How Autos Work

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An in depth introduction to Automobiles

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I. Introduction

Automobile, the self-propelled vehicle, changed the world during the 20th century, particularly in the industrialized nations. From the growth of suburbs to the development of elaborate road and highway systems, the so-called horseless carriage has forever altered the modern landscape. The manufacture, sale, and servicing of automobiles have become key elements of industrial economies. But along with greater mobility and job creation, the automobile has brought noise and air pollution, and automobile accidents rank among the leading causes of death and injury throughout the world. But for better or worse, the 1900s can be called the Age of the Automobile, and cars will no doubt continue to shape our culture and economy well into the 21st century.

Our great-grandfather was a true pioneer of automobile era and the Quraishi Family is the First Family of Autmotive Industry. Our great grandfather imported his first vehicle in 1905 and became the first Asian outside Japan to import his own automobile. He parlayed his passion for cars into a business when he opened Asia’s First Auto Dealership in 1911.

Automobiles are classified by size, style, number of doors, and intended use. The typical automobile, also called a car auto, motorcar, and passenger car, has four wheels and can carry up to six people, including a driver. Larger vehicles designed to carry more passengers are called vans, minivans, omnibuses, or buses. Those used to carry cargo are called pickups or trucks, depending on their size and design. Minivans are van-style vehicles built on a passenger car frame that can usually carry up to eight passengers. Sport-utility vehicles, also known as SUVs, are more rugged than passenger cars and are designed for driving in mud or snow.

In 2001 manufacturing plants in more than 35 countries produced 39.5 million passenger cars. About 7.3 million passenger vehicles were produced in North America in 2001.

The automobile is built around an engine. Various systems supply the engine with fuel, cool it during operation, lubricate its moving parts, and remove exhaust gases it creates. The engine produces mechanical power that is transmitted to the automobile’s wheels through a drivetrain, which includes a transmission, one or more driveshafts, a differential gear, and axles. Suspension systems, which include springs and shock absorbers, cushion the ride and help protect the vehicle from being damaged by bumps, heavy loads, and other stresses. Wheels and tires support the vehicle on the roadway and, when rotated by powered axles, propel the vehicle forward or backward. Steering and braking systems provide control over direction and speed. An electrical system starts and operates the engine, monitors and controls many aspects of the vehicle’s operation, and powers such components as headlights and radios. Safety features such as bumpers, air bags, and seat belts help protect occupants in an accident.

II. Power System

Gasoline (petrol) internal-combustion engines power most automobiles, but some engines use diesel fuel, electricity, natural gas, solar energy, or fuels derived from methanol (wood alcohol) and ethanol (grain alcohol). The purpose of a gasoline car engine is to convert gasoline into motion so that your car can move. Currently the easiest way to create motion from gasoline is to burn the gasoline inside an engine. Therefore, a car engine is an internal combustion engine — combustion takes place internally.

Almost all cars today use a reciprocating internal combustion engine because this engine is:

  • Relatively efficient (compared to an external combustion engine)
  • Relatively inexpensive (compared to a gas turbine)
  • Relatively easy to refuel (compared to an electric car)

These advantages beat any other existing technology for moving a car around.

Most gasoline engines work in the following way: Turning the ignition key operates a switch that sends electricity from a battery to a starter motor. The starter motor turns a disk known as a flywheel, which in turn causes the engine’s crankshaft to revolve. The rotating crankshaft causes pistons, which are solid cylinders that fit snugly inside the engine’s hollow cylinders, to move up and down. Fuel-injection systems or, in older cars, a carburetor deliver fuel vapor from the gas tank to the engine cylinders.

The pistons compress the vapor inside the cylinders. An electric current flows through a spark plug to ignite the vapor. The fuel mixture explodes, or combusts, creating hot expanding gases that push the pistons down the cylinders and cause the crankshaft to rotate. The crankshaft is now rotating via the up-and-down motion of the pistons, permitting the starter motor to disengage from the flywheel.

If you put a high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas. You can use that energy to propel a thing into motion. This fact is behind a car engine. A cycle is created that allows one to set off explosions hundreds of times per minute, and that energy is harnessed to drive the car.

Almost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867. The four strokes are:

  • Intake stroke
  • Compression stroke
  • Combustion stroke
  • Exhaust stroke

Here’s what happens as the engine goes through its cycle:

The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline. This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work. Then the piston moves back up to compress this fuel/air mixture making the compression stroke. Compression makes the explosion more powerful. When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline and combustion stroke begins. The gasoline charge in the cylinder explodes, driving the piston down. Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tail pipe. This is exhaust stroke. Now the engine is ready for the next cycle, so it intakes another charge of air and gas and the cycle continues.

A. Engine

The basic components of an internal-combustion engine are the engine block, cylinder head, cylinders, pistons, valves, crankshaft, and camshaft.

The lower part of the engine, called the engine block, houses the cylinders, pistons, and crankshaft. The components of other engine systems bolt or attach to the engine block. The block is manufactured with internal passageways for lubricants and coolant. Engine blocks are made of cast iron or aluminium alloy and formed with a set of round cylinders.

The core of the engine is the cylinder, with the piston moving up and down inside the cylinder. Most cars have more than one cylinder (four, six and eight cylinders are common). In a multi-cylinder engine, the cylinders usually are arranged in one of three ways: inline, V or flat (also known as horizontally opposed or boxer). See below for more details.

The upper part of the engine is the cylinder head. Bolted to the top of the block, it seals the tops of the cylinders. Pistons compress air and fuel against the cylinder head prior to ignition. The top of the piston forms the floor of the combustion chamber. A rod connects the bottom of the piston to the crankshaft. Lubricated bearings enable both ends of the connecting rod to pivot, transferring the piston’s vertical motion into the crankshaft’s rotational force, or torque. The pistons’ motion rotates the crankshaft at speeds ranging from about 600 to thousands of revolutions per minute (rpm), depending on how much fuel is delivered to the cylinders.

Fuel vapor enters and exhaust gases leave the combustion chamber through openings in the cylinder head controlled by valves. The typical engine valve is a metal shaft with a disk at one end fitted to block the opening. The other end of the shaft is mechanically linked to a camshaft, a round rod with odd-shaped lobes located inside the engine block or in the cylinder head. Inlet valves open to allow fuel to enter the combustion chambers. Outlet valves open to let exhaust gases out.

A gear wheel, belt, or chain links the camshaft to the crankshaft. When the crankshaft forces the camshaft to turn, lobes on the camshaft cause valves to open and close at precise moments in the engine’s cycle. When fuel vapor ignites, the intake and outlet valves close tightly to direct the force of the explosion downward on the piston.

B. Engine Types

The blocks in most internal-combustion engines are in-line designs or V designs. In-line designs are arranged so that the cylinders stand upright in a single line over the crankshaft. In a V design, two rows of cylinders are set at an angle to form a V. At the bottom of the V is the crankshaft. In-line configurations of six or eight cylinders require long engine compartments found more often in trucks than in cars. The V design allows the same number of cylinders to fit into a shorter, although wider, space. Another engine design that fits into shorter, shallower spaces is a horizontally opposed, or flat, arrangement in which the crankshaft lies between two rows of cylinders.

Inline Engine V6 Engine
Flat Engine  

Engines become more powerful, and use more fuel, as the size and number of cylinders increase. Most modern vehicles have 4-, 6-, or 8-cylinder engines, but car engines have been designed with 1, 2, 3, 5, 12, and more cylinders.

Diesel engines, common in large trucks or buses, are similar to gasoline internal-combustion engines, but they have a different ignition system. Diesels compress air inside the cylinders with greater force than a gasoline engine does, producing temperatures hot enough to ignite the diesel fuel on contact. Some cars have rotary engines, also known as Wankel engines, which have one or more elliptical chambers in which triangular-shaped rotors, instead of pistons, rotate.

Electric motors have been used to power automobiles since the late 1800s. Electric power supplied by batteries runs the motor, which rotates a driveshaft, the shaft that transmits engine power to the axles. Commercial electric car models for specialized purposes were available in the 1980s. General Motors Corporation introduced a mass-production all-electric car in the mid-1990s.

Automobiles that combine two or more types of engines are called hybrids. A typical hybrid is an electric motor with batteries that are recharged by a generator run by a small gas- or diesel-powered engine. These hybrids are known as hybrid electric vehicles (HEVs). By relying more on electricity and less on fuel combustion, HEVs have higher fuel efficiency and emit fewer pollutants. Several automakers have experimented with hybrids.

In 1997 Toyota Motor Corporation became the first to mass-produce a hybrid vehicle, the Prius. It became available in Japan in 1997 and in North America in 2000. The first hybrid available for sale in North America, the Honda Insight, was offered by Honda Motor Co., Ltd., in 1999. Honda later introduced a hybrid version of the Honda Civic. In August 2004 the Ford Motor Company became the first U.S. automaker to release a hybrid vehicle when it began production of the Ford Escape Hybrid, the first hybrid sport- utility vehicle (SUV). The Escape Hybrid was released for the 2005 model year.

C. Displacement (CC)

The combustion chamber is the area where compression and combustion take place. As the piston moves up and down, you can see that the size of the combustion chamber changes. It has some maximum volume as well as a minimum volume. The difference between the maximum and minimum is called the displacement and is measured in liters or CCs (Cubic Centimeters, where 1,000 cubic centimeters equals a liter). Here are some examples:

A chainsaw might have a 40 cc engine. A motorcycle might have a 500 cc or a 750 cc engine. A sports car might have a 5.0 liter (5,000 cc) engine. Most normal car engines fall somewhere between 1.5 liter (1,500 cc) and 4.0 liters (4,000 cc) If you have a 4-cylinder engine and each cylinder displaces half a liter, then the entire engine is a “2.0 liter engine.” If each cylinder displaces half a liter and there are six cylinders arranged in a V configuration, you have a “3.0 liter V-6.”

Generally, the displacement tells you something about how much power an engine can produce. A cylinder that displaces half a liter can hold twice as much fuel/air mixture as a cylinder that displaces a quarter of a liter, and therefore you would expect about twice as much power from the larger cylinder (if everything else is equal). So a 2.0 liter engine is roughly half as powerful as a 4.0 liter engine.

You can get more displacement in an engine either by increasing the number of cylinders or by making the combustion chambers of all the cylinders bigger (or both).

D. Parts of an Engine

The parts of an engine vary depending on the engine’s type. For a four-stroke engine, key parts of the engine include the crankshaft, one or more camshafts and valves. For a two-stroke engine, there may simply be an exhaust outlet and fuel inlet instead of a valve system. In both types of engines, there are one or more cylinders and for each cylinder there is a spark plug, a piston and a crank A single sweep of the cylinder by the piston in an upward or downward motion is known as a stroke and the downward stroke that occurs directly after the air-fuel mix in the cylinder is ignited is known as a power stroke.

Piston: A piston is a cylindrical piece of metal that moves up and down inside the cylinder.

Piston rings: Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes:

  • They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the sump during compression and combustion.
  • They keep oil in the sump from leaking into the combustion area, where it would be burned and lost. Most cars that “burn oil” and have to have a quart added every 1,000 miles are burning it because the engine is old and the rings no longer seal things properly.

Connecting rod: The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and the crankshaft rotates. It transmits motion or power from one moving part to another, especially the rod connecting the crankshaft of a motor vehicle to a piston. Also called pitman

Valves: The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Note that both valves are closed during compression and combustion so that the combustion chamber is sealed.

Crank shaft: The crank shaft turns the piston’s up and down motion into circular motion just like a crank on a jack-in-the-box does.

Spark plug: The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur. The spark must happen at just the right moment for things to work properly.

Sump: The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom of the sump (the oil pan).

E. Combustion and Explosion

All internal combustion engines depend on the chemical process of combustion and explosion, that is the reaction of a fuel with oxygen. See also: stoichiometry.

The most common fuels in use today are made up of hydrocarbons and are derived from petroleum. These include the fuels known as diesel, gasoline and liquefied petroleum gas. Some have theorized that in the future hydrogen might replace such fuels. The advantage of hydrogen is that its combustion produces only water (the chief disadvantage of using hydrogen is that presently no method exists for efficiently producing it in quantities sufficient to power internal combustion engines on a large scale). This is unlike the combustion of hydrocarbons which also produces carbon dioxide – a major cause of global warming.

Whatever the choice of fuel, all internal combustion engines rely on the effects of a controlled explosion, where a gaseous fuel reacts with oxygen. The explosion products (hot gases) occupy a larger volume than the original compressed fuel/air mixture and the resulting high pressure in the cylinders drives the engine’s pistons down. Relieving the pressure after this has occurred (either by opening a valve or exposing the exhaust outlet) allows the piston to return to its uppermost position (Top Dead Center – TDC). The piston can then proceed to the next phase of its cycle (which varies between engines). The resulting heat from the explosion is a waste product and is removed from the engine either by an air or liquid cooling system. (An ideal, 100% efficient engine would run and remain at ambient temperature and convert all the energy in the fuel to kinetic energy – not into heat).

All internal combustion engines must have a means of ignition to promote combustion. Most engines use either an electrical or a compression heating ignition system. Electrical ignition systems generally rely on a lead-acid battery and an induction coil to provide a high voltage electrical spark to ignite the air-fuel mix in the engine’s cylinders. This battery can be recharged during operation using an alternator driven by the engine. Compression heating ignition systems rely on the heat already present in the compressed air in the engine’s cylinders to ignite the fuel when it is injected.

F. How an Engine works

Each movement of the piston from top to bottom or from bottom to top is called a stroke. The piston takes two strokes (an upstroke and a downstroke) as the crankshaft makes one complete revolution. When the piston is at the top of a stroke, it is said to be at top dead center. When the piston is at the bottom of a stroke, it is said to be at bottom dead center. These positions are rock positions.

The enclosed end of a cylinder has two openings. One of the openings, or ports, permits the mixture of air and fuel to enter, and the other port permits the burned gases to escape from the cylinder. The two ports have valves assembled in them. These valves, actuated by the camshaft, close off either one or the other of the ports, or both of them, during various stages of engine operation. One of the valves, called the intake valve, opens to admit a mixture of fuel and air into the cylinder. The other valve, called the exhaust valve, opens to allow the escape of burned gases after the fuel-and-air mixture has burned. Later you will learn more about how these valves and their mechanisms operate.

The following paragraphs explain the sequence of actions that takes place within the engine cylinder: the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. Since these strokes are easy to identify in the operation of a four-cycle engine, that engine is used in the description. This type of engine is called a four-stroke-Otto-cycle engine, named after Dr. N. A. Otto who, in 1876, first applied the principle of this engine. Each stroke corresponds to one full stroke of the piston, therefore the complete cycle requires two revolutions of the crankshaft to complete.

Intake or Admission Stroke

The first stroke in the sequence is the intake stroke. During this stroke, the piston is moving downward and the intake valve is open. This downward movement of the piston produces a partial vacuum in the cylinder, and air and fuel rush into the cylinder past the open intake valve, the exhaust valve is meanwhile held shut by a spring. This action produces a result similar to that which occurs when you drink through a straw. You produce a partial vacuum in your mouth, and the liquid moves up through the straw to fill the vacuum.

Compression Stroke

When the piston reaches bottom dead center at the end of the intake stroke (and is therefore at the bottom of the cylinder) the intake valve closes and seals the upper end of the cylinder. Now both intake and exhaust valves are closed. As the crankshaft continues to rotate, it pushes the connecting rod up against the piston. The piston then moves upward and this upward movement compresses the combustible mixture in the cylinder. This action is known as the compression stroke .

In gasoline engines, the mixture is compressed to about one-eighth of its original volume. (In a diesel engine the mixture may be compressed to as little as one-sixteenth of its original volume.) This compression of the air-fuel mixture increases the pressure within the cylinder. Compressing the mixture in this way makes it more combustible; not only does the pressure in the cylinder go up, but the temperature of the mixture also increases.

Power or Expansion Stroke

As the piston reaches top dead center at the end of the compression stroke (and is therefore at the top of the cylinder), the ignition system produces an electric spark. The spark ignites the fuel-air mixture. The intake and exhaust valves are closed. Having been ignited, the fuel-air mixture burns. In burning, the mixture gets very hot and expands in all directions. The pressure rises to about 600 to 700 pounds per square inch. Since the piston is the only part that can move, the force produced by the expanding gases forces the piston down. This force, or thrust, is carried through the connecting rod to the crankpin on the crankshaft. The crankshaft is given a powerful twist. Since it is the only stroke and event that furnishes power to the crankshaft, it is usually called the power stroke, although it is sometimes called the expansion stroke for purposes of instruction. This turning effort, rapidly repeated in the engine and carried through gears and shafts, will turn the wheels of a vehicle and cause it to move along the highway.

Exhaust Stroke

After the fuel-air mixture has burned, it must be cleared from the cylinder. Therefore, the exhaust valve  is opened by the cam/lifter mechanism as the power stroke is finished and the piston starts back up on the exhaust stroke. The piston forces the exhausted fuel of the cylinder past the open exhaust valve.

The four strokes (intake, compression, power, and exhaust) are continuously repeated as the engine runs.

Intake Stroke Compression Stroke
Power Stroke Exhaust Stroke

Valve Trains and Camshaft

The valve train consists of the valves and a mechanism that opens and closes them. The opening and closing system is called a camshaft. The camshaft has lobes on it that move the valves up and down, as shown in the attached Figure.

Most modern engines have what are called overhead cams. This means that the camshaft is located above the valves, as you see in Figure 5. The cams on the shaft activate the valves directly or through a very short linkage. Older engines used a camshaft located in the sump near the crankshaft. Rods linked the cam below to valve lifters above the valves. This approach has more moving parts and also causes more lag between the cam’s activation of the valve and the valve’s subsequent motion. A timing belt or timing chain links the crankshaft to the camshaft so that the valves are in sync with the pistons. The camshaft is geared to turn at one-half the rate of the crankshaft. Many high-performance engines have four valves per cylinder (two for intake, two for exhaust), and this arrangement requires two camshafts per bank of cylinders, hence the phrase “dual overhead cams.”

Valves let the air/fuel mixture into the engine and the exhaust out of the engine. The camshaft uses lobes (called cams) that push against the valves to open them as the camshaft rotates; springs on the valves return them to their closed position. This is a critical job, and can have a great impact on an engine’s performance at different speeds.

The key parts of any camshaft are the lobes. As the camshaft spins, the lobes open and close the intake and exhaust valves in time with the motion of the piston. It turns out that there is a direct relationship between the shape of the cam lobes and the way the engine performs in different speed ranges. To understand why this is the case, imagine that we are running an engine extremely slowly — at just 10 or 20 revolutions per minute (RPM) — so that it takes the piston a couple of seconds to complete a cycle. It would be impossible to actually run a normal engine this slowly, but let’s imagine that we could. At this slow speed, we would want cam lobes shaped so that:

Just as the piston starts moving downward in the intake stroke (called top dead center, or TDC), the intake valve would open. The intake valve would close right as the piston bottoms out.

The exhaust valve would open right as the piston bottoms out (called bottom dead center, or BDC) at the end of the combustion stroke, and would close as the piston completes the exhaust stroke. This setup would work really well for the engine as long as it ran at this very slow speed.

But what happens if you increase the RPM? Let’s find out.

When you increase the RPM, the 10 to 20 RPM configuration for the camshaft does not work well. If the engine is running at 4,000 RPM, the valves are opening and closing 2,000 times every minute, or 33 times every second. At these speeds, the piston is moving very quickly, so the air/fuel mixture rushing into the cylinder is moving very quickly as well. When the intake valve opens and the piston starts its intake stroke, the air/fuel mixture in the intake runner starts to accelerate into the cylinder. By the time the piston reaches the bottom of its intake stroke, the air/fuel is moving at a pretty high speed. If we were to slam the intake valve shut, all of that air/fuel would come to a stop and not enter the cylinder. By leaving the intake valve open a little longer, the momentum of the fast-moving air/fuel continues to force air/fuel into the cylinder as the piston starts its compression stroke. So the faster the engine goes, the faster the air/fuel moves, and the longer we want the intake valve to stay open. We also want the valve to open wider at higher speeds — this parameter, called valve lift, is governed by the cam lobe profile.

Any given camshaft will be perfect only at one engine speed. At every other engine speed, the engine won’t perform to its full potential. A fixed camshaft is, therefore, always a compromise. This is why carmakers have developed schemes to vary the cam profile as the engine speed changes.

Camshaft Arrangements

There are several different arrangements of camshafts on engines. We’ll talk about some of the most common ones. You’ve probably heard the terminology: Single overhead cam (SOHC), Double overhead cam (DOHC) and Pushrod. Let’s start by looking at single overhead cams.

Single Overhead Cams This arrangement denotes an engine with one cam per head. So if it is an inline 4-cylinder or inline 6-cylinder engine, it will have one cam; if it is a V-6 or V-8, it will have two cams (one for each head).

The cam actuates rocker arms that press down on the valves, opening them. Springs return the valves to their closed position. These springs have to be very strong because at high engine speeds, the valves are pushed down very quickly, and it is the springs that keep the valves in contact with the rocker arms. If the springs were not strong enough, the valves might come away from the rocker arms and snap back. This is an undesirable situation that would result in extra wear on the cams and rocker arms.

A single overhead cam (SOHC)

On single and double overhead cam engines, the cams are driven by the crankshaft, via either a belt or chain called the timing belt or timing chain. These belts and chains need to be replaced or adjusted at regular intervals. If a timing belt breaks, the cam will stop spinning and the piston could hit the open valves.

Double Overhead Cam (DOHC)

A double overhead cam engine has two cams per head. So inline engines have two cams, and V engines have four. Usually, double overhead cams are used on engines with four or more valves per cylinder — a single camshaft simply cannot fit enough cam lobes to actuate all of those valves.

The main reason to use double overhead cams is to allow for more intake and exhaust valves. More valves means that intake and exhaust gases can flow more freely because there are more openings for them to flow through. This increases the power of the engine.

Pushrod Engines

Like SOHC and DOHC engines, the valves in a pushrod engine are located in the head, above the cylinder. The key difference is that the camshaft on a pushrod engine is inside the engine block, rather than in the head.

The cam actuates long rods that go up through the block and into the head to move the rockers. These long rods add mass to the system, which increases the load on the valve springs. This can limit the speed of pushrod engines; the overhead camshaft, which eliminates the pushrod from the system, is one of the engine technologies that made higher engine speeds possible.

The camshaft in a pushrod engine is often driven by gears or a short chain. Gear-drives are generally less prone to breakage than belt drives, which are often found in overhead cam engines.

D. Fuel Supply

The internal-combustion engine is powered by the burning of a precise mixture of liquefied fuel and air in the cylinders’ combustion chambers. Fuel is stored in a tank until it is needed, then pumped to a carburetor or, in newer cars, to a fuel-injection system.

The carburetor controls the mixture of gas and air that travels to the engine. It mixes fuel with air at the head of a pipe, called the intake manifold, leading to the cylinders. A vacuum created by the downward strokes of pistons draws air through the carburetor and intake manifold. Inside the carburetor, the airflow transforms drops of fuel into a fine mist, or vapor. The intake manifold delivers the fuel vapor to the cylinders, where it is ignited.

All new cars produced today are equipped with fuel injection systems instead of carburetors. Fuel injectors spray carefully calibrated bursts of fuel mist into cylinders either at or near openings to the combustion chambers. Since the exact quantity of gas needed is injected into the cylinders, fuel injection is more precise, easier to adjust, and more consistent than a carburetor, delivering better efficiency, gas mileage, engine responsiveness, and pollution control. Fuel-injection systems vary widely, but most are operated or managed electronically.

High-performance automobiles are often fitted with air-compressing equipment that increases an engine’s output. By increasing the air and fuel flow to the engine, these features produce greater horsepower. Superchargers are compressors powered by the crankshaft. Turbochargers are turbine-powered compressors run by pressurized exhaust gas.

Lubrication System

The lubrication system makes sure that every moving part in the engine gets oil so that it can move easily. The two main parts needing oil are the pistons (so they can slide easily in their cylinders) and any bearings that allow things like the crankshaft and camshafts to rotate freely. In most cars, oil is sucked out of the oil pan by the oil pump, run through the oil filter to remove any grit, and then squirted under high pressure onto bearings and the cylinder walls. The oil then trickles down into the sump, where it is collected again and the cycle repeats.

Fuel System

The fuel system pumps gas from the gas tank and mixes it with air so that the proper air/fuel mixture can flow into the cylinders. Fuel is delivered in three common ways: carburetion, port fuel injection and direct fuel injection.

In carburetion, a device called a carburetor mixes gas into air as the air flows into the engine. In a fuel-injected engine, the right amount of fuel is injected individually into each cylinder either right above the intake valve (port fuel injection) or directly into the cylinder (direct fuel injection).

How Fuel Injectors work?

In trying to keep up with emissions and fuel efficiency laws, the fuel system used in modern cars has changed a lot over the years. The 1990 Subaru Justy was the last car sold in the United States to have a carburetor; the following model year, the Justy had fuel injection. But fuel injection has been around since the 1950s, and electronic fuel injection was used widely on European cars starting around 1980. Now, all cars sold in the United States have fuel injection systems. In this article, we’ll learn how the fuel gets into the cylinder of the engine, and what terms like “multi-port fuel injection” and “throttle body fuel injection” mean. We’ll also find out how performance chips can give your engine more power.

The Fall of the Carburetor

For most of the existence of the internal combustion engine, the carburetor has been the device that supplied fuel to the engine. On many other machines, such as lawnmowers and chainsaws, it still is. But as the automobile evolved, the carburetor got more and more complicated trying to handle all of the operating requirements. For instance, to handle some of these tasks, carburetors had five different circuits: Main circuit – Provides just enough fuel for fuel-efficient cruising Idle circuit – Provides just enough fuel to keep the engine idling Accelerator pump – Provides an extra burst of fuel when the accelerator pedal is first depressed, reducing hesitation before the engine speeds up Power enrichment circuit – Provides extra fuel when the car is going up a hill or towing a trailer Choke – Provides extra fuel when the engine is cold so that it will start In order to meet stricter emissions requirements, catalytic converters were introduced. Very careful control of the air-to-fuel ratio was required for the catalytic converter to be effective. Oxygen sensors monitor the amount of oxygen in the exhaust, and the engine control unit (ECU) uses this information to adjust the air-to-fuel ratio in real-time. This is called closed loop control — it was not feasible to achieve this control with carburetors. There was a brief period of electrically controlled carburetors before fuel injection systems took over, but these electrical carbs were even more complicated than the purely mechanical ones.

At first, carburetors were replaced with throttle body fuel injection systems (also known as single point or central fuel injection systems) that incorporated electrically controlled fuel-injector valves into the throttle body. These were almost a bolt-in replacement for the carburetor, so the automakers didn’t have to make any drastic changes to their engine designs.

Gradually, as new engines were designed, throttle body fuel injection was replaced by multi-port fuel injection (also known as port, multi-point or sequential fuel injection). These systems have a fuel injector for each cylinder, usually located so that they spray right at the intake valve. These systems provide more accurate fuel metering and quicker response.

When You Step on the Gas

The gas pedal in your car is connected to the throttle valve — this is the valve that regulates how much air enters the engine. So the gas pedal is really the air pedal.

A partially open throttle valve

When you step on the gas pedal, the throttle valve opens up more, letting in more air. The engine control unit (ECU, the computer that controls all of the electronic components on your engine) “sees” the throttle valve open and increases the fuel rate in anticipation of more air entering the engine. It is important to increase the fuel rate as soon as the throttle valve opens; otherwise, when the gas pedal is first pressed, there may be a hesitation as some air reaches the cylinders without enough fuel in it.

Sensors monitor the mass of air entering the engine, as well as the amount of oxygen in the exhaust. The ECU uses this information to fine-tune the fuel delivery so that the air-to-fuel ratio is just right.

The Injector

A fuel injector is nothing but an electronically controlled valve. It is supplied with pressurized fuel by the fuel pump in your car, and it is capable of opening and closing many times per second.

Inside a fuel injector

When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing the pressurized fuel to squirt out through a tiny nozzle. The nozzle is designed to atomize the fuel — to make as fine a mist as possible so that it can burn easily.

A fuel injector firing

The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width, and it is controlled by the ECU.

Fuel injectors mounted in the intake manifold of the engine

The injectors are mounted in the intake manifold so that they spray fuel directly at the intake valves. A pipe called the fuel rail supplies pressurized fuel to all of the injectors.

In order to provide the right amount of fuel, the engine control unit is equipped with a whole lot of sensors. Let’s take a look at some of them.

Engine Sensors

In order to provide the correct amount of fuel for every operating condition, the engine control unit (ECU) has to monitor a huge number of input sensors. Here are just a few:

Mass airflow sensor – Tells the ECU the mass of air entering the engine

Oxygen sensor(s) – Monitors the amount of oxygen in the exhaust so the ECU can determine how rich or lean the fuel mixture is and make adjustments accordingly

Throttle position sensor – Monitors the throttle valve position (which determines how much air goes into the engine) so the ECU can respond quickly to changes, increasing or decreasing the fuel rate as necessary

Coolant temperature sensor – Allows the ECU to determine when the engine has reached its proper operating temperature

Voltage sensor – Monitors the system voltage in the car so the ECU can raise the idle speed if voltage is dropping (which would indicate a high electrical load)

Manifold absolute pressure sensor – Monitors the pressure of the air in the intake manifold The amount of air being drawn into the engine is a good indication of how much power it is producing; and the more air that goes into the engine, the lower the manifold pressure, so this reading is used to gauge how much power is being produced.

Engine speed sensor – Monitors engine speed, which is one of the factors used to calculate the pulse width There are two main types of control for multi-port systems: The fuel injectors can all open at the same time, or each one can open just before the intake valve for its cylinder opens (this is called sequential multi-port fuel injection). The advantage of sequential fuel injection is that if the driver makes a sudden change, the system can respond more quickly because from the time the change is made, it only has to wait only until the next intake valve opens, instead of for the next complete revolution of the engine.

Engine Controls and Performance Chips

The algorithms that control the engine are quite complicated. The software has to allow the car to satisfy emissions requirements for 100,000 miles, meet EPA fuel economy requirements and protect engines against abuse. And there are dozens of other requirements to meet as well.

The engine control unit uses a formula and a large number of lookup tables to determine the pulse width for given operating conditions. The equation will be a series of many factors multiplied by each other. Many of these factors will come from lookup tables. We’ll go through a simplified calculation of the fuel injector pulse width. In this example, our equation will only have three factors, whereas a real control system might have a hundred or more.

Pulse width = (Base pulse width) x (Factor A) x (Factor B)

In order to calculate the pulse width, the ECU first looks up the base pulse width in a lookup table. Base pulse width is a function of engine speed (RPM) and load (which can be calculated from manifold absolute pressure). Let’s say the engine speed is 2,000 RPM and load is 4. We find the number at the intersection of 2,000 and 4, which is 8 milliseconds.


In the next examples, A and B are parameters that come from sensors. Let’s say that A is coolant temperature and B is oxygen level. If coolant temperature equals 100 and oxygen level equals 3, the lookup tables tell us that Factor A = 0.8 and Factor B = 1.0.

Factor A
Factor B

So, since we know that base pulse width is a function of load and RPM, and that pulse width = (base pulse width) x (factor A) x (factor B), the overall pulse width in our example equals:

8 x 0.8 x 1.0 = 6.4 milliseconds

From this example, you can see how the control system makes adjustments. With parameter B as the level of oxygen in the exhaust, the lookup table for B is the point at which there is (according to engine designers) too much oxygen in the exhaust; and accordingly, the ECU cuts back on the fuel.

Real control systems may have more than 100 parameters, each with its own lookup table. Some of the parameters even change over time in order to compensate for changes in the performance of engine components like the catalytic converter. And depending on the engine speed, the ECU may have to do these calculations over a hundred times per second.

Performance Chips

This leads us to our discussion of performance chips. Now that we understand a little bit about how the control algorithms in the ECU work, we can understand what performance-chip makers do to get more power out of the engine.

Performance chips are made by aftermarket companies, and are used to boost engine power. There is a chip in the ECU that holds all of the lookup tables; the performance chip replaces this chip. The tables in the performance chip will contain values that result in higher fuel rates during certain driving conditions. For instance, they may supply more fuel at full throttle at every engine speed. They may also change the spark timing (there are lookup tables for that, too). Since the performance-chip makers are not as concerned with issues like reliability, mileage and emissions controls as the carmakers are, they use more aggressive settings in the fuel maps of their performance chips.


The theory behind Commonrail was originally developed by researchers at Zurich University. This simple yet elegant theory is based on the assumption that if you continue to push diesel into a tank, the pressure inside will rise and the tank itself will become a hydraulic accumulator (or rail), i.e. a reserve of pressurised fuel ready for use. This technology was first applied to diesel engines in late 80s. First came Unijet Commonrail engines.

Diesel engine development has centred around the commonrail as its rising star in the area of fuel distribution technology. Premium makes such as the Merc E-class and quite a few MPVs are using commonrail diesel technology in Thailand.

There are only few pickups with commonrail technology at the moment but sources say that the rest of the pack will follow suit.

Until recently, there has been growing concern on the issue of the electronically-controlled diesel commonrail’s fuel efficiency in comparison to older direct fuel injection technology which uses a mechanical pump or VE mechanical pump.

First of all, commonrail technology was developed in order to get optimal performance and overcome the lingering problem of incomplete fuel combustion. Other benefits were supposed to be enhanced fuel efficiency and less exhaust emissions.

However, it all depends on how much output carmakers desire as well. Horses eat grass, engines drink petrol. A few drops of fuel will not result in a lot of horsepower because commonrail technology was not made by aliens. High output requires quite a lot of fuel regardless of whatever engine technology is being put to use.

One reason why the high-tech commonrail diesel block is as thirsty as its regular diesel counterpart is due to the increased power or maximum output and decreased exhaust emissions.

Say the diesel commonrail engine delivers better acceleration, engine response and cargo-hulling ability due to a more powerful engine. If fuel consumption is on a par with its predecessor or dated diesel technology _ it’s not a surprise.

The key issue here is that a more powerful engine requires optimal combustion so that every drop of fuel is used to its potential in squeezing out every horse from the engine.

So if a diesel commonrail engine is clearly giving you better performance, while consuming just a little bit more fuel than its dated diesel counterpart – you are using your fuel to its optimal potential.

Confused? Say we have two diesel engines, one with commonrail technology and the other with regular fuel injection. And say that both engines are supposed to produce the same level of performance or horsepower.

This example will naturally allow the commonrail engine to be more fuel efficient and produce less emissions.

However, if the commonrail engine is more powerful, the end result might not necessarily allow it to be more fuel efficient than the conventional diesel engine.

For your information, commonrail diesels require enormous amounts of oil pressure when compared to the conventional type. The fuel injector has around six to seven pinholes for the fuel to be sprayed out. Each injector receives data processed from several sensors in order to determine the right amount of fuel to be distributed/sprayed in tandem with the right amount of air mixture.

That said, modern commonrail diesels should have the same rate of fuel consumption against its dated conventional diesel counterpart as long as maximum output or power are on the same levels.

According to an independent study conducted by a certain university, the commonrail diesel had a slight advantage over the conventional diesel engine in fuel efficiency under controlled driving conditions. However, during practical usage and driving conditions, the results were the opposite.

Why? Simply put, different driving styles.

A commonrail diesel customer is likely to be someone who likes performance with a heavy foot, so to speak. A conventional diesel customer is someone who is satisfied with the car’s performance and drives slowly without forcing the issue.

Which diesel pickup suits you will depend on your personal requirements.

In the future, more and more pickup brands will use commonrail technology which gives better acceleration, smooth, quiet and does less damage to the environment and the air around us.

The switch to commonrail stems from the fact that fuel combustion is more complete and environment-friendly.

It can be likened to the scenario where petrolheads changed from the conventional carburetor to electronic fuel distribution.

D. Exhaust System

The exhaust system carries exhaust gases from the engine’s combustion chamber to the atmosphere and reduces, or muffles, engine noise. Exhaust gases leave the engine in a pipe, traveling through a catalytic converter and a muffler before exiting through the tailpipe.

Chemical reactions inside the catalytic converter change most of the hazardous hydrocarbons and carbon monoxide produced by the engine into water vapor and carbon dioxide.

The conventional muffler is an enclosed metal tube packed with sound-deadening material. Most conventional mufflers are round or oval-shaped with an inlet and outlet pipe at either end. Some contain partitions to help reduce engine noise.

Car manufacturers are experimenting with an electronic muffler, which uses sensors to monitor the sound waves of the exhaust noise. The sound wave data are sent to a computer that controls speakers near the tailpipe. The system generates sound waves 180 degrees out of phase with the engine noise. The sound waves from the electronic muffler collide with the exhaust sound waves and they cancel each other out, leaving only low-level heat to emerge from the tailpipe.

Exhaust System

The exhaust system includes the exhaust pipe and the muffler. Without a muffler, what you would hear is the sound of thousands of small explosions coming out your tailpipe. A muffler dampens the sound. The exhaust system also includes a catalytic converter.

Emission Control

The emission control system in modern cars consists of a catalytic converter, a collection of sensors and actuators, and a computer to monitor and adjust everything. For example, the catalytic converter uses a catalyst and oxygen to burn off any unused fuel and certain other chemicals in the exhaust. An oxygen sensor in the exhaust stream makes sure there is enough oxygen available for the catalyst to work and adjusts things if necessary.

E. Cooling and Heating System

Combustion inside an engine produces temperatures high enough to melt cast iron. A cooling system conducts this heat away from the engine’s cylinders and radiates it into the air.

In most automobiles, a liquid coolant circulates through the engine. A pump sends the coolant from the engine to a radiator, which transfers heat from the coolant to the air. In early engines, the coolant was water. In most automobiles today, the coolant is a chemical solution called antifreeze that has a higher boiling point and lower freezing point than water, making it effective in temperature extremes. Some engines are air cooled, that is, they are designed so a flow of air can reach metal fins that conduct heat away from the cylinders.

A second, smaller radiator is fitted to all modern cars. This unit uses engine heat to warm the interior of the passenger compartment and supply heat to the windshield defroster.

What Can Go Wrong?

So you go out one morning and your engine will turn over but it won’t start… What could be wrong? Now that you know how an engine works, you can understand the basic things that can keep an engine from running. Three fundamental things can happen: a bad fuel mix, lack of compression or lack of spark. Beyond that, thousands of minor things can create problems, but these are the “big three.” Based on the simple engine we have been discussing, here is a quick run-down on how these problems affect your engine:

Bad fuel mix

A bad fuel mix can occur in several ways:

  • You are out of gas, so the engine is getting air but no fuel.
  • The air intake might be clogged, so there is fuel but not enough air.
  • The fuel system might be supplying too much or too little fuel to the mix, meaning that combustion does not occur properly.
  • There might be an impurity in the fuel (like water in your gas tank) that makes the fuel not burn.

Lack of compression 

If the charge of air and fuel cannot be compressed properly, the combustion process will not work like it should. Lack of compression might occur for these reasons: Your piston rings are worn (allowing air/fuel to leak past the piston during compression). The intake or exhaust valves are not sealing properly, again allowing a leak during compression. There is a hole in the cylinder. The most common “hole” in a cylinder occurs where the top of the cylinder (holding the valves and spark plug and also known as the cylinder head) attaches to the cylinder itself. Generally, the cylinder and the cylinder head bolt together with a thin gasket pressed between them to ensure a good seal. If the gasket breaks down, small holes develop between the cylinder and the cylinder head, and these holes cause leaks.

Lack of spark

The spark might be nonexistent or weak for a number of reasons:

  • If your spark plug or the wire leading to it is worn out, the spark will be weak.
  • If the wire is cut or missing, or if the system that sends a spark down the wire is not working properly, there will be no spark.
  • If the spark occurs either too early or too late in the cycle (i.e. if the ignition timing is off), the fuel will not ignite at the right time, and this can cause all sorts of problems.

Other Factors

Many other things can go wrong. For example:

  • If the battery is dead, you cannot turn over the engine to start it.
  • If the bearings that allow the crankshaft to turn freely are worn out, the crankshaft cannot turn so the engine cannot run
  • If the valves do not open and close at the right time or at all, air cannot get in and exhaust cannot get out, so the engine cannot run.
  • If someone sticks a potato up your tailpipe, exhaust cannot exit the cylinder so the engine will not run.
  • If you run out of oil, the piston cannot move up and down freely in the cylinder, and the engine will seize.

In a properly running engine, all of these factors are within tolerance. As you can see, an engine has a number of systems that help it do its job of converting fuel into motion. Most of these subsystems can be implemented using different technologies, and better technologies can improve the performance of the engine.

Variable Valve Timing

There are a couple of novel ways by which carmakers vary the valve timing. One system used on some Honda engines is called VTEC. VTEC  (Variable Valve Timing and Lift Electronic Control) is an electronic and mechanical system in some Honda engines that allows the engine to have multiple camshafts. VTEC engines have an extra intake cam with its own rocker, which follows this cam. The profile on this cam keeps the intake valve open longer than the other cam profile. At low engine speeds, this rocker is not connected to any valves. At high engine speeds, a piston locks the extra rocker to the two rockers that control the two intake valves.

Some cars use a device that can advance the valve timing. This does not keep the valves open longer; instead, it opens them later and closes them later. This is done by rotating the camshaft ahead a few degrees. If the intake valves normally open at 10 degrees before top dead center (TDC) and close at 190 degrees after TDC, the total duration is 200 degrees. The opening and closing times can be shifted using a mechanism that rotates the cam ahead a little as it spins. So the valve might open at 10 degrees after TDC and close at 210 degrees after TDC. Closing the valve 20 degrees later is good, but it would be better to be able to increase the duration that the intake valve is open.

Ferrari has a really neat way of doing this. The camshafts on some Ferrari engines are cut with a three-dimensional profile that varies along the length of the cam lobe. At one end of the cam lobe is the least aggressive cam profile, and at the other end is the most aggressive. The shape of the cam smoothly blends these two profiles together. A mechanism can slide the whole camshaft laterally so that the valve engages different parts of the cam. The shaft still spins just like a regular camshaft — but by gradually sliding the camshaft laterally as the engine speed and load increase, the valve timing can be optimized.

Several engine manufacturers are experimenting with systems that would allow infinite variability in valve timing. For example, imagine that each valve had a solenoid on it that could open and close the valve using computer control rather than relying on a camshaft. With this type of system, you would get maximum engine performance at every RPM. Something to look forward to in the future…

Air-intake and Starting Systems

Air-intake System

Most cars are normally aspirated, which means that air flows through an air filter and directly into the cylinders. High-performance engines are either turbocharged or supercharged, which means that air coming into the engine is first pressurized (so that more air/fuel mixture can be squeezed into each cylinder) to increase performance. The amount of pressurization is called boost. A turbocharger uses a small turbine attached to the exhaust pipe to spin a compressing turbine in the incoming air stream. A supercharger is attached directly to the engine to spin the compressor.

When people talk about race cars or high-performance sports cars, the topic of turbochargers usually comes up. Turbochargers also appear on large diesel engines. Jim Autos biggest seller Hilux Vigo comes equipped with a turbocharger. A turbo can significantly boost an engine’s horsepower without significantly increasing its weight, which is the huge benefit that makes turbos so popular!

What Is a Turbocharger?

Turbochargers are a type of forced induction system. They compress the air flowing into the engine. The advantage of compressing the air is that it lets the engine squeeze more air into a cylinder, and more air means that more fuel can be added. Therefore, you get more power from each explosion in each cylinder. A turbocharged engine produces more power overall than the same engine without the charging. This can significantly improve the power-to-weight ratio for the engine. In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds of up to 150,000 rotations per minute (rpm) — that’s about 30 times faster than most car engines can go. And since it is hooked up to the exhaust, the temperatures in the turbine are also very high.

Multiple-Cylinder Engines

The discussion so far has concerned a single-cylinder engine. A single cylinder provides only one power impulse every two crankshaft revolutions in a four-cycle engine. It delivers power only one-fourth of the time. To provide for a more continuous flow of power, modern engines use four, six, eight, or more cylinders. The same series of cycles take place in each cylinder.

In a four-stroke cycle, six-cylinder engine, for example, the cranks on the crankshaft are set 120 degrees apart. The cranks for cylinders 1 and 6, 2 and 5, and 3 and 4 are in line with each other. The cylinders fire or deliver the power strokes in the following order: 1-5-3-6-2-4. Thus, the power strokes follow each other so closely that a continuous and even delivery of power goes to the crankshaft.


In a gasoline engine, the valves must open and close at the proper times with regard to piston position and stroke. In addition, the ignition system must produce the sparks at the proper time so that the power strokes can start. Both valve and ignition system action must be properly timed if good engine performance is to be obtained.

Valve Timing

Valve timing refers to the exact times in the engine cycle that the valves trap the mixture and then allow the burned gases to escape. The valves must open and close so that they are constantly in step with the piston movement of the cylinder they control. The position of the valves is determined by the camshaft; the position of the piston is determined by the crankshaft. Correct valve timing is obtained by providing the proper relationship between the camshaft and the crankshaft.

When the piston is at top dead center, the crankshaft can move 15° to 20° without causing the piston to move up and down any noticeable distance. This is one of the two rock positions of the piston. When the piston moves up on the exhaust stroke, considerable momentum is given to the exhaust gases as they pass out through the exhaust valve port. If the exhaust valve closes at top dead center, a small amount of the gases will be trapped and will dilute the incoming fuel-air mixture when the intake valves open. Since the piston has little downward movement while in the rock position, the exhaust valve can remain open during this period and thereby permit a more complete scavenging of the exhaust gases.

Ignition Timing

Ignition timing refers to the timing of the sparks at the spark plug gap with relation to the piston position during the compression and power strokes. The ignition system is timed so that the sparks occurs before the piston reaches top dead center on the compression stroke. That gives the mixture enough time to ignite and start burning. If this time were not provided, that is, if the spark occurred at or after the piston reached top dead center, then the pressure increase would not keep pace with the piston movement.

At higher speeds, there is still less time for the fuel-air mixture to ignite and bum. To make up for this lack of time and thereby avoid power loss, the ignition system includes an advance mechanism that functions on speed.

Classification Of Engines

Engines for automotive and construction equipment may be classified in several ways: type of fuel used, type of cooling employed, or valve and cylinder arrangement. They all operate on the internal combustion principle. The application of basic principles of construction to particular needs or systems of manufacture has caused certain designs to be recognized as conventional.

The most common method of classification is based on the type of fuel used; that is, whether the engine burns gasoline or diesel fuel.

Gasoline Engines Versus Diesel Engines

Mechanically and in overall appearance, gasoline and diesel engines resemble one another. However, many parts of the diesel engine are designed to be somewhat heavier and stronger to withstand the higher temperatures and pressures the engine generates. The engines differ also in the fuel used, in the method of introducing it into the cylinders, and in how the air-fuel mixture is ignited. In the gasoline engine, we first mix air and fuel in the carburetor. After this mixture is compressed in the cylinders, it is ignited by an electrical spark from the spark plugs. The source of the energy producing the electrical spark may be a storage battery or a high-tension magneto.

The diesel engine has no carburetor. Air alone enters its cylinders, where it is compressed and reaches a high temperature because of compression. The heat of compression ignites the fuel injected into the cylinder and causes the fuel-air mixture to burn. The diesel engine needs no spark plugs; the very contact of the diesel fuel with the hot air in the cylinder causes ignition. In the gasoline engine the heat compression is not enough to ignite the air-fuel mixture; therefore, spark plugs are necessary.

Arrangement Of Cylinders

Engines are also classified according to the arrangement of the cylinders. One classification is the in-line, in which all cylinders are cast in a straight line above the crankshaft, as in most trucks. Another is the V-type, in which two banks of cylinders are mounted in a “V” shape above the crankshaft, as in many passenger vehicles. Another not-so-common arrangement is the horizontally opposed engine whose cylinders mount in two side rows, each opposite a central crankshaft. Buses often have this type of engine.

The cylinders are numbered. The cylinder nearest the front of an in-line engine is numbered 1. The others are numbered 2, 3,4, and so forth, from the front to rear. In V-type engines the numbering sequence varies with the manufacturer.

The firing order (which is different from the numbering order) of the cylinders is usually stamped on the cylinder block or on the manufacturer’s nameplate.

Valve Arrangement

The majority of internal combustion engines also are classified according to the position and arrangement of the intake and exhaust valves. This classification depends on whether the valves are in the cylinder block or in the cylinder head. Various arrangements have been used; the most common are the L-head, I-head, and F-head.  The letter designation is used because the shape of the combustion chamber resembles the form of the letter identifying it.


In the L-head engines, both valves are placed in the block on the same side of the cylinder. The valve-operating mechanism is located directly below the valves, and one camshaft actuates both the intake and exhaust valves.


Engines using the I-head construction are called valve-in-head or overhead valve engines, because the valves mount in a cylinder head above the cylinder. This arrangement requires a tappet, a push rod, and a rocker arm above the cylinder to reverse the direction of the valve movement. Only one camshaft is required for both valves. Some overhead valve engines make use of an overhead camshaft. This arrangement eliminates the long linkage between the camshaft and the valve.


In the F-head engine, the intake valves normally are located in the head, while the exhaust valves are located in the engine block. This arrangement combines, in effect, the L-head and the I-head valve arrangements. The valves in the head are actuated from the camshaft through tappets, push rods, and rocker arms (I-head arrangement), while the valves in the block are actuated directly from the camshaft by tappets (L-head arrangement).

How to Make everything faster

Using all of this information, you can begin to see that there are lots of different ways to make an engine perform better. Car manufacturers are constantly playing with all of the following variables to make an engine more powerful and/or more fuel efficient.

Increase displacement – More displacement means more power because you can burn more gas during each revolution of the engine. You can increase displacement by making the cylinders bigger or by adding more cylinders. Twelve cylinders seems to be the practical limit.

Increase the compression ratio – Higher compression ratios produce more power, up to a point. The more you compress the air/fuel mixture, however, the more likely it is to spontaneously burst into flame (before the spark plug ignites it). Higher-octane gasolines prevent this sort of early combustion. That is why high-performance cars generally need high-octane gasoline — their engines are using higher compression ratios to get more power.

Stuff more into each cylinder – If you can cram more air (and therefore fuel) into a cylinder of a given size, you can get more power from the cylinder (in the same way that you would by increasing the size of the cylinder). Turbochargers and superchargers pressurize the incoming air to effectively cram more air into a cylinder.

Cool the incoming air – Compressing air raises its temperature. However, you would like to have the coolest air possible in the cylinder because the hotter the air is, the less it will expand when combustion takes place. Therefore, many turbocharged and supercharged cars have an intercooler. An intercooler is a special radiator through which the compressed air passes to coofttttttl it off before it enters the cylinder.

Let air come in more easily – As a piston moves down in the intake stroke, air resistance can rob power from the engine. Air resistance can be lessened dramatically by putting two intake valves in each cylinder. Some newer cars are also using polished intake manifolds to eliminate air resistance there. Bigger air filters can also improve air flow.

Let exhaust exit more easily – If air resistance makes it hard for exhaust to exit a cylinder, it robs the engine of power. Air resistance can be lessened by adding a second exhaust valve to each cylinder (a car with two intake and two exhaust valves has four valves per cylinder, which improves performance — when you hear a car ad tell you the car has four cylinders and 16 valves, what the ad is saying is that the engine has four valves per cylinder). If the exhaust pipe is too small or the muffler has a lot of air resistance, this can cause back-pressure, which has the same effect. High-performance exhaust systems use headers, big tail pipes and free-flowing mufflers to eliminate back-pressure in the exhaust system. When you hear that a car has “dual exhaust,” the goal is to improve the flow of exhaust by having two exhaust pipes instead of one.

Make everything lighter – Lightweight parts help the engine perform better. Each time a piston changes direction, it uses up energy to stop the travel in one direction and start it in another. The lighter the piston, the less energy it takes.

Inject the fuel – Fuel injection allows very precise metering of fuel to each cylinder. This improves performance and fuel economy.

Difference between Diesel and Petrol Engine

In a diesel engine, there is no spark plug. Instead, diesel fuel is injected into the cylinder, and the heat and pressure of the compression stroke cause the fuel to ignite. Diesel fuel has a higher energy density than gasoline, so a diesel engine gets better mileage.

Rudolf Diesel developed the idea for the diesel engine and obtained the German patent for it in 1892. His goal was to create an engine with high efficiency. Gasoline engines had been invented in 1876 and, especially at that time, were not very efficient.

The main differences between the gasoline engine and the diesel engine are:

  • A gasoline engine intakes a mixture of gas and air, compresses it and ignites the mixture with a spark. A diesel engine takes in just air, compresses it and then injects fuel into the compressed air. The heat of the compressed air lights the fuel spontaneously.
  • A gasoline engine compresses at a ratio of 8:1 to 12:1, while a diesel engine compresses at a ratio of 14:1 to as high as 25:1. The higher compression ratio of the diesel engine leads to better efficiency.

Gasoline engines generally use either carburetion, in which the air and fuel is mixed long before the air enters the cylinder, or port fuel injection, in which the fuel is injected just prior to the intake stroke (outside the cylinder). Diesel engines use direct fuel injection — the diesel fuel is injected directly into the cylinder.

The diesel engine has no spark plug, it intakes air and compresses it, and it then injects the fuel directly into the combustion chamber (direct injection). It is the heat of the compressed air that lights the fuel in a diesel engine.


The injector on a diesel engine is its most complex component and has been the subject of a great deal of experimentation — in any particular engine it may be located in a variety of places. The injector has to be able to withstand the temperature and pressure inside the cylinder and still deliver the fuel in a fine mist. Getting the mist circulated in the cylinder so that it is evenly distributed is also a problem, so some diesel engines employ special induction valves, pre-combustion chambers or other devices to swirl the air in the combustion chamber or otherwise improve the ignition and combustion process.

One big difference between a diesel engine and a gas engine is in the injection process. Most car engines use port injection or a carburetor rather than direct injection. In a car engine, therefore, all of the fuel is loaded into the cylinder during the intake stroke and then compressed. The compression of the fuel/air mixture limits the compression ratio of the engine — if it compresses the air too much, the fuel/air mixture spontaneously ignites and causes knocking. A diesel compresses only air, so the compression ratio can be much higher. The higher the compression ratio, the more power is generated.

Some diesel engines contain a glow plug of some sort. When a diesel engine is cold, the compression process may not raise the air to a high enough temperature to ignite the fuel. The glow plug is an electrically heated wire (think of the hot wires you see in a toaster) that helps ignite the fuel when the engine is cold so that the engine can start. According to Cley Brotherton, a Journeyman heavy equipment technician:

“All functions in a modern engine are controlled by the ECM communicating with an elaborate set of sensors measuring everything from R.P.M. to engine coolant and oil temperatures and even engine position (i.e. T.D.C.). Glow plugs are rarely used today on larger engines. The ECM senses ambient air temperature and retards the timing of the engine in cold weather so the injector sprays the fuel at a later time. The air in the cylinder is compressed more, creating more heat, which aids in starting.”

Smaller engines and engines that do not have such advanced computer control use glow plugs to solve the cold-starting problem.

If you have ever compared diesel fuel and gasoline, you know that they are different. They certainly smell different. Diesel fuel is heavier and oilier. Diesel fuel evaporates much more slowly than gasoline — its boiling point is actually higher than the boiling point of water. You will often hear diesel fuel referred to as “diesel oil” because it is so oily. Diesel fuel evaporates more slowly because it is heavier. It contains more carbon atoms in longer chains than gasoline does (gasoline is typically C9H20, while diesel fuel is typically C14H30).

It takes less refining to create diesel fuel, which is why it is generally cheaper than gasoline.

Diesel fuel has a higher energy density than gasoline. On average, 1 gallon (3.8 L) of diesel fuel contains approximately 155×106 joules (147,000 BTU), while 1 gallon of gasoline contains 132×106 joules (125,000 BTU). This, combined with the improved efficiency of diesel engines, explains why diesel engines get better mileage than equivalent gasoline engines.

Diesel engines have never really caught on in passenger cars. During the late 1970’s, diesel engines in passenger cars did see a surge in sales because of the OPEC oil embargo (over half a million were sold in the U.S.), but that is the only significant penetration that diesel engines have made in the marketplace.

Even though they are more efficient, there are eight historical problems that have held diesel engines back:

  • Diesel engines, because they have much higher compression ratios (20:1 for a typical diesel vs. 8:1 for a typical gasoline engine), tend to be heavier than an equivalent gasoline engine.
  • Diesel engines also tend to be more expensive.
  • Diesel engines, because of the weight and compression ratio, tend to have lower maximum RPM ranges than gasoline engines. This makes diesel engines high torque rather than high horsepower, and that tends to make diesel cars slow in terms of acceleration.
  • Diesel engines must be fuel injected, and in the past fuel injection was expensive and less reliable
  • Diesel engines tend to produce more smoke and “smell funny”.
  • Diesel engines are harder to start in cold weather, and if they contain glow plugs, diesel engines can require you to wait before starting the engine so the glow plugs can heat up.
  • Diesel engines are much noisier and tend to vibrate.
  • Diesel fuel is less readily available than gasoline

One or two of these disadvantages would be OK, but a group of disadvantages this large is a big deterrent for lots of people. The two things working in favor of diesel engines are better fuel economy and longer engine life. Both of these advantages mean that, over the life of the engine, you will tend to save money with a diesel. However, you also have to take the initial high cost of the engine into account. You have to own and operate a diesel engine for a fairly long time before the fuel economy overcomes the increased purchase price of the engine. The equation works great in a big diesel tractor-trailer rig that is running 400 miles every day, but it is not nearly so beneficial in a passenger car.

As mentioned, the list above contains historical disadvantages for diesel engines. Many of the new diesel engine designs using advanced computer control are eliminating many of these disadvantages — smoke, noise, vibration and cost are all declining. In the future, we are likely to see many more diesel engines on the road.

III. Drivetrain

The rotational force of the engine’s crankshaft turns other shafts and gears that eventually cause the drive wheels to rotate. The various components that link the crankshaft to the drive wheels make up the drivetrain. The major parts of the drivetrain include the transmission, one or more driveshafts, differential gears, and axles.

A. Transmission

The transmission, also known as the gearbox, transfers power from the engine to the driveshaft. As the engine’s crankshaft rotates, combinations of transmission gears pass the energy along to a driveshaft. The driveshaft causes axles to rotate and turn the wheels. By using gears of different sizes, a transmission alters the rotational speed and torque of the engine passed along to the driveshaft. Higher gears permit the car to travel faster, while low gears provide more power for starting a car from a standstill and for climbing hills.

The transmission usually is located just behind the engine, although some automobiles were designed with a transmission mounted on the rear axle. There are three basic transmission types: manual, automatic, and continuously variable.

A manual transmission has a gearbox from which the driver selects specific gears depending on road speed and engine load. Gears are selected with a shift lever located on the floor next to the driver or on the steering column. The driver presses on the clutch to disengage the transmission from the engine to permit a change of gears. The clutch disk attaches to the transmission’s input shaft. It presses against a circular plate attached to the engine’s flywheel. When the driver presses down on the clutch pedal to shift gears, a mechanical lever called a clutch fork and a device called a throwout bearing separate the two disks. Releasing the clutch pedal presses the two disks together, transferring torque from the engine to the transmission.

An automatic transmission selects gears itself according to road conditions and the amount of load on the engine. Instead of a manual clutch, automatic transmissions use a hydraulic torque converter to transfer engine power to the transmission.

Instead of making distinct changes from one gear to the next, a continuously variable transmission uses belts and pulleys to smoothly slide the gear ratio up or down. Continuously variable transmissions appeared on machinery during the 19th century and on a few small-engine automobiles as early as 1900. The transmission keeps the engine running at its most efficient speed by more precisely matching the gear ratio to the situation. Commercial applications have been limited to small engines.

B. Front- and Rear-Wheel Drive

Depending on the vehicle’s design, engine power is transmitted by the transmission to the front wheels, the rear wheels, or to all four wheels. The wheels receiving power are called drive wheels: They propel the vehicle forward or backward. Most automobiles either are front-wheel or rear-wheel drive. In some vehicles, four-wheel drive is an option the driver selects for certain road conditions; others feature full-time, all-wheel drive.

The differential is a gear assembly in an axle that enables each powered wheel to turn at different speeds when the vehicle makes a turn. The driveshaft connects the transmission’s output shaft to a differential gear in the axle. Universal joints at both ends of the driveshaft allow it to rotate as the axles move up and down over the road surface.

In rear-wheel drive, the driveshaft runs under the car to a differential gear at the rear axle. In front-wheel drive, the differential is on the front axle and the connections to the transmission are much shorter. Four-wheel-drive vehicles have drive shafts and differentials for both axles.

IV. Support Systems

Automobiles would deliver jolting rides, especially on unpaved roads, without a system of shock absorbers and other devices to protect the auto body and passenger compartment from severe bumps and bounces.

A. Suspension System

The suspension system, part of the undercarriage of an automobile, contains springs that move up and down to absorb bumps and vibrations. In one type of suspension system, a long tube, or strut, has a shock absorber built into its center section. Shock absorbers control, or dampen, the sudden loading and unloading of suspension springs to reduce wheel bounce and the shock transferred from the road wheels to the body. One shock absorber is installed at each wheel. Modern shock absorbers have a telescoping design and use oil, gas, and air, or a combination to absorb energy.

Luxury sedans generally have a soft suspension for comfortable riding. Sports cars and sport-utility vehicles have firmer suspensions to improve cornering ability and control over rough terrain.

Older automobiles were equipped with one-piece front axles attached to the frame with semi-elliptic leaf springs, much like the arrangement on horse-drawn buggies. Front wheels on modern cars roll independently of each other on half-shafts instead of on a common axle. Each wheel has its own axle and suspension supports, so the shock of one wheel hitting a bump is not transferred across a common axle to the other wheel or the rest of the car. Many rear-axle suspensions for automobiles and heavier vehicles use rigid axles with coil or leaf springs. However, advanced passenger cars, luxury sedans, and sports cars feature independent rear-wheel suspension systems.

Active suspensions are computer-controlled adjustments of the downward force of each wheel as the vehicle corners or rides over uneven terrain. Sensors, a pump, and hydraulic cylinders, all monitored and controlled by computer, enable the vehicle to lean into corners and compensate for the dips and dives that accompany emergency stops and rapid acceleration.

B. Wheels and Tires

Wheels support the vehicle’s weight and transfer torque to the tires from the drivetrain and braking systems. Automobile wheels generally are made of steel or aluminum. Aluminum wheels are lighter, more impact absorbent, and more expensive.

Pneumatic (air-filled) rubber tires, first patented in 1845, fit on the outside rims of the wheels. Tires help smooth out the ride and provide the automobile’s only contact with the road, so traction and strength are primary requirements. Tire treads come in several varieties to match driving conditions.

V. Control Systems

A driver controls the automobile’s motion by keeping the wheels pointed in the desired direction, and by stopping or slowing the speed at which the wheels rotate. These controls are made possible by the steering and braking systems. In addition, the driver controls the vehicle’s speed with the transmission and the gas pedal, which adjusts the amount of fuel fed to the engine.

A. Steering

Automobiles are steered by turning the front wheels, although a few automobile types have all-wheel steering. Most steering systems link the front wheels together by means of a tie-rod. The tie-rod insures that the turning of one wheel is matched by a corresponding turn in the other.

When a driver turns the steering wheel, the mechanical action rotates a steering shaft inside the steering column. Depending on the steering mechanism, gears or other devices convert the rotating motion of the steering wheel into a horizontal force that turns the wheels.

Manual steering relies only on the force exerted by the driver to turn the wheels. Conventional power steering uses hydraulic pressure, operated by the pressure or movement of a liquid, to augment that force, requiring less effort by the driver. Electric power steering uses an electric motor instead of hydraulic pressure.

B. Brakes

Brakes enable the driver to slow or stop the moving vehicle. The first automobile brakes were much like those on horse-drawn wagons. By pulling a lever, the driver pressed a block of wood, leather, or metal, known as the shoe, against the wheel rims. With sufficient pressure, friction between the wheel and the brake shoe caused the vehicle to slow down or stop. Another method was to use a lever to clamp a strap or brake shoes tightly around the driveshaft.

A brake system with shoes that pressed against the inside of a drum fitted to the wheel, called drum brakes, appeared in 1903. Since the drum and wheel rotate together, friction applied by the shoes inside the drum slowed or stopped the wheel. Cotton and leather shoe coverings, or linings, were replaced by asbestos after 1908, greatly extending the life of the brake mechanism. Hydraulically assisted braking was introduced in the 1920s. Disk brakes, in which friction pads clamp down on both sides of a disk attached to the axle, were in use by the 1950s.

An antilock braking system (ABS) uses a computer, sensors, and a hydraulic pump to stop the automobile’s forward motion without locking the wheels and putting the vehicle into a skid. Introduced in the 1980s, ABS helps the driver maintain better control over the car during emergency stops and while braking on slippery surfaces.

Automobiles are also equipped with a hand-operated brake used for emergencies and to securely park the car, especially on uneven terrain. Pulling on a lever or pushing down on a foot pedal sets the brake.

VI. Electrical System

The electrical system consists of a battery and an alternator. The alternator is connected to the engine by a belt and generates electricity to recharge the battery. The battery makes 12-volt power available to everything in the car needing electricity (the ignition system, radio, headlights, windshield wipers, power windows and seats, computers, etc.) through the vehicle’s wiring.

The automobile depends on electricity for fuel ignition, headlights, turn signals, horn, radio, windshield wipers, and other accessories. A battery and an alternator supply electricity. The battery stores electricity for starting the car. The alternator generates electric current while the engine is running, recharging the battery and powering the rest of the car’s electrical needs.

Early automotive electrical systems ran on 6 volts, but 12 volts became standard after World War II (1939-1945) to operate the growing number of electrical accessories. Eventually, 24- or 48-volt systems may become the standard as more computers and electronics are built into automobiles.

The starting system consists of an electric starter motor and a starter solenoid. When you turn the ignition key, the starter motor spins the engine a few revolutions so that the combustion process can start. It takes a powerful motor to spin a cold engine. The starter motor must overcome:

  • All of the internal friction caused by the piston rings
  • The compression pressure of any cylinder(s) that happens to be in the compression stroke
  • The energy needed to open and close valves with the camshaft
  • All of the “other” things directly attached to the engine, like the water pump, oil pump, alternator, etc.

Because so much energy is needed and because a car uses a 12-volt electrical system, hundreds of amps of electricity must flow into the starter motor. The starter solenoid is essentially a large electronic switch that can handle that much current. When you turn the ignition key, it activates the solenoid to power the motor.

A. Ignition System

The ignition system supplies high-voltage current to spark plugs to ignite fuel vapor in the cylinders. There are many variations, but all gasoline-engine ignition systems draw electric current from the battery, significantly increase the current’s voltage, then deliver it to spark plugs that project into the combustion chambers. An electric arc between two electrodes at the bottom of the spark plug ignites the fuel vapor.

In older vehicles, a distributor, which is an electrical switching device, routes high-voltage current to the spark plugs. The distributor’s housing contains a switch called the breaker points. A rotating shaft in the distributor causes the switch to open and close, interrupting the supply of low-voltage current to a transformer called a coil. The coil uses electromagnetic induction to convert interruptions of the 12-volt current into surges of 20,000 volts or more. This high-voltage current passes back to the distributor, which mechanically routes it through wires to spark plugs, producing a spark that ignites the gas vapor in the cylinders. A condenser absorbs excess current and protects the breaker points from damage by the high-voltage surge. The distributor and other devices control the timing of the spark-plug discharges.

In modern ignition systems, the distributor, coil, points, and condenser have been replaced by solid-state electronics controlled by a computer. A computer controls the ignition system and adjusts it to provide maximum efficiency in a variety of driving conditions.

Spark Timing

The ignition system on your car has to work in perfect concert with the rest of the engine. The goal is to ignite the fuel at exactly the right time so that the expanding gases can do the maximum amount of work. If the ignition system fires at the wrong time, power will fall and gas consumption and emissions can increase.

The spark plug fires before the piston reaches top dead center.

When the fuel/air mixture in the cylinder burns, the temperature rises and the fuel is converted to exhaust gas. This transformation causes the pressure in the cylinder to increase dramatically and forces the piston down.


In order to get the most torque and power from the engine, the goal is to maximize the pressure in the cylinder during the power stroke. Maximizing pressure will also produce the best engine efficiency, which translates directly into better mileage. The timing of the spark is critical to success.

There is a small delay from the time of the spark to the time when the fuel/air mixture is all burning and the pressure in the cylinder reaches its maximum. If the spark occurs right when the piston reaches the top of the compression stroke, the piston will have already moved down part of the way into its power stroke before the gases in the cylinder have reached their highest pressures.

To make the best use of the fuel, the spark should occur before the piston reaches the top of the compression stroke, so by the time the piston starts down into its power stroke the pressures are high enough to start producing useful work.

Work = Force * Distance

In a cylinder:

  • Force = Pressure * Area of the piston
  • Distance = Stroke length

So when we’re talking about a cylinder, work = pressure * piston area * stroke length. And because the length of the stroke and the area of the piston are fixed, the only way to maximize work is by increasing pressure. Timing The timing of the spark is important, and the timing can either be advanced or retarded depending on conditions.

The time that the fuel takes to burn is roughly constant. But the speed of the pistons increases as the engine speed increases. This means that the faster the engine goes, the earlier the spark has to occur. This is called spark advance: The faster the engine speed, the more advance is required.

Other goals, like minimizing emissions, take priority when maximum power is not required. For instance, by retarding the spark timing (moving the spark closer to the top of the compression stroke), maximum cylinder pressures and temperatures can be reduced. Lowering temperatures helps reduce the formation of nitrogen oxides (NOx), which are a regulated pollutant. Retarding the timing may also eliminate knocking; some cars that have knock sensors will do this automatically.

Next we’ll go through the components that make the spark. Let’s start with the spark plug.

Spark Plug

The spark plug is quite simple in theory: It forces electricity to arc across a gap, just like a bolt of lightning. The electricity must be at a very high voltage in order to travel across the gap and create a good spark. Voltage at the spark plug can be anywhere from 40,000 to 100,000 volts.

The spark plug is in the center of the four valves in each cylinder.

The spark plug must have an insulated passageway for this high voltage to travel down to the electrode, where it can jump the gap and, from there, be conducted into the engine block and grounded. The plug also has to withstand the extreme heat and pressure inside the cylinder, and must be designed so that deposits from fuel additives do not build up on the plug.

Spark plugs use a ceramic insert to isolate the high voltage at the electrode, ensuring that the spark happens at the tip of the electrode and not anywhere else on the plug; this insert does double-duty by helping to burn off deposits. Ceramic is a fairly poor heat conductor, so the material gets quite hot during operation. This heat helps to burn off deposits from the electrode.

Some cars require a hot plug. This type of plug is designed with a ceramic insert that has a smaller contact area with the metal part of the plug. This reduces the heat transfer from the ceramic, making it run hotter and thus burn away more deposits. Cold plugs are designed with more contact area, so they run cooler.

The carmaker will select the right temperature plug for each car. Some cars with high-performance engines naturally generate more heat, so they need colder plugs. If the spark plug gets too hot, it could ignite the fuel before the spark fires; so it is important to stick with the right type of plug for your car.

The Coil

The coil is the device that generates the high voltages required to create a spark. It is a simple device — essentially a high-voltage transformer made up of two coils of wire. One coil of wire is called the primary coil. Wrapped around it is the secondary coil. The secondary coil normally has hundreds of times more turns of wire than the primary coil.

Current flows from the battery through the primary winding of the coil.

The primary coil’s current can be suddenly disrupted by the breaker points, or by a solid-state device in an electronic ignition.

If you think the coil looks like an electromagnet, you’re right — but it is also an inductor. The key to the coil’s operation is what happens when the circuit is suddenly broken by the points. The magnetic field of the primary coil collapses rapidly. The secondary coil is engulfed by a powerful and changing magnetic field. This field induces a current in the coils — a very high-voltage current (up to 100,000 volts) because of the number of coils in the secondary winding. The secondary coil feeds this voltage to the distributor via a very well insulated, high-voltage wire.

The Distributor

The distributor handles several jobs. Its first job is to distribute the high voltage from the coil to the correct cylinder. This is done by the cap and rotor. The coil is connected to the rotor, which spins inside the cap. The rotor spins past a series of contacts, one contact per cylinder. As the tip of the rotor passes each contact, a high-voltage pulse comes from the coil. The pulse arcs across the small gap between the rotor and the contact (they don’t actually touch) and then continues down the spark-plug wire to the spark plug on the appropriate cylinder. When you do a tune-up, one of the things you replace on your engine is the cap and rotor — these eventually wear out because of the arcing. Also, the spark-plug wires eventually wear out and lose some of their electrical insulation. This can be the cause of some very mysterious engine problems.

Older distributors with breaker points have another section in the bottom half of the distributor — this section does the job of breaking the current to the coil. The ground side of the coil is connected to the breaker points.

A cam in the center of the distributor pushes a lever connected to one of the points. Whenever the cam pushes the lever, it opens the points. This causes the coil to suddenly lose its ground, generating a high-voltage pulse.

The points also control the timing of the spark. They may have a vacuum advance or a centrifugal advance. These mechanisms advance the timing in proportion to engine load or engine speed.

Spark timing is so critical to an engine’s performance that most cars don’t use points. Instead, they use a sensor that tells the engine control unit (ECU) the exact position of the pistons. The engine computer then controls a transistor that opens and closes the current to the coil.

Solid State Ignition

In recent years, you may have heard of cars that need their first tune-up at 100,000 miles. One of the technologies that enables this long maintenance interval is the distributorless ignition.

Instead of one main coil, distributorless ignitions have a coil for each spark plug, located directly on the spark plug itself.

The coil in this type of system works the same way as the larger, centrally-located coils. The engine control unit controls the transistors that break the ground side of the circuit, which generates the spark. This gives the ECU total control over spark timing.

Systems like these have some substantial advantages. First, there is no distributor, which is an item that eventually wears out. Also, there are no high-voltage spark-plug wires, which also wear out. And finally, they allow for more precise control of the spark timing, which can improve efficiency, emissions and increase the overall power of a car.

VII. Safety Features

Manufacturers continue to build lighter vehicles with improved structural rigidity and ability to protect the driver and passengers during collisions.

Bumpers evolved as rails or bars to protect the front and rear of the car’s body from damage in minor collisions. Over the years, bumpers became stylish and, in some cases, not strong enough to survive minor collisions without expensive repairs. Eventually, government regulations required bumpers designed to withstand low-speed collisions with less damage. Some bumpers can withstand 4-km/h (2.5-mph) collisions with no damage, while others can withstand 8-km/h (5-mph) collisions with no damage.

Modern vehicles feature crumple zones, portions of the automobile designed to absorb forces that otherwise would be transmitted to the passenger compartment. Passenger compartments on many vehicles also have reinforced roll bar structures in the roof, in case the vehicle overturns, and protective beams in the doors to help protect passengers from side impacts.

Seat belt and upper-body restraints that relax to permit comfort but tighten automatically during an impact are now common. Some car models are equipped with shoulder-restraint belts that slide into position automatically when the car’s doors close.

An air bag is a high-speed inflation device hidden in the hub of the steering wheel or in the dash on the passenger’s side. Some automobiles have side-impact air bags, located in doors or seats. At impact, the bag inflates almost instantaneously. The inflated bag creates a cushion between the occupant and the vehicle’s interior. Air bags first appeared in the mid-1970s, available as an optional accessory. Today they are installed on all new passenger cars sold in the United States.

Air bags inflate with great force, which occasionally endangers a child or infant passenger. Some newer automobile models are equipped with switches to disable the passenger-side air bags when a child or infant is traveling in the passenger seat. Automakers continue to research ways to make air-bag systems less dangerous for frail and small passengers, yet effective in collisions.

VIII. History

The history of the automobile actually began about 4,000 years ago when the first wheel was used for transportation in India. In the early 15th century the Portuguese arrived in China and the interaction of the two cultures led to a variety of new technologies, including the creation of a wheel that turned under its own power. By the 1600s small steam-powered engine models had been developed, but it was another century before a full-sized engine-powered vehicle was created.

In 1769 French Army officer Captain Nicolas-Joseph Cugnot built what has been called the first automobile. Cugnot’s three-wheeled, steam-powered vehicle carried four persons. Designed to move artillery pieces, it had a top speed of a little more than 3.2 km/h (2 mph) and had to stop every 20 minutes to build up a fresh head of steam.

As early as 1801 successful but very heavy steam automobiles were introduced in England. Laws barred them from public roads and forced their owners to run them like trains on private tracks. In 1802 a steam-powered coach designed by British engineer Richard Trevithick journeyed more than 160 km (100 mi) from Cornwall to London. Steam power caught the attention of other vehicle builders. In 1804 American inventor Oliver Evans built a steam-powered vehicle in Chicago, Illinois. French engineer Onésiphore Pecqueur built one in 1828.

British inventor Walter Handcock built a series of steam carriages in the mid-1830s that were used for the first omnibus service in London. By the mid-1800s England had an extensive network of steam coach lines. Horse-drawn stagecoach companies and the new railroad companies pressured the British Parliament to approve heavy tolls on steam-powered road vehicles. The tolls quickly drove the steam coach operators out of business.

During the early 20th century steam cars were popular in the United States. Most famous was the Stanley Steamer, built by American twin brothers Freelan and Francis Stanley. A Stanley Steamer established a world land speed record in 1906 of 205.44 km/h (121.573 mph). Manufacturers produced about 125 models of steam-powered automobiles, including the Stanley, until 1932.

A Internal-Combustion Engine

Development of lighter steam cars during the 19th century coincided with major developments in engines that ran on gasoline or other fuels. Because the newer engines burned fuel in cylinders inside the engine, they were called internal-combustion engines.

In 1860 French inventor Jean-Joseph-Étienne Lenoir patented a one-cylinder engine that used kerosene for fuel. Two years later, a vehicle powered by Lenoir’s engine reached a top speed of about 6.4 km/h (about 4 mph). In 1864 Austrian inventor Siegfried Marcus built and drove a carriage propelled by a two-cylinder gasoline engine. American George Brayton patented an internal-combustion engine that was displayed at the 1876 Centennial Exhibition in Philadelphia, Pennsylvania.

In 1876 German engineer Nikolaus August Otto built a four-stroke gas engine, the most direct ancestor to today’s automobile engines. In a four-stroke engine the pistons move down to draw fuel vapor into the cylinder during stroke one; in stroke two, the pistons move up to compress the vapor; in stroke three the vapor explodes and the hot gases push the pistons down the cylinders; and in stroke four the pistons move up to push exhaust gases out of the cylinders. Engines with two or more cylinders are designed so combustion occurs in one cylinder after the other instead of in all at once. Two-stroke engines accomplish the same steps, but less efficiently and with more exhaust emissions.

Automobile manufacturing began in earnest in Europe by the late 1880s. German engineer Gottlieb Daimler and German inventor Wilhelm Maybach mounted a gasoline-powered engine onto a bicycle, creating a motorcycle, in 1885. In 1887 they manufactured their first car, which included a steering tiller and a four-speed gearbox. Another German engineer, Karl Benz, produced his first gasoline car in 1886. In 1890 Daimler and Maybach started a successful car manufacturing company, The Daimler Motor Company, which eventually merged with Benz’s manufacturing firm in 1926 to create Daimler-Benz. The joint company makes cars today under the Mercedes-Benz nameplate (see DaimlerChrysler AG).

In France, a company called Panhard-Levassor began making cars in 1894 using Daimler’s patents. Instead of installing the engine under the seats, as other car designers had done, the company introduced the design of a front-mounted engine under the hood. Panhard-Levassor also introduced a clutch and gears, and separate construction of the chassis, or underlying structure of the car, and the car body. The company’s first model was a gasoline-powered buggy steered by a tiller.

French bicycle manufacturer Armand Peugeot saw the Panhard-Levassor car and designed an automobile using a similar Daimler engine. In 1891 this first Peugeot automobile paced a 1,046-km (650-mi) professional bicycle race between Paris and Brest. Other French automobile manufacturers opened shop in the late 1800s, including Renault. In Italy, Fiat (Fabbrica Italiana Automobili di Torino) began building cars in 1899.

American automobile builders were not far behind. Brothers Charles Edgar Duryea and James Frank Duryea built several gas-powered vehicles between 1893 and 1895. The first Duryea, a one-cylinder, four-horsepower model, looked much like a Panhard-Levassor model. In 1893 American industrialist Henry Ford built an internal-combustion engine from plans he saw in a magazine. In 1897 he used an engine to power a vehicle mounted on bicycle wheels and steered by a tiller.

B Early Electric Cars

For a few decades in the 1800s, electric engines enjoyed great popularity because they were quiet and ran at slow speeds that were less likely to scare horses and people. By 1899 an electric car designed and driven by Belgian inventor Camille Jenatzy set a record of 105.8810 km/h (65.79 mph).

Early electric cars featured a large bank of storage batteries under the hood. Heavy cables connected the batteries to a motor between the front and rear axles. Most electric cars had top speeds of 48 km/h (30 mph), but could go only 80 km (50 mi) before their batteries needed recharging. Electric automobiles were manufactured in quantity in the United States until 1930.

IX. Automobiles in the 20th Century

For many years after the introduction of automobiles, three kinds of power sources were in common use: steam engines, gasoline engines, and electric motors. In 1900 more than 2,300 automobiles were registered in New York City; Boston, Massachusetts; and Chicago, Illinois. Of these, 1,170 were steam cars, 800 were electric cars, and only 400 were gasoline cars. Gasoline-powered engines eventually became the nearly universal choice for automobiles because they allowed longer trips and faster speeds than engines powered by steam or electricity.

But development of gasoline cars in the early 1900s was hindered in the United States by legal battles over a patent obtained by New York lawyer George B. Selden. Selden saw a gasoline engine at the Philadelphia Centennial Exposition in 1876. He then designed a similar one and obtained a broad patent that for many years was interpreted to apply to all gasoline engines for automobiles. Although Selden did not manufacture engines or automobiles, he collected royalties from those who did.

Henry Ford believed Selden’s patent was invalid. Selden sued when Ford refused to pay royalties for Ford-manufactured engines. After eight years of court battles, the courts ruled in 1911 that Selden’s patent applied only to two-stroke engines. Ford and most other manufacturers were using four-stroke engines, so Selden could not charge them royalties.

Improvements in the operating and riding qualities of gasoline automobiles developed quickly after 1900. The 1902 Locomobile was the first American car with a four-cylinder, water-cooled, front-mounted gasoline engine, very similar in design to most cars today. Built-in baggage compartments appeared in 1906, along with weather resistant tops and side curtains. An electric self-starter was introduced in 1911 to replace the hand crank used to start the engine turning. Electric headlights were introduced at about the same time.

Most automobiles at the turn of the 20th century appeared more or less like horseless carriages. In 1906 gasoline-powered cars were produced that had a style all their own. In these new models, a hood covered the front-mounted engine. Two kerosene or acetylene lamps mounted to the front served as headlights. Cars had fenders that covered the wheels and step-up platforms called running boards, which helped passengers get in and out of the vehicle. The passenger compartment was behind the engine. Although drivers of horse-drawn vehicles usually sat on the right, automotive steering wheels were on the left in the United States.

In 1903 Henry Ford incorporated the Ford Motor Company, which introduced its first automobile, the Model A, in that same year. It closely resembled the 1903 Cadillac, which was hardly surprising since Ford had designed cars the previous year for the Cadillac Motor Car Company. Ford’s company rolled out new car models each year, and each model was named with a letter of the alphabet. By 1907, when models R and S appeared, Ford’s share of the domestic automobile market had soared to 35 percent.

Ford’s famous Model T debuted in 1908 but was called a 1909 Ford. Ford built 17,771 Model T’s and offered nine body styles. Popularly known as the Tin Lizzy, the Model T became one of the biggest-selling automobiles of all time. Ford sold more than 15 million before stopping production of the model in 1927. The company’s innovative assembly-line method of building the cars was widely adopted in the automobile industry.

By 1920 more than 8 million Americans owned cars. Major reasons for the surge in automobile ownership were Ford’s Model T, the assembly-line method of building it, and the affordability of cars for the ordinary wage earner.

Improvements in engine-powered cars during the 1920s contributed to their popularity: synchromesh transmissions for easier gear shifting; four-wheel hydraulic brake systems; improved carburetors; shatterproof glass; balloon tires; heaters; and mechanically operated windshield wipers.

From 1930 to 1937, automobile engines and bodies became large and luxurious. Many 12- and 16-cylinder cars were built. Independent front suspension, which made the big cars more comfortable, appeared in 1933. Also introduced during the 1930s were stronger, more reliable braking systems, and higher-compression engines, which developed more horsepower. Mercedes introduced the world’s first diesel car in 1936. Automobiles on both sides of the Atlantic were styled with gracious proportions, long hoods, and pontoon-shaped fenders. Creative artistry merged with industrial design to produce appealing, aerodynamic automobiles.

Some of the first vehicles to fully incorporate the fender into the bodywork came along just after World War II, but the majority of designs still had separate fenders with pontoon shapes holding headlight assemblies. Three companies, Ford, Nash, and Hudson Motor Car Company, offered postwar designs that merged fenders into the bodywork. The 1949 Ford was a landmark in this respect, and its new styling was so well accepted the car continued in production virtually unchanged for three years, selling more than 3 million. During the 1940s, sealed-beam headlights, tubeless tires, and the automatic transmission were introduced.

Two schools of styling emerged in the 1950s, one on each side of the Atlantic. The Europeans continued to produce small, light cars weighing less than 1,300 kg (2,800 lb). European sports cars of that era featured hand-fashioned aluminum bodies over a steel chassis and framework.

In America, automobile designers borrowed features for their cars that were normally found on aircraft and ships, including tailfins and portholes. Automobiles were produced that had more space, more power, and smoother riding capability. Introduction of power steering and power brakes made bigger cars easier to handle. The Buick Motor Car Company, Olds Motor Vehicle Company (Oldsmobile), Cadillac Automobile Company, and Ford all built enormous cars, some weighing as much as 2,495 kg (5,500 lb).

The first import by German manufacturer Volkswagen AG, advertised as the Beetle, arrived in the United States in 1949. Only two were sold that year, but American consumers soon began buying the Beetle and other small imports by the thousands. That prompted a downsizing of some American-made vehicles. The first American car called a compact was the Nash Rambler. Introduced in 1950, it did not attract buyers on a large scale until 1958. More compacts, smaller in overall size than a standard car but with virtually the same interior body dimensions, emerged from the factories of many major manufacturers. The first Japanese imports, 16 compact trucks, arrived in the United States in 1956.

In the 1950s new automotive features were introduced, including air conditioning and electrically operated car windows and seat adjusters. Manufacturers changed from the 6-volt to the 12-volt ignition system, which gave better engine performance and more reliable operation of the growing number of electrical accessories.

By 1970 sales of foreign and domestic compacts accounted for about one-third of all passenger cars sold in the United States. American cars were built smaller, but with increased engine size and horsepower. Heating and ventilating systems became standard equipment on even the least expensive models. Automatic transmissions, power brakes, and power steering became widespread. Styling sometimes prevailed over practicality—some cars were built in which the engines had to be lifted to allow simple service operations, like changing the spark plugs. Back seats were designed with no legroom.

In the 1970s American manufacturers continued to offer smaller, lighter models in addition to the bigger sedans that led their product lines, but Japanese and European compacts continued to sell well. Catalytic converters were introduced to help reduce exhaust emissions.

During this period, the auto industry was hurt by the energy crisis, created when the Organization of Petroleum Exporting Countries (OPEC), a cartel of oil-producing countries, cut back on sales to other countries. The price of crude oil skyrocketed, driving up the price of gasoline. Large cars were getting as little as 8 miles per gallon (mpg), while imported compacts were getting as much as 35 mpg. More buyers chose the smaller, more fuel-efficient imports.

Digital speedometers and electronic prompts to service parts of the vehicle appeared in the 1980s. Japanese manufacturers opened plants in the United States. At the same time, sporty cars and family minivans surged in popularity.

Advances in automobile technology in the 1980s included better engine control and the use of innovative types of fuel. In 1981 Bayerische Motoren Werke AG (BMW) introduced an on-board computer to monitor engine performance. A solar-powered vehicle, SunRaycer, traveled 3,000 km (1,864 mi) in Australia in six days.

X. New Technologies

Pollution-control laws adopted at the beginning of the 1990s in some of the United States and in Europe called for automobiles that produced better gas mileage with lower emissions. The California Air Resources Board required companies with the largest market shares to begin selling vehicles that were pollution free—in other words, electric. In 1997 General Motors became the first to begin selling an all-electric car, the EV1, to California buyers. The all-electric cars introduced so far have been limited by low range, long recharges, and weak consumer interest.

Engines that run on hydrogen have been tested. Hydrogen combustion produces only a trace of harmful emissions, no carbon dioxide, and a water-vapor by-product. However, technical problems related to the gas’s density and flammability remain to be solved.

Diesel engines burn fuel more efficiently, and produce fewer pollutants, but they are noisy. Popular in trucks and heavy vehicles, diesel engines are only a small portion of the automobile market. A redesigned, quieter diesel engine introduced by Volkswagen in 1997 may pave the way for more diesels, and less pollution, in passenger cars.

While some developers searched for additional alternatives, others investigated ways to combine electricity with liquid fuels to produce low-emissions power systems. Two automobiles with such hybrid engines, the Toyota Prius and the Honda Insight, became available in the late 1990s. Prius hit automobile showrooms in Japan in 1997, selling 30,000 models in its first two years of production. The Prius became available for sale in North America in 2000. The Honda Insight debuted in North America in late 1999. Both vehicles, known as hybrid electric vehicles (HEVs), promised to double the fuel efficiency of conventional gasoline-powered cars while significantly reducing toxic emissions. The Ford Motor Company introduced the first U.S.-made hybrid when it began production for the Ford Escape Hybrid in August 2004. The 2005 model year Escape was also the first hybrid in the sport-utility vehicle (SUV) category.

Computer control of automobile systems increased dramatically during the 1990s. The central processing unit (CPU) in modern engines manages overall engine performance. Microprocessors regulating other systems share data with the CPU. Computers manage fuel and air mixture ratios, ignition timing, and exhaust-emission levels. They adjust the antilock braking and traction control systems. In many models, computers also control the air conditioning and heating, the sound system, and the information displayed in the vehicle’s dashboard.

Expanded use of computer technology, development of stronger and lighter materials, and research on pollution control will produce better, “smarter” automobiles. In the 1980s the notion that a car would “talk” to its driver was science fiction; by the 1990s it had become reality.

Onboard navigation was one of the new automotive technologies in the 1990s. By using the satellite-aided global positioning system (GPS), a computer in the automobile can pinpoint the vehicle’s location within a few meters. The onboard navigation system uses an electronic compass, digitized maps, and a display screen showing where the vehicle is relative to the destination the driver wants to reach. After being told the destination, the computer locates it and directs the driver to it, offering alternative routes if needed.

Some cars now come equipped with GPS locator beacons, enabling a GPS system operator to locate the vehicle, map its location, and if necessary, direct repair or emergency workers to the scene.

Cars equipped with computers and cellular telephones can link to the Internet to obtain constantly updated traffic reports, weather information, route directions, and other data. Future built-in computer systems may be used to automatically obtain business information over the Internet and manage personal affairs while the vehicle’s owner is driving.

During the 1980s and 1990s, manufacturers trimmed 450 kg (1,000 lb) from the weight of the typical car by making cars smaller. Less weight, coupled with more efficient engines, doubled the gas mileage obtained by the average new car between 1974 and 1995. Further reductions in vehicle size are not practical, so the emphasis has shifted to using lighter materials, such as plastics, aluminum alloys, and carbon composites, in the engine and the rest of the vehicle.

Looking ahead, engineers are devising ways to reduce driver errors and poor driving habits. Systems already exist in some locales to prevent intoxicated drivers from starting their vehicles. The technology may be expanded to new vehicles. Anticollision systems with sensors and warning signals are being developed. In some, the car’s brakes automatically slow the vehicle if it is following another vehicle too closely. New infrared sensors or radar systems may warn drivers when another vehicle is in their “blind spot.”

Catalytic converters work only when they are warm, so most of the pollution they emit occurs in the first few minutes of operation. Engineers are working on ways to keep the converters warm for longer periods between drives, or heat the converters more rapidly.

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