Dual CBS for large sports tourers

Honda has further advanced Combi Brake, which will work simultaneously on the front and rear wheels by operation of the pedal (left lever) only, to develop dual CBS for application to much larger sports models. Based on the front double disk brake and rear disk brake, this not only brakes the front and rear wheels at the same time by applying the pedal, but also applies braking force on the rear wheel when the right lever is operated. The dual CBS enabled to efficiently decelerate and reduce nosedive.

Mechanism of dual CBS

In the dual CBS, the hydraulic pressure generated on operation of the right lever will act on the pistons on both ends of “three-pot” calipers on the left and right of the front. The braking force generated then will move the calipers on the left to generate new hydraulic pressure on the secondary master cylinder.

The hydraulic pressure will act on the pistons on both ends of three-pot calipers through the proportional control valve, PCV, having the function of pressure reduction, to general braking force on the rear wheel. Furthermore, the hydraulic pressure generated by operation of the pedal will act on the piston in the middle of three-pot calipers in the fore and aft. Similarly to the lever brake, the braking force generated on the front calipers on the left will generate hydraulic pressure in the secondary master cylinder, which will act on the pistons on both ends of the rear calipers. As the result, braking force higher than the time of lever operation will be generated on the rear wheel since all three pistons of the calipers are actuated.

Because of these mechanisms, the dual CBS turns out to be CBS also when the lever is operated unlike the case of Combi Brake. In addition to it, distribution characteristics different from the time of operating pedal will be obtained.

Braking force distribution characteristics of dual CBS

The above figure shows the braking force distribution characteristics of dual CBS. The characteristics of pedal brake lies on the ideal braking force distribution characteristic diagram at the time of maximum loading, similarly to the case of Combi Brake.

The characteristics at the time of using the right lever brake, on the other hand, exist on the underside along the ideal braking force distribution characteristics in case of a single rider, which indicates the braking force is distributed rather largely on the front wheel. As the braking force on the front wheel is increased, the braking force on the rear wheel increases at first, then goes down after passing the peak. Such unique distribution characteristics are obtained from the characteristics of PCV exclusively of motorcycles with the function of pressure reduction.

When both the pedal and lever are used, the distribution is in the region lying between the two braking force distribution characteristics, depending on the manner of distribution. This will make it easy to obtain a distribution closer to the ideal braking force distribution.

The above figure compares the deceleration generated by combination of operation of the lever and pedal on completed vehicles between the one equipped with conventional brake and that equipped with dual CBS. The directional axis diagonally to the right (blue) indicates lever input while the directional axis diagonally to the left (red) shows pedal input and the direction along the axis of ordinate (yellow) represents the deceleration generated by combination of respective inputs.

The figure on the left shows the deceleration generated by the combined operation of lever and pedal in the conventional brake system. It can be seen that both of the values of input and generated deceleration are low in the single operation by pedal input while high deceleration generated by the combination with lever input takes place in a partly limited input distribution area surrounded by green.

The figure on the right shows the deceleration generated by dual CBS. It can be seen that the operation of pedal alone enables to yield high input and high deceleration and that the area in which high deceleration can be generated is expanded. This means that riders can generate high deceleration much more easily.