Honda Worldwide | Technology Close-up



	Two types of CBS, Combi Brake (Single CBS) and dual CBS Honda's CBS can be largely classified into two types; Combi brake adopted for scooters, medium sized motorcycles and American custom models and dual CBS used by large sports and large tourers. The main purpose of the two types is the same; to increase the deceleration obtained on appllication of the pedal brake (or the left lever), which was previously relatively lower during the application of the rear wheel brake alone. To achieve the purpose, it was made possible to apply the brakes simultaneously on the front and rear wheels by operation of the pedal (or the left lever). In case of dual CBS, furthermore, it was made possible to apply the brakes simultaneously on the front and rear wheels when the right lever was operated, to reduce nosedive.

Mechanical Combi Brake for small scooters

A number of small scooters are equipped with mechanical drum brakes. The mechanical Combi Brake is a system designed for small scooters. On application of the left lever, the brakes will work simultaneously on the front and rear wheels through the equalizer. On input of low power, however, the front wheel brake efficacy is checked to bring nosedive closer to the former level caused by operation of the left lever. Thanks to the system, a high degree of deceleration is effectively obtained through a single operation of the left lever.

Fluid pressure type Combi Brake for medium-sized models

Fluid pressure type Combi Brakes were developed for large scooters, medium-sized touring bikes and American custom cruisers. Hydraulic pressure created by application of the pedal (or the left lever) is conveyed simultaneously to the front and rear wheel brakes. Similar to mechanical Combi Brakes, they are equipped with delay valves to cut hydraulic pressure to assure no brake will work on the front wheel at input of low power. The hydraulic pressure type Combi Brake is similarly effective to the mechanical Combi Brake; a high degree of deceleration can be effectively obtained by operation of the pedal (or the left lever) only.

Braking force distribution characteristics of combination brakes to front and rear wheels

The above figure shows the braking force distribution characteristics of the Combi Brake of a certain model, to front and rear wheels. The axis of abscissa represents the braking force of the front wheel while the axis of ordinate the braking force of rear wheel. The curve connecting blue points indicates an ideal braking force distribution characteristics in case of a single rider while the same connecting red points the ideal braking force distribution characteristics in case of maximum loading.

The maximum deceleration on a road surface having a friction coefficient occurs immediately before the simultaneous lock of the front and rear wheels. Individual points denote ideal braking force distribution on a road surface µ. Ideal braking force distribution characteristics are obtained by connecting points of ideal braking force distributions of respective friction coefficients. On a road surface with friction coefficient (µ) of 0.2 in case of single rider (green circle), for example, the figure shows that it is better if the braking force on the rear wheel was made larger than the front wheel. In case of 1.0 (yellow circles), on the other hand, it will be better if the distribution on front wheel brake was increased.

The riders will make either higher or lower distribution from the ideal braking force distribution characteristics. Making higher distribution will indicate that braking force distribution on rear wheel is larger while making lower distribution will show the braking force distribution on front wheel is larger.

The dark blue line denotes the braking power distribution characteristics into the front and rear wheel on operation of pedal (or the left lever) of the Combi Brake. Being positioned above the ideal braking force distribution characteristic diagram, the braking force distribution on rear wheel is larger. On operation of the right lever, braking force will take place on the front wheel only so that the distribution will be on the green line of front wheel braking force line.