Ground-Breaking Brakes

GROUND-BREAKING BRAKES

HONDA HAS RELEASED YET another in its series of novel braking systems. Soon to be available on the 1996 ST1100 sport-tourer, it has the giant name “LBS-ABSTCS.” Decoded, this means “Linked Braking System/Antilock Brake System/Traction Control System,” and marries the linked-brake setup of the CBR1000F with the ABS-TCS of the ST1100.

In the Linked Braking System, actuation of the hand brake lever sends fluid to two of the three pistons in each of the front pair of calipers. Reaction torque from one of these calipers in turn drives a submaster cylinder that sends Huid (through a separate circuit) to two of the three pistons in the single rear caliper. Actuating the foot brake pedal sends fluid to the center pistons of all three calipers.

Why link front and rear brakes? Because many riders lack emergency braking technique, using only one or the other brake, or both but in wrong proportion. LBS maximizes total braking by proportioning brake torque to wheel load.

ABS, properly used, prevents over-braking to the point of control loss. TCS is intended to prevent wheelspin during acceleration. or on low-traction surfaces.

ABS works like this: Lach brake circuit has two master cylinders—one rider-controlled, the other (called a modulator) controlled by the ABS computer. If you begin to lock a wheel, the computer, informed by a wheel-speed sensor, causes the modulator to do two basic things: ( 1 ) It closes a valve, sealing the rider’s master cylinder out of the circuit; and (2) it then pulls fluid out of the brake circuit, causing the locking

wheel to release and maintain directional control.

When the computer senses wheel release, it reverses these actions, first raising line pressure back to the rider’s original value, then rejoining the rider’s master cylinder to the brake circuit. If the wheel again begins to lock, the cycle repeats itself many times per second, thereby holding wheel braking at the maximum consistent w ith available traction. Thus, when ABS operates, it alternates rapidly between two states-one in which it samples the rider’s braking demand, and the other in which it prevents that demand from causing wheel locking and loss of control. In normal braking, when no incipient wheel-locking occurs, ABS does nothing and braking is entirely rider-controlled.

Two miniature twin-piston modulators are used in Honda’s new ABS II system, one per wheel. One front modulator piston controls the pressure sent to the hand lever-controlled caliper pistons, while the other controls pressure to the single inner pistons. Likewise, rear modulator action is split betw'een the two brake circuits acting on the rear caliper.

A metering valve delays front-brake application slightly, slowing brake dive. A proportioning valve moderates the rise of rear-brake line pressure as harder braking transfers weight to the front.

A similar system has also been developed, for use on cable-braked scooters and light motorcycles. Honda calls it M.C.-ABS, or Motor-Controlled ABS. Don’t even ask how it works. -Kevin Cameron