Antilock Brakes / Traction Control Systems: Description and Operation

SYSTEM OUTLINE

ABS

1. INPUT SIGNALS

1. Speed sensor signal
The speed of the wheels is detected and input to TERMINALS FL+, FR+, RL+ and RR+ of the brake ECU.

2. Stop light SW signal
A signal is input to TERMINAL STP of the brake ECU when the brake pedal is depressed.

2. ABS SYSTEM OPERATION
During sudden braking the brake ECU has signals input from each sensor, which controls the current to the solenoid inside the actuator and lets the hydraulic pressure acting on each wheel cylinder escape to the reservoir. The pump inside the actuator is also operating at this time and it returns the brake fluid from the reservoir to the master cylinder, thus preventing locking of the vehicle wheels.

If the brake ECU judges that the hydraulic pressure acting on the wheel cylinder is insufficient, the current on the solenoid is controlled and the hydraulic pressure is increased. Holding of the hydraulic pressure is also controlled by the brake ECU, by the same method as above. Pressure reduction, holding and increase are repeated to maintain vehicle stability and to improve steerability during sudden braking.