General System Description
SYSTEM DESCRIPTIONThe Anti-lock Brake System (ABS) works on all four wheels. A combination of wheel speed sensor and Electronic Hydraulic Control Unit (EHCU) can determine when a wheel is about to stop turning and adjust brake pressure to maintain best braking.
This system helps the driver maintain greater control of the vehicle under heavy braking conditions.
NOTE: The Electronic Hydraulic Control Unit (EHCU) comprises the Hydraulic Unit (H/U) and the Coil Integrated Module.
Under normal driving conditions, the Anti-lock Brake System functions the same as a standard power assisted brake system. However, with the detection of wheel lock-up, a slight bump or kick-back will be felt in the brake pedal. This pedal "bump" will be followed by a series of short pedal pulsations which occurs in rapid succession. The brake pedal pulsation will continue until there is no longer a need for the anti-lock function or until the vehicle is stopped. A slight ticking or popping noise may be heard during brake applications when the Anti-lock features is being used.
When the Anti-lock feature is being used, the brake pedal may rise even as the brakes are being applied. This is also normal. Maintaining a constant force on the pedal will provide the shortest stopping distance.
CIRCUIT DESCRIPTION
The circuit consists of the starter switch, stoplight switch (vehicle W/O cruise control), brake switch (vehicle with Cruise control), hydraulic unit, coil integrated module (SIM), wheel speed sensor, G sensor, 4WD indicator, ABS warning light, BRAKE warning light, 4WD control unit, voice relay, and data link connector.
When the service brake is applied while in the running mode, the EHCU (Electronic Hydraulic Control Unit) judges which wheel is about to lock by using the wheel rotation speed signals sent from the wheel speed sensors. And the brake fluid pressure applied to the four wheels is controlled by a hydraulic unit to prevent the wheels from locking.
Based on the wheel rotation speed signals input from the wheel speed sensor, the EHCU sends out signals to the hydraulic unit to increase, maintain or decrease the brake fluid pressure. The hydraulic unit uses these signals to control the fluid pressure which is applied to the calipers of the disc brakes of the front wheels. The system also controls the fluid pressure applied to the rear wheels at the same time.