Anti-Lock/Traction Control: Description
The Anti-Lock Brake System (ABS) limits wheel slip automatically during braking thereby maintaining vehicle stability.
Anti-Lock Brake System (ABS) consists of a hydraulic unit with 4 solenoid switching valves, 4 speed sensors, an Electronic Control Unit (ECU), relays and wiring harness. See Fig 1 .
An ANTI-LOCK indicator light, located on the instrument panel, lights up when the ignition is turned on. This indicator light goes out once engine is started, indicating ABS is ready for operation.
The ABS activates at speeds greater than 8 MPH. When vehicle speed is greater than 3 MPH, the built-in electronic test monitor will start checking the ABS. If a fault is found, the warning light will come on. When the ABS light is on, the ABS is switched off. The vehicle will then convert to conventional braking.
If battery voltage is less than 10.5 volts with the ignition on and test speed is exceeded, the ABS will remain off until the alternator increases voltage output to more than 10.5 volts. The ABS warning light will then go out.
Automatic stability control with traction control (ASC+T) represents a further development of the system. ASC+T adds the feature of braking control at the rear wheels, depending on degree of slippage and road speed. It can brake the spinning wheel and direct torque to the wheel with better traction thereby eliminating the need for a limited-slip differential.
The same principle as ABS is applied to wheel slip when accelerating (wheel spin) by the ASC system. By controlling throttle opening and ignition timing, ASC reduces torque to the driven wheel if excessive wheel slip occurs during acceleration. More effective transmission of power to the road surface is achieved, and lateral forces remain high.
Because an automatic control system can react more quickly and precisely than the driver, active safety is improved with these systems.
As the amount of spin required for optimum propulsion in deep snow, for instance, is very high, the system can be switched off for this operating range.
Whenever the ignition is switched on, the ASC+T system is in operation. The indicator lamp goes off when the engine is started. As soon as the system is activated, for example if the accelerator setting is excessive for the given road conditions, the ASC lamp in the instrument cluster flashes. If the ASC+T system fails or is switched off, the ASC lamp remains on.