Antilock Brake/Traction Control System
PURPOSEThe Anti-lock Brake System/Traction Control System (ABS/TCS) allows for two-way communication between the following two systems:
1. The ABS consists of electronic and hydraulic components. It allows for control of braking force so that locking of the wheels can be avoided.
The ABS:
1) Ensures proper tracking performance through steering wheel operation.
2) Enables obstacles to be avoided through steering wheel operation.
3) Ensures vehicle stability by preventing flat spins.
2. The TCS is mainly effective for vehicle starting or acceleration on slippery road surfaces. It minimizes drive wheel slipping and enhances vehicle stability. The system helps to reduce the mental stress on the driver during delicate accelerator pedal control.
ABS (ANTI-LOCK BRAKE SYSTEM) OPERATION
- When the vehicle speed is less than 10 km/h (6 MPH) this system does not work.
- The Anti-lock Brake System (ABS) has self-test capabilities. The system turns on the ABS warning lamp for 1 second after turning the ignition switch ON. The system performs another test the first time the vehicle reaches 6 km/h (4 MPH). A mechanical noise may be heard as the ABS performs a self-test. This is a normal part of the self-test feature. If a malfunction is found during this check, the ABS warning lamp will come on.
- During ABS operation, a mechanical noise may be heard. This is a normal condition.
ABS HYDRAULIC CIRCUIT
TRACTION CONTROL SYSTEM (TCS) OPERATION
- This system is designed to limit wheel slip during acceleration by cutting fuel to selected cylinders and changing transmission shift schedule.
The Anti-lock Brake System/Traction Control System (ABS/TCS) control unit monitors wheel speed slips through the ABS wheel sensors and determines the desired torque reduction needed to minimize wheel spin.
The torque reduction by the ABS/TCS control unit may result in a combination of fuel cutoff and change shift timing of the transmission.
The torque reduction is sent from the ABS/TCS control unit through the data link to the Engine Control Module (ECM) and Transmission Control Module (TCM). The ECM will cut off fuel and/or TCM change shift schedule to achieve torque reduction.
The TCS will be enabled when the TCS switch is in the ON position (TCS OFF indicator not illuminated), and if the catalytic converter temperature is within normal operating range.
- This system has a self-diagnostic function. When the ignition switch is initially turned "ON", the SLIP indicator lamp and TCS OFF indicator lamp light. If there is no problem with the ABS and TCS, both indicator lamps will go out as soon as the engine starts.
- The TCS OFF switch cancels the TCS function. The TCS OFF indicator lamp then lights to indicate that the TCS is not operating.
- This system utilizes a fuel-cut function to control drive torque. If fuel cut continues for an extended period of time during high-speed operations, the catalyst may melt and deteriorate. During continued TCS operations, the system will sometimes suspend the drive torque control function, preventing catalyst melting and deterioration.
SYSTEM COMPONENTS
SYSTEM DESCRIPTION
Sensor
The sensor unit consists of a gear-shaped sensor rotor and a sensor element. The element contains a bar magnet around which a coil is wound. The sensor is installed on the back side of the brake rotor. Sine-wave current is generated by the sensor as the wheel rotates. The frequency and voltage increase(s) as the rotating speed increases.
Control Unit
ABS Function
The control unit computes the wheel rotating speed by the signal current sent from the sensor. Then it supplies a DC current to the actuator solenoid valve. It also controls ON-OFF operation of the valve relay and motor relay. If any electrical malfunction should be detected in the system, the Anti-lock Brake System (ABS) warning lamp is turned on. In this condition, the ABS will be deactivated, and the vehicle's brake system reverts to normal operation.
TCS function
Drive wheel slippage is detected by the 4-wheel rotating speed signal. When the wheel slip becomes excessive, the Traction Control System (TCS) operates, causing the SLIP indicator lamp to flash. And, at the same time, a fuel-cut signal to be sent to the Engine Control Module (ECM) and a signal requiring a change in the shift schedule is sent to the Transmission Control Module (TCM). When the TCS OFF switch is used to cancel TCS function, the TCS OFF indicator lamp will light. (TCS does not activate.) In case of a malfunction in the TCS, both the SLIP indicator lamp and the TCS OFF indicator lamp will light, while shutting down the TCS system operation. The vehicle will operate in the same way as a vehicle not equipped with the TCS.
Actuator
The actuator contains:
- An electric motor and pump
- Two relays
- Eight solenoid valves, each inlet and outlet for:
- LH front
- RH front
- LH rear
- RH rear
These components control the hydraulic circuit. The Anti-lock Brake System (ABS) control unit directs the actuator to increase, hold or decrease hydraulic pressure to all or individual wheels.
ABS Actuator Operation