Anti-Lock Brakes/Traction Control & VDC: Description
The Anti-Lock Brake System (ABS) prevents wheel lock-up during abrupt braking or when braking on slippery surfaces. The system detects wheel rotation rate and electronically controls fluid pressure applied to brakes. The Traction Control System (TCS) limits wheel spin during acceleration on slippery surfaces by cutting fuel to certain cylinders and changing transmission shift points. It also closes the throttle valve to reduce engine torque. The driver is informed that the system is in operation by a flashing SLIP indicator lamp. In addition to the ABS/TCS function, VDC detects the driver's steering operation amount and brake operation amount from the steering angle sensor and pressure sensor. Using the information from the yaw rate/side G sensor and wheel speed sensors, VDC judges the driving condition (conditions of understeer and oversteer) to improve stability by controlling the brake on 4 wheels and engine output. See Fig 1.
Many electronic control units are used on a vehicle, and each control unit shares information and links with other control units during operation (not independent). Controller Area Network (CAN) is a serial communication line for real time application. It is an on-vehicle multiplex communication line with high data communication speed and excellent error detection ability. In CAN communication, control units are connected with 2 communication lines (CAN H line, CAN L line) allowing a high rate of information transmission with less wiring. Each control unit transmits/receives data but selectively reads required data only. See Fig 2.
When starting the engine, or just after starting the vehicle, the brake pedal may vibrate or the motor operating noise may be heard from the engine compartment. This is normal during the operation check. Depending on road circumstances, the vehicle may have a sluggish feel. This is not abnormal, because the optimum traction has the highest priority by the TCS operation.