Antilock Brakes / Traction Control Systems: Description and Operation
BRAKE CONTROL: VEHICLE STABILITY CONTROL SYSTEM: SYSTEM DIAGRAM
Communication table:
SYSTEM DESCRIPTION
1. SYSTEM DESCRIPTION
HINT
The skid control ECU is built into the VSC actuator.
(a) ABS (Anti-lock Brake System)
The ABS helps prevent the wheels from locking when the brakes are applied firmly or on a slippery surface.
(1) Operation description
The skid control ECU detects wheel lock conditions by receiving vehicle speed signals from each speed sensor, and sends control signals to the pump motor and solenoid valve to prevent the wheels from locking by controlling the brake fluid pressure of each wheel cylinder.
The ABS warning light and SLIP indicator light come on when the ABS system malfunctions.
(b) EBD (Electronic Brake Force Distribution)
The EBD control utilizes the ABS, performing proper brake force distribution between the front and rear wheels in accordance with the driving conditions. When the brakes are applied while cornering, it also controls the braking forces of the rear right and rear left wheels, helping to maintain vehicle stability.
(1) Operation description
The skid control ECU receives speed signals from each speed sensor to detect the slip conditions of the wheels and sends control signals to the solenoid.
The solenoid valve controls the brake fluid pressure of each wheel cylinder, and divides the control power properly between the front and rear wheels and the rear right and rear left wheels.
The ABS and BRAKE warning lights and SLIP indicator light come on to indicate malfunctions in the EBD system.
(c) BA (Brake Assist)
The primary purpose of the brake assist system is to provide auxiliary brake force to assist drivers who cannot generate a brake force large enough during emergency braking, thus helping to maximize the vehicle's braking performance.
(1) Operation description
The skid control ECU receives speed signals from each speed sensor and the fluid pressure signal from the master cylinder pressure sensor to determine whether brake assist is necessary. If brake assist is deemed necessary, the skid control ECU sends control signals to the pump motor and solenoid. The pump and the solenoid valve then control the pressure applied to each wheel cylinder. The ABS warning light and the SLIP indicator light come on to indicate malfunctions in the BA system.
(d) Changing of TRAC, AUTO LSD and VSC operation permission / disablement through VSC OFF switch
(1) Changing modes
Through the VSC OFF switch, the vehicle can be changed to normal mode, TRAC OFF mode, AUTO LSD mode and VSC OFF mode.
2WD vehicles and 4WD vehicles in 2H mode
HINT
* o: Illuminated
* -: Not illuminated
4WD vehicles in H4L mode
HINT
* o: Illuminated
* -: Not illuminated
4WD vehicles in L4L mode
HINT
* o: Illuminated
* -: Not illuminated
(2) Drive mode and each function
HINT
* o: Operates
* -: Does not operate
(e) TRAC (Traction Control) (for 2WD vehicles or 4WD vehicles in 2H mode)
The TRAC system helps prevent the drive wheels from slipping if the driver presses down on the accelerator pedal excessively when starting off or accelerating on a slippery surface.
(1) Operation description
The skid control ECU detects the vehicle's slip condition by receiving signals from each speed sensor and the ECM via CAN communication.
The skid control ECU controls engine torque with the ECM via CAN communication and brake fluid pressure through the pump and solenoid valve. The SLIP indicator light blinks when the system is operating. The SLIP indicator light comes on when the TRAC system malfunctions.
(f) VSC (Vehicle Stability Control)
The VSC system helps prevent the vehicle from slipping sideways when front or rear wheel skidding occurs while cornering.
(1) Operation description
The skid control ECU determines the vehicle condition by receiving signals from the speed sensor, yaw rate and deceleration sensor and steering angle sensor. The skid control ECU controls driving torque with the ECM via CAN communication, and brake fluid pressure with the solenoid valve.
The SLIP indicator light blinks when the system is operating. When there is a malfunction in the VSC system, the SLIP indicator light comes on.
The VSC OFF switch stops VSC operation.
(g) A-TRAC (Active Traction Control) (for 4WD)
During rugged off-road driving, this system controls the engine output and the brake fluid pressure that is applied to the slipping wheel and distributes the drive force that would have been lost through the slippage to the remaining wheels in order to achieve an LSD (Limited Slip Differential) effect.
HINT
The A-TRAC system operates when the 4WD control switch is set to 4L or 4H.
(1) Operation description
The SLIP indicator light blinks when the system is operating. The SLIP indicator light comes on to indicate a malfunction in the A-TRAC system.
(h) AUTO LSD (Auto Limited Slip Differential)
For 2WD vehicles and 4WD vehicles in 2H mode, the AUTO LSD will operate with the VSC OFF switch on (approximately 1 second) and the accelerator pedal depressed.
The AUTO LSD system is used to restrain brake pressure and reduce differential movement, thus transmitting drive torque to the other drive wheel to ensure startability under the following conditions:
Wheels run off the road.
Drive wheels slip when starting on a slope with one wheel on snow/ice.
HINT
Depressing the brake pedal cancels control of the AUTO LSD system.
(1) Operation description
The SLIP indicator light blinks and the AUTO LSD indicator light remains on when the system is operating.
The SLIP indicator light comes on to indicate a malfunction in the AUTO LSD system.
When the vehicle is in normal mode and the VSC OFF switch is pressed for 3 seconds or more, AUTO LSD operation becomes possible. During AUTO LSD mode, the combination meter's AUTO LSD indicator light and VSC OFF indicator light illuminate, and TRAC operation is disabled.
When the vehicle speed is more than 50 km/h (31 mph), the vehicle automatically returns to normal mode. When the vehicle speed is 50 km/h (31 mph) or less, the vehicle returns to AUTO LSD mode.
(i) Trailer Sway Control
Trailer sway control is a part of VSC. If the vehicle is towing a trailer with an inappropriate hitch load, trailer sway could be caused by crosswinds, imbalance caused by the load, or the driver's steering. Trailer sway control reduces trailer sway by controlling the engine output and the braking of each wheel.
2. ABS with EBD, BA, TRAC and VSC OPERATION
(a) The skid control ECU calculates vehicle stability tendency based on the signals from the 4 wheel speed sensors, the yaw rate and deceleration sensor and the steering angle sensor. In addition, it evaluates the results of the calculations to determine whether any control actions (control of the engine output torque by electronic throttle control and of the brake fluid pressure by the VSC actuator) should be implemented.
(b) The SLIP indicator light blinks to inform the driver that the VSC system is operating. The SLIP indicator light also blinks when traction control is operating, and the operation being performed is displayed.
3. FAIL-SAFE FUNCTION
(a) When a failure occurs in the ABS with BA, TRAC and VSC systems, the ABS warning light and SLIP indicator light come on, and the operation of those systems is prohibited. In addition to this, when a failure which disables the EBD operation occurs, the BRAKE warning light comes on and EBD operation is prohibited.
(b) If control is prohibited due to a malfunction during operation, control is disabled gradually to avoid sudden vehicle instability.
4. INITIAL CHECK
(a) When the vehicle speed first reaches approximately 23 km/h (14 mph) or more after the ignition switch is turned ON, each solenoid valve and the motor of the VSC actuator are sequentially activated to perform electrical checks. During the initial check, the operating sound of the motor can be heard from the engine compartment, but this does not indicate a malfunction.
5. FUNCTION OF COMPONENTS
