System Description

HINT:

The skid control ECU is located within the brake actuator assy.

1. ABS

   (Anti-lock Brake System)

   The ABS helps prevent the wheels from locking when the brakes are applied firmly or when braking on a slippery surface.

   Fig 1: ABS System Description Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   Operation description 

   The skid control ECU detects wheel lock condition by receiving vehicle speed signals from each speed sensor, and sends control signals to the pump motor and solenoid valve. The pump motor and solenoid valve avoid wheel lock by controlling the hydraulic pressure of each wheel cylinder.

   The ABS warning light comes on when the ABS system is malfunctioning.

2. EBD

   (Electronic Brake force Distribution)

   The EBD control utilizes ABS, realizing proper brake force distribution between the front and rear wheels in accordance with driving conditions.

   In addition, when braking while cornering, it also controls the brake forces of the right and left wheels, helping to maintain vehicle behavior.

   Fig 2: EBD System Description Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Operation description 

The skid control ECU receives the speed signal from each speed sensor to detect the slip condition of the wheels and sends the control signal to the solenoid.

The solenoid valve controls the hydraulic pressure of each wheel cylinder and splits the control power properly between the front and rear wheels and the right and left wheels.

Both of the ABS and BRAKE warning lights come on to indicate a malfunction in the EBD system.

1. Based on the signals received from the 4 wheel speed sensors, the skid control ECU calculates the speed of each wheel and deceleration, and checks wheel slipping condition. According to the slipping condition, the skid control ECU controls the pressure holding valve and pressure reduction valve in order to adjust the fluid pressure of each wheel cylinder.

1. When a failure occurs in the ABS system, the ABS warning light comes on and operation is prohibited.

   In addition to this, when a failure which disables EBD operation occurs, the brake warning light comes on as well and operation is prohibited (see FAIL-SAFE CHART  ).