System Description

HINT:

The skid control ECU forms a single unit with the brake actuator.

1. ABS (Anti-lock Brake System)

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

   Fig 1: ABS - System Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   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 comes on when the ABS system malfunctions.

2. EBD (Electronic Brake force Distribution)

   The EBD control utilizes the ABS, realizing the proper brake force distribution between the front and rear wheels in accordance with the driving conditions and vehicle load. In addition, when the brakes are applied while cornering, it also controls the braking forces of the right and left wheels, helping to maintain vehicle stability.

   Fig 2: EBD - System Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   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 right and left wheels. The BRAKE warning light comes on to indicate malfunctions in the EBD system.

1. Based on the signals received from each of the 4 wheel speed sensors, the skid control ECU calculates the speed and deceleration of each wheel, and checks the wheel slippage conditions. The ECU controls the pressure holding valve and pressure reduction valve in order to adjust the brake fluid pressure of each wheel cylinder in accordance with the slippage conditions.

1. When a failure occurs in the ABS system, the ABS warning light comes on and its operation is prohibited. In addition to this, when a failure which disables the EBD operation occurs, the brake warning light comes on and its operation is prohibited.

   If control is prohibited due to a malfunction during operation, control is disabled gradually to avoid sudden vehicle instability.

1. When the vehicle speed first reaches approximately 4 mph (6 km/h) or more after the ignition switch is turned to ON, each solenoid valve and the motor of the brake actuator are sequentially activated to perform electrical checks. During the initial check, the operating sound of the solenoid valve and motor can be heard from the engine compartment, but this does not indicate a malfunction.