System Description

SYSTEM DESCRIPTION
HINT:

The skid control ECU is located within the brake actuator assembly.
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: Brake Actuator Assembly - Communication Diagram
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  1. 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: Brake Actuator Assembly - Communication Diagram
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  1. 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.
ABS with EBD OPERATION
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.
FAIL SAFE FUNCTION
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.

FUNCTION OF COMPONENTS

Components	Function
Brake actuator assembly	Composed of the holding solenoid valve, pressure reduction solenoid valve, pump motor, reservoir, etc., and adjusts the brake fluid pressure applied to each wheel cylinder. Houses the skid control ECU.
Skid Control ECU	Calculates brake control in accordance with sensor signals.
Speed sensor	Detects speed of each wheel and inputs the data into the skid control ECU.
Master cylinder	Generates pressure according to pedal effort.
Stop light switch	Illuminates the brake light when the brake pedal is depressed. (Sends brake on signal to the skid control ECU)
Solenoid relay	Supplies power to each solenoid. Housed in the skid control ECU.
Motor relay	Supplies power to the pump motor. Housed in the skid control ECU.
ABS warning light	Comes on to inform the driver that a malfunction in the ABS has occurred. Blinks to output DTC.
BRAKE warning light	Comes on to inform the driver that the parking brake is on when the system is normal or the brake fluid has decreased. Simultaneously comes on with the ABS warning light to inform the driver that both ABS and BED cannot operate.