BRAKE CONTROL SYSTEM

Info Added 2017-04-18


  1. FUNCTION OF MAIN COMPONENTS

    Component Function
    Brake Actuator Assembly Skid Control ECU

    Judges the vehicle driving condition based on the signals from each sensor and switch, and sends the brake control signals to the brake actuator.


    • Detects the operation of the parking brake.

    • Requests steering torque assist during cooperative control with EPS.

    • Requests torque distribution between the front and rear wheels during cooperative control with AWD.*1
    Solenoid Valves

    • The hydraulic circuit has 2 master cylinder cut solenoid valves, 2 reservoir cut solenoid valves, 4 pressure holding solenoid valves and 4 pressure reduction solenoid valves.

    • Change the fluid path based on the signals from the skid control ECU during the operation of the brake control system functions, in order to control the fluid pressure applied to the wheel cylinders.
    Pump Motor Drives the pumps inside the brake actuator.
    Solenoid Relay (Built into Skid Control ECU) Supplies power to the solenoid valves.
    Motor Relay (Built into Skid Control ECU) Supplies power to the pump motor.
    Master Cylinder Pressure Sensor Assembled in the brake actuator, detects the master cylinder pressure.
    Spiral Cable with Sensor Sub-assembly Steering Sensor Detects the steering direction and angle of the steering wheel.
    Airbag Sensor Assembly Yawrate Sensor

    • The airbag sensor assembly incorporates the yawrate sensor and acceleration sensor.

    • The yawrate sensor detects the vehicle's yaw rate.

    • The acceleration sensor detects the vehicle's longitudinal and lateral deceleration.

    • The airbag sensor assembly sends the detection signals from the yawrate sensor and acceleration sensor to the skid control ECU via CAN communication.
    Acceleration Sensor
    Power Steering ECU Assembly Receives the signal of steering torque assist request from the skid control ECU.
    Speed Sensors Detect the wheel speed of each of the 4 wheels.
    Stop Light Switch Assembly Detects the brake pedal depressing signal.
    Brake Pedal Load Sensing Switch Detects the brake pedal depressing signal.
    Brake Master Cylinder Reservoir Sub-assembly Brake Fluid Level Warning Switch Detects the brake fluid level.
    Electric Parking Brake Switch Assembly VSC OFF Switch Enables the driver to select the "Normal Mode", "TRC OFF Mode", or "VSC OFF Mode".
    Brake Hold Switch Switches the brake hold function on and off.
    4WD ECU Assembly*1 Operates in cooperation with the skid control ECU to control the torque distribution between the front and rear wheels.
    Network Gateway ECU Relays and transmits each CAN communication data signal.
    ECM

    • Sends the throttle position signal, accelerator pedal position signal and engine speed signal to the skid control ECU.

    • Based on the signals from the skid control ECU, controls the engine output.
    Combination Meter Assembly ABS Warning Light Each of the lights and buzzers inform the driver of system operations, malfunctions, or control restriction conditions. Also, messages are displayed on the multi-information display in response to system abnormalities and system malfunction.
    Brake Warning Light (Red /Yellow)
    Slip Indicator Light
    VSC OFF Indicator Light
    Brake Hold Operated Indicator Light
    Brake Hold Stand-by Indicator Light
    Multi-information Display
    Buzzer
    Master Warning Light
    Millimeter Wave Radar Sensor Assembly*2 Sends the brake control request signal from the pre-collision safety system to the skid control ECU.
    Engine Stop and Start ECU*3 Receives a brake hold request signal and performs brake hold control.

    *1: AWD models

    *2: Models with Toyota safety sense

    *3: Models with stop and start system

  2. SYSTEM CONTROL


    1. The brake control system has the following system/functions:

      Control Outline
      Anti-lock Brake System (ABS) Helps prevent the wheels from locking when the brakes are applied firmly or when braking on a slippery surface.
      Electronic Brake Force Distribution (EBD) EBD control utilizes ABS, realizing proper brake force distribution between the front and rear wheels in accordance with the driving conditions. In addition, during braking while cornering, it also controls the brake forces of the right and left wheels, helping maintain vehicle stability.
      Brake Assist The primary purpose of brake assist is to provide supplementary brake force to assist a driver who cannot generate a large brake force during emergency braking, thus helping to utilize the vehicle's braking performance.
      Traction Control (TRC) Helps restrain the slippage of the drive wheels if the driver depresses the accelerator pedal excessively when starting off or accelerating on a slippery surface.
      Vehicle Stability Control (VSC) Helps restrain sideways slippage of the vehicle during a strong understeer tendency or strong oversteer tendency while cornering.
      Engine Output Control during TRC or VSC Operation Transmits an engine output control signal from the skid control ECU to the ECM to limit the engine output while the TRC or VSC is being activated.
      Trailer Sway Control If the tongue load is not properly adjusted while towing a trailer, trailer sway may be caused due to crosswinds, bumpy roads, steering operation, etc. Trailer sway control detects sway and regulates the brake of each wheel and the engine output in order to suppress trailer sway.
      Hill-start Assist Control When starting uphill, this control maintains the brake hydraulic pressure to all 4 wheels, in order to momentarily help prevent the vehicle from descending backward.
      Brake Hold As the driver depresses the brake pedal and the vehicle comes to a stop, this function maintains the hydraulic pressure of the 4 wheels in order to keep the vehicle stopped.
      Cooperative Control with EPS Effects cooperative control with the power steering ECU assembly in order to provide steering assist in accordance with the operating conditions of the vehicle.
      Cooperative Control with AWD System*1 This performs cooperative control with the 4WD ECU assembly in order to control the drive torque of the front and rear wheels in accordance with the operating conditions of the vehicle.
      Dynamic Radar Cruise Control Brake*2 When the millimeter wave radar sensor assembly determines that a large amount of deceleration is required based on the distance to the preceding vehicle and the relative vehicle speed during the dynamic radar cruise control system operation, the skid control ECU operates the brake system according to the signal from the ECM.
      Pre-collision Brake*2 When the millimeter wave radar sensor assembly determines that the possibility of a collision is high or an unavoidable collision condition exists, the skid control ECU activates the pre-collision brake assist or the pre-collision brake according to the signal from the millimeter wave radar sensor assembly.

      *1: AWD models

      *2: Models with Toyota Safety Sense

  3. FAIL-SAFE


    1. If a failure occurs in the skid control ECU, sensors, or brake actuator assembly, the system continues performing brake control by excluding the failed area and using only the areas that are operating normally.

  4. DIAGNOSIS


    1. If the skid control ECU detects a malfunction in the brake control system, the warning lights or indicator light illuminate. At the same time, a Diagnostic Trouble Code (DTC) is stored in the memory of the skid control ECU.

    2. This system has a sensor signal check (test mode) function.

    3. For details of DTCs and check function, refer to the Repair Manual.