BRAKE CONTROL SYSTEM


  1. FUNCTION OF MAIN COMPONENTS

    Component Function
    Brake Actuator Assembly

    • Solenoid Valve

    • Master Cylinder Cut Solenoid Valve

    • Reservoir Cut Solenoid Valve

    		 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 each wheel cylinder.
    Master Cylinder Pressure Sensor Built into the brake actuator, detects the master cylinder pressure assembly.
    Skid Control ECU

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

    • Based on signals from various sensors, outputs the emergency brake signal control signals.
    Motor Relay Supplies power to the pump motor.
    Solenoid Relay Supplies power to the solenoid valves.
    Combination Meter Assembly Brake System Warning Light

    • Illuminates to alert the driver when the skid control ECU detects a malfunction in the EBD.

    • Illuminates to alert the driver when the brake fluid level is low.

    • Illuminates when an abnormal brake booster assembly vacuum warning switch assembly*5 or vacuum sensor assembly*4 value is detected.
    ABS Warning Light Illuminates to alert the driver when the skid control ECU detects a malfunction in the ABS.
    Slip Indicator Light

    • Blinks to inform the driver when the TRC and VSC are operational.

    • Illuminates to alert the driver when the skid control ECU detects a malfunction in the TRC or VSC.
    VSC OFF Indicator Light Illuminates to inform the driver when VSC OFF mode is selected.
    Master Warning Light Illuminates when the warning message is displayed in the multi-information display.
    Multi-information Display

    • Displays an information message when TRC OFF mode is selected.

    • Displays a warning message when the skid control ECU detects a malfunction in the ABS or EBD.
    Combination Switch Assembly VSC OFF Switch Enables the driver to select "Normal Mode", "TRC OFF Mode", or "VSC OFF Mode".
    Air Conditioning Control Assembly Hazard Warning Signal Switch Transmits a hazard warning light on/off request signal to the skid control ECU.
    Brake Pedal Load Sensing Switch Detects the brake pedal load.
    Stop Light Switch Assembly Detects when the brake pedal is depressed.
    Semiconductor PWR Integration ECU Stop Light Control Relay Illuminates or flashes the stop lights in accordance with the signals from the stop light switch assembly and skid control ECU.
    Parking Brake Switch Assembly Detects the parking brake pedal status.
    Speed Sensor Detect the wheel speed of each of the 4 wheels.
    Yawrate Sensor

    • Detects the vehicle's longitudinal and lateral acceleration.

    • Detects the vehicle's yaw rate.
    Steering Sensor Detects the direction and angle of the steering wheel.
    Power Steering ECU Assembly Controls the steering assist torque based on the signals received from the skid control ECU.
    Front Steering Control ECU*1 Controls the turning angle of the front wheels based on the signals received from the skid control ECU.
    Rear Steering Control ECU*1 Controls the turning angle of the rear wheels based on the signals received from the front steering control ECU.
    Absorber Control ECU*2 Controls the damping force based on the signals received from the skid control ECU.
    Driving Support ECU Assembly*3 Makes a request for brake control to the skid control ECU.
    ECM

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

    • Controls the engine output based on the signals received from the skid control ECU.
    Main Body ECU (Multiplex Network Body ECU) Transmits the parking brake switch signal to the skid control ECU.
    Engine Stop and Start ECU*4 Receives a brake hold request signal and performs brake hold control.
    Central Gateway ECU (Network Gateway ECU) Relays data between buses.

    *1: Models with Lexus dynamic handling system

    *2: Models with adaptive variable suspension system

    *3: Models with pre-collision system

    *4: Models with stop and start system

    *5: Models without stop and start system

  2. SYSTEM CONTROL


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

      Control Function
      Anti-lock Brake System (ABS) The 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) The EBD utilizes ABS, achieving proper brake force distribution between the front and rear wheels in accordance with the driving conditions. In addition, during braking while cornering, the EBD also controls the brake force of the right and left wheels, helping maintain vehicle stability.
      Brake Assist

      • The primary purpose of brake assist is to provide an auxiliary brake force to assist a driver who cannot generate a large brake force during emergency braking, thus helping utilize the vehicle's braking performance.

      • If the brake booster malfunctions and the skid control ECU judges that the brake pedal force applied by the driver is not sufficient to ensure adequate braking force, brake assist is used to enhance the braking force.
      Traction Control (TRC) The TRC helps restrain the slippage of the drive wheels if the driver depresses the accelerator pedal excessively when starting off or while accelerating on a slippery surface.
      Vehicle Stability Control (VSC) The VSC helps restrain sideways slippage of the vehicle during a strong front wheel skid or strong rear wheel skid, which may occur while cornering.
      VSC and Cooperative Control with EPS*1 or VSC+*2 This performs cooperative control with the power steering ECU assembly, front steering control ECU*3 and rear steering control ECU*3 in order to provide steering assist in accordance with the operating conditions of the vehicle.
      Hill-start Assist Control When starting uphill, this control maintains the brake hydraulic pressure on all 4 wheels, in order to momentarily prevent the vehicle from descending backward.
      Radar Cruise Control Brake*4 When the driving support ECU 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 driving support ECU assembly.
      Pre-collision Brake*4 When the driving support ECU 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 driving support ECU assembly.
      Emergency Brake Signal In the case of emergency braking, the emergency brake signal flashes the stop lights to alert drivers in following vehicles.

      *1: Models for General countries

      *2: Models for Europe

      *3: Models with Lexus dynamic handling system

      *4: Models with pre-collision system

  3. FAIL-SAFE


    1. If a malfunction occurs in the skid control ECU, sensors, or brake actuator assembly, the system continues performing brake control by excluding the malfunctioning 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 DTC and check function, refer to the Repair Manual.