BRAKE CONTROL SYSTEM(w/ Vacuum Brake Booster)


  1. CONSTRUCTION


    1. The brake actuator assembly consists of the brake actuator portion and skid control ECU.

      B005660C01
      *a Brake Actuator Portion *b Skid Control ECU

    2. The brake actuator portion consists of 2 master cylinder cut solenoid valves, 4 pressure holding solenoid valves, 4 pressure reduction solenoid valves, 2 pumps, 2 reservoirs and a master cylinder pressure sensor.

      B0056IVC01
      *1 Brake Actuator Assembly *2 Master Cylinder Pressure Sensor
      *3 No. 1 Master Cylinder Cut Solenoid Valve *4 No. 2 Master Cylinder Cut Solenoid Valve
      *5 Pressure Holding Solenoid Valve *6 Pump
      *7 Pressure Reduction Solenoid Valve *8 Reservoir
      *a From Master Cylinder *b Rear Brake LH
      *c Rear Brake RH *d Front Brake LH
      *e Front Brake RH - -

  2. OPERATION


    1. ABS and EBD


      1. Based on the signals received from the 4 speed sensors, the skid control ECU calculates the speed of each wheel, and checks the wheel slipping conditions. In accordance with the slipping condition, the skid control ECU controls each solenoid valve in the brake actuator assembly in order to adjust the fluid pressure of each wheel cylinder in the following 3 modes: pressure increase, pressure holding and pressure reduction modes.

        B0056VLC04
        *1 Pressure Holding Solenoid Valve *2 Pressure Reduction Solenoid Valve
        *3 Port A *4 Port B
        *a Pressure Increase Mode *b Pressure Holding Mode
        *c Pressure Reduction Mode *d To Wheel Cylinder
        *e From Wheel Cylinder - -
        Brake Actuator Assembly Operation in ABS and EBD
        Item Pressure Increase Mode Pressure Holding Mode Pressure Reduction Mode
        Pressure Holding Solenoid Valve (Port A) Off (Open) On (Closed) ←
        Pressure Reduction Solenoid Valve (Port B) Off (Closed) ← On (Open)
        Wheel Cylinder Pressure Increases Holds Reduces

    2. Brake Assist


      1. In the event of emergency braking, the skid control ECU determines the driver's intention based on the speed of the pressure increase in the master cylinder determined by the master cylinder pressure sensor signal. If the skid control ECU judges the need for additional brake assist, pressure is generated by the pump in the brake actuator assembly and directed to the wheel cylinder to apply a large amount of fluid pressure.

        B00569DC03
        *a Rear Brake LH *b Rear Brake RH
        *c Front Brake LH *d Front Brake RH
        Brake Actuator Operation in Brake Assist
        Item Brake Assist Not Activated Brake Assist Activated
        Pump Off On
        No. 1 Master Cylinder Cut Solenoid Valve (1) Port (A) Off (Open) On*
        No. 2 Master Cylinder Cut Solenoid Valve (2) Port (B) Off (Open) On*
        Pressure Holding Solenoid Valve (3) Port (C) Off (Open) ←
        (4) Port (D) Off (Open) ←
        (5) Port (E) Off (Open) ←
        (6) Port (F) Off (Open) ←
        Pressure Reduction Solenoid Valve (7) Port (G) Off (Closed) ←
        (8) Port (H) Off (Closed) ←
        (9) Port (I) Off (Closed) ←
        (10) Port (J) Off (Closed) ←

        Tech Tips

        *: The solenoid valve switches the hydraulic pressure between "open" and "closed" in accordance with the operating conditions by adjusting continually.

    3. TRC


      1. The fluid pressure generated by the pump is regulated by the master cylinder cut solenoid valve to the required pressure. Thus, the wheel cylinders of the drive wheels are controlled in the following 3 modes: pressure increase, pressure holding and pressure reduction modes to control the slippage of the drive wheels. Each pressure holding solenoid valve and the pressure reduction solenoid valve is turned on or off in accordance with the ABS and EBD operation patterns.

        B0056AZC02
        *a Rear Brake LH *b Rear Brake RH
        *c Front Brake LH *d Front Brake RH
        Brake Actuator Operation in TRC
        Item TRC Operation
        Not Activated Pressure Increase Mode Pressure Holding Mode Pressure Reduction Mode
        Pump Off On ← ←
        No. 1 Master Cylinder Cut Solenoid Valve (1) Port (A) Off (Open) On* ← ←
        No. 2 Master Cylinder Cut Solenoid Valve (2) Port (B) Off (Open) ← ← ←
        Front Brake Pressure Holding Solenoid Valve (5) Port (E) Off (Open) On (Closed) ← ←
        (6) Port (F) Off (Open) On (Closed) ← ←
        Pressure Reduction Solenoid Valve (9) Port (I) Off (Closed) ← ← ←
        (10) Port (J) Off (Closed) ← ← ←
        Rear Brake Pressure Holding Solenoid Valve (3) Port (C) Off (Open) On* On (Closed) ←
        (4) Port (D) Off (Open) On* On (Closed) ←
        Pressure Reduction Solenoid Valve (7) Port (G) Off (Closed) ← ← On (Open)
        (8) Port (H) Off (Closed) ← ← On (Open)

        Tech Tips

        *: The solenoid valve switches the hydraulic pressure between "open" and "closed" in accordance with the operating conditions by adjusting continually.

    4. VSC


      1. The VSC, by the way of solenoid valves, controls fluid pressure generated by the pump and applies it to the brake wheel cylinder of each wheel in the following 3 modes: pressure increase, pressure holding and pressure reduction modes. As a result, the tendency of front wheel skid or rear wheel skid is controlled.

      2. In front wheel skid restraining control, the brakes of the front wheel on the outer circle of the turn and the rear wheels are applied. Also, depending on whether the brake is on or off and also depending on the condition of the vehicle, there are circumstances in which the brake might not be applied to the wheels even if the wheel is targeted for braking. The following diagram shows the hydraulic circuit in pressure increase mode as it controls a front wheel skid condition while the vehicle is making a right turn. In other operating modes, the pressure holding valve and the pressure reduction valve are turned on or off in accordance with the ABS and EBD operation patterns.

        B0056UKC02
        *a Rear Brake LH *b Rear Brake RH
        *c Front Brake LH *d Front Brake RH
        Brake Actuator Operation in VSC (Front Wheel Skid Restraining)
        Item VSC Operation
        Not Activated Pressure Increase Mode Pressure Holding Mode Pressure Reduction Mode
        Pump Off On ← ←
        No. 1 Master Cylinder Cut Solenoid Valve (1) Port (A) Off (Open) On* ← ←
        No. 2 Master Cylinder Cut Solenoid Valve (2) Port (B) Off (Open) On* ← ←
        Front Brake Pressure Holding Solenoid Valve (5) Port (E) Off (Open) On* On (Closed) ←
        (6) Port (F) Off (Open) On (Closed) ← ←
        Pressure Reduction Solenoid Valve (9) Port (I) Off (Closed) ← ← On (Open)
        (10) Port (J) Off (Closed) ← ← ←
        Rear Brake Pressure Holding Solenoid Valve (3) Port (C) Off (Open) On* On (Closed) ←
        (4) Port (D) Off (Open) On* On (Closed) ←
        Pressure Reduction Solenoid Valve (7) Port (G) Off (Closed) ← ← On (Open)
        (8) Port (H) Off (Closed) ← ← On (Open)

        Tech Tips

        *: The solenoid valve switches the hydraulic pressure between "open" and "closed" in accordance with the operating conditions by adjusting continually.

      3. During the rear wheel skid restraining control, the brakes of the front and rear wheels on the outer circle of the turn are applied. Also, depending on whether the brake is on or off and also depending on the condition of the vehicle, there are circumstances in which the brake might not be applied to the wheels even if the wheel is targeted for braking. The following diagram shows the hydraulic circuit in pressure increase mode, as it controls the rear wheel skid condition while the vehicle is making a right turn. In other operating modes, the pressure holding valve and the pressure reduction valve are turned on or off in accordance with the ABS and EBD operation patterns.

        B00564BC02
        *a Rear Brake LH *b Rear Brake RH
        *c Front Brake LH *d Front Brake RH
        Brake Actuator Operation in VSC (Rear Wheel Skid Restraining)
        Item VSC Operation
        Not Activated Pressure Increase Mode Pressure Holding Mode Pressure Reduction Mode
        Pump Off On ← ←
        No. 1 Master Cylinder Cut Solenoid Valve (1) Port (A) Off (Open) On* ← ←
        No. 2 Master Cylinder Cut Solenoid Valve (2) Port (B) Off (Open) On* ← ←
        Front Brake Pressure Holding Solenoid Valve (5) Port (E) Off (Open) On* On (Closed) ←
        (6) Port (F) Off (Open) On (Closed) ← ←
        Pressure Reduction Solenoid Valve (9) Port (I) Off (Closed) ← ← On (Open)
        (10) Port (J) Off (Closed) ← ← ←
        Rear Brake Pressure Holding Solenoid Valve (3) Port (C) Off (Open) On* On (Closed) ←
        (4) Port (D) Off (Open) On (Closed) ← ←
        Pressure Reduction Solenoid Valve (7) Port (G) Off (Closed) ← ← On (Open)
        (8) Port (H) Off (Closed) ← ← ←

        Tech Tips

        *: The solenoid valve switches the hydraulic pressure between "open" and "closed" in accordance with the operating conditions by adjusting continually.

    5. Steering Cooperative Control


      1. The operation of the solenoid valves under the steering cooperative control is the same as the TRC or VSC operation.

    6. Hill-start Assist Control and Brake Hold


      1. Hill-start assist control and brake hold operation are performed by closing the master cylinder cut solenoid valves after the driver operates the brake pedal and leaving a certain amount of hydraulic pressure created by the pump in the wheel cylinder. The diagram below shows the hydraulic circuit in the pressure holding mode.

        B0056WBC03
        *a Rear Brake LH *b Rear Brake RH
        *c Front Brake LH *d Front Brake RH
        Brake Actuator Operation in Hill-start Assist Control and Brake Hold
        Item Hill-start Assist Control and Brake Hold Operation
        Not Activated Pressure Holding Mode Pressure Reduction Mode
        No. 1 Master Cylinder Cut Solenoid Valve (1) Port (A) Off (Open) On (Closed) On (Open)
        No. 2 Master Cylinder Cut Solenoid Valve (2) Port (B) Off (Open) On (Closed) On (Open)
        Front Brake Pressure Holding Solenoid Valve (5) Port (E) Off (Open) ← ←
        (6) Port (F) Off (Open) ← ←
        Pressure Reduction Solenoid Valve (9) Port (I) Off (Closed) ← ←
        (10) Port (J) Off (Closed) ← ←
        Rear Brake Pressure Holding Solenoid Valve (3) Port (C) Off (Open) ← ←
        (4) Port (D) Off (Open) ← ←
        Pressure Reduction Solenoid Valve (7) Port (G) Off (Closed) ← ←
        (8) Port (H) Off (Closed) ← ←