BRAKE CONTROL SYSTEM DETAILS


  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 sends the brake control signals to the brake actuator.
    Solenoid Valve (10) Changes 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 that is applied to the wheel cylinders.
    Pump Motor Drives the pumps inside the brake actuator.
    Solenoid Relay Supplies power to the solenoid valves.
    Motor Relay Supplies power to the pump motor.
    Motor Failsafe Relay Cuts the power to the motor when the motor relay malfunctions.
    Master Cylinder Pressure Sensor Assembled in the brake actuator, detects the master cylinder pressure.
    Steering Angle Sensor Detects the steering direction and angle of the steering wheel.
    Yaw Rate Sensor Detects the yaw rate and the longitudinal and lateral acceleration and deceleration of the vehicle body.
    Speed Sensors Detect the wheel speed of each of the 4 wheels.
    Stop Light Switch Detects the brake pedal depressing signal.
    Parking Brake Switch Detects when the parking brake lever is pulled up.
    VSC OFF Switch Enables the driver to select the "Normal Mode", "TRC-OFF Mode", or "VSC-OFF Mode".
    Main Body ECU (Multiplex Network Body ECU) Transmits the parking brake switch signal to the skid control ECU.
    ECM

    • Sends the throttle position signal, accelerator pedal position signal engine speed signal, park/neutral position switch signal to the skid control ECU.

    • Based on the signals receives from the skid control ECU, controls the engine output.
    Power Steering ECU Operates cooperatively with the skid control ECU to control the steering assist torque.
    Combination Meter Assembly ABS Warning Light Lights up to alert the driver when the skid control ECU detects a malfunction in the ABS.
    Brake Warning Light

    • Lights up together with ABS warning light to alert the driver when the skid control ECU detects the malfunction not only in the ABS but also in the EBD.

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

    • Lights up to inform the driver when the parking brake lever is pulled up.
    Slip Indicator Light

    • Illuminates to alert the driver if the TRC or VSC system malfunctions.

    • Illuminates to inform the driver of "TRC-OFF mode" or "VSC-OFF mode" being selected.

    • Blinks to inform the driver when the TRC or VSC operates.
    VSC OFF Indicator Light

    • Blinks to alert the driver if the TRC or VSC system malfunctions.

    • Illuminates to inform the driver of "VSC-OFF mode" being selected.
    Multi Buzzer

    • Emits a warning sound to inform the driver during VSC operation.

    • Sounds once when the vehicle reaches a speed of approximately 5 km/h (3 mph) or more while the parking brake is applied.

  2. SYSTEM CONTROL


    1. Control List


      1. The brake control system (ABS with EBD, Brake Assist, TRC, VSC and VSC+) has the following controls:

        Control Outline
        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 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 behavior.
        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 ensure the vehicle's braking performance.
        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 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, such as may occur 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.
        VSC+ (Cooperative Control with EPS) Effects cooperative control with the power steering ECU in order to provide steering assist in accordance with the operating conditions of the vehicle.

    2. Anti-lock Brake System (ABS)


      1. The ABS prevents the wheels from locking during sudden braking or braking on a slippery surface. This provides the proper braking force when the vehicle slips, thus ensuring vehicle stability and excellent braking performance.

        A0116U4E01

    3. Electronic Brake Force Distribution (EBD)


      1. This function controls the brake force that acts on the rear wheels in accordance with the changes in the vehicle conditions such as load factors or deceleration, in order to ensure excellent braking performance.

        A0116EGE01

      2. During cornering braking, this function controls the brake force that acts on the left and right wheels in accordance with the vehicle conditions at that time. This ensures vehicle stability and excellent braking performance.

        A0116FNE01

    4. Brake Assist


      1. In the brake assist, based on the signals from the master cylinder pressure sensor, the skid control ECU calculates the speed and the amount of the brake pedal application and then determines the intention of the driver to make an emergency braking. If the skid control ECU determines that the driver intends the emergency braking, this function activates the brake actuator to increase the brake fluid pressure, which increases the brake force.

        A0116OFE01

    5. Traction Control (TRC)


      1. The TRC helps prevent the drive wheels from slipping if the driver depresses the accelerator pedal excessively when starting off or accelerating on a slippery surface. Simultaneously with the hydraulic brake control of the drive wheels, the skid control ECU requests the ECM to effect engine output control. This produces the drive force that suits the driving conditions, in order to ensure the proper start-off acceleration.

        A0116SXE01

    6. Vehicle Stability Control (VSC)


      1. The followings are two examples that can be considered as circumstances in which the tires exceed their lateral grip limit. The VSC is designed to help control the vehicle behavior by controlling the engine output and the brakes at each wheel when the vehicle is under one of the conditions indicated below.

        A0116JBE01

      2. To determine the condition of the vehicle, sensors detect the steering angle, vehicle speed, vehicle's yaw rate, and the vehicle's lateral acceleration, which are then calculated by the skid control ECU.

      3. Whether or not the vehicle is in the state of front wheel skid is determined by the difference between the target yaw rate and the vehicle's actual yaw rate. When the vehicle's actual yaw rate is smaller than the yaw rate (a target yaw rate that is determined by the vehicle speed and steering angle) that should be rightfully generated when the driver operates the steering wheel, it means the vehicle is making a turn at a greater angle than the locus of travel. Thus, the skid control ECU determines that there is a large tendency to front wheel skid.

        A0116D1E01

      4. Whether the vehicle is in the state of the rear wheel skid or not is determined by the values of the vehicle's slip angle and the vehicle's slip angular velocity (time-dependent changes in the vehicle's slip angle). When the vehicle's slip angle and the slip angular velocity are large, the skid control ECU determines that the vehicle has a large rear wheel skid tendency

        A0116HGE01

      5. When the skid control ECU determines that the vehicle has a tendency to front wheel skid or rear wheel skid, it decreases the engine output and applies the brake of a front or rear wheel to control the vehicle's yaw moment. The basic operation of the VSC is described below. However, the control method differs depending on the vehicle's characteristics and driving conditions.

      6. When the skid control ECU determines that there is a large front wheel skid tendency, it takes countermeasures in accordance with the extent of that tendency. The skid control ECU controls the engine output and applies the brakes of the front wheels and rear wheel of the inner circle of the turn in order to help restrain the front wheel skid tendency.

        A0116DVE01

      7. When the skid control ECU determines that there is a large rear wheel skid tendency, it takes countermeasures in accordance with the extent of that tendency. It applies the brakes of the front and rear wheels of the outer circle of the turn, and generates an outward moment of inertia in the vehicle, in order to restrain the rear wheel skid tendency. Along with the reduction in the vehicle speed caused by the braking force, excellent vehicle stability is ensured.

        A0116M5E01

    7. Engine Output Control during TRC or VSC Operation


      1. During the TRC or VSC operation, the skid control ECU outputs the engine output control signal to the ECM. Upon receiving this signal, the ECM inhibits the engine output.

        A0116SOE01

    8. VSC+ (Cooperative Control with EPS)


      1. If the driver suddenly applies the brakes on a road surface with a considerable difference in friction coefficient between the right and left wheels, the difference in the brake force between the right and left wheels will cause the vehicle posture to become unstable and create a yaw moment. In this state, the skid control ECU controls the ABS and VSC to stabilize the vehicle posture. At the same time, it effects cooperative control with the EPS to provide steering torque assist, which facilitates the driver's steering maneuvers to stabilize the vehicle posture.

        A0116UDE01

      2. If the driver suddenly starts off or accelerates on a road surface with a considerable difference in friction coefficient between the right and left wheels, the slippage of a drive wheel will cause the vehicle posture to become unstable and negatively affect its acceleration performance. In this state, the skid control ECU causes the TRC to control the hydraulic brake of the slipping drive wheel, and requests the ECM to effect engine output control. At the same time, it effects cooperative control with the EPS to provide steering torque assist, which facilitates the driver's steering maneuvers to stabilize the vehicle posture.

        A0116PUE01

      3. When the skid control ECU determines a front wheel skid tendency, it controls the VSC to dampen the front wheel skid. At the same time, it effects the cooperative control with the EPS to provide steering torque assist, which controls the driver's steering maneuvers to stabilize the vehicle posture. Steering torque assists are provided to inform the driver of the front wheel skid, and to prevent the driver's excessive turning of the steering wheel. In the assist for preventing excessive turning, it increases the resistance to counter the driver's steering effort, if the driver turns the steering wheel excessively.

        A0116V6E01

      4. When the skid control ECU determines a rear wheel skid tendency, it controls the VSC to dampen the rear wheel skid. At the same time, it effects the cooperative control with the EPS to provide steering torque assist, which facilitates the driver's steering maneuvers in the direction to correct the rear wheel skid.

        A0116CIE01

  3. FUNCTION


    1. VSC OFF Switch


      1. The operation of the VSC and TRC functions can be stopped by the VSC OFF switch. While the vehicle is running off the shoulder of the road or running on the dirt road, the engine output control is stopped to maintain drive torque.

      2. The VSC OFF switch can select the 3 modes (Normal Mode, TRC-OFF Mode, VSC-OFF Mode). When the VSC OFF switch is pressed briefly, TRC-OFF Mode is entered and the TRC function will be disabled. When the VSC OFF switch is pressed and held for 3 seconds or more, VSC-OFF Mode is entered and the TRC and VSC functions will be disabled.

      3. After the ignition switch is turned off in the TRC-OFF Mode or VSC-OFF Mode, turning the ignition switch on again selects the Normal Mode. The system also enters Normal Mode automatically when the vehicle speed increases.

        A0116VUE01

      4. The operations of the brake control functions in each mode are as follows:

        Item Brake Control Function Slip Indicator Light VSC OFF Indicator Light
        TRC VSC
        Normal Mode ○ ○ - -
        TRC-OFF Mode X ○ Light ON -
        VSC-OFF Mode X X* Light ON Light ON

        • ○: Controllable

        • X: Not Controllable

        Tech Tips

        *: The control is effected during braking or while the yaw rate is large.

  4. CONSTRUCTION


    1. Brake Actuator Assembly


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

      2. The actuator portion regulates the hydraulic brake pressure to each wheel cylinder.

        A0116KRE01

      3. The brake actuator is constructed with the following hydraulic circuit:

        A0116KUE01

    2. Speed Sensor


      1. An active type speed sensor is used. This sensor contains a Hall IC.

      2. The sensor rotor, which consists of N and S poles that are arranged in a circle, is integrated with the hub bearing inner race.

      3. An active type speed sensor uses a Hall IC to detect magnetic field changes caused when the sensor rotor rotates, and the sensor outputs the detected information to the skid control ECU as digital pulses.

      4. To detect the vehicle speed, the frequency of the output pulses is used. Because the active type sensor outputs digital pulses, it can detect vehicle speeds even when the vehicle is nearly stationary.

        A0116S3E01

    3. Yaw Rate Sensor


      1. The yaw rate sensor is built into the acceleration sensor.

      2. The yaw rate sensor detects acceleration in the horizontal forward-backward and left-right directions using the signals from two acceleration sensors, which are fitted at an angle of 45° to the front and back directions of the vehicle body, and transmits signals to the skid control ECU.

        A0116GEE01

        Note

        After replacing the yaw rate sensor, or the skid control ECU, initialization of the yaw rate sensor is required. For the actual procedure, refer to the Repair Manual.

    4. Steering Angle Sensor


      1. The steering angle sensor detects the steering direction and angle, and sends this signal to the skid control ECU.

      2. The steering angle sensor contains two sets of magnetic reluctance elements that detect the rotational movement of a magnet that is built into the detection gear. Thus, the sensor detects the changes that occur in the magnetic reluctance elements along with the rotational movement of the detection gear, in order to detect the rotational movement of the steering wheel.

        A0116MUE01

        Note

        Do not remove the steering angle sensor from the spiral cable. If there is a malfunction in the steering angle sensor, replace the spiral cable with steering angle sensor.

  5. OPERATION


    1. ABS with EBD


      1. Based on the signals received from the 4 speed sensors, the skid control ECU calculates each wheel speed and deceleration, and checks wheel slipping conditions. 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 the each wheel cylinder in the following 3 modes: pressure reduction, pressure holding, and pressure increase modes.

        A0116KZE01
        Not Activated Normal Braking - -
        Activated Increase Mode Holding Mode Reduction Mode
        Pressure Holding Valve (Port A) OFF (Open) ON (Close) ←
        Pressure Reduction Valve (Port B) OFF (Close) ← ON (Open)
        Wheel Cylinder Pressure Increase Hold Reduce

    2. Brake Assist


      1. In the event of emergency braking, the skid control ECU detects 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 and directed to the wheel cylinder to apply a greater fluid pressure than the master cylinder.

        A0116O2E01
        A0116DIE01
        Item Port Not Activated Activated
        Master Cylinder Cut Solenoid Valve (1) (A) OFF (Open) ON*
        (2) (B) OFF (Open) ON*
        Pressure Holding Solenoid Valve (3) (C) OFF (Open) ←
        (4) (D) OFF (Open) ←
        (5) (E) OFF (Open) ←
        (6) (F) OFF (Open) ←
        Pressure Reduction Solenoid Valve (7) (G) OFF (Closed) ←
        (8) (H) OFF (Closed) ←
        (9) (I) OFF (Closed) ←
        (10) (J) OFF (Closed) ←
        Pump OFF ON

        Tech Tips

        *: The solenoid valve controls the hydraulic pressure between "open" and "close" according to the operating condition 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 reduction, pressure holding, and pressure increase modes to control the slippage of the drive wheels. The diagram below shows the hydraulic circuit in the pressure increase mode when the TRC is activated. The pressure holding solenoid valve and the pressure reduction solenoid valve are turned on/off according to the ABS with EBD operation pattern.

        A0116NRE01
        A0116NIE01
        Item Port Not Activated Activated
        Increase Mode Holding Mode Reduction Mode
        Master Cylinder Cut Solenoid Valve (1) (A) OFF (Open) ON* ← ←
        (2) (B) OFF (Open) ON* ← ←
        Front Brake Pressure Holding Solenoid Valve (3) (C) OFF (Open) ← ← ON (Closed)
        (6) (F) OFF (Open) ← ← ON (Closed)
        Pressure Reduction Solenoid Valve (7) (G) OFF (Closed) ← ← ON (Open)
        (10) (J) OFF (Closed) ← ← ON (Open)
        Brake Wheel Cylinder Pressure Right - - Increase Hold Reduce
        Left - - Increase Hold Reduce
        Rear Brake Pressure Holding Solenoid Valve (4) (D) OFF (Closed) ON (Closed) ← ←
        (5) (E) OFF (Closed) ON (Closed) ← ←
        Pressure Reduction Solenoid Valve (8) (H) OFF (Closed) ← ← ←
        (9) (I) OFF (Closed) ← ← ←
        Brake Wheel Cylinder Pressure Right - - - - -
        Left - - - - -
        Pump OFF ON ← ←

        Tech Tips

        *: The solenoid valve controls the hydraulic pressure between "open" and "closed" according to the operating condition by adjusting continually.

    4. VSC


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

        A0116UNE01

      2. In the front wheel skid restraining control, the brake of the wheels of the inner circle of the turn is applied. Also, depending on whether the brake is on or off and 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 diagram below shows the hydraulic circuit in the pressure increase mode, as it controls the front wheel skid condition while the vehicle makes a right turn. In other operating modes, the pressure holding valve and the pressure reduction valve are turned on/off according to the ABS with EBD operation pattern.

        A0116DKE01
        Item Port Not Activated Activated
        Increase Mode Holding Mode Reduction Mode
        Master Cylinder Cut Solenoid Valve (1) (A) OFF (Open) ON* ← ←
        (2) (B) OFF (Open) ON* ← ←
        Front Brake Pressure Holding Solenoid Valve (3) (C) OFF (Open) ← ON (Closed) ←
        (6) (F) OFF (Open) ← ON (Closed) ←
        Pressure Reduction Solenoid Valve (7) (G) OFF (Closed) ← ← ON (Open)
        (10) (J) OFF (Closed) ← ← ON (Open)
        Brake Wheel Cylinder Pressure Right - - Increase Hold Reduce
        Left - - Increase Hold Reduce
        Rear Brake Pressure Holding Solenoid Valve (4) (D) OFF (Open) ON (Closed) ← ←
        (5) (E) OFF (Open) ← ON (Closed) ←
        Pressure Reduction Solenoid Valve (8) (H) OFF (Closed) ← ← ←
        (9) (I) OFF (Closed) ← ← ON (Open)
        Brake Wheel Cylinder Pressure Right - - Increase Hold Reduce
        Left - - - - -
        Pump OFF ON ← ←

        Tech Tips

        *: The solenoid valve controls the hydraulic pressure between "open" and "closed" according to the operating condition by adjusting continually.

      3. In 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 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 diagram below shows the hydraulic circuit in the pressure increase mode, as it controls the rear wheel skid condition while the vehicle makes a right turn. In other operating modes, the pressure holding valve and the pressure reduction valve are turned on/off according to the ABS with EBD operation patterns.

        A0116L2E01
        Item Port Not Activated Activated
        Increase Mode Holding Mode Reduction Mode
        Master Cylinder Cut Solenoid Valve (1) (A) OFF (Open) ON* ← ←
        (2) (B) OFF (Open) ON* ← ←
        Front Brake Pressure Holding Solenoid Valve (3) (C) OFF (Open) ON (Closed) ← ←
        (6) (F) OFF (Open) ← ON (Closed) ←
        Pressure Reduction Solenoid Valve (7) (G) OFF (Closed) ← ← ←
        (10) (J) OFF (Closed) ← ← ON (Open)
        Brake Wheel Cylinder Pressure Right - - - - -
        Left - - Increase Hold Reduce
        Rear Brake Pressure Holding Solenoid Valve (4) (D) OFF (Open) ← ON (Closed) ←
        (5) (E) OFF (Open) ON (Closed) ← ←
        Pressure Reduction Solenoid Valve (8) (H) OFF (Closed) ← ← ON (Open)
        (9) (I) OFF (Closed) ← ← ←
        Brake Wheel Cylinder Pressure Right - - - - -
        Left - - Increase Hold Reduce
        Pump OFF ON ← ←

        Tech Tips

        *: The solenoid valve controls the hydraulic pressure between "open" and "closed" according to the operating condition by adjusting continually.

    5. VSC+ (Cooperative Control with EPS)


      1. The operation of the solenoid valves under the cooperative control with EPS is the same as the brake control functions (ABS, TRC, VSC) operation.

  6. FAIL-SAFE


    1. In the event of a malfunction in the ABS, skid control ECU prohibits the brake control system.

    2. In the event of a malfunction in the EBD, the brake system is operated as long as possible even if the ABS is prohibited. If the EBD control becomes impossible, the brake warning light illuminates to inform the driver of that. In this case, the brake system is operated in the same condition as the brake system without the brake control system.

    3. In the event of a malfunction in the TRC and/or VSC, skid control ECU prohibits the TRC and VSC operation.

    4. If a communication malfunction occurs between the skid control ECU and the steering angle sensor, yaw rate sensor, or ECM, the skid control ECU stops the TRC and VSC.

    5. When the ECM detects the DTC (Diagnostic Trouble Code), it will disable the TRC and VSC.

  7. DIAGNOSIS


    1. If the skid control ECU detects a malfunction in the brake control system (ABS with EBD, brake assist, TRC, VSC and VSC+), then the ABS warning light, brake warning light, VSC OFF indicator light, or slip indicator light illuminate either individually or as a group according to the function in which the malfunction has been detected, to alert the driver of the malfunction.

    2. At the same time, the DTCs (Diagnostic Trouble Codes) are stored in memory.

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

    4. For details of the DTCs that are stored in skid control ECU memory and the DTCs that are output through the sensor signal check functions, see the Repair Manual.