BRAKE CONTROL SYSTEM DETAILS

  1. FUNCTION OF MAIN COMPONENTS

    Component Function
    Combination Meter Assembly Brake System Warning Light (Red Indicator)

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

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

    • Lights up to inform the driver of the electric parking brake system condition.
    ABS Warning Light Lights up 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 or VSC is operational.

    • Lights up to alert the driver when the skid control ECU detects a malfunction in the TRC and/or VSC.
    VSC OFF Indicator Light Lights up to inform the driver when VSC OFF mode is selected.
    Multi-information Display

    • Displays a message to inform the driver when in TRC OFF Mode.

    • Displays a warning message to alert the driver when the skid control ECU detects a malfunction in the brake control function.
    Multi Buzzer Emits a warning sound to alert the driver when the skid control ECU detects a malfunction in the TRC and/or VSC.
    Steering Angle Sensor Detects the direction and angle of the steering wheel.
    Yaw Rate Sensor (Built-in Deceleration Sensor)

    • Detects the vehicle's longitudinal and lateral acceleration.

    • Detects the vehicle's yaw rate.
    Speed Sensor Detects the wheel speed of each of the 4 wheels.
    Stop Light Switch Assembly Detects the brake pedal depressing signal.
    Brake Actuator Assembly 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 applied to the wheel cylinders.
    Motor Relay (Built into Skid Control ECU) Supplies power to the pump motor.
    Solenoid Relay (Built into Skid Control ECU) Supplies power to the solenoid valves.
    Master Cylinder Pressure Sensor Built into the brake actuator, detects the master cylinder pressure.
    VSC OFF Switch Enables the driver to select the Normal Mode, TRC OFF Mode, or VSC OFF Mode.
    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.
    Electric Parking Brake ECU Sends the electric parking brake condition 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.
    Power Steering ECU Assembly Operates cooperatively with the skid control ECU to control the steering assist torque.

  2. SYSTEM CONTROL

    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, achieving 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 driver 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.
    Cooperative Control with Electric Power Steering (EPS) The cooperative control with the power steering ECU provides steering assistance in accordance with the operating conditions of the vehicle.

    1. Anti-lock Brake System (ABS)

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

        A010F6ME01
        Text in Illustration (Illustration Provides Conceptual Image)
        *A Models with ABS *B Models without ABS
        *a Brake Operation - -

    2. Electronic Brake Force Distribution (EBD)

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

        A010FITE01

      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.

        A010FI6E01

    3. Brake Assist

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

        A010FD6E01

    4. 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 makes a request to 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.

        A010FL5E01

    5. Vehicle Stability Control (VSC)

      1. The following are 2 examples that can be considered 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:

        A010FUWE01

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

      3. Whether or not the vehicle is experiencing a 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 target yaw rate (a target yaw rate is determined based on the vehicle speed and steering angle) that should be generated when the driver operates the steering wheel, it means the vehicle is making a turn at a greater angle than the target locus of travel. Thus, the skid control ECU determines that there is a large front wheel skid tendency.

        A010FK7E01

      4. Whether or not the vehicle is experiencing a rear wheel skid 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 is large, and the slip angular velocity is also large, the skid control ECU determines that the vehicle has a large rear wheel skid tendency.

        A010FJPE01

      5. When the skid control ECU determines that the vehicle exhibits a tendency to experience a front wheel skid or a rear wheel skid, it decreases the engine output and applies the brakes of the front or rear wheels 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 rear wheel on the inner circle of the turn in order to help restrain the front wheel skid tendency.

        A010FAZE01

      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. In some cases, the skid control ECU applies the brake of the rear wheels, as necessary.

        A010FANE01

    6. Cooperative Control with Electric Power Steering (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 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.

        A010FEVE01

      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 makes a request to 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.

        A010FUKE01

      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 assist is provided to inform the driver of a front wheel skid (a), and to prevent the driver's excessive turning of the steering wheel (b). In the assist for preventing excessive turning (b), it increases the resistance to counter the driver's steering effort, if the driver turns the steering wheel excessively.

        A010FNCE01

      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 cooperative control with the EPS to provide steering torque assist, which facilitates the driver's steering maneuvers in the appropriate direction to correct the rear wheel skid.

        A010FR1E01

  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 a dirt road, the engine output control is stopped to maintain drive torque.

        A010F9BE01
        Text in Illustration
        *1 VSC OFF Indicator Light *2 VSC OFF Switch
        *3 Multi-information Display - -

      2. The VSC OFF switch can select 3 modes (Normal Mode, TRC OFF Mode, and VSC OFF Mode).

      3. Briefly pressing the VSC OFF switch in Normal Mode selects the TRC OFF Mode.

      4. Pressing and holding the VSC OFF switch for 3 seconds or more with the vehicle stopped selects the VSC OFF Mode, disabling the TRC and VSC functions.

      5. Briefly pressing the VSC OFF switch in the TRC OFF Mode or VSC OFF Mode or turning the ignition switch (engine switch*) off returns to the Normal Mode.

        • *: Models with entry and start system

          A010FP4E01

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

        Item Brake Control Function VSC OFF Indicator Light Multi-information Display
        TRC VSC
        Normal Mode ○ ○ - -
        TRC OFF Mode X ○ - Displays
        VSC OFF Mode X X* Illuminates -

        Tech Tips

        ○: Controllable

        X: Not controllable

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

  4. CONSTRUCTION

    1. Steering Angle Sensor

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

        A010FFA

    2. Yaw Rate Sensor

      1. This sensor has a built-in deceleration sensor.

      2. The yaw rate sensor detects the vehicle's yaw rate.

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

        A010FCQ

    3. Speed Sensor

      1. An active type speed sensor is used. This sensor contains a sensor IC, which consists of 2 Magnetic Resistance Elements (MREs).

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

        A010FQ6E01

    4. Brake Actuator

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

        A010FPDE05
        A010FBQE04
        Component
        (1), (4) Master Cylinder Cut Solenoid Valve
        (2), (3) Reservoir Cut Solenoid Valve
        (5), (6), (7), (8) Pressure Holding Solenoid Valve
        (9), (10), (11), (12) Pressure Reduction Solenoid Valve

  5. OPERATION

    1. Speed Sensor

      1. The active type speed sensor uses a sensor 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 (vehicle speed signal).

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

        A010FW4E01

    2. 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 wheel slipping conditions. In accordance with the slipping condition, the skid control ECU controls each solenoid valve in the brake actuator in order to adjust the fluid pressure of each wheel cylinder in the following 3 modes: pressure reduction, pressure holding, and pressure increase modes.

        A010FRAE01
        Pressure Mode Increase Mode Holding Mode 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

    3. 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 and directed to the wheel cylinder to apply a greater fluid pressure.

        A010F6DE01
        A010FDME04
        Item Brake Assist Not Activated Brake Assist Activated
        Pump Off On
        Master Cylinder Cut Solenoid Valve (1) Port (A) Off (Open) On (Closed)
        (4) Port (D) Off (Open) On (Closed)
        Reservoir Cut Solenoid Valve (2) Port (B) Off (Closed) On (Open)
        (3) Port (C) Off (Closed) On (Open)
        Pressure Holding Solenoid Valve (5) Port (a) Off (Open) Off (Open)
        (6) Port (b) Off (Open) Off (Open)
        (7) Port (c) Off (Open) Off (Open)
        (8) Port (d) Off (Open) Off (Open)
        Pressure Reduction Solenoid Valve (9) Port (e) Off (Closed) Off (Closed)
        (10) Port (f) Off (Closed) Off (Closed)
        (11) Port (g) Off (Closed) Off (Closed)
        (12) Port (h) Off (Closed) Off (Closed)

    4. 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 pressure holding solenoid valve and the pressure reduction solenoid valve are turned on or off in accordance with the ABS and EBD operation patterns.

        A010FG0E01
        A010FSQE04
        Item TRC Operation
        Not Activated Pressure Increase Mode Pressure Holding Mode Pressure Reduction Mode
        Pump Off On On On
        Master Cylinder Cut Solenoid Valve (1) Port (A) Off (Open) On (Closed) On (Closed) On (Closed)
        (4) Port (D) Off (Open) On (Closed) On (Closed) On (Closed)
        Reservoir Cut Solenoid Valve (2) Port (B) Off (Closed) On (Open) On (Open) On (Open)
        (3) Port (C) Off (Closed) On (Open) On (Open) On (Open)
        Front Brake Pressure Holding Solenoid Valve (5) Port (a) Off (Open) Off (Open) On (Closed) On (Closed)
        (8) Port (d) Off (Open) Off (Open) On (Closed) On (Closed)
        Pressure Reduction Solenoid Valve (9) Port (e) Off (Closed) Off (Closed) Off (Closed) On (Open)
        (12) Port (h) Off (Closed) Off (Closed) Off (Closed) On (Open)
        Wheel Cylinder Pressure Right - Increases Holds Reduces
        Left - Increases Holds Reduces
        Rear Brake Pressure Holding Solenoid Valve (6) Port (b) Off (Open) On (Closed) On (Closed) On (Closed)
        (7) Port (c) Off (Open) On (Closed) On (Closed) On (Closed)
        Pressure Reduction Solenoid Valve (10) Port (f) Off (Closed) Off (Closed) Off (Closed) Off (Closed)
        (11) Port (g) Off (Closed) Off (Closed) Off (Closed) Off (Closed)
        Wheel Cylinder Pressure Right - - - -
        Left - - - -

    5. VSC

      1. The VSC, by way of the solenoid valves, controls the fluid pressure 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.

        A010F99E02

      2. In the front wheel skid restraining control, the brake of the front and rear wheels on the inner circle of the turn is 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 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 solenoid valve and the pressure reduction solenoid valve are turned on or off in accordance with the ABS and EBD operation patterns.

        A010FVXE01
        Item VSC Operation
        Not Activated Pressure Increase Mode Pressure Holding Mode Pressure Reduction Mode
        Pump Off On On On
        Master Cylinder Cut Solenoid Valve (1) Port (A) Off (Open) On (Closed) On (Closed) On (Closed)
        (4) Port (D) Off (Open) On (Closed) On (Closed) On (Closed)
        Reservoir Cut Solenoid Valve (2) Port (B) Off (Closed) On (Open) On (Open) On (Open)
        (3) Port (C) Off (Closed) On (Open) On (Open) On (Open)
        Front Brake Pressure Holding Solenoid Valve (5) Port (a) Off (Open) Off (Open) On (Closed) On (Closed)
        (8) Port (d) Off (Open) On (Closed) On (Closed) On (Closed)
        Pressure Reduction Solenoid Valve (9) Port (e) Off (Closed) Off (Closed) Off (Closed) On (Open)
        (12) Port (h) Off (Closed) Off (Closed) Off (Closed) Off (Closed)
        Wheel Cylinder Pressure Right - Increases Holds Reduces
        Left - - - -
        Rear Brake Pressure Holding Solenoid Valve (6) Port (b) Off (Open) On (Closed) On (Closed) On (Closed)
        (7) Port (c) Off (Open) Off (Open) On (Closed) On (Closed)
        Pressure Reduction Solenoid Valve (10) Port (f) Off (Closed) Off (Closed) Off (Closed) Off (Closed)
        (11) Port (g) Off (Closed) Off (Closed) Off (Closed) On (Open)
        Wheel Cylinder Pressure Right - Increases Holds Reduces
        Left - - - -

      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 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 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 solenoid valve and the pressure reduction solenoid valve are turned on or off in accordance with the ABS and EBD operation patterns.

        A010FUBE01
        Item VSC Operation
        Not Activated Pressure Increase Mode Pressure Holding Mode Pressure Reduction Mode
        Pump Off On On On
        Master Cylinder Cut Solenoid Valve (1) Port (A) Off (Open) On (Closed) On (Closed) On (Closed)
        (4) Port (D) Off (Open) On (Closed) On (Closed) On (Closed)
        Reservoir Cut Solenoid Valve (2) Port (B) Off (Closed) On (Open) On (Open) On (Open)
        (3) Port (C) Off (Closed) On (Open) On (Open) On (Open)
        Front Brake Pressure Holding Solenoid Valve (5) Port (a) Off (Open) On (Closed) On (Closed) On (Closed)
        (8) Port (d) Off (Open) Off (Open) On (Closed) On (Closed)
        Pressure Reduction Solenoid Valve (9) Port (e) Off (Closed) Off (Closed) Off (Closed) Off (Closed)
        (12) Port (h) Off (Closed) Off (Closed) Off (Closed) On (Open)
        Wheel Cylinder Pressure Right - - - -
        Left - Increases Holds Reduces
        Rear Brake Pressure Holding Solenoid Valve (6) Port (b) Off (Open) Off (Open) On (Closed) On (Closed)
        (7) Port (c) Off (Open) On (Closed) On (Closed) On (Closed)
        Pressure Reduction Solenoid Valve (10) Port (f) Off (Closed) Off (Closed) Off (Closed) On (Open)
        (11) Port (g) Off (Closed) Off (Closed) Off (Closed) Off (Closed)
        Wheel Cylinder Pressure Right - - - -
        Left - Increases Holds Reduces

    6. Cooperative Control with EPS

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

  6. FAIL-SAFE

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

  7. DIAGNOSIS

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

    2. This system has a speed sensor and a VSC OFF switch check function.

    3. For details of DTC and the check function, refer to the corresponding Repair Manual for this model.