BRAKE CONTROL SYSTEM


  1. OUTLINE


    1. The brake actuator and the skid control ECU have been integrated and a hydraulic brake booster is provided, thus optimizing the hydraulic circuit and offering a weight reduction.

    2. Brake control functions (ABS with EBD, Brake Assist, TRC, VSC and Hill-start Assist Control) are provided.

    3. An electronically controlled brake system is used to control the hydraulic pressure at the 4 wheels.

    4. A regenerative brake cooperative control is used.

    5. A VSC OFF switch is provided.

    6. An emergency brake signal is used. This signal is provided to indicate that strong braking is being performed by the driver.

  2. PRECAUTION


    1. When the brake control system is activated, the brake pedal may shudder, which is a normal occurrence of the system in operation and should not be considered a malfunction.

    2. The TRC and VSC functions control brake hydraulic pressure and motive force to ensure vehicle stability. Therefore, operate the VSC OFF switch (stop the operation of the TRC and VSC functions) only when it is necessary.

  3. MAIN FEATURES


    1. Electronically Controlled Brake System


      1. In this system, the conventional brake booster portion has been discontinued. Instead, it consists of a hydraulic brake booster, brake actuator and brake booster pump assembly.

      2. During normal braking, fluid pressure generated by the hydraulic brake booster does not directly actuate the wheel cylinders, but serves as a hydraulic pressure signal. Instead, the actual control pressure is obtained by regulating the fluid pressure of the brake booster pump assembly, which actuates the wheel cylinders.

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      3. When the skid control ECU detects a fault in the system, brake force can be ensured by applying the brake using the fluid pressure boosted by the hydraulic brake booster.

    2. Regenerative Brake Cooperative Control


      1. Regenerative braking consists of a resistance force that is generated at the rotational axle in the reverse direction of the rotation of the generator (MG2) that is generating electricity. The greater the generated amperage (battery charging amperage), the greater the resistance force will be.

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        Text in Illustration
        *1 MG1 *2 Inverter
        *3 Engine *4 MG2
        *a Rotating direction to electricity generation *b Resistance
        *c Brake Force - -

      2. The drive wheels and MG2 are joined mechanically. When the drive wheels rotate MG2 and cause it to operate as a generator, a regenerative brake force of MG2 is transmitted to the drive wheels. Based on the signals from the skid control ECU, this force is controlled by the hybrid system, which controls the generation of electricity.

      3. The regenerative brake cooperative control does not rely solely on the braking force of the hydraulic brake system to supply the brake force required by the driver. Instead, by effecting cooperative control with the hybrid system, this control provides a joint braking force provided by the regenerative braking and the hydraulic braking. As a result, this control minimizes the loss of the kinetic energy associated with the normal hydraulic braking, and recovers this energy by converting it into electrical energy.

      4. The apportioning of the brake force between the hydraulic braking and the regenerative braking varies by the vehicle speed and braking time.

      5. The apportioning of the brake force between the hydraulic braking and the regenerative braking is accomplished by controlling the hydraulic braking so that the total brake force of the hydraulic braking and the regenerative braking matches the brake force required by the driver.

      6. If the regenerative braking becomes inoperative due to a malfunction in the hybrid system, the brake system disables cooperative control so that the entire brake force required by the driver is supplied by the hydraulic brake system.

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    3. VSC


      1. previous models, the brake control functions (ABS, TRC, VSC) and the EPS (Electronic Power Steering) were controlled individually. In contrast, new models use the VSC, which uses cooperative control with the EPS. This system effects the controls integrated with the brake control functions and the EPS in accordance with driving conditions. Thus, it realizes dynamic performance of the vehicle's ability to "run, turn and stop" and ensures excellent driving stability and drivability.

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