BRAKE CONTROL SYSTEM


  1. SYSTEM CONTROL


    1. The following 2 examples can be considered as circumstances in which the tires exceed their lateral grip limit. VSC is designed to help control the vehicle behavior by controlling the engine output and the brakes at each wheel when the vehicle is subject to one of the conditions indicated below.

      A018GK9C01
      *a Front Wheel Skid Tendency *b Rear Wheel Skid Tendency

    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 experiencing understeer 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 understeer tendency.

      A018GQ5C01
      *a Actual Locus of Travel (Actual Yaw Rate) *b Locus of Travel Based on the Target Yaw Rate

    4. Whether or not the vehicle is experiencing oversteer 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 oversteer tendency.

      A018GDUC01
      *a Direction of Travel of the Vehicle's Center of Gravity *b Movement of Vehicle
      B003YTW Slip Angle - -

    5. When the skid control ECU determines that the vehicle exhibits a tendency to experience either understeer or oversteer, it decreases the engine output and applies the brakes of individual wheels to control the vehicle's yaw moment. The basic operation of the VSC functions 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 understeer tendency, it takes countermeasures in accordance with the extent of that tendency. The skid control ECU controls engine output and applies the brakes of both front wheels and the rear wheel on the inside of the turn in order to help restrain the understeer tendency.

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      B003YU9 Brake Force B003YTW Control Moment

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

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      B003YU9 Brake Force B003YTW Control Moment