BRAKE CONTROL SYSTEM


  1. SYSTEM CONTROL


    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 motive force and the brakes at each wheel when the vehicle is under one of the conditions indicated below.

      A00Z097C03
      *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 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.

      A00Z06OC02
      *a Actual Locus of Travel (Actual Yaw Rate) *b Locus of Travel (Based on the Target Yaw Rate)

    4. Whether the vehicle is in the state of 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.

      A00Z00KC02
      *a Direction of Travel of the Vehicle's Center of Gravity *b Slip Angle
      *c Movement of Vehicle - -

    5. When the skid control ECU determines that the vehicle has a tendency to front wheel skid or rear wheel skid, it decreases the motive force 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 motive force 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.

      A00Z050C01
      *a Making a Right Turn - -
      A00Z06S Brake Force A00Z09X Control Moment

    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.

      A00Z04CC02
      *a Making a Right Turn - -
      A00Z06S Brake Force A00Z09X Control Moment