System Outline

If the brake pedal is depressed suddenly, the ABS controls the hydraulic pressure of the brake cylinders on all four of the wheels to automatically prevent the wheels from locking and to ensure the directional and steering stability of the vehicle. Under the situation, the skid control ECU controls the solenoids in the actuators, using the signals from the sensors to move the brake fluid to the reservoir in order to release the braking pressure applied to the wheel cylinders. Also, if the skid control ECU detects that the fluid pressure in the wheel cylinder is insufficient, the ECU controls the solenoids in the actuators to increase the braking pressure.

The skid control ECU with actuator assembly distributes appropriate brake-force to the front and rear wheels (Brake-force distribution control for the front and rear wheels) according to the driving conditions. It also makes effective use of rear wheel brake-force to match the vehicle load when decelerating, resulting in a reduction in the brake pedal force required and ensuring effective braking. When braking during a turn, the ECU controls the brake-force distribution to the right and left wheels (Brake-force distribution control for the right and left wheels) to ensure stability and vehicle braking.

The skid control ECU recognizes emergency braking by assessing the speed at which the brake pedal is being applied and the amount that the brake travels, and controls the braking force to supply a firmer brake-force for the emergency braking.

Unexpected road conditions, emergency situations, and any other external factors may cause a large under- or over-steer of the vehicle. If this occur, the VSC system automatically controls the driving power and wheel brakes to reduce the under- or over-steer.

To reduce a large over-steer :

If the VSC system determines that the over-steer is large, it activates the brakes for the outer turning wheels depending on the degree of the over-steer to produce moment toward the outside of the vehicle and reduce the over-steer.

To reduce a large under-steer :

If the VSC system determines that the under-steer is large, it controls the driving power and activates the front wheel brakes and rear inner side wheel brake to reduce the under-steer.

If there is malfunction in the VSC system, the VSC indicator lights up to warn the driver.

Due to cooperative control with hybrid vehicle control ECU, the skid control ECU controls the hydraulic brake to collect as much electrical energy as possible by making the best use of regenerative brake.

The skid control ECU also improves the stability of the vehicle, performing cooperative control with the power steering ECU to give steering torque assistance, corresponding to driving conditions.

An electric charge is stored in brake control power supply. If the voltage of vehicle electricity declines, the electric charge will be released to cover the electric supply to the system.

The skid control ECU monitors the system component parts electrically. If there is an abnormality in the ECU, sensor signal or actuator, the remaining parts without an abnormality will continue the braking operation.

Even if the ABS is shut off due to a malfunction in the oil pressure source, braking is still available as the master cylinder pressure is still generated manually by the driver.

If the regenerative brake is shut off because of an abnormality in communication with the hybrid vehicle control ECU, control will be changed to use only the oil pressure brake to generate all the braking force.