System Description

FUNCTION DESCRIPTION
1. Electronically Controlled Brake System
  1. The electronically controlled brake system detects the amount that the brake pedal is depressed based on signals from the brake pedal stroke sensor. The system uses the skid control ECU to adjust the pressure supplied from the hydraulic pressure source for each wheel, generating optimal braking force.
2. Regenerative Braking Cooperative Control
  1. This control performs cooperative control with regenerative braking that is specific to hybrid vehicles to efficiently charge the HV battery.
3. Steering Cooperative Control
  1. Performs cooperative control with the power steering ECU in order to provide steering torque assist in accordance with present vehicle dynamics.
4. Anti-lock Brake System (ABS)
  1. The ABS helps prevent the wheels from locking when the brakes are applied firmly or when braking on a slippery surface.
5. Electronic Brake Force Distribution (EBD)
  1. EBD control utilizes the ABS, realizing proper brake force distribution between the front and rear wheels in accordance with the driving conditions. In addition, when braking while cornering, it also controls the brake force applied to the right and left wheels, helping to stabilize vehicle behavior.
6. Brake Assist (BA)
  1. The primary purpose of BA is to provide supplementary brake force to assist a driver who cannot generate a large brake force during emergency braking, thus helping ensure the vehicles braking performance.
7. Traction Control (TRAC)
  1. The TRAC helps restrain the slippage of the drive wheels if the driver depresses the accelerator pedal excessively when starting off or accelerating on a slippery surface.
8. Vehicle Stability Control (VSC)
  1. The VSC helps restrain sideways slippage of the vehicle during a strong front wheel skid or strong rear wheel skid during cornering.
9. Hill-start Assist Control
  1. The hill-start assist control generates four-wheel hydraulic pressure when the brake pedal is further depressed while the vehicle is stationary in order to prevent the vehicle from moving backward.

FUNCTION OF COMPONENTS

Component		Function
Brake Booster with Master Cylinder	Brake Actuator	Consists of 4 switching solenoid valves, 2 pressure control solenoid valves, 4 pressure holding solenoid valves, and 4 pressure reduction solenoid valves. The regulator pressure sensor, the wheel cylinder pressure sensor and the accumulator pressure sensor are installed in the brake actuator. Changes the brake fluid path based on the signals from the skid control ECU during the operations of the ABS with EBD, BA, TRAC, VSC and hill-start assist control in order to control the fluid pressure that is applied to the wheel cylinders.
	Hydraulic Brake Booster	Generates hydraulic pressure in accordance with the amount of effort applied to the brake pedal by the driver. When a malfunction occurs in the brake system, the hydraulic brake booster supplies the fluid pressure (which is generated by the brake pedal effort) directly to the wheel cylinders.
	Stroke Simulator	Provides a pedal stroke during braking in accordance with the drivers pedal effort.
Brake Actuator	Skid Control ECU	Monitors the driving conditions of the vehicle in accordance with the signals received from the sensors and through cooperative control with the hybrid vehicle control ECU and power steering ECU calculates the required amount of braking force, and controls the brake actuator. Judges the vehicle driving condition based on signals from each sensor, and controls ABS with EBD, BA, TRAC, VSC and hill-start assist control. Operates the brake booster pump to control accumulator pressure based on accumulator pressure sensor signal.
Skid Control ECU	Solenoid Relay	Built into the skid control ECU, supplies and cuts off power to the solenoid valves in the brake actuator.
	Motor Relay	Built into the skid control ECU, supplies power to the brake booster pump. Ensures power to the brake booster pump by using the rest relay if the skid control ECU malfunctions.
	Relief Valve	Built into the skid control ECU, returns the brake fluid to the reservoir tank to prevent excessive pressure if the pump operates continuously due to a malfunction of the accumulator pressure sensor.
	Linear Solenoid Valve	Controls the wheel cylinder pressure to generate a braking force responsive to the braking force requirement when the brake pedal is depressed normally.
	Switching Solenoid Valve	Switches the brake hydraulic path when the brake control system is activated.
	Control Solenoid Valve	Controls the hydraulic pressure that is applied to the wheel cylinders during brake control.
	Regulator Pressure Sensor	Converts the fluid pressure generated by the hydraulic brake booster into electrical signals and transmits them to the skid control ECU. Accordingly, the skid control ECU determines the braking force required by the driver.
	Wheel Cylinder Pressure Sensor	Detects the fluid pressure that acts on the respective wheel cylinders and transmits them to the skid control ECU in the form of feedback. Accordingly, the skid control ECU monitors the fluid pressure of the wheel cylinders and controls the control solenoid valve, in order to achieve the optimal wheel cylinder pressures.
	Accumulator Pressure Sensor	Constantly detects the brake fluid pressure in the accumulator and transmits the signals to the skid control ECU. Accordingly, the skid control ECU controls the pump motor.
Brake Booster Pump	Accumulator	Stores the hydraulic pressure that was generated by the pump. The accumulator is filled with high pressure nitrogen gas.
Brake Booster Pump	Pump and Pump Motor	Draws up the brake fluid from the reservoir tank and provides high hydraulic pressure to the accumulator.
Speed Sensor		Detects the wheel speed of each wheel.
Brake Pedal Stroke Sensor		Directly detects the extent of the brake pedal stroke operated by the driver.
Steering Angle Sensor		Detects the steering direction and angle of the steering wheel.
Yaw Rate and Acceleration Sensor		Detects the vehicles yaw rate. Detects the vehicles longitudinal and lateral acceleration and deceleration.
Reservoir Tank		Stores brake fluid.
Brake Fluid Level Warning Switch		Detects a low brake fluid level.
Parking Brake Switch		Detects parking brake operation.
VSC OFF Switch		Enables the driver to select normal mode, TRAC off mode, or VSC off mode.
Stop Light Switch		Detects brake pedal operation.
Stop Light Control Relay		Illuminates the stop lights when hill-start assist control and brake control system (models with dynamic radar cruise control) is operating.
Skid Control Buzzer*1		Sounds the buzzer to alert the driver that the distance to the preceding vehicle ahead has become shorter during pre-collision operation. Sounds the buzzer to alert the driver that the distance to the preceding vehicle ahead has become shorter during radar cruise control operation.
Power Steering ECU		Performs cooperative control with the skid control ECU, in order to control the steering assist force in accordance with information received from the skid control ECU.
Main Body ECU (Instrument Panel Junction Block)		Transmits the parking brake signal to the skid control ECU.
Hybrid Vehicle Control ECU		Actuates regenerative braking upon receiving a signal from the skid control ECU. Sends the actual regenerative braking control value to the skid control ECU. Transmits the shift state signal to the skid control ECU. Controls the drive force based on an output control request signal received from the skid control ECU while the VSC function or TRAC function is operating.
Combination Meter	ABS Warning Light	Illuminates to alert the driver when the skid control ECU detects a malfunction in the ABS or BA.
	Brake Warning Light/Red (Malfunction)	Illuminates to alert the driver that the skid control ECU detects a malfunction in the apportioning of the brake. Illuminates to inform the driver when the parking brake is applied or the brake fluid is low.
	Brake Warning Light/Yellow (Minor Malfunction)	Illuminates to alert the driver that a minor malfunction which does not affect the braking force has occurred in the brake system.
	VSC OFF Indicator Light	Illuminates to inform the driver when VSC off mode is selected.
	Slip Indicator Light	Blinks to inform the driver when the ABS, TRAC, VSC, or hill-start assist control operates.
	Master Warning Light	Lights up to alert the driver when the skid control ECU detects a malfunction in the brake control system.
	Multi-information Display	Shows a warning message to alert the driver when the skid control ECU detects a malfunction in the brake control system.
	Meter Buzzer	Emits a warning sound to inform the driver when hill-start assist control operation is started or finished. Sounds continuously to inform the driver if there is a hydraulic pressure malfunction.

*1: w/ Dynamic Radar Cruise Control System