BRAKE CONTROL SYSTEM

FUNCTION OF MAIN COMPONENTS

Component			Function
Brake Booster with Master Cylinder Assembly	Skid Control ECU		Operates the brake actuator assembly and brake actuator to control the brake fluid pressure of each wheel based on signals from each sensor and ECU. Performs regenerative cooperative brake control by communicating with each ECU.
	Master Cylinder		Generates brake fluid pressure in accordance with the depression amount of the brake pedal.
	Stroke Simulator		Generates a natural brake pedal feel in response to depression of the brake pedal by the driver.
	Brake Master Cylinder Reservoir Assembly	Brake Fluid Level Warning Switch	Detects when the brake fluid level is low.
	Brake Actuator	Regulator	Supplies pressurized brake fluid which is controlled by the linear solenoid valve to the servo chamber when the skid control ECU is operating. Supplies brake fluid pressure from the accumulator to the servo chamber when the skid control ECU is not operating or during back-up when the skid control ECU is malfunctioning.
		Linear Solenoid Valve (SLA, SLR)	Adjusts the regulator to control the servo pressure as requested.
		Gap Hold Valve (SGH)	During normal control, transmits the brake fluid pressure generated by the depression of the brake pedal by the driver to the stroke simulator. During a malfunction, seals the brake fluid pressure of the gap hold chamber.
		Stroke Simulator Cut Valve (SSA)	Allows the stroke simulator pressure to flow to the brake master cylinder reservoir assembly such as when the system is malfunctioning.
		Relief Valve	Opens to prevent excessive fluid pressure if the pump motor operates continuously such as during a malfunction of the accumulator pressure sensor.
		Accumulator Pressure Sensor(Pacc)	Detects the accumulator brake fluid pressure and is used to control the pump motor.
		Servo Pressure Sensor(Psrv)	Detects the fluid pressure of the servo chamber.
		Stroke Simulator Pressure Sensor(Prct)	Detects the brake fluid pressure in the stroke simulator which is generated by the depression of the brake pedal by the driver.
Brake Actuator Assembly			Independently controls the brake fluid pressure of the 4 wheels when ABS, TRC, VSC, etc. is operating.
Brake Booster Pump Assembly	Pump Motor		Pumps the brake fluid from the brake master cylinder reservoir assembly to the accumulator.
Brake Booster Pump Assembly	Accumulator		Accumulates brake fluid supplied by the pump motor under pressure.
Speed Sensor			Detects the wheel speed of each of the 4 wheels.
Airbag Sensor Assembly	Yawrate Sensor		Detects the angular velocity of the vehicle.
Airbag Sensor Assembly	Acceleration Sensor		Detects the longitudinal and lateral acceleration of the vehicle.
Steering angle Sensor			Detects the steering direction and angle of the steering wheel.
Stop Light Switch Assembly			Detects when the brake pedal is depressed.
Electric Parking Brake Switch Assembly	VSC OFF Switch		Disables TRC and VSC functions when pressed.
Electric Parking Brake Switch Assembly	Brake Hold Switch		Turns the brake hold function on/off.
Brake Pedal Stroke Sensor Assembly			Detects the stroke distance of the brake pedal.
Front Door Courtesy Light Switch Assembly (Driver Side)			Outputs whether the driver door is open or closed to the skid control ECU.
Hybrid Vehicle Control ECU			Controls the regenerative braking force via communication with the skid control ECU during regenerative cooperative braking. Also, controls drive force when TRC or VSC is operating.
Inverter with Converter Assembly	MG ECU		Sends information regarding the motor to the skid control ECU during regenerative cooperative braking.
ECM			Controls the engine output based on signals received from the hybrid vehicle control ECU.
Parking Brake ECU Assembly			Sends the electric parking brake condition to the skid control ECU. Controls the parking brake actuator assembly based on the signals received from the skid control ECU.
Power Steering ECU Assembly			Controls the steering assist torque based on signals received from the skid control ECU during steering cooperative control.
Millimeter Wave Radar Sensor Assembly*			Sends brake request signals to the skid control ECU.
Network Gateway ECU			Relays data between buses.

*: Models with Toyota Safety Sense

SYSTEM CONTROL

The brake control system has the following system/functions:

Control	Outline
Anti-lock Brake System (ABS)	Helps prevent the wheels from locking when the brakes are applied firmly or when braking on a slippery surface.
Electronic Brake Force Distribution (EBD)	EBD control utilizes ABS, realizing proper brake force distribution between the front and rear wheels in accordance with the driving conditions. In addition, during braking while cornering, it also controls the brake forces of the right and left wheels, helping maintain vehicle stability.
Brake Assist	The primary purpose of brake assist is to provide supplementary brake force to assist a driver who cannot generate a large brake force during emergency braking, thus helping to utilize the vehicle's braking performance.
Traction Control (TRC)	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.
Vehicle Stability Control (VSC)	Helps restrain sideways slippage of the vehicle during a strong understeer tendency or strong oversteer tendency while cornering.
Hill-start Assist Control	When starting uphill, this control maintains the brake hydraulic pressure to all 4 wheels, in order to momentarily help prevent the vehicle from descending backward.
Brake Hold	As the driver depresses the brake pedal and the vehicle comes to a stop, this function maintains the hydraulic pressure of the 4 wheels in order to keep the vehicle stopped.
Cooperative Control with EPS	Effects cooperative control with the power steering ECU assembly in order to provide steering assist in accordance with the operating conditions of the vehicle.
Dynamic Radar Cruise Control Brake*	When the millimeter wave radar sensor assembly determines that a large amount of deceleration is required based on the distance to the preceding vehicle and the relative vehicle speed during the dynamic radar cruise control system operation, the skid control ECU operates the brake system according to the signal from the hybrid vehicle control ECU.
Pre-collision Brake*	When the millimeter wave radar sensor assembly determines that the possibility of a collision is high or an unavoidable collision condition exists, the skid control ECU activates the pre-collision brake assist or the pre-collision brake according to the signal from the millimeter wave radar sensor assembly.

*: Models with Toyota Safety Sense

FAIL-SAFE

If a malfunction is detected in the brake system, the fail-safe function operates. Depending on the type of malfunction, the fail-safe function informs the driver via warning indicators in the combination meter assembly and continues brake control via the use of non-malfunctioning parts. Also, when the system is not operating, the fluid pressure generated in the brake master cylinder by the depression of the brake pedal works as a back-up mechanism to ensure braking force.

DIAGNOSIS

A diagnosis function is provided in consideration of serviceability in order to simplify the inspection of systems. For details of the diagnosis function, refer to Repair Manual.