System Description

COMPONENTS AND FUNCTION

Components	Functions
Skid control ECU*	Calculates brake control in accordance with sensor / ECU signals or communication with hybrid ECU
Brake control power supply assembly*	Charges capacitor inside unit and supplies power source to system by discharging when voltage of vehicle's power source drops
Speed sensor	Detects speed of each wheel and inputs data into skid control ECU
Pedal stroke sensor*	Detects brake pedal stroke and inputs data into skid control ECU
Yaw rate / deceleration sensor*	Detects forward / rearward and lateral acceleration, and then inputs data into skid control ECU
Steering angle sensor	Detects steering wheel angle and steering wheel direction, and then inputs data into skid control ECU
Accumulator	Accumulates fluid pressure generated by pump
Accumulator pressure sensor (PACC)	Detects accumulator pressure and inputs data into skid control ECU
Master cylinder	Generates pressure according to pedal effort
Brake fluid reservoir	Stores master cylinder system / power supply system brake fluid Brake fluid level warning switch built into reservoir detects decrease of brake fluid
Stroke simulator	Generates smooth pedal stroke in accordance with pedal effort during system control
Stroke simulator cut valve (SCSS)	Changes intake / cutoff of brake fluid from master cylinder to stroke simulator Sends oil pressure generated in master cylinder to stroke simulator during system control Cuts brake fluid flow from master cylinder to stroke simulator when system is not controlling
Master cylinder pressure sensor 1 (PMC) Master cylinder pressure sensor 2 (PMC2)	Detects fluid pressure inside master cylinder and inputs data into skid control ECU
Relief valve	Releases brake fluid into reservoir and prevents excessively high power supply system pressure when pump operates continuously due to malfunctions in parts such as accumulator oil pressure sensor
Wheel cylinder pressure sensor	Detects pressure in each wheel cylinder and inputs data into skid control ECU
ABS NO. 1 relay ABS NO. 2 relay	Supplies power to each solenoid according to skid control ECU signals Supplies power to skid control ECU Supplies electricity and maintains operating condition for brake system when power switch is OFF
ABS MTR relay ABS MTR 2 relay	Supplies power to each motor according to skid control ECU signals Drives relay 1 under normal condition and drives relay 2 under ABS operation Substitutes relay operation when one relay malfunctions
Changeover solenoid valve (SMC1, SMC2)	Changeover solenoid valve switches brake hydraulic pressure passage depending on whether system is in operation or not operation
Linear solenoid valve (SLA##, SLR##)	Controls wheel cylinder hydraulic pressure according to regenerative braking force in order to generate braking force required by driver under normal brake operation Controls hydraulic pressure of each wheel cylinder under ABS, VSC brake operation SLA## adjusts pressure increase level SLR## adjusts pressure decrease level
Stop light switch	Illuminates brake light when brake pedal is depressed (sends brake ON signal to skid control ECU)
BRAKE warning light (Red)	Informs driver that there is trouble with ECB (normal brake) by turning on Informs driver when parking brake is applied and brake fluid level drops by turning on
BRAKE warning light ((Yellow) Brake Control warning light)	Informs driver when there is trouble with ECB or problem with brake system that has no influence on driving, by turning on
ABS warning light	Informs driver that there is trouble with ABS by illuminating light
VSC warning light	Informs driver that there is trouble with Enhanced VSC by illuminating light
SLIP indicator	Informs driver that Enhanced VSC and ABS are operating by blinking light
Skid control buzzer	Informs driver when there is trouble with hydraulic pressure source or power source by continuous buzzer sound Informs that Enhanced VSC is operating by intermittent buzzer sound

HINT:

*: The "initialization of linear solenoid valve and calibration" must be performed when the skid control ECU, actuator, stroke sensor, yaw rate (deceleration) sensor, brake control power supply assembly, and steering sensor are replaced (see INITIALIZATION ). It is necessary to perform zero point calibration of the yaw rate (deceleration) sensor (see CALIBRATION ).

OPERATION DESCRIPTION
1. ECB (Electronically Controlled Brake):
  The skid control ECU receives signals from the pedal stroke sensor, master cylinder sensor and wheel cylinder pressure sensor. Based on these signals, the skid control ECU calculates necessary braking force for each wheel. The necessary hydraulic pressure braking force signal is sent to the hybrid control ECU via CAN communication. The skid control ECU receives a braking force (regenerative braking force) signal from the hybrid control motor via CAN communication. The ECU calculates the necessary hydraulic pressure braking force based on the necessary braking force and regenerative braking force.
  
  Necessary hydraulic pressure is supplied to each wheel by adjusting the brake accumulator (hydraulic pressure source) pressure with each solenoid valve. If there is a problem with the braking function, the normally operating parts will maintain brake control as a fail-safe.
  
  Fig 1: CAN Communication System Diagram (1 Of 3)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. ABS with EBD and Enhanced VSC:
  The skid control ECU receives a vehicle speed signal from each speed sensor and detects wheel's slip condition and then sends a control signal to the solenoid.
  
  The solenoid valve controls each wheel cylinder's hydraulic pressure and optimizes hydraulic pressure allocation to each wheel cylinder.
  
  Fig 2: CAN Communication System Diagram (2 Of 3)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
3. BA (Brake Assist):
  The skid control ECU receives the brake pedal stroke sensor signal and hydraulic pressure signal from the master cylinder pressure sensor and determines whether brake assist operation is necessary or not. If it is determined that brake assist operation is necessary, the ECU changes target hydraulic pressure applied to each wheel.

Fig 3: CAN Communication System Diagram (3 Of 3)