Description & Operation

WARNING: For warnings and procedures regarding vehicles equipped with Anti-Lock Brake Systems (ABS), see appropriate ANTI-LOCK article.

WARNING: Read service precautions before proceeding with any service procedure. See SERVICE PRECAUTIONS .

An ECB (Electronically Controlled Brake) system has been adopted in the brake control system. The ECB system calculates the required braking force based on the amount of pedal effort and force applied by the driver. Then, this system applies the required braking force (which consists of a regenerative brake force generated by MG2 and a brake force generated by the hydraulic brake system) and effectively absorbs the energy.

The ECB ECU, which controls this system, is integrated into the skid control ECU, and effects comprehensive control together with the hydraulic brake control system (consisting of ABS with EBD, brake assist and an optional Enhanced VSC system). The optional Enhanced VSC system provides the steering assist in order to facilitate steering operation of the driver depending on vehicle situations by effecting cooperative control in conjunction with EPS, in addition to the VSC system that gives the general braking control function.

On the 2004 Prius, the motor traction control system has been adopted. This system minimizes a slippage of the drive wheels and generates the appropriate drive force for road surface condition by applying the hydraulic brake control to the wheels that are slipping, in addition to the control function protecting the planetary gear and the motor that has been provided by the THS system on the previous model.

The conventional brake booster portion has been discontinued. Instead, it consists of brake input, power supply, and hydraulic pressure control portions. During normal braking, the fluid pressure generated by the master cylinder does not directly actuate the wheel cylinders, but serves as a hydraulic pressure signal. Instead, the actual control pressure is obtained by regulating the fluid pressure of the hydraulic power source in the brake actuator, which actuates the wheel cylinders.