Electric Parking Brake System Description
Overview
The electric parking brake system replaces the traditional parking brake pedal or lever and linkage with an electrically controlled parking brake mechanism in the rear calipers. This reduces driver effort and provides additional features such as:
- Simple electric switch operation
- Parking brake release upon acceleration
- Automatic rollaway prevention
The system is controlled by the VSA modulator-control unit.
Function
The electric parking brake system has following functions.
Manual Operating Function
The electric parking brake can be manually applied and released using the switch. Pulling up on the electric parking brake switch applies the parking brake. Firmly applying the brake pedal and pushing down on the electric parking brake switch releases it.
Automatic Operating Function - Drive Away Assist
The electric parking brake is released automatically when the vehicle is driven away from a stop with the driver's seat belt buckled. Problems in the electric parking brake switch circuits do not affect automatic apply and release.
Automatic Operating Function - Request From Other System
While the electric servo brake system is preventing vehicle movement during automatic brake hold control, the electric parking brake system may operate automatically. This will occur after a specific time period has elapsed based on commands sent from the electric servo brake system.
Automatic Adjusting Function
Because the parking brake is automatically adjusted whenever applying the parking brake, the electric parking brake needs no adjustment. And, if the vehicle is driven 625 miles (1, 000 km) without applying the parking brake, the parking brake is automatically applied and released while vehicle is at a short stop, and adjusts the remaining brake pads.
Reclamp Function - High Temperature Reclamp
Brake disc temperature is calculated from the vehicle's kinetic energy as it stops, because loss of clamping force can occur when brake system components contract as they cool. If the calculated brake temperature exceeds a predetermined threshold, the high temperature reclamp function reapplies the electric parking brake actuators after a cool-down time has elapsed to compensate for any loss of clamping force. In order to accommodate this function, the VSA modulator-control unit may be kept on for a period of time after the turning the vehicle to the OFF (LOCK) mode. Depending on when high temperature reclamp occurs, the driver may notice the motor noise.
Reclamp Function - Roll-Away Reclamp
The roll-away reclamp function reapplies the parking brake if wheel movement is detected after the electric parking brake is applied.
Emergency Brake Function
In an emergency situation, such as a failure of the conventional brake system, the electric parking brake system performs the emergency brake function by activating the electric parking brake switch continuously. There are two controls depending on the state of the electric servo brake system.
- In cases where the electric servo brake system can perform the servo control:
The electric parking brake system sends the brake control request to the electric servo brake system which applies the emergency brake using the servo control.
- In cases where the electric servo brake system can not perform the servo control:
The electric parking brake system controls the electric parking brake actuator so that the wheels do not lock, and applies the emergency brake instead of the electric servo brake system. However, if the wheel speed signal is abnormal, the anti-lock control is not performed.
Ignition OFF Apply Function
The electric parking brake system can apply the parking brake automatically when the vehicle is turned to the OFF (LOCK) mode based on customer preferences. It may be necessary to temporarily cancel this function in certain service procedures. Refer to How To Temporarily Cancel Automatic Electric Parking Brake . For more information on how to turn on or off the automatic parking brake function, refer to the owner's manual.
Maintenance Mode
The electric parking brake system has a brake pad maintenance mode functional test. This test fully releases the parking brake mechanism so that brake service, such as rear pad replacement, can be done. Maintenance mode can be activated by the HDS.