Parking Brake System: Description and Operation
Electric Parking Brake
All new Cayenne models feature an electrically operated parking brake, which can be controlled conveniently by means of a button at the left of the steering wheel. The electric parking brake can be activated manually using this button and deactivated when the footbrake is pressed. It is also released automatically following manual activation when the driver's intention to drive off is detected via the accelerator pedal. The electric parking brake therefore increases comfort and safety when the vehicle is parked.
Functions
Activating when the vehicle is stationary Conditions:
- Vehicle speed less than 1.4 mph (2.2 km/h)
- At least one valid wheel signal per axle
- Press operating control
Display:
Function light comes on in the instrument cluster and on the operating control
Emergency operation:
If there is not at least one valid wheel signal available on each axle, the electric parking brake can be applied and the vehicle reliably held under the following conditions:
- Ignition off
- Operating control pressed for longer than 10 seconds
Releasing when the vehicle is stationary Conditions:
- Ignition on
- Brake pedal actuated
- Pull operating control
Display:
Function light goes out (on instrument cluster and operating control)
Automatic electric parking brake release when driver's intention to drive off is detected on the flat (gradient of less than 5°)
Conditions:
- Engine running
- Gear selected (PDK = selector lever in D or R, manual transmission = clutch pressed)
- Accelerator pedal pressed
- Driver's seat belt fastened
- Driver's door closed
Automatic electric parking brake release when driver's intention to drive off is detected on a gradient of more than 5° (Drive-Off Assistant)
Conditions:
- Engine running
- Gear selected (PDK = selector lever in D or R, manual transmission = clutch pressed)
- Accelerator pedal pressed
- Driver's seat belt fastened
- Driver's door closed
- Gradient angle > 5°
NOTE: If the driver's door is not closed or the driver's seat belt is not fastened, the electric parking brake will not be released automatically when the driver attempts to drive off. The message "Release electric parking brake" appears on the multifunction display in the instrument panel. The brake warning light on the instrument panel and the indicator light on the operating control start to flash. The parking brake must be released manually.
The Drive-Off Assistant is activated if a gradient angle of more than 5° is detected. The downgrade force is calculated in the PSM control unit from the gradient angle signal. In communication with the DME control unit, the system calculates at which engine torque the parking brake has to be released. In other words, the parking brake is released slowly only when the driver has pressed the accelerator pedal far enough.
Display:
Function light goes out (on instrument cluster and operating control)
Emergency braking - vehicle deceleration of 0.8 g
In dangerous situations, it is possible to decelerate very sharply and stop the vehicle using the electric parking brake instead of the footbrake.
Conditions:
- Vehicle speed above 2.2 mph (3.5 km/h)
- A valid wheel signal per axle
- Press operating control continuously
Display:
- Function light flashes (on instrument cluster and operating control)
- Warning tone
Text message "The emergency brake function is deactivated when switch is released" is displayed on the instrument cluster.
Note on emergency braking:
Vehicle deceleration of 0.8 g is requested as long as the operating control is actuated. The PSM control unit implements this request in a controlled braking function. If a speed of below approx. 1.2 mph (2 km/h) is reached, the EPB takes over complete braking and stopping of the vehicle.
Special functions
1. Brake test stand (T0V (MOT)) mode, automatic activation upon detection of roller operation
The braking action of the parking brake can be tested at any time on a roller-type test stand. The system automatically switches to test mode as soon as one axle is driven while the other is stationary. The service brakes of the front and rear axle can be tested normally. To test the parking brake, the button must be pressed continuously until the highest braking torque is reached or the vehicle jumps out of the test stand.
2. EPB emergency release
The emergency release function should be used only if the brake can no longer be released electrically (actuating element itself is faulty)
1 Undo the oval-head screw on the back of the actuator using an Allen key (a/f 3).
2 Access the emergency release screw using an Allen key (a/f 3).
3 Turn approx. 300 turns in counter-clockwise direction until there is a noticeable increase in torque. The fully released position of the brake shoes is then reached.
Control unit
Sensors
PSM signals
Speed signal - Wheel speeds are detected in order to execute the various functions depending on vehicle speed.
Longitudinal acceleration - The gradient is detected in order to activate/deactivate the Drive-Off Assistant.
Output signals to the PSM hydraulic unit - Targeted build-up of brake pressure during emergency braking.
Clutch sensor
The clutch sensor is only installed on vehicles with manual transmission. It is located on the clutch master cylinder in order to detect the position of the master piston. The piston contains a permanent magnet for this purpose. The different positions of the magnet generate certain field strengths, which can be used to determine the sensor position. The sensor supplies up to three different signals, which provide information about the position of the piston: clutch pedal actuated, piston travel and clutch fully depressed.
