Principle Of Operation
Principle of Operation
Parking Brake Control
Two separate controls are provided to operate the parking brake functions.
1. The Push Button, located in the instrument panel to the left of the steering wheel is used for the basic function. This will apply and release the parking brake when the vehicle is stationary and provide "Dynamic Braking" when the vehicle is driven depending on the vehicle speed.
When the vehicle is stationary, it functions as an ON/OFF (momentary) push button. Only in the Dynamic Braking mode, the brake is applied for as long as the button is pressed.
2. The action field in the menu of the control display provides a second control. The menu screen is activated and controlled by the driver to activate or deactivate the "Automatic Hold" parking brake function.
This function can also be activated and deactivated with the free programmable button on the multifunction steering wheel (if set in the Control Display).
Indicator Lights
The driver is informed of the parking brake system status by an indicator light in the instrument cluster. When a fault is present, an additional message in the Control Display will provide more information. The parking brake control module communicates via the PT-CAN and K-CAN Busses. The light is activated as part of the pre-drive check when the ignition is switched on.
Indication
In the basic function, application of the parking brake is indicated by a red LED in the brake symbol and by the letter P on the inside. The letters "PARK" are illuminated in the indicator light for as long as the parking brake is applied.
The P symbol indicates that the requested status of "release" or "apply" is reached. When the parking brake is operated while driving (Dynamic Braking), an acoustic warning signal is additionally activated (multiple gong).
Automatic Hold Indication
Standby of the automatic hold function is indicated by the green lettering "AUTO-P" integrated in the light. The parking brake signal is additionally indicated when the automatic hold function is active and the vehicle is stopped. The parking brake symbol lights up in green because the hold function is activated by the DSC with all 4 wheel (service) brakes.
After the brake has been released when starting off (automatically), the green parking brake symbol goes out and only the green standby indication "AUTO-P" remains active. The transition from hydraulic to mechanical mode takes place automatically when the engine is switched off. The light changes from green to red indicating the parking brake is applied and the DSC (service brakes) are released.
Additional Indication
The driver is alerted of parking brake malfunctions by a yellow indicator light in the instrument cluster. In addition, the same symbol is illuminated in the variable indicator warning field and briefly explained by a text note.
In addition to the parking brake status, the variable indicator light is also made available to other control modules. It is only used by the parking brake control module for specific faults.
When the variable indicator light appears, the fault is explained in the Check Control display accompanied by additional information in the Control Display (Condition Based Service).
Indication Examples:
Basic Parking Brake Function with the EMF
Situation: "Ignition ON" and the engine is not running. When the vehicle is stationary, the parking brake is released or applied by pressing the push button. The light in the instrument cluster is either not lit or is red. The lettering "PARK" is illuminated while the brake is released or applied. Pressing the button while the vehicle is rolling triggers the dynamic braking function.
Changing from the EMF to DSC: When the EMF is applied and the engine is started, the system changes over to the service brakes using the DSC. The EMF is not released until the service brakes are applied. The light is permanently red and the transfer is not indicated to the driver (transparent).
Changing from DSC to EMF: When automatic hold is activated or the ignition is switched "OFF" (even if automatic hold was not activated), the service brakes are released after the changeover to the EMF takes place. If automatic hold was activated, the indicator light changes from green to red. If the service brakes are applied, they will be released after the changeover to EMF. The indicator light will remain red during this changeover.
Parking Brake Function with DSC (Service Brakes)
Situation: "Engine Running". When the push button is pressed, the service brakes are released or applied by the DSC and the indicator light is either off or red. When the vehicle is moving and the push button is pressed, Dynamic Braking is applied.
The parking brake push button acts as a switch at speeds below 3 km/h, pressing the push button once will trigger an immediate function change. The brakes are released before starting off by pressing the push button. When attempting to start off without releasing the parking brake, the DSC will further increase the service brake pressure and a warning (gong) will alert the driver. When the parking brake is set and the driver exits the vehicle (CAN signal - driver's seat occupancy) with the engine running, the EMF parking brake will be applied in addition to the DSC service brakes.
Ignition Key Removed (Rest Status)
When the parking brake is applied, the P-light remains on for a certain period indicating "brake hold" to the driver. The parking brake can be released at any time by pressing the push button until the ignition key is removed (car wash function). The rest status is assumed when the ignition key is removed. The parking brake can not be released when the ignition key removed (child safety). The ignition key must be inserted and the ignition switched on to release the parking brake.
Automatic Hold Function
The Automatic Hold function is activated by selecting "Auto P" in the Control Display (or MFL free programmable button) only when the engine is running and the hood is closed (or the hood contact switch is in the service position). It then remains operational until the next time the engine is switched off. When selected, the vehicle is automatically held by the service brakes each time it comes to a stop. This also applies when the Automatic Hold function is requested and the vehicle is stationary.
When the vehicle is stationary, the brake pressure that the driver applies from the brake pedal is "locked in". When the vehicle comes to a stop without operating the brake pedal (roll to a stop), hydraulic pressure is built up by the DSC pump. Increased pressure will be automatically supplied if the vehicle begins to roll (detected by the wheel speed sensors).
When the automatic transmission is engaged in a drive gear, the brakes will be automatically released by pressing on the accelerator pedal. The next time the vehicle stops it will be automatically held by the service brakes. The standby status of the automatic mode is indicated by the green lettering "Auto-P". When the vehicle is stationary, the parking brake symbol is additionally illuminated in green.
The Automatic Hold function is deactivated by selecting "OFF" in the Control Display (or MFL free programmable button). This will not change the current parking brake status. This means when the vehicle is stationary, it remains held hydraulically after selecting "Auto-P OFF". The parking brake indicator light will change from green to red and the "Auto-P" indicator will go out.
The Automatic Hold function is always aborted when the push button is pressed and must be reactivated by selecting "ON" in the Control Display (or MFL button). When the engine is switched "OFF" in the Automatic Hold function, the EMF will apply the parking brake.
The parking brake can be released at any time by pressing the push button until the ignition key is removed (car wash function). The parking brake will apply after the ignition key has been removed.
Automatic Hold Safety Control
Release of the Automatic Hold function by pressing the accelerator pedal is based on two safety functions.
Situation: Hood open. Automatic release of the service brakes when the accelerator pedal is pressed is inhibited when the hood is open (CAN signal - hood contact switch) while the engine is running.
In this situation, the parking brake can only be released by pressing the push button (Automatic Hold deactivation). When the hood is closed, the Automatic Hold must be selected again by the driver. This situation also applies when the luggage compartment (trunk) lid is open and Reverse is engaged.
Situation: The driver exits the vehicle. When the driver exits the vehicle (CAN signal - driver 5 seat occupancy) with the engine running, the automatic release of the service brakes by pressing the accelerator pedal is inhibited. The EMF parking brake will also be applied and the transmission will automatically stiff to the P-position.
When the driver re-enters the vehicle (CAN signal - driver's seat occupancy), the brake pedal must be pressed and a transmission drive gear must be engaged to drive off. The brake light switch signal requests the EMF to release the parking brake. The Automatic Hold function must be selected again by the driver.
Dynamic Braking
Two separate controls are required by law for brake operation, the brake pedal and hand-brake lever were previously used. In the E65/E66, the footbrake and the push button in the dashboard fulfills the requirements.
When the vehicle is moving and the engine is "OFF", the EMF parking brake is applied when pressure is maintained on the push button at speeds below 3 km/h. During this situation, the parking brake is applied for 0.8 seconds. For the next 2 seconds there is an increase in the braking power and the rate of deceleration is maintained as long as the push button is pressed.
The Dynamic Braking tunction is active while the vehicle is rolling at speeds above 3 km/h (when the ignition is in position KLR or KL1 5) when pressure is maintained on the push button. This maintains vehicle stability by preventing overbraking of the rear axle using DSC hydraulic pressure build-up application to the service brakes. The required brake pressure is made available as fast as possible by the DSC.
Since braking takes place hydraulically on all four wheels, higher deceleration rates are possible with minimum operating force as compared to the EMF parking brakes. This controlled braking contributes to increased vehicle safety. For safety reasons, traffic is warned when Dynamic Braking is active by the brake lights.
To avoid incorrect operation, the "Release Parking Brake" display and gong draw the driver 5 attention to Dynamic Brake operation. This function should only be used in exceptional circumstances.
When Dynamic Braking is activated until the vehicle comes to a stop, the vehicle will remain held by the service brakes and the red P-indicator light remains on. If the brake pedal is pressed during this operation, the DSC interprets this as a higher priority and will override the parking brake function.
Exiting the dynamic emergency braking function: After emergency braking the vehicle to a stop, the vehicle will remain held by the service brakes even after releasing the parking brake push button. The service brakes will not be released until the push button is pressed again.