Safety Concept
Safety Concept
Fault Messages
The EMF and DSC control modules monitor the system for faults and alert the driver. A fault has different priorities depending on driving situations: vehicle stationary/moving and starting off/deceleration. To avoid damage, faults in the EMF actuating mechanism like cable breakage and stretch (actuating range exceeded) are detected by the Hall sensors in the motor
If the EMF control module is defective, fault messages will not be available. The instrument cluster recognizes the absence of the normally active parking brake message (alive-enable) over the PT-CAN Bus and will display a fault message. The safety concept is based on a staged shut down strategy. In addition to the yellow warning light, information is available in the Control Display.
General Parking Brake Fault Concept
Fault division between DSC and EMF control module: DSC faults that only affect the parking brake will result in a shut down of the hydraulic function (Dynamic Braking not possible). These are typically faults that result in a shut down of the ABS functions and Manual Emergency Mode will be assumed by the EMF. If the fault is only a CAN Bus fault, Dynamic Braking will be possible.
Shut Down Stage of "Manual Emergency Mode"
This will only apply when the EMF actuating unit is not in operation and is implemented for one of the following DSC faults:
- DSC control module defect
- Electrical defect (example: wiring harness)
- Sensor fault (brake pressure sensor, wheel speed sensors)
- EMF actuator fault, DSC hydraulic unit
- CAN communication fault
Shut Down Stage "Only Dynamic Braking Available"
This stage will provide Dynamic Braking by the DSC hydraulic service brakes in the event of an EMF actuating failure.
- Fault in the actuating motor Hall sensors
- Actuating motor fault
- Fault in control electronics
- Fault in actuating mechanism (mechanical)
- Electrical faults
Shut Down Stage "Total Shut Down"
- Parking brake control module failure
- Push button fault
- Electrical faults including voltage supply
All fault codes are stored in the EMF control module and is also informed of the DSC control module fault status.
Fault Regeneration
It a fault is detected, the system remains in the current stage until the ignition is switched "OFF". A shut down situation will not be deactivated until the faulty component is operating correctly. If the fault is not present during the next restart, the shut down stage is cancelled to resume normal operation. Component tests are carried out continually, even during the shut down situation.
The fault information remains stored in the fault code memory. If correct function of the component cannot be determined after a fault has occurred, the parking brake will remain in the safe, shut down state until the next workshop visit with the exception of: CAN timeout error; overvoltage and temperature protection. After properly repaired, the fault can be deleted with the DISplus.
Regeneration of CAN Faults
CAN timeout faults can be regenerated. The shut down stage is cancelled if the signal is received correctly for a certain period of time.
Monitoring and Fault Detection
Electrical faults monitoring: The wiring to the EMF control module including the actuator motor are monitored for breaks or shorts to B+ and ground.
Hydraulic interface monitoring: The DCS checks the plausibility of the deceleration request by the parking brake during Dynamic Braking and the hydraulic Hold Function. If the request and feedback do not agree within a defined time (5 seconds), the corresponding shut down stage is assumed and a fault code will be stored.
Input signals monitoring: In the event of a faulty input signal, the entire system is shut down with a Check Control error message and a stored fault code.
Parking brake push button monitoring: The push button signals are continually monitored (hardwired to the EMF control module). In the event of a push button plausibility fault, the entire parking brake system is shut down and the "Parking Brake Push Button Defective" fault code is stored. The DSC control module also checks the plausibility of the parking brake push button signals that are transmitted via the CAN Bus (from the EMF control module). If faulty, the "Parking Brake Push Button Signals via CAN Implausible" fault code is stored and partial shut down is carried out (Dynamic Braking is not possible).
Speed signals monitoring: Total shut down of the parking brake system will occur with the loss of all 3 speed inputs.
- The direct digital wheel speed signal (separate hard wire backup, front left) is continually checked for the plausibility of the signal edge change.
- The plausibility of the reference speed signal from the DSC over the PT-CAN Bus and the direct digital wheel speed signal is continually and mutually checked.
- The reference speed signal from the DSC is compared with the automatic transmission output speed.
Fault codes:
- Direct wheel speed signal implausible or faulted
- DSC speeds implausible or no message
- EGS automatic transmission output speed implausible or no message
Hall sensors monitoring: The plausibility of the actuating motor Hall sensors is continually checked. When there are deviations that are out of tolerance, partial shut down (only Dynamic Braking available) is implemented and the "Parking Brake Actuating Unit Defective, Plausibility of Hall Sensors" fault code will be set.
In addition, the plausibility of the position is checked during the actuating motor operation. When the Hall sensor signal is not received, the parking brake system is shut down and a fault code will be set.
EMF actuating unit monitoring: After the ignition is switched on and a fault is present, it will be detected before a required parking brake function is active.