Electric parking brake, function - GF42.20-P-0001RF
Model 205, 253
Block diagram (except AMG vehicles with engine 177)
Block diagram (for AMG vehicles with engine 177)
Function requirements - electric parking brake (EFB), general
- "Circuit 15R ON" status
Electronic parking brake (EFB), general
The electronic parking brake makes it possible to hold the vehicle at a standstill on gradients even in the absence of the driver, the braking parts being held de-energized in the brake position by a self-locking mechanical effect. The Electronic Stability Program control unit (except AMG vehicles with engine 177) or the electric parking brake control unit (for AMG vehicles with engine 177) actuates the left electric parking brake actuator motor and the right electric parking brake actuator motor.
Activation takes place manually via the electric parking brake switch or automatically depending on the driving condition. Depending on the operating condition of the electric parking brake (EFB) the driver's wish is converted into a corresponding tension force build up or reduction in the actuator motors.
The electronic parking brake (EFB) consists of the following subfunctions:
- Function sequence for release parking brake (manual, via electric parking brake switch)
- Function sequence for automatically release parking brake (Comfort-Go)
- Function sequence for emergency braking
- Function sequence for dynamometer test mode
- Function sequence - child safety lock
- Function sequence - display concept/acoustic signal
Function sequence for release parking brake (manual, via electric parking brake switch)
The "circuit 15R ON" status required to release the parking brake is sent by the electronic ignition lock control unit to the chassis FlexRay for the Electronic Stability Program control unit (except AMG vehicles with engine 177) or to the periphery CAN for the electric parking brake control unit (for AMG vehicles with engine 177).
The parking brake release is requested by actuating the electric parking brake switch. The Electronic Stability Program control unit (except AMG vehicles with engine 177) or the electric parking brake control unit (for AMG vehicles with engine 177) directly reads in the status of the electric parking brake switch.
As soon as the Electronic Stability Program control unit (except AMG vehicles with engine 177) or the electric parking brake control unit (for AMG vehicles with engine 177) has simultaneously actuated the left and right electric parking brake actuator motors, and the electric parking brake has been completely released, it generates a signal for the parking brake indicator lamp (red). The parking brake indicator lamp (red) in the instrument cluster then goes off.
The electric parking brake switch must be actuated for a sufficient length of time for release to be detected.
Additional function sequences - automatically release parking brake (Comfort-Go)
The electric parking brake is released if the following conditions are satisfied:
- Engine running.
- Selector lever position "D" or "R" engaged (in vehicles with automatic transmission).
- Trunk lid/liftgate is closed (for selector lever position "R" or engaged reverse gear).
- Driver seat belt inserted.
- The driver actuates accelerator pedal
- Release clutch pedal with gear engaged (on vehicles with manual transmission).
When the driver seat belt is not fastened, the electric parking brake is released if the following conditions are satisfied:
- Driver door is closed.
- Gear range changed from selector lever position "P"
- Vehicle speed exceeds 3 km/h
Function sequence for automatically release parking brake (Comfort-Go)
The automatically release parking brake function is performed once there is a sufficiently high drive torque on the rear axle wheels to overcome the prevailing grade resistance corresponding to the road gradient.
The following signals of the individual control units are sent over each CAN bus or FlexRay to the Electronic Stability Program control unit (except AMG vehicles with engine 177) or to the electric parking brake control unit (for AMG vehicles with engine 177):
- Accelerator pedal position (over accelerator pedal sensor), drive train and engine running status, by the CDI control unit (with diesel engine) or the ME-SFI [ME] control unit (with gasoline engine) over the engine CAN, powertrain control unit and the chassis FlexRay (except AMG vehicles with engine 177) or the periphery CAN (for AMG vehicles with engine 177)
- Current selector lever position, from DIRECT SELECT lever to steering column tube module control unit, over the chassis FlexRay (except AMG vehicles with engine 177) or over the chassis FlexRay and the periphery CAN with the electronic ignition lock control unit interface (for AMG vehicles with engine 177)
- Road inclination (at vehicle standstill), from Supplemental Restraint System control unit, over the dynamics CAN, to the Electronic Stability Program control unit, over the chassis FlexRay, to the electronic ignition lock control unit and over the periphery CAN
- Total transmission ratio, from fully integrated transmission control unit over the drive train CAN, powertrain control unit and the periphery CAN (for AMG vehicles with engine 177) or the electronic ignition lock control unit and chassis FlexRay (except AMG vehicles with engine 177)
The driver door status message (from left front door control unit) is sent to the electronic ignition lock control unit over the interior CAN. The trunk lid/liftgate status is read in directly by the rear SAM control unit. The rear SAM control unit sends all messages to the Electronic Stability Program control unit (except AMG vehicles with engine 177) or to the electric parking brake control unit (for AMG vehicles with engine 177) for evaluation. Along with the required signals for the wheel speeds, the Electronic Stability Program control unit (except AMG vehicles with engine 177) or the electric parking brake control unit (for AMG vehicles with engine 177) sends this information to the chassis FlexRay (except AMG vehicles with engine 177) or the periphery CAN (for AMG vehicles with engine 177).
The Electronic Stability Program control unit (except AMG vehicles with engine 177) or the electric parking brake control unit (for AMG vehicles with engine 177) is woken up by the corresponding FlexRay or CAN messages, whereby it then releases the parking brake through actuating the integrated actuator motors on both rear brake calipers. If a fault prevents the electric parking brake from being released, the instrument cluster displays the "Release parking brake" message and a warning tone is sounded.
Function sequence for emergency braking
If the electric parking brake switch is operated and held when driving, the Electronic Stability Program control unit (except AMG vehicles with engine 177) or the electric parking brake control unit (with AMG vehicles with engine 177) recognizes a braking request.
The request is received by the following control units:
- From the instrument cluster
- From the rear SAM control unit
The vehicle is now braked via the service brake. The rear SAM control unit activates the brake light actuation. The instrument cluster displays the "Release parking brake" message and a warning tone is also sounded.
Additional function requirements for roller brake test stand
- Front wheel "stationary" and rear wheels turn slowly (roller brake test stand).
- A test must be performed after bedding-in the service brake.
- Engine running.
- Selector lever position "N"
Function sequence for dynamometer test mode
To enable the electric parking brake to be tested on the brake test stand, a roller dynamometer test mode is integrated in the Electronic Stability Program control unit (except AMG vehicles with engine 177) or in the electric parking brake control unit (with AMG vehicles with engine 177).
If the vehicle is on the brake test stand and the brake test stand rollers are activated, this is recognized automatically by the Electronic Stability Program control unit (except AMG vehicles with engine 177) or the electric parking brake control unit (with AMG vehicles with engine 177) through the RPM difference at the rear wheels compared with the front wheels, whereupon it switches to the roller dynamometer test mode.
When roller dynamometer test mode is activated, the inspector can gradually raise the tension force of the electric parking brake by actuating the electric parking brake switch multiple times until the rear axle wheels lift out of the rollers of the brake test stand at a correspondingly high tension force.
The following variables/values can be evaluated by checking a vehicle on the brake test stand:
- Rolling resistance
- Braking power
- Deviation in brake force between right and left rear wheel
- Start of locking tendency
Function requirements for child safety lock
- Status "Circuit 15R OFF"
- Transmitter key removed
Function sequence - child safety lock
When the transmitter key is removed or with circuit 15R OFF, operating the electric parking brake switch does not lead to actuation of the left and right electric parking brake actuator motors to release the brake by the Electronic Stability Program control unit (except AMG vehicles with engine 177) or by the electric parking brake control unit (for AMG vehicles with engine 177).
This should prevent unintended deactivation of the electric parking brake and, as such, serves as an additional protection against the vehicle rolling away on slopes or inclines.
Function requirements for display concept/acoustic signal
- Circuit 30
Function sequence - display concept/acoustic signal
The following display tools are available for the display of function and condition of the electric parking brake:
- Parking brake indicator lamp (red)
- Parking brake warning lamp (yellow)
- Diverse status/warning messages via the instrument cluster
- Acoustic warnings
The different displays and acoustic signals are actuated depending on the current operating condition of the electric parking brake.
| Error condition | Display actuation | Display | Acoustic signal | Instrument cluster message |
|---|---|---|---|---|
| Electric parking brake actuated | Permanently | Parking brake indicator lamp (red) | - | - |
| Faulty electric parking brake (permanent fault, service required) | Continuously/flashing | Parking brake warning lamp (yellow)/parking brake indicator lamp (red) | - | Parking brake "P" See operator's manual! |
| Electric parking brake malfunction, electric parking brake inoperative | Flashing | Parking brake warning lamp (yellow) | - | Parking brake inoperative! "P" |
| Attempted release of electric parking brake in child safety lock mode, ignition must be switched on (circuit 15R ON) | Permanently | Parking brake indicator lamp (red) | - | Parking brake! "P" To release switch on ignition! |
| Conditions for automatic release not met OR Emergency stop with parking brake |
Flashing | Parking brake indicator lamp (red) | Bleep-interval | Parking brake! "P" Release brake! |
| Electrical function schematic for electric parking brake | Model 205 except code 990 (AMG car docs./desig. plate allocation) | PE42.20-P-2050-97FBA | |
| Model 205 with code 990 (AMG car docs./desig. plate allocation) | PE42.20-P-2050-97FBB | ||
| Overview of system components for electric parking brake | GF42.20-P-9998RF |