Auto Start Stop Function
Auto Start Stop Function
Operating principle
The Auto Start Stop function switches off the combustion engine under defined conditions when the vehicle is stopped and therefore contributes to reducing fuel consumption when the vehicle is stationary.
The Auto Start Stop function can be manually deactivated and activated by way of the Start/Stop switch in the center console.
The Start Stop function is available only after the engine, transmission and battery have reached operating temperature.
If the vehicle is stopped by brake operation and the brake pedal is held, the Auto Start Stop function switches off the engine after approx. 1 - 2 seconds.
In Stop mode, the energy supply is provided by the vehicle battery. Energy forms that can otherwise be used only with running engine are buffered where necessary (hydraulic impulse oil storage), replaced (electric oil pump for transmission) or lead to Stop mode being terminated if power is requested (e.g. power steering). All systems remain functional, the ignition remains switched on and communication systems remain active.
Stop mode is ended by an active driver request "Restart" and may also be ended by a request from the DME control unit, e.g.:
- if the total energy requirement of the vehicle systems for the battery cannot be covered (charge condition of the battery, too many loads switched on)
- if the automatic air conditioning/heating with residual heat function cannot guarantee that the set temperature can be maintained without running the engine, e.g. at very low and very high outside temperatures
The restart must also be possible in the engine run-out phase without the starter having to be engaged (by pre-injection of the engine). Otherwise a restart must be initiated only after engine run-out.
Restarting is also prevented:
- if the presence of the driver is not guaranteed, i.e. driver's door is open or driver's seat belt is not fastened,
- if the hood is open.
Start Stop coordinator
The Start Stop coordinator processes the input data of the management functions shown in the following illustration and outputs the data for controlling the engine and starter.
Enabling transition to Stop mode:
- Vehicle standstill with depressed brake. The selector lever must be in one of the selector lever positions D, N, P or in the manually selected driving position 1 or 2
- The driver is detected in the sense of the safety strategy, i.e. the seat belt on the driver's side is fastened, the driver's door is closed and the brake is depressed
- The hood is closed
- The engine, battery and transmission have reached operating temperature
- The vehicle has been driven for at least 1.5 seconds and at a speed of more than 1.2 mph (2 km/h) since the last automatic engine stop
- The engine stop is possible up to a downhill or uphill gradient of 10 %. During an engine stop on uphill gradients, the vehicle is held by maintaining the brake pressure (PSM)
- No Sport mode active
- ESP-OFF not active
- Auto Start Stop function is not deactivated by way of the deactivation button
- A/C max is not active
- No Defrost mode active
- Vehicle is not in Off-road mode
- Level control is not taking place
- Rear fog light is not switched on
- No trailer detected
- Manoeuvering mode not detected
Start requests (restart):
- Vehicle moves
- Manoeuvering mode is detected
- Selector lever R is engaged
- Activation of Sport mode
- Shift to a gear that is not permitted in Start Stop mode
- Restart in selector lever position D or N or manually selected driving position 1 or 2 by
- Releasing the footbrake or
- Pressing the accelerator
- Activation of the function ESP-OFF, A/C- Max, Defrost, Off-road mode or level adjustment
- Falling brake pressure
- Energy level falls below the maximum permitted energy that can be tapped from the vehicle battery for each engine stop
If no Stop enable signal is provided by the coordinator before a maximum time since vehicle standstill is exceeded, i.e. speed = 0 mph, Stop operation is prohibited for this standstill phase.
Unfastening the seat belt or opening of the driver's door during an engine stop prevent an automatic start until all safety conditions have been met again and the footbrake is pressed.
Restricted Auto Start Stop function, e.g if
- the battery charge is insufficient
- non vehicle-internal test processes are taking place, e.g. automatic engine diagnosis
NOTE: Automatic engine restart is possible if one of these states occurs after the engine has been switched off automatically.
Displays:
If the engine has been switched off automatically by the Auto Start Stop function and the driver has been detected in the vehicle (safety strategy), the indicator light in the multi-function display on the instrument panel lights up green.
Start-Stop indicator on the instrument cluster:
The Stop function is displayed on the TFT display by a green pictogram which goes out after restart.
If a stop is not possible, this is indicated by a yellow Start Stop icon on the TFT display. This case applies if the Start Stop function detects that:
- at least one prerequisite for the Stop function is not met, or
- at least one exemption condition of the Auto Start Stop function is present.
If the Start Stop function fails, the display shows the message "Start/stop mode deactivated". This message must be acknowledged once in each ignition cycle.
Unfastening the seat belt or opening the driver's door with subsequent release of the brake lead to deactivation of the Auto Start Stop function since driver absence in the sense of the safety strategy is then assumed. The engine must be started manually.
Control units involved
Bus systems involved
Involved components
