Automatic Engine Stop, Function - GF08.30-P-3001RFH

Engine 274.920 in model 205.047/147/247 

Engine 274.920 in model 205.053/054/253 

Engine 274.920 in model 253.353/953 

Engine 274.920 in model 253.354/954 

Engine 651.921 in model 205.012/212 

Engine 654.920 in model 205.013/213 

The subfunction "automatic engine stop function" is considered and described from the point of view of the hybrid drive system.

We will not go into more detail here about internal signals and function sequences of the internal combustion engine and the A/T.

Function requirements for an automatic engine stop - general points 

• Hybrid drive system "READY"
• Engine running.
• System diagnosis complete and fault-free
• Engine hood closed
• No Crash event occurred in the driving cycle
• Vehicle speed< 160 km/h
• Transmission oil temperature > 0°C

The automatic engine stop in hybrid vehicles is equivalent to electrical driving.

Automatic engine stop - general points 

An automatic engine stop is initiated if this is meaningful as part of the system optimization and the requested drive torque can be generated purely electrically. For automatic engine stop the internal combustion engine is switched off by the CDI control unit (N3/9) (for a diesel engine) or the ME-SFI [ME] control unit (N3/10) (for a gasoline engine) without switching off terminal 15.

The following listed read in signals are just related to the release for the automatic engine stop from external systems such as:

• High-voltage on-board electrical system
• V on-board electrical system
• vehicle climate control
• Regenerative braking system

The CDI control unit or the ME-SFI [ME] control unit reads in the following signals for release of the automatic engine stop:

• Climate control control unit (N22/1) via the CAN network:
  • A/C status
• Electronic Stability Program control unit (N30/4), via the CAN network:
  • Wheel speed
  • Engine stop prohibition
  • Engine start request
• Battery management system control unit (N82/2) via the CAN network:
  • Voltage of high-voltage battery (A100g1)
  • Temperature of high-voltage battery
• Power electronics control unit (N129/1) via the CAN network:
  • Status of the electrical machine (A79/1)
  • Torque of electrical machine
  • Rotational speed of electrical machine
• Fully integrated transmission control unit (Y3/8n4) via the CAN network:
  • Gear range status
  • Wet clutch status
  • Transmission oil temperature
  • Status of the electrical auxiliary oil pump (M42)
• Supplemental Restraint System control unit (N2/10)
  • Direct crash signal
• Supplemental Restraint System control unit via the CAN network
  • Indirect crash signal
  • Status of driver seat belt
• Front SAM control unit (N10/6) via the CAN network:
  • Engine stop prohibition
  • Engine start request
  • Signal that engine hood is closed
• Left front door control unit (N69/1) via the CAN network
  • Contact switch signal (left front door)

If the internal combustion engine is off (e.g automatic engine stop), the oil supply for the A/T is secured over the electrical auxiliary oil pump.

If the internal combustion engine is off (e.g. automatic engine stop), the fuel supply is influenced appropriately over the FSCU (N118).

If the automatic start/stop intervals exceed an established number in a certain time, the automatic engine stop is suppressed for a certain period of time.

Function sequence of an automatic engine stop 

The CDI control unit or the ME-SFI [ME] control unit continuously performs a system diagnosis and assesses the function requirements for an automatic engine stop.

The status of the electric auxiliary oil pump is checked before triggering of the automatic engine stop and then immediately actuated or actuated during triggering of the automatic engine stop by the fully integrated transmission control unit. The electric auxiliary oil pump secures the hydraulic system's oil supply in the automatic transmission when the internal combustion engine is switched off.

The combustion engine is switched off by the CDI control unit or the ME-SFI control unit if certain internal combustion engine prerequisites are fulfilled and all of the following prerequisites and approvals have been granted:

• Vehicle speed< 160 km/h
• Transmission oil temperature > 0°C
• gear range plausible
• Adequate vacuum in the brake booster
• Enable issued by ESP®.
• Engine hood closed
• no crash event
• the condition of the 12-V on-board electrical system is OK and release has been issued
• Charge level of high-voltage battery is sufficient
• oil supply to A/T secured
• Driver door closed
• Driver seat belt applied
• interior temperature can be regulated with the current coolant temperature of the internal combustion engine.
• Climate control control unit has issued approval.

The CDI control unit or the ME-SFI [ME] control unit makes the request via the CAN network to the fully integrated transmission control unit for actuation of the wet clutch or engine separator clutch in order to disconnect the combustion engine from the drive. After appropriate feedback via the opened wet clutch or engine separator clutch, the CDI control unit or ME-SFI [ME] control unit switches the combustion engine off.

If during the automatic engine stop a release is retracted or a prerequisite is no longer fulfilled, the internal combustion engine will automatically be started without any defined action on the part of the driver.

	Electrical function schematic for automatic engine stop		PE08.30-P-2053-97FBH
	Overview of system components, hybrid drive system		GF08.30-P-9999RFH