Automatic Engine Start, Function - GF08.30-P-3002LFH

Engine 276 in model 222.057/157 

Engine 276 in model 222.163 

Engine 276 in model 222.173 

Engine 651.9 in model 222.004/104 

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

Function requirements for an automatic engine start - general points 

• Hybrid drive system "READY"
• Engine stops after an automatic engine stop (electrical operation)
• System diagnosis complete and fault-free
• No crash event in this driving cycle
• Engine hood closed

Automatic engine start - general points 

An automatic engine start is initiated if the vehicle needs energy for the traction which cannot be delivered purely electrically or if changes in system conditions requires starting of the internal combustion engine. Starting of the internal combustion engine is requested by the CDI control unit (N3/9) (for a diesel engine) or the ME-SFI [ME] control unit (N3/10) (for a gasoline engine). Start of the internal combustion engine takes place according to the specifications of the aggregate coordinator interface in the CDI control unit or the ME-SFI [ME] control unit over

• the starter (M1) (e.g. in electric mode)

  or

• The electrical machine (A79/1) (for vehicle standstill), requested via the CAN network for power electronics control unit (N129/1)

  or

• the starter and the electrical machine together (in electrical mode), requested via the CAN network from the power electronics control unit

The internal combustion engine start can only take place over the electrical machine if the vehicle is stationary and the charge level of the high-voltage battery (A100g1) is adequately high.

During electric mode with the wet clutch (except model 222.173) or engine separator clutch (model 222.173) open, starting is always done initially by the starter up to a certain engine speed.

Once this starting speed is reached, the wet clutch or engine separator clutch is closed to take the combustion engine to idle speed via the drive train.

Internal signals from the combustion engine which are read in for automatic engine start are described in the associated document.

Information about starting the combustion engine with the starter and the electric machine are described in the associated document.

Torque influencing requests and signals to the torque coordinator interface in the CDI or ME-SFI [ME] control unit are described in the associated document.

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

Further information about the fuel supply during an automatic engine start is described in the associated document.

The CDI control unit or the ME-SFI [ME] control unit reads in the following signals for an automatic engine start over the electrical machine:

• 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:
  • High-voltage battery voltage
  • Temperature of high-voltage battery
• Power electronics control unit via the CAN network:
  • Status of electrical machine
  • Torque of electrical machine
  • Rotational speed of electrical machine
• Fully integrated transmission control unit (Y3/8n4) via the CAN network:
• Gear range status
• Status of wet clutch (except model 222.173)
• Status of engine separator clutch (model 222.173)
• 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)

Function sequence for automatic engine start 

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

If one of the following listed releases is retracted or a condition is no longer fulfilled, the internal combustion engine is started.

Starting of the combustion engine is initiated in the following cases:

• Vehicle speed > 160 km/h
• Transmission oil temperature < 0°C
• The vacuum in the brake booster is not adequate
• Electronic Stability Program has canceled the enable
• 12-V energy management has canceled the enable.
• Charge level of the high-voltage battery under the limit value
• Oil supply for the automatic transmission via the electric auxiliary oil pump not safeguarded
• driver identified as absent
• Interior temperature cannot be regulated with the current coolant temperature of the internal combustion engine
• Climate control, control unit has retracted approval.

An automatic engine start can occur for every engaged gear range. If the vehicle is brought to a standstill after electric operation and the driver door is opened, the driver is reminded about the continuing driving readiness of the vehicle.

For an engaged gear range "P" or "N" the internal combustion engine is started as a reminder.

For an engaged gear range of "D" or "R", an indication occurs in the instrument cluster (A1).

For an automatic engine start during the vehicle standstill the required motor-generated torque from the electrical machine is calculated by the CDI control unit or the ME-SFI [ME] control unit. In order to prevent an automatic engine stop and for an opened engine hood an automatic engine start, the signal about the status of the engine hood is also read in via the CAN network from the CDI control unit or the ME-SFI [ME] control unit.

The CDI or ME-SFI [ME] control unit requests actuation of the wet clutch or engine separator clutch via the CAN network from the fully integrated transmission control unit in order to connect the combustion engine with the automatic transmission.

Further information concerning actuation of the wet clutch or engine separator clutch is available in the associated documents.

After receiving feedback that the wet clutch or engine separator clutch is closed, the CDI or ME-SFI [ME] control unit sends a request via the CAN network to actuate the electric machine in order to start the combustion engine.

Recognition of the start end takes place over the engine speed or, in the case of a torque-led start, over a differential torque assessment between the torque generated by the electrical machine and the torque from the internal combustion engine.

	Electrical function schematic for automatic engine start		PE08.30-P-2052-97SEH
	Overview of system components, hybrid drive system		GF08.30-P-9999LFH