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

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 start 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, the A/T, the RBS and the 12 V on-board electrical 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).
• the electrical machine (A79/1) (for vehicle standstill), requested via the CAN network for power electronics control unit (N129/1).
• 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 electrical operation with an opened wet clutch, starting always occurs first over the starter up to a certain rotational speed of the internal combustion engine.

If this starting speed is reached then the internal combustion engine is subsequently up to idle speed over the drive through closing the wet clutch.

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

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
  • 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)

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 internal combustion engine is initiated if

• Vehicle speed > 160 km/h
• Transmission oil temperature < 0°C
• The vacuum in the brake booster is not adequate
• Enable canceled by ESP®.
• 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 canceled 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 "D" or "R" an indication occurs in the multifunction display (A1p13) in the IC (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 control unit or the ME-SFI [ME] control unit requests actuation of the wet clutch via the drive train CAN from the fully integrated transmission control unit in order to connect the internal combustion engine with the automatic transmission.

After receiving the respective feedback over the closed wet clutch the CDI control unit or the ME-SFI [ME] control unit requests actuation of the electrical machine from the power electronics control unit via the CAN network in order to start the internal combustion engine.

The end of the starting procedure is detected via the engine speed or, in the case of a torque-led start, by means of a differential torque assessment between the motorized torque generated by the electric machine and the torque from the combustion engine.

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