Automatic engine start, function - GF08.30-P-3002FLM

ENGINE 276.952 in MODEL 212.095 as of model year 2014 

ENGINE 651.924 in MODEL 212.098/298 as of model year 2014 

The subfunction "automatic engine start function" is considered and described from the point of view of the hybrid system. Information for partial function "Energy management start-stop function" for the 12-V on-board electrical system is documented in the function description "Energy management of start-stop function". Information about the subfunction "engine timing start-stop function" is document from the point of view of the engine timing of the internal combustion engine in the function description "engine timing start-stop".

Function requirements for an automatic engine start - general points

• Hybrid drive "READY" (green or yellow)
• The engine is stationary after an automatic engine stop (electrical driving mode)
• 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) (for example in electrical driving mode)
• The electrical machine (A79/1) (at vehicle standstill), requested via the hybrid CAN (CAN L) from the power electronics control unit (N129/1)

The start of the combustion engine over the electrical machine alone can only take place if the vehicle is stationary and the charge level of the high-voltage battery (A100g1) is adequately high. During electric driving mode for an open wet clutch starting is always initially over the starter up to a certain rotational speed of the 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.

Internal signals from the internal combustion engine which are read in for the automatic engine start are described in the following document:

• Engine timing, start/stop function 

Information about starting the internal combustion engine with the starter and the electrical machine are described in the following document:

• Starting, function 

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

• Torque coordination, function 

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:

• Regenerative braking system control unit (N30/6), wheel speed over chassis CAN 1 (CAN E1)
• Wheel speed
• Engine stop prohibition
• Engine start request
• Automatic air conditioning control and operating unit (N22/7), status of air conditioning system via interior CAN (CAN B) and chassis CAN 1
• Battery management system control unit (N82/2) via hybrid CAN (CAN L)
• high-voltage battery voltage (A100g1)
• Temperature of high-voltage battery
• Power electronics control unit (N129/1) via hybrid CAN
• 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 drive train CAN (CAN C)
• Gear range status
• Transmission oil temperature
• Status of the electric transmission oil pump (M42)
• Wet clutch status
• Supplemental restraint system control unit (N2/10), direct crash signal
• Supplemental restraint system control unit via chassis CAN 1
• Indirect crash signal
• Status of driver seat belt
• Signal engine hood closed (with code (U60) Pedestrian protection)
• Front SAM control unit with fuse and relay module (N10/1) via the chassis CAN 1
• Air conditioning status
• Engine stop prohibition
• Engine start request
• Signal from the door contact on the front left
• Signal engine hood closed (with code (551) Antitheft alarm system (ATA))

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.

The start 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
• RBS has retracted a release
• 12-V energy management has its release retracted
• Charge level of the high-voltage battery is below the threshold value
• Oil supply of the AT over the electric transmission oil pump not secured
• Driver identified as absent
• Interior temperature cannot be regulated with the current coolant temperature of the internal combustion engine

An automatic engine start can occur for every engaged gear range. If the vehicle is brought to a standstill after electric driving mode 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 chassis CAN 1 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. Additional information concerning actuation of the wet clutch is described in the following document:

• Wet clutch, function 

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 hybrid CAN in order to start the internal 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.