Automatic engine stop, function - GF08.30-P-3001FLM

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 stop 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 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".

Function requirements for an automatic engine stop - general points

• Hybrid drive "READY" (green)
• 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 mode 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 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 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
• 12 V on-board electrical system
• Vehicle climate control
• Regenerative braking system

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

• engine timing, start/stop 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 documents:

• Torque coordination for a hybrid drive system, function 
• Torque coordination, function 

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

• Automatic air conditioning control and operating unit (N22/7), status of air conditioning system via interior CAN (CAN B) and chassis CAN 1 (CAN E1)
• Regenerative braking system control unit (N30/6), wheel speed via chassis CAN 1
• Wheel speed
• Engine stop prohibition
• Engine start request
• 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 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)
• 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 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))

If the combustion engine is off (e.g. automatic engine stop), the oil supply for the AT is secured over the electrical transmission oil pump. Additional information about the oil supply for the AT is described in the following document:

• Oil supply for automatic transmission, function 

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 electrical transmission oil pump is checked before triggering the automatic engine stop and then immediately actuated or actuated during triggering the automatic engine stop by the fully integrated transmission control unit. The electric transmission oil pump safeguards the hydraulic system's oil supply in the automatic transmission when the internal combustion engine is switched off. The internal combustion engine is switched off by the CDI control unit or the ME-SFI [ME] control unit if certain internal combustion engine conditions are fulfilled and all of the following conditions and releases have been awarded:

• Vehicle speed < 160 km/h
• Transmission oil temperature > 0°C
• Gear range plausible
• Adequate vacuum in the brake booster
• RBS has issued a release
• 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 adequate
• Oil supply to A/T secured
• Driver door closed
• Driver seat belt buckled
• Interior temperature can be regulated with the current coolant temperature of the internal combustion engine
• Interior temperature can be regulated with the current coolant temperature
• AAC control and operating unit has issued a release

The CDI control unit or the ME-SFI [ME] control unit makes the request via the drive train CAN to the fully integrated transmission control unit () for actuation of the wet clutch in order to disconnect the internal combustion engine from the drive. After appropriate feedback the CDI control unit or the ME-SFI [ME] control unit switches the internal combustion engine off over the opened wet clutch. Additional information concerning actuation of the wet clutch is described in the following document:

• Wet clutch, function 

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. Additional information and descriptions of the automatic engine start can be found in the following documents:

• Automatic engine start function 
• Engine timing, start/stop function 
• Starting, function