Deactivation of hybrid drive system, function - GF08.30-P-1004FLH

ENGINE 276.952 in MODEL 212.095 up to model year 2014 

ENGINE 651.924 in MODEL 212.098/298 up to model year 2014 

Function requirements for deactivating a hybrid drive system, general points 

• Hybrid system "READY" (yellow or green)

Deactivating a hybrid drive system - general points 

In order to deactivate the hybrid system the CDI control unit (N3/9) (for a diesel engine) or ME-SFI [ME] control unit (N3/10) (for a gasoline engine) makes the request to the battery management system control unit (N82/2) to switch off the contactor (A100s1). The CDI control unit or ME-SFI [ME] control unit assesses is status and controls discharging of the intermediate circuit over the power electronics control unit (N129/1) and retracts the release of system readiness.

To do this the CDI control unit or ME-SFI [ME] control unit reads in the following sensors and signals:

• Battery management system control unit via the hybrid CAN (CAN L)
• High-voltage battery voltage (A100g1)
• Status of the contactor over hybrid CAN
• Temperature of high-voltage battery
• Power electronics control unit via the hybrid CAN
• Status of the electrical machine (A79/1)
• Voltage status of the intermediate circuit discharge

Function sequence for deactivation of the hybrid drive system 

The CDI control unit or ME-SFI [ME] control unit makes the request from the battery management system control unit via the hybrid CAN under the conditions described more precisely below for switching off of the contactor.

Switching off path

The switching off path is used for severe system failures (e.g. CAN failure) in order to power down the high voltage on-board electrical system and the HD. The status hybrid system "READY" is retracted after powering down, the internal combustion engine is switched off and the vehicle is no longer ready to drive.

If a very serious system failure is detected on the hybrid system, the CDI control unit or the ME-SFI [ME] control unit transmits a shut-down signal over the switching off path to the power electronics control unit (N129/1) to shut down the hybrid system.

After successful switching off of the contactor the battery management system control unit alters the status of the contactor and sets the status in the hybrid CAN. In the case of failure of the status signal and message failure the CDI control unit or the ME-SFI [ME] control unit sets the status of the contactor to a substitute value.

If the information is present over the switched off contactor in a crash case, the CDI control unit or the ME-SFI [ME] control unit requests active discharging of the intermediate circuit capacitor from the power electronics control unit via the hybrid CAN.

In order to secure discharging of the intermediate circuit, the power electronics control units checks the voltage after opening of the contactor and reports this via the hybrid CAN to the CDI control unit or the ME-SFI [ME] control unit. In the case of signal and message failure the CDI control unit or the ME-SFI [ME] control unit sets the voltage information respectively to a substitute value. If the maximum discharge time does not reach the minimum value of the voltage after the procedure, a fault memory entry takes in the CDI control unit or the ME-SFI [ME] control unit.

After successful switching off the high-voltage on-board electrical system the CDI control unit or the ME-SFI [ME] control unit retracts system readiness of the hybrid drive system. The CDI control unit or the ME-SFI [ME] control unit transmits this status via the chassis CAN (CAN E) to the IC (A1), which switches off the display "READY". The CDI control unit or the ME-SFI [ME] control unit retracts the system readiness "READY" of the hybrid system after taking back of the system readiness and discharge of the intermediate circuit and switches off the internal combustion engine if necessary.

The vehicle is no longer ready to drive without the system readiness "READY" (yellow or green).