Recuperative braking, function - GF42.22-P-1010FLH

MODEL 212.095 with ENGINE 276.952 up to model year 2014 

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

Function requirements for regenerative braking system, general

• Hybrid system "READY" (yellow or green)
• Selector lever position "D"
• Vehicle speed > 0 km/h

Regenerative braking, general 

In regenerative braking, only a part, or at low braking, the entire braking torque is generated by the electrical machine (A79/1). The high-voltage battery is charged with the electrical energy produced in the process (A100g1). The CDI control unit (N3/9) (for diesel engine) or ME-SFI [ME] control unit (N3/10) (for gasoline engine) reads in the following signals for regenerative braking:

• Battery management system control unit (N82/2) via hybrid CAN (CAN L)
• Voltage of high voltage battery
• Temperature of high voltage battery
• Regenerative braking system control unit (N30/6) via chassis CAN (CAN E)
• Wheel speed
• Requested regenerative braking torque over chassis CAN
• Power electronics control unit (N129/1) via hybrid CAN
• Status of electric machine
• Available torque from electric machine
• Torque of electric machine
• Rotational speed of electric machine
• Charging voltage/current, signal

Regenerative braking system function sequence 

The CDI control unit or the ME-SFI [ME] control unit forecasts the current status of the maximum available regenerative braking torque, which can be generated by the electrical machine. This then sends it over the chassis CAN to the regenerative braking system control unit. To do so, it permanently reads in the status of the torque available from the electric machine over the hybrid CAN as sent by the power electronics control unit. The CDI or ME-SFI [ME] control unit uses the calculated charge level for the high-voltage battery and the maximum tolerable charging current to forecast the maximum available regenerative braking torque. The regenerative braking system control unit divides the overall braking torque moment requested by the driver according to the driving condition into a regenerative (to be implemented by the drivetrain) part and a hydraulic (to be implemented over the wheel brake) braking torque moment.

If the required overall brake torque can be generated by regeneration alone or together with the internal combustion engine's deceleration fuel shutoff, the distribution into an additional hydraulic portion is no longer required.

Additional information on deceleration fuel shutoff is available in the following document:

• Deceleration mode, function 

In the event of an emergency stop, or a fault in the hybrid system, the braking torque is generated hydraulically only. The regenerative braking torque portion is requested by the regenerative braking system control unit over the chassis CAN from the CDI or MESFI [ME] control unit. The CDI or ME-SFI [ME] control unit sends the request for a generated torque to the power electronics control unit over the hybrid CAN. This actuates the electrical machine as a generator and it thereby generates the requested regenerative braking torque. The actual realized braking torque, set by the power electronics control unit, is forwarded by the CDI or the ME-SFI [ME] control unit over the chassis CAN back to the regenerative braking system control unit. This checks the realization of the requested overall braking torque and hydraulically regulates as required, or it sends a new request to the CDI or the ME-SFI [ME] control unit.

The three-phase AC voltage generated during regenerative braking by the electrical machine is converted by the power electronics control unit into high-voltage DC voltage and supplied to the high-voltage battery.