Recuperative Braking, Function - GF42.22-P-1010GRH

MODEL 166 with ENGINE 276.821 

The subfunction "regenerative braking, function" is considered and described from the point of view of the hybrid system.

We will not go into more detail here about internal signals and function sequences of the regenerative braking system.

Function requirements for regenerative braking system, general 

• Hybrid drive system "READY"
• 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 (A100g1) is charged with the electrical energy generated here.

For regenerative braking, the ME-SFI [ME] control unit (N3/10) reads in the following signals via the CAN network:

• Battery management system control unit (N82/2)
  • High-voltage battery voltage
  • Temperature of high-voltage battery
• Electronic Stability Program control unit (N30/4)
  • Wheel speed
  • Requested regenerative braking torque
• Power electronics control unit (N129/1)

• Status of electrical machine
• Available torque from electrical machine (regenerative braking torque)
• Torque of electrical machine
• Rotational speed of electrical machine
• Charging voltage/current, signal

Regenerative braking system function sequence 

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. It sends this to the Electronic Stability Program control unit via the CAN network. To do so, it permanently reads in the status of the torque available from the electrical machine over the CAN network as sent by the power electronics control unit. The ME-SFI [ME] control unit uses the calculated charge level of the high-voltage battery and the maximum tolerable charging currents to forecast the maximal available regenerative braking torque.

The Electronic Stability Program control unit divides the overall braking torque requested by the driver according to the driving condition into regenerative (to be implemented by the drive train) and hydraulic (to be implemented over the service brake) braking torque. 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.

In the event of a full-stop braking action or a fault in the hybrid drive system, the braking torque is generated hydraulically only. The Electronic Stability Program control unit requests the regenerative braking torque proportion from the ME-SFI [ME] control unit via the CAN network. The ME-SFI [ME] control unit transmits the request for regenerative torque to the power electronics control unit via CAN network. This actuates the electrical machine as a generator and it thereby generates the requested regenerative braking torque. The braking torque that has actually been implemented, which has been transmitted from the power electronics control unit, is relayed by the ME-SFI [ME] control unit back to the Electronic Stability Program control unit via the CAN network.

This checks the realization of the requested overall braking torque and hydraulically regulates as required, or it sends a new request to the ME-SFI [ME] control unit.

The 3-phase AC voltage generated during regenerative braking by the electric machine is converted by the power electronics control unit into high-voltage DC voltage and supplied to the high-voltage battery.

	Electrical function schematic for regenerative braking		PE08.30-P-2068-97NAH
	Overview of system components, hybrid drive system		GF08.30-P-9999GRH