On-board electrical system function - GF54.10-P-0004GM

MODEL 164.1 as of model year 2009 

MODEL 164.8, 251.0/1 as of model year 2009 

Function requirements, general 

• Circuit 30 ON

On-board electrical system control, general 

The on-board electrical system provides electrical power, the objective being to ensure that the engine can start reliably and that all the electrical consumers have a stable power supply.

In the on-board electrical system only the low voltage network (12 V) is described, for hybrid vehicles (164.195) the correlation between the high voltage and low voltage networks is also described. A comprehensive description of the high voltage network is provided in the function description for the hybrid drive system.

The on-board electrical system consists of the following components:

• AC generator (G2) (for power generation, except model 164.195)
• DC/DC converter control unit (N83/1) (for power generation, on model 164.195)
• Battery (G1) (for energy storage and power supply with engine OFF)
• Additional battery (G1/7)
• With code (U80) 115V socket in load compartment:
  • DC/AC converter control unit (115 V socket) (N24/3)
  • 115 V socket (X58/34) with integrated socket microswitch (X58/34s1)
• 12 V sockets
• All electrical components that affect the performance of the on-board electrical system

The on-board electrical system encompasses the following subfunctions:

• Function sequence for actuation of AC generator (except model 164.195) 
• Function sequence for power transfer of high voltage/low voltage on-board electrical system (for model 164.195) 
• Consumer shutoff function sequence 
• Power supply via additional battery function sequence 

Further subfunctions are described in :

• DC/AC converter function 
• Pyrofuse actuation function (model 164.8 with engine 642 or model 164.195) 

Function sequence for actuation of AC generator (except model 164.195) 

The alternator is controlled by the CDI control unit (N3/9) (for diesel engine) or the ME-SFI control unit (N3/10) (for gasoline engine). The CDI control unit or the ME-SFI control unit calculates the specified values for the on-board electrical system. The alternator is controlled on the basis of this calculation. The CDI control unit or the ME-SFI [ME] control unit communicates with the alternator via the drive train LIN (LIN C1).

The CDI control unit or the ME-SFI [ME] control unit is active as the master control unit for the alternator.

Function sequence for power transfer of high voltage/low voltage on-board electrical system (for model 164.195) 

Because of the hybrid drive used, the vehicle is equipped with an additional high-voltage on-board electrical system (U = 300 V). The energy management module in the power electronics control unit (N129/1) regulates the energy flows in the high-voltage system along with the voltage conversion and energy exchange with the 12 V on-board electrical system. To do this the power electronics control unit communicates over the hybrid CAN (CAN L) with the DC/DC converter control unit and the battery management system control unit (A100n1). In order to ensure a permanent supply of electrical energy, the DC/DC converter control unit is designed as a bidirectional DC voltage converter which generates a high and low DC voltage and transfers this between the high-voltage on-board electrical system and the 12 V on-board electrical system.

The following components are involved in the high-voltage energy management:

• High-voltage battery module (A100) (Energy storage and supply at engine OFF)
• Power electronics control unit
• DC/DC converter control unit

Consumer shutoff function sequence 

The consumer shutoff is decentralized only to ensure that in the event of any drop in power (poor batter charge level) the most important vehicle functions are maintained for as long as possible. When required, all control units in the vehicle change over automatically to power reduction mode or they switch to a quiescent state (shutoff). In the same manner, the control units are also switched off in the event of overvoltage in order to prevent malfunctions and damage to the consumers. As soon as the on-board electrical system voltage stabilizes again, the control units are automatically activated again.

Power supply via additional battery function sequence 

In order to shift the transmission into the "P" position even when the on-board electrical system malfunctions, the intelligent servo module for DIRECT SELECT (A80) is also powered through the EIS control unit (N73) from the additional battery. The capacity of the additional battery is 1.2 Ah.

The function sequence for power supply via the additional battery comprises the following subfunctions:

• Charging of additional battery function sequence 
• Additional battery state recognition function sequence 

Additional function requirements for charging additional battery 

• Voltage of additional battery U6V
• On-board power supply voltage U < 15.5 V

Charging of additional battery function sequence 

The additional battery is continuously charged while the engine is running after battery state recognition is performed. The additional battery is charged over the front SAM control unit (N10). The additional battery is only charged as long as the battery state recognition is interrupted. To prevent any overloading of the additional battery the charging current is limited. A diode prevents the additional battery from feeding back into the on-board electrical system.

Additional battery state recognition function sequence 

A simple battery state recognition function is integrated in the front SAM control unit in order to provide information about the availability of electrical energy from the additional battery. This function is performed directly after the engine is started. If the engine is switched off while battery state recognition is being performed, recognition is aborted and the measurements and results obtained by that point are discarded. In addition to the battery state recognition, the voltage of the additional battery is also constantly checked. To perform this check, charging must be stopped for t = 20 ms. The check is performed every t = 5 s.

12 V sockets: 

The sockets are designed for accessories up to max. P = 180 W (model 164) or P = 240 W (model 251). The maximum current consumption of I = 20 A may not be exceeded. When all sockets in the vehicle are used, the maximum current consumption is I = 55 A. The sockets can also be used with circuit 15 OFF. An emergency shutoff system ensures that the on-board power supply voltage does not drop too much. If the on-board power supply voltage is too low, the sockets are switched off automatically. This leaves enough power to start the engine.

On model 164.1 and on model 251, there is:

• One socket in the front passenger footwell
• Two sockets on the center console in the rear
• One socket in the load compartment on the right-hand side trim

The sockets in the front passenger footwell and the cargo area are jointly fused. The sockets in the rear are also jointly fused.

On model 164.8, there is:

• One socket on the center console
• One socket in the load compartment on the left-hand side trim

On-board electrical system, location of components	MODEL 164.1 as of model year 2009	GF54.10-P-0004-01GQ
	MODEL 164.8 as of model year 2009	GF54.10-P-0004-01GM
	MODEL 251.0/1 as of model year 2009	GF54.10-P-0004-01GV
On-board electrical system block diagram		GF54.10-P-0004-02GM
DC/AC converter function	MODEL 164.1 as of model year 2009 with CODE U80 (115 V socket in load compartment) MODEL 164.8, 251.0/1 as of model year 2009 with CODE U80 (115 V socket in load compartment)	GF54.10-P-2005GM
Deploying of pyrofuse, function	MODEL 164.1 (except 164.195) with ENGINE 272 as of model year 2010MODEL 164.195 as of model year 2009 MODEL 164.8 with ENGINE 273 as of model year 2010MODEL 164.8 with ENGINE 642 as of model year 2009	GF91.60-P-2011GM
Overview of system components of on-board electrical system control		GF54.10-P-9995GM