GF54.10-P-0004GM on-Board Electrical System Function

GF54.10-P-0004GM On-board Electrical System Function

General function requirements
^ Terminal 30

On-board electrical system control, general
The on-board electrical system provides electrical power, with the intention of ensuring that the engine will start 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 cars the correlation between high voltage and low voltage networks.
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, for model 164.195)
- Battery (G1) (for energy storage and power supply with engine OFF)
- Additional battery (G1/7)
- With code (U80) 115 V socket in load compartment: DC/AC converter control unit (115 V socket) (N24/3) and 115 V socket (X58/34) with integrated socket microswitch (X58/34s1)
- 12 V sockets
- All electrical components that affect the performance of the onboard electrical system

The on-board electrical system consists of the following component functions:
^ 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 partial functions are described in separate documents:
^ 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 AC generator is controlled by the ME-SFI [ME] control unit (N3/10) (gasoline engine) or the CDI control unit (N3/9) (diesel engine). The ME-SFI [ME] control unit or the CDI control unit calculates the specified values for the on-board electrical system, and then, based on this computation, the AC generator is activated. Communication with the AC generator and requests to it takes place over the drive LIN (LIN C1).
The engine control unit is active as a master control unit for the AC generator.

Function sequence for power transfer of high voltage/low voltage on-board electrical system, function (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 from and to the 12 V on-board electrical system. To do this the power electronics control unit communicates with the DC/DC converter control unit and the battery management system control unit (A100n1) through the hybrid CAN (CAN L).
In order to achieve a permanent supply of electrical energy, the DC/DC converter control unit is designed as a bidirectional DC voltage converter, which generates high and low DC voltage and transfers this between the high-voltage 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 the control units in the vehicle are switched automatically to power reduction or they switch into a quiescent state (shutoff).
In the same manner the control units are also switched off in the event of any overvoltage as a safeguard against 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 be able to shift the transmission to position "P" even when the on-board electrical system has malfunctioned, the intelligent servo module for DIRECT SELECT (A80) has an additional second power supply applied to it over the EIS [EZS] control unit (N73) from the additional battery. The capacity of the additional battery is 1.2 Ah.

The power supply via additional battery function sequence 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 U ≥6 V
^ 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). Charging is only interrupted while battery state recognition is being performed. 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 for the additional battery is integrated into the front SAM control unit to provide information about the availability of 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 battery state recognition, the voltage of the additional battery is continuously 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.
On model 164.1 and model 251, the sockets can only be used with circuit 15 ON.
On model 164.8, 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 model 251 there is
- One socket in the front passenger footwell,
- Two sockets on the center console in the rear and
- One socket in the load compartment on the right-hand side trim.

The sockets in the front passenger footwell and load compartment are fused together, as are the sockets in the rear.

On model 164.8 there is
- One socket on the center console and
- One socket in the load compartment on the left-hand side trim.