GF54.10-P-0003LE Energy Management, Function

GF54.10-P-0003LE Energy Management, Function

General function requirements
^ Terminal 30

Energy management, general
The energy management system manages the supply and consumption of electrical energy with the aim of ensuring the starting ability of the engine and a stable power supply to all electrical consumers.

In the energy management system, only the low voltage network (12 V) is described; for hybrid cars the correlation between high voltage and low voltage networks is also described. A detailed description of the high voltage network is provided in the function description of the hybrid drive systems.

This is accomplished using the following subfunctions:
^ Alternator actuation, function
^ Energy management, function
^ Energy transfer of high-voltage/low-voltage on-board electrical system, function (model 221.095/195)

Further partial functions are described in separate documents:
^ Engine off energy management, function
^ Engine on energy management, function

Depending on the engine mounted in the vehicle, either the CDI control unit (N3/9) (with diesel engine) or the ME-SFI [ME] control unit (N3/10) (with gasoline engine) is installed. The term "engine control unit" is used below to refer to both control unit types.

Alternator actuation, function
Control of the alternator (G2) is performed according to the requests made by engine control unit. The engine control unit calculates the specified voltage values from the specified values from the on-board electrical system management system. The alternator is controlled on the basis of this calculation. Communication with the alternator and requests to it take place via the drive LIN (LIN C1).

The engine control unit is active as a master control unit for the AC generator.
On model 221.095/195, the alternator is only activated if the energy provided by the DC/DC converter control unit (N83/1) from the high-voltage on-board electrical system is not sufficient.

Energy management, function
The energy management system monitors the capacity of the onboard electrical system and actively intervenes in balancing energy requirements. The aim is to ensure a stable power supply for the electrical consumers in the 12 V on-board electrical system.

The following components are involved in energy management:
- On-board electrical system battery (G1) (power storage and supply when the engine is off)
- Battery sensor (B95) (monitoring of charge level)
- Alternator (energy generation)
- DC/DC converter control unit (on model 221.095/195) (energy supply)
- From high-voltage electrical system to low-voltage electrical system for vehicle operation
- From low-voltage electrical system to high-voltage electrical system for charging discharged high-voltage battery (A100g1))
- Engine control unit (alternator actuation, high-voltage on-board electrical system control)
- Front SAM control unit with fuse and relay module (N10/1) (control of energy management)

The energy requirements of all electrical consumers are defined based on the state of the on-board electrical system battery, which is permanently monitored by the battery sensor. The battery sensor uses various voltage, current and temperature measurements to compute parameters that serve as the basis for energy management.
Energy management influences the power output of the alternator or of the DC/DC converter control unit such as to achieve a balanced, positive charge/discharge ratio in the on-board electrical system battery and provide for fuel-efficient operation of the vehicle.

Model 221.095/195:
The 12 V on-board electrical system is supplied with energy primarily via the DC/DC converter control unit. Energy is supplied to the 12 V on-board electrical system via the DC/DC converter control unit as follows:
- with engine OFF or during boost mode: from the energy stored in the high-voltage battery
- with engine ON: from the energy generated in the integrated starter alternator (A79)

If the energy provided by the DC/DC converter control unit cannot cover the power requirement, the alternator is activated as an auxiliary power source.

Energy transfer of high-voltage/low-voltage on-board electrical system, function (model 221.095/195)
Because of the hybrid drive used, the vehicle is equipped with an additional high-voltage on-board electrical system (U = 140 V). The energy management module in the ME-SFI [ME] control unit regulates the energy flows in the high-voltage on-board electrical system along with the voltage conversion and energy exchange from and to the 12 V on-board electrical system.
In addition, the ME-SFI [ME] control unit communicates with the DC/DC converter control unit via the drive train sensor CAN (CAN I) and with the alternator via the drivetrain LIN. The 12 V on-board electrical system is supplied with energy primarily from the high-voltage on-board electrical system ("buck mode").

For this purpose, energy is supplied to the 12 V on-board electrical system via the DC/DC converter control unit as follows:
- with engine OFF or during boost mode: from the energy stored in the high-voltage battery
- with engine ON: from the energy generated in the integrated starter alternator

In the case of extremely low outside temperatures, the 12 V on- board electrical system may assist the high-voltage on-board electrical system via the DC/DC converter control unit in order to ensure the starting ability of the engine ("boost mode").

The following components are involved in the high-voltage energy management:
- High-voltage battery module (energy storage and supply at engine OFF)
- Integrated starter alternator (energy generation for high-voltage on-board electrical system)
- Engine control unit (energy management and alternator management)
- Battery management system control unit (N82/2) (on model 221.095/195) (monitoring of high-voltage battery charge level)
- DC/DC converter control unit (energy conversion from high voltage to low voltage)
- Power electronics control unit (N129/1) (regulation of integrated starter alternator)