System functions
The following system functions of the power supply system are described:
- Power management with engine running:
"Basic Power Management" functions with standard equipment and "Advanced Power Management" with High equipment level
- Emergency operation in the event of bitserial data interface failure
- Energy management even when engine is not running:
Power supply for control units, consumer cutoff of auxiliary consumers and off-load current monitoring
- Data transfer for power supply
Power management
The power management system is the most important component of the energy management system.
The power management system is a software package in the engine control unit (DME or DDE).
When the engine is running, the power management system regulates the alternator voltage.
Depending on the vehicle's equipment, there are 2 versions of the power management:
- Basic Power Management (BPM)
- on vehicles with standard equipment and only a few items of special equipment
Basic Power Management controls the idle speed.
Basic Power Management also specifies the charge voltage according to demand.
- Advanced Power Management (APM)
- on vehicles with High equipment level, e.g. with the following items of special equipment:
- CCC: Car Communication Computer
- M-ASK: Multi-audio system controller
- BMW "Professional" radio in US version
- Telephone in US version.
Advanced Power Management is only available with the intelligent battery sensor. Advanced Power Management gives precise consideration to the current battery condition: The intelligent battery sensor reads the corresponding data.
When the engine is running, the power management system regulates the following:
- Alternator voltage regulation
When the engine is running, the alternator generates a variable voltage, the alternator voltage.
This variable alternator voltage is regulated by the power management according to the following criteria:
- Nominal value for alternator voltage:
The respective nominal value for alternator voltage depends on how many electrical consumers are switched on.
- Battery temperature:
To prevent the battery from overheating, the optimum charge voltage is regulated.
The alternator voltage is regulated by the engine control unit (DME or DDE).
The alternator should always deliver as much current as the electrical consumers need.
The engine control unit adapts the alternator voltage as follows, depending on the consumers in use:
- By increasing engine speed
- By increasing excitation current to alternator coils
The data is exchanged via the bitserial data interface.
- Battery charging regulation
On vehicles without intelligent battery sensor, the battery temperature (for example) is calculated.
On vehicles with intelligent battery sensor, the battery condition is recorded precisely by the intelligent battery sensor.
- Load-dependent reduction of some consumers
- Only on vehicles with High equipment level and intelligent battery sensor
On vehicles with intelligent battery sensor, consumers may be reduced or even switched off altogether, even if the engine is running.
This consumer cutoff reduces current consumption in critical situations.
This ensures that the battery is not discharged.
The affected consumers are either switched off completely of their power output is reduced.
On vehicles with diesel engine, the power consumption of the electric auxiliary heater is regulated.
- Basic Power Management (BPM)
Emergency operation in the event of bitserial data interface failure
If the bitserial data interface between the engine control unit and the alternator is interrupted, the alternator voltage will be regulated to a constant 14.3 V.
Energy management system
The energy management system is software package in several control units, e.g.:
- CAS: Car Access System
- JBE: Junction Box Electronics
- Engine control unit: DME or DDE).
The energy management system monitors and regulates the power supply, even when the engine is not running.
- Power supply for control units
To ensure that the vehicle retains its starting capability, there are two additional terminals for permanent current (terminal 30):
- Terminal 30g (active)
- Terminal 30g-f (cutoff in case of fault, only on vehicles with High equipment level).
These new terminals allow consumers to be cut off and off-load current to be monitored when the vehicle is our of use.
- Auxiliary consumer cutoff
Terminal 30g (terminal 30 active): Terminal 30g means "active continuous positive": Components with power supply via terminal 30g are switched off according to time.
The Car Access System (CAS) uses terminal 30g as follows to effect a time-controlled cutoff of control units and components with power supply: Approximately 30 minutes after terminal R is switched OFF, the power supply for these components is switched off. This prevents the battery from being subjected to excess load by the electrical consumers for too long when the vehicle is out of use.
- Control unit cutoff in case of fault
Cutoff in case of fault is only available on vehicles with High equipment level (e.g. on vehicles with CCC or M-ASK).
Cutoff in case of fault helps to maintain the vehicle's ability to start.
All control units and components on terminal 30g-f are cut off if any of the following faults develop:
- Control units frequently woken up after terminal R is switched OFF: Some control units do not "go to sleep", but rather remain active.
- Prolonged undervoltage on bus systems
- Data buses do not go to "sleep" after terminal R is switched OFF.