System functions

The power supply system comprises the following functions:

• Electric energy management
• Power management
• Variable charge voltage
• Idle-speed increase
• Reduction of load peaks
• Consumer shutdown
• Off-load current monitoring
• Terminal 30g relay

Electric energy management 

The electric energy management monitors and controls the vehicle's energy requirements. The monitoring and control functions are performed by the interconnection of various components. The energy management links functions, signals and maps for generating and outputting control signals.

• Components of the energy management system:
  • Battery
  • Intelligent battery sensor (IBS)
  • Bit-serial data interface (BSD)
  • DME or DDE
  • Engine
  • Power management (microcontroller)
  • Micro-power module (MPM)

    >From 09/2005, MPM function is integrated into the body-gateway module (KGM)

  • Alternator
  • Terminal 30g relay
  • Consumers on terminal 30/terminal 30g
• Function/systems involved in energy management:
  • Power management
  • Car Access System (CAS)
• Signals/characteristic curves in energy management system:
  • Current flow to consumers
  • Increased idling speed
  • Battery charge current
  • Nominal value for charge voltage
  • Reduced fuel consumption
  • Terminal 15 wake-up wire

Power management 

The power management is on the one hand part of the electrical energy management system. Power management is software stored in the DME or DDE and in the intelligent battery sensor that is used for controlling the vehicle's energy requirements.

Power management comprises the functions controlled by the software in the DME / DDE and in the IBS:

• Variable charge voltage for the battery by adapting the charge voltage from the alternator to that required by the battery
• Increased idling speed to boost the alternator's output
• Reduction of load peaks through power reduction when the vehicle's electrical system is unable to provide the energy needed (vehicle electrical system deficiency)
• Auxiliary consumers switched off via CAN messages when engine has reached its limit of starting capability
• Off-load current monitoring

Power management links the input signals with the characteristic curves stored in an EPROM (Erasable Programmable Read-Only Memory) and generates the output signals to control energy requirements.

• Power management components:
  • DME or DDE
  • EPROM
  • Microcontroller
• Power management input signals:
  • Battery voltage (U)
  • Current (I ±)
  • Temperature (T)
• Characteristic curves
  • Battery voltage (U)
  • Current (I ±)
  • Temperature (T)
• Output signals
  • Idle-speed control
  • Nominal value for charging voltage
  • Auxiliary consumer shutdown
  • Load peak reduction

Power management registers the battery charge state and the battery condition.

• Battery charge balance 

  The charge balance of the battery is determined by the charge quantity flowing into and out of the battery. Two counters are provided in the power management to give a running balance of the battery's charge state. One of the counters counts the charge quantity taken up by the battery. Another counter counts the charge quantity discharged from the battery. At the factory, the counters are calibrated for the battery fitted. The IBS transmits the data to power management in the DME / DDE. Data is transmitted via the bitserial data interface (BSD). The difference between the two charge levels is the battery charge state (SoC: "State of Charge"). Following an engine shutdown, the power management computes the current battery charge state for the next engine start.

• Battery condition 

  The battery condition (SoH: "State of Health") is derived from the drop in battery voltage and the current drawn during engine start. These data are measured by the IBS during the starting procedure. The average value of the starting current in the start phase and the value of the voltage dip are transmitted to the DME / DDE via the bit-serial data interface (BSD). The starting procedure is indicated to the IBS by currents greater than 200 amperes (A). The "engine running" signal is output by the DME / DDE as soon as the engine starts. The power management system calculates the battery's internal resistance from the average value of the starting current and the value of the voltage dip. Conclusions about the battery's condition can be drawn from its internal resistance.

Variable charging voltage 

The variable charging voltage for the battery ensures that an optimal battery charge state is maintained, even in unfavorable driving situations. Unfavorable driving situations are, e.g. city traffic and driving in congested traffic.

The charging voltage varies, depending on

• Battery temperature and
• Consumer current.

  Battery temperature 

  The temperature-dependent adjustment of the battery charging voltage prevents an undesirable increase of the battery temperature during recharging.

  Moreover, the battery temperature remains lower, even at higher ambient temperatures. This reduces the amount of gas generated during charging and the amount of distilled water consumed.

  Consumer current 

  The level of consumer current is measured by the IBS and transmitted to the power management via the bit - serial data interface (BSD). From this, the power management derives the charging voltage level to be generated by the alternator. This charging voltage nominal value, as derived by the power management, determines the level of the charging voltage generated by the alternator. This determines the battery charge current, which in turn influences the battery charging process, and ultimately the vehicle's consumer current.

Idling speed increase 

The idling speed of the engine is raised by the DME / DDE to 750 RPM if the specified battery charging voltage level is not achieved.

The idling speed is raised when

• the alternator is at full capacity

  and

• the battery charge state is too low.

Load peak reduction 

If the charge state of the battery does not improve, even after the idling speed has been increased, the peak load in the vehicle electrical system is reduced. The peak load reduction is achieved by the following actions:

• Pulsing the load with pulse width modulation (PWM) signals

  In this process, consumers (e.g. the electric auxiliary heater) are switched on and off for defined times. To pulse the electric auxiliary heater, the power management outputs a PWM signal in the DME / DDE, depending on the energy available. The PWM signal contains the information for the maximum switch-on power available for the electric auxiliary heater. The frequency of the PWM signal is fixed at 160 Hertz (Hz).

• Power draw reduced to a certain percentage.
• Individual consumers are switched off in extreme situations when the power reduction achieved through pulsing and reduced consumption is insufficient.

The load on the vehicle electrical system is reduced according to the table:

Priority of consumers	Power reduction	Control unit
Heated rear window	Pulsing	IHKA
Seat heating	level 2	SM
Seat heating	50 %	SM
Active seat	Off	SM
Heater blower	75 %	IHKA
Steering wheel heating	Pulsing	SZL
Heater blower	50 %	IHKA
Mirror heating	Off	TM >from 09/2005: KGM
Heated rear window	Off	IHKA
Seat heating	Off	SM
Steering wheel heating	Off	SZL
Active seat ventilation	Off	SM
Heater blower	25 %	IHKA

Consumer shutoff 

Consumers are switched off according to different criteria and are split into the following categories:

• Convenience consumers
  • Heated rear window
  • Seat heating
  • Steering wheel heating

  The convenience consumers are automatically switched off when the engine is switched off. The convenience consumers can only be switched on again after the engine has been restarted.

• Legally prescribed auxiliary consumers
  • Parking lights
  • Hazard warning lights

  Legally prescribed auxiliary consumers must still be operational when the engine has been switched off, as long as this is possible. These auxiliary consumers are not deactivated, even if the battery's limit of starting capability has been reached.

• Auxiliary consumers
  • independent heating
  • Independent ventilation
  • Communications components
    • Displays
    • Terminal 30g
    • Telematic services

  The auxiliary consumers listed can still be switched on after the engine has been switched off. The auxiliary consumers are automatically switched off when the battery reaches its limit of starting capability. A CAN message from the DME / DDE prompts the shutdown.

• System-related run-on
  • Electric radiator fan

  System-related run-on components can remain operational for a certain time after the engine has been switched off.

Off-load current monitoring 

If the vehicle is out of use (from 68 minutes after terminal R OFF) and the battery current exceeds 80 milliamperes (mA) (default setting), a fault memory entry is stored in the DME / DDE.

Terminal 30g relay 

The terminal 30g relay prevents a higher off-load current, e.g. one caused by a defective consumer, with a predefined consumer shutoff. The terminal 30g relay is actuated by the CAS. The "g" indicates that terminal 30g is an active terminal.

The connections that are switched on and off through the terminal 30g relay are shown on the system circuit diagram.

Subject to change.