Power Management

Power Management

Advanced Power Management, APM
The power management a subsystem of the energy management. The power management is run from the engine control unit (DME or DDE: Digital Engine Electronics or Digital Diesel Electronics).
While driving, the power management regulates power consumption of the most important electrical consumers and the power output of the alternator, as well as the battery charge.

Brief component description
The following components for voltage supply are described:
- Battery
- Alternator
- Intelligent battery sensor
- Digital Motor Electronics or Digital Diesel Electronics

Battery
The capacity of the built-in battery depends on the engine used and the vehicle equipment. Selection criteria for the required capacity are:
- the cold-start behavior of the engine
- the standby current consumption of the vehicle
- the energy requirement of the auxiliary consumer units (auxiliary heater, telephone, etc.)

Alternator
With the engine running, the alternator generates a variable charging voltage for battery charge. The variable charging voltage is influenced by the power management depending on the temperature and current by the DME/DDE raising the engine speed.

IBS: Intelligent battery sensor
The intelligent battery sensor (IBS) is a mechatronic component with its own microcontroller for monitoring the battery condition. The IBS continuously measures the following values on the battery:
- Voltage
- Charge and discharge current
- Battery temperature







For data transfer, the IBS is connected to the DME (Digital Motor Electronics) or DDE (Digital Diesel Electronics) via a local interconnect network bus (LIN bus).

DME or DDE: Digital Motor Electronics or Digital Diesel Electronics

The DME or DDE contribute to the voltage supply as follows: If the alternator voltage falls, DME/DDE increase the engine speed depending on the requirement. The software for this is called "power management".

System functions
The following system functions are described for power management ("Advanced Power Management"):
- Reduction or shutdown of individual electrical consumer
- Control of the electric auxiliary heater
- Idle speed increase.
- Optimized charging voltage and vehicle voltage.
- Identification of poor charge balance.







Reduction or shutdown of individual electrical consumer
The shutdown of individual consumer units or reduction of the power consumption lowers the power consumption in critical situations. This prevents the battery from discharging. The power management controls the switch-off of individual consumers or reduction in the power consumption using requests (messages) to the relevant control units.

With the engine running
With the engine running, individual functions are divided into two classes:
- Class A: A reduction in the power consumption or a shutdown of these consumers is only perceived by the driver to a limited extent or after a delay.
A shutdown of individual class A consumer units or reduction in the power consumption is only activated under the following 2 conditions:
- Battery charge state in the critical range
- High utilization of capacity of the alternator or reduced utilization of capacity of the alternator due to excess temperature.

- Class B: A reduction in the power consumption or a switch-off of these functions is detected by the driver immediately.
Shutdown of individual Class B electrical consumers or reduction of the power consumption is only activated under the following condition:
- Battery charge state in the critical range (close to the startability limit)

In the event of alternator fault
- In the event of an electrical or mechanical fault on the alternator (reduced alternator availability), the power consumption of Class A and Class B electrical consumers is reduced by the allowable maximum amount in order to lower the power demand from the vehicle electrical system.
- If alternator load is reduced due to excessive temperature (protective function), only the power consumption of Class A electrical consumers is reduced by the maximum amount allowable.

In the event of an engine shutdown (MSA)
To prevent excessive power consumption when the engine is switched off (MSA function), power consumption of Class A electrical consumers is reduced by the maximum amount allowable and that of Class B consumers by Reduction no. 1 (see table below).

With the engine off and the ignition switched on
With the engine off and the ignition switched on, consumers are not switched off or their power consumption is not reduced.

Class A electrical consumers

Under the conditions described, the following measures for class A consumers are executed in succession:







Class B electrical consumers

Under the conditions described, the following measures for class B consumers are executed in succession:







When the battery charge state moves out of the critical range, the functions become 100 % available again.

IMPORTANT: When the shutdown of individual consumer units or the reduction of power consumption is activated, the displays remains active (LEDs remain lit).

Control of the electric auxiliary heater
On vehicles with diesel engines and without independent heating, the heat exchanger for the heating system is heated additionally with an electric auxiliary heater based on the PTC principle. The electric auxiliary heater is one of the consumer units that need a relatively high amount of power (up to 1300 W) and it is thus regulated by power management. Furthermore, two other electric auxiliary heaters (300 W each) are used in the rear on vehicles with rear air conditioning. These high electrical loads are regulated as follows:
- The IHKA control unit controls the electric auxiliary heater (via LIN bus) and the FKA control unit controls both electric auxiliary heaters in the rear passenger compartment (with a pulse-width modulated signal).
- The power management in the DDE regulates the maximum electrical power output of the electric auxiliary heater (signal in a CAN signal).
The maximum power output of the electric auxiliary heater depends on the utilization of the alternator.
- The electric auxiliary heater regulates the heater output of the heating register depending on the specifications of the power management.

Idle speed increase
To prevent a negative charge balance of the battery, the power management can request an increase in the idle speed of the combustion engine. Depending on the engine version, the idle speed is raised by up to 200 rpm. An idle speed increase is activated under the following preconditions:
- Quality of the calculated battery charge state adequate and battery charge state below a specified limit.
- High utilization of capacity of the alternator for a certain period.

Optimal charge and vehicle voltage

Vehicle without intelligent alternator control (IGR)
The power management controls the alternator voltage as a function of the following criteria:
- Battery temperature: A cold battery loads less current, so the charging voltage should be higher than for a warm battery. The temperature of the battery is determined by the IBS and sent to the DME or DDE across the LIN bus.
- Protection of the battery against sustained excessive voltage and sustained discharge in the case of a poor state of charge.
- Request from components of the vehicle electrical system and functions (e.g. exterior lights or Dynamic Stability Control): minimum or maximum necessary voltage. These limit values must not be undershot or exceeded, as otherwise there can be functional limitations or function failures.
This rule is to ensure adequate charge of the battery. The aim is a charge of 100 %.

Vehicle with intelligent alternator control (IGR)
Unlike the normal control of the battery charge, the intelligent alternator control prevents 100 % charging of the battery. The battery charge goes to the range of 75 - 85 % of the maximum possible charge. This means that the battery remains "chargeable" to permit energy recovery in the vehicle overrun phase.
The power management co-ordinates the various requirements for the vehicle voltage:
- Battery: Nominal voltage depends on the temperature of the battery. Minimum and maximum voltage to permanently protect against excessive voltage and discharge with poor state of charge. In cycles, the intelligent alternator control is suppressed; this permits 100 % battery charge to achieve full battery capacity for a sustained period (regeneration).
- Components of the vehicle electrical system and functions (e.g. exterior lights or Dynamic Stability Control): minimum or maximum necessary voltage. These limit values must not be undershot or exceeded, as otherwise there can be functional limitations or function failures.
- Operating condition of the IGR: Energy recovery in the overrun phases, partial alternator relief (no battery discharge permitted) or alternator relief (return of the energy from the battery into the vehicle electrical system).

Identification of poor charge balance

With high specification vehicles with high load on the vehicle electrical system, the vehicle electrical system can be suppressed, particularly at excessively high ambient temperatures. The following reasons are possible:
- High power requirements for the electric fans from the heating and air conditioning system and the heat management system.
- Reduced performance of the alternator at high temperatures.

The APM monitors the charge balance continuously by integrating the battery current measured by the IBS. If a bad charge balance is detected, then take the following action:
- Idle speed increase.
- Reduce the class B electrical consumer (heating fan to 75% or 50%).
- Adaptation of the vehicle switch points with 8-gear automatic transmission 8HP90 to increase the engine speed measured.

Notes for Service department

General notes

NOTICE: Procedure in the event of a customer complaint with regard to malfunctions

In the event of customer complaints with regard to malfunctions related to the reduction in power consumption or shutdown of individual electrical consumers, use the following procedure:
- Run the "Reduction of electrical consumers" testing procedure. Information on the reduction or shutdown (point in time, duration and functions concerned) is shown in the testing procedure.
- Check the function with activation via diagnosis (component activation or testing procedure for function check).
- If appropriate, inform the customer regarding the situation.

We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.