Voltage Supply
Voltage Supply
Voltage supply
The power management is the most important component of the energy management. The power management system is a software package in the engine control unit (Digital Motor Electronics, DME). The power management regulates the alternator voltage with the engine running.
The intelligent battery sensor helps to reduce consumer units or switch them off completely as required, even while the engine is running. This consumer unit shutdown lowers the power consumption in critical situations. This prevents the battery from discharging.
New as of 08/2008:
Within the framework of Efficient Dynamics, a CO2 measure that is implemented is intelligent alternator control.
Brief description of components
The following components for power supply are described:
Intelligent battery sensor
The intelligent battery sensor (IBS) evaluates the current quality of the battery. The IBS has its own control unit.
The IBS is part of the battery negative terminal. The IBS regularly measures (cyclically) the following values:
- Battery voltage
- Charge current
- Discharge current
- Temperature of the battery
Alternator
The alternator is connected to the DME control unit across a bit-serial data interface.
The alternator interchanges data with the DME control unit across a bit-serial data interface. The alternator provides the DME control unit with information, e.g. type and manufacturer. This enables the DME control unit to adapt control of the alternator to the alternator model fitted.
System functions
The following system functions are described:
Voltage supply
The power supply of the DME control unit is as follows:
the ignition starter switch signals terminal 15 On to the DME control unit (separate pin). In response, the DME control unit activates the DME main relay. The DME main relay thus supplies other inputs of the DME control unit with voltage. The Digital Motor Electronics main relay also ensures the power supply for other control units and components. For memory functions, the DME control unit still requires a sustained power supply via terminal 30. The earth connection of the DME control unit is ensured via a number of pins that are connected to one another in the control unit. The battery voltage is monitored continuously by the DME control unit. With a battery voltage of less than 2.5 Volts or greater than 24 Volts, a fault is entered. The diagnosis only becomes active 3 minutes after engine start-up. This means that the effects of the starting operation or starting assistance on the battery voltage are not detected as faults.
Activation of the alternator
For the alternator with bit-serial data interface, the following functions are implemented in the DME control unit:
- Switching the alternator on and off on the basis of defined parameters
- Specification of the maximum permitted power consumption of the alternator
- Calculation of the input torque for the alternator from the power consumption
- Control of the reaction of the alternator with addition of high power consumers (load-response function)
- Diagnosis of the data line between alternator and DME control unit
- Storage of any faults that occur on the alternator in the fault code memory of the DME control unit
- Activation of the charge control lamp in the instrument cluster via bus connection
The main function of the alternator is also ensured in the event of interruption of the communication between the alternator and DME control unit. The following fault causes are distinguishable by the fault code memory entries:
- Overheating protection:
the alternator is overloaded. For safety reasons, the alternator voltage is reduced until the alternator has cooled down again (the charge control lamp does not light up).
- Mechanical fault:
the alternator is mechanically blocked. Or the belt drive is defective.
- Electrical fault:
defect in the exciter diode, interruption in the excitation coil, overvoltage due to defective regulator.
- Communication failure:
defective cable between DME control unit and alternator.
An interruption or short circuit in the alternator coils will not be detected.
Intelligent alternator regulation
The core principle of the intelligent alternator control is an extension of the charge strategy of the vehicle battery. The battery is no longer fully charged. Depending on various environmental conditions (e.g. outside temperature, battery age), it is charged to a defined degree.
In contrast to conventional charge strategies, energy recuperation now only takes place in the coasting phases of the vehicle. The alternator excitation is the maximum. Electrical energy is generated and fed into the battery. Fuel is not consumed. The available kinetic energy affects the alternator via the wheels of the of the coasting vehicle and the engine: Electrical energy is generated by recuperation.
In the acceleration phases of the vehicle, the alternator is not excited. This means that no energy - and thus no fuel - is used to generate electrical energy.
Depending on the driving profile, the intelligent alternator control can reduce CO2 by up to 3 % and thus save energy. This function does not lead to drops in performance that can be perceived by the customer.
Components involved
Communication of the engine management system with the intelligent battery sensor as well as with the alternator takes place across the bit-serial data interface. The information from the intelligent battery sensor is used to calculate the charge and age status of the battery in power management.
Power management is the software in the engine management system that is responsible for all calculation in the area of energy management. The software also handles control processes of the intelligent alternator control. Other information is delivered by the control units connected to the bus system. The collated information is used to derive the general conditions that also influence the charging process.
An AGM battery is always installed on account of its greater cycle resistance.
Charge state and voltage control
In contrast to control of the charge voltage, intelligent battery control prevents charging up to 100 %. The battery charging goes up to the range between 70 % to 80 % of the maximum possible charge.
In cycles, the intelligent alternator control is suppressed.
This permits 100 %battery charging to achieve full battery capacity for a sustained period (regeneration). Accordingly, with intelligent alternator control, the alternator voltage is more frequently in the low voltage range to achieve better battery charging.
No liability can be accepted for printing or other errors. Subject to changes of a technical nature