Voltage Supply
Voltage Supply
Voltage supply
The power management is the most important element of the energy management. Power management is software in the engine control unit (Digital Engine Electronics DME). When the engine is running, the power management system regulates the alternator voltage. With the aid of the intelligent battery sensor, consumers may be reduced or even switched off altogether, even if the engine is running. This consumer shutdown lowers the power consumption in critical situations. This prevents the battery from discharging.
Intelligent generator control is implemented as a CO2 measure as part of BMW EfficientDynamics.
The graphic below shows a parts overview of the engine wiring harness.
Brief component description
The following components for voltage supply are described:
Intelligent battery sensor
The intelligent battery sensor (IBS) evaluates the current quality of the battery. The intelligent sensor is secured to the negative battery terminal. The intelligent battery sensor is connected to the engine control unit over the bit-serial data interface (BSD).
The intelligent battery sensor is an extremely important component for energy management in the vehicle network.
The IBS regularly (cyclically) measures the following values:
- Battery voltage
- Charge current and discharge current
- Temperature of the battery terminal
The designation "intelligent" with the battery sensor refers to an integrated microcontroller with a software proportion. Upstream processing of especially time-critical measured variables is carried out by the processor. The results are then forwarded (with a lower data rate) to the engine control unit.
Alternator
The alternator is also connected to the DME control unit over a bit-serial data interface. The alternator exchanges data with the DME control unit using a bit-serial data interface. The alternator sends the DME control unit information on type and manufacturer, for example. The DME control unit uses this to adapt the voltage setting dependent on the state of charge of the battery as well as the driving condition.
The alternator keeps the vehicle voltage at the required level as long as it is at less than 100 % capacity. Above this the voltage may collapse dependent on the vehicle electrical system load. The alternator also supplies all electrical consumer units during driving. The controller adjusts the output voltage of the electrically excited alternator with uncontrolled rectifier by adjusting the excitation current.
Starter motor
The starter has the job of rotating the crankshaft of the internal combustion engine at the minimum speed that is necessary for starting up (starting speed).
The starter that is used is coordinated with the engine of the respective vehicle model. The output can be up to 1000 Watts depending on the model.
Engine starting is initiated by pressing the start/stop button. The CAS control unit switches voltage through to the starter relay via terminal 50L. The starter pinion is engaged in the ring gear of the flywheel using the starter relay and the intermediate gearbox or planetary gear train
Once the starter pinion has been engaged, the crankshaft of the combustion engine is rotated with the starting speed by the direct current motor of the starter motor. The DC motor is supplied with voltage via terminal 30 to do this. Once the internal combustion engine has started, a freewheeling clutch on the starter pinion prevents the starter pinion from being driven by the flywheel. This could damage the starter motor due to the large gear ratio between the starter pinion and the ring gear (approx. 12 : 1). Then the starter pinion automatically disengages.
System functions
The following system functions are described:
Voltage supply
The voltage supply to the DME control unit is as follows: The ignition starter switch signals over terminal 15 ON to the DME control unit (separate pin). The DME control unit then activates the DME main relay. This cause the DME main relay to supply voltage to other inputs of the DME control unit. The DME main relay also ensures the voltage supply to other control units and components. The DME control unit still needs a continuous voltage supply from terminal 30 for memory functions. The DME control unit ground connection is assured by several pins connected to each other in the control unit. The battery voltage is regularly monitored 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 ensures that the effects of the starting operation or starting aid on the battery voltage will not be registered as a fault.
Activation of the alternator
The following functions have been implemented in the DME control unit for the alternator with bit-serial data interface:
- Switching the alternator on and off on the basis of defined parameters
- Specification of the maximum permissible excitation current
- Calculation of the alternator drive torque and output current
- Control of the reaction of the alternator with addition of high power consumers (load-response function)
- Diagnosis for the data line between the alternator and DME control unit
- Storage of faults which develop in the alternator in the fault memory of the DME control unit
- Activation of the charge indicator light in the instrument panel via bus connection
The principal function of the alternator is also guaranteed when communication between the alternator and DME control unit is interrupted. The following fault causes are distinguishable by the fault 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).
- Rotation fault: The alternator is, for instance, mechanically blocked. Or the belt drive is defective.
- Electrical fault: Exciter diode defective, excitation coil has been interrupted, overvoltage or undervoltage due to defective controller.
- Communication failure: Line between DME control unit and alternator faulty.
An interrupt or short circuit in the coils of the alternator cannot be detected.
Intelligent generator control
The core principle of intelligent generator control is an extension of the charge strategy for the battery. The battery is no longer fully charged, but is charged to a defined level depending on various ambient conditions (e.g. ambient temperature, battery age).
In contrast to conventional charge strategies, energy recovery now only takes place in the overrun phases of the vehicle. The alternator excited to the maximum amount during these phases. Electrical energy is generated and fed into the battery.
Fuel is not consumed. The kinetic energy available from the coasting vehicle drives the alternator via the wheels and engine Electrical energy is generated through energy recovery.
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.
The intelligent generator control can save, depending on the driving profile, up to 3 % CO2 and therefore energy. There are no power losses for the customer from this function.
Engine control communication with the intelligent battery sensor as well as the alternator is over the bit-serial data interface. The state of charge and age of the battery is calculated in the power management using the information from the intelligent battery sensor.
Power management is the software in the engine control that is responsible for all calculations in the energy management field. The software also carries out control processes of the intelligent generator control.
Further information is delivered by the control units connected to the bus system. Conditions that affect the charging procedure are derived from the collected information.
An AGM battery is always installed due to the higher cycle resistance.
State of charge and voltage control
Unlike the normal control of the charging voltage, intelligent alternator control prevents a 100 % battery charge. The battery charge goes up to the range between 70 to 80 % of the maximum possible charge.
Intelligent generator control is suppressed cyclically. This permits a 100-percent battery charge to achieve full battery capacity on a continuing basis (regeneration).
With intelligent generator control, the alternator voltage is correspondingly more frequently in the low voltage range to achieve a better battery charge.
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