Starter Motor: Description and Operation
Starter Unit, Active Hybrid
Starter unit, active hybrid
The starter unit enables comfortable starting of the combustion engine from a vehicle standstill or during electric driving via the starter generator.
An auxiliary battery is provided so that the vehicle electrical system is not affected. This auxiliary battery is necessary because a sufficient voltage supply e.g. for driving stability control systems must be ensured while the vehicle is driving.
To avoid overcharging the auxiliary battery, the cut-off relay is closed when a certain engine speed is exceeded. However, to ensure that the cut-off relay is not loaded, the closing action must take place at the smallest possible load: To achieve this, the DC/DC converter in the electrical machine electronics (EME) adjusts the vehicle voltage to the voltage of the auxiliary battery. The cut-off relay then remains closed until the combustion engine is switched off again.
In case of a fault in the high-voltage system or in the intelligent battery sensor of the auxiliary battery, the cut-off relay remains closed.
Brief component description
The following components for voltage supply are described:
- Auxiliary battery
- Intelligent battery sensor for auxiliary battery
- Cut-off relay
- Starter motor generator
Auxiliary battery for starter unit
The starter unit enables comfortable starting of the engine from a standstill or while driving. The auxiliary battery provides power to the starter generator. The auxiliary battery is installed at the rear right in the luggage compartment. The auxiliary battery is a 40 Ah AGM battery.
The auxiliary battery is also equipped with an intelligent battery sensor and a safety battery terminal.
The safety battery terminal is activated by the Crash Safety Module (ACSM) in the event of a crash.
The starter unit enables comfortable starting of the engine from a standstill or while driving. The auxiliary battery provides power to the starter generator. The auxiliary battery is a 40 Ah AGM battery.
The starter generator delivers a high charge current to the auxiliary battery at high engine speeds (approx. 2700 rpm). The excess power is diverted to the vehicle electrical system (cut-off relay closes) so as to prevent the auxiliary battery from being overcharged during long high-speed journeys. This excess power is sensibly used by consumers that always available.
In its normal state the auxiliary battery is sufficiently charged (state of charge higher than 90 %). The only consumer is the starter generator, which draws approx. 200 As charge for every starting operation. Since there are no high charge currents flowing, the off-load voltage will vary. The charging voltage can thus set to a relatively low value above the open-circuit voltage. The open-circuit voltage must at all times be lower than the charging voltage of the system battery. This prevents the switching condition from being reached too quickly.
After the combustion engine is started, the nominal voltage is slowly increased starting from the voltage of the auxiliary battery. After each increase in the battery voltage the current into the auxiliary battery is measured via the intelligent battery sensor. This prevents the power output of the starter generator from exceeding 500 W.
Intelligent battery sensor for auxiliary battery
The intelligent battery sensor is connected via the LIN bus to the electrical machine electronics (EME).
The intelligent battery sensor is a mechatronic component with its own microprocessor. The following measured variables are recorded for the purpose of monitoring the battery condition:
- Terminal voltage
- Charge current and discharge current
- Temperature of the battery terminal
Cut-off relay of starter unit
The auxiliary battery and the starter generator are connected to the 12 V vehicle electrical system via the cut-off relay. The cut-off relay is activated by the electrical machine electronics (EME) via a control line. When activated the cut-off relay is closed.
The cut-off relay is supplied by the rear right power distribution box with terminal 30B.
Starter motor generator
The starter generator is integrated in the belt drive. Using a starter generator means that a second belt tensioner is required.
The crankshaft starter generator enables a comfortable transition from electric driving to driving powered by the combustion engine. The energy supplied by the auxiliary battery makes it possible to quickly start the engine with very low noise without requiring an additional torque in the electrical machine.
The crankshaft starter generator is connected to the digital motor electronics (DME) via a local interconnect network bus (LIN).
If there is a fault in the DC/DC converter or the high-voltage system, the starter generator can take over the supply of the 12 V electrical system.
System functions
The following system functions for the starter unit are described:
- Functional networking
Functional networking
The following system overview shows the functional networking using the example of F10. not illustrated: Functional networking with front electronic module (FEM), e.g. F30.
Notes for Service department
General notes
WARNING:
Hybrid cars have an additional high-voltage electrical system which has its own safety regulations to be observed. Work on live high-voltage components is expressly prohibited. Prior to every operation which involves a high-voltage component, it is essential to disconnect the high-voltage system from the voltage supply and to secure it against unauthorized return to service.
1. Switch off ignition.
2. Remove the high-voltage safety connector.
3. Prevent the high-voltage safety connector from being reinserted.
4. Switch the ignition on.
5. Always wait 10 seconds until the "High-voltage system switched off" Check Control message (ID 636) appears in the instrument cluster.
Vehicles in storage or parked for extended periods: Recharge the high-voltage battery at regular intervals
Just as with system batteries, the high-voltage batteries in stored vehicles and cars that remain parked for extended periods must be recharged at regular periodic intervals to avoid total discharge and the attendant damage. Recharge at the same recharging intervals prescribed for the system battery (Instructions for recharging the high-voltage battery).
Diagnosis instructions
NOTICE: Auxiliary battery: Register battery replacement.
After installing a new auxiliary battery, the service function for registering battery replacement must be run. This is necessary to inform the electrical machine electronics (EME) that a new auxiliary battery has been installed in the vehicle. All measured data of the battery condition are reset.
NOTICE: Observe the service function.
The diagnosis system provides the following service functions for the high-voltage battery and the starter unit:
- Start-up of the high-voltage battery
- Evaluating the battery state of charge
- Auxiliary battery: Register battery replacement
Path: Service functions > Body > Voltage supply > Hybrid vehicle
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