Drive Motor/Generator: Description and Operation
Drive Active Hybrid
Drive Active Hybrid
The BMW Active Hybrid is a full hybrid. This hybrid vehicle allows purely electrical driving in city traffic, a boost function for dynamic acceleration as well as coasting with the internal combustion engine switched off. The hybrid vehicle also has energy management that can achieve an anticipatory drive control by networking with the navigation system.
Example F10 with active hybrid 5:
The drive of the BMW Active Hybrid 5 consists of a 6-cylinder in-line engine (N55B30M0) with BMW TwinPower Turbo technology, an 8-speed automatic gearbox (GA8P70HZ) and an electrical machine.
With the Active Hybrid 5, the BMW 535i achieves a reduction in the fuel consumption figures and emission values of more than 10%.
The electric drive of the Active Hybrid 5 enables purely electrical - and therefore emission-free - driving at speeds up to 60 km/h. With an average speed of 35 km/h, the high-voltage battery provides sufficient energy to enable purely electrical driving over a distance of up to 4 kilometers. Moreover, a hybrid-specific engine start-stop function enables an additional increase in efficiency by consistently switching off the combustion engine when stopping at traffic lights or in traffic jams.
The drive has a power output of 250 kW or 340 bhp. The maximum torque is 450 Nm.
The Active Hybrid 5 accelerates in 5.9 seconds from 0 to 100 km/h. The fuel consumption varies between 6.4 and 7.0 litres per 100 kilometres. This means a CO2 emission of 149 to 163 grams per kilometer (values in accordance with EURO test cycle, depending on the selected tyre format).
Brief component description
The following components of the drive are described:
- Automatic gearbox with electric gearbox oil pump
- Electrical machine with rotor position sensor
- Electrical machine electronics (EME)
- Starter motor generator
- Electric vacuum pump
- Controllable engine mounts
- Exhaust flap
GA8P70HZ automatic gearbox with electric gearbox oil pump
The automatic gearbox is equipped with a separating clutch. The separating clutch and the electrical machine are fitted in one joint housing. The separating clutch is designed as a wet multi-plate clutch.
The separating clutch is used in certain operating states to disconnect the combustion engine from the electrical machine and the remaining power train. This takes place for example with purely electrical driving as well as in the coasting driving mode. So that the connection and disconnection of the combustion engine is not noticeable, the separating clutch has high actuating precision.
In the same way as all clutches and multi-plate brakes of the automatic gearbox, the separating clutch is operated by the mechatronics module. At static pressure, the separating clutch is opened. This means that gearbox oil pressure is required to close the clutch. This is provided either by the electric gearbox oil pump or the mechanical oil pump.
With the separating clutch opened, the mechanical oil pump is driven by the electrical machine. This means that if the electrical machine fails and the gearbox oil temperature is below 0 °C, the separating clutch cannot be closed and the vehicle cannot be driven off.
The electric gearbox oil pump is a vane-type pump in the same way as the mechanical oil pump. The electric gearbox oil pump is driven by a brushless DC motor. The control electronics is integrated in the housing of the electric transmission oil pump and is activated by the electronic transmission control (EGS). The electric gearbox oil pump can be operated as of a gearbox oil temperature of 0 °C.
To insulate the torsional vibrations, a torsional-vibration damper is used in the automatic gearbox. The torsional-vibration damper sets up the mechanical connection between the flywheel of the combustion engine and the separating clutch.
Electrical machine with rotor position sensor
The electrical machine, including separating clutch, is installed between the combustion engine and the automatic gearbox. The electrical machine consists of stator (inside) and rotor (outside). The rotor replaces the flywheel of the combustion engine. The electrical machine is designed as a permanently excited electric motor (synchronous) with a maximum output of 39 kW.
The electrical machine has the following functions:
- Electrical driving
- Support for the combustion engine (boost)
- Electrical brake (recuperation = energy recuperation)
- Alternator
For boosting (electrical acceleration), up to 210 Nm additional electromotive torque can be provided.
The rotor position sensor records the exact position of the rotor or the electrical machine. The rotor position sensor is constructed in the same way as a synchronous motor. The specially shaped rotor is connected to the rotor of the electrical machine. The stator is connected to the stator of the electrical machine. The voltages induced by turning the rotor in the coils of the stator are evaluated by the Electrical Machine Electronics (EME) and the rotor position angle is calculated.
The rotor position angle is imperative for exact, field-oriented control of the electrical machine in order to create the voltages at the coils of the stator that match the position of the rotor.
The coils of the electrical machine must not exceed a certain temperature during operation. This is why a representative temperature in one of the coils is measured using a temperature sensor (NTC).
The Electrical Machine Electronics (EME) evaluate the signals from the temperature sensor. The EME reduces the power output of the electrical machine if the temperature of the coils approaches maximum permitted value.
Electrical machine electronics (EME)
The Electrical Machine Electronics (EME) integrate the following components:
- Inverters for controlling the electrical machine
- DC/DC converter (2.4 kW) for transferring energy in both 12 V electrical system and high-voltage electrical system
- Control unit
The EME controls the starter unit (auxiliary battery with an intelligent battery sensor and cut-off relay).
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.
Electric vacuum pump
Various components of the engine rely on the supply of a partial vacuum. The engine has a mechanical vacuum pump the necessary partial vacuum. The vacuum supply must also be ensured in phases in which the engine is switched off. This is why the vacuum system has been extended to include an electric vacuum pump. As soon as the partial vacuum in the system falls short of a certain threshold value, the electric vacuum pump is activated. The partial vacuum is measures by a partial vacuum sensor in the brake booster; this is already familiar from vehicles with the automatic engine start/stop function.
Controllable engine mounts
The engine has engine mounts that can be enabled, familiar from vehicles with diesel engines. The engine mounts that can be enabled are set by means of partial vacuum to hard or soft to ensure a comfortable start and idling of the combustion engine. As soon as the partial vacuum is no longer applied to the engine mounts, they are switched to hard. The electric changeover valve of the controllable engine mounts is activated by the Digital Engine Electronics (DME).
Exhaust flap
The height requirements with regard to acoustics mean that the exhaust system is fitted with a controllable exhaust flap. This is activated by the Digital Engine Electronics (DME). The exhaust flap is opened and/or closed by a vacuum or electrically.
- Adjustment by vacuum
The DME activates an electric changeover valve that applies partial vacuum to a diaphragm canister. The supply with partial vacuum is from the vacuum system.
The following graphic shows for example an exhaust flap that is opened and closed by a vacuum.
- Electric adjustment
The exhaust control flap is driven via an axially arranged electric motor with integrated gearing and integrated electronics.
The following graphic shows for example an exhaust flap that is opened and closed electrically.
System functions
The following system functions are described for the drive:
- Functional networking
- Electrical driving
- Support for the combustion engine (boost)
- Electrical braking (energy recovery)
- ECO PRO mode, for example coasting
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.
Electrical driving
The electrical machine is a synchronous motor integrated in the housing of the 8-speed automatic gearbox. The connection between the electric drive and gearbox is by means of a separating clutch. The operating temperature is regulated via the cooling system of the combustion engine. The electrical machine with its 40 kW power output provides a torque of 210 Newton-meters even from a standstill. The electrical machine is supplied by a lithium-ion battery specially developed for the vehicle. The high-voltage battery unit is surrounded by a high-strength housing. It is fitted in the luggage compartment between the wheelhouses. The high-voltage battery unit consists of 96 storage cells. The high-voltage battery unit has an independent cooling system and provides usable energy of 675 Watt hours.
Support for the combustion engine (boost)
During strong acceleration, for example overtaking operations, power output is called up from the electrical machine in addition to that from the combustion engine. This means that maximum power output is available. The accelerator pedal has to be pressed down firmly (kick-down). The revolution counter shows the current engine speed. At the same time, all 4 arrows on the left-hand side light up. The boost function can be used up to a driving speed of 160 km/h.
Electrical braking (energy recovery)
Electric braking enables braking energy recuperation. Here, the electrical machine works as an alternator and brakes the drive wheels. The energy that is generated is used to charge the high-voltage battery unit via the Electrical Machine Electronics (EME).
The decisive input variables for electric braking are the accelerator pedal angle and the brake pedal path.
- The brake pedal path is measured by the brake pedal path sensor and read in by the Dynamic Stability Control (DSC).
- The accelerator pedal angle is measured by the accelerator pedal module and read in by the Digital Engine Electronics (DME).
With the brake pedal not operated but an accelerator pedal angle of 0°, the electrical machine is operated as an alternator. The Electrical Machine Electronics (EME) activate the electrical machine in such a way that brake force results for the complete vehicle that corresponds to a conventional vehicle in the over-run mode. The extent of energy recuperation is still at a low level here.
When the brake pedal is operated, a response threshold must first be overcome during which there is no hydraulic braking. However, the brake pedal path is already being evaluated and with the help of the electrical machine a greater brake force than in the purely over-run mode is created.
When the brake pedal is operated beyond the response threshold, both brake interventions are simultaneously active, because now hydraulic braking is added for braking energy recuperation. The braking force generated by the electrical machine is increased as the brake pedal path increases, until the maximum is reached.
Electric braking with the help of the drive train only affects the rear axle. The brake force on the rear axle must not exceed a certain level relative to that on the front axle. Otherwise, driving stability would be impaired. This is also why the maximum deceleration that can be achieved through braking energy recuperation is limited. The maximum permitted brake force by electric braking depends on monitoring of the slip, lateral acceleration and control interventions in the driving dynamics system. This ensures that the vehicle in also remains in a stable driving state during braking energy recuperation at all times. Here, the Dynamic Stability Control (DSC) contributes to the amount of fuel saved from the point of view of active safety.
If the high-voltage battery unit is already fully charged, no more electrical energy can be stored. This special state can be a reason why braking energy recuperation cannot be possible, but it rarely occurs. The operating strategy means that during normal driving an adequately large reserve is kept in the state of charge of the high-voltage battery unit. It is deliberate that energy is drawn from the high-voltage battery unit at regular intervals. This keeps the state of charge within a range that also allows for space to store electrical energy generated by electrical braking on long hill descents.
ECO PRO mode
The ECO PRO mode is activated using the driving experience switch. As default, the COMFORT program is set. To activate the ECO PRO mode: With terminal 15 towards, the driving experience switch must be moved towards COMFORT until ECO PRO appears in the instrument cluster (display of ECO PRO mode, see Owner's Handbook).
Intelligent control of energy management and the heating and air conditioning system forms the cornerstone of ECO PRO. A real life reduction in consumption of up to 10 % can be achieved.
- Another accelerator pedal characteristic curve and altered shifting times of the automatic gearbox, the driver is supported in a consumption-optimized driving style.
- Reduction of electrical loads such as seat heating, mirror heating and heated rear window.
- More efficient control of the heater/air conditioning system
- Number and length of possible phases for engine shutdown (MSA) are maximized.
- Coasting: yet another consistent increase in efficiency
The shutdown of the combustion engine means this is possible not only at a standstill and in city traffic, but also when driving fast. If the combustion engine is not required, it can also be switched off by the hybrid drive while the vehicle is being driven. For this, the vehicle must be in the ECO PRO mode and the driver must not press the accelerator pedal. Up to a speed of 160 km/h, the combustion engine is then switched off and a separating clutch separates it from the rest of the drive train. The BMW Active Hybrid subsequently runs silently and without emissions on the roadway without the influence of engine drag-torque. In order to ensure unrestricted operation of all safety functions and convenience functions, a small amount of the kinetic energy is converted into electric energy by recuperation.
In order to implement energy management that is even more strongly aligned to maximum efficiency, the range of functions of the Electrical Machine Electronics (EME) in the BMW Active Hybrid have been extended to include an anticipatory analysis of the driving situation.
To this end, the Electrical Machine Electronics (EME) are networked with the series standard navigation system 'Professional'. This means it is possible to evaluate the data at an early stage that indicate a change in the outside conditions or in the driver request. In addition, the Electrical Machine Electronics (EME) also control operation of auxiliary components and convenience functions to achieve the greatest possible efficiency. The comprehensive networking enables the Electrical Machine Electronics to implement intelligent energy management and thus optimize the operating strategy of the complete vehicle under all conditions.
If, for example, a downward incline ahead is determined, all of the electric energy stored in the high-voltage battery unit can be used to support the drive. Reason: The high-voltage battery unit is recharged by the recuperation when the subsequently travels downhill. It is also possible to achieve an almost complete charge of the high-voltage battery unit in good time before reaching the destination to enable maximum electrical vehicle operation in the area of the destination.
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 normal 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 normal 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
- Evaluate state of charge of battery.
- Auxiliary battery: Register battery replacement
Path: Service functions > Body > Voltage supply > Hybrid vehicle
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