BMW & MINI to Develop its Own Electric Engines

With BMW’s first consumer electric car the MINI E, it wasn’t a BMW powerplant but an AC Propulsion unit that produced power. However it looks like BMW and MINI will be taking electric engine development in house. At last week’s Innovation Days in Munich BMW announced that it will be working on full electric and hybrid drivetrains in house as it allows for better integration within other BMW Group components.

Official Release: Targeted electrification of current BMW and MINI models is today already contributing towards the efficiency advantage achieved in all relevant vehicle segments. The number of electrically powered vehicle components has been consistently increased within the framework of Efficient Dynamics. Examples of this are the electromechanical power steering system, which is still unique in many segments, as well as on-demand electrical actuation of numerous ancillary components. These systems no longer obtain their power supply directly from the combustion engine. Hence fuel consumption is lowered and the energy contained in the fuel utilised to a greater extent to enhance driving dynamics.

The electricity required for the electrically driven components is obtained to the best possible extent using brake energy regeneration. With this recuperation technology featured as standard in all BMW and MINI models, generator operation is focused on the vehicle’s overrun and braking phases. Thanks to this technology, energy in the form of heat that normally escapes unused from the brake discs of conventional vehicles is utilised purposefully.

BMW ActiveHybrid technology and electric mobility: crucial pillars of the Efficient Dynamics strategy. The BMW Group is constantly pressing ahead with electrification through the further development of hybrid technology and electric powertrains. Like BMW ActiveHybrid technology, electric mobility also constitutes a supporting pillar within the Efficient Dynamics strategy. The importance of these forms of drive technology in high-volume automobile production is dependent on technological advancement as well as political and economical framework conditions alike. Electrification plays a key role on the way to emission-free mobility. The establishing of electric mobility as a sustainable solution for motorised individual transport requires in the long term not only an energy supply infrastructure that is adapted to suit everyday requirements, but also electric power generation from regenerative sources.

Electrification of the powertrain: BMW Group is focusing on in- house development.

The electrification of the drivetrain poses a particularly high potential for achieving a reduction in fuel consumption and emission levels. In the series production models BMW ActiveHybrid 7 and BMW ActiveHybrid X6, both of which are equipped with BMW ActiveHybrid technology, the power required for the electric drive functions is obtained to a large extent by means of brake energy regeneration. Additionally required electric energy is gained by means of an efficiency-optimising shift of the engine operating point. Furthermore, a significant efficiency advantage is achieved through switching off the engine during idling as well as the supporting effect of the electric motor in obtaining particularly dynamic acceleration.

Plug-in hybrid concepts facilitate charging of the vehicle with energy from the main power supply system. In both cases the achievable vehicle range in purely electrical operation is highly dependent on the capacity of the storage systems. The attributes of the electric motor influence vehicle characteristics in terms of agility, power development and range, whilst the power electronics secure the effective interaction between the energy storage unit and the electric powertrain. In the case of these key components for hybrid and electric vehicles, the BMW Group places the emphasis on in-house development and production. For this purpose the globally unique technological expertise in the drive system sector is also being extended to the field of electric mobility. In this way, high-voltage storage units, electric motors and power electronics can be precisely adapted to the requirements of each model.

High-voltage storage units: flexible modular system facilitates model-specific configuration in the vehicle. In the BMW ActiveHybrid 7, the energy supply to the mild hybrid system is provided by a remarkably compact lithium-ion battery comprising 35 single cells, which is integrated into the luggage compartment. It delivers 0.8 kilowatt hours (kWh) of energy, providing a maximum vehicle output of 19 kW.

In order to meet the power and energy requirement of future hybrid and electric vehicles to the full, the BMW Group has achieved unmatched flexibility in the model-specific configuration of high-voltage storage units through a modular development concept. Each storage unit of a hybrid or electric vehicle comprises a different number of modules, which in turn each consist of a specific number of battery cells. These are interconnected in series in order to match the power and energy capacity requirements of each vehicle.

Due to the available installation space of this conversion concept, the integration of the new BMW high-voltage storage unit into the BMW ActiveE required three storage units of different size and shape. They are installed within the area of the centre tunnel, at the front and at the rear of the vehicle. The storage units contain several modules of three different sizes, the designs of which have identical cell sizes, structures and subcomponents, each of them having a different number of cells. The three storage units provide the BMW ActiveE’s 125 kW electric motor with 30 kWh of power.

The lithium-ion cells used in both models are characterised by high energy density and cyclic stability. In order to utilise the benefits of a modular system even more effectively, the BMW Group is working together with other car manufacturers to introduce common standards for the size of individual battery cells. A considerable reduction in costs can be achieved through this standardisation and production in large quantities. On hybrid models featured to date, around 60 percent of the cost of the electric drive system are solely attributable to the battery cells, this being as much as 75 percent in the case of an electric vehicle.

Better performance and longer range through BMW Group innovations for electronic, battery management, housing and cooling system. For a comprehensive optimisation of the high-voltage storage unit the BMW Group also utilises its technological expertise in the development of further battery system components. These include specific components for the interconnection of the cells themselves and the battery system with the vehicle as well as the integrated control unit and electronic components in the proximity of the cells, including sensors for battery management. In addition to safety monitoring, exceptionally efficient battery management guarantees operation control as well as accurate state detection and various diagnostic functions.

The battery housing and model-specific mounting elements developed by the BMW Group ensure comprehensive protection of the high-voltage storage unit from environmental influences and a structurally stable integration into the vehicle. Moreover, the high-voltage storage systems are equipped with practice-oriented cooling technology. The temperature of a battery system rises both due to power loss during operation as well as to external thermal input as a result of high ambient temperatures. Therefore, when lithium-ion storage units are used in vehicles, they are normally fitted with a battery cell cooling system.

The in-house development concept and the increase in manufacturing expertise in the area of high-voltage storage systems allow the BMW Group to use its technological know-how especially for maximising power output and the range and lifespan of the battery through effective battery management, intelligent operation strategies and optimum heat management. Over and above that, the high quality level of the storage systems is also guaranteed by the close coordination between component development and production. BMW Group develops made-to-measure power electronics.

The power electronics responsible for the interaction between the battery and the electric motor are also developed by the BMW Group exclusively for each specific vehicle. The power electronics serve both as an inverter for the power supply from the battery to the electric motor as well as a voltage transducer interacting between the high-voltage storage unit and the 12-volt onboard power system. Furthermore, highly sophisticated software control provides for the best possible current flow between the battery and the electric motor, which also acts as a generator during overrun phases. On plug-in hybrid and purely electrically powered vehicles the battery charging function is incorporated into the power electronics.

Whatever the task, the power electronics must be able to control the required current flows variably and according to each situation. Thus the power requirements from the onboard power system vary between several hundred watts and two to three kilowatts, depending on the driving situation. The electric motor of a purely electrically powered vehicle requires energy for constant power outputs ranging from 20 to 60 kW. In particularly dynamic driving situations, significantly higher ratings are temporarily achieved. In their function as a battery charger, the power electronics operate, depending on the power available from the socket, within a range between three and as much as 20 kW. Inverter, voltage transducer and charging electronics require a cooling system that is especially adapted to demands in order to ensure their permanent and efficient functioning at the ideal operating temperature.

Electric motor: optimum efficiency through cutting-edge technology expertise. The BMW Group also focuses on company-specific solutions in the development of electric motors, also bringing to bear its worldwide leading technological expertise in the field of drive systems for the benefit of driving pleasure from the power socket. Like petrol and diesel engines, electric motors designed by the BMW Group are characterised by an exceptionally high degree of efficiency. Moreover, the development strategy offers the possibility to realise an electric powertrain that is designed to match the individual character of specific hybrid and electric models. Irrespective of this, all variants within the electric drive portfolio set standards not only though their efficiency and power development, but also through superior qualities in

terms of acoustic and vibration characteristics that fulfil the premium standard required of BMW Group brands. When choosing a design principle with which the highest demands on a drive system in the premium segment can be fulfilled, the BMW Group decided in favour of the development of a so-called hybrid synchronous motor (HSM). Thanks to their particularly favourable power-to-weight ratio, electric motors of this type offer the ideal prerequisites for efficient mobility. In addition to the superior power density, the high level of operational effectiveness poses a further advantage. In terms of overall efficiency, the hybrid synchronous motor surpasses asynchronous and permanent-magnet synchronous motors by up to five percent. Furthermore, an electric motor featuring the HSM principle excels through the fact that it is able to achieve 95 percent efficiency across a particularly wide load range. Thus, in direct comparison with other types of electric motor featuring the same battery technology, it is possible to achieve a significantly longer range.

A characteristic feature of electric motors is their high level of torque, which is available from standstill. In spite of this principle-related attribute, electric motors also have differing response characteristics. In order to do justice to the typical character of both BMW and MINI in terms of power output, designers of electric motors attached great importance to both a spontaneous response and a stable torque up to a high load range. In these respects too, the hybrid synchronous motor poses significant advantages compared to other types of electric drive. Furthermore, the electric motor developed by the BMW Group is characterised by exceptionally quiet and smooth running qualities. In this area, BMW makes consistent use of synergies from the development and production of particularly smooth- running internal combustion engines. Hence the hybrid synchronous motor also meets the demands on a drive system designed for premium automobiles with regard to acoustic and vibration characteristics.