BMW’s “CO2 Champion” Performance Concept is a Plug-in Diesel Hybrid; 50 km/31 mile All-Electric Range; Thermo-electric Generator for Waste Heat Recovery
30 August 2009
|The powertrain of the plug-in hybrid BMW Vision EfficientDynamics. Click to enlarge.|
BMW has provided more details on the concept car it will unveil at the upcoming Frankfurt Motor Show—a concept that Dr. Norbert Reithofer, Chairman of the Board of Management of BMW AG, called a “CO2 champion” that will demonstrate “a whole new dimension of driving pleasure with regards to efficiency with performance” during a press conference late in July. (Earlier post.)
The plug-in full hybrid BMW Vision EfficientDynamics all-wheel drive concept car is powered by a 1.5-liter, three-cylinder turbodiesel; two electric motors, one on each axle; and a 10.8 kWh lithium-polymer battery pack. Overall system output is 262 kW (356 hp), with maximum torque of 800 N·m (590 lb-ft).
|The BMW Vision EfficientDynamics. Click to enlarge.|
BMW Vision EfficientDynamics is able to run completely under electric power for up to 50 km (31 miles), with the power of the turbodiesel engine alone, or through an infinite combination of the three power sources. Depending on driving conditions and the driver’s particular requirements, the two electric motors may be used both for accelerating and for regenerating energy when applying the brakes and in overrun.
BMW Vision EfficientDynamics is neither a mere variant of a production car built for maximum efficiency nor a purely visionary study completely separated from series development. Rather, all the technologies contributing to the car’s outstanding efficiency come from a development process conceived for regular production. Indeed, some of these technologies are already in use in current BMW models, others are approaching production standard or have already proven their functional benefits in practical tests and in prototypes.—BMW
Objectives. The purpose of the high-performance concept study was to visualize the dynamic performance typical of a BMW against the backdrop of future demands in sustained mobility, according to the company. The specific development aim was to provide the performance of a BMW M Car and a highly emotional character combined with the fuel economy and emission management of a modern small car in the premium class.
Engine. Through its compact dimensions, the three-cylinder fits neatly in front of the rear axle like in an mid-engined sports car, despite the two seats at the rear. Fuel is injected by the latest generation of common-rail direct injection, and the turbocharger features variable intake geometry for maximum efficiency.
Engine output is 120 kW (163 hp), peak torque 290 N·m (214 lb-ft). The output per liter of 80 kW (109 hp) achieved in this way sets a new record in diesel technology. The power delivered by the turbodiesel is conveyed to the rear axle by means of a newly developed, minimum-consumption version of BMW’s direct-clutch gearbox with six speeds for maximum efficiency and flexibility.
Motors. BMW said the concept’s development engineers followed the principle of “Best of Hybrid”, choosing the optimum combination of a hybrid synchronous motor on the front axle and a full-hybrid system at the rear.
The rear axle comes with a second-generation full-hybrid system corresponding to the technology introduced for the first time in the BMW ActiveHybrid 7 production model. (Earlier post.) Running as an electric motor, the compact electric power unit positioned between the combustion engine and the double-clutch gearbox develops a consistent 25 kW and is able to reach a peak of up to 38 kW.
Maximum torque, again, is 290 N·m or 214 lb-ft, the power developed in this way serving, depending on driving conditions, either to support the combustion engine or for all-electric motoring.
A second electric motor acts on the front axle. This power unit, a hybrid synchronous motor, offers permanent output of 60 kW and peak torque of 220 N·m or 162 lb-ft. Extra power of 84 kW is available for a period of up to 30 seconds; for 10 seconds the electric motor is even able to develop 104 kW. Power is transmitted through a two-stage, single-speed reduced-ratio gearbox.
Battery pack. The energy cells featured in BMW Vision EfficientDynamics are housed in a chassis element running from front to rear through the middle of the car. Overall, BMW Vision EfficientDynamics comes with a total of 98 lithium-polymer cells, each offering a capacity of 30 Ah and developing continuous output of 600 Amps at a voltage of 3.7 V. For a period of 30 seconds, each cell is even able to develop maximum output of 1,200 Amps.
Serial arrangement of the lithium-polymer cells serves to generate nominal voltage of 364 V, and the gross storage capacity of the battery is 10.8 kWh. Offering an unusually high discharge capacity of 80%, the battery delivers 8.6 kWh for driving the car.
Overall weight of the entire energy storage system is 85 kg or 187 lb. Through their optimum dimensions tailored to the specific qualities and features of the car, the lithium-polymer cells, together with the operating strategy chosen with a concept of energy management looking ahead at upcoming requirements, reduces the thermal load acting on the battery to such an extent that there is no need for active cooling.
Connected to the regular European domestic power mains (220 V, 16 Amps), the system requires a maximum of 2½ hours to fully charge the lithium-polymer cells. Wherever a power source with higher voltage and amperage (380 V, 32 Amps) is available, the charge time is an even shorter 44 minutes at the very most.
In addition to the electrical energy storage system, BMW Vision EfficientDynamics comes with a conventional fuel tank at the rear end of the central chassis tunnel, offering a capacity of 25 liters (6.6 gallons US). Running on diesel fuel alone, BMW Vision EfficientDynamics is able to cover a distance of approximately 650 km (400 miles) with the combustion engine. With the extra range of up to 50 kilometers in the all-electric mode, the car offers an overall cruising range of approximately 700 kilometers (435 miles).
Thermo-electric generator. One objective of BMW’s engineers was, wherever possible, to further reduce the loss of energy still quite substantial even on the most efficient combustion engines. A water-cooled Thermo-Electrical Generator (TEG) is integrated in the exhaust system of BMW Vision EfficientDynamics, serving to convert a lot of the thermal energy contained in the exhaust emissions into electric power. (Earlier post.)
This technology uses the Seebeck effect generating a certain voltage through a temperature gradient within metal-based semi-conductors. The Vision EfficientDynamics Thermo-Electrical Generator, which has already proven its practical qualities in a BMW 5 Series test car, develops maximum output of up to 200W.
The pipes and manifolds in the exhaust system are designed in this case to maintain the full power and all the characteristics typical of the combustion engine also when using this generator system.
Forward-looking Energy Management. Having the individual system components on board BMW Vision EfficientDynamics networked with one another enables implementation of a forward-looking system of energy management using information gathered by the sensors of the driver assistance units fitted in the car.
Data provided, for example, by the rain sensor or Active Cruise Control with its Stop & Go function as well as by the navigation system, and subsequently evaluated by the central control unit, offers an overview of current and upcoming driving conditions.
Then, evaluating such data, the on-board computer is able to forecast driving conditions on the stretch of road immediately ahead, such calculations serving to prepare the car for upcoming requirements and make efficient use of the energy available through optimum operation of all systems.
Should the high-performance central computer establish, for example, that the driver is about to take the motorway, the power used for running the cooling system is reduced for a certain period in advance, on the assumption that the short increase in coolant temperature resulting from such an energy-saving measure will quickly be set off by the higher speed of the car on the motorway. Another example of such pre-conditioning is the regeneration of energy from the air conditioning, from EPS Electronic Power Steering and the Brake Assistant.
The management system considers not only data collected within the car, but also data coming from other vehicles (Car 2 Car) or from sensors fitted on buildings or bridges (Car 2 Infrastructure), thus enabling the driver, say, to avoid traffic congestion in good time or find parking space far more quickly.
The services already offered by BMW ConnectedDrive to avoid traffic congestion and speed up the process of finding parking space are therefore being enhanced by further components and features serving above all to provide even greater efficiency.
Further features of intelligent energy management on BMW Vision EfficientDynamics allow the driver to influence the efficiency of the car. By adding an Eco Mode to the existing system of Dynamic Drive Control, for example, this new concept car enables the driver to reduce fuel consumption and emissions through the individual style of motoring.
This is done by a display in the instrument cluster instructing the driver to accelerate, apply the brakes and—in the manual mode—shift gears with maximum efficiency. In the automatic mode, in turn, the electronic control unit adjusts the gearshift map on the double-clutch gearbox and the control map of the electronic gas pedal to current driving conditions also in the interest of enhanced fuel economy.
Aerodynamics. Measuring only 1.24 metres or 48.8" in height and with a sweeping, arch-like roofline, BMW Vision EfficientDynamics offers the slender silhouette of a classic Gran Turismo. With the combustion engine fitted in front of the rear axle, the designers have furthermore succeeded in giving the car a very low and sleek front end, with the flow of air depending on driving conditions being further smoothened by active louvers in the radiator closing completely whenever the need for cooling air is relatively low.
This efficient function follows in the footsteps of the active air flap control already used as a feature of BMW EfficientDynamics in many of BMW’s current production models. And as a further highlight, BMW Vision EfficientDynamics guides air smoothly and exactly as required into the car through an active air intake at the front.
Numerous details in the design of the body are based on the know-how BMW has gained in Formula 1, a number of body elements serving as air deflectors and guide vanes, as on the BMW Sauber F1. Designed as ducts, for example, the A-pillars serve to channel the flow of air in the same way as the rear lights with their wing profile.
The underfloor of the car is fully covered from front to rear and from one side to the other, thus maintaining a smooth surface to avoid any air swirl liable to increase fuel consumption. Slender openings around the front air dam guide the air flowing in specifically into two closed ducts leading inside the front air dam to the wheel arches where the air comes out again through a very slim aperture at high speed, flowing just next to the outer wheel flanks. This air jet rests on the front wheels like a curtain and is therefore referred to most appropriately as the air curtain with its highly stabilizing effect.
To further optimize the aerodynamic qualities of the entire vehicle and keep rolling resistance to a minimum, BMW Vision EfficientDynamics comes with tires and rims of quite unusual size on a sports car. The tires measure 195/55 in their width-to-height ratio, while large 21-inch rims provide a contact surface on the road otherwise offered only by a much wider tire.
In combination with the sophisticated axle kinematics, this ensures particularly agile driving behaviour. The extra-large rim covers extending over part of the tire flanks add to the unique, very different look of BMW Vision EfficientDynamics from the side.
The blade profile integrated in the rims serves furthermore to reduce the negative effect of the turning wheels on the overall aerodynamics of the car. In all, these features optimizing the aerodynamic qualities of the car give the BMW Vision EfficientDynamics concept car a very low drag factor (CX) of 0.22.
Materials. The chassis and suspension of BMW Vision EfficientDynamics are made completely of aluminium, the roof and the outer skin on the large doors are made almost completely of a special polycarbonate glass automatically darkening as a function of the light shining on the car.
Performance and fuel consumption. Anticipated acceleration from a standstill to 100 km/h is 4.8 seconds, with a top speed of 250 km/h (155 mph) (electronically limited). Applying the criteria of the EU test cycle currently prescribed by law, BMW Vision EfficientDynamics offers projected average fuel consumption of 3.76 liters/100 km (62.6 mpg US), with CO2 emissions of 99 grams/kilometer.
These consumption and emission figures are measured on a consistent internal power balance, meaning that the batteries and storage media for electrical energy maintain the same charge level throughout the entire test cycle (with the same level at the beginning and end) and are charged while driving only by the car’s on-board systems.
As a plug-in hybrid, BMW Vision EfficientDynamics is able to cover the entire fuel consumption drive cycle under electric power alone. Then, to subsequently charge the lithium-polymer cells to the same status as when setting off, all the driver has to do is connect the car to an external power grid. To determine the consumption of electric power, the only requirement is to compare the charge level of the battery before and after the test cycle.
Applying this measurement process, the BMW Vision EfficientDynamics concept car consumes 17.5 kWh per 100 kilometers, equal to a CO2 emission rating of 50 grams per kilometer in the EU test cycle based on the EU electricity mix.
To determine the total volume of CO2 emissions when driving in the all-electric mode, new standards for measuring the level of fuel consumption are currently being prepared for hybrid and electric cars with a plug-in power supply. Applying this calculation method, the CO2 emission ratings generated by BMW Vision EfficientDynamics are reduced further to just one-third of the original figure of 99 grams per kilometer.
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