Overview: BMW Concept Active E
BMW’s Concept Active E, unveiled at the end of last year, is a good example of a (somewhat upmarket) plug-in electric vehicle.
Based on the Einser coupé, and a more glamorous follow-up to the Mini E, BMW’s latest Concept has a 170PS electric motor mounted between the rear wheels, with Li-ion battery packs in the now-abandoned transmission tunnel, in the place where the fuel tank used to be, and in the former engine compartment. Because of the need to house the power electronics on top of the traction motor, the boot has shrunk to 200l.
The motor’s 250Nm helps coax this heavy (1800kg) car up to 100km/h in around nine seconds. Maximum speed is electronically limited to 90mph. BMW expects a real-world range of around 100 miles. To prevent the car’s operating range from shrinking in hot weather, the battery back features a temperature controller with liquid coolant.
Typically of current automotive electric motors, the BMW’s is a synchronous device with permanent magnets. Synchronous motors are less prone to lose torque at higher rotational speeds, traditionally a weakness of electric motors.
The power electronics that steal the coupé’s boot space control the supply of current to the motor and from the generator — the motor and generator being the same thing. The system also provides electrical power (by means of a voltage transformer) to the vehicle’s regular network, as the BMW has no separate 12V battery.
Modern automotive electric motors also work in reverse, as generators. This allows them to capture some of the vehicle’s surplus kinetic energy during overrun and braking, and to feed it into the battery pack as ‘free’ power. In the case of the Active E, substantial ‘engine braking’ and energy capture take place on releasing the accelerator. Clearly this electromagnetic braking only acts on the drive wheels — we wonder what would be the result of releasing the accelerator sharply on a slippery down-gradient.
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BMW estimates that, in urban traffic, around three quarters of all deceleration manoeuvres can be carried out without the need for the mechanical brakes. Fortunately, the brake energy regeneration system triggers the vehicle’s brake lights.
On-board charge management allows the Li-ion pack to be recharged from a power outlet at a public charging station, from a normal domestic socket or from a special wall box. Fed 230V A.C., the battery pack can be fully charged from a high-current power outlet (50A) in around three hours.
BMW has invested some lateral thought in the Active E. The car’s on-board system can talk to a remote mobile phone, providing the owner with information about the current state of charge and allowing the owner to activate the car’s climate control system remotely. There is even a timer that allows the driver to pre-heat or cool the car before a trip.
BMW’s (and its customers’) experiences with the Mini E — the first part of ‘Project i’ — have given the company significant pointers to what will be required of future production electric vehicles. The next stage of Project i is to develop a second trial fleet of electric vehicles, this time based on the Concept Active E. Like the Minis before them, these vehicles are intended for everyday use in a large-scale field trial. The lessons learned over the coming months will feed into the development of an electrically-powered serial production vehicle which the BMW Group will put on the market under a sub-brand of BMW in the next five years.
Click here to see our article about the Active E trial prototype.
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