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President-elect' Barack Obama has promised that 'half of all cars purchased by the federal government will be plug-in hybrids or all-electric by 2012.' Some of this requirement can be met by Chevrolet Volts and plug-in versions of the Toyota Prius, but there is a need for plug-ins which can offer more, in terms of both size and performance. This article describes a generic powertrain for sedans the size of a Chevrolet Malibu, Ford Taurus or Dodge Charger and larger, and for all sizes of SUV. The article starts with the specification and then offers explanations for the various choices.
The plug-in battery pack needs to be modular, to provide users with a choice of AER (All-Electric Range), from some 20 miles at city speeds to over 60 miles on freeways at the legal limit. Assuming an average electricity consumption of 250 Wh per mile in the city, the available capacity of the smallest pack needs to be 5 kWh. Because the state-of-charge swing needs to be less than 75% to improve battery life, the nominal battery capacity will be around 7 kWh. The battery pack will be located under the trunk floor, in what was the spare wheel well. Consequently, run-flat tires will be fitted as standard.
The base engine could be an E85/gasoline version of a small I-4, similar to the 100 bhp unit in the Volt. The optional more powerful engine might be a turbocharged version of the same engine, producing some 150 bhp on gasoline and 180 bhp on E85. Perhaps surprisingly, the more powerful engine should use less E85 than the base engine when cruising because it will have properly implemented flexible fuelling (see Saab BioPower), unlike most other systems claimed to be optimal. Most systems adjust ignition and injection timing, but Saab uses variable boost turbocharging to modify the effective compression ratio to take full advantage of the higher octane rating of most biofuels. The result is that the 'mpg gap' between gasoline and E85 can close to the point where it costs less per mile to use E85.
The engine will be connected to the front wheels via a dual-clutch transmission (DCT), which combines the efficiency of a manual transmission with the ease of use of an automatic. The engine and transmission will be mounted in the conventional transverse position, under the hood. Because the DCT operates here as part of a parallel hybrid configuration, engine power can normally be delivered even more smoothly than a DCT or conventional automatic operating on its own.
The 'foundation technology' for the powertrain is a surge power unit, mounted inside the transmission tunnel down the centerline of the vehicle. The Malibu, Taurus and Charger are already available with a conventional 4WD system requiring a transmission tunnel which is large enough, with some minor fettling, to take a surge power unit. The surge power unit will, in its basic form, drive (and be driven, during regenerative braking) by the rear wheels, via the rear final drive.
The sketch indicates where the key components will be located in the vehicle. The surge power unit will have an available energy capacity of some 500 Wh, with a peak output power rating of over 260 bhp (~200 kW), and be kept topped up by the plug-in battery, and the engine when the battery is flat. Most importantly, the surge power unit should have the ability to return over 60% of the kinetic energy of the vehicle during a full brake/accelerate cycle. This contrasts with the less than 35% returned by most current hybrid drives. For the FBI (and police?), a more powerful version should be available which the front as well as rear wheels, via a 4WD version of the DCT. Cars with V-8 engines will become so 'last millennium'.