Fraunhofer wheel hub motor — Credit: Fraunhofer IFAM
A car with a motor in each wheel was invented by none other than Ferdinand Porsche and demonstrated widely in the early 1900’s. It was a hybrid car that used both batteries and a generator to produce electricity for the motors mounted in the hub of each wheel. It was a big vehicle, and heavy, but it could do 56 kph (35 mph), which at the time set road speed records. It’s time may have come again.
It seems likely that one of the main tracks for ‘clean’ cars of the future (the future near and far) is electricity driven. This should be a cause for a total rethinking of how motor transport is designed and manufactured. Researchers at the Fraunhofer Institute (Germany) call it ‘electromobility’ and they built a car with motors in the hubs of each wheel, similar in concept to that built by Porsche. There is no conventional engine – making the engine space another boot (or trunk, as Americans would say). This wheel hub motor is a sophisticated blend of electric motor and high-tech electronics. There are other wheel hub motors available today, but the Fraunhofer model has no external electronics, few control wires, and greater power.
The biggest issue with wheel hub drive was, and is, the handling. Like all-wheel-drive on conventional cars, the tendency for wheels with independent drive is to create difficult handling. This is compounded by the relatively heavy wheels and the potential strength of the hub’s electric motor. The Fraunhofer design compensates for these effects by redesigning the chassis of the vehicle to redistribute weight, and through computer controlled coordination between the motors/wheels. The result is handling scarcely different than standard vehicles.
One advantage of the hub motor is that it does away with the complexities and mechanical vulnerability of the conventional ‘drive train’ – transmissions, drive shafts, and differential units. In fact, it makes electronic control of ‘all-wheel-drive’ (or 4 wheel drive) almost automatic.
Another advantage of the hub motor is the direct channeling of braking energy into recharging the vehicle batteries. Although not yet achieved, it is expected that the braking effect will ultimately be electrical and a conventional braking system will only be used for backup and emergencies.
Several carmakers and component suppliers are interested in hub motors. Michelin, for one, is developing a system it calls the Active Wheel. As well as an electric motor to drive the wheel, it contains a second electric motor to operate an active suspension system that is also built into the wheel hub. Michelin reckons this arrangement, which is now being tested in cars, could make other conventional parts, like shock absorbers, unnecessary.
Such a wheel would, in effect, transform Michelin from being a tyremaker into an engine and suspension supplier as well. Many other such changes are coming for the companies in the automotive business, say the Fraunhofer engineers, because some parts will no longer be required for electric vehicles, but other new parts will be needed instead. So as electric propulsion takes hold, it will not just be the shape and the dynamics of the vehicles themselves that will change, but also those of automotive companies, too.
[Source: The Economist]