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Reinventing the wheel poses other environmental considerations

08 August 2013

In the push to reduce carbon emissions and meet government targets, vehicle manufacturers are looking for ways that allow them to incorporate new elements into existing designs.

One such innovative element is an electric motor housed inside the wheel hub, but this configuration raises certain issues, not least being the need to protect the motor from the aggressive nature of its working environment.

It’s not such a new idea, the wheel motor; Ferdinand Porsche sold 300 cars with electric in-wheel motors more than a century ago. The ready availability of cheap petrol put an end to that. Now, the tables have turned and economic and environmental costs are bringing the potential for in-wheel motors back.

Ken Stewart of Protean Electric – a company that is developing in-wheel motor technology - says the philosophy behind the idea is simple: “Why not put the torque at the wheel? That’s where you need it.” The idea also has the advantage of freeing up space inside the vehicle. “Not only does the motor fit inside wasted space,” Stewart says, “you don’t need drive shafts, transmission, differential or any mechanical connections. You just press the throttle pedal, which sends a command along a wire to provide more torque at the wheel.” 

Protean is currently testing its wheel motor on prototypes and expects to go into serial production in 2014. One of the main uses Protean sees in the medium term is for fleet operators who can improve the carbon footprint of their fleet by making all their cars into hybrids with two electric-driven and two conventionally driven wheels, all controlled by smart software.

But if the wheel is an ideal home for the motor in some ways, in others it’s the worst possible place. It’s subject to vibration and road irregularities, it gets splashed with water, and it is often knocked against curbs. So the seals protecting in-wheel motors have a difficult job to do – not least, they have to keep foreign matter out of the gap between the rotor and the stator.

According to Tony Fagg of seals specialist, Trelleborg, this application requires that the seals meet a combination of thermal and physical challenges and cope with the wide variety of conditions under which the seal has to work. “It has needed a number of design and material iterations during development to meet these demands,” says Mr Fagg. “The car could be parked in a puddle in Alaska that freezes overnight, but when the motor starts, the seal quickly reaches a potential friction heat of 160 degrees Celsius.”

Meanwhile, the testing continues; and while nothing has failed yet, Mr Fagg expects that small changes will still be necessary. Ken Stewart acknowledges that this is a critical design point for the motor, but he expresses confidence that Trelleborg’s solution will work.

Protean Electric has been making in-wheel motors since 2005. The company’s products have featured in a variety of prototype vehicles, from a Mini Cooper to a Brabus Mercedes and a Vauxhall delivery van. Though now based in Detroit, its engineering is in Farnham, UK and there are plans for a production facility in China.

Trelleborg’s Tony Fagg is pleased with the way this project has come together. “This has been a real international affair, combining our expertise from around the world. The Trelleborg manufacturing and development facility in Malta has the knowledge of materials to engineer the right elastomer and will be carrying out volume production.

“We’ve been able to call on the assistance of our facilities in England in the initial stages. Tewkesbury has the skill to manufacture prototypes, and our site in Bridgewater has the specialist test equipment needed. In addition, we’ll be able to serve the factory in China with our global supply chain management network and give local support from our marketing company there.

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