Hub dreams

An electric motor mounted in a wheel hub could be the way forward for hybrid vehicles. Jon Excell reports.

Claims about startling innovations that will ‘forever change the way we get from A to B’ are pretty common in the automotive industry, and most can be taken with a pinch of salt.

But when the person making these claims is the former vice-president of DaimlerChrysler, a man who over the course of his 37-year career has become a respected figure in the global automotive industry, you tend to sit up and take notice.

The man is Richard Schaum, the company is Wavecrest, and the innovation in question is the adaptive motor, a high torque, high-efficiency electric motor that can be mounted in a car’s wheel hub.

Schaum was ‘happily retired’, spending time with his family and his yacht when Wavecrest approached him. He found the lure of an exciting engineering project too hard to resist. ‘I got so excited I came back to work again,’ he said. Schaum now heads a group of engineers in the company’s recently-opened Detroit development centre.

Wavecrest recently demonstrated its motor at EVS20, the 20th International Electric Vehicle Symposium and Exhibition held in California. The company removed the petrol powertrain from a Smart Roadster and installed adaptive motors in its rear wheels.

Described by Schaum as a ‘beautiful installation’, the 14in dia, 20kW motors demonstrated extraordinary levels of torque – over 700 Nm each.

While the motor has its immediate origins in the work of Russian physicists Alexander Pyntikov and Boris Maslov the concept has an intriguing historical precedent.

In 1898 Austrian coachbuilder Jakob Lohner hired a 25-year-old graduate as his chief engineer, and commissioned him to devise a quietly-elegant electrical propulsive system that wouldn’t insult the delicate sensibilities of the wealthier classes in the way that the ‘primitive’ combustion engines of the time did.

The student placed two electrical motors as bushings of the front wheels in such a way that its rotors turned with the wheels, so both stators were fixed by a rigid axis and to the suspension.

When the groundbreaking 1 tonne vehicle first appeared at the World Exhibition of Paris in April 1900 it astonished the automobile world.

That student’s name was Ferdinand Porsche, and this was his first design.

The principle of Wavecrest’s adaptive motor is not so very different from Porsche’s concept. A cylindrical stator frame (the stationary part of the motor) is fixed to the wheel axle. The power supply is fixed within the stator frame, while a number of electro-magnets are mounted on its outer surface. A cylindrical rotor frame (the moving part of the motor) is then coupled via bearings to the wheel axle, and permanent magnets distributed along its inner surface surround the electromagnetic stator segments.

Schaum explained that in a model application an adaptive motor would be used to drive each wheel of a vehicle. Each motor is controlled by microprocessors embedded in the control system, while decision-making algorithms track and analyse vehicle performance, instantaneously identify load requirements and precisely deliver energy. The system also makes use of regenerative braking – re-using energy generated during braking.

While the prototype shown at EVS20 was a ‘pure’ electric vehicle, Schaum said that the main application of the technology is likely to be in hybrids.

These vehicles typically operate either in series (operating solely on electricity, but containing a combustion engine that generates additional electricity) or in parallel (containing an electric system and a combustion system and capable of operating on either).

Despite the great promise of hybrid engines, it’s estimated that on most, up to 10 per cent of the engine power is lost as energy as it is transferred through the gears and shafts to the wheels.

Wheel hub motors present a tempting alternative for hybrid designers. By replacing a central energy source with wheel-mounted motors they could eliminate much of the drivetrain and its associated energy losses.

Schaum said that one of the things that really attracted him to the company was the potential to develop what he calls ‘full vector control’ – the ability to precisely control the behaviour of the individual wheels. He said that although efforts have so far been confined to one axle, the ultimate plan is to put motors at each corner of the vehicle, allowing unprecedented manoeuvrability.

‘If you want to park the car we can rotate one wheel clockwise and the other anticlock-wise, and make it turn in very tight corners,’ he said.

Returning to the torque characteristics of the motors, Schaum dismissed suggestions that vehicles equipped with such motors would be sluggish. Electric motors are able to provide maximum torque as soon as they start up, he said. This could give vehicles equipped with hub motors sports car-like acceleration from a standing start.

Clearly the technology is still in its infancy and Schaum’s team is involved in a frenzied process of continual tweaking. The Smart Roadster ‘drives beautifully’ he said, but the team is now trying to improve its manoeuvrability. ‘We have bits and pieces of traction control and stability control, but the aim for 2004 is toget all these functions working in a way that we can demonstrate all the potential capabilities to various tier 1 suppliers as well as whoever else wants to listen,’ he added. Schaum said it’s likely that the first multi-axle application will be on commercial hybrid vehicles.

With General Motors recently winning a contract for 56 hybrid electric buses in Seattle, he pointed to a growing trend in the US towards hybrid stop-and-go delivery vehicles, and said that the motors have great potential on vehicles operated by the likes of UPS and FEDEX.

This is because without the need for differentials, axle shafts, gearboxes and transmissions there’s a lot more room for passengers or goods. ‘Hub motors let you maximise the interior volume of the vehicle,’ he said.

The final stage is for the motors to be used on production cars, although Schaum said that he doesn’t really see the technology making an impact here until 2007.

However, while ‘full vector’ control of four wheels is still just around the corner, single wheels present fewer problems and the company’s first commercially available product, an electric folding bicycle, has just gone into production.

With motors mounted in the rear hub, the TidalForce M-750 is said to provide an exceptionally smooth and powerful ride. ‘The only thing you can hear is the tyres,’ said Schaum, ‘and what’s really impressive is the low-end torque: you just accelerate away from a rest – it’s remarkable.’

The M-750 differs from other electric bikes in that it doesn’t need a planetary gearset to multiply the torque in the motor. It simply has a battery in the front hub and a motor in the rear hub.

Schaum said that because of its quiet operation and low heat signature the bike, which starts at $1,750 (£1,000), is perfect for the armed forces, and the company is currently bidding for potential military contracts.

Helped, no doubt, by the expertise of company chairman Gen Wesley Clarke, who just happens to be former head of NATO.