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01 September, 2005

The September 2005 issue of Drives & Controls magazine contains a special report on the trend towards electric propulsion for almost every form of transport. This article provides some extra information on some of the companies that are gearing up to support the growing demand for specialised electric motors for vehicle applications

Electric Transport Extra: Motoring towards a new market

The prospect of a potentially lucrative new market opening up for EV (electric vehicle) motors has spawned a cottage industry of motor developers hoping to cash in on this specialist market. They are designing machines to meet the demand for light, rugged motors that will deliver plenty of torque, especially at low speeds.

Some of these developers are tweaking standard motor designs; others have gone back to the drawing board to come up with radically new machines, tailored to the demands of the EV market. Many are based in the US.

One of the best-established developers is Colorado-based UQM Technologies, which was founded in 1967 to produce fibreglass parts for various applications including kit cars. It then turned its attention to developing an all-composite battery-powered vehicle and, as a result, started to experiment with motor technologies.

This led to the development of a patented permanent magnet motor design and matching controls. A typical UQM motor has a stator winding with a high pole count and a hollow rotor fitted with rare-earth magnets. A patented control method allows the high-efficiency motors to deliver both high output torque at low speeds, and continuous power at high speeds.

UQM has supplied motors to GM, BMW, Humvee and has picked up several US Government and military development contracts.

A more recent arrival is Utah-based Raser Technologies, formed in 2003, which claims to have found a way of making a few, simple changes to a conventional motor design that yield significant increases in power, performance and efficiency without needing exotic materials. It claims that its Symetron motors (shown above) deliver more torque than conventional machines at a lower cost per kW and in a smaller, lighter frame.

For example, Raser claims that one of its motors has demonstrated the highest torque density (35Nm/l) of any currently available drive system. It says that the 67kg air-cooled motor, which is 32cm in diameter and 20cm long, can deliver 570Nm of torque continuously for at least 60s.

Raser is spearheading a new consortium which aims to develop "next generation" hybrid electric vehicles, which use an electric motor as their main form of propulsion and can be plugged into the mains for recharging. They will operate in an all-electric mode for the first 30-80km of a journey, achieving the equivalent of 1.2-2.35 l/100km (100-200 mpg).

Wavecrest Laboratories was founded in Virginia in 2000 to develop and commercialise a multi-phase brushless DC motor said to deliver high efficiencies and torque levels at high and low speeds. The patented design, called the Adaptive Motor, uses a rotor that surrounds and rotates about a central stator consisting of a series of independently controlled electromagnets driven by a proprietary control module.

In 2004, WaveCrest launched its first commercial products - high-performance electric bicycles. It has also developed a propulsion system for electric scooters.

Another novel multi-phase machine is the Chorus Meshcon motor, developed by a "virtual company" registered in Gibraltar but with operations spread around the world. Chorus Motors says that its machine achieves five times the torque of conventional three-phase motors by "spoofing" the drive electronics into thinking it is operating at a higher speed.

The technology which, can be applied to motors ranging from a few hundred Watts to several Megawatts, has potential applications away from electric vehicles. Chorus has been working with Boeing to test a motor that can propel a Boeing 767 on the ground.

There are EV motor developers based in Europe as well. Perhaps the best-known is Cedric Lynch, whose brushless DC motor has a disc armature formed from hard-drawn copper, interleaved with low-loss steel. There are permanent magnets on both sides of the disc, doubling the flux density and shortening the magnetic path. The result is a motor, available in ratings up to 22kW, 120V, with high efficiencies, and high power-to-weight and power-to-volume ratios.

The Lynch motors, which are made in Devon by LMC, have been used to propel a variety of vehicles including bicycles, airships, boats and go-karts. The technology has also been licenced to the US lawn-mower giant Briggs & Stratton. The British developers of the 225km/h Connaght hybrid electric sportscar (shown above) are using a 13kW Lynch motor to boost the low-speed torque of the vehicle`s V10 petrol engine.

A rather more specialised British development is the PowerBeam - a cylindrical energy storage device containing two contra-rotating rotors that spin at 25,000-50,000 rpm. For a passenger car, the 250mm-diameter cylinder would be about 2m long and would store about 1kWh. The developers say that it will provide a better way of capturing regenerative energy and delivering torque boosts than a battery.

As well as the specialised motor developers, companies are emerging to supply complete drivetrain for electric and hybrid vehicles. One example is the Canadian company Azure Dynamics which supplies complete drive systems for commercial and military vehicle customers around the world. For example, Azure recently signed a deal with the UK`s SEV Group to supply 1,000 drivetrains for EVs over a two-year period.

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