EUREKA APRIL 2003 COVER FEATURE STORY

Flat motors put vehicle design in a spin

A new motor is expected to bring big benefits to both electric vehicles and domestic appliances. Tom Shelley reports

A flat, permanent magnet wheel motor and drive is claimed to have about double the overall efficiency of other motors used or proposed for electric vehicles.

Developed primarily for electric bicycles, the motor and drive combination is unique in that back emf and surplus power is extracted from non energised poles at all points in the drive cycle. You could say that it saves energy by giving with one hand and taking some of it back again with the other.

It is smoother and more efficient than conventional systems, and is aimed at the growing electric and hybrid vehicle market, including the nearly 3 million electric bicycles now made each year in China.

The Ultra motor is in fact a whole family of motors invented by Russian engineer Professor Vasiliy Shkondin, and made by him and colleagues in a small firm 100km South of Moscow. Professor Shkondin learned his trade as an electromechanical apprentice in the Russian Navy, although he subsequently moved into academia. The original inspiration may well have been advanced and super quiet submarine motors, but nobody is saying.

The 750W motor shown to Eureka was mounted on the front wheel of a bicycle, as part of an evaluation being undertaken by Chris Roberts, a former Pera consultant now working for himself in a small village near Melton Mowbray. The motor was between 40 and 45mm thick and 380mm in diameter and was enclosed in a solid looking aluminium housing. It was powered by three 12V 10Ah motorcycle batteries mounted in the cycle saddlebags. It was said to have 10 ferrite permanent magnet poles on its rotor and 12 electromagnetic poles on its stator. Maximum output torque was said to be 120Nm.

As well as regenerating power during braking, we were told that it makes use of the fact that back emf is generated in each electromagnet coil, when it is not powered. This energy is extracted according to the amount of surplus power that the drive decides it is supplying to the motor. The motor is said to collect up to 30% of the power associated with back emf when subjected to normal loads and speeds. This is claimed to at least double the potential range of electric vehicles compared to those powered using more conventional technology.

The motor exhibits relatively low field breakdown so torque and back emf are less spiky than usual. The motor did exhibit some slight cogging when the bicycle was ridden very slowly uphill, but generally it runs very smooth and completely silent. Part of the problem was, apparently, that your Eureka editor found it a strange experience to ride a bicycle driven at the front, with consequent wheelspin at the steering end, and so proceeded with extreme caution. Motor performance was not helped by the batteries being only partly charged. On a full charge, we were told that range was about 25km.


Variant with stator poles on inside and magnets on outer rotor


Motor with similar intended function but with outer stator poles and magnets on inner rotor

Professor Shkondin has developed around 70 variants based on the same basic technology. His factory, apparently, contains prototypes of electric bicycles or different types and power, electric motorcycles, wheelchairs and small cars reminiscent of the 'Bond Bug'. One design, weighing 20kg, is intended to fit into a 16in wheel rim. Power output is 4kW and maximum torque 600Nm. Torque generally is claimed to be two to four times greater than that possible with conventional gearboxes.

According to Justin Martin, commercial director of the Ultra Motor Company, an enterprise based in the Isle of Man, it will be marketing four different concepts: Ultra slim, Ultra compact, Ultra efficient and Ultra durable. "We think we can double the range of battery electric vehicles from a typical 53 miles to 100 miles, and reduce the 0 to 30mph 7s acceleration time showed by cars such as the Ford Thimk! to 4.5 to 5s. The bigger you go, the more torque and output power you get per unit weight. With sensible use of polymers it should be possible to reduce weight."

Whereas personal electric vehicles remain under something of a cloud in the UK, largely thanks to the Sinclair C5, other countries, without the same bad experience, are grasping the opportunities. There are now some 260 makers of electric bicycles world-wide. In China, the bicycle is still the principle mode of transport. The government there is not keen to encourage universal use of cars, or even mopeds with 50cc internal combustion engines, because of concerns about major pollution problems in its cities. China is believed to have produced between 2.5 and 3 million electric bicycles in 2002 the next largest producers are Japan and India. In the USA, it is possible to put 750W motors on bicycles, without getting into motorcycle legislation. In Europe, the figure is 250W. A 250W electric bicycle equipped with same 30Ah of batteries, should have a range of about 75km. The company intends to offer DIY kits to convert any make or model of bicycle into an adaptive 'pedelec' - a regular bicycle with a motor attached to its frame and a throttle on its handlebars.

Because the motors do not depend on rare earth metals, they are cheap to make. As well as motor vehicles, Martin believes the slim weight, high torque and smooth running low speed characteristics make the motors and drives eminently suitable for washing machines and other domestic appliances. The motors could be mounted directly on the backs of the washing machine drums and do away with the need for a belt drive, or the space required to mount the motor beneath the drum. Martin and his colleagues, in Isle of Man based Flintstone Technologies, have long experience of technology transfer from Russia, previous successful transfers include Keronite hard coatings for light alloys and Hardide fully dense tungsten carbide.

Pointers

The motors are flat, multi-poled types optimised for low speeds and high torque

The permanent magnets are ferrite, making the motors low cost

High efficiency and smooth running is ensured by using back emf from the non-energised motor windings

Eureka says: "Its about time to took a second serious look at the electric vehicle business as well as seeing what other electrical products the new motor might allows to be redesigned."

Euro motors zip along

Not only Russian and Chinese but leading European motor makers continue to come up with ideas and products to meet the challenge of designing commercially viable electric vehicles.

The Spingo, developed by Gloucestershire based Aphid designs, powers kick scooters to speeds approaching 20mph, for up to 25 miles on a single charge. At its heart is a maxon RE40 motor normally delivering 150W of power. The motor weighs only 480g but, controlled electronically through Aphid's pulse width modulator, it can produce almost 200W. Neodymium iron boron magnets allow miniaturisation and a running efficiency of up to 92%. No load current at 48V is 5mA. The whole motor pack weighs 4kg including batteries.

AEG Lafert motors are also proving to be of interest to European electric vehicle designers, again with permanent magnets. Fitted to a Lepton electric scooter, 1.8kW motors give a top speed of 45km/h and 0 to 50km/h acceleration in 6.5 to 7s. Weight with lead acid batteries is 133kg. On an electric micro car, 4kW motors deliver a maximum torque of 50Nm and give a top speed of 45km/h. Range is 85km and weight is 440kg with batteries or 280kg without.

Ultra motor temporary web site
justinmartin@iom.com

For more technical developments see www.eurekamagazine.co.uk

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