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Race Winning Motor Turns To Machine Tools

Electric Vehicles Motors

Published in: Drives and Controls, November/December 1996

A flat motor used in race winning high speed vehicles and boats is now being launched as an industrial drive in a down-rated version. Its low weight and high efficiency make it particularly suitable for machine tools and robotics.

A motor with a disc shaped armature, which has found great success in powering racing vehicles, is now being offered in a down-rated version as a compact industrial drive for applications which require high power in a compact form.

The Lynch Disc-Armature motor which was originally developed for traction applications in a partnership between the inventor Cedric Lynch and London Innovation, a company which specialises in the development of new products from first concept to industrial production.

The principle of the iron-less ‘pancake’ motor has been known for years, but Lynch’s design is thought to be the first to combine the advantages of the disc armature with those of the traditional traction motor with laminated core. Because the armature is in the shape of a disc, rather than a cylinder as in conventional DC motors, the copper conductors and magnetic flux are used more effectively, and cooling is increased. As a result, power to weight ratios and efficiencies are higher than for conventional small traction motors.

To improve efficiency further, thick conductors of low resistance are used. High power and torque at low speed result from high magnetic flux acting on both sides of the armature.

The commutator is an integral part of the motor, making the motor more compact and rugged. There are no commutator connections to break down; cross connections are made at the armature periphery where cooling is at its maximum. Brush life is claimed to be many thousands of hours.

Control of the Lynch motor is simple, as no-load speed is proportional to voltage, and speed falls only slightsly as increasing load is applied. Maximum speed is self-regulated and regenerative braking is possible. A constant speed ‘shunt’ characteristic ensures the motor will not over-speed on no load.

Richard Fletcher of London Innovation sees the Lynch motor replacing hydraulic motors in machine tool and robotics applications, where its small size allows it to be placed close to the point of application at the head, rather than at the hub. He claims that in machine tool applications the motor will give two or three times the power of a conventional motor of the same size, at over 90% efficiency.

A range of standard flange mountings is offered. As the shafts are mounted from the outside of the motors, shaft sizes and types can be changed easily and motors can be supplied with integral geared or splined shafts made to order.

In traction applications the motors give continuous power output from 1kW on 12V to 8.5kW on 48V, and in appropriate circumstances they can be run at 60V giving 10.5kW power. (For short periods in racing vehicles they can give even higher power). The motors weigh between 8.5 and 11kg, and a single motor weighing less than 10kg is powerful enough to drive a light car at up to 50mph. The industrial version is down-rated 50% to ensure long life, but this still gives 4kW output on 48V for a weight of less than 11kg.

Shaft speed is generally lower for a given power output, thus requiring less gearing. At present, more powerful motors running at higher voltages are offered with twin armatures. But if demand warrants it, the Lynch Motor Company can offer motors with larger armatures, giving perhaps 20kW continuous output for traction or 10kW for industrial drives. These motors should weigh under 20kg and measure about 250mm in diameter.

The Lynch Motor Company, a division of London Innovation, has been producing Lynch motors in its factory in Devon since 1993. The motors are firmly established in lightweight traction applications in both vehicles and boats, and are now also being used in light aircraft, powered gliders and as a compressor drive in airships. Achievements include: the Countess of Arran’s World Waterspeed Record for an electric hydroplane in 1989; first place in its class in the French Electric Grand Prix in 1991; record 205km range of the Lynch Electrobike (London to Birmingham) in 1992; and the first electric sail drive for a four berth yacht in 1993.

In 1995 the first Lynch engined Ford Fiesta was exhibited at the Geneva Motor Show, and the Lynch motor is now becoming popular in electric go-karts. Over 500 motors have been sold to Asmo of Switzerland for karts, and this year electric karts fitted with Lynch motors are leading the international championship and have established a 24 hour endurance record of 970 miles.

Richard Fletcher of London Innovation believes that in the debate between AC and DC drives, the Lynch motor tips the balance in favour of DC in sizes of up to about 20 or 30kW. “The Lynch motor offers excellent low speedperformance and sophisticated control characteristics with less complexity and a lower number of power output devices than AC drives,” he adds.

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