APME: Economic Examples

Trouble-free electric drives

Modern cars require a large number of electric motors. While at one time electrically operated windows were regarded as a luxury; now cars of all types rely on electric motors for a wide range of functions, many of them critical to safety such as door locking systems, anti-lock braking, windscreen washer spray pump, and mirror and headlamp adjustment. Several other features also use electric motors, for example engine cooling, in-car climate control and seat adjustment. As hybrid vehicles and ultimately fuel cell propulsion come on to the market, we will see yet more applications of electric motors in cars.

Electric motors used in automotive applications require engineering materials with high temperature resistance, dimensional stability, low wear and friction (for gear trains), easy mouldability and chemical resistance. The main use of engineering plastics in automotive electric motors is in the production of drive (gear) housing. And the low coefficient of friction of many engineering plastics means that they are increasingly chosen to produce the gear trains themselves. Their benefits include smooth, quiet and maintenance free operation. For gear trains where the use of lubricants must be avoided, self-lubricating plastics are used.

But the most powerful advantages of plastic gears may be the design opportunities they afford. Gear geometries impractical in metal are often easy to mould in plastic, and they can reduce drive size weight, and cost. For example, a common arrangement of two external spur gears with a large ratio demands a wide center distance. However, the same ratio can be achieved in a smaller space by replacing an external gear with an internal gear that, while difficult to machine in metal, is easy to mould in plastic.