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09/10/2005
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Tom Shelley reports on an innovation that reduces electrical noise from motors in cars and saves space at the same time
New small motors have been developed for the automotive market with all their suppression components in the motor end caps.
Engineers at Johnson Electric, a company which started out in Hong Kong and makes vast numbers of motors in China, but undertakes its R&D in the USA, concluded that the closer the suppression circuitry is to the source of electrical noise, the more effective it will be.
They therefore decided to mount all the suppression components in the same motor end cap that carries the brush gear. The result is a plastic, moulded end cap with various pockets. These containing: positive and negative motor terminals, a chip capacitor, an inductor, a PTC thermistor, two brush assemblies and a bearing.
The chip capacitor is connected between the positive and negative motor terminals. The inductor coil is connected between the positive terminal and the motor brush. The other brush is connected to the negative terminal and the motor housing through the PTC thermistor.
This arrangement will reduce electrical noise at a time when more electronic controllers are being used in cars and smaller motors have higher current densities going through their brushes, creating more noise.
Johnson Electric
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Author
Tom Shelley
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