Recently various kinds of position sensors have been used in automotive subsystems which include Electronic Fuel Injection, Active Suspension and Exhaust Gas Recirculation (EGR). Because a potentiometer has a simple structure in which a brush slides on a resistor surface, it has many advantages such as high temperature applications, low cost, high signal level and almost infinite resolution compared to other kinds of position sensors that are magnetic or optical in nature. The potentiometer is considered to have the highest potential for a position sensor.
However, conventional potentiometers sometimes lose their linearity after use under severe conditions such as engine vibration (dither). They can endure only tens of millions of cycles of dither. This linearity error is thought to result from the following process:
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1st stage:
The resistive element wears by numerous cycles of slides.
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2nd stage:
The wear debris are generated and are deposited between resistor and brush.
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3rd stage:
Contact resistance increases as the contact area between resistor and brush decreases, since debris act as an insulator.
In order to prolong the sliding life of a potentiometer, the wear of both the resistive element and the brush must be reduced.
Carbon resistors consist of binder resin, carbon black, and some fillers that reinforce the resistors. By choosing these materials well, we have succeeded in developing a potentiometer that has a lifetime of more than one billion cycles of dither, preserving the initial linearity throughout this period of use.