Sensing Wheel Technology Changes
Sensing Wheel Technology Changes
Wheel speed sensors have evolved over the years, but still are important undercar components.
Motor Age — As long as vehicles have been rolling, the speed of the load-carrying wheels has been an issue. When I was a young boy watching western movies in the 1960s, I could always tell when a wagon was going to crash, because the camera would focus on a wood-spoked, steel-tired wagon wheel that was obviously spinning faster than it should. Those wooden wheels had a hard wood hub spinning on a hard wood axle; there was no bearing at all except for the animal fat-based grease that was packed in between the components.
In the course of the story, a crisis situation would come about that caused the draft animals to bolt and carry the wagon too far too fast (usually hurtling along through boulder-strewn cactus country or on the rim of a 1,000-foot promontory). Then a wheel would come off, tossing the wagon’s cargo and passengers far and wide amid splintered boards accompanied by a suitably exciting explosion of dust and debris.
I’d remember those scenes as I rode in the back seat of the family car on vacation trips while looking out the side window at the blur of the spinning wheels on the vehicles we were passing. And as I watched, I’d wonder how fast a car would have to go before the wheels came off the way those wooden wagon wheels did.
For years, vehicle road speed was measured at the output shaft except on old Volkswagen beetles, which had the speedometer cable fed through the hollow left front wheel spindle with its square end poking through a matching hole in the left front wheel bearing dust cap and a small snap ring to hold the end of the cable in place. The old VW engineers had a way of doing things like that: smooth and simple, easy to troubleshoot and easy to repair. Heck, the gas gauge on older bugs was even mechanical; it used a short cable-and-sheath affair that led from the float lever in the tank right up to the gauge.
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Source: Motor Age
