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By Design News Staff -- Design News, December 2, 2002
A bad assumption?
I must comment on your cover story, "Tires going high-tech" (DN 10.07.02, p.66), which discusses tire pressure monitoring systems under development. A tire inflation monitoring system should not be based on the faulty assumption that a "smaller" underinflated wheel will rotate faster than a fully inflated tire. A tire's revolution rate is a direct function of the tire's undeflected outside tread surface circumference and the distance traveled. When a tire is underinflated, its footprint merely lengthens. A radial belted tire's tread circumference will not change as it is inflated, underinflated, or deflected. Wheel-to-road slip will not be detectable until the inflated is so very low the tire will slip on the wheel. At that point, the tire will lose any ability to transfer forces to the rim and axle, and the vehicle will be dangerously difficult to control. An inflation monitoring system must give an earlier warning.
—Robert M. Allen, Design News reader
We did it already!
With regard to your cover story on tire pressure monitoring systems, in 1971 we built an off-road truck, with 300 ton payload capacity, and individually monitored all tire pressures and temperatures. We more than doubled the off-road tire tread life and completely eliminated low pressures. The tires were 36-51 78 ply rating (1000/78-51 in today's nomenclature—Ed.). The cold inflation pressure was 100 psig. The wheel load was 1/8th of the gross weight of over 1,000,000 lbs.
—Bryant Trenary, Design News reader
A better approach
RE: Tire pressure story. This story was interesting and I believe that the Michelin engineers, with their TIPM system, offer the best solution. However, I am curious why they believe that individual air pressure transducers are required at each wheel? With a computer-controlled sampling system, you would be able to valve-in to each wheel pressure through their pneumatic tubing that connects to a port through the wheel bearing. If the system was programmed to cycle the air pressure from each tire to a single air pressure transmitter, they would be able to eliminate the rim-mounted pressure sensors (transducers) and utilize a single air pressure transmitter. This would also eliminate the radio signal based system they envision. The sensing of the individual tire pressure via pneumatic tubing and the port through the wheel bearing would also serve as the conduit for adding or removing air from the tire in dynamic response to the conditions experienced by each tire. It would just be a matter of computer controlled synchronism of the sampling and the air pressure adjustment via stationary valves, a simpler and less costly system.
I am an Instrument and Control Engineer with 20 years of experience in the food processing industry and now working on systems in the nuclear industry.
—Paul Bunnell, Design News reader
Humpty Dumpty could have used him
The childhood toy that inspired me to pursue engineering (DN Editorial 10.07.02) was an Erector Set, specifically the Rocket Launcher set. It came with an electric motor and mechanical transmission. I built the rocket launcher only once, but used the kit to (try) to make things I saw around me. The most practical that I built was a lathe which I then used for several Cub Scout projects. I believe my dad bought the Erector Set for me out of frustration. He complained to my mother, "He always tears his new toys apart." To which my mom replied, "Yes, but he always puts them back together."
—John Myers, Polkaudio
Busy, busy
What childhood toy inspired me to go into engineering? Was it the Tinker Toys and Lincoln Logs at age 3? Was it the Gilbert Erector Set at age 7? Was it the chemistry set at age 10? Or was it the toys we made ourselves? The battleships we made out of scrap lumber? The tree houses in the woods? Fixing the discarded broken alarm clock? The go-cart and mini-bike we built from lawn mowers and bicycles? Replacing motor brushes in our mother's hand mixer? Maintaining and modifying our family and personally owned cars? I'm not sure if any of these projects motivated me to go into engineering. I think these were the playthings of inquisitive, analytical, logical children.
—Gene Polan, DaimlerChrysler AG
Vel Satis gets thumbs down
The Renault Vel Satis (DN 10.21.02, p.40), while employing very forward thinking in the technology and design department, has once again missed the boat in style. Obviously Renault is an extremely successful automaker in the European market but if they ever wish to seriously make another attempt in the U.S., the Vel Satis is not going to get them here. Renault is remembered in the U.S. as a low quality auto-maker from previous models such as the horrible Le Car; to break out of that classification would require something spectacular in style, quality, and value. That is something that has yet to be seen from Renault, or any other French automaker for that matter.
—George Rothgery, Storm Products, Microwave Business Unit
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