On-the-fly Tire Pressure Adjustment

About time we listened to you...

Watching Matt's Off Road Recovery videos I am reminded that going off road often means letting air out of the tires until the internal pressure is more like 10 PSI instead of 30 PSI. Higher pressures work well on the highway. You have less rolling resistance, better control and the tires don't get over heated. Lower pressures off road give you better grip on iffy surfaces like mud and sand. Getting back on the highway after an off road adventure, you want to pump up your tires back up to 30 PSI. This usually means carrying a portable air compressor with you, and if you have very large tires, spending a quarter hour or more waiting for your tires to reach highway pressure.

Of course, you need to stop the vehicle and get out to perform these operations. The military gets around this by having an air system built into the wheels and axles, an expensive proposition that few civilians can afford.

It occurred to me that it might be possible to build a system into the wheel with no mechanical connection to the rest of the vehicle. A small air compressor would be mounted to the wheel inside the tire and would be controlled by a radio signal, much like Tire Pressure Monitoring Systems do now. The only real problem we would have is providing power to the electric motor that will drive the air compressor. This could be done by turning the wheel into a generator. A ring of magnets would be mounted to the vehicle some where around the brakes, and a set of coils of wire would be mounted to the wheel so that they are in close proximity to to the magnets. When the wheel turns, the coils of wire would pass through the magnetic field, electricity is generated, the motor drives the air compressor and the tire is inflated.

Given that we would want to keep the weight as low as possible and the low speed of the wheel, this wheel mounted generator would probably not be able to generate much power. It might be enough to do the job. You might have to drive a mile at a lower speed before the tires were inflated enough to handle highway speeds. You would however, be moving as opposed to being stopped waiting for your portable air compressor to do the job. An experimental model would have to be built and tested. 

If that arrangement is not adequate, we might want to add battery packs, which are heavy, or a bladder to hold a supply of high pressure air. It would be in the shape of a small inner tube that would hug the wheel and so not interfere with the deformation of the tire often encountered when crawling over rocks.