self-inflating tyre

The up-and-down bouncing action of a car in normal driving ought to be enough to compress air through a valve to keep a tyre inflated if it has sprung a slow leak. This would have to be a microprocessor controlled system which let the correct amount of air in (or out, in hot weather) to keep the tyre at the correct pressure, plus it would have to trigger an alert to the driver that the car must be taken to a tyre repair shop immediately. If the car stayed stationary for any length of time (i.e. parked for hours, not stopped at the lights etc) it would disable the ignition so that the mechanism was not abused, especially since severe damage would occur if someone were stupid enough to drive on the rims.