Pneumatically operable switch unit for monitoring tire pressure

摘要

An insulating cup-shaped body (29) that is screwed into the rim (11) of a vehicle wheel prevents conduction of heat (generated by the brakes, for example) from heating the metallic body (16) that forms a reference pressure chamber closed off by a membrane (17) from the inflated interior of a vehicle tire. The membrane (17) is set slightly within the rim of the cup for protection during tire changes. The chamber and switch housing (16) and a spool (27) for the coil of a resonant circuit form a preassembled unit that is snapped into the insulating cup and cemented into place. The relatively large coil diameter adds to the economy of the device, permitting the use of a small capacitor. The temperature of the gas sealed in the reference pressure chamber (18) by closure of the filling bore with a steel ball (25) follows the temperature of the interior of the tire and reliably opens the resonant circuit if the tire pressure falls below a prescribed limit. The condition of the resonant circuit is sensed by a fixed miniature oscillator mounted on the axle.