Tire pressure detecting switch

Claim 1

A tire pressure detecting device mounted on a vehicle wheel assembly including a rotatable wheel with a wheel rim carrying a tire and a stationary element supported on a wheel axle, comprising a revolving part secured to said rim for moving therewith along a circular path and a fixed part secured to said stationary element and disposed adjacent said circular path, said revolving part comprising a first housing portion extending through said wheel rim and a second housing portion extending at an angle thereto at the side of said rim carrying said tire, said first and second housing portions being secured to and communicating with each other, a shaft member rotationally mounted in said first housing portion, and having an inner end portion projecting in the radial direction of said wheel, a magnet mounted on said inner end portion of said shaft member and producing a magnetic field, a spring means rotationally biasing said shaft member into an operative position, a movable member exposed on its one end to tire pressure and extending substantially tangential to said wheel rim and slidably guided in said second housing portion and being movable in response to a pressure drop in said tire, said movable member being engageable with said shaft member to lock said shaft member and said magnetic member in said inoperative position, said movable member being movable upon tire pressure drop to unlock the said shaft member to permit turniNg said magnetic member into said operative position under the action of said spring means, and a guide element received in said second housing for guiding said movable member and made of a material having a low coefficient of friction to insure an instantaneous response of said movable member to said tire pressure variations even under very high centrifugal forces, said fixed part comprising a switch element responsive to said magnetic field of said magnetic member while in said operative position, to produce a signal for a warning system.