Tire pressure alarm system

Claim 1

A tire pressure alarm system comprising a standard dual wheel lug bolt on a vehicle wheel modified by the provision of a tapped hole in the end thereof; a body threaded into said tapped hole; means forming a guide passageway in said body and through said lug bolt; a sensing rod of electrically conductive material slidably mounted in said guide passageway for longitudinal reciprocation in one direction and in the opposite direction thereto; one end of said rod protruding in said one direction through said lug bolt on the inside of the vehicle wheel; a flange cap member on the other end of said rod; means biasing said rod in said one direction; annular pressure responsive means sealed in said body to form an inflatable chamber, embracing said sensing rod and engaging said cap member to urge said rod in said opposite direction; a fill pipe for exposing said inflatable chamber to a source of gas pressure; duct means connecting said fill pipe to the interior of a tire on said vehicle wheel; and signal means for indicating when said pressure responsive means is overcome by said biasing means, including: an energized electrical sensing circuit with a contact brush therein; said brush being positioned at a point in the path of rotation of said one end of said sensing rod to be engaged thereby only when said sensing rod is in its overcome position; said sensing circuit being conditioned to be overloaded when said sensing rod contacts said brush; an electrical signal circuit; a signal device in said signal circuit; and a switch device operative to open said sensing circuit and close said signal circuit when said sensing circuit is overloaded.