Tire pressure detector

Claim 1

A pressure detector for a tire having an inflating valve, comprising: a cap-like casing having a closed upper portion and an open lower portion; a hollow adaptor made of an insulating material and having an upper end engaging said open lower portion of said casing, a lower end adapted to engage and open the inflating valve to permit flow of air from the tire into said adaptor, and an inward protrusion projecting from an inner wall of said adaptor; a detector assembly including a battery unit and a signal generating unit which are mounted within said casing; a pressure-actuated switch unit mounted within said adaptor for connecting electrically said battery unit to said signal generating unit so as to activate said signal generating unit when pressure inside the tire is insufficient, said switch unit including: a resilient disc member disposed in said lower end of said adaptor, said disc member having a peripheral portion secured to said inner wall of said adaptor and forming an air chamber in said lower end of said adaptor to be communicated with an interior of the tire, and a central portion moving in accordance with pressure inside the tire; an annular conductive piece disposed on an upper surface of said inward protrusion of said adaptor and connected electrically to one of said battery unit and said signal generating unit; a first contact unit having a conductive tubular body which is disposed on said central portion of said disc member and which extends slidably through said inward protrusion of said adaptor, said tubular body having a peripheral flange which projects outwardly from an upper end thereof and which extends above said conductive piece; a second contact unit including a hollow conductive seat member which is mounted within said adaptor above said tubular body and which has an internally threaded portion, said seat member being connected electrically to the other one of said battery unit and said signal generating unit, said second contact unit further including an adjustment rod which has an externally threaded portion that engages said internally threaded portion of said seat member; and a spring having one end abutting said adjustment rod and another end abutting said tubular body to bias said tubular body toward said disc member, said adjustment rod being movable within said seat member to adjust biasing force of said spring; whereby, when pressure inside the tire is sufficient to overcome said biasing force of said spring, said disc member biases said tubular body such that said peripheral flange of said tubular body is spaced from said conductive piece to disconnect electrically said signal generating unit from said battery unit, and when pressure inside the tire is insufficient to overcome said biasing force, said spring biases said tubular body such that said peripheral flange of said tubular body contacts said conductive piece to connect electrically said signal generating unit to said battery unit.