Abstract: Tire pressure monitors are incorporated in vehicles having penumatic tires (14) to continuously or periodically measure the air pressure within the tires and to alert the driver should the pressure in one of the tires fall below a predetermined value. A self-contained battery powered rf transmitter unit (10) is affixed within the drop center (22) of each wheel (12) and includes a pressure sensing switch (84). The battery is contained within a housing (20) mounted to the external surface of the wheel adjacent a fill valve (30) through which electrical wires (50) are routed to the transmitter (11). The transmitter emits a pulse every 33 seconds when the air pressure within the tire is above a prescribed value. A receiver (13), located in the passenger compartment of the vehicle, receives the signal(s) from the transmitters and counts the number of signals received over a given time period established by an internal pulse generator.

Abstract: Tire pressure monitors are incorporated in vehicles having pneumatic tires to continuously or periodically measure the air pressure in the tires and to alert the driver should the pressure in one of the tires fall below a predetermined value. A self-contained generator-transmitter unit is affixed to each wheel, each unit monitoring the air pressure in the tire associated therewith and generating an RF signal when the pressure falls below a predetermined value. A receiver, located in the passenger compartment of the vehicle, receives the signal(s) from the generator-transmitter units to indicate a low tire condition to the vehicle operator. The generators operate only during rotation of the wheels which effect relative rotation between two members in each generator, one member carrying a permanent magnet and the other carrying an inductor.