The present invention relates to transmitter units each attached to a rim wheel of a tire for gathering and transmitting information regarding the tire including the air pressure in the tire, for the purpose of monitoring the condition of the tire, and to tire condition monitoring apparatuses having such transmitter units.
For monitoring the condition of the tires of a vehicle from its passenger compartment, wireless type tire condition monitoring apparatuses have been proposed. One such apparatus includes a plurality of transmitters and a receiver. Each of the transmitters is installed in a different one of the tires and attached to the rim wheel of the tire. The receiver is installed in a body frame of the vehicle. Each transmitter detects the condition of the corresponding tire including the air pressure and the temperature in the tire. The transmitter then wirelessly transmits a signal including detection data of the tire condition via an antenna. The signal is received by the receiver through an antenna, and information regarding the tire condition is shown on a display provided in the passenger compartment. The driver is thus allowed to monitor the condition of the tires of the vehicle constantly.
Typically, each transmitter includes a circuit board defining an electronic circuit and a housing accommodating the circuit board. The electronic circuit includes a plurality of electronic components including a pressure sensor and a signal treatment element, which are formed on the circuit board.
Conventionally, the transmitters of a wireless type tire condition monitoring apparatus are attached to tire rim wheels by means of attachment structures described in, for example, U.S. Pat. Nos. 6,549,125 and 6,672,150 and Japanese Laid-Open Patent Publication No. 2003-312221. In these structures, one or more studs project from and are fixed to the outer circumferential surface of each rim wheel through welding or swaging. Each of the studs is received in a hole defined in a portion of the housing of each transmitter. In this state, a clump member is attached to the stud, thus fixing the transmitter housing to the outer circumferential surface of the rim wheel.
However, for forming the studs on the outer circumferential surface of the rim wheel, it is necessary to define a hole in each rim and a threaded portion in each stud or bond the stud with the rim wheel through welding. That is, the conventional attachment structures are complicated to assemble, making it difficult to attach the transmitters. Also, if the studs are fixed to the rim wheels through welding, the heat generated by the welding decreases the strength of the welded portion of each rim wheel, resulting in non-uniform strength of the rim wheel as a whole.