Abstract:
A system for interrogating a tire sensor. The disclosure provides a wheel ( 2 ) including a sensor ( 14 ) and an electrical conductor ( 18, 20 ) extending about a rotational axis ( 4 ) of the wheel ( 2 ), the sensor ( 14 ) being electrically coupled to said electrical conductor ( 18, 20 ). Communication between the sensor and a remote interrogating apparatus is thereby improved.

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates to a system for interrogating a tire sensor. 
   DESCRIPTION OF RELATED ART 
   It is known to monitor the characteristics of a tire through use of one or more Surface Acoustic Wave (SAW) sensors. Such sensors are generally mounted inside the tire and are electrically connected to an antenna by virtue of which signals may be communicated between the sensor and a remote transmitter/receiver. A problem associated with this prior art system is that, as the tire rotates in use, the sensor and associated antenna also rotate. Accordingly, the position of the sensor and antenna rapidly oscillates relative to the position of the transmitter/receiver and this can complicate interpretation of signals transmitted between the sensor and transmitter/receiver. 
   SUMMARY OF THE INVENTION 
   A first aspect of the present invention provides a wheel comprising a sensor electrically coupled to an electrical conductor within the structure of the wheel. The sensor may be a SAW sensor. The sensor may be capacitively coupled to the electrical conductor. The electrical conductor may be a rim of the wheel and/or elements within a tire mounted on the wheel. The tire elements may be reinforcing components within the tire. The tire elements may, for example, be a metal rim or braid. Furthermore, the sensor may be electrically coupled to the electrical conductor by means of a dipole or antenna. The dipole/antenna is preferably positioned within the wheel so as to excite an electromagnetic wave travelling around the wheel. The antenna may be a helical antenna. 
   A second aspect of the present invention provides a valve for a tire, wherein the valve comprises a sensor and dipole or antenna, wherein the dipole or antenna is electrically coupled to both the sensor and a body of the valve. The body of the valve is preferably metallic and adapted for connection with a wheel rim. Said connection may be an electrical connection. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: 
       FIG. 1  is a first embodiment of the present invention; 
       FIG. 2  is a second embodiment of the present invention; 
       FIG. 3A  is a side view of a valve body for use in connection with the present invention; 
       FIG. 3B  is a cross-sectional side view of the valve body shown in  FIG. 3A ; 
       FIG. 3C  is an end view of the valve body shown in  FIG. 3A ; 
       FIG. 4A  is a side view of a further valve body for use in connection with the present invention; 
       FIG. 4B  is a cross-sectional side view of the valve body shown in  FIG. 4A ; 
       FIG. 4C  is an end view of the valve body shown in  FIG. 4A ; and 
       FIG. 5  is a cross-sectional partial view of a wheel according to the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   A wheel  2  according to the present invention is shown in  FIG. 5  of the accompanying drawings. The wheel  2  is shown in cross-section taken through a plane in which a rotational axis  4  of the wheel  2  lies. As the wheel  2  is symmetrical about the rotational axis  4 , only the portion of wheel  2  located above the rotational axis  4  is shown in  FIG. 5 . The construction of a conventional automobile wheel will be well known to those skilled in the art and a detailed description thereof will not be necessary. Nevertheless, for the sake of completeness, it will be understood that the wheel  2  shown in  FIG. 5  comprises a wheel hub  6  upon which a pneumatic tire  8  is mounted. A valve  10  extends through an aperture in the wheel hub  6  so as to allow air to be forced into the cavity  12  between the tire  8  and the hub  6 . The valve  10  has a one-way characteristic so that air maybe admitted into the cavity  12  without being released therefrom (unless a release mechanism within the valve is activated). The tire  8  may be thereby conveniently inflated on the wheel hub  6 . 
   In accordance with the present invention, the valve  10  is provided with a sensor (such as a SAW sensor) for monitoring characteristics such as tire pressure and temperature. A SAW sensor  14  is shown in  FIG. 5  located in a slot defined in the body of the valve  10 . The sensor  14  is electrically connected to a helical antenna  16  which itself is mechanically mounted to the body of the valve  10 . The antenna  16  is located sufficiently close to the rim  18  of the hub  6  and the reinforcing elements  20  located within the tire side wall to induce an electro-magnetic wave therein. The antenna  16  may be located sufficiently close to the rim  18  and/or the reinforcing elements  20  so that the rim  18  and/or elements  20  lie within the near magnetic field generated by the antenna  16  when the sensor  14  activates. 
   Only some of the reinforcing elements  20  of the tire  8  are shown in  FIG. 5  and those that are shown are illustrated in a schematic manner. A reader skilled in the art will be familiar with the arrangement of the reinforcing elements  20  in a pneumatic automobile tire. 
   An enlarged view of the valve  10  is shown in  FIG. 2  of the accompanying drawings. As an alternative to the valve  10 , the valve  30  shown in  FIG. 1  of the accompanying drawings may be mounted to the wheel hub  6 . It will be seen with reference to  FIG. 1  that, rather than mounting the SAW sensor in a slot as in the case of the valve  10  shown in  FIG. 2 , the valve  30  shown in  FIG. 1  comprises a SAW sensor  32  secured to the valve body  34  by means of a mounting bracket  36 . The valve  30  of  FIG. 1  also comprises a helical antenna  38  secured to the valve body  34  and electrically connected to the sensor  32 . 
   With particular reference to  FIGS. 1 and 2  it will be seen that in the case of each valve  30 , 10  a helical antenna  38  (or, alternatively, a short dipole) is mechanically attached to a valve and electrically connected to a SAW sensor. The location of the antenna/dipole and sensor is such that, when the valve is secured to a wheel, the antenna/dipole and sensor are located inside a tire mounted on the wheel rim. One terminal of the sensor is also connected to a metal body of the valve. In this way, the valve body may be employed as an RF “counterweight”. Each valve may be capacitively coupled to a wheel rim. The dipole/antenna is positioned inside the tire in such a way that it excites an electro-magnetic wave which travels around the tire as a result of reflections from the metal wheel rim and tire braid. Effectively, the tire operates as an electro-magnetic waveguide and spreads an electro-magnetic field across the whole tire. Accordingly, the tire walls radiate the electromagnetic wave around the whole circumference of the wheel. This is in contrast to use of a conventional antenna which operates as a point source. In the present invention, the entire wheel effectively operates as an antenna. This increases the sector within which a sensor can be excited by an interrogation pulse and considerably simplifies the interrogation process. 
   In the valve  30  of  FIG. 1 , the SAW sensor is mounted to the valve by means of a mounting bracket. However, in the valve  10  of  FIG. 2 , the SAW sensor is mounted directly on the valve body. Valve bodies suitable for directly receiving a sensor are illustrated in  FIGS. 3 and 4  of the accompanying drawings. Each of the valve bodies  50 , 60  shown in  FIGS. 3 and 4  respectively define a slot  52 , 62  in which a sensor may be located. Each slot  52 , 62  is defined in the associated valve body so as to cut across the air passageway  54 , 64  through which, in use, inflation air is admitted into the tire cavity  12  (see  FIG. 5 ). In this way, when the sensor is located in the slot, inflation air passing through the valve passes around the sensor. The sensor is thereby exposed to the inflation air and may monitor the characteristics thereof. The slot  52 , 62  is also provided in that portion of the valve body which remains located within the tire cavity  12 . In this way, the sensor may also monitor the characteristics of the air within the tire during a normal use of the associated wheel. 
   The present invention is not limited to the specific embodiments described above. Alternative arrangements will be apparent to those skilled in the art.