It is known to monitor the characteristics of a tyre through use of one or more Surface Acoustic Wave (SAW) sensors. Such sensors are generally mounted inside the tyre 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 tyre 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.

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 tyre mounted on the wheel. The tyre elements may be reinforcing components within the tyre. The tyre 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 electro-magnetic wave travelling around the wheel. The antenna may be a helical antenna.

A second aspect of the present invention provides a valve for a tyre, 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.

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

A wheel 2 according to the present invention is shown in Figure 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 Figure 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 Figure 5 comprises a wheel hub 6 upon which a pneumatic tyre 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 tyre 8 and the hub 6. The valve 10 has a one-way characteristic so that air may be admitted into the cavity 12 without being released therefrom (unless a release mechanism within the valve is activated). The tyre 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 tyre pressure and temperature. A SAW sensor 14 is shown in Figure 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 tyre 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 tyre 8 are shown in Figure 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 tyre.

An enlarged view of the valve 10 is shown in Figure 2 ofthe accompanying drawings.

As an alternative to the valve 10, the valve 30 shown in Figure 1 of the accompanying drawings may be mounted to the wheel hub 6. It will be seen with reference to Figure I that, rather than mounting the SAW sensor in a slot as in the case of the valve 10 shown in Figure 2, the valve 30 shown in Figure 1 comprises a SAW sensor 32 secured to the valve body 34 by means of a mounting bracket 36. The valve 30 of Figure 1 also comprises a helical antenna 38 secured to the valve body 34 and electrically connected to the sensor 32.

With particular reference to Figures 1 and 2 it will be seen that in the case of each valve 30,10 a helical antenna (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 locate inside a tyre 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 tyre in such a way that it excites an electro-magnetic wave which travels around the tyre as a result of reflections from the metal wheel rim and tyre braid. Effectively, the tyre operates as an electro-magnetic waveguide and spreads an electro-magnetic field across the whole tyre. Accordingly, the tyre walls radiate the electro- magnetic 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 Figure 1, the SAW sensor is mounted to the valve by means of a mounting bracket. However, in the valve 10 of Figure 2, the SAW sensor is mounted directly on the valve body. Valve bodies suitable for directly receiving a sensor are illustrated in Figures 3 and 4 of the accompanying drawings. Each of the valve bodies 50,60 shown in Figures 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 tyre cavity 12 (see Figure 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 tyre cavity 12. In this way, the sensor may also monitor the characteristics of the air within the tyre 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.