Embodiments of the present invention relate to monitoring system sensors and methods of constructing the same. In particular, embodiments of the present invention relate to water-resistant tyre-pressure monitoring system sensors and methods of constructing the same.

Tyre-pressure monitoring systems (TPMSs) monitor the fluid pressure in pneumatic tyres of a vehicle. Such systems are used to provide a warning if an inflation fluid pressure in the tyre falls below a predetermined level. In some instances, the temperature of the fluid in the pneumatic tyres (or the temperature of a part of the tyres) is also monitored.

TPMSs are particularly advantageous when used in relation to large off-road vehicles as are typically used in, for example, the mining industry. Using a TPMS to monitor inflation fluid pressure in vehicle tyres allows issues to be readily identified and appropriate action taken - such as re-inflation of the tyre. Maintaining the inflation fluid pressure in the tyres of a vehicle at appropriate levels can help to reduce tyre maintenance costs, improve fuel efficiency of the vehicle, and reduce downtime for the vehicle.

A TPMS includes a sensor which is mounted with respect to a tyre of a vehicle in order to sense the inflation fluid pressure in the tyre. The TPMS sensor may, for example, be mounted within the tyre (an internal sensor) or to a valve of the tyre (an external sensor). The TPMS sensor is typically linked to a control unit by a radio frequency communication channel. The TPMS sensor transmits, for example, an identifier for the sensor and a signal representative of the inflation fluid pressure of a tyre to the control unit. The control unit may include a predetermined fluid pressure associated with the identifier. The control unit may, for example, trigger the actuation of an alarm in the event that the fluid pressure sensed by the sensor is below or above the predetermined fluid pressure (or outside of a predetermined range). Of course, the control unit may be configured to perform various different steps and this is just one example. The temperatures and/or pressures sensed by the TPMS sensor are time stamped and logged in a receiver. The log may be used to identify slow leaks and overheating (due to, for example, excessive speed, overloading or poor driving style). In some arrangements the receiver is configured to pass the received information to a third party system which may log and/or transmit the information (perhaps via the internet) for off vehicle analysis and decision making.

During operational life of a TPMS sensor, the sensor is exposed to various different fluid pressures and temperatures, vibrations, forces associated with rotation of the tyre, and various different fluids. It is not uncommon for a tyre to contain various different fluids due to poor maintenance practices - for example, water may be present within the tyre due to the water in the air used to inflate the tyre. Other fluids, such as coolants, may also be deliberately introduced into a tyre to inhibit corrosion of the wheel or tyre, or to disperse heat. Water and other fluids can cause corrosion and/or can short circuit electrical components of the sensor.

The sensor must be sufficiently durable so as to provide consistently accurate fluid pressure measurements throughout a reasonable operating life. Prior attempts to provide sensors which are protected from potentially damaging fluids include embedding a sensing element and circuit board in a hard compound such as an epoxy resin. However, in such arrangements, the accurate readings of the fluid pressure in the tyre are either impossible or difficult as the fluid pressure is not transmitted to the sensing element through the epoxy resin. Some attempts have been made to provide a tube (a "snorkel") which passes through the epoxy resin and puts the sensing element in fluid communication with the interior of the tyre. Such snorkels are not, however, effective in all circumstances - particularly, in relation to tyres which contain a relatively large quantity of potentially damaging fluid. The snorkel arrangements are also thought to be ineffective even if only a small quantity of fluid is present - even condensation may be an issue (particular, in the presence of salty contaminants). Furthermore, the hard compounds are prone to failure and cracking during operation - particularly at the joints between the compound and the various parts of the sensor. Such cracks allow the ingress of potentially damaging fluid to parts of the sensor. Conformal coatings, such as parylene and acrylic based coatings, also do not allow for the consistent accurate transmission of fluid pressure to the sensing element of the TPMS sensor during operation and/or suffer from cracking and/or are prone to failure and/or move under the forces associated with rotation of the tyre. Some coatings are, for example, prone to the formation of gas bubbles during decompression which can exert forces on the sensing element of the TPMS sensor.

There is, therefore, a need to provide a TPMS sensor in which the components of the sensor are adequately protected from potentially damaging fluids and which are durable. Embodiments of the present invention seek to ameliorate one or more problems associated with the prior art.

Accordingly, an aspect of the present invention provides a sensor for use with a monitoring system, the sensor comprising: a main body at least partially defining a vented volume; a sensor circuit including a sensor element, the sensor circuit being at least partially housed in the chamber of the main body; and a protective elastomeric gel which covers an operative part of the sensor element, wherein an open part of the volume is provided adjacent the protective elastomeric gel such that the gel can expand into the open part of the volume.

The sensor circuit may include a circuit board. The sensor circuit may include one or more other components. The sensor may further comprise an attachment arrangement securing at least part of the sensor circuit to the main body. The attachment arrangement may comprise a thermosetting polymer. The thermosetting polymer may be an epoxy resin. The elastomeric gel may be a layer of elastomeric gel which covers at least a part of the attachment arrangement. The elastomeric gel may cover at least part of a juncture between the attachment arrangement and the main body. The volume may be a chamber and the open part of the volume may be defined between the elastomeric gel and a lid of the sensor. The lid may define one or more vents. The volume may be a chamber and the open part of the volume may be defined between the elastomeric gel and an end surface of the main body. The sensor may further comprise a valve attachment arrangement which is configured to be secured to the valve of a tyre. The volume may be vented through the valve attachment arrangement. The sensor may be configured to be secured within a tyre. The open part of the volume may be sized and/or shaped to help to prevent bubbles formed in the elastomeric gel causing a substantive force to be applied to the operative part of the sensor element. Another aspect of the present invention provides a tyre-pressure monitoring system including one or more sensors.

Another aspect of the present invention provides a vehicle including one or more sensors.

Another aspect of the present invention provides a vehicle including a tyre- pressure monitoring system. Another aspect of the present invention provides a method of manufacturing a sensor for use in a monitoring system, the method comprising: providing a main body at least partially defining a vented volume; providing a sensor circuit including a sensor element, the sensor circuit being at least partially housed in the chamber of the main body; and providing a protective elastomeric gel which covers an operative part of the sensor element, wherein an open part of the volume is provided adjacent the protective elastomeric gel such that the gel can expand into the open part of the volume.

The sensor circuit may include a circuit board. The sensor circuit may include one or more other components. The method may further comprise providing an attachment arrangement securing at least part of the sensor circuit to the main body. The attachment arrangement may comprise a thermosetting polymer. The thermosetting polymer may be an epoxy resin. The method may further comprise reducing the fluid pressure around the thermosetting polymer before the thermosetting polymer is cured. Providing the elastomeric gel may comprise providing a layer of elastomeric gel which covers at least a part of the attachment arrangement. The elastomeric gel may be provided such that the elastomeric gel covers at least part of a juncture between the attachment arrangement and the main body. The method may further comprise providing a lid, wherein the volume is a chamber and the open part of the volume is defined between the elastomeric gel and the lid of the sensor. The lid may define one or more vents. The volume may be a chamber and the open part of the volume may be defined between the elastomeric gel and an end surface of the main body. The method may further comprise providing a valve attachment arrangement which is configured to be secured to the valve of a tyre. The volume may be vented through the valve attachment arrangement. The sensor may be configured to be secured within a tyre. The open part of the volume may be sized and/or shaped to help to prevent bubbles formed in the elastomeric gel causing a substantive force to be applied to the operative part of the sensor element.

Embodiments of the present invention are described herein, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a cross-sectional view of a TPMS sensor;

Figure 2 shows a cross-sectional view of a TPMS sensor;

Figure 3 shows a cross-sectional view of a TPMS sensor;

Figure 4 shows a cross-sectional view of a TPMS sensor;

Figure 5 shows a schematic and simplified view of a TPMS; and

Figure 6 shows a vehicle.

With reference to figures 1 , 5 and 6, an embodiment of the present invention comprises a tyre-pressure monitoring system sensor 10 for use with a tyre- pressure monitoring system (TPMS) 100 for a vehicle 300. The sensor 10 comprises a main body 8. The main body 8 forms an enclosure for other parts of the sensor 10. The main body 8 may be formed from plastic or metal, for example.

The main body 8 at least partially defines a chamber 3. In embodiments, the main body 8 also defines an access aperture 31 of the chamber 3. The access aperture 31 may comprise an open side of the chamber 3 defined by the main body 8 - the chamber 3 forming a receptacle.

In embodiments, the sensor 10 includes a lid 32 which at least partially covers the access aperture 31 . The lid 32 defines one or more vents 12 (which may each comprise a hole through the entire depth of the lid 32). The or each vent 12 provides fluid communication between the chamber 3 and the atmosphere around at least part of the sensor 10. The lid 32 may be adhered or welded to the main body 8. A solvent weld may be used to couple the lid 32 to the main body 8.

The lid 32 may fit within a peripheral recess defined by the main body 8 substantially adjacent the access aperture 31 such that the lid 32 (when fitted) sits flush with a surface of the main body 8.

The lid 32 may also define an antenna aperture 33 configured to receive at least part of an antenna 9 therethrough. The antenna aperture 33 may be configured to receive the antenna 9 in a substantially tight fit such that the passage of fluid through the antenna aperture 33 is inhibited by the received antenna 9. In embodiments, the lid 32 provides mechanical support to an antenna 9 which passes through the antenna aperture 33. This mechanical support helps to stop forces which have a component which is perpendicular to a longitudinal axis of the antenna 9 from damaging the connection between the antenna 9 and other parts of the sensor 10 (and sensor circuit). In embodiments, a dimension (e.g. a width or diameter) of a part of the antenna 9 which is located within the chamber 3 is larger than the corresponding dimension of the antenna aperture 33. Thus, when the lid 32 is fitted, the part or the antenna 9 abuts against the lid 32 to inhibit axial movement of the antenna through the antenna aperture 33 - which may otherwise damage a coupling between the antenna 9 and other parts of the sensor 10 (and sensor circuit). The part may be configured to be adjacent the lid 32 or to abut the lid 32 when the lid 32 is in place on the main body 8.

Within the chamber 3 is a sensor element 7. The sensor element 7 is configured output an electrical signal dependent on a sensed fluid pressure - which may be a sensed gas pressure.

The sensor element 7 may be mounted to a circuit board 4 - such as a printed circuit board (PCB). One or more other components 5 are also mounted to the circuit board 4. Just one other component 5 is depicted in the figures showing embodiments of the invention, however, this is for illustrative purposes only and it will be appreciated that a plurality of other components 5 of various shapes and sizes may be provided. The or each other component 5 may include components such as resistors, capacitors, diodes, integrated circuits, transistors, and the like.

A power source 6 is provided. The power source 6 may comprise one or more batteries 6 which are located within the chamber 3. The or each battery 6 (or other power source 6) may be in electrical communication with the circuit board 4 and/or the one or more other components 5 and/or sensor element 7 and/or the antenna 9. In the depicted embodiment of figure 1 , two batteries 6 are provided.

The sensor element 7 and/or the or each battery 6 and/or the one or more other components 5 and/or the antenna 9, form a sensor circuit which is configured to sense a fluid pressure and transmit a signal representative of the fluid pressure to other parts of the TPMS. It will be appreciated that the sensor circuit may comprise a wide variety of different components and that these may be coupled together to form a circuit by a means other than a circuit board 4. The chamber 3 is at least partially filled with an epoxy resin body 1 . The epoxy resin body 1 secures parts of the sensor circuit within the chamber 3. In embodiments, the epoxy resin body 1 fills a deepest region of the chamber 3 with respect to the access aperture 31 . In embodiments, the epoxy resin body 1 is coupled to at least part of the circuit board 4 (if provided), this part of the circuit board 4 may be a first side of the circuit board 4.

The epoxy resin body 1 may substantially surround one or more of the parts of the sensor circuit. For example, the epoxy resin body 1 may substantially surround one or more components of the sensor circuit which are mounted on the first side of the circuit board 4. The epoxy resin body 1 does not entirely surround the sensor element 7, however. In particular, the epoxy resin body 1 does not entirely cover an operative part of the sensor element 7 - the operative part of the sensor element 7 being the part which is used to detect fluid pressure. In embodiments, the epoxy resin body 1 does not cover any of the sensor element 7 (as depicted in figure 1 ). In other embodiments, the epoxy resin body 1 covers part (e.g. the sides) of the sensor element 7. In embodiments, the epoxy resin body 1 does not cover any part of a second side of the circuit board 4 or the components 5 mounted thereon (the second side of the circuit board 4 generally opposing the first side across a depth of the circuit board 4).

The epoxy resin body 1 may cover at least part of the or each battery 6 (or other power source 6).

In embodiments, the epoxy resin body 1 extends substantially across an entire cross-section of the chamber 3 in a plane which is substantially parallel to a plane of the circuit board 4 (for provided) and/or a base/end surface of the chamber 3. A gel layer 2 is provided and may cover at least part of the second side of the circuit board 4 (i.e. the side which is remote from the epoxy resin body 1 in the embodiment depicted in figure 1 ). The gel layer 2 covers at least part of the sensor element 7. In embodiments, the gel layer 2 covers the operative part of the sensor element 7.

The gel layer 2 may cover substantially all of the second side of the circuit board 4. The gel layer 2 may cover one or more other components 5 at least partially - other one or more other components 5 being mounted to the second side of the circuit board 4. In embodiments, one or more other components 5 extend through the gel layer 2 into an open portion of the chamber 3. The open portion of the chamber 3 is defined between the gel layer 2 and the lid 32. In embodiments, the gel layer 2 covers at least part of the or each battery 6 (or other power source 6). In embodiments, all of the components 5 are covered by the gel layer 2.

In embodiments, the antenna 9 extends through the gel layer 2 and may pass through the open portion of the chamber 3 and through the antenna aperture 33 in the lid 32. As will be appreciated, in this embodiment, the antenna 9 extends from the second side of the circuit board 4 (if provided).

In embodiments, the gel layer 2 is a layer which extends substantially across an entire cross-section of the chamber 3 in a plane which is substantially parallel to a plane of the circuit board 4 (if provided). The gel layer 2 may delineate a protected portion of the chamber 3 from the open portion of the chamber 3.

The open portion of the chamber 3 is in fluid communication with the fluid around the sensor 10 - via the or each vent 12. Thus, the operative part of the sensor element 7 is exposed to this fluid only through the gel layer 2. The gel layer 2 is sufficiently flexible to transmit variations in fluid pressure within the open portion of the chamber 3 to the operative part of the sensor element 7.

In embodiments, the gel layer 2 protects the sensor element 7 from direct exposure to potentially damaging fluids which may be present in the tyre - and which may have entered the open portion of the chamber 3 through the or each vent 12. The gel layer 2 may also act to limit or prevent exposure of at least one of the one or more other components 5 and/or the or each battery 6 (or other power source 6) and/or the circuit board 4 and/or at least part of the antenna 9 (e.g. a base of the antenna 9) to potentially damaging fluids.

In embodiments in which the gel layer 2 covers at least part of the or each battery 6 (or other power source 6), gases which may produced by the or each battery 6 (or other power source 6) during its operation are expelled into the gel layer 2. Bubbles of the gases within the gel layer 2 will, over time, move through the gel layer 2 to the open portion of the chamber 3 where they are then released from the chamber 3 through the or each vent 12. Small amounts of gas liberated slowly may diffuse through the gel layer 2 without forming bubbles. If bubbles do form, they may not burst except following a severe decompression, but shrink and disappear as the gas diffuses out of the gel layer 2. In embodiments, the or each battery 6 (or other power source 6) is located remotely from the sensor element 7. In embodiments, the or each battery 6 is positioned such that the or each sensor element 7 is not between the or each battery 6 (or other power source 6) and the adjacent surface of the gel layer 2.

In the event of a rapid decrease in fluid pressure around the sensor 10, then bubbles of gas may form in the gel layer 2 - the gas having been, for example, previously absorbed by components or otherwise present in the gel. However, these bubbles of gas are, over time, released to the open portion of the chamber 3. The provision of the open portion of the chamber 3 helps to prevent the bubbles being trapped and causing inaccurate measurements by the sensor element 7. The bubbles, therefore, do not cause a substantive force to be applied to the operative part of the sensor element 7 because the open portion of the chamber 3 allows for expansion of the gel layer 2 as a result of the gas bubbles.

The gel layer 2 is sufficiently flexible to seal, substantially, the circuit board 4 (if provided), and/or one or more other components 5 and/or the or each battery 6 (or other power source 6) from the open portion of the chamber 3 (and any potentially damaging fluids therein) even in the event of cracking occurring in junctures between the epoxy resin body 1 and other parts of the sensor 10. Such cracking may, for example, occur between the epoxy resin body 1 and the main body 8. The antenna 9 may be a helically wound conductor which is encased in a flexible body of cylindrical form. The flexible body protects the conductor of the antenna 9 but allows the antenna 9 to flex in the event of, for example, impact with another object. The flexible body may be sufficiently rigid to support, at least partially, the antenna 9. The flexible body may be resiliently biased such that the antenna 9 extends away from the main body 8 of the sensor 10 substantially perpendicular to a longitudinal axis thereof.

In operation, the sensor element 7 senses a fluid pressure within the tyre. A signal representative of the fluid pressure (and maybe also an identifier of the sensor 10) is sent via the antenna 9 to other parts of the TPMS. The or each other component 5 of the sensor 10 may be configured to process a signal from the sensor element 7 for transmission via the antenna 9, or otherwise prepare the signal for transmission. The antenna 9 is sized and shaped for radio-frequency transmission of a signal. It will be appreciated that other forms of transmission may be used and that these may or may not require the use of an antenna 9. The sensor 10 depicted in figure 1 and the variations thereof discussed above are configured to be fitted inside the tyre 200 of a vehicle 300. In these and other embodiments, the sensor 10 is configured to be fitted within the tyre 200 on a side wall of the tyre 200. In embodiments, the sensor 10 is secured within the tyre 200 by the use of a bracket. The bracket may include a flexible adhesive pad for adhesion to an internal surface of the tyre 200. The bracket includes an arrangement to secure the sensor 10 thereto. This arrangement may comprise one or more spigots which are each configured to be received by respective one or more recesses in the main body 8 of the sensor 10. In embodiments, two spigots are provided and the main body 8 has a corresponding two recesses. The recesses are located at opposing ends of the main body 8 - which may be elongate. The sensor 10 may be configured to be fitted inside the tyre 200 such that the or each vent 12 faces towards a main internal inflation volume of the tyre 200.

Embodiments of the present invention include a tyre-pressure monitoring system sensor 10 which is configured for external fitting.

With reference to figure 2, an embodiment comprises a sensor 10 for external fitting. In other words, in this embodiment (and others) the sensor 10 is configured to be fitted to the valve of a tyre 200 - not within the inflated volume of the tyre 200. The valve to which the sensor 10 of this and other embodiments is configured to be fitted may be the valve of the tyre 200 through which inflation fluid is delivered to inflate the tyre 200. In some embodiments, the sensor 10 is configured to be fitted to a port of a tyre 200 which does not include a valve. The port may be a dedicated port for a TPMS sensor. In some embodiments a fitting, such as a T-shaped fitting, is provided so that the sensor 10 can be connected via the valve used to inflate the tyre 200 and inflation fluid can be supplied to the tyre (via the fitting) without requiring removal of the sensor 10.

The sensor 10 in these (and other) embodiments includes a main body 8 which is, in this example, substantially formed of an epoxy resin body 1 . The main body 8 is formed around at least part of the sensor circuit of this embodiment (which may be the same as the sensor circuit described above) and may be formed around at least part of the circuit board 4 (if provided), and/or the antenna 9, and/or one or more batteries 6 (or other power source 6), and/or one or more of the other components 5. A first side of the circuit board 4 (if provided) may be substantially entirely covered by the epoxy resin body 1 . In embodiments, at least part (e.g. a peripheral region) of a second side of the circuit board 4 (which opposes the first side across a depth of the circuit board 4) is covered by the epoxy resin body 1 .

The main body 8 defines a chamber 3 towards the second side of the circuit board 4 (if provided).

In embodiments, the chamber 3 is defined towards a first end of the sensor 10.

The sensor 10 includes a sensor element 7 (as discussed in relation to other embodiments) which is located with respect to the chamber 3 such that an operative part of the sensor element 7 is open to the chamber 3. In embodiments, the sensor element 7 is mounted on the second side of the circuit board 4 (if provided). The epoxy resin body 1 may cover at least part of the sensor element 7 - for example, one or more sides of the sensor element 7. In embodiments, however, none of the sensor element 7 is covered by the epoxy resin body 1 . The sensor element 7 is in electrical communication one or more other components 5 and/or the circuit board 4 and/or the antenna 9, and/or the or each battery 6 (or other power source 6). An antenna 9 may extend from the first side of the circuit board 4 (if provided) - or otherwise away from the first end of the sensor 10.

The or each battery 6 (or other power source 6) may be located with respect to the circuit board 4 (if provided) towards the first side thereof. The or each battery 6 (or other power source 6) may be adjacent the antenna 9.

A gel layer 2 is provided within the chamber 3 such that the operative part of the sensor element 7 is substantially covered by the gel layer 2. The gel layer 2 may cover at least part of the one or more other components 5. One or more other components 5 may extend through the gel layer 2 and into an open part of the chamber 3.

The open part of the chamber 3 is defined between the gel layer 2 and a lid 32 which is located at the first end of the sensor 10.

The lid 32 at least partially closes an open end of the chamber 3. The lid 32 may define, or is secured to, a valve attachment arrangement 121 which is configured for attachment to the valve of the tyre 200 of a vehicle 300 - to provide for fluid communication between an inflation fluid volume of the tyre 200 and the open part of the chamber 3 of the sensor 10.

The lid 32 may be formed from plastic or metal. The valve attachment arrangement 121 may include a threaded portion configured to engage a corresponding thread of a valve of a tyre 200. As will be noted, the sensor 10 of the embodiment depicted in figure 2 and the variants described herein include an open portion of the chamber 3 as discussed above in relation to figure 1 . The same advantages may, therefore, be realised.

The sensor 10 described herein with reference to figure 2 may be an internal sensor too. In such embodiments, the lid 32 defines a vent 121 instead of a valve attachment arrangement 121 . The vent 121 permits fluid communication between an inflation fluid volume of the tyre and the open part of the chamber 3. An arrangement may be provided to secure the sensor 10 inside the tyre 200 - for example, to an internal wall of the tyre 200.

Another embodiment of a TPMS sensor 10 for external fitting is depicted in figure 3.

In this and similar embodiments, the sensor 10 comprises main body 8 which includes a carrier 8a and an operative module 8b. The carrier 8a defines a cavity which is suitable to receive the operative module 8b. The carrier 8a also defines a valve aperture 1 1 1 which is configured to receive at least part of a valve of a tyre 200 of a vehicle 300.

A valve attachment member 1 1 may be secured to the valve aperture 1 1 1 . The valve attachment member 1 1 may include a threaded attachment arrangement which is configured to be secured to a correspondingly threaded valve of a tyre 200. The valve attachment member 1 1 may include an O-ring 1 12 (or other sealing arrangement) to help to provide a substantially fluid tight seal between the carrier 1 1 a and the rest of the valve attachment member 1 1 .

The carrier 8a and operative module 8b may both have a substantially circular cross-section. The cavity defined by the carrier 8a is generally cylindrical in shape. An internal surface of the carrier 8a includes an inwardly facing threaded surface 81 which is configured to mate with a correspondingly threaded outer surface of the operative module 8b - the operative module 8b having a generally cylindrical outer shape at least in the region of the threaded outer surface. The correspondingly threaded surfaces of the carrier 8a and operative module 8b may be provided towards an end of the sensor 10 at which the valve attachment member 1 1 is located. An O-ring 10 (or other sealing arrangement) may be provided within the cavity defined by the carrier 8a and located such that it substantially seals a juncture between the carrier 8a and the operative module 8b. The O-ring 10 (or other sealing arrangement) may be located adjacent the threaded surfaces of the carrier 8a and the operative module 8b.

Thus, the operative module 8b may be coupled to the carrier 8a, by inserting the operative module 8b into the cavity defined by the carrier 8a until the respective threads thereof contact each other. The operative module 8b is then rotated with respect to the carrier 8a to complete the coupling of the operative module 8b and the carrier 8a. In embodiments, the operative module 8b and carrier 8a are rotated with respect to each other until the O-ring 10 is compressed between the operative module 8b and the carrier 8a to provide a seal between the operative module 8b and the carrier 8a. The carrier 8a may substantially surround an outer circumferential wall of the operative module 8b when they are coupled together. This helps to prevent the inadvertent decoupling of the operative module 8b from the carrier 8a when the sensor 10 is being fitted to a valve of a tyre 200. The operative module 8b defines a chamber 3 which contains an epoxy resin body 1 which may be provided in an enclosure 82. The epoxy resin body 1 contains and/or substantially surrounds one or more batteries 6 (or other power source 6) which are in electrical communication with a circuit board 4 and/or one or more other components 5 and/or a sensing element 7 - which form a sensor circuit as generally discussed above (also as discussed above, the circuit board 4 need not be provided in some embodiments).

At least part of the circuit board 4 (if provided) and/or one or more other components 5 is substantially covered by the epoxy resin body 1 . The epoxy resin body 1 is located between the valve attachment member 1 1 and the circuit board 4 in the constructed sensor 10. In embodiments, the epoxy resin body 1 covers at least part, or substantially the entire of, a first side of the circuit board 4. The sensor element 7 is positioned in this embodiment on the second side of the circuit board 4 (if provided) such that an operative part of the sensor element 7 faces away from the circuit board 4 and the epoxy resin body 1 and the valve attachment member 1 1 .

A gel layer 2 is provided which covers at least the operative part of the sensor element 7. In embodiments, the gel layer 2 covers at least part of the circuit board 4 (if provided) which may include at least part of, or substantially the entire of, the second side of the circuit board 4. One or more other components 5 may be at least partially covered by the gel layer 2. A part of one or more of the other components 5 may extend through the gel layer 2.

The antenna 9 may be formed, in this embodiment, by a helically wound conductor which extends along a length of the operative module 8b. In embodiments, the antenna 9 extends from the circuit board 4. The antenna 9 extends away from the valve attachment member 1 1 (and the second side of the circuit board 4 (if provided)). In embodiments, the antenna 9 extends around an internal circumference of the operative module 8b. The antenna 9 may be encased - partially or entirely - in epoxy resin 1 a which may or may not be integrally formed with the epoxy resin body 1 . In embodiments, the antenna 9 is self-supporting and does not require encasement in epoxy resin 1 a. In embodiments, the antenna 9 is supported by one or more support members such as annular rings provided within the operative module 8b.

In this embodiment, an open part of the chamber 3 is defined by the gel layer 2, an end wall of the operative module 8b, and the antenna 9 (and any material which encases the antenna 9 or otherwise supports the antenna 9).

The open part of the chamber 3 is in fluid communication with the valve attachment arrangement 1 1 . This fluid communication may be provided around the epoxy resin body 1 or through tubes defined by the epoxy resin body 1 .

In embodiments, one or more abutment members (not shown), such as ribs, may be provided to ensure the correct positioning of the operative module 8b within the carrier 8a.

In embodiments, the enclosure 82 may include one or more longitudinal channels to ensure fluid communication between the open part of the chamber 3 and the valve attachment arrangement 1 1 . In embodiments which do not include the enclosure 82, then the one or more longitudinal channels may be provided in the epoxy resin body 1 and the epoxy resin 1 a which encases the antenna 9 (again, if provided). A distal end of the epoxy resin 1 a (remote from the epoxy resin body 1 ) may include one or more further channels (generally radial) to ensure this fluid communication. The one or more further channels may be provided in the enclosure 82 if provided. In embodiments, a damping member is sandwiched between the distal end of the epoxy resin 1 a (and enclosure 82 if provided) and an end wall of the operative module 8b - to reduce any rattling.

As will be appreciated, an open part of the chamber 3 is also provided in accordance with this embodiment (and its variants).

Another embodiment of a TPMS sensor 10 for external fitting is depicted in figure 4. In this embodiment, a carrier 8a comprises an enclosure which may be formed of plastic or metal, for example. The carrier 8a houses an operative module 8b which may be formed from a rigid material. The operative module 8b may also be formed from metal or plastic, for example. The operative module 8b forms a receptacle which houses an antenna 9 towards a closed end thereof. In embodiments, a circuit board 4 is housed towards an open end of the chamber 3.

The antenna 9 is embedded in an epoxy resin body 1 which may substantially fill a depth of the operative module 8b in which the antenna 9 is located.

The antenna 9 is in electrical communication with a circuit board 4, and/or one or more batteries 6 (or other power source 6), and/or a sensor element 7 - generally forming a sensor circuit as discussed above. As discussed in relation to other embodiments, the circuit board 4 need not be provided.

The or each battery 6 (or other power source 6) may also be embedded in the epoxy resin body 1 . The battery 6 (or other power source 6) may be located beside the sensor element 7 and may be covered by or protrude through the gel layer 2. The circuit board 4 (if provided) is at least partially covered by the epoxy resin body 1 . One or more other components 5 may also be at least partially covered by the epoxy resin body 1 - for example, components 5 mounted on a first side of the circuit board 4.

The sensor element 7 may be mounted such that it extends from a second side of the circuit board 4 (a side which opposes the epoxy resin body 1 ). As discussed above in relation to other embodiments, the sensor element 7 may or may not be partially covered by the epoxy resin body 1 . The operative part of the sensor element 7 is not covered by the epoxy resin body 1 .

A gel layer 2 is provided which at least partially covers the sensor element 7. The gel layer 2 covers an operative part of the sensor element 7 - see the above discussion concerning other embodiments. The gel layer 2 may cover one or more other components 5. In embodiments, one or more components 5 extend through the gel layer 2.

In the depicted embodiment, the sensor element 7 is located towards the open end of the operative module 8b. In embodiments, the sensor element 7 faces the open end of the operative module 8b.

A lid 32 is secured to the open end of the operative module 8b so as to at least partially close the open end. The lid 32 may be welded (e.g. using a solvent weld or friction spin welding) to the operative module 8b. The lid 32 defines a valve aperture 1 1 1 . A valve attachment arrangement 1 1 is fitted to the valve aperture 1 1 1 in the same manner as discussed above in relation to figure 3, for example.

An open part of the chamber 3 is defined between the gel layer 2 and the lid 32. The operative module 8b may be secured within the carrier 8a by an adhesive - for example. In other embodiments, the operative module 8b is secured within the carrier 8a by an interference fit or correspondingly threaded parts or abutment of the operative module 8b between the lid 32 and an opposing end wall of the carrier 8a.

The provision of an operative module 8b in the embodiment depicted in figure 4 and its variants reduces the need for a juncture between the carrier 8a and the epoxy resin body 1 (a juncture which is prone to cracking due to changes in the relative sizes of the carrier 8a and the epoxy resin body 1 ).

As will be appreciated, aspects of the embodiments depicted and described in relation to the embodiments disclosed herein are interchangeable. Particularly, in the case of the external sensors 10 depicted in figures 2-4, various aspects have been described which are interchangeable between the depicted and described embodiments.

It has been found that the depth of the gel layer 2 over the sensor element 7 may ideally be around 1 mm or around 2mm and may be around 2.35mm. The depth of the gel layer 2 over the sensor element 7 may, in embodiments, be between around 1 mm and around 4.5mm, or around 2mm to 3mm. The depth of the gel over the circuit board 4 may be around 1 mm to 2mm or about 1 .6mm. In embodiments, a grid (not shown) is embedded in the gel layer 2. The grid may provide support for at least part of the gel which forms the gel layer 2. The grid may define pockets which may be filled with gel of the gel layer 2. The grid may be contained entirely, or substantially entirely, within the gel layer 2 or may only be partially embedded in the gel layer 2 (and may extend from a surface of the gel layer 2). The grid may be placed before the gel layer 2 is formed. The walls of the grid may act as baffles. The grid may be pre- primed to help adhesion of the gel thereto. The use of the grid may negate the need to prime other parts of the sensor 10.

The gel layer 2 may be formed from silicone elastomeric gel which may be Qgel310 (available from ACC Silicones Ltd of Bridgwater, UK). The gel layer 2 may have a viscosity of about 1000 mPa.s before it is cured (as measured using a Brookfield viscometer at 23 °C ± 2 °C and at a relative humidity of 65%). The cured gel layer 2 may have a cone penetration of about 7mm for a 19.5g cone (the cone having an approximate 6.5 mm foot).

As will be appreciated other forms of gel layer 2 may be used in accordance with embodiments of the invention.

In embodiments, the open part of the chamber 3 has a depth (for example, between the gel layer 2 and the lid 32 or an opposing wall) of around 3mm or around 4mm. The depth of the open part of the chamber 3 may be between around 3mm and around 4mm. The depth may be about 3.7mm.

In embodiments, the volume of gel in the gel layer 2 may be substantially equal to the volume of the open part of the chamber 3. In embodiments, the volume of the open part of the chamber 3 is greater than the volume of gel in the gel layer 2. In embodiments, the depth of the gel layer 2 is substantially equal to the depth of the open part of the chamber 3. In embodiments, the depth of the open part of the chamber 3 is greater than the depth of the gel layer 2.

The open part of the chamber 3 may be provided adjacent to substantially all of the components of the sensor circuit. The open part of the chamber 3 may be provided across substantially an entire side of the circuit board 4 (if provided. The open part of the chamber 3 may be provided adjacent the sensor element 7 and at least one other component 5 of the sensor circuit. The open part of the chamber 3 may be defined between a surface of the gel layer 2 and a vent 12. The open part of the chamber 3 may be defined between a surface of the gel layer 2 and an end surface of the main body 8. The open part of the chamber 3 may be defined between the gel layer 2 and a lid 32.

In embodiments, the open part of the chamber 3 is in fluid communication with the environment around the sensor 10 (for example the inflation volume of a tyre 200). In embodiments, the open part of the chamber 3 is in substantially free (unrestricted) fluid communication with the environment around the sensor 10 through one or more vents. As will be appreciated, the open part of the chamber 3 allows the gel layer 2 to expand (for example, as the result of bubbles forming and/or expanding therein) without the expected expansion applying a substantive force on the operative part of the sensor element 7 - which would cause inaccurate measurements by the sensor element 7. In other words, the open part of the chamber 3 allows for a degree of substantially free or uninhibited expansion of the gel layer 2.

In embodiments the sensor element 7 is a micromachined piezoresistive silicone type sensor. Other pressure sensors may be used instead for the sensor element 7.

The epoxy resin body 1 of embodiments may have a pre-cured viscosity of between 0.1 and 0.3 Pa.s measured by a Brookfield viscometer DB-E at 22 °C ± 1 °C. Once cured the epoxy resin body 1 may have a Shore Hardness (BS2782 method 365B) >70. The epoxy resin may be ER1448 (available from Electrolube a division of HK Wentworth Ltd of Leicestershire, UK).

According to embodiments, the epoxy resin body 1 may cover, at least partially, all components of the sensor circuit. The operative part of the sensor element 7 should, however, be free from the epoxy resin body 1 to allow for unimpeded operation. In embodiments, at least part of the or each battery 6 (or other power source 6) is not covered in the epoxy resin body 1 such that gases expelled by the or each battery 6 can escape. The part of the or each battery 6 which is not surrounded by the epoxy resin body 1 may be covered by the gel layer 2.

In manufacturing a sensor 10 in accordance with embodiments of the invention the operative part of the sensor element 7 may be directly exposed to the gel layer 2 so that the pressure on the surface of the gel is accurately transmitted to the surface of the operative part of the sensor element 7.

In some instances, the sensor element 7 is mounted to the circuit board in a standard SO8 surface mount integrated circuit package that has a vent in the top thereof. In such instances, at least part (and maybe the whole) of the top of the integrated circuit package is removed to allow direct contact of the operative part of the sensor element 7 and the gel layer 2.

In embodiments, the sensor element 7 and a substantial part of a package in which the sensor element 7 is housed are covered by the gel layer 2. In embodiments, one or more electrical conductors which extend from a package in which the sensor element 7 is housed (and form a part of that package) are substantially covered by the gel layer 2. The or each electrical conductor may be configured for connection (e.g. by soldering) to another conductor which may be part of a circuit board. The one or more conductors which extend from the package may be all of the conductors which extend from the package. In embodiments, a package in which the sensor element 7 is housed has an external surface which is substantially covered by the gel layer 2. In embodiments, the external surface is a surface which faces away from the sensor element 7. In embodiments, the package includes one or more internal surfaces which are substantially covered by the gel layer 2. In embodiments, the or each internal surface substantially faces the sensor element 7. In other embodiments a die of the sensor element 7 is wire bonded directly to circuit board 4 before the gel layer 2 is applied. In relation to the construction of sensors 10 in accordance with embodiments, the epoxy resin body 1 may be poured into a mould. The mould may be the main body 8 or a part thereof (such as the operative module 8b) depending on the embodiment. In embodiments, the mould does not form part of the completed sensor 10 but in embodiments the mould becomes part of the sensor 10.

Parts of the sensor circuit - such as the circuit board 4 - may then be positioned on or in the uncured epoxy resin body 1 . In embodiments, the air pressure around the epoxy resin body 1 is then reduced (in other words the body 1 is exposed to an increasing vacuum. This may be done is stages or steps to prevent excessive foaming of the body 1 . In embodiments, the pressure is dropped to around 3000 Pa. Any cavities formed in the body 1 may be refilled with epoxy resin on returning the body 1 to atmospheric pressure.

This pressure reduction helps to remove air from bubbles and cavities within the body 1 . The epoxy resin body 1 may be cured by leaving the body for at least 24 hours at room temperature and then at a temperature of about 60°C for at least 4 hours before the gel layer 2 is formed.

In embodiments, it is important to make sure that the epoxy resin body 1 is sufficiently cured before the gel layer 2 is formed so that the epoxy resin body 1 does not interfere with the curing of the gel layer 2. Surfaces of the sensor circuit components which are to be covered by the gel layer 2 may be primed and allowed to dry, for example, for one hour. The gel to form the gel layer 2 is then poured into place to form the gel layer 2. The gel layer 2 may be subjected to a reduced air pressure prior to curing (i.e. is exposed to an increasing vacuum) in much the same manner as the epoxy resin body 1 as described above - e.g. in steps or stages. This process may negate, in some embodiments, the need for at least part of the top of the integrated circuit package of the sensor element 7 to be removed.

In embodiments, the senor circuit includes a temperature sensor (a thermistor) which may be one of the one or more other components 5 discussed above. The temperature sensor may be located adjacent the sensor element 7. The temperature sensor may, therefore, be at least partially covered by the gel layer 2. In embodiments, the temperature sensor is covered by the gel layer 2.

The temperature sensor is configured to output a signal representative of a sensed temperature. This signal may be transmitted to other parts of the TPMS via the antenna 9 - for example.

The sensor 10 according to embodiments may be configured to operate in fluid pressures up to about 1400kPa or 2000kPa. In embodiments in which one or more other components 5 extend through the gel layer 2 into the open part of the chamber 3, the or each other component 5 may be resistant to the potentially damaging fluids which may be present in the tyre 200. The gel layer 2 is an example of an elastomeric gel which may be used in accordance with embodiments of the invention. As will be understood, the gel provides protection against potentially damaging fluids which include, for example, water. The gel may, therefore, be impermeable or substantially impermeable. The gel is sufficiently flexible to allow for movement of the various parts of the sensor 10 without failure of the gel. The gel is sufficiently viscous when cured that the gel does not substantially drift when subjected to the normal forces associated with the use of the gel in a TPMS sensor. The gel may also be substantially non-conductive to electricity. The gel of the gel layer 2 may have elastic cross-links which, once the gel is cured, provide the gel layer 2 with a "memory" of its cured position.

As will be understood, embodiments including a sensor 10 configured for external fitting to a tyre, the chamber 3 of the sensor 10 is vented through the valve attachment arrangement 1 1 . The term "vented" as used herein is intended to indicate that the chamber 3 (which is vented) is not entirely isolated from the environment surrounding the sensor 10.

The epoxy resin body 1 is an example of an attachment arrangement for attaching at least part of the sensor circuit to the main body 8. In embodiments, other thermosetting polymers may be used instead of the epoxy resin body 1 . The attachment arrangement is substantially non-conductive to electricity.

One or more batteries 6 have been provided as an example of a power source 6. Other possible power sources 6 may scavenge power from the environment including from electromagnetic radiation and/or movement of the power source 6.

As will be understood, embodiments of the present invention include a sensor 10 for a TPMS. Embodiments of the present invention also include a TPMS incorporating such a sensor. The TPMS may include a control unit 101 , and/or one or more display units 102, and/or one or more alarm or monitoring units 103 (see figure 5, for example).

Embodiments of the present invention also include a tyre 200 including a sensor 10. Embodiments of the present invention may further include a vehicle 300 including a tyre 200 according to embodiments of the invention.

Although embodiments of the present invention have been described with reference to a tyre-pressure monitoring system and sensor 10, embodiments of the present invention may be directed to pressure sensor for other uses - for example, a diving depth gauge. Moreover, in other embodiments, the sensor element 7 is configured to sense some other parameter and not fluid pressure - for example, temperature. The sensor 10 may, however, be a sensor for use in a pressure monitoring system and may be a pressure sensor 10. The pressure monitoring system may be a tyre-pressure monitoring system.

It will be appreciated that, in some embodiments, a lid need not be provided and that the chamber 3 may not be enclosed or substantially enclosed. For example, in the embodiment depicted in figure 1 the lid 32 may be omitted. Thus, as will be appreciated the main body 8 may at least partially define a volume which may be a chamber 3 (which may or may not be enclosed or substantially enclosed). As will be appreciated, the embodiments depicted in figures 1 -4, and the described variants thereof, may have respective chambers 3 which are not enclosed or substantially enclosed and that, therefore, include a volume at least partially defined by the main body 8 but not necessarily a chamber 3.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.