GB2542136A

GB2542136A - Wheel loosening sensor

Info

Publication number: GB2542136A
Application number: GB1515898.3A
Authority: GB
Inventors: Broadfield Gary
Original assignee: Wheely Safe Ltd
Current assignee: Wheely Safe Ltd
Priority date: 2015-09-08
Filing date: 2015-09-08
Publication date: 2017-03-15
Also published as: GB201515898D0

Abstract

A wheel loosening sensor 100 for fitting in a recess 204 on an internal surface of a wheel 200 and for detecting movement of the wheel away from a wheel hub 202, the wheel loosening sensor comprising: a transmitter configured to transmit a signal when movement of the wheel away from the wheel hub is detected; and an antenna 130 in electrical communication with the transmitter and configured such that at least part of the antenna is deeper within the recess than the transmitter when the wheel loosening sensor is fitted within the wheel. The wheel loosening sensor may comprise a protrusion (312, Fig.3) in which at least part of the antenna is located. The protrusion may have a smaller cross sectional area than the main body (302). The sensor may comprise a removable cap (401, Fig.4) covering the protrusion which may have one or more ridges configured to create an interference fit with the recess to retain the sensor in position. Also claimed is a wheel comprising a recess on an internal surface; a wheel loosening sensor assembly or kit of parts comprising a sensor and a spacer (530,Fig.5); and a vehicle comprising a wheel having a recess.

Description

WHEEL LOOSENING SENSOR

Technical field

The invention relates to wheel loosening sensors configured to detect loosening and/or loss of a wheel of a vehicle. More specifically, the invention relates to, but is not limited to, wheel loosening sensors configured to detect relative movement between a wheel and an axle of a vehicle. For example, sensors may be held against an axle or wheel hub when the wheel is securely fixed to a vehicle, but may experience movement away from the axle or wheel hub if the wheel loosens.

Background

Sensors and systems for notifying when a wheel of a vehicle is not securely fitted to the vehicle improve safety. Such sensors and systems allow preventative action to be taken prior to a wheel being lost, which prevents accidents and damage to vehicles, pedestrians and street furniture.

One such system is disclosed in WO2011/121334 and comprises a battery, a transmitter and a detector, or switch, operated by a coil spring. Such systems may be fitted to standard vehicle wheels that may have a steel construction by fitting a bracket to one or more wheel nuts, the bracket holding the sensor against the wheel. However, this is not always possible on alloy wheels, as the outer surface of the wheel may be significantly contoured. In addition, the addition of a wheel loosening sensor to the outer surface of an alloy wheel would not be conducive with the overall appearance of the alloy wheel.

Summary

The inventors have appreciated that a wheel loosening sensor may be positioned against an inner surface of an alloy wheel. That is, a wheel loosening sensor may be positioned between an inner surface of a wheel and the wheel hub or axle. In exemplary configurations, a wheel loss sensor may be positioned in a recess in an inner surface of a wheel. In such arrangements, the inventors have appreciated that it may be challenging to achieve adequate propagation of signals transmitted from the sensor such that they may be received by a controller device of the a wheel loosening alarm system.

Exemplary methods and apparatus described herein aim to alleviate or obviate one or more errors associated with the prior art, including those discussed herein.

According to the invention in one aspect, there is provided a wheel loosening sensor for fitting in a recess on an internal surface of a wheel and for detecting movement of the wheel away from a wheel hub, the wheel loosening sensor comprising: a transmitter configured to transmit a signal when movement of the wheel away from the wheel hub is detected; and an antenna in electrical communication with the transmitter and configured such that at least part of the antenna is deeper within the recess than the transmitter when the wheel loosening sensor is fitted within the wheel.

Optionally, the wheel loosening sensor further comprises a housing comprising a main body, in which the transmitter is located, and a protrusion, in which at least part of the antenna is located.

Optionally, the protrusion has a cross sectional area less than a cross sectional area of the main body.

Optionally, the main body and the protrusion each has a substantially circular cross section, and wherein a cross sectional radius of the protrusion is less than a cross sectional radius of the main body.

Optionally, the wheel loosening sensor further comprises a cap covering at least part of the protrusion.

Optionally, the recess comprises an aperture extending to an external surface of the wheel, and wherein the cap is configured to extend to be at least level with the external surface of the wheel.

Optionally, the cap is removable.

Optionally, the cap is configured to provide an interference fit within the recess to retain the wheel loosening sensor within the recess.

Optionally, the cap comprises one or more ridges configured to provide the interference fit.

Optionally, the cap comprises a visual indicator identifying the type of wheel loosening sensor fitted within the wheel.

Optionally, the wheel loosening sensor further comprises a battery, wherein the antenna is configured such that it is deeper within the recess than the battery when the wheel loosening sensor is fitted within the wheel.

According to a further aspect of the invention, there is provided a wheel comprising a recess on an internal surface thereof, wherein the recess is configured to receive a wheel loosening sensor for detecting movement of the wheel away from a wheel hub.

Optionally, the wheel further comprises an aperture extending from a base of the recess to an external surface of the wheel.

Optionally, the aperture has a cross sectional area less than a cross sectional area of the recess.

Optionally, the recess comprises a first section from the internal surface of the wheel and a second section from the first section to the base of the recess, and wherein the first section is wider than the second section and configured to accommodate movement of a first part of the wheel loosening sensor relative to a second part of the wheel loosening sensor.

Optionally, the aperture further comprises a flange retaining section configured to retain a flange of a cap to be fitted to a protrusion of the wheel loosening sensor and configured to extend into the aperture.

Optionally, the wheel further comprises a wheel loosening sensor as described herein fitted within the recess.

According to the invention in a further aspect, there is provided a wheel loosening sensor assembly, comprising: a wheel loosening sensor for fitting in a recess on an internal surface of a wheel and for detecting movement of the wheel away from a wheel hub; and a spacer configured to retain the sensor in a position spatially displaced from the wheel hub.

Optionally, the spacer is configured to restrict heat transfer from the wheel hub to the sensor and/or to dissipate heat from the wheel hub.

Optionally, the spacer comprises a thermal insulator material.

Optionally, the spacer comprises one or more cooling fins comprising a thermal conductor material.

Optionally, the one or more cooling fins are positioned on an outer surface of the spacer.

According to a further aspect of the invention, there is provided a wheel as described herein, comprising a wheel loosening sensor assembly as described herein.

According to a further aspect of the invention, there is provided a kit of parts comprising: a wheel loosening sensor for fitting in a recess on an internal surface of a wheel and for detecting movement of the wheel away from a wheel hub; and a spacer configured to retain the sensor in a position spatially displaced from the wheel hub.

The transmitter may be within a water tight housing that is permanently sealed, and at least two electrical terminals are exposed at an exterior of the housing, the transmitter being configured to transmit a signal when the at least two electrical terminals are disconnected. An electrically conductive element may be biased away from the at least two electrical terminals and configured to electrically connect the two electrical terminals when the bias is overcome.

Optionally, the electrically conductive element comprises a disc spring configured to bias the electrically conductive element away from the at least two terminals.

Optionally, one or more spring elements of the disc spring are configured to contact the at least two electrical terminals when the bias is overcome.

Optionally, the electrically conductive element is mounted on a backing plate.

Optionally, the backing plate comprises one or more of; stainless steel; a polycarbonate; and an extruded metal material.

Optionally, the wheel loosening sensor further comprises a gasket secured to the housing surrounding the at least two electrical terminals, wherein the electrically conductive element is coupled to the gasket.

Optionally, the gasket comprises a resiliently deformable material configured to bias the electrically conductive element away from the at least two electrical terminals.

Optionally, the gasket forms a water tight seal with the exterior of the housing.

Optionally, the gasket forms a water tight seal with the backing plate.

Optionally, the gasket is secured to the housing and/or the backing plate by an adhesive.

Optionally, the sensor further comprises an extruded spring holder configured to extend along a sidewall of the sensor to cover the gasket.

Optionally, at least part of the housing comprises first and second parts ultrasonically welded together.

Optionally, at least part of the housing comprises a moulded plastics material, and wherein the at least two electrical terminals are moulded into the moulded plastics material.

Optionally, the sensor is configured to be coupled to a wheel, such that the bias is overcome when the wheel is securely fitted.

According to the invention in another aspect, there is provided a kit of parts comprising: a sensor according to any preceding claim; and one or more caps configured to be fitted to the sensor and to cover at least partly the protrusion.

Brief description of the drawings

Figure 1 is a section through a wheel loosening sensor;

Figure 2 is a section through a wheel loosening sensor fitted within a recess of a wheel;

Figure 3 is a section through a wheel loosening sensor fitted within a recess of a wheel;

Figure 4 is a section through a wheel loosening sensor fitted within a recess of a wheel; and

Figure 5 is a section through a wheel loosening sensor fitted within a recess of a wheel. Detailed description

Generally, disclosed herein are methods and apparatus for detecting loosening of a vehicle wheel and for transmitting a signal to a device of a wheel loosening alarm system. Exemplary methods and apparatus are configured to transmit such a signal in challenging radio frequency (RF) environments.

Figure 1 shows a section through an exemplary wheel loosening sensor 100. The sensor comprises a housing 102 that may be permanently sealed such that it is water tight. Electronics for operation of the sensor 102 are sealed within the housing 102.

First and second electrical terminals 104,106 are exposed at an exterior of the housing 102. That is, the first and second electrical terminals 104, 106 pass through the housing 102, such that they are electrically connected to the electronics therein and provide electrical contact points that may be accessed externally. In the exemplary sensor of Figure 1, the first and second electrical terminals 104, 106 are each electrically connected to a circuit within the housing 102 and are separated from each other so as to form an open circuit. The circuit within the housing is operable in a first state when the first and second electrical terminals 104, 106 are electrically connected, and operable in a second state when the first and second electrical terminals 104, 106 are electrically disconnected. Further, in the exemplary sensor of Figure 1, the first and second electrical terminals 104, 106 are statically sealed within the housing 102 and may be moulded into the housing 102 when, for example, the housing comprises a plastics material.

An electrically conductive element 108 is biased away from the first and second electrical terminals 104, 106. When the sensor 100 is in an open configuration, the electrically conductive element 108 is biased away from the first and second electrical terminals 104, 106 such that the electrically conductive element 108 is not in contact with at least one of the first and second electrical terminals 104, 106. When the sensor 100 is in a closed configuration, the bias acting on the electrically conductive element 108 is overcome and the electrically conductive element 108 electrically connects the first and second electrical terminals 104, 106. The electrically conductive element 108 may be a spring, such as a disc spring 114.

The electrically conductive element 108 is mounted on a backing plate 116. The backing plate 116 may comprise any material having a stiffness sufficient to hold the electrically conductive element 108 in the correct orientation with the first and second electrical terminals 104, 106. That is, the backing plate 116 is configured to present the electrically conductive element 108 to the first and second electrical terminals 104, 106 such that they are electrically connected when the biasing force acting on the electrically conductive element 108 is overcome. Exemplary backing plates 116 may comprise stainless steel and/or polycarbonate. The backing plate 116 may have a thickness in a range from 0.1 mm to 0.6 mm or in a range from 0.2 mm to 0.4 mm. Exemplary sensors take advantage of creating a very thin switch system in the knowledge that the backing plate will gain further strength from surfaces in the wheel loss application such as the very solid hub of a wheel. A gasket 118 is secured to the housing 102 such that it surrounds the first and second electrical terminals 104, 106. The gasket 118 may be a ring gasket. The gasket 118 may comprise a compressible material that may be resiliently deformable, such that it at least partly provides the force biasing the electrically conductive element 108 away from the first and second electrical terminals 104, 106. The gasket 118 may be adhered to the housing 102, for example, by a double sided adhesive tape. The backing pate 116 is secured to the gasket 118 and may be adhered to the gasket 118, for example, using a double sided adhesive tape. The gasket 118 may comprise a material that is impervious to water and is secured to the housing 102 and the backing plate 116, such that water may not ingress a void 120 comprising the electrically conductive element 108 and the first and second electrical terminals 104, 106.

As the gasket 118 is compressible and provides a water tight seal it allows for movement of the electrically conductive element 108 towards and away from the first and second electrical terminals 104, 106 without the need for dynamic seals between elements that move relative to each other.

The housing 102 may comprise front and rear portions 102a, 102b configured to be connected together to form a permanent and static seal 122. The seal 122 may, for example, be formed by ultrasonic welding. The rear portion 102b of the housing 102 may comprise a plastics material. The first and second electrical terminals 104, 106 may be moulded into the rear portion 102b of the housing 102, such that they are in contact with the electronics within the housing 102 and are exposed to an exterior of the housing 102. The rear portion 102b comprises a raised area 124 within the void 120 and on which the first and second electrical terminals 104, 106 are exposed.

The housing 102 and the electronics within it may be termed the transmission engine. The electronics comprise a printed circuit board 126, a battery 128 and an antenna spool 130. The printed circuit board 126 comprises a transmitter configured to transmit a signal from the antenna spool 130. When the first and second electrical terminals 104, 106 are electrically disconnected, the electronics are configured such that an alert signal is transmitted from the antenna spool 130. The alert signal may be received by a further unit that may be in the vehicle and configured to provide a warning to the driver of the vehicle.

It is noted that the arrangement described above is exemplary and the methods and apparatus disclosed herein may be used in conjunction with various sensor designs. Certain features of the wheel loosening sensor described above (and any other wheel loosening sensor) may be adapted to accommodate the features disclosed herein. For example, the antenna spool may be extended and/or moved, as set out below.

Figure 2 shows the exemplary wheel loosening sensor 100 of Figure 1 fitted to a vehicle between an inner surface of the wheel 200 and the wheel hub 202. A recess 204 is formed in the wheel 200 on an inner surface. As used herein, the term inner surface of the wheel is the surface that would typically abut the wheel hub 202. The recess 204 comprises a retaining surface 206 against which the wheel loosening sensor 100 may be retained in a closed position when the wheel 200 is secured to the vehicle. In the exemplary arrangement of Figure 2, the retaining surface 206 is the bottom surface of the recess 204, although other configurations are possible.

In the arrangement shown in Figure 2, the antenna coil 130 of the wheel loosening sensor 100 is required to transmit a signal to a further device of a wheel loosening alarm system, such as a controller (not shown). In order to facilitate this, the wheel comprises an aperture 208 extending from a base of the recess 204 to the outer surface 210 of the wheel 200. The aperture 208 removes a section of the wheel such that emitted signals may be propagated away from the sensor 100 towards the controller. The aperture 208 provides an air medium through which RF radiation can propagate. Without the aperture 208, the wheel loosening sensor 100 may be in situation similar to a Faraday’s cage and from which RF radiation may not propagate.

Referring to Figure 3, a wheel loosening sensor 300 may comprise a protrusion 312 configured to extend into an aperture 308. Exemplary wheel loosening sensors 100, 300 may be disc shaped. The disc may have a circular, rectangular or any other shaped top elevation. Specific exemplary wheel sensors 100, 300 have a circular disc shape. The protrusion 312 may extend from a top or bottom surface of the disc shaped wheel sensor 300. That is, the protrusion 312 may extend from a surface 314 of the wheel loosening sensor 300 that is in a plane transverse (and in exemplary wheel sensors 300, substantially perpendicular) to an axis 316. The axis 316 may be aligned with the direction of travel of a first part of the wheel loosening sensor 316 with respect to a main body 318 of the wheel sensor 300 during opening and closing of the wheel sensor 300. A housing 302 may comprise the protrusion 312 and the main body 318.

It is noted that relative terms such as top, bottom, left and right are used herein for descriptive purposes and need not limit the scope of the methods and apparatus disclosed.

The protrusion 312 comprises an antenna coil 330. In the exemplary wheel sensor 300, the antenna coil 330 has been moved from a location around the periphery of the disc shaped wheel sensor 300 into the protrusion 312. However, in other exemplary wheel sensors the antenna coil 330 may be extended such that it is located around the periphery of the disc shaped wheel sensor 300 and extends up into the protrusion 312. By placing at least part of the antenna coil 330 in the protrusion 312, the antenna coil is closer to an outer surface of the

In the exemplary wheel loosening sensor 300, the protrusion 312 has a cross sectional area less than the main body 318 of the wheel loosening sensor 300. The exemplary wheel loosening sensor 300 has a substantially circular cross section and the cross sectional radius of the protrusion 312 is less than the cross sectional radius of the main body 318. The cross sectional radius of the protrusion 312 may be 50% or less of the cross sectional radius of the main body 318. The cross sectional radius of the protrusion 312 may be in a range from 3 mm to 6 mm and, in a particular exemplary wheel loosening sensor 100, 300, may be substantially 4 mm.

In such exemplary wheel loosening sensors 300, the wheel 320 may comprise an aperture 308 extending from the base of a recess 304 to an external surface 310 of the wheel 320, wherein the aperture 308 has a cross sectional area smaller than the recess 304. The dimensions of the wheel loosening sensor 300 dictate the dimensions of the recess 304 in the wheel 320. The components of the wheel loosening sensor 300, e.g. the transmitter and the battery, are such that the recess must be relatively large, when compared to the dimensions required by the antenna coil 330. As the aperture 308 is aimed at improving propagation of RF signals from the antenna coil 330, the aperture 308 need not be as large as the recess 304. Reducing the cross sectional dimensions of the aperture 308 retains more structural integrity of the wheel 320. In addition, a reduced cross sectional area of the aperture 308 improves the appearance of the wheel 320. The wheel loosening sensors disclosed herein relate particularly to alloy wheels for which appearance is an important factor.

The protrusion 312 allows the antenna coil 330 to be placed above the transmitter, which is formed on a PCB 326. This allows the transmitter to be deeper in the recess 304 or aperture 308 than the transmitter and, therefore, closer to the external surface 310 of the wheel 320. The antenna coil 330 is also above the battery 328 and all other active features of the wheel loosening sensor 300.

As mentioned above, the wheel 200, 320 comprises a recess 204, 304 in an internal surface. The recess 204, 304 may comprise a first section and a second section. The first section runs from the internal surface to the second section. The second section runs from the first section to the base of the recess 204, 304. Exemplary wheel loosening sensors 100, 300 comprise a first part and a second part. The first part may comprise the backing plate 116, 316 and the second part may comprise the housing 102, 302. As shown in Figures 2 and 3, the backing plate 116, 316 may extend up the sides of the wheel loosening sensor 100, 300 such that it overlaps the housing 102, 302. The first part of the wheel loosening sensor 100, 300 may therefore be wider than the second part of the wheel loosening sensor 100, 300. As such, the first section of the recess 204, 304 may be wider than the second part of the recess 204, 304 and may be configured to accommodate movement of the first part of the wheel loosening sensor 100, 300.

The wheel 200, 320 may also comprise an aperture 208, 308 extending from the base of the recess 204, 304 to an external surface 210, 310 of the wheel 200, 320. The aperture may improve propagation of an RF radiation signal from the antenna coil 230, 330 of the wheel loosening sensor 100, 300. The cross sectional area of the aperture 208, 308 may be less than the cross sectional area of the recess 204, 304. The aperture 308 may be configured to receive the protrusion 312.

As shown in Figure 4, a wheel loosening sensor 400 may comprise a cap 401 configured to cover at least partly a protrusion 412. The cap 401 may be removable from the wheel loosening sensor 400.

The cap 401 may be configured to extend into the aperture 408 at least as far as an external surface 410 of the wheel 420. In this way, the cap prevents water and debris from entering the aperture 408 by plugging the aperture 408. For improved resistance to the ingress of water and debris, the cap 412 may be configured for an interference fit within the aperture 408. The cap 412 may be manufactured from a deformable material, such as a rubber or plastics material to provide a seal between the internal wall of the aperture 408 and the cap 412. In addition, the cap 412 and/or the internal wall of the aperture 408 may comprise one or more protrusions or ridges configured to retain the cap 412 within the aperture 408.

The cap 412 may comprise a visual indicator, such as a colour indicator, that may indicate information relating to the sensor. For example, the visual indicator may identify the type of sensor fitted.

There may be a plurality of caps 412 that may be fitted to the wheel loosening sensor 400. Each cap 412 may comprise a different visual indicator and/or a different length. The length of the cap 412 determines how far into the aperture 408 the cap extends. Therefore, by providing a plurality of caps 412 having different lengths, a single wheel loosening sensor 400 may be used for a plurality of different wheels 420 having different thicknesses. A different cap 412 may be fitted, such that the cap 412 extends to be flush with an external surface 410 of the wheel 420.

The aperture 408 may comprise a flange retaining section 422 configured to accommodate and retain a flange 424 of the cap 412.

The antenna cap 412 is a cost effective solution that may utilise a simple moulding (which may be rubber or soft plastics) which fills the aperture 408 to the exterior surface of the wheel 420 with a much tighter fit than the protrusion 412. The cap 412 could be coloured for sensor identification purposes and could comprise small ribs on the outer surface to aid retention of the sensor when pushing into the alloy wheel during the fitting process. Varying aperture depths caused by differing wheel designs can effectively be visually plugged by varying the length of the antenna cap 412 itself.

Figure 5 shows a wheel loosening sensor 500 positioned within an internal recess 504 of a wheel 520. The wheel loosening sensor 500 may comprise one or more features of the wheel loosening sensors in Figures 1-4 and may, in a specific exemplary arrangement, be substantially the same as the sensor in Figure 1. The wheel is secured against a wheel hub 502. The recess 504 in the wheel 520 is deep enough to accommodate the wheel loosening sensor 500 and a spacer 530. The recess 504 comprises a retaining lip 532 that defines an aperture 508. The retaining lip 532 retains the sensor 500 within the recess 504. The aperture 508 allows propagation of RF signals from an antenna of the sensor 500.

The spacer 530 is configured to hold the sensor 500 in a position displaced from the wheel hub 502. The wheel hub 502 may get hot during operation of a vehicle, for example due to friction caused by braking. Therefore, the spacer 530 may be configured to prevent or reduce heat transfer from the wheel hub 502 to the sensor 500. The spacer is also configured to translate to the sensor 500 any displacement of the wheel 520 from the wheel hub 502. The spacer 530 may therefore be formed of a material having sufficient stiffness to translate that displacement.

The exemplary spacer 530 of Figure 5 is cylindrical and has a void within. However, other spacers are possible within the scope of the invention. For example, the spacer may be a solid mass of material, may be a composite and/or laminar and may be different cross sectional shapes.

Exemplary spacers may comprise a material with relatively poor heat transfer properties (an insulator), which prevents heat from the wheel hub 502 transferring to the sensor 500. For example, the spacer 530 may be manufactured, at least in part, from a plastics material. Other exemplary spacers may be formed from an aluminium extrusion, which has the benefit of being cheap and the material will have substantially the same thermal characteristics as an alloy wheel. For example, the aluminium spacer will have substantially equal thermal expansion and contraction properties of alloy wheels. Exemplary spacers may comprise one or more cooling fins around an outer surface or around an inner surface, within a void. This may be particularly useful when using aluminium spacers.

Another advantage of using a spacer 530, as in Figure 5, is that the sensor 500 can be positioned more consistently with the recess 504 of the wheel 520 by varying the spacer height for various wheel thicknesses. Also with the antenna being closer to the outer surface of the wheel, RF transmission power is improved.

In other exemplary arrangements, the recess 504 may comprise air flow channels to allow air to flow over the sensor for allowing heat to be dissipated from the wheel hub 502. The air flow channels may be formed in the sidewalls of the recess 504. The air flow channels may be configured to have increased air flow therethough as a result of rotation of the wheel 520. For example, the air flow channels may form a spiral or helix around the sidewall of the recess 504. A wheel loosening sensor assembly may comprise the sensor 500 and the spacer 530.

It is noted that Figures 1 to 4 each show wheel loosening sensors. Whilst some features of the wheel loosening sensors change between the figures, many of the features remain the same but are not described in respect of each figure in the interests of brevity. However, appropriate features from any of the sensors in Figures 1 to 4 may be combined with the sensors of the other of Figures 1 to 4.

The skilled person will be able to envisage other embodiments of the invention without departing from the scope of the appended claims.

Claims

CLAIMS:

1. A wheel loosening sensor for fitting in a recess on an internal surface of a wheel and for detecting movement of the wheel away from a wheel hub, the wheel loosening sensor comprising: a transmitter configured to transmit a signal when movement of the wheel away from the wheel hub is detected; and an antenna in electrical communication with the transmitter and configured such that at least part of the antenna is deeper within the recess than the transmitter when the wheel loosening sensor is fitted within the wheel.

2. A wheel loosening sensor according to claim 1, further comprising a housing comprising a main body, in which the transmitter is located, and a protrusion, in which at least part of the antenna is located.

3. A wheel loosening sensor according to claim 2, wherein the protrusion has a cross sectional area less than a cross sectional area of the main body.

4. A wheel loosening sensor according to claim 3, wherein the main body and the protrusion each has a substantially circular cross section, and wherein a cross sectional radius of the protrusion is less than a cross sectional radius of the main body.

5. A wheel loosening sensor according to any of claims 2 to 4, further comprising a cap covering at least part of the protrusion.

6. A wheel loosening sensor according to claim 5, wherein the recess comprises an aperture extending to an external surface of the wheel, and wherein the cap is configured to extend to be at least level with the external surface of the wheel.

7. A wheel loosening sensor according to claim 5 or 6, wherein the cap is removable.

8. A wheel loosening sensor according to any of claims 5 to 7, wherein the cap is configured to provide an interference fit within the recess to retain the wheel loosening sensor within the recess.

9. A wheel loosening sensor according to claim 8, wherein the cap comprises one or more ridges configured to provide the interference fit.

10. A wheel loosening sensor according to any of claims 6 to 8, wherein the cap comprises a visual indicator identifying the type of wheel loosening sensor fitted within the wheel.

11. A wheel loosening sensor according to any preceding claim, further comprising a battery, wherein the antenna is configured such that it is deeper within the recess than the battery when the wheel loosening sensor is fitted within the wheel.

12. A wheel comprising a recess on an internal surface thereof, wherein the recess is configured to receive a wheel loosening sensor for detecting movement of the wheel away from a wheel hub.

13. A wheel according to claim 12, further comprising an aperture extending from a base of the recess to an external surface of the wheel.

14. A wheel according to claim 13, wherein the aperture has a cross sectional area less than a cross sectional area of the recess.

15. A wheel according to claim 13 or 14, wherein the recess comprises a first section from the internal surface of the wheel and a second section from the first section to the base of the recess, and wherein the first section is wider than the second section and configured to accommodate movement of a first part of the wheel loosening sensor relative to a second part of the wheel loosening sensor.

16. A wheel according to any of claims 12 to 15, wherein the aperture further comprises a flange retaining section configured to retain a flange of a cap to be fitted to a protrusion of the wheel loosening sensor and configured to extend into the aperture.

17. A wheel according to any of claims 12 to 16, further comprising a wheel loosening sensor according to any of claims 1 to 11 fitted within the recess.

18. A wheel loosening sensor assembly, comprising: a wheel loosening sensor for fitting in a recess on an internal surface of a wheel and for detecting movement of the wheel away from a wheel hub; and a spacer configured to retain the sensor in a position spatially displaced from the wheel hub.

19. A wheel loosening sensor assembly according to claim 18, wherein the spacer is configured to restrict heat transfer from the wheel hub to the sensor and/or to dissipate heat from the wheel hub.

20. A wheel loosening sensor assembly according to claim 19, wherein the spacer comprises a thermal insulator material.

21. A wheel loosening sensor assembly according to claim 19 or 20, wherein the spacer comprises one or more cooling fins comprising a thermal conductor material.

22. A wheel loosening sensor assembly according to claim 21, wherein the one or more cooling fins are positioned on an outer surface of the spacer.

23. A wheel according to any of claims 12 to 16, comprising a wheel loosening sensor assembly according to any of claims 18 to 22.

24. A kit of parts comprising: a wheel loosening sensor for fitting in a recess on an internal surface of a wheel and for detecting movement of the wheel away from a wheel hub; and a spacer configured to retain the sensor in a position spatially displaced from the wheel hub.

25. A vehicle comprising one or more wheels according to claim 17 or 23.

26. A wheel loosening sensor substantially as herein described with reference to the accompanying drawings.

27. A wheel substantially as herein described with reference to the accompanying drawings.