WO2010092171A2

WO2010092171A2 - Piezoelectric power generator

Info

Publication number: WO2010092171A2
Application number: PCT/EP2010/051847
Authority: WO
Inventors: Geoff Haswell
Original assignee: Piezotag Limited
Priority date: 2009-02-13
Filing date: 2010-02-15
Publication date: 2010-08-19
Also published as: GB0902395D0; DE112010000690T5; WO2010092171A3

Abstract

A piezoelectric power generator includes piezoelectric material and an actuator for deflecting the piezoelectric material for the purpose of generating electrical charge. The actuator is arranged for reciprocating movement along a first axis in response to external forces, and is preferably constrained against deviation from said axis via one or more suspension members, by means of which the actuator is suspended. The piezoelectric material may be carried on the underside of the actuator, for deflection into a recess. The actuator may carry circuitry for collecting charge, with the piezoelectric material in electrical contact with said circuitry via a conductor extending through an aperture in the actuator in floating, preferably resiliently biased, contact with the circuitry.

Description

Piezoelectric power generator

The present invention relates to a piezoelectric power generator, more particularly, but not exclusively, to a piezoelectric power generator for use in a rotatable object, such as a vehicle tyre. The invention also relates to a vehicle tyre monitoring apparatus and a telemetry unit for transmitting data from within a rotating object such as a vehicle tyre.

A tyre monitoring apparatus for recording pressure and temperature data within a tyre, e.g. for predicting tyre failure, is known from EP1549515. The apparatus includes a power generator having an actuator mass arranged to deflect piezoelectric material in response to external forces, in order to generate electrical charge to power the apparatus. Advantageously, control circuitry for the apparatus forms part of the actuator mass.

It is an object of the invention to provide alternatives and/or improvements to the principles of construction and operation of the power generator and/or the tyre monitoring apparatus described in EP 1549515.

According to one aspect of the invention there is provided a piezoelectric power generator including piezoelectric material and an actuator for deflecting the piezoelectric material for the purpose of generating electrical charge, wherein the actuator is arranged for reciprocating movement along a first axis in response to external forces, and wherein the actuator is constrained against deviation from said axis via one or more suspension members, by means of which the actuator is movably suspended.

The suspension and constraint of the actuator according to this aspect of the invention is believed to provide a more efficient and robust arrangement than the power generator of EP1549515, e.g. by reducing problems of wear and chatter between contacting parts and improving power generation by reducing the transfer of radial forces from the actuator to the piezoelectric material.

The actuator is preferably suspended in a housing by an annular suspension member or by an array of separate suspension members which define an annulus for the actuator. An inner region of the or each suspension member is preferably integral with or connected to a n peerriinphheerrvy o off t thhee a accttuuaattoorr..

In preferred embodiments, the actuator is circular and the annular suspension member or array of suspension members define a circular annulus for the actuator.

The piezoelectric material and actuator are preferably mounted in a housing, which preferably includes a base member and a cover member, wherein an outer region of the or each suspension member is clamped between the base member and the cover member. However, in other embodiments, an outer region of the actuator is anchored in the cover member for movement relative to said base member. In such cases, the cover member is preferably of resilient material for permitting reciprocating movement of the actuator along said axis in response to external forces, and is more preferably configured or reinforced to prevent significant radial deviation of the actuator from said axis in response to external forces.

The annular suspension member, array of suspension members or resilient cover is preferably arranged to act as a diaphragm, by means of which potential radial deviation of the actuator in response to external forces is transferred into up or down movement along said axis. This is believed to improve the efficiency of the generator.

A connection between the or each suspension member and the actuator is preferably of a rocker or ball and socket type articulating joint. More preferably, an inner region of the or each suspension member has a rounded profile, which is located in a complimentarily formed groove or recess in a periphery of the actuator.

The piezoelectric material is preferably arranged for deflection into a recess upon movement of the actuator and is carried for movement with the actuator in response to external forces. More preferably, the piezoelectric material is concentric with said recess.

The actuator preferably carries circuitry for collecting charge from the piezoelectric material, and the piezoelectric material is in communication with said circuitry. The piezoelectric element is preferably in electrical contact with said circuitry via a conductor extending through an aperture in the actuator and which is in floating, preferably resilient Iy biased, contact with the circuitry. The conductor preferably has a first end affixed to the piezoelectric element and an unsecured second end arranged for contact with the circuitry.

The piezoelectric material is preferably in the form of a disc, preferably of piezoceramic material. The disc and recess are preferably circular in plan view.

Circuitry for collecting charge from the piezoelectric material preferably forms part of the actuator. In one embodiment, the actuator includes a tray defining a compartment in which a printed circuit board is secured in place, e.g. via an epoxy potting compound. The PCB is preferably arranged in electrical communication with the piezoelectric material. The PCB preferably includes sensor circuitry, in order to provide tyre-monitoring functions. More particularly, the sensor circuitry is preferably connected to one or more sensors for monitoring parameters (e.g. pressure and temperature) local to the generator.

The above aspect of the invention may incorporate any one or more of the essential or preferred features of any one or more of the other aspects of the invention set forth herein.

According to another aspect of the invention, there is provided a piezoelectric power generator including piezoelectric material and an actuator for deflecting the piezoelectric material for the purpose of generating electrical charge, wherein the piezoelectric material is arranged for deflection into a recess upon movement of the actuator, and wherein the piezoelectric material is arranged for movement with the actuator in response to external forces.

The arrangement according to this aspect of the invention is believed to provide a more robust arrangement than the power generator of EPl 549515, e.g. by obviating relative movement between the piezoelectric material and the actuator and so avoiding a striking action of the actuator against the piezoelectric material.

The above aspect of the invention may incorporate any one or more of the essential or preferred features of any one or more of the other aspects of the invention set forth herein. A further aspect of the invention provides a piezoelectric power generator including piezoelectric material and an actuator for deflecting the piezoelectric material for the purpose of generating electrical charge, wherein the actuator carries circuitry for collecting charge from the piezoelectric element, and the piezoelectric element is in electrical contact with said circuitry via a conductor extending through an aperture in the actuator and which is in floating, preferably resiliency biased, contact with the circuitry.

The circuitry for collecting charge from the piezoelectric element preferably forms part of the actuator for deflecting the piezoelectric element. In one embodiment, the actuator is in the form of a tray defining a compartment in which a printed circuit board is secured in place, e.g. via an epoxy potting compound, and wherein the connector extends through an aperture in the tray.

The invention also provides a tyre incorporating a piezoelectric power generator according to any one or more of the above aspects of the invention.

The invention further provides a tyre monitoring unit for mounting in a vehicle tyre incorporating a piezoelectric power generator according to any one or more of the above aspects of the invention.

A further aspect of the invention further provides a piezoelectric power generator for mounting in vehicle tyre, the piezoelectric power generator including piezoelectric material and an actuator for deflecting the piezoelectric material for the purpose of generating electrical charge, wherein the generator includes a cover element intended for securing the generator to the vehicle tyre in use, wherein the actuator is anchored in the cover member and arranged reciprocating movement along a first axis in response to external forces for deflecting said piezoelectric material.

The cover member is preferably of resilient material for permitting said reciprocating movement. The above aspect of the invention may incorporate any one or more of the essential or preferred features of any one or more of the other aspects of the invention set forth herein.

The invention further provides a tyre incorporating a piezoelectric power generator according to the above aspect of the invention and/or a tyre monitoring unit for monitoring pressure and or temperature within a tyre incorporating a piezoelectric power generator according to the above aspect of the invention.

The power generators described herein have particular advantage in vehicles tyres, wherein the forces generated when the tyre is in motion can be harnessed to generate electrical charge. However, other motion-related applications will be apparent.

Other aspects and features of the invention will be readily apparent from the claims and following description, made by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a schematic cross-sectional view of a tyre monitoring unit configured for mounting in a vehicle tyre, taken along a first centre line;

Figure 2 is an enlarged view of the circled region in Figure 1 , showing the actuator in a rest position;

Figure 3 is a schematic cross-section through the tyre monitoring unit of Figure 1, taken along a second centreline perpendicular to said first centreline.

Figure 4 is an enlarged view of the circled region in Figure 3;

Figure 5 is an exploded perspective view from above of the unit from Figure 1;

Figure 6 is similar to Figure 5, showing the components of the unit from below;

Figure 7 is a schematic side view of a modified tyre monitoring unit; Figure 8 is a schematic cross-section through the unit of Figure 7 along line A-A;

Figure 9 is a schematic cross-section through the unit of Figure 8 along line B-B; and

Figure 10 is an exploded perspective view from above of the unit from Figure 7.

Referring firstly to Figures 1 to 6, there is shown a tyre monitoring unit 100, which incorporates a piezoelectric power generator for battery-less power generation within the unit 100. In particular, the unit 100 includes piezoelectric material 110 and an actuator 112, wherein the actuator 112 is intended deflect the piezoelectric material 110 in response to external forces acting on the unit 100, for the purpose of generating electrical charge.

The piezoelectric element 110 and actuator 112 are mounted in a housing 102, which preferably encases the piezoelectric element 110 and actuator 112, thereby preventing debris from within the tyre from contact with the piezoelectric element 110 or actuator 112. In this embodiment, the housing 102 includes a base member 104 and a cover member 106, which cooperate to encase the piezoelectric element 110 and actuator 112. The cover member 106 is affixed to the base member 104 via threaded pins 108 (see Figures 3 and 4), although other means of connection between the base member 104 and cover member 106 may be preferred, e.g. an ultrasonic welded connection or staking.

The actuator 112 is movably mounted within the housing 102. More particularly, the actuator 112 is arranged for reciprocating movement along an axial centre line X of the unit 100, that is to say movement up and down as viewed in Figure 1. More preferably, the actuator 112 is constrained against deviation from the axial centre line X (e.g. side-to-side movement as viewed in Figure 1), so as to remain substantially concentric with the axial centre line X of the unit 100. The piezoelectric element 110 and actuator 112 are also concentric with said centreline X.

In the illustrated embodiment, the actuator 112 is constrained against deviation from the axial centre line X using an annular support member 114, in the form of a ring of resilient material, e.g. polyurethane. The annular support member 114 is preferably configured to act as a diaphragm, by means of which potential radial deviation of the actuator in response to external forces is transferred into up or down movement. This is believed to improve the efficiency of the generator. The same or a similar constraining effect may be achieved using an array of support members, spaced from one another around the periphery of a centrally arranged actuator, to create a trampoline- or diaphragm-type effect, by means of which the actuator 112 is suspended within the housing, and wherein the support members cooperate to permit up and down movement of actuator, whilst restraining the actuator from side to side movement.

An inner region of the support member 114 is connected to (or may be integral with) the periphery of the actuator 112 and an outer region of the support member 114 is anchored within the housing 102. Hence, it should be clear that the actuator 112 is suspended within the housing 102 by the support member 114. Again, the same or a similar constraining effect may be achieved using an array of support members.

As can be seen most clearly from Figures 1 and 2, an outer region 130 of the support member 114 is clamped between the base member 104 and the cover member 106, so as to be fixed in place on the housing 102. The inner region 132 of the support member 114 has an enlarged, rounded profile which is located in a complimentarily formed annular groove 134 in an outer wall 136 of the actuator 112, thereby forming a ball and socket type joint wherein the actuator 112 is able to articulate relative to the inner region of the support member, e.g. during movement of the actuator 112 along the axial centre line X under the action of centrifugal forces acting on the unit 100 when mounted inside a rotating vehicle tyre.

The actuator 112 in Figures 1 to 6 includes a generally circular tray 116 defining a compartment 118. A printed circuit board (PCB) 120 is mounted in the compartment 118 on the tray, and so contributes to the actuator mass for deflecting the piezoelectric element 110. As will be described in more detail below, the PCB 120 is in electrical communication with the piezoelectric element 110.

The PCB 120 includes: a rectifier for converting an alternating current output from the piezoelectric element 110 into a direct current output; an energy storage element in the form of a series of a capacitors, which store the direct current output from the rectifier (until required); and a DC-DC controller for regulating the voltage output from the capacitors. The preferred embodiment uses ultra low leakage type capacitors, to ensure that as high a percentage as possible of the generated charge is retained and that internal leakage is kept to a minimum. Modified embodiments may include a rechargeable battery for the storage of the generated charge.

In this embodiment, the PCB 120 includes a microprocessor, a radio frequency (RF) transmitter, sensor circuitry and control circuitry, in order to provide tyre monitoring functions. More particularly, the sensor circuitry is connected to one or more sensors, e.g. a sensor capsule 122 mounted on the tray 116 and/or other sensors external to or partially projecting from the housing 102, for monitoring parameters (e.g. pressure and temperature) local to the unit 100. The sensor, controlling processor, RF transmitter and other electronic devices may be provided as an ASIC.

The PCB 120 may be securably located on the tray 116 using a potting compound (not shown). The potting compound can be of any suitable type, e.g. a two-part epoxy adhesive, and contributes to the actuator mass for deflecting the piezoelectric element 110. However, it should be noted that in other embodiments the PCB and/or sensors etc may be located remote from the actuator 112.

As can be seen most clearly in Figure 2, the base member 104 defines a curved recess 105. The radius of curvature extends in a single axis only, as can be seen by comparison between Figures 2 and 3. The underside of the actuator 112 (or a covering element mounted on the piezoelectric element 110) has a curvature which matches the radius of curvature of the recess 105. The piezoelectric element 110 is arranged for deflection into the recess 105 in response to movement of the actuator 112, whereby the piezoelectric element 110 conforms to the curvature of the recess 105 and the underside of the actuator 112. It is suggested that such 'nested' deflection of piezoelectric material, particularly piezoceramic material, can protect the internal structure of the piezoelectric material, e.g. as described in US2005/0082949.

Hence, in preferred embodiments, it may be preferable for the piezoelectric material to be arranged for deflection into a recess upon movement of the actuator, e.g. if carried for movement with the actuator in response to external forces. The piezoelectric material may preferably be concentric with said recess. The recess may preferably have a curved profile and a contact portion of the actuator may preferably have a complimentary curved profile for nesting within the radius of curvature of the recess. More preferably, the radius of curvature of the recess may extend along a single axis only.

Referring now to Figures 3 and 4, it can be seen that the piezoelectric element 110 is coupled for movement with the actuator 112. More particularly, the piezoelectric element 110 is carried by the actuator 112.

As can be seen most clearly in Figure 5, the piezoelectric element 110 is mounted on substrate 140, which is attached to the underside of the tray 116. In the illustrated embodiment, the substrate 140 is attached to the tray 116 via threaded pins 124 arranged along a radial centre line of the element 110. The pins 124 extend through a radial flange 126 on the tray 116 and are secured in place via nuts 128. However, the substrate 140 may be otherwise attached to the tray 116, e.g. by hot staking or riveting.

The piezoelectric element 110 is effectively sandwiched between the underside of the tray 116 and the substrate 140. A covering shim (not shown) may be provided over the piezoelectric element 110, to defend the integrity of the piezoelectric material under deflection.

In this embodiment, the piezoelectric element 110 is in the form of a circular disc, preferably of piezoceramic material. The substrate 140 is also preferably in the form of a circular disc, more preferably a disc having a greater diameter than the piezoelectric disc 110. The recess 105 is also circular and the actuator 112 and piezoelectric disc 110 are preferably concentric with said recess 105.

The substrate 140 is preferably of electrically conductive material. A conductor 138 provides electrical communication between the piezoelectric element 110 and the PCB 120, whereby pulses of electrical charge are passed from said piezoelectric element 110 to the PCB 120 via said substrate 140 and conductor 138. As can be seen most clearly in Figure 4, the connector 138 has a first end clamped in place between the substrate disc 140 and the tray 116, and a second end extending through an aperture 142 in the tray 116, so as to be arranged for contact with the PCB 120. In a preferred embodiment, the connector 138 is not affixed to the PCB 120, but is instead resiliency arranged in abutment with a contact portion 144 of the PCB 120. In other embodiments, the connector 138 may be fixed to the PCB 120 by a soldered or clamped joint.

The unit 100 is preferably configured for attachment to a footing, for use in locating the unit 100 on an internal surface of the tyre (preferably on a portion of the tyre which is directly opposite the road-contacting surface of the tyre). In the illustrated embodiment, the housing 102 (in this case, a portion of the base member 104) includes an annular channel or groove 146 for snap-fitting engagement in a complimentary aperture 148 in a footing 150. In use, the footing 150 is secured to the tyre, e.g. using adhesive. In other embodiments, the housing may be encapsulated in a patch which is then secured to an internal surface of the tyre

Operation of the unit 100 is substantially the same as the units described and illustrated in WO2004/030949, the content of which is incorporated herein by reference, and so will not be described in detail. However, the basic operation is as follows:

When the wheel is in rotation, centrifugal forces urge the tray 116 in the direction of the base member 104 (e.g. along axial centre line X) from a rest position (e.g. as indicated in Figure 4) in order to deflect the piezoelectric material 110 into the recess 105. More particularly, as the tray 116 is urged in the direction of the base member 104, the substrate 140 acts as a simply supported beam across the recess 105 and the curvature of the underside of the tray 116 causes bending of the piezoelectric material 110 into the recess 105 over the unsupported region of the substrate 140. When the area of the tyre adjacent the unit 100 comes into contact with the road surface, it suddenly deforms, causing a sudden change in the centrifugal forces experienced by the actuator 112. This causes a change in the deflection of the piezoelectric element 110. The changes in the deflected state of the piezoelectric element 110 from its rest position during rotation of the tyre generate pulses of electrical charge, which are communicated to the PCB 120. The collected charge is intended for use in powering the sensor circuitry of the PCB 120. Although the unit 100 is intended for battery-less power generation, the unit 100 may be modified to include a battery or other electrical energy store, in addition to the piezoelectric arrangement.

It will be understood that the unit 100 has a piezoelectric power generator including piezoelectric material 110 and an actuator 112 for deflecting the piezoelectric material for the purpose of generating electrical charge, wherein the piezoelectric material and an actuator are provided in a housing 102, and wherein the actuator is arranged for reciprocating movement along a first axis X in response to external forces and is constrained against deviation from said axis via one or more suspension members, by means of which the actuator is movably suspended within the housing.

It will also be understood that the unit 100 has a piezoelectric power generator including piezoelectric material 110 and an actuator 112 for deflecting the piezoelectric material for the purpose of generating electrical charge, wherein the piezoelectric material is arranged for deflection into a recess 105 upon movement of the actuator, and wherein the piezoelectric material is arranged for movement with the actuator in response to external forces.

A modified tyre monitoring unit 200 is illustrated in Figure 7 to 10. As with the unit 100, the unit 200 has a piezoelectric power generator including piezoelectric material 202 and an actuator 204 for deflecting the piezoelectric material 202 for the purpose of generating electrical charge. The piezoelectric material 202 and actuator 204 are mounted in a housing and the actuator 204 is suspended within the housing for reciprocating movement along a first axis X in response to external forces. The piezoelectric material 202 is arranged for deflection into a recess 218 (having a radius of curvature which extends in a single axis only) upon movement of the actuator 204, and the piezoelectric material 202 is arranged for movement with the actuator 204 in response to external forces.

The housing has a base 206 and a cover 208. However, in this embodiment, the cover 208 is in the form of a patch by means of which the unit 200 can be secured at its intended operating location, e.g. on an internal surface of a tyre. The cover 208 encapsulates the base 206, actuator 204 and piezoelectric material 202. The actuator 204 is generally circular in plan view and is intended for carrying control circuitry for the unit 200. However, in this embodiment the actuator 204 is suspended directly from the cover 208, without the need for additional suspension or support members (e.g. the annular ring 114 of the unit 100). This reduces the number of components and net weight of the unit 200 in use.

As can be seen, the cover 208 includes an annular recess 210 for locating a circumferential lip 212 of the actuator 204. The cover 208 is of resilient material, specifically a material which permits reciprocating movement of the actuator 204 along the axis X (i.e. up and down, as viewed in Figures 8 and 9) in response to external forces, e.g. centrifugal forces in rotary applications.

The cover 208 is preferably reinforced or configured to constrain the actuator 204 against deviation from said axis X, and so act as a diaphragm, by means of which potential radial deviation of the actuator 204 in response to external forces is transferred into up or down movement along said axis X. In this embodiment, the base 206 is a rigid element (compared with the resilient nature of the cover 208) and extends upwards in to the cover 208, specifically in the region immediately adjacent the recess 210, in order to provide local rigidity to prevent lateral movement of the actuator 204. This is shown, by way of example only, in Figures 8 and 9, in which upstanding portions 214 of the base 206 extend into sockets 216 formed in the cover 208. The base 206 may include a plurality of such upstanding portions 214, e.g. defining a generally circular array, or may define a single annular upstand, for example.

Operation of the unit 200 is generally the same as for the unit 100 of Figures 1 to 6, wherein centrifugal forces will urge the actuator 204 in the direction of the base 206 in order to deflect the piezoelectric material 110 into the recess 218 in the base 206. Again, the curvature of the underside of the actuator 206 causes bending of the piezoelectric material 202 into the recess 218.

It should be noted that a spacer element 220 is preferably provided below the piezoelectric material 202, between the actuator 204 and the base 206. The purpose of the spacer element 220 is to shift the neutral radius of bending that occurs when the actuator causes the piezoelectric material 202 to bend is below the piezoelectric material 202 during bending, so that all of the piezoelectric material 202 is in compression during bending, thereby improving power generation. Accordingly, the piezoelectric material 202 must be fixedly secured to the spacer element 220, so that the combination of piezoelectric material 202 and spacer element 220 reacts as a single composite unit, under bending. In this embodiment, the spacer element 220 is carried by the actuator 204.

Claims

1. A piezoelectric power generator including piezoelectric material and an actuator for deflecting the piezoelectric material for the purpose of generating electrical charge, wherein the piezoelectric material and actuator are provided in a housing, wherein the actuator is arranged for reciprocating movement along a first axis in response to external forces, and wherein the actuator is constrained against deviation from said axis via one or more suspension members, by means of which the actuator is movably suspended within the housing.

2. A power generator according to claim 1 wherein the actuator is suspended in the housing by an annular suspension member or by an array of separate suspension members which define an annulus for the actuator.

3. A power generator according to claim 2 wherein an inner region of the or each suspension member is integral with or connected to a periphery of the actuator.

4. A power generator according to any of claims 1 to 3 wherein the actuator is circular and the annular suspension member or array of suspension members defines a circular annulus for the actuator.

5. A power generator according to any preceding claim wherein the housing includes a base member and a cover member, and wherein an outer region of the or each suspension member is clamped between the base member and the cover member.

6. A power generator according to any preceding claim wherein the housing includes a base member and a cover member, and wherein an outer region of the actuator is anchored in the cover member for movement relative to said base member.

7. A power generator according to claim 6 wherein the cover member is of resilient material for permitting reciprocating movement of the actuator along said axis in response to external forces.

8. A power generator according to claim 7 wherein the cover is configured or reinforced to prevent significant radial deviation of the actuator from said axis in response to external forces.

9. A power generator according to any preceding claim wherein the piezoelectric material is arranged for deflection into a recess upon movement of the actuator and is carried for movement with the actuator in response to external forces.

10. A power generator according to claim 9 wherein the piezoelectric material is concentric with said recess.

11. A power generator according to any preceding claim wherein the actuator carries circuitry for collecting charge from the piezoelectric material, and the piezoelectric material is in communication with said circuitry.

12. A power generator according to claim 11 wherein the piezoelectric element is in electrical contact with said circuitry via a conductor extending through an aperture in the actuator and which is in floating, preferably resiliently biased, contact with the circuitry.

13. A power generator according to claim 12 wherein the conductor has a first end affixed to the piezoelectric element and an unsecured second end arranged for contact with the circuitry.

14. A piezoelectric power generator including piezoelectric material and an actuator for deflecting the piezoelectric material for the purpose of generating electrical charge, wherein the piezoelectric material is arranged for deflection into a recess upon movement of the actuator, and wherein the piezoelectric material is arranged for movement with the actuator in response to external forces.

15. A power generator according to claim 14 wherein the piezoelectric material is mounted adjacent an underside of the actuator.

16. A power generator according to claim 14 or claim 15 wherein the piezoelectric material is arranged to be concentric with said recess.

17. A power generator according to any of claims 14 to 16 wherein the piezoelectric material is mounted on a substrate material carried by the actuator, wherein the substrate is configured to act as a simply supported beam across the recess and the actuator includes a curved portion intended for bending the piezoelectric material into the recess over the unsupported region of the substrate.

18. A power generator according to any of claims 14 to 17 wherein the piezoelectric material and an actuator are provided in a housing, wherein the actuator is arranged for reciprocating movement along a first axis in response to external forces, and wherein the actuator is constrained against deviation from said axis via one or more suspension members, by means of which the actuator is movably suspended within the housing.

19. A power generator according to claim 18 wherein the actuator is suspended in the housing by an annular suspension member or by an array of separate suspension members which define an annulus for the actuator.

20. A power generator according to claim 19 wherein an inner region of the or each suspension member is integral with or connected to a periphery of the actuator.

21. A power generator according to any of claims 18 to 20 wherein the actuator is circular and the annular suspension member or array of suspension members defines a circular annulus for the actuator.

22. A power generator according to any of claims 18 to 21 wherein the housing includes a base member and a cover member, and wherein an outer region of the or each suspension member is clamped between the base member and the cover member.

23. A power generator according to any of claims 18 to 22 wherein the housing includes a base member and a cover member, and wherein an outer region of the actuator is anchored in the cover member for movement relative to said base member.

24. A power generator according to claim 23 wherein the cover member is of resilient material for permitting reciprocating movement of the actuator along said axis in response to external forces.

25. A power generator according to claim 24 wherein the cover is configured or reinforced to prevent significant radial deviation of the actuator from said axis in response to external forces.

26. A power generator according to any of claims 14 to 25 wherein the actuator carries circuitry for collecting charge from the piezoelectric material, and the piezoelectric material is in communication with said circuitry.

27. A power generator according to claim 26 wherein the piezoelectric element is in electrical contact with said circuitry via a conductor extending through an aperture in the actuator and which is in floating, preferably resiliently biased, contact with the circuitry.

28. A piezoelectric power generator including piezoelectric material and an actuator for deflecting the piezoelectric material for the purpose of generating electrical charge, wherein the actuator carries circuitry for collecting charge from the piezoelectric element, and the piezoelectric element is in electrical contact with said circuitry via a conductor extending through an aperture in the actuator and which is in floating, preferably resiliently biased, contact with the circuitry.

29. A power generator according to claim 31 wherein the conductor has a first end affixed to the piezoelectric element and an unsecured second end arranged for contact with the circuitry.

30. A tyre incorporating a piezoelectric power generator according to any one of claims 1 to 13, 14 to 27 or 28 to 29.

31. A tyre monitoring unit for mounting in a vehicle tyre including sensors for monitoring pressure and or temperature within a tyre, and incorporating a piezoelectric power generator according to any one of claims 1 to 13, 14 to 27 or 28 to 29.

32. A piezoelectric power generator for mounting in vehicle tyre, the piezoelectric power generator including piezoelectric material and an actuator for deflecting the piezoelectric material for the purpose of generating electrical charge, wherein the generator includes a cover element intended for securing the generator to the vehicle tyre in use, wherein the actuator is anchored in the cover member and the cover member is of resilient material for permitting reciprocating movement of the actuator along a first axis in response to external forces for deflecting said piezoelectric material.

33. A power generator according to claim 32 wherein the cover is configured or reinforced to prevent significant radial deviation of the actuator from said axis in response to external forces.

34. A power generator according to claim 33 wherein the actuator is circular and the cover provides an annular support for the actuator.

35. A power generator according to any of claims 32 to 34 wherein the piezoelectric material is arranged for deflection into a recess upon movement of the actuator.

36. A power generator according to any of claims 32 to 35 wherein the piezoelectric material and is carried for movement with the actuator in response to external forces.

37. A power generator according to claim 35 wherein the piezoelectric material is mounted on a substrate material carried by the actuator, wherein the substrate is configured to act as a simply supported beam across the recess and the actuator includes a curved portion intended for bending the piezoelectric material into the recess over the unsupported region of the substrate.

38. A power generator according to any of claims 32 to 37 wherein the actuator carries circuitry for collecting charge from the piezoelectric material, and the piezoelectric material is in communication with said circuitry.

39. A power generator according to claim 38 wherein the piezoelectric element is in electrical contact with said circuitry via a conductor extending through an aperture in the actuator and which is in floating, preferably resiliently biased, contact with the circuitry.

40. A power generator according to claim 39 wherein the conductor has a first end affixed to the piezoelectric element and an unsecured second end arranged for contact with the circuitry.

41. A tyre incorporating a piezoelectric power generator according to any one of claims 32 to 40.

42. A tyre monitoring unit for monitoring pressure and or temperature within a tyre, incorporating a piezoelectric power generator according to any one of claims 32 to 40.

43. A power generator according to any of claims 9 to 10, 14 to 27 or 35 wherein a spacer element is provided below the piezoelectric material, between the actuator and the recess, so that the neutral radius of bending that occurs when the actuator causes the piezoelectric material to bend is below the piezoelectric material, so that all of the piezoelectric material is in compression during bending.

44. A power generator according to claim 43 wherein the piezoelectric material is fixedly secured to the spacer element, so that the combination of piezoelectric material and spacer element reacts as a single composite unit, under bending.