An energy harvesting device

Abstract

A piezoelectric energy harvesting device 10 comprises a base 12 having a mounting section 14 and a support section 16, a beam 22 having first and second ends, and a piezoelectric element mounted on th

Description

Field of the Invention This invention relates to a device for energy harvesting, particularly to a piezoelectric device that can be used to harvest electricity from movement, such as within vehicle tyres. Background to the Invention Hitherto, there has been a desire to harvest electricity energy from moving bodies, for example in vehicle tyres, and whilst various methods and devices have been proposed, there are often flawed for various reasons. Commonly, a piezoelectric element is used so that deformation of the moving body can deform the piezoelectric element and create electricity. One previously proposed arrangement bonds a piezoelectric element directly to the inner liner of a vehicle tyre. When installed in this manner, the piezoelectric element is subjected to, large uncontrollable cyclic strain, non-uniform bending and high stress concentration at bond points, especially where the tyre is subject to abnormal conditions such as potholes or the tyre hitting a curb. These uncontrollable strains often result in fatigue in the piezoelectric element, leading to microcracking and early electrical degradation over time, and can also result in a complete mechanical failure of the piezoelectric material and / or its electrical connections. It should also be noted that the environment inside a tyre is inhospitable and temperatures can exceed 125°C, which, in combination with mechanical vibrations causing damage to solder joints and adhesives, can result in existing devices failing. The outcome is a product lifetime inconsistent with the typical tyre service life. Clearly, in a tyre, where the number of cycles during use will be very high, failure of the piezoelectric element relatively early in the lifespan of the tyre results in the energy harvesting device becoming redundant soon after installation. In other arrangements, battery-powered sensors are placed inside tyres; however, these then need to be replaced regularly, and oftentimes before the tyre needs replacing. In order to service and / or replace the battery, the tyre to which it is affixed will need to be removed prior to the tyre itself having passed its useful lifespan, which can cause damage to the tyre and increased labour costs for a customer. Whilst some devices can be placed in the rim of a wheel, rather than on a tyre, the information returned is limited as the device cannot monitor tyre deformation or strain in the tyre wall, which can be critical information in determining tyre lifespan and integrity. Another major limitation of battery configurations is that in order to increase the lifespan of the system, the amount of data gathered and transmitted must be limited to manage power usage, often leading to missing data trends or delays in detecting incidents. This can result in reduced safety levels because problems with the tyre cannot be identified over the lifespan of the tyre or, due to the restriction on monitored parameters, key data cannot be transmitted, thereby missing structural problems within the tyre. A further concern with existing systems that employ batteries is that those batteries usually decrease in capacity when exposed to the temperatures experienced within tyres, for example, over 100°C. This reduces the lifespan of sensing devices, again, making them ineffective before the device in which they are arranged has reached the end of its useful life. Summary of the Invention Accordingly, the present invention is directed to an energy harvesting device comprising: a base member having a mounting section and a support section, with the support section being spaced apart from the mounting section; and a beam component having a first edge and an opposing second edge; wherein, the beam component is mounted on the mounting section of the base member, with the first edge of the beam component being arranged on the mounting section or on the opposite side of the mounting section from the support section, wherein the second edge of the beam component is arranged to be on the side of the support section distal from the mounting section; and wherein a piezoelectric element is mounted on or adjacent the beam component, such that deformation of the beam component results in deformation of the piezoelectric element. Thus, the present invention provides a piezoelectric energy harvesting device that addresses problems associated with stress and fatigue in the piezoelectric element. This is undertaken by way of removing the piezoelectric element from direct contact with the deforming surface to which the device is attached. A cantilever structure is created that distances the piezoelectric element from the surface on which it is installed, thereby allowing deformation of the piezoelectric element, without the piezoelectric element experiencing the cyclic strain and direct stress experienced in existing solutions. The device of the present invention has a base member that is fixed to a surface, such as a tyre liner, and the cantilever beam component is mounted upon the base portion, with at least part of the beam component free or partially constrained, with a piezoelectric element connected to the beam component. As such, the beam component provides damping to the piezoelectric element, thereby reducing the strain thereupon. The piezoelectric element may be mounted directly upon the beam component, for example by adhesive, or it may be attached indirectly to the beam component, for example, upon another part that is in contact with the beam component. Similarly, the piezoelectric element could be contained embedded, or partially embedded, into the beam component, for example, by overmoulding or sandwiching the piezoelectric element within the beam component. In some arrangements, there may be a benefit to the piezoelectric element being in contact with, but not fixedly connected to, the beam component, so that deformation of the beam component results in deformation of the piezoelectric element, but the piezoelectric element has a degree of autonomy with respect to movement relative to the beam component. The support section is arranged to provide support to the second edge of the beam component, with a space provided between the beam component and the base section. Effectively, the beam component is raised from the surface of the base member with a gap between the two in order to allow the beam component to flex. The beam component, particularly the area adjacent the second end of edge of the beam component, may be allowed to slide relative to the support section, rather than being affixed thereto. As a result, the beam component experiences different and controllable deformation, compared to that seen by the base member which experiences stress and strains dictated by the surface on which it is installed. That said, it is preferable that the position of the beam component is controlled and maintains close contact with the support section of the device to reduce uncontrolled motion such as vibration. Therefore, preferably, the support section of the base member comprises an opening and the beam component passes through the opening. The opening may be in the form of a slot, aperture, gap or other opening in, or on, the support section. The result of the opening is, ideally, that the beam component has a defined path along the support section, so that movement of the beam component relative to the support section is substantially predetermined and it may be restricted to a sliding movement in a specific direction, relative to the support section. It will be appreciated that other ways to reduce undesirable movement of the beam component may be employed, for example, tracks or guide elements that restrict the movement of the beam component to specific directions or attachment using flexible materials such as elastomers which allow controlled relative movement. In one arrangement, a second piezoelectric element is provided on or adjacent the beam component. The beam component may be provided with a plurality of piezoelectric elements so that deformation of the beam component results in multiple piezoelectric elements deforming, thereby generating more energy in the device for each deformation of the beam component. It may be that the plurality of piezoelectric elements is arranged so that piezoelectric elements are stacked on top of one another, aside one another, or they be positioned at different locations on the beam component, such as one on a first side of the beam component and one on an opposite side of the bean component. In one arrangement, the base member comprises a second support section on the opposite side of the mounting section from the first support section, and the beam component may be connected to the mounting section at a position between its first edge and its second edge, and, optionally, a further piezoelectric element is mounted on the beam component between the mounting section and the second edge. The device may comprise a double-cantilever structure in which a first end, or first beam component extends from the mounting section in a first direction, and a second end of the beam component, or a second beam component extends from the mounting section in a different direction. Each beam component, or part of the beam component, can be provided with a piezoelectric element, thereby increasing the energy harvested in a single deformation of the body to which the device is attached. This may be particularly advantageous where the deformation is experienced in more than one direction, in which case the beam components can be offset from one another so that a first beam component is in a first direction, or plane, and the second beam component extends in a different direction or plane. It is particularly advantageous that the energy harvesting device is provided with one or more components selected from a group comprising: a capacitor; an energy storage component; a wireless transmitter; and a sensor device. The sensor, or sensors, may monitor temperature, humidity, pressure, force or other parameters. The energy storage component may be an energy accumulator, such as a battery, a capacitor or another storage element that can allow the energy to be used at a later time. By providing an energy accumulator, such as a capacitor, the energy can be stored and used to power the sensors and any other components contained within the device. In some arrangements, the device may be provided with a wireless receiver so that it can be programmed and / or adjusted to more efficiently store and use the energy harvested during use, which may be based upon the historically sensed parameters. The invention extends to energy harvesting arrangement comprising: a tyre; and an energy harvesting device as described herein; wherein the energy harvesting device is connected to the internal surface of the tyre. The energy harvesting device can be placed within a tyre so that deformation of the tyre during use can result in energy generation in the device. This allows energy to be generated that can then be used to power sensing devices and other components, such as short-range transmitters, thereby allowing the monitoring of the conditions within the tyre and the forces acting upon the tyre during operation. Such monitoring of parameters within the tyre can be important for determining degradation the information received from the device can be used to prolong the life of the tyre. Therefore, the use of then energy harvesting device in accordance with the present invention can reduce the number of tyres used and can result in reduced numbers of tyres being burned or sent to landfill. As the tyre rotates, deformation in the inner liner of the tyre upon which the energy harvesting device is mounted caused relative motion between the tyre liner and the piezoelectric element, with the cantilever arrangement converting the motion into controlled bending and controlled stain. Thus, the piezoelectric element experiences reduced peak strain, more uniform stress distribution, and improved fatigue life. The cantilever provides mechanical impedance matching between the large, low-frequency, tyre deformation and the piezoelectric element’s optimal strain range. Thus, the cantilever acts as a mechanical filter and its design geometry incorporates stress managing and / or transforming elements. Peak liner strain is attenuated before reaching the piezoelectric element, thereby protecting the piezoelectric element from, excessive bending, compression and shear forces. The energy harvesting device can be used to power a tyre pressure monitoring system and the sensors contained therein. As the energy harvesting device can operate without any external power, it can be used in enclosed spaces, such as within tyres or in sealed environments that are subject to mechanical strain. This allows the device to operate in conditions that other devices cannot. Furthermore, the reliance on battery technology is reduced, which can provide longer lifetimes to the devices in which the energy harvesting arrangement is installed. A further advantage of the present invention is that, because the power supply is not limited as with battery technology, more data can be accumulated and transmitted over the lifespan of the device. This can allow for on-going monitoring of the body to which the energy harvesting device is connected, which can improve safety and reliability of the body, because defects and concerns can be more readily identified and actioned before failure occurs. This can lead to ‘intelligent products’ being produced that can provide feedback on parameters for the lifetime of the product. The energy harvesting device can be used in other arrangements where a surface experiences sufficient deformation. For example, an energy harvesting device according to the present invention can be embedded into or attached onto: footwear, especially within the soles; skis or snowboards; surf boards; boats; aircraft wings; turbine blades; vehicle suspension; walkways and bridges; support structures in buildings; road markers, such as cat’s eyes to produce power to light LEDs; unit load devices; railway tracks or rolling stock (rail sleepers, bogies); industrial conveyor belts, prosthetic limbs or orthotics; sporting equipment (tennis rackets, bicycle frames, helmets); military clothing or devices, marine structures (buoys, offshore platforms, moorings); pipelines (oil / gas pipes subject to vibration); agricultural machinery (tyres, chassis under field conditions); mining equipment; packaging / shipping containers (impact and vibration monitoring); and / or automotive body panels or chassis members. As such, the structural integrity, mechanical forces experienced and / or other parameters can be monitored in the listed situations and environments to increase the safety and lifespan of the body being monitored. Brief Description of the Drawings An embodiment of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a device according to the present invention; Figure 2 is a side view of the device of Figure 1; Figure 3 is an exploded view of the device of Figure 1; Figure 4 shows a first view of the device of Figure 1 when employed in a tyre; and Figure 5 shows a second view of the arrangement in Figure 4. Detailed Description of the Exemplary Embodiment Figures 1 to 5 show an energy harvesting device 10. The energy harvesting device 10 has an elongate base member 12, the base member 12 having a length L and a width W, and the base member 12 comprising a flexible material. The base member 12 has a mounting section 14 arranged at a first end 12a and a support section 16 at the second, opposite end 12b, with the mounting section 14 and the support section 16 being spaced apart along the length L of the base member 12. The region of the base member 12 between the mounting section 14 and the support section 16 has a top surface that is lower than that of both the top of the mounting section 14 and the top of the support section 16, which creates a substantially U-shaped profile when viewed from the side, as shown in Figure 2. The support section 16 is provided with a slot 18 therein, with the slot 18 being arranged across the width W of the base member 12, and substantially perpendicular to the length L of the base member 12. The mounting section 14 is provided with apertures 20 in its top surface. Mounted on top of the mounting section 14 is the first end of an elongate beam component 22. The beam component 22 extends from the mounting section 14 and passes through the slot 18 of the support section 16, and the beam component is a little longer than the distance between the mounting section 14 and the support section 16, so that the second end of the beam component 22 protrudes from the slot 18 in the support section 16. The second end of the beam component 22 is not fixedly attached to the support section 16, so that it can move relative to the slot 18. An elongate piezoelectric element 24, is arranged on top of the beam component 22 and is adhered thereto, with a first end of the piezoelectric element 24 being arranged adjacent the first end of the beam component 22. The piezoelectric element 24 has a width less than that of the beam component 22 and a length less than the length of the beam component 22, such that the piezoelectric element 24 extends partway along the beam component 22. The piezoelectric element 24 can be sunk into the beam component 22, so that it is not visible from a side view, as shown in Figure 2. Mounted on top of the first end of the beam component 22 and the first end of the piezoelectric element 24 is a housing 26, which is provided with an aperture 28 in its lower surface. Also in the lower surface of the housing 26 are two contact apertures 30. The housing 26 comprises external walls that create a volume within the housing into which components may be fitted. The housing is fitted to the base member 12 by way of screws 32 arranged to pass through the apertures 28 in the lower surface of the housing, through corresponding apertures in the beam component 22 and into the apertures 20 in the mounting section 14. This fixes the housing 26 onto the base member 12 and holds the beam component 22 and the piezoelectric element 24 in place. The contact apertures 30 are positioned to be above the piezoelectric element 24 when the housing 26 is mounted on the base member 12. An adhesive pad 34 is placed on top of the screws 32, with the adhesive pad 34 having adhesive on both its top side and bottom side. The adhesive pad 34 is sized to cover the screws 32, but not to fill the area of the inside of the housing 26, thereby leaving a gap above the contact apertures 30. Surface-mount technology pads 36 are positioned in the contact apertures 30, such that they are in contact with the piezoelectric element 24. On top of the adhesive pad 34 sits circuitry in the form of a printed circuit board 38, which is arranged on top of the surfacemount technology pads 36, so that the printed circuit board 38 is in contact with the piezoelectric element 24 via the surface-mount technology pads 36. Thus, electricity generated by the piezoelectric element 24 can be provided to the printed circuit board 38. A housing lid 40 is connected to the top surface of the housing 26 by screws 42, thereby closing the top of the housing 26 with the circuitry therewithin, and so reducing the risk of particulate ingress and providing some shielding to the circuitry from the environment in which the device is placed. Figures 4 and 5 show the energy harvesting device 10 installed on the inner liner of a tyre 50. As can be seen, as the tyre 50 moves along a surface 52, it deforms to create a flat section where it contacts with the surface 52. As the tyre 50 deforms, because the energy harvesting device 10 is affixed to the inner liner of the tyre 50, the base member 12 of the energy harvesting device 10 also deforms. At the same time as the base member 12 deforming, the beam component 22 and the associated piezoelectric element 24 also deform. The base member 12 bends more than the piezoelectric element 24, due to the cantilever structure created by the beam component 22, particularly as the second, free end of the beam component can slide within the slot 18. As such, the bending strain on the piezoelectric element 24 is less than that of the base member 12. This reduced bending strain results in reduced fatigue in the piezoelectric element 24, thereby increasing its longevity. The base member is, preferably, manufactured from a material that is flexible and / or resiliently yieldable, so that it is able to repeatedly flex, preferably without noticeable fatigue. Clearly, a rigid material or a material that will readily fatigue before the piezoelectric material will be unsuitable because the base member will mechanically fail prior to the piezoelectric element. The material employed for the beam component can be selected according to the degree of bending required. For example, a stiffer material may be used to reduce the bending on the piezoelectric element, or a less stiff material to provide more bending on the piezoelectric element. The choice of stiffness for the beam component may depend upon the purpose of the energy harvesting and the degree of cyclic strain to which the surface on which the device is mounted is subjected. The beam component may comprise one or more of the following materials and structures: spring metals; composite material, for example, glass fibre with an epoxy resin matrix material; polymers; and elastomers. Similarly, the shape of the beam component may be adapted according to the intended purpose. For example, the beam component may be a straight, curved or tapered component, and it may be of constant or variable thickness. The beam component may comprise a plurality of layers connected to one another. In essence, the energy harvesting device can provide a mechanical mounting arrangement for the piezoelectric element, which can be employed in a body that experienced cyclic strain. As the piezoelectric element is mounted on a compliant beam component, which creates a cantilever structure, the piezoelectric element is mechanically decoupled from the strains experienced by the body to which is it attached. The cantilever structure allows the piezoelectric element to experience controlled bending or displacement in response to flexing during rotation, whilst limiting peak strain, stress, and fatigue that would otherwise occur with direct liner attachment. The circuitry of the present invention can be provided with a processing unit that can control the amount of energy stored, how that is stored and where in the system it may be stored. The processor may itself use information received from one or more sensors in the energy harvesting device to appropriately manage the energy harvesting. Similarly, the device may be provided with non-volatile memory in order to store information, which may be accessed later on. The energy harvesting device may be provided with a reserve battery, so that the if the device is stationary for an extended period, there is still a supply of energy available to the device. This reserve battery may be charged during operation of the energy harvesting device. It will be appreciated that under high load and low-pressure conditions, stresses in the beam component should, preferably, remain below a safe fraction of the flexural strength of the material used to manufacture the same. Where one end of the piezoelectric device is fixed to the mounting section, the resulting pivot mechanism enables repeatable, single-point bending and can act as part of a deflection-limiting safety mechanism. In some cases, components may be combined and / or integrated to reduce the number of components. For example, the piezoelectric element and the beam component to which it is connected may be a single structure. Similarly, the housing may be integral with the base member. It will also be appreciated that the components described as being integral may also be manufactured separately, for example the mounting section and the support section may be separate parts. In its broadest sense, the energy harvesting device of the present invention is structured to reduce the strain on a piezoelectric element. The piezoelectric element is removed from direct forces experienced by the body to which is attached. The present invention allows the forces to which the piezoelectric element is subjected to be more readily controlled, thereby reducing the strain via mechanical coupling. The forces applied to the piezoelectric element can be adjusted by adjusting the stiffness of the relevant parts, thereby allowing the proportion of forces experienced by the body to which the device is attached to be scaled accordingly. Thus, the present invention may allow for some torsional forces experienced by the body to be reduced or filtered from being applied to the piezoelectric element, and the degree of bending experienced by the piezoelectric 5 element can be scaled so that only a portion of that is applied to the piezoelectric element. The cantilever arrangement described herein is one example of how that may be achieved. One of more features described herein in relation to a specific embodiment or arrangement may be incorporated into another embodiment or arrangement described 10 herein.

Claims

1. An energy harvesting device comprising:a base member having a mounting section and a support section, with the support section being spaced apart from the mounting section; and a beam component having a first edge and an opposing second edge; wherein, the beam component is mounted on the mounting section of the base member, with the first edge of the beam component being arranged on the mounting section or on the opposite side of the mounting section from the support section,wherein the second edge of the beam component is arranged to be on the side of the support section distal from the mounting section; andwherein a piezoelectric element is mounted on or adjacent the beam component and is coupled to the beam component, such that deformation of the beam component results in deformation of the piezoelectric element.

2. An energy harvesting device according to claim 1, wherein the support section of the base member comprises an opening and the beam component passes through the opening.

3. An energy harvesting device according to claim 1 of claim 2, wherein a second piezoelectric element is provided adjacent the beam component such that the second piezoelectric element is also coupled to the beam component.

4. An energy harvesting device according to any preceding claim, wherein:the base member comprises a second support section on the opposite side of the mounting section from the first support section; andthe beam component is connected to the mounting section at a position between its first edge and its second edge.

5. An energy harvesting device according to claim 4, wherein a further piezoelectric element is mounted on the beam component between the mounting section and the second support section.

6. An energy harvesting device according to any preceding claim, wherein the device is provided with one or more components selected from a group comprising: a capacitor; a battery; a wireless transmitter; and a sensor device.

57. An energy harvesting arrangement comprising:a tyre; andan energy harvesting device according to any preceding claim;wherein the energy harvesting device is connected to the internal surface of the10 tyre.A

Images