WO1997019474A1

WO1997019474A1 - Generating energy from piezoelectric effect

Info

Publication number: WO1997019474A1
Application number: PCT/NL1996/000466
Authority: WO
Inventors: Gerrit Oudakker; Maarten Jongejan
Original assignee: Ocean Power Technologies, Inc.
Priority date: 1995-11-24
Filing date: 1996-11-25
Publication date: 1997-05-29
Also published as: AU7591196A

Abstract

An electric generator is invented, comprising: drive elements, such as one or more vanes or propellors or fans, for converting a fluid flowing around said drive elements into a rotating or pivoting motion; transmission elements for converting said rotating or pivoting motion into a cyclic relative motion between: at least a part of electric power generating elements of piezoelectric material, and actuator elements, engaging said power generating elements, such as to generate a deformation of said power generating elements. In one embodiment, there is a crankshaft such that web like piezoelectric material is alternating stretched and relaxed by rotation of the crankshaft.

Description

Generating energy from piezoelectric effect.

The invention is concerned with the field of genereting electrical power from the movement of a fluid, e.g. wind or a water current, or moving waves or the rocking motion of water. Materials are known, e.g. polymers from the group of polyvinylidene fluoride, that with deformation generate a galvanic potential differenc as result of its piezoelectric property. There are publications about water driven electical power generators, that generate a galvanic power by cyclic deformation of the piezoelectric material. According to a known embodiment (see the article "Plastic cables pull power from the see", New Scientist, January 14, 1995, page 19), the material is therefor lenghtwise stretched like a rubber band. To this end, the material webs with one end are anchored to the sea bed, while the other end is anchored to a body floating on the sea level. No description is given of the system to adapt the system to the variations in the wave movement. With heavy swells, there is a risk that e.g. the material webs will break, and/or the floating body will repeatedly be drawn under water. With minor swells, the floating body will hardly be able to stretch the material webs to generate electricity. This is one of the reasons why the effectiveness of the system will be far from an optimum. The invention proposes several alternative energy generating systems, each with their own objects and solutions of problems with known systems.

In the first place the invention proposes, to adapt the recognition to apply piezo-electric material for use with a flow or current movement of a fluid, different from a swelling or waving motion. With that the technique is made available to generate electric power from wind or water current. To this end, in one aspect it is proposed to provide drive elements, such as one or more vanes or propellors or fans, for converting a fluid flowing around said drive elements into a rotating or pivoting motion, transmission elements for converting said rotating or pivoting motion into a cyclic relative motion between electric power generating elements of piezo-electric material, and actuator elements, engageing said power generating elements. The cyclic relative motion can be a reciprocating motion, e.g. provided by a crankshaft mechanism, but can be an ongoing movement in one direction as well, e.g. a continuous rotating movement in one direction. The drive elements can be adapted to generate a continuing movement in one direction, but can be adapted to generate a reciprocative rotating or pivoting motion as well, regardless of the nature of the flow of the fluid (continuous or discontinuous in one direction, or alternating in the opposite direction). Examples of this part of the invention are as follows:

The drive elements drive a shaft in a continuous rotation in one direction through a transmission. Actuator elements embodied by pins or stubs, spaced apart in circumferential and lengthwise direction of the shaft, project in sideway directions from the shaft, like the pins of the drive shaft of a music box. The shaft is surrounded by tongues, clamped with their one longitudinal end and facing the shaft with their opposite longitudinal end, and the lengtwise direction is substantially in radial direction w.r.t. the axis of the shaft, like the soundtongues of a music box. The tongues are sized and directed such that they project into the orbital space of the pins such that during rotation of the shaft a pin engages the free longitudinal end of a respective tongue in line with said pin, such that said tongue is deflected to some extend, before the pin disengages from said tongue due to further rotation of the shaft. The deflection and, if the pin disengages, again reflexing of the tongue, possibly followed by flexural vibrating of the tongue, will generate an electric power due to the piezo electric nature of the tongue. For each revolution of the shaft, e.g. one or several pins will engage the same tongue. The tongue can be designed such that its fexural rigidity decreases lineairly from its clamped longitudinal end towards its free longitudinal end, such that the flexural deformation is constant over its length, ensuring a smooth generation of piezo electricity over its length. For that purpose, the tongues can e.g. have a constant thickness or a constant width. In an alternative, the shaft is fixed, and the tongues are driven by the drive elements through the transmission elements, such that they rotate around the shaft. In another embodiment the system is designed such that more or less pins and tongues will mutually engage, depending on the working circumstances. Pins can therefor e.g. be selectively retracted into the shaft. They will only be extended if the prevailing need for electric power rises, and/or if the fluid flow is more powerful, and/or the drive elements give more power to the shaft. According to another embodiment the tongues are part of a shell, the shaft penetrates deeper or less deeper into this shell. The shaft is provided with pins spaced apart in the lengtwise direction of the shell. The shell is provided with radial inward projecting tongues over its complete length. Depending on the ratio of penetration of the shaft into the shell, more pins and tongues will mutually engage. The adjustment of the shaft w.r.t. the shell is e.g. stepwise to make sure that the pins always work reliably with the respective tongues. The actuation of the adjustment is e.g. through the drive elements based on the compressive force they experience from the fluid flow. If the fluid flow is strong (e.g. at high wind speeds) or if the fluid flow is used at high effectiveness by the drive elements (e.g. large speed of vanes with variable speed), the compressive force applied to the drive elements by the fluid flow in flow direction wil be bigger. By supporting the drive elements e.g. elastically yielding, or otherwise displaceable with backward function in the direction of flow of the fluid, said change of compressive force can be transferred into a displacement, to be used to control the ratio of penetration of the shaft into the shell, possibly through the intermediate of a transmission device.

According to another embodiment a crankshaft is continuously driven in rotation in one direction by the drive elements. This crankshaft is a transmission element to transmit a rotating movement into a cyclic reciprocating movement. Connected to the stepped parts of the crankshaft, acting as actuator elements, are the one longitudinal ends of webs of piezo electric material such that those ends will reciprocate during rotation of the crankshaft. This connection will be clear to the skilled man, since it does not differ from the way in which a piston rod is connected to a crankshaft. The opposite longitudinal ends of the webs are anchored, and the webs are of a length such that they will be strained elastically with each rotation of the crankshaft. In a further development of this example care is taken that one or some of the webs will not be strained by the rotation of the crankshaft. Therefore, those webs are anchored with the aid of a spring-element. The elastic behaviour of the spring- element is selected such that it is weaker than the web, such that a load will strain the spring in stead of the web. By designing the spring such that it can be locked, the spring action can be selectively switched off. If the spring is switched off, the web of piezo electric material itself will strain, and generate power. In another variant, the crankshaft could be split, such that parts of the crankshaft can be selectively disconnected, and will therefore not be rotated by the drive elements. By providing a slip coupling between the split parts of the crankshaft, it is possible as well to have parts of the crankshaft rotating at different speeds, such that stepless engaging/disengaging of one or more webs is allowed (such that the more webs are engaged the higher the couple due to stronger fluid flows). The above embodiments are not intended to limit the scope of the invention. Other embodiments are feasible as well, to which belong those in which one or more details of two or more of the above embodiments are combined into another embodiment. In a further aspect of the invention, provisions are provided to engage more or less electric power generating elements if the system is active. With that it is possible to adapt to the prevailing energy needs, the changing drive power of the drive elements or the changes in the movement of the fluid driving the drive elements. This aspect also comprises generating electric power from the wave movement or swell of the fluid, next to the generating from a flow or current of the fluid. For this reason it is proposed, to provide switching means to selectively disengage one or more electric power generating means from the actuator elements. Above several embodiments for this aspect of the invention have already been illustrated. With rotation- or circumferencing motion it is also meant here a circumferencing motion different from a pure movement around the axis, such as e.g. with drive elements following an endless course, e.g. directed along end wheels such that they drive one of those wheels or another transmission element. The invention is further illustrated by the at this moment most preferred, non-limiting embodiments shown in the drawings. Fig. 1 shows a first alternative, in front view. Fig. 2 shows a second alternative, in a partly broken, longitudinal cross section. Fig. 1 shows an eccentrically journalled shaft body 1, driven by drive elements (not shown). The shaft body 1 is e.g. drivingly coupled to vanes, propellors or other drive elements, through the intermediate of a gear transmission, known as such. The shaft body 1 extends substantially parallel and substantially in the centre of a ring body 2, which is substantially circular in this embodiment. Pre-stressed web elements of piezo electric material 3 extend between the shaft body and the ring body in substantial radial directions. They have a fixed position w.r.t. the ring body 2 and for that reason e.g. mounted with their one longitudinal end to the ring body 2 which is fixed w.r.t. the shaft body 1, while their opposite end is mounted to a bearing element (not shown) closely surrounding the shaft body 1 and fixed w.r.t. the shaft body 1. When the shaft body 1 rotates within the ring body 2, the web elements will be cyclic alternating further stretched and (partly) relaxed. In an alternative embodiment, the ring body 2 is elongated, e.g. a cilinder. According to another alternative, the ring body 2 is driven in rotation by the drive elements and eccentrically journalled, while the shaft body 1 is fixed w.r.t the ring body 2. The web elements 3 can then be designed such that they rotate with the ring body. The shaft body 1 can further be part of a crankshaft (not shown), to provide the eccentric journalling of the shaft body.

Fig. 2 shows how a transmission element 11 (preferably a sprocket wheel) is mounted to an eccentrically journalled shaft body 10, driven by drive elements possibly through the intermediate of transmission elements. This transmission element 11 drives pinion wheel elements 12, each driving a crankshaft 13. The shaft body 10 also penetrates a shell body 14, which does not rotate w.r.t. the shaft body 10. Pre- stressed web elements of piezo electric material 3 extend substantially in radial direction between the shell body 14 and a respective crankshaft element 13. When the shaft body 10 rotates, the crankshaft elements 13 are rotated such that the web elements 3 are cyclically stronger stressed and (partly) relaxed. With the transmission using the elements 11 and 12, the rotating speed of the crankshafts is substantially increased, such that the stretching frequence of the web element is increased. One system of pinion gear element 12 and crankshaft element 13 with element 3, or as many of those systems as can be positioned along the circumference of the transmission element 11, an all numbers in between, are feasible. Further alternatives are e.g. combinations of individual details of above illustrated embodiments. The web elements can be wire like and they do not have to be pre- stressed.

Claims

1. Electric generator comprising: drive elements, such as one or more vanes or propellors or fans, for converting a fluid flowing around said drive elements into a rotating or pivoting motion;

- transmission elements for converting said rotating or pivoting motion into a cyclic relative motion between: - at least a part of electric power generating elements of piezo-electric material, and

- actuator elements, engageing said power generating elements , such as to generate a deformation of said power generating elements.

2. System according to claim 1, piezo electical material is alternating stretched by a alternating distance between an eccentric journalled pivoting or rotating part and a counter part that is substantially fixed w.r.t. said rotating or pivoting part.

3. System according to claim 2, the ratating part is a crankshaft .

4. System according to claim 2 or 3 , the piezo electical material extends radially between the pivoting or rotating part and the counter part, the one part extends within the other part and the parts preferably have substantial parallel axis.