WO2009065411A1

WO2009065411A1 - Device for generating electrical energy

Info

Publication number: WO2009065411A1
Application number: PCT/DK2008/000415
Authority: WO
Inventors: Anders Ostergaard Clausen
Original assignee: Danfoss A/S
Priority date: 2007-11-21
Filing date: 2008-11-20
Publication date: 2009-05-28
Also published as: DE102007055508B4; DE102007055508A1

Abstract

The invention concerns a device (1) for generating electrical energy with at least one piezo element (6, 7). It is endeavoured to enable local generation of electrical energy. For this purpose, at least one thermal expansion element (2) is in active connection with the piezo element (6, 7).

Description

Device for generating electrical energy

The invention concerns a device for generating electrical energy with at least one piezo element.

Such a device is known from US 6,407,484 B1. A piezo element is suspended between two carriers, which are connected to each other by means of two roof-shaped elements. If a force acts upon the ridge of the roof-shaped elements, the piezo element is stretched, and converts mechanical energy into electrical energy. For short, this process is called "generation of electrical energy". In the opposite direction, the piezo element contracts on its own.

US 7,183,937 B2 describes a device for measuring the air pressure in a tyre, the measuring signal being transmitted to the outside in a wireless manner. The electrical energy required to supply the sensors and for the transmission power is generated by an arrangement of piezo elements, which are fixed on the tyre, the tyre here forming the carrying arrange- ment. When the tyre is deformed, also the piezo elements are deformed, thus generating the electrical energy.

The invention is based on the task of enabling local generation of electrical energy.

With a device as mentioned in the introduction, this task is solved in that at least one thermal expansion element is in active connection with the piezo element.

A thermal expansion element is an element, which changes its expansion in connection with a temperature change. For example, the thermal expansion element extends its length, when the temperature rises, and re- duces its length, when the temperature falls. In this connection, often small temperature differences of a few degrees centigrade, or even a fraction of one degree centigrade, will be sufficient to cause a length change. The piezo element and the thermal expansion element are connected to each other. When the thermal expansion element expands or contracts, the piezo element is deformed, thus converting mechanical energy to electrical energy. As in many places, the temperature, to which the thermal expansion element is exposed, is continuously changing; a generation of electrical energy simply by means of the temperature change in the envi- ronment is possible in this way. For example, the temperature in a room with windows, but without any additional measures, will already change due to a more or less intense sun radiation. The temperature change caused by this will be sufficient to generate a certain amount of electrical energy.

Preferably, the piezo element and the thermal expansion element are connected to a carrying device. In this connection, the carrying device does not have to be made in one piece. It is only essential that the expansion change of the thermal expansion element can cause a deformation of the piezo element. The use of a carrying device will give more freedom when locating the thermal expansion element and the piezo element in relation to each other.

Preferably,/the thermal expansion element is arranged in parallel to the piezo element. When the thermal expansion element changes its length, the piezo element is exposed to a tensile stress. As the tension direction is parallel to the polarisation direction of the piezo element, a length change causes a tension generation.

It is preferred that the thermal expansion element is arranged in parallel to several piezo elements. This gives two advantages. Firstly, the same length change of the thermal expansion element will generate a corre- spondingly larger electrical energy. At least, this applies if the thermal expansion element provides a force, which is sufficient to activate several piezo elements at the same time. Secondly, such an arrangement ensures that the bending stress of the piezo element remains small.

This is particularly the case, if the piezo elements surround the thermal expansion element in a uniform manner. For example, opposite sides of the thermal expansion element can be provided with one piezo element. When the thermal expansion element changes its length, the two piezo elements will be equally expanded, and the risk that the thermal expansion element or the piezo elements are bent excessively is kept small.

In an alternative embodiment it may be provided that the thermal expansion element acts transversely to the piezo element. When the thermal expansion element changes its length, the piezo element is bent, thus generating electrical energy.

Preferably, the piezo element is arranged between at least two thermal expansion elements having opposite active directions. With this embodi- ment, the force acting upon the piezo element can be increased, as now two thermal expansion elements are used to compress or stretch the piezo element. At the same time, the distance across which the piezo element is compressed, is increased. These two features increase the amount of generated electrical energy.

Preferably, the piezo element is connected to a rectifier. Depending on the forces acting upon it, the piezo element generates positive or negative voltages. The use of a rectifier may ensure that constantly a voltage with a desired equal polarity is available, which simplifies the further treatment of an electrical energy generated in this way. Preferably, the piezo element is connected to an energy storage. Thus it is possible also to have electrical energy available also if, at the moment when the electrical energy is required, no temperature change takes place. An energy storage can have different embodiments. In the simplest case, a capacitor with a sufficient capacity is used. Also the use of a rechargeable battery, which can also be called an accumulator, is possible.

Preferably, the thermal expansion element has the form of a bellows element. Bellows elements are, for example, known from thermostatic radia- tor valve top parts. They change their length with a sufficient force during a temperature change.

Alternatively, the thermal expansion element can comprise a piston guided in a cylinder. The piston limits a pressure chamber, which comprises a fill- ing, whose volume changes during a temperature change. The filling can be a gas, a liquid or a solid, for example a wax.

Alternatively, the thermal expansion element may comprise a chamber that is closed by a membrane. In this case, a temperature change will de- form the membrane, which will then act directly or indirectly, for example via a tappet or the like, upon the piezo element. Basically, all embodiments of a thermal expansion element can be imagined, in which a volume change occurs, if the temperature of the environment of the thermal expansion element changes.

Preferably, the thermal expansion element has a filling, which is, at least partly, gaseous. A gaseous filling causes a relatively large length change in accordance with the temperature. This applies for both activation directions. At the same time, a sufficient force is made available for acting upon the piezo element. Preferably, the thermal expansion element is connected to an external tank. The external tank then contains the same filling as the thermal expansion element. When, then, the external tank is acted upon by the environmental temperature, the extension of the thermal expansion element changes to an accordingly larger degree. Thus, both the activation length of the thermal expansion element in relation to the temperature and, in certain cases, also the force of the thermal expansion element can be increased.

It is also advantageous, if the thermal expansion element acts upon the piezo element via a gear arrangement. The gear arrangement causes a change of force and travel. Depending on the piezo element used, the gear arrangement can ensure that the thermal expansion element acts upon the piezo element with a reduced force, however, with a longer travel. Of course, also a reversed design of the gear arrangement is possible.

It is preferred that the gear arrangement has a transmission lever. The transmission lever can be one-armed or two-armed. The details depend on the available space.

It is preferred that the thermal expansion element generates a force of at least 15 N. Thus, a thermal expansion element as the one known from thermostatic radiator valve top parts can be used. Here, safety springs of approximately 70 N are already used today. A force of at least 15 N will be sufficient for most piezo elements to generate sufficient electrical energy.

Preferably, the thermal expansion element has a longitudinal extension coefficient of at least 0.25 mm/K. Piezo elements are available, which supply electrical voltage already at a length change of the thermal expansion element of 0.001 mm. This change corresponds to a temperature change of 0.004⁰C. Already smaller temperature changes in the environ- ment of the thermal expansion element will then be sufficient to generate an electrical energy. A temperature change of this small size can practically not be felt by a human being in a room. However, it often exists. Also rooms, which are heated by a thermostatically controlled heating, have temperature fluctuations around the desired value, the temperature fluctuations often being larger than the 0.004⁰C mentioned above.

Preferably, the piezo element supplies an operating energy for an electrical motor. The motor can then be used to displace elements. In a radiator thermostat top part, for example, the electric motor can be used to displace a desired value.

Preferably, the motor and the piezo element are arranged in a common housing, from which an outlet element of the motor projects to the outside. The outlet element of the motor can, for example, be a rotating shaft. However, it is also possible that the motor is a linear motor. In this case, the outlet element has the form of a tappet. Of course, next to the motor and the piezo element also further parts of the device can be arranged in the housing, for example an energy storage and a treatment arrangement.

The invention also concerns a thermostatic radiator valve top part with such a device. The device for generating electrical energy can then be used for many purposes. Many thermostatic radiator valve top parts have an electrical motor for the adjustment of a desired value. The electrical energy required to drive this motor can then be provided by the piezo element, which again is activated by a thermal expansion element. Then, the thermal expansion element that is available in the valve top part anyway can be used to act upon the piezo element. However, also an additional element can be used.

The invention also concerns an alarm system for fire and/or smoke. The alarm system usually requires batteries, so that it can be driven independ- ently. If such an alarm system is provided with at device, at least in the area of its sensors, which provides electrical energy by means of a deformation of a piezo element caused by temperature influences, the periodic battery replacement can be avoided.

In the following, the invention is described on the basis of a preferred embodiment in connection with the drawings, showing:

Fig. 1 a schematic view of a first embodiment of a device for gen- erating electrical energy,

Fig. 2 a perspective view of a second embodiment of a device for generating electrical energy,

Fig. 3 a third embodiment of a device for generating electrical energy,

Fig. 4 a schematic view of a thermostatic radiator valve top part,

Fig. 5 an alarm system for fire and/or smoke,

Fig. 6 a fourth embodiment of a device for generating electrical energy,

Fig. 7 a fifth embodiment of a device for generating electrical energy,

Fig. 8 a sixth embodiment of a device for generating electrical energy,

Fig. 9 a seventh embodiment of a device for generating electrical energy, Fig. 10 the embodiment according to Fig. 6 with a motor,

Fig. 11 the embodiment according to Fig. 10 in a housing, and

Fig. 12 the embodiment according to Fig. 6 as a smoke alarm.

Fig. 1 is a schematic view of a device 1 for generating electrical energy. Here, the electrical energy is generated by a conversion of mechanical energy into electrical energy.

The device 1 has a thermal expansion element 2, in the present case in the form of a bellows element. The thermal expansion element 2 has a folded outer wall 3, which surrounds a hollow inner chamber, not shown in detail, in which a filling is arranged, which is in an at least partly gaseous state. When the temperature changes (rises), to which the thermal expansion element 2 is exposed, the gas filling expands and stretches the thermal expansion element 2. When the temperature falls, the thermal expansion element 2 contracts. Caused by the accordion-like outer wall 3, such an increase or reduction of the length of the thermal expansion element 2 is possible.

The thermal expansion element 2 is arranged between two carriers 4, 5, one carrier 4 being, for the purposes of the following explanation of this embodiment, regarded as a carrying arrangement, as it is fixedly placed in a housing that is not shown in detail. The second carrier 5, however, can be moved in the direction of or away from the first carrier 4 by the thermal expansion element 2. However, the device 1 also works, if none of the carriers 4, 5 are fixedly arranged.

Two piezo elements 6, 7 are arranged between the carriers 4, 5. The piezo elements 6, 7 are both fixedly connected to the two carriers 4, 5, that is, they can be loaded by both stress and pressure in parallel to the expansion direction of the thermal expansion element.

As appears from, for example, Fig. 2, the piezo elements 6, 7 can be con- nected to the carriers 4, 5 by means of rivets 8.

When the thermal expansion element 2 expands, the length of the two piezo elements 6, 7 is increased, that is, they are exposed to tensile stress. When the thermal expansion element 2 contracts, also the piezo elements 6, 7 contract. Both movements make the piezo elements 6, 7 generate an electrical voltage, which can be supplied to a treatment arrangement 13 via cables 9-12. An energy store 14 is connected to said treatment arrangement 13, for example in the form of a capacitor or a rechargeable battery, that is, an accumulator.

The piezo elements 6, 7 will be activated, already when the length of the thermal expansion element 2 has increased by 0.001 mm. The thermal expansion element 2 is made so that such an increase occurs already with a temperature increase of 0.004°. Thus, the length change or expansion coefficient of the thermal expansion element amounts to at least 0.25 mm/K. The force thus generated by the thermal expansion element 2 amounts to at least 15 N. If a thermal expansion element like the one that is at the moment applied in many radiator thermostat valve top parts is used, this provides a substantial force surplus, as such thermal expansion elements 2 generate a larger force. Thus, preferably, a bellows element is used as thermal expansion element 2, the bellows element having a relatively soft outer wall 3 and being filled with an aggressive filling, that is, a filling, whose volume changes relatively much in connection with a temperature change.

If the electrical energy does not have to be stored, the energy store 14 and, in certain cases, also the treatment arrangement 13 can be avoided. As only relatively small temperature changes in the environment of the thermal expansion element 2 are required to generate electrical energy, it must be assumed that the device 1 can continuously supply electrical energy. Temperature changes below 0.05⁰C can hardly be felt by a human 5 being. However, they happen in many cases, for example, if the room, in which the device 1 is located, is heated by a thermostatically controlled radiator. Also with a fast responding control such temperature variations can practically not be avoided. o Fig. 2 shows a modified embodiment, in which the same elements have the same reference numbers. For reasons of clarity, the treatment arrangement 13 and the energy storage 14 are not shown here.

Here, the thermal expansion element 2 has a different embodiment. It has5 a tappet 15, which is supported at the carrier 5. Further, the thermal expansion element 2 has a body 16, which is supported at the carrier 4. The body 16 may contain a solid filling, for example, a wax. If the temperature in the environment of the thermal expansion element 2 increases, the wax expands and pushes the tappet 15 out of the body 16. This exposes the 0 piezo elements 6, 7 to a tensile stress and their length increases, so that an electrical energy can be supplied via the cables 9, 10 or 11 , 12.

In the embodiment according to Figs. 1 and 2, the piezo elements 6, 7 are exposed to a tensile stress and steered. Fig. 3 shows a modified embodi-5 ment, in which, for reasons of clarity, the carrying arrangement with the carriers 4, 5 is not shown. Same elements and elements with the same functions are provided with the same reference numbers as in Figs. 1 and 2.

o Here, the thermal expansion element 2 has the same embodiment as in

Fig. 2. The tappet 15 that projects from the body 16, however, does not stress the piezo element 6 in its longitudinal direction, but in a transverse direction. As appears from a comparison of the Figs. 3a and 3b, the piezo element 6 is bent, when the tappet 15 is pressed out of the body 16. Also with such a bending stress, the piezo element 6 supplies a voltage via the cables 9, 10. This voltage can, if required, be treated by the treatment ar- rangement 13 and stored in the energy storage 14.

Fig. 4 is a strictly schematic view of a radiator thermostat valve top part 17, which acts upon a valve element 18 interacting with a valve seat 19. Thus, the valve element 18 controls the inlet of heating fluid from an inlet 20 into a radiator pipe 21.

In a manner known per se, the thermostatic valve top part 17 has a thermostatic element 22, which expands at a temperature rise, thus moving the valve element 18 closer to the valve seat 19. At a temperature fall, the valve element 18 is lifted from the valve seat 19. The thermostatic element 22 can be made in the same way or similar to the thermal expansion element 2 in the device according to Fig. 1.

A motor 23, which is fixed in a housing 24 of the thermostatic valve top part 17, changes the length of the thermostatic element 22 inside the housing, and thus also the desired value. With an unchanged length of the thermostatic element 22, moving the thermostatic element 22 away from the valve seat 19 will cause the release of a larger opening cross-section between the valve element 18 and the valve seat 19.

The motor 23 is an electric motor. In order to activate the motor, an electrical energy is therefore required. This electrical energy is supplied by the arrangement 1, in which, in this embodiment, the carrier 5 is fixed at the housing 24 via a piston 25. If the temperature of the thermal expansion element 2 changes during a temperature change, the other carrier 4 will be displaced, thus exposing the piezo elements 6, 7 to tension or pressure, so that they provide an electrical power, which can be stored in the energy storage to be made available for the activation of the motor 23 on need. In a manner not shown in detail, the motor 23 can comprise a control device, which can be controlled via a radio signal or the like, to start the motor 23.

Fig. 5 shows a fire or smoke alarm arrangement 26, which is part of a system for fire or smoke alarm. Also here, a device 1 for electrical energy generation is arranged in a housing 27 and supplies electrical energy via the energy storage 14 to a transmitter 28, which is also arranged in the housing 27. The required information to be transmitted is obtained by means of a sensor 29.

Fig. 6 shows an embodiment, which in principle corresponds to that of Fig. 1. The thermal expansion element 2 and the piezo element 6 are arranged in a common housing 30, so that the thermal expansion element 2 presses the piezo element 6 against the housing 30. In this case, the housing 30 forms a carrying arrangement. In this embodiment, the piezo element 6 is stressed by pressure and tension.

A rectifier 31 is arranged between the piezo element 6 and the treatment arrangement 13. In dependence of its force activation in the tension and the pressure directions, the piezo element 6 supplies a positive and a negative voltage. The rectifier 31 ensures that a voltage with the same polarity is always available at the treatment arrangement 13.

Fig. 7 shows a modified embodiment, in which the piezo element 6 is suspended between two bellows elements 2a, 2b. The two bellows elements 2a, 2b are supported at the housing 30.

In the embodiment according to Fig. 8, the bellows element 2 is connected to an external tank 32 via a pipe 33, through which a filling of the thermal expansion element 2 can get to and from the tank 32. If the tank 32 is ex- posed to the environment temperature, the filling inside expands. The tank 32 has a constant volume, meaning that the filling can only escape into the thermal expansion element 2. The extension of the thermal expansion element 2 then changes to an increased degree in dependence of the 5 temperature.

With the embodiment according to Fig. 9, the thermal expansion element 2 is connected to the piezo element 6 via a gear arrangement 34. The gear arrangement 34 has a two-armed lever 35, which can be swivelled around0 a rotation point 36, which is connected to the housing 30. An arm 37 facing the thermal expansion element 2 is longer than an arm 38 facing the piezo element 6. When the thermal expansion element 2 expands, the piezo element 6 is compressed by a smaller distance. The relation between the compression and the expansion occurs from the relation be-5 tween the lengths of the arms 37, 38. The smaller compression of the piezo element 6 occurs together with larger force activation.

It applies for all embodiments that the piezo element 6 is not only connected to the thermal expansion element 2 via a connection transferring0 pressure, the connection also transfers tensional forces. Accordingly, the thermal expansion element 2 will extend the length of the piezo element 6 again, if the temperature falls and the thermal expansion element 2 decreases its extension. 5 In the arrangement according to Fig. 10, the device according to Fig. 6 is connected to an electric motor 23, whose output element 39 can adopt practically any desired activation elements. In the simplest case, the output element 39 is an output shaft, which rotates on activation of the motor 23. If the motor 23 is a linear motor, the output element 39 can also be a o tappet. In the embodiment according to Fig. 11, the device according to Fig. 10 is arranged in a housing 40, in which the motor 23, the thermal expansion element 2, the piezo element 6, the rectifier 31 , the treatment arrangement 13 and the energy store 14 are arranged in a housing 24. Merely the out- put element 39 projects to the outside. Of course, the housing 24 can also comprise activation elements, for example for controlling the motor 23.

The embodiment according to Fig. 12 in principle corresponds to the embodiment according to Fig. 5. However, it has been generalized. A sensor 40, which is connected to the energy storage 14, can be acted upon by some external influence value 41. One example is a smoke alarm, whose sensor 40 establishes the presence of smoke. In a similar manner, a fire alarm can be made, whose sensor 40 detects fire, light, heat or the like. The sensor 40 can also be a hygrometer, an anemometer, a temperature sensor or the like. It receives its energy from the piezo element 6.

For reasons of simplicity, the thermal expansion element 2 is shown as a bellows element. In principle, however, any element can be used, in which, during a change of the environment temperature, a volume change of a filling, that is, a fluid, a gas or a solid, causes an extension change, in particular a length change, which again can be used to compress or bend a piezo element. It can, for example, also be a piston-cylinder arrangement or a chamber, which is ended by a membrane.

The influencing temperature can be a room temperature, an outdoor temperature etc. However, also the temperature of a small, local area can be used, which is detected by means of some kind of "remote sensor".

Additionally, the combination of thermal expansion element 2 and piezo element 6 can also be used as temperature sensor, that is, a certain voltage occurs at a certain temperature. The piezo element 6 can be used individually (so-called bulk) or in combination with one or more other piezo elements (so-called "stack"). In the latter case, the statements in the description with regard to one single piezo element also apply for the "stack".

Claims

Patent Claims

1. Device for generating electrical energy with at least one piezo ele- ment, characterised in that at least one thermal expansion element

(2) is in active connection with the piezo element (6, 7).

2. Device according to claim 1 , characterised in that the piezo element (6, 7) and the thermal expansion element (2) are connected to a carrying device (4, 5).

3. Device according to claim 1 or 2, characterised in that the thermal expansion element (2) is arranged in parallel to the piezo element (6, 7).

4. Device according to claim 3, characterised in that the thermal expansion element (2) is arranged in parallel to several piezo elements (6, 7).

5. Device according to claim 4, characterised in that the piezo elements (6, 7) surround the thermal expansion element (2) in a uniform manner.

6. Device according to claim 2, characterised in that the thermal expan- sion element (2) acts transversely to the piezo element (6).

7. Device according to one of the claims 2 to 6, characterised in that the piezo element (6) is arranged between at least two thermal expansion elements (2a, 2b) having opposite active directions.

8. Device according to one of the claims 1 to 7, characterised in that the piezo element (6, 7) is connected to an energy storage (14).

9. Device according to one of the claims 1 to 8, characterised in that the piezo element is connected to a rectifier.

10. Device according to one of the claims 1 to 9, characterised in that the thermal expansion element (2) has the form of a bellows element (3).

11. Device according to one of the claims 1 to 9, characterised in that the thermal expansion element (2) comprises a piston guided in a cylin- der.

12. Device according to one of the claims 1 to 9, characterised in that the thermal expansion element (2) comprises a chamber that is closed by a membrane.

13. Device according to one of the claims 10 to 12, characterised in that the thermal expansion element (2) has a filling, which is, at least partly, gaseous.

14. Device according to one of the claims 1 to 13, characterised in that the thermal expansion element (2) is connected to an external tank (32).

15. Device according to one of the claims 1 to 14, characterised in that the thermal expansion element (2) acts upon the piezo element (6) via a gear arrangement (34).

16. Device according to claim 16, characterised in that the gear arrangement (34) has a transmission lever (35).

17. Device according to one of the claims 1 to 16, characterised in that the thermal expansion element (2) generates a force of at least 15 N.

18. Device according to one of the claims 1 to 17, characterised in that the thermal expansion element (2) has a longitudinal extension coefficient of at least 0.25 mm/K.

19. Device according to one of the claims 1 to 18, characterised in that the piezo element (6) supplies an operating energy for an electrical motor (23).

20. Device according to claim 19, characterised in that the motor (23) and the piezo element (6) are arranged in a common housing (24), from which an outlet element (39) of the motor (23) projects to the outside.

21. Thermostatic radiator valve top part with a device according to one of the claims 1 to 20.

22. Alarm system for fire and/or smoke with a device according to one of the claims 1 to 20.