WO2008101533A1

WO2008101533A1 - Power generator using an electro-active polymer

Info

Publication number: WO2008101533A1
Application number: PCT/EP2007/010474
Authority: WO
Inventors: Willem Johan Anton Teulings
Original assignee: Continental Automotive France
Priority date: 2007-01-22
Filing date: 2007-12-03
Publication date: 2008-08-28
Also published as: FR2911733A1; FR2911733B1

Abstract

The invention relates to a power generator that uses an electro-mechanical transducer including a layer of an electro-active polymer material (10) provided between two electrodes (12, 12', 14, 14'). The layer of electro-active polymer material (10) is built into a bellows (2) made of a flexible material surrounding a universal joint-type connection between two non-aligned shafts (4, 6) and rotated therewith. The layer of electro-active polymer material (10) and the electrodes (12, 12', 14, 14') extend longitudinally relative to two shafts (4, 6), the electrodes (12, 12', 14, 14') being provided in facing positions on either side of the layer of electro-active polymer material (10).

Description

Electric generator using an electroactive polymer

The present invention relates to an electric generator using an electroactive polymer.

The field concerned by the present invention is in particular the field of automobile construction. In this field, a growing number of sensors and actuators are used. Their power supply poses some problems. In the design of the vehicle for example, it is necessary to provide passages of power cables. The increasing number of cables causes an increase in the mass of copper used in the vehicle. Given these elements, it is also necessary to provide a battery capable of supplying power to all these components. The batteries used therefore become more and more powerful and more and more heavy. This leads to heavier vehicles and therefore greater fuel consumption.

We also note that some electronic devices are in permanent movement relative to the chassis of the vehicle; it is therefore necessary to provide flexible cables for the power supply of these devices. Such cables are very expensive because they have to withstand very high stresses.

In the case where a mobile sensor is to be powered, an electric battery can also be integrated in the sensor, but this causes problems of maintenance, service life, size, recycling and costs. There are also wireless sensors and without on-board electrochemical energy source. They are equipped with a receiver / transducer receiving electromagnetic energy from a transmitting antenna. This technology consumes a lot of electricity because only a small part of the energy emitted by the antenna is received at the receivers. In addition, as the transmission distance increases, the risk of electromagnetic disturbance increases.

The idea at the origin of the present invention is to use electroactive polymers (known in particular under the English abbreviations EAP for "ElectroActive Polymer") to produce an electricity generator delocalized in a motor vehicle. One of the aims of the invention is to offer the possibility of replacing certain sensors powered by a wire by wireless sensors and without on-board electrochemical energy source (such sensors are said to be "autarkic"). The wireless transmission of electrical energy to supply sensors can be done only over short distances, it is necessary to have a nearby electrical generator and mechanically secured to the wireless sensor. This can be particularly interesting for fully mobile sensors (tire pressure sensor for example), sensors located in places in constant motion but whose amplitude is limited by relative to the chassis of the vehicle (wheel speed sensor on the triangle or suspension height sensor / attitude height) or sensors near high temperature devices such as elements of an exhaust or an element of the exhaust gas treatment chain. The present invention then proposes an electric generator comprising an electromechanical transducer comprising at least one layer of electroactive polymer material each disposed between two electrodes.

According to the present invention, the layer of electroactive polymer material is integrated into a bellows of flexible material axially surrounding a cardan-type connection between two non-aligned shafts and rotated with them, and the layer of electroactive polymer material and the electrodes extend longitudinally with respect to the shafts, the electrodes being arranged opposite one another on either side of the layer of electroactive polymer material. To be able to follow the permanent deformations of the electroactive material, the electrodes must also be flexible. This can be achieved by choosing electrodes in the form of metal sheets (aluminum / steel) but more advantageously still polymers of conductive material.

In this way, the electroactive polymer material is, during a rotation, sometimes compressed, sometimes stretched. An alternating electric field therefore appears and a corresponding potential difference is created between the electrodes. This electric generator is operational as soon as it is rotated.

In order to make best use of the deformations of the bellows, a layer of electroactive polymer material forms a continuous sleeve, and at least two pairs of electrodes are distributed around the periphery of the sleeve of electroactive polymer material, two electrodes of the same pair of electrodes. electrodes facing each other by being separated by the electroactive polymer sleeve. The two pairs of electrodes preferably cover almost the entire inner and outer surface of the sleeve made of electroactive polymer material. In this way, it is possible to optimize the energy recovery related to the deformation of the sleeve. In this embodiment having several pairs of electrodes, a preferred variant can be provided in which two pairs of electrodes surround the electroactive polymer sleeve, each electrode being electrically insulated from the other electrodes, and in which also each electrode extends over about 180 ° at the periphery or inside the sleeve.

It is also possible to provide another variant in which three or four pairs of electrodes surround the electroactive polymer sleeve, each electrode being electrically insulated from the other electrodes, and in which also each electrode extends over approximately 120 °, respectively 90 ° to the periphery or inside the sleeve. In order to power an electronic device such as an electronic sensor, an electric generator according to the invention advantageously also comprises means for transforming the output voltage of at least one pair of electrodes, such as, for example, a down converter. DC-DC voltage (such as a Buck converter) preceded by a single or double recovery stage.

To promote power generation when the generator has several pairs of electrodes, the electrodes are advantageously connected to a recovery capacitor, each pair of electrodes being associated with a single or double rectifier stage. The present invention also relates to a protective bellows for a cardan type connection of two non-aligned shafts, characterized in that it incorporates an electric generator as described above. In such a protective bellows, the electrodes preferably extend substantially over the entire length of the bellows to benefit the best deformations in it during its rotation. The present invention also relates to a shaft rotation sensor, characterized in that it comprises an electric generator as described above, and in that this generator is integral with the shaft whose rotation speed and / or the angular position is measured.

Details and advantages of the present invention will emerge more clearly from the description which follows, made with reference to the appended diagrammatic drawings in which:

FIG. 1 schematically shows a gimbal bellows used for producing a generator according to the invention,

FIG. 2 illustrates the stress in the polymer layer of the bellows of FIG. 1 at point A; FIG. 3 represents the stresses in the polymer layer for point A 'of FIG. 1,

FIG. 4 is a front view of the bellows and the electric generator of FIG. 1,

FIG. 5a is an electrical diagram illustrating the supply of a position sensor from an electrical generator according to the invention with double rectification and provided with two electrodes,

FIG. 5b is an electrical diagram illustrating the supply of a position sensor from an electrical generator according to the invention with double rectification and provided with two pairs of electrodes, FIG. 6 is an electrical diagram illustrating the supplying a position sensor from an electrical generator according to the invention with simple rectification and provided with two pairs of electrodes FIG. 7 is an electrical diagram of an angular position sensor including a level shift stage,

FIG. 8 is an electrical diagram for the use of a generator according to the invention with a wheel speed sensor with JK or D ₁ rocker. FIG. 9 represents the "raw" output voltage of a pair of electrodes. ,

FIG. 10 schematically represents the scaled voltage (Vsc of FIG. 7) by means of the resistive network R / 1000R,

FIG. 11 schematically represents the output voltage Vo of FIG. 7, and FIG. 12 schematically represents the waveform of the signal Vs of FIG. 8.

Figure 1 shows a bellows 2 protecting a connection, for example by gimbal, between two axes 4 and 6 inclined axially with respect to one another. The first axis 4 drives for example the second axis 6 in rotation. There is such a bellows at a wheel of a motor vehicle and at the connection of the wheel shaft at the output of the gearbox (in traction vehicles). The shaft 4 is then for example a transmission shaft connected to a differential and the shaft 6 is for example a wheel shaft. The articulation between these two shafts is protected by the bellows 2 inside which there may be a lubricant. The bellows 2, in a conventional manner, is in the form of a tubular sleeve with longitudinal corrugations. Thus, a cross section through the bellows is circular in shape but the diameter of the section varies depending on the longitudinal position of the cross section.

The original idea underlying the present invention is to integrate an electric generator in such a bellows. This generator uses electroactive polymer materials. When such a material is deformed, an electric field appears on its surface. This phenomenon is reversible and thus when such a material is subjected to an electric field it extends or retracts, depending on the orientation of the field. The use of such a material is therefore advantageous in the present application since the bellows 2 is deformed permanently when the shaft 4 drives the shaft 6 in rotation.

In such an application, it is not possible to use piezoelectric materials because the deformations experienced by the bellows greatly exceed the limited elasticity of most piezoelectric materials. In addition, the electroactive polymer materials have the advantage of having a high specific energy density. It is thus possible to generate 0.4 J / g with such materials. Large deformations are also acceptable by these materials (often greater than 250% of the initial length) and their cost is very interesting. In the field For example, electroactive polymers based on acrylic elastomer, silicone, polyurethane, fluoro-silicones, fluoroelastomers, isoprene, polybutadiene, natural rubber or latex can be used. The performance of such dielectric elastomeric materials is very interesting. FIG. 2 represents on an enlarged scale a longitudinal section made in the bellows 2 at the zone A of FIG. 1. This section makes it possible to appreciate the structure of the interior of the bellows 2. The external surface of the bellows 2 is formed an outer layer 8 made of a flexible material such as, for example, rubber. The material usually used for the production of a similar bellows can be used here. Inside the bellows, protected by the outer layer e, there is an electrical generator comprising in particular a layer of an electroactive polymer material, hereinafter referred to as the EAP layer 10. An outer electrode 12 is disposed between the EAP layer 10 and the outer layer 8 while an inner electrode 14 is disposed facing the outer electrode 12 on the opposite face of the EAP layer 10, inside the bellows 2.

The electrodes 12 and 14 extend longitudinally with respect to the bellows 2. Thus, during the rotation of the bellows 2, driven by the rotation of the shafts 4 and 6, the electroactive polymer material between the electrodes is in the same state. stretching or compression. FIG. 4 shows an end view of the bellows 2 of FIG. 1. It should be noted that, in the embodiment shown, the electric generator inside the bellows 2 has two external electrodes 12 and 12 'and two electrodes. 14 and 14 '. For best efficiency, each of the electrodes extends over the entire length of the bellows 2 or, preferably at least over the entire length of the corrugated portion of the bellows 2, that is to say the entire length of the bellows 2 is deforming. Of course, the electrodes are always separated by the EAP layer 10 so that the latter also extends preferably over the entire length of the bellows 2 or preferably over at least the entire length of the corrugations of this bellows. This EAP layer 10 thus preferably resumes the shape of the outer layer 8. It has only a very slightly smaller diameter and possibly a different thickness.

As can be seen in FIG. 4, each of the electrodes 12, 12 ', 14, 14' extends over approximately 180 °. The outer electrodes 12, 12 'as well as the inner electrodes 14, 14' are separated from each other by insulating elements 16 extending in each case over the entire length of the corresponding electrodes. It is advantageous to choose electrodes in conducting polymer material, since the thermal and mechanical properties will be closer to those of the EAP material only in the case of metal electrodes (eg steel or aluminum sheets).

In summary, there is therefore a corrugated tubular sleeve with longitudinal corrugations of electroactive polymer material inside which are two inner electrodes extending longitudinally and covering each time about 180 ° the inner face of the sleeve of electroactive polymer material. . The outer face of the sleeve of electroactive polymer material is in turn covered by two outer electrodes extending longitudinally and in the form of a half sleeve covering the sleeve of electroactive polymer material. Each outer electrode is disposed facing an inner electrode, the electroactive polymer material thus forming the dielectric of a pair of electrodes (inner electrode and corresponding outer electrode).

The embodiment shown is a preferred embodiment that has two pairs of electrodes. However, it is conceivable to use only one pair of electrodes. These electrodes are then facing and preferably extend at most 180 ° around the longitudinal axis of the bellows 2. Thus, it is preferable to use a sleeve of electroactive polymer material and to cover all its inner surface and any its outer surface of electrodes (except of course insulating elements necessary to separate the electrodes). Two pairs of electrodes are then preferably provided but it may be envisaged to have more than two pairs of electrodes without departing from the scope of the present invention.

In FIGS. 2 and 3, the arrows 18 schematically represent the stresses in the EAP 10 layer. FIG. 2 corresponds to a section in zone A of FIG. 1 in which the electroactive polymer material is stretched, while FIG. at the same cut but when the trees have rotated 180 °, that is to say when the same material is in the area A 'of Figure 1. The electroactive polymer material is compressed.

The electric generator thus produced provides an alternating voltage at the electrodes. The latter is not directly usable by a sensor or other electronic device. It should therefore be straightened and adapted. For the embodiment shown in FIG. 4, it is proposed to use a processing unit 20 (including a single or double rectification stage - as shown in FIGS. 5a, 5b and 6 - as well as a switching power supply 26), allowing the conversion of a voltage of a given value to another value, having very good electrical efficiencies, and potentially reversible. This is for example a DC-DC step down converter, usually called Buck converter. As shown in this FIG. 4, each input of the processing unit 20 is connected to an electrode of a pair of electrodes according to the polarity of the generated voltage. The processing unit 20 then makes it possible to obtain a DC voltage Vo at the output.

In order to bias the electroactive material to a point of optimum electromechanical efficiency, it is possible to use a bi-directional power supply in place of the switching power supply 26, but it is then necessary to dispense with the stage rectification between the electrodes and bi-directional power supply.

This voltage source can be used to power a sensor. A first application of such a self-powered sensor is a speed sensor and / or wheel position. It is noted in fact that the signal provided by the electrodes is an alternating signal identifiably linked by a computer to the angular position of the bellows, and therefore of the same frequency as the rotation of the corresponding wheel. It is therefore easy to deduce the position of the wheel by analyzing the signal supplied by the electrodes of the electric generator (see Fig. 11). It is also possible, using the signal obtained, to know the angular velocity of the wheel (see Fig. 12). In order to be able to use this electrical generator integrated in the bellows 2 as a speed and / or position sensor, it must be ensured that the rotation of the bellows is synchronous with the rotation of the wheel, that is to say with Trees 4 and 6. Usually, the bellows are mounted by clamping using a collar or equivalent means. It is necessary to provide a bellows mounting 2 on the shafts 4 and 6 in a predetermined position to allow the indexing of the angular position of the wheel. This can be obtained mechanically in a very simple way by providing for example a polarizer. Just provide one or more teeth on the shafts and corresponding recesses on the bellows 2. It can thus ensure a known position of the bellows 2 with the shafts 4 and 6 throughout the life of the bellows 2. In addition, when the mounting of a new bellows, it can resume exactly the same position as the defective bellows.

FIGS. 5a, 7 and 8 show electrical diagrams making it possible, from the signal received by a pair of electrodes 12, 14 or 12 ', 14', to supply a position and / or speed sensor. In FIG. 5a, a pair of electrodes 12, 14 is connected to a bridge-type rectifier bridge of Graetz 22. This bridge is then connected to terminals A and B of a capacitor C (designed to withstand high voltages) as well. at the terminals of a switching power supply 26. At the output of this power supply, the position and / or speed sensor 28 is connected. This sensor 28 is preferably associated with an antenna 30 for emitting electromagnetic signals 31 indicating the result of the measurement made by the sensor 28. Figure 7 shows an electrical diagram for mounting a wheel position sensor with level shift. The signal coming from a pair of electrodes 12, 14 passes into a voltage divider (resistors 1000R1 and R1) and is then processed by an operational amplifier 29 associated with resistors R2 to provide a signal Vo representative of the position of the wheel.

Figure 8 shows a mounting for a wheel speed sensor. Here we find a divider bridge (resistors 1000R and R) which is associated with an electronic flip-flop 32, for example a flip-flop of JK or D type. A signal Vs representative of the speed of the wheel is then obtained at the output. Fig. 9 shows the output voltage across a pair of electrodes. In the example given here, there is a voltage amplitude of about 2000 V, but with an offset of 500 V (the numerical values are given by way of illustrative example but are not limiting). This is because the relationship between the output voltage and the stress level is not linear for the electroactive materials. The curve shown in Figure 9 is not entirely representative of reality since the output voltage is not quite a sinusoidal function, although periodic.

Figure 10 shows the voltage of Figure 9 scaled. This voltage is obtained at the output of a resistive network R1 / 1000 R1 and corresponds to the voltage Vsc of FIG. 7. Since this voltage can be of negative value, a stage with the operational amplifier 29 is provided to shift the level of this tension. The output voltage of this amplifier is shown in Fig. 11 (Vo in Fig. 7). It is exploitable by an automobile computer to identify the angular position of the axis around the bellows. The output voltage of a pair of bellows electrodes scaled by a resistive network Vsc can also be introduced into the electronic flip-flop 32 (as shown in FIG. 8), whose output (Vs) will be exploitable for evaluate the speed of rotation of the axis around bellows. FIG. 12 then gives the waveform of the signal Vs obtained. It should be noted that the electronic flip-flop 32 can be implemented in a software way or not. FIG. 5b shows for its part an embodiment of a voltage generator according to the invention and provided with two pairs of electrodes, each of the pairs being associated with a rectifier bridge similar to that of FIG. 5a, said bridge the rectifier being connected to the terminals A and B of a capacitor C as well as to the terminals of a switching power supply 26. At the output of this switching power supply 26, the position and / or velocity sensor 28 is connected. This sensor 28 is preferably associated with an antenna 30 for emitting electromagnetic signals 31 indicating the result of the measurement made by the sensor 28. Figure 6 also shows an electrical diagram for the use of the generator as an electric generator. Here the two pairs of electrodes are used. There is a similar arrangement to that of FIG. 4, involving here two diodes D and a capacitor C. The electrodes are thus connected to the terminals A and B of the capacitor C and to a switching power supply 26. The output terminals are recovered at this switching power supply 26 a DC voltage that can be used to power a sensor 28 or any other electronic device.

As can be seen from the foregoing, the generator described above makes it possible to provide a source of energy from two shafts driven in rotation, the two shafts being not aligned in the axial direction. This energy source is advantageously used to power sensors and make them autarkic sensors to measure quantities including the rotation that is the source of energy. In the case of a wheel and the mounting of a generator at a gimbal bellows, the energy source thus obtained can be used as a speed and angular position sensor for electronic systems known as ABS and ESP or equivalent electronic systems.

The generator according to the invention has the great advantage of not being cumbersome, of being integrated into an existing and durable organ and of being able to be implanted in a motor vehicle in places that are difficult to access because they are at the level of a room movement (the wheel for example).

The present invention is not limited to the preferred embodiment described above by way of non-limiting example and to the variants mentioned. It also relates to the embodiments within the scope of the skilled person.

Claims

An electric generator comprising an electromechanical transducer comprising at least one layer of electroactive polymer material (10) each disposed between two electrodes (12, 12 ', 14, 14'), characterized in that the layer of electroactive polymer material ( 10) is integrated with a bellows (2) of flexible material surrounding a cardan-type connection between two non-aligned shafts (4, 6) and rotated with them, and in that the layer of electroactive polymer material (10) and the electrodes (12, 12 ", 14, 14) 'extend longitudinally with respect to the shafts (4, 6), the electrodes (12, 12', 14, 14 ') being arranged opposite one another on either side of the layer of electroactive polymer material (10).

Electric generator according to claim 1, characterized in that a layer of electroactive polymer material (10) forms a continuous sleeve, and in that at least two pairs of electrodes (12, 12 ', 14, 14') are distributed at the periphery of the sleeve of electroactive polymer material, two electrodes of the same pair of electrodes facing each other being separated by the electroactive polymer sleeve (10).

Electric generator according to Claim 2, characterized in that two pairs of electrodes surround the electroactive polymer sleeve (10), in that each electrode (12, 12 ', 14, 14') is electrically insulated from the other electrodes, and in that each electrode (12, 12 ', 14, 14') extends about 180 ° at the periphery or inside the sleeve.

4. Electrical generator according to one of claims 1 to 3, characterized in that it further comprises means (20) for transforming the output voltage at the supply level of conventional electronic sensors, at least one pair of electrodes.

5. Electrical generator according to one of claims 2 or 3, characterized in that at least two pairs of electrodes are connected to a recovery capacitor C each pair of electrodes (12, 12 ', 14, 14') being associated with a single or double rectifier.

6. Bellows (2) protection for a cardan type connection of two shafts (4, 6) not aligned in the axial direction, characterized in that it integrates an electric generator according to one of claims 1 to 5.

7. bellow (2) protection according to claim 6, characterized in that the electrodes (12, 12 ', 14, 14') extend substantially over the entire length of the bellows (2).

8. shaft rotation sensor, characterized in that it comprises an electric generator according to one of claims 1 to 5, and in that this generator is integral with the shaft (6) whose rotation speed and / or the angular position is measured through the output voltage of the electric generator.