JP2008147304A - Thermoelectric conversion element - Google Patents

Abstract

Provided is a thermoelectric conversion element capable of simplifying the structure of the entire element and thus simplifying the manufacturing process.
A thermoelectric conversion element 15 includes a thermoelectric material 16 having a skutterudite crystal structure, a pair of permanent magnets 17 and 18 disposed so as to face each other with the thermoelectric material 16 interposed therebetween, Means for generating a temperature gradient ΔT3 in the direction perpendicular to the direction of the magnetic field B2 generated by the thermoelectric material 16, and the thermoelectric material 16 spaced apart in the circumferential direction n orthogonal to the direction of the magnetic field B2 and the direction of the temperature gradient ΔT3, respectively. A pair of electrodes 19 and 20 are provided.
[Selection] Figure 4

Description

  The present invention relates to a Nernst effect, a thermoelectric conversion element that uses both the Nernst effect and the Seebeck effect, and an exhaust heat recovery device for an internal combustion engine including the thermoelectric conversion element.

  In recent years, thermoelectric conversion elements using the Seebeck effect are known as devices for converting thermal energy into electrical energy. Here, the Seebeck effect is a phenomenon in which when a temperature difference is applied to both ends of a semiconductor, a potential difference is generated between both ends of the semiconductor due to the movement of electrons generated between the high-temperature end and the low-temperature end.

  As such an element, for example, there is an element composed of two types of semiconductors, an n-type thermoelectric semiconductor and a p-type thermoelectric semiconductor. As shown in FIG. 6, this element includes an n-type thermoelectric material 100 made of an n-type semiconductor and a p-type thermoelectric material 101 made of a p-type semiconductor. Then, one end 100a of the n-type thermoelectric material 100 and one end 101a of the p-type thermoelectric material 101 are connected via the heat collecting electrode plate 102, and heat is radiated to the other ends 100b and 101b of the both thermoelectric materials 100 and 101, respectively. Electrode plates 103 and 104 are attached. In this element, when the heat collecting electrode plate 102 is heated by the heat from the heat source, the heat collecting electrode plate 102 is transmitted to the heat radiating electrode plates 103 and 104 via the n-type thermoelectric material 100 and the p-type thermoelectric material 101. Heat is dissipated by the heat radiation electrode plates 103 and 104. At this time, due to the Seebeck effect, a negative potential is generated in the heat dissipation electrode plate 103 of the n-type thermoelectric material 100, and a positive potential is generated in the heat dissipation electrode plate 104 of the p-type thermoelectric material 101. The generated voltage between 104 can be taken out as electric power.

On the other hand, in recent years, for example, a thermoelectric conversion element described in Patent Document 1 is well known in order to improve electric characteristics such as a power generation voltage and power generation efficiency in the thermoelectric conversion element. As shown in FIG. 7, this element has a saddle-type structure in which an n-type thermoelectric material 110 and a p-type thermoelectric material 111 are joined via a heat collecting electrode plate 112 as a basic element. Thus, a plurality of basic elements are connected in series. By connecting a plurality of basic elements in series via the heat dissipation electrode plate 113 in this way, the total number of the n-type thermoelectric material 110 and the p-type thermoelectric material 111 is increased, so that the electrical characteristics of the element can be improved. it can. Further, in this element, since the n-type thermoelectric material 110 and the p-type thermoelectric material 111 can be arranged in a planar shape, the entire structure of the element can be made thin.
JP 2004-014995 A

  By the way, when a structure in which a plurality of basic elements are connected in series via a heat dissipation electrode plate, such as a thermoelectric conversion element described in Patent Document 1, the following problems cannot be ignored. .

  That is, the structure of the entire element becomes complicated, and the process for manufacturing the element also becomes complicated. In particular, such a tendency becomes conspicuous when an element described in Patent Document 1 is arranged on a fluid pipe or the like having a curved outer periphery. That is, as shown in FIG. 8, when the thermoelectric conversion element 121 is arranged on the outer periphery of the member 120 whose outer periphery is bent, the thermoelectric material and the electrode of the element are respectively matched with the outer peripheral shape of the member 120. Since it needs to be processed, the process for manufacturing the element is further complicated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a thermoelectric conversion element capable of simplifying the structure of the entire element and thus simplifying the manufacturing process.

In the following, means for achieving the above object and its effects are described.
The invention according to claim 1 intersects a thermoelectric material having a skutterudite crystal structure, a pair of permanent magnets disposed so as to face each other with the thermoelectric material interposed therebetween, and a magnetic field direction generated by the permanent magnet. The gist is provided with a means for generating a temperature gradient in the direction in the thermoelectric material, and a pair of electrodes disposed on the thermoelectric material apart from each other in the direction intersecting the magnetic field direction and the temperature gradient direction.

  According to the configuration, the voltage generated between the electrodes can be increased by using the Nernst effect and increasing the lengths of the thermoelectric material and the permanent magnet in the direction intersecting the magnetic field direction and the temperature gradient direction. Here, when the thermoelectric material is placed in a magnetic field, the electrical characteristics of the thermoelectric material change, but holes are more likely to affect the change than the electrons of the thermoelectric material. Therefore, a higher Nernst effect can be obtained with a thermoelectric material having a higher hole mobility. In this regard, according to the above configuration, since the thermoelectric material has a skutterudite-type crystal structure in which the hole mobility is higher than the electron mobility, the Nernst effect can be enhanced, and power generation The voltage can be further increased. As a result, the structure of the entire element can be simplified, and the manufacturing process thereof can be simplified as compared with a configuration in which the generated voltage is increased by dividing the element including the thermoelectric material into a plurality of parts. It becomes like this. In this case, the pair of electrodes may be spaced apart in the direction intersecting with the magnetic field direction and the temperature gradient direction, respectively, but these electrodes are spaced apart in directions orthogonal to the magnetic field direction and the temperature gradient direction, respectively. It is desirable for enhancing the Nernst effect.

  The invention according to claim 2 is summarized in that, in the thermoelectric conversion element according to claim 1, the pair of electrodes is disposed on each side surface of the thermoelectric material in a direction intersecting the magnetic field direction.

According to this configuration, since the electrodes can be separated as much as possible, the voltage generated between the electrodes can be further increased by the Nernst effect.
The gist of the invention according to claim 3 is that, in the thermoelectric conversion element according to claim 1 or 2, the pair of electrodes are arranged in the thermoelectric material so as to be separated in the direction of the temperature gradient.

According to this configuration, the generated voltage between the electrodes can be further increased by using the Seebeck effect in addition to the Nernst effect.
Further, as such a thermoelectric conversion element, a thermoelectric material containing CoSb ₃ can be employed as described in claim 4.
Furthermore, by having such an element structure, for example, as described in claim 5, even an element in which the thermoelectric material has a cylindrical shape can be manufactured easily. .

  The invention according to claim 6 comprises the thermoelectric conversion element according to any one of claims 1 to 5, wherein the thermoelectric material has a side surface in the direction in which the temperature gradient is generated of an exhaust pipe of an internal combustion engine. The gist is to be disposed so as to be in contact with the outer peripheral surface.

  According to this configuration, the heat energy discharged to the outside from the exhaust pipe of the internal combustion engine can be recovered as electric energy, and the fuel efficiency of the internal combustion engine can be improved. Further, the temperature range of about 300 ° C. to 600 ° C. at which the power generation efficiency of the thermoelectric material having a skutterudite crystal structure is large is substantially equal to the temperature change range of the exhaust pipe during operation of the internal combustion engine. A higher conversion efficiency from energy to electrical energy can be ensured.

  In order to increase the recovery efficiency, a thermoelectric material having a cylindrical shape as described in claim 5 is provided, and the thermoelectric material is brought into contact with and covers the outer peripheral surface of the exhaust pipe. It is preferable to employ a configuration that is arranged.

  Hereinafter, a thermoelectric conversion element and an exhaust heat recovery apparatus for an internal combustion engine using the thermoelectric conversion element according to the present invention will be described with reference to FIGS. In the following, first, the principle of power generation of the thermoelectric conversion element will be described with reference to FIGS. 1 to 3, and then an exhaust heat recovery apparatus for an internal combustion engine using the thermoelectric conversion element will be described with reference to FIG.

  First, the principle of power generation by the Seebeck effect will be described with reference to FIG. Here, the thermoelectric conversion element is formed in a rectangular parallelepiped shape. As shown in FIG. 1, the thermoelectric material 1 is provided with electrodes 2 and 3 on one side surface 1a and a side surface 1b located on the opposite side of the side surface 1a. In such a thermoelectric conversion element, a Seebeck voltage Vs having a magnitude corresponding to the temperature gradient ΔT1 is generated between the electrodes 2 and 3 by making one of the side surfaces 1a and 1b high and keeping the other low. To do.

  Next, the principle of power generation by the Nernst effect will be described with reference to FIG. As shown in FIG. 2, the thermoelectric material 4 is provided with permanent magnets 5 and 6 so as to cover one side surface 4a and a side surface 4b opposite to the side surface 4a. Further, in the thermoelectric material 4, electrodes 7 and 8 are disposed on the side surfaces 4c and 4d that are orthogonal to the side surfaces 4a and 4b and in parallel with each other at positions facing the thermoelectric material 4, respectively. ing. In such a thermoelectric material 4, by keeping one of the side surfaces 4e and 4f orthogonal to the side surfaces 4a to 4d at a high temperature and the other at a low temperature, a Nernst voltage Vn having a magnitude corresponding to the temperature gradient ΔT2 is obtained. It occurs between the electrodes 7 and 8. Here, the direction of the magnetic field B1 generated by the permanent magnets 5 and 6, the direction in which the temperature gradient ΔT2 is generated, and the direction m in which the electrodes 7 and 8 are disposed are perpendicular to each other.

  Subsequently, the structure of the thermoelectric conversion element using both the Seebeck effect and the Nernst effect described above will be described with reference to FIG. In the following description, members having the same functions as those of the thermoelectric conversion element shown in FIG. 2 are denoted by the same reference numerals and description thereof is omitted. In the thermoelectric conversion element shown in FIG. 2, in the thermoelectric material 4, the electrodes 7 and 8 are disposed at positions facing each other across the thermoelectric material 4. In the thermoelectric conversion element shown in FIG. 3, these electrodes are arranged. 9, 10 are spaced apart in the direction in which the temperature gradient ΔT2 occurs. Specifically, the electrodes 9 and 10 are end portions on the opposite sides of the side surfaces 4c and 4d on which the electrodes 9 and 10 are arranged so that the distance between the electrodes 9 and 10 in the direction in which the temperature gradient ΔT2 occurs is the longest. Respectively.

Further, the thermoelectric material 4 is made of CoSb ₃ having a skutterudite crystal structure. A material having a skutterudite type crystal structure has material characteristics in which electron mobility is higher than hole mobility. In this thermoelectric conversion element, the Seebeck voltage Vs is generated between the electrodes 9 and 10 because the electrodes 9 and 10 are separated in the direction of the temperature gradient ΔT2. Further, in this thermoelectric conversion element, the electrodes 9 and 10 are spaced apart from each other in the direction m perpendicular to the direction of the magnetic field B1 and the direction of the temperature gradient ΔT2, so that the Nernst voltage is between the electrodes 9 and 10. Vn is generated. That is, in the thermoelectric conversion element shown in FIG. 3, an effect combining the Seebeck effect and the Nernst effect can be obtained, and a voltage Vs + Vn obtained by adding the Seebeck voltage Vs and the Nernst voltage Vn is generated. In this thermoelectric conversion element, the voltage Vs + Vn is increased by increasing the lengths of the thermoelectric material 4, the electrode 9, and the electrode 10 in the direction m perpendicular to the direction of the magnetic field B1 and the direction in which the temperature gradient ΔT2 is generated. Can do.

Next, an embodiment in which the thermoelectric conversion element shown in FIG. 3 is used in an exhaust heat recovery device for an internal combustion engine will be described with reference to FIG.
As shown in FIG. 4, a thermoelectric conversion element 15 formed in a cylindrical shape with an end is in contact with the outer peripheral surface of the exhaust pipe 14 of the internal combustion engine. The thermoelectric conversion element 15 is roughly arranged at a thermoelectric material 16 made of CoSb ₃ having a skutterudite-type crystal structure, and at each end 16a, 16b in the longitudinal direction of the exhaust pipe 14 in the thermoelectric material 16. The permanent magnets 17 and 18 are configured. These permanent magnets 17 and 18 generate a magnetic field B 2 in the longitudinal direction of the exhaust pipe 14. The exhaust pipe 14 is made of a material having nonmagnetic characteristics, for example, aluminum, even in a state where the exhaust pipe 14 is heated and heated to a high temperature. As a result, the magnetic fluxes of the magnets 17 and 18 pass through the exhaust pipe 14, and the magnetic flux passing through the thermoelectric material 16 is reduced by that amount, thereby preventing the magnetic field strength from being lowered. An insulating member such as silicon or mica is interposed between the exhaust pipe 14 and the thermoelectric conversion element 15, and the exhaust pipe 14 and the thermoelectric conversion element 15 are electrically disconnected.

  Further, a heat insulating member such as glass wool or ceramic wool is interposed between the exhaust pipe 14 and the permanent magnets 17 and 18 to suppress heat transfer from the exhaust pipe 14 to the permanent magnets 17 and 18. I am doing so. In general, magnetic members such as the permanent magnets 17 and 18 have a characteristic that the magnetic field becomes weaker as the temperature increases. For this reason, when the temperature of the permanent magnets 17 and 18 rises due to the heat transmitted from the exhaust pipe 14 to the thermoelectric conversion element 15, the Nernst effect of the thermoelectric conversion element 15 may be reduced. Therefore, by interposing a heat insulating member between the exhaust pipe 14 and the permanent magnets 17 and 18 as described above, such a decrease in Nernst effect is suppressed.

  Furthermore, as shown in the enlarged view of FIG. 4, an electrode 19 is disposed on one end surface 16 c in the circumferential direction of the thermoelectric material 16 on the outermost side in the radial direction of the thermoelectric material 16. An electrode 20 is disposed on the inner end 16 d in the radial direction of the thermoelectric material 16 on the other end face 16 d in the circumferential direction of the thermoelectric material 16.

  According to such a thermoelectric conversion element, when exhaust gas flows into the exhaust pipe 14 by operating the internal combustion engine, the inner peripheral surface of the thermoelectric material 16 that is in contact with the outer peripheral surface of the exhaust pipe 14 is exposed to the outside air. It becomes high temperature compared with the outer peripheral surface cooled by being carried out. Therefore, a temperature gradient ΔT3 is generated in the radial direction of the thermoelectric material 16. Since the electrodes 19 and 20 are spaced apart in the direction in which the temperature gradient ΔT3 is generated, the Seebeck voltage Vs is generated between the electrodes 19 and 20. Further, in this thermoelectric conversion element, the electrodes 19 and 20 are spaced apart from each other along the circumferential direction n orthogonal to the direction of the magnetic field B2 and the direction in which the temperature gradient ΔT3 occurs. The Nernst voltage Vn is generated between 20. That is, the thermoelectric conversion element 15 can obtain an effect that combines the Seebeck effect and the Nernst effect, and generates a voltage Vs + Vn obtained by adding the Seebeck voltage and the Nernst voltage. In the thermoelectric conversion element 15, the generated voltage is increased by increasing the lengths of the thermoelectric material 16 and the permanent magnets 17 and 18 in the circumferential direction n orthogonal to the direction of the magnetic field B2 and the direction of the temperature gradient ΔT3.

As described above in detail, according to the present embodiment, the following effects can be obtained.
(1) A pair of permanent magnets 17 and 18 disposed so as to face each other with the thermoelectric material 16 interposed therebetween, and a temperature gradient ΔT3 in a direction perpendicular to the direction of the magnetic field B2 generated by the permanent magnets 17 and 18 are given to the thermoelectric material 16. Each electrode by utilizing the Nernst effect and increasing the length of the thermoelectric material 16 and the permanent magnets 17 and 18 in the circumferential direction n orthogonal to the direction of the magnetic field B2 and the direction of the temperature gradient ΔT3. The voltage generated between 19 and 20 can be increased. Here, when the thermoelectric material 16 is placed in a magnetic field, the electrical characteristics of the thermoelectric material 16 change. However, the holes are more likely to affect the change than the electrons of the thermoelectric material 16. Therefore, a higher Nernst effect can be obtained with a thermoelectric material having a higher hole mobility. In this regard, in the thermoelectric conversion element 15, since the thermoelectric material 16 has a skutterudite type crystal structure in which the hole mobility is higher than the electron mobility, specifically, CoSb ₃ is adopted, the Nernst The effect can be enhanced and the generated voltage can be further increased. As a result, the structure of the entire element can be simplified and the manufacturing process thereof can be simplified as compared with the configuration in which the generated voltage is increased by dividing the element including the thermoelectric material 16 into a plurality of elements. It becomes like this. In this case, the pair of electrodes 19 and 20 may be spaced apart from each other in the direction intersecting with the direction of the magnetic field B2 and the direction of the temperature gradient ΔT3, but the electrodes 19 and 20 are separated from each other with the direction of the magnetic field B2 and the temperature gradient ΔT3. In order to enhance the Nernst effect, it is desirable to dispose them in a circumferential direction n orthogonal to the directions.

  (2) Since the pair of electrodes 19 and 20 are disposed on the end faces 16c and 16d of the thermoelectric material 16 in the circumferential direction n orthogonal to the direction of the magnetic field B2, the voltage generated between the electrodes 19 and 20 due to the Nernst effect Can be further increased.

  (3) Since the pair of electrodes 19 and 20 are spaced apart from each other in the direction of the temperature gradient ΔT3 and disposed on the thermoelectric material 16, by utilizing the Seebeck effect in addition to the Nernst effect, The generated voltage can be further increased.

(4) Even if the thermoelectric material 16 is an element having a cylindrical shape like the thermoelectric conversion element 15, it can be easily manufactured.
(5) By disposing the thermoelectric conversion element 15 in the exhaust pipe 14 of the internal combustion engine, the heat energy discharged from the exhaust pipe 14 to the outside can be recovered as electric energy, and the fuel efficiency of the internal combustion engine is improved. Will be able to. Further, the temperature range of about 300 ° C. to 600 ° C. at which the power generation efficiency of the thermoelectric material 16 having the skutterudite crystal structure is large is substantially equal to the temperature change range of the exhaust pipe 14 during operation of the internal combustion engine. Also, higher conversion efficiency from heat energy to electrical energy can be ensured.

In addition, the said embodiment can also be implemented as the following forms which changed this suitably, for example.
As shown in FIG. 5, a thermoelectric conversion element 30 having a laminated structure in which a plurality of thermoelectric materials 31 and 32 and magnets 33, 34, and 35 are sequentially laminated may be employed. By adopting such a laminated structure, the generated voltage can be further increased.

  In the above embodiment, the exhaust pipe 14 is formed from a material having non-magnetic characteristics, but may be formed from a magnetic material, for example, magnetic stainless steel. Further, in this case, the magnetic field strength caused by the magnetic flux of the permanent magnets 17 and 18 passing through the exhaust pipe 14 by interposing a material having non-magnetic characteristics between the exhaust pipe 14 and the thermoelectric conversion element 15. It is desirable to suppress the decrease in the above.

  In order to protect the thermoelectric conversion element 15, for example, when a member covering the thermoelectric conversion element is provided, the same member is also formed of a nonmagnetic material in order to suppress a decrease in magnetic field strength as much as possible. It is desirable to suppress the decrease in magnetic field strength.

  In the above embodiment, the heat insulating member is interposed between the permanent magnets 17 and 18 and the exhaust pipe 14, but the inner peripheral surface of the thermoelectric conversion element 15 is used to suppress the temperature rise of the permanent magnets 17 and 18. It is also possible to employ a configuration in which a heat insulating member is disposed between the whole and the exhaust pipe 14. However, in this case, there is a concern that the Seebeck effect is lowered due to the decrease in the temperature gradient ΔT3. For this reason, it is desirable to set the material and shape of the heat insulating member in consideration of the balance between the Nernst effect and the Seebeck effect in the thermoelectric conversion element 15.

  In the above embodiment, the electrode 19 and the electrode 20 are disposed on the outermost and innermost sides in the radial direction on the end faces 16c and 16d in the circumferential direction of the thermoelectric material 16, respectively. If the pair of electrodes are disposed at positions separated from each other in the direction, power generation by the Seebeck effect can be performed. Further, even if the electrodes 19 and 20 are arranged at the same position in the radial direction, power generation by the Nernst effect can be performed.

In the above embodiment, CoSb ₃ is adopted as the thermoelectric material 16, but other skutterudite-type crystals such as RhSb ₃ , IrSb _3, etc., including other materials in addition to the CoSb ₃ A material having a structure may be employed.

  In the above embodiment, the exhaust pipe is exemplified as a means for heating the thermoelectric element and generating a temperature gradient in the thermoelectric element, but other heat recovery devices such as an EGR pipe may be applied.

The schematic diagram for demonstrating the Seebeck effect. The schematic diagram for demonstrating the Nernst effect. The schematic diagram which shows the structure of a thermoelectric conversion element. The perspective view of an exhaust heat recovery device. The schematic diagram which shows the modification of the thermoelectric conversion element of an exhaust heat recovery apparatus. The schematic diagram which shows the structure about the conventional thermoelectric conversion element. The schematic diagram which shows the structure about the other conventional thermoelectric conversion element. The perspective view which shows the structure about the other conventional thermoelectric conversion element.

Explanation of symbols

  1, 4, 16, 31, 32, 100, 101 ... thermoelectric material, 1a, 1b, 4a-4f ... side face, 2, 3, 7-10, 19, 20 ... electrode, 5, 6, 17, 18, 21 , 33, 34, 35 ... permanent magnet, 14 ... exhaust pipe, 15, 30, 121 ... thermoelectric conversion element, 16a, 16b ... end, 16c, 16d ... end face, 100, 110 ... n-type thermoelectric material, 100a, 101a ... one end, 100b, 101b ... the other end, 101, 111 ... p-type thermoelectric material, 102, 112 ... heat collecting electrode plate, 103, 104, 113 ... heat radiation electrode plate, 120 ... member.

Claims (6)

A thermoelectric material having a skutterudite-type crystal structure;
A pair of permanent magnets arranged to face each other with the thermoelectric material interposed therebetween;
Means for causing the thermoelectric material to generate a temperature gradient in a direction intersecting with the direction of the magnetic field generated by the permanent magnet;
A thermoelectric conversion element comprising: a pair of electrodes disposed in the thermoelectric material apart from each other in a direction intersecting with the magnetic field direction and the temperature gradient direction. In the thermoelectric conversion element according to claim 1,
The pair of electrodes is disposed on each side surface of the thermoelectric material in a direction intersecting the magnetic field direction. In the thermoelectric conversion element according to claim 1 or 2,
The pair of electrodes are disposed on the thermoelectric material so as to be separated from each other in the temperature gradient direction. In the thermoelectric conversion element as described in any one of Claims 1-3,
The thermoelectric conversion element, wherein the thermoelectric material contains CoSb ₃ . In the thermoelectric conversion element as described in any one of Claims 1-4,
The thermoelectric conversion element is characterized in that the thermoelectric material is formed in a cylindrical shape with ends. Comprising the thermoelectric conversion element according to any one of claims 1 to 5,
An exhaust heat recovery device for an internal combustion engine, wherein the thermoelectric material is disposed such that a side surface in a direction in which the temperature gradient is generated contacts an outer peripheral surface of an exhaust pipe of the internal combustion engine.

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