FR3041156A1 - THERMO ELECTRIC MODULE AND DEVICE, ESPECIALLY FOR GENERATING AN ELECTRICAL CURRENT IN A MOTOR VEHICLE - Google Patents

Abstract

The present invention relates to a thermoelectric module comprising a plurality of electric thermoelectric elements (1n, 1p) having a first coefficient of expansion, in the form of a cylinder or of a right prism and having a central recess, capable of generating an electric current under the action of a temperature gradient exerted between a first said outer face defined by an outer periphery surface and a second inner so-called face defined by an inner periphery surface, a first fluid being intended to flow through the central recess and a second fluid being intended to circulate around the outer periphery, and an envelope (4) obtained in a material having a second coefficient of expansion less than the first coefficient of expansion of the electric thermoelectric elements (1n, 1p) and capping the latter, said envelope (4) comprising at least one compensating volume (5) of the dilation in which extends at least one deformable element (6) resting on the inner wall of the casing (4) and at least one thermoelectric element (1n, 1p).

Description

The present invention relates to a module and a thermoelectric device, in particular for generating an electric current in a motor vehicle.

In the automotive field, has already been proposed electric thermo devices, also called electric thermo generators or TEG according to the acronym "ThermoElectric Generator", using so-called electric thermo elements, to generate an electric current in the presence of a temperature gradient between two of their opposite faces according to the phenomenon known as the Seebeck effect. These devices comprise a stack of first tubes, intended for the circulation of the exhaust gases of an engine, and second tubes, intended for the circulation of a heat transfer fluid of a cooling circuit. The electrical thermo elements are sandwiched between the tubes so as to be subjected to a temperature gradient from the temperature difference between the hot exhaust gases and the cold cooling fluid.

Such devices are particularly interesting because they make it possible to produce electricity from a conversion of the heat coming from the exhaust gases of the engine. They thus offer the possibility of reducing the fuel consumption of the vehicle by replacing, at least partially, the alternator usually provided therein to generate electricity from a belt driven by the engine crankshaft. .

It has already been developed by the applicant annular thermal electrical elements in which the temperature gradient for generating the electric current is imposed between two of their opposite cylindrical faces, the hot fluid and the cold fluid flowing coaxially, one inside the ring and the other outside. This type of thermoelectric elements presents integration difficulties which lead to the commitment of a large amount of material burdening the cost and increasing the thermal inertia of the device.

In order to overcome these drawbacks, the applicant has developed a thermoelectric module comprising annular-shaped thermoelectric elements in which the first fluid and the second fluid circulate transversely relative to one another. Such a thermoelectric module is shown in FIG. 1 and comprises a plurality of annular-shaped electric thermoelectric elements 11, 1p arranged in the longitudinal extension of one another in a coaxial manner, with for example an alternation of elements N-type thermoelectric thermocouples and P-type thermoelectric elements. Each thermoelectric element ln, lp comprises fins 2 extending from the outer periphery, transversely and radially. These fins 2, usually obtained in aluminum or stainless steel and crimped onto the outer diameter of the rings of the thermoelectric elements ln, lp, make it possible to promote heat exchange with the hot exhaust gases flowing through the said rings. fins 2, a cold fluid flowing in the center of the electric thermoelectric elements through an aluminum tube 3, and extracting the maximum of heat from the exhaust gases flowing in an envelope 4 covering said thermoelectric elements ln, lp and the fins 2 between said fins 2 for transferring said heat to thermoelectric materials.

In this type of assembly, the thermoelectric elements ln, lp bear against the end walls of the cylindrical casing 4 and differential expansions appear between the different elements which are obtained in different materials. Thus, the thermoelectric elements ln, lp generally consisting of Bismuth and Tellurium (Bi2Te3), the tube 3 being obtained from aluminum and the casing 4 being obtained in molded ceramic, extruded mica or alumina which have very different coefficients, by a factor of 2 to 3, longitudinal dimensional deviations of several millimeters may appear, said dimensional differences being liable to damage either the envelope 4 or the electric thermo elements ln, lp. For example, the casing 4 undergoes a small longitudinal expansion, represented by the arrow a, while the tube 3 undergoes a large longitudinal expansion, represented by the arrow b, when the exhaust gas has a temperature of about 650 ° C circulate in said casing 4. The invention proposes to improve the situation and concerns for this purpose a thermoelectric module comprising a plurality of electric thermo elements having a first coefficient of expansion, said electric thermo elements being capable of generating an electric current under the action of a temperature gradient exerted between a first so-called outer face and a second so-called inner face, said electric thermoelectric elements being stacked in a stacking direction, said module further comprising a layer obtained in a material having a second coefficient of expansion less than the first coefficient of expansion of the elements thermo electric and styling the latter, said module comprising at least one compensation volume of the expansion, located in the extension of said electric thermo elements in said stacking direction and wherein extends at least one deformable element.

It is clearly understood that the compensation volume and the deformable element or elements make it possible to absorb the differences in length, in particular between the rigid ceramic body and the electric thermoelectric elements, deviations which can be of several millimeters during the operation at high temperature. , of the order of 650 ° C, and prevent a rupture either ceramic or thermoelectric elements.

According to one aspect of the invention, said electric thermo elements are in the form of cylinder or straight prism and having a central recess. Said outer faces are defined by outer periphery surfaces of the electric thermo elements. Said inner faces are defined by inner periphery surfaces of said electric thermo elements. A first fluid is for circulating through the central recess and a second fluid is for circulating around the outer periphery.

According to one aspect of the invention, said material having a second coefficient of expansion forms a casing covering said thermoelectric elements.

Said envelope may include the one or more expansion compensation volumes.

Said deformable element may be supported on an inner wall of the casing and / or on at least one thermoelectric element.

According to one aspect of the invention, said deformable element consists of a washer obtained in a flexible material and resistant to temperatures up to 800 ° C.

According to an exemplary embodiment, said deformable element consists of a graphite washer.

Advantageously, each washer forming a deformable element has a thickness greater than 2 mm.

According to one aspect of the invention, said deformable element consists of a spring washer.

Advantageously, the spring washer is obtained in a metal alloy having a melting point greater than 1000 ° C. and a coefficient of thermal expansion at 20-100 ° C. of less than 15 × 10 -6 K 1.

According to one aspect of the invention, the spring washer is obtained in a metal alloy comprising at least iron, nickel and chromium.

According to an exemplary embodiment, the spring washer consists of a Belleville washer and / or a corrugated washer.

According to another aspect of the invention, said deformable element consists of a pneumatic chamber.

According to one aspect of the invention, the electric thermo elements are stacked on a tube, said tube extending in the central recesses of said electric thermo elements and in a central recess of said one or more deformable element (s). The invention also relates to a thermoelectric device comprising a plurality of modules as described above.

Advantageously, said device is configured to be positioned in a motor vehicle exhaust gas conduit so that said gases circulate in the envelope, said gases defining the second fluid. The invention will be better understood in the light of the following description which is given only as an indication and which is not intended to limit it, accompanied by the attached drawings among which: FIG. 1 is a sectional view longitudinal view of an electrical module of the prior art comprising a plurality of thermal electric elements capped by an envelope, FIG. 2 is a diagrammatic representation in longitudinal section of a thermoelectric module according to the invention, FIG. a schematic representation in longitudinal section of an alternative embodiment of the thermoelectric module according to the invention.

In the figures, identical or similar elements bear the same references.

As illustrated in FIG. 2, the invention relates to a thermoelectric module, said module comprising at least one thermoelectric element 1, here a plurality of thermoelectric elements 11, 1p, in the form of a cylinder or of a right prism and having a central recess, capable of generating an electric current under the action of a temperature gradient exerted between a first so-called outer face defined by an outer periphery surface and a second so-called inner face defined by an inner periphery surface, the second fluid being intended to circulate through the central recess and the first fluid being intended to circulate around the outer periphery, and an envelope 4 covering the said thermoelectric element (s) 1.

It will be noted that the outer and inner faces of the electric thermoelectric elements 1 are for example circular. However, more generally, any section of rounded shape, such as an oval shape for example, and / or polygonal is possible.

Such elements operate, according to the Seebeck effect, by making it possible to create an electric current in a load connected between the inner and outer faces of the thermoelectric elements ln, lp subjected to the temperature gradient. In a manner known to those skilled in the art, such elements consist, for example, of Bismuth and Tellurium (BIT2Te3).

The thermoelectric elements may be, for a first part, elements lp of a first type, said P, making it possible to establish a difference of electric potential in a direction, said positive, when they are subjected to a temperature gradient given, and, for the other part, elements ln of a second type, said N, allowing the creation of a difference of electric potential in an opposite direction, said negative, when they are subjected to the same temperature gradient .

Said electric thermoelectric elements 1 represented consist of a ring in one piece. They may however be formed of several pieces each forming an angular portion of the ring.

The outer surface has, for example, a radius of between 1.5 and 4 times the radius of the inner surface. It could be a radius equal to about 2 times that of the inner surface.

Each thermoelectric element 1 has, for example, two opposite parallel flat faces. In other words, the ring constituting the thermoelectric element 1 is of rectangular annular section.

Said thermoelectric elements lp, ln are arranged, for example, in the longitudinal extension of one another, in particular in a coaxial manner, and the P-type thermoelectric elements alternate with the N-type thermoelectric elements, according to a direction D. They are, in particular, of identical shape and size. They may, however, have a thickness, that is to say a dimension between their two planar faces, different from one type to another, particularly depending on their electrical conductivity.

Said thermoelectric elements lp, ln are, for example, grouped in pairs, each pair being formed of a said P type thermoelectric element and a said N type thermoelectric element, and said module is configured to allow a current flow between the first surfaces of the electric thermoelectric elements 1 of the same pair and a flow of current between the second surfaces of each of the electric thermoelectric elements 1 of the same pair and the thermoelectric element 1 adjacent to the neighboring pair. In this way, a series circulation of the electric current is ensured between the electric thermoelectric elements lp, ln arranged next to one another in the direction D.

For the circulation of fluids, the module according to the invention may comprise a cold liquid circulation channel in contact with said second surface of said thermoelectric elements lp, ln.

According to the above, the cold liquid circulation channel is unique, placed in the center of the module, and consists of an aluminum tube for example. According to one variant, a plurality of cold liquid circulation channels may be provided.

The said liquid circulation channel or channels are, for example, of circular section.

Thus, said module comprises a cold liquid circulation tube 3 on which are mounted a plurality of electric thermoelectric elements 1 of the same type alternating in the direction of longitudinal extension D of the tube 3 with a thermoelectric element of the other type said direction D corresponding to a stacking direction of said electric thermo elements.

Said module may further comprise electrical insulation means, not shown in the figures, arranged between two faces vis-à-vis neighboring electric thermo elements lp, ln according to the longitudinal extension direction D of the tube 3.

Said module may further comprise first electrical connection means, not shown in the figures, connecting the outer periphery surfaces of two of said thermoelectric elements, provided adjacent and of different types. Said first electrical connection means comprise, for example, a layer of electrically conductive material, in particular copper and / or nickel, coating said thermoelectric elements lp, ln.

Said module may also comprise secondary exchange surfaces, in particular fins 2, with the second fluid. In this way, the exchange surface between the electric thermoelectric elements 1 and said second fluid is increased. Said fins 2 are arranged, for example, transversely, in particular radially to said electric thermo elements 1. They are here positioned parallel to each other with a spacing allowing a good heat exchange with the second fluid while limiting the losses of charges. Said fins 2 may be off-center with respect to said thermoelectric elements lp, ln, in particular elongated on the side of the arrival of the second fluid.

Said fins 2 may comprise a catalytic coating to ensure a catalytic conversion of toxic components of the second fluid. In the case of exhaust gas, said module can in this way equip a catalytic converter in addition or substitution of the components conventionally used for catalysis in such equipment.

Said fins 2 are fixed, for example, on said first electrical connection means, in particular by crimping and / or brazing.

The module may further comprise second electrical connection means establishing an electrical connection between the inner periphery surfaces 11b of two of said adjacent thermoelectric elements 1, of different types and not connected by said first electrical connection means.

In other words, said first and second electrical connection means connect in pairs said electric thermoelectric elements 1 so as to establish an electrical circulation in series between said thermoelectric elements 1 of the module.

According to the invention, the casing 4 which has a second coefficient of thermal expansion less than the first coefficient of thermal expansion of the electric thermoelectric elements 1 comprises a so-called expansion compensation volume 5 in which at least one deformable element 6 extends. here bearing on the inner wall of the casing 4, at one end of said casing 4, and on an electric thermo element 1. In the embodiment shown in FIG. 1, said deformable element consists of a circular washer 6 obtained in a flexible material and resistant to temperatures up to 800 ° C. Said washer 6 consists, for example, in a graphite washer having a thickness greater than 2 mm, and in the central hole of which the tube 3 extends. However, it is obvious that the compensation volume 5 can receive several deformable elements 6 such as graphite washers. It will be noted that the dimensions of the compensation volume 5, as well as the dimensions and the number of deformable elements, can easily be determined by those skilled in the art and will depend in particular on the dimensions of each thermoelectric module and the expansion coefficients of the components. electric thermo elements 1, tube 3 and casing 4.

According to an alternative embodiment, not shown in the figures, the thermoelectric module according to the invention comprises two compensation volumes, a compensation volume 5 at each of the ends of the casing 4, in order to compensate for a very large expansion, in particular in the case of modules of great length for example.

Thus, the compensation volume 5 and the deformable element or elements 6 make it possible to absorb the differences in length between the rigid ceramic body of the envelope 4 and the electric thermoelectric elements 1 and / or the tube 3, which can be several millimeters when operating at high temperature, of the order of 650 ° C. In this way, the expansion of the various elements is absorbed in order to prevent a rupture of either the ceramic envelope 4 or the electric thermoelectric elements 1.

In a second exemplary embodiment, with reference to FIG. 3, the envelope 4 which, in the same manner as above, has a second coefficient of thermal expansion less than the first coefficient of thermal expansion of the electric thermoelectric elements 1 comprises a volume 5 said compensation of the expansion in which extends at least one deformable element 6 here bearing on the inner wall of the casing 4, at one end of said casing 4, and on a thermoelectric element 1. This embodiment differs from that previously described in that the deformable element 6 consists of a spring washer such as a Belleville washer or a corrugated washer for example in the central hole of which the tube 3 extends. spring washer is advantageously obtained in a metal alloy having a melting point greater than 1000 ° C. and a coefficient of thermal expansion at 20-100 C of less than 15xl0 "6K" 1. Said spring washer may for example be obtained in a metal alloy comprising at least iron, nickel and chromium.

In the same way as before, the thermoelectric module according to the invention may comprise two compensation volumes, a compensation volume 5 at each end of the envelope 4 without departing from the scope of the invention.

Incidentally, the deformable element or elements 6 may consist of any deformable element well known to those skilled in the art such as a pneumatic or hydraulic chamber for example.

It is understood that the present invention is in no way limited to the embodiments described above and that many modifications can be made without departing from the scope of the appended claims.

Claims (13)

"CLAIMS" 1. Thermoelectric module comprising a plurality of electric thermo elements (ln, lp) having a first coefficient of expansion, said electric thermo elements being capable of generating an electric current under the action of a temperature gradient exerted between a first said outer face and a so-called inner second face, said electric thermoelectric elements being stacked in a stacking direction, said module further comprising a layer (4) obtained in a material having a second coefficient of expansion less than the first coefficient of expansion of the thermoelectric elements (ln, lp) and styling them, said module comprising at least one compensation volume (5) of the expansion, located in the extension of said electric thermo elements in said stacking direction and in which extends to at least one deformable element (6). 2. Module according to claim 1 wherein said deformable element (6) consists of a washer obtained in a flexible material and resistant to temperatures up to 800 ° C. 3. Module according to claim 2 wherein said deformable element (6) consists of a graphite washer. 4. Module according to any one of claims 2 or 3 wherein each washer forming a deformable element (6) has a thickness greater than 2 mm. 5. Module according to claim 1 wherein said deformable element (6) consists of a spring washer. 6. Module according to claim 1 wherein the spring washer is obtained in a metal alloy having a melting point greater than 1000 ° C and a coefficient of thermal expansion at 20-100 ° C of less than 15x10 "6 K'1. 7. Module according to any one of claims 5 or 6 wherein the spring washer is obtained in a metal alloy comprising at least iron, nickel and chromium. 8. Module according to any one of claims 5 to 7 wherein the spring washer consists of a belleville washer. 9. Module according to any one of claims 5 to 7 wherein the spring washer consists of a wave washer. 10. Module according to claim 1 wherein said deformable element (6) consists of a pneumatic chamber. 11. Module according to any one of claims 1 to 10 wherein the electric thermo elements (ln, lp) are stacked on a tube (3), said tube (3) extending in central recesses of said thermoelectric elements ( ln, lp) and in a central recess of said one or more deformable element (s) (6). 12. Thermoelectric device comprising at least one module according to any one of claims 1 to 11 above. 13. Thermoelectric device according to claim 12 configured to be positioned in a motor vehicle exhaust gas duct.