Patent Application
20180315915
The present invention relates to a thermoelectric module and a thermoelectric device, in particular intended to generate an electric current in a motor vehicle.
In the automotive field thermoelectric devices, also termed thermoelectric generators (TEG), have already been proposed using so-called thermoelectric elements enabling generation of an electric current in the presence of a temperature gradient between two of their opposite faces by the phenomenon known as the Seebeck effect. These devices comprise a stack of first tubes, intended for the circulation of the exhaust gases from an engine, and second tubes, intended for the circulation of a heat transfer fluid from a cooling circuit. The thermoelectric elements are sandwiched between the tubes so as to be subjected to a temperature gradient resulting from the temperature difference between the hot exhaust gases and the cold cooling fluid.
Such devices are of particular interest because they enable production of electricity by conversion of heat coming from the exhaust gases of the engine. They therefore offer the possibility of reducing the fuel consumption of the vehicle through being substituted, at least in part, for the alternator usually provided therein to generate electricity by means of a belt driven by the crankshaft of the engine.
There have already been developed by the applicant thermoelectric elements of annular shape in which the temperature gradient enabling generation of the electric current is imposed between two of their opposite cylindrical faces, the hot fluid and the cold fluid circulating coaxially, one inside the ring and the other outside it. This type of thermoelectric element is difficult to integrate and this leads to the use of a large quantity of material adding to the unit cost and increasing the thermal inertia of the device.
To remedy these disadvantages, the applicant has developed a thermoelectric module including thermoelectric elements of annular shape in which the first fluid and the second fluid circulate transversely relative to one another. A thermoelectric module of this kind is represented in
To channel the hot gases across the fins 2, there is usually employed a cylindrical enclosure capping the fins 2 of the thermoelectric elements 1 that are assembled in the form of a cylindrical pencil, the thermoelectric elements pencil 1 being inserted in the cylindrical enclosure the inside diameter of which is adjusted to suit the outside diameter of the fins 2 which then have a circular shape. In order to produce a thermoelectric generator, a plurality of pencils can be assembled together, the number of pencils depending on the required electrical power.
The various elements of these thermoelectric modules are generally assembled by brazing and this type of assembly by brazing is generally not the optimum. Actually, this type of assembly necessitates compatibility of the materials to be assembled in order to accommodate the differential expansion stresses of the various elements and problems with brazing the chosen alloy or alloys.
The invention proposes to improve on the situation to optimize assembly and to that end concerns a thermoelectric module comprising at least one plurality of cylindrical thermoelectric elements comprising a circular central opening receiving a central tube, said thermoelectric elements being adapted to generate an electric current because of a temperature gradient exerted between a first, so-called exterior face defined by an exterior periphery surface and a second, so-called interior face defined by an interior periphery surface, a first fluid being intended to circulate through the central tube and a second fluid being intended to circulate around the exterior periphery, said central tube being made of aluminum and having a wall thickness between 150 and 500 μm inclusive.
This is therefore a tube enabling mechanical assembly, that is to say by expansion of its section.
According to various embodiments of the invention, separately or in combination:
The invention also concerns a thermoelectric device comprising a plurality of modules as described above.
Said device is advantageously configured to be positioned in a motor vehicle exhaust gas pipe so that said gases circulate between the fins, said gases defining the second fluid.
The invention will be better understood in the light of the following description which is given by way of illustration only and not to limit the invention, accompanied by the appended drawings in which:
In the figures, identical or analogous elements carry the same references.
As shown in
It will be noted that the exterior face 11a and the interior face 11b of the thermoelectric elements 1 are for example circular. However, more generally, any section of rounded shape, such as an oval shape for example, and/or a polygonal shape, is possible.
Elements of this kind operate in accordance with the Seebeck effect, enabling an electric current to be created in a load connected between the interior face 11b and the exterior face 11a of the thermoelectric elements 1n,1p subjected to the temperature gradient.
The thermoelectric elements could be, for a first part, elements 1p of a first, so-called P type, enabling an electric potential difference to be established in a so-called positive direction when they are subjected to a given temperature gradient, and, for the other part, elements 1n of a second so-called N type enabling the creation of an electric potential difference in an opposite, so-called negative direction when they are subjected to the same temperature gradient.
Said thermoelectric elements 1 represented are constituted of a one-piece ring. They could however be formed from a plurality of parts each forming an angular portion of the ring.
The exterior surface 11a has, for example, a radius between 1.5 and 4 times inclusive the radius of the interior surface 11b. This could be a radius equal to approximately twice that of the interior surface 11b.
Said thermoelectric element 1 has, for example, two opposite parallel plane faces. In other words, the ring constituting the thermoelectric element 1 is of rectangular annular shape.
Said thermoelectric elements 1p, 1n are disposed, for example, longitudinally in line with one another, in particular in a coaxial manner, and the type P thermoelectric elements alternate with the type N thermoelectric elements in a direction D. They are in particular of identical shape and size. They could however have a thickness, that is to say a dimension between their two plane faces, different from one type to another, in particular as a function of their electrical conductivity.
Said thermoelectric elements 1p, 1n are, for example, grouped in pairs, each pair being formed of one of said type P thermoelectric elements and one of said type N thermoelectric elements, and said module is configured to enable circulation of current between the first surfaces of the thermoelectric elements 1 of the same pair and circulation of current between the second surfaces of each of the thermoelectric elements 1 of said same pair and the adjacent thermoelectric element 1 of the adjacent pair. This ensures that the electric current flows in series between the thermoelectric elements 1p, 1n disposed one alongside the other in the direction D.
Said module further comprises electrical insulation means 6 disposed between two facing faces of adjacent thermoelectric elements 1p, 1n in the longitudinal direction D in which the tube 5 extends.
Referring to
Said module advantageously comprises secondary exchange surfaces, in particular fins 2, for exchanges with the exhaust gases. This increases the area of exchange between the thermoelectric elements 1 and the exhaust gases. Said fins 2 are disposed transversely, for example, in particular radially relative to said thermoelectric elements 1. Here they are positioned parallel to one another with a gap enabling good exchange of heat with the second fluid whilst limiting head losses.
Said fins 2 could comprise a catalytic coating to provide catalytic conversion of toxic components of the second fluid. In the case of exhaust gas, said module could therefore equip a catalytic converter in addition to instead of the catalysis components conventionally used in such equipments.
Said fins 2 are constituted of circular washers comprising a flange 8 fastened to the interior edge of said washers, said flange 8 having a width greater than the thickness of said fin 2.
In this embodiment, the flanges 8 of the fins 2 extend on only one side of said fins 2. However, it is obvious that the flanges 8 could extend on either side of the fins 2 without this departing from the scope of the invention.
Said fins 2 are fixed to the exterior electrode 6 by crimping as described in detail hereinafter.
In this embodiment, the fins 2 are plane and extend parallel to one another; however, in order to improve the performance of the fins 2, that is to say the convection between the hot exhaust gases and the fins 2, said fins 2 could be corrugated.
In an ancillary manners, said fins 2 could have a rough surface state, produced by sandblasting for example, in order also to improve the efficacy of said fins.
Moreover, the module also comprises second electrical connection means 9 establishing an electrical connection between the interior periphery surfaces of two adjacent thermoelectric elements 1 of different types not connected by said electrical connection means 8.
In other words, said first electrical connection means 7 and said second electrical connection means 9 connect said thermoelectric elements 1 two by two so as to establish a series electrical circuit between said thermoelectric elements 1 of the module.
Referring to
The exterior surface of the central tube 5 includes an electrical insulation layer 10 the thickness of which is between 25 and 150 μm inclusive. This electrical insulation layer 10 is made of alumina. This layer enables prevention of a short circuit between all the pairs of thermoelectric elements 1n,1p. Its thickness enables insulation of the aluminum of the central tube 5 from the tubular interior electrode 9 whilst not constituting too high a thermal resistance. Moreover, the tubular interior electrode 9 is made of copper with a thickness between 80 and 300 μm inclusive. The external surface of the tubular interior electrode 9 includes a so-called diffusion barrier layer 11 to prevent diffusion of the brazing elements, said diffusion barrier 11 having a thickness between 1 and 10 μm inclusive. This diffusion barrier 11 is preferably made of nickel. It enables prevention of diffusion of the brazing elements to the adjoining layer and vice versa. Moreover, between the interior face of the thermoelectric element 1 and the diffusion barrier layer 11, a brazed joint 12 having a thickness between 5 and 100 μm inclusive is deposited, said brazed joint 12 being made of a metal alloy including aluminum or tin. The interior face of the thermoelectric element 1 advantageously includes a so-called second diffusion barrier layer 13 having a thickness between 1 and 10 μm inclusive. This second diffusion barrier 13 is constituted of a plurality of layers made of metal or metal alloys and an external nickel layer in contact with the brazed joint 12. Each thermoelectric element 1 has a thickness between 1 and 10 mm inclusive and is preferably made of magnesium silicide or manganese silicide. It will be noted that the edge of the interior face of the thermoelectric elements 1 are beveled. These bevels 14 enable prevent of flash on the brazed joint 12.
Moreover, referring to
It will be noted that the edges of the exterior face of the thermoelectric elements 1 are chamfered. These chamfers 19 enable prevention of flash on the brazed joint 16.
It will be seen that these various layers described in detail above enable optimized assembly and robustness of the thermoelectric module.
It is understood that the present invention is in no way limited to the embodiments described above and that modifications can be made thereto without departing from the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1558643 | Sep 2015 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2016/052259 | 9/9/2016 | WO | 00 |
