DE102010030259A1 - Thermoelectric module for internal combustion engine of motor car, has semiconductor elements that are arranged in interstice formed between hot and cold sides, where remaining volume of interstice is filled by insulating material - Google Patents

Abstract

The module (1) has p-doped and n-doped semiconductor elements (7) arranged alternately in interstice formed between hot side (2) and cold side (4), where 70% of surfaces of hot and cold sides are contacted with the elements. Interstice is filled by 70% of the elements and remaining volume is filled by insulating material. Heat conductivity of thermoelectric module is adjusted between 40-60% of total temperature difference between hot and cold sides based on arrangement of elements in interstice so that temperature difference between the sides is reduced. Independent claims are included for the following: (1) method of manufacturing thermoelectric module; and (2) motor car.

Description

The present invention relates to a thermoelectric module for generating electrical energy, for. B. from the exhaust of an internal combustion engine, by means of a generator. This means, in particular, a generator for converting thermal energy of an exhaust gas into electrical energy, that is to say a so-called thermoelectric generator.

The exhaust gas from an engine of a motor vehicle has thermal energy, which can be converted by means of a thermoelectric generator into electrical energy, for example, to fill a battery or other energy storage or electrical loads to supply the required energy directly. Thus, the motor vehicle is operated with a better energy efficiency, and it is available for the operation of the motor vehicle energy to a greater extent.

Such a thermoelectric generator has at least a plurality of thermoelectric conversion elements. Thermoelectric materials are of a type that can effectively convert thermal energy into electrical energy (Seebeck effect) and vice versa (Peltier effect). Such thermoelectric conversion elements preferably have a multiplicity of thermoelectric elements which are positioned between a so-called hot side and a so-called cold side. Thermoelectric elements include z. B. at least two semiconductor elements (p- and n-doped), which are mutually provided on their upper and lower sides (towards the hot side or cold side) with electrically conductive bridges. Ceramic plates or ceramic coatings and / or similar materials serve to insulate the metal bridges and are thus preferably arranged between the metal bridges. If a temperature gradient is provided on both sides of the semiconductor elements, a voltage potential forms between the ends of the semiconductor element. The charge carriers on the hotter side are increasingly excited by the higher temperature in the conduction band. Due to the difference in concentration in the conduction band, charge carriers diffuse on the colder side of the semiconductor element, which results in the potential difference. In a thermoelectric module, numerous semiconductor elements are electrically connected in series. So that the generated potential difference of the serial semiconductor elements does not cancel each other out, alternate semiconductor elements with different majority charge carriers (n- and p-doped) are always brought into direct electrical contact. By means of a connected load resistor, the circuit can be closed and thus electrical power can be tapped.

It has already been tried to provide corresponding thermoelectric generators for use in motor vehicles, especially passenger cars. However, these were usually very expensive to manufacture and characterized by a relatively low efficiency. Thus, no serial production could be achieved.

On this basis, it is an object of the present invention, at least partially solve the problems described with reference to the prior art. In particular, a thermoelectric module is to be specified, which is suitable for versatile applications, and which allows improved efficiency in terms of the conversion of provided thermal energy into electrical energy while taking into account the introduced amount of costly semiconductor material.

These objects are achieved with a thermoelectric module according to the features of patent claim 1 and by a method for producing a thermoelectric module according to the features of claim 5. Advantageous embodiments of the device according to the invention and the integration of these devices in higher-level units and their use are dependent on formulated claims. It should be noted that the features listed individually in the claims in any technologically meaningful way, can be combined with each other and show other embodiments of the invention. The description, in particular in conjunction with the figures, further explains the invention and leads to additional embodiments of the invention.

• a) höchstens 70% der ersten Fläche oder/und der zweiten Fläche ist mit Halbleiterelementen kontaktiert, und
• b) höchstens 70% des Zwischenraums ist durch die Halbleiterelemente ausgefüllt.

The thermoelectric module according to the invention has at least one hot side with a first surface and a cold side with a second surface and an intermediate space between the hot side and the cold side, wherein in the intermediate space a plurality of p- and n-doped semiconductor elements is alternately arranged alternately electrically connected to each other. In the thermoelectric module at least one of the two conditions is fulfilled:

• a) at most 70% of the first surface and / or the second surface is contacted with semiconductor elements, and
• b) at most 70% of the gap is filled by the semiconductor elements.

In this case, the remaining volume of the gap between the semiconductor elements is filled by an insulating material and the thermal conductivity of the thermoelectric module at an operating point by the at least one condition a) and b) is set so that between 40% and 60% of the total temperature difference of hot side and cold side drops over the thermoelectric module.

It is very particularly preferred that both conditions a) and b) are satisfied.

The thermoelectric device proposed here is composed in particular in layers or in layers, in particular with a plurality of (identical) modules to form a thermoelectric generator. In particular, a plurality of interconnected modules form a thermoelectric generator. The thermoelectric module is arranged in particular in a housing in which a plurality of thermoelectric modules can be arranged together as a unit for forming a thermoelectric generator.

In particular, the thermoelectric module additionally has sealing means which limit the gap for the semiconductor elements in the installation space and terminate to the outside. Preferably, in particular at the ends of the module, connecting elements are provided which electrically contact the respective semiconductor elements of the thermoelec tric module situated at the ends of the module and can thus pass on the electric current generated in the thermoelectric module to a memory or consumer of a motor vehicle.

The semiconductor elements are in particular arranged side by side between the first surface and the second surface, wherein the first surface and the second surface in particular form the outer boundary of the thermoelectric module. In this case, the first and second surfaces form a heat transfer layer, which enables a heat transfer from the thermoelectric module to the fluids flowing around the thermoelectric module. Here, the first surface as a hot side, in particular with a fluid with elevated temperature, for. As an exhaust gas, and the second surface as a cold side, in particular with a fluid low temperature, for. As a coolant, in heat-transmitting connection. As a result, a temperature difference is formed across the thermoelectric module between the first surface and the second surface, which as a result of the "Seebeck effect" generates an electrical voltage via semiconductor elements which are mutually electrically interconnected.

The semiconductor elements have at their respective either the hot side or the cold side facing the ends of metallic bridges through which the semiconductor elements are electrically conductively connected to each other. These metallic bridges can be arranged both on the side surfaces of the respective semiconductor elements and on the respective end faces. The metallic bridges are in turn electrically insulated from the hot side or cold side, so that an unwanted current transition between not over the metallic bridges electrically interconnected semiconductor elements can not be done here. The semiconductor elements each have an end face on their ends facing the hot side and the cold side, with which they are contacted with the first surface or with the second surface in the sense of the present invention. It does not matter here that the respective ends z. B. are provided with metallic bridges, or that the metallic bridges with respect to the hot or cold side have an additional electrical insulation. Here, the areal coverage of the first or second area by the respective end face of the semiconductor elements is important because this Flächenbeaufschlagung simultaneously describes the space efficiency or land use of the hot side or cold side or between this hot side and cold side gap. In other words, this also means that in each case a cross-sectional area is present at the respective end faces of the semiconductor elements, which is summed up on the respective hot side or cold side for all semiconductor elements at most 70% of the entire first surface and / or the entire second surface.

The first surface and the second surface is limited by the space available for the semiconductor elements, that is, the first surface or second surface and the gap extends z. B. between the respective present sealing means at the respective end of the thermoelectric module. Thermoelectric semiconductor elements can be arranged on these surfaces or within this intermediate space. So far, it has been assumed that the highest possible space utilization of this gap or the highest possible space utilization on the hot side or cold side is required to a to allow high conversion of the available thermal energy into electrical energy due to the thermoelectric generator. The space utilization and the selection of the filling material were directed (preferably exclusively) according to the requirements of the mechanical or chemical stability of the module. The present invention has for the first time recognized that the utilization of space and the selection of filling material must be used to adapt the thermal resistances of the individual functional layers, because the temperature distribution between the exhaust gas, the hot side, the cold side and the coolant can be designed to increase performance.

x:

Höhe des Moduls, d. h. dem Abstand zwischen der Heißseite und der Kaltseite des Moduls,

λ_TE:

Wärmeleitfähigkeit des thermoelektrischen Materials der Halbleiterelemente,

λ_Füllung:

Wärmeleitfähigkeit des Füllmaterials (insbesondere des Isolationsmaterials),

A_TE:

Fläche senkrecht zum Wärmestrom des thermoelektrischen Materials (insbesondere Querschnitt durch die Halbleiterelemente),

A_Füllung:

Fläche senkrecht zum Wärmestrom des Füllmaterials (insbesondere Querschnitt durch Zwischenräume).

The producible electrical power of the thermoelectric module results, in simple terms, from the product of the thermoelectric efficiency of the module and the heat flow Q occurring on the hotter side of the thermoelectric module. In general, the thermoelectric efficiency increases with increasing thermal resistance of the functional layer between the first surface and the second surface, as this increases the temperature difference between the hot and the cold side. In contrast, the flowing heat flow decreases due to the increased thermal resistance. This means in particular that the electrical power is a function of the thermal resistance of the thermoelectric module. The thermal resistance of the thermoelectric module results from the thermal conductivity of the thermoelectric material, the geometric dimensions of the thermoelectric semiconductor elements and the thermal conductivity of the filling material (in particular of the insulating material) and the geometric dimensions of the filling material. Thus, neglecting thermal contact resistances for the thermal resistance of the module (R _module ), the following relationship applies: R _modulus = x / (λ _TE · A _TE + λ _filling · A _filling ), With

x:

Height of the module, ie the distance between the hot side and the cold side of the module,

λ _TE :

Thermal conductivity of the thermoelectric material of the semiconductor elements,

λ _filling :

Thermal conductivity of the filling material (in particular of the insulating material),

A _TE :

Area perpendicular to the heat flow of the thermoelectric material (in particular cross section through the semiconductor elements),

A _filling :

Area perpendicular to the heat flow of the filling material (in particular cross-section through spaces).

The convective resistance (R _convective ) results too R _convective = 1 / (α * A) where α indicates the heat transfer coefficient and A the corresponding considered surface. The smallest unit area A _EZ , which is considered here for the comparison of R _convective and R _module , corresponds to the cross-sectional area of a so-called unit cell. The unit cell comprises the region of a thermoelectric module, which in each case comprises an n- and p-doped semiconductor element and the filling material arranged therebetween, in particular insulation material. Thus: A _TE + A _filling = A _EZ

The existing total temperature difference between z. B. a passing on the hot side exhaust gas and a flowing past the cold side coolant divides in the ratio of the thermal resistances R _convective (respectively for the hot side and for the cold side) and R _module . The temperature difference thus present between the hot side and the cold side of the thermoelectric module behaves proportionally to the thermal resistance of the thermoelectric module R _module . The heat flow Q that can be converted into electrical current by the semiconductor elements thus results correspondingly from the ratios of these resistors R _convective and R _module to one another and behaves inversely proportional to R _module . Further heat flows in the thermoelectric element are the Peltier heat flux, and the ohmic heat flow, which is caused by the ohmic resistance of the semiconductor materials of the thermoelectric elements.

The heat flow Q flowing through the thermoelectric module is calculated accordingly from the quotient ΔT / R _module , where ΔT is the temperature difference between the hot side (T _{h, TM} ) and the cold side (T _{k, TM} ) and R _{modulus is} the thermal resistance of the thermoelectric module indicates. Thus, the producible electric power of the thermoelectric module by the thermal resistance of the thermoelectric module are significantly affected. Depending on the material of the semiconductor, a heat flow flows from the hot side to the cold side via the semiconductor elements. The higher the specific thermal conductivity of the semiconductor material, the lower the temperature difference available between the hot side and the cold side end of the semiconductor element available for electric power generation. The invention has made a significant adjustment mm between the one hand for the power generation of important semiconductor material, which connects the hot side with the cold side on the one hand to generate electricity from the temperature difference but on the other just also heat-conducting, and on the other hand, improved heat insulation between the hot and cold side, such that a large temperature difference exists at the respective ends of the semiconductor elements on the hot side and on the cold side, respectively, and a large heat flow flows via the semiconductor elements from the hot side to the cold side of the thermoelectric module.

Therefore, it is proposed by the present invention in particular that the gap between hot and cold side is no longer completely filled by semiconductor element material, but on the contrary a large part, the available on the hot side or cold side for semiconductor elements or between hot - and cold side present space is filled by thermal insulation material. In particular, the remaining volume of the gap between the semiconductor elements is filled by an insulating material, wherein the thermal conductivity of the thermoelectric module at a (predetermined) operating point of the thermoelectric module by the specified conditions a) and / or b) is set so that between 40% and 60% of the total temperature difference of the hot side and cold side, so the total temperature difference between z. B. a flowing past on the hot side of the exhaust gas and a flowing past the cold side coolant drops above the thermoelectric module. In other words, this means that for a predetermined operating point of the thermoelectric module, the sum of the convective resistances R _convective the hot side and the cold side of the thermoelectric module between 80% and 120% of the value of the thermal resistance of the thermoelectric module R _module .

As the thermal resistance of the thermoelectric module increases, the temperature difference between the hot side and the cold side of the thermoelectric module, which can be used for power generation, increases. The thermoelectric efficiency benefits approximately linearly from an increasing temperature difference. However, the flowing heat flow through the thermoelectric module decreases as the total resistance (sum of R _convective and R _modulus ) increases with increasing thermal resistance of the thermoelectric module. There is thus a power maximum of the overall arrangement as a function of the thermal resistance. As an approximation one can assume that the electrical power is maximum when half of the total temperature difference (exhaust gas / coolant) drops over the thermoelectric module. Ie. it should roughly apply: R _{convective hot side} + R _{convective cold side} = R _module

The thermal resistance of the thermoelectric module can be adjusted, inter alia, on the degree of filling, wherein the term "degree of filling" describes the space utilization and / or the area utilization in the space of the thermoelectric module by the semiconductor elements, according to the above conditions a) and b). The adjustment of the thermal resistance of the thermoelectric module can also be achieved by non-constant cross sections of the semiconductor elements and / or by porous semiconductor elements. When all the gap between hot side and cold side available for semiconductor element mounting is filled by semiconductor elements, or when the area available on the hot side and cold side for semiconductor elements is completely contacted by semiconductor elements, the degree of filling is 1 or 100%. If only half of the said intermediate ridge is filled by semiconductor elements or only half of the area mentioned on the hot side and cold side is contacted by semiconductor elements, the degree of filling is 0.5 or 50%. When air is used as the insulating material, in a 0.5 degree pad, the thermal resistance of the thermoelectric module is about twice that of a 1 pad. The reason is the smaller available area through which the heat flow can flow. The degree of filling allows the thermal resistance of the thermoelectric module to be adjusted so that a maximum of electrical power can be generated. Ie. much less (expensive) thermoelectric material is needed and at the same time the electrical power is increased by adjusting the thermal resistance of the thermoelectric module.

Simulations have confirmed these findings. An exemplary result is shown in the following table: filling level insulation material λ _eff T _{h, TM Tk, TM} Q _Parasitic Q _TM efficiency P _el I-1 [-] [W / mK] [° C] [° C] [W] [W] [-] [W] 0.9 air 1.2 164 95 0,006 1.92 1.52 0,029 0.66 air 0.9 183 95 0,025 1.81 1.83 0.034 0.3 air 0.5 240 95 0.092 1.42 2.51 0,038 Table 1: Simulation results for a filling degree variation

It can be seen that with decreasing degree of filling the effective thermal conductivity (λ _eff ) decreases. The effective thermal conductivity here describes a substitute value for a unit cell, which consists of the parallel path of the thermoelectric element and the insulating material, that is: (λ _TE · A _TE + λ _filling · A _filling ) / (A _TE + A _filling ) = λ _eff

Due to the decreasing effective thermal conductivity, the temperature difference across the module (T _{h, TM} : 164 to 240 ° C in relation to T _{k, TM} : 95 ° C) increases, which in turn has a positive influence on the efficiency (efficiency: 1, 52 to 2.51). This results in an overall increase in electrical power (P _el ) by 30%, while reducing the thermoelectric material used by 66%. The results shown assume a predetermined operating point and a predetermined convective heat transfer. The thermoelectric module is in fact also adapted to specific requirements (eg differences between internal combustion engine diesel / Otto in the exhaust gas enthalpy) during operation.

Q _Parasitic is the entering portion of the heat flow on the hot side of the modules, which does not flow through the thermoelectric material but through the insulation material arranged in parallel (air in the example above).

In addition to the increase in performance, the temperature on the hot side of the thermoelectric module (T _{h, TM} ) can also be adjusted by varying the parameter degree of filling, so that overheating during operation of a thermoelectric module in an exhaust system can be avoided.

An operating point here is a state for which the thermoelectric module is to be designed and which is generally present at the installation site of the thermoelectric module. The operating point includes z. As exhaust gas temperatures, coolant temperatures, exhaust gas mass flow, coolant mass flow, etc.

In particular, it is proposed that between the hot side and the cold side and between two adjacent semiconductor elements a plurality of different thermal insulation materials - in particular viewed along a semiconductor element from the hot side to the cold side - are arranged. Ceramic spacers are particularly advantageously used here, which space the thermoelectric elements from one another and fix them with regard to their positioning. These can fill the entire installation space between the hot side and the cold side and between the semiconductor elements. Preferably, however, a mica material is used instead of a ceramic or in addition thereto. Particularly preferably, the space between the semiconductor elements and between hot side and cold side is filled exclusively or additionally by air or by a vacuum. This achieves thermal isolation matched to heat flow so that power dissipation parasitic heat flows within the thermoelectric module parallel to the thermoelectric material are minimized. By virtue of the module according to the invention, the usable electrical power can be maximized and at the same time the use of cost-intensive semiconductor material can be reduced. In addition, there are advantages through a possible weight reduction, because large parts of the gap between the hot side and cold side should now be filled with air.

According to a particularly advantageous embodiment, the thermoelectric module is tubular. In other words, this also means that the first surface and the second surface are generally arranged concentrically with one another and the intermediate space is formed in the manner of a hollow cylinder between them. Accordingly, the first surface and the second surface are most preferably shown with a tube of different diameters, wherein the inner tube inside and the outer tube outside can be embossed by a heat transfer fluid.

In a tubular embodiment of the thermoelectric module preferably at least a portion of the semiconductor elements is annular shaped and each contacted with an outer peripheral surface and an inner peripheral surface with the hot side or with the cold side. The outer or inner peripheral surface then forms the end face of the semiconductor element which contacts the hot side or cold side of the thermoelectric module. The term annular means that the semiconductor element images at least a portion of a circular ring. Such shaped semiconductor elements are to be proposed in particular for at least partially tubular thermoelectric modules. In this case, the hot side and the cold side respectively form the outer and the inner peripheral surface of a tube, so that a double tube wall is formed, in whose intermediate space the semiconductor elements are arranged. A thermoelectric module constructed in this way is flowed through by a fluid through a channel formed by the inner circumferential surface of the tube and overflowed by another fluid on the outer circumferential surface, so that a temperature difference can be generated across the double tube wall. The semiconductor elements are in particular circumferentially closed executed in the form of a circular ring and arranged inside the double tube wall one behind the other.

The semiconductor elements may in particular also have the shape of a circular ring segment. The semiconductor elements are then arranged side by side or one behind the other along an axial direction of the tube. The circular ring shape may in particular correspond to a circular shape, but also oval embodiments are possible. With regard to the interconnection of the semiconductor elements, it is, for example, also possible for the semiconductor elements to have a 180 ° circular ring shape, which are then alternately electrically connected to one another offset.

Another particular embodiment of the thermoelectric module comprises that the semiconductor elements are separated from one another by spacers made of at least ceramic or mica. Even if a material of the spacers is sufficient on a regular basis, a combination of the two types of spacers may also be useful if necessary.

Particularly suitable ceramics are the following materials: AIN (aluminum nitride), Al ₂ O ₃ (aluminum oxide), Al ₂ TiO ₅ (aluminum titanium oxide).

I

= Cs, K, Na, NH4, Rb, Ba, Ca

M

= Li, Fe⁺⁺ oder⁺⁺⁺, Mg, Mn⁺⁺ oder⁺⁺⁺, Zn, Al, Cr, V, Ti

T

= Be, Al, B, Fe⁺⁺⁺, Si

A

= Cl, F, OH, O (Oxy-Glimmer), S.

Mica are phyllosilicates in which the unitary structure of an octahedral sheet (Os) exists between two opposite tetrahedral leaves (Ts). These sheets form a layer separated from adjacent layers by areas of non-hydrated interlayer cations (I). The sequence is: ... I Ts Os Ts I Ts Os Ts .... The Ts have the composition T ₂ O ₅ . The coordinating anions around the octahedral coordinated cations (M) consist of oxygen atoms of neighboring Ts and anions A. The coordination of the interlayer cations is nominally 12-fold, with a simplified formula that can be written as follows: IM _2-3 X _1-0 T _-1 O ₁₀ A ₂ in which

I

= Cs, K, Na, NH4, Rb, Ba, Ca

M

= Li, Fe ⁺⁺ or ⁺⁺⁺ , Mg, Mn ⁺⁺ or ⁺⁺⁺ , Zn, Al, Cr, V, Ti

T

= Be, Al, B, Fe ⁺⁺⁺ , Si

A

= Cl, F, OH, O (oxy-mica), S.

Very particular preference is given here to the following materials: Micanites (that is to say, in particular, mica fragments which are pressed together with synthetic resin to form large mica films and baked) with high heat-conducting resistances.

According to a further particularly advantageous embodiment of the thermoelectric module, the semiconductor elements are uniformly arranged on the first surface and / or the second surface or in the intermediate space. By uniform is meant here in particular that the semiconductor elements are arranged at least in one direction in each case at equal distances from each other. This ensures, in particular, that equidistant spacings are provided between the semiconductor elements, which, for example, each make up approximately between 30% and 50% of the respective cross-sectional area of a semiconductor element.

• a) höchstens 70% der ersten Fläche oder/und der zweiten Fläche werden mit Halbleiterelementen kontaktiert, und
• b) höchstens 70% des Zwischenraums wird durch die Halbleiterelemente ausgefüllt; wobei

das übrige Volumen des Zwischenraums zwischen den Halbleiterelementen durch ein Isolationsmaterial ausgefüllt wird. Weiter erfolgt die Anordnung so, dass die Wärmeleitfähigkeit des Moduls bei einem Betriebspunkt des thermoelektrischen Moduls durch die wenigstens eine Bedingung a) und b) so eingestellt wird, dass zwischen 40% und 60% der Gesamttemperaturdifferenz von Heißseite und Kaltseite über dem thermoelektrischen Modul abfällt.It is further proposed a method for producing a thermoelectric module, in particular a module according to the invention, wherein the thermoelectric module at least one hot side with a first surface and a cold side with a second surface and one between the hot side and the Cold side disposed gap, wherein in the intermediate space a plurality of p- and n-doped semiconductor elements are arranged alternately, which are alternately electrically connected to each other. In the arrangement of the semiconductor elements, at least one of the two conditions is fulfilled:

• a) at most 70% of the first surface and / or the second surface are contacted with semiconductor elements, and
• b) at most 70% of the gap is filled by the semiconductor elements; in which

the remaining volume of the gap between the semiconductor elements is filled by an insulating material. Next, the arrangement is such that the thermal conductivity of the module at an operating point of the thermoelectric module by the at least one condition a) and b) is set so that between 40% and 60% of the total temperature difference from the hot side and cold side above the thermoelectric module drops.

According to a further aspect of the invention, a method for producing a thermoelectric module is proposed, wherein the thermoelectric module has at least one hot side with a first surface and a cold side with a second surface and an intermediate space between the hot side and the cold side, wherein in the intermediate space a plurality of p- and n-type semiconductor elements are alternately arranged, which are mutually electrically connected to each other. In addition, for an assumed operating point of the thermoelectric module, the sum of the convective resistances of the hot side and the cold side of the thermoelectric module is between 80% and 120% of the value of the thermal resistance of the thermoelectric module.

The method mentioned above can also be used to produce the thermoelectric modules according to the invention. Therefore, for explanation of the arrangement, connection, etc., the complete description will be fully made to the descriptions thereof.

Furthermore, it is proposed that the thermoelectric module according to the invention is used to generate electrical energy from the exhaust gas of a mobile combustion engine.

Furthermore, a motor vehicle is proposed with an internal combustion engine, an exhaust system, at least one cooling circuit and at least one thermoelectric module according to the invention or a thermoelectric module according to the invention, wherein in the motor vehicle, the exhaust system with the hot side and the cooling circuit are connected to the cold side of the thermoelectric module. The exhaust system may in particular have an exhaust gas recirculation line, in which the thermoelectric module is integrated. Furthermore, the hot side of the thermoelectric module can also be overflowed by a medium that itself is heated by the exhaust gas, so that the thermoelectric module, as protection against overheating, outside the exhaust system can be arranged.

The invention and the technical environment will be explained in more detail with reference to FIGS. It should be noted that the figures show particularly preferred embodiments of the invention, but this is not limited thereto. They show schematically:

1 a variant of a thermoelectric generator in a motor vehicle;

2 a variant of a thermoelectric module;

3 : an embodiment of a semiconductor element;

4 : a further embodiment variant of a thermoelectric module;

5 a further embodiment of a semiconductor element;

6 a third embodiment of a thermoelectric module;

7 a detail of the third embodiment of the thermoelectric module; and

8th : Qualitative course of the efficiency, the heat flow and the electrical power as a function of the thermal resistance of the thermoelectric module.

1 shows a variant of a thermoelectric generator 12 in a motor vehicle 30 , The car 30 has an internal combustion engine 31 , an exhaust system 32 and a cooling circuit 33 on. Inside the exhaust system 32 is a thermoelectric generator 12 arranged, consisting of several thermoelectric modules 1 that exists in a common housing 13 are arranged. The individual thermoelectric modules 1 are at least partially with semiconductor elements 7 be filled and be on a hot side 2 with a first surface 3 from an exhaust 17 and on a cold side 4 with a second surface 5 from a coolant 18 overflows. In this case, the first surface extends 3 and the second surface 5 each between the respective ends 15 of the thermoelectric module 1 ,

2 shows an embodiment of a thermoelectric module 1 , where a cold side 4 and opposite a hot side 2 are provided, between which there is a gap 6 extends. The gap 6 is bounded laterally by sealants 14 that the gap 6 between the hot side 2 and cold side 4 Seal against external media fluid-tight or gas-tight. Furthermore, forms in the by the sealing means 14 laterally limited space 6 on the hot side 2 the first area 3 and on the cold side 4 the second area 5 out. In the gap 6 between the hot side 2 and the cold side 4 is a plurality of p-doped and n-doped semiconductor elements 7 alternately arranged one behind the other and via metallic bridges 10 alternately connected to each other so that an electric current generated as a result of the Seebeck effect and the thermoelectric module 1 from one end 15 to the other end 15 can flow through. The semiconductor elements 7 are opposite the hot side 2 or the cold side 4 through insulation 23 electrically insulated, with the insulation 23 but a good heat transfer from the hot side 2 or the cold side 4 towards the semiconductor elements 7 should allow. The semiconductor elements 7 are separated from each other by a distance 27 separated, wherein between the semiconductor elements 7 an insulation material 24 is arranged, which is the semiconductor elements 7 electrically isolated from each other. The insulation material 24 at the same time has good thermal insulation properties, allowing heat transfer from the hot side 2 to the cold side 4 by means of insulation 24 should be prevented. This can cause the temperature difference 19 between the hot side 2 and the cold side 4 for power generation of the thermoelectric module 1 be used efficiently. The temperature difference 19 is thus regularly lower than the total temperature difference caused by the temperature of the exhaust gas on the hot side 2 and by the temperature of the refrigerant on the cold side 4 is formed. The inside of the thermoelectric module 1 generated electric current is through at the respective ends 15 of the thermoelectric module 1 provided connection elements 16 discharged to the outside.

3 shows an embodiment of a semiconductor element 7 that in the in 2 shown thermoelectric module 1 can be used. Here is a cuboid semiconductor element 7 shown with side surfaces 21 and with end faces 22 at the respective end areas 20 , At the end areas 20 are power transmission areas 11 arranged, here at the end face 22 with metallic bridges 10 (see also 2 ) to contact. The current transfer areas 11 can also be in the end area 20 on the side surfaces 21 be arranged. The semiconductor element 7 has a cross-sectional area 28 (or closing surface). Due to the arrangement within a thermoelectric module 1 with a hot side 2 and a cold side 4 is located on the semiconductor element 7 a temperature difference 19 between the respective end regions 20 at.

4 shows a further embodiment of a thermoelectric module 1 , Here is a tubular thermoelectric module 1 shown by an inner channel 34 from the exhaust 17 is flowed through, so that here the hot side 2 of the thermoelectric module 1 is trained. Over the outer surface of the tubular thermoelectric module 1 flows according to a coolant 18 , so that forms a temperature difference over the double-walled tube. Inside the thermoelectric module 1 are between the hot side 2 and the cold side formed by the outer pipe peripheral surface 4 Semiconductor components 7 arranged so that as a result of the thermoelectric effect between the ends 15 of the thermoelectric module 1 An electric current is generated, which is connected via connecting elements 16 is discharged to a battery or consumers of a motor vehicle. The semiconductor elements 7 are within a space 6 arranged laterally through the sealing means 14 is limited in the axial direction and in the radial direction on the one hand by the first surface 3 on the hot side 2 and on the other side through the second surface 5 on the cold side 4 of the thermoelectric module 1 , The semiconductor elements 7 are opposite the first surface 3 or the second surface 5 through the insulation 23 electrically isolated.

5 shows a further embodiment of a semiconductor element 7 that in the in 4 shown thermoelectric module 1 can be used. The semiconductor element shown here 7 has an annular shape, so that the outer peripheral surface 8th of the semiconductor element 7 with the in 4 shown cold side contacted and the inner peripheral surface 9 of the semiconductor element 7 with the hot side 2 of the thermoelectric module 1 out 4 contacted. Above the semiconductor element 7 thus falls one temperature difference 19 between inner peripheral surface 9 and outer peripheral surface 8th from. The semiconductor element 7 still has side faces 21 on, between those on the outer peripheral surface 8th or on the inner peripheral surface 9 Current transfer surfaces 11 arranged inside the thermoelectric module 1 for forwarding an electric current with metallic bridges 10 (not shown here) are connectable. The current transfer areas 11 can also be on the side surfaces 21 near the inner peripheral surface 9 or near the outer peripheral surface 8th be arranged.

6 shows a third embodiment of a thermoelectric module 1 , with one here 4 proposed tubular thermoelectric module 1 is shown. Here, too, semiconductor elements 7 between a hot side 2 and a cold side 4 arranged so that, due to the mutual connection of the semiconductor elements 4 through metallic bridges 10 an electric current from one end 15 of the thermoelectric module 1 can be generated to the other end and from there by connection elements 16 an external memory or a consumer can be supplied. At the respective ends 15 of the thermoelectric module 1 are sealing elements 14 provided the gap 6 between the hot side 2 and the cold side 4 in an axial direction limit and between which the first surface 3 and the hot side 2 and the second surface 5 on the cold side 4 form. On the first surface 3 or the second surface 4 are semiconductor elements 7 arranged, which contact this surface. It is irrelevant according to the invention that here metallic bridges 10 or an insulation 23 between semiconductor element 7 and first surface 2 or second surface 5 are arranged so that a "direct" contact does not occur. The semiconductor elements 7 have a distance 27 up, which - like on the right side of the 6 shown - by spacers 25 is produced. The spacer 25 can be made in several parts. in 6 two spacers are shown, one is on an outer circumference in the region of the cold side 4 and another on an inner periphery in the region of the hot side 2 arranged. Thus, as shown here, different spacers 25 arranged seen in the radial direction. Between the spacers 25 , which are preferably made of ceramic or mica, can air 29 or a vacuum, so that the most efficient thermal insulation between the hot side 2 and cold side 4 is reached. air 29 and spacers 25 So serve here as insulation material 24 as in the left area of the 6 shown. There are preferably equal distances 27 between the semiconductor elements 7 at least in one direction 26 of the thermoelectric module 1 in front.

7 shows a detail of the third embodiment of the thermoelectric module 1 , Inside the thermoelectric module 1 is, in the axial direction at the respective ends 15 by sealing elements 14 and in the radial direction through a first surface 3 and a second area 5 limited, a gap 6 arranged. Inside the gap 6 are the semiconductor elements 7 arranged.

8th shows the course of the efficiency 36 , the heat flow 37 and the electrical power 35 depending on the thermal resistance 38 of the thermoelectric module applied on the horizontal axis. With increasing thermal resistance 38 of the thermoelectric module increases the useful for generating electricity temperature difference between the hot side and cold side of the thermoelectric module. The thermoelectric efficiency 36 benefits approximately linearly from a rising temperature difference.

However, the flowing heat flow decreases 37 through the thermoelectric module, as with increasing thermal resistance 38 of the thermoelectric module also increases the total resistance (sum of R _convective and R _module ). There is thus a power maximum of the overall arrangement as a function of the thermal resistance 38 , It can be approximated that the electric power 35 maximum is when half of the total temperature difference (exhaust / coolant) should apply to the thermoelectric module drops.

LIST OF REFERENCE NUMBERS

1

Thermoelectric module

2

hot side

3

First surface

4

cold side

5

Second surface

6

gap

7

Semiconductor element

8th

Outer peripheral surface

9

Inner peripheral surface

10

Metallic bridge

11

Current transfer surface

12

Thermoelectric generator

13

casing

14

sealant

15

End module

16

connecting element

17

exhaust

18

coolant

19

temperature difference

20

end

21

side surface

22

face

23

insulation

24

insulation material

25

spacer

26

direction

27

distance

28

Cross sectional area

29

air

30

motor vehicle

31

internal combustion engine

32

exhaust system

33

Cooling circuit

34

Inner canal

35

electrical power

36

efficiency

37

heat flow

38

thermal resistance

Claims (7)

Thermoelectric module ( 1 ), at least having a hot side ( 2 ) with a first surface ( 3 ) and a cold side ( 4 ) with a second surface ( 5 ) as well as between the hot side ( 2 ) and the cold side ( 4 ) arranged intermediate space ( 6 ), wherein in the intermediate space ( 6 ) a plurality of p- and n-doped semiconductor elements ( 7 ) which are alternately electrically interconnected, characterized in that at least one of the two conditions is met: a) at most 70% of the first area ( 3 ) and / or the second surface ( 5 ) is equipped with semiconductor elements ( 7 ), and b) at most 70% of the space ( 6 ) is through the semiconductor elements ( 7 ) completed; and the remaining volume of the gap ( 6 ) between the semiconductor elements ( 7 ) by an insulating material ( 24 ), and wherein the thermal conductivity of the thermoelectric module ( 1 ) at an operating point by which at least one condition a) and b) is set such that between 40% and 60% of the total temperature difference of hot side ( 2 ) and cold side ( 4 ) above the thermoelectric module ( 1 ) drops. Thermoelectric module ( 1 ) according to claim 1, wherein the thermoelectric module ( 1 ) is tubular. Thermoelectric module ( 1 ) according to claim 1 or 2, wherein the semiconductor elements ( 7 ) from each other by spacers ( 8th ) are separated from at least ceramic or mica. Thermoelectric module ( 1 ) according to one of the preceding claims, wherein the semiconductor elements ( 7 ) on the first surface ( 3 ) and / or the second surface ( 5 ) or evenly spaced in the space. Method for producing a thermoelectric module ( 1 ), wherein the thermoelectric module ( 1 ) at least one hot side ( 2 ) with a first surface ( 3 ) and a cold side ( 4 ) with a second surface ( 5 ) as well as between the hot side ( 2 ) and the cold side ( 4 ) arranged intermediate space ( 6 ), wherein in the intermediate space ( 6 ) a plurality of p- and n-doped semiconductor elements ( 7 ) arranged alternately which are alternately electrically connected to each other, characterized in that the arrangement of the semiconductor elements ( 7 ) is carried out so that for an operating point of the thermoelectric module ( 1 ) the sum of the convective resistances of the hot side ( 2 ) and the cold side ( 4 ) of the thermoelectric module ( 1 ) between 80% and 120% of the value of the thermal resistance of the thermoelectric module ( 1 ) is. Use of a thermoelectric module ( 1 ) according to one of the claims 1 to 4 or a module ( 1 ) produced according to claim 5 for generating electrical energy from the exhaust gas of a mobile internal combustion engine ( 31 ). Motor vehicle ( 30 ) with an internal combustion engine ( 31 ), an exhaust system ( 32 ), at least one cooling circuit ( 33 ) and at least one thermoelectric module ( 1 ) according to one of the claims 1 to 4 or a module ( 1 ) produced according to claim 5, wherein in the motor vehicle ( 30 ) the exhaust system ( 32 ) with the hot side ( 2 ) and the cooling circuit ( 33 ) with the cold side ( 4 ) of the thermoelectric module ( 1 ) are connected.

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