POWER GENERATOR FOR VEHICLE

A power generator includes thermoelectric transducers configured so that the band gap energy of an intrinsic semiconductor part disposed between an n-type semiconductor part and a p-type semiconductor part is lower than each band gap energy of the n-type semiconductor part and the p-type semiconductor part. The power generator is used in a vehicle that includes an exhaust pipe serving as a heat supplier. The thermoelectric transducers are supplied with heat from the exhaust pipe through an insulating member. The thermoelectric transducers are installed in such a manner that a portion of the surface of the intrinsic semiconductor part is in contact with the surface of the insulating member (heat supply surface).

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of Japanese Patent Application No. 2016-011615, filed on Jan. 25, 2016, which is incorporated by reference herein in its entirety.

BACKGROUND

Technical Field

The present disclosure relates to a power generator for a vehicle, and more particularly to a power generator for a vehicle that incorporates a thermoelectric transducer.

Background Art

There are various thermoelectric transducers based on the Seebeck effect. For such a thermoelectric transducer to produce an electromotive voltage, there needs to be a temperature difference between the two kinds of metals or semiconductors forming the thermoelectric transducer. Thus, power generation using the thermoelectric transducer requires a device that maintains the temperature difference, such as a cooler. WO 2015125823 A1 discloses a semiconductor single crystal that can be used as a thermoelectric transducer capable of generating power without the temperature difference.

Specifically, the semiconductor single crystal disclosed in WO 2015125823 A1 includes an n-type semiconductor part, a p-type semiconductor part, and an intrinsic semiconductor part disposed between the n-type semiconductor part and the p-type semiconductor part, and the band gap energy of the intrinsic semiconductor part is set to be lower than each band gap energy of the n-type semiconductor part and the p-type semiconductor part. If the semiconductor single crystal having this configuration is heated to fall within a predetermined temperature range, electrons in the valence band of the intrinsic semiconductor part is excited into the conduction band, even if there is no temperature difference between the n-type semiconductor part and the p-type semiconductor part. The electrons excited into the conduction band moves to the n-type semiconductor part, which has a lower energy, and the holes formed in the valence band moves to the p-type semiconductor part, which has higher energy. As a result of these movements, the carriers (electron and holes) are unevenly distributed, and the semiconductor single crystal serves as a power generating material with the p-type semiconductor part serving as a positive electrode and the n-type semiconductor part serving as a negative electrode. The semiconductor single crystal having this configuration used as a thermoelectric transducer can generate electric power when the temperature of the thermoelectric transducer is within the predetermined temperature range, even if there is no temperature difference between the n-type semiconductor part and the p-type semiconductor part.

In addition to WO 2015125823 A1, JP 2004-011512A is a patent document which may be related to the present disclosure.

SUMMARY

To efficiently use the heat emitted by components of a vehicle, such as an automobile, a power generator including the semiconductor single crystal disclosed in WO 2015125823 A1 as a thermoelectric transducer can be installed in various sites in the vehicle. When this kind of power generator is installed, it is favorable to be able to efficiently generate electric power based on the characteristics of the thermoelectric transducer.

The present disclosure has been made to address the problem described above, and an object of the present disclosure is to provide a power generator for a vehicle, which includes a thermoelectric transducer configured so that the band gap energy of an intrinsic semiconductor part disposed between an n-type semiconductor part and a p-type semiconductor part is lower than each band gap energy of the n-type semiconductor part and the p-type semiconductor part, and in which the thermoelectric transducer is mounted on the vehicle in such a manner as to efficiently generate electric power.

A power generator for a vehicle according to the present disclosure includes a thermoelectric transducer including an n-type semiconductor part, a p-type semiconductor part, and an intrinsic semiconductor part disposed between the n-type semiconductor part and the p-type semiconductor part. A band gap energy of the intrinsic semiconductor part is lower than each band gap energy of the n-type semiconductor part and the p-type semiconductor part. The power generator is used in a vehicle that includes a heat supplier configured to supply heat to the thermoelectric transducer. The thermoelectric transducer is supplied with heat from a heat supply surface, which is a surface of the heat supplier or a surface of an intermediate member between the thermoelectric transducer and the heat supplier. The thermoelectric transducer is installed in such a manner that at least a portion of a surface of at least the intrinsic semiconductor part of a surface of the thermoelectric transducer is in contact with the heat supply surface.

The thermoelectric transducer may include a first thermoelectric transducer and a second thermoelectric transducer. The power generator may further include an electrode that electrically connects the first thermoelectric transducer and the second thermoelectric transducer to each other. At least a portion of the surface of at least the intrinsic semiconductor part of the surface of the first thermoelectric transducer may be in contact with a first portion of the heat supply surface. At least a portion of the surface of at least the intrinsic semiconductor part of the surface of the second thermoelectric transducer may be in contact with a second portion of the heat supply surface, which is different from the first portion.

The electrode may connect an end portion of the n-type semiconductor part of the first thermoelectric transducer on a side opposite to the intrinsic semiconductor part and an end portion of the p-type semiconductor part of the second thermoelectric transducer on a side opposite to the intrinsic semiconductor part.

The electrode may include: a positive electrode that connects an end portion of the n-type semiconductor part of the first thermoelectric transducer on a side opposite to the intrinsic semiconductor part and an end portion of the n-type semiconductor part of the second thermoelectric transducer on a side opposite to the intrinsic semiconductor part to each other; and a negative electrode that connects an end portion of the p-type semiconductor part of the first thermoelectric transducer on a side opposite to the intrinsic semiconductor part and an end portion of the p-type semiconductor part of the second thermoelectric transducer on a side opposite to the intrinsic semiconductor part to each other.

The power generator may be configured so that a heat flux received, from the heat supply surface by a surface of the electrode on a side of the heat supply surface is lower than a heat flux received from the heat supply surface by a surface of the intrinsic semiconductor part of each of the first thermoelectric transducer and the second thermoelectric transducer.

The electrode may be installed to face the heat supply surface with an air layer interposed therebetween.

The power generator may further include a heat insulator interposed between the surface of the electrode and the heat supply surface.

The power generator may further include a heat insulator installed between the heat supply surface and an end portion of the n-type semiconductor part of the thermoelectric transducer on a side opposite to the intrinsic semiconductor part or an end portion of the p-type semiconductor part of the thermoelectric transducer on a side opposite to the intrinsic semiconductor part.

The thermoelectric transducer may include a plurality of thermoelectric transducers. The power generator may include the plurality of thermoelectric transducers in a form of a thermoelectric transducer module. The thermoelectric transducer module may include a transducer stack formed by the plurality of thermoelectric transducers electrically connected to each other and a housing that houses the transducer stack. The housing may serve as the intermediate member, or the housing and an insulating member interposed between the housing and the plurality of thermoelectric transducers may serve as the intermediate member. The heat supply surface for at least some of the plurality of thermoelectric transducers forming the transducer stack may be an inner surface of the housing or a surface of the insulating member on a side of the plurality of thermoelectric transducers.

The thermoelectric transducer module may be installed in such a manner that an outer surface of the housing opposite to the inner surface of the housing is in contact with the surface of the heat supplier.

The heat supply surfaces may include a first heat supply surface and a second heat supply surface. Of the surface of the thermoelectric transducer, a first portion of the surface of the intrinsic semiconductor part may be in contact with the first heat supply surface, and a second portion of the surface of the intrinsic semiconductor part is in contact with the second heat supply surface.

The heat supplier may include a plurality of heat suppliers. At least a portion of the surface of at least the intrinsic semiconductor part of the surface of the thermoelectric transducer may be in contact with the heat supply surface of each of the plurality of heat suppliers.

The heat supplier may be an exhaust pipe of an internal combustion engine mounted on the vehicle. In addition, if the heat supplier includes a plurality of heat suppliers, one of the plurality of heat suppliers may be an exhaust pipe of an internal combustion engine mounted on the vehicle.

According to the power generator for a vehicle of the present disclosure, the thermoelectric transducer is configured so that the band gap energy of the intrinsic semiconductor part disposed between the n-type semiconductor part and the p-type semiconductor part is lower than each band gap energy of the n-type semiconductor part and the p-type semiconductor part, and the thermoelectric transducer is installed in such a manner that at least a portion of the surface of at least the intrinsic semiconductor part is in contact with the heat supply surface. If a temperature difference is produced in such a manner that the temperature of the n-type semiconductor part or the p-type semiconductor part having a relatively higher band gap energy is higher than the temperature of the intrinsic semiconductor part, it becomes difficult for the thermoelectric transducer having the configuration described above to efficiently produce an electromotive voltage. According to the installation method according to the power generator, however, the thermoelectric transducer can be installed on the vehicle in such a manner that heat input to the intrinsic semiconductor part is ensured. As a result, the temperature difference in the manner described above is less likely to be produced, and the thermoelectric transducer can efficiently produce the electromotive voltage. Thus, efficient power generation can be achieved.

DETAILED DESCRIPTION

In the following, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same reference numerals denote the same or similar components.

First Embodiment

First, with reference toFIGS. 1 to 7, a first embodiment of the present disclosure will be described.FIG. 1is a diagram showing an application example of a power generator10for a vehicle according to the first embodiment of the present disclosure.FIG. 2is a schematic perspective view showing a configuration of each thermoelectric transducer12of the power generator10shown inFIG. 1.

[Installation Site of Power Generator in Vehicle]

The installation site of the power generator10according to the present embodiment is not particularly limited. For example, as shown inFIG. 1, the power generator10is installed on an exhaust pipe2, in which exhaust gas from an internal combustion engine1mounted on a vehicle flows. In the example shown inFIG. 1, heat of the exhaust gas flowing in the exhaust pipe2is supplied to each of thermoelectric transducers12via the exhaust pipe2. Thus, in this example, the exhaust pipe2serves as a “heat supplier” according to the present disclosure. Examples of the heat supplier other than the exhaust pipe2that is a component of the vehicle and supplies heat to the thermoelectric transducer12include a cylinder block and a cylinder head of the internal combustion engine1, a cooling water hose in which engine cooling water for cooling the internal combustion engine1flows, a radiator for cooling the engine cooling water, a transmission associated with the internal combustion engine, and a battery that accumulates electric power used by the vehicle. In addition, the temperature of the heat supplier when supplying heat is higher than the temperature of the ambient atmosphere (atmospheric air, in the present embodiment) of the thermoelectric transducer12. The power generator10according to the present embodiment includes a transducer stack14formed by a plurality of thermoelectric transducers12electrically connected to each other, although details of the configuration of the power generator10will be described later with reference toFIG. 5.

In the example shown inFIG. 2, the thermoelectric transducer12has the shape of a prism. The thermoelectric transducer12has an n-type semiconductor part12aat one end and a p-type semiconductor part12bat the other end. The thermoelectric transducer12further has an intrinsic semiconductor part12cbetween the n-type semiconductor part12aand the p-type semiconductor part12b.

FIGS. 3A and 3Bare conceptual diagrams showing statuses of the band gap energy of the thermoelectric transducer12shown inFIG. 2. InFIGS. 3A and 3B, the vertical axes indicate the energy of an electron, and the horizontal axes indicate the distance L (seeFIG. 2) from an end face12aesof the thermoelectric transducer12on the side of the n-type semiconductor part12a.

As shown inFIGS. 3A and 3B, in the n-type semiconductor part12a, the Fermi level f is in the conduction band, and in the p-type semiconductor part12b, the Fermi level f is in the valence band. In the intrinsic semiconductor part12c, the Fermi level f is at the middle of the forbidden band existing between the conduction band and the valence band. The band gap energy corresponds to the difference in energy between the uppermost part of the valence band and the lowermost part of the conduction band. As can be seen from these drawings, the band gap energy of the intrinsic semiconductor part12cof the thermoelectric transducer12is lower than the band gap energies of the n-type semiconductor part12aand the p-type semiconductor part12b. Note that the length ratio between the n-type semiconductor part12a, the p-type semiconductor part12band the intrinsic semiconductor part12cshown inFIGS. 3A and 3Bis just an example, and the ratio can vary depending on how the thermoelectric transducer (semiconductor single crystal)12is formed. The band gap energy of the n-type semiconductor part12a, the p-type semiconductor part12band the intrinsic semiconductor part12ccan be measured in inverse photoelectron spectroscopy, for example.

The thermoelectric transducer (semiconductor single crystal)12having the characteristics described above (that is, the band gap energy of the intrinsic semiconductor part12cis lower than the band gap energies of the n-type semiconductor part12aand the p-type semiconductor part12b) can be made of a clathrate compound (inclusion compound), for example. As an example of the clathrate compound, a silicon clathrate Ba8Au8Si38may be used.

The thermoelectric transducer12according to the present embodiment can be manufactured in any method, as far as the method can produce the thermoelectric transducer12having the characteristics described above. If the thermoelectric transducer12is made of, for example, the silicon clathrate Ba8Au8Si38, the manufacturing method described in detail in International Publication No. WO 2015125823 A1 can be used, for example. The manufacturing method can be summarized as follows. That is, Ba powder, Au powder and Si powder are weighed in the ratio (molar ratio) of 8:8:38. The weighed powders are melted together by arc melting. The melt is then cooled to form an ingot of the silicon clathrate Ba8Au8Si38. The ingot of the silicon clathrate Ba8Au8Si38prepared in this way is crushed into grains. The grains of the silicon clathrate Ba8Au8Si38are melted in a crucible in the Czochralski method, thereby forming a single crystal of the silicon clathrate Ba8Au8Si38. The thermoelectric transducer12shown inFIG. 2is provided by cutting the single crystal of the silicon clathrate Ba8Au8Si38prepared in this way into the shape of a prism (more specifically, the shape of a rectangular parallelepiped). The shape of the thermoelectric transducer is not limited to the rectangular parallelepiped, and the thermoelectric transducer may have any shape provided by cutting the single crystal into a desired shape, such as a cube or a column.

[Principle of Power Generation]

FIG. 3Ais a conceptual diagram showing a status of thermal excitation of the thermoelectric transducer12when the thermoelectric transducer12is heated to a predetermined temperature. If the thermoelectric transducer12is heated to a temperature T0 (seeFIG. 4described later) or higher, electrons (shown by black dots) in the valence band are thermally excited into the conduction band, as shown inFIG. 3A. More specifically, if heat is supplied and energy exceeding the band gap energy is thereby supplied to an electron located in an uppermost part of the valence band, the electron is excited into the conduction band. In the process where the temperature of the thermoelectric transducer12increases, a condition can occur in which such thermal excitation of electrons occurs only in the intrinsic semiconductor part12c, which has a relatively low band gap energy.FIG. 3Ashows a status of the thermoelectric transducer12in which the thermoelectric transducer12is heated to a predetermined temperature (such as the temperature T0) that can allow such a condition to occur. In this status, no electrons are thermally excited in the n-type semiconductor part12aand the p-type semiconductor part12b, which have a relatively higher band gap energy.

FIG. 3Bis a conceptual diagram showing movement of an electron (shown by the black dot) and a hole (shown by a white dot) when the thermoelectric transducer12is heated to the predetermined temperature described above. As shown inFIG. 3B, electrons excited into the conduction band move toward a part of lower energy, that is, toward the n-type semiconductor part12a. On the other hand, holes formed in the valence band as a result of the electrons being excited move toward a part of higher energy, that is, toward the p-type semiconductor part12b. The carriers are unevenly distributed in this way, so that the n-type semiconductor part12ais negatively charged, and the p-type semiconductor part12bis positively charged, and therefore, an electromotive force occurs between the n-type semiconductor part12aand the p-type semiconductor part12b. Thus, the thermoelectric transducer12can generate power even if there is no temperature difference between the n-type semiconductor part12aand the p-type semiconductor part12b. This principle of power generation differs from the Seebeck effect, which produces an electromotive force based on a temperature difference. The power generator10using the thermoelectric transducer12requires no temperature difference and therefore a cooling part that provides the temperature difference and therefore can be simplified in configuration.

FIG. 4is a graph showing a relation between an electromotive voltage and the temperature of the thermoelectric transducer12. The term “electromotive voltage” of the thermoelectric transducer12used herein refers to the potential difference between an end portion of the thermoelectric transducer12on the side of the p-type semiconductor part12bserving as a positive electrode and an end portion of the thermoelectric transducer12on the side of the n-type semiconductor part12aserving as a negative electrode. More specifically, the relation shown inFIG. 4shows temperature characteristics of the electromotive voltage produced when the thermoelectric transducer12is heated in such a manner that no temperature difference is produced between the n-type semiconductor part12aand the p-type semiconductor part12b. Note that the temperature range in which the electromotive voltage is produced differs depending on the composition of the thermoelectric transducer.

As shown inFIG. 4, the electromotive voltage is produced when the thermoelectric transducer12is heated to the temperature T0 or higher. More specifically, as the temperature of the thermoelectric transducer12increases, the electromotive voltage also increases. A possible reason why the electromotive voltage increases as the temperature increases as shown inFIG. 4is that, as the amount of heat supplied increases, the number of electrons and holes that can be excited in the intrinsic semiconductor part12c, which has a relatively low band gap energy, increases. As shown inFIG. 4, the electromotive voltage reaches a peak value at a certain temperature T1 and decreases as the thermoelectric transducer12is further heated beyond the temperature T1. A possible reason for this is that, as the temperature of the thermoelectric transducer12increases, not only electrons and holes in the intrinsic semiconductor part12cbut also electrons and holes in the n-type semiconductor part12aand the p-type semiconductor part12bare thermally excited.

[Method of Installing Thermoelectric Transducer (Transducer Stack) on Exhaust Pipe and Overall Configuration of Power Generator]

As can be seen fromFIG. 4described above, power generation by using the thermoelectric transducer12is possible if the temperature of the thermoelectric transducer12falls within a predetermined range. More favorably, efficient power generation is possible if the temperature of the thermoelectric transducer12is close to the temperature T1 at which the peak electromotive voltage is achieved. Thus, to achieve efficient power generation using the thermoelectric transducers12on the vehicle, a heat supplier, which can supply heat to the thermoelectric transducers12so that the temperature of each of the thermoelectric transducers12approaches a temperature suitable for power generation, is selected from among components of the vehicle, and the thermoelectric transducers12are installed on the selected heat supplier. More specifically, the temperature of the exhaust gas in the exhaust pipe2decreases as it flows downstream, and therefore, the wall temperature of the exhaust pipe2is lower in downstream parts of the exhaust pipe2than in upstream parts. When the exhaust pipe2is used as the heat supplier as in the present embodiment, the installation site of the thermoelectric transducer12on the exhaust pipe2along the direction of flow of the exhaust gas is determined so that a heat source that allows efficient power generation is provided.

(Issue with Efficient Power Generation)

As described above, the thermoelectric transducer12is configured to produce an electromotive voltage as a result of the movement of electrons and holes caused by the electrons in the intrinsic semiconductor part12cbeing thermally excited when the thermoelectric transducer12is supplied with heat from the heat supplier. If a temperature difference is produced in the thermoelectric transducer12in such a manner that the temperature of the intrinsic semiconductor part12cis higher than the temperature of the n-type semiconductor part12aand the p-type semiconductor part12b, thermal excitation of electrons in the intrinsic semiconductor part12cis promoted compared with thermal excitation of electrons in the n-type semiconductor part12aand the p-type semiconductor part12b. This is favorable, rather than an issue. However, depending on the installation of the thermoelectric transducer12, a temperature difference may be produced in such a manner that the temperature of one or both of the n-type semiconductor part12aand the p-type semiconductor part12bis higher than the temperature of the intrinsic semiconductor part12c. As the temperature difference in this manner increases, electrons are more easily thermally excited in the one or both of the n-type semiconductor part12aand the p-type semiconductor part12b. This may make it harder for the thermoelectric transducer12to produce the electromotive voltage. To achieve efficient power generation using the thermoelectric transducers12, it is useful to prevent occurrence of the temperature difference in the latter manner. To this end, each of the thermoelectric transducers12(transducer stack14) is favorably installed on the heat supplier in such a manner as to ensure heat input to the intrinsic semiconductor part12c.

(Method of Installing Thermoelectric Transducer (Transducer Stack) According to First Embodiment)

In view of the above description, according to the present embodiment, the transducer stack14, which is a stack of thermoelectric transducers12, is installed on an outer surface of the exhaust pipe2in the arrangement shown inFIG. 5described below.

FIG. 5is a schematic diagram showing a specific configuration of the power generator10according to the first embodiment of the present disclosure. InFIG. 5and other drawings, for the sake of clarity of the arrangement of the thermoelectric transducers12, the n-type semiconductor part12aand the p-type semiconductor part12bof the thermoelectric transducer12are distinguished by color. The intrinsic semiconductor part12cbetween the n-type semiconductor part12aand the p-type semiconductor part12blies around the boundary between the parts12aand12b. In the example shown inFIG. 5, the transducer stack14is installed on a flat part of the exhaust pipe2. However, the transducer stack14may be installed in conformity to the curved outer surface of a cylindrical exhaust pipe2.

As shown inFIG. 5, in the transducer stack14, adjacent thermoelectric transducers12are connected in series with each other with an electrode16interposed therebetween. That is, the transducer stack14includes the thermoelectric transducers12and the electrodes16. The electrode16may be made of a metal material, such as copper, that has low electrical resistance. According to the principle of power generation of the thermoelectric transducer12described above, the p-type semiconductor part12bserves as a positive electrode, and the n-type semiconductor part12aserves as a negative electrode. Therefore, an electric current caused by the electromotive force produced by power generation flows from the p-type part to the n-type part. In the present embodiment, in order to ensure that the electric current smoothly flows while maximizing the potential difference between the opposite ends of the electrode16, the electrode16is configured to connect an end portion12ae(seeFIG. 2) of the n-type semiconductor part12aon the opposite side to the intrinsic semiconductor part12cof one thermoelectric transducer12(which corresponds to a “first thermoelectric transducer” according to the present disclosure) and an end portion12be(seeFIG. 2) of the p-type semiconductor part12bon the opposite side to the intrinsic semiconductor part12cof another thermoelectric transducer12(which corresponds to a “second thermoelectric transducer” according to the present disclosure) to each other. In other words, the electrode16is configured to connect parts having the highest band gap energy to each other.

More specifically, the surface of the end portion12aeof the n-type semiconductor part12aincludes an end face12aesand a portion of the side surface of the n-type semiconductor part12athat is close to the end face12aes. Similarly, the surface of the end portion12beof the p-type semiconductor part12bincludes an end face12besand a portion of the side surface of the p-type semiconductor part12bthat is close to the end face12bes. In the example shown inFIG. 5, the electrode16connects the end face12aesand the end face12besto each other. However, according to the present disclosure, any electrode that connects the end portions of adjacent thermoelectric transducers (the end portion of the n-type semiconductor part on the opposite side to the intrinsic semiconductor part and the end portion of the p-type semiconductor part on the opposite side to the intrinsic semiconductor part) to each other can be used. Thus, as an alternative to the example described above, the electrode16may be configured to connect the portion of the side surface of the n-type semiconductor part12athat is close to the end face12aesand the portion of the side surface of the p-type semiconductor part12bthat is close to the end face12besto each other.

The way of stacking of the thermoelectric transducers12is not particularly limited. In the example shown inFIG. 5, the transducer stack14is provided with the thermoelectric transducers12stacked in series with each other in a serpentine form. With the transducer stack14, by appropriately determining the number of thermoelectric transducers12stacked, any desired level of electromotive voltage can be produced under the temperature condition of the thermoelectric transducers12expected from the heat supply from the exhaust pipe2.

The power generator10according to the present embodiment is characterized in that each thermoelectric transducer12forming the transducer stack14is installed on the exhaust pipe2in the manner described below. That is, as shown inFIG. 5, each thermoelectric transducer12is installed with a portion of the surface of the intrinsic semiconductor part12cin contact with the surface (more specifically, outer surface) of the exhaust pipe2with an insulating member18interposed therebetween. In the example of the shape of the thermoelectric transducer12shown inFIG. 5, the portion of the surface of the intrinsic semiconductor part12cis a surface of the intrinsic semiconductor part12cincluded in the side surface of the thermoelectric transducer12facing the exhaust pipe2(insulating member18).

The insulating member18is provided to suppress a leakage of the electric current from the thermoelectric transducer12to the exhaust pipe2(metal member). Thus, the insulating member18is interposed not only between the thermoelectric transducer12and the exhaust pipe2but also between the electrode16and the exhaust pipe2. The power generator10is required to transfer the heat of the exhaust gas (from the internal combustion engine1), which is a heat source, from the exhaust pipe2, which is a heat supplier, to each thermoelectric transducer12through the insulating member18. Therefore, the insulating member18is made of a material that has a higher electrical resistance than that of the electrode16and high thermal conductivity. Such a material is silicon nitride, aluminum nitride, aluminum oxide, or boron nitride, for example.

In the configuration shown inFIG. 5, the insulating member18interposed between each thermoelectric transducer12and the exhaust pipe2corresponds to an “intermediate member” according to the present disclosure. And the surface of the insulating member18on the side of the thermoelectric transducer12corresponds to a “heat supply surface” according to the present disclosure. If the surface of the heat supplier is in direct contact with the thermoelectric transducer, the surface of the heat supplier corresponds to the “heat supply surface” according to the present disclosure.

Furthermore, each thermoelectric transducer12according to the present embodiment is installed in such a manner that a portion of the surface of the intrinsic semiconductor part12cis in contact with the heat supply surface with the entire side surface of the thermoelectric transducer12facing the exhaust pipe2(more specifically, insulating member18) in contact with the surface of the insulating member18(that is, heat supply surface). The aforementioned entire side surface includes not only the side surface of the intrinsic semiconductor part12cbut also the side surfaces of the n-type semiconductor part12aand the p-type semiconductor part12b.

(Overall Configuration of Power Generator)

The power generator10is provided with an electrical circuit20that is configured to connect the opposite ends of the transducer stack14by conductive wires. The electrical circuit20is opened and closed with a switch22. Electrical equipment (such as a light)24mounted on the vehicle is connected to the electrical circuit20. The switch22is opened and closed under the control of an electronic control unit (ECU)26mounted on the vehicle.

With the power generator10configured as described above, during activation of the vehicle system, the transducer stack14is enabled to generate power by closing the switch22when the temperature of the thermoelectric transducers12reaches a temperature suitable for power generation as a result of heat from the exhaust gas being supplied to the thermoelectric transducers12via the exhaust pipe2and the insulating member18. In the present embodiment, the heat source is the exhaust gas, so that the exhaust heat of the internal combustion engine1can be recovered by the power generation. In addition, the electric power obtained by the power generation by the transducer stack14can be supplied to the electrical equipment24. The switch22may be replaced with a variable resistor. In this example, the electric power supplied from the transducer stack14to the electrical equipment24can be controlled in more detail by adjusting the resistance of the variable resistor. Vehicle equipment that receives the electric power is not limited to the electrical equipment24, and a battery that accumulates electric power may be connected to the electrical circuit20instead of or in addition to the electrical equipment24, for example.

Although not shown inFIG. 5, the transducer stack14is covered with a protective cover. In addition, the transducer stack14is fixed to the exhaust pipe2with an attachment not shown in the drawing.

[Advantage of Method of Installing Thermoelectric Transducer (Transducer Stack) According to First Embodiment]

FIGS. 6A and 6Bare diagrams for illustrating an advantage of the method of installing the thermoelectric transducer12according to the first embodiment.FIG. 6Ashows the thermoelectric transducer12installed in the method according to the present embodiment, as with the configuration shown inFIG. 5.FIG. 6Bshows the thermoelectric transducer installed in a method other than the method according to the present embodiment. More specifically, in the installation method shown inFIG. 6B, the thermoelectric transducer is installed on the heat supplier in such a manner that the end face of the n-type semiconductor part having the highest band gap energy is in contact with the heat supply surface, rather than the surface of the intrinsic semiconductor part being in contact with the heat supply surface.

If the thermoelectric transducer is installed as shown inFIG. 6B, more heat is supplied to the n-type semiconductor part than to the intrinsic semiconductor part. As a result, a temperature difference is produced in such a manner that the temperature of the intrinsic semiconductor part is lower than the temperature of the n-type semiconductor part. Thus, it is difficult to efficiently provide an electromotive voltage of the thermoelectric transducer as described above. To the contrary, according to the installation method according to the present embodiment shown inFIG. 6A, since the surface of the intrinsic semiconductor part12cis in contact with the heat supply surface (surface of the insulating member18), heat can be reliably input to the intrinsic semiconductor part12chaving a relatively low band gap energy. Thus, a temperature difference is less likely to be produced in such a manner that the temperature of the n-type semiconductor part12aor the p-type semiconductor part12bhaving a relatively high band gap energy is higher than the temperature of the intrinsic semiconductor part12c, so that the electromotive voltage of the thermoelectric transducer12can be efficiently provided. In addition, since heat can be reliably input to the intrinsic semiconductor part12c, the intrinsic semiconductor part12ccan be more likely to be supplied with as much heat from the heat supplier as possible even when the amount of heat supplied from the heat supplier is less than the ideal amount.

Next,FIGS. 7A and 7Bare diagrams for illustrating an advantage of the manner of stacking of the thermoelectric transducers12according to the first embodiment.FIG. 7Ashows the thermoelectric transducers12stacked in the manner according to the present embodiment, as with the configuration shown inFIG. 5.FIG. 7Bshows thermoelectric transducers stacked in another manner. More specifically, in both of the left and right configurations according to the stacking manner shown inFIG. 7B, the surface of the intrinsic semiconductor part of the lowermost thermoelectric transducer is in direct contact with the heat supply surface, and any other thermoelectric transducers have one or more thermoelectric transducers and electrodes placed below it between itself and the heat supply surface. In these configurations, the electrodes are disposed on the intrinsic semiconductor parts having a relatively low band gap energy.

If the thermoelectric transducers are stacked in the manner shown inFIG. 7B, the heat from the exhaust gas (heat source) is inevitably supplied to the thermoelectric transducers other than the lowermost thermoelectric transducer through the other thermoelectric transducers and the electrodes. To the contrary, in the stacking manner according to the present embodiment shown inFIG. 7A, a portion of the surface of the intrinsic semiconductor part12cof each thermoelectric transducer12of the transducer stack14is in contact with a different portion of the heat supply surface (surface of the insulating member18) (the portion corresponds to a “first portion of the heat supply surface” or a “second portion of the heat supply surface” according to the present disclosure). With such a configuration, unlike each of the configurations shown inFIG. 7B, the surfaces of the intrinsic semiconductor parts12cof all the thermoelectric transducers12forming the transducer stack14are in contact with the heat supply surface without any other thermoelectric transducer12interposed therebetween. As a result, the intrinsic semiconductor part12cof each individual thermoelectric transducer12can receive an approximately equal heat flux (amount of heat passing through a unit area per unit time) from the heat supply surface.

In the stacking manner according to the present embodiment shown inFIG. 7A, the electrode16is configured to connect the end face12aesof the n-type semiconductor part12aof one thermoelectric transducer12and the end face12besof the p-type semiconductor part12bof another thermoelectric transducer12to each other. Since the electrodes16are disposed to electrically connect the parts having the highest band gap energy to each other, the electromotive voltage can be efficiently provided, and heat can be reliably input to each intrinsic semiconductor part12c.

Second Embodiment

Next, with reference toFIGS. 8 to 12, a second embodiment of the present disclosure will be described.

FIG. 8is a schematic perspective view showing an overall configuration of a power generator30for a vehicle according to the second embodiment of the present disclosure. The power generator30according to the present embodiment includes a plurality of thermoelectric transducers12as components of a thermoelectric transducer module32. In the present embodiment, as in the first embodiment, the exhaust pipe2is used as an example of the heat supplier that supplies heat to the thermoelectric transducers12. The thermoelectric transducer module32is installed on the exhaust pipe2. In the following, a method of installing the thermoelectric transducer module32will be described in more details.

FIG. 9is a partial perspective view showing an internal structure of the thermoelectric transducer module32shown inFIG. 8.FIG. 10is a cross-sectional view of the thermoelectric transducer module32and the exhaust pipe2taken along the line A-A inFIG. 8. As shown in these drawings, the thermoelectric transducer module32includes the transducer stack14formed by a stack of a plurality of thermoelectric transducers12and a housing32athat houses the transducer stack14. The housing32ais formed to surround the transducer stack14. The housing32ais attached to a flat part of the exhaust pipe2with an attachment not shown. The housing32ais favorably made of a material having a high thermal conductivity and, for example, can be made of a metal, such as aluminum.

The housing32ahas a first wall part32a1that faces the exhaust pipe2when the thermoelectric transducer module32is installed. The first wall part32a1is shaped to conform to the outer surface (which is flat in an example of the present embodiment) of the exhaust pipe2. Once the thermoelectric transducer module32is installed on the exhaust pipe2, the outer surface of the first wall part32a1is in direct contact with the outer surface of the exhaust pipe2. The transducer stack14is provided with one side surface thereof facing an inner surface of the first wall part32a1with the insulating member18interposed therebetween.

The housing32ahas a second wall part32a2having an inner surface opposed to the inner surface of the first wall part32a1. The transducer stack14is disposed with a side surface thereof opposite to the above-described one side surface facing the first wall part32a1facing the second wall part32a2with the insulating member18interposed therebetween.

With such a configuration, the heat from the exhaust gas is transferred to the transducer stack14through the exhaust pipe2, the housing32aand the insulating member18. More specifically, the housing32areceives the heat from the exhaust gas at the outer surface of the first wall part32a1opposite to the inner surface of the first wall part32a1. Each thermoelectric transducer12of the transducer stack14receives heat from the inner surface of the first wall part32a1through the insulating member18and from the inner surface of the second wall part32a2through the insulating member18. In short, in the present embodiment, again based on the same concept as in the first embodiment, each thermoelectric transducer12is installed with the intrinsic semiconductor part12cin contact with the heat supply surface (surface of the insulating member18). Heat can therefore be supplied to the intrinsic semiconductor part12cof each thermoelectric transducer12from two directions (the first wall part32a1and the second wall part32a2).

In the present embodiment, the housing32a(wall parts32a1and32a2) and the insulating member18that are interposed between each thermoelectric transducer12and the exhaust pipe2correspond to the “intermediate member” according to the present disclosure. Moreover, the surfaces of the insulating members18that are located on the side of the thermoelectric transducer12and are in contact with the first wall part32a1and the second wall part32a2correspond to the “heat supply surfaces” (more specifically, a “first heat supply surface” and a “second heat supply surface”) according to the present disclosure. Further, the portions of the surface of the intrinsic semiconductor part12cthat are in contact with the surfaces of the insulating members18corresponding to the first and second heat supply surfaces correspond to a “first portion” and a “second portion” according to the present disclosure, respectively.

Next, an advantage of the method of installing the thermoelectric transducer (transducer stack) according to the present embodiment will be described.FIGS. 11A and 11Bare diagrams for illustrating an advantage of the method of installing the thermoelectric transducer12according to the second embodiment by focusing on an individual thermoelectric transducer12.FIG. 11Bshows the thermoelectric transducer installed in a method other than the method according to the present disclosure when the thermoelectric transducer receives heat from two directions (from the first and second wall parts). In the example of the installation method shown inFIG. 11B, the surface of the intrinsic semiconductor part is not in contact with any of the two heat supply surfaces in the two directions, and the end faces of the n-type semiconductor part and the p-type semiconductor part having the highest band gap energy are in contact with the respective opposed heat supply surfaces. With this configuration, more heat is supplied to the n-type semiconductor part and the p-type semiconductor part than to the intrinsic semiconductor part.

FIG. 11Ashows the thermoelectric transducer12installed in the method according to the present embodiment, as with the configuration shown inFIGS. 8 to 10. With the configuration according to the present embodiment, as shown inFIG. 11A, heat can be reliably supplied to the intrinsic semiconductor part12cthrough the insulating members18from both of the first wall part32a1and the second wall part32a2. Compared with the configuration according to the first embodiment in which heat is supplied in one direction, heat can be more uniformly input to each thermoelectric transducer12.

FIGS. 12A and 12Bare diagrams for illustrating an advantage of the manner of stacking of the thermoelectric transducers12according to the second embodiment.FIG. 12Bshows examples of the manlier of stacking of the thermoelectric transducers that is possible when heat is supplied in two directions. The manner of stacking of the thermoelectric transducers in these examples is the same as that shown inFIG. 7B. In both of the left and right configurations according to the stacking manner shown inFIG. 12B, the surfaces of the intrinsic semiconductor parts of the two thermoelectric transducers closest to the first and second wall parts of the housing are in direct contact with the two heat supply surfaces.

FIG. 12Ashows the thermoelectric transducers12stacked in the manner according to the present embodiment, as with the configuration shown inFIGS. 8 to 10. According to this stacking manner, on the sides of the first and second wall parts32a1and32a2, the surfaces of the intrinsic semiconductor part12cof each thermoelectric transducer12of the transducer stack14are in contact with different portions of the respective heat supply surfaces. As a result, the intrinsic semiconductor part12cof each individual thermoelectric transducer12can receive an approximately equal heat flux from the two heat supply surfaces.

In the stacking manner according to the present embodiment shown inFIG. 12A, the electrode16electrically connects the parts having the highest band gap energy to each other. Therefore, even when heat is supplied in two directions, the electromotive voltage can be efficiently provided, and heat can be reliably input to each intrinsic semiconductor part12c.

With the power generator30according to the present embodiment, main components for thermoelectric power generation are modularized as described below. That is, the power generator30has the thermoelectric transducer module32that includes the transducer stack14that is a stack of a plurality of thermoelectric transducers12and the housing32awhich not only serves to house and protect the transducer stack14but also serves as an intermediate member for transferring heat from the exhaust pipe2to the transducer stack14. With the power generator30, thermoelectric power generation using the thermoelectric transducers12can be achieved simply by installing the thermoelectric transducer module32on the exhaust pipe2and forming the electrical circuit20.

In the transducer stack14in the thermoelectric transducer module32, the thermoelectric transducers12are stacked in a serpentine form along the first wall part32a1of the housing32ainstalled to conform to the outer surface of the exhaust pipe2. When the thermoelectric transducers12are stacked in this manner, placing the thermoelectric transducer module32in such a manner that the first wall part32a1is in conformity to the outer surface of the exhaust pipe2(or the second wall part32a2is in conformity to the outer surface of the exhaust pipe2) as described above is favorable because an adequate area of the housing32acan be used for heat transfer from the exhaust pipe2. However, the stacking pattern of the thermoelectric transducers12is not limited to this pattern, and any stacking pattern is possible as far as it meets the requirement that at least a portion of the surface of the intrinsic semiconductor part12cof each thermoelectric transducer12is in contact with the “heat supply surface”. The shape of the housing for the transducer stack differs depending on the stacking pattern. The orientation of the thermoelectric transducer module with respect to the exhaust pipe2can be appropriately determined from the viewpoint of efficiency of heat transfer to the transducer stack depending on the stacking pattern and the shape of the housing.

In this second embodiment, an example has been described in which each thermoelectric transducer12receives heat from two heat supply surfaces (in two directions). However, according to the present disclosure, the surface of the intrinsic semiconductor part of the thermoelectric transducer can be in contact with three or more heat supply surfaces. For example, in a configuration in which thermoelectric transducers having the shape of a rectangular parallelepiped are stacked to form a transducer stack having the shape of a rod, and the rod-shaped transducer stack is housed in a housing having the shape of a rectangular parallelepiped, three or four of the four inner side surfaces of the housing may be in contact with the surface of the intrinsic semiconductor part. The configuration in which the four inner side surfaces (that is, all the side surfaces) are used as heat supply surfaces corresponds to a configuration in which the whole of the surface of the intrinsic semiconductor part is in contact with the heat supply surface, as shown inFIG. 21described later.

In this second embodiment, an example has been described in which the heat supply surfaces for all the thermoelectric transducers12forming the transducer stack14are the surfaces of the insulating members18on the side of the thermoelectric transducers12. However, the heat supply surfaces for only some of the plurality of thermoelectric transducers forming the transducer stack housed in the housing of the thermoelectric transducer module according to the present disclosure may be the surfaces of the insulating members on the side of the thermoelectric transducers. In an arrangement that requires no insulating member between the housing and the thermoelectric transducers, the heat supply surfaces for at least some of the plurality of thermoelectric transducers forming the transducer stack may be the inner surface of the housing. This holds true for transducer stacks42and64described later.

Third Embodiment

Next, with reference toFIGS. 13 and 14, a third embodiment of the present disclosure will be described.

FIG. 13is a schematic perspective view showing an overall configuration of a power generator40for a vehicle according to the third embodiment of the present disclosure. The power generator40according to the present embodiment includes a transducer stack42. A plurality of thermoelectric transducers12forming the transducer stack42are connected in series with each other with an electrode44interposed between every adjacent two of the thermoelectric transducers12, as shown inFIG. 13. The stacking pattern of the transducer stack42is the same as that of the transducer stack14according to the first embodiment, for example. The power generator40differs from the power generator10according to the first embodiment in arrangement of the electrodes44. The following description will be focused on the difference.

As shown inFIG. 13, each electrode44that connects two thermoelectric transducers12to each other is disposed not to be in contact with any of the exhaust pipe serving as the heat supplier that supplies heat to the transducer stack42and the insulating member18serving as the intermediate member that transfers the heat. In other words, there is an air layer46between the surface of the electrode44and the surface of the exhaust pipe2(heat supply surface).

FIGS. 14A and 14Bare diagrams for illustrating an advantage of the arrangement of the electrodes44according to the third embodiment.FIG. 14Bshows the arrangement of the electrode16according to the first embodiment. In this arrangement, the surface of the electrode16is in direct contact with the surface of the insulating member18serving as the heat supply surface. The electrode16made of metal basically has a higher thermal conductivity than the thermoelectric transducer12. Therefore, with the arrangement shown inFIG. 14B, the electrode16has a stronger tendency to receive heat than the thermoelectric transducer12. As a result, the heat supplied to the electrode16through the insulating member18is easily transferred to the parts of the thermoelectric transducer12that are in contact with the electrode16(that is, the end faces12aesand12besof the n-type semiconductor part12aand the p-type semiconductor part12bhaving the highest band gap energy).

On the other hand, in the arrangement according to the present embodiment shown inFIG. 14A, there is the air layer46between the surface of the electrode44and the surface of the exhaust pipe2, and the surface of the electrode44is not in contact with the surface of the exhaust pipe2. With such an arrangement, heat is transferred through the air layer46from the surface of the exhaust pipe2(heat supply surface) to the surface of the electrode44on the side of the exhaust pipe2. Thus, the heat flux received by the surface of the electrode44from the surface of the exhaust pipe2in this heat transfer is lower than the heat flux received by the surface of the intrinsic semiconductor part12cof the thermoelectric transducer12via heat conduction from the surface of the insulating member18(heat supply surface). As a result, heat input from the electrode44to the n-type semiconductor part12aand the p-type semiconductor part12bcan be reduced. As a result, a temperature difference is less likely to be produced in such a manner that the temperature of the n-type semiconductor part12aor the p-type semiconductor part12bhaving a relatively high band gap energy is higher than the temperature of the intrinsic semiconductor part12c. Thus, efficient power generation can be achieved.

Fourth Embodiment

Next, with reference toFIG. 15, a fourth embodiment of the present disclosure will be described. In the third embodiment described above, the power generator40has the air layer46between the surface of the electrode44and the surface of the exhaust pipe2(heat supply surface). However, according to the present disclosure, the specific arrangement for reducing the heat flux received by the surface of the electrode on the side of the heat supply surface compared with the heat flux received by the surface of the intrinsic semiconductor part12cof the thermoelectric transducer from the heat supply surface is not limited to the arrangement in the example described above, and the arrangement described below with reference toFIG. 15is also possible, for example.

FIG. 15is a diagram for illustrating an arrangement of the electrode44in a power generator50for a vehicle according to the fourth embodiment of the present disclosure. In the power generator50shown inFIG. 15, instead of the air layer46, a heat insulator52(which corresponds to a “heat insulator” according to the present disclosure) is disposed between the surface of the electrode44and the surface of the exhaust pipe2(heat supply surface). More specifically, the heat insulator52is made of a material (such as ceramics) that has a lower thermal conductivity than that of the electrode44. The arrangement using the heat insulator52can also reduce the heat transfer from the exhaust pipe2to the electrode44. As a result, the temperature difference in the manner described above is less likely to be produced, and efficient power generation can be achieved. The heat insulator52may be a separate member attached to the surface of the electrode44or a coating layer applied to the surface of the electrode44, for example.

Fifth Embodiment

Next, with reference toFIGS. 16 and 17, a fifth embodiment of the present disclosure will be described.

FIG. 16is a schematic diagram showing an overall configuration of a power generator60for a vehicle according to the fifth embodiment of the present disclosure. The power generator60according to the present embodiment is provided with a thermoelectric transducer module62. The thermoelectric transducer module62includes a transducer stack64and the housing32adescribed above with regard to the second embodiment. The plurality of thermoelectric transducers12forming the transducer stack64are connected in series with each other with an electrode66interposed between every adjacent two of the thermoelectric transducers12, as shown inFIG. 16. The configuration of the transducer stack64is the same as the transducer stack14or42described above except for the arrangement of the electrode66.

The arrangement of the electrode66according to the present embodiment is equivalent to the arrangement in which heat is supplied to each thermoelectric transducer12in two directions to which the same concept of the electrode44according to the third embodiment is additionally applied. That is, as shown inFIG. 16, each electrode66that connects two thermoelectric transducers12is disposed not to be in contact with any of the wall parts32a1and32a2of the housing32aand the insulating member18that serve as the intermediate member for transferring heat to the transducer stack64. In other words, an air layer68is provided between the surface of the electrode66and the surface of the first wall part32a1(heat supply surface) and between the surface of the electrode66and the surface of the second wall part32a2(heat supply surface).

FIGS. 17A and 17Bare diagrams for illustrating an advantage of the arrangement of the electrode66according to the fifth embodiment.FIG. 17Bshows the arrangement of the electrode16according to the second embodiment. In the arrangement shown inFIG. 17B, the electrode16is in direct contact with the surface of the insulating member18serving as the heat supply surface on both of the sides of the first wall part32a1and the second wall part32a2.

On the other hand, in the arrangement according to the present embodiment shown inFIG. 17A, there is the air layer68between the surface of the electrode66and the surface of the first wall part32a1(heat supply surface) and between the surface of the electrode66and the surface of the second wall part32a2(heat supply surface), and the electrode66is not in contact with any of the wall parts32a1and32a2. With such an arrangement, both on the sides of the first wall part32a1and the second wall part32a2, the heat flux received by the surface of the electrode66from the surfaces of the wall parts32a1and32a2(heat supply surfaces) is lower than the heat flux received by the surface of the intrinsic semiconductor part12cof the thermoelectric transducer12from the surface of the insulating member18(heat supply surface). As a result, heat input from the electrode66to the n-type semiconductor part12aand the p-type semiconductor part12bcan be reduced, and efficient power generation can be achieved.

Sixth Embodiment

Next, with reference toFIG. 18, a sixth embodiment of the present disclosure will be described. As with the relation between the configuration according to the third embodiment shown inFIG. 14Aand the configuration according to the fourth embodiment shown inFIG. 15, the configuration according to the fifth embodiment shown inFIG. 17Acan be modified into the configuration shown inFIG. 18described below.

FIG. 18is a diagram for illustrating an arrangement of the electrode66in a power generator70for a vehicle according to the sixth embodiment of the present disclosure. In the power generator70shown inFIG. 18, instead of the air layer68, a heat insulator72having the same configuration as the heat insulator52is disposed between the surface of the electrode66and the surface of the wall part32a1of the housing32a(heat supply surface) and between the surface of the electrode66and the surface of the wall part32a2of the housing32a(heat supply surface). The arrangement using the heat insulator72can also reduce the heat transfer from the wall parts32a1and32a2to the electrode66. As a result, heat input from the electrode66to the n-type semiconductor part12aand the p-type semiconductor part12bcan be suppressed, and efficient power generation can be achieved.

In the first to sixth embodiments described above, the power generator10,30,40,50,60or70is provided with the transducer stack14,42or64formed by a plurality of thermoelectric transducers12. However, the present disclosure is not necessarily limited to the power generators including a plurality of thermoelectric transducers in the form of a transducer stack, and the power generator according to the present disclosure may include only one thermoelectric transducer.

FIG. 19is a diagram for illustrating another method of installing the thermoelectric transducer12shown inFIG. 2. An exhaust pipe82of a vehicle that incorporates a power generator80shown inFIG. 19includes an exhaust pipe main part82a. The exhaust pipe main part82ahas, on the outer surface thereof, a fin part82bextending in a direction perpendicular to the direction of the flow path of the exhaust pipe82. The thermoelectric transducer12of the power generator80is installed on the fin part82bwith the insulating member18interposed therebetween. In addition, a heat insulator84(which corresponds to the “heat insulator” according to the present disclosure) is interposed between the surface of the exhaust pipe main part82a(heat supply surface) and the end portion12ae(more specifically, the end face12aes) of the n-type semiconductor part12a. The heat insulator84is made of a material (such as ceramics) that has a lower thermal conductivity than that of the thermoelectric transducer12. With such a configuration, although the end portion12aeof the n-type semiconductor part12a, that is, the part having the highest band gap energy, is disposed close to the heat supply surface, heat input to that part can be suppressed. As an alternative to the configuration shown inFIG. 19, the heat insulator84may be disposed between the end portion12beof the p-type semiconductor part12band the heat supply surface. With any of the configuration shown inFIG. 19and the alternative thereto, again, heat can be supplied to the thermoelectric transducer12while a temperature difference can be less likely to be produced in such a manner that the temperature of the n-type semiconductor part12aand the p-type semiconductor part12bhaving a relatively high band gap energy is higher than the temperature of the intrinsic semiconductor part12c.

FIG. 20is a diagram for illustrating another method of installing the thermoelectric transducer12shown inFIG. 2. An exhaust pipe92of a vehicle that incorporates a power generator90shown inFIG. 20includes an exhaust pipe main part92a. The exhaust pipe main part92ahas, on the outer surface thereof, a protrusion92bprotruding in a direction perpendicular to the direction of the flow path of the exhaust pipe92. The thermoelectric transducer12of the power generator90is installed on the protrusion92bwith the insulating member18interposed therebetween. As shown inFIG. 20, the thermoelectric transducer12is not in contact with the heat supply surface (surface of the insulating member18) at the whole of the side surface thereof on the side of the exhaust pipe92but only at the side surface of the intrinsic semiconductor part12cand the side surface of a part of the thermoelectric transducer12close to the intrinsic semiconductor part12c. With such a configuration, heat can be intensively input to the intrinsic semiconductor part12chaving a lower band gap energy than the n-type semiconductor part12aand the p-type semiconductor part12b. Thus, with this configuration, the temperature difference in the manner described above is less likely to occur. The protrusion92bmay be an intermediate member that is separated from the exhaust pipe92and transfers heat from the exhaust pipe92to the thermoelectric transducer12. According to the present disclosure, any method of installing the thermoelectric transducer is possible including the example shown inFIG. 20, as far as it ensures that, of the surface of the thermoelectric transducer, at least a portion (one side surface, if the thermoelectric transducer has the shape of a prism, for example) of at least the surface of the intrinsic semiconductor part is in contact with the heat supply surface.

FIGS. 21A and 21Bare diagrams for illustrating another method of installing the thermoelectric transducer12shown inFIG. 2. In a power generator100shown inFIG. 21A, the thermoelectric transducer12is installed on the exhaust pipe2with an intermediate member102and the insulating member18interposed therebetween.FIG. 21Bis a cross-sectional view of the thermoelectric transducer12and the surrounding structure taken along the line B-B inFIG. 21A. As can be seen from these drawings, the thermoelectric transducer12is inserted into a through-hole102aformed in the intermediate member102, and the surface of the intrinsic semiconductor part12cand a part of the thermoelectric transducer12close to the intrinsic semiconductor part12cis covered with the intermediate member102with the insulating member18interposed therebetween. Inside the through-hole102a, the whole of the side surface of the thermoelectric transducer12is in contact with the surface of the insulating member18(heat supply surface). That is, in this configuration, unlike the configurations in which only a portion of the surface of the intrinsic semiconductor part12cis in contact with the heat supply surface, such as the configuration shown inFIG. 5, the whole of the surface of the intrinsic semiconductor part12cis in contact with the surface of the insulating member18(heat supply surface). According to this configuration, heat from the exhaust gas is supplied from the exhaust pipe2to the thermoelectric transducer12through the intermediate member102and the insulating member18. With such a configuration, again, heat can be intensively input to the intrinsic semiconductor part12chaving a relatively low band gap energy.

FIGS. 22A and 22Bare diagrams for illustrating another manner of stacking of the thermoelectric transducers12shown inFIG. 2. In a power generator110shown inFIG. 22A, again, each thermoelectric transducer12is installed on the exhaust pipe2with the insulating member18interposed therebetween. Of course, as in the other examples, each thermoelectric transducer12is disposed with the intrinsic semiconductor part12cin contact with the heat supply surface (surface of the insulating member18).

FIG. 22Bis a plan view of the thermoelectric transducer12viewed in the direction of the arrow C inFIG. 22A. As can be seen from these drawings, end faces12besof the p-type semiconductor parts12bserving as a positive electrode of adjacent thermoelectric transducers12(which correspond to the “first thermoelectric transducer” and the “second thermoelectric transducer” according to the present disclosure) are electrically connected to each other by an electrode112(which corresponds to a “positive electrode” according to the present disclosure), and end faces12aesof the n-type semiconductor part12aserving as a negative electrode of the adjacent thermoelectric transducers12are electrically connected to each other by an electrode114(which corresponds to a “negative electrode” according to the present disclosure). The transducer stack of a plurality of thermoelectric transducers12is not limited to the stack including the thermoelectric transducers12connected in series with each other, such as those in the examples described above, and a stack including the thermoelectric transducers12connected in parallel with each other, such as the configuration shown inFIGS. 22A and 22B, is also possible. As an alternative, the transducer stack according to the present disclosure may be a combination of a series connection of a plurality of thermoelectric transducers12and a parallel connection of a plurality of thermoelectric transducers12. In addition, the combination may not be on a thermoelectric transducer basis. For example, a plurality of thermoelectric transducers are connected in series with each other to form a transducer stack that provides a desired electromotive voltage, and a plurality of thermoelectric transducer modules each including such a transducer stack may be connected in parallel with each other.

Furthermore, in the configuration shown inFIGS. 22A and 22B, as with the configuration according to the third embodiment, an air layer116is provided between the surface of the electrode114on the side of the exhaust pipe2and the surface of the exhaust pipe2(heat supply surface). As an alternative, as with the configuration according to the fourth embodiment, the heat insulator52may be disposed between the surface of the electrode114on the side of the exhaust pipe2and the surface of the exhaust pipe2(heat supply surface).

FIG. 23is a diagram for illustrating another method of installing the thermoelectric transducer12shown inFIG. 2. In a power generator120shown inFIG. 23, each thermoelectric transducer12is supplied with heat from two heat suppliers of a vehicle, more specifically, a housing of a battery122and a cooling water hose124. With such a configuration, the intrinsic semiconductor part12cof each thermoelectric transducer12is in contact with the surface of the battery122and the surface of the cooling water hose124(that is, the heat supply surfaces of the two heat suppliers). The housing of the battery122is made of resin, and the cooling water hose124is made of rubber. That is, these heat suppliers are made of materials having high insulating properties. Thus, this configuration corresponds to an example in which there is no insulating member18serving as the intermediate member, and the surface of the heat supplier serves as the heat supply surface with which the thermoelectric transducer12is in contact.

According to the present disclosure, as an alternative to the two heat suppliers in the example shown inFIG. 23, three or more heat suppliers may be used to supply heat to a thermoelectric transducer. Furthermore, in the configuration shown inFIG. 23, the heat source of the housing of the battery122is the battery122itself, and the heat source of the cooling water hose is the engine cooling water (from the internal combustion engine1). The plurality of heat suppliers according to the present disclosure do not have to have different heat sources as in the configuration of the example shown inFIG. 23, and a plurality of heat suppliers that share the same heat source (engine cooling water), such as a radiator and the cooling water hose, can also be used.

The embodiments and modifications described above may be combined in other ways than those explicitly described above as required and may be modified in various ways without departing from the scope of the present disclosure.