Abstract:
A thermoelectric generator comprising: at least a high-temperature heat source using a high-temperature fluid; at least a low-temperature heat source using a low-temperature fluid lower in temperature than the high-temperature fluid; and a plurality of thermoelectric elements arranged in parallel between the high-temperature heat source and the low-temperature heat source; wherein at least selected one of the high-temperature heat source and the low-temperature heat source is connected with a frame surrounding the plurality of thermoelectric elements.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a thermoelectric generator for generating power, by the Seebeck effect, due to a temperature difference across thermoelectric elements.  
         [0003]     2. Description of the Related Art  
         [0004]     A conventional thermoelectric generator is disclosed in Japanese Unexamined Patent Publication No. 11-40863. In this generator a plurality of thermoelectric elements (thermoelectric generating modules) are arranged in parallel and are held between a high-temperature heat source (heat absorption structure on the high temperature side) and a low-temperature side heat source (heat radiation structure on the low temperature side), so that electric power is generated due to the temperature difference across the high-temperature heat source and the low-temperature heat source.  
         [0005]     One of the surfaces of the high-temperature heat source and the low-temperature side heat source in contact with the thermoelectric elements is held integrally with an elastic flat plate, and a plurality of flat metal plates are independently coupled to each of a plurality of thermoelectric elements. A thickness variation, if any, in the thermoelectric elements is absorbed by the elastic flat plate, so that all the thermoelectric elements are in satisfactory thermal contact with each other.  
         [0006]     In order to prevent the displacement of a plurality of the thermoelectric elements held by the high-temperature heat source and the low-temperature heat source, however, the thermoelectric elements are each coupled to a flat metal plate and, therefore, the assembly thereof requires considerable labor.  
         [0007]     The patent document described above discloses the provision of a guide rib on the outer periphery of the flat metal plate to facilitate the positioning. The surface roughness and the flatness of the flat metal plate, however, may be deteriorated during the rib machining process, thereby adversely affecting the originally-intended satisfactory thermal contact.  
       SUMMARY OF THE INVENTION  
       [0008]     In view of the problem described above, the object of this invention is to provide a thermoelectric generator in which a plurality of thermoelectric elements are held between the high-temperature heat source and the low-temperature heat source while maintaining a satisfactory thermal contact with the high-temperature heat source and the low-temperature heat source, and the plurality of the thermoelectric elements can be assembled easily.  
         [0009]     In order to achieve this object, according to this invention, there is provided a thermoelectric generator employing the technical means described below.  
         [0010]     In order to accomplish the above object, according to a first aspect of the present invention, there is provided a thermoelectric generator comprising: at least a high-temperature heat source using a high-temperature fluid; at least a low-temperature heat source using a low-temperature fluid lower in temperature than the high-temperature fluid; and a plurality of thermoelectric elements arranged in parallel between the high-temperature heat source and the low-temperature heat source; wherein at least a selected one of the high-temperature heat source and the low-temperature heat source is connected with a frame surrounding the plurality of the thermoelectric elements.  
         [0011]     Without deteriorating the surface roughness and the parallelism of the surfaces of each high-temperature heat source and each low-temperature heat source in contact with a plurality of thermoelectric elements, a satisfactory thermal contact is secured while making it possible to set a plurality of the thermoelectric elements in position, thereby eliminating the need to couple the plurality of the thermoelectric elements to the high-temperature heat source or the low-temperature heat source for an improved assembly performance.  
         [0012]     The plurality of the thermoelectric elements are connected in series or in parallel to each other. In the case where the lead wires extending from the thermoelectric elements are twisted or brazed to each other or connected by connectors or the like, the lead wires from the thermoelectric elements project or otherwise hamper the assembly work. Under an external vibration load, on the other hand, stress is concentrated at the roots of the lead wires in view of the fact that the forward ends of the lead wires are free, thereby sometimes breaking the lead wires.  
         [0013]     According to a second aspect of the present invention, the plurality of the thermoelectric elements are connected electrically to each other through a plurality of conducting portions arranged on the frame.  
         [0014]     According to this invention, the unnecessary projection of the lead wires described above is eliminated, and the assembly work is thus eased. Also, as the lead wires are fixed on conducting portions, the risk of breakage under an external vibration load is eliminated.  
         [0015]     In the second aspect of connection, as a third aspect of the present invention, the plurality of the conducting portions can be connected by brazing.  
         [0016]     Moreover, as a fourth aspect of the present invention, the plurality of the conducting portions may be connected by inserting the lead wires of the plurality of the thermoelectric elements into holes formed in the conducting portions. As a result, the lead wires can be connected to the conducting portions by one touch while brazing is eliminated.  
         [0017]     Moreover, according to a fifth aspect of the present-invention, the direction in which the lead wires are arranged and the holes are formed is coincident with the direction in which the plurality of the thermoelectric elements are inserted into the frame. As a result, The lead wires of the plurality of the thermoelectric elements can be inserted into holes while thermoelectric elements are inserted into the frame for an improved workability.  
         [0018]     The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a schematic diagram showing a general configuration including an engine.  
         [0020]      FIG. 2  is an exploded perspective view showing a general configuration of a thermoelectric generator.  
         [0021]      FIG. 3  is a plan view showing a frame according to a first embodiment.  
         [0022]      FIGS. 4A, 4B  are a plan view and a side view, respectively, showing the manner in which the lead wires of the thermoelectric elements arranged in the frame of  FIG. 3  are connected to each other.  
         [0023]      FIG. 5  is a plan view showing a frame according to a second embodiment.  
         [0024]      FIGS. 6A, 6B  are a plan view and a side view, respectively, showing the manner in which the lead wires of the thermoelectric elements arranged in the frame of  FIG. 5  are connected to each other.  
         [0025]      FIG. 7  is a sectional view taken in line A-A in  FIG. 6 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     A first embodiment of the invention is explained. A thermoelectric generator  100  according to the invention is used for an automotive vehicle having a water-cooled engine  10 , in which the waste heat energy generated by the cooling of the engine  10  is recovered as electric energy. First, the basic configuration of the thermoelectric generator  100  is explained with reference to FIGS.  1  to  4 . In this connection,  FIG. 1  is a schematic diagram showing a general configuration including an engine  10 ,  FIG. 2  is an exploded perspective view showing a general configuration of a thermoelectric generator  100 ,  FIG. 3  is a plan view showing a frame  140  according to a first embodiment, and  FIGS. 4A, 4B  are a plan view and a side view, respectively, showing the manner in which the lead wires  131  of the thermoelectric elements  130  arranged in the frame of  FIG. 3  are connected to each other.  
         [0027]     As shown in  FIG. 1 , the engine  10  includes an engine cooling water circuit  20  and a radiator  21 . The cooling water in the engine  10  is circulated by a water pump  11  through the engine cooling water circuit  20  and the radiator  21 . The heat radiation of the radiator  21  cools the cooling water and the operating temperature of the engine  10  is appropriately controlled. The engine cooling water circuit  20  includes a bypass  22  for bypassing the radiator  21  and a thermostat  23  for controlling the cooling water flow rate to the radiator  21  or the bypass  22 .  
         [0028]     The thermoelectric generator  100  is arranged between the radiator  21  and the bypass  22  in the engine cooling water circuit  20 . The cooling water (the high-temperature water corresponding to the high-temperature fluid according to the invention) flowing out of the engine  10  flows through a high-temperature heat source  110  described later. The cooling water (the low-temperature water corresponding to the low-temperature fluid according to the invention) after passing through the radiator  21  flows through a low-temperature heat source  120  described later.  
         [0029]     The thermoelectric generator  100  is explained in detail. As shown in  FIG. 2 , the thermoelectric generator  100  has a plurality of thermoelectric elements  130 , which are disposed between the high-temperature heat sources  110  and the low-temperature heat sources  120  alternately stacked and which generate power utilizing the Seebeck effect. Three high-temperature heat sources  110 , four low-temperature heat sources  120 , and ninety-six thermoelectric elements  130  (sixteen between each pair of heat sources  110 ,  120  in six stages) are used as thirteen layers in all. A heat conductive grease is coated or a heat conductive sheet is interposed to decrease the contact heat resistance between each high-temperature heat source  110  and the corresponding thermoelectric elements  130  and between each low-temperature heat source  120  and the corresponding thermoelectric elements  130 . The direction along which the heat sources  110 ,  120  are stacked is hereinafter called the vertical direction as in  FIG. 2 .  
         [0030]     The high-temperature heat source  110  is a flat container formed of a pair of plates arranged center-to-center and peripherally molded. The high-temperature heat source  110  has an expansion  111  at an end thereof and bolt holes  112  for insertion of bolts  171  at the central portion thereof. An inner fin (not shown) to transmit the heat of the high-temperature water efficiently to the thermoelectric elements  130  is inserted in the high-temperature heat source  110 .  
         [0031]     As a basic form of the high-temperature heat source  110 , large-diameter pipes  113  extending downward and small-diameter pipes  114  extending upward and adapted to be coupled to each other to communicate with the interior of the corresponding high-temperature heat source  110  are formed on the expansion  111 . A circumferential groove is formed at the forward end of each small-diameter pipe  114  and has an O-ring  115  mounted therein.  
         [0032]     Of the high-temperature heat sources  110  stacked in a plurality of layers, the uppermost stage includes a high-temperature inlet pipe  116  and a high-temperature outlet pipe  117  in place of the small-diameter pipes  114 , and the lowest stage does not include a large-diameter pipe  113 .  
         [0033]     The low-temperature heat source  120  is different from the high-temperature heat source  110  in that the expansion  121  is located at such a position as to clear the expansion  111  of the high-temperature heat source  110 , but is identical with the high-temperature heat source  110  in the other points. The low-temperature heat source  120  has a central bolt hole  122  in which an inner fin (not shown) is inserted to efficiently transmit heat to the low-temperature water from the thermoelectric elements  130 . The expansion  121  includes large-diameter pipes  123  and small-diameter pipes  124  each carrying an O-ring  125 . The low-temperature heat source  120  in the uppermost stage includes a low-temperature inlet pipe  126  and a low-temperature outlet pipe  127  in place of the small-diameter pipes  124 , while the low-temperature heat source  120  in the lowest stage does not include a large-diameter pipe  123 .  
         [0034]     The thermoelectric element  130  is well known and generates power using the Seebeck effect (or generates heat using the Peltier effect). It is formed of a P-type semiconductor and a N-type semiconductor connected in series by a metal electrode. The lead wires  131  for connecting the P-type semiconductor and the N-type semiconductor are projected from an end of the thermoelectric element  130  at two points. Each thermoelectric element  130  is in the shape of a square having each side of about 40 mm, and sixteen thermoelectric elements  130  are arranged in parallel (in one plane) between each pair of the high-temperature heat source  110  and the low-temperature heat source  120 . The thermoelectric elements  130  are connected in series by the lead wires  131  (the connecting method is described in detail later).  
         [0035]     According to this invention, a frame  140  is arranged to position and connect the plurality of the corresponding thermoelectric elements  130 . Each frame  140 , which is made of a resin material has, as shown in  FIG. 3 , a profile of a square smaller than the heat sources  110 ,  120  and a thickness smaller than the thermoelectric elements  130  (about one half as thick as the thermoelectric elements  130 ). Two openings  141  are formed in the frame  140 , and eight thermoelectric elements  130  are inserted closely in each opening  141  (the frame  140  surrounds a plurality of the thermoelectric elements  130 ).  
         [0036]     Two bolt holes  142  corresponding to the bolt holes  112 ,  122  of the heat sources  110 ,  120  are formed between the two openings  141 . Incidentally, a cylindrical protrusion to be inserted into the bolt holes  112 ,  122  of the opposed heat sources  110 ,  120  is formed on the outer periphery of each bolt hole  142 , so that the frame  140  and the heat sources  110 ,  120  can be set in position at the time of assembly.  
         [0037]     A plurality of conducting portions  143  of copper plates are coupled on the outer periphery of the frame  140  and at positions between the openings  141  corresponding to the lead wires  131  of the thermoelectric elements  130 . This frame  140  makes up a printed board. In the middle stage on the left and right sides in  FIG. 3 , the conducting portions  143  extend in vertical direction, and an insulating portion  144  of a coating material is formed on the surface of the intermediate portion (indicated by dashed line in  FIG. 3 ) of each conducting portion for insulation from the exterior.  
         [0038]     Using the frames  140 , the thermoelectric generator  100  is assembled in the following way. Specifically, as shown in  FIGS. 4A, 4B , the frame  140  is arranged on the upper side surface of each of the heat sources  110 ,  120  and coupled by adhesive or the like. In the process, as described above, the frame  140  is positioned by the bolt holes  112 ,  122 ,  142  with respect to the heat sources  110 ,  120 .  
         [0039]     Next, sixteen thermoelectric elements  130  are inserted into the openings  141  of each frame  140  in such a manner that the lead wires  131  and the conducting portions  143  coincide with each other in position. Each lead wire  131  is soldered (or brazed according to the invention) to the corresponding conducting portion  143 , after which the surface of the lead wires  131  is subjected to a waterproofing process with a silicon agent or the like. The sixteen thermoelectric elements  130  are positioned on each frame  140  on the upper side surface of the heat sources  110 ,  120  while at the same time being connected in series (electrically connected).  
         [0040]     Next, as shown in  FIG. 2 , the low-temperature heat sources  120  (having mounted the thermoelectric elements  130  thereon) and the high-temperature heat sources  110  (having mounted the thermoelectric elements  130  thereon) are stacked alternately with each other from the lower side, and the low-temperature heat source  120  (having mounted no thermoelectric element  130  thereon) is set in the uppermost stage. In the process, the small-diameter pipes  124  of a given low-temperature heat source  120  are inserted into the large-diameter pipes  123  of the low-temperature heat source  120  in the immediately upper stage, and both are connected by the O-ring  125  interposed between the inner peripheral surface of each large-diameter pipe  123  and the outer peripheral surface of the corresponding small-diameter pipe  124 . The large-diameter pipes  123 , the small-diameter pipes  124  and the O-rings  125  thus establish communication between the plurality of the low-temperature heat sources  120 , and the low-temperature inlet pipe  126  and the low-temperature outlet pipe  127  are opened to the upper side of the uppermost low-temperature heat source  120 .  
         [0041]     In similar fashion, the small-diameter pipes  114  of a given high-temperature heat source  110  is inserted into the large-diameter pipes  113  of the high-temperature heat source  110  in the immediately upper stage, and both are connected to each other through the O-rings  115 . The large-diameter pipes  113 , the small-diameter pipes  114  and the O-rings  115  establish mutual communication between the plurality of the high-temperature heat sources  110 , with the high-temperature inlet pipe  116  and the high-temperature outlet pipe  117  open to the upper side of the uppermost high-temperature heat source  110 .  
         [0042]     Next, a lower plate  150  is set under the lowermost stage of the low-temperature heat source  120 , and an upper plate  160  above the uppermost stage of the low-temperature heat source  120 . A plurality of the high-temperature heat sources  110 , the low-temperature heat sources  120  and the thermoelectric elements  130  are held between the upper plate  160  and the lower plate  150  and integrally fixed with each other by bolts  171  and nuts  172 . A thermoelectric generator  100  in which the thermoelectric elements  130  are in opposed relation with the heat sources  110 ,  120  under a predetermined surface pressure is thus formed.  
         [0043]     The high-temperature inlet pipe  116  and the high-temperature outlet pipe  117  of the thermoelectric generator  100  are connected to the upstream side of the radiator  21  of the engine cooling water circuit  20 . The low-temperature inlet pipe  126  and the low-temperature outlet pipe  127 , on the other hand, are connected to the downstream side of the radiator  21 .  
         [0044]     In the thermoelectric generator  100  described above, after starting the engine  10 , the cooling water increases in temperature and exceeds a predetermined temperature (say, 90° C.), and thermostat  23  opens to the radiator  21 . Then, the high-temperature water flowing out of the engine  10  flows into the plurality of the high-temperature heat sources  110  through the high-temperature inlet pipe  116  of the thermoelectric generator  100  and flows into the radiator  21  through the high-temperature outlet pipe  117 .  
         [0045]     The low-temperature water that has passed through the radiator  21  flows through a plurality of the low-temperature heat sources  120  from the low-temperature inlet pipe  126 , and returns to the engine  10  through the low-temperature outlet pipe  127 .  
         [0046]     The plurality of the thermoelectric elements  130  are subjected to a temperature difference due to the high-temperature water flowing through the high-temperature heat sources  110  and the low-temperature water flowing through the low-temperature heat sources  120 , so that power is generated with a predetermined power generation capacity. The electric power produced by this power generating operation is stored in a battery charger (battery) not shown or used for the operation of various auxiliary equipment.  
         [0047]     As long as the cooling water remains at lower than a predetermined temperature (say, 90° C.), the radiator  21  is closed by the thermostat  23 , and the cooling water flows through the bypass  22  thereby to promote the warming-up of the engine  10 .  
         [0048]     As described above, in the thermoelectric generator  100  with a plurality of the thermoelectric elements  130  interposed between each pair of the heat sources  110 ,  120 , the assembly work thereof consumes a considerable labor. According to this invention, however, the provision of the frames  140  makes it possible to set a plurality of the thermoelectric elements  130  in position while at the same time securing a satisfactory thermal contact with the plurality of the high-temperature heat sources  110  and the low-temperature heat sources  120  without adversely affecting the surface roughness and parallelism of the contact surface of the high-temperature heat sources  110  and the low-temperature heat sources  120  with the thermoelectric elements  130 . Thus, the connection of the plurality of the thermoelectric elements  130  to the high-temperature heat sources  110  or the low-temperature heat sources  120  as explained in “Description of the Related Art” is eliminated to provide an improved assembly performance.  
         [0049]     Further, the plurality of the thermoelectric elements  130  are connected to each other by soldering through a plurality of the conducting portions  143  arranged on each frame  140 . Therefore, the protrusion of each lead wire  131  and, hence, an obstacle to the assembly work are eliminated. Also, the lead wires  131  are fixed on the conducting portions  143  and therefore not easily broken under an external vibration load.  
         [0050]     Next, a second embodiment of the invention is explained with reference to FIGS.  5  to  7 . In the second embodiment, the method of connecting the lead wires  131  is different from the first embodiment.  
         [0051]     Specifically, the conducting portions  143  of each frame  140  are formed with holes  143   a  through which the lead wires  131  of the thermoelectric elements  130  are inserted. In addition, the frame  140  is formed with lower holes  145  corresponding to the holes  143   a . The direction in which the holes  143   a  and the lower holes  145  are formed is coincident with the direction in which the thermoelectric elements  130  are inserted into the openings  141  of the frame  140  (the direction in which the heat sources  110 ,  120  are stacked). Also, the forward end of each lead wire  131  of the thermoelectric elements  130  is bent into the same direction as the direction in which the holes  143   a  and the lower holes  145  are formed.  
         [0052]     At the time of mounting the thermoelectric elements  130 , the thermoelectric elements  130  are inserted into the openings  141  of each frame  140 , while at the same time fitting by inserting the lead wires  131  into the holes  143   a  (lower holes  145 ) (mechanical connection).  
         [0053]     As a result, the soldering is eliminated unlike in the first embodiment, and the lead wires  131  can be connected to the conducting portions  144  by one action for an improved workability.  
         [0054]     The direction of the lead wires  131  and the holes  143   a  is not limited to those in the embodiments described above, but may be changed as required by the restrictions of design or fabrication.  
         [0055]     Finally, other embodiments are explained. According to the first and second embodiments, the cooling water (high-temperature water) flowing out of the engine  10  in the engine cooling water circuit  20  and the cooling water (low-temperature water) after passing through the radiator  21  are used as the high- and low-temperature fluids, respectively, of the thermoelectric generator  100 . Alternatively, the exhaust gas of the engine  10  may be used as the high-temperature fluid, and cooling water in an exclusive cooling water circuit other than the engine cooling water circuit  20  may be used as the low-temperature fluid.  
         [0056]     Also, in the embodiments explained above, a plurality of the heat sources  110 ,  120  are stacked to hold a plurality of sets of the thermoelectric elements  130 . As an alternative, the thermoelectric elements  130  may be held by one high-temperature heat source  110  and one low-temperature heat source  120  with equal effect.  
         [0057]     While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.