WO2015059549A1

WO2015059549A1 - Cooler and electric power converter

Info

Publication number: WO2015059549A1
Application number: PCT/IB2014/002190
Authority: WO
Inventors: Shinichi Miura
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2013-10-24
Filing date: 2014-10-22
Publication date: 2015-04-30
Also published as: JP2015082950A

Abstract

Provided are a cooler (10) elongated in its external shape as viewed in a stacking direction with semiconductor devices and an electric power converter in which the coolers (10) are stacked. The cooler (10) includes a refrigerant supply port (11a) for taking refrigerant into the cooler (10), a refrigerant discharge port (lib), a refrigerant supply passage (12), a plurality of branch passages (13), nozzles (15) for jetting the refrigerant from the branch passage (13), and a refrigerant discharge passage (18). The refrigerant supply port (11a) is provided at an end in the longitudinal direction of the cooler (10). The refrigerant supply passage (12) is connected to the refrigerant supply port (11a), extending in the longitudinal direction of the cooler (10). Each of a plurality of the branch passages (13) is branched from the refrigerant supply passage (12), extending in parallel in the short side direction of the cooler (10). The nozzles (15) jet the refrigerant against a cooler side plate (10a) in contact with the semiconductor device (21).

Description

COOLER AND ELECTRIC POWER CONVERTER

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to a cooler which is to be stacked with a semiconductor device and an electric power converter using the same cooler. The electric power converter which requires the cooler is a device which converts direct current power from a battery to alternating current power and supplies the power to a traveling motor in a hybrid vehicle, for example.

2. Description of Related Art

[0002] The electric power converter which supplies electric power to a large output device represented by a traveling motor of a hybrid vehicle often includes a plurality of power transistors. For example, an inverter circuit of a three phase alternating current motor includes three pairs of a power transistor for its upper arm and a power transistor for its lower arm, totaling to at least six power transistors. If the electric power converter includes a voltage converter circuit as well as the inverter circuit, it further includes at least two power transistors. Because the power transistor for use in electric power conversion of a large output device produces a large calorific value, it absolutely requires a cooler.

[0003] A cooler for cooling a plurality of semiconductor devices each having a large calorific value such as the power transistor effectively and an electric power converter using the same cooler have been disclosed in Japanese Patent Application Publication No. 2008-198751 (JP 2008-198751 A). The electric power converter disclosed in JP 2008-198751 A has a structure in which a plurality of flat sheet type semiconductor devices and a plurality of flat sheet type coolers are stacked alternately. The semiconductor device is typically a power card in which a semiconductor element is molded with resin. The power card is sometimes called semiconductor module or sometimes called power module. In the meantime, generally, the "power transistor" means a transistor configured to control electric power and is, typically, an insulated gate bipolar transistor (IGBT).

[0004] In the electric power converter disclosed in JP 2008-198751 A, the flat sheet type semiconductor device accommodating the semiconductor elements is sandwiched with the coolers from both sides. Because the plurality of the semiconductor devices and the plurality of the coolers are stacked alternately, every semiconductor device is cooled from both sides. The electric power converter of JP 2008-198751 A achieves a high cooling efficiency because the total contact area between the semiconductor device and the cooler is large.

[0005] As its cooler, the technology of JP 2008-198751 A adopts a so-called impingement -jet type. More specifically, the cooler has a refrigerant passage which is divided to three layers by partition walls in the stacking direction with the semiconductor devices. Then, the partition wall located between an outside refrigerant passage and a central refrigerant passage is provided with jet holes which jet cooling medium from the central refrigerant passage into the outside refrigerant passage. Jetted refrigerant collides with a rear surface of a cooler side plate in contact with the semiconductor device. In the impingement-jet type cooler, its cooling effect is raised by bringing refrigerant into collision with the rear surface of the side plate in contact with a cooling object. A detail of the impingement -jet type cooler has been described in, for example, Japanese Patent Application Publication No. 2011-166113 (JP 2011-166113 A). In the meantime, the refrigerant in the cooler of JP 2008-198751 A is liquid, typically, water or LLC (long life coolant).

[0006] Because the impingement-jet type cooler has a number f jet ports (nozzles) for jetting refrigerant along a flow direction of refrigerant (or because an opening for refrigerant has an elongated nozzle along the flow direction), pressure loss is large in comparison with a cooler in which refrigerant simply flows. Passage resistance of the nozzle is one of causes for the pressure loss. The cooler of JP 2008-198751 A has an elongated shape as viewed in the stacking direction with the semiconductor devices. More specifically, the shape is rectangular. A refrigerant supply port is provided at an end in the longitudinal direction of the elongated cooler and a refrigerant discharge port is provided at the other end. Then, refrigerant flows along the longitudinal direction inside the cooler. While refrigerant flows along the longitudinal direction, it is jetted from the nozzles. Because the cooler of JP 2008-198751 A is provided with a number of the nozzles along the longitudinal direction of the cooler, the pressure loss between its upstream and downstream is large. That is, a difference in pressure of refrigerant between the upstream and the downstream is large. As a result, a difference is produced in cooling efficiency between the upstream and the downstream of refrigerant.

SUMMARY OF THE INVENTION

[0007] In views of the above-described problems, the present invention provides a technology for reducing the difference in pressure of refrigerant between the upstream and the downstream in the impingement-jet type cooler which is to be stacked with the semiconductor devices during use. In addition, the present invention provides an electric power converter having an excellent cooling efficiency in which such a cooler is stacked with the semiconductor devices.

[0008] In the cooler of JP 2008-198751 A, refrigerant passages in which refrigerant flows are provided in the longitudinal direction thereof and a plurality of nozzles are provided in the refrigerant passages. The nozzles are arranged in line in the longitudinal direction of the cooler. Because the cooler of JP 2008-198751 A is provided with a plurality of nozzles over a long distance in the longitudinal direction of the cooler, the difference in pressure between the upstream and the downstream of the nozzles is large. In the meantime, the "longitudinal direction" and "short side direction" of the cooler means "longitudinal direction" and "short side direction" of an elongated shape as viewed from the stacking direction with the semiconductor device.

[0009] Accordingly, according to an aspect of the present invention, there is provided a cooler in which a plurality of passages extending in the short side direction of the cooler are provided and nozzles are provided in each of the passages. By setting a distance between the upstream and the downstream of the nozzle short, the difference in pressure between the upstream and the downstream is reduced. In the meantime, by providing the passages each having nozzles in a plural number and in parallel and further providing each passage with the nozzles, reduction of the total area of the nozzles is prevented.

[0010] The cooler is elongated in its external shape as viewed in the stacking direction with the semiconductor device. Although the external shape of the cooler is typically rectangular, the edges on both ends in the longitudinal direction may be curved or in a wedge shape.

[0011] The cooler includes a refrigerant supply port configured to take refrigerant into the cooler and a refrigerant discharge port configured to discharge refrigerant which has passed through the inside of the cooler. The refrigerant supply port is provided at an end in the longitudinal direction of the cooler. The cooler includes a refrigerant supply passage, a plurality of branch passages and a refrigerant discharge passage inside thereof. The refrigerant supply passage is connected to the refrigerant supply port at an end thereof and extends in the longitudinal direction of the cooler while the other end is closed. The plurality of branch passages are branched from halfway of the refrigerant supply passage and extend in parallel to each other while its distal ends are closed. The plurality of the branch passages extend in the short side direction of the cooler. Each branch passage is provided with nozzles. The nozzles are configured to jet refrigerant against a rear face of a cooler side plate in contact with the semiconductor device. The nozzle of each branch passage has an elongated shape in the short side direction (i.e., a direction in which the branch passage extends) of the cooler. The refrigerant discharge passage is configured to introduce refrigerant jetted from the nozzle to the refrigerant discharge port.

[0012] The above-described cooler includes a plurality of the branch passages which extend in the short side direction of the cooler and further, each of the branch passages is provided with nozzles. That is, the cooler produces a flow of refrigerant in the short side direction and refrigerant is jetted from the nozzle inside such a short branch ^{■ ■ ■ ■ ■■} 5

passage. Compared to a case where the cooler is provided with nozzles in the longitudinal direction, a distance between the upstream side end portion and the downstream side end portion of the nozzle is short so that the difference in pressure therebetween is small. If expressing comprehensively, although the cooler of JP 2008-198751 A is provided with long nozzles in the flow direction of refrigerant, the cooler of the present invention is provided with a plurality of short nozzles in the flow direction of refrigerant. Consequently, the distance between the upstream end and the downstream end of the nozzle is decreased so as to reduce the difference in pressure.

[0013] In the meantime, the "elongated nozzle in the short side direction of the cooler" may be a nozzle whose opening is elongated in the short side direction of the cooler or a group of nozzles in which a plurality of nozzles having a small-diameter opening are arranged in line in the short side direction of the cooler. The plurality of the small-diameter nozzles arranged in line, when viewed macroscopically, is equivalent to a nozzle having an elongated opening. Further, this type of the nozzles may be provided in line in a direction perpendicular to the flow direction of refrigerant.

[0014] According to another aspect of the present invention, there is provided a cooler which can be stacked with a semiconductor device containing a semiconductor element. The cooler includes a case. The external shape of the case is an elongated shape as viewed in the stacking direction with the semiconductor devices. Then, the case includes a refrigerant supply port, a refrigerant discharge port, a refrigerant supply passage, a plurality of branch passages, nozzles and a refrigerant discharge passage. The refrigerant supply port is provided at an end in the longitudinal direction of the case so that refrigerant is taken into the case. The refrigerant discharge port discharges the refrigerant which has passed through the inside of the cooler. The refrigerant supply passage is connected to the refrigerant supply port and extends in the longitudinal direction of the case. The plurality of the branch passages are branched from the refrigerant supply passage and extend in parallel in the short side direction of the case. The nozzle has an elongated shape in the short side direction. The nozzle is provided in each of the plurality of the branch passages and is configured to jet the refrigerant from the branch passage toward a side plate of the case in contact with the semiconductor device. The refrigerant discharge passage is configured to introduce the refrigerant jetted from the nozzle to the refrigerant discharge port.

[0015] In the aforementioned cooler, by using an advantage of the plurality of the branch passages, an area of each refrigerant flow intake of one of the plurality of the branch passages may be made different from the area of the refrigerant flow intake of other branch passage. That is, the flow rates of the plurality of the branch passages are differentiated. This is valid when the semiconductor devices to be stacked include semiconductor elements each having a different calorific value. That is, by arranging the branch passages so as to oppose each semiconductor element and further adjusting the area of the refrigerant flow intake of each branch passage corresponding to the calorific value of each semiconductor element, it is possible to achieve a cooler whose cooling capacity is different between respective portions to meet the calorific value of each semiconductor element.

[0016] The aforementioned cooler should be stacked with the semiconductor device which contains a first and second semiconductor element each having a different calorific value. Because the flow rate of refrigerant on a side near the refrigerant supply port of the cooler is larger than that on a far side, the semiconductor device and the cooler are stacked such that a semiconductor device having a large calorific value is located on the side near the refrigerant supply port. That is, if the second semiconductor element has a smaller calorific value than the first semiconductor element, the semiconductor device and the cooler should be stacked such that the second semiconductor element is located farther from the refrigerant supply port than the first semiconductor element in the longitudinal direction of the cooler. , Then, a first branch passage should be provided so as to oppose the first semiconductor element and a second branch passage should be provided so as to oppose the second semiconductor element. Further, the area of the refrigerant flow intake of the second branch passage should be set smaller than the area of the refrigerant flow intake of the first branch passage. With the above-described structure, the flow rate of the first branch passage near the refrigerant supply port increases while conversely, the flow rate of the second branch passage far from the refrigerant supply port decreases. The larger the flow rate, the higher the cooling capacity is. In the abovementioned stacked unit in which the coolers and the semiconductor devices are stacked, the cooling capacities of the branch passages can be differentiated from each other corresponding to the calorific value of each of the first semiconductor element having a relatively large calorific value and the second semiconductor element having a relatively small calorific value. That is, the above-described technology contributes to improvement of the cooling capacity of the electric power converter including a plurality of the semiconductor elements' each having a different calorific value. In the meantime, the stacked unit of the semiconductor devices and the coolers is a major unit of the electric power converter.

[0017] , If the refrigerant discharge port is arranged near the refrigerant supply port, compactness of the stacked unit (electric power converter) can be achieved as follows. That is, the refrigerant supply ports and the refrigerant discharge ports of each of the plurality of the coolers stacked with the plurality of the semiconductor devices are arranged on a side face in the longitudinal direction of the cooler. Then, a refrigerant supply pipe which is connected to the plurality of the refrigerant supply ports and a refrigerant discharge pipe which is connected to the plurality of the refrigerant discharge ports are arranged such that they extend in parallel in the stacking direction along a side face of the stacked unit of the semiconductor devices and the coolers. In the electric power converter of the above-mentioned JP 2008-198751 A, the refrigerant supply pipe and the refrigerant discharge pipe are arranged on both sides of the stacked unit. Contrary to this, in the electric power converter of the present invention, the refrigerant supply pipe and the refrigerant discharge pipe are arranged on one side of the stacked unit. By arranging the refrigerant supply pipe and the refrigerant discharge pipe side by side, the refrigerant supply pipe and the refrigerant discharge pipe can be centralized so as to achieve space saving of the electric power converter.

[0018] Further, there may be a case where load is applied to the stacked unit in which a plurality of the semiconductor devices and a plurality of the coolers are stacked from both sides in the stacking direction. By applying load, the adhesion between the semiconductor device and the cooler is intensified so as to improve its cooling capacity. To withstand the load, a reinforcement rib may be provided between the branch passages adjacent to each other inside the cooler. Both ends of the reinforcement rib may be in contact with each of two side plates opposing each other in the stacking direction. Between the branch passages adjacent to each other means a wall which partitions adjacent branch flows. The wall is used as a reinforcement which withstands the load in the stacking direction.

[0019] Further, the electric power converter may further include a step-up circuit, a first power conversion circuit and a second power conversion circuit. Here, the step-up circuit is configured to boost a voltage of a battery. The first power conversion circuit is configured to convert direct current power of the battery to alternating current power and supply the power to a traveling motor. The second power conversion circuit is configured to convert alternating current power of a generator to direct current power and supply the , power to the battery. The first semiconductor element may be a power transistor in the step-up circuit or a power transistor in the first power conversion circuit, and the second semiconductor element may be a power transistor in the second power conversion circuit.

[0020] According to the impingement-jet type cooler which is to be stacked with the semiconductor device and the electric power converter including the semiconductor devices and the coolers of the present invention as described above, the difference in pressure of refrigerant in the flow direction flowing through the cooler can be reduced, so that the cooling capacity of the cooler can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: FIG. 1 is a perspective view of a stacked unit according to an embodiment of the present invention;

FIG. 2 is a sectional view of a cooler taken along the line II-II in FIG. 1;

FIG. 3 is a sectional view of the cooler taken along the line III-III in FIG. 2;

FIG. 4 is a perspective view of a branch passage;

FIG. 5 is a sectional view of the cooler taken along the line V-V in FIG. 2;

FIG. 6 is a sectional view of the cooler taken along the line II-II in FIG. 1 or a diagram indicating a positional relationship between branch passages each having a different refrigerant flow intake and semiconductor elements each having a different calorific value;

FIGs. 7 A and 7B are graphs showing a relationship between an arrangement of the refrigerant passages and a flow rate of the branch passages based on a simulation result according to the embodiment;

FIGs. 8A and 8B are graphs showing a relationship between an arrangement of the refrigerant passages and a pressure loss of the branch passages based on a simulation result according to the embodiment;

FIG. 9 is a block diagram of electric system of a hybrid vehicle containing the electric power converter according to the embodiment; and

FIG. 10 is a perspective view showing a hardware structure of the electric power converter according to the embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0022] A cooler and a stacked unit using the same of an embodiment will be described with reference to the drawings. FIG. 1 shows a perspective view of a stacked unit 20. The stacked unit 20 is a device in which five flat sheet type coolers 10 and four flat sheet type power modules 21 are stacked. The five coolers 10 are arranged in parallel to each other. The power module 21 is arranged between adjacent coolers 10. Although not shown here, load is applied to the stacked unit 20 from both sides in the stacking direction so that the cooler 10 and the power module 21 are fitted to each other. Because the cooler 10 and the power module 21 are fitted to each other, the stacked unit 20 secures an intensified cooling efficiency.

[0023] The cooler 10 has a case and liquid refrigerant passes through the inside of the case so as to cool the adjacent power module 21. The refrigerant is, typically, water or long life coolant (LLC).

[0024] A refrigerant supply port 11a for taking in refrigerant and a refrigerant discharge port lib for discharging refrigerant which has passed through the inside of the cooler 10 are provided on one side face of each cooler 10. The refrigerant supply port 11a and the refrigerant discharge port lib are provided on one side face in the longitudinal direction of each cooler 10. A refrigerant supply pipe 23 and a refrigerant discharge pipe 24 are arranged in parallel such that they oppose the one side face. The refrigerant supply pipe 23 and the refrigerant discharge pipe 24 oppose the one side face of each cooler 10 and extend in the stacking direction. In other words, the refrigerant supply pipe 23 and the refrigerant discharge pipe 24 extend along the one side face of the stacked unit 20. The refrigerant supply pipe 23 is connected to the refrigerant supply port 11a of each cooler 10 and the refrigerant discharge pipe 24 is connected to the refrigerant discharge port lib of each cooler 10. An arrow Fl in the figure indicates a flow-in direction of refrigerant and an arrow F2 indicates a discharge direction of refrigerant. Meanings of symbols Fl and F2 are the same in subsequent drawings. Refrigerant is supplied from a pump (not shown) to the refrigerant supply pipe 23 in a direction indicated by the arrow Fl and then supplied to each cooler 10 through the refrigerant supply port 11a. Refrigerant absorbs heat from an adjacent device (power module 21) during passage through each cooler 10 and flows into the refrigerant discharge pipe 24 through the refrigerant discharge port lib. Finally, refrigerant flows in a direction indicated by the arrow F2 and flows toward a radiator (not shown). After cooled by the radiator, refrigerant flows to each cooler 10 through the refrigerant supply pipe 23 again by means of a pump (not shown).

[0025] An internal structure of the cooler 10 will be described with reference to FIGs. 2 through 4. FIG. 2 shows a sectional view of the cooler 10 taken along the line II-II in FIG. 1. FIG. 2 is a sectional view in the longitudinal direction of the cooler 10. As illustrated clearly by FIG. 2, the cooler 10 is in an elongated shape as viewed in the stacking direction (Z-axis direction) with the power module 21. In the figure, its Z axis corresponds to the stacking direction, its X axis corresponds to the longitudinal direction of the cooler 10 and its Y axis corresponds to the short side direction of the cooler 10. In the meantime, in FIG. 2, the symbols Fl and F2 indicate a flow direction of refrigerant. In the refrigerant supply pipe 23, refrigerant flows toward the deep side from forward of the paper surface (symbol Fl) and in the refrigerant discharge pipe 24, refrigerant flows from the deep side of the paper toward forward thereof (symbol F2). FIG. 3 shows a sectional view of the cooler taken along the line III-III in FIG. 2. FIG. 3 is a sectional ' view in the short side direction of the cooler 10. In the meantime, in FIG. 3, to distinguish two power modules which sandwich the cooler 10, a power module below in the figure is indicated with reference numeral 21a and a power module above the cooler 10 is indicated with reference numeral 21b.

[0026] The refrigerant supply port 11a for taking in refrigerant and the refrigerant discharge port lib for discharging refrigerant which has flown through the inside of the cooler 10 are provided on one side face in the longitudinal direction of the cooler 10. A refrigerant supply passage 12, four branch passages 13-1, 13-2, 13-3 and 13-4, and a refrigerant discharge passage 18 are provided inside the cooler 10. In the meantime, if the four branch passages 13-1, 13-2, 13-3 and 13-4 are generally named in a following description, they are expressed as "branch passage 13".

[0027] In the refrigerant supply passage 12, an end 12a thereof is connected to the refrigerant supply port 11a and the other end 12b thereof is closed. The refrigerant supply passage 12 extends straight in the longitudinal direction along an end side in the short side direction of the cooler 10. Each of the four branch passages 13 is branched from halfway of the refrigerant supply passage 12. The four branch passages 13 are branched from the refrigerant supply passage 12 in succession in the flow direction. The passage sectional area of each of the branch passages 13-1 and 13-2 is larger than the passage sectional area of each of the branch passages 13-3 and 13-4, which will be described in detail below.

[0028] The branch passage 13 extends straight in the short side direction of the cooler 10 and a distal end thereof is closed. As illustrated clearly in FIG. 3, a partition plate 14 which is perpendicular to the stacking direction is provided substantially in the center of the stacking direction (Z-axis direction) inside the cooler 10. The partition plate 14 defines the branch passage 13. One side (upper side of the partition plate 14 in FIG. 3) of the partition plate 14 corresponds to the branch passage 13 and the other side (lower side of the partition plate 14 in FIG. 3) corresponds to an after-branch discharge passage 16. The after-branch discharge passage 16 is continuous to a refrigerant discharge passage 18.

[0029] Each of the branch passages 13 is provided with a nozzle 15 which extends in an extending direction of the branch passage 13, that is, in the short side direction of the cooler 10. In other words, the nozzle 15 is provided in the partition plate 14 which defines the branch passage 13. The distal end of the nozzle 15 is directed to the rear face of the side plate 10a in contact with the power module 21a. The nozzle 15 jets refrigerant which flows through the branch passage 13 toward the rear face of the side plate 10a. A branch passage is provided with a plurality of the nozzles 15 in parallel to each other. The plurality of the nozzles 15 are provided in line along a direction perpendicular to the flow direction. Each of the nozzles 15 is elongated along the flow direction of refrigerant.

[0030] The rear face of the side plate 10a is provided with a plurality of fins 17. The distal end of the nozzle 15 is in contact with a top end of the fin 17. In the meantime, the "rear face of the side plate 10a" corresponds to an inside face of the cooler 10.

[0031] A flow of refrigerant inside the cooler 10 will be described. Refrigerant flowing through the refrigerant supply pipe 23 flows into the cooler 10 through the refrigerant supply port 11a. Refrigerant flows into each of the branch passages 13 from the refrigerant supply passage 12. Refrigerant flowing into the branch passage 13 is jetted against the rear face of the side plate 10a through the nozzle 15. Refrigerant jetted to the rear face of the side plate 10a flows between the plurality of the fins 17 into the refrigerant discharge passage 18. Finally, refrigerant flows from the refrigerant discharge passage 18 into the refrigerant discharge pipe 24 through the refrigerant discharge port lib. Heavy lines with an arrow in FIGs. 2 and 3 indicate a flow of refrigerant.

[0032] A cooling effect of the cooler 10 will be described. The power module 21a is in contact with the side plate 10a of the cooler 10 and a power transistor PT is molded inside the power module 21a. The power transistor PT is arranged at a position opposed to the branch passage 13. Refrigerant flowing through the branch passage 13 is jetted from the nozzle 15 and collides with the rear face of the side plate 10a. Refrigerant collides with the rear face of the side plate 10a so as to cool the side plate 10a effectively. The side plate 10a is opposed to the power transistor PT so that heat from the power transistor PT is transmitted to the side plate 10a and transferred to refrigerant colliding with the rear face of the side plate 10a effectively. In the meantime, the fins 17 provided on the rear face of the side plate 10a also contributes to improvement of cooling capacity. The cooler 10 in which refrigerant is brought into collision with the rear face of the cooler side plate 10a which opposes the cooling object (power transistor PT in this case), thereby intensifying the cooling efficiency is called impingement-jet type.

[0033] In the meantime, as regards a layout of the branch passage 13, the partition plate 14, the nozzles 15 and the fins 17, see FIG. 4. FIG. 4 is a perspective view showing the interior of a branch passage 13. In the meantime, in FIG. 4, the partition plate 14 is represented such that it is cut out halfway. A hatched face of the partition plate 14 corresponds to a cut-out face. Heavy lines with an arrow in FIG. 4 indicate a flow of refrigerant. From FIG. 4, it is well understood that refrigerant enters the branch passage 13 from the refrigerant supply passage 12, collides with the rear face of the side plate 10a through the elongated nozzles 15 provided in the partition plate 14, passes between the plurality of the fins 17 and flows into the refrigerant discharge passage 18 through the after-branch discharge passage 16. In the meantime, in FIG. 4, reference numeral 10b indicates a reinforcement rib which constitutes the side wall of the branch passage 13. The reinforcement rib 10b will be described later.

[0034] One of features of the cooler 10 will be described. The cooler 10 is a so-called impingement-jet type cooler. Refrigerant is jetted from the nozzle 15 in the branch passage 13 and collides with the rear face of the side plate 10a in contact with the cooling object. As illustrated clearly in FIG. 2, the branch passage 13 extends in the short side direction (Y-axis direction) of the cooler 10 and the nozzle 15 also extends in an elongated shape along the short side direction. The width of the nozzle 15 is small in order to jet refrigerant from the nozzle 15 vigorously. The pressure loss of refrigerant in the nozzle 15 is large due to the small width. However, the nozzle 15 extends in the short side direction of the cooler 10 and compared to a case where the nozzle extends in the longitudinal direction of the cooler, the length of the nozzle is smaller. A cooler in which the nozzle extends in the longitudinal direction of the cooler is referred to as conventional cooler in a following description.

[0035] Because in the cooler 10 of the embodiment, the length of the nozzle 15 is smaller compared to the conventional cooler, a difference in pressure between the upstream and the downstream of the nozzle 15 in the branch passage 13 is small. By providing the cooler 10 with the nozzle for jetting refrigerant along the short side direction of the cooler, the length of the nozzle in the flow direction of refrigerant is reduced thereby decreasing the difference in pressure between the upstream and the downstream. In the meantime, as illustrated clearly in FIG. 2, by providing with the plurality of the branch passages 13 (13-1,; 13-2, 13-3, 13-4) along the longitudinal direction of the cooler 10, a number of the nozzles is secured. In other words, by increasing the number of the short nozzles, the cooler 10 secures an identical flow rate of refrigerant (flow rate of refrigerant jetted from the nozzles) to the conventional coolers. Thus, the cooler 10 of the present embodiment can achieve a higher cooling efficiency than conventionally due to the small pressure loss while securing an identical flow rate of refrigerant to the conventional coolers. [0036] Next, another feature of the cooler 10 will be described with reference to FIG. 5. FIG. 5 is a sectional view of the cooler 10 taken along the line V-V in FIG. 2. That is, FIG. 5 corresponds to a cross sectional view of the cooler 10 between the adjacent branch passages 13. As shown in FIG. 5, the cooler 10 has the reinforcement ribs 10b in contact with the two side plates 10a, 10c both ends of which are opposed to each other in the stacking direction (Z direction in the figure), the reinforcement ribs 10b being provided between the adjacent branch passages 13. As described above, the stacked unit 20 receives a compression load in the stacking direction. In the cooler 10, the compression load in the stacking direction is received by the reinforcement rib 10b. Thus, the cooler 10 is never crushed by the compression load.

[0037] Next, still another feature of the cooler 10 will be described with reference to FIG. 6. FIG. 6 is a similar diagram to FIG. 2. To help understanding, some reference numerals indicated in FIG. 2 are omitted and widths of refrigerant flow intakes the plurality of the branch passages 13 are indicated with symbols. In the meantime, because the heights of the refrigerant flow intakes are identical, a difference in width of the refrigerant flow intakes is equivalent to a difference in area of the refrigerant flow intakes.

[0038] In the cooler 10, a width W2 (area) of the refrigerant flow intakes of the branch passages 13-3, 13-4 arranged far from the refrigerant supply port 11a is smaller than a width W2 (area) of the refrigerant flow intakes of the branch passages 13-1, 13-2 arranged near the refrigerant supply port 11a. Thus, the flow rate of refrigerant flowing through the branch passages 13-3, 13-4 arranged far from the refrigerant supply port 11a is smaller than the flow rate of refrigerant flowing through the branch passages 13-1, 13-2 arranged near the refrigerant supply port 11a. Thus, the cooling capacity at a position opposing the branch passages 13-3, 13-4 arranged far from the refrigerant supply port 11a is relatively lower than the cooling capacity at a position opposing the branch passages 13-1, 13-2 arranged near the refrigerant supply port 11a. In other words, the cooling capacity at the position opposing the branch passages 13-1, 13-2 arranged near the refrigerant supply port 11a is relatively higher than the cooling capacity at the position opposing the branch passages 13-3, 13-4 arranged far from the refrigerant supply port 11a. Therefore, it is recommendable to arrange a cooling object having a high calorific value at the position opposing the branch passages 13-1, 13-2 and arrange a cooling object having a low calorific value at the position opposing the branch passages 13-3, 13-4. In FIG. 6, a power module 21 in contact with the cooler 10 is represented with a phantom line and four power transistors PT1, PT2 molded in the power module 21 are also represented with a phantom line. In FIG. 6, a difference in the magnitude of calorific value is schematically indicated with the size of a rectangle indicating the power module. In the power module 21, the power transistors PT1 having a large calorific value are arranged at positions opposing the branch passages 13-1, 13-2 and the power transistors PT2 having a small calorific value are arranged at positions opposing the branch passages 13-3, 13-4.

[0039] In the meantime, differentiating the area of the refrigerant flow intake of the branch passage means providing a local cooling capacity with a difference depending on a distance from the refrigerant supply port without changing the whole cooling capacity of the entire cooler. By decreasing the cooling capacity of a portion which does not need a large cooling capacity, the cooling capacity of other portions can be increased. This structure of the cooler 10 is valid for a case where the power module contains a plurality of power transistors each having a different calorific value.

[0040] Further, in the cooler 10, the refrigerant supply passage 12 and the refrigerant discharge passage 18 are parallel to each other and the directions of the flows therein are inverse to each other. This structure contributes to reducing the difference in flow rate of refrigerant and the pressure loss in the plurality of the branch passages 13 which are branched from the refrigerant supply passage 12 in a direction perpendicular thereto and arranged in parallel to each other. This fact has been confirmed through simulation. FIGs. 7A, 7B and FIGs. 8A, 8B show examples of the results of the simulation. The passage structure for use in the simulation is as follows. A refrigerant supply passage fin and a refrigerant discharge passage fout which extend in parallel to each other are set up. Five branch passages (fl-f5) which extend in a direction perpendicular to the refrigerant supply passage fin are provided from the upstream of the refrigerant supply passage fin toward the downstream thereof. The areas of the refrigerant flow intakes and the passage sectional areas of the plurality of the branch passages are identical. A distal end of the branch passage is connected to the refrigerant discharge passage fout. In a case of FIG. 7A, the refrigerant supply port (qin) and the refrigerant discharge port (qout) are provided on the same side. That is, the refrigerant supply passage fin and the refrigerant discharge passage fout are parallel to each other and the directions of flows thereof are inverse to each other. In a case of FIG. 7B, the refrigerant supply port (qin) and the refrigerant discharge port (qout) are provided on opposite sides of the branch passage. That is, the refrigerant supply passage fin and the refrigerant discharge passage fout are parallel to each other and the directions of flows thereof are identical.

[0041] Lower graphs of FIGs. 7A and 7B show the flow rate of each branch passage. FIGs. 8A and 8B indicate pressure loss in each branch passage in each case of FIGs. 7 A and 7B. In case of FIG. 7 A, the flow rate of a branch passage fl nearest the refrigerant supply port qin is the largest. However, a difference in flow rate between the branch passage fl nearest the refrigerant supply port qin and the farthest branch passage f5 was 0.21 [L/min]. In the meantime, a pressure loss between the refrigerant supply port qin and the refrigerant discharge port qout was 0.72 [kPaJ. Contrary to this, in case of FIG. 7B, the flow rate of the branch passage fl near the refrigerant supply port qin is the smallest. Then, a difference in flow rate between the branch passage fl nearest the refrigerant supply port qin and the farthest branch passage f5 was 0.79 [L/min]. In the meantime, the pressure loss between the refrigerant supply port qin and the refrigerant discharge port qout was 1.10 [kPa].

[0042] As understood from the simulation result, in case of FIG. 7A, the difference in flow rate among the plurality of the branch passages can be made smaller than the case of FIG. 7B, and the pressure loss between the upstream and the downstream of the plurality of the branch passages can be reduced. Reduction of the difference in pressure loss contributes to improvement of the cooling capacity. [0043] Further, as illustrated by FIG. 7 A, if the areas of the flow intakes of the plurality of the branch passages are identical, the flow rate of the branch passage fl arranged near the refrigerant supply port is larger than the flow rate of the branch passage f5 arranged far from the refrigerant supply port. Thus, if the areas of the refrigerant flow intakes of the plurality of the branch passages are differentiated as shown in FIG. 6, preferably, the area of the refrigerant flow intake of the branch passage arranged near the refrigerant supply port is larger than the area of the refrigerant flow intake of the branch passage arranged far therefrom.

[0044] Finally, the electric power converter which employs the cooler 10 and the stacked unit 20 described above will be described. The electric power converter of the present embodiment is a device which is mounted on a hybrid vehicle and converts direct current power of a battery to alternating current power, which is to be supplied to a motor while it converts alternating current power generated by the motor to direct current power, which is to be supplied to the battery. First, the whole electric system of the hybrid vehicle will be described.

[0045] FIG. 9 shows a block diagram of an electric system of a hybrid vehicle 2. The hybrid vehicle 2 includes two motors 45, 46 and an engine 41. Of the two motors, a first motor 45 is mainly for traveling and a second motor 46 is mainly for power generation. However, if the vehicle exerts a strong braking, the power generation is executed also by the first motor 45. Further, if a high output torque is required, the second motor 46 also exerts a driving force for traveling. In the meantime, an output of the first motor 45 is larger than an output of the second motor 46.

[0046] The driving_^ force by the two motors 45, 46 and the engine 41 is adjusted by a power distribution mechanism 42. The power distribution mechanism 42 is a planetary gear in which an output shaft of the engine 41 is connected to a sun gear, art output shaft of the second motor 46 is connected to a carrier and an output shaft of the first motor 45 is connected to a ring gear. By adjusting respective brakes and clutches of the planetary gear appropriately, the entire output torque of the engine 41 and the two motors 45, 46 is transmitted to an axle 43 or the output torque of the engine 41 is distributed to the axle 43 and the second motor 46. When the output of the engine 41 is transmitted to the second motor 46, the second motor 46 acts as a power generator. In the meantime, the axle 43 is connected to driving wheels 47 through a differential gear 44.

[0047] An electric power converter 30 includes a first inverter circuit 5, a second inverter circuit 6 and a step-down/-up circuit 4. In the hybrid vehicle 2, driving voltages of the first motor 45 and the second motor 46 are higher than the output voltage of a battery 3. Then, the step-down/-up circuit 4 can execute both a step-up operation of raising a voltage of the battery 3 up to a voltage suitable for driving of the motor and a step-down operation of lowering a voltage of an electric power generated by the motor to an output voltage of the battery. The step-down/-up circuit 4 includes a filter capacitor 49 which stores the electric power of the battery 3 temporarily, a reactor 7, two power transistors PT3, and two diodes. Each diode is connected to each power transistor PT3 in anti-parallel. The power transistor PT3 is typically an IGBT. The power transistor PT3 is operated according to a drive signal (PWM signal) supplied from a controller (not shown). By adjusting the drive signal supplied from the controller, the step-down/-up circuit 4 raises a voltage from the battery side toward the inverter circuit side, and conversely lowers the voltage from the inverter circuit side toward the battery side. Because the circuit structure of the step-down/-up circuit 4 of FIG. 1 and its operation have been well known, a detailed description thereof is omitted.

[0048] The first inverter circuit 5 and the second inverter circuit 6 have basically the same circuit structure. Any inverter circuit has 3 sets of two-power transistors PT1, PT2 pairs. The three sets of the series-connected circuits are connected in parallel. The diode is connected to each power transistor in anti-parallel. A capacitor 9 (8) is connected to an input end of each inverter circuit. The capacitors 8, 9 are provided to smooth a current to be input to the inverter circuit. Reference symbol PT1 indicates a power transistor of the first inverter circuit 5 and reference symbol PT2 indicates a power transistor of the second inverter circuit 6. [0049] As described above, the first motor 45 mainly for traveling is larger than the second motor 46 mainly for power generation. Thus, calorific value of the power transistor PTl in the first inverter circuit 5 is larger than the calorific value of the power transistor PT2 in the second inverter circuit 6. Further, the step-down/-up circuit 4 supplies the first inverter circuit 5 having a large output with electric power. Thus, the calorific value of the power transistor PT3 in the step-down/-up circuit 4 is also larger than the calorific value of the power transistor PT2 in the second inverter circuit 6.

[0050] FIG. 10 shows a hardware structure of the electric power converter 30. Capacitor units 32, 33, the stacked unit 20 and a control board 34 are accommodated within a case 31 of the electric power converter 30. The capacitor unit 32 corresponds to a capacitor 49 in the circuit block diagram (FIG. 9). The capacitor unit 33 corresponds to the capacitor 8 and the capacitor 9 in the circuit block diagram (FIG. 9). In the meantime, each of the capacitor units 33, 34 accommodates a plurality of film type capacitor elements. The stacked unit 20 is a unit in which a plurality of the power modules 21 and a plurality of the coolers 10 are stacked. A plurality of power transistors are molded in each of the power modules 21 with resin. The power transistors molded in the power module 21 correspond to the power transistors PTl, PT2, and PT3 in the circuit block diagram (FIG. 9).

[0051] As described above, the calorific value of the power transistor PTl is larger than the calorific value of the power transistor PT2. Further, the calorific value of the power transistor PT3 is also larger than the calorific value of the power transistor PT2. In the cooler 10, by differentiating the areas of the refrigerant flow intakes of the plurality of the branch passages, the cooling capacity can be changed corresponding to a position of the cooler. Particularly, it is efficient to increase the cooling capacity of a branch passage near the refrigerant supply port 11a of the. cooler to be higher than the cooling capacity of a branch passage far from the refrigerant supply port 11a. Then, in the cooler 10, the area of the refrigerant flow intake of the branch passage arranged near the refrigerant supply port 11a should be set larger than the area of the refrigerant flow intake of the branch passage arranged far therefrom, and at the same time, the power module 21 should be arranged so that the power transistor PTl (or PT3) opposes the branch passage arranged near the refrigerant supply port 11a while the power transistor PT2 opposes the branch passages 13-3, 13-4 arranged far therefrom. If speaking repeatedly, the power transistor PTl is a power transistor in the first inverter circuit 5 which converts electric power of the battery 3 to driving electric power for the first motor 45 mainly for traveling and the power transistor PT2 is a power transistor in the second inverter circuit 6 which converts electric power generated by the second motor 46 to electric power for charging the battery 3. Further, the power transistor PT3 is a power transistor in the step-up circuit (step-down/-up circuit 4) which boosts a voltage of the battery 3.

[0052] What should be noted concerning a technology described in the above embodiments will be described. The power module 21 is equivalent to an example of the semiconductor device to be stacked with the cooler 10.

[0053] Although it is preferable that the refrigerant supply port is provided on the face on one side in the longitudinal direction of the cooler, it is acceptable if the refrigerant supply port is provided on an end side in the longitudinal direction. For example, the refrigerant supply port may be provided on an end side in the longitudinal direction of a face in contact with the semiconductor device. Alternatively, the refrigerant supply port may be provided on an end side in the longitudinal direction of a face which intersects with the short side direction.

[0054] Typically, the semiconductor element contained in the semiconductor device which opposes the cooler is a power transistor as used in the embodiment. However, the semiconductor element contained in the semiconductor device which opposes the cooler may be any other semiconductor element than the power transistor.

[0055] In the embodiment, the cooler 10 is applied to the electric power converter of a hybrid vehicle. It is also preferable that the cooler of the embodiment is applied to the electric power converter of an electric vehicle having no engine.

Claims

1. A cooler which can be stacked with a semiconductor device accommodating a semiconductor element, the cooler being elongated in its external shape as viewed in a stacking direction with the semiconductor device, the cooler comprising:

a refrigerant supply port provided on an end in a longitudinal direction of the cooler, the refrigerant supply port being configured to take refrigerant into the cooler;

a refrigerant discharge port configured to discharge the refrigerant which has passed through the inside of the cooler;

a refrigerant supply passage connected to the refrigerant supply port, the refrigerant supply passage extending in the longitudinal direction of the cooler;

a plurality of branch passages branched from the refrigerant supply passage, the plurality of branch passages being extending in parallel to each other in a short side direction of the cooler;

nozzles having an elongated shape in a short side direction, the nozzles being provided in each of the plurality of the branch passages, and the nozzles being configured to jet the refrigerant from the branch passage toward a cooler side plate in contact with the semiconductor device; and

a refrigerant discharge passage configured to introduce the refrigerant jetted from the nozzle to the refrigerant discharge port.

2. The cooler according to claim 1, wherein

an area of a refrigerant flow intake of one of the plurality of the branch passages is different from the area of a refrigerant flow intake of other branch passage.

3. The cooler according to claim 1 or 2, wherein

the nozzles are provided in line in a direction perpendicular to a flow direction of the refrigerant. ^■ - ' . · · ^■ 23

4. The cooler according to claim 1, further comprising:

a reinforcement rib provided between the branch passages adjacent to each other, both ends of the reinforcement rib being in contact with each of two side plates opposing each other in a stacking direction, and in the stacking direction the semiconductor device and the cooler being stacked.

5. A cooler which can be stacked with a semiconductor device accommodating a semiconductor element, the cooler comprising:

a case whose external shape is an elongated shape as viewed in a stacking direction with the semiconductor device, the case including a refrigerant supply port, a refrigerant discharge port, a refrigerant supply passage, a plurality of branch passages, nozzles and a refrigerant discharge passage,

the refrigerant supply port being provided at an end in a longitudinal direction of the case, the refrigerant supply port being configured to take the refrigerant into the case, the refrigerant discharge port being configured to discharge the refrigerant which has passed through the inside of the cooler,

the refrigerant supply passage being connected to the refrigerant supply port, the refrigerant supply passage extending in the longitudinal direction of the case,

the plurality of the branch passages being branched from the refrigerant supply passage, the plurality of the branch passages extending in parallel in a short side direction of the case,

the nozzle having an elongated shape in the short side direction, the nozzle being provided in each of the plurality of the branch passages, the nozzle being configured to jet the refrigerant from the branch passage toward a side plate of the case in contact with the semiconductor device,

the refrigerant discharge passage being configured to introduce the refrigerant jetted from the nozzle to the refrigerant discharge port.

6. The cooler according to claim 5, wherein the area of a refrigerant flow intake of one of the plurality of the branch passages is different from the area of the refrigerant flow intake of other branch passage.

7. An electric power converter, comprising:

a plurality of semiconductor devices;

a plurality of coolers according to claim 1 or 2;

a refrigerant supply pipe provided on one side face in the longitudinal direction of the cooler, the refrigerant supply pipe being connected to each of the refrigerant supply ports of the plurality of the cooler;

a refrigerant discharge pipe provided on the one side face in the longitudinal direction of the cooler, the refrigerant discharge pipe being connected to each of the refrigerant discharge ports of the plurality of the coolers,

the refrigerant supply pipe and the refrigerant discharge pipe opposing the one side face, the refrigerant supply pipe and the refrigerant discharge pipe extending in parallel to each other in the stacking direction.

8. The electric power converter according to claim 7, wherein

the cooler includes a reinforcement rib which is provided between the branch passages adjacent to each other, both ends of the reinforcement rib are in contact with each of two side plates opposing each other in a stacking direction, and in the stacking direction the semiconductor device and the cooler are stacked.

9. An electric power converter, comprising

a semiconductor device which includes a first semiconductor element and a second semiconductor element, the second semiconductor element being arranged farther from the refrigerant supply port in the longitudinal direction than the first semiconductor element while having a smaller calorific value than the first semiconductor element,

a cooler according to claim 2 or 6, in which a first branch passage and a second branch passage are provided, the first branch passage being arranged to oppose the first semiconductor element while the second branch passage being arranged to oppose the second semiconductor element and the second branch passage having a smaller refrigerant flow intake area than that of the first branch passage.

10. The electric power converter according to claim 9, wherein

the cooler has a reinforcement rib whose both ends are in contact with each of two side plates opposing each other in the stacking direction, the reinforcement rib being provided between the branch passages adjacent to each other.

11. The electric power converter according to claim 9 or 10, further comprising: a step-up circuit configured to boost a voltage of a battery;

a first power conversion circuit configured to convert direct current power of the battery to alternating current power, the first power conversion circuit being configured to supply the power to a traveling motor; and

a second power conversion circuit configured to convert alternating current power of a generator to direct current power, the second power conversion circuit being configured to supply the power to the battery, wherein

the first semiconductor element is a power transistor in the step-up circuit and the second semiconductor element is a power transistor in the second power conversion circuit.

12. The electric power converter according to claim 9 or 10, further comprising: a step-up circuit configured to boost a voltage of a battery;

a second power conversion circuit configured to convert alternating current power of a generator to direct current power, the second power conversion circuit being configured to supply the power to the battery, wherein the first semiconductor element is a power transistor in the first power conversion circuit and the second semiconductor element is a power transistor in the second power conversion circuit.