Inverter-integrated electric compressor and assembly method therefor

An IGBT serving as a heat-generating electrical component mounted on the lower surface of a lower board serving as a control circuit board of an inverter is disposed in abutment with a heat-dissipating flat section provided on an inner wall of an inverter box provided on the outer periphery of a housing so that the heat of the IGBT is dissipated toward the housing. Moreover, a spacer member is interposed between the lower board and the IGBT so as to fill a space between the lower board and the IGBT, and the spacer member is rigid enough that the lower board and the IGBT are prevented from being displaced toward and away from each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inverter-integrated electric compressor particularly suitable for use in a vehicle air conditioner and formed by installing an inverter inside an inverter box provided on the outer periphery of a housing, and to an assembly method therefor.

This application is based on Japanese Patent Application No. 2010-027733, the content of which is incorporated herein by reference.

2. Description of Related Art

In recent years, in addition to vehicles that run using internal combustion engines, vehicles that run by utilizing electric power, such as electric vehicles, hybrid vehicles, and fuel-cell-powered vehicles, are rapidly being developed and made commercially available. In many air conditioners for such vehicles that utilize electric power, electric compressors having motors that operate with electric power as a driving source are used as compressors for compressing and supplying a refrigerant.

Similarly, in some air conditioners for vehicles that run using internal combustion engines, compressors that are driven by the internal combustion engines via electromagnetic clutches are replaced by electric compressors so as to solve the problem of reduced drivability caused by the intermittency of the electromagnetic clutches.

A common example of an electric compressor of this type is a sealed electric compressor in which a compression mechanism and a motor are integrally built inside a housing. Furthermore, the sealed electric compressor is capable of supplying electric power input from a power source to the motor via an inverter and variably controlling the rotation speed of the compressor in accordance with the air-conditioning load.

In a proposed example of an electric compressor driven via an inverter in this manner, a control circuit board and the like that constitute the inverter are accommodated within an inverter box formed integrally with the outer periphery of the housing of the electric compressor so that the inverter is integrated with the electric compressor, and heat-generating electrical components, like power-controlling semiconductors, such as smoothing capacitors, that minimize the ripple of current supplied to the control circuit board and the like, and insulated gate bipolar transistors (IGBTs) are accommodated within the inverter box (for example, see Japanese Unexamined Patent Application, Publication No. 2003-153552 and the Publication of Japanese Patent No. 3786356).

In the integrated-type electric compressor discussed in Japanese Unexamined Patent Application, Publication No. 2003-153552, the heat-generating electrical components, such as IGBTs, mounted on the lower surface of the circuit control board of the inverter, with a gap therebetween, within the inverter box are in abutment with the bottom surface of the inverter box, that is, a heat-dissipating flat section (heat sink) thermally connected to the outer wall of the housing of the electric compressor, via a heat dissipation sheet composed of silicon rubber, as shown in FIG. 1 of the publication, whereby the heat of the electrical components is dissipated toward the housing.

In the integrated-type electric compressor discussed in the Publication of Japanese Patent No. 3786356, the heat-generating electrical components mounted on the lower surface of the circuit control board of the inverter, with a gap therebetween, within the inverter box are disposed directly in abutment with the bottom surface of the inverter box (housing), as shown in FIG. 2 of the publication, whereby the heat of the electrical components is dissipated toward the housing.

In order to maximize the heat dissipation effect for the heat-generating electrical components in such an inverter-integrated electric compressor, it is preferable that the electrical components be fastened to the bottom surface of the inverter box, that is, the heat-dissipating flat section of the housing, by using fastening members, such as screws, or be bonded thereto via an adhesive sheet or the like so that the electrical components and the heat dissipation surface are fixed and thermally connected to each other.

Because such an inverter-integrated electric compressor in general is directly attached to an engine of a vehicle, the inverter-integrated electric compressor constantly receives vibrations from the engine, vibrations from the vehicle body, rotational vibrations from the motor, and the like when the vehicle is running. The vibrations are also applied to the control circuit board of the inverter, causing the control circuit board to resonate mainly in the thickness direction thereof within the inverter box.

Therefore, with the configuration of the inverter-integrated electric compressor discussed in Japanese Unexamined Patent Application, Publication No. 2003-153552 and the Publication of Japanese Patent No. 3786356, relative displacement repeatedly occurs between the electrical components, mounted on the lower surface of the control circuit board with a gap therebetween and fixed to the bottom surface (i.e., the heat-dissipating flat section) of the inverter box by fastening or bonding, and the control circuit board vibrating in the thickness direction thereof. As a result, metal fatigue accumulates in lead terminals (pin terminals) that connect the electrical components to the control circuit board, possibly leading to deformation or breakage of the lead terminals with long-term use.

On the other hand, when assembling the inverter, the multiple electrical components are first arranged on the bottom surface (i.e., the heat-dissipating flat section) of the inverter box with their lead terminals oriented upward and are fastened thereto using screws or the like. Subsequently, the control circuit board is placed thereon from above, and the multiple lead terminals of the electrical components are inserted into lead-terminal through-holes in the control circuit board before the lead terminals are each soldered to the control circuit board. Therefore, an assembly procedure that involves a difficult and complicated positioning process is necessary, and moreover, the soldering process needs to be performed within the inverter box of the electric compressor. For this reason, the main body of the electric compressor needs to be conveyed in the assembly line of the inverter, resulting in extremely poor workability for assembling the inverter and its surrounding area.

BRIEF SUMMARY OF THE INVENTION

In view of these circumstances, an object of the present invention is to provide an inverter-integrated electric compressor that can effectively dissipate the heat of a heat-generating electrical component mounted on a control circuit board of an inverter, prevent a lead terminal that connects this electrical component to the control circuit board from breaking due to vibration, and provide satisfactory workability for assembling the inverter and its surrounding area, as well as providing an assembly method therefor.

In order to solve the aforementioned problems, the present invention employs the following solutions.

Specifically, an inverter-integrated electric compressor according to a first aspect of the present invention includes an inverter box provided on an outer periphery of a housing; an inverter having a control circuit board and accommodated within the inverter box; an electrical component mounted on one surface of the control circuit board and constituting the inverter; and a heat-dissipating flat section provided on an inner wall of the inverter box. The electrical component is disposed in abutment with the heat-dissipating flat section directly or via a heat conducting member so as to dissipate heat of the electrical component toward the housing. A spacer member is interposed between the control circuit board and the electrical component so as to fill a space between the control circuit board and the electrical component. The spacer member is rigid enough that the control circuit board and the electrical component are prevented from being displaced toward and away from each other.

With the first aspect of the present invention, the spacer member fills the space between the control circuit board and the electrical component and prevents these two components from being displaced toward and away from each other so that relative displacement between these two components is eliminated even when they receive vibration, thereby eliminating the possibility of breakage of a lead terminal of the electrical component due to metal fatigue. Moreover, since the electrical component is in abutment with the heat-dissipating flat section, the heat of the electrical component can be effectively dissipated.

Furthermore, in the above-described aspect, it is desirable that the inverter-integrated electric compressor further include a pressing member that presses at least the electrical component, among the control circuit board, the electrical component, and the spacer member, toward the heat-dissipating flat section.

With the above-described configuration, since the electrical component is pressed toward the heat-dissipating flat section by the pressing member, the heat dissipation effect for the electrical component can be enhanced.

Furthermore, in the above-described aspect, it is preferable that the inverter-integrated electric compressor further include a bonding member that bonds the spacer member to at least one of the control circuit board and the electrical component.

Since the spacer member can be fixed to the control circuit board or the electrical component by providing the aforementioned bonding member, not only are the control circuit board and the electrical component prevented from being displaced toward and away from each other, but relative displacement between the two components in the planar direction is also prevented. Therefore, breakage of the lead terminal of the electrical component is prevented more effectively. In addition, since the spacer member can be fixed to the control circuit board and the electrical component without being dependent on fastening members, such as screws, the workability for assembling the inverter and its surrounding area can be improved. It is desirable that both a surface of the control circuit board and a surface of the electrical component be provided with bonding members.

Furthermore, in the above-described aspect, the spacer member may be composed of an elastic material and may be elastically interposed between the control circuit board and the electrical component.

Accordingly, since the spacer member itself acts as a vibration absorbing member, breakage of the electrical component due to vibration can be effectively prevented, and the electrical component can be pressed toward the heat-dissipating flat section by the elastic force of the spacer member without the use of fastening members, such as screws. Therefore, the workability for assembling the inverter and its surrounding area can be improved, and the heat dissipation effect for the electrical component can be enhanced.

In order to solve the aforementioned problems, an assembly method for an inverter-integrated electric compressor according to a second aspect of the present invention is provided, in which a bonding member for bonding the spacer member to at least one of the control circuit board and the electrical component is provided. In this case, the bonding member is composed of a heat-weldable joining material, and the assembly method includes sub-assembling the control circuit board, the electrical component, and the spacer member in advance; forming an inverter-board assembly by applying heat to the control circuit board, the electrical component, and the spacer member so as to heat-weld the joining material; and installing the inverter-board assembly into the inverter box.

With the second aspect of the present invention, the inverter-board assembly can be assembled outside the inverter box, and lead terminals of a plurality of electrical components can be sub-assembled by inserting them into the control circuit board in advance, whereby the workability for assembling the inverter and its surrounding area can be dramatically improved.

Accordingly, with the inverter-integrated electric compressor and the assembly method therefor according to the present invention, the heat of the heat-generating electrical component mounted on the control circuit board of the inverter can be effectively dissipated, the lead terminal that connects this electrical component to the control circuit board can be prevented from breaking due to vibration, and the workability for assembling the inverter and its surrounding area can be improved.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of an inverter-integrated electric compressor and an assembly method therefor according to the present invention will be described below with reference to the drawings.

First Embodiment

A first embodiment of the present invention will be described below with reference toFIGS. 1 to 3.FIG. 1is a vertical sectional view for explaining the schematic configuration of an inverter-integrated electric compressor according to this embodiment. An inverter-integrated electric compressor1is a compressor used in a vehicle air conditioner, and the driving rotation speed thereof is controlled by an inverter.

The inverter-integrated electric compressor1has an aluminum-alloy housing2serving as an outer shell. The housing2is constituted of a compressor housing3and a motor housing4that are tightly fastened to each other with a bearing housing5interposed therebetween by using a bolt6.

A commonly known scroll compression mechanism8is fitted within the compressor housing3. A stator11and a rotor12that constitute a motor10are fitted within the motor housing4. The scroll compression mechanism8and the motor10are linked with each other via a main shaft14, and the scroll compression mechanism8is driven by rotating the motor10. The main shaft14is rotatably supported by a main bearing15held by the bearing housing5and a sub-bearing16held by an end of the motor housing4.

The end of the motor housing4is provided with a refrigerant intake port (not shown), and the refrigerant intake port is connected to an intake pipe of a refrigeration cycle so that low-pressure refrigerant gas is taken into the motor housing4. This refrigerant gas cools the motor10by flowing through the motor housing4and is subsequently taken in by the scroll compression mechanism8where the refrigerant gas is compressed to become high-temperature high-pressure refrigerant gas. The refrigerant gas is then discharged to a discharge pipe of the refrigeration cycle through a discharge port (not shown) provided at an end of the compressor housing3.

The motor10is driven via an inverter21, and the rotation speed thereof is variably controlled in accordance with the air-conditioning load. The inverter21is integrated with the inverter-integrated electric compressor1and is formed by installing, for example, a plurality of control circuit boards, i.e., an upper board25A and a lower board25B, one on top of the other within an inverter box23formed integrally with the outer periphery of the housing2and having a rectangular shape in plan view. The inverter21is electrically connected to the motor10via an inverter output terminal, a lead wire, a motor terminal, and the like that are not shown in the drawings.

The inverter box23has a structure in which, for example, a peripheral wall27thereof is formed integrally with an upper portion of the motor housing4, and an upper opening thereof is closed by a cover member28in a liquid-tight manner. The inverter box23has a depth that can accommodate the upper board25A and the lower board25B constituting the inverter21, while maintaining a predetermined distance therebetween in the vertical direction. A bottom surface29of the inverter box23serves as an outer wall of the motor housing4, and a flat and horizontal heat-dissipating flat section31is formed therein. The upper board25A and the lower board25B are disposed in parallel with the heat-dissipating flat section31.

The upper board25A is fastened to, for example, board-fastening bosses34, formed in the four corners of the inverter box23, by using screws35. The lower board25B is fastened to board-fastening bosses36, formed at a position one step lower than that of the board-fastening bosses34, by using screws37, and is positioned at about an intermediate height between the upper board25A and the heat-dissipating flat section31. For example, the upper board25A is a CPU board on which a device, such as a CPU (not shown), that operates at low voltage is mounted, whereas the lower board25B is a power board on which multiple heat-generating devices, such as IGBTs41, are mounted. In this embodiment, only the upper board25A and the lower board25B are shown as the devices that constitute the inverter21, whereas other devices are not shown in the drawings.

The bottom surface29of the inverter box23is partly or entirely provided with, for example, a plate-like heat conducting member43composed of a highly thermally conductive material, such as an aluminum alloy. Techniques used for fixing the heat conducting member43to the bottom surface29include fastening using screws44, using an adhesive, fitting, and casting. The heat conducting member43is in abutment with the motor housing4composed of an aluminum alloy.

Electrical components, such as the IGBTs41, are mounted on the lower side of the lower board25B. Multiple lead terminals (pin terminals)41aof the IGBTs41extend through a spacer member45, to be described later, and are inserted into lead-terminal insertion holes25h(seeFIG. 5A), formed in the lower board25B, from below so as to be connected to the lower board25B by soldering. The lower surface of each IGBT41is in abutment with the heat conducting member43so that heat generated by the IGBT41is dissipated toward the heat-dissipating flat section31via the heat conducting member43. Alternatively, the heat conducting member43may be omitted, and the IGBTs41may be disposed in direct abutment with the heat-dissipating flat section31.

The spacer member45is interposed between the lower board25B and the IGBTs41. Although the spacer member45has a rectangular parallelepiped shape with a rectangular shape in plan view that conforms to the contour shape that collectively surrounds the multiple IGBTs41, the spacer member45may alternatively be, for example, small segments provided individually on the respective IGBTs41. The lead terminals41aof the IGBTs41extend through the spacer member45so as to be connected to the lower board25B.

The upper and lower surfaces of the spacer member45are respectively in abutment with the lower surface of the lower board25B and the upper surface of each IGBT41without any gaps therebetween. Specifically, the spacer member45fills the space between the lower board25B and the IGBTs41.

Various conceivable examples of the material used for forming the spacer member45include metal, hard resin, soft resin, an elastic material such as rubber or sponge, and a fibrous material such as paper, cloth, or felt. However, the spacer member45must be rigid enough that the lower board25B and the IGBTs41are prevented from being displaced toward and away from each other when the spacer member45is attached between the two components25B and41. For this reason, if the spacer member45is to be composed of an elastic material or a fibrous material, it might be necessary to elastically interpose the spacer member45in a compressed state between the two components25B and41, depending on the circumstances. This example will be described later in a fourth embodiment and a fifth embodiment.

Furthermore, screws48vertically extend through the lower board25B, the spacer member45, and the IGBTs41so as to fasten these three components25B,45, and41to the heat conducting member43(i.e., the heat-dissipating flat section31). The screws48serve as pressing members that press the IGBTs41toward the heat-dissipating flat section31. As an alternative to the three components25B,45, and41being collectively fastened to the heat conducting member43in this manner, the IGBTs41alone may be fastened to the heat conducting member43by, for example, forming through-holes, through which the heads of the screws48can pass, in the lower board25B and the spacer member45. In other words, at least the IGBTs41need to be pressed toward the heat conducting member43.

When assembling the inverter21, as shown inFIG. 3, an inverter-board assembly51is sub-assembled in advance by stacking the lower board25B, the spacer member45, and the IGBTs41one on top of the other, inserting the lead terminals41aof the IGBTs41into the lower board25B from below and soldering the lead terminals41athereto from above, and inserting the screws37and48into the lower board25B from above. Then, after setting the inverter-board assembly51within the inverter21and tightening the screws37and48so as to fix the inverter-board assembly51within the inverter box23, the upper board25A is placed and fixed thereon using the screws35(seeFIG. 1). By subsequently performing a necessary wiring process, the inverter21is completed. Finally, the inverter21is closed using the cover member28.

In the inverter-integrated electric compressor1having the above-described configuration, low-pressure refrigerant gas circulating in the refrigerant cycle is taken into the motor housing4through the refrigerant intake port (not shown) and flows through the motor housing4so as to be taken in by the scroll compression mechanism8. The refrigerant gas compressed to a high-temperature high-pressure state in the scroll compression mechanism8travels through the discharge pipe via the discharge port (not shown) provided at the end of the compressor housing3so as to circulate in the refrigerant cycle.

During this time, in the inverter box23, the low-temperature low-pressure refrigerant gas flowing through the motor housing4absorbs working heat generated by the IGBTs41, serving as heat-generating devices of the inverter21, via the heat-dissipating flat section31serving as an outer wall of the motor housing4and the heat conducting member43having high thermal conductivity. Consequently, the upper board25A and the lower board25B constituting the inverter21set within the inverter box23can be forcedly cooled.

In particular, since the electrical components, such as the IGBTs41, serving as heat-generating devices mounted on the lower board25B serving as a power board are disposed such that the lower surfaces thereof are in abutment with the heat conducting member43, the working heat thereof is directly dissipated toward the heat-dissipating flat section31and the motor housing4via the heat conducting member43. Therefore, the lower board25B serving as a power board, which especially generates a large amount of heat, can be efficiently cooled.

In this embodiment, the spacer member45is interposed between the lower board25B and the IGBTs41so that this spacer member45fills the space between the lower board25B and the IGBTs41. In addition, since the spacer member45is rigid enough that the two components25B and41are prevented from being displaced toward and away from each other, relative displacement between the lower board25B and the IGBTs41does not occur even when, for example, the lower board25B resonates with external vibrations or vibrations from the motor10.

Therefore, conventional accumulation of metal fatigue of the lead terminals41acaused by relative displacement between the lower board25B and the IGBTs41occurring due to the lower board25B vibrating alone relative to the IGBTs41is avoided, thereby reliably eliminating the possibility of deformation and breakage of the lead terminals41a. Furthermore, since the IGBTs41are pressed toward the heat-dissipating flat section31by the screws48, the heat of the IGBTs41can be dissipated more efficiently toward the heat-dissipating flat section31.

The screws48extending through the lower board25B, the spacer member45, and the IGBTs41are fastened to the heat conducting member43, whereby the IGBTs41are pressed against the heat conducting member43. Therefore, this eliminates the conventional need for an extremely difficult and complicated assembly process involving aligning the IGBTs41on the heat conducting member43in advance, fixing the IGBTs41thereon using screws or the like, placing the lower board25B in alignment with the lead terminals41a, and performing soldering, whereby the workability for assembling the inverter21and its surrounding area can be significantly improved.

When sub-assembling the inverter-board assembly51, since the assembly work can be performed outside the inverter21, the main body of the electric compressor does not need to be conveyed in the assembly line of the inverter, whereby the workability for assembling the inverter21and its surrounding area can also be improved in this respect. The screws48serving as pressing members that press the IGBTs41toward the heat-dissipating flat section31can conceivably be replaced with other bias members, such as springs and clips.

Second Embodiment

Next, a second embodiment of the present invention will be described with reference toFIG. 4andFIGS. 5A to 5C.

InFIG. 4andFIGS. 5A to 5C, components that are the same as those in the first embodiment shown inFIGS. 1 to 3are given the same reference numerals, and descriptions thereof will be omitted.

In the second embodiment, bonding layers62are formed on both upper and lower surfaces of a spacer member61. The bonding layers62function as bonding members for bonding the spacer member61to the lower board25B and the IGBTs41, and can conceivably be composed of an adhesive material, such as an adhesive or double-sided tape, or a heat-weldable joining material, such as solder layers or adhesive resin layers. Although only one bonding layer62may be provided on one of the upper and lower surfaces of the spacer member61, it is preferable that both the upper and lower surfaces be provided with bonding layers62.

Unlike the first embodiment, the IGBTs41are simply bonded to the lower surface of the spacer member61via the bonding layer62without being screwed onto the heat conducting member43. Furthermore, because the spacer member61is also bonded to the lower board25B by the bonding layer62, positional displacement of the IGBTs41and the spacer member61relative to the lower board25B does not occur. The lower surfaces of the IGBTs41abut on the heat conducting member43so that the heat of the IGBTs41is dissipated toward the heat conducting member43.

Since both the upper and lower surfaces of the spacer member61are bonded to the lower board25B and the IGBTs41via the bonding layers62, not only are the lower board25B and the IGBTs41prevented from being displaced toward and away from each other, but relative displacement between the two components25B and41in the planar direction is also prevented. Therefore, breakage of the lead terminals41aof the IGBTs41is prevented more effectively.

In addition, in view of the fact that the spacer member61can be fixed to the lower board25B and the IGBTs41without being dependent on fastening members, such as screws, and that the lower board25B, the spacer member61, and the IGBTs41can be sub-assembled in advance, the workability for assembling the inverter21and its surrounding area can be significantly improved. Moreover, since it is not necessary to form holes for extending screws through the lower board25B, strength reduction of the lower board25B can be avoided.

If the spacer member61is composed of a material with no vibration absorbability, such as metal or hard resin, the bonding layers62may have cushioning properties so as to be given vibration absorbability and to lightly press the IGBTs41toward the heat conducting member43with the elastic force of the bonding layers62, thereby preventing the IGBTs41from being lifted upward from the heat conducting member43and satisfactorily ensuring the heat dissipation effect for the IGBTs41.

FIGS. 5A to 5Cillustrate an assembly method of the inverter21according to the second embodiment. In this case, the bonding layers62are composed of a heat-weldable material, such as solder layers or adhesive resin layers. First, as shown inFIG. 5A, a sub-assembly process is performed in advance by stacking the lower board25B, the spacer member61, and the IGBTs41one on top of the other. Next, as shown inFIG. 5B, heat is applied to these three components25B,61, and41so as to heat-weld the bonding layers62thereto, thereby forming the inverter-board assembly51. Then, as shown inFIG. 5C, the inverter-board assembly51is disposed within the inverter box23and is fastened to the board-fastening bosses36using the screws37. Finally, a wiring process is performed so that the inverter21is completed, and the inverter21is closed using the cover member28.

With such an assembly method, the inverter-board assembly51can be assembled outside the inverter box23, and the lead terminals41aof the plurality of IGBTs41can be sub-assembled in advance by inserting them into the lower board25B, whereby the workability for assembling the inverter21and its surrounding area can be dramatically improved. In particular, if the bonding layers62are solder layers, the heating process for the bonding layers62and the soldering process between the lower board25B and the IGBTs41can be performed at the same time, thereby reducing the number of assembly steps and enhancing manufacturability.

Third Embodiment

InFIG. 6, components that are the same as those in the second embodiment shown inFIG. 4are given the same reference numerals, and descriptions thereof will be omitted.

In the third embodiment, the IGBTs41are fastened to the heat conducting member43using screws71. Furthermore, recesses73for accommodating the heads of the screws71are formed in the lower surface of a spacer member72. Bonding layers62similar to those in the second embodiment are used for bonding and positioning between the IGBTs41and the spacer member72and between the spacer member72and the lower board25B.

With this configuration, the IGBTs41alone are first fastened to the heat conducting member43using the screws71, thereby ensuring reliable heat dissipation. The recesses73in the lower surface of the spacer member72may alternatively be through-holes extending through the spacer member72, the bonding layers62, and the lower board25B.

Fourth Embodiment

InFIG. 7, components that are the same as those in the third embodiment shown inFIG. 6are given the same reference numerals, and descriptions thereof will be omitted.

In the fourth embodiment, a spacer member81is composed of an elastic material, such as rubber, and the spacer member81is elastically interposed between the lower board25B and the IGBTs41. Specifically, the spacer member81is given a slightly large thickness in advance so that when the screws37that fasten the lower board25B to the board-fastening bosses36within the inverter box23are loosened, the lower board25B is slightly lifted upward from the board-fastening bosses36by the elastic force of the spacer member81.

Accordingly, since the spacer member81itself acts as a vibration absorbing member, resonance of the lower board25B can be effectively suppressed. Although the screws71are used to fasten the IGBTs41to the heat conducting member43, even if the screws71were to be omitted, the heat dissipation effect for the IGBTs41would still be satisfactorily ensured since the IGBTs41are pressed toward the heat conducting member43by the elastic force of the spacer member81, and the workability for assembling the inverter21and its surrounding area can also be improved.

Fifth Embodiment

Next, a fifth embodiment of the present invention will be described with reference toFIG. 8.

InFIG. 8, components that are the same as those in the fourth embodiment shown inFIG. 7are given the same reference numerals, and descriptions thereof will be omitted.

In the fifth embodiment, a spacer member91is composed of a porous or foamed elastic material, such as sponge or urethane foam, and this spacer member91is elastically interposed between the lower board25B and the IGBTs41.

Although the IGBTs41are not fastened to the heat conducting member43with screws or the like, since the IGBTs41are pressed toward the heat conducting member43by the elastic force of the spacer member91elastically interposed between the lower board25B and the IGBTs41, the heat dissipation effect for the IGBTs41is satisfactorily ensured.

Furthermore, because the spacer member91is composed of a porous or foamed elastic material, the strength of the elastic force of the spacer member91sandwiched between the lower board25B and the IGBTs41can be readily set.

It should be noted that the present invention is not to be limited to the first to fifth embodiments described above. For example, modifications, such as appropriately combining the configurations of the first to fifth embodiments, are permissible so long as they do not depart of the scope of the claims.