Patent Publication Number: US-2004052660-A1

Title: Electric compressor

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to an electric compressor for a refrigeration cycle used in an automotive air conditioner to compress a refrigerant.  
       [0002] Japanese Laid-Open Utility Model Publication No. 62-12471 and Japanese Laid-Open Patent Publication No. 2002-5024 each describe an electric compressor having an inverter, which drives an electric motor, attached to an outer surface of a compressor housing, which houses a compression mechanism. To cope with the heat generated from the inverter, in Japanese Laid-Open Utility Model Publication No. 62-12471, the low temperature refrigerant flowing through the electric compressor exchanges heat with a switching device, which forms the inverter, through the compressor housing. Such a structure is advantageous in that a mechanism for cooling the inverter, such as a radiator or a fan, is not required.  
       [0003] However, Japanese Utility Model Publication No. 62-12471 only describes that the switching device is attached to, or contacts, the outer surface of the electric compressor housing. There is no disclosure of how to improve the heat exchange efficiency between the compressor housing and the switching device.  
       [0004] When the inverter is attached to the compressor, part of the inverter projects outward from the compressor housing. This enlarges the electric compressor. Space is limited when installing the compressor in an automobile. Thus, enlargement of the compressor must be avoided. To keep the electric compressor compact, the height of the part of the inverter projecting from the compressor housing must be lowered. Among the electric components included in the inverter, a plurality of large electrolysis capacitors are used in a smoothening circuit. To lower the height of the projecting part of the inverter, the layout of electrolysis capacitors must be changed. However, in the prior art, sufficient consideration has not been given to the layout of the electrolysis capacitors.  
       SUMMARY OF THE INVENTION  
       [0005] It is an object of the present invention to provide an electric compressor that is compact and increases the efficiency for exchanging heat between the switching device and the compressor housing.  
       [0006] To achieve the above object, the present invention provides an electric compressor for use in a refrigeration circuit. The electric compressor includes a housing having an outer surface, an electric motor, and a compression mechanism accommodated in the housing for being driven by the electric motor. An inverter is attached to the outer surface of the housing to drive the electric motor. The inverter includes a switching device having a heat radiating surface. A groove having a wall is formed in the outer surface of the housing. The switching device is inserted in the groove so that the heat radiating surface contacts the wall of the groove.  
       [0007] A further aspect of the present invention is an electric compressor including a housing having a cylindrical wall with an outer surface and an axis, an electric motor, and a compression mechanism accommodated in the housing. When operated, the compression mechanism is driven by the electric motor. An inverter is attached to the outer surface of the cylindrical wall to drive the electric motor. The inverter includes a plurality of cylindrical electrolysis capacitors, each having an axis. The axes of the electrolysis capacitors are parallel to one another and parallel to the axis of the cylindrical wall.  
       [0008] Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009] The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
     [0010]FIG. 1 is a cross-sectional view of an electric compressor according to a preferred embodiment of the present invention;  
     [0011]FIG. 2 is a side view showing the electric compressor;  
     [0012]FIG. 3 is a cross-sectional view taken along line  3 - 3  in FIG. 2;  
     [0013]FIG. 4 is an exploded perspective view showing a switching device assembly of the electric compressor;  
     [0014]FIG. 5 is an exploded perspective view showing electrolysis capacitors of the electric compressor;  
     [0015]FIG. 6 is a cross-sectional view of a switching device assembly in another embodiment of the present invention; and  
     [0016]FIG. 7 is a cross-sectional view of a switching device assembly in a further embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0017] An electric compressor  10  according to a preferred embodiment of the present invention will now be discussed with reference to FIGS.  1  to  5 . The electric compressor  10  is incorporated in a refrigeration cycle of an automotive air conditioner.  
     [0018] Referring to FIGS. 1 and 2, the electric compressor  10  has a compressor housing  11  including a first housing member  21  and a second housing member  22 . The first housing member  21 , which is an aluminum alloy casting, has a cylindrical wall  23 . The second housing member  22  is also an aluminum alloy casting. The first housing member  21  and the second housing member  22  are coupled to each other to define a hollow portion  24  in the compressor housing  11 .  
     [0019] As shown in FIG. 1, a rotary shaft  27  is rotatably supported in the first housing member  21 . An axis L of the rotary shaft  27  coincides with an axis of the electric compressor  10 . The cylindrical wall  23  extends around the rotary shaft  27  so that the axis of the cylindrical wall  23  coincides with the axis L of the rotary shaft  27 .  
     [0020] An electric motor  25  and a compression mechanism  26  are accommodated in the hollow portion  24 . The electric motor  25  includes a stator  25   a , which is fixed to an inner surface  23   a  of the cylindrical wall  23 , and a rotor  25   b , which is arranged on the rotary shaft  27  radially inward from the stator  25   a . The electric motor  25  rotates the rotary shaft  27  with power supplied from the stator  25   a.    
     [0021] As shown in FIG. 2, the first housing member  21  has a suction port  31 . The second housing member  22  has a discharge port  32 . An external refrigeration circuit  61 , which includes a condenser  62 , an expansion valve  63 , and an evaporator  64 , connect the suction port  31  and the discharge port  32 . The external refrigeration circuit  61  and the electric compressor  10  form the refrigeration cycle of the automotive air conditioner.  
     [0022] As shown in FIG. 1, the compression mechanism  26  includes a fixed scroll  26   a  and a movable scroll  26   b . When the rotary shaft  27  rotates, the movable scroll  26   b  orbits relative to the fixed scroll  26   a  to compress refrigerant gas. Accordingly, when the electric motor  25  drives the compression mechanism  26 , low temperature, low pressure refrigerant gas is drawn into the compression mechanism  26  from the evaporator  64  through the suction port  31 . The compression mechanism  26  compresses the drawn refrigerant gas to produce high temperature, high pressure refrigerant gas and sends the refrigerant gas to the condenser  62  through the discharge port  32 .  
     [0023] Referring to FIG. 3, the first housing member  21  includes a retainer  36  projecting from a part of the outer surface  23   b  of the cylindrical wall  23 . The retainer  36  includes side walls  37 , which extend integrally from the outer surface  23   b  of the cylindrical wall  23 , and a cover  38 , which is fixed to the top of the side walls  37  to cover the opening of the side walls  37 . A retaining chamber  35  is defined in the retainer  36 .  
     [0024] The retaining chamber  35  has a bottom surface  35   a , which is part of the outer surface  23   b  of the cylindrical wall  23 . The retaining chamber  35  also has side surfaces  35   b , which are the inner surfaces of the side walls  37 . In other words, the bottom surface  35   a  and side surfaces  35   b  of the retaining chamber  35  are defined by parts of the first housing member  21 . The bottom surface  35   a  in the retainer  36  is curved along the cylindrical wall  23 . The retaining chamber  35  further has a top surface  35   c , which is the inner surface of the cover  38 . In the retaining chamber  35 , the distance between the bottom surface  35   a  and the top surface  35   c  decreases at the middle section of the retaining chamber  35  and increases at the peripheral sections on each side (left and right sides as viewed in FIG. 3) of the retaining chamber  35 .  
     [0025] An inverter  41 , which drives the electric motor  25 , is retained in the retainer  36 . The inverter  41  supplies the stator  25   a  of the electric motor  25  with power in accordance with a command from an air conditioner ECU (not shown).  
     [0026] As shown in FIGS.  3  to  5 , the inverter  41  includes a first circuit board  42  and a second circuit board  43 , which are for use in a power system, and a third circuit board  44 , which is for use in a control system. A switching device assembly  70 , a capacitor  46 , and electric components of the power system that configure an inverter circuit (not shown), such as a transformer, are connected to the first circuit board  42 . The switching device assembly  70  includes a plurality of switching devices  45  (six in the preferred embodiment).  
     [0027] A plurality of electrolysis capacitors  47  (five in the preferred embodiment), which are electric components of the power system configuring the inverter circuit, are mounted on the plane  43   a  of the second circuit board  43 . The electrolysis capacitors  47  are cylindrical and configure a smoothening circuit. The smoothening circuit stabilizes the battery voltage applied to a power system circuit of the inverter  41 . The electrolysis capacitors  47  occupy much space in the retaining chamber  35 . Thus, the second circuit board  43  is separated from the first circuit board  42  to efficiently use the limited space in the retaining chamber  35  of the retainer  36 . A driver  48  mounted on the third circuit board  44  intermittently controls the switching devices  45  in accordance with commands from, for example, the air conditioner ECU.  
     [0028] As shown in FIG. 3, relatively large electric components, such as the switching device assembly  70  and the capacitor  46  are connected to the lower surface  42   a  of the first circuit board  42 . The lower surface  42   a  of the first circuit board  42  faces towards the bottom surface  35   a  of the retaining chamber  35 . The third circuit board  44  is arranged between the first circuit board  42  and the cover  38  in the retainer  36 . The first circuit board  42  and the third circuit board  44  are arranged in the retainer  36  in a superimposed manner. The first circuit board  42  is fixed to the compressor housing  11  by bolts (not shown). The third circuit board  44  is fixed to the first circuit board  42  by bolts (not shown).  
     [0029] Resin molding, such as insert molding, is performed to integrate the six switching devices  45  into the switching device assembly  70 . Resin molding is performed by arranging the switching devices  45  in two rows and filling connecting resin  57  into the space between the switching devices  45  so as to connect the switching devices  45 .  
     [0030] The six switching devices  45  of the switching device assembly  70  each include a body  45   a  and three terminals  45   b  extending from one end of the body  45   a . Among the three terminals  45   b , two are bent. The remaining terminal  45   b  extends straight from the end of the body  45   a . Due to such configuration, the wiring pattern (not shown) of the circuit board  42 , to which the distal portions of the terminals  45   b  are connected, is not dense.  
     [0031] The six switching devices  45  are arranged in two rows in the longitudinal direction of the switching device assembly  70 . The bent terminals  45   b  of the switching devices  45  in each row are aligned in the longitudinal direction. The straight terminal  45   b  is arranged between the bent terminals  45   b  in each switching device  45 .  
     [0032] As shown in FIG. 3, the switching device assembly  70  is the component that projects the most from the first circuit board  42 . If a component projecting from the first circuit board  42  is arranged in the central portion of the retainer  36  where the distance between the bottom surface  35   a  and the top surface  35   c  of the retaining chamber  35  is small, the distance between the lower surface  42   a  of the first circuit board  42  and the outer surface of the cylindrical wall  23  must be increased. This enlarges the retainer  36 , which in turn, enlarges the electric compressor  10  in the radial direction (i.e., the direction perpendicular to the axis L).  
     [0033] However, in the preferred embodiment, the switching device assembly  70  is connected to the first circuit board  42  at the peripheral section (left side as viewed in FIG. 3) where the distance between the bottom surface  35   a  and the top surface  35   c  of the retaining chamber  35  is large. Such arrangement of the switching device assembly  70  enables the first circuit board  42  to be positioned near the cylindrical wall  23 . As a result, the size of the retainer  36  may be reduced, and the electric compressor  10  may be made more compact.  
     [0034] The arrangement of the switching device assembly  70 , which is a projecting component, in one side of the retaining chamber  35  provides a relatively large space from the middle portion of the retaining chamber  35  to the other side (right side as viewed in FIG. 3) of the retaining chamber  35  between the first circuit board  42  and the bottom surface  35   a  of the retaining chamber  35 . In this space, the electrolysis capacitors  47 , which occupy much space, are arranged in a row in the circumferential direction of the cylindrical wall  23 . Accordingly, the layout of the switching device assembly  70  in one side of the retainer  36  not only enables the size of the electric compressor  10  to be reduced in the radial direction but also enables efficient usage of the space in the retainer  36 .  
     [0035] As shown in FIGS. 3 and 5, the plane  43   a  of the second circuit board  43  is perpendicular to the axis L of the compressor housing  11 . As a result, the axes of the parallel electrolysis capacitors  47  are parallel to the axis L of the compressor housing  11 .  
     [0036] The second circuit board  43  has a flat surface and a bent portion at the middle in correspondence with the bottom surface  35   a  of the retaining chamber  35 . The five electrolysis capacitors  47  are connected to the second circuit board  43  in a manner forming a line that is bent at the middle so as to follow the curve of the bottom surface  35   a.    
     [0037] A resin capacitor holder  49  fixes the five electrolysis capacitors  47  to the compressor housing  11 . The capacitor holder  49  has five holding portions  49   a  to hold the five electrolysis capacitors  47 . The capacitor holder  49  is formed so that the line defined by the holding portions  49   a  is bent at the middle in accordance with the bent line of the electrolysis capacitors  47 .  
     [0038] When the electrolysis capacitors  47  are held in the holding portions  49   a , the capacitor holder  49  is fastened to the compressor housing  11  by bolts  60  (refer to FIG. 5). This holds the electrolysis capacitors  47  between the capacitor holder  49  and the bottom surface  35   a  of the retaining chamber  35 .  
     [0039] A resin sheet  50  is arranged on the bottom surface  35   a  of the retaining chamber  35  to separate the bottom surface  35   a  from the capacitor  46  and the electrolysis capacitors  47 . The sheet  50  may be made of rubber as long as it has superior elastic and heat conducting properties. That is, the capacitor  46  and the electrolysis capacitors  47  indirectly contact the bottom surface  35   a  of the retaining chamber  35  by means of the sheet  50 .  
     [0040] As shown in FIGS. 3 and 4, a groove  51  is formed in the outer surface  23   b  of the cylindrical wall  23  of the compressor housing  11  in the retaining chamber  35 . More specifically, a first wall  52  and a second wall  53 , which are parallel to the axis L, define the groove  51 . The side wall  37  of the retainer  36  that is located near the switching device  45  serves as the first wall  52 . The second wall  53  is extended from the outer surface  23   b  of the cylindrical wall  23  in the retainer  36 . A part of the outer surface  23   b  of the cylindrical wall  23  (bottom surface  35   a  of the retaining chamber  35 ) functions as a bottom surface  51   a  of the groove  51 , which connects the first wall  52  and the second wall  53 .  
     [0041] As shown in FIG. 4, an inner surface  52   a  of the first wall  52  faces towards an inner surface  53   a  of the second wall  53  in the groove  51 . The inner surfaces  52   a  and  53   a  of the first and second walls  52  and  53  are inclined relative to a vertical line S, which is perpendicular to a horizontal plane extending through the axis L of the rotary shaft  27  as viewed in FIG. 3.  
     [0042] The switching devices  45  each have a heat radiating surface  45   c , which is faced to the associated inner surface  52   a  or  53   a  of the groove  51 . In other words, the switching device assembly  70  has six heat radiating surfaces  45   c , three on each side of the switching device assembly  70  (FIG. 4).  
     [0043] The heat radiating surface  45   c  is the surface of the body  45   a  from which a conducting portion of a transistor, which forms the switching device  45 , is exposed. The conducting portion is encircled in each heat radiating surface  45   c  in FIG. 4.  
     [0044] When the switching device assembly  70  is received in the groove  51 , the heat radiating surface  45   c  of each switching device  45  contacts the corresponding inner surface  52   a  or  53   a  of the groove  51 . More specifically, in the row of the three switching devices  45  that are closer to the first wall  52 , the heat radiating surfaces  45   c  contact the inner surface  52   a  of the first wall  52 . Further, in the row of the three switching devices  45  that are closer to the second wall  53 , the heat radiating surfaces  45   c  contact the inner surface  53   a  of the second wall  53 .  
     [0045] An elastic sheet  54  is arranged between the heat radiating surfaces  45   c  of the switching devices  45  and the inner surfaces  52   a  and  53   a  of the groove  51 . The elastic sheet  54  is made of rubber or resin. Further, the sheet  54  has a superior heat conducting property.  
     [0046] When the switching device assembly  70  is received in the groove  51 , a flat fastening plate  55  is fixed to the compressor housing  11  to cover the opening of the groove  51 . The fastening plate  55  functions as a fastening member and a pressure applying body.  
     [0047] The lower surface of the fastening plate  55  (as viewed in FIG. 3) presses the switching device assembly  70  in a direction parallel to the vertical line S. As described above, the heat radiating surfaces  45   c  of the switching device  45  and the inner surfaces  52   a  and  53   a  of the groove  51  are inclined relative to the vertical line S. Accordingly, when the fastening plate  55  presses the switching device assembly  70  in the direction parallel to the vertical line S, the heat radiating surfaces  45   c  of the switching devices  45  are pressed strongly against the inner surfaces  52   a  and  53   a  of the groove  51  through the sheet  54 . In the preferred embodiment, the fastening plate  55  functions to press the switching devices  45  against the inner surfaces  52   a  and  53   a  of the groove  51 .  
     [0048] As shown in FIG. 4, a plurality of insertion holes  55   a  are extend through the fastening plate  55 . The terminals  45   b  of the switching devices  45  are inserted through the corresponding insertion holes  55   a . Then, the fastening plate  55  is fastened to the compressor housing  11  by bolts  58 . After the first circuit board  42  is fixed to the compressor housing  11 , the terminals  45   b  projecting out of the insertion holes  55   a  of the fastening plate  55  are soldered.  
     [0049] Referring to FIGS.  1  to  3 , a refrigerant gas passage  33  connecting the suction port  31  to the compression mechanism  26  passes by the groove  51  in the compressor housing  11 . More specifically, the refrigerant gas passage  33  is defined between the inner surface  23   a  of the cylindrical wall  23  and the outer surface of the stator  25   a  of the electric motor  25  at a location corresponding to the groove  51 . The refrigerant gas passage  33  extends parallel to the axis L of the rotary shaft  27 .  
     [0050] The low temperature refrigerant gas directed toward the compression mechanism  26  from the suction port  31  flows through the refrigerant gas passage  33  to cool the switching devices  45 . Heat exchange between the switching devices  45  and the cooler cylindrical wall  23  is performed mainly at locations where the heat radiating surfaces  45   c  of the switching devices  45  contact the corresponding inner surfaces  52   a  and  53   a  of the groove  51 .  
     [0051] The preferred embodiment has the advantages described below.  
     [0052] (1) The groove  51  is formed in the outer surface  23   b  of the compressor housing  11 . In other words, the bottom surface  51   a  and inner surfaces  52   a  and  53   a  of the groove  51  are provided by the compressor housing  11 , the temperature of which is low. Accordingly, the compressor housing  11  cools the switching devices  45  more easily in comparison to, for example, when the switching devices  45  are arranged outside the groove  51 . This improves the heat exchange efficiency between the switching device  45  and the compressor housing  11  in comparison to the heat exchange described in, for example, Japanese Laid-Open Utility Model Publication No. 62-12471. Further, this cools the inverter  41  in a preferable manner, improves the durability of the inverter  41 , and stabilizes the operation of the inverter  41 .  
     [0053] (2) The fastening plate  55  connected to the compressor housing  11  presses the switching device assembly  70  against the inner surfaces  52   a  and  53   a  of the groove  51 . As a result, the heat radiating surfaces  45   c  of the switching devices  45  come into close contact with the corresponding inner surfaces  52   a  and  53   a  of the groove  51 . This improves the heat exchange efficiency between the switching devices  45  and the compressor housing  11 .  
     [0054] (3) In comparison to when providing a groove  51  for each switching device  45 , the accommodation of the switching devices  45  in the single groove  51  reduces the machining cost of the compressor housing  11 .  
     [0055] (4) The switching device assembly  70 , which is formed from the unit of the switching devices  45 , is inserted in the groove  51 . Accordingly, the switching devices  45  are inserted in the groove  51  at the same time by inserting the switching device assembly  70 . This simplifies assembly of the electric compressor  10 .  
     [0056] (5) The inner surfaces  52   a  and  53   a  of the groove  51  are inclined relative to the vertical line S of the groove  51  so that the distance between the inner surfaces  52   a  and  53   a  of the groove  51  decreases as the bottom surface  51   a  of the groove  51  becomes closer. Accordingly, the heat radiating surfaces  45   c  of the switching devices  45  come into close contact with the corresponding inner surfaces  52   a  and  53   a  of the groove  51  as if a wedge is inserted into the compressor housing  11 . This further improves heat exchange efficiency between the switching device  45  and the compressor housing  11 .  
     [0057] (6) The elastic sheet  54  is arranged between the heat radiating surfaces  45   c  of the switching devices  45  and the corresponding inner surfaces  52   a  and  53   a  of the groove  51 . Accordingly, elastic deformation of the sheet  54  absorbs dimensional differences and increases contact between the heat radiating surfaces  45   c  of the switching devices  45  and the corresponding inner surfaces  52   a  and  53   a  of the groove  51 . Further, the superior heat conductance of the sheet  54  further improves the heat exchange efficiency between the switching devices  45  and the compressor housing  11 . The elastic sheet  54  also protects the switching devices  45  from impacts, or the like, applied to the compressor housing  11 .  
     [0058] (7) In the compressor housing  11 , the refrigerant gas passage  33 , which connects the low pressure side of the external refrigeration circuit  61  (the side in which the evaporator  64  is located) to the compression mechanism  26 , passes by the groove  51 . Accordingly, the low temperature refrigerant gas that passes by the groove  51  effectively cools the switching devices  45 .  
     [0059] (8) The inverter  41  is retained in the retaining chamber  35  of the compressor housing  11 . The bottom surface  35   a  and side surface  35   b  of the retaining chamber  35  are part of the compressor housing  11 . This reduces the number of components in comparison to when preparing a retainer separately from the compressor housing  11  (e.g., when retaining the inverter  41  in a case and attaching the case to the compressor housing  11 ). Further, the inverter  41  is surrounded by the compressor housing  11 , which has high rigidity. This is effective for protecting the inverter from external impacts.  
     [0060] (9) The elastic sheet  50  separates the electrolysis capacitors  47  and the capacitor  46  from the bottom surface  35   a  of the retaining chamber  35 . Accordingly, elastic deformation of the sheet  50  absorbs dimensional differences and increases contact of the electrolysis capacitors  47  and the capacitor  46  against the bottom surface  35   a  of the retaining chamber  35 . Further, the superior heat conductance of the sheet  50  further improves the heat exchange efficiency of the capacitors  46  and  47  with the compressor housing  11 . The elastic sheet  50  also protects the capacitors  46  and  47  from impacts, or the like, applied to the compressor housing  11 .  
     [0061] (10) The switching device assembly  70  is connected to the first circuit board  42  after arranging the switching device assembly  70  in the groove  51 . Accordingly, by adjusting the insertion of the terminals  45   b  of the switching devices  45  for the first circuit board  42 , dimensional differences of each portion is absorbed and the heat radiating surfaces  45   c  of the switching devices  45  come into close contact with the corresponding inner surfaces  52   a  and  53   a  of the groove  51 . This further improves heat exchange efficiency between the switching devices  45  and the compressor housing  11 .  
     [0062] (11) The axes M of the electrolysis capacitors  47  are parallel to each other and to the axis L of the rotary shaft  27  (cylindrical wall  23 ). For example, in comparison to when the axes M of the electrolysis capacitors  47  are arranged in a direction perpendicular to the axis L of the cylindrical wall  23  or when the electrolysis capacitors  47  are not arranged in the same direction, the projecting height of the inverter  41  (retainer  36 ) from the cylindrical wall  23  is decreased. Thus, the electric compressor  10  does not have to be enlarged in the radial direction.  
     [0063] (12) The electrolysis capacitors  47  are arranged in a row along the outer surface  23   b  of the cylindrical wall  23 . Accordingly, in comparison to, for example, when arranging the electrolysis capacitors  47  in a stacked manner, the projecting height of the inverter  41  (retainer  36 ) from the cylindrical wall  23  is decreased.  
     [0064] (13) The electrolysis capacitors  47  are held between the capacitor holder  49  and the cylindrical wall  23 . In other words, the capacitor holder  49  fixes the electrolysis capacitors  47  to the compressor housing  11 . In comparison to, for example, when indirectly fixing the electrolysis capacitors  47  to the compressor housing  11  with the second circuit board  43 , the fastening of the electrolysis capacitors  47  to the compressor housing  11  is guaranteed. This improves vibration resistance of the electrolysis capacitors  47 . Thus, the electric compressor  10  of the preferred embodiment is especially desirable under harsh vibration conditions, such as in an automobile.  
     [0065] (14) The electrolysis capacitors  47  are connected to the second circuit board  43 , which is separated from the first circuit board  42 . By separating the second circuit board  43  from the first circuit board  42 , freedom of layout for the second circuit board  43  increases in the compressor housing  11 . In other words, freedom of layout for the electrolysis capacitors  47  increases.  
     [0066] (15) The electrolysis capacitors  47  are arranged between the first circuit board  42  and the cylindrical wall  23 . Due to the difference in the shapes of the first circuit board  42 , which is flat, and the cylindrical wall  23 , which is curved, it is difficult to arrange electric components in the space between the first circuit board  42  and the cylindrical wall  23 . However, in the preferred embodiment, the electrolysis capacitors  47  are arranged in the space in an orderly manner along the outer surface  23   b  of the cylindrical wall  23 . The layout of the electrolysis capacitors  47  in the space between the first circuit board  42  and the cylindrical wall  23 , which would otherwise be dead space, is extremely effective for decreasing the height that the inverter  41  projects from the cylindrical wall  23 .  
     [0067] It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.  
     [0068] As shown in FIG. 6, the groove  51  may be formed so that its opposing inner surfaces  52   a  and  53   a  are parallel to each other. In this case, the heat radiating surfaces  45   c  of the switching devices  45  in the switching device assembly  71  are parallel to the vertical line S.  
     [0069] As shown in FIG. 7, a third wall  59  may be arranged between the first wall  52  and the second wall  53 . In this case, the compressor housing  11  has two grooves  51 . Three of the switching devices  45  are arranged in each of the grooves  51 . A switching device assembly  72 , which is formed by integrating three switching devices  45 A into a switching device assembly  72  with resin, is inserted in each groove  51 .  
     [0070] In the embodiments of FIGS.  1  to  7 , the sheet  54  arranged between the heat radiating surfaces  45   c  of the switching devices  45  and the inner surfaces  52   a  and  53   a  of the groove  51  may be eliminated. Further, the heat radiating surfaces  45   c  of the switching devices  45  may come into direct contact with the corresponding inner surfaces  52   a  and  53   a  of the groove  51 .  
     [0071] Instead of bending the row of the electrolysis capacitors  47  at the middle, the row of the electrolysis capacitors  47  may be linear.  
     [0072] The electrolysis capacitors  47  may be stacked upon one another.  
     [0073] In the embodiments of FIGS.  1  to  7 , the capacitor holder  49  may be eliminated, and the second circuit board  43  may be fixed to the compressor housing  11  or the other circuit boards  42  or  44  by bolts. In other words, the electrolysis capacitors  47  may be indirectly connected to the compressor housing  11  through the second circuit board  43 . This would decrease the number of components.  
     [0074] In the embodiments of FIGS.  1  to  7 , the second circuit board  43  may be eliminated and wires may be connected directly to the electrolysis capacitors  47 . In this case, by integrating the electrolysis capacitors  47  with resin beforehand, the electrolysis capacitors  47  may easily be attached to the compressor housing  11 .  
     [0075] In the embodiments of FIGS.  1  to  7 , in addition to the plane  43   a  of the second circuit board  43 , the electrolysis capacitors  47  may be arranged on the plane on the other side of the second circuit board  43 .  
     [0076] The present invention may be applied to an electric compressor in which the electric motor is separated from the compression mechanism. In this case, the inverter is arranged in the compressor housing, which accommodates the compression mechanism.  
     [0077] The present invention may be applied to an electric compressor in which the electric motor and compression mechanisms are arranged in different compressor housings. In this case, the inverter may be arranged in the compressor housing accommodating the electric motor or in the compressor housing accommodating the compression mechanism.  
     [0078] The present invention may be embodied in a so-called hybrid compressor, which uses an automotive drive source, or an engine, as another compressor drive source.  
     [0079] The compression mechanism  26  does not have to be a scroll type mechanism and may be a piston type, vane type, or helical type mechanism.  
     [0080] The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.