BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to assembly methods of a motor housing and a stator core of a sealed type motor-driven compressor.  
         [0002]     In a sealed type motor-driven compressor, a sealed housing accommodates, for example, a scroll type compressor mechanism and an electrical motor for driving the mechanism. The motor includes a rotational shaft, a rotor, and a stator. The rotational shaft of the motor is rotationally supported at a middle portion of a motor housing, which forms part of the sealed housing. The rotor is securely fitted to the outer circumferential surface of the rotational shaft. The stator is securely fitted to the inner circumferential surface of the motor housing through shrink fitting. The stator includes a cylindrical stator core and coils arranged along the inner circumference of the stator core. A technique for shrink-fitting the stator to the motor housing is disclosed in, for example, Japanese Laid-Open Patent Publication Nos. 2000-224787 and 2003-269335.  
         [0003]     When the motor housing is formed of aluminum, which has smaller modulus of elasticity than iron, a pressure rise in the motor housing causes a relatively great increase of the inner diameter of the motor housing, as compared to the case in which the motor housing is formed of iron. Chlorofluorocarbon or carbon dioxide is used as refrigerant gas charged in a refrigerating circuit of a vehicle air conditioner. The maximum charging pressure of chlorofluorocarbon gas is approximately 1 to 2 MPa, while that of carbon dioxide is equal to or greater than 10 MPa. As long as the pressure in the motor housing is maximally 1 to 2 MPa, the stator is prevented from loosening with respect to the motor housing by a fastening interference defined in shrink fitting of the stator core and the motor housing. However, if carbon dioxide is used as the refrigerant, the pressure equal to or greater than 10 MPa is applied to the motor housing.  
         [0004]     Accordingly, if carbon dioxide is used as the refrigerant and the motor housing formed of aluminum is employed, the motor housing must have a relatively large wall thickness for preventing the increase of the inner diameter of the motor housing. However, this increases the dimensions and weight of the compressor. Alternatively, the shrink fitting of the stator core and the motor housing may be performed with a sufficiently large fastening interference such that an effective fastening interference is maintained even if the inner circumference of the motor housing is increased. However, to provide a sufficiently large fastening interference, the shrink fitting must be performed at a relatively high temperature, leading to lowering of the strength of the motor housing, which is formed of aluminum. It is thus extremely difficult to increase the fastening interference for the shrink fitting.  
         [0005]     In contrast, if the motor housing is formed of iron, the increase of the inner diameter of the motor housing, which is caused by the high pressure applied by the refrigerant gas, is extremely small. However, the motor housing formed of iron increases the weight of the compressor.  
       SUMMARY OF THE INVENTION  
       [0006]     Accordingly, it is an objective of the present invention to provide a novel assembly method of a motor housing and a stator core capable of providing a sufficiently large fastening interference between the motor housing and the stator core for suppressing loosening of the stator core with respect to the motor housing, which is otherwise caused by a relatively high pressure produced by refrigerant gas.  
         [0007]     To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, the invention provides a method of assembling a sealed type motor-driven compressor having a cylindrical motor housing and an annular stator core fastened to the interior of the motor housing. The method includes fastening the stator core to the motor housing by mechanically deforming at least one of the motor housing and the stator core.  
         [0008]     Other aspects and advantages of the 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 longitudinal cross-sectional view showing an embodiment of a motor-driven compressor according to the present invention;  
         [0011]      FIG. 2  is a partially omitted cross-sectional view showing a motor portion of the compressor of  FIG. 1 ;  
         [0012]      FIG. 3  is a cross-sectional view showing a fastening interference between a motor housing and a stator core before assembly;  
         [0013]      FIG. 4  is a cross-sectional view showing an elastically deformed state of the motor housing such that the stator core is fitted to the motor housing;  
         [0014]      FIG. 5  is a partially omitted cross-sectional view showing a motor portion of a modification of the embodiment of the present invention; and  
         [0015]     FIGS.  6 ( a ) to  6 ( c ) are cross-sectional views each showing a modification of the assembly method of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     With reference to FIGS.  1  to  4 , an embodiment of an assembly method of a stator core and a motor housing of a sealed type motor-driven compressor  10  according to the present invention will be described.  
         [0017]     The compressor  10  includes a sealed housing  11  having a housing body  12  and a front housing  13 . The housing body  12  is formed of aluminum through forging and has a lidded, horizontal cylindrical shape. The front housing  13  is securely connected to a front opening end (as viewed to the right in  FIG. 1 ) of the housing body  12 . The housing body  12  includes a compressor housing  14 , a motor housing  15 , and a rear housing  16  (as viewed to the left in  FIG. 1 ). The compressor housing  14  is located in a front portion of the housing body  12 . The motor housing  15  has a relatively small diameter and is formed integrally with a rear end of the compressor housing  14 . The rear housing  16  is formed integrally with a rear end of the motor housing  15 .  
         [0018]     The compressor housing  14  accommodates a scroll type compressor mechanism  17 . The mechanism  17  includes a base plate  18 , a fixed scroll  19 , and a revolving scroll  20 . The base plate  18  is securely fitted to a stepped portion of an inner circumferential surface  14   a  of the compressor housing  14 . The fixed scroll  19  is securely fitted to the inner circumferential surface of a front opening of the compressor housing  14 . The revolving scroll  20  is arranged between the base plate  18  and the fixed scroll  19 . A compression chamber  21  is defined by the fixed scroll  19  and the revolving scroll  20 . Further, a suction chamber  22  is defined in the compressor housing  14  and at a rear side of the base plate  18 .  
         [0019]     A discharge chamber  23  is defined in the front housing  13 . Refrigerant gas is drawn from the suction chamber  22  to the compression chamber  21  through a suction port  18   a , which is defined in the base plate  18 , and is compressed in the compression chamber  21 . The refrigerant gas is then discharged to the discharge chamber  23  through a discharge port  19   a , which is defined in the fixed scroll  19 . The refrigerant gas is, for example, carbon dioxide.  
         [0020]     An outlet  13   a  is defined in the front housing  13  for supplying the compressed refrigerant gas to an external refrigerating circuit. An inlet  16   a  is defined in the rear housing  16  for introducing the refrigerant gas from the external refrigerating circuit to the suction chamber  22 .  
         [0021]     A stator  31  is securely fitted to the inner circumferential surface of the motor housing  15 , which forms part of an electrical motor M. The stator  31  includes a stator core  32 , teeth  32   a , and coils  33 . The stator core  32  is formed of iron. The teeth  32   a  are formed on the inner circumference of the stator core  32  and the coils  33  are each wound around the corresponding one of the teeth  32   a . A boss portion  16   b  is formed integrally with an inner rear side of the rear housing  16 . Likewise, a boss portion  18   b  is formed integrally with the rear side of the base plate  18 .  
         [0022]     A rotary shaft  28  is rotationally supported by a pair of bearings  29 ,  30  between the boss portions  16   b ,  18   b . An eccentric pin  34  is disposed at a distal end of the rotary shaft  28  and is connected to a boss portion  20   a , which is formed integrally with a rear side of the revolving scroll  20 , through a bearing. A rotor  35  is securely fitted to the outer circumferential surface of the rotary shaft  28 .  
         [0023]     When an alternating current is supplied from a non-illustrated power supply to the coils  33 , electromagnetic attractive force is produced by the stator  31  and the rotor  35 , such that the rotary shaft  28  is rotated. This revolves the eccentric pin  34 , thus permitting the revolving scroll  20  to revolve in a state prohibited from rotating. In this manner, the compressor mechanism  17  compresses the refrigerant gas.  
         [0024]     The main portion of the present invention will hereafter be described.  
         [0025]      FIG. 2  is a lateral cross-sectional view showing the motor housing  15  and the stator core  32 . In the illustrated embodiment, the motor housing  15  includes first, second, and third expanded portions  15   b ,  15   c ,  15   d  and first, second, and third fastening interference portions  15   e ,  15   f ,  15   g . Each of the fastening interference portions  15   e  to  15   g  is formed integrally with the motor housing  15  and is arranged between the corresponding adjacent ones of the first to third expanded portions  15   b  to  15   d . First, second, and third fastening surfaces S 1 , S 2 , S 3  are each formed along the arched inner circumferential surface of the corresponding one of the first to third fastening interference portions  15   e  to  15   g . The first to third fastening surfaces S 1  to S 3  are fastened to an outer circumferential surface  32   b  of the stator core  32  at three respective positions by a predetermined fastening force.  
         [0026]     The stator core  32  is assembled with the motor housing  15  by the following method.  
         [0027]      FIG. 3  shows the state of the motor housing  15  and the stator core  32  before assembly. In this state, as viewed with respect to the axis of the stator core  32 , the first to third fastening surfaces S 1  to S 3  of the first to third fastening interference portions  15   e  to  15   g  are located radially inward compared to the outer circumferential surface  32   b  of the stator core  32 . The distance between the outer circumferential surface  32   b  of the stator core  32  and each of the fastening surfaces S 1  to S 3 , as viewed with respect to the axis of the stator core  32 , is defined as a fastening interference δ. In the illustrated embodiment, the fastening interference δ is set to, for example, 200 μm. The fastening interference of the motor housing  15  as a whole is set to 2×δ=400 μm.  
         [0028]     With reference to  FIG. 4 , the second and third expanded portions  15   c ,  15   d  are received by a lower pressing tool  36  having a pair of slanted support surfaces  36   a ,  36   b  at opposing sides. In this state, an upper pressing tool  37  presses the outer circumferential surface of the first expanded portion  15   b  downward, that is, radially inward. The lower and upper pressing tools  36  and  37  elastically deform the first to third expanded portions  15   b  to  15   d  such that the first to third fastening interference portions  15   e  to  15   g  are displaced radially outward.  
         [0029]     Accordingly, referring to  FIG. 4 , the fastening surfaces S 1  to S 3  are spaced from the positions corresponding to the outer circumferential surface  32   b  of the stator core  32 . Each of the resulting distances between the fastening surfaces S 1  to S 3  and the positions corresponding to the outer circumferential surface  32   b  of the stator core  32  is defined as fitting interference ε. Although it is theoretically possible to set the fitting interference ε to 0 μm, the fitting interference ε must be set to approximately 50 μm, in order to absorb manufacturing errors of the motor housing  15  and the stator core  32  and facilitate the assembly.  
         [0030]     As illustrated in  FIG. 4 , the stator core  32  is then inserted into the motor housing  15  with the fitting interference ε maintained. In this state, pressing by the pressing tools  36 ,  37  is released, each of the first to third fastening interference portions  15   e  to  15   g  is restored to the original state by elastic shape-restoring force. Each fastening surface S 1  to S 3  is restored in accordance with the distance corresponding to the fitting interference ε because of the fastening interference δ. Each fastening surface S 1  to S 3  is thus securely fastened to the outer circumferential surface  32   b  of the stator core  32 . In this manner, without using the shrink fitting, the stator core  32  is securely fastened to the motor housing  15 .  
         [0031]     A forming angle defined by the fastening surface S 1  to S 3  of each fastening interference portion  15   e  to  15   g  with respect to the center of the motor housing  15  in the circumferential direction is set to, for example, 5 to 30 degrees. If this forming angle is excessively small, the fastening interference portions  15   e  to  15   g  may be deformed. If the forming angle is excessively large, the predetermined fastening interference δ is hard to ensure. It is thus preferred that the forming angle is set to 10 to 20 degrees.  
         [0032]     Referring to  FIG. 2 , in the state that the motor housing  15  is assembled with the stator core  32 , clearances G 1 , G 2 , G 3  are each defined between the inner circumferential surface of the corresponding one of the first to third expanded portions  15   b  to  15   d  and the outer circumferential surface  32   b  of the stator core  32 . Each of the clearances G 1  to G 3  defines a passage for guiding the refrigerant gas drawn to the motor housing  15  through the inlet  16   a  to the suction chamber  22 .  
         [0033]     The refrigerant gas, which is carbon dioxide, sealed in the refrigerating circuit is introduced into the compressor  10 . Thus, when the compressor  10  actually operates, a relatively high pressure exceeding 10 MPa is applied to the compressor  10 . However, in the illustrated embodiment, the fastening interference  2 δ of 400 μm is provided. Thus, even if the high pressure acting on the inner circumferential surface  15   a  of the motor housing  15  increases the inner diameter of the motor housing  15  such that the motor housing  15  loosens with respect to the stator core  32  by, for example, 147 μm, a sufficiently great fastening force is maintained between the stator core  32  and the motor housing  15 .  
         [0034]     The illustrated embodiment has the following advantages.  
         [0035]     (1) In the illustrated embodiment, the first to third expanded portions  15   b  to  15   d  of the motor housing  15  are pressed radially inward from the outer side by using the pressing tools  36 ,  37 . The fastening surfaces S 1  to S 3  of the first to third fastening interference portions  15   e  to  15   g  are thus displaced radially outward in accordance with the fastening interference δ and the fitting interference ε. As a result, each fastening surface S 1  to S 3  is slightly spaced from the position corresponding to the outer circumferential surface  32   b  of the stator core  32 .  
         [0036]     In this state, the stator core  32  is inserted into the motor housing  15  and the pressing tools  36 ,  37  are released. This allows the first to third fastening interference portions  15   e  to  15   g  to be pressed against the outer circumferential surface  32   b  of the stator core  32 . It is thus possible to easily ensure the fastening interference δ larger than that of the shrink fitting or shrink cooling. Accordingly, without employing a complicated technique with the shrink fitting and the shrink cooling, the stator core  32  is securely fastened to the motor housing  15 .  
         [0037]     (2) In the illustrated embodiment, since carbon dioxide is used as refrigerant gas, a relatively high pressure is applied to the compressor  10 , as compared to the case in which chlorofluorocarbon is employed. Further, the motor housing  15 , to which the stator core  32  is fastened, can be formed of aluminum by forging at a relatively small wall thickness, for example, 4 mm. This reduces the weight of the compressor  10 , as compared to the case in which the motor housing  15  is formed through casting and has a relatively large wall thickness.  
         [0038]     The present invention may be embodied in the following modified forms.  
         [0039]     The modification of  FIG. 5  is different from the illustrated embodiment in the number of the expanded portions and that of the fastening interference portions. In  FIG. 5 , first to fourth expanded portions  15   b ,  15   c ,  15   d ,  15   h  are formed in the motor housing  15 . Further, first to fourth fastening interference portions  15   e ,  15   f ,  15   g ,  15   i  are disposed between the corresponding adjacent ones of the expanded portions  15   b ,  15   c ,  15   d ,  15   h . First to fourth fastening surfaces S 1  to S 4  are formed respectively in the first to fourth fastening interference portions  15   e ,  15   f ,  15   g ,  15   i.    
         [0040]     Thus, the outer circumferential surface  32   b  of the stator core  32  is fastened to the motor housing  15  at four positions corresponding to the first to fourth fastening surfaces S 1  to S 4 . In this modification, before assembling the motor housing  15  with the stator core  32 , the motor housing  15  is pressed from four directions corresponding to the expanded portions  15   b ,  15   c ,  15   d ,  15   h  at opposing vertical positions and opposing horizontal positions.  
         [0041]     In the modification of FIGS.  6 ( a ) to  6 ( c ), the motor housing  15  has a cylindrical shape and the stator core  32  has a substantially triangle cross-sectional shape. First to third fastening interference portions  32   c ,  32   d ,  32   e  are each formed at an outer circumferential portion of the stator core  32 . Referring to  FIG. 6 ( b ), the outer circumferential surface of the motor housing  15  is pressed at three positions, radially inward from the outer side. This expands the portions of the motor housing  15  corresponding to the first to third fastening interference portions  32   c  to  32   e  in radial outward directions.  
         [0042]     As a result, a fitting interference ε is defined between each of the first to third fastening surfaces S 1  to S 3  of the first to third fastening interference portions  32   c  to  32   e  and the inner circumferential surface  15   a  of the motor housing  15 . In this state, the stator core  32  is inserted into the motor housing  15  and the motor housing  15  is released from the pressed state of  FIG. 6 ( b ). Accordingly, with reference to  FIG. 6 ( c ), the motor housing  15  is deformed to restore the original cylindrical shape such that the motor housing  15  is pressed against the first to third fastening surfaces S 1  to S 3  of the first to third fastening interference portions  32   c  to  32   e  of the stator core  32 . In this manner, the stator core  32  is fastened to the motor housing  15  in accordance with a predetermined fastening interference δ.  
         [0043]     Each of the modifications of  FIGS. 5 and 6  has the same advantages as those of the illustrated embodiment.  
         [0044]     The present invention may be further modified as follows.  
         [0045]     As long as a resulting fastening interference exceeds that of shrink fitting or shrink cooling, the motor housing  15  and the stator core  32  may be fastened together by different methods. The methods include, for example, mechanical deformation of either the motor housing  15  or the stator core  32  or both of the motor housing  15  and the stator core  32 .  
         [0046]     The motor housing  15  may be deformed by a different method other than pressing. For example, a plurality of tension tools may be employed at a plurality of positions of the outer circumferential surface of the motor housing  15 . The tools thus apply tensile force to the motor housing  15 , thus deforming the motor housing  15 .  
         [0047]     Further, for deforming the stator core  32 , pressing or tension tools may be employed at a plurality of positions of the inner circumferential surface of the stator core  32 . The tools thus apply pressing or tensile force to the stator core  32 , thus deforming the stator core  32 .  
         [0048]     The method employed in the illustrated embodiment, the mechanical elastic deformation of the motor housing or the stator core  32  may be combined with the shrink fitting or shrink cooling.  
         [0049]     Other different methods may be employed, the circumferential dimension of the inner circumferential surface  15   a  of the motor housing  15  may be larger than that of the outer circumferential surface  32   b  of the stator core  32  and the stator core  32  may be fastened to the motor housing  15  through deformation of the motor housing  15 .  
         [0050]     The motor housing  15  may be formed of a metal material other than aluminum that has a thermal expansion coefficient different than that of the iron material forming the stator core  32 .  
         [0051]     An increased number of expanded portions may be formed in the motor housing  15 . However, for ensuring a predetermined fastening interference, it is preferred to deploy three to five expanded portions in the motor housing  15 .  
         [0052]     An increased number of fastening interference portions  32   c  to  32   e  may be formed in the stator core  32 . However, for ensuring a predetermined fastening interference, it is preferred to deploy three to five fastening interference portions in the stator core  32 .  
         [0053]     Further, the motor housing  15  may be formed with an oval or triangle or square cross-sectional shape.  
         [0054]     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.
A sealed type motor-driven compressor includes a cylindrical motor housing and an annular stator core fastened to the interior of the motor housing. A method of assembling the compressor includes fastening the stator core to the motor housing by mechanically deforming at least one of the motor housing and the stator core. It is thus possible to set the fastening interference between the motor housing and the stator core to a sufficiently great level for suppressing loosening of the stator core with respect to the motor housing, which may otherwise be caused by a relatively high pressure produced by refrigerant gas.