Patent Publication Number: US-2022235769-A1

Title: Scroll compressor

Description:
This application claims the priorities to the Chinese patent applications Nos. 201910465901.0 and 201920805084.4 filed with the China National Intellectual Property Administration on the same day of May 30, 2019 and titled “SCROLL COMPRESSOR”, both of which are incorporated herein by reference. 
     FIELD 
     The present application relates to a scroll compressor, and more specifically, to a scroll compressor capable of preventing an axial compliance mounting mechanism from failing. 
     BACKGROUND 
     This section only provide background information related to this disclosure, which may not be necessarily the prior art. 
     A scroll compressor may be applied in, for example, a refrigeration system, an air conditioning system, and a heat pump system. The scroll compressor includes a compression mechanism for compressing a working fluid (e.g., a refrigerant), a main bearing housing for supporting the compression mechanism, a rotating shaft for driving the compression mechanism, and a motor for driving the rotating shaft to rotate. The compression mechanism includes a non-orbiting scroll and an orbiting scroll that orbits relative to the non-orbiting scroll. The non-orbiting scroll and the orbiting scroll each include an end plate and a spiral vane extending from one side of the end plate. When the orbiting scroll orbits relative to the non-orbiting scroll, a series of moving compression chambers with volume gradually decreasing from a radial outer side to a radial inner side are formed between the spiral vane of the non-orbiting scroll and the spiral vane of the orbiting scroll, so that the working fluid is compressed. 
     During the normal operation of the scroll compressor, a good seal needs to be achieved between a tip end of the spiral vane of one of the non-orbiting scroll and the orbiting scroll and an end plate of the other of the non-orbiting scroll and the orbiting scroll. On the other hand, for example, in a case of excessive pressure in the compression chamber of the scroll compressor, the spiral vane can be separated from the end plate to unload the high-pressure fluid, thereby avoiding damage to the compression mechanism. 
     In view of this, the non-orbiting scroll is mounted to the main bearing housing via an axial compliance mounting mechanism, such that the non-orbiting scroll can axially move a certain distance relative to the orbiting scroll. The axial compliance mounting mechanism generally includes bolts and sleeves located outside the bolts. Bolts are inserted into mounting holes of the non-orbiting scroll to screw the non-orbiting scroll to the main bearing housing. Sleeves are also inserted into the mounting holes of the non-orbiting scroll and are provided between heads of the bolts and the main bearing housing, such that a certain gap is formed between the heads of the bolts and the non-orbiting scroll to enable axial movement of the non-orbiting scroll. 
     SUMMARY 
     The inventor of the present application found that the bolts of the axial compliance mounting mechanism are liable to be loose or fractured. To this end, reasons for the fatigue damage of the bolts have been deeply studied, and a solution that can improve the fatigue strength of the bolts has been proposed. 
     An object of the present application is to provide a scroll compressor that can prevent or reduce damage to the axial compliance mounting mechanism. 
     According to an aspect of the present application, a scroll compressor is provided. The scroll compressor includes a non-orbiting scroll, an orbiting scroll, a main bearing housing and an axial compliance mounting mechanism. The non-orbiting scroll has a non-orbiting scroll end plate and a non-orbiting scroll vane extending from one side of the non-orbiting scroll end plate. The orbiting scroll has an orbiting scroll end plate and an orbiting scroll vane extending from one side of the orbiting scroll end plate. The orbiting scroll is configured to orbit relative to the non-orbiting scroll, so that a series of compression chambers for compressing working fluid are formed between the non-orbiting scroll vane and the orbiting scroll vane. The main bearing housing is fixedly mounted to a housing of the scroll compressor, and has a bearing surface for slidably supporting the orbiting scroll end plate. The axial compliance mounting mechanism is configured to fixedly connect the non-orbiting scroll to a connecting portion of the main bearing housing, such that the non-orbiting scroll is movable by a predetermined distance in an axial direction. The non-orbiting scroll further has a flange extending radially outward from a peripheral wall portion of the non-orbiting scroll. The flange has a first surface facing the non-orbiting scroll end plate, a second surface facing the orbiting scroll end plate, and a mounting hole extending from the first surface to the second surface for receiving the axial compliance mounting mechanism. The flange has an axial geometric center position between the first surface and the second surface, and the flange is positioned such that the axial geometric center position is located to be closer to the orbiting scroll end plate than an axial middle position of the peripheral wall portion. A height of the flange between the first surface and the second surface is H 1 ; a distance between an axial position of an equivalent acting point of force borne by the axial compliance mounting mechanism and the second surface is h 1 ; a distance between the first surface and an end surface of the connecting portion is H 2 , a distance between the second surface and the end surface is h 2 ; and a distance between the axial position of the equivalent acting point and the end surface is h, and h=h 1 +h 2 . The scroll compressor is such configured that the axial position of the equivalent acting point of the force applied to the axial compliance mounting mechanism is offset from the axial geometric center position toward the main bearing housing during normal operation. 
     In the scroll compressor according to the present application, the axial position of the equivalent acting point of the force applied to the axial compliance mounting mechanism is offset toward the main bearing housing relative to the axial geometric center position, so that the distance h can be reduced, that is, a distance D of the arm of force from the axial position of the equivalent acting point to a fracture position P can be reduced, and therefore bolt fracture can be significantly alleviated or prevented. 
     In some examples, an outer contour of the axial compliance mounting mechanism and/or an inner contour of the mounting hole of the flange have convex sections, such that the axial position of the equivalent acting point is offset from the axial geometric center position toward the main bearing housing. 
     In some examples, the convex sections are in the form of a curved surface or a shoulder forming a step. 
     In some examples, the flange includes an extension portion extending from the second surface in the axial direction toward the main bearing housing and beyond a top surface of the non-orbiting scroll vane. 
     In some examples, the connecting portion of the main bearing housing that engages with the axial compliance mounting mechanism extends in the axial direction toward the flange and beyond the bearing surface. 
     In some examples, the axial compliance mounting mechanism includes a bolt and a sleeve located outside the bolt. Or, the axial compliance mounting mechanism includes a shouldered bolt. 
     In some examples, 0&lt;h 2 /H 1 &lt;0.3; 0&lt;h 2 /H 2 &lt;0.3; 0&lt;h/H 1 &lt;0.6; or 0&lt;h/H 2 &lt;0.6. 
     According to the present application, a scroll compressor is further provided. The scroll compressor includes a non-orbiting scroll, an orbiting scroll, a main bearing housing and an axial compliance mounting mechanism. The non-orbiting scroll has a non-orbiting scroll end plate and a non-orbiting scroll vane extending from one side of the non-orbiting scroll end plate. The orbiting scroll has an orbiting scroll end plate and an orbiting scroll vane extending from one side of the orbiting scroll end plate. The orbiting scroll is configured to orbit relative to the non-orbiting scroll, so that a series of compression chambers for compressing working fluid are formed between the non-orbiting scroll vane and the orbiting scroll vane. The main bearing housing has a bearing surface for slidably supporting the orbiting scroll end plate. The axial compliance mounting mechanism is configured to fixedly connect the non-orbiting scroll to a connecting portion of the main bearing housing, such that the non-orbiting scroll is capable of moving a predetermined distance in an axial direction. The non-orbiting scroll further has a flange extending radially outward from a peripheral wall portion of the non-orbiting scroll. The flange has a first surface facing the non-orbiting scroll end plate, a second surface facing the orbiting scroll end plate, and a mounting hole extending from the first surface to the second surface for receiving the axial compliance mounting mechanism. A height of the flange between the first surface and the second surface is H 1 ; a distance between an axial position of an equivalent acting point of force borne by the axial compliance mounting mechanism and the second surface is h 1 ; a distance between the first surface and an end surface of the connecting portion is H 2 ; a distance between the second surface and the end surface is h 2 ; and a distance between the axial position of the equivalent acting point and the end surface is h, and h=h 1 +h 2 . The flange and/or the connecting portion extend toward each other in the axial direction, such that the second surface of the flange extends beyond the top surface of the non-orbiting scroll vane and/or the end surface of the connecting portion extends beyond the bearing surface. 
     In the scroll compressor according to the present application, the flange and the connecting portion of the main bearing housing extend toward each other, so that the distance h can be reduced, that is, a distance D of arm of force from the axial position of the equivalent acting point to a fracture position P can be reduced, and therefore bolt fracture can be significantly alleviated or prevented. 
     In some examples, 0&lt;h 2 /H 1 &lt;0.3; 0&lt;h 2 /H 2 &lt;0.3; 0&lt;h/H 1 &lt;0.6; or 0&lt;h/H 2 &lt;0.6. 
     In some examples, the axial compliance mounting mechanism includes a bolt and a sleeve located outside the bolt. Or, the axial compliance mounting mechanism includes a shouldered bolt. 
     In some examples, the scroll compressor is such configured that the axial position of the equivalent acting point is offset toward the main bearing housing relative to the axial geometric center position between the first surface and the second surface during normal operation. 
     In some examples, an outer contour of the axial compliance mounting mechanism or an inner contour of the mounting hole of the flange has a convex section, such that the axial position of the equivalent acting point is offset toward the main bearing housing relative to the axial geometric center position. 
     In some examples, the convex section is in the form of a curved surface or a shoulder forming a step. 
     From the following detailed description, other application fields of the present application will become more apparent. It should be understood that, although these detailed descriptions and specific examples show preferred embodiments of the present application, these detailed descriptions and specific examples are for the purpose of illustration, rather than to limit the present application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of one or more embodiments of the present application will become more readily understood from the following description with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic perspective view of a scroll compressor according to an embodiment of the present application; 
         FIG. 2  is a schematic partial cross-sectional view of the scroll compressor shown in  FIG. 1 ; 
         FIG. 3  is a schematic partial enlarged view of the scroll compressor shown in  FIG. 2 ; 
         FIG. 4  is a schematic partial cross-sectional view of a scroll compressor according to another embodiment of the present application; 
         FIG. 5  is a schematic partial enlarged view of a non-orbiting scroll of the scroll compressor shown in  FIG. 4 ; 
         FIG. 6  is a schematic partial cross-sectional view of a scroll compressor according to yet another embodiment of the present application; 
         FIG. 7  is a schematic partial enlarged view of the non-orbiting scroll of the scroll compressor shown in  FIG. 6 ; 
         FIG. 8  is a schematic partial cross-sectional view of a scroll compressor according to another embodiment of the present application; 
         FIG. 9  is a schematic partial enlarged view of a main bearing housing of the scroll compressor shown in  FIG. 8 ; 
         FIG. 10  is a schematic view of parameters associating the axial compliance mounting mechanism with the non-orbiting scroll and the main bearing housing of the scroll compressor; 
         FIGS. 11 a  to 11 d    are schematic views of parameters provided according to various embodiments of the present application; 
         FIG. 12  is a graph showing the effect of the scroll compressor according to the present application; and 
         FIG. 13  is a schematic view showing a location of bolt failure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments will now be described more comprehensively with reference to the accompanying drawings. 
     Exemplary embodiments are provided so that the present application will be thorough and will more fully convey the scope to those skilled in the art. Many specific details such as examples of specific components, devices, and methods are described to provide a thorough understanding of various embodiments of the present application. It will be clear to those skilled in the art that the exemplary embodiments may be implemented in many different forms without using specific details, none of which should be construed as limiting the scope of the present application. In some exemplary embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The overall structure of a scroll compressor  100  will be described below with reference to  FIG. 1 . As shown, the compressor  100  includes a housing  11 , a compression mechanism CM, a motor  16 , a rotating shaft (also referred to as a drive shaft or a crankshaft)  14 , and a main bearing housing  15 . 
     The housing  11  may include a cylindrical body  11   a , a top cover  11   b  located at the top end of the cylindrical body  11   a , and a bottom cover  11   c  located at the bottom end of the cylindrical body  11   a . The housing  11  forms a closed space in which the compression mechanism CM, the motor  16 , the rotating shaft  14  and the main bearing housing  15  are accommodated. A partition plate  11   d  may further be provided between the top cover  11   b  and the cylindrical body  11   a . The partition plate  11   d  divides the closed space of the housing  11  into a high-pressure side and a low-pressure side. The high-pressure side is defined by the partition plate  11   d  and the top cover  11   b , and the low-pressure side is defined by the partition plate  11   d , the cylindrical body  11   a , and the bottom cover  11   c.    
     The cylindrical body  11   a  is provided with an inlet port (not shown) for introducing the working fluid with a suction pressure into the housing  11 . The top cover  11   b  is provided with an outlet port  11   e  for discharging the working fluid with discharge pressure compressed by the compression mechanism CM out of the housing  11 . During the operation of the scroll compressor  100 , the low-pressure working fluid is introduced into the compressor  100  via the inlet port (introduced to the low-pressure side in the example shown in  FIG. 1 ), sucked into the compression mechanism CM, discharged to the high-pressure side after being compressed, and finally discharged out of the scroll compressor  100  via the outlet port  11   e.    
     The compression mechanism CM includes a non-orbiting scroll  12  fixed to the housing  11  (specifically, the cylindrical body  11   a ) and an orbiting scroll  13 . The motor  16  is configured to drive the rotating shaft  14  to rotate, which in turn drives the orbiting scroll  13  to orbit relative to the non-orbiting scroll  12  (i.e., a center axis of the orbiting scroll moves around a central axis of the non-orbiting scroll, but the orbiting scroll does not rotate around its own center axis) to compress the working fluid. The orbiting movement is realized via an Oldham coupling  17  (referring to  FIG. 2 ). 
     The non-orbiting scroll  12  may be fixed relative to the housing  11  in any suitable manner. As shown, the non-orbiting scroll  12  is fixedly mounted to the main bearing housing  15  by bolts, which will be described in detail later. The non-orbiting scroll  12  may include a non-orbiting scroll end plate  122 , a non-orbiting scroll vane  124  extending from one side of the non-orbiting scroll end plate  122 , and an outlet  121  located approximately at a central portion of the non-orbiting scroll end plate  122 . For ease of description, the radially outermost portion of the non-orbiting scroll vane  124  is referred to as a peripheral wall portion  126  herein. As shown in  FIG. 2 , the non-orbiting scroll  12  further has a flange  128  extending radially outward from an outer peripheral surface of the peripheral wall portion  126 . The flange  128  is provided therein with a mounting hole  127  for receiving an axial compliance mounting mechanism, so as to be connected to the main bearing housing  15 . 
     The orbiting scroll  13  may include an orbiting scroll end plate  132 , an orbiting scroll vane  134  formed on one side of the orbiting scroll end plate  132 , and a hub  131  formed on the other side of the orbiting scroll end plate  132 . The non-orbiting scroll vane  124  and the orbiting scroll vane  134  can be engaged with each other, so that a series of moving compression chambers with volume gradually decreasing from a radial outer side to a radial inner side are formed between the non-orbiting scroll vane  124  and the orbiting scroll vane  134  during operation of the scroll compressor, so as to compress the working fluid. The hub  131  is engaged with an eccentric crank pin of the rotating shaft  14  and is driven by the eccentric crank pin. 
     The main bearing housing  15  is adapted to support the orbiting scroll end plate  132  of the orbiting scroll  13 . The orbiting scroll end plate  132  orbits on a bearing surface  155  of the main bearing housing  15  (referring to  FIG. 2 ). The main bearing housing  15  may be fixed with respect to the housing  11  of the scroll compressor  100  by any suitable means. 
     In order to achieve fluid compression, an effective sealing is required between the non-orbiting scroll  12  and the orbiting scroll component  13 . 
     On the one hand, during the normal operation of the scroll compressor, a radial sealing is also required between a side surface of the spiral vane  124  of the non-orbiting scroll  12  and a side surface of the spiral vane  134  of the orbiting scroll  13 . The radial sealing between the two is generally achieved by a centrifugal force of the orbiting scroll  13  during orbiting movement and a driving force provided by the rotating shaft  14 . In a case that incompressible foreign matter (e.g., solid impurities and liquid refrigerant) enters the compression chamber and gets stuck between the spiral vanes  124  and  134 , the spiral vanes  124  and  134  can be temporarily separated from each other in the radial direction to allow the foreign matter to pass through, thereby preventing the spiral vanes  124  and  134  from being damaged, so as to provide the scroll compressor  100  with radial compliance. 
     On the other hand, during the normal operation of the scroll compressor, an axial sealing is further required between a tip of the spiral vane  124  of the non-orbiting scroll  12  and the end plate  132  of the orbiting scroll  13 , and between a tip of the spiral vane  134  of the orbiting scroll  13  and the end plate  122  of the non-orbiting scroll  12 . In a case of excessive pressure in the compression chamber of the scroll compressor, the fluid in the compression chamber leaks to the low-pressure side through a gap between the tip of the spiral vane  124  of the non-orbiting scroll  12  and the end plate  132  of the orbiting scroll  13  and a gap between the tip of the spiral vane  134  of the orbiting scroll  13  and the end plate  122  of the non-orbiting scroll  12  to achieve unloading, thereby providing the scroll compressor  100  with axial compliance. 
     In order to provide axial compliance, the non-orbiting scroll  12  is mounted to the main bearing housing  15  via the axial compliance mounting mechanism  18 . Referring to  FIG. 2 , the axial compliance mounting mechanism  18  includes a bolt  181  and a sleeve  182  located radially outside the bolt  181 . The bolt  181  has a stem portion  1813 , a head portion  1811  located at one end of the stem portion  1813 , and a threaded portion  1817  located at the other end of the stem portion  1813 . The head portion  1811  has an abutting surface  1812  for abutting against an upper end surface  1821  (referring to  FIG. 3 ) of the sleeve  182  and an upper surface (first surface)  1281  of the flange  128 . The threaded portion  1817  is configured to be able to be screwed into a threaded hole  151  of the main bearing housing  15 . The sleeve  182  is further received in a mounting hole  127  of the flange  128  of the non-orbiting scroll  12  and is located between the head portion  1811  and the upper surface  153  of the main bearing housing  15 , thereby positioning the head portion  1811  such that the non-orbiting scroll  12  is capable of moving a predetermined distance in the axial direction. 
     The inventor found that the bolts of the existing axial compliance mounting mechanism are liable to be loose or fractured. The reason why the bolts are liable to be loose or fractured is analyzed below with reference to  FIG. 13 . Forces borne by the bolts are very complicated, and thus are simplified for ease of understanding the cause of the fracture. The bolt is liable to be broken or failed at the position P indicated by the dashed line, at an upper threaded joint between the bolt  3  and the main bearing housing  2 . With respect to the distance from the flange  128 , the “upper threaded joint” is referred to herein as a proximal joint. As described above, when the orbiting scroll (not shown in  FIG. 13 ) orbits relative to the non-orbiting scroll  1 , a vane side contact force (acting force) is generated due to the centripetal acceleration, and is transmitted to the bolt  3  via the sleeve  4 . It is generally considered that an equivalent acting point of the force F applied to the bolt  3  by the non-orbiting scroll  1  corresponds to an axial geometric center point of the flange of the non-orbiting scroll  1 . A distance between the position P and the force F is D, so that a moment M (product of the force F and the distance D) is generated with the position P as the fulcrum. The moment M causes the bolt to be easily broken at the position P. The present application aims to alleviate or prevent the bolt from being broken by reducing the distance D. For the ease of description herein, it is assumed that a distance between the position P and an upper surface  2   a  of the main bearing housing  2  (i.e., an axial height of a counterbore  2   b ) is unchanged in various embodiments. In this way, by reducing the distance h from the upper surface  2   a  of the main bearing housing  2  to the equivalent acting point of the force F, it is possible to alleviate or prevent fracture of the bolt. 
     When the compressor is operating normally, the orbiting scroll exerts force on the sleeve through the flange (lug) of the non-orbiting scroll. Generally, the flange of the non-orbiting scroll is fitted in the sleeve with face-to-face contact, so the force applied to the sleeve can be regarded as forces distributed over a certain contact area. When the effect of these distributed forces is equivalent to a concentrated force (the force F described herein), the position of the concentrated force F is the axial position of the equivalent point of the force F described herein. 
     In order to reduce the distance h, the flange  182  of the non-orbiting scroll is located at a lower half of the peripheral wall portion  126  close to the main bearing housing  15 . Preferably, the flange extends radially outward from an end of the peripheral wall portion  126  (the lower surface  1283  of the flange  182  is substantially flush with the top surface of the vane  124 ). 
       FIGS. 1 to 3  show an example of reducing the distance h by modifying an outer contour of a sleeve  182 . As shown, the outer contour (outer peripheral surface) of the sleeve  182  is not of a cylindrical shape with a constant diameter, but has a convex section  1828 . A dashed line C 1  in  FIG. 2  represents the axial geometric center position of the flange  128 , and a dashed line C 2  corresponds to a maximum diameter portion  1829  of the convex section  1828  and therefore represents a position (i.e., the axial position of the equivalent acting point of the force F) where the sleeve contacts with the mounting hole  127  of the flange  182 . The convex section  1828  tapers from the maximum diameter portion  1829  toward the upper surface (first surface)  1281  and the lower surface (second surface)  1283  of the flange  128 . In examples shown, the sleeve  182  may further have a straight section  1827  with a constant diameter located adjacent to the main bearing housing  15 . In  FIG. 2 , a distance from the position P to the axial position C 2  of the equivalent acting point is obviously shorter than a distance from the position P to the axial geometric center position C 1 . 
     It will be appreciated that the present application is not limited to the specific embodiments illustrated. For example, the convex section  1828  may only taper from the maximum diameter portion  1829  toward the first surface  1281  of the flange  128 , and there is a constant diameter from the maximum diameter portion  1829  to an end adjacent to the main bearing housing  15 . In this case, the axial position of the equivalent acting point can be further offset downward, that is, the distance from the position P to the equivalent acting point of force can be further reduced. In the examples shown, the convex section  1828  is in the form of a curved surface. However, it should be understood that the convex section  1828  may also be in the form of a shoulder forming a step or the like. In the shown examples, the sleeve  182  and the bolt  181  are separate components. However, it should be understood that the sleeve  182  and the bolt  181  may be integrated as one piece, that is, a shouldered bolt. 
     It can be seen from the above content that it is possible to alleviate or prevent fracture of the bolt  181  by providing the outer contour of the axial compliance mounting mechanism  18  with a convex section, which causes the axial position C 2  of the equivalent acting point to be lower than the axial geometric center position C 1 . 
       FIGS. 4 and 5  show an example of reducing the distance h by modifying an inner contour (shape of an inner wall) of a mounting hole  227  of a flange  228 . As shown, the inner contour (shape of the inner wall) of the mounting hole  227  is not of a cylindrical shape with a constant diameter, but has a convex section  2272 . Therefore, a sleeve  282  may have a cylindrical shape with a constant diameter. Similar to the examples shown in  FIGS. 1 to 3 , a dashed line C 2  corresponds to a maximum diameter portion  2279  of the convex section  2272  and therefore represents a position (i.e., the axial position of the equivalent acting point of the force F) where the mounting hole contacts with the sleeve  282 . The convex section  2272  tapers from the maximum diameter portion  2279  toward the upper surface (first surface)  2281  and the lower surface (second surface)  2283  of the flange  228 . In examples shown, the mounting hole  227  may further have a straight section  2271  with a constant diameter located adjacent to the upper surface (first surface)  2281 . In  FIG. 4 , a distance from the position P to the axial position C 2  of the equivalent acting point is obviously shorter than a distance from the position P to the axial geometric center position C 1 . 
     It will be appreciated that the present application is not limited to the specific embodiments illustrated. For example, the convex section  2272  may have any other suitable form, as long as the axial position C 2  of the equivalent acting point is below the axial geometric center position C 1 . 
       FIGS. 6 and 7  show another example of reducing the distance h by modifying the structure of a flange  328 . As shown, the flange  328  further has an extension portion  3285  extending downward in the axial direction from a lower surface (second surface)  3283 , so that a lower end surface (third surface)  3284  of the extension portion  3285  is below a top surface of the non-orbiting scroll vane  124 . In this example, a mounting hole  327  of the flange  328  may have a constant inner diameter, and a sleeve  382  may also have a constant outer diameter substantially equal to the inner diameter of the mounting hole  327 . 
     In the example shown in  FIGS. 6 and 7 , the dashed line C 1  still represents an axial geometric center position between an upper surface (first surface)  3281  and the lower surface (second surface)  3283 , and the dashed line C 2  corresponds to an axial geometric center position between the upper surface (first surface)  3281  and the lower end surface (third surface)  3284  and therefore represents an axial position of the equivalent acting point of the force F applied to the bolt. In this example, by extending the length of the mounting hole  327  toward the main bearing housing  15 , the axial position of the equivalent acting point is offset toward the main bearing housing  15 , thereby reducing a distance from the position P to the axial position of the equivalent acting point, i.e., reducing the distance h. 
       FIGS. 8 and 9  show another example of reducing the distance h by modifying the structure of the main bearing housing  15 . As shown, the main bearing housing  15  has a connecting portion  452  for threaded engagement with a bolt  481 . The connecting portion  452  may extend toward the flange such that an upper end surface  453  of the connecting portion  452  is higher than a bearing surface  455  for supporting an end plate  432  of the orbiting scroll  13 , and more preferably, the connecting portion  452  is close to a lower surface  4283  of a flange  428 . As described above, for the ease of description herein, it is assumed that a distance between the position P and an upper surface of the main bearing housing (i.e., an axial height of a counterbore) is unchanged in each embodiment. Therefore, in the examples shown in  FIGS. 8 and 9 , by extending the connecting portion  452  toward the flange  428 , the position P is offset toward the flange  428 , thereby reducing the distance h. 
     The inventor has further made a finite element analysis on some parameters related to the axial compliance mounting mechanism  18 . By optimizing the design of some parameters, the bolt fracture can also be alleviated or prevented. Reference is made to  FIG. 10  below to understand the parameters related to alleviating or preventing bolt fracture. The components in  FIG. 10  that are the same as those in  FIG. 8  are denoted by the same reference numerals as in  FIG. 8 . 
     As shown in  FIG. 10 , the height of the flange  428  between the first surface  4281  and the second surface  4283  is indicated by H 1 . A distance between an axial position C 2  of the equivalent acting point of the force applied by the flange  428  to the axial compliance mounting mechanism and the second surface  4283  is indicated by h 1 . A distance between the first surface  4281  and the end surface  453  of the connecting portion  452  is indicated by H 2 . A distance between the second surface  4283  and the end surface  453  is indicated by h 2 . A distance between the axial position C 2  of the equivalent acting point and the end face  453  is indicated by h, and h=h 1 +h 2 . 
     Through finite element analysis, the inventor found that bolt fracture can be significantly alleviated or prevented in a case that the following conditions are met: 0&lt;h 2 /H 1 &lt;0.3; 0&lt;h 2 /H 2 &lt;0.3; 0&lt;h/H 1 &lt;0.6; or 0&lt;h/H 2 &lt;0.6. 
     The inventor has further performed tests within these parameter ranges with respect to various embodiments described above.  FIG. 11 a    corresponds to the embodiment shown in  FIGS. 1 to 3 , and  FIG. 11 b    corresponds to the embodiment shown in  FIGS. 4 and 5 . In the examples shown in  FIG. 11 a    and  FIG. 11 b   , h 1 /H 1 =0.25, and h=14.5. The tests show that this parameter can significantly alleviate or prevent bolt fracture. 
       FIG. 11 c    corresponds to the embodiment shown in  FIGS. 8 and 9 . In the example shown in  FIG. 11 c   , h 2 /H 2 =0.06, h/H 2 =0.36, and h=9.3. Tests show that this parameter can significantly alleviate or prevent bolt fracture.  FIG. 11 d    corresponds to the embodiment shown in  FIGS. 6 and 7 . In the example shown in  FIG. 11 d   , h 2 /H 2 =0.10, h/H 2 =0.55, and h=14.3. Tests show that this parameter can significantly alleviate or prevent bolt fracture. 
     The inventor has further tested moments generated at the position P at different distances h under the same force. In these tests, structures of the flange, the main bearing housing and the axial compliance mounting mechanism are the same, and only value of the distance h is varied. The test results are shown in Table 1 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Force  
                 Distance  
                 Moment at position 
               
               
                 F (N) 
                 h (mm) 
                 P (N * mm) 
               
               
                   
               
             
            
               
                 3000 
                  8.2 
                 2803 
               
               
                 3000 
                 10.2 
                 3229 
               
               
                 3000 
                 12.2 
                 3665 
               
               
                 3000 
                 14.2 
                 4105 
               
               
                 3000 
                 16.2 
                 4546 
               
               
                 3000 
                 18.2 
                 4975 
               
               
                 3000 
                 20.2 
                 5418 
               
               
                 3000 
                 22.2 
                 5851 
               
               
                 3000 
                 24.2 
                 6289 
               
               
                   
               
            
           
         
       
     
     A graph is drawn according to Table 1, referring to  FIG. 12 .  FIG. 12  more intuitively shows that the smaller the distance h is, the smaller the moment at the position P is. Therefore, by reducing the distance h, bolt fracture can be significantly alleviated or prevented. 
     While the present application has been described with reference to the exemplary embodiments, it will be appreciated that the present application is not limited to the specific embodiments described and illustrated in detail herein. The person skilled in the art can make various variants to the exemplary embodiments without departing from the scope defined by the claims. It should further be understood that, provided that there is no contradiction in technical solutions, the features in the various embodiments can be combined with each other, or can be omitted.