Abstract:
A compressor has a housing and a cylinder block. The housing includes suction and discharge chambers. The cylinder block is fixed to the housing via a valve plate assembly. The valve plate assembly forms suction and discharge ports and suction and discharge valves. A partition wall is formed with the housing, and separates the suction chamber and the discharge chamber. The housing includes a first surface, and the cylinder block includes a second surface. At least one of the first and second surfaces is concave in shape. The cylinder block is screwed to the housing at the partition wall or a position closer to the central axis of the housing than the partition wall by a bolt so that the first surface faces the second surface.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a compressor. More particularly, the present invention relates to a structure of the compressor that improves sealing performance at facing surfaces of a housing and a cylinder block. 
     A piston type compressor such as a swash plate type compressor generally includes suction and discharge chambers defined in a housing such that a partition wall separates the suction and discharge chambers. A cylinder block facing the suction and discharge chambers is disposed in the housing so as to sandwich a valve plate assembly. Cylinder bores each slidably accommodate respective pistons. Refrigerant gas in the suction chamber is sucked into the cylinder block and the refrigerant gas in the cylinder block is discharged to the discharge chamber by reciprocation of the pistons. Due to the suction and discharge of the refrigerant gas, large pressure difference arises at the partition wall. 
     To improve sealing performance at the partition wall, Japanese Unexamined Patent Publication No. 11-303743 discloses a compressor that includes the convex end of a cylinder head facing the partition wall of the housing. 
     Sealing performance at the partition wall improves because pressure applied to the partition wall increases due to the convex end of the cylinder head. However, an unwanted effect is that sealing performance at the cylinder head adjacent to the outer periphery is deteriorated because pressure applied to the surface of the cylinder head adjacent to the outer periphery reduces. 
     Particularly, high sealing performance is required when refrigerant gas such as carbon dioxide is used in the compressor in a state of a relatively high pressure condition. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above-mentioned problems traceable to large pressure difference between a suction chamber and a discharge chamber by improving sealing performance at mutual facing surfaces between a housing and a cylinder block. 
     According to the present invention, a compressor has a housing and a cylinder block. The housing includes suction and discharge chambers. The cylinder block is fixed to the housing via a valve plate assembly. The valve plate assembly forms suction and discharge ports and suction and discharge valves. A partition wall is formed with the housing, and separates the suction chamber and the discharge chamber. The housing includes a first surface, and the cylinder block includes a second surface. At least one of the first and second surfaces is concave in shape. The cylinder block is screwed to the housing at the partition wall or a position closer to the central axis of the housing than the partition wall by a bolt so that the first surface faces the second surface. 
     Pressure is applied to the partition wall by screwing the cylinder block to the housing. Since at least one of the first and second surfaces is concave in shape, pressure is applied to the first and second surfaces adjacent to the outer periphery after screwing the cylinder block to the housing by the bolt. 
     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 
     The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. 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: 
     FIG. 1 is a longitudinal cross-sectional view of a swash plate type variable displacement compressor according to an embodiment of the present invention; 
     FIG. 2 is a longitudinal cross-sectional view of a front housing and a cylinder block used for the compressor in FIG. 1; and 
     FIG. 3 is a longitudinal cross-sectional view of a swash plate type variable displacement compressor according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will now be described with reference to FIGS. 1 through 3. The left side and the right side in FIGS. 1 through 3 correspond to the front side and the rear side, respectively. 
     As shown in FIG. 1, a first bolt  4  screws a front housing  1  to a rear housing  2  via a gasket  3 , thus constructing a housing  5  of a compressor. The front housing  1  provides a step  6  inside. A retainer plate  7 , a discharge valve plate  8 , a valve plate  9  and a suction valve plate  10  are fitted onto the step  6 . A suction chamber  12  and a discharge chamber  13  are defined between the retainer plate  7  and a front end wall  11  of the front housing  1  such that a partition wall  14  separates the suction chamber  12  and the discharge chamber  13  from each other. 
     A cylinder block  15  is fitted onto the suction valve plate  10  in the front housing  1 , and a second bolt  16  fixes the cylinder block  15  to the front housing  1 . The cylinder block  15 , the front housing  1  and the rear housing  2  rotatably support a drive shaft  17 . The drive shaft  17  protrudes its front end outside the front housing  1 , and connects with a driving source such as an engine or a motor of a vehicle, which is not shown. In the rear housing  2 , a lug plate  18  is secured to the drive shaft  17 , and a swash plate  19  engages with the lug plate  18 . The drive shaft  17  extends through a through hole, which is formed through the center of the swash plate  19 . A pair of guide pins  20  extending from the swash plate  19  is slidably fitted into a pair of guide holes  21  formed with the lug plate  18 . The guide pins  20  engages with the guide holes  21  so that the swash plate  19  integrally rotates with the drive shaft  17 , and the swash plate  19  is tiltably supported by the drive shaft  17  so as to slide along the axis of the drive shaft  17 . Also, the lug plate  18  is rotatably supported by a thrust bearing  22 , which is disposed on the inner surface of a rear end wall of the rear housing  2 . 
     A plurality of cylinder bores  23  is defined in the cylinder block  15  so as to surround the drive shaft  17 , and the cylinder bores  23  each slidably accommodate respective pistons  24 . The pistons  24  each engage with the periphery of the swash plate  19  through a pair of shoes  25 . As the swash plate  19  rotates with the drive shaft  17 , the pistons  24  each reciprocate in the direction of the axis of the drive shaft  17  in the associated cylinder bores  23  through shoes  25 . 
     Due to movement of the piston  24  from a top dead center toward a bottom dead center, refrigerant gas in the suction chamber  12  flows into a suction port  26  of the valve plate  9 , and pushes a suction reed valve of the suction valve plate  10  aside, then flows into the cylinder bore  23 . Due to movement of the piston  24  from the bottom dead center toward the top dead center, the refrigerant gas flows into a discharge port  27  of the valve plate  9 , and pushes a discharge reed valve of the discharge valve plate  8  aside, then flows into the discharge chamber  13 . 
     As shown in FIG. 2, the suction chamber  12  and the discharge chamber  13  are defined in the front housing  1  such that the partition wall  14  separates the suction chamber  12  and the discharge chamber  13 , and the retainer plate  7  abuts against a first surface  28  including the rear end of a step  6  and the rear end of the partition wall  14 . Meanwhile, cylinder bores  23  and a through hole  29  for inserting the drive shaft  17  are defined in the cylinder block  15 , and the suction valve plate  10  abuts against a second surface  30 . The first and second surfaces  28 ,  30  face each other through the retainer plate  7 , the discharge valve plate  8 , the valve plate  9  and the suction valve plate  10 , and both the first and second surfaces  28 ,  30  are concave in shape. 
     The concave first and second surfaces are exaggeratedly illustrated in FIG. 2. A first distance or a first concave depth A along the central axis  31  as indicated by a double headed arrow is defined from the first surface  28  to a hypothetical surface  281  which extends between end points  282  in the front housing  1  as indicated by a vertical double-dotted line. Similarly, a second distance or a second concave depth B along the central axis  31  as indicated by a double headed arrow is defined from the second surface  30  to a hypothetical surface  301  which extends between end points  302  on the cylinder block  15  as indicated by another vertical double-dotted line. When the end points  282  and  302  contact in the first housing  1 , a sum of the distances A and B ranges from 0.01 mm to 0.2 mm, preferably, from 0.05 mm to 0.1 mm. 
     The cylinder block  15  is screwed to the front housing  1  by the second bolt  16  at an axis  32  for fastening the second bolt  16 , which is closer to the central axis  31  of the front housing  1  than the partition wall  14 . Since the axis  32  is located inside the partition wall  14 , the front housing  1  and the cylinder block  15  deform a little, such that the first and second surfaces  28 ,  30  become mutual parallel planes relative to each other by fastening the second bolt  16 . Thereby, pressure is applied to the first and second surfaces  28 ,  30  at the rear end of the partition wall  14 , and sealing performance is ensured. Also, since the first and second surfaces are originally concave in shape, higher pressure is applied to the step  6  of the front housing  1  and the cylinder block  15  adjacent to the outer periphery in comparison with pressure applied to the rear end of the partition wall  14  when pressure applied to the rear end of the partition wall  14  is increased by screwing the cylinder block  15  to the front housing  1  by the second bolt  16 . 
     In the present embodiment, both the first surface  28  of the front housing  1  and the second surface  30  of the cylinder block  15  are concave in shape. However, the present invention is not limited to the embodiment described above. One of the first and second surfaces  28 ,  30  may be concave in shape, and the other may be flat in shape. The similar advantageous effects are obtained. 
     Also, as shown in FIG. 3, the first surface of a front housing  41  and the second surface of a cylinder block  42  are concave in shape as well as those in the embodiment described above. A second bolt  44  may screw the cylinder block  42  to the front housing  41  at a partition wall  43  of the front housing  41 . In such a state, pressure is applied to the rear end of the partition wall  43  by screwing the second bolt  44 , and sealing performance is ensured. Also, pressure is applied to the cylinder block  42  adjacent to the outer periphery by screwing the second bolt  44 , and sealing performance is ensured. 
     According to the present invention described above, at least one of the first surface of the housing and the second surface of the cylinder block is concave in shape, and the cylinder block is screwed to the housing at the partition wall or a position closer to the central axis of the housing than the partition wall. Thereby, pressure is applied to the rear end of the partition wall by screwing the second bolt, and pressure is also applied to the cylinder block adjacent to the outer periphery by screwing the second bolt, thus ensuring high sealing performance. Accordingly, the present invention is especially available in using a compressor in a state of a relatively high pressure condition such that the compressor compresses refrigerant gas such as carbon dioxide. 
     Therefore, 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 of the appended claims.