Abstract:
A compressor includes a piston reciprocating in a cylinder bore. The piston draws refrigerant into and discharges refrigerant from a compression chamber, which is formed between the piston and a valve plate. The valve plate has a discharge port connecting the compression chamber to the discharge chamber. A guide passage facilitates the flow of the refrigerant from the compression chamber to the discharge port. The guide passage is defined in the compression chamber when the piston is located at the top dead center position. This decreases pressure losses that would otherwise occur when the piston is near the top dead center position.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a piston type compressor. More particularly, the present invention pertains to a compressor that decreases pressure loss at the last stage of piston discharge strokes. 
     Japanese Unexamined Patent Publications Nos. 8-261150 and 10-68382 disclose piston type compressors. 
     FIG. 11 illustrates part of the piston type compressor of the publications. A piston  81  is reciprocally housed in a cylinder bore  82 . A valve plate  95  separates the cylinder bore  82  from a suction chamber  83  and from a discharge chamber  84 . The valve plate  95  includes a main plate  85 , a first sub plate  89  and a second sub plate  91 . The first and second sub plates  89 ,  91  sandwich the main plate  85 . A suction port  86  and a discharge port  87  are formed in the valve plate  95 . The first sub plate  89  includes a suction valve flap  88 . The suction valve flap  88  corresponds to the suction port  86 . The second sub plate  91  has a discharge valve flap  90 . The discharge valve flap  90  corresponds to the discharge port  87 . 
     A compression chamber  92  is defined by the end face of the piston  81  and the first sub plate  89  in the cylinder bore  82 . When the piston  81  is moved from the top dead center position to the bottom dead center position, that is, when the piston  81  is in the suction stroke, refrigerant gas in the suction chamber  83  is drawn into the compression chamber  92  through the suction port  86  and the suction valve flap  88 . When the piston  81  moves from the bottom dead center position toward the top dead center position, that is, when the piston  81  is in the discharge stroke, the gas in the compression chamber  92  is compressed to a predetermined pressure. The gas is then discharged to the discharge chamber  84  through the discharge port  87  and the valve flap  90 . 
     As shown in FIG. 12, the ports  86  and  87  are located radially inside of the wall of the cylinder bore  82 . 
     When the piston  81  is at the last stage of the discharge stroke, that is, when the piston  81  is in the vicinity of the top dead center position, gas in the compression chamber  92  flows to the discharge port  87  through a narrow space between the end of the piston  81  and the first sub plate  89 . This causes a pressure loss. The pressure loss decreases the compression efficiency of the compressor. 
     Compressors that are used in vehicle air conditioners typically use fluorocarbon as refrigerant. However, the recent trend is to replace fluorocarbon by carbon dioxide to decrease the influence of the refrigerant on the environment. 
     Carbon dioxide refrigerant requires a higher compression rate (for example, ten times higher) than fluorocarbon refrigerant. Thus, the pressure loss mentioned above is much more significant in compressors using carbon dioxide as a refrigerant. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an objective of the present invention to provide a compressor that decreases pressure loss at the last stage of the piston discharge stroke. 
     To achieve the above objective, the present invention provides a compressor. The compressor comprises a housing, a cylinder bore formed in the housing, a suction chamber formed in the housing, a discharge chamber formed in the housing. A discharge port connects the discharge port to the cylinder bore. A piston is located in the cylinder bore. The piston moves from a top dead center position to a bottom dead center position to draw refrigerant gas into the cylinder bore from the suction chamber. The piston moves from the bottom dead center position to the top dead center position to discharge refrigerant gas to the discharge chamber. A compression chamber is defined by an enclosure. The enclosure is formed by the piston and the housing. A guide passage facilitates the flow of compressed gas from the compression chamber to the discharge port. The guide passage is defined in the enclosure when the piston is located substantially at the top dead center position. 
     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 partial cross-sectional view illustrating a compressor according to a first embodiment of the present invention; 
     FIG. 2 is a cross-sectional view taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a cross-sectional view of the compressor shown in FIG. 1; 
     FIG. 4 is a cross-sectional view taken along line  4 — 4  of FIG. 3; 
     FIG. 5 is a partial cross-sectional view illustrating a compressor according to a second embodiment; 
     FIG. 6 is a cross-sectional view taken along line  6 — 6  of FIG. 5; 
     FIG. 7 is a partial cross-sectional view illustrating a compressor according to a third embodiment; 
     FIG. 8 is a cross-sectional view taken along line  8 — 8  of FIG. 7; 
     FIG. 9 is a partial cross-sectional view illustrating a compressor according to a fourth embodiment; 
     FIG. 10 is a cross-sectional view taken along line  10 — 10  of FIG. 9; 
     FIG. 11 is a partial cross-sectional view illustrating a prior art compressor; and 
     FIG. 12 is a cross-sectional view taken along line  12 — 12  of FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A variable displacement compressor  10  according to a first embodiment of the present invention will now be described with reference to FIGS. 1 to  4 . The compressor  10  is used in an air conditioner. 
     As shown in FIG. 3, the compressor  10  is a variable displacement type compressor. The compressor  10  uses carbon dioxide as the refrigerant. A front housing  12  and a rear housing  13  are secured to a cylinder block  11 . A valve plate  14  is located between the cylinder block  11  and the rear housing  13 . The cylinder block  11 , the front housing  12 , the rear housing  13  and the valve plate  14  form the housing of the compressor  10 . A crank chamber  15  is defined between the front housing  12  and the cylinder block  11 . A suction chamber  16  and a discharge chamber  17  are defined in the rear housing  13 . 
     The cylinder block  11  and the front housing  12  rotatably support a drive shaft  18  by means of radial bearings  19 ,  20 . A rotor  21  is fixed to the drive shaft  18  in the crank chamber  15 . A swash plate  23  is supported on the drive shaft  18  in the crank chamber  15 . The swash plate  23  is permitted to incline with respect to and slide along the axis L of the drive shaft  18 . The swash plate  23  is coupled to the rotor  21  by a hinge mechanism  24 . The swash plate  23  rotates integrally with the rotor  21 . The swash plate  23  is moved between a maximum inclination position shown by solid lines in FIG. 3 and a minimum inclination position shown by broken line. 
     As shown in FIG. 4, the cylinder block  11  has cylinder bores  25 , the number of which is seven in this embodiment. The cylinder bores  25  are all located at the same distance from the axis L of the drive shaft  18  and are spaced apart at equal angular intervals about the axis L of the shaft  18 . As shown in FIG. 3, a piston  26  is accommodated in each cylinder bore  25 . Each piston  26  is coupled to the swash plate  23  by pair of shoes  27 . The swash plate  23  converts rotation of the drive shaft  18  into reciprocation of each piston  26  in the associated cylinder bore  25 . 
     The valve plate  14  includes a main plate  28 , first sub plate  29  and second sub plate  30 . The first and second sub plates  29  and  30  sandwich the main plate  28 . The main plate  28  has suction ports  31  and discharge ports  32 . Each suction port  31  and each discharge port  32  correspond to one of the cylinder bores  25 . The first sub plate  29  has suction valve flaps  33 , each of which corresponds to one of the suction port  31 . The second sub plate  30  has discharge valve flaps  34 , each of which corresponds to one of the discharge ports  32 . The suction ports  31  connect the suction chamber  16  with the cylinder bores  25 . The discharge ports  32  connect the discharge chamber  17  with the cylinder bore  25 , respectively. The maximum opening degree of each discharge valve flap  34  is restricted by a retainer  35 . 
     The end face of each piston  26  and the first sub plate  29  define a compression chamber  36  in the associated cylinder bore  25 . The walls of the cylinder bores  25 , the valve plate  14 , and the pistons  26 , which are accommodated in the cylinder bores  25  form the compression chambers  36 . That is, the housing of the compressor  10  and the pistons  26  form an enclosure defining the compression chambers  36  in the cylinder bores  25 . 
     When each piston  26  is moved from the top dead center position to the bottom dead center position, that is, when each piston  26  is in the suction stroke, refrigerant gas in the suction chamber  16  is drawn into the associated compression chamber  36  through the suction port  31  and the suction valve flap  33 . When each piston  26  is moved from the bottom dead center to the top dead center, that is, when each piston  26  is in the discharge stroke, the gas in the associated compression chamber  36  is compressed to a predetermined pressure. The gas is then discharged to the discharge chamber  17  through the associated discharge port  32  and the associated valve flap  34 . 
     The discharge chamber  17  is connected to the crank chamber  15  by a supply passage  38 . An electromagnetic valve  37  is installed in the rear housing  13  to regulate the supply passage  38 . The crank chamber  15  is connected to the suction chamber  16  by a bleeding passage  39 . The bleeding passage  39  has a throttle. The electromagnetic valve  37  regulates the amount of refrigerant gas that flows from the discharge chamber  17  to the crank chamber  15 . The pressure of the crank chamber  15  is determined by the rate of gas flow from the discharge chamber  17  to the crank chamber  15  through the valve  37  and the rate of gas flow from the crank chamber  15  to the suction chamber  16  through the bleeding passage  39 . That is, the pressure of the crank chamber  15  is adjusted by opening and closing the valve  37 . 
     A controller (not shown) controls current to the electromagnetic valve  37  based on external information such as the temperature detected by a passenger compartment temperature sensor and a target temperature set by a temperature setter. When the valve  37  is closed, the pressure in the crank chamber  15  is lowered, which moves the swash plate  23  to the maximum inclination position. When the valve  37  is opened, the crank chamber pressure is increased, which moves the swash plate  23  to the minimum inclination position. In this manner, the displacement of the compressor  10  is controlled by opening and closing the valve  37 . 
     The number of suction ports  31  and the number of discharge ports  32  are both seven. As shown in FIG. 4, the suction chamber  16  and the discharge chamber  17  are separated by an annular wall  40 , which extends from the inner surface of the rear housing  13 . Each suction port  31  is located at the opposite side of the wall  40  from the corresponding discharge port  32 . The second sub plate  30  is not illustrated in FIG.  4 . 
     As shown in FIGS. 1 and 2, part of each suction port  31  and part of each discharge port  32  are located radially inside of the wall of the corresponding cylinder bore  25 . The rest of each suction port  31  and the rest of each discharge port  32  are radially outside of the corresponding cylinder bore  25 . 
     The thermophysical property of carbon dioxide allows the volume of each cylinder bore  25  to be relatively small. Thus, the diameter of each cylinder bore  25  is approximately half of the diameter of a cylinder bore in a compressor using fluorocarbon as refrigerant. The diameter of each cylinder bore  25  is about ten to twenty millimeters. The diameter of the suction ports  31  and the discharge ports  32  is about four to five millimeters. 
     The wall  40  separates the suction chamber  16  from the discharge chamber  17 . In other words, the wall  40  is located between the suction ports  31  and the discharge ports  32 . Therefore, if the size of the cylinder bores  25  and the ports  31 ,  32  are in the above mentioned range, part of each suction port  31  or part of each discharge port  32  can be located radially outside of wall of the corresponding cylinder bore  25 . 
     As shown in FIGS. 1 and 3, the end of each piston  26  is machined to have a chamfered surface  41 . The open end of each cylinder bore  25  is also machined to include a chamfered surface  42 . As shown in FIG. 1, when the piston  26  is substantially at the top dead center position, that is, when the piston  26  at the final stage of the discharge stroke, the piston chamfered surface  41  and the cylinder chamfered surface  42  define an annular guide passage  43  in the compression chamber  36 . The guide passage  43  extends about the entire circumference of the piston  26  and communicates with the discharge port  32 . 
     The cross-sectional area of the guide passage  43  is determined to reduce the friction applied to the refrigerant gas flowing through the passage  43 . However, if the volume of the space at the end of each piston  26 , or the volume of dead space, is too large when the piston  26  is at the top dead center position, the volumetric efficiency of the compressor  10  deteriorates. The cross-sectional area of the guide passage  43  is determined such that the compressor volumetric efficiency does not deteriorate significantly. Specifically, the width of each of the chamfered surfaces  41 ,  42  is between 0.5 and 1.0 millimeters. The “width” refers to a measurement taken along the face of the chamfered surface  41 ,  42 . 
     As shown in FIG. 1, at the last stage of the discharge stroke, that is, when the piston  26  is in the vicinity of the top dead center, the top clearance, or the space between the piston end and the first sub plate  29  is relatively narrow (for example, one millimeter). In this state, refrigerant gas in the area far from the discharge port  32 , that is, refrigerant gas in the vicinity of the suction port  31 , smoothly flows along the arrow of FIG. 1 in the guide passage  43  toward the discharge port  32 . Also, refrigerant gas is moved radially outward from the center of the piston end toward the periphery as the piston  26  moves closer to the first sub plate  29 . The gas is then smoothly conducted to the discharge port  32  by the guide passage  43 . Some refrigerant gas flows directly to the discharge port  32  through the narrow space between the piston end and the first sub plate  29 . 
     The embodiment of FIGS. 1 to  4  has the following advantages. 
     In the discharge stroke of a piston  26 , refrigerant gas in the compression chamber  36  is smoothly conducted to the discharge port  32  through the guide passage  43 . Thus, the pressure loss at the last stage of the discharge stroke is reduced, which improves the compression efficiency of the compressor  10 . The compressor  10  uses carbon dioxide as the refrigerant. Thus, the refrigerant is compressed to a relatively high pressure. However, since the pressure loss at the last stage of the discharge stroke is reduced, the construction shown in FIGS. 1 to  4  is particularly suitable for compressors using carbon dioxide. The guide passage  43  is located along the entire circumference of the end of each piston  26 . Thus, a relatively large amount of refrigerant gas is smoothly conducted to the discharge port  32  through the guide passage  43 , which further reduces the pressure loss. 
     As shown in FIGS. 1 and 2, part of each suction port  31  and part of each discharge port  32  are radially outside of the cylinder bore  25 . This arrangement of the ports  31 ,  32  does not prevent the guide passage  43  from smoothly conducting refrigerant gas to the discharge port  32 . 
     The chamfered surfaces  41 ,  42  formed on each piston  26  and each cylinder bore  25  define the guide passage  43 . The chambers  41 ,  42  are easily formed by machining, which reduces the manufacturing costs. Further, the chamfered surfaces  41 ,  42  are formed more easily than grooves. Also, forming the chamfered surfaces  41 ,  42  eliminates the corners, at which stress concentrates, from the pistons  26  and the cylinder bores  25 . The durability of the compressor  10  is therefore improved. 
     The chamfered surfaces  41 ,  42  are formed both on the pistons  26  and the cylinder bores  25  to form the guide passages  43 . Therefore, even if the chamfered surface  41  on each piston  26  is small, the chamfered surface  42  formed on the cylinder bore  25  guarantees that the guide passage  43  has a sufficient size. 
     The chamfered surface  42  in each cylinder bore  25  smoothly conducts gas from the compression chamber  36  to the discharge port  32 , which reduces the pressure loss in the vicinity of the inlet of the discharge port  32 . 
     FIGS. 5 and 6 illustrate a second embodiment. In the embodiment of FIGS. 5 and 6 is the same as the embodiment of FIGS. 1 to  4  except for the shape of ports  31 ,  32 . 
     As shown in FIGS. 5 and 6, the suction port  31  and the discharge port  32  are inclined with respect to the axis of the cylinder bore  25 . Specifically, the ports  31 ,  32  extend in the direction of gas flow caused by the chamfered surface  41  of the piston  26 . The axes of the ports  31 ,  32  extend symmetrically to each other and substantially at a right angle to the chamfered surface  41 . The ports  31 ,  32  are also substantially parallel to the angle of the chamfered surface  42 . 
     In addition to the advantages of the embodiment of FIGS. 1 to  4 , the embodiment of FIGS. 5 and 6 has the following advantages. 
     In the discharge stroke of each piston  26 , the chamfered surface  41  pushes refrigerant gas in the associated compression chamber  36  in the direction of the discharge port  32 . The gas is smoothly guided to the discharge port  32  by the chamfered surface  42 . Therefore, pressure loss caused when gas flows through the discharge port  32  is suppressed. Accordingly, the pressure loss at the last stage of the discharge stroke is further reduced. 
     The distance between the ports  31 ,  32  increases toward the suction chamber  16  and the discharge chamber  17  as shown in FIG.  5 . Therefore, even if the cylinder bore  25  has a relatively small diameter, the ports  31 ,  32  are positively connected to the cylinder bore  25  without reducing the thickness of the wall  40  or without reducing the size of the ports  31 ,  32 . 
     FIGS. 7 and 8 illustrate a third embodiment. The third embodiment is the same as the embodiment of FIGS. 1 to  4  except for the shape of chamfered surfaces  45  of the piston  26 . 
     As shown in FIGS. 7 and 8, the width of the chamfered surface  45  formed on each piston  26  increases toward the discharge port  32 . The cylinder block  11  has the chamfered surface  42 , which is the same as the chamfered surface  42  illustrated in FIGS. 1 to  4 . When the piston  26  reaches the vicinity of the top dead center position, that is, at the last stage of the discharge stroke, the chamfered surfaces  42 ,  45  define a guide passage  46 , which extends along the circumference of each piston  26 . The cross-sectional area of the guide passage  46  increases toward the discharge port  32 . 
     The maximum width of the chamfered surface  45  is slightly greater than the width (for example, 0.5 to 1.0 mm) of the chamfered surfaces  41 ,  42  of the embodiment of FIGS. 1 to  4 . The volume of the space when the piston  26  is at the top dead center position, or the volume of the dead space, is smaller than that of the embodiment of FIGS. 1 to  4 . 
     In addition to the advantages of the embodiment of FIGS. 1 to  4 , the embodiment of FIGS. 7 and 8 has the following advantages. 
     The width of the chamfered surface  45  decreases at locations that are farther away from the discharge port  32 . Thus, compared to the embodiment of FIGS. 1 to  4 , the compressor of FIGS. 7 and 8 has a smaller dead space, which improves the compression efficiency. 
     The illustrated embodiments may be modified as follows. 
     The guide passage does not need to be formed along the circumference of the end face of the pistons  26 . For example, as shown in FIGS. 9 and 10, a groove  48  may be formed on the piston end face to define a central guide passage  49  to conduct gas in the compression chamber  36  to the discharge port  32 . In the embodiment of FIGS. 9 and 10, the ports  31 ,  32  are radially inside the wall of the cylinder bore  25 . The groove  48  extends along a diametral line connecting the ports  31 ,  32 . The depth of the groove  48  is, for example, 0.5 to 1.0 mm. As in the embodiment of FIGS. 1 to  4 , the chamfered surfaces  41 ,  42  are formed. At the last stage of the discharge stroke of each piston  26 , the refrigerant gas can flow in the central guide passage  49  in addition to the peripheral guide passage  43 . The chamfered surfaces  41 ,  42  may be omitted. Permitting gas to flow along the central guide passage  49 , which is defined by the groove  48 , reduces the pressure loss at the last stage of the discharge stroke. In this case, the refrigerant is not limited to carbon dioxide but may be fluorocarbon. 
     The chamfered surfaces may be replaced by grooves. For example, a groove having an L-shaped cross-section may be formed between the circumferential surface and the end face of each piston  26 . Also, a groove having an L-shaped cross-section may be formed in the inner wall of each cylinder bore  25 . In this case, the grooves face each other to define a guide passage. 
     Furthermore, a guide passage may be defined by a groove formed in the valve plate  14 . For example, an annular groove may be formed in the valve plate  14  at the position corresponding to the boundary of each piston  26  and the associated cylinder bore  25 . The groove  48  of FIGS. 9 and 10 may be replaced by a groove that is formed on the valve plate  14  and extends along the line connecting each suction port  31  with the corresponding discharge port  32 . 
     It is sufficient to machine just one of the parts that define each compression chamber  36  to form a guide passage. That is, at least one of the cylinder block  11 , the pistons  26  the valve plate  14  may be machined to form a guide passage. Guide passages may be defined only by the chamfered surfaces  41  formed on the pistons  26 . Alternatively, the guide passage may be defined only by the chamfered surfaces  42  formed on cylinder block  11 . If two or more parts are machined to define the guide passages, chamfered surfaces and grooves may be combined to define guide passages. For example, the chamfered surface  41  ( 45 ) of each piston  26  may be combined with a groove formed on the inner wall of the associated cylinder bore  25  to define a guide passage. 
     The guide passages need not extend along the entire circumference of the corresponding piston  26 . For example, each guide passage may extend along the half circumference of each piston  26  that corresponds to the discharge port  32 . 
     The guide passage may be defined by means other than chamfered surfaces and grooves formed on the cylinder block  11 , the valve plate  14  and the pistons  26 . For example, the end face of each piston  26  may be inclined such that the distance between the valve plate  14  and the piston end face increases toward the discharge port  32 . 
     The present invention may be embodied in compressors other than compressors using carbon dioxide as refrigerant. For example, the present invention may be embodied in compressors using fluorocarbon as the refrigerant. 
     The structure of the illustrated and preferred embodiments may be used in compressors other than single-headed piston type variable displacement compressors. For example, the present invention may be embodied in wobble plate type compressors and fixed displacement compressors. 
     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. 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 and equivalence of the appended claims.