Patent Publication Number: US-2005142016-A1

Title: Heat insulating structure in piston type compressor

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a heat insulating structure in a piston type compressor, in which a piston is reciprocated in accordance with the rotation of a rotary shaft to draw refrigerant gas from a suction pressure region to a compression chamber as well as to discharge the refrigerant gas from the compression chamber to a discharge pressure chamber.  
      In a piston type compressor (cf. Unexamined Japanese Patent Application Publication No. 2001-515174), refrigerant gas is introduced into a compression chamber. The temperature of the introduced refrigerant gas in the compression chamber affects the performance of the compressor. As the temperature is higher, the density of the refrigerant gas in the compression chamber is lower, so that the performance of the compressor deteriorates. On the other hand, as the temperature is lower, the density of the refrigerant gas in the compression chamber is higher, so that the performance of the compressor improves.  
      By compressing the refrigerant gas, its temperature rises. Thus, heat is transmitted from the compressed refrigerant gas to a wall that defines the compression chamber, and the temperature of the wall rises. After compressing and discharging the refrigerant gas, the refrigerant gas is newly introduced into the compression chamber. The newly introduced refrigerant gas receives the heat from the wall, and its temperature rises. Therefore, if the temperature of the wall substantially rises or the wall has high heat conductivity, the temperature of the refrigerant gas in the compression chamber substantially rises before compression, and the performance of the compression deteriorates.  
      The present invention is directed to boosting the heat insulating characteristics of the compression chamber in a piston type compressor.  
     SUMMARY OF THE INVENTION  
      According to the present invention, a heat insulating structure in a piston type compressor includes a heat insulating member. The piston type compressor includes a cylinder block and a cover housing connected to the cylinder block, a piston is accommodated in a cylinder bore defined in the cylinder block to define a compression chamber. A suction pressure region and a discharge pressure region are defined in the cover housing. The piston is reciprocated in the cylinder bore in accordance with rotation of a rotary shaft so that refrigerant gas is drawn from the suction pressure region to the compression chamber and discharged from the compression chamber to the discharge pressure region. The heat insulating member has a predetermined shape and is located in the cylinder block. The heat insulating member has an inner peripheral surface that defines the cylinder bore. 
    
    
     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 compressor according to a first preferred embodiment;  
       FIG. 2  is a cross-sectional view of the compressor taken along the line I-I in  FIG. 1 ;  
       FIG. 3  is a cross-sectional view of the compressor taken along the line II-II in  FIG. 1 ;  
       FIG. 4  is a partially enlarged cross-sectional view of the compressor when a piston is located at its top dead center according to the first preferred embodiment;  
       FIG. 5  is a partially enlarged cross-sectional view of the compressor when the piston is located at its bottom dead center according to the first preferred embodiment;  
       FIG. 6  is a partially enlarged cross-sectional view of a compressor according to a second preferred embodiment;  
       FIG. 7  is a partially enlarged cross-sectional view of a compressor according to a third preferred embodiment;  
       FIG. 8  is a partially enlarged cross-sectional view of a compressor according to a fourth preferred embodiment;  
       FIG. 9A  is a partially enlarged cross-sectional view of a compressor according to a fifth preferred embodiment;  
       FIG. 9B  is a cross-sectional view of the compressor taken along the line III-III in  FIG. 9A ;  
       FIG. 10A  is a partially enlarged cross-sectional view of a compressor according to a sixth preferred embodiment;  
       FIG. 10B  is a cross-sectional view of the compressor taken along the line IV-IV in  FIG. 10A ;  
       FIG. 11  is a partially enlarged cross-sectional view of a compressor according to a seventh preferred embodiment; and  
       FIG. 12  is a partially enlarged cross-sectional view of a compressor according to an eighth preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      A first preferred embodiment will be described with reference to  FIGS. 1 through 5 , in which the present invention is applied to a piston type variable displacement compressor.  
      As shown in  FIG. 1 , the housing of a piston type variable displacement compressor  10  includes a cylinder block  11  of aluminum, a front housing  12  of aluminum and a rear housing or cover housing  13  of aluminum. The front housing  12  is joined to the front end of the cylinder block  11 , and the rear housing  13  is joined to the rear end of the cylinder block  11  through a valve plate  14  and gasket type valve forming plates  15 ,  16 . The cylinder block  11 , the front housing  12  and the rear housing  13  are combined by a screw  53 . As shown in  FIGS. 4 and 5 , the valve forming plate  15  includes a metallic plate  152  and rubber layers  153 ,  154  that are respectively provided on the surfaces of the metallic plate  152 . In a similar manner, the valve forming plate  16  includes a metallic plate  162  and rubber layers  163 ,  164  that are respectively provided on the surfaces of the metallic plate  162 .  
      The front housing  12  and the cylinder block  11  define a pressure control chamber  121  and rotatably support a rotary shaft  18  through radial bearings  19 ,  20 , respectively. The rotary shaft  18  extends in the pressure control chamber  121  and protrudes to the outside therefrom. The rotary shaft  18  receives driving power from a vehicle engine  17  as an external drive source through a pulley (not shown) and a belt (not shown).  
      A lug plate  21  is mounted on the rotary shaft  18 , and a swash plate  22  is supported on the rotary shaft  18  so as to slide in and incline with respect to the axial direction of the rotary shaft  18 . A connection member  23  is mounted on the swash plate  22 , and a guide pin  24  is mounted on the connection member  23 . A guide hole  211  is formed in the lug plate  21 . The head portion of the guide pin  24  is slidably inserted into the guide hole  211 . The cooperation of the guide hole  211  and the guide pin  24  allows the swash plate  22  to incline with respect to the axial direction of the rotary shaft  18  and to rotate together with the rotary shaft  18 . The inclination of the swash plate  22  is guided by the slide guide relation between the guide hole  211  and the guide pin  24  and the slide support of the rotary shaft  18 .  
      As the middle part of the swash plate  22  moves toward the lug plate  21 , an inclination angle of the swash plate  22  is increased. The swash plate  22  comes into contact with the lug plate  21  to restrict the maximum inclination angle. At the position of the swash plate  22  indicated by the solid line in  FIG. 1 , the inclination angle of the swash plate  22  is the maximum. As the middle part of the swash plate  22  moves toward the cylinder block  11 , the inclination angle of the swash plate  22  is decreased. At the position of the swash plate  22  indicated by the two-dot chain line in  FIG. 1 , the inclination angle of the swash plate  22  is the minimum.  
      As shown in  FIGS. 1, 2  and  4 , a plurality of holes  111  are formed through the cylinder block  11  for forming compression chambers. A cylindrical-shaped heat insulating member  30  of synthetic resin is press-fitted into each of the hole  111 . The inner peripheral surface of the cylinder block  21  that defines the hole  111  is covered by the heat insulating member  30 .  
      A piston  25  of aluminum is accommodated in each of the heat insulating members  30 . Only one piston  25  is shown in  FIG. 2 . The piston  25  includes a cylindrical-shaped head portion  252  and a neck portion  253  as shown in  FIG. 1 . The head portion  252  is inserted into the heat insulating member  30 , and the neck portion  253  is engaged with the swash plate  22  through a pair of shoes  26 . The rotational movement of the swash plate  22  is converted into the reciprocating movement of the piston  25 , and the piston  25  is reciprocated in the heat insulating member  25 . The inside of the heat insulating member  30  is a cylinder bore  43  for reciprocating the piston  25  therein, and the heat insulating member  30  has an inner peripheral surface  431  that defines the cylinder bore  43  as shown in  FIGS. 2 and 3 . A compression chamber  112  is defined by the piston  25 , the heat insulating member  30  and the valve forming plate  15  in the inside of the heat insulating member  30  (the cylinder bore  43 ) as shown in  FIG. 1 .  FIG. 5  shows a state where the piston  25  is located at its bottom dead center.  
      As shown in  FIGS. 1 and 3 , the rear housing  13  and the valve plate  14  define a suction chamber or suction pressure region  27  and a discharge chamber or discharge pressure region  28  that are separated by an annular partition wall  29 . The suction chamber  27  is located on the radially outer side of the rear housing  13  and surrounds the discharge chamber  28  around an axial line  181  of the rotary shaft  18 . The compression chamber  112  is separated from the suction chamber  27  and the discharge chamber  28  by the valve plate  14 . The valve forming plates  15 ,  16  and a retainer  31  are combined with the valve plate  14  by a screw  32 .  
      As shown in  FIGS. 4 and 5 , a suction port  141  is formed in the valve plate  14  and the valve forming plate  16 , and a discharge port  142  is formed in the valve plate  14  and the valve forming plate  15 . A suction valve  151  is formed in the valve forming plate  15 , and a discharge valve  161  is formed in the valve forming plate  16 . Gaseous refrigerant in the suction chamber  27  pushes away the suction valve  151  and is drawn into the compression chamber  112  through the suction port  141  by the movement of the piston  25  from the right to the left as seen in  FIG. 1 .  
      A regulating recess  301  is formed on the end face of the heat insulating member  30  near the valve forming plate  15 , and a metallic member  302  is mounted on the bottom of the regulating recess  301 . The suction valve  151  comes into contact with the metallic member  302  at the bottom of the regulating member  301  to regulate its opening degree. The drawn gaseous refrigerant in the compression chamber  112  pushes away the discharge valve  161  and is discharged into the discharge chamber  28  through the discharge port  142  by the movement of the piston  25  from the left to the right as seen in  FIG. 1 . The discharge valve  161  comes into contact with the retainer  31  to regulate its opening degree.  
      As shown in  FIG. 1 , an inlet  33  for introducing the gaseous refrigerant into the suction chamber  27  and an outlet  34  for discharging the gaseous refrigerant from the discharge chamber  28  are formed in the rear housing  13 . The inlet  33  and the outlet  34  is interconnected by an external refrigerant circuit  35  on which a heat exchanger  36  for obtaining heat from the refrigerant, a fixed throttle  37 , a heat exchanger  38  for transmitting heat from the surrounding air to the refrigerant and an accumulator  39  are arranged. The accumulator  39  feeds the only gaseous refrigerant to the compressor  10 . The refrigerant in the discharge chamber  28  flows into the suction chamber  27  via the outlet  34 , the heat exchanger  36 , the fixed throttle  37 , the heat exchanger  38 , the accumulator  39  and the inlet  33 .  
      The discharge chamber  28  and the pressure control chamber  121  are interconnected by a supply passage  40  formed in the cylinder block  11 . The pressure control chamber  121  and the suction chamber  27  are interconnected by a bleed passage  41  formed in the cylinder block  11  and the rear housing  13 . The refrigerant in the pressure control chamber  121  flows out to the suction chamber  27  through the bleed passage  41 .  
      An electromagnetic displacement control valve  42  is arranged on the supply passage  40 . When the displacement control valve  42  is de-energized, the displacement control valve  42  is closed so that the refrigerant does not flow from the discharge chamber  28  to the pressure control chamber  121  through the supply passage  40 . Since the refrigerant in the pressure control chamber  121  flows out to the suction chamber  27  through the bleed passage  41 , the pressure in the pressure control chamber  121  falls. Therefore, the inclination angle of the swash plate  22  is increased, and the displacement is increased. When the displacement control valve  42  is energized, the displacement control valve  42  is opened so that the refrigerant flows from the discharge chamber  28  to the pressure control chamber  121  through the supply passage  40 . Therefore, the pressure in the pressure control chamber  121  rises, the inclination angle of the swash plate  22  is decreased and the displacement is decreased. In the first preferred embodiment, carbon dioxide is used as the refrigerant.  
      According to the first preferred embodiment, the following advantageous effects are obtained.  
      (1-1) In accordance with the movement of the piston  25  from the right to the left as seen in  FIG. 1 , the refrigerant gas in the suction chamber  27  is drawn into the compression chamber  112  through the suction port  141 . In accordance wit the movement of the piston  25  from the left to the right as seen in  FIG. 1 , the refrigerant gas in the compression chamber  112  is compressed and discharged into the discharge chamber  28  through the discharge port  142 . As the refrigerant gas in the compression chamber  112  is compressed, the temperature thereof rises. However, synthetic resin or the material for the heat insulating member  30  has heat conductivity lower than aluminum or the material for the cylinder block  11 . Thus, the heat insulating member  30  having the inner peripheral surface  431  that defines the cylinder bore  43  is hard to be heated by the refrigerant gas in the compression chamber  112 , and the temperature of the heat insulating member  30  substantially does not rise. Therefore, a small amount of heat is transmitted from the heat insulating member  30  to the refrigerant gas that is newly drawn into the compression chamber  112  after compressing and discharging the previously drawn refrigerant gas. Namely, the temperature of the refrigerant gas in the compression chamber  112  is substantially prevented from being increased by the heat insulating member  30 . The heat insulating member  30  enhances the heat insulating characteristics of the compression chamber  112  and contributes to the improvement in the performance of the piston type variable displacement compressor  10 .  
      (1-2) The heat insulating member  30  having a predetermined shape or the cylindrical shape is made thicker to enhance the heat insulation effectiveness.  
      (1-3) The heat insulation member  30  is made of synthetic resin that has low heat conductivity. The heat insulating member  30  reduces the heat transmission from the cylinder block  11  of aluminum, which has high heat conductivity, to the refrigerant gas in the compression chamber  112 . Thus, the heat insulating member  30  contributes to the improvement in the performance of the compressor.  
      (1-4) If the piston type variable displacement compressor  10  becomes unusable, the heat insulating member  30  is removed from the hole  111  and is recyclable.  
      (1-5) Carbon dioxide is used as refrigerant under the pressure higher than when chlorofluorocarbon is used. Thus, small flow rate is required. When the flow rate is small, it is important to prevent the refrigerant gas in the compression chamber  112  from being heated. The piston type variable displacement compressor  10  using carbon dioxide as the refrigerant is suitable for the application of the present invention.  
      In the present invention, the following preferred embodiments are practiced as shown in  FIGS. 6 through 12 . In these preferred embodiments, similar elements are referred to by the same reference numerals as the first is preferred embodiment.  
      In a second preferred embodiment as shown in  FIG. 6 , a heat insulating member  44  includes a cylindrical portion  441  and a flange  442  that is located at the end of the cylindrical portion  441  near the valve plate  14  and is integrated with the cylindrical portion  441 . The cylindrical portion  441  is inserted into the hole  111 , and the flange  442  is sandwiched between the cylinder block  11  and the valve plate  14 . Since the flange  442  is sandwiched between the cylinder block  11  and the valve plate  14 , the cylindrical portion  441  is held in the hole  111  without following the reciprocating movement of the piston  25 .  
      In a third preferred embodiment as shown in  FIG. 7 , the cylinder block  11  is formed with a protrusion  114  on its inner peripheral surface that defines the hole  111 . A cylindrical-shaped heat insulating member  45  is inserted into the hole  111  and sandwiched between the protrusion  114  and the valve plate  14 . Thus, the heat insulating member  45  is held in the hole  111  without following the reciprocating movement of the piston  25 .  
      In a fourth preferred embodiment as shown in  FIG. 8 , a valve forming plate  15 A is made of metal, and a seal ring  46  is interposed between the cylinder block  11  and the valve forming plate  15 A near the outer periphery of the cylinder block  11  so as to surround the axial line  181  of the rotary shaft  18  and all of the is heat insulating members  44 . The flange  442  of the heat insulating member  44  serves to seal the compression chamber  112 , so that the refrigerant gas is prevented from leaking along the surface of the valve forming plate  15 A from the compression chamber  112  to a hole  115  that is formed in the cylinder block  11  for inserting the rotary shaft  18  therein. The seal ring  46  prevents the refrigerant gas from leaking along the surface of the valve forming plate  15 A from the compression chamber  112  to the outside of the compressor.  
      In a fifth preferred embodiment as shown in  FIGS. 9A and 9B , a heat insulating member  47  includes a cylindrical portion  471  and an end wall  472 . The cylindrical portion  471  is inserted into the hole  111 , and the end wall  472  is in contact with the valve forming plate  15 A of metal and faces the top end surface of the piston  25 . The heat insulating member  47  is sandwiched between the protrusion  114  and the valve plate  14 . Thus, the heat insulating member  47  is held in the hole  111  without following the reciprocating movement of the piston  25 . The end wall  472  has formed therein a suction hole  473  facing the suction port  141  and a discharge hole  474  facing the discharge port  142 . The refrigerant gas in the suction chamber  27  is drawn into the compression chamber  112  through the suction port  112  and the suction hole  473  while the refrigerant gas in the compression chamber  112  is discharged into the discharge chamber  28  through the discharge hole  474  and the discharge port  142 . The end wall  472  further improves the heat insulating characteristics of the compression chamber  112 .  
      In a sixth preferred embodiment as shown in  FIGS. 10A and 10B , a cylinder block  11  A includes an annular base block  48  of aluminum and an annular block  49  of synthetic resin. The base block  48  includes a radially outer portion  481 , a radially inner portion  482  and an end wall  483 , and the annular block  49  is interposed between the radially outer portion  481  and the radially inner portion  482  to surround the axial line  181  of the rotary shaft  18 . A plurality of the cylinder bores  43  are formed in the annular block  49 . Namely, the annular block  49  or a heat insulating member of synthetic resin has the inner peripheral surface  431  that defines the cylinder bore  43 . The end wall  483  has formed therein a through hole  484  corresponding to each of the cylinder bore  43 . The piston  25  is inserted into the cylinder bore  43  through the through hole  484 . The above structure, in which a plurality of the cylinder bores  43  are formed in the annular block  49  of heat insulating material or synthetic resin, is more productive than a structure in which a plurality of cylinder bores are respectively formed in a plurality of heat insulating members.  
      In a seventh preferred embodiment as shown in  FIG. 11 , the peripheral surface of the head portion  252  of the piston  25  is covered with a coating layer  50  made of the same material as the heat insulating member  45 . The structure, in which the heat insulating member  45  and the coating layer  50  are made of material having the same coefficient of linear expansion, facilitates control of the clearance between the inner peripheral surface  431  of the heat insulating member  45  and the surface of the coating layer  50  in thermal expansion.  
      In an eighth preferred embodiment as shown in  FIG. 12 , a disc-shaped heat insulating member  51  is bound to a top end surface  251  of the piston  25  to cover the top end surface  251 . The heat insulating member  51  further improves the heat insulating characteristics of the compression chamber  112 .  
      According to the present invention, the following alternative embodiments are practicable.  
      (1) In the seventh preferred embodiment, the coating layer  50  is made of the same material as the heat insulating member  45 . However, the coating layer is made of material that has abrasive resistance higher than the heat insulating member or sliding characteristics better than the heat insulating member, so that the lifetime of the compressor improves. Furthermore, the coating layer is provided in the other preferred embodiments.  
      (2) Hard rubber or ceramics is used as material for the heat insulating member having the inner peripheral surface that defines the cylinder bore.  
      (3) The cylindrical-shaped heat insulating member includes two parts, or a radially inner part and a radially outer part that are made of different synthetic resins. Synthetic resin having high abrasive resistance (e.g. polytetrafluoroethylene) is used as the synthetic resin for the radially inner part.  
      (4) The present invention is applicable to a piston type compressor in which the discharge chamber is defined on the outer peripheral side of the rear housing  13  so as to surround the suction chamber around the axial line  181  of the rotary shaft  18 .  
      (5) The present invention is applicable to a piton type fixed displacement compressor.  
      (6) The present invention is applicable to a compressor in which refrigerant other than carbon dioxide is used.  
      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.