Patent Publication Number: US-6213727-B1

Title: Variable displacement compressor and outlet control valve

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a variable displacement compressor that controls the inclination of a drive plate by adjusting the amount of refrigerant gas bled from a crank chamber. More particularly, the invention pertains to an outlet control valve used in such a compressor. 
     A typical variable displacement compressor has a drive shaft, which is rotatably supported in a crank chamber defined in the compressor housing. The housing includes a cylinder block. Cylinder bores are formed in the cylinder block. A piston is reciprocally housed in each cylinder bore. An inclined drive plate, or swash plate, is supported by the drive shaft in the crank chamber. The swash plate rotates integrally with and inclines with respect to the drive shaft. The swash plate converts rotation of the drive shaft into reciprocation of the pistons. 
     The inclination of the swash plate varies in accordance with the pressure in the crank chamber. The stroke of the pistons is changed according to the inclination angle of the swash plate, which varies the displacement of the compressor. To control the crank chamber pressure, either the flow rate of refrigerant gas delivered to the crank chamber or the flow rate of refrigerant gas released from the crank chamber must be controlled. 
     To control the amount of gas delivered to the crank chamber, an inlet control valve is located in a passage connecting the discharge chamber to the crank chamber. The crank chamber is connected to a suction chamber by a bleeding passage. A fixed restrictor is formed in the bleeding passage. The control valve adjusts the amount of refrigerant gas supplied to the crank chamber from the discharge chamber, thereby setting the crank chamber pressure to a desired level. 
     To control the amount of gas released from the crank chamber, an outlet control valve is located in a bleeding passage, which connects the crank chamber to the suction chamber. When a piston compresses refrigerant gas in the associated cylinder bore, refrigerant gas in the cylinder bore leaks into the crank chamber between the surface of the piston and the wall of the cylinder bore. The leaking gas is referred to as blowby gas. The blowby gas increases the pressure of the crank chamber. The outlet control valve adjusts the amount of refrigerant flowing from the crank chamber to the suction chamber thereby setting the crank chamber pressure to a desired pressure. 
     Using the outlet control valve, the crank chamber pressure is changed in accordance with the amount of refrigerant gas bled from the crank chamber. Therefore, to quickly change the crank chamber pressure, sufficient blowby gas must be constantly supplied to the crank chamber. However, blowby gas is a mere byproduct of gas compression by the piston. Thus, it is difficult to quickly change the crank chamber pressure using only blowby gas. Further, the amount of blowby gas is varied according to the rotation speed of the swash plate. Particularly when the swash plate speed is low, the amount of blowby gas is not sufficient. Therefore, the inclination of the swash plate, or the compressor displacement, cannot be changed quickly. 
     Providing a constant, adequate supply of blowby gas to the crank chamber is difficult. To avoid this problem, a supply passage may be provided to supply refrigerant gas from the discharge chamber to the crank chamber. However, the diameter of the supply passage needs to be extremely small (for example, 0.1 to 0.5 millimeters). Forming such narrow passages in compressor housings with a drilling machine shortens the life of the drilling machine. Compressor housings having such a supply passage are therefore not suitable for mass production. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an objective of the present invention to provide a variable displacement compressor and an outlet control valve that quickly adjust the compressor displacement and are suitable for mass production. 
     To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a variable displacement compressor for varying displacement according to the inclination of a drive plate located in a crank chamber is provided. The compressor includes a suction pressure zone, the pressure of which is a suction pressure, and a discharge pressure zone, the pressure of which is a discharge pressure. The compressor also includes a bleeding passage for bleeding refrigerant gas from a crank chamber to the suction pressure zone and valve for regulating the bleeding passage. The valve controls the flow of refrigerant gas from the crank chamber to the suction pressure zone such that the valve adjusts the pressure of the crank chamber, and the inclination of the drive plate varies in accordance with the pressure in the crank chamber. The valve has a valve body, which adjusts the opening area of the bleeding passage, an adjuster body, which acts on the valve body, and a housing that houses the adjuster body. A supply passage is formed between the adjuster body and the housing to guide refrigerant gas from the discharge pressure zone to the crank chamber. 
     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 accompaning drawings in which: 
     FIG. 1 is a cross-sectional view illustrating a variable displacement compressor according to a first embodiment of the present invention; 
     FIG. 2 is an enlarged cross-sectional view illustrating an outlet control valve in the compressor of FIG. 1; 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is a cross-sectional view like FIG. 3, illustrating a second embodiment; and 
     FIG. 5 is an enlarged cross-sectional view illustrating an outlet control valve according to a third embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will now be described with reference to FIGS. 1 to  3 . 
     As shown in FIG. 1, a front housing  2  and a rear housing  4  are secured to a cylinder block  1 . Cylinder bores  1   a  (only one is shown) are formed in the cylinder block  1 . A valve plate  5  is located between the cylinder block  1  and the rear housing  4 . A crank chamber  3  is defined between the front housing  2  and the cylinder block  1 . The cylinder block  1 , the front housing  2  and the rear housing  4  form the compressor housing. 
     The valve plate  5  includes a suction valve plate  6  and a discharge valve plate  7 . The suction valve plate  6  has suction valve flaps  6   a,  each of which corresponds to one of the cylinder bores  1   a.  The discharge valve plate  7  has discharge valve flaps  7   a,  each of which corresponds to one of the cylinder bores  1   a . A suction chamber  8  and a discharge chamber  9  are defined in the rear housing  4 . Suction ports  5   a  and discharge ports  5   b  are formed in the valve plate  5 . Each cylinder bore  1   a  is connected to the suction chamber  8  by one of the suction ports  5   a.  Also, each cylinder bore  1   a  is connected to the discharge chamber  9  by one of the discharge ports  5   b.    
     A drive shaft  12  is rotatably supported by a pair of bearings  13  in the cylinder block  1  and the front housing  2 . The drive shaft  12  is coupled to an external drive source, or engine E, by a pulley, a belt and an electromagnetic clutch (none of which is shown). A rotating support  14  is secured to the drive shaft  12  in the crank chamber  3 . The rotating support  14  rotates integrally with the drive shaft  12 . A thrust bearing  15  is located between the rotating support  14  and the inner wall of the front housing  2 . The rotating support  14  has a support arm  14   a.  A guide slot  14   b  is formed in the support arm  14   a.  A drive plate  17  is fitted about the drive shaft  12 . The drive plate  17  has a front projection, from which a pin  16  extends. The pin  16  is engaged with the guide slot  14   b.  Cooperation of the pin  16  and the support arm  14   a  allows the drive plate  17  to rotate integrally with the drive shaft  12 . 
     A sleeve  19  is slidably fitted to the drive shaft  12 . The sleeve  19  is coupled to a boss  17   a  of the drive plate  17  by a pair of coupling pins  20  (only one is shown). The sleeve  19  allows the drive plate  17  to move along the axis of the drive shaft  12 , and the pins  20  allow the drive plate  17  to pivot about the pins  20 . A wobble plate  18  is fitted about the boss  17   a  of the drive plate  17  to be rotatable relative to the drive plate  17 . A guide rod  21  located in the crank chamber  3  prevents the wobble plate  18  from rotating while allowing the plate  18  to incline. The wobble plate  18  is coupled to each piston  22  by a piston rod  23 . A spring seat  24  is fitted to the drive shaft  12 . A coil spring  25  is fitted about the drive shaft  21  between the spring seat  24  and the sleeve  19 . The spring  25  urges the plates  17 ,  18  to left as viewed in FIG. 1, or in a direction increasing the inclination of the plates  17 ,  18 . 
     As shown in FIG. 1, the discharge chamber  9  is connected to the suction chamber  8  by an external refrigerant circuit  30 . The external refrigerant circuit  30  and the compressor form a vehicle cooling circuit. The refrigerant circuit  30  includes a condenser  31 , an expansion valve  32  and an evaporator  33 . The expansion valve  32  maintains a pressure difference between the condenser  31  and the evaporator  33 . Also, the expansion valve  32  controls the amount of refrigerant supplied to the evaporator  33  in accordance with the thermal load applied to the circuit  30 . The expansion valve  32  is feedback controlled based on the temperature at the outlet of the evaporator  33  and on the pressure at the inlet or the outlet of the evaporator  33 . Accordingly, the amount of circulating refrigerant in the circuit  30  is controlled such that the degree of superheating of gasified refrigerant in the evaporator  33  is maintained at a proper level. 
     When the drive shaft  12  is rotated by the external drive source E, the inclined drive plate  17  is rotated. The rotation of the drive plate  17  causes the wobble plate  18  to wobble. The wobbling movement of the wobble plate  18  is converted into reciprocation of each piston  22 . Each piston  22  reciprocates with a stroke corresponding to the inclination of the plates  17 ,  18 , which draws refrigerant gas from the suction chamber  8  to the associated cylinder bore  1   a , and discharges compressed refrigerant gas from the cylinder bore  1  to the discharge chamber  9 . 
     The inclination of the plates  17 ,  18  is determined based on a moment resulting from centrifugal force, a moment resulting from the force of the spring  25  and a moment resulting from the gas pressure applied to the pistons  22 . The moment based on centrifugal force and the moment based on the spring  25  always act to increase the inclination of the plates  17 ,  18 . The moment based on the gas pressure acts to decrease the inclination of the plates  17 ,  18 . The moment based on the gas pressure is generated by the compression reaction force acting on the pistons  22  that are performing a compression stroke, the pressure in the cylinder bores  1   a  of the pistons  22  that are performing a suction stroke and the pressure (Pc) in the crank chamber  3 . 
     Changing the crank chamber pressure Pc permits the plates  17 ,  18  to be at any inclination between the minimum inclination and the maximum inclination. The stroke of the pistons  22 , or the compressor displacement, is controlled in accordance with the inclination of the plates  17 ,  18 . Specifically, when the crank chamber pressure Pc is increased and the moment based on the gas pressure is greater than the sum of the moment based on centrifugal force and the moment based on the spring force, the inclination of the plates  17 ,  18  is decreased. The minimum inclination of the plates  17 ,  18  is three to five degrees. The inclination of the plates  17 ,  18  is represented by their angle relative to a plane perpendicular to the axis of the drive shaft  12 . When the crank chamber pressure Pc is lowered and the moment based on the gas pressure is smaller than the sum of the moment based on centrifugal force and the moment based on the spring force, the inclination of the plates  17 ,  18  is increased. The inclination of the plates  17 ,  18  is unchanged when the moment based on the gas pressure and the sum of the moment based on rotation and the moment based on the spring force are in balance. 
     An outlet control valve  40  will now be described with reference to FIG.  2 . The outlet control valve  40  includes a first valve housing  41 , a second valve housing  42  and a plug  43 . The second valve housing  42  is secured to the bottom of the first housing  41  and the plug  43  is located in the second valve housing  42 . The first valve housing  41 , the second valve housing  42  and the plug  43  form the housing of the control valve  40 . 
     The second valve housing  42  is cylindrical and has annular steps formed on the inner wall. The lower end of the plug  43  is engaged with one of the annular steps. A disk spring  44  is engaged with another annular step. The disk spring  44  urges the plug  43  downward preventing the plug  43  from moving in the second valve housing  42 . 
     A seal ring  45  is fitted between the inner wall of the second valve housing  42  and a groove formed in the circumferential surface of the plug  43 . A valve chamber  46  is formed below the plug  43 . A pressure sensing element, or diaphragm  54 , is located between the first valve housing  41  and the second valve housing  42 . A pressure sensing chamber  53  is defined between the diaphragm  45  and the plug  43 . 
     An annular step  47  is formed in the inner wall of the second valve housing  42  in the axial center of the valve chamber  46 . The step  47  divides the valve chamber  46  into an upper portion (suction pressure zone) and a lower portion (crank chamber pressure zone). A valve body  50  is movably housed in the valve chamber  46 . The valve body  50  contacts the step  47 , which serves as a valve seat, to disconnect the upper portion of the valve chamber  46  from the lower portion. 
     Ports  48 ,  49  are formed in the wall of the second valve housing  42 . The ports  48  connect the upper portion of the valve chamber  46  to the suction chamber  8  by a passage  35  formed in the compressor. The ports  49  connect the lower portion to the crank chamber  3  by a passage  36  formed in the compressor. The crank chamber  3  is connected to the suction chamber  8  by a bleeding passage, which includes the passage  36 , the ports  49 , the valve chamber  46 , the ports  48  and the passage  35 . The valve body  50  is moved to change its position in the valve chamber  46 . Accordingly, the area of the space between the valve body  50  and the step  47 , or the opening amount of the bleeding passage, is varied. 
     A guide hole  51  extends in the plug  43  along the axis of the control valve  40 . A pressure sensing rod  52  extends through the guide hole  51  and slides with respect to the plug  43 . The lower end of the rod  52  is coupled to the valve body  50  and the upper end of the rod  52  is coupled to the lower side of the diaphragm  54  by a connector  55 . The valve body  50 , the rod  52  and the connector  55  are moved integrally along the axis of the control valve  40 . 
     Pressure sensing ports  56  are formed in the wall of the second valve housing  42  above the seal ring  45 . The pressure sensing ports  56  are connected to the suction chamber  8  and to the pressure sensing chamber  53  via a space defined between the plug  43  and the inner wall of the second valve housing  42 . Thus, the pressure of the suction chamber  8 , or the suction pressure Ps, is applied to the pressure sensing chamber  53  by the pressure sensing ports  56 . 
     An adjuster  57  is threaded into the first valve housing  41 . A hole  57   a  is formed in the center of the adjuster  57   a  to communicate the interior of the first valve housing  41  with the atmosphere. A ball seat  61  is attached to the upper side of the diaphragm  54 . A spring receiver  59  is located above the ball seat  61  with a ball  60  in between. A spring  58  is located between the spring receiver  59  and the adjuster  57 . A target value Pset of the suction pressure Ps is determined by the sum of the force of atmospheric pressure, which acts on the diaphragm  54 , and the force of the spring  58 . The target value Pset is adjusted by changing the axial position of the adjuster  57 . 
     In the embodiment of FIGS. 1 to  3 , a pressure sensing mechanism is formed by the pressure sensing rod  52 , the pressure sensing chamber  53 , the diaphragm  54 , the connector  55 , the pressure sensing ports  56 , the adjuster  57 , the spring  58 , the spring receiver  59 , the ball  60  and the ball seat  61 . The pressure sensing mechanism actuates the valve body  50  in accordance with changes in the suction pressure Ps. 
     A guide hole  62  extends in the lower portion of the second valve housing  42  along the axis of the control valve  40 . An adjuster rod  63  extends in and slides along the guide hole  62 . A mushroom-shaped stopper  63   a  is formed at the upper end of the adjuster rod  63 . A flange  64  is removably attached to the stopper  63   a.  A spring  65  extends between the flange  64  and the lowest step formed in the second valve housing  42 . The spring  65  urges the adjuster rod  63  toward the valve body  50  through the flange  64 . As a result, the stopper  63   a  is constantly pressed against the valve body  50 . In other words, the adjuster rod  63  is operably coupled to the pressure sensing mechanism by the valve body  50 . 
     A lower surface  63   b  of the adjuster rod  63  is exposed to the pressure of the discharge chamber  9 , or the discharge pressure Pd. As shown in FIGS. 2 and 3, the diameter of the guide hole  62  is slightly greater than that of the adjuster rod  63  (FIGS. 2 and 3 illustrate the diameter difference is in an exaggerated manner). A space  66  is formed between the guide hole  62  and the adjuster rod  63 . The space  66  connects the lower portion of the control valve  40  with the discharge chamber  9  thereby drawing refrigerant gas to the ports  49 . Some of the refrigerant gas in the discharge chamber  9  is thus conducted to the crank chamber  3  by the ports  49 . Since the space  66  is very narrow, the space  66  functions as a fixed restriction. 
     In addition to blowby gas leaking to the crank chamber  3  from the cylinder bores  1   a , refrigerant gas flowing through the space  66  is also supplied to the crank chamber  3 . 
     Changes of the suction pressure Ps, which is applied to the pressure sensing chamber  53 , actuate the pressure sensing mechanism, which includes the diaphragm  54 . Accordingly, the axial position of the valve body  50  is changed, which varies the opening amount of the bleeding passage ( 36 ,  49 ,  46 ,  48 ,  35 ). When the valve body  50  contacts the step  47 , the bleeding passage is closed. At this time, flow of refrigerant gas from the crank chamber  3  to the suction chamber  8  is stopped. As a result, gas is supplied to the crank chamber  3  via the cylinders  1   a  (blowby gas) and via the space  66 , which increases the crank chamber pressure Pc. The increase of the crank chamber pressure Pc decreases the inclination of the plates  17 ,  18 . Accordingly, the displacement of the compressor is decreased. 
     When the valve body  50  is separated from the step  47 , or when the bleeding passage is open, refrigerant gas flows from the crank chamber  3  to the suction chamber  8 . If the amount of refrigerant gas flowing from the crank chamber  3  to the suction chamber  8  via the bleeding passage is greater than the total amount of blowby gas and gas flowing through the space  66 , the crank chamber pressure Pc is lowered and the inclination of the plates  17 ,  18  is increased. If the amount of refrigerant gas entering the crank chamber  3  is equal to the amount of refrigerant gas escaping from the crank chamber  3 , the crank chamber pressure Pc does not change. The inclination of the plate  17 ,  18  is determined, accordingly. 
     The valve sensing mechanism actuates the valve body  50  such that the suction pressure Ps is substantially equal to the target value Pset. A pressure Ps′ at the outlet of the evaporator  33  represents the thermal load. The role of the compressor in the refrigerant circuit is to control the pressure Ps′ to a desired level. Therefore, the compressor feedback controls the inclination of the plates  17 ,  18 , or the compressor displacement, by the control valve  40  such that the suction pressure Ps, which is substantially equal to the pressure Ps′, is maintained at the target value Pset. 
     When the pressure of refrigerant gas discharged from the compressor to the refrigerant circuit  30 , or the discharge pressure Pd, is relatively great, pressure loss in the passages of the refrigerant circuit  30  is increased. This increases the difference between the pressure Ps′ at the evaporator outlet and the suction pressure Ps. For example, the greater the discharge pressure Pd is, the smaller the suction pressure Ps is than the pressure Ps′ at the evaporator outlet. 
     The adjuster rod  63  compensates the difference between the suction pressure Ps and the pressure Ps′ thereby maintaining the pressure Ps′ to a desired level. Specifically, the higher the discharge pressure Pd is, the greater the power of the adjuster rod  63  to lift the entire pressure sensing mechanism by the valve body  50  is. The axial urging force of the adjuster rod  63 , which is determined in accordance with the discharge pressure Pd, acts against the axial urging force of the spring  58  through the valve body  50  and the parts of the pressure sensing mechanism ( 52 ,  55 ,  54 ,  61 ,  60 ,  59 ). In other words, the adjuster rod  63  adjusts the target value Pset of the suction pressure Ps in accordance with the level of the discharge pressure Pd. Therefore, even if the discharge pressure Pd is so high that there is a great difference between the suction pressure Ps and the pressure Ps′, the opening of the control valve  40  is controlled such that the pressure Ps′ is stabilized in a desired pressure range. 
     The illustrated embodiment of FIGS. 1 to  3 , has the following advantages. 
     Sufficient refrigerant gas is constantly supplied to the crank chamber  3  by blowby gas from the cylinder bores  1   a  and gas flowing through the space  66 . Therefore, although the compressor uses the outlet control valve  40 , the inclination of the plates  17 ,  18  is quickly changed. 
     The space  66 , which conducts refrigerant gas from the discharge chamber  9  to the crank chamber  3 , is formed by the clearance between the adjuster rod  63  and the guide hole  62  in the outlet control valve  40 . Therefore, there is no need to form a passage for supplying gas from the discharge chamber  9  to the crank chamber  3 , which reduces the manufacturing cost. Thus, the compressor having the illustrated valve  40  is suitable for mass production. 
     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. Particularly, it should be understood that the invention may be embodied in the following forms. 
     As shown in FIG. 4, the diameter of the adjuster rod  63  may be substantially the same as the diameter of the guide hole  62 . In this case, one or more grooves  67  are formed in the circumferential surface of the rod  63 . The number of the grooves  67  is three in the drawing. The grooves  67  function in the same way as the space  66  of FIGS. 2 and 3. Alternatively, guide grooves  68  may be formed in the inner wall of the guide wall  62  as illustrated by two-dot chain line in FIG.  4 . 
     The plug  43 , the disk spring  44 , the seal ring  45  and the ports  56  may be omitted. That is, as shown in FIG. 5, the upper portion of the valve chamber  46  may function as the pressure sensing chamber  53  and the chamber  53  may be connected to the suction chamber  8  by the passage  35 . This valve functions like the valve  40  of FIG.  2 . 
     As a pressure sensing body, a bellows may replace the diaphragm  54 . 
     The control valve  40  of FIGS. 2 and 5 is a self-controlled type, which operates in accordance with the suction pressure Ps. However, the present invention may be embodied in an externally controlled type control valve, which is controlled by electrical signals supplied from an outside controller. 
     The outlet control valve according to the illustrated embodiments may be used in compressors other than the compressor of FIG. 1, which has the drive plate  17  and the wobble plate  18 . For example, the present invention may be embodied in swash plate type compressors, in which an inclined swash plate reciprocates pistons. 
     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.