Patent Publication Number: US-6217293-B1

Title: Variable displacement compressor

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a variable displacement compressor for vehicle air-conditioning system. More specifically, the present invention relates to a variable displacement compressor having a drive plate for reciprocating pistons, the inclination angle of which is varied. 
     FIGS. 3 and 4 show a conventional variable displacement compressor. A drive shaft  102  is rotatably supported in a housing  101 . The housing  101  includes cylinder bores  101   a,  a crank chamber  103 , a suction chamber  104 , and a discharge chamber  105 . A piston  106  is accommodated in each cylinder bore  101   a  to reciprocate. A rotor  107  is fixed to the drive shaft  102  in the crank chamber  103 . A drive plate, or a swash plate  108 , is accommodated in the crank chamber  103 . The drive shaft  102  penetrates the swash plate  108 . A hinge mechanism  109  is located between the rotor  107  and the swash plate  108 . The hinge mechanism  109  rotates the swash plate  108  together with the drive shaft  102  and the rotor  107  and permits the swash plate  108  to incline with respect to the drive shaft  102 . The pistons  106  are coupled to the swash plate  108 . 
     The drive shaft  102  is connected to an external drive source, or an engine  110 , of the vehicle without a clutch mechanism such as an electromagnetic clutch. The drive shaft  102  is constantly driven while the engine  110  is running. The swash plate converts the rotation of the drive shaft  102  into reciprocation of each piston  106 . Each piston  106  draws refrigerant gas from the suction chamber  104  to the corresponding cylinder bore  101   a  and compresses the gas. Then, the refrigerant gas is discharged from the cylinder bore  101   a  to the discharge chamber  105 . 
     A pressurizing passage  111  connects the crank chamber  103  to the discharge chamber  105 . A bleeding passage  112  connects the crank chamber  103  to the suction chamber  104 . A displacement control valve  113  is located in the pressurizing passage  111 . The control valve  113  is an electromagnetic valve and moves a valve body  113 b by exciting and de-exciting a solenoid  113   a.  This opens and closes the pressurizing passage  111 . When the solenoid  113   a  is excited, the control valve  113  closes the pressurizing passage  111 . When the solenoid  113   a  is de-excited, the control valve  113  opens the pressurizing passage  111 . 
     As shown in FIG. 3, when the pressurizing passage  111  is closed, the refrigerant gas does not flow from the discharge chamber  105  to the crank chamber  103 . Accordingly, the pressure in the crank chamber  103  decreases and the inclination angle of the swash plate  108  increases. This increases the piston stroke and displacement of the compressor. As shown in FIG. 4, when the pressuring passage  111  is opened, the refrigerant gas flows from the discharge chamber  105  to the crank chamber  103 . Accordingly, pressure in the crank chamber  103  increases and the inclination angle of the swash plate  108  decreases. This decreases the piston stroke and displacement of the compressor. 
     A suction passage  114  is formed in the housing  101  and connects an external refrigerant circuit to the suction chamber  104 . A shutter  115  engages the rear end of the drive shaft  102  and slides along the axis of the drive shaft  102 . The shutter  115  moves with the swash plate  108  and selectively opens and closes the suction passage  114 . As shown in FIG. 3, when the swash plate  108  is positioned at its maximum inclination angle by the excitation of solenoid  113   a,  the shutter  115  opens the suction passage  114 . Accordingly, the refrigerant gas flows from the external refrigerant circuit to the suction chamber  104 . As shown in FIG. 4, when the swash plate  108  is positioned at its minimum inclination angle by the demagnetization of the solenoid  113 a, the shutter  115  closes the suction  114 . Accordingly, refrigerant gas does not flow from the external refrigerant circuit to the suction chamber  104 . This stops the circulation of refrigerant gas between the external refrigerant circuit and the compressor. 
     The control valve  113  includes an electromagnetic valve and suddenly opens the pressurizing passage  111  when the solenoid  113   a  is demagnetized. Accordingly, high-pressure refrigerant gas of the discharge chamber  105  suddenly flows into the crank chamber. This suddenly increases pressure in the crank chamber  103  and reduces the inclination angle of the swash plate  108 . This increases friction on the engaging parts of the hinge mechanism  109 , the swash plate  108  and the drive shaft  102 , which produces vibration and noise. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to control the sudden change of pressure in the crank chamber and slows the change of inclination angle of the drive plate in a variable displacement compressor. 
     To achieve the above objective, the present invention provides a variable displacement compressor that varies the displacement in accordance with the inclination angle of a drive plate located in a crank chamber. The compressor is structured as follows. A piston is connected to the drive plate and is reciprocated by movement of the drive plate. An adjusting mechanism for adjusting the pressure in the crank chamber includes a control passage connected to the crank chamber for permitting passage of a fluid and a control valve located in the control passage for selectively opening and closing the control passage. The inclination of the drive plate is varied in accordance with pressure in the crank chamber and the piston stroke varies in accordance with the drive plate inclination to vary the displacement. A fixed restrictor is located in the control passage, to limit the flow rate of the fluid in the control passage. 
     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 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. 
     FIG. 1 is a cross sectional view of a variable displacement compressor according to one embodiment of the present invention; 
     FIG. 1A is an enlarged view of the encircled area  1 A of FIG. 1; 
     FIG. 2 is a cross sectional view of the variable displacement compressor of FIG. 1 when the swash plate is minimally inclined; 
     FIG. 3 is a cross sectional view of a prior art variable displacement compressor; and 
     FIG. 4 is a cross sectional view of the variable displacement compressor of FIG. 3 when the swash plate is minimally inclined. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A variable displacement compressor according to one embodiment of the present invention will now be described. As shown in FIGS. 1 and 2, a front housing  11  is joined and secured to the front end of a cylinder block  12 . A rear housing  13  is joined and secured to the rear end of the cylinder block  12  through a valve plate  14 . As shown in FIG. 1A, the valve plate  14  includes a main plate  14   a,  a first sub-plate  14   b,  a second sub-plate  14   c,  and a retainer plate  14   d.  The first sub-plate  14   b  is located on the front side of the main plate  14   a.  The second sub-plate  14   c  is located on the rear side of the main plate  14   a.  The retainer plate  14   d  is located on the rear side of the second sub-plate  14   c.    
     A crank chamber  15  is defined between the front housing  11  and the cylinder block  12 . A drive shaft  16  passes through the crank chamber  15  and is rotatably supported by the front housing  11  and the cylinder block  12 . 
     A pulley  17  is rotatably supported at the front end of the front housing  11  through an annular bearing  18  and is secured to the drive shaft  16 . The pulley  17  is connected to an outer drive source, or an engine  20 , without a clutch mechanism such as an electromagnetic clutch. Accordingly, the engine  20  rotates the drive shaft  16  through a belt  19  and the pulley  17 . 
     A rotor  22  is secured to the drive shaft  16  in the crank chamber  15 . A drive plate, or a swash plate  23 , is inclinably and slidably supported by the drive shaft  16 . The swash plate  23  slides along the axis L of the drive shaft  16 . The drive shaft  16  penetrates a through hole  23   a  in the center of the swash plate  23 . A hinge mechanism  24  is located between the rotor  22  and the swash plate  23 . 
     The hinge mechanism  24  will now be described. A pair of guide pins  21  (only one shown) are attached to the front surface of the swash plate  23 . Each of the guide pins  21  includes a spherical head  21   a.  A support arm  25  projects from the rear surface of the rotor  22 . The support arm  25  includes a pair of guide holes  25   a.  Each spherical head  21   a  of the guide pins  21  is received in the corresponding guide hole  25   a.    
     The engagement of the guide pin  21  with the support arm  25  causes the swash plate  23  to rotate integrally with the drive shaft  16  and the rotor  22 . The engagement also permits the swash plate  16  to move along the axis L of the drive shaft  16  and to incline with respect to the drive shaft  16 . As the swash plate  23  moves toward the cylinder block  12 , the inclination angle of the swash plate  23  decreases. A spring  26  is located between the rotor  22  and the swash plate  23 . The spring  26  urges the swash plate  23  rearward, or toward its minimum inclination. As shown in FIG. 1, when the swash plate  23  abuts against the rotor  22 , the swash plate  23  is positioned at its maximum inclination. 
     A shutter bore  27  is formed in the center of the cylinder block  12 . A cylindrical shutter  28 , which has one closed end, is slidably accommodated in the shutter bore  27 . An opener spring  29  is located between a step on the inner surface of the shutter bore  27  and the shutter  28  and urges the shutter  28  toward the swash plate  23 . 
     The rear end of the drive shaft  16  is received in the shutter  28 . A radial bearing  15  is fixed to the inner surface of the shutter  28  and rotatably supports the drive shaft  16 . The radial bearing  30 , together with the shutter  28 , slides axially on the drive shaft  16 . 
     A suction passage  32  is formed in the center of the rear housing  13  and the valve plate  14 . The inner end of the suction passage  32  is open to the shutter bore  27 . A positioning surface  33  is formed on the valve plate  14  around the opening of the suction passage  32 . The shutter  28  has a shutting surface  34 , which can contact the positioning surface  33 . When the shutting surface  34  contacts the positioning surface  33 , the suction passage  32  is disconnected from the shutter bore  27 . 
     A thrust bearing  35  is located between the swash plate  23  and the shutter  28  and is slidably supported on the drive shaft  16 . The thrust bearing  35  is held between the swash plate  23  and the shutter  28  by the force of the opener spring  29 . 
     The swash plate  23  moves rearward (rightward in FIG. 1) as its inclination angle decreases. In this movement, the swash plate  23  pushes the shutter  28  through the thrust bearing  35 . Accordingly, the shutter  28  moves toward the positioning surface  33  against the force of the opener spring  29 . When the shutting surface  34  of the shutter  28  contacts the positioning surface  33 , the swash plate  23  is positioned at its minimum inclination angle. The minimum inclination angle of the swash plate  23  is slightly greater than zero degrees. The inclination angle of the swash plate  23  is measured with respect to a plane perpendicular to the axis L of the drive shaft  16 . 
     Cylinder bores  12   a  (only one shown) are formed in the cylinder block  12 . A single-headed piston  36  is accommodated in each of the cylinder bores  12   a.  Each piston  36  is coupled to the periphery of the swash plate  23  through a pair of shoes  37 . Each piston  36  reciprocates in the corresponding cylinder bore  12   a  as the swash plate  23  rotates. 
     A suction pressure zone, or a suction chamber  38 , is formed in the rear housing  13 . A discharge pressure zone, or a discharge chamber  39 , is also formed in the rear housing  13 . A suction port  40  and a discharge port  42  are formed in the main plate  14   a  to correspond to each cylinder bore  12   a.  A suction valve  41  is formed in the first sub-plate  14   b  to correspond to each suction port  40 . A discharge valve  43  is formed in the second sub-plate  14   c  to correspond to each discharge port  42 . A retainer  31  is formed in the retainer plate  14   d  to correspond to each discharge valve  43 . 
     When the piston  36  moves from the top dead center position to the bottom dead center position, refrigerant gas in the suction chamber is drawn to the cylinder bore  12   a  through the suction port and the suction valve  41 . When the piston  36  moves from the bottom dead center position to the top dead center position, refrigerant in the cylinder bore  12   a  is compressed to a predetermined pressure and is discharged to the discharge chamber  39  through the discharge port  42  and the discharge valve  43 . The retainer  31  determines the maximum opening position of the discharge valve  43 . 
     A thrust bearing  44  is located between the rotor  22  and the inner wall of the front housing  11 . A thrust bearing  44  receives a compression reaction force applied to the pistons  36  through the swash plate  23 , hinge mechanism  24 , and the rotor  22 . 
     The suction chamber  38  is connected to the shutter bore  27  through a passage  45 , which is formed in the valve plate  14 . When the shutter  28  contacts the positioning surface  33 , the passage  45  is disconnected from the suction passage  32 . An axial passage  46  is formed in the drive shaft  16  to connect the crank chamber  15  with the inside of the shutter  28 . A pressure release passage  47  is formed in the wall of the shutter  28 . The inside of the shutter  28  is connected to the internal space of the shutter bore  27  through the release passage  47 . The axial passage  46 , the release passage  47 , and the passage  45  form a bleeding passage. The bleeding passage connects the crank chamber  15  to the suction chamber  38 . The release passage  47  functions as a fixed restrictor and restricts the flow of refrigerant from the crank chamber  15  to the suction chamber  38 . 
     A control passage, or a pressurizing passage  48 , connects the discharge chamber  39  to the crank chamber  15 . A displacement control valve  49 , which is an electromagnetic valve, is installed in the rear housing  13 . The control valve  49  is located in the pressurizing passage  48  and selectively opens and closes the pressurizing passage  48 . 
     The control valve  49  will now be described in detail. The control valve  49  includes a valve chamber  50 , which is located in the pressurizing passage  48 , and a valve hole  52 , which is connected to the valve chamber  50 . A spherical valve body  51  located in the valve chamber  50  to face the valve hole  52 . The valve chamber  50  and the valve hole  52  form part of the pressurizing passage  48 . 
     A solenoid  53  includes a fixed metal core  54 , a movable metal core  55 , and a coil  56 . A rod  57  transmits the movement of the movable core  55  to the valve body  51 . An opener spring  58  urges the valve body  51  to open the valve hole  52  through the movable core  55  and the rod  57 . The coil  56  is arranged around the fixed core  54  and the movable core  55 . 
     When the solenoid  53  is excited, that is, when electric current is supplied to the coil  53 , an electromagnetic attraction force is generated between the cores  54 ,  55 . This moves the movable core  55  toward the fixed core  54  against the force of the opener spring  58 . As a result, the valve body  51  closes the valve hole  52  as shown in FIG.  1 . When the solenoid is de-excited, that is, when the supply of electric current to the coil  56  is stopped, the electromagnetic attraction force between the cores  54 ,  55  disappears. Accordingly, the force of the opener spring  58  causes the movable core  55  to move away from the fixed core  54 , and as shown in FIG. 2, the valve body  51  opens the valve hole  52 . 
     The pressurizing passage  48  includes an upstream passage  48   a,  which is located between the discharge chamber  39  and the valve chamber  50  of the control valve  49 , and a downstream passage  48   b,  which is located between the valve chamber  50  and the crank chamber  15 . The upstream passage  48   a  is formed in the rear housing  13 . The downstream passage  48   b  is formed in the rear housing  13 , the valve plate  14 , and the cylinder block  12 . 
     A fixed restrictor  59  is located in the pressurizing passage  48 . The restrictor  59  is formed by reducing the cross-sectional area of a small part of the pressurizing passage  48 . The restrictor  59  is preferably located in the downstream passage  48   b.  In detail, the restrictor  59  is formed as shown in FIG.  1 A. That is, a part of the downstream passage  48   b  that is located in the main plate  14   a  of the valve plate  14  has a smaller diameter than the remainder of the passage. 
     An external refrigerant circuit  61  connects the suction passage  32  to the discharge chamber  39 . The external refrigerant circuit  61  includes a condenser  62 , an expansion valve  63 , and an evaporator  64 . 
     A temperature sensor  65  is located near the evaporator  64 . The temperature sensor  65  detects the temperature of the evaporator  64  and outputs a detection signal to a computer  66 . The computer  66  controls the excitation and de-excitation of the solenoid  53  according to the detection signal from the temperature sensor  65 . When the detected temperature falls below a predetermined temperature while the air-conditioner switch  67  is on, the computer  66  de-excites the solenoid  53 . Frost occurs in the evaporator  64  at temperatures below the predetermined temperature. When the air-conditioner switch  67  is turned off, the computer  66  also de-excites the solenoid  53 . 
     As shown in FIG. 2, when the solenoid  53  is de-excited, the control valve  49  opens the pressurizing passage  48 . Accordingly, the high-pressure refrigerant gas of the discharge chamber  39  flows to the crank chamber  15  through the pressurizing passage  48 , which increases the pressure in the crank chamber  15 . As a result, the swash plate  23  is moved to the minimum inclination and the displacement of the compressor is minimized. 
     When the swash plate  23  is at the minimum inclination, the shutter  28  contacts the positioning surface  33  and closes the suction passage  32 . Accordingly, refrigerant gas cannot flow from the external refrigerant circuit  61  to the suction chamber  38 , and circulation of refrigerant gas between the external refrigerant circuit  61  and the compressor is stopped. 
     Since the minimum inclination angle of the swash plate  23  is not zero degrees, the pistons  36  continue to reciprocate with a very short stroke. Accordingly, a small amount of refrigerant gas continues to be drawn from the suction chamber  38  to the cylinder bores  12   a  and discharged from the cylinder bores  12   a  to the discharge chamber  39 . That is, when the inclination angle of the swash plate  23  is minimized, refrigerant gas circulates through the discharge chamber  39 , the pressurizing passage  48 , the crank chamber  15 , the axial passage  46 , the release passage  47 , the suction chamber  38 , and the cylinder bores  12   a.  The lubricant oil contained in the refrigerant gas also circulates and lubricates parts of the compressor. 
     When the solenoid  53  is excited, the pressurizing passage  48  is closed as shown in FIG.  1 . Since refrigerant gas from the crank chamber  15  continuously flows to the suction chamber  38  through the axial passage  46 , the release passage  47  and the passage  45 , the pressure in the crank chamber  15  is lowered gradually. As a result, the swash plate  23  moves from the minimum inclination to the maximum inclination angle, and the displacement of the compressor is maximized. When the swash plate  23  moves away from the minimum inclination position, the shutter  28  opens the suction passage  32 . Accordingly, refrigerant gas flows from the external refrigerant circuit  61  to the suction chamber  38 . This permits the circulation of refrigerant between the external refrigerant circuit  61  and the compressor. 
     The fixed restrictor  59  is located in the pressurizing passage  48 . When the pressurizing passage  48  is suddenly opened by the de-excitation of the solenoid  53 , the restrictor  59  limits the flow rate of refrigerant from the discharge chamber  39  to the crank chamber  15 . Accordingly, pressure in the crank chamber  15  gradually increases and the inclination angle of the swash plate  23  gradually decreases. Therefore, strong friction between the guide pin  21  and the support arm  25  and between the swash plate  23  and the drive shaft  16  is prevented. This reduces vibration and noise. 
     Under the normal operation of the compressor, the compression load applied to the pistons  36  is received in a stable manner by the thrust bearing  44  through the swash plate  23 , the hinge mechanism  24  and the rotor  22 . However, it has been confirmed by the inventors&#39; experiments that, if the inclination angle of the swash plate  23  is suddenly reduced, the compression load from the pistons  36  is applied in an unstable manner to the swash plate  23  and is not properly received by the thrust bearing  44 . This causes the swash plate  23  to move in an unstable manner and produces excessive force on the joint between the guide pin  21  and the support arm  25 , which generates chatter. The restrictor  59  prevents this problem. 
     The fixed restrictor  59  is located in the downstream passage  48   b  of the pressurizing passage  48 , between the control valve  49  and the crank chamber  15 . The restrictor  59  reduces the flow rate of refrigerant that flows from the control valve  49  to the crank chamber  15 . When the flow rate of refrigerant is reduced, atomized lubricant oil in the refrigerant gas is more easily separated from the gas and adhered to the inner wall of the suction passage  48 . The lubricant oil adhered to the inner wall is then moved to the crank chamber  15  by the flow of the refrigerant gas. The lubricant oil in the crank chamber  15 , which has been separated from the refrigerant gas, remains in the crank chamber  15  for a relatively long time. Therefore, the sliding surfaces located in the crank chamber  15  are adequately lubricated. 
     If the fixed restrictor  59  were located in the upstream passage  48   a,  lubricant oil separated from the refrigerant gas by the restrictor  59  would tend to remain in the control valve  49  and not easily reach the crank chamber  15 . 
     The fixed restrictor  59  is simply formed by reducing the diameter of an opening in a section of the pressurizing passage  48 . 
     The fixed restrictor  59  is formed in the valve plate  14 , and more specifically, in the main plate  14   a.  This facilitates forming the restrictor  59 , compared to forming a restrictor in the cylinder block  12 . If a restrictor were formed in the cylinder block  12 , small-diameter drilling would be necessary, which is troublesome and expensive. In contrast, in the present embodiment, the restrictor  59 , which may have an arbitrary diameter, can be easily and precisely formed in the main plate  14 a by punching before assembling the main plate  14   a.    
     The present invention can further be embodied as follows. 
     The fixed restrictor  59  may be formed in other part of the valve plate  14 , that is, the first sub-plate  14   b,  the second sub-plate  14   c  or the retainer plate  14   d.    
     The fixed restrictor  59  may be located in other parts of the downstream passage  48   b.    
     The fixed restrictor  59  may be formed in the upstream passage  48   a.    
     The fixed restrictor  59  may be formed in the control valve  49 . 
     A pin having a diameter smaller than the pressurizing passage  48  may be arranged inside the pressurizing passage  48  to function as a fixed restrictor. 
     Opposite to the embodiments of FIGS. 1 and 2, the solenoid of the control valve may be excited to open the pressurizing passage  48  and de-excited to close the passage  48 . In this case, the excitation of the solenoid suddenly opens the pressurizing passage  48 . However, the fixed restrictor  59  prevents a sudden increase of pressure in the crank chamber  15 . 
     The control valve  49  and the fixed restrictor  59  may be located in the bleeding passage that connects the crank chamber  15  to the suction chamber  38 . In this case, the control valve  49  controls the flow of refrigerant gas from the crank chamber  15  to the suction chamber  38 , thus controlling the displacement of the compressor. Though the excitation or de-excitation of the solenoid  53  suddenly opens the bleeding passage, the fixed restrictor  59  prevents a sudden decrease of pressure in the crank chamber  15 , thus preventing a sudden increase of the inclination angle of the swash plate  23 . 
     Other types of control valves may be used instead of an electromagnetic valve. For example, a control valve having a pressure sensitive member such as bellows may be used. In this case, the pressure sensitive member moves a valve body in accordance with the pressure (suction pressure) of refrigerant gas drawn to the compressor. The movement of the valve body adjusts the opening size of a valve hole. In addition to the pressure sensitive member, the control valve may include a solenoid that variably urges the valve body. In this case, the forces applied to the valve body from the pressure sensitive member and the solenoid determine the opening size of the valve hole. 
     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.