Patent Publication Number: US-6659733-B1

Title: Variable displacement compressor

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a variable displacement compressor capable of changing its displacement by changing the crank chamber pressure. 
     FIG. 5 shows a swash plate compressor to be used in a vehicle air conditioner. A crank chamber  82  is defined between a front housing  80  and a cylinder block  81 . A drive shaft  83 , which is driven by a vehicle engine, is supported by the crank chamber  82  and the cylinder block  81 . The crank chamber  82  contains a lug plate  84  that rotates integrally with the drive shaft  83 . A swash plate  85  is connected to the lug plate  84  through a hinge mechanism  102 . 
     A plurality of cylinder bores  86  are defined in the cylinder block  81 . Each cylinder bore  86  contains a piston  87 . The drive shaft  83  rotates the swash plate  85  to make each piston  87  connected to the swash plate  85  reciprocate between a top dead center position and a bottom dead center position within the cylinder bores  86 . The stroke of each piston  87  is changed depending on the inclination angle of the swash plate  85  to change the displacement of the compressor. 
     A valve plate  88  is located between the cylinder block  81  and a rear housing  89 . The rear housing  89  contains a suction chamber  90  and a discharge chamber  91 . As each piston  87  reciprocates, a refrigerant gas in the suction chamber  90  is caused to flow into the cylinder bore  86 . After the refrigerant gas is compressed in the cylinder bore  86 , it flows into the discharge chamber  91 . 
     The inclination angle of the swash plate  85  is determined by controlling the internal pressure of the crank chamber  82  (crank chamber pressure) with an electromagnetic control valve  93 . A supply passage  92  connects the discharge chamber  91  and the crank chamber  82  to each other through the electromagnetic control valve  93 . The electromagnetic control valve  93  controls the quantity of refrigerant gas flowing into the crank chamber  82  through the supply passage  92 . A bleed passage  94  connects the crank chamber  82  and the suction chamber  90  to each other. The refrigerant gas in the crank chamber  82  is allowed to flow into the suction chamber  90  through the bleed passage  94  constantly at a predetermined flow rate. 
     When no electric current is supplied to the control valve  93 , the valve  93  opens fully. Thus, the refrigerant gas is introduced to the crank chamber  82  at the maximum flow rate through the supply passage  92 . This increases the crank chamber pressure to cause the swash plate  85  to assume the minimum inclination angle. The control valve  93  closes when an electric current is supplied thereto, and the refrigerant gas cannot flow from the discharge chamber  91  into the crank chamber  82 . This reduces the crank chamber pressure to cause the swash plate  85  to assume the maximum inclination angle. 
     The swash plate  85  assumes the maximum inclination angle and the minimum inclination angle when it abuts against the lug plate  84  and against a restriction ring  101  fixed to the drive shaft  83 , respectively. 
     The clearance between the drive shaft  83  and the front housing  80  is sealed with a lip seal  95 . The distal end of the drive shaft  83  protrudes outward through the housing. An electromagnetic clutch  96  is attached to that end of the drive shaft  83 . The electromagnetic clutch  96  includes a fixed clutch disc  96   c  supported by the front housing  80 , a movable clutch disc  96   a  fixed to the distal end of the drive shaft  83  to oppose the fixed clutch disc  96   c , and an electromagnetic coil  96   b  for moving the movable clutch disc  96   a . When an electric current is supplied to the electromagnetic coil  96   b , the movable clutch disc  96   a  is brought into contact with the fixed clutch disc  96   c  to transmit the driving force of an engine E to the drive shaft  83 . 
     A thrust bearing  97  is located between the lug plate  84  and the front housing  80 . The inner end of the drive shaft  83  is inserted to an insertion hole  98  defined in the cylinder block  81  and is supported therein. The insertion hole  98  contains a support spring  100 , which is a compression spring. The support spring  100  is located between a snap ring  99  contained in the insertion hole  98  and a thrust bearing  103  attached to the inner end of the drive shaft  83 . The support spring  100  urges the drive shaft  83  axially forward with respect to the front housing  80  (leftward in FIG.  5 ). The support spring  100  controls axial backlash of the drive shaft  83 . 
     When a power switch of the air conditioner is turned off or when the engine E is stopped, the supply of electric current to the electromagnetic clutch  96  and to the control valve  93  is interrupted. Thus, the control valve  93  opens fully to let the refrigerant gas flow through the supply passage  92  into the crank chamber  82 . Here, the crank chamber pressure increases temporarily to an excessively high degree due to the abrupt inflow of the gas. The swash plate  85  having moved to the minimum inclination angle position (indicated by the chain double-dashed line in FIG. 5) is then pressed against the restriction ring  101  with an excessive force. As a result, the drive shaft  83  retracts along its axis against the force of the support spring  100 . 
     The displacement of the compressor is sometimes minimized to reduce the load of the compressor applied to the engine E during acceleration of a vehicle. In this case, the refrigerant gas flows rapidly into the crank chamber  82  as soon as the control valve  93  opens fully, which increases the crank chamber pressure temporarily to an excessively high degree. Thus, the drive shaft  83  retracts axially. 
     The retraction of the drive shaft  83  moves the pistons  87  toward the valve plate  88 . Thus, each piston  87  impinges upon the valve plate  88  at the top dead center position and causes hammering or vibration. 
     The retraction of the drive shaft  83  also moves the movable clutch disc  96   a  of the electromagnetic clutch  96  backward. This brings the movable clutch disc  96   a  into contact with the fixed clutch disc  96   c , although the electromagnetic coil  96   b  is demagnetized. As a result, the two clutch discs  96   a  and  96   c  generate friction, abnormal noise and heat. 
     Further, if the drive shaft  83  retracts, the axial position of the drive shaft  83  changes with respect to the lip seal  95  held in the front housing  80 . Normally, the drive shaft  83  is in contact with the lip seal  95  at a predetermined axial position. The drive shaft  83  has a foreign matter such as sludge deposited on its outer surface at a position spaced from the predetermined axial position. Therefore, if the axial position of the drive shaft  83  changes with respect to the lip seal  95 , the sludge is caught between the lip seal  95  and the drive shaft  83 . This lowers the sealing performance of the lip seal  95  and permits gas leakage from the crank chamber  82 . 
     To solve the problems described above, it is possible to use a support spring  100  having a greater force so that the drive shaft  83  is not retracted by an excessively increased crank chamber pressure. In this case, however, excessive loads are applied to the thrust bearings  97  and  103 , which causes power loss in the compressor. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a variable displacement compressor capable of preventing shifting of the drive shaft in the axial direction. 
     In order to attain the above object, the present invention provides a compressor capable of changing its displacement depending on the internal pressure of the crank chamber. The compressor has a housing. The housing contains a cylinder block and a valve plate to be connected to the cylinder block. The cylinder block contains cylinder bores and a supporting hole. A piston is housed in each cylinder bore to compress gas drawn into the cylinder bore through the valve plate. The compressed gas is discharged from the cylinder bore through the valve plate. A drive shaft supported in the housing has an end portion to be inserted into the supporting hole. A drive plate is connected operationally to the pistons to convert the rotation of the drive shaft into reciprocating motions of the pistons. The drive plate is supported on the drive shaft and can incline. The drive plate inclines between a maximum inclination angle position and a minimum inclination angle position depending on the internal pressure of the crank chamber. The inclination angle of the drive plate determines the piston stroke and the compressor displacement. A movable body is housed in the supporting hole to be able to move in the axial direction. The end portion of the drive shaft is supported in the cylinder block through the movable body. An urging member urges the movable body toward the drive plate to bring the former into abutment against the latter. The movable body moves along the axis of the drive shaft as the drive plate is inclined. When the drive plate is located at the minimum inclination angle position, the valve plate receives force from the drive plate through the movable body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view showing a variable displacement compressor according to a first embodiment of the present invention, with the swash plate assuming the maximum inclination angle; 
     FIG. 2 is a partial enlarged cross-sectional view of the compressor shown in FIG. 1; 
     FIG. 3 is a cross-sectional view showing the compressor shown in FIG. 1, with the swash plate assuming the minimum inclination angle; 
     FIG. 4 is a cross-sectional view showing a variable displacement compressor according to a second embodiment; and 
     FIG. 5 is a cross-sectional view showing a prior art variable displacement compressor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described by way of a first embodiment referring to FIGS. 1 to  3 , in which the present invention is embodied in a swash plate variable displacement compressor employed in a vehicular air conditioner. 
     As shown in FIG. 1, the compressor  10  has a housing composed of a front housing  11 , a cylinder block  12 , a rear housing  13  and a valve plate  14 . The cylinder block  12  is fixed to the front housing  11 . A crank chamber  15  is defined between the front housing  11  and the cylinder block  12 . The rear housing  13  is fixed to the cylinder block  12  through the valve plate  14 . 
     A drive shaft  16  is rotatably supported in the front housing  11  and the cylinder block  12 . The drive shaft  16  is driven by a vehicular engine E as an external drive source. The drive shaft  16  is supported in the front housing  11  through a radial bearing  17 . A first end  16   a  of the drive shaft  16  extends outward through the front housing  11 . A supporting hole  18  is defined substantially at the center of the cylinder block  12 . A second end  16   b  of the drive shaft  16  is located in the supporting hole  18 . The second end  16   b  is supported in the cylinder block  12  through a cylindrical body  19 , or a movable body, located in the supporting hole  18 . 
     A supporting cylinder  11   a  is formed at the distal end of the front housing  11 . A lip seal  20  is located between the drive shaft  16  and the supporting cylinder  11   a  to seal the crank chamber  15 . The lip seal  20  contains a plurality of lip rings and a plurality of backup rings which are built up alternately. The drive shaft  16  is brought into contact with the lip seal  20  at a predetermined axial position. 
     An electromagnetic clutch  21  is located between the first end  16   a  of the drive shaft  16  and the engine E. The electromagnetic clutch  21  selectively transmits the driving force of the engine E to the drive shaft  16 . The electromagnetic clutch  21  contains a rotor  23  serving as a fixed clutch disc, a hub  24 , an armature  25  serving as a movable clutch disc, and an electromagnetic coil  26 . The rotor  23  is rotatably supported at the front end of the front housing  11  through an angular bearing  22 . A belt  27  is wrapped around the rotor  23  to transmit the power of the engine E to the rotor  23 . The hub  24 , which is resilient, is fixed to the front end of the drive shaft  16 . The hub  24  supports the armature  25 . The armature  25  is located to oppose the rotor  23 . The electromagnetic coil  26  is supported on the front wall of the front housing  11  to oppose the armature  25  across the rotor  23 . 
     When the electromagnetic coil  26  is magnetized, or when the electromagnetic clutch  21  is turned on, the armature  25  is pulled by the rotor  23  into contact with the rotor  23  against the resilience of the hub  24 . Thus, the driving force of the engine E is transmitted to the drive shaft  16 . When the electromagnetic coil  26  is demagnetized in this state, or when the electromagnetic clutch  21  is turned off, the armature  25  is spaced from the rotor  23  to interrupt transmission of power from the engine E to the drive shaft  16 . 
     A lug plate  30  is fixed to the drive shaft  16  within the crank chamber  15 . A thrust bearing  31  is located between the lug plate  30  and the internal wall surface of the front housing  11 . A hinge mechanism  33  connects the lug plate  30  to a swash plate  32 , or a drive plate. 
     The swash plate  32  is supported on the drive shaft  16  to incline with respect to the drive shaft  16  and to move along the drive shaft  16  axially. The swash plate  32  has a counterweight  36  protruding toward the lug plate  30 . The swash plate  32  also has an abutting portion  34  protruding toward the cylinder block  12 . 
     As shown in FIGS. 1 and 3, the hinge mechanism  33  is composed of a pair of guide pins  38  extending from the swash plate  32  and a pair of supporting arms  37  extending from the lug plate  30 . A guide hole  37   a  is formed through each supporting arm  37  at the distal end portion thereof. The guide pins  38  are inserted into the opposing guide holes  37   a  respectively. The hinge mechanism  33  rotates the swash plate  32  integrally with the drive shaft  16 . The hinge mechanism  33  also guides the movement of the swash plate  32  in the axial direction of the drive shaft  16  and the inclination of the swash plate  32 . 
     A first coil spring  39 , which is a compression spring, is fitted on the outer surface of the drive shaft  16  between the lug plate  30  and the swash plate  32 . The first coil spring  39  urges the swash plate  32  backward (rightward in FIG. 1) to reduce the inclination angle of the swash plate  32 . 
     A plurality of cylinder bores  40  are defined in the cylinder block  12  to extend in the axial direction of the drive shaft  16 . The cylinder bores  40  are defined at predetermined intervals on a circle centered on the axis of the drive shaft  16 . Each cylinder bore  40  contains a single-headed piston  41 . Each piston  41  is connected to the swash plate  32  through a pair of shoes  42   a . The rotational motion of the swash plate  32  is converted through the shoes  42   a  into reciprocating motion of the pistons  41  in the cylinder bores  40 . 
     A suction chamber  43  and a discharge chamber  44  are defined in the rear housing  13  to form a suction pressure region and a discharge pressure region, respectively. The valve plate  14  has a suction port  45 , a suction valve  46 , a discharge port  47  and a discharge valve  48  for each cylinder bore  40 . In the stroke in which a piston  41  travels from the top dead center position to the bottom dead center position, the refrigerant gas in the suction chamber  43  opens the suction valve  46  and flows through the suction port  45  into the opposing cylinder bore  40 . In the stroke in which the piston  41  travels from the bottom dead center position to the top dead center position, the refrigerant gas in the cylinder bore  40  is compressed to a predetermined pressure and then opens the discharge valve  48  and is discharged through the discharge port  47  into the discharge chamber  44 . 
     An axial passage  50  is defined in the drive shaft  16  to connect the crank chamber  15  to the supporting hole  18 . A communicating port  49  is defined in the valve plate  14  to connect the supporting hole  18  to the suction chamber  43 . In this embodiment, the axial passage  50 , the supporting hole  18  and the communicating port  49  constitute a bleed passage for bleeding the gas from the crank chamber  15  into the suction chamber  43 . 
     A supply passage  51  is defined through the cylinder block  12 , the valve plate  14  and the rear housing  13  to connect the crank chamber  15  to the discharge chamber  44 . An electromagnetic control valve  52  is located in the supply passage  51  to change the flow rate of refrigerant gas flowing from the discharge chamber  44  into the crank chamber  15 . The electromagnetic control valve  52  is controlled based on external commands. 
     The electromagnetic control valve  52  is an electromagnetic proportional control valve and has a solenoid  57  containing a coil  53 , a fixed iron core  54 , a movable iron core  55  and a return spring  56 . The return spring  56  urges the movable iron core  55  away from the fixed iron core  54 . When an electric current is supplied to the coil  53 , the movable iron core  55  shifts toward the fixed iron core  54  against the force of the return spring  56 . A valve body  59  is connected to the movable iron core  55 . A valve hole  58  is defined in the supply passage  51 . The movable iron core  55  makes the valve body  59  change the opening degree of the valve hole  58  depending on the value of electric current supplied to the coil  53 . 
     As shown in FIG. 2, a cylindrical supporting hole  18  is defined through the cylinder block  12  to extend along the axis of the drive shaft  16 . The cylindrical body  19  is contained in the supporting hole  18  to be movable in the axial direction. The cylindrical body  19  is brought into sliding contact with the inner surface of the supporting hole  18 . The cylindrical body  19  has a large-diameter portion  60  and a small-diameter portion  61 . 
     A radial bearing  62  is fixed to the inner surface of the large-diameter portion  60 . The second end  16   b  of the drive shaft  16  is supported in the cylindrical body  19  to rotate through the radial bearing  62  and to move axially . A thrust bearing  63  is located between the end face of the cylindrical body  19  and the abutting portion  34  of the swash plate  32 . The thrust bearing  63  permits rotation of the swash plate  32  and the cylindrical body  19  relative to each other. 
     A step  64  is formed between the large-diameter portion  60  and the small-diameter portion  61 . A second coil spring  66  is located as an urging member between the step  64  and a snap ring  65  fixed to the inner circumference of the supporting hole  18 . 
     The second coil spring  66  urges the cylindrical body  19  toward the swash plate  32  such that the thrust bearing  63  abuts against the abutting portion  34  of the swash plate  32 . The second coil spring  66  also urges the drive shaft  16  forward through the cylindrical body  19 , the thrust bearing  63 , the swash plate  32 , the hinge mechanism  33 , the first coil spring  39  and the lug plate  30 . As a result, axial backlash of the drive shaft  16  is suppressed. 
     The inclination angle of the swash plate  32  is determined by various moments acting upon it, including a moment based on the centrifugal force acting upon the rotating swash plate  32 ; moments based on the inertia forces of the reciprocating pistons  41 ; moments based on the forces of the coil springs  39  and  66 ; and a moment based on the gas pressure acting upon each piston  41 . The moment based on the gas pressure includes the moment based on the internal pressure of the crank chamber  15  (crank chamber pressure) and the moment based on the internal pressure of each cylinder bore  40  (bore pressure). 
     In this embodiment, the inclination angle of the swash plate  32  is controlled by changing the crank chamber pressure with the control valve  52 . A reduction in the crank chamber pressure increases the inclination angle of the swash plate  32  and increases the stroke of each piston  41 . As a result, the displacement of the compressor is increased. Meanwhile, an increase in the crank chamber pressure reduces the inclination angle of the swash plate  32  and reduces the stroke of each piston  41 . As a result, the displacement of the compressor is reduced. If the compressor is stopped, and the crank chamber pressure is equalized with the bore pressure, the swash plate  32  is located at the minimum inclination angle position by the forces of the springs  39  and  66 . 
     As shown in FIG. 1, when the counterweight  36  abuts against the lug plate  30 , the swash plate  32  is located at the maximum inclination angle position. Meanwhile, as shown in FIG. 3, when the cylindrical body  19  abuts against the valve plate  14 , the swash plate  32  is regulated to be at the minimum inclination angle position. Here, the cylindrical body  19  does not block the communicating port  49 . 
     The suction chamber  43  and the discharge chamber  44  are connected to each other through an external refrigerant circuit  70 , as shown in FIG.  1 . The external refrigerant circuit  70  includes a condenser  71 , an expansion valve  72  and an evaporator  73 . A controller  74  controls the value of electric current to be supplied to the control valve  52  to change the opening degree thereof based on external information from various sensors or selecting switches (not shown). 
     The operation of the compressor having the constitution described above will be described below. 
     When a request for cooling is output to the controller  74  when the engine E is operating, the electromagnetic clutch  21  connects the drive shaft  16  to the engine E based on a command from the controller  74 . Thus, the compressor is started to allow each piston  41  to reciprocate with a stroke that depends on the inclination angle of the swash plate  32 . As a result, the refrigerant gas circulates through the external refrigerant circuit  70  and the compressor. 
     When the controller  74  reduces the opening degree of the control valve  52 , the quantity of refrigerant gas flowing into the crank chamber  15  is reduced to lower the crank chamber pressure. This increases the inclination angle of the swash plate  32  and increases the stroke of each piston  41  and the displacement of the compressor  10 . 
     When the controller  74  increases the opening degree of the control valve  52 , the flow rate of refrigerant gas flowing into the crank chamber  15  increases, which increases the crank chamber pressure. This reduces the inclination angle of the swash plate  32 , the stroke of each piston  41 , and the displacement of the compressor  10 . 
     The cylindrical body  19  is pressed against the swash plate  32  by the second coil spring  66 . Thus, the cylindrical body  19  moves along the drive shaft  16  with the inclination of the swash plate  32 . 
     If cooling is interrupted or the engine E is stopped in when the displacement of the compressor  19  is the maximum or the crank chamber pressure is low, the electromagnetic clutch  21  is turned off, which interrupts the supply of electric current to the electromagnetic control valve  52 , and the valve  52  opens fully. Thus, the refrigerant gas flows at a large flow rate from the discharge chamber  44  into the crank chamber  15 . The flow rate of refrigerant gas from the crank chamber  15  through the bleed passage ( 50 ,  18 ,  49 ) into the suction chamber  43  is not very large, so the crank chamber pressure increases rapidly, and the swash plate  32  rushes toward the minimum inclination angle position against the force of the second coil spring  66 . As shown in FIG. 3, when the cylindrical body  19  abuts against the valve plate  14 , the swash plate  32  is located at the minimum inclination angle position and retracts no further. 
     The force based on the crank chamber pressure that urges the swash plate  32  toward the minimum inclination angle position is received by the valve plate  14  through the cylindrical body  19  and exerts no influence on the drive shaft  16 . Thus, the drive shaft  16  does not retract even if the crank chamber pressure is increased excessively. The second coil spring  66  moderates the impact of the cylindrical body  19  against the valve plate  14 . 
     Since axial movement of the drive shaft  16  is prevented, the various problems as described in the paragraphs of the prior art section, axial dislocation of the drive shaft  16  relative to the lip seal  20 , contact between the armature  25  and the rotor  23  when the clutch  21  is turned off, and impingement of pistons  41  against the valve plate  14  are solved. 
     The mechanism of preventing axial movement of the drive shaft  16  is housed in the supporting hole  18  of cylinder block  12 . This helps to miniaturize the compressor  10 . 
     The electromagnetic control valve  52  can change the crank chamber pressure rapidly compared with a control valve that changes the crank chamber pressure in accordance with the operation of a pressure-sensing element, such as bellows, that depends on the suction pressure. Therefore, the compressor in this embodiment, which has the electromagnetic control valve  52 , can change the displacement rapidly while preventing movement of the drive shaft  16 . 
     The control valve  52  fully opens the supply passage  51  to increase the crank chamber pressure, when no electric current is supplied thereto. This causes the compressor to have the minimum displacement when it is stopped. Thus, the compressor  10  is started with the minimum load or the minimum displacement whenever cooling is restarted or the engine E is restarted. 
     The supporting hole  18  is cylindrical. Therefore, the supporting hole  18  can be machined easily. 
     The present invention may be modified as follows. 
     The present invention may be applied to a clutchless type compressor having no electromagnetic clutch  21  (shown in FIG. 1 or  3 ) and having a pulley  75  fixed to the drive shaft  16 , as shown in FIG.  4 . 
     In the compressor shown in FIG. 4, the control valve  52  is not located in the supply passage  76  connecting the discharge chamber  44  to the crank chamber  15 . Instead, the electromagnetic control valve  52  is located in the bleed passage  77  connecting the crank chamber  15  to the suction chamber  43 . In this case, the control valve  52  controls the flow rate of gas bled from the crank chamber  15  into the suction chamber  43 . Further, both the supply passage and the bleed passage may be provided with control valves respectively. 
     The electromagnetic control valve  52  may have a pressure-sensing mechanism (bellows and the like) which moves the valve body  59  depending on the pressure in the suction chamber  43 . 
     The electromagnetic control valve  52  may be of the type that is switched simply to the fully closed state and to the fully open state based on on/off of supply current. 
     The electromagnetic control valve may be located apart from the housing of the compressor.