Abstract:
An integrated capacity control valve for a variable capacity refrigerant compressor includes an integral pressure sensor that is continuously coupled to a discharge port of the valve for measuring the refrigerant discharge pressure. A plunger of the control valve is disposed within a passage coupling the compressor crankcase to the discharge port, and is positioned by pneumatic and electric control elements to regulate the refrigerant suction pressure. The plunger has intersecting axial and lateral bores that define a continuous passage between the discharge port and a cavity in which the pressure sensor is retained so that the sensor is continuously exposed to the discharge pressure regardless of the plunger position, and refrigerant discharge pressure in the lateral bore produces a bias force on the plunger that compensates the pneumatic suction pressure setpoint for a pressure drop between the evaporator and the suction port of the valve.

Description:
FIELD OF THE INVENTION 
   This invention relates to a two-port capacity control valve for a variable capacity refrigerant compressor, and more particularly to a pneumatic regulating control valve that is electrically biased to adjust the pneumatic regulation setpoint. 
   BACKGROUND OF THE INVENTION 
   Variable capacity refrigerant compressors have been utilized in automotive air conditioning systems, with the compressor capacity being controlled by a control valve that is either pneumatically-operated or electrically-operated. In either case, the control valve typically varies the pressure in a crankcase of the compressor to control the compressor capacity. In a particularly economical arrangement, the compressor includes an internal bleed passage coupling the crankcase to suction (low-side) refrigerant pressure, and the control valve controls refrigerant flow though a control passage coupling the crankcase to discharge (high-side) refrigerant pressure by controlling the position of a plunger relative to the control passage. In pneumatically-operated control valves, the plunger is positioned by a bellows or diaphragm that is responsive to suction pressure, whereas in electrically-operated control valves, the plunger is positioned by the armature of a solenoid that is energized by a system controller. In general, pneumatically-operated control valves offer superior stability, while electrically-operated control valves offer superior flexibility. Accordingly, it has been proposed to integrate both pneumatic and electric control elements into a single control valve to obtain inherently stable and flexible suction pressure control. In such integrated control valves, the pneumatic control element establishes a predefined regulation setpoint for the suction pressure, and the electric control element is variably energized to bias the pneumatic element, effectively adjusting the regulation setpoint. See, for example, the U.S. Pat. Nos. 6,439,858 and 6,126,405, which are incorporated herein by reference. 
   SUMMARY OF THE PRESENT INVENTION 
   The present invention is directed to an improved integrated capacity control valve for a variable capacity refrigerant compressor, wherein the valve includes an integral pressure sensor that is continuously coupled to a discharge chamber of the valve for measuring the compressor discharge pressure. A plunger of the control valve is disposed within a passage coupling the compressor crankcase to the discharge chamber, and is positioned by pneumatic and electric control elements to regulate the suction pressure of the compressor. The plunger has intersecting axial and lateral bores that define a continuous passage between the discharge chamber and a cavity in which the pressure sensor is retained so that the sensor is continuously exposed to the discharge pressure regardless of the plunger position, and discharge pressure in the lateral bore produces a bias force on the plunger that compensates the pneumatic suction pressure setpoint for a pressure drop between the evaporator and the suction port of the compressor. The solenoid armature is pressure balanced and includes a movable coil that interacts with a stationary pole piece including one or more permanent magnets. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a cross-sectional view of an integrated capacity control valve according to this invention. 
       FIG. 2  graphically depicts variation in a suction pressure setpoint of the control valve of  FIG. 1  as a function of electrical activation of the control valve. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawing, the reference numeral  10  generally designates a compressor capacity control valve according to the present invention. The control valve  10  is designed to be mounted in the rear head of variable capacity refrigerant compressor such that the ports  12 ,  14  and  16  are respectively placed in communication with chambers containing the compressor suction, discharge and crankcase pressures, with the O-rings  18  and  19  positioned to prevent leakage from the discharge port  14  to the suction or crankcase ports  12 ,  16 . A third O-ring  20  prevents leakage between the crankcase port  16  and atmosphere. The illustrated arrangement of valve ports is particularly advantageous since it matches the rear head refrigerant chamber configuration most commonly utilized in variable capacity compressors, facilitating fluid coupling between the control valve ports and the respective refrigerant chambers. 
   The purpose of the control valve  10  is to control the pressure in the crankcase chamber as a means of controlling the compressor capacity. In the illustrated embodiment, increasing the crankcase pressure causes the compressor pumping capacity to decrease, and decreasing the crankcase pressure causes the compressor pumping capacity to increase. The compressor includes an internal bleed valve between its crankcase and suction chambers to establish a full capacity compressor when the discharge chamber is isolated from the crankcase chamber, and the control valve  10  variably couples the discharge and crankcase chambers to raise the crankcase pressure to reduce the compressor capacity. 
   The suction, discharge and crankcase ports  12 ,  14  and  16  extend laterally in order through a pressure port  22  that includes an internal axial bore  24  coupling the ports  12 ,  14 ,  16 . The inboard end of the bore  24  terminates in a suction chamber  25  that houses a pneumatic bellows  26 , and a plunger  30  disposed within the bore  24  is press-fit into the outboard end of bellows  26  as shown. The bellows  26  includes an internal spring  32  axially aligned with the bore  24 , and the inboard end of bellows  26  is seated against a setpoint adjustment screw  34  threaded into the inboard end of pressure port  22 . As explained below, the screw  34  can be manually rotated to change the bellows spring force applied to plunger  30  for purposes of adjusting a pneumatic setpoint pressure of the control valve  10 . 
   The plunger  30  includes an inboard portion  30   a  having a relatively small diameter and an outboard portion  30   b  having a diameter that is larger than the inboard portion  30   a . The inboard portion  30   a  fits closely within the portion of bore  24  that couples the suction and discharge ports  12  and  14 , but loosely within the portion of bore  24  that couples the discharge and crankcase ports  14  and  16 , allowing a flow of discharge refrigerant between bore  24  and the inboard portion  30   a  of plunger  30 . The outboard portion  30   b  of the plunger  30  is sized to fit closely within the portion of bore  24  that couples the discharge and crankcase ports  14  and  16 , so that the plunger  30  can be axially positioned to control refrigerant flow from the discharge port  14  to the crankcase port  16 . In general, inboard movement of the plunger  30  decreases the refrigerant flow to decrease the crankcase pressure, thereby increasing the compressor capacity, while outboard movement of the plunger  30  increases the refrigerant flow to increase the crankcase pressure, thereby decreasing the compressor capacity. The outboard portion  30   b  of plunger  30  is provided with balance grooves  31  that tend to fill with refrigerant during operation of the compressor  10 . Lubricating oil is ordinarily suspended in the refrigerant, and the oil captured in the grooves  31  tends to laterally balance plunger  30  within the bore  24 , minimizing the force required to axially displace plunger  30 . 
   Bellows spring  32  produces an outboard force or bias on plunger  30  that is countered by an opposing pneumatic force proportional to the amount by which the suction pressure in chamber  25  exceeds a sub-atmospheric air pressure internal to the bellows  26 . When the suction pressure achieves a calibrated setpoint, the spring force and pneumatic forces balance and the control valve  10  is in equilibrium. If system conditions cause the suction pressure to deviate from the setpoint, the bellows  26  expands or contracts, producing a corresponding axial movement of the plunger  30  within the bore  24  to counteract the suction pressure deviation and bring the control valve  10  back into equilibrium. For example, when the suction pressure increases due to increased air conditioning load, the bellows  26  contracts to produce inboard movement of the plunger  30 . This reduces the discharge-to-crankcase refrigerant flow (and hence, the crankcase pressure), which produces increased compressor capacity. The increased compressor capacity eventually lowers the suction pressure, allowing bellows  26  to expand somewhat so that the compressor capacity is decreased to a level that maintains the suction pressure at the calibrated setpoint. Rotating the screw  34  to adjust its axial position within the pressure port  22  changes the bias force of bellows spring  32 , and therefore the suction pressure setpoint. For example, adjusting the screw  34  to decrease its axial penetration into the pressure port  22  decreases the outboard spring force on plunger  30 , which requires a corresponding reduction in the suction pressure if the pneumatic and spring forces are to be maintained in equilibrium; in other words, the suction pressure setpoint is correspondingly decreased. The opposite effect is achieved, of course, by rotating the screw  34  to increase its axial penetration into the pressure port  22 . 
   The outboard end of pressure port  22  is received within a cylindrical housing member  40 , compressing an O-ring seal  42  therebetween. The housing member  40  is part of a solenoid assembly  44  that when electrically activated biases plunger  30  in the inboard direction, effectively counteracting the force of bellows spring  26 . This reduces the suction pressure setpoint just as though the screw  34  were adjusted to decrease its axial penetration into the pressure port  22  as described above. The solenoid force is proportional to the level of electrical activation so that the suction pressure setpoint can be controlled as graphically depicted in  FIG. 2 , where the solenoid activation level is depicted as a pulse-width-modulation (PWM) duty cycle. 
   The solenoid assembly  44  additionally includes a set of permanent magnets  45  and  46  disposed between the housing element  40  and an inner pole piece  48 , and a cup-shaped spool  50  carrying a movable coil  52 . The spool  50  is secured to the outboard end of plunger  30 , and a housing element  54  is secured to the housing element  40 , defining an internal cavity  56  in which the spool  50  can move axially with the plunger  30 . A spring  58  disposed about plunger  30  between the spool  50  and the outboard end of pressure port  22  biases spool  50  and plunger  30  to the retracted position shown in  FIG. 1 , effectively aiding the spring force of bellows spring  26 . In the illustrated limit position, the inboard end of plunger  30  rests against the housing element  54  about an aperture  60  axially aligned with the bore  24 . The flexible conductors  62  couple the movable coil  52  to the terminals  64 , and electrically energizing coil  52  via terminals  64  produces a magnetic field that attracts the spool  50  toward the permanent magnet  46 , biasing the spool  50  and plunger  30  inboard against the force of springs  58  and  32 . 
   Internal measurement of the discharge pressure is achieved by providing intersecting lateral and axial bores  70  and  72  within the plunger  30  and securing a pressure sensor  74  to the inboard face of housing element  54  about the opening  60 . The pressure sensor  74 , which may be a top-hat stainless steel diaphragm-type sensor, compresses an O-ring  76  against an outboard surface of the housing element  54 , and is held in place by the base housing element  78  and the housing insert  80 . Discharge refrigerant is coupled through the plunger bores  70 ,  72  into the aperture  60  of housing element  54  and the inner periphery of the pressure sensor  74 . The discharge refrigerant also enters the cavity  56  (primarily when plunger  30  is displaced inboard from the limit position depicted in  FIG. 1 ), and one or more openings  77  formed in the spool  50  ensure pressure equalization across the base of spool  50  during its movement. 
   The discharge refrigerant pressure acting on the inner periphery of pressure sensor  74  produces flexure of its diaphragm, and the mechanical strain associated with the flexure is detected by a piezo-resistor circuit (not depicted) formed on the exterior surface of the diaphragm. The piezo-resistor circuits are wire-bonded to bond pads formed on a circuit board  82  (which may also support signal conditioning circuitry), and the circuit board circuitry is coupled to the connector terminals  84  via the wires  86 . The circuit board  82  has a central opening for receiving the outboard end of pressure sensor  74 , and is held in place by the housing element  88  and the connector  90 . The connector  90  is secured to the outboard end of base housing piece  78  as shown, and supports the terminals  64  and  84  in an insulative insert  92 . An O-ring  94  compressed between the connector  90  and the housing piece  78  seals the enclosed area  96  from environmental pressures so that the pressure measured by sensor  74  can be calibrated to indicate the absolute discharge pressure, as opposed to a gauge pressure that varies with ambient or barometric pressure. 
   The continual presence of discharge pressure in the lateral bore  70  of plunger  30  creates a small but significant force that biases the plunger  30  inward. This discharge pressure bias effectively aids the suction pressure in suction chamber  25 , thereby compensating for diminution of the refrigerant pressure between the evaporator of the air conditioning system and the suction chamber of the compressor. The compensation is fairly accurate since the evaporator-to-compressor refrigerant pressure diminution or drop is substantially proportional to the discharge pressure. Accordingly, the suction pressure setpoint of the control valve  10  actually occurs at the evaporator instead of the compressor suction port  12 . Although this sort of compensation is known per se in pneumatically-operated valves, it is provided at no additional cost in the control valve  10  since the lateral bore  70  is already provided for purposes of discharge pressure measurement. 
   In operation, the energization of movable coil  52  is pulse-width-modulated to dither the plunger  30  within the bore  24  to control the refrigerant pressure in the compressor crankcase. The configuration of solenoid assembly  44  with the movable coil  50  and stationary permanent magnets  45  and  46  significantly reduces the electrical power required to activate the valve  10 , compared to a conventional fixed-coil design. The power requirement is additionally reduced by the balance grooves  31 , which minimize the frictional forces acting on the plunger  30 . In one implementation of this invention, for example, the maximum required coil current was only 300 mA, compared to a 1000 mA maximum current requirement in a conventional fixed-coil design, and the average current requirement under all operating conditions was reduced by at least 67%, compared to a conventional fixed-coil design. This reduction in the power requirement is particularly important in automotive applications because the generated electrical power is limited, particularly at low engine speeds. The system cost is also significantly reduced compared with a conventional approach because the discharge pressure is continuously and accurately measured by the internal sensor  74 . And finally, the discharge pressure in the lateral bore  70  of plunger  30  compensates for the evaporator-to-compressor refrigerant pressure drop so that the control valve  10  can effectively regulate the refrigerant pressure upstream of the compressor suction port. 
   While the present invention has been described in reference to the illustrated control valve  10 , it will be recognized that various modifications in addition to those mentioned above will occur to those skilled in the art. For example, a diaphragm can be substituted for the bellows  26 , if desired. Also, the control valve may be modified to include integral suction pressure measurement through the inclusion of an additional pressure sensor and auxiliary suction port. Further, the pressure sensor  74  may be replaced with a temperature sensor since the relationship between pressure and temperature of refrigerant in a closed volume system is known, and so on. Accordingly, capacity control valves incorporating such modifications may fall within the intended scope of this invention, which is defined by the appended claims.