Abstract:
A valve assembly having a valve body, a piston, a modulating plug, a valve cover adjoining the valve body, and a throttling member. The valve body has an inlet and outlet port, a partition with a valve seat separating the valve body into a first and second flow passage. The piston has a throughbore including an orifice, reciprocably mounted in the valve body and movable between a first and second position. The modulating plug, in abutting contact with the piston and reciprocably mounted in the valve body, gradually moves between an open position, permitting a main fluid flow, and a closed position engaging the valve seat, blocking the main fluid flow. The throttling member is adapted to insure a gradual alteration of the cross-section of the orifice upon piston movement. A method of gradually opening the valve assembly modulating plug is also set forth.

Description:
CROSS-REFERENCE TO RELATED CASES 
   The present application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/424,120 filed Nov. 5, 2002, the disclosure of which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to a valve assembly with a variable piston orifice and the method of controlling the valve assembly&#39;s main stage position. 
   BACKGROUND OF THE INVENTION 
   In certain prior art constructions pertaining to pilot operated valves, such as U.S. Pat. No. 3,020,925 to Randall et al. and U.S. Pat. No. 6,105,608 to Katzman, conventional pressure regulating valves control pilot flow through the use of a diaphragm and spring arrangement. A range or pilot spring forces the diaphragm to cover an inlet passage, preventing pilot flow from traveling into a cavity above the piston. The set point of a valve is the pressure at which pilot flow lifts the diaphragm and causes the main stage to open. The range spring has to be manually adjusted so that the force needed to move the diaphragm is set at a predetermined level. Tightening an adjusting stem for the range spring increases the spring force acting on the diaphragm. As the spring force is increased, the diaphragm is held closed until the pilot flow reaches higher pressures. When the forces reach this limit, the diaphragm responds and allows fluid into a cavity above the piston. The fluid will cause the piston to move and opens the main stage, thus allowing the flow of fluid through main flow path. The advantage of this type of conventional regulating valve is that the pilot flow permitted through the seat will vary in proportion to the pressure force acting on the diaphragm. Higher pressure gives more pilot flow, resulting in more main stage movement. The disadvantages of this arrangement are that the valve must be manually adjusted, the valve will only respond to pressure signals, and the valve does not automatically change in response to or proportional to a significant change in pilot flow. Also, the pressures to which the diaphragm will respond are limited by the range spring characteristics. 
   A variation of the above-discussed conventional regulated valve is shown in a printed publication namely Refrigerating Specialties Bulletin 23-11 published in January 1997 by the Parker Hannifin Corporation, the assignee of the present invention. In this variation, the range spring can be adjusted by means of a cam rotated by an electric motor. This allows the set point of the valve to be adjusted remotely. Also, the valve set point can be controlled by parameters other than pressure, e.g. temperature. The disadvantage with this type of valve is that the motor is expensive and the mechanical parts will wear. Because of the wear, as well as normal variability in the parts, it is difficult to accurately set the pressure at which the valve will respond. 
   Another variation of the pressure-regulated valve shown in the above mentioned Bulletin 23-11 involves utilizing a proportional solenoid to meter the pilot flow. Thus the diaphragm and spring are eliminated. Instead, flow is metered by a solenoid plunger. As voltage to the solenoid coil is increased, the solenoid plunger moves to increase the pilot flow. The advantage of this type of valve is that the pilot flow can be directly controlled by a voltage signal. The control signal can respond to either pressure or temperature being sensed remotely. One disadvantage of this type of valve is that a solenoid generally has a significant amount of hysteresis. Since the pilot flow needed to slightly open the main stage is nearly the same as the pilot flow needed to hold the valve fully open, it is difficult to control the main stage to a position that is truly proportional to the input signal. Another example of a solenoid operated valve is shown in prior art reference U.S. Pat. No. 5,078,240 to Ackermann et al. Again, like the above reference solenoid metered valve, the disadvantage to this type of valve control is that the valve is either open or closed, and not modulated. 
   Another method of controlling the valve main stage involves directly coupling the modulating plug to an electric motor. These types of valve controls are set forth in a printed publication, namely Sporlan Bulletin 100-40, published in May, 2000 which details the use of a stepper motor for valve control manufactured by The Sporlan Valve Company Washington, Mo., and in a printed publication, namely Hansen Technologies Bulletin R629a, published in February, 2002, which details the use of a sealed motor for valve control manufactured by Hansen Technologies, Burr Ridge, Ill. The disadvantages of these constructions are that these motors are expensive and freeze in position in the event of a power failure. This can be a dangerous circumstance and requires costly and complex controls to overcome. 
   Prior art designs have used tapered pins to regulate the inlet to the piston chamber and to regulate the flow from the pressure chamber. Examples of these types of constructions are shown in U.S. Pat. No. 1,046,236 to Wagner and U.S. Pat. No. 2,694,544 to Hall, respectively. Although these constructions provide better control of the valve, they do not make the valve position automatically responsive to or proportional to a significant change in pilot flow. 
   Other prior art designed valves have a fixed orifice in the piston that allows a steady amount of fluid to pass once flow enters the gap or region above the piston. Such a construction is set forth in a printed publication entitled “Inlet Pressure Regulators” published in February, 1991 by the Refrigeration Specialties Division of the Parker Hannifin Corporation, the assignee of the present invention. With the fixed orifice, the main stage (or modulating plug) has a tendency to swing fully open due to the sudden change in pressure forces. This is due to the sudden decrease in force holding the modulating plug closed, while the forces acting in the opposite direction remain the same. If the device controlling the pilot flow continues to supply the same rate of flow, forces from the pilot flow will remain constant. 
   SUMMARY OF THE INVENTION 
   A feature of the present invention is to provide a valve assembly comprised of: a valve body with an inlet and an outlet port having a partition wall with a valve seat separating the valve body into a first flow passage and a second flow passage; a piston, with a throughbore including an orifice, reciprocally mounted in said valve body and movable between a first position and a second position; a modulating plug in abutting contact with the piston, reciprocally mounted in the valve body and gradually movable between an open position, which permits fluid flow from the first flow passage to the second flow passage, and a closed position engaging the valve seat, which blocks the fluid flow from the first flow passage to the second flow passage; a valve cover adjoining the valve body; and a throttling member, connected to the valve cover and extending into the throughbore and through the orifice, adapted to insure a gradual alteration of the cross-section of the piston orifice upon reciprocation of the piston between the first and second positions. 
   Another feature of the noted valve assembly includes having a throughbore in the valve cover for receiving a pilot fluid flow. Yet another feature of the noted valve assembly includes having a connecting passage in the valve body leading from the first flow passage to a gap between the valve body and the valve cover. 
   Another feature includes having the gradual alteration of the piston orifice cross-sectional area being proportional to the volume of the pilot flow passing through the piston orifice. A further feature includes having the gradual alteration of the piston orifice cross-sectional area change with the travel of the piston. An added feature includes having the piston orifice being fully closed when the piston is in the first position and being in its maximum open position when the piston is in the second position. 
   Still another feature in the noted valve assembly includes having the throttling member take the form of a tapered pin that is received within the piston throughbore. Further, the throttling member can have a cross-sectional area that gradually decreases from a first end to a second end. Yet further, the throttling member can be a fixed diameter disk that is received within the piston throughbore and the piston throughbore has a cross-section surface area that gradually increases from a first end to a second end. 
   Another feature of the present invention provides a method of gradually opening the modulating plug of the valve assembly. The valve assembly is similar to the noted valve assembly previously discussed, and the method includes the steps of: directing a flow of pilot fluid into an area between the valve cover and the valve body; increasing the pilot fluid forces on a first end of the piston, gradually moving the piston and the modulating plug, reciprocally mounted in the valve body, between a first position and a second position, wherein the first position includes having the throttling member sealingly closing the throughbore piston orifice; equalizing the forces acting upon the modulating plug; gradually increasing the pilot fluid flow forces acting upon the upper end of the modulating plug such that the modulating plug gradually moves to a fully opened position; and gradually opening the main fluid flow passage within the valve body. A further feature of the noted method has the step of gradually increasing the forces comprised of increasing the amount of fluid flow passing through the piston orifice. Still yet another feature of the noted method has the gradual movement of the modulating plug being proportional to the volume of the pilot fluid flow introduced to the valve assembly. 
   A further feature of the noted method has the gradual increase in pilot fluid forces acting upon the upper end of the modulating plug being a linear increase in fluid forces. Yet further, the fluid forces acting upon the upper end of the modulating plug can be a non-linear increase in fluid forces. 
   Yet another feature of the noted method has the equalization of the fluid forces acting upon the modulating plug occurring substantially simultaneously with the movement of the piston. And yet a further feature has the equalization of the fluid forces being reactive to an increase in the forces acting upon the piston. Further features and advantages of the present invention will become apparent to those skilled in the art upon review of the following specification in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a valve assembly according to the present invention. 
       FIG. 2  is an enlarged cross-sectional view of the circled area, defined by line  2 — 2  in  FIG. 1  showing a piston assembly in a closed position. 
       FIG. 3  is a further cross-sectional view of the valve assembly similar to that of  FIG. 1 , showing the piston assembly in an open position. 
       FIG. 4  is an enlarged cross-sectional view of the circled area, defined by line  4 — 4  in  FIG. 3 , showing the piston assembly in an open position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings, and particularly to  FIG. 1 , a pilot operated regulating valve assembly  10 , according to the present invention, is shown. Among other uses, regulating valve  10  can be used to modulate the flow of common refrigerants and fluids approved for use in refrigeration systems in order to maintain constant upstream (or inlet) pressure during load fluctuations, for example. 
   Regulating valve assembly  10  is comprised of a valve body  12  having an inlet port  27  defined by a first main flow passage  28  and an outlet port  29  defined by a second main flow passage  30 . Valve body  12  also has a first cylindrical cavity  31 , located in its upper portion, and a second cavity  32 , located in its lower portion. A narrow, generally cylindrical central passage  55 , best seen in  FIG. 3 , fluidly connects first main flow passage  28  with second main flow passage  30 . A central portion  53  of valve body  12  defines this central passage  55 . Central portion  53 , at the lower end of passage  55 , is provided with an annular rim surface or knob-like surface  57  throughout the circumferential extent of central portion  53 . Valve body  12  further has a narrow passage  59  which extends from first main flow passage  28  to the upper end of valve body  12 . 
   A valve cover  18 , located on top of valve body  12 , has a stepped through cylindrical passage  36 , best seen in  FIG. 2 , for receiving a pilot fluid flow. Stepped passage  36  includes an upper, wider portion  37  which receives a locking nut  49 , and a lower, narrow portion  38  which leads into a cylindrical gap  73  located between valve cover  18  and valve body  12 . 
   A cylindrical piston  22  is received in and adapted for reciprocal movement within first cylindrical cavity  31  of valve body  12  and, at one end of its stroke, its upper surface is located adjacent to valve cover  18 , with gap  73  separating this top surface therefrom. As best seen in  FIG. 2 , an upper portion  34  of a throttling member, such as, for example, a tapered pin  33 , is retained within passage upper portion  37  in valve cover  18  by locking nut  49 . A throttling member lower portion  35  is received within a stepped central bore, having a lower bore portion  41 , in piston  22 . An outer spacer  50  and inner spacer  51  are positioned on the upper and lower surfaces of nut  49 , respectively. Outer spacer  50  can take the form of a compressed spring. Inner spacer  51  can take the form of nut  49 , and has a lateral slot milled through its bottom portion to permit fluid flow. Valve cover passage lower portion  38  is larger than the diameter of throttling member  33 , thus allowing throttling member  33  to find piston orifice  40 . Due to the close fit between pin  33  and piston lower bore portion  41 , if pin  33  is not fully aligned with piston bore portion  41 , then piston  22  could be prevented from moving freely. To avoid any impeded movement of piston  22 , pin  33  and attached nut  49  can move laterally (due to outer spacer spring  50 ) within lower bore portion  41  while allowing pilot fluid flow to pass therethrough. The axial extent of throttling member  33  can be adjusted via a threaded portion of throttling member upper portion  34  by nut  49 , and pin  33  is thereafter locked into an axial position by means of upper and lower spacers  50 ,  51 . A pilot fluid flow adapter  44 , affixedly received within valve cover passage  36 , functions as the inlet for pilot fluid flow. 
   As best seen in  FIGS. 1 and 3 , a contoured modulating plug  20 , having an upper sculpted portion  67  and a stepped cylindrical lower portion  68 , is interposed between a lower surface of piston  22  and a closing spring  24 . Modulating plug upper portion  67  is in abutting contact with piston  22  and is located substantially within valve body first cylindrical cavity  31 . Modulating plug lower portion  68  is in biasing contact with closing spring  24  that is fixedly located within valve body second cavity  32 . Modulating plug  20  includes a midportion  69  having a maximum outside diameter greater than the maximum lateral extent of modulating plug upper portion  67  and the diameter of plug lower portion  68 . The maximum outside diameter of plug midportion  69  is greater than the inside diameter of annular rim surface  57  of valve body central portion  53 . 
   The operation of the present invention will now be discussed.  FIGS. 1 and 2  show a closed valve assembly  10  wherein modulated plug  20  is held in a closed position by closing or biasing spring  24 . In this position the peripheral portion of modulating plug midportion  69  is biased into sealing contact with valve body annular rim surface  57 . As a result, main fluid is unable to flow between first and second main flow passages,  28  and  30  respectively. This lack of main fluid flow increases the fluid pressure force in first main flow passage  28 , acting on plug lower portion  68 , thereby holding modulating plug  20  in a closed position. 
   A pilot fluid flow, represented by arrows  80 , is introduced into valve assembly  10  through adapter  44 , and flows into valve cover passage  36 . It should be noted that pilot fluid flow  80  could, alternatively, be introduced into cylindrical gap  73  through an unimpeded passage  59 , being fed from first main flow passage  28 , if so desired. Pilot fluid flow  80  from adapter  44 , via passages  36  and  38 , fills cylindrical gap  73  and exerts and builds up pressure on the top surface of piston  22 . Since a minimal amount of pilot fluid flow  80  will leak around pin  33  while in its substantially closed position, as well as around the periphery of piston  22 , pressure will not build in gap  73  until the pilot fluid flow exceeds this leakage. It should be noted that unlike prior art designs in which pilot flow can travel through the piston via a fixed orifice hole extending through the piston, pilot fluid flow  80  is trapped in gap  73  (with the exception of the noted leakages) while piston  22  remains in the closed position shown in  FIGS. 1 and 2 . When the pressure within gap  73  becomes sufficient to overcome the forces (i.e. the opposing biasing force exerted by closing spring  24  and pressure in flow passage  28 ) holding modulating plug  20  closed, piston  22  together with modulating plug  20  are forced inwardly (into the position shown in  FIGS. 3 and 4 ), thereby allowing main fluid to flow from first flow passage  28  into second flow passage  30 . Pilot fluid flow  80  then flows through a side passage  42  in piston  22  and joins the main fluid. 
   Piston orifice  40  is substantially closed by throttling member  33  when piston  22  is in its outermost stroke position, shown in  FIGS. 1 and 2 , and valve assembly  10  is in a closed position. In the prior art, the piston orifice area is both small and fixed, so the pilot fluid flow required to initially move the piston (and modulating plug) is nearly the same as the flow needed to hold the piston (and modulating plug) in a fully open position. In the present invention, the opening (the annular area between orifice diameter  40  and throttling member  33  outer diameter) within piston  22  increases as piston  22  travels inwardly. Since throttling member  33  is tapered, such that its cross section is smaller at lower portion  35  than at upper portion  34 , the increase in the annular area between orifice  40  and tapered throttling member  33  allows more pilot flow  80  to pass therethrough as piston  22  travels inwardly relative to throttling member  33 . As the opening becomes greater when piston  22  moves inwardly, more pilot fluid is needed to continue to force piston  22  inwardly since more fluid is allowed to pass through the increasing annular orifice opening. This effectively increases the difference between the pilot fluid flow needed to just barely open modulating plug  20  and the pilot fluid flow needed to fully open modulated plug  20 . 
   Throttling member  33  can readily take the form of other design variations in addition to that of the previously-described tapered pin and continue to function as long as the cross-sectional area between throttling member  33  and orifice  40  gradually increases as piston  22  travels inwardly. For example, throttling member  33  can have a constant outer diameter with longitudinal slits that increases in area closer to lower portion  35 . In another embodiment, throttling member  33  can be of constant diameter, while the diameter of piston bore  41  increases during inward movement of piston  22 . 
   The present invention also addresses the fluctuating pressures within valve assembly  10  as modulating plug  20  begins to move. Referring specifically to  FIGS. 3 and 4 , as soon as modulating plug  20  begins to move slightly inwardly, the fluid pressure in first main flow passage  28  is suddenly reduced. Therefore, the fluid pressure force acting to hold modulating plug  20  closed suddenly decreases, which typically (in prior art designs) causes modulating plug  20  to suddenly move to a fully open position. However, in the present invention, the fluid pressure forces acting on the top surface of piston  22  also decrease with the inward movement of modulating plug  20 . The fluid pressure forces within gap  73  decrease since fluid is allowed to flow through the gradually enlarging cross-sectional opening of piston orifice  40 . If the pilot fluid flow rate remains constant, forces from pilot fluid flow  80  decrease as the cross-section of piston orifice  40  increases. As soon as the piston orifice cross-section increases, a new equilibrium is established and piston  22  is prevented from moving further downward until pilot fluid flow  80  increases, thus providing additional force to move piston  22  inwardly. Valve assembly  10  reacts to changing pressure requirements the instant that modulating plug  20  moves off valve body annular rim surface  57 . As the pilot device increases the fluid flow, forces from the fluid flow will cause piston  22  to move further inwardly, thus gradually increasing the cross-section of piston orifice  40 . This continues until the pilot device allows the maximum amount of flow, when piston  22  is at its maximum inward stroke position (as shown in  FIGS. 3 and 4 ), and modulating plug  20  is in its fully open position. For each position of the pilot fluid flow device, there is only one corresponding position of modulating plug  20 . 
   It should be noted that the present invention is not limited to the specified preferred embodiments and principles. Those skilled in the art to which this invention pertains may formulate modifications and alterations to the present invention. These changes which rely upon the teachings by which this disclosure has advanced are properly considered within the scope of this invention as defined by the appended claims.