Abstract:
In a silently operating pilot-operated flow regulating valve, a main valve element is not allowed to vibrate freely, e.g., in lateral direction in an opened state and cannot constitute a noise source because while the main valve element is brought into its open position, an urging force acts upon the main valve element so as to tilt it into vibration suppressing contact with the valve seat whereby vibration of the main valve element is restricted.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a pilot-operated flow regulating valve including a main valve element arranged in a flow passage to which high-pressure fluid is supplied, a circular valve seat formed in said flow passage, said main valve element facing said valve seat, a pressure receiving member arranged with its front surface exposed to the fluid in said flow passage, said pressure receiving member being moveable in accordance with a differential pressure between a fluid pressure applied to said front surface in a first portion of said flow passage and a pressure in a pressure control chamber bounded by a rear surface of said pressure receiving member, a driving force transmitting member interposed between said pressure receiving member and said main valve element so as to move said pressure receiving member and said main valve element in directions such that said main valve element moves towards said valve seat into a first, completely seated position and away from said valve seat into other positions allowing a fluid flow through said valve seat, a pilot passage connecting said pressure control chamber with said second portion of said flow passage located at a side of said valve seat opposite to said pressure receiving member, a leak passage of small cross-sectional area permitting leak of fluid between said pressure control chamber and said first portion of said flow passage, urging means for urging said main valve element in a direction opposite to a driving direction of said pressure receiving member, and a pilot passage constant differential-pressure regulating valve which opens when a differential pressure between an inlet and an outlet of said pilot passage becomes higher than a given pressure in order to keep said differential pressure essentially constant In operation of said pilot-operated flow regulating valve the differential pressure between the inlet and the outlet sides of the valve is kept constant to thereby regulate the flow rate of fluid through said valve seat. 
     2. Discussion of the Related Art 
     In flow regulating valves in general the differential pressure between the inlet and outlet sides of the valve is regulated by a solenoid such that the flow rate is controlled in accordance with the set differential pressure. For extremely high fluid pressures, however, the solenoid needs to be strong and has to have a huge size when directly actuating the main valve element, compared with the cross-sectional area of the flow passage for the fluid. Strong solenoids are expensive. Said combination lacks practicability. 
     To avoid said drawback it is known in practice to use pilot-operated types of flow regulating valves for a high pressure applications. Unlike a simple pilot-operated on/off valve, pilot-operated flow regulating flow valves need a constant differential-pressure regulating pilot valve for opening and closing a pilot passage. The solenoid then only needs to be strong enough to actuate the pilot valve which is actuatable by much less force than the main valve element. As a result, a small sized, cheap solenoid, preferably a proportional solenoid, can be used, the actuating force of which is proportional to the value of the current supplied to its coil. 
     In a conventional pilot operated flow regulating valve the main valve element is arranged in a flow passage for high-pressure fluid and faces the valve seat formed in the flow passage. At the rear side of a pressure receiving member a pressure control chamber is defined. The front surface of the pressure receiving member is exposed to the fluid in the first portion of said flow passage so that the pressure receiving member moves in response to different pressures applied to its front and rear surfaces. A driving force transmitting member is interposed between said pressure receiving member and the main valve element. Also, a pilot passage connects said pressure control chamber with a second portion of the flow passage located below said valve seat opposite the pressure receiving member front surface. A leak passage of small cross-sectional area permits leak of fluid between the pressure control chamber and said first portion of the flow passage. Urging means urge the main valve element in a direction opposite to the driving direction of said pressure receiving member. Said design of a pilot operated flow regulating valve is known from practice. In said conventional pilot-operated flow regulating valve said main valve element when lifted from its valve seat is in a state that it can freely vibrate, e.g. in lateral direction. If said main valve element occasionally vibrates because of the fluid flow and repeatedly collides with its surrounding, e.g. the valve seat, disturbing noise is produced. Said phenomenon is known as “valve rattling”. Furthermore, excessive wear may develop at the main valve element and/or at the valve seat. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a silent pilot-operated flow regulating valve wherein the main valve element does not vibrate freely, e.g. in lateral direction, when said main valve element opens the flow passage. Said main valve element should not constitute a noise source. 
     According to a first aspect of the invention in said other positions of said main valve element at least one of said urging means and said driving force transmitting member forces said main valve element into a vibration suppressing contact with only a portion of said circular valve seat. 
     According to a further aspect of the invention while said main valve element is opened or brought into one of said other positions an urging force of said urging means acts upon said main valve element so as to tilt the same and to thereby restrict vibration of said main valve element. 
     Whenever the main valve element clears the flow passage for fluid through the valve seat the urging force of the urging means acts upon the main valve element so as to tilt it and to thereby restrict vibration of the main valve element. Consequently, the main valve element is prevented from vibrating freely while opened so that the pilot-operated flow regulating valve never constitutes a noise source. In particular the urging force is tilting the main valve element laterally and into a vibration suppressing contact with only a part of the circular valve seat. In a structurally simple way said tilting effect is produced at the main valve element either by the urging means or the force transmitting member or by the mechanical co-action of both. This intentional contact is maintained by said urging force in said other positions of said main valve element, i.e. as long as said main valve element is not completely seated on said circular valve seat. Since the main valve element is tilted laterally into the vibration suppressing contact with only a part of the circular valve seat, an opening remains between the main valve element and the valve seat allowing the fluid flow. The intentionally created vibration suppressing contact hinders the valve element from vibrating, mainly in lateral direction, and thus avoids the generation of disturbing noise. Furthermore, since the main valve element is hindered to vibrate freely dangerous and sudden collisions between the main valve element and the valve seat are avoided. The life duration of the valve is increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will be described with the help of the drawing. In the drawing is: 
     FIG. 1 a longitudinal sectional view of a first embodiment of a pilot-operated flow regulating valve, showing an open state, 
     FIG. 2 an enlarged sectional view of a detail of FIG. 1, 
     FIG. 3 a longitudinal sectional view of the first embodiment, showing a closed state, 
     FIG. 4 a longitudinal sectional view of a second embodiment of a pilot-operated flow regulating valve, showing an open state, and 
     FIG. 5 a schematic block diagram illustrating a refrigerating cycle containing a pilot-operated flow regulating valve defining a pressure reducing device of said refrigerating cycle. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 5 illustrates a refrigerating cycle for a car air-conditioner operating, for example, with carbonic acid gas as a refrigerant Carbonic acid gas as a refrigerant needs considerably higher operating pressure than conventional refrigerants in turn requiring special pressure and flow control measures. The refrigerant is compressed by a compressor  1  and is passed through a radiator  2  arranged outside a vehicle compartment and further through a pressure reducing device, i.e. an expansion valve, constituted by a pilot-operated flow regulating valve  10 . From said valve  10  the refrigerant is supplied to an evaporator  4  constituting an interior radiator. After temporarily being accumulated in an accumulator  5  the refrigerant is returned to the compressor  1 . In a heat exchanger  6  heat is exchanged between the refrigerant which is about to be introduced into the compressor  1  and the refrigerant which has just passed through radiator  2 . 
     In a first embodiment of said pilot-operated flow regulating valve  10  in FIGS. 1 to  3  an inlet pipe  11  introduces high-pressure carbonic acid gas as the refrigerant A passage connecting said inlet pipe to an outlet hole  13  constitutes a refrigerant passage  12 . Between a first portion  12   b  and a second portion  12   a  of said refrigerant passage  12  a valve seat  15  is formed defined by a circular hole with a circular sealing edge having a central axis. 
     In said second portion  12   a  a main valve element  16  is arranged upstream of valve seat  15  so as to face valve seat  15  from upstream. Main valve element  16  is urged by a compression coil spring  17 , constituting an urging means, arranged coaxially with said main valve  16  longitudinal axis in a direction such that it is pressed against valve seat  15  from an upstream side. 
     Main valve element  16  has a conical surface facing valve seat  15 . In a first, completely seated position, i.e. when said main valve is closed, said conical surface abuts against the entire circular circumference of valve seat  15 . In an apex of main valve element  16  a recess  16   a  is formed with a flat bottom surface. Said first portion  12   b  between valve seat  15  and outlet hole  13  is made cylindrical with a constant inner diameter much larger than the diameter of valve seat  15 . Within said cylindrical portion a piston-like pressure receiving member  20  is axially moveably received at a location such that it does not close outlet hole  13 . Pressure receiving member  20  has an effective pressure receiving area larger than the pressure receiving area of main valve element  16 . 
     Pressure receiving member  20  is urged in a direction towards valve seat  15  by a compression coil spring  21 . A rear side of said pressure receiving member  20  confines within said cylindrical portion a pressure control chamber  22 . Pressure receiving member  20  receives at its front surface the pressure of the refrigerant in said first portion  12   b  and receives the pressure in the pressure control chamber  22  at its rear surface. Pressure control chamber  22  and first portion  12   b  communicate via a leak hole  23  of small cross-sectional area. Leak-hole  23  can e.g. be formed in pressure receiving member  20  or in the housing. A driving rod  19  (a driving force transmitting member) is interposed between pressure receiving member  20  and main valve element  16 . Pressure receiving member  20  and main valve element  16  move together in directions such that said main valve element  16  moves towards and away from valve seat  15 . As soon as said main valve is closed, said main valve element  16  is completely seated by its conical surface against the circular edge of valve seat  15 . In other positions main valve element  16  clears an opening of variable cross-section for the fluid passing through valve seat  15 . 
     Driving rod  19  has an outer diameter much smaller than the inner diameter of recess  16   a  of main valve element  16  and the inner diameter of the circular hole of valve seat  15 . Driving rod  19  is positioned eccentrically with respect to main valve element  16 , i.e. the longitudinal axis of driving rod  19  is laterally offset with respect to the longitudinal axis of main valve element  16  or at least with respect to the longitudinal axis of coil spring  17 . 
     Driving rod  19  has an end portion passed through valve seat  15  and abutting against the bottom surface of recess  16   a  of main valve element  16 . Driving rod  19  is not fixed to main valve element  16 . It may be optionally fixed to pressure receiving member  20 . 
     Said first portion  12   a  of passage  12  and pressure control chamber  22  communicate with each other via a pilot channel  24 . Within pressure control chamber  22  a pilot valve element  26  is arranged facing a pilot valve seat  25  formed at the mouth of pilot channel  24 . pilot channel  24  may be formed by a pipe or the like. Pilot valve element  26  e.g. is attached to a distal end of a valve pusher piston  27  which is arranged moveably in directions towards and away from pilot valve seat  25 . The other end of valve pusher piston  27  abuts against an end face of a moveable iron core of a solenoid  30 . Moveable iron core  32  is urged by a compression coil spring  33  having constant spring force in a direction such that the pilot valve element  26  is pressed against pilot valve seat  25  by the force of said compression coil spring  33 . The force by which the pilot valve element  26  is pressed against pilot valve seat  25  decreases with increasing current supplied to a coil  31  of solenoid  30 , because these electromagnetic driving force acting upon the moveable iron core  32  acts counter to the urging force of compression coil spring  33 . 
     Provided that the value of the current supplied to coil  31  is fixed, said pilot element  26  is lifted from said pilot valve seat  25  if the differential pressure between the upstream and downstream sides of said pilot valve seat  25  (i.e. the differential pressure between the upstream second portion  12   a  of passage  12  and said pressure control chamber  22 ) becomes higher than a given value. Said pilot valve closes if the differential pressure becomes lower than said given value. By respective motions of pilot valve element  26  said differential pressure is kept essentially constant. Said differential pressure is at a maximum when no current is supplied to coil  31 . 
     If pressure in said first downstream portion  12   b  of passage  12  increases, pressure receiving member  20  moves in a direction bringing said main valve element  16  into its first completely seated closing position, as shown in FIG.  3 . If the pressure in said downstream first portion  12   b  decreases, pressure receiving member  20  is moved in a direction to open the main valve or to move said main valve element  16  in at least one of said other positions (away from valve seat  15 ), as shown in FIG.  1 . Thanks to such operations the flow rate of the refrigerant flowing from inlet pipe  11  to outlet hole  13  is kept constant. Accordingly, by varying the value of the current supplied to coil  31  it is possible to adjust the flow rate of the refrigerant as desired. 
     During such operations as mentioned above, while the driving rod  19  tends to push main valve element  16  off from valve seat  15 , the urging force of compression coil spring  17  acts upon main valve element  16  and tilts it, since driving rod  19  is positioned eccentrically with respect to main valve element  16  and compression coil spring  17 . In FIG. 2 spring end turn  17   a  is abutting an abutment surface  16   c  of said main valve element  16 . Due to said tilting action the conical surface of main valve element  16  is pressed against a part of the ridge line of circular valve seat  15  (FIG. 2) whereby vibration of main valve element  16  is restricted and as a consequence, any generation of noise is suppressed. 
     In a second embodiment in FIG. 4 said compression coil spring  17  which urges the main valve element  16  towards valve seat  15 , has no end turns formed at its opposite ends (or at least on one of its opposite ends), so that while the main valve element  16  is forced into said other positions, the urging force of the compression coil spring  17  acts upon the main valve element  16  and tilts it into vibration suppressing contact e.g. with the ridge line of valve seat  15 . “No end turn formed” means that no end turn does extend in a plane perpendicular to the longitudinal axis of the compression coil spring. Instead, in FIG. 4 the last spring turn extends, e.g. with essentially the same turn pitch as the other spring turns, towards a freely terminating turn end of said last spring turn which protrudes at a certain laterally offset location related to the respective axes of the coil spring  17  and/or main valve element  16 . Said last spring turn even can be cut off perpendicularly to the core line of said last spring turn. 
     In FIG. 2 the tilting function forcing main valve element  16  in vibration suppressing contact with the circular valve seat  15  is achieved by the lateral offset between rod  19  and the longitudinal axis of coil spring  17  and of main valve element  16 . 
     In the embodiments described having no coil spring end turn but an offset protruding free end of the last spring turn the tilting function for the main valve element is achieved by an offset force transmission from said free end of the last spring turn onto the abutment surface  16   c  of said main valve element  16 . Additionally or alternatively even said abutment surface  16   c  of said main valve element  16  can be inclined by an angle smaller than 90° with respect to the longitudinal axis of said main valve element  16 . 
     With this arrangement, i.e. a compression coil spring  17  having no end turn but a sidewardly protruding free end of the last spring turn and/or the inclined abutment surface  16   c,  the main valve element  16  will be tilted due to the eccentrically transmitted urging force of the compression coil spring  17 , even if the driving rod  19  is positioned coaxially with the longitudinal axis of main valve element  16 . Vibration of main valve element  16  efficiently is avoided thereby preventing generation of noise. 
     In a further not shown embodiment driving rod  19  and main valve element  16  may be positioned coaxially, but the compression coil spring  17  then may be positioned eccentrically with respect to these members, i.e. laterally offset to the longitudinal axes of main valve element  16  and driving  19 . The compression coil spring even may have a protruding turn end contacting the main valve element  16 . Furthermore, the present invention can be applied to various types of pilot-operated flow regulating valves differing from the shown and described embodiments in use or in the design of its individual components, etc.