Abstract:
A hydraulic latching spool valve has at movable piston and valve cage defining two seats. In the valve cage, a moveable piston is operable to move the valve into open and closed positions. A spring positioned in a pilot close chamber urges the piston to close. A pulse of fluid pressure at a pilot open chamber causes the piston to open. A latching chamber is formed on the interior of the piston, the latching chamber being exposed to supply pressure when the piston is in the open position. Accordingly, in the open position, supply fluid in the latching chamber generates sufficient latching force to overcome opposing forces generated by the sprig. The supply pressure holds the piston in the open position until a pulse of fluid pressure is applied to the pilot close chamber, thereby causing the valve to close.

Description:
BACKGROUND OF INVENTION 
     This invention relates generally to a hydraulic latching spool valve and more specifically concerns a valve having a latching chamber formed in the interior of an elongate movable piston. The latching chamber is in fluid communication with the supply pressure to the valve and has an area exposed to the supply pressure that generates sufficient latching force to overcome opposing forces and latch the valve in the open position after an initial pulse of open fluid pressure. 
     Hydraulic valves are used in a variety of applications to control flow in hydraulic circuits. While pilot operated poppet valves have been employed for many years, recent changes in control system design have rendered traditional poppet valves less than optimal. With traditional valves, hydraulic pilot pressure is applied and maintained in order to open the valve and keep it in an open position. A poppet valve that was designed for use in a traditional hydraulic system is disclosed in U.S. Pat. No. 5,901,749 assigned to Gilmore Valve Co., the assignee of the present invention. The valve disclosed in this patent requires constant pilot pressure to stay open. If pilot pressure unintentionally drops for any reason, the valve will close because of spring force. This sometimes results in the unintentional closure of a valve. 
     Maintaining a constant pilot pressure to keep the valve open has a number of drawbacks. 
     Any hydraulic system can be troubled by leaks, and keeping a valve under constant pilot pressure may be difficult if there are leaks in the system. Further, maintaining constant pilot pressure requires energy. Thus, control systems have shifted to a design in which pilot pressure need only be pulsed in order to open the valve, and then released. There is, therefore, a need for a valve design capable of latching in the open position after only a brief pulse of pilot pressure. The term “pulsed” as used herein means that a pilot is opened and pressurized fluid is directed to a desired apparatus, for example the present invention, for 2 to 3 seconds, and then the fluid is vented and pressure falls to zero psi. 
     A previous attempt to address this need can be found in U.S. Pat. No. 6,209,565, however the device described suffers from several problems. For example, the device is needlessly complicated. It uses two pistons, i.e. the pilot open piston and a second piston (called a head) in the latching piston assembly. Two moving pistons require additional seals that increase the potential for leakage and failure. There is, therefore, a need for a simple, elegant valve that does not require constant pilot pressure in order to keep it in an open position. 
     SUMMARY OF INVENTION 
     The present invention provides a simple valve design that is able to remain open without constant pilot pressure, and that minimizes the risk of leakage due to the fluid pressure holding the valve open. Briefly, the present invention is a hydraulic latching spool valve which is adapted to be inserted into a valve chamber in a body. Some end users of the hydraulic latching spool valve have bodies that receive the valve and others do not. Therefore the hydraulic latching spool valve may be sold with or without a body. The valve body defines a supply port, a function port, a vent port, a pilot close port, and a pilot open port. The supply port is connected to a pressurized fluid source which delivers supply pressure to the spool valve. The pilot close port is connected to a close pilot to deliver close fluid to the spool valve when the close pilot is pulsed. The pilot open port is connected to an open pilot to deliver open fluid to the spool valve when the open pilot is pulsed. 
     The spool valve itself comprises a valve cage, a seal assembly carried by a moveable elongate piston, a spring, a pilot open chamber, a pilot close chamber, and a latching chamber. The valve cage is sized and arranged to be inserted into the valve chamber of the body. The valve cage defines an upper circular seat positioned between a valve supply port and a valve function port, and a lower circular seat positioned between the valve function port and a valve vent port. The seal assembly is carried by an elongate moveable piston. The piston moves from a closed position, in which the seal assembly is engaged with the first seat and disengaged with the second seat, to an open position, in which the seal assembly is engaged with the second seat and disengaged with the first seat. The spring is positioned within a chamber in fluid communication with the pilot close port and urges the piston into the closed position. The pilot open chamber is in fluid communication with the pilot open port and serves to retain fluid that exerts pressure on the head of the piston, causing the piston to move from a closed position to an open position where the piston is actuated. 
     The latching chamber is formed within the interior of the elongate moveable piston and is in fluid communication with the supply pressure when the valve is in the open position. The latching chamber has an area exposed to the supply pressure that generates sufficient latching force to overcome the opposing forces generated by the spring and the supply pressure acting against the piston. Thus, when the open pilot is pulsed, the elongate moveable piston moves to the open position and supply pressure fills the latching chamber. The piston is then held in the open position until the close pilot is pulsed, which added pressure combines with the pressure exerted by the spring to force the piston into the closed position. These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the preferred embodiment thereof which is illustrated in the appended drawings, which drawings are incorporated as a part hereof. 
     It is to be noted, however, that the appended drawings illustrate only a typical embodiment of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1 is a section view of a portion of the body and of the hydraulic latching spool valve of the present invention. The internal valve components are in the closed position. 
     FIG. 2 is a section view of the hydraulic latching spool valve of FIG. 1, except the internal valve components are in the open position. 
     FIG. 3 is an exploded view of the hydraulic latching spool valve showing the three-dimensional structure and spatial relationship of the valve components. 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings and first to FIGS. 1 and 2, a preferred embodiment of the present hydraulic latching spool valve is generally designated by the numeral  10 . FIG. 1 shows the spool valve  10  in the closed position, while FIG. 2 shows spool valve  10  in the open position. 
     In FIG. 1, a body  12  surrounds the hydraulic latching spool valve  10 . The body  12  defines a valve chamber  13 , a pilot open port  14 , a pilot close port  16 , a vent port  18 , a function port  20 , and a supply port  22  which are each in communication with valve chamber  13 . At its upper end, valve body  12  defines a threaded access opening  24  which is adapted to threadably engage a hex plug  26  which is sealed with respect to body  12  by an o-ring  28 . A valve cage  30  is inserted in the valve chamber  13  of body  12 , and is sealed with respect to valve body  12  by first upper valve cage seal assembly generally identified by the numeral  32 , comprised of an o-ring  27  and two flanking backup rings  25  and  29 , second upper valve cage seal assembly generally identified by the numeral  34 , comprised of an o-ring  31  and a backup ring  33 , first lower valve cage seal assembly generally identified by the numeral  36 , comprised of an o-ring  37  and a backup ring  35 , and second lower valve cage seal assembly generally identified by the numeral  38 , comprised of an o-ring  41  and a backup ring  39 . These seal assemblies and others described herein are better seen in FIG.  3 . 
     Valve cage  30  acts as a piston receptacle and guide, and further defines upper circular seat  40  and lower circular seat  42 . The upper end of valve cage  30  defines a piston and spring section having an internal cylindrical surface which defines a piston chamber  43  for receiving a piston  44 . Piston  44  has an upper cylindrical section and a lower stem section, and is sealed with respect to piston chamber  43  by first piston seal assembly generally identified by the numeral  46 , comprised of an o-ring  45  and two flanking backup rings  75  and  47 , and second piston seal assembly generally identified by the numeral  48 , comprised of an o-ring  51  and two flanking backup rings  49  and  53 . Immediately below the upper cylindrical portion of piston  44 , an annular seal gland  68  is positioned about the piston stem. Seal gland  68  defines a circular seal recess adapted to receive an upper piston stem seal assembly generally identified by the numeral  60 . 
     Upper piston stem seal assembly  60  is comprised of an o-ring  61  and a circumferential PEEK seal  63 . The lower end of the stem of piston  44  maintains a lower piston stem seal assembly generally identified by the numeral  62 , comprised of an o-ring  67  and a circumferential PEEK seal  65 . A spacer  74  is provided in supporting engagement between upper piston stem seal assembly  60  and lower piston stem seal assembly  62 . The bottom of the stem of piston  44  is also adapted to receive a gland nut  70  into which is positioned a cotter pin  72  which secures gland nut  70  against inadvertent rotation relative to the piston stem. 
     The top portion of piston  44  defines an opening adapted to receive stationary plug  50 . Stationary plug  50  is positioned between the underside of hex plug  26  and the upper end of piston  44 . Stationary plug  50  is sealed with respect to the opening in the upper end of piston  44  by latching piston seal assembly generally identified by the numeral  52 , the seal assembly being comprised of an o-ring  57  and two flanking backup rings  55  and  59 . 
     Piston  44  further defines an internal latching chamber  54 , having a cylindrical shape and having a wide diameter at its upper end. Latching chamber  54  is in fluid communication with supply port  22  by means of fluid port  56  located at the lower end of piston  44 . Between piston  44  and valve cage  30 , a spring  58  is operably located to bias piston  44  towards the closed position. 
     FIG. 1 shows hydraulic latching spool valve  10  in the closed position. Lower piston stem seal assembly  62  and lower circular seat  42  are engaged, while upper piston stem seal assembly  60  and upper circular seat  40  are disengaged. Thus, vent port  18  and function port  20  are in fluid communication with one another. 
     FIG. 2 shows hydraulic latching spool valve  10  in the open position. Upper piston stem seal assembly  60  and upper circular seat  40  are engaged, while lower piston stem seal assembly  62  and lower circular seat  42  are disengaged. Thus, function port  20  is in fluid communication with supply port  22 . Supply pressure fills latching chamber  54 . 
     The operation of hydraulic latching spool valve  10  is as follows. The “normal” condition of hydraulic latching spool valve  10  is as shown in FIG. 1, where spring  58  maintains the valve mechanism in the closed position with lower piston stem seal assembly  62  in sealing engagement with lower circular seat  42 , thus blocking supply pressure from supply port  22  from communication with function port  20 . At this point, function port  20  is open to vent port  18 . 
     To open the valve, the open pilot is pulsed, causing pilot open pressure to flow into pilot open chamber  64  and to act on the upper end of piston  44 , thus driving the piston downward and moving upper piston stem seal assembly  60  into sealing engagement with upper circular seat  40 . This piston and valve seal movement causes isolation of vent port  18  from function port  18  and allows supply pressure to communicate with function port  18  and latching chamber  54 . This open position of hydraulic latching spool valve  10  is shown in FIG.  2 . 
     As piston  44  moves into the open position, latching chamber  54  is also placed in fluid communication with supply port  22  by means of fluid port  56 . Supply fluid enters latching chamber  54  at fluid port  56  near its lower end and fills the latching chamber. As supply fluid fills the upper end of latching chamber  54  the fluid imparts pressure against piston  44  and stationary plug  50 . The effect of this pressure is to force piston  44  in a downward direction. Because of the area of the upper portion of latching chamber  54 , identified by arrows “L”, the force imparted by fluid in the latching chamber is sufficient to overcome the combined opposing force of spring  58  and the supply pressure impacting piston  44  at spacer  74  indicated by arrow “P”. Thus, the fluid in latching chamber  54  serves to latch the valve in the open position. Pilot open pressure goes to zero psi and the valve remains open because of the differential forces acting on piston  44 . 
     To close the valve, the close pilot is pulsed, causing pilot close pressure to flow into pilot close chamber  66 . The fluid pressure in pilot close chamber  66  acts on piston  44  forcing it in an upward direction. The force of the pilot close pressure, in combination with spring  58 , is sufficient to overcome the force imparted by fluid in latching chamber  54 . Piston  44  moves upwardly, returning the valve to its normally closed position. 
     FIG. 3 is an exploded view of a preferred embodiment of the present invention. The diagram shows the orientation of each component of hydraulic latching spool valve  10  relative to the others. Beginning at the top row, left to right, the parts are: hex plug  26 ; o-ring  28 ; stationary plug  50 ; stationary plug seal assembly  52 ; first piston seal assembly  46 ; latching chamber  54 ; piston  44 ; spring  58 ; second piston seal assembly  48 ; seal gland  68 ; upper piston stem seal assembly  60 ; access opening  24 ; valve cage  30 ; spacer  74 ; lower piston stem seal assembly  62 ; gland nut  70 ; cotter pin  72 ; first upper valve cage seal assembly  32 ; second upper valve cage seal assembly  34 ; first lower valve cage seal assembly  36 ; and second lower valve cage seal assembly  38 . 
     The invention has several advantages. Using only one moveable piston, the valve can be latched in the open position after only a brief pulse of pilot open pressure. Once the pilot open pressure is pulsed, fluid fills the latching chamber and maintains the valve in the open position even after pilot open pressure is removed. The valve remains open until pilot close pressure is applied. 
     Another advantage of the invention is that the risk of leakage due to the latching fluid pressure is reduced because the fluid is contained within a latching chamber located in the interior of the piston. This is preferable to the situation in which the latching fluid fills a chamber between the piston body and the valve cage because if the latching fluid fills a chamber between the piston body and the valve cage there is a risk of leakage along the various seal points between the piston body and the valve cage. 
     In view of the foregoing it is evident that the present invention is one well adapted to attain all of the advantages and features hereinabove set forth, together with other advantages and features which are inherent in the apparatus disclosed herein. 
     As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its spirit or essential characteristics. The present embodiment is, therefore, to be construed as merely illustrative and not restrictive, the scope of the invention being indicated by the claims rather than the foregoing description, and all changes which come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.