Abstract:
A decouple check-relief valve for use in a hydraulic fluid circuit is provided that has a cylinder guide housing which travels during the check function of the valve. The cylindrical guide housing has a clearance parameter, allowing for the selection of an optimal check response time. A dampening disk is provided inside the cylindrical guide housing, traveling within the guide during the relief function of the valve. The dampening disk has a separate clearance parameter, allowing for the selection of an optimal dampening capacity and fluid circuit stability. As such, the check and relief clearance parameters are independent of each other to allow both the check and relief functions of the valve to be optimized.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to valves and, more specifically, a check-relief valve for use in hydraulic fluid circuits. 
     Check-relief valves are well known in the art. Such valves essentially combine the functions of both check and relief valves into one body. Check valves control the direction of flow of fluid, allowing fluid flow to travel only in the direction of lower pressure. Check valves prevent backpressure from reversing the flow of a fluid circuit. Relief valves serve as a vent for excessive backpressure. When backpressure exceeds a threshold level, a relief valve will open to prevent backpressure from increasing and damaging the fluid circuit. The advantage of check-relief valves is the conservation of space gained by bringing two functions into a single body. 
     Conventional cartridge-style check-relief valves comprise a guide with a centrally-located stem. The stem is connected to the dampening disk at one end of the stem and is critical to the relief function of the valve. The guide and stem combination ride within a base or plug. The guide has a seat on the side opposite the plug. The valve normally remains in a closed position, which is where no fluid flows past the valve. In operating as a check valve, pressure drives the guide and stem combination of the conventional device into the plug, forcing the seat to move to an open position and allow fluid flow. When fluid flows past seat, the valve is said to be in the check position. The greater the clearance between the outer diameter of the dampening disk and the inner diameter of the plug, the greater the rate of fluid flow past the dampening disk and the faster the valve will be able to move into the check position. A check spring, which is of the helical compression type, works to resist the movement of the guide and stem combination and will reseat the valve upon a certain diminished level of pressure. 
     In operating as a relief valve, backpressure of a threshold level will drive the dampening disk and stem combination of the conventional device away from the plug. Because the seat already is in the closed position, a gap opens between the stem and seat, allowing the backpressure to vent. When fluid flows through the gap between the stem and the seat, the valve is said to be in the relief position. A relief spring, which also is of the helical compression type, works to resist the motion of the dampening disk and stem combination and will return the stem to a closed position upon a certain diminished level of backpressure. The smaller the clearance between the outer diameter of the dampening disk and the inner diameter of the plug, the greater the dampening capacity of the disk and the greater the stability of the system will be. 
     With conventional cartridge-style check-relief valves, it is desired to have a large clearance between the plug and the dampening disk in order to optimize the performance of the check function and minimize the time needed to move the valve into the check position. In a hydrostatic pump situation, a flash check time is partially desired when beginning operation from a cold start. Yet, it also is desirable to have a small clearance between the plug and dampening disk in order to maximize the dampening capacity of the valve when moving into the relief position. This leads to greater stability through the fluid circuit. In a hydrostatic pump situation, greater dampening capacity is desired when operating at higher temperatures. 
     A disadvantage of conventional cartridge-style check-relief valves is that the clearance parameter is restricted only to one value. As such, both the check and relief functions of the valve are governed by the same clearance parameter. Essentially, this means that one of the functions, check or relief, must be compromised as it is only possible to optimize one function at a time. Either there will be a large clearance between the outer diameter of the dampening disk and the inner diameter of the plug, which benefits the check function, or the clearance will be small, which benefits the relief function. 
     It is therefore a principal object of this invention to provide a check-relief valve that allows for a quick check response time while still allowing for sufficient relief dampening and fluid circuit stability. 
     Another object of this invention is to provide a check-relief valve that allows for separate clearance parameters for both the check as well as the relief functions of the valve. 
     A further object of this invention is to provide a check-relief valve with separate check and relief clearance parameters that minimizes the number of components. 
     Another object of this invention is to provide a check-relief valve with separate check and relief clearance parameters than conserves physical space. 
     Yet another object of this invention is to create a check-relief valve with separate check and relief clearance parameters that minimizes manufacturing time and cost. 
     These and other objects will be apparent to those skilled in the art. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed towards a cartridge-style check-relief valve for use in a hydraulic fluid circuit. When the pressure in the check direction exceeds the backpressure, the present invention serves as a check valve and the valve seat opens. When the backpressure exceeds a calibrated level while the valve is in the closed position, the present invention serves as a relief valve and the valve stem opens to vent the backpressure. 
     The present invention utilizes a cylindrical guide housing that alters the clearance parameter used in the check and relief positions. As such, one clearance parameter may be used for the check position, while a different clearance parameter may be used for the relief. Separate clearance parameters allow both the check and relief positions to be optimized. 
     The present invention and the advantages provided thereby will be more fully understood upon further study of the following description of certain embodiments of the invention and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the components of a conventional cartridge-style check-relief valve; 
         FIG. 2  is a perspective view of the components of the present invention, decoupled check-relief valve; 
         FIG. 3  is a side view of a hydrostatic pump; 
         FIG. 4  is a process and instrument schematic of a hydraulic fluid circuit for the present invention; 
         FIG. 5  is a sectional view of the decoupled check-relief valve of  FIG. 4  in the closed position; 
         FIG. 5A  is a sectional view similar to  FIG. 5 ; 
         FIG. 6  is a sectional view of the decoupled check-relief valve of  FIG. 4  in the check position; 
         FIG. 6A  is a sectional view similar to  FIG. 6 ; 
         FIG. 7  is a sectional view of the decoupled check-relief valve of  FIG. 4  in the relief position; and 
         FIG. 7A  is a sectional view similar to FIG.  7 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described as it applies to its preferred embodiment. It is not intended that the present invention be limited to the preferred embodiment. It is intended that the invention cover all modifications and alternatives that may be included within the spirit and scope of the invention. 
     With reference to  FIG. 1 , a perspective drawing of the components of a conventional cartridge-style check-relief valve is shown. A dampening disk or nut  10  is attached to the bottom  12  of stem  14 . A relief spring  16  rests on the dampening disk and presses against a conventional guide  18 . Relief spring  16  is a helical compression spring with a constant spring diameter. The guide  18  forces a seat  20  against the head  22  of stem  14 . A check spring  24  is attached to the bottom  12  of stem  14 . Check spring  24  is a helical compression spring with a decreasing spring diameter. The end of spring  24  that engages with the bottom  12  of stem  14  has a smaller spring diameter than the opposite end of spring  24 . All of these components typically are inserted within a cavity  26  ( FIG. 5 ) of the end cap  30  of a hydrostatic pump  32  (FIG.  3 ). The components typically are retained within the end cap  30  by a plug  34  which attaches to the end cap  30  (FIG.  5 ). 
     The primary difference between the present invention and the conventional check-relief spring depicted in  FIG. 1  is the cylindrical guide housing  36  shown in FIG.  2 . Guide housing  36  is attached to the seat  20  and encloses the dampening disk or nut  10  and the relief spring  16 . Guide housing  36  has protrusions  38  that span part of the length of the guide. As the guide housing  36  moves to the check position, protrusions  38  ride within the cavity  26  of the pump end cap  30  (FIG.  5 ). The protrusions  38  center the guide housing  36  and minimize friction between the cavity  26  and the guide housing  36 . The guide housing  36  also has a smooth lower portion  40 , just beyond the reach of the protrusions  38 . As the guide housing  36  moves to the check position, the smooth lower portion  40  rides within the recess  42  of plug  34  (FIG.  5 ). Lower portion  40  of guide housing  36  has an inner and outer diameter. The dampening disk  10  rides inside guide housing  36  against the inner diameter of lower portions  40 . The diameter of dampening disk  10  can be varied to achieve a desired clearance between the dampening disk  10  and the inner diameter of the lower portion  40  of guide housing  36 . In addition, the inner diameter of the recess  42  ( FIG. 5 ) can be varied to achieve a desired clearance between recess  42  and the outer diameter of the lower portion  40  of guide housing  36 . 
       FIG. 3  shows a side valve of variable displacement pump  32 . Pump  32  includes two decoupled check-relief valves  44  and  46  (not shown) in the end cap  30  of pump  32 . In the preferred embodiment, cavity  26  is machined into pump end cap  30  (FIG.  5 ). The decoupled check-relief valve, as shown in  FIG. 2 , is received within cavity  26  of pump end cap  30 . Plug  34  is attached to the exterior of pump end cap  30  to support and retain the decoupled check-relief valve  44 . Typically, plug  34  is attached to the pump end cap  30  with threads. Alternatively, plug  34  can be integrated into pump end cap  30  or any other portion of variable displacement pump  32 . The present invention can be adapted for use in other locations on a hydrostatic pump. Further, the present invention can be adapted for use with other components on a hydraulic fluid circuit as well as other applications. 
       FIG. 4  shows a process and instrument schematic of a hydraulic fluid circuit  48  that has been adapted to use two decoupled check-relief valves  44  and  46  of the present invention. One decoupled check-relief valve  44  has a system pressure port  50  and a charge pressure port  52 . The other decoupled check-relief valve  46  has a system pressure port  43  and a charge pressure port  56 . 
     In describing the process of the hydraulic fluid circuit  48  as shown in  FIG. 4 , charge pump  58  draws suction flow from a reservoir  60  through line  62 , which passes through a filter  64 . The charge pressure leaves charge pump  58  through line  66 . Charge relief valve  68  ensures that the charge pressure leaving charge pump  58  does not exceed a certain threshold level. Charge relief valve  68  vents excess pressure through line  70 . Charge pressure flows through displacement control valve  72 . Control handle  74  regulates displacement control valve  72 , throttling charge pressure through line  76  or case flow through line  78  to variable displacement pump  32 . Input shaft  80  drives cylinder block assembly  82  of variable displacement pump  32 . The variable displacement pump  32  draws charge pressure from line  84  and creates high pressure, which leaves the cylinder block assembly  82  through line  86 . Case flow also leaves variable displacement pump  32  through line  88 , which passes the case flow through a heat exchanger  90  or a heat exchanger bypass  92  and back to the receiver  60 . High pressure leaving variable displacement pump  32  then flows into cylinder block assembly  94  of fixed displacement motor  96 . High pressure in cylinder block assembly  94  drives outputs shaft  98 . The cylinder block assembly  94  then returns charge pressure through charge line  84  back to variable displacement pump  32  and the rest of the flow circuit. Loop flushing module  100  includes charge pressure relief valve  102 , which prevents charge pressure from exceeding a certain threshold level. 
     When high pressure flowing into port  50  on decoupled check-relief valve  44  exceeds a certain threshold level, valve  44  moves to the relief position to allow high pressure to pass from port  50  to port  52 . Should charge pressure at port  52  exceed the pressure at port  50 , valve  44  moves to the check position to allow the charge flow to pass from port  52  to port  50 . 
     Decoupled check-relief valve  46  operates in a similar manner. When system pressure flowing into port  54  on decoupled check-relief valve  46  exceeds a certain threshold level, valve  46  moves to the relief position to allow the system pressure to pass from port  54  to port  56 . Should charge pressure at port  56  exceed the pressure at port  54 , valve  46  moves to the check position to allow the charge pressure to pass from portion  56  to port  54 . 
       FIGS. 5-7  show the operation of the present invention and  FIGS. 5A-7A  have been arranged on one sheet to more clearly illustrate the operation.  FIG. 5  shows the valve  44  in the closed or neutral position, where the seat  20  of the decoupled check-relief valve  44  is pressed against sealing surface  104  of cavity  26  within end cap  30 . In this position, the pressure at port  50  (hereinafter referred to as “P2”) is greater than the pressure at port  52  (hereinafter referred to as “P1”). If P 1  exceeds P 2 , then the valve will move into the check position depicted in FIG.  6 . While in the closed position, P 2  also must be less than the relief pressure setting, which is a parameter controlled by the relief spring  16  and set according to the desired application. If P 2  exceeds the relief pressure setting, then the valve will move into the relief position shown in FIG.  7 . While in the closed position, the combined force of P 2  pushing on guide housing  36  and the spring force of check spring  24  push the seat  20  firmly against seating surface  104 . This creates a seal against the seating surface  104  that prevents fluid from getting past the seat. In addition, the force of P 1  pushing on the head  22  of stem  14  pushes the head  22  firmly against the seat  20 . This creates a seal against port  106  in seat  20 , preventing fluid from seeping through port  106 . 
     If P 1  exceeds P 2 , then the pressure of P 1  against the stem  14  and the seat  20  will drive the valve into the check position, as shown in FIG.  6 . At this point, the force created by P 1  on the surface of stem  14  and seat  20  overcomes the resisting force created by P 2  and the spring force created by check spring  24 . Check spring  24  compresses against the bottom wall of recess  42  of plug  24  as the combination of stem  14 , seat  20 , cylindrical guide housing  36  and dampening disk  10 , in unison, push on spring  24 . The valve assembly then shifts to the right, creating a gap between seat  20  and seating surface  104 , creating a check fluid path between seat  20  and seating surface  104 . As the valve assembly moves to the check position, the relief spring  16  is not compressed. The relief spring  16  and the dampening disk  10  shift along with the rest of the valve assembly  44  and the dampening disk  10  maintains its position with respect to the guide housing  36 . 
     A check clearance  108  exists between the outer diameter of cylindrical guide housing  36  and the inner diameter of recess  42  in plug  34 . This check clearance  108  regulates the check function of the valve. It is desirable for the check clearance  108  to be large to ensure a rapid check response, particularly during cold start operations. This greater check clearance will allow the guide housing  36  to quickly plunge into recess  42  of plug  34 . The specific check clearance depends upon the application and desired needs of check-relief valve  44 . 
     The check function also can be regulated by varying the parameters of the check spring  24 . The characteristics, including the number of coils, the spring diameter, and the wire diameter, can be altered to vary the spring constant and performance of spring  24 , depending upon the application and desired needs of check-relief valve  44 . 
     If P 2  exceeds the relief pressure setting, then the force created by P 2  on the dampening disk  10  will drive the valve into the relief position, as shown in FIG.  7 . Specifically, the force created by P 2  on the bottom surface of dampening disk  10  will cause the combination of the dampening disk  10  and stem  14 , in unison, to push upon and compress relief spring  16 . The cylindrical guide housing  36  and seat  20  cannot move with the dampening disk  10  and stem  14  as they are retained by the seating surface  104 . Therefore, relief spring  16  is forced to compress inside cylindrical guide housing  36  as dampening disk  10  shifts to the relief position. As the relief spring  16  compresses inside guide housing  36 , the dampening disk  10  and stem  14  shifts to the left to create a gap between port  106  and head  22  of stem  14 . This creates a relief fluid path through port  106 . 
     The relief pressure setting is a parameter governed primarily by the characteristics of relief spring  16 . The relief pressure setting can be altered depending upon the application and desired needs of check-relief valve  44 . 
     A relief clearance  110  exists between the outer diameter of dampening disk  10  and the inner diameter of cylindrical guide housing  36 . This relief clearance  110  regulates stability of the relief function of the valve. It is desirable for relief clearance  110  to be small to provide dampening and stability, particularly at hotter operating temperatures. This smaller relief clearance increases dampening, which prevents the valve from suddenly and drastically shifting to the vent position. This makes for a more stable fluid circuit. Further, the dampening also prevents the head  22  of stem  14  from slamming back into port  106  of seat  20 . Dampening also prevents high frequency oscillation of stem  14 , thereby eliminating valve squeal. The specific relief clearance depends upon the application and desired needs of check-relief valve  44 . 
     The relief function also can be regulated by varying the parameters of the relief spring  16 . The characteristics, including the number of coils, the spring diameter, and the wire diameter, can be altered to vary the spring constant and performance of spring  16 , depending upon the application and desired needs of check-relief valve  44 . 
     Because the addition of cylindrical guide housing  36 , and check clearance parameter associated with the check function is separate from the relief clearance parameter associated with the relief function. In addition, these two clearance parameters can be selected independently to optimize both of the check and relief functions, depending upon the application and desired needs. Specifically, check clearance  108  ( FIG. 6 ) can be selected to vary the speed of the check function. Similarly, relief clearance  110  ( FIG. 7 ) can be selected to vary the dampening speed of the relief function. 
     Whereas the invention has been shown and described in connection with the preferred embodiments thereof, it will be understood that many modifications, substitutions, and additions may be made which are within the intended broad scope of the following claims. From the foregoing, it can be seen that the present invention accomplishes at least all of the stated objectives.