Abstract:
A valve apparatus is disclosed for use in regulating the flow of fluid between a closed hydraulic loop and a fluid source in a hydraulic circuit, where the valve apparatus provides up to four different functions including a check valve, a neutral valve, a relief valve and a pressure rise rate valve. The apparatus includes a valve seat for selectively permitting fluid communication between the closed hydraulic loop and the fluid source, a sleeve member and a relief poppet in the valve seat, a relief compression spring inside the sleeve and positioned adjacent the relief poppet and the base of the slidable member, a valve guide and an accumulator piston slidably mounted within the valve guide to define an accumulator volume therein.

Description:
CROSS REFERENCE 
   This patent application claims the benefit of U.S. Provisional Patent Application No. 60/681,369 filed on May 16, 2005, which is incorporated herein by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   This invention relates generally to the design of valves and, more particularly, to the design of a combination check valve, neutral valve, pressure rise rate valve and pressure relief valve for use in a hydraulic component such as a hydrostatic transmission or integrated hydrostatic transaxle using a closed hydraulic circuit to connect a pump and a motor. 
   Check valves, neutral valves, pressure rise rate valves, and pressure relief valves are known in the art. Generally, a check valve restricts fluid flow in one direction while a relief valve is used to reduce pressure spikes in the hydraulic circuit. A combination check valve and pressure relief valve is disclosed in commonly owned U.S. Pat. No. 6,691,512, the terms of which are incorporated herein by reference. A neutral valve will permit the flow of a hydraulic fluid from the closed circuit to a sump or reservoir when the component is at or near neutral to permit a wider neutral band. The use of neutral valves in a hydrostatic apparatus is disclosed in U.S. Pat. No. 4,674,287. Lastly, a pressure rise rate valve regulates how quickly pressure rises in a hydraulic system. In order to accomplish these functions in a single hydraulic component, it is generally required to use multiple valves. 
   SUMMARY OF THE INVENTION 
   A multifunction valve is provided for use in regulating the flow of fluid between a first fluid side and a second fluid side in a hydraulic component such as a hydraulic pump. The first fluid side, or closed loop hydraulic circuit, is understood to have a high pressure side and a low pressure side when the component is in operation. The second fluid side, or source of make-up fluid, may be either a sump or reservoir, or it may comprise charge fluid provided by a charge pump or the like. In essence, any source of make-up fluid for the hydraulic circuit may be considered the second fluid side or fluid source within the scope of this invention. 
   The valve assembly has a check valve function, permitting it to open when the pressure in the closed loop hydraulic circuit is sufficiently low to permit oil to be brought into the circuit from a sump or reservoir. The valve assembly also comprises a neutral valve function, permitting the valve to open the closed loop hydraulic circuit to the sump or reservoir when the component is at or near neutral. The valve assembly also has a pressure relief valve function permitting the valve to open when the pressure in the closed loop hydraulic circuit exceeds a desired amount that is set depending upon the application. Finally, the valve assembly in accordance with the present invention provides a pressure rise rate valve function that permits the valve to open the closed loop hydraulic circuit for a limited time to moderate pressure spikes. 
   The various functions of this valve apparatus are integrally formed as part of the same structure; i.e., each function is present in a single valve assembly comprised of multiple parts but all operating together in a single structure as opposed to multiple valves. While all four functions described herein are present in a valve in accordance with the preferred embodiment, it will be understood that fewer than all four functions could be present in keeping with the present invention. 
   In general, the relative values of the pressure set points for the valve&#39;s four functions are as follows: P check &lt;P neutral &lt;P Pressure Rise Rate &lt;P Relief . As system pressure varies along this relative pressure continuum, the multifunction valve automatically responds, configuring its components to achieve the four functions described herein. Some overlap of these functions necessarily occurs during rapid transitions in system pressure. 
   A better understanding of these and other advantages, objects, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth illustrative embodiments and which are indicative of the various ways in which the principles of the invention may be employed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, reference may be had to the following drawings in which: 
       FIG. 1  is a perspective view of a hydraulic pump in which a valve assembly constructed in accordance with the present invention may be mounted. 
       FIG. 2  is a top plan view of the pump shown in  FIG. 1 . 
       FIG. 3  is a cross-sectional, front view of the pump of  FIG. 2 , along line  3 - 3 . 
       FIG. 4  is a top plan view of the end cap portion of the pump of  FIG. 1 , with certain of the components removed for clarity. 
       FIG. 5  is a perspective view of a multifunction valve assembly in accordance with the present invention. 
       FIG. 6  is an exploded view of the valve assembly shown in  FIG. 5 . 
       FIG. 7  is a cross-sectional view of the end cap in  FIG. 4 , along line  7 - 7 , showing the check valve function of two valves, one in the open position (left) and one in the closed position (right), and where one of the valves is shown rotated 90 degrees with respect to the other valve. 
       FIG. 8  is a cross-sectional view similar to that shown in  FIG. 7 , with the neutral valve portion of the valve assemblies in the open position. 
       FIG. 9  is a cross-sectional view of the valve in accordance with the present invention, during nominal operating conditions, where the neutral valve portion of the valve assembly is in the closed position. 
       FIG. 10  is a cross-sectional view of the valve shown in  FIG. 9 , where the pressure rise rate valve portion of the valve assembly is in the open position. 
       FIG. 11  is a cross-sectional view of the valve shown in  FIG. 9 , where the pressure rise rate valve portion of the valve assembly is in the fully closed position. 
       FIG. 12  is a cross-sectional view of the valve shown in  FIG. 9 , where the pressure rise rate valve portion of the valve assembly is in the fully closed position and the relief valve portion is open. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Turning now to the figures, wherein like reference numerals refer to like elements, there is generally illustrated in  FIGS. 5-12  a multifunction valve  10 . 
   A preferred application for valve  10  is shown in  FIGS. 1-4 , which depict pump assembly  40 , comprising a pump housing  52  on which is mounted end cap  54  to form a sump  60  in which is located a rotable cylinder block  55 . A plurality of pistons  57  are mounted in cylinder block  55  and engage moveable swash plate  58 . A pump input shaft  53  extends into housing  52  to engage and drive cylinder block  55  as well as charge pump  62 . It will be understood that this depicted application of valve  10  is exemplary only, and valve  10  could be used in a wide variety of applications. 
   End cap  54  as shown in  FIGS. 1-4 ,  7  and  8  comprises hydraulic porting, and located therein are a pair of system ports  42  (shown here as plugged) a bypass valve  43 , a case drain  45  (plugged), a charge inlet  46  (plugged) and a valve passage  34  (containing valves  10  retained by plugs  30 ). Charge pump  62 , shown here as a gerotor style charge pump, receives fluid through charge inlet passage  47 , and charged fluid is provided to the system by means of charge outlets  49  and charge gallery  48 . A charge pressure relief valve  44  is also provided. 
   Since the construction of hydraulic pumps such as pump  40  and charge pump  62  are well known in the art, it will not be explained in greater detail here. The reader is referred to U.S. Pat. Nos. 5,555,727 and 6,494,686, the terms of which are incorporated herein by reference, for further explanation on the operation of such pumps. 
   Valve assembly  10  is shown most clearly in  FIGS. 5 ,  6 , and  9 . Sleeve  23  is mounted inside valve seat  22 . Relief poppet  24  and relief compression spring  26  are mounted in sleeve  23 , and head  24   a  of relief poppet  24  acts against relief compression spring  26  to move head  24   a  into and out of contact with inner seat surface  32  to control the flow of fluid through openings  31  formed in valve seat  22 . 
   Sleeve  23  also has an external base  23   a  having openings  23   c  formed therein to permit fluid to pass into and out of the internal volume of sleeve  23  and also to provide a surface against which accumulator piston  25  rests. Internal to sleeve  23  is internal base portion  23   b , which is contacted by spring  26 . A series of ribs  25   a  may optionally be provided on accumulator piston  25  to disrupt any laminar flow of fluid across accumulator piston  25 , lessening the bleed of fluid between the fluid sides, thereby permitting a more efficient pressure rise rate valve function. 
   Guide  27  comprises a threaded portion  27   a  that is threaded into seat  22  and an inner passage  33  in which accumulation piston  25  is slidably mounted. It will be understood that other means for attaching guides  27  to seat  22  are contemplated by the present invention, without limitation, such as welding or crimping. Check compression spring  28  is mounted about an outer surface of guide  27  and is located inside a portion of plug  30 , the check compression spring retained on the valve guide by means of rib  27   c  for ease of assembly and installation in the end cap  54 . 
   The check valve feature of the present invention is shown most clearly in  FIG. 7 , where the valve on the left hand side of the figure has the check valve in the open position, while the valve on the right hand side has the check valve in the closed position. A valve passage  34 , having inner surface  34   a , is formed in end cap  54  for the mounting of both valve assemblies  10 ; in the preferred embodiment depicted, valve passage  34  extends through the entire end cap  54  and intersects both system ports  42 . Valve passage  34  also has a narrower central passage  36 , where the reduced diameter of central passage  36  compared to valve passage  34  permits the forming of two seat surfaces  35  against which the external surface of valve seat  22  may rest to close the check valve function. It will be understood that this design is not required; for example, separate port passages may be formed in end cap  54  for the two valves. It will also be understood that although the illustrated embodiment of the check valve function is described using a check compression spring, it is well known in the art that the check valve function can be accomplished without use of a check compression spring whereby a valve assembly can be oriented vertically within a hydraulic component, the check valve feature accomplished by the valve assembly working against, and being returned by, gravity and system pressure. 
   Check compression spring  28  acts against both head surface  27   b  of guide  27  and an inner surface of plug  30 . This arrangement permits a first assembly consisting of guide  27  and seat  22 , and the components therein, to move axially with respect to plug  30 . Thus, when the pressure in charge gallery  48  exceeds the pressure in one of the system ports  42  by a predetermined amount, as determined by the spring constant of check compression spring  28 , the first assembly will move toward plug  30 , and off seat surface  35 , permitting fluid to flow from charge gallery  48  to that valve&#39;s corresponding system port  42 . A series of flow channels  18 , bounded by a plurality of channel ribs  18   a  on the external surface of seat  22 , are used to improve the flow of fluid between seat  22  and inner surface  34   a  of valve passage  34  when the check valve is in the open position. As will be understood, the other system port will be under high pressure at that point, so the other check valve remains closed, as shown in  FIG. 7 . 
   In describing the neutral valve, pressure rise rate valve, and relief valve functions of the present invention, reference will be made to various internal volumes formed in valve assembly  10 , as denoted in  FIGS. 8-12 , when it is assembled. For convenience of description, these volumes are labeled as follows: volume  15   a  inside guide  27  and adjacent one end of accumulator piston  25 ; volume  15   b  inside seat  22  but external to sleeve  23 ; volume  15   c  inside sleeve  23  where relief compression spring  26  is located; volume  15   d  adjacent openings  39 ; volume  15   e  inside valve seat  22  adjacent opening  31 ; and volume  15   f  inside plug  30  and adjacent opening  29  in guide  27 . 
   Opening  29  is formed in one end of guide  27  to permit fluid communication between volume  15   a  and volume  15   f . Openings  39  in the head of seat  22  permit fluid communication between volumes  15   b ,  15   c ,  15   d  (valve seat internal volume) and central passage  36  by way of clearance around relief poppet  24 . It will also be understood that when relief poppet  24  is lifted off inner surface  32  of valve seat  22 , fluid in volume  15   e  communicates with volume  15   d . It will be further understood that when valve assembly  10  is in its nominal operating condition, such as is shown in  FIG. 9 , where relief poppet  24  is seated against inner surface  32 , volumes  15   a ,  15   e  and  15   f  are at system pressure, while volumes  15   b ,  15   c  and  15   d  are at charge pressure (i.e., the pressure in channel  36  through its connection with charge gallery  48 . 
   The neutral valve function of the present invention will now be described with respect to  FIGS. 8 and 9 . As is known, a neutral valve operates to open the system port to the sump or reservoir when the pressure in the system port is at or near neutral, providing a wider neutral band for the component. The neutral valve function is shown in the open position in  FIG. 8 , where sleeve  23  is in a position where it does not block flow through cross holes  19  formed in seat  22 . Thus, when system pressure in volumes  15   a  and  15   e  is sufficiently low, spring  26  acts to locate sleeve  23  in the position shown in  FIG. 8 , and fluid is permitted to flow from system ports  42  through cross holes  19 , through the clearance around relief poppet  24 , and out passages  39  to central passage  36  and charge gallery  48 . As system pressure increases, piston  25  forces sleeve  23  to the right, to the position shown in  FIG. 9 , thus causing some compression of spring  26  and flow through cross holes  19  is stopped. During the valve&#39;s transition from open to closed positions, a tapering of the leading edge  23   d  of sleeve  23  produces a smooth metering effect in the flow reduction, helping to prevent abrupt starts from neutral that can translate to jerking of the hydraulic component. 
   In the following discussion of the pressure rise rate valve and relief valve functions of the present invention, it will be understood that  FIGS. 9-12  show the condition of valve assembly  10  components when installed in end cap  54  and under the fluid conditions described below. The system loop in this description comprises system ports  42 . 
   The pressure rise rate valve function of the present invention gives this valve the ability to quickly open when there is a rapid pressure rise in the closed hydraulic loop to permit fluid to exit the system loop, while then permitting the valve to more slowly close as the system maintains this higher pressure. Thus, by closing in a controlled manner, this valve moderates the pressure rise rate in its associated system port  42 . When a valve with this capability is used in a typical application such as a lawn and garden tractor, the pressure rise rate valve softens the ride and prevents the tractor from jerking when a high acceleration force is provided by the user. Such valves are sometimes referred to as “easy ride” valves. This pressure rise rate valve feature is shown most clearly by a comparison of  FIGS. 9 ,  10  and  11 . 
   In  FIG. 9  the system is in a typical operating condition with stable, constant fluid pressure, with volumes  15   a  and  15   e  being at system pressure. Poppet  24  remains at zero displacement, shown as position  90   a.    
   If a rapid transition from one system pressure level to another occurs, also called a spike, the pressure increase will first appear at volume  15   e  and outside opening  29  (volume  15   f ); the rate of change of the pressure in volume  15   a  is delayed due to the relatively small diameter of opening  29 . The increased pressure on head  24   a  of relief poppet  24  will tend to move relief poppet  24  to the left in  FIG. 10 . Given the force applied by the fluid pressure at volume  15   a  and the incompressibility of the fluid, movement of sleeve  23  and accumulator piston  25  towards volume  15   a  is resisted, resulting in the compression of relief spring  26  so that head  24   a  is displaced from seat  32  to position  90   b  from position  90   a , as shown in  FIG. 10 . Fluid is now permitted to flow from opening  31  past relief poppet head  24   a  and out passages  39 . The typical distance of travel of relief poppet  24  is thousandths of an inch to provide effective pressure rise rate moderation. 
   It will be understood that the components of valve  10  react with varying speeds depending on which component is moving and the conditions under which they are moving. For example, when relief poppet  24  moves from surface  32  of valve seat  22 , it does so nearly instantaneously compared to the length of time it will then remain off surface  32 , though this separation time is only on the order of tenths or hundredths of milliseconds. The period of time it takes for relief poppet  24  to return to surface  32  will be controlled in part by the volume of accumulator  15   a  and the cross-section of opening  29 , as previously discussed. 
   It will also be understood that diameter D 1  of the accumulator piston  25  in passage  33  is greater than diameter D 2  of volume  15   e  against the portion of head  24 A adjacent thereto. Thus, a balance of forces will exist at the point of contact between internal sleeve base  23   b  and the end of spring  26 . At the occurrence of a pressure spike in system port  42 , the pressure in volume  15   a  is somewhat lower than the pressure in volume  15   e  (and outside opening  29 ) resulting in a flow of fluid into volume  15   a  through opening  29  that is moderated by the size of opening  29 . As pressure increases in volume  15   a , a second assembly comprising accumulator piston  25 , sleeve  23  and relief compression spring  26  is moved to the right in these figures, because the diameter D 1  is greater than diameter D 2 , again moving relief poppet  24  against seat  32  to close off the fluid passage between a system port  42  and charge gallery  48 , thus completing the pressure rise rate valve function. Thus, when the pressure in volume  15   a  approaches the pressure in volume  15   e , the pressure acting on the greater cross-sectional area of accumulator piston  25  provides a larger force to the right in these figures than the leftward force generated in volume  15   e  against relief poppet head  24   a , causing movement of accumulator piston  25 , sleeve  23 , spring  26  and relief poppet  24 , if unseated, to the right. 
   The pressure rise rate valve function is completed when head  24   a  is pushed against inner seat  32  to close the relief fluid passage between a system port  42  and charge gallery  48 . The length of time to closure depends in part on the initial system pressure and the differential pressure between volume  15   a  and volumes  15   f  and  15   e , and the resulting amount of increased compression of spring  26 . 
   As system pressure continues to rise, the system pressure differential compensation action described above will ultimately cause the second assembly to reach the position shown in  FIG. 11 , where sleeve  23  is completely against surface  22   a  of seat  22 . At this point, the pressure rise rate valve feature as previously described is no longer provided. As shown in  FIG. 12 , spring  26  can still be compressed if system pressure in volume  15   e  continues to rise. This increased pressure would result in relief poppet  24  compressing spring  26  and lifting off inner seat surface  32 , to again permit system pressure to discharge to the charge outlet side through openings  39  (i.e., again placing volumes  15   d  and  15   e  in communication). However, since the entire inner second assembly can no longer move to the right, the valve assembly cannot close off this connection. Thus, the pressure rise rate valve feature is limited to a maximum pressure at which point valve  10  acts as a simple pressure relief valve. 
   While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure.