Abstract:
A relief valve for a hydraulic machine that combines a poppet valve assembly and a pilot valve assembly together using a connector pin wherein internal fluid passageways within the poppet and pilot spools provide a fluid flow path between the inlet of the valve and a cavity disposed between the poppet and pilot. As a result of the internal passageways fluid is metered to the interior cavity to provide additional control and stability within the relief valve.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to hydraulic devices. More specifically this invention relates to a relief valve for a hydraulic device. 
     Traditionally, low leakage relief valves utilize a direct acting poppet and low pressure rise rate valves are pilot operated. Direct acting poppet valves have a tendency to be unstable unless a very high rate spring or special geometry is used. The use of a high rate spring increases the pressure rise rate proportionately. Thus, there is a need to combine a poppet with a pilot to have functioning of both within a valve at a low cost. Attempts have been made to met this need; however, typically a traditional style pilot operation combined with a poppet is unstable. Additional problems exist with complex machining needed to accomplish the combination thus adding to manufacturing costs. 
     Therefore, a principal object of the present invention is to provide a poppet relief valve that improves control of the valve. 
     Another object of the present invention is to minimize manufacturing costs associated with a poppet relief valve. 
     Yet another object of the present invention is to provide a poppet relief valve that minimizes instability therein. 
     These and other objects, features or advantages of the present invention will become apparent from the specification and claims. 
     BRIEF SUMMARY OF THE INVENTION 
     A poppet relief valve for a hydraulic device. The relief valve contains a poppet and a pilot that matingly and detachably connect with one another. The poppet moves relative to the pilot and the pilot has a seat for receiving a pilot ball that is biased against the pilot. A poppet spool is disposed through a cavity of the poppet and has at least one internal passageway disposed therein. Similarly a pilot spool is disposed through a cavity in the pilot and has at least one internal passageway disposed therein. The poppet and pilot spools are connected and through the use of the internal passageways of each to provide fluid communication from a first area within an inlet of a poppet housing to a second area between the poppet and pilot. Said fluid communication functions to meter fluid flow from the first area to the second area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a poppet relief valve in a first position; 
         FIG. 2  is a sectional view of a poppet relief valve in a second position; and 
         FIG. 3  is a sectional view of a poppet relief valve in a third position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The figures show a relief valve  10 . The relief valve  10  comprises a poppet housing  12  with a centrally located cavity  14  in fluid communication with a valve inlet  16  at a first end and a fluid outlet  18  adjacent the cavity  14  to provide fluid flow communication with a tank (not shown). Adjacent the inlet  16  within the cavity  14  is a first area  20  wherein the inlet  16  provides pressure. The poppet housing additionally has a poppet seat  21  therein for receiving a poppet  22 . 
     Disposed within the cavity  14  is poppet  22  and a pilot  24  wherein the first end of the pilot matingly and detachably connects to the poppet  22  within cavity  14  as shown in  FIGS. 1-3 . The second end of the pilot forms a pilot seat  26  having a milled flat. A second area  28  is disposed between the poppet and pilot  22 ,  24  within cavity  14  of the poppet housing. The poppet  22  additionally has a cavity  30  disposed therein that extends the distance of the poppet  22 . Similarly the pilot  24  has a cavity  31  disposed therein that extends the distance of the pilot  24 . 
     A poppet spool  32  is disposed within the cavity  30  of poppet  22 . The poppet spool  32  extends from within the first area  20  through the cavity  30  of spool  22  to a larger diametered portion of the cavity  30  in the second area  28 . The spool  32  has cross-drilled holes or a radial passageway  34  disposed therein that intersects axial passageway  36  disposed within spool  32  and surrounded by sidewall  38 . Thus, both the radial and axial passageways  34  are internal passageways disposed within the spool  32 . The axial passageway  36  extends through the spool  32  to a connection pin  40  that connects the spool  32  and axial passageway  36  to pilot spool  42 . 
     Pilot spool  42  is disposed within the cavity  31  of the pilot  24  and comprises a head portion  44  that is of greater diameter than a stem portion  46  that extends away from the head portion  44 . Additionally disposed within the stem  46  of the pilot spool  42  is a radial passageway  48  that is in fluid flow communication with axial passageway  36  of the poppet spool  32  via axial passageway  49 . Surrounding the stem  46  of the pilot spool  42  and engaging the head  44  of pilot spool  42  at a first end and engaging the pilot  24  at a second end is a biasing spring  50 . Biasing spring  50  biases the pilot  24  away from the pilot spool  42  wherein the spring force of biasing spring  50  must be overcome for the poppet and pilot  22  and  24  to engage. 
     A hex plug  52  slidably receives the poppet housing  12  within hex plug cavity  54 . Disposed within the cavity  54  of hex plug  52  and engaging seat  26  in a first position as shown in  FIG. 1  is a pilot ball  56  wherein the area between the pilot ball  56  and the pilot spool  42  is considered a third area  58 . Pilot ball  56  is biased against the seat  26  of the pilot  24  by a ball retainer  60  disposed within cavity  54  of hex plug  52 . Biasing the ball retainer  60  and thus pilot ball  56  against seat  26  is a pilot spring  62  that is also disposed within cavity  54  of hex plug  52 . The pilot spring  62  may be tensioned by a tensioning device  64  that in combination with the nut element  66  is adjustable to provide proper tensioning. 
     In operation as shown in  FIG. 1  when pressure at the first area  20  is below a threshold pressure of the relief valve  10  the pressure acting on both ends of the poppet  22  are equal. This pressure is communicated to both sides of the poppet  22  within the relief valve  10 . Specifically, because the second area  28  is larger than the first area  20  there is a net force acting on the poppet  22  to push the poppet  22  against seat  21  of poppet housing  12 . When in the first position as shown in  FIG. 1  a low leaking interface is created. 
     As inlet pressure increases at the first area  20  this pressure is communicated through the poppet spool  32  and pilot spool  42  to the second area  28  via internal radial passageways  34 ,  48  and internal axial passageway  36 ,  49 . The pressure in the second area  28  thus acts upon the pilot ball  56 . As the pressure acting on the third area  58  increases to match the force supplied by the pilot spring  62  the pilot ball  56  begins to move off the seat  26  of pilot  24 . As the pilot ball  56  moves off the pilot seat  26  the pressure in the second and third areas  28 ,  58  is routed to the fluid outlet  18  tank port via the milled flat on the pilot seat  26  and the seat  21  of poppet housing  12 . The passageways located in the poppet spool  32  restrict the total amount of oil flow into the second and third areas  28 ,  58  to less than their individual capacities. As the pilot ball  56  moves axially off the pilot seat  26  the pressure in the second area  28  decreases. This pressure imbalance acting on the pilot mechanism  24  moves the entire pilot assembly axially toward the pilot ball  56  against the force generated by the pilot spring  62 . 
     As the passageways in the poppet spool  32  begin to close as a result of the axial movement the flow into the second area  28  decreases further. This decrease in flow increases the pressure imbalance acting on the pilot mechanism  24 . This in turn closes the passageways completely in the poppet spool  32  within the poppet  22  as shown in  FIG. 2 . 
     With the passageways closed the inlet pressure at the first area  20  acts upon the poppet  22  and seat  21  interface. With the pressure acting on the poppet/seat interface and the pressure acting upon the poppet in the second area  28  at or near tank pressure there is a higher pressure imbalance acting on the poppet. This higher pressure imbalance moves the poppet  22  axially toward the pilot ball  56 . The poppet spool  32 /pilot spool  42  assembly continues to move axially to contact the pilot ball  56  and completely move it off the pilot seat  26  as shown in  FIG. 3 . 
     The axial movement of the poppet  22  is regulated by the axial position of the radial passageway  34  within poppet spool  32 . As the pilot ball  56  moves axially either direction the pilot assembly follows. As the pilot assembly moves axially the poppet  22  follows to open and close as is required by the amount of flow through the valve varies. The pilot assembly works in conjunction with the poppet  22  to maintain a constant differential pressure acting on the poppet  22  regardless of the flow through the valve. 
     As the pressure at the first area  20  decreases to below the threshold pressure the pilot spring  62  pushes the ball retainer  60  and pilot ball  56  back onto the pilot seat  26 . The pilot mechanism assembly is pushed axially along with the pilot ball  56 . As the pilot ball  56  seats or closes the flow path through the pilot seat  26  the pressure in the second and third areas  28 ,  58  increase from tank pressure. This pilot assembly movement opens the radial passageway  34  and allows the pressure in the second area  28  to equalize with the pressure at the first area  20 . As the pressure in the first and second areas  20 ,  28  approach equilibrium the poppet  22  acquires a net force acting to close the valve. 
     Thus, by having the passageways  34 ,  38 ,  49  and  50  disposed within the poppet spool  32  and the pilot spool  42  fluid is able to be metered through the poppet and pilot spools  32 ,  42  to provide a minimal rise in pressure during operation. In a preferred embodiment the internal leakage rate of the valve is reduced to ten drops per minute. Thus, more control and stability is provided throughout the relief valve  10 . Also, the passageways are easily machined within the spools minimizing complex geometries and reducing manufacturing costs. Consequently, at the very least, all of the stated objectives have been met. 
     It will be appreciated by those skilled in the art that other various modifications could be made to the device without the parting from the spirit in scope of this invention. All such modifications and changes fall within the scope of the claims and are intended to be covered thereby.