Abstract:
A hydraulic valve has a main poppet that engages and disengages a valve seat to control the flow of fluid between an inlet and an outlet. Movement of the main poppet is governed by a pilot valve element the opens and closes a pilot passage in the main poppet. The pilot valve element is slideably received in a bore in an armature. The armature is biased toward the main poppet by a first spring and a second spring biases the pilot valve element outward from armature bore and toward the main poppet. The second spring has a lesser spring rate than the first spring. Upon engagement of the pilot valve element with the main poppet continued application of the engaging force causes the second spring to collapse and the pilot valve element to slide within the armature, thereby absorbing some of the force that could otherwise adversely affect the valve.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to pilot operated hydraulic valves, and more particularly to such valves which incorporate mechanisms that compensate for the effect that change in a pressure differential across the valve has on flow through the valve.  
         [0003]     2. Description of the Related Art  
         [0004]     There is a current trend in hydraulic systems to use electrical control and the electrically operated hydraulic valves. This type of control simplifies the hydraulic plumbing as the control valves do not have to be located in close proximity to the operator cab and facilitates computerized operation of various machine functions.  
         [0005]     A solenoid actuated pilot valve is a well known electrically operated device that controls the flow of hydraulic fluid. This valve has nose port at an end of a bore, a side port that opens laterally into the bore, and a valve seat between the ports. A poppet engages and disengages the valve seat to close and open a fluid path between the two ports. Fluid flows through the valve in a forward direction from the side port to the nose port. A bidirectional valve also is able to control flow in a reverse direction, from the nose port to the side port.  
         [0006]     Movement of the poppet is governed by pressure in a control chamber on a remote side of the poppet from the valve seat. Energizing an electromagnetic coil moves an pilot valve element that opens a pilot passage through the poppet, thereby releasing pressure in the control chamber so that the poppet can move away from the valve seat. The flow through some types of pilot operated poppet valves can be varied by controlling the level of electrical current applied to the electromagnetic coil and thus the distance that the poppet moves away from the valve seat. The resultant fluid flow is related to the electrical current level and these valves are referred to as proportional valves. When the electromagnetic coil is deenergized, a spring biases the pilot valve element to block the pilot passage so that pressure increases in the control chamber and forces the poppet against the valve seat, closing the valve.  
         [0007]     When a conventional pilot operated, poppet valve is commanded to close and the electric current is removed from the solenoid coil, the electromagnetic force diminishes quickly. This results in the pilot valve element moving faster in response to the spring force than the speed at which the poppet moves toward the valve seat. Therefore, the pilot valve element is forcibly pushed into an opening of the pilot passage in the poppet, which over time adversely affects the pilot valve element and the opening of the pilot passage.  
         [0008]     When fluid is flowing in the reverse direction through the valve, the flow force pushes the poppet against the pilot valve element collapsing the spring that acts on the pilot valve element. This action drives the pilot valve element into the pilot passage in the poppet which also adversely affects the service life of the valve.  
         [0009]     Therefore, it is desirable to provide a mechanism that balances or reduces these forces that drive the pilot valve element into the pilot passage of the poppet.  
       SUMMARY OF THE INVENTION  
       [0010]     A hydraulic control valve comprises a body having a first bore with a valve seat formed therein. A first port opens transversely into the first bore on one side of the valve seat and a second port communicates with the first bore on another side of the valve seat. A main poppet selectively engages and disengages the valve seat to control flow of fluid between the first and second ports, and a control chamber is formed within the first bore on one side of the main poppet. The main poppet has a pilot passage with openings into the control chamber and the second port.  
         [0011]     An actuator includes an armature that moves within the body and that has a second bore therein. A first spring biases the armature with respect to the body. A pilot valve element is slideably received within the second bore to selectively open and close the pilot orifice as the armature moves. That opening and closing action controls pressure within the control chamber in a conventional manner used in prior pilot operated valves. A second spring biases the pilot valve element with respect to the armature. The second spring has a lesser spring rate than the first spring, wherein upon engagement of the pilot valve element with the main poppet, further application of a force that pushes the pilot valve element and the main poppet together causes the second spring to collapse and the pilot valve element to slide within the armature. This latter sliding action absorbs some of the force that could otherwise adversely affect the service life of the valve.  
         [0012]     In a preferred embodiment of the hydraulic control valve, the pilot valve element has a member that limits the amount that the pilot valve element is able to slide within the armature toward the main poppet.  
         [0013]     A bidirectional version of a hydraulic valve incorporating the present invention also is disclosed. That valve&#39;s pilot passage also opens into the first port and check valves are located at the pilot passage openings into both ports. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a cross sectional view through a solenoid operated hydraulic valve according to the present invention;  
         [0015]      FIG. 2  is a cross sectional view through a second embodiment of a solenoid operated hydraulic valve; and  
         [0016]      FIG. 3  is a schematic diagram of a hydraulic circuit that utilizes hydraulic valves according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     With reference to  FIG. 1 , a solenoid operated hydraulic valve  10  comprises a cylindrical cartridge type body  14  mounted in a longitudinal first bore  16  of a valve manifold  12 . The valve manifold  12  has a transverse first conduit  15  which opens into first port  18  at the side of the first bore  16 . A second conduit  19  extends through the valve manifold  12  and communicates with a second port  20  at the interior end of the first bore  16 . A valve seat  22  is formed in the first bore  16  between the first and second ports  18  and  20 .  
         [0018]     A main poppet  24  slides within the first bore  16  with respect to the valve seat  22  to selectively control flow of hydraulic fluid between the first and second ports  18  and  20 . An aperture  26  is centrally located in the main poppet  24  and extends from a first opening at the second port  20  to a second opening into a control chamber  28  on the remote side of the main poppet. The poppet aperture  26  has a shoulder  33  spaced from the first opening.  
         [0019]     The nose of the main poppet  24  has a frustoconical surface  23  that in the closed state of the valve engages the valve seat  22 . The frustoconical surface  23  terminates at a cylindrical nose  21  that projects into second port  20 .  
         [0020]     A first check valve  34  forms a flow control element that is located in a first pressure passage  25  in the main poppet  24  between the shoulder  33  and the first opening to allow fluid to flow only from the poppet aperture  26  into the second port  20 . A flow control element comprising a second check valve  37  is located within the main poppet  24  in a transverse second pressure passage  38  that extends between the first port  18  and the poppet aperture  26  adjacent the shoulder  33 . The second check valve  37  limits fluid flow in the passage  38  to only a direction from the poppet aperture  26  into the first port  18 . Both flow passages controlled by the first and second check valves  34  and  37  are in constant communication with the aperture  26  in the main poppet  24 .  
         [0021]     The opening of the poppet aperture  26  into the control chamber  28  is closed by a flexible pilot seat  30  that has a pilot aperture  27  there through. The pilot seat  30  is held in place by a snap ring  31 . A double helical spring  32  within the poppet  24  biases the pilot seat  30  with respect to the shoulder  33  of the poppet aperture  26 . Opposite sides of the pilot seat  30  are exposed to the pressures in the control chamber  28  and a pilot passage  35  that extends through the double helical spring  32  in the main poppet  24 .  
         [0022]     The valve manifold  12  has a first control passage  52  extending between the control chamber  28  and the first port  18  with a flow control element comprising a third check valve  50  in that passage  52 . The third check valve  50  that allows fluid to flow only in the direction from the first port  18  to the control chamber  28 . A second control passage  56  is provided in the valve manifold  12  and has another flow control element, specifically a fourth check valve  54 , therein which limits fluid flow only from the second port  20  into the control chamber  28 . Both of these control passages  52  and  56  have first and second flow restricting orifices  53  and  57 , respectively. Note that the control chamber  28  is connected directly to a control port  59  in the valve manifold  12  that enables external devices to be connected to the control chamber as will be described.  
         [0023]     Movement of the main poppet  24  is controlled by a solenoid actuator  36  comprising an electromagnetic coil  39 , an armature  42  and a pilot valve element  44 . The armature  42  is positioned within a bore  40  through the valve body  14  and is biased toward the main poppet  24  by a first, or modulating, spring  45  that exerts a force which can be varied by an adjusting screw  41  threaded into an exposed end of the cartridge bore  40 . The electromagnetic coil  39  is located around and secured to valve body  14 . The armature  42  slides within the cartridge bore  40  away from main poppet  24  in response to an electromagnetic field created by applying electric current to the electromagnetic coil  39 .  
         [0024]     The pilot valve element  44  is slideably received in a second bore  46  of the tubular armature  42 . A second spring  48 , that engages a snap ring  51  secured to the pilot valve element, biases the pilot valve element  44  outward from that second bore  46  so that a proximate end with a conical tip  62  enters the pilot aperture  27 . A remote end  43  of the pilot valve element  44  is recessed within second bore  46  from the adjacent end of the armature  42  when the hydraulic valve  10  is in the closed state as illustrated. That pilot valve element remote end  43  has an aperture therein within which a pull pin  47  is press fitted. The pull pin  47  has an exterior head that engages a washer  49  which is held between the end of the armature  42  and the first spring  45 . A gap is created between the washer  49  and the adjacent end  43  of the pilot valve element  44  that allows the pilot valve element to slide upward within the armature  42  against the force of the second spring  48 . The first spring  45  has a significantly greater spring rate than the second spring  48  so that force applied to the tip of the pilot valve element  44  will produce that sliding action before the armature  42  compresses the first spring, as will be described.  
         [0025]     In the de-energized state of the electromagnetic coil  39 , the first spring  45  forces the armature  42  toward the main poppet  24 , while the second spring  48  forces the pilot valve element  44  outward from the armature so that the conical tip  62  enters and closes the pilot aperture  27 . This combined action results in the pilot valve element tip  62  closing the pilot passage  35  and blocking fluid communication between the control chamber  28  and both the first and second ports  18  and  20 . At the same time the third and fourth check valves  50  and  54  also block any fluid from exiting the control chamber  28  while allowing the pressure in the control chamber to be at least as great as the higher pressure at the first and second ports. As a consequence, the pressure within the control chamber  28  resists forces that tend to move the main poppet  24  from the main valve seat  22  and open the hydraulic valve  10 .  
         [0026]     Energizing the solenoid actuator  36  enables the hydraulic valve  10  to proportionally control the flow of hydraulic fluid between the first and second ports  18  and  20 . Electric current applied to the electromagnetic coil  39  generates an electromagnetic field which draws the armature  42  into the solenoid actuator  36  and away from the main poppet  24 . The magnitude of that electric current determines the degree to which the valve opens and thus the amount of fluid flow through the valve is proportional to that current. The valve is bidirectional being able to control fluid flow in either direction between the ports.  
         [0027]     When the pressure at the first port  18  exceeds the pressure at the second port  20 , the higher pressure is communicated to the control chamber  28  through orifice  53 , first pressure passage  52  and the third check valve  50 . The solenoid actuator&#39;s electromagnetic field causes the armature  42  to move upward in  FIG. 1  which also draws the pull pin  47  and the pilot valve element  44  upward. This action moves the pilot valve element tip  62  away from the main poppet  24 , thereby opening the pilot aperture  27  and releasing pressure in the control chamber  28  to the second port  20  which in this instance has a lower relative pressure. As a result, a greater pressure from the first port  18  acts on surface  58  of the main poppet than acts on the main poppet surface in the control chamber  28 . That pressure difference forces the frustoconical surface  23  away from valve seat  22 , thereby opening direct communication between the first and second ports  18  and  20 . The resultant opening allows fluid to flow in a forward direction through the hydraulic valve  10  from the first port  18  to the second port  20 .  
         [0028]     Movement of the main poppet  24  continues until a pressure/force balance is established across the main poppet due to constant flow through the effective opening of the pilot aperture  27 . Thus, the size of this valve opening and the flow rate of hydraulic fluid there through are determined by the position of the armature  42  and pilot valve element  44 , which in turn controlled by the magnitude of current in electromagnetic coil  39 .  
         [0029]     Fluctuation of the load and supply pressures produces a varying pressure differential across the valve that may affect the magnitude of electrical current required to operate the valve. In hydraulic valve  10 , the effect that the pressure differential has on the main poppet  24  is counterbalanced by the flexible pilot seat  30  that is biased by the double helical spring  32 . The double helical spring  32  enables the pilot seat  30  to move in response to changes in the pressure differential across the main poppet  24 . Such movement effectively alters the axial position of the pilot seat  30  to offset the effects of pressure differential changes on the pilot valve. The design flexibility of the pilot seat is determined based on the spring rate of the double helical spring  32 .  
         [0030]     When the solenoid actuator  36  is deenergized to close the hydraulic valve  10 , the high rate modulating, first spring  45  drives the armature  42  toward the main poppet  24 . The pilot valve element  44  is carried along with the movement of the armature  42  until the conical tip  62  engages the pilot seat  30  of the main poppet  24 . That engagement resists further motion of the pilot valve element  44 , thereby collapsing the second spring  48  and allowing the armature  42  to slide over the pilot valve element. Therefore, some of the force, that in prior valves was transferred to the wall of the pilot aperture  27  in the main poppet  24 , is absorbed by the collapse of the second spring  48 .  
         [0031]     When the hydraulic valve  10  controls flow in the reverse direction, pressure in the second port  20  exceeds the pressure in the first port  18 . In this case the higher second port pressure is communicated into the control chamber  28  through orifice  57 , the second control passage  56 , and the fourth check valve  54 . Upon the electromagnetic coil  39  being energized, the pilot valve element  44  moves out of the pilot aperture  27  releasing the pressure in the control chamber  28  and allowing the second port&#39;s pressure to move the main poppet  24  away from the valve seat  22 . This proportional flow control is similar to that described previously for flow in the forward direction.  
         [0032]     However, as the pressure in the second port  20  drives the main poppet  24  against the pilot valve element tip  62 , the first spring  45  collapses to absorb some of that force and mitigate the potential adverse affects on the pilot valve element tip and the pilot aperture  27 .  
         [0033]     In addition, the collapsing pilot valve element design with the dual springs  45  and  48  enables the main poppet  24  to travel a greater distance within the first bore  16  than the amount that the armature  42  of the solenoid actuator  36  is able to travel. Note that the gap in the control chamber  28  in which the main poppet  24  moves is greater that the gap above the upper end of the armature  42 . Therefore, when the armature  42  reaches the extreme upward end of its travel, the pilot valve element  44  is capable of further upward motion within the second bore  46  in the armature, which allows the main poppet  24  to move farther upward away from the valve seat  22 . This increased travel distance of the main poppet  24  increases the flow through the valve.  
         [0034]     For example, when the hydraulic valve  10  is controlling the flow of fluid from the second port  20  to the first port  18  pressure is greater in the second port. That greater pressure is applied to the relatively large surface area at the nose  21  of the main poppet  24 . Although the armature may be at the extreme upward end of its travel, the main poppet still is forced farther open as the pilot valve element moves upward within the armature collapsing the second spring  48 .  
         [0035]      FIG. 2  illustrates a second hydraulic valve  70  which incorporates the present invention. That second hydraulic valve  70  has a cylindrical valve body  72  that is mounted within an aperture of a manifold  74  which has first and second fluid passages  76  and  78 . The first fluid passage opens through a first port  80  in the valve body  72 , while the nose of the valve body has a second port  82  in communication with the second passage  78 . The valve body  72  has a tubular configuration with an internal bore  84  in which a main poppet  86  is slidably received to selectively engage a valve seat  88  to open and close communication between the first and second ports  80  and  82 .  
         [0036]     The end of the poppet  86 , that is remote end from the valve seat, has a recess within which a valve piston  87  is received, thereby defining an intermediate chamber  89  there between. Fluid passages  91  extend through the valve piston  87  between the intermediate chamber  89  and a control chamber  92  on the opposite side of the poppet  86 . Thus the intermediate and control chambers  89  and  92  are in constant fluid communication with each other. A control port  95  enables the control chamber  92  to be connected to an external device, as will be described.  
         [0037]     The main poppet  86  has a pilot passage  90  between the second port  82  and the intermediate chamber  89  on the opposite side from the valve seat  88 . A first check valve  93  in a branch passage permits fluid to flow only from the pilot passage  90  to the first port  80 . A second check valve  94  allows fluid flow only from the in the pilot passage  90  into the second port  82 . A first control passage  96  extends between the first port  80  to the intermediate chamber  89  and on into the control chamber  92  and has a third check valve  98  therein that allows fluid to flow through that passage only in a direction to the control chamber. A second control passage  100  extends between the second port  82  and the intermediate and control chambers  89  and  92  with a fourth check valve  102  that enables fluid to flow only from that second port to those chambers.  
         [0038]     The second hydraulic valve  70  has a solenoid actuator  106  with an electromagnetic coil  108  within which an armature  110  is slideably received. A first spring  118  presses a washer  120  against an end surface of the armature  110  thereby biasing the armature toward the main poppet  86 . The solenoid actuator  106  has a pilot valve element  111  that comprises a pilot pin  112  attached to a pilot poppet  114 , which may be separate pieces or formed as a single piece. The elongated, tubular pilot pin  112  extends through a bore in the armature  110  and into an aperture within the valve piston  87 . An end of the pilot pin  112  that is within the solenoid actuator  106  has an annular rib  121  that abuts the washer  120  in the illustrated state of the valve and limits downward travel of the pilot pin. The opposite end of the pilot pin  112 , that extends into the piston  87 , is attached to the pilot poppet  114  which selectively engages a pilot aperture  116  where the pilot passage  90  opens into the intermediate chamber  89 . A second spring  122  biases the pilot poppet  114  away from the opposite end of the armature  110  and into the pilot aperture  116  to close that aperture. A third spring  123  biases the valve piston  87 , and thus the main poppet  86 , away from the solenoid actuator  106 .  
         [0039]     As with the first valve  10  in  FIG. 1 , pressure at the second port  82  can exert force on the main poppet  86  and valve piston  87  which causes the pilot valve element  111  to slide within the armature  110  and absorb forces that otherwise could damage the sealing surfaces of the pilot poppet  114  and the pilot aperture  116 . The ability of the pilot valve element  111  to move with respect to the position of the armature  110  also enables the main poppet  86  to move a greater distance with respect to the main valve seat  88  than the distance that the armature  110  is able to move.  
         [0040]      FIG. 3  illustrates an exemplary hydraulic circuit  200  for an excavator in which the hydraulic valve  10  or  70  is utilized. The hydraulic circuit  200  employs four such valves as four control valves  201 - 204  which couple a boom cylinder  206  to a pump supply line  208  and a tank return line  210 . The cylinder  206  has a head chamber  211  and a rod chamber  212 . A first control valve  201  connects the pump supply line  208  to the rod chamber  212  and a second control valve  202  provides a connection between the pump supply line and the head chamber  211 . The third control valve  203  couples the rod chamber  212  to the tank return line  210 , while the fourth control valve  204  provides a similar connection between the head chamber  211  and the tank return line  210 .  
         [0041]     A first pressure relief valve  214  connects the control port  59  or  95  of the third control valve  203  to the tank return line  210  when pressure within the rod chamber  212  of cylinder  206  exceeds a predefined threshold. That action releases the pressure in the control chamber  28  or  92  of the third control valve  203  thereby allows its main poppet  24  or  86  to open in response to the pressure in the rod chamber  212  to open. Thus a path in created between the rod chamber  212  and the tank return line  210  which relieves the excessive pressure within that chamber. This arrangement utilizes a relatively low flow and physically small pressure relief valve  214  and enables the third control valve  203  to act as the primary pressure relief conduit. A similar pressure relief valve  216  is provided at the control port  59  or  95  of the fourth control valve  204  to open that control valve in response to excessive pressure within the head chamber  211  of the cylinder  206 .  
         [0042]     The cylinder  206  for the boom of an excavator has a piston rod  255  with a relatively large diameter. Therefore, the head chamber  211  has a significantly greater volume than rod chamber  212  when the piston is centered within the cylinder. As a consequence, fluid must flow to and from the head chamber  211  at a greater rate than fluid exhausting from the rod chamber  212  in order to move the piston rod at the same speed in both directions. Therefore, the control valves  202  and  204  for the head chamber  211  must provide a larger flow path than the control valves  201  and  203  for the rod chamber  212 . This is accomplished by taking advantage of the capability of the first and second hydraulic valves  10  and  70  design that allows their main poppets  24  and  86  to travel a greater distance than the respective solenoid armature  42  and  110 .  
         [0043]     That additional motion is enabled by releasing pressure within the valve&#39;s control chamber  28  or  92  which is accomplished by first and second pressure release valves  220  and  222  that are high flow, on/off type valves. Specifically, the first pressure release valve  220  is connected between the control port  59  or  95  of the second control valve  202  and when opened, relieves the pressure within the associated control chamber  28  or  92  to the tank return line  210 . Thus, even after the armature has reached the extreme upward end of its travel in  FIGS. 1 and 2  and the main poppet  24  or  86  engages the pilot valve element  44  or  111  which closes the pilot passage  35  or  90 , the control chamber pressure is released to tank via the first pressure release valve  220 . With the pressure in the control chamber  28  and  92  released, fluid pressure at the second port  20  or  82  exerts a force that causes the pilot valve element  44  or  111  to slide, or collapse, with in the armature  42  or  110 . That motion allows the main poppet  24  or  86  to open farther than otherwise would be permitted by the armature of the solenoid actuator. Therefore, the second control valve  202  is able to convey a greater fluid flow from the supply line into the head chamber  211  when rapid piston movement is required.  
         [0044]     Similarly, the second pressure release valve  222  couples the control port  59  or  95  of the fourth control valve  204  to the tank return line  210 , thereby relieving any pressure within the respective control chamber  28  or  92  and allowing the associated main poppet  24  or  86  to move into a further open position. This enables the fourth control valve  204  to convey a greater fluid flow from the head chamber  211  to the tank return line  210 , when rapid piston movement is required in the opposite direction.  
         [0045]     The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.