Patent Publication Number: US-7213502-B2

Title: Robustly stable servo-controlled metering poppet valve

Description:
TECHNICAL FIELD 
   The present disclosure relates generally to valve assemblies, and more particularly to a poppet valve assembly that can hydraulically lock a poppet valve member in one of a plurality of different positions with respect to a valve seat. 
   BACKGROUND 
   Poppet valves are used in a variety of hydraulic systems such as those used to control different systems on work machines. A poppet valve typically consists of a housing with at least one input and one output hydraulic port. Inside the housing is a poppet valve member seated in a valve seat such that when the poppet valve member is in contact with the valve seat, the input and the output ports are not fluidly connected. When the poppet valve member is moved away from the valve seat by an actuator, then the input and output ports are fluidly connected and hydraulic fluid can flow across the valve seat. Typically, the housing also contains a control chamber hydraulically connected in a number of different manners, such as a position follower model described in U.S. Pat. No. 6,745,992 B2, a flow amplifying model described in U.S. Pat. No. 5,819,532, or a force feedback model as in U.S. Pat. No. 6,869,060 B2, all of which involve the poppet valve member being exposed to hydraulic pressure on at least one control hydraulic surface. In this manner the motion of the poppet valve member can be at least partially controlled and de-sensitized to differences in pressure between the input and the output ports. 
   A problem with these methods of controlling the poppet valve member is that the pump and line pressure changes can affect poppet control volume dynamics. This occurs because the control volume is always fluidly connected to the hydraulic system. As the pressure in the system fluctuates, the poppet valve member may move at differing rates due to the hydraulic connections of the ports to the control chamber, making accurate control difficult and unpredictable. This same problem renders it difficult to maintain the poppet valve member at a selected location away from its seat. 
   One possible solution to this problem is to use spool valves rather than poppet valves in hydraulic systems, such as that described in U.S. Pat. No. 5,186,212. Spool valves include a spool valve member that slides back and forth inside a bore of a housing to open and close fluid ports. An advantage of spool valves is that they are pressure balanced and can therefore be precisely positioned regardless of pressure differences. Spool valves, however, have a disadvantage in that they necessarily have a radial clearance between the spool valve member and the housing, so they inherently leak. This can cause problems when the spool valves are used in work machine applications such as loaders, such as where it might be desirable to keep the loader bucket in a lifted position over a prolonged period of time. 
   The present disclosure is directed to one or more of the problems set forth above. 
   SUMMARY OF THE INVENTION 
   In one aspect, a valve assembly includes a poppet valve assembly fluidly connected to a pilot valve assembly. The poppet valve assembly includes a hydraulic control chamber and a fluid passage, including a valve seat, extending between a first port and a second port. The poppet valve assembly further includes a poppet valve member with a control hydraulic surface exposed to hydraulic pressure inside the control chamber. The poppet valve member has a plurality of positions with different flow areas across the valve seat, and includes a position in which there is no flow area because the poppet valve member is in contact with the valve seat. The pilot valve assembly has a first configuration wherein the control chamber is fluidly connected to the first port, a second configuration wherein the control chamber is fluidly connected to the second port, and a third configuration wherein the control chamber is fluidly isolated from both the first port and the second port. 
   In another aspect, a machine comprises a chassis and a poppet valve assembly, which includes a head port, a rod port, a pump port and a drain port, attached to the chassis. The machine further includes a hydraulic cylinder fluidly connected to the head port and the rod port. The poppet valve assembly includes a poppet valve member with a control hydraulic surface exposed to fluid pressure in a control chamber, and is movable to a plurality of positions with different flow areas across the valve seat. Further, the machine includes means, such as a pilot valve assembly, for stopping the poppet valve member at each of the plurality of positions at least in part by fluidly isolating the control chamber. 
   In yet another aspect, a method for operating a valve assembly comprises a step of moving a poppet valve member with respect to a valve seat. This movement is done at least partially by exposing a control hydraulic surface of the poppet valve member to hydraulic pressure in a control chamber. The poppet valve member is stopped at a position away from the valve seat at least partially by fluidly isolating the control chamber. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of the poppet valve assembly fluidly connected to the pilot valve assembly in the first configuration, both of which are electrically connected to the electrical controller, according to the present disclosure; 
       FIG. 2  is a schematic view of the poppet valve assembly of  FIG. 1  in the second configuration according to the present disclosure; 
       FIG. 3  is a schematic view of the poppet valve assembly of  FIGS. 1 and 2  in the third configuration according to the present disclosure; 
       FIG. 4  is a schematic view of the valve assembly that includes a first, second, third, and fourth poppet valve assembly according to  FIG. 1  coupled to a hydraulic cylinder according to the present disclosure; 
       FIG. 5  is a diagrammatic view of a backhoe-type work machine including a valve assembly according to the present disclosure; 
       FIG. 6   a  is a graph of hydraulic cylinder position shown as a percentage as a function of time; 
       FIG. 6   b  is a graph of the position of a poppet valve member in a valve assembly coupled to the hydraulic cylinder as a function of time; 
       FIG. 6   c  is a graph of pressure differential across the valve seat in the hydraulic system coupled to the hydraulic cylinder as a function of time; and 
       FIG. 6   d  is a graph of the configuration of a pilot valve assembly in the valve assembly as a function of time. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , there is shown a valve assembly  21  electrically connected to an electrical controller  13  according to the present disclosure. The valve assembly  21  includes a pilot valve assembly  40  and a poppet valve assembly  30 . The poppet valve assembly includes a poppet valve member  31  with a control hydraulic surface  35 . Poppet valve member  31  is movable with respect to a valve seat  32 , which may be a conical valve seat formed on a valve body. The poppet valve assembly  30  also includes a position sensor  60 , such as a linear variable displacement transducer (LVDT) or some other suitable device known to those skilled in the art, electrically connected to the electrical controller  13  to determine the displacement of the poppet valve member  31  with respect to the valve seat  32 . The control hydraulic surface  35  is exposed to hydraulic pressure in a control chamber  36  inside the poppet valve assembly  30 . The poppet valve assembly  30  further includes an input port  34  connected to a pressure source, such as a pump  25 , an output port  33  on an opposite side of the valve seat  32 , and a first and second pressure sensor  61 ,  62  connected to the electrical controller  13  operable to detect a pressure differential across the valve seat  32 . The pilot valve assembly  40  includes a pilot valve member  42  and an electrical actuator  41  operably controlled by the electrical controller  13 . The actuator  41  could be any suitable actuator including but not limited to a piezo or a solenoid. The pilot valve assembly  40  is shown in a first configuration  40   a  wherein the output port  33  is fluidly isolated from control chamber  36 , and the input port  34  is fluidly connected to the control chamber  36  via the pilot valve member  42 . The actuator  41  biases the pilot valve assembly  40  to be in the first configuration  40   a  as shown in  FIG. 1 .  FIG. 2  shows the valve assembly  21  in a second configuration  40   b  electrically connected to the electrical controller  13 . In the second configuration  40   b , the input port  34  is fluidly isolated, but the output port  33  is fluidly connected to the control chamber  36  via the pilot valve member  42 .  FIG. 3  shows a valve assembly  31  in a third configuration  40   c  electrically connected to the electrical controller  13 . In the third configuration  40   c , the control chamber  36  is fluidly isolated from both the input port  34  and the output port  33  by the pilot valve member  42 . 
   It will be appreciated by one skilled in the art that the pilot valve member  42  is shown as a three-way valve by way of example only, and that the spirit and scope of this disclosure includes any such means for connecting the control chamber  36 , the input port  34  and the output port  33  in the first configuration  40   a , the second configuration  40   b  and the third configuration  40   c  as disclosed above. One possible alternative could include a combination of two two-way valves operably coupled to two actuators and the control chamber  36 , the input port  34  and the output port  33 , respectively. Further, it should be recognized that the actuator  41  described above can include a piezo, a solenoid or any other means of altering the configuration of the pilot valve member  40 . In the illustrated embodiment, pilot valve member  40  is a spool, but it could be an appropriately biased poppet valve member. Finally, it should be recognized that the pump  25  connected to the input port  34  is not necessary to the valve assembly  21  as herein disclosed, and is only meant to show an example fluid connection without limitation to scope or spirit of the disclosure. In a similar manner, the position sensor  60 , the first pressure sensor  61 , and the second pressure sensor  62  are not necessary to ensure correct operation of the disclosure, but are herein included as an example of a desired embodiment. 
   Referring to  FIG. 4 , there is shown a valve assembly  121  containing a pump port  37  and a drain port  38  wherein like elements are assigned like numbers to the previous Figures. The valve assembly  121  is fluidly connected to a hydraulic cylinder  12  via a head port  22  and a rod port  23 . The valve assembly  121  further includes a first poppet valve assembly  51 , a second poppet valve assembly  52 , a third poppet valve assembly  53 , and a fourth poppet valve assembly  54  each with a respective first pilot valve assembly  56 , a second pilot valve assembly  57 , a third pilot valve assembly  58 , and a fourth pilot valve assembly  59 . Movement of cylinder  12  is accomplished by activating different pairs of the valve assemblies in a conventional manner. 
   Referring to  FIG. 5 , a backhoe type work machine  10  is provided utilizing the valve assembly  121  herein disclosed. It will be recognized that similar elements are indicated by similar numbers to the previous Figures. The backhoe type work machine  10  includes a chassis  11 , an implement  14  whose movement is controlled by a hydraulic cylinder  12  and an electronic controller  13 . The valve assembly  121  is also attached to the chassis  11 . As shown, the valve assembly  21  is attached to a head port  22  and a rod port  23  of the hydraulic cylinder  12 . An electrical connection  24  connects the electronic controller  13  with the position sensor  60 , the first pressure sensor  61  and the second pressure sensor  62  positioned inside of each poppet valve assembly  30 . The electrical connection  24  also operably connects the electronic controller  13  with each pilot valve assembly  40  of the valve assembly  121 . 
   It will be recognized by one skilled in the art that the description of the backhoe type work machine  10  is not intended to limit the spirit or scope of this disclosure, and it is envisioned that the work machine  10  could be any suitable work machine with a chassis  11 , an electronic controller  13 , an implement  14 , and a hydraulic cylinder  12 , such as a bulldozer, a compactor, or any other work machine known to those skilled in the art. Further, it should be recognized that although only one valve assembly  121  and one hydraulic cylinder  12  are discussed in this disclosure, it is contemplated that there could be more than one valve assembly  121  attached to the chassis  11 , which could each control a different hydraulic cylinder  12  associated with the same or a different implement. 
   Referring to  FIGS. 6   a – 6   d , there is provided an example of the inter-relation between the hydraulic cylinder  12 , the position of the poppet valve member  31  relative to the valve seat  32 , the hydraulic pressure of the pump port  37 , and the configuration of the pilot valve assembly  40 . The graphs show an example procedure in opening the hydraulic cylinder  12  in two stages from 0% where the cylinder  12  is fully closed to 100% where the cylinder  12  is fully open. In this example only the first poppet valve assembly  51  and the third poppet valve assembly  53  as shown in  FIG. 4  are used, along with their respective pilot valve assemblies  55 ,  57 , because the cylinder  12  is being extended. The first pilot valve assembly  55  will move the poppet valve member  31  away from the valve seat  32  of the first poppet valve assembly  51  to fluidly connect the pump port  37  with the head port  22  of the hydraulic cylinder  12  in order for hydraulic fluid to open the hydraulic cylinder. Simultaneously, the third pilot valve assembly  57  will introduce hydraulic fluid to the control chamber  36  of the third poppet valve assembly  53  and move the poppet valve member  31  away from the valve seat  32  of the third poppet valve assembly  53 , fluidly connecting the rod port  23  of the hydraulic cylinder  12  with the drain port  38  of the valve assembly  21 . In this way the hydraulic fluid will drain from the rod port  23  of the hydraulic cylinder  12 , allowing the hydraulic cylinder  12  to open as described in  FIG. 6   a . It will be recognized that if the hydraulic cylinder  12  were moving in the direction opposite of that described above, then the second and fourth poppet valve assemblies  52 ,  54  would be utilized, along with their respective pilot valve assemblies  56 ,  58  in a similar manner recognizable to one skilled in the art. 
     FIG. 6   c  shows the hydraulic pressure of the pump port  37  at some level from time t=0 to time t=3, then the hydraulic pressure temporarily decreases at t=4 and resumes at t=5 until t=10. The hydraulic pressure then increases to some higher pressure from t=10 to t=11, at which point it temporarily decreases again at t=16, but otherwise remains constant from t=11 to t=20. 
   It will further be observed that  FIG. 6   b  describes the displacement of the poppet valve member  31  from the valve seat  32  from time t=0 through t=20, while  FIG. 6   d  describes the configuration of the pilot valve assembly  40 . From time t=0 through t=1,  FIG. 6   b  shows that the poppet valve member  31  is moving away from the valve seat  32 . During this time  FIG. 6   d  shows that the pilot valve assembly  40  is in the second configuration  40   b , and  FIG. 6   a  shows that the hydraulic cylinder  12  is accelerating. 
   From time t=1 through time t=3,  FIG. 6   a  shows the motion of the hydraulic cylinder  12  to be relatively linear. During this time the poppet valve member  31  is hydraulically locked in position by the pilot valve assembly  40  in the third configuration  40   c  as shown in  FIG. 6   d . Similar movement in the hydraulic cylinder  12  is observed from time t=5 through t=7. 
     FIG. 6   c  shows that the hydraulic pressure drops from t=3 through t=4, and then returns to its former level from t=4 through t=5. During this time,  FIG. 6   a  shows that the movement of the hydraulic cylinder  12  remains linear.  FIGS. 6   d  and  6   b  illustrate that this is accomplished at least in part by the pilot valve assembly  40  moving the poppet valve member  31  further away from the valve seat  32  from t=3 through t=4, and then returning the poppet valve member  31  to its former position from t=4 through t=5. By moving the poppet valve member  31  away from the valve seat  32 , the flow area across the valve seat  32  is increased, which compensates for the temporarily lowered hydraulic pressure. When  FIG. 6   c  shows the hydraulic pressure level returning to normal,  FIG. 6   d  shows the pilot valve assembly  40  moving the poppet valve member  31  back to its previous position in  FIG. 6   b.    
   From time t=7 through t=8,  FIG. 6   a  shows the motion of the hydraulic cylinder  12  decreasing. During this time  FIG. 6   d  shows that the pilot valve assembly  40  is in the first configuration  40   a , which causes the poppet valve member  31  to move into contact with the valve seat  32  as shown in  FIG. 6   b . Once in contact with the valve seat  32  at time t=8,  FIG. 6   d  shows that the pilot valve assembly  40  is in the third configuration  40   c , hydraulically locking the poppet valve member  31  in position. As seen in  FIG. 6   a , during this time the hydraulic cylinder  12  remains motionless, as there is no flow area across the valve seat  32  of the valve assembly  21 , even when  FIG. 6   c  shows the hydraulic pressure increasing from time t=10 through t=11. 
   Graphs  6   a–d  demonstrate a similar behavior of the hydraulic cylinder  12  from time t=12 through t=20 as to the behavior observed from time t=0 through t=8, even though  FIG. 6   c  shows an increase in hydraulic pressure. Despite this increase,  FIG. 6   a  shows the hydraulic cylinder  12  moving at the same rate as it did previously. It will be seen by examination of  FIG. 6   b  that this is because the poppet valve member  31  is displaced to a distance closer to the valve seat  32 . By decreasing the displacement of the poppet valve member  31 , the increased hydraulic pressure is at least partially compensated for. It will further be observed that because the hydraulic pressure is higher from time t=12 through t=12.5, the pilot valve assembly  40  needs to be in the second configuration  40   b  for a lesser amount of time to move the poppet valve member  31 , as seen in  FIGS. 6   b  and  6   d . It will be noticed that the time to move the poppet valve member  31  back into position is decreased in a similar manner, as shown in  FIGS. 6   b  and  6   d . It should also be observed that when a  FIG. 6   c  shows a temporary fluctuation in hydraulic pressure from time t=15 through t= 17 ,  FIGS. 6   b  and  6   d  show the pilot valve assembly  40  and poppet valve member  31  being moved to compensate in a manner similar to time t=3 through t=5. In this manner the hydraulic pressure variance is at least partially compensated for, and the motion of the hydraulic cylinder  12  remains relatively linear, as observed in  FIG. 6   a.    
   It will be appreciated by one skilled in the art that  FIGS. 6   a – 6   d  are merely demonstrative, and are not intended to limit the spirit or scope of this disclosure in any way with respect to time or degree of motion of any element of the valve assembly  121 . It is contemplated that the pilot valve assembly  40  could have different flow areas through the first configuration  40   a  and the second configuration  40   b  such that the movement of the poppet valve member  31  could be controlled with higher precision, allowing for greater uniformity in observed hydraulic cylinder  12  movement. 
   INDUSTRIAL APPLICABILITY 
   This disclosure contemplates the valve assembly  121  disclosed herein specifically to manipulate a hydraulic cylinder  12  attached to a work machine implement  14  connected to the chassis  11  of a backhoe type work machine  10  as provided in  FIG. 5 . In one embodiment herein contemplated, the valve assembly  121  would include a pump port  37  and a drain port  38  fluidly connected via a plurality of poppet valve assemblies  51 ,  52 ,  53 ,  54  to the head port  22  and the rod port  23  of the hydraulic cylinder  12 . 
   The actuator  41  of a pilot valve assembly  40  is operable to move the pilot valve member  42  to effect either fluid connection or fluid isolation of the control chamber  36  of the poppet valve assembly  30 .  FIG. 1  shows that when the pilot valve assembly  40  is moved into the first configuration  40   a , the control chamber  36  is fluidly connected to the input port  34  of the poppet valve assembly  30 . This will allow pressurized hydraulic fluid to fill the control chamber  36 , which will cause hydraulic pressure on the poppet valve member  31  via the control hydraulic surface  35 . This will result in the poppet valve member  31  moving into contact with the valve seat  32 , reducing and ultimately removing a flow area across the valve seat  32 . It will be noted that the actuator  41   a  is biased such that the natural state of the pilot valve assembly  40  is in this first configuration  40   a  in order to prevent unintentional movement of the associated hydraulic cylinder  12  and work machine implement  14 . 
   Similarly, when the pilot valve assembly  40  is in the second configuration  40   b , the control chamber  36  is fluidly connected to the output port  33  of the poppet valve assembly  30  as shown by  FIG. 2 . Because the output port  33  will be at a lower pressure than the control chamber  36 , hydraulic fluid will flow out of the control chamber  36 , resulting in a negative pressure across the control hydraulic surface  35  of the poppet valve member  31 . This will cause the poppet valve member  31  to move away from the valve seat  32 , creating a flow area across the valve seat  32  between the input port  34  and the output port  33  of the poppet valve assembly. 
   In the third configuration  40   c , the control chamber  36  is fluidly isolated from either the input port  34  or the output port  33  by the pilot valve assembly  40  as shown in  FIG. 3 . It will be recognized that because the control chamber  36  is fluidly isolated, the poppet valve member  31  is hydraulically locked into position because the hydraulic chamber  36  contains a certain amount of hydraulic fluid that will neither compress nor expand. This will result in the poppet valve member  31  being almost completely immobile regardless of changes in the pressure differential between the pump port  37  and the drain port  38  of the valve assembly  21  as shown in  FIGS. 6   b  and  6   d.    
   One skilled in the art will recognize that in  FIG. 4  the input port  34  of the first and fourth poppet valve assemblies  51 ,  54  would be connected to the pump port  37 , while their output ports  33  would be connected to the head port  22  and the rod port  23  of the hydraulic cylinder  12 , respectively. Likewise, the output port  33  of the second and third poppet valve assemblies  52 ,  53  will be connected to the drain port  38  while their input ports are connected to the head port  22  and rod port  23  of the hydraulic cylinder  12 , respectively. 
   The advantages in control from this valve assembly  121  will be apparent to one skilled in the art. It is contemplated that the work machine operator will make a control change that will be interpreted by the electronic controller  13 . The electronic controller  13  will then gather data such as the pressure differential between the first pressure sensor  61  and the second pressure sensor  62 , and the position of the poppet valve member  31  in relation to the valve seat  32  via the position sensor  60 . The electronic controller  13  then directs the actuator  41  of the pilot valve assembly  40  to move the pilot valve member  42  in a manner as shown in  FIGS. 6   b–d . If the pressure differential is high, then the poppet valve member  31  will be displaced less from the valve seat  32  than if the pressure differential were low as seen in  FIGS. 6   b  and  6   c . In this manner, the fluid pressure on the hydraulic cylinder  12  will be controlled and the movement of the hydraulic cylinder  12  will be effectively the same whether the pressure differential is high or low, as shown in  FIG. 6   a . Thus, the results that the work machine operator observes will be almost uniform, however the internal positioning of the valve assembly  121  may differ. In this way the problems of difficult and unpredictable controls may be significantly lessened. An additional improvement in the current valve assembly  121  as disclosed is that a poppet valve member  31  can be moved to a location away from the valve seat  32  and hydraulically locked in place via fluid isolation of the control chamber  36  for a prolonged period of time. The valve will not inherently leak because it is not a spool valve, and because it is fluidly isolated it is de-sensitized to the pressure changes that characterized difficulties with previous poppet valve designs. 
   It will be appreciated that the embodiment described above is merely exemplary, and multiple other configurations involving at least one poppet valve assembly  30  and at least one pilot valve assembly  40  herein disclosed are contemplated. Those skilled in the art will appreciate that other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.