Abstract:
A 4-way 3-position direct acting tandem center neutral valve has two 3-way, 2-position poppet valves configured so as to provide 4-way, 3-position tandem center neutral valve functions so that it is direct acting and essentially zero leak.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This claims the benefit of U.S. Provisional Patent Application No. 60/636,150 filed Dec. 15, 2004. 
     
    
     STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       FIELD OF THE INVENTION 
       [0003]    This invention relates to hydraulic control valves, and in particular to 4-way 3-position valves. 
       BACKGROUND OF THE INVENTION 
       [0004]    In a tandem center neutral hydraulic control valve, the load, for example, a double-acting hydraulic cylinder, is held in a particular position if the power is off to the valve. In other words, the load is held in the position it was in when the valve was turned off. 
         [0005]    Prior tandem center neutral hydraulic control valves have typically been 4-way, 3-position solenoid operated spool valves. Spool valves inherently have clearances that result in leakage, which is undesirable in a tandem center neutral valve, since the whole idea is to hold the load at a particular position. In other prior tandem center neutral valves, a master/slave arrangement was used in which the master was a spool valve that produced a pilot pressure to control a slave valve that may have been a poppet valve, to hold the poppet valve closed or to open it. Such valves have leakage in the spool sections and also are not, in the case of the master/slave valve, direct acting since the solenoid that controls the master valve is to produce a pilot pressure, that in turn controls the slave valve. Therefore, a need exists for a direct acting, zero leak 4-way 3-position (4/3) tandem center neutral hydraulic control valve. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention provides an improved 4-way 3-position tandem center neutral direct acting valve by providing a pair of 3-way 2-position poppet valves in a system that achieves the objectives of a 4-way 3-position tandem center neutral valve. 
         [0007]    In particular, the two solenoid-operated poppet valves are incorporated in a circuit such that one of them has its center port connected to a source of pressure, with the center port of the other poppet valve connected to tank. The normally open-to-center ports of both poppet valves are connected to one another and are connected to the load by a pressure operated normally biased closed one-way valve that in the absence of its pilot override pressure does not permit flow back to the normally open ports of the poppet valves from the load. 
         [0008]    The normally closed ports of the poppet valves may also be connected to the load by a pressure operated normally biased closed one-way valve that in the absence of its pilot override pressure does not permit flow back to the normally open ports of the poppet valves from the load. For example, if the load is a double acting hydraulic cylinder, these ports can be connected to the bore side of the cylinder and the other ports can be connected to the rod side, downstream from the one-way valve. The pilot pressure for operating the one-way valve is dependent on the pressure at the normally-closed ports of the poppet valves. The pilot pressure for the other one-way valve, if provided, is dependent on the pressure at the normally open ports of the poppet valves. 
         [0009]    In this configuration, actuating the second poppet valve connects the source of pressure to the normally-closed port, which also provides the override pressure to open the one-way valve to permit reverse flow from the load to the normally-open port of the first poppet valve that is connected via the center port of that poppet valve to tank. When the second poppet valve is actuated, the normally-open port of that valve is blocked. When a sufficient volume of fluid or pressure has been supplied to the load by actuation of the second poppet valve, that poppet valve can be de-energized. This holds the pressure delivered to the load by the second poppet valve, and directs the source of pressure to tank via the normally-open port of the second valve that is connected to tank via the center port of the first valve. The pressure of the load maintains the one-way valve open to flow in the normally-closed direction of the one-way valve. 
         [0010]    When the first poppet valve is energized, while maintaining the second poppet valve de-energized, the normally-closed port of the second poppet valve is opened to tank via the center port of the first valve. In addition, the normally-open port of the first valve is blocked, which blocks the flow of fluid from the pressure source. This has the effect of delivering the fluid from the pressure source flowing through the second valve to the load, through the one-way valve. The pilot pressure on the one-way valve coming from the normally-closed port of the second poppet valve is relieved in this state of energization of the first poppet valve. The pilot pressure on the other one-way valve, if provided, coming from the normally-open ports of the first and second poppet valves will hold the other one-way valve in the open position to allow flow from the bore side of the cylinder to tank. If the first poppet valve is deenergized, the first one way check valve will hold the load until the pilot override pressure is once again supplied to the first one way check valve, for example by energizing the second poppet valve. If the second poppet valve were to also be energized while energizing the first poppet valve, flow from the pump source is directed to tank and flow from the rod side of the load would be blocked by the first one way check valve and also by both poppet valves, and flow from the bore side of the load would be blocked by the second check valve, if provided. 
         [0011]    This provides a zero-leak direct acting valve that can be used as a 4-way 3-position tandem center neutral valve, which is solenoid operated. 
         [0012]    Other objects and advantages of the invention will be apparent from the detailed description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a front plan view of a valve of the invention; 
           [0014]      FIG. 2  is a top plan view of the valve of  FIG. 1 ; 
           [0015]      FIG. 3  a side plan view of the valve; 
           [0016]      FIG. 4  is a cross-sectional view from the plane of the line  4 - 4  of  FIG. 1 ; 
           [0017]      FIG. 5  is a cross-sectional view from the plane of the line  5 - 5  of  FIG. 1 ; 
           [0018]      FIG. 6  is a cross-sectional view from the plane of the line  6 - 6  of  FIG. 1 ; 
           [0019]      FIG. 7  is cross-sectional view from the plane of the line  7 - 7  of  FIG. 2 ; 
           [0020]      FIG. 8  is a cross-sectional view from the plane of the line  8 - 8  of  FIG. 3 ; 
           [0021]      FIG. 9  is a cross-sectional view from the plane of the line  9 - 9  of  FIG. 3 ; and 
           [0022]      FIG. 10  is a schematic circuit diagram of the valve of  FIGS. 1-9 , incorporated into an electrohydraulic system. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]      FIGS. 1-9  illustrate a valve  40  of the invention and  FIG. 10  is a hydraulic circuit of the valve  40  integrated into a hydraulic system. The numbers used in  FIG. 10  to identify passages and components correspond to the numbers used throughout  FIGS. 1-9  to identify the corresponding passages and components. 
         [0024]    Referring particularly to  FIGS. 1-9 , the valve  40  includes two identical 3-way 2-position solenoid-operated spring return poppet valves  24  and  25 . The poppet valves  24  and  25  may be of any suitable construction, with the construction described in U.S. Pat. No. 5,111,840 being one possibility and the valve disclosed herein. The description of the construction and operation (col. 3, line 10-col. 5, line 62) of the poppet valve disclosed in U.S. Pat. No. 5,111,840 is hereby incorporated by reference as if fully set forth herein. As is well known, a poppet valve differs from a spool valve in that in a poppet valve a surface of the poppet valve element seats axially against a valve seat, whereas in a spool valve, the valve spool is axially slidable in a valve bore to create a radial seat, which requires there to be a clearance, however small, between the outside diameter of the valve spool and the inside diameter of the valve bore, which inevitably results in some amount of leakage. A poppet valve, having an axially abutting surface against a valve seat, has zero leakage, and therefore is preferred in some applications over a spool valve, for example where load holding is desired. 
         [0025]    Each valve  24  and  25  is solenoid-operated and is spring return. As is well known with 3-way 2-position poppet valves, a common port is in the middle of the valve with a normally-open port on one side and a normally-closed port on the other side of the center port. When the solenoid of the valve is de-energized, the spring moves the poppet valve sealing element against the seat that is adjacent to the normally-closed port, which closes that port in the de-energized position and opens the normally-open port in the de-energized position of the valve. When the solenoid is energized, the poppet valve sealing element is urged by the solenoid against the operation of the spring to seat against the seat that is adjacent to the normally-open port of the solenoid valve, which closes that port and opens the normally-closed port of the solenoid valve. With reference to  FIG. 10 , the center port of valve  24  is identified by reference number  16 , the normally-open port is identified by reference number  6 , and the normally-closed port is identified by reference number  17 . For valve  25 , the center port is reference number  19 , the normally open port is reference number  4  and the normally-closed port is reference number  20 . Valves  24  and  25  are illustrated in their normal positions in  FIG. 10 . 
         [0026]    The pressure supply line is passageway  1  throughout the drawings and this is shown in  FIG. 10  as being supplied by a pump or other source S of pressurized hydraulic fluid, which draws its fluid from tank or reservoir  22  that is or near atmospheric pressure. Reference number  22  also denominates the ports and passageways that are connected to the reservoir or tank, for example port  22  in  FIG. 7  which is connected to the tank. In addition, tank  22 , represented by port  22 , is connected to the center port  16  of valve  24  via passageway  7  ( FIG. 9) and 21  ( FIG. 10 ) and these passages are connected to port  22 , which is connected to the tank or reservoir source of fluid at or near atmospheric pressure. 
         [0027]    Port  1  which receives pressurized fluid from the pump S communicates with passageway  2  as illustrated in  FIG. 7  and  FIG. 10  and passageway  2  communicates with passageway  3  as illustrated in  FIG. 8 . Passageway  3  is in direct communication with center port  19  of valve  25  as illustrated in  FIGS. 8 and 10 . Normally-open port  18  of valve  25  communicates with passageway  5  through passageway  4  as illustrated in  FIG. 6  and is in communication with passageway  6  as illustrated in  FIGS. 6 and 10 . Passageway  6  is in direct communication with normally-open port  15  of valve  24  and passageway  5  communicates with pressure operated normally biased closed one-way check valve  26  as illustrated in  FIG. 7 . Flow from passageway  5  toward check valve  26  can flow through the check valve  26  to passageway  9  without a significant restriction, but cannot flow in the reverse direction unless a pilot pressure is applied to valve  26  via passageway  13 . A pressure at port  18  also lifts the ball of the one-way check valve  28  off its seat, with the pressure from port  18  being communicated to piston chamber  27  ( FIG. 7 ) of valve  28  via passages  4 ,  5  and  8 , to permit flow in the direction from port A to the normally closed port  20  of valve  25 . Pressurizing passageway  27  moves piston  30  that pushes a pin to lift the ball of the check valve  28  off of its seat, so as to permit flow from passageway  29  to passageways  14 ,  11  and  12  if valve  24  is energized. If there is no significant pressure at port  18  of valve  25 , then one way check valve  28  is closed to flow in the direction from port A to line  14  by its spring and any pressure on it from port A. Although a pressure at port  18  will open valve  28  to flow in the normally closed direction, that flow is from port A and no significant flow or leakage is permitted from port B. 
         [0028]    Passageway  9  is connected to port B ( FIG. 1  and  FIG. 10 ) which as illustrated in  FIG. 10  can be connected to a load. As illustrated, this load may be the rod side of a hydraulic actuator H. Port A of the valve  40  is connected to another load, which as illustrated in  FIG. 10  may be the bore side of the hydraulic actuator H. The two loads connected to the ports A and B may be independent of one another, but as illustrated in  FIG. 10  they are opposite sides of the piston of the same hydraulic actuator. A pressure at port  20  of valve  25  also lifts the ball of one-way check valve  26  off its seat, with the pressure from port  20  being communicated to piston chamber  14  ( FIG. 7 ) of valve  26  via passages  10 ,  11  and  13 , to permit flow in the direction from port B to the normally open port  15  of valve  24 . Pressurizing piston chamber  14  moves piston  30  that pushes a pin to lift the ball of the check valve  26  off of its seat, so as to permit flow from the opposite side of the ball through passageway  9  to passageways  5  and  6 . If there is no significant pressure at port  20  of valve  25 , then one way check valve  26  is closed to flow in the direction from port B to line  5  by its spring and any pressure on it from port B. While a particular valve for the one way valves  26  and  28  has been illustrated, any type of one way valve that is opened by a pilot pressure to flow in the normally closed direction could be substituted for these valves. Although a pressure at port  20  will open valve  26  to flow in the normally closed direction, that flow is from port B and no significant flow or leakage is permitted from port A. 
         [0029]    Thus, the valve  40  operates as follows. With both valves  24  and  25  de-energized, pressure from the source S will be directed by valve  25  through port  18  of valve  25  to the normally open port  15  of valve  24  which is connected to tank  22 . Flow and pressure from the bore side of the cylinder H (port A) will be directed to the normally biased closed one-way valve  28  and therefore will be blocked. Thus, with both valves de-energized, the position of the actuator H is held constant against further retraction. 
         [0030]    If it is desired to further extend the actuator H, valve  25  is energized which places port  20  and port A in communication with the source of pressure S to provide a flow of fluid under pressure to the bore side of the actuator H. The pressure at port  20  holds the one-way check valve  26  open, which permits flow from the rod side of the actuator H to flow to normally open port  15  of valve  24  and from there to tank  22 . Thus, the piston of actuator H extends. When the new position desired of the actuator H is reached, valve  25  can be de-energized to hold that position. 
         [0031]    When it is desired to retract the actuator H, valve  24  is energized and valve  25  is not energized which places the bore side of actuator H, via port A, in communication with the tank  22 . Flow from the bore side is blocked from flowing to tank  22  by the one-way check valve  28 . Similarly, with valve  24  energized and valve  25  de-energized, fluid from the source flows through one-way check valve  26  to port B, in the normally open direction through valve  26 , and therefore to the rod side of actuator H. Port  15  of valve  24  is blocked when valve  24  is actuated so pressure from the source cannot flow to tank through valve  24 . As pressure builds in passageway  5 , due to valve  28  blocking flow in the normally closed position, the ball on the one-way valve  28  is lifted off of its seat. Thus fluid from the bore side can flow directly to tank through the valve  24 . When the retraction position desired is reached, valve  24  is de-energized which will permit the pressure at port A and B to equalize and when equalized the valve  26  shuts off against flow in the direction from port B to tank through the valve  26  (a light spring biasing the valve  26  closed is illustrated in  FIG. 10  and may be provided to aid in closing the valve in a near equalized pressure state across the valve, which holds the cylinder H in position, and valve  28  shuts off against flow in the direction from port A to tank through the valve  28  (a light spring biasing the valve  28  aids in closing the valve in a near equalized pressure state across the valve). As such, with a load being held against further extension of the actuator H, there will be no pressure at port A to open valve  26 , and therefore flow from port B will be blocked by valve  26 . Similarly, there will be no pressure at port  15  to open valve  28  and therefore flow from port A will be blocked by valve  28 . Thus, when both valves  24  and  25  are de-energized, the actuator H is held in position both from extending further or retracting further, with essentially zero leakage, so as to hold its position every time and with direct acting valves which do not require pilot pressures for operation. 
         [0032]    The valve  40  may also include an adjustable pressure relief valve  23  of any suitable configuration, as illustrated in  FIGS. 5 and 10 . The purpose of the pressure relief valve  23  is to relieve any excess pressures that occur in the lines between the valve  25  and the source of pressure S. Pressure relief valve  23  is connected to passageway  2  at its inlet and by passageway  21  to tank  22 . 
         [0033]    Many modifications and variations to the preferred embodiment described will be apparent to those skilled in the art. Therefore, the invention should not be limited to the embodiment described, but should be defined by the claims which follow.