Abstract:
A swing cylinder oscillation control circuit and valve for oscillating booms connects two hydraulic cylinders with a shuttle valve and two check valves to provide the higher cylinder pressure to a fluid inlet and a lower cylinder pressure to a fluid outlet of a fast-opening and a slow-closing check valve. The fast-opening and slow-closing check valve uses a poppet and spring to set a valve opening pressure and uses internal flow connections to a large diameter piston that works with mechanically adjustable piston and poppet strokes to control the time for valve closing.

Description:
BACKGROUND OF THE INVENTION 
     A typical hydraulic system for a backhoe loader swing function is shown in FIG.  1 . The manually operated direction control valve with pressure and tank connections is used to provide flow into one of two cylinders which function to oscillate a boom, and out of the opposite cylinder. A hydraulic hose or tube connects the piston rods of the cylinders such that when one cylinder extends, the other retracts. The rods of these cylinders are mechanically connected to the boom and control the rotation or swing function of the boom and any bucket attached thereto. With this system, the directional control valve is activated to start and maintain swing motion, and is centered, thus blocking all flow, to stop the swing motion. When this valve is centered, inertia of the moving boom and the bucket mass causes continued motion rather than an instantaneous stop. This continued motion compresses the fluid (especially any entrained air) in the cylinder that the boom and bucket are moving towards, thus resulting in a very high pressure in that cylinder. This high pressure stores energy much like a spring and creates a force that then causes the boom and the bucket to then move in the opposite direction, where the same phenomenon occurs. This oscillating motion eventually decays, but it delays the operator from continuing with digging or other work functions until the boom and the bucket stop. This also inhibits precise position control. 
     It is therefore a principal object of this invention to provide a swing cylinder oscillation control circuit and valve for oscillating booms which permits smooth deceleration at any stopping point in the swinging of the boom by sensing high pressure in one of the two cylinders that pivot or oscillate the boom. 
     A further object of this invention is to provide a swing cylinder oscillation control circuit and valve for oscillating booms which will permit an instantaneous stop of the oscillation of the boom by overcoming the inertia of the moving boom. 
     These and other objects will be apparent to those skilled in the art. 
     BRIEF SUMMARY OF THE INVENTION 
     A swing cylinder oscillation control circuit and valve for oscillating booms has a hydraulic circuit of four valves incorporated into a typical boom control system. A shuttle valve is used to connect the higher pressure of one of the cylinders used to oscillate the boom to the inlet of a variable pressure check valve. Two standard check valves then connect the lower pressure of one or the other of the cylinders to the outlet of a variable pressure check valve. The variable pressure check valve is set to be closed at normal operating pressures and will open only when the pressure difference between the cylinders exceeds a set value, e.g., when the boom and the bucket swing momentum creates a high pressure in one cylinder. The variable pressure check valve opens at one pressure differential commonly known as the “crack pressure”, and closes at another pressure differential, commonly known as the “re-seat pressure”. The crack and re-seat pressures are controlled to be adjustable and to be independent of each other. This valve then functions in the system by opening a flow connection between the two cylinders as soon as any swing “overshoot” causes a high pressure difference. The amount of fluid to be transferred through this connection is controlled by accurately setting both the crack and re-seat pressure of the variable pressure check valve. Transferring the proper amount of fluid from the high pressure cylinder to the low pressure cylinder at the onset of any swing “overshoot,” then results in a smooth end-of-motion for the boom and the bucket swing, and provides precise position control. 
     A variable pressure check valve consists of a poppet with a sealing seat which slides in a bore; a piston which slides in a separate larger bore; a spring between the poppet and piston; a sleeve and retainer assembly containing the valve; and internal passages which interconnect these components. In normal operation, the spring holds the poppet against the seat, blocking flow from the inlet to the outlet. Inlet pressure is communicated through an orifice in the poppet to the top of the piston, and outlet pressure is communicated through a hole in the poppet to the bottom of the piston. The difference between higher inlet and lower outlet pressure creates a force on the piston holding it in the position shown and maintaining the spring force on the poppet. When the inlet-to-outlet pressure difference exceeds a pre-set value control by the poppet seat area and installed spring force, the poppet lifts creating a connection from the inlet to the outlet. This will cause the inlet and outlet pressures to begin to equalize. As this pressure difference decreases, the force on the piston decreases and the spring, normally in compression, will tend to cause the piston to lift. As the piston lifts, the spring compression is reduced therefore lowering the spring force that acts on the poppet. Since the spring force and the poppet seat area control the inlet-to-outlet pressure difference, this reduced force results in a reduced pressure difference or a re-seat pressure, that causes the valve to close. The opening and closing pressure are therefore determined by the poppet seat area; the spring strength and stiffness; and the difference between the poppet and piston strokes which can be controlled accurately and independently of each other. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS AND PHOTOS 
     FIG. 1 is a schematic view of a prior art hydraulic system for a backhoe loader swing function; 
     FIG. 2 is a view similar to that of FIG. 1 but shows the shuttle valve, variable pressure check valve, and standard check valves which have been added to the system of FIG. 1; and 
     FIG. 3 is a cross-sectional view of the variable pressure check valve of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The prior art system of FIG. 1 includes a frame  10 , a pivotal boom  12 , and first and second hydraulic cylinders  14  and  16  which are pivotally secured to the frame and the boom for oscillating the boom. The numeral  18  designates the piston for cylinder  14 , and the numeral  20  designates the piston for cylinder  16 . Piston rods  26  connect the pistons to the boom. The boom is pivotally connected to the frame  10  by means of the pivotal connection  28 . 
     A first conduit  30  interconnects the cylinders  14  and  16  above the respective pistons thereof. A directional control valve  32  used by the operator to control the movement of boom  12  through the cylinders  14  and  16  is connected to the lower portion of each of the cylinders by conduits  34  and  36 , respectively. It is this configuration of FIG. 1 that is unable to smoothly deal with the inertia of the moving boom and bucket mass, and which cannot achieve an instantaneous stop of the boom during its pivotal motion. 
     With reference to FIG. 2, the improvement of this invention over the conventional structure in FIG. 1 is illustrated. Similar numerals have been shown in FIG. 2 which correspond to like components in FIG.  1 . Attention is directed to the first and second hydraulic zones  22  and  24  above and below each of the pistons  18  and  20 , respectively. Added to the system of FIG. 1, as shown in FIG. 2, is a first hydraulic control line  38  which interconnects conduits  34  and  36 . A second hydraulic control line  40  is parallel to line  38  and also interconnects lines  34  and  36 . A shuttle valve  42  is imposed in line  38 , and conventional directional check valves  44  and  46  are imposed in line  40  in spaced condition. A variable pressure check valve  48  is imposed between the shuttle valve  42  and line  40  at a point in between the check valves  44  and  48 . 
     With reference to FIG. 3, the details of the variable pressure check valve  48  are disclosed. A valve body  50  has first and second bores  52  and  54  with the bore  52  having a diameter greater than that of the poppet seat  60 . End cap  55  closes the “upper” end of bore  52 . A fluid inlet port  56  is located at one end of the bore  54  and a valve seat  60  is formed adjacent thereto. A poppet valve body  62  is slidably mounted in the bore  54  and includes a valve element  64  which is adapted to engage valve seat  60  to close inlet port  56  at times. The numeral  66  designates an outlet port in the second bore  54  which is located in spaced condition with respect to the valve seat  60  and the inlet port  56 . 
     Poppet valve body  62  has a head portion  68 . Again, the poppet valve body  62  slidably engages the inner wall  70  of bore  54 . 
     A piston  72  is slidably mounted within the first bore  52  which has a center portion  74 , a first end space  76 , and a second end space  78 . 
     A longitudinal bore  80  is located on the longitudinal center line of poppet valve body  62  and has a small orifice  82  which connects the bore  80  with the inlet port  56 . A hollow stem  84  extends from the inner end of poppet valve body  62 , and slidably extends through center bore  86  in piston  72 , and terminates in the first end space  76  of bore  52 . A spring  88  surrounds stem  84  and has its opposite ends engaging piston  72  and poppet valve body  62 . A passageway  90  is located in the poppet valve body  62  and connects the outlet port  66  with the end space  78  “below” piston  72 . The dimensional arrows  92  and  94  reflect the respective strokes of the poppet valve body  62  and the piston  72 . 
     The design of the pressure check valve  48  can be varied and is determined by the area of valve seat  60 , the strength of spring  88  and its spring rate or stiffness, and the difference between the poppet and piston strokes as indicated by the arrows  92  and  94 , respectively. It is seen that the poppet and piston strokes can be controlled accurately and independently of each other. 
     As previously indicated, the variable pressure check valve  48  is set to be closed at normal operating pressures and will open only when the pressure differential between the cylinders  14  and  16  exceeds a predetermined value. The spring  88  is typically set to establish a crack pressure of 3300 psi. When the poppet valve element  64  opens to connect the inlet port  56  with the outlet port  56 , the fluid pressures within the cylinders commence to equalize, and the piston  72  moves “upwardly” which lowers the “re-seat” pressure to slowly close the poppet valve element  64  on seat  60 . When this takes place, the fluid pressure returns the piston  72  to the position shown in FIG.  3 . 
     This is accomplished, as previously discussed, as the boom is being pivoted (i.e., “normal operation”) the spring  88  holds the poppet valve element  64  against the seat  60 , blocking flow from the inlet  56  to the outlet  66 . Inlet pressure is communicated through the orifice  82  in the lower end of the poppet valve body  62  to the top of the piston  72 , and outlet pressure is communicated through the orifice  90  in the poppet valve body  62  to the end space  78  “underneath” piston  72 . The difference between the higher inlet pressure at port  56  and the lower outlet pressure at port  66  creates a force on the piston  72  holding it in the position shown in FIG.  3  and maintaining the force of spring  88  on the poppet valve body  62 . When the inlet-to-outlet pressure difference exceeds a pre-set value (e.g., 3,300 psi) created by the area of the bottom of the poppet valve body  62  surrounded by seat  60 , the fluid pressure at port  56  overcomes the “downward” force of the spring  88 , and the poppet valve body lifts creating a fluid connection from the inlet  56  to the outlet  66 . This will cause the inlet and outlet pressures to equalize. The shuttle valve  42  will allow the high fluid pressure created in the bottom  24  of either cylinder to trigger the infusion of high fluid pressure to inlet  56  regardless of which cylinder develops this high pressure because of bringing the boom to a stop during its pivotal movement in one direction or another. As seen in FIG. 2, high fluid pressure moving in either direction through line  38  towards shuttle valve  42  will be diverted towards the inlet  56  of the variable pressure check valve  48 . When that pressure from one cylinder or another maximizes when the boom stops, and if that pressure at inlet  56  is sufficient to lift the poppet valve body  62  from seat  50 , the system begins to do its work by alleviating the slack imposed by the high inertial-induced pressures. 
     When the inlet and outlet pressures begin to equalize upon being in communication with each other, the force on the “top” of piston  72  decreases. This is because the force on the “top” of piston  72  in space  76  is the high inlet pressure communicated through orifice  82  and hollow stem  84 . As the inlet pressure begins to decrease, creating a decrease in pressure differential, when inlet and outlet pressure join upon the opening of poppet valve body  62 , the downward force on the piston  72  decreases and the spring will tend to cause the piston  72  to lift. As the compression in spring  88  thereupon decreases, the spring force on the poppet valve body similarly decreases which results in reduced pressure differential (or a re-seat pressure) that causes the poppet valve body  62  to close on seat  60 . 
     As also described above, the crack and re-seat pressures are controlled to be adjustable and to be independent of each other. This valve then functions in the system by opening a flow connection between the two cylinders as soon as any swing “overshoot” causes a high pressure difference. The amount of fluid to be transferred through this connection is controlled by accurately setting both the crack and re-seat pressure of the variable pressure check valve. Transferring the proper amount of fluid from the high pressure cylinder to the low pressure cylinder at the onset of any swing “overshoot” then results in a smooth end-of-motion for the boom and the bucket swing, and provides precise position control. 
     The passageway  90  in poppet valve body member  62  allows reduced fluid pressure from outlet  66  to be normally “under” the piston  72 , but also allows the fluid to vacate space  78  as the re-seat pressure assumes control and the piston  72  moves downwardly as the pressure differential between inlet and outlet pressure decreases. 
     The variable pressure check valve  48  is mounted within the circuit shown in FIG. 2 with the inlet  56  being adjacent to shuttle valve  42  and the outlet  66  being connected to line  40  between check valves  44  and  48 . 
     It is therefore seen that the check valve  48  will automatically sense the high pressure in one of the cylinders  14  and  16  which will exert “upward” pressure on the poppet valve body  62  to cause it to move upwardly, which will cause the piston  72  to move “upwardly” to overcome the crack pressure of spring  88 , whereupon the pressure differential in the cylinders  14  and  16  will start to equalize to create the “re-seat” pressure and which will allow the slow closing of the poppet valve as described heretofore. This phenomenon will provide smooth deceleration at any stopping point in the oscillation path of the boom  12 . Transferring the proper amount of fluid from the high pressure cylinder to the low pressure cylinder at the onset of any swing “overshoot” results in a smooth end-of-motion for the boom and provides for precise position control. 
     It is therefore seen that this invention will achieve at least all of its stated objectives.