Patent Publication Number: US-7913491-B2

Title: Hydraulic flow control system and method

Description:
TECHNICAL FIELD 
     This invention relates to the control of double-acting hydraulic cylinders e.g. in earth-moving equipment. In particular, this invention relates to use of flow regeneration to control double-acting cylinders in load-lowering and other operations where the cylinder rod extends under the influence of a load during the operation. 
     BACKGROUND 
     Use of flow regeneration circuits in controlling double-acting cylinders, including cylinders with a main directional control valve, is known. U.S. Pat. No. 6,267,041 (Skiba et al.) discloses a fluid regeneration circuit for a hydraulic cylinder having a directional control valve, wherein the regeneration flow path includes a separate regeneration valve between the rod end and head end. The regeneration valve is under the control of a controller and directs flow from the rod end to either the head end or to the system tank during certain rod extending operations. However, such systems cannot accommodate certain operations where flow from the rod end to both the head end and to the tank are desired, or where regenerative flow to the head end is required at relatively low rod extension speeds, such as controlled load-lowering e.g. in a wheel loader. Rather, the circuit disclosed in the Skiba et al patent provides regeneration flow only for rod speeds and/or rod extension demands greater than a preselected threshold. 
     The present disclosure thus seeks to improve upon existing cylinder control apparatus and methods to mitigate one or more of these shortfalls. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect of the disclosure, apparatus is disclosed for controlling a double-acting hydraulic cylinder during a load-induced rod-extending operation, the cylinder being activated by fluid supplied from a reservoir by a pump, the cylinder having a rod end, a head end, a piston connected to rod for engaging the load, the cylinder piston being urged toward the rod end by the load during the operation. The apparatus includes a cylinder activating circuit including an activation valve for providing a flow path from the pump to the cylinder head end. The apparatus also includes a flow regeneration circuit fluidly connecting the cylinder rod end and the cylinder head end and configured for providing flow from the cylinder rod end to the cylinder head end during rod extension, the regeneration circuit including a regeneration flow valve. The apparatus further includes a controller operatively connected to the regeneration flow valve and the activation valve, the controller being responsive to rod-extending rate demands from an operator to control the activation valve to provide flow from the pump to the head end and to control the regeneration valve to provide flow from the rod end to the head end. The cylinder activating circuit also includes a return flow path between the cylinder rod end and the fluid reservoir, and a return valve positioned in the return flow path and configured to control flow from the cylinder rod end to the fluid reservoir. Both the return valve and the activation valve are controllable by the controller independently from the regeneration flow valve. 
     In another aspect of the present disclosure, a method is disclosed for controlling a double-acting hydraulic cylinder during load-induced rod-extending movement, the cylinder being activated by pressurized hydraulic fluid supplied from a reservoir by a pump and an activation circuit including a directional control valve for selectively directing the pressurized fluid to the cylinder head end or the rod end, the activation circuit also including a return flow path from the rod end to the reservoir for fluid displaced from the rod end during rod-extension. The method includes providing a regeneration flow path from the rod end to the head end, and controlling fluid flow to the head end during the load-induced rod-extension. The controlling method element includes independently controlling the fluid flow from the rod end through the regeneration path to the head end and independently controlling the fluid flow from the pump to the head end, and restricting the flow of displaced fluid from the rod end to the reservoir along the return path independently from controlling the flow through the regeneration path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic showing apparatus for controlling a double-acting hydraulic cylinder during a load-induced rod-extending operation, specifically a load-lowering operation; 
         FIG. 2  is a flow chart showing elements of a method for controlling a double-acting hydraulic cylinder during a load-induced rod-extending operation; 
         FIG. 3  is a chart showing flow coefficients versus directional control valve position and regeneration valve position, for the apparatus in  FIG. 1 ; and 
         FIG. 4  is a graph showing valve command versus operator rod extension rate demand, for the regeneration valve and the directional control valve of the apparatus in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     In one aspect of the disclosure, apparatus is disclosed for controlling a double-acting hydraulic cylinder during a load-induced rod-extending operation. The double-acting cylinder is of the type activated by fluid supplied from a reservoir by a pump, the cylinder having a rod end, a head end, and a piston connected to a rod for engaging the load. During the operation, the cylinder piston is urged toward the rod end by the load. With reference to  FIG. 1 , double-acting cylinder  12 , as would be readily understood by one skilled in the art, includes rod end  14 , head end  16 , and piston  18  connected to rod  20  for engaging/supporting load  22 . In some applications, such as the load-lowering operation in  FIG. 1 , cylinder  12  may be oriented with the rod extension direction in the direction of the force on the load tending to extend the rod, such as the force of gravity designated “G” in  FIG. 1 . However, the present disclosure also is intended to provide cylinder control in other load-induced rod extension operations such as for other cylinder orientations and for loads due to forces other than gravity. 
     Also in accordance with the first aspect of the disclosure, the control apparatus may include a cylinder activating circuit including an activation valve for providing a flow path from the pump to the cylinder head end. As depicted in  FIG. 1 , cylinder  12  is activated by pressurized hydraulic fluid from tank/reservoir  24  and pump  26  via a cylinder activation circuit designated generally by the numeral  28 . Circuit  28  includes conduits  30  and  32  operatively connected to allow fluid flow to and from rod end  14  and head end  16 , respectively, during a cylinder operation. Conduits  30  and  32  may be protected against pressure overloads such as by pressure relief valves  46  and  48 , respectively. One skilled in the art would understand for a cylinder operation requiring rod extension, with piston  18  moving toward rod end  14 , a flow out of rod end  14  through conduit  30  would be required. Also during such an operation, a flow into head end  16  through conduit  32  should occur during certain operating conditions in order to prevent the formation of voids in head end  16 . 
     Cylinder activation circuit  28  also may include directional control valve  34  that can provide control over the flow from pump  26  through conduit  32  to cylinder head end  16  during load-lowering or other load-induced rod-extension operation. As depicted in  FIG. 1 , control valve  34  is a directional control valve for selectively connecting output from pump  26  to conduit  30  or  32 , depending on the cylinder piston movement required for the desired operation. As depicted, directional control valve  34  may be spool-activated such that movement of the spool element to the right would complete a flow path from pump  26  through conduit  32  to head end  16 , while a leftward movement would complete a flow path from pump  26  through conduit  30  to rod end  14 . 
     Furthermore, as depicted, directional control valve  34  may also be a four-position four-way valve configured to provide a return flow path from cylinder rod end  14  or head end  16  to reservoir  24 , such as by conduit  36 , again depending upon the required cylinder operation as discussed above. Also as depicted in  FIG. 1 , directional control valve  34  may be a proportional valve for metering pressurized flow in accordance with a desired cylinder activation rate, such as may be provided by a suitable controller, such as controller  38 , using operator input from e.g. joystick  40  or other operator interface equipment. The control connection  42  between controller  38  and the directional control valve may be electrical, hydraulic, or pneumatic, as is convenient. 
     More specifically, and as shown in  FIG. 1 , direction control valve  34  is a pilot-controlled four-position, four-way valve. Regarding the four positions, namely positions  34   a ,  34   b ,  34   c , and  34   d , from right to left, the  34   b  position is the neutral position, the  34   a  position is for cylinder retraction, and both  34   c  and  34   d  positions are for cylinder rod extension. The  34   c  position does not allow any return flow from rod end  14  to tank (reservoir)  24  along conduit  30  and conduit  36 . However, the  34   d  position allows some return flow from rod end  14  to tank (reservoir)  24 , but restricts the flow at position  34   d  as represented by orifice designation  35  in  FIG. 1 , for reasons that will be clear from the subsequent discussion. 
     As discussed above and depicted in  FIG. 1 , cylinder  12  may be oriented such that lowering load  22  against the force of gravity will cause extension of rod  20 , causing a decrease in the cylinder volume portion at rod end  14  and an increase the cylinder volume portion at head end  16 . In some conventional apparatus and systems, all the fluid necessary to fill the expanding head end volume is supplied through the cylinder activation circuit from the fluid reservoir via the pump. In certain situations, however, the capacity of the activation circuit may be unable to supply hydraulic fluid to the cylinder at a rate sufficient to occupy the expanding head end volume for a desired rod extending rate. For example, apparatus configuration and/or operating conditions such as those required to supply hydraulic fluid under pressure to other hydraulic systems serviced by the same pump and reservoir, such as systems  44  depicted in  FIG. 1 , may put undo constraints on the rates at which the rod can be extended without encountering void formation in the head end of the cylinder. 
     Still in accordance with the first aspect of the disclosure, the control apparatus includes a flow regeneration circuit fluidly connecting the cylinder rod end and the cylinder head end. The flow regeneration circuit is configured for providing flow from the cylinder rod end to the cylinder head end during rod extension and includes a regeneration flow valve. As depicted in  FIG. 1 , flow regeneration circuit  50  may include conduit  52  interconnecting conduits  30  and  32  providing the required flow connection between the rod end  14  and head end  16 . One skilled in the art would appreciate that one or both ends of conduit  50  alternatively could be connected directly to the rod and head ends to provide the desired regeneration flow path. Regeneration circuit  50  further includes regeneration valve  54 , which may be a proportional valve as depicted in  FIG. 1  and may be operatively connected to controller  38  via connection  56 . Regeneration circuit  50 , as depicted, is separately controllable from directional control valve  34  and is configured to provide regeneration flow only from rod end  14  to head end  16 , and may include a check valve  58  and/or a regeneration valve  54  specifically configured for one-way flow. 
     Still further in accordance with a first aspect of the disclosure, the control apparatus may include a controller  38  operatively connected to the activation valve  34  and the regeneration valve  54  to provide, respectively, flow from the pump  26  to the head end  16  and flow from the rod end  14  to the head end  16 , during the load-induced rod-extending operation. As disclosed herein and discussed previously, controller  38 , which may include a microprocessor, is configured to independently control both directional control valve  34  and regeneration control valve  54  during the load-induced rod-extending operation. Due to the cylinder geometry, specifically the volume occupied by the rod  20  in the cylinder rod end  14 , the fluid exiting rod end  14  during a incremental rod extension movement is less than the corresponding volume increase in the cylinder head end  16  such that the regeneration flow through regeneration circuit  50  alone would be unable to supply sufficient flow to the head end  16 . Hence, the controller  38  is configured to provide sufficient additional pressurized flow from pump  26  through directional control valve  34 , to supply the additional hydraulic fluid to head end  16  to make up the short-fall in the regeneration flow for certain operating conditions to be discussed hereinafter. 
     Still in accordance with a first aspect of the disclosure, the cylinder activating circuit also includes a return flow path between the cylinder rod end and the fluid reservoir, and a return valve positioned in the return flow path and configured to control flow from the cylinder rod end to the fluid reservoir independently from the control of the regeneration valve. As depicted in  FIG. 1  spool-activated directional control valve  34  is configured to provide a return flow path from rod end  14  via conduit  30  to tank/reservoir  24  via conduit  36  but also provide the function of the return valve to totally restrict (i.e. cut-off) return flow in certain valve positions, specifically position  34   c , or to permit some return flow in other valve positions, such as position  34   d . Specifically, directional control valve  34  may be configured to restrict return flow from the rod end  14  through the return path during a load-induced rod extending operation, such as the load-lowering operation depicted. That is, directional control valve  34  may be configured to include the function of a return flow valve such that, under the control of controller  38 , pump  26  provides pressurized fluid to conduit  32 , and thus to cylinder head end  16 , during the rod extending operation, but fluid displaced from rod end  14  is totally restricted from traveling back to the fluid reservoir  24  for spool positions corresponding to rate demands less than a predetermined value. The return flow restriction provided by valve  34  may thus providing full regeneration to head end  16  (except for inadvertent leakage) through regeneration circuit  50  for certain situations, such as controlled load-lowering. Moreover, in situations, where only a minimum amount of flow to head end  16  from reservoir  24  via pump  26  through directional control valve  34  and conduit  32  would be required, the present apparatus and methods affording additional flow capacity for operation of other hydraulic systems such as systems  44 , due ti the preferential supply from rod end  14  to head end  16  via regeneration circuit  50 . Such a flow control configuration would also maximize the allowable rate of rod extension, consistent with the prevention of cavitation and void formation in the head end and related conduits. 
     Furthermore, directional control valve  34  and controller  38  may be configured to allow some flow via the return path  36  for load lowering rates greater than or equal to the predetermined rod extension rate demand value, thus permitting operation of the cylinder  12  in situations requiring a very high rate of rod extension and necessitating a higher rate of fluid flow out of cylinder rod end  14  than can be accommodated by regeneration circuit  50  alone. Such situations may include a “quick-drop” of load  22 , or a lowering of the rod to a standby position, such as ground level, during a shut-down. Other possible situations include rapid rod positioning, and maintenance operations. 
     In the  FIG. 1  depiction, directional control valve  34  is configured to prevent return flow through conduit  36  for a rightward spool movement less than a specific distance from the depicted neutral position, but to allow some return flow from rod end  14  to tank  24  for spool movement a rightward distance greater than or equal to the specified distance, which distance would correspond to the desired predetermined lowering rate, as discussed above. 
     For example,  FIG. 3  shows the metering (represented by a flow coefficient) provided by one possible configuration of four-position, four-way direction control valve  34  shown in  FIG. 1 . The  34   b  neutral position is where the spool displacement is between about −6 mm˜ and about +6 mm. At this neutral position, only an internal flow path in valve  34  (not shown) from pump  26  back to tank  24  is open, while the flow paths to head end  16  and rod end  14  via respective conduits  32  and  30  are closed. The internal flow coefficient from pump  26  back to tank  24  depicted as “A” in  FIG. 3 . The  34   a  position for rod retraction operation is where the spool displacement in directional control valve  34  is between about +6 mm to about +16 mm. At this valve position, the pump  26  flow is directed to rod end  14  through conduit  30  with the flow coefficient depicted as “C” in  FIG. 3 . The return flow from head end  16  is directed to tank  24  through conduits  32  and  36  and is depicted the applicable flow coefficient is depicted as “D” in  FIG. 3 . 
     The  34   c  position In  FIG. 1 , corresponding to cylinder extension under a load, is where the spool displacement is between about −6 mm to about −11 mm in the  FIG. 3  configuration. At this valve position, the pump  26  flow is directed to head end  16  through the flow path conduit  32 . The return to-tank flow path from rod end  14  stays closed, at this valve position. Hence, the flow from rod end  14  is not directed to tank  24 , but is essentially totally regenerated to head end  16  through regeneration valve  54  as shown in  FIG. 3 , with a flow coefficient designated by curve “F”. 
     In directional control valve  34  of  FIG. 1 , the  34   d  position is where the spool displacement is between about −11 mm to about −16 mm. At this valve position, pump  26  flow is directed to head end  16  through the flow path of conduit  32  and the applicable flow coefficient is depicted as “B” in  FIG. 3 . The return-to-tank flow path from rod end  14 , through conduit  30  to directional control valve  34 , and then through conduit  36  is, however, partially open as depicted in  FIG. 3  as having a flow coefficient “E”. The return flow from rod end  14  is therefore “restrictedly” directed to tank  24 , while the majority of the flow from rod end  14  is regenerated to head end  16  through regeneration path conduit  52 . The regeneration path flow coefficient “F” is shown in  FIG. 3  only for illustration, as directional control valve  34  is separate from regeneration valve  54 , and regeneration valve  54  and directional control valve  34  are controlled independently. One skilled in the art would be able to readily construct a suitable directional control valve for the above and similar configurations given this disclosure. 
     Controller  38 , which as stated above may include a microprocessor, is configured to control directional control valve  34 , which includes a return flow restriction function, and independently control regeneration valve  54 , to accommodate the desired rod-extension rate input from joystick  40 . The microprocessor memory in controller  38  may have stored relationships (“maps”) of joystick position/deflection versus rod extending rate, and/or spool travel versus rod extending rate. One skilled in the art also would be able to provide a controller having the functions and capabilities discussed above and to achieve the methods to be discussed hereinafter, and also to provide the programming logic for the controller to implement those functions, based on the present disclosure. 
     Still further, control apparatus  10  also may include a sensor  64  operatively connected to controller  38  via connection  66  to provide signals from which can be determined one or more of rod position, rod movement direction, and rate of rod movement (velocity), as one of ordinary skill in the art would appreciate. In this respect, directional control valve  34  may be configured to additionally allow return flow from the rod end  14  directly to tank/reservoir  24  for conditions (not shown) in addition to a rod extension demand rate greater than or equal to the predetermined value, such as for a stationary rod situation or for very small rod extension rates (velocities) less than or equal to a second predetermined value. Again, one skilled in the art would be able to configure directional control valve  34  and controller  38  to accomplish this additional function. 
     It should also be appreciated by one skilled in the art that various modifications of the disclosed control apparatus may be made consistent with this disclosure. For example, a separate return valve could be used, such as return valve  60  (shown dotted) appropriately positioned such as in portion  30   a  of conduit  30 , and under the control of controller  38 , such as by independent connection  62 . Such a construction would simplify the design of the directional control valve  34 , although it would involve a separate, controllable component. Also, although not depicted, a separate conduit could be provided directly interconnecting rod end  14  (or conduit  30 ) with conduit  36  (or reservoir  24 ), in which the separate return flow control valve  60  could be positioned if, for example, the directional control valve was not configured to include a rod end return path. 
     As is evident from the above description, the disclosed control apparatus may be provided as part of a new, integrated machine or vehicle for a load-induced rod-extending operations, such as wheel loader  68  depicted in  FIG. 1 , or may be provided as control equipment such as in kit form to retro-fit existing equipment already having a double-acting cylinder, reservoir, pump, etc., to the extent such existing components were not incompatible with the above disclosed components and functions or with the following control method aspect of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     In accordance with another aspect of the present invention, methods are disclosed for controlling apparatus having a double-acting hydraulic cylinder during load-induced rod-extending operation, where the cylinder is activated by pressurized hydraulic fluid supplied from a reservoir by a pump, and the cylinder activation circuit includes a control valve for directing pressurized fluid to the cylinder head end during the operation. The apparatus to be controlled by the method to be described hereinafter may also include a return flow path from the rod end to the reservoir for fluid displaced from rod end during rod extension. Such an apparatus has been discussed previously in relation to  FIG. 1 . 
     Specifically, the method of controlling a double-acting cylinder during load induced rod-extending movement designated generally by the numeral  100  in the flow chart of  FIG. 2  includes providing a regeneration flow path from the rod end to the head end, as is shown schematically at block  110 . As discussed previously in respect to the apparatus  10  shown in  FIG. 1 , the apparatus to be controlled may include a conduit with a controllable regeneration valve connected between the conduits used to supply the rod end and the head end from the pump of the activation circuit, or a separate conduit between the cylinder rod end and the cylinder head end. Providing the regeneration flow path includes activating the controllable regeneration flow valve, which may be a proportional valve for controlling the flow rate through the regeneration flow path. 
     Method  100  further includes controlling the fluid to the head end during the load-included rod extension by controlling the flow through the regeneration flow path and directing flow from the cylinder activation circuit to the head end, as is represented by block  112  of  FIG. 2 . More specifically, controlling the flow to the cylinder head end, as would be understood from the present disclosure, may be accomplished by independently controlling both the regeneration valve  54  and the directional control valve  34 . Moreover, for apparatus such as depicted in  FIG. 1 , having a proportional regeneration valve and as well as a proportional directional control valve  34 , the controlling may be in respect to the desired rate of rod extension, such as by the use of a suitably programmed controller such as controller  38  activating the respective valves. 
     For example,  FIG. 4  shows a modulation (control) scheme for directional control valve  34  and regeneration valve  54 , for one possible load-induced rod extending operation, using the apparatus depicted in  FIG. 1 . In operation, the operator&#39;s rate demand is translated by controller  38  to provide separate commands to regeneration valve  54  and directional control valve  34 . For “small” operator rate demands such as less than a threshold value (e.g. less than about 15%), only regeneration valve  54  is opened an amount depicted by curve “H” in  FIG. 4 , while directional control valve  34  stays “closed” in respect to flow from pump  26  to head end  16 . This regeneration-flow-only condition allows controlled extension of rod  20  during e.g. rod positioning, and thus smoother operation, without intercepting any pump flow from other functions. 
     For “medium” operator rate demands (e.g. between about 15% and about 60%), during e.g. load-lowering, regeneration valve  54  is open and directional control valve  34  is shifted to the  34   c  position, where the flow path from pump  26  to head end  16  is opened a relative amount depicted by curve “I” in  FIG. 4  but where the return flow path from rod end  14  to tank  24  is closed, as discussed previously. 
     For “high” operator rate demands (e.g. between about 60% and about 100%), for e.g. “quick-drop” operation regeneration valve  54  is open and directional control valve  34  is shifted to the  34   d  position, where the return-to-tank flow path is opened but restricted. The opening amount of the return flow restriction is not shown in  FIG. 4 . This modulation scheme provides a “soft coupling” of the synchronization between directional control valve  34  and regeneration valve  54 . One skilled in the art would be able to provide a suitably programmed controller to carry out the control scheme discussed above, and similar schemes. 
     Method  100  further includes restricting the flow of fluid displaced from the rod end to the reservoir along the return path, as shown in block  114  of  FIG. 2 . The flow restricting function can be accomplished using a suitable return valve which can be a proportional valve (such as the specially configured directional control valve  34  or alternative separate valve  60 , both shown in  FIG. 1 ), and which is controlled separately from the regeneration flow valve  54 . As discussed previously in relation to the apparatus of  FIG. 1 , totally preventing flow along the return path from the displaced flow from the rod end of the cylinder during preselected conditions of rod extension has the advantage of directing essentially 100% of the displaced fluid through the regeneration flow path, thus minimizing the volume of any pressurized fluid required to be supplied from pump  26 , as discussed previously. 
     Method  100  further includes totally restricting (i.e. shutting off) the flow from rod end  14  to reservoir  24  along the return path only for certain rod extending rates demanded by an operator, such as rates less than a predetermined rate. This method element is represented by logic block  116  in the  FIG. 2  flow chart, which depicts a method element that restricts displaced rod end fluid from flowing along the return path for rod extending rates less than a predetermined rate, that is, for e.g. controlled load-lowering, but also permits restricted flow along the return path for rod extending demand rates greater than or equal to the predetermined rate, for e.g. “quick-drop”. As would be understood, the control of the respective valves may be accomplished using a suitably programmed microprocessor-based controller, such as controller  38  depicted in  FIG. 1 . One skilled in the art would be able to provide suitable programming for such a controller given the above disclosure. 
     It would be apparent to those skilled in the art that various modifications and variations can be made to the disclosed apparatus and method for controlling a double-acting hydraulic cylinder during load induced rod extending movement. Other embodiments will be apparent to those skilled in the art from consideration of this specification and practice of the disclosed apparatus and method. It is intended that the specification and examples be considered as exemplary only, with a true scoping indicated by the following claims and their equivalents.