Patent Publication Number: US-2010122528-A1

Title: Hydraulic system having regeneration and supplemental flow

Description:
TECHNICAL FIELD  
     The present disclosure relates generally to a hydraulic system, and more particularly, to a hydraulic system having regeneration and supplemental flow. 
     BACKGROUND  
     Hydraulic machines such as, for example, dozers, loaders, excavators, motor graders, and other types of heavy equipment use one or more hydraulic actuators to accomplish a variety of tasks. These actuators are fluidly connected to a pump of the machine that provides pressurized fluid to chambers within the actuators. As the pressurized fluid moves into or through the chambers, the pressure of the fluid acts on surfaces of the chambers to affect movement of the actuators and a connected work tool. When the pressurized fluid is drained from the chambers, it is returned to a low pressure sump of the machine. 
     One problem associated with this type of hydraulic arrangement involves efficiency. In particular, the fluid draining from the actuator chambers to the sump often has a pressure greater than a pressure of the fluid already within the sump, especially when the actuators are moving in a direction aligned with the pull of gravity (i.e., when actuator movement is being assisted by a weight of the tool and any associated load). As a result, the higher pressure fluid draining into the sump still contains some energy that is wasted upon entering the low pressure sump. This wasted energy reduces the efficiency of the hydraulic system. 
     Another problem associated with the hydraulic arrangement described above involves flow capacity. That is, the various valves and passageways of the system that control flow to and from the actuators place restrictions on fluid supplying and draining from the actuators. As a result of the restrictions, the flow to and from the actuators may be limited, thereby causing the actuators to move slower than desired. 
     One attempt to alleviate the problems described above is disclosed in U.S. Patent Application Publication No. 2007/0186548 (the &#39;548 publication) by Smith et al. published on Aug. 16, 2007. Specifically, the &#39;548 publication discloses a hydraulic system including a first actuator, a second actuator, a pump, and a tank. The hydraulic system further includes a first arrangement of valves associated with control of fluid flow from the pump to the first actuator and from the first actuator to the tank, and a second arrangement of valves associated with control of fluid flow from the pump to the second actuator and from the second actuator to the tank. The hydraulic system also includes an independent metering valve connected between the first and second arrangements of valves. During a retraction of the first actuator, the independent metering valve is opened to allow fluid forced from the first actuator to enter and move the second actuator during a regeneration event, and/or to enter and be stored within an accumulator for later use. The fluid stored within the accumulator may then be directed to a suction side of the pump to selectively supplement pump flow that is directed to the first and second actuators. 
     Although the hydraulic system described in the &#39;548 publication may help improve efficiency and flow capacity by implementing regeneration and supplementing pump flow, it may be suboptimal. Specifically, the hydraulic system may utilize a large number of components to supports its operations, thereby increasing a cost and a complexity of the system. Further, because the supplemental flow from the accumulator is directed into the pump before passing to the first and second actuators, the flow may still be restricted and be flow limited by the number of valves and passageways within the system. 
     The disclosed hydraulic system is directed to overcoming one or more of the problems set forth above. 
     SUMMARY  
     In one aspect, the present disclosure is directed to a hydraulic system. The hydraulic system may include pump, a tank, a first actuator having a head-end and a rod-end, and a first valve arrangement configured to control fluid flow from the pump to the first actuator and from the first actuator to the tank. The hydraulic system may also include a second actuator having a head-end and a rod-end, and a second valve arrangement configured to control fluid flow from the pump to the second actuator and from the second actuator to the tank. The hydraulic system may further include a third valve arrangement fluidly connected between the first and second valve arrangements to receive pressurized fluid from the pump in parallel with the first and second valve arrangements, the third valve arrangement being configured to facilitate fluid regeneration of and supplemental flow to at least one of the first and second actuators. 
     In another aspect, the present disclosure is directed to a method of operating a hydraulic system. The method may include pressurizing a fluid, directing a first flow of the pressurized fluid to move a first actuator, and directing a second flow of the pressurized fluid to move a second actuator. The method may further include directing a third flow of the pressurized fluid in parallel with at least one of the first and second flows of pressurized fluid to move at least one of one of the first and second actuators at an increased velocity, and directing pressurized fluid from the first actuator to the second actuator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a diagrammatic illustration of an exemplary disclosed machine; and 
         FIG. 2  is a schematic illustration of an exemplary disclosed hydraulic system that may be used in conjunction with the machine of  FIG. 1 ; 
         FIG. 3  is a schematic illustration of an exemplary disclosed hydraulic system that may be used in conjunction with the machine of  FIG. 1 ; 
         FIG. 4  is a schematic illustration of an exemplary disclosed hydraulic system that may be used in conjunction with the machine of  FIG. 1 ; and 
         FIG. 5  is a schematic illustration of an exemplary disclosed hydraulic system that may be used in conjunction with the machine of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION  
       FIG. 1  illustrates an exemplary machine  10  having multiple systems and components that cooperate to accomplish a task. Machine  10  may embody a fixed or mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation, or any other industry known in the art. For example, machine  10  may be an earth moving machine such as a loader, an excavator, a dozer, a backhoe, a motor grader, a dump truck, or any other earth moving machine. Machine  10  may include an linkage system  12  configured to move a work tool  14 , and a prime mover  16 , for example a combustion engine, that provides power to linkage system  12 . 
     Linkage system  12  may include structure affected by fluid actuators to move work tool  14 . Specifically, linkage system  12  may include a boom member (i.e., a lifting member)  17  vertically pivotal about a horizontal axis  28  relative to a work surface  18  by a pair of adjacent, double-acting, hydraulic cylinders  20  (only one shown in  FIG. 1 ). Linkage system  12  may also include a single, double-acting, hydraulic cylinder  26  connected to tilt work tool  14  relative to boom member  17  vertically about a horizontal axis  30 . Boom member  17  may be pivotally connected to a frame  32  of machine  10 . 
     For purposes of simplicity,  FIG. 2  illustrates the composition and connections of only hydraulic cylinders  20  and  26 . It should be noted, however, that machine  10  may include other hydraulic actuators of similar composition connected to move the same or other structural members of linkage system  12  in a similar manner, if desired. 
     As shown in  FIG. 2 , each of hydraulic cylinders  20  and  26  may include a tube  34  and a piston assembly  36  arranged to form a first pressure chamber  38  and a second pressure chamber  40 . In one example, a rod portion  36 a of piston assembly  36  may extend through second pressure chamber  40 . As such, second pressure chamber  40  may be associated with a rod-end  44  of its respective cylinder, while first pressure chamber  38  may be associated with an opposing head-end  42  of its respective cylinder. 
     First and second pressure chambers  38 ,  40  may each be selectively supplied with pressurized fluid and drained of the pressurized fluid to cause piston assembly  36  to displace within tube  34 , thereby changing an effective length of hydraulic cylinders  20 ,  26 . A flow rate of fluid into and out of first and second pressure chambers  38 ,  40  may relate to a velocity of hydraulic cylinders  20 ,  26 , while a pressure differential between the first and second pressure chambers  38 ,  40  may relate to a force imparted by hydraulic cylinders  20 ,  26  on the associated linkage members. An expansion (represented by arrow  46 ) and a retraction (represented by an arrow  47 ) of hydraulic cylinders  20 ,  26  may function to assist in moving work tool  14 . 
     To help regulate filling and draining of first and second chambers  38 ,  40 , machine  10  may include a hydraulic system  48  having a plurality of interconnecting and cooperating fluid components. In particular, hydraulic system  48  may include valve stack  50  at least partially forming a circuit configured to receive pressurized fluid from an engine-driven pump  52  and to discharge fluid to a tank  53  or other low pressure reservoir. Valve stack  50  may include a lift valve arrangement  54 , a tilt valve arrangement  56 , and an auxiliary valve arrangement  58  fluidly connected to receive pressurized fluid from pump  52  in parallel fashion. In one embodiment, valve arrangements  54 - 58  may include bodies bolted to each other to form valve stack  50 . In another embodiment, each of valve arrangements  54 - 58  may be stand-alone arrangements, connected only by way of fluid conduits, if desired. It is contemplated that a greater number, a lesser number, or a different configuration of valve arrangements may be included within valve stack  50 , if desired. For example, a swing valve arrangement (not shown) configured to control a swinging motion of linkage system  12 , one or more attachment valve arrangements (not shown), one or more travel valve arrangements, and other suitable valve arrangements may be included in valve stack  50 . 
     Each of lift, tilt, and auxiliary valve arrangements  54 - 58  may regulate the motion of their associated fluid actuators. Specifically, tilt valve arrangement  54  may have elements movable to control the motion of hydraulic cylinder  20  associated with boom member  17 ; tilt valve arrangement  56  may have elements movable to control the motion of hydraulic cylinder  26  associated with work tool  14 ; and auxiliary valve arrangement  58  may have elements movable to affect the motion of any or both of hydraulic cylinders  20 ,  26 . 
     Valve arrangements  54 - 58  may be connected to regulate flows of pressurized fluid to and from hydraulic cylinders  20 ,  26  via common passages. Specifically, valve arrangements  54 - 58  may be connected to pump  52  by way of a common supply passage  60 , and to tank  53  by way of a common drain passage  62 . Lift, tilt, and auxiliary valve arrangements  54 - 58  may be connected in parallel to common supply passage  60  by way of individual fluid passages  66 ,  68 ,  70 , respectively, and in parallel to common drain passage  62  by way of individual fluid passages  72 ,  74 , and  76 , respectively. A pressure compensating valve  78  and/or a check valve  79  may be disposed within each of fluid passages  66 - 70  to provide a unidirectional supply of fluid having a substantially constant flow to valve arrangements  54 - 58 . Pressure compensating valves  78  may be movable in response to a differential pressure between a flow passing position and a flow blocking position, such that a substantially constant flow of fluid is provide to valve arrangements  54 - 58 , even when a pressure of the fluid directed to pressure compensating valves  78  varies. It is contemplated that, in some applications, pressure compensating valves  78  and/or check valves  79  may be omitted, if desired. For example, pressure compensating valve  78 , in one embodiment, may be omitted from auxiliary valve arrangement  56  to increase a flow capacity thereof. 
     Each of lift, tilt, and auxiliary valve arrangements  54 - 58  may be substantially identical, and each may include four independent metering valves (IMVs). Of the four IMVs, two may be generally associated with fluid supply functions, while two may be generally associated with drain functions. For example, lift valve arrangement  54  may include a head-end supply valve  80 , a rod-end supply valve  82 , a head-end drain valve  84 , and a rod-end drain valve  86 . Similarly, tilt valve arrangement  56  may include a head-end supply valve  88 , a rod-end supply valve  90 , a head-end drain valve  92 , and a rod-end drain valve  94 . And, although not specific to a head-end or a rod-end of a particular cylinder, auxiliary valve arrangement  58  may include a first supply valve  96 , a second supply valve  98 , a first drain valve  100 , and a second drain valve  102 . 
     Head-end supply valve  80  may be disposed between fluid passage  66  and a fluid passage  104  leading to first chamber  38  of hydraulic cylinder  20  to regulate a flow of pressurized fluid to first chamber  38 . Head-end supply valve  80  may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow into first chamber  38 , and a second end-position, at which fluid flow is blocked from first chamber  38 . It is contemplated that head-end supply valve  80  may include additional or different elements such as, for example, a fixed-position valve element or any other valve element known in the art. It is also contemplated that head-end supply valve  80  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. It is further contemplated that head-end supply valve  80  may be configured to allow fluid from first chamber  38  to flow through head-end supply valve  80  during a regeneration event when a pressure within first chamber  38  exceeds a pressure of pump  52  and/or a pressure of the chamber receiving the regenerated fluid. 
     Rod-end supply valve  82  may be disposed between fluid passage  66  and a fluid passage  106  leading to second chamber  40  of hydraulic cylinder  20  to regulate a flow of pressurized fluid to second chamber  40 . Rod-end supply valve  82  may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow into second chamber  40 , and a second end-position, at which fluid is blocked from second chamber  40 . It is contemplated that rod-end supply valve  82  may include additional or different valve elements such as, for example, a fixed-position valve element or any other valve element known in the art. It is also contemplated that rod-end supply valve  82  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. It is further contemplated that rod-end supply valve  82  may be configured to allow fluid from second chamber  40  to flow through rod-end supply valve  82  during a regeneration event when a pressure within second chamber  40  exceeds a pressure of pump  52  and/or a pressure of the chamber receiving the regenerated fluid. 
     Head-end drain valve  84  may be disposed between fluid passage  104  and fluid passage  74  that leads to common drain passage  62  to regulate a flow of pressurized fluid from first chamber  38  of hydraulic cylinder  20  to tank  53 . Head-end drain valve  84  may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow from first chamber  38 , and a second end-position, at which fluid is blocked from flowing from first chamber  38 . It is contemplated that head-end drain valve  84  may include additional or different valve elements such as, for example, a fixed-position valve element or any other valve element known in the art. It is also contemplated that head-end drain valve  84  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. 
     Rod-end drain valve  86  may be disposed between fluid passage  106  and fluid passage  72  that leads to common drain passage  62  to regulate a flow of pressurized fluid from second chamber  40  of hydraulic cylinder  20  to tank  53 . Rod-end drain valve  86  may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow from second chamber  40 , and a second end-position, at which fluid is blocked from flowing from second chamber  40 . It is contemplated that rod-end drain valve  86  may include additional or different valve elements such as, for example, a fixed-position valve element or any other valve element known in the art. It is also contemplated that rod-end drain valve  86  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. 
     Head-end supply valve  88  may be disposed between fluid passage  68  and a fluid passage  108  leading to first chamber  38  of hydraulic cylinder  26  to regulate a flow of pressurized fluid to first chamber  38 . Head-end supply valve  88  may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow into first chamber  38 , and a second end-position, at which fluid flow is blocked from first chamber  38 . It is contemplated that head-end supply valve  88  may include additional or different elements such as, for example, a fixed-position valve element or any other valve element known in the art. It is also contemplated that head-end supply valve  88  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. It is further contemplated that head-end supply valve  88  may be configured to allow fluid from first chamber  38  to flow through head-end supply valve  88  during a regeneration event when a pressure within first chamber  38  exceeds a pressure of pump  52  and/or a pressure of the chamber receiving the regenerated fluid. 
     Rod-end supply valve  90  may be disposed between fluid passage  68  and a fluid passage  110  leading to second chamber  40  of hydraulic cylinder  26  to regulate a flow of pressurized fluid to second chamber  40 . Specifically, rod-end supply valve  90  may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow into second chamber  40 , and a second end-position, at which fluid is blocked from second chamber  40 . It is contemplated that rod-end supply valve  90  may include additional or different valve elements such as, for example, a fixed-position valve element or any other valve element known in the art. It is also contemplated that rod-end supply valve  90  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. It is further contemplated that rod-end supply valve  90  may be configured to allow fluid from second chamber  40  to flow through rod-end supply valve  90  during a regeneration event when a pressure within second chamber  40  exceeds a pressure of pump  52  and/or a pressure of the chamber receiving the regenerated fluid. 
     Head-end drain valve  92  may be disposed between fluid passage  108  and fluid passage  74  that leads to common drain passage  62  to regulate a flow of pressurized fluid from first chamber  38  of hydraulic cylinder  26  to tank  53 . Specifically, head-end drain valve  92  may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow from first chamber  38 , and a second end-position, at which fluid is blocked from flowing from first chamber  38 . It is contemplated that head-end drain valve  92  may include additional or different valve elements such as, for example, a fixed-position valve element or any other valve element known in the art. It is also contemplated that head-end drain valve  92  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. 
     Rod-end drain valve  94  may be disposed between fluid passage  110  and fluid passage  74  leading to common drain passage  62  to regulate a flow of pressurized fluid from second chamber  40  of hydraulic cylinder  26  to tank  53 . Rod-end drain valve  94  may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow from second chamber  40 , and a second end-position, at which fluid is blocked from flowing from second chamber  40 . It is contemplated that rod-end drain valve  94  may include additional or different valve element such as, for example, a fixed-position valve element or any other valve elements known in the art. It is also contemplated that rod-end drain valve  94  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. 
     First supply valve  96  may be disposed between fluid passage  70  and fluid passage  108  leading to first chamber  38  of hydraulic cylinder  26  to regulate a flow of pressurized fluid to first chamber  38 . First supply valve  96  may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow into first chamber  38 , and a second end-position, at which fluid flow is blocked from first chamber  38 . It is contemplated that first supply valve  96  may include additional or different elements such as, for example, a fixed-position valve element or any other valve element known in the art. It is also contemplated that first supply valve  96  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. It is further contemplated that first supply valve  96  may be configured to allow fluid from first chamber  38  to flow through first supply valve  96  during a regeneration event when a pressure within first chamber  38  exceeds a pressure of pump  52  and/or a pressure of the chamber receiving the regenerated fluid. 
     Second supply valve  98  may be disposed between fluid passage  70  and fluid passage  104  leading to first chamber  38  of hydraulic cylinder  20  to regulate a flow of pressurized fluid to first chamber  38 . Second supply valve  98  may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow into first chamber  38 , and a second end-position, at which fluid is blocked from first chamber  38 . It is contemplated that second supply valve  98  may include additional or different valve elements such as, for example, a fixed-position valve element or any other valve element known in the art. It is also contemplated that second supply valve  98  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. It is further contemplated that second supply valve  98  may be configured to allow fluid from first chamber  38  to flow through second supply valve  98  during a regeneration event when a pressure within first chamber  38  exceeds a pressure of pump  52  and/or a pressure of the chamber receiving the regenerated fluid. 
     First drain valve  100  may be disposed between fluid passage  108  and fluid passage  76  leading to common drain passage  62  to regulate a flow of pressurized fluid from first chamber  38  of hydraulic cylinder  26  to tank  53 . First drain valve  100  may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow from first chamber  38 , and a second end-position, at which fluid is blocked from flowing from first chamber  38 . It is contemplated that first drain valve  100  may include additional or different valve elements such as, for example, a fixed-position valve element or any other valve element known in the art. It is also contemplated that first drain valve  100  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. 
     Second drain valve  102  may be disposed between fluid passage  104  and fluid passage  76  leading to common drain passage  62  to regulate a flow of pressurized fluid from first chamber  38  of hydraulic cylinder  20  to tank  53 . Specifically, second drain valve  102  may include a variable-position. spring-biased valve element that is solenoid actuated and configured to move to any position between a first end-position, at which fluid is allowed to flow from first chamber  38 , and a second end-position, at which fluid is blocked from flowing from first chamber  38 . It is contemplated that second drain valve  102  may include additional or different valve elements such as, for example, a fixed-position valve element or any other valve element known in the art. It is also contemplated that second drain valve  102  may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in any other suitable manner. 
       FIGS. 3-5  illustrate exemplary operations of hydraulic system  48 .  FIGS. 3-5  will be discussed in more detail in the following section to further illustrate the disclosed concepts. 
     INDUSTRIAL APPLICABILITY  
     The disclosed hydraulic system may be applicable to any machine that includes multiple fluid actuators where flow capacity, cost, and efficiency are issues. The disclosed hydraulic system may provide high flow capacity by supplementing flow to and from hydraulic actuators of the system, and low cost by providing the supplemental flow with relatively few components. The disclosed hydraulic system may provide increased efficiency by facilitating cylinder-to-cylinder and in-cylinder regeneration, and by minimizing a pressure drop associated with filling or draining of the cylinders. The operation of hydraulic system  48  will now be explained. 
     As shown in  FIG. 2 , hydraulic cylinders  20  and  26  may be movable by fluid pressure in response to an operator input. In particular, fluid may be pressurized by pump  52  and selectively directed to head-end and rod-end supply valves  80 ,  82 ,  88 ,  90 ,  96 , and  98 . In response to an operator input to either extend or retract piston assembly  36  relative to tube  34 , head-end or rod-end supply valves  80 ,  82 ,  88 ,  90  may be moved toward the open position to direct the pressurized fluid to the appropriate one of first and second chambers  38 ,  40 . Substantially simultaneously, head-end or rod-end drain valves  84 ,  86 ,  92 ,  94  may be moved toward the open position to direct fluid from the appropriate one of the first and second chambers  38 ,  40  to tank  53  to create a force differential across piston assembly  36  that causes piston assembly  36  to move. 
     For example, if an extension of hydraulic cylinder  26  is requested (i.e., if movement of hydraulic cylinder  26  in the direction of arrow  46  is requested), head-end supply valve  88  may be moved toward the open position to direct pressurized fluid from pump  52  to first chamber  38 . Substantially simultaneous to the directing of pressurized fluid to first chamber  38 , rod-end drain valve  94  may be moved toward the open position to allow fluid from second chamber  40  to drain to tank  53 . The high pressure within first chamber  38  and the low pressure within second chamber  40  may together create a force differential across piston assembly  36  that causes piston assembly  36  to move and extend from tube  34 . During the extension of hydraulic cylinder  26 , head-end drain valve  92  and rod-end supply valve  90  may be maintained in their closed positions. 
     If a retraction of hydraulic cylinder  20  is requested (i.e., if movement of hydraulic cylinder  20  in the direction of arrow  47  is requested), rod-end supply valve  82  may be moved toward the open position to direct pressurized fluid from pump  52  to second chamber  40 . Substantially simultaneous to the directing of pressurized fluid to second chamber  40 , head-end drain valve  84  may be moved toward the open position to allow fluid from first chamber  38  to drain to tank  53 . The high pressure within second chamber  40  and the low pressure within first chamber  38  may together create a force differential across piston assembly  36  that causes piston assembly  36  to move and retract back into tube  34 . During the retraction of hydraulic cylinder  20 , head-end supply valve  80  and rod-end drain valve  86  may be maintained in their closed positions. 
     As shown in  FIG. 3 , auxiliary valve arrangement  58  may be utilized to selectively increase a velocity of hydraulic cylinders  20 ,  26  during an extension by facilitating supplemental flow to first chamber  38  of head-ends  42 . For example, during the extension of hydraulic cylinder  26 , pressurized fluid may be directed from pump  52  to first chamber  38  by way of common supply passage  60 , fluid passage  68 , head-end supply valve  88 , and fluid passage  108 . Simultaneously, pressurized fluid may be directed in parallel from pump  52  to first chamber  38  via common supply passage  60 , fluid passage  70 , first supply valve  96 , and fluid passage  108 . During the supplemented extension of hydraulic cylinder  26 , head-end drain valve  92 , rod-end supply valve  90 , second supply valve  98 , first drain valve  100 , and second drain valve  102  may be maintained in their closed positions. The additional flow of fluid may help to speed up movement of hydraulic cylinder  26 . The extension speed and efficiency of hydraulic cylinder  20  may be increased in a similar manner. 
     Auxiliary valve arrangement  58  may also be utilized to increase a velocity of hydraulic cylinders  20 ,  26  during a retraction by supplementing flow from head-ends  42 . For example, during the retraction of hydraulic cylinder  20 , fluid already within first chamber  38  may be drained to tank  53  by way of fluid passage  104 , head-end drain valve  84 , fluid passage  72 , and common drain passage  62 . Simultaneously, fluid may be directed in parallel from first chamber  38  to tank  53  via fluid passage  104 , second drain valve  102 , fluid passage  76 , and common drain passage  62  During the supplemented retraction of hydraulic cylinder  20 , head-end supply valve  80 , rod-end drain valve  86 , first supply valve  96 , second supply valve  98 , and first drain valve  100  may be maintained in their closed positions. The additional flow of fluid from first chamber  38  may help to speed up the retracting movement of hydraulic cylinder  20 . The retraction speed of hydraulic cylinder  26  may be increased in a similar manner. 
     As shown in  FIG. 4 , auxiliary valve arrangement  58  may facilitate cylinder-to-cylinder regeneration. For example, during a retraction of hydraulic cylinder  20  aligned with the pull of gravity, the fluid exiting first chamber  38  may have a pressure as high as or even higher than the pressure imparted by pump  52 . As such, rather than directing this exiting fluid to tank  53  where the energy of the highly pressurized fluid would be wasted, the pressurized fluid may instead be directed for reuse within hydraulic cylinder  26  by way of auxiliary valve arrangement  58 . Specifically, the highly pressurized fluid exiting first chamber  38  of hydraulic cylinder  20  may be directed through fluid passage  104 , second supply valve  98 , first supply valve  96 , and fluid passage  108  to first chamber  38  of hydraulic cylinder  26 . Check valve  79  of auxiliary valve arrangement  58  may help inhibit undesired pump interaction with the regenerated fluid. During cylinder-to-cylinder regeneration, head-end supply valve  80 , head-end drain valve  84 , rod-end drain valve  86 , rod-end supply valve  90 , head-end supply valve  88 , head-end drain valve  92 , first drain valve  100 , and second drain valve  102  may be at least partially, if not fully, closed. That is, in some situations, because of a volume ratio between first and second chambers  38 ,  40 , there may be excess regenerative fluid and some of that fluid may need to be drained back to tank  53  by way of head-end drain valve  84 , rod-end drain valve  86 , head-end drain valve  92 , first drain valve  100 , and/or second drain valve  102 . In other situations, the regenerated fluid may be insufficient and, in these situations, one of the supply valves of the cylinder receiving the regenerated fluid may be partially or even completely open, if desired. The fluid being directed from hydraulic cylinder  20  to hydraulic cylinder  26 , because of its pressure, may cause pressure check valve  79  associated with auxiliary valve arrangement  58  to close and inhibit fluid flow in reverse direction to pump  52 . In this manner, the energy associated with the fluid being forced from hydraulic cylinder  20  during gravity-assisted retraction may be at least partially recouped and utilized to move hydraulic cylinder  26 . Regeneration of fluid from hydraulic cylinder  26  to hydraulic cylinder  20  may be accomplished in a similar manner. 
     As shown in  FIG. 5 , auxiliary valve arrangement  58  may be further used to facilitate in-cylinder regeneration. That is, instead of or in addition to passing highly pressurized fluid from one of hydraulic cylinders  20 ,  26  to the other, that fluid may be reused within the same cylinder. For example, during a retraction of hydraulic cylinder  20  aligned with the pull of gravity, the highly-pressurized fluid exiting first chamber  38  may be directed through fluid passage  104 , head-end supply valve  80 , rod-end supply valve  82 , and fluid passage  106 , to second chamber  40 . During in-cylinder regeneration of hydraulic cylinder  20 , head-end drain valve  84  and rod-end drain valve  86  may at least partially, if not fully, closed positions. That is, in some situations, because of a volume ratio between first and second chambers  38 ,  40 , there may be excess regenerative fluid and some of that fluid may need to be drained back to tank  53  by way of head-end drain valve  84  and/or rod-end drain valve  86 . The fluid being directed from first chamber  38  of hydraulic cylinder  20  to second chamber  40  of hydraulic cylinder  26 , because of its pressure, may cause check valve  79  associated with lift valve arrangement  54  to close and inhibit fluid flow to pump  52 . In this manner, the energy associated with the fluid being forced from hydraulic cylinder  20  during retraction may be recouped and reutilized within hydraulic cylinder  20 . In-cylinder regeneration of hydraulic cylinder  26  may be accomplished in a similar manner. 
     The inclusion of auxiliary valve arrangement  58  may afford several benefits. In particular, auxiliary valve arrangement  58  may facilitate supplemental flow to any of the hydraulic cylinders included within machine  10 , and from those cylinders to tank  53 . The supplemental flow may allow for increased velocity movements of work tool  14 . Further, auxiliary valve arrangement  58  may facilitate both cylinder-to-cylinder and in-cylinder regeneration, thereby increasing an efficiency of machine  10 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed hydraulic system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed hydraulic system. For example, although head-ends  42  of hydraulic cylinders  20 ,  26  are shown and described as being connected to receive supplemental flow from pump  52  by way of auxiliary valve arrangement  58 , one or both of hydraulic cylinders  20 ,  26  could be connected in an inverse manner such that the supplemental flow is alternatively directed to rod-ends  44 , if desired. Further, although pre-pressure compensating valves are described as being included in one exemplary embodiment, it is contemplated that post-compensating valves, makeup valves, relief valves, bypass valves, and other commonly known elements may additionally or alternatively be included within hydraulic system  48 , if desired. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.