Meterless hydraulic system having multi-actuator circuit

A hydraulic system is disclosed. The hydraulic system may have a pump, a rotary actuator, a linear actuator, and a closed-loop circuit fluidly connecting the pump to the rotary and linear actuators. The hydraulic system may also have at least one valve configured to switch fluid flow direction from the pump through the linear actuator during fluid flow in a single direction through the rotary actuator.

TECHNICAL FIELD

The present disclosure relates generally to a hydraulic system and, more particularly, to a meterless hydraulic system having a multi-actuator circuit.

BACKGROUND

A conventional hydraulic system includes a pump that draws low-pressure fluid from a tank, pressurizes the fluid, and makes the pressurized fluid available to multiple different actuators for use in moving the actuators. In this arrangement, a speed of each actuator can be independently controlled by selectively throttling (e.g., restricting) a flow of the pressurized fluid from the pump into each actuator. For example, to move a particular actuator at a high speed, the flow of fluid from the pump into the actuator is restricted by only a small amount. In contrast, to move the same or another actuator at a low speed, the restriction placed on the flow of fluid is increased. Although adequate for many applications, the use of fluid restriction to control actuator speed can result in flow losses that reduce an overall efficiency of a hydraulic system.

An alternative type of hydraulic system is known as a meterless hydraulic system. A meterless hydraulic system generally includes a pump connected in closed-loop fashion to a single actuator or to a pair of actuators operating in tandem. During operation, the pump draws fluid from one chamber of the actuator(s) and discharges pressurized fluid to an opposing chamber of the same actuator(s). To move the actuator(s) at a higher speed, the pump discharges fluid at a faster rate. To move the actuator with a lower speed, the pump discharges the fluid at a slower rate. A meterless hydraulic system is generally more efficient than a conventional hydraulic system because the speed of the actuator(s) is controlled through pump operation as opposed to fluid restriction. That is, the pump is controlled to only discharge as much fluid as is necessary to move the actuator(s) at a desired speed, and no throttling of a fluid flow is required.

An exemplary meterless hydraulic system is disclosed in a technical document titled “Test Bed 1—Heavy Mobile Equipment” by Zimmerman et al. presented in the Jun. 14, 2010 annual meeting of the National Science Foundation. In this document, a meterless hydraulic system is described that has a multi-actuator circuit. The hydraulic system includes an over-center, variable displacement pump connected in closed-loop fashion to a travel motor and a hydraulic cylinder. Isolation valves are associated with both the travel motor and the hydraulic cylinder to allow sequential operation of the two actuators. Pairing of multiple actuators with a single pump helps to reduce a number of pumps required for the hydraulic system.

Although the meterless hydraulic system of the technical document described above discloses a multi-actuator circuit, the system may still be less than optimal. In particular, the system does not provide for simultaneous use of the travel motor and hydraulic cylinder, much less simultaneous use with independent speed control or simultaneous use with reversing actuation directions.

The hydraulic system of the present disclosure is directed toward solving one or more of the problems set forth above and/or other problems of the prior art.

SUMMARY

In one aspect, the present disclosure is directed to a hydraulic system. The hydraulic system may include a pump, a rotary actuator, a linear actuator, and a closed-loop circuit fluidly connecting the pump to the rotary and linear actuators. The hydraulic system may also include at least one valve configured to switch fluid flow direction from the pump through the linear actuator during fluid flow in a single direction through the rotary actuator.

In another aspect, the present disclosure is directed to a method of operating a hydraulic system. The method may include pressurizing fluid with a pump, directing fluid pressurized by the pump to a motor and a linear actuator, and returning fluid from the motor and linear actuator to the pump via a closed-loop circuit. The method may also include receiving an indication of operator desired movement of the motor and linear actuator, and adjusting operation of the pump based on the indication. Adjusting operation of the pump may include adjusting operation of the pump based on only desired movement of the motor when movement of the linear actuator is not desired, adjusting operation of the pump based on only desired movement of the linear actuator anytime movement of the linear actuator is desired, and adjusting operation of the motor based on desired movement of the motor when movement of both the motor and the linear actuator is desired.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary machine10having multiple systems and components that cooperate to accomplish a task. Machine10may embody a fixed or mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation, or another industry known in the art. For example, machine10may be an earth moving machine such as an excavator (shown inFIG. 1), a dozer, a loader, a backhoe, a motor grader, a dump truck, or any other earth moving machine. Machine10may include an implement system12configured to move a work tool14, a drive system16for propelling machine10, a power source18that provides power to implement system12and drive system16, and an operator station20situated for manual control of implement system12, drive system16, and/or power source18.

Implement system12may include a linkage structure acted on by fluid actuators to move work tool14. Specifically, implement system12may include a boom22that is vertically pivotal about a horizontal axis (not shown) relative to a work surface24by a pair of adjacent, double-acting, hydraulic cylinders26(only one shown inFIG. 1). Implement system12may also include a stick28that is vertically pivotal about a horizontal axis30by a single, double-acting, hydraulic cylinder32. Implement system12may further include a single, double-acting, hydraulic cylinder34that is operatively connected between stick28and work tool14to pivot work tool14vertically about a horizontal pivot axis36. In the disclosed embodiment, hydraulic cylinder34is connected at a head-end34A to a portion of stick28and at an opposing rod-end34B to work tool14by way of a power link37. Boom22may be pivotally connected to a body38of machine10. Body38may be pivotally connected to an undercarriage39and movable about a vertical axis41by a hydraulic swing motor43. Stick28may pivotally connect boom22to work tool14by way of axis30and36.

Numerous different work tools14may be attachable to a single machine10and operator controllable. Work tool14may include any device used to perform a particular task such as, for example, a bucket, a fork arrangement, a blade, a shovel, a ripper, a dump bed, a broom, a snow blower, a propelling device, a cutting device, a grasping device, or any other task-performing device known in the art. Although connected in the embodiment ofFIG. 1to pivot in the vertical direction relative to body38of machine10and to swing in the horizontal direction, work tool14may alternatively or additionally rotate, slide, open and close, or move in any other manner known in the art.

Drive system16may include one or more traction devices powered to propel machine10. In the disclosed example, drive system16includes a left track40L located on one side of machine10, and a right track40R located on an opposing side of machine10. Left track40L may be driven by a left travel motor42L, while right track40R may be driven by a right travel motor42R. It is contemplated that drive system16could alternatively include traction devices other than tracks such as wheels, belts, or other known traction devices. Machine10may be steered by generating a speed and/or rotational direction difference between left and right travel motors42L,42R, while straight travel may be facilitated by generating substantially equal output speeds and rotational directions from left and right travel motors42L,42R.

Power source18may embody an engine such as, for example, a diesel engine, a gasoline engine, a gaseous fuel-powered engine, or any other type of combustion engine known in the art. It is contemplated that power source18may alternatively embody a non-combustion source of power such as a fuel cell, a power storage device, or another source known in the art. Power source18may produce a mechanical or electrical power output that may then be converted to hydraulic power for moving hydraulic cylinders26,32,34and left travel, right travel, and swing motors42L,42R,43.

Operator station20may include devices that receive input from a machine operator indicative of desired machine maneuvering. Specifically, operator station20may include one or more operator interface devices46, for example a joystick, a steering wheel, or a pedal, that are located proximate an operator seat (not shown). Operator interface devices46may initiate movement of machine10, for example travel and/or tool movement, by producing displacement signals that are indicative of desired machine maneuvering. As an operator moves interface device46, the operator may affect a corresponding machine movement in a desired direction, with a desired speed, and/or with a desired force.

As shown inFIG. 2, hydraulic cylinders26,32,34may each include a tube48and a piston assembly50arranged within tube48to form a first chamber52and an opposing second chamber54. In one example, a rod portion50A of piston assembly50may extend through an end of second chamber54. As such, second chamber54may be considered the rod-end chamber of hydraulic cylinders26,32,34, while first chamber52may be considered the head-end chamber.

First and second chambers52,54may each be selectively supplied with pressurized fluid and drained of the pressurized fluid to cause piston assembly50to displace within tube48, thereby changing an effective length of hydraulic cylinders26,32,34and moving work tool14(referring toFIG. 1). A flow rate of fluid into and out of first and second chambers52,54may relate to a translational velocity of hydraulic cylinders26,32,34, while a pressure differential between first and second chambers52,54may relate to a force imparted by hydraulic cylinders26,32,34on the associated linkage structure of implement system12.

Swing motor43, like hydraulic cylinders26,32,34, may be driven by a fluid pressure differential. Specifically, swing motor43may include first and second chambers (not shown) located to either side of a pumping mechanism such as an impeller, plunger, or series of pistons (not shown). When the first chamber is filled with pressurized fluid and the second chamber is drained of fluid, the pumping mechanism may be urged to move or rotate in a first direction. Conversely, when the first chamber is drained of fluid and the second chamber is filled with pressurized fluid, the pumping mechanism may be urged to move or rotate in an opposite direction. The flow rate of fluid into and out of the first and second chambers may determine an output velocity of swing motor43, while a pressure differential across the pumping mechanism may determine an output torque. It is contemplated that a displacement of swing motor43may be variable, if desired, such that for a given flow rate and/or pressure of supplied fluid, a speed and/or torque output of swing motor43may be adjusted.

Similar to swing motor43, each of left and right travel motors42L,42R may be driven by creating a fluid pressure differential. Specifically, each of left and right travel motors42L,42R may include first and second chambers (not shown) located to either side of a pumping mechanism (not shown). When the first chamber is filled with pressurized fluid and the second chamber is drained of fluid, the pumping mechanism may be urged to move or rotate a corresponding traction device (40L,40R) in a first direction. Conversely, when the first chamber is drained of the fluid and the second chamber is filled with the pressurized fluid, the respective pumping mechanism may be urged to move or rotate the traction device in an opposite direction. The flow rate of fluid into and out of the first and second chambers may determine a velocity of left and right travel motors42L,42R, while a pressure differential between left and right travel motors42L,42R may determine a torque. It is contemplated that a displacement of left and right travel motors42L,42R may be variable, if desired, such that for a given flow rate and/or pressure of supplied fluid, a speed and/or torque output of travel motors42L,42R may be adjusted.

As illustrated inFIG. 2, machine10may include a hydraulic system56having a plurality of fluid components that cooperate to move work tool14(referring toFIG. 1) and machine10. In particular, hydraulic system56may include, among other things, a first meterless circuit58, a second meterless circuit60, a third meterless circuit62, and a charge circuit64. First meterless circuit58may be a bucket circuit associated with hydraulic cylinder34and left travel motor42L. Second meterless circuit60may be a boom circuit associated with hydraulic cylinders26and right travel motor42R. Third circuit62may be a stick circuit associated with hydraulic cylinder32and swing motor43. Charge circuit64may be in selective fluid communication with each of first, second, and third meterless circuits58,60,62. It is contemplated that additional and/or different configurations of meterless circuits may be included within hydraulic system56such as, for example, an independent circuit associated with each separate actuator (e.g., hydraulic cylinders32,34,26, left travel motor42L, right travel motor42R, and/or swing motor43), if desired.

In the disclosed embodiment, each of first, second, and third meterless circuits58,60,62may be substantially identical and include a plurality of interconnecting and cooperating fluid components that facilitate the use and control of the associated actuators. For example, each meterless circuit58,60,62may include a pump66fluidly connected to its associated rotary and linear actuators in parallel via a closed-loop formed by upper-side and lower-side (relative toFIG. 2) passages. Specifically, each pump66may be connected to its rotary actuator (e.g., to left-travel motor42L, right travel motor42R, or swing motor43) via a first pump passage68and a second pump passage70. In addition, each pump66may be connected to its linear actuator (e.g., to hydraulic cylinder26,32, or34) via first and second pump passages68,70, a rod-end passage72, and a head-end passage74. To cause the rotary actuator to rotate in a first direction, first pump passage68may be filled with fluid pressurized by pump66, while second pump passage70may be filled with fluid exiting the rotary actuator. To reverse direction of the rotary actuator, second pump passage70may be filled with fluid pressurized by pump66, while first pump passage68may be filled with fluid exiting the rotary actuator. During an extending operation of a particular linear actuator, head-end passage74may be filled with fluid pressurized by pump66, while rod-end passage72may be filled with fluid returned from the linear actuator. In contrast, during a retracting operation, rod-end passage72may be filled with fluid pressurized by pump66, while head-end passage74may be filled with fluid returned from the linear actuator.

Each pump66may have variable displacement and be controlled to draw fluid from its associated actuators and discharge the fluid at a specified elevated pressure back to the actuators in two different directions. That is, pump66may include a stroke-adjusting mechanism, for example a swashplate, a position of which is hydro-mechanically adjusted based on, among other things, a desired speed of the actuators to thereby vary an output (e.g., a discharge rate) of pump66. The displacement of pump66may be adjusted from a zero displacement position at which substantially no fluid is discharged from pump66, to a maximum displacement position in a first direction at which fluid is discharged from pump66at a maximum rate into first pump passage68. Likewise, the displacement of pump66may be adjusted from the zero displacement position to a maximum displacement position in a second direction at which fluid is discharged from pump66at a maximum rate into second pump passage70. Pump66may be drivably connected to power source18of machine10by, for example, a countershaft, a belt, or in another suitable manner. Alternatively, pump66may be indirectly connected to power source18via a torque converter, a gear box, an electrical circuit, or in any other manner known in the art. It is contemplated that pumps66of different circuits may be connected to power source18in tandem (e.g., via the same shaft) or in parallel (via a gear train), as desired.

Pump66may also be selectively operated as a motor. More specifically, when an associated actuator is operating in an overrunning condition, the fluid discharged from the actuator may have a pressure elevated higher than an output pressure of pump66. In this situation, the elevated pressure of the actuator fluid directed back through pump66may function to drive pump66to rotate with or without assistance from power source18. Under some circumstances, pump66may even be capable of imparting energy to power source18, thereby improving an efficiency and/or capacity of power source18.

During some operations, it may be desirable to cause movement of a linear actuator without causing movement of the associated rotary actuator within the same circuit. For this purpose, each of meterless circuits58,60,62may be provided with isolation valves76capable of substantially isolating the rotary actuator from its associated pump66and linear actuator. Isolation valves76, in the disclosed embodiment, may be on/off type valves that are solenoid-actuated toward a flow-passing position and spring-biased toward a flow-blocking position. When isolation valves76are in the flow-passing position, fluid may flow substantially unrestricted between first and second pump passages68,70by way of the rotary actuator. When isolation valves76are in the flow-blocking position, fluid flows within first and second pump passages68,70may not pass through and substantially affect the motion of the rotary actuator. In addition to isolating the rotary actuator from operation of pump66and movement of the linear actuator, isolation valves76may also function as load-holding valves, hydraulically locking movement of the rotary actuator, when the rotary actuator has a non-zero displacement and isolation valves76are in their flow-blocking positions.

The linear actuator of each meterless circuit58,60,62may likewise be provided with valves used for isolation of the linear actuator. In particular, each of meterless circuits58,60,62may be provided with four valves, including a first rod-end valve78, a second rod-end valve80, a first head-end valve82, and a second head-end valve84. First rod-end valve78may be positioned between first pump passage68and rod-end passage72. Second rod-end valve80may be positioned between second pump passage70and rod-end passage72. First head-end valve82may be positioned between first pump passage68and head-end passage74. Second head-end valve84may be positioned between second pump passage70and head-end passage74. Like isolation valves76, valves78,80,82,84may be on/off type valves that are solenoid-actuated toward a flow-passing position, and spring-biased toward a flow-blocking position. To isolate a linear actuator from its associated pump66and rotary actuator and to hydraulically lock movement of the linear actuator, all of valves78,80,82,84may be moved to their flow-blocking positions.

Valves78,80,82,84, in addition to facilitating isolation of the associated linear actuator, may also provide flow-switching functionality. In particular, there may be times when movement of the rotary actuator in the first direction and retraction of the linear actuator is desired, while at other times movement of the rotary actuator in the first direction and extension of the linear actuator is desired. During the first situation, pump66may be required to pressurize first pump passage68and rod-end passage72, while during the second situation, pump66may be required to pressurize first pump passage68and head-end passage74. Valves78,80,82,84may facilitate these operations. For example, when first pump passage68is pressurized by pump66and retraction of the linear actuator is desired, first rod-end valve78may be moved to its flow-passing position such that rod-end passage72and second chamber54of the linear actuator are also pressurized. At this same time, second head-end valve84may be in its flow-passing position such that fluid discharged from first chamber52passes through head-end passage74to second pump passage70and back to pump66. In contrast, when first pump passage68is pressurized by pump66and extension of the linear actuator is desired, first head-end valve82may be moved to its flow-passing position such that head-end passage74and first chamber52of the linear actuator are also pressurized. At this same time, second rod-end valve80may be in its flow-passing position such that fluid discharged from second chamber54passes through rod-end passage72to second pump passage70and back to pump66. Similar movements of valves78,80,82,84may be initiated to provide for movement of the rotary actuator in the second direction during extensions and retractions of the linear actuator.

In some embodiments, valves78,80,82, and84may be used to facilitate fluid regeneration within the associated linear actuator. For example, when valves80,84are moved to their flow passing positions and valves78,82are in their flow-blocking positions, high-pressure fluid may be transferred from one chamber to the other of the linear actuator via valves80,84, without the fluid ever passing through pump66. Similar functionality may alternatively be achieved by moving valves78,82to their flow-passing positions while holding valves80,84in their flow-blocking positions.

It will be appreciated by those of skill in the art that the respective rates of hydraulic fluid flow into and out of first and second chambers52,54of hydraulic cylinders26,32,34during extension and retraction may not be equal. That is, because of the location of rod portion50A within second chamber54, piston assembly50may have a reduced pressure area within second chamber54, as compared with a pressure area within first chamber52. Accordingly, during retraction of hydraulic cylinders26,32,34, more hydraulic fluid may be forced out of first chamber52than can be consumed by second chamber54and, during extension, more hydraulic fluid may be consumed by first chamber52than is forced out of second chamber54. In order to accommodate the excess fluid discharge during retraction and the additional fluid required during extension, each of meterless circuits58,60,62may be provided with two makeup valves86and two relief valves88that connect first and second pump passages68,70to charge circuit64via a common passage90.

Makeup valves86may each be a variable position valve that is disposed between common passage90and one of first and second pump passages68,70and configured to selectively allow pressurized fluid from charge circuit64to enter first and second pump passages68,70. In particular, each of makeup valves86may be solenoid-actuated from a first position at which fluid freely flows between common passage90and the respective first and second pump passage68,70, toward a second position at which fluid from common passage90may flow only into first and second pump passage68,70when a pressure of common passage90exceeds the pressure of first and second pump passages68,70by a threshold amount. Makeup valves86may be spring-biased toward their second positions, and only moved toward their first positions during operations known to have need of positive or negative makeup fluid. Makeup valves86may also be used to facilitate fluid regeneration between first and second pump passages68,70within a particular circuit, by simultaneously moving together at least partway to their first positions.

Relief valves88may be provided to allow fluid relief from each meterless circuit58,60,62into charge circuit64when a pressure of the fluid exceeds a set threshold of relief valves88. Relief valves88may be set to operate at relatively high pressure levels in order to prevent damage to hydraulic system56, for example at levels that may only be reached when hydraulic cylinders26,32,34reach an end-of-stroke position and the flow from the associated pumps66is nonzero, or during a failure condition of hydraulic system56. Each pair of relief valves88may connect to first and second pump and head- and rod-end passages68-74via different resolvers92, such that a higher-pressure fluid of first pump and rod-end passages68,72may be relieved to common passage90via set of resolvers92, and a higher-pressure fluid of second pump and head-end passages70,74may be relieved to common passage90via a remaining resolver92.

Charge circuit64may include at least one hydraulic source fluidly connected to common passage90described above. In the disclosed embodiment, charge circuit64has two sources, including a charge pump94and an accumulator96, which may be fluidly connected to common passage90in parallel to provide makeup fluid to meterless circuits58,60,62. Charge pump94may embody, for example, an engine-driven, variable displacement pump configured to draw fluid from a tank98, pressurize the fluid, and discharge the fluid into common passage90. In one embodiment, charge pump94may be an over-center pump that allows for peak-shaving operations, as will be described in more detail below. Accumulator96may embody, for example, a compressed gas, membrane/spring, or bladder type of accumulator configured to accumulate pressurized fluid from and discharge pressurized fluid into common passage90. Excess hydraulic fluid, either from charge pump94or from meterless circuits58,60,62(i.e., from operation of pumps66and/or the rotary and linear actuators) may be directed into either accumulator96or into tank98by way of a charge relief valve100disposed in a return passage102. Charge relief valve100may be movable from a flow-blocking position toward a flow-passing position as a result of elevated fluid pressures within common passage90and return passage102. A manual service valve104may be associated with accumulator96to facilitate draining of accumulator96to tank98during service of charge circuit64.

Hydraulic system56may be provided with means for recuperating fluid power. In particular, hydraulic system56may include at least one high-pressure accumulator106. In the disclosed embodiment, two high-pressure accumulators106are utilized and separated by a two-position (e.g., flow-passing and flow-blocking), solenoid-actuated, combining valve107. One or both of accumulators106, depending on system demands, may be selectively connected to particular ones of meterless circuits58,60,62via combining valve107to either accumulate excess pressurized fluid or to discharge previously accumulated fluid. Accumulators106may be fluidly connected to first and second pump passages68,70via accumulator passages108and110, respectively, and via a common passage112. Accumulator valves114may be disposed between common passage112and accumulator passages108,110and configured to selectively control fluid flow between individual meterless circuits58,60,62and accumulators106. Accumulator valves114may be two-position (flow-blocking and flow-passing), solenoid actuated valves that are spring-biased toward flow-blocking positions. A manual service valve116may be associated with accumulators106to facilitate draining of accumulators106to tank98via a passage118during service.

In some embodiments, a valve120may be disposed within a passage122that connects accumulators106to common passage90. Valve120may be a two-position (flow-blocking and flow-passing), solenoid-activated valve that is spring biased toward the flow-blocking position. Valve120may be used to facilitate peak-shaving operations. That is, any time accumulators106have excess pressurized fluid (or any time pressurized fluid is directed to already full accumulators), the fluid may be directed through passage122and valve120into charge circuit64. This fluid may then be utilized in several different ways, for example to fill low-pressure accumulator96, to provide makeup fluid to meterless circuits58,60,62if there is current demand, or to drive charge pump94in a direction that reduces a load on or adds capacity to power source18. It is contemplated that valve120may also help protect accumulator96from damaging pressure spikes, in some applications. That is, valve120may be used to isolate accumulator96from excessive pressures, and only open when the pressures of passage122are below a threshold pressure. Alternatively, an additional isolation valve150may be provided and directly associated with accumulator96, if desired.

During operation of machine10, the operator of machine10may utilize interface device46to provide a signal that identifies a desired movement of the various linear and/or rotary actuators to a controller124. Based upon one or more signals, including the signal from interface device46and, for example, signals from various pressure sensors126and/or position sensors (not shown) located throughout hydraulic system56, controller124may command movement of the different valves and/or displacement changes of the different pumps and motors to advance a particular one or more of the linear and/or rotary actuators to a desired position in a desired manner (i.e., at a desired speed and/or with a desired force).

Controller124may embody a single microprocessor or multiple microprocessors that include components for controlling operations of hydraulic system56based on input from an operator of machine10and based on sensed or other known operational parameters. Numerous commercially available microprocessors can be configured to perform the functions of controller124. It should be appreciated that controller124could readily be embodied in a general machine microprocessor capable of controlling numerous machine functions. Controller124may include a memory, a secondary storage device, a processor, and any other components for running an application. Various other circuits may be associated with controller124such as power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other types of circuitry.

An alternative embodiment of first meterless circuit58is illustrated inFIG. 3. Like first meterless circuit58ofFIG. 2, first meterless circuit58ofFIG. 3includes pump66connected to left travel motor42L and hydraulic cylinder34via first and second pump and rod- and head-end passages68-74in closed-loop manner. In contrast to the embodiment ofFIG. 2, however, first meterless circuit58ofFIG. 3includes a single spool valve128in place of valves78,80,82,84.

Spool valve128may be a five-position, solenoid-operated valve, that is spring biased toward a flow-blocking position. In the flow-blocking position, fluid flow between pump66and hydraulic cylinder34may be blocked. From the first position, spool valve128may be moved upward (relative toFIG. 3) one step to a second position, at which first pump passage68is fluidly connected with rod-end passage72and second pump passage70is fluidly connected with head-end passage74. Further upward movement of spool valve128may achieve the third position, at which second pump passage70is simultaneously fluidly connected with both rod- and head-end passages72,74. From the first position, spool valve128may also be movable downward one step to a fourth position, at which first pump passage68is fluidly connected with head-end passage74and second pump passage70is fluidly connected with rod-end passage72. Further downward movement of spool valve128may achieve the fifth position, at which first pump passage68is simultaneously fluidly connected with both rod- and head-end passages72,74.

The third and fifth positions may be used in a tool float mode of operation. That is, when in the third and fifth positions, work tool14may be allowed to float or move under the influence of an outside force (e.g., gravity or a load on work tool14). When in these positions, fluid may be allowed to flow directly from first chamber52to second chamber54and vice versa, without first passing through pump66. This functionality may provide for faster movement of work tool14and a reduced load on pump66and power source18.

In the embodiment ofFIG. 3, left travel motor42L may only be isolated from pump66and hydraulic cylinder34via displacement control, as described above. It is contemplated, however, that isolation valves76may additionally be included in the embodiment ofFIG. 3, if desired.

Industrial Applicability

The disclosed hydraulic system may be applicable to any machine where improved hydraulic efficiency and performance is desired. The disclosed hydraulic system may provide for improved efficiency through the use of meterless technology. The disclosed hydraulic system may provide for enhanced performance through the selective use of a novel fluid storage configuration. Operation of hydraulic system56will now be described.

During operation of machine10, an operator located within station20may command a particular motion of work tool14in a desired direction and at a desired velocity by way of interface device46. One or more corresponding signals generated by interface device46may be provided to controller124indicative of the desired motion, along with machine performance information, for example sensor data such a pressure data, position data, speed data, pump displacement data, and other data known in the art.

In response to the signals from interface device46and based on the machine performance information, controller124may generate control signals directed to pumps66,94and to valves76,78,80,82,84,86,114,120,150. For example, to rotate left travel motor42L at an increasing speed in the first direction, controller124may generate a control signal that causes pump66of first meterless circuit58to increase its displacement and discharge fluid into first pump passage68at a greater rate. In addition, controller124may generate a control signal that causes isolation valves76to move toward and/or remain in their flow-passing positions. After fluid from pump66passes into and through left travel motor42L via first pump passage68, the fluid may return to pump66via second pump passage70. To reverse the motion of left travel motor42L, the output direction of pump66may be reversed. If, during the motion of left travel motor42L, the pressure of fluid within either of first or second pump passages68,70becomes excessive (for example during an overrunning condition), fluid may be relieved from the pressurized passage to tank98via relief valves88and common passage90. Alternatively or additionally, the pressurized fluid may be directed into accumulators106via accumulator passages108or110, valves114, and common passage112. In contrast, when the pressure of fluid within either of first or second pump passages68,70becomes too low, fluid from charge circuit64may be allowed into meterless circuit58via common passage90and makeup valves86.

During the motion of left travel motor42L, the operator may simultaneously request movement of hydraulic cylinder34. For example, the operator may request via interface device46that hydraulic cylinder34be retracted at an increasing speed. When this occurs, controller124may generate a control signal that causes pump66of first meterless circuit58to increase its displacement and discharge fluid into first pump passage68at a greater rate. In addition, controller124may generate a control signal that causes first rod-end valve78and second head-end valve84to move toward and/or remain in their flow-passing positions. At this time, second rod-end valve80and first head-end valve82may be in their flow-blocking positions. As fluid from pump66passes into second chamber54of hydraulic cylinder34via first pump and rod-end passages68,72, fluid may be discharged from first chamber52back to pump66via head-end and second pump passages74,70.

The motion of hydraulic cylinder34may be reversed in two different ways. First, the operation of pump66may be reversed, thereby reversing the flows of fluid into and out of hydraulic cylinder34. Although satisfactory in some situations, this method of reversing cylinder motion may only be possible when the displacement of left travel motor42L is also simultaneously reversed (so as to maintain travel in a desired constant direction) or when the left travel motor42L is already stopped and isolated from hydraulic cylinder34. Otherwise, the motion of hydraulic cylinder34may be reversed by switching the positions of first and second pump and rod- and head-end valves78,80,82,84. If, during the motion of hydraulic cylinder34, the pressure of fluid within either of first or second pump passages68,70becomes excessive (for example during an overrunning condition), fluid may be relieved from the pressurized passage to tank98via relief valves88and common passage90. Alternatively or additionally, the pressurized fluid may be directed into accumulators106via accumulator passages108,110, valves114, and common passage112. In contrast, when the fluid pressure becomes too low, fluid from charge circuit64may be allowed into meterless circuit58via common passage90and makeup valves86.

As described above, desired operation of the rotary and linear actuators may drive displacement control of pumps66. When both rotary and linear actuator motion is simultaneously desired within a single circuit, however, directional displacement control of the associated pump66may be driven based solely on the desired motion of the linear actuator (although the displacement magnitude of pump66may be based on flow requirements of both the rotary and linear actuator). At this time, in order to cause the rotary actuator to move in a desired direction at a desired speed and/or with a desired torque, the displacement of the rotary actuator may be selectively varied.

As also described above, hydraulic cylinder34may discharge more fluid from first chamber52during retracting operations than is consumed within second chamber54, and consume more fluid that is discharged from second chamber54during an extending operation. During these operations, accumulator valves114may be selectively opened to allow the excess fluid to enter and fill accumulators106(when the excess fluid has a sufficiently high pressure, for example during an overrunning condition) or to exit and replenish meterless circuit58, thereby providing a neutral balance of fluid entering and exiting pump66.

Regeneration of fluid may be possible during retracting operations of hydraulic cylinder34, when the pressure of fluid exiting first chamber52of hydraulic cylinder34is elevated (e.g., during motoring retracting operations). Specifically, during the retracting operation described above, both of makeup valves86may be simultaneously moved toward their flow-passing positions. In this configuration, makeup valves86may allow some of the fluid exiting first chamber52to bypass pump66and flow directly into second chamber54. This operation may help to reduce a load on pump66, while still satisfying operator demands, thereby increasing an efficiency of machine10. In some embodiments, makeup valves86may be held partially closed during regeneration to facilitate some energy dissipation that improves controllability.

In the disclosed embodiments of hydraulic system56, flows provided by pump66may be substantially unrestricted such that significant energy is not unnecessarily wasted in the actuation process. Thus, embodiments of the disclosure may provide improved energy usage and conservation. In addition, the meterless operation of hydraulic system56may, in some applications, allow for a reduction or even complete elimination of metering valves for controlling fluid flow associated with the linear and rotary actuators. This reduction may result in a less complicated and/or less expensive system.

The disclosed hydraulic system may provide for fluid power storage and reuse between multiple, closed-loop, meterless circuits. That is, the configuration of hydraulic system56may allow for excess fluid power from one closed-loop meterless circuit to be accumulated and later used within another closed-loop meterless circuit. In addition, because the power is retained in fluid form and directly transferred from circuit to circuit without transformation, an efficiency of the process may be high.

The disclosed hydraulic system may also provide for enhanced pump overspeed protection. In particular, during overrunning retracting operations of hydraulic cylinders26,32,34, when fluid exiting first chambers52has elevated pressures, the highly-pressurized fluid may be rerouted back into second chambers54via makeup valves86, without the fluid ever passing through pumps66. Not only does the rerouting help to improve machine efficiencies, but the bypassing of pumps66may also reduce a likelihood of pumps66overspeeding.

The disclosed hydraulic system may further provide for improved pressure protection from damaging spikes. In particular, because pressure relief of meterless circuits58,60,62may be provided at dual locations via resolvers92(at locations within first and second upper- and lower-side passages68-74), the likelihood of damaging pressure spikes developing in these areas is reduced.

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 valves114,76,78,80,82, and84are shown and described as being two-position, on/off type valves, it is contemplated that these valves could alternative be proportional in nature to facilitate additional functionality. For example, if accumulator valve114were proportional, accumulators106could be simultaneously charged by each of first, second, and third meterless circuits58,60,62, even if all three circuits have different pressures. In this situation, accumulator charging would be done at the lowest pressure and some throttling might be required. In addition, although pumps66are described as being over-center type pumps, it is contemplated that pumps66may alternatively be unidirectional pumps, if desired. In this situation, energy transferred through the pump (i.e., from any rotary and/or linear actuators) will be limited to a single direction. 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.