Abstract:
A method and system for operating a machine having first and second movable elements, first and second hydromechanical movers for moving the first and second movable elements, respectively, and first and second hydraulic pumps linked to the first and second hydromechanical movers, respectively. Movement requests for moving the first and second movable elements are processed such that the movement command to the second hydromechanical mover is reduced by a variable amount based on the magnitude of the first movement request. For commanded first hydromechanical mover movements below a certain level, flow to the second hydromechanical mover may optionally not be reduced.

Description:
TECHNICAL FIELD 
       [0001]    This patent disclosure relates generally to excavators and other machines having a meterless hydraulic system capable of actuating multiple functions at a given time via hydromechanical movers, and, more particularly to arrangements for adapting such a system to provide a more user-friendly experience during high acceleration movement of one of the functions. 
       BACKGROUND 
       [0002]    Unlike a typical hydraulic system having a single hydraulic pump feeding a plurality of valves to control an associated plurality of hydraulic actuators and hydraulic motors (herein included in the term “hydromechanical movers”) for various functions, a “meterless” hydraulic control system controls one or more hydraulic actuators and/or motors associated with separate movements or functions by controlling a flow rate from a dedicated pump associated with those hydromechanical movers. Thus, while proportional or throttling valves are utilized in prior art metered systems to meter fluid to control movement of each hydromechanical mover, the flow to each hydromechanical mover in a meterless system is controlled directly by controlling the associated pump. The dedicated pump or pumps may be of any suitable type including variable displacement or fixed displacement, wherein the flow from the pump to the actuator chambers is varied in order to control the speed and extent of the movement. 
         [0003]    In prior art meterless arrangements, pump controlled circuits known as Displacement Controls (DC) utilize a variable displacement pump with a constant speed driver, while Electro-Hydrostatic Actuators (EHA) utilize a fixed displacement pump with a variable speed driver. In either case, the system is able to move multiple functions simultaneously more efficiently than prior systems. Although this is generally a substantial benefit, the response that the operator experiences from the machine in certain circumstances is sometimes unsettling for operators accustomed to more traditional equipment. 
         [0004]    For example, in an excavator having a traditional hydraulic system, when an operator “comes out of the hole” by commanding swing at the same time as commanding the boom up sharply, the swing pump and associated motor speed response is naturally sluggish due to the simultaneous hydraulic requirements of the boom actuator(s). In comparison, a meterless system is able to fully supply both functions, with the result that the swing movement may occur much more vigorously than the operator had anticipated based on his or her experience with traditional metered systems. This may lead to operator surprise or discomfort. 
         [0005]    It will be appreciated that this background section sets forth a collection of concepts that the inventors considered in their contemplations regarding the invention. This background section does not, however, purport to be or to describe prior art except as expressly noted. Rather, it describes certain inventor observations and ideas based on those observations. 
       SUMMARY 
       [0006]    In one aspect of the disclosure, there is described a machine having meterless hydraulic actuation of a plurality of functions, the machine having a first movable element, a first hydromechanical mover for moving the first movable element, and a first hydraulic pump linked to the first hydromechanical mover to supply hydraulic fluid thereto and receive hydraulic fluid therefrom. A second movable element is included as well as a second hydromechanical mover for moving the second movable element, and a second hydraulic pump, distinct from the first hydraulic pump, linked to the second hydromechanical mover to supply hydraulic fluid thereto and receive hydraulic fluid therefrom. 
         [0007]    A user interface for receiving movement requests for moving the first and second movable elements is included in the machine, as is a controller for generating movement commands to the first and second hydromechanical movers based on the received first and second movement requests. The movement command to the second hydromechanical mover is reduced by a variable amount based on the magnitude of the first movement request. 
         [0008]    In another embodiment, a method is described for adjusting movement of movable elements in a machine having meterless hydraulic actuation of a plurality of functions. The method includes receiving a first movement request for movement of a first machine element, the first machine element being actuated by a first hydromechanical mover having a first hydraulic pump linked to the first hydromechanical mover to supply hydraulic fluid thereto and receive hydraulic fluid therefrom. The method further includes receiving contemporaneously with the first movement request a second movement request for movement of a second machine element, the second machine element being actuated by a second hydromechanical mover having a second hydraulic pump, distinct from the first hydraulic pump, to supply hydraulic fluid thereto and receive hydraulic fluid therefrom. Movement commands are generated for the first and second hydromechanical movers based on the received first and second movement requests, wherein generating the second movement command includes applying to the second request a variable rate based on the magnitude of the first movement request. 
         [0009]    In yet another embodiment, a controller for controlling first and second hydromechanical movers linked to first and second movable elements in a machine is described. Each hydromechanical mover includes a separate respective hydraulic pump for supplying pressurized hydraulic fluid to, and receiving pressurized hydraulic fluid from, the hydromechanical mover. The controller includes a computer-readable memory having thereon computer-executable instructions including instructions for receiving a first movement request for movement of the first movable element, receiving contemporaneously with the first movement request a second movement request for movement of the second movable element, and generating movement commands to the first and second hydromechanical movers based on the received first and second movement requests. Generating the second movement command includes applying to the second request a variable rate based on the magnitude of the first movement request. 
         [0010]    Other features and advantages of the described principles will be apparent from the detailed specification, taken in conjunction with the attached drawing figures, of which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a side elevational view of a machine incorporating aspects of this disclosure; 
           [0012]      FIG. 2  is a schematic view of a hydraulic system according to this disclosure including a hydraulic circuit, including actuators, motors, pumps and pressure transducers; 
           [0013]      FIG. 3  is a schematic control architecture view of the pump displacement control of  FIG. 2  including data and command signaling; 
           [0014]      FIG. 4  is a simplified plot showing boom circuit flow and a correlated swing circuit flow limit according to an embodiment of the disclosure; and 
           [0015]      FIG. 5  is a flow chart of a process for establishing a swing circuit flow based on a boom circuit flow to replicate a behavior of a metered hydraulic system according to an embodiment of the disclosed system and method. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    This disclosure relates to machines  100  that utilize hydromechanical movers (identified generally as  102 ) to control movement of moveable subassemblies of the machine, such as arms, booms, implements, or the like, as well as rotation of the assemblies of the machine  100 . For the purposes of this disclosure and the appended claims, the term “hydromechanical movers” will be used to refer to both actuators and motors that are hydraulically operated by a pump. More specifically, the disclosure relates to such so-called meterless hydraulic systems  104  utilized in machines  100 , such as the excavator  106  illustrated in  FIG. 1 , used to control rotation or extension and retraction of such hydromechanical movers  102 . While the arrangement is illustrated in connection with an excavator  106 , the arrangement disclosed herein has universal applicability in various other types of machines  100  as well. The term “machine” may refer to any 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, the machine may be a wheel loader or a skid steer loader. Moreover, one or more implements may be connected to the machine  100 . Such implements may be utilized for a variety of tasks, including, for example, brushing, compacting, grading, lifting, loading, plowing, ripping, and include, for example, augers, blades, breakers/hammers, brushes, buckets, compactors, cutters, forked lifting devices, grader bits and end bits, grapples, blades, rippers, scarifiers, shears, snow plows, snow wings, and others. 
         [0017]    The excavator  106  of  FIG. 1  includes a cab  108  that is swingably supported on an undercarriage  110  that includes a pair of rotatably mounted tracks  112 . The swinging function is implemented via a hydromechanical mover in the form of a hydraulic motor  408  (see  FIG. 3 ). In the meterless system illustrated, a dedicated pump  406  is provided for operation of the swing motor  408 , as will be appreciated by those of skill in the art. Returning to  FIG. 1 , the hydraulic motor for implementing the cab swing movement may be fixed to the cab  108  and rotatably linked via a ring gear or other arrangement to the undercarriage  110 . Alternately, it may be fixed to the undercarriage  110  and rotatably linked to the cab  108 . 
         [0018]    The cab  108  includes an operator station  114  from which the machine  100  may be controlled. The operator station  114  may include, for example, an operator control  115  for controlling the rotation or extension and refraction of the hydromechanical movers  102 . The operator control  115  may be of any appropriate design. By way of example only, the operator control  115  may be in the form of joystick, such as illustrated in  FIG. 1 , a dial, a switch, a lever, a combination of the same, or any other arrangement that provides the operator with a mechanism by which to identify the movement commanded. The operator station  114  may further include controls such as a hydraulic lockout switch  113 , or an on/off switch  111  as shown in  FIG. 2 . 
         [0019]    The cab  108  may further include an engine  116 , and at least a portion of the meterless hydraulic system  104 . The engine  116  may be an internal combustion engine or any type power source known to one skilled in the art now or in the future. 
         [0020]    A front linkage  118  includes a boom  120  that is pivotably supported on the cab  108 , a stick  122  pivotably coupled to the boom  120 , and an implement  124  pivotably coupled to the stick  122 . While the implement  124  is illustrated as a bucket  126 , the implement  124  may alternately be, for example, a compactor, a grapple, a multi-processor, thumbs, a rake, a ripper, or shears. 
         [0021]    Movement of the boom  120 , stick  122 , and implement  124  is controlled by a number of hydromechanical movers  102  in the form of actuators  130 ,  132 ,  134 . The boom  120  is pivotably coupled to cab  108  at one end  136 . To control movement of the boom  120  relative to the cab  108 , a pair of actuators  130  are provided on either side of the boom  120 , coupled at one end to the cab  108 , and at the other end to the boom  120 . 
         [0022]    The stick  122  is pivotably coupled to the boom  120  at a pivot connection  138 . Movement of the stick  122  relative to the boom  120  is controlled by the actuator  132  that is coupled at one end to the boom  120 , and at the other end to the stick  122 . The actuator  132  is pivotably coupled to the stick  122  at a pivot connection  140  that is spaced from the pivot connection  138  such that extension and retraction of the actuator  132  pivots the stick  122  about pivot connection  138 . 
         [0023]    The implement  124  is pivotably coupled to the stick  122  at pivot connection  142 . Movement of the implement  124  relative to the stick  122  is controlled by actuator  134 . The actuator  134  is coupled to the stick  122  at one end. The other end of the actuator  134  is coupled to a four-bar linkage arrangement  144  that includes a portion of the stick  122  itself, as well as the implement  124  and a pair of links  146 ,  148 . The actuator  134  is extended in order to move the implement  124  toward the cab (counterclockwise in the illustrated embodiment), and retracted in order to move the implement  124  away from the cab (clockwise in the illustrated embodiment). 
         [0024]    Movement of the actuator  132  is controlled by the meterless hydraulic system  104 , which is shown in greater detail in  FIG. 2 . While the operation of the hydraulic system  104  is explained below with regard to actuator  132 , this explanation is equally applicable to the other actuators  130 ,  134 , and other actuators operated by a similar meterless hydraulic system  104 . Further, similar hydraulic supply arrangements are provided for operation of the swing motor  408 . 
         [0025]    The actuator  132  includes a cylinder  162  in which a piston  164  is slidably disposed. A rod  166  is secured to the piston  164 , and extends from the cylinder  162 . In this way, the piston  164  divides the interior of the cylinder  162  into a rod chamber  168  and a cap side chamber  170 . In operation, as the actuator  132  is extended, hydraulic fluid flows from the rod chamber  168  and hydraulic fluid flows into the cap side chamber  170  as the piston  164  and rod  166  slide within the cylinder  162  to telescope the rod  166  outward from the actuator  132 . Conversely, as the actuator  132  is retracted, hydraulic fluid flows into the rod chamber  168  and hydraulic fluid flows out of the cap side chamber  170  as the piston  164  and rod  166  slide within the cylinder  162  to retract the rod  166  into the cylinder  162 . Flow of hydraulic fluid to and from the rod and cap side chambers  168 ,  170  proceeds through a rod side fluid connection  172  and a cap side fluid connection  174 , respectively, that are fluidly coupled to respective ports  176 ,  178  opening in the rod or cap side chambers  168 ,  170  in the cylinder  162 . 
         [0026]    Flow between the rod and cap side chambers  168 ,  170  through the rod side and cap side fluid connections  172 ,  174  is provided by a pump  180  wherein the flow rate from the pump may be varied. In this way, the pump  180  controls the operation of actuator  132 , rather than so-called metering valves. Any suitable pump type may be used, including without limitation, variable displacement radial pumps with reversing valve (sized for minimal losses), unidirectional axial piston pumps with a reversing valve, and so on, as well as the variable displacement type pump described below. 
         [0027]    In the illustrated implementation, the pump  180  is a variable displacement pump  180 , which includes a swash plate  181 , the angle of which determines the positive or negative displacement of the pump  180 , and volume of flow from the pump  180 . It will thus be appreciated that the displacement of the pump  180 , and, accordingly, the flow rate is controlled in order to control both the direction and volume of the flow of hydraulic fluid to provide extension and retraction of the actuator  132  as commanded by the operator. While a reversible variable displacement pump  180  is illustrated, the pump  180  may alternately be a fixed displacement pump wherein the speed may be varied by an associated driving motor. The pump  180  may operate as a pump to positively pump fluid from one fluid connection  172 ,  174  to the other  172 ,  174 , or a motor as fluid flows from one fluid connection  172 ,  174  to the other  172 ,  174 . 
         [0028]    It will be appreciated by those of skill in the art that the respective volumes of hydraulic fluid flowing into and out of the rod and cap side chambers  168 ,  170  during extension and refraction of the actuator  132  are not equal. This is a result of the difference in surface area of the piston  164  on the rod and cap side chambers  168 ,  170 ; that is, the surface area of the piston  164  where the rod  166  extends from the piston  164  is less than the surface area of the piston  164  facing the cap side chamber  170 . Consequently, during retraction of the actuator  132 , more hydraulic fluid flows from the cap side chamber  170  than can be utilized in the rod chamber  168 . Conversely, during extensions of the actuator  132 , additional hydraulic fluid is required to supplement the hydraulic fluid flowing from the rod chamber  168  in order to fill the cap side chamber  170 . To receive this excess hydraulic fluid and provide this supplemental hydraulic fluid, a charge circuit  182  and make-up hydraulic circuit  184  may be provided, as shown in  FIG. 2 . 
         [0029]    The charge circuit  182  includes at least one hydraulic fluid source, two of which are provided in the illustrated embodiment. The illustrated charge circuit  182  includes an accumulator  186  that may be utilized to provide a source of pressurized hydraulic fluid or that may be charged with excess hydraulic fluid through a charge conduit  188 . The illustrated charge circuit  182  additionally includes a tank  190  from which hydraulic fluid may be provided by a second pump  192  through the charge conduit  188 . Excess hydraulic fluid, either from the second pump  192  or operation of the actuator  132  may be returned to either the accumulator  186 , or to the tank  190  by way of a charge pilot valve  198  disposed in a charge pilot conduit  200 , which is fluidly connected to return conduit  201 . The charge pilot valve  198  is operated as a result of fluid pressure in the conduit  200  along the inlet side of the charge pilot valve  198 , although an alternate method of operation may be provided. In this embodiment, the pump  180  and the second pump  192  are both operated by a prime mover  194 , such as the engine  116 , through a gearbox  196 . In an alternate embodiment, one or both of the pumps  180 ,  192  may be connected directly to the engine  116  or prime mover  194  shaft with no speed ratio change. The pump  180  and/or the second pump  192  may alternately be operated by a battery or other power storage arrangement. It will further be appreciated that the second pump  192  may be selectively operated, or continuously operated, as in the illustrated embodiment, depending upon the arrangement provided. 
         [0030]    The make-up hydraulic circuit  184  includes a make-up conduit  202  that is fluidly coupled to the charge conduit  188 , a make-up valve  204 , a rod side make-up conduit  206  and a cap side make-up conduit  208 , which are fluidly coupled to the rod side fluid connection  172  and the cap side fluid connection  174 , respectively. The make-up valve has three positions. The first, central default position  210  prevents flow to or from each of conduits  202 ,  206 ,  208 . Alternatively, the central default position may be constructed such that conduit  208  is connected to conduit  202  by an orifice (not shown), and conduit  206  is connected to conduit  202  by an orifice (not shown); this connection using orifices may be desirable if the pump  180  does not return to a perfect zero displacement when commanded to neutral. 
         [0031]    In order to operate the make-up valve  204 , pilot connections  216 ,  218  are provided from the rod and cap side make-up conduits  206 ,  208 , respectively. Thus, the make-up valve  204  is operative as a result of a minimum pressure differential between the pilot connections  216 ,  218 . While very little flow occurs through the pilot connections  216 ,  218 , it will be appreciated that the pressure from the rod side fluid connection  172  is applied to the pilot connection  216  by way of the rod side make-up conduit  206 . Similarly, the pressure from the cap side fluid connection  174  is applied to the pilot connection  218  by way of the cap side make-up conduit  208 . 
         [0032]    The make-up circuit  184  may include check valves  220 ,  222  that are operative at set pressure differentials between the make-up conduit  202  and the rod side and cap side fluid connections  172 ,  174 , respectively. It will be appreciated that the check valves  220 ,  222  will unseat to permit flow if the pressure within the make-up conduit  202  is sufficiently greater than the pressures in rod side and cap side fluid connections  172 ,  174 , respectively. The check valves  220 ,  222  may include any device for limiting flow in a piping system to a single direction known by one skilled in the art now and in the future. 
         [0033]    Turning now to  FIG. 3 , this figure is a schematic view of the control architecture  400  of the pump displacement control of  FIG. 2  including data and command signaling. In particular, the illustrated control architecture  400  includes a human machine interface (HMI)  401  which allows the machine to receive operator commands and translate them into a machine operable form such as a digital or analog command or signal. Examples of the HMI  401  include without limitation the related structures of  FIG. 1 , namely operator control  115  for controlling the operation of the hydromechanical movers  102 , which control may be in the form of a joystick, a dial, a switch, a lever, a combination of the same, or any other arrangement by which the operator may command a movement, as well as a hydraulic lockout switch  113 , on/off switch  111 , etc. 
         [0034]    In addition to the HMI  401 , the architecture  400  includes a controller  403  for receiving interface commands  402 ,  412  from the HMI  401 . In the illustrated example, the first interface command  402  may be a boom movement command and the second interface command  412  may be a swing movement command. 
         [0035]    The controller  403  may comprise one or more processors, e.g., microprocessors, for generating and transmitting control signals  404 ,  405  based on received data and commands. The controller  403  may operate specifically by the computerized execution of computer-readable instructions stored on a nontransitory computer-readable medium such as a RAM, ROM, PROM, EPROM, optical disk, flash drive, thumb drive, etc. 
         [0036]    The controller  403  is operable to receive commands and data from the HMI  401  and optionally to receive actuator or element movement data, e.g., for position and/or acceleration, from machine sensors, and control pump flow for each pump on the basis of received commands and data. In the illustrated embodiment, a first command  404  and a second command  405  are output from the controller  403  to be provided to a first hydraulic pump  406  and to a second hydraulic pump  407  respectively. Each of the first hydraulic pump  406  and the second hydraulic pump  407  is configured to provide pressurized fluid at a commanded rate. The first hydraulic pump  406  is fluidly linked via hydraulic circuit  410  to supply pressurized fluid to a swing motor  408 , while the second hydraulic pump  407  is fluidly linked via hydraulic circuit  411  to supply pressurized fluid to a boom hydraulic actuator  409 . In an alternative embodiment, the hydraulic actuators  408 ,  409  are situated to power other independent machine functions requiring coordinated rate-based control. 
         [0037]    Due to the independent nature of each hydraulic circuit, the illustrated meterless configuration is able to fully supply pressurized fluid responsive to received operator commands. Depending upon the number of functions operated at a given time, this response may differ from the response of an otherwise equivalent machine using a unitary metered circuit instead of multiple meterless circuits as noted above. As also noted above, the differing response may be disconcerting to the user who is actually accustomed to a more sluggish response when controlling certain machine movements simultaneously. 
         [0038]    A primary context in which this difference may be noticeable to the operator is when the machine is commanded to lift the boom at a high rate of speed or acceleration, while simultaneously swinging to move the bucket to or from a pile. This movement is sometimes referred to as “coming out of the hole.” In a traditional metered system, the raising of the boom in an abrupt manner decreases the hydraulic flow to the swing motor, resulting in a variable and somewhat sluggish swing motion anytime the boom is commanded to undergo substantial upward motion. 
         [0039]    In the illustrated system, this response is mimicked by independently electronically controlling multiple pumps in a variable manner with the control rate being established based on other simultaneously commanded movements. In a specific embodiment, the allowed rate of swing movement is constrained by a variable amount based on the rate of boom lift commanded. In further embodiment, this is accomplished by reducing the flow in the hydraulic circuit  410  associated with the swing motor  408  by a variable amount based on the simultaneously commanded rate of boom movement. 
         [0040]    As will be discussed in greater detail hereinafter, the controller  403  implements the rate reduction scheme summarized above by reducing the swing flow command  404  by an amount dictated by any simultaneous boom lift command  405 . The quantitative behavior of the system in this regard will be discussed with reference to  FIG. 4 , after which the operations of the controller  403  to impose swing rate limits will be discussed with reference to  FIG. 5 . 
         [0041]    Turning now to  FIG. 4  for the moment, this figure illustrates a set of correlated flow plots showing hydraulic circuit flow command and flow command limits for swing and boom up functions according to an embodiment of the disclosure. In particular, the boom curve  450  illustrates an increasing rate boom up user boom up command on the horizontal axis and a corresponding flow command from the controller  403  on the vertical axis. As can be seen, the issued flow command tracks the user command proportionally. 
         [0042]    In an embodiment, this results in a swing flow limit curve as shown in plot  460 . In the lower portion  461  of the swing flow limit curve, the flow available to the swing motor is unlimited except by the limit of the associated pump output F max . This lower portion  461  represents the region in which the correlated instantaneous boom up flow command has not exceeded a predetermined rate B t . After this point, the flow limit for the swing function changes. In particular, in region  462 , the correlated instantaneous boom up flow command exceeds the predetermined rate B t . 
         [0043]    In this region, wherein the user boom command exceeds the predetermined boom rate threshold B t , the swing flow limit curve is not proportional to the user swing command, but rather is decreased by a rate that is related to the contemporaneous boom flow command  450 . In an embodiment, the swing motor flow limit is adjusted such that the boom flow and swing flow remain constant, mimicking the “maxing out” of a fixed flow metered system. 
         [0044]    Thus, the swing motor flow limit S L  can be written in this embodiment as S L =F max  when the boom flow B F  is less than B T , and S L =M−B F  when B F  exceeds B T , where M is a maximum chosen flow rate for both the boom and swing circuits combined. In an embodiment, M=B T +F max . Although in a traditional metered system this would imply that there is no flow available for other hydraulic functions at such a time, in an embodiment, the flows to other actuators (other than the swing motor) in the meterless system are not affected by the flow limits imposed on the swing motor circuit. 
         [0045]    The controller function that provides this swing flow derating behavior will be discussed in greater detail with respect to the flow chart of  FIG. 5 . In particular, FIG,  5  is a flow chart of a process  500  for treating swing flow commands and boom flow commands in an interdependent manner to produce a user experience that simulates that provided by a traditional metered system. 
         [0046]    At stage  501  of process  500 , the controller  403  receives a boom movement command and a swing movement command, e.g., from the HMI  401 . Subsequently at stage  502 , the controller  403  determines whether the received boom movement command correlates to a boom actuator flow rate exceeding the predetermined flow threshold B T . If it is determined at stage  502  that the received boom movement command correlates to a boom actuator flow rate that does not exceed the predetermined boom flow threshold B T , then the process  500  continues to stage  503 , wherein the controller provides pump flow commands to the swing circuit pump and boom circuit pump corresponding to the received boom flow and swing flow commands. In this stage, the boom circuit flow and swing circuit flow are independent. 
         [0047]    If, however, it is determined at stage  502  that the received boom movement command correlates to a boom actuator flow rate exceeding the predetermined flow threshold B T , then the process  500  branches to stage  504  instead, wherein the controller  403  provides a pump flow command to the boom circuit pump corresponding to the received boom flow command and provides a pump flow command to the swing circuit corresponding to the received swing flow command decreased by an amount dependent on the pump flow command to the boom circuit. For example, the pump flow command to the swing circuit may be decreased to keep the sum of the boom flow and swing flow constant as discussed above. Alternatively, the pump flow command to the swing circuit may be decreased by a multiplicative factor based on the pump flow command to the boom circuit pump. 
         [0048]    The flow commands issued to the hydraulic pumps may be digital or analog signals, and may be of any suitable type and nature. For example, in an implementation employing a variable displacement pump for each circuit, the pump flow commands may be signals adapted to drive a solenoid setting a hydraulic actuator or swashplate affecting pump displacement. In contrast, in an implementation employing fixed displacement electrically driven pumps, the pump flow commands may be electric drive signals adapted to drive the motor for each pump (or to cause the motor to be driven) at the prescribed speed to produce the desired flow rate. 
       INDUSTRIAL APPLICABILITY 
       [0049]    The described system and method may be applicable to any meterless hydraulically-actuated excavator machine having independent variable flow pumps for executing boom movement and swing movement, or more generally any machine having a meterless hydraulic system controlling multiple independent dimensions of movement. The described system allows for the benefits of meterless systems, e.g., efficiency, lowered emissions, etc., to be attained while maintaining certain desired behavior associated with metered systems wherein certain dimensions of movement (e.g., boom and swing) may interact. 
         [0050]    In particular, in an embodiment wherein the machine is a meterless excavator, the boom and swing movements are coupled such that for low boom flows, the swing motion is unaltered but for high boom flows the swing flow is reduced to provide a coupled feel relative to the boom and swing functions. Thus, for example, when the machine is “coming out of the hole” with high boom upward acceleration, the user experiences an artificially sluggish swing response more akin to that of a metered system. This allows the user to control the meterless machine in much the same way that he or she controlled the metered machine, without encountering disconcerting changes in machine behavior and without having to change their habits of control and operation. Not only does this modification in meterless operation improve the user experience, but it also avoids the expense of retraining trained personnel to switch over from metered to meterless machines. 
         [0051]    It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated. 
         [0052]    Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. 
         [0053]    Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.