Hydraulic control system having cylinder flow correction

A hydraulic control system is disclosed. The hydraulic control system may have a hydraulic actuator, a valve arrangement, and an operator input device configured to generate a first signal indicative of a desired hydraulic actuator velocity. The hydraulic control system may also have a sensor configured to generate a second signal indicative of an actual flow rate of fluid entering the hydraulic actuator, and a controller. The controller may be configured to determine a desired flow rate of fluid into the hydraulic actuator based on the first signal; to estimate the actual flow rate based on the desired flow rate, a correction flow rate, and a system response model; and to determine the actual flow rate based on the second signal. The controller may also be configured to make a comparison of the estimated and determined actual flow rates of fluid, and to determine the correction flow rate based on the comparison.

TECHNICAL FIELD

The present disclosure relates generally to a hydraulic control system, and more particularly, to a hydraulic control system that implements cylinder flow correction.

BACKGROUND

Machines such as wheel loaders, excavators, dozers, motor graders, and other types of heavy equipment use multiple actuators supplied with hydraulic fluid from one or more pumps on the machine to accomplish a variety of tasks. These actuators are typically velocity controlled based on, among other things, an actuation position of an operator interface device. In particular, when an operator moves a particular interface device to a specific displaced position, the operator expects a corresponding hydraulic actuator to move at a predetermined velocity in a desired direction. This predetermined velocity and associated fluid flow into the actuator required to produce the velocity are, however, generally fixed within permanent relationship maps during testing of a similar test machine at a manufacturing facility, and may not account for machine-to-machine variability. Accordingly, every machine may behave somewhat differently when actuated in the same manner by the same operator. If left unchecked, this variability could cause reduced machine control, performance, and efficiency.

One attempt to reduce the effects of machine-to-machine variability in the control of a position-in, velocity-out hydraulic system is disclosed in U.S. Pat. No. 6,775,974 that issued to Tabor on Aug. 17, 2004 (the '974 patent). In particular, the '974 patent describes a hydraulic system having a joystick movable by an operator to produce an electrical signal indicative of a direction and a desired rate at which a corresponding hydraulic actuator is to move. The hydraulic system also has a pressure sensor configured to sense a system pressure at an electro-hydraulic proportional valve associated with the hydraulic actuator, and a controller in communication with the joystick, the pressure sensor, and the electro-hydraulic proportional valve. The controller is configured to request a desired velocity for the hydraulic actuator based on the electrical signal, and determine varying forces acting on the hydraulic actuator based on a signal from the pressure sensor. The controller is further configured to determine a unique valve flow coefficient, which characterizes fluid flow through the particular electro-hydraulic proportional valve, that is required to achieve the desired velocity. Activation of the electro-hydraulic valve is then performed based on the valve flow coefficient.

Although the system of the '974 patent may be potentially helpful in reducing machine-to-machine variability, it may still be less than optimal and lack applicability. In particular, the system of the '974 patent may fail to consider system delays inherent to pump and cylinder response, as well as valve behavior during cylinder movement. In addition, the system may lack applicability to machines where pressure variations at the valve do not substantially affect flow through the valve.

The disclosed hydraulic control system is directed to overcoming 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 control system. The hydraulic control system may include a hydraulic actuator, a valve arrangement configured to meter pressurized fluid into the hydraulic actuator, and an operator input device configured to generate a first signal indicative of a desired velocity of the hydraulic actuator. The hydraulic control system may also include a sensor configured to generate a second signal indicative of an actual flow rate of fluid entering the hydraulic actuator, and a controller in communication with the valve arrangement, the operator input device, and the sensor. The controller may be configured to determine a desired flow rate of fluid into the hydraulic actuator based on the first signal; to estimate the actual flow rate of fluid entering the hydraulic actuator based on the desired flow rate of fluid, a correction flow rate, and a system response model; and to determine the actual flow rate of fluid entering the hydraulic actuator based on the second signal. The controller may also be configured to make a comparison of the estimated and determined actual flow rates of fluid entering the hydraulic actuator, and to determine the correction flow rate based on the comparison.

In another aspect, the present disclosure is directed to a method of operating a machine. The method may include receiving an operator input indicative of a desired velocity of a hydraulic actuator, and determining a desired flow rate of fluid into the hydraulic actuator based on the desired velocity. The method may further include estimating an actual flow rate of fluid entering the hydraulic actuator based on the desired flow rate of fluid, a correction flow rate, and a system response model; and sensing an actual flow rate of fluid entering the hydraulic actuator. The method may additionally include making a comparison of the estimated and sensed actual flow rates of fluid entering the hydraulic actuator, and determining the correction flow rate based on the comparison.

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 a material moving machine such as the loader depicted inFIG. 1. Alternatively, machine10could embody an excavator, a dozer, a backhoe, a motor grader, a dump truck, or another similar machine. Machine10may include, among other things, a linkage system12configured to move a work tool14, and a prime mover16that provides power to linkage system12.

Linkage system12may include structure acted on by fluid actuators to move work tool14. Specifically, linkage system12may include a boom (i.e., a lifting member)17that is vertically pivotable about a horizontal axis28relative to a work surface18by a pair of adjacent, double-acting, hydraulic cylinders20(only one shown inFIG. 1). Linkage system12may also include a single, double-acting, hydraulic cylinder26connected to tilt work tool14relative to boom17in a vertical direction about a horizontal axis30. Boom17may be pivotably connected at one end to a body32of machine10, while work tool14may be pivotably connected to an opposing end of boom17. It should be noted that alternative linkage configurations may also be possible.

Numerous different work tools14may be attachable to a single machine10and controlled to perform a particular task. For example, work tool14could embody a bucket (shown inFIG. 1), 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 another task-performing device known in the art. Although connected in the embodiment ofFIG. 1to lift and tilt relative to machine10, work tool14may alternatively or additionally pivot, rotate, slide, swing, or move in any other appropriate manner.

Prime mover16may embody an engine such as, for example, a diesel engine, a gasoline engine, a gaseous fuel-powered engine, or another type of combustion engine known in the art that is supported by body32of machine10and operable to power the movements of machine10and work tool14. It is contemplated that prime mover may alternatively embody a non-combustion source of power, if desired, such as a fuel cell, a power storage device (e.g., a battery), or another source known in the art. Prime mover16may produce a mechanical or electrical power output that may then be converted to hydraulic power for moving hydraulic cylinders20and26.

For purposes of simplicity,FIG. 2illustrates the composition and connections of only hydraulic cylinder26and one of hydraulic cylinders20. It should be noted, however, that machine10may include other hydraulic actuators of similar composition connected to move the same or other structural members of linkage system12in a similar manner, if desired.

As shown inFIG. 2, each of hydraulic cylinders20and26may include a tube34and a piston assembly36arranged within tube34to form a first chamber38and a second chamber40. In one example, a rod portion36aof piston assembly36may extend through an end of second chamber40. As such, second chamber40may be associated with a rod-end44of its respective cylinder, while first chamber38may be associated with an opposing head-end42of its respective cylinder.

First and second chambers38,40may each be selectively supplied with pressurized fluid and drained of the pressurized fluid to cause piston assembly36to displace within tube34, thereby changing an effective length of hydraulic cylinders20,26and moving work tool14(referring toFIG. 1). A flow rate of fluid into and out of first and second chambers38,40may relate to a velocity of hydraulic cylinders20,26and work took14, while a pressure differential between first and second chambers38,40may relate to a force imparted by hydraulic cylinders20,26on work tool14. An expansion (represented by an arrow46) and a retraction (represented by an arrow47) of hydraulic cylinders20,26may function to assist in moving work tool14in different manners (e.g., lifting and tilting work tool14, respectively).

To help regulate filling and draining of first and second chambers38,40, machine10may include a hydraulic control system48having a plurality of interconnecting and cooperating fluid components. Hydraulic control system48may include, among other things, a valve stack50at least partially forming a circuit between hydraulic cylinders20,26, an engine-driven pump52, and a tank53. Valve stack50may include a lift valve arrangement54, a tilt valve arrangement56, and, in some embodiments, one or more auxiliary valve arrangements (not shown) that are fluidly connected to receive and discharge pressurized fluid in parallel fashion. In one example, valve arrangements54,56may include separate bodies bolted to each other to form valve stack50. In another embodiment, each of valve arrangements54,56may be stand-alone arrangements, connected to each other only by way of external fluid conduits (not shown). It is contemplated that a greater number, a lesser number, or a different configuration of valve arrangements may be included within valve stack50, if desired. For example, a swing valve arrangement (not shown) configured to control a swinging motion of linkage system12, one or more travel valve arrangements, and other suitable valve arrangements may be included within valve stack50. Hydraulic control system48may further include a controller58in communication with valve arrangements54,56to control corresponding movements of hydraulic cylinders20,26.

Each of lift and tilt valve arrangements54,56may regulate the motion of their associated fluid actuators. Specifically, lift valve arrangement54may have elements movable to simultaneously control the motions of both of hydraulic cylinders20and thereby lift boom17relative to work surface18. Likewise, tilt valve arrangement56may have elements movable to control the motion of hydraulic cylinder26and thereby tilt work tool14relative to boom17. During a lowering movement of boom17and a downward tilting movement of work tool14, hydraulic cylinders20,26may be assisted by the force of gravity. In contrast, during upward lifting and tilting movements, hydraulic cylinders20,26may be working against the force of gravity.

Valve arrangements54,56may be connected to regulate flows of pressurized fluid to and from hydraulic cylinders20,26via common passages. Specifically, valve arrangements54,56may be connected to pump52by way of a common supply passage60, and to tank53by way of a common drain passage62. Lift and tilt valve arrangements54,56may be connected in parallel to common supply passage60by way of individual fluid passages66and68, respectively, and in parallel to common drain passage62by way of individual fluid passages72and74, respectively. A pressure compensating valve78and/or a check valve79may be disposed within each of fluid passages66,68to provide a unidirectional supply of fluid having a substantially constant flow to valve arrangements54,56. Pressure compensating valves78may be pre- (shown inFIG. 2) or post-compensating (not shown) valves 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 provided to valve arrangements54and56, even when a pressure of the fluid directed to pressure compensating valves78varies. It is contemplated that, in some applications, pressure compensating valves78and/or check valves79may be omitted, if desired.

Each of lift and tilt valve arrangements54,56may be substantially identical and 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 arrangement54may include a head-end supply valve80, a rod-end supply valve82, a head-end drain valve84, and a rod-end drain valve86. Similarly, tilt valve arrangement56may include a head-end supply valve88, a rod-end supply valve90, a head-end drain valve92, and a rod-end drain valve94.

Head-end supply valve80may be disposed between fluid passage66and a fluid passage104that leads to first chamber38of hydraulic cylinder20, and be configured to regulate a flow rate of pressurized fluid into first chamber38in response to a flow command from controller58. Head-end supply valve80may 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 chamber38, and a second end-position at which fluid flow is blocked from first chamber38. It is contemplated that head-end supply valve80may 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 valve80may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in another suitable manner.

Rod-end supply valve82may be disposed between fluid passage66and a fluid passage106leading to second chamber40of hydraulic cylinder20, and be configured to regulate a flow rate of pressurized fluid into second chamber40in response to a flow command from controller58. Rod-end supply valve82may 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 chamber40, and a second end-position at which fluid is blocked from second chamber40. It is contemplated that rod-end supply valve82may 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 valve82may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in another suitable manner.

Head-end drain valve84may be disposed between fluid passage104and fluid passage72, and be configured to regulate a flow rate of pressurized fluid from first chamber38of hydraulic cylinder20to tank53in response to a flow command from controller58. Head-end drain valve84may 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 chamber38, and a second end-position at which fluid is blocked from flowing from first chamber38. It is contemplated that head-end drain valve84may 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 valve84may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in another suitable manner.

Rod-end drain valve86may be disposed between fluid passage106and fluid passage72, and be configured to regulate a flow rate of pressurized fluid from second chamber40of hydraulic cylinder20to tank53in response to a flow command from controller58. Rod-end drain valve86may 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 chamber40, and a second end-position at which fluid is blocked from flowing from second chamber40. It is contemplated that rod-end drain valve86may 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 valve86may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in another suitable manner.

Head-end supply valve88may be disposed between fluid passage68and a fluid passage108that leads to first chamber38of hydraulic cylinder26, and be configured to regulate a flow rate of pressurized fluid into first chamber38in response to a flow command from controller58. Head-end supply valve88may 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 chamber38, and a second end-position at which fluid flow is blocked from first chamber38. It is contemplated that head-end supply valve88may 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 valve88may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in another suitable manner.

Rod-end supply valve90may be disposed between fluid passage68and a fluid passage110that leads to second chamber40of hydraulic cylinder26, and be configured to regulate a flow rate of pressurized fluid into second chamber40in response to a flow command from controller58. Specifically, rod-end supply valve90may 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 chamber40, and a second end-position, at which fluid is blocked from second chamber40. It is contemplated that rod-end supply valve90may 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 valve90may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in another suitable manner.

Head-end drain valve92may be disposed between fluid passage108and fluid passage74, and be configured to regulate a flow rate of pressurized fluid from first chamber38of hydraulic cylinder26to tank53in response to a flow command from controller58. Specifically, head-end drain valve92may 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 chamber38, and a second end-position at which fluid is blocked from flowing from first chamber38. It is contemplated that head-end drain valve92may 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 valve92may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in another suitable manner.

Rod-end drain valve94may be disposed between fluid passage110and fluid passage74, and be configured to regulate a flow rate of pressurized fluid from second chamber40of hydraulic cylinder26to tank53in response to a flow command from controller58. Rod-end drain valve94may 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 chamber40, and a second end-position at which fluid is blocked from flowing from second chamber40. It is contemplated that rod-end drain valve94may 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 valve94may alternatively be hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in another suitable manner.

Pump52may have variable displacement and be load-sense controlled to draw fluid from tank53and discharge the fluid at a specified elevated pressure to valve arrangements54,56. That is, pump52may include a stroke-adjusting mechanism96, for example a swashplate or spill valve, a position of which is hydro-mechanically adjusted based on a sensed load of hydraulic control system48to thereby vary an output (e.g., a discharge rate) of pump52. The displacement of pump52may be adjusted from a zero displacement position at which substantially no fluid is discharged from pump52, to a maximum displacement position at which fluid is discharged from pump52at a maximum rate. In one embodiment, a load-sense passage (not shown) may direct a pressure signal to stroke-adjusting mechanism96and, based on a value of that signal (i.e., based on a pressure of signal fluid within the passage), the position of stroke-adjusting mechanism96may change to either increase or decrease the output of pump52and thereby maintain the specified pressure. Pump52may be drivably connected to prime mover16of machine10by, for example, a countershaft, a belt, or in another suitable manner. Alternatively, pump52may be indirectly connected to prime mover16via a torque converter, a gear box, an electrical circuit, or in any other manner known in the art.

Tank53may constitute a reservoir configured to hold a supply of fluid. The fluid may include, for example, a dedicated hydraulic oil, an engine lubrication oil, a transmission lubrication oil, or any other fluid known in the art. One or more hydraulic circuits within machine10may draw fluid from and return fluid to tank53. It is also contemplated that hydraulic control system48may be connected to multiple separate fluid tanks, if desired.

Controller58may embody a single microprocessor or multiple microprocessors that include components for controlling valve arrangements54,56based on, among other things, input from an operator of machine10and one or more sensed operational parameters. Numerous commercially available microprocessors can be configured to perform the functions of controller58. It should be appreciated that controller58could readily be embodied in a general machine microprocessor capable of controlling numerous machine functions. Controller58may include a memory, a secondary storage device, a processor, and any other components for running an application. Various other circuits may be associated with controller58such as power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other types of circuitry.

Controller58may receive operator input associated with a desired movement of machine10by way of one or more interface devices98that are located within an operator station of machine10. Interface devices98may embody, for example, single or multi-axis joysticks, levers, or other known interface devices located proximate an onboard operator seat (if machine10is directly controlled by an onboard operator) or located within a remote station offboard machine10. Each interface device98may be a proportional-type device that is movable through a range from a neutral position to a maximum displaced position to generate a corresponding displacement signal that is indicative of a desired velocity of work tool14caused by hydraulic cylinders20,26, for example a desired tilting and/or lifting velocity of work tool14. The lifting and tilting desired velocity signals may be generated independently or simultaneously by the same or different interface devices98, and be directed to controller58for further processing.

One or more maps relating the interface device position signals, the corresponding desired work tool velocities, associated flow rates, valve element positions, system pressures, and/or other characteristics of hydraulic control system48may be stored in the memory of controller58. Each of these maps may be in the form of tables, graphs, and/or equations. In one example, desired work tool velocity and commanded flow rates may form the coordinate axis of a 2-D table for control of head- and rod-end supply valves80,82,88,90. The commanded flow rates required to move hydraulic cylinders20,26at the desired velocities and corresponding valve element positions of the appropriate valve arrangements54,56may be related in the same or another separate 2- or 3-D map, as desired. It is also contemplated that desired velocity may alternatively be directly related to the valve element position in a single 2-D map. Controller58may be configured to allow the operator to directly modify these maps and/or to select specific maps from available relationship maps stored in the memory of controller58to affect actuation of hydraulic cylinders20,26. It is also contemplated that the maps may be automatically selected for use by controller58based on sensed or determined modes of machine operation, if desired.

Controller58may be configured to receive input from interface device98and to command operation of valve arrangements54,56in response to the input and based on the relationship maps described above. Specifically, controller58may receive the interface device position signal indicative of a desired work tool velocity, and reference the selected and/or modified relationship maps stored in the memory of controller58to determine desired flow rates for the appropriate supply and/or drain elements within valve arrangements54,56. In conventional hydraulic systems, the desired flow rates would then be commanded of the appropriate supply and drain elements to cause filling of particular chambers within hydraulic cylinders20,26at rates that correspond with the desired work tool velocities. However, machine-to-machine variability (e.g., variability between supply and drain valve elements, pumps, and actuators) could result in performance variability of the conventional systems that is unexpected and/or undesired. In fact, in some systems, machine-to-machine variability has been shown to account for up to 30% error in the desired work tool velocities (i.e., velocities that are 30% lower higher than the desired velocities). Accordingly, controller58, as will be described in more detail in the following section, may be configured to accommodate the machine-to-machine variability by selectively correcting the desired flow rates mapped out for individual valve arrangements based on monitored and modeled performance factors.

Controller58may rely, at least in part, on measured flow rates of fluid entering each hydraulic cylinder20,26to account for machine-to-machine variability. The measured flow rates may be directly or indirectly sensed by one or more sensors102,103. In the disclosed embodiment, each of sensors102,103may embody a magnetic pickup-type sensor associated with a magnet (not shown) embedded within the piston assembly36of different hydraulic cylinders20,26. In this configuration, sensors102,103may each be configured to detect an extension position of the corresponding hydraulic cylinder20,26by monitoring the relative location of the magnet, indexing position changes to time, and generating corresponding velocity signals. As hydraulic cylinders20,26extend and retract, sensors102,103may generate and direct the velocity signals to controller58for further processing. It is contemplated that sensors102,103may alternatively embody other types of sensors such as, for example, magnetostrictive-type sensors associated with a wave guide (not shown) internal to hydraulic cylinders20,26, cable type sensors associated with cables (not shown) externally mounted to hydraulic cylinders20,26, internally- or externally-mounted optical sensors, rotary style sensors associated with a joint pivotable by hydraulic cylinders20,26, or any other type of sensors known in the art. It is further contemplated that sensors102,103may alternatively only be configured to generate signals associated with the extension and retraction positions of hydraulic cylinders20,26, with controller58then indexing the position signals according to time and thereby determining the velocities of hydraulic cylinders20,26based on the position signals from sensors102,103. From the velocity information provided by sensors102,103and based on known geometry and/or kinematics of hydraulic cylinders20,26(e.g., flow areas), controller58may be configured to calculate the flow rates of fluid entering hydraulic cylinders20,26. That is, the flow rate of fluid entering a particular cylinder may be calculated by controller58as a function of that cylinder's velocity and its cross-sectional flow area.

FIG. 3illustrates an exemplary flow-correcting operation performed by controller58.FIG. 3will be discussed in more detail in the following section to further illustrate the disclosed concepts.

INDUSTRIAL APPLICABILITY

The disclosed hydraulic control system may be applicable to any machine that includes multiple fluid actuators where controllability, productivity, and efficiency are issues. The disclosed hydraulic control system may enhance controllability, productivity, and efficiency by selectively correcting desired flow rates commanded of individual valve arrangements based on monitored and modeled performance factors. Operation of hydraulic control system48will now be explained.

During operation of machine10, a machine operator may manipulate interface device98to request a corresponding movement of work tool14. The displacement position of interface device98may be related to an operator desired velocity of work tool14. Interface device98may generate a position signal indicative of the operator desired velocity of work tool14during manipulation, and direct this position signal to controller58for further processing.

Controller58may receive the operator interface device position signal (Step300) and reference the maps stored in memory to determine a desired velocity for the appropriate cylinder20,26of hydraulic control system48and the corresponding desired flow rate (Step305) that should cause that cylinder20,26to move at the desired velocity. Controller58may then apply a correction flow rate to the desired flow rate, and command the resulting total flow rate of the appropriate supply and drain elements of valve arrangements54,56to move the corresponding hydraulic cylinder20,26at the desired velocity requested by the operator (Step320). In the disclosed embodiment, the correction flow rate may be an arrangement-specific flow rate that is added to or subtracted from the desired flow rate. In another embodiment, however, the correction flow rate may instead be or additionally include a scaling factor that multiplies the desired flow rate for a certain arrangement by a particular amount.

In some embodiments, the correction flow rate may first be limited, if desired, before being applied to the desired flow rate for the certain arrangement. For example, controller58may be configured to compare a magnitude of the correction flow rate to a magnitude of the desired flow rate (Step310), and set the magnitude of the correction flow rate about equal to the magnitude of the desired flow rate (Step315) when the correction flow rate magnitude is greater than the desired flow rate magnitude. By limiting the correction flow rate, it may be ensured that the correction flow rate will not result in a total flow rate that is excessive or a total flow rate that is in a direction opposite the work tool movement direction that is desired by the operator. For example, if the desired flow rate for a particular valve arrangement is 50 lpm (liters per minute), but the correction flow rate is −55 lpm, the resulting total flow rate would be −5 lpm, resulting in a cylinder movement direction that is opposite to that being requested. Instead, in this example, the correction flow rate may be limited to −50 lpm, such that the total flow rate would instead be 0 lpm. It is contemplated that steps310-315may be omitted, if desired.

The correction flow rate applied to the desired flow rate may be determined through the use of a system response model. In particular, controller58may provide the desired flow rate determined in Step305as input to the system response model to estimate how hydraulic control system48will respond to a valve arrangement command to meter the desired flow rate into a corresponding cylinder. In the disclosed embodiment, the system response model may consist of three different portions, including a pump response portion, a cylinder response portion, and a valve behavior portion. Each portion of the system response model may include one or more equations, algorithms, maps, and/or subroutines that function to predict the physical response and/or behavior of the specified portion of hydraulic control system48. Each of the equations, algorithms, maps, and/or subroutines may be developed during manufacture of machine10and periodically updated and/or uniquely tuned based on actual operating conditions of individual machines10.

At about the same time as (e.g., just before or just after) commanding the appropriate one of valve arrangements54,56to meter fluid at the total flow rate about equal to the desired flow rate plus the correction flow rate, controller58may run the pump portion of the system response model to determine how pump52(referring toFIG. 2) might respond to the flow rate metering commanded by controller58(Step325). That is, the pump portion of the system response model may be used by controller58to estimate a delay between a time when the flow rate metering command is issued by controller58to the appropriate valve arrangement54,56, and a time when adjusting mechanism96(referring toFIG. 2) begins to adjust the displacement of pump52and respond to system pressure fluctuations caused by the metering. That is, even after the flow rate metering command is issued by controller58, some time may lapse before system pressure droops and pump52mechanically responds to the droop with increased displacement that raises pressure back up to where it should be maintained. During this time, fluid flow through the system (e.g., through the corresponding valve arrangement into the appropriate cylinder) may fluctuate, resulting in changing velocities of the cylinder. In addition to estimating the associated pump response time delay, the pump portion of the system response model may also be configured to model the actual pump flow that is directed to the corresponding valve arrangement54,56(Step330). This information concerning the pump's output may subsequently be used for control of pump52and/or other functions of machine10.

After completion of Step325, controller58may be configured to run the cylinder delay and valve behavior portions of the system response model to determine an estimated actual flow through the corresponding valve arrangement54,56to the appropriate hydraulic cylinder20,26at a particular instant in time following issuance of the metering command (Step335). Specifically, controller58may use the cylinder delay portion of the system response model to estimate a delay between the time when adjusting mechanism96begins to adjust the displacement of pump52and respond to system pressure fluctuations caused by the commanded metering, and a time when effects of the adjusting are experienced by the corresponding hydraulic cylinder. In other words, the cylinder response model may be used by controller58to determine the delay between a displacement adjustment of pump52and a change in the actual flow rate into and velocity of the corresponding hydraulic cylinder20,26caused by the adjustment. Controller58may then use the valve behavior portion of the system response model to determine how movements of the corresponding valve arrangement54,56may affect cylinder velocity after the time when the displacement adjustment of pump52has affected the cylinder velocity (i.e., after the cylinder response delay period). In other words, after the displacement of pump52has been adjusted to change the flow rate of fluid directed into the corresponding hydraulic cylinder20,26, the valve behavior portion may then be utilized by controller58to model how movements of the corresponding valve arrangement54,56may affect that flow rate.

Based on information from the system response model, controller58may be configured to estimate an actual flow rate of fluid entering the corresponding hydraulic cylinder20,26at any point in time, and compare that estimated actual flow rate to an actual flow rate measured by way of sensors102,103(Step340). This comparison may provide an indication as to how well the total flow rate metering commanded of valve arrangements54,56(i.e., desired flow rate+correction flow rate) results in the operator desired velocity of work tool14. In particular, an error value substantially proportional to the difference between the estimated actual and the measured actual flow rates may be generated during Step340and used by controller58to adjust the correction flow rate during a subsequently requested movement of hydraulic cylinders20,26(i.e., during a subsequent control cycle when the system response model is again utilized). In other words, the correction flow rate utilized in Step320during a current machine movement may be a correction flow rate adjusted during an immediately previous control cycle. In the disclosed example, the adjustments from sequential cycles may be integrated to form the correction flow rate (Step350).

In some situations, controller58may be configured to consider the movement direction requested by the operator in Step300. Specifically, controller58may be configured to determine if the requested movement of work tool14is in general alignment with the force of gravity (Step345) (i.e., when the requested flow direction causes the corresponding hydraulic cylinder20,26to move with or against gravity), and respond differently according to the determination. When the requested movement is against the force of gravity (e.g., when work tool14is lifting or tilting upward), control may proceed through step350, as described above. However, when the requested movement is in alignment with the force of gravity (e.g., when work tool14is lowering or tilting downward), controller58may be configured to maintain without change the correction flow rate determined during the immediately previous control cycle utilizing the system response model (Step355) (i.e., the adjustment to the correction flow rate may not be integrated). In this manner, the effects of gravity causing a cylinder to move faster than possible with the commanded flow rate of fluid may be avoided and the integrity of the correction flow rate preserved, thereby providing stability to hydraulic control system48.

The disclosed hydraulic control system48may help to improve the control, productivity, and efficiency of machine10. Specifically, hydraulic control system48may be configured to monitor actual flow rates of fluid supplied to hydraulic cylinders20,26, and tailor corresponding flow rate commands to better match actual velocities of hydraulic cylinders20,26to velocities desired and requested by the operator of machine10. In this manner, machine-to-machine variability may be reduced, allowing for enhanced control, productivity, and efficiency.