US20140060030A1 - Hydraulic accumulator health monitor - Google Patents

Abstract

A system and method to diagnose the operational health of a hydraulic accumulator are provided. The system can include a hydraulic accumulator selectively coupled to a hydraulic actuator, such as a swing motor. The accumulator can be charged by movement of the actuator. A pressure sensor can be associated with the accumulator to determine an accumulator pressure. A controller can be connected to the pressure sensor. The controller can determine a charge curve based on a relationship between an actuator operational parameter associated with the actuator movement and the accumulator pressure. The controller can compare the charge curve to a previously defined charge curve or range to determine an error between the charge curve and the previously defined charge curve or range. The degree of the error can be associated with the operational health of the accumulator, and if too large, the operator may be notified of the status.

Description

RELATED APPLICATIONS
• This application is based upon and claims the benefit of priority from U.S. Provisional Application No. 61/695,344 by Pengfei Ma et al., filed Aug. 31, 2013, the contents of which are expressly incorporated herein by reference.
TECHNICAL FIELD
• The present disclosure relates to hydraulic accumulators and more particularly to monitoring and determining the health of the hydraulic accumulator.
BACKGROUND
• Pre-charge pressure of a hydraulic accumulator needs to be periodically checked after installation in a hydraulic system to ensure operational health of the accumulator. Typical solutions for detecting the accumulator health involve connecting a gas pressure gauge and/or a modular kit to a gas valve of the hydraulic accumulator, when the machine is stopped and the fluid in the hydraulic accumulator is not pressurized. The gas pressure gauge provides a reading of the pre-charge pressure. Depending on such readings, the hydraulic accumulator is either re-charged or completely overhauled or replaced. Hence, typical solutions required physically connecting the hydraulic accumulator to the pressure gauge. However, the accumulator can be located on a machine such that it is difficult to access and couple the gas pressure gauge.
• In one example, German Patent Number DE102005052640 relates to a method involving determination of a difference in accumulator volume using a flow regulator with constant adjustable flow rate and an actuating valve with preset response time. The method also involves determination of pressure values before and after the fluid withdrawal from a hydraulic accumulator using a pressure sensor based on its recalled calculated accumulator volume at an empty state.
SUMMARY OF THE DISCLOSURE
• In one embodiment, a system to diagnose the operational health of a hydraulic accumulator is provided. The system can include a hydraulic actuator and a hydraulic accumulator selectively coupled to the hydraulic actuator. The hydraulic accumulator can be charged as a result of movement of the actuator. A pressure sensor can be associated with the hydraulic accumulator to determine an accumulator pressure. A controller can be in communication with the pressure sensor. The controller can determine a relationship between an actuator operational parameter associated with the movement of the actuator and the accumulator pressure. The controller can compare the relationship to a previously defined relationship (or range) to determine an error, if any, between the relationship and the previously defined relationship.
• In another embodiment, a method of diagnosing an operational health of a hydraulic accumulator is provided. Another step may include moving an actuator to charge a hydraulic accumulator selectively coupled to the actuator. Another step may include storing an accumulator pressure during the movement of the actuator to define a relationship between an actuator operational parameter associated with the movement of the actuator and the accumulator pressure. Another step may include comparing the relationship to a previously defined relationship to determine an error, if any, between the relationship and the previously defined relationship.
• In another embodiment, a machine is provided having a pump, a hydraulic actuator selectively moved by fluid provided by the pump, and a hydraulic accumulator fluidly coupled to the hydraulic actuator. The hydraulic accumulator is configured to be charged with pressurized fluid resulting from movement of the actuator. A pressure sensor is associated with the hydraulic accumulator to determine an accumulator pressure. A controller is in communication with the pressure sensor. The controller is configured to determine a relationship between an actuator operational parameter associated with the movement of the actuator and the accumulator pressure, and compare the relationship to a previously defined relationship to determine an error, if any, between the determined relationship and the previously defined relationship. The degree of error may be associated with the operational health of the hydraulic accumulator.
• Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a block diagram of an exemplary system having a hydraulic accumulator and a controller, according to one embodiment of the disclosure;
• FIG. 2 is a diagrammatic view of the hydraulic accumulator in an initial state;
• FIG. 3 is a diagrammatic view of the hydraulic accumulator at an intermediate state;
• FIG. 4 is a diagrammatic illustration of an exemplary disclosed machine operating at a worksite with a haul vehicle;
• FIG. 5 is a schematic illustration of an exemplary disclosed hydraulic control system that may be used with the machine ofFIG. 4;
• FIG. 6 is a diagram of a process of determining the health of an accumulator; and
• FIG. 7 is a graphical view of change in accumulator pressure with respect to position of a machine during charging.
DETAILED DESCRIPTION
• FIG. 1 illustrates anexemplary system100 including ahydraulic accumulator102, apressure sensor104, afluid source106 and acontroller108, according to one embodiment of the present disclosure. Thesystem100 may be embodied in any machine such as excavators, wheel loaders, tractors and other machinery. Thehydraulic accumulator102 may be a piston-based accumulator, a bladder-based accumulator, membrane/spring-biased accumulator, or other kind of pressurized fluid storage device that can be selectively charged and discharged. One or more valves (not shown) may be associated with thesystem100 to selectively control charging and discharging of the accumulator. For example, one or more valves may be open to permit charging and/or discharging of the accumulator, whereas one or more valves (same or different) may be closed to permit charging and/or discharging.
• Hydraulic accumulator102 may embody pressure vessels filled with a compressible gas that are configured to store pressurized fluid for future use by the hydraulic system. The compressible gas may include, for example, nitrogen, argon, helium, or another appropriate compressible gas. As fluid in communication with the accumulator exceeds a predetermined pressure of the accumulator, the fluid may flow into accumulator to charge. Because the gas therein is compressible, it may act like a spring and compress as the fluid flows into the accumulator. When the pressure of the fluid drops below the predetermined pressure of the accumulator, the compressed gas may expand and urge the fluid from within the accumulator to exit or discharge.
• As shown inFIGS. 2-3, one example ofhydraulic accumulator102 may include a first chamber302 (FIG. 3), such as a working fluid or oil chamber, asecond chamber304, such as a compressible fluid or gas chamber, and aseparator306 disposed between thechambers302,304. Thefirst chamber302 may be configured to be filled with a first fluid. In one embodiment, the first fluid may include oil, lubricating fluid, or any other fluid associated with hydraulic machinery. Thesecond chamber304 of thehydraulic accumulator102 may be filled with a gas or any other compressible fluid via agas valve308. In one embodiment, the gas may be nitrogen. Theseparator306 of thehydraulic accumulator102 may be configured to separate the first fluid andsecond chambers302,304 to keep the fluid contained therein substantially isolated from one another.
• Thehydraulic accumulator102 may include afirst end cap310 associated with thesecond chamber304 and asecond end cap312 associated with thefirst chamber302. Theseparator306 may be a piston having one ormore seals314 to reduce the risk of fluid from one chamber entering into the other chamber. Theseparator306 is movable within thehydraulic accumulator102 to reduce or increase the volume of the respective chambers.Additional seals315 may be provided in thefirst end cap310 and thesecond end cap312 of thehydraulic accumulator102. Similarly, in case of a bladder-based accumulator, theseparator306 may be flexible membrane or an expandable separator being movable between an expanded configuration and a compressible configuration. Thehydraulic accumulator102 is sized to have a pre-charge pressure capacity to pressurize accumulated fluid within thefirst chamber302, e.g., for energy recovery, which is sequentially released from thefirst chamber302 at the pressure associated with the charged pressure of thesecond chamber304. The pre-charge pressure can be determined by the pressure capacity and difference between the first andsecond chambers302,304.
• To determine the pressure associated with thehydraulic accumulator102, thepressure sensor104 may be connected upstream or downstream of thefirst chamber302 of thehydraulic accumulator102. Thepressure sensor104 may be configured to monitor and provide to thecontroller108 pressure readings of the fluid in thefirst chamber302 during charging and discharging of thehydraulic accumulator102. In one embodiment, the pressure readings may either be provided continuously or after pre-determined intervals of time. In one example, thepressure sensor104 can be a fluid or oil pressure sensor.
• Thefirst chamber302 of thehydraulic accumulator102 can be connected to thefluid source106, such as a fixed or variable displacement hydraulic pump, or a hydraulic actuator as later described. Thefirst chamber302 of thehydraulic accumulator102 is configured to receive and deliver fluid at a flow rate during accumulator charging and discharging modes, respectively. Parameters related to the pump such as flow rate, flow direction, and the like may vary. It should be understood that any other device which may regulate a flow of the fluid may also be utilized. One or more valves may be associated with thefirst chamber302 such that after discharging of thehydraulic accumulator102, the valve is configured to prevent charging at specified periods, such as later described.
• As shown inFIG. 1, thecontroller108 may be connected to thepressure sensor104. Thecontroller108 may be configured to receive and process the pressure readings taken by thepressure sensor104. Moreover, thecontroller108 may determine an approximate pre-charge pressure of thehydraulic accumulator102. Also, thecontroller108 may be configured to determine or estimate frictional forces associated with theseparator306 of thehydraulic accumulator102. For example, determination of such frictional forces may be useful to determine the effectiveness of theseals314 of a piston-based accumulator.
• In one embodiment, thecontroller108 may include acomparator202 to diagnose a health of thehydraulic accumulator102. Thecomparator202 may compare at least one of the pre-charge pressure, the frictional forces with a predefined threshold range of pre-charge pressure and the frictional forces associated with thehydraulic accumulator102 to diagnose the health of thehydraulic accumulator102. In another embodiment, thecomparator202 may be an independent or separate module connected to thecontroller108 by known methods.
• Thecontroller108 and/orcomparator202 may include a processor unit, input and output ports, an electronic storage medium for executable programs and threshold values, random access memory, a data bus, and the like. The functionality of thecontroller108 and/orcomparator202 may further include other activities not described herein. Thecontroller108 may include a memory, a secondary storage device, a clock, and one or more processors that cooperate to accomplish a task consistent with the present disclosure. Numerous commercially available microprocessors can be configured to perform the functions of thecontroller108. It should be appreciated thatcontroller108 could readily embody a general machine controller capable of controlling numerous other functions of a machine. Various known circuits may be associated withcontroller108, including signal-conditioning circuitry, communication circuitry, and other appropriate circuitry. It should also be appreciated thatcontroller108 may include one or more of an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a computer system, and a logic circuit configured to allowcontroller108 to function in accordance with the present disclosure.
• Also, thecontroller108 and/or thecomparator202 may retrieve or store the pressure readings in adatabase110. Thedatabase110 may store historical data values related to the threshold range of pre-charge pressure and frictional forces of thehydraulic accumulator102. Thedatabase110 may utilize data structures, index files, or any other data storage and retrieval technique, without any limitation. It should be understood that theexemplary system100 may include other components not described herein.
• In one example, a process for determining the pre-charge pressure of thehydraulic accumulator102. Initially, thefirst chamber302 of thehydraulic accumulator102 is connected to the fluid source106 (such as, e.g., a pump or a hydraulic actuator). Fluid pressure may be driven to a minimum working pressure or zero such as, e.g., by withdrawing the fluid from the first chamber302 (that is, discharging fluid from the first chamber302) such that thehydraulic accumulator102 is in an minimum volume state as shown inFIG. 2. In the piston-based accumulator, at the minimum working pressure, theseparator306 of thehydraulic accumulator102 may be in contact with walls of thefirst chamber302. Hence, thefirst chamber302 may be reduced to a minimum or zero volume state, while thesecond chamber304 may be at a maximum volume state, resulting in a minimum working pressure. Here, the pressure readings of the fluid pressure of thefirst chamber302 at a minimum or zero volume may be monitored by thepressure sensor104.
• In one example, the pre-charge pressure of thehydraulic accumulator102 is defined as the pressure of the inert gas or compressible fluid filled in thesecond chamber304 when thehydraulic accumulator102 is in the minimum volume state. The fluid pressure recorded by thepressure sensor104 at the minimum volume state is at a minimum working pressure or zero.
• Subsequently, thehydraulic accumulator102 may be charged by providing the fluid to thefirst chamber302.FIG. 3 illustrates an intermediate state of thehydraulic accumulator102 during the charging or discharging cycle. During charging, the fluid is provided to thefirst chamber302 by thefluid source106, at the pre-determined flow rate via aport316 located near thefirst chamber302. In one embodiment, the pump may be driven to minimum or low flow such as, e.g., about 30 lpm or less. Substantially faster rates can be more difficult to measure and control due to temperature increase and other factors. The pressure readings of the fluid pressure may be simultaneously monitored by thepressure sensor104.
• As the fluid is filled in thefirst chamber302, theseparator306 is pushed towards thesecond chamber304 of thehydraulic accumulator102. For a certain interval of time, the pressure of the fluid may continue to remain zero or minimal until the frictional forces associated with theseparator306 are overcome and theseparator306 begins to move away from thesecond end cap312.
• When theseparator306 starts moving, the volume associated with thefirst chamber302 increases as the fluid fills into thefirst chamber302, causing a corresponding decrease in the volume associated with the compressible fluid filled in thesecond chamber304. At this time, the pressure of the fluid may change at a first rate and then transition to a second rate. It may be observed that the first rate of change in the fluid pressure with time is greater than the second rate of change in the fluid pressure with time, as a rapid change to the first rate and subsequent gradual transitioning to the second rate.
• Subsequently, thecontroller108 may determine an approximate pre-charge pressure of thehydraulic accumulator102 based on the monitored transition pressure. In one embodiment, the determination may be based on the second transition pressure. In another embodiment, the determination of the approximate pre-charge pressure of thehydraulic accumulator102 may be based on a correlation of the first and second transition pressures. The correlation may include any mathematical function of the first and second transition pressure readings or the derivation of the approximate pre-charge pressure based on statistical analysis of the first and second transition pressure readings. In one embodiment, thecontroller108 may calculate an average of the first and second transition pressures to determine the approximate pre-charge pressure of thehydraulic accumulator102.
• It should be understood that the determined approximate pre-charge pressure may be substantially equivalent to the pressure of thehydraulic accumulator102 at the minimum volume state. The rate of change of the gas pressure with time during charging and discharging of thehydraulic accumulator102 may be proportional to the comparatively slower rate of change the fluid pressure with time recorded by thepressure sensor104. The slower rates may be easier to read and control.
• Thecontroller108 may also be adapted to notify an operator if at least one of the determined pre-charge pressure and the frictional forces is not within the predefined threshold range. It should be understood that the notification may be provided to indicate that the determined approximate pre-charge pressure and/or the frictional forces of thehydraulic accumulator102 may either be lower or higher than acceptable performance Moreover, the notification provided by thecontroller108 may be a visual feedback like an alert message, an audio feedback like a warning alarm, or any other type of feedback. Based on the notification, one or more remedial actions such as re-charging of thehydraulic accumulator102, overhauling of thehydraulic accumulator102 or replacement of theseals314 in case of the piston-based accumulator may be performed.
• Theaccumulator102 can be fluidly coupled to a hydraulic actuator circuit of a machine, such as, e.g., a swing circuit or a hydraulic cylinder circuit.FIG. 4 illustrates anexemplary machine610 having multiple systems and components that cooperate to excavate and load earthen material onto anearby haul vehicle612. In the depicted example,machine610 is a hydraulic excavator having a swing circuit with a swing motor. It is contemplated, however, that machine10 could alternatively embody another swing-type excavation or material handling machine, such as a backhoe, a front shovel, a dragline excavator, or another similar machine. Alternatively, the machine could have a hydraulic cylinder circuit (boom, stick, and/or tool circuit) coupled to the accumulator, such as an excavator, a wheel loader, or another similar machine. In other words, a hydraulic actuator, such as a swing motor or a hydraulic cylinder, may be coupled to the accumulator.Machine610 may include, among other things, an implementsystem614 configured to move awork tool616 between adig location618 within a trench or at a pile, and adump location620, for example overhaul vehicle612.Machine610 may also include anoperator station622 for manual control of implementsystem614. It is contemplated thatmachine610 may perform operations other than truck loading, if desired, such as craning, trenching, and material handling.
• Implementsystem614 may include a linkage structure acted on by fluid actuators to movework tool616. Specifically, implementsystem614 may include aboom624 that is vertically pivotal relative to awork surface626 by one or more adjacent, double-acting, hydraulic cylinders628 (only one shown inFIG. 6) Implementsystem614 may also include astick630 that is vertically pivotal about ahorizontal pivot axis632 relative to boom624 by a double-acting,hydraulic cylinder636 Implementsystem614 may further include a double-acting,hydraulic cylinder638 that is operatively connected to worktool616 to tiltwork tool616 vertically about ahorizontal pivot axis640 relative to stick630.Boom624 may be pivotally connected to aframe642 ofmachine610, whileframe642 may be pivotally connected to anundercarriage member644 and swung about avertical axis646 by aswing motor649.Stick630 may pivotally connectwork tool616 to boom624 by way ofpivot axes632 and640. It is contemplated that a greater or lesser number of fluid actuators may be included within implementsystem614 and connected in a manner other than described above, if desired.
• Numerousdifferent work tools616 may be attachable to asingle machine610 and controllable viaoperator station622.Work tool616 may include any device used to perform a particular task such as, for example, a bucket, a fork arrangement, a blade, a shovel, or any other task-performing device known in the art. Although connected in the embodiment ofFIG. 4 to lift, swing, and tilt relative tomachine610,work tool616 may alternatively or additionally rotate, slide, extend, open and close, or move in another manner known in the art.
• Operator station622 may be configured to receive input from a machine operator indicative of a desired work tool movement. Specifically,operator station622 may include one ormore input devices648 embodied, for example, as single or multi-axis joysticks located proximal an operator seat (not shown).Input devices648 may be proportional-type controllers configured to position and/or orientwork tool616 by producing a work tool position signal that is indicative of a desired work tool speed and/or force in a particular direction. The position signal may be used to actuate any one or more ofhydraulic cylinders628,636,638 and/orswing motor649. It is contemplated that different input devices may alternatively or additionally be included withinoperator station622 such as, for example, wheels, knobs, push-pull devices, switches, pedals, and other operator input devices known in the art.
• As illustrated inFIG. 5,machine610 may include ahydraulic control system650 having a plurality of fluid components that cooperate to move implement system614 (referring toFIG. 4). In particular,hydraulic control system650 may include afirst circuit652 associated withswing motor649, and at least asecond circuit654 associated withhydraulic cylinders628,636, and638.First circuit652 may include, among other things, aswing control valve656 connected to regulate a flow of pressurized fluid from apump658 to swingmotor649 and fromswing motor649 to a low-pressure tank660 to cause a swinging movement ofwork tool616 about axis646 (referring toFIG. 4) in accordance with an operator request received viainput device648.Second circuit654 may include similar control valves, for example a boom control valve (not shown), a stick control valve (not shown), a tool control valve (not shown), a travel control valve (not shown), and/or an auxiliary control valve connected in parallel to receive pressurized fluid frompump658 and to discharge waste fluid totank660, thereby regulating the corresponding actuators (e.g.,hydraulic cylinders628,636, and638).
• Swing motor649 may include ahousing662 at least partially forming a first and a second chamber (not shown) located to either side of animpeller664. When the first chamber is connected to an output of pump658 (e.g., via afirst chamber passage666 formed within housing662) and the second chamber is connected to tank660 (e.g., via asecond chamber passage668 formed within housing662),impeller664 may be driven to rotate in a first direction (shown inFIG. 5). Conversely, when the first chamber is connected totank660 viafirst chamber passage666 and the second chamber is connected to pump658 viasecond chamber passage668,impeller664 may be driven to rotate in an opposite direction (not shown). The flow rate of fluid throughimpeller664 may relate to a rotational speed ofswing motor649, while a pressure differential acrossimpeller664 may relate to an output torque thereof.
• Pump658 may be configured to draw fluid fromtank660 via aninlet passage680, pressurize the fluid to a desired level, and discharge the fluid to first andsecond circuits652,654 via adischarge passage682. Acheck valve683 may be disposed withindischarge passage682, if desired, to provide for a unidirectional flow of pressurized fluid frompump658 into first andsecond circuits652,654. Pump658 may embody, for example, a variable displacement pump (shown inFIG. 5), a fixed displacement pump, or another source known in the art. Pump658 may be drivably connected to a power source (not shown) ofmachine610 by, for example, a countershaft (not shown), a belt (not shown), an electrical circuit (not shown), or in another suitable manner. Alternatively, pump658 may be indirectly connected to the power source ofmachine610 via a torque converter, a reduction gear box, an electrical circuit, or in any othersuitable manner Pump658 may produce a stream of pressurized fluid having a pressure level and/or a flow rate determined, at least in part, by demands of the actuators within first andsecond circuits652,654 that correspond with operator requested movements.Discharge passage682 may be connected withinfirst circuit652 to first andsecond chamber passages666,668 viaswing control valve656 and first andsecond chamber conduits684,686, respectively, which extend betweenswing control valve656 andswing motor649.
• Tank660 may constitute a reservoir configured to hold a low-pressure 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 systems withinmachine610 may draw fluid from and return fluid totank660. It is contemplated thathydraulic control system650 may be connected to multiple separate fluid tanks or to a single tank, as desired.Tank660 may be fluidly connected to swingcontrol valve656 via adrain passage688, and to first andsecond chamber passages666,668 viaswing control valve656 and first andsecond chamber conduits684,686, respectively.Tank660 may also be connected to low-pressure passage688. Acheck valve690 may be disposed withindrain passage688, if desired, to promote a unidirectional flow of fluid intotank660.
• Swing control valve656 may have one or more elements that are movable to control the rotation ofswing motor649 and corresponding swinging motion of implementsystem614.Swing control valve656 may include an element configured as spool, or independent metering valve (IMV) configuration.
• To driveswing motor649 to rotate in a first direction (shown inFIG. 5),swing control valve656 can have a first configuration to allow pressurized fluid frompump658 to enter the first chamber ofswing motor649 viadischarge passage682 andfirst chamber conduit684, and to allow fluid from the second chamber ofswing motor649 to drain totank660 viasecond chamber conduit686 anddrain passage688. To driveswing motor649 to rotate in the opposite direction,swing control valve656 can have a second configuration to communicate the second chamber ofswing motor649 with pressurized fluid frompump658, and to allow draining of fluid from the first chamber ofswing motor649 totank660. It is contemplated that both the supply and drain functions ofswing control valve656 may alternatively be performed by a single valve element associated with the first chamber and a single valve element associated with the second chamber, or by a single valve element associated with both the first and second chambers, if desired.
• Controller700 (an example of previously referencedcontroller108 inFIG. 1) may be in communication with the different components ofhydraulic control system650 to regulate operations ofmachine610. For example,controller700 may be in communication with the element(s) ofswing control valve656 infirst circuit652 and with the element(s) of control valves (not shown) associated withsecond circuit654. Based on various operator input and monitored parameters,controller700 may be configured to selectively activate the different control valves in a coordinated manner to efficiently carry out operator requested movements of implementsystem614.Controller700 may be connected to inputdevice648 such that current position of the input device is an input for the controller. Based on the current position ofinput device648, the controller may determine and command the appropriate operation of the machine components for a desired task.
• Hydraulic control system650 may be fitted with anenergy recovery arrangement704 that is in communication with at leastfirst circuit652 and configured to selectively extract and recover energy from waste fluid that is discharged fromswing motor649. Energy recovery arrangement (ERA)704 may include, among other things, a recovery valve block (RVB)706 that is fluidly connectable betweenpump658 andswing motor649, an accumulator708 (an example of previously referencedaccumulator102 inFIG. 1) configured to selectively communicate withswing motor649 viaRVB706. In the disclosed embodiment,RVB706 may be fixedly and mechanically connectable to one or both ofswing control valve656 andswing motor649, for example directly tohousing662 and/or directly tohousing697.RVB706 may include afirst passage712 fluidly connectable tofirst chamber conduit684, and asecond passage714 fluidly connectable tosecond chamber conduit686.Accumulator708 may be fluidly connected toRVB706 via aconduit716.
• RVB706 may house aselector valve720, acharge valve722 associated withaccumulator708, and adischarge valve724 associated withaccumulator708 and disposed in parallel withcharge valve722.Selector valve720 may automatically fluidly communicate one of first andsecond passages712,714 with charge and dischargevalves722,724 based on a pressure of first andsecond passages712,714. Charge and dischargevalves722,724 may be selectively movable in response to commands fromcontroller700 to fluidly communicateaccumulator708 withselector valve720 for fluid charging and discharging purposes.
• Selector valve720 may be a pilot-operated, 2-position, 3-way valve that is automatically movable in response to fluid pressures in first andsecond passages712,714 (i.e., in response to a fluid pressures within the first and second chambers of swing motor649). In particular,selector valve720 may include avalve element726 that is movable from a first position (shown inFIG. 5) at whichfirst passage712 is fluidly connected to charge and dischargevalves722,724 via aninternal passage728, toward a second position (not shown) at whichsecond passage714 is fluid connected to charge and dischargevalves722,724 viapassage728. Whenfirst passage712 is fluidly connected to charge and dischargevalves722,724 viapassage728, fluid flow throughsecond passage714 may be inhibited byselector valve720 and vice versa. First andsecond pilot passages730,732 may communicate fluid from first andsecond passages712,714 to opposing ends ofvalve element726 such that a higher-pressure one of first orsecond passages712,714 may causevalve element726 to move and fluidly connect the corresponding passage with charge and dischargevalves722,724 viapassage728.
• Charge valve722 anddischarge valve724 may be a solenoid-operated, variable position, 2-way valve that is movable in response to a command fromcontroller700 to allow fluid frompassage728 to enter or exitaccumulator708. In particular, each of the charge and dischargevalves722,724 may include avalve element734 or738, respectively. For instance, thevalve element734 is movable between a first position (shown inFIG. 5) at which fluid flow frompassage728 intoaccumulator708 is inhibited, and a second position (not shown) at whichpassage728 is fluidly connected toaccumulator708. Whenvalve element734 is away from the first position (i.e., in the second position or in an intermediate position between the first and second positions) and a fluid pressure withinpassage728 exceeds a fluid pressure withinaccumulator708, fluid frompassage728 may fill (i.e., charge)accumulator708.Valve element734 may be spring-biased toward the first position and movable in response to a command fromcontroller700 to any position between the first and second positions to thereby vary a flow rate of fluid frompassage728 intoaccumulator708. Acheck valve736 may be disposed betweencharge valve722 andaccumulator708 to provide for a unidirectional flow of fluid intoaccumulator708 viacharge valve722.
• Valve element738 is movable between a first position (not shown) at which fluid flow fromaccumulator708 intopassage728 is inhibited, and a second position (shown inFIG. 5) at whichaccumulator708 is fluidly connected topassage728. Whenvalve element738 is away from the first position (i.e., in the second position or in an intermediate position between the first and second positions) and a fluid pressure withinaccumulator708 exceeds a fluid pressure withinpassage728, fluid fromaccumulator708 may flow intopassage728. Valve element138 may be spring-biased toward the first position and movable in response to a command fromcontroller700 to any position between the first and second positions to thereby vary a flow rate of fluid fromaccumulator708 intopassage728. Acheck valve740 may be disposed betweenaccumulator708 anddischarge valve724 to provide for a unidirectional flow of fluid fromaccumulator708 intopassage728 viadischarge valve724.
• The operational parameters monitored bycontroller700, in one embodiment, may include a pressure of fluid within first and/orsecond circuits652,654. For example, one ormore pressure sensors739 may be strategically located within first chamber and/orsecond chamber conduits684,686 to sense a pressure of the respective passages and generate a corresponding signal indicative of the pressure directed tocontroller700. It is contemplated that any number ofpressure sensors739 may be placed in any location within first and/orsecond circuits652,654, as desired. It is further contemplated that other operational parameters such as, for example, speeds, temperatures, viscosities, densities, etc. may also or alternatively be monitored and used to regulate operation ofhydraulic control system650, if desired.
• Moreover, operational parameters monitored bycontroller700, in one embodiment, may include accumulator pressure. For example, anaccumulator pressure sensor741 may be associated withaccumulator708 and configured to generate signals indicative of a pressure of fluid withinaccumulator708, if desired. Theaccumulator pressure sensor741 may be disposed betweenaccumulator708 anddischarge valve724. It is contemplated, however, that theaccumulator pressure sensor741 may alternatively be disposed betweenaccumulator708 andcharge valve722 or directly connected toaccumulator708 in some fashion, if desired. Signals frompressure sensors739 andaccumulator pressure sensor741 may be directed tocontroller700 for use in regulating operation of charge and/or dischargevalves722,724 and/or for use in monitoring the operational health of the accumulator. In one example, theaccumulator pressure sensor741 is an example of thepressure sensor104 shown inFIG. 1.
• Controller700 may be configured to selectively causeaccumulator708 to charge and discharge, thereby improving performance ofmachine610. In particular, a typical swinging motion of implementsystem614 instituted byswing motor649 may consist of segments of time during whichswing motor649 is accelerating a swinging movement of implementsystem614, and segments of time during whichswing motor649 is decelerating the swinging movement of implementsystem614. The acceleration segments may require significant energy fromswing motor649 that is conventionally realized by way of pressurized fluid supplied to swingmotor649 bypump658, while the deceleration segments may produce significant energy in the form of pressurized fluid that is conventionally wasted through discharge totank660. Both the acceleration and the deceleration segments may requireswing motor649 to convert significant amounts of hydraulic energy to swing kinetic energy, and vice versa. After pressurized fluid passes throughswing motor649, however, it still contains a large amount of energy. If the fluid passing throughswing motor649 is selectively collected withinaccumulator708 during the deceleration segments, this energy can then be returned to (i.e., discharged) and reused byswing motor649 during the ensuing acceleration segments.Swing motor649 can be assisted during the acceleration segments by selectively causingaccumulator708 to discharge pressurized fluid into the higher-pressure chamber of swing motor649 (viadischarge valve724,passage728,selector valve720, and the appropriate one of first andsecond chamber conduits684,686), alone or together with high-pressure fluid frompump658, thereby propellingswing motor649 at the same or greater rate with less pump power than otherwise possible viapump658 alone.Swing motor649 can be assisted during the deceleration segments by selectively causingaccumulator708 to charge with fluid exitingswing motor649, thereby providing additional resistance to the motion ofswing motor649 and lowering a restriction and cooling requirement of the fluid exitingswing motor649. In other examples, the stored energized fluid in theaccumulator708 can be directed to other functions, such as a second hydraulic circuit where the stored energized fluid can be reused.
• The actuator operational parameters may also be monitored bycontroller700. For example, sensor(s)743 may be associated with the generally horizontal swinging motion ofwork tool616 imparted by swing motor649 (i.e., the motion offrame642 relative to undercarriage member644). For example,sensor743 may embody a rotational position or speed sensor associated with the operation ofswing motor649, an angular position or speed sensor associated with the pivot connection betweenframe642 andundercarriage member644, a local or global coordinate position or speed sensor associated with any linkage member connectingwork tool616 toundercarriage member644 or withwork tool616 itself, a displacement sensor associated with movement ofinput device648, or any other type of sensor known in the art that may generate a signal indicative of a swing position, speed, acceleration, force, or other swing-related parameter ofmachine610. The signal generated by sensor(s)743 may be sent to and recorded bycontroller700 during each excavation work cycle. It is contemplated thatcontroller700 may derive a swing speed based on a position signal fromsensor743 and an elapsed period of time, if desired. In another example, thecontroller700 may determine a position (angular or linear—depending on the actuator) during a full or partial actuation cycle (either swing or stroke cycle).
• Alternatively or additionally, sensor(s)743 may be associated with the vertical pivoting motion ofwork tool616 imparted by hydraulic cylinders628 (i.e., associated with the lifting and lowering motions ofboom624 relative to frame642). Specifically,sensor743 may be an angular position or speed sensor associated with a pivot joint betweenboom624 andframe642, a displacement sensor associated withhydraulic cylinders628, a local or global coordinate position or speed sensor associated with any linkage member connectingwork tool616 to frame642 or withwork tool616 itself, a displacement sensor associated with movement ofinput device648, or any other type of sensor known in the art that may generate a signal indicative of a pivoting position or speed ofboom624. It is contemplated thatcontroller700 may derive a pivot speed based on a position signal fromsensor743 and an elapsed period of time, if desired. Again, sensor may be also associated with the hydraulic cylinder to measure acceleration or force.
• In yet an additional embodiment, sensor(s)743 may be associated with the tilting force ofwork tool616 imparted byhydraulic cylinder638. Specifically,sensor743 may be a pressure sensor associated with one or more chambers withinhydraulic cylinder638 or any other type of sensor known in the art that may generate a signal indicative of a tilting force ofmachine610 generated during a dig and dump operation ofwork tool616. Signals frompressure sensors743 may be directed tocontroller700 for use in regulating operation of charge and/or dischargevalves722,724 and/or for use in monitoring the operational health of the accumulator.
• FIG. 6 depicts a diagram of aprocess1000 for determining the operability or health of the accumulator. Before initiating the process, it is desirable to park the machine on level ground for consistent readings. Further, the implement and/or linkages of the machine may be placed in a predefined position. Atstep1010, the actuator can be moved in a manner to direct pressurized fluid from a chamber of the actuator to the accumulator for charging the accumulator to a desired pressure, such as a fully charged working pressure (Pacc). The controller may command appropriate machine components for this operation. It would be desirable to maintain the implement and/or linkages of the machine at the predefined position during the movement of the actuator. Moreover, it would desirable to move the actuator at full speed. Prior to step1010, the accumulator can be fully discharged to a minimum working pressure (Paccmin).
• Thecontroller700 may record and store the value of the minimum working pressure. For instance, one or more maps relating the accumulator pressure and the actuator position, speed, acceleration and/or force, for hydraulic cylinders and/or swing motors may be stored in the memory ofcontroller700. Each of these maps may include a collection of data in the form of tables, graphs, and/or equations. In one example, desired accumulator pressure range and actuator operational parameter (position, speed, acceleration, or force) may form the coordinate axis of a 2-D table for monitoring the accumulator health (seeFIG. 7). The charging rate and/or discharging rate of the accumulator at the desired actuator operational parameter (position, speed, acceleration, or force) may be related in another separate 2-D map or together with the desired actuator operational parameter in a single 3-D map.Controller700 may 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 ofcontroller700 for desired accumulator health monitoring. It is contemplated that the maps may additionally or alternatively be automatically selectable based on modes of machine operation.
• Atstep1020, a relationship can be determined (e.g., with the controller) by continuously recording the actuator operational parameter and the accumulator pressure during charging of the accumulator. The relationship could also be determined during discharging of the accumulator, in which such case the cycle may begin with at least a partially, if not fully, charged accumulator, as appreciated by those skilled in the art. For example, the relationship may be a single point plot. Alternatively, the relationship may be series of single points on a plot, which may even be characterized to define a charging curve can be determined (e.g., with the controller) by continuously recording the actuator operational parameter and the accumulator pressure. This can show the relationship of the rise in accumulator pressure from minimum working pressure to the fully charged working pressure and an actuator operational parameter, such as, e.g., the position of the actuator, during the charging of the accumulator. Atstep1030, the determined relationship, such as, e.g., the charging curve, can be compared (e.g., with the controller) to a previously defined relationship or range to determine the amount of error, if any, between the relationships or range at a selected pressure or position (see, e.g.,FIG. 7). The previously defined charging curve or range may be preprogrammed within the memory of the controller at the manufacturing facility, programmed within the memory during operation of the machine, downloaded to the memory from an external controller, or other methods known in the art.
• If the error is outside of a predefined threshold range (i.e., the accumulator is not healthy), the controller can send a signal to the operator for notification of a potential accumulator issue. The notification provided by the controller may be a visual feedback like an alert message, an audio feedback like a warning alarm, or any other type of feedback. Based on the notification, one or more remedial actions such as re-charging of thehydraulic accumulator708, overhauling of thehydraulic accumulator708 or replacement of its seals in case of the piston-based accumulator may be performed. However, if the error is inside a predefined threshold range (i.e., the accumulator is healthy), the controller can send a signal to the operator for notification of a healthy accumulator or send no signal.
INDUSTRIAL APPLICABILITY
• On usage, thehydraulic accumulator102 or708 may lose the pre-charge pressure due to a variety of reasons. For example, reasons may be component failure such as, e.g., piston seal failure in the piston-based accumulator or bladder failure in the bladder-based accumulator. Further, gain in pre-charge pressure can be attributed by leakage of fluid between the chambers of the accumulator, such as, e.g., from thefirst chamber302 ofaccumulator102 into thesecond chamber304 or from chamber to gas chamber as an example. Accordingly, if the pre-charge pressure is too high or too low, then thehydraulic accumulator102 or708 may require servicing or overhauling. Hence, the health of thehydraulic accumulator102 or708 may require to be checked once every few months or at least once a year after installation in a machine.
• Determining the health of theaccumulator102 or708 may overcome some of the problems of connecting a pressure gauge and/or a modular kit to the gas valve, such as, e g.,valve308 of thehydraulic accumulator102, where accessibility is an issue, or where operator or service time is unnecessarily required. The systems and methods described herein may relate to an automated process for monitoring and diagnosing the health of thehydraulic accumulator102 or708, without requiring physical connection to a gas valve, i.e., without use of a gas gauge or sensor. The systems and methods described herein may determine an approximate pre-charge pressure and/or frictional values associated with the separator of thehydraulic accumulator102 or708 to improve diagnosis of the accumulator health.
• The diagnosis of the health and the determination of the approximate pre-charge pressure and/or the frictional values may be performed in real time by monitoring the pressure readings provided by thepressure sensor104 or741, and subsequently performing the necessary processing of the readings required for the determination.
• Thecontroller108 or700 may determine if the approximate pre-charge pressure determined by the controller lies within the predefined threshold range. If the approximate pre-charge pressure is either too high or too low, that is, outside the range, then the operator may be suitably notified. Based on the notification, one or more remedial actions such as re-charging of thehydraulic accumulator102 or708 replacement of the seal may be performed.
• In case of the piston-based accumulator, the systems and methods described herein may determine the seal effectiveness of theseparator306. If the determined frictional values of the separator, such as, e.g., theseparator306, lie within the predefined threshold range it may be indicative that the seals of thehydraulic accumulator102 or708 are in an acceptable condition and its seals may be retained. For example, loss in pre-charge pressure can be due to component failure such as piston seal failure or bladder failure such that fluid leakage occurs from the second chamber to the first chamber, or gas leakage from the chamber to the atmosphere. Gain in pre-charge pressure can be due to fluid leakage from the first chamber into the second chamber.
• Theexemplary process1000 for determining the operational health of a hydraulic accumulator is shown inFIG. 6. As previously mentioned, the accumulator could be tied to various embodiments of actuators such as, e.g., a swing motor or a hydraulic cylinder. For example, the process can be applied to themachine610 with theswing motor649 and theaccumulator708 shown inFIGS. 4-5. Themachine610 can be preferably park on level ground, with the linkage preferably at a predefined position and thestick630 preferably positioned vertically or fully extended. For a swing motor, the operator can move theinput device648 to a position to rotate themachine610 at a desired swing speed, such as full swing speed, between two points of the actuator operational parameters. For example, theswing motor649 can rotate between first and second angular positions x1, x2 in order to fully discharge theaccumulator708 to a first pressure or the minimum working pressure (Paccmin) as sensed by theaccumulator pressure sensor741. Thecontroller700 may record and store the value of the minimum working pressure. After rotating themachine610, the operator can quickly pull theinput device648 back to neutral. Thecontroller700 can continuously record the swing speed and/or the relative angular position and the accumulator charge pressure during swing travel between the first and second angular positions x1, x2 to a second pressure, such as, e.g., the fully charged working pressure (Pacc) to define a charge curve (step1010 and step1020).
• For a hydraulic cylinder, the operator can move theinput device648 to a position to move the machine linkage at a desired speed between two points of the actuator operational parameters. For example, after fully discharging the accumulator, thehydraulic cylinder628 can be moved between first and second linear positions. Thecontroller700 may record and store the value of the minimum working pressure, and thecontroller700 can continuously record the relative linear position and the accumulator charge pressure during movement between the first and second positions to a second pressure, such as, e.g., the fully charged working pressure (Pacc) to define a charge curve.
• Returning to the swing motor configuration, the charge curve can be determined to show the relationship of the rise in accumulator pressure from minimum working pressure (Paccmin) to the fully charged working pressure (Pacc) and the angular position change of theswing motor649 during the charging of theaccumulator708. Moreover,FIG. 7 is arepresentative plot1100 showing the relationship between the actuator operational parameter1102 (shown as swing angular position) and theaccumulator pressure1104 during charging. The determined charge curve, for example, curve TD1, can be compared to a previously definedcharge curve1120 at a selected operational parameter such as angular position x3 to determine the degree of error E between the curves TD1 and1120, if any, (see step1030). If the error is outside of a predefined threshold range such as, e.g., plus or minus about 10-20% of previously defined charge curve1120 (i.e., theaccumulator708 can be determined to be not healthy), thecontroller700 can send a signal to the operator for notification of a potential accumulator issue. Warning strategies can be implemented to notify the operator of degree of failure and when to service accumulator. However, if the error is inside a predefined threshold range (i.e., the accumulator can be determined to be healthy), thecontroller700 can send a signal to the operator for notification of a healthy accumulator or send no signal.FIG. 7 depicts an exemplary determined curve TD1 greater than the previously defined threshold charge curve orrange1120 which may suggest fluid leakage from thefirst chamber302 into thesecond chamber304; and an exemplary determined curve TD2 that is less than the previously defined threshold charge curve orrange1120 which may suggest fluid leakage from the gas chamber into the oil chamber, or into the atmosphere.
• While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.

Claims (20)

What is claimed is:

1. A system to diagnose a health of a hydraulic accumulator, the system comprising:

a hydraulic actuator;

a hydraulic accumulator fluidly coupled to the hydraulic actuator, wherein the hydraulic accumulator is configured to be charged from movement of the actuator;

a pressure sensor associated with the hydraulic accumulator to determine an accumulator pressure; and

a controller in communication with the pressure sensor, the controller configured to:

determine a relationship between an actuator operational parameter associated with the movement of the actuator and the accumulator pressure; and

compare the relationship to a previously defined relationship to determine an error, if any, between the determined relationship and the previously defined relationship.

2. The system ofclaim 1, wherein the controller configured to:

determine a charge curve based on the relationship between the actuator operational parameter associated with a movement of the actuator and the accumulator pressure; and

compare the charge curve to a previously defined charge curve to determine an error between the charge curve and the previously defined charge curve.

3. The system ofclaim 1, wherein the actuator is a swing motor.

4. The system ofclaim 3, wherein the actuator operational parameter is a swing angular position.

5. The system ofclaim 3, wherein the actuator operational parameter is a swing angular speed.

6. The system ofclaim 1, wherein the controller is configured to notify an operator if the error is outside a predefined threshold range.

7. The system ofclaim 1, wherein the actuator is a hydraulic cylinder.

8. The system ofclaim 7, wherein the actuator operational parameter is a linear position of the hydraulic cylinder.

9. The system ofclaim 7, wherein the actuator operational parameter is a speed of the hydraulic cylinder.

10. The system ofclaim 1, wherein a valve is fluidly coupled between the actuator and the hydraulic accumulator for selective charging of the hydraulic accumulator.

11. A method of diagnosing an operational health of a hydraulic accumulator, the method comprising:

moving a hydraulic actuator to charge a hydraulic accumulator fluidly coupled to the actuator,

storing an accumulator pressure during the movement of the actuator;

determining a relationship between an actuator operational parameter associated with the movement of the actuator and the accumulator pressure; and

comparing the determined relationship to a previously defined relationship to determine an error, if any, between the determined relationship and the previously defined relationship.

12. The method ofclaim 11, further comprising:

determining a charge curve based on the relationship between the actuator operational parameter associated with a movement of the actuator and the accumulator pressure; and

comparing the charge curve to a previously defined charge curve to determine an error between the charge curve and the previously defined charge curve.

13. The method ofclaim 11, wherein the moving an actuator to a position step includes rotating a swing motor between a first position and a second position.

14. The method ofclaim 13, wherein the actuator operational parameter includes a swing angular position.

15. The method ofclaim 11, further including reducing the hydraulic accumulator to a minimum accumulator pressure prior to the moving step.

16. The method ofclaim 11, further including notifying an operator if the error is outside a predefined threshold range about the relationship.

17. The method ofclaim 11, wherein the moving an actuator to a position step includes moving a hydraulic cylinder between a first position and a second position.

18. The method ofclaim 17, wherein the actuator operational parameter includes a linear position.

19. A machine comprising:

a pump;

a hydraulic actuator selectively moved by fluid provided by the pump;

a hydraulic accumulator fluidly coupled to the hydraulic actuator, wherein the hydraulic accumulator is configured to be charged with pressurized fluid resulting from movement of the actuator;

a pressure sensor associated with the hydraulic accumulator to determine an accumulator pressure; and

a controller in communication with the pressure sensor, the controller configured to:

determine a relationship between an actuator operational parameter associated with the movement of the actuator and the accumulator pressure; and

compare the relationship to a previously defined relationship to determine an error, if any, between the determined relationship and the previously defined relationship.

20. The machine ofclaim 19, wherein the hydraulic actuator is a hydraulic swing motor, and the actuator operational parameter is a swing angular position.

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