This disclosure is directed toward power machines. More particularly, this disclosure is directed toward leveling systems for buckets or other implements on lift arm assemblies of power machines, including compact articulate loaders with extendable (e.g., telescoping) lift arm assemblies.
Power machines, for the purposes of this disclosure, include any type of machine that generates power to accomplish a particular task or a variety of tasks. One type of power machine is a work vehicle. Work vehicles, such as loaders, are generally self-propelled vehicles that have a work device, such as a lift arm (although some work vehicles can have other work devices) that can be manipulated to perform a work function. Work vehicles include loaders, excavators, utility vehicles, tractors, and trenchers, to name a few examples.
Different types of power machines, such as articulated and other loaders, can include lift arm assemblies, such as may be used to execute work functions using implements secured to the lift arm assemblies. For example, hydraulic circuits can be operated to move a lift arm assembly to raise or lower, or otherwise manipulate, a bucket or other implement that is coupled to a lift arm of the lift arm assembly. As a bucket or other implement is raised and lowered, or otherwise manipulated, it can be advantageous to control the attitude of the implement (i.e., the orientation of the implement relative to ground, a horizontal plane, or another reference), such as to maintain the implement at an appropriately constant attitude (e.g., substantially parallel to ground).
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Some power machines, such as front-end loaders and utility vehicles, can include telescoping lift arm assemblies and associated hydraulically operated implement-leveling systems. In some embodiments of the disclosure, an implement-leveling system can include a hydraulic leveling circuit that can provide improved leveling performance, including with regard to particular modes of operation in which particular hydraulic cylinders of the implement-leveling systems may be subjected to particular types of loading (e.g., compression or tension). For example, some embodiments of the disclosure can include appropriately placed and configured restriction orifices that are configured to prevent run out or desynchronization of various hydraulic cylinders within the hydraulic leveling circuit during particular work operations.
In some embodiments, a hydraulic assembly for a telescoping lift arm assembly is provided. The telescoping lift arm assembly can include a main lift arm portion, a telescoping lift arm portion configured to move telescopically relative to the main lift arm portion, and an implement supported by the telescoping lift arm portion. The hydraulic assembly can include an extension cylinder, a leveling cylinder, a main control valve, a flow combiner/divider, a first restriction orifice, and a second restriction orifice. The extension cylinder can be configured to move the telescoping lift arm portion relative to the main lift arm portion. The leveling cylinder can be configured to adjust an attitude of the implement relative to the telescoping lift arm portion. The main control valve can be configured to control commanded movement of the extension and leveling cylinders. The flow combiner/divider can be configured to hydraulically link the extension cylinder with the leveling cylinder for synchronized operation of the extension cylinder and the leveling cylinder. The first restriction orifice can be arranged in a first hydraulic flow path between a rod end of the leveling cylinder and the flow combiner/divider. The second restriction orifice can be arranged in a second hydraulic flow path between a base end of the extension cylinder and the main control valve. The first restriction orifice can be configured to restrict flow from the rod end of the leveling cylinder during extension of the leveling and extension cylinders to maintain synchronization of the leveling and extension cylinders. The second restriction orifice can be configured to restrict flow from the base end of the extension cylinder during retraction of the leveling and extension cylinders, to maintain synchronization of the leveling and extension cylinders.
In some embodiments, another hydraulic assembly for a telescoping lift arm assembly is provided. The telescoping lift arm assembly can include a main lift arm portion, a telescoping lift arm portion configured to move telescopically relative to the main lift arm portion, and an implement supported by the telescoping lift arm portion. The hydraulic assembly can include an extension cylinder, a leveling cylinder, a main control valve, a combiner divider, and a lock valve. The extension cylinder can be configured to move the telescoping lift arm portion relative to the main lift arm portion. The leveling cylinder can be configured to adjust an attitude of the implement relative to the telescoping lift arm portion. The main control valve can be configured to control commanded movement of the extension and leveling cylinders. The flow combiner/divider can be configured to hydraulically link a rod end of the extension cylinder with a rod end of the leveling cylinder for synchronized operation of the extension cylinder and the leveling cylinder. The lock valve can be arranged in a first hydraulic flow path between a rod end of the extension cylinder and the flow combiner/divider. The lock valve can be configured to move to a first configuration during the commanded movement of the extension and leveling cylinders and to a second configuration when there is no commanded movement of the extension and leveling cylinders. The first configuration of the lock valve can permit hydraulic flow between the rod ends of the extension and leveling cylinders. The second configuration of the lock valve can block hydraulic flow between the rod ends of the extension and leveling cylinders.
In some embodiments, still another hydraulic assembly for a telescoping lift arm assembly is provided. The telescoping lift arm assembly can include a main lift arm portion, a telescoping lift arm portion configured to move telescopically relative to the main lift arm portion, and an implement supported by the telescoping lift arm portion. The hydraulic assembly can include an extension cylinder, a leveling cylinder, a main control valve, a flow combiner/divider, a first restriction orifice, and a pilot-operated check valve. The extension cylinder can be configured to move the telescoping lift arm portion relative to the main lift arm portion. The leveling cylinder can be configured to adjust an attitude of the implement relative to the telescoping lift arm portion. The main control valve can be configured to control commanded movement of the extension and leveling cylinders. The flow combiner/divider can be configured to hydraulically link the extension cylinder with the leveling cylinder for synchronized operation of the extension cylinder and the leveling cylinder. The first restriction orifice can be arranged in a first hydraulic flow path between a rod end of the leveling cylinder and the flow combiner/divider. The pilot-operated check valve can be arranged in the first hydraulic flow path in parallel with the first restriction orifice. The first restriction orifice can be configured to restrict flow from a base end of the leveling cylinder upon a compression of the leveling cylinder by an external load during retraction of the extension and leveling cylinders, to maintain synchronization of the leveling and extension cylinders. The pilot-operated check valve can be configured to permit flow along the first hydraulic flow path during the commanded movement of the extension and leveling cylinders, absent the compression of the leveling cylinder by the external load.
This Summary and the Abstract are provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary and the Abstract are not intended to identify key features or essential features of the claimed subject matter, nor are they intended to be used as an aid in determining the scope of the claimed subject matter.
The concepts disclosed in this discussion are described and illustrated by referring to exemplary embodiments. These concepts, however, are not limited in their application to the details of construction and the arrangement of components in the illustrative embodiments and are capable of being practiced or being carried out in various other ways. The terminology in this document is used for the purpose of description and should not be regarded as limiting. Words such as “including,” “comprising,” and “having” and variations thereof as used herein are meant to encompass the items listed thereafter, equivalents thereof, as well as additional items.
As used herein in the context of multiple actuators, unless otherwise defined or limited, “synchronized” refers to an orientation or a movement of the actuators that maintains a particular relative angle between the actuators. For example, synchronized hydraulic cylinders may be configured so that a particular relative angle between the extension axes of the cylinders is maintained when the cylinders are at rest, when the cylinders are actuated to extend or retract, or when the cylinders are otherwise in motion. In some cases, actuators undergoing synchronized movement may exhibit slight variations in relative angle due to power fluctuations, mechanical loading, or other factors. Actuators may still be considered to be “synchronized” provided that such variations are transient (e.g., being remedied in a relatively short time compared to the total time of the relevant synchronized extension, retraction, or other movement) or minimal (e.g., deviating from a fully synchronized relative angle by 5° or less at a distal end thereof).
For some operations, performance of power machines can be improved by maintaining synchronization between a plurality of actuators, including sets of related hydraulic cylinders. For example, some power machines can include an extendable (e.g., telescoping) lift arm with multiple hydraulic cylinders. An extension cylinder can control the extension and retraction of the lift arm, and a leveling cylinder can control the orientation of an associated structural member (e.g., a link in a multi-bar linkage that supports a tilt cylinder or an implement on the lift arm). Maintaining synchronized orientation and movement of such extension and leveling cylinders can help to reduce undesired tilting of an attached implement during extension or retraction of the lift arm such as can improve load retention or other aspects of operation of the implement. Further, appropriate synchronization of such extension and leveling cylinders can reduce the need for more active tilt control during certain power machine operations, such as might otherwise be provided by a tilt cylinder supported on the lift arm, and an associated hydraulic or electronic control architecture.
To achieve synchronized movement of hydraulic cylinders, it is generally necessary to maintain an appropriate ratio for the hydraulic flows to the cylinders. For example, for cylinders of the same size, synchronized movement can be maintained with a 1:1 flow ratio (i.e., with equal flow to each of the cylinders for any given movement). For cylinders of different sizes, however, different flow ratios may be required.
In some arrangements, synchronized actuators can be operated by a common power source or can receive operational flow from a common hydraulic circuit. For example, a set of synchronized hydraulic cylinders, including a set of extension and leveling cylinders as discussed above, can sometimes be provided with pressurized flow from a common hydraulic pump via a shared hydraulic circuit. Correspondingly, some hydraulic systems can include control devices, such as flow combiner/dividers, which can help to distribute appropriate ratios of hydraulic flow to certain cylinders within the system and can thereby help to ensure synchronized movement of those cylinders.
In some conventional arrangements, however, some power machine operations can result in sub-optimal performance of a flow combiner/divider, or other effects that can result in loss of synchronization of the cylinders. For example, when synchronized cylinders are being actuated to extend, a tension load on a first of the cylinders can cause overly rapid evacuation of hydraulic fluid from the rod end of that cylinder. Particularly if a second of the cylinders is not subjected to a similar tension load, this rapid evacuation of hydraulic fluid from the first cylinder can result in a loss of synchronization between the two cylinders and, in some cases, cavitation within the base end of the first cylinder.
As another example, a compressive load on a first cylinder of a synchronized set of cylinders, when the cylinders are being actuated to retract, can cause overly rapid evacuation of hydraulic fluid from the base end of that cylinder. Particularly if a second cylinder of the set is not subjected to a similar compressive load, this rapid evacuation of hydraulic fluid from the first cylinder can also result in a loss of synchronization between the cylinders and, in some cases, cavitation within the rod end of the first cylinder.
Additionally, some conventional flow combiner/dividers are configured to operate most effectively when there is commanded flow through the associated hydraulic system. Correspondingly, when a hydraulic system does not have appropriate commanded flow, imbalanced loading on cylinders within the system (e.g., greater compressive loading on a first cylinder than on a second cylinder) can push flow through a flow combiner/divider so as to desynchronize the cylinders. For example, in some configurations of a hydraulic circuit for work machines, a flow combiner/divider can be arranged to provide a hydraulic flow path between particular (e.g., rod) ends of two synchronized cylinders. Thus, the flow combiner/divider can help to ensure synchronized commanded movement of the cylinders by appropriately rationing the commanded hydraulic flow between cylinders. However, for this arrangement (and others), an imbalanced loading on the cylinders, in the absence of appropriate commanded flow through the circuit, can push flow from one cylinder to the other via the flow combiner/divider and thereby desynchronize the cylinders.
Embodiments of the invention can address these issues, and others, by providing systems and methods for regulating hydraulic flow relative to synchronized hydraulic actuators, both during and in the absence of commanded hydraulic flow. Thus, some embodiments can result in better maintained synchronization between hydraulic cylinders, as compared to conventional systems, both during commanded movement of the cylinders and when the cylinders are stationary. Disclosed embodiments include power machines, such as small articulated loaders, and hydraulic assemblies for power machines, including power machines with lift arm assemblies and implement-leveling systems.
In some embodiments, a hydraulic circuit for a set of synchronized hydraulic cylinders can include one or more restriction orifices, which can be arranged in the hydraulic circuit to reduce flow to or from particular parts of the cylinders during particular operations or under particular loading of the cylinders. In some embodiments, a hydraulic circuit for a set of synchronized hydraulic cylinders can include one or more lock valves, which can be arranged in the hydraulic circuit to block flow to or from particular parts of the cylinders during particular operations or under particular loading of the cylinders. In some embodiments, one or more flow-blocking arrangements can be provided to selectively block or reduce flow to or from particular parts of the cylinders during particular operations or under particular loading of the cylinders. For example, some embodiments can include blocking arrangements that include a restriction orifice and a check valve arranged in parallel, or a multi-position valve that includes a one-way flow position and a restricted flow position.
Some embodiments can be particularly useful to help to maintain synchronization between hydraulic cylinders in implement-leveling systems. For example, some implement-leveling systems can include a plurality of hydraulic cylinders that are configured for synchronized interoperation, to manipulate an implement while also substantially maintaining a particular attitude for the implement. Correspondingly, some embodiments of the invention can include hydraulic assemblies that include one or more appropriately located and configured restriction orifices or other blocking arrangement and one or more lock valves that are appropriately located and configured to help to restrict or fully block flow relative to particular ends of the hydraulic cylinders during particular operating states of the relevant power machine. For example, restriction orifices can be arranged in combination with pilot-operated or other check valves to restrict flow into or out of rod or base ends of particular hydraulic cylinders when the cylinders are under tension or compression due to loading of an associated implement. This can result in more reliable synchronization of the cylinders during a variety of commanded movements. As another example, a controllable lock valve can be arranged to selectively block flow between rod (or base) ends of two cylinders when no movement of the cylinders is commanded. This can also result in more reliable synchronization of the cylinders, including during loading of the associated implement.
These concepts can be practiced on various power machines, as will be described below. A representative power machine on which the embodiments can be practiced is illustrated in diagram form in
Certain work vehicles have work elements that can perform a dedicated task. For example, some work vehicles have a lift arm to which an implement such as a bucket is attached such as by a pinning arrangement. The work element, i.e., the lift arm can be manipulated to position the implement to perform the task. In some instances, the implement can be positioned relative to the work element, such as by rotating a bucket relative to a lift arm, to further position the implement. Under normal operation of such a work vehicle, the bucket is intended to be attached and under use. Such work vehicles may be able to accept other implements by disassembling the implement/work element combination and reassembling another implement in place of the original bucket. Other work vehicles, however, are intended to be used with a wide variety of implements and have an implement interface such as implement interface 170 shown in
On some power machines, implement interface 170 can include an implement carrier, which is a physical structure movably attached to a work element. The implement carrier has engagement features and locking features to accept and secure any of a number of different implements to the work element. One characteristic of such an implement carrier is that once an implement is attached to it, the implement carrier is fixed to the implement (i.e. not movable with respect to the implement) and when the implement carrier is moved with respect to the work element, the implement moves with the implement carrier. The term implement carrier as used herein is not merely a pivotal connection point, but rather a dedicated device specifically intended to accept and be secured to various different implements. The implement carrier itself is mountable to a work element 130 such as a lift arm or the frame 110. Implement interface 170 can also include one or more power sources for providing power to one or more work elements on an implement. Some power machines can have a plurality of work element with implement interfaces, each of which may, but need not, have an implement carrier for receiving implements. Some other power machines can have a work element with a plurality of implement interfaces so that a single work element can accept a plurality of implements simultaneously. Each of these implement interfaces can, but need not, have an implement carrier.
Frame 110 includes a physical structure that can support various other components that are attached thereto or positioned thereon. The frame 110 can include any number of individual components. Some power machines have frames that are rigid. That is, no part of the frame is movable with respect to another part of the frame. Other power machines have at least one portion that can move with respect to another portion of the frame. For example, excavators can have an upper frame portion that rotates with respect to a lower frame portion. Other work vehicles have articulated frames such that one portion of the frame pivots with respect to another portion for accomplishing steering functions.
Frame 110 supports the power source 120, which can provide power to one or more work elements 130 including the one or more tractive elements 140, as well as, in some instances, providing power for use by an attached implement via implement interface 170. Power from the power source 120 can be provided directly to any of the work elements 130, tractive elements 140, and implement interfaces 170. Alternatively, power from the power source 120 can be provided to a control system 160, which in turn selectively provides power to the elements that capable of using it to perform a work function. Power sources for power machines typically include an engine such as an internal combustion engine and a power conversion system such as a mechanical transmission or a hydraulic system that is capable of converting the output from an engine into a form of power that is usable by a work element. Other types of power sources can be incorporated into power machines, including electrical sources or a combination of power sources, known generally as hybrid power sources.
Power machine 100 includes an operator station 150 that includes an operating position from which an operator can control operation of the power machine. In some power machines, the operator station 150 is defined by an enclosed or partially enclosed cab. Some power machines on which the disclosed embodiments may be practiced may not have a cab or an operator compartment of the type described above. For example, a walk behind loader may not have a cab or an operator compartment, but rather an operating position that serves as an operator station from which the power machine is properly operated. More broadly, power machines other than work vehicles may have operator stations that are not necessarily similar to the operating positions and operator compartments referenced above. Further, some power machines such as power machine 100 and others, whether they have operator compartments, operator positions or neither, may be capable of being operated remotely (i.e. from a remotely located operator station) instead of or in addition to an operator station adjacent or on the power machine. This can include applications where at least some of the operator-controlled functions of the power machine can be operated from an operating position associated with an implement that is coupled to the power machine. Alternatively, with some power machines, a remote-control device can be provided (i.e. remote from both the power machine and any implement to which is it coupled) that is capable of controlling at least some of the operator-controlled functions on the power machine.
Loader 200 includes frame 210 that supports a power system 220 that can generate or otherwise provide power for operating various functions on the power machine. Frame 210 also supports a work element in the form of lift arm assembly 230 that is powered by the power system 220 and that can perform various work tasks. As loader 200 is a work vehicle, frame 210 also supports a traction system 240, which is also powered by power system 220 and can propel the power machine over a support surface. The lift arm assembly 230 in turn supports an implement interface 270 that includes an implement carrier 272 that can receive and secure various implements to the loader 200 for performing various work tasks and power couplers 274, to which an implement can be coupled for selectively providing power to an implement that might be connected to the loader. Power couplers 274 can provide sources of hydraulic or electric power or both. The loader 200 includes a cab 250 that defines an operator station 255 from which an operator can manipulate various control devices to cause the power machine to perform various work functions. Cab 250 includes a canopy 252 that provides a roof for the operator compartment and is configured to have an entry 254 on one side of the seat (in the example shown in
The operator station 255 includes an operator seat 258 and the various operation input devices 260, including control levers that an operator can manipulate to control various machine functions. Operator input devices can include a steering wheel, buttons, switches, levers, sliders, pedals and the like that can be stand-alone devices such as hand operated levers or foot pedals or incorporated into hand grips or display panels, including programmable input devices. Actuation of operator input devices can generate signals in the form of electrical signals, hydraulic signals, and/or mechanical signals. Signals generated in response to operator input devices are provided to various components on the power machine for controlling various functions on the power machine. Among the functions that are controlled via operator input devices on power machine 100 include control of the tractive system 240, the lift arm assembly 230, the implement carrier 272, and providing signals to any implement that may be operably coupled to the implement.
Loaders can include human-machine interfaces including display devices that are provided in the cab 250 to give indications of information relatable to the operation of the power machines in a form that can be sensed by an operator, such as, for example audible and/or visual indications. Audible indications can be made in the form of buzzers, bells, and the like or via verbal communication. Visual indications can be made in the form of graphs, lights, icons, gauges, alphanumeric characters, and the like. Displays can be dedicated to provide dedicated indications, such as warning lights or gauges, or dynamic to provide programmable information, including programmable display devices such as monitors of various sizes and capabilities. Display devices can provide diagnostic information, troubleshooting information, instructional information, and various other types of information that assists an operator with operation of the power machine or an implement coupled to the power machine. Other information that may be useful for an operator can also be provided. Other power machines, such walk behind loaders may not have a cab nor an operator compartment, nor a seat. The operator position on such loaders is generally defined relative to a position where an operator is best suited to manipulate operator input devices.
Various power machines that can include and/or interact with the embodiments discussed below can have various different frame components that support various work elements. The elements of frame 210 discussed herein are provided for illustrative purposes and should not be considered to be the only type of frame that a power machine on which the embodiments can be practiced can employ. As mentioned above, loader 200 is an articulated loader and as such has two frame members that are pivotally coupled together at an articulation joint. For the purposes of this document, frame 210 refers to the entire frame of the loader. Frame 210 of loader 200 includes a front frame member 212 and a rear frame member 214. The front and rear frame members 212, 214 are coupled together at an articulation joint 216. Actuators (not shown) are provided to rotate the front and rear frame members 212, 214 relative to each other about an axis 217 to accomplish a turn.
The front frame member 212 supports and is operably coupled to the lift arm 230 at joint 216. A lift arm cylinder (not shown, positioned beneath the lift arm 230) is coupled to the front frame member 212 and the lift arm 230 and is operable to raise and lower the lift arm under power. The front frame member 212 also supports front wheels 242A and 242B. Front wheels 242A and 242B are mounted to rigid axles (the axles do not pivot with respect to the front frame member 212). The cab 250 is also supported by the front frame member 212 so that when the front frame member 212 articulates with respect to the rear frame member 214, the cab 250 moves with the front frame member 212 so that it will swing out to either side relative to the rear frame member 214, depending on which way the loader 200 is being steered.
The rear frame member 214 supports various components of the power system 220 including an internal combustion engine. In addition, one or more hydraulic pumps are coupled to the engine and supported by the rear frame member 214. The hydraulic pumps are part of a power conversion system to convert power from the engine into a form that can be used by actuators (such as cylinders and drive motors) on the loader 200. Power system 220 is discussed in more detail below. In addition, rear wheels 244A and 244B are mounted to rigid axles that are in turn mounted to the rear frame member 214. When the loader 200 is pointed in a straight direction (i.e., the front frame portion 212 is aligned with the rear frame portion 214) a portion of the cab is positioned over the rear frame portion 214.
The lift arm assembly 230 shown in
Other lift arm assemblies can have different geometries and can be coupled to the frame of a loader in various ways to provide lift paths that differ from the radial path of lift arm assembly 230. For example, some lift paths on other loaders provide a radial lift path. Others have multiple lift arms coupled together to operate as a lift arm assembly. Still other lift arm assemblies do not have a telescoping member. Others have multiple segments. Unless specifically stated otherwise, none of the inventive concepts set forth in this discussion are limited by the type or number of lift arm assemblies that are coupled to a particular power machine.
The description of power machine 100 and loader 200 above is provided for illustrative purposes, to provide illustrative environments on which the embodiments discussed below can be practiced. While the embodiments discussed can be practiced on a power machine such as is generally described by the power machine 100 shown in the block diagram of
The lift arm assembly shown in
In the lift arm assembly 350, the lift arm 316 is pivotally attached to a frame 310 at a pivot attachment or coupling 312. The lift arm assembly 350 has a variable length level link 328, in the form of a leveling cylinder that is pivotally attached to frame 310 at a pivot attachment or coupling 326. In example embodiments, it has been found that improved leveling performance over a range of lift arm positions is achieved with the pivot attachment 326 of leveling cylinder 328 positioned above and behind (i.e., toward an operator compartment of the power machine) the pivot attachment 312 of the lift arm 316. In some embodiments, it has been found that the pivot attachment 326 of the leveling cylinder 328 can advantageously be positioned above and rearward of the pivot attachment 312 of the lift arm such that a line of action 324 extending between pivot attachments 312 and 326 forms an angle θ, relative to a horizontal direction, of at least approximately 105° . However, this geometrical relationship is not required in all embodiments.
A leveling link 322 is also provided in each of the lift arm assemblies to facilitate the mechanical self-leveling functions. The leveling link 322, which is a fixed length link, includes three pivot attachments. First, the leveling link 322 is pivotally attached to the lift arm 316 at the pivot attachment 314. The pivot attachment 314 can be to the telescoping lift arm portion 318 in the lift arm 316. A second pivot attachment on the leveling link 322 is a pivot attachment 320 between the leveling cylinder 328 and the leveling link 322. The third pivot attachment on the leveling link 322 is a pivot attachment 338 between a tilt cylinder 340 and the leveling link 322.
As also noted above,
The leveling cylinder 328 can be, in the embodiment shown in
As noted above, the lift arm assembly shown in
The second four-bar linkage 350b includes the leveling link 322, the tilt cylinder 340, the lift arm 316 and the implement carrier 334. The pivot attachments for the second four-bar linkage include the pivot attachment 314 between the lift arm 316 and the leveling link 322, the pivot attachment 330 between the lift arm 316 and the implement carrier 334, the pivot attachment 332 between the tilt cylinder 340 and the implement carrier 334, and the pivot attachment 338 between the tilt cylinder 340 and the leveling link 322. A notable feature of the lift arm assembly discussed with reference to
As also alluded to above, different configurations are possible for implement-leveling systems, including differently configured linkages and actuators than are shown in
For example,
In several aspects, the lift arm assembly 450 includes similar components as the lift arm assembly 350, including two four-bar linkages 450a, 450b that can be controlled by associated hydraulic cylinders to provide improved implement-leveling operations. For example, in the lift arm assembly 450, a main lift arm portion 416 is pivotally attached to a frame 410 at a pivot attachment or coupling 412. The main lift arm portion 416 is also slidably coupled to a telescoping lift arm portion 418, which extends along the outside of the main lift arm portion 416 and forward of a forward end thereof. In other embodiments, a telescoping portion of a lift arm can be otherwise configured, such as to extend within a main portion of a lift arm. An extension cylinder 419 within the main lift arm portion 416 can be selectively commanded to extend or retract, in order to extend or retract the telescoping lift arm portion 418 with respect to the lift arm 416. A variable length leveling link 428 configured as a hydraulic cylinder is also pivotally attached to frame 410 at a pivot attachment or coupling 426. The variable length leveling link 428 can be selectively commanded to extend or retract by commanding extension or retraction of a leveling cylinder 421.
A fixed length leveling link 422 is also provided to facilitate the leveling functions. Unlike leveling link 322, for example, the leveling link 422 includes pivot attachments at only two locations, although other configurations are possible. First, the leveling link 422 is pivotally attached to the telescoping lift arm portion 418 at a pivot attachment (not shown), thus helping to define the first four-bar linkage 450a, as formed by the main lift arm portion 416, the telescoping lift arm portion 418, the variable length leveling link 428, and the fixed length leveling link 422, i.e., with two separate variable length links. The second pivot attachment on leveling link 422 is a pivot attachment 420 between the leveling cylinder 428, the leveling link 422, and a tilt cylinder 440, thus helping to define the second four-bar linkage 450b, as formed by the telescoping lift arm portion 416, the tilt cylinder 440, the leveling link 422, and part of the implement carrier 434. The pivot attachment 420 can provide independent rotational coupling between the leveling cylinder 428 and both the leveling link 422 and the tilt cylinder 440, such that each of the leveling link 422 and the tilt cylinder 440 can rotate independently about the pivot attachment 420 with respect to the leveling cylinder 428.
The implement carrier or interface 434 is configured to allow the bucket 436 or other implement (not shown) to be mounted on lift arm assembly 450, including at a pivot attachment 430 to the telescoping lift arm portion 418. The implement carrier 434 is also pivotally attached, via a pivot attachment 432, to tilt cylinder 440.
To help level the bucket 436 or other implement during movement of the lift arm assembly 450, the leveling cylinder 428 can be hydraulically coupled to the extension cylinder 419 that controls extension and retraction of telescoping portion 418 of lift arm 416. Thus, as the extension cylinder 419 extends/retracts to extend/retract the telescoping lift arm portion 418 relative to the main lift arm portion 416, the leveling cylinder 428 can also simultaneously and synchronously extend/retract. Thus, through appropriate synchronization between the extension and leveling cylinders 419, 428 the leveling link 422, including the pivot attachment 420, can be moved in synchronization with the telescoping lift arm portion 416, and the attitude of the bucket 436 or another implement can be substantially maintained.
As noted above, during operation of a leveling cylinder and an extension cylinder, hydraulic communication may be maintained between the two cylinders, such as between the base ends of both cylinders and between the rod ends of both cylinders, in order to effect appropriately synchronized movement, and, for example, to maintain synchronization between the two cylinders when the cylinders are not moving. Accordingly, hydraulic circuits for leveling cylinders and extension cylinders can include hydraulic flow lines that connect the cylinders together. However, without appropriate regulation of hydraulic flow, uneven loading on the two cylinders during certain operations can sometimes result in undesired loss synchronization. Thus, for example, embodiments of the invention can include appropriately disposed and configured restriction orifices and other flow-control devices in order to selectively restrict flow between leveling and extension cylinders, including during particular operational modes for the relevant power machines.
In this regard, the description herein of hydraulic circuit 700 with reference to
In the hydraulic circuit 700, an implement pump 702, which can be an example of the implement pump 224B of
As also noted above, in some implementations, the leveling cylinder 710 and the extension cylinder 712 can be utilized in a lift arm assembly similar to either of the lift arm assemblies 350, 450 (see
In the embodiment illustrated in
The flow combiner/divider 718 is illustrated with a simplified schematic in
In the illustrated embodiment of
In other embodiments, other configurations are possible, including configurations in which flow combiner/dividers are provided along two hydraulic flow paths out of a main control valve, and configurations in which such flow combiners/dividers are configured to operate only as flow dividers and not as flow combiners. For example, some embodiments can include a flow combiner/divider that is generally similar to the flow combiner/divider 718 but that is located along the second flow path 708. In such an arrangement, for example, the flow combiner/divider can be configured to divide flow to base ends 730, 732 of the cylinders 710, 712 during commanded extension of the cylinders 710, 712 and to operate as a flow divider relative to the base ends 730, 732 of the cylinders 710, 712 during commanded retraction of the cylinders 710, 712.
Generally, the hydraulic circuit in
In any case, various components of the hydraulic circuit 700, including components of the flow combiner/divider 718, may be sized or otherwise configured in various ways according to various expected operational parameters or specifications. For example, various components of the hydraulic circuit 700 may be sized or otherwise configured based on expected loads, desired hydraulic pressure drops, and other parameters for particular expected operating conditions. As such, the particular sizes and configurations of components illustrated in
As noted above, the leveling cylinder first line 720 provides fluid communication between the flow combiner/divider 718 and the rod end 714 of the leveling cylinder 710. In the embodiment illustrated in
Because the first leveling restriction orifice 726 is arranged in parallel with the first leveling check valve 724, although flow from the flow combiner/divider 718 toward the rod end 714 of the leveling cylinder 710 can pass relatively uninhibited through the first leveling check valve 724, flow in the reverse direction is diverted to pass through the first leveling restriction orifice 726, due to the one-way nature of the first leveling check valve 724. Accordingly, flow from the rod end 714 of leveling cylinder 710 towards the flow combiner/divider 718 is generally limited by the first leveling restriction orifice 726. Thus, during commanded extension of the cylinders 710, 712, flow from the rod end 714 of the leveling cylinder 710 may be restricted by the restriction orifice 726 of the noted flow-blocking arrangement.
To control hydraulic flow between the rod end 716 of the extension cylinder 712 and the MCV 704, the flow combiner/divider 718, and rod end 714 of the leveling cylinder 710, the extension cylinder first line 722 includes a selective lock valve 728 disposed between the flow combiner/divider 718 and the rod end 716 of the extension cylinder 712. The selective lock valve 728 is movable between an open position (not shown), in which fluid flow between flow combiner/divider 718 is permitted, and a closed position (as shown in
In some cases, the selective lock valve 728 can be configured to automatically move into the open position when the leveling cylinder 710 and the extension cylinder 712 are commanded to extend or retract, as also discussed below. Similarly, the selective lock valve 728 can be configured to automatically move into the closed position when the leveling cylinder 710 and the extension cylinder 712 are not being commanded to extend or retract, as also discussed below. The selective lock valve 728 is shown in
Opposite the MCV 704 from the first line 706, the second line 708 provides a flow path between the MCV 704, the base end 730 of the leveling cylinder 710, and the base end 732 of the extension cylinder 712. The second line 708 includes a leveling cylinder second line 734 that leads to the leveling cylinder 710, and an extension cylinder second line 736 that leads to the extension cylinder 712.
The leveling cylinder second line 734 provides fluid communication between the MCV 704 and the base end 730 of the leveling cylinder 710 and includes another flow-blocking arrangement that includes a check valve 738 and a second leveling restriction orifice 740 that are arranged in parallel with each other. In some embodiments, the check valve 738 is a spring-biased pilot-operated check valve, although other configurations are possible for the check valve and for the flow-blocking arrangement in general.
The check valve 738 is arranged on the leveling cylinder second line 734 such that flow from the MCV 704 toward the base end 730 of the leveling cylinder 710 may flow through the check valve 738 to the base end 730 of the leveling cylinder 710 during commanded extension of the cylinders 710, 712. Conversely, flow from the base end 730 of the leveling cylinder 710 toward the MCV 704 through the check valve 738 is generally prevented. Thus, as also discussed below, flow from the base end 730 of the leveling cylinder 710 during commanded retraction of the cylinders 710, 712 may generally be diverted through the restriction orifice 740. Further, because the second leveling restriction orifice 740 is arranged in parallel with the check valve 738, although flow from the MCV 704 toward the base end 730 of the leveling cylinder 710 (e.g., during commanded extension of the cylinders 710, 712) can pass generally uninhibited through the check valve 738, flow in the reverse direction (e.g., during commanded retraction of the cylinders 710, 712) is generally diverted to pass through the second leveling restriction orifice 740. Accordingly, flow from the base end 730 of leveling cylinder 710 towards the MCV 704 is generally limited by the second leveling restriction orifice 740.
In some cases, however, operation of the pilot-operated check valve 738 can result in relatively unimpeded flow through the check valve 738 from the base end 730 of the leveling cylinder 710 to the MCV 704, including during commanded retraction of the cylinders 710, 712. For example, in the illustrated configuration, the check valve 738 is operably coupled to the leveling cylinder first line 720 through a pilot line 742. As such, if the hydraulic pressure within the leveling cylinder first line 720 is sufficiently high (e.g., to overcome the biasing force of a spring element of the check valve 738), the pressurization of the pilot line 742 can open the check valve 738, thereby allowing for hydraulic fluid to flow generally unrestricted from the base end 730 of the leveling cylinder 710 to the MCV 704.
Accordingly, for example, during a commanded retraction of the cylinders 710, 712 with the leveling cylinder 710 under a tension load, pressure in the pilot line 742 may be relatively high, resulting in the check valve 738 being opened for relatively unimpeded flow of hydraulic fluid from the base end 730 of the leveling cylinder 710. In contrast, for example, during a commanded retraction of the cylinders 710, 712 with the leveling cylinder 710 under a compression load (e.g., during back dragging, as also discussed below), pressure in the pilot line 742 may be insufficient to open (or keep open) the check valve 738, thereby resulting in flow from the base end 730 of the leveling cylinder 710 being diverted through the restriction orifice 740. As also discussed below, this can help to avoid collapse of the leveling cylinder 710 during some operations.
In the illustrated example, the pilot line 742 connects to the leveling cylinder first line 720 downstream of the first leveling check valve 724 and the first leveling restriction orifice 726 (i.e., closer to leveling cylinder 710 and opposite the flow combiner/divider 718 from the MCV 704). However, in other embodiments, other configurations are possible. For example, the pilot line 742 can alternatively connect to the leveling cylinder first line 720 upstream of first leveling check valve 724 and the first leveling restriction orifice 726 (i.e., farther from leveling cylinder 710 and on an opposing side of the restriction orifice 726 than is shown).
The extension cylinder second line 736 provides fluid communication between the MCV 704 and the base end 732 of the extension cylinder 712. The extension cylinder second line 736 includes another flow-blocking arrangement that includes a second extension check valve 744 and a second extension restriction orifice 746 arranged in parallel with each other. The second extension check valve 744 is arranged on the extension cylinder second line 736 such that flow from the MCV 704 toward the base end 732 of the extension cylinder 712 is generally uninhibited by the second extension check valve 744, while flow in the reverse direction (i.e., from the base end 732 of the extension cylinder 712 toward the MCV 704) through the second extension check valve 744 is generally prevented.
Because the second extension restriction orifice 746 is arranged in parallel with the second extension check valve 744, flow from the MCV 704 toward the base end 732 of the extension cylinder 712 can pass generally uninhibited through the second extension check valve 744, whereas flow in the reverse direction is diverted through the second extension restriction orifice 746 due to the one-way nature of the second extension check valve 744. Accordingly, flow from the base end 732 of the extension cylinder 712 is generally limited by the second extension orifice 746. Thus, for example, flow from the MCV 704 to the base end 732 of the extension cylinder 712 during extension of the cylinders 710, 712 may be generally unimpeded, passing through the check valve 744. In contrast, flow from the extension cylinder 712 to the MCV 704 during commanded retraction of the cylinders 710, 712 may be diverted through the restriction orifice 746 and be restricted accordingly.
As noted above, different sizes, different relative locations, or other variations on aspects of the components of the hydraulic circuit 700 can be employed in other embodiments. For example, a particular range of absolute and relative sizes of the restriction orifices 726, 740, 746 may be appropriate for a particular configuration of the cylinders 710, 712, the MCV 704, the flow combiner/divider 718, and the pump 702, for a particular range of expected operating conditions (e.g., hydraulic pressures and pressure drops), and for a power machine such as the loaders 200, 300, 400 with lift arm assemblies similar to those described above. However, other ranges of absolute and relative sizes for these or other restriction orifices may be appropriate for other configurations and expected operating conditions, or for other power machines or lift arm assemblies.
The hydraulic circuit 700 as illustrated and described, and other hydraulic circuits according to the disclosure can be useful to help ensure synchronized operation of the cylinders 710, 712, or other cylinders, as well as to otherwise improve system performance, including in particular operating conditions. In some cases, for example, as further discussed below, the hydraulic circuit 700 and, in particular, the arrangement of the check valves 724, 738, 744 and the restriction orifices 726, 740, 746 in the example flow-blocking arrangements of
Referring again to
Referring again to
However, because of the configuration of the flow-blocking arrangement that includes the first leveling check valve 724 and the first leveling restriction orifice 726, fluid that is drawn out of the rod end 714 of the leveling cylinder 710 during a commanded extension of the cylinders 710, 712 is diverted around the check valve 724 and through the first leveling restriction orifice 726. Accordingly, flow out of the rod end 714 of the leveling cylinder 710 during extension of the cylinders 710, 712 can be substantially restricted, particularly in comparison with the relatively unimpeded flow from the rod end 716 of the extension cylinder 712 (i.e., along the extension cylinder first line 722). Thus, with appropriate configuration of the restriction orifice 726 (and other relevant components), cavitation in the base end 730 of the leveling cylinder 710 can be avoided, and appropriately synchronized movement of the cylinders 710, 712 can be maintained. In addition, passing hydraulic fluid through the restriction orifice 726 can aid in the combining performance of the combiner/divider valve 718, because it can provide pressure to appropriately balance the combiner/divider valve.
Meanwhile, still considering a commanded extension of the cylinders 710, 712, the configuration of the check valve 738 and the second extension check valve 744 allows hydraulic fluid to flow relatively freely into the base ends 730, 732 of the cylinders 710, 712 to affect the desired synchronized extension of the cylinders 710, 712. Further, as alluded to above, when the operator commands the cylinders 710, 712 to extend or retract, the lock valve 728 is configured to be moved (e.g., automatically moved) to the open position, such that hydraulic fluid can move freely out of the rod end 716 of extension cylinder 712.
Similar considerations can also apply when an implement is loaded and the operator commands the cylinders 710, 712 to retract. In this case, for example, the compressive force imparted on the extension cylinder 712 by the force of gravity on the loaded implement creates a tendency for the hydraulic fluid to be drawn relatively rapidly out of the base end 732 of the extension cylinder 712. This, in turn, may result in (and exacerbate) cavitation within the rod end 716 of the extension cylinder 712, and can cause the extension cylinder 712 to compress relatively rapidly. If not appropriately checked, this relatively rapid compression of the extension cylinder 712 can also cause a loss of synchronization between the cylinders 710, 712. As a result, the attitude of the implement during the commanded retraction of the cylinders 710, 712 may not be appropriately maintained, the implement may tilt forward, and material on the implement can be inadvertently rolled out.
However, because of the configuration of the second extension check valve 744 and the second extension restriction orifice 746, fluid that is drawn out of the base end 732 of the extension cylinder 712 during a commanded retraction of the cylinder 710, 712 is diverted around the check valve 744 and through second extension orifice 746. Accordingly, flow out of the base end 732 of the extension cylinder 712 can be substantially restricted, particularly in comparison with relatively unimpeded flow from the base end 730 of the leveling cylinder 710, due to activation of the check valve 738 via the pilot line 742 (as also discussed below). Thus, with appropriate configuration of the restriction orifice 746 (and other relevant components, such as the pilot-operated check valve 738), cavitation in the rod end 716 of the extension cylinder 712 can be avoided, and appropriately synchronized movement of the cylinders 710, 712 can be maintained. In addition, passing hydraulic fluid through the restriction orifice 726 can aid in the dividing performance of the combiner/divider valve 718, because it can provide pressure to appropriately balance the combiner/divider valve.
Meanwhile, still considering a commanded retraction of the cylinders 710, 712, the configuration of the first leveling check valve 724 and the lock valve 728 allows hydraulic fluid to flow freely into the rod ends 714, 716 of the cylinders 710, 712. As noted above, the lock valve 728 can be controlled to open when movement (e.g., retraction) of the cylinders 710, 712 is commanded, thus allowing hydraulic fluid to flow freely into or out of the rod end 716 of the cylinder 712. Further, the tensile force maintained on the leveling cylinder 710 (e.g., by the bucket 436), in combination with pressurization resulting from the commanded retraction, will generally maintain a relatively elevated pressure of the hydraulic fluid in the leveling cylinder first line 720. Because the pilot line 742 is in fluid communication with the leveling cylinder first line 720, this relatively elevated pressure can cause the check valve 738 to remain open, as also noted above. As such, hydraulic fluid can also flow relatively freely out of the base end 730 of leveling cylinder 710 to the MCV 704, bypassing the restriction orifice 740 to flow through the open check valve 738, and synchronization of the cylinders 710, 712 can be maintained.
In some embodiments, synchronization can also be maintained during other commanded movements. For example, in some cases, it can be desirable to perform a function commonly known as “back dragging” in which an implement (e.g., bucket) edge engages the ground as the power machine moves backward, thereby allowing the implement to smooth (or otherwise condition) the ground or other surface. With a telescopic loader, the backward movement of the implement (e.g., the bucket 436) for a back dragging operation can be accomplished using a telescopic function of a lift arm assembly (e.g., as opposed to using a travel function of a power machine as a whole). For some lift arm assemblies, however, back dragging operations can also result in imbalanced loading of leveling and extension cylinders. Referring again to
Referring again to
However, because the leveling cylinder 710 is being compressively loaded by the implement, pressure within the leveling cylinder first line 720 correspondingly drops, despite pressurized flow into the leveling cylinder first line 720 from the MCV 704 via the flow combiner/divider 718. As such, with sufficient compressive loading of the leveling cylinder 710 (e.g., as may be sufficient to substantially increase the risk of cavitation), the pressure within the pilot line 742 will be reduced until it is no longer sufficiently high to maintain the check valve 738 in an open state. With the check valve 738 thus closed, fluid flowing out of the base end 730 of the leveling cylinder 710 toward the MCV 704 is diverted around the check valve 738 to pass through the second leveling restriction orifice 740. Accordingly, flow out of the base end 730 of the leveling cylinder 710 can be substantially restricted, with corresponding reduction of the risk of cavitation in the leveling cylinder 710. Thus, with appropriate configuration of the restriction orifice 740 (and other relevant components, such as the check valve 738), cavitation in the rod end 714 of the leveling cylinder 710 can be avoided, and appropriately synchronized movement of the cylinders 710, 712 can be maintained.
Appropriate control may also be needed to maintain a synchronized orientation of leveling and extension cylinders when no movement of the cylinders is commanded. For example, when no movement is being commanded for the cylinders 710, 712 (i.e., when there is no commanded fluid flow in the hydraulic circuit 700), various external forces can act on the cylinders 710, 712. These forces can push flow through the flow combiner/divider 718, which may tend to function best only during commanded hydraulic flow, and can thereby urge the cylinders 710, 712 out of a desired synchronized orientation.
To prevent loss of synchronization of a set of cylinders, as also alluded to above, a lock valve can be provided in order to prevent certain hydraulic flows when no movement of the cylinders is commanded. For example, the lock valve 728 in the hydraulic circuit 700 is configured to selectively block the flow path between the rod end 716 of the extension cylinder 712 and the rod end 714 of the leveling cylinder 710. Accordingly, the lock valve 728 can prevent flow between the rod ends 714, 716 of the two cylinders 710, 712, via a connection in the flow combiner/divider 718 and can thereby help to maintain the synchronized orientation of the cylinders 710, 712 when flow is not commanded. Further, as noted above, the solenoid of the lock valve 728 can be configured to be energized whenever flow is commanded for the hydraulic circuit 700 (i.e., whenever movement of the cylinders 710, 712 is commanded) in order to move the lock valve 728 to the open position and thereby permit flow between the rod ends 714, 716 of the cylinders 710, 712. Also as noted above, although the lock valve solenoid 728 is illustrated as an electrically controlled valve, other configurations are possible, including lock valves that are configured to be controlled via pilot pressure to unlock (i.e., to permit flow) when movement of the relevant cylinders is commanded.
As also noted above, particular sizes and other aspects of the restriction orifices 726, 740, 746 can be selected in order to appropriately accommodate expected flow rates, pressure drops, loading, and other relevant aspects of particular systems and particular operations. Similarly, other components, such as the check valves 724, 738, 744, the pump 702, the MCV 704, the flow combiner/divider 718, or other orifices, valves, check valves, pumps, cylinders, and so on can also be customized as appropriate for particular power machines or operating conditions.
In this regard, the description herein of hydraulic circuit 800 with reference to
In the hydraulic circuit 800, an implement pump 802, which can be an example of the implement pump 224B of
As also noted above, in some implementations, the leveling cylinder 810 and the extension cylinder 812 can be utilized in a lift arm assembly similar to either of the lift arm assemblies 350, 450 (see
In the embodiment illustrated in
The flow combiner/divider 818 is illustrated with a simplified schematic in
In the illustrated embodiment of
In other embodiments, other configurations are possible, including configurations in which flow combiner/dividers are provided along two hydraulic flow paths out of a main control valve, and configurations in which such flow combiners/dividers are configured to operate only as flow dividers and not as flow combiners. For example, some embodiments can include a flow combiner/divider that is generally similar to the flow combiner/divider 818 but that is located along the second flow path 808. In such an arrangement, for example, the flow combiner/divider can be configured to divide flow to base ends 830, 832 of the cylinders 810, 812 during commanded extension of the cylinders 810, 812 and to operate as a flow divider relative to the base ends 830, 832 of the cylinders 810, 812 during commanded retraction of the cylinders 810, 812.
Generally, the hydraulic circuit in
In any case, various components of the hydraulic circuit 800, including components of the flow combiner/divider 818, may be sized or otherwise configured in various ways according to various expected operational parameters or specifications. For example, various components of the hydraulic circuit 800 may be sized or otherwise configured based on expected loads, desired hydraulic pressure drops, and other parameters for particular expected operating conditions. As such, the particular sizes and configurations of components illustrated in
As noted above, the leveling cylinder first line 820 provides fluid communication between the flow combiner/divider 818 and the rod end 814 of the leveling cylinder 810. In the embodiment illustrated in
Because the first leveling restriction orifice 826 is arranged in parallel with the first leveling check valve 824, although flow from the flow combiner/divider 818 toward the rod end 814 of the leveling cylinder 810 can pass relatively uninhibited through the first leveling check valve 824, flow in the reverse direction is diverted to pass through the first leveling restriction orifice 826, due to the one-way nature of the first leveling check valve 824. Accordingly, flow from the rod end 814 of leveling cylinder 810 towards the flow combiner/divider 818 is generally limited by the first leveling restriction orifice 826. Thus, during commanded extension of the cylinders 710, 812, flow from the rod end 814 of the leveling cylinder 810 may be restricted by the restriction orifice 826 of the noted flow-blocking arrangement.
To control hydraulic flow between the rod end 816 of the extension cylinder 812 and the MCV 804, the flow combiner/divider 818, and rod end 814 of the leveling cylinder 810, the extension cylinder first line 822 includes a selective lock valve 828 disposed between the flow combiner/divider 818 and the rod end 816 of the extension cylinder 812. The selective lock valve 828 is movable between an open position (not shown), in which fluid flow between flow combiner/divider 818 is permitted, and a closed position (as shown in
In some cases, the selective lock valve 828 can be configured to automatically move into the open position when the leveling cylinder 810 and the extension cylinder 812 are commanded to extend or retract, as also discussed below. Similarly, the selective lock valve 828 can be configured to automatically move into the closed position when the leveling cylinder 810 and the extension cylinder 812 are not being commanded to extend or retract, as also discussed below. The selective lock valve 828 is shown in
Opposite the MCV 804 from the first line 806, the second line 808 provides a flow path between the MCV 804, the base end 830 of the leveling cylinder 810, and the base end 832 of the extension cylinder 812. The second line 808 includes a leveling cylinder second line 834 that leads to the leveling cylinder 810, and an extension cylinder second line 836 that leads to the extension cylinder 812.
The leveling cylinder second line 834 provides fluid communication between the MCV 804 and the base end 830 of the leveling cylinder 810 and includes another flow-blocking arrangement that includes a check valve 838 and a second leveling restriction orifice 840 that are arranged in parallel with each other. In some embodiments, the check valve 838 is a spring-biased pilot-operated check valve, although other configurations are possible for the check valve and for the flow-blocking arrangement in general.
The check valve 838 is arranged on the leveling cylinder second line 834 such that flow from the MCV 804 toward the base end 830 of the leveling cylinder 810 may flow through the check valve 838 to the base end 830 of the leveling cylinder 810 during commanded extension of the cylinders 810, 812. Conversely, flow from the base end 830 of the leveling cylinder 810 toward the MCV 804 through the check valve 838 is generally prevented. Thus, as also discussed below, flow from the base end 830 of the leveling cylinder 810 during commanded retraction of the cylinders 810, 812 may generally be diverted through the restriction orifice 840. Further, because the second leveling restriction orifice 840 is arranged in parallel with the check valve 838, although flow from the MCV 804 toward the base end 830 of the leveling cylinder 810 (e.g., during commanded extension of the cylinders 810, 812) can pass generally uninhibited through the check valve 838, flow in the reverse direction (e.g., during commanded retraction of the cylinders 810, 812) is generally diverted to pass through the second leveling restriction orifice 840. Accordingly, flow from the base end 830 of leveling cylinder 810 towards the MCV 804 is generally limited by the second leveling restriction orifice 840.
In some cases, however, operation of the pilot-operated check valve 838 can result in relatively unimpeded flow through the check valve 838 from the base end 830 of the leveling cylinder 810 to the MCV 804, including during commanded retraction of the cylinders 810, 812. For example, in the illustrated configuration, the check valve 838 is operably coupled to the leveling cylinder first line 820 through a pilot line 842. As such, if the hydraulic pressure within the leveling cylinder first line 820 is sufficiently high (e.g., to overcome the biasing force of a spring element of the check valve 838), the pressurization of the pilot line 842 can open the check valve 838, thereby allowing for hydraulic fluid to flow generally unrestricted from the base end 830 of the leveling cylinder 810 to the MCV 804.
Accordingly, for example, during a commanded retraction of the cylinders 810, 812 with the leveling cylinder 810 under a tension load, pressure in the pilot line 842 may be relatively high, resulting in the check valve 838 being opened for relatively unimpeded flow of hydraulic fluid from the base end 830 of the leveling cylinder 810. In contrast, for example, during a commanded retraction of the cylinders 810, 812 with the leveling cylinder 810 under a compression load (e.g., during back dragging, as also discussed below), pressure in the pilot line 842 may be insufficient to open (or keep open) the check valve 838, thereby resulting in flow from the base end 830 of the leveling cylinder 810 being diverted through the restriction orifice 840. As also discussed below, this can help to avoid collapse of the leveling cylinder 810 during some operations.
In the illustrated example, the pilot line 842 connects to the leveling cylinder first line 820 downstream of the first leveling check valve 824 and the first leveling restriction orifice 826 (i.e., closer to leveling cylinder 810 and opposite the flow combiner/divider 818 from the MCV 804). However, in other embodiments, other configurations are possible. For example, the pilot line 842 can alternatively connect to the leveling cylinder first line 820 upstream of first leveling check valve 824 and the first leveling restriction orifice 826 (i.e., farther from leveling cylinder 810 and on an opposing side of the restriction orifice 826 than is shown).
The extension cylinder second line 836 provides fluid communication between the MCV 804 and the base end 832 of the extension cylinder 812. The extension cylinder second line 836 includes another flow-blocking arrangement that includes a two-position counterbalance valve 850. In particular, the counterbalance valve 850 includes a first position 854 with a spring-biased check valve and a second position 852 with a restriction orifice, is biased towards the first position 854 as a default, and is configured to be hydraulically actuated based on flow through a pilot line 856 from the flow line 822 and a counterbalance pilot line 858 from an outlet side of the first position 854.
Accordingly, the counterbalance valve 850 is configured so that the check valve of the first position 854 generally allows relatively unimpeded flow from the MCV 804 toward the base end 832 of the extension cylinder 812, such as during commanded extension of the cylinders 810, 812. And the restriction orifice of the second position 852 restricts flow from the base end 832 of the extension cylinder 812 to the MCV 804, such as during commanded retraction of the cylinders 810, 812. Further, through operation of the pilot lines 856, undesired flow in some operating conditions can be avoided. For example, at low flow hydraulic rates, during retraction of the cylinders 810, 812, leakage through the restriction orifice of the second position 852 could result in collapse of the extension cylinder 812 and a corresponding desynchronization of the cylinders 810, 812 collectively. However, due to the operation of the pilot line 856 and the default orientation of the counterbalance valve 850 in the first position 854, flow from the base end 832 of the cylinder 812 to the MCV 804 is generally prevented unless the rod end 816 of the extension cylinder 812, as reflected along the extension cylinder first line 822, is sufficiently pressurized. Thus, at relatively low flows, pressure within the pilot line 856 may initially (or otherwise) be small enough that the counterbalance valve 850 initially (or otherwise) remains in (or returns to) the first position 854, so that an appropriate pressure drop across the counterbalance valve 850 can be maintained and potential collapse of the extension cylinder 812 under compression loading can be avoided.
As noted above, different sizes, different relative locations, or other variations on aspects of the components of the hydraulic circuit 800 can be employed in other embodiments. For example, a particular range of absolute and relative sizes of the restriction orifices 826, 840 or of the second position 852 of the counterbalance valve 850 may be appropriate for a particular configuration of the cylinders 810, 812, the MCV 804, the flow combiner/divider 818, and the pump 802, for a particular range of expected operating conditions (e.g., hydraulic pressures and pressure drops), and for a power machine such as the loaders 200, 300, 400 with lift arm assemblies similar to those described above. However, other ranges of absolute and relative sizes for these or other restriction orifices may be appropriate for other configurations and expected operating conditions, or for other power machines or lift arm assemblies. Similarly, the required pilot pressure for movement of a counterbalance valve for flow from a base end of a cylinder (or otherwise) can be selected from a wide range of pressures to provide appropriate operation for particular use cases or system configurations.
The hydraulic circuit 800 as illustrated and described, and other hydraulic circuits according to the disclosure can be useful to help ensure synchronized operation of the cylinders 810, 812, or other cylinders, as well as to otherwise improve system performance, including in particular operating conditions. In some cases, for example, as further discussed below, the hydraulic circuit 800 and, in particular, the arrangement of the check valves 824, 838, the restriction orifices 826, 840, and the counterbalance valve 850 in the example flow-blocking arrangements of
Referring again to
Referring again to
However, because of the configuration of the flow-blocking arrangement that includes the first leveling check valve 824 and the first leveling restriction orifice 826, fluid that is drawn out of the rod end 814 of the leveling cylinder 810 during a commanded extension of the cylinders 810, 812 is diverted around the check valve 824 and through the first leveling restriction orifice 826. Accordingly, flow out of the rod end 814 of the leveling cylinder 810 during extension of the cylinders 810, 812 can be substantially restricted, particularly in comparison with the relatively unimpeded flow from the rod end 816 of the extension cylinder 812 (i.e., along the extension cylinder first line 822). Thus, with appropriate configuration of the restriction orifice 826 (and other relevant components), cavitation in the base end 830 of the leveling cylinder 810 can be avoided, and appropriately synchronized movement of the cylinders 810, 812 can be maintained. In addition, passing hydraulic fluid through the restriction orifice 826 can aid in the combining performance of the combiner/divider valve 818, because it can provide pressure to appropriately balance the combiner/divider valve.
Meanwhile, still considering a commanded extension of the cylinders 810, 812, the configuration of the check valve 838 and the second extension check valve 844 allows hydraulic fluid to flow relatively freely into the base ends 830, 832 of the cylinders 810, 812 to affect the desired synchronized extension of the cylinders 810, 812. Further, as alluded to above, when the operator commands the cylinders 810, 812 to extend or retract, the lock valve 828 is configured to be moved (e.g., automatically moved) to the open position, such that hydraulic fluid can move freely out of the rod end 816 of extension cylinder 812.
Similar considerations can also apply when an implement is loaded and the operator commands the cylinders 810, 812 to retract. In this case, for example, the compressive force imparted on the extension cylinder 812 by the force of gravity on the loaded implement creates a tendency for the hydraulic fluid to be drawn relatively rapidly out of the base end 832 of the extension cylinder 812. This, in turn, may result in (and exacerbate) cavitation within the rod end 816 of the extension cylinder 812, and can cause the extension cylinder 812 to compress relatively rapidly. If not appropriately checked, this relatively rapid compression of the extension cylinder 812 can also cause a loss of synchronization between the cylinders 810, 812. As a result, the attitude of the implement during the commanded retraction of the cylinders 810, 812 may not be appropriately maintained, the implement may tilt forward, and material on the implement can be inadvertently rolled out.
However, because of the configuration of the second extension check valve 844 and the second extension restriction orifice 846, fluid that is drawn out of the base end 832 of the extension cylinder 812 during a commanded retraction of the cylinder 810, 812 is diverted around the check valve 844 and through second extension orifice 846. Accordingly, flow out of the base end 832 of the extension cylinder 812 can be substantially restricted, particularly in comparison with relatively unimpeded flow from the base end 830 of the leveling cylinder 810, due to activation of the check valve 838 via the pilot line 842 (as also discussed below). Thus, with appropriate configuration of the restriction orifice 846 (and other relevant components, such as the pilot-operated check valve 838), cavitation in the rod end 816 of the extension cylinder 812 can be avoided, and appropriately synchronized movement of the cylinders 810, 812 can be maintained. In addition, passing hydraulic fluid through the restriction orifice 826 can aid in the dividing performance of the combiner/divider valve 818, because it can provide pressure to appropriately balance the combiner/divider valve.
Meanwhile, still considering a commanded retraction of the cylinders 810, 812, the configuration of the first leveling check valve 824 and the lock valve 828 allows hydraulic fluid to flow freely into the rod ends 814, 816 of the cylinders 810, 812. As noted above, the lock valve 828 can be controlled to open when movement (e.g., retraction) of the cylinders 810, 812 is commanded, thus allowing hydraulic fluid to flow freely into or out of the rod end 816 of the cylinder 812. Further, the tensile force maintained on the leveling cylinder 810 by the bucket 436, in combination with pressurization resulting from the commanded retraction will generally maintain a relatively elevated pressure of the hydraulic fluid in the leveling cylinder first line 820. Because the pilot line 842 is in fluid communication with the leveling cylinder first line 820, this relatively elevated pressure can cause the check valve 838 to remain open, as also noted above. As such, hydraulic fluid can also flow relatively freely out of the base end 830 of leveling cylinder 810 to the MCV 804, bypassing the restriction orifice 840 to flow through the open check valve 838, and synchronization of the cylinders 810, 812 can be maintained.
In some embodiments, synchronization can also be maintained during other commanded movements. For example, during back dragging operations, the leveling cylinder 810 can become loaded in compression and the extension cylinder 812 can become loaded in tension during a commanded retraction of the cylinders 810, 812. For similar reasons as discussed above, this can tend to cause cavitation in the rod end 814 of the leveling cylinder 810, relatively rapid flow of hydraulic fluid out of the base end 830 of the leveling cylinder 810, and the resulting loss of the desired synchronization of the leveling and extension cylinders 810, 812.
However, because the leveling cylinder 810 is being compressively loaded by the implement, pressure within the leveling cylinder first line 820 correspondingly drops, despite pressurized flow into the leveling cylinder first line 820 from the MCV 804 via the flow combiner/divider 818. As such, with sufficient compressive loading of the leveling cylinder 810 (e.g., as may be sufficient to substantially increase the risk of cavitation), the pressure within the pilot line 842 will be reduced until it is no longer sufficiently high to maintain the check valve 838 in an open state. With the check valve 838 thus closed, fluid flowing out of the base end 830 of the leveling cylinder 810 toward the MCV 704 is diverted around the check valve 838 to pass through the second leveling restriction orifice 840. Accordingly, flow out of the base end 830 of the leveling cylinder 810 can be substantially restricted, with corresponding reduction of the risk of cavitation in the leveling cylinder 810. Thus, with appropriate configuration of the restriction orifice 840 (and other relevant components, such as the check valve 838), cavitation in the rod end 814 of the leveling cylinder 810 can be avoided, and appropriately synchronized movement of the cylinders 810, 812 can be maintained.
Appropriate control may also be needed to maintain a synchronized orientation of leveling and extension cylinders when no movement of the cylinders is commanded. For example, when no movement is being commanded for the cylinders 810, 812 (i.e., when there is no commanded fluid flow in the hydraulic circuit 800), various external forces can act on the cylinders 810, 812. These forces can push flow through the flow combiner/divider 818, which may tend to function best only during commanded hydraulic flow, and can thereby urge the cylinders 810, 812 out of a desired synchronized orientation.
To prevent loss of synchronization of a set of cylinders, as also alluded to above, a lock valve can be provided in order to prevent certain hydraulic flows when no movement of the cylinders is commanded. For example, the lock valve 828 in the hydraulic circuit 800 is configured to selectively block the flow path between the rod end 816 of the extension cylinder 812 and the rod end 814 of the leveling cylinder 810. Accordingly, the lock valve 828 can prevent flow between the rod ends 814, 816 of the two cylinders 810, 812, via a connection in the flow combiner/divider 818, and can thereby help to maintain the synchronized orientation of the cylinders 810, 812 when flow is not commanded. Further, as noted above, the solenoid of the lock valve 828 can be configured to be energized whenever flow is commanded for the hydraulic circuit 800 (i.e., whenever movement of the cylinders 810, 812 is commanded) in order to move the lock valve 828 to the open position and thereby permit flow between the rod ends 814, 816 of the cylinders 810, 812. Also as noted above, although the lock valve solenoid 828 is illustrated as an electrically controlled valve, other configurations are possible, including lock valves that are configured to be controlled via pilot pressure to unlock (i.e., to permit flow) when movement of the relevant cylinders is commanded.
As also noted above, particular sizes and other aspects of the restriction orifices 826, 840 and of the restriction orifice in the second position 852 of the counterbalance valve 850 can be selected in order to appropriately accommodate expected flow rates, pressure drops, loading, and other relevant aspects of particular systems and particular operations. Similarly, other components, such as the check valves 824, 838, the check valve in the first position 854 of the counterbalance valve 850, the pump 802, the MCV 804, the flow combiner/divider 818, or other orifices, valves, check valves, pumps, cylinders, and so on can also be customized as appropriate for particular power machines or operating conditions.
In this regard, similarly to the hydraulic circuit 800, the hydraulic circuit 900 includes an implement pump 902 and a main control valve (MCV) 904 that can selectively direct hydraulic flow along either of hydraulic flow lines 906, 908 in order to control synchronized movement of a leveling cylinder 910 and an extension cylinder 912. In particular, during commanded retraction of the cylinder 910, 912, hydraulic flow is directed by the MCV 904 along the flow line 906 to be divided by a flow divider 918 before reaching rod ends 914, 916 of the cylinders 910, 912. In contrast, during commanded extension of the cylinders 910, 912, hydraulic flow is directed by the MCV 904 along the flow line 908 to be divided by a flow divider 920 before reaching base ends 930, 932 of the cylinders 910, 912.
Conversely, during commanded extension of the cylinders 910, 912, flow from the rod ends 914, 916 of the cylinders 910, 912 bypasses the flow divider 918, and during commanded retraction of the cylinders 910, 912, flow from the base ends 930, 932 of the cylinders 910, 912 bypasses the flow divider 920. For example, flow from the rod end 914 of the leveling cylinder 910 during extension of the cylinders 910, 912 passes through a directional bypass that includes a spring-biased check valve 924 that is arranged in parallel with a flow restriction 922 of the flow divider 918, but not included in the flow divider 918. Similarly, flow from the rod end 916 of the extension cylinder 912 and from the base ends 930, 932 of the leveling and extension cylinders 910, 912 during extension and retraction of the cylinders 910, 912, respectively, will pass around the flow dividers 918, 920 through associated check valves (not numbered). In contrast, flow from the MCV 904 to the rod ends 914, 916 of the cylinder 910, 912 or from the MCV 904 to the base ends 930, 932 of the cylinders 910, 912 would be blocked by the check valve 924 and other similarly placed check valves (not numbered) and thereby routed through the restriction orifices of the flow dividers 918, 920 (e.g., the restriction orifice 922) to be appropriately divided between the cylinders 910, 912. Among other benefits, this arrangement can allow the flow dividers 918, 920 to serve as flow dividers only (i.e., not also as flow combiners), which may improve overall system functionality due to the tendency of some flow dividers/combiners to work less well as combiners than as dividers. Further, the reduced restriction of flow to the MCV 904 through the check valves outside of the flow dividers 918, 920 (e.g., the check valve 924), rather than through the restriction orifices of the flow dividers 918, 920 (e.g., the restriction orifice 922) can help to maintain stability for flow-blocking arrangements configured as counterbalance valves, including the counterbalance valves further discussed below.
As alluded to above, the hydraulic circuit 900 includes a set of three flow-blocking arrangements that are configured similarly to flow-blocking arrangements discussed above with respect to the hydraulic circuit 800 of
Generally, the flow-blocking arrangements are configured and operate similarly to corresponding flow-blocking arrangements in
As noted for other components discussed above, some flow dividers may exhibit a different or more complex configuration than is illustrated for the flow dividers 918, 920. Correspondingly, the principles discussed herein with regard to the hydraulic circuit 900 can be still be usefully employed in hydraulic circuits that include differently configured flow dividers or other components.
Although the examples above focus on synchronized movement of cylinders, some similar arrangements can be used for other purposes. For example, similar hydraulic circuits can be used to ensure a controlled desynchronized movement of cylinders, such as extension or retraction of one cylinder by a fraction of or excess percentage relative to extension or retraction of another cylinder. In some embodiments, this controlled desynchronized movement can be implemented using hydraulic circuits similar to those discussed herein, but with differently sized restriction orifices. For example, restriction orifices such as the restriction orifices 726, 740, 746 can be sized in some cases to provide a ratio of flow for synchronized movement and can be sized in other cases to provide a ratio of flow for non-synchronized movement. Correspondingly, although some examples herein describe fixed orifices arranged to provide a desired pressure drop, other embodiments can include one or more variable orifices (e.g., located similarly to the restriction orifices 726, 740, 746) that can be adjusted to provide desired pressure drops for particular operating conditions.
Although the examples above focus on synchronized movement of cylinders, some similar arrangements can be used for other purposes. For example, similar hydraulic circuits can be used to ensure a controlled desynchronized movement of cylinders, such as extension or retraction of one cylinder by a fraction of or excess percentage relative to extension or retraction of another cylinder. In some embodiments, this controlled desynchronized movement can be implemented using hydraulic circuits similar to those discussed herein, but with differently sized restriction orifices. For example, restriction orifices such as the restriction orifices 726, 740, 746 can be sized in some cases to provide a ratio of flow for synchronized movement and can be sized in other cases to provide a ratio of flow for non-synchronized movement. Correspondingly, although some examples herein describe fixed orifices arranged to provide a desired pressure drop, other embodiments can include one or more variable orifices (e.g., located similarly to the restriction orifices 726, 740, 746) that can be adjusted to provide desired pressure drops for particular operating conditions.
Some discussion above, focuses in particular on control and synchronization of sets of leveling and extension cylinders (e.g., the cylinders 710, 712 of
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail to the disclosed embodiments without departing from the spirit and scope of the concepts discussed herein.
This application claims priority to U.S. Provisional Patent Application No. 62/809,275, filed Feb. 22, 2019, and U.S. patent application Ser. No. 16/799,685, filed Feb. 24, 2020, the entireties of both of which are incorporated herein by reference.
Number | Date | Country | |
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62809275 | Feb 2019 | US |
Number | Date | Country | |
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Parent | 16799685 | Feb 2020 | US |
Child | 17522180 | US |