Patent Publication Number: US-2021180287-A1

Title: Loader lift arm

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 15/957,170, filed on Apr. 19, 2018, which published as U.S. Publication No. 2018/0305889 A1 on Oct. 25, 2018, which claims the benefit of U.S. Provisional Application No. 62/487,153, which was filed on Apr. 19, 2017, the contents of which are hereby incorporated in their entireties. 
    
    
     BACKGROUND 
     The present disclosure is directed toward power machines. More particularly, the present disclosure is directed toward lift arm and related structures for moving or handling material with an implement mounted on the lift arm structure. 
     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. 
     Power machines typically include a frame, at least one work element, and a power source that can provide power to the work element to accomplish a work task. One type of power machine is a self-propelled work vehicle. Self-propelled work vehicles are a class of power machines that include a frame, work element, and a power source that can provide power to the work element. At least one of the work elements is a motive system for moving the power machine under power. 
     Typically, power machines include a lift arm structure pivotally mounted to the frame of the power machine, with one or more lift actuators coupled between the frame and the lift arm structure to raise and lower the lift arm structure during work operations. For example, the lift arm structure can be used to raise and lower a bucket to move material. Designing lift arm structures which are less complex to manufacture but which are sufficiently strong to endure high load stresses on the lift arm structure is challenging. Further, many lift arm structure designs adversely affect visibility for the operator of the power machine. 
     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. 
     SUMMARY 
     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. The 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. 
     Disclosed embodiments include power machines, lift arm structures, implement carriers, follower link structures, and driver link structures which improve manufacturability of the power machine, reduce component failures of the power machine, and improve power machine design and functionality. In some exemplary embodiments, lift arm structures include cast lower lift arm portions which directly pivotally couple to cast implement carrier plates. The cast lower lift arm portions include contoured upper ends which are sleeved onto contoured lower ends of upper lift arm portions to control stress points and to reduce stresses on welds between the upper and lower lift arm portions. In some embodiments, the follower link structures include cast follower links which are configured to be positioned at least partially outside of the lift arm structure to improve rear visibility for an operator of the power machine. In some embodiments, the driver link structures are configured to be at least partially laterally spaced from the frame of the power machine such that they laterally overlap with innermost surfaces on the lift cylinder, but such that as the lift arm is raised the laterally overlapping portions are moved above the innermost surfaces of the lift cylinder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating functional systems of a representative power machine on which embodiments of the present disclosure can be advantageously practiced. 
         FIG. 2  is a front perspective view of a power machine on which embodiments disclosed herein can be advantageously practiced. 
         FIG. 3  is a rear perspective view of the power machine shown in  FIG. 2 . 
         FIG. 4  is a side view illustration of components of another power machine on which embodiments disclosed herein can be advantageously practiced. 
         FIGS. 5 and 6  are perspective view illustrations of a lift arm structure of the power machine shown in  FIG. 4 . 
         FIG. 7  is a perspective view of a cast lower lift arm portion of the lift arm structure illustrated in  FIGS. 5 and 6  in accordance with exemplary embodiments. 
         FIG. 8  is a perspective view illustration of contoured ends of the cast lower lift arm portion and of a main or upper lift arm portion in accordance with some exemplary embodiments. 
         FIG. 9  is a first perspective view of a cast implement carrier plate in accordance with some exemplary embodiments. 
         FIG. 10  is a machine side view of the implement carrier plate shown in  FIG. 9 . 
         FIG. 11  is an end view of the implement carrier plate shown in  FIG. 9 . 
         FIG. 12  is a second perspective view of the implement carrier plate shown in  FIG. 9 . 
         FIGS. 13 and 14  are perspective views of an implement carrier assembly including two cast implement carrier plates as shown in  FIG. 9 , with a structural tube extending therebetween. 
         FIG. 15  is a perspective view illustration showing the exemplary implement carrier embodiment rotatably coupled to the cast lower lift arm portions. 
         FIG. 16  is a rear view illustration of a portion of the power machine showing a cast follower link configuration in accordance with some exemplary embodiments. 
         FIG. 17  is a partial perspective view of the power machine showing the follower link configuration of  FIG. 16 . 
         FIG. 18  is an illustration of the cast follower link members connected by a structural tube. 
         FIGS. 19-21  are side view illustrations showing a relational positioning of a pivot attachment between a driver link of the power machine and the lift arm structure relative to a top end of a lift cylinder base in accordance with some exemplary embodiments. 
         FIG. 22  is another illustration of the relationship between the driver link pivot and the base end of the lift cylinder in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     This discussion uses illustrative embodiments to disclose various concepts. 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. 
     The disclosed embodiments include power machines, lift arm structures, implement carriers, follower link structures, and driver link structures which improve manufacturability, reduce component failures, and improve power machine design. In some exemplary embodiments, lift arm structures include cast lower lift arm portions. The cast lower lift arm portions can be directly pivotally coupled to cast implement carrier plates. The cast lower lift arm portions can include, in some embodiments, contoured upper ends which are sleeved onto contoured lower ends of upper lift arm portions to control stress points and to thereby reduce stresses on welds between the upper and lower lift arm portions. 
     In some embodiments, the follower link structures include cast follower links which are configured to be positioned at least partially outside of the lift arm structure to improve rear visibility for an operator of the power machine. Also, in some embodiments, the driver link structures are configured to be at least partially laterally spaced from the frame of the power machine such that they laterally overlap with innermost surfaces on the lift cylinder, but such that as the lift arm is raised the laterally overlapping portions are moved from below the innermost surfaces of the lift cylinder to above the innermost surfaces of the lift cylinder such that the driver link does not damage the lift cylinder. This allows for more efficient use of space to improve design features without requiring the width of the power machine to be increased. 
     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  FIG. 1  and one example of such a power machine is illustrated in  FIGS. 2-3  and described below before any embodiments are disclosed. However, as mentioned above, the embodiments below can be practiced on any of a number of power machines, including power machines of different types from the representative power machine shown in  FIGS. 2-3 . 
     Power machines, for the purposes of this discussion, include a frame, at least one work element, and a power source that can provide power to the work element to accomplish a work task. One type of power machine is a self-propelled work vehicle. Self-propelled work vehicles are a class of power machines that include a frame, work element, and a power source that can provide power to the work element. At least one of the work elements is a motive system for moving the power machine under power. 
       FIG. 1  shows a block diagram illustrating the basic systems of a power machine  100  upon which the embodiments discussed below can be advantageously incorporated and can be any of a number of different types of power machines. The block diagram of  FIG. 1  identifies various systems on power machine  100  and the relationship between various components and systems. As mentioned above, at the most basic level, power machines for the purposes of this discussion include a frame, a power source, and a work element. The power machine  100  has a frame  110 , a power source  120 , and a work element  130 . Because power machine  100  shown in  FIG. 1  is a self-propelled work vehicle, it also has tractive elements  140 , which are themselves work elements provided to move the power machine over a support surface and an operator station  150  that provides an operating position for controlling the work elements of the power machine. A control system  160  is provided to interact with the other systems to perform various work tasks at least in part in response to control signals provided by an operator. 
     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 for performing the task. The implement, in some instances 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  FIG. 1 . At its most basic, implement interface  170  is a connection mechanism between the frame  110  or a work element  130  and an implement, which can be as simple as a connection point for attaching an implement directly to the frame  110  or a work element  130  or more complex, as discussed below. 
     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 implements to the work element. One characteristic of such an implement carrier is that once an implement is attached to it, it 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 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 is capable of moving 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 is capable of providing 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. 
       FIG. 1  shows a single work element designated as work element  130 , but various power machines can have any number of work elements. Work elements are typically attached to the frame of the power machine and movable with respect to the frame when performing a work task. In addition, tractive elements  140  are a special case of work element in that their work function is generally to move the power machine  100  over a support surface. Tractive elements  140  are shown separate from the work element  130  because many power machines have additional work elements besides tractive elements, although that is not always the case. Power machines can have any number of tractive elements, some or all of which can receive power from the power source  120  to propel the power machine  100 . Tractive elements can be, for example, track assemblies, wheels attached to an axle, and the like. Tractive elements can be mounted to the frame such that movement of the tractive element is limited to rotation about an axle (so that steering is accomplished by a skidding action) or, alternatively, pivotally mounted to the frame to accomplish steering by pivoting the tractive element with respect to the frame. 
     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 or not they have operator compartments or operator positions, 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. 
       FIGS. 2-3  illustrates a loader  200 , which is one particular example of a power machine of the type illustrated in  FIG. 1  where the embodiments discussed below can be advantageously employed. Loader  200  is a track loader and more particularly, a compact tracked loader. A track loader is a loader that has endless tracks as tractive elements (as opposed to wheels). Track loader  200  is one particular example of the power machine  100  illustrated broadly in  FIG. 1  and discussed above. To that end, features of loader  200  described below include reference numbers that are generally similar to those used in  FIG. 1 . For example, loader  200  is described as having a frame  210 , just as power machine  100  has a frame  110 . Track loader  200  is described herein to provide a reference for understanding one environment on which the embodiments described below related to track assemblies and mounting elements for mounting the track assemblies to a power machine may be practiced. The loader  200  should not be considered limiting especially as to the description of features that loader  200  may have described herein that are not essential to the disclosed embodiments and thus may or may not be included in power machines other than loader  200  upon which the embodiments disclosed below may be advantageously practiced. Unless specifically noted otherwise, embodiments disclosed below can be practiced on a variety of power machines, with the track loader  200  being only one of those power machines. For example, some or all of the concepts discussed below can be practiced on many other types of work vehicles such as various other loaders, excavators, trenchers, and dozers, to name but a few examples. In particular, the features of power machine frames described below can be utilized on wheeled loaders as well. An example embodiment of such a wheeled loader, commonly referred to as a skid-steer loader, is illustrated in  FIG. 4 . 
     Loader  200  includes frame  210  that supports a power system  220 , the power system can generate or otherwise providing power for operating various functions on the power machine. Frame  210  also supports a work element in the form of a lift arm structure  230  that is powered by the power system  220  and 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 structure  230  in turn supports an implement carrier interface  270 , which includes an implement carrier  272  that can receive and securing various implements to the loader  200  for performing various work tasks and power couplers  274 , which are provided to selectively provide power to an implement that might be connected to the loader. The loader  200  can be operated from within a cab  250  from which an operator can manipulate various control devices  260  to cause the power machine to perform various functions. Cab  250  can be pivoted back about an axis that extends through mounts  254  to access components as needed for maintenance and repair. 
     Referring still to  FIGS. 2 and 3 , the elements of frame  210  discussed herein are provided for illustrative purposes and are not the only type of frame that a power machine on which the embodiments can be practiced can employ. Frame  210  of loader  200  includes an undercarriage or lower portion  211  of the frame and a mainframe or upper portion  212  of the frame that is supported by the undercarriage. A tailgate  280  is provided in the rear of the machine to selectively provide access to an engine compartment. The mainframe  212  of loader  200  is attached to the undercarriage  211  such as with fasteners or by welding the undercarriage to the mainframe. Mainframe  212  includes a pair of upright portions  214 A and  214 B located on either side and toward the rear of the mainframe that support lift arm structure  230  and to which the lift arm structure  230  is pivotally attached. The lift arm structure  230  is illustratively pinned to each of the upright portions  214 A and  214 B. The combination of mounting features on the upright portions  214 A and  214 B and the lift arm structure  230  and mounting hardware (including pins used to pin the lift arm structure to the mainframe  212 ) are collectively referred to as joints  216 A and  216 B (one is located on each of the upright portions  214 ) for the purposes of this discussion. Joints  216 A and  216 B are aligned along an axis  218  so that the lift arm structure is capable of pivoting, as discussed below, with respect to the frame  210  about axis  218 . Other power machines may not include upright portions on either side of the frame, or may not have a lift arm structure that is mountable to upright portions on either side and toward the rear of the frame. For example, some power machines may have a single arm, mounted to a single side of the power machine or to a front or rear end of the power machine. Other machines can have a plurality of work elements, including a plurality of lift arms, each of which is mounted to the machine in its own configuration. Frame  210  also supports a pair of tractive elements  242 A and  242 B on either side of the loader  200 , which on loader  200  are track assemblies. 
     The lift arm structure  230  shown in  FIG. 1  is one example of many different types of lift arm structures that can be attached to a power machine such as loader  200  or other power machines on which embodiments of the present discussion can be practiced. The lift arm structure  230  has a pair of lift arms  234  that are disposed on opposing sides of the frame  210 . A first end of each of the lift arms  234  is pivotally coupled to the power machine at joints  216  and a second end  232 B of each of the lift arms is positioned forward of the frame  210  when in a lowered position as shown in  FIG. 2 . The lift arm structure  230  is moveable (i.e. the lift arm structure can be raised and lowered) under control of the loader  200  with respect to the frame  210 . That movement (i.e. the raising and lowering of the lift arm structure  230 ) is described by a travel path, shown generally by arrow  237 . For the purposes of this discussion, the travel path  237  of the lift arm structure  230  is defined by the path of movement of the second end  232 B of the lift arm structure. 
     Each of the lift arms  234  of lift arm structure  230  as shown in  FIG. 2  includes a first portion  234 A and a second portion  234 B that is pivotally coupled to the first portion  234 A. The first portion  234 A of each lift arm  234  is pivotally coupled to the frame  210  at one of the joints  216  and the second portion  234 B extends from its connection to the first portion  234 A to the second end  232 B of the lift arm structure  230 . The lift arms  234  are each coupled to a cross member  236  that is attached to the first portions  234 A. Cross member  236  provides increased structural stability to the lift arm structure  230 . A pair of actuators  238 , which on loader  200  are hydraulic cylinders configured to receive pressurized fluid from power system  220 , are pivotally coupled to both the frame  210  and the lift arms  234  at pivotable joints  238 A and  238 B, respectively, on either side of the loader  200 . The actuators  238  are sometimes referred to individually and collectively as lift cylinders. Actuation (i.e., extension and retraction) of the actuators  238  cause the lift arm structure  230  to pivot about joints  216  and thereby be raised and lowered along a fixed path illustrated by arrow  237 . Each of a pair of control links  217  are pivotally mounted to the frame  210  and one of the lift arms  232  on either side of the frame  210 . The control links  217  help to define the fixed travel path of the lift arm structure  230 . The lift arm structure  230  shown in  FIG. 2  is representative of one type of lift arm structure that may be coupled to the power machine  100 . Other lift arm structures, with different geometries, components, and arrangements can be pivotally coupled to the loader  200  or other power machines upon which the embodiments discussed herein can be practiced without departing from the scope of the present discussion. For example, other machines can have lift arm structures with lift arms that each has one portion (as opposed to the two portions  234 A and  234 B of lift arm  234 ) that is pivotally coupled to a frame at one end with the other end being positioned in front of the frame. Other lift arm structures can have an extendable or telescoping lift arm. Still other lift arm structures can have several (i.e. more than two) portions segments or portions. Some lift arms, most notably lift arms on excavators but also possible on loaders, may have portions that are controllable to pivot with respect to another segment instead of moving in concert (i.e. along a pre-determined path) as is the case in the lift arm structure  230  shown in  FIG. 2 . Some power machines have lift arm structures with a single lift arm, such as is known in excavators or even some loaders and other power machines. Other power machines can have a plurality of lift arm structures, each being independent of the other(s). 
     An exemplary implement interface  270  is provided at a second end  234 B of the arm  234 . The implement interface  270  includes an implement carrier  272  that can accept and securing a variety of different implements to the lift arm  230 . Such implements have a machine interface that is configured to be engaged with the implement carrier  272 . The implement carrier  272  is pivotally mounted to the second end  234 B of the arm  234 . Implement carrier actuators  235  are operably coupled the lift arm structure  230  and the implement carrier  272  and are operable to rotate the implement carrier with respect to the lift arm structure. 
     The implement interface  270  also includes an implement power source  274  available for connection to an implement on the lift arm structure  230 . The implement power source  274  includes pressurized hydraulic fluid port to which an implement can be coupled. The pressurized hydraulic fluid port selectively provides pressurized hydraulic fluid for powering one or more functions or actuators on an implement. The implement power source can also include an electrical power source for powering electrical actuators and/or an electronic controller on an implement. The implement power source  274  also exemplarily includes electrical conduits that are in communication with a data bus on the excavator  200  to allow communication between a controller on an implement and electronic devices on the loader  200 . 
     The lower frame  211  supports and has attached to it a pair of tractive elements  242 A and  242 B. Each of the tractive elements  242 A and  242 B has a track frame that is coupled to the lower frame  211 . The track frame supports and is surrounded by an endless track, which rotates under power to propel the loader  200  over a support surface. Various elements are coupled to or otherwise supported by the track frame for engaging and supporting the endless track and cause it to rotate about the track frame. For example, a sprocket is supported by the track frame and engages the endless track to cause the endless track to rotate about the track frame. An idler is held against the track by a tensioner (not shown) to maintain proper tension on the track. The track frame also supports a plurality of rollers, which engage the track and, through the track, the support surface to support and distribute the weight of the loader  200 . 
     Display devices are provided in the cab 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. 
     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  FIG. 1  and more particularly on a loader such as skid-steer loader  200 , unless otherwise noted or recited, the concepts discussed below are not intended to be limited in their application to the environments specifically described above. 
       FIG. 4  is a side view of a portion, including a lift arm structure  330 , of a power machine  300 , which is another power machine on which disclosed embodiments can be implemented.  FIG. 5  illustrates a portion of the lift arm structure  330  of  FIG. 4 . In  FIG. 4 , frame  310  and lift arm structure  330  of power machine  300  are illustrated, while other power machine components are omitted to better illustrate certain features. In power machine  300 , lift arm structure  330  includes a pair of main lift arm portions  334 . Each of the main lift arm portions  334  includes a first portion  334 A and a second portion  334 B that is pivotally coupled to the first portion  334 A. The first portion  334 A of each main lift arm  334  is pivotally coupled to the frame  310  (which represents a first end  332 A of the lift arm  334 ) at one of the joints  316  and the second portion  334 B extends from its connection to the first portion  334 A to a second end  332 B of the lift arm  334 . The main lift arm portions  334  are each coupled to a cross member  336  that is attached to the first portions  334 A and to a cross member  335  that is attached to the second portions  334 B. 
     An implement carrier  372  is rotatably mounted, by a pivotal attachment  371 , to cast lower lift arm portions  339 . Although not necessarily a part of the power machine  300 , an implement  373  is shown mounted on implement carrier  372  for illustrative purposes. In an exemplary embodiment, implement  373  is a bucket type of implement for a loader type of power machine. 
     On each side of frame  310 , a lift cylinder or actuator  338  is pivotally attached to the frame at pivot attachment  338 A. The lift cylinder  338  is also pivotally attached at pivot attachment  338 B to the lift arm structure  330 . The first portion  324 A acts as a follower link and is pivotally attached at pivot attachment  316  to frame  310  and at pivot attachment  375 B to the second or main portion  334 B of the lift arm structure  330 . A driver link  380  is pivotally attached at pivot attachment  380 A to frame  310  and at pivot attachment  380 B to lift arm structure  330  (on the main or second portion  334 B). The driver link, the follower link, the frame of the loader and the rest of the lift arm provide a four-bar linkage arrangement for the lift arm assembly  330 . More detailed discussions of these various components are provided below with reference to  FIGS. 5-22 . 
     Lift Arm Structure 
       FIGS. 5-6  shows the lift arm structure  330  in greater detail.  FIG. 7  illustrates an embodiment of lower lift arm portion  339  that is formed from a casting in greater detail, and  FIG. 8  illustrates features of upper or main lift arm portion  334  and cast lower lift arm portion  339  at a junction  332  where the two lift arm portions are welded together. While some embodiments of lift arm structures may not have cast lower lift arms, the embodiment shown in  FIGS. 5-8  illustrate cast lower lift arms. Near the junction  332  between the respective main lift arm portions  334  and cast lower lift arm portions  339 , the lower lift arm portions  339  sloping downwardly more dramatically than the main portion from the main lift arm portions  334  (in some embodiments, the main lift arm portions need not slope downwardly) a “knee” is formed in exemplary embodiments. The term knee is used to describe the departure area between the main portion and the lower portion, even when, as is the case in the embodiment shown in  FIGS. 5-6 , there is no movable joint between the main lift arm portion and the lower lift arm portion. As shown in  FIGS. 5-6 , the two (left and right) cast lower lift arm portions  339  can have the same features, but can be mirror or reverse images of each other or at least substantially similar. While in this respect the cast lower lift arm portions may not be identical, a description of only one cast lower lift arm portion is provided below. Those of skill in the art will understand that the features discussed on one cast lower lift arm portion  339  can be implemented on a corresponding lower lift arm portion for the opposite side of the lift arm structure and that other features, not discussed herein may be present on one or the other without departing from the scope of this discussion. 
     Cast lower lift arm portions  339 , in this embodiment, have hollow interiors and several cast features that provide improvements over conventional lower lift arm portions that are formed from one or more pieces of steel welded or otherwise fastened together. For example, cast lower lift arm portions  339  are formed to include inward offset or bend regions  396  which taper the width of the lift arm structure  330  from a width which is wider than the frame of the power machine down to a width necessary for attachment of the implement carrier and any attached implement. Forming this laterally inward bend or offset using traditional methods requires the welding of multiple different individual metal plates or pieces, which causes manufacturing to be more expensive and complex, and introduces a large number of welds, which can fail under exposure to repeated high stresses. Using a cast lower lift arm portion or member, the laterally inward bend or offset  396  can be formed to narrow the lift arm structure without requiring additional metal pieces or welds. This simplifies manufacturing, and produces a stronger lower lift arm portion which is less prone to stress failures. Further, using a cast lower lift arm portion allows for tighter control of tolerances of the part shape and dimensions than can be reasonably be achieved by welding multiple pieces together. If such dimensions are not tightly controlled, they can result in configurations in which the tilt cylinder (not shown) can be over-extended or over-retracted and thereby damaged or other misalignments can introduce unwanted stresses into the lift arm. 
     In lift arm structure  330 , cast lower lift arm portions  339  include other features such as pivot attachment bores or apertures  390  for connecting the tilt cylinder (not shown) between lower lift arm portion  339  and the implement carrier  372  (shown in  FIG. 4 ), and pivot attachment bores or apertures  392  for the pivotal attachment of the implement carrier directly to the cast lower lift arm portion. Also, structural tube bores or apertures  394  are formed in the lower lift arm portions and configured to receive a structural tube  335  that is a cross-member that extends between respective left and right lower lift arm portions  339  to provide strength and stability by resisting torque and other forces introduced into the lift arm. 
       FIG. 7  provides a perspective view of a cast lower lift arm portion  339  according to one illustrative embodiment. Cast lower lift arm portion  339  includes features which strengthen the lift arm structure and allow for deformation of portions of the cast material to reduce stress on welds between the lower lift arm portion  339  and structural tube  335 , or between lower lift arm portion  339  and upper or main lift arm portion  334 . For example, cast lower lift arm portion  339  includes a boss  402  surrounding structural tube aperture  394  to facilitate cast material deformation to absorb load stresses and thereby prevent transfer of those stresses to welds between the structural tube and lower lift arm portion  339 . Also, lower lift arm portion  339  includes a contoured top end  405  which is configured to be received at least partially into a corresponding contoured bottom end  410  (shown in  FIG. 8 ) of the upper or main lift arm portion  334 , with the contoured ends joined at a junction  332 . The shapes of the contoured ends and resulting junction  332  control the placement of the highest tension and compression stress points to reduce stress on welds between the upper and lower lift arm portions. 
     Referring more specifically to  FIG. 8 , contoured bottom end  410  of upper or main lift arm portion  334  is sleeved over part of contoured top end  405  of cast lower lift arm portion  339 . A weld is placed in a channel  415  (the weld is not shown in  FIG. 8 ) formed between contoured ends  405  and  410  of cast lower lift arm portion  339  and upper or main lift arm portion  334 . The shapes of the contoured ends of lift arm portions  339  and  334  are designed to control the location of the highest tension (under load) point between the upper and lower lift arm portions, and the highest compression (under load) point between the two lift arm portions. For example, with the contour illustrated in  FIG. 8 , point  420  represents an example of the highest tension point, while point  425  is an example of the highest compression point. To control the location of these points, and to provide for regions of controlled deformation of one or both lift arm portions  334  and  339 , a protruding kink section  430  is formed by the contoured top end  405  of the cast lift arm portion  339 . A corresponding inlet kink section  435  is formed in the contoured bottom end  410  of upper or main lift arm portion  334  and is configured to receive the protruding kink section  430 . This configuration forms a top extending member  440  of the upper or main lift arm portion  334 , with the top extending member  440  extending further toward the knee region of lower lift arm portion  339  than other parts of the upper or main lift arm portion  334 . A bottom extending member  445  is also formed by the contoured bottom end  410  of the upper or main lift arm portion  334  and is separated from top extending member  440  by inlet kink section  435 . In this configuration, with top extending member  440  extending further than bottom extending member  445 , the top extending member is configured to bend, deflect or deform slightly under heavily loaded conditions to absorb stresses and thereby reduce the stresses on weld  415 . 
     Implement Carrier Structure 
       FIGS. 9-12  illustrate one embodiment of a cast implement carrier plate  500  of implement carrier  372  shown in  FIG. 4 .  FIGS. 13-14  are perspective view illustrations of implement carrier  372 , which includes two cast implement carrier plates  500  coupled together with a structural tube  510  that is a cross-member welded to each plate  500 . Each cast implement carrier plate  500  is configured to be pivotally attached or coupled to a different one of the pair of lower lift arm portions  339  of the lift arm structure at respective pivot attachments  371  discussed above and as shown in  FIG. 15 . The two (left and right) cast implement carrier plates can have the same features, but can be mirror or reverse images of each other. While the cast implement carrier plates may be mirror images of each other instead of identical, a description of only one implement carrier plate is shown in  FIGS. 9-12  and discussed herein for brevity&#39;s sake. In some embodiments, each of the left and right cast implement carrier plates may have features that differ from the other that are not discussed herein. None of those differences will cause the implement carrier plates to depart from the scope of this discussion. 
     As shown best in  FIGS. 9-12 , each cast implement carrier plate  500  has a rear or power machine side  520  and an opposing front or implement interface side  530 . The implement interface side  530  is configured to directly interface the implement (in other words, the casting itself is positioned directly against the implement). On rear side  520 , each plate  500  has bores or apertures  540  for pivot attachment  371  (shown in  FIG. 4 ) to pivotally attach the cast plate to lower lift arm portions  339 . On the same rear side, each plate also includes bores or apertures  545  for pivot attachments between a tilt cylinder (not shown) and the cast plate to control tilt functions for an implement mounted on the implement carrier  372 . On an inside end of each of the cast implement carrier plates, a structural tube or cross-member receiving collar  550  is included in the casting. Further, each structural tube receiving collar has side apertures  555  formed therein to allow for welds  560  (shown in  FIGS. 13-14 ) and for improved deformability of collars  550  to absorb stress forces on the implement carrier plate  500 . By allowing deformation of the cast implement carrier material in the region of collar  550 , stress forces on welds  560  and  565  between the collar and the structural tube  510  are reduced. 
     Carrier plate  500  has a tilt stop machined surface  570  configured to contact the lower lift arm portion  339  or other stop surface to prevent further movement (in one direction) of the implement carrier relative to the lift arm portion. Surface  570  is machined onto the cast implement carrier plate to tightly control the maximum degree of extension of the tilt cylinder to prevent damage to the cylinder due to over-extension. Also, other surfaces of carrier plate  500  can be machined after casting to closely control dimensions and tolerances. For example, bores  540  and  545  can be machined, as can the aperture within collar  550 . 
     After casting carrier plate  500  and machining any necessary surfaces, the implement locking mechanisms can be added to the carrier plate. For example, as shown in  FIGS. 13 and 14 , levers  580 , spring mechanisms  585 , and locking pins  590  can be added. These locking components are used for locking an implement into its position mounted on the implement interface side  530  of the cast plates  500 . 
     Follower Link Structure 
       FIGS. 16-17  show partial rear and rear perspective views of power machine  300  illustrating follower links  375  in accordance with some exemplary embodiments.  FIG. 18  illustrates the follower links  375  and structural tube  610  that is a cross-member separate from the power machine  300 . In some embodiments, follower links  375  are formed as single pieces using a casting technique. In other embodiments, follower links can be otherwise constructed. 
     The follower links  375  include a structural tube (or cross-member) receiving collar  630  and an extension member  640  which extends from the collar  630  down to a pivot bore  650  used to provide the pivot attachment  375 A (also referred to as pivot  316  on  FIG. 4 ) to upright portions  615  of frame  310 . The extension member has a first portion  641  which is at least partially in-line with a main portion of the lift arm structure of the power machine when viewed from directly behind the power machine and a second portion  642  positioned outward from the first portion such that the link casting lift arm attachment point is outside of the lift arm structure. The first portion  641  can be angled outward to transition between positions which are in-line with the main portions of the lift arm and positions which are outward. By positioning the follower link outside of the main lift arm portion, visibility from an operator compartment rearward is advantageously improved. The structural tube  610  extends between the collar  630  of each of the follower links  375 . The collar  630  allows the follower link material to twist or deform to reduce the stress on the weld between the structural tube and the follower link. As shown in  FIG. 17 , a pivot attachment  375 B couples the lift arm structure  330  to the follower link  375 . 
     Using a cast material for follower links  375  provides numerous advantages. For example, using a casting allows close control of dimensions and tolerances between the lift arm pivot bore  650  and the pivot bore in collar  630 . It also allows material to be removed from the follower link casting, while at the same time making the follower link stronger due in part to less usage of welds. As can be seen in  FIG. 16 , extension members  640  of follower links  375  are positioned outside of upper or main lift arm portions  334  from collar  630  at least part of the way toward the pivotal attachments of the follower links to the upright portions  615  of the power machine frame. This provides improved rear visibility for an operator of the power machine. 
     Driver Link Structure and Path 
       FIGS. 19-21  illustrate portions of the power machine  300  with the lift arm structure in various states of being raised, by lift cylinder  338 , relative to the fully lowered state shown in  FIG. 4 . Of particular importance, power machine  300  is configured such that the paths of the driver link  380  and lift cylinder  338  can allow these components to be placed in close proximity to each other and to the frame  310 , without the driver link  380  contacting the lift cylinder  338 . The driver link  380  and follower link  375  are configured such that when the driver link pivot attachment  380 B to the lift arm structure  330  crosses the lift cylinder  338 , the pivot attachment  380 B is above the uppermost or top position  660  of the base of the lift cylinder. Pivot attachment  380 A is positioned behind a rear axle of the loader as is shown in  FIG. 19 . 
     The driver link is configured such that the main lift arm portion pivot attachment  380 B follows a movement arc that moves above the top  660  of the lift cylinder body as the main lift arm portion is raised and lowered by the lift cylinder.  338 . In some embodiments, when the main lift arm portion is in a fully lowered position, the main lift arm portion pivot attachment  380 B of the driver link is positioned rearward of the top  660  of the lift cylinder body, but when the main lift arm portion is in a fully raised position, pivot attachment  380 B is positioned forward of the top of the lift cylinder body. In addition, the main lift arm portion pivot attachment  380 B is positioned behind and above the pivot attachment  380 A throughout its travel path from a fully lowered position (as is shown in  FIG. 19 ) to a fully raised position (as is shown in  FIG. 21 ). 
     As can be seen in  FIG. 4 , when the lift arm structure  330  is down and the lift cylinder  338  is fully retracted, the pivot attachment  380 B is below the top  660  of the base of the lift cylinder. As the lift cylinder is extended ( FIGS. 19-21 ) to raise the lift arm, the pivot  380 B is higher than the top  660  of the lift cylinder base when the pivot passes (inward of) the lift cylinder. This configuration allows these components to be placed closer together and doesn&#39;t require widening of the power machine.  FIG. 22  shows the pivot  380 B having an outermost surface  670  at a positon laterally from the frame  310  of the power machine that would interfere with the inner most surface  680  of the base of the lift cylinder  338 , but which is positioned to be above the top  660  of the base of the lift cylinder when the pivot  380 B passes near the lift cylinder. In some embodiments, the maximum distance between the driver link  380  and the frame is greater than the minimum distance between the tilt cylinder and the frame, while at least a portion of the driver link is positioned between the tilt cylinder and the frame. Stated another way, a portion of the driver link  380  extends beyond the closest position of the lift cylinder  338  relative to the frame. As shown in  FIG. 22 , the driver link  380  has a clevis  384  on an end at which the driver link is coupled to the lift arm. The clevis end allows a main portion  382  the driver link to be narrow so as to be positioned closer to the frame of the machine. 
     Although the present disclosure has been described by referring to various embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the disclosure.