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BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a self-propelled vehicle having a front lift arm assembly. More particularly, the present invention relates to a work machine with a lift arm assembly having a boom stop thereon.  
         [0002]     A wheeled work machine includes a frame attached to an operator compartment such as a cab. A cargo support is attached to the frame behind the cab. A lift arm assembly is attached to the frame generally in front of the cab and centered on a longitudinal center line of the work machine. The lift arm assembly is movable with respect to the frame and can be attached to one or more work tools such as a bucket. The wheeled work machine is suited for use as a utility vehicle for various tasks.  
         [0003]     Many loaders include boom stops to render a raised lift arm assembly inoperable. One example of a boom stop is disclosed in U.S. Pat. No. 5,009,566. The lift arm includes a hydraulic cylinder having a cylinder body attached to the frame of the skid steer loader and an extensible rod attached to the lift arm assembly. When the rod is fully extended from the cylinder body, the boom stop is positioned between the cylinder body and the lift arm assembly, thus preventing the rod from retracting into the cylinder body.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention is directed to a self-propelled, wheeled work machine having a lift arm assembly pivotably coupled to a front of a frame assembly at a frame pivot. The lift arm assembly includes a pair of spaced-apart lift arms and an extensible lift cylinder. The lift arms are relatively close together so the lift arm assembly is positioned in center portions of the frame. The lift cylinder is pivotably coupled to the lift arms at a lift cylinder connection pivot, and is pivotably coupled to the frame assembly such that extension of the lift cylinder moves the lift arms with respect to the frame assembly about the frame pivot.  
         [0005]     A boom stop is pivotably coupled to the lift cylinder connection pivot. The boom stop is movable from an inoperable position adjacent to and retained with the lift arms, to an operable position wherein an end of the boom stop engages the frame assembly and prevents lowering the lift arms with respect to the frame assembly. The boom stop is releasably held with a latch coupled to one of the lift arms. The latch includes a bracket on the boom stop having a retractable pin resiliently urged into an engaged position. In the engaged position, the pin engages a bracket on the one lift arm to hold the boom stop in the inoperable position.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a side elevation view of a work machine constructed in accordance with the present invention;  
         [0007]      FIG. 2  is a fragmentary side elevation view of a portion of a work machine frame with a lift arm assembly in a lowered position with respect to the frame;  
         [0008]      FIG. 3  is a side elevation view of the lift arm assembly in a raised position with respect to the portion of the frame shown in  FIG. 2 ;  
         [0009]      FIG. 4  is a perspective view of a portion of the lift arm assembly shown in  FIGS. 2 and 3 ;  
         [0010]      FIG. 5  is a plan view of the lift arm assembly shown in  FIG. 4 ;  
         [0011]      FIG. 6  is a plan view of a portion of the lift arm assembly shown in  FIG. 5 ; and  
         [0012]      FIG. 7  is an enlarged side view of a portion of the side view of  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]      FIG. 1  is side elevation view of an exemplary work machine  10 . The work machine  10  includes a frame  12  supported with front and rear wheel assemblies  14 ,  16  respectively. The frame  12  is attached to a cab  18  that defines an operator compartment  20  having an operator platform, and a seat  22 , and operator controls  24 . The work machine also includes an engine, not shown, typically disposed between the seat  22  and the rear wheel assembly  16  and attached to the frame  12 . The frame  12  also is connected to a cargo support  26 , which is disposed behind the seat  22  in the example. A lift arm assembly  28  is positioned in front of the seat  22  and attached to the front portion of frame  12 . The lift arm assembly  28  is adapted to receive a removable tool  30 , such as a bucket  32  shown in  FIG. 1 .  
         [0014]     In a typical example, the frame  12  is a rigid frame assembly that provides generally no frame articulation between the front and rear wheel assemblies  14 ,  16 . The frame  12  is illustrated as including longitudinal members  34  extending from the front wheel assembly  14  toward the rear wheel assembly  16 . The frame includes a cargo support portion  36 , a middle portion  38 , and a lift arm support portion  40 . The lift arm support portion  40  is particularly strengthened to resist bending or twisting from loads carried with lift arm assembly  28 . The middle portion  38  is adapted to provide a stable mount for the cab  18  and can be suited to accommodate a transverse mounted engine.  
         [0015]     The engine can power either or both of the wheel assemblies  14 ,  16  to move the work machine  10 . The engine is connected to one or both of the wheel assemblies  14 ,  16 , with mechanical drives, hydraulic motors or other suitable devices for power transmission. In the illustrated embodiment, hydraulic drive motors are used to drive the wheels. The wheel assemblies  14 ,  16  can include suspension systems coupled to the frame  12 . A steering linkage can be coupled to the front wheels, rear wheels, or both. In the illustrated embodiment, the wheels are steered using hydraulic cylinders. Controls  24  for the operation of the work machine  10  are mounted in the operator compartment  20 .  
         [0016]     The cab  18  defines the operator compartment  20 . The cab  18  in the example includes a canopy  42  and lights  44 . A windshield, windows and doors can also be provided, if desired. The operator compartment  20  includes an instrument cluster and dash  46  generally disposed in front of the seat  22 , and includes gauges, controls and the like useful for comfort of the operator and operation of the work machine  10 . The seat  22  can include one or more bucket seats or a common bench seat for two or more riders.  
         [0017]     More detailed descriptions of a work machine, such as the exemplary work machine  10 , are found in U.S. Patent Application Publication No. 2003073400; and also in U.S. Pat. No. 6,729,830, which are both incorporated by reference into this disclosure.  
         [0018]      FIG. 1  also shows the lift arm assembly  28  connected to the lift arm support portion  40  of the frame  12 . The remote end of the lift arm  28  can be connected to an interface  48  that provides attachments to various tools  30 . Such tools  30  can include buckets, grapples, brooms, augers or other tools. The lift arm assembly  28  is coupled to the frame  12  in such a manner that it can be moved with respect to the frame  12 . Movement of the lift arm assembly  28  is effected through the use of hydraulic actuators that receive power from the engine.  
         [0019]      FIG. 2  is a more detailed view of the lift arm assembly  28  as coupled to the frame  12 . The lift arm assembly  28  is coupled to a mast assembly  50  that is included in the lift arm support portion  40  of the frame  12 . The mast assembly  50  includes a pair of opposing side mast plates  52 A and  52 B (shown in the elevation view of  FIGS. 3, 4  and  7 ). A cross member  54  is attached to and extends between the side mast plates  52 A and  52 B, and a pair of spaced brace plates  56 A and  56 B ( FIG. 7 ) that are positioned to the inside of the side mast plates  52 A and  52 B. The brace plates  56 A and  56 B are suitably braced to support a tilt cylinder  72  at upper end portions  57 A and  57 B of the brace plates  56 A and  56 B.  
         [0020]     The lift arm assembly  28  is pivotably movable with respect to the mast assembly  50 . The lift arm assembly  28  includes a lift cylinder indicated generally at  58  positioned between the brace plates  56 A and  56 B, with the cylinder base supported at a pivot  60 . Lift arms  62 , which are joined together with cross members, are pivoted between the mast plates  52 A and  52 B. The lift arms  62  are also pivotably coupled to the rod end of lift cylinder  58  at a connection  66 . The remote or outer ends of the lift arms  62  have a tilt link  68  connected thereto at pivot  70 . Tilt cylinder  72  is coupled to upper ends  57 A and  57 B of the spaced brace plates  56 A and  56 B at tilt cylinder pivot  74 , the rod end of tilt cylinder  72  is connected to the tilt link  68  at tilt cylinder connection pivot  76 . The tilt link  68  is pivotably coupled to a connector link  78 .  
         [0021]     The connector link  78  and the remote ends of the lift arms are adapted to be coupled to a tool. In one example as described above, the lift arms  62  and links  78  are coupled to an attachment plate  48  that can be used to support one of several tools. Other examples include the lift arms and links being connected to quick exchange brackets or the lift arms and links may be connected directly to the tool with pin connections.  
         [0022]     In the example shown, the lift cylinder  58  and tilt cylinder  72  are hydraulic cylinders and each includes a body or cylinder portion and an extensible rod. The lift cylinder body portion  86  is shown in  FIG. 2  coupled to the mast frame assembly  50  and the extensible rod  84  is coupled to the lift cylinder connection  66 . The tilt cylinder body portion is shown in Figures coupled to the mast frame assembly  50  and the extensible rod  84  coupled to the link  68 . Other configurations are possible. The cylinders  58  and  72  are actuated with operator controls and are powered by the engine.  
         [0023]      FIGS. 2, 3  and  7  also show a lift arm or boom stop  80  having one end pivotably coupled to the rod end pivot  66  of  58 . A latch assembly  82  retains the outer end of the boom stop  80  relative to one lift arm. The lift arm or boom stop  80  is held by the latch assembly  82  in a first, stored or inoperative position, with the boom stop  80  generally extending along the length of the lift arm assembly  28 . The lift arm or boom stop  80  is shown coupled to the latch assembly  82 . The boom stop  80  in the first stored position does not interfere with the operation of the lift arm assembly  28  and the tool  30 .  
         [0024]      FIGS. 3 and 7  show the lift arms  62  (and thus lift arm assembly) in a raised position with respect to the frame assembly  50  lift cylinder. Rod  84  is extended from the body  86  of the lift cylinder  58  to place the lift arms  62  in the raised position. The lift cylinder  58  can be controlled to extend the rod  84  from the body  86  and thus vary the height of the lift arms  62 .  FIGS. 3 and 7 , however, show the lift arms  62  in a generally fully raised position.  
         [0025]     The lift arm or boom stop  80  is also shown disposed in a second, or operative, position in  FIGS. 3 and 7 , positioned to prevent downward movement of the lift arm assembly  28 . In the second position, the latch assembly  82  is released and the outer or remote end  80 A of the boom stop moves down as the boom stop pivots about the lift cylinder connection pivot  66 . The remote end  80 A of the boom stop  80  seats against the offset portion  55  of cross member  54  between the side plates  52 A and  52 B, or other sturdy member or portion of the frame assembly  50 . If the lift cylinder  58  is slightly retracted, the boom stop  80  becomes wedged or otherwise secured in the offset portion  55 , and this prevents further retraction of the lift cylinder  58  or downward movement of the lift arm assembly until the lift arm assembly is raised.  
         [0026]     The boom stop is stopped right on the vehicle frame, so the boom stop has a large area to rest upon, and the boom stop does not extend along the lift cylinder rod. The boom stop is independent from the lift cylinder. The offset portion  55  also tilts upwardly slightly to retain the boom stop  80  positively. The remote end of the boom stop is trimmed at a mating angle.  
         [0027]     Extension of the lift cylinder  58  permits manual removal of the remote end of the boom stop  80  from the raised outer edge of the offset frame portion  55 . The lift arm assembly is raised sufficiently to provide clearance. The boom stop  80  then can be manually placed in the first stored or inoperative position again and latched in place with latch assembly  82 .  
         [0028]      FIGS. 4 and 5  show additional views of the pair of lift arms  62 , boom stop  80 , and latch assembly  82 . In the example shown, the boom stop  80  is mounted between the pair of lift arms  62  and is formed out of a U-shaped bar or strut for strength. The boom stop  80  includes a connection plate  88  that is a portion of the latch assembly  82 . The latch assembly  82  in the example includes an S-shaped bracket  90  attached to one of the lift arms  62  and containing a spring-loaded pin  92 . The spring-loaded pin  92  includes a spring  93 , a handle  94  that extends through slot  96  in the S-shaped bracket  90 , and a tip or end  95  that projects from an end wall of bracket  90  and will fit into a hole  102  provided in the connection plate  88  to retain the boom stop  80  in the first inoperative or stored position.  
         [0029]     The pin  92  is resiliently urged to an engaged position  98 , and is movable from the engaged position  98  of the handle to a disengaged position  100 . In the engaged position  98 , also shown in  FIG. 6 , the tip  95  of the pin  92  extends through hole  102  on the connection plate  88 . The spring  93  holds the pin  92  in place and secures the boom stop  80  in the first position and along the lift arms  62 . The pin  92  also carries a keeper  104  for the spring  93  to retain the spring  93  in position on the pin  92 . In one example, the keeper  93  is a snap ring. When the handle  94  is pulled toward the disengaged position  100 , the spring  93  is compressed between the keeper  104  and a middle bar  106  of the S-shaped bracket  90 . The pin  92  slides out of the hole  102  of the connection plate  88 , and the boom stop  80  is decoupled from the bracket  90  of the latch assembly  82 .  
         [0030]     When the handle  94  is released the spring  93  urges the tip  95  away from the bracket  90  and the latch assembly  82  is ready for coupling to the boom stop  80 . The connection plate  88  includes an angled lip portion  108  that guides the tip  95  of the pin  92  back into the hole  102  as the boom stop  80  is moved into the first position. The tip  95  slides along the lip  108  and then extends through the hole  102  to lock the boom stop  80  into the first position. The connection plate  88  in the example also includes a resilient bumper  110  that mates with a resilient button  112  attached to the bracket  90 . The resilient material for the bumper  110  and button  112 , such as rubber or another elastomeric material serves to prevent the boom stop  80  from rattling during operation of the machine  10 . In another example, the connection plate  88  can be attached to one of the lift arms and the bracket  90  and spring would be attached to the boom stop.  
         [0031]     The boom stop latch assembly  82  can be released to drop the remote end down and the boom stop will pivot as the lift arm assembly is raised. The remote end of the boom stop  80  will slide along the raised front edge of offset portion  55  until the edge of the tapered end  80 A of the boom stop  80  is over the front edge of the offset section  55 . The remote end then swings to the position of  FIGS. 3 and 7  under gravity against a vertical frame section  55 A as the lift arms are raised. When the lift arms are lowered, the cooperating tapered end  80 A will seat securely on the tilted upper surface of offset frame portion  55 . The boom stop cannot be manually moved back to its stored or inoperative position until the lift arms are raised again sufficiently to provide clearance for pivoting the boom stop upwardly.  
         [0032]     Although the present invention has now been described with reference to preferred 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 invention.

Summary:
A work machine has a lift arm assembly pivotably coupled to a frame assembly at a forward frame pivot. The lift arm assembly includes a pair of spaced-apart lift arms and an extensible lift cylinder. The lift cylinder is pivotably coupled to the lift arms at a lift cylinder connection pivot. The lift cylinder is pivotably coupled to the frame assembly such that extension of the lift cylinder moves the lift arms with respect to the frame assembly about the frame pivot. A boom stop is pivotably coupled to the lift cylinder connection pivot. The boom stop is movable from an inoperable position with a remote end adjacent the lift arms to an operable position wherein the boom stop engages the frame assembly and prevents lowering movement of the lift arms with respect to the frame assembly. The lift arm assembly also can include a latch assembly coupled to one of the lift arms for holding the boom stop in the inoperable position.