Abstract:
The present invention relates to a forklift having a traversing carriage for moving longitudinally along a frame of the forklift, an outer guide rail for guiding the carriage being disposed relatively low to the operator cockpit so as to minimize the obstruction of operator visibility of the surrounding terrain.

Description:
This application is a continuation of U.S. Patent application Ser. No. 09/882,009, filed on Jun. 15, 2001, now abandoned which is a continuation-in-part of U.S. Patent application Ser. No. 09/286,152, filed Apr. 5, 1999, entitled “High Visibility Rough Terrain Forklift with Tight Turning Radius and Extensible Boom,” now abandoned, and claims priority to Provisional Patent Application No. 60/232,786, filed Sep. 15, 2000, hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a traversing boom system. More particularly, the present invention relates to a traversing boom system for a forklift providing a high degree of operator visibility. 
     BACKGROUND OF THE INVENTION 
     Forklifts have long been known in the construction industry and typically comprised a frame having a front and rear set of opposing wheels, an engine and drivetrain, an operator cockpit, and a load handling attachment at the end of a boom. Forklifts having a high level of maneuverability were usually preferred for the transport and placement of loads in and around construction sites. The typical construction site also required, for safe and efficient operation, that a forklift provide its operator with a high level of visibility of the terrain surrounding the forklift. Such a forklift is described in application Ser. No. 09/286,152 which is incorporated herein by reference and of which this application is a continuation-in-part. Operator visibility of the terrain surrounding a forklift was crucial to avoid injury to personnel working thereabout and to avoid damaging nearby structures, waterlines or electrical lines. When provided with a high degree of visibility of the surrounding terrain, an operator could quickly and efficiently operate the forklift with confidence it was being done safely. 
     Prior to transporting a load, a forklift operator would usually engage the load with the load handling attachment at the end of the boom, lift the load from the surface upon which it rested by elevating the boom, and adjust the boom and load to a transport configuration. The transport configuration positioned the load at a sufficient distance from the ground to ensure that neither the load nor the load handling attachment of the boom would inadvertently encounter the ground during transportation. The load elevation varied according to the terrain and would necessarily be greater when the terrain was rough than when the terrain was relatively even. Stability dictated, however, that the load not be positioned too far above the forklift center of gravity. Other aspects of the environment in which the forklift was used also limited the elevation of the load in the transport configuration. For example, a forklift employed to move a load from a construction site into a building might have been required to pass through a doorway. At that time, the vertical elevation of the boom, load handling attachment or load could be no higher than the vertical opening of the doorway. 
     Forklifts having a variable reach or extensible boom were also well known in the construction industry. An extensible boom was usually pivotally connected to the forklift&#39;s frame, at, for example, a rearward portion thereof, and extended forward over the frame. The operator cockpit was typically mounted at the side of the frame between the front and rear wheels. The engine was often placed at the side of the frame opposing the operator cockpit or at the rear of the frame adjacent to the pivotal connection between the boom and the frame. As known to those of ordinary skill in the art, the extensible boom was employed to facilitate the handling of a load at a location to which the forklift could not travel. For example, placement or retrieval of a load on a second or higher floor of a building could require the forklift operator to elevate and extend the boom to place or retrieve the load. 
     Alternatively, some forklifts have mounted the boom pivot to a traversing boom carriage capable of travelling along portions of the forklift length rather than being pivotally mounted directly to the forklift&#39;s frame in a fixed manner. Traversing boom carriages typically employed a hydraulically controlled boom carriage mounted to a pair of parallel rails that enabled the boom carriage, and thus the boom attached thereto, to traverse the rails longitudinally towards the front or rear of the forklift frame. 
     As is known to one of ordinary skill in the art, traversing boom carriages were employed to increase the load handling ability of a forklift. For example, delivery of a load to the second or higher floor of a building with a fixed boom-pivot required raising the boom to the necessary angle, extending the boom to the approximate desired length to positioning the load handling device adjacent to the delivery area and then performing an iterative process involving adjusting the length and height of the boom to transport the load laterally to the desired position while maintaining the load of a constant elevation. A traversing boom carriage eliminated this iterative process by allowing the forklift operator to position the load adjacent to the delivery area and simply causing the boom carriage to traverse forward to locate the load in the delivery area. The traversing carriage provided a simple manner of obtaining lateral movement of the load while maintaining it at a relatively constant elevation. 
     The traversing carriage of the traversing boom type forklift added a new factor to the transport configuration of forklifts. As known to those skilled in the art, the boom carriage was typically positioned at or near its rearward most position at the rear of the forklift frame for stability. However, the guide rails along which the carriage traveled, as well as the carriage itself, obstructed the forklift operator&#39;s view of the terrain on the side of the forklift opposite the operator&#39;s cockpit when the forklift was in the transport configuration. The outermost guide rails and the carriage became the limiting factors of operator visibility of that terrain. 
     SUMMARY OF THE INVENTION 
     It is one of the principal objectives of the present invention to provide a rough terrain forklift that provides optimum terrain visibility to an operator. 
     It is another objective of the present invention to provide a forklift having a boom pivotally mounted on a traversable carriage and an engine mounted between frame rails. 
     It is still another objective of the present invention to provide a forklift having a low overall profile and optimum terrain visibility to an operator. 
     It is yet another objective of the present invention to provide a forklift having a traversing boom carriage. 
     It is another objective of the present invention to provide a forklift having a traversing boom carriage mounted on guide rails that facilitate optimum operator visibility of the terrain surrounding the forklift. 
     It is an additional objective of the present invention to provide a forklift having a traversing boom carriage mounted on a pair of guide rails, one or both of which are located low on the forklift to facilitate optimum operator visibility of the terrain surrounding the forklift. 
     It is a further objective of the present invention to provide a forklift having a pair of boom carriage guide rails, the outer one of the guide rails being lower than the inner guide rail. 
     It is yet another objective of the present invention to provide a traversing boom carriage for a forklift having the outer one of a pair of legs longer than the inner one of the pair of legs to accommodate a vertical offset of a pair of corresponding guide rails on the forklift. 
     It is still another objective of the present invention to provide a traversing boom forklift in which the carriage is guided by a single set of guide tracks. 
    
    
     These and other objectives of the present invention will become apparent upon review of the attached written description including the figures and claims. 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of one embodiment of the forklift of the present invention with a traversing boom carriage in a rearward position and showing, in phantom, the boom carriage in a forward position. 
     FIG. 2 is a perspective view of one embodiment of the traversing boom carriage of the present invention. 
     FIG. 3 is a left side elevational view of the traversing boom carriage depicted in FIG.  2 . 
     FIG. 4 is a front side cross-sectional view of one embodiment of the guide rails of the present invention and an elevational view of the carriage of the present invention mounted therein. 
     FIG. 5A is a front side elevational view of one embodiment of the forklift of the present invention with the frame and guiderails in cross-section to illustrate the operator&#39;s line of sight over the frame to the terrain adjacent to the carriage guide rails as well as the operator&#39;s line of sight if the outer guide rails were of equal elevation to the inner guide rail as with prior art traversing boom guide rails. 
     FIG. 5B is a broader view of the illustration of FIG. 5A indicating the increased view of the terrain provided by the embodiment of the present invention depicted in FIG.  5 A. 
     FIG. 6 is a right side elevational view of one embodiment of the forklift of the present invention with the boom carriage in a rearward position. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a perspective view of a forklift  10  representing one embodiment of the present invention. As shown in FIG. 1, the forklift  10  comprises a mainframe  12  with a front set of wheels  14  and a rear set of wheels  18  coupled to a front axle  22  and a rear axle (not shown) respectively. An engine  26  (see FIG. 5) and drivetrain (not shown) are located between a left frame rail  28  and a right frame rail  30  of the mainframe  12  to deliver power to the front  22  and/or rear (not shown) axles. An engine casing (not depicted) may enclose the engine  26  to protect the engine  26  from foreign objects and to protect the operator from injury. A cockpit  32  is mounted to the left frame rail  28  of the mainframe  12  for housing an operator  88  (See FIG.  5 ). Additionally, the cockpit  32  houses controls (not shown) known to one of ordinary skill in the art for operating the various mechanical features described herein. 
     A load handling device  34  is pivotally mounted to a first end  36  of a boom  38 . Other handling devices, such as a loading fork, bucket, crane hook, or other load handling device known in the art, may be employed with the present invention. The boom  38  shown in FIG. 1 is a telescoping extensible boom. The boom  38  may alternatively be a fixed length boom, or other boom known in the art. The load handling device  34  is selectively tiltable using a hydraulic load handling cylinder (not shown) as is known to those skilled in the art. 
     A second end  42  of the boom  38  is pivotally mounted to a boom carriage  44 . Two hydraulic boom cylinders  46  are connected between the boom  38  and the boom carriage  44  along either side of the boom carriage  44 . The hydraulic boom cylinders  46  operate to raise and lower the boom first end  36 . As the hydraulic boom cylinders  46  extend to raise the boom first end  36  the load handling cylinder may contract to maintain the load handling device  34  level to the ground. Similarly, as the hydraulic boom cylinders  46  contract to lower the boom  38 , the load handling cylinder may extend to maintain the load handling device  34  level to the ground. The load handling cylinder may be extended or contracted independent of the hydraulic boom cylinders  46 . 
     The embodiment depicted in FIG. 1 is a rough terrain forklift  10  allowing a tight turning radius, having a low profile, a centrally mounted engine  26  and drivetrain and the mainframe  12  as described in application Ser. No. 09/286,152. Additionally, the pivotal mount of the boom  38  is elevated from the mainframe  12  to provide the operator  88  of the forklift  10  with optimum visibility of the terrain surrounding the forklift  10  as described in application Ser. No. 09/286,152. The boom carriage  44  and rail configuration of the present invention can be employed with any type of boom, hydraulic system, or frame configuration. 
     FIGS. 2 and 3 illustrate one embodiment of the boom carriage  44  of the present invention. The boom carriage  44  has a left side plate  48  and a right side plate  50 . The side plates  48 ,  50  are each affixed one to the other by a top brace  52  and a diagonal brace  54  which extend therebetween. The carriage depicted in FIG. 1 shows top and diagonal braces  52 ,  54  of different configurations than those depicted in FIG.  2 . Other configurations will become evident to one of ordinary skill in the art. The braces  52 ,  54  can be affixed to the side plates  48 ,  50  by any other manner known in the art. The side plates  48 ,  50  each provide a boom pivot  56 ,  58  respectively, for rotatably mounting the boom  38  thereto as well as hydraulic support portions  60 ,  62  respectively, for attaching the hydraulic boom cylinders  46  thereto. Mounting of the boom  38  and hydraulic boom cylinders  46  to the boom carriage  44  may be accomplished in any manner known to those of ordinary skill in the art. 
     Each side plate  48 ,  50  comprises a guide track engaging portion, which in FIG. 2 comprises rollers  63 ,  64 ,  65 ,  66  rotatably mounted thereto. The carriage right side plate  50  is provided with a front roller  63  and a rear roller  64 . The carriage left side plate  48  is provided with a front roller  65  and a rear roller  66 . The rollers  63 ,  64  attached to the carriage right side plate  50  may be referred to herein collectively as the outer rollers  63 ,  64  (indicating the outermost relationship of the rollers  63 ,  64  with respect to the operator) and the rollers  65 ,  66  attached to the carriage left side plate  48  may be referred to herein collectively as the inner rollers  65 ,  66  (indicating the innermost relationship of the rollers  65 ,  66  with respect to the operator  88 ). Other guide track engaging portions consistent with the principles set forth herein are contemplated. 
     As shown in FIG. 3, the carriage right side plate  50  is longer than the carriage left side plate  48  so that it extends farther below the top brace  52  so as to vertically offset the outer rollers  63 ,  64  below the inner rollers  65 ,  66 . In one embodiment, the outer rollers  63 ,  64  are vertically offset approximately 4.5 inches below the inner rollers  65 ,  66 , as measured from their respective axes of rotation. That is, the outer rollers  63 ,  64  are located approximately 4.5 inches farther below the top brace  52  than are the inner rollers  65 ,  66 . As described more fully below, the outer rollers  63 ,  64  engage an outer guide track  83  and the inner rollers engage an inner guide track  81  to guide the carriage  44  as it traverses the forklift  10 . 
     In one embodiment, the overall length of the boom carriage  44  has a relatively shorter length than previous carriages, enabling the boom carriage  44  to be further removed from an operator&#39;s view when in a rearward position such as when configured for travel as depicted in FIG.  6 . In one embodiment, the boom carriage  44  is approximately 83 inches long, as measured from the centerline of the front left roller  65  to the centerline of the rear left roller  66 . According to well known principals of physics, shortening the length of the boom carriage  44  increases the loads experienced by the rollers  63 ,  64 ,  65 ,  66  due to the moment created by the weight of the load and the boom  38 . The shorter carriage length reduces the moment arm of the boom carriage  44 , which increases the amount of force exerted on the rollers  63 ,  64 ,  65 ,  66  and, therefore, the guide tracks  81 ,  83 . In one embodiment, the increased loads are partially sustained by using larger diameter rollers  63 ,  64 ,  65 ,  66  than previous designs. For example, the rollers  63 ,  64 ,  65 ,  66  are approximately 5⅞ inches in diameter in one embodiment. The rollers  63 ,  64 ,  65 ,  66  may utilize roller bearings, as opposed to the bronze bushings used in past designs, to help compensate for the increased loading caused by the shortened boom carriage  44  of this embodiment. Other carriage lengths and roller diameters, consistent with the principals set forth herein, are contemplated. 
     As shown in FIG. 4, the left frame rail  28  comprises an inner guide rail  68  and the right frame rail  30  comprises an outer guide rail  70 . The terms inner and outer are again used with reference to the cockpit  32  and the operator  88  therein. The outer guide rail  70  is vertically offset from the inner guide rail  68  to accommodate the offset between the outer rollers  63 ,  64  and the inner rollers  65  and  66 . The inner and outer guide rails  68 ,  70  respectively each have a lower rail portion  72 ,  74 , an upper rail portion  76 ,  78 , and a side rail portion  80 ,  82 , respectively, defining an inner guide track  81  and an outer guide track  83  to accommodate the guide track engaging portions depicted as inner rollers  65 ,  66  and outer rollers  63 ,  64  respectively. Lower rail portions  72 ,  74 , may, optionally, be readily replaceable to absorb the wear and tear to which the lower rail portions  72 ,  74  are subjected. In this embodiment, the lower rail portions  72 ,  74  are replaceably secured to the respective upper rail portions  76 ,  78  by bolts, as shown, or by any other manner known to those of ordinary skill in the art. The rollers  63 ,  64 ,  65 , and  66  operate within the respective guide tracks  81 ,  83  allowing the boom carriage  44  to traverse the guide rails  68 ,  70  in the conventional manner of traversing boom forklifts as will be understood by one of ordinary skill in the art. The figures depict the right front roller  63  and the right rear roller  64  both being accommodated in the outer guide track  83  as well as the left front roller  65  and the left rear roller  66  both being accommodated in the inner guide track  81 . This configuration differs to prior traversing boom configurations that employed a pair of opposing upper guide tracks for the rear rollers and a distinct pair of opposing lower guide tracks for the front rollers to vertically offset the front rollers from the rear rollers. Eliminating this vertical offset in the present invention allows the guide tracks to be lowered the maximum amount to provide the maximum visibility of the terrain possible. Manufacture of the present guide tracks  81 ,  83 , is also simpler than prior guide tracks. It will become evident to one of ordinary skill in the art, however, that the offset of the present invention between the inner and outer rails could be accomplished, with concomitant benefits, on a forklift employing separate pairs of guide tracks for the front and rear rollers. 
     The rollers  63 ,  64 ,  65 ,  66  are accommodated in the guide rails  68 ,  70  such that each roller  63 ,  64 ,  65 ,  66  contacts either the lower rail portion  72 ,  74  or the upper rail portion  76 ,  78  depending on the loading of the boom carriage  44 . For example, generally, when the load  20  handling device  34  is loaded, a downward force is transferred through the boom carriage  44  in front of the center of gravity of the boom carriage  44 , the moment created by the load will cause the front rollers  63 ,  65  to ride along the lower rail portions  72 ,  74  and the rear rollers  64 ,  66  to ride along the upper rail portions  76 ,  78 . The side rail portions  80 ,  82  provide lateral support to the rollers  63 ,  64 ,  65 ,  66  and are configured to prevent the boom carriage  44  from escaping the guide tracks  81 ,  83  defined by the guide rails  68 ,  70 . 
     In one embodiment, the height of the guide rails  68 ,  70 , measured from the lowest surface of the lower rail portion  72 ,  74  to the uppermost surface of the upper rail portion  76 ,  78 , is approximately 8.66 inches. The height of the guide tracks  81 ,  83 , measured from the lowest surface of the upper rail portion  76 ,  78  to the uppermost surface of the lower rail portion  72 ,  74 , is approximately 5.91 inches. The width of the guide rails  68 ,  70 , measured from the innermost surface to the outermost surface of the guide rails  68 ,  70 , is approximately 2.8 inches. The thickness of the side rail portions  80 ,  82  is approximately 0.75 inches. The thickness of the lower rail portion  72 ,  74  is approximately 0.75 inches. The thickness of the upper rail portion  76 ,  78  is approximately 2.0 inches. Additionally, in this embodiment, the guide rails  68 ,  70  may be constructed of welded steel plates. Alternatively, the guide rails  68 ,  70  may be constructed from formed steel channels formed, by way of example only, by extrusion. In the embodiment depicted in FIGS. 1 and 4, guide rails  68 ,  70  are attached to the frame rails  28 ,  30 , respectively, by welding. Alternate methods of attaching the guide rails  68 ,  70  to the frame rails  28 ,  30 , such as bolting, will be evident to one of ordinary skill in the art. The guide tracks  81 ,  83  of the present invention may alternatively be formed into the frame rails  28 ,  30  themselves, such as by forging or machined therein. Other methods for providing the guide tracks  81 ,  83  of the present invention will become apparent to one of ordinary skill in the art. 
     As described above with respect to FIGS. 2 and 3, the outer rollers  63 ,  64  are located approximately 4.5 inches below the inner rollers  65 ,  66  in one embodiment. This offset is illustrated in FIG. 4 as distance a. Other magnitudes of offset a are contemplated. In the same embodiment, the center of the outer guide track  81  is located approximately 4.5 inches, or other dimension a, lower than the center of the inner guide track  83  to accommodate the offset of the rollers  63 ,  64 ,  65 ,  66 . Offsetting the guide tracks  81 ,  83  lowers the uppermost surface of the outer guide rail  70  thereby increasing the operator&#39;s visibility of the terrain thereadjacent by a distance b as depicted in FIG.  5 B. The inner guide rail  68  may also be lowered with respect to prior inner guide rails. Indeed, in one embodiment of the present invention, which is not depicted, the inner guide rail  68  is lowered to an elevation equal to the outer guide rail  70  and the carriage left and right side plates  48 ,  50  are, accordingly, of equal length. In either configuration, the carriage left and right side plates  48 ,  50  must be of sufficient height to elevate the carriage top brace  52  over the engine.  26  or other equipment which resides between the frame rails  28 ,  30 . However, when physical limitations prevent the lowering of the inner guide rail  68  to the same lowered elevation as desired for the outer guide rail  70 , the vertical offset a of the present invention as depicted in FIGS. 4,  5 ,  5 A and  5 B provide increase terrain visibility without requiring a lowered inner guide rail  68 . Such physical limitations may include, by way of example only, mountings (not depicted) for the cockpit  32  or access holes in the inner frame rail  28  to provide access to the engine, transmission or drivetrain. 
     The lower limit of the outer guide rail  70  will be dictated by the desired ground clearance and the desired maximum loading capability of the forklift  10 . In one embodiment, it has been found that the inner and outer frame rails  28  and  30  need be approximately 16 inches high and 21.5 inches high, respectively, when comprised of approximately 1.5 inch thick welded plate steel for a forklift  10  having a recommended lifting capacity of 8,000 lbs. Other configurations are contemplated and will be recognized by one of ordinary skill in the art. 
     One or more of the rollers  63 ,  64 ,  65 ,  66  may comprise a thrust slide or an adjustable roller with a cam-like mechanism for adjusting its thrust, or position of the roller  63 ,  64 ,  65 ,  66  from side to side. For example, the inner rollers  65 ,  66  may be adjustable rollers and the outer rollers  63 ,  64  may be fixed rollers to promote acquiring a perfect fit between the boom carriage  44  and the offset guide rails  68 ,  70  during the assembly of the forklift  10 . 
     The traversing motion of the boom carriage  44  along the guide rails  68 ,  70  may be facilitated by one or a pair of carriage hydraulic cylinders  84 , one located along each of the guide rails  68 ,  70 . As shown in FIG. 1, the offset rails  68 ,  70  may traverse the length of the mainframe  12  allowing the boom carriage  44  to traverse the length of the mainframe  12 . FIGS. 1 and 6 depict the boom carriage  44  in a fully rearward, or nearly fully rearward, position which may constitute a transport configuration. The transport configuration is designed to promote a higher degree of visibility when the forklift  10  is in motion as well as to allow transport of the forklift  10  without the load encountering the earth. In the transport configuration, the boom carriage  44  is entirely out of the line of sight of the operator  88  housed in the cockpit  32  when looking towards the terrain adjacent to the outside rail  70 . Therefore, as depicted in FIG. 6, the short length of the boom carriage  44  of the present invention assures that the increased operator visibility provided by the lowered outer guide rail  70  of the present invention is appreciable by the operator. Moreover, locating the engine  26  immediately below the carriage  44  in its depicted location in FIG. 6 assures that the engine  26  remains out of the sight of the operator regardless of the position of the carriage  44 . FIG. 6 also depicts a front carriage stop  92  proximate the foremost portion of the guide rails  68 ,  70 . A rear carriage stop (not depicted) may also be located proximate to the rearmost portion of the guide rails  68 , 70 . FIG. 1 also illustrates, in phantom, the boom carriage  44  in a forward position. 
     FIG. 5A illustrates the increased visibility provided by the offset guide rails  68 ,  70 . As described above, the cockpit  32  is located along the left frame rail  28 . When the operator  88  housed in the cockpit  32  looks towards the terrain adjacent to the right frame rail  30 , and the boom carriage  44  is in a rearward position to remove it from the operator&#39;s line of sight, the operator&#39;s view is limited by the height of the outer guide rail  70 . In FIG. 5, the operator&#39;s line of sight over the offset guide rails  68 ,  70  of the present invention is demonstrated by line A. Line B illustrates what the operator&#39;s line of sight would have been had the outside guide rail  70  been located at an elevation equal to the inner guide rail  68  in the traditionally configuration. FIG. 5B demonstrates the additional terrain which the operator is able to view as a result of the present invention. By lowering the outside guide rail  70  of the present invention the operator&#39;s view of the surrounding terrain is increased by the distance b shown in FIG.  5 B. 
     Although the engine  26  and drivetrain may be mounted to the mainframe  12  in a number of configurations, using the offset rails  68 ,  70 , in conjunction with a centrally mounted engine  26  and drivetrain affords a further increase of visibility. 
     For all of the above reasons, the forklift  10  of the present invention increases an operator&#39;s visibility of the surrounding terrain. 
     It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is, therefore, intended that such changes and modifications be covered by the appended claims.