Abstract:
A boom of a wheeled loader or digger is pivoted about a horizontal axis in a fork. Yaw adjustment is provided by opposed taper plugs which constitute a spindle of the boom. The taper portions of the plugs are eccentric with respect to the bearing portions and may be rotationally adjusted to correct misalignment of the boom in yaw. A threaded fastener locks the taper plugs to the boom.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a boom, for example of a wheeled loader or digger, and particularly to yaw adjustment for alignment of the boom with the fork to which it is mounted. 
       BACKGROUND OF THE INVENTION 
       [0002]    Telescopic booms are typically mounted to loaders and diggers in order to provide adjustable reach. Such booms are pivoted with respect to a chassis, which may be wheeled or tracked, and which is commonly self-propelled. In one example the boom is horizontally pivoted to the rear of a wheeled chassis so as to extend forwardly; a driver&#39;s cab is provided on the chassis at the side of the boom, and the long axis of the boom is offset to one side of the centreline of the chassis. Such a boom may be raised and lowered by hydraulic ram, and include one or more telescopic sections which may be advanced or retracted on demand to adjust the reach thereof. 
         [0003]    It is desirable for the long axis of the boom to be parallel to the fore and aft centreline of the chassis. However the chassis mounting of the boom typically consists of a welded fabrication of many steel plate components, and it may be problematic to ensure that the pivot axis of the boom is perpendicular to the fore and aft centreline of the vehicle whilst maintaining other tolerances and dimensional requirements. In particular the pivot axis may be defined in separate steel plate components having bores which are independently machined, and line boring after fabrication may be impractical. Furthermore distortion of the fabricated assembly may occur during welding thereof. 
         [0004]    It will be appreciated that any misalignment of the long axis of the boom is magnified at maximum boom extension, and that such misalignment becomes apparent after assembly of the boom to the chassis. 
         [0005]    It would be desirable to provide yaw adjustment of the boom after manufacture and assembly of the device to which the boom is fitted. 
       SUMMARY OF THE INVENTION 
       [0006]    According to a first aspect of the invention there is provided a boom assembly comprising a support having forks, and a boom pivoted between the forks on a spindle about a substantially horizontal pivot axis, wherein the spindle includes a circular bearing portion for the forks and a circular boom portion for the boom, the boom portion being eccentric with respect to the bearing portion so that rotation of the spindle moves the beam in yaw with respect to the forks. 
         [0007]    In one embodiment the boom comprises a circular through hole tapering inwardly from respective ends towards the middle, and the spindle comprises two plugs, one each insertable into a respective end of said through hole, each plug having a circular tapered portion to match the respective taper of the through hole, and a circular pivot bearing portion for engagement in a respective fork, wherein the tapered portion of each plug is eccentric with respect to the bearing portion. 
         [0008]    Such an arrangement permits yaw adjustment by relative rotation of the spindle, in particular one or both of the plugs. The plugs provide the spindle of the boom upon locking of the taper portions of the plug and with the taper portions of the through bore. 
         [0009]    In one embodiment a threaded fastener is provided to draw the plugs together, thereby to make them immovable with respect to the boom. The threaded fastener may pass through one of the plugs to engage the other, and may furthermore be captive so as to separate the plugs upon unscrewing thereof. 
         [0010]    Separate plugs provides for easy assembly of the boom and fork, and moreover the tapered plugs permits relatively easy location of each plug in the mouth of the through bore; this avoid the necessity of aligning the boom and fork to a close accuracy before inserting the usual one-piece spindle. 
         [0011]    The arrangement of the invention allows adjustment of the yaw angle after a period of use, or upon replacement of components of the boom assembly. 
         [0012]    According to a second aspect of the invention there is provided a method of adjusting yaw of a boom assembly of the invention, the method comprising positioning the boom in the forks; inserting the plugs through a respective fork into the through hole from either side, the tapered portions of the plugs being in sliding engagement with the through hole; rotating one or more of the plugs to adjust the yaw angle of said boom with respect to the forks; and bringing the plugs into taper locking engagement with the through hole to render the plugs rotationally immovable with respect to the through hole. 
         [0013]    Other features of the invention will be apparent from the claims appended hereto, and from the description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Other features of the invention will be apparent from the following description of an embodiment of the invention described by way of example only in the accompanying drawings in which:— 
           [0015]      FIG. 1  is a side elevation of an exemplar self-propelled loader having a telescopic boom assembly. 
           [0016]      FIG. 2  is a plan view of the loader of  FIG. 1 . 
           [0017]      FIG. 3  is a schematic cross-section on the pivot axis of the boom assembly of  FIG. 1 , illustrating the principles of the invention. 
           [0018]      FIG. 4  is a schematic axial cross-section through a tapered eccentric plug of the invention. 
           [0019]      FIG. 5  is a schematic perspective view of a tapered eccentric plug of the invention. 
           [0020]      FIG. 6  is a cross-section corresponding to  FIG. 3 , and illustrating a practical embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The accompanying drawings of  FIGS. 1-5  are schematic and illustrative; they do not represent particular dimensions or proportions and are intended to convey the principles of the invention without dimensional limitation or absolute diagrammatic accuracy. 
         [0022]    With reference to  FIGS. 1 and 2  a wheeled self-propelled loader  10  comprises a chassis  11  having four wheels  12  rotatable about parallel axes  13 ,  14 . A fore and aft centreline of the loader has an axis  15  which is orthogonal to the axes  13 ,  14 , and defines a straight direction of travel. The loader may have a skid-steer chassis whereby direction is determined by braking one or more wheels whilst driving other wheels; however a conventional steerable chassis may also be provided, or a chassis with tracks. 
         [0023]    A driver&#39;s cab  16  is provided at one side of the chassis, and a telescopic boom  17  is pivoted to the rear of the chassis about pivot axis  18 , so as to lie alongside the cab  15 . Such an arrangement provides a vehicle of compact dimensions when the boom assembly  17  is retracted. 
         [0024]    The boom  17  may be raised or lowered by hydraulic ram  19  pivoted on the vehicle at vehicle pivot  21 , and on the boom at boom pivot  22 . Raising and lowering is in the direction indicated by double headed arrow  20 . 
         [0025]    The boom  17  comprises an outer section  23 , and a single telescopic inner section  24  which may be extended or retracted by a driver under hydraulic control in the direction indicated by double headed arrow  25 . As illustrated the inner section of the boom carries a fork  26 , but other attachments are possible, including a grab, a bucket or the like, of conventional kind. 
         [0026]    It is desirable that the long axis  27  of the boom ( FIG. 2 ) is parallel to the fore and aft axis  15  so as to minimize yaw misalignment, as represented by double headed arrow  28 . 
         [0027]    As described so far, the loader of  FIGS. 1 and 2  is conventional. The chassis comprises a steel fabrication to which upstanding arms  29 ,  30  are provided, and which define the pivot axis  18 . The boom is typically fork mounted on the axis  18  by a pivot pin in corresponding through holes (not shown) of the arms  29 ,  30 . 
         [0028]      FIG. 3  illustrates a somewhat simplified embodiment of the invention, corresponding components having the reference numerals of  FIGS. 1 and 2 . The upstanding arms  29 ,  30  define a fork into which the outer section  23  of the boom is pivoted about pivot axis  18 . 
         [0029]    Each arm  29 ,  30  defines a through aperture on axis  18  in which is provided a respective circular plain bearing  31 ,  32 . The outer section  23  also defines a through bore  33 , which is inwardly tapered from the opposite outer sides to the middle, so that the minimum diameter is at the centre, and substantially aligned with the long axis  27  of the boom. A plain diameter portion may be provided at the outer and middle portions of the through bore  33 , but the tapered portion should be straight, smooth and continuous, as will become apparent. 
         [0030]    The pivot pin for the boom assembly comprises two separate and similar plugs  34 ,  35 , which each comprise a fixed diameter circular bearing portion  36  and a tapered circular nose portion  37  to correspond to a respective tapered portion of the through bore  33 . 
         [0031]    The bearing portions  36  have a diameter corresponding to the plain bearings  31 ,  32  so as to provide pivoting support for the boom assembly  17 . 
         [0032]    The left plug  34  (as viewed) includes a female thread  38  at the tapered end, whereas the right plug  35  has a through hole  39  at a clearance diameter for a threaded bolt  40 , which engages the female thread  38  in use. It will be understood that tightening the bolt  40  draws the plugs  34 ,  35  together, and against the tapered surfaces of the through bore  33 , so that in use the plugs  34 ,  35  can become immovable with respect to the outer section  23  yet provide for pivoting thereof about the pivot axis  18  in the respective circular bearings  31 ,  32 . A centre clearance  41  is provided between the plugs  34 ,  35  in the assembly condition (as illustrated) to avoid bottoming thereof. 
         [0033]    The right plug  35  is illustrated in  FIGS. 4 and 5 . The plain diameter of the circular bearing portion  36 , and the tapered nose portion  37  can be clearly seen. The tapered nose portion is however symmetrically eccentric, with maximum eccentricity at the bottom, as viewed. Accordingly upon rotation thereof the nose portion  37  will shift transversely relative to the bearing portion  36  between the solid outline of  FIG. 4  to the chain-dot outline of  FIG. 4 , and back again. By this means rotation of the plug  35  causes relative fore and aft movement of the corresponding side of the outer section  23  with respect to the arm  29 , and hence movement of the boom assembly in the yaw direction. 
         [0034]    The plug  34  has the same exterior form as the plug  35 , but as noted above the through hole  39  is replaced by a female thread  38 . The plug  34  may be rotated relative to the outer section  23  to cause relative movement with respect to the arm  30 . 
         [0035]    The plugs  34 ,  35  may be rotated in situ by any suitable means, for example a peg spanner engageable in recesses  42  ( FIG. 4 ), or by external flats of the plugs  34 ,  35 . 
         [0036]    In use the outer section  23  is placed between the arms  29 ,  30 , and the plugs  34 ,  35  are inserted to position the boom. The boom is extended, to maximize yaw error at the free end of the inner section  24 , and the yaw discrepancy measured. If out of tolerance, one or both plugs  34 ,  35  are rotated to slew the boom assembly until parallel with the fore and aft centreline  15 . In this condition the bolt  40  is tightened to draw the tapered portions  37  into friction locking engagement with the tapered surfaces of the bore  33 , thus rendering them immovable with respect to the outer section  23 . 
         [0037]    Certain components and minor features are omitted in the cross-section of  FIG. 3  in order to improve clarity, for example grease passages, and thrust washers between the outer section  23  and arms  29 ,  30 . 
         [0038]    A typical plug  34 ,  35  may have a maximum diameter of around 60 mm, a bearing length of around 50 mm, an overall length of around 130 mm and included taper angle of 7.5°. The taper offset may be around 1 mm, which is sufficient to give a corrective yaw movement within manufacturing tolerances of the described embodiment. 
         [0039]      FIG. 6  corresponds to  FIG. 3  and shows a practical embodiment of the invention. Constructional details of the arm  29 ,  30  differ, and the bolt  40  is retained within the plug  35  so as to urge the plugs  34 ,  35  apart upon unscrewing, thereby to break the taper lock with the through bore  33  on demand. In the alternative a hydraulic fitting may be provided to permit the clearance  41  to be pressurized, thereby to break the tapered engagement. The boom is typically a box section in order to reduce mass thereof whilst retaining strength and stiffness. 
         [0040]    The invention has been described in relation to a wheeled loader. It will however be apparent that the invention may be applied to any fork mounted boom having a substantially horizontal pivot, whether on a self-propelled vehicle or not. 
         [0041]    The materials of the invention are conventional, being suitable grades of steel and bearing materials of a kind habitually used in machines with booms, in particular construction machinery. 
         [0042]    Variants and modifications of the invention are possible within the scope of the appended claims.