Light Weight Boom Construction

Abstract

A truck mounted crane has a three-part, extensible boom in which telescopic motion is accomplished by a pair of extension cylinders contained within the boom. Frictional forces between the slidably mounted boom sections are minimized by improved pad assemblies positioned at selected bearing points. Support members in the form of rollers are positioned within the boom immediately above the lower extension cylinder to not only prevent the extension cylinder from buckling under full load conditions, but to support the outer boom section when it is retracted inward. The result is a reduction in the size and weight of the extension cylinders and a consequent reduction in boom weight.

Description

BACKGROUND OF THE INVENTION

The field of the invention is telescopic booms for truck mounted cranes, and particularly boom constructions which have minimum cross section, size and weight for a given length and load capacity.

Of primary concern in the design of truck mounted telescopic booms is the overall weight of the boom sections and drive means used to extend and retract the boom sections in a telescopic motion. For every pound added to the weight of the boom, either the load capacity must be decreased or the amount of the counterweight must be increased to prevent the truck from tipping under full load conditions. However, the weight of the boom and its counterweight must be borne by the truck and an increase in either affects the size, weight and cost of the overall crane. Therefore, considerable effort is made to reduce the weight of the boom sections and the weight of the drive system used to extend and retract them.

Hydraulic extension cylinders are commonly used to control boom reach and they contribute significantly to the weight of the boom. To reduce the overall boom weight, therefore, it is desired to minimize the size of the extension cylinders. Typically, the cylinder end of such an extension cylinder is pinned to the lower end of an inner boom section and its rod end is pinned to the outer end of a telescopically mounted outer boom section. As a result, when fully extended the extension cylinder is exceedingly long and slender and when axially loaded, the extension cylinder bends, or bows significantly. To prevent the extension cylinder from buckling, lateral support must be provided by the walls of the boom sections in which it lies. In so called "step type" telescopic booms it has been the practice to provide such lateral support for the extension cylinder by locating a divider plate within the outer boom section immediately above the cylinder. Although such divider plates prevent the extension cylinder from buckling, they add appreciable weight to the boom. In the alternative, the diameter of the extension cylinder must be increased substantially to prevent buckling.

In a three-part, telescopic, step type boom in which an extension cylinder is contained within and lies along the length of the mid section, a divider plate is typically provided not only to support the extension cylinder as described above, but also to support the outer boom section when it is retracted, or telescoped inward, into the mid boom section. The divider plate prevents the outer boom section from tipping downward and damaging the extension cylinder which lies beneath.

To minimize frictional losses between the slidable telescopic boom sections and to thereby further reduce the size of the extension cylinders, either pads or rollers are positioned at appropriate load bearing points on each boom section. The pads are typically formed from a synthetic material such as nylon and they are either fastened directly to the boom section or are loosely retained within a shallow recess formed on the boom section. Due to the high shearing forces developed during telescopic motion of the boom sections, pads fastened with bolts tend to loosen rapidly as the holes in the pads become elongated under stress. On the other hand, when the pads are loosely confined in a shallow recess, they occasionally lift out and fall free of the boom. A lightweight and reliable pad assembly is therefore needed.

SUMMARY OF THE INVENTION

The present invention relates to a means of reducing the overall weight of a telescopic boom by eliminating divider plates within the boom and providing spaced support means in place of the divider plate which not only engage and support another boom section, but also provide lateral support for an extension cylinder located beneath. The invention includes a series of support means which connect to the walls of the boom section and which are positioned along its length. Each support means is positioned immediately above the extension cylinder contained within the boom section and directly below a retracted outer boom section. The support means thus serves a dual purpose of providing lateral support for the extension cylinder which prevents it from buckling under high axial loads, and provides support for the outer boom section when it is retracted.

A general object of the invention is to eliminate the need for a heavy divider wall within a boom section. In the preferred embodiment of the invention the support means includes a pair of rollers which connect to the sidewalls of the boom section and are positioned to allow the outer boom section to ride over them when retracted. The outer boom section is thus prevented from tipping downward against the extension cylinder. The rollers also serve to minimize frictional forces which impede telescopic motion and they therefore contribute to a reduction in the size of the extension cylinder.

Another general object of the invention is to provide lateral support for the extension cylinder contained within the boom section. By positioning the rollers between the extension cylinder and the retracted outer boom section, the rollers limit the lateral movement of the extension cylinder when it bends and thus prevents the cylinder from buckling under maximum load conditions. This lateral support allows a substantial reduction in the size of the extension cylinder.

A more specific object of the invention is to provide support rollers which serve to carry a retracted outer boom section and which provide lateral support for an extension cylinder located beneath. When maximum loading is approached, the rod on the extension cylinder bows upward and bears against the bottom side of the rollers. A contact point is thus made and when a load is applied to the boom rapidly, the cylinder rod impacts with the rollers. The rollers are rotatably connected to and suspended between the sidewalls of the boom section and each includes a sleeve made of a relatively soft material which will not damage the cylinder rod during impact.

Still another specific object of the invention is to provide an improved means of slidably mounting an outer boom section to an inner boom section. A lower pad assembly is mounted on the outer end of the inner boom section and slidably bears against the bottom surface of the outer boom section. An upper pad assembly is formed on the lower end of the outer boom section and slidably bears against the inner surface of the top wall of the inner boom section. A set of rollers are contained within the inner boom section and are positioned to bear against the bottom surface of the outer boom section as it is retracted inward to thus further reduce frictional forces generated during retraction and extension.

A more specific object of the invention is to provide an improved means of attaching and retaining the pads to the boom section. Each pad assembly includes a base to which a metal frame member is fastened. The frame member is spaced slightly above the surface of the base and it contains an opening into which a pad is placed. A retainer plate which is larger than the opening is bonded to the bottom surface of the pad to prevent the pad from lifting out of the opening during operation.

Other objects and advantages of the invention will become apparent from the description which follows. In the description reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made to the claims herein for interpreting the breadth of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation view of a truck crane which includes the present invention,

FIG. 2 is a schematic representation of a fully loaded extensible boom which includes the present invention,

FIG. 3 is a cross section of part of the boom shown in FIG. 2 when not fully loaded,

FIG. 4 is a cross section of another part of the boom shown in FIG. 2 when not fully loaded,

FIG. 5 is a view in cross section of the boom of FIG. 4 taken on the plane .ident.--5, and

FIG. 6 is an exploded perspective view of a pad assembly which forms part of the boom in FIGS. 2 and 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, a truck mounted crane has a three-part boom 1 which includes a nonextensible base section 2, a mid, or inner, extensible and retractable section 3, and an outer extensible and retractable section 4. The lower end of the base section 2 is rotatably mounted to a revolving frame 5 for pivotal motion in a vertical plane about a pivot point 6, and the boom 1 is raised and lowered by an elevation cylinder 8 which connects between the revolving frame 5 and a bracket 9 welded to the sides of the base boom section 2. The boom 1 supports a tip assembly 7 which is attached to the outer end of the outer boom section 4.

Referring specifically to FIG. 2, the length, or reach, of the boom 1 is determined by a pair of extension cylinders 10 and 11. The cylinder end 12 of the first extension cylinder 10 is pinned to the lower end of the base section 2 and its rod end 13 is pinned to the outer end of the mid section 3. The base section 2 has a generally rectangular cross sectional shape formed by a pair of side walls, a top wall and a bottom wall. The mid section 3 has a similar shape smaller in size and it telescopes within the base section 2 when the first hydraulic extension cylinder 10 is retracted. The outer boom section 4 is similarly slidably mounted for telescopic motion within the mid boom section 3. The cylinder end 14 of the second extension cylinder 11 is pinned at the lower end of the mid boom section 3 and its rod end 15 is pinned at the outer end of the outer boom section 4.

Frictional forces between the telescoping boom sections 2, 3 and 4 are reduced by a set of pad assemblies and rollers. Sliding engagement of the base boom section 2 and the mid boom section 3 is secured by a lower pad assembly 16 attached at the outer end of the base boom section 2 on its bottom wall, and an upper pad assembly 17 attached at the inner end of the mid boom section 3 on its top wall. Similarly, sliding engagement of the mid boom section 3 and the outer boom section 4 is secured by a lower pad assembly 18 attached at the outer end of the boom section 3 on its bottom wall, and an upper pad assembly 19 located at the inner end of the boom section 4 on its top wall. The pad assemblies 16, 17, 18 and 19 are all similar in construction and will be described in more detail hereinafter.

The three-part boom illustrated in FIG. 2 is shown fully extended and loaded. As a result, the mid and outer boom sections 3 and 4 are noticeably bowed from the downward load force applied to the tip assembly 7. This bowing, or bending, results from the lateral component of the load force, whereas the axial component of the load force acts along the length of the boom. This axial component of the load force is applied to each of the extension cylinders 10 and 11, and as a result, they also bow, or bend upward. To prevent the cylinders 10 and 11 from buckling under this axial load, support means are provided within each of the boom sections 3 and 4. More specifically, a pair of rollers 23 and 20 are connected to span between the sidewalls of the mid boom section 3 and are positioned immediately above the rod of the first hydraulic extension cylinder 10. The first roller 23 is located approximately one half the length of the rod from its pinned end 13, and the second roller 20 is positioned immediately below the inner end of the outer boom section when it is fully extended. Additionally, a pad 21 is attached to the lower end of the mid boom section 3 and is positioned immediately above the first extension cylinder 10 to provide support at the outer end of its cylinder portion. Similarly, a roller 22 is connected to span between the sidewalls of the outer boom section 4 and is positioned immediately above the rod of the second extension cylinder 11. The roller 22 is positioned approximately one half the length of the rod from its pinned end 15. A pad 24 connects to the lower end of the outer boom section 4 and is positioned directly above the cylinder portion of the second extension cylinder 11 to provide further lateral support.

Although it is apparent from FIG. 2 that the rollers 23 and 20 provide lateral support for the rod of the first extension cylinder 10 and thus prevent it from bending excessively under axial loading, these rollers serve a second purpose when the load is removed from the boom and the outer boom section 4 is retracted inward. More specifically, as this operation is performed the outer boom section 4 telescopes within the mid boom section 3 and reaches a point at which its center of gravity passes over the lower pad assembly 18. When this occurs, the lower end of the outer boom section 4 tips downward. The rollers 23 and 20 are positioned to catch and support the outer boom section 4 when this occurs, and to thus prevent it from striking the rod of the first hydraulic cylinder 10. The rollers 23 and 20 thus provide both lateral support for the extension cylinder 10 and support for the outer boom section 4 when it is retracted inward.

Referring to FIG. 5, the rollers 20, 22 and 23 are identical in construction and each includes a circular cylindrical steel body portion 25 which is constricted over the central portion of its length to form a spindle 26. A nylon sleeve 27 is formed around the spindle 26 to provide a relatively soft surface against which the rod of the cylinder 10 may impact without damage. Trunions 28 and 29 are formed on the ends of each roller and each is rotatably connected to one of the boom section side walls by respective sleeve bearings 30 and 31. The sleeve bearings 30 and 31 are fastened to respective annular shaped retainer plates 32 and 33 which in turn are welded to the boom section side walls. The roller shown in FIG. 5 engages and supports the outer boom section 4 which is positioned above it. The extension cylinder rod 10 passes beneath the roller, and when the boom 1 is heavily loaded, the cylinder 10 bows upward and its rod bears against the sleeve 27.

With the exception of their size and manner of attachment, the pad assemblies 16, 17, 18 and 19 are substantially identical. Referring to FIG. 6, each pad assembly includes a base portion which is formed by a rectangular base plate 33 fastened to a set of three lateral support members 34, 35 and 36. The support members 34-36 extend across the width of the boom section to which they are attached and are welded to the underside of the base plate 33 to form a rigid base which will withstand the large forces exerted downward on the pad assembly. Three threaded openings 37 are formed in the lateral support member 34 and a frame member 38 is fastened thereto by a set of three bolts 39. The frame member 38 is rectangular in shape and roughly the size of the base plate 33. It includes a downward turned flange 40 along its front edge and a set of three holes 43 are formed in the flange 40 in alignment with the threaded holes 37 in the lateral support member 34. A bar shaped clamping member 44 is fastened against the front surface of the flange 40 by the bolts 39 which pass through the holes 43 and engage the threaded openings 37. The frame member 38 has a pair of large rectangular shaped openings 41 and 42 formed completely through it, and when fastened to the base, these openings form a pair of side-by-side recesses.

The frame member 38 is spaced slightly above the base plate 33 and a pair of pads 45 and 46 of substantially rectangular shape are disposed in the recesses formed by the openings 41 and 42. The pads 45 and 46 are formed of a bearing material such as nylon and they fit loosely within the respective openings 41 and 42. The pads 45 and 46 are substantially thicker than the frame member 38 and, therefore, they extend above its surface. The forward and rearward edges of the pads 45 and 46 are beveled and the top surface of each is greased.

To prevent the pads 45 and 46 from lifting out of their respective recesses, a pair of relatively thin retainer plates 47 and 48 are bonded to their bottom surfaces with an epoxy cement. The retainer plates 47 and 48 are disposed between the bottom surface of the frame member 38 and the top surface of the base plate 33 and each is slightly larger than its associated opening 41 and 42. The pads 45 and 46 are thus loosely held in place within the recesses and the forces generated by the sliding engagement of the pads 45 and 46 are taken by the frame member 38. Forces tending to lift the pads 45 and 46 out of their respective recess are relatively small, and therefore, the retainer plates 47 and 48 are sufficient to prevent the pads from being lifted out of the recesses. It should be apparent to those skilled in the art that a number of variations can be made to the pad assembly described herein without departing from the spirit of the invention. For example, a single retainer plate may be used for both of the pads 45 and 46, or a single pad may be used. Also, instead of gluing the retainer plates to the pads, other fastening means such as screws can be used, or the retainer plate can be formed as an integral part of the pad.

The invented boom is shown, somewhat schematically, in FIG. 2 in a fully loaded position in which the lower extension cylinder 10 is bowed upward against the pad 21 and the rollers 23 and 20, and the upper extension cylinder 11 is bowed upward against the pad 24 and the roller 22. As shown in FIGS. 3 and 4, however, when the load is reduced the boom 1 straightens and the axial loading on the extension cylinders 10 and 11 is reduced. As a result, the cylinders 10 and 11 straighten and disengage from the pads 21 and 24 and the rollers 20, 22 and 23.

As shown in FIGS. 3 and 4, a pad 49 is attached to the underside of the cylinder 10 at the outer end of its cylinder portion, and a pad 50 is attached to the underside of the extension cylinder 11 at the outer end of its cylinder portion. When the extension cylinders 10 and 11 sag, or bow downward, due to their own weight, the pads 49 and 50 rest against the bottom walls of the respective boom sections 3 and 4. Additionally, however, the pads 49 and 50 prevent the respective cylinders 10 and 11 from buckling under maximum loading. Referring specifically to FIG. 5, the pad 50 includes a steel plate 55 which is welded to the underside of the cylinder 11 and is braced by a pair of angle irons 56 and 57 welded to either side. A block 58 of nylon bearing material is fastened to the bottom surface of the plate 55 by a pair of screws 59. The width of the plate 55 is only slightly smaller than the inside dimension of the outer boom section 4, and therefore, when the cylinder 11 bows in the sideways direction under heavy axial loading, the plate 55 contacts the sidewalls of the outer boom section 4 and inhibits further bowing.

When the boom is fully loaded as shown in FIG. 2, the outer boom section 4 does not engage the roller 20 mounted to the mid boom section 3, but instead, bears heavily against the upper pad assembly 19 and the lower pad assembly 18. However, when the load is removed and the outer boom section 4 is retracted as shown in FIG. 4, the outer boom section 4 tips downward into engagement with the roller 20. It should be apparent to those skilled in the art that when performing the dual function described herein, the rollers offer a number of advantages. However, other forms of spaced support members will also suffice. For example, pads may be substituted for one or more of the rollers and particularly for example, the roller 22 in the outer boom section 4 which serves only to provide lateral support for the rod of the extension cylinder 11.

Claims

I claim:

1. In a telescopic boom having an inner boom section containing an extension cylinder which is connected thereto and lies along a substantial part of its length, and having an outer boom section slidably connected to the inner boom section to telescope therewithin between a retracted and extended position, the improvement comprising:

a set of supports spaced along the length of the inner boom section and positioned between the extension cylinder contained therein and the outer boom section when in its retracted position, each support extending completely across the interior of said inner boom section to connect with opposing side walls thereof,

wherein each support not only engages and carries said retracted outer boom section, but also engages and provides lateral support for said extension cylinder when it bends under heavy loads.

2. The telescopic boom as recited in claim 1 in which said supports are rollers which rotatably connect with the opposing side walls of said inner boom section.

3. The telescopic boom as recited in claim 2 in which each roller includes a sleeve made of a relatively soft material which will not damage said extension cylinder when it engages the roller.

4. The telescopic boom as recited in claim 2 in which a plate is fastened to the extension cylinder at a point intermediate its ends and said plate extends sideways in both directions from said cylinder to provide sideways support for said cylinder by engaging one of the sidewalls of said inner boom section when said cylinder bows in sideways direction under axial loading.

5. The telescopic boom as recited in claim 2 in which said outer boom section contains a second extension cylinder which is connected thereto and lies along a substantial part of its length, and there is a second set of supports spaced along the length of the outer boom section and positioned above said second extension cylinder to provide lateral support therefor under heavy loads.

6. The telescopic boom as recited in claim 1 in which the slidable connection of said outer boom section to said inner boom section is obtained by a pair of pad assemblies and each pad assembly includes:

a base having a top surface, said base being connected to one of said boom sections;

a frame member connected to said base and extending over said top surface, said frame member having an opening therethrough which forms a recess;

a pad disposed within said opening and having a bearing surface which extends above said frame member to slidably engage the other of said boom sections; and

a retainer plate disposed between the base and frame member and connected to said pad, said retainer plate having outer dimensions larger than the opening in said frame member.

7. The telescopic boom as recited in claim 6 in which said frame member includes a flange which is fastened to said base to separate said frame member from the top surface of said base and said retainer plate is disposed within the space provided by this separation.

8. The telescopic boom as recited in claim 6 in which said retainer plate is bonded to the pad.