Trapezoidal Telescoping Crane Boom

Abstract

A crane boom comprises plural extensible and retractable telescoping sections each of which is trapezoidal in cross section. The trapezoidal cross sectional shape imparts to a boom of given weight greater lifting capacity or longitudinal rigidity and greater lateral stability than any other cross sectional shape. The trapezoidal cross section allows for a much more efficient placement of wear pads between boom sections and web stiffeners on the sides and bottoms of the sections. Adequate internal space is provided for boom extending and retracting means whether hydraulic or mechanical.

Description

BACKGROUND OF THE INVENTION

Heretofore in the art, the booms and boom sections of telescoping crane booms, such as the type used on mobile carriers and constructed to be extended and retracted by hydraulic rams or cables in conjunction with hydraulic rams, or the like, have been generally rectangular in cross-section. Two or more box-shaped boom sections are correspondingly proportioned so that they telescopically slide in each other to provide a boom of appropriate length. Generally, booms are constructed of between two to five telescopic boom sections.

As rectangular cross-section booms have been designed to lift loads of greater weight the vertical walls of the boom sections have been made higher, increasing the rectangular cross-section and putting more material in the vertical walls to increase the rigidity of the boom in the longitudinal direction and thus increase the strength of the boom. It has been found, however, that the height to which the rectangular cross-section can be increased is limited by the width of the rectangular cross-section. When a rectangular boom carrying a load is extended, and particularly when the boom is rotated on its carrier in the extended position, the nose of the boom has a tendency to twist about the longitudinal axis of the boom and lay over on its side. To combat this, the rectangular cross-section of the boom is made wider and in some cases the cross-section is square in shape. However, it has been found that while this provides greater lateral rigidity to the boom, it adds excessive weight to the boom itself, such that rectangular cross-section booms cannot be made wide enough to give proper lateral rigidity without adding a disproportionate amount of excessive weight to the boom.

A rectangular cross-sectioned boom also has other design limitations. A crane boom is primarily a cantilevered beam, a moment carrying member, and in a telescopic boom the telescoping sections must fit closely inside each other with as little side, top and bottom play as possible. The width is therefore limited to such an extent that there is not sufficient room to properly stiffen the vertical web members of the rectangular cross-section, so that all stiffening is obtained in the thickness of the metal used. Massive shear forces are therefore present at the points of concentrated loads when the boom is in extended position, that is, within the socket area or overlap area of adjacent extended telescopic sections.

Additionally, excessive transverse stresses are developed on the top and bottom members of the rectangular cross-sectioned boom sections. Adjacent telescopic sections are guided and supported within each other normally by means of rollers or wear pads on the inner end of one section bearing on the inside of the top member of the section into which it slides, and on the outer end of each section bearing on the outside of the bottom member of the adjacent section housed therein. Because of the configuration of one rectangular member nested within another rectangular member the wear pads or rollers, which are points of concentrated loads between sections, are located a substantial distance inwardly from the side walls of the rectangular sections and with such a configuration it is impossible to locate the wear pads beneath the vertical web members of the succeeding boom section. For this reason, in rectangular cross-section booms, the wear pads between adjacent sections cause excessive transverse bending stresses to be developed in the top and bottom members of a rectangular cross-sectioned boom.

The boom art therefore requires a break-through in the design of telescopic booms which will enable the strength and rigidity to weight ratio in both longitudinal and lateral directions to be substantially increased, thus enabling a boom of a given weight to be capable of lifting considerably heavier loads than a prior art boom of the same weight. Triangular cross-sectioned telescopic booms have been used in machinery where the majority of the load is along the longitudinal axis of the boom, but such an arrangement, while it approaches a solution to the design problem of lateral rigidity, since the base of the cross-section is much wider than the apex of the triangular cross-section, it is not suitable for use in a cantilevered crane boom which functions as a load carrying beam. A boom having a cross-section of an equilateral triangle with longitudinally extending chord members of equal cross-sectional area in each corner of the triangular configuration provides a good column design which efficiently functions as a compression member but it will not efficiently function as a cantilevered load lifting beam. The main reason is that the chord at the apex of the triangular cross-section cannot provide sufficient track or bearing area for the wear pads of the adjacent inner section and tremendous concentrated forces would, therefore, be present at the apex of the triangular section. Additionally, a triangular cross-section restricts the inner area available in a boom for the positioning of the operating hydraulic cylinders to such a great extent that this restriction alone makes a triangular cross-sectional boom impracticable.

Therefore, up until the present time, the art is without a solution to the problem of a more efficient design for a telescopic boom which will enable the art to move on and produce telescopic booms capable of lifting greater loads than is presently possible with known designs.

SUMMARY OF THE INVENTION

In accordance with the present invention, a telescoping preferably hydraulically operated crane boom of the type commonly used on mobile carriers is provided. The boom is characterized by the fact that the several boom sections are trapezoidal in cross section and preferably the wider base of the trapezoid is lowermost and its sides, which are of equal length, converge upwardly. The trapezoid is symmetrical and has its major axis disposed in a vertical plane. This construction greatly increases the lifting efficiency of the crane boom and its economy in terms of lifting capacity to weight ratio. In comparison to other cross sectional forms, the total boom and its sections are more rigid in the longitudinal direction or in the plane in which the lifted load is suspended. The boom is also more stable laterally and more resistant to lateral deformation and twisting. When a heavy load is suddenly released, as when dumping a bucket of concrete, vertical whipping or springing upwardly of the boom is greatly lessened due to the greater rigidity inherent in the trapezoidal shape. In comparison to other specific cross sectional shapes commonly employed, as much as 50 per cent more lifting capacity can be obtained or three times as much rigidity in the vertical plane and up to seven times more rigidity laterally.

The trapezoidal configuration possesses other marked advantages over rectangular and other shapes. Additional room is provided for side and bottom web stiffeners and for front and rear lateral guides without increasing the space between telescoping sections which must be maintained to a minimum. Additionally, the wear pads or bearings between adjacent sections of the boom may be located substantially in direct alignment with the reinforced side webs and this important feature has not been possible with other cross sectional shapes, including rectangular. The trapezoidal shape also provides adequate internal chamber space for hydraulic rams and associated components.

BRIEF DESCRIPTION OF DRAWING FIGURES

FIG. 1 is a front perspective view of a retracted trapezoidal telescoping crane boom embodying the invention;

FIG. 2 is a side elevation of the boom facing in the opposite direction to that depicted in FIG. 1;

FIG. 3 is a plan view of the retracted boom;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is an enlarged front end elevational view of the boom;

FIG. 6 is a similar rear end elevational view;

FIG. 7 is an enlarged fragmentary cross section taken on line 7--7 of FIG. 3;

FIG. 8 is a similar section taken on line 8--8 of FIG. 4;

FIG. 9 is a side elevational view of the boom extended, on a considerably reduced scale;

FIG. 10 is an enlarged side elevational view of the portion A in FIG. 9;

FIG. 11 is a similar view of the portion B in FIG. 9;

FIG. 12 is a similar view of the portion C in FIG. 9;

FIG. 13 is a similar view of the portion D in FIG. 9; and

FIG. 14 is an enlarged transverse vertical section taken on line 14--14 of FIG. 10.

DETAILED DESCRIPTION

Referring to the drawings in detail, wherein like numerals designate like parts throughout, the numerals 20, 21, 22 and 23 designate, respectively, the base section, inner mid section, outer mid section, and the fly section of the telescoping boom assembly. As shown particularly in FIGS. 1, 5 and 6, each of the individual boom sections is trapezoidal in cross section and in each case the wide base of the trapezoidal boom section is lowermost and the upwardly converging sides are of equal length so that the trapezoid is symmetrical about its neutral axis. The trapezoid, forming the basis of the cross sectional shape of each of the boom sections, is elongated in the vertical plane, FIG. 5, that is to say, the depth of the trapezoid in the vertical plane through its center is greater than its maximum width at the base.

As best shown in FIG. 9 where the boom assembly is fully extended, the sections 20, 21 and 22 possess a number of common structural features, to be described in detail, whereas the fly section 23, while possessing the characteristic trapezoidal shape, differs in its details from the other boom sections.

The base section 20, which is the outermost of the boom sections and therefore has the largest trapezoidal cross section, embodies a top plate 24 extending for its entire length and relatively thin side walls or webs 25 which diverge downwardly from the longitudinal edge portions of the top plate in a symmetrical manner with respect to a theoretical central vertical plane through the boom. The base section 20 further comprises a relatively thin bottom web 26 bounded along its longitudinal edges by continuous bars or rails 27 of increased thickness and rigidity. The elements 26 and 27 make up the lower base of the trapezoidal base section 20. The elements 24 through 27 are all integrally joined in a very secure manner by welding.

At spaced intervals along the length of the base section 20, side web stiffeners 28 are provided on the outer faces of the side webs 25 and welded thereto with their upper and lower ends welded to the top plate 24 and bars 27, respectively. As clearly shown in FIG. 14, the web stiffeners 28 lie within the longitudinal edges of the elements 24 and 27. As shown in FIG. 7, each web stiffener 28 is a channel member having its open side facing the adjacent side web 25. In a similar manner, bottom web stiffeners 29 are provided at spaced intervals along the bottom web 26 to reinforce the same against buckling and, as shown at FIGS. 3 and 4, the stiffeners 28 and 29 may be disposed at similar locations along the boom section 20. While the spacing of the web stiffeners is not extremely critical, they are preferably spaced apart by distances which approximate the depth of the trapezoidal boom section to which they are applied. FIG. 8 illustrates the channel construction of the bottom web stiffeners 29 whose open sides face the web 26.

The base section 20 is equipped at its rear end with a suitably reinforced main pivot unit 30 for the entire boom which is attachable in a conventional manner to the mobile carrier. Near its mid point and on its bottom, the boom base section is also equipped with a reinforced connector 31 for the boom lifting cylinder indicated in phantom lines at 32 in FIG. 2. At its forward end, the base section 20 carries an underslung transverse box member 33 which receives the lower forward wear plates or pads 34 and their conventional holders.

At the forward end region of the base section 20 where this section receives the extended inner mid section 21 in socketed relationship, and is therefore subjected to great stresses, the top plate 24 is reinforced by an overlay plate 35. Additionally, in this region, side longitudinal reinforcing bars 36 are employed preferably between the forward four web stiffeners 28 and directly under the top plate 24 to greatly reinforce the welded joints so as to resist the greatest wear pad stress. Suitable diagonal braces 37 are also preferably employed on opposite sides of the base section, as shown in the drawings, to render the structure further rigid in the critical region of high stress. At the extreme forward end of the base section 20 and depending from its top plate 24 is a stabilizing means 38 for the inner mid section 21 when the boom is fully retracted, preventing the boom sections from shifting laterally or twisting relative to one another.

The inner and outer mid sections 21 and 22 of the telescoping crane boom are very similar in construction to the base section 20 except that they are not equipped with the elements 30 and 31 and are of successively smaller trapezoidal cross sectional shape for close interfitting relationship with each other and with the base section 20. It is therefore believed that it is unnecessary to completely describe the boom mid sections 21 and 22, and in the drawings primed and double-primed reference numerals corresponding to the numerals employed for various components of the base section 20 are used to designate the identical parts in the inner and outer mid sections 21 and 22. Except for differences in size, the construction and functioning of these various detailed elements on the boom sections 20, 21 and 22 are identical.

The inner and outer mid sections 21 and 22 contain one other feature of difference from the base section 20 in that both of the former are provided at their rear ends and tops with laterally spaced wear pads 39 mounted in holders 40, FIG. 6, having reinforcing and bracing means 41 and 42 at the rear end of the particular boom section. The base section 20 requires no upper wear pads since it does not operate inside of another boom section.

It may now be observed by referring particularly to FIGS. 5 and 6 that with the trapezoidal construction of the individual boom sections, the lower wear pads 34, 34' and 34" may be located directly under the side webs 25, 25' and 25" so as to receive directly the forces or loads transmitted through these webs. This advantageous arrangement of wear pads or rollers, in some cases, is not readily attainable when rectangular cross sectional boom sections are employed because the lower pads as well as the upper pads must be arranged somewhat inwardly of the side webs. In such cases, when the boom is loaded, the top and bottom plates or webs of the boom sections have a tendency to distort or bow transversely, and in this respect, one of the significant advantages of the trapezoidal configuration is that it allows the placement of the lower forward wear pads directly under the side webs of the next innermost boom section.

Since various load capacities and lengths of booms are involved in practice, precise sizes and dimensions of the trapezoidal sections are somewhat variable. However, proportional limits can be defined. Using the vertical height of the trapezoidal section, FIG. 14, for unity, then the width of the top plate 24 will measure from 0.35 to 0.6 of unity and the bottom assembly or plate including the elements 26 and 27 will measure from 0.8 to 1.1 of unity. Also, as is well known, all beams including cantilever beams have a neutral axis and for greatest beam efficiency, the masses above and below the neutral axis should be nearly as equal as possible and these masses should be as distant as possible from the neutral axis. The theoretical neutral axis of the trapezoidal base section 20 is indicated at 43 in FIG. 14 for illustrative purposes. The mass above this axis including the top plate 24 is approximately equal to the mass below the neutral axis including web 26 and bars 27 and associated elements. As is apparent in FIG. 14, the major mass elements 24 and 26-27 are located as far as possible on opposite sides of the neutral axis.

While the forwardmost or fly section 23 of the boom has the same characteristic trapezoidal shape and embodies a similar top plate 44, side webs 45, and bottom web 46 reinforced at its edges by longitudinal bars 47, the various web stiffeners and bracing on the base section 20 and mid sections 21 and 22 is unnecessary and need not be employed. This is true because the fly section 23 is customarily extended during use only when relatively light loads are being handled and not under heavy loads. Therefore, the fly section is never subjected to the high degrees of stress that the other boom sections receive. Since the fly section 23 has no boom section telescoped within it, it also requires no forward wear plates or pads similar to the pads 34, 34' and 34". However, the fly section 23 does require and is equipped with the upper rear bearing pads or rollers, in some instances, and these are conventional elements in the art. The fly section carries the conventional nose assembly 48 shown in phantom lines in FIGS. 2 and 13.

The telescopic crane boom may be extended and retracted by any desired hydraulic means or by mechanical cable means, or the like. Preferably, it is hydraulically operated and a preferred operating means of this character is illustrated somewhat schematically in phantom lines in the drawings. Referring particularly to FIGS. 10 through 13, the piston rod 49 of the first ram is secured as at 50 to the back of base section 20 and the cylinder 51 of this first ram is pivoted at 52 to the rear of inner mid section 21, the forward end of this ram cylinder extending freely into the inner mid section 21, FIG. 11.

A box element 53 is pivoted at 54 to the rear of outer mid section 22 and extends forwardly with a free end terminating adjacent the forward end of the outer mid section, FIG. 12. The cylinder end 55 of another ram is pivoted at 56 to the rear end of inner mid section 21 and extends forwardly into and through the box 53 and the rod end 57 of this ram is pivotally connected at 58 to the forward terminal end of the box 53, as shown in FIG. 12.

Finally, the cylinder end 59 of a third ram, FIG. 11, is pivotally connected at 60 to the rear end of outer mid section 22 and the forward end of this cylinder 59 terminates within and near the forward end of mid section 22. The rod 61 of this third ram extends forwardly into the fly section 23, FIG. 13, and is pivotally connected therewith at 62. The arrangement provides for full extension of the boom as illustrated in FIG. 9 and the full retraction thereof to the condition shown in FIGS. 1 and 2 and all adjusted positions in between the two extremes. Preferably, each of the hydraulic rams, above-described, is an individually actuated double acting ram.

As shown in the drawings, the boom fly section 23 is preferably reinforced between its side webs 45 with a centrally located transverse brace web 45' which extends continuously for the full length of the fly section. Additionally, front lateral guides or pads 63, 63' and 63" are provided on opposite sides of the base section 20 and inner and outer mid sections 21 and 22 to stabilize and guide the interfitting boom sections laterally. Similarly, rear lateral guides or pads 64, 64' and 64" are provided on opposite sides of the two boom mid sections and the fly sections 23, FIG. 6.

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof but it is recognized that various modifications are possible within the scope of the invention claimed.

Claims

I claim:

1. A telescoping crane boom comprising a base section for the boom having means to pivot it about one end thereof, at least one additional extensible and retractable boom section telescopically engaged within the base section with means connected thereto adapted to load only the outer free end of the crane boom, power means to extend and retract the telescoping boom, all sections of the telescoping boom being trapezoidal in transverse cross section and including upwardly converging side webs, a relatively narrow top plate secured to the side webs and a relatively wide bottom plate unit secured to the side webs, a reinforcement for the top plate of at least the base section of the boom adjacent the forward end of the base section to resist stresses produced thereon by extension and loading of the next forwardmost boom section having upper wear pads bearing against the top plate of the base section, and said reinforcement comprising an overlayplate mounted on said top plate, and a pair of side reinforcing bars adjacent the overlay plate and near the tops of the side webs and secured thereto and to said top plate.

2. The structure of claim 1, and plural longitudinally spaced web stiffeners secured to said side webs of at least said base section of the boom.

3. The structure of claim 2, and additional transverse longitudinally spaced web stiffeners for said bottom plate unit secured thereto.

4. The structure of claim 3, and a pair of longitudinal side reinforcing bars extending along the lower corners of at least said base section of the boom and secured to said side and bottom web stiffeners, said side webs and bottom plate unit formed of relatively thin gage material for lightness.

5. The structure of claim 4, and all of said web stiffeners comprising channel bars having their open sides facing and abutting the webs to which they are welded.

6. A telescoping crane boom comprising a base section for the boom having means to pivot it about one end thereof, at least one additional extensible and retractable boom section telescopically engaged within the base section with means connected thereto adapted to load only the outer free end of the crane boom, power means to extend and retract the telescoping boom, all sections of the telescoping boom being trapezoidal in transverse cross section and including upwardly converging side webs, a relatively narrow top plate secured to the side webs and a relatively wide bottom plate unit secured to the side webs, a pair of laterally spaced wear elements on the bottom plate unit of at least said base section near the forward end thereof to receive directly the bottom plate unit of the next forwardmost additional boom section, and said wear elements disposed directly under the side webs of said next forwardmost additional boom section for transmitting forces directly thereto.

7. The structure of claim 6 in which the cross sectional height of any boom section is unity and the width of said top plate is from 0.35 to 0.6 of unity and the width of said bottom plate unit is from 0.8 to 1.1 of unity.

8. The structure of claim 6, and a pair of upper wear elements interposed between the top plates of the two boom sections and being located substantially directly above side side webs of the next forwardmost additional boom section for transmitting forces directly thereto whereby the side webs function substantially as columns to absorb said forces, and means to retain the upper wear elements on the next additional forwardmost boom section.

9. A telescopic crane boom as set forth in claim 6 in which said bottom plate unit of at least one of said boom sections includes a pair of longitudinal reinforcing bars extending along the lower corners of the boom section connected beneath the side webs thereof, and a bottom web of relatively thin gage material connected between said pair of longitudinal reinforing bars.