US3628612A

US3628612A - Mounting arrangement for bulldozer blades

Info

Publication number: US3628612A
Application number: US855908A
Authority: US
Inventors: Richard K Liess; Donald E Ribbing; Visvaldis A Stepe; Eugene M Wilson
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1969-09-08
Filing date: 1969-09-08
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21

Abstract

A mounting and control arrangement for supporting a bulldozer blade upon a tractor by means of a C-frame. The blade is centrally secured to the C-frame by a universal ball joint. Hydraulic angling jacks are interconnected between each leg of the C-frame and a guide member slidably mounted on a T-shaped bar respectively secured to each C-frame leg. A triangular brace supports each end of the blade and is secured to the respective guide members by a ball joint. The angling jacks are pivotally connected to the C-frame legs and the guide members by means of ball joints to reduce stresses with the pivotal connection between the angling jacks and the guide members preferably being a trunnion mounting having a pivot axis perpendicularly related to the axis of the pivot joint between each angling jack and the C-frame.

Description

[72] inventors Richard K. Liess Peoria; Donald E. Ribbing, Juliet; Visvaldis A. Stepe, Willow Springs; Eugene M. Wilson, ,lloliet, all oi ill. [21] Appl. No. 855,908 [22] Filed Sept. 8, 1969 [45] Patented l)ec.2l,l97l [73] Assignee Caterpillar Tractor Co.

Peoria, 111.

[54] MOUNTING ARRANGEMENT FOR BULLDOZER BLADES 8 Claims, 8 Drawing Figs.

[52] 11.8. C1 172/804, 172/805 [51] int. (11 E0213/76 [50] Field oil Search 172/805, 803, 804, 806

[56] References Cited UNITED STATES PATENTS 2,636,289 4/1953 Pryor 172/804 Primary Examiner-Robert E. Pulfrey Assistant Examiner-Stephen C. Pellegrino Attarney-Fryer, Tfensvold, Feix, Phillips & Lempio ABSTRACT: A mounting and control arrangement for supporting a bulldozer blade upon a tractor by means of a C- frame. The blade is centrally secured to the C-frame by a universal ball joint. Hydraulic angling jacks are interconnected between each leg of the C-frame and a guide member slidably mounted on a T-shaped bar respectively secured to each C-frame leg. A triangular brace supports each end of the blade and is secured to the respective guide members by a ball joint. The angling jacks are pivotally connected to the Gimme legs and the guide members by means of lball joints to reduce stresses with the pivotal connection between the angling jacks and the guide members preferably being a trunnion mounting having a pivot axis perpendicularly related to the axis of the pivot joint between each angling jack and the C-frame.

PNVENTORS K. LIESS E. RIBBING VISVALDIS A. STEPE EUGENE M. WILSON RICHARD DONALD SHEET 2 OF 4 PATENTED 01562! M PATENIED HECZI mm SHEET 3 OF 4 INVENTORS RICHARD K. LIESS DONALD E. RIBBING VISVALDIS A. STEPE EUGENE M. WILSON V M ATTORNEYS PATENTEU DECZI I97! SHEET [1F Q ENTORS I R NG [NV RICHARD K LI 5 DONALD E VISVALDIS A STEPE BY EUGENE M. WILSON M w 2? I I ATTO EYS MOUNTING ARRANGEMENT FOR BULLDGZEIM BLADES The present invention relates to a mounting arrangement for a bulldozer blade and more particularly to such an arrangement where hydraulic motors are employed to permit angling, pitching and tilting of the blade during operation.

Bulldozer blades of the type contemplated by the present invention are commonly employed to move large quantities of earth or other material. Forces acting upon the blade must be transferred through the mounting arrangement to the tractor. For reliable operation over long periods of time, the construction of components within the mounting arrangement, their interrelation and interconnection must be carefully selected to minimize stress and wear within the mounting arrangement.

The present invention provides a mounting arrangement which is particularly effective to overcome these problems while facilitating adjustment of the blade during operation. More particularly, the present invention provides a novel arrangement and interconnection of the hydraulic jacks which function to control angling of the blade. The arrangement and interconnection of these components is made even more effective when combined with the remaining components and particularly the pivotal joints of the mounting arrangement which support the blade.

In many mounting arrangements for bulldozer blades, hydraulic angling cylinders are mounted on each side of the bulldozer blade support frame so that the blade may be angled to either side to accommodate varying types of material and different environments. It is desirable that the angling cylinders be capable of sufficiently shifting the blade to permit proper sidecasting of material. At the same time, it is desirable to mount the bulldozer blade as close as possible to the tractor to further reduce stresses in the blade and mounting arrangement and to improve stability of the tractor. Accordingly, the construction, arrangement, and interconnection of components for angling the blade is believed to be critical. It is further desirable that these components be interconnected in such a manner that slight misalignment does not tend to bind the hydraulic angling cylinders which could adversely increase stress and wear within the mounting arrangement.

Accordingly, it is an object of the present invention to provide a mounting arrangement for supporting a bulldozer blade upon a tractor while minimizing stress and wear within various components of the mounting arrangement.

It is a more particular object of the invention to provide an arrangement and interconnection of components for angling the blade to serve the same purpose as above.

It is another object of the invention to provide such a mounting arrangement which permits substantial angling of the blade while maintaining in close relation to the tractor.

It is still another object to provide such a mounting arrangement wherein components for angling the blade are arranged and interconnected in a manner which minimizes stress and wear within the mounting arrangement.

Yet another object is to select the arrangement and interconnection of the angling components as well as of other portions of the mounting arrangement to minimize stress and wear throughout the entire interconnection between the bulldozer blade and the tractor.

The above objects are clarified and additional objects and advantages of the present invention are believed to be apparent from the following description having reference to the accompanying drawings.

In the drawings:

FIG. 1 is a plan view of the forward end of a tractor including the present mounting arrangement for supporting a bulldozer blade;

FIG. 2 is a fragmentary side view in elevation of the mounting arrangement for the bulldozer blade of FIG. 1;

FIG. 3 is a view taken along section lines III-III of FIG. 2;

FIG. 4 is a perspective view of another embodiment of the mounting arrangement in association with a bulldozer blade;

FIG. 5 is a fragmentary view with parts in section of a slidable guide member for interconnecting a triangular brace associated with the blade to a hydraulic motor for controlling angling of the blade;

FIG. 6 is a fragmentary side view of another embodiment of the slidable guide member; and

FIGS. 7 and 3 are views taken along section lines VII-VII and VIII-VIII respectively of FIG. 6.

A mounting arrangement according to the present invention is illustrated in FIG. I for supporting a bulldozer blade 11 upon a tractor partially shown at 12. The blade is supported upon the tractor by a C-frame I3 which includes an intermediate portion l4 transversely arranged across the front of the tractor. The blade II is centrally supported for universal oscillation relation to the C-frame by a ball joint indicated at 16. The C-frame also includes leg portions 17 and I8 which extend along respective sides of the tractor and are pivoted to the tractor at 19 and 21.

Hydraulic jacks

22 and 23 are pivotally interconnected between the forward end of the tractor and the C-frame for raising and lowering the blade 11.

A pair of hydraulic jacks indicated at 24 are arranged upon respective sides of the tractor for adjusting the angle of blade Ill. Each hydraulic angling jack 24 is pivotally interconnected between the C-frame at 26 adjacent the pivotal interconnection 119 and 211 and slidable guide members indicated at 27. With the cylinders 28 of the jacks 24 being pivotally connected at 26 to the C-frame, the other extendible portion or rod 29 of each jack is secured to the respective guide member by a pivot joint 3i. Each pair of pivotal interconnections 26, 3B for the respective angling jacks is arranged to permit generally free oscillation of the jack about axes which are perpendicular to each other.

The guide members 27 are slidably mounted upon T-shaped bars 32 which are secured to the respective C-frame legs. Each of the guide members 27 forms an elongated slot 33 (see FIGS. 2 and 3) for receiving the respective T-shaped bars. Referring also to FIG. 2, triangular braces 34 each include upper and

lower members

36 and 37 which are respectively pivoted to the ends of the blade 11 by

ball joints

38 and 39. The triangular braces 34 are also pivotally connected to the respective guide members 27 by ball joints indicated at 41.

The blade I1 is preferably formed with forwardly angled end portions II which provide for adequate side shifting of material with reduced motion in the angling jaclts 24. This combination of features further contributes to reduced stress in the mounting assembly and closer coupling of the blade to the tractor.

The particular arrangement and interconnection of the components of the lift arrangement as described, for example, with respect to FIGS. I and 2, has been found to significantly reduce stress and wear within various portions of the mounting arrangement. Within the present arrangement, it has been found that wear is most noticeable upon the T-shaped bars 32. Referring now particularly to FIG. 3, the construction of the T-shaped bar 32 is particularly contemplated to simplify replacement of those portions which are most susceptible to wear. As shown in FIG. 3, each T-shaped bar includes a bifurcated upright 42 secured to the respective C-frame leg 18 as by welding indicated at 43. An elongated plate 44 is secured to both sides of the bifurcated upright 42, for example, by a plurality of cap screws such as those indicated at 46. As is also apparent from FIG. 3, the balljoint 4B for securing each triangular brace 34 to the respective guide member 27 includes a ball 47 secured to each guide member 27 and a socket 43 formed by each of the triangular braces 34.

Another embodiment of the mounting arrangement is illustrated in FIG. 4. Components which are generally the same as those indicated in FIG. I are labeled by similar primed numerals. It is apparent that the construction and arrangement of components in the mounting assembly of FIG. 4 is generally the same as for that in FIG. 1. However, in the embodiment of FIG. 4, the extendible rods 29' of the angling jacks 24' are pivotally interconnected at 26 to the C-frame. The cylinder portions 2% are pivotally connected to the respective guide members 27' by pivotal joints 31" which are trunnion mountings permitting relatively free oscillation between the cylinders 28' and the guide members 27'.

With the cylinders 28' supported intermediate their ends upon the respective guide members 27', the blade may be angled a greater amount because the cylinders extend into unused space just behind the blade. Additionally, positioning the cylinders adjacent the blade permits them to remain at substantially a fixed relationship with the blade even during maximum angling. With this arrangement, the length of the C- frame legs may be somewhat decreased so that the blade is maintained in closer relation to the tractor thus reducing stresses in the mounting arrangement and improving stability of the tractor. Still further, the exposed rod ends of the angling cylinders 24' are afforded somewhat greater protection since they are not adjacent the blade.

As was noted above, maximum stress and wear tends to occur within the slidable guide members 27' and the T-shaped bars 32'. A preferred construction for these components to minimize the above problems is illustrated in FIG. with yet another embodiment being illustrated in FIGS. 6-8.

Referring first to FIG. 5 in combination with FIG. 4, the guide member 27' is formed with upper and

lower elements

51 and 52 which form a cylindrical hole 53 for receiving the cylinder 28'. The

elements

51 and 52 mate at the sides of the cylinder 28 and are secured together for example by cap screws indicated at 54. The elongated slot 33 for receiving the T-shaped bar 32 is formed by the lower element 52. The ball 47' to which the triangular brace 34' is secured is also integrally formed together with the lower element 52. The trunnion mounting 31' is formed by pins 56 and 57 which extend vertically from the cylinder 28. Coaxial bores 58 and 59, in which bearings 60 are mounted for support of pins 56, 57, are formed respectively by the upper and lower

guide member elements

51 and 52.

All edges of the slider member 27' which contact the slide rail 32' are chamfered as indicated at 50 to reduce wear during motion of the slide member upon the rail. Preferably the angle of the chamfer is 7.

Referring now to FIGS. 6-8, another embodiment of the guide member 27' is formed with two

side elements

61 and 62 for receiving the cylinder 28'. The

elements

61, 62 are joined below the cylinder 28 for example by welding as indicated at 63. The elongated slot 33 for receiving the T-shaped bar 32' is formed by both of the

elements

61, 62 when they are secured together. In this embodiment, the trunnion mounting 31' includes a trunnion 64 encompassing the cylinder 28 and having vertically extending

pins

66 and 67. The upper and

lower pins

66 and 67 are carried by bearings 68 mounted respectively within bores 69. The bores 69 are respectively formed by a plate 71 secured between the

side elements

61, 62, for example by a plurality of bolts, one of which is indicated at 72 (see FIG. 8) and by the

mating elements

61, 62 adjacent the slot 33'. In this embodiment, the elongated plate 44' of the T-shaped bar 42 is replaceably mounted by capscrews 46 in a similar manner as described above with reference to FIG. 3. However, in the embodiment as shown in FIG. 8 the bifurcated upright 42' is formed as an integral portion of the respective C-frame leg indicated at 18' for additional strength. The ball 47 is again formed as an integral portion of one of the elements, for example that indicated at 61.

What is claimed is:

1. A mounting and control arrangement for supporting a bulldozer blade at one end of a tractor having a C-frame including legs pivoted to respective sides of the vehicle and an intermediateportion transversely arranged at the one end of the tractor comprising a ball joint securing a central portion of the blade with the intermediate C-frame portion,

a T-shaped bar secured to each C-frame leg,

a guide member slidably mounted on each T-shaped bar,

a triangular brace secured to each guide member by a ball joint, each brace including upper and lower brace members respectively and pivotally secured to upper and lower portions of the blade at one end thereof, the upper members of the braces being hydraulicjacks,

hydraulic angling jack having extendible portions interconnected between each guide member and the C-frame relatively adjacent its pivotal connection to the tractor, the interconnections with the guide members being pivot joints permitting generally free oscillation between the angling jacks and the guide members about a generally vertical axis, the interconnections with the C-frame pivotally permitting oscillation between the angling jacks and the C-frame about axes generally perpendicular to the axes of the pivot joints, and

wherein the blade has end portions angling forwardly from the central portion to provide for adequate side shifting of material by the blade when the blade is angled in either direction with reduced motion of the angling jacks and reduced stress in the mounting arrangement while concurrently permitting the blade to be supported in closer relation to the tractor.

2. The invention of claim I wherein the T-shaped bars are formed by bifurcated members secured to the C-frames and extending upwardly therefrom, and elongated plates arranged in generally horizontal relation above both of the bifurcated members to which they are respectively secured,

each plate being replaceably secured to both sides of the respective bifurcated members, and wherein the pivots between the brace members and the blade are formed by ball joints.

3. The invention of claim 2 wherein the extendible portions of each angling jack include a cylinder pivoted to the respective C-frame and a rod interconnected to the respective guide member by the pivotjoint.

4. A mounting and control arrangement for supporting a bulldozer blade at one end of a tractor having a C-frame including legs pivoted to respective sides of the vehicle and an intermediate portion transversely arranged at the one end of the tractor comprising a ball joint arranged between a central portion of the blade and the intermediate C-frame portion,

a T-shaped bar secured to each C-frame leg, the T-shaped bars being formed by bifurcated members secured to the C-frames and extending upwardly therefrom, and elongated plates arranged in generally horizontal relation above both of the bifurcatedmembers to which they are respectively secured, each plate being replaceably secured to both sides of the respective bifurcated member, guide member slidably mounted on each T-shaped bar, each guide means comprising two structural elements being secured together to form a longitudinal slot for receiving the respective elongated plate and a longitudinal opening thereabove for receiving the rod, each guide member having cylindrical bearing surfaces in vertically aligned relation above and below the longitudinal opening respectively,

a triangular brace secured to each guide member by a ball joint, each brace including upper and lower brace members respectively and pivotally secured to upper and lower portions of the blade at one end thereof, the upper members of the braces being hydraulic jacks, and hydraulic angling jack having extendible portions interconnected between each guide member and the C-frame relatively adjacent its pivotal connection to the tractor, the interconnections with the guide members being pivotable trunnion mountings including the respective bearing surfaces in the guide members and permitting generally free oscillation between the angling jacks and the guide members about a generally vertical axis, the interconnections with the C-frame pivotally permitting oscillation between the angling jacks and the C-frame about axes generally perpendicular to the axes of the pivot joints.

5. The invention of claim Al wherein the ball joint for securing the triangular brace to each guide member comprises a ball integrally formed with one of the structural elements.

6. A mounting and control arrangement for supporting a bulldozer blade at one end of a tractor having a C-frame including legs pivoted to respective sides of the vehicle and an intermediate portion transversely arranged at the one end of the tractor comprising a ball joint for supporting a central portion of the blade upon the intermediate C-frame portion,

a T-shaped bar secured to each C-frame leg,

guide members forming elongated slots for slidably receiving the respective T-shaped bars, each guide member comprising two structural elements being secured together to form a generally cylindrical bore, the two structural elements of each guide member mating and being secured together above and below the cylindrical bore,

a triangular brace secured to each guide member by a ball joint, a portion of the ball joint being integrally formed with an inner one of the structural elements, each brace including upper and lower brace members respectively and pivotally secured to upper and lower portions of the blade, and

a hydraulic angling jack having extendible portions respectively interconnected between each guide member and the respective C-frame relatively adjacent its pivotal connection to the tractor, the interconnection between one extendible portion of each jack and the C-frame being a pivot joint permitting generally free oscillation about a horizontal axis, the other extendible portion of each jack penetrating the cylindrical bore of the respective guide member and being supported therein by a trunnion mounting for substantially free oscillation about a vertical axis.

7. The invention of claim 6 wherein the one extendible portion of each angling jack is its rod and the other extendible portion of each anglingjack is its cylinder.

8. A mounting and control arrangement for supporting a bulldozer blade at one end of a tractor having a C-frame ineluding legs pivoted to respective sides of the vehicle and an intermediate portion transversely arranged at the one end of the tractor comprising a ball joint for supporting a central portion of the blade upon the intermediate C-frame portion,

a T-shaped bar secured to each C-frame leg,

guide members forming elongated slots for slidably receiving the respective T-shaped bars, each guide member comprising two structural elements being secured together to form a generally cylindrical bore,

a triangular brace secured to each guide member by a ball joint, a portion of the ball joint being integrally formed with one of the structural elements, each brace including upper and lower brace members respectively and pivotally secured to upper and lower portions of the blade,

a hydraulic angling jack having extendible portions respectively interconnected between each guide member and the respective C-frame relatively adjacent its pivotal connection to the tractor, the interconnection between one extendible portion of each jack and the C-frame being a pivot joint permitting generally free oscillation about one axis, the other extendible portion of each jack penetrating the cylindrical bore of the respective guide member and being supported therein by a trunnion mounting for substantially free oscillation about another axis generally perpendicular to the one axis for the pivot joint between the one extendible jack portion and the C-frame, and

wherein the two structural elements of each guide member mate and are secured together at the respective sides of the cylindrical bore, the ball of the ball joint for the respective brace being integrally formed with a lower one of the structural elements which also forms the elon ated slot for receiving the T-shaped bar, the structura elements also including coaxial and vertically aligned bores serving as bearings for the trunnion mounting, the other extendible portion of each jack having radially extending pins which are received by the respective bores in the structural elements.

Claims

1. A mounting and control arrangement for supporting a bulldozer blade at one end of a tractor having a C-frame including legs pivoted to respective sides of the vehicle and an intermediate portion transversely arranged at the one end of the tractor comprising a ball joint securing a central portion of the blade with the intermediate C-frame portion, a T-shaped bar secured to each C-frame leg, a guide member slidably mounted on each T-shaped bar, a triangular brace secured to each guide member by a ball joint, each brace including upper and lower brace members respectively and pivotally secured to upper and lower portions of the blade at one end thereof, the upper members of the braces being hydraulic jacks, a hydraulic angling jack having extendible portions interconnected between each guide member and the C-frame relatively adjacent its pivotal connection to the tractor, the interconnections with the guide members being pivot joints permitting generally free oscillation between the angling jacks and the guide members about a generally vertical axis, the interconnections with the C-frame pivotally permitting oscillation between the angling jacks and the C-frame about axes generally perpendicular to the axes of the pivot joints, and wherein the blade has end portions angling forwardly from the central portion to provide for adequate side shifting of material by the blade when the blade is angled in either direction with reduced motion of the angling jacks and reduced stress in the mounting arrangement while concurrently permitting the blade to be supported in closer relation to the tractor.

2. The invention of claim 1 wherein the T-shaped bars are formed by bifurcated members secured to the C-frames and extending upwardly therefrom, and elongated plates arranged in generally horizontal relation above both of the bifurcated members to which they are respectively secured, each plate being replaceably secured to both sides of the respective bifurcated members, and wherein the pivots between the brace members and the blade are formed by ball joints.

3. The invention of claim 2 wherein the extendible portions of each angling jack include a cylinder pivoted to the respective C-frame and a rod interconnected to the respective guide member by the pivot joint.

4. A mounting and conTrol arrangement for supporting a bulldozer blade at one end of a tractor having a C-frame including legs pivoted to respective sides of the vehicle and an intermediate portion transversely arranged at the one end of the tractor comprising a ball joint arranged between a central portion of the blade and the intermediate C-frame portion, a T-shaped bar secured to each C-frame leg, the T-shaped bars being formed by bifurcated members secured to the C-frames and extending upwardly therefrom, and elongated plates arranged in generally horizontal relation above both of the bifurcated members to which they are respectively secured, each plate being replaceably secured to both sides of the respective bifurcated member, a guide member slidably mounted on each T-shaped bar, each guide means comprising two structural elements being secured together to form a longitudinal slot for receiving the respective elongated plate and a longitudinal opening thereabove for receiving the rod, each guide member having cylindrical bearing surfaces in vertically aligned relation above and below the longitudinal opening respectively, a triangular brace secured to each guide member by a ball joint, each brace including upper and lower brace members respectively and pivotally secured to upper and lower portions of the blade at one end thereof, the upper members of the braces being hydraulic jacks, and a hydraulic angling jack having extendible portions interconnected between each guide member and the C-frame relatively adjacent its pivotal connection to the tractor, the interconnections with the guide members being pivotable trunnion mountings including the respective bearing surfaces in the guide members and permitting generally free oscillation between the angling jacks and the guide members about a generally vertical axis, the interconnections with the C-frame pivotally permitting oscillation between the angling jacks and the C-frame about axes generally perpendicular to the axes of the pivot joints.

5. The invention of claim 4 wherein the ball joint for securing the triangular brace to each guide member comprises a ball integrally formed with one of the structural elements.

6. A mounting and control arrangement for supporting a bulldozer blade at one end of a tractor having a C-frame including legs pivoted to respective sides of the vehicle and an intermediate portion transversely arranged at the one end of the tractor comprising a ball joint for supporting a central portion of the blade upon the intermediate C-frame portion, a T-shaped bar secured to each C-frame leg, guide members forming elongated slots for slidably receiving the respective T-shaped bars, each guide member comprising two structural elements being secured together to form a generally cylindrical bore, the two structural elements of each guide member mating and being secured together above and below the cylindrical bore, a triangular brace secured to each guide member by a ball joint, a portion of the ball joint being integrally formed with an inner one of the structural elements, each brace including upper and lower brace members respectively and pivotally secured to upper and lower portions of the blade, and a hydraulic angling jack having extendible portions respectively interconnected between each guide member and the respective C-frame relatively adjacent its pivotal connection to the tractor, the interconnection between one extendible portion of each jack and the C-frame being a pivot joint permitting generally free oscillation about a horizontal axis, the other extendible portion of each jack penetrating the cylindrical bore of the respective guide member and being supported therein by a trunnion mounting for substantially free oscillation about a vertical axis.

7. The invention of claim 6 wherein the one extendible portion of each angling jack is its rod and the other extendible portion of each angling jack is its cylinder.

8. A Mounting and control arrangement for supporting a bulldozer blade at one end of a tractor having a C-frame including legs pivoted to respective sides of the vehicle and an intermediate portion transversely arranged at the one end of the tractor comprising a ball joint for supporting a central portion of the blade upon the intermediate C-frame portion, a T-shaped bar secured to each C-frame leg, guide members forming elongated slots for slidably receiving the respective T-shaped bars, each guide member comprising two structural elements being secured together to form a generally cylindrical bore, a triangular brace secured to each guide member by a ball joint, a portion of the ball joint being integrally formed with one of the structural elements, each brace including upper and lower brace members respectively and pivotally secured to upper and lower portions of the blade, a hydraulic angling jack having extendible portions respectively interconnected between each guide member and the respective C-frame relatively adjacent its pivotal connection to the tractor, the interconnection between one extendible portion of each jack and the C-frame being a pivot joint permitting generally free oscillation about one axis, the other extendible portion of each jack penetrating the cylindrical bore of the respective guide member and being supported therein by a trunnion mounting for substantially free oscillation about another axis generally perpendicular to the one axis for the pivot joint between the one extendible jack portion and the C-frame, and wherein the two structural elements of each guide member mate and are secured together at the respective sides of the cylindrical bore, the ball of the ball joint for the respective brace being integrally formed with a lower one of the structural elements which also forms the elongated slot for receiving the T-shaped bar, the structural elements also including coaxial and vertically aligned bores serving as bearings for the trunnion mounting, the other extendible portion of each jack having radially extending pins which are received by the respective bores in the structural elements.