GB2104475A - Crane slewing mechanism - Google Patents

Abstract

A slewing mechanism for a folding boom crane of a type which is mounted to a vehicle includes a bearing block (23), a rotatable pivot pin (21) located within the bearing block for supporting a pillar of the crane, a rack (35) extending into the bearing block for meshing engagement with motion translating elements (32) of the pivot pin, and fluid actuated pistons (34) for imparting reciprocating linear motion to the rack. Linear motion of the rack (35) causes rotary motion to be imparted to the pivot pin (21). The motion translating elements (32) of the pivot pin comprise rod-like elements which are disposed in spaced-apart parallel relationship around the circumference of the pivot pin (21) in the manner of pinion teeth and, although the elements are normally held captive to the pivot pin, such elements are individually removable from the pivot pin and are replaceable in the event that they should be worn excessively or be damaged. <IMAGE>

Description

SPECIFICATION Crane slewing mechanism This invention relates to a slewing mechanism for a crane.

The slewing mechanism has particular but nonexclusive application in a crane of a type which is suitable for mounting to a truck and which has a folding boom. Such a crane is usually mounted to a chassis structure rearwardly of a truck cabin and is employed for lifting loads onto and from the loadcarrying table or platform of the truck.

Slewing mechanisms which currently are employed in truck mounted cranes have a main pivot pin which is carried in a bearing block for rotation about a vertical axis. The main pin comprises a lower extension of the king post of the crane and it is formed with a pinion which meshes with a horizontally disposed rack. Translational (reciprocating) motion is imparted to the rack by hydaulic pistons and such motion causes rotation of the pinion/main pin and hence, causes slewing of the crane about the axis of the main pin. The pinion is formed by gear cutting the main pin and, thus, the pinion is formed as an integral part of the main pin.

Such prior art slewing mechanisms suffer the disadvantage that, if high torsional loads, particularly shock loads, are imposed on the main pin, the pinion teeth are caused to shear and the entire main pin must then be replaced. This problem can be alleviated to a certain extent by manufacturing the pinion/main pin from high tensile steel, but a complete solution would require that the pinion teeth be increased substantially in size. However, it has not been feasible to increase the size of the pinion to a sufficient extent to accommodate all possible shock loads because, apart from the unacceptably high cost of so doing, an appropriate dimensional increase would result in such a large increase in the overall size of the slewing mechanism that it could not be accommodated within the confined space that is available in most vehicles for mounting a crane.

The present invention seeks to avoid the above stated problem of prior art devices by providing a slewing mechanism having a main pivot pin which is provided with replaceable rack-engaging motion translating elements. Such elements may be formed from a material which has the capacity to withstand normally expected torsional loads and, in the event that one or more of the elements may be damaged by unexpectedly high shock loads, only the elements themselves will need to be replaced.

Thus, the present invention provides a slewing mechanism for a crane and which comprises: a bearing block, a pivot pin located within the bearing block for rotation about its own axis, and a rack projecting into the bearing block. The rack is engageable with motion translating elements of the pivot pin in a manner such that linear motion of the rack imparts rotational motion to the pivot pin, and the motion translating elements are normally held captive to the pivot pin for meshing engagement with the rack but are removable from the pivot pin and replaceable in the event that they should become excessively worn or damaged.

The motion translating elements may be formed as teeth of a sleeve type pinion which is fitted and held captive to the pivot pin but which is removable and replaceable in the event that any of the teeth should become worn or damaged. However, the motion translating elements preferably comprise a plurality of longitudinally extending rods which are disposed in spaced-apart parallel relationship around the circumference of the pivot pin for meshing engagement with the rack.

The motion translating elements may be removable from the pivot pin either individually or collectively. However, when in the form of rods, the motion translating elements preferably are individually slidable from the pivot pin in the direction of their respective longitudinal axes.

The pivot pin preferably includes upper and lower flanges and, in such case, the motion translating elements would extend in the longitudinal direction between the flanges. When in the forms of rods, the motion translating elements most preferably locate in part in individual grooves which extend between the flanges of the pivot pin, such that the elements project outwardly from the body of the pivot pin in a manner similar two teeth of a pinion.

The motion translating elements most preferably comprise high tensile steel rods, and they may be held captive to the pivot pin by tack welding them in position. Following assembly of the motion translating elements to the pivot pin, if any one or more of the elements is or are to be removed from the pivot pin this can be achieved by drilling or otherwise machining into the weld metal. In an alternative arrangement, the motion translating elements may be held captive to the pivot pin by locking screws or the like.

The invention will be more fully understood from the following description of a preferred embodiment of a slewing mechanism for a truck self-loading crane. The description is given with reference to the accompanying drawings wherein: Figure 1 illustrates a general arrangement of a truck self-loading crane with the boom thereof shown in three (alternative) positions, Figure 2 shows an elevation view of a (lower) slewing mechanism portion of the crane as illustrated in Figure 1, Figure 3 shows an elevation view of the slewing mechanism as seen in the direction of arrow 3 as shown in Figure 2, Figure 4 shows a sectional plan view of the slewing mechanism as viewed in the direction of section plane 4-4 as shown in Figure 3, and Figure 5 shows a sectional elevation view of the slewing mechanism as viewed in the direction of section plane 5-5 as shown in Figure 4, but with a main pivot pin of the mechanism being illustrated in full elevation.

As shown in Figure 1 of the drawings, the crane comprises a slewing mechanism 10 which is mounted to a supporting structure 11. The supporting structure would normally from a part of the chassis or sub-frame of a truck (not shown) and be located immediately behind the cabin of the truck.

A pillar or so-called king post 12 is rigidly mounted to the slewing mechanism 10 and, as such, is rotated about the vertical axis of the slewing mechanism when a main pivot pin of the slewing mechanism is itself caused to rotate.

Afirst boom section 13 is pivotably mounted to the upper end of the kind post 12 and is coupled to a lower section of the king post by a telescopic ram 14.

Also, a second boom section 15 is connected to the first section 13 by way of a pivot pin and knuckle 16, and a second telescopic ram 17 connects between the first boom section 13 and the knuckle. The second ram 17 when actuated causes the second boom section 15 to pivot relative to the first section 13.

A third boom section 18 is located telescopically within the second section 15 and is extendable with actuation of a third ram 19. A sling cleat 20 is affixed to the end of the third boom section 18.

With appropriate hydraulic drive to the rams 14,17 and 19, the boom can be located in or be extended to any one of a number of positions between an initial folded position and a fully extended position.

The arrangement per sue of the king post and boom sections as shown in Figure 1 is not significantly different from corresponding arrangements in prior art crane structures, and, in the context of the present invention, the significant features reside in the slewing mechanism 10 as illustrated in detail in Figures 2 to 5.

The slewing mechanism 10 comprises a main pivot pin 21 which is fitted with a thrust bearing collar 22, a housing (i.e., a bearing block) 23, and a pair of horizontally opposed piston cylinders 24 affixed to the housing 23.

As best seen from Figure 5, the pivot pin 21 includes an upper portion 25 which projects upwardly from the housing 23 and a lower portion 26 which locates within the housing. The lower portion 26 of the pivot pin is formed approximately midway along its length with a circumferential groove 27, and the groove may be considered as being defined by vertically spaced flange or shoulder portions 28 of the pivot pin.

The pivot pin 21 is rotatable within the housing 23 and is supported by a bearing bush 29 and a sleeve 30.

Although not shown in the drawings, a cap plate would normally be welded onto the upper portion 25 of the pivot pin 21 and a corresponding base plate would be welded to the bottom of the king post 12 (Figure 1). Then, the slewing mechanism 10 would be coupled to the king post 12 by bolting the cap and base plates together. Also, the housing 23 is formed with a base plate 31 which is bolt connected or welded to the supporting framework of a truck to which the crane is in use mounted.

A number of longitudinally extending motion translating elements 32 are located around the periphery of the groove 27, the elements having the function of and being somewhat similar in construction to pinion teeth. However, it is stressed that the elements are not formed as conventional pinion teeth, in the sense that they are not gear cut to form an integral part of the pivot pin itself. Rather, the respective motion translating elements 32 comprise separate pins or rods which are inserted into and are removable from sockets 33 which are formed within the pivot pin.

The sockets 33 are formed as holes which are located around a required pitch circle diameter and which are drilled into the pivot pin 21 from the lower end thereof prior to formation of the groove 27 in the pivot pin. Thus, the holes are drilled and, thereafter, the groove 27 is machined to a depth corresponding to one-half of the diameter of the drilled holes. By this procedure, a series of semi-circular channels are exposed during the machining of the groove 27, the channels effectively extending between the flanges or shoulders 28 of the pivot pin.

After drilling of the sockets 33 and formation of the groove 27, the rods (motion translating elements) 32 are inserted into the respective sockets 33 in the longitudinal direction of the pivot pin and the rods are thereafter tack welded in position. Then, if it is required at any time that one or more of the rods 32 should be removed, the tack welding is drilled away and such elements may be extracted from the pivot pin and be replaced.

The rods 32 have a circular-section which may be preserved along the full longitudinal length of the rods or, as shown in Figure 4 of the drawings, after the rods have been fitted in the respective sockets the outer margin of the rods may be machined so that they are each provided with a flat or arcuate surface.

A piston 34 is located in each of the cylinders 24, and a square-section rack 35 extends between and interconnects the two pistons.

The rack 35 is disposed horizontally for translation back and forth within the cylinders 24 and through the housing 23. Hydraulic fluid is admitted to one or the other of the cylinders 24 so as to effecttransla- tion of the rack 35 in a reciprocating manner, and the rack is provided with teeth 36 which engage with the pivot pin rods 32 to impart rotational movement to the pivot pin 21 with reciprocating motion of the rack 35.

Thus, hydraulic fluid is admitted to one or the other of the cylinders 24 to effect slewing of the crane which is mounted above the slewing mechanism 10.

Adjustable bearing pads 37 are located within the housing 23 and bear against the rack 35 to hold the rack in positive meshing engagement with the pivot pin rods 32. The bearing pads 37 may be adjusted positionally to accommodate any wear in the rack and/or pivot pin rods.

Claims (11)

1. A crane slewing mechanism comprising a bearing block, a rotatable pivot pin located within the bearing block and supported for rotation about its own axis, a rack extending into the bearing block and engagable with motion translating elements of the pivot pin in a manner such that linear motion of the rack causes rotary motion to be imparted to the pivot pin, and means for imparting reciprocating linear motion to the rack; characterised in that the motion translating elements of the pivot pin are normally held captive to the pivot pin for meshing engagement with the rack but are removable from the pivot pin and replaceable in the event that they should become excessively worn or damaged.

2. The mechanism as claimed in claim 1 characterised in that the motion translating elements comprise a plurality of longitudinally extending rods which are disposed in spaced-apart parallel relationship around the circumference of the pivot pin for meshing engagement with the rack.

3. The mechanism as claimed in claim 2 characterised in that the rods are individually slidable from the pivot pin in the direction of their respective longitudinal axes.

4. The mechanism as claimed in claim 2 or claim 3 characterised in that each of the rods has a substantially circular cross-section.

5. The mechanism as claimed in any one of claims 2 to 4 characterised in that the pivot pin includes upper and lower flanges, and in that the rods extend in a longitudinal direction between the flanges.

6. The mechanism as claimed in claim 5 characterised in that the rods are located in part within respective grooves which extend in a longitudinal direction between the flanges.

7. The mechanism as claimed in claim 6 characterised in that respective ones of the grooves are formed coincident with holes which extend through one of the flanges and into the other flange, each hole forming a socket in which one of the rods is located.

8. The mechanism as claimed in claim 7 characterised in that the rods are tack-welded in position in the respective sockets.

9. The crane slewing mechanism substantially as illustrated in Figures 2 to 5 of the accompanying drawings and substantially as hereinbefore described with reference thereto.

10. A crane incorporating a slewing mechanism as claimed in any one of the preceding claims.

11. A crane substantially as illustrated in Figures 1 to 5 and substantially as hereinbefore described with reference thereto.