GB2053149A - Telescopic crane booms - Google Patents

Abstract

Locking means remotely operable are provided to lock together adjacent sections of a telescopic boom when partly extended and the locking means transfer the load from one section to an adjacent section. In this way, rams or other extending means can be used for telescoping operations but can then be relieved of loads resulting from using the boom. As shown pins at 9, 10 can respectively lock together sections 2, 3 and 3, 4 of boom 1 by passing through apertures in selected ones of reinforcing plates 11 spaced along the sections 2, 3. Eight different boom extensions are thus available. <IMAGE>

Description

SPECIFICATION Crane Booms This invention relates to telescopic crane booms and in particular booms which are to form part of a mobile truck or vehicle mounted crane.

Rams which are housed in the boom sections of telescopic crane booms are generally long and in order to keep the boom weight to a minimum are slender. In such cranes it will be appreciated that much of the load of the frame when in use is taken by the ram cylinder walls which have to resistto inward telescoping of the sections when under the effect of the load. It thus happens that, particularly in large telescopic boom cranes, the lifting capacity of the crane is very much limited by the ram capacity.

Increase of ram wall thickness is not an attractive option since this increases the total boom weight which is a limited and undesirable possibility with truck mounted cranes.

Afurther problem with telescopic boom cranes, particularly those with longer booms, is that the long piston rods come under great strain when the boom is extended and under load and tend to bucke. The greater the extension, clearly the greater the susceptibility to buckling and the greater must be the load reduction.

Because of such problems with known boom constructions, for some large cranes the maximum load with the boom even fractionally extended may be reduced by as much as 50% of the maximum load for a fully retracted boom. This is despite the structural strength of the booms section's permitting a much higher duty. Of course when the boom sections are fully closed, the thrust is carried by the boom sections rather than the ram or rams and the full structural limit of the boom may be realised.

The invention has therefore been made with these points in mind and it is an object of the invention to overcome or mitigate the aforesaid disadvantages.

According to the invention, there is provided a telescopic crane boom which comprises two or more boom sections telescopically movable relative one another and extendable and retractable by driving means operating between adjacent sections, and locking means remotely operable to lock together adjacent sections when they are at least partially extended relative one another so as to transfer load from one adjacent section to the other.

The provision of the locking means which are preferably a remotely operable pin on one section capable of engaging in one or more holes in the other section, enables the stress from an upper or outer section to be transferred to a lower or inner section substantially without significant stress on the extension means which can thus be relieved of large loads which might destroy or damage the drive means.

Semi-tower cranes whose tower portions are pinned whilst in a strictly vertical position have been proposed. However, it has not been the practice in telescopically adjustable boom cranes to relieve the rams or other drive means of the stress by locking means between sections such as can be remotely operable from the crane cab, so that the crane operator may choose the required boom extension irrespective of the angle of elevation of the boom and then lock the boom sections together and so relieve the ram or rams of its or their duty. This allows loads to be lifted which take full advantage of the structural strength of the boom, which increases the crane capacity for a given all up weight. This is most important for truck mounted mobile cranes where it is important to keep the weight of the boom to a minimum.

The drive means are preferably hydraulic rams, an extensible ram being mounted between each adjacent pair of sections. However, other drive means such as a screw can be used.

Preferably, the locking means comprises a pin carried by one section and movable into one of a plurality of holes in the adjacent section, which holes has additional local reinforcement over the remainder of the boom section material.

Suitably, this pin is formed with the pin actuator at least partially located within the pin to reduce to a minimum the amount of space taken up by a locking means. This is important since any protrusion on the underside of the boom is liable to damage by the hoist rope when the boom is at its maximum angle.

So that the crane operator will know when the locking means can be operated, it is preferred that cam means be provided on one adjacent section to contact a switch on the other which is actuated by the cam means when the relative extension of adjacent boom sections is such that its locking means can be operated to lock the adjacent sections in that relative position of extension.

An embodiment of a telescopic crane boom according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure lisa side elevation of a boom according to the invention in its retracted position and shown mounted on a vehicle as part of a mobile crane; Figure 2 is an elevation of the extended telescopic crane boom according to the invention; Figure 3 is an enlarged elevation of the junction of two adjacent sections of the boom of Figure 2; Figure 4 is a further enlarged part section of the locking arrangement taken on line 4-4 of Figure 3; Figure 5 is a further part section of the locking arrangement taken on line 5-5 of Figure 4; Figure 6 is a section similar to Figure 5 showing the locking arrangement engaged between the two sections of the boom; and Figure 7 is a section similar to Figure 4 but showing the locking arrangement engaged between the two sections of the boom.

The boom 1 shown in Figures 1 and 2 has three boom sections 2, 3 and 4. Section 2 is extendable from section 3 by means of a first hydraulic ram 5 including a ram cylinder 5a and a piston rod Sb whilst section 3 is extendable from section 4 by means of a second hydraulic ram 7 including a ram cylinder 7a and a piston rod 7b.

At the ends of sections 3 and 4 are spaced pairs of flanges 8 and 8a and across the underside of these are fitted plates 8b. These plates carry the locking means between sections to be described in more detail below. Housings 9 and 10 cover these plates 8b to enclose the locking means and the housing 9 is shown in more detail in Figures 3 to 7. Housing 10 contains similar parts to housing 9 and will not be separately described.

At intervals along the sections 2 and 3 are horse-shoe shaped reinforcing plates 11 in which there are holes 15 in line with corresponding holes 15a in the sections 2 and 3. These holes are of a size to receive a locking pin axially slidably mounted in a sleeve 16a fixed between the lowerflange of the section 3 and the plate Sb; the holes 15 and 15a and pins 16 together comprise the locking means.

Each pin 16 is hollow and within it is a linear actuator in the form of a rotatable screw (not shown) positioned within a tube 17a in turn positioned within a cover 17. The screw engages with a non-rotatable nut (not shown) fixed to the bottom of the tube in the pin 16. The tube 17a is itself fixed to the pin 16 by means of a small pin 24. The screw is rotated by a motor 20 which drives the screw through a right angle worm gear positioned within a casing 22.

When the pin 16 reaches its lower disengaged limit position as shown in Figures 4 and 5, a limit switch 18 is actuated by a roller 25 mounted on a switch arm 27 acting on the underside of a bracket 26 fixed to the pin 16. Similarly, when the pin reaches its upper engaged limit position as shown in Figures 6 and 7 where the pin 16 transmits stress from one boom section to the other, the switch 18 is operated in the opposite direction by the roller 25 acting on the underside of an arm 29 forming part of the bracket 26. When operated, the switch 18 energises electrical circuits (not shown) to indicate the position of the pin to the operator, e.g. by the illumination of a lamp. The motor can be electrically operated or operated, for example, hydraulically or pneumatically.Instead of a single switch 18, one can have two switches, one of which is operated in the upper engaged limit position of the pin 16 and the other of which is operated in the lower discharge limit position of the pin 16.

By providing the screw within the pin 16, the housings 9 and 10 can be relatively small and compact.

Aligned with each reinforcing plate 11 and hole 15a and positioned on the sides of the sections 2 and 3 are cams 12 which contact a switch 13 fixed to the sections 3 and 4 respectively. When a cam 12 operates a switch 13, this can be used to indicate that the pin 16 is in line with one of the holes 15 to enable the locking pin to be engaged with one of the holes 15.

As will be seen from the drawings, in the boom shown, eight different boom extension lengths are obtained, six of these being pinned positions and two being fully retracted positions; each position can be about 2m apart. Clearly, additional positions can be provided if required.

As shown in Figure 1, the boom 1 can be mounted on a vehicle 50 to provide a mobile crane, the elevation of the boom being controlled by means of hydraulic rams 52. As will be appreciated, the locking means can be brought into operation irrespective of the angle of elevation of the boom.

Claims (12)

1. A telescopic crane boom which comprises two or more boom sections telescopically movable relative one another and extendable and retractable by drive means operating between adjacent sections, and locking means remotely operable to lock together adjacent sections when they are at least partially extended relative one another so as to transfer load from one adjacent section to the other.

2. A crane boom as claimed in Claim 1 in which the locking means are capable of locking adjacent sections together in one of a plurality of positions when at least partially extended relative one another.

3. A crane boom as claimed in Claim 1 or Claim 2 in which the drive means comprise a hydraulic ram operating between the or each adjacent pair of sections of the boom.

4. A crane boom as claimed in any preceding claim in which the locking means comprises a pin carried by one adjacent section and movable into an aligned one of a plurality of holes in the other adjacent section.

5. A crane boom as claimed in Claim 4 in which each hole has additional local reinforcement over the remainder of the boom section material.

6. A crane boom as claimed in Claim 4 or Claim 5 in which at least part of the actuating means for the pin are located within the pin.

7. A crane boom as claimed in any of claims 4 to 6 in which the pin is movable by means including a mating screw and nut and means for rotating the screw and nut relative one another.

8. A crane boom as claimed in any of claims 4 to 7 in which limit switch means are provided which are operated by movement of the pin to show whether the pin is engaged in a hole or disengaged.

9. A crane boom as claimed in any preceding claim in which cam means are provided on one adjacent section to contact a switch on the other which is actuated by the cam means when the relative extension of adjacent boom sections is such that the locking means can be operated to lock the adjacent sections in that relative position of extension.

10. A crane boom as claimed in any preceding claim and further comprising means for elevating the boom in an upright plane so as to adjust the elevation of the boom relative the horizontal, the locking means being operable irrespective of the elevation of the boom.

11. A telescopic luffing crane boom substantially as herein described with reference to the accompanying drawings.

12. A mobile crane having a boom as claimed in any preceding claim.