Traversing hoists – Boom position lock
Reexamination Certificate
1999-03-18
2001-04-17
Brahan, Thomas J. (Department: 3652)
Traversing hoists
Boom position lock
C212S348000
Reexamination Certificate
active
06216895
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a locking device for telescopic sections of a telescopic jib, and more particularly to the jib of a crane or mobile crane having such a locking device.
Crane jib telescopic sections are lockable in the extended condition to, among other things, relieve the load on the telescoping system. This applies especially when use is made of entraining means, for example piston/cylinder units, for extending the telescopic sections in bringing one telescopic section after the other into the extended or retracted positions.
For locking telescopic sections use is made mostly of locking pins, which engage from one telescopic section into a receiving portion of the adjoining telescopic section. In earlier practice such pins were retracted from the outer side of a surrounding telescopic section inward into a receiving portion of the telescopic section located within. On the one hand, this is an unsightly disadvantage, since exposed locking units spoil the neat design of the jib as a whole. On the other hand, such conventional jibs and pinning systems necessitate disposing a power supply (hydraulics, pneumatic system, etc) to the pinning means on the outer side of the jib, which is a technical complication to be avoided.
In a very early practice, such as disclosed in U.S. Pat. No. 4,036,372 a locking system with locking pins engage from an inner telescopic section outwards into receiving portions of an outer telescopic section, as a result of which the locking system could be disposed in the interior of the jib, thus obviating the need of locating power supplies on the outer side of the jib. However, the drawback in this system is that each of the locking pins engages the upper or lower plates of the telescopic section, i.e. at locations at which maximum bending stresses (tension at the top, compression below) occurs due to the external loads. In addition to this the release device described in this patent operates with double-acting cylinders and is thus, for this reason alone, relatively complicated.
Known from EP O 661 213 Al is a locking device for telescopic sections in which a locking pin guided in an inner telescopic section is able to engage a receiving portion in an outer telescopic section. This document describes the use of spring-biased locking pins in which the pin is maintained in a locked position by the force of a spring, whilst the inner end of the pin can be engaged by a hydraulic release device to return the pin into the released position in overcoming the force of a spring. A parallel description of the same design is described in U.S. Pat. No. 5,628,416.
In the last-mentioned locking device only a single locking pin is provided for locking two telescopic sections, this locking pin engaging the top flange shells of the jib sections in the middle. Thus, here too, there is again the disadvantage that the passages for the locking pins are provided just in the cross-sectional zone of the jib profile where maximum tensile stresses occur and, therefore, the structure of the jib sections is interrupted at an unsuitable location due to the recesses.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a locking device for telescopic jibs which obviates the above mentioned drawbacks of prior art, it being more particularly the intention to provide a locking device which permits a necessary structural weakening of the jib profile with minimum disadvantage to stability.
This object is achieved in accordance with the invention in that two locking pins, each of a locking unit, are arranged on each inner telescopic section so that they can be caused to engage with two oppositely located receiving portions in the vertical side webs of the outer telescopic section, i.e. preferably in the middle portion of the side webs.
The special advantage afforded by the locking device in accordance with the invention is that the receiving portions and passages needed for the locking pins are disposed in a zone of the jib in which the bending load forces produce bending stresses in the jib of no significance. In loading a jib or its telescopic sections when lifting a load a maximum tensile stress occurs on the upper side of the profile and a maximum compressive stress materializes on the underside.
This also applies to the side webs of the profile, a zone materializing, however, which is substantially stress-neutral in the middle portion of the side web. In accordance with the invention it is just in this substantially stress-neutral zone that the locking units are now disposed so that the structural weakening materializing from the necessary passages in the webs are of minimum disadvantage to the stability in this case. Since the bending stresses occurring in this case are relatively slight, this weakening of the structure is minimal and acceptable.
In one preferred embodiment of the present invention the release device comprises a hydraulic actuating cylinder arranged on a piston/cylinder unit, more particularly on the head of the cylinder at the piston output end parallel to the longitudinal axis thereof. The aforementioned piston/cylinder unit serves to extend or retract the telescopic sections and is thus already provided with a hydraulic system. This hydraulic system can be made use of simultaneously to actuate the hydraulic actuating cylinder, which is arranged to advantage space-savingly parallel to the longitudinal axis of the piston/cylinder unit.
The release device preferably comprises a lever, which converts the actuation of the hydraulic actuating cylinder so that an engaging end of the lever is moved substantially in the axial direction of the locking pins. By means of such a lever simple and reliable conversion of the direction of movement of the actuating cylinder by 90° is assured.
The engaging end of the lever is preferably configured so that on axial travel of the piston/cylinder unit it can be brought into engagement with a clasp at the inner end of the locking pin. For this purpose the engaging end of the lever advantageously comprises a T-shaped protuberance which can be brought into engagement with a longitudinally slotted clasp on the inner end of the locking pin, thus making it possible to bring this release device into the respective position suitable for releasing the locking pins by the method of the release device with the head of the piston/cylinder unit. When the device is moved each time to the suitable location by position monitoring, the engaging end of the lever of the release device engages the inner clasp of the locking pin so that the locked position can be released when the hydraulic cylinder is set in motion. In this arrangement it needs to be assured that the jib sections are retained at all times either by means of the locking pins or are locked in place by an entraining device.
In one embodiment of the locking device in accordance with the invention the release device is arranged on the head of the piston/cylinder unit above an entraining device for extending the telescopic sections, the locking pins being located parallel to the entraining pins. In this arrangement the entraining device may be a conventional assembly having extensible entraining pins and receiving portions provided therefor in the telescopic sections
In a further advantage aspect of the locking device in accordance with the invention the outer end of the locking pins comprises a nose protruding opposite to the telescopic extension direction. In the locked condition of two sections the nose clasps the adjoining part of the receiving portion behind the outer wall of the outer section.
Unlike the fully surrounding safety collars as proposed in prior art (see EP O 661 231 Al) a nose such as above permitting hook attachment to the outer telescopic section thus ensuring that the pin in the locked condition of two telescopic sections cannot be accidentally retracted, has the advantage that when the lock is released, i.e. when the telescopic cylinder is extended somewhat with the inner section to enable the locking pi
Erdmann Gerd
Richter Frank
Birch & Stewart Kolasch & Birch, LLP
Brahan Thomas J.
Grove U.S. L.L.C.
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