GB2127073A - Workhead with elastomeric pivots - Google Patents

Abstract

This invention provides a tamping workhead (10) having a vertically movable carriage (25) mounting a tamping support unit (20), said unit (20) carrying a vibratory motor (22) and ballast tamping blades (21), an elongated non- circular tube (41) fixed in said carriage (25) on an axis about which the support unit (20) is to pivot, said support unit (20) having fixed plates (42) proportioned to closely fit over the ends of said tube (41), a pair of elastomer bushings (43) having an outer shape like the tube (41) cross section and being forced fitted one into each end of said tube (41) so as to be spaced along said axis, said bushings (43) having bonded inner sleeves (44), and means (51-55) including a shaft (51) passing through said sleeves (44) and said plates (42) for locking the plates (42) and sleeves (44) against relative rotation, whereby the support unit (20) can pivot about said axis by resiliently deflecting said bushings (43). <IMAGE>

Description

SPECIFICATION Workhead with elastomeric pivots This invention relates generally to railroad track maintenance equipment and more particularly concerns a tamping workhead with elastomeric pivots.

Railroad tamping workheads such as those disclosed in United States Patent No. 3,725,156 to Anderson, issued December 7, 1972, are subject to extremely severe working conditions. The workheads carry powerful vibration motors which shake the workheads as well as the track ballast, and hydraulic actuators drive into the ballast, and tilt and squeeze the tamping blade sets thereby imposing heavy strains on the workhead parts. Typically, the working environment is dirty, and the work cycle is rapid and repeated over and over during a working day.

Under such conditions, workhead pivot bearings require careful lubrication maintenance and, even so, rapid wear is inevitable. As soon as even slight bearing wear occurs, the workheads become noisy and further wear is accelerated leading to the need for major overhaul and replacement.

According, it is the primary aim of the invention to provide a tamper workhead that is strong and gives good control of the tamping blades, but which does not use conventional bearings or other rubbing parts to mount the blades for tilting and squeezing motions. A collateral object of the invention is to provide such a workhead that is quieter in operation and reduces vibration transmitted back to the tamper frame.

It is also an object to provide a workhead of the above type in which the structure permitting blade tilting and squeezing is extremely close fitting so as to minimize wear-inducing clearances and eventual heavy wear, noisy operation and repair.

Another object is to provide a workhead of the foregoing character in which the blade tilting and squeezing axes require no lubrication, thus simplifying and reducing maintenance costs, and making it less likely that an inadvertent service lapse will result in premature failure.

Yet another object is to provide a workhead as characterized above that is nevertheless economical to manufacture.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: Figure 1 is a fragmentary side elevation of a portion of a tamper showing a workhead embodying the present invention; Figure 2 is an enlarged side elevation of the workhead shown in Figure 1; Figure 3 is a partial section taken approximately along line 3-3 in Figure 2; Figure 4 is an enlarged section taken approximateliy along line 4-4 in Figure 2; Figure 5 is an end elevation with parts removed of the structure shown in Figure 4; Figure 6 is a section taken approximately along line 6-6 in Figure 4; and Figure 7 is a perspective of one of the bushings used in the workhead of Figure 1.

While the invention will be described in connection with a preferred embodiment, it will be understood that I do not intend to limit the invention to that embodiment. On the contrary, I intend to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Turning now to Figure 1,there is shown a workhead 10 embodying the invention mounted on columns 11 forvertical movement. The columns 11 are fixed in a tamper frame 12 riding on a railroad track 13 of which a rail 14 and ties 15 are shown. The workhead 10 includes four tamper support units 20, each carrying a pair of tamper blades 21 and a vibratory motor 22. The units 20 are arranged so that lowering the workhead 10 positions a pair of blades 21 on either side of the tie 15 to be tamped, with blade pairs being both inside and outside of the overlying rail 14.

Each tamper support unit 20 is mounted on one of a pair of lower workhead carriages 25, and both such carriages 25 are in turn mounted on an upper workhead carriage 26 that is guided on the columns 11. The illustrated workhead 10 is a dual pivot workhead, which means that hydraulic actuators 27 extending between the lower carriage 25 and the support units 20 can pivot the units about axes defined by pivot asssemblies 28 and 29, two assemblies 28 being illustrated, to squeeze the blades 21 under the ties 15. In addition, actuators 31 extending between the upper and lower carriages 26, 25 pivot the lower carriages, and thus the support units 20, about axes defined by pivot assemblies 32 to tilt the blades 21 under the rail 14. In this way, the critical ballast area beneath both the tie and rail is reached for effective compaction.

In accordance with the invention, the pivot assemblies 28, 29, 32 utilize elastomer bushings with there being no play or clearance between relatively moveable parts other than through the elastomeric material of the bushings. Since the pivot assemblies are similar except for overall length, the assemblies 32 being axially shorter than the assemblies 28,29, only the assembly 28 will be described in detail with it being understood that the general description applies to all.

The assembly 28 includes an elongated noncircular tube 41 fixed in the lower workhead carriage 25 on the axis about which the associated support unit 20 is to pivot. Preferably, the cross-section is substantially square. The associated support unit 20 includes fixed plates 42 proportioned to closely fit over the ends of the bearings 56. A pair of elastomer bushings 43 having an outer shape like the tube cross-section, in this case substantially square, are force-fitted one into each end of the tube so that they are spaced along the pivot axis. The elastomer, conventionally rubber, bodies of the bushings 43 are bonded to inner metallic sleeves 44 into which a keyway 45 is cut. The sleeves 44, together with a relatively thin, cylindrical band of elastomer material surrounding the sleeve ends, extend axially from each end of the bushings (see Figure 7).

The outer shape of the bushings 43 and the inner tube shape are proportioned so that there is a very tight interference fit, requiring something on the order of a ten ton press force to place the bushings in the tube. The elastomer material is thus compressed between the tube 41 and the inner bushing sleeves 44.

The bushing sleeves 44 are locked to the support unit plates 42 by a shaft 51 passing through the sleeves 44 and the plates 42. Keys 52 fix the shaft 51 against rotation with the sleeves 44. The ends of the shaft 51 are flattened on two opposite sides (see Figure 5), and a slot 53 in a locking plate 54 is closely fitted on each shaft end and the locking plates are secured to the adjacent plates 42 by a plurality of screws 55. Thus, the bushing sleeves 44 become rotationally rigid with the support unit plates 42.

In order to maintain properfirm alignment without play or clearance in the assembly 28, metallic bushings 56, preferably steel, are closely fitted on the ends of the shaft 51 and are interposed between the shaft and the holes in the plates 42 through which the shaft passes. The axial length of the bushings 56 is such that the bushings are driven tightly against the outer ends of the bushing sleeves 44 by the locking plates 54 as the plates are tightly screwed to the unit plates 42. This tight engagement should be sufficient to require slight distortion of the elastomer of the bushings 43, with the result that the assembly is tightly locked against all relative movement accept through the resilience of the body portions of the bushings 43.

Extending the associated actuator 27 will thus rotate the bushing sleeves 44 within the tube 41 by circumferentially resiliently distorting the elastomer material of the bushings 43. There is no rubbing movement of parts along this pivot axis. It can thus be seen that conventional bearings requiring conventional lubrication maintenance have been eliminated mounting the blades 21 for tilting and squeezing movement.

The resilience within the several pivot axes also results in a workhead that is quieter in operation and which reduces vibration transmitted back from the motors 22 to the tamperframe 12.

The pivot axes assemblies of the workhead 10 are extremely close fitting so as to eliminate clearances between relatively moving parts which inherently eventually wear, producing a noisy assembly that quickly becomes progressively worse requiring repair and replacement.

Despite these advantages, those skilled in the art will appreciate that the workhead 10 is economical to manufacture since it avoids conventional bearings and lubrication systems for those bearings.

Claims (4)

1. In a tamping workhead having a vertically moveable carriage mounting a tamping support unit, said unit carrying a vibratory motor and ballast tamping blades, the improvement comprising, in combination, an elongated non-circular tube fixed in said carriage on an axis about which the support unit is to pivot, said support unit having fixed plates proportioned to closely fit over the ends of said tube, a pair of elastomer bushings having an outer shape like the tube cross section and being forced fitted one into each end of said tube so as to be spaced along said axis, said bushings having bonded inner sleeves, and means including a shaft passing through said sleeves and said plates for locking the plates and sleeves against relative rotation, whereby the support unit can pivot about said axis by resilliently deflecting said bushings.

2. The combination of claim 1 in which said means includes metallic bushings closely fitted on the ends of said shaft which are driven tightly against the outer ends of said bushing sleeves so that there is no play or clearance between said carriage and said support unit other than through the resillience of said bushings.

3. A combination of claim 1 in which said tube and the outer shape of said bushings are substantially square in cross-section.

4. Atamping workhead substantially as hereinbefore described with reference to the accompanying drawings.