Mobile ballast tamper

#The present invention relates to improvements in a mobile machine for tamping ballast underneath a track consisting of two rails fastened to a plurality of spaced ties resting on the ballast, and more particularly to tamping machines which comprise a frame, a tamping unit vertically movably mounted on the frame and including a pair of vibratory tamping tools for tamping ballast under a respective one of the ties whereby the track is pressed upwardly, and means mounted on the frame for holding the track in position against the upward pressure to limit the upward movement of the track to a level controlled by a reference system.

#In track leveling operations wherein the track is lifted and ballast is tamped under the lifted ties, the track is sometimes raised beyond the desired grade because of switching delays in the control circuit for the track lifting tools and/or excessive compaction of the tamped ballast, etc. This causes errors in the leveled track. Various proposals have been made to avoid such errors, i.e. to control the lifting operation accurately and dependably and/or to control undue ballast pressure on the track, but they tend to increase the operating time and/or to produce uneven, and sometimes, insufficient ballast compaction. In an effort to overcome these disadvantages, it has been proposed to hold the track in position against the upward tamping pressure so that the track cannot rise above the desired grade.

#U.S. Pat. Nos. 3,744,428, dated July 10, 1973, and 3,910,195, dated Oct. 7, 1975, for example, disclose mobile ballast tamping machines with means mounted in the region of the tamping tools for holding the track in a fixed vertical position against upward pressure beyond a controlled grade. The disclosed track holding means comprise one or two closely spaced bearing rollers or rams pressed against the associated track rails by hydraulic motors to assume desired vertical positions controlled by a reference system in relation to which the track is leveled. These track holding devices have been successfully used in track leveling operations, but in some instances, particularly where several adjacent ties were tamped simultaneously, the locally limited transmission of downward pressure forces on the associated rails by the track holding devices of known structure has tended to produce irregularities in the track level.

#The above and other objects, advantages and features of the present invention will become more apparent from the following detailed description of certain now preferred embodiments thereof, taken in conjunction with the accompanying schematic drawing wherein

#FIG. 1 is a partial side elevational view of a mobile track tamper incorporating one embodiment of the track holding means according to this invention;

#FIG. 2 is a side elevational view of another embodiment of the track holding means; and

#Referring now to the drawing, wherein like reference numerals designate like parts functioning in a like manner in all figures, and first to FIG. 1, there is shown a mobile machine for tamping ballast underneath a track consisting of two rails 12, 12 fastened to a plurality of spaced ties S.sub.1, S.sub.2, S.sub.3 and S.sub.4 resting on ballast (not shown). Frame 2 of the machine is mounted on undercarriages 3, 3 for advancement along the track in the direction of the horizontal arrow shown in FIG. 1. Carrier frame 6 for tamping unit 4 is supported on guide beam 26 for movement in the direction of the track, the guide beam being fixed on machine frame 2 and hydraulic motor 5 being connected to the tamping unit carrier frame for moving the carrier frame in this direction. Tamping unit 4 is vertically movably mounted on support columns 27, 27 of carrier frame 6 and a conventional power-actuated drive is provided to move the tamping unit up and down. The tamping unit has at least one pair of vibratory tamping tools for tamping ballast under a respective one of the ties whereby the track is pressed upwardly, the illustrated unit including two pairs of vibratory tamping tools 7 spaced for simultaneously tamping two adjacent ties. The tamping unit further comprises means for actuating the tamping tools for imparting thereto a ballast tamping movement whereby the ballast is tamped under the respective ties, the illustrated actuating means including a central vibrating drive 9 and hydraulic motors 8 for reciprocating the tamping tools. Tamping units of this general type are well known and more fully disclosed and claimed, for instance, in U.S. Pat. No. 3,357,366, dated Dec. 12, 1967.

#While one particular embodiment of tamping head has been illustrated, the present invention is not limited thereto and any tamping unit with a pair of vibratory tamping tools reciprocable to tamp ballast under a tie positioned between the tools may be used in combination with the track holding means of this invention. In the embodiment of the invention illustrated in FIG. 1, the track holding means includes counterpressure beam 13 extending above each track rail 12 in the direction thereof in the region of the tamping tools. The counterpressure beam has three points of engagement with the associated rail, two points of engagement 14, 16 at the ends of the beam and intermediate point of engagement 15 centered therebetween and between the pairs of tamping tools. Each point of engagement is constituted by bearing surface 17 projecting from beam 13 towards the associated rail and adapted for gliding engagement therewith. These bearing surfaces form rams pressing against the rail under the downward pressure of power-actuated drives 11 which are linked to the counterpressure beam in the region of each beam end. The illustrated drives are hydraulic motors 10 whose upper ends are mounted on tamping unit carrier frame 6.

#This arrangement of the counterpressure beam on the tamping unit has the advantage that the vertical adjustment of the tamping tools and the track holding beam may be observed by the operator at the same time so as to exclude the possibility of damage to the beam during advancement of the machine from tamping station to tamping station. Since in most tampers, the tamping tools may also be moved laterally, i.e. transversely to the track, to center the tools over the rails, the mounting of the counterpressure beam on the tamping unit will automatically center the beams over the associated rails at the same time that the tamping tools are so centered, thus assuring proper alignment of the beams and rails in track curves, for example. The longitudinal movement of the tamping unit with the counterpressure beams is particularly useful in the illustrated arrangement for simultaneous tamping of several adjacent ties since this enables the end points of engagement 14 and 16 to be positioned in alignment with the adjacent, partially tamped ties while the intermediate point of engagement 15 is centered in the region of the ties to be tamped.