US2825472A - Selective travel draft gear - Google Patents

Description

B. E. PETERSON 2,825,472

SELECTIVE TRAVEL DRAFT GEAR March 4, 1958 8 Sheets-Sheet 1 Filed Nov. 5. 1955 INVENTOR.

Ii l 14M MM WJ, fi zm w/ W March 4, 1958 B. E. PETERSON 2,325,472

SELECTIVE TRAVEL DRAFT GEAR Filed Nov. 3, 1955 8 Sheets-Sheet 2 IN VEN TOR.

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' SELECTIVE TRAVEL. DRAFT GEAR Filed Nov. 3, 1955 8 Sheets-Sheet 3 IN V EN TOR.

A B E 4 N 7 B. E. PETERSON 2,825,472

SELECTIVE TRAVEL DRAFT GEAR March 4, 1958 8 Sheets-Sheet 4 Filed Nov. 3, 1955 INVENTOR.

Mardi 1958 B. E. PETERSON ,825,

SELECTIVE TRAVEL DRAFT GEAR 8 Sheets-Sheet 5 Filed Nov. 3, 1955 I INVENTOR.

Marnh 4, 1958 PETERSON 2,825,472

SELECTIVE TRAVEL DRAFT GEAR 8 Sheets-Sheet 6 Filed Nov. 5. 1955 March 4, 1958 B. E. PETERSON 2,825,472

SELECTIVE TRAVEL DRAFT GEAR 8 Sheets-Sheet 7 Filed NOV. 3, 1955 INVENTOR. Wm

March 4, 1958 B. E. PETERSON 2,825,472

SELECTIVE TRAVEL DRAFT GEAR Filed Nov. 3, 1955 8 Sheets-Sheet 8 FREE FALL (INCHES) T u P CLOSURE (mm-ass) 4 ig-1f IN V EN TOR.

Un ed m iimm 2,325,472 SELECTIVE TRAVEL BRA-FT GEAR Bertil E. Peterson, Chicago, 111., assi'gn'or to Cardwell Westinghouse Company, a corporation of Delaware Application November 3, 1955, Serial No. 544,782

9 Claims. (Cl. 2133-22) This invention relates to a shock absorber for railway freight cars and more particularly to a selective travel type draft gear.

The principal object of the invention is to provide a draft gear; that is adapted for use in a standard A. A. R. draft pocket and offers increased travel and capacity in buff; that is adapted for use with standard draft gear attachments; that includes energy absorption means for reducing loading impacts, particularly those associated with buff loads, and dampening recoil effects; and that may beforeshortened for facilitating insertion in the draft gear pocket.

Generally speaking this is accomplished by locating separate cushioning units within the draft pocket on opposite sides of a transverse Wall that forms a portion of a novel yoke that is movable within the draft pocket. The yoke is keyed to a conventional coupler for applying draft to the front cushioning unit and supports the front cushioning unit for abutment with the coupler shank for applying buff to both cushioning units in series.

The transverse yoke wall carries a friction wedge bar that is movable therewith and that extends rearwardly thereof for sliding frictional engagement with friction shoes that are housed within suitable pockets formed in a rear follower. The shoes are yieldably urged into contact with the wedge bar so that movement of the yoke relative to the rear follower develops frictional energy dissipation. In addition the draft gear may be foreshortcned and held against expansion by keying the wedge bar against movement relative to the rear follower.

Other objects and advantages of the invention will be apparent during the course of the following description.

In the accompanying drawings forming a part of this specification and in which like numerals are employed to designate like parts throughout the same;

Fig. l is a horizontal section through familiar parts of a freight car showing the draft gear applied;

Fig. 2 is a vertical section of the same;

Fig. 3 is a horizontal section showing the relations of the relative parts in buff;

Fig. 4 is a horizontal section through familiar parts of a freight car and showing another embodiment of the draft gear applied;

Fig. 5 is a vertical section of the same;

Fig. 6 is a horizontal section showing the relations ofthe relative parts in bud;

Figs. 7, 8, and 9 are cross-sectional views taken on the lines 7-7, 8-8, and 9-9, respectively, of Fig. 4;

Fig. 10 is a perspective view of the yoke employed with a draft gear in accordance with the second embodiment;

Patented Mar. 4, 1958 Figs. '11 and 12 are perspective views of the front and rear followers, respectively;

Fig. 13 is a perspective view of the wedge bar and shearpin; V I p t Fig. 14 is a side view illustrating the manner in which the shear (pin mounted in the wedge bar cooperates with the rear follower and temporarily holds the draft gear compressed for handling, shipping, and installing;

Fig.15 is a capacity curve for the rubber-friction gear of Figs. 4 to 14, in-accordance with the standard A. A. R. capacity or drop test, and indicates the high capacity and controlled recoil of the gear; and

Fig; 1 6 is a fragmentary cross-sectional view corresponding generally to that of Fig. 9, but is taken through a modifiedrea'r'follower that offers varied energy absorpti'O'h "characteristics. 7

Referring now to the drawings and particularly to Figs. 1 to 3, a simplified form of draft gear constructed in accordance with the concepts of the invention is designated generally'at 2t and'is shown applied in a draft gear pocket of standard size in accordance with the requirements of the Association of American Railroads for cars used in interchange. The gear is 'sh't'iw'n' in the familiar surroundings of center 'sillszl, front and rear draft lugs 22 and 2 3, respectively, coupler butt or shank 24 slotted as at 25 to receive a horizontal draft key 26 and having a coupler horn 27 spaced forw'ardl'y of a striking plate 28 to allow inward travel of the coupler shank, coupler carrier iron 29 and draft gear carrier irons 30. These parts are so familiar that no specific description is deemed necessary.

without modifying the standard draft gearattachmentsand associated portions of the car frame. The gear consists of a novel yoke generally indicated at 32 that is movable not only during the application of draft loads but also while bud loads are applied, front and rear cushioning units generally indicated at 33 and 34, fesp'ectively, and engaging the opposite faces of a rear tr'ansver'se wall 35 of the yoke 32, and front and rear follower members 36 and 37, respectively. H V

The were is shown, for ilhist'rative purposes only, as being of the vertical-plane, horizontal key type and has its side arms 38 integrally connected to the rear transverse wall as by" top ana barium wall portions designat d 39 and 40. respectively. The yoke', which is preferably of cast steel. is open at its forward face and the coupler shank 24 applies buff loads to the draftg'e'ar by direct engagement with the from follower 36. It may be seen that the yoke with the from stops 22 and V I 36 definesa chamber for the front cushioning unit 33 and with the rear steps 23 and rear follower defines a separate chamber for the rear cushioning unit 34.

The front follower 36 is provided with forwardly otfand rearward movements, and as best seen in Figs. 1 and 3, the yoke is constructed and arranged t6 acc'oinniodate" front follower 3. r T such .movementswithoutcreating any j'co'nflicfwitlr the adjacentportions of the frontstops.

The cushioning units 33 and 34 may be of any selected frh'e front follower 136 Shaw's in perspective in Fig. 1 1.

may also be identicalwith the follower-of the previous embodiment and also includes, a forwardly offset portion.

' 142 that spaces the coupler horn an increased distance set 42 .of the' front follower 36 forcing that follower against the front cushioning unit 33 which in turn transmus the bulf forces through the transverse wall 35 of the yoke to the rear cushioning unit 34 which-reacts against the'rear follower 37 that is in abutting engagement with therear draftlugs 23; Since the yoke is movable, bothgcushioning unitswill yield, to provide a relatively long and smooth high energy cushioning action for a the buff loads; iThe movement of the yoke during buff occurs due to forces which are transmitted from the coupler butt th rough'the front cushioning unit. to the rear transverse ,wall 35 of the yoke'and no butf loads are applied by the key 26 to the side arms 38 of the yoke..

-It-'should'be apparent from Figs. 1 and 2. that when draft loads are applied, thegear functions in the conventional manner in that draftforces are transmitted from the coupler shank 24 tothe yoke S2-through the draft key 26. Forward movement of the yoke compresses the front cushioningunitonly and allows the rear cushioning unit to expand and take up any slack. Thus draft' forces cause the transverse wall 35 ,of the yoke to'move forwardly and compress the front cushioning unit 33 against e the frontfollower 36 which in turn abuts against th f ont draft gear lugs 22..

' Thus the front cushioning unit acts to cushionboth buffand draft loads whereas the rear cushioning unit is active only in .the case of buff loads. The overall ar-' rangement of the parts is simple and compact and entirely eliminates the necessity of thestandard type yoke while at the same time being considerably less expensive to man-v ufacture than comparable selective travel type ,draft gears.

' Another embodiment-ofa selective travel draft gear is 7 shown in Figs. 4 to 14 and in this case is of the rubberfrict on type which not only affords highercapacity both in buff anddraft but also reduces impact efiects because of its'energy, absorption characteristics and more irnporw tantlylimits recoil effects and of the gear l 7 The rubber-friction gear of this invention is adapted for applicationfin a standard. draft pocket and cooperates withstandard 'draft' gear attachments'and the freight car dampens multiple vibrations frame in substantially the same manner as the gear of Figs l to 3. For ease of description the corresponding parts of the 'cfar'frame arenumbered identically.

The rubber-friction. gear also consists of 'a, novel yoke.

' 132 that. is movable notonly during the'applicationfof draft loads but also while'butfloads'a re applied, front and rear cushioning units generally indicated at 133 and 134;

respectively, and engaging the opposite faces of a rearv transverse wall ,135'of the yoke132, front and rear fol- 'lower members '136 and 137, respectivelyriand an energy absorbing friction system .101L- a a The yoke asr shown in perspective in Fig. 10 is again illustrated" as being of the vertical-plane horizontal key torn wall portions designated 139; and 140, respectively, which extend forwardly. from the rear transverse wall 135.' Structurallythe yoke maybe identical withrthe -60. r. Y H Y unit 134 and rear follower with'its friction system already from the striking plate and permits the desired overtravel in bulf. 7

The rear follower 137, as bestseen inFigs. 4,. 9, and

12, consists of front and rear plates designated 104 and 105, respectively, that are spaced apart by suitable horizontal reinforcing ribs 106 and vertical reinforcing ribs 107 which are constructed and arranged to define laterally spaced apart opposedfriction shoe pockets 108 and 109. The plates 104and 105 are centrally apertured as indi cated at 110. and 111 to receive an elongated wedge bar 112 which is provided with a' shouldered head113 that mounts in countersunk fashion J within the shouldered aperture 102 provided in the rear transverse wall 135 and which is" formed with a' rearwardly tapering portion-1'14 that telescopes within the apertured' rear follower and extends completely therethrough as indicated'inFig'iA. Each of the friction shoe pockets contains a springpack 116 that reacts against the vertical rib 107' and applies, 7

pressure to a pair of identically shaped wedgelike shoes 117 that are arranged in overlapping relationship within the pocket. Manufacturing advantages are gained from the factthat the vertical-ribs 107 are arranged'to'run parallel with the adjacent surface of the tapered wedgejbar since this. permits all of thewedge shoes to be shaped identically. 'i

In Figs. 4 and-9the spring pack 116is shown in the.

form ofrubber bar elements secured on opposite sides of a perforated plate, and the arrangement of the pocket,

spring'packand'shoes is such that when the draft-gear a in itsnormal release position which is the position in which the gearis shown in Figs. 4 and 5, the spring units will' be precompressed an amount sufiicient to insure that. V V

they will operate along the relatively straight line portion of their lead deflection curve.

The cushioning units 133 and134 again may be of any selected typebut are here 'shownin Figs. 4, 7,-and8fas.

the rubber spring type and are composed-10f a plurality of perforated plates 1 43 and rubber bars 144 on each side of the plates 143 and spacer plates 145 interposed between the cushioningielements. .Itfwill be'noted that the front cushioning ufnit is of a smaller. cross-section than the rear cushioning unit, as is necessary. to provide clearance for the .topandb'ottomwalls 139'and'140of the yoke. 4 a

In theca'se of the ruhber frictiondraft gear an'extra spacer or backinglplate 145isprovided adjacent the;for-- ward face of the transverse Wall'135, and aswill become more'clear. presently, this additional plate performs "the important function of uniformly distributing the trans;

mitted Q buff loads so that the yoke 132iand wedge 'bar move rearwardly in unison. Furthermore, the rear cushaccommodatingthe wedge bar 112. V

In assembling the gear, the wedge "bar 112 is passed through the transverse wall'135 of the yo ke' so' .thatthe shouldered head'113 nests within the shouldered aperture 102 formed in the transverse wall. The rearcushioning in place therein is telescoped over thewedge bar 112'and a type and has itsside arms 138merging with top and hotyoke employed i connection with the-embodiment of 'Figs. 1 to 3;,however, for accommodating the energy ab:

sorbing system 101, t-he' yoke is. provided with ashouldered aperture .102, that extends completely through its .rear transverse wall 135..., 1 a

the parts are precompress'ed to'a degree'sufiicient to cause a'vertical-bore 118 formed adjacent the rear e'nd'of'the wedge bar to clear the rear wall of the rear-follower. l The retaining pin 119 may. then be inserted in rhe -pore; I 118 to hold the parts in compres sed relationandrthisiis gbest shownin Figs. 4 and .14; This arrangement greatly facilitates handling, shipping, and insta llingthed'raft gear.

.It should be apparentthat aftersufiiciently compressing the rear'cushioning unit, the front) cushioning unit will have adequate mounting clearance and may be easily inserted at the time of installation of the gear'in a draft pocket. 7 M me ioning unit is arranged with a longitudinal bore146 for a is installed; the load willpermit the pm 119 to fall through the bore 118 and release the gear.

When buff loads are applied as indicated by the arrow B in Fig. 6, the coupler butt 24 forces the front follower 136 inwardly to compress both cushioning units as explained in the case of the previous embodiment. This action again results in part from the fact that the entire yoke moves rearwardly and in the present instance this movement of the yoke relative to the rear follower 137 brings into play the energy absorbing system composed of the wedge bar 112 and cooperating friction shoes 117 urged into engagement therewith by the spring packs 116. The portion of the buff load which is not absorbed by the front cushioning unit is transmitted by the backing or spacer plate 145 adjacent the yoke wall and urges both the yoke and the wedge bar rearwardly. Thus there is relative sliding movement between the wedge bar 112 and the friction shoes, and due to the lateral pressures existing therebetween, a regulated amount of energy is dissipated frictionally.

Furthermore, due to the tapered arrangement of the wedge bar, the friction forces increase in the case of the larger buff loads which necessarily produce a greater buff travel. The energy absorbed by the friction system effects important reductions in the impacts that are actually transmitted to the car but even more importantly the friction system is operative during both inward andoutward movement of the wedge bar so that the energy of recoil resulting from severe buif loads is also dissipated frictionally.

In the case of draft loads only the front cushioning unit will be compressed, but the forward movement of the yoke wall, through shouldered engagement, carries the wedge bar forwardly and once again results in relative movement between the wedge bar and wedge shoes so that the gear also dissipates a portion of the energy of the draft load. In this case, however, the friction forces are somewhat reduced with respect to the forces associated with buff loads. Even in the case of draft the energy of recoil is dissipated frictionally.

In one form of the rubber-friction draft gear, the arrangement gives up to 3 inches travel in buff and 1% inches travel in draftin all a total of 5 /2 inches which is in acordance with the standards of the Association of American Railroads. The pressures acting on the faces of the wedge shoes in full buff are 4600 pounds, in full draft 1500 pounds, and in neutral position 2400 pounds. This gear offers the relatively high capacity of approximately 50,000 foot pounds in buff and 17,000 foot pounds in draft with controlled recoil, and this also compares favorably with the requirement of the Association of American Railroads that a draft gear be capable of withstanding 18,000 foot pounds in buff.

A typical capacity curve for the gear is shown in Fig. 5.

This curve is based on the standard A. A. R. capacity or.

drop test and the cross hatched area 120 between the closure curve 121 and recoil curve 122 represents the amount of energy absorption. Furthermore, the recoil curve indicates only a 22 /2 percent recoil so that when the buff loads are removed from the gear, it almost immediately returns to its neutral position with but a minimum of undesired vibrations. I

As to the details of construction, the yoke is preferably made of cast steel; the spacer plate adjacent the yoke wall is preferably a A: inch steel plate. The friction shoes and wedge bar may be of mild steel or hardened steel and the rubber elements in the spring packs and in the cushioning units should be of approximately 72 durometer hardness.

The spring packs which urge the shoes into frictional engagement with the wedge bar may take other forms in accordance with the desired energy dissipation characteristics. One such obvious modification involves the use of a coil spring in lieu of the rubber spring units and if desired the spring pockets 108 and 109 could be en- 6 larged by appropriately modifying the rear follower i131 in order to accommodate springs of desired capacity.

Another possible modification is shown in the fragmentary view of Fig. 16 wherein the rear follower is modified to accommodate a hydraulic system for loading the friction shoes. In this arrangement the friction pockets 108 and 109 are cylindrical in form and constitute cylinders for the reception of a pair of opposed main pistons 124. The pistons 124 are hollowed as at 125 and these chambers 125 communicate at their outer ends with the cylinders 108 and 109 through restricted ports 126 arranged in an annular ring in the piston wall. The chambers 12S receive a secondary piston 127 and a return spring 128. The secondary piston slides back and forth in the chamber 125 while a suitable O-ring 131 prevents undesired leakage.

The cylinders are filled with a suitable fiuid 127 and a bias spring 128 and are sealed at their outer ends by suitable plates 129 that are affixed to the follower 1'37. Leakage at the inner ends of the cylinders is prevented 'by suitable O-rings 130 provided on the piston 124.

When loads are applied to a gear having this hydraulic system for loading the friction shoes, movement of the wedge bar 112 in the rearward direction is resisted by friction between the shoes 117 and the wedge bar and this is dependent upon the functioning of the hydraulic system. If the loads are sharply applied large pressures are developed since the inward movement of the main piston is completed in a short time and by this time the volume of hydraulic fluid displaced by such movement must pass through the restricted ports 126 and into the hollowed chamber. Less suddenly applied loads, though of comparable magnitude, develop lower friction shoe pressures.

The pressures developed by any particular load may, of course, be regulated by varying the size of the ports and/ or the viscosity of the hydraulic liquid.

it should be understood that this specific description of the invention is for the purpose of complying with Section 112 of Title 35 of the U. S. Code, and that the appended claims should be construed as broadly as the prior art will permit.

I claim:

1. In a railway car, the combination with a draft pocket having spaced stops therein; of a pair of cushioning units lying in line within the pocket with their remote ends reacting between said stops when in their release position, front and rear follower members between the remote ends of said units and the stops, a yoke having a transverse rear wall mounted in said pocket for movement in either longitudinal direction from its release position, said rear wall lying between and in contact with the adjacent ends of the units and having an open front end, a coupler having a shank attached to the yoke for applying draft to the front one of said cushioning units through said yoke and movable through the open front end of rear one of said cushioning units into cooperating en-' gagement with said second friction means whereby relative movement between said yoke and said rear follower causes relative movement between said first and second friction means to develop a frictional dissipation of energy.

2. In a railway car, the combination with a draft pocket having spaced stops therein; of front and rear cushioning units lying in line within the pocket with their remote ends reacting between said stops when in their release position, front and rear follower members between the remote ends of said units and'th'e stops, a

yoke having a transverse pocket for, movement in either longitudinal: directlon means and develops -a r i ie r iq fih ebflweenrear wall mounted in said from its release position, 'said;rear wall lying between the adjacent ends of, said cushioning units, s aid yoke including, a connection means extending forwardly from said rear wall,-a wedge bar in thrust engagement with a 7 comprising ,a yoke having ,a transverse "rear Wall and,

saidyoke and movable therewith said wedge bar extending rearwardly from said transverse wall through said rear cushioning unit and said rear follower member, said ivedgebar havingopposed friction surfaces converging toward said rear follower member, transversely spaced friction, shoes carried by said rear 'followerand yieldably engaging the friction surfaces of said wedge bar,

and a coupler having a shank in lost-motion connection with saidconnectionmeans ,of the yoke, said-shank being inthrust relation with the front one of said cushioning units-for applying buff forces to said rear unit through said front unit, said lost motion connection accommodating rearward'movement of said coupler shank relative to said yoke. V t

'3. In a railway car, the combination with a draft pocket having spaced stops therein; of front' and rear cushioning units lying in line' Within the pocket, front,

and rear follower members between the remote ends of said units and the stops, a movable yoke having a transverse wall lying between the adjacent ends of the cash ioning units, a shouldered wedge bar countersunk in said transverse wall and extending rearwardly through friction surfaces converging toward'said rear follower member, a backing plate between the front cushioning unit and the transverse wall for moving said yoke andwedge bar rearwardly in unison, friction shoes carried by said rear follower: and yieldably engaging the fl'iC': tion surfaces of said wedge bar, and a coupler having a shank in lost motion connection to the yoke for applying draft to said front cushioning unit through said yoke and positioned abutting engagement with said front cushioning unit to apply buff directly thereto whereby both ,of said units operate in buff and only said front unit operates in draft. V r 7 V t 4. In a railway car, the combination with a draft pocket having spacedtstops therein; of a pair of cushioning units lying in line within the pocket with their remote tends reacting between said stops'when in their release position, front and rear follower members hetweentthe remote ends of said units and the steps, a

yoke having a transverse wall mounted insaid pocketfor movement in either longitudinal direction from its releaseposition, said rear wall lying between and in contact with the adjacent ends of the units, a coupler having a shank attached to the yoke, and energy dissipating means comprising first friction means mounted in said yoke and movable therewith and second friction saidtransverse wall, said rear cushioning unit, and said,

rear follower member, said Wedge bar having opposed, 3

a 1.8 i 6. Ina railway car'of the H carrying spaced front and rear lugs defimng a draft pocket and having, a coupler movable' into' and out 'of said pocketin response; tobnfi-and draft jloads-"respeev tively;. adraftfgear for mounting in saidv'pocket and transversely spaced arms extending forwardly'from staid, wall for lost-motion connection to said coupler, 831d arms being spaced apart on opposite sides of'said cou-. pler to define therebetween a central opening greaterin cross section'than saidcoupler to allowvmovementxof, said coupler through said yoke arms towards said, rear t wall; said yoke being mounted in said pocket for movement in either longitudinal direction from'its release position, front and rear cushioning units in line OHHOP'," posite sides of said transverse 'wall with the adjacent ends of said units reacting against said wall and with the, remote ends of said unit s reacting'between; said lugs,

when said gear is in its release position, ajrear follower between said rear cushioning unit and said rearqlugs cushioning unit into engagement between said shoes. r

7. In a railway car of the type having a center ,sill carrying spaced front and rear lugs defining a, draft pocket and' having a coupler movable into :and out of said pocket inresponse to buff and draft loads respectively;

a'draft gear for mounting in said pocket and comprising a yoke having a transverse r'ear wall and transversely; spaced arms extending forwardly from said wallfor lostmotion connection to said'coupler, said arms being spaced apart on opposite sides offsaid coupler to define therebetween a central opening greater in cross section than 7 said coupler to allow movement of said coupler through said yoke arms towards said, rear wall, said'yoke being 7 mountedin said pocket for movement-in eithertlongi-:

tudinal' direction from its release position, front and rear cushioning units in' line on opposite sides of said transverse wall with the adjacent ends of saidunitsre-j 'acting against said wall and with the remote ends of means carried by said rear follower, at least one of said friction meanstextending through the rear one of said cushioning units into cooperating engagement with the other friction means whereby relative movement between,

said yoke and said rear follower causes relative'mo'vethem between said first and second'friction means to develop a frictional'dissipation of energy.

'5. The arrangement of claim 4 wherein onerof said' frictionmeans comprises a wedge bar'having opposed friction surfaces converging towards the other of said I friction means, said other friction means comprising friction shoes-yieldably urged into contact with'said friction surfaces whereby relative inward movement'of said yoke and said rear follower causes relative inward movement between said first and second friction means to develop oprogressively increasing energy dissipation'and relative outward movement of said yoke and said rearrfollo'wer causescorresponding outward movement of said friction progressively decreasing energy said units'reacting between saidilugs when said gear is in its release position, a rear followerbetween saidl rearv cushioning unit and said rear lugs, friction shoes mounted in said follower in transversely spaced relationship and yieldably urged towards each other, ;a friction bar thrust engagement with said 'yoke and movable ,therewith, said bar extending'rearwardly from saidtransverse wall through said rear cushioning unit and into said 7 rear follower into engagement between said-shoes.

8. In a railway car of the type having a centerlsill; carrying spaced front and rear lugs-defining a draft a pocket and having a coupler movable into andout of said pocket in response to buff and draft loads respe'ctively; a'draft gear for mounting in said pocket and comprising a yoke having a transverse rear wall and loop- ,shape'd'armsextending forwardly in" transversely spaced relation from opposite edges of'said wall to form a pair of transversely spaced apart rearwardly facing 'co-' 1 operating abutment surfaces, said rear wall having' a centralraperture bounded by forwardly facing internal shoulders, a shouldered wedge bar countersunk in said rear wall in, abuting engagement with said 'internah shoulders and extending rearwardly therethrough, a front] cushioning unit reacting between said rear wall and said' cooperating abutment surfaces, a rear cushioning unit telescoped over said rearwardly extending wedge bar with its forward end reacting against said rear walLa'rear follower telescoped over said rearwardly extending wedge bar to bear against the rear end of said rear cushioning unit, transversely spaced friction'shoes carried by said' rear follower and yieldably urged into engagementwith I'said wedge bar, said 'wedgebar having a slot adjacent type having; a center i its rear end and said cushioning unit being compressible to expose said slot behind the rear follower, and a keying element in said slot and overlying said rear follower to hold the gear together with said rear cushioning unit under compression.

9. A movable yoke comprising a transverse rear wall providing forwardly and rearwardly facing spring seat surfaces and loop-shaped arms extending forwardly in transversely spaced relation from opposite edges of said wall to form a pair of rearwardly facing cooperating abutment surfaces, each of said arms having a portion extending forwardly of said abtument surfaces having mating longitudinal slots.

References Cited in the file of this patent UNITED STATES PATENTS Ritter Oct. 1, 1901 Kinne Oct. 29, 1935 Munro et a1. July 16, 1940 Hobson Oct. 1, 1940 Haseltine Oct. 19, 1948 Willison et al Jan. 2, 1953 Wolfe July 14, 1953 U. 5-, DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,825,472 March 4, 1958 Bertil E. Peterson ified that error appears in the printed specification It is hereby cert rrec-tion and that the said Letters of the above numbered patent requiring 00 Patent should read as corrected below. 4

Column 9, line 6, beginning with "9a A movable yoke" strike out all to and including longitudinal slots in line 13, comprising claim 9; in the heading to the printed specification, line 6, for "9 Claims," read Signed and sealed this 20th day of May 1958,

Attest:

KARL AXLINE ROBERT c. WATSON Comissioner of Patents Attesting Officer

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