US2911112A

US2911112A - Draft gear for railroad cars

Info

Publication number: US2911112A
Application number: US467118A
Authority: US
Inventors: William K Maccurdy
Original assignee: Southern Pacific Co
Current assignee: Southern Pacific Co
Priority date: 1954-11-05
Filing date: 1954-11-05
Publication date: 1959-11-03
Anticipated expiration: 1976-11-03

Description

Nov. 3, 1959 W. K. MaCCURDY 2,911,112

DRAFT GEAR FOR RAILROAD CARS Filed Nov. 5, 1954 5 Sheets-Sheet l Nov. 3, 1959 w. K. MaCcuRDY l DRAFT GEAR FOR RAILROAD CARS 5 Sheets-Sheet 2 Filed Nov. 5, 1954 IN V EN TOR.

W/LL/AM KM CURDY Bmm A TTORNEVS NOV. 3, 1959 W. K. MaCCURDY 2,911,112

DRAFT GEAR FOR RAILROAD CARS INVENTOR. WILL/AM KMMCURDY IWW/ @@Mm A T TORNEKS Nov. 3, 1959 w. K. MaCcuRDY DRAFT GEAR FOR RAILROAD CARS 5 Sheets-Sheet 4 Filed Nov. 5. 1954 --q/Ioa JNVENToR. W/LL/AMKM CURDY ATTORNEYS Nov. 3, 1959 w. Kt. MaCURDY DRAFT GEAR FOR RAILROAD CARS 5 Sheets-Sheet 5 Filed Nov. 5, 1954 INVENTOR. W/LL/AM K M CURDV [im 4( 444km A 7' TOR/VEYS 2,911,112 DRAFT-GEAR roR RAILROAD cARs william K. Maccurdy, Menld Park, Ca1if.,assignor, by mesne assignments, to Southern Pacific Company, San

Francisco, Calif., a corporation of Delaware l, f Applicare@ November s, 1954, serial No. 467,118

' #13 Claims. (cl. 213-8) This invention relates to and in general has for its object the provision of improved draft gear for railroad cars. v

As is well known in the industry, a very substantial loss is suffered annually by railroads as a result of freightk damaged by the jarring of freight cars during the operation thereof particularly in retarder yards. This loss still occurs in spite of the fact that many attempts have K been made to devise satisfactory mechanisms for cushioning the impact to which freight cars aresubjected and to devise systems for controlling and limiting the speeds of cars in retarderv yards.

lMorespeciiically one of the objects ofthis inventionY is the provision of draft gear including a draft sill paralleling vthe main sill of a freight car and longitudinally movable relative thereto under the influence of an impact to which the car is subjected; a hydraulic press mounted on one of said sills; two sets of interdigitated friction plates operatively disposed in said press, one set being secured to `one sill and the other set to the other sill; a hydraulic pump mounted on one of said sills and operatively connected to said hydraulic press; and means responsive to the relative movement of said sills for actuating said hydraulic pump thereby to activate said hydraulic press and squeeze said friction plates and .thereto restrain the relative movement of said sills.

A further object of this invention is the provision in draft gear such as above described of friction plates movable with the draft sill and which are maintained under' tension rather than compression during the dampening action" of vthe draft gear.

Still another object of this invention is the provision of `draft gear of the character described, wherein the hydraulic pump is provided with a metering pin for controlling the pressure developed throughout the working medium.

The invention possesses other advantageous features, some of which, with the foregoing, willbeV set forth at length in the following description where those forms of the invention which have been selected for illustration in the drawings accompanying and forming a part of the vpresent specification, are outlined in full. In said drawings, several forms ofthe invention are shown, but it is to be understood that it is not limited to such forms, since the invention as set forth in the claims may be embodied in other forms.

Referring to the drawings:

."Figure 1A is a top plan view of the end of a freight car'sub-frarne including draftA gear embodying vthe objects of myv inventionand with portions thereof broken away to better illustrate Aits construction. l

' Figure 1B is a continuation of the sub-frame and draft gear disclosed in Figure 1A, its right-hand end terminating at about the longitudinal midpoint of the sub-frame.

Figure 2A'is a vertical midsection of the structure illustrated in Figure 1A.

Figure 2B is avertical midsectitni of the structure illus-.

fr ICC 2 trated in Figure lB, with portions thereof broken awa to better illustrate its construction.

Figure 3 is a transverse vertical section taken on the section-line 3-3 of Figure 2B. A i

,Figure 4 is a view similar to that illustrated in the right-hand end of Figure 2B, but somewhat enlarged and showing the piston of the hydraulic pump at the end of its work stroke.

Figure 5 is an enlarged vertical transverse section taken on the section line 5-5 of Figure 2B.

Figure 6 is an enlarged transverse vertical section taken on the section line 6-6 of Figure 2A.

Figure 7 is a top lplan viewof a modified formof hydraulic pump actuating element.

Figure 8 is a longitudinal vertical' section of the hydraulic pump actuating element illustrated in Figure 7.

Figure 9 is a right-hand end elevationof theistructure shown in Figure 8. f

Figure 10-is'a top plan view of an alternate friction plate assembly. f

Figure 1l is a vertical midsection of the assembly illustrated in Figure l0. Y

Figure 12 is a right-hand end elevation of Figure 10.

vGeneral Description Briefly the structure disclosed in Figures lA to 6 in-V -;clusive comprises a freight car sub-frame including a main sill extending the length thereof. Mounted adjacent the'main sill in parallelism therewith is a draft sill protruding beyond the main sillat each end thereof.

Supported by the main silll intermediate'its lends is a .hydraulic press and operatively disposed therein are two` interdigitated sets of friction plates, one fastened to the main sill and the other fastened to and movable with the'draft sill.

I Car sub-frame and sill assem'bly" More specifically the structure disclosed in Figures 1Ai to 6 inclusive comprises a freight car body center sill 11 surrounding a draft sill 12 `and representing the under- Vframe of the car body. Forming a part of said underframe are end sills 13, bolsters 14,` crossbearers 15 and cross ties 16, all essentially of standard design and modifiedl only to accommodate for the wider spacing of the center sill 11 and to provide proper support and clearg ance for the sliding draftsill 12. Most radically affected bythese requirements is the combined center plate and bolster bottom tie 17 shown in the drawing as a single casting, *but which can be of built-up welded design.

Coupler assembly Associated with each end of the draft sill 12 is a standard coupler 18 provided with a slotted shank 19, a coupler carrier 20, coupler yoke 21, coupler key 22, yoke carrier 23,V draft gear 24,' front draft lugs 25 and `rear draftlugs 26. As is well known in the art, this lstructure willabsorb bufng shocks Aof certain magnitudes before affecting the car body center sill 11. How-l Mounted on one of the sills is a hydraulic' pump operatively associated with the hydraulic press, and'- ing .hydnaulically actuated friction mechanism generally indicated by the reference numeral 28. Preferably one such assembly and mechanism is installed at each end of the vfreight car. Y

Spring return centering assembly -lugs33 securedto thetop flanges thereof serving as seats or stops for follower plates 30. Similarly and for a like purpose, lugs 34 .are attached to the center sill bottom tie plates 35. Optionally the springs 29 can be housed in tubes 36, a rod 37 r'extending `through the springs 29 and follower plates 30 withppositive clearance, being used to vfacilitate the installation and removal of the springs. It *will be seen that as a result of this construction, the movementzof the draft sill 12 relative to the centersill 11 in either direction rwill compress the springs in an amount. proportional to the relative movement between these sills, and that the springs will exert an yequal and opposite reaction on the sills.

Friction plate assembly ably, and as illustrated, the

plates

38 and 39 are of inverted V-shape to provide forgreater column strength when the plates function under compression but can beY made flat if, as shown in Figures 10, l1 and l2, they are `made to function under tension.

Removably secured to the draft sill 12 and movable therewith are a pair of longitudinally spaced plates 40 reinforced by ribs 41, the sliding friction plates 38 being accommodated between the plates 40 and therefore con-A strained to move therewith under the pushing action of one of the plates 40.= Y

Forming a stationary or fixed retainer for the friction plates 39 are two laterally spaced pairs of posts 42, there being one pair of such posts located on each side 'of the sliding friction plates 38 and each such pair of posts being welded to a longitudinally extending side plate 43. Welded between and to the upper ends of the posts 42 is a pressure block 44 having an inverted V-shaped bottom conforming to the contour of the

friction plates

38 and 39. Bolted to and across the bottom of the center sill 11 (Figure 6) below the

plates

38 and 39 is a tie plate 45 and 'mounted on the plate 45 is a vertically movable pressure block or saddle 46 for supporting the two interdigitated sets of friction plates 38 and-39, the plates 39 being confined with the retainer formed by the .posts 42 and plates 43. Here it should be noted that the ends of the stationary friction plates 39 abut the posts 42 and are therefore restrained against longitudinal movement, that the sliding friction plates 38 pass between the posts 42 with positive clearance but4 are seated between the plates 40 and are therefore constrained to move with the draft sill 12.

To clear the pressure block 44 the top flanges ofthe draft sill V12 are cut out and the sill reinforced at this point .by angles 47. Formed as an integral part of the center sill 11 is a top tie plate 48, the center thereof being'cut out for the snug reception vof the top ofthe pressure block 44. These'expedients Vare resorted to only because the draft gear here under consideration is being installed on a freight car sub-frame of conventional con-` struction, and not on a sub-frame specifically designedto accommodate such draft gear.

Hydraulic pump assembly Associated with the friction mechanism 28 above vdescribed is a hydraulic pump assembly generally designated by the reference numeral 49 and a hydraulic press generally designated by the Vreference numeral 50.

As best shown in Figures 4 and 5, the hydraulic pump 49 comprises a master cylinder 51 secured to the center sill bottom plate 52, a piston 53 operatively disposed within the cylinder 51, a piston rod 54 secured to said piston, across head 55 secured to the free end of said piston rod, and a mechanical linkage between the cross head and the draft sill 12 whereby any movement of the latter relative to the center sill 11 will actuate the piston 53. To this end, there is pivoted to the cross head 55 a pair of opposed channels 56,l these channels 1in turn being pivoted at their ends to the upper ends of depending links 57. The lower end of each of the links 57 is pivoted to a bracket 58 bolted or otherwise secured to the draft sill 12. Secured to the sill bottom plate 52 are a pair of guide members 59 of I-beam cross-section for constraining the cross head 55 and channels 56 to move vertically and thereby causing the piston 53 to move withinA the cylinder 51. Any translatory motion of the draft sill 12 from its neutral or center position as illustrated in Figure 2B, will cause thelinks 57 and channels 56 to move from their positions as shownin Figure 2B toward their positions as shown in Figure 4 and perforce cause the piston to travel downwardly.

From an inspection of Figure 4 it will be noted that the piston 53`is provided with an `axial bore 60 having a restricted throat 60a and intersected by a transverse bore 60h. Mounted-on the lower end of the cylinder 51 coaxially therewith is a metering pin 61 extending into bore 60 and so Vshaped as to control the rate of ow ofworking medium through the restricted throat 60EL and thus determine the desired pressure. Connected to the bottom of the cylinder 51 are

conduits

62 and 63, the former communicating with the hydraulic press 50 and the latter to the lower end of a relief Valve 64. Connected with the upper end of the cylinder 51 and with the upper endy Hydraulic press Secured to the center sill bottom plate 45 is a closed cylinder 68 and slidably disposed within said cylinder is a piston 69 supported by an intermediate spring 76. Supported by the cylinder 68 adjacent its side walls, is a pair of diametrically opposed springs 71 extending through the top of the cylinder and through the plate 45 into engagement with the pressure block or saddle 46, thereby to subject the friction plates 3S and 39 to an initial predetermined pressure.

As best indicated in Figure 6, the conduit 62 communicates with the lower end of the cylinder 68 whereby the conduit 67 is connected to the upper end thereof. kEstablishing communication between the upper and lower ends of the cylinder 68 is a conduit 72, a check valve 73 being interposed in this conduit so as to permit only the downward ow of working medium therethrough.

Operation out the rest ofthe hydraulic system, all in accordance.

with'well known hydraulic principles. There is essentially no flow of liquid in the usual sense, except from below to above the piston 53, but rather there is a shock or pressure wave transmitted through the liquid which acts directly against the piston 69 'and which in turn must be sure'so developed bythe pump assembly istr'ansmitted through the conduit 62 to the cylinder 68 of the hydraulic press 50 thereby to activate the piston 69 and compress the interdigitated sets of

friction plates

38 and 39. Since one set of plates is fixed to the car main sill11, and since the other set moves with the draft sill 12, any movement ofthe draft sill' away from its neutral or` center position will be retarded by the compression of the two sets of friction plates. Furthermore since the compression of the friction plates proceeds in response to the relative movement of the two sills, the draft gear described may be characterized as being of the servo type. t

Preferably the braking action of the friction plates 38 and 39V should be proportional' to the impact on the draft `sill 12 causing relative motion between the two sills. Since the movement ofthe draft sill 12 is proportional to such impact, it can be said that the braking of the friction plates should be proportional to the movement of the draft sill. In the modification of the device above described, the movement of the pump piston 53 is not directlyproportional to the movement of the draft sill 12, but rather a function of tan a, a being the angle between the links 57 and a vertical reference line. To compensate for this, and to make the pressure applied by the hydraulic press 50 to the

friction plates

38 and 39 directly proportional; tothe impact on the draft sill, the metering pin 61 jof the hydraulic pump piston 53 may be shaped as requied; vThe same `objective could of course be attained 4by any analogous method which will vary the flow of the working medium in the same manner during the stroke. I

' Modified hydraulic pump assembly Y u lIn .Figures 7,

v

8 and 9 still another alternative for making the braking action of the

friction plates

38 and 39 directly. proportional to the movement vof the draft sill 12` has 'been illustrated. Here the system is exactly the same as shown in Figures 1A to 6 inclusive, except with respect Vto the mechanism for activating the hydraulic pump. For purposes of ready reference and comparison, all parts to which no kchange has been made will be identied by the corresponding reference numerals 'used in conjunction with Figures 1A to 6 inclusive', whereas new or altered parts will be indicated by a new set of reference numerals beginning with the number 100.

Included in the modified hydraulic pump assembly generally designated by the reference numeral 100 'is the cylinder 51 which asv previously described is secured to theV center sill bottom plate 52; piston 53, piston rod 54, and a crosshead 101 having oppositely inclined upper faces 101a and 1010. Mounted on the bottom plate 52 are four guides 102 of T-cross section fortconstrainingv the crosshead 101 and the piston rod 54 to move only vertically. Secured to the draft sill 12 is a mounting plate 103 and fastened thereto is a cross-head actuating plate 104, provided on its lower side with a pair of opposed and converging inclined planes 104@L and v 104b respectively, complementary to the faces 101a and 1011. Slidably mounted in the top and bottom plates of the fore be easily fashioned tol translate the movement of the piston 53 into a force applied by the hydraulic press

to'the friction plates

38 and 39 such that the braking force effected 'bythe plates 38 rand 39 will be directly proportional to any impact to which the draft sill maybe subjected and which is suflicient to effect any appreciable movement of the draft sill.

Alternatey construction of friction plat-e lzllssnembly In the friction plate assemblyY illustratdgin Figures Y 1A', 2A and'6, the movement of the draft sill 12 is transmitted to slidable friction plates 38 by the pushing vaction of the trailing plate 40. Aspreviously stated the column strength of a relatively thin plate is low and it is for that reason that friction plates of V shape section are resorted to in'F-ig'ures 1A, 2A yand 6. Although a relativelythin but long plate lacks strength when yplacedunder longitudinal compression, it nevertheless has considerable'lo'n- 'gitudinal tensional strength. In the modification illustrated in Figures l0, 1.1 and 12, advantage is taken of this phenomena by so arranging the friction plate assembly that thetsliding friction plates 38 are pulled by the draftnsill 12 in response to any movement of said sill in either' direction. Here again the reference numerals heretofore used will be applied to identical'parts and new reference numerals beginning with 200, reserved for` new or modified parts or elements. More specifically the friction plater assembly disclosed l in Figures 10, 11 and 12 and generally indicated by the reference numeral 200, include a first set of relatively long and narrow sliding friction plates 201 interdigitated cylinder 51 and in the center sill bottom plate-.'52, are a The-"springs-106 therefore serve to maintain the crosshead v 1.0' 1 y in positive and sliding engagement with the inclined planes 104EL and 104i.

it As a result of this construction Ait will be seen that any movement of the draft sill 12 in either direction will serve to depress the crosshead 101 and its associated pis-,

ton 53, and that the downward movement of thepiston is a straight line function of the movement of the draft sfil'l412. 'The'contourof thenmetering p in ,61; can therewith a second yset of relatively short stationary or fixed friction plates 202. Disposed between the ends ofplates 201 in abutment with shoulders -201a formed on the ends offthe plates 201 are follower bars 203. Secured to the draft sill l`2'in'wardly of the follower bars 203 and in contact therewith are lugs 204. To securely lock the ends of the friction plates 201 to the follower barsI 203;' filler blocks 205 are snugly fitted between the `uppermost friction plate 201 and the top of the draft 'sill 12 and between the lowermost friction plate 201 and the draft sill bottom plate 206. As a result of this construction the ends of the slidable friction plates are interdigitated with and irmlysecured to the followerbars'v 203, .the bars 203 being in contact with the lugs 204.` Consequently draft sill 12 moves to the left asv viewed in Fig. 1l, and the left-handvlugs 204 'will serve to, pull the friction` plates 201 to ,thev leftover the stationary friction plates 202. When the draft sill moves to. the right as viewed in Figure 1l, the right-hand lugs 204 will pull the plates 201 to the right. In each case the plates 201 operate'under tension rather than under compres-' sion whereby ,all possibility oftbuckling isobviated. Asin'the cas'eof the friction plate assembly illus-A trated in FiguresflA, 2A .and 6, the stationary friction plates 202 are housed by the posts 42 welded to the side plates 43 and to an X-shaped block 207 tted between the upper ends of the posts 42. The lower ends of the posts 42 are welded to the center sill bottom tie plate 4S which in turn is bolted to the center sill 11.

Disposed beneath the lowermost friction plate 202 and forming a support therefor is a block208. The remainder of the assembly is identical to the assembly originally describedv and therefore the elements thereof bear the same reference numerals.

It is evident that in all modifications of the general Vcombination herein described a moderate end fimpacton,r

thetdraft sill willl produce a moderate pressure on the friction plates resulting in a moderate retardation vin the relative movement between the draft sill and the centerV sill. Under a larger impact load, the velocity ofthe draft;

sill will be greater, thereby resulting in a greater velocity of the piston of the hydraulic pump and the application ofv a greater pressure by the hydraulic press tothe fricv tion plates. l'In' other words the pressure applied'to the 1. Draft gear for a railroad car having a stationaryv part and almovable part movable relative to said stationary part in opposite directions from normal at-rest position, said draft kgear comprising: a hydraulic press having opposed, spaced pressure plates; a stack of first and second sets of interdigitated friction plates operatively disposed in said press in confronting face to face relationship With and between said pressure plates -for compression thereby, the friction plates of one set of plates being arranged for sliding movement over the friction plates of the other `set of plates; one of said sets of friction plates vbeing'connected to said stationary part of said railroad car and the second of said sets of friction plates connected to and movable with said relatively movable part of said car, spring means biasing said pressure plates together; a hydraulic pump for actuating said hydraulic press; and means for actuating said hydraulic pump in response to movement of said movable part relative to said stationary part in a direction away from said normal at-rest position.

2. Draft gear such as defined in claim 1 wherein said hydraulic pump includes a cylinder; a piston slidable in said cylinder and formed with an axial bore; and a `tapered metering pin secured to one end of said cylinder coaxiall-ytherewith and extending into said bore for determining the rate of flow of liquid through said bore thus determining the pressure applied to said hydraulic press.

V3. Draft gear for railroad cars comprising: a car subframe sill; a draft sill paralleling said sub-frame sill and arrangedA for longitudinal movement relative thereto; means engaging said sills and biasing said draft sill against movement relative to said subfrarne sill in a direction away from a normal at-rest position; a rst set of friction plates fixed to said subframe sill;-a second set of friction plates fixed to said draft sill, the plates of said second set being interdigitated with the friction plates of s'aid first set to form a stack; a hydraulic press mounted on one of said sills and having opposed pressure plates straddling said interdigitated friction plates andv engaging the outerl faces of the outer plates of the stack; a `hy draulicpump mounted on one of said sills; means for conducting fluid between the pump and press for actuating said press by the pump; and means responsive to movement of said draft sill in a direction away from said normal at-rest position forV actuating said pump.

4. Draft gear such as defined in claim 3 wherein said hydraulic pump includes a cylinder; apiston S'lidable in said cylinder and .formed with Van axial f bore; and a tapered metering pin secured to one end of said cylinder coaxially therewith and extending into said bore for determining the flow of liquid through said bore'thereby to determine the pressure applied to said hydraulic press.

5. Draft gear for `a railroad car having a stationary part and a movable part movable relative to said stationaryv part in opposite directions from a normal at-rest position, said draft gear comprising: a hydraulic press; first and second sets of interdigitated friction plates disposed in confronting Vface to face relationship in said press for the application of compressive force thereby to the plates; normal to their faces, the-friction plates of one set of :plates being arranged for sliding movement, over'the friction plates of said second setv of friction plates, the plates of the first set being connected to and movable withV said movable part and the plates of the second set being connected to said stationary part; means operatively connected to said plates and biasing said plates together; and means for actuating said .hydraulic press in response to movement of said movable part of Ythe car relative to said stationary part and in aldirection away from said normal at-rest position, thereby to squeeze said plates together. y

l 6. Draft gear fora railroad car having a stationary part anda movable part movable relative to said stationary part in opposite directions from a normal yat-rest position, said draft gear comprising: a hydraulic press; first and second sets of interdigitated friction plates disposed in confronting face to face relationship in said press for the application of compressive force thereby to the plates normal to their faces, the friction plates of one set of plates being arranged for sliding movement over the friction plates of said second set and the plates of the first set being connected to andv movable with said movable part and the plates of the second set being connected to said stationary part; a hydraulic pump .for actuating said hydraulic press, said pump including `a cylinder, a piston slidable'in said cylinder and formed with anA axial bore; a tapered metering pin secured'to one end of said cylinder coaxial -therewith and extending into said bore for determining the pressure applied to the hydraulic press; and means responsive to movement of said movable part of the carrelative to said stationary part and in a direction away from said normal alt-rest position for actuatingsaid hydraulic pump,

7. Draft gear for railroad cars comprising: a car subframe sill; a draft sill paralleling said subframe sill and arranged 'for longitudinal movement relative thereto in opposite directions from a normal art-rest position; a rst set of friction plates fixed to said frame sill; a second set of friction plates fixed to said draft sill, the plates of said second set being interdigitated in confronting face V'to face relationship with the friction plates of said first set to form a stack; a hydraulic press mounted on one of said sills and acting on the outer faces of the outer plates of the stack to compress said plates; a hydraulic pump mounted on one of said sills for actuating said press; means responsive to movement of said draft sill relative to said subframe sill and in a direction away from said normal at-rest position for actuating said pump, said pump including a'cylinder and a piston slidablevtherein and formed with an axial bore; and ay tapered metering pin secured to one end of said cylinder coaxially therewith `and extending into said bore for determining the flow of liquid through said bore thereby to determine the pressure applied to said hydraulic press Vby the pump,

8. Draft gear for a railroad car having a stationary part and a movable part movable relative to said stationary part in opposite directions from a normal at-rest position, said draft gear comprising: a hydraulic press; first and second sets of interdigitated friction plates operatively disposed in confronting face `to face relationship in said press for the application of compressive force thereby to the plates normal to their faces, the plates Vof one of said sets being connected to and movable with said relatively movable part of said railroad car and being arranged for sliding movement parallel to the planes of their faces over the plates of the other of said sets, the plates of said other of said setsbeing connected to said stationary part of said car; and means connected to one of said parts responsive to movement of said movable part of said car relative to said stationary part and ina direction away from said normal at-rest position for actuating the press to compress the plates.

9. Draft gear as ydefined in 'claim 8 wherein said last named means includes a cylinder, a piston in said cylinder and co-operating therewith to define -a pressure chamber, means responsive to said relative movement in said direction to move said piston in a direction to reduce the size of said pressure chamber, means providing for fluid iiow from said chamber, and means for variably restricting said iiow to vary the pressure within said chamber during .said piston movement, .said includingmeans for transmitting the uid pressure within said pressure charn-l l0. Draft gear .as deiined in claim 9 wherein said means for variably restricting said flow comprises means defining an axial bore in said piston and a tapered metering pin secured to one end of said cylinder coaxial with said bore and movable into said bore for variably restricting the flow of uid through said bore to vary the pressure within said chamber.

1l. Draft gear as defined in claim 8 wherein said last named means is responsive to the rate of movement of said movable part relative to said stationary part in a direction away from said normal at-rest position.

12. Draft lgear as defined in claim 8 wherein said last named means is responsive to the rate of movement and displacement of said movable part relative -to said stationary part and in a direction away from said normal at-rest postion.

13. In a railway car having an underframe member and a draft sill member mounted on said underframe member for longitudinal movement relative thereto in opposite directions from a normal `at-rest position, the combination of two sets of friction plates with the plates of one set interdigitated with those of the other in confronting face to face relationship to form a stack with the faces of the plates parallel to the direction of movement of the draft sill member, means connecting the plates of the rst set to said underframe member against longitudinal movement relative thereto, means connecting the plates of the second set to the draft sill member for movement Itherewith longitudinally of said underfrarne member, means responsive to movement of said draft sill member relative to said underframe member vand in a direction away from said normal at-rest position to apply a'compressive force to said stack of plates normal to the faces thereof, said last named means including a cylinder mounted on one of said members, a piston reciprocably mounted within said cylinder, means carried by said cylinder and biasing said piston in one direction relative to said cylinder, co-operating means on the other of said members and on said piston and responsive to longitudinal movement of said draft sill member relative to said underframe member and in a direction away from said normal at-rest position to move said piston in the direction opposite to said direction of said first mentioned piston movement to provide -a working pressure within said cylinder at `one side of said piston, means for conducting fluid between the parts of the cylinder at opposite sides of the piston for controlling said working pressure at said one side of the piston, Aand means engaging the outer faces of the outer plates of said stack and responsive to said working pressure within said cylinder at said one side of said piston to apply a compressive force to said stack of plates normal to the faces thereof.

References Cited in the le of this patent UNITED STATES PATENTS