US3534871A - Hydraulic buffer - Google Patents

Description

Oct. 20, 1970 R. D. RUMSEY HYDRAULIC BUFFER 4 Sheets-Sheet 1 Filed Dec. 1, 1967 IAIVENIOR Qu/v 00064 ,45 Pun L55) [WW I 4 A'I [ORAL-Jo Oct. 20, 1970 R. D. RUMSEY 3,

HYDRAULIC BUFFER Filed Dec. 1, 1967 4 Sheets-Sheet 2 4 Fan/M 0006095 04455) Filed Deb. 1, 1967 4 Sheets-Sheet 5 R 0 T A E I Pea/N 000G445 Ramsay 12 ,A ATTORA/EYS United States Patent Oflice 3,534,871 Patented Oct. 20, 1970 US. Cl. 21343 24 Claims ABSTRACT OF THE DISCLOSURE An anti-creep hydraulic railroad car draft gear buffer has a cylinder and piston arrangement normally hydraulically locked against relative reciprocal bufiing operation. Responsive to predetermined pullout or draft stroke force a two-way pressure relief poppet valve controlling fluid transfer passageway in the piston opens by differential pressure fluid action on the ValVe and the piston to stretch a hollow piston rod and compress a hollow valve stem anchored at its distal end within the rod. Under predetermined compression or bufiing force the valve opens in response to fluid pressure differential acting to compressively shorten the piston rod and stretch the valve stem.

This invention relates to hydraulic buffers and more particularly concerns buffers of the heavy duty, reciprocal type which are especially useful in railroad car draft gear installations.

Heretofore hydraulic railroad car end draft gear has been equipped with buffers having metering schedules which reduce the orifice area in proportion to stroke, usually in a parabolic manner, developing relatively uniform force under impacts on the order of to 12 miles per hour. This type of draft gear performs well during humping operations and is widely utilized on piggy-back fiat cars and auto-rack cars. Most of these units have a buff travel of approximately 9 to 11 inches and a draft travel of 2 to 3 inches, or an average total travel of approximately 12 inches per car end.

In view of the fact that prior buffers have been designed to have relatively constant force during a decelerating velocity, they are generally designed with relatively wide open orifices near the beginning of the stroke, and in fact, throughout most of the stroke if the schedule is parabolic. Therefore, at low closure speed or opening speeds, such buffers are free to travel with almost no resistance. This free travel occurs in the range of speeds up to 2 to 3 miles per hour. It thus becomes obvious that during train motion, if for example, 50 cars in the center of the train are equipped with the prior type of buffer, with 12 inches of available travel per car end, there would be a capability of 100 feet variation in train length. Since each one of the buffer units could extend or retract at a velocity, for example, of 1 mile per hour, a relative speed between the front of the train and rear of the train can easily reach a level in excess of miles per hour, resulting in couplers being pulled out, or the train as a whole buckling in the middle causing a derailment and wreck. It is strongly suspected that many, if not most, of recent train wrecks are attributable to this cause.

It is, accordingly, an important object of the present invention to provide a hydraulic buffer which overcomes the deficiencies of the prior constructions and which will eliminate creeping in or out at low velocities under low load.

Another object of the invention is to provide a hydraulic buffer which is substantially locked against extension or contraction but is responsive to predetermined draft or buffing loads.

Another object of the invention is to provide a new and improved hydraulic buffer which remains substantially insensitive to low velocity impacts but is able to absorb high velocity impacts by metered hydraulic fluid displacement therein.

Still another object of the invention is to provide a hydraulic buffer especially suitable for controlling relative movement of the cars in the train to safe limits.

It is a further object of the invention to provide novel control valve means in a hydraulic buffer utilizing the elasticity of materials to control operation of hydraulic displacement valving automatically responsive to internal hydraulic pressures within the buffer in operation.

Other objects, features and advantages of the present invention will be readily apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a top plan view of a hydraulic bufler embodying features of the invention.

FIG. 2 is an end elevational view of the buffer looking from the plane of line IIlI of FIG. 1.

FIG. 3 is an enlarged fragmentary longitudinal sectional detail view taken substantially along the the line IIIIII of FIG. 1.

FIG. 4 is an enlarged fragmentary longitudinal sectional detail view taken substantially along the line IVIV of FIG. 1.

FIG. 5 is an enlarged fragmentary longitudinal sectional detail view taken substantially along the line V-V of FIG. 1.

FIG. 6 is an end elevational view of the piston taken substantially along the line VI-VI of FIG. 4.

FIG. 7 is an enlarged fragmentary longitudinal sectional detail view similar to FIG. 4 but showing the relationship of the valve and the piston during a compression bufling stroke.

FIG. 8 is an enlarged fragmentary longitudinal sectional detail view similar to FIG. 4 but showing the relationship of the control valve and the piston during a return bufling stroke.

Although the buffer illustrated to exemplify the invention may be found useful in numerous and varied situations wherein a substantially locked, anti-creep relationship is desired between spaced structures which must under predetermined load, thrust, impact, etc., conditions be permitted to move relative to one another for stress relief, the specific buffer construction shown is especially suited for installation in railroad car end draft gear. Therein, one of the relatively movably structures may be fixedly related in a more or less rigid relation to the railroad car frame, and the other of the relatively movable structures comprises a coupler by which the associated end of the car is coupled to another car or railroad engine. In such a railroad car draft gear high pull out and impact load forces must be resisted and accommodated by the bulfer. For example, a tolerable load level up to which buffing may not be needed in modern car constructions and with modern lading techniques is on the order of 300,000 pounds. Beyond this force level, buffing is desirable. These operating conditions are met by the buffer of the present invention. That is, the bulfer is so constructed and arranged that it remains substantially hydraulically locked until a predetermined force level, i.e., approximately 300,- 000 pounds is reached. Thereupon, bufiing action either during a pull out or draft stroke or under coupling thrust, sudden deceleration impact, and the like, takes place with internal pressures within the bufler building up and automatically releasing the buffer from its normally substantially hydraulically locked condition to effect energy-absorbing buffing displacement of hydraulic fluid within the self-contained hydraulic system in the buffer. Having reference to FIG. 1, S and SS represent, schematically,

spaced structures which are liable to, and under certain operating conditions must be permitted to have relative movement toward or away from one another, such as in the draft gear of a railroad car. Between these structures is installed the illustrated buffer which is of the rectilinear telescopically operable type including a housing of generally elongated form having on one end thereof means '11 for attaching it operatively to the structure S. Extending from the opposite end of the housing 10 is a piston rod 12 having means 13 on its outer end for attachment of the buffer to the structure SS.

Within the housing 10, the piston rod 12 has mounted on its inner end a piston 14 (FIG. 4) which is reciprocably operable within a hollow cylinder 15 which is desirably a heavy walled cylindrical tube capable of withstanding the order of magnitude of internal pressures which must be sustained in operation of the buffer. Desirably, mounting of the cylinder 15 within the housing 10 is such that a hydraulic fluid reservoir space 17 is provided about the cylinder by a preferably monolithic sturdy cast housing casing 18 which is longer than the cylinder. At its end from which the piston rod 12 projects, the cylinder 15 is mounted in fixed relation to the casing 18 and concentric with the piston rod 12 by means of a combination flanged mounting fitting and piston rod tubular bearing member 19 which is partially telescopically engaged within the associated end portion of the cylinder, has a lateral thrust flange 20 engaging a thrust seat 21 of the housing casing and is provided with an outward tubular centering extension 22 which is telescoped into an end opening 23 through the casing and of larger diameter than the outside diameter of the piston rod but of smaller diameter than the inside diameter of the cylinder. An annular pressure seal about the piston rod 12 is provided by packing 24 within the bore of the opening 23 between the end of the flange extension 22 and a packing gland retainer flange 25 secured to the end of the casing in packing compressing relation as by means of screws 27, with dynamic compression on the packing by means of thrust springs 28 acting toward the flange 25 from within the adjacent end of the flange extension 22. A protective dirt shield about the outwardly projecting portion of the piston rod 12 is provided by an accordian type flexible boot 29 secured at its inner end to the flange 25 and at its outer end to the outer end portion of the piston rod.

Within the bearing member 19 a cylindrical surface 30 of substantial length affords a stable sliding bearing for the piston rod 12. Adjacent to the inner end of the bearing surface 30 is provided an O ring dynamic seal 31 about the piston rod. To drain off hydraulic fluid that may enter the bearing between the seal 31 and the packing 24, an annular collection groove 32 in the bearing surface 30 communicates through a duct 33 with the reservoir 17 at the perimeter of the flange 20. Leakage past the flange member 19 through the joint with the cylinder 15 is substantially prevented by a sealing ring 34.

At its opposite end (FIG. 5) the cylinder 15 is mounted concentrically relative to the piston 14 by means of a closure flange member 35 which has inner end portion rabbet grooved seat 37 onto which the adjacent end of the cylinder is telescopically engaged, with a static sealing ring 38 substantially preventing leakage through the joint. Concentricity of the closure flange member 35 is maintained by telescopic entering engagement thereof within an end opening 39 in the housing casing 18 of slightly larger diameter than the outside diameter of the cylinder 15 so as to permit assembly into the casing of the cylinder 15, the bearing flange member 19, the piston rod 12 and the piston 14 as a unit. Attachment of the closure flange member to the housing casing is by means of a lateral flange 40 secured as by means of socket head cap screws 41 to the adjacent end of the casing.

In addition to its other functions, the closure flange member 35 provides part of the buffer end attaching means 11. To this end, the outer end portion of the member 35 has a central integral stem 42 of substantial diameter projecting from a concave bearing recess 43 which is desirably contoured on a complementary radius to a confronting convex bearing surface 44 of a retaining nut 45 which is threadedly engaged onto the stem 43 to attach the associated end of the buffer in swiveled relation to the structure S depicted in FIG. 1.

Operatively, hydraulic fluid such as an oil suitable for this purpose fills the cylinder 15 and a substantial volume of replenising hydraulic fluid is maintained in the reservoir 17 into which there is a filler opening closed by plug 47 (FIG. 4) with an adjacent liquid level gauge for checking purposes. Desirably a drain opening, closed by a plug 49 (FIG. 5) is provided in the bottom of the head end portion of the casing 18, that is, adjacent to the end closure flange 35.

According to the present invention, means are provided to ontrol displacement of hydraulic fluid within the cylinder 15 past the piston in such a manner as to effect a substantial normal hydraulically locked condition until substantially predetermined internal pressure is developed within the cylinder, whereupon automatic release of the piston for relative telescopic bufl'lng action within the cylinder occurs. Although for some purposes it may be desired to have the automatic pressure responsive release from the locked condition operate in only one direction of reciprocal relative movement of the piston and cylinder, for railroad car draft gear installation, the construction and relationship of the control device is such as to be pressure responsively releasable in both respective directions of reciprocal operation. To this end, the piston 14 has passageway therethrough controlled by valve means comprising a poppet valve member 50 which is mounted for relative reciprocal movement within the piston, but is held normally in fixed relation thereto by a valve stem 51 fixedly anchored to the piston rod 12.

In a desirable construction and relationship, the valve stem 51 is fixedly secured to the valve member 50 by having an end portion of the stem telescoped into a central outwardly opening bore 52 in the valve member and secured therein in suitable manner as by means of brazing. From the valve member, the stem 51 extends along a concentric bore 53 and of a length substantially throughout the length of the pisto rod to a dead end adjacent to the outer end of the rod (FIG. 3). Adjacent to the dead end, anchoring means desirably in the form of a pair of crossingly related pins 54 and 55 extend through aligned bores in axially spaced adjacent relation in the piston rod and the valve stem, with the ends of the pins entirely within the perimeter of the piston rod. Hydraulic fluid leakage past the anchoring pins is prevented by means such as O-rings 57 adjacent to their opposite ends. Endwise displacement of the pin 54 is prevented by a locking relation thereto of a member 58 threadedly mounted on the outer end portion of the piston rod 12 and comprising a coupling nut which is part of the end coupling 13 and having an inner convex face 59 which is on a complementary radius to a central outwardly opening concave recess 60 in the end face of the piston rod, providing a swivel coupling joint with the structure SS (FIG. 1). Unintentional displacement of the member 58 from its operative coupling head and pin-locking position on the piston rod is prevented by a staking pin 61. Endwise displacement of the anchoring pin 55 is prevented by locking means, conveniently comprising a retainer ring 62 for the adjacent end of the boot 29.

For the reasons that will be presently described, the valve stem 51 is constructed as a tube. Therefore, to strengthen the anchorage of the valve stem to the piston rod, an anchoring plug 63 is secured within the outer end portion of the hollow valve stem and through which the anchoring pins 54 and 55 extend in a close fitting relation. For fixed attachment of the plug 63 to the valve stem, it is desirably brazed thereto. The plug 63 also provides means for drainage from the space afforded between the piston rod bore 53 and the valve stem through a port 64 in the valve stem wall reinforced by the plug. Within the plug is an angular passage 65 which connects the port 64 with the chamber in the tubular valve stem. Adjacent to but spaced from the valve member 50, the space between the bore 53 and the valve stem 51 is closed by a dynamic sealing ring 67 (FIG. 4) which may be of the piston ring type.

For the purposes of the present invention, the passageway through the piston 14 and controlled by the valve 50 comprises a plurality of branches 68 opening through the front or head face of the piston (FIGS. 4 and 6), herein shown as four in number, equally spaced apart in a circumferential direction and located on a circle intermediate the outer perimeter of the piston and a central bore 69 opening through that face of the piston and within which the innermost end of the valve member 50 is slidably received with a front end valve surface 70 exposed to the hydraulic fluid in the cylinder. Within the piston 14, the respective passage branches 68 extend to an annular, radially inwardly opening distribution groove 71 at the inner end of a substantial stepped enlargement of the bore through the piston and generally aligned with the inner end of the piston rod 12 onto which the inner end portion of the piston is threadedly engaged and secured against torsional displacement as by means of a set screw 72. Normally, displacement of hydraulic fluid from in front of the piston through the passage branches 68 by way of the groove 71 is blocked by the valve 50 which for this purpose has a cylindrical external control surface 73 on a maximum outer perimeter intermediate annular flange portion 74 of the valve member slidably coacting with a complementary annular internal seat surface 75 on the piston between the groove 71 and an annular radially inwardly opening discharge groove 77 Within the piston. Communication between the groove 77 and the back face of the piston 14 is effected through a plurality herein four, equally spaced axially extending ducts 78 in the piston having blind ends adjacent to the groove 77 and communicating therewith through respective ports 79. At their outer ends, the displacement ducts 78 are controlled by an annular check valve 80 which is biased by a Wavy spring 81, seated on a retainer shoulder ring 82, into closing relation to the ducts 78 to permit only rearward discharge from the controlled ends of the ducts and prevent return flow therethrough.

For displacement of the hydraulic fluid from the back of the piston 14 a plurality, herein four equally spaced passageway branches 83 extend forwardly from respective check valve by-passing notches 84 into the body of the piston on about the same diameter thereof as the ducts. 78. Interiorly of the piston the branches 83 deadend and communicate through respective angular ports 85 with a stepped annular discharge groove 87 of smaller diameter than the discharge groove 77 and defined by an axially extending annular internal seat 88 slidably engaged by a. fluid displacement blocking axially extending complementary stepped cylindrical control surface 89 of the valve member 50.

It will thus be observed that normally hydraulic fluid displacement through the piston 14 by way of the passageway atforded by the passageway branches 68 and 83 and the discharge grooves in the piston providing part of the passageway, is completely blocked by the valve 50, so that a substantially hydraulically locked condition prevails. Thereby relatively low magnitude or load or velocity forces imparted by the structures S and SS during pull out or draft on the one hand or compressive impact will be restricted without bufling action by the buffer, thus avoiding creeping, elognation or contraction of the buffer which has been found undesirable when multiplied by the number of buffers in the draft gear of a train of railroad cars. This anti-creep feature is controlled to function within a safe operating range, and when the internal hydraulic pressure on either end of the piston 14 reaches a predetermined load value, the valve 50 acting as a relief valve meters hydraulic fluid through the piston substan tially proportional to pressure to effect a buffing action. This involves relative reciprocal movement of the valve 50 and the piston 14 which is herein automatically ac complished in response to predetermined hydraulic operating pressures by having the piston rod 12 and the valve stem 51 serve as pressure responsive means. For this purpose, the piston rod and the valve stem, by rea son of their tubular construction, length and suitable material, have suflicient elastic relative longitudinal stretching and compression ability to serve, in effect, as relief valve fuse structure. Spring tube material is used in the valve stem 51 and of substantially thinner wall section and smaller diameter than the piston rod 12, thus affording a desirable differential in stretching and compression under the same hydraulic force, preferably amounting to about twice the extent of elongation or shortening in length movement relative to the piston rod.

For example, as related to a railroad car end draft gear buffer, resistance to opening of the valve 50, in either direction, may be controlled to a force level of about 300,000 pounds. Above that force level, opening of the valve 50 will progress as the force builds up to approximately 400,000 pounds at full opening, automatically assuming the proper degree of opening incremently within the closed to full open range proportionate to the pressure. It will be understood, of course, that the extent of relative stretching and compression of the piston rod and the valve stem must be calculated to be well within the elastic limits of the materials for which they are respectively made.

Illustrative of the action which takes place during a compression buffing stroke, hydraulic pressure acts on the front or crown face of the piston 14 as depicted by the arrows 90 in FIGS. 4 and 7. Simultaneously, hydraulic pressure transmitted through the passageway branches 68 thrust against a rearwardly facing annular pressure receiving surface 91 on the valve member 50 forwardly of the groove 71 as indicated by the force arrows 92. Since the area of the surface 91 is greater than the front end area 70 of the valve there is a forward, valve stemstretching force applied to the valve member simultaneously with a rearward piston rod compressing force which causes correlated relative axial movements of the piston and valve member'to cause the control surface 73 of the valve and the seat surface 75 of the piston to separate and provide a pressure escape relief gap to the discharge groove 77 and thence by way of the ducts 78 and past the check valve 80 to the chamber area rearwardly of the piston. Thereby closing action of the buffer occurs with accompanying energy absorption as the fluid escapes through the bufling metering restriction provided by the gap between the valve and the piston. Typically, during the bufling strOke the piston rod -12 may compress as much as inch while the tubular valve stem rod 51 may stretch about /s inch, for a full opening of the annular buffing metering orifice to y inch under maximum hydraulic compression load of 400,000 pounds.

To accommodate larger volume of fluid displacement during buffing than can be received into the working cylinder chamber back of the piston, one or more fluid by-pass ports 93 through the valve member 50 lead radially inwardly from the annular area of the discharge groove 77 to communication with the interior of the tubular valve stem 51 serving as an auxiliary fluid reservoir 94 (FIG. 4) and which is in communication with the reservoir 17 through a return tube 95 and the end closure flange 35 (FIG. 5). For this purpose the tube 95 is of a smaller outside diameter than the inside diameter of the valve stem 51, is of a length great enough to remain in constant communication with the auxiliary reservoir 94 throughout the range of reciprocal relative telescopic movements of the piston 14 and the cylinder 15, and is slidably received through a central clearance bore 97 through the valve member 50 with a dynamic fluid seal 98 substantially preventing pressure fluid leakage through the sliding joint, just as a similar dynamic seal 99 substantially prevents pressure fluid leakage through the sliding joint between the valve member and the bore 69 in the piston.

At the end closure flange 35, the fluid return tube 95 has its associated end portion fixedly secured within a counterbore 100 having a blind end bore continuation 101 into the enclosure flange communicating with a lateral duct 102 extending to the reservoir 17 adjacent to the near end of the cylinder 15. Thus, a continuously open return duct or passage is provided between the reservoir 17 and the auxiliary reservoir 94.

At the end of any compression buffing stroke, the annular fluid displacement metering orifice between the valve flange 74 and the piston closes by re-engagement of the valve surface 73 and the seat 75, brought about by return of the piston rod 12 and the valve stem 51 toward their normal condition, and return means function to restore the buffer to an extended, normal starting condition, even in the absence of a pull out force applied thereto. For this purpose, a return spring 103 of the coiled compression type is mounted about the piston rod end portion of the housing casing 18, with one end of the return spring thrusting against a shoulder 104 provided by the housing and the opposite end thrusting against a suitable abutment movable with the piston rod 12, and in this instance comprising the structure SS (FIG. 1). In a typical example, where the operating forces required to close the buffer are in excess of 300,000 pounds, the spring may have a return thrust force of on the order of 1900 pounds at neutral or starting position of the buffer.

Return bufling is effected by metered leakage displacement of hydraulic fluid from in back of the piston 14 along its outer perimeter and past piston ring 105 (FIG. 4) mounted in an annular groove 107 which intersects the passageway branches 68 and is slightly wider and deeper than the piston ring. Through this arrangement, the piston ring has a limited range of axial displacement in the groove 107 such that during compression stroke it serves as a check valve against any substantial leakage from the passageway branches 68 past the outer perimeter of the piston, but during return stroke the piston ring unseats and permits metered leakage displacement of hydraulic fluid from back of the piston into the groove 107 and past the inner perimeter of the piston ring which is slightly larger in diameter than the root of the groove 107. It will be observed that a scraper ring 108 carried by the piston 14 between its crown end and respective pockets 109 of the passageway branches 68 opening through the outer perimeter of the piston substantially precludes high pressure leakage thereby and, especially during compression stroke affords a hydraulic balance for the piston within the cylinder by action of the pressurized hydraulic fluid about the outer perimeter of the piston between the piston ring 105 and the scraper ring 108.

In order to afford a suitable range of pullout opening of the buffer, the normal, neutral relative position of the piston 14 Within the cylinder is located a spaced longitudinal interval from the end flange 19, such, for example, as about 3 inches, where a total bufling travel of the piston within the cylinder may be about l1 inches. Stopping of piston return at the neutral position is effected by a ring valve 110 which is normally maintained by means of a coiled compression spring 111 at substantially the neutral position and serves to block further displacement of hydraulic fluid around the piston when it reaches the neutral position during a return stroke and thus resumption of the normally hydraulically locked condition of the buffer. For this purpose, the ring valve 110 is secured, as shown, to one end portion of the spring 111, and the spring is anchored at its opposite end portion, as shown, to the inner end portion of the bearing flange member 19. In its end which engages the back of the piston, the ring valve 110 carries an annular sealing ring 112. A sealing relationship between the perimeter of the confronting perimeter of the ring valve and the wall of the cylinder 15 is effected by a piston ring 113. Through this arrangement, while the piston 14 may freely separate from the ring valve 110 during a compression or closing buffing stroke, on re-engagement of the piston with the ring valve 110 the return bufling stroke terminates and the hydraulically locked condition of the piston is resumed,

Hydraulic fluid which has been displaced into the reservoir 17 in the course of a compression bufiflng stroke, returns to the cylinder chamber from the gravity fed replenishing supply in the reservoir 17, by way of the passageway 102 in the closure flange 35 (FIG. 5) and a replenishing duct 114 leading therefrom to an annular distribution groove 115 in the bottom of a recess 117 in the inner face of the member 35. Relatively free replenishing displacement of hydraulic fluid by way of the groove 115 under return stroke suction is permitted by unseating of a ring shaped disk valve 118 from its normally closed position over the groove 115 as biased by means of a wave spring 119 held under slight compression by a retaining flange 120 secured into the recess 117 as by means of screws 121. Thus, during compression strokes displacement through the groove 115 and the replenishing duct 114 is substantially precluded by the check valve 118, but replenishing fluid is readly drawn into the cylinder chamber.

During a pullout or draft stroke force on the buffer as effected by relative separating pull of the structures S and SS, hydraulic pressure is generated between the piston 14 and the end member 19 within the cylinder 15. This hydraulic pressure exerts an inward longitudinal force, as indicated by the arrows 122 (FIGS. 4 and 8) on the back of the piston 14, tending to stretch the piston rod 12. Simultaneously, the same pressure is exerted through the passageway branches 83 and the ports 85 not only inwardly on the piston 14 within the groove 87, but rearwardly against a generally axially inwardly facing annular surface 123 of the valve member 50 exposed within the groove 87, as indicated by force arrows 124, tending to compress the valve stem 51. In a typical railroad car end draft gear buffer, when the pullout pressure exceeds 300,- 000 pounds, the piston 14 and the control valve 50 begin to move relatively axially until the pressure separates the cylindrical valve surface 89 from the valve seat 88 to open an annular metering orifice from the groove 87 into the discharge groove 77, reaching a maximum open condition at about 400,000 pounds load. At this maximum load the poppet valve stem 51 will have been contracted by about 4; inch and the piston rod stretched by about of an inch, for a total displacement opening of about inch. Hydraulic fluid thus displaced from the back of the piston area of the cylinder chamber escapes by way of the return tube 95 to the reservoir 17 and by way of the replenishing duct 114 to the cylinder inwardly of the piston. During pullout relief valve opening, the control surface 73 of the valve by reason of its substantial length maintains a closed condition with the confronting control sur'face 75 of the piston.

Inasmuch as the pullout or draft forces are much less likely to exceed the fuse release or pressure relief gradient in a railroad car end draft gear buffer than the compression bufling forces exerted, for example, during car coupling operations involving often severe bumping, the extent of relative pullout movement of the piston and cylinder may be generally expected to be only partially through the pullout differential distance permitted from the neutral position, in any pullout force application. Therefore, a slower recovery or return of the piston and cylinder to the normal neutral position after a pullout stroke may be permitted than is desirable for recovery from a compression buffing stroke. Herein such recovery after a pullout stroke is not forced, such as recovery after a compression stroke is forced by the return spring 103, but is permitted to result from operating forces generated in normal operation wherein restricted bleeding displacement of hydraulic fluid from in front of the piston 14 through the passageway branches 68, the groove 107 and thence along the valve perimeter past the relaxed piston ring 105 which has a split 125 for this purpose, to the rear of the piston until the cylinder chamber back of the piston is replenished and the neutral position of the piston and cylinder attained.

It will be understood that variations and modifications may be effected without departing from the spirit and scope of the novel concepts of this invention.

I claim as my invention:

1. A hydraulic buffer of the type to be mounted between two structures subject to movement toward and away from each other and which movement should be resisted in at least one direction, comprising:

means defining a housing having opposite ends and provided therein with a hollow hydraulic fluid cylinder between said ends;

means on one end of said housing for operative association with one of said structures;

a piston reciprocably mounted in said cylinder and having a fluid transfer passageway therethrough and a thrust surface facing in an axial direction;

a piston rod projecting from said piston through the opposite end of said housing and having an outer end;

means on said outer end of said piston rod for operative association with the other of said structures; and

valve means mounted in said piston to reciprocate therewith and including means yieldable in response to a predetermined hydraulic pressure but normally operative to positively hold said valve means in position to close said passageway, thereby to hydraulically substantially lock said piston and cylinder and restrain said movement in said one direction until said predetermined hydraulic pressure is generated in said cylinder, and to open in said axial direction of said piston thrust surface when said predetermined hydraulic pressure is generated and thrusts against said piston thrust surface, and a pressure thrust surface on said valve facing axially opposite to said piston thrust surface and against which said predetermined hydraulic pressure thrusts to force said yieldable means to yield, whereby in response to the opposite pressure thrusts on said surfaces, respectively, said valve is caused to open in said axial direction of said piston thrust surface to relieve the hydraulic pressure in said cylinder and permit movement in said one direction to the extent of pressure relief thus effected.

2. A hydraulic buffer according to claim 1, in which said valve means comprise a poppet relief valve member and said yieldable responsive means comprise elastic relief valve fuse structure connecting said valve member and said piston together.

3. A hydraulic buffer according to claim 2, in which said fuse structure comprise a valve stem fixedly related to said piston and said valve member being mounted in relatively movable relation to the piston.

4. A hydraulic buffer according to claim 1, in which said valve means and said piston have surfaces engaging to block fluid flow through said passageway, and said yieldable means comprises an elastic stem anchored at one end to said piston rod and at the other end to said valve member and yieldable in response to said predetermined hydraulic pressure on said axially facing surfaces to enable movement of the valve member relative to the piston to separate said normally engaging surfaces and open said passageway thereby.

5. In a hydraulic buffer according to claim 4, said piston and said valve member having an angular discharge groove as part of said passageway therebetween, respective axially extending and radially facing confronting slidably related control surfaces on said piston and said valve member at respective opposite sides of said groove and normally closing said groove from the remainder of said passageway, and respective oppositely generally axially facing pressure responsive surfaces on said valve member within said passageway adjacent to said control surfaces normally spaced from said groove.

6. In a hydraulic buffer according to claim 5, passageway branches leading from one end of said piston to one of said axially facing surfaces, and passageway branches leading from the other end of said piston to the other of said axially facing surfaces.

7. A hydraulic buffer according to claim 1, said piston rod being tubular, said valve member having a tubular stem, said valve stem and piston rod being concentrically telescopically related, said means automatically responsive to said predetermined pressure comprising respectively oppositely axially facing pressure thrust surfaces on said valve member and said piston whereby said predetermined hydraulic pressure effects respectively opposite pressure thrust on said surfaces causing said piston rod to compress axially and said valve stem to stretch whereby to effect said opening of said valve means, and additional respectively oppositely facing pressure responsive surfaces on said valve member and said piston reacting to predetermined hydraulic pressure in the op posite direction in said cylinder to effect compression on said valve stem and stretching of the piston rod to effect opening of the valve means for hydraulic pressure relief and movement of the piston in said opposite direction.

8. A hydraulic buffer of the type to be mounted between two structures subject to movement toward and away from each other and which movement should be resisted in at least one direction, comprising:

.means defining a housing having opposite ends and provided therein with a hollow hydraulic fluid cylinder between said ends;

means on one outer end of said housing for operative association with one of said structures;

a piston reciprocably mounted in said cylinder and having fluid transfer passageway therethrough;

a piston rod projecting from said piston through the opposite end of said housing;

means on the outer end of said piston rod for operative relation to the other of said structures; and

means normally hydraulically substantially locking said piston and cylinder to restrain said movement in one direction until a predetermined hydraulic pressure is generated in said cylinder, comprising:

a poppet valve member relatively reciprocably mounted across said passageway in said piston,

means normally holding said valve member in position to close said passageway,

axially extending and radially facing confronting relatively slidably engaged control surfaces on said valve member and said piston having a limited range of axial engagement and normally blocking flow through said passageway when said valve is in closed position, and

relatively oppositely axially facing differential area surfaces on said piston and said valve member exposed to hydraulic fluid pressure generated in said fluid cylinder and said passageway, said valve holding means being responsive to said predetermined hydraulic fluid pressure exerted against said differential area surfaces to allow relative axial movement of the valve member toward said piston area surface to separate said control surfaces and thereby open said passageway.

9. A hydraulic buffer according to claim 8, in which said piston rod is hollow to adjacent its outer end, and said valve holding means comprising at least in part a spring stem extending fixedly from said valve member through the hollow piston rod and fixedly anchored to the piston rod adjacent to said outer end and being yieldable in response to said predetermined hydraulic fluid pressure exerted against said differential area surfaces in allowing said relative axial movement of the valve member and the piston.

10. A hydraulic buffer according to claim 9, in which said spring stem comprises a tube of substantially smaller wall section than the wall section of said piston rod, and said piston rod is also yieldable under said predetermined hydraulic fluid pressure exerted against said differential area surfaces but in the opposite direction from said stern in the operation of said automatically responsive means.

11. A hydraulic buffer according to claim 10, in which said stem serves as a hydraulic fluid reservoir.

12. A hydraulic buffer according to claim 11, in which said stern has adjacent to its anchored end a drain passage between the reservoir therein and the area between the stem and the piston rod, and means reinforcing the stem in the area of the drain passage.

13. A hydraulic buffer according to claim 1.1, in which said housing has a reservoir outside of said cylinder, and a fluid conduit means connecting the stem reservoir and said housing reservoir.

14. A hydraulic buffer according to claim 13, in which said connecting means comprise a return tube extending slidably through said valve member and having an end portion secured to said housing, with a passage connecting said end portion with said housing reservoir.

15. A hydraulic buffer according to claim 14, having a check valved replenishing connection between said connecting passage and the interior of said cylinder.

16. A hydraulic buffer of the type to be mounted between two structures subject to movement toward and away from each other and which movement should be resisted in at least one direction, comprising:

means defining a housing having opposite ends and provided therein with a hollow hydraulic fluid cylinder between said ends;

a piston reciprocably mounted in said cylinder and having fluid transfer passageway therethrough;

a piston rod projecting from said piston through the opposite end of said housing; means normally hydraulically substantially locking said piston and cylinder to restrain said movement in one direction until a predetermined hydraulic pressure is generated in said cylinder, comprising valve means normally blocking hydraulic fluid transfer through said passageway throughout a substantial working pressure range, and means automatically responsive to said predetermined hydraulic pressure to open said valve means; push-pull swivel connection means on an outer end of said housing opposite to said piston rod for connection to one of said structures and having an annular concave surface on said outer end and a member carried by said outer end and spaced from said surface having a complementary convex annular surface confronting said concave surface; and

push-pull swivel connection means on the outer end portion of said piston rod for connection to the other of said structures including a concave end surface on said rod and a member .mounted on said end portion and having a complementary annular convex surface facing in the opposite direction from said concave end surface.

17. A hydraulic buffer of the type to be mounted between two structures subject to movement toward and away from each other and which movement should be resisted in at least one direction, comprising:

means defining a housing having opposite ends and provided therein with a hollow hydraulic fluid cylinder between said ends;

means on one outer end of said housing for operative association with one of said structures;

a piston reciprocably mounted in said cylinder and having fluid transfer passageway therethrough;

a piston rod projecting from said piston through the opposite end of said housing;

means on the outer end of said piston rod for operative relation to the other of said structures;

means normally hydraulically substantially locking said piston and cylinder to restrain said movement in one direction until a predetermined hydraulic pressure is generated in said cylinder, comprising valve means normally blocking hydraulic fluid transfer through said passageway throughout a substantial working pressure range, and means automatically responsive to said predetermined hydraulic pressure to open said valve means;

said piston rod being hollow to adjacent its outer end;

said valve means comprising a valve member having a stern extending longitudinally through the hollow piston rod and having an end portion adjacent said end of the piston rod;

an anchoring pin extending through the adjacent end portions of the piston rod and the stem; and

a member for connecting the outer end of the piston rod to said other of said structures mounted on the piston rod in retaining relation to said pin.

18. A hydraulic buffer of the type to be mounted between two structures subject to movement toward and away from each other and which movement should be resisted in at least one direction, comprising:

means defining a housing having opposite ends and provided therein with a hollow hydraulic fluid cylinder between said ends;

means on one outer end of said housing for operative association with one of said structures;

a piston reciprocably mounted in said cylinder and having fluid transfer passageway therethrough;

a piston rod projecting from said piston through the opposite end of said housing;

means on the outer end of said piston rod for operative relation to the other of said structures;

means normally hydraulically substantially locking said pisto? and cylinder to restrain said movement in one direction until a predetermined hydraulic pressure is generated in said cylinder, comprising valve means normally blocking hydraulic fluid transfer through said passageway throughout a substantial working pressure range, and means automatically responsive to said predetermined hydraulic pressure to open said valve means;

a bore in said piston rod extending from said piston to adjacent the outer end of the piston rod;

a valve stem extending from said valve means through said bore and having an outer end adjacent to said outer end of the piston rod;

an anchoring pin extending through said piston rod and said stem;

a protective boot about said piston rod having one end attached to said housing and having its opposite end adjacent to said one end of the piston rod; and

means securing said opposite end of the boot to the piston rod and retaining said pin against displacement.

19. A hydraulic buffer of the type to be mounted between two structures subject to movement toward and away from each other and which movement should be resisted in at least one direction, comprising:

means defining a housing having opposite ends and provided therein with a hollow hydraulic fluid cylinder between said ends;

means on one outer end of said housing for operative association with one of said structures;

a piston reciprocably mounted in said cylinder and having fluid transfer passageway therethrough;

a piston rod projecting from said piston through the opposite end of said housing;

means on the outer end of said piston rod for operative relation to the other of said structures;

means normally hydraulically substantially locking said piston and cylinder to restrain said movement in one direction until a predetermined hydraulic pressure is generated in said cylinder, comprising valve means normally blocking hydraulic fluid transfer through said passageway throughout a substantial working pressure range, and means automatically responsive to said predetermined hydraulic pressure to open said valve means;

said valve means comprising a valve member operable within said piston;

said passageway extending in part through said piston under the control of said valve member, and in part extending along the perimeter of said piston; and

a ring valve in slideable engagement with the inner cylinder wall, controlling that part of the passage way around the perimeter of the piston, said valve abutting against a shoulder on the piston thereby closing said passageway in one direction of relative movement of the piston and cylinder, and separating from said shoulder thereby opening said passageway in the opposite direction of relative movement of the piston and cylinder.

20. In a hydraulic buffer according to claim 19, said ring valve comprising a piston ring, the perimeter of the piston having a groove wider than the piston ring and communicating with said passageway in the piston.

21. A hydraulic buffer according to claim 19, said ring valve having means sealingly engaging the inner wall of the cylinder and sealing means separably engageable with the piston and including biasing means normally thrusting the ring valve toward the piston.

22. Inahydraulic bufier:

a hydraulic cylinder having an inner cylindrical surface;

a piston reciprocably operable in pressure strokes in said cylinder and having a perimeter confronting said surface;

fluid passageway for displacement of hydraulic fluid from one end of the piston to the opposite end of the piston along and between said perimeter of the piston and said surface; and

a control valve mounted in said cylinder spaced from one end of the cylinder and attached to the cylinder at said one end and being separable from said opposite end of the piston but being in intercepting relation to said opposite end of the piston when the piston moves toward said one end of the cylinder;

said valve having sealing engagement with said cylinder surface and effecting sealing engagement with said piston when the piston reaches the valve and thereby blocking flow of fluid along the piston perimeter to stop advance of the piston toward said References Cited UNITED STATES PATENTS 3,150,779 9/1964 Holm 213--8 3,257,000 6/1966 Cope 21343 3,334,757 8/1967 Peterson 213-8 3,368,698 2/ 1968 Cardwell 213-43 3,400,833 9/1968 Powell 2138 3,411,635 11/1968 Powell 213-8 3,412,870 11/1968 Rollins 2l3-8 DRAYTON E. HOFFMAN, Primary Examiner US. Cl. X.R.

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