US3760955A

US3760955A - Hydraulic cushioning unit

Info

Publication number: US3760955A
Application number: US00195236A
Authority: US
Inventors: V Hawthorne
Original assignee: Keystone Industries Inc
Current assignee: Keystone Industries Inc
Priority date: 1970-07-06
Filing date: 1971-11-03
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25

Abstract

A hydraulic unit for a railway cushioning device has improved head assemblies which close the ends of an outer reservoir housing and a cylinder contained in the housing to provide a strong, relatively light weight, and easily manufactured unit. The head assemblies comprise pairs of nested cylinder and reservoir heads. The head assemblies are located at each end of the unit and cooperate with the reservoir housing and cylinder to provide passages, including orifices, and valves for regulating flow of hydraulic fluid through the unit, and thereby absorb energy, in response to movement of a piston which slides in the cylinder. The orifices are located in the cylinder and include a small restricted orifice located adjacent one end of the cylinder and beyond the limit of travel of the piston, which permits the piston to move to the limit of its travel in the draft direction and provides hydraulic control for cushioning train action forces.

Description

United States Patent [1 1 Hawthorne 1 1 Sept. 25, 1973 HYDRAULIC CUSl-llONlNG UNIT [75] Inventor: Vaughn T. Hawthorne,

Mechanicsburg, Pa. [73] Assignee: Keystone Industries, Inc., Chicago,

Ill.

[22] Filed: Nov. 3, 1971 21 Appl. No.: 195,236

Related US. Application Data [63] Continuation-impart of Ser. No. 52,265, July 6, 1970,

Pat. No. 3,682,324.

3,495,719 2/1970 Peppers 213/8 Primary Examiner-James B. Marbert A!torney-Albert W. Bicknell et al.

[57] ABSTRACT A hydraulic unit for a railway cushioning device has improved head assemblies which close the ends of an outer reservoir housing and a cylinder contained in the housing to provide a strong, relatively light weight, and easily manufactured unit. The head assemblies comprise pairs of nested cylinder and reservoir heads. The head assemblies are located at each end of the unit and cooperate with the reservoir housing and cylinder to provide passages, including orifices, and valves for regulating flow of hydraulic fluid through the unit, and thereby absorb energy, in response to movement of a piston which slides in the cylinder. The orifices are located in the cylinder and include a small restricted orifice located adjacent one end of the cylinder and beyond the limit of travel of the piston, which permits the piston to move to the limit of its travel in the draft direction and provides hydraulic control for cushioning train action forces.

24 Claims, 4 Drawing Figures HYDRAULIC CUSHIONING UNIT This application is a continuation-in-part application of my copending U. S. Pat. application Ser. No. 52,265, filed July 6, I970, now Patent No. 3,682,324.

This invention relates to improvements in a hydraulic unit for a railway car cushioning device of the type adapted to be connected to a coupler of a railway car for cushioning forces that may be imposed on the coupler. In particular, the invention pertains to such a hydraulic unit having improved head assemblies and cylinder construction.

The present invention provides a number of improvements for a hydraulic unit for use in a railway cushioning device. The unit comprises a reservoir housing and a cylinder that contain a hydraulic fluid. The cylinder is mounted in the reservoir housing to define a generally annular reservoir space therebeween and the ends of the cylinder and the ends of the reservoir are closed by head means comprising improved head assemblies, each of which includes a pair of nested reservoir and cylinder heads. A piston rod carries a piston which slides in the cylinder, and the piston rod extends from the unit and engages a coupler assembly and aspring return assembly of the railway cushioning device.

The reservoir and cylinder of thepresent unit are connected by passages and orifices, some with valves therein, which form a hydraulic circuit for absorbing and dissipating energy by controlling the flow of the hydraulic fluid caused by movement of the piston.

To provide improved hydraulic cushioning characteristics in the unit, the cylinder is provided with a plurality of longitudinally spaced orifices in the buff end of the cylinder and a single small restricted orifice in the draft end of the cylinder, the orifices being located to communicate between the cylinder and reservoir space. The small restricted orifice permits the piston to move to its furthest draft position for cushioning the relative movements which occur between the cars ofa moving train. The restricted orifice is located adjacent the draft end of the cylinder beyond the travel of the piston. Thus, the restricted orifice is always open and is the only such orifice for fluid flow from one side of' the piston when the piston is at or near its draft position.

Nested pairs of reservoir and cylinder heads cooperate to form return passages that connect the reservoir space to the cylinder through check valves which are located in the cylinder heads. Portions of the return passages are formed in one of the adjacent contacting surfaces of the reservoir and cylinder heads. This construction facilitates manufacturing of the check valves.

The reservoir and cylinder heads have large areas that are in direct face-to-face contact with each otherv to provide mutual support and give the assembled pair of heads strength. At the same time this construction keeps the axial length and the weight of the unit at a minimum. Also, the heads sealingly contact each other circumferentially adjacent the piston rod, instead of being spaced apart at such location, and this arrangement reduces the number of piston rod seals that are' needed. Thus, the unit of the present invention is more compact and lighter in weight than those prior art devices which had two pairs of spaced apart reservoir and cylinder heads.

Accordingly, it is the primary object of the present invention to provide a strong, compact hydraulic unit for a railway cushioning device.

Another object of the present invention is to provide compact, strong reservoir and cylinder head assemblies for closing'the ends of a reservoir housing and a cylinder of a hydraulic unit for a railway cushioning device.

Still another object of the present invention is to provide a hydraulic unit for a railway cushioning device having improved characteristics in cushioning impacts due to the relative, train action movements which occur between cars of a moving train.

Another object of the present invention is to provide a hydraulic unit for a railway cushioning device which is easily and economically manufactured.

These and other objects and advantages of the present invention will become apparent from the subsequent detaileddescription taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a cross-sectional view of a railway car sill containing a hydraulic cushioning device embodying the present invention;

FIG. 2 is an enlarged cross-sectional view of the hydraulic unit shown in FIG. 1, and taken on the line 2-2 in FIG. 3;

FIG. 3 is an enlarged cross-sectional view, with por tions broken away, taken along the line 3-3 of FIG. 2; and

FIG. 4 is an enlarged cross-sectional view, with portions broken away, taken along the line 4-4 of FIG. 2.

In the drawings a longitudinally extending center sill,

designated generally at 20, of a railway car is rigidly connected to portions of the car underframe structure, not shown. As seen'in FIGS. 3 and 4, the sill 20 has an open bottom and a channel-shaped configuration, including a top wall 21, spaced depending side walls 22, and laterally extending flanges 23 at the lower edges of the side walls 22. A cushioning device, in this instance of the type to be connected to a coupler at the end of the car, is mounted within the sill 20. The device comprises three principal assemblies (FIG. 1), namely, a coupler yoke assembly designated generally 26, a spring return assembly designated generally 27, and a hydraulic unit, embodying the present invention, designated generally 28. The

assemblies

26 and 27 which are operatively interconnected in end-to-end relation to the unit 28, are only briefly described herein, but are more fully described in my above-identified copending application.

The hydraulic cushioning unit 28 has a piston rod 30 which operatively connects the unit 28 to the

other assemblies

26 and 27. As shown in FIGS. 1 and 2, the piston rod 30 projects axially through both ends of the hydraulic unit 28 and is rigidly secured at one of its outer extremities to a rod end member 32 (FIG. 1) which interfits in a recess 33 in the adjacent end of the yoke assembly .26. The yoke assembly 26 comprises a casting having an elongated generally boxlike configuration Draft and buff forces are transmitted from the coupler stem 34 through the yoke assembly 26 and into the hydraulic cushioning unit 28, through the rod end member 32 and the rod 30. The hydraulic cushioning unit 28 cushions both buff and draft impacts, and if an impact is greater than the cushioning capacity of the unit, any excessive coupler forces will be imposed directly on buff or draft stops that are secured to the sill 20, by means of a pair of massive integral side projections or ears that extend outwardly from the yoke. (The buff and draft stops and the ears of the yoke are not shown herein but are fully shown and described in my above-identified copending application.) Thus, coupler forces, when the device is in its furthest buff or draft position, are transmitted directly from the yoke to the sill without being imposed on the hydraulic unit 28.

The return spring assembly 27 urges the device including the unit 28 toward a predetermined or neutral position, in this instance at the limit of piston travel in the draft end of the cylinder. The return spring assembly 27 includes a cylindrical helical compression spring 49 (FIG. 1) which is disposed between a bracket 51 at one end of the spring 49 and a movable disk-shaped spring follower 53 at the opposite end of the spring 49, the bracket 51 being secured to the sill 20 by bolts 52 (FIG. 1). The follower 53 is rigidly carried on an elongated spring rod 55 which extends through an elongated central tubular passage provided in a bolster center filler 59. The right-hand end of the spring rod 55, as seen in FIG. 1, abuts the left-hand end of the rod 30, the right end of the spring rod 55 being preferably tapered to fit in a cooperating axial recess (not shown) in the end of the rod 30. Thus, the rod 30, the spring 49, and the spring rod 55 are, in this instance, disposed in coaxial alignment.

As best seen in FIG. 2, the hydraulic cushioning unit 28, is supported on bars 63 secured to the flanges 23. The hydraulic unit 28 is held in longitudinal position by abutting an extension 65 of the center filler 59 at the left end of the unit as seen in FIGS. 1 and 2 and abutment bars 67 at the right end of the unit. Both the extension 65 and bars 67 are rigidly secured to the sill 20, as by welding.

The hydraulic unit 28 comprises a tubular reservoir housing 71 and a cylinder 72 which are held in generally concentric spaced relation and are closed at their opposite ends by head assemblies, each assembly comprising a reservoir head 73 or 74 and a

cylinder head

75 or 76. The reservoir housing 71 extends between and is welded to the reservoir head 73 at the bufi end of the unit and to the head 74 at the draft end of the unit. The cylinder 72 extends between the cylinder head 75 at the buff end of the unit and the cylinder head 76 at the draft end of the unit. The reservoir heads 73 and 74 and the cylinder heads 75 and 76, thus, cooperate with each other and with other structures yet to be described to close the ends of the reservoir housing 71 and the cylinder 72. The cylinder 72 is spaced concentrically a small distance inwardly from the reservoir housing 71 to define a generally annular reservoir space 77 therebetween. The cylinder heads 75 and 76 respectively are in nesting or interfitting engagement and in face-to-face contact, as is indicated at the interfaces 81 (FIG. 2), with the reservoir heads 73 and 74, respectively.

A piston 82 on the rod 30 is slidable longitudinally in the cylinder 72. The piston 82 has a piston ring 83 mating reservoir head, as shown, to form the head assemblies which cooperate with the rod 30 space. and sealing structure to close the corresponding ends of both the cylinder 72 and reservoir housing 71. The cylinder heads and 76 preferably have a forced fit in recess 85 of the reservoir heads 73 and 74, respectively, and are secured to their respective reservoir heads by means of bolts 91 (FIGS. 3 and 4). Upon assembly, the cylinder 72 is tightly received in annular grooves 0r recesses 92 located in the cylinder heads 75 and 76 and is clamped in that position by means of the reservoir heads 73 and 74 and reservoir housing 71 which are welded together as shown. This arrangement facilitates assembly of the hydraulic unit during manufacture and disassembly of the unit for repairs, and also avoids possible distortion of the cylinder 72 during assembly.

In the present form, the cylinder heads 75 and 76 are of cast iron and have relatively large generally annular surface areas that bear against complementary surface areas on the reservoir heads 73 and 74 which are forgings. The nested head arrangement provides mutual support between the cylinder head and reservoir head, and consequently the assemblies are adapted to withstand relatively great hydraulic pressures which may develop in the cylinder. In other words, when one of the cast

iron cylinder heads

75 or 76 is acted upon by high pressure fluid in the cylinder, the cooperating forged reservoir head 73 or 74, against which it bears, acts to reinforce and stiffen that cylinder head.

Each of the reservoir heads 73 and 74 has an inner annular lip 93 which extends axially into the opening 86 of the associated

cylinder head

75 or 76. The lip 93 serves to position or locate the cylinder head on its associated reservoir head. The cylinder heads 75 and 76 each have circumferential areas in the opening 86 that engage corresponding areas on their associated reservoir heads 73 or 74 adjacent the rod 30 and form a seal therebetween. Consequently, only one seal (to be described hereinafter) is needed at each end of the unit 28 for the pair of assembled heads.

The piston rod 30 is carried at each end of the unit 28 by a relatively long bushing 94 provided in the reservoir heads 73 and 74. Each bushing 94 has an opening 95 through which the piston rod 30 extends, and each has a shoulder 96 which abuts against the reservoir head 73 or 74. The bushing 94 has a forced fit in the opening 84 of its associated head 73 or 74. The bushing 94 is held in place by a radially extending lip 97 on the cylinder head that abuts the inner end of the bushing.

As mentioned above, a seal is provided at each end of the unit in the reservoir heads 73 and 74 around the piston rod 30. A preferred form of seal comprises a pressure ring 102 which is forced against a packing ring 103 by a plurality of springs such as 101. The packing ring 103 in turn bears against a wiper ring housing 104 containing a wiper ring 105. The parts of the seal are held in place in the bore 84 by a retaining ring 106 at the outer end of the seal and by the end of the bushing 94 at the inner end of the seal.

The present unit avoids the use of mechanism to compensate for changes in volume in the system. It will be noted that the piston rod 30 projects from opposite sides of the piston 82 and is long enough to extend beyond both ends of the unit 28 through the openings 84 in the head assemblies. As the piston is shifted from one end of the cylinder to the opposite end, fluid is displaced from one side of the cylinder to the other by piston movement, and the rod 30 does not affect displacement. Also, it will be noted that a portion of the wall of the reservoir housing 71 is fitted with removable filler plugs 111 for filling the reservoir space 77 and cylinder 72 with a suitable hydraulic fluid to a level indicated by the dashed line 112. The space above the line 1 12 contains air when the unit is filled, and the air can expand and contract as required to compensate for changes in volume of the hydraulic fluid due to temperature and other changes. During operation of the unit the air is likely to be mixed with the hydraulic fluid. The volume of air in the reservoir is likely to gradually increase due to normal very slight seepage of fluid out and air in along the rod through the seals. Such seepage of fluid helps keep the packing rings 103 moist and lubricated.

In FIG. 2, the piston 82 is illustrated in full lines at the right-hand or draft end of the cylinder 72, which, in this instance, is also its neutral position. During a buff inpact, the piston 82 may be forced to the opposite or buff end of the cylinder 72, as seen in dashed lines at 113, and, of course, the spring assembly 27 will absorb energy and tend to 'retum the piston to the neutral position. To hydraulically dissipate energy in the unit, the wall of the cylinder 72 is provided with a plurality of metering openings or main orifices 115 in the buff end of the cylinder and a single restricted orifice 1 16, hereinafter more fully described. The main orifices 1 15 permit flow of the hydraulic fluid from the interior of the cylinder 72 into the annular reservoir space 77 during movement of the piston 82. The size and arrangement of the main orifices l 15 axially and circumferentially of the cylinder 72 was arrived at empirically. It should be noted that the first main orifice 115 is located to the left of the restricted orifice 116 but is to the right of the middle of the cylinder 72, the cylinder 72 being imperforate between the first orifice 115 and the restricted orifice 116. In a typical unit having a piston that travels a maximum of ten inches from end to end, the first orifree 115 is located about 6 inches from the cylinder head 75 and about 5 and its inches from the orifice 116, for reasons that will, hereinafter, be explained.

The hydraulic system of the present unit is considered to be a compact, closed system in that when a volume of fluid is forced out of the cylinder 72 on one side of the'piston 82 an equal volume of fluid is drawn into the cylinder at the other side of the piston 82. Fluid enters the cylinder at the other end through any orifices, such as 115, that happen to be on the other side of the piston 82 at that instant. In addition, the cylinder heads 75 and 76 are provided with openings or passages, such as 123, which connect with other passages provided in the head assemblies that connect, in turn, to the reservoir space 77. These additional openings and passages permit fluid to be drawn into the cylinder even when the piston is at or near an end of the cylinder. It will be noted that when the piston 82 has traveled to either end 6 of its stroke in the cylinder there is no opening in the side of the cylinder through which fluid can be drawn as the piston begins movement away from that end. As the piston moves away and uncovers openings 115 behind it, such openings 115 also permit fluid to flow into the cylinder.

A check valve, indicated generally as 121 in the

head

75 and 141 in the head 76, is associated with each return passage 123 and is mounted in its associated cylinder head to permit fluid to be drawn into the cylinder from the reservoir space 77 and to prevent fluid from being forced out of the cylinder through the passages or openings 123. In the present instance four check valves 121 and passages 123 are provided in the cylinder head 75 at the buff end of the cylinder and seven check valves 141 and passages 123 are provided in the cylinder head 76 at the draft end of the cylinder. As is best seen in FIGS. 2 and 4, each check valve 121 comprises a ball member 112 which is contained in its associated passage or opening 123 extending generally axially but sloping downwardly from the piston side of the cylinder head. Each passage 123 has at its inner end a set of cast guide lugs 124 on which the ball 122 rides. To form the lower end 125 of the passage 123 and a seat 127 for the associated ball 122 of the check valves 121, the guide lugs 124 have been machined and the

heads

75 and 76 have been drilled out as shown to communicate with pockets 126, hereinafter described. The balls 122 are mounted in the enlarged upper endof their associated passages 123, in the piston side of the cylinder head. They are retained in position by a circular wire ring 131 which is installed in an annular groove 132 formed in the cylinder head. By slanting the passages 123 and their associated lugs 124 downwardly, the balls 122 will move toward the closed position unless forced away from their seats by fluid moving into the cylinder through their passages 123.

It will be noted that the head 75 is identical to the head 76 except that three of the passages have not actually been completed in this head. Three pockets 123-A of the cylinder head 75, as seen in FIG. 4, have not been drilled out and do not contain balls 122. This resulted from using the same basic form of casting for both

heads

75 and 76. In the head 76, on the other hand, all seven of the passages 123 have been drilled.

As was indicated above, the lower end 125 of each of the passages 123 opens into an associated radial passage or pocket 126. In this instance the pockets 126 are formed at the head interfaces and in the reservoir heads. Again, identical forgings are used for the reservoir heads 73 and 74. Consequently, the head 73 has three blind pockets 126, aligned with but not connected to the undrilled pockets 123-A.

As is shown in FIG. 3, the pockets 126 are located circumferentially about the lower periphery of the reservoir .head and extend radially outwardly, with their outer edges 134 located radially outwardly of the periphery 135 of the cylinder head. The pockets 126 open into a generally annular passage 136. The outer surfaces of the cylinder heads are notched, as indicated at 137, forming entrances to the radial passages or pockets 126.

It will be understood that the various return passages for connecting the reservoir space 77 to the interior of the cylinder 72 and their associated check valves provide substantial resistance to fluid flow. It is apparent from the drawings that these return passages decrease in cross sectional area as they get further from the reservoir space and closer to the cylinder. In addition, each associated passage twists and turns inwardly upon itself, generally l80, which results in turbulence when fluid flows through them at relatively high velocity. These factors cause significant fluid flow pressure losses inthese passages and the kinetic energy of the fluid is dissipated through the system as the fluid is forced out from one end of the cylinder through the orifices 1 15, through the reservoir space 77, into the passage 136, through the pockets or passages 126, and through the openings or passages 123 into the other end of the cylinder. By making the pockets 126 relatively small, greater pressure loss occurs in the pockets, and at the same time large surfaces of the cylinder head and reservoir head between the pockets 126 are in face-to-face contact, to provide the advantage of increased head assembly strength heretofore mentioned.

As mentioned above, in the cylinder head 76 there are seven passages or openings 123 and seven associated check valves 141 to avoid unnecessarily high pressure during heavy buff impacts. Except as to number, the passages and check valves 141 are identical to those previously described, so no further description is believed necessary.

At each end of the unit 28, in the bushing 94 is an annular collector passage 143 which is connected to one or more passages 144 (FIGS. 2, 3, and 4) in the reservoir head. The collector passage 143 collects most of the hydraulic fluid that may pass from the cylinder between the bushings 94 and the rod 30. Passages 144, in turn, connect to several of the pockets 126, and the fluid, except for the very small amount that seeps through the sealing ring 103, is returned to the several pockets 126 (FIGS. 3 and 4) and hence to the reservoir space 77.

To add flow capacity so that still larger buff and draft impacts can be cushioned without damage to the unit, a normally closed pressure relief valve is provided in each end of the cylinder, preferably, in the periphery of the cylinder heads 75 and 76. The pressure relief valve permits flow of hydraulic fluid from the cylinder 72 through an associated relief passage into the reservoir space 77. The pressure relief valve opens when the pressure of the hydraulic fluid reaches a predetermined high level in the respective end of the cylinder. A pressure relief valve 146 in the cylinder head 75 is operable to open when pressure within the adjacent end of the cylinder reaches a high level, such as when a high coupler force is experienced. The valve 146 comprises a movable valve body 147 having an enlarged head 151 contacting a ball 152. The ball 152 engages a corresponding valve seat 153 formed at the end of an associated relief passage 154 which extends axially through the cylinder head. The valve body 147 fits within a spring 155 which forces the ball 152 toward its nor-' mally closed position against the valve seat 153. One end of the spring 155 presses against the head 151, and at the other end, the spring engages the reservoir head 73. A small generally radial relief passage 156 is formed in the cylinder head 75 to connect the pressure relief passages 154, with the reservoir space 77 when when valve 146 is open. A similar pressure relief valve 157 is located in the cylinder head 76 and the parts thereof similarly have the same numbers as the pressure relief valve 146.

The restricted orifice 116, briefly mentioned above, is located adjacent the cylinder head 76 at the draft end of the cylinder and to the right of all the main orifices 1 15 as seen in FIGS. 1 and 2. The orifice 116 is considerably smaller than any of the main orifices 1 15 (three sixty-fourths inch as compared to five-sixteenths inch and three-eighths inch, for example) and thus has a very small flow capacity compared to an orifice 115. Consequently, when the piston is to the right of all the orifices 115 (as seen in FIG. 2) and moving toward the orifice 116, the small flow capacity of the orifice 116 permits the unit to effectively cushion relatively small coupler forces. To facilitate forming the orifice 1 16, its outer end 161 is enlarged. Preferably, the restricted orifice 116 is located in the cylindrical wall of the cylinder 72 and is positioned to be open at every position of the piston relative to the cylinder. In this instance, the restricted orifice 116 is located beyond the limit of travel of the piston 82, and about one inch from the end edge of the cylinder 72. The limit of travel of the piston in the draft direction is limited by the draft stops, heretofore described and never contacts the draft end of the cylinder. The restricted orifice 116 is always on one side of the piston for every position of said piston relative to said cylinder so that fluid may flow from the cylinder through this orifice when the piston moves in the draft direction. Thus, whenever the piston moves only a small distance away from its neutral position, as

would normally occur during relative movement between cars due to train action, the restricted orifice 1 16 limits flow and thus retards movement of the piston back to its neutral position. The orifice 116, also, prevents hydraulic fluid from being trapped in the draft end of the cylinder. No hydraulic forces will be improved on the cylinder head 76 if the piston remains in the draft position, and, as was heretofore mentioned, in such case all coupler forces in a draft direction will be transmitted directly from the coupler through the yoke assembly 26 to center sill 20.

' As indicated above, the use of the separate reservoir and cylinder heads nested together to form head assemblies provides a number of manufacturing advantages. For instance, since the cylinder heads are cast iron, the relatively complicated structure for the

check valves

121 and 141 and for the

relief valves

146 and 157 are easily formed by casting them in the cylinder heads and 76. At the same time good strength is assured for the assembly since each of the

cast cylinder heads

75 or 76 is backed up by a high strength, forged reservoir head 73 or 74. Also the reservoir heads 73 and 74 at both ends of the unit are identical as forged, and the cylinder heads 75 and 76 at both ends of the unit are identical as cast. The difi'erences between the cylinder heads are the result of machining, the head 76 having .only four of the passages 123 drilled through for check valves. This mode of construction results in significant cost reduction without a corresponding sacrifice of high quality production.

In operation, the cushioning of the buff and draft impacts by the unit 28 is due to the resistance to movement of the piston 82 provided by the fluid. Unlike most prior art units the pressure losses in the fluid are not concentrated solely at the cylinder orifices 1 15 and 116.1nstead pressure losses are distributed through the system and energy is absorbed at the orifices and also in the other passages formed in the unit. Consequently, a considerable pressure, on the order of 1,000

to 1,500 pounds per square inch or more, may be developed in the reservoir 77 during a major buff impact.

When a buff impact occurs, the coupler and yoke assembly 26, the piston rod 30, and the piston 82 all move toward the left. However, the spring returnassembly 27 urges the hydraulic unit 28 to the right toward its neutral position. As the piston moves to the left in the cylinder 72, the pressure of the hydraulic fluid in the left end of the cylinder 72 increases and causes the check valves 121 to close. The hydraulic fluid is, therefore, forced from the cylinder through the main orifices 1 by the piston and into the reservoir space 77. Nor-- mally, unless a predetermined pressure is exceeded, the pressure relief valve 146 remains closed. The pressure in the left end of the cylinder increases to a maximum pressure, depending on the size of the impact. As the pressure in the left end of the cylinder increases, the pressure in the reservoir space also increases, and the pressure in the right end of the cylinder decreases. Thus, the fluid flows from the reservoir space 77 to the right end of the cylinder 72, first through passages 123 at the right end of the piston 82. A small quantity of fluid also flows through the restricted orifice 116 into the cylinder. As the openings 115 are progressively covered by the piston 82, the capacity for flow from the cylinder decreases. If the coupler force is great enough, eventually the piston will reach the limit of its travel at the left end of the cylinder and any remaining force will be transmitted from the yoke directly to the sill. If the force is all absorbed in the hydraulic unit and the spring assembly 27, which is more likely, the piston 82' will stop short of the left limit, and the spring assembly 27 will begin to move the piston back to the right toward its neutral position. As mentioned above if the impact of the force is so great that the pressure in the cylinder exceeds a certain amount, the valve 146 will open to supplement the openings 115.

When the force of the buff impact has been absorbed, the compressed return spring 49 urges the piston rod 30 and piston 82 toward the right to their draft or neutral position, and the stored energy of the spring will be dissipated hydraulically. This unit avoids an undesirable rebound effect in about the same way it provides cushioning in the draft direction, by controlling fluid flow as the piston moves back from the left toward the right. As this movement occurs, the pressure of the fluid in the right end of the cylinder increases, and the check valves 141 close. The pressure of the fluid in the left end of the cylinder decreases. Should the pressure in the right end of the cylinder exceed a certain amount, the pressure relief valve 157 will open. Assuming the prior buff impact had moved the piston to the left of one or more of the orifices 115, the fluid flows out through any of the main orifices 115 that are to the right of the piston, and into the reservoir space 77. A small quantity of fluid also flows out through the orifice 116 into the reservoir space 77. As pressure in the reservoir space 77 increases, the fluid will flow into the left end of the cylinder through the main orifices 115 to the left of the piston. A pressure decreases in the left end of the cylinder opens the check valve 121, and the fluid also flows through these valves into the cylinder.

As the piston 82 moves toward the right end of the cylinder 72, it passes the rightmost main orifice 115 and from that point on, the fluid flows out of the right end of the cylinder, mainly through the restricted orifice 116 until the piston 82 reaches its draft position.

A small amount of fluid is intentionally bypassed from one side of the piston 82 to the other through the gap in the piston ring 83.

As is well known, whan a train of cars is moved along a track, the cars continually move relative to one another as a result of changes in the track grade and train operation. This relative movement is commonly referred to as train action. It is desirable to cushion the impacts caused by the coupler forces during such train action. It should be recognized that since train action is continually occurring during operation of a train, the piston 82 is almost never at the neutral position, but instead is to the left of that position. The cushioning required during train action is different from that required during coupling or starting a car from a standstill when very large buff and draft impacts may occur,

"and the same orifices which provide the principal cushioning effect for the buff impact of coupling and the draft impact when moving a car from a standstill are not entirely suitable to also perform this task. In the present invention, cushioning of draft and buff train action forces is provided by displacement of fluid through the relatively small orifice 116 into the reservoir space 77 and by controlled leakage across the piston ring 83. In cushioning a small buff impact, for example, the piston 82 is forcedto the left until the spring 49 has absorbed the force. Fluid is displaced by the piston 82 outwardly through the numerous openings into the reservoir space 77 and fluid enters the right end of the cylinder through the check valves 141, all without much efiort. The spring 49 will then release its stored energy by shifting the piston 82 to the right and this will close the check valves 141. Fluid to the right of the piston 82 is forced through the small orifice 116 and also through the gap in the piston ring. Hence, in small draft impacts, energy is dissipated merely by forcing fluid through the small orifice 116 and across the piston ring. During such relatively small movements of the piston 82 following train action impacts and during normal train operation, the

pressure relief valves

146 and 157 remain closed. Thus, the cushioning impacts resulting from such relative movements is controlled principally by the separate small restricted orifice 116.

As can be seen from the foregoing description, the present invention provides an improved reservoir head and cylinder head assembly for closing the ends of a reservoir housing and cylinder. Each cylinder head is in contacting face-to-face abutment about its center with its respective reservoir head. The arrangement of the contactingpairs of reservoir and cylinder heads results in a compact and strong assembly. Further, the present invention simplifies installation and arrangement of the valves and passages in the heads to enhance energy absorption throughout the system. In addition, the present invention provides a relatively small restricted orifice that is always open, and located in the draft end of the cylinder and longitudinally spaced from the main orifices to provide cushioning for the relatively small impacts that result from train action.

Although the invention has been described with particular reference to certain structural embodiments thereof, it is to be understood that various modifications and equivalents may be resorted to without departing from the scope of the invention.

I claim:

1. A hydraulic unit for a railway car cushioning device, comprising a housing enclosing a single cylinder fixed in said housing and forming a reservoir space therebetween, said unit being substantially liquid tight for containing a hydraulic fluid, orifice means in said cylinder for providing flow communication between said cylinder and said reservoir space, a piston rod extending into said housing and cylinder and having a piston thereon adapted to slidable travel in said cylinder and thereby circulating said fluid through said cylinder and reservoir space, said unit being adapted to be operatively connected to a spring assembly for forcing said piston toward one end of said cylinder and having a neutral position at one end of said cylinder, said orifice means including a plurality of main orifices in longitudinally spaced relation adjacent the other end of said cylinder and a single restricted orifice smaller than any of said main orifices and located adjacent said one end of said cylinder in spaced relation from said plurality of main orifices, said single restricted orifice always being open to provide direct communication between the inside of said cylinder and said reservoir space, said single restricted orifice providing restricted fluid flow to cushion relatively small train action forces and said main orifices providing greater fluid flow to cushion greater forces.

2. A hydraulic unit according to claim 1 in which said restricted orifice is located between said one end of said cylinder and said piston for every position of said piston relative to said cylinder.

3. A hydraulic unit according to claim 1 in which said restricted orifice is located in longitudinal spaced rela tion from the nearest of said plurality of main orifices and said cylinder is imperforate therebetween.

. 4. A hydraulic unit for a railway car cushioning device, comprising a reservoir housing, a cylinder positioned within said reservoir housing, said reservoir housing and said cylinder being closed at their respective ends forming a substantially liquid-tight unit for containing hydraulic fluid, a piston rod extending into said cylinder and having a piston thereon adapted to slidably travel in said cylinder and normally positioned at one end of said cylinder, check valve means at each end of said cylinder for permitting flow from said reservoir space into said cylinder, pressure relief valve means at each end of said cylinder, each pressure relief valve means permitting flow from said cylinder into said reservoir space when the pressure in the end of said cylinder associated with each pressure relief valve means exceeds a certain amount, and orifice means for providing flow communication between said cylinder and said reservoir space including one or more main orifices adjacent the other end of said cylinder and a restricted orifice located at said one end of said cylinder beyond said piston for every position of said piston relative to said cylinder.

5. A hydraulic unit according to claim 4, wherein said check valve means and said pressure relief valve means are located in heads at the ends of said cylinder, and said restricted orifice is located in said cylinder.

6. A hydraulic unit for a railway car cushioning device, comprising a reservoir housing, a single cylinder fixed in position within said reservoir housing and forming a reservoir space therebetween, head means for closing each end of said reservoir housing and said cylinder to form a substantially liquid-tight unit for containing hydraulic fluid, a piston rod extending axially into said cylinder through said head means, and adapted to operatively engage a coupler and a return spring assembly, a piston slidable in said cylinder and mounted on said piston rod, orifice means in said cylinder for passing said fluid between said cylinder and said reservoir space, said orifice means including a restricted orifice positioned at one end of said cylinder to be on one side of said piston at every position of said piston relative to said cylinder and a plurality of longitudinally spaced main orifices in said cylinder between the other end of said cylinder and said restricted orifice, said single restricted orifice always being open to provide direct communication between the inside of said cylinder and said reservoir space.

7. A hydraulic unit according to claim 6, further comprising a relief valve for each end of said cylinder and respectively mounted in said head means, each of said relief valves having an associated relief passage formed in the respective head means and operable for discharging fluid from said cylinder to said reservoir space when the fluid pressure in the end of said cylinder associated with said relief valve exceeds a predetermined amount.

8. A hydraulic unit according to claim 6, further I comprising at least one check valve for each end of said cylinder and respectively mounted in said head means, each of said check valves having an associated return passage including a portion passing through its associated head means and each being operable to open and to permit-fluid flow into said cylinder from said reservoir space as said piston moves away therefrom and to close its associated return passage at all other times.

9. A hydraulic unit according to claim 6, wherein each head means is an assembly, each assembly'comprising an inner cylinder head member and an outer reservoir head member for respectively closing said cylinder and said reservoir housing, said inner cylinder and outer reservoir head members being nested together in face'to-face contact. 10. A hydraulic unit according to claim 9, wherein check valve means and relief valve means are provided in each assembly and include passage means located in said head members and valves located in said cylinder head members, and said restricted orifice is located in said cylinder.

11. A hydraulic unit for a railway car cushioning device, comprising a reservoir housing, a cylinder positioned within said reservoir housing defining a reservoir space therebetween, a pair of head assemblies closing the opposite ends of said reservoir housing and said cylinder, said unit being substantially liquid-tight and adapted to contain hydraulic fluid, a piston rod extending axially into said cylinder and through one of said head assemblies, a piston on said piston rod and slidable in said cylinder, means for passing said fluid from said cylinder to said reservoir space and back to said cylinder in response to movement of said piston, each of said head assemblies comprising an outer reservoir head and an inner cylinder head in abutting face-toface relationship, said abutting heads having circumferentially extending surfaces in engagement around and adjacent said piston rod.

12. A hydraulic unit according to claim 11, wherein said means for passing fluid includes a plurality of passages in each head assembly, each such passage having a valve mounted in its associated cylinder head memher, said passages in said head assemblies connecting said cylinder and said reservoir space, said valves being circumferentially spaced about the periphery of its associated cylinder head member, said passages extending generally radially outwardly from said valves to said reservoir space, said reservoir head member and said cylinder head member being in abutting engagement between said passage means.

13. A hydraulic unit according to claim 12, wherein at least some of said passages include pockets formed in a surface in one head member of said assembly and covered by the other head member of said assembly, said pockets extending generally radially outwardly from said valves toward said reservoir space.

14. A hydraulic unit according to claim 13, wherein said pockets are formed in the periphery of each reservoir head member, said pockets extending radially outwardly from said valves and communicating with said reservoir space.

inder, said reservoir housing and said cylinder defining a reservoir space therebetween and being adapted to 15. A hydraulic unit according to claim 12, wherein said valves include check valves that are associated with return passages for permitting flow from said reservoir space into said cylinder, and a relief valve that is associated with a relief passage for permitting flow from said cylinder to said reservoir space.

16. A hydraulic unit according to claim 12, wherein each of said valves includes a return passage extending through its associated cylinder head member and having a ball seat, and a ball member in said return passage operable to move off its seat and open its return passage to fluid flow upon said piston moving away from said ball member and to engage its seat and close its return passage at all other times.

17. A hydraulic unit according to claim 16, wherein each of said return passages slopes generally downwardly from said cylinder toward said reservoir head member, said ball member being mounted in said return passage and tending to roll down said slope to engage its seat and close its return passage, said ball member being lifted off its seat to open the passage upon movement of said piston away from said ball member.

18. A hydraulic unit according to claim 12, wherein said valves include a relief valve havinga valve body mounted on its associated passage, a spring forcing said valve body to a closed position in said associated passage, said spring engaging said valve body at one end and engaging said reservoir head member at the otherv end.

19. A hydraulic unit according to claim 11, wherein said means for passing said fluid includes a single orifice located at one end of said cylinder beyond the limit of piston travel and a plurality of longitudinally spaced main orifices located in said other end of said cylinder, said single orifice being more restricted than any of said plurality of main orifices and always open to permit fluid flow between said cylinder and said reservoir sace.

20. A hydraulic unit for a railway car cushioning device, comprising a reservoir housing, a cylinder positioned within said reservoir housing, head means for closing the ends of said reservoir housing and said cylcontain hydraulic fluid, a piston rod extending axially into said cylinder, said piston rod having a piston slidably mounted in said cylinder, orifice means for passing fluid from said cylinder to said reservoir space, each head means having at least one return passage containing a check valve for returning fluid from said reservoir space into said cylinder, the cross-sectional area of said return passage being smallest at said check valve and being progressively larger toward the end adjacent said reservoir space. I

21. The hydraulic unit according to claim 20, wherein there are a plurality of check valves in each of said head means and a separate return passage is provided for each of said check valves.

22. The hydraulic unit according to claim 20, wherein said return passages turn sharply to increase turbulence and thereby absorb energy in said passage.

23. A railway car cushioning device, comprising a spring assembly and a hydraulic unit operatively connected together, said unit having a housing enclosing a cylinder, said housing and cylinder defining a reservoir space, said unit being substantially liquid tight and adapted to contain a hydraulic fluid, orifice means for providing flow communication between said cylinder and said reservoir space, a piston rod extending into said housing and cylinder and having a piston thereon adapted to slidably travel in said cylinder thereby circulating said fluid through said cylinder and reservoir space, said spring assembly forcing said piston toward a neutral position relative to said cylinder and adjacent the draft end thereof, said orifice means including a plurality of main orifices in longitudinally spaced relation in the buff end of said cylinder and a single restricted orifice located adjacent said draft end of said cylinder in spaced relation from said plurality of main orifices, and a pressure relief valve at each end of said cylinder, said single restricted orifice and said spring assembly cooperating to cushion buff and draft forces smaller than a predetermined magnitude, said single restricted orifice and said spring assembly cooperating with said main orifices to cushion buff and draft forces of a greater magnitude, and said orifice means and said spring assembly cooperating with said relief valves to cushion buff and draft forces of a'still greater magnitude.

24. A hydraulic unit as in claim 23, wherein said piston has a neutral position adjacent the draft end of said cylinder, a coupler force moving said piston from said neutral position. toward said buff end of said cylinder to store energy in said spring assembly and to dissipate energy by fluid flow through said main orifices, the energy stored in said spring being dissipated by fluid flow through said orifice means as said piston returns to its neutral position.

Claims

3. A hydraulic unit according to claim 1 in which said restricted orifice is located in longitudinal spaced relation from the nearest of said plurality of main orifices and said cylinder is imperforate therebetween.

4. A hydraulic unit for a railway car cushioning device, comprising a reservoir housing, a cylinder positioned within said reservoir housing, said reservoir housing and said cylinder being closed at their respective ends forming a substantially liquid-tight unit for containing hydraulic fluid, a piston rod extending into said cylinder and having a piston thereon adapted to slidably travel in said cylinder and normally positioned at one end of said cylinder, check valve means at each end of said cylinder for permitting flow from said reservoir space into said cylinder, pressure relief valve means at each end of said cylinder, each pressure relief valve means permitting flow from said cylinder into said reservoir space when the pressure in the end of said cylinder associated with each pressure relief valve means exceeds a certain amount, and orifice means for providing flow communication between said cylinder and said reservoir space including one or more main orifices adjacent the other end of said cylinder and a restricted orifice located at said one end of said cylinder beyond said piston for every position of said piston relative to said cylinder.

8. A hydraulic unit according to claim 6, further comprising at least one check valve for each end of said cylinder and respectively mounted in said head means, each of said check valves having an associated return passage including a portion passing through its associated head means and each being operable to open and to permit-fluid flow into said cylinder from said reservoir space as said piston moves away therefrom and to close its associated return passage at all other times.

9. A hydraulic unit according to claim 6, wherein each head means is an assembly, each assembly comprising an inner cylinder head member and an outer reservoir head member for respectively closing said cylinder and said reservoir housing, said inner cylinder and outer reservoir head members being nested together in face-to-face contact.

10. A hydraulic unit according to claim 9, wherein check valve means and relief valve means are provided in each assembly and include passage means located in said head members and valves located in said cylinder head members, and said restricted orifice is located in said cylinder.

11. A hydraulic unit for a railway car cushioning device, comprising a reservoir housing, a cylinder positioned within said reservoir housing defining a reservoir space therebetween, a pair of head assemblies closing the opposite ends of said reservoir housing and said cylinder, said unit being substantially liquid-tight and adapted to contain hydraulic fluid, a piston rod extending axially into said cylinder and through one of said head assemblies, a piston on said piston rod and slidable in said cylinder, means for passing said fluid from said cylinder to said reservoir space and back to said cylinder in response to movement of said piston, each of said head assemblies comprising an outer reservoir head and an inner cylinder head in abutting face-to-face relationship, said abutting heads having circumferentially extending surfaces in engagement around and adjacent said piston rod.

12. A hydraulic unit according to claim 11, wherein said means for passing fluid includes a plurality of passages in each head assembly, each such passage having a valve mounted in its associated cylinder head member, said passages in said head assemblies connecting said cylinder and said reservoir space, said valves being circumferentially spaced about the periphery of its associated cylinder head member, said passages extending generally radially outwardly from said valves to said reservoir space, saiD reservoir head member and said cylinder head member being in abutting engagement between said passage means.

15. A hydraulic unit according to claim 12, wherein said valves include check valves that are associated with return passages for permitting flow from said reservoir space into said cylinder, and a relief valve that is associated with a relief passage for permitting flow from said cylinder to said reservoir space.

18. A hydraulic unit according to claim 12, wherein said valves include a relief valve having a valve body mounted on its associated passage, a spring forcing said valve body to a closed position in said associated passage, said spring engaging said valve body at one end and engaging said reservoir head member at the other end.

20. A hydraulic unit for a railway car cushioning device, comprising a reservoir housing, a cylinder positioned within said reservoir housing, head means for closing the ends of said reservoir housing and said cylinder, said reservoir housing and said cylinder defining a reservoir space therebetween and being adapted to contain hydraulic fluid, a piston rod extending axially into said cylinder, said piston rod having a piston slidably mounted in said cylinder, orifice means for passing fluid from said cylinder to said reservoir space, each head means having at least one return passage containing a check valve for returning fluid from said reservoir space into said cylinder, the cross-sectional area of said return passage being smallest at said check valve and being progressively larger toward the end adjacent said reservoir space.

23. A railway car cushioning device, comprising a spring assembly and a hydraulic unit operatively connected together, said unit having a housing enclosing a cylinder, said housing and cylinder defining a reservoir space, said unit being substantialLy liquid tight and adapted to contain a hydraulic fluid, orifice means for providing flow communication between said cylinder and said reservoir space, a piston rod extending into said housing and cylinder and having a piston thereon adapted to slidably travel in said cylinder thereby circulating said fluid through said cylinder and reservoir space, said spring assembly forcing said piston toward a neutral position relative to said cylinder and adjacent the draft end thereof, said orifice means including a plurality of main orifices in longitudinally spaced relation in the buff end of said cylinder and a single restricted orifice located adjacent said draft end of said cylinder in spaced relation from said plurality of main orifices, and a pressure relief valve at each end of said cylinder, said single restricted orifice and said spring assembly cooperating to cushion buff and draft forces smaller than a predetermined magnitude, said single restricted orifice and said spring assembly cooperating with said main orifices to cushion buff and draft forces of a greater magnitude, and said orifice means and said spring assembly cooperating with said relief valves to cushion buff and draft forces of a still greater magnitude.

24. A hydraulic unit as in claim 23, wherein said piston has a neutral position adjacent the draft end of said cylinder, a coupler force moving said piston from said neutral position toward said buff end of said cylinder to store energy in said spring assembly and to dissipate energy by fluid flow through said main orifices, the energy stored in said spring being dissipated by fluid flow through said orifice means as said piston returns to its neutral position.