US3392849A

US3392849A - Railway hydraulic cushioning device

Info

Publication number: US3392849A
Application number: US538052A
Authority: US
Inventors: Robert A Rasmussen
Original assignee: Pullman Inc
Current assignee: Pullman Standard Inc; Pullman Inc
Priority date: 1966-03-28
Filing date: 1966-03-28
Publication date: 1968-07-16
Anticipated expiration: 1985-07-16

Description

July 16, 1968 R. A. RASMUSSEN RAILWAY HYDRAULIC CUSHIONING DEVICE 2 Sheets-Sheet 1 Filed March 28, 1966 WV I K 0n hm mm 6 V P r\ 1 mm w Ir: j

INVENTOR ROBERT A. RASMUSSE N ATT'Y y 6, 1968 R. A. RASMUSSEN RAILWAY HYDRAULIC CUSHIONING DEVICE 2 Sheets-Sheet 2 Filed March 28, 1965 INVENTOR ROBERT A. RASMUSSEN ATT'Y.

United States Patent 3,392,849 RAILWAY HYDRAULIC CUSHIONING DEVICE Robert A. Rasmussen, Ogden Dunes, Ind., assignor to Pullman Incorporated, Chicago, 11]., a corporation of Delaware Filed Mar. 28, 1966, Ser. No. 538,052 3 Claims. (Cl. 21343) ABSTRACT OF THE DISCLOSURE A hydraulic cushion device disposed between the railroad car coupler and the lading carrying structure of the railroad car comprising a fluid filled cylinder having a fixed cylinder head, a unitary piston assembly in the cylinder reciprocal between the head and one end of the cylinder for extending and contracting the cushion device, the piston head assembly having an orifice defined by a shank abuttable with the cylinder head in the extended position, the shank having a bore aligned with the orifice, a tubular piston rod attached to the shank and extending through the head, port means in the shank and a flexible boot fixed to the head and the piston rod, passage means in the head providing fluid communication between the cylinder bore and the boot, a metering pin attached to the one end of the cylinder and extending through the orifice, and a return spring disposed between the outer end of the rod and the cylinder.

SPECIFICATION The present invention relates to hydraulic cushion devices, and more particularly to an improved piston head assembly for a hydraulic cushion device of the type which may be used in cushioned underframe railway cars for providing car body and lading protection.

A hydraulic cushion unit of the type to which the present invention relates is disclosed in US. Patent 3,- 003,436. The hydraulic cushion unit comprises generally a hydraulic fluid filled cylinder in which there is reciprocally disposed a fluid displacement means which may be in the form of a piston head having fixed to one face thereof an end of a tubular piston rod. The piston rod extends through an intermediate cylinder head fixed inwardly of an open end of the cylinder. Fixed to the outwardly extending end of the cylinder is a base plate against which there abuts one end of a return spring means, the other end of which abuts against another base plate which closes off the other end of the cylinder.

The cylinder and fluid displacement means are movable between a neutral extended and contracted position. During the extension and contraction of the cushion unit, hydraulic fluid flows between a high pressure chamber defined between the forward face of the piston head and the closed end of the cylinder and a low pressure chamber defined between the rear face of the piston head and the intermediate cylinder head.

A flexible reservoir is attached between the intermediate cylinder head and the outwardly extending end of the piston rod. The reservoir communicates with the low pressure chamber by way of the fluid passages through the intermediate cylinder head and serves to receive hydraulic fluid displaced by the piston rod during the contraction of the cushion unit.

The hydraulic cushion unit is preferably of the type having an approximately constant resisting force travel characteristic. To this end the piston head is provided with an orifice which is aligned with the piston rod bore having ports providing fluid communication with the low pressure chamber. Extending through the orifice is a metering pin which is constructed so as to vary the fluid Patented July 16, 1968 flow through the orifice in a manner achieving the approximate substantially constant resisting or cushioning force. The metering pin is fastened at one end to the base of the follow-up plate so as to form a fluid tight seal.

The above generally described hydraulic cushion is primarily characterized by a structure utilizing only static seals which result in a substantially trouble free and leak proof unit.

The principal object of the present invention is to provide a cushion unit of the foregoing type with a new and improved piston head construction.

It is a further object taken in conjunction with the foregoing object to provide a unitary piston head construction having incorporated therein a stop means for limiting the extension of the cushion unit to the neutral position.

Briefly, the piston head of the present construction is formed from a forging or casting including a head having an axial orifice and a shank extending from one face thereof. The shank is formed with a bore which is axially aligned with the orifice and the piston rod bore. The bore of the shank communicates with the low pressure chamber in the cylinder by way of angularly spaced ports formed therein. Moreover, the shank is attached to the tubular piston rod so as to form a continuation of the latter and is formed at its end connected to the piston rod with an outer diameter greater than that of th outer diameter of the piston rod. The portion of the shank extending above the outer diameter of the piston rod serves as an abutment surface or stop which limits the travel of the piston rod assembly in the extended or neutral position of the cushion unit.

Further objects and features will hereinafter appear.

In the drawings:

FIG. 1 is a fragmentary view, partially in section, of a hydraulic cushion unit embodying the piston head construction of the present invention and showing the unit in the neutral extended position thereof;

FIG. 2 is a longitudinal cross sectional view showing the unit in the contracted position;

FIG. 3 is a fragmentary cross sectional view of the piston head construction of the present invention; and

FIG. 4 is a front elevational view of the piston head.

Referring now to the drawings, there is shown a hydraulic cushion unit or device 10 embodying the piston head construction of the present invention and comprising generally a hydraulic fluid filled cylinder 11, a fluid displacement means 12 reciprocal within the cylinder 11, a flexible reservoir in the form of a boot 13 which is statically connected at one end to the cylinder 11 and at the other end to the fluid displacement means 12, a metering pin 14 for controlling the fluid flow from a high pressure chamber 15 and a low pressure chamber 16, and a return spring means 17 disposed between the cylinder 11 and the fluid displacement means 12.

The cylinder is formed from a tube 18 made of steel or the like and of which one end has fixed thereto a base plate 19. Inwardly of the open end 22 is an intermediate cylinder head 23, having an axial opening 24. The intermediate cylinder head 23 may be suitably fixed within the bore 21 by means of snap rings. A sealing ring may be disposed between the contacting surfaces of the cylinder head 23 and the inner wall of the cylinder 11 to form a fluid tight seal.

The fluid displacement means 12 comprises generally a piston head assembly 25 which is reciprocable within the cylinder bore 21. The piston head assembly in accordance with the present invention is formed from a forging or a casting and includes a piston head 26 formed with an axial orifice 30. Extending from the inner face of the head 26 is a shank 27 having a bore 28 which is axially aligned with the orifice 30. The shank 27 at its inner end is formed with a grooved recess 29 which receives one end of a tubular piston rod 31. It is to be noted that the shank 27 is formed at its end connected to the tubular piston rod 31 with an outer diameter greater than the outer diameter of the tubular piston rod 31. This forms in the nature of an abutting surface or stop 32 which strikes the inner face of the intermediate cylinder head 23 in the neutral position as shown in FIG. 1. Extending between the stop 32 and the piston head 26 are radially spaced vertical reinforcing ribs 33.

To facilitate the fastening of the shank 27 to the end of the piston rod 31 the portion of the shank 27 overlying the piston rod and the grooved recess 29 is formed with a plurality of angularly spaced openings 34 into which a Weld is inserted for fixing the rod 31. The shank 27 is further formed with lengthwise and angularly spaced ports 36 which provide fluid communication between the bore 28 of the cylinder and the low pressure chamber 16.

The high pressure face 38- of the piston head 26 is formed with a recess 39 into Which there is positioned a lengthwise movable flap valve 41 which serves to permit communication directly between the high pressure chamber and

low pressure chambers

15 and 16 during the return movement of the unit 10 from its contracted to extended positions for reasons more fully to be explained hereinafter. The flap valve 41' is movable between a position overlying a plurality of elongate ports 42 which are formed in the piston head radially outwardly of the shank 27 to a position clear of the openings against a snap ring 43 seated within the recess.

Seated Within a groove formed in the periphery of the piston head 26 is a guide and sealing ring 47 which is preferably formed from a laminated phenolic resin. The guide and sealing ring 47 is constructed so that the outer guiding surface thereof extends about the outer periphery of the piston head 26 and thereby precludes metal to metal contact of the latter with the cylinder Wall.

Fixed to the other end of the tubular piston rod and closing off same is a second base plate 45 which is fastened to a closure or tie block 46 fixed within the end of the bore 37 as by welding.

To obtain an energy absorbing or resisting force which remains as close as practically possible to a substantially constant value during each increment of travel of the unit from its fully extended neutral position as shown in FIG. 1 to the fully contracted or compressed position as shown in FIG. 2, there is provided the metering pin 14. The metering pin 14 serves to meter the flow of the fluid through the orifice 30 by varying the effective flow area thereof.

The metering pin is formed from a forging having integrally formed at one end thereof an annular attaching flange 51 for fastening the pin 14 on the base plate 19. As shown in particular in FIG. 2 the forged metering pin includes an elongate body portion 52 of substantially constant diameter along the length thereof and is machined to be snugly slidable within the orifice 30.

Formed along the length of the metering pin body 52 is a plurality of spaced flutes 53, each of Which vary similarly in cross section along the length thereof so that upon relative movement between the cylinder 11 and the piston head 26 moving along the metering pin flutes 53, there is provided a varying effective orifice area which imparts a substantially constant force travel characteristic to the cushioning device. To this end the flutes 53 are designed to conform substantially with the relationship x A,.-- A 1 3 wherein A is the orifice area of any position x over the total nominal stroke a (length of the surface in which the flutes are formed), and A is the initial orifice area defined by the orifice 30 and the flutes 53 at the beginning of the stroke under conditions where a completely rigid body is being cushioned.

It is of course to be understood that the design of the flutes 53 may be varied somewhat from the above relationship to achieve the desired constant force characteristic for any given situation. For a more detailed description of the flutes 53 and the fluid metering achieved thereby, reference is made to the aforementioned patent.

The flexible boot 13, Which serves as a reservoir for hydraulic fluid displaced by the piston rod 31;during the contraction of the hydraulic cushion unit 10, may be formed from a fluid impervious flexible material capable of resisting the corosive effects that the hydraulic fluid may have andcapable of withstanding the pressures imposed thereon during use without rupturing.

The boot 13 is formed at one end with a head which is clamped by means of a snap ring clamp arrangement 56 to the intermedite cylinder head 23. At its other end the boot 13 is reverscly turned and the terminal end is also formed with a head 57. The head abuts along one side against a ring 58 fixed to the piston rod 31. On its other side the bead 57 is clamped by Way of a sleeve 59 which is slidable over the piston rod 31 and fixed at its outer end by way of a snap ring 61 against axial movement. In this manner the reversely turned end of the boot 13 is held clamped to the piston rod 31.

The return spring means 17 interposed between the

base plates

19 and 45 and which serve to return the hydraulic cushion 10 to the neutral position of FIG. 1 may be a plurality of springs arranged in tandem.

Assuming that the hydraulic cushion device 10 is employed in a cushioned underframe railway car and is interposed between the lading supporting and the coupler mounting structures thereof, in the absence of shock impact at the couplers the components of the hydraulic cushion device assume the neutral position shown in FIG. 1. Upon shock impact in either buff or draft, the cylinder 11 and the piston head 25 move relatively to each other toward the compressed or contracted position illustrated in FIG. 2. As the cushioning unit 10 contracts under the impact of the force being cushioned, the metering pin 14 displaces hydraulic fluid contained within the piston rod 31 through the ports 36 into the low pressure chamber 16 and through the annular opening 24 into the boot 13, causing the latter to expand.

At the same time the hydraulic fluid flow, initiated by the relative movement of the piston head 26 and the cylinder 11, is directed from the high pressure'chamber 15 to the low pressure chamber 16 via the orifice 30, the shank bore 28 and the ports 36, thence the hydraulic fluid flows into the boot 13. The rate of flow into the orifice 30 is controlled by way of the metering pin 14 and the flutes 53 formed thereon by varying the effective orifice area in a manner which achieves a substantially constant resisting force for each increment of travel of the components. During the contraction of the unit, the force of the fluid on the high pressure face 38 of the piston head causes the flap valve 41 to overlie the ports 42 formed in the piston head. In this manner fluid flow through the ports 42 is precluded during contraction of the cushion unit 10.

Contraction of the unit 10 continues until the open end of the cylinder 11 contacts the closure plate or base plate 45. After the shock has been fully dissipated, the return spring means 17 are operative to return the hydraulic cushion device components to the initial neutral position.

During the relative extension of the cylinder 11 and the piston head 25, the pressure in the low pressure chamber 16 is greater than that which occurs in the high pressure chamber 15; thus, the force of the fluid in the ports 42 acting upon the flap valve 41 are operative to displace the latter from overlying position and against the snap ring 43. This permits addiiional fluid flow area to evacuate the hydraulic fluid in the chamber 16 to the high pressure chamber 15. At the same time, the fluid returns also through the ports 36 and via the gradually increasing orifice area into the high pressure chamber 15. Thus, the flow of hydraulic fluid into the high pressure chamber 15 is always adequate to assure that the latter is filled and thereby maintain the pressure forces in the low pressure chamber 16 and boot 13 at a minimum. These conditions assure proper operation of the cushion unit should an impact be encountered before the unit has returned to its neutral position.

Return movement of the cushion unit occurs when the stop 32 abuts against the intermediate cylinder head 23.

What is claimed is:

1. In a hydraulic cushion device comprising a fluid filled cylinder, a first base plate fixed at one end of said cylinder, an intermediate cylinder head fixed within the bore of said cylinder, a unitary piston head assembly reciprocable within said cylinder bore for movement between said base plate and said intermediate cylinder head to and from an extended position and a contracted position, said piston head assembly including a piston head having an axial orifice, a shank integrally extending from one face of said piston head and having the free end thereof abuttable against said intermedite cylinder head in the extended position thereof, said shank being formed with a bore axially aligned with said orifice, a tubular piston rod fixed at one end within said shank and extending through said intermediate cylinder head outwardly of said open end of said cylinder and having a bore coaxial with said shank bore, radially disposed port means formed in said shank, a flexible boot fixed between said intermediate cylinder head and said outwardly extending end of said piston rod, hydraulic fluid passage means through said intermediate cylinder head providing hydraulic fluid passage means between said cylinder bore and said flexible boot, a second base plate fixed to said outwardly extending end of said tubular piston rod, a metering pin fixed to said first base plate and extending through said piston head orifice, and a reiurn spring disposed between said first and second base plates.

2. The invention as defined in claim 1 wherein said unitary piston head is formed from a casting and said free end of said shank is formed with an outer diameter greater than the outer diameter of said piston rod and thereby forming a stop abuttable against said intermediate cylinder head in the neutral position of said piston head assembly.

3. The invention as defined in claim 1 wherein said piston head is formed with ports providing fluid communication between said closed end of said cylinder and the open end thereof, said ports being spaced radially outwardly of said shank, and wherein flap valve means are disposed over said ports for precluding fluid communication therethrough during movement of said piston head assembly to said contracted position and open communication during movement to said neutral position.

References Cited UNITED STATES PATENTS 3,164,262 1/1965 Price et a1. 2l38 3,176,856 4/1965 Smith 2l343 3,194,415 7/1965 Rasmussen 2l343 3,232,443 2/1966 Smith 213-8 DRAYTON E. HOFFMAN, Primary Examiner,