US3917075A

US3917075A - Hydro-pneumatic cushion gear for railway car

Info

Publication number: US3917075A
Application number: US532804A
Authority: US
Inventors: Willis Harding Knippel
Original assignee: Pullman Inc
Current assignee: Pullman Standard Inc; Pullman Inc
Priority date: 1974-12-16
Filing date: 1974-12-16
Publication date: 1975-11-04
Anticipated expiration: 1992-11-04

Abstract

In a railway car underframe center sill structure, an end-of-car cushion unit of the hydro pneumatic type for absorption of buff forces and located in the cushion pocket at the end of the center sill and coupled with the yoke and coupler arrangement. The cushion unit has a moveable hydraulic fluid containing cylinder connecting with the yoke and coupler arrangement and fixed piston having its inner piston rod end connected in the center sill and its outer piston head orificed within the cylinder to receive reciprocably a central metering pin fixed in the cylinder for transfer of hydraulic fluid to either side of the piston head and in and out of draft chamber portions of the cylinder. A moveable gas piston is in the inner end of the fixed piston and has gas under pressure on the piston inner end, the piston outer side being in hydraulic fluid communication with the orifice. The gas piston has a rolling seal connection and stop within the fixed piston. A rolling seal in the form of a boot connects the cylinder and piston and acts as a dust protector for the piston rod. An alternate form of gas piston slidingly floats in the hydropneumatic chamber in the fixed piston. The cushion arrangement is also provided with buff cylinder stops that hit the striker and provided with recessed draft cylinder stops near the outer end of the cylinder.

Description

United States Patent 11 1 Knippel Nov. 4, 1975 HYDRO-PNEUMATIC CUSHION GEAR FOR RAILWAY CAR Willis Harding Knippel, Palos Park, Ill.

Assignee: Pullman Incorporated, Chicago, Ill.

Filed: Dec. 16, 1974 Appl. No.: 532,804

[75] Inventor:

[56] References Cited UNITED STATES PATENTS 6/1970 Powell 213/43 8/1971 Knippel 213/8 Primary ExaminerM. Henson Wood, .lr. Assistant ExaminerGene A. Church Attorney, Agent, or FirmRichard J. Myers [57] ABSTRACT In a railway car underframe center sill structure, an

end-of-car cushion unit of the hydro pneumatic type for absorption of buff forces and located in the cushion pocket at the end of the center sill and coupled with the yoke and coupler arrangement. The cushion unit has a moveable hydraulic fluid containing cylinder connecting with the yoke and coupler arrangement and fixed piston having its inner piston rod end connected in the center sill and its outer piston head orificed within the cylinder to receive reciprocably a central metering pin fixed in the cylinder for transfer of hydraulic fluid to either side of the piston head and in and out of draft chamber portions of the cylinder. A moveable gas piston is in the inner end of the fixed piston and has gas under pressure on the piston inner end, the piston outer side being in hydraulic fluid communication with the orifice. The gas piston has a rolling seal connection and stop within the fixed piston. A rolling seal in the form of a boot connects the cylinder and piston and acts as a dust protector for the piston rod. An alternate form of gas piston slidingly floats in the hydropneumatic chamber in the fixed piston. The cushion" arrangement is also provided with buff cylinder stops that hit the striker and provided with recessed-draft cylinder stops near the outer end of the cylinder.

31 Claims, 7 Drawing Figures Sheet 1 of 4 3,917,075

U.S. Patent Nov. 4, 1975 N T mm 3 mm ON 9 US. Patent Nov. 4, 1975 Sheet 2 of4 3,917,075

U.S. Patent Nov. 4, 1975 Sheet 3 of4 3,917,075

HYDRO-PNEUMATIC CUSHION GEAR FOR RAILWAY CAR BACKGROUND OF THE INVENTION 1. Field of the Invention:

This invention relates to end-of-car hydraulic cushioning for railway cars to absorb buff forces.

2. Description of the Prior Art It is well known in the prior art to place an end-of-car cushion unit of the hydraulic liquid type in the end of railway car center sill and connect the cushion unit to a yoke and coupler assembly for the absorption of buff and draft forces placed on the railway car, as shown for example in US. Pat. Nos. 3,275,164; 3,458,054; 3,583,573; and 3,599,802. These arrangements employ a mechanical return spring about the outer peripheries of the intercoupled cylinder and piston of the hydraulic cushion unit. The spring is subject to wear and tear and extra friction limiting the smooth operation of the cushion unit. It is desirable to eliminate these problems. Also, it is desirable to have a more compact unit to meet the special requirements of the center sill .end construction. Also, it desirable to develop a cushion unit where the high hydraulic pressure would not be impinged upon the outer boot of the cushion unit, which high pressure could rupture the boot. Yet is is desirable to have the boot protect the piston rod of the unit. It is these desirable objects that the subject invention accomplishes.

SUMMARY The inventive design disclosed herein provides for a railway car cushion unit that eliminates high pressures on the cushion boot, yet retains the boot as a dust cover for the cushion piston rod. In conjunction with this objective, the inventive design also utilizes a cushion unit using a gas piston to replace the mechanical spring of conventional type cushion units, whereby the return of the cushion unit to a neutral position after contracting under a buff force is accomplished smoothly and with considerably reduced friction and wear and tear on the parts, such as in the case with the mechanical spring type. The gas pressure moving piston, so called gas piston, is connected to the fixed hydraulic piston of the cushion unit by a rolling seal or by a sliding seal when the piston is to be free floating.

These and other objectives will become apparent from reference to the following description, appended claims and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of a railway car underframe end illustrating the novel center sill cushion pocket with the pneumatic hyrdaulic cushion unit for end of car cushioning;

FIG. 2 is a sectional end view of the center sill hydropneumatic cushion gear, and coupler structure taken along line 22 of FIG. 1;

FIG. 3 is a longitudinal elevational sectional view taken along line 33 of FIG. 2 and illustrates the neutral extended position of the hydro-pneumatic cushion gear just before a buff load is applied;

FIG. 3a is an enlarged sectional view of a portion of Flg. 3 showing the outer boot seal, the draft and buff port and valve means to the draft chamber, and the sliding dynamic seal means between the hydraulic cylinder and piston rod of the hydro-pneumatic cushion gear; 7

FIG. 4 is longitudinal sectional view similiar to FIG. 3 but with the hydro-pneumatic cushion gear in the collapsed position and ready to expand by operation of the return mechanism or gas piston andalso ready to ac cept a draft force in excess of the force of the return mechanism;

FIG. 5 is longitudinal elevational sectional view similiar to FIG. 3 but with a modified form of free floating gas piston with a sliding seal; and

FIG. 6 is longitudinal section view of the modified free floating gas piston with sliding seal of FIG. 5 but in the position shown in FIG. 4.

DESCRIPTION OF THE PREFERED EMBODIMENTS With reference now to the drawing and in particular with reference to FIGS. 1 and 2, there is shown a portion of a railroad car 2, in phantom line, having a center sill structure 4 with a gear containing end portion 6 having a cushion pocket 8 in which is located a cushion unit 10 of a hydropneumatic (gas to oil) gear 11. The cushion unit has a piston means 12 having a piston rod 13 fixed to the base plate 14 which is fixed and trapped between rear buff stop 16 and rear draft stop 18 attached to the center sill 4. A cylinder 20 is reciprocably disposed in a longitudinal moveable direction about the piston 12 and at its outer end 22 is integrally attached to the yoke 23 of the hydropneumatic gear 11 which carries the coupler 24 held by coupler pin 25. The outer end 26 of the center sill 4 is provided with a striker 27. The outer or front end is provided with

front draft stops

29, 29 for engagement with cylinder shoulders 30, 30 and with front buff stops 28, 28 for engagement with the yoke shoulders 31, 31 (on the outer flange 34 of the coupler housing 35) of the moveable yoke 23. The forward draft stops 29, 29 ride in cylinder recesses 30a, 30a. The center sill 4 is provided with a center sill reinforcement 33 and an end sill 32. At the inner end or rear of the gear 11 the base plate 14 is provided with a flange 15 having draft surfaces 15a, 15a for engagement with

rear draft stops

18, 18 and buff surfaces 15b, 15b for the rear buff stops l6, 16. A flexible boot 36 that acts as a dust cover for the piston rod covers piston rod and connects therewith the cylinder 20.

With reference now to FIGS. 3, 3a and 4 it is seen that the cushion unit 10 has its cylinder 20 moveably and reciprocably disposed about the fixed piston means 12 which includes piston head 37 that forms a forward hydraulic chamber 38 with the

interior walls

39 and 40 of the cylinder 20. The front wall 40 was a metering pin 41 extending rearwardly therefrom and through a metering orifice 42 in the piston head 37. The piston head has a piston ring 43 about its outer periphery that forms a sliding sealing engagement with the cylindrical wall 39. The piston head 37 at its outer peripheral portion inward its ring 43 is provided with a plurality of circumferentially spaced connecting

ports

44, 44a communicating chamber 38 with outer annular draft chamber 45 that surrounds the piston rod 13 and is bounded by the piston head 37, the cylinder wall 39 and the slidingannular seal arrangement 46 being fixed on the rear end 47 of the cylinder 20. The seal arrangement 46 is of the sliding seal type between the piston rod and the cylinder and includes the packing gland 48 and the dynamic sliding seal means 49 that is comprised of a plu- 3 rality of stacked \/-shaped or chevron type peripheral seat rings 50 of seal material between a rear retaining ring 51 and forward annular spring means 52. The forward port 53 of the boot 36 is also attached to the rear end 47 of the cylinder and the outer surface of the piston rod 13 at 54. The boot seal prevents dust from getting on the piston rod and adjacent sliding seal means The central portion of the piston rod 13 forms a piston rod chamber 55 containing hydraulic fluid as defined by the inner cylindrical piston rod wall 56 and the rear wall or cap 57. A gas piston 58 is reciprocably disposed within said chamber 55 and forms a rolling seal with the piston rod wall 56 by the attached rolling seal or flexible boot member 59. The chamber 55'communicates with the orifice 42 and with the draft chamber 45 by way of cut-out area or porting 60 and passage or port 600 in the piston head 37. A draft valve means 61 in the form of a slide ring 61a, slidable along piston rod outer peripheral groove 62 during draft acting forces, blocks off porting or passage 60a to terminate fluid communication between the draft chamber 45 and the piston rod chamber 55. Buff valve means 63 in the form of a slide ring 64 slidable along the piston head outer peripheral groove 65 during buff acting forces, blocks off the passages or ports 44 to terminate fluid communication between the draft chamber 45 and the front cylinder chamber 38.

The piston rod 13 fixedly supports within its chamber 55 an annular spider member 66 that has ports 67 for introducing hydraulic fluid from the metering orifice 42 into chamber 55. The member 66 also acts as a stop or abutment for the gas piston member 58. A gas receiving chamber or accumulator 68 is formed between the gas piston member 58 and the left end wall 57 of the piston rod 13 into which nitrogen gas is introduced under pressure by way of pre-charge valve means 69. The gas piston is allowed to compress the gas in the gas chamber when buff forces imperige upon the coupler much like the usual mechanical return spring around the cushion unit is compressed in a conventional manner as shown for instance in US. Pat. No. 3,599,802. The compressed gas moves the gas piston, hydraulic fluid and cylinder to the right when the buff forces are removed from the coupler. FIGS. and 6 show a modified form of gas piston which is a sliding gas piston 70 having a piston ring 71 and sliding seal 72 engaging with the interior of the piston rod and has no floating seal 59 and no spider member 66. The reciprocation of the piston 70 is limited by the stop surface 57a on the element 57 and the stop surface 37a on the element 37.

i In operation a buff force on the coupler 24 moves the cylinder over a piston means 12 toward the base plate 14 forcing the hydraulic fluid or oil out of the front cylinder chamber 38 and into the draft chamber 45 by way of

passages

60 and 60a and ring valve 61 and the oil moves into the piston rod chamber 55 by way of orifices 42 forcing the

gas piston

58 or 70 to the left compressing the gas in accumulator chamber 68. Once the buff force is removed from the coupler draft forces may take over and move the cylinder 20 in reverse manner with the fluid leaving the draft chamber 45 via ports 44 and ring valve member 64 into the front cylin der chamber 38. Also when the

accumulator gas piston

58 or 70 is compressing the gas in the accumulator chamber 68 the hydraulic cylinder and the coupler can return to the neutral position once the buff forces are removed whether or not any draft forces are acting on 4 the coupler because of the stored energy of the compressed nitrogen gas in the accumulator chamber.

Thus what is provided is a novel cushion unit which utilizes a gas piston arrangement in longitudinal alignment with the hydraulic piston and cylinder means and replaces the mechanical spring of the conventional type unit whereby the return of the cushion unit to a neutral position, after contracting under a buff force, is accomplished smoothly and with considerably reduced friction and wear and tear on the parts. The rolling seal or the sliding seal of the gas piston reduces wear and tear on the cushion unit components. The novel porting of hydraulic fluid between the front cylinder chamber, the draft chamber and the piston rod chamber gives a smooth operation to the cushioning unit.

The foregoing description and drawings merely explain and illustrate the invention and the invention is not limited thereto, except insofar as the appended claims are so limited, as those skilled in the art who have the disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.

What is claimed is:

1. In a railway car including a car coupler and a hollow open end center sill structure having a cushion pocket therein and a hydraulic cushion unit in the pocket and attached to the car coupler and receiving 1 buff and draft forces;

a rear buff stop means on the center .sill structure, rear draft stop means on the center sill structure outwardly of the buff stop means,

said cushion unit having a cushion base plate held between said rear buff stop means and said rear draft stop means,

said cushion unit having piston means including a piston rod fixedly attached to the outer forward end of said base plate and a piston head, and

said cushion unit including a hydraulic cylinder reciprocally movable over said piston head and piston rod forwardly of the rear end of said piston rod.

2. In a railway car including a car coupler and a hollow open end center sill structure having a cushion pocket therein and a hydraulic cushion unit in the pocket and attached to the car coupler and receiving buff and draft forces;

'a rear buff stop means on the center sill structure, rear draft stop means on the center sill structure outwardly of the buff stop means,

said cushion unit having piston means including a piston rod fixedly attached to the outer forward end of said base plate and a piston head.

said cushion unit including a hydraulic cylinder reciprocally movable over said piston head and'piston rod forwardly of the rear end of said piston rod; and 1 front buff stop means and front draft stop means outwardly of said rear buff and draft stop means on said center sill structure engageable with said cylinder means and said coupler.

3. The invention according to claim 2, and

said front buff stop means being mounted outwardly of said front draft stop means.

4. The invention according to claim 2, and

said front buff stop means engaging with said coupler and said front draft stop means engaging with said cylinder means.

5. The invention according to claim 2, and

said front buff stop means being at the outer end of the center sill structure.

6. The invention according to claim 2, and

said front buff stop means being mounted outwardly of said front draft stop means, and

said front buff stop means being at the outer end of the center sill structure.

7. The invention according to claim 2, and

said front buff stop means being at the outer end of the center sill structure, and

striker means at the outer end of the center sill structure, said front buff stop means being engageable with said striker means.

8. The invention according to claim 2, and

said cylinder means having a recessed shoulder, and

said front draft stop means being engageable with said recessed shoulder.

9. In a railway car, a center sill end structure having a cushion pocket, a hydro-pneumatic shock absorber cushion unit comprising;

piston means fixedly attached to said center sill end structure,

cylinder means reciprocally movable over said piston means,

said center sill end structure having buff and draft stop means coupled with said cylinder means for limited movement of the latter,

said cylinder means at its outer forward end including a coupler subject to buff end draft forces,

dyamic seal means slidable relatively between the piston means and the cylinder means, and

a dust seal boot connecting the outer periphery of the piston means and the inner end of the cylinder means and encircling said dyamic seal means to prevent dust from forming on said seal means.

10. The invention according to claim 9, and

said piston means including a piston head and a piston rod having a hollow tubular member having an inner end portion,

cap means on the inner end portion of said piston means,

a free moving piston in said tubular member,

said free moving piston being within the hollow portion of said piston rod and movable between the cap means and the piston head, i

a flexible rolling seal means including a boot connecting with said free moving piston and with the tubular member and defining with said cap means a gas receiving first chamber and with the cylinder means a second chamber for hydraulic fluid, and

said cap means being adapted for introduction of a gaseous fluid into the gas receiving first chamber and said rolling seal means being an interface between the first chamber and the second chamber.

11. The invention according to claim 10, and

a stop member in the tubular member engageable with and limiting movement of said free moving piston.

12. The invention according to claim 10, and

said cylinder means defining an outer third chamber, a metering pin extending in said third chamber, said piston head having an orifice in fluid communication with the second and third chambers and said metering pin extending from the outer end of the third chamber inwardly into the orifice for controlling the flow of fluid from the third chamber into the second chamber as defined between the free moving piston and the piston head.

13. The invention according to claim 12, and

a draft chamber formed between said piston rod and said cylinder means, said piston head having an outerperipheral portion provided with port means for transferring fluid between the third chamber andsaid draft chamber.

14. The invention according to claim 10, and

a stop member in the tubular member engageable with and limiting movement of said free moving piston, and

15. The invention according to claim 13, and

said port means including a first fluid pathway communicating between the second chamber and the draft chamber'and a first movable valve means for blocking fluid communication of the fluid in the first fluid pathway upon extension of the cushion unit,

said port means having a fluid pathway communicating between the third chamber and said draft chamberand a second movable valve means for closing off said first pathway upon compression of the cushionunit under buff forces.

16. The invention according to claim 9, and

cap means on the inner end portion of said piston means,

a free moving piston in said tubular member,

said free moving piston being within the hollow portion of said piston rod and movable between the cap means and the piston head,

a rolling seal means connecting with said free moving piston and with the tubular member and defining with said cap means a gas receiving first chamber and with the cylinder means a second chamber for hydraulic fluid, and

said cap being adapted for introduction of a gaseous fluid into the gas receiving first chamber and said rolling seal means being an interface between the first chamber and the second chamber.

17. The invention according to claim 16, and

18. The invention according to claim 16, and

19. The invention according to claim 18, and

a draft chamber formed between said piston rod and said cylinder means. said piston head having an outer peripheral portion provided with port means for transferring fluid between the third chamber and said draft chamber.

20. The invention according to claim 16, and

a stop member in the tubular member engageable with and limiting movement of said free moving piston. and

21. The invention according to claim 18, and

a draft chamber formed between said piston rod and said cylinder means, said piston head having an outer peripheral portion provided with port means for transferring fluid between the third chamber and said draft chamber.

22. The invention according to claim 21, and

said cap means having a shoulder to limit movement of said free moving piston.

23. The invention according to claim 21, and

said free moving piston being engageable with said piston head.

24. The invention according to claim 9, and

cap means on the inner end portion of said piston means,

a free moving piston in said tubular member,

sliding seal means surrounding said free moving piston and engageable with the interior surface of said piston rod and defining with said cap means a gas receiving first chamber and with the cylinder means a second chamber for hydraulic fluid, and sliding seal means forming a seal between the first chamber and the second chamber, said free moving piston being freely slidable between the cap means and the piston head, and

25. The invention according to claim 24, and

26. The invention according to claim 24, and

27. The invention according to claim 26, and

28. The invention according to claim 24, and

29. The invention according to claim 27, and

said port means including a first fluid pathway communicating between the second chamber and the draft chamber and a first movable valve means for blocking fluid communication of the fluid in the first fluid pathway upon extension of the cushion unit, and

said port means having a fluid pathway communicating between the third chamber and said draft chamber and a second movable valve means for closing off said first pathway upon compression of the cushion unit under buff forces.

30. In a railway car, a center sill end structure having a cushion pocket, a hydro-pneumatic shock absorber cushion unit comprising;

piston means fixedly attached to said center sill end structure, r z' cylinder means reciprocally movable over' said piston means,

said center sill end structure having buff and draft stop means coupled with said cylinder means for i tion of said piston rod and movable" between the cap means and the piston head,

a flexible rolling seal means including .aboot connecting with said free moving piston and with the tubular member and defining with said cap means a gas receiving first chamber andI'with-the cylinder means a second chamber for hydraulic fluid, and

said cap means being adapted for introduction of a gaseous fluid into the gas receiving first chamber and said rolling seal means being an interface between the first chamber and the second chamber,

31. In a railway car, a center sill end structure having a cushion pocket, a hydro-pneumatic shock absorber cushion unit comprising;

piston means fixedly attached to said center sill end structure,

cylinder means reciprocally movable over said piston means,

said center sill end structure having buff and draft stop means coupled with said cylinder means for limited movement of the latter.

dyamic seal means slidable relatively between the piston means and the cylinder means,

cap means on the inner end portion of said piston means,

a free moving piston in said tubular member,

10 said free moving piston being within the hollow portion of said piston rod and movable between the cap means and the piston head. sliding seal means surrounding said free moving piston and engageable with the interior surface of said piston rod and defining with said cap means a gas receiving first chamber and with the cylinder means a second chamber for hydraulic fluid, said sliding seal means forming a seal between the first chamber and the second chamber, said free moving piston being freely slidable between the cap means and the piston head, and said cap means being adapted for introduction of a gaseous fluid into the gas receiving first chamber and said rolling seal means being an interface between the first chamber and the second chamber.

Claims

1. In a railway car including a car coupler and a hollow open end center sill structure having a cushion pocket therein and a hydraulic cushion unit in the pocket and attached to the car coupler and receiving buff and draft forces; a rear buff stop means on the center sill structure, rear draft stop means on the center sill structure outwardly of the buff stop means, said cushion unit having a cushion base plate held between said rear buff stop means and said rear draft stop means, said cushion unit having piston means including a piston rod fixedly attached to the outer forward end of said base plate and a piston head, and said cushion unit including a hydraulic cylinder reciprocally movable over said piston head and piston rod forwardly of the rear end of said piston rod.

2. In a railway car including a car coupler and a hollow open end center sill structure having a cushion pocket therein and a hydraulic cushion unit in the pocket and attached to the car coupler and receiving buff and draft forces; a rear buff stop means on the center sill structure, rear draft stop means on the center sill structure outwardly of the buff stop means, said cushion unit having a cushion base plate held between said rear buff stop means and said rear draft stop means, said cushion unit having piston means including a piston rod fixedly attached to the outer forward end of said base plate and a piston head, said cushion unit including a hydraulic cylinder reciprocally movable over said piston head and piston rod forwardly of the rear end of said piston rod, and front buff stop means and front draft stop means outwardly of said rear buff and draft stop means on said center sill structure engageable with said cylinder means and said coupler.

3. The invention according to claim 2, and said front buff stop means being mounted outwardly of said front draft stop means.

4. The invention according to claim 2, and said front buff stop means engaging with said coupler and said front draft stop means engaging with said cylinder means.

5. The invention according to claim 2, and said front buff stop means being at the outer end of the center sill structure.

6. The invention according to claim 2, and said front buff stop means being mounted outwardly of said front draft stop means, and said front buff stop means being at the outer end of the center sill structure.

7. The invention according to claim 2, and said front buff stop means being at the outer end of the center sill structure, and striker means at the outer end of the center sill structure, said front buff stop means being engageable with said striker means.

8. The invention according to claim 2, and saId cylinder means having a recessed shoulder, and said front draft stop means being engageable with said recessed shoulder.

9. In a railway car, a center sill end structure having a cushion pocket, a hydro-pneumatic shock absorber cushion unit comprising; piston means fixedly attached to said center sill end structure, cylinder means reciprocally movable over said piston means, said center sill end structure having buff and draft stop means coupled with said cylinder means for limited movement of the latter, said cylinder means at its outer forward end including a coupler subject to buff end draft forces, dyamic seal means slidable relatively between the piston means and the cylinder means, and a dust seal boot connecting the outer periphery of the piston means and the inner end of the cylinder means and encircling said dyamic seal means to prevent dust from forming on said seal means.

10. The invention according to claim 9, and said piston means including a piston head and a piston rod having a hollow tubular member having an inner end portion, cap means on the inner end portion of said piston means, a free moving piston in said tubular member, said free moving piston being within the hollow portion of said piston rod and movable between the cap means and the piston head, a flexible rolling seal means including a boot connecting with said free moving piston and with the tubular member and defining with said cap means a gas receiving first chamber and with the cylinder means a second chamber for hydraulic fluid, and said cap means being adapted for introduction of a gaseous fluid into the gas receiving first chamber and said rolling seal means being an interface between the first chamber and the second chamber.

11. The invention according to claim 10, and a stop member in the tubular member engageable with and limiting movement of said free moving piston.

12. The invention according to claim 10, and said cylinder means defining an outer third chamber, a metering pin extending in said third chamber, said piston head having an orifice in fluid communication with the second and third chambers and said metering pin extending from the outer end of the third chamber inwardly into the orifice for controlling the flow of fluid from the third chamber into the second chamber as defined between the free moving piston and the piston head.

13. The invention according to claim 12, and a draft chamber formed between said piston rod and said cylinder means, said piston head having an outer peripheral portion provided with port means for transferring fluid between the third chamber and said draft chamber.

14. The invention according to claim 10, and a stop member in the tubular member engageable with and limiting movement of said free moving piston, and said cylinder means defining an outer third chamber, a metering pin extending in said third chamber, said piston head having an orifice in fluid communication with the second and third chambers and said metering pin extending from the outer end of the third chamber inwardly into the orifice for controlling the flow of fluid from the third chamber into the second chamber as defined between the free moving piston and the piston head.

15. The invention according to claim 13, and said port means including a first fluid pathway communicating between the second chamber and the draft chamber and a first movable valve means for blocking fluid communication of the fluid in the first fluid pathway upon extension of the cushion unit, said port means having a fluid pathway communicating between the third chamber and said draft chamber and a second movable valve means for closing off said first pathway upon compression of the cushion unit under buff forces.

16. The invention according to claim 9, and said piston means including a piston head and a piston rod having a hollow tubular member having an inner end portion, CAP means on the inner end portion of said piston means, a free moving piston in said tubular member, said free moving piston being within the hollow portion of said piston rod and movable between the cap means and the piston head, a rolling seal means connecting with said free moving piston and with the tubular member and defining with said cap means a gas receiving first chamber and with the cylinder means a second chamber for hydraulic fluid, and said cap being adapted for introduction of a gaseous fluid into the gas receiving first chamber and said rolling seal means being an interface between the first chamber and the second chamber.

17. The invention according to claim 16, and a stop member in the tubular member engageable with and limiting movement of said free moving piston.

18. The invention according to claim 16, and said cylinder means defining an outer third chamber, a metering pin extending in said third chamber, said piston head having an orifice in fluid communication with the second and third chambers and said metering pin extending from the outer end of the third chamber inwardly into the orifice for controlling the flow of fluid from the third chamber into the second chamber as defined between the free moving piston and the piston head.

19. The invention according to claim 18, and a draft chamber formed between said piston rod and said cylinder means, said piston head having an outer peripheral portion provided with port means for transferring fluid between the third chamber and said draft chamber.

20. The invention according to claim 16, and a stop member in the tubular member engageable with and limiting movement of said free moving piston, and said cylinder means defining an outer third chamber, a metering pin extending in said third chamber, said piston head having an orifice in fluid communication with the second and third chambers and said metering pin extending from the outer end of the third chamber inwardly into the orifice for controlling the flow of fluid from the third chamber into the second chamber as defined between the free moving piston and the piston head.

21. The invention according to claim 18, and a draft chamber formed between said piston rod and said cylinder means, said piston head having an outer peripheral portion provided with port means for transferring fluid between the third chamber and said draft chamber.

22. The invention according to claim 21, and said cap means having a shoulder to limit movement of said free moving piston.

23. The invention according to claim 21, and said free moving piston being engageable with said piston head.

24. The invention according to claim 9, and said piston means including a piston head and a piston rod having a hollow tubular member having an inner end portion, cap means on the inner end portion of said piston means, a free moving piston in said tubular member, said free moving piston being within the hollow portion of said piston rod and movable between the cap means and the piston head, sliding seal means surrounding said free moving piston and engageable with the interior surface of said piston rod and defining with said cap means a gas receiving first chamber and with the cylinder means a second chamber for hydraulic fluid, and sliding seal means forming a seal between the first chamber and the second chamber, said free moving piston being freely slidable between the cap means and the piston head, and said cap means being adapted for introduction of a gaseous fluid into the gas receiving first chamber and said rolling seal means being an interface between the first chamber and the second chamber.

25. The invention according to claim 24, and a stop member in the tubular member engageable with and limiting movement of said free moving piston.

26. The invention according to claim 24, and said cylinder means defining an outer third chamber, a metering pin extEnding in said third chamber, said piston head having an orifice in fluid communication with the second and third chambers and said metering pin extending from the outer end of the third chamber inwardly into the orifice for controlling the flow of fluid from the third chamber into the second chamber as defined between the free moving piston and the piston head.

27. The invention according to claim 26, and a draft chamber formed between said piston rod and said cylinder means, said piston head having an outer peripheral portion provided with port means for transferring fluid between the third chamber and said draft chamber.

28. The invention according to claim 24, and a stop member in the tubular member engageable with and limiting movement of said free moving piston, and said cylinder means defining an outer third chamber, a metering pin extending in said third chamber, said piston head having an orifice in fluid communication with the second and third chambers and said metering pin extending from the outer end of the third chamber inwardly into the orifice for controlling the flow of fluid from the third chamber into the second chamber as defined between the free moving piston and the piston head.

29. The invention according to claim 27, and said port means including a first fluid pathway communicating between the second chamber and the draft chamber and a first movable valve means for blocking fluid communication of the fluid in the first fluid pathway upon extension of the cushion unit, and said port means having a fluid pathway communicating between the third chamber and said draft chamber and a second movable valve means for closing off said first pathway upon compression of the cushion unit under buff forces.

30. In a railway car, a center sill end structure having a cushion pocket, a hydro-pneumatic shock absorber cushion unit comprising; piston means fixedly attached to said center sill end structure, cylinder means reciprocally movable over said piston means, said center sill end structure having buff and draft stop means coupled with said cylinder means for limited movement of the latter, said cylinder means at its outer forward end including a coupler subject to buff end draft forces, dyamic seal means slidable relatively between the piston means and the cylinder means, said piston means including a piston head and a piston rod having a hollow tubular member having an inner end portion, cap means on the inner end portion of said piston means, a free moving piston in said tubular member, said free moving piston being within the hollow portion of said piston rod and movable between the cap means and the piston head, a flexible rolling seal means including a boot connecting with said free moving piston and with the tubular member and defining with said cap means a gas receiving first chamber and with the cylinder means a second chamber for hydraulic fluid, and said cap means being adapted for introduction of a gaseous fluid into the gas receiving first chamber and said rolling seal means being an interface between the first chamber and the second chamber.

31. In a railway car, a center sill end structure having a cushion pocket, a hydro-pneumatic shock absorber cushion unit comprising; piston means fixedly attached to said center sill end structure, cylinder means reciprocally movable over said piston means, said center sill end structure having buff and draft stop means coupled with said cylinder means for limited movement of the latter, said cylinder means at its outer forward end including a coupler subject to buff end draft forces, dyamic seal means slidable relatively between the piston means and the cylinder means, said piston means including a piston head and a piston rod having a hollow tubular member having an inner end portion, cap means on the inner end portion of said piston means, a free moving piston in said tubular memBer, said free moving piston being within the hollow portion of said piston rod and movable between the cap means and the piston head, sliding seal means surrounding said free moving piston and engageable with the interior surface of said piston rod and defining with said cap means a gas receiving first chamber and with the cylinder means a second chamber for hydraulic fluid, said sliding seal means forming a seal between the first chamber and the second chamber, said free moving piston being freely slidable between the cap means and the piston head, and said cap means being adapted for introduction of a gaseous fluid into the gas receiving first chamber and said rolling seal means being an interface between the first chamber and the second chamber.