US3868911A

US3868911A - Railway car suspension motion control system

Info

Publication number: US3868911A
Application number: US372851A
Authority: US
Inventors: John C Schultz
Original assignee: Houdaille Industries Inc
Current assignee: Vibratech Inc
Priority date: 1973-06-22
Filing date: 1973-06-22
Publication date: 1975-03-04
Anticipated expiration: 1992-03-04

Abstract

A filled hydraulic system controls bounce, pitch and roll vibrational movements of a railroad car by controlling displacement of hydraulic fluid in and between double-acting hydraulic cylinder units connected between the car body and at least one truck frame, there being check valves and a main pressure responsive spool valve in the system.

Description

United States Patent 1 1 1111 3,868,911 Schultz 1 1 Mar. 4, 1975 [5 RAILWAY CAR SUSPENSION MOTION 3,614,931 10/1971 Adler 105/164 3,717,104 2 1973 Law et al. 105/182 R x CONTROL SYSTEM [75] Inventor: John C. Schultz, Buffalo, NY. [73] Assignee: Houdaille Industries, Inc., Buffalo,

[22] Filed: June 22, 1973 [21] Appl. No.: 372,851

[52] US. Cl 105/164, 105/199 A, 105/210 [51] Int. Cl. B611 3/08, B611 5/24, B6lf 5/50 [58] Field of Search... 105/164, 182 R, 210, 199 A [56] References Cited UNITED STATES PATENTS 2,505,256 4/1950 Poage 105/210 2,520,944 9/1950 Lynn et al 105/164 X Primary E.\'aminerM. Henson Wood, Jr.

Assistant Examiner-Howard Beltran Attorney, Agent, or FirmHill, Gross, Simpson, Van Santen, Steadman, Chiara & Simpson [57] ABSTRACT A filled hydraulic system controls bounce, pitch and roll vibrational movements of a railroad car by controlling displacement of hydraulic fluid in and between double-acting hydraulic cylinder units connected between the car body and at least one truck frame, there being check valves and a main pressure responsive spool valve in the system.

22 Claims, 5 Drawing Figures PATENTEDW 41975 SHEET 2 BF 3 A I W 5] '5' 34:

PATENTEDHAR 41915 3.868.911 SHEET 3 BF 3 Ffga5 RAILWAY CAR SUSPENSION MOTION CONTROL SYSTEM This invention relates to the control of motions of railroad cars related to their suspension systems, and is more particularly concerned with a new and improved hydraulic system for this purpose.

Pertinent elements involved in the suspension system of a railroad car are the car body, bolsters, suspension springs and truck assemblies. Basically, the car body is supported at four corners by springs which rest on the truck frames, this being generally accomplished through a swivel plate connection between the car body and each bolster. This constitutes a mass elastic system. When track irregularities and force and speed disturb the elastic system at its natural frequency, large undesirable oscillations of the car body result. In running operation, a car body basically has three modes of vibration, that is, bounce wherein the entire car body vibrates vertically in phase, pitch wherein the two ends vibrate vertically 180 out of phase, and roll wherein the vibrations are transverse to the length of the car and are 180 out of phase. Resonant disturbances which are sustained for any length of time result in a build-up of car body oscillation amplitudes to undesirable levels. Track surface irregularities which predominantly produce these disturbances are variations of the cross level of the tracks and rail joints. American railroads stagger the joints. Therefore, cars are subjected to disturbances which contribute to the roll mode.

Conventionally, the railroad car body is supported through center plates on bolsters, carried on springs on the truck frames riding on the wheel and axle assembly. During major roll motion the weight of the car transfers to the side bearing on and between the car and bolster and the center plate separates. The suspension springs compress to virtually solid condition on the side toward which the roll extends and expand on the other side. The wheel opposite the roll direction lifts from the track. Permitting the roll to build sufficiently in magnitude may result in extremely high forces being imposed on the bolster and side frame about the center bearing requiring high endurance strength in these components. If wheel lift occurs while negotiating a curve or during a lateral disturbance, derailment may result.

On bad track, the roll problem occurs in a speed range of about to 30 miles per hour, requiring the engineer to take the train through this range as rapidly as possible or to slack off and pass through this speed range where track conditions are more desirable.

Vertical or bounce frequency is in the order of 2.5 cps and the roll frequency is in the order of 0.5 cp's. Therefore, ordinary shock absorbers which will sufficiently damp the roll oscillations are much too stiff for nornal vertical or bounce conditions.

An important object of the present invention is to overcome the foregoing and other disadvantages, deficiencies, inefficiencies, shortcomings and problems in railroad car suspension systems, and to attain important advantages and improvements and new and improved results through the system to be hereinafter described and which will satisfy the requirements for roll control as well as providing for efficient bounce and pitch control.

Another object of the present invention is to provide a new and improved railroad car suspension control system wherein all three basic modes of vibration are controlled in a simple, efficient and highly effective manner, wherein vibrations in the roll mode, especially, are effectively controlled.

A further object of the invention is to provide a new and improved filled hydraulic system for controlling railroad car suspension, and involving an advantageous automatic, self-adjusting valve arrangement.

Still another object of the invention is to provide a new and improved control valve arrangement for railroad car suspension systems.

Yet another object of the invention is to provide a new and improved vibration damping system for railroad cars.

Other objects, features and advantages of the invention will be readily apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings although variations and modifications may be effected without departing from the spirit and scope of the novel concepts embodied in the disclosure, and in which:

FIG. 1 is a simplified, illustrative fragmentary end elevational view, partially in section, of a railroad car embodying features of the present invention.

FIG. 2 is a schematic illustration of the manner in which bounce and pitch are controlled in the railroad car suspension; and

FIGS. 3,4 and 5 illustrate various progressive phases in roll control in the railroad car suspension.

Referring, first, to FIG. 1, a typical railroad car is exemplified which may be a passenger car but in the example shown, comprises a freight car having a body 10 and suspension including a pair of trucks 11 on each of which the body is mounted through the medium of swivel center plate means 12 on a bolster 13 extending transversely under the car and having its opposite ends mounted on coil springs 14 supported by truck frame 15 carried by the journals extending from the opposite ends of an axle 17 of flanged car wheels 18 riding on track rails 19.

According to the present invention, a new and improved control system for damping bounce, pitch and roll is provided and which is mounted on and between the car body 10 and the suspension 11. Either or both of the trucks 11 of the car may be equipped with the control system. For this purpose, at each side of the truck 11 a double-acting hydraulic fluid displacement unit 20 is coupled to and between the body 10 and the truck frame 15 by suitable flexible joint means 21 such as universal joints to permit lateral and turning movements between the car body and the truck. In the present instance, the units 20 comprise rectilinear cylinder and piston assemblies each comprising a cylinder 22 having an upper end thereof coupled to the car body 10, and a piston rod 23 extending from the lower end of the cylinder coupled to the truck frame with a protective flexible boot 24 about the portion of the piston rod which projects beyond the cylinder. If preferred, mounting of the hydraulic units 20 may be reversed, that is, the piston rod 23 in each instance attached to the car body and the opposite end of the cylinder 22 attached to the truck frame 15. As best seen in FIG. 2, the hydraulic units 22 are of the double-ended cylinder type, although single-ended cylinders could be used where rod displacement is accounted for by design. In the present instance, the cylinders 22 are such that the piston rod 23 in each instance extends through the opposite ends of the cylinder and with a piston 25 fixed on the piston rod normally located intermediate the ends of the working chamber within the cylinder, dividing such working chamber into an upper subchamber 27 and a lower subchamber 28. On its upper end, the cylinder 22 has means defining a replenishing chamber 29 which is partially filled with hydraulic fluid through a suitable port normally closed by a filler plug 30 positioned so as to insure the proper air to oil relationship when the unit is in the installed attitude for servicing purposes. Suitable check valved replenishing communication between the reservoir 29 and the working chamber within the cylinder 22 is provided for in any well-known manner to insure a continously filled operating system and make up and fluid leakage. Apart from providing replenishing fluid, the chamber 29 serves as a place for the increased oil volume in the system which occurs due to thermal expansion. At its free end portion the piston rod 23 extends into the reservoir chamber 29 and on moving into the chamber 29, may compress the air in the chamber.

Means providing hydraulic displacement connections between the units comprise a preferably flexible conduit or duct 31 communicating with the upper working subchamber 27 and a preferably flexible duct or conduit 32 communicating with the lower subchamber 28. First valve means are provided in the hydraulic displacement connections automatically responsive to hydraulic pressure in said connections as generated by the units 20 for controlling displacement therethrough and thereby damping relative bounce and pitch motions between the car body and the suspension. Additonal, pressure-sensitive valve means are provided in the hydraulic displacement connections inactive relative to bounce and pitch but operating automatically responsive to hydraulic pressue in the connections as generated by the units 20 to damp roll motion between the car body and the suspension. These valve means are desirably housed within a housing which may be in the form ofa block 33 with which the

ducts

31 and 32 communicate.

In a desirable construction, as exemplified in FIG. 2, the valve means functioning to control and damp relative bounce and pitch motions comprise a set of check valves for the hydraulic circuit associated with each of the units 20. Such valves include a check valve 34 permitting relatively free hydraulic fluid displacement from the duct 31 to the duct 32 of each of the hydraulic units 20, and a check valve 35 which is normally biased as by means of a spring 37 for resisting hydraulic fluid displacement from the duct 32 to the duct 31 of each of the hydraulic units 20. Suitable means, (not shown) may be provided for adjusting the biasing thrust of the spring 37 in each instance.

Roll motion damping valve means comprises a reciprocating mounted spool valve member 38 mounted in a bore 39 and normally maintained centered therein by biasing means such as respective coiled compression springs 40 thrusting towards the respective opposite ends of the valve. Each of the ducts 32 communicates with a respective one end of the bore 39, and through the bore with the companion duct 31 by way of a respective blind end bore 41 in the adjacent end portion of the valve 38 and one or more side ports 42 near the inner end of the respective bore 41 and a communication groove 43 in the perimeter of the valve spool registering with a port 44 from which a branch passage 45 connects with the seat for the check valve 35 and a branch passage 47 connects with the check valve 34. Communication between the ducts 31 is effected by way of adjacently spaced ports 48 near the longitudinal center of the bore 39 and a peripheral groove 49 in the valve 38 bracketing the ports 48.

In operating condition, the hydraulic system as described is self-contained and is filled with suitable hydraulic fluid such as oil, and vibration damping in the several modes of capability of the system is effected automatically. For example, FIG. 2 demonstrates damping of bounce vibrations wherein the entire body vibrates vertically in phase,-and pitch vibrations wherein the two ends of the car vibrate vertically out of phase. The solid directional arrows represent hydraulic fluid displacement during compression wherein the distance between the car body 10 and the truck 11 reduces by yielding of the springs 14 as where the wheels 18 strike a raised rail joint. Although many prior sus' pension systems offer little damping for such vibrational motions, the present system efficiently damps such motions. During the compression movement, the upper subchambers 27 of the hydaulic units 22 contract and the lower subchambers 28 expand. Hydraulic fluid from the upper chambers 27 displaces through the ducts 31 past the check valves 34 which raise from their seats 50 as shown in full outline and the displaced fluid finds its way freely through the passage 47 bypassing the check valve 35 to the lower subchambers 28 through the ducts 32. Any slight rolling movement is compensated for by stabilizing displacement between the ends of te ducts 31 through the ports 48. Damping during rebound occurs by closing of the check valve 34, thereby compelling return flow as indicated by the dashed arrows in FIG. 2 through the biased check valve 35. As shown in dash outline in FIG, 2, the check valve during rebound closes against its seat 50 and the check valve 35 is moved by the returning hydraulic fluid from its seat 51 against the bias of the spring 37 which thus restricts return flow and damps the rebound. During bounce and pitch damping, the spool valve 38 remains inactive, serving as a passive flow passage member in connecting the

ducts

31 and 32. Inasmuch as hydraulic pressures are substantially equal at each side of the hydraulic system during bounce and pitch vibrations, the valve 38 is held inactive even though the pressure exerted during rebound, especially, may be of fair magnitude.

During a roll movement as indicated by the directional arrow R in FIGS. 3,4 and 5, the car body 10 tilts either to the left or to the right relative to the frame 15 of the truck 11, a rightward tilt being shown by way of example. In FIG. 3, line pressue conditions at initial roll movement are shown. In this condition, the lower subchamber 28 of the left-hand cylinder 22 and the uppper subchamber 27 of the right-hand cylinder 22 will expel fluid and the opposite subchambers will expand. The tendency to expel fluid by the lower left-hand subchamber 28 will be resisted by te check valve 35 connected with the duct 32 from that subchamber and the flow from the upper right-hand subchamber 27 will displalce through its duct 31 past the right-hand check valve 34 with little resistance. This provides a pressure differential from the left-hand circuit toward the righthand circuit across the pressure sensitive spool valve 38 tending to shift it toward the right as shown in FIG. 3, and fluid thus displaced from the right-hand circuit flows to the left-hand circuit through the ports 48. As transition to roll mode occurs, as shown in FIG. 4, the differential pressure across the valve 38 causes it to move against the bias of right-hand spring 40 and gradually to throttle communication between the ports 48. At the same time, the valve 38 moves toward restricting movement of fluid thorugh the ports 44. This gradually increases resistance to the roll movement in a smooth manner as the car body tilt progresses to the point where right-hand tilt stop bearing 52 on the car body engages tilt stop bearing 53 on the bolster 13 and the corresponding tilt stop bearings at the left side of the car increase their normal spaced relation and the center bearing plates 33 may partially separate.

As shown in FIG. 5, as the rolling motion reaches maximum, the bolster l3 tilts, compressing the springs 14 at the right side, and the pressure differential across the valve 38 reaches maximum wherein the valve completely shuts off communication between the ports 48 so that no bypass of fluid can occur therethrough. At this time the valve 38 also greatly increases the resistance to displacement of fluid in the hydrualic system by throttling the ports 44 to minimum flow, thereby thoroughly damping the rolling motion. By the same token, return to normal attitude will be resisted until the valve 38 centers.

It will be understood, of course, that roll toward the left will be controlled in the same manner as control of roll to the right as has been described, since the control system is equal and complementary in each direction.

Not only viscous damping for vertical control, but also viscous damping for control of roll oscillations is provided by the present system. In roll oscillation damping the oscillations will not be permitted to build up to undesirable amplitudes wherein wheel lift, derailment or high component loading might occur.

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

1 claim as my invention:

1. A system for controlling operational vibrations of a rail-road car body relative to its suspension, comprisdouble-acting hydraulic fluid displacement units having means for coupling them to and between the respective opposite sides of the car body and suspension;

means providing hydraulic displacement connections between said units;

first valve means in said connections automatically responsive to hydrualic pressure in said connections as generated by said units controlling displacement through the connection and thus damping relative bounce and pitch motions between the car body and the suspension; and

additional pressure-sensitive valve means in said connections inactive relative to bounce and pitch but operating automatically responsive to hydraulic pressure in said connections as generated by said units to damp roll motion between the car body and suspension.

2. A system according to claim 1, wherein said actuators comprise piston and cylinder devices wherein the cylinder has means for flexibly connecting it to one of said body or suspension and the piston has a piston rod including means for flexibly connecting it to either the car body or the suspension alternatively to the cylinder.

3. A system according to claim 1, wherein said hydraulic units have respective working subchambers, said hydraulic displacement connections comprising respective ducts communicating with said subchambers, the ducts connecting one of the chambers of the units being normally in free communication with one another, and the ducts communicating with others of the subchambers having communication with the freely communicating ducts through said valve means.

4. A system according to claim 1, wherein said pressure-sensitive valve means comprise a spool valve and means normally biasing the spool valve into an inactive position, said spool valve providing passageways for generally free communication of said hydraulic connections therethrough in the inactive position of the spool valve, said spool valve being responsive to roll motion displacement of hydraulic fluid from said units in opposition to said biasing means to throttle said passageways and thereby damp said roll motiom.

5. A system according to claim 4, wherein said first valve means comprise check valves cooperating with said spool valve in effecting roll motion damping.

6. A system according to claim 1, wherein said first valve means cooperate with said pressure-sensitive valve means in effecting damping of roll motion between the car body and suspension.

7. A system according to claim 1, wherein said hydraulic units are linearly acting cylinder and piston devices having the piston dividing the cylinder into upper and lower working subchambers, said connections comprising ducts leading from the upper subchamber and connected for normally generally free communication between one another, said lower subchambers having ducts in communication therewith, and passage means effecting communication between the upper subchamber ducts and the lower subchamber ducts,

and said first valve means being in displacement con-,

trolling relation to said ducts in said passage means.

8. A system according to claim 7, wherein said pressure-sensitive valve means in part provide said passage means and control displacement between said upper subchamber ducts and between said lower subchamber ducts and the upper subchamber ducts.

9. In combination with a railroad car having a body and suspension means comprising a truck having rail running wheels supporting a truck frame on which are mounted springs carrying a bolster on which the body is mounted, a system for controlling operational vibrations between the car body and the suspension comprising:

double-acting hydraulic fluid displacement units having means coupling them at respectively opposite sides of the truck to the truck frame and to the car body;

means providing hydraulic displacement connections between said units;

first valve means in said connections automatically responsive to hydraulic pressure in said connections as generated by said units controlling displacement through the connections and thus damp ing relative bounce and pitch motions between the car body and the suspension; and additional pressure-sensitive valve means in said connections inactive relative to bounce and pitch, but operating automatically responsive to hydraulic pressure in said connections as generated by said units to damp roll motion between the car body and suspension.

10. In a combination according to claim 9, wherein said actuators comprise piston and cylinder devices in which the cylinder has means for flexibly coupling it to one of said car body or truck frame and the piston has a piston rod including means for flexibly connecting it to either the car body or the truck frame alternatively to the cylinder.

11. In a combination according to claim 9, wherein said hydraulic units have respective working subchambers, said hydraulic displacement connections comprising respective ducts communicating with said subchambers, the ducts connecting one of the chambers of the units being normally in free communication with one another, and the ducts communicating with others of the subchambers having communication with the freely communicating ducts through said valve means.

12. In a combination according to claim 9, wherein said pressure-sensitive valve means comprise a spool valve and means normally biasing the spool valve into an inactive postion, said spool valve providing passageways for generally free communication of said hydraulic connections therethrough in the inactive position of the spool valve, said spool valve being responsive to roll motion displacement of hydraulic fluid from said units in opposition to said biasing means to throttle said passageways and thereby damp said roll motion.

13. In a combination according to claim 12, wherein said first valve means comprise check valves cooperating with said spool valve in effecting roll motion damp ing.

14. In a combination according to claim 9, wherein said first valve means cooperate with said pressuresensitive valve means in effecting damping of roll motion between the car body and suspension.

15. In a combination according to claim 9, wherein said hydraulic units are linearly acting cylinder and piston devices having the piston dividing the cylinder into upper and lower working subchambers, said connections comprising ducts leading from the upper subchamber and connected for normally generally free communication between one another, said lower subchambers having ducts in communication therewith, passage effecting communication between the upper subchamber ducts and the lower subchamber ducts, and said first valve means being in displacement controlling relation to said ducts in said passage means.

16. In a combination according to claim 15, wherein said pressure-sensitive valve means in part provide said passage means and control displacement between said upper subchamber ducts and between said lower subchamber ducts and the upper subchamber ducts.

17. A system for controlling operational vibrations of a railroad car body relative to its suspension, comprising:

double-acting hydraulic fluid displacement units having means for coupling them to and between the respective opposite sides of the car body and suspension;

means providing hydraulic displacement connections between said units;

first valve means in said connections for controlling displacement therethrough and thus damping relative bounce and pitch motions between the car body and the suspension;

pressure-sensitive valve means in said connections inactive relative to bounce and pitch but operating to damp roll motion between the car body and suspension;

said hydraulic units having respective working subchambers and said hydraulic displacement connections comprising respective ducts communicating with said subchambers;

the ducts connecting one of the chambers of the units being normally in free communication with one another, and the ducts communicating with others of the subchambers having communication with the freely communicating ducts through said valve means; and

said first valve means comprising check valves operating to permit relatively free flow in one direction between the ducts which are companion to each of the hydraulic units and resist and damp flow in the opposite direction between the companion ducts.

18. A system according to claim 17, wherein said pressure-sensitive valve means comprise a reciprocable spool valve providing controllable passage means for displacement of fluid between said ducts.

19. A system according to claim 18, including ports under the control of said spool valve and through which ports said ducts communicate.

20. In combination with a railroad car having a body and suspension means comprising a truck having rail running wheels supporting a truck frame on which are mounted springs carrying a bolster on which the body is mounted, a system for controlling operational vibrations between the car body and the suspension, comprising:

means providing hydraulic displacement connections between said units;

pressure-sensitive valve means in said connections inactive relative to bounce and pitch, but operating to damp roll motion between the car body and suspension;

said hydraulic units having respective working subchambers and hydraulic displacement connections comprising respective ducts communicating with said subchambers;

21. In a combination according to claim 20, wherein said pressure-sensitive valve means comprise a reciprocable spool valve providing controllable passage means for displacement of fluid between said ducts.

22. In a combination according to claim 21, including ports under the control of said spool valve and through which ports said ducts communicate.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3 868 911 DATED 3 March 4, 1975 rr-rvrzr-rror s John C. Schultz It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, lines 55 and 56 for "reciprocatlng" read --reciprocatlng- Column 4, line 32, for "te" read --the--. Column 4, line 53, for "pressue" read --pressure-. Column 4, line 55, for "uppper" read --upper-. Column 4, line 59, for "te" read --the--. Column 4, line 62, for "plalce" read -p1ace--. Column 5, line 7, for "thorugh" read --through-. Column 6, line 19, for "motlom" read mot'ron-. Column 7, line 46, after "passage" insert means-.

Signed and sealed this 10th day of June 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks

Claims

1. A system for controlling operational vibrations of a railroad car body relative to its suspension, comprising: double-acting hydraulic fluid displacement units having means for coupling them to and between the respective opposite sides of the car body and suspension; means providing hydraulic displacement connections between said units; first valve means in said connections automatically responsive to hydrualic pressure in said connections as generated by said units controlling displacement through the connection and thus damping relative bounce and pitch motions between the car body and the suspension; and additional pressure-sensitive valve means in said connections inactive relative to bounce and pitch but operating automatically responsive to hydraulic pressure in said connections as generated by said units to damp roll motion between the car body and suspension.

7. A system according to claim 1, wherein said hydraulic units are linearly acting cylinder and piston devices having the piston dividing the cylinder into upper and lower working subchambers, said connections comprising ducts leading from the upper subchamber and connected for normally generally free communication between one another, said lower subchambers having ducts in communication therewith, and passage means effecting communication between The upper subchamber ducts and the lower subchamber ducts, and said first valve means being in displacement controlling relation to said ducts in said passage means.

9. In combination with a railroad car having a body and suspension means comprising a truck having rail running wheels supporting a truck frame on which are mounted springs carrying a bolster on which the body is mounted, a system for controlling operational vibrations between the car body and the suspension comprising: double-acting hydraulic fluid displacement units having means coupling them at respectively opposite sides of the truck to the truck frame and to the car body; means providing hydraulic displacement connections between said units; first valve means in said connections automatically responsive to hydraulic pressure in said connections as generated by said units controlling displacement through the connections and thus damping relative bounce and pitch motions between the car body and the suspension; and additional pressure-sensitive valve means in said connections inactive relative to bounce and pitch, but operating automatically responsive to hydraulic pressure in said connections as generated by said units to damp roll motion between the car body and suspension.

13. In a combination according to claim 12, wherein said first valve means comprise check valves cooperating with said spool valve in effecting roll motion damping.

14. In a combination according to claim 9, wherein said first valve means cooperate with said pressure-sensitive valve means in effecting damping of roll motion between the car body and suspension.

17. A system for controlling operational vibrations of a railroad car body relative to its suspension, comprising: double-acting hydraulic fluid displacement units having means for coupling them to and between the respective opposite sides of the car body and suspension; means providing hydraulic displacement connections between said units; first valve means in said connections for controlling displacement therethrough and thus damping relative bounce and pitch motions between the car body and the suspension; pressure-sensitive valve means in said connections inactive relative to bounce and pitch but operating to damp roll motion between the car body and suspension; said hydraulic units having respective working subchambers and said hydraulic displacement connections comprising respective ducts communicating with said subchambers; the ducts connecting one of the chambers of the units being normally in free communication with one another, and the ducts communicating with others of the subchambers having communication with the freely communicating ducts through said valve means; and said first valve means comprising check valves operating to permit relatively free flow in one direction between the ducts which are companion to each of the hydraulic units and resist and damp flow in the opposite direction between the companion ducts.

20. In combination with a railroad car having a body and suspension means comprising a truck having rail running wheels supporting a truck frame on which are mounted springs carrying a bolster on which the body is mounted, a system for controlling operational vibrations between the car body and the suspension, comprising: double-acting hydraulic fluid displacement units having means coupling them at respectively opposite sides of the truck to the truck frame and to the car body; means providing hydraulic displacement connections between said units; first valve means in said connections for controlling displacement therethrough and thus damping relative bounce and pitch motions between the car body and the suspension; pressure-sensitive valve means in said connections inactive relative to bounce and pitch, but operating to damp roll motion between the car body and suspension; said hydraulic units having respective working subchambers and hydraulic displacement connections comprising respective ducts communicating with said subchambers; the ducts connecting one of the chambers of the units being normally in free communication with one another, and the ducts communicating with others of the subchambers having communication with the freely communicating ducts through said valve means; and said first valve means comprising check valves operating to permit relatively free flow in one direction between the ducts which are companion to each of the hydraulic units and resist and damp flow in the opposite direction between the companion ducts.