US3330422A

US3330422A - Hydraulic cushion device for railway cars

Info

Publication number: US3330422A
Application number: US463297A
Authority: US
Inventors: Robert A Rasmussen
Original assignee: Pullman Inc
Current assignee: Pullman Standard Inc; Pullman Inc
Priority date: 1965-06-11
Filing date: 1965-06-11
Publication date: 1967-07-11
Anticipated expiration: 1984-07-11
Also published as: DE1530207A1; CH458426A; DE1530207C3; NL6601539A; BE676914A; DE1530207B2; CH459289A

Description

July ll, 1967 R. A. RAsMussEN HYDRAULIC CUSHION DEVICE FOR RAILWAY CARS Filed June ll, 1965 5 Sheets-Sheet l Y ROBERT A. RA SM USSEN ATT'Y.'

July 1l, 1967 R. A. RAsMUssEN 3,330,422

HYDRAULIC CUSHION DEVICE FOR RAILWAY CARS f /NvE/vToR ROBERT A. RASMUSSEN swf? July 11, 1967 R. A. RAsMUssEN 3,330,422

HYDRAULIC CUSHION DEVICE FOR RAILWAY CARS Filed June l1, 1965 5 Sheets-Sheet 3 INVENTOR lROBERT A. RASMSSEN ATT'Y.

July 1l, 1967 R. A. RAsMussr-:N 3,330,422

HYDRAULIC CUSHION DEVICE FOR RAILWAY CARS Filed June ll, 1965 5 Sheets-Sheet 4 LLL! i |||||I l I Illl NVNTOR RBERT A. RASMUSSEN BY w ATT'Y.

July 11, 1967 R. A. RAsMussEN 3,330,422

HYDRAULIC CUSHION DEVICE FOR RAILWAY CARS Filed June 11. 1965 5 Sheets-Sheet 5 United States Patent O 3,330,422 HYDRAULIC CUSHIGN DEVICE FOR RAILWAY CARS Robert A. Rasmussen, Portage, Ind., assignor to Pullman Incorporated, Chicago, Ill., a corporation of Delaware Filed June 11, 1965, Ser. No. 463,297 8 Claims. (Cl. 213-43) ABSTRACT OF THE DISCLOSURE A hydraulic cushioning device for use in railway vehicles including a uid filled cylinder having a piston assembly reciprocal therein with a flexible boot closing off the open end of the cylinder by attachment of one end of the boot at the open end of the cylinder and the other end to the piston assembly. The flexible boot is formed of two superposed chord plies in which one of the plies has a chord angle varying between about 32 and about 59 and the chord angle of the other ply is supplementary thereto. The boot is formed with beaded ends at each end of which one beaded end is clamped to an intermediate cylinder head adjacent the open end of the cylinder and the other end is clamped to a tubular piston rod of the piston assembly. The piston assembly clamping means includes a clamping ring fixed to the piston rod of the piston assembly and a second coacting clamping `ring slidable lengthwise of the piston rod which is held in clamping relationship by means of a snap ring seated within a groove formed in the piston rod.

The present invention relates to hydraulic cushion devices of the type employed in cushion under-frame railway vehicles wherein the coupler carrying structure and the lading supporting structures are relatively slidable lengthwise of each other and the hydraulic cushion device is interposed for interaction between the aforementioned structures to absorb a portion of the impact energy and thereby prevent lading damage.

The hydraulic cushion device, to which the present invention relates, comprises generally a hydraulic uid filled cylinder and a fluid displacement means including a piston head and piston rod. The cylinder and fluid displacement means are arranged to reciprocate relative to each other between a neutral extended position and to a contracted position upon impact to either the cylinder or fluid displacement means. Relative movement of the cylinder and fluid displacement means is operative to displace the hydraulic fluid from a high pressure chamber to a low pressure chamber which results in absorbing a portion of the kinetic energy of the impact force.

Communication between the high pressure chamber and the low pressure chamber is established by way of an oriiice having a metering pin associated therewith. The metering pin serves to vary the effective orifice area during contraction of the cushion device so as to impart a substantially constant force travel characteristic to the cushion unit.

The hydraulic cushion device is characterized by a construction which utilizes solely static seals. To this end there is employed a iiexible boot reservoir which closes off the open end of the cylinder and accommodates the hydraulic uid displaced by the piston rod of the uid displacement means.

Heretofore a return spring disposed about the cylinder between the remote ends of the fluid displacement means and cylinder has been used to return the cushion device components to the neutral position. During the return movement of the cushion device, the hydraulic fluid ow is reversed from the exible boot reservoir and low pressure chamber and the hydraulic uid flows from the low ICC pressure chamber to till the volume of the high pressure chamber preparatory to receiving another impact.

The utilization of the return spring, while resulting in satisfactory cushion operation under some circumstances, presents a problem with respect to the installation of the cushion unit in a cushion underframe car. Such problems may be created Iby the limited space available in the car for accommodating the diameter of the spring disposed about the cylinder. Moreover, the return spring which is applied under compression also may require the use of special equipment or tools to assemble and disassemble the same from the cushion unit.

lt is the principal object of the present invention to provide a new and improved cushion unit of the aforedescribed type wherein the iiuid pressure forces of the hydraulic fluid in the flexible boot reservoir are utilized to provide the necessary force for returning the cushion unit components from the contracted to the neutral extended positions thereof.

It is a further object to provide the cushion unit of the generally aforedescribed type having a iiexible boot reservoir with a new and improved clamping arrangement for attaching the boot between the cylinder and fluid displacement means so as to form a fluid tight seal in the presence of the high fluid pressure forces to which the cushion unit is subject during use.

Further objects and features will hereinafter appear.

FlG. 1 is a cross sectional View of the cushion unit embodying the present invention with the components thereof shown in the contracted position;

FIG. 2 `is a fragmentary cross sectional view of the cushion unit of FIG. l, but showing the flexible boot reservoir in the deiiated state prior to the introduction of hydraulic fluid therein;

FIG. 3 is a fragmentary cross sectional view similar to FIG. 2 but showing the flexible boot reservoir filled with hydraulic fluid and with the components thereof in the neutral extended position;

FIG. 4 is a fragmentary cross sectional view similar to FIG. 3 but showing the flexible boot reservoir in its fully extended position when the cushion unit components are in the contracted position;

FIG. 5 is an enlarged fragmentary view of the piston rod and showing in section the flexible boot reservoir clamped at one end to the piston rod;

FIG. 6 is an enlarged fragmentary View of the piston rod and showing in section the flexible boot reservoir clamped to the intermediate cylinder head.

FIG. 7 is an enlarged view of the flexible boot reservoir in the deflated state thereof with some of the structure broken away to show underlying details;

FIG. 8 is a view similar to FIG. 7 but showing the flexible boot reservoir in its maximum inflated state;

FIG. 9 is a fragmentary cross sectional view of the iiexible boot reservoir construction; and

FIG. l0 is a fragmentary cut-away perspective view of the iiexible boot reservoir structure.

Referring now to the figures there is shown a hydraulic cushion device 10 comprising essentially a hydraulic iiuid filled cylinder 11; a fluid displacement means 12 which is reciprocable relative to the cylinder 11 between the neutral extended position shown for example in FIG. 3 to a contracted position shown in FIG. 4 for displacing dluid from a high pressure chamber 13 to a low pressure chamber 14; a flexible boot reservoir 15 connected between the cylinder 11 and the fluid displacement means 12 for receiving a portion of the hydraulic fluid displaced during contraction; and a metering pin 16 for metering the flow between the high pressure chamber 13 and the low pressure chamber 14.

As shown in the gures the cylinder 11 is formed from a cylindrical tube 17 which may be made from a suit- 3 able steel or the like. Fixed as by welding to one end of the tube 17 is a follower or base plate 18.

The fluiddisplacement means 12 includes a piston head 19 and a tubular piston rod 21 of which lone end is fixed to the low pressure face 22 of the piston head 19. The

other end of the tubular piston rod 21 extends outwardly through the open end of the cylinder 11. Fixed to the outwardly extending end as by a fastening stud 23 threaded into a fastening block 24 fixed within the piston rod bore 26, is a second base plate 27.

As shown, the high pressure face 28 of the piston head 19, which may be formed from suitable metal such as cast iron, is formed with a conical feed surface 29 which merges with an axial orifice 31. The axial orifice 31 -is coaxial with the piston rod borer36 Iand the latter cornmunicates with the low pressure chamber via an array `of ports 32 formed in the tubular piston rod 21 adjacent the piston head 19. Moreover, the piston rod 21 is of lesser diameter than an axial -opening 33 in an Iintermediate cylinder head 34 so that there is defined between the outer circumference of the tubular pistonrod 21 and the inner circumference of the axial opening 13 an annular passage 36 which provides communication between the low pressure chamber 14 and the flexible boot reservoir 15. Thus, hydraulic fluid communication between the high Vpressure: chamber 13 and the flexible boot reservoir 15 is established via the piston head orifice 31, the piston rod bore 26, the array of ports 32, the low pressure chamber 14, and the annular passage 36.

Preferably, -as shown in FIGS. 710, the flexible boot reservoir is made from rubber having reinforcing cords and 35 imbedded therein. In accordance with the more or less conventional manufacturing practice, the ply of cords 30 are applied on an inner rubber liner 40 and are separated from the overlying second ply of cords 'by a skim coat 45 which is also applied over the cords 35. The exterior of the boot 15 is formed by an outer liner 50. In the manufacturing process the inner liner 40, skim coats 45 and outer liner 50 form 'more or less an homogenous mass so that there are no visible planes of demarcation therebetween, as illustrated for clarity. VThe angles at which the

cords

30 and 35 are positioned with respect to the horizontal are arranged to `impart strength to the exible boot reservoir 15 so that the latter may serve las the means for running the cushion unit from the compressed position to the extended position after the force of impact applied to the cushion unit has been dissipated. To this end it has been discovered that the cord angle of the lower ply of cords 30 in the extended position be about 32 with respect to the horizontal, as shown, and the cord angle of the upper ply of cords 35 be the supplement of the lower cord angle or about 148. In the fully compressed position of the cushion unit in which the flexible boot is filled with hydraulic uid, the cord -angles of the cords are arranged so as not to exceed about 59 and 121, respectively.

Thus, it should be readily apparent that the fiexible boot reservoir is radially expansible under the pressure Vof the hydraulic fluid received therein during the contraction of the cushion unit 10 from the extended to the contracted positions. Such radial expansion is permitted Aby way of the increase in the cord angles of the cord plies 30 and 35. At the same time the increase in the cord angles causes the boot to be shortened in its overall length. However, since the ply of

cords

30 and 35 are imbedded in the rubber to assume Ia normal or extended position of about 32, there is imparted to the boot a linear force acting between the cylinder 11 and the fluid displacement means 12 which tends to return the latter two components to the neutral position as more fully to be explained hereafter.

At each end the boot 15 is formed with a bead 37 which is formed about a wire 38. The beads '37-37 serve to provide a clamping sector for attach- 4 ment to the piston rod 21 and the intermediate cylinder head 34.

As shown in particular in FIGS. 15, one end 15a of the boot reservoir 15 is reversely turned or folded inwardly and the associated bead 37 is clamped between a first clamping ring 39 which is fixed to the periphery of the piston rod 21 as by welding and a clamping sleeve 41 slidable on the piston rod 21. The clamping sleeve 41 has fixed to one end a second clamping ring 42 which when positioned yadjacent to the first clamping ring 39 coacts with the latter to clampingly grip the beaded end 37. The outer peripheries of the first and second clamping rings 39 and 42 .are each inclined so that the boot reservoir is not subject to sharp edges and is permitted to contact the piston rod periphery along the length thereof. The other end of the clamping sleeve 41 extends outwardly toward the follower plate 27 and is fixed against longitudinal movement by means of a snap ring 43 seated within a groove 44 formed in the periphery of the piston rod 21 as shown in particular in FIG. 4.

The above described clamping arrangement is particularly advantageous in that the clamping sleeve 41 is fixed at the area of low stress concentra-tion of the tubular piston rod. In this connection it is to be noted that the groove 44 into which the snap ring is fastened overlies the plug 24 adjacent the follower plate 27 where the pressure forces and bending moment is at a minimum so that the groove 44 does not affect the strength of the piston rod 21. Moreover, the snap ring as is readily .apparent upon an inspection of FIG. 2, showing the condi-tion of the lboot reservoir 15 without hydraulic fluid stored therein lies inboard ofthe reversely bent portion 15a `and facilitates the installation without Yinterference from the boot 15.

The other beaded end 37 is clamped to the intermediate cylinder head 34 disposed between the open end of Y the cylinder 11 and the base plate 18.

To this end, the intermediate cylinder head 34 includes an annular-body member 46 which is'fixed within the bore of the cylinder 17 as by snap rings 47. To form a uid tight seal at the inner cylinder. wall a quadrant ring 48 may be seated within a peripheral groove. The inboard face of the annular body member 46 is formed with a circular recess 49, Seated within the recess 49 and held fixed therein as'by a snap ring 51 is an annular orifice plate 52 having the opening 33 which is of greater diameter than the outer periphery of the piston rod 21 and forms therewith the annular passageway 36 providing fluid communication between the low pressure chamber 14 and the flexible boot reservoir 15.

The bead end 37 of the flexible boot reservoir 15 isV securely clamped between the inner face of the orifice plate 52 and shoulder 53 formed by a second circular recess 54 located inwardly of the recess 49. The beaded end 37 of the rubber boot is formed of greater thickness than the distance between the shoulder 53 and the inner face of the orifice plate 52 so that it is compressed therein and firmly clamped to the intermediate cylinder head 34.

The metering pin 16 which serves to control the hy- Vdraulic fiuid ow through the piston orifice 31 includes a metering body 56 slidable within the piston head yorifice 31 and is of substantially constant diameter along the length thereof. The metering pin 16 may be made from a forging having an annular attachment flange integrally formed on one end thereof and is inserted through anV the length of the metering body 56. rIhe flutes 57 are formed to coact with the piston head orifice 31 by varying the effective cross sectional area of the latter in a manner such that the hydraulic fluid pressure forces within the high pressure chamber 13 remain substantially constant during the contraction of the cushion device 10.

To maintain and return the fluid displacement means 12 and the cylinder 11 in the neutral position in the absence of impact at either end `of the cushion unit, the pressure forces of the hydraulic fluid reacting on the flexible boot may be used. To this end, the hydraulic fluid, which may be poured through the opening accommodating the metering pin 16 prior to the insertion of the latter, is present in a sufficient quantity to exert pressure forces within the flexible boot reservoir in the extended neutral position which pressure forces increase upon the application of an impact force to either end of the cushion unit, This causes the boot 15 to expand radially as heretofore described and thereby causing the chord angles of the

cords

30 and 35 to be changed causing a linear force to be applied between the cylinder 11 and fluid displacement means 12. As shown in particular in FIGS. 3 and 4, the pressure forces of the hydraulic fluid Within the flexible boot reservoir act on an area defined by the annular cross-section of the boot at the reversely turned end and shall hereinafter be designated as the reaction area. The total pressure forces yof the reaction area are operative on the reversely turned end 15a of the boot reservoir 15 also to apply a substantially linear force parallel to the longitudinal axis of the piston rod 21 in a direction causing the fluid displacement means 12 and cylinder 11 to assume the neutral extended position. Thus the pressure forces of the hydraulic fluid and the boot construction tend to return the cushion unit to its extended position.

Upon impact to either

base plate

18 or 27 the fluid displacement means 12 and the cylinder move relatively to each other to the contracted position shown in FIGS. 1 and 4. During this relative movement, hydraulic fluid is displaced into the boot reservoir under increased pressure thereby to radially expand the flexible boot reservoir 15. As shown in FIG. 4 upon -radial expansion of the boot 15 there is a corresponding increase in the reaction area along with the change in the angles of the cords and 35 such that the total linear reaction force on the reversely turned end 15 also is increased. Thus, when the impact force has been dissipated, the force exerted by the boot is Operative to return the fluid displacement means 12 and the cylinder 11 to the neutral position Assuming now that the cushion device 10 of the present invention is employed in a cushion underframe railway and interposed between the sliding sill (not shown) and the stationary sill (not shown). In the absence of an impact on the sliding sill the cushion device 10 assumes the neutral position shown in FIG. l.

Upon impact to the sliding sill at either end thereof the cushion unit 10, the fluid displacement means 12 and the cylinder 11 telescope relatively to each other toward the contracted position shown in FIG. l. As the unit 10 contracts, the piston head 19 and the base plate 18 move toward each other whereupon the piston rod 21 displaces hydraulic fluid Within the low pressure charnber 14 into the flexible boot 15 reservoir via the annular opening 36.

At the same time, hydraulic fluid displaced from the high pressure chamber 13 flows through piston head orifice 31 of gradually diminishing cross-sectional area into the piston rod bore 26. From the piston rod bore 26 the hydraulic fluid flows into the low pressure chamber 14 via the array of ports 32.

The hydraulic fluid is discharged into the low pressure chamber 14 at a relatively high velocity which creates considerable turbulence. The turbulence is caused at least in part by the radially directed flow of the hydraulic fluid impinging directly against the bore wall so as to dissipate much of the kinetic energy of the impact in the form of heat.

When the cusbion device 10 has completed its travel, the flexible boot reservoir 15 contains the increased hydraulic fluid displaced by the piston rod 21 as shown in FIG. 3. The increased volume which is under increased pressure radially expands the boot 15 causing a shortening of the boot length as heretofore described. The radial expansion increases the reaction area and thereby the linear force applied by the boot between the cylinder 11 and the piston rod 21 to return the cushion to the neutral position shown in FIG. 2.

What is claimed is:

1. In a hydraulic cushion unit comprising a cylinder having a bore, a first base plate fixed to one end of said cylinder, a piston head reciprocable within the bore of said cylinder and having an axial orifice, said piston head defining a high pressure chamber on one side thereof with said first base plate and a low pressure chamber on the opposite side thereof, a tubular piston rod fixed at one end to said piston head with the other end extending through the open end of said cylinder, said tubular piston rod having a bore coaxially disposed relative to said axial orifice, a second base plate fixed to said other end of said piston rod, a flexible boot reservoir having beads at each end thereof, said flexible boot reservoir having a reversely turned end portion which is turned inwardly into said boot, an intermediate cylinder head having an orifice, said intermediate cylinder head being fixed to said cylinder and including an orifice and an annular clamping means for holding one of said beaded ends of said flexible boot reservoir clamped to said intermediate cylinder head, a first clamping ring fixed on said piston rod, a second clamping ring slidable on said piston rod to coact with said first clamping ring for clamping said beaded end on said reversely turned end portion on said piston rod, one of said first and second clamping rings having an inclined peripheral surface underlying said reversely turned end, retaining means on said piston rod for retaining said second clamping means in clamping relationship with said first clamping ring, and hydrauilc fluid filling said cylinder, said piston head and said cylinder being movable relatively to each other from an extended neutral position to a contracted position upon impact at said base plates and thereby to displace fluid from said high pressure chamber into said low pressure chamber and said flexible boot reservoir.

2. In a hydraulic cushion unit comprising a cylinder having a bore, a first base plate fixed to one end of said cylinder, a .piston head reciprocable within the bore of said cylinder and having 'an axial orifice, said piston head defining a high pressure chamber on one side thereof with said first base plate and a low pressure chamber on the opposite side thereof, a tubular piston rod fixed at one end to said piston head with the other end extending through the open end of said cylinder, said tubular piston rod having a bore coaxially disposed relative to said axial orifice, a second base plate fixed to said other end of said piston rod, a flexible boot reservoir having beads at each end thereof, said flexible boot reservoir having a reversely turned end portion which is turned into said boot, an intermediate cylinder head having an orifice, said intermediate cylinder head being fixed Within said cylinder and including a recess and an annular plate clamping one beaded end of said flexible boot reservoir thereto, said annular plate having an opening defining with said piston rod an annular passage, a first clamping ring fixed on said piston rod and disposed within the confines of said boot inwardly of said bead on said reversely turned end, said first clamping ring having a peripheral surface inclined toward said intermediate cylinder head, a second clamping ring slidable on said piston rod and disposed for engagement with the reversely turned end portion of said boot, said second clamping ring having a peripheral surface inclined in an vopposite direction from the inclined surface on said rst clamping ring, retaining means on said piston rod for retaining said other beaded end in clamping relationship with said iirst clamping ring, and hydraulic uid filling s-aid cylinder, said piston head and said `cylinder being movable relatively to each other from an extended neutral position to a contracted position upon impact at said base plates and thereby to displace fluid from said high pressure chamber into said low pressure chamber and said ilexible boot reservoir.

3. The invention as deiined in claim 2 wherein said retaining means comprises an elongate sleeve of which one end en-gages said second clamping ring and the other Vend lies adjacent to said second base plate, and snap ring means seated in a groove in said piston rod abutting said other end of said sleeve.

4. The invention as defined in claim 2 wherein said cylinder is iilled with hydraulic fluid in a quantity suicient to cause said llexible boot reservoir to be radially' expanded by the pressure forces exerted by said hydraulic fluid and thereby to create a reaction force tending to maintain said piston head in said neutral position.

5. The invention as defined in claim 4 wherein said flexible boot reservoir is constructed so as to be further radially expanded upon travel of said cushion device to said contracted position upon the application of an impact force to said cushion device, whereby the corresponding increase of the pressure forces of said hydraulic fluid within said ilexible boot reservoir create a reaction force causing the piston head and cylinder to return to Y the neutral position when the impact force has dissipated.

6. The invention as deiined in claim 2 wherein said flexible boot reservoir is formed of rubber having reinforcing cording permitting radial expansion thereof while 35 substantially precluding longitudinal elongation.

7. The invention as defined in claim 6 wherein said cording comprises two superposed plies of cord of which one ply is arranged to provide between the extended and contracted position of said cushion unit a cord angle Varying between about 32 to 59 with respect to a reference line parallel to the longitudinal axis of said flexible boot reservoir and the other is arranged to provide supplementary cord angles thereto.

8. A hydraulic cushion unit comprising a hydraulic iluid lled cylinder having a closed end and an open end, a fluid displacement means reciprocable within said cylinder between a neutral extended position and a contracted position, and a flexible boot reservoir connected between said cylinder and said fluid displacement means for receiving hydraulic fluid displaced during reciprocation of said fluid displacement means and said cylinder, said exible boot reservoir comprising a rubber boot having two superposed cord plies embedded therein, one of said plies having a cord angle varying between about 32 and 59 as said cylinder and said uid displacement means reciprocate relative to each other, said other of said plies having cord angles varying between rangles supplementary to said one cord ply range of cord angles.

References Cited UNITED STATES PATENTS 2,893,104 7/1959 Hancock 267-65 X 2,920,885 1/ 1960 Niclas 267-65 3,033,557 5/1962 Harris 267-65 3,038,717 6/1962 Bank 267-65 3,043,582 7/1962 Hirtreiter 267-65 3,148,869 9/1964 |Peterson 267-1 ARTHUR L. LA POINT, Primary Examiner.

DRAYTON E. HOFFMAN, Examiner.

Claims

1. IN A HYDRAULIC CUSHION UNIT COMPRISING A CYLINDER HAVING A BORE, A FIRST BASE PLATE FIXED TO ONE END OF SAID CYLINDER, A PISTON HEAD RECIPROCABLE WITHIN THE BORE OF SAID CYLINDER AND HAVING AN AXIAL ORIFICE, SAID PISTON HEAD DEFINING A HIGH PRESSURE CHAMBER ON ONE SIDE THEREOF WITH SAID FIRST BASE PLATE AND A LOW PRESSURE CHAMBER ON THE OPPOSITE SIDE THEREOF, A TUBULAR PISTON ROD FIXED AT ONE END TO SAID PISTON HEAD WITH THE OTHERE END EXTENDING THROUGH THE OPEN END OF SAID CYLINDER, SAID TUBULAR PISTON ROD HAVING A BORE COAXIALLY DISPOSED RELATIVE TO SAID AXIAL ORIFICE, A SECOND BASE PLATE FIXED TO SAID OTHER END OF SAID PISTON ROD, A FLEXIBLE BOOT RESERVOIR HAVING BEADS AT EACH END THEREOF, SAID FLEXIBLE BOOT RESERVOIR HAVING A REVERSELY TURNED END PORTION WHICH IS TURNED INWARDLY INTO SAID BOOT, AN INTERMEDIATE CYLINDER HEAD HAVING AN ORIFICE, SAID INTERMEDIATE CYLINDER HEAD BEING FIXED TO SAID CYLINDER AND INCLUDING AN ORIFICE AND AN ANNULAR CLAMPING MEANS FOR HOLDING ONE OF SAID BEADED ENDS OF SAID FLEXIBLE BOOT RESERVOIR CLAMPED TO SAID INTERMEDIATE CYLINDER HEAD A FIRST CLAMPING RING FIXED ON SAID PISTON ROD, A SECOND CLAMPING RING SLIDABLE ON SAID PISTON ROD TO COACT WITH SAID FIRST CLAMPING RING FOR CLAMPING SAID BEADED END ON SAID REVERSELY TURNED END PORTION ON SAID PISTON ROD, ONE OF SAID FIRST AND SECOND CLAMPING RINGS HAVING AN INCLINED PERIPHERAL SURFACE UNDERLYING SAID REVERSELY TURNED END, RETAINING MEANS ON SAID PISTON ROD FOR RETAINING SAID SECOND CLAMPING MEANS IN CLAMPING RELATIONSHIP WITH SAID FIRST CLAMPING RING, AND HYDRAUILC FLUID FILLING SAID CYLINDER, SAID PISTON HEAD AND SAID CYLINDER BEING MOVABLE RELATIVELY TO EACH OTHER FROM AN EXTENDED NEUTRAL POSITION TO A CONTRACTED POSITION UPON IMPACT AT SAID BASE PLATES AND THEREBY TO DISPLACE FLUID FROM SAID HIGH PRESSURE CHAMBER INTO SAID LOW PRESSURE CHAMBER AND SAID FLEXIBLE BOOT RESERVOIR.