DE1920866U - HYDRAULIC LONG-STROKE SHOCK ABSORBER DEVICE FOR RAILWAY CARS. - Google Patents

Description

H May

Bullman Incorporated, Chicago. 111 ". PPE.

Hydrauli see Eanghub shock absorber device for railroad cars .

The invention relates generally to shock absorber devices and, more particularly, to hydraulic shock absorber devices. Device for use in railroad cars in which the coupling carrier and the load carrier construction contribute impact on the clutches Carriages are movable relative to each other in the longitudinal direction, the hydraulic shock absorber device between the said parts is arranged and to prevent damage to the cargo a hawker Impact energy destroyed »

The shock absorber device according to the invention consists in essential from .; one filled with hydraulic fluid Cylinder and a KLuidum displacement device. Cylinder and displacement device are arranged to each other that they are at one on the. Cylinder or

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impact shock exerted on the displacement device straight out relative to each other; an extended or extended. Neutral position in a shortened Able to shift position with a relative movement of the cylinder and the fluid displacement device - In the shortened position, the displacement device is able to remove the fluid from a high pressure chamber in a lower pressure chamber too. displace, in such a way that a Part of the kinetic energy of the impact is destroyed

To ensure an additional volume of the low-pressure chamber, the cylinder and the displacement— installation of an expandable sleeve or cuff assigned «In the neutral or«; extended position of the device, the expandable cuff is deflated, while that of the lower pressure chamber is open the impact of the device absorbed pluid volume expanding the cuff to accommodate the predetermined volume. displaced pluidum. to the Episode has «

The hydraulic shock absorber device is also one between the pluidum displacer and associated with the cylinder arranged return spring,

which the named components after the destruction of the Force of impact from the foreshortened position into the Moved back to neutral position · During the return movement in the neutral position, the direction of flow of the displaced fluid is reversed, which is now in the Way flows from the low pressure chamber to the high pressure chamber that the flexible cuff container in turn is emptied "

The shock absorber device described above is generally between a clutch carrier structure and a relative to this movable load carrier installed, so that the device has a rope of the force acting on the clutches capable of destroying »! The size of the energy transferred to the charge carrier is at such a value held that no damage occurs to the load carried by the load carrier.

Railway vehicles with coupling carrier and load carrier construction that can be moved relative to one another in the longitudinal direction of the car can be constructed in the form of a shock-absorbing base frame, one of which is the couplings has supporting, movable in the longitudinal direction of the undercarriage, or can be a load have supporting, platform-like component, the

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in the longitudinal direction of the car relative to the couplings supporting underframe is movably mounted »In both vehicle constructions of the type generally described above, an interaction between the coupling and the load carrier part is reached by two sets of stop arrangements, one of which is on the coupling carrier part and the other attached to the load carrier is.

Both sets of stops consist of spaced apart arranged soling members, each with a. Stop in the neutral or extended position of the shock absorber device is able to come into contact with one of its two ends · With one on one of the Impact impact acting on clutches can do that to the Side of the impact, the stop member attached to the coupling carrier pushes the shock absorber device against the opposite, to compress or close the stop member attached to the load carrier. shorten · this way the shock absorber device destroys a rope of the kinetic energy of the impact, so that the remaining, transferred to the charge carrier rope of the energy is below the value at which damage to the load carried by the load carrier would occur

After, the annihilation of the impact force represents the

between, the pluidum displacer and the Cylinder effective return spring the shock absorber device back to their neutral, extended position. At the same time, the one attached to the coupling carrier part is also attached Stop link j, which dampens the shortening of the shock » had initiated a device through which stretching end in its normal or neutral position pushed so that the two stop sets attached to the load carrier and the coupling carrier part, respectively able to come into contact with one end of the shock absorber * As mentioned, during the Bending movement reverses the pluidum flow direction, so that the flexible cuff is deflated

The above-described mode of operation of the shock absorber device occurs in the event of an impact shock in one direction and as long as there is no impact at the other end of the car before the device has returned to its neutral position.However, if an impact shock acts in the other direction before the shock absorber pre-adjustment again has assumed its neutral position, the impact on the opposite clutch has a rapid ^{reversal of direction of the stops provided on the clutch carrier part to the I 1} OIge, so that the return spring does not find any resistance and the shock absorber device tends to expand faster

State makes it necessary. That the fluid flow from the cuff container and from the low pressure chamber goes so far that the volume of fluid in these trees. with one at the Eedjuaierungs- _; Degree of the decreasing volume of the flexible cuff adapted speed decreases and this: fluid is returned to the tree provided for it in the chain as a division of the device. "If the hydraulic flow is not fast enough, the flexible" cuff tries to expand and to. stretch in order to provide the required volume for the fluid in it. set, while a part of the high pressure chamber is only partially filled, so that a negative pressure is generated therein. If, in this state of the partially filled and stretched cuff and the high pressure chamber in the cylinder, which is under negative pressure, another impact is exerted on the clutches, then the shock absorber device is unable to ensure sufficient force counteracting the impact and a further amount of hydraulic fluid that likewise : can be as large as the amount displaced at the first impact, additionally introduced into the container formed by the cuff. This makes the flexible sleeve beyond its intended: fit; stretched and stretched, which affects the operation of the shock absorber device and under

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under certain circumstances even at one point in rupturing the cuff can lead.

I was concerned with veriaeid-ang these difficulties and hard parts The invention In the first Mule with the Creation of a shock absorber device for the above Generally described Arty with means for eliminating the hi rather occurred in such devices Has disadvantages

To. For this purpose, such a known shock dating device, which defines a cylinder, a fluid displacement device that can be moved back and forth in a straight line in the cylinder, defines a high-pressure chamber and a lower pressure chamber in the cylinder, as well as a cuff formed by a flexible or resilient cuff, is provided with outer surfaces Has the chamber connected to the lower pressure chamber, provided according to the invention with a device for ensuring a sufficiently rapid return flow of the hydraulic fluid from the container formed by the cuff and from the Hlederdruol & ammer into the high pressure chamber in the event of a rapid sequence of oppositely directed impact forces to prevent excessive stretching and expansion the flexible cuff as well as the creation of a negative pressure in the high pressure chamber

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The invention also provides a hydraulic shock absorber device for use in railroad car constructions » the one cylinder filled with hydraulic fluid in which a linearly reciprocating cylinder Fluid displacement device is arranged, which in turn divides in a shortening movement from a neutral out the pluiduin from a siisusr. High pressure chamber and able to displace from a low-pressure chamber / as well as a chamber formed by a flexible or resilient sleeve for receiving a rope of the displaced Hydraulic fluid with one on the high pressure side of the Fluxdum displacement has arranged arrangement, which responds to a predetermined! pressure in the low pressure chamber and an additional backflow volume between Low pressure and high pressure chamber guaranteed.

For a better understanding, the invention is now based on the drawings explained in more detail «Show it

1 shows a partial section through a hydraulic shock absorber device with the features of the invention in their extended or »neutral division,

Hg · 2 a Pig. 1. cut similar part, in which. However, the shock absorber device according to the invention is in its shortened position which it assumes in the event of an impact.

»3 a partial cross-section through the cylinder and the Pluidum displacement device together with the latter associated office flow arrangement according to the invention, on a larger scale,

Pig 4 is an end view of the portion shown in Pig 3;

Pig · «. 5 »" 6 and 7 schematic representations of the invented hydraulic shock absorber device according to the invention with reflux or hydraulic fluid compensation arrangement, from which specifically the reflux path of the hydraulic fluid when moving the shock absorber device from the shortened position according to Pigv 5 in a middle position according to Pig. 6 and in the fully extended position according to Pig ·. 7 he si oh cloth is.

Pig «8 shows a partial section through a arranged in the cylinder of a shock absorber device according to the invention Piston head with a different design

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shape of the return flow arrangement according to the invention, enlarged scale, and

Pig ·. 9 is a practical section taken along line 9-9 in FIG Pig »8..

In the drawings is a hydraulic shock absorber device according to the invention 10 shown, which essentially consists of a cylinder 11 filled with hydraulic fluid one arranged in the cylinder 11 for the purpose of displacement of the pluidum. a high pressure chamber into a lower pressure chamber 13 or H back and forth in a straight line in the cylinder movable pluidum displacement device 12, one between the cylinder 11 and the 3 & uidum displacement » device 12 inserted flexible sleeve or · container 16, which has a predetermined volume for receiving part of the displaced when the device was shortened Hydraulic fluid provides a lioseielstauge 17 for dimensioning the flow between the high pressure and the median pressure chamber 13 or 14 and a reset spring 18 for resetting the pluidum displacement device 12 and the cylinder 11 is in the Sieutralstellung after the shortening of the Device causing impact shock has been destroyed is·

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According to the invention, the shock absorber device is provided with a high-speed reversal or return flow arrangement, which is inserted between the high-pressure chamber 13 and the low-pressure chamber 14 and is arranged on the pluidum displacement device 12, which when predetermined pressure forces are reached in the low-pressure chamber during the return movement in the door direction a sufficiently high reflux yoxl hydraulic fluid from the. the container formed by the cuff and the low-pressure chamber into the high-pressure chamber guaranteed "

According to: Figures 1 to 4, the cylinder 11 consists of one cylindrical tube 21 made of steel ο »the like ·, on one of which The end of a basil or driver plate 22 attached, is welded on, for example, which extends beyond the outer urofang of the pipe 21 and a holding- edge 23 for the return spring 18 forms. Inward from At the open end of the cylinder, a central cylinder head 26 is fastened in the cylinder bore 24, the one next to the open cylinder head At the end of a cuff chamber 27 for receiving the flexible cuff 16

The length of the cuff sub-chamber 27 can thus be increased be that a hanging shoulder 28 is set, on which a provided on the middle cylinder head conversion

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Catch flange 30 is held by means of a snap ring 29, which rests on a retaining ring 31 attached to the central part of the cylinder head 26. A sliding compression ring 32 is provided between the retaining ring 31 and the circumferential flange 30, which is urged against an O-shaped sealing ring 33 by a plurality of clamp members distributed radially at intervals and compresses it to form a fluid-tight seal along the bore wall. . · .. ". (Akt ^.

The Pluidum ~ displacement device 12 has a J piston head 38 on which one end of a tubular Piston rod 39 is attached, the other end through the axial opening 36 of the cylinder head 26 from the open Cylinder end exits and defines an annular opening 41 together with this opening. The piston head 38 places on one side together with the cylinder head 22 the high pressure chamber 13 and on its other side together with the central cylinder head 26 and the flexible sleeve 16, the low-pressure chamber 14 is fixed

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The scope of the order made of cast steel, for example Piston head: 38 has a small distance voxL of the inner wall of the cylinder guide 24 · In an im The circumferential groove 42 provided for the piston head is a sealing and miter ring 43, which is preferably made of layered phenolic resin and sized so is that it forms a seal on the inner wall of the cylinder bore 24 «,

The front of the piston has a circular shape. Well 44 with a practical, planar or level Floor surface 46 provided by. which leaves a rearwardly directed truncated cone or "funnel surface 47, which in a band edge 48 surrounding an axial opening 49 provided in the piston head 38 passes over.

The tubular piston rod 39 consists of a hollow tubular rod with a bore 51 arranged coaxially with respect to the piston head opening 49. On that of the piston head 38 distal end of the piston rod, a second base plate 52 is attached to the shaft 53 of a; Fastener 54 may be attached with an externally threaded head 56 which is screwed into the internally threaded end of the piston rod 39 is. Inward of the fastening member 54 in the piston rod bore 51 can be a non-return valve assembly

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be provided for filling the device 10 with fluid. When using the check valve »the hydraulic— fluid is filled in via this valve before the base plate 52 is attached to the piston rod 39.

The flexible sleeve 16 can be made of a flexible and resilient fluid-tight material, for example Rubber «and is at one end for example in the middle of a hose clamp on the extension 37 of the middle cylinder head 26 attached. At the other end, the cuff is turned upside down and so is it attached to the piston rod 39 by means of a hose clamp. According to Mg. .1 is the cuff in the extended or neutral division of the hydraulic Shock absorber device 10 in practical from ELuidum deflated while in the foreshortened position the device by a rope of the displaced during the shortening movement of the device 10 KLuidums is extended and filled out, as later Will be explained in more detail yet · It is, however, too. note that the volume of the displaced ELuidums taken up by the cuff 16 is only so large that the cuff is not expanded further than: Volume of the cuff chamber 27 is.

On the base plate 22 is the coaxial through the

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Piston head opening extending into the piston rod bore Throttle rod 17 attached * which is used to control the: fluid flow from the high-pressure chamber 13 to the low- pressure chamber 14 is used. The flow between them both pressure chambers is preferably carried out in such a way that the shock absorber device 10 during their shortening movement practically constant force / displacement properties are awarded »For this purpose, the scope of the Throttle rod longitudinal sinkings 58 planned » with the help of which the effective cross-sectional area of the opening 49 through which the pluidum flows through during the shortening movement. The grooves 53 are formed so that they with the Piston head opening 49 interact and the pressure forces in the high pressure chamber 15 during a relative movement of the piston head 38 opposite the cylinder 11 approximately keep constant by changing the effective cross-sectional area of the opening on belt 48 in accordance with the Total cross-sectional area of the area enclosed by the band 48 Recesses 58 is changed · In this context it should be noted that the total effective cross-sectional area is greatest in the extended position of the device and gradually down to a minimum value decreases at the end of the shortening movement, at which they have a noticeable flow from the high pressure chamber to the low pressure chamber 14 switches off «

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The maximum length of the shock absorbing device 10 in the expanded state is given by one on the outer periphery attached to the piston rod 39, for example snwelded Limit stop ring 61 limited, which may be provided with an inclined surface, which in the extended position of the goal direction on a complementary inclined surface on the inside of the middle Cylinder head 26 abuts.

To produce a connection between the piston rod bore 51 and the low-pressure chamber 14 has the piston rod 39 next to, the piston head 38 a row from. openings 62 on "whereby between the low pressure" chamber 14 and the high pressure chamber 13 a connection is created, the one. Flow of hydraulic fluid via the piston head opening 49 and the grooves 58, the piston rod bore 51 <and the openings 62 allows.

The cylinder 11 and the fluid displacement device device 12 from the shortened taken in an impact. Position in the normal or neutral extended position according to Hg «1 bringing back spring 18 is disposed between the base plates 22 and 52 and may be selected from a number of one behind the other arranged springs 18a, and 18 are made.

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According to Pig. 2, in the compressed position of the shock absorber device 10, the throttle rod 17 is oriented relative to the piston head in such a way that practically the entire flow through the grooves 58 and the opening 49 is interrupted. During the return movement of the piston head 38 and the cylinder into the neutral position, on the other hand, the throughput of hydraulic fluid increases gradually, while the effective opening cross-sectional area, which, as mentioned, is determined by the depth of the grooves 58 and by the opening edge 48 » Under certain conditions during the operation of the railroad car _9, for example when a series of faster and oppositely directed impact forces are exerted on the shock absorber device 10, the return movement of the cylinder 11 and piston head 38 takes place within a relatively short period of time and much faster than the hydraulic fluid through the gradually increasing cross-sectional area of the opening is able to flow through in order to keep the high-pressure chamber 13 in the filled state. Under these circumstances, the volume of liquid within the total volume of the pressure chamber H and the flexible sleeve 16 is greater than the volume for which the device is designed, while the volume of fluid in the high pressure chamber is less than the intended volume.

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pressure chamber and fluid located in the flexible cuff 16 thus causes the cuff to expand in radial and longitudinal direction over the limits of the Cuff chamber 27 * This excessive expansion of the cuff 16 can result in a further reduction in the ratio cause the sleeve to burst or tear between the cylinder and piston under the action of the spring.

In addition, the lack of a sufficient amount of hydraulic fluid in the high pressure chamber 13 »which keeps it filled, a negative pressure is generated in this chamber, so that the resistance or the energy destruction capacity of the gate direction in the event of an impact impact acting on the device at this moment far below the rated power of the door direction. ”At the same time, the hydraulic fluid would enter the low-pressure chamber 14 and be displaced into the flexible sleeve 16, whereby the latter would be expanded even further.

To avoid this undesirable condition is therefore a volume equalization «- or Mckflußordnung for the; Hydraulic fluid provided, which is used to increase the hydraulic fluid volume within the flexible sleeve 16 and to keep the corset pressure chamber H below the value, in which an expansion of the cuff 16 takes place out of the boundaries of the cuff chamber 27

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and which keeps the Hoehdruokkammer 13 filled.

According to the Pig * 3 and 4- this can be done by creating an arrangement responsive to the fluid pressure can be effected, which in the event of an insufficient throughput of hydraulic fluid by the effective opening cross-section during the bending stroke of the shock absorber device 10 ensures increased fluid throughput, whereby the

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correct volume equilibrium of the fluid is maintained. For this purpose, on the one hand, the piston head 33 is provided with a number of angularly spaced openings 64 and, on the other hand, an annular valve member 66 overlying these openings 64 is inserted into the circular recess or depression provided on the side 65 of the piston head 38 facing the high pressure chamber , which can consist of a ring-shaped metal disc *

This valve member 66 is normally urged into seat contact by a number of spring fingers 67, which with Help of a retaining ring 68 on the surface 6? of the piston head 38 are attached * Hing and springs are means; Screws 69 attached to piston head 38

8 and 9 is a further embodiment a hydraulic fluid compensation provided on the piston head

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arrangement shown *. In the provided in the piston head recess 44 an annular valve disc 66 is used, which is loosely received by the recess 44 and drawn up by broken lines from a lying over the apertures 64 position to an in Pig x 8, adapted to move from the openings remote position, the extent of the outward movement of the annular disk away from the openings 64 is limited by a spring ring 69 which is inserted into a groove 70 formed along a wall 73 of the recess 44.

During the compression stroke when the shock absorber device Moved into the shortened position, the valve disc 66 is through the. Pressure of the acting on them Fluid in sealing contact via the openings 64 pushed at the Piaehe 46, while in the backward movement that prevailing in the low pressure chamber 14, over the openings 64 acting on the valve ring disk 66 pushes the disk 66 from above the openings in a lying position against the stop ring 69 so that the hydraulic fluid can freely pass through the openings 64 to. able to flow

In operation, the shock absorber device 10 according to the invention is between the ßleitträger 7t · and a carriage fixed carrier 72 one. Railway car with shock-absorbing lower *

frame used, like this, in the Pig »5 to 7 schematised, is shown. With this arrangement, the base plates are in the neutral position of the shock absorber device 10 in contact with the respective buffer stops 74 »74 or with the slide support stops 76, 76, which are movable along with the carriage couplings (not shown) Slide supports 71 are attached

When an impact shock hits the right end of the slide beam 71 acts, the force of the impact force moves the Slide carrier relative to the carriage-fixed carrier 72 according to FIGS. 5 and 6 to the left, the one with the slide carrier moved and the base plate 22 touching stops 76, 76 the shock absorber device against the Opposite, on the left side located stops 74,74 of the wagenfeaten carrier press.

While compressing or shortening the shock absorbers er device 10 move the piston head 38 and the base plate 22 against each other, the latter on the latter fixed throttle rod 17 that in the piston rod bore 31 located hydraulic fluid via the opening row 62 out into the Hiederdruokkammer 14 "and over the hanging opening 41 eats the flexible cuff container 16 displaced "

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At the same time, the pluid displaced from the high-pressure chamber flows over the gradually decreasing Cross-sectional area at the opening 49 in the piston rods bore 51 »through the row of openings 62 into the lower pressure chamber 14 and through the bing opening 41 into the flexible cuff 16

The hydraulic fluid is flowing at a relatively high speed displaced into the low pressure chamber 14, which results in considerable turbulence. This Turbulence is caused, at least in part, by the radial causes directed flow of hydraulic fluid, which is directly on the inner wall of the cylinder 11- hits and thereby destroys a: & large rope of kinetic energy in the form of heat «

After completing its stroke, the shock absorber device is 10 completely compressed and the throttle rod 17 and the piston head 38 are aligned with one another in such a way that that the latter is somewhat behind the ends of the grooves 58 located. In this position of the piston head 38 and the throttle rod 17 there is practically no flow through the opening 49

the other end / normally, that is, when / no impact impact acts, that acting between the base plates 22 and 52 can

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Reset spring 18 to expand the shock absorber device, whereupon the base plate touching the right slide support stops 76 'moves the slide support 71 into the neutral position moved back according to Fig. 7. During the mck movement the shock absorber device in the neutral position according to Fig. 6 is the flow direction of the hydraulic fluid vice versa, so that the shock absorber device is enabled again, its energy-destroying Exercise function. The return movement of the shock absorber device 10 in the neutral division under the action of the spring 18 takes place alone normally during a such a period of time that the hydraulic fluid at a rate through the constantly increasing opening cross section is able to flow, in which the Pressure forces in the low pressure chamber 14 and in the flexible cuff container or container tube 16 to a minimum be held and that gradually increases Senden volume of the high pressure chamber 13 is practically completely filled with fluid. The cuff container is thus not subjected to any substantial expansion beyond the cuff chamber 27 and it is in the high pressure chamber 14 generates practically no negative pressure.

The following is the mode of operation of the reflux arrangement according to FIGS. 1 ~ 4 explained »In the absence of a significant pressure increase of the hydraulic fluid in the

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of the piston opening 49 may not be sufficient to allow the fluid to flow through this opening with such Speed to enable the high pressure chamber 13 to be kept in a fully filled condition * In this Pail can have an excessive amount of hydraulic fluid in the low- pressure chamber and remain in the expandable cuff 16. This excessive amount of pluidum in the Low pressure chamber 14 and in the cuff 16 leads to a corresponding increase in pressure in these ropes, the in the absence of a means of releasing the pressure, the cuff will expand excessively leads.

The relationships described appear even more clearly in appearance when there is an impact on the left side in the same direction as the slide carrier 71 moves occurs before a noticeable stooping movement of the shock absorber device 10 has occurred.

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The pressure chamber remains the valve member 66, which is exposed to such pressure forces via the openings 64 is, under the action of the peder fingers 67 and the pressure forces of the pluidum in the high pressure chamber 13 in Seat contact. Palis, however, the return time of the shock j damper device 10 from the compressed into the extended position would be significantly shortened, the effective opening cross-sectional area could increase

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In this case the slide carrier is moved to the right, the left slide carrier stop 76 being out of contact with the base plate according to: Pig * 6 ". The slide carrier 71 therefore no longer offers any resistance to the force of the return spring 18, so that the piston head 38 and the cylinder 11 are displaced more quickly into the neutral position. This accelerated movement of the piston head 38 and cylinder 11 does not allow sufficient fluid flow through the throttled piston head opening 49 t so that the excessive volume of hydraulic fluid within the lower pressure chamber 14 creates pressure forces which are applied to the inner surface of the annular valve member 66. If these pressure forces are so great that the counteracting force of the valve ring member 66 holding spring fingers 67 is overcome, this is; The valve member is displaced from its seat contact via the openings 64, so that the hydraulic fluid is able to flow unhindered through these openings into the high-pressure chamber 14. The force of the spring fingers is preferably adjusted so that the pingers yield to hydraulic fluid forces that are below the value at which a substantial expansion of the cuff 16 out of the boundaries of the cuff chamber 27 takes place. In this way, the hydraulic fluid return forces acting on the flexible sleeve 16 are kept below the value

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at which there is a tendency towards undue expansion the cuff occurs

If, on the other hand, the return flow arrangement according to FIGS. 8 and 9 is used, the pressure forces of the hydraulic fluid within the corset pressure chamber 14 displace the ring-shaped valve member 66 into the position shown by dashed lines in Pig 8 as soon as the bending movement of the device is initiated ·

After returning to the neutral position and during the return movement, the high-pressure chamber 13 is practically completely filled with hydraulic fluid. If an impact shock is now applied before or immediately after the moment in which the device has reached the neutral position according to FIG. 7, the full volume of the high pressure chamber 13 is available for absorbing the impact force on one. If the value drops below the spring finger, the valve member 66 comes to rest again via the openings 64 and interrupts the flow of hydraulic fluid through these openings.

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Claims (4)

J E31 * n.g. SS protection claims 1. Hydraulic shock absorber device, "consisting of a bored cylinder having a cylinder head at one end and inward from the other end in the cylinder bore a central cylinder head having an axial opening are attached, one arranged in the cylinder bore, on one side together with the the first-mentioned cylinder head defining a high-pressure chamber and a low-pressure chamber on the other side, reciprocable between the two cylinder heads, having an axial opening Piston head, one connected at one end to the piston head and penetrating the axial opening tubular piston rod on which stop means which can be brought into contact with the central cylinder head are provided that keep the piston head at a minimum distance from the central cylinder head, formed between the stop means and the piston head in the tubular piston rod openings, one between the middle cylinder head and the flexible cuff container inserted into the piston rod, one at the other end of the tubular Piston rod attached another cylinder head, between the cylinder bore and the flexible one - 28 - Reservoir provided fluid channels, a throttle rod attached to the first-mentioned cylinder head and penetrating the basket head opening, which defines a gradually decreasing flow cross-section when the piston head moves in the direction of the first-mentioned cylinder head, and hydraulic fluid filling the cylinder, characterized in that in the piston (38) in In the radial direction outward from the piston head opening (49), several openings (64) arranged at angular distances from one another are formed and on the side of the piston head (38) facing the first-mentioned cylinder head (22) an annular plate (66) is held which extends into one of the openings (64) is able to shift the covering position when the piston head (38) moves from a position next to the central cylinder head (26) into a position next to the first-mentioned cylinder head (22) and which moves away into one of the openings (64) Able to shift position when the piston Ko pf (38) is moved to the position next to the central cylinder head (26). 2. Device according to claim 1, characterized in that that it has a spring means (67) which the annular plate member (66) during the movement of the iiolbenkopfs (38) in sight of the first-mentioned cylinder head (22) pushes into cover contact with the openings (64), but during the return movement of the piston head (38) - 29 - into the position next to the central cylinder head (26) under the action of the pressure forces of the hydraulic fluid located in the low pressure chamber gives way. 3. Device according to claim 1, characterized in that that the annular plate member (66) in a side facing the first-mentioned cylinder head (22) the piston head (38) provided recess (.44) is arranged. 4. Apparatus according to claim 3, characterized in that that within the recess (44) a stop ring (69) to limit the outward movement of the annular Plate member (66) is provided, 5. Device according to claim 2, characterized in that that the spring device (67) consists of a number of angular spacings distributed on the piston head (38) attached and the annular plate member (66) resiliently contacting spring fingers. * 4 * * ul «ö« ta ** «« * »·; si * «« eh »Wlft 4w« JJ Mi. SI ·. ^