DE8800694U1 - Hydraulic cylinder with dimensionally stable piston guide - Google Patents

Description

Applicant &igr; Dipl. Ing.Adalbert Huperz Meisenweg Nr. 3, 6832 Hockenheim

Inventor Dipl.-Ing. Adalbert Huperz Meisenweg No. 3, 6832 Hockenheim and

Dipl.-Ing. Harald Solmitz Kantstrasse 8, 6800 Mannheim 1

Hydraulic cylinder with dimensionally stable piston guide

The invention relates to a hydraulic cylinder which, in contrast to the versions mentioned, consists of an outer jacket tube with an internal pressure-balanced guide tube. The guide tube accommodates the piston, whereby a constant sealing gap between the piston and the guide tube is maintained largely independent of the prevailing hydraulic operating pressure, since the guide tube is practically not subject to any branch-dependent expansion.

This design is particularly suitable for high-pressure hydraulics of more than 1000 bar and is equally advantageous for the synchronous and differential cylinder designs.

The use of ever higher pressures in hydraulic systems leads to increased problems in cylinder construction. The increase in fluid pressures requires increasingly thick-walled cylinder dimensions in the common load units, which are necessary not only for reasons of strength, but also in the conventional design with a single-walled cylinder wall due to their pressure-dependent expansion. These elastic wall deformations of the cylinder

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tube results in undesirable gap expansions between the piston and the surrounding cylinder tube. The gap enlargement causes considerable sealing difficulties on the piston in the case of liquid piston sealing due to the pure gap resistance effect or when using special piston seals, especially since in this high-pressure range it is not uncommon for the gap to increase by more than a power of ten compared to the smaller original gap specified during production.

If there is a pure gap seal between the cylinder tube and the piston, i.e. a seal without the use of sealing elements, the fluid losses at the gap increase in proportion to the cube of the gap width. In addition, the use of low-viscosity media, such as water, increases the leakage losses. In addition, if the gap is large, the piston is more likely to move off-center, which means that a concentric gap is no longer formed, and the leakage can multiply again by up to 2.5 times the fourth that occurs with a concentric gap.

The physical phenomena described cause unacceptable "power losses" which, in high and ultra-high pressure hydraulic systems, cannot rule out strong local heating in the piston area and the associated consequential damage due to energy conversion.

If the seal between the cylinder tube and the piston is made using an additional piston seal, then in such cases conventional collar, stuffing box seals or the like regularly fail, since the seal is no longer adequately supported by the pressure-dependent gap expansion described. The reason for this is that the supporting element usually associated with the seal

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ring can only be dimensioned to match the narrow original gap that exists during production. As a result, during the piston movement the sealing material migrates into the sealing gap with a drastic increase in the gap and at the same time the high fluid pressure prevailing. When the pressure drops, the elastic cylinder tube contracts again and crushes the piston seal. This destructive process is further limited by trapped dirt particles that form longitudinal grooves in the cylinder tube. Wear on the piston rods and cylinder bore due to excessive edge pressure on the guide bushes is also dangerously promoted by the formation of an unacceptably large gap.

The invention is based on the object of remedying this problem by means of an expedient solution in order to create precisely functioning hydraulic cylinders with or without the use of sliding seals with low leakage, low friction losses and a considerable service life for use in general hydraulics, in particular in water operation in the field of high and ultra-high pressure hydraulics. In addition, the cylinder drive should be characterized by a design that is easy to assemble and economical to manufacture. The invention solves this problem in a hydraulic cylinder of the type in that two cylinder heads equipped with conventional hydraulic connections receive a cylinder casing tube from both sides in a centered manner and, braced by tie rods, form a unit which receives a guide tube surrounded by a plurality of pressure chambers arranged one behind the other in an aligned manner, whereby the pressure chambers communicate with the pressure fluid available for the piston drive via the bores of the guide or cylinder tube for the purpose of pressure equalization on the guide tube, and whereby each of the pressure chambers is embedded between the cylinder casing and the guide tube in an elastically pre-stressed manner, closed by flexible seals, and the guide tube receives the drive piston including the associated piston rod bearing centrally, whereby

if piston seals are used, these are divided into two seal packages and are constantly and automatically under functional hydraulic contact pressure with the help of two check valves compactly housed in the piston, and that a commercially available static seal type ensures the hermetic external closure of the cylinder unit according to the invention.

These measures of the invention ensure that the sealing gap is maintained between the guide tube and the piston, regardless of changing fluid pressures. This is because the different hydraulic pressures occurring in the guide tube are transferred in sections to the pressure chambers arranged in close succession between the guide tube and the casing tube, i.e. hydraulic pressure equalization is largely achieved on the guide tube, unaffected by axial piston movements and the different pressure differences occurring on the piston, whereby this component, which is crucial for maintaining the desired small sealing gap, remains dimensionally stable.

When using piston seals, the extremely space-saving and simple check valve construction integrated in the piston, which takes over the function of hydraulically operated pressure inlet valves, ensures optimal radial form instability when the two piston seal packages are hydraulically pressed onto the guide tube, without causing the seals to shift within their piston embedding during load change operation or seal wear.

The stabilization measures taken according to the invention on both the guide tube and the piston seals are important prerequisites for the perfect sliding behavior between the piston seals and the guide tube, whereby the pressure equalization via cylinder bores keeps the guide tube running surface free of holes, which, however, requires an additional control unit.

A further advantageous characteristic feature of the invention relates to an increase in the durability of the cylinder casing tube, which is necessary in rare cases, to protect against cracking in a load unit subject to exceptionally high dynamic stress.

Without affecting the dimensional stability of the guide tube and thus the sealing gap between the piston and the guide tube*, the modular principle can be used to replace the simple cylinder jacket tube with a double jacket tube, the hollow space of which is formed by its double wall and closed on both sides and is pumped up hydrostatically with pressure ■ _{( )} .

This variant allows the use of the conveying medium as a static pre-stressing agent within the double-walled casing to achieve a considerable increase in the fatigue strength _of the cylinder material, which is subject to high dynamic stress. However, the inventive design of the hydraulic cylinder does not allow any deformation to be transferred from the double-walled casing to the guide tube, since the guide tube is elastically cushioned relative to the double-walled casing.

The invention thus allows a composite technology in which the inclusion of the known prestressing process for increasing the fatigue strength of a double-shell cylinder tube prestressed by means of hydrostatic pressure does not have a harmful effect on the dimensionally stable guide between the piston and the guide tube.

In the following, the invention is explained in more detail using the example of a double-acting cylinder that is pressure-balanced via guide tube bores and whose alternately drivable piston has seals using Fig. 1, Fig. 2 and Fig. 3. The figures show»

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Fig.l shows an axially sectioned hydraulic oil calibration cylinder according to the invention to illustrate its concept and functioning.

Fig.2 a section through the details of the guide tube and piston with the piston rods on both sides to highlight the effectiveness of the piston seal and special assembly requirements with regard to the piston equipped with seals in connection with the guide tube.

Fig*3 an axial half section to illustrate the inclusion of a hydrostatically prestressed

Double cladding tube jacket in the cylinder construction

in order to increase the fatigue strength of this component.

The cylinder casing tube (1) is firmly clamped between the head pieces (3) and (4) by means of tie rod screws (2). Each of the head pieces is provided with a pressure connection designed as a threaded bore (5) or (15), which opens into the annular channel (6) or (14). If, on the one hand, pressure medium is pumped to the reciprocally driven piston (C-10) via the threaded bore (5), the ring channel (6) and the bores (7) of the guide tube (8), then on the other hand the pumped medium is displaced via the bore (9) of the guide tube (8), the ring channel (11), the bores (12) of the adapter sleeve (13) and the ring channel ( ¹⁴ ) and the threaded bore (15). An opposite flow direction causes the drive on the piston (10) to be reversed. The guide tube (8), which accommodates the piston drive shown in more detail in Fig. 2, is accommodated centrally on both sides, namely in the head piece (3) through bore (16) and in the head piece (4) through bore (17) via the intermediately mounted adapter sleeves.

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(18). In addition, between the fitting sleeve (18) on the one hand and the projecting annular front surface (19) on the other hand, there are a number of pressure chambers (20) arranged one behind the other, which are embedded between the cylinder casing tube (1) and the guide tube (8). The length of each pressure chamber (20) is defined by the spacer ring (21). The pressure chambers (20) arranged in a row and enclosing the guide tube (8) are sealed off from one another by means of flexible seals (22), whereby these seals (22) themselves are closed on both sides by elastic support rings (23). All chamber elements (21), (22), (23) arranged one after the other are clamped against the circumferentially projecting end face (19) by means of the adapter sleeve (13), support ring (24), packings (25) and adapter sleeve (18) by * the action of the threaded ring (26) screwed into the head piece (4). A prescribed, empirically determined torque is used to tighten the thread of part (26). The condition for the clamping process of the chamber elements* arranged around the guide tube (8) is free axial mobility of the guide tube (8) and its adjacent parts. These are the bearing bracket (2?) and elsewhere the bearing bracket (28) including the O-ring (30) encapsulated by the support rings (29) and (31). The guide tube not only accommodates these movable parts, but also the alternately driven piston (10) in alignment. In turn, the guide tube (8) is fixed* via the adjacent parts (27), (28)» (29)# (30), (31) by screwing the threaded ring (32) tight, which provides clear support for all parts located between the threaded rings (26) and (32).

A large number of pore-like micro-holes (33) arranged in a circle in the guide tube (8), which are assigned to each pressure chamber (20) in an analogous manner, enable the liquid to be fed into all pressure chambers (20) in accordance with the hydraulic pressure difference occurring at the piston (10). This means that

during a communicating fluid transfer between the interior and the pressure chambers (20) located on the outside of the guide tube (8). The pressure equalization thus caused ensures the shape instability of the guide tube ($) to a large extent, independent of any pressure fluctuations of the conveying medium that occur depending on the position or axial load of the piston.

The pressure-dependent expansion of the cylinder casing tube ( &igr; ) is not prevented. The breathing of the cylinder casing tube (1)

A mutual flow of the porous micro _- holes (33) is achieved, thus providing a cleaning effect which protects the micro-holes (33) from contamination or

blockages. The cylinder tube enlargement caused by the elastic expansion has no influence on the tightness of the pressure chambers (20), since the sealing elements (22) and (23) selected for such sealing cases follow the breathing-like cylinder tube movement without difficulty.

On both sides, the piston rods (10.01) and (10,02) of the piston (10) are guided and sealed in the sealing packages (34) and (35), which consist of guide, support and sealing rings and are located inside the bearing flange (27) and (28). The threaded rings (36) and (37) have the task of ensuring the appropriate contact pressure on the piston rods (10.01) and (10.02) for the piston rod seals. The soft seals (38) and (39) including the additional dirt scraper rings (40) and (41) are designed to prevent leakage; the leakage to the threaded connections (42) and (43) is ensured by a conventional drainage system using ring channels and bores. The threaded rings (26), (36) and (32), (37) are screwed in for the purpose of sealing against the outside using Teflon tape as a sealing agent. The packing (25) and O-rings seal against the hydraulically increasing working pressure.

' - 9 (30) and (48) hermetically sealed.

The advance of the piston (10) is limited by a conventional end position damping. The damping piston parts (10.03) or (10.04) are immersed in the bores (44) or (45), each of which has a screw-in throttle (46) or (47), in the end position area of the working stroke. In the process, the liquid volume is displaced either via the corresponding throttle (46) or (47), until the drive piston comes to a stop in a controlled manner via a dampened braking path.

Explanations_to_Ficj_._2

The guide tube (8) with the holes (7) and (9) as well as the micro holes (33) together with the complete double-sided piston rod are shown in Fig. 1.

In the piston (10) there are two conical radial bores (10.06) and (10.10) offset by 180° on the piston circumference, see enlarged section A of Fig. 2. The conical bore countersinks serve as valve seats for the check balls (10.07) and (10.11). Both balls are simultaneously subject to the restoring force of the spring-loaded clamping ring (10.08) that surrounds them and which lies in a circle in the circumferential groove (10.09) of the piston (10). As an alternative to the clamping ring machine element (10.08), the O-ring is also suitable for this component.

The check balls (10.07) and (10.11) take over the function of pressure inlet valves, which always put the sealing package (10.17) and (10.18) under hydraulic contact pressure with the highest fluid pressure that alternates on the opposite effective face of the disk-like piston (10). The hydraulic force flow, which depends on the ^piston thrust force, thus comes through the bores (10.13), (10.05 ) _to the check valves, depending on the direction of travel of the piston (10).

ball (10.07), bore (10.06) or bore (10.16), ring channel (10.14), bores (10.15), (10.12), check ball (10.11), bore (10.10) of the piston seal as hydraulic clamping force. In this way, the piston sealing packages (IC.17) and (10.18), also consisting of guide, support and sealing rings, always maintain their defined position with optimally appropriate preload, even under alternating loads on the piston (10), which is an important prerequisite for the necessary internal radial form stability of the slider, rwisch ;n j. piston QO) and guide tube (8). j

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\ All elements of the sealing p:*.kete (10.17) and (10,18) to;"

Pistons (10) receive their basic mechanical preload through

J Tighten the threaded union (10.04). The assembly process for applying the mechanical basic preload for the sealing packages (10.17) and (10.18) is provided inside the _guide tube (8), since after mechanical application of the preload,

j Due to the pre-tensioning of the thread outside the guide tube (8), the insertion of the piston (10) into the guide tube (8) is very difficult if the seal packages (10.17) and (10.8) are too ^expanded .

To implement the project, the piston rod (10.01) is held at its flats (10.19) using an open-end wrench (Wl) and the threaded union (10.04), which is positively connected to the guide tube (8) by the plug-in tool (W 2) via the bore (9) and (10.20), is rotated to achieve the desired joint.

Explanations_to_Fi0j.3

According to the modular principle, a double jacket tube (50) replaces the single cylinder jacket tube (1). The maximum operating pressure is extracted from the pressure curve of the conveying medium via the feed valves (51), which are basically designed according to the type of valve in the piston (10) (see "Explanations for section A of Figure 2").

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filtered and introduced between the walls of the double-cladding pipe jacket | (5Ö). This process achieves the formation of a resting hydrostatic liquid layer between the two walls of the pipe jacket and thus a pre-stress to protect against threshold stresses of the conveying medium» which act on the inner wall of the double-cladding pipe jacket (50)»

The result is a considerable increase in the fatigue strength of the dynamically stressed cylinder material while avoiding deformation of the guide tube (8) due to the effect of the hydraulically prestressed double cladding tube (50), since the dimensionally stable guide tube (8) is elastically cushioned by the pressure chambers (10) with the chamber elements (21), (22), (23).

Furthermore, the invention teaches, while maintaining the underlying principle, that the same effect occurs when the pressure medium is fed via cylinder tube bores for the purpose of guide tube stabilization. The pressure chamber charging is no longer carried out from the inside via guide tube bores, but from the outside via cylinder tube bores with liquid pressure, which, however, requires an additional hydraulic control device. The advantage of this more complex design is that it maintains a bore-free guide tube running surface and the optimal prerequisite for the seal-friendly sliding behavior that this provides.

This variant of the invention is shown and explained in more detail in the drawing Fig. 4 using the embodiment of a synchronous cylinder that is pressure-balanced via cylinder tube bores and thus dimensionally stable in its piston guide, which has an additional hydraulic control device and whose alternately drivable piston has seals.

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The cylinder structure shown is, apart from minor modifications, identical to the representation shown in Fig. I. Only the micro-bores (33) in the guide tube (8) are omitted. The spacer rings (21), which define the length of the pressure chambers (20), are no longer accommodated on the outside of the cylinder casing tube (1) but on the inside of the guide tube (8) so that the pressure chambers (20) move from the inside to the outside, where they are supplied with pressure fluid via conically chamfered blind bores (52) by means of the self-sealing hose pieces or tubes sealed at the end or similarly designed connecting elements (53), whereby the connecting elements (53) between the blind bores (52) and (54) are pre-tensioned when the control block (55) is mounted on the two head pieces (3) and (4). The control block (55), a component of the control device, is flanged onto the head pieces (3) and (4) of the synchronous cylinder and is hydraulically connected through the bores (5), (56) and (15), (57) and the associated sealing elements, such as the support ring (58) and O-ring (56) or the support ring (60) and O-ring (61), as well as the usual leakage drains (42) and (43). The control block (55) accommodates the control piston (63) in its bore (62) which is aligned parallel to the piston (10), whereby the sealing lengths of the piston (10) and the control piston (63) are kept the same. The disc-shaped control piston (63) is held centrally in the plain bearings (64) and (65) on both sides via its piston rods (63.1) and (63.2) and sealed by the elements (66) and (67), whereby the plain bearings (64) and (65) are screwed firmly and Teflon-sealed using threaded rings (68) and (69).

The piston rods (10.02) and control piston rod (63.2) are connected to one another in a form-fitting manner but without transverse forces via the torsion-resistant coupling "K" shown, whereby the force flow from the piston (lö) to the control piston (63) is achieved. Of course, the implementation of a

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second coupling arrangement of the same type between the piston rods«? (10.01) and (63.1)*

As a result, a synchronous operation based on a drag effect is achieved between the equally long pistons (10) and the control piston (63), which results in the functional control of the pressure chambers (20) by the control piston (63) and, as a result, a bore-free running surface of the guide tube (8) that is good for piston seals.

Claims (1)

Protection claims 1. Dimensionally stable piston guide for hydraulic cylinders, in particular high-pressure hydraulic cylinders for axial plain bearing with simultaneous pressure fluid sealing through pure friction action or the use of sealing elements, characterized in that in the bore (16) of the head piece (3) and bore (17) of the head piece (4) in advance with intermediate fitting sleeves (13) and (18) the guide tube (8) is both centrally located and a plurality of pressure chambers (20) arranged one behind the other are embedded between the guide tube (0) and the cylinder tube (1), the pressure chambers (20) being closed off from one another by means of flexible seals (22) and elastic support rings (23) and on the one hand between the projecting annular end face (19) of the head piece (3) and on the other hand U through the threaded nut (26) screwed into the head piece (4) under force-locking preload, whereby the support ring (24), packings (25), adapter sleeve (18) and (13) are included in this connection. In turn, the guide tube (8) with the inserted bearing brackets (27) and (28) as well as the O-ring (30) encapsulated by the support rings (29) and (31) are subject to a form-locking between the threaded ring (26) and the threaded ring (32) screwed into the head piece (3). The piston (10) is axially freely movable and aligned in the guide tube (8) and its ij Piston rods (10..5^* and (10.02) on both sides in the central bores the bearing glasses (28) and (27). A pressure medium communication for hydraulically pressurizing the surfaces of the piston (10) with liquid exists to the threaded hole (*> via ring channel (6) and several holes (7) as well as to the threaded hole (15) via ring channel (14), several holes (12), ringkgSi?: ^x) and several holes (9), while to each individual pressure channel (20) via the multitude of pore-like micro-holes (33) arranged in a circle in the guide tube (8) there is also an associated communication of the pressure medium. "&igr;'&igr;&igr;&igr; · : Dimensionally stable piston guide for hydraulic cylinders according to claim 1, characterized in that the two sealing packages (10.17) and (10.18) located circumferentially in the piston (10) are mechanically clamped by a threaded coupling (10.04) and are additionally subjected to alternating hydraulic loading within their butt joint either via hydraulic bores (10.13), (10.05) and ball (10.07) or via hydraulic bore (10.16), ] ring channel (10.14), hydraulic bores (10.15), (10.12) and ball (10.11). &igr; and ball (10.07) in the countersink of the hydraulic bore (10.06) as well as ball (10.11) in the countersink of the hydraulic bore (10.10) are held together spring-loaded by means of a clamping ring (10.08). Dimensionally stable piston guide for hydraulic cylinders according to claim 1, characterized in that first the force-fitting clamping process &idigr; of the plurality of pressure chambers (20) embedded between the cylinder casing tube (1) and the guide tube (8) j and arranged one behind the other, consisting of the chamber elements spacer ring (21), flexible seals (22) and elastic support rings (23), is carried out by means of a threaded ring screw connection (26) during the assembling process with free axial mobility of the guide tube (8), and only after the aforementioned assembling process is the guide tube (8) fixed in place with the aid of the threaded screw connection (32). Dimensionally stable piston guide for hydraulic cylinders according to claims 1 to 3, characterized in that, with a smooth bore surface of the guide tube (8) in the sliding area of the piston (10), the cylinder casing tube (1) has conically chamfered blind bores (52) which are opposite the similar blind bores (54) of the control block (55), a component of an additional control device flanged to the head pieces (3) and (4). The hydraulic connections between the pressure chambers (20) and the guide bore (62) of the control block (55) are provided between the blind bores (52) and (54) by means of the self-sealing connecting elements (53) inserted under prestress, whereby bore [' (62) a control piston aligned parallel to the piston (10), arranged next to one another without offset and having the same length as the sealing (63), whose piston rods (63.1) and (63.2) are mounted centrally on both sides in the plain bearings (64) and (65) and by means of the &bull; ■ · a · ■ &bull;&bull;&bull;&bull;tt · · Elements (67) are sealed. Control piston rod (63.1) or (63.2) is coupled to control piston rod (10.02) or (10.01) in a form-fitting manner but without transverse force by at least one coupling ¹¹ K" for the purpose of a synchronous movement sequence of the two pistons. Hydraulic pressure compensation between the interior of the guide tube (8) and the pressure chambers (20) is provided starting from the piston (10) on the one hand via the bore (9), annular bore (11), bores (12), annular bore (14), bore (15)/(57), guide bore (62) of the control piston (63V, blind bores (54), connecting elements (53), blind bores (52) and on the other hand via bore (7), annular channel (6), bore (5)/(56), guide bore (62) of the control piston (63), blind bores (54), connecting elements (53), blind bores (52). 5. Dimensionally stable piston guide for hydraulic cylinders according to claim 1 to 4, characterized in that instead of the simple cylinder casing tube (1) there is a double casing tube (50) which can be charged hydrostatically via feed valves (51) and which is cushioned against the guide tube (8) by the elastic pressure chambers (20) with the chamber elements (21), (22), (23), which causes a decoupling of shape changes of the double casing tube (50) on the guide tube (8). >cyl2 &bull; I » (I I · < > »· ·· ( Il II·· 5 '' ti &iacgr;&iacgr;&iacgr;&iacgr;; ·· !· Il ·· Il