EP0739450B1 - Seal for a piston-cylinder unit - Google Patents

Abstract

PCT No. PCT/CH95/00259 Sec. 371 Date Jul. 10, 1996 Sec. 102(e) Date Jul. 10, 1996 PCT Filed Nov. 9, 1995 PCT Pub. No. WO96/15368 PCT Pub. Date May 23, 1996The device comprises a cylinder (3) and a piston (7) which is guided free of contact relative to the cylinder (3). A gap seal (12) is provided between the lateral surfaces (15, 14) of the cylinder (3) and of the piston (7). The gap seal (12) has a very thin and uniform annular cross section. The lateral surfaces (14, 15) of the cylinder liner (4) and of the piston (7) are essentially smooth and comprise a material with a linear thermal coefficient of expansion which is lower relative to steel. The precise maintenance of the sealing gap and the central guidance of the piston (7) in the cylinder liner (4) is ensured through two guides (8, 9) connected rigidly with the housing (5). These guides (8, 9) are elastic in the direction of the central axis (2) of the piston-cylinder unit and highly rigid transversely to the central axis (2). The arrangement formed with the aid of these guides (8, 9) of a gap sealing between piston (7) and cylinder (3) with minimum gap is free of contact and no abrasion of sealing material develops wherein the motions of the piston (7) are guided precisely centrally to the cylinder (3).

Description

The invention relates to a sealing arrangement on a piston-cylinder unit, with one in a cylinder with one Cylinder liner longitudinally movable in the direction of a central axis Piston, with a piston skirt and a non-contact Gap seal between cylinder liner and piston skirt for sealing a liquid under pressure or gaseous medium, the piston-cylinder unit is installed in a housing.

Sealing arrangements of this type take place in a known manner Use with compressors, servo motors, volumetric flasks or Stirling free-piston engines, which are equipped with a gaseous, or in the case of servomotors or volumetric pistons also interact with liquid medium. Special problems now occur wherever the piston-cylinder unit both sliding friction-free and lubricant-free to be operated. For example, with oxygen compressors, or compressors for the food industry the case. Known compressors of this type have a piston-cylinder unit, in which the Seal between piston and cylinder by means of a labyrinth seal is formed. The piston must be in the cylinder as centrally as possible to avoid touching the piston skirt to avoid on the cylinder wall and corresponding To prevent damage or seizure. To this The piston with one is sufficient to meet the guiding conditions Provide piston rod, which is mounted in a cross head and is led. This crosshead is in turn known Way on a crank rod from a rotating crankshaft driven. In this way, the necessary generates oscillating movements of the piston, the desired guidance of the piston in the cylinder through the crosshead is guaranteed. Corresponding compressors are in the Technical book "Piston Compressor" by K.H. Küttner, Springer publishing house 1991, pages 236 and following. A disadvantage this version is now that between the piston skirt and very narrow gaps are not provided in the cylinder wall can be, but a relatively large game necessary is. On the one hand, this is due to the running play of the crosshead guide conditioned, and on the other hand by the fact that oil-free compressors have a much longer design need as oil-lubricated piston compressors. Through the The deflections or deviations become long of the piston from the central axis is getting bigger, and that free play, or the gap between the piston and cylinder must therefore be kept large. This requires then the arrangement of labyrinth seals to the desired seal between the pressure side of the piston and to reach the unpressurized side. Because the piston with the translatory movements in the direction of the central axis cannot be kept exactly on this axis, shows the sealing gap between the piston skirt and cylinder wall not a circular cross-section, but the cross-section is mostly crescent-shaped. As a result, the thickness of the gap on one side almost doubles can, and accordingly the tightness in this area decreases significantly. This asymmetry of the sealing gap leads to significant problems and is undesirable, can however, cannot be avoided with such compressors. The leakage losses in the area of the Poetry.

From DE-B 19 33 159 is a piston-cylinder unit for one Stirling piston engine known in which the centering of the piston and the seal between the piston and cylinder done via O-rings. However, this arrangement shows in the Practice only a very short lifespan because the sealing rings can wear out very quickly when operating without lubricant, and thus the centering and sealing no longer guaranteed is. In addition, the abrasion of the seals gets in the circuit of the print medium, which is normally not allowed is and can also lead to significant interference. This solution can also be used with lubricant-free Operation accurate guidance of the piston on the central axis and cannot be achieved during long-term operation.

It is an object of the present invention to provide a sealing arrangement to create a piston-cylinder unit at which of the pistons performs translatory movements, which are exactly centered on the cylinder, and where the Piston no emigration movements in relation to the central axis of the cylinder, the sealing gap has its circular shape Maintains cross-section and does not assume a sickle shape, and can be made minimally small during assembly the piston-cylinder unit no radial axis displacements arise between piston and cylinder, i.e. an exact central assembly of all components is possible, and further measures are provided to touch the wall between piston skirt and cylinder liner due to thermal Prevent stretching.

This object is achieved in the characterizing part of the claim 1 defined characteristics solved. Beneficial Further developments of the invention result from the features of the dependent claims.

The guidance of the piston according to the invention ensures precise guidance of the translatory movements of the piston along the central axis of the cylinder and prevents deviating Movements perpendicular to this central axis. Thereby there is the advantage that between the piston skirt and the cylinder wall set a minimal sealing gap can be, and therefore the need for arrangement no labyrinth seals. It also exists no danger that the cross section of the sealing gap is a takes on a crescent shape, and thereby the sealability the sealing arrangement would be reduced. With correct position Assembling the piston and cylinder will make the seal opposite the pressurized side of the piston the very thin sealing gap that can be achieved with this arrangement guaranteed. Through conical centering the components of the piston and the cylinder result in the Advantage that these parts are aligned exactly on the same axis and be held in that position. It will ensured that the piston and the cylinder do not touch anywhere during the movement, and the annular gap is constant throughout the operating period remains. The connection of the cylinder to the machine housing is also done via a conical centering, or over several elastic brackets. At least three brackets are attached to the housing, whereby elastic tongues, over a lateral surface of a housing part of the cylinder, the radial positioning and thus centering of the cylinder determine. When the cylinder is not assembled and housing define holding surfaces on the elastic Tongues have an inner diameter which is smaller than the outer diameter of the lateral surface on the housing part of the Cylinders. This gives the advantage of a radial / backlash-free mounting and mounting of the cylinder opposite the housing. The outer surface on which the elastic Mounts can be used as an outer surface or as an inner surface be formed, and the holding surfaces on the brackets are accordingly directed inwards or outwards. Another advantage of the arrangement is that the components of the piston and the cylinder, namely the piston skirt and the cylinder liner, which define the boundary surfaces form the gap of the gap seal, from one material exist, which has a very small coefficient of thermal expansion having. Such materials are known per se and in the present case it will contain more nickel Steel or sintered graphite or coal selected. The different Components have the same possible thermal Strains at the same temperatures, the linear Thermal expansion coefficient at least by a factor of 4 should be smaller than that of unalloyed steel, or Iron. This ensures that in the event of temperature differences practically no additional between piston and cylinder Changes in the sealing gap occur.

By using graphite on at least one of the components of the piston or cylinder, which are the boundary surfaces of the gap of the gap seal will form a additional security against damage to the sealing surfaces reached in the event of a malfunction. Such could occur when due to external influences such as lateral Blows or an earthquake, any deviations of the Axes occur. In this case there would be no gnawing of the touching parts, but that Part, which consists of sintered graphite, or with coated with a layer of nickel graphite would be ground down. This has the advantage that after a Running-in time of the sealing gap would be set independently, and the piston-cylinder device are operated normally could. However, this embodiment also has the other one Advantage that pistons and cylinders are practical at the beginning a Passitz can be assembled and by appropriate Shrink the component from sintered graphite, or with the Nickel graphite layer, i.e. the piston skirt or the cylinder liner, ground in, and the sealing gap by running in is trained. This possibility can be used if minimal sealing gaps are required, and the correspondingly high costs for breaking in and subsequent removal of the abrasion can be accepted. Instead of sintered graphite or coatings of nickel graphite, other materials can also be used which have the same thermal properties and have the same emergency running properties. The mentioned However, materials prove to be particularly suitable.

This also applies to thermal loads on the piston components and the cylinder during operation and any resulting changes in length no deviations of the piston and the cylinder from the central axis possible are, the individual components are made using elastic Clamping elements put together, which in the direction the axis of the conical centerings or the central axis Act. Through the interaction of the conical centers and the clamping forces have the advantage that even with Radial temperature differences between the components No additional play arises in the direction of the components always in the axial direction in the conical guides stay pressed. This ensures compliance the concentricity between piston and cylinder.

In the sealing arrangement according to the invention there is each of the two spaced guides several plate-shaped spring elements. The proposed one Arrangement of the guides with the spring elements provides the Advantage that the piston, which oscillating linear movements centered exactly on its central axis and to be led. The guides have no parts move against each other and subject to sliding wear are. The piston is guided through the two guides and centered that it is non-contact with the cylinder can perform a purely axial relative movement. This e.g. in a lubricant-free oxygen processor, or at a lubricant-free piston of a Stirling free-piston engine. The spring elements of the individual guides are in arranged on a plane which is approximately perpendicular to the central axis of the oscillating moving machine element stands. The main spring parts are on this level, which are plate-shaped. This arrangement of Main spring parts allows a calculation of the movement and Spring data in a known manner, so that the movements of the machine element can be determined exactly. in the The outer area of the long main spring parts are shorter auxiliary spring parts arranged, at right angles to the main spring parts, so that these auxiliary spring parts approximately parallel to Central axis run. The connection of the auxiliary spring parts with the main spring parts via an additional connecting element, which with appropriate fasteners for the fixed connection of the ends of the main and auxiliary spring parts Is provided. By arranging this additional Connection element between each auxiliary spring part and the associated main spring part, there is the advantage that the spring element is rigid in the angled area is, and the deformations of the spring elements only in the plate-shaped areas take place. The individual auxiliary spring parts and main spring parts, as well as the connecting elements, can be very according to the technical specifications manufacture precisely so that they both affect the installation Dimensional stability as well as strength values the desired Have values. This exact agreement with the given Masses and strength values can be with conventional Manufacturing methods achieve because the spring parts and the connecting elements have simple shapes. The single ones Components can also be easily checked and parts which deviate from the norm data, are easily eliminated. The assembly of each spring element from several individual spring parts allows adaptation to different Requirements and brings the significant advantage with the fact that no parts of the spring elements during manufacture deformed, for example, must be bent. The plate-like design of the individual spring element parts allows precise processing to the desired at any time Dimensions, e.g. by grinding too. The main and the Auxiliary spring parts are normally flat plates.

The plate-shaped spring elements of each guide expediently arranged centrally symmetrically, so that from the central axis in the plane of the guide four, extend six or more spring element parts radially outwards. Odd numbers of spring element parts in the plane the tour is possible, each expediently includes Spring element, however, a main spring part, which itself extends symmetrically on both sides of the central axis. Thereby, that between the spring elements, which lie in one plane, the same angles are included, results the advantage that the machine element on the central axis is centered exactly symmetrically.

The dimensions of the long main spring parts and the short ones Auxiliary spring parts are chosen in a known manner so that the rigidity of the two guides that guide the piston, across the central axis at least by the factor 100 is larger than in the direction of the central axis. Depends on the desired precision in the area of the sealing gap and the lateral forces that occur are guides with a Stiffness ratio of 500 and more used. In the The device according to the invention now has further advantages, by the force absorption, the rigidity or the movement paths by adapting the individual spring element parts can be changed. The stiffness ratio leaves not only by changing the dimensions, for example of the plate-shaped spring parts change, but also in that at least two auxiliary spring parts or main spring parts spaced parallel to each other, or the auxiliary as well as the main spring part so formed are. If you do not want to change the spring constant, so in a tour in two at a distance from each other arranged levels two groups of plate-shaped spring elements be arranged. This leads to an increase in Load capacity of the corresponding guide with approximately the same Stiffness ratio. With all these different Arrangements and embodiments can always the same basic elements of main spring parts, auxiliary spring parts and fasteners are used so that the Calculation bases are simplified, and so is manufacturing the individual parts is made considerably easier. Another The advantage is that the main spring part of the individual spring elements formed in one or two parts can be. If the guide is arranged at the end of an axis, it can be advantageous to make the main spring parts in one piece train, since they then with the help of a central connecting element can be connected to the axis. Becomes however, the guide somewhere in the axis area of the machine element arranged, it is often useful to the main spring parts run in two parts, and then against the central axis directed inner ends of the main spring parts by appropriate fastening devices with the axis connect to.

With the claimed combination of elements that the Seal arrangement according to the invention can be formed Guide the pistons in a cylinder so precisely that a lubricant-free one Operation is enabled, and yet sealing gaps between piston and cylinder of minimal dimensions become possible. By using two identical Guides that are spaced from each other, the piston is guided exactly along the central axis, and disturbing movement deviations are avoided. So that will it is possible, for example, the piston or the piston rod a free piston engine, e.g. a Stirling engine without Use lubricant in the cylinder, namely the working and displacement pistons. Pollution of the pressure medium due to abrasion or lubricant residues completely avoided. The same applies to statements from oxygen compressors to, or to, compressors with other media that are not lubricated or abrasion may be contaminated. The inventive Sealing arrangement requires no lubricant and provides also make sure that there is no abrasion in the area during operation of the sealing gap arises.

Fig. 1

einen Längsschnitt durch einen schematisch dargestellten Kompressor, mit elektromagnetischem Antrieb,

Fig. 2

einen Längsschnitt durch den Kolben-Zylinder-Bereich des Kompressors gemäss Fig. 1, mit einem beschichteten Kolben,

Fig. 3

eine frontale Teilansicht einer der in Fig. 1 und 2 dargestellten Führungen für den Kolben,

Fig. 4

einen Ausschnitt aus einer Führung mit doppelten Federelementen und zweiteiligen Hauptfederteilen,

Fig. 5

einen Ausschnitt aus einer Führung mit zweiteiligen Hauptfederteilen und paarweise angeordneten Haupt- und Hilfsfederteilen,

Fig. 6

einen Ausschnitt aus Fig. 1, mit elastischer Halterung für den Zylinder am Gehäuse, und

Fig. 7

eine Ansicht der Anordnung gemäss Fig. 6 in Richtung der Zentralachse, mit einem Teilschnitt durch Zylinder und Kolben.

The invention is explained in more detail below with the aid of drawings which illustrate exemplary embodiments. Show it:

Fig. 1

2 shows a longitudinal section through a schematically represented compressor, with an electromagnetic drive,

Fig. 2

2 shows a longitudinal section through the piston-cylinder area of the compressor according to FIG. 1, with a coated piston,

Fig. 3

2 shows a frontal partial view of one of the guides for the piston shown in FIGS. 1 and 2,

Fig. 4

a section of a guide with double spring elements and two-part main spring parts,

Fig. 5

a section of a guide with two-part main spring parts and main and auxiliary spring parts arranged in pairs,

Fig. 6

a section of Fig. 1, with elastic holder for the cylinder on the housing, and

Fig. 7

6 in the direction of the central axis, with a partial section through the cylinder and piston.

1 shows a longitudinal section through a compressor 1, only the upper part is shown, but the lower part is centrally symmetrical is the same. The compressor 1 has an electric drive in a housing 5, which consists of a fixed magnetic coil 10 and a longitudinally movable Anchor 11 exists. The armature 11 is with a piston rod 6 connected, the piston rod 6 and armature 11 the Have common central axis 2 and in the direction of this Central axis 2 are translationally movable. The piston rod 6 is supported on two guides 8 and 9 and exactly centered guided, these two guides 8 and 9 with Are spaced from each other. At the front end 16 of the Piston rod 6 is a piston 7 with a piston skirt 13 attached. This piston 7 is from a cylinder liner 4 surround which is part of a cylinder 3. The cylinder 3 is in turn connected to the housing 5 and forms part of the same. The cylinder 3 includes one Working space 18 for the pressure medium and has in a known Show intake valves 19 and exhaust valves 20. Between the piston skirt 13 and the cylinder liner 4 is a gap seal 12 formed, the piston 7 without contact is guided in the cylinder liner 4. This configuration A non-contact gap seal is achieved by the inventive Design and arrangement of the two guides 8, 9 enables. In the example shown, it is for example possible with a piston diameter of 45 mm Form a gap width of 0.01 mm on the gap seal.

The piston 7 is assembled from several parts. The piston rod 6 has a plate-shaped flange 21, which forms the holder for the cylindrical piston jacket 13. A second plate-shaped flange 22 interacts with the other end of the piston jacket 13 and is connected to the front end 16 of the piston rod 6 via an elastic clamping element 23 and a clamping nut 24. The two plate-shaped flanges 21, 22 have conical edge regions 25 and 25 '. The two end faces of the piston skirt 13 are also conical. The conical edge region 25 of the plate-shaped flange 21 centers and guides the piston jacket 13 exactly centrally to the central axis 2. The elastic clamping element 23 generates a constant clamping force in the direction of the central axis 2 and ensures that even with length changes due to temperature changes, the piston jacket 13 is always exactly centered between the two plate-shaped flanges 21, 22 is clamped. The elastic clamping element 23 consists of a plate spring. The piston skirt 13 is made of sintered graphite in the example shown, and the clamping between the two conical edge regions 25 and 25 'of the plate-shaped flanges 21, 22 ensures a permanent pressure preload and secure mounting for the sintered body 13. The for the piston skirt 13 and the cylinder liner 4 materials used have a linear thermal expansion coefficient, which is at least four times smaller than that of unalloyed steel, the latter being 11.1x10 ^-6 per degree Kelvin. A high-alloy nickel steel with eg 36% nickel can have a linear expansion coefficient of 0.9x10 ^-6 per degree Kelvin.

The cylinder liner 4 is elastic on the one hand Clamping element 26 and fastening element 27, and on the other hand supported by a conical centering 28 in the cylinder 3 and centered. The elastic tensioning element 26 also exists from a disc spring, but can also from others known elastic elements can be formed. In case of Changes in length of the cylinder liner 4 due to temperature differences the cylinder liner is always in the direction of the central axis pressed against the conical centering 28. Thereby it is also ensured on the cylinder liner that this is always free of play and no deviations occur with respect to the central axis 2.

About the alignment of the cylinder 3 and the cylinder liner 4 to ensure on the central axis 2 is on the housing part 61 of the cylinder 3 also between the cylinder 3 and the housing 5 a conical centering 29 is formed. The connection between cylinder 3 and housing 5 does not take place Connection elements 30 shown in the area of the conical Centering 29. Since the conical centering 29 both the housing 5, as well as the cylinder 3, from the same Material, there are no thermal ones Axial movements to be expected. The conical centers between the individual components of the cylinder 3 and Pistons 7 ensure that the individual components are accurate be assembled and formed centrally to the central axis 2 thus the prerequisites for training the desired minimal gap at the gap seal 12.

Center the two guides 8 and 9 and guide the piston rod 6, or the piston 7 so that the lateral surface 14 of the piston skirt 13 without contact and exactly parallel to Cylinder surface 15 of the cylinder liner 4 runs. This about the entire length of the translatory movements of the piston 7 in the direction of arrows 31. The first guide is 8 arranged in the immediate vicinity of the piston 7 and the second Guide 9 at the rear end 17 of the piston rod 6. This Guides 8, 9 are aligned on two levels 32, 33, which are approximately at right angles to the central axis 2. The two Levels 32, 33 and thus the two guides 8, 9 arranged at a distance from one another in the direction of the central axis 2, this distance due to storage conditions, as well as the design of the compressor is.

Each of the two guides 8, 9 consists of several spring elements 34, which can best be seen from FIG. 3. This Spring elements 34 each consist of a two-part long Main spring part 35 and two short auxiliary spring parts 36, which at the outer ends 37 of the main spring part 35 rigidly attached and connected to the housing 5. The Auxiliary spring parts 36 are approximately at right angles to the main spring part 35 arranged and thus run approximately parallel to Central axis 2. The rigid connection between the outer Ends 37 of the main spring part 35 and the auxiliary spring parts 36 is produced by means of connecting elements 38. The spring elements 34 are on the one hand via the auxiliary spring parts 36 and Fasteners 39 fixed to the housing 5, and on the other hand via the main spring parts 35, and the flanges 40 and Clamping elements 41 with the oscillating piston rod 6 and the piston 7 firmly connected. The two guides 8, 9 are exactly the same, but as shown in Fig. 1 is recognizable, arranged mirror-inverted. The leadership and Centering the piston 7 is so precise that between the piston 7 and the cylinder liner 4 only a very thin one Gap 12 is necessary. This can seal the piston chamber 18 take place through a contactless gap seal 12, and no seals are necessary and available, which are abraded or worn by relative movements would. That by the spring elements 34 of each guide 8, 9 formed spring system is designed so that the Stiffness in the direction of the planes 32, 33 at least around the Factor 100 is greater than its stiffness in the direction the central axis 2. In the example shown in FIG. 1 the rigidity across the central axis 2 is approx. 200 times higher than in the direction of the central axis 2. For this purpose, spring parts made of hardened spring steel with a thickness of 1.18 mm. There are two spring elements 34 per guide 8, 9 available, which are arranged at right angles to each other and each from two main spring parts 35 and two auxiliary spring parts 36 exist. The main spring parts 35 have a length of approx. 13 cm and the auxiliary spring parts a length of approx. 2.2 cm. This enables a piston stroke of 20 mm. The piston diameter is 45 mm and the oscillation frequency is 50 Vibrations per second.

Fig. 2 shows another embodiment of the piston 7, the remaining parts of the compressor 1 are configured identically, as in Fig. 1. In cylinder 3 is again a cylinder liner 4 used, which is made of a high-nickel steel, manufactured in the example shown of the type 36% Ni-Alloy is. The centering and clamping of the cylinder liner 4 in Cylinder 3 also takes place here via the conical centering 28, and the elastic clamping element 26, and the fastening elements 27. The piston 7 also consists of several Divide. A piston skirt 44 is between one of the Piston rod 6 outgoing plate-shaped flange 42 and clamped a second plate-shaped flange 43. The Tension is achieved by the elastic tensioning element 23 in the Form a plate spring, and the clamping nut 24 is generated. Here is the clamping nut 24 on the front end 16 of the piston rod 6 screwed on. The piston skirt 44 consists of high nickel steel. On the outer surface 45 of this piston skirt 44 is a coating 46 made of suitable nickel graphite angry, e.g. in the composition of 15-25% by weight graphite and 75-85% nickel. This coating 46 forms the interface of the gap seal 12 the cylinder liner 4. The conical edge areas 47 and 47 ' point at both ends of the cylindrical piston skirt 44 here an inclination, which in relation to the piston skirt 44 causes a tension. This is because of the chosen one Material steel permissible and advantageous.

Both in the embodiment of the piston 7 according to FIG. 1, 2, the dimensions of the piston skirt 13, or 44 and the cylinder liner 4 from the beginning chosen so that when assembling the components in the areas the gap seal 12 forms the smallest possible gap becomes. In sealing arrangements between the piston 7 and the Cylinder liner 3, in which a very uniform circular cross-section is requested, and at the same time the thickness the gap of the gap seal 12 should be absolutely minimal, it is possible to the diameter of the piston skirt 44 and the Select cylinder liner 4 so that almost a Passitz or a relatively strict sliding fit arises. By careful The sintered graphite material of the piston jacket can shrink 13, or the coating 46 rubbed against the piston skirt 44 and thereby creates a very narrow gap seal 12 will. It is also possible to choose the material combinations between To replace cylinder liner 4 and piston skirt 13. The exact guidance of the piston 7 over the guides 8 and 9, as well as the conical centering of the various components of the piston 7 and the cylinder 3 enable in any case the formation of a very tight and non-contact gap seal 12, and thus the lubricant-free operation. There the piston 7 in normal operation without contact in the cylinder liner 4 runs, there is no abrasion, which also means the pollution of the print medium is prevented.

FIG. 3 shows a guide 8, 9 as shown in FIG. 1 or 2 is used as a partial view in the direction of the central axis 2. It can be seen that in each of the levels 32 or 33 two spring elements 34 are arranged, between the Spring elements 34, seen in the circumferential direction, are the same Angles are included. Each of the spring elements 34 is made thereby from two main spring parts 35, two auxiliary spring parts 36 and two connecting elements 38. The connecting elements 38 turned ends of the short auxiliary spring parts 36 are fasteners 39 on the housing 5 of the compressor 1 rigidly attached. The piston rod 6, which is moved axially oscillating has a flange 40 on, and a clamping element 41, which for connection the inner ends 53 of the main spring parts 35 with the flange 40 serves. The short auxiliary spring parts 36 are made of flat, rectangular plates formed. The main spring parts 35 are trapezoidal and wider towards the outer end 37 than at the inner end 53. The shape of the spring parts 35, 36 is in a known manner by the desired spring characteristics certainly. Ribs 55 are arranged on the flange 40, which stop surfaces 56 for the inner ends 53 of the Form main spring parts 35. Through these ribs 55 and the corresponding stop surfaces 56, and the corresponding Shape of the inner ends 53 of the main spring parts 35, their position relative to the piston rod 6 is precisely determined. In this position, the inner ends 53 of the Main spring parts 35 with the help of the clamping element 41 and Screws 58 clamped and held.

Fig. 4 shows a guide 50, which in principle the arrangements 1 and 2 corresponds. However, it is on each guide 50 two spaced apart Levels 51, 52 are present, in each of which spring elements 34 are arranged are. The two levels 51, 52 run parallel to each other and approximately at right angles to the central axis 2 the piston rod 6. As described and shown for Fig. 3 there are two in each of the levels 51, 52 Spring elements 34 are arranged, in which between the spring elements 34, seen in the circumferential direction, the same angle are included. In addition to the flange 40 and Clamping element 41 are two centering plates on piston rod 6 here 54 and a spacer 57 arranged. Here the centering plates 54 have the ribs 55 with the stop faces 56 on. The inner ends 53 of the pair arranged spring parts 35 are between a centering plate 54 and the flange 40, or the clamping element 41 clamped. The clamping force is generated by means of the screws 58. This arrangement of a guide shown in Fig. 4 50 with two spring levels 51, 52 can be larger longitudinal and Take up lateral forces. However, it leaves the same Movements to, such as that shown and described in Fig. 1 simple execution. Freedom in particular the linearly oscillating movement of the piston rod 6 and the associated piston 7 in the direction of arrows 31 guaranteed. The embodiment described in FIGS. 3 and 4 the two-part main spring parts 35 is particular useful where on the central axis 2 before and 50 further machine elements arranged behind the guide which are a plug-in of continuous one-piece Do not allow spring elements 34 on the piston rod 6. in the but also the production of the main spring parts 35 facilitated because they have smaller dimensions, and if necessary, individual parts of a spring element 34 can be replaced are. But it is quite possible and in the sense of the invention, e.g. in plane 33 in Fig. 1, one-piece Use main spring parts 35. These have a central Bore on and can be pushed onto the piston rod 6 and then clamped.

5 shows a further embodiment of an inventive one Guide for a sealing arrangement shown in each spring element 34 both the main spring parts 35, as well as the auxiliary spring parts 36 in pairs in parallel and are arranged at a distance from each other. The connection of the inner ends 53 of the main spring parts 35 with the flange 40 the piston rod 6 takes place in the same way as for FIG. 3, or 4 described. The connecting element 38 between the outer ends of the main spring parts 35 and the abutting ones The ends of the auxiliary spring parts 36 are designed accordingly and has contact surfaces for the paired arrangement of the parallel springs. For connecting the auxiliary spring parts 36 with the housing 5 are corresponding fastening and Clamping elements 60 available. The organization of the leadership with parallel springs 35 leads to one in both longitudinal directions of movement symmetrical spring characteristic with accordingly more favorable voltage curve. The one shown in Fig. 1 simple spring points because of the bending and force relationships in the clamping areas for the forward or Backward movement of the machine element is not the same Spring characteristic. In relation to the zero point the positive and negative characteristics of the single spring not symmetrical.

In all the described embodiments of the guides 8, 9 it turns out to be useful in each of the levels 32, 33, or 51, 52 to arrange at least two spring elements 34, which are centrally symmetrical to the central axis 2 and their orientation axes, seen in the circumferential direction, Cross at an angle of 90 °. Provided the design conditions and the forces that arise require it However, the spring elements can also be at an angle of 60 ° or 45 ° to each other. Accordingly then in the area of the oscillating piston 7 and Housing 5 more attachment and positioning points provided. Regardless of the different possible configurations of the guides ensure exact centering along the linearly oscillating piston 7 the central axis 2 and a reduction of the deviations from this central axis 2 as a result of transverse forces, which are minimal Gap between the moving piston and the fixed one Cylinder liner 4 and thus non-contact gap seals allows.

6 and 7 show a further advantageous embodiment the connection between the cylinder 3 and the housing 5. The housing part 61 of the cylinder 3 has a cylindrical Shell surface 62, which is exactly centric to the central axis 2 is formed. At least 5 are on the housing three, in the example shown four elastic mounts 65 arranged. These four brackets 65 are radial each 90 ° offset and fastening parts 67 and known fasteners 68, e.g. Screws, attached to the housing 5. Each bracket 65 has an elastic tongue 69 on the free end of a holding surface 64 is arranged. To the Holding surface 64 closes an outwardly diverging surface oblique guide surface 63. The housing 5 is in the further a stop surface 66 is arranged, which in a radial plane to the central axis 2 and the support and mounting surface forms for the housing part 61 of the cylinder 3. Before assembling the cylinder 3 with the housing 5 machined the holding surfaces 64 of the marked brackets 65 so that they limit an inside diameter which is smaller than the outer diameter of the outer surface 63 am Housing part 61. If the housing part 61 of the cylinder 3 in Pushed in the direction of the central axis 2 between the brackets 65, the tongues 69 are elastically deformed, and between the outer surface 62 on the cylinder 3 and the holding surfaces 64 on the brackets 65 becomes a backlash-free fit educated. The deformation of the elastic tongues 69 on the Brackets 65 cause four equal, against the central axis 2 directed radial forces, which the housing part 61 and thus the cylinder 3 with respect to the central axis 2 Center without play. In the centered installation position is the housing part 61 of the cylinder 3 on the stop surface 66 of the housing 5 and is by means of known connecting elements 30, e.g. Screws, connected to the housing 5. This embodiment of the connections between cylinders 3 and housing 5 ensures a backlash-free centering and fastening, in which the influence of the connecting elements 30 avoided on the centricity of the arrangement becomes. Furthermore, it is also possible for the outer surface 62 on an annular collar, or in a groove on the opposite the housing 5 facing end face 70 of the housing part 61 to arrange. The outer surface 62 is then an outer surface or designed as an inner surface. The brackets 65 are then arranged accordingly in the interior of the housing 5, and the holding surfaces 64 on the elastic tongues 69 are then dependent on the orientation of the lateral surface 61 directed inwards or outwards. In the case where the elastic tongues 69 holding surfaces 64 arranged on the outside have, which in a collar or a groove on the housing part 61 engage, the initial diameter is not in assembled condition larger than the diameter of the Shell surface 62 on the housing part 61 of the cylinder 3. Die play-free leadership is, as described above, at guaranteed each embodiment.

Claims (13)

1. Sealing arrangement for a piston-cylinder unit, having a piston (7) which is longitudinally movable in the direction of a central axis (2) in a cylinder (3) with a cylinder liner (4), having a piston skirt (13) and a contactless gap seal (12) between cylinder liner (4) and piston skirt (13), for sealing off a pressurized liquid or gaseous medium, the piston-cylinder unit being installed in a housing (5), characterized in that the piston (7) is rigidly connected to two guides (8, 9; 50), which are disposed a distance apart from one another in the direction of the central axis (2) and fastened to the housing (5), parts (35) of said guides (8, 9; 50) are movable to a limited extent in the direction of the central axis (2), and guide the piston (7) elastically in the direction of the central axis (2), the guides (8, 9; 50) at right angles to the central axis (2) are at least 100 times stiffer than in the direction of the central axis (2), and hold the piston (7) exactly centrically relative to the central axis (2), the piston skirt (13) and the cylinder liner (4), which lie opposite one another in the region of the gap seal (12), have substantially smooth lateral surfaces (14, 15), and said sub-regions (4, 13) of the cylinder (3) and of the piston (7) are made cf materials having a coefficient of linear thermal expansion which is at least 4 times lower than that of plain steel.
2. Sealing arrangement according to claim 1, characterized in that the piston (7i and the cylinder (3) are composed of a plurality of structural parts (13, 21, 22 and 3, 4 respectively), and said structural parts are mutually clamped in conical centring devices (25, 28), and centred without play relative to the central axis (2).
3. Sealing arrangement according to claim 1 or 2, characterized in that a housing part (61) of the cylinder (3) is clamped relative to the housing (5) in a conical centring device (29), or said housing part (61) via a lateral surface (62) is guided without play by means of at least three elastic holding devices (65) fastened to the housing (5) and is clamped axially against a stop face (66) of the housing (5), and the housing part (61), and hence the cylinder (3), is centred without play relative to the central axis (2).
4. Sealing arrangement according to one of claims 1 to 3, characterized in that elastic clamping elements (23, 26) are disposed on the structural parts of the piston (7) and/or of the cylinder (3) which are assembled, and said elastic clamping elements (23, 25) act in the direction cf the axis of the conical centring device (25, 28, 29).
5. Sealing arrangement according to one of claims 1 to 4, characterized in that the piston skirt (13) of the piston (7) which delimits the gap of the gap seal (12) is made of sintered graphite, and the cylinder liner (4) of the cylinder (3) which delimits said gap is made of steel with a high nickel content.
6. Sealing arrangement according to one of claims 1 to 4, characterized in that the piston skirt (44) of the piston (7) and the cylinder liner (4), which delimit the gap of the gap seal (12), are made of steel with a high nickel content, and the surface (14) of the piston skirt (44) directed towards said gap is coated with a nickel graphite layer.
7. Sealing arrangement according to one of claims 1 to 6, characterized in that each of the two guides (8, 9; 50) comprises a plurality of plate-like spring elements (34) which are disposed in a plane (32, 33; 51, 52) extending substantially at right angles to the central axis (2) of the piston (7), each of the spring elements (34) is firmly connected on the one hand in the region of the central axis (2) to the piston (7) and on the other hand in the region of the outer ends of the spring elements (34) to the housing (5), each of the spring elements (34) comprises at least one long main spring part (35), which lies in the plane (32, 33; 51, 52) at right angles to the central axis (2), and at each end directed towards the housing (5) at least one short auxiliary spring part (36), which is disposed substantially parallel to the central axis (2), a connecting element (38) is disposed between each auxiliary spring part (36) and the associated main spring part (35), and the auxiliary spring parts (36) are connected by said connecting elements (38) rigidly to the outer ends (37) of the main spring parts (35).
8. Sealing arrangement according to claim 7, characterized in that each of the two guides (8, 9; 50) comprises at least two centrosymmetric spring elements (34), which are disposed in a plane (32, 33; 51, 52) at right angles to the central axis (2) of the piston (7) and radially cut said central axis (2), angles each of identical size being formed between the spring elements (34) viewed in a peripheral direction.
9. Sealing arrangement according to claim 7, characterized in that at least one of the guides (8, 9; 50) comprises two planes (51, 52) with spring elements (34), said planes (51, 52) extending parallel to one another and in the direction of the central axis (2), at a distance from one another, as well as at right angles to the central axis (2).
10. Sealing arrangement according to claim 7, characterized in that each of the spring elements (34) comprises a one- or multi-part main spring part (35) and two pairs each of parallel-running auxiliary spring parts (36).
11. Sealing arrangement according to claim 7, characterized in that each of the spring elements (34) comprises a pair of parallel, one- or multi-part main spring parts (35) and two pairs each of parallel-running auxiliary spring parts (36).
12. Sealing arrangement according to one of claims 1 to 11, characterized in that the piston (7), cylinder (3) and guides (8, 9; 50) are parts of a Stirling free-piston engine.
13. Sealing arrangement according to one cf claims 1 to 11, characterized in that piston (7), cylinder (3) and guides (8, 9; 50) are parts of a compressor (1) with a linearly oscillating drive (10, 11).

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