EP0572774B1 - Housing for a power cylinder - Google Patents

Description

The invention relates to a housing for a working cylinder, with a cylinder tube, which consists of an inner tube and a coaxially arranged outer tube enclosing the inner tube radially on the outside with direct contact, the inner tube being a metal tube and the outer tube being a plastic tube.

Such a housing is disclosed in US-A-4 884 493. Its strength is determined by the outer tube, which is made of a composite fiber material and comprises a plurality of tortuous fibers. Since the material is relatively porous, there is an inner tube made of metal inside the outer tube, which ensures the necessary fluid tightness.

The fiber structure of the outer tube allows high strength with a low weight, but is associated with a relatively complex and therefore cost-intensive production method. The inner tube seems to have little influence on the strength to take and, apart from the sealing function, only to act as a carrier for the fiber material.

From the German utility model G 82 04 795.5, a housing emerges that has an inner tube made of plastic material which ensures good sliding properties and which is encased by an outer tube made of metal to improve the impact resistance. Here, however, it has proven to be problematic to permanently provide a high-quality surface quality in the area of the inner surface of the plastic pipe, along which a piston slides during operation. There are also high demands on the manufacturing accuracy of the metallic outer tube, since the plastic tube used conforms to the inner contour of the outer tube and takes it over practically. As a result, it can be difficult, among other things, to attach fastening devices for sensors serving to query the position in the case of relatively thin metal pipes in the area of the outer circumference, since appropriate measures can have a negative effect on the contour accuracy.

It is the object of the present invention to provide a housing of the type mentioned at the outset which, while maintaining small wall thicknesses and allowing diverse contours of the outer peripheral area, offers high wear resistance and shape accuracy in the running area of the piston.

This object is achieved in that the plastic tube forming the outer tube consists of unreinforced plastic material.

In this way, the inner surface of the cylinder tube forming the running area for the piston continues to be made of extremely wear-resistant and true-to-shape material, which can also be within the necessary roughness depths without any problems Lets hold values. The metal tube forming the inner surface is also largely responsible for the strength of the housing. For the enveloping outer tube, it is therefore possible to use plastic material of lower strength, particularly since it is not exposed to dynamic loads and therefore no high demands have to be made of the abrasion resistance. At the same time, the use of plastic material for the outer tube enables a diverse contouring of the outer circumference with little effort, so that, for example, fastening grooves for sensors can be provided without problems. The latter, in conjunction with the realizable small wall thicknesses, means that very reliable position queries can be carried out with regard to the piston, which in this case carries a permanent magnet, the magnetic field of which radiates through the wall of the cylinder tube to the outside and can actuate the magnetic field-sensitive sensor.

Although it is already known to manufacture cylinder tubes entirely from plastic material, reference is made to DE 30 20 390 C2. There, however, it is imperative to maintain a uniform wall thickness of the cylinder tube over the entire circumference, since any formations would impair the dimensional stability of the inner contour with which the piston works directly. Such an impairment is not present in the configuration according to the invention.

Advantageous developments of the invention are listed in the subclaims.

The inner tube and / or the outer tube of the cylinder tube are expediently designed as extruded parts, with which any contours can be realized without problems.

The housing also expediently has cylinder covers arranged on the end face of the cylinder tube, which consist entirely of plastic material, which can also be an unreinforced plastic. The connection to the cylinder tube is made directly between the cylinder cover and the outer tube, and in addition to a snap or snap connection or a welded connection, at least one cylinder cover can in particular also be formed in one piece with the outer tube. This results in a housing with a very small number of components, and any fastening part that may be necessary to fix the housing can be molded directly onto one of the cylinder covers made of plastic material.

Fig. 1

eine erste Bauform des erfindungsgemäßen Gehäuses in Seitenansicht, wobei der oberhalb der Mittellinie liegende Bereich durch einen Längsschnitt aufgebrochen ist, und wobei das Gehäuse einen Bestandteil eines fertigen Arbeitszylinders darstellt, indem es noch einen Kolben und eine Kolbenstange führt,

Fig. 2

einen vergrößerter Ausschnitt des zylinderdeckelseitigen Endbereiches einer weiteren Bauform des Gehäuses im Längsschnitt und

Fig. 3

ein weiteres Ausführungsbeispiel eines Gehäuses im Querschnitt, wobei strichpunktiert ein in einer Befestigungsnut sitzender Sensor für die Positionsabfrage eines Kolbens angedeutet ist.

The invention is explained in more detail below with reference to the accompanying drawing. In this show:

Fig. 1

a first design of the housing according to the invention in side view, the above the center line lying area is broken up by a longitudinal section, and wherein the housing is a component of a finished working cylinder by still leading a piston and a piston rod,

Fig. 2

an enlarged section of the cylinder cover end portion of a further construction of the housing in longitudinal section and

Fig. 3

a further embodiment of a housing in cross section, with a dash-dotted sensor in a mounting groove for the position query of a piston is indicated.

In Fig. 1, a particularly pneumatically actuated cylinder 1 is shown, in which a first design of a housing 2 is realized. The latter has a cylinder tube 3 with, for example, a circular cross-sectional contour, which is closed at both ends by a cylinder cover 4, 5. The housing space 6 delimited by the cylinder tube 3 and the two cylinder covers 4, 5 is suitable for the axially displaceable receiving of a piston 7, which is provided with a piston rod 8, for example. The latter extends from the piston 7 coaxially through the housing space 6 towards one of the Cylinder cover 4, which has a feed-through opening 9 through which the piston rod 8 projects outwards. For guidance and / or sealing between piston rod 8 and through opening 9, a schematically indicated guide and / or seal arrangement 13 is expediently used in the latter.

In principle, it could be a continuous piston rod 8, which also penetrates the second cylinder cover 5 in a manner comparable to the first cylinder cover 4. According to the example, however, one (14) of the two working chambers 14, 15 separated from one another by the piston 7 in the housing space 6 is rodless, so that the associated cylinder cover 5, with the exception of a connection opening 16, has a closed wall. Said connection opening 16 opens into the working chamber 14, as is also the case for a connection opening 17 in the first cylinder cover 4 with respect to the working chamber 15. The connection openings 16, 17 allow the connection of suitable connecting lines in order to supply or discharge pressure medium and thereby move the piston 7 with its piston rod 8 back and forth in the direction of the housing longitudinal axis 18.

The cylinder tube 3 is composed of two tube elements, namely an inner tube 23 and one in the area of its outer lateral surface directly Contact tightly enclosing outer tube 24. Outer tube 24 and inner tube 23 are accordingly arranged coaxially and concentrically with each other.

The inner tube 23 consists of metal with high abrasion resistance, with stainless steel or stainless steel being used as the material in the exemplary embodiment. This material also allows the maintenance of very small wall thicknesses without having to suffer from strength disadvantages. The metal tube 26 thus present can be produced with relatively little effort, very true to size and with extremely small tolerances, and the inner surface 25 swept by the piston 7 during its movement can also be machined very precisely and equipped with an extremely low surface roughness, so that it runs more smoothly and with less wear Run of the piston 7 is guaranteed. The inner tube 23 designed as a metal tube 26 is preferably an extruded part cut to the desired length, which can have the desired final shape directly during manufacture by means of suitable calibration measures. If required, however, it is easily possible to connect fine reworking with regard to the inner surface 25, for example by honing.

In the exemplary embodiment, the inner tube 23 is enclosed by the outer tube 24 over its entire axial length, both tubes are preferably of the same length, so that they end flush with one another. The outer tube 24 is a plastic tube 27, which consists of preferably unreinforced plastic material, which is relatively inexpensive. Reinforcement is not necessary since the strength of the cylinder tube 3 is largely determined by the metal tube 26. Nevertheless, the outer tube 24 will also be included in the strength function in order to make the overall wall thickness of the cylinder tube 3 as small as possible. The outer tube 24 is also preferably an extruded part or an extruded part cut to the desired length, the requirements for dimensional accuracy being lower, since it does not perform a guiding function with respect to the piston 7. In the normal case, the proportion of wall thickness of the cylinder tube 3 which is due to the outer tube will be greater than that which is due to the metallic inner tube 23.

It is envisaged that the outer tube 24 and the inner tube 23 touch directly with the mutually facing peripheral surfaces. Even without aids, the two tubes 23, 24 are fixed relative to one another both in the circumferential direction and in the axial direction. This is achieved, for example, by measures which bring about radial bracing between the tubes 23, 24 which are pulled onto one another.

In order to achieve the above, the inner tube 23 and outer tube 24 can in principle be axially pressed into one another in the cold state. However, the relative hold is preferably ensured by a so-called shrink fit, which is the case in the exemplary embodiment. Here, the outer tube 24 and the inner tube 23 are initially in a separate state, the inner diameter of the plastic tube 27 provided as the outer tube 24 being somewhat smaller than the outer diameter of the metal tube provided as the inner tube. The plastic tube 27 is then heated until an expansion is achieved which allows the metal tube 26 to be inserted without problems. Here, for example, total tolerances of approximately 0.5 mm are bridged between the outer diameter of the metal tube 26 and the inner diameter of the plastic tube 27. If the plastic material of the plastic tube 27 is polyoxymethylene (POM), heating to 160 ° C can result in an expansion of approximately 0.6 mm if one assumes a nominal cylinder tube diameter between 32 and 40 mm , so that assembly is possible without effort. As a result of better dimensional accuracy, the tolerances to be bridged can also be lower for other plastic materials. This is the case, for example, if the outer tube is made from polyvinyl chloride (PVC). In any case, the inner tube 23 is cooled by the latter after the outer tube 24 has been pushed on clasped tightly or spanned.

In principle, it would also be possible to extrude or extrude a metal tube 26 and a plastic tube 27 simultaneously, in such a way that the two tubes are extruded directly into one another. This coaxial extrusion then results in a tube-in-tube strand with an outer plastic tube and a metallic inner tube, which only has to be cut to the length of the desired cylinder tube 3.

To save weight, it is of great advantage if at least one of the existing cylinder covers 4, 5 is also made of plastic. For example, both cylinder covers 4, 5 are plastic parts made of, in particular, unreinforced plastic material. The latter suitably corresponds to that used for the associated outer tube 24. So that no complex connection measures that increase the overall width and / or the weight are required, it is advantageous here if the connection between a respective cylinder cover 4, 5 and the cylinder tube 3 is a permanent connection, as in the exemplary embodiment.

A snap connection 28 is located between the cylinder cover 4 on the right in FIG. 1 and the cylinder tube 3 in front. A hollow cylindrical extension 29 of the cylinder cover 4 is placed coaxially on the outer tube 24 and engages in a complementary circumferential groove 34 of the outer tube 24 with a radially inward protruding, in particular circumferential locking projection 33. Alternatively or in addition, a radially outwardly projecting ring projection of the outer tube 24 can also engage in a corresponding locking recess on the inner circumference of the extension 29. Once snapped on, the snap connection 28 can only be released by destroying one of the two connected parts.

Also in the case of the cylinder cover 5 shown on the left in FIG. 1, the outer tube 24, which is made of plastic, acts as the connection partner of the cylinder tube 3. However, there is a welded connection 35, more precisely: a friction welded connection. Again, the cylinder tube 3 with the corresponding axial end region 36 is inserted into a sleeve-like extension 29 'of the cylinder cover 5, and it can additionally be immersed in an annular axial recess 37 of the cover part adjoining the extension 29'. The end face 38 of the outer tube 24 is advantageously beveled in the manner of a circumferential bevel and bears against a complementary inclined surface 39 at the base of the axial recess 37. The bevel is practically the circumferential one Broken outer edge of the outer tube 24, and there is a larger contact area in terms of amount compared to blunt contact. This is important for the welding process, since the friction welding connection 35 is present in the contact area between the end face 38 and the inclined surface 39.

While in the case of a snap connection 28 it may be expedient to provide a seal 40, in particular axially between the cylinder tube 3 and the cylinder cover 4, such measures are unnecessary in the case of a welded connection.

Also in the case of the housing 2 'of FIG. 2, no seal between the cylinder tube 3 and cylinder cover 5' is required. Here, a cylinder cover 5 'and the plastic tube 27 form a one-piece structural unit, in that they were produced as a single component, in particular as part of a plastic injection molding process. The internal assembly of the metal tube 26 can be done in a manner as has already been explained with reference to FIG. 1.

Above all, if it is intended to carry out a contactless magnetic position inquiry of the piston, the metal tube 26 should consist of non-magnetizable and non-magnetic material, as is the case for the stainless steel used in the example. In connection with a In addition, it is advantageous to query the position to design the cylinder tube 3 in a design based on the principles of the construction variant shown in FIG. 3. According to FIG. 3, a fastening groove 42 is provided on the outer circumference, that is to say in the area of the outer lateral surface 41 of the outer tube 24, which extends in the direction of the longitudinal axis 18 of the housing and is formed in one piece with the outer tube 24 and serves to releasably hold a sensor 43 indicated by dash-dotted lines . The fastening groove 42 is, for example, embedded in a rib-like tubular projection 44 which is radially raised in the circumferential direction of adjacent regions of the lateral surface 41 and extends in the longitudinal direction of the outer tube 24. The fastening groove 42 is designed as a dovetail groove, but can also be contoured differently, for example as a T-groove. The axial length of the fastening groove 42 and the pipe protrusion 44 which may be present can correspond to that of the outer pipe 24 or is designed for the entire housing design in such a way that it extends only to the beginning of the extensions 29, 29 ', possibly attached cylinder cover 4, 5. It goes without saying that further, parallel fastening grooves 42 can be provided distributed over the circumference of the outer tube 24. With a corresponding wall thickness of the outer tube 24, the fastening groove 42 can be inserted directly into the wall of the outer tube 24 without an additional radial projection.

When a fastening groove 42 is formed and / or when a tubular projection 44 is formed in or on the outer tube 24, with regard to the contouring of the inner surface 45 of the outer tube 24 in the region of the inner surface 45 of the outer tube 24 radially on the inside opposite the fastening groove 42 or the tubular projection 44 Irregularities occur, which are indicated by the dot-dash line at 46. These would trigger functional impairments if a piston were to be guided directly because of the runout caused. In the present case, this is not the case since the metal tube 26 is still interposed, which does not transmit the irregularity 46 to its inner surface 25.

1 and 2 it can also be seen that a fastening part 47 is also integrally formed on at least one of the cylinder covers 5,5 ', which makes it possible to fix the housing 2 at the place of use on a component provided for this purpose. In the case of FIG. 2, this results in a one-piece design of the outer tube 24, cylinder cover 5 'and fastening part 47, which enables simple production with a small number of components. The attachment part is e.g. an eye and / or an external thread.

Large dimensional tolerances regularly occur when shaping plastic components. For a cylinder tube with a nominal diameter of 40 mm, they amount to approximately ^± 0.3 mm.

These are easily compensated for when the additional metal tube 26 is used according to the invention. The fact that the outer tube 24 is made of plastic material leaves a very large margin for the design of the outer contour, without any adverse effects on the guidance accuracy with respect to the piston 7.

In the case of FIGS. 2 and 3, the same reference numbers as in FIG. 1 have been used for corresponding components.

Claims (14)

1. Housing for an operating cylinder (1), with a cylinder tube (3) comprised of an inner tube (23) and a coaxially-aligned outer tube (24) firmly surrounding the radial outside of the inner tube (23) with direct contact, wherein the inner tube (23) is a metal tube (26) and the outer tube (24) a plastic tube, characterized in that the plastic tube (27) forming the outer tube (24) is made of unreinforced plastic material.
2. Housing according to claim 1, characterized in that the outer tube (24) is made of polyvinylchloride (PVC) or of a polyacetal, in particular polyoxymethylene (POM).
3. Housing according to claim 1 or 2, characterized in that the inner tube (23) is made of special steel.
4. Housing according to any of claims 1 to 3, characterized in that the metal tube (26) is made of non-magnetizable and/or non-magnetic material.
5. Housing according to any of claims 1 to 4, characterized in that the outer tube (24) of plastic material is an extrusion-moulded or extruded part.
6. Housing according to any of claims 1 to 5, characterized in that the inner tube (23) made of metal is an extrusion-moulded or extruded part.
7. Housing according to claim 6 in conjunction with claim 5, characterized in that the cylinder tube (3) is comprised of simultaneously coaxial inner and outer tubes (23, 24) extruded into one another.
8. Housing according to any of claims 1 to 6, characterized in that the inner tube (23) and the outer tube (24) are pressed axially into one another.
9. Housing according to any of claims 1 to 6, characterized in that, in the separated state, the inside diameter of the outer tube (24) is less than the outside diameter of the inner tube (23), with the inner tube being firmly clamped, expediently in a shrink-fit, by the outer tube which is temporarily heated and thereby temporarily expanded for insertion into the former.
10. Housing according to any of claims 1 to 9, characterized in that at least one fixing groove (42) or fixing projection running longitudinally and suitable for sensor mounting is integrally moulded on to the outer surface (41) of the plastic outer tube (24).
11. Housing according to claim 10, characterized in that the fixing groove (42) is formed directly in the wall of the outer tube (42) in a radially-raised, rib-like tube projection (44).
12. Housing according to any of claims 1 to 11, characterized in that the cylinder tube (3) is provided on at least one and expediently on both end faces with a cylinder cover (4, 5, 5') made of in particular unreinforced plastic material.
13. Housing according to claim 12, characterized in that the cylinder tube (3) is permanently joined to one or more of the cylinder covers (4, 5, 5') made of plastic material, for example by means of a snap or catch connection (28) or by means of a welded joint (35), in particular in the form of a friction welded joint, or by integral moulding wherein on the cylinder tube (3) side the outer tube (24) made of plastic material forms the connection partner.
14. Housing according to claim 12 or 13, characterized in that one or more cylinder covers made of plastic has a one-piece integral mounting section (47) for external fixing of the housing (2).

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