Actuator with a non-rotatable piston rod

The invention relates to a druckmittelbeaufschlagbare piston-cylinder unit having a piston rod which at least in the the associated cylinder cover sealed by a seal against the escape of pressure medium passing through length region having a deviating from the circular cross-section cross-section, the one associated with the cylinder, penetrated by the piston rod associated bearing component which performs the piston rod for longitudinal displacement, the piston rod is in the the associated cylinder cover region passing through the largest part of the circumference of circular cross-sectional surface sections formed with the same radius, the forming at regular angular intervals of extending longitudinally ball raceways sections are interrupted , and is fixed to the cylinder cover of the penetrated by the piston rod bearing component, which in turn comprises in alignment with the longitudinally extending ball races ball tracks, and in the existing between the outer surface of the piston rod and the inner surface of the bearing component gap rows of the ball races of the piston rod on the one hand and the ball races of the bearing component rolling bearing balls are arranged on the other, and being provided in the cylinder cover in a surrounding the piston rod with radial clearance groove a sealing ring having a cross-sectional shape of the piston rod corresponding complementary passage opening

The piston rod of manufactured today druckmittelbeaufschlagbaren piston-cylinder units, that is pneumatic or hydraulic cylinders, have at least in the during the working stroke of the associated cylinder cover traversed forming longitudinal section generally cylindrical in shape, which the sealing of the required between the piston rod and of the passage opening in the cylinder cover gap against pressure loss and discharge of the pressure medium by means of conventional ring seals - there are O-rings or lip seals - allows. Due to the cylindrical shape of the piston rod emerging from the cylinder end of the piston rod is not secured against rotation, especially since the cylinder is firmly connected to the piston rod has a concentric circular boundary, which is also not secured in the circumferential direction within the cylinder against rotation. If such piston-cylinder units are used in structures in which they must advance and retreat components which must be maintained during the stroke in relation to the longitudinal central axis of the piston-cylinder unit against rotation exactly secure alignment, additional guides Müsen be provided securing the piston rod against rotation. Regardless of whether they are in series or parallel arrangements provided to the piston rod and connected to their guides, the length or width of the piston-cylinder unit increased significantly. Moreover, the construction of the piston-cylinder unit complex and the number of components required and the cost of its processing and assembly is increased as compared to a secured not against rotation simple piston-cylinder unit significantly.

From DE-A-3435 964, a proposal for the design of a piston-cylinder unit of the aforementioned kind is known in which the - in cross section, for example elliptical piston rod by an inserted in the penetrated by the piston rod cylinder cover guide bush with complementary (elliptical ) opening cross section is secured against rotation. By planar juxtaposition of the piston rod in the guide bush but creates a especially at the beginning of the piston stroke, ie upon actuation of the cylinder from the rest position effective friction (Ruhreibung), which may result in a jerky movement of the piston rod, which is undesirable for many applications. About the design and arrangement of the outlet of the pressure medium from the piston-cylinder unit preventing seal this publication is not removable.

From US-A-3,994,539 a piston-cylinder unit of the type mentioned is known, which basically circular cross-section shaped piston rod may be provided on opposite sides with sharpened flats. The document can not be removed if these flats only serve as raceways for the longitudinal ball bearing, the piston rod leading in the housing, or whether they should also bring about a rotation of the piston rod in conjunction with a complementary through hole of the cylinder cover or the outer housing of the longitudinal ball bearings.

The invention is based on the object to provide a piston-cylinder unit in which a, the outer dimensions of the piston-cylinder unit at most slightly magnified, the piston rod against rotation locking self guide is integrated, the rotation is no friction or loss has compressed air to a row.

This object is achieved in that the bearing member is rotatably mounted on the piston facing away from the outside of the cylinder cover arranged so that the ball raceways are arc-shaped concave in cross-section, and that the sealing ring in the connecting area between the cylinder cover (18) and the bearing component (46) and as lip seal ring is formed, the sealing lips are directed into the interior of the piston-cylinder unit. The piston rod is therefore basically similar to a formed by a linear-motion bearings with ball bearings against rotation secured longitudinally displaceably guided wave, but that does not occur in such waves problem of sealing the piston rod against the built-up by the pressure medium in the interior of the piston-cylinder unit pressure by a special lip seal ring with the cross-sectional shape of the piston rod adapted through-opening is achieved.

In a preferred embodiment of the invention the piston rod with a number of is staggered at regular angular intervals, radially projecting and provided in the working stroke direction extending lengthwise wedges, which are respectively provided on both sides in the transition zone to adjoining, circular in cross-sectional area portion with the ball raceways, the bearing component into alignment is provided on the longitudinal wedges with grooves in which the ball raceways of the bearing component are provided. This configuration with the under the name "Ball Spline" become known linear motion bearings corresponding rotation has proven itself. In the arrangement of three runs in the circumferential direction of the longitudinal splines on the piston rod provide a total of six rows of circumferentially oriented balls on the one hand a slight longitudinal displacement, on the other hand, an angle play between the piston rod and the cylinder at high acting moments is prevented.

Alternatively, the embodiment also be such that the piston rod with a number of staggered at regular angular intervals, radially depressed, the ball raceways forming longitudinal grooves is provided, where the ball tracks forming longitudinal grooves are associated in a corresponding angular displacement in the inner surface of the bearing component. This simplified embodiment is particularly useful in cases where relatively small force acting in the circumferential direction and to rotate the piston rod trying moments occur.

In an advantageous embodiment of the invention are - again in accordance with the aforementioned linear motion bearings-circumferentially to the ball raceways displaced deeper feedback longitudinal grooves in the inner surface of the bearing component provided, which are connected at both ends to the adjacent ends of the respective associated ball raceway, so that with a stroke of the piston rod arriving at one end of the associated ball raceway in the bearing component bearing balls displaced in the return-grooves in the continuation of the piston rod movement and returned against the stroke direction of the piston rod on this.

It is advantageous when the rolling on the ball raceways and recirculated in the recirculation grooves rows of bearing balls is associated with a bearing-balls in the bearing member holder Direction cage in the fields of the ball raceways of the piston rod lying opposite each have a slot , through which the bearing balls can pass only partially, while it is closed in the area of ​​return-grooves respectively towards the piston rod. Thus disassembly of the bearing part of the piston rod is possible without the balls to escape from the bearing component.

If the piston rod has projecting longitudinal wedges, the inventively provided lip seal ring is preferably designed such that it has a circularly limited outer diameter that is greater than the over the end face of the longitudinal splines of the piston rod measured diameter, and at its edge a to the cylindrical inner surface the receiving groove sealing peripheral elastic sealing lip is provided, and that along which the cross-sectional shape of the piston rod complementary correspondingly shaped inner passage opening a further closed all round and continuous sealing on the outer surface of the piston rod elastic sealing lip is provided, pointing in the same direction between the two sealing lips, a peripheral , is formed to the cylinder interior is open towards the pressure chamber, which measured between the outer and the inner sealing lip radial dimensions in the areas of the longitudinal splines of the piston rod assigned are lower than in the intermediate circumferential areas.

When the piston rod, however, is provided with a number of the ball tracks forming longitudinal grooves, the lip seal ring is so formed that it has a circularly limited outer diameter that is larger than the maximum diameter of the piston rod , and at its edge a cylindrical at the inner surface of the receiving groove is sealing peripheral elastic sealing lip is provided, and along which the cross-sectional shape of the piston rod complementary correspondingly shaped inner passage opening is further closed all round and continuously provided on the outer surface of the piston rod sealing elastic sealing lip, pointing in the same direction between the two sealing lips, a peripheral , is formed to the cylinder interior is open towards the pressure chamber, which measured between the outer and the inner sealing lip radial dimensions in the areas of the longitudinal grooves of the piston rod assigned are greater than in the intermediate circumferential areas.

The invention is explained in more detail in conjunction with the drawings in the following description of two embodiments, specifically:<ul><li>1 shows a longitudinal central section through a first embodiment of a formed as a pneumatic cylinder piston-cylinder unit, the piston rod is secured in the inventive manner against rotation.</li><li>Fig. 2 is a sectional view seen in the direction of arrows 2-2 in Fig. 1;</li><li>Figure 3 is a plan view of the envisaged for sealing of the piston rod lip sealing ring, viewed in the direction of the arrow 3 in Fig. 4.</li><li>Figure 4 is a sectional view of the lip sealing ring, viewed in the direction of arrows 4-4 in FIG. 3. FIG.</li><li>Figure 5 shows an enlarged detail of Figure 1 located in inside the dash-dotted circle 5 part of the piston-cylinder unit..; </li><li>6 is a longitudinal cross-section through a second embodiment of a formed as a pneumatic cylinder piston-cylinder unit, the piston rod is secured in the inventive manner against rotation.</li><li>Fig. 7 is a sectional view seen in the direction of arrows 7-7 in Figure 6;</li><li>Figure 8 is a plan view of the envisaged for sealing of the piston rod lip sealing ring, viewed in the direction of the arrow 8 in FIG. 9;</li><li>Figure 9 is a sectional view of the lip sealing ring, viewed in the direction of the arrows 9-9 in FIG. 8; and</li><li>FIG. 10 is an enlarged detail of the lying in Figure 6 within the dashed circle 10 portion of the piston-cylinder unit.</li></ul>

The shown in Figure 1, designated in its entirety with 10 piston-cylinder unit is acted upon by compressed air as the working medium double-acting pneumatic cylinders with cushioning, which corresponds with respect to its basic structure known pneumatic cylinder of this kind, so that its construction so far not described in detail must be, especially since the invention intended to prevent distortion of its piston rod 12 with other types, such as single-acting and non-damped pneumatic cylinders in the same way can be realized as well as in by a hydraulic fluid as the working fluid actuatable piston-cylinder units.

The piston-cylinder unit 10 thus comprises the actual, at one end by a closed cylinder cover 14 and at the other end sealed by a provided with a circular cross-section central through hole 16 for the piston rod 12 cylinder cover 18 cylinders 20th In the cylindrical bore 22 of the cylinder bore into two variable size work spaces 24, 24 'sectioning and the hole inner wall defining a sealing piston 26 is slidably mounted. The assembled from multiple, not described in detail parts piston 26 is centrally the piston rod passes through the reduced diameter cylindrical inner end 28 12 and held by a nut screwed onto the free end of the sleeve 30 on the piston rod end.

The measures provided in the cylinder covers 14 and 18 compressed air ports 32, 34 are indicated by dashed lines in Fig. 1 only.

The piston rod 12 has in the reduced to the diameter, cylindrical end portion 28 adjoining region 36 - in deviation from the conventional circular cross-sectional shape - to be seen in Figure 2 cross-section, in which a generally circular basic cross section at 120 ° circumferentially offset longitudinal wedges each. 38 radially protrude, which in rounded merging into the circular cross-section shaped waveband transition regions 40 ball raceways for rows of bearing balls 42 (FIG. 1) forming, of which so one row each longitudinal wedge on each side. On the other hand runs every ball series in each of the longitudinal groove 44 in a surrounding bearing part 46, which is centered in the cylinder cover 18 mounted and screwed secured with the cylinder cover against rotation. This fitting is carried out - in the case shown - with mounting screws 48, of which FIG 1 only one is shown, and which serve simultaneously to the piston-cylinder unit 10 of forming a through hole 50 in a part of a larger construction support plate. to secure 52 of the in Figure 1, only one -. dash-dotted hatched - portion is shown.

In Fig. 1, the piston rod 12 is shown in the retracted completely into the piston-cylinder unit 10 position in which the working chamber 24 its maximum and the working chamber 24 'has its minimum size. The length of the provided with the longitudinal splines 38 section 36 of the piston rod 12 is chosen such that it extends even by the bearing component 46 passes and something comes out of that shown in Fig. 1 left-most end of the bearing component 46. The portion 36 still closes the outside then a cylindrical piston rod section 54 to, on the one of the piston rod 12, depending on the loading of the working spaces 24, 24 'with compressed air toward or her to be moved - component is mounted, from - not shown Assume the that he may its relative rotational position with respect to the longitudinal center axis of the piston-cylinder unit 10 does not change, because it may have, for example, projecting pins which have 12 engage in the associated mating holes in the fully extended end position of the piston rod.

The rotation of the piston rod 12 thus occurs through the longitudinal wedges 38 laterally supporting and in turn supported in the longitudinal grooves 44 in the bearing component 46 Ball series. With each stroke, the bearing balls roll 42 onto the associated raceways of section 36 and the bearing part 46 and thus also change their position in the longitudinal direction. To make this possible, and to bring the balls anyway over the entire length of the bearing component 46 for supporting, are those formed in the bearing component 46 tracks are circumferentially offset lower return-grooves 56 provided at their ends not shown arcuate connecting portions with each other are such that when contouring at one end of the longitudinal grooves 44 exiting bearing balls 42 transgressed on the respective connecting portion in the associated feedback longitudinal groove and be returned to this in the opposite direction of rolling to the other end of the longitudinal groove 44th This return-grooves 56 are dimensioned so as to completely accommodate the bearing balls, so do not roll in these areas on the piston rod portion 36th A suitably designed cage 58 of plastic holds the bearing balls 42 so that it partially by a respective prescribed therein slot can pass on the piston rod portion 36 in the longitudinal grooves 44 to the ball raceways, while the lower return-grooves 56 against the piston rod closes. Even when completely pulled out from the storage device 46 piston rod 12, the bearing balls 42 are thus retained by the cage 58 in the bearing part 46, so that thus during disassembly or assembly of the piston-cylinder unit 10 is not the risk of loss of individual bearing balls 42 there. In so far described corresponds to the scope, the rotation of the piston rod 12 delivered under the name "Ball Spline" from the company THK Europe GmbH, Dusseldorf linear motion bearings, thus allowing a centrally managed and secured against twisting motion of a shaft in a bearing component, but no allow axial seal against gaseous or liquid pressure medium.

In order to ensure this when used for anti-rotation of a piston rod indispensable seal, according to the invention which are arranged separately in Fig. 3 and 4 illustrated lip seal 60 in a circumferential, cylindrical at the bottom of the groove accommodating groove 62 (Fig. 1 and 5) which on the one hand in the cylinder cover 18 and on the other hand seals on the outer surface of the piston rod portion 36th

For this purpose, the lip seal ring has an outer annular and an inner corresponding to the cross sectional shape of the piston rod portion 36 of limited radial portion 64 on the on the working space 24 of the piston-cylinder unit the opposite side of a metallic support disc 66 is supported in the receiving groove. The support disk is held clamped between a radial surface of the cylinder cover 18 and the bearing component 46th A at the outer periphery of the radial portion 64 is set, pointing in the direction of the working space 24 encircling sealing lip 68 is biased sealingly against the circumferential or bottom surface of the receiving groove 62 and one of the contour shape of the inner boundary following sealing lip 70 on the piston rod portion 36. The lip seal ring made of elastomeric plastic 60 thus forms an open towards the working space 24 circulating pressure chamber 72 in which builds the respectively prevailing in the pressure chamber 24 pressure and the sealing lips 68, 70 in addition presses against the associated sealing surfaces. A strong pressing of the sealing lip 70 on the piston rod portion 36 is performed but then only if the working chamber 24 is pressurized with compressed air, ie, when the piston rod is retracted into the interior of the piston-cylinder unit. The relative movement between the section 36 and the sealing lip 70 is then directed in the direction of the free end of the sealing lip, whereby the wear is relatively low, provided that the surface of the piston rod portion 36 is performed with sufficient smoothness. On the other hand, the working chamber 24 'is pressurized with compressed air to extend the piston rod 12, the pressure chamber 24 is vented, that is, there is no, the sealing lip 70 with additional pressure on the surface of the piston rod abutting pressure. Even so far is a premature wear of the sealing lip is not to be feared.

In the figures 6 to 10 one described with respect to the above in connection with Figures 1 to 5 the piston-cylinder unit 10 is modified piston-cylinder unit 10 'is shown, but only with respect to the - of the cross-sectional shape - different from the circular cross-section cylinder cover 18 traversing length range of the piston rod 12 and the resulting different arrangement of the ball tracks on the piston rod and a correspondingly changed form of the lip seal ring is different from the piston-cylinder unit 10th To avoid unnecessary repetition, therefore the mentioned modifications will be described below, while it is sufficient for the rest, to refer to the previous description of the piston-cylinder unit 10, especially functionally identical parts of the two embodiments in the figures 1 to 5 on the one hand and 6 to 10 On the other hand provided with the same reference numerals.

A major difference of the piston-cylinder unit 10 'in comparison with the piston-cylinder unit 10 is that instead of the longitudinal splines 38 of the piston rod 12 of the first embodiment here in cross section arcuate concave grooves 39 (Figures 6 and 7) are provided, forming the piston rod side ball raceways. The length range marked with these ball raceways 36 '(Fig. 7) of the piston rod 12 accordingly has a slightly larger diameter than the portion 36 of the piston rod 12 of the piston-cylinder unit 10. Accordingly, the sealing on the piston rod sealing lip 70' of the lip sealing ring 60 (figures 8, 9 and 10) and one of the cross-sectional shape of the area 36 'complementary corresponding course.

Incidentally, if the two embodiments 10 and 10 'is largely in line with the decisions taken at the piston-cylinder unit 10 embodiment is basically suitable for the rotation of the piston rod against higher, turning it examined moments, on the other hand in the design of the piston cylinder unit 10 'of the lip seal ring 60' has a less complex and therefore easier in the manufacturing mold.