DE8915484U1 - Piston-cylinder unit with anti-twisting piston rod - Google Patents

Abstract

Actuator unit (10) which can be acted upon by compressed air and whose piston rod (12) is secured against rotation by a plurality of ball tracks being provided at least in the longitudinal area (36) passing through the allocated cylinder lid (32), which ball tracks are distributed over the periphery of the piston rod and run in the longitudinal direction of the piston rod. A bearing component (46), through which the piston rod (12) passes, is fastened to the outside of the cylinder lid (32) removed from the piston, which bearing component (46) is in turn provided with ball tracks in alignment with the ball tracks of the piston rod (12), rows of bearing balls (42) being provided in the intermediate space between the outer surface of the piston rod (12) and the inner surface of the bearing component (46), which bearing balls (42) roll on the ball tracks of the piston rod (12) on the one hand and the ball tracks of the bearing component (46) on the other hand. In the connecting area between the cylinder lid (32) and the bearing component (46), a lip sealing ring (60) having a passage opening corresponding in complementary fashion to the cross-sectional shape of the piston rod (12) is provided in an encircling location groove (62) surrounding the piston rod (12) at a radial distance, the sealing lips (68; 70) of which lip sealing ring (60) are directed into the interior of the actuator (10). <IMAGE>

Description

The invention relates to a piston-cylinder unit that can be pressurized with compressed air, with a piston rod that has a cross-section of circular cross-section at least in the length region that passes through the associated cylinder cover and is sealed against the escape of compressed air by a seal. has a different cross-section, to which a bearing component is assigned which is connected to the cylinder in a rotationally fixed manner and through which the piston rod passes, which guides the piston rod in a longitudinally displaceable manner but is secured against rotation.

The piston rods of today's pressure-operated piston cylinder units, i.e. pneumatic or hydraulic cylinders, are at least in the length that passes over the associated cylinder cover during the working stroke. section has a cylindrical £■*%·■:* , which enables the gap required between the piston rod and the passage opening in the cylinder cover to be sealed against pressure loss and leakage of the pressure medium by means of conventional ring seals - be they O-rings or lip seals. The cylindrical shape of the piston rod is the The end of the piston rod exiting the cylinder is not secured against twisting, especially since the cylinder, which is firmly connected to the piston rod, has a concentric circular boundary which extends in the circumferential direction within the cylinder is also not secured against rotation. If such piston-cylinder units are used in constructions in which they have to push and pull back components which, during the stroke, are in a position relative to the longitudinal center axis of the piston-cylinder unit, must be kept in an alignment that is precisely secured against twisting, additional guides must be provided to secure the piston rod against twisting. Regardless of whether the guides are arranged in series or parallel to the piston rod and connected to it.

3g bound guides, the overall length or width of the piston-cylinder unit increases considerably. In addition, the structure of the piston-cylinder unit

more complex and the number of components required as well as the effort required for their processing and assembly increases significantly compared to a simple piston-cylinder unit that is not secured against rotation.

From DE-OS 34 35 964 a proposal for the design of a piston-cylinder unit of the type mentioned at the beginning is known, in which the piston rod - elliptical in cross-section - is secured against rotation by a guide bush with a complementary (elliptical) opening cross-section inserted in the cylinder cover through which the piston rod passes. However, the flat contact of the piston rod in the guide bush creates friction (frictional friction) that is particularly effective at the beginning of the piston stroke, i.e. when the cylinder is actuated from a rest position, which can lead to a jerky movement of the piston rod, which is undesirable for many applications. Nothing can be inferred from this publication about the design and arrangement of the seal that prevents the pressure medium from escaping from the piston-cylinder unit.

The invention is based on the object of creating a piston-cylinder unit in which a self-guide is integrated which only slightly increases the external dimensions of the piston-cylinder unit and secures the piston rod against rotation, whereby the rotation lock does not result in stiffness or the loss of compressed air.

This object is achieved according to the invention in that the piston rod in the area passing through the associated cylinder head is formed over the largest part of the circumference by surface sections with a circular arc shape in cross-section and the same circular radius, which are arranged at equal angular intervals from radially protruding or recessed ball tracks running in the longitudinal direction.

I I ■ I · t» II*

sections, that on the outside of the cylinder cover facing away from the piston, a bearing component through which the piston rod passes is fastened, which in turn has ball races in alignment with the longitudinal ball races, wherein rows of bearing balls rolling on the ball races of the piston rod on the one hand and the ball races of the bearing component on the other hand are arranged in the space between the outer surface of the piston rod and the inner surface of the bearing component, and that in the connection area between the cylinder cover and the bearing component, in a circumferential receiving groove surrounding the piston rod at a radial distance, a lip sealing ring with a passage opening complementary to the cross-sectional shape of the piston rod is provided, the sealing lips of which are directed towards the interior of the piston-cylinder unit. The piston rod is therefore basically designed similarly to a longitudinally displaceable shaft secured against rotation by a linear motion bearing with ball guides, but the problem of sealing the piston rod against the pressure medium, which does not occur with such shafts, is eliminated.

by a special lip sealing ring with a passage opening adapted to the cross-sectional shape of the piston rod.

In a preferred embodiment of the invention, the piston rod is provided with a number of longitudinal wedges offset at equal angular intervals, projecting radially and running in the working stroke direction, each of which is provided with the ball raceways on both sides in the transition area to the adjoining surface section with a circular cross-section, the bearing component being provided with longitudinal grooves in alignment with the longitudinal wedges, in which the ball raceways of the bearing component are provided. This embodiment with a linear motion bearing known as the "ball spline"

The corresponding anti-rotation device has proven to be effective. When three longitudinal wedges running in the circumferential direction are arranged on the piston rod, a total of six rows of balls aligned around the circumference ensure easy longitudinal movement on the one hand, while on the other hand angular play between the piston rod and the cylinder is prevented even when high moments are applied.

Alternatively, the design can also be such that the piston rod is provided with a number of radially recessed longitudinal grooves that form the ball raceways and are offset at equal angular intervals. The longitudinal grooves that form the ball raceways are assigned to these grooves at a corresponding angular offset in the inner surface of the bearing component. This simplified embodiment is particularly suitable in cases in which comparatively small moments occur that act in the circumferential direction and attempt to twist the piston rod.

In an advantageous development of the invention - again in accordance with the linear motion bearings mentioned - deeper return longitudinal grooves are provided in the inner surface of the bearing component, offset in the circumferential direction from the ball races, which are connected at both ends to the adjacent ends of the respective associated ball race, so that the bearing balls arriving at one end of the associated ball race in the bearing component during a stroke of the piston rod are displaced into the return longitudinal grooves as the piston rod movement continues and are returned via these in the opposite direction to the stroke direction of the piston rod.

In this case, it is useful if the rows of bearing balls rolling on the ball raceways and returning in the return longitudinal grooves are assigned a cage that holds the bearing balls in the bearing component, which cage is located in the area opposite the ball raceways of the piston rod.

&bull;".J

has a slot through which the bearing balls can only partially pass, while in the area of the longitudinal grooves of the rear

■ is closed towards the piston rod. This means

■ 5 dismantling of the bearing component from the piston rod is possible .

' without the balls escaping from the bearing component

: can.

' If the piston rod has projecting longitudinal keys,

the lip sealing ring provided according to the invention is preferably designed in such a way that it has a circularly limited outer diameter which is larger than the diameter measured over the front surface of the longitudinal wedges of the piston rod, and on the edge of which a cylindrical see inner surface of the receiving groove sealing circumferential

elastic sealing lip is provided, and that along the j inner passage opening, which is shaped complementarily to the cross-sectional shape of the piston rod, a further completely closed and uninterruptedly on the outer surface the piston rod is provided with an elastic sealing lip, whereby between the two sealing lips pointing in the same direction a circumferential pressure chamber is formed which is open towards the inside of the cylinder and whose radial dimensions measured between the outer and the inner sealing lip sions in the areas associated with the longitudinal wedges of the piston rod are smaller than in the areas in between in the circumferential direction.

If, however, the piston rod is provided with a number of longitudinal grooves forming the cooling raceways, the lip sealing ring is designed in such a way that it has a circularly limited outer diameter that is larger than the maximum diameter of the piston rod, and on the edge of which a circumferential elastic sealing lip is provided that seals against the cylindrical inner surface of the receiving groove. and along the ä&r -Suerachnittsfora of the piston rod complementary correspondingly shaped inner passage opening

In the sealing arrangement, a further elastic sealing lip is provided which is closed all around and seals continuously on the outer surface of the piston rod, whereby a circumferential pressure chamber which is open towards the inside of the cylinder is formed between the two sealing lips pointing in the same direction, the radial dimensions of which, measured between the outer and inner sealing lips, are larger in the areas associated with the longitudinal grooves of the piston rod than in the areas lying between them in the circumferential direction.

The invention is explained in more detail in the following description of two embodiments in conjunction with the drawing, which shows:

Fig. 1 is a longitudinal section through a first

Embodiment of a piston-cylinder unit designed as a pneumatic cylinder, the piston rod of which is secured against rotation in the manner according to the invention;

Fig. 2 is a sectional view, seen in the direction of arrows 2-2 in Fig. 1;

Fig. 3 is a plan view of the sealing element for the

Lip sealing ring provided on the piston rod, seen in the direction of arrow" 3 in Fig. 4;

Fig. 4 is a sectional view of the lip seal ring, seen in the direction of arrows 4-4 in Fig.

3;

Fig. 5 an enlarged detail of the in Fig. 1

within the dash-dotted circle 5 part of the piston-cylinder-sine

Ness;

Fig. 6 a longitudinal center section through a second embodiment of a piston-cylinder unit designed as a pneumatic cylinder, the piston rod of which is secured against rotation in the manner according to the invention

is secured;

Fig. 7 is a sectional view taken in the direction of arrows 7-7 in Figure 6;

Fig. 8 is a plan view of the lip sealing ring provided for sealing the piston rod , seen in the direction of arrow 8 in Figure 9;

Fig. 9 is a sectional view of the lip seal ring, seen in the direction of arrows 9-9 in Figure 8; and

Fig. 10 an enlarged detail of the in Figure 6

The part of the piston-cylinder unit located within the dash-dotted circle.

The one shown in Figure 1, in its entirety with 10

The piston-cylinder unit referred to is a double-acting pneumatic cylinder with end-position cushioning that can be pressurized with compressed air as the working medium, the pneumatic cylinder known in terms of its basic structure of this Type, so that its construction does not need to be described in detail, especially since the protection against twisting of its piston rod sought according to the invention also applies to other types of construction, e.g. single-acting and undamped pneumatic cylinders as well as to pneumatic cylinders with a

Hydraulic fluid as working medium

Piston-cylinder units can be implemented in the same way.

The piston-cylinder unit 10 therefore has the actual cylinder head 14, which is closed at one end and at the other end by a central bore opening IS with a circular cross-section for the pistons. rod 12 provided cylinder cover IS closed Cylinder 20. In the cylindrical bore 22, the cylinder 20 is a piston 26 which divides the bore into two variable-size working spaces 24, 24' and seals against the inner wall bordering the bore. The piston 26, which is assembled from several parts not described individually, is penetrated centrally by the cylindrical inner end 28 of the piston rod 12, which is reduced in diameter, and is held in place by a sleeve 30 screwed onto the free end at the piston rod end. held.

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

The piston rod 12 has in the area 36 adjoining the reduced diameter cylindrical end section 28 - deviating from the usual circular cross-sectional shape - the cross-section shown in Fig. 2, in which from a basically circular base cross-section, each offset by 120° in the circumferential direction Longitudinal wedges 38 project radially, which in rounded transition areas 40 transition into the circular cross-sectional shaft area form ball raceways for rows of bearings

Balls 42 (Fig. 1) are formed, each of which has a &iacgr;

row on each side of each longitudinal wedge. On the other hand , each row of balls runs in a longitudinal groove·, 44 in a ';

Surrounding bearing component 46, which is centered in the cylinder cover 18 and secured to the cylinder cover against;,

rotation is secured. This screw connection ■-;'

* in the case shown - with fastening screws 48, i

&bull;· 1 rf ·

of which only one is shown in Fig. 1, and which at the same time also serve to fasten the piston-cylinder unit 10 as a whole in a through hole 50 in a support plate 52 forming part of a larger construction, of which only a part - hatched with dash-dot lines - is shown in Fig. 1,,

In Fig. 1, the piston rod 12 is shown in the position completely retracted into the cylinder unit IC, in which the working chamber 24 has its maximum size and the working chamber 24' has its minimum size. The length of the section 36 of the piston rod 12 provided with the longitudinal groove 38 is selected such that it still extends through the bearing component 46 and emerges slightly from the bearing component 46 at the end on the left in Fig. 1. The section 36 is then connected to the outside by a cylindrical piston rod section 54, on which a component (not shown) can be mounted that can be moved back and forth by the piston rod 12 depending on the pressurization of the working spaces 24, 24' with compressed air, and which is assumed not to change its relative rotational position with respect to the longitudinal center axis of the piston-cylinder unit 10 because, for example, it may have projecting pins that must engage in associated matching bores in the fully extended end position of the piston rod 12.

The rotational locking of the piston rod 12 is therefore carried out by the rows of balls which support the longitudinal wedges 38 laterally and which in turn are supported in the longitudinal grooves 44 in the bearing component 46. During the working stroke, the bearing balls 42 roll on the associated raceways of the section 36 and the bearing component 46 and thus also change their position in the longitudinal direction. In order to make this possible and to still allow the balls to bear over the entire length of the bearing component 46, deeper return longitudinal grooves 56 are provided, offset in the circumferential direction from the raceways formed in the bearing component 46.

provided, which are connected to one another at their ends via circular arc-shaped connecting sections (not shown), so that during the rolling movement, bearing balls 42 emerging from the longitudinal grooves 44 at one end pass over the respective connecting section into the associated return longitudinal groove and are returned in this in the opposite rolling direction to the other end of the longitudinal groove 44. These return longitudinal grooves 56 are dimensioned such that they completely accommodate the bearing balls, which therefore do not roll on the piston rod section 36 in these areas. A suitably designed cage 58 made of plastic holds the bearing balls 42 in such a way that they can partially pass through a slot provided in the area of the longitudinal grooves 44 to the ball tracks on the piston rod section 36, while it closes off the deeper return longitudinal grooves 56 against the piston rod. Even when the piston rod 12 is completely pulled out of the bearing component 46, the bearing balls 42 are therefore held back in the bearing component 46 by the cage 58, so that when disassembling or assembling the piston-cylinder unit 10, there is no risk of losing individual bearing balls 42. To the extent described so far, the anti-twisting device of the piston rod 12 corresponds to the linear motion bearings supplied under the name "Ball Spline" by THK Europe GmbH, Düsseldorf, which therefore enable a centrally guided and anti-twisting movement of a shaft in a bearing component, but do not allow axial sealing against gaseous or liquid pressure media.

In order to ensure this sealing, which is essential when used to prevent a piston rod from rotating, the lip seal 60 shown separately in Fig. 3 and 4 is arranged in a circumferential, cylindrical receiving groove 62 (Fig. 1 and 5) at the base of the groove, which seals on the one hand in the cylinder cover 18 and on the other hand on the outer surface of the piston rod section 36.

&bull; · . · ic·

For this purpose, the lip sealing ring has an outer circular and an inner radial section 64^ ^u Ser, which is limited according to the cross-sectional shape of the piston rod section 36 on the working chamber 24 of the piston

The support disk is clamped between a radial surface of the cylinder cover 18 and the bearing component 46. A circumferential sealing lip 68, which is placed on the outside of the cylinder section 64 and points in the direction of the working chamber 24, rests under pre-tension in a sealing manner on the circumferential or bottom surface of the receiving groove 62 and a sealing lip 70, which follows the outline of the inner boundary, rests on the piston rod section 36. The lip sealing ring 60 made of elastomeric plastic thus forms a circumferential pressure chamber 72 that is open towards the working chamber 24, in which the pressure prevailing in the pressure chamber 24 builds up and additionally presses the sealing lips 68, 70 onto the associated sealing surfaces. However, a strong pressure of the sealing lip 70 onto the piston rod section 36 only occurs when the working chamber 24 is pressurized with compressed air, i.e. 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 towards the free end of the sealing lip, whereby the wear on the sealing lip is relatively low, provided that the surface of the piston rod section 36 is sufficiently smooth. On the other hand, if the working chamber 24' is pressurized with compressed air in order to extend the piston rod 12, the pressure chamber 24 is vented, i.e. there is no overpressure exerted on the sealing lip 70 with additional pressure on the surface of the piston rod. In this respect, too, there is no risk of premature wear of the sealing lip.

In Figures 6 to 10, a piston arrangement which differs from the one described above in connection with Figures 1 to 5 is shown.

Cylinder unit 10 modified piston-cylinder unit 10' is shown, which, however, only differs in relation to the cross-sectional shape - which deviates from the circular cross-section - of the length region of the piston-cylinder unit 10 passing through the cylinder cover 18.

g rod 12 and the resulting different arrangement of the ball races on the piston rod as well as a correspondingly modified shape of the lip seal ring from the piston-cylinder unit 10. To avoid unnecessary repetition, only the modifications mentioned are described below, while it is otherwise sufficient to refer to the preceding description of the piston-cylinder unit 10, especially since functionally identical parts of the two embodiments in the drawing figures 1 to 5 on the one hand and 6 to 10 on the other hand are provided with the same reference numerals.

A significant difference between the piston-cylinder unit 10' and the piston-cylinder unit 10 is that instead of the longitudinal wedges 38 of the piston rod of the first embodiment, circular-arc-shaped concave longitudinal grooves 39 (Figures 6 and 7) are provided in the cross-section _here , which form the ball tracks on the piston rod side. The longitudinal region 36' (Figure 7) of the piston rod 12 provided with these ball tracks accordingly has a slightly larger diameter than the region 36 of the piston rod 12 of the piston-cylinder unit 10. Accordingly, the sealing lip 70' of the lip sealing ring 60 (Figures 8, 9 and 10) sealing on the piston rod also has a cross-sectional shape complementary to the region 36'.

3Q tär corresponding course.

Otherwise, the two embodiments 10 and 10' are largely identical, whereby the design of the piston-cylinder unit 10 is basically suitable for securing the piston rod against higher moments that tend to twist it, while the design according to the piston-cylinder unit 10' of the

Lip sealing ring 60' has a less complex and therefore easier to manufacture shape.

Claims (7)

!■Ill· ·· ■■· ·· ·· "Protection claims 1. Piston-cylinder unit that can be pressurized with compressed air, with a piston rod that has a cross-section that differs from a circular cross-section at least in the length range that passes through the associated cylinder cover and is sealed against the escape of compressed air by a seal, to which a bearing component that is connected to the cylinder in a rotationally fixed manner and through which the piston rod passes is assigned, which guides the piston rod so that it can move longitudinally but is secured against rotation, characterized, that the piston rod (12) in the area (36; 36') passing through the associated cylinder cover (la) is formed over the major part of the circumference by surface sections with a circular arc in cross section and the same circular radius. which are arranged at equal angular intervals from radial protruding or recessed sections forming longitudinally extending ball raceways (40; 39), dsS on the piston-walled outside of the cylinder cover (18) a bearing component (46) is fixed through which the piston rod (12) passes, which in turn has ball tracks (44) in alignment with the longitudinal ball tracks (40; 39), wherein in the space between the outer surface of the piston rod (12) and the 'Zc. .-surface of the Rows of bearing balls (42) rolling on the ball tracks (40; 39) of the piston rod on the one hand and the ball tracks (44) of the bearing component (46) on the other hand are arranged in the intermediate space of the bearing component (46), and that in the connection area between the cylinder cover (18) and the bearing component (46) in a circumferential receiving groove (62) surrounding the piston rod at a radial distance a lip sealing ring (60) with one of the cross-sectional shapes &bull;2 a passage opening complementary to the piston rod is provided, the sealing lips (68; 70; 70') of which are directed towards the interior of the piston-cylinder unit (10; 10').
5 2. Piston-cylinder unit according to claim 1, characterized in that the piston rod (12) is provided with a number of longitudinal wedges (38) offset at regular angular intervals , projecting radially and running in the working stroke direction , which are each provided with the ball raceways (40) on both sides in the transition area to the adjoining surface section with a circular cross-section, and that the bearing component (46) is provided with longitudinal grooves in alignment with the longitudinal wedges, iis which the Ball raceways (44) of the bearing component are formed. 3. Piston-cylinder unit according to claim 1, characterized in that the piston rod (12) is provided with a number of radially recessed grooves offset at equal angular intervals. ten, which form the ball raceways (39) is provided with longitudinal grooves to which are assigned, at a corresponding angular offset in the inner surface of the bearing component (46), the longitudinal grooves forming the ball raceways (44) of the bearing component. 4. Piston-cylinder unit according to one of claims 1 to 3, characterized in that deeper return longitudinal grooves (56) are provided in the inner surface of the bearing component (46) offset in the circumferential direction to the ball raceways, which are connected at their two ends to the adjacent ends of the respectively associated ball raceway (44), so that the bearing balls (42) arriving at one end of the associated ball raceway in the bearing component (46) during a stroke of the piston rod (12) are displaced into the return longitudinal grooves (56) as the piston rod movement continues and are returned via these against the stroke direction of the piston rod. &bull;&bull;■j ■ .-■ 5. Piston-cylinder unit according to claim 4, characterized in that the rows of bearing balls (42) rolling on the ball raceways (40; 44; 39) and guided back in the return longitudinal grooves (56) are assigned a cage {58} which holds the bearing balls in the bearing component (45), which has a slot in the area opposite the ball raceways of the piston rod {12} through which the bearing balls (42) can only partially pass, while in the area of the return longitudinal grooves (56) it is largely closed towards the piston rod (12). 6. Piston-cylinder unit according to claim 2, characterized in that the lip sealing ring (60) has a circularly limited outer diameter which is larger than the across the end faces of the longitudinal wedges of the piston rod (12) measured diameter, and on the edge of which a circumferential elastic sealing lip (68) is provided which seals against the cylindrical inner surface of the receiving groove (62), and that along the cross-sectional shape of the piston rod (12) complementary, correspondingly shaped inner passage opening, a further elastic sealing lip (70) is provided which is closed all around and seals continuously on the outer surface of the piston rod, wherein between the two sealing lips (68; 70) pointing in the same direction, a circumferential pressure chamber (72) open towards the inside of the cylinder: is formed, the radial dimensions of which measured between the outer and the inner sealing lip (68; 70) are smaller in the areas assigned to the longitudinal wedges (38) of the piston rod than in the circumferential direction areas in between. 7. Piston-cylinder unit according to claim 3, characterized in that the lip sealing ring (60') has a circularly limited outer diameter which is larger than the Maximum diameter of the piston rod (12) and whose edge has a circumferential elastic sealing lip sealing the cylindrical inner surface of the receiving groove (62) : .A (68) is provided, and that along the inner passage opening, which is shaped complementarily to the cross-sectional shape of the piston rod (12), a further elastic sealing lip [70'] is provided which is closed all around and seals continuously on the outer surface of the piston rod, wherein between the two sealing lips (68; 70') pointing in the same direction, a pressure chamber (72) is formed which is open towards the interior of the cylinder, the radial dimensions of which, measured between the outer and inner sealing lips, are larger in the areas assigned to the longitudinal grooves (39) (piston rod (22)) than in the areas lying between them in the circumferential direction.