EP1415069A1

EP1415069A1 - Device for transforming a rotational movement into a backwards and forward movement

Info

Publication number: EP1415069A1
Application number: EP02707993A
Authority: EP
Inventors: Stefan Battlogg
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-08-06
Filing date: 2002-03-28
Publication date: 2004-05-06
Also published as: US20040154567A1; WO2003014535A1; US6951148B2

Abstract

A device for transforming a rotational movement into a backwards and forward movement, comprising a cam element (5) which is arranged on a driven carrier shaft (1) and provided with an eccentric control area (4), in addition to a cam follower (9) which can be displaced or pivoted by said cam element (5). The cam element (5) is rotationally mounted in a flexible encompassing element (6) which is movably connected to the cam follower (9) on a plane which is perpendicular to the axis of rotation (8) of the cam element (5). The flexible encompassing element (6) surrounds the eccentric control surface (4) of the cam element (5) and a non-driven bearing surface (3) for the cam follower (9).

Description

Device for converting a rotary movement into a reciprocating movement

The invention relates to a device for converting a rotary movement into a reciprocating movement, in particular cam control, valve train for internal combustion engines of motor vehicles or the like, with at least one cam element arranged on a driven carrier shaft and having an eccentric control surface and with a cam element displaceable by the cam element. or pivotable cam follower element, in particular a valve lifter or the like, the cam element being rotatably arranged in a flexible enclosing element which is movably connected to one end of the cam follower element in a plane perpendicular to the axis of rotation of the cam element.

Since conventional valves of internal combustion engines require return springs for the closure, which have to exert considerable forces, positive guides have also been proposed which require weaker return springs or make them unnecessary. A special embodiment of such a positive guidance can be found, for example, in DE 37 00 715 A, in which the cam element is loosely surrounded by a flexible enclosing element which is connected to the valve actuating element. The cam element therefore runs around in the enclosing element. Various further developments of this type of positive guidance are described in WO 01/12958 A and WO 01/12959 A. When using these enclosing elements, the friction occurs between the circumferential surface of the cam element and the inside surface of the enclosing element, and it has therefore also been proposed to introduce a friction-reducing medium via radial channels in the cam element between the circumferential surface and the enclosing element.

Since the encircling element is particularly exposed to relatively high tensile forces from the reciprocating cam follower element when the repulsion acceleration is braked, that part of the encircling element opposite the connection area is pressed firmly onto the circumference of the cam element. Conversely, the part of the area enclosing the connection area Enclosing element shortly before returning to the starting position exposed to correspondingly high compressive forces, since the return acceleration is braked, and pressed onto the circumference of the cam element. In both cases, outlet openings lying in these areas are sealed by the enclosing element, and a very high pressure would be required to supply the lubricant. For example, a pressure of 2 to 5 bar is present in conventional cylinder heads, and at least 10 times the pressure should be able to be applied in order to push the enclosing element away from the circumference and to allow the medium to escape. (The values in this example refer to oil lubrication). Only partial lubricant films are created and mixed friction occurs, the coefficient of friction of which does not become less than 0.1.

The invention has now set itself the task of significantly improving the friction conditions in a device of the type mentioned, and this is achieved in that the flexible enclosing element, the eccentric control surface of the

Cam element and a non-driven contact surface for that

Surrounds cam follower. A non-driven contact surface is primarily understood to mean a cylindrical contact surface fixed to the device, for example on a bearing element of the carrier shaft. In this way, depending on the shape of the cam, the contact surface between the

Cam element and the enclosing element in length by at least one

Third, with conventional cam shapes even up to two thirds can be reduced. Since that

Cam element is also narrower than the enclosing element - at least on one side, preferably on both sides adjoins the cam element in particular a cylindrical end region of a bearing element - the friction-generating contact surface is also narrower than in the conventional designs.

The non-driven contact surface can, however, also be formed on a ring or the like, for example rotatably mounted on the bearing element, so that a minimal back and forth rotation of the contact surface is possible, which changes due to the slightly alternating changing geometric relationships between the connection point of Enclosing element sets with the cam element and the wandering control surface. Although it is already known from WO 98/26 161 A to divide the control cam area into two components, namely the cam element and a bearing element, this is done there for reasons of easier manufacture and adjustment of the closed position stop, since no basic circle machining of a cam element is required is.

Further friction-reducing measures can be the arrangement of roller bearings between each bearing element and the carrier shaft and / or the cam element, and / or the arrangement of a rotatably mounted roller in the eccentric control surface of the cam element and / or the formation of feed channels for a friction-reducing medium, in particular lubricating oil, to the friction-generating contact surfaces.

In the cases mentioned above, in which high tensile or compressive forces occur, these are transferred directly to the bearing elements by the design according to the invention, so that the sliding or rolling bearings between the bearing elements and the carrier shaft are relieved. In order to relieve the load on the bearing of the cam follower element, it is provided in a further preferred embodiment that the end of the cam follower element connected to the enclosing element is guided in a guide fixed to the device.

The reduction in the friction-generating contact surfaces further reduces the amount of heat that is generated, the removal of which is facilitated if the standing base circle area is part of the camshaft bearing and can be connected directly to the housing, in particular the cylinder head, and reduces the need for lubricant.

The preferably cylindrical contact surface can furthermore also have a central flat point at which the enclosing element is slightly spaced, so that heat-related play compensation for the cam follower element is also provided in a simple manner. The cam element is limited to the eccentric area, i.e. the usual base circle area is not or only partially formed.

The positive guidance of the cam follower element eliminates the usual massive return springs, which must have conventional valve drives, for example. However, a small restoring force can be an advantage. In a preferred embodiment, in which the cam follower element is articulated on the enclosing element by means of a bearing pin, the restoring force can act on the bearing pin in that the bearing pin is acted on by an elastic element against the contact surface fixed to the device. For example, a leg spring or the like can be used to generate the restoring force, which is supported on the one hand on the bearing pin and on the other hand on the bearing element or the like. A preferred embodiment provides that the bearing pin has at least one exposed end area, and an elastically flexible band made of steel, rubber or the like is guided around the exposed end area and the bearing element.

The device according to the invention thus contains at least two closed belts or loops, namely the tensile enclosing element for the positive guidance of the cam follower element and the elastic band for resetting the cam follower element.

In a further preferred embodiment, the enclosing element is also formed by an elastic band, which is preferably provided with an expansion limiter, and cooperates with a cam element which can be radially retracted and extended on the carrier shaft in order to change the size of the cam stroke. In the case of valve drives, such devices are referred to as variable valve controls, the radial displaceability of the cam element being achievable by increasing control surfaces which are provided between the cam element and the driven carrier shaft if the carrier shaft is, for example, axially displaceable, or between the cam element and a control shaft are provided, which are rotatably arranged in the hollow cylindrical carrier shaft. In a further embodiment, the cam element can also be positively guided, for example by a crank mechanism or the like.

The invention will now be described in more detail with reference to the figure of the accompanying drawings.

Show it: 1 is an exploded view of the individual components of a first embodiment of a device according to the invention, FIG. 2 is a side view,

Fig. 3 is a section along the line III-III of Fig. 2 and Fig. 4 is a longitudinal section through the first embodiment.

Fig. 5 shows a longitudinal section through a second embodiment of an inventive

Contraption,

Fig. 6 shows a section along the line VI-VI of Fig. 5, Fig. 7 enlarges the control cam area of Fig. 5 and

Fig. 8 is an oblique view of the second embodiment.

9 is a side view of a third embodiment of the device according to the invention,

Fig. 10 is a section along the line X-X of Fig. 9 and

11 shows a longitudinal section through the third embodiment according to FIG. 9.

12 is an exploded view of the individual components of a fourth embodiment of the device according to the invention,

13 shows a longitudinal section through the fourth embodiment,

14 and 16 each enlarge the connection area between the enclosing element and the cam follower element and

15 is a section along the line XV-XV of FIG. 13th

17 shows an exploded view of the individual components of a fifth embodiment of the device according to the invention, FIG. 18 shows a longitudinal section through the fifth embodiment, the

Cam follower abuts the contact surface,

19 enlarges the connection area between the enclosing element and the successor element,

20 shows a section along the line XX-XX of FIG. 18, FIG. 21 shows a longitudinal section similar to FIG. 18, the cam element being rotated by 180 °,

22 enlarges the bearing area of the cam element from FIG. 21,

Fig. 23 is a section along the line XXIII-XXIII of Fig. 22 and

Fig. 24 is a schematic oblique view of the device. 25 is an exploded view of the individual components of a sixth embodiment of the device according to the invention,

26 shows a longitudinal section through the sixth embodiment, the cam follower resting on the contact surface, FIG. 27 enlarges the connection area between the enclosing element and the cam follower,

28 shows a section along the line XXVIII-XXVIII of FIG. 26,

29 shows a longitudinal section similar to FIG. 26, with the cam follower element being rotated through 180 °, FIG. 30 shows a section along the line XXX-XXX of FIG. 29 and FIG. 31 shows a side view of the sixth embodiment.

32 and 33 are longitudinal sections through a seventh embodiment of the device according to the invention, the cam follower in each case abutting the contact surface, FIG. 34 oblique views of the carrier shaft and the cam element in three different positions and

35 and 36 sections along the line XXXV-XXXV of Fig. 32 and the line XXXVI-XXXVI of Fig. 33th

37 and 38 are sections through an eighth embodiment of the device according to the invention, the cam follower in each case abutting the contact surface.

39 and 40 are schematic end views of a cam element positively guided by means of a crank mechanism in two different positions.

A device according to the invention for converting a rotary movement into a reciprocating, rectilinear or pivoting movement comprises a driven carrier shaft 1, on which a cam element 5 with an eccentric control surface 4 is fixed in a manner not shown. The eccentric control surface 4 reciprocates a cam follower element 9, which is held against it, in accordance with its guidance or mounting. The preferred application of the device is shown in all exemplary embodiments, namely as valve control of internal combustion engines. However, the use of such devices can also be used, for example, in cam controls of machine tools, in special gearboxes or the like, the cam follower element 9 shown in FIGS Embodiments forms a valve lifter, the application is designed accordingly.

A central hub-like area 16 of the cam element 5 is rotatably supported on one or both sides on or in a bearing element 10, on which an annular or sleeve-shaped end area 11 is formed with a particularly cylindrical outer surface. A flexible enclosing element 6, for example a fabric tape or the like, surrounds the eccentric control surface 4 of the cam element 5 and the outer surface of the end region 11 of each bearing element 10, and has a holder 12 on which the cam follower element 9 is arranged in an articulated manner. The hinge axis runs parallel to the axis of rotation 8 of the carrier shaft 1. The rotation of the cam element 5 leads to an oscillating movement of the enclosing element 6, which, however, due to its connection with the cam follower element 9, cannot twist, but is continuously lifted all around from the outer surface of the end region 11 becomes. The cam follower element 9 is transferred from a contact surface 3, in which the cam follower element 9 has the shortest distance to the axis of rotation 8, and which forms part of the outer surface of the end region 11, into a position at a maximum distance from the axis of rotation 8 when the maximum of the eccentric Control surface 4 of the cam element 5 is effective, and retracted into the basic position during further rotation. In the case of the valve train, the closed position is the basic position and the maximum removed position is the open position of the valve plate 13.

1 to 4 show a first embodiment, in which the bearing elements 10 are only shown schematically as a piece of cladding tube with end rings, which are fixed, for example, in holders fixed to the housing, or — as FIG. 8 shows — with corresponding ones

Fastening parts are provided. The cam element 5 has an eccentric

Control surface 4 bearing cam region, the axial extent of which is shorter around the two annular end regions 11 of the bearing elements 10 than its central region 16 fixed on the carrier shaft. The enclosing element 6 has approximately one

Width that corresponds to the axial extent of the central cam region 16, so that the enclosing element 6 surrounds part of the cylindrical peripheral surface of the two end regions 11 and the eccentric control surface 4 of the cam element 5. Since only the eccentric control surface 4 has to slide on the inner surface of the enclosing element 6, the friction-generating contact surface is smaller than half the inner surface of the enclosing element 6. As mentioned, this is connected in an articulated manner via its holder 12 to the cam follower element 9, so that between the enclosing element 6 and the cylindrical outer surface serving as contact surface 3 of the two end regions 11, which are fixed to the housing as parts of the bearing elements 10 there is no friction. The division into contact surfaces with friction and those without friction can be seen particularly well from FIG. 3, in which the cam element 5 is cut with the eccentric control surface 4, whereas the axially offset end region 11 can be seen in plan view.

5 to 8, the carrier shaft 1 is formed by a bundle of support rods 2, so that a simple positive connection between the carrier shaft 1 and the cam element 5 is given. The carrier shaft 1 is driven by a drive wheel, not shown, which, like the cam element 5, has a corresponding bore pattern in the center. The cam element 5 has a lateral annular groove in which the end region 11 of a bearing element 10 engages. A roller bearing 15, for example a needle bearing or the like, is inserted between the core region 16, as shown in FIG. 7 on an enlarged scale. Due to the interlocking of the end region 11 and the cam element 10, the entire width of the enclosing element 6 lies against the contact surface 3 of the end region 11 and surrounds the eccentric control region 4 of the cam element 5. As can be seen from the enlarged illustration in FIG. 7, the contact surface 3 has a central flattening 17, so that a play compensation, for example in the case of heat-related changes in length of the cam follower element 9, is possible. 8 shows the embodiment from the side facing away from the bearing element 10.

In the embodiment according to FIGS. 9 to 11, which largely corresponds to the embodiment according to FIGS. 1 to 4, two recesses are formed in the cam element 5 and the remaining central web receives a pin 14 on which a roller 7 can be rotated per recess by means of a roller bearing is mounted, the arrangement and the cam shape being chosen so that the peripheral surface of the two rollers 7 fall in the central region of the eccentric control surface 4. As can be seen above all from FIG. 10, only a short transition section 18 remains on both sides of the rollers 7, in which the peripheral surface of the cam element 5 comes into contact with the enclosing element 6. Since the rollers 7 roll in the encircling element 5 during the rotation of the cam element 5, the friction-generating contact surfaces are again significantly reduced. In this embodiment, too, it is of course possible to install a roller bearing 15 between the carrier shaft 1 and the core area 16 of the cam element 5.

12 to 16 show an embodiment in which two cam elements 5 are formed with a common central region 16, each cam element 5 having a radial recess 20 and forming a complete ring 22 in this region. The central region 16 of the cam elements 5 is connected in a rotationally fixed manner to the carrier shaft 1 and the two rings 22, which each hold a roller bearing 15, are rotatably mounted on the two tubular bearing elements 10. As can be seen from FIG. 14 or 16, an annular gap 23 remains between the carrier shaft 1 and the bearing elements 10, so that production inaccuracies of the carrier shaft 1 do not require any reworking. The recess 20 leaves a space for a guide sleeve 81 drawn up to the holder 12 between the closure element 6 and the cam follower element 9, which is limited to two diametrically opposed webs 83 of the cylinder head 80 and whose width corresponds to the recess 20. The two parts of the rotating cam element 5 rotate past the raised guide sleeve 81 for the cam follower element 9 on both sides. In this embodiment, the encircling element 6 is provided with a central cutout, which corresponds to the recess 20 or, as shown in FIG. 12, is formed from two loops which are held together by the holder 12 or the bearing pin 62 of the plunger head 61. The cam element 5 can have an edge shoulder in order to prevent the enclosing element 6 from slipping off. The bearing elements 10 are fixed by means of hold-down devices 84 on upstanding webs of the cylinder head 80.

17 to 24, an embodiment is shown in which a common cam element 5 is assigned to two cam follower elements 9. The cam element 5 shown in an oblique view in FIG. 17 therefore has a ring 22 at each end and a central region 16 with a five-sided opening. The cam element 5 is arranged in a torsion-proof manner on a five-sided carrier shaft 1, the bearing of which is carried out via the bearing elements 10 and via rings which are fixed or loosely arranged at their end regions 11, on which the two rings 22 of the cam element 5 are rotatably supported, in each case by means of a roller bearing 15 , The enclosing element 6 has no cutouts and has a plug opening in the holder 12 formed in a sleeve 19, into which a bearing pin 62 is inserted, which protrudes on both sides, and is connected to a plunger head 61 at each end. In this embodiment too, the guide 81 for each cam follower 9 is pulled up to the bearing sleeve 10.

The space between the two guides 81 is so large that the cam element 5 can rotate, with FIGS. 21 and 23 showing the position in which the valve plate 13 is most open from the valve seat.

This version also shows a possibility of supplying a friction-reducing medium, for example lubricating oil, to the individual bearing surfaces. For this purpose, the carrier shaft 1 has a central feed channel and radial outlet openings 25 which merge into bores 26 of the cam element 5. The bores 26 open into the contact area with the enclosing element 6 on the circumference of the cam element 5 and in the region of the roller bearings 15 (FIG. 22). A further bore 27 extends through the holder 12 to a bore 28 in the sleeve 19, in which the bearing pin 32 having a circumferential groove 29 is arranged. The bearing pin 62 is provided with an axial channel 30 which is connected to the circumferential groove 29 by a bore, not shown. The medium emerging from the channel 30 is distributed on the sliding surfaces of the guide sleeves 81 for the plunger head 62.

25 to 31 show a sixth exemplary embodiment, in which two cam elements 5 are again provided in the central region 16 and are surrounded by a common enclosing element 6. The central region 16 is provided with a non-circular bore 21 and arranged on the carrier shaft 1 in a rotationally fixed manner, the cross-sectional shape of which is composed of three more curved arches and three less curved arches, which alternate with one another. At the central area 16 two cylindrical extensions are formed, the outer

Have bearing surfaces, and are internally supported in two sleeve-shaped bearing elements 10. The bearing sleeves 10 are in two closed bearing rings 85 each

Cylinder block 80 fixed, on which in turn raised guide sleeves 81 are provided. In the holder 12 of the enclosing element 6, an extended bearing pin 62 is inserted, on which, similar to the embodiment according to FIG. 17, a tappet head 61 of a cam follower element 9 is rotatably mounted on both sides. The ends 63 of the bearing pin 62 each protrude through a slot 82 in the bearing rings 85 and are urged against the bearing sleeves 10 in the above part by a band made of rubber, a clip made of spring steel or another elastic element 31. The lateral slipping of the element 31 is prevented by a collar 64 (Fig. 27). As the comparison of FIGS. 26 and 29 as well as 28 and 30 shows, the elastic elements 31 are stretched by the cam element 5 during the downward movement of the cam follower elements 9, that is to say when the valves are opened, and generate a force that supports the return, which in some applications is not Can be an advantage. Substantially stronger return springs engaging directly on the cam follower elements 9 are, after all, dispensed with by the positive guidance of the enclosing element 6. Instead of the band shown, other spring devices, such as leg springs or the like, can also be provided.

25 and 27 in particular that the tappet head 61 has an undercut insertion groove for the tappet of the cam follower element 9. It can be inserted from the side and is thus rotatably mounted in the plunger head 61.

32 to 40 show designs which enable an adjustment of the cam stroke and can therefore be used above all as a variable valve control.

In the embodiment according to FIGS. 32 to 36, the carrier shaft 1 is arranged so as to be longitudinally displaceable in the bearing elements 10 and has a cutout 41 in each area in which a cam follower element 9 is to be actuated, which has a sloping surface 42 and lateral parallel flats is provided. A cam element 5, which has an approximately U-shaped cutout on the side opposite the eccentric control surface 4, is guided on the parallel flats so that it can be pushed out and pushed in vertically. 34 and 36 clearly show that the cam element 5 which does not protrude over the circumference of the bearing element 10 in a lowest position when the carrier shaft 1 is moved to the left of the inclined surface 42 rising in a wedge shape and transferred to the maximum extended position shown in FIG. 34 below or FIG. 35.

The rest of the construction corresponds essentially to that of FIG. 25, so that these details need not be repeated here. Only the enclosing element 6 is designed to be elastically stretchable, since, as can be seen above all from the comparison of FIGS. 35 and 36, it must lengthen and shorten.

A reversibly extendable enclosing element 6 has already been described in the aforementioned WO 01/12959 A, to which reference is made. The enclosing element 6 is, for example, a seamless loop which is produced from threads or fibers in a textile rounding technique. The encircling element preferably has threads made of a tensile-strength material that extend in the circumferential direction and that form an expansion limitation. A fabric-like loop can be provided with a friction-reducing coating at least in the area of the inwardly protruding elevations, which are formed by the crossing threads.

The elastic enclosing element 6 can dispense with the elastic elements 31 shown in FIGS. 32 and 33, since it likewise exerts a restoring force on the bearing pin 62. Due to the elasticity of the encircling element 6, it can be advantageous if it contains stiffeners in the transverse direction, that is to say in the axial direction of the carrier shaft, for example in the form of reinforcing ribs 43 which have inserted or glued-in pins. The cross stiffeners prevent the pulling in of unsupported parts of the enclosing element 6 in the region of the cam element 5.

37 and 38, a rotatable control shaft 44 is arranged in the carrier shaft 1 for the radial movement of the cam element 5, on which an eccentric, spirally rising control surface 49 is formed. The course of the adjustment of the cam element 5 can be seen from the comparison of the two FIGS. 37 and 38. In the extended position according to FIG. 37, the cam element 5 is held by the hook-like core area of the control shaft 34. If the control shaft 34 is rotated counterclockwise in the carrier shaft 31, the cam element 5 resting on the spiral control surface 49 migrates inside until the position without stroke according to FIG. 38 is reached. In this, the cam element 5 lies within the cylindrical outer surface of the bearing element 10 or the annular region 11 of the bearing element 10, so that the contracted enclosing element 6 lies all around on the annular region 11 and any friction is avoided, since the cam element 5 rotates without contact.

39 and 40 show an embodiment in which the cam element 5 is forcibly extended and retracted. A control shaft 44 in the interior of the carrier shaft 1 has a slot 45 in which a link 48 is rotatably mounted on a bearing pin 46. The second end of the link 48 is arranged on a bearing journal 47, which is mounted in the interior of the cam element 5, the cam element 5 being approximately U-shaped and extending in a guide of the carrier shaft 1 or a guide sleeve arranged on the carrier shaft 1. and is arranged insertable. The positive guidance thus represents a crank mechanism that can be rotated through an angle of approximately 120 °. FIG. 39 shows a partial stroke and FIG. 40 shows the full stroke of the cam element 5.

In the embodiments according to FIGS. 32 to 40, the enclosing element 6 forms on both sides a rectilinear bridging of the transition area between the non-rotatable contact surface 3 and the eccentric control surface 4, which changes when the stroke changes. 32 to 40 for the stroke adjustment of the cam element 5 can also be used if the contact surface 3 is provided on the driven carrier shaft 1 or on a part which rotates with the carrier shaft.

Claims

Patent claims:

1. Device for converting a rotary movement into a reciprocating movement, in particular cam control, valve train for internal combustion engines of motor vehicles or the like, with at least one cam element (5) arranged on a driven carrier shaft (1) and having an eccentric control surface (4) with a cam follower element (9) which can be displaced or pivoted by the cam element (5), in particular a valve tappet or the like, the cam element (5) being rotatably arranged in a flexible enclosing element (6) which is in a direction relative to the axis of rotation (8) of the cam element (5) vertical plane is movably connected to one end of the cam follower element (9), characterized in that the flexible enclosing element (6) the eccentric control surface (4) of the cam element (5) and a non-driven contact surface (3) for the

Surrounds cam follower (9).

2. Apparatus according to claim 1, characterized in that the contact surface (3) on a bearing element (10) of the carrier shaft (1) is provided on which the carrier shaft (1) and / or the cam element (5) is rotatably mounted.

3. Apparatus according to claim 1 or 2, characterized in that a roller bearing (15) is arranged between the bearing element (10) and the carrier shaft (1) and / or the cam element (5).

4. Apparatus according to claim 2 or 3, characterized in that the bearing element (10) has an annular end region (11), and the cam element (5) in the end region (11) has an inner part (16).

5. Device according to one of claims 1 to 4, characterized in that the end of the cam follower element (9) connected to the enclosing element (4) is guided in a guide (81) fixed to the device.

6. Device according to one of claims 1 to 5, characterized in that a roller bearing is arranged in the eccentric control surface (4) of the cam element (5).

7. The device according to claim 6, characterized in that at least one rotatably mounted roller (7) is provided as the rolling bearing.

8. Device according to one of claims 1 to 7, characterized in that the carrier shaft (1) and the cam element (5) supply channels (25, 26) for a friction-reducing medium to the bearing surfaces of the rolling bearing (15) and preferably also to the eccentric control surface (4).

9. Device according to one of claims 1 to 8, in which the cam follower (9) on the enclosing element (6) is articulated by means of a bearing pin (62), characterized in that the bearing pin (62) by an elastic element against the device-fixed contact surface ( 3) is applied.

10. The device according to claim 9, characterized in that the bearing pin (62) has at least one exposed end region, and an elastically flexible band (31) made of steel, rubber or the like. Around the exposed

End region and the bearing element (10) is guided.

11. Device according to one of claims 1 to 10, characterized in that the cam element (5) on the carrier shaft (1) is arranged radially extendable and retractable, and the enclosing element (6) is designed to be elastic.

12. The apparatus according to claim 11, characterized in that between the radially extendable and retractable cam element (5) and the carrier shaft (1) rising control surfaces (42) are formed.

13. The apparatus according to claim 11, characterized in that in the carrier shaft (1) a control shaft (44) is movable, and between the radially extendable and retractable cam element (5) and the control shaft (44) rising control surfaces (49) are formed ,

4. Device according to one of claims 11 to 13, characterized in that the radially extendable and retractable cam element (5) is positively guided.