ADJUSTMENT DRIVE FOR A STEERING COLUMN, MOTOR-ADJUSTABLE STEERING COLUMN FOR A MOTOR VEHICLE, AND METHOD FOR ADJUSTING A BEARING ASSEMBLY OF AN ADJUSTMENT DRIVE

Abstract

A motor adjustment drive for a vehicle steering column includes a threaded spindle with an axis. The threaded spindle engages a spindle nut. A drive unit and a gear wheel which is connected to the spindle nut or the threaded spindle for rotation therewith is driveable to rotate by the drive unit and is rotatably mounted in a bearing housing between two outer bearing rings that are axially supported at the bearing housing. The outer bearing rings each have, on their sides facing one another, a circumferential outer bearing face that is coaxial to the axis. Each outer bearing face lays opposite a bearing face embodied on the end side at the gear wheel. An outer bearing ring is axially resiliently supported at the bearing housing via an elastic element, which exerts an axial force that biases the two outer bearing rings toward each other.

Claims

1.-17. (canceled)

18. An adjustment drive for a steering column that is adjustable by motor for a motor vehicle, comprising: a spindle nut, a threaded spindle with an axis, said threaded spindle engaging in the spindle nut, a drive unit, and a gear wheel connected to the spindle nut or the threaded spindle for rotation therewith, the gear wheel configured to be rotated about the axis by the drive unit and which is rotatably mounted about the axis in a bearing housing in a bearing arrangement between two outer bearing rings that are axially supported at the bearing housing, wherein the outer bearing rings each have, on their sides facing one another, a circumferential outer bearing face that is coaxial to the axis, each said outer bearing face positioned opposite a bearing face formed on the end side at the gear wheel, wherein at least one of the outer bearing rings is supported in an axially resilient manner at the bearing housing by way of an elastic preloading element configured to exert a preloading force that axially biases the two outer bearing rings against one another.

19. The adjustment drive of claim 18 wherein the preloading element comprises a ring-shaped spring element.

20. The adjustment drive of claim 18 wherein the preloading element is supported at a securing element that is connected to the bearing housing.

21. The adjustment drive of claim 18 wherein the preloading element comprises a securing element.

22. The adjustment drive of claim 21 wherein the securing element comprises fastening means for affixment inside the receiving space.

23. The adjustment drive of claim 18 wherein the preloading element is an integral securing element.

24. The adjustment drive of claim 18 comprising rolling bodies positioned between the gear wheel and the outer bearing rings.

25. The adjustment drive of claim 18 wherein one of the outer bearing rings is supported at the bearing housing at a counter bearing in an axially rigid manner.

26. The adjustment drive of claim 18 wherein the bearing housing comprises a hollow cylindrical receiving space in which the outer bearing rings and the gear wheel are arranged coaxially in relation to the axis.

27. A steering column that is adjustable by motor for a motor vehicle, comprising a carrying unit configured to attach to a vehicle body, an actuating unit held by the carrying unit, a steering spindle rotatably mounted about a longitudinal axis in the carrying unit, and an adjustment drive connected to the carrying unit and to the actuating unit, via which the actuating unit is adjustable relative to the carrying unit, wherein the adjustment drive comprises: a spindle nut, a threaded spindle with an axis, said threaded spindle engaging in the spindle nut, a drive unit, and a gear wheel connected to the spindle nut or the threaded spindle for rotation therewith, the gear wheel configured to be rotated about the axis by the drive unit and which is rotatably mounted about the axis in a bearing housing in a bearing arrangement between two outer bearing rings that are axially supported at the bearing housing, wherein the outer bearing rings each have, on their sides facing one another, a circumferential outer bearing face that is coaxial to the axis, each said outer bearing face positioned opposite a bearing face formed on the end side at the gear wheel, wherein at least one of the outer bearing rings is supported in an axially resilient manner at the bearing housing by way of an elastic preloading element configured to exert a preloading force that axially biases the two outer bearing rings against one another.

28. A method for setting a bearing arrangement of an adjustment drive for a steering column that is adjustable by motor for a motor vehicle, comprising a threaded spindle with an axis, said threaded spindle engaging in a spindle nut, and a gear wheel which is connected to the spindle nut or the threaded spindle for rotation therewith and which is rotatably mounted about the axis in a bearing housing in a bearing arrangement between two outer bearing rings that are axially supported at the bearing housing, wherein an outer bearing ring is supported in an axially resilient manner at the bearing housing by way of an elastic preloading element, the method comprising: applying an axial preloading force to the preloading element, applying a load moment to the gear wheel and measuring the load moment, measuring a bearing state variable that is correlated with the load moment, comparing the measured bearing state variable with a predetermined state target value, when the measured bearing state variable deviates from the state target value: modifying the axial preloading force, and when the measured bearing state variable attains the state target value: affixing the preloading element in an axial preloading position at the bearing housing and completing the setting process.

29. The method of claim 28, further comprising: applying a breakaway torque as load moment for rotational driving of the gear wheel and measuring the breakaway torque in the process as a correlating bearing state variable, comparing the measured breakaway torque as a bearing state variable with a predetermined torque target value as a state target value, when the measured breakaway torque as a bearing state variable is smaller than the predetermined torque target value as a state target value: increasing the axial preloading force, and when the breakaway torque as a bearing state variable attains the predetermined torque target value as a state target value: affixing the preloading element in an axial preloading position at the bearing housing and completing the setting process.

30. The method of claim 28, further comprising: applying a tilting moment as a load moment across the axis on the gear wheel and measuring a displacement of the gear wheel relative to the bearing housing in the process as a correlating bearing state variable, comparing the measured displacement as a bearing state variable with a predetermined stiffness threshold as a state target value, when the measured displacement as a bearing state variable is greater than the predetermined stiffness threshold as a state target value: increasing the axial preloading force, and when the measured displacement as a bearing state variable attains the predetermined stiffness threshold as a state target value: affixing the preloading element in an axial preloading position at the bearing housing and completing the setting process.

31. The method of claim 28 wherein the preloading force is measured when the preloading force is applied.

32. The method of claim 28 wherein the preloading force is exerted on a securing element that is arranged in front of an outer bearing ring.

33. The method of claim 32 wherein the securing element is movable relative to the bearing housing in the direction of the preloading force and embodied to affix itself at the bearing housing against the preloading force.

34. A method for setting a bearing arrangement of an adjustment drive for a steering column that is adjustable by motor for a motor vehicle, comprising a threaded spindle with an axis, said threaded spindle engaging in a spindle nut, and a gear wheel which is connected to the spindle nut or the threaded spindle for rotation therewith and which is rotatably mounted about the axis in a bearing housing in a bearing arrangement between two outer bearing rings that are axially supported at the bearing housing, wherein an outer bearing ring is supported in an axially resilient manner at the bearing housing by way of an elastic preloading element, comprising the steps of: applying an axial preloading force to the preloading element, measuring the axial preloading force, comparing the measured preloading force with a predetermined target preloading force, when the measured preloading force deviates from the predetermined target preloading force: modifying the axial preloading force, and when the measured preloading force attains the predetermined target preloading force: affixing the preloading element in an axial preloading position at the bearing housing and completing the setting process.

Description

DESCRIPTION OF THE DRAWINGS

[0105] Below, advantageous embodiments of the invention are described in more detail on the basis of the drawings. In detail:

[0106] FIG. 1 shows a schematic perspective view of a steering column according to the invention,

[0107] FIG. 2 shows a further perspective view of the steering column according to the invention as per FIG. 1, from a different viewing angle,

[0108] FIG. 3 shows a longitudinal section along the threaded spindle axis through an adjustment device of a steering column as per FIGS. 1 and 2 in a perspective view,

[0109] FIG. 4 shows a longitudinal section as in FIG. 3 in a side view,

[0110] FIG. 5 shows a pulled-apart illustration of the spindle drive as per FIGS. 3 and 4,

[0111] FIG. 6 shows a longitudinal section through the bearing arrangement of a spindle drive as in FIG. 4 when setting the bearing arrangement,

[0112] FIG. 7 shows a second embodiment of an adjustment device in a view as in FIG. 4,

[0113] FIG. 8 shows a third embodiment of an adjustment device in a view as in FIG. 4,

[0114] FIG. 9 shows a fourth embodiment of an adjustment device in a view as in FIG. 4,

[0115] FIG. 10 shows a fifth embodiment of an adjustment device in a view as in FIG. 4.

EMBODIMENTS OF THE INVENTION

[0116] In the various figures, the same parts are always provided with the same designations, and are therefore in each case also generally only referred to or mentioned once.

[0117] FIG. 1 shows, from obliquely top right, a steering column 1 according to the invention in a schematic perspective view of the rear end in relation to the direction of travel of a vehicle (not illustrated here), where the steering wheel (not illustrated here) is held in the operating region. FIG. 2 shows a steering column 1 in a view from the opposite side, i.e., as seen from top right.

[0118] The steering column 1 comprising a carrying unit 2, which is embodied as a console that comprises fastening means 21 in the form of fastening bores for attachment to a vehicle body (not illustrated here). The carrying unit 2 holds an actuating unit 3, which is received in a casing unit 4—which is also referred to as a guide box or box-section swinging fork.

[0119] The actuating unit 3 has a steering column tube 31, in which a steering spindle 32 is mounted to be rotatable about a longitudinal axis L, said steering spindle extending axially in the longitudinal direction, i.e., in the direction of the longitudinal axis L. Formed at the rear end of the steering spindle 32 is a fastening portion 33, a steering wheel (not illustrated here) being attachable thereon.

[0120] In order to realize a longitudinal adjustment, the actuating unit 3 is received in the casing unit 4 so as to be telescopically displaceable in the direction of the longitudinal axis L in order to be able to position the steering wheel that is connected to the steering spindle 32 forward and backward in the longitudinal direction relative to the carrying unit 2, as indicated by the double-headed arrow parallel to the longitudinal axis L.

[0121] The casing unit 4 is mounted in a pivot bearing 22 at the carrying unit 2 in a manner to be pivotable about a horizontal pivot axis S that is transverse to the longitudinal axis L. In the rear region, the casing unit 4 is connected to the carrying unit 2 via an actuating lever 41. As a result of a rotational movement of the actuating lever 41 by means of an illustrated actuating drive 6 (see FIG. 2), the casing unit 4 can be pivoted relative to the carrying unit 2 about the pivot axis S that lies horizontally in the installed state, as a result of which it is possible to adjust a steering wheel, attached to the fastening portion 33, in the height direction H, as indicated by the double-headed arrow.

[0122] A first adjustment drive 5 for adjusting the longitudinal position of the actuating unit 3 relative to the casing unit 4 in the direction of the longitudinal axis L comprises a spindle drive with a spindle nut 51 with a female thread 74 extending along an axis G, a threaded spindle 52 engaging therein; i.e., the male thread of said threaded spindle is screwed into the corresponding female thread 74 of the spindle nut 51. The threaded spindle axis of the threaded spindle 52 is identical to the axis G and extends substantially parallel to the longitudinal axis L.

[0123] The spindle nut 51 is mounted in a bearing housing 53 so as to be rotatable about the axis G, said bearing housing being securely connected to the casing unit 4. In the direction of the axis G, the spindle nut 51 is axially supported at the casing unit 4 via the bearing housing 53, as will still be explained in more detail below.

[0124] With a fastening element 54 embodied at the rear end thereof, the threaded spindle 52 is connected to the actuating unit 3 via a transmission element 34, to be precise in a manner fixed in the direction of the axis G or the longitudinal axis L and stationary in respect of rotation about the axis G. As a result of the spindle nut 51 that is driveable to rotate and the threaded spindle 52 that is stationary in respect of rotation, a so-called plunger spindle drive is realized.

[0125] The transmission element 34 extends from the actuating unit 3 through a slot-shaped passage opening 42 in the casing unit 4. In order to adjust the steering column 1 in the longitudinal direction, the transmission element 34 can be moved freely along in the passage opening 42 in the longitudinal direction.

[0126] The adjustment drive 5 has an electric servomotor 55, by means of which the spindle nut 51 is driveable to rotate in respect of the axis G relative to the stationary threaded spindle 52. As a result, it is possible—depending on the direction of rotation of the servomotor 55—to displace the threaded spindle 52 in the direction of the axis G in translational fashion relative to the spindle nut 51 such that, accordingly, the actuating device 3 connected to the threaded spindle 52 is adjusted in the direction of the longitudinal axis L relative to the casing unit 4 connected to the spindle nut 51. The drive of the spindle nut 51 and the support of the spindle nut 51 in the direction of the axis G at the casing unit 4 will still be explained in detail further down.

[0127] In FIG. 2, which shows a perspective view of the steering column 1 from the side lying at the back in FIG. 1, it is possible to recognize how a second adjustment drive 6 for adjusting the height direction H is attached to the steering column 1. This adjustment drive 6 comprises a spindle nut 61, in the female thread 74 of which a threaded spindle 62 engages along an axis G. The threaded spindle 62 is mounted so as to rotatable about the axis G in a bearing housing 63, which is fastened at the casing unit 4, axially supported, in the direction of the axis G, at the casing unit 4 and driveable, optionally in both directions of rotation, by an electric servomotor 65 so as to be rotatable about the axis G. This will still be explained in detail further down.

[0128] The spindle nut 61 is attached in a stationary manner in respect of a rotation about the axis G at one end of the two-arm actuating lever 41, which is mounted at the carrying unit 22 so as to be are rotatable about a pivot bearing 23, the other arm of said actuating lever being connected, with the other end thereof, to the casing unit 4.

[0129] By rotating the threaded spindle 61, it is possible—depending on the direction of rotation of the servomotor 65—to displace the spindle nut 61 in translational fashion relative to the threaded spindle 62 in the direction of the axis G such that, accordingly, the casing unit 4, which is connected to the spindle nut 41 via the actuating lever 41, together with the adjusting device 3 received therein can be adjusted up or down in the height direction H relative to the carrying unit 2, as indicated by the double-headed arrow. The drive of the threaded spindle 62 and the support of the threaded spindle 62 in the direction of the axis G at the casing unit 4 will still be explained in detail below.

[0130] FIG. 3 and FIG. 4 present a longitudinal section through the bearing housing 63 of the adjustment drive 6 along the axis G in different views.

[0131] A gear wheel 7 designed according to the invention is fastened to the threaded spindle 62 for rotation therewith in respect of the axis G. The gearwheel 7 has a core element 71 made out of plastics, which is preferably produced from a thermoplastic such as PP, POM or the like as a plastics injection moulded part. At its outer circumference, the gearwheel 7 comprises at the core element 71 a circumferential toothing 72 that is coaxial to the axis G, said toothing being embodied as a worm toothing in the illustrated example such that the gearwheel 7 forms a worm wheel. A worm 66 that is driveable to rotate by the servomotor 65 engages in the toothing 72.

[0132] In the region of a central connecting portion 73, which forms a connecting piece, the core element 71 is connected to the threaded spindle 62 for rotation therewith. By way of example, the connection can be embodied as a substance-to-substance bond by virtue of the core element 71 being moulded onto the threaded spindle 62 in the process of injection moulding to the threaded spindle 62. In addition or as an alternative thereto, an interlocking and/or any other type of fastening may be provided.

[0133] Bearing rings 8 of the gear wheel 7 are fixedly connected to the core element 71. Each bearing ring 8 has a ring-shaped bearing face 81 that is coaxial to the axis G and embodied as the ball-bearing raceway. As seen from the core element 71, the two bearing faces 81 run to the outside, in an end-side conical manner. Expressed differently, the ball-bearing raceways are at an angle to the axis G.

[0134] Axially, the bearing rings 8 comprise support portions 82 that are directed against one another in the direction of the axis G, said support portions directly lying against one another in the shown example such that the bearing rings 8 are directly supported against one another in the direction of the axis G. In particular, no plastics material of the core element 71 is situated between the support portions 82 of the bearing rings 8 that are in contact with one another.

[0135] The bearing rings 8 are preferably embodied as sheet metal shaped parts, particularly preferably as press/punch parts made of sheet steel. For the purposes of connection to the gear wheel 7, the plastics of the core element 71 is injection moulded onto the bearing rings 8 and the latter is thus embedded into the core material 71 in a substance-to-substance bonded and interlocking manner, apart from the bearing faces 81 that are exposed to the outside on the end side. Optionally, provision can be made of a fixing element 83, at which the two bearing rings 8 are positioned relative to one another and held during the insert moulding with plastics such that they lie against one another axially in the direction of the axis G. However, the fixing element 83 can also be omitted. Alternatively, it is also conceivable to directly connect the bearing rings 8 prior to insert moulding, for example by point welding or the like.

[0136] The bearing faces 81 from the inner rings of a rolling-element bearing arrangement 9, which comprises ball bearings 91 that are held in a rotatable manner in a ball-bearing cage 92 and that are arranged so is to roll in the axial bearing gap between said ball-bearing raceways of the bearing faces 81 and corresponding ball-bearing raceways in outer bearing rings 93. As seen from the gear wheel 7, the outer bearing rings 93 are supported axially to the outside on both end sides by way of elastic spring elements 94, which form preloading elements, elastomeric rubber rings in the shown example, against axial counter bearings in the form of securing rings 95, which in turn are connected in a manner stationary in the axial direction of the axis G to the bearing housing 53, for example by wedging, caulking or jamming. The spring element 94 likewise can be embodied as a wave spring or disk spring.

[0137] In the embodiment illustrated in FIG. 4, spring elements 94 that are embodied as preloading elements are arranged in both end sides of the gear wheel 7, said spring elements being supported axially at the bearing housing 63 by the two securing rings 94 and being elastically braced axially. Here, the spring force acts as a preloading force F on the bearing faces 81 via the outer bearing rings 93 and the ball bearings 91, and so the gearwheel 7 is preloaded between the rolling element bearing arrangements 9 axially.

[0138] For affixing purposes, the securing rings 95 can have at their outer circumference fastening means 951, for example partly or completely circumferential cutting edges that protrude to the outside and that bury themselves in an interlocking plastic manner into the inner wall of the bearing housing 63. Preferably, the cutting edges are inclined against the axis G such that the fastening means 951 have a barb-like embodiment. As a result, the securing rings 95 can be moved axially only in the direction against the gear wheel 7 in the bearing housing 63. As a result of the preloading force F that acts in the assembled state, the securing rings 95 are loaded oppositely, as a result of which the fastening means 951 cling to the inner wall of the bearing housing 63 as a result of their barb-like embodiment. Expressed differently, the securing rings 95 have a self-affixing embodiment.

[0139] An axial preloading force F is applied during the assembly of the rolling-element bearing arrangement 9 for the purposes of avoiding bearing play in the direction of the axis G. It is applied by the securing rings 95, the spring elements 94 embodied as preloading elements and the ball bearings 91 on the bearing faces 81 of the bearing rings 8 on the bearing rings 8, as indicated by force arrows in FIG. 4. The preloading force F is maintained during the entire service life by the elastic spring elements 94 that act as preloading elements. As a result, the two bearing rings 8 are pressed against one another axially, wherein the force F acting on the bearing faces 81 during operation is transmitted completely in the power flow through the bearing rings 8. What is advantageous here, in particular, is that the plastics material of the core element 71 is not situated in the power flow between the bearing rings 8, i.e., it is not subjected to pressure. This unloading ensures that the plastics material is not plastically deformed by flowing.

[0140] FIG. 5 shows the individual parts of the gear wheel 7 and of the rolling-element bearing arrangement 9 pulled apart in an exploded illustration in the direction of the axis G.

[0141] FIG. 6 shows an adjustment drive 6 during setting in a setting device, which comprises an axially movable compression column 96 and a counter bearing 97 that is stationary relative thereto. By means of a source of force (not illustrated here), the compression column 96 can have applied a preloading force F thereto, the latter consequently serving as pressing-in force.

[0142] In order to set the rolling-element bearing arrangements 9, the one securing element 95, which lies to the left in FIG. 6, is axially supported at the counter bearing 97 while the other securing ring 95, situated at the right in the drawing, is pressed against the gear wheel 7 in the axial direction with the preloading force F by way of the compression column 96. Here, the securing ring 95 is initially displaced as far as against the spring element 94 by way of the above-described barb-shaped embodiment of the fastening means 951. Upon contact, the spring element 94 is axially compressed by the preloading force F and the preloading force F is introduced into the rolling-element bearing arrangement.

[0143] The magnitude of the preloading force F with which the gear wheel 7 is preloaded in the rolling-element bearing arrangement 9 can be effected depending on a breakaway torque M that has to be applied to turn the gear wheel 7. To this end, the gear wheel 7 is driven to rotate, for example by the servomotor 66 of the drive unit. Alternatively, as per FIG. 3, 4, 6, 7 or 8, in the case of a rotational spindle drive, in which the threaded spindle 62 is connected to the gear wheel 7 for rotation therewith, the drive can be brought about by an external adjustment drive (not illustrated here), which drives the threaded spindle 62 to rotate.

[0144] The breakaway torque M can be measured by means of suitable sensors, for example by way of torque sensors, or by way of a motor current of the servomotor 65 or an external adjustment drive.

[0145] During the rotating drive, the axial preloading force F is applied by the compression column 96 on the bearing arrangement proceeding from a predetermined start value and said preloading force is increased continuously or step-by-step and preferably measured by means of suitable force sensors in the process. As a result, there is an increase in the bearing friction, and the measured breakaway torque M, which correlates to the preloading force F, likewise increases.

[0146] The measured breakaway torque M is compared, preferably automatically, to a predetermined torque target value.

[0147] If the measured breakaway torque M is less than the predetermined torque target value, this means that the bearing play is still too large, or the preload is still too small, and so the required rigidity of the bearing arrangement and play-free running under load conditions during operation are not yet ensured. In this case, the preloading force F is increased, and the measured breakaway torque M is measured again and compared to the torque target value.

[0148] The aforementioned steps are run through until the measured breakaway torque M as bearing state variable attains the predetermined torque target value as state target value. In the axial position attained in the process, in the preloading position, the securing ring 95 and hence the spring element 94 are affixed relative to the bearing housing 63. The axial affixment can be effected by virtue of the barb-shaped fastening means 951 being buried in the inner wall of the bearing housing 63 in an interlocking plastic manner as a result of the preloading force F exerted by the spring element 94 and then securing this in the preloaded position during unloading or retraction of the compression column 96. As an alternative or in addition thereto, an affixment can be brought about by substance-to-substance bonding, for example welding or the like, or by means of additionally inserted fastening means.

[0149] As an alternative or in addition thereto, the preload can be set depending on the bending stiffness of the adjustment drive 6. To this end, the bearing arrangement is subjected to bending by a tilt moment K, which is introduced transversely into the threaded spindle 62. The radial deflection x occurring in the process, which is measured by means of a path measuring device 99, is a measure for the stiffness. It is dependent on the preloading force F, with a high preloading force F correlating with a low deflection x and, accordingly, a high stiffness

[0150] The deflection x, which serves as a correlating bearing state variable, corresponds to a displacement of the gear wheel 7, for example a tilt in the bearing housing 63, which is produced by the tilt moment that serves as load moment. The measured deflection x is compared to a reference value of a maximum admissible displacement that is assigned to a stiffness threshold corresponding to the state target value.

[0151] The required stiffness is not provided for as long as the measured deflection x is greater than a predetermined stiffness threshold. In this case, the preloading force F is increased until the measured deflection x is less than or equal to the stiffness threshold within predetermined tolerance ranges.

[0152] Setting the preload can be effected by regulating the breakaway torque M or the tilt moment K, or else by taking account of both load moments M and K.

[0153] Alternatively, the preload can be set by regulating the applied and measured preloading force; if the latter attains a predetermined threshold, the so-called target preloading force, the preloading element is affixed and setting the preloading force is completed.

[0154] FIG. 7 shows a second embodiment in which the outer bearing ring 93 lying to the left in the drawing is axially supported against an axial counter bearing 67 that is formed by a moulding of the bearing housing 63 embodied as a shoulder, instead of the one securing ring 95. Moreover, this embodiment has only one spring element 94, which is embodied as an O-ring made of rubber-elastic material, said spring element being arranged to the right in the drawing between the outer bearing ring 93 and the securing ring 95.

[0155] FIG. 8 shows a third embodiment which has two securing rings 95, like the embodiment as per FIG. 6, but only one spring element 94, which is embodied as an O-ring or similar elastic element, like in FIG. 7.

[0156] In respect of the bearing of the gearwheel 7, the fourth embodiment as per FIG. 9 has a similar design, in principle, as the embodiment presented in FIGS. 4 and 6. However, in contrast thereto, this is a plunger spindle drive, in which the threaded spindle 62 engages in a thread in the spindle nut 61 that is connected to the gearwheel 7, i.e., it is not connected to the gearwheel 7 for rotation therewith.

[0157] The fifth embodiment as per FIG. 10 is distinguished by virtue of at least one of the securing rings 95, or else both securing rings 95, inherently having an axial spring-elastic embodiment. As it were, the preloading element according to the invention has an integrated embodiment in at least one securing ring 95.

[0158] The embodiments shown in FIGS. 7, 8, 9 and 10 can be set as described in relation to FIG. 6.