U.S. patent application number 12/453010 was filed with the patent office on 2009-10-29 for arrangement for automatic running gap control on a two or multi-stage turbine.
Invention is credited to Peter Broadhead, Harald Schiebold, Thomas Wunderlich.
Application Number | 20090269190 12/453010 |
Document ID | / |
Family ID | 34854112 |
Filed Date | 2009-10-29 |
United States Patent
Application |
20090269190 |
Kind Code |
A1 |
Wunderlich; Thomas ; et
al. |
October 29, 2009 |
Arrangement for automatic running gap control on a two or
multi-stage turbine
Abstract
On a two or multi-stage turbine, expansion rings are provided in
all stages at the sides of the rotors for passive, continuous
running gap control whose thermal expansion and contraction
behavior corresponds to that of the rotors and which are connected
to radially moveable upstream and downstream stator vanes (5, 7).
The downstream stator vanes are assembled to the upstream stator
vanes via a bridge (16; 17, 18) which is axially and
circumferentially fixed and located flexibly in the radial
direction on the outer casing (10) of the turbine. The stator vanes
(6) arranged between the rotor disks are integrally connected to
the bridge or, as separate components, held axially and
circumferentially on the bridge to take up rolling and tilting
moments.
Inventors: |
Wunderlich; Thomas; (Berlin,
DE) ; Schiebold; Harald; (Berlin, DE) ;
Broadhead; Peter; (Derby, GB) |
Correspondence
Address: |
SHUTTLEWORTH & INGERSOLL, P.L.C.
115 3RD STREET SE, SUITE 500, P.O. BOX 2107
CEDAR RAPIDS
IA
52406
US
|
Family ID: |
34854112 |
Appl. No.: |
12/453010 |
Filed: |
April 27, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11088840 |
Mar 25, 2005 |
7524164 |
|
|
12453010 |
|
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Current U.S.
Class: |
415/173.7 |
Current CPC
Class: |
F01D 11/24 20130101;
F01D 11/18 20130101; F05D 2240/11 20130101; F01D 25/26
20130101 |
Class at
Publication: |
415/173.7 |
International
Class: |
F01D 11/00 20060101
F01D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2004 |
DE |
10 2004 016 222.0 |
Claims
1. An arrangement for automatic running gap control on a turbine
having at least two stages, comprising first and second rotors
within an outer casing, shroud segments moveably arranged around
the rotors, stator vanes positioned upstream, between and
downstream of these rotors, an expansion ring associated to each of
the rotors which is connected to radially moveable, upstream stator
vanes and to radially moveable, downstream stator vanes and whose
thermal expansion behaviour compares with that of the rotors, a
bridge connecting the upstream and downstream stator vanes at outer
platforms thereof, the bridge being axially and circumferentially
fixed and radially located on the outer casing, the intermediate
stator vanes and shroud segments being attached to the bridge.
2. An arrangement in accordance with claim 1, wherein the bridge
includes a first half bridge and a second half bridge which is
axially, radially and circumferentially held on the first half
bridge, with the intermediate second stator vanes being integrally
connected to the second half bridge.
3. An arrangement in accordance with claim 2, wherein the first
half bridge comprises a multitude of bending-resistant,
circumferentially arranged supporting elements, with a
circumferential gap provided between each of them, and a stiff
attaching ring attached to the outer casing of the turbine to which
the supporting elements are connected via radially flexible links,
with a radial gap provided between the free ends of the ring and
the supporting elements.
4. An arrangement in accordance with claim 2, wherein the first
half bridge and the second half bridge include a plurality of
circumferentially arranged half-bridge elements, and each of the
first half-bridge elements is located slideably in the radial
direction by a guiding sleeve and a guiding pin which slideably
engages the guiding sleeve, one of the guiding pin and the guiding
sleeve attached to the half-bridge element and the other of the
guiding pin and the guiding sleeve attached to and extending from
the outer casing.
5. An arrangement in accordance with claim 1, wherein the bridge
includes a plurality of circumferentially arranged full-bridge
elements which locate, at free ends thereof, in the outer platforms
of the upstream and the downstream stator vanes.
6. An arrangement in accordance with claim 5, wherein the
intermediate stator vanes are integrally connected to the
full-bridge elements.
7. An arrangement in accordance with claim 5, wherein the
intermediate stator vanes are separate components axially, radially
and circumferentially fixed to the full-bridge elements.
8. An arrangement in accordance with claim 6, wherein each of the
full-bridge elements includes a radially slideable connection to
the outer casing comprising a guiding sleeve and a guiding pin
slideably engaging the guiding sleeve, one of the guiding pin and
the guiding sleeve attached to the full-bridge element and the
other of the guiding pin and the guiding sleeve attached to the
outer casing, each of the intermediate stator vanes including a
locating web which engages a circumferential groove of a retaining
ring.
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. An arrangement in accordance with claim 1, comprising seals
positioned between the outer platform of the downstream stator
vanes and the outer casing.
14. An arrangement in accordance with claim 3, comprising a split
ring fixing ring for axial fixation between the supporting elements
and the half-bridge elements.
15. An arrangement in accordance with claim 3, wherein the
supporting elements and the half-bridge elements are stiffened by
reinforcing elements.
16. An arrangement in accordance with claim 5, comprising seals
positioned between the full-bridge element and the outer
casing.
17. An arrangement in accordance with claim 5, comprising a split
ring fixing ring for axial fixation between the full-bridge
elements and the separate intermediate stator vanes.
18. An arrangement in accordance with claim 5, wherein the
full-bridge elements are stiffened by reinforcing elements.
Description
[0001] This application claims priority to German Patent
Application DE 10 2004 016 222.0 filed Mar. 26, 2004, the entirety
of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] This invention relates to an arrangement for
automatic--passive--running gap control on a two or multi-stage
turbine which comprises at least first and second rotors within an
outer casing, with stator vanes arranged upstream, between and
downstream of these rotors, respectively.
[0003] On the turbine of aircraft engines, the clearance between
the blade tips of the rotor and the casing adjacent to it or
another stationary component are desirably kept as small as
possible to minimize performance and fuel losses and ensure high
efficiency of the engine in all flight phases. However, this is
problematic in that the rotating and stationary components are
subject to different dynamic loads and to different thermal loads,
in particular in the various flight phases such as take-off,
acceleration, continuous operation or deceleration, with their
expansion and contraction characteristics deviating
accordingly.
[0004] The clearance (running gap, blade gap) between the rotating
blade tips and the stationary casing parts adjacent to the blade
tips must be large enough to prevent rubbing between the stationary
and the rotating components as they expand under transient
conditions. Under continuous operating conditions, this clearance
will, however, grow to an extent that efficient use of the energy
input is not ensured.
[0005] In order to keep the running gap as constant and as small as
possible in all operating phases to effectively use the energy
input while preventing the rotating blade tips of the rotor from
contacting the adjacent, stationary area of the casing in the
take-off phase, a great variety of solutions for running gap
control has been presented.
[0006] The known "active" solutions for setting the size of the
running gap comprise the supply of cold compressor air or hot
combustion gases to the casing or to the liner segments
(interlayers) connected to it, using their expansion or contraction
to actively control the gap size or adapting the expansion behavior
of the stator to the thermal and dynamic expansion behavior of the
rotor in the various operating phases.
[0007] "Active" systems for running gap control are, however,
disadvantageous in that they incur a loss of compressor work or a
reduction of turbine efficiency, respectively. Moreover, adequate
control of the gap width between blade tips and liner segments is
not possible in all operating phases. Finally, active systems are
expensive since they require valve and control devices.
[0008] In order to resolve the problems associated with active gap
control, Specification GB 2061396 proposes an arrangement provided
in the casing interior for automatic "passive" running gap control
between the blade tips and the liner segments arranged on the inner
side of the turbine casing of a single-stage turbine. In the case
of this "passive" running gap control, the liner segments, which
are arranged remotely above the tips of the rotor blades, are held
at the outer platforms of the stator vanes of the turbine on one
side and at the outer platforms of a subsequent stator vane on the
other side, while the inner platforms of the stator vane segments
on both sides are each connected to a ring element (expansion ring)
whose reaction to a certain thermal load corresponds to the thermal
behavior of the rotor. Thus, in the event of an expansion or a
contraction of the rotor, the ring elements connected to the
platforms will become larger or smaller to the same extent as the
rotor, the moveably held stator vane segments will be shifted and
the liner segments attached to the vane segments will be set
relatively to the rotor and in correspondence with the degree of
expansion and contraction of the rotor.
[0009] This design, which also comprises a special fixation of the
stator vanes to enable their radial movement, ensures the formation
of a constant running gap between blade tips and liner segments in
all operating phases of the engine. The arrangement described in
the above is, however, unsuitable for two or multi-stage
turbines.
[0010] Based on the radial setting of the liner segments in
accordance with the expansion and contraction behavior of the rotor
known from Specification GB 2061396, the present invention, in a
broad aspect, provides an arrangement for two or multi-stage
turbines for passively setting a running gap that is constant in
various operating phases.
BRIEF SUMMARY OF THE INVENTION
[0011] It is a particular object of the present invention to
provide solution to the above problems by an arrangement for
automatically controlling the running gap width on a two or
multi-stage turbine designed in accordance with the features
described herein. Further features and advantageous embodiments of
the present invention will be apparent from the description
below.
[0012] In accordance with the state of the art, at least one
expansion ring is associated with each of the at least two rotors
whose expansion and contraction behavior under changing thermal
load agrees with that of the rotors. The expansion rings are
connected to the stator vanes located immediately upstream and
downstream of the turbine, so that the upstream and downstream
stator vanes are adjusted in accordance with the thermal load. The
outer platforms of the upstream and downstream stator vanes are
connected to each other by means of a bridge, which is fixed in the
axial and circumferential direction and is moveably located in the
radial direction. The intermediate stator vanes are either
integrally or separately provided on the moveable bridge between
the rotors. The rolling and tilting moments acting upon these are
taken up by the axially and circumferentially retained bridge
elements and, if applicable, an additional axial attachment on the
free vane side. Also provided on the bridge so formed are separate
or integral shroud segments.
[0013] This type of bridge design provides, for the first time for
two or multi-stage turbines, a passive gap width control
individually optimised for each rotor stage in accordance with the
thermal rotor movement, which, in addition, is less expensive than
the active systems hitherto known for gap width control on
two-stage turbines.
[0014] In accordance with a further important feature of the
present invention, the bridge comprises a first half bridge and a
second half bridge which is axially, radially and circumferentially
held on the first half-bridge and which is integral with the
intermediate stator vanes. The first half bridge forms a segmented
inner casing of bending-resistant, circumferentially spaced
supporting segments, with each supporting segment being firmly
connected to a stiff ring attached to the outer casing by means of
a radially flexible mounting or link.
[0015] However, the first half bridge can also be located slideably
in the radial direction on the outer casing by means of a pin and
sleeve or other fastening system.
[0016] In another development of the present invention, the bridge
can include full-bridge elements at which the intermediate stator
vanes and the shroud segments are separately held or integrally
provided, with the intermediate stator vanes being held on the free
side in a circumferential groove. In an embodiment of the present
invention, the full-bridge elements are located radially by means
of a guiding pin engaging a guiding sleeve.
[0017] In yet another embodiment of a full bridge, the individual
full bridge elements are connected to the outer casing by means of
a radially flexible link. The braces are either held on a fixing
ring by means of a groove or immediately connected to a stiff ring
attached to the outer casing by means of a flange. In this variant,
a supporting segment with integrated stator vane and integrated
shroud segment is axially and circumferentially fixed on the bridge
elements.
[0018] In another development of the present invention, axial
location of bridge elements, supporting elements or intermediate
stator vanes is accomplished by means of a piston ring-type fixing
ring which engages a groove provided in the component to be
located.
[0019] In a further development of the present invention, the
bridges or the half-bridge elements (supporting elements),
respectively, and the full-bridge elements are stiffened by
reinforcing elements (ribs).
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Embodiments of the present invention are more fully
described in the light of the accompanying drawings. In the
drawings,
[0021] FIG. 1 is a partial view of a two-stage turbine with a
two-part bridge which automatically adapts to the expansion
behavior of the rotors, with shroud segments held on this bridge,
and with an intermediate stator vane,
[0022] FIG. 2 is an isometric view of a half bridge of the two-part
bridge forming a segmented inner casing in the direction of
arrowhead A in FIG. 1,
[0023] FIG. 3 is another embodiment of a bridge formed by
half-bridge elements which is located slideably in the radial
direction,
[0024] FIG. 4 is a one-piece full bridge consisting of full-bridge
elements located slideably in the radial direction, with shroud
segments integral with the full bridge and intermediate stator
vanes,
[0025] FIG. 5 is a full bridge according to FIG. 4, but with the
stator vane being provided separately on the respective full-bridge
element,
[0026] FIG. 6 is a full bridge according to FIG. 4, in which the
shroud segments of the first stage are separately manufactured and
attached to the full-bridge element,
[0027] FIG. 7 is a full bridge with supporting elements separately
mounted to the full-bridge elements and with integrated stator vane
and shroud segment, with the full-bridge elements being held on the
outer casing by means of a fixing ring and a radially flexible link
connected to the fixing ring, and
[0028] FIG. 8 is a full bridge according to FIG. 7, in which the
radially flexible links are firmly connected to a stiff ring
attached on the outer casing.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The two-stage turbine partially shown in FIG. 1 in schematic
representation comprises a first rotor 1 and a second rotor 2, each
with a row of rotor blades 3 or 4, respectively. A first or second
stator vane row with first or second stator vanes 5, 6
respectively, is arranged upstream of the first or second rotor 1,
2, respectively. The principle of radial adjustment of the first
and second shroud segments 8a, 8b forming a first and a second
shroud and arranged remotely of the blade tips 3a, 4a is
essentially identical with the design described in Specification
GB-A-2061396 and is, therefore, not represented herein. This
principle is only explained in that a one-piece expansion ring (not
shown) is associated with each of the two rotors 1 and 2 of the
two-stage turbine whose expansion behaviour agrees with that of the
adjacent rotor 1 or 2, respectively. The expansion ring (not shown)
associated with the first rotor 1 is connected to the first stator
vanes 5, which are moveably located radially to the respective
outer casing 10 of the turbine via the respective outer platform 9
on the turbine inlet side, while the expansion ring (not shown)
adjacent to the second rotor 2 is connected to a likewise radially
moveable outer platform 11 for a stator vane row (not shown) on the
outlet side of the turbine. The respective radial movement of the
stator vanes 5 on the inlet side and of the downstream stator vanes
7 on the outlet side is indicated by a double arrow 12 or 13,
respectively.
[0030] With a first and second running gap 14, 15 being left, the
shroud segments 8a, 8b opposite the blade tips 3a, 4a are adjusted
relative to the blade tips 3a, 4a in accordance with the movement
transmitted by the expansion rings (not shown), on the one hand,
onto the moveable first stator vanes 5 and their outer platforms 9
and, on the other hand, to the outer platforms 11 of the downstream
stator vanes 7 of the rearward stator vane row and from these to a
bridge 16. The bridge 16, which connects the outer platforms 9 of
the first (forward) stator vanes 5 with the outer platforms 11 of
the rearward (downstream) stator vanes 7, comprises, in the present
embodiment, a first half bridge 17 followed by a second half bridge
18. The second half bridge 18 is integrally connected to the
intermediate stator vanes 6 and to the second shroud segments 8b.
The first shroud segments 8a, in the present embodiment, are
separately manufactured and held on the bottom side of the first
half bridge 17 and on the outer platforms 9 of the first stator
vanes 5.
[0031] The first half bridge 17 includes supporting elements 19
arranged in the circumferential direction and provided with bending
resistance by reinforcing elements 30. A circumferential gap 20 is
left between two each supporting elements 19. A mount 21 provided
on the supporting element 19 serves for both, location or retention
of the first shroud segments 7 and axial and radial retention of
the inflow-side end of the second half bridge 18 with integrated
shroud segments 8 and second stator vanes 6. Connected to the side
of the circumferentially spaced, bending-resistant supporting
elements 19 which faces the outer casing 10 are thin, radially
flexible links 22 which, at the free end, transit into a
circumferential, one-piece, stiff attaching ring 23 whose angled
mounting flange 23a with holes 23b serves for firm connection to
the outer casing 10. On the side of the supporting element 19
resting on the outer platform 9 of the stator vanes 5, a radial gap
24 exists between the stiff supporting element 19 and the stiff
attaching ring 23 so that, by virtue of the flexible connection via
the braces 22 and the supporting elements 19 being interrupted by
the circumferential gaps 20, radial movement between the attaching
ring 23 and the supporting elements 19 is possible, but with the
loads produced by the stator vanes 6 of the second turbine stage
being axially and circumferentially transmittable.
[0032] The second half bridge 18, which circumferentially includes
half-bridge elements 18a and to which the second stator vanes 6 of
the turbine arranged upstream of the second rotor 2 and the second
shroud segments 8b are attached, is radially held, on the
outlet-side end, on the outer platforms 11 of the stator vanes (not
shown) arranged behind (downstream of) the second rotor 2. The
second half bridge 18 locates, on a web 25 connected to each
half-bridge element 18a, the outlet-side end of the
circumferentially spaced supporting elements 19 of the half bridge
17 by means of a one-piece, slotted fixing ring 26 in the axial
direction, by means of an abutment 27 in the radial direction, and
by means of locating pins 28 in the circumferential direction.
[0033] The bridge 16 described in light of the FIGS. 1 and 2,
including the first half bridge 17 and the second half bridge 18
into which the second shroud segments 8b and the second stator
vanes 6 for the second turbine stage are integrated, provides for
continuous, "passive" gap width control automatically adapting to
variations in thermal expansion also on multi-stage turbines. The
supporting elements 19 of the half bridge 17 and the half-bridge
elements 18a of the second half bridge 18 are stiffened by
reinforcing elements 30, 29 such that the forces acting upon the
stator vanes 6 can be taken up. The radial position of the first
half bridge 17 and of the second half bridge 18 or the half-bridge
elements 18a, respectively, is determined by their location on the
outer platform 9 and the outer platform 11. Any thermal expansion
of the bridge 16 is taken up by the circumferential gaps 20 between
the supporting elements 19 and by the radial gap 24. While the
radially flexible links 22 compensate any relative movement between
the supporting elements 19 and the attaching ring 23 of the half
bridge 17, the radial gap 24 remaining between the supporting
elements and the ring provides for thermal compensation. The half
bridge 17 takes up the rolling and tilting moments of the second
stator vanes 6 integrated into the half-bridge elements 18a of the
second half bridge 18, with the radially flexible links 22
transmitting the axial and circumferential forces acting upon the
second (intermediate) stator vanes 6 into the outer casing 10 via
the stiff attaching ring 23 separated from the supporting element
19 by the radial gap 24.
[0034] FIG. 3 shows another embodiment of a bridge 16 including two
half bridges 17, 18 by means of which the stator vanes 5, 7
immediately upstream and downstream of the rotors 1 and 2 of a
two-stage turbine are connected to each other to provide for a
passive running gap control adapted to the thermal loading of the
rotors. The stiffened supporting elements 19 of the first half
bridge 17, arranged with circumferential gaps (not shown) left
between them, are each connected to a separately manufactured first
shroud segment 8a held on the outer platform 9 of the first stator
vane 5. The half-bridge elements 18a of the second half bridge 18,
arranged one behind the other in the circumferential direction and
provided with integral second stator vanes 6 and second shroud
segments 8b each, are axially and radially held on the outer
platform 11 of the downstream stator vanes 7 and on the respective
supporting element 19 of the first half bridge 17. By means of a
guiding pin 31 extending inwards from the outer casing 10 and a
guiding sleeve 32 formed onto the half bridge 17, and thus the
bridge 16 (17, 18) as a whole, is located slideably in the radial
direction, and additionally held axially and circumferentially. A
retaining ring 34 (FIG. 4) prevents the bridge from rotating around
the guiding pin 31.
[0035] FIGS. 4, 5 and 6 show embodiments of the inventive assembly
of stator vanes to stator vanes by means of a bridge 16 connecting
the stator vanes 5, 7 for passive running gap control on a
two-stage turbine, in which the circumferentially arranged bridge
elements form a one-piece bridge 16 (full bridge), and the
individual full-bridge elements 16a--as in the embodiment according
to FIG. 3--are radially located by means of a guiding pin 31
extending from the casing 10 and a guiding sleeve 32 formed onto
the full-bridge elements 16a.
[0036] In the embodiment according to FIG. 4, the first and second
shroud segments 8a, 8b and the second (intermediate) stator vanes 6
are an integral part of the full-bridge element 16a. The
full-bridge elements 16a are held at the ends in the outer platform
9 of the first stator vanes 5 and the outer platform 11 of the
stator vanes 7 arranged downstream of the second rotor 2 to take up
the tilting and rolling moments originating at the second stator
vanes 6. The second stator vanes 6, which are integral with the
full-bridge elements 16a, are provided with a locating web 33 at
their inner platform 6a which engages an annular groove of a
circumferential retaining ring 34 to secure the respective second
stator vanes 6 against rotation.
[0037] The embodiment in FIG. 5 with full-bridge elements 16a
located slideably in the radial direction (31, 32) differs from the
embodiment according to FIG. 4 in that the respective second stator
vanes 6 are not integral with the respective full-bridge element
16a, but are separably connected to the full-bridge elements 16a by
means of known fastening structures and, in particular, by means of
a fixing ring 26 (see FIG. 1) to take up the axial loads acting
upon the second stator vanes 6. In the case of the full-bridge
elements 16a located slideably in the radial direction according to
FIG. 6--other than in the embodiments to FIGS. 4 and 5--both, the
respective second stator vane 6 and the first and second shroud
segments 8a, 8b are provided as separate components.
[0038] FIGS. 7 and 8 show yet other embodiments of the inventive
design with stator vanes assembled to stator vanes by means of a
full-bridge element 16a. Here, the full-bridge element 16a provided
with a separate first shroud segment 8a is held on the outer
platform 9 of the first stator vane 5 and on the outer platform 11
of the outlet-side stator vanes 7. Seals 35 are provided between
the outer casing 10 and the full-bridge elements 16a. In addition,
the full-bridge elements 16a provided with bending-resistance by
means of reinforcing elements 29 are retained via a radially
flexible link 22 either by a fixing ring 26 (FIG. 7) as in the
embodiment with a half bridge according to FIG. 1, or by means of a
stiff attaching ring 23 (FIG. 8) attached to the outer casing 10,
as in the embodiment according to FIG. 1. If axially attached via
the fixing ring 26, a transmission element 37 is provided to
discharge the bridge circumferential load to the casing 10. The
second stator vane 6 and the second shroud segment 8b form a
one-piece component 36 which is flexible in the connecting area 36a
between stator vane and shroud segment and which is axially,
radially and circumferentially fixed to the bridge element 16a and
also axially held on the outer platform 11.
LIST OF REFERENCE NUMERALS
[0039] 1 First rotor [0040] 2 Second rotor [0041] 3 Rotor blade of
1 [0042] 3a Blade tips [0043] 4 Rotor blade of 2 [0044] 4a Blade
tips [0045] 5 First (upstream) stator vanes [0046] 6 Second
(intermediate) stator vanes [0047] 6a Inner platform [0048] 7
Downstream stator vanes [0049] 8a, 8b First/second shroud segments
[0050] 9 Outer platform of 5 [0051] Outer casing [0052] 11 Outer
platform of 7 [0053] 12 Double arrow (radial movement) [0054] 13
Double arrow (radial movement) [0055] 14 First running gap [0056]
Second running gap [0057] 16 Bridge [0058] 16a Full-bridge element
[0059] 17 First half bridge [0060] 18 Second half bridge [0061]
17a, 18a Half-bridge element [0062] 19 Supporting elements of 17
[0063] 20 Circumferential gap of 17 [0064] 21 Mount of 19 [0065] 22
Radially flexible link [0066] 23 Stiff attaching ring of 17 [0067]
23a Mounting flange [0068] 23b Hole [0069] 24 Radial gap of 17
[0070] 25 Web of 18a [0071] 26 Fixing ring [0072] 27 Abutment
[0073] 28 Locating pings [0074] 29 Reinforcing elements of 18
[0075] 30 Reinforcing elements of 17 [0076] 31 Guiding pin [0077]
32 Guiding sleeve [0078] 33 Locating web [0079] 34 Retaining ring
[0080] 35 Seal [0081] 36 One-piece component (supporting element)
[0082] 36a Flexible connecting area [0083] 37 Transmission
element
* * * * *