FRICTION CLUTCH WITH INTERMEDIATE PLATE MOUNTING
SYSTEM
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates generally to a multi-disk friction clutch.
More particularly, the present invention relates to a multi-disk friction clutch having
means for promoting uniform engagement and wear of the friction disks.
Description of the Related Art
[0002] Friction clutches for use in transmitting rotational torque between a motor
vehicle engine and a transmission are well known in the art. One known friction
clutch design includes two friction disks, a pressure plate, an intermediate plate, and a
clutch cover mounted for rotation about a common axis. The clutch disks, pressure
plate and intermediate plate are axially moveable relative to each other so that the
pressure plate may be moved relative to the cover to press the two friction disks and
the interposed intermediate plate axially against an engine flywheel. A series of drive
straps, each generally including one or more resilient elements that are layered to
form a leaf spring, are placed around the peripheries of the intermediate plate and
pressure plate to provide a biasing force against the plates. During engagement of the
clutch, the intermediate plate, pressure plate and friction disks are pressed against the
engine flywheel, such that rotation of the flywheel causes rotation of the friction
disks. During disengagement of the clutch, the drive straps bias the intermediate plate
and pressure plate in a direction away from the flywheel to separate the intermediate
plate and pressure plate from the friction disks.
[0003] A basic problem with conventional friction clutches is that the
intermediate plate is uncontrolled during engagement and disengagement of the
clutch. In other words, it is generally difficult to achieve simultaneous engagement of
the intermediate plate and the pressure plate with the friction disks and simultaneous
disengagement of the friction disks from the interposed intermediate plate. If the
friction disks are engaged sequentially rather than simultaneously, the friction

material on one friction disk may be consumed more rapidly than the friction material
on the other friction disk, thereby reducing the useful life of the clutch.
[0004] To ensure virtually simultaneous engagement of the friction disks, several
designs have been proposed that force the travel of the intermediate plate to closely
coincide with pressure plate travel. One Icnown design incorporates a mechanism that
includes a separator element bolted to the radially outer side of the intermediate plate
and a lever attached to the mid-point of the drive straps that bias the pressure plate.
Engagement of the separator element with the lever limits axial movement of the
intermediate plate to approximately half of the axial movement of the pressure plate
during engagement and disengagement of the clutch. Accordingly, the friction disks
are engaged by the intermediate plate and pressure plate nearly simultaneous,
providing substantially uniform wear of the friction disks and a smooth engagement
of the clutch.
[0005] One limitation of the aforementioned design is that it requires a hole
and/or slot to be machined into the radially outer surface of the intermediate plate to
connect the mechanism. Another limitation is that the mechanism must be affixed to
the intermediate plate using a separate fastener(s), which, together with the machined
holes and/or slot in the intermediate plate, add to the complexity and cost of
manufacturing the prior art clutch assembly. Still another limitation is that the
separator element must directly engage the lever to protect the drive straps from direct
and damaging engagement by the separator element, and to provide a more precise
control of the displacement of the pressure plate relative to the intermediate plate.
Yet another limitation is that maximum axial movement of the intermediate plate is
generally uncontrolled, permitting the connected drive straps to be overextended and
damaged.
[0006] Accordingly, there exists a need for a simplified device that can be easily
and cost effectively affixed to a clutch to achieve the desired control of intermediate
plate travel relative to the pressure plate.
SUMMARY OF THE INVENTION
[0007] In a preferred embodiment of the present invention a friction clutch is
provided that includes a clutch cover, an intermediate plate that is spaced apart from

an engine flywheel, a first friction disk positioned between the flywheel and the
intermediate plate, a pressure plate spaced apart from the intermediate plate and a
second friction disk positioned between the intermediate plate and the pressure plate.
The clutch further includes at least one first drive strap for applying a load to the
intermediate plate, at least one second drive strap for applying a load to the pressure
plate and at least one separator arm attached to the intermediate plate. The separator
arm engages the second drive strap such that axial movement of the intermediate plate
relative to the clutch cover is a fraction of the corresponding axial movement of the
pressure plate during engagement and disengagement of the clutch.
[0008] In another embodiment of the present invention, at least one fastener is
provided for removably connecting the first drive strap to the cover. The intermediate
plate is configured to slide axially on a portion of the fastener that extends beyond the
cover. The axial movement of the intermediate plate is limited by the fastener to
prevent permanent deformation of or otherwise damage the first drive strap.
[0009] Among other advantages, the separator arm of the present invention can be
attached to the intermediate plate using existing fasteners, i.e., the fasteners used to
secure the first drive straps to the intermediate plate, thereby eliminating one or more
manufacturing steps. Another advantage is that the separator arm material can be
readily tailored to the requirements of a particular clutch assembly to reduce friction
between the separator arm and the engaged second drive strap. Unlike the prior art,
the separator arm can directly engage the second drive strap, without the use of a
lever. Still another advantage is that the intermediate plate can be easily removed
from the clutch to facilitate repair or replacement of the friction disks. Yet another
advantage is that axial movement of the intermediate plate is precisely controlled to
prevent damage to the first drive straps during operation of the clutch
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a diagrammatic representation of a double-disk friction clutch
according to a preferred embodiment of the present invention;
[0011] FIG. 2 is a partial sectional view of the clutch of FIG. 1;
[0012] FIG. 3 A is a side view of a separator arm shown in FIG. 2 according to a
preferred embodiment of the present invention;

[0013] FIG. 3B is a front cross-sectional view of the separator arm of FIG. 3A;
[0014] FIG. 4 is a partial cross-sectional view of the clutch of FIGS. 1 and 2
showing a separator arm according to an alternate embodiment of the present
invention;
[0015] FIGS. 5 A and 5B are front views of the separator arm of FIG. 4 illustrating
the preferred methods of connecting a head portion of the separator arm to a base
portion;
[0016] FIG. 6 is a partial cross-sectional view of the clutch of FIGS. 1 and 2
showing a separator arm according to another alternate embodiment of the present
invention;
[0017] FIG. 7 is a partial cross-sectional view of the clutch of FIG. 6 showing the
separator arm and a friction reducing member;
[0018] FIG. 8 is a cross-sectional view of the friction reducing member of FIG. 7;
[0019] FIG. 9 is a partial cross-sectional view of the clutch of FIG. 7 showing an
alternate embodiment of the friction reducing member; and
[0020] FIG. 10 is a cross-sectional view of the friction reducing member of FIG.
9.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] Referring now to the drawings, the preferred embodiments of the present
invention are shown in detail. Referring to FIG. 1, a diagrammatic representation of a
double-disk friction clutch 20 is illustrated, while a partial sectional view of clutch 20
is illustrated in FIG. 2. Clutch 20 includes a cover 22 that is detachably secured to a
flywheel 24 of an internal combustion engine (not illustrated). Within cover 22 is
disposed a first friction disk 26 adjacent flywheel 24 and an intermediate plate 28
adjacent first friction disk 26. A second friction disk 30 is disposed adjacent a
transmission-facing side 32 of intermediate plate 28 and a pressure plate 34 is
disposed adjacent a transmission-facing side 36 of second friction disk 30. First and
second friction disks 26, 30 are secured for rotation on a transmission input shaft 38,
but are axially moveable in relation thereto.
[0022] Intermediate plate 28 and pressure plate 34 are secured for rotation with
cover 22 and, like friction disks 26 and 30, are axially moveable in relation thereto.

In the illustrated embodiment, pressure plate 34 abuts a diaphragm spring 40 that
moveably connects pressure plate 34 to a release mechanism 42. Release mechanism
42 is selectively controlled by a vehicle operator to engage and disengage clutch 20.
However, it will be appreciated that the present invention can be used with a variety
of clamp-load generating release mechanisms besides a diaphragm spring. One
example well known in the art is the use of a plurality of levers and compression
springs. Another alternative is a centrifugally actuated clutch having both an
intermediate plate and a pressure plate. In the centrifugally actuated clutch, the
clamping load is generated by pivoted weights, which swing radially outwardly with
rotation of the clutch assembly.
[0023] Referring now to FIGS. 1 and 2, intermediate plate 28 and pressure plate
34 are moveably connected to cover 22 by first and second drive straps 44 and 46,
respectively. Drive straps 44, 46 preferably include a plurality of resilient elements
that are layered together to form a leaf spring, as is known in the art. First drive strap
44 provides a force on intermediate plate 28 for biasing intermediate plate 28 in a
direction toward pressure plate 34. Similarly, second drive strap 46 provides a force
against pressure plate 34 to ensure that pressure plate 34 is in continuous contact with
diaphragm spring 40. In return, diaphragm spring 40 applies a clamping force against
pressure plate 34 when engagement of clutch 20 is desired. While FIGS. 1 and 2
show only one drive strap 44,46 for each of intermediate plate 28 and pressure plate
34, respectively, a plurality of drive straps 44 and 46 are preferably distributed about
the peripheries of intermediate plate 28 and pressure plate 34.
[0024] Referring exclusively to FIG. 2, a first end 48 of second drive strap 46 is
fixedly secured to a flange portion 50 of pressure plate 34 by a fastener 52, such as a
rivet or the like. A second end 54 of second drive strap 46 is removably connected to
cover 22 by a fastener 56, such as a threaded bolt or the like. A washer 58 may be
disposed between a head 59 of fastener 56 and second drive strap 46 to ensure
adequate contact pressure is distributed over second end 54 of second drive strap 46.
[0025] Referring still to FIG. 2, a first end 60 of first drive strap 44 is fixedly
secured to intermediate plate 28, while a second end 62 of first drive strap 44 is
removably connected to cover 22. To facilitate easy removal of intermediate plate 28
from clutch 20, first drive strap 44 is preferably attached to cover 22 by a threaded

fastener 64, such as a threaded bolt or the like. Once secured to cover 22, a
significant portion of threaded fastener 64 extends beyond cover 22. This "extended"
portion of threaded fastener 64 is preferably provided with a generally cylindrical
sleeve 66 that extends between first drive strap 44 and a head 68 of threaded fastener
64. A washer 70, such as a beveled washer, may be provided between sleeve 66 and
first drive strap 44 to increase the clamping force applied by threaded fastener 64
against first drive strap 44. Similarly, a generally fiat washer 72 may be provided
between head 68 and sleeve 66, or a flange may be provided on head 68, to ensure
that sufficient contact pressure is distributed from head 68 through the fastened
components.
[0026] Intermediate plate 28 preferably includes a lug portion 74 through which
threaded fastener 64 and sleeve 66 extend to moveably secure intermediate plate 28 to
cover 22. As illustrated in FIG. 2, lug portion 74 is provided with an aperture 76
therethrough that is sized to slidingly receive sleeve 66, so that intermediate plate 28
is free to slide on sleeve 66 during operation. The length of sleeve 66, or the degree
of axial movement afforded to intermediate plate 28, will generally depend on various
factors, including, but not limited to, the size of clutch 20 and the amount of travel
needed to compensate for wear in first friction disk 26. However, care must be taken
to ensure that the axial movement afforded intermediate plate 28 does not
permanently deform or otherwise damage first drive strap 44. Accordingly, washer
72 acts as a "stop" against which intermediate plate 28 is precluded from further axial
travel.
[0027] First end 60 of first drive strap 44 is fixedly secured to intermediate plate
28 by a fastener 78, such as a rivet or the like. Fastener 78 is also used to attach a
separator arm 79 to intermediate plate 28 for movement therewith. In a preferred
embodiment, separator arm 79 is made of a relatively high strength material, such as
metal or plastic, and includes a base portion 80 secured to intermediate plate 28 and a
head portion 82 that engages second drive strap 46. Head portion 82 preferably
engages second drive strap 46 proximate a mid-point between fastener 52 and fastener
56, for reasons that will be explained below, but may engage other points on second
drive strap 46 as required. Head portion 82 preferably includes a substantially flat
land 77 where it contacts second drive strap 46 to reduce contact pressure and friction.

[0028] Referring to FIGS. 3A and 3B, base portion 80 includes an aperture 84
therethrough that is sized to receive fastener 78 and a lip 86 that extends along at least
a portion of base 80. Once assembled onto intermediate plate 28, lip 86 abuts first
drive strap 44 and substantially prevents rotation of separator arm 79 about a
longitudinal axis (not shown) of fastener 78 during operation of clutch 20.
Alternatively, lip 86 may take other forms, such as, for example, lip 86' illustrated in
FIGS. 4-8.
[0029] Referring to FIG. 4, an alternate embodiment of the present invention is
shown in detail. In this embodiment, a clutch 20' is provided that is substantially
similar to clutch 20 described in the first embodiment with a least one exception,
namely, the configuration of separator arm 79. In this embodiment, a separator arm
79' is provided that includes a separate base portion 80' that is secured to a head
portion 82' prior to assembly of separator arm 79' onto intermediate plate 28. As
illustrated in FIG. 5A, head portion 82' may be secured to base portion 80' by press
fitting a shaft 87 on head portion 82' into an aperture 88 in base portion 80'.
Alternatively, other methods may be used to secure head portion 82' to base portion
80', such as using snap hooks, as illustrated in FIG. 5B, or welding head portion 82'
to base portion 80'. An advantage of the embodiment illustrated in FIG. 4 is that head
portion 82' can be manufactured out of a low friction material, such as PTFE, whereas
base portion 80' can be manufactured out of a second, perhaps less costly material.
[0030] Referring to FIGS. 6, 7 and 9, another alternate embodiment of the present
invention is shown in detail. In this embodiment, a separator arm 79" is provided
that includes a generally round head portion 82", as opposed to substantially flat head
portion 82 provided in the preferred embodiment. Separator arm 79" provides a
concentrated point of contact between head portion 82" and second drive strap 46,
which more precisely defines the axial movement of intermediate plate 28.
[0031] Optionally, in clutch assemblies that exhibit a relatively high level of
friction between separator arm 79" and second drive strap 46, a friction reducing
member 90 may be disposed between second drive strap 46 and head portion 82", as
illustrated in FIG. 7. However, friction reducing member 90 is not necessary due to
the friction reducing characteristics of separator arm 79 and adequate control of the

displacements of intermediate plate 28 and pressure plate 34 can be achieved with the
simplified intermediate plate control system.
[0032] Referring to FIG. 8, friction reducing member 90 includes a contoured
surface 92 that engages head portion 82" and a duct 94 therethrough for receiving
second drive strap 46. Friction reducing member 90 may be manufactured out of any
suitable friction reducing material, such as PTFE.
[0033] Referring to FIGS. 9 and 10, an alternate embodiment of friction reducing
member 90 is shown in detail. In this embodiment a friction reducing member 90' is
provided that includes a pair bendable clamps 96 that are bent around second drive
strap 46 and an contoured portion 98 that engages head portion 82". An advantage of
this embodiment is that can be more cost effectively manufactured, such as by
stamping the shape of friction reducing member 90' out of a suitable metal.
[0034] Advantages of the present invention will become apparent upon review of
the assembly and operation of clutch 20, as described herein below. In the assembly
of clutch 20, first clutch disk 26 is moved into contact with flywheel 24 and then a
pre-assembled cover assembly, which includes intermediate plate 28, second friction
disk 30, pressure plate 34, diaphragm spring 40 and cover 22, are secured to flywheel
24. Cover 22 may be divided into two parts for simpler assembly and disassembly of
the intermediate plate 28, however, such a division of cover 22 is not necessary.
[0035] When clutch 20 is disengaged, that is, when diaphragm spring 40 is moved
to the position shown in FIG. 1, pressure plate 34 automatically moves away from
flywheel 24 due to the biasing force of second drive strap 46. Virtually
simultaneously, intermediate plate 28 automatically moves away from flywheel 24
due to the biasing force of first drive strap 44. However, due to the contact of
separator arm 79 proximate the mid-point of second drive strap 46, the axial distance
intermediate plate 28 moves is approximately one-half the axial distance pressure
plate 34 moves. In this manner, it is ensured that first and second friction disks 26, 30
are disengaged virtually simultaneously. It will be appreciated that axial movement

of intermediate plate 28 relative to pressure plate 34 can be easily modified by
altering the point of engagement between separator arm 79 and second drive strap 46.
For example, the dimensions of separator arm 79 can be modified to alter the
engagement point of separator arm 79 on second drive strap 46.

[0036] When clutch 20 is engaged, the various components move in a direction
opposite the direction of disengagement, i.e., to the left in FIG. 1. Again, due to the
engagement of separator arm 79 with second drive strap 46, intermediate plate 28 will
move approximately one-half the distance pressure plate 34 moves. In this manner, it
is ensured that first and second friction disks 26, 30 are engaged virtually
simultaneously and smoothly, due to axial movement of intermediate plate 28 relative
to cover 22 being a precisely defined fraction of the corresponding axial movement of
pressure plate 34. Additionally, axial movement of intermediate plate 28, and
indirectly pressure plate 34, is limited by fasteners 64 to substantially prevent first and
second drive straps 44, 46 from becoming damaged due to excessive wear in friction
disk 26, 30.
[0037] Among other advantages, separator arm 79 can be attached to intermediate
plate 28 using existing fasteners, i.e., fastener 78 used to secure first drive strap 44 to
intermediate plate 28, thereby eliminating one or more manufacturing steps. Another
advantage is that the material of separator arm 79, more particularly head portion 82,
can be easily tailored to the requirements of a particular clutch assembly to reduce
friction between separator arm 79 and second drive strap 46, and decrease component
wear. Unlike the prior art, separator arm 79 can be engaged directly with second
drive strap 46, without the use of a lever. Still another advantage is that intermediate
plate 28 can be easily removed from clutch 20 to facilitate repair or replacement of
friction disks 23, 30. Yet another advantage is that axial movement of intermediate
plate 28 is precisely controlled by fasteners 64 to prevent damage to first and second
drive straps 44, 46 during operation of clutch 20.
[0038] Although certain preferred embodiments of the present invention have
been described, the invention is not limited to the illustrations described and shown
herein, which are deemed to be merely illustrative of the best modes of carrying out
the invention. A person of ordinary skill in the art will realize that certain
modifications and variations will come within the teachings of this invention and that
such variations and modifications are within its spirit and the scope as defined by the
claims.

WE CLAIM
1. A friction clutch (20) comprising:
- a flywheel (24) rotatable about an axis of rotation;
- a clutch cover (22) fixed to the flywheel (24) for rotation therewith;
- an intermediate plate (28) spaced apart from the flywheel (24) and
disposed within the cover (22);
- a first friction disk (26) positioned between the flywheel (24) and
intermediate plate (28);
- a pressure plate (34) disposed within the cover (22) between the
intermediate plate (28) and the cover (22) and spaced apart from the
intermediate plate (28);
- a second friction disk (30) positioned between the intermediate plate (28)
and the pressure plate (34);
characterized in that,
a first drive strap (44) disposed between the intermediate plate (28) and
the cover (22), the first drive strap (44) rotatively fixing the intermediate
plate (28) to the cover (22) and biasing the intermediate plate (28) away
from the flywheel (24);
- a second drive strap (46) disposed between the pressure plate (34) and
the cover (22), the second drive strap (46) rotatively fixing the pressure

plate (34) to the cover (22) and biasing the pressure plate (34) away from
the flywheel (24); and
- a separator arm (79) attached to the intermediate plate (28) at a point of
attachment of the first drive strap (44), the separator arm (79) engaging
the second drive strap (46) such that axial movement of the intermediate
plate (28) relative to the clutch cover (22) is a fraction of the
corresponding axial movement of the pressure plate (34) during
engagement and disengagement of the clutch (20).
2. The clutch (20) as claimed in claim 1, wherein the separator arm (79)
comprises at least one shoulder (86) to inhibit rotation of the separator
arm (79) relative to the intermediate plate (28).
3. The clutch (20) as claimed in claim 1, wherein the separator arm (79)
comprises a head portion (82) that engages the second drive strap (46)
and a base portion (80) connected to the intermediate plate (28).
4. The clutch (20) as claimed in claim 3, wherein the portion (82) comprises
a substantially flat land (77) where the separator arm (79) contacts the
second drive strap (46).
5. The clutch (20) as claimed in claim 3, wherein the base portion (80)
comprises an aperture (84) therethrough that receive a fastener (78) to
connect the separator arm (79) and the first drive strap (44) to the
intermediate plate (28).

6. The clutch (20) as claimed in claim 3, wherein the head portion (82) is
made separate from the base portion (80) and secured thereto.
7. The clutch (20) as claimed in claim 6, wherein the head portion (82) is
secured to the base portion (80) by a press fit connection.
8. The clutch (20) as claimed in claim 6, wherein the head portion (82) is
secured to the base portion (80) by a snap-together connection.
9. The clutch (20) as claimed in claim 1, wherein a friction reducing member
(90) is disposed between the separator arm (79) and the second drive
strap (46).
10. The friction clutch (20) as claimed in claim 1, wherein at least one
fastener (64) that removably connects the first drive strap (44) to the
cover (22), the intermediate plate (28) configured to slide axially on a
portion of the fastener (64) that extends beyond the cover (22).

11. The friction clutch (20) as claimed in claims 1 to 10, wherein a sleeve (66)
is disposed between the fastener (64) and the intermediate plate (28).
12. The friction clutch (20) as claimed in claims 1 to 11, wherein the
intermediate plate (28) comprises a lug portion (74) having an aperture
(76) therethrough that is sized to slidingly receive the sleeve (66).

13. The friction clutch (20) as claimed in claims 1 to 12, wherein the fastener
(64) is configured to limit axial movement of the intermediate plate (28).
14. The friction clutch (20) as claimed in claims 1 to 13, wherein a separator
arm (79) attached to the intermediate plate (28) the separator arm (79)
engaging the second drive strap (46) such that axial movement of the
intermediate plate (28) relative to the clutch cover (22) is a fraction of the
corresponding axial movement of the pressure plate (34) during
engagement and disengagement of the clutch (20).
15. The friction clutch (20) as claimed in claims 1 to 14, wherein the separator
arm (79) having a head portion (82) that engages the second drive strap
(46) and a base portion (80) connected to the intermediate plate (28).
16. The friction clutch (20) as claimed in claims 1 to 15, wherein the fastener
(64) is configured to limit axial movement of the intermediate plate (28).
17. The friction clutch (20) as claimed in claims 1 to 16, wherein a separator
arm (79) having a base portion (80) fixed to the intermediate plate (28)
and a head portion (82) engaging the second drive strap (46) so as to
follow deflection of the second drive strap (46) at a location of
engagement there between such that axial travel of the intermediate plate
(28) relative the clutch cover (22) associated with moving between a
clutch engaged condition and a clutch disengaged condition is a fraction
of the corresponding axial movement of the pressure plate (34) during
engagement and disengagement of the clutch (20).

18. The friction clutch (20) as claimed in claims 1 to 17, wherein the head
portion (82) is circumferentially and axially offset from the base portion
(80) and cantilevered over the first drive strap (44), thereby permitting
deflection of the first drive strap (44) toward the head portion (82) in the
engaged condition.
19. The friction clutch (20) as claimed in claims 1 to 18, wherein the head
potion (82) engages the second drive strap (46) directly.
20.The friction clutch (20) as claimed in claims 1 to 19, wherein a friction
reducing member (90) is disposed between the head portion (82) and the
second drive strap (46).
21. The friction clutch (20) as claimed in claims 1 to 20, wherein the head
potion (82) having a substantially flat land (77) where the separator arm
(79) contacts the second drive strap (46).
22.The friction clutch (20) as claimed in claims 1 to 21, wherein the base
portion (80) having an aperture (84) there through that receives a
fastener (78) to connect the separator arm (79) and the first drive strap
(44) to the intermediate plate (28).
23. The friction clutch (20) as claimed in claims 1 to 22, wherein the head
potion (82) is made separate from the base portion (80) and secured
thereto.

24. The friction clutch (20) as claimed in claims 1 to 23, wherein the head
potion (82') secured to the base portion (80')by a press fit connection.
25. The friction clutch (20) as claimed in claims 1 to 24, wherein the head
potion (82')s secured to the base portion (80') by a snap-together
connection.

A friction clutch (20) is provided that includes a clutch cover (22), an
intermediate plate (28) that is spaced apart from an engine flywheel (24), a first
friction disk (26) positioned between the flywheel (24) and the intermediate plate
(28), a pressure plate (34) spaced apart from the intermediate (28) and a
second friction disk (30) positioned between the intermediate plate (28) and the
pressure plate (34). The clutch (20) further includes a first drive strap (44) for
applying a load to the intermediate plate (28), a second drive strap (46) for
applying a load to the pressure plate (34) and a separator arm (879) attached to
the intermediate plate (28). The separator arm (79) engages the second drive
strap (46) such that axial movement of the intermediate plate (28) relative to the
clutch cover (22) is a friction of the corresponding axial movement of the
pressure plate (34) during engagement and disengagement of the clutch (20).