This invention relates to clutches and in particular to
the manufacture of clutch driven plates. Such driven plates, hereinafter referred
to as being of the type described, include an annular steel disc which carries friction
elements on either side of its outer peripheral zone and is connected at its inner
periphery with a drive hub (often via a spring and friction damping arrangement),
the outer peripheral zone is formed into a series of axial corrugated resilient
segments which provide axial cushioning when the driven plate is clamped between
a pressure plate and an associated engine flywheel when the clutch is engaged to
provide a smoother take-up of drive. Such driven plate constructions are well known
and examples are shown in, for example the Applicant's co-pending UK Application
number 04 06518.1.
The manufacture of such driven plates is a relatively costly
and time consuming operation since the steel segmented disc which supports the friction
elements requires detailed shaping and heat treatment to achieve the desired shape
and long term resilience.
It is an object of the present invention to provide an
improved method of manufacture of a segmented disc for use in a driven plate of
the type described.
Thus according to the present invention there is provided
a method of manufacturing a segmented disc for a clutch driven plate of the type
described comprising the steps of:-
- blanking out the disc to its final segmented form;
- positioning the blanked disc on a support fixture;
- positioning electrical induction heating means adjacent the segmented portion
of the blanked disc and heating the segmented portion using the induction electrical
heating means to the austenitic temperature;
- removing the induction heating means from the blanked disc;
- crimping the segmented portion of the disc between crimping dies;
- quenching the segmented portion of the disc to modify the carbon structure of
the segmented portion (partially to martensite and sorbite) to increase its hardness;
- and reheating the segmented portion of the disc to temper the segmented portion.
This method enables a segmented disc to be produced in
a shorter production time and at a lower cost since the disc does not need to be
moved form the support fixture once positioned there. Also no metal forming is carried
out after the heat treatment steps.
Preferably, the re-heating for tempering is carried out
by the electrical induction heating means.
Alternatively, the re-heating for tempering carried out
by further heating means (e.g. by placing in a furnace).
The quenching is preferably achieved by passing cooling
fluid through cavities in the crimping dies.
The electrical induction heating means may be moved radially
and/or axially towards and away from the segmented portion of the disc for the heating
and re-heating portions of the method.
The present invention also provides a clutch driven plate
which includes a segmented disc produced by the above method and an apparatus for
carrying out the above method.
Such an apparatus comprises a support fixture on which
the blanked disc is placed, electrical induction heating means moveable between
a heating position adjacent the segmented portion of the blanked disc and a retracted
position clear of the blanked disc, and crimping dies moveable towards the segmented
portion of the blanked disc to crimp the disc therebetween when the heating means
is in its retracted position, the crimping dies including internal cooling cavities
to enable the quenching process to be carried out.
The present invention will now be described, by way of
example only, with reference to the accompanying drawings in which:-
- Figure 1 shows a plan view of a clutch driven plate which includes a segmented
disc manufactured by the method of the present invention;
- Figure 2 shows a section on the line A-A of figure 1;
- Figure 3 shows the blank from which the segmented disc is formed, and
- Figures 4 and 5 show diagrammatically vertical sections through an apparatus
for carrying out the method of the present invention.
Referring to the drawings, the clutch driven plate 10 comprises
a central drive hub 11, a surrounding so-called compound damping centre 12 and an
outer support disc 13 sandwiched between a pair of friction members 14a and 14b.
As is conventional, the compound centre includes inner
idle rattle damping springs 15 and outer main damping springs 16. Outer main springs
16 act between central plate 17 and side plates 18 which are rivetted together at
19. Rivets 19 also secure support disc 13 to the side plates 18. The compound centre
also includes a frictional damping means 12a to resist circumferential movement
between support member 13 and hub 11.
Since the precise details of the compound damping centre
12 form no part of the present invention and any suitable form of damping centre
may be employed no further details will be given. The invention is also applicable
to driven plates with single stage torsional damping or even no torsional damping
The support disc 13 is of annular form as is most clearly
seen in Figure 3. The outer portion of the support disc is divided into a series
of circumferentially spaced segments 20 which are axially corrugated and can move
in an axial sense independently of each other and which support the two friction
members 14a, 14b therefrom.
Both friction members 14a and 14b are of annular form.
The outer frictional engaging surface of each friction member is formed as a series
of circumferentially spaced pads 21 separated by grooves 22 (see figure 1). Alternatively
the friction engaging surface can be of flat form without grooves 22.
The support member 13 includes series of outer rivet holes
20a, 20b for securing the friction members 14a, 14b in position as will be described.
Also inner rivet holes 20c are provided through which rivets 19 extend and locating
holes 20d which are used during manufacture of the driven plate. Friction members
14a, 14b include circumferentially alternating holes 25 and 26 (see figures 1 and
2). Holes 25 are counter sunk and receive rivets 27 which secure the relevant friction
member to the support member 13. Holes 26 provide clearance for the ends of the
rivets 27 which secure the other friction member to the support member 13.
When the clutch is engaged and the driven plate is compressed
between a pressure plate and a flywheel the axial corrugations of the segments 20
are compressed to provide axial cushioning of the clutch engagement in the known
In accordance with the present invention the segmented
disc 13 is manufactured by a method which comprises the following steps:-
- blanking out the disc 13 to the flat finished form shown in figure 3 which includes
all the holes 20a, 20b, 20c and 20d and the fully defined segments 20;
- positioning the blanked disc 13 on a support fixture 30 (see figure 4) on which
the blank is located by locating pins 31 which extend through locating holes 20d
in the blanked disc,
- positioning electrical induction heating coils (32) adjacent the segmented portion
20 of the blanked disc and heating the segmented portion using the coils to the
austenitic temperature (this modifies its carbon structure to increase its resilience);
- removing the induction heating coils from the blanked disc;
- crimping the segmented portion 20 of the disc between crimping dies (33) to
give the segments 20 their axially corrugated form;
- quenching the segmented portion 20 of the disc to modify the carbon structure
of the segmented portion (partially to martensite and sorbite) to increase its hardness;
- and reheating the segmented portion 20 of the disc to temper the segmented portion
When carrying out the above method the electrical induction
heating coils 32 may be moved into and out of their operational position over the
segmented portion 20 of the disc 13 by radial and/or axial movement. Similarly the
crimping dies 33 may be moved into and out of their operational position on either
side of the disc 13 by radial and/or axial movement.
The reheating of the disc for the tempering operation may
be carried out using the heating coils 32 or by removing the disc 13 from the support
structure 30 and placing the disc in a furnace.
The quenching is achieved by passing cooling fluid (e.g.
water) through cavities 34 formed in the crimping dies 33. As can be seen from figure
5, the crimping dies have a corrugated crimping surface 35 which gives segments
20 of the disc their axial corrugation.
The initial heating of the blanked disc is timed to ensure
that the carbon structure of the segments 20 of the disc 13 changes from a ferrite
form to an austenitic form to increase the resilience of the segments 20. Similarly
during the quenching phase of the method the quenching is timed to ensure that the
carbon structure of the segments 20 changes to martensite and sorbite to increase
the hardness of the segments. Experience shows that there is a transition area between
the outer segments 20 and the radially inner area containing the holes 20c where
the hardness of the disc 13 is even lower than the hardness of the radially inner
The present invention thus provides a method of manufacturing
a segment disc for a clutch driven plate of the type described which is particularly
suited to automatic assembly of the driven plate, which is economic (particularly
in the heat used), and which gives good control of the heat treatment of the disc
and the accuracy of the dimensions and physical properties of the disc.