The present invention relates to torsional vibration dampers and in particularly to torsional vibration dampers suitable for use in a friction clutch.

The present invention aims to provide a torsional vibration damper having a high torsional stiffness.

The present invention provides a torsional vibration damper comprising a driving member and a driven member mounted for rotation relative thereto, first and second end caps mounted on the members, and resilient means interposed between the end caps to resist said relative rotation, the resilient means comprising two resilient members mounted side by side. The resilient members may be at substantially the same distance from the axis of the damper.

Preferably the torsional vibration damper further comprises auxiliary resilient means interposed between the end caps and acting to resist said relative rotation after a predetermined initial rotation.

Preferably the torsional vibration damper further comprises stop means which limits movement of the end caps against the auxiliary resilient means.

Conveniently one end cap has a projection, the auxiliary resilient means being mounted on the projection.

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Optionally the end cap has a stud and the auxiliary resilient means has a hole therein for mounting it on the stud.

Preferably the end cap has a hole therein and the auxilary resilient means has a stud thereon for engagement with the hole.

In a preferred embodiment the torsional vibrational damper further comprises a packing member between the driving member and the driven member the packing member being frictionally rotatable relative to the driving member or the driven member ^" .

Optionally the torsional vibrational damper comprises a plurality of packing members circumferentially spaced around the damper.

The packing member or members may be mounted on the driving member.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which :-

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Fig 1 is a section through a clutch driven plate assembly including a torsional vibration damper according to a first embodiment of the present invention;

Fig 2 is a view of the assembly of fig 1 without the side plates and hub;

Fig 3 is a view of a side plate of the assembly of fig 1; Fig 4 is an enlarged view of one of the end caps of fig l;

Fig 5 and Fig 6 are views of an elastomeric buffer of the assembly of Fig 1,

Fig 7 is a section through a clutch driven plate assembly including a torsional vibration damper according to a second embodiment of the invention,

Fig 8 is a view, similar to Fig 2 , of the assembly of Fig 7, nd

Fig 9 is a graph showing the torque characteristic of the a ^~ ^ bly of Figs 1 to 6.

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Referring to Fig 1, a clutch driven plate comprises a driven member in the form of a hub 10 having a radially extending hub flange 12.

A driving member in the form of an annular carrier plate 14 has a central aperture 15.

Two annular friction facings 18,20 are mounted one on either side of an outer region 22 of the carrier plate 14. Two annular support plates 24,26 are mounted one on either side of an inner region 28 of the carrier plate 14. The central apertures 30 of the support plates 24,26 are the same size as the central aperture 16 of the carrier plate 14. The carrier plate 14 is fitted over the flange 12 so that it is rotatable relative to the flange.

Two annular side plates 40,42 as shown in Fig 3 are mounted one on either side of the hub flange 12. The side plates 40,42 are secured to the hub flange 12 by rivets 44 and extend radially outw rds on either side of the carrier plate 14.

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The carrier plate 14 and support plates 24,26 each have eight apertures which are aligned to form carrier- windows 46. The side olates 40,42 each have eight side Plate windows 48 which are aligned with the carrier windows 46.

Referring to Fig 2 a pair of end caps 50,52 is mounted in each carrier window 46. Each end cap 50,52 comprises a back plate 54 which rests against a respective end 56,58 of one of the carrier windows 46, a stop 60 protruding from the back plate 54 near it:: radially outer end 62, and an end cap projection 63 protruding from the back plate near its radially inner end 66. A stud 64 protrudes from one end cap projection 63 (shown in fig 4), and a buffer 68, having a hole 67 therein, (shown in fig 5) is mounted on the stud such that it extends beyond the end of the stud. In this embodiment the buffer is of elastomeric material. On the other end cap 50, an abutment surface 70 is formed opposite the buffer 68.

Four lugs 72, (see figs 1 and 3) one on either side of each end cap 50,52, extend out through opposite side

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plate windows 48 and rest against the ends 73, 74 of the side plate windows 43. A spring mounting 76 protrudes from each lug 72.

A pair of helical springs 80 is mounted on each pair of opposite spring mountings 76. ^~ ach pair of springs 80 comprises an inner spring 82 and an outer spring 84.

Eight packing members 86 are riveted to each of the support plates 24,26. Each packing member 86 fits between two of the carrier windows 46 and is shaped such that its edges 88 coincide with the ends 56,58 of the carrier windows 46. The packing members 86 are in frictional contact with the side plates 40,42.

In operation, rotation of the carrier plate 14 relative to the hub 10 and side plates 40,42 causes one end 56 of the carrier window 46 to move towards the opposite end 74

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of the side plate window 48. This urges the two end caps 50,52 together against the force of the springs 80,82,84 which act as main resilient means. After further rotation the buffer 63 contacts the abutment surface 70. The buffer 68 then acts as an auxiliary resilient means and further rotation is against the force of the springs 80,82,84 and the buffer 68. This increases the torque required for further rotation. If enough torque is applied the stops 60 come into contact (as shown in dotted outline in Fig 2) preventing further rotation. In the embodiment shown , the total possible rotation in either direction is 7.5 degrees.

Rotation of the carrier 14 relative to the side plates is also damped by friction between the packing members 86 and the side plates 40,42.

Referring to Figs 7 and 8, the second embodiment differs form the first in that the packing members 86 are replaced by a pair of packing disks 90,92. The packing disks are the same shape and thickness as the support plates 94,96 but they are countersunk to receive the heads 98 of the rivets 100.

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The end caps 102, 104 of the second embodiment are identical to each other. Instead of the stud 64 in the first embodiment, each end cap 102,104 has a hole 106 and the buffer 108 has a stud 110 for inserting in the hole in one end cap 104. The buffer 108 is also glued onto the end cap 104. The buffer can be attached to the end cap 104 by glue only, so that the holes 106 in the end caps 102,104 and the stud 110 on the buffer 108 are not needed.

Fig 9 shows the estimated torque characteristics of the driven plate assembly of the first embodiment of the invention. The first stage a represents the torque provided by the springs before the buffers come into operation at a rotation of 6.25. Thereafter the buffers provide extra torque. Curve b shows the characteristic for buffers made of Hytrel b4075 and b shows the characteristic for buffers of Hytrel 6346. The springs alone provide a torque equal to the maximum engine torque, the buffers only coming into operation to smooth out irregularities in the torque applied to the driven plate.

As an alternative to the helical springs the main resilient means could be made from elastomeric material.

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