Twin mass flywheel sub-assembly for a motor vehicle

A twin mass flywheel sub-assembly comprising a pair of axially spaced side plates for connection with an associated first flywheel mass, a force transmitting member for connection with an associated second flywheel mass and being disposed at least partially between the side plates. A plurality of linkages connect the side plates and the force transmitting member, each linkage comprising a first link pivotally connected to the side plates, a second link pivotally connected to the force transmitting member, and a pivot for pivotally connecting the first and second links. The linkages being arranged to move in a generally radially outward direction as the sub-assembly rotates thereby controlling relative rotation of the side plates and force transmitting member. One of the flywheel masses may have cushioning springs to engage the other flywheel mass at the limits of relative rotation of the flywheel masses.

The present invention relates to a twin mass flywheel arrangement for 
absorbing or compensating for torsional vibrations such as can arise in a 
vehicle transmission assembly. 
More particularly, the invention relates to a twin mass flywheel of the 
type described in WO 89/01097 in which two coaxial flywheel masses which 
are mounted for limited angular rotation relative to each other; and a 
plurality of pivotal linkages interconnect the two flywheel masses each 
comprising a first link pivotally connected one of the flywheel masses, 
and a second link pivotally connected to the other of the flywheel masses, 
and means for pivotally connecting the first and second links. 
A problem arises due to the pivotal linkage striking one of the flywheel 
masses at extremes of relative rotation, thereby causing noise. A proposal 
for the use of cushioning means at the limits of relative rotational 
movement is disclosed in WO 92/14076. The cushioning means disclosed 
therein have problems due to the conflicting requirements of resilience on 
one hand and wear resistance on the other hand. 
It is an object of the present invention to provide a twin mass flywheel of 
the above type with improved cushioning means. 
According to the invention there is provided a twin mass flywheel for a 
vehicle comprising two co-axially arranged flywheel masses which are 
mounted for limited angular rotation relative to each other; and a 
plurality of pivotal linkages interconnecting the two flywheel masses each 
linkage comprising a first link pivotally connected to one of the flywheel 
masses, a second link pivotally connected to the other of the flywheel 
masses, and a pivot for pivotally connecting the first and second links, 
said linkage being arranged to tend to move radially outwardly as the 
flywheel rotates, at least one of the flywheel masses having cushioning 
means thereon to engage the other flywheel mass at the limits of said 
relative rotation in at least one direction of relative rotational 
movement characterised in that the cushioning means on said one flywheel 
mass engages a radially outer marginal portion of the other flywheel mass. 
Preferably one flywheel mass comprises a hub, a first annular plate fast 
with the hub and a pair of annular side plates spaced axially apart and 
fast with the hub, and the second flywheel mass is mounted on the hub and 
comprises a second annular plate with a pair of flange plates fixed 
thereon having portions located between the side plates, and the 
cushioning means act between the side plates and the flange plates at said 
limits. 
Preferably the flange plates of the second flywheel each have a pair of 
diametrically opposed radially outwardly projecting arms thereon, the arms 
on one flange plate being aligned with arms on the other flange plate, and 
the cushioning means being mounted in aligned apertures in the two side 
plates. 
Preferably the first annular plate has a cylindrical outer side wall 
forming an annular cavity around the hub and said side plates and flange 
plates are located within the cavity, and the radially outer ends of the 
arms engage friction damping devices fixed relative to the radially inner 
surface of the cylindrical wall.

With reference to FIGS. 1 to 6 of the accompanying drawings there is 
illustrated a twin mass flywheel 10 comprising two flywheel masses 11 and 
12. One flywheel mass 11 is fixed on a flange of a crankshaft of an 
internal combustion engine (not shown) by way of a central hub 14 and 
bolts 18. In use a friction clutch (not shown) could be secured to the 
second flywheel mass 12. Under normal drive conditions the flywheel masses 
11, 12 rotate in a counter-clockwise direction in the view shown in FIG. 
1A as indicated by the arrow D. The flywheel mass 12 is mounted on the 
central hub 14 via a bearing 19. 
The flywheel mass 11 comprises the hub 14 which is fixed to the crankshaft 
and first annular plate 15 fixed to the hub 14 by the bolts 16. The first 
annular plate 15 is a sheet steel pressing having an outer cylindrical 
side wall 13. 
The annular plate 15, hub 14, and outer wall 13 form an annular cavity A, 
the base of which is formed by the plate 15. A pair of annular sheet steel 
side plates 26 and 27 are located within the annular cavity A. The side 
plates 26 and 27 are mirror images of each other, and the side plate 27 is 
shown in FIG. 4 and FIG. 4C. The side plate 26 adjacent the first annular 
plate is fixed thereto by pegs or dowels 17 that engage holes 20 spaced 
around the outer periphery of each side plate. 
The other side plate 27 is axially spaced from side plate 26 and the two 
plates 26 and 27 are held apart by circumferentially spaced axially 
inwardly indented areas 21 on each side plate which abut each other. The 
two plates 26 and 27 can be secured together by spot welding, or by screw 
fasteners, rivets etc. in the abutting areas. 
The second flywheel mass 12 is arranged at the open end of said cavity A 
and is mounted rotatably to the first flywheel mass 11 by way of the 
bearing 19. The bearing 19 is non-rotatably mounted on the hub 14 and is 
secured in place between a flange 28 on the hub and the plate 15. The 
outer race of the bearing 19 is non-rotatably mounted by an interference 
fit in the centre of the second flywheel mass 12. 
The second flywheel mass 12 further includes a hub part 30 and a pair of 
annular flange plates 31 32, the hub part 30 is secured to the flywheel 
mass 12 by spaced set screws 34 (see FIG. 6). The two flange plates 31 32 
are mirror images of each other and one flange plate 31 is shown in FIG. 
3. The two flange plates 31 and 32 each have a radially inner annular 
portion 35 with two diametrically opposed radially extending lugs 36 
thereon which are formed axially inwardly of the annular portion so that 
when the two plates 31 and 32 are secured back-to-back on the hub part 30 
by rivets 37 the aligned lugs 36 on each plate 31 and 32 abut. 
Relative rotation between the two flywheel masses 11 and 12 is controlled 
by a plurality of, preferably four, pivotal linkages 40 circumferentially 
spaced around the flywheel masses, and by two friction damping means 50 
located on the inner surface of the wall 13. Each pivotal linkage 40, only 
one 40A of which is described in detail, comprises a first link 41 
pivotally mounted between the spaced annular portions 35 of the flange 
plates 31 of the second flywheel mass 12 by way of a pivot 43, and a 
second link 42 pivotally mounted on the side plates 26 27 of the flywheel 
mass 11 by way of pivot 44. The two links 41 and 42 are pivotally 
connected to each other by means of a third pivot 45. 
It will be noted from FIG. 1B that the pivot 43 is positioned radially 
inwardly of the pivots 44 and 45. The first link 41 is formed as a bob 
weight mass having a greater mass at its end remote from the pivot 43, and 
adjacent the pivot 45 between the two links 41 and 42. The link 41 also 
has its centre of mass off-set towards its leading edge considering the 
link 41 relative to its normal drive direction. By off-setting the centre 
of mass in this manner the centrifugal bob weight effect of the link 41 is 
increased in the normal drive direction of rotation D. 
The second link 42 comprises a pair of parallel arms which are arranged one 
on each axial side of the bob weight 41. Each pair of arms 42 located one 
on each axial side of the bob weight 41 extend from the pivot 45 through 
an aperture 22 in an inclined side of a respective indented area 21 of 
each side plate 26 27 to connect with a pivot 44 on the axially outer side 
of said side plates. The side plates 26, 27 have circumferentially spaced 
radial slots 23 extending radially outwardly from the inner periphery 
thereof, to accomodate radial movement of the pivot 45. 
The friction damping means comprise leaf springs 50 (see FIGS. 7 & 8) fixed 
relative to the outer wall 13 which are deformable by the relative 
movement of the lugs 36 on the flange plates 31 32. As the flange plates 
31 32 move relative to first annular plate 15, the radially outer edges of 
the lugs 36 cause the leaf springs 50 to deform and resist the movement. 
The springs 50 are so shaped as to provide increasing resistance with 
increasing relative rotational displacement between the two flywheel 
masses 11 and 12. The springs are held against movement relative to wall 
13 by tangs 50a which engage slots 51 in side plates 26, 27. 
Alternative, or additional friction damping means (not shown) could be 
provided by a stack of friction washers, located on the hub 14 to operate 
between the annular plate 15 and the hub part 30. Alternate friction 
washers may be driven by the hub 14 of the first flywheel mass 12, and the 
hub part 30 of the second flywheel mass 12. The washers may be urged 
together by a Belleville spring, such a friction damping means is shown in 
British Patent Application GB-A-2 198 808. 
Resilient cushioning means 54, 55 are fixed between the side plates 26 27, 
to cushion the relative movement between the two flywheel masses at the 
limits of the angular relative rotation. The first cushioning means 54 
comprise resilient stops, preferably in the form of helical compression 
springs, which are located on the "drive" side of the lugs 36. The springs 
are located in sets of aligned apertures 28 on the two side plates. One 
end of each spring 54 is held in an end cap 56 fixed at one end of the 
respective aligned set of apertures 28, and the other end of each springs 
54 is located in an end cap 57 which is slideably mounted in the 
respective set of aligned apertures 28. At the limits of relative 
rotational movement, in the drive direction D, the lugs 36 will each abut 
said end caps 57 and thereafter such movement will be resisted by the 
springs 54. 
The lugs 36 on the flange plates 31, 32 have notches 38 therein to 
accomodate a predetermined relative movement between the flywheel mass 11 
and 12 before the springs 54 begin to operate. 
The second cushioning means 55 each comprise resilient stops, preferably an 
elastomeric cylinder, held between two end caps 58 59, and which are 
located on the "over run" side of the lugs . The elastomeric cushioning 
means 55 are located between the end caps 58 59 in second sets of aligned 
apertures 29 on the two side plates 26, 27. At the limits of relative 
rotational movement of the flange plates 31 32 in the over-run direction 
the lugs 36 will each abut a respective end cap 58 which is slideably 
mounted in the respective apertures 29. Thereafter, further such movement 
will be resisted by the elastomeric cushioning means. 
The open end of the first flywheel mass 11 is enclosed by a cover plate 60 
fixed to the open end of the cylindrical wall 13. A resilient seal 61 is 
clamped between the second flywheel mass 12 and the flange plate 32 and 
engages the cover plate 60. The seal 61 is preferably a sheet metal 
diaphragm. The cavity `A` may be filled with a viscous damping medium such 
as grease. 
Operation of the twin mass flywheel shown in FIG. 1 to 6 will now he 
described. Under no-load conditions, with the engine rotating at high 
speeds centrifugal force acts on the pivotal linkages 40 and particularly 
on the bob weights 41 and urges the linkages in a radially outward 
direction. At higher rotational speeds the centrifugal force is greater 
and whilst this does not affect the configuration it greatly affects the 
force required to move the flywheel mass 12 relative to the flywheel mass 
11. 
If the clutch is engaging or is engaged and torque is transmitted from the 
engine to the flywheel mass 11 and then to flywheel mass 12 there is a 
tendency for the two masses to rotate relative to each other. At 
relatively low speeds when the influence of centrifugal force is small the 
flywheel masses move readily relative to each other. However at high 
speeds the influence of centrifugal force is much greater and relative 
rotation of the flywheel masses requires greater force. 
The envelope of movement of the bob weights 41 is shown at 40B in FIG. 1A. 
In extreme drive conditions the linkage 40 is stretched and under 
conditions of over-run the effects are similar except that in the 
embodiments described the link 42 folds under the bob weight 41. 
The two resilient cushioning means 54, 55 form resilient travel end stops 
to prevent shock loading in extreme high torque loading conditions when 
the flywheel masses approach the limit of their permitted relative 
rotational movement. Such conditions are most likely to occur at low 
flywheel rotation speeds when the centrifugal controlling force of bob 
weights 41 is lowest. 
If the cavity `A` is filled with grease then the movement of the pivots 
linkages 40 between the two extremes, is damped by the grease, in that the 
grease provides resistance to the movement of the linkages and must flow 
around the bob weights 41 as they move through the respective chambers 46. 
As indicated above, the bob weights 41 are assymetrically shaped having an 
offset mass to give different effects in the drive direction of relative 
rotation as compared with the overrun direction of relative rotation. The 
mass is off-set to the leading edge of the bob weight in the drive 
condition. This has the additional effect of moving the neutral position 
in the at-rest condition towards the overrun side of the flywheel and 
gives a longer drive condition travel. 
FIG. 9 shows a modified form of cushioning means in which a rubber block 70 
is positioned adjacent each end cap 56 in series with each spring 54'. 
Each spring 54' acts against a plate 71 which compresses the adjacent 
rubber block 70. Thus in drive direction D when lug 36 contacts end cap 
57' spring 54' is compressed and moves plate 71 which also compresses 
block 70 until plate 71 contacts end cap 56'. The interaction of spring 
54' and rubber block 70 depends on the relative spring rates of the spring 
and block and can be chosen to give a variety of different operating 
characteristics depending on the vehicle in which the flywheel is to be 
used. 
Movement in the opposite direction is cushioned by the contact of lug 36 
with a plate 72 which overlies a rubber block 73 which is supported by an 
end cap 74.