EP1119716A1

EP1119716A1 - Twin mass flywheels

Info

Publication number: EP1119716A1
Application number: EP00951709A
Authority: EP
Inventors: Anthony John Curtis; Alastair John Young
Original assignee: AP TMF Ltd
Current assignee: AP TMF Ltd
Priority date: 1999-08-10
Filing date: 2000-08-04
Publication date: 2001-08-01
Also published as: WO2001011258A1; GB0107339D0; GB2358693A; AU6456600A

Abstract

A twin mass flywheel (10) for use in drive lines has an input mass (11) for connection with an associated engine and an output mass (12) for connection with an associated driveline, these masses being relatively rotatable via a support bearing (13) acting therebetween against the action of a torsional damping means (14, 15, 16, 17) to damp torsional vibrations in the associated driveline. The input mass (11) has a central disc portion (11b) and a separately formed outer annular main mass portion (11c), the outer annular main mass portion having a recess (11e) in which the outer periphery of the central disc portion (11b) is received, and the inner and outer mass portions being secured together (11f) for co-rotation. The outer mass portion (11c) may carry additional mass in the form of blocks (70) located in a volume of an annular zone between the masses which is not swept by linkages (14) which connect the masses (11, 12) and act as part of the torsional damping means.

Description

WO 01/11258 PCT/GB0O/O3O29

TWIN MASS FLYWHEELS

This invention relates to twin mass flywheels, hereinafter referred to as of the kind specified, for use in drive lines, the flywheel comprising an input mass for connection with an associated engine and an output mass for connection with an associated driveline, said masses being relatively rotatable via a support bearing acting therebetween against the action of a torsional damping means to damp torsional vibrations in the associated driveline

It is an object of the present invention to provide a twin mass flywheel of the kind specified which is economical to construct

It is a further object of the present invention to provide a twin mass flywheel of the kind specified which is of a compact construction

Thus according to the present invention there is provided a twin mass flywheel of the kind specified in which the input mass comprises a central disc portion and a separately formed outer annular main mass portion, the outer annular main mass portion having a recess in which the outer periphery of the central disc portion is received, and the inner and outer mass portion's being secured together for co-rotation

This arrangement enables a high inertia to be provided in relatively small envelope

The outer and central portions may be secured together by circumferentially spaced rivets or similar fastening means Alternatively, for example, the outer and central portions may be welded together by laser or beam welding

The outer main mass portion may carry a starter ring This starter ring may be formed integrally on the outer mass portion or may be a separate component Additional mass may be secured to the outer main mass portion.

Typically the outer main mass portion may be of a cast construction and the central portion may be of a pressed sheet construction.

The outer main mass portion may be secured to the central portion in a substantially axially mid region of the outer portion to provide better axial balancing of the outer portion relative to the central portion.

The outer portion may be centred relative to the central portion by contact between circumferentially spaced locating zones on one portion which contact a peripheral zone of the other portion. For example, circumferential spaced radially projecting locating zones on the outer periphery of the central portion may contact a radially inwardly facing peripheral zone of the recess.

The recess in the outer main mass portion which receives the outer periphery of the central disc portion may comprise a stepped bore with a smaller diameter portion of the stepped bore of relative short axial extent contacting the periphery of the central disc portion. With such a construction dimensional accuracy of the recess can be limited to this relative short smaller diameter portion of the stepped bore thus reducing manufacturing costs.

In an alternative arrangement the central disc portion may initially be of a dished configuration and during assembly of the input mass the central disc portion is pulled flat into contact with the outer main mass portion thus forcing the outer periphery of the central portion to bite into the outer portion.

In yet a further alternative design gripping teeth formed on the outer periphery of the central portion are forced into the outer main mass portion prior to further securing together of the central and outer portions. In yet a further alternative the step in the bore may be peened over to hold the central portion in position prior to further securing together of the central and outer portions. The invention also provides a method of balancing the input mass after the outer and inner portions have been secured together This balancing may be achieved by drilling first balancing holes in a first annular surface of the outer portion. Preferably the entire twin mass flywheel is balanced after completion of its assembly by drilling second balancing holes in a second annular surface of the outer portion of the input mass Conveniently the first annular surface may face axially and the second annular surface may face radially

The invention further provides a method (and a jig for carrying out the method) of centring the central and outer portions of the input mass relative to each other on a jig which centres these two components relative to the intended axis of rotation of the input mass Such a jig may include a first set of spring-loaded jaws which centre the central portion and a second set of spring-loaded jaws which centre the outer portion

Preferably the support bearing is carried on a bearing support member which is centred relative to and secured to the central portion of the input mass

The invention also provides a twin mass flywheel of the kind specified in which the torsional damping means includes a plurality of circumferentially spaced linkages disposed in an annular zone between the masses, the linkages interconnecting the masses to damp torsional vibrations in the associated vehicle driveline and each moving through a swept volume in said annular zone as said masses rotate relative to each other, the flywheel also including additional mass secured to one or both flywheel masses at circumferentially spaced locations in the non-swept volume of said annular zone

This arrangement enables the inertia of the flywheel to be increased to promote improved engine smoothness without increasing the space occupied by the flywheel

The additional mass may comprise separate masses rivetted or otherwise secured to the relevant flywheel mass Alternatively the additional mass may be cast, forged or otherwise formed integrally with the relevant flywheel mass The additional masses may also act as abutments which spring damping means may act, to further resist the relative rotation of the flywheel masses

The present invention will now be described by way of example only, with reference to the accompanying drawings in which. -

Figure 1 is a side view of a twin mass flywheel embodying the present invention,

Figures 2 and 3 show sections on lines B-Bl and B2-B3 of figure 1 respectively,

Figures 4 shows part of figure 2 on a larger scale,

Figure 5 shows a further part of figure 1 on a larger scale,

Figure 6 shows part of a casting mould for an in situ moulded plain bearing,

Figure 7 shows an alternative in situ moulded plain bearing,

Figures 8 and 9 show perspective views of an alternative form of twin mass flywheel embodying the present invention,

Figure 10 shows a section through a still further form of twin mass flywheel embodying the present invention,

Figure 11 shows a modification of the input mass of the flywheel of figure 10,

Figures 12 and 13 show a further modification of the input mass,

Figure 14 shows a further alternative form of input mass using sheerpins and adhesive bonding, Figure 15 shows a further alternative form of input mass using welding;

Figure 16 and 17 shows a further alternative form of input mass employing an initially dished central portion;

Figures 18A and 18B show a further alternative form of input mass employing gripping teeth;

Figure 19 shows yet a further alternative form of input mass employing peening.

Figure 20 shows details of a centring jig for the outer and central input mass portions,

Figures 21 and 22 show alternative methods of centring a bearing support member relative to the central portion of the flywheel input mass

Referring to figures 1 to 5 a twin mass flywheel 10 comprises an input flywheel mass 11 [carrying a starter ring 1 1 a] and an output flywheel mass 12 which are mounted for limited relative rotation about a common axis A- A via a plain bearing arrangement 13 described in detail below carried on a bearing support block l id Relative rotation of the input and output flywheel members is opposed by a damping means in the form of bob-weight linkages 14, compression spring assemblies 15, elastomeric springs 16, and a radially inner multi-plate friction damper 17 All these damping means act in parallel between the input and output flywheel masses

In accordance with the invention the input flywheel mass 1 1 is of a composite construction having pressed metal central disc portion 1 lb and a forged outer annular portion 1 lc which are welded together by a weld bead 1 If and are centred relative to each other by contact between the outer periphery of disc portion 1 lb and annular surface 1 le on outer portion 1 lc The output flywheel mass 12 is of a cast metal construction The two flywheel masses are held in an assembled state, prior to attachment to the associated engine crankshaft by screws 18 see Figure 1, on the same pitch circle diameter as bolt holes 19 As is conventional the twin mass flywheel is bolted to the crankshaft by attachment bolts 19a which extend through circumferentially spaced bolt holes 19 in bearing support block 1 Id and input flywheel mass disc portion 1 lb By using this composite input flywheel mass construction a high inertia can be provided in a relatively small envelope and complex metal forming operations are also avoided.

Compression spring assemblies 15 each act between a first abutment 20 (see figure 1 ) which is forged out of input flywheel 11 and a second abutment 21 which is cast into output flywheel 12. By forming both of the abutments integrally with the respective flywheel masses the number of separate components in the flywheel is significantly reduced and the axial space required is also reduced since separate spring abutment members are eliminated

Each compression spring assembly may comprise an outer compression spring 15a and an inner compression spring 15b with the operation of the inner compression spring 15b being timed to be delayed by several degrees from the commencement of the operation of the outer compression spring 15a.

Alternatively, one pair of diametrically opposite compression springs 15 may be arranged to operate before the other pair of diametrically opposite compression springs during the relative rotation of the two flywheel masses

The springs 15a and 15b have a natural shape in which their longitudinal axes are straight When mounted between abutments 20 and 21 the springs are deflected to an acute shape by a sheet metal support member 40 which will be described further below

Figure 1 shows the flywheel in its central or neutral position and, with the flywheel rotating in the direction of arrow D, in the normal drive condition a relative rotation of P (see Figure 5) occurs before abutments 21 are contacted by spring chairs 15c which fit around the end of the springs 15 Springs 15 are non-operational in the overrun condition when abutments 21 tend to move away from springs 15

The elastomeric compression springs or blocks 16 (see figure 5) are each supported on the input mass 11 between end plates 16a in a window 22 pressed out of input flywheel mass 11 by a sheet metal casing member 41 Member 41 has end portions 41a and 41b which are respectively curved around a radially outer abutment 24 which is pressed out of input flywheel mass 1 1 and around the bottom edge 22a of window 22

The end plates 16a are acted upon by abutments 23 on a ring 23a which is secured to output flywheel mass 12 by rivets 23b The end plates 16a have wings 16b which extend between abutments 23 and output mass 12 and tabs 16c which hook under the radially inner edge of block 16 Each elastomeric spring block 16 is also located against radially outwards movement to mass 1 1 by radially outer abutment 24

The elastomeric springs 16 are therefore confined within windows 22 between the two flywheel masses 1 1 and 12 As will be appreciated the blocks 16 operate to damp relative rotation of the flywheel masses in the end zones of the relative rotation both in the drive and overrun conditions Blocks 16 operate in the drive condition after a relative rotation of Q and in the overrun condition after a relative rotation of R Further details of blocks 16 are set out in the Applicant's co-pending UK patent application No 98 28399 7

Each bob- weight linkage 14 comprises a bob-weight 25 which is pivotally mounted on output flywheel mass 12 via a cantilevered pivot pin 26 and a bush 27 which is press fit into the bob- weight The linkage is completed by a flexible link 28 which is connected at one end with the input flywheel mass 1 1 via a rivet 29 and at its other end with a bob- weight 25 via a rivet 30

Each rivet 29 extends through a mounting tab 40a of support member 40 The other end 40b of spring support member 40 rests on outer radially abutment 24

The details of pivotal connections 28 and 29 are again described in greater detail in the previously referred to co-pending application no 98 28399 7

As can be seen from figure 1 , pivots 29 are located radially within compression spring assemblies 15 This allows a longer length for links 28 so that the total permitted relative rotation between the input and output flywheel masses can be increased.

Bob-weights 25 are also shaped having a cut-out portions 25a, to concentrate their mass as radially far outwards as possible

Output mass 12 is provided with radially outwardly projecting lugs 45 which move in circumferentially extending slots 46 between radially inwardly extending lugs 47 on input mass 1 1 Relative rotation between mass 1 1 and 12 in the drive condition is limited by contact between surfaces 47a and 45a on lugs 47 and 45 and in the overrun condition by contact between surfaces 47b and 45b

The multi-plate friction damper 17 is best seen in Figure 4 This damper comprises discs 50 and 51 which are splined onto output mass 12 at 50a and 51a respectively, the disc 52 which is splined at 52a onto a first bearing carrier 60 which has a radially inwardly extending portion 60d which is bolted to input flywheel mass disc portion 1 lb by bolts 19a and further discs 53 and 54 which are splined at 53a and 54a to an annular band 55 which is itself splined at 55a onto spines 52a of disc 52 The friction damper is completed by a pair of belleville springs 56 which act between disc 50 and a second bearing carrier 61 which is secured via rivets 23b to output flywheel mass 12

This basic form of friction damping device is described in the Applicant's co-pending patent application No WO96/29525 and includes co-operating ramps formed on discs 50 and 54 which are indicated diagramatically at 57 in figure 4 As described in co-pending application No WO96/29525, after the two flywheel masses have rotated relative to each other through a given angle from the neutral or central position, the ramps come into operation and force the discs 50 and 54 apart against the action of belleville springs 56 to generate increasing friction from damping device 17 The device can be arranged to generate no friction in the central region before the ramps become operative or can have its axial loading adjusted to ensure that friction is generated at all times The precise set-up of the friction damper depends on the desired operating characteristics of the flywheel In accordance with the Applicant's co-pending UK Patent Application No 9918716 3 the above referred to bearing carriers 60 and 61 have concentric generally axially extending portions 61a and 60a respectively between which a plain bearing sleeve 80 which is formed in situ is located The bearing is completed by a belleville spring 62 which acts between radially extending regions 60c and 61c of the bearing carriers to bias the regions 60c and 61c apart and hence axially load the output flywheel mass 12 to the left, as viewed in figure 4, relative to the input mass 11 In effect disc 52 which is sandwiched between the input and output flywheel masses acts as an axial thrust bearing support member

To provide further support for the relative rotation of the flywheel masses 1 1 and 12 axially facing support pads 66 are provided at circumferentially spaced locations around the input mass 1 1 These pads contact the confronting surface 12a of the output mass 12 to control any tendency of the two flywheel masses to move axially or tilt relative to each other during relative rotation

Pads 66 could replace disc 52 to take axial loading or could supplement disc 52 to control tilt to a given level

The beanng support block 1 Id is preferably manufactured from cast metal and, in order to avoid problems due to local radial distortion of the support block when attachment bolts 19a are fully tightened the radially outer surface 1 lg of block 1 Id may be sized to be positioned with a slight clearance from the bearing carrier 60 and the carrier 60 may be supported against radially inward movements by annular washer 65 through which the attachment bolts 19a extend This washer is also provided to prevent the attachment bolts digging into the cast support l id Alternatively earner 60 may be supported on support lid

The plain bearing sleeve 80, as indicated above, is formed in situ between the carriers 60 and 61 using a mould arrangement part of which is shown diagrammatically in Figure 6 Essentially the mould comprises two platens 81 and 82 which support the bearing carriers 60 and 61 with their radially extending portions 60c and 61c in contact with each other to seal off one end of a void between the bearing supports within which the bearing sleeve 80 will be moulded. The other end of the void is sealed by the platen 82 Platen 82 includes injection nossles 83 through which polymeric bearing material is injected When the bearing material is solidified the supports 60 and 61 together with the in situ moulded sleeve 80 are removed from the mould and the supports 60 and 61 are moved axially and/or rotated relative to each other to crack the bond between the sleeve 80 and one or both of the supports 60 and 61 to provide a functioning bearing The bearing is then subsequently mounted in its operational position in the flywheel with the two radially extending portions 60c and 61c spaced apart as shown, for example, in figure 4

The moulding process may be modified by providing differential temperature control to the platens This can be achieved by providing one or both of the platens with a cooling water gallery which cools one or both carriers 60 or 61 so that the in situ moulded bearing sleeve does not attach itself to the or each cooled carrier This obviates the need to crack the carriers from the moulded sleeve 80 If the or each platen is cooled sufficiently the bearing sleeve may shrink back slightly from the cooled carrier(s) to give a working clearance

Alternatively differential temperature of the platens can be achieved by applying heat rather than cooling

In a further alternative arrangement in place of platen cooling one or both of the carriers may be coated in a release agent prior to insertion into the mould to remove the need to, or at least facilitate, cracking of the carriers from sleeve 80

Clearly one big advantage of forming the bearing sleeve by in situ moulding is that absolute accuracy of the internal and external diameters of the bearing sleeve is guaranteed without the need for any expensive machining or any particularly high manufacturing accuracies

The material from which the bearing sleeve is moulded may, for example, comprise modified or unmodified thermoplastic or thermosetting polymers For example, PEEK (poly ether ether ketone) with fillers such as glass fibre, carbon fibre and/or friction modifiers such as molybdenum disulphide may be used Alternatively PES (polyethersulphone) with similar fillers and modifiers may be used

The bearing construction shown in Figure 4 may be modified, for example, by moving belleville spring 62 to the position occupied by disc 52 and forming bearing sleeve 80 with an integral radially extending portion 80a (see Figure 1) which replaces disc 52 and acts as an axial thrust bearing Bearing sleeve 80 with the radially extending portion 80a may be cast in situ by a suitable modification of the mould platens shown in Figure 6

If desired the bearing sleeve 80, with or without radially extending portion 80a, may be directly moulded or otherwise formed into portions of flywheel mass 12 and support 1 Id or an axially extended portion of flywheel mass 11 This arrangement requires appropriate modification of the mould platens shown in Figure 6

In accordance with a further aspect of the present invention the input flywheel mass 1 1 is provided with additional mass 70 at circumferentially spaced positions around the input mass to increase the inertia of the flywheel This additional mass is located generally in the annular zone between the flywheel masses within which the bob weight linkages 14 operate but is located to the side of the linkages in a non swept volume of this annular zone This extra mass is forged into the outer annular portion l ie of the input mass and includes the spring abutments 20

The provision of this additional mass increases the inertia of the flywheel which increases its torsional damping capabilities and thus promotes engine smoothness It also allows the ratio of input flywheel mass to output flywheel mass to be tuned Typically this input to output mass ratio is in the range 60-40 to 70-30 Choosing the desired value for this ratio is a balance between the requirement to have a high input mass to give maximum torsional damping effect and a requirement to lower the input mass to produce a more free revving engine Also the thermal capacity and hence mass of the output mass must be sufficient to absorb the heat which may be generated by the clutch plate which engages the output mass

All these factors have to be taken into account when choosing the input to output mass ratio and additional mass blocks, whether integral or separate, can be used on the input or output mass to adjust this ratio and also the overall inertia of the flywheel Figures 8 and 9 show perspective views of part of an alternative form of one piece input flywheel mass 1 11 in which equivalent components to those shown in Figures 1 to 7 have been marked with reference numerals increased by 100 The input flywheel mass 111 has separate additional mass blocks 170 which are riveted to the input mass pressing 170a. The separate additional blocks 170 also include spring abutments 120 which are contacted by compression spring assemblies 115

As can be clearly seen from Figure 8 blocks 170 are located to the side of linkages 1 14 in the non-swept volume of the annular zone between the flywheel masses in which the linkages operate.

Figure 10 shows an alternative form of twin mass flywheel 200 comprising an input mass 21 1 and an output mass 212 which is supported by a bearing 213 carried on a bearing support member 214 which is secured to the input mass 21 1

The relative rotation of the input and output masses 21 1 and 212 is controlled by a torsional damping means in the form of bob-weight damping linkages 215 which are connected between the masses, compression springs 216 A which act between the masses, rubber and travel springs 216B and a friction pack 217 which also acts between the masses All these elements of the torsional damping means act in parallel between the masses

Since the present invention is not concerned with the details of any of the elements of the torsional damping means these elements will not be further described If the reader wishes to find further details of these damping elements these can be obtained from the following earlier applications of the Applicant

Bob-weight damping linkage - Applicant's application no WO96/38681 Compression springs - Applicant's application no WO 96/38681 Rubber end travel springs - Applicant's application no WO 96/38681 Friction pack - Applicant's application no WO 96/29525 As with the flywheel shown in figures 1 to 6 the input mass of the twin mass flywheel is of a composite construction a central disc portion 218 and an outer annular main mass portion 219

As can be seen from figure 10, the main outer mass portion 219 carries an engine starter ring 220 and a sheet metal annular ring 221 which includes an added mass portion 222a which projects axially beyond the output mass 212 and the cover 223 of the associated clutch and a radially inwardly extending flange 222b which includes a slot 222c to accommodate linkage rivet 215a

The central disc portion 218 of the input mass is of a pressed sheet metal construction of relatively small thickness, typically 4mm, whilst the outer main mass portion 219 is of a cast construction and includes an internal recess 224 within which the outer periphery of the central disc portion 218 is received The central disc portion may be subjected to a surface hardening process such as nitriding

The central and outer portions 218 and 219 are riveted together by rivets not visible in figure 10 The general plane of the central disc portion 218 is located in a substantially axially mid region 219a of the outer main mass portion 219 so that the outer main portion is better balanced in an axial sense relative to the central portion

The bearing support member 214 is secured to the central portion 218 of the input mass by the attachment bolts 225 which also secure the entire twin mass flywheel to the crankshaft of an associated engine (not shown) Additional elements are provided to secure the bearing support member to the central disc portion 218 during assembly of the twin mass flywheel Two examples of alternative methods of securing the bearing support member 214 to the central portion 218 are illustrated in figures 21 and 22 In figure 21 the bearing support member 214 is centred relative to the central disc portion 218 by two dowels 226 and the bearing support member is secured to the central disc portion by a pair of set screws 227 This attachment is further augmented by the attachment bolts 225 which also pass through the bearing support member 214 and central disc portion 218 as mentioned above In figure 22, the bearing support member 214 is centred relative to the central disc portion 218 by ring dowels 228 which surround bores 229 and 230 in the bearing support member 214 and central disc portion 218 respectively and through which the attachment bolts (not shown) ultimately extend when the flywheel is secured to the associated engine crankshaft Again the bearing support member 214 and central disc portion 218 are held together during assembly of the flywheel by a pair of set screws 227

As can be seen from figure 10, the central portion of the input mass 21 1 is of an extremely compact axial dimension so that the total axial width X of the flywheel in the central region is relatively small This is a particularly important feature of the present invention allowing the flywheel of the present invention to be installed in confined engine compartments applications (e g front wheel drive vehicles) where the axial length of the flywheel and thus associated clutch and transmission housings is of significant importance

By manufacturing the outer main mass portion 219 as a cast component the necessary inertia of the input mass can be maintained and the construction of the input mass is also extremely economical and compact

Figures 1 1 shows a modified form of input mass in which outer main mass portion 219 has a recess 224 in the form of a stepped bore having a smaller diameter portion 231 which contacts the outer periphery of the central disc portion 218 This construction has the advantage that dimensional accuracy need only be maintained over the relatively short smaller diameter portion 231 of recess 224 thus reducing manufacturing costs

In the arrangement shown in figures 12 and 13, the outer periphery of the central disc portion 218 is provided with a number of radially projecting tabs 232 which contact the smaller damped portion 231 of recess 224

In the arrangement shown in figure 14, the outer main mass portion 219 is secured to the central disc portion 218 by circumferentially spaced shear pins 233 and by adhesive bonding In the arrangement shown in figure 15, the central disc portion 218 is welded at 219a to the outer main weight portion 219 by, for example, laser or a beam welding process

Referring to figures 16 and 17, these show yet a further alternative form of input mass in which the central disc portion 18 is initially of a dished configuration, as shown in figure 16, and the central portion 218 is pulled flat against the outer main mass portion 219 using rivets 234 This causes the corner 218a of the central disc portion to bite into a tapering portion 224a of recess 224 This provides a pre-stressed central disc portion 218 which assists in maintaining concentricity of the central portion 218 and outer main mass portion 219 during use of the flywheel

In the arrangement shown in figure 18A and 18B, the outer periphery of the central disc portion 218 is provided with a series of circumferentially spaced gripping teeth 235 which as the central disc portion 218 is pressed onto the reduced diameter portion 231 of recess 224 bite into the reduced diameter portion 231 to locate the outer main mass portion 219 relative to the central disc portion 218 The gripping effect of these teeth is further augmented by rivets, bonding, welding or other suitable securing means

Figure 19 shows an arrangement in which the reduced diameter portion 231 of recess 224 is peened over at 236 to retain the central disc portion 218 in position relative to the outer main mass portion 219 Again this attachment is augmented by further securing means such as rivets, welding or adhesive etc

Figure 20 shows diagrammatically the basic principles of an automatic centring jig used to centre the central disc portion 218 and the outer main mass portion 219 relative to an intended axis of rotation Z of the input mass

The jig comprises a first set of spring loaded jaws 240 which are spring-loaded radially outwardly as indicated by arrows 241 into contact with aperture 242 formed in the centre of disc portion 218 These jaws centre the disc portion 218 relative to axis Z A second centre of jaws shown diagrammatically at 243 are biased radially inwardly as indicated by arrows 244 into contact with the outer periphery 245 of the main disc portion 219 and centralise the main disc portion relative to intended axis of rotation Z. The bias of the jaws 240, 243 may be achieved by any suitable means such as springs, pneumatic or hydraulic pressure or magnetic force Alternatively, the jig may have its jaws brought into centring contact with the central and outer portion manually (e.g. by winding a separate handle for each set of jaws ) or the jig may have fixed jaws into which the central and outer portions are inserted for centring.

With the two input mass portions 218 and 219 centralised by the jig these portions are then secured together by, for example, rivets 246 to produce a correctly centred input mass

The input mass is balanced after the outer and inner portions have been secured together This balancing may be achieved by drilling balancing holes in a first annular surface of the outer portion. Preferably the entire twin mass flywheel is balanced after completion of its assembly by drilling balancing holes in a second annular surface of the outer portion of the input mass Conveniently the first annular surface may face axially and the second annular surface may face radially

As will readily be appreciated the composite flywheel input mass constructions described above, which utilise a central disc portion and a separately formed outer annular main mass portion in which the central portion is received, can be used with a wide variety of twin mass flywheels of the kind specified and are not limited to use with any particular type of torsional damping means

Claims

1 A twin mass flywheel of the kind specified in which the input mass comprises a central disc portion and a separate formed outer annular main mass portion, the outer annular main mass portion having a recess in which the outer periphery of the central disc portion is received, and the inner and outer mass portion's being secured together for co-rotation

2 A flywheel according to claim 1 in which the outer and central portions are secured together by circumferentially spaced rivets or similar fastening means

3 A flywheel according to claim 1 in which the outer and central portions are welded together

4 A flywheel according to claim s 1 to 3 in which the outer main mass portion is of a cast construction and the central portion is of a pressed sheet construction

5 A flywheel according to any one of claims 1 to 4 in which the outer main mass portion is secured to the central portion in a substantially axially mid region of the outer portion to provide better axial balancing of the outer portion relative to the central portion

6 A flywheel according to any one of claims 1 to 5 in which the outer portion is centred relative to the central portion by contact between circumferentially spaced locating zones on one portion which contact a peripheral zone of the other portion

7 A flywheel according to claim 6 in which circumferential spaced radially projecting locating zones on the outer periphery of the central portion contact a radially inwardly facing peripheral zone of the recess A flywheel according to any one of claims 1 to 7 in which the recess in the outer main mass portion which receives the outer periphery of the central disc portion comprises stepped bore with a smaller diameter portion of the stepped bore of relative short axial extent contacting the periphery of the central disc portion

A flywheel according to any one of claims 1 to 8 in which the central disc portion is initially of a dished configuration and during assembly of the input mass the central disc portion is pulled flat into contact with the outer main mass portion thus forcing the outer periphery of the central portion to bite into the outer portion

A flywheel according to any one of claims 1 to 9 in which gripping teeth formed on the outer periphery of the central portion are forced into the outer main mass portion prior to further securing together of the central and outer portions

A flywheel according to claim 8 in which the step in the bore is peened over to hold the central portion in position prior to further securing together of the central and outer portions

A method of balancing the input mass of a flywheel according to any one of claims 1 to 1 1 after the inner and outer portions have been secured together comprising drilling first balancing holes in a first annular surface of the outer portion of the input mass

A method of balancing a complete flywheel of the kind specified after balancing the input mass using the method of claim 12 and completion of the assembly of the flywheel, the method comprising drilling second balancing holes in a second annular surface of the outer portion of the input mass

A method according to claim 13 in which the first balancing holes are drilled in an axially facing first annular surface and the second balancing holes are drilled in a radially facing second annular surface A method of centring the central and outer portions of the input mass of a flywheel according to claim 1 , said method comprising placing the central and outer input mass portions into a jig which centres these two components relative to the intended axis of rotation of the input mass.

A method according to claim 15 in which the jig centres the central portion using a first set of spring-loaded jaws and centres the outer portion using a second set of spring-loaded jaws.

A method according to claim 15 or 16 in which the support bearing is carried on a support member which is centred relative to an secured relative to the central portion of the input mass.

A flywheel according to any one of claims 1 to 11 in which additional mass is secured to the outer main mass portion.

A flywheel according to claim 18 in which the torsional damping means includes a plurality of circumferentially spaced linkages in an annular zone between the masses, the linkages interconnecting the masses to damp torsional vibrations in the associated vehicle driveline and each moving through a swept volume in said annular zone as said masses rotate relative to each other, the flywheel also including additional mass secured to one or both flywheel masses at circumferentially spaced locations in the non- swept volume of said annular zone.

A twin mass flywheel of the kind specified in which the torsional damping means includes a plurality of circumferentially spaced linkages disposed in an annular zone between the masses, the linkages interconnecting the masses to damp torsional vibrations in the associated vehicle driveline and each moving through a swept volume in said annular zone as said masses rotate relative to each other, the flywheel also including additional mass secured to one or both flywheel masses at circumferentially spaced locations in the non-swept volume of said annular zone. A flywheel according to any one of claims 18 to 20 in which additional mass comprises separate masses rivetted or otherwise secured to the relevant flywheel mass

A flywheel according to any one of claims 18 to 20 in which the additional mass is cast, forged or otherwise formed integrally with the relevant flywheel mass

A flywheel according to any one of claims 18 to 22 in which the additional mass may also act as abutments against which spring damping means act to further resist the relative rotation of the flywheel masses

A flywheel according to any one of claims 1 to 11 or 18 to 23 in which the support bearing is a plain bearing cast in situ between the input and output masses or between bearing carriers connected with a respective one of the input and output masses

A flywheel of the kind specified constructed and arranged substantially as hereinbefore described with reference to and as shown in any one of the accompanying drawings