GB2276433A

GB2276433A - Two-part flywheel

Info

Publication number: GB2276433A
Application number: GB9405779A
Authority: GB
Inventors: Bernhard Schierling; Stefan Gebauer; Ralf Till
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Sachs AG
Priority date: 1993-03-24
Filing date: 1994-03-23
Publication date: 1994-09-28
Anticipated expiration: 2014-03-23
Also published as: BR9401256A; ES2082712B1; GB9405779D0; FR2704915A1; ES2082712A2; FR2704915B1; ES2082712R; DE4309551A1; GB2276433B; DE4309551C2

Description

2276433 TWO-PART FLYWHEEL The invention relates to a two-part flywheel for

an internal combustion engine of a motor vehicle of the kind comprising a primary mass which is secured on the end of the engine crankshaft concentric with its axis, a secondary mass which is mounted on the primary mass, and a torsion spring device between the two masses for transmitting torque and damping torsional vibrations, and having a clutch pressure plate secured by a flange to a corresponding attachment face on the secondary mass, and a clutch plate interposed between the pressure plate and the secondary mass.

Two-part flywheels of the kind stated above are known in various forms. For example from German OLS 34 12 961 there is known a two-part flywheel in which the pressure plate of the friction clutch and the clutch plate are secured to the secondary mass by screws.

The assembly processes for two-part flywheels are being automated to an increasing extent. Accordingly, it is worth striving to enable the pressure plate and the clutch disc to be secured to the secondary mass by a robot.

A robot can bring the pressure plate automatically into the correct position if for example a location mark, capable of being recognised by robots, is provided on the secondary mass. However, such a solution cannot always be achieved economically.

According to the present invention in a two-part flywheel of the kind set forth, a locking means is provided between the primary and secondary masses, the 2 locking means having a locked position, in which it prevents relative rotation of the masses, and being releasable into an unlocked position in which relative rotation is permitted.

The arrangement of the locking means, or rotation lock, between the two masses, which may be undertaken for example by the supplier of the flywheel, means that on the initial assembly of an engine it is possible to maintain the exact position of both masses, in relation to the engine parts. In this way, -when the robot recognises the location of the crankshaft, it also knows the locations of the two masses, and can place the pressure plate in the correct position so that the holes for the attachment screws are lined up with the threads. This provides an easy and cheap way of using automatic assembly for the clutch pressure plate and clutch plate. The locking means can be released at the earliest after insertion of the screws into the threads or at the latest before the engine is put into operation. The rotation lock enables easy automatic assembly of a two-part flywheel onto a crankshaft of an internal combustion engine even when a torsion spring arrangement is provided between the two masses and has a very low spring stiffness over the initial part of its travel.

The locking means is preferably locked with the torsion spring arrangement in its neutral position. This is advantageous because on subsequent release of the rotation lock no relative movement takes place between the two masses. Moreover it is just in this neutral position that the locking process by the manufacturer of the flywheel is easy to perform.

3 The process of releasing the locking means can take place either automatically on assembly of the pressure plate, or equally well after assembly of the pressure plate, according to the nature and position of the means chosen. It is then advantageous if wall regions of the primary mass extend opposite the attachment face for the pressure plate on the secondary mass, and axially spaced therefrom. With such a disposition rotation locks with or without an automatic release action can be employed.

Thus, a non-automatically releasable locking means can be provided by a threaded insert being arranged in a threaded hole in the secondary mass at least at one position and parallel to the axis of rotation, the insert being screwed in before assembly of the pressure plate so that it locates the two masses relative to one another either frictionally or mechanically and being removed through a corresponding opening in the pressure-plate flange after assembly. In this arrangement the threaded insert passes right through the secondary mass and it engages in an adjacent surface region of the primary mass. This arrangement is particularly advantageous and simple insofar as a screw-thread which is already present for attachment of the pressure plate can be employed and after removal of the threaded insert a corresponding attachment screw can be inserted.

A particularly simple solution is provided by the locking means being released at least on screwing in of one of the attachment screws attaching the pressure plate to the secondary mass. In this way no separate unlocking process is required.

4 Such automatic release can be performed where the locking means comprises a locking element retained on the outer periphery of the secondary mass adjacent a threaded hole by its own stress and having, in the locked position, a rotationally secure connection to the primary mass, and on insertion of the attachment screw into the threaded hole the element moves automatically from the locked position into the unlocked position. The locking element preferably resembles a leaf spring, having an end region engaging in a groove in the primary mass open towards the secondary mass to form the locking connection by engaging circumferential faces on the primary mass. A pin projects into the threaded hole and is urged radially inwardly by the locking element in its locked position but is forced radially outwards during the process of screwing in the attachment screw.

Another advantageous kind of automatically released rotation lock envisages that a threaded insert with a screw thread for an attachment screw is arranged in the secondary mass in an opening, and adjacent the primary mass, and in alignment with a through bore for the attachment screw and is held by the engagement of its external profile in an internal profile in the secondary mass at least circumferentially free of play and secure against rotation, and is urged axially by the force of a spring towards the primary mass, and with the attachment screw not tightened engages, circumferentially free of play by means of a projection or its external profile, in a corresponding recess in the primary mass, and when the attachment screw is tightened it is held on the secondary mass in a position remote from the primary mass and thereby the projection or the external profile is held out of engagement with the recess in the primary mass. Such a device is advantageous because completely standard attachment screws can be employed and the entire device is held against rotation.

An automatically released locking means which is particularly secure in operation provides that there is arranged in attachment faces of the secondary mass a through bore parallel to the axis of rotation and in which an axially-extending portion adjacent the attachment face has a right-hand thread and an axially-extending portion adjacent the _primary mass has a left-hand thread, there being inserted in the left-hand thread a threaded insert which, before the pressure plate is mounted, has a projection directed towards the primary mass and engaging at least circumferentially in a mechanical way in a recess in the primary mass, and which has a dowel pin directed towards the attachment face and having a slight projection beyond the attachment face, and the attachment screw has a central longitudinal hole, in the internal profile of which the external profile of the dowel pin can engage to prevent relative rotation but allow axial displacement, and when the attachment screw is inserted to mount the pressure plate, the threaded insert is automatically moved away from the primary mass and the projection comes out of engagement with the recess. Such a construction is both particularly secure in operation in the locked position and also during the unlocking process which automatically coincides with the action of attaching the pressure plate.

in a further embodiment it is proposed that a clip should be arranged on the secondary mass in the neighbourhood of at least one threaded hole for an attachment screw, the clip having a main body with 6 radially outer and inner portions separated by a fold, the radially outer portion engaging the attachment face and extending outwardly beyond it, and the radially inner portion of the main body projecting radially inwards and, before attachment of the pressure plate, having a portion which stands away from the attachment face, and a tongue projecting from the main body axially over the outside diameter of the secondary mass, and radially spaced from it, and being cranked to extend radially inwards so that its end is in the threaded hole, the crank engaging in -a recess in the primary mass and so forming a rotation lock which is automatically released, on screwing the pressure plate to the secondary mass, by a tilting movement of the main body about the fold, in which the radially inner portion of the main body comes into engagement with the attachment face, whilst the radially outer portion of the main body lifts away from the attachment face, so that the tongue is moved away from the primary mass towards the pressure plate and the crank on the tongue comes out of engagement with the recess. Such a rotation lock is distinguished in particular by the low-cost nature of the locking element in the form of a clip.

It is further proposed that, to locate the clip laterally, in addition to the tongue, there are two further tongues which, before the pressure plate is mounted, engage the outside diameter of the secondary mass. In this way the clip can be pre-assembled onto the secondary mass and is then secure against loss.

The material and construction of the clip are chosen in such a way that a permanent plastic deformation occurs on unlocking following mounting of the pressure plate. In this way it is ensured that on 7 any possible subsequent replacement of the clutch plate or the pressure plate the clip does not return to the locking position. Locking is no longer necessary in any such repair process.

In order to be able to provide sufficient freedom of movement for the clip an appropriate recess for receiving the tongue is advantageously provided in the secondary mass.

It is furthermore advantageous to -provide radially extending grooves in the attachment face at the or each position where there is a clip, the width of the grooves corresponding to the width of the main body and their depth to the thickness of the material of the clips. In this way there is obtained a circumferentially extending unbroken smooth engaging surface for the flange of the pressure plate.

The main body of the clip is provided in the unstressed condition with a bulge extending radially inwards of the fold and over the threaded hole and having an opening for receiving the attachment screw. This construction secures the clip additionally during the assembly process and prevents it escaping radially outwards.

The invention -will now be further explained in conjunction with the accompanying drawings. In the drawings:

Figure 1 shows the upper half of a longitudinal section through a twopart flywheel with a separately inserted threaded insert; 8 Figure 2 is a partial longitudinal section through a two-mass flywheel with an automatically releasable locking element; Fiúfure 3 is a partial section and also a section III-III through a locking element with a thread; Figure 4 is a partial longitudinal section through a locking element with a left-hand thread; Figures 5-8 show a partial longitudinal section and elevation of a plastically deformable clip.

Figure 1 shows the upper half of a longitudinal section through a twopart flywheel 1 comprising a primary mass 2 and a secondary mass 3. It is arranged concentrically with respect to an axis of rotation 5, this axis 5 being that of a crankshaft 4 of an internal combustion engine. The primary mass 2 is arranged securely on the crankshaft 4 and together with a cover 11 it forms a chamber which is concentric with the axis 5 and in which are arranged a number of circumferentially spaced coil springs 10. A hub disc 9 projects radially inwardly into this chamber and has corresponding radially projecting fingers which are in rotationally secure engagement with the individual coil springs 10. The hub disc 9 is connected securely in its radially inner region to the secondary mass 3 which is axially offset from the primary mass 2. The secondary mass 3 is mounted to be rotatable but axially located on a hub 7 by means of a bearing 6 in its radially inner region and the hub 7 is screwed to the crankshaft 4 of the engine together with a cover 8. A driving and engaging clutch, known in principle, is arranged on the secondary mass 3 and comprises a pressure plate 12 and a driven clutch plate 16. The 9 pressure plate 12 comprises a clutch housing 13 as well as a diaphragm spring 14 and a pressure plate 15, the pressure plate 15 being connected in a circumferentially secure manner to the clutch housing 13 but mounted to be axially movable and acted on by the diaphragm spring 14 in a direction to cause the clutch plate 16 to be gripped frictionally. The clutch housing 13 is provided in its radially outer region with a flange 18 which extends substantially radially (perpendicular to the axis 5) and is secured to a correspondingly shaped attachment face 17 of the secondary mass 3 by means of screws 23. The two-part flywheel 1 together with the friction clutch is placed between the crankshaft 4 and a gearbox, not shown, and it damps torsional vibrations by means of the elasticity of the coil springs 10. Additional friction devices or similar damping elements could be provided.

After the two-part flywheel 1 has been mounted on the crankshaft 4 the pressure plate 12 and the clutch plate 16 are assembled, by screwing the plate 12 to the secondary mass 3. In order to be able to automate this process it is necessary for the robot to place the pressure plate 12 in the exact angular position on the secondary mass so that threaded holes 20 provided in the secondary mass 3 to receive attachment screws 23 are aligned with openings 22 in the flange 18 of the clutch housing 13. It is relatively easy for the robot to recognise the angular position of the crankshaft, for example, which means that it can also recognise the position of the primary mass. Provided that the secondary mass is in a fixed position relative to the primary mass, it can associate the arrangement of the openings 22 in the clutch housing 13 to match the threaded holes 20. For this purpose there is provided between the primary mass 2 and secondary mass 3 a locking means which comprises a threaded insert 21. This is inserted in a threaded hole 20, which extends parallel to the axis 5, in place of an attachment screw 23 or independently of one of the attachment screws 23. The threaded insert 21 is screwed into the threaded hole 20 far enough for it to emerge on the rear face of the secondary mass 3 and there to engage a corresponding region of the primary mass 2, here the face of the cover 11 which is adjacent the secondary mass 3. The threaded insert 21 can be screwed in on completion of the flywheel 1 so that it achieves a predetermined disposition between the two masses 2 and 3. In this arrangement the threaded insert 21 can achieve the locking by friction or equally well by mechanical engagement if an appropriate notch is provided in the cover 11. The relative location of the two masses 2 and 3 during the locking process takes place preferably in the neutral position of the torsion spring device, that is to say, with the springs 10 in their unstressed state. In fact any other of the possible range of relative angles can be used but then there is a torque present when the locking is released so relative rotation will occur. In the present case the two- part flywheel is supplied in the locked condition and is mounted on the crankshaft 4. Subsequently the clutch plate 16 and pressure plate 12 are placed in position by the robot with the f lange 18 against the attachment face 17. By virtue of the fixed position of the crankshaft in a new engine it is possible for the robot to recognise the position of the secondary mass 3 and to place the pressure plate 13 circumferentially so that the openings 22 for the attachment screws 23 line up exactly with the threaded holes 20 and the screws 23 can be inserted. it is possible to extract the threaded insert 21 and thereby release the lock as soon as the screws 23 have been 11 inserted into the corresponding holes 20 However, it is also possible to remove the insert 21 only after the screws 23 have been tightened. In this connection it is of minor importance whether the threaded hole 20 in which the insert 21 was present is provided with an attachment screw 23 or not. It is entirely possible to provide a separate threaded hole in the secondary mass 3 which is not used after removal of the insert 21.

Figure 2 shows a locking means or rotation lock in a two-part flywheel 1, which is releaseed automatically during mounting of the clutch disc and pressure plate. Only the outer profile of the primary mass 2 is illustrated; its remaining construction and operation is the same as that shown in Figure 1, and corresponding reference numerals have been applied to corresponding parts. A locking element 28 of the locking means is arranged at the outer periphery of the secondary mass 3 and in fact directly radially outside a threaded hole 20 for an attachment screw 23. The element 28 is shaped like a leaf spring and is secured to the secondary mass 3 by means of a rivet 29 at that end of it which is nearest the attachment face 17. BY virtue of its own internal stress the element 28 is urged radially inwards at that end of it which is furthest from the rivet 29. That end projects into a circumferentially extending groove 24 in the primary mass 2 and there it engages, in a manner preventing relative rotation, between circumferentially spaced faces 25 on the primary mass. Moreover by virtue of its own radially inwardly directed stress the element 28 bears against the head of a pin 27 which projects through the secondary mass 3 and into the threaded hole 20. In the position shown the locking element 28 is in the locked position. After the clutch plate and pressure plate have been mounted and after the pressure 12 plate has been orientated the attachment screws 23 can be inserted, in the manner described already, through the openings 22 in the flange 18 of the clutch housing 13 and can be screwed into the threaded holes 20. In this arrangement at least that screw 23 which is inserted into the hole 20 provided with the locking element 28 is of such a form that it has on the leading end of its thread a conical projection 26. The length of the attachment screw 23 is selected so that as it is screwed into the threaded hole 20 its projection 26 forces the pin 27 radially outwards so- that the locking element 28 is displaced to a position further away from the axis of rotation, in which it lies in the circumferential groove 24 but comes out of engagement with the f aces 25. In this way the locking action is automatically released when the attachment screws 23 are inserted. It is possible to provide such locking elements 28 at several circumferentially spaced points.

In Figure 3 there is illustrated a further embodiment of an automatically released rotation lock. In this arrangement the secondary mass 3 has provided in it, on the side which is adjacent the primary mass 2, at least one internal profile 35 with a through-bore 30 for an attachment screw 23, and with two flat, parallel, circumferentially spaced faces 37. A threaded insert 32 forming the locking means is received in the bore 30 and is guided by these faces 37 and has an external profile corresponding to the faces 37. In this way the threaded insert 32 is guided so as to be movable radially but held against rotation. The insert 32 is pre-loaded by a spring 36 to urge it axially in a direction towards the primary mass 2 and in the locked position it is axially spaced from the secondary mass 3 in the region of the opening 30. The insert 32 is provided with a projection 33 which, in 13 the locked position, engages in a non-rotating manner in a corresponding recess 31 in the primary mass 2.

With the two masses 2 and 3 in the locked position the clutch plate and the pressure plate can be placed by a robot in an appropriate orientation on the attachment face 17 and the attachment screws can be inserted and tightened. In this arrangement the particular attachment screw which is inserted through the opening is screwed into the threaded hole 20 of the insert 32 and the insert 32 is automatically displaced, against the force of the spring 36j- away from the primary mass to release the engagement between the projection 33 and the recess 31, and into abutment with the secondary mass 3. Thus, the flange 18 of the pressure plate 12 is secured by tightening of the screws 23 and the threaded insert 32 is released into its unlocked position.

In Figure 4 there is shown a further variant of a rotation lock between the primary mass 2 and the secondary mass 3. In at least one opening in the secondary mass 3 for an attachment screw there is formed adjacent the attachment face 17 a right-hand thread portion 20 and adjacent the primary mass 2 a left-hand thread portion 39. A threaded insert 40 forming the locking means is inserted in the left-hand thread portion 39 and has a projection 33 directed towards the primary mass 2, and in the locked position this projection engages mechanically in a corresponding recess 31 in the primary mass 2. The threaded insert 40 furthermore has a dowel pin 42 directed away from the primary mass 2. In the locked position the pin 42 projects slightly beyond the attachment face 17. This dowel pin 42 has a non-circular cross-section. An attachment screw 38 which is to be mounted at this position has a right-hand thread 41 and an axial hole 14 43 of which the cross-section matches that of the dowel pin 42. When the flywheel is assembled with the clutch plate and the pressure plate 12 the attachment screw 38 is placed with its hole 43 over the dowel pin 42 and it is screwed into the thread 20 in the secondary mass 3. As the two components 38, 40 are secured together against rotation but can slide axially in relation to one another this insertion of the screw 38 moves the insert 40 in the left-hand thread 39, away from the primary mass 2, to release it into the unlocked position. In this way the projection -33 comes out of engagement with the recess 31 and the rotation lock is automatically released.

In Figures 5 to 8 there is shown a further example of an automatically released rotation lock. A clip 44 forming the locking means is arranged on the secondary mass 3 adjacent a threaded hole 20 for an attachment screw. The cross-section of the clip 44 is illustrated in Figures 5 and 6, with the clip in its advanced and retracted position and Figures 7 and 8 show views from the front and from above. The clip 44 has a main body 45 which is of substantially rectangular shape and has an opening 48 through which an attachment screw can be inserted. The main body 45 is provided with a radially inner portion having a bulge 47 which, before assembly of the pressure plate 12 and the attachment screw, stands away from the secondary mass 3. A fold 46 separates the bulge 47 from a radially outer portion of the main body 45. The fold and the radially outer portion engage the attachment face 17, and on mounting of the pressure plate 13 the outer end of the flange 18 engages the fold 46. A central tongue 50 extends from the main body 45 axially over the outside diameter of the secondary mass 3 and radially spaced from it and its end 52 is cranked in radially and thereby forms a is crank 51. The end 52 engages in the threaded hole 20 in the secondary mass 3. Before the pressure plate is mounted the crank 51 is placed so that it engages in a non-rotational manner in a circumferential recess 53 in the primary mass 2 and thereby forms the locking means. For trouble- free location of the clip 44 on the secondary mass 3 it is provided with two further tongues 54 each being spaced from the tongue 50, one in each circumferential direction. These two tongues 54 are inclined radially inwards and engage against the outside diameter of the secondary mass-3 for support in relation to the end 52 of the tongue 50. Furthermore, there is provided in the secondary mass 3 in the region of the end 52 of the tongue 50 a substantially radially extending notch 55 which allows the end 52 freedom of movement in an axial direction. As is shown in particular in Figure 5 a radially extending groove 49 is provided in the secondary mass 3 in the region of engagement of the main body 45 of the clip 44 and it has a shape matching that of the main body 45 and a depth corresponding to the thickness of the material of the clip 44. This groove 49 serves to provide a f lat engaging surface in a circumferential direction for the flange 18 when the pressure plate 12 is mounted.

When the clutch pressure plate and clutch plate are mounted, on tightening of the attachment screws the flange 18 moves towards the secondary mass 3 so that the clip 44 experiences deformation of the bulge 47, causing the main body 45 of the clip 44 to pivot about the fold 46 in such a way that the radially outer portion of the main body swings away from the primary mass 2 so that the tongue 50 moves in the direction of the arrow A, its crank 51 coming out of engagement with the notch 53 in the primary mass 2, as a result of a corresponding tilting movement of the end 52, so that 16 the rotation lock is automatically released into its unlocked position. The deformation of the clip 44 in this connection is preferably plastic so that a resilient return motion is no longer possible.

17

Claims

1. A two-part flywheel for an internal combustion engine of a motor vehicle of the kind set forth, in which a locking means is provided between the primary and secondary masses, the locking means having a locked position, in which it prevents relative rotation of the masses, and being releasable into an unlocked position in which relative rotation is permitted,

2. A two-part flywheel as claimed in claim 1, in which the locking means is operated with the torsion spring arrangement in its neutral position.

3. A two-part flywheel as claimed in claim 1 or claim 2, in which the locking means is released automatically on assembly of the pressure plate.

4. A two-part flywheel as claimed in claim 1 or claim 2, in which the locking means is released after assembly of the pressure plate.

5. A two-part flywheel as claimed in any preceding claim, in which wall regions of the primary mass extend opposite the attachment face for the pressure plate on the secondary mass, and spaced therefrom.

6. A two-part flywheel as claimed in claim 5, in which the locking means comprises a threaded insert arranged in a threaded hole in the secondary mass at least at one position and parallel to the axis of rotation the insert being screwed in before assembly of the pressure plate so that it locates the two masses relative to one another either frictionally or 18 mechanically and being removed through a corresponding opening in the pressure plate flange after assembly.

7. A two-part flywheel as claimed in claim 5, in which the locking means is released at least when one of the attachment screws attaching the pressure plate to the secondary mass is inserted.

8. A two-part flywheel as claimed in claim 7, in which the locking means comprises a locking element retained on the outer periphery of the secondary mass adjacent a threaded hole by its own stress, and having in the locked position a rotationally secure connection to the primary mass, and on insertion of the attachment screw into the threaded hole the element moves automatically from the locked position to the unlocked position.

9. A two-part flywheel as claimed in claim 8, in which the locking element resembles a leaf spring having an end region engaging in a groove in the primary mass open towards the secondary mass to form the locking connection by engaging circumferential faces on the primary mass.

10. A two-part flywheel as claimed in claim 8 or claim 9, in which a pin projects substantially perpendicular to the axis into the threaded hole from outside, the pin being urged radially inwardly by the locking element in its locked position, and on insertion of the screw being forced radially outwardly to displace the locking element radially outwardly, into the unlocked position.

11. A two-mass flywheel as claimed in claim 7, in which a threaded insert having a thread for an 19 attachment screw is arranged in the secondary mass in an opening and adjacent the primary mass, and in alignment with a through bore for the attachment screw, and is held by the engagement of its external profile in an internal profile of the secondary mass at least circumferentially free of play and secure against rotation and is urged axially by the force of a spring towards the primary mass, and with the attachment screw not tightened engages, circumferentially free of play by means of a projection or its external profile in a corresponding recess in the primary mass, and when the attachment screw is tightened it is held on the secondary mass in a position remote from the primary mass and thereby the projection or the external profile is held out of engagement with the recess in the primary mass.

10. A two-part flywheel as claimed in Claim 7, in which there is arranged in the attachment face of the secondary mass a through bore parallel to the axis and in which an axially-extending portion adjacent the attachment face has a right-hand thread and an axial ly-extending portion adjacent the primary mass has a left-hand thread, there being inserted in the left-hand thread a threaded insert which, before the pressure plate is mounted, has a projection directed towards the primary mass and engaging at least circumferentially in a mechanical way in a recess in the primary mass and has a dowel pin directed towards the attachment face and projecting slightly beyond the attachment face, and the attachment screw has a central longitudinal hole, in the internal profile of which the external profile of the dowel pin can engage to prevent relative rotation but allow axial displacement, and when the attachment screw is inserted to mount the pressure plate, the threaded insert is automatically moved away from the primary mass and the projection comes out of engagement with the recess.

13. A two-part flywheel as claimed in claim 7, in which a clip is arranged on the secondary mass in the neighbourhood of at least one threaded hole for an attachment screw, the clip having a main body engaging the attachment face with radially outer and inner portions separated by a fold, the radially outer portion engaging the attachment face and extending outwardly beyond it, and the radiall-y inner portion projecting radially inwards, and before attachment of the pressure plate having a portion which stands away from the attachment face, a tongue projecting from the main body axially over the outside diameter of the secondary mass and radially spaced from it, and being cranked to extend radially inwards so that its end is in the threaded hole, the crank engaging in a recess in the primary mass and so forming the locking means, which is automatically released on screwing the pressure plate to the secondary mass, by a tilting movement of the main body about the fold, in which the radially inner portion of the main body comes into engagement with the attachment face whilst the radially outer portion of the main body lifts away from the attachment face, so that the tongue is moved away from the primary mass in a direction towards the pressure plate and the crank on the tongue comes out of engagement with the recess.

14. A two-part flywheel as claimed in claim 13, in which in order to locate the clip laterally, in addition to the tongue there are two further tongues which, before the pressure plate is mounted, engage the outside diameter of the secondary mass.

21

15. A two-part flywheel as claimed in claim 13 or claim 14, in which the clip experiences a permanent plastic deformation when the pressure plate is mounted.

16. A two-part flywheel as claimed in claim 15, in which a recess is provided in the secondary mass between the end of the threaded hole adjacent the primary mass, or the engagement point for the clip, and the outside diameter of the secondary mass, for receiving the tongue on release of the locking means.

17. A two-part flywheel as claimed in claim 16, in which radially extending grooves are provided in the attachment face at the or each position where there is a clip, the width of the grooves corresponding to the width of the main body and their depth corresponding to the thickness of the material of the clip.

18. A two-part flywheel as claimed in claim 17, in which the main body of the clip has in its unstressed condition a bulge extending radially inwards of the fold and over the threaded hole, and an opening is provided in the bulge for the attachment screw.

19. A two-part flywheel of the kind set forth substantially as described herein with reference to and as illustrated in Figure 1 of the accompanying drawings.

20. A two-part flywheel of the kind set forth substantially as described herein with reference to and as illustrated in Figure 2 of the accompanying drawings.

21. A two-part flywheel of the kind set forth substantially as described herein with reference to and as illustrated in Figure 3 of the accompanying drawings.

22 22. A two-part flywheel of the kind set forth r substantially as described herein with reference to and as illustrated in Figure 4 of the accompanying drawings.

23. A two-part flywheel of the kind set forth substantially as described herein with reference to and as illustrated in Figure 1 of the accompanying drawings.