GB2197428A - Method of manufacturing an apparatus for damping torsional vibrations - Google Patents

Abstract

A torsional vibration damping apparatus includes a divided flywheel having two flywheel elements (3,4) which are capable of relative angular movement against the action of a damping device which includes an annular chamber (30) at least partly filled with a viscous material such as grease. During manufacture, at least the part of the apparatus which defines the chamber (30) is raised to a rotational speed sufficient to distribute the viscous material around the chamber to define a uniform radially inner level and to expel air bubbles, prior to dynamic balancing. <IMAGE>

Description

SPECIFICATION Method of manufacturing an apparatus for damping torsional vibrations The invention relates to a method of manufacturing an apparatus for damping torsional vibrations, e.g. in the transmission line of a vehicle, the apparatus having at least two flywheel masses which are mounted for rotation with respect to each other against the action of damping means, one of which flywheel masses may be connected to an engine and the other to a gearbox, e.g. via a clutch such as a friction clutch, and at least one of the flywheel masses having a chamber which can be at least partly filled with a pasty or viscous medium and houses damping means which oppose relative rotation between the flywheel masses.

The basic object of the invention is to develop a method of manufacturing such apparatuses which enables a simple, rapid and economical as well as functionally reliable assembly of the apparatus to be obtained. A further object of the invention is to improve the performance of such apparatuses and their working life.

This is achieved according to the invention in that, prior to the dynamic balancing of the apparatus, at least the flywheel element which is provided with the chamber is raised to a rotational speed for distributing the medium over the circumference of the chamber at a radially inner level which is as constant as possible.

By means of the method according to the invention the result is obtained that, when the chamber is filled with a pasty medium which undergoes as far as possible no change or only a slight change in its state and hence at least no substantial change in its viscosity throughout the range of temperatures that will occur, a uniform distribution of the medium or a uniform level of filling thereof round the circumference of the chamber is obtained, so that a very accurate dynamic balancing of the apparatus is possible.

The at least partial filling of the chamber may, in many different constructional forms of the apparatus, advantageously take place before the flywheel mass provided with the chamber is raised to a centrifugal speed which causes the distribution. It may, however, be particularly advantageous if, during the filling of the chamber with a viscous medium, at least the flywheel element provided with the chamber is rotated at a speed which produces the uniform distribution of the medium round the circumference of the said chamber. For many applications, however, it may instead be appropriate if, during the introduction of the viscous medium into the chamber, at least the flywheel element provided with the said chamber is rotated initially at a speed below the dynamic balancing speed.

In order to achieve reliable distribution of the viscous medium in the chamber it is advantageous if the centrifugal speed is of the order of from two to fifteen times the dynamic balancing speed. It is suitable if the centrifugal speed is at least of the same order of magnitude as the speed at which the internal combustion engines, with which apparatus according to the invention will be used, could be operated.

The above mentioned high centrifugal speeds further make it possible to prevent the presence of individual air occlusions between the component parts being maintained, since they are removed as a result of the substantial centrifugal force acting on the viscous medium. It is thus ensured that, after the apparatus itself has been put into operation, even after a relatively long period of operation, no imbalance will occur as a result of subsequent absorption of air occlusions by the viscous medium. In order to enable accurate dynamic balancing to be obtained and to prevent the subsequent occurrence of any additional imbalance, it is advantageous if the rotational speed to which the apparatus is raised prior to the dynamic balancing is of the order of 4000 to 7000 revolutions per minute and preferably of the order of about 5000 to 6000 revolutions per minute.Moreover; it may be advantageous if, with a view to obtaining reliable distribution of the viscous medium within the chamber, at least the flywheel element provided with the chamber is kept at the centrifugal speed for between 30 seconds and three minutes, and it is preferable if this period is of the order of one minute. This centrifugal period is dependent upon the viscosity of the medium employed, as well as upon the centrifugal speed which is employed.

In order to reduce the period for which the centrifugal force is operative and at the same time to achieve a reliable distribution of the viscous medium within the chamber, it may be particularly advantageous if at least the flywheel mass provided with the chamber is heated and/or the viscous medium is heated prior to its introduction into the chamber.

Such heating also enables the centrifugal speed to be reduced. The temperature to which the flywheel mass and/or the viscous medium is or are raised may be of the order of magnitude of between 80 degrees centigrade and 250 degrees centigrade.

In many constructional embodiments of an apparatus according to the invention, it may be advantageous if the viscous medium is injected or forced into the chamber of the already assembled flywheel mass through a closable opening which opens into the said chamber. It may moreover be advantageous if the entire apparatus is assembled prior to this filling operation. For other construcfional forms of apparatuses according to the;invention, it may, however, be advantageous if instead the introduction of the viscous medium into the chamber and the distribution thereof within it take place prior to the assembly or fitting together of the two flywheel masses.Such at least partial filling of the chamber makes possible not only better operation of the flywheel element provided with this chamber, but also the introduction of the viscous medium through those parts of the chamber which will be closed by the fitting together of the two flywheel masses. The last-mentioned possibility has, in particular, the advantage that no addition filling hole with sealing or closing means is necessary. For many applications, it may be advantageous if the apparatus is dynamically balanced only after the two flywheel masses which form the apparatus have been assembled together. The dynamic balancing speed may furthermore be between 400 and 2,000 revolutions per minute.

For other applications or constructional forms of apparatuses according to the invention, it may however be appropriate is instead the flywheel mass provided with the chamber for the viscous medium and the other flywheel mass are dynamically balanced individually, i.e.

separately, and are only assembled together afterwards. A pasty substance, such as a lubricant, grease or the like are advantageously suitable for use as the viscous medium.

The invention will be explained in greater detail with reference to Figs. 1 to 3, in which: Figure 1 is a section through an apparatus according to the invention, Figure la shows the detail X of Fig. 1 on an enlarged scale, Figure 2 is an elevational view of the apparatus according to Fig. 1 as seen in the direction of the arrow 11, without the clutch and partly broken away, and Figure 3 is a section through a further embodiment.

The torque-transmitting apparatus 1 shown in Figs. 1, 1a and 2 for compensating for torsional impulses includes a flywheel 2 which is subdivided inbto two flywheel elements 3 and 4. The flywheel element 3 is fixed by fixing screws 6 to a crankshaft 5 of an inter nal combustion engine not shown in more detail. A disengagable friction clutch 7 is secured to the flywheel element 4. Between the pressure plate 8 of the friction clutch 7 and the flywheel element 4, there is provided a clutch disk 9 which is mounted on the input shaft 10 of a gearbox which is not shown in more detail. The pressure plate 8 of the friction clutch 7 is urged in the direction towards the flywheel element 4 by a diaphragm spring 12 which is mounted for rocking movement on the clutch cover plate 11.By operating the friction clutch 7, the flywheel element 4 and hence also the flywheel 2 or the internal combustion engine can be coupled with and uncoupled from the gearbox input shaft 10. Between the flywheel element 3 and the flywheel element 4, there is provided a first, radially outer damper 13 as well as a second, radially inner damper 14 connected in parallel therewith which permit relative rotation between the two flywheel elements 3 and 4.

The two flywheel elements 3 and 4 are mounted on a bearing unit 15 for relative rotation with respect to each other. The bearing unit 1 5 includes a rolling bearing in the form of a single row ball bearing 16. The outer race ring 17 of the rolling bearing 16 is located in a recess 18 in the flywheel element 4 and the inner race ring 19 of the rolling bearing 16 is located on a cylindrical spigot 20 which is provided on the flywheel elements 3, extends in the direction away from the crankshaft 5 and projects into the recess 18.

The inner race ring 19 is engaged as a press fit on the spigot 20 and is clamped between a shoulder 21 on the spigot 20 or the flywheel element 3 and a retaining washer 22 which is fixed against the end of the spigot 20 by means of rivets 22a.

As is apparent more particularly from Fig.

1 a, the bearing 16 is axially secured with respect to the flywheel element 4 by its outer race ring 1 7 being clamped axially, with the interposition of two L-section rings 23, 24 between a shoulder 25 on the flywheel element 4 and an annular disk 27 which is rigidly fixed by rivets 26 to the said flywheel element 4.

The radially inwardly projecting limbs 23a, 24a of the rigs 23, 24 extend radially partly over the inner race ring 19 and are supported axially against the latter, so that they serve at the same time as sealing means for the bearing 16. In order to ensure reliable sealing of the bearing 16, the radially extending limbs 23a, 24a are each urged axially towards the respective end surface of the inner race ring 1 9 by means of a corresponding force accumulator in the form of a plate spring 28 or 29.

Between the inner race ring 19 and the outer surface 20a of a recessed part of the spigot 20 on the flywheel element 3 there is provided a sealing ring 37 which is fitted in a radial annular groove 37a in the said surface 20a.

It can be understood from Fig. 1 that the flywheel element 3 forms a housing which delimits an annular chamber 30 in which the dampers 13, 14 are accommodated. The flywheel element 3 which contains the annular chamber 30 is composed essentially of two housing parts 31, 32. The two housing parts 31, 32 which delimit the annular chamber 30 consists of castings. The housing part 32 has on its circumference an axial cylindrical projection 32a by means of the inner surface 35 of which the housing part 32 is centred on anouter surface 34 of the housing part 31. The axial securing together of the two housing parts 31, 32 is effected by means of radial pins 38 which are fitted in the region of the centring surfaces 34, 35.The housing part 32 supports on a shoulder 39 a starter ring 40 which engages axially partly over the pins 38, so that they cannot become radially displaced.

In order to seal the annular chamber 30 outwardly, a seal 36 is provided which is located between the pins 38 and the chamber 30.

The two dampers 13, 14 have a common output part in the form a radial flange 41 which is located axially between the two housing parts 31, 32. The flange 41 is, as is evident more particularly from Fig. 2, fixed for rotation by its inner part with the annular disk part 27 by means of a sliding joint 42, the disk part 27 being secured by rivets 26 to the end of the axial projection 43 which is provided on the flywheel element 4 and extends in the direction towards the crankshaft 5.

The flange 41 has on its outer circumference radially projecting arms 44 which are the parts that act against the force accumulators, in the form of coil springs 45, of the outer damper 13. Radially inwardly of the openings 46 for the coil springs 45, which openings 46 are located circumferentially between the radially projecting arms 44, the flange 41 has arcuate windows 47 in which the force accumulators, in the form of coil springs 48, of the inner damper 14 are accommodated. Radially between the openings 46 and the windows 47, the flange 41 is in the form of circumferentially extending webs 49 which interconnect the radially projecting arms 44 or the radial parts 50 of the flange 41 that are located circumferentially between the windows 47.

The radial parts 50 constitute the parts of the flange 41 which act against the coil springs 48.

The radially outer part of the annular chamber 30 forms an annular passage-like or toruslike housing space 51 in which the projecting arms 44 of the flange 41 engage.

The annular passage-like housing space 51 for the force accumulators 45 is formed essentially by circumferentially extending axial depressions 52, 53 which are located in the radial regions of the housing parts 31, 32 and into which those portions of the force accumulators 45 which project outwardly on both sides of the flange 41 extend. The radially inner part of the annular housing space 51 is closed, except for a small clearance 54, by the webs 49 of the flange 41.

As is apparent from Fig. 1, the axial depressions 52, 53 are so shaped in cross-section that their arcuate extent conforms at least ap proximately to the circumference of the crosssection of the force accumulators 45. Thede pressions 52, 53 thus form supporting or guiding regions for the force accumulators 45, against which regions the force accumulators 45 can support themselves. As a result of the conformity of the supporting surfaces provided by the depressions 52, 53 with the circumferences of the force accumulators 45, the wear which takes place as a result of the friction of the turns of the force accumulators 45 against the wall surfaces of the depressions 52, 53 can be substantially reduced, since the supporting surface area between the springs 45 and the depressions 52, 53 is increased.

in order to prevent or reduce wear on the radial supporting region of the annular passage-like housing space 51 for the springs 45, a steel strip 81 having a high degree or hardness is provided, which steel strip 81 extends round the circumference of the annular passage-like housing space 51 and surrounds the springs 45. The steel strip 81 is made cylindrical and is fitted in a groove 81 which is formed by a radial incision or a radial rebate.

When the apparatus 1 is rotating, the springs 45 are supported by the turns thereof against the steel strip 81 due to the centrifugal force acting on them.

In order to actuate the force accumulators 45, circumferentially acting abutment members 55, 55a are fitted in the depressions 52, 53 on both sides of the projecting arms 44, which abutment members provide circumferentially acting supports for the force accumulators 45. The circumferentially acting abutment members 55, 55a are formed by component parts, such as for example forgings or pressings, which are shaped to conform with depressions 52, 53 and ridigly connected by means of rivets 58 to the housing parts 31, 32. The circumferentially facing end surfaces of the circumferentially acting abutment members 55, 55a are flattened so as to act better against the force accumulators 45.

As can be appreciated from Fig. 2, the abutment members 55, 55a provided on both sides of each projecting arm 44 on the flange 41 have a greater circumferential extent than the projecting arms 44, so that, in the embodiment illustrated, in the rest position of the apparatus shown in Fig. 2, the projecting arms 44 are located centrally with respect to the abutment members 55, 55a project circumferentially equal amounts in both directions respectively from the projecting arms 44.

Radially inwardly of the annular passage-like housing space 51, the housing parts 31, 32 have parts 60, 61 that provide confronting arcuate surfaces between which there is an annular gap 62 for the flange 41.

In the embodiment according to Figs. 1 and 2, the width of this annular gap 62 is somewhat greater than the thickness of the part of the flange 41, located within it, so that a clearance 54 is available on at least one side of the flange 41.

Radially inwardly of the annular gap 62, the housing parts 31, 32 have axial depressions 63, 64 into which the parts of the inner coil springs 48 which project on both sides re spectively of the flange 41 at least partly pro ject.

As is apparent from Fig. 1, the axial depressions 63, 64 are so shaped in cross-section that their arcuate extent conforms, at least in the radially outer region thereof, with the circumference of the cross-section of the coil springs 48, so that the springs 48 are held or guided at least axially by the depressions 63, 64.

In a similar manner to the outer depressions 52, 53, the inner depressions 63, 64 extend round the entire circumference of the apparatus. This is advantageous since for example the pre-cast depressions 52, 53 and 63, 64 can then be finished by a turning operation. In order to actuate the force accumulators or coil springs 48, circumferentially acting abutment members 65, 66 are provided in the depressions 63, 64 which form circumferential supports for the coil springs 48. These circumferentially acting abutment members 65, 66 are formed similarly to the circumferentially acting abutment members 55, 55a and are likewise riveted to the housing parts 31, 32.The circumferentially acting abutment members 65, 66, which are located on opposite sides respectively of the radial parts 50 of the flange 41, are of a greater circumferential extent than the parts 50 which serve for actuating the springs 48. The arrangement of the abutment members 65, 66 in relation to the radial parts 50 is however such that the circumferentially acting abutment members 65, 66, in the rest condition of the apparatus 1, project in one direction with respect to the parts 50, whereas the surfaces of the abutment mem bers 65, 66 and parts 50 which face in the other direction may be flush with each other.

Moreover, the offsetting of the abutment members 65, 66 with respect to the radial parts 50 is such that two circumferentially successive abutment members 65 or 66 are offset in opposite rotational directions with re spect to the corresponding radial parts 50 of the flange 41. As a result of this arrangement, the inner springs 48 form two groups of springs, namely 48a and 48b which come into operation in successive stages.

The webs 49 of the flange 41 are so di mensioned in relation to the inner depressions 63, 64 that the coil springs 48 are supported radially against the said webs 49 at least while they are being subjected to the action of centrifugal force.

This is advantageous, since the flange may be made of steel which is at least casehar dened, so that wear on the radial supporting parts for the springs 48 can be reduced.

As is clear from Fig. 2, spring end caps 59 are provided between the radial arms 44 or the circumferentially acting abutment members 55, 55a and those ends of the springs 45 which face towards them, the circumferences of which spring end caps 59 correspond to the cross-section of the annular passage-like housing space 51.

Each of the spring end caps 59 has a projection 59a of slightly tapered conical shape which projects axially into a corresponding spring 45. The extremity 59b of the projection 59a is of conical shape in the embodiment shown, but it could instead be of part spherical shape. By so shaping the spring end caps 59, it is ensured that, if during operation of the apparatus one of these end caps slips out of the corresponding spring end, an automatic guiding or threading thereof irito the spring will take place when the end cap is acted on again or the spring expands, so that neither the spring nor the end cap will be damaged.

Movement of the spring end craps 59 out of the springs can occur when the outbr- springs 45 are compressed and the apparatC$/'I is rotating at a relatively high speed. In this situation, the friction occurring betweeri the turns of the springs 45 and the radial portions of the housing parts 31, 32 which support them may be so high that the springs 45 cannot at least fully expand in the event of an impulse occurring due to a sudden load reversal. Due to the displacement of the viscous medium produced by the radial arms 44 during the load reversal impulse, which viscous medium is distributed outwardly again under the action of centrifugal force, the spring end caps 59 may be forced off the ends of the non-expanded springs 45.

A viscous medium or lubricant, such as for example grease, may be provided in the annular chamber 30. The level of the viscous medium or lubricant may moreover reach at least as far as the middle region or axis of the outer springs 45 of the damper 13 while the apparatus 1 is rotating. In the embodiment shown, it is advantageous if this level reaches at least as far as the outer parts of the turns of the inner coil springs 48, so that wearreducing lubrication is available at least between the said turns and the radial parts which support them, in the present case the webs 49 of the flange 41. In the apparatus 1 shown, it is advantageous if the filling of viscous medium or lubricant reaches approximately as far as the axis of the inner coil springs 48. Due to the association of the annular chamber 30, which contains a viscous medium or a lubricant, with the flywheel ele ment 3 connected with the engine and due to the spatial separation thereof from the flywheel element 4 which carries the friction clutch 7, any influence on the viscous medium or lubricant of the heat produced in connection with the friction clutch is excluded.

Furthermore, there is provided between the annular chamber 30 or the housing part 32 and the flywheel element 4 an outwardly open annular duct or annular gap 68 which, in conjunction with ventilating ports 69 further im proves the cooling effect. The ventilation ports 69 are located radially inwardly of the friction surface 4a of the flywheel element 4 for the clutch disk 9.

As is apparent more particularly from Fig. 2, the flange 41 has a central opening 71, the contour of which comprises radial profilings 72 engaging with counter-profilings 73 which are provided on the outer circumference of the annular disk part 27 connected to the flywheel element 4. The profilings 72 and counter-profilings 73 which form the axial sliding joint 42 enable reliable alignment of the flange 41 between the two housing parts 31, 32 to be effected, so that the clearance 54 between the annular passage 62 and the flange 41 can be made very small. The sliding joint 42 also enables the axial tolerances between the various contact or supporting surfaces of the component parts to be enlarged.

As is apparent more particularly from Fig.

1 a, a seal 74 is provided between the inner region of the housing part 32 and the annular disk 27 or the axial projection 43 on the flywheel element 4. The seal 74 comprises an annular, axial resilient disk 75, the radially inner part of which is supported against an annular component part 76 fixed to the axial projection 43 and the radially outer part of which is axially secured against the radially inner region of the housing part 32. The sealing disk 75, which is axially deformable like a plate spring, carries on its radially outer and inner parts coatings 75a, 75b, such as plastics coatings, which are applied, for example by spraying them on. These coatings 75a, 75b should have a low coefficient of friction as well as a certain degree of elastic or plastic deformability.The radially outer rim part of the sealing disk 75 is socketed in a sealing manner in an annular support 80. The socketing of the radially outer part of the sealing disk 75 is effected in such a manner that the sealing disk 75 can undergo a variation of its conicity. The parts 80b of the annular support 80 which engage over the outer circumference of the sealing disk are received in an axial incision or in an axial rebate 77 formed in the radially inner region of the housing part 32. In order to secure the outer part of the sealing disk axially, the annular support 80 has a flanged over part 80a which engages over the inner edge 32b of the housing part 32. The annular support 80 forms an annular fulcrum bearing for the sealing disk 75 which is deformable like a plate spring.

The annular component part 76, which is formed with a sealing surface that cooperates with the sealing disk 75, has a radially inner disk-like part 76a which is clamped axially between the end surface of the axial projection 43 and the disk-like part 27 as well as an outer annular part 76b against which the sealing disk bears under axial prestress in such a manner as to form a seal.

The radially outer parts 76b of the annular component part 76 are offset in the axial direction away from the annular component part 27 which is provided with the counter-profillings 73 of the sliding joint 42. As is clear from Fig. 1, the seal 74 seals off the annular chamber 30 from the annular gap 68 between the two flywheel elements 3 and 4.

In order to enable the two flywheelele- ments 3 and 4 to be joined together axially, the inside diameter of the sealing disk 75 is greater than the outside diameter of the radial projections or counter-profilings 73. The part 76b of the annular component part 76 against which the sealing disk is axially supported extend radially outwards further than the counter-profilings.

The sliding joint 42 and the seal 74 make possible a particularly simple assembly of the torque transmitting device 1, since the two flywheel elements 3 and 4 are first pre-assembled and are then connected together axially by fitting and securing the retaining washer 22 axially against the end surface of the projection 20. For this purpose, first of all the seal 74 is pre-mounted on the flywheel element 3 and the rolling bearing 16 is securely fitted in the flywheel element 4. During the assembly of the two flywheel elements 3 and 4, the inner race 19 of the rolling bearing is slid onto the seating 20a on the axial spigot 20 of the housing part 31 and the counter-profilings 73 are brought into engagement with the profilings 72.Moreover, during the sliding together of the two flywheel elements 3 and 4, the radially inner part 75b of the sealing disk 75 comes into engagement with the coacting sealing surface on the part 76b of the component part 76, so that the sealing disk 75 undergoes deflection like a plate spring and bears under prestress against the part 76b.

The fiunal axial fixing together of the two flywheel elements 3 and 4 is effected, as already mentioned, by securing the washer 22 to the spigot 20. The manner in which the apparatus according to Figs. 1, la and 2 operates is described below.

When rotation occurs of the flywheel element 4 with respect to the flywheel element 3 from the rest position shown in Fig. 2, the flange 41 is driven via the sliding joint 42 so that first the inner springs 48b are compressed between the circumferentially acting stops 65, 66 and the radial parts 50. After the angle of relative rotation 79 has been transversed in one direction or the angle of relative rotation 80 has been transversed in the other direction, the radial parts 50 come into engagement with the ends of the inner springs 48b, so that, during further relative rotation between the two flywheel elements 3 and 4, the springs 48a will be compressed in addition to the springs 48b.After the angle of relative rotation 79a has been transversed in one direction or the angle of relative rotation 90a has been transversed in the other direction, the outer springs 45 will be acted on by the radially projecting arms 44, so that, when a further relative rotation takes place, the springs between the circumferentially acting abutment members 55, 55a and the radially projecting arms 44 will be compressed. In the embodiment illustrated, the angle 79 corresponds to 6the angle 79a and the angle 90 to the angle 90a, so that the springs 48a and the springs 45 will be come operative simulta neously. Thus, in the embodiment shown in Figs. 1 and 2, a two-stage spring characteristic curve is obtained.The angles 79, 90, 79a and 90a could, however, be equal in only some cases or have different values, so that a spring characteritic curve having at least three stages in each direction of rotation, or a spring characteristic curve having at least two stages in one direction of rotation and at least three stages in the other direction is possible.

Furthermore, the circumferentially acting abutment members 65, 66 as indicated at 65a in chain-dotted lines in Fig. 2, could be set back with respect to the ends of the springs 48b in the flange, so that there is no spring action because of the elimination of the relative rotation of the two flywheel elements 3 and 4 over a predetermined angle, and there may then perhaps be only hydraulic or viscous damping and/or frictional damping.

In the embodiment illustrated, the simultaneous compression of the springs 48a, 48b and 45 takes place until at least the inner springs 48a become locked solid, so that the relative rotation between the two flywheel elements 3 and 4 is limited. When relative rotation takes place between the two flywheel elements 3 and 4, frictional damping is produced by friction of the outer springs 45 against the wall surfaces of the depressions 52, 53 or against the steel strip 81 as well as by friction of the sealing disk 75 against the part 76b. Frictional damping also takes place between the radially inner springs 48 and the radial surfaces by which they are supported.

The frictional damping that occurs between the springs 45, 48 and the surfaces which support them radially is dependent on the speed of rotation, this damping becoming greater as the speed of rotation increases. In addition, damping is produced by turbulence or dispiacement of the viscous or pasty medium contained in the annular chamber 30. In particular, the viscous medium present in the practically closed annular passage-like housing space 51 produces a hydraulic or viscous damping, since the spring end caps 59 act like pistons within the said annular passagelike housing space.During compression of the outer springs 45, the springs end caps 59 acted against by the projecting arms 44 are moved in the direction towards the spring end caps that are supported against the circumferentially acting abutment members 55, 55a, so that the viscous medium which is present in the springs is forced out mainly through the clearance 54 which acts like a throttle. A further part of the viscous medium is forced between the spring end caps 59 and the wall surfaces of the annular passage-like housing space 51. The viscous medium, which is first forced inwardly, is then distributed uniformly over the circumference as a result of the centrifugal force acting on it. During the expansion of the outer springs 45, the viscous medium that is present on the side of the spring end caps 59 and the wall surfaces of the annular passage-like housing space 51.The viscous medium,which is first forced inwardly, is then distributed uniformly over the circumference as a result of the centrifugal force acting on it. During the expansion of the outer springs 45, the viscous medium that is present on the side of the spring end caps 59 remote from the respective springs 45 is similarly forced past the spring end caps as well as through the clearance 54 and, due to the centrifugal force acting on it once again fills up the spaces containing the springs 45. The damping produced by the viscous medium is dependent upon the centrifugal force acting on the medium, which means therefore that the damping becomes greater as the rotational speed increases.

The parts of the radially inner springs 48 which become immersed in the viscous medium also produce a viscous or hydraulic damping effect as a result of turbulence.

By forming axial recesses or openings in at least some of the spring end caps, as well as by suitably dimensioning the clearance 54 on the outer circumference of the spring end caps, the amount of damping produced by the viscous medium can be varied or made to suit the circumstances existing at any given time.

Moreover, the viscous or hydraulic damping effect can adjusted by providing only some of the springs 45 with end caps 59. Spring end caps may also be provided between the ends of at least one inner spring 48 and the corresponding radial part or parts 50 of the flange 41.

As is apparent more particularly from Fig. 2, the part 3a of the flywheel element 3 has on its outer circumference radial projections 86 in each of which a screw threaded bore 87 is provided for the attachment of a friction clutch 7. Some of the projections 86 also have bores 88 for the reception of pins which ensure accurate locating of the clutch cover plate with respect to the part 3a during assembly.

The radial projections 86 enable the construction of the flywheel element 3 to be simplified. In addition, better cooling of the part 3a and of the clutch mounted thereon is obtained by the radial recesses 86a between the radial projections 86, since circulation of air can take place between the cover plate and the recesses 86a.

The radial projections 86 furthermore enable the part 3a to be made thicker for any given mass in the region of the friction surfaces 4a.

The radial projections 86 furthermore enable the part 3a to be made thicker for any given mass in the region of the friction surfaces 4a so that overheating in this region can be avoided.

A variation of the damping effect produced by the viscous medium can moreover be achieved by giving the annular passage-like housing space 51 a non-uniform cross-section at least over parts of the longitudinal extent of at least one spring 45, so that in the regions of larger cross-section a relatively small amount of damping is obtained and in the regions of smaller cross-section a greater amount of damping is obtained. Athough this variation in the cross-section of the annular passage-like housing space may be provided at any desired position or even at several different positions, it is particularly suitable if such variations or enlargements of cross-sectional area are located in the positions occupied by the end parts of the springs 45 when the latter are uncompressed. The variations of cross-section may moreover be either abrupt or progressive.It is furthermore particularly advantageous if the enlargements of crosssectional area are provided in the region of the radially inner half of the annular housing space 51. Such an enlargement is shown in Fig. 2 and indicated by the reference numeral 89. This enlargement 89 is formed in the flange 41 which delimits or closes the annular passage-like housing space 51 on the radially inner side. The enlargements could, however, be formed instead by suitably shaping the depressions 52, 53 which delimit the annular passage-like housing spaces 51.

The introduction of the viscous material into the chamber 30 may take place before the assembly or fitting together of the two flywheel elements 3, 4. Such an at least partial filling of the chamber 30 enables the viscous medium to be introduced through those parts of the chamber which are closed by the fitting together of the flywheel elements 3, 4.

In the embodiment according to Figs. 1, 1 a and 2 these parts extend between the inner edge of the sealing disk 75 and the spigot 20 flywheel element 3 is rotated up to a speed which, as a result of the centrifugal force acting on the viscous medium, ensures a reliable distribution of this viscous medium round the circumference of the chamber 30. Such a procedure ensures that, during the filling of the chamber 30 with a pasty medium, which undergoes as far as possible no change of state or only the minimum possible amount of such change over the range of temperatures that occur and consequently undergoes no substantial change in its viscosity, a uniform distribution or a uniform level of filling is obtained over the entire circumference of the chamber 30, so that thereafter a very precise balancing of the apparatus 1 is possible.

The centrifugal speed may be between 4000 and 7000 revolutions per minute, and is preferably of the order of about 5000 to 6000 revolutions per minute.

The flywheel element 3 provided with the chamber may be dynamically balanced prior to being assembled with the other flywheel element 4. Moreover, the other flywheel element 4 may also be dynamically balanced separately so that, after the two elements have been fitted together, the apparatus 1 is dynamically balanced. It may however be appropriate if, instead, the balancing takes place only after the assembly of the two elements 3, 4.

The centrifugal speed which produces reliable distribution of the viscous medium in the chamber may be of the order of 4000 to 7000 revolutions per minute and preferably between 5000 and 6000 revolutions per minute. The centrifugal time may be between 30 seconds and 3 minutes and should advantageously, however, be of the order of the magnitude of one minute. A reduction of the centrifugal speed as well as of the centrifugal time can be obtained by heating the flywheel or the viscous medium or both before the chamber is filled. By such heating, improved distribution of the viscous medium in the chamber is achieved.

The dynamic balancing of the flywheel elements 3 and 4 or of the entire apparatus 1 may take place at a speed of between 400 and 2000 The dynamic balancing of the flywheel elements 3 and 4 or of the entire apparatus 1 may take place at a speed of between 400 and 2000 revolutions per minute.

In the embodiment shown in Fig. 3 of an apparatus 1, the side wall 103a nearer to the engine of the flywheel element 103 has at least one bore 191 formed in it, through which the viscous medium, such as grease, can be introduced into the chamber 130.

After the filling up with the viscous medium, the bore 191 is closed by means of a sealing plug 192. The sealing plug 192 may be pressed into the bore 191, In the embodiment shown according to Fig. 3, the sealing plug 192 has a groove 193 in which is fitted a sealing ring 194 which is in sealing contact with the wall surface of the bore 191. The cover plate 132 which delimits the chamber 130 on one side is constituted by a sheet metal pressing which is fixed against the end surface of the axial projection 131 by riveted connections 138. In order to prevent escape of the lubricant from the chamber 130 due to the action thereon of centrifugal force, a seal 136 is provided radially inwardly of the riveted connections 138.

Between the radially inner parts of the cover plate 132 and a shoulder on the flywheel element 104 there is axially clamped a platespring-like sealing element 175 which seals the chamber from the outside.

The two flywheel elements 103 and 104 are mounted for rotation with respect to each other by means of a rolling bearing 116.

Claims (16)

1. A method of manufacturing an apparatus for damping torsional vibrations, e.g. in the transmission line of a vehicle, the apparatus having at least two flywheel masses which are mounted for rotation with respect to each other against the action of damping means, one of which flywheel masses may be connected to an engine and the other to a gearbox, e.g. via a clutch such as a friction clutch, and at least one of the flywheel masses having a chamber which can be at least partly filled with a pasty or viscous medium and houses damping means which oppose relative rotation between the flywheel masses characterised in that, prior to the dynamic balancing of the apparatus (1; 101), at least the flywheel element (3, 103) which is provided with the chamber (30; 130) is raised to a rotational speed for distributing the medium over the circumference of the chamber (30; 130) at a radially inner level which is as constant as possible.

2. A method according to claim 1, characterised in that at least partial filling of the chamber (30; 130) takes place before the flywheel mass (3; 103) is raised to a centrifugal speed which causes the distribution.

3. A method according to claim 1, characterised in that the at least partial filling of the chamber (30; 130) takes place while the flywheel mass (3; 103) is rotating.

4. A method according to one of claims 1 to 3, characterised in that the centrifugal speed is from two to fifteen times the dynamic balancing speed.

5. A method according to one of claims 1 to 4, characterised in that the rotational speed to which at least the flywheel mass (3; 103) provided with a chamber which can be at least partly filled with a viscous medium is raised prior to the dynamic balancing is of the order of 4000 to 7000 revolutions per minute and preferably between 5000 and 6000 revolutions per minute.

6. A method according to one of claims 1 to 5, characterised in that the flywheel mass (3; 103) is kept at the centrifugal speed for between 30 seconds and 3 minutes, and preferably for a period of the order of 1 minute.

7. A method according to one of claims 1 to 6, characterised in that at least the flywheel mass (3; 103) provided with the chamber (30; 130) is heated in order to obtain easier and better distribution of the viscous medium.

8. A method according to one of claims 1 to 7, characterised in that the viscous medium is heated before being introduced into the chamber (30; 130).

9. A method according to one of claims 1 to 8, characterised in that the flywheel mass (3; 103) and/or the viscous medium is or are heated to a temperature between 80 degrees centigrade and 250 degrees centigrade.

10. A method according to one of claims 1 to 9, characterised in that the viscous is injected or forced into the chamber (130) of the (already assembled) flywheel mass (103) through a closable opening (191) which opens into the said chamber.

11. A method according to one of claims 1 to 10, characterised in that the entire apparatus (1; 101) is assembled prior to the filling of the chamber (30; 130) with a viscous medium.

12. A method according to one of claims 1 to 10, characterised in that the viscous medium is first distributed in the chamber (30; 130) of the appropriate flywheel mass (3; 103) and thereafter the two flywheel masses are assembled together.

13. A method according to one of claims 1 to 12, characterised in that the completely assembled apparatus (1; 101) is dynamically balanced.

14. A method according to one of claims 1 to 13, characterised in that the dynamic balancing speed is between 400 and 2000 revolutions per minute.

15. A method according to one of claims 1 to 14, characterised in that, prior to the assembly of the apparatus (1; 101), the flywheel mass (3; 103) provided with the chamber (30; 130) for the viscous medium and the other flywheel element are dynamically balanced separately.

16. A method according to one of claims 1 to 15, characterised in that a pasty substance, such as a lubricant, a fat or the like, is used as the viscous medium.