Abstract:
A torsional vibration damper comprising an input member for connection with a vehicle engine and an output member for connection with a vehicle transmission, the members being mounted for limited relative rotation about a common axis against a damping means comprising one or more circumferentially acting compression springs. Each spring acts between a first abutment formed as an integral part of the input member and a second abutment formed as an integral part of the output member. The damper may also include one or more elastomeric springs or blocks which are subjected to compression in end zones of the relative rotation of the input and output members. Other inventive features of the damper include support members for avoiding fouling of the elastomeric springs or blocks by the compression springs and the use of cantilevered pivot pins for the connection of bob-weight connecting linkages connected between the input and output members. Various friction damping arrangements are also disclosed which can be speed and/or displacement dependent. A method of assembling the damper is also disclosed.

Description:
FIELD OF THE INVENTION 
     This invention relates to torsional vibration dampers (hereinafter referred to as torsional vibration dampers of the kind specified) which comprise an input member for connection with a vehicle engine and an output member for connection with a vehicle transmission, the members being mounted for limited relative rotation about a common axis against a damping means to damp torsional vibrations in the engine/transmission. 
     Such torsional vibration dampers are often in the form of a twin mass flywheel in which the input and output members comprise input and output flywheel masses mounted for relative rotation via a support bearing acting between the masses. 
     Alternatively the input and output members can be of relatively small mass as shown, for example, in the Figures of the Applicant&#39;s earlier British patent application No. 98 03046.3. 
     BACKGROUND OF THE INVENTION 
     The damping means of such torsional vibration dampers can take a wide range of forms, for example, the damping means may comprise one or more of the following: 
     one or more circumferentially acting compression springs; 
     one or more circumferentially acting elastomeric compression blocks; 
     one or more friction devices; 
     one or more hydraulic damping devices, and 
     one or more bob-weights connecting linkages (which generate speed dependent damping) connected between the members. 
     Such torsional vibration dampers therefore tend to be relatively complex devices which consist of a relatively large number of individual parts and are therefore relatively expensive to manufacture. 
     There is also a requirement to provide an axially compact torsinal vibration damper. 
     SUMMARY OF THE INVENTION 
     It is an objective of the present invention to provide a torsional vibration damper of the kind specified with fewer individual parts which is therefore easier and cheaper to manufacture. 
     It is a further objective of the present invention to provide a torsional vibration damper of the kind specified which is of an axially compact design. 
     Thus according to one aspect of the present invention in a torsional vibration damper of the kind specified the damping means comprises one or more circumferentially acting compression springs, the or each spring acting between a first abutment formed as an integral part if the input member and a second abutment formed as an integral part of the output member. 
     Such a construction is particularly advantageous when the torsional vibration damper is a twin mass flywheel with the input mass formed as a single piece sheet metal pressing with integral first spring abutments and the output mass is a cast component with integrally cast second spring abutments. 
     The construction is also particularly compact in an axial sense which is an important feature of twin mass flywheels for use in congested engine compartments particularly when the engine is disposed transversely relative to the vehicle. 
     The torsional vibration damper may also include one or more elastomeric springs or blocks which are subjected to compression in end zones of the relative rotation of the input and output members. 
     In accordance with a further aspect of the present invention such elastomeric springs or blocks are mounted on one of the input or output members between first circumferentially facing abutments formed on or carried by said member and are acted upon by further circumferentially facing abutments formed on or carried by the other member. The elastomeric springs or blocks may also be located radially by a radially outer abutment formed on one of the input or output members. In a preferred and particularly convenient construction both the first circumferentially facing abutments and the radial abutment of each elastomeric spring or block are formed integrally on the input member which may conveniently be formed as a single piece pressing. 
     Each elastomeric spring or block may be supported by a sheet metal casing member which sits in a window in the input or output member which supports the block or spring. 
     In accordance with a further aspect of the present invention in a torsional vibration damper of the kind specified which includes circumferentially acting compression springs, the circumferentially acting compression springs are each supported at a radially inner location by a support member (typically of general channel configuration) to avoid fouling adjacent elastomeric springs or blocks which are located radially inwardly of the compression springs. The spring support members deflect the compression springs from their natural straight configuration to an accurate form which bridges the elastomeric springs or blocks. 
     In a particularly convenient arrangement, in a vibration damper employing bob-weight connecting linkages, the compression spring support member may rest at one end on the radially outer abutment associated with each elastomeric springs or block and may be also fastened at the other end to a pivot pin of an adjacent associated bob-weight connecting linkages. 
     In accordance with a further aspect of the present invention a torsional vibration damper of the type specified may also be provided with a friction damping device whose frictional damping effect varies with the amount of relative rotation of the input and output members of the damper. 
     For example, such a rotation dependent damping device may comprise a friction member which is carried by the input or output member and biased into contact with a surface on the other of the input or output members to provide frictional damping. The surface against which the friction member is biased may be in the form of a cam surface orientated with respect to the axis of relative rotation of the input and output members so that the contact pressure of the friction member on the surface increases with relative rotation between the input and output members. The friction member may be arranged to contact the surface only in the last end portion of the relative rotation. In a particularly convenient arrangement the member which is biased into contact with the surface may also act as a stop which co-operates with abutments on the other of the input or output members to limit the relative rotation between the input and output members. 
     In accordance with a still further aspect of the present invention, in a torsional vibration damper which includes bob-weight connecting linkages, the bob-weights may each be pivotally mounted on one of the input and output members by a cantilevered pivot pin. Each bob-weight may be free to move axially to a limited extent on its cantilevered pin. 
     The use of cantilevered pivot pins further reduces the axial dimensions of the torsional vibration damper. 
     Each linkage may be completed by a single flexible link pivoted at one end on the associated bob-weight and at its other end on the other of the input or output members. The single flexible link may conveniently be located on the input member side of the bob-weight. 
     In a further construction the cantilevered pivot pins and the main support bearing which supports the input and output members for relative rotation are both retained in position by a common retaining member. 
     The bob-weight may be mounted on the cantilevered pin via a bearing bush which is a press fit in the bob-weight. Similarly the flexible link may be pivoted to the bob-weight via a second bush which is a press fit in the bob-weight and a rivet which carries its own collar and which extends through the second bush. 
     The flexible link may be pivoted on the other of the input or output members via a stud or other fixing on which the link is sandwiched between a flange formed on a sleeve surrounding the stud or other fixing and a washer. 
     In accordance with a still further aspect of the present invention a twin mass flywheel of the kind specified includes a friction damping device whose friction damping effect varies with the speed of rotation of the flywheel. 
     The damping effect may be arranged to decrease (or increase) with the speed of rotation depending on the operating characteristics required from the flywheel. For example, the friction damping device may comprise a friction block supported on one flywheel mass which is biased into rubbing contact with the other flywheel mass and is disposed so that, as the speed or rotation of the flywheel mass increases, the centrifugal effect on the friction block tends to reduce the contact pressure of the block on the other flywheel thus reducing the friction force generated. 
     The variation in friction forces of the above friction block arrangement can also be made angularly dependent by arranging the block to make contact with circumferentially ramped surfaces on the other flywheel mass. 
     In accordance with a still further aspect of the present invention in a torsional vibration damper of the kind specified which includes bob-weight linkages and circumferentially acting compression springs interconnecting the input and output members the total permitted relative rotation of the input and output members can be increased by connecting the linkages with the input or output member which supports the compression springs radially inboard of the compression springs thus allowing longer linkages to be employed. 
     In yet a further alternative construction the damping means may comprise a single plate friction damper in which the single friction plate is biased against the input or output member or a component carried thereby by a belleville spring or other axially acting spring member which acts against the other of the input or output members. This simple instruction again saves axial space. 
     The present invention also provides a method of assembly of a torsional vibration damper of the kind specified which includes one or more cantilevered pin mounted bob-weight connecting linkages, said method including the steps of: 
     assembling one or more bob-weight connecting linkages; 
     pivotally connecting one end of the or each linkage to one of the input or output members; 
     inserting respective locating pin through a respective locating aperture in said one of the input or output members and into a first cantilevered pivot pin bore at the other end of the or each linkage through which the cantilevered pivot pin is to extend; 
     completing the assembly of the remainder of the torsional vibration damper onto the input and output members; 
     placing the other of the input and output members over said one member with second cantilever pin bore(s) in said other member in line with the locating Pin(s), and 
     inserting the cantilevered pin(s) into said first bore(s) thus displacing said locating pin(s) from said first bore(s) and connecting the or each linkage with said other member. 
     Preferably the cantilevered pin(s) are inserted into the second cantilevered pin bore(s) prior to the placing of the other member over said one member and the locating pin(s) are displaced from the first bore(s) as the other member is lowered onto said one member. 
     In such an arrangement the method preferably includes the further step of securing to said other member a common retaining member for the main support bearing and the cantilevered pin(s) prior to placing the other member over said one member. 
     Such an arrangement necessitates the mounting of the main support bearing on the other of said input or output members prior to placing said other member over said one member. 
     The invention also provides a torsional vibration damper assembled by the above method in which one of the input or output members includes a locating pin aperture in axial alignment with the or each cantilevered pivot pin. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now me described, by way of example only, with reference to the present invention in which: 
     FIG. 1 is s side view of a torsional vibration damper in the form of a twin mass flywheel embodying the various aspects of the present invention; 
     FIGS. 2 and 3 are sectors outlines X-X and Y-Y respectively of FIG. 1; 
     FIG. 4 shows the top half of FIG. 2 on a larger scale; 
     FIG. 5 shows the bottom half of FIG. 2 on a larger scale; 
     FIG. 6 shows the top half of FIG. 3 on a larger scale; 
     FIG. 7 shows the bottom half of FIG. 3 on a larger scale; 
     FIG. 8 shows part of FIG. 1 on a larger scale; 
     FIG. 9 shows details of an elastomeric spring of block used in the twin mass flywheel of FIG. 1 on a larger scale; 
     FIG. 10 shows details of a rotation dependant friction damper used in the twin mass flywheel of FIG. 1 on a larger scale; 
     FIG. 11 shows diagramatically a method of assembly of the twin mass flywheel of FIG. 1; 
     FIG. 12 shows an alternative form of torsional vibration damper embodying the present invention, and 
     FIG. 13 shows a form of speed dependent friction damping which constitutes another aspect of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 to  8 , a twin mass flywheel  10  comprises an input flywheel mass  11 , carrying a starter ring  11   a  and additional inertia rings  11   f  and  11   g  (see FIGS. 2 and 3) which are welded in position, and an output flywheel mass  12  which are mounted for limited relative rotation about a common axis A-A via a plain bearing  13  carried on a bearing support block  11   d . Relative rotation of the input and output flywheel members is opposed by a damping means in the form of bob-weight connecting linkages  14 , compression spring assemblies  15 , elastomeric springs  16 , radially outer friction damping devices  17   a  and a radially inner single plate friction damper  17   b . All these damping means act in parallel between the input and output flywheel masses. 
     Input flywheel mass  11  is of a pressed metal construction and the output flywheel mass  12  is of a cast metal construction. These two flywheel masses are centred relative to each other during assembly via annular surfaces  11   b  and  12   b  respectively and are held in an assembled state, prior to attachment to the associated engine crankshaft by studs  18  (see FIG.  8 ). As is conventional the twin mass flywheel is bolted to the crankshaft by attachment bolts  19   a  which extend through circumferentially spaced bolt holes  19  in bearing support block  11   d  and input flywheel mass  11 . 
     Compression spring assemblies  15  each act between a first abutment  20  (see FIG. 8) which is pressed 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. As can be seen from FIGS. 3 and 6, abutments  20  extend diagonally across the diameter of the associated spring  15  thus ensuring good contact. 
     Each compression spring assembly may comprise an outer compression spring  15   a  and an inner compression spring  15   b  with the operation of the inner compression spring  15   b  being timed to be delayed by several degrees from the commencement of the operation of the outer compression spring  15   a.    
     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  15   a  and  15   b  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. 
     FIG. 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 occurs before abutments  21  are contacted by spring chairs  15   c  which fir around the end of the springs. 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 FIGS. 8 and 9) are each supported on the input mass  11  between end plates  16   a  in a window  22  pressed out of input flywheel mass  11  by a sheet metal casing member  41 . Member  41  has end portions  41   a  and  41   b  which (see FIG. 4) are respectively curved around a radially outer abutment  24  which is pressed out of input flywheel mass  11  and around the bottom edge  22   a  of window  22 . 
     The end plates  16   a  are acted upon by abutments  23  on a ring  23   a  which is secured to output flywheel mass  12  by rivets  23   b . The end plates  16   a  have wings  16   b  which extend between abutments  23  and output mass  12  and tabs  16   c  which hook under the radially inner edge of block  16 . Each elastomeric spring block  16  is also located against radially outwards movement relative to mass  11  by radially outer abutment  24 . 
     The elastomeric springs  16  are therefore confined within windows  22  between the two flywheel masses  11  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. 
     Each bob-weigh 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  11  via a rivet  29  and at its other end with a bob-weight  25  via a rivet  30 . 
     Each rivet  29  has a head  29   a  which engages an annular seating  11   c  on input mass  11 . An axial spacer is mounted on rivet  29  between a mounting tab  40   a  of support member  40  and a riveted head  29   b  of rivet  29 . Surrounding spacer  31  is a metal bush  32  which is riveted into link  28  with relative rotation of link  28  relative to input mass  11  occuring between bush  32  and spacer  31 . The other end  40   b  of spring support member  40  rests on outer radially abutment  24 . 
     The pivotal connection of link  28  with bob-weight  25  via rivet  30  comprises a bush  33  which is pressed into bob-weight and on axial spacer  34  which surrounds rivet  30  . Head  30   a  of rivet  30  is recessed at  25   a  into bob-weight  25  and a washer  35 , also partly recessed into bob-weight  25  at  25   b , is clamped between link  28  and bob-weight  25  by riveted head  30   b.    
     As can be seen from FIG. 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  25   a , to concentrate their mass as radially far outwards as possible. 
     Each radially outer friction device  17   a , there are sic in total, comprises a plunger  45  slideable in a bore  46  in output mass  12 . The plunger has a head portion  47  having arcuate friction surfaces  48  and  49  for frictional contact with arcuate ramp surfaces  50  and  51  respectively formed on the inside of the rim portion  11   e  of input mass  11 . As can be seen from FIG. 8, after a relative rotation of Z in the drive condition surfaces  49  and  51  come into contact and plunger  45  is pressed into bore  46  against the action of belleville springs  52  as the relative rotation increases further to increase the contact pressure and hence the frictional damping generated. Thus the friction device  17   a  provides frictional resistance to the relative rotation of the flywheel masses in the last end portion of this relative rotation in the drive condition. This frictional resistance also increases with increasing relative rotation in the last end portion of rotation. 
     Similarly after a relative rotation of W in the overrun condition, surfaces  48 ,  50  come into contact and provide an increasing frictional resistance to further relative rotation in the last end portion of the relative rotation. 
     The curvatures of the co-operating arcuate surfaces  49 ,  51  and  48 ,  50  are arranged to be such that the arcuate surfaces  48 ,  49  approach their co-operating surfaces  50 ,  51  so that the surfaces  48 ,  49  make substantially full face contact with their co-operating cam surface  50 ,  51  immediately on coming into contact and maintain this full face contact for their entire contact period to ensure maximum frictional contact area in each end portion of relative rotation. The invention is not however limited to such arcuate surface contact. 
     Plunger  45  is held against radially outward movement relative output mass  12  by a pin  53  which engages in an oversize hole  54  in plunger  45 . This prevents contact between surfaces  48  and  50  and surfaces  49  and  51  in the central portion (Z+W) of the relative rotation of the flywheel masses between ram surfaces  50  and  51 . 
     Each plunger  45  also has a pin portion  55  which extends into a slot  56  in input mass portion  11   e  and in the drive condition eventually contacts end  57  of slots  56  to limit the relative rotation of the flywheel masses. When this contact of pin  55  with slot end  57  occurs force is transmitted from input mass  11  to output mass  12  via pin  55  end plunger head  47  to contact surface  58  of output mass  12 . 
     Similarly in the overrun condition relative rotation is limited by contact between pin  55  and the end  59  of slot  56 . In this contact condition the force is again transmitted from pin  55  and plunger head  47  to output flywheel  12  via surface  60  on the output mass. 
     The single plate friction damper  17   b  comprises an annular friction ring  61  which is splined at  62  onto bearing support member  11   d  and which is pressed against ring  23   a  which rotates with output mass  12  by a belleville spring  62  which reacts against input mass  11 , friction ring  61  may be coated with, for example, sprayed on sintered friction material to increase the friction damping generated. This friction damper  17   b  provides continuous friction damping which damps all relative rotation the flywheel masses. 
     The flywheel shown in FIGS. 1 to  10  may be assembled by the method shown diagrammatically in FIG.  11 . 
     Essentially this method comprises the steps of: 
     assembling the bob-weight connecting linkages by connecting each link  28  with its bob-weight  25  via pivot  30 ; 
     pivotally connecting one end of each linkage to one of the input mass  11  via pivot  29 ; 
     inserting a series of locating pins  70  through respective locating apertures  71  in the input mass  11  and into bushes  27 ; 
     completing the assembly of the remainder of the torsional vibration damper onto the input and output masses; 
     placing the output mass over the input mass with the bores  12   c  in line with the locating pins  70 , and 
     inserting the cantilevered pins  26  into the bushes  27  thus displacing said locating pins  70  from the bushes  27  and connecting the linkages with the output mass. 
     The cantilevered pins  26  are inserted into bores  12   c  (which are serrated) prior to placing the output mass  12  over the input mass  11  and the locating pins  70  are displaced from the bushes  27  as the output mass  12  is lowered onto the input mass  11  which also carries the bearing support  11   d.    
     The main support bearing  13  is mounted onto the output mass  12  member prior to placing the output mass over the input mass and a common retaining member  75  for the main support bearing and the cantilevered pins  26  is also secured to the output mass  12  by rivets  23   b  prior to the joining of the two masses. 
     The axial dimension T of the torsional vibration damper is reduced by the use of direct abutments for springs  15  and  16  on the input and output members (thus avoiding the use of space-taking separate abutment members) and by the use of the cantilevered pins  26  for the mounting of the bob-weights (thus avoiding the need to support the pin on both sides of the bob-weight.) 
     It is possible to mount the elastomeric springs  16  on the input flywheel mass  11  without the use of casing members  41  as shown, for example, in FIG. 12 in which abutments  23  carried by output mass  12  and abutments  22   a  formed on input mass  11  contact plates  16 ′ located on each side of each spring  16 . 
     Also, the torsional vibration damper may be modified to include in place of, for example, outer friction devices  17   a  speed dependent friction damping devices each of the form shown diagrammatically in FIG.  13 . Each such device comprises a spring bow  135  which is rivetted at  136  to the input wheel mass  11  and which carries a friction block  137  which is biased into contact with a portion  138  of the outer periphery of the output flywheel mass  12 . Due to the centrifugal effect on the friction block  137 , as the speed of rotation of the flywheel increases the contact pressure of block  137  on portion  138  decreases thus reducing the friction generated by the friction damping device. The damper may also be made sensitive to the relative rotation of the flywheel masses by making portion  138  of the outer periphery of mass  12  in the form of a ramp surface so that the friction generated by block  137  increases as the relative rotation of the flywheel masses increases.