Abstract:
A torsional damper with a hub assembly and a disc assembly has coil springs disposed therebetween. The coil springs are disposed in pockets defined in part by apertures in opposed cover plates. The apertures have sharply angled end portions providing deflection relief near the ends of the coil springs.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of Provisional Application 60/965,271, filed Aug. 17, 2007 the disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of torsional vibration dampers in general, and more specifically, to friction clutches having torsional vibration dampers. 
     BACKGROUND OF THE INVENTION 
     Torsional vibrations are the rotational irregularities of a rotatingly driven component. In a vehicle drivetrain, torsional vibrations are caused by the forces generated within a combustion engine by the combustion of gases during the periodic combustion process. Torsional vibrations of the second or third order which originate from the engine, as a result of the ignition frequency of four or six cylinder engines, respectively, are predominant in the vehicle driveline. Torsional vibrations not only emanate from the engine power pulses but also from torque spikes and from abrupt changes in driveline torque due to rapid engine acceleration and deceleration. 
     Torsional vibrations cause premature wear to driveline components as well as audible noise. In a conventional driveline, the flywheel, which is rigidly connected to the crankshaft, will generate high reaction forces on the crankshaft. Torque irregularities from a periodic combustion also engine adds additional stress in the form of high frequency torques to the transmission. Furthermore, when a manual transmission is in neutral, gear rattle occurs, which is also an audible event, due to the teeth of meshing gears lifting away from another and then striking each other as a result of high frequency torque fluctuations. 
     Along with gear rattle, order based responses from the second or third engine order may be passed through the drivetrain and into the body structure. This sound can be greatly amplified if the components forming the sound are excited at their resonant frequencies. 
     Torsional vibration issues are further compounded by efforts to improve vehicle efficiency. Reductions in vehicle size and weight as well as reductions in driveline component inertia, such as flywheel masses, as well as reductions in transmission oil viscosity have added to the existing torsional vibration challenges. Lower drivetrain inertia results in a higher natural frequency of the drivetrain. As the engine rotational speed passes through the drivetrain natural frequency, resonant frequency occurs. The input displacement of a system is amplified at resonant frequency. 
     It is well known in the art to incorporate torsional vibration damping mechanisms in a dry clutch. As rotation occurs, the energy storage means within the damper, typically coil springs, provide the rotational compliance between the rotating elements. Another component of the damper is hysteresis, which is provided by friction producing elements. The hysteresis cooperates with the energy storage component of the damper to remove energy from the system. The prior art is replete with friction clutches with dampers for attenuating torsional vibrations. A variety of spring arrangements have been employed to provide frictional force for damping. 
     The coil springs are typically disposed in spring pockets circumferentially located around a clutch hub. Compression of the springs is typically limited by a stop disposed between the hub and the disc limiting relative rotation therebetween. The springs provide some isolation between the engine and transmission of firing pulses of the engine and other engine speed fluctuations. However, point loading between the springs and the spring pockets occurs at ends of the springs, producing wear of one or both parts. Also, within the range of travel permitted by the stop or stops, the springs tend to move relatively freely within the pockets, bowing and rubbing against the sides of the pockets. This spring motion and wear may potentially lead to the springs breaking, or to an increase in the size of the spring pocket, diminishing the dampening effectiveness of the clutch and potentially enabling the spring to escape the clutch driven disc assembly. 
     It is desired to minimize such wear and the associated loss of damper effectiveness by improving the interface between the components to increase the effective life of the dampers. 
     SUMMARY OF THE INVENTION 
     A torsional damper with a hub assembly and a disc assembly has coil springs disposed therebetween. The coil springs are disposed in pockets defined in part by apertures in opposed cover plates. The apertures have sharply angled end portions providing deflection relief near the ends of the coil springs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a clutch incorporating a representative damper. 
         FIG. 2  is a front view of a driven disc incorporating a representative damper. 
         FIG. 3  is a cross-sectional view of the driven disc of  FIG. 2  along section A-A. 
         FIG. 4  is an exploded perspective view of the driven disc of  FIG. 2 . 
         FIG. 5  is a front view of a spring cover plate incorporating the improved spring aperture of the present invention. 
         FIG. 6  is a sectional view in the directions of arrows  7  of  FIG. 5 . 
         FIG. 7  is a sectional view in the directions of arrows  8  of  FIG. 5 . 
         FIG. 8  is a sectional view in the directions of arrows  9  of  FIG. 5 . 
         FIG. 9  is a broken out perspective view of an aperture of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a cross-sectional view of a representative friction torque device  1  into which the present invention may be incorporated is shown. The friction torque device  1  comprises a driving member  12  having an axis of rotation  2 . A cover  14  is coupled to the driving member  12  for rotation therewith. A pressure plate  16  is coupled to the cover  14  for rotation therewith. A driven disc  10  is coupled to an axially extending driven shaft  5  for rotation therewith. Although driven disc  10  is shown splined to driven shaft  5 , it should be apparent to those skilled in the art that any suitable means known in the art may be substituted for a splined coupling. The driven disc  10  is interposed between the driving member  12  and the pressure plate  16 . 
     Referring now to  FIGS. 2 and 3 , representative driven disc  10  is shown. Driven disc  10  is not intended to show the only possible application of the present invention. Driven disc  10  incorporates a torsional damper  15 . Driven disc  10  comprises a rotatable disc assembly  20  which includes a first plate or disc plate  40  having a plurality of apertures  22 . A plurality of friction pads  50  are attached to disc plate  40  for frictional engagement with pressure plate  16  and driving member  12 . A hub assembly  30  includes a hub  70  secured to a pair of facing spring cover plates  100 . Spring cover plates  100  have a plurality of apertures  32  disposed therein. Disc plate and spring cover plate apertures  22 ,  32  are at least partially aligned. Energy storage means in the form of coil springs  80  are disposed within apertures  22 ,  32 . Disc assembly  20  is rotatable relative to hub assembly  30 . Coil springs  80  absorb torque as a function of relative rotation between the hub  70 , via spring cover plate  100  and disc plate  40 . Torsional damper  15  includes first plate  40  and cover plates  100  and springs  80 . 
     In  FIGS. 2 and 3 , exemplary driven disc  10  comprises a rotatable disc assembly  20  having disc plate  40  fixedly attached to reinforcing plates  60  by a plurality of rivets  21 . Reinforcing plates  60  each have a plurality of apertures  62  at least partially aligned with apertures  22  in disc plate  40 . Hub assembly  30  includes a pair of facing spring cover plates  100  fixedly attached to hub  70  by a plurality of rivets  31 . While plates  60  are shown on opposite sides of disc plate  40 , other arrangements are easily anticipated by those skilled in the art, including having plates  60  on a single side of disc plate  40 , having no reinforcing plates, or having more than two reinforcing plates. A benefit of reinforcing plates is that it enables the use of a thinner plate  40 , beneficially reducing the rotating inertia of driven disc  10 . Yet alternatively, cover plates  100  could incorporate reinforcing plates. However, with regard to the operation of the damping mechanism, the use or non use of reinforcing plates is not critical. Thicker plates can be employed as might be required to sustain the anticipated loading within torsional damper  15 . Spring reaction features within apertures  62 ,  22  may be in part or in entirely defined by apertures in reinforcing plates or the disc plate to the extent that the either of apertures  62 ,  22  are smaller than the other. The combinations and arrangements of reinforcing plates, if any, are not critical to the present invention. Another factor that is not significant is whether the first plate is part of the disc assembly and the cover plates part of the hub assembly, or vice versa, with the first plate part of the hub assembly and the cover plates part of the disc assembly. Although that is not the usual arrangement in a driven disc of a frictional clutch, such an approach could be used in a driven disc, or any other torsional damper application. 
     Energy storage means  80  are disposed within apertures  22 ,  32 ,  62  for absorbing torque as a function of relative rotation between hub assembly  30  and disc assembly  20 . 
     Coil springs  80  are operatively disposed between the disc assembly  20  and the hub assembly  30 . More specifically, coil springs  80  contact disc plate  40  and reinforcing plates  60  at a first end and first spring cover plates  100  at a second end. Inner coil springs (not shown) radially disposed within coil springs  80  contact a feature  35  within apertures  32  at a first end and disc plate  40 . As the disc assembly  20  rotates relative to hub assembly  30 , torque is absorbed as a function of the resulting spring and friction damping. 
       FIGS. 5-9  show plate  100  in greater detail, and in particular show improved apertures  32  in spring cover plate  100 . Damper pockets  11 , best seen in  FIG. 3 , are defined by apertures  32  in oppositely disposed spring cover plates  100  with aligned spring apertures  32 . Apertures  32  are characterized by parallel pocket lips or edges  11  extending in the axial direction from the surface of plate  100 . 
     Pocket geometry plus spring preload together has been discovered to make a very significant difference in pocket wear, and by association, spring wear. These factors are particularly important with longer damper springs. The resulting optimal shape is surprising relative to past design approaches. In the past, the outer edges of the spring pockets typically took on a smooth arcuate shape. The arcuate shape restricts the displacement of the coil spring during compression and extension cycling to the arcuate shape of pocket  11 . That results in constant engagement of the spring with the outer edges of the spring pocket along the entire length of the spring. Such a shape seems intuitively appropriate, as it is concentric with the plate and allows the spring to deflect along the same path that the relatively rotating pockets are moving in. However, the constant engagement results in both pocket wear and spring wear. It has been discovered that the area most severely affected by the constraint is that near the ends of the spring. The inventive flat shape of the damper pockets and the corresponding apertures  32  provides the spring with sufficient room to deflect more while still being retained in pockets  11 . The result has been a significant reduction in both spring wear and pocket wear, in turn resulting in increased damper durability. 
     Pocket  11  still captures the ends of the spring by defining an inside diameter near the same size as the outside diameter of coil spring  80 . Ends of apertures  32  are provided with flat sections  35  that extend into aperture  32 . Flat sections help retain springs  80  and can provide a surface for engagement of ends of inner coil springs, should such inner coil springs be employed in the damper. The particularly beneficial improvement is the more rapid transition that the pocket provides from fully retained to a low restriction condition. Angled edge portions  11 C and  11 D of aperture  32  increase the space available to spring A much closer to the ends of the spring than the prior art concentric arc configuration did. Potentially, a single diameter arc with a center eccentric to and smaller than the old concentric arc could provide an advantage similar to the present invention. However, the eccentric arc may not be possible to employ without compromising the outer diameter of the plate  100  if the apertures  32  are located too close to the periphery of the plate  100 . Accordingly, the illustrated embodiment has outer edge parallel  11 B to inner edge  11 A, in effect drawing a chord across the new arc. Portions  11 C and  11 D could be alternatively straight lines or arcs. In the illustrated embodiment, portions  11 C and  11 D are defined by an arc of approximately one half the radius of plate  32 . The resultant larger cross section damper pocket provides spring  80  with increased freedom of movement in the pocket. Outer edge  11 B is essentially a chord across the smaller diameter arc. Outer edge  11 B extends approximately one half the length of aperture  32 , with aperture  32  being measured from flat section  35  to flat section  35 . The larger section of the resultant pockets  11  limits spring contact against the pockets to the end or dead coils, greatly reducing wear on both the spring and the pocket. 
     Axial spring preload is also a factor. Too much or too little longitudinal preload has been discovered to contribute to spring and pocket wear. Twenty percent of spring capacity has been determined to be a particularly beneficial value of spring preload. The preload is a function of the spring&#39;s free length relative to the length of the spring pocket with the assembly in the unloaded condition. By unloaded, it is meant that the clutch driven disc does not have a torsional load applied to it. Assembly of the driven disc requires chamfers on the springs and coining or chamfers on the pocket. It is to be appreciated that too much spring preload deteriorates in-vehicle performance of the damper  15  because of insufficient enough torsional absorption capacity, while too little promotes pocket wear, and leads to durability issues. The above described configuration is particularly beneficial to the use of inner coil springs. 
     The foregoing discussion discloses and describes the preferred embodiment of the present invention. However, one skilled in the art will readily recognize from such discussion and the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined in the following claims.