Abstract:
An actuation module of a centrifugal clutch incorporates a plurality of actuating weights mounted on pivot links. The weights pivot radially outwardly under centrifugal forces induced by rotation of the actuation module. One weight is secured to each of the pivot links, and springs counter the radially outward movements of the weights. Each weight defines a slot; a roller is disposed in each of the slots. Each slot defines a pair of spaced walls; each of the rollers is rotatable on an axle secured between one pair of walls. The rollers engage cam ramps that rotate with the module but are axially displaceable with respect thereto for engagement and disengagement of the clutch. Each pair of walls is oriented in direction of pivotal movement of its associated weight. A roller thrust plate is secured between each roller and the wall of the slot spaced farthest away from the pivot link.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates generally to improvements in centrifugal modules of automatically actuated clutches. More particularly, the invention relates to improvements in high speed functioning of weight and roller structures contained in such centrifugal modules, and commensurately to reduced wear rates of rollers subject to centrifugal forces within the modules. 
     2. Description of the Prior Art 
     Automatically actuated centrifugal clutches employed with heavy-duty electromechanical highway line-haul truck transmissions include so-call centrifugal actuation modules that house centrifugally actuated weights. The centrifugal modules are affixed to engine flywheel rings, and each of a plurality of centrifugally actuated weights is adapted to swing in an arc about a pivot link fixed to the module housing structure. As such, the weights contained within the modules are radially outwardly movable against resistive spring forces as a function of engine speed; the higher the speed, the greater the movement between limits. Rollers attached to the weights are adapted to roll atop ramp segments that are cammed for clutch engagement and disengagement, as will be appreciated by those skilled in the art. 
     The rollers operate under relatively high centrifugal forces, and thus give rise to issues that work against satisfactory operation of the modules over the useful lives of the clutches. For example, in one centrifugal module rigidly attached to an engine flywheel ring, the rollers are supported for rotation on axles fixed in slots provided in the weights. The mass of the rollers subjects the rollers to centrifugal forces that urge the sides of the rollers into walls of the slots. The result is an accelerated wear of the rollers, and scouring of the slot walls. The condition is exacerbated at higher clutch rotation speeds at which the operative centrifugal forces become higher. Thus, a need exists to avoid premature deterioration of the rollers, along with scouring of the walls of the slots subject to such roller contact, particularly under higher clutch rotation speeds associated with centrifugal clutch operation at highway line-haul speeds. 
     SUMMARY OF THE INVENTION 
     The present invention provides improved operation of an actuation module of a centrifugally actuated vehicular clutch. The actuation module incorporates a plurality of clutch engagement actuating weights. The weights are mounted on pivot links that are adapted to permit the weights to pivot radially outwardly under centrifugal forces induced by rotation of the actuation module. One weight is secured to each of the pivot links, and in one described embodiment, a set of springs counters the radially outward movement of the weights. 
     Each weight defines a slot, and a roller is disposed in each of the slots. Each slot defines a pair of spaced walls, and each of the rollers is rotatable on an axle secured between the pair of walls. The rollers engage cams (ramps) that rotate with the module but are axially displaceable with respect to the module for engagement and disengagement of the clutch. Each of the rollers, as well as each of the associated pairs of walls, is oriented in a direction of pivotal movement transverse to the longitudinal axis of its associated weight. A roller thrust plate is secured between each roller and the wall of the slot spaced farthest away from the pivot link to avoid deterioration of the roller and commensurate scouring of the slot wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a centrifugal clutch assembly that incorporates the clutch roller thrust plate of the present invention. 
     FIG. 2 is an enlarged perspective view of a centrifugally actuated weight-spring clutch actuation (engagement) module, shown as part of the clutch assembly of FIG. 1, that incorporates the thrust plate of the subject invention. 
     FIG. 3 is an enlarged side view of one of the centrifugal weights employed in the centrifugal module of FIG. 2, demonstrating a first embodiment of a thrust plate and roller arrangement for the centrifugal clutch of the present invention. 
     FIG. 4 is a perspective view of the embodiment of the thrust plate of FIG.  3 . 
     FIG. 5 is an enlarged perspective cut away view of a portion of the centrifugal clutch of FIG. 1, demonstrating interaction of a roller system of the clutch actuation module with a ramp segment of a clutch actuation ramp plate. 
     FIG. 6 is a fragmentary side view of an alternate thrust plate and roller arrangement for the centrifugal clutch of the present invention. 
     FIG. 7 is a face view of the alternate embodiment of the thrust plate shown in FIG.  6 . 
     FIG. 8 is a fragmentary side view of another alternate thrust plate and roller arrangement for the centrifugal clutch of the present invention. 
     FIG. 9 is a perspective view of the alternate embodiment of the thrust plate structure shown in FIG.  8 . 
     FIG. 10 is a fragmentary side view of yet another alternate thrust plate and roller arrangement for the centrifugal clutch of the present invention. 
     FIG. 11 is a perspective view of the alternate embodiment of the thrust plate structure shown in FIG.  10 . 
     FIG. 12 is a fragmentary side view of still another alternate thrust plate and roller arrangement for the centrifugal clutch of the present invention. 
     FIG. 13 is a perspective view of the alternate embodiment of the thrust plate structure shown in FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring initially to FIG. 1, an automatically actuated centrifugal clutch  10  is designed for use in a motor vehicle, not shown. The clutch  10  is enshrouded between a bell housing  12  of a transmission (also not shown) and a flywheel housing  14  coupled externally to the bell housing  12 . The centrifugal clutch  10  is of the normally unengaged type that relies upon engine speed to initiate actuation, and hence engagement. The clutch may be used with an electromechanical style automatic transmission, and is employed in vehicles that are normally without a clutch pedal. 
     The flywheel housing  14  envelops an engine flywheel  16  that is bolted to an engine crankshaft  26  for direct rotation therewith. In the embodiment described, a pair of friction plates  18 ,  20  includes friction linings  21 ,  23 , secured to the plates  18 ,  20  via fasteners (not shown), which may be rivets, bolts, or adhesives, etc. The friction plates are adapted to be releasably clasped between the flywheel  16 , an intermediate plate  22 , and a pressure plate  24 . The friction plates  18 ,  20  are directly attached to, and rotate with, a transmission input shaft  27 . Those skilled in the art will appreciate that the transmission input shaft  27  is positioned coaxially with respect to the engine crankshaft  26 , but is axially spaced therefrom as depicted. 
     The engine crankshaft  26  is affixed to the engine flywheel  16 . For this purpose, the shaft  26  extends through an aperture  28  of the flywheel housing  14  as shown. A circumferentially extending flywheel ring  30  is rigidly affixed to the flywheel  16 , and an external clutch cover  32  is secured to the flywheel ring. In some cases, the ring  30  and cover  32  may be the same part, and this invention is intended to cover such cases. The clutch cover  32 , the pressure plate  24 , and the intermediate plate  22  are all affixed to the flywheel ring  30  in a manner such that all of the respectively described members are permitted to move axially, though non-rotatably, in reference to the flywheel ring. Thus, as the flywheel ring  30  spins during operation of the vehicle engine, the described coupled members all rotate together at the same speed as the ring  30 . 
     Indeed all members as will be described herein rotate with the flywheel ring  30  with the exception of the pair of friction plates  18 ,  20  that are respectively clasped, i.e. “clutched”, between the flywheel  16 , the axially movable intermediate plate  22 , and axially moveable pressure plate  24 , as described above. In addition, it will be appreciated that all of the plates, apart from the plates  18 ,  20  are annular in shape, as required to permit the transmission input shaft  27  to pass through the centers of each of the plates that rotate with the flywheel ring  30 . 
     Continuing reference to FIG. 1, any leftward movement of the pressure plate  24  actuates the clutching of the friction plates  18 ,  20 . Referring now also to FIG. 2, in order to initiate such clutching, a centrifugal module  40  is provided, the module having a circumferentially arranged plurality of weights  64  that are pivotally disposed within a housing  72  of the centrifugal module  40 . The weights are attached to pivot links  66  fixed to a rear portion (hidden) of the housing  72 , and are adapted to swing radially outwardly against centrifugal force induced upon them by engine speed. The amount of angular pivotal movement of the weights  64  is controlled by compression springs  68 ,  70  that are secured between the weights  64  and the internal diameter  74  of the module housing  72 . 
     Making reference now to FIGS. 3 and 4, one of the centrifugal weights  64  is shown isolated from the normally circumferentially arranged plurality of centrifugal weights  64  (FIG.  2 ). It will thus be appreciated that each centrifugal weight  64  pivots in an arc S about a pivot link  66  that is fixed to the noted rear portion of the module housing  72 . To the extent that the module  40  (FIG. 2) rotates at variable rates of speed, the springs  68  and  70  will be effective to limit movement of the pivotal weight  64  along arc S as a function of amount of centrifugal force on the weight  64 . In FIG. 3, it will be apparent that the springs  68  and  70  are supported against a spring seat  65  adapted to hold the springs fixedly in-place on the internal diameter  74  of the housing  72 . 
     Continuing reference to FIG. 3, in combination with FIG. 5, it will further be appreciated that rollers  46 ,  48  are supported on axles  94  that extend between parallel walls  96  of a slot  98  formed within each weight  64 . The axles  94  extend parallel to an axis a-a that forms a longitudinal axis of the weight  64 . The rollers  46 ,  48  are thus adapted to move in a direction transverse to the longitudinal axis a-a of the weight  64 . It will further be appreciated that each of the rollers  46 ,  48  has a mass that will be subjected to centrifugal forces as the weight  64  is centrifugally rotated. Thus, the rollers  46 ,  48  will tend to be slung radially outwardly, i.e. to be urged in a direction of the arrow F, so as to create a scouring of the wall  96  positioned farthest away from the pivot link  66 , hereinafter called the “outer wall.” In some cases, the interaction between the outer wall  96  and the rollers can create conditions under which the clutch assembly  10  will be unable to disengage. The issue is particularly exacerbated by the fact that the weight  64  is formed typically of cast iron, a relatively soft material compared to the typically hardened steel material of the rollers  46 ,  48 . 
     In order to alleviate such scouring, and to avoid premature demise of the rollers  46 ,  48 , a thrust plate  80 , best shown in FIG. 4, is interposed between the outer wall  96  and the rollers  46 ,  48 . The thrust plate of the described embodiment is formed of VESPEL®, a plastic composite material. Alternatively, a carbon steel or a brass material can be used. The thrust plate material in any event will be formed of bearing grade material in order to assure an adequate useful life of the actuation module. Finally, the thrust plate  80  includes a pair of apertures  88 ,  90  through which extend axles  94  for support of the rollers  46 ,  48 , as will be appreciated by those skilled in the art. 
     Referring in more detail to FIG. 5, the weight  64  has been cut away to better reveal action of the rollers  46 ,  48 , which move radially outwardly in direction R along ramp segments  44  of a clutch ramp plate  36 . The rollers  46 ,  48  are fixed within the slots  98  of the weights  64  as noted above, and thus move to cause the ramp plate  36  to move leftwardly (FIG. 1) against the force of a resilient diaphragm spring  34  (FIG.  1 ). This action produces the clutching action earlier described, wherein the friction plates  18 ,  20  become coupled, i.e. rotationally locked, to the flywheel  16 , as will be appreciated by those skilled in the art. 
     Turning momentarily back to FIG. 1, the ramp plate  36  directly engages the diaphragm spring  34 , as previously noted. In accordance with this described embodiment, an annular drive reaction plate  38  (FIGS. 1 and 5) of a thin spring metal is interposed between the ramp plate  36 , ramp segments  44  and rollers  46 ,  48  of the centrifugal clutch actuation module  40 . In the described embodiment, the plate  38  is formed of high carbon spring steel, such as SAE 1080 spring steel. The drive reaction plate includes apertures  42  (FIG. 5) for receiving and capturing a plurality of the ramp segments  44  that are circumferentially angularly distributed about the ramp plate  36 , each segment being rigidly secured to the ramp plate  36 . In the described embodiment, the apertures  42  are also generally rectangular in shape, so as to closely circumscribe the ramp segments  44 , as desirable for greatest effectiveness. 
     Those skilled in the art will appreciate that normally the diaphragm spring  34  is preloaded in order to reduce amount of clutch plate travel required to achieve plate clamp load sufficient to engage the clutch. Typically, the amount of preload in clutches adapted for use in heavy-duty vehicles is measured in the thousands of pounds. Accordingly, at a clutch rotation of approximately 1400 RPM, the preload force of the diaphragm spring  34  in the described embodiment is overcome (approximately 4000 pounds). At this point, the weights  64  will tend to swing outwardly along arc S (FIG. 3) rather abruptly, fully compressing the springs  68 ,  70 , and causing the radially outwardly end  67  of the weight  64  to swing into the internal diameter  74  of the module housing  72 . The resultant noise can be audible to an operator of a vehicle depending on effectiveness of the dampening of engine noise, which can vary from one vehicle to another. Referring now more particularly to FIG. 4, those skilled in the art will appreciate that for purposes of dampening noise created when the weight  64  strikes the internal diameter  74 , the thrust plate  80  includes a spring tab portion  84  that is angularly attached at  86  to the roller thrust plate portion  82 . In the described embodiment, the spring tab portion  84  is adapted to make a dampened contact with a strike surface  92  formed in the internal diameter  74 , as shown (FIG.  3 ). 
     For optimized operation, circumferentially spaced pairs of the spring-loaded rollers  46 ,  48  are adapted to directly engage respective ramp segments  44  of the type shown in FIG.  5 . The drive reaction plate  38  further includes apertures  50  for attaching the plate  38  directly to the ramp plate  36  via fasteners  52  (FIG.  1 ), which may be bolts or rivets for example. The plate  38  also includes a plurality of spaced resilient straps  54  having apertures  56  to permit the attachment of the straps  54  to connection lugs  58  (FIG. 1) of the module  40 . 
     The spring metal straps  54  (FIG. 5) of the plate  38  are secured to the lugs  58  to provide a resilient axial relative movement capability between the ramp plate  36  and the module  40 ; no relative rotational movement is enabled by the connection. Such a connection facilitates operation of a pair of wear ramps  60 ,  62  (FIG. 5) employed to compensate for wear of the friction linings of the friction plates  18 ,  20 . 
     Intended operation of the centrifugal clutch assembly  10  is as follows. As the speed of the engine increases, e.g. as measured in revolutions per minute of the crankshaft  26 , the weights  64  (FIG. 2) will be urged radially outwardly against the compressive forces of the springs  68 ,  70 . Centrifugal forces on the weights will cause the weights to pivot radially outwardly a distance proportional to the engine speed. In the described embodiment, the clutch  10  will remain disengaged at idle speeds in the range of 750 rpm, as the forces of the springs  68 ,  70  will be sufficient to counter the centrifugal forces on the weights  64  at that engine speed. Upon additional engine fueling rates, the engine speed will progress to higher values resulting in clutch actuation movement initiated by the rollers  46 ,  48  against the ramps  44 . By the time the clutch assembly  10  is rotating at speeds in the range of 900 to 1200 rpm, the clutch  10  will be fully engaged, and the friction disks  18 ,  20  fully clutched. 
     FIGS. 6 and 7 display an alternative embodiment of a thrust plate  80 ′ for intended use in the weight and roller structures  64 ,  46  of the invention. The thrust plate  80 ′ is without a spring tab portion  84  of the first described embodiment, and may be particularly suitable for environments in which highly preloaded diaphragm spring systems are not applicable, or in environments where likelihood of abrupt force changes are minimal. 
     FIGS. 8 and 9 depict an additional embodiment of a U-shaped thrust plate  100  that includes a pair of parallel side portions  102 ,  104  connected by a transverse connective portion  106 . The side portion  102  is adapted to be secured to end portions of the axles  94  that extend outside of the slot  98 . The thrust plate  100  is preferably formed of spring steel for enhancing clip-on resiliency. Obviously, the connective portion  106  is sized to fit over the end  67  of the weight  64  and into the slot  98  as shown. Apertures  108  in the side portion  102  accommodate the axles  94 , while slotted openings  110  and  112  are adapted to slip over the portion of the axles  94  disposed within the slot  98 , as will be appreciated by those skilled in the art. 
     FIGS. 10 and 11 depict yet another embodiment of a thrust plate  80 ″ that is a variation of the thrust plate  80  of the first described embodiment of FIGS. 3 and 4. The thrust plate  80 ″ has a tab portion  84 ′ that is analogous to the spring tab portion  84  employed in the first described embodiment. However, in the thrust plate  80 ″ the tab  84 ′ is formed orthogonally at  86 ′ to the roller thrust plate portion  82 ′. As such, the spring tab portion  84 ′ is formed to permanently lie against the upper surface  69  of the weight  64 , and thus provides no damping function similar to the spring tab portion  84  of the embodiment of FIGS. 3 and 4. 
     Finally, the embodiment of a thrust plate  120  as displayed in FIGS. 12 and 13 is adapted to provide protection of an oil fitting cap  130 . The cap  130  covers an oil fitting (not shown) for assuring sufficient lubrication of the described shafts  94  and rollers  46 ,  48 . For this purpose, a side flange  122  is orthogonally connected at  124  to a roller thrust plate portion  126 . As in all except one of the previously described embodiments, a pair of apertures  128  and  132  are provided to accommodate the axles  94  for securement of the thrust plate  120  to the weight and roller structure  64 ,  46 . 
     It is to be understood that the above description is intended to be illustrative and not limiting. Many embodiments will be apparent to those skilled in the art upon reading the above description. For example, although only a single thrust plate has been described in reference to each pair of rollers  46 ,  48 , an opposing thrust plate may be employed at the opposite ends of the rollers for other reasons, such as dimensional tolerance variations of the ramp segments, as one example. The scope of the invention should be determined, however, not with reference to the above description, but with reference to the appended claims with full scope of equivalents to which such claims are entitled.