Abstract:
A clutch ramp reaction plate is adapted to be positioned adjacent a centrifugal actuation module of a centrifugally actuated vehicular clutch. The ramp reaction plate includes attached individually machined ramp segments manufactured separately from the ramp reaction plate. In one embodiment, the ramp segments are made from a powdered metal process to assure uniform tolerances. In an alternate embodiment, the ramp segments are formed of hardened stamped steel material. The ramp reaction plate is machined to accept the segments, which includes a surface hardness higher than that of the ramp reaction plate to accommodate wear resistance. The ramp segments can be impregnated with lubricants or polytetrafluoroethylene materials to reduce rolling friction and wear between the ramp surfaces and mass weight rollers of the centrifugal actuation module that interacts with the ramp surfaces. The segments are attached to the ramp reaction plate by means of fasteners including bolts, rivets, or adhesives.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    This invention relates generally to improvements in the manufacture of ramp modules for ramp reaction plates adapted to interface with weight and roller centrifugal modules of automatic centrifugal clutches. More particularly, the invention relates to improvements in ramp modules affixed to ramp reaction plates, and commensurately to improved operation of vehicular clutches.  
           [0003]    2. Description of the Prior Art  
           [0004]    Automatically actuated centrifugal clutches include actuation modules of the type including centrifugal weights affixed to vehicular clutch covers. The weights are radially movable against spring loads as a function of engine speed. Several issues work against ideal operation of the modules over the useful lives of the clutches. For example, individually machined ramp units normally formed on and integral to the ramp reaction plates require very close manufacturing tolerances for each individual ramp profile. The process is expensive, slow, and works against achievement of manufacturing efficiencies.  
           [0005]    In addition, the existence of tolerance variations in profile ramp angles creates nonuniform movements of the centrifugal mass weight rollers, giving rise to uneven performance of the centrifugal module during clutch actuation. As a result, the centrifugal module is vibration prone in one aspect of its less than satisfactory operation. In addition, to the extent that the tolerance variations limit proper interaction of the mass weight rollers and ramp reaction plate reaction modules during actuation, the overall efficiency and performance of the clutch actuation module suffers.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention facilitates improved operation of a centrifugal actuation module in a centrifugally actuated vehicular clutch. In the described embodiment, a clutch ramp reaction plate is positioned adjacent the centrifugal actuation module. The ramp reaction plate is manufactured apart from individually machined ramp segments that are separately attached to the ramp reaction plate. In one embodiment, the ramp segments are made from a powdered metal process to assure that the tolerances are uniform from one ramp segment to the next. In an alternate embodiment, the ramp segments are formed of a hardened stamped steel material. The ramp reaction plate is machined to accept the segments. The segments include surface hardnesses that are higher than that of the ramp reaction plate to accommodate wear resistance.  
           [0007]    The use of separate manufacturing processes for the ramp segments assures that they can be hardened in bulk from a harder material than that of the ramp reaction plate. In addition, the powdered metal ramp segments can be impregnated with lubricants or polytetrafluoroethylene materials to reduce rolling friction and wear between the ramp surfaces and the mass weight actuated rollers interacting with the surfaces.  
           [0008]    The segments are attached to the ramp reaction plate by means of various fasteners including bolts, rivets, or adhesives. In one described embodiment, a special lip permits the strength requirement of the fastener to be reduced to the extent that the lip is adapted to resist centrifugal forces acting on the segment. Use of separately manufactured segments substantially reduces manufacturing costs, and assures higher product quality with lower tolerance variations.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a cross-sectional view of a normally open centrifugal clutch that incorporates the improved clutch drive ramp reaction plate of the present invention.  
         [0010]    [0010]FIG. 2 is a view of one embodiment of a clutch actuation ramp reaction plate of the centrifugal clutch of FIG. 1, including a plurality of ramp segments affixed to the plate for interaction with a weight roller system of a centrifugal weight-spring clutch actuation module of the clutch of FIG. 1.  
         [0011]    [0011]FIG. 3 is an enlarged perspective view of one of the ramp segments.  
         [0012]    [0012]FIG. 4 is a perspective end view of a centrifugal weight spring clutch actuation module included in the centrifugal clutch of FIG. 1.  
         [0013]    [0013]FIG. 5 is a perspective face view of a second embodiment of the clutch drive ramp reaction plate of the present invention.  
         [0014]    [0014]FIG. 6 is an alternate embodiment of the drive ramp reaction plate segment employed in the ramp reaction plate of FIG. 5.  
         [0015]    [0015]FIG. 7 is an elevation view along lines  7 - 7  of the ramp reaction plate segment of FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0016]    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 shroud or 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 is normally used with an electromechanical style automatic transmission, and is employed in vehicles that are normally without a clutch pedal.  
         [0017]    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 , which are bonded, riveted, or welded to the plates  18 ,  20 . 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.  
         [0018]    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. The clutch cover, the pressure plate  24 , and the intermediate plate  22  are all affixed to the flywheel ring  30 . (In some embodiments, the ring  30  is equivalent to the cover  32 .) 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  rotates during operation of the vehicle engine, the described coupled members all rotate together at the same speed as the ring  30 .  
         [0019]    All members described herein rotate with the flywheel ring  30  with the exception of the pair of friction plates  18 ,  20  that are clasped, i.e. “clutched”, between the axially movable flywheel  16 , the intermediate plate  22 , and the pressure plate  24  as described above. Any leftward movement of the pressure plate  24  actuates the clutching of the friction plates  18 ,  20 . 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 .  
         [0020]    Referring now also to FIGS.  2 - 4 , in order to initiate such clutching, a centrifugal module  40  is provided, the module having a circumferentially arranged plurality of weights  64  pivotally disposed within a housing  72  of the module  40 . The weights are attached to pivot links  66  fixed to 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 .  
         [0021]    A ramp reaction plate  36  (FIGS. 1 and 2) directly engages a resilient diaphragm  34  (FIG. 1). It will be appreciated that rollers  46 ,  48  (FIG. 4) move radially outwardly under centrifugal forces induce upon the rollers by the weights  64 . The axially fixed but radially movable rollers, however, directly engage the ramp segments  44  (FIG. 2), fixed to the axially movable ramp reaction plate  36  to cause the ramp reaction plate  36  to move leftwardly (FIG. 1) against the force of the diaphragm  34 . This action produces the earlier described “clutching”, 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.  
         [0022]    In accordance with this invention, and referring now particularly to FIGS. 2 and 4, the annular ramp reaction plate  36  is interposed against the centrifugal clutch actuation module  40 . Individually manufactured ramp segments  38 ,  42 ,  44 ,  50  are circumferentially spaced about the planar face  54  of the ramp reaction plate  36 , each segment being rigidly secured to the ramp reaction plate  36  by rivets, bolts, or via an adhesive. As alluded to earlier, corresponding sets of circumferentially spaced spring-loaded rollers  46  are designed to directly engage corresponding ramp segments  38 ,  42 ,  44 ,  50 .  
         [0023]    As the speed of the engine increases, e.g. measured in revolutions per minute of the crankshaft  26 , the weights  64  will be urged radially outwardly against the compressive forces of 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 650 to 850 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  38 ,  42 ,  44 , and  50 . By the time the clutch assembly  10  is rotating at speeds in the range of 1200 to 1500 rpm, the clutch  10  will be fully engaged, and the friction disks  18 ,  20  fully clutched.  
         [0024]    Against this background, and referring now particularly to FIG. 3, the ramp segment  38  is representatively shown in greater detail. All of the ramps segments  38 ,  42 ,  44 ,  50  are identical in their features; only their relative positions about the annular ramp reaction plate  36  vary. Ideally, the segments and their corresponding interactive rollers  46  are circumferentially spaced apart in regular angular intervals for achievement of an optimal centripetal force balance, to the extent that the masses of the weights, rollers, and ramp segments all rotate with the engine flywheel.  
         [0025]    Each ramp segment  38  is comprised of an integral, one-piece metallic member including a boss defined by a raised portion  76  integral to but situated atop a base plate  80 . Ideally, the ramp segments are formed in a batch process to assure consistent uniformity of hardnesses and dimensions of said segments. The raised portion  76  is angled to the base plate  80  in the described embodiment. The portion  76  incorporates a dwell portion  78  contiguously abutted by an angled cam portion  79 . The rollers  46  engage the angled cam portion  79  during the clutch actuation phase described above. At and above clutch engagement speeds, however, the rollers engage and remain contact with the dwell portion  78 .  
         [0026]    For accommodating the rollers  46 , the raised portion  76 , which is generally rectangular in shape, is disposed along a longitudinal axis b-b, which does not dictate orientation of the separate axis a-a of the base plate  80 . As apparent in FIG. 3, the two axes do not coincide or run together. Moreover in the embodiment of FIG. 3, the base  80  of the ramp segment  38  incorporates a lip  82  disposed orthogonally to the base  80 . The lip has a corresponding arcuate shape of, and is sized to capture, the interior diameter  84  of the annular ramp reaction plate  36 .  
         [0027]    Those skilled in the art will appreciate that the lip produces the structural strength requirement of the segment  38 . This is because, especially at high revolutions per minute, centrifugal forces imposed on ramp segments  38  will be effectively transferred to the lips  82  and, in turn, to the internal diameter  84  of the plate  36 . As such, a single rivet (not shown) may be installed into an aperture  86  to securely attach the segment  38  to the face  54  of the plate  36 .  
         [0028]    [0028]FIG. 5 represents another embodiment of the ramp reaction plate  36 ′ which incorporates attached ramp segments  38 ′,  42 ′,  44 ′, and  50 ′. Referring now also to FIG. 6 and FIG. 7, the ramp segment  38 ′ is shown in greater detail. The segment  38 ′ includes a raised portion  76 ′ as well as an oval base plate  80 ′, having a major axis a′-a′. The segment  38 ′, however, is without the lip  82 . Thus two rivets or connectors (not shown) are inserted through apertures  88  and  90  to secure the segment  38 ′ to the ramp reaction plate  36 ′. The segments  36 ′ are substantially similar to segments  36  and all other respects, and cooperate with the rollers  46  in the same manner.  
         [0029]    In each of the noted embodiments, the segments  38 ,  38 ′ may be formed of a powdered metal composition to insure consistent uniformity of size and shape. Alternatively, the segments  38 ,  38 ′ may be formed as a hardened stamped metal part, i.e. steel in the disclosed embodiment. Maintaining such uniformity is difficult when the manufactured plates already include the segments; in such cases the segments must be separately finished while comprising an integral part of the plate. Processes for achieving uniformity under such circumstances have not been satisfactory. For example, in some cases it has been virtually impossible to achieve uniform hardnesses among segments integrally affixed to the plate.  
         [0030]    Finally, in accordance with the disclosed invention, shape of the segments  38 ,  38 ′ can be readily varied to achieve various performance characteristics, strictly as a function of clutch actuation dynamics. The invention thus adds a dimension of significant versatility, in addition to reducing manufacturing costs, assuring higher product quality, and achieving smaller tolerance variation from part to part.  
         [0031]    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. 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.