Abstract:
A clutch travel stop limits the amount of vehicular clutch travel adjustment normally permitted for compensating clutch component wear. The stop is attached to a centrifugal weight and roller clutch actuation module to control the amount of permissible wear of clutch components including, for example, friction plate linings. In one embodiment, the stop is defined by a protuberance, such as an integrally formed radially extending lug integrally affixed to an outer circumferential periphery of the housing of the centrifugal module. The lug is positioned to arrest relative movement between respective flanges of a clutch cover and the centrifugal module to limit adjustment of the clutch so that an over-adjustment condition is avoided. Potential damage to critical clutch components is thereby minimized, such as damage to flywheel and pressure plate components caused by fasteners that become exposed after clutch linings retained by the fasteners to the friction disc have become worn.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The present invention relates to vehicular clutch adjustments made to compensate for increased clutch component travel resulting from clutch wear, and to overall enhancements in the utility of automatic wear compensation mechanisms used in clutches for such purposes. More particularly, the invention relates to a device for limiting an otherwise permissible amount of wear adjustment of a centrifugal clutch, so that an over-adjustment condition may be avoided, and potential for damage to critical clutch components may be reduced.  
           [0003]    2. Description of the Prior Art  
           [0004]    Clutch wear mechanisms of the type affixed to vehicular clutch covers are used to compensate for clutch friction lining wear over the functional life of a clutch. In centrifugal clutches, such mechanisms are typically directly affixed between clutch covers of vehicular clutch assemblies and housings of centrifugal weight and roller modules, and are secured to the respective structures via traditional fasteners, including rivets or bolts.  
           [0005]    Although clutch wear compensation mechanisms have improved over time, such mechanisms have not always been successful in protecting critical components of the clutch under conditions of extreme wear, particularly the clutch linings associated with rotary clutch friction plates or discs. In some instances, the fasteners, such as rivets for example, that secure the linings to the discs become exposed after the linings are worn. The exposed rivets then become prone to causing mechanical damage to the flywheel and pressure plate surfaces.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a clutch travel limit or stop for a vehicular clutch to limit amount of clutch travel adjustment otherwise normally permitted for compensation of clutch component wear. The stop is employed in such clutches to limit the amount of permissible wear of the internal clutch components, such as friction disc linings. In addition, the stop is employed to eliminate or reduce the effect of over-adjustment of the clutch via a cam segment wear compensation mechanism.  
           [0007]    In one described embodiment, the stop is defined by a protuberance, such as an integrally formed lug, fixed to an outer circumferential periphery of the housing of a centrifugal weight and roller compensation module. The lug is positioned proximally to a clutch flywheel ring or attached clutch cover segment for limiting axial travel of the ring relative to the module housing, and in turn for limiting amount of permissible adjustment of the clutch so that an over-adjustment due to an over-worn condition may be avoided. Potential damage to critical clutch components is thereby minimized, such as damage to flywheel and pressure plate components caused by exposed fasteners, such as rivets, after the clutch linings secured by the rivets to the friction disc have become substantially worn. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a cross-sectional view of a normally open centrifugal clutch assembly that includes the clutch adjustment travel stop of the present invention.  
         [0009]    [0009]FIG. 2 is a perspective cut away view of a portion of the clutch assembly of FIG. 1, showing components of a centrifugal module employed in one described embodiment of the assembly, including the travel stop system of the present invention.  
         [0010]    [0010]FIG. 3 is a side view of the same embodiment revealing additional components of the clutch assembly of FIG. 1.  
         [0011]    [0011]FIG. 4 is a cross-sectional view of a second embodiment of the travel stop system of the present invention.  
         [0012]    [0012]FIG. 5 is a cross-sectional view of a third embodiment of the travel stop system of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0013]    Referring initially to FIG. 1, an automatically actuated centrifugal clutch assembly  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.  
         [0014]    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 bonded friction linings  21 ,  23  secured by traditional fasteners including rivets, bolts, or welds. 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.  
         [0015]    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 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  rotates during operation of the vehicle engine, the described coupled members all rotate together at the same speed as the ring  30 .  
         [0016]    Indeed all members as will be described herein always 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 fixed flywheel  16 , the axially movable intermediate plate  22 , and the axially movable 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 .  
         [0017]    Continuing reference to FIG. 1, leftward movement of the pressure plate  24  actuates the clutching of the friction plates  18 ,  20 . Referring now also to FIGS. 2 and 3, in order to initiate such clutching, a centrifugal module  40  is provided, the module having a plurality of circumferentially arranged weights  35  pivotally disposed within a housing  38  of the centrifugal module  40 . The weights are attached to pivot links  37  fixed to the housing  38 , and are adapted to swing radially outwardly via centrifugal force induced by engine speed. The amount of angular pivotal movement of the weights  35  is controlled by compression springs  39  that are secured between the weights  35  and the internal diameter  41  of the housing  38 .  
         [0018]    The weights  35  along with rollers (not shown) move radially outwardly under centrifugal forces induced by rotation of the engine, as the rollers are attached to the weights. The rollers are axially fixed to the weights  35 , and interact with axially movable ramp segments (also not shown) affixed to a ramp plate  36  (FIG. 1). The centrifugally actuated rollers urge the ramp plate leftwardly against the force of a resilient diaphragm spring  34 . 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.  
         [0019]    The ramp plate  36  (FIG. 1) directly engages the diaphragm spring  34  as depicted in FIG. 1. Thus, it will be appreciated by those skilled in the art that the clutch assembly  10  is automatically actuated as a function of the rotary speed of the crankshaft  26 . As the speed of the engine increases, e.g. measured in revolutions per minute of the crankshaft  26 , the weights  35  will be urged radially outwardly against the compressive forces of the springs  39 . 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  39  will be sufficient to counter the centrifugal forces on the weights  35  at that relatively low engine speed. Upon additional engine fueling rates, the engine speed will progress to higher values, resulting in clutch actuation movement initiated by the described rollers against the ramp plate  36 . By the time the clutch assembly  10  is rotating at speeds in the range of 1400 rpm, the clutch  10  will be fully engaged, and the friction discs  18 ,  20  fully clutched.  
         [0020]    In accordance with this invention, and referring now particularly to FIG. 3, a plurality of travel stop lugs  42  are disposed circumferentially in spaced regular angular intervals about the external periphery of the housing  38  of the module  40 . As was earlier noted, the clutch cover  32  is bolted to the flywheel ring  30 . In FIG. 3, it is apparent that the clutch cover periphery has openings through which can be seen one of a plurality of intermediate plate drive straps  44  arranged to circumferentially connect the intermediate plate  22  to the clutch cover  32  by way of connection bolts  46  and  48 . This permits the intermediate plate to move axially, or along an axis a-a that defines coincident centerlines of the clutch assembly  10  and the centrifugal module  40 . Similarly, the pressure plate  24  is attached to the clutch cover  32  via a plurality of pressure plate drive straps  50  that connect the cover to the pressure plate via connection rivets  52  and bolts  54 .  
         [0021]    As the friction linings  21  and  23  become worn during the useful life of the clutch, the rollers of the centrifugal module could begin to lose effectiveness with respect to interacting with ramps of the ramp plate  36  for maintaining sufficient clutching forces, as those skilled in the art will appreciate. Thus, a friction wear mechanism is defined by a circumferentially disposed pair of cam segments  60  and  62  (FIG. 2) fixed between a travel lug flange contact surface  56  of the cover  32  and a flange  64  of the housing  38 . The segments  60  and  62  rotate relative to one another to accommodate the slack that occurs due to wear, axially spreading respective flanges apart to achieve this desired effect.  
         [0022]    A major issue of wear compensation mechanisms such as the cam segments  60  and  62  is their inability to avoid damage to components of the clutch after the wear has progressed beyond certain limits. Thus, even though wear slack has been taken up by the segments  60  and  62 , a point can be reached when the friction facings have become so worn that the fasteners retaining the facings to the friction discs  18 ,  20  become exposed and begin to scour and otherwise damage the surfaces of the flywheel  16 , the intermediate plate  22 , and the pressure plate  24 .  
         [0023]    To avoid this condition, the travel lugs  42  have contact surfaces  66  adapted to engage a complementary radially extending flange contact surface  56  of the cover  32  after a prescribed distance D is accommodated for slack due to friction lining wear (FIG. 3). Thus at the point that the lugs  42  engage the surface  56 , no further wear adjustment will be achieved by the cam segments  60  and  62 . The distance D therefore defines the full wear travel of the centrifugal module  40  relative to the clutch cover  32 . The lugs  42  will also provide a travel limit for protection of the drive straps  44  and  50  during shipment of the clutch, as drive straps are occasionally overstressed during movements that occur prior to installation of such clutch assemblies in vehicles.  
         [0024]    Referring now to FIGS. 4 and 5, second and third embodiments  42 ′ and  42 ″ of the clutch travel stop lug  42  are shown. Referring to FIG. 4, the travel stop lug  42 ′ is shown in cross-section as a cup-shaped structure that is secured to a threaded stud  58 ′ that extends from the rear  43 ′ of the module  40 . In cross-section, the travel stop lug  42 ′ has an axially depending leg  45  with a contact surface  66 ′, and a complementary threaded aperture  68  for securement to the threaded stud  58 ′ of the module  40 . In accordance with the aforedescribed concept of the invention, the contact surface  66 ′ is adapted to engage the flange contact surface  56 ′ prior to complete wear of the friction linings  21 ,  23 , thus avoiding issues of over adjustment attributable to wear compensation. Although the second embodiment of the travel stop lug  42 ′ may be cup-shaped, the stop lug  42 ′ may also be into two separate pieces, wherein the cross-section will still be as shown in FIG. 4. In addition, there will normally be a nut (not shown) secured to the threaded stud  58 ′ for affixing the lug  42 ′ in place against the rear  43 ′ of the module  40 .  
         [0025]    Finally, FIG. 5 displays a travel stop lug  42 ″ that is in the form of a washer circumferentially disposed within an annular slot  47  in the body of the housing  38 ″. Similarly, the lug  42 ″ has a contact surface  66 ″ adapted to limit against likelihood of over adjustment attributable to wear compensation.  
         [0026]    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.