Abstract:
A belt driving pulley, as typically used in a belt driven, drum-type drain cleaning machine and/or any other belt driven machinery, is disclosed wherein slippage between the pulley and the motor drive shaft occurs if a predetermined resisting torque is applied to the pulley by the belt.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention generally relates to sewer cleaning machines having a belt driven drum, or basket, which typically stores therein, and drives, a pipe cleaning cable or ““snake”.” More particularly the present invention teaches a unique and novel friction, clutch driven, pulley attached to the output shaft of the driving electric motor, or other prime mover, whereby the friction clutch will slip upon encountering a predetermined resisting torque, thereby preventing damage to the “snake” should the “snake” encounter extreme resistance outside the design parameters of the sewer cleaning machine and/or cable.  
         DESCRIPTION OF PRIOR ART  
         [0002]    Torque limiting mechanisms have been used in prior art sewer cleaning machines to protect the sewer cleaning cable, or “snake”, from being damaged if the sewer cleaning “snake” encounters an extreme torque, or resistance, whereby the yield point of the “snake” material may be exceeded. Generally the prior art torque limiting mechanisms fall into two categories, axial in-line mechanisms positioned in-line with the cleaning cable and pulley mechanisms attached to the driving motor&#39;s torque out-put, or drive, shaft. Following are typical prior art patents relating to both types of mechanisms:  
           [0003]    In-Line Mechanisms:  
           [0004]    U.S. Pat. No. 3,574,878 issued on Apr. 13, 1971 to Harold S. Ardsley for a “Power Rooter With Safety Clutch” teaches an in-line clutch assembly having diametrically, spring loaded clutch elements (balls) that cooperate with axial grooves that circumferentially slip upon experiencing a predetermined resistance torque.  
           [0005]    U.S. Pat. No. 3,742,548 issued on Jul. 3, 1973 to Peter L. Ciaccio for a “Safety Overload Clutch For Sewer-Rodding Machines and the Like, With Loading Indicator” discloses a pair of axial, in-line, “ratchet” toothed couplings, biased together by a coil spring that slidingly slip, with respect to one another, upon experiencing a predetermined limiting torque.  
           [0006]    U.S. Pat. No. 5,618,123 issued on Apr. 8, 1997 to Robert Pulse for a “Coupling Device For Sewer And Drain Cleaning Cable” teaches an in-line coupling having diametrical shear pins that shear when the coupling experiences a predetermined torque.  
           [0007]    U.S. Pat. No. 5,657,505 issued to Michael P. Gallagher et al. on Aug. 19, 1997 for a “Drain Cleaning Apparatus” discloses a drain cleaning machine having an engaging/disengaging double cone clutch by which the operator may manually engage and/or disengage the motor drive shaft from the sewer cleaning “snake” during the sewer cleaning operation.  
           [0008]    Drive Pulley Mechanisms:  
           [0009]    U.S. Pat. No. 5,033,990 issued to Arthur Silverman on Jul. 23, 1991 for a “Pulley Having Spring Loaded Release Mechanism” teaches a split V-belt pulley assembly, axially biased together by a helical spring, whereby the pulley sheaves are caused to axially separate when a predetermined torque, acting upon the V-belt passing between the pulley sheaves, is surpassed thereby permitting the V-belt to slip with respect to the pulley sheaves.  
           [0010]    U.S. Pat. No. 6,381,798 issued to Michael J. Rutkowski et al. for a “Spring Clutch For Drain Cleaning machines” on May 7, 2002 teaches a belt driven drum-type drain cleaning machine in which the driving motor supports are spring biased to tension the drive belt whereby drive belt slippage occurs in response to the imposition of a predetermined torque on the drain cleaning cable during use of the machine.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    The present invention generally relates to a drain cleaning machine of the belt driven, drum-type, design. More specifically, the present invention discloses a belt driving pulley assembly, attached to and rotating with the motor drive shaft, wherein the pulley will slip, with respect to the motor drive shaft, if a predetermined resisting torque is applied to the pulley by the drive belt.  
           [0012]    The torque limiting pulley comprises a central hub having a radially extending rotor preferably at one end thereof. Rotably positioned upon the central hub, adjacent the rotor, is a V groove pulley preferably having a lubricant impregnated bearing positioned between the inside diameter of the pulley and the external diameter of the central hub, whereby the pulley may be permitted to rotate independently of the central hub.  
           [0013]    A first friction material disc, coaxial with the central hub, is positioned between the pulley and the rotor. A second friction material disc, also coaxial with the central hub, is positioned on the opposite side of the pulley whereby the pulley is contiguously interposed between the first and second friction material discs.  
           [0014]    A pressure plate disc, coaxial with the central hub, positioned on the opposite side of the second friction material disc, is spring biased toward the second friction material disc whereby the axial force applied to the pressure plate disc causes the pulley to be frictionally held between the rotor and the pressure plate disc. Thus the pulley will rotate with the motor drive shaft until a predetermined resisting torque is applied to the pulley by the drive belt, whereupon the pulley will slip between the first and second friction material discs thereby preventing over torquing the drain cleaning cable causing damage thereto and/or stalling the motor.  
           [0015]    The torque value at which the pulley will slip between the first and second friction material discs, is determined by the axial spring force applied to the pressure plate disc by the biasing spring and the frictional properties of the friction material discs. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 presents a perspective view of a belt driven basket-type drain cleaning machine having a torque limiting clutch embodying the present invention.  
         [0017]    [0017]FIG. 2 presents an exploded perspective of the belt driven basket-type drain cleaning machine shown in FIG. 1.  
         [0018]    [0018]FIG. 3 presents a crossectional view taken along line  3 - 3  in FIG. 2 showing the elements and element arrangement of my torque limiting clutch driven pulley.  
         [0019]    [0019]FIG. 4 presents an exploded perspective of the torque limiting clutch driven pulley shown in FIG. 3.  
         [0020]    [0020]FIG. 5 presents a crossectional view similar to that shown in FIG. 3 illustrating an alternate embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    [0021]FIGS. 1 and 2 present a typical belt driven basket-type drain cleaning machine  10  having an electric driving motor  12 , driving basket  14  by way of an endless drive belt  16  typically wrapping about the circumference of basket  14 . Attached to the out-put shaft  18  of motor  12 , for driving belt  16 , is clutch driven pulley assembly  20 .  
         [0022]    Referring now to FIGS. 3 and 4, pulley assembly  20  comprises a central hub  25  adapted to be mounted upon motor output shaft  18 . Central hub  25  includes rotor  34  and cylindrical, or tubular, portion  32 , receiving therein motor output shaft  18 . Provided within rotor  34  is internally threaded bore  36  receiving therein set screw  38  for rigidly attaching central hub  25  to motor output shaft  18  as illustrated in FIG. 3.  
         [0023]    Although a set screw  38  as illustrated in FIGS. 3 and 4 as a preferred method for attaching central hub  25  to motor output shaft  18 , any other means may be used such as a “woodruff key,” a splined motor output shaft with matching internal spline receiving grooves within the cylindrical portion of central hub  25 , a diametrically orientated roll-pin extending through central hub  25  and the motor drive shaft  18  or any other suitable means for affixing a rotating element upon a rotatable drive shaft. However, if a “woodruff key” or the splined shaft coupling arrangement were to be used, additional means would necessarily have to be added to prevent axial movement of central hub  25  upon motor output shaft  18  such as a threaded retaining nut threaded upon the distal end of motor output shaft  18  similar to that shown in the alternate embodiment illustrated in FIG. 5.  
         [0024]    Although rotor  34  is illustrated as being integral with cylindrical portion  32 , rotor  34  may also be attached to cylindrical portion  32  by any other suitable means such as a “woodruff key” a splined coupling or any other suitable means for attaching rotating elements one to the other whereby they rotate as a single integral unit with motor output shaft  18 . Further, although rotor  34  is illustrated as being at a distal end of tubular portion  32 , rotor  34  may be positioned at any convenient axial location on tubular portion  32 .  
         [0025]    A rotatable V-groove pulley  40  is coaxially positioned upon the cylindrical portion  32  of central hub  25  as illustrated in FIG. 3.  
         [0026]    Preferably an “OILITE” (OILITE is a registered trademark of Beemer Precision, Inc. of Fort Washington Pa.) oil impregnated bronze bearing  41 , or equal, is positioned between the outer periphery of cylindrical portion  32  and the inside diameter of pulley  40  so that pulley  40  may rotate about cylindrical portion  32 . A first friction disc  42  is coaxially positioned between rotor pressure plate  28  of rotor  34  and the first frictional face plate  46  of pulley  40 . A second friction disc  44  is coaxially positioned between the second frictional face plate  48  of pulley  40  and coaxial pressure plate disc  52 . Spaced axially apart from pressure plate disc  52 , as illustrated in FIG. 3, is retaining disc  54 . Pressure plate  52  is keyed to central hub  25  such that plate  52  and disc  54  rotate with central hub  25 . Although pressure plate  52  is illustrated as being keyed to  
         [0027]    As self locking nut  86  is threaded onto cylindrical portion  32  belleville spring  84  is proportionately compressed thereby applying an axial force against pressure plate disc  52  whereby pulley  40  is frictionally held between friction discs  42  and  44  such that as central hub  25  rotates with and upon motor output shaft  18 , pulley  40  also rotates therewith, thereby rotating basket  14  which in turn rotates drain cleaning cable  22 .  
         [0028]    Similar to the embodiment shown in FIGS. 3 and 4, pulley  40 , will begin to slip when a threshold or limiting torque is experienced by cable  22 .  
         [0029]    Although FIGS. 3 and 4 teach use of a spring clip  56  and groove  33  to retain coil spring  58  between plates  52  and  54 , it is also possible to use a self locking nut in their place as illustrated in the alternative embodiment illustrated in FIG. 5.  
         [0030]    Use of a self locking nut, as illustrated in FIG. 5 in place of a groove  33  and spring clip  56 , illustrated in FIGS. 3 and 4, permits varying the axial force applied to pressure plate  52  whereby the slip threshold of pulley  40  may be varied by varying the axial load applied to compression spring  58  and/or belleville spring  82 . Whereas, by use of a coil spring  58  and a retaining spring clip  56  in groove  33  only one limiting resistive torque may be accommodated.  
         [0031]    While I have described above the principles of my invention in connection with specific preferred embodiments, it is to be clearly understood that this description is made only by way of example and not as a limitation of the scope of my invention as set forth in the accompanying claims.