Patent Publication Number: US-2010119295-A1

Title: Snap-Lock Engagement Pulley

Description:
TECHNICAL FIELD 
     The invention relates to a pulley for rotatable engagement with an object. 
     BACKGROUND OF THE INVENTION 
     A pulley is a type of wheel configured for changing direction of an applied force, transmitting rotational motion, or realizing a mechanical advantage. A pulley typically conveys force and motion transmitted to it via a drive element, such as a belt. 
     In order to change direction of an applied force or to realize a mechanical advantage, pulleys are often anchored in place, i.e. attached to objects such as mounting brackets or structural panels. Such attachment is typically accomplished via conventional assembly techniques, which generally include use of common fasteners, such as screws or rivets. 
     Often, however, pulley attachment via common fasteners requires use of a lubricating agent and/or a bearing to reduce the pulley&#39;s operating friction and to extend its service life. Consequently, use of such fasteners may add time to the assembly process, as well as to the cost and weight of the finished product. 
     SUMMARY OF THE INVENTION 
     A wheel having an axis of rotation and a flexible projection portion is provided. The flexible projection portion is configured for rotatable snap-lock engagement with an object that includes an aperture of a specified diameter. 
     The wheel may also have a first side face orthogonal to the axis of rotation, a second side face parallel to the first side face, and an annular portion arranged between the first face and the second face. Additionally, the flexible projection portion may include multiple flexible projections arranged concentrically on the first side face on a pitch diameter relative to the axis of rotation. 
     The wheel may further include engagement portions arranged on the flexible projections orthogonal to the axis of rotation. Such engagement portions would have an outer diameter that is greater than the pitch diameter and would be arranged to spring back for snap-lock engagement when pushed through the aperture, wherein the aperture&#39;s diameter is smaller than the outer diameter of the engagement portions. The engagement portions may further include lead-in chamfers for reducing a force required to push the engagement portions through the aperture. 
     The wheel may be configured as a unitary structure formed from plastic. The wheel may also be configured to operate as a pulley by including a groove on the annular portion&#39;s perimeter for receiving a drive element. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional fragmentary side view of a pulley snap-lock engaged with an object; 
         FIG. 2  is a schematic cross-sectional fragmentary side view of the pulley shown in  FIG. 1  in the process of being engaged with the object; 
         FIG. 3  is a schematic side view of the pulley shown in  FIGS. 1 and 2  snap-lock engaged with the object; 
         FIG. 4  is a schematic isometric perspective view of the pulley shown in  FIG. 3  snap-lock engaged with the object shown in a fragmentary view; 
         FIG. 5  is a flow chart illustrating a method of assembling a pulley with an object. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows a cross-sectional view of a pulley  10  snap-lock engaged with an object  12 , such as, for example, a window regulator mechanism for a vehicle. The pulley  10  is a type of a wheel configured for rotation around an axis A for changing direction of an applied force, transmitting rotational motion, or realizing a mechanical advantage. The object  12  has an aperture  14  with a diameter  16 . The object  12  has a flange thickness  18  at the aperture  14 . The object  12  may be a mounting bracket or a structural panel for supporting the pulley  10  during operation. 
     The pulley  10  has a first side face  20  which is configured orthogonally with respect to the axis A. The first side face  20  has a reaction surface  21 , similarly orthogonal to the axis A, and configured to contact the object  12  during the pulley&#39;s assembly and engagement with the object  12  The pulley  10  also has a second side face  22  which is configured parallel to the first side face  20 . An annular portion  24  bridges the first side face  20  and the second side face  22  on the pulley&#39;s perimeter. Annular portion  24  includes a groove  26  for receiving a drive element (not shown), such as a belt. 
     The pulley  10  includes flexible projections  28  arranged on the first side face  20  on a pitch diameter  30  concentrically with respect to the axis A. The flexible projections  28  include engagement portions  32 . Engagement portions  32  have an outer diameter  34  that is greater than the pitch diameter  30 . The flexible projections  28  have a length  33  between the reaction face  21  and the engagement portions  32 . Length  33  is configured to be greater than the flange thickness  18  of the object in order to facilitate rotational movement of the pulley  10  relative to the object  12 . The flexible projections  28  are arranged to function as a bearing surface, to thereby facilitate rotational engagement of the pulley  10  with the object  12  after the assembly is complete. 
     The engagement portions  32  include a lead-in chamfer  36 . The lead-in chamfer  36  is incorporated into the engagement portions for reducing insertion force F required to push the engagement portions  32  through the aperture  14  in the object  12 . The diameter  16  of the aperture is smaller than the outer diameter  34  of the engagement portions  32  in order to facilitate rotational movement of the pulley  10  relative to the object  12 . 
     As shown in  FIG. 2 , the engagement portions  32  flex toward the axis A during assembly of the pulley  10  into the object  12 . The engagement portions&#39; outer diameter  34  contracts to diameter  16  under the influence of the insertion force F, thereby permitting the engagement portions  32  to pass through the aperture  14 . Following the engagement portions  32  passing through the aperture  14 , the engagement portions spring back to their original shape, where their outer diameter  34  is restored. When the engagement portions  32  spring back to restore the outer diameter  34  behind the flange thickness  18 , the snap-lock engagement of the pulley  10  with the object  12  is complete (as shown in  FIG. 2 ). 
     The insertion force F may be provided by an assembly apparatus shown in part by an installation fixture  38 . The fixture  38  may be used to align the pulley, and be configured to apply the force F on the second side face  22  and/or on the groove  26  of the pulley  10 . A load cell (not shown) may be incorporated into the installation fixture to sense the insertion force F. Assembly of the pulley  10  into the object  12  is controlled by a controller  40  in electronic communication with the assembly apparatus, in response to the force F sensed by the load cell, as shown in  FIG. 2 . 
     The controller  40  is programmed with an algorithm to control the pulley  10  assembly based on a predicted fluctuation of insertion force F during assembly. In general, the force F can be expected to vary between an initial magnitude corresponding to the engagement of the engagement portions  32  with object  12  at aperture  14 , a force drop representing spring back of the flexible projections  28  during their snap-lock engagement with the object  12 , and a sharp increase representing contact between the reaction surface  21  and the object  12 . The expected force fluctuation may be established empirically during design and development of the pulley and its assembly operation. 
     The pulley  10  as described may comprise a unitary structure formed from an engineering plastic. Such construction may utilize any of the appropriate materials known by those skilled in the art, formulated to reduce the pulley&#39;s rotating friction at the reaction face  21  and at the flexible projections  28 . The utilization of such materials for construction of pulley  10  is therefore likely to enhance the pulley&#39;s performance and extend its service life. 
     A method of assembling a pulley with an object is shown in  FIG. 5  and is described below with respect to the pulley  10  of  FIGS. 1-4 . In block  100  the method includes aligning flexible projections  28  arranged on the pulley with the aperture  14  having a diameter that is smaller than the outer diameter of the engagement portions  32 . The pulley&#39;s flexible projections  28  are arranged on a pitch diameter  30  concentric with the pulley&#39;s axis of rotation A, and configured with engagement portions  32  having an outer diameter  34  that is greater than the pitch diameter  30 . In block  102  the engagement portions  32  are pushed into the aperture  14 , and snap-lock engagement of the flexible projections with the object is sensed in block  104 . 
     The sensing of the flexible projections&#39; spring back for snap-lock engagement may be accomplished via recognizing an increase in load representing engagement of the engagement portions  32  with the object  12 . Sensing also includes recognizing a load drop representing spring back of the flexible projections  28  signifying snap-lock engagement of the pulley with the object. Sensing may additionally include recognizing a load increase representing a hard stop, i.e. contact of the pulley&#39;s reaction surface  21  with the object  12 . The load increase representing a hard stop is more abrupt and greater than the load increase representing engagement of the engagement portions  32  with the object. Hence, pushing the engagement portions into the aperture may be performed until the hard stop is sensed. 
     According to the method, aligning, pushing and sensing may be performed automatically by the assembly apparatus, shown in part by the installation fixture  38  in  FIG. 2 . The assembly apparatus may also employ a load cell (not shown), and an electronic controller  40  programmed with an algorithm and in electronic communication with the load cell, as described above in connection with  FIG. 2 . The installation and alignment of the pulley may therefore be accomplished by the installation fixture  38 . The sensing may be performed by the load cell, which may be incorporated into the installation fixture  38 . The control of the assembly operation may be performed by the electronic controller  40  in response to the load sensed by the load cell. In the alternative, the aligning, pushing and sensing functions may be performed manually by an operator, i.e. a human being (not shown). 
     The snap-lock engagement pulley  10  provides a cost efficient, mass efficient, and assembly labor efficient pulley design, by reason of the pulley attachment being achieved without a separate fastener, such as a bolt, a screw, or a rivet. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.