Abstract:
An engine accessory belt drive includes a self-aligning pulley assembly including a relatively stationary outer assembly and a universally pivotable inner assembly supported by the outer assembly and able to be locked in position by tightening of a fastener. During alignment of the self-aligning pulley with the belt, the fastener is maintained in the loose position, allowing limited universal pivoting of the rotational axis of the pulley as a result of belt tension forces which act to align the pulley. After the pulley is aligned, the fastener is tightened to fix the rotational axis of the pulley and the inner assembly in the aligned position of the pulley. Features of the inner and outer assemblies of the pulley assembly are also described.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a self-aligning pulley and an engine accessory belt drive incorporating such a pulley.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is known in the art to use pulleys and belts to drive automotive engine accessories such as alternators, air conditioning compressors, power steering pumps, and the like. Proper alignment of these pulleys and belts is necessary for the quiet operation of the belt drive. Typically, in volume production, the accessories are all mounted on brackets that have tolerances which can cause misalignment. Short belt spans are more critical than long spans because the belts lack flexibility over short spans to compensate for any misalignment of the pulleys.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention provides a self-aligning pulley assembly for use in a tensioned belt drive, wherein the pulley may need alignment.  
           [0004]    The present invention also provides an engine accessory belt drive which has a self aligning pulley assembly to correct pulley to belt misalignment in the belt drive.  
           [0005]    In a preferred embodiment, a self-aligning pulley assembly according to the invention includes a relatively stationary outer assembly and a universally pivotable inner assembly supported by the outer assembly.  
           [0006]    The inner assembly includes a pulley for engaging a belt, a bearing rotatably supporting the pulley on a rotational axis, and support members having convex part-spherical outer surfaces, and inner portions engaging and supporting the bearing.  
           [0007]    The outer assembly includes a relatively stationary support, guide members carried by the support and having recessed surfaces engagable with the spherical outer surfaces of the support members, an axle defining a relatively fixed support axis and extending through the guide members and the inner assembly, and a fastener associated with the axle and adjustable between loose and tight positions for, respectively, movably or fixedly holding the recessed surfaces of the guide members against the spherical surfaces of the support members;  
           [0008]    During self-alignment of the pulley with a belt, the fastener is maintained in the loose position, allowing limited universal pivoting of the rotational axis of the pulley to self-align the pulley with the direction of motion and tilt of the belt surface. After the pulley is aligned, the fastener is tightened (moved to the tight position) to fix the rotational axis of the pulley and the inner assembly in the aligned position of the pulley.  
           [0009]    These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a front end view of a portion if an engine accessory belt drive including a self-aligning pulley assembly according to the invention.  
         [0011]    [0011]FIG. 2 is a fragmentary isometric view of the drive showing the pulley assembly in cross section prior to alignment.  
         [0012]    [0012]FIG. 3 is a view similar to FIG. 2 but showing the pulley assembly after alignment and tightening of the fastener.  
         [0013]    [0013]FIG. 4 is an exploded view of the pulley assembly shown in an aligned position.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]    Referring first to FIG. 1 of the drawings in detail, numeral  10  generally indicates a front view of a portion of an engine accessory belt drive according to the invention. Drive  10  includes a crank pulley  12  that acts as a main drive pulley for the accessory drive  10 . In a first belt run  14 , a conventional multigroove first drive belt  16  extends around the crank pulley  12 , a power steering pulley  18 , a first idler pulley  20 , an AC (air conditioning) compressor pulley  22 , and a first tensioner pulley  24 , back to the crank pulley  12 .  
         [0015]    In a second belt run  26 , a second drive belt  28  extends around a second track of the crank pulley  12  to an alternator pulley, not shown, and back around a water pump pulley  30  to the crank pulley  12 . In a third belt run  32 , a third drive belt  34  extends around the power steering pulley  18 , an idler pulley  36 , an additional accessory pulley, not shown, and back around a second tensioner pulley  38  to the power steering pulley  18 . The second and third belt runs are illustrated here to show the complex nature of an accessory drive for a modern engine, which requires driving of multiple accessories from the engine crankshaft crank pulley  12 .  
         [0016]    Referring back to the first belt run  14 , it is noted that belt spans between pulleys are relatively long, except for spans designated  40  and  42  which extend between the first tensioner pulley  24  and the AC and crank pulleys  22 ,  12 , which are quite short due to the arrangement of the accessories to be driven by the belt. The short spans  40 ,  42  have limited flexibility to adjust for misalignment of the tensioner pulley with direction of belt motion and, thus, create the possibility of noise created at the interface of the belt with the tensioner pulley if the pulley is misaligned.  
         [0017]    In addition, the first tensioner pulley  24  is rotatably mounted on a tensioner lever  44  which has a pivot axis  45 . When a tensioner load  46  is applied upon a first end  47  of the tensioner lever  44 , the resulting moment about the pivot axis  45  results in application of a belt tensioning force  48  against the first drive belt  16 . As the belt  16  expands or stretches in service, the lever  44  will pivot to take up the slack and may increase the angular engagement of the tensioner pulley  24  with the belt  16 , increasing the potential for noise from misalignment of the belt and pulley.  
         [0018]    To avoid the problems which may result from misalignment of the first tensioner pulley  24  and the drive belt  16 , the pulley  24  is made part of a self-aligning pulley assembly  50 , a preferred embodiment being shown in FIGS.  2 - 4 . In assembly  50 , the tensioner pulley  24  is rotatably supported, for engagement with belt  16 , by a bearing  52 , preferably of the low friction roller or ball type. Other bearing types suitable for a particular application could be utilized, if desired.  
         [0019]    Bearing  52  supports the pulley  24  for rotation on a rotational axis  54 . The bearing is, in turn, supported by a pair of support members  56 . Each support member  56  has a convex part-spherical outer surface  58  and an inner portion  60  engaging and supporting one side of bearing  52 . Thus, bearing  52  is supported on both sides by the inner portions  60  of the support members  56 . The pulley  24 , bearing  52  mounted on rotational axis  54 , and the pair of support members  56 , together constitute a universally pivotable inner assembly  62 .  
         [0020]    The pair of support members  56  engage a pair of guide members  64  wherein each guide member  64  has a recessed inner surface  66  engaging the convex part-spherical outer surface  58  of one of the support members  56 . The recessed surfaces  66  may be concave part-spherical surfaces, but could have other configurations, such as conical.  
         [0021]    An axle  68  defines a support axis  70 , which is fixed in relation to the pivotable inner assembly  62  and the rotational axis  54  of the pulley. Axle  68  forms part of a fastener  72  formed as a bolt having a head  73  at one end and an opposite threaded end  74 .  
         [0022]    A spacer  75  is disposed between an outer face  76  of one of the guide members  64  and the head  73  of the fastener bolt  72 . The spacer  75  is received in an opening  77  in an arm  78  of two bifurcated arms  78 ,  80  that form a support at the pulley end of the tensioner lever  44 . The other bifurcated arm  80  includes a threaded opening  82  into which the threaded end  74  of the fastener bolt  72  is received. The support  78 ,  80 , the spacer  75 , the guide members  64  and the fastener bolt  72  define a relatively stationary outer assembly  84  fixed in the pulley end of the tensioner lever  44 .  
         [0023]    In assembly of the self-aligning pulley assembly  50  to the tensioner lever  44 , the pivotable inner assembly  62  is first formed. This includes fixing the outer race of bearing  52  within the first idler pulley  24  and inserting the support members  56  against the bearing inner race. The support members  56  engage and support the bearing inner race both radially and axially by cylindrical and radial surfaces  86 ,  88 , respectively, of the support members.  
         [0024]    The guide members  64 , which form part of the relatively stationary outer assembly, are then placed with their recessed inner surfaces  66  (preferably part spherical) engaging the part spherical convex outer surfaces  58  of the support members  56 . The spacer  75  is inserted into the opening  77  in the bifurcated arm  78  of the tensioner lever  44 , and the inner assembly  62 , together with guide members  64 , is slid into position between the bifurcated arms  78 ,  80  with flat outer faces  76  of the guide members respectively engaging an inner face of the bifurcated arm  80  and an inner face of the spacer  75 .  
         [0025]    The fastener bolt  72  is then inserted through axially-aligned openings, including an opening  90  in the spacer  75 , support openings  92  in the guide members  64 , clearance openings  94  in the support members  56  and a central opening  96  in the inner race of bearing  52 , and the bolt is threaded into the threaded opening  82  of bifurcated arm  80 . At this point, the bolt may be loosely applied so that the inner assembly  62  remains free to pivot in any direction, within limits of the clearance openings  94  in the support members. Thus, the rotational axis  54  of the tensioner pulley  24  may be positioned to be coaxial with or canted at a limited angle with respect to the support axis  70  of the axle  68  formed by the fastener bolt  72 .  
         [0026]    During assembly of the accessory belt drive  10 , the tensioner lever  44  is mounted on its pivot axis  45  and a tensioner loading device, such as a spring or piston not shown, is connected to the first end  47  of the lever  44  for urging the lever  44  clockwise, as seen in FIG. 1, toward the belt tensioning position. The lever is initially retracted with the pulley  24  backed away from its operative position so that the first drive belt  16  may be installed around the other pulleys  12 ,  18 ,  20  and  22 . The pulley fastener bolt  72  is loosened or remains loose at this time so that the pulley  24  and inner assembly  62  with the rotational axis  54  are free for self-alignment.  
         [0027]    When the belt  16  is in place, the tensioner lever  44  is released and the pulley  24  is urged against the smooth back side of the multi-grooved drive belt  16 . The reaction forces of the belt on the tensioner pulley then act to pivot the pulley  24 , the inner assembly  62  and the rotational axis  54  into an aligned position of the pulley  24  with the belt  16 , thus self-aligning the pulley. Should the tensioner pulley  24  not become fully aligned by a single release of the tensioner lever  44 , the lever may be retracted and released a few times to urge the pulley  24  into better alignment. Also, cranking of the engine to move the belt around the pulleys may also be helpful in obtaining better alignment, if needed.  
         [0028]    When the tensioner pulley  24  is properly aligned, the fastener bolt  72  is then tightened, causing frictional engagement of the convex surfaces  58  of the support members  56  with the recessed or concave surfaces  66  of the guide members  64  to lock the inner assembly  62  in place in the outer assembly  84 . The tensioner pulley  24  is thereby fixed in the aligned position against the drive belt  16  so that the operation of the accessory drive  10  may be operated with minimal belt/pulley misalignment.  
         [0029]    The structure and method of assembly of the engine accessory drive of the invention thus combine to provide alignment of a tensioner or idler pulley in an accessory belt drive without requiring severe tolerance requirements in the design and manufacture of the mounting components for the particular pulley application involved. The invention is particularly effective in the exemplary application described wherein mounting of the pulley on the end of a pivoting tensioner arm would require close tolerances of the assembled components in order to maintain the degree of alignment of the belt and pulley that is desirable for quiet operation of the accessory drive. This is particularly important in view of the short belt runs indicated in FIG. 1 of the drawings, which make the problems of misalignment more severe than is the case for longer belt runs where flexibility of the belt may be sufficient to accommodate greater degrees of misalignment.  
         [0030]    While the axle  68  of the exemplary embodiment described is formed as a fastener bolt  72  supported at both ends, the invention could also be applied to an axle supported at one end as a cantilever beam wherein the fastener could be a nut threaded on the end of the axle.  
         [0031]    The use of the term relatively stationary is intended to convey that the outer assembly of the pulley assembly is stationary relative to the inner assembly, which is pivotable. When the outer assembly is mounted on the end of a tensioner lever, the outer and inner assemblies are, of course, movable with the lever, but the outer assembly remains relatively stationary as compared to the pivotable inner assembly.  
         [0032]    While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.