Abstract:
An idler pulley with an integral bearing carrier insert comprising: a pulley body having a peripheral surface for accepting and retaining an endless belt; and a tubular bearing carrier insert forming a central hub along a perpendicular axis of the idler pulley body, the hub having an inner circumferential surface and an outer circumferential surface.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of pulleys. In particular, the invention relates to plastic idler pulleys adapted with an integral bearing carrier insert, and to a method for manufacturing such plastic idler pulleys. 
     Plastic idler pulleys are known in the art as taught by U.S. Pat. Nos. 6,220,635; 6,200,513; 6,181,239; 6,120,401; 6,102,822; 6,090,001; 6,086,809; 6,032,635; 5,830,046; 5,782,709; 5,725,448; 5,724,930 and 5,176,580. Such plastic idler pulleys have heretofore been made by either molding-in a bearing, incorporated as an insert in the molding process, or by force fitting a bearing into a molded bore in the plastic part. For example, U.S. Pat. Nos. 4,468,210 and 4,473,363 describe examples of a plastic outer pulley body molded on a metal disc; and U.S. Pat. Nos. 4,913,688 and 5,476,423 describe examples of a two-step assembly wherein first a plastic outer pulley body is molded and then the metal insert is placed into the already molded pulley body. 
     Traditionally, when a pulley produced by the one-step process of compression molding the plastic pulley body about the metal insert, the insert is physically altered to include one or more projections such as radially extending scallops or knurls on the outer periphery of the insert. 
     Pulleys are also produced by the two-step process wherein a metal insert is attached to a molded plastic outer pulley by forcing the insert into the bore of the pulley. An adhesive, such as epoxy, is generally applied between the outer metal surface of the insert and the inner surface of the plastic pulley body to assist in bonding the insert to the pulley body. In each of the methods, the bearing retention is less than desirable since the clamping force which secures the bearing is dependent upon the modulus of the plastic material and upon the surface of the outer bearing race. Typically, the outer bearing is smooth and made from material having relatively little affinity for the plastic pulley. Furthermore, asymmetric forces which may occur during the molding process can distort the bearing to an out-of-round condition, thereby, shortening its useful life. For example, when an idler pulley is subjected to a heavy radial load from a belt, such as a timing belt, entrained therearound, the pulley and the bearing are slightly deformed and, since the deformation patterns of the plastic pulley and the insert are different, a slight clearance is defined between the inner surface of the pulley and the outer surface of the bearing. This clearance becomes wider as the radial force from the belt increases and over time, results in the wear of the fit surfaces of the pulley and the outer surface of the bearing, thus decreasing the joining force between the pulley and the bearing. The process of bonding with an adhesive presents undesirable clean-up and environmental problems. Accordingly, there is a need, particularly in the area of an endless drive belt of a vehicle accessories drive system, for a plastic pulley with a metal insert that may be easily manufactured without the problems associated with prior art pulleys. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided an idler pulley having a moldable pulley body with a rigid bearing carrier insert integrally formed in the pulley body for accepting a bearing member. The bearing member may be fitted into the rigid bearing carrier insert either before or after molding. 
     In one aspect of the invention, the bearing member is installed into the integrally formed moldable idler pulley body and rigid tubular bearing insert before molding. 
     In another aspect of the invention, the bearing member is fitted into the tubular bearing carrier insert of the molded idler pulley after the idler pulley is formed. 
     In yet another aspect of the invention, the metal bearing insert is fitted into the bore of the tubular shell and the tubular shell having the bearing insert fitted therein is inserted into the bore of the plastic pulley body. 
     The material selected for the construction of the tubular shell is a suitably strong and rigid material which is compatible with the plastic material of the pulley body and with the metal bearing insert. 
     The tubular shell may be adapted to provide a hoop/clamping force sufficient to afford superior bearing retention and to resist unbalanced forces during molding and maintain bearing concentricity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates one embodiment of the idler pulley with integral bearing carrier insert of the present invention; 
         FIG. 2  is a cross-section of the idler pulley of  FIG. 1  taken along lines  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a mold which may be used to make an idler pulley having an integral barrier carrier insert; 
         FIG. 4  is a cross-section taken along lines  4 - 4  of  FIG. 3 ; and 
         FIG. 5  is a cross-sectional view of the mold of  FIG. 3  after a plastic material has been inserted into the mold cavity to make the idler pulley of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings,  FIGS. 1 and 2  illustrate an idler pulley  10  comprising a molded plastic body  12  having an integral tubular bearing carrier insert  14  centrally positioned in the pulley body  12 . The tubular bearing carrier insert  14  is incorporated between the plastic body of the pulley and an outer bearing race  15  of bearing  16 . The bearing  16  may be fitted into the insert either before or after molding. 
     The idler pulley  10  of the invention may be from a wide variety of polymeric materials, provided that they are distortion resistant at ambient and higher temperatures. It also is generally desirable, particularly for automotive applications, that the polymeric materials used to make the pulley  10  have a low-temperature resiliency. Suitable polymeric materials include thermoplastic and thermosetting materials, such as polyamides. e.g., polyphthalamtides, nylons, particularly nylon-6, nylon-6,6, nylon-4,6; nylon 6,10; nylon 9; nylon 11 and nylon-12; polyesters, epoxy resins; phenolic resins; polyurethanes; high density polyolefins, e.g., polyethylene; and the like. The polymeric material used to manufacture the body  12  of the pulley  10  may be compounded with additional fillers, modifiers or reinforcing agents as determined for a particular application. In a preferred aspect of the invention the polymeric material contains a reinforcing material, such as a fibrous glass reinforcing material. Useful modifiers include lubricants such as polytetrafluoroethylene, silicone, graghite, molybdenum disulfide, ultra high molecular weight polyethylene. Other suitable modifiers include thermoplastic materials, rubber, etc. Fillers may be glass beads, carbon black, minerals such as calcium carbonate, wollastonite, mica, clay, talc etc. The reinforcing agent may be glass fibers, long glass fibers, aramid, carbon fibers, etc. 
     The outer peripheral surface of the pulley  10  comprises a plurality of protrusions  20  and recesses  22 . The protrusions may be in the form of V-shaped projections and recesses, truncated V-shaped projections and recesses, and any other useful design. In a preferred aspect of the invention, the peripheral surface of the pulley  10  comprises a metal or ceramic liner  18  to provide enhanced abrasion resistance. The liner  18  may be of any suitable material which has the desired resistance to abrasion, and is sufficiently deformable so that it can be used in the practice of the invention. Steel or aluminum having a thickness in the approximate range of about 0.010-0.050 inch is preferred. 
     The tubular insert  14  may be manufactured from steel, aluminum, zinc, brass, or any other suitably rigid and strong material. The insert  14  may also be coated or plated to enhance adhesion to the particular polymeric material selected for the body  12  of the idler pulley  10 . For example, a brass or zinc plating over a steel tubular insert shell increases the chemical affinity of the insert for a thermoplastic phenolic material, especially if the phenolic material also incorporates any of several classes of adhesion-enhancing ingredients such as sulfur, silica, acrylates, vinyl acetates, low molecular weight polyamides, etc. The outer surface of the tubular insert  14  may contain interlocking means  13  such as knurls, splines, indents, holes, and the like to provide an irregular outer surface of said tubular insert  14  for the purpose of enhancing the mechanical interlock of the insert  14  with the plastic body  12 . The inner surface of the tubular insert  14  may be provided with means  24 , such as a stepped profile or detents, to accurately locate and align the bearing  16  during assembly, or the surface of the insert during molding. 
     Referring now to  FIGS. 3-5 , the idler pulley  10  is formed using a three-section mold (or a two-section mold for flat pulleys), designated generally by the reference numeral  26 . The first, or base section  28  has a cylindrical center portion  30  having an outside diameter approximately equal to the inside diameter of the tubular insert  14 . The second section  32  has at least two segmented sections  34  so that the completed pulley can be easily removed. The segments  34 , when in the molding position, form an annular opening. The inner periphery of the segments  34  has a plurality of projections  36  and recesses  38  corresponding to the shape of the recesses  22  and projections  20 , respectively of the peripheral surface of the pulley  10 . The third section  40  has a central opening  42  which has an inside diameter approximately equal to the outside diameter of the tubular insert  14 . The third section  40  also has at least one injection port  44  through which the plastic material is injected into the mold  26 . The mold sections may be clamped together by any suitable clamping means, such as bolts  45 , as illustrated. 
     To make the pulley  10 , the second section  32  is assembled on the first section  28  and the tubular insert  14  is inserted over the cylindrical center portion  30  of the first portion  28  and the third section  40  is assembled on the top of the second section  32  and the mold  26  is clamped together by the clamping means. 
     The pulley  10  is made by injecting a suitable polymeric material through the injection port(s)  44  under sufficient pressure, e.g., about 500-30,000 psi, to fill the cavity and, if present, to deform the metal liner  18 , causing it to conform to the projections  36  and recesses  38  in the segments  34 . 
     Various changes and modifications may be made to the idler pulley having an integral bearing carrier insert of the present invention, and to the method of manufacturing such idler pulley in light of the above disclosure without departing from the scope and spirit of the appended claims.