Patent Publication Number: US-2017356541-A1

Title: Fastener-Free Idler Pulley

Description:
FIELD OF INVENTION 
     The present disclosure relates to an idler pulley mounting system and a method of manufacture and assembly. 
     BACKGROUND 
     Many systems having belt-driven components include an idler pulley in the system. One example of a pulley system  10  for an internal combustion engine is shown in  FIG. 1 . A crankshaft pulley  12  coupled to the crankshaft of the engine (not shown) is the driver that provides the torque for the driven-components: air conditioner (A/C), water pump and fan, power steering pump (P/S), and an alternator, which are coupled to pulleys  24 ,  28 ,  20 , and  26 , respectively. In the example in  FIG. 1 , two idler pulleys  30  and  32  are included. A serpentine belt  40  rides on the periphery if all of the pulleys. Idler pulleys serve the function of causing belt  40  to wrap around a sufficient portion of the periphery of a driving or driven pulley so that there is enough friction to prevent belt slippage. Such an example is shown in  FIG. 1  with idler pulley  30 . If belt  40  is made shorter and idler pulley  30  is not included, belt  40  would stretch straight across between A/C pulley  24  and P/S pulley  20  making the circumferential contact between belt  40  and pulleys  24  and  20  less. Another reason for an idler pulley is to reduce the distance between adjacent pulleys to minimize belt flapping. Two examples of long uninterrupted belt runs, if idler pulleys  30  and  32  were removed, would be between crank pulley  12  and P/S pulley  20  and between P/S pulley  20  and A/C pulley  24 . 
     In  FIG. 1 , two idler pulleys are shown. If the locations of the various pulleys in an engine package could be optimized for the front end accessory drive system, idler pulleys could in some situations be obviated. However, packaging is accomplished to satisfy many goals. Thus, idler pulleys are added as needed. In some applications, there are multiple belts for an internal combustion engine and many idler pulleys. 
     One example of an idler pulley-shaft assembly in an exploded view is shown in  FIG. 2 . Pulley  52  is coupled to a bearing  58 . Pulley  52  and bearing  58  are slip fit over a shaft  60  that extends from an engine cover  62 . A bolt  54  is slid through a washer  56  and bearing  58 . Threads of bolt  54  are engaged with threads  64  of shaft  60 . Bolt  54  is tightened to secure idler pulley  52  against engine cover  62 . Bolt  54  and washer  56  keep pulley  52  from coming off shaft  60  as well keeping the inner portion of bearing  58  from rotating. The outer portion of bearing  58  and pulley  52  rotate. Bearing  58  can be a ball bearing, a roller bearing, or any suitable bearing type. In some alternatives, washer  56  is integrated with bolt  54 . Particularly in engines with multiple idler pulleys, it is desirable to obviate the bolt and washer (or bolt with integrated washer) and mount the idler pulley without fasteners. 
     SUMMARY 
     To obviate the bolt and washer used in the prior art, an idler pulley system is disclosed that includes: a shaft having a circumferential groove, a bearing having an inner race, the inner race having a circumferential ridge with the ridge engaged with the groove of the shaft, and an idler pulley mounted on the bearing. 
     The idler pulley system, in some embodiments, an axial slot is formed in the inner race of the bearing, an axial slot is formed on the shaft with the axial slot on the shaft aligned with the axial slot on the inner race, and a key is inserted into the aligned axial slots. In another embodiment, stakes formed by a chisel are formed in the shaft proximate an interface of the shaft and the inner race. 
     The idler pulley is press fit onto an outer race of the bearing forming an interference fit. 
     The bearing is pressed onto the shaft to cause the ridge of the inner race to seat into the groove of the shaft and the resulting clearances between the inner race and the ridge provides a slip fit. 
     The bearing is either a ball bearing with the balls disposed between the inner race and an outer race of the bearing or a needle bearing with needles disposed between the inner race and the outer race. 
     Also disclosed is idler pulley system having a shaft with a circumferential ridge, a bearing having an inner race and an outer race, and a circumferential groove on the inner race. The ridge is engaged with the groove. 
     In some embodiments, an axial slot is formed in the inner race of the bearing, an axial slot is formed on the shaft, and the axial slot on the shaft is aligned with the axial slot on the inner race. A key is inserted into the aligned axial slots. In other embodiments, stakes are formed by a chisel, the stakes being proximate an interface of the shaft and the inner race. 
     The idler pulley is press fit onto an outer race of the bearing forming an interference fit. 
     Also disclosed is a method to fabricate and install an idler pulley system that includes: fabricating a roller bearing having an inner race having a first circumferential feature, fabricating a second circumferential feature on a shaft, press fitting a pulley onto an outer race of the roller bearing, and pressing the bearing/pulley assembly over the shaft with the first and second circumferential features engaging. 
     In some embodiments, the first circumferential feature is a ridge and the second circumferential feature is a groove. In other embodiments, the first circumferential feature is a groove and the second circumferential feature is a ridge. 
     The roller bearing is one of a ball bearing and a needle bearing. 
     In some embodiments, the method also includes: forming an axial keyway in the shaft, forming an axial keyway in the inner race of the bearing, aligning the keyways, and inserting a key into the keyways. In other embodiments, the shaft is staked to the inner race of the bearing. 
     One advantage according to the present disclosure is that part count and cost is reduced. The assembly operation of threading the bolt into the shaft is now obviated. Instead the idler pulley is snapped onto the shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a front-end accessory drive according to the prior art; 
         FIG. 2  is an illustration of a idler pulley in an exploded view according to the prior art; 
         FIGS. 3 and 4  are representations each showing a bearing and a shaft according to embodiments of the disclosure; 
         FIGS. 5 and 6  are cross sections of the bearings and shafts of  FIGS. 3 and 4 , respectively; 
         FIGS. 7 and 8  are end view each showing an idler pulley assembly according to embodiments of the disclosure; and 
         FIG. 9  is a flow chart to manufacture and assemble an idler pulley assembly showing embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
     A bearing  300  has an outer race  302  and an inner race  304  with a plurality of balls  306  contained between races  302  and  304 . An idler pulley (not shown) is press fit (interference fit) or molded onto outer race  302 . In the embodiment shown in  FIG. 3 , inner race  304  has a circumferential ridge  310  that extends into toward the center. A shaft  312  that is coupled to an engine cover  316 , a portion of which is shown in  FIG. 3 , has a circumferential groove  314  formed therein. A central axis of bearing  300  and shaft  312  is axis  318 . When aligned, the two are coupled by moving bearing  300  in the direction of arrows  320  to slip fit bearing  300  over shaft  312 . Inner race  304  forms a slip fit with shaft  312 . Groove  314  of shaft  312  engages with ridge  310  of bearing  300 . Bearing  300  is pressed onto shaft  312  for groove  314  to engage with ridge  310 . Otherwise, inner race  302  and shaft  312  are dimensioned to provide a slip fit. 
     An alternative configuration in  FIG. 4  shows a bearing  400  with an inner race  404  that has a circumferential groove  410 . Balls  406  are contained between inner race  404  and outer race  402 . A shaft  412  coupled to an engine cover  416  has a circumferential ridge  414  that engages with groove  410  when bearing  400  is slid over shaft  412  along central axis  418  in the direction of arrows  420 . 
     A portion of the bearing and shaft shown in  FIG. 3  are shown in  FIG. 5  in cross section. Ridge  310  of bearing  300  engages with groove  314  of shaft  312 . In  FIG. 6 , bearing  400  has groove  410  that engages with ridge  414  of shaft  412 . 
     The groove and ridge on the inner race of the bearing and the shaft keep the idler pulley from coming off the shaft in the axial direction. Additionally, the inner race of the bearing should not rotate with respect to the shaft. To prevent that, in one embodiment, a key is provided in  FIG. 7 , which shows one embodiment of an idler pulley system  500 . An idler pulley  512  is mounted onto an outer race  502  of a bearing. The bearing also includes an inner race  504  and balls or needles  506  between races  502  and  504 . Both inner race  504  and a shaft  510 , onto which inner race  504  is mounted, are provided with an axial groove, a keyway. A key  520  is inserted into the aligned keyways in inner race  504  and shaft  510 . 
     An alternative embodiment for preventing relative rotation of the shaft and the inner race is shown in  FIG. 8 , which shows an idler pulley system  550 . An idler pulley  562  is mounted on an outer race  554  of a bearing. Balls or needles  556  are contained between outer race  552  and an inner race  554 . Idler pulley  562  and the bearing are slid over a shaft  560 . A chisel or staking punch is used to deform the metal in a few places around the periphery of shaft  560  to form an interference fit in those locations. In 
       FIG. 6 , three such stakes  570  are shown. As races  552  and  554  of the bearing are hardened by heat treating, staking is applied to shaft  560  to deform material to engage with race  552 . 
     Referring to  FIG. 9 , a number of alternative embodiments for manufacturing and assembling the idler pulley assembly. In box  700 , the idler pulley is fabricated; in block  702 , a bearing is fabricated. The inner race has a circumferential ridge. The bearing may be a ball bearing, a needle bearing, or any suitable alternative. In block  704 , a circumferential groove is machined into a shaft. In embodiments including a keyway: an axial keyway is machined into the inner race of the bearing in block  710  and an axial keyway is machined into the shaft in block  712 . In block  720 , the pulley is press fit onto the outer race of the bearing. In an alternative embodiment not shown in  FIG. 9 , the pulley is molded onto the outer race of the bearing. In block  730 , the pulley/bearing assembly is pressed over the shaft causing the ridge to engage with the groove. In alternatives with the key pressed into keyway, the keyways on the bearing and the shaft are aligned and then a key is inserted into the aligned keyways in block  740 . Alternatively, in systems using staking, a chisel is used to deform material proximate the interface of the shaft and the inner race of the bearing, in block  750 , to thereby prevent relative rotation of those two components. 
     In  FIG. 9 , the inner race of the bearing has a ridge that engages with the groove of the shaft. In an alternative, the bearing has a groove and the shaft has a ridge. 
     A front-end accessory drive for an internal-combustion engine is described as one system to which the present disclosure applies. The present disclosure applies to any system including belt-driven accessories in which an idler pulley is included. 
     While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, efficiency, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.