Abstract:
A pair of tapered roller bearings, which are located between two machine components, such as a pinion shaft and its carrier, to enable the one component to rotate relative to the other one, is set to a desired dimensional preload with the aid of a gauge and the force preload in the bearing is determined to verify that it is within acceptable limits. The gauge is interposed between a raceway and rolling elements of the second bearing to measure the size of a spacer required to give the two bearings the correct dimensional preload. The gauge also exerts a known axial force on the bearings, and while that force is maintained, the torque required by the bearings is measured. That torque divided by the axial load gives a torque signature. Thereafter, the gauge is removed, the spacer is selected and installed, and the bearings are installed in their operative positions. The spacer sets the bearings with a desired dimensional preload. Then, with the desired dimensional preload in the bearings, the torque required by the bearings is measured. The force preload in the bearings is calculated by dividing the measured torque at the desired dimensional preload by the torque signature.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     This invention relates in general to opposed antifricton bearings and more particularly to a process for setting such bearings in preload and for verifying the force preload. 
     One can find rotating shafts in a wide variety of machinery, and when such shafts carry heavy loads or must rotate with a good measure of precision, they are often supported on antifricton bearings. Usually the antifriction bearings arranged in a pair, with the bearings of the pair being adjusted against each other to a desired setting. Typical of the bearings are single row tapered roller bearings. When positioned with the large ends of the tapered rollers in the two bearings presented away from each other (indirect mounting) or the large ends of the rollers presented toward each other (direct mounting), displacement of one race of one of the bearing axially will change the setting for the two bearings. 
     Where the axis of rotation must remain perfectly stable, such as in the pinion assemblies for automotive differentials or in machine tool spindles, the bearings that support the rotating components should operate in a condition of preload, which is characterized by an absence of clearances, both axial and radial, in the bearings. Typically, preload, like end play where clearances exist, is considered in the context of an axial dimension (e.g. 0.002 in. preload), but the real and more meaningful measure of preload is in the context of the internal forces captured by the opposed bearings. In this regard, several pairs of bearings identical in size and configuration, all set to the same dimensional preload could well lock in different internal forces, that is to say, different force preloads. Pinion assemblies for automotive differentials illustrate the problems and uncertainties one encounters in connection with setting the bearings. The typical pinion assembly has a carrier, a pinion shaft provided with a pinion at its one end, and a pair of tapered roller bearings which support the shaft in the carrier. When the carrier is attached to the main housing of a differential, the pinion meshes with a ring gear, and to insure that the mesh is proper, the bearings must be set to preload. 
     Typically, the procedure for adjusting the bearings in a pinion assembly involves fitting the shaft to the carrier with one of the tapered rollers of the bearing seated along the raceways for that bearing. Thereupon, measurements are taken from the other bearing to determine the size of a spacer, which, when installed, will impart the proper preload to the two bearings. The assembly procedure is then completed using the spacer. Thereafter, the torque required to rotate the shaft is measured to see if it falls within acceptable limits. But torque does not provide a very good measure of preload, because in identical pinion assemblies set to the same force preload, torque can vary as much as ±20%. In view of this variance, some pinion assemblies which exhibit torque outside the accepted range may actually have an acceptable force preload. This can lead to expensive disassembly and reassembly. Then again, some that exhibit a torque within the acceptable range may actually have an unacceptable force preload. And too much force preload can lead to early failure of the bearings. On the other hand, too little force preload may permit excursions into end play owing to differential thermal expansions between the carrier and shaft during operation. End play detracts for the stability of the pinion shaft and may allow the pinion to assume positions which lead to wear and create annoying noise. 
     SUMMARY OF THE INVENTION 
     The present invention resides in a process for setting opposed antifriction bearings with a desired dimensional preload and verifying that the force preload is acceptable. To this end, machine components are assembled with one of the bearings in place between them. The other bearing has a gauge interposed in it and the gauge provides measurement for determining the size of a spacer which will give the bearings a desired dimensional preload. The gauge also exerts a known axial force on the bearings, and while that force is exerted the torque required by the bearings is measured. This provides a torque signature. When the other bearing is assembled without the gauge and with the spacer installed to provide the desired dimensional preload, the torque is again measured, and from this new torque and the torque signature, one can determine the load, that is the force preload, in the bearings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a pinion assembly, the bearings of which have been set and verified in accordance with the present invention; 
     FIG. 2 is an exploded sectional view of the pinion assembly with the gauge interposed between components of one of the bearings of the assembly; 
     FIG. 3 is a perspective view, partially broken away and in section, of the pinion assembly, with the gauge fitted to one of its bearings; and 
     FIG. 4 is an enlarged sectional view of the gauge and the bearing to which it is fitted. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The process for setting bearings in preload and verifying that preload in terms of force finds utility in connection with a wide variety of machinery employing shafts mounted on opposed tapered roller bearings. Actually, its utility extends to opposed bearings that enable a machine component to rotate relative to another machine component with a good measure of stability, and this requires that the bearings be in preload. Typical of such an arrangement is a pinion assembly A which is bolted to the housing of an automotive differential to engage and rotate the ring gear in the differential. 
     The pinion assembly A includes (FIG. 1) a carrier  2 , a pinion shaft  4  that extends through the carrier  2 , head and tail bearings  6  and  8 , respectively, which support the pinion shaft  4  in the carrier  2 , a yoke  10  fitted to the tail end of the pinion shaft  4 , and a nut  12  threaded over the end of the pinion shaft  4  to retain the yoke  10  firmly on the shaft  4 . The bearings  6  and  8  enable the shaft  4  to rotate about an axis X and are set to a condition of preload, so that the axis X remains perfectly stable with respect to the carrier  2 . To this end, the bearings  6  and  8  are mounted in opposition in the indirect configuration, with the preload setting being controlled by a sleeve  14  and a spacer  16  that are located around the shaft  4 , with the spacer  16  being against a reference surface  18  on the end of the sleeve  14 . 
     The carrier  2  is actually a subhousing which is bolted to the main housing of the differential. It has two bearing seats  20  and  22 , the former for the head bearing  6  and the latter for the tail bearing  8 . 
     The shaft  4  extends through the carrier  2  where the bearing seats  20  and  22  of the carrier  2  surround it. The shaft  4  projects out of the head end of the carrier  2 , and here it is provided with a pinion  30 . The back of the pinion  30  forms a shoulder  32  at the head end of the shaft  4 , with the shoulder  32  being squared off with respect to the axis X. The shaft  4  also projects out of the tail end of the carrier  2 , and here it is provided with a spline  34  and beyond the spline  34  with a reduced end  36  which is threaded. 
     Each bearing  6  and  8  includes (FIGS. 1 &amp; 2) an inner race in Fe form of a cone  40 , and outer race in the form of a cup  42 , rolling elements in the form of tapered rollers  44 , and a cage  46 . The rollers  44  lie in a single row between the cone  40  and the cup  44 , while the cage  46  maintains the correct spacing between the rollers  44  and further holds the rollers  44  around the cone  40  when the cone  40  is removed from the cup  42 , so that the cone  40 , rollers  44 , and cage  46  form a cone assembly. 
     The cone  40  has a tapered raceway  50 , which is presented outwardly away from the axis X, and a thrust rib  52  at the large end of the raceway  50 . On the end of the thrust rib  52  the cone  40  has a back face  54 , and at its opposite end, beyond the small end of the raceway  50 , the cone  40  has a front face  56 . Both the back face  54  and front face  56  are squared off with respect to the axis X. 
     The cup  42  has a tapered raceway  58 , which is presented inwardly toward the axis X, and a back face  60  at the small end of the raceway  58 . The back face  60  is also squared off with respect to the axis X. 
     The tapered rollers  44  fit between the cone  40  and cup  42  with their tapered side faces against the raceways  50  and  58  and their large end faces against the thrust rib  52 . Indeed, the thrust rib  52  prevents the rollers  44  from moving up the raceways  50  and  58  and out of the space bet n the cone  40  and cup  42 . The rollers  44  are on apex, meaning that the conical envelopes formed by their tapered side faces have their apices at a common point along the axes X. The conical envelopes formed by the raceways  50  and  58  have their apices at the same point 
     The cones  40  of the two bearings  6  and  8  fit over the pinion shaft  4 , each with an interference fit. The back face  54  for the cone  40  of the head bearing  6  bears against the shoulder  32  on the pinion  30 , whereas the back face  54  for the cone  40  of the tail bearing  8  bears against the yoke  10  which is held firmly against it by the nut  12 . The sleeve  14  and spacer  16  also fit around the shaft  4  when they lie between the two cones  40 . Indeed, the sleeve  14  and spacer  16  are damped snugly between the front faces  56  on the two cones  40 . The cup  42  for the head bearing  6  fits into the bearing seat  20  in the carrier  2 , whereas the cup  42  for the tail bearing  8  fits into the other bearing seat  22 , there being interference fits between the cups  42  and their respective bearing seats  20  and  22 . Moreover, the back faces  60  of the two cups  42  bear firmly against the ends of their respective bearing seats  20  and  22 . The rollers  44  for the two bearings  6  and  8  lie between the raceways  50  and  58  on the cones  40  and cups  42  of those bearings  6  and B. Here their tapered side faces contact the raceways  50  and  58 , whereas their large end faces bear against the thrust ribs  52 . Since the bearings  6  and  8  are in preload, no clearances exists between any of the rollers  44  and the raceways  50  and  58  between which they are located. 
     The thickness of the spacer  16  controls the magnitude of the preload in the bearings  6  and  8 , and to determine the thickness required to provide the proper preload, one must know the distance that the front face  56  for the cone  40  of the tail bearing  6  will locate from the reference surface  18  at the end of the sleeve  14  when the bearings  6  and  8  are in a condition of zero end play, that is to say, when there is neither end play nor preload in the bearings  6  and  8 . This distance cannot be measured when the cone  40  of the tail bearing  8  is around the shaft  4  in its operating position, since its front face  56  is too obscured for such a measurement. Instead a gauge B (FIGS.  2 - 4 ), which in effect projects the raceway  58  of the cup  42  for the tail bearing  8  and the reference surface  18  of the sleeve  14  out of the carrier  2 , is utilized. 
     The gauge B is employed with the pinion assembly A partially assembled, that is to say, assembled to the extent that the pinion shaft  4  extends through the carrier  2  with is head bearing  6  in place and the rollers  44  of that bearing seated against the raceways  50  and  58  of it cone  40  and cup  42  (FIG.  3 ). The partial assembly further includes installation of the cup  42  for the tail bearing  8  in its seat  22  in the carrier  2  and placement of the sleeve  14  over the pinion shaft  4  and against the front face  56  for the cone  40  of the head bearing  6 . 
     The gauge B basically includes (FIG. 4) a male element  66  and a female element  68  which are located essentially end to end and in addition an intervening element  70  which extends between the male and female elements  66  and  68 . The gauge B also has a spring  72  which urges the male and female elements  66  and  68  apart. 
     Both the male element  66  and the female element  68  fit over the intervening element  70  where they are capable of shifting axially with respect to it and to each other. The male element  66  has a tapered surface  76  which is presented outwardly away from the axes X. The taper of the surface  76  conforms to the taper of the raceway  58  on the cup  42  of the tail bearing  8  and is further of a diameter small enough to enable the male element  66  to fit into the cup  42  of the bearing  8 . When so fitted, the tapered surface  76  seats perfectly against the raceway  58 , which provides one of two conical envelopes employed by the gauge B. Essentially the female member  68  lies axially beyond the male member  66 . It has a tapered surface  78  which is presented inwardly toward the axis X. Its taper and size conform to the other conical envelope employed by the gauge B, that is the envelope formed by the outwardly presented faces of the rollers  44  for the tail bearing  8 . After all, when the tail bearing  8  is assembled in its operating condition, the tapered rollers  44  that surround its cone  40  seat against the tapered race raceway  58  of its cup  42 —or in other words the two conical envelopes are then coincident. The intervening element  70  fits within the male and female elements  66  and  68  such that the two elements  66  and  68  can slide over it. Thus, the male and female elements  66  and  68  may each assume infinite positions with respect to the intervening element  70  and with respect to each other as well. The intervening element  70  has an inner end  80  which is configured to seat against the reference surface  18  on the sleeve  14  and an outer end  82  which is configured to fit against the front face  56  of the cone  40  for the tail bearing  8 . The two ends  80  and  82  lie a fixed and known distance a apart 
     The spring  72  fits around the intervening element  70  and between the male and female elements  66  and  68  and urges them apart. It may take the form of a Belleville spring or even a coil spring. Irrespective of its configuration, it carries a strain sensor  84  which senses the strain in the spring  72  and produces a signal that reflects that strain. The signal is monitored by instruments which basically convert the strain into the distance between the male and female elements  66  and  68 , and further into the force exerted by the spring  72  on the two elements  66  and  68 . 
     The male element  66  and the female element  68  possess equivalent diameters d along their respective tapered surfaces  76  and  78  (FIGS.  2  &amp;  4 ). The equivalent diameters d are separated by an axial distance b, and that distance varies, although slightly, between different pairs of bearings  6  and  8 . 
     In order to ascertain the axial dimension c (FIG. 1) for the spacer  16  required to provide the bearings  6  and  8  with the proper dimensional preload p, the gauge B installed over the tail end of the partially assembled pinion assembly A (FIGS.  3  &amp;  4 ). In particular, the gauge B is lowered over the pinion shaft  4  at the tail end of the assembly A far enough to enable the tapered surface  76  on its male element  66  to seat against the tapered raceway  58  for the tail cup  42  and also far enough to enable the inner end  80  of the intervening element  70  to seat against the reference surface  18  on the sleeve  14 . The male element  66  and intervening element  70  thus assume fixed positions with respect to the head bearing  6 . Thereupon, the cone assembly for the tail bearing  8 , that is its cone  40  together with its tapered rollers  44  and cage  46 , is inserted into the female element  68 . The rollers  44  seat against the raceway  50  of the cone  40  and also against the tapered surface  78  of the female element  68 . While the front face  56  of the cone  40  is presented opposite the outer end  82  of the intervening element  70 , it remains separated from the outer end  82  at this juncture. The cone  40  of the tail bearing  6  thus becomes a positional race, the axial position of which along the shaft  4  determines the setting for the bearings  6  and  8 . 
     The reduced end  36  of the pinion shaft  4  projects out of the gauge B, and an assembly yoke  90  is fitted over it, so that the yoke  90  bears against the back face  54  of the tail cone  40 . Finally, the threads on the reduced end  36  of the shaft  4  are engaged with an assembly nut  92  which is turned down against the yoke  90 . Indeed, the nut  92  forces the female element  68  downwardly against the bias of the spring  72  until the front face  56  of the cone  40  (FIG. 3) comes against the outer end  82  of the intervening element  70  of the gauge B. In other words, the assembly nut  92  is tightened far enough to clamp the cone  40  of the head bearing  6 , the sleeve  14 , the intervening element  70  of the gauge B, and the cone  40  of the tail bearing  8  all tightly together between the pinion  30  and the assembly yoke  90 . The spring  72  compresses, and the sensor  84  applied to it produces a signal reflecting the distance the female element  68  moves toward the male element  66 . This determines the distance b between the like diameters d on the male and female elements  66  and  68 . 
     When the instrument registers the measured distance b, the pinion shaft  4  should rotate relative to the carrier  2 . This insures that the rollers  44  of the head bearing  6  seat property against the raceways  56  and  58  and thrust rib  52  of that bearing, and that the rollers  44  of the tail bearing  8  seat properly against the raceway  50  and the thrust rib  52  of the tail cone  40  and also against the tapered surface  78  of the female element  68  on the gauge B. The rotation is imparted to the pinion shaft  4  at the assembly yoke  90  which is temporarily on it. Not only does the instrument that is attached to the sensor  84  register the distance b between the diameters d on the tapered surfaces  76  and  78  of the male and female elements  66  and  68 , respectively, but it also determines the force exerted by the spring  72 . The torque required to maintain the rotation is also measured. The force represents a temporary or assembly load in the bearings  6  and  8  with the gauge B interposed between the cup  42  and the cone assembly of the tail bearing  8 . 
     From the distance b measured by the gauge B and the fixed distance a that the intervening element  70  spaces the tail cone  40  from the reference surface  18  on the sleeve  14 , one can calculate the axial dimension c for the spacer  16  which will provide the desired dimensional preload p to the two bearings  6  and  8 . In particular: 
     
       
         
           c=a−b+p−i 
         
       
     
     The formula takes into account the change i in the axial dimension owning to the interference fit of the cone  40  for the tail bearing  8 . 
     From the force f registered by the instrument to which the sensor  84  is connected and the torque t applied to the assembly yoke  90 , one can obtain a torque signature s for the two bearings  6  and  8 . In particular: 
     
       
         
           s=t/f 
         
       
     
     Once the torque signature s is known, one can calculate the force preload in the bearing simply by measuring the torque required to rotate its pinion shaft  4 , that is to say: 
     
       
         
           f=t/s 
         
       
     
     And indeed, once the pinion assembly A is fully assembled (FIG. 1) with the rollers  44  of its tail bearing  8  seated against not only the raceway  50  of its cone  40 , but also against the raceway  58  of its cup  42 , and further with spacer  16  and the the operating yoke  10  and nut  12  in place, the force preload in the bearings  6  and  8  is measured to insure that it falls within acceptable limits. In this regard, the spring  72  of the gauge B applies some preload to the bearings  6  and  8 , with that preload insofar as the tail bearing  8  is concerned being transferred between the cone  40  and cup  42  through the gauge B and rollers  44  instead of directly through the rollers  44 . The preload imparted by the gauge B produces a torque signature s for the two bearings  6  and  8 . That signature then becomes the basis for ascertaining the force preload in the fully assembled pinion assembly A and verifying that it falls within acceptable limits. In particular, the torque signature s remains the same for the bearings  6  and  8  irrespective of preload. The torque t varies with preload. Thus, using the torque signature and the torque t measured for the assemble pinion assembly A, one determines the force preload using the formula: 
       f=t/s   
     The procedure for setting bearings and verifying force preload may be used for bearings mounted in the direct configuration as well, that is to say, with bearings having the large ends of the rollers in the two rows presented toward each other. Moreover, for some measurements it may be desirable to have the tapered surfaces  76  and  78  on a single gauge element where they are a fixed distance apart and the ends  80  and  82  on end-to-end elements with the spring  72  between those elements, so that the distance between the ends  80  and  82  becomes the measured distance. Basically, the procedure, irrespective of the location of the tapered surfaces  76  and  78  and the ends  80  and  82 , uses the difference between a measured distance and a fixed distance to determine the size of a spacer which will provide opposed bearings with the proper setting.