Abstract:
A bolted joint which is formed by using a bolt having a tapered shoulder to cold form a deformable sleeve in order to provide a “zero-clearance” fit. Specifically, preferably a plurality of bolted joints are used to join a ring gear to a differential case. As the bolts are installed into the differential case and ring gear, tapered shoulders on the bolts dilate deformable sleeves until outer diameters of the sleeves contact internal walls of through holes in the differential case.

Description:
RELATED APPLICATION (PRIORITY CLAIM) 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/708,265, filed Aug. 15, 2005, which is hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The present application generally relates to bolted joints, and more specifically relates to a zero-clearance bolted joint such as for use in joining a ring gear to a differential case. 
     One application in which bolted joints have been attempted to be used is in joining a ring gear to a differential case. However, generally the bolted joints are not capable of keeping the gear from moving in relation to the differential case. This is because the bolts are not capable of producing enough tension to keep the gear from slipping which in turn causes the bolts to back out of the joint. 
     One current method of joining a ring gear to a differential case utilizes matching circular patterns of a plurality of through holes on the differential case and a plurality of tapped holes on the ring gear. This design has raised concerns with the hole position tolerance capability of the manufacturing plants. As a result, the challenge is to develop a way of fastening the differential case to the ring gear that will be forgiving of alignment and minimize gear slippage while the ring gear is submitted to a substantial load for a number of cycles. 
     OBJECTS AND SUMMARY 
     An object of an embodiment of the present invention is to provide a zero-clearance bolted joint which can be used, for example, to join a ring gear to a differential case. 
     Another object of an embodiment of the present invention is to provide a zero-clearance bolted joint which can be used as a way of fastening a differential case to a ring gear that is forgiving of alignment and minimizes gear slippage while the ring gear is submitted to a substantial load for a number of cycles. 
     Briefly, and in accordance with at least one of the foregoing objects, an embodiment of the present invention provides a bolted joint which is formed by using a bolt having a tapered shoulder to cold form a deformable sleeve in order to provide a “zero-clearance” fit. Specifically, preferably a plurality of bolted joints are used to join a ring gear to a differential case. As the bolts are installed into the differential case and the ring gear, tapered shoulders on the bolts dilate deformable sleeves until the outer diameters of the sleeves contact internal walls of through holes in the differential case. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, wherein like reference numerals identify like elements in which: 
         FIG. 1  is a cross-sectional view of a bolted joint which is in accordance with an embodiment of the present invention, showing the condition prior to applying a shear load; 
         FIG. 2  is similar to  FIG. 1 , but shows the bolted joint after a shear load has been applied, showing maximum movement between the differential case and ring gear; 
         FIG. 3  shows the sleeve before installation of the bolt; 
         FIG. 4  shows the sleeve after installation of the bolt; 
         FIG. 5  provides a graph of the tensile load on the bolt vs. time, due to cold forming the sleeve during installation; 
         FIG. 6  provides a graph of the torque (in lb-ft) on the ring gear vs. angle of rotation (in degrees) between the ring gear and differential case; 
         FIG. 7  is a top view of the bolt; 
         FIG. 8  is a top view of the sleeve; 
         FIG. 9  is a side, cross-sectional view of the sleeve, taken along line  9 - 9  of  FIG. 8 ; 
         FIG. 10  shows a section of the differential case; 
         FIG. 11  is a cross-sectional view taken along line  11 - 11  of  FIG. 10 ; 
         FIG. 12  shows a section of the ring gear; 
         FIG. 13  is a cross-sectional view taken along line  13 - 13  of  FIG. 12 ; 
         FIG. 14  shows an alternative embodiment which includes a retention feature; 
         FIG. 15  shows a close up, detailed view of a circled portion of  FIG. 14 ; and 
         FIG. 16  shows a preferred bolt for use with the present invention. 
     
    
    
     DESCRIPTION 
     While the present invention may be susceptible to embodiment in different forms, there are shown in the drawings, and herein will be described in detail, embodiments thereof with the understanding that the present description is to be considered an exemplification of the principles of the invention and is not intended to limit the invention to that as illustrated and described herein. 
     The present invention is directed to a zero-clearance bolted joint which can be used, for example, as a way of fastening a differential case to a ring gear that is forgiving of alignment and minimizes gear slippage while the ring gear is submitted to a substantial load for a number of cycles. 
     As shown in  FIGS. 1 and 2 , the bolted joint consists of a bolt  20  having a head  22  which preferably has a hexagon profile  24  as shown in  FIG. 7 . Of course, the head  22  may have a profile other than hexagon. A threaded portion  26  is provided on a shaft portion  28  of the bolt  20 , proximate an opposite end  30  of the bolt  20 . An adhesive  32 , such as Precoat  80 , may be applied to a section  34  of the threaded portion  26  of the bolt  20 , such that the adhesive  32  as applied allows for a finger effort start for one revolution after first engagement with the ring gear, as will be described below. As shown in  FIGS. 1-4 , a tapered shoulder  44  is provided generally between the threaded portion  26  and the head  22  of the bolt  20 . With regard to material, the bolt  20  may be formed of, for example, ESS-M1A170-B Grade 8 or 8.2. As will be discussed more fully hereinbelow, the shoulder  44  may instead be provided as rounded (see  FIG. 16 ), and this is actually preferred for reasons discussed later hereinbelow. 
     In addition to the bolt  20 , the bolted joint also includes a sleeve  46  as shown in  FIGS. 1-4 ,  8  and  9 . As shown in  FIGS. 8 and 9 , the sleeve  46  is generally circular having a throughbore  48 . As such, the sleeve  46  has an inner diameter  50  and an outer diameter  52 . Preferably, the inner diameter  50  of the sleeve  46  is smaller than the width or diameter  36  of the shaft portion  28  of the bolt  20 , such that the tapered shoulder  44  of the bolt  20  deforms the sleeve  46  when the bolt  20  is installed, i.e., is threadably engaged with the ring gear  42 . Preferably, the outer diameter  52  of the sleeve  46  is smaller than a diameter  54  of a corresponding aperture or through hole  56  which is provided in a differential case  58 , such that the sleeve  46  can be inserted in the through hole  56  in the differential case  58 . Additionally, preferably a diameter  60  of the head portion  22  of the bolt  20  is larger than the diameter  54  of the through hole  56  in the differential case  58 . As such, when installed, the head  22  of the bolt  20  seats against the differential case  58 , as shown in  FIGS. 1 ,  2  and  4 . The sleeve  46  may be formed of, for example, AISI 1010 steel. 
     With regard to the differential case  58 ,  FIG. 10  shows a section of the differential case  58 , illustrating the aperture or through hole  56  provided therein.  FIG. 11  is a cross-sectional view taken along line  11 - 11  of  FIG. 10 . With regard to the ring gear  42 ,  FIG. 12  shows a section of the ring gear  42 , illustrating a tapped hole  40  provided therein.  FIG. 13  is a cross-sectional view taken along line  13 - 13  of  FIG. 12 . 
       FIG. 3  shows the condition of the sleeve  46  before the bolt  20  is installed. As shown, the shape of the sleeve  46  is consistent with that which is shown in  FIG. 9 . During installation of the bolt  20 , the head  22  of the bolt  20  is rotated causing the threaded portion  26  of the bolt  20  to thread into the tapped hole  40  which is provided in the ring gear  42 . As the threaded portion  26  threads into the hole  40 , the tapered shoulder  44  of the bolt  20  cold forms the sleeve  46 , as shown in  FIG. 4  (see also  FIGS. 1 and 2 ), thereby causing the outer surface  64  of the sleeve  46  to contactably engage an internal wall  62  of the differential case  58 , thereby providing a “zero-clearance” fit.  FIG. 5  provides a graph of the tensile load on the bolt vs. time, due to cold forming the sleeve during installation 
     To fully join the ring gear to the differential case, preferably a plurality of bolted joints are used.  FIG. 1  shows the bolted joint prior to applying a shear load, and  FIG. 2  shows the bolted joint after a shear load has been applied, showing maximum movement between the differential case  58  and ring gear  42 . As shown, while the differential case  58  moves sideways relative to the ring gear  42  and the bolt  20 , the bolt  20  and sleeve  46  resist the relative movement between the differential case  58  and the ring gear  42  which additionally reduces the tendency of the bolt  20  to back out of the joint, preferably even when the differential case  58  is submitted to a substantial load for a number of cycles.  FIG. 6  provides a graph of the torque (in lb-ft) on the ring gear vs. angle of rotation (in degrees) between the ring gear and differential case. 
       FIG. 14  shows a preferred embodiment of sleeve  46  (identified as  46   a  in  FIG. 14 ), wherein a retention feature is provided, specifically three depressions  66   a , equally spaced, on the external surface  64   a  of the sleeve  46   a , and an internal lip or protrusion  67   a . The retention feature provides that the bolt  20  and sleeve  46   a  can be supplied such that the sleeve  46   a  is retained on the bolt  20 , ready for installation in a differential case and ring gear, and this is preferred.  FIG. 15  shows a close up, detailed view of a circled portion of  FIG. 14 . 
       FIG. 16  shows a preferred bolt  20   a  for use with the present invention. The bolt  20   a  includes a radius or rounded portion  21   a . The purpose of the radius  21   a  is to provide a smoother transition when entering the sleeve  46 , and to decrease the load required to extrude the sleeve  46 . 
     While embodiments of the present invention are shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from the spirit and scope of the disclosure.