Patent Publication Number: US-2015063999-A1

Title: Press fit keyed outer race in stator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/870,327, filed Aug. 27, 2013, which application is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of stator assemblies, particularly the operative connection between the stator body and outer race, and more particularly to the functional attachment of the stator and the outer race. 
     BACKGROUND OF THE INVENTION 
     Torque converters are used with automatic transmissions in motor vehicles to allow for transmission of torque from the engine to the transmission. Stator assemblies are used to direct fluid flow from the turbine to the pump in the torque converter to maintain rotation of the torque converter. Stator assemblies include a one-way clutch (clutch) that allows the stator to rotate with the pump and turbine at higher speed ratios and prevents stator rotation in the opposite direction at lower speed ratios including vehicle launch, for example. 
     The clutch includes an outer race that is functionally connected to the stator. By functionally attached is meant that a component or device is connected either directly or indirectly to a second component and causes that second component to function. For example, the outer race of the clutch contacts or is attached to the stator and allows the stator to rotate (freewheel) with the torque converter at high speed ratios and prevents stator rotation at lower speeds enabling the stator to redirect fluid flow to the torque converter pump. 
     Several difficulties must be overcome in the manufacture of a stator assembly. To reduce cost, stators are usually fabricated from softer metals, such as aluminum, while outer races are customarily constructed from harder materials, such as steel, to withstand the torque applied to the clutch. Because of the high fluid temperatures developed during operation of a torque converter, the stator and outer race will expand at different rates as each will have different coefficients of thermal expansion, with the aluminum of the stator expanding faster than the steel outer race. This can reduce the durability of the stator assembly as the functional attachment between the stator and outer race can be significantly altered. 
     Alternative designs use radial projections, or lugs, cast in the stator housing to drive slots in the outer race. In order to assemble the two components, some lash is present in the joint. Therefore, when the clutch locks, the rotating stator lug will collide against the stationary outer race slot. These collisions cause the harder outer race to eventually wear the softer stator lug. 
     Moreover, the design of stator assemblies usually necessitates the use of close tolerances between the stator and outer race to provide the most efficient operation. It is less expensive to machine smooth cylindrical surfaces on a lathe rather than mill surfaces with projections in the inner surface of the stator what would be used to form the functional attachment with the outer race. 
     U.S. Pat. No. 5,056,581 to Tarawa, et al., which patent is incorporated herein by reference in its entirety, discloses a method for forming a stator-outer ring (outer race) in which the outer race is forged to include projections distributed on the outer edge of the race. The stator is formed by molding or casting using the outer race as an insert. This method forms a close connection between the outer race and stator but requires expensive molding and forging processes. U.S. Pat. No. 8,197,202 to Olsen, et al., which patent is incorporated herein by reference in its entirety, discloses a stator housing with precast grooves to improve durability of a press-fit connection with the outer race, which has teeth or projections on the edge of the outer race that fit into the precast grooves. This connection can be altered by differences in thermal expansion. 
     Thus, it can be seen that there remains a need in the field to provide a stator assembly in which lash can be reduced or eliminated, the problems of different rates of thermal expansion can be overcome, and smooth surfaces can be used to manufacture the stator assembly. 
     SUMMARY OF THE INVENTION 
     The present invention broadly an outer race for a stator assembly comprising: a body; an outer circumferential edge; a plurality of keys extending radially outward from the outer circumferential edge, each of the plurality of keys having a thickness, a pair of opposing sides, and an outer key edge extending between each one of the pair of opposing sides; at least one spline projecting from at least one of the two opposing sides; and, an inner circumferential edge. In a preferred embodiment, a plurality of splines project transversely from both opposing sides of each key. 
     The present invention also broadly comprises a stator assembly comprising: a stator and an outer race. The stator includes: a stator body; an outer circumferential stator edge; an inner circumferential edge; an outer surface; and, an inner circumferential surface including a plurality of recesses; a plurality of blades distributed on the inner surface. The outer race, includes: a body; an outer circumferential edge; a plurality of keys extending radially outward from the outer circumferential edge, each of the plurality of keys having a thickness, a pair of opposing sides, and an outer edge extending between each one of the pair of sides; at least one spline projecting from at least one of the two opposing sides; and, an inner circumferential edge. Each of the at least one spline form grooves within respective stator recesses when the outer race is pressed into the stator body. 
     The invention also broadly comprises a method of fabricating a stator assembly wherein a stator includes: a stator body; an outer circumferential stator edge; an inner circumferential edge; an outer surface; and, a inner circumferential surface including a plurality of recesses; a plurality of blades distributed on the inner surface; and, wherein an outer race includes: a body; an outer circumferential edge; a plurality of keys extending radially outward from the outer circumferential edge, each of the plurality of keys having a thickness, a pair of opposing sides, and an outer edge extending between each one of the pair of sides; at least one spline projecting from at least one of the two opposing sides; and, an inner circumferential edge; 
     wherein each of the at least one spline forms grooves within respective stator recesses when the outer race is pressed into the stator body with the method comprises positioning each of the keys over the slots; and, pressing the keys into the stator slots in an axial direction. The plurality of splines form grooves within the stator slots when the outer race is pressed into the stator body. 
     One object of the invention is to supply a stator assembly that maintains efficient operation in a high heat environment. 
     A second object of the invention is to provide a stator-outer race connection in which lash is reduced or eliminated. 
     A third object of the invention is to present a stator assembly in which the parts are easily machined. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The nature and mode of the operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing Figures, in which: 
         FIG. 1  is a top view of the front side of the outer race of the present invention; 
         FIG. 2  is an enlarged top perspective view of one of the keys extending from the outer race of the present invention; 
         FIG. 3  is a top view of the stator assembled with outer race of the present invention; 
         FIG. 4  is a top view of the rear side of the stator assembly of the present invention; and, 
         FIG. 5  is an enlarged top view of one of the keys of the outer race pressed into the body of the stator in the stator assembly of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical structural elements of the invention. It also should be appreciated that figure proportions and angles are not always to scale in order to clearly portray the attributes of the present invention. 
     While the present invention is described with respect to what is presently considered to be the preferred embodiments, it is understood that the invention is not limited to the disclosed embodiments. The present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. It should be appreciated that the term “substantially” is synonymous with terms such as “nearly”, “very nearly”, “about”, “approximately”, “around”, “bordering on”, “close to”, “essentially”, “in the neighborhood of”, “in the vicinity of”, etc., and such terms may be used interchangeably as appearing in the specification and claims. It should be appreciated that the term “proximate” is synonymous with terms such as “nearby”, “close”, “adjacent”, “neighboring”, “immediate”, “adjoining”, etc., and such terms may be used interchangeably as appearing in the specification and claims. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described. 
       FIG. 1  is a top view of the outer race  100  of the present invention. Outer race  100  (“race  100 ”) includes body  112  and outer circumferential edge  114  (“edge  114 ”). Keys  116  project from edge  114 . In a preferred embodiment, keys  116  are integral with edge  114 . By integral is meant that the component parts are formed together as a single unit. Each of keys  116  possesses opposing sides  116   b  and a key edge  116   a  extending between opposing sides  116   b.  In addition, keys  116 , along with outer race  100  as a whole, have a depth or thickness extending from the rear surface seen in  FIG. 2  to an opposing front surface (not seen in  FIG. 1 ). 
     Outer race  100  also includes inner circumferential edge  118  (“edge  118 ”). In the embodiment shown, a plurality of interior struts  120  extend radially inward from edge  118 . In the same embodiment, inclined ramps  122  extend part of the distance between the individual struts  120  along inner circumferential edge  118 . Shoulder  124  indicates where the slope of ramp  122  ends. 
       FIG. 2  is a top perspective view of one of keys  116 . In the preferred embodiment shown, key  116  is shown as integral with outer edge  114  and body  112 . In other embodiments, keys  116  may be welded onto outer edge  114 . Splines  117  project transversely from opposing sides  116   b.  Splines  117  can be seen as extending the width or thickness  116   c  of key  116 . 
       FIG. 3  is a top view of stator  200 . Stator  200  includes outer stator edge  202  (“outer edge  202 ”) and inner stator edge  208  (“edge  208 ”). Between edges  202  and  208  are a plurality of stator blades  204  which extend radially inward from outer stator edge  202  to stator body  206 . Inner edge  208  is preferably smooth and incorporates a plurality of slots  210  that are integral with edge  208 . As explained below, keys  116  are pressed into slots  210  with splines  117  forming transverse grooves  217  into the sidewalls of slots  210 . 
       FIG. 4  is a top view of the rear side of stator assembly  400 . This view depicts the assembly of stator  200  with the one way clutch which includes outer race  100  and inner race  300 . 
     Stator  200  has a thickness extending between the front side (not seen in  FIG. 3  or  4 ) and the rear side. As a consequence, inner stator edge  208  includes an inner surface that extends between the front side and rear side of stator  200 . Preferably, this inner surface is smooth, meaning it does not include projections extending radially inward from the inner surface. This smooth inner surface provides the advantage of easier and less expensive machining of the inner surface to effect a functional connection with outer race  100 . 
     Struts  120  extend from inner circumferential edge  118  toward inner race  300 . Rollers  126  are positioned between ramp  122  and outer inner race edge  304 . Adjacent to each roller  126  is spring  128 . Rollers  126  contact and roll on outer inner race edge  304 . Inner race  300  includes inner race body  302 . Teeth  308  extend radially inward from inner circumferential edge  306  of inner race  300 . 
     In the freewheeling condition, outer race  100  and stator  200 , connected by splines  117 , rotate together in the direction of the arrow Put in arrow. Springs  128  push rollers  126  farther onto ramp  118  where there is a larger gap between inner edge  118  and outer edge  306  of inner race  300 . This allows outer race  100  and stator  200  to rotate freely. In the locked condition, stator  200  and outer race  100  rotate in the opposite direction forcing roller  126  to be wedged between inner edge  118  and outer edge  306  of inner race  300 . This prevents stator  200  from rotating enabling it to reverse the fluid flow exiting the turbine and entering the pump of the torque converter. 
       FIG. 5  is a top view of one of keys  116  pressed into body  206  of stator  200 . 
     Keys  116  will include at least one spline  117  projecting form at least one side  116   b.  Preferably, a plurality of splines  117  will project transversely from each opposing side  116   b  on all keys  116 . Inner stator edge  208  is located slightly radially outward from outer circumferential edge  114  of outer race  100 . Preferably, stator  200 , including the walls of slots  210 , is fabricated from a softer material than outer race  100 . For example, stator  200  may be fabricated from aluminum, while outer race  100  is fabricated from steel. Stator body  206  is seen surrounding grooves  217 . 
     Before the press fit takes place with outer race  100  and stator  200  axially aligned to be pressed into the assembly, splines  117  extend past the slot  210  sidewalls. During the press fit operation, the harder material of splines  117  cut out and fit into individual transverse grooves  217  from the inner walls of slots  210  resulting in individual splines  117  that are closely fit into grooves  217 . This close, transverse fit provides the advantage of preventing stator  200  from pulling away from outer race  100  when the temperature of the torque converter and fluid increases during long term operation of the vehicle. The close fit with in the transverse grooves acts to keep stator  200  and outer race  100  in the same relative positions even while stator  200  expands radially faster than outer race  100  when heated,. 
     A further advantage is provided by the close fit in that there is very little if any open space between splines  117  and the walls of grooves  217 . Therefore, when the torque converter launches (moves) a vehicle from a stopped position, the torque applied to the stator by the fluid returning from the turbine to the pump will create a rotational force in the clutch-locked direction on the stator  200  against outer race  100  preventing rotation of stator  200 . Any small spaces or gaps between stator  200  and outer race  100  will result in collisions that wear on the softer stator  200 . The close fit between splines  117  of outer race  100  and grooves  217  in stator  200  eliminates or greatly reduces gaps between the contact point between stator  200  and outer race  100  thereby eliminating or greatly reducing the wear on the stator caused by lash. 
     Thus it is seen that the objects of the invention are efficiently obtained, although changes and modifications to the invention should be readily apparent to those having ordinary skill in the art, which changes would not depart from the spirit and scope of the invention as claimed. 
     PARTS LIST 
       100  outer race 
       112  outer race body 
       114  outer circumferential edge 
       116  keys 
       116   a  outer key edge 
       116   b  opposing side of key 
       116   c  depth (thickness) of key 
       118  inner circumferential edge 
       120  strut 
       122  inclined ramp 
       124  shoulder 
       126  roller 
       128  spring 
       117  spline 
       200  stator 
       202  outer stator edge 
       204  stator blade 
       206  stator body 
       208  inner stator edge 
       210  stator slot 
       217  transverse grooves 
       300  inner race 
       302  inner race body 
       304  outer edge of inner race 
       306  inner edge of inner race 
       400  stator assembly