Abstract:
A high performance sprag clutch assembly and replacement system for a land motor vehicle transmission, which utilizes a commercially available sprag assembly popular among high performance enthusiasts in combination with newly manufactured inner and outer races to achieve the maximum rated torque capacity is disclosed. The outer race and stator end cap components have been designed to reduce the overall axial length to adapt the sprag clutch assembly to the limited axial space within the stator component of the torque converter of various transmissions. The interlocking stator caps function to reduce race eccentricity under load to ensure that each individual sprag element carries the torque equally to prevent the sprag elements from being rolled over in operation causing severe damage. A plurality of interchangeable inner races adapt the present sprag clutch system for use with GENERAL MOTORS, FORD, and CHRYSLER transmission input shaft configurations.

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. 60/365,911 filed Mar. 21, 2002, entitled Improved Sprag Clutch Assembly. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to the field of one-way clutches for use in land motor vehicles and, more particularly, to a high performance sprag clutch assembly for use in the torque converter stator of an automatic transmission. 
   The original concept of the sprag clutch was developed in the late 1940s. Since that time sprag clutches have been used as driving members in many automatic transmissions worldwide. Sprag clutches are a specific class of one-way clutches. The unique feature of one-way clutches is that they can maintain high torque capacity in one direction and no torque capacity in the other direction. 
   The geometric design characterizing sprag clutch operation basically involves unidirectional wedging of the surfaces of multiple-cam structures denoted as dogleg sprags or sprag elements between two races, which enclose the sprags. The primary role of the sprag clutch in the present application is to allow the stator component within a torque converter in an automatic transmission to be driven by the torque converter in only one direction. This occurs at high load conditions during which the sprag elements are wedged in the drive mode to prevent relative motion between the inner and outer races. In this mode and during the transition to engagement, the wedged sprags transmit torque from the outer race to the inner race of the clutch. 
   Reliable sprag clutch operation requires a number of contributing design factors. (1) The clutch design must force all of the sprags to work together in phase throughout their operating range (so-called “phasing”) such that the sprags equally share the load within small tolerance variations. (2) All sprags should be individually energized, axially aligned, and as free as possible of parasitic friction that subtracts from the normal energizing forces. (3) Adequate race proportions, concentricity, material, heat treatment, and surface finish are essential. Thus, the clutch is no better than the races used in its fabrication. (4) The clutch must be adequately lubricated. Lubrication requirements will vary significantly depending on application details. 
   The typical problem in sprag clutch design is to achieve the greatest possible torque capacity in a minimum of space. Maximum and minimum sprag lengths are usually governed by practical considerations. For example, the maximum length is limited by the ability to heat-treat without distortion; and the minimum length is governed by the division of the axial space available between sprag and the energizing means (i.e. cages). 
   There are several known prior art patents that are available in the field and their discussion follows. One example of a prior art one-way clutch is disclosed in U.S. Pat. No. 5,779,014 to Kinoshita et al., which teaches a one-way clutch mounting structure including an outer ring, an inner ring and a plurality of clutch members interposed between the inner and outer rings. In this one-way clutch the outer ring is mounted in a housing, which is part of a stator. The housing has an annular section and a side section, which together define a pocket wherein the outer ring is mounted. The outer ring includes a spiral engaging means providing an integrated structure between the stator housing and the outer ring. 
   Another example of a prior art one-way clutch for a torque converter is disclosed in U.S. Pat. No. 5,760,514 to Taniguchi et al., which provides a one-way clutch for a plastic stator capable of preventing the inner circumferential surface of the outer ring of the one-way clutch from being deformed during shrinkage of the plastic stator in the manufacturing process. Thus, the outer ring integrally formed with the plastic stator is not required to be further machined after the integration, which reduces production costs. 
   U.S. Pat. No. 6,481,549 to Kroll et al. discloses an overrunning clutch for a torque converter wherein the stator consists of glass reinforced plastic which is injected around the overrunning clutch outer ring so that machining of the outer ring is no longer necessary after integration in the stator. 
   U.S. Pat. No. 5,881,556 to Matsuoka discloses a stator for a torque converter with thrust supporting structures without using a thrust bearing on at least one axial end thereby facilitating reduction of the axial dimensions thereof. 
   While these devices fulfill their respective, particular objectives and requirements, the aforementioned patents do not disclose the high performance sprag clutch assembly of the present invention, which substantially departs from the conventional concepts and designs of the prior art. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is a high performance sprag clutch assembly, which utilizes a standard, commercially available sprag assembly in combination with the newly manufactured inner and outer races of the present invention to achieve the maximum rated torque capacity and to minimize manufacturing costs. The present outer race and stator cap components have been designed to reduce the overall axial length of the sprag clutch assembly in order to adapt a BORG WARNER (Part No. 27306 AM) sprag assembly, which is popular among racing enthusiasts, to the limited axial space within the stator component of the torque converter. Interlocking stator caps function to reduce eccentric loading of the races in operation to ensure that each individual sprag element carries the torque equally and to prevent the sprag elements from being rolled over in operation. A plurality of interchangeable inner races having different internal spline configurations adapt the present sprag clutch assembly for use with various transmission shafts including twenty-seven-tooth spline shafts, thirty-two-tooth stator support shafts, and various other shaft spline configurations utilized in GENERAL MOTORS, FORD, and CHRYSLER transmissions. 
   There has thus been outlined, rather broadly, the important features of the present invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. 
   Other features and technical advantages of the present invention will become apparent from a study of the following description and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features of the present invention are set forth in the appended claims. The invention itself, however, as well as other features and advantages thereof will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures, wherein: 
       FIG. 1  is a composite view illustrating the components of a typical sprag clutch labeled Prior Art; 
       FIG. 2  is a composite diagram illustrating the sprag clutch in the drive mode (clutch engaged) and the freewheeling mode (clutch disengaged); 
       FIGS. 3A–3C  show partial sections of the sprag clutch illustrating the phasing of the sprags throughout the entire operating range; 
       FIG. 4  is an elevational view of the improved sprag clutch assembly of the present invention; 
       FIG. 5A  is an elevational view of the inner race of the present sprag clutch; 
       FIG. 5B  is a cross-sectional view of the inner race taken along the section line  5 B— 5 B of  FIG. 5A ; 
       FIG. 6A  is an elevational view of the outer race of the present sprag clutch; 
       FIG. 6B  is a cross-sectional view of the outer race taken through the section line  6 B— 6 B of  FIG. 6A ; 
       FIG. 7A  is an exploded cross-sectional view of the present sprag clutch showing the details of the stator cap components; and 
       FIG. 7B  is a cross-sectional view showing the components of the present sprag clutch in an assembled condition. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Prior to describing the present invention in detail it may be beneficial to briefly review the structure and function of a typical sprag clutch in an automatic transmission. With reference to the drawings there is shown therein a sprag clutch in accordance with the prior art, indicated generally at  100  and illustrated in  FIG. 1 . 
   The primary components of the sprag clutch  100  consist of the sprag assembly, indicated generally at  110 , an inner race  112 , an outer race  115 , two end bearings  116 , and two retaining rings  118  (only one shown). The sprag assembly  110  typically consists of a plurality of sprag elements or sprags  105  held in place by two concentric cages  107 ,  108  positioned between the inner and outer races  112 ,  115  as most clearly shown in  FIG. 2 . A stamped, spring-steel ribbon  109  located between the cages  107 ,  108  pre-loads the sprags  105  evenly to distribute the load during engagement. This is accomplished by spring tabs (not shown) that are formed on the spring ribbon  109  each of which is in contact with a sprag  105 . The end bearings  116  and the retaining rings  118  align the sprag assembly  110  axially between the inner and outer races  112 ,  115 . 
   In most sprag clutch applications the inner race  112  overruns the outer race  115  in the same direction at about twice the outer race speed. Since no load is applied to the sprag assembly  100  in this state, this condition is regarded as freewheeling ( FIG. 2  at the right). The ribbon  109  keeps each element in constant contact with the inner race  112  so that engagement and torque transfer, when required, can be both rapid and coincident for all the sprag elements  105 . This occurs when the sprag elements  105  are wedged (i.e. locked) in the drive mode to prevent relative motion between the inner and outer races  112 ,  115  as shown ( FIG. 2  at the left). In this mode and during the transition to engagement, the wedged sprag elements  105  transmit torque directly from the outer race  17  to the inner race  15 . 
   Phasing of the sprag elements  105  is achieved by the use of the two cages  107 ,  108  that are held concentric by their respective races  112 ,  115 . The outer cage  108  controls the sprags  105  near their outer race contact and the inner cage  107  controls the sprags  105  near the inner race contact. By accurately sizing and spacing the cage openings wherein they are disposed, the sprags  105  can be contoured and fitted so they move in unison throughout their entire operating range.  FIGS. 3A–3C  show the relationship of sprags  105  and cages  107 ,  108  during the driven mode ( FIG. 3A ), transition mode ( FIG. 3B ), and freewheeling mode ( FIG. 3C ). 
   Thus, it will be appreciated that multiple forces act upon the sprag elements  105 . In the drive mode the inner race  112  experiences the wedging force transmitted by the sprag assembly  105  from the outer race  115 . In the freewheeling mode the centrifugal force acting on the sprag assembly  100  during high differential speeds tends to load the sprag elements  105  against the inner race  112 , which contributes largely to the total drag force. An additional secondary force is produced by the spring tabs (not shown) acting on the sprag elements  105 , which generates frictional drag on the inner race  112 . 
   An assumption made by most manufacturers is that the clutch races  1112 ,  115  are precisely concentric when the sprag elements  105  first engage and begin to transmit torque. Unfortunately, this condition is not easily achieved in actual practice. Depending on the clutch, sprag element angle, and spring design, the races  112 ,  115  are forced into an eccentric condition and a substantial percentage of the sprag elements  105  never carry any of the torque. The few remaining load-bearing sprag elements  105  in such condition can be overloaded and rolled over causing clutch failure. The effect of the eccentric push on bearings associated with the races  112 ,  115  is sometimes damaging to the bearings. 
   One reason for the eccentric loading is that the loaded sprags  105  in the larger radial sprag space between the races have a greater cam rise per degree of rotation than the loaded sprags  105  in the smaller radial sprag space caused by the eccentricity. Thus, as the torque is increased the races  112 ,  115  are held eccentric or are forced into a position of greater eccentricity depending on the extent of the original offset. 
   The present invention has been developed to minimize these problems and will now be described in detail. With reference to  FIG. 4  there is shown therein an improved sprag clutch in accordance with the present invention, indicated generally at  10 . The sprag clutch  10  is comprised of an inner race  15 , an outer race  17 , a sprag assembly  110  and a pair of opposed stator caps  25  ( FIG. 7A ). A sprag assembly  110  manufactured under the tradename BORG WARNER (Part No. 27306 AM) or another similar sprag assembly is desirable for this purpose. 
   The primary role of the present sprag clutch assembly  10  is to allow the rotating, shaft-mounted stator wherein it is installed to be driven in only one direction. In the present application the inner race  15  is always stationary. The sprag clutch  10  engages (i.e. locks up) when the torque converter is loaded. When the load decreases and parasitic drag on the stator increases, the stator, which is connected to the outer race  17  freewheels. 
   In a typical embodiment the inner race  15  is a cylindrical construction including an internal spline  12  formed in the inside diameter as shown in  FIGS. 5A and 5B . In the embodiment shown the internal spline  12  consists of twenty-seven teeth  14  for mating engagement with a 27 tooth spline pattern on the transmission input shaft  16  (shaft is shown withdrawn for clarification). In accordance with the present invention the inner race  15  is provided in other spline configurations so as to be interchangeable for different applications. For example, the inner race  15  is provided in alternative embodiments (not shown) adaptable to a 32 tooth stator support shafts utilized in FORD transmissions and various other spline patterns. 
   Referring to  FIGS. 6A and 6B  the details of the present outer race  17  are illustrated. The outer race  17  includes a plurality of slots  18  formed on the circumference, which engage mating key structures (not shown) formed on the inside diameter (I.D.) of the stator component to provide positive engagement and to ensure rotation of the stator during operation. As shown in cross-section in  FIG. 6B , the outside diameter (O.D.) of the outer race  17  as at  40  is machined in a stepped configuration to provide interlocking engagement with the stator end caps  25  ( FIGS. 7A and 7B ). 
   The stator end caps, indicated generally at  25 , are designed to secure the inner and outer races  15 ,  17  in coaxial alignment with the sprag assembly  110 . Thus, it will be appreciated that the stator end caps  25  provide essentially the same function as the end bearings  116  and retaining rings  118  of the prior art sprag clutch  100 . A plurality of oil slots  32  extending inwardly as most clearly shown in  FIG. 4  provides continuous lubrication to the sprag assembly  110  and inner race  15 . 
   The counterbores  30 ,  35  wherein the inner and outer races  15 ,  17  engage the stator end caps  25  are machined to hold precise concentricity tolerances to ensure that, when the sprag clutch  10  is assembled as shown in  FIG. 7B , the races  15 ,  17  are maintained in concentric relation. Thus, potential for eccentric loading of the inner and outer races  15 ,  17  and the rollover of sprags  105  is minimized. 
   Further, when the present sprag clutch  10  is assembled such that the inner and outer races  15 ,  17  are interlocked within the counterbores  30 ,  35  in the stator end caps  25 , the overall axial length as at “X” ( FIG. 7B ) is reduced to a minimum to meet the space restrictions for this application. 
   Although not specifically illustrated in the drawings, it should be understood that additional equipment and structural components will be provided as necessary and that all of the components described above are arranged and supported in an appropriate fashion to form a complete, operative, and Sprag Clutch Assembly incorporating features of the present invention. For example, it is anticipated that the present sprag clutch assembly may be provided in a kit form including at least one interchangeable inner race for various torque converter stator applications. In addition, the present sprag clutch assembly may be included within a complete torque converter rebuild kit having other torque converter components. 
   Moreover, although illustrative embodiments of the invention have been described, a latitude of modification, change, and substitution is intended in the foregoing disclosure, and in certain instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of invention.