Abstract:
A transmission gear unit includes a carrier including a first disc formed with a first chamfer, and a second disc, a one-way clutch including a first ring contacting the second disc, and a second ring, located radially outboard of and surrounding the first ring, and formed with a second chamfer, and pinion shafts, each shaft supported on the first disc and first ring, engaging the first and second chamfers and supporting a pinion thereon.

Description:
This application is a continuation of U.S. application Ser. No. 11/701,663, filed Feb. 2, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a planetary gear unit for an automatic transmission, and more particularly to an assembly that includes a planet pinion carrier connected to a powdered metal plate of a one-way clutch. 
     2. Description of the Prior Art 
     A conventional Ravigneaux gearset includes a carrier containing two sets of planet pinions, long pinions and short pinions. Each pinion set includes several pinions. Each pinion is mutually spaced angularly about a central axis, each short pinion meshing with a corresponding long pinion. There are two sun gears, a short sun gear meshing with the short pinions, and a long sun gear meshing with the long pinions. A ring gear meshes with the long pinions. 
     Both planet pinion sets are supported for rotation on the carrier. Each long pinion is in mesh with a short pinion, the ring gear, and the long sun gear. Each short pinion is in mesh with a long pinion and the short sun gear. 
     Ravigneaux gearsets are used in many automatic transmissions due to their compact size. A Ravigneaux gearset can be used in lieu of two simple planetary gearsets to produce four forward speeds and a reverse gear. They are smaller, and require fewer components than two simple planetary gearsets because they have one ring gear, and one carrier. Their manufacturing and assembly costs compare favorably to those of simple planetary gearsets. 
     Frequently a Ravigneaux gear unit is controlled by a hydraulically actuated friction brake, which alternately holds the carrier against rotation on a transmission casing and releases the carrier to rotate freely. A one-way clutch is often arranged in parallel with the friction brake between the casing and planet carrier. The rings of the one-way clutch are formed from powdered metal, but the other components of the carrier assembly are machined from cast iron. There is a need to integrate such one-way clutches into the carrier assembly using mechanical connections. But the components of the integrated assembly that are fabricated from powdered metal and those that are fabricated from cast iron have substantially different material stiffness and strength properties. For example, pinion carriers are less expensive, more rigid and have better pinion window tolerances when made from cast iron than from powdered metal. 
     The joint between a cast iron carrier and a powder metal clutch ring must radially locate both parts, axially retain both parts, and carry torque. Conventional methods for joining the two dissimilar materials include a spline and a snap ring, but these require excessive axial space; a shearing spline, which would create high radial loads on the thin powder metal clutch ring; or a press fit, which would not carry the high loading. 
     There is a need in the automatic transmission industry for an integrated carrier assembly comprising both a one-way clutch of powder metal and other components of machined cast iron that overcomes these and other problems associated with integrating and mechanically joining the dissimilar metals. 
     SUMMARY OF THE INVENTION 
     A transmission gear unit includes a carrier including a first disc formed with a first chamfer, and a second disc, a one-way clutch including a first ring contacting the second disc, and a second ring, located radially outboard of and surrounding the first ring, and formed with a second chamfer, and pinion shafts, each shaft supported on the first disc and first ring, engaging the first and second chamfers and supporting a pinion thereon. 
     The joint between a cast iron carrier and a powder metal clutch ring must radially locate both parts, axially retain both parts, and carry torque. The method accurately machines a radial pilot in both the carrier and the one-way clutch ring to locate the two parts radially. The method provides unmachined clearance holes in the clutch ring, which holes correspond with the long pinion shafts in the carrier assembly to carry the torque. After the clutch ring and clutch rocker assembly is installed over the long pinion shafts, the pinion shafts are orbital formed or riveted to fill the hole clearance and retain the rocker assembly axially. 
     Advantages provided by the invention include excellent radial location for the clutch ring to the carrier, the clutch ring is removed from the pinion stack path, thereby improving pinion window tolerances, it requires no additional axial space, as compared to a powdered metal rocker and conventional carrier assembly, and the one-way clutch is completely removable, thereby allowing flexibility for cost vs. shift quality across different vehicle platforms. 
     By splitting the powder metal rocker clutch cam ring from the cast iron carrier, an original equipment manufacturer (OEM) can source manufacture of the planet carrier separately from manufacture of the rocker one-way clutch components. In this way, the OEM can assemble the rocker one-way clutch assembly, or have a supplier assemble the one-way clutch and ship it to the OEM ready to install on the planet carrier. By splitting the rocker clutch cam ring from the planet carrier, an OEM can employ business entities proficient in powdered metal fabrication to manufacture the one-way clutch and entities proficient in fabricating machined castings for the pinion carrier. 
     The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       These and other advantages will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
         FIG. 1  is a side cross section of a Ravigneaux gear set for an automatic transmission; 
         FIG. 2  is a front-side perspective view of the carrier assembly shown in  FIG. 1 ; and 
         FIG. 3  is a rear-side perspective view of the carrier assembly shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1-3 , a planetary gear assembly  10  of the Ravigneaux type located in a transmission case  12  includes a first sun gear  14 , connected by a spline  16  to a rotating shaft; a second sun gear  20 , connected by a spline  22  to a rotating shaft; a planet pinion carrier assembly  26 , which is supported for rotation and includes long planet pinions  28 , each spaced angularly about an longitudinal axis  30 , supported on the carrier  26  and meshing with sun gear  14 . The gear assembly  10  includes a set of short planet pinions (not shown), each spaced angularly about axis  30 , supported on carrier  26  and meshing with sun gear  20  and a long pinion  28 . The gear assembly  10  further includes a ring gear  18  surrounding the long pinions  28 , short pinions and sun gears  14 ,  20  and engaged with the long pinions  28 . 
     The carrier assembly  26  includes a first disc  32  formed with axial holes  34  spaced angularly about axis  30  joined to a second disc  36  spaced axially from the first disc and formed with axial holes  38 , each second hole being aligned a first hole  34 ; and pinion shafts  40  each supported on the carrier  26  and extending axially through a first hole  34  and a second hole  38 . Discs  32  and  36  are formed integrally as a unitary component, preferably as a casting of cast iron. Bearings  42 ,  43 , fitted between the outer surface of each pinion shaft  40  and the inner surface of a corresponding long pinion  28 , support the long pinions  28  in rotation on the pinion shafts  40 . 
     The transmission case  12  is formed at an inner surface with axial spline teeth  42 , which are engaged with external spline teeth  44  formed on the circumferential periphery of the outer ring  46  of a rocker one-way clutch  48 . The outer ring  46  of one-way clutch  48  is secured to the case  12  by a snap ring  49 . An inner ring  50  of clutch  48  is guided to its correct radial position on a pilot surface  52  formed on carrier disc  36 . 
     Carrier  26  includes a member  54  having a web  56  located axially between axial spaced portions of the long pinion  40 . Member  54  further includes posts  58 , which encircle the short pinions and long pinions  40 , and axial external spline teeth  60 , which are angularly spaced about axis  30 , aligned with posts  58  and offset angularly from the pinion shafts  40  and long pinions  28 . An axial end of member  54  bears against the clutch ring  50  and the opposite axial end of member  54  bears against the carrier disc  32 .  FIG. 2  shows that the web provides spaces into which pinions  28  and pinion shafts  40  are located. 
     A hydraulically actuated friction brake  62  includes clutch plates  64 , which are spaced mutually and rotatably secured to the case  12  by engagement with spline teeth  42 . Frictions discs  66 , each interleaved between successive clutch plates  64 , are rotatably secured to the member  54  by engagement with its spline teeth  60 . A hydraulically actuated brake piston  67  produces a drive connection between the case  12  and carrier  26  when it moves leftward, thereby forcing the plates  64  and discs  66  into mutual frictional contact against the outer ring  46  of one-way clutch  48 . 
       FIG. 2  shows angularly spaced holes  68  formed in carrier disc  32  and angularly spaced holes  70  formed in web  54  and aligned with holes  68 . The short pinions are supported in rotation on short pinion shafts (not shown) located in holes  68  and  70 . The short pinion shafts secure member  54  to carrier  26  for rotation as a unit due to the short pinion shafts being fitted through holes  68  and  70 . 
     The mechanical connection that joins the cast iron carrier  26  and the powder metal clutch ring  50  must locate both parts radially, axially secure the parts mutually, and transmit torque about axis  30 . To accomplish these, mating radial pilot surfaces  52  are accurately machined in both carrier disc  36  and clutch ring  50 , thereby locating disc  36  and ring  50  at their correct radial positions. Unmachined clearance holes  72  having chamfered surfaces  74  are formed in the clutch ring  50 . The mutually aligned holes  38 ,  34  in the carrier discs  32 ,  36  receive the long pinion shafts  40  of the Ravigneaux carrier assembly  26 , and allow a portion of each pinion shaft to extend axially through holes  38  and into a hole  72  in the clutch ring  50 . After the clutch ring  50  is installed over the pilot  52  and over the long pinion shafts  40 , the pinion shafts are orbital formed or riveted into holes  72 , thereby retaining the components of the rocker assembly  26 , including clutch ring  50 , in their correct axial positions.  FIG. 1  shows that orbital forming the pinion shafts  40  peens material  76 ,  78  located at the outer periphery of countersunk, conical holes  80 ,  82  in the pinion shafts over chamfered surfaces  74 ,  86  in the opposite ends of the pinion shafts  40 . 
     A method for assembling the planetary gear unit includes (a) pre-assembling each long pinion gear  28  with bearings  42  and  43  and washers  90  and  92  into the carrier assembly  26 ; (b) installing a pinion shaft  40  through hole  38  and through the long pinion gear  28  with bearings  42  and  43  and washers  90  and  92  and then through hole  34  with each pinion shaft  40  extending past the first disc through hole  38 ; (c) forming the first disc with a first pilot surface  52  radially spaced from the axis and extending along the axis. The first ring  50  is formed with a second pilot surface  53  substantially parallel to the first pilot surface. The second pilot surface  53  is engaged with the first pilot surface  52  while installing the first ring  50 . The outer clutch ring  46  is installed and aligned axially with the first ring and located radially outboard of the first clutch ring  50 . Then (d) the pinion shafts  40  are orbital formed or riveted to axially retain the first ring  50  to the carrier assembly  26  and to prevent the pinion shafts  40  from moving axially relative to carrier assembly  26 . 
     In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.