Abstract:
An assembly for stabilizing a gear unit of a transmission for an automotive vehicle includes a first component fixed against displacement along an axis, a carrier facing the first component, supported for rotation about the axis, and supporting planet pinion thereon, and springs located between the first component and the carrier, producing axial forces distributed angularly around the axis and applied to the carrier.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to the kinematic arrangement of an automatic transmission, and, more particularly to stabilizing a planetary pinion carrier using a preload. 
         [0003]    2. Description of the Prior Art 
         [0004]    In a planetary gear unit of the type used in automatic transmissions for motor vehicles planetary pinions are supported for rotation on a carrier comprising discs that are spaced axially to provide space for the pinions. The carrier is usually piloted into its correct position in the assembly on pilot surfaces formed in adjacent components. 
         [0005]    For example, one of the carrier discs may be piloted into position on a spline and the other disc on the race of a one-way clutch (OWC). The race may not be perfectly round, and the spline may not be perfectly centered on the clutch race. 
         [0006]    These features produce an inherent imbalance in the carrier, causing the carrier to tip on its spline and generate a large force that causes the carrier to track the out-of-round clutch race. When the carrier is piloted on imperfect interfaces, large impact loads are generated when the carrier is forced back to a centerline by the outer race profile. These impact loads on the carrier tend to upset the rocker element of the OWC, causing the rocker to pivot toward engagement when it should retract to an over-running position. When the carrier is impacted by the outer race, actuating springs, which urge the rocker toward engagement, can be destroyed and the clutch&#39;s function lost. 
         [0007]    A need exits in the industry for a technique that avoids over-constraining the gearset and maintaining the carrier aligned with the centerline during no torque, coast events. 
       SUMMARY OF THE INVENTION 
       [0008]    An assembly for stabilizing a gear unit of a transmission for an automotive vehicle includes a first component fixed against displacement along an axis, a carrier facing the first component, supported for rotation about the axis, and supporting planet pinion thereon, and springs located between the first component and the carrier, producing axial forces distributed angularly around the axis and applied to the carrier. 
         [0009]    The stabilization springs prevent over-constrainting the gearset and keep the carrier aligned with the axis. 
         [0010]    The preload applied to the carrier by the stabilization springs, counteracts the inherent imbalance that causes an initial tipping moment on the carrier. The preload force of the springs applies a greater moment to the carrier than the imbalance force, thereby preventing tipping of the carrier. By preventing this tipping, the carrier can not follow the race. When the race is no longer contacted by the carrier, impact loads are eliminated and the rocker of the one-way clutch remains retracted during over running conditions, preventing damage to the rocker springs. 
         [0011]    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 
         [0012]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a cross section of a portion of the kinematic assembly for an automatic transmission that includes a Ravigneaux gear set; 
           [0014]      FIG. 2  is a side view of a disc for a brake assembly of the kinematic assembly; 
           [0015]      FIG. 3  is front view of a subassembly containing a series of springs located in the assembly of  FIG. 1 ; and 
           [0016]      FIG. 4  is a cross section taken at plane  4 - 4  of the spring subassembly of  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    Referring to  FIG. 1 , 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 drum  18 ; a second sun gear  20 , connected by a spline  22  to a rotating drum  24 ; 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 carrier assembly  26  further includes a set of short planet pinions  32 , each spaced angularly about axis  30 , supported on carrier  26  and meshing with sun gear  20  and the long pinion  28 . The gear assembly  10  further includes a ring gear  34  engaged with the long pinions  28  and arranged coaxially with the sun gears  14 ,  20  and pinions  28 ,  32 . 
         [0018]    The carrier assembly  26  includes a first disc  36 , connected by a spline  38  to a shaft  40 ; a second disc  42 , spaced axially from the first disc; and a third disc  44 , located between the end discs  36 ,  42 . The carrier discs  36 ,  42 ,  44  support pinion shafts  46 ,  48 , on which pinions  28 ,  32  are supported for rotation on bearings  50 ,  52 , respectively. 
         [0019]    The transmission case  12  is formed at an inner surface with axially directed spline teeth  54 , which are engaged with external spline teeth  56  formed on the circumferential periphery of the outer ring  58  of a rocker one-way or overrunning clutch  60 . U.S. Pat. No. 7,383,930 discloses the structure and operation of a rocker one-way clutch similar to clutch  60 , the entire disclosure of which is incorporated herein by reference. 
         [0020]    An annular pilot recess  64  on the inner ring  62  of clutch  60  is engaged by carrier disc  42  and guides disc  42  into its assembled position within the case  12 , and spline  38  pilots carrier disc  36  to its correct position within the case. 
         [0021]    The disc  70  of a hydraulically-actuated friction disc brake drum  72  faces clutch  60  and carrier discs  42 ,  44 .  FIG. 2  illustrates that the disc  70  is formed with external spline teeth  74 , which engage teeth formed on the inner surface of case  12 . Internal spline teeth  76  engage spline teeth formed on friction discs  78  of a hydraulically-actuated brake  80 . A snap ring  81  secures disc  70  against axial movement relative to the case  12 . The disc  70  is also formed with cylindrical bosses  82 , which are angularly spaced about axis  30 . 
         [0022]    A spring subassembly  90 , shown in  FIGS. 3 and 4 , includes a circular plate  92  formed with angularly spaced spring retainers  94  that extend axially from the surface of the plate. A helical coiled compression spring  96 , is retained in position on plate  92  at each retainer  94  due to frictional engagement of the inner surface of the spring with the radial outer surface of the retainer. 
         [0023]      FIGS. 1A and 1B  show that the spring subassembly  90  is installed such that each of its springs  96  is aligned with and frictionally engages one of the bosses  82  on disc  70 . A spacer shim  98  in the form of a circular disc, fitted between plate  92  and the axial surface  100  of carrier disc  42 , is installed such that springs  96  produce a preload directed axially rightward on a thrust bearing  101  located between sun gear  14  and the spacer shim  98 . 
         [0024]    The axially directed preload applied by the spring subassembly  90  to thrust bearing  100  is transmitted axially across sun gear  14 ; plate  102 , which is secured to and rotates with sun gear  14 ; a second thrust bearing  104 , contacting plate and sun gear  20 ; sun gear  20 ; and a third thrust bearing  106  to the inner surface of carrier disc  36 . This arrangement of sun gears  14 ,  20  and thrust bearings  102 ,  104 ,  106  permits the spring subassembly  90  to remain secured against rotation on clutch disc  70  and to transmit the preload to the rotating carrier. 
         [0025]    The preload counteracts an inherent imbalance that causes an initial tipping moment on the carrier  26 . For the carrier  26  to tip, a gap must open between the thrust bearing  106  and the carrier disc  36 . The preload force of stabilization springs  96  closes this gap and requires a force to open it. By adjusting the thickness of shim  98 , the spring preload applies a greater moment to the carrier  26  than the imbalance force, preventing the carrier from tipping out of alignment with axis  30 . By preventing this tipping, the carrier  26  can not follow the race  62  of overrunning clutch  60 . When the race  62  is no longer contacted by the carrier  26 , impact loads are eliminated. This allows the rocker of clutch  60  to remain retracted during overrunning conditions, and prevents damage to the rocker springs of the clutch. 
         [0026]    Throughout this description use of the terms “overrunning clutch” and “one-way clutch” apply both to a clutch and a brake. An overrunning brake alternately engages to secure a component of the kinematic arrangement against rotation in one direction relative the case  12  and disengages to release the component to rotate freely in the opposite direction. A overrunning clutch alternately engages to secure two components of the kinematic arrangement against relative rotation when the speed of a first component is greater than that of a second component in one direction and disengages to release the components to rotate relative to one another when the speed of the second component is greater than that of the first component. 
         [0027]    The helical coiled compression springs  96  may be replaced in the spring subassembly  90  by a Belleville spring that engages disc  70  and produces a preload axial force on thrust bearing  101 . The preload force of the Belleville spring is transmitted axially to the rotating carrier disc  36 . 
         [0028]    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.