Abstract:
An engine starter comprises a housing with a planetary gear arrangement provided within the housing. The planetary gear arrangement includes a ring gear configured to pivot about an axis. The ring gear includes a face oriented substantially perpendicular to the axis, the face including a plurality of detents provided as a plurality of ribs and a plurality of depressions on the face. A torque limiter is positioned adjacent to the face of the ring gear within the housing of the engine starter. The torque limiter includes a plurality of projecting members engaging the plurality of detents on the ring gear when the ring gear pivots about the axis. The torque limiter is provided as a plate including a central hole, a body portion, and a perimeter portion. The plurality of projecting members comprise a plurality of spring fingers extending from the body portion at an angle.

Description:
FIELD 
       [0001]    This application relates to the field of engine starters, and more particularly to torque absorbing or limiting components in an engine starter. 
       BACKGROUND 
       [0002]    Many engine starters include a planetary gear system that transmits power from an electric starter motor to a pinion configured to engage an engine ring gear. The planetary gear system typically includes a sun gear connected to the output shaft of the electric motor. A plurality of planet gears revolve around the ring gear. The planet gears also engage teeth provided on an outer ring gear in the planetary gear system. 
         [0003]    Engine starters may encounter excessive torque in the radial direction of the output shaft of the starter. For example, the torque associated with initial rotation of the electric motor, a slow turning pinion, or a jammed pinion may all result in excessive torque to the planetary gear system. When the planetary gear system encounters excessive torque, the planet gears may grind against the teeth of the outer ring gear. After time, the teeth of the planet gears grinding against the teeth of the ring gear may result in excessive wear or even failure of the planetary gear system. 
         [0004]    In view of the foregoing, it would be advantageous to provide an engine starter having torque absorbing features provided in association with the planetary gear system of the starter. It would also be advantageous if such torque absorbing features could be easily incorporated into the engine starter. 
       SUMMARY 
       [0005]    An engine starter comprises a housing with a planetary gear arrangement provided within the housing. The planetary gear arrangement includes a ring gear configured to pivot about an axis. The ring gear includes a face oriented substantially perpendicular to the axis, the face including a plurality of detents provided as a plurality of ribs and a plurality of depressions on the face. An output shaft is connected to the planetary gear arrangement such that the planetary gear arrangement is configured to drive the output shaft. A pinion provided on the output shaft. 
         [0006]    A torque limiter is positioned adjacent to the face of the ring gear within the housing of the engine starter. The torque limiter includes a plurality of projecting members engaging the plurality of detents on the ring gear when the ring gear pivots about the axis. The torque limiter is provided as a plate including a central hole, a body portion, and a perimeter portion. The plurality of projecting members comprise a plurality of spring fingers extending from the body portion at an angle. The plurality of spring fingers are provided as cut out portions of the body portion such that an opening is provided in the body portion in association with each of the plurality of spring fingers. The plurality of spring fingers each include a end tip portion that is bent away from the rest of the spring finger such that the end tip portion is generally parallel to the main body portion. 
         [0007]    The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. Furthermore, while it would be desirable to provide an engine starter that includes one or more of the foregoing or other advantageous features as may be apparent to those reviewing this disclosure, the teachings disclosed herein extend to those embodiments which fall within the scope of the appended claims, regardless of whether they include the above-mentioned features accomplish or provide one or more of the above-mentioned advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a cutaway view of an embodiment of an engine starter having a torque limiter; 
           [0009]      FIG. 2  shows a perspective view of a ring gear of a planetary gear mechanism of the engine starter of  FIG. 1 ; 
           [0010]      FIG. 3  shows a perspective view of a ring gear side of a torque limiter configured to engage the ring gear of  FIG. 2 ; and 
           [0011]      FIG. 4  shows a perspective view of the opposite side of the torque limiter of  FIG. 3 . 
       
    
    
     DESCRIPTION 
       [0012]    With reference to  FIG. 1 , an electric engine starter or cranking motor  10  is illustrated. The starter  10  is provided in a housing  12 . The housing  12  includes a solenoid chamber  52  which encloses a solenoid (not shown). The housing  12  also includes a drive chamber  54 , which encloses an electric motor (not shown), a planetary gear system  14 , an overrunning clutch  16  and a pinion gear  18 . The overrunning clutch  16  and the pinion gear  18  are both provided upon a pinion drive shaft  20 . 
         [0013]    The electric motor provided within the housing  12  is a direct current motor. The direct current motor includes an armature and an armature shaft. The motor further has a means for developing field flux (also not illustrated) which may take the form of a plurality of permanent magnets. 
         [0014]    The armature shaft of the direct current motor is connected to the sun gear (not shown) of the planetary gear mechanism  14 . The sun gear is provided at the center of the planetary gear mechanism  14  along the same axis  21  as the pinion drive shaft  20 . A plurality of planet gears (not shown) are positioned about and engage the sun gear. Each of the planet gears is provided on a post  22 . The posts  22  holding the planet gears are connected to a rotatable platform  24  which, in turn, is connected to the pinion drive shaft  20 . The planet gears rotate about the sun gear within a ring gear  30 . 
         [0015]    With reference now to  FIGS. 1 and 2 , the ring gear  30  generally cylindrical or cup-shaped. The ring gear  30  includes an open rear end  32 , a circular sidewall  34 , and a forward face  36 . The open rear end  32  is positioned on the electric motor side of the ring gear and abuts a metal plate  48  positioned within the housing  12 . The output shaft  20  of the electric motor passes through the metal plate  48  and into the interior of the ring gear  30  to engage the sun gear. 
         [0016]    A torque limiter  60  is provided adjacent to the ring gear  30  on the pinion-side of the ring gear  30 . Accordingly, the forward face  36  of the ring gear  30  abuts the torque limiter  60 . As explained in further detail below, the torque limiter  60  is provided as a plate comprising a plurality of spring fingers. The spring fingers engage detents  42  on the forward face  36 , allowing the ring gear to rotate slightly in the radial direction about the axis  21  (i.e., in a circular direction about the axis  21 ). As best seen in  FIG. 2 , the detents  42  are provided as a plurality of elongated radial ribs  56  formed upon the forward face  36 . A recess or depression  58  is provided between each pair of ribs  56 . Each rib  56  is generally smooth and rounded such that a smooth rounded contour is provided when moving across the rib  56  from one depression  58  to the next. 
         [0017]    The interior portion of the ring gear  30  includes a planetary gear track  38  including a plurality of teeth  40  provided on the interior surface of the circular sidewall  34 . The teeth of the planet gears engage the teeth  40  of the planetary gear track  38  and the planet gears circle the planetary gear track  38  as they rotate about the sun gear. 
         [0018]    The rotatable platform  24  is rotatably positioned within the ring gear  30 . In particular, as the planet gears rotate, the posts  22  holding the planet gears also rotate. Because the posts  22  are connected to the platform  24 , the platform  24  also rotates with the planet gears. As shown in  FIG. 2 , the ring gear  30  includes a hole  41  in its front face. The platform  24  is connected to the pinion drive shaft  20  through this hole  41 . Accordingly, rotation of the platform  24  results in rotation of the pinion drive shaft  20 . 
         [0019]    The shaft  20  drives a starter drive that is comprised of the overrunning clutch  16  and a pinion gear  18 . The pinion gear  18  is adapted to be moved into mesh with the ring gear of an engine. The shell  26  of the overrunning clutch has a helical splined connection to the shaft  20 , which is not illustrated. During operation of the starter motor, after the engine fires and the pinion begins to rotate at excessive speeds, the overrunning clutch prevents translation of this excessive speed back to the planetary gear mechanism  14  and the electric motor. 
         [0020]    The housing  12  includes an end nose portion  50 . The nose portion  50  has an access opening (not shown) which allows the pinion gear  18  to be moved into mesh with a ring gear of an engine. 
         [0021]    The housing  12  also includes a solenoid chamber or compartment  52 . A solenoid (not shown) is held within the solenoid chamber  52 . The plunger of the solenoid engages a shift lever  44  which extends between the solenoid chamber  52  and the drive housing  54 . The shift lever  44  includes arms  46  that extend from an end portion and engage the overrunning clutch  16 . It can be appreciated that when shift lever  44  is pivoted in the counter-clockwise direction by action of the solenoid in the solenoid chamber, the arms  46  will engage surface of the clutch  16  to push the overrunning clutch  16  and pinion  18  to the right, in  FIG. 1 , to a position where pinion  18  will mesh with the ring gear of the engine. Likewise, solenoid action against the shift lever causing clockwise movement of shift lever  44  causes surface  28  to be engaged by the arms  46  of the shift lever  44 , thereby causing the pinion  18  to be pulled out of mesh with the engine ring gear. 
         [0022]    With reference now to  FIGS. 3 and 4 , a more detailed view of the torque limiter  60  is shown. The torque limiter  60  is generally provided as a metal plate comprising a body portion  62 , a central hole  64 , and a perimeter portion  66 . 
         [0023]    The body portion  62  of the torque limiter includes a generally flat surface  63  provided within a body plane. A plurality of projecting members  68  extend from the body portion  66  and engage the plurality of detents  42  on the ring gear. In the embodiment of  FIGS. 3 and 4 , the plurality of projecting members  68  are provided as spring fingers  68  which extend from the flat surface  63  of the body portion  62  at an angle. In one embodiment, the spring fingers  68  extend from the flat surface  63  of the body portion  62  at an angle between 30° and 60° relative to the body plane. The spring fingers  68  may be formed by stamping the fingers out of the flat surface  63  of the body portion and bending the fingers away from the flat surface at an angle. Accordingly, an opening  70  may be provided in the body portion  62  in association with each of the spring fingers  68 . In particular, the openings  70  are formed in the area in the body portion  62  where the spring fingers  68  were cut out of the flat surface  63 . 
         [0024]    Each of the spring fingers  68  includes an elongated portion  72  and an integral end tip portion  74 . The end tip portion  74  is provided on the end of the spring finger  68  that is most distant from the flat surface  63 . The end tip portion  74  angles away from the elongated portion  72  of the spring finger such that the end tip portion  74  is generally parallel to the flat surface  63  of the body portion  62 . This angled relationship between the end tip portion  74  and the elongated portion  72  may be provided by bending the end tip portion  74  on the elongated portion  76  when the spring finger  68  is bent away from the flat surface  63  of the body portion  62 . As shown in  FIG. 1 , the end tip portions  74  of the spring fingers  68  contact the detents  42  in the ring gear  30 , holding the ring gear in place within the housing. In particular, with reference to  FIGS. 2 and 3 , the end tip portions  74  extend into the depressions  58  and abut the ribs  56  on the face  36  of the ring gear. 
         [0025]    Returning to  FIGS. 3 and 4 , the central hole  64  of the torque limiter  60  is defined by an interior lip that extends from the flat surface  63 . The central hole is configured to provide a passage between the rotatable platform  24  of the planetary gear mechanism  14  and the output shaft  20  of the engine starter  10 , allowing the output shaft  20  to be connected to the planetary gear mechanism  14 . 
         [0026]    The perimeter portion  66  of the torque limiter  60  includes an outer lip  78  that extends around the perimeter of the torque limiter  60 . A plurality of tabs  80  are provided on the outer lip  78  in the form of rounded knobs. These knobs  80  are configured to engage slots or recesses formed in the housing  12 . The slots in the housing are also rounded and complimentary in shape to the knobs  80 . Accordingly, when the knobs  80  are fitted into the slots in the housing  12 , the knobs secure the torque limiter  60  in place within the housing  12 , preventing the torque limiter  60  from rotating about the axis  21 . 
         [0027]    In operation of the engine starter  10 , when the ring gear  30  is exposed to excessive torque, the torque limiter  60  provides a dampening feature for the ring gear, limiting wear to the teeth  40  of the ring gear  30 . In particular, when the ring gear experiences excessive torque, the forces of the planet gears against the ring gear encourage the ring gear  30  to pivot about the axis  11 . The degree of ring gear  30  pivot within the housing is dependent upon the amount of torque encountered by the ring gear. In particular, when the ring gear  30  begins to rotate about the axis  21 , the ribs  56  on the face  36  of the ring gear  30  are forced against the spring fingers  68  of the torque limiter  60 . As the spring fingers  68  ride up the contoured surface of the ribs  56 , the spring fingers  68  flex back toward the flat surface  63  of the torque limiter body portion  62 . This force provided by the spring fingers  68  against the ribs  56  of the ring gear  30  increases as the spring fingers flex. When the ring gear  30  is exposed to sufficient torque, the ring gear  30  rotates such that the spring fingers  68  slide completely past the ribs and into the next subsequent depression  58  on the ring gear This rotation action by the ring gear  30  provides a torque dampening feature for the engine starter, allowing the planetary gear system to minimize wear caused by excessive torque events. When the excessive torque is removed, the ring gear  30  remains in the last incremental orientation encountered during the excessive torque event, with the spring fingers  68  sliding down into the closest depressions  58  on the ling gear. 
         [0028]    Although the present invention has been described with respect to certain preferred embodiments, it will be appreciated by those of skill in the art that other implementations and adaptations are possible. Moreover, there are advantages to individual advancements described herein that may be obtained without incorporating other aspects described above. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.