Abstract:
A limited slip planetary gear transmission comprising an input member, an output member, a planetary gear set coupled between the input member and the output member, the planetary gear set having a sun gear, and a brake member directly coupled to the sun gear, the brake member controls an output torque of the planetary gear set by controlling a speed of the sun gear.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a limited slip planetary gear transmission, and in particular, to a limited slip planetary gear transmission having a brake member engaging a rotating portion of a planetary gear set for controlling an output torque of the planetary gear transmission. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to planetary gear sets. Planetary gear sets are typically unitary assemblies comprising a sun gear, carrier, pinions, and a ring gear. The planetary gear set subassembly is then incorporated into a larger mechanical device, such as an automotive transmission. The output power or torque of the larger device into which a planetary gear set is incorporated is routinely controllable. For certain applications it would be desirable to control the torque output of the planetary gear set proper by directly controlling the torque of one or more of the planetary gear set components such as the sun gear or carrier. 
         [0003]    Representative of the art is U.S. Pat. No. 5,106,351 which discloses a transfer case for a four wheel drive vehicle providing a central shaft defining a first output concentrically surrounded by a forward high/low drive range gear set and an aft dual planetary inter-axle differential gear set. A range clutch collar is disposed between the gear sets for selectively providing four wheel drive low range, neutral, and full-time four wheel drive high range. Likewise, a mode sleeve is disposed between the gear sets for selectively locking the differential gear set when the vehicle is shifted into its four wheel low range. Inner and outer relatively rotational drum housings surround the aft dual planetary differential gear set for defining an annular viscous fluid coupling chamber therebetween. The inner drum is formed with internal annulus gear teeth meshed with a portion of the dual planetary gear set for rotation with the first output shaft while the outer drum is interconnected to a second output for providing full-time four wheel drive differentiation with limited slip between the first and second outputs. 
         [0004]    What is needed is a limited slip planetary gear transmission having a brake member engaging a rotating portion of a planetary gear set for controlling an output torque of the planetary gear transmission. The present invention meets this need. 
       SUMMARY OF THE INVENTION 
       [0005]    The primary aspect of the invention is to provide a limited slip planetary gear transmission having a brake member engaging a rotating portion of a planetary gear set for controlling an output torque of the planetary gear transmission. 
         [0006]    Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
         [0007]    The invention comprises a limited slip planetary gear transmission comprising an input member, an output member, a planetary gear set coupled between the input member and the output member, the planetary gear set having a sun gear, and a brake member directly coupled to the sun gear, the brake member controls an output torque of the planetary gear set by controlling a speed of the sun gear. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention. 
           [0009]      FIG. 1  is a cross-sectional view of the preferred embodiment. 
           [0010]      FIG. 2  is an exploded view of the embodiment in  FIG. 1 . 
           [0011]      FIG. 3  is a cross-sectional view of an alternate embodiment. 
           [0012]      FIG. 4  is an exploded view of the embodiment in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]      FIG. 1  is a cross sectional view of the inventive transmission. Carrier  20  rotates about an axis A-A. Carrier  20  may be press fit on a rotating shaft (not shown). 
         [0014]    A plurality of pinion gears  90  are journalled to carrier  20 . Each pinion gear  90  meshes with ring gear  30  and sun gear  10 . Sun gear member  11  further comprises a shaft which is coaxial with carrier  20  about axis A-A. In this embodiment sun gear  10  is frictionally engaged with brake  40  through sun gear member  11 . 
         [0015]    Ring gear  30  rotates upon sun gear member  11  through bearing  81 . Ring gear  30  rotates upon carrier  20  through bearing  80 . In this embodiment the power output is through ring gear  30  and the power input is through carrier  20 . 
         [0016]    Brake  40  comprises a housing  50 , and interleaved plates  60  and  70 . Plates  60  comprise a frictional material known in the clutch and brake arts. Plates  70  comprise a frictional material known in the clutch and brake arts. Plates  60  are mounted to housing  50 . Plates  70  are mounted to sun gear member  11 . Piston  41  urges plates  60  into frictional engagement with plates  70 . Frictional engagement between plates  60  and plates  70  applies a drag torque to sun gear member  11 , thereby slowing rotation of sun gear  10 , which in turn reduces the output torque of the device. Brake  40  may also comprise other types of brakes as known in the art, such as a cone or band brake. In an alternate embodiment piston  41  may further comprise a pneumatic or hydraulic cylinder connected to a control system (not shown). 
         [0017]    In  FIG. 1  the device is configured as a planetary gear set where sun  10  is the reaction gear and the carrier  20  is the input to create an output speed increase at ring  30 . In an alternative embodiment ring  30  could be the input resulting in a speed reduction at output carrier  20 . Sun  10  would be held fixed to create the speed ratio, but could also be slipped to vary the output speed, each selected speed using brake  40 . 
         [0018]    To illustrate operation, assume that the transmission is used as a speed increaser wherein ring  30  is the output and carrier  20  is the input. The ratio of the transmission when sun  10  is held to no rotation by brake  40  is: 
         [0000]    
       
         
           
             1 
             
               ( 
               
                 1 
                 + 
                 
                   S 
                   R 
                 
               
               ) 
             
           
         
       
     
       Where, 
       [0019]    S is number of teeth on sun  10 
 
R is the number of teeth on ring  30 
 
         [0020]    In this example sun  10  has 12 teeth and ring  30  has 60 teeth so that the ratio is 0.83:1. If carrier  20  is spinning at 1,000 RPM with 12 Nm torque and sun  10  is not rotating due to application of brake  40  then ring  30  spins at 1,200 RPM and at a torque of 10 Nm. It is possible to slip brake  40  to have any speed less than 1,200 RPM at ring  30 . If the desired speed of ring  30  is 1100 RPM the applied force to brake  40  can be reduced to allow sun  10  to slip. 
         [0021]    To calculate the slip speed required at sun  10  the following calculation is used: 
         [0000]      ( R+S )ωCARRIER= R ωRING+ S ωSUN
 
         [0000]    ωCARRIER is the speed of the carrier
 
ωRING is the speed of the ring
 
ωSUN is the speed of the sun
 
         [0022]    In this case the slip speed of sun  10  is 500 RPM to slow ring  30  to 1100 RPM from 1200 RPM. The power loss is simply the product of the change in speed at ring  30  and the torque at ring  30  as shown in the equation: 
         [0000]    
       
         
           
             Ploss 
             = 
             
               
                 
                   2 
                    
                   π 
                 
                 
                   60 
                    
                   
                       
                   
                    
                   s 
                    
                   
                     / 
                   
                    
                   min 
                 
               
                
               
                 ( 
                 
                   Δω 
                    
                   
                       
                   
                    
                   RING 
                 
                 ) 
               
                
               
                 ( 
                 TRing 
                 ) 
               
             
           
         
       
     
         [0000]    The power lost from slipping ring  30  is approximately 105 Watts. The torque at sun  10  is lower at 2 Nm because the speed at sun  10  is higher at 500 RPM. The power loss is easier to manage at a higher speed because the required force applied to plate  60  and plate  70  is lower. The lower applied force allows reduction of the overall physical size of plate  60 , plate  70 , and housing  50 . 
         [0023]      FIG. 2  is an exploded view of the embodiment in  FIG. 1 . O-rings  51  prevent debris from entering the housing and reaching the plates  60 ,  70 . O-rings  51  are also used to seal piston  41  as a pressure boundary. Housing cover  52  is fixed to the housing  50  using bolts  53 . A plate  60  bears upon an end plate  54 . 
         [0024]    Snap ring  82  retains bearing  81  in ring carrier  31 . Deflector  33  directs oil into the gear mesh interface between pinion  90  and sun  10 . Ring gear  30  is retained between ring carrier  31  and ring carrier  32 . Snap ring  83  retains bearing  80  in ring carrier  32 . 
         [0025]    In this embodiment, three pinion gears  90  are journalled to carrier  20 , although more pinions may be used depending upon the needs of a user. Sun gear  10  is press fit on an outer surface of sun gear member  11 . 
         [0026]      FIG. 3  is a cross-sectional view of an alternate configuration. In this embodiment, the brake mechanism is applied to the carrier  300 , wherein the embodiment in  FIG. 1  the brake mechanism is applied to the sun gear  10 . 
         [0027]    In this embodiment two ring gears ( 100 ,  500 ) share a common carrier  300  with a compound pinion  200 , where the carrier is the reaction element. Ring  100  is the input to create a speed increase at output ring  500 . Carrier  300  is the reaction member that is prevented from rotating or is slipped using brake  400 . As noted for the embodiment in  FIG. 1 , the power flow may be in either direction, namely, with input through ring carrier  501  and output through ring carrier  101  for a speed decrease transmission. 
         [0028]    Ring gear  100  is disposed on an inner surface of ring carrier  101 . Ring gear  100  meshes with a plurality of compound pinions  200 . Compound pinions  200  are journalled around carrier  300 . Each compound pinion  200  comprises two gears, namely, gear  201  and gear  202 . Each gear  201  and gear  202  has a different number of teeth. Ring gear  100  meshes with each gear  201 . 
         [0029]    Ring gear  500  is disposed on an inner surface of a ring carrier  501 . Ring gear  500  meshes with each gear  202  on each compound pinion  200 . 
         [0030]    Band brake  400  frictionally engages an outer circumferential surface  301  of carrier  300 . Band brake comprises a band  401  upon which is mounted frictional material  402 . Frictional material  402  frictionally engages surface  301 . Band brake  400  operates in a manner known in the art using a mechanical means to constrict the band upon surface  301 , thereby increasing the frictional force applied to the carrier. Such means can include but are not limited to an electric actuator, a pneumatic or hydraulic piston, an Acme-type screw or simple lever (none shown). 
         [0031]    In operation, each gear comprises a predetermined number of teeth. Each gear may have any number of teeth as known in the art as required by a user. In the instant embodiment ring  100  has 107 teeth. Compound pinion  200  has two gear teeth profiles. Gear  201  has 13 teeth that mesh with ring  100  and gear  202  has 17 teeth that mesh with ring  500 . Ring  500  has 111 teeth. 
         [0032]    If ring  100  is rotated at 1,000 RPM and carrier  300  is held fixed (no rotation) by brake  400  then ring  500  will spin at 1,260 RPM. The speed of ring  500  can be decreased by allowing carrier  300  to slip by partially releasing brake  400 . For example, to achieve 10% slip at ring  500 , carrier  300  must be slipped so that carrier  300  spins at 485 RPM. The change in speed at ring  500  and ring carrier  501  is 126 RPM, but the increase in speed of carrier  300  allowed by the 10% slip means a lower torque must be managed by brake  400  making it possible to have a smaller applied force to the braking mechanism. 
         [0033]      FIG. 4  is an exploded view of the embodiment in  FIG. 3 . In this embodiment, three compound pinions  200  are journalled to carrier  300 . Band brake  400  is disposed radially outwardly of carrier  300 . This arrangement allows the transmission to have a thin profile thickness T, allowing use in confined areas. 
         [0034]    The inventive device makes speed control simple and precise. The control system can monitor the speed and/or torque at the output and at the reaction member enabling the slipping element to constantly be varied to enable a constant speed at the output. 
         [0035]    There are several methods that can be used to measure the torque of the slipping or braked element. Some examples of torque measurement are load cells and the use of an elastic element such as torsion or compression springs. The elastic element has a known spring rate which can be used with a measured angular or linear displacement to measure torque. 
         [0036]    Although forms of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.