Abstract:
A planetary transmission comprising an input member, an output member, a planetary gear assembly mechanically disposed between the input member and the output member, a centrifugal clutch mechanically disposed between the input member and the output member, a one-way clutch mechanically disposed between the input member and the output member, the one-way clutch for directly coupling the input member and the output member from zero rotational speed up to a first rotational speed, the centrifugal clutch for directly coupling the input member and the output member from a second rotational speed greater than zero rotational speed to a third rotational speed which is in excess of the first rotational speed, and a brake member for selectively controlling rotation of the planetary gear assembly.

Description:
FIELD OF THE INVENTION 
     The invention relates to a planetary transmission, and more particularly to a planetary transmission having a centrifugal clutch and a one-way clutch for selectively directly coupling an input member and an output member. 
     BACKGROUND OF THE INVENTION 
     Switchable planetary transmissions are intended to provide adequate speed to accessory assemblies, such as an air conditioner compressor, alternator, steering pump or any other kind of auxiliary at engine idling speeds without causing those assemblies to race out of specification at high engine speeds, which may cause damage. This makes it possible to guarantee the operation of the vehicle electrical system, steering system or AC system even if the accessory assembly size might be reduced. Reduced accessory speed at high engine revs leads to lower power losses giving higher maximum performance. 
     Representative of the art is U.S. Pat. No. 4,827,799 which discloses an infinitely variable planetary transmission is used in a vehicle, such as motorcycle and remote-control model car. The transmission includes a driven shaft journalled within the end bore of an input shaft. A sun gear is sleeved rigidly on the driven shaft. A planet gear carrier is sleeved rotatably on the driven shaft and serves as a power output member. A first centrifugal clutch is interposed between a ring gear and the input shaft so that, when the rotational speed of the input shaft is increased, the ring gear rotates synchronously with the input shaft. A set of planet gears are mounted rotatably on the carrier and meshed with the ring and sun gears. A second centrifugal clutch includes friction shoes mounted on the carrier, and a rim clutch sleeved rigidly on the driven shaft. A uni-directional bearing limits the driven shaft to rotate only in the same direction as the input shaft. When the input shaft rotates at a low speed, the sun gear is fixed by the limiting action of the unidirectional bearing so that the rotational speed ratio of the carrier to the input shaft is low. When the input shaft rotates at a high speed, the second centrifugal clutch interengages the carrier and the driven shaft so that the ring and sun gears rotate in the same direction, achieving a high rotational speed ratio of the carrier to the input shaft. 
     What is needed is a planetary transmission having a centrifugal clutch and a one-way clutch for selectively directly coupling an input member and an output member. The present invention meets this need. 
     SUMMARY OF THE INVENTION 
     The primary aspect of the invention is to provide a planetary transmission having a centrifugal clutch and a one-way clutch for selectively directly coupling an input member and an output member. 
     Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
     The invention comprises a planetary transmission comprising an input member, an output member, a planetary gear assembly mechanically disposed between the input member and the output member, a centrifugal clutch mechanically disposed between the input member and the output member, a one-way clutch mechanically disposed between the input member and the output member, the one-way clutch for directly coupling the input member and the output member from zero rotational speed up to a first rotational speed, the centrifugal clutch for directly coupling the input member and the output member from a second rotational speed greater than zero rotational speed to a third rotational speed which is in excess of the first rotational speed, and a brake member for selectively controlling rotation of the planetary gear assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG. 1  is a cross sectional view of the transmission. 
         FIG. 2  is a rear perspective view of the transmission. 
         FIG. 3  is a front perspective view of the centrifugal clutch. 
         FIG. 4  is a front elevation view of the centrifugal clutch. 
         FIG. 5  is section  5 - 5  from  FIG. 4 . 
         FIG. 6  is a cross sectional view of the roller clutch. 
         FIG. 7  is a detail of the roller clutch. 
         FIG. 8  is a chart showing transmission torque as a function of engine RPM. 
         FIG. 9  is an exploded perspective view. 
         FIG. 10  is a schematic of the control system for the transmission. 
         FIG. 11  is a perspective view of the transmission and the band brake. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a cross sectional view of the transmission. Transmission  100  is a compact unit which is installed on the end of an internal combustion engine crankshaft. 
     Transmission  100  comprises input member  13 . Input member  13  is connected to an engine crankshaft using a bolt  11 . Inertial member  12  is connected to input member  13 . 
     Input member  13  further comprises a carrier member  13   a . Input member  13 , inertial member  12  and carrier member  13   a  are connected to form an input assembly. Carrier member  13   a  is a portion of input member  13 . 
     Disposed about carrier member  13   a  is a plurality of planetary gears  14 . Each planetary gear  14  rotates about a spindle  15 . 
     Disposed radially outward from the carrier member  13   a  is ring gear  16 . Each planetary gear  14  engages ring gear  16  and sun gear  17 . 
     Ring gear  16  rotates about carrier member  13   a  on bearing  18  and upon output member  19  on bearing  20 . 
     Carrier member  13   a , planetary gears  14 , spindles  15 , and ring gear  16  comprise the planetary gear assembly. 
     Brake member band brake band  24  engages surface  25  of ring gear  16 . Band brake may comprise one known in the art. For example, the band brake disclosed in U.S. Pat. No. 4,881,453 which is incorporated herein by reference in its entirety. 
     Sun gear  17  is disposed on output member  19 . 
     Output member  19  comprises a belt bearing surface  21 . Belt bearing surface may have any required profile including multi-ribbed as shown. 
     One-way clutch  22  is disposed directly between input member  13  and output member  19 . This arrangement does not decouple carrier  13   a  from crankshaft (CRK) as is taught in the prior art. 
     Centrifugal clutch  40  is press fit onto input member  13 . Friction rim  41  engages an inner surface  191  of output member  19 . 
     Portions  27  and  28  prevent debris from entering the transmission, and also provide structural support. 
     The inventive transmission has two operating modes. The first is when the band brake is not engaged. The second is when the band brake is engaged. 
     First Operating Mode 
     In the first operating mode, a crankshaft (not shown) rotates input member  13 , and therefore carrier member  13   a . Inertial member  12  is slaved to the input member  13  and will not be further described. 
     Since the centrifugal clutch  40  is not engaged and the band brake is not engaged, ring gear  16  is free to rotate. 
     In this mode one-way clutch  22  is engaged, therefore causing output member  19  to rotate in unison with and at the same speed as input member  13 . 
     In this mode for engine speeds up to approximately 4300 RPM the output member is driven by the one-way clutch  22 . For speeds exceeding approximately 4300 RPM the centrifugal clutch is engaged with the output member  19  and the one-way clutch is disengaged due to the centripetal effects on the roller pins, see  FIG. 7 . 
     In the first operating mode the torque flow is from input member  13 , (and for speeds less than ˜4300 RPM) directly through one-way clutch  22  and then through output member  19  to a belt (not shown), (and for speeds greater than ˜4300 RPM) directly through the centrifugal clutch  40  and then through output member  19  to a belt. 
     Second Operating Mode 
     In the second operating mode band brake  24  is engaged. This prevents ring gear  16  from rotating. When ring gear  16  is locked, rotation of carrier member  13   a  causes each planetary gear  14  to rotate about each respective spindle  15 . Rotation of each planetary gear  14  causes sun gear  17  to be driven in the same rotational direction as the input member  13 , but at a greater speed having a ratio of approximately 2:1. Since sun gear  17  and output member  19  are being driven at a greater speed than input member  13 , one-way clutch  22  is overridden and disengages. 
     In the second operating mode the torque flow is from input member  13  (and thereby through carrier member  13   a ) through planetary gears  14 , through sun gear  17  to output carrier  19 . Since one-way clutch  22  and centrifugal clutch  40  are disengaged, there is no torque transmitted through one-way clutch  22  or centrifugal clutch  40 . 
       FIG. 2  is a rear perspective view of the transmission. Centrifugal clutch  40  is disposed between input member  13  and output member  19 . 
       FIG. 3  is a front perspective view of the centrifugal clutch. Clutch  40  comprises stretchable friction ring  41  and inner ring  42 . Disposed between friction ring  41  and inner ring  42  are weights  43  and frictional elements  44 . Inner ring  42  comprises a guide  420  for locating guiding and retaining weights  43  and elements  44 . 
     Friction ring  41  comprises a stretchable elastomeric material. For example, suitable materials may comprise EPDM rubber having a tensile modulus of approximately 30N to 50N at approximately 2% to approximately 4% elongation and with a coefficient of friction (COF) approximately 1.5 to approximately 3.0. This material would have a temperature performance range of approximately −45° C. to approximately 160° C. 
     Another suitable material comprises high temperature HNBR. In addition to providing the given modulus and COF of EPDM, HNBR also provides oil resistance and has a temperature range of approximately −25° C. to approximately +160° C. 
     High temperature urethane is the third available material. The urethane COF range is approximately 2.0 to approximately 3.0, while providing good oil resistance and temperature resistance equivalent to HNBR. 
       FIG. 4  is a front elevation view of the centrifugal clutch. Sides  441  and  442  of elements  44  comprise an angular offset from a radius R. Sides  431  and  432  of weights  43  comprise an angular relation α from a radius R. Sides  442  slidingly engage sides  431 . Sides  441  slidingly engage sides  432 . 
     The angular relation of sides  431 ,  432 ,  441 ,  442  assure that weights  43  and elements  44  remain in contact as weights  43  and elements  44  move radially outward as clutch  40  spins. 
     Inner ring  42  comprises radially projecting members  420 . Members  421  hold weights  43  and elements  44  in proper relation so that torque may be transmitted from inner ring  42 , to members  421  through elements  44  to the friction ring  41  and therefrom to output member  19 . 
     By way of example and not of limitation, each weight  43  weighs approximately 17 gm and each element  44  weighs approximately 7 gm. 
       FIG. 5  is section  5 - 5  from  FIG. 4 . Guide  420  radially projects from inner ring  42 . Each weight  43  and element  44  is engaged with guide  420  by a groove  433  (for weight  43 ) and groove  443  (for element  44 ). 
     In operation the centrifugal force generated by the mass of each weight  43  and element  44  forces each to move radially outwardly against the friction ring  41 . As the rotational speed increases the force exerted by each weight and element also increases. This increases the normal force exerted by the friction ring  41  on the inner surface  191  of output member  19 . The frictional force is the product of the normal force and the coefficient of friction. 
       FIG. 6  is a cross sectional view of the roller (one-way) clutch. Clutch  22  comprises an inner race  220 , an outer race  221 , a bearing  230  and bearing  231 . Bearings  230  and  231  are ball bearings. Inner race  220  is press fit on input member  13 . 
       FIG. 7  is a detail of the roller clutch. Clutch  22  comprises outer race  221 . Outer race  221  comprises tangs  224  which extend radially inward toward inner race  220 , but do not contact inner race  220 . Also included is an inclined surface  225 . Roller  222  is disposed between the inclined surface  225  and inner race  220 . A spring member  223  presses against roller  222  with a predetermined force. 
     Inclined surface  225  has a slight divergent angular separation from a tangent taken with relation to the inner race at the point where roller  22  contacts the inner race. This has the effect of establishing an acute angle between the inclined surface  225  and the tangent to the inner race. 
     In operation the convergent nature of inclined surface  225  and inner race  220  causes roller  222  to be locked or “trapped” therebetween, causing the inner race  220  and outer race  221  to rotate in locked fashion. When the inner race is rotated in the opposite direction, or, when the outer race is rotated faster than the inner race, the divergent nature of the inclined surface  225  and inner race causes rollers  222  to be disengaged, thereby prevent a transfer of torque between the inner and outer races.  FIG. 7  is a detail representing a plurality of such components in the one-way clutch  22 . 
     The torque capacity of the one-way clutch is approximately 200 N. The position of each roller is a function of its centrifugal force.
 
 F=mv   2   /r N  
 
     Where F is the centrifugal force
         m is the mass of the roller in kg   v is the tangential velocity in m/sec   r is the radius in meters   N is Newtons       

     At a predetermined speed, based upon the mass of each roller, the rotational speed of the clutch, and the spring rate of spring  223 , each roller will begin to move radially outwardly along the inclined surface. This will ultimately cause each roller to disengage from the inner race, thereby causing the inner race to disengage from the outer race. This stops all torque transmission between the inner race and the outer race. 
       FIG. 8  is a chart showing transmission torque as a function of engine RPM. The chart shows that at approximately 4300 RPM the one-way roller clutch  22  begins to disengage as described for  FIG. 7 . Simultaneously, the centrifugal clutch  40  begins to engage. At approximately 6000 RPM each roller  222  is fully disengaged, thereby disengaging the one-way clutch  22 . At the same time the centrifugal clutch  40  is developing greater amounts of frictional force between the friction ring  41  and inner surface  191 . As a result the centrifugal clutch is able to progressively increase the amount of torque transmitted from the input member  13  across clutch  40  to the output member  19 . 
       FIG. 9  is an exploded perspective view. 
       FIG. 10  is a schematic of the control system for the transmission. Vacuum actuator  201  is connected to a vehicle vacuum system  210 . Vacuum actuator is also connected to E3 controller  300 , known in the art. E3 controller  300  is connected to a vehicle battery  301 . 
     Speed sensor  302  provides an engine speed signal to the E3 controller. The E3 controller can be programmed to actuate the vacuum actuator  201  based upon predetermined engine speeds. For example, at engine idle the band brake is “ON” and therefore the vacuum actuator is “ON” and the band  24  is engaged with surface  25 . This stops rotation of ring gear  16 . This causes the output member  19  to rotate at a speed greater than the speed of input member  13 . This in turn causes the accessories to be driven at an appropriate speed at engine idle. Engine idle is typically ˜700 RPM to 900 RPM. The transmission ratio is typically in the range of approximately 2:1. 
     At speeds greater that ˜2000 RPM the vacuum actuator is “OFF” which allows ring gear  16  to rotate. The engine speed signal is from speed sensor  302 . Rotation of ring gear  16  causes output member  19  to rotate at the same speed as the input member  13 . However, due to the smaller radius of output member  19 , the accessories are driven at a normally slower speed, thereby reducing the amount of power normally required to run the accessories at higher engine speeds. The diameter of output member  19  is typically ˜90 mm. By comparison, the typical diameter of a crankshaft pulley is in the range of approximately 150 mm to 175 mm. 
       FIG. 11  is a perspective view of the transmission and the band brake. Band  24  of band brake  200  engages surface  25  of ring gear  16 . Band comprises friction material  24   a.    
     Band brake  200  is operated by a vacuum actuator  201 . Vacuum actuator  201  is connected to band  24  by linkage  202 . Linkage  202  is guided by guide member  203 . Guide member  203  restricts linkage  202  such that linkage  202  moves in a substantially linear direction along its major axis A-A. Band  24  is connected at a first pivot  204  to the base  206 . Band  24  is connected to a second pivot  205  on an end of linkage  202 . 
     Linear movement of linkage  202  causes second pivot  205  to tightly engage surface  25 . Without guide member  203  second pivot  205  can be pushed radially outward by surface  25  during operation, which in turn can diminish the effectiveness of the band brake. 
     Base  206  of band brake  200  is mounted to a mounting surface, such as an engine, using bolts  207 . 
     Vacuum actuator  201  is connected to a vehicle vacuum system and is controlled based upon the engine speed. 
     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 and method without departing from the spirit and scope of the invention described herein.