Abstract:
An electrically actuated continuously variable transmission with a first pulley having a first pulley portion for fixed connection to an engine shaft and an axially movable second pulley portion for placement about the engine shaft. An electric actuator coaxially coupled to the second pulley portion moves the second pulley portion with respect to the first pulley portion when the electric actuator moves the second pulley portion to change spacing between the first and second pulley portions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/567,468, filed May 3, 2004, which application is hereby incorporated by reference along with the application designated by Attorney Docket No. 13054-244, entitled Electrical Actuator for Continuously Variable Transmission, filed in the names of John M. Starkey, Enrico N. Manes, and Benjamin J. Rumley on May 2, 2005. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]     This invention relates generally to transmissions, and more particularly to methods and apparatus for actuation of continuously variable transmissions.  
       BACKGROUND OF THE INVENTION  
       [0003]     Transmissions are devices that transform the speed and torque in vehicles using gears, belts, or other drive components. Most transmission designs use discrete speed ratios: low ratios for acceleration, hill climbing, and heavy hauling, and high ratios for higher-speed travel. They use multiple parallel gear sets between input and output shafts. By changing which gear set carries the loads between the shafts, the speed ratio between the input and output shafts is altered.  
         [0004]     Transmissions have also been designed that are continuously variable (CVTs). These generally use friction to transfer load from an input shaft to an output shaft. By altering the radial position of friction rollers, belts, or other components, the speed ratio is changed.  
         [0005]     A typical CVT design  10  is shown in  FIGS. 1 and 2 . It uses a driving (primary) pulley  12 , a wide v-belt  14 , and a driven (secondary) pulley  16 . The speed ratio is adjusted by altering the width of the driving  12  and driven  16  pulleys, so that the v-belt  14  contacts at varying radii on the pulleys  12  and  16 .  FIG. 1  shows the CVT  10  operating at a lower speed ratio where the driven pulley halves  18  and  20  are separated and the v-belt  14  contacts the pulley halves  18  and  20  at a small radius. The driven pulley halves  18  and  20  are squeezed together by a spring under these conditions, forcing the belt  14  at the output end to contact at a large radius. This configuration offers maximum torque magnification and speed reduction.  FIG. 2  shows the CVT operating in a higher speed ratio where the pulley halves  22  and  24  of the driving pulley  12  are positioned close together, forcing the v-belt  14  to contact the pulley halves  22  and  24  at a larger radius and increasing the velocity of the v-belt  14 . The increased velocity of the v-belt  14  works against the spring force of the driven pulley  16 , forcing the driven pulley halves  18  and  20  apart where the v-belt  14  contacts the driven pulley halves  18  and  20  at a smaller radius. This configuration offer maximum speed magnification.  
         [0006]     Most current CVTs rely upon fixed-design mechanical or hydraulic actuation that cannot be easily changed to respond to differing demands, such as varying vehicle cargo loads and operator performance demands. Accordingly, there is need for a CVT actuation system that is more flexible and adaptable than the current state of technology.  
       SUMMARY OF THE INVENTION  
       [0007]     According to one aspect of the present invention, a coaxial electrical actuator is provided for a continuously variable transmission with first and second pulleys interconnected by a belt. The first pulley is connected to an engine shaft and has a first pulley portion and a second pulley portion axially movable with respect to the first pulley portion. An armature for connection about the engine shaft is adapted for threaded connection to one of the first or second pulley portions. A stator coil for positioning adjacent the armature causes rotation of the armature when energized so that rotation of the armature with respect to the pulley, in response to energization of the stator coil during use, changes the axial spacing between the first and second pulley portions.  
         [0008]     According to another aspect of the present invention, a method for electrically actuating a continuously variable transmission having first and second pulleys interconnected by a belt is provided. The first pulley is adapted for mounting on an engine shaft and has a first pulley portion and an axially movable second pulley portion. An armature is provided adjacent the engine shaft so as to normally rotate therewith and is rotatably coupled to the first or second pulley portion so as to move one pulley portion axially with respect to the other pulley portion in response to relative rotation between the armature and the pulley. A stator coil is provided adjacent the armature. Energizing the stator coil to cause the armature to rotate relative to the pulley changes the axial spacing between the first and second pulley portions.  
         [0009]     According to a further aspect of the present invention, an electrically actuated continuously variable transmission has a first pulley with a first pulley portion for fixed connection to an engine shaft and an axially movable second pulley portion for placement about the engine shaft. An electric actuator coaxially coupled to the second pulley portion moves the second pulley portion with respect to the first pulley portion when the electric actuator moves the second pulley portion to change the spacing between the first and second pulley portions.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of a continuously variable transmission of the prior art at a lower speed ratio.  
         [0011]      FIG. 2  is a perspective view of a continuously variable transmission of the prior art at a higher speed ratio.  
         [0012]      FIG. 3  is a cross-sectional view of an embodiment of a coaxially mounted electrical actuator in accordance with the present invention, in a lower speed ratio configuration.  
         [0013]      FIG. 4  is a cross-sectional view of the electrical actuator of  FIG. 3 , shown in a higher speed ratio configuration.  
         [0014]      FIG. 5  is a cross-sectional view of another embodiment of a coaxially mounted electrical actuator in accordance with of the present invention.  
         [0015]      FIG. 6  is a cross-sectional view of the electrical actuator of  FIG. 5 , shown in a higher speed ratio configuration.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0017]      FIGS. 3 and 4  show a pulley  26  and a coaxially mounted electrical actuator  28  for a continuously variable transmission (CVT) in accordance with one embodiment of the present invention. The pulley has a fixed pulley half or portion  30  and a movable pulley half or portion  32  interconnected by a belt  34 . The electrical actuator includes an armature  36  and a stator coil  38 . A cover  40  connected to the movable pulley half  32  protects the coaxially mounted electrical actuator.  
         [0018]     The fixed pulley half  30  is fixedly connected to the engine shaft  42 , such as with a key  44 , and has an externally threaded, preferably self-locking pitch, portion  46  and an armature stop  48 . The movable pulley half is positioned about the engine shaft, adjacent the fixed pulley half. Movement of the movable pulley half  32  is effected by movement of the armature  36 , which is connected to movable pulley half  32  by way of a thrust bearing  50 . During a shift operation of the transmission, the threaded portion  46  of the fixed pulley half  30  co-acts with rotation of the armature  36  to move the movable pulley half  32  with respect to the fixed pulley half  30  to change the speed ratio of the transmission. The armature stop  48  limits movement of the movable pulley half  32  with respect to the fixed pulley half  30 , setting the maximum low speed ratio of the transmission.  
         [0019]     The armature  36  shown in the  FIGS. 3 and 4  includes a nut mounted on the fixed pulley half  32  and normally spins at the same rate as the engine shaft  42 . The armature nut has an internally threaded, preferably self-locking pitch, portion  52  which mates with the threaded portion  46  of the fixed pulley half  30 . The armature  36  has a magnetized portion  54  and, together with stator  38 , forms an electric motor coaxially mounted on the engine shaft.  
         [0020]     The stator coil  38  is fixed to an external wall of the engine  56 . During a shift operation, it is selectively energized to create an alternating electrical field that acts upon the magnetized portion  54  of the armature  36 , causing it to rotate with respect to the threaded portion  46  of the fixed pulley half  30 . Such relative motion causes the movable pulley half  32  to move toward or away from the fixed pulley half  30 , depending upon the direction of rotation of the armature  36 . Movement of pulley half  32  toward fixed pulley half  30  decreases the spacing between the pulley halves, which forces the belt  34  toward the outer edge of the pulley, as shown in  FIG. 4 , effectively increasing the speed ratio of the transmission. Movement of pulley half  32  away from fixed pulley half  30  increases the spacing between the pulley halves and allows the belt to move toward the center of the pulley, as shown in  FIG. 3 , effectively decreasing the speed ratio of the transmission.  
         [0021]     Alternating electric current may be continuously supplied to the stator coil  38  during a shift operation to either slow down or speed up the rotation of the armature relative to the engine shaft and the fixed pulley. Alternatively, electric current may be supplied to the stator coil  38  in appropriately timed pulses to incrementally move the armature  36 , e.g., in stepwise fashion. When power is removed from the stator coil  38 , the movable pulley half  32  preferably remains stationary with respect to the fixed pulley half  30 , due in part to the self-locking thread connection between the threaded portion  46  and the armature nut  36 . This reduces power consumption of the coaxial electrical actuator  28 , as well as stator coil heating, because actuation of the stator coil  38  is only required when change of the speed ratio is desired.  
         [0022]     The CVT incorporating the present invention may be operated in open-loop fashion, e.g., by energizing the stator coil as a simple function of engine speed or, in certain embodiments, simply by means of suitable control switches connected to the stator coil. Alternatively, an electronic control system is provided which is responsive to engine speed and throttle position. Such an electronically controlled CVT may operate open-loop but preferably operates as a closed-loop control system responsive to feedback indicative of the actual state of the transmission, which may be measured, for example, in terms of the position of the movable pulley.  
         [0023]     In another embodiment of the present invention providing a coaxially mounted electrical actuator  128  for a pulley  126  of a continuously variable transmission, shown in  FIGS. 5 and 6 , the movable pulley half  132  has an externally threaded sleeve portion  133  that is in threaded communication with the internal threads  152  of the armature nut  136 . The two pulley halves  130  and  132  are splined together  135  to rotate at the same speed at all times, and to allow the engine shaft  142  to transmit its torque to both pulley halves  130  and  132 . The armature nut  136  is in communication with the fixed pulley half  130  by way of a thrust bearing  150  and normally spins with the rotation of the engine shaft  142 . Manipulation of the alternating electric field of the stator coil  138  so that the armature nut  136  spins faster or slower than the engine shaft  142  rotation will cause the movable pulley half  132  to move axially toward or away from the fixed pulley half  130 . Movement of the movable pulley half  132  forces the belt  134  to move toward the outer edges of the pulley halves  130  and  132 , as shown in  FIG. 5 , or toward the center of the pulley halves  130  and  132 , as shown in  FIG. 6 , altering the speed ratio of the transmission.  
         [0024]     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. For example, while a threaded connection is described above for the armature and the pulley, unthreaded connections are also contemplated. One such actuator comprises an electric solenoid, e.g., a three-position or other multi-position solenoid, mounted on an external wall of the engine with its longitudinal axis parallel to the engine shaft and with its plunger coupled to the movable pulley half so as to move the pulley half in response to an electrical signal.  
         [0025]     Another form of electric actuator may include an electromagnetic actuator as in a loudspeaker, e.g., with a magnetic collar about the engine shaft coupled to an electromagnetic coil fixed to the engine. The magnetic collar may, for example, be similar to the armature of  FIG. 3  but without threads (coupled to an unthreaded sleeve that is otherwise like threaded sleeve  46  on the fixed pulley of  FIG. 3 ), and the fixed electromagnetic coil may be similar to the stator of  FIG. 3 . Other forms of linear electric actuators are also contemplated, such as linear stepper motors.  
         [0026]     The electrical actuator of the present invention may also be used in other ways, such as, for example, a starter motor for an internal combustion engine. The armature may be moved toward the engine, effectively disengaging the movable pulley from the belt, and contacting the armature stop so as to apply torque directly to the engine shaft, turning the engine shaft for starting. The electrical actuator may also be used as a power source—as an auxiliary electric motor or in certain applications as the primary electric motor—in a hybrid vehicle of the type that uses an electric motor and internal combustion engine to power the vehicle. For example, the electric actuator may be sized to provide significant drive torque to the transmission pulley to augment the torque used to drive the vehicle.