Abstract:
This disclosure generally includes description of a secondary driven clutch system for a continuously variable transmission. The secondary driven clutch system may be coupled adjacent a shaft that is rotatable about a longitudinal axis. The system may include a movable sheave including a slot, where the movable sheave may be movable closer to or further from a stationary sheave along the longitudinal axis. The slot may be generally at an angle from the longitudinal axis and configured to reduce the longitudinal force needed to move the moveable sheave along the shaft along the longitudinal axis, as compared to a slot generally parallel to the longitudinal axis.

Description:
BACKGROUND 
       [0001]    This disclosure relates generally to clutch for a continuous variable transmission (CVT) more particularly to the driven clutch of a CVT, and specifically to a system for reducing the amount of force needed to control the driven clutch an electronic CVT (eCVT). 
         [0002]    Split sheave, belt-driven, continuously variable transmissions (CVT&#39;s) are used in a variety of recreational type off-road vehicles such as snowmobiles, golf carts, all-terrain vehicles (ATV&#39;s), and the like. CVT&#39;s, as their name implies, do not require shifting through a series of forward gears, but rather provide a continuously variable ratio that automatically adjusts as the vehicle speeds up or slows down, thus providing relatively easy operation for the rider. 
         [0003]    A typical CVT transmission is made up of a split sheave primary drive clutch connected to the output of the vehicle engine (often the crankshaft) and split sheave secondary driven clutch connected (often through additional drive train linkages) to the vehicle axle. An endless, flexible, generally V-shaped drive belt is disposed about the clutches. Each of the clutches has a pair of complementary sheaves, one of the sheaves being movable with respect to the other. The effective gear ratio of the transmission is determined by the positions of the movable sheaves in each of the clutches. The primary drive clutch has its sheaves normally biased apart (e.g., by a coil spring), so that when the engine is at idle speeds, the drive belt does not effectively engage the sheaves, thereby conveying essentially no driving force to the secondary driven clutch. The secondary driven clutch has its sheaves normally biased together (e.g., by a torsion spring working in combination with a helix-type cam, as described below, so that when the engine is at idle speeds the drive belt rides near the outer perimeter of the driven clutch sheaves. 
         [0004]    The spacing of the sheaves in the primary drive clutch usually may be controlled by centrifugal flyweights. Centrifugal flyweights are typically connected to the engine shaft so that they rotate along with the engine shaft. As the engine shaft rotates faster (in response to increased engine speed) the flyweights also rotate faster and pivot outwardly, urging the movable sheave toward the stationary sheave. The more outwardly the flyweights pivot, the more the moveable sheave is moved toward the stationary sheave. This pinches the drive belt, causing the belt to begin rotating with the drive clutch, the belt in turn causing the driven clutch to begin to rotate. Further movement of the drive clutch&#39;s movable sheave toward the stationary sheave forces the belt to climb outwardly on the drive clutch sheaves, increasing the effective diameter of the drive belt path around the drive clutch. Thus, the spacing of the sheaves in the drive clutch changes based on engine speed. The drive clutch therefore can be said to be speed sensitive. 
         [0005]    As the sheaves of the drive clutch pinch the drive belt and force the belt to climb outwardly on the drive clutch sheaves, the belt (not being relatively stretchable) is pulled inwardly between the sheaves of the driven clutch, decreasing the effective diameter of the drive belt path around the driven clutch. This movement of the belt outwardly and inwardly on the drive and driven clutches, respectively, smoothly changes the effective gear ratio of the transmission in variable increments. 
         [0006]    Split-sheave, belt driven CVTs are typically purely mechanical devices, that is, the mechanical parameters are established when the CVT is assembled. Once the CVT is assembled, the gear ratio depends on these set mechanical parameters. For example, the gear ratio depends on the distance between the drive clutch sheaves. The distance between the drive clutch sheaves is determined by the amount of force produced by the flyweights against the movable sheave. As the flyweights are attached to the engine shaft, the amount of the flyweight force depends on the speed of rotation of the engine shaft. Thus, with these prior devices, it is difficult to modify the gear ratio without disassembling the CVT and readjusting the mechanical parameters. 
         [0007]    Conversely, electronic CVTs control the distance between the sheaves in controlled electrically and electronically via stepper motors, gear and sprocket drives, and the like. The motor may force the sheaves together to control the distance of the belt from the shaft, thus controlling the ratio and speed. This offers advantageous of flexibility of design and control. 
         [0008]    As noted above, the secondary driven clutch sheaves may be held apart via a spring, or other biasing device. A certain amount of force is needed to overcome the biasing force to move the driven sheaves together. The size, or biasing force, of the spring, and the size of the motor are considerations when designing a secondary driven eCVT clutch system. What is needed is a system for reducing the amount of energy needed to control a secondary driven eCVT clutch. 
       SUMMARY 
       [0009]    The present disclosure is directed to systems and methods which provide relatively lower power and motor size to control a secondary driven eCVT clutch. The moveable sheave in the clutch system may include a generally angled slot, which guide rollers reside in to impart force on the sheave. The sheave may be coupled to a position system, which may be driven by a motor, to move the moveable sheave with respect to a non-moveable sheave. The angular slot may reduce the amount of longitudinal force required to move the moveable sheave. This may decrease the power and size of the motor needed to control the movement of the moveable sheave, when compared to a sheave with a generally longitudinal slot. 
         [0010]    The foregoing has outlined rather broadly the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure as set forth in the appended claims. The novel features which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The accompanying drawings, which are incorporated in and form part of the specification in which like numerals designate like parts, illustrate embodiments of the present disclosure and together with the description, serve to explain the principles of the disclosure. In the drawings: 
           [0012]      FIG. 1  is plan view of a CVT system according to an embodiment of the disclosure. 
           [0013]      FIG. 2  is plan view of a driven eCVT clutch system according to an embodiment. 
           [0014]      FIG. 3  is plan view of a driven eCVT clutch system according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  shows a plan view of a CVT system  100 . System  100  may include a primary drive pulley  110 , a secondary driven pulley  120 , and a belt  130 . Each of primary drive pulley  110  and secondary driven pulley  120  may include a fixed or stationary sheave (not shown) and a moveable sheave (not shown). The moveable sheave may be moved with respect to the stationary sheave to allow belt  130  to move within the pulleys  110 ,  120 . This may change the distance of belt  130  with respect to the drive  112  and driven shafts  122 , thereby changing an effective gear ratio, which in turn changes the speed of driven shaft. Typically drive shaft  112  is coupled to the shaft of a motor, and runs at a generally constant speed, once the motor ramps up to speed. 
         [0016]    Primary drive pulley  110  may be mounted and/or generally coupled to drive shaft  112 . Similarly, a secondary driven pulley  120  may be coupled to a driven shaft  122 . This may be accomplished via many known methods and systems. Any method or system of coupling capable of being used for this purpose may be used. This disclosure is not limited by the method or system of coupling of the pulleys to the respective shafts. 
         [0017]    As shown, if the moveable sheave of the primary drive pulley  110  is moved away from the stationary sheave, belt  130 A would ride further down in primary drive pulley  110 . This would cause the speed of driven shaft  122  to generally decrease. If the moveable sheave of secondary driven pulley  122  is moved away from the stationary sheave, this would cause the belt  130 A to ride lower in the driven pulley  120 , which would cause the rotational speed of driven shaft  122  to generally increase (if the primary drive shaft  112  speed was held constant). In this manner, the ration of speed of the relatively constant rotational speed of the drive shaft  112  and the driven shaft  122  can be constantly varied and controlled. 
         [0018]      FIG. 2  shows a secondary driven clutch system  200  according to an embodiment. System  200  may include a stationary sheave  202 , a moveable sheave  210 , a driven shaft  204  and a belt  206 . Moveable sheave  210  may be moved with respect to stationary sheave  202 , which causes belt  206  to move toward and away from shaft  204 . This would cause the ration of rotational speed of the drive shaft (not shown) to driven shaft  204  to change, and thereby change the speed of the vehicle this system  200  is a part of. 
         [0019]    Moveable sheave  210  may include one or more slot(s)  212 . Within slot  212  may be roller(s)  220 . Moveable sheave  210  may be coupled to a position motor (not shown), which may be controlled to control the position of moveable sheave  210  with respect to stationary sheave  202 . The position motor may be couples to the rollers in any manner which may be operable to impart force upon moveable sheave  210 . It will be appreciated that this may be accomplished with many configurations, and the scope of this disclosure is not limited by the configuration, system and/or method of coupling a positional motor to moveable sheave  210 . 
         [0020]    Through roller(s)  220 , force may be transmitted to moveable sheave  210  from the position system, which includes position motor. The relative movement of moveable sheave  210  with respect to stationary sheave  202  may be determined by the shape of slot(s)  212 . In the embodiment shown in  FIG. 2 , the shape of slot(s)  212  is generally helical, with a helix angle HA of about 20 degrees as measured from longitudinal axis  230 . Longitudinal axis  230  is generally parallel to driven shaft  204 . HA may be in the range of about 5-50 degrees. 
         [0021]    The force imparted upon moveable sheave  210  by the position system may be generally represented by a radial force RF generated by belt  206 , and is transformed by the shape of slot(s)  212  to a normal force NF, and axial force AF. Axial force AF pushes moveable sheave  210  toward stationary sheave  202 . The larger the helix angle of HA, the larger axial force AF, which may result in less power required from an electric positional motor (not shown) to move moveable sheave  210  toward stationary sheave  202 . The motor must also be sized with enough initial torque to start the movement of moveable sheave  210  toward stationary sheave  202 . However, the size, power, and cost of the positional motor may be reduced. 
         [0022]    Moveable sheave  210  may typically be biased away from stationary sheave  202  via a spring. The positional motor must be sized to overcome this biasing force. With the design of slot(s)  212 , the size, power, and/or cost, and/or combinations thereof, of the positional motor may be generally reduced then if slot(s)  212  were generally parallel to longitudinal axis  220 . 
         [0023]    The relative motion between moveable sheave  210  and stationary sheave  202  may be determined and/or defined by the configuration of slot  212 , which guides roller  220 . Helix angle HA of slot  212  aids in moving moveable sheave  210 , resulting lower initial torque and lower power requirements for positional motor. 
         [0024]      FIG. 3  shows a portion of drive system  300  used for moving a moveable sheave. System  300  may include a positional motor  302 , coupled to a position sprocket  304 , position belt  310 , sheave sprocket  306 , and a stationary sheave  308 . Position belt  310  may contact and generally encircle a portion of position sprocket  304  and sheave sprocket  306 . 
         [0025]    In an embodiment, position belt  310  may be a toothed-type belt or other belt suitable for use in this system. Belt  330  contacts sheave  308  in a manner described above to impart force upon the secondary driven clutch. 
         [0026]    In an embodiment, change of the position of the moveable sheave (not shown) may be accomplished in the following manner. Positional motor  302  may rotate sheave sprocket  306  via position belt  310  and positional sprocket  304 . This may cause moveable sheave to move because sheave sprocket  304  may be coupled (either directly or indirectly) to moveable sheave. Sheave sprocket  306  may be coupled to moveable sheave any suitable manner, including but not limited to, intertwined splines, worm or other gear, or any other manner suitable for this purpose. 
         [0027]    As movable sheave moves toward stationary sheave  308 , the distance R belt  330  is from the shaft may increase, thereby increasing the rotational speed of the secondary driven clutch. 
         [0028]    The relative motion between moveable sheave and stationary sheave  308  may be determined and/or defined by the configuration of slot  212 , which guides roller  220 . Helix angle HA of slot  212  aids in moving moveable sheave, resulting lower initial torque and lower power requirements for positional motor  302 . 
         [0029]    Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods, and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. The disclosure disclosed herein may suitably be practiced in the absence of any element that is not specifically disclosed herein.