Abstract:
A method of controlling the speed of the output of a V-belt drive having an output driven pulley driven by a V-belt from an input driver pulley wherein the rotational speed of the driver pulley is determined, the ratio of the effective belt drive diameters of the driver and driven pulleys are determined and the effective belt to drive diameter of at least one of the pulleys is adjusted to provide a preselected speed of the drive output.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to V-Belt drives and more particularly to a method of controlling the speed of a driven shaft not withstanding variations in the speed of a driver shaft. 
     2. Description of Background Art 
     A V-Belt power transmission drive including a driver pulley, a driven pulley and a V-belt interconnecting the pulleys is a common method of transmitting torque from a prime mover to a load. While the angular velocity i.e., rotational speed, of the driven pulley is normally not equal to the rotational speed of the driver pulley, as determined by the ratio of the circumference of the driven pulley to the circumference of the driver pulley, the speed of the driven pulley is normally directly proportional to the speed of the drive pulley. 
     One use of such V-belt drives is in driving the generator of a vehicle. Such generators conventionally have optimal operating speeds. The generator is driven from the automobile engine, the speed of which varies, so that the speed of the generator correspondingly varies. 
     Therefore, in such operation of the vehicle, the generator may not be operating at the optimal speed at all times and must be designed to operate over a wide range of driven speeds. 
     In other applications incorporating V-belt transmissions, the prime mover has a speed-versus-torque relationship different from the speed-versus-torque relationship of the load. Where the speed of the load is caused to be directly proportional to the speed of the prime mover, the prime mover must be sufficiently oversized to permit the torque output of the prime mover at any speed to satisfy the torque requirement of the load at the operating speed thereof. Such oversizing is undesirable for economic concerns, space requirements, ease of maintenance, etc. 
     SUMMARY OF THE INVENTION 
     The present invention comprehends a method of controlling the speed of rotation of a load driven by a drive system including a driver pulley, a driven pulley and a V-belt engaged therebetween. 
     In the illustrated embodiment, one or both of the pulleys comprises a variable diameter pulley and include illustratively a movable pulley piece movable with respect to a stationary pulley piece. As the movable pulley piece is adjusted in relation to the stationary pulley piece, the effective diameter of the variable diameter pulley changes, thereby changing the ratio between the driver pulley and the driven pulley. 
     In the illustrated embodiment, the engine is directly connected to the driver pulley. The driven pulley is directly connected to a load, an automotive generator having a preselected speed-versus-torque relationship. A V-belt interconnects the driver pulley to the driven pulley. 
     The rotational speed of the driver pulley is sensed and a corresponding speed signal is generated. The position of the movable pulley piece of the variable diameter pulley is adjusted in accordance with the speed signal, thereby modulating the effective diameter of the variable diameter pulley in accordance with the load requirements. The invention comprehends an improved method of controlling this function. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will be apparent from the following description taken in connection with the drawings, wherein: 
     FIG. 1 is a graph illustrating the relationship between the rotational speed of the driver pulley and the driven pulley, for both a conventional V-belt power transmission drive and a V-belt power transmission drive incorporating the present invention; 
     FIG. 2 is a graph illustrating the relationship between the rotational speed of a generator and the operating efficiency of the generator; 
     FIG. 3 is a schematic perspective view of a drive system embodying the present invention; 
     FIG. 4 is a diametric section taken substantially along the line 4--4 of FIG. 3 illustrating the variable diameter driver pulley; 
     FIG. 5 is a schematic perspective view similar to that of FIG. 2, but illustrating a drive system utilizing a different method of sensing the driver pulley speed; 
     FIG. 6 is a schematic diagram of the electric control utilized in the prevent invention; 
     FIG. 7 is a schematic diagram illustrating another electric control system useful in practicing the invention; 
     FIG. 8 is a schematic diagram illustrating still another electric control system useful in practicing the invention; and, 
     FIG. 9 is a schematic diagram illustrating yet another electric control system useful in practicing the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A V-belt power transmission drive 15 includes a driver pulley 18 connected to a prime mover engine 16, a load or driven pulley 20 connected to a rotating load 21 and a V-belt 22 engaged therebetween. 
     FIG. 1 compares the relationship between the angular velocity, or rotational speed N d  of the driver pulley 18, versus the ratio of the driven pulley speed N L  to the driver pulley speed N d  for a V-belt power transmission drive, embodying the invention with the prior art V-belt drives. 
     A first curve 10 illustrates the relationship between the driver pulley speed (N d ) and the ratio of driven pulley speed to drive pulley speed (N L  /N d ) for a conventional V-belt power transmission drive. For any driver pulley speed (N d ), the ratio of driven pulley speed to driver pulley speed, (N L  /N d ) remains constant. Thus, as N d  increases, N L  increases proportionately. 
     A second curve 12, including segments a, b, and c, illustrates the relationship between the drive pulley speed (N d ) and the ratio of driven pulley speed to driver pulley speed (N L  /N d ) for a V-belt power transmission drive incorporating the present invention. Segment &#34;a&#34; of curve 12 illustrates the speed wherein the ratio of driven pulley speed to driver pulley speed decreases linearly as the driver pulley speed increases, i.e., the driven pulley speed remains constant over this range of driver pulley speeds. 
     The segments &#34;b&#34; and &#34;c&#34; of the second curve 12 illustrate the ranges of driver pulley speeds beyond the maximum limits of adjustment of the driver pulley diameter. 
     FIG. 2, illustrates the relationship between the speed of a typical automotive generator and the operating efficiency thereof. As indicated at a point E in FIG. 2, there exists an optimum speed for operation of the generator. 
     FIG. 3 illustrates a power transmission drive for carrying out the method of the present invention. As shown, V-belt drive 15 includes motor 16 having an output shaft 23 and variable diameter driver pulley 18 including a movable pulley piece 19a, and a stationary pulley piece 19b connected to output shaft 23 . Driven pulley 20 is connected to rotating load 21 and V-belt 22 is engaged between driver pulley 18 and driven pulley 20. 
     A magnetic pickup 26, coupled to a controller 28, senses the successive juxtaposition of projections 30a of a gear 30, driven with pulley piece 19b for generating a speed signal representing the rotational speed of driver pulley 18. 
     A servo motor 34 electrically coupled to the controller 28 includes a shaft 29 supported by a bearing 30 and connected to a lever arm 36 connected to movable pulley piece 19a. A position sensor 38, discussed further below, is mechanically connected to shaft 29. Position sensor 38 is electrically coupled to controller 28, to generate a signal representative of the angular position of lever arm 36 about the axis of shaft 29, and thus representative of the position of movable pulley piece 19a. 
     As motor 16 rotates driver pulley 18, V-belt 22 causes driven pulley 20 to rotate. The speed of the driver pulley 18 is sensed by magnetic pickup 26. Controller 28 in response to the speed signal, provides an output signal to servo motor 34 causing servo motor 34 to be repositioned. The repositioning of servo motor 34 rotates lever arm 36, thereby moving movable pulley piece 19a axially with respect to stationary pulley piece 19b as seen in FIG. 4. 
     A spring 40 is provided coaxially on a hub portion 42 of fixed pulley piece 19band is compressed between the movable pulley piece 19a and a spring retainer 44 fixed to hub portion 42. A U-section guide ring 48 is mounted through a bearing 50 on the outer periphery of hub portion 42 of movable pulley piece 19a. A slide portion 36a of lever arm 36 is received in the guide ring 48. 
     Selective positioning of lever arm 36 moves movable pulley piece 19a axially of hub portion 42, thereby correspondingly increasing or decreasing the space between movable pulley piece 19a and stationary pulley piece 19b. 
     For example, when movable pulley piece 19a is moved axially away from the stationary pulley piece 19b, V-belt 22 moves radially inwardly relative to hub portion 42 to decrease the effective diameter of driver pulley 18. 
     Correspondingly, when movable pulley piece 19a is moved axially towards stationary pulley piece 19b the V-belt 22 moves radially outwardly relative to hub portion 42 thereby increasing the effective diameter of drive pulley 18. 
     Such change in the effective diameter of drive pulley 18 correspondingly changes the ratio of driver pulley diameter to load pulley diameter. 
     As seen in FIG. 5, a tachometer 26b is connected to drive pulley 18 by a belt 52 and pulleys 54 and 56. Tachometer 26b is electrically coupled to controller 28 and provides an alternate method of sensing the rotational speed of the driver pulley 18. 
     FIG. 6 illustrates a method of controlling the rotation of the V-belt power transmission device embodying the present invention. 
     The speed signal indicating the rotational speed of driver pulley 18 is provided by sensor 26 to controller 28 including a rotary amplifier 58, a summing junction 59 and a servoamplifier 60. 
     A position sensor 38a includes a potentiometer 61, a voltage source 62 and a sliding contact 63 mechanically connected to lever arm 36 (FIG. 3) and electrically coupled to summing junction 59. 
     Summing junction 59 generates an error signal which is amplified by servoamplifier 60. Servomotor 34 responds to the amplified error signal generated by servoamplifier 60, thereby causing servomotor 34 to rotate and varying the effective diameter of driver pulley 18. 
     A change in the rotational speed of motor 16 causes a change in the rotational speed of drive pulley 18, the change being sensed by sensor 26. An amplified error signal, generated by controller 28, causes servomotor 34 to rotate, thereby varying the effective diameter of drive pulley 18. 
     Thus, the ratio of driven pulley diameter to driver pulley diameter and, correspondingly load pulley speed to driver pulley speed is modified as a function of driver pulley speed in accordance with a desired parameter. The parameter for the particular application may comprise an operating curve for example, established by the resistance characteristics of potentiometer 61. 
     An alternate method of sensing the angular position of lever arm 36 is illustrated in FIG. 7. A position sensor 38b includes a magnetic core 70 mechanically connected to lever arm 36 and slidably movable through primary and secondary windings 72a and 72b of a differential transformer 72. Differential transformer 72 generates an output signal correspondingly to the position of core 70 magnetically interconnecting primary and secondary windings 72a and 72b. Thus the output signal of differential transformer 72 is directly proportional to the position of lever arm 36 and hence, the effective diameter of driver pulley 18. 
     FIG. 8 illustrates still another alternate method of sensing the angular position of lever arm 36. A position sensor 38c includes a magnetic sensor 75 having magnetized metal plate 76 connected to lever arm 36. A signal generated by magnetic sensor 75 is proportional to the position of magnetized metal plates 76 in respect to the secondary windings of the magnetic sensor 75. 
     FIG. 9 illustrates yet another method of sensing the position of lever arm 36. A variable capacitor 77 includes a movable plate 78 mechanically coupled to lever arm 36. An oscillator 79, includes an amplifier 80 coupling capacitator 77 to a voltage converter 81 to generate a voltage having a frequency determined by the capacitance of variable capacitor 77. A position sensor 38d comprising oscillator 79 and voltage converter 81 generates a voltage representative to the rotational position of lever arm 36. 
     The foregoing disclosure of specific embodiments is illustrative of the broad inventive concepts comprehended by the invention.