Abstract:
The present invention provides a system and method for automatically adjusting a continuously variable transmission (CVT) in a motorized vehicle. A microprocessor processor in the vehicle receives data about the operating status of the vehicle from a plurality. Examples of vehicle data include vehicle speed, motor speed, throttle position, current draw from a battery, and battery level. A servo motor is in mechanical communication with the CVT and provides an axial force to adjust the CVT. The microprocessor uses lookup tables of optimal set points for vehicle data to instruct the servo motor to adjust the transmission ratio of the CVT according to the vehicle data provided by the sensors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of and priority to U.S. Provisional Patent Application No. 60/783,108 filed Mar. 14, 2006 the technical disclosures of which are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD OF INVENTION 
     The present invention relates generally to a continuously variable transmission (CVT) and specifically to a system and method for providing an automated adjustment to a CVT. 
     BACKGROUND OF THE INVENTION 
     A transmission is any mechanical linkage that converts an input torque to an output torque. It usually involves a series of gears that have differing diameters, allowing a first gear at a first rotation rate to link to a second gear rotating at a second rate. The most common application for transmissions is in a vehicle. For example, a car may have an automatic transmission or a manual transmission. A bicycle has a simple transmission that links the pedals to the hub of the rear wheel. 
     Transmissions allow an input force to be converted into a more useful and appropriate output. However, by using gears and linkages, a typical transmission may only have 4 or 5 ratios available. For example, a four speed automatic transmission in a car has only 4 sets of output gears to couple to the engine&#39;s input. A ten speed bike has only ten ratios of input to output. A need exists for a transmission that is not limited by the number of gears. Yet, to place a larger number of gears into a transmission increases its costs and weight and space requirements. 
     A continuously variable transmission (CVT) is a transmission that eliminates the need for a specified number of gears. Instead it allows an almost limitless number of input to output ratios. This is a benefit because it allows an output to be achieved (i.e. the speed of a vehicle) at an optimal input (i.e. the rpm of the engine). For example, an engine might be most efficient at 1800 rpm. In other words, the peak torque output for the engine might be achieved at this engine rpm, or perhaps the highest fuel economy. Consequently, it may be desirable to run at a specified RPM for an economy mode or a power mode. Yet, in third gear, the car might be going faster at 1800 ipm than the driver desires. A continuously variable transmission would allow an intermediate ratio to be achieved that allowed the optimal input to achieve the desired output. 
     CVT transmissions have a variator for continuously variable adjustment of the ratio. A customary structure is a belt drive variator having two pairs of beveled pulleys and rotating a torque-transmitter element therein, such as a pushing linked band or a chain. The beveled pulleys are loaded with pressure from the transmission oil pump in order, on one hand, to actuate the ratio adjustment and, on the other, to ensure a contact pressure needed for transmission of the torque upon the belt drive element. Another usual structure is a swash plate variator in semi-toroidal or fully toroidal design. 
     Examples of CVTs are exemplified by U.S. Pat. Nos. 6,419,608 and 7,011,600 assigned to Fallbrook Technologies of San Diego, Calif., the contents of which are hereby incorporated by reference. In each of those applications the axial movement of a rod or an axial force (as indicated by numeral 11 in each reference) is used to vary the input-to-output ratio of such transmissions. 
       FIG. 1  is a prior art schematic representation depicting the operation of manually controlled CVT or variator in a light electric vehicle, such as a scooter. As shown in  FIG. 1 , a manual push button control box  101  has buttons corresponding to a signal output  108  of 0%  102 , 25%  103 , 50%  104 , 75%  105 , and 100%  106  sent to a microprocessor  112 . The microprocessor output can be shown on a display  150 . The microprocessor  112  interfaces with a motor control board  114  which receives power from a battery pack  118 . 
     A servo motor  120  engages a 90-degree gearbox  122  which provides an axial force  130  to a variator (CVT)  132  in contact with the rear wheel  134 . The rear wheel  134  is powered by a chain  136  or other equivalent means connected to a drive motor  140  (e.g., Briggs &amp; Stratton ETEK). 
     The speed of the drive motor  140  is regulated by a current sent by a motor control device  144 . The motor control device  144  is regulated by a throttle  146  and is powered by the battery  118 . 
     While a user of the electric vehicle can manually shift gears using the push button control, it would be desirable to have an automatic shifting transmission to permit an electric scooter to operate in a power mode or an economy mode. Consequently, a need exists to automatically adjust the input to output ratio based upon one or more input variables. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system and method for automatically adjusting a continuously variable transmission (CVT) in a motorized vehicle, such as a battery powered scooter. A microprocessor processor in the vehicle receives data about the operating status of the vehicle from a plurality. Examples of vehicle data include vehicle speed, motor speed, throttle position, current draw from a battery, battery level, CVT setting, control settings of a motor control device, wind direction, wind speed, and tire pressure. A servo motor is in mechanical communication with the CVT and provides an axial force to adjust the CVT. The microprocessor uses lookup tables of optimal set points for vehicle data to instruct the servo motor to adjust the transmission ratio of the CVT according to the vehicle data provided by the sensors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a prior art schematic representation depicting the operation of a manually controlled variator in a light electric vehicle; 
         FIG. 2  is a schematic representation depicting the operation of automatically controlled variator in a light electric vehicle in accordance with one embodiment of the present invention; 
         FIG. 3A  is a schematic representation of the automatic operation of the shifter in accordance with one embodiment of the present invention; 
         FIG. 3B  is a schematic representation of the 90° gearbox in accordance with one embodiment of the present invention; 
         FIG. 4A  is a schematic representation of a linear actuator in accordance with an alternative embodiment of the present invention; 
         FIG. 4B  is a schematic representation of a servo motor mounted on the rear wheel in accordance with an alternate embodiment of the present invention; 
         FIG. 4C  is a schematic representation of an alternate servo motor design in accordance with another embodiment of the present invention; and 
         FIG. 4D  is a schematic representation of the servo motor in communication with a hub that contains the variator in accordance with another alternate embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  is a schematic representation depicting the operation of an automatically controlled variator in a light electric vehicle in accordance with one embodiment of the present invention. Instead of a push button control box  101  to manually control the transmission ratio of a CVT as shown in  FIG. 1 , the present invention uses one or more automatically-generated variables to automatically adjust the variator (CVT). 
     The amount of current being drawn from the motor control device  144 , as provided by sensor  244 , comprises an automatically generated variable that can be used as an input signal to the microprocessor  112 . Motor controllers such as those available from Altrax of Grants Pass, OR can be used. Motor current draw is a function of throttle position and the state of the vehicle. For example:
         Full throttle at 0 mph=full current draw   Full throttle at 35 mph down a hill=low current draw       

     Another automatically generated variable supplied to the microprocessor  112  is the speed of the scooter, which is provided by a speed sensor  236  mounted on the front wheel  136 . In the preferred embodiment, multiple magnets (e.g., 16) are mounted around the rim of the front wheel  136 . All of the magnet poles are arranged in the same direction. The front wheel sensor  236  is mounted in a bracket from the wheel axel and wired into microprocessor  112 . The microprocessor  112  counts a pulse when a magnet passes the sensor  236 . The number of pulses in a given time period denotes the speed of the wheel, which is used to extrapolate the speed of the vehicle. This input is used in the calculation of optimized shifting to set a ratio in the variator  132 . 
     Motor speed data provided by sensor  240  is another automatic variable that might be fed to the microprocessor  112 . The motor speed sensor  240  operates on the same principle as the front wheel sensor  236 . The signal provided by the sensor  240  gives a motor RPM value, which can be used to verify the transmission ratio using the following calculation:
 
Motor RPM/fixed gear reduction/variator gear reduction
 
     The variator gear reduction is derived from the front wheel speed sensor  236  and can be used to validate vehicle speed or transmission ratio to the “set ratio” of the control system. 
     Other examples of automatically generated variables include, but are not limited to:
         Position of the throttle   Current draw from the battery   Variator setting   Battery level   Control settings of the motor control device (e.g., linear or s-curve),   Wind Direction   Wind speed   Tire pressure       

     External data may also be provided to the microprocessor via a blue tooth antenna  260 . 
     The twist throttle  146  gives the motor controller  144  an input signal from the rider. Based on the amount the throttle  146  is twisted, it increases a resistance value to the main motor controller  144 , which then translates this resistance value into voltage and current supplied to the drive motor  140 . In the preferred embodiment the throttle is rated for 0-5 k resistance. 
       FIG. 3A  is a schematic representation of the automatic operation of the shifter in accordance with one embodiment of the present invention. In one embodiment, the microprocessor  112  comprises a basic stamp board available from Parallax, Inc. of Rocklin, Calif. The microprocessor  112  can be programmed to generate lookup tables to provide optimum set points for variable inputs (described above) to obtain either the best performance or optimal efficiency of the scooter system. 
     In the example depicted in  FIG. 3A , the microprocessor  112  receives data from the front wheel speed sensor  236  and current draw sensor  244 . The microprocessor  112  then outputs a signal to the servo  120 , which in turn provides an axial force to the variator  332  to shift in an optimal manner that minimizes current draw  244  or power drain so as to provide optimal efficiency. The data sampling speed and servo adjustment speed are adjusted to minimize power drain on the system that would otherwise cancel the efficiency gains. 
     As shown in  FIG. 2 , microprocessor output can be shown on a display  150 . This is an “on board” display of inputs and outputs that allows the user to verify settings and measurements during the testing phase. Examples of display readouts include:
         Wheel count   Current amps   Voltage in (current sensor for motor)   Motor RPM   Wheel RPM   Mile per hour (MPH)       

       FIG. 3B  is a schematic representation of the 90° gearbox in accordance with one embodiment of the present invention. The gearbox  322  comprises a servo  320  mounted with bolts  310  to the scooter frame (not shown). A coupler  323  is disposed between a threaded (worm) shaft  324  and the servo  320 . Upon rotation of the threaded shaft  324 , the wheel  326  rotates as depicted by numeral  328 , causing the shift shaft  330  to rotate. Such rotation of the shift shaft  330  is converted into an axial force. 
     The 90° gearbox setup is used to provide a mechanical advantage (i.e. 36:1) and to reduce the size of the protrusion from the side of the scooter. 
     When the system is turned on the servo motor  320  is driven towards home until the shift shaft  330  contacts the home sensor  250  (shown in  FIG. 2 ). The servo is stopped and the microprocessor  112  sets the internal electronic home position, registering voltage, turns, and rotation direction. In response to inputs from the sensors, based on the last known servo position a comparison is made between the current position and the “called” position. The microprocessor  112  then drives the servo  320  to the “called” position. 
       FIG. 4A  is a simplified schematic representation of a linear actuator in accordance with an alternative embodiment of the present invention. This embodiment uses a rack and pinion setup and can be mounted up inside of the scooter. The end  416  of the threaded shaft  424  is adapted to couple between a first tooth-like member  412  and a second tooth-like member  414 . As the servo motor rotates the shaft end  416 , the first tooth-like member  412  is driven axially and thereby provides an axial force to a member  410  that is in communication with the tooth-like member  412  and a variator (not shown). 
       FIG. 4B  is a schematic representation of a servo motor mounted on the rear wheel in accordance with an alternate embodiment of the present invention. The servo motor  420  is connected to a shaft  430  having a threaded portion  424  adapted to couple with a threaded variator shaft (not shown). The internal threaded portion  424  allows space for the variator shaft to be pulled in and out. The servo motor  420  turns the shaft  430  thereby causing the threaded portion  424  to move the variator shaft in or out, thus adjusting the variator. 
       FIG. 4C  is a schematic representation of an alternate servo motor design in accordance with another embodiment of the present invention. Like the embodiment depicted in  FIG. 4B , the servo motor  420  in this embodiment is also mounted at the rear wheel of the scooter. However, in this embodiment, the servo motor  420  is connected to a shaft  430  having a splined portion  425  adapted to couple with a variator shaft (not shown). The servo motor  420  turns the splined shaft  430 , thereby creating an axial force on the variator shaft, thus adjusting the variator. 
       FIG. 4D  is a schematic representation of the servo motor in communication with a hub that contains the variator in accordance with another alternate embodiment of the present invention. In this embodiment, a hub  1102  containing the variator is mounted at the rear wheel of the scooter (not shown), and the servo motor is mounted up in the scooter. The rear hub  1102  includes a housing having an axial force that encloses and protects a pulley system coupled to cables  1012  and  1014 . These cables  1012 ,  1014  in turn are connected to the servo motor  420 , which alternately pulls cable  1012  or cable  1014  in order to adjust the variator inside the hub  1102 . 
     The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.