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A system for enhanced ratio control in a continuously variable transmission (CVT) includes a ratio control element positionable by an actuator in response to an actuator command to establish various CVT ratios in the CVT. At least one sensor generates a train of pulses indicative of speed of rotatio

A system for enhanced ratio control in a continuously variable transmission (CVT) includes a ratio control element positionable by an actuator in response to an actuator command to establish various CVT ratios in the CVT. At least one sensor generates a train of pulses indicative of speed of rotation of a predetermined rotary member of the CVT. A measured CVT ratio generator derives information of an actual CVT ratio out of at least the train of pulses to give a measured value of CVT ratio. A filter processes the measured value of CVT ratio in a manner to refine the information of the actual CVT ratio to give an estimated value of CVT ratio. A command generator determines the actuator command such that the actuator command remains unaltered when a deviation of the estimated value of CVT ratio from a desired value of CVT ratio stays within a dead zone. A filter and command generator manager narrows the dead zone to meet precision requirement upon determination that the desired value of CVT ratio has been accomplished and adjusts filter gain at the filter in a manner to keep amplitude at frequency of noise that is contained in the measured value of CVT ratio within the narrowed dead zone.

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1. A system for enhanced ratio control in a continuously variable transmission (CVT) including a ratio control element positionable by an actuator in response to an actuator command to establish various CVT ratios in the CVT, the system comprising:a measured CVT ratio generator obtaining information

1. A system for enhanced ratio control in a continuously variable transmission (CVT) including a ratio control element positionable by an actuator in response to an actuator command to establish various CVT ratios in the CVT, the system comprising:a measured CVT ratio generator obtaining information of an actual CVT ratio established in the CVT to give a measured value of CVT ratio; a filter processing the measured value of CVT ratio in a manner to refine the information of the actual CVT ratio to give an estimated value of CVT ratio; a command generator determining the actuator command such that the actuator command remains unaltered when a deviation of the estimated value of CVT ratio from a desired value of CVT ratio stays within a dead zone; and a filter and command generator manager narrowing the dead zone to meet precision requirement upon determination that the desired value of CVT ratio has been accomplished and adjusting the filter to gain requirement for keeping the magnitude of signal at frequency of noise within the narrowed dead zone. 2. The system as claimed in claim 1, further comprising:a noise estimator determining amplitude and frequency of noise contained in the measured value of CVT ratio, and wherein the filter and command generator manager determines the filter gain based on the estimated amplitude at the estimated frequency of noise and the dead zone. 3. The system as claimed in claim 2, further comprising a desired CVT ratio generator generating the desired value of CVT ratio in response to a vehicle speed indicative of speed of rotation of an output member of the CVT and operator torque demand.4. The system as claimed in claim 3, wherein, upon determination that the desired value of CVT ratio has been accomplished when the precision requirement is present, the filter and command generator manager provides the narrowed dead zone, which is narrower than dead zone provided upon determination that the desired value of CVT ratio has been accomplished when the precision requirement is absent.5. The system as claimed in claim 4, wherein the filter and command generator manager determines the filter gain so as to suppress the amplitude of noise below a value resulting from subtracting from the width of the narrowed dead zone a sum of minimum interval in CVT ratio that can be attained by the actuator and minimum interval in CVT ratio that can be measured by the measured CVT ratio generator.6. The system as claimed in claim 4, wherein the dead zone is greater in width than a sum of minimum interval in CVT ratio that can be attained by the actuator, minimum interval in CVT ratio that can be measured by the measured CVT ratio generator, and minimum amplitude of noise.7. The system as claimed in claim 4, wherein the narrower the dead zone, the lower the gain at frequency of noise.8. The system as claimed in claim 4,wherein the at least one sensor includes an input speed sensor generating a first train of pulses indicative of speed of rotation of an input member of the CVT and an output speed sensor generating a second train of pulses indicative of speed of rotation of an output member of the CVT; wherein the filter includes a low pass filter; wherein the measured CVT ratio generator gives, as the measured value of CVT ratio, a ratio between speed of rotation of the input member and speed of rotation of the output member, which speeds are determined based on frequency of the first train of pluses and frequency of the second train of pulses, respectively; and wherein the filter gain at frequency of noise is lower during operation with CVT ratios used at low speeds of rotation of the output member than it is during operation with CVT ratios used at high speeds of rotation of the output member. 9. The system as claimed in claim 4,wherein the at least one sensor includes an input speed sensor generating a first train of pulses indicative of speed of rotation of an input member of the CVT and an output speed sensor generating a second train of pulses indicative of speed of rotation of an output member of the CVT; wherein the filter includes a band reject filter; wherein the measured CVT ratio generator gives, as the measured value of CVT ratio, a ratio between speed of rotation of the input member and speed of rotation of the output member, which speeds are determined based on frequency of the first train of pluses and frequency of the second train of pulses, respectively; and wherein the lower the speed of rotation of one of the input and output members of the CVT, the lower the frequency to be cut off at the band reject filter. 10. The system as claimed in claim 4, wherein the precision requirement is present when the desired value of CVT ratio has accomplished one of the largest CVT ratio and the smallest CVT ratio.11. The system as claimed in claim 4, wherein the CVT is an infinitely variable transmission (IVT) having a geared neutral point (GNP), and wherein there is the requirement for precision in holding a predetermined value of CVT ratio needed accomplish the GNP.12. The system as claimed in claim 4, wherein the filter includes an observer that receives, as inputs, the actuator command as well as the measured value of CVT ratio to provide the estimated value of CVT ratio.13. The system as claimed in claim 1, wherein the filter and command generator manager increases control gain used in determining the actuator command at the command generator after narrowing the dead zone.14. A method for enhanced ratio control in a continuously variable transmission (CVT) including a ratio control element positionable by an actuator in response to an actuator command to establish various CVT ratios in the CVT, the method comprising:obtaining information of an actual CVT ratio established in the CVT to give a measured value of CVT ratio; processing the measured value of CVT ratio in a manner to refine the information of the actual CVT ratio to give an estimated value of CVT ratio; determining the actuator command such that the actuator command remains unaltered when a deviation of the estimated value of CVT ratio from a desired value of CVT ratio stays within a dead zone; and narrowing the dead zone to meet precision requirement upon determination that the desired value of CVT ratio has been accomplished and adjusting the filter to gain requirement for keeping the magnitude of signal at frequency of noise within the narrowed dead zone. 15. The method as claimed in claim 14,further comprising determining amplitude and frequency of noise that may be contained in the measured value of CVT ratio, and wherein the processing the measured value of CVT ratio includes determining filter gain based on the amplitude at the frequency of noise and the dead zone. 16. The method as claimed in claim 15, wherein the precision requirement is present when the desired value of CVT ratio matches with a precision required value of CVT ratio.17. The method as claimed in claim 16, wherein the precision requirement is absent when the desired value of CVT ratio fails to match with the precision required value of CVT ratio.18. The method as claimed in claim 17, wherein the precision required value of CVT ratio is the largest CVT ratio.19. The method as claimed in claim 18, wherein the precision required value of CVT ratio is the smallest CVT ratio.20. The method as claimed in claim 17, wherein the narrowed dead zone is provided upon determination that the desired value of CVT ratio has been accomplished when the desired value of CVT ratio and the precision required value of CVT ratio match with each other, and the narrowed dead zone is narrower than dead zone provided upon determination that the desired value of CVT ratio has been accomplished when the desired value of CVT ratio and the precision required value of CVT ratio fail to match with each other.21. A system for enhanced ratio control in a continuously variable transmission (CVT) including a ratio control element positionable by an actuator in response to an actuator command to establish various CVT ratios in the CVT, the system comprising:sensor means for generating a train of pulses indicative of speed of rotation of a predetermined rotary member of the CVT; means for deriving information of an actual CVT ratio established in the CVT out of at least the train of pulses to give a measured value of CVT ratio; filter means for processing the measured value of CVT ratio in a manner to refine the information of the actual CVT ratio to give an estimated value of CVT ratio; means for determining the actuator command such that the actuator command remains unaltered when a deviation of the estimated value of CVT ratio from a desired value of CVT ratio stays within a dead zone; means for narrowing the dead zone to meet precision requirement upon determination that the desired value of CVT ratio has been accomplished; and adjusting filter gain at the filter means in a manner to keep amplitude at frequency of noise within the narrowed dead zone. 22. A computer readable storage medium having stored thereon data indicative of instructions readable by a microprocessor for carrying out enhanced ratio control in a continuously variable transmission (CVT), the CVT including a ratio control element positionable by an actuator in response to an actuator command to establish various CVT ratios in the CVT, the computer readable storage medium comprising:instructions for obtaining information of an actual CVT ratio established in the CVT to give a measured value of CVT ratio; instructions for processing the measured value of CVT ratio in a manner to refine the information of the actual CVT ratio to give an estimated value of CVT ratio; instructions for determining the actuator command such that the actuator command remains unaltered when a deviation of the estimated value of CVT ratio from a desired value of CVT ratio stays within a dead zone; and instructions for narrowing the dead zone to meet precision requirement upon determination that the desired value of CVT ratio has been accomplished and adjusting the filter to gain requirement for keeping the magnitude of signal at frequency of noise within the narrowed dead zone.