Method and system for controlling rate of change of ratio in a continuously variable transmission

Abstract

Systems and methods for efficiently and effectively controlling the rate of change of ratio, not simply the ratio, in a CVT. By controlling the rate of change of ratio, the acceleration or deceleration of a vehicle can be controlled in an efficient manner. Furthermore, the rate of change of ratio can be controlled by controlling the clamping pressure of the pulleys and/or differential pressure between the pulleys with minimal slip by using a servo control mechanism adapted for control by a system controller based on equilibrium mapping and other control parameters.

1 . An apparatus for optimizing the operation of a continuously variable transmission (CVT) on a vehicle having a powertrain, said CVT having hydraulically operated primary and secondary pulleys with varying effective diameters, and a drive belt coupling the primary pulley to the secondary pulley, comprising:
 a control computer adapted to receive driver input and send commands to the powertrain depending on the transmissible torque;   programming associated with said control computer for carrying out the operations of controlling primary and secondary pulley pressure of a CVT to achieve a commanded clamping pressure in response to an input torque command and commanded ratio rate or shift velocity based on a mapping of empirical data relating to pressure, ratio rate, and torque;   a primary pump fluidly connected to said primary pulley;   a secondary pump fluidly connected to said secondary pulley;   wherein said primary and secondary pumps are not fluidly connected; and   wherein the pressure on said secondary pulley is raised instead of lowering the pressure on said primary pulley when said CVT is shifted toward low gear.   
     
     
         2 . An apparatus as recited in  claim 1 , further comprising a hydraulic servo control system adapted for control of said primary and secondary pulley pressure in response to said control computer. 
     
     
         3 . A hybrid electric vehicle, comprising:
 a continuously variable transmission (CVT);   said CVT having hydraulically operated primary and secondary pulleys with varying effective diameters;   a drive belt coupling the primary pulley to the secondary pulley;   a primary pump fluidly connected to said primary pulley;   a secondary pump fluidly connected to said secondary pulley;   wherein said primary and secondary pumps are not fluidly connected;   wherein the pressure on said secondary pulley is raised instead of lowering the pressure on said primary pulley when said CVT is shifted toward low gear;   an internal combustion engine coupled to the CVT;   an electric motor coupled to the output of the internal combustion engine;   a system controller configured to operate said motor simultaneously with said engine and apply motor torque to said engine output to maintain engine power or torque output substantially along a predetermined operating line;   wherein said system controller is adapted to send commands to said motor and said engine depending on driver input and transmissible torque;   said system controller further configured to control rate of change of ratio of said continuously variable transmission;   wherein said system controller dynamically varies acceleration and deceleration of said vehicle by varying motor torque and rate of change of ratio of said continuously variable transmission; and   programming associated with said system controller for carrying out the operations of controlling primary and secondary pulley pressure of a CVT to achieve a commanded clamping pressure in response to an input torque command and commanded ratio rate or shift velocity based on a mapping of empirical data relating pressure, ratio rate, and torque.   
     
     
         4 . A hybrid electric vehicle as recited in  claim 3 , further comprising a hydraulic servo control system adapted for control of said primary and second pulley pressure in response to said system controller.