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AVTC Model Based Design Curriculum Development Project Continuously Variable Transmission Continuously Variable Transmission ππ€ , ππ€ Power Driver Request Engine Controller ππ , π π Load Engine Transmission Mode Selector (P, D, R) Desired Vehicle Speed Transmission Controller Vehicle Speed ππ , π π Driveline Final Drive Major Components of a CVT β’ Unlike other transmission systems, a CVT is simple in concept as it only has three major components β A drive pulley - Connected to input shaft β A driven pulley - Connected to output shaft β A belt Changes from low to high pulley ratio Continuously Variable Transmission β’ The CVT is an automatic transmission with a continuously variable range of torque/speed ratios β’ Instead of gears, the transmission uses a pair of variable size pulleys and a fixed length belt β’ As the diameter of one pulley becomes larger the other correspondingly becomes smaller β’ Ratio of pulley sizes is analogous to ratio of gear sizes Illustrated by: W. Rebel Basic principle of operation β’ Pulleys consist of conical pulley halves β’ Two sheaves of one pulley move closer together while the two sheaves of the other pulley move farther apart β’ If two cones of one pulley are far apart, the diameter of the pulley becomes smaller β’ Conversely, when they are closer together, the diameter of the pulley is larger β’ The ratio changes as the respective pulley diameters change with a constant length belt Illustrated by: W. Rebel Advantages of CVTβs β’ Uninterrupted power transfer from engine to drive shaft β’ Smooth transition as pulley ratio changes β’ Ability to operate engine at optimal performance over a wide range of vehicle speeds β’ Convenience similar to an automatic transmission β’ Engine can operate at most efficient speed or at speed to produce peak power β’ A separate clutch is not necessarily required http://en.wikipedia.org/wiki/File:Toyota_Super_CVT-i_01.JPG Disadvantages of CVTs β’ Relatively low efficiency, e.g. 88% β’ Can not handle high torque demands β’ Not robust, repairs can be expensive Simulink Model of a Continuously Variable Transmission Review and test β’ How many gear ratios are possible with a CVT? β β β β 0 1 8 Infinite β’ The length of a drive belt is constant in a CVT β True β False β’ Which one of the following components are NOT a part of a CVT? β β β β Drive pulley Driven pulley Synchonizer Driving belt References β’ Chao-Hsu Yao. Automotive Transmissions: Efficiently Transferring Power from Engine to Wheels. ProQuest: Discovery Guides, http://www.csa.com/discoveryguides/auto/review.pdf 2008. β’ βContinuous Variable Transmission (CVT),β https://d2t1xqejof9utc.cloudfront.net/files/19153/eti_19_CVTransmission.pdf?1363 999370.
