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AVTC Model Based Design Curriculum Development
Project
Continuously Variable Transmission
Continuously Variable Transmission
Request
Vehicle Speed
Mode Selector (P, D, R)
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EngineDriver Power Driveline𝑇 𝑇 ,𝑛𝑇 𝑇 𝑇 ,𝑛𝑇Transmission
Transmission Controller
Load
Desired Vehicle Speed
Major Components of a CVT
• Unlike other transmission systems, a CVT is simple in concept as it only has three major components– A drive pulley
- Connected to input shaft
– A driven pulley- Connected to output shaft
– A belt
Changes from low to high pulley ratio
Continuously Variable Transmission
• The CVT is an automatic transmission with a continuously variable range of torque/speed ratios
• Instead of gears, the transmission uses a pair of variable size pulleys and a fixed length belt
• As the diameter of one pulley becomes larger the other correspondingly becomes smaller
• Ratio of pulley sizes is analogous to ratio of gear sizes Illustrated by: W. Rebel
Basic principle of operation
• Pulleys consist of conical pulley halves• Two sheaves of one pulley move closer
together while the two sheaves of the other pulley move farther apart
• If two cones of one pulley are far apart, the diameter of the pulley becomes smaller
• Conversely, when they are closer together, the diameter of the pulley is larger
• The ratio changes as the respective pulley diameters change with a constant length belt Illustrated by: W. Rebel
Advantages of CVT’s
• Uninterrupted power transfer from engine to drive shaft
• Smooth transition as pulley ratio changes• Ability to operate engine at optimal
performance over a wide range of vehicle speeds
• Convenience similar to an automatic transmission
• Engine can operate at most efficient speed or at speed to produce peak power
• A separate clutch is not necessarily requiredhttp://en.wikipedia.org/wiki/File:Toyota_Super_CVT-i_01.JPG
Disadvantages of CVTs
• Relatively low efficiency, e.g. 88%• Can not handle high torque demands• Not robust, repairs can be expensive
Simulink Model of a Continuously Variable Transmission
Review and test• How many gear ratios are possible with a CVT?
– 0– 1– 8– Infinite
• The length of a drive belt is constant in a CVT– True– False
• Which one of the following components are NOT a part of a CVT?– Drive pulley– Driven pulley– Synchonizer– Driving belt
References
• Chao-Hsu Yao. Automotive Transmissions: Efficiently Transferring Power from Engine to Wheels. ProQuest: Discovery Guides, http://www.csa.com/discoveryguides/auto/review.pdf 2008.
• “Continuous Variable Transmission (CVT),” https://d2t1xqejof9utc.cloudfront.net/files/19153/eti_19_CVTransmission.pdf?1363999370.