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.