AVTC Model Based Design Curriculum Development Project

Continuously Variable Transmission

Request Vehicle Speed Mode Selector (P, D, R) Engine Power Transmission 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 required

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, “Continuous Variable Transmission (CVT),”