A CVT commonly used in hybrid vehicles achieves its variable drive ratio primarily through

• A. Planetary gear sets
• B. Hydraulic torque converter
• C. Dual clutch arrangement
• D. Belt running between variable width pulleys

Answer: (D)

A CVT changes the gear ratio by adjusting the effective diameters of the driving and driven pulleys with a belt running between them. As the pulleys change width, the belt climbs to a larger diameter on one pulley and a smaller diameter on the other, or vice versa. This lets the ratio vary continuously rather than in steps, which is ideal for keeping the engine or motors in their most efficient operating range in hybrid systems.

Other mechanisms deliver ratios differently: planetary gear sets provide finite, predefined ratios; a hydraulic torque converter is a fluid coupling that doesn’t set a true variable ratio like a CVT; and a dual-clutch transmission shifts between discrete gears. The belt between variable-width pulleys is the mechanism that enables a true continuous range of drive ratios.