During which torque converter phase does the engine's torque output increase at the transmission input?

During which torque converter phase does the engine's torque output increase at the transmission input?

• A. Coupling Phase
• B. Multiplication Phase
• C. Lock-Up
• D. Cool-Down

Answer: (B)

Torque converters boost the engine’s torque at the transmission input during the phase where the fluid flow between the impeller and turbine creates a torque multiplier. When the engine powers the impeller and the turbine hasn’t caught up yet, the stator redirects the circulating fluid to amplify the torque transferred to the transmission. This multiplication can make the input torque higher than the engine torque, especially at low speeds with more slip. As speed increases, slip decreases and the multiplier falls off; once the converter locks up, there’s little to no multiplication and the input torque closely follows the engine torque (minus small losses). The cool-down stage isn’t about torque transfer, and the lock-up stage eliminates slip rather than multiplying torque. So the phase where the engine’s torque output increases at the transmission input is the torque multiplication phase.

Torque converters boost the engine’s torque at the transmission input during the phase where the fluid flow between the impeller and turbine creates a torque multiplier. When the engine powers the impeller and the turbine hasn’t caught up yet, the stator redirects the circulating fluid to amplify the torque transferred to the transmission. This multiplication can make the input torque higher than the engine torque, especially at low speeds with more slip. As speed increases, slip decreases and the multiplier falls off; once the converter locks up, there’s little to no multiplication and the input torque closely follows the engine torque (minus small losses). The cool-down stage isn’t about torque transfer, and the lock-up stage eliminates slip rather than multiplying torque. So the phase where the engine’s torque output increases at the transmission input is the torque multiplication phase.