Fashionable torque converters use electro hydraulic Command with the lock-up clutch. The hydraulic circuit which locks/unlocks the torque converter clutch is managed making use of hydraulic valves. The valves are actuated immediately or indirectly by solenoids. Torque converter equations of motion are ruled by Leonhard Euler's eighteenth century turbomachine equation: https://torque-converter-clutch77418.blogproducer.com/41013679/a-simple-key-for-torque-converter-clutch-unveiled