Modern-day torque converters use electro hydraulic Handle for that lock-up clutch. The hydraulic circuit which locks/unlocks the torque converter clutch is managed making use of hydraulic valves. The valves are actuated directly or indirectly by solenoids. Torque converter equations of motion are ruled by Leonhard Euler's eighteenth century turbomachine equation: https://donovanyyvuq.theobloggers.com/40232324/torque-converter-clutch-things-to-know-before-you-buy