A hydrodynamic torque converter (1) with a lock-up clutch (6) in a clutch space, (9) and with a piston (7) for activating of the lock-up clutch (6). The piston (7) separates the clutch space (9) from a piston chamber (10). The piston (7), via the application of pressure, can be moved, from a starting position in which the lock-up clutch (6) is disengaged, in the engaging direction of the lock-up clutch (6). The piston (7) has at least a closable opening (11) through which hydraulic fluid can flow from the piston chamber (10) into the clutch space (9). The opening (11) is open if either the piston (7) is away from the starting position and/or if a fluid pressure in the piston chamber (10), compared to the clutch space (9), is elevated. The closing element (12, 13) is tongue-shaped element which serves closing and opening of the opening (11).