A hydraulic power transmission device includes a front cover, a torque converter main body, a lock-up device, and a dynamic damper. The dynamic damper has a base plate, inertia rings and lid members that configure an inertial body, viscosity attenuation portions, and an elastic coupling portion. The base plate is fixed to an output plate. The inertial body can move in the rotation direction relative to the base plate. The viscosity attenuation portions can generate a variable hysteresis torque according to the relative speed difference between the base plate and the inertial body.

A hydraulic power transmission device includes a front cover, a torque converter main body, a lock-up device, and a dynamic damper. The dynamic damper has a base plate, inertia rings and lid members that configure an inertial body, viscosity attenuation portions, and an elastic coupling portion. The base plate is fixed to an output plate. The inertial body can move in the rotation direction relative to the base plate. The viscosity attenuation portions can generate a variable hysteresis torque according to the relative speed difference between the base plate and the inertial body.

A torque converter includes a torsional damper assembly. The torsional damper assembly includes a damper. The damper has an electromagnetic coil and a magnetorheological fluid. The electromagnetic coil is positioned such that a magnetic field from the electromagnetic coil adjusts a viscosity of the magnetorheological fluid when a current flows through the electromagnetic coil.

A torque converter includes a torsional damper assembly. The torsional damper assembly includes a damper. The damper has an electromagnetic coil and a magnetorheological fluid. The electromagnetic coil is positioned such that a magnetic field from the electromagnetic coil adjusts a viscosity of the magnetorheological fluid when a current flows through the electromagnetic coil.