Torque converter for vehicle

1. A torque converter for a vehicle, comprising:

a front cover;

an impeller which is coupled to the front cover and rotates together with the front cover;

a turbine which is disposed at a position facing the impeller;

a reactor which is positioned between the impeller and the turbine and changes a flow of oil flowing from the turbine to the impeller;

a lock-up clutch which has a piston that directly connects the front cover and the turbine; and

a torsional damper which includes a pair of retaining plates that receives driving power of an engine from the turbine or the lock-up clutch, and a driven plate that is disposed between the retaining plates, the torsional damper being coupled to the lock-up clutch and absorbing impact and vibration applied in a rotation direction;

wherein multiple spring assembly seating portions are formed in the retaining plates, spring assemblies are disposed in the multiple spring assembly seating portions so as to impart elasticity in a direction from a circumference of the torsional damper to an rotation axis,

the driven plate has an approximately circular plate shape, multiple curved portions and multiple edge portions are formed on an outer circumferential surface of the driven plate, each of the curved portions has a curvature that is more gradual than an imaginary circumference defined by a maximum diameter of the driven plate, and

the spring assemblies are in contact with the curved portions to apply elasticity to the curved portions.

2. The torque converter of claim 1 , wherein:

the torsional damper includes:

three spring assembly seating portions, three spring assemblies, three curved portions, and the three edge portions.

3. The torque converter of claim 1 , wherein:

lengths of the multiple curved portions are approximately equal to one another.

4. The torque converter of claim 1 , wherein:

intervals between the multiple spring assembly seating portions are approximately equal to one another.

5. The torque converter of claim 1 , wherein:

each of the spring assemblies includes a spring, and a spring seat which is coupled to the spring and has a hemispheric shape, and

the spring seat is disposed such that a portion, which defines a curved surface of the hemispheric shape, is in contact with the curved portion.

6. The torque converter of claim 1 , wherein:

each of the spring assemblies includes a spring, and a spring seat which is coupled to the spring and disposed to be in contact with the curved portion,

the spring seat has a stopper that protrudes in a lateral direction of the spring assembly, and

the stopper prevents the edge portion of the driven plate and the spring assembly from intersecting and passing each other.