Torsion spring

A throttle valve device comprising:

• a torsion spring that is assembled and used in the throttle valve device for increasing and decreasing an opening degree of an intake passage or an exhaust passage of an internal-combustion engine, the torsion spring comprising:
• two coil springs connected with each other so that torsion directions are opposite from each other;
• and
• a hook disposed between the two coil springs, and
• a valve object housed in the intake passage or the exhaust passage to be rotatable to increase and decrease the opening degree of the intake passage or the exhaust passage, wherein
• of the two coil springs, one side spring arranged at one side in an axial direction biases the valve object to a closing side, and the other side spring arranged at the other side in the axial direction biases the valve object to an opening side,
• at least one coil spring of the two coil springs and the hook connected with each other defines a clearance therebetween, and a dimension of the clearance is larger than an average value of clearances between coil turns of the at least one coil spring,
• the hook defined by bending a wire element has a hook gap in the axial direction, one end of the hook in the axial direction being connected to the other end of the one side spring in the axial direction, the other end of the hook in the axial direction being connected to the one end of the other side spring in the axial direction,
• the throttle valve device further comprises:
• one side bush arranged at an inner circumference of the one side spring, and having an outer periphery surface in contact with the inner circumference of the one side spring, and
• the other side bush arranged at an inner circumference of the other side spring, and having an outer periphery surface in contact with the inner circumference of the other side spring, wherein a gap is defined between the one side bush and the other side bush in the axial direction,
• a spring gap is defined in the axial direction between a first turn of coil turns of the one side spring located the most other side in the axial direction, and a first turn of coil turns of the other side spring located the most one side in the axial direction, in the state where the torsion spring is assembled to the one side bush and the other side bush,
• the gap defined between the one side bush and the other side bush in the axial direction is defined as a bush gap,
• while extending from a tip end of the hook toward the other end of the one side spring in the axial direction, the hook gap is smaller than the bush gap up to a predetermined position, and becomes larger than the bush gap when passing the predetermined position, and
• the spring gap is larger than the bush gap.