Coil spring

A coil spring including a wire formed into a helical shape, and being arranged in such a state that it is compressed between a lower spring seat and an upper spring seat of a strut-type suspension, wherein the upper spring seat is not parallel to the lower spring seat, the coil spring comprising:

• a lower end turn portion which is in contact with the lower spring seat;
• an upper end turn portion which is in contact with the upper spring seat;
• an effective portion between the lower end turn portion and the upper end turn portion;
• and
• a force line, which is a straight line, connecting a center of force applied to the lower end turn portion and a center of force applied to the upper end turn portion in a state in which the force which compresses the effective portion is applied to the lower end turn portion and the upper end turn portion,
• wherein:
• the force line is inclined obliquely at angles with respect to the lower spring seat and the upper spring seat,
• the effective portion is cylindrical about an axis of the effective portion with a substantially constant pitch along the axis in its free shape which is not compressed, the free shape being exhibited in an unassembled state in which the coil spring is not arranged between the lower spring seat and the upper spring seat of the strut-type suspension, and
• with respect to a coordinate system in which the force line is assumed as a Z-axis, the effective portion is cylindrical with a substantially constant pitch and a substantially constant coil diameter in a direction along the Z-axis in its compressed shape which is compressed to a specified height between the lower spring seat and the upper spring seat which is not parallel to the lower spring seat.