Method of designing torsion bars used for trunk lid

A design method of torsion bars used for a trunk lid, each of the torsion bars being given a target shape in a state where the trunk lid is closed, and being given a free shape in a free state where the torsion bars are unhitched from the trunk lid, the design method of the torsion bar having the free shape comprising:

• (a) a step of inputting design specifications including target torque occurring in each of the torsion bars in the target closed shape, a rotational angle by which a movable end of each of the torsion bars is rotated from the target closed shape to the open shape, the target closed shape to be specified by coordinates of bending points of the torsion bars, and a wire diameter of each of the torsion bars;
• (b) a step of creating a center line model having the target closed shape on the basis of the coordinates of the bending points;
• (c) a step of geometrically and statically creating the free shape corresponding to the target closed shape, and creating a center line model of the free shape on the basis of coordinates of bending points of the free shape;
• (d) a step of creating a center line model of the open shape on the basis of the center line model of the free shape, and rotating the center line model of the open shape by the rotational angle to thereby create a center line model of an analyzed closed shape;
• (e) a step of obtaining difference torque between the target torque and analyzed torque of the analyzed closed shape;
• (f) a step of comparing the center line models of the analyzed closed shape and the target closed shape with each other to thereby obtain a difference vector occurring between corresponding bending points for the analyzed closed modified shape and the target closed shape;
• and
• (g) a step of changing the center line model so as to decrease the amplitudes of the difference torque and the difference vector, when the amplitudes of the difference torque and the difference vector are not both within predetermined tolerances, respectively, and returning to the step (d), or a step of finishing the design method of the torsion bar, when the amplitudes of the difference torque and the difference vector are both within predetermined tolerances, respectively.