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The purpose of this study is to validate a reverse engineering based design method for automotive trunk lid torsion bars (TLTB) in order to determine a free, or unloaded, shape that meets a target closed shape as well as a specified torque. A TLTB is a trunk lid component that uses torsional restoring force to facilitate the lifting open of a trunk lid, as well as to maintain the open position. Bend points and torque of a TLTB at a closed trunk position are specified by a car maker. Conventionally, a TLTB supplier determines bend points of the free shape by rotating the given bend points from a closed position around a certain axis to satisfy the specified torque at the closed position. Bend points of a deformed TLTB shape in the closed position often do not match the target bend points given by a car maker when designed by the conventional method, which can potentially cause interference issues with surrounding components.

The MacPherson strut is widely used in the automotive industry. Many investigations regarding the minimization of damper friction force have been published; however, this is not the case with vehicle self steer. There are several methods to reduce the amount of vehicle self steer. The objective of this paper is to minimize vehicle self steer with respect to spring force line position. To investigate the relationship between vehicle self steer and spring force line, a mathematical model of suspension system was developed and then solved to obtain the optimum force line position that minimizes vehicle self steer. The solution to the mathematical model found was that the force line must pass through the upper mount center in order to minimize vehicle self steer, or the force line must be on the same plane as the kingpin axis. Sensitivity analysis was performed to investigate the variability of the force line position on vehicle self steer.

Coil spring force line control is an important aspect of spring design for coil-over-shock suspension type applications, such as MacPherson strut and coil-over-shock trailing arm applications, from the standpoint of riding comfort, steering stability and damper durability. A method based on simple statics to determine a unique spring force line for damper friction minimization has previously been investigated. Typically that method led to a unique specification of the spring force line, and a tolerance was arbitrarily determined. However, there are actually an infinite number of force line positions that obtain the same damper friction. Therefore, the spring force line determined by the conventional method is only a sufficient condition, but not a necessary condition to minimize the damper friction. Targeting a different spring force line position may contribute to reducing a cost of spring.