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In McPherson strut applications for automotive suspension systems, the desired coil spring reaction force vector (FLP: force line position) that minimizes damper friction and king pin moment is typically determined by Statics/Kinematics calculations. There is not a device available on the open market today which can mimic the coil spring reaction force vector within the suspension system. Such a programmable coil spring reaction force vector generator, named “Universal Spring”, was developed in 2003 (USPG2003), and was then improved in 2013 (USPG2013) from the standpoint of accuracy, durability and reliability. The device is actuated by six hydraulic cylinders constructing a Stewart platform type parallel mechanism. Accuracy of FLP generated by USPG2013 is 1.1mm at maximum in ϕ80mm area around strut axis.

As for the McPherson strut, a force from the tire acts on the shock absorber producing a bending moment, which causes an increase in the friction acting on the shock absorber. Reducing the friction is one of the most important issues to improve the riding comfort of an automobile. The bending moment can be reduced by controlling the load axis of the coil spring assembled with the shock absorber. In order to control the load axis, several types of coil springs have been recently reported. This paper proposes another shape-controlled coil spring, called L-shape. The L-shape spring has the following advantages: (1) The load axis can be precisely controlled with ease; (2) Additional space is unnecessary; (3) Manufacturing tractability is increased. The proposed L-shape spring is validated analytically and experimentally in this paper. The effect of the L-shape spring for reducing the friction on a shock absorber is also experimentally confirmed.