Design Optimization of Trunk Lid Torsion Bar Type Trunk Lid Pop Up Mechanism 2019-28-0111
Trunk lid (TL) can be opened using hydraulic or pneumatic balancers, coil springs, torsion bars or combination of the above. TL Opening Mechanism specific to Trunk Lid Torsion Bar (TLTB) is being discussed in the paper. After de-latching, TL should open smoothly and stop at such a height that it is visible from driver seat. The system consists of a four bar linkage mechanism, in which the fixed link is formed by BIW Bracket. Connecting link, TL Hinge Arm and Torsion bar arm form the other three links. Hinge has its one end attached to TL and the other end to BIW bracket. Torsion bar arm transfers torque to TL hinge through the connecting link. Major challenges in designing TLTB mechanism are part tolerances, C.G position and Weight variations in individual parts, Torsion bar Raw Material variation, uncertain friction in the system etc. If above challenges are not addressed properly, then issues like TL not popping up to desired level consistently and smoothly and hard closing may occur. TL pops up when torque due to torsion bar is greater than the combination of torque due to TL weight and friction at linkages. Considering the above challenges and drop in elasticity of TLTB with time, upper and lower values of torques are derived. When lower value torque of torsion bar is greater than the upper value torque of TL weight torque and friction torque, TL always opens. If effects of the tolerances are not considered then pop up of TL is uncertain. The difference between these torques should be optimal so as to ensure smooth pop up. This paper outlines the design optimization of Trunk Lid Pop up Mechanism while addressing afore mentioned challenges.