Front Suspension Joint Integrity Analysis for Addressing Noise Issue Due to Torque Loss at Lower Control Arm Joint

The lower control arm (LCA) is a part of the front suspension system which is mounted on chassis with flexible rubber bushing through-bolted joint which allows the control arm to swing up and down, absorb road bumps and reduce noise and vibrations as front wheels roll over bump or potholes. In bolted joints, torque is applied so as the joint develops a certain preload that is higher than the external loads and losses acting on the joint. But the loss of preload is evident over time which causes quality problems, reworks, or even joint failures. While moving over speed breakers/obstacles abnormal squeak noise is observed in the vehicle due to torque loss in the LCA joint. The intent of this study is to determine preload requirements in LCA joint and various factors contributing to preload loss by performing joint integrity analysis in CAE. Road load data acquisition (RLDA) with Wheel Force Transducer (WFT) is performed for different testing tracks. Loads on the LCA joint are simulated from ADAMS using WFT data along with shear loads due to suspension travel and misalignment. Preload generated due to applied torque is analytically calculated and experimentally validated by the Ultrasonic method.

High fidelity LCA joint is modeled and simulated in CAE to study the contact pressure distribution at the contact area between mating surfaces of components and the influence of uneven contact on preload loss. With the use of Fuji paper Influence of serrated washers on mating surface and friction effects on preload are studied. LCA bracket face angularity considering worst tolerances of joint components is analyzed to capture the maximum loss of preload in compensating the tolerances. The effect of service load in a permanent set of LCA joint leading to loss of preload is also determined using CAE. The study helps in taking appropriate design countermeasures considering all factors to avoid torque loss issues.