Optimization of Propeller shaft design to eliminate Launch Undulation (Lateral shake) and Vibration level

During vehicle launches in 1st gear, a lateral shake (undulation) and a pronounced metallic hitting noise were observed in the underbody. The noise was identified as the propeller shaft's second universal joint (UJ) yoke striking the fuel tank mounting bracket. Sensitivity to these issues varied with acceleration inputs: light pedal input during a normal 1st gear launch on a flat road resulted in minimal undulation, whereas wide open throttle (WOT) conditions in 1st gear produced significant lateral shake and intensified hitting noise. Further investigation revealed that the problem persists across all gears and occurs consistently during normal driving conditions, with continuous impact between the propeller shaft yoke and the fuel tank mounting bracket. Extensive experimental measurements at the vehicle level indicated that these issues were primarily caused by the center-mounted propeller shaft joint deviating from its central position and rotating eccentrically under torque. This eccentric movement was linked to the improper propeller shaft split ratio and shorter fitting length. A detailed design study combined with vehicle-level experiments (Design of Experiments, DOE) confirmed that these factors significantly contribute to the positional shift of the second UJ connection and its resulting eccentric behavior. This study provides a comprehensive approach to addressing the issue, focusing on reducing vibrations transmitted to the floor and seats and give NVH refinement through the propeller design optimization. By doing so, it ensures improved vehicle performance without compromising other critical parameters.