An Analytical Methodology for Engine Gear Rattle and Whine Assessment and Noise Simulation 2019-01-0799

In automotive engine gears are needed to transmit engine rotation and torque. A major application is to drive balance shafts in I3 and I4 engines which are not internally balanced. The gears can lead to NVH issues appearing as either broad band rattling noise, or narrow band tonal whine. Rattle is due to teeth single and/or double-sided impacts from backlash and teeth separations. Source of rattle is primarily pulsation in the torque. Whine is due to gear mesh frequencies and the occurring contact forces causing vibration of the gears pair. The conflicting behavior between gear rattle and whine is a well-known error state issue. Resolving one may result in aggravating the other one. For example, reducing gear teeth backlash can prevent or mitigate rattling noise, however, due to increase in the contact forces and sliding friction at the gear teeth whining noise may get worse. Balance shaft design architecture, defining mass and inertia distribution and positioning inside the engine, and gear geometry and micro-geometry are critical design elements influencing gear noise. Early on analytical assessment can ensure a gear system design with an acceptable NVH performance. The analytical assessment can cover the excitation source and extend through the transmitting under different engine speed and loading conditions. Additionally, design sensitivity and robustness studies involving gear lash, pressure angle, tip relief, teeth crowning, etc. can be investigated and used in deriving the design. In this presentation, a CAE methodology based on a multiphysics approach for engine gear rattle and whine evaluation will be reviewed. The method combine and/or apply results and outputs from various analytical domains involving engine modal analysis, multibody dynamics (MBD) and acoustic analysis to perform gear noise risk assessment. The assessment includes source-path analysis of gear rattle and whine and vibration evaluation of a detailed flexible engine model. The vibration data from the exterior surface of the engine goes through engine acoustic analysis for noise simulation and acoustic hot spots identification and panel contribution to the noise. Analysis under different engine loading conditions with results in both time and frequency domains including gear order cuts and color map plots will be presented. Various sensitivity analyses involving different gear backlash levels and micro-geometry modifications will be investigated.