Modeling and analysis of gear rattle in automotive transmissions

In recent years, attainment of high quality in automotive vibration and sound has become a major effort in automotive vehicle refinement programs. In Europe and Asia, the vast majority of passenger cars are equipped with manual transmissions and diesel engines. Compared with automatic transmissions, manual shifts offer lower cost, better fuel efficiency, and more a greater sense of being in control of the car. However, unlike automatic transmissions, manual transmissions do not have the high viscous damping inherent to a hydrodynamic torque converter to suppress the impacting of gear teeth oscillating through their gear backlash. Therefore, a significant level of noise can be produced by the gear rattle and transmitted both inside the passenger compartment and outside the vehicle. Gear rattle, idle shake, and other noise generated by low frequency vibration phenomena in the automobile driveline have become an important concern to automobile manufacturers in their pursuit of an increase in perceived sound quality.; Gear rattle is produced by the impacting of gear teeth through their unloaded mesh backlash as a response to engine torque fluctuations. Not only is rattle noise audibly objectionable, but it may also be misconstrued as an impending transmission failure leading to warranty returns. The complexity of torsional vibrations and various nonlinearities of the manual transmission present many challenges for the analysis of torsional vibration characteristics and gear rattle behavior. Despite intensive research in the past, numerical difficulties in handling nonlinearity have prohibited the development of general criteria in transmission design to alleviate the rattle.; The objective of this dissertation is to investigate and develop a complete modeling method considering all the components of the powertrain, with robust numerical techniques for study of the gear rattle phenomenon. The aim of the modeling and analysis effort is to conduct parametric studies and provide design guidelines for powertrain development and refinement. The dissertation focuses on the following:; First, based upon a comprehensive understanding of the powertrain system, a decoupled torsional vibration model is developed. This model separates the system into two parts with a baseline model and a rattle model to simplify the analysis. The validity of the decoupled model is determined by implementing and comparing it with a full model. Second, a numerical technique based on Finite Elements in Time domain (FET) is derived and implemented for the analysis of rattle dynamics. The numerical integration algorithm is a key component for efficient and accurate numerical investigations. The FET algorithm is compared with the Stiff ODE algorithms of MATLAB to show its efficiency and effectiveness.; Third, with the developed decoupled model and numerical tools, a parametric study is conducted for design applications. These parametric studies yield the effects of the key design parameters on the effective indices of rattle dynamics. This allows the designer to evaluate trade-offs among various designs without resorting to expensive and inefficient palliative measures.