a b s t r a c tThis work proposes an original non-intrusive approach to detect and quantify rattle noise in automotive gearboxes operating under non-stationary conditions by means of vibration or instantaneous angular speed measurements. Rattle noise is produced by vibro impacts between teeth of unloaded gears excited by the engine acyclism. It appears during acceleration or deceleration phases and its detection requires the analysis of nonstationary signals. In order to take advantage of the repetitive nature of the impacts, an angle/time cyclostationary approach is introduced. Rattle noise is thus characterized through the angle/time duality: the cyclic frequency expressed in events per revolution is directly linked to the periodicity of the impacts while their frequency content is expressed in Hertz. The proposed detection method uses an order/frequency spectral coherence and may be applied either on vibration signals or instantaneous angular speed signals. For validation purposes, a specific instrumentation of a gearbox is set up. The relative speed of the unloaded meshing gears is observed by means of optical encoders to directly detect the instants of impact which then serve as a basis for validation of the non-intrusive detection method proposed in this paper.
The acoustic and vibratory analysis represent an essential research axis in the automotive industry because these phenomena directly affect the appreciation of the customer when using a vehicle. Indeed, the combustion engine represents the main source of mechanical energy but it generates an acyclic torque because of the explosions. This acyclism is responsible for noise and vibration fatigue. To reduce NVH issues, a possible mean is to use a Multiple Tuned Mass Damper (MTMD) adapted to rotating machine. The purpose of this paper is to propose a framework for the design of this type of MTMD. To achieve this goal, an optimization strategy is implemented in the non-rotating and rotating case to determine the optimal distribution of the MTMD frequencies. It is based on the minimization of the elastic strain energy of the transmission chain near the torsion mode. In addition, a dedicated reduced order method is proposed to reduce the calculation costs link to the modeling of the system by the finite element method and the optimization process. However, conventional reduction order methods are not suitable for this type of problem where the shape of the modes of the main structure and the MTMD are varying according to the rotation speed. To overcome this problem, a multi-model approach is employed. Finally, the influence of the number of absorbers composing the MTMD as well as the structural damping of the absorbers and their mass on the performance of the optimal solution is presented in the non-rotating and rotating case.
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