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Driveline clunk during static engagements on vehicles with automatic transmissions is a phenomenon that can adversely affect customer perception of vehicle quality. Tuning a vehicle's static engagement characteristics for superior shift quality demands a good understanding of the inputs to the vehicle driveline, the response of the driveline, and the sensitivity of the vehicle to such inputs. This paper describes a case study conducted on a rear wheel drive vehicle with an automatic transmission and independent rear suspension to understand and reduce the severity of driveline engagement clunk to acceptable levels. Finally, the results of the study are used to develop guidelines for such vehicles to ensure superior shift quality during static engagements.

A customer's perception of vehicle quality very closely parallels the noise vibration and harshness (NVH) characteristics of the vehicle. Consequently, automotive manufacturers are investing significant resources into optimizing the NVH performance of their vehicles. Automatic transmission shift quality is one of a number of attributes where NVH optimization is critical towards providing customers with a pleasant driving experience. This paper addresses various aspects of understanding, quantifying and optimizing a vehicle's shift quality characteristics. Following an introductory treatment of automatic transmission planetary gear systems, the interaction between the engine/transmission system during shifts is summarized. Various shift quality metrics used to quantify a vehicle's response and its sensitivity to transient inputs are provided. Approaches to manage the engine torque output during the shifts are discussed.