Abstract This paper demonstrates the use of a system level model that includes torsional models of a Cummins diesel engine and an Allison transmission to study and improve system NVH behavior. The study is a case where the two suppliers of key powertrain components, Cummins Inc. and Allison Transmission Inc., have collaborated to solve an observed NVH problem for a vehicle customer. A common commercial tool, Siemens' AMESim, was used to develop the drivetrain torsional system model. This paper describes a method of modelling and calibration of baseline engine and transmission models to identify the source of vibration. Natural frequencies, modal shapes, and forced response were calculated for each vehicle drive gear ratio to study the torsional vibration. Several parametric studies such as damping, inertia, and stiffness were carried out to understand their impact on torsional vibration of the system. The best solution was then selected based on the system study and implemented in the vehicle for validation. Finally, the aim of this paper is to demonstrate the successful use of an analysis led design approach by collaborating suppliers (Cummins and Allison) to identify drivetrain NVH problems and options for solutions. Such an approach can be used in early phases of vehicle integration to achieve optimized drivetrain system design, to the benefit of the end customer and the component suppliers. Introduction Vehicle drivability and smoothness of operation has quickly become a key customer requirement of the automotive industry [ 1]. This presents engine and transmission integration challenges to vertically integrated suppliers, as well as to component suppliers. Non-optimal configurations can result in torsional vibration issues that are not only a significant source of noise and harsh drive quality, but can, in some cases, also damage the drivetrain. Optimal drivetrain design for reduced Noise, Vibration and Harshness (NVH) is very challenging, particularly since the different components making up the drivetrain (engine, transmission, axle, etc.) usually come from multiple suppliers performing their design functions independently. Solving drivetrain NVH problems requires a system level model to characterize and eliminate incompatibilities. Fuel efficiency and emission regulations have been the major driving forces behind large engine development in recent decades. Engine downsizing is one of the techniques utilized to improve fuel economy and reduce carbon dioxide emissions. While 4-cylinder engines are lighter, and can provide higher fuel efficiency than 6-cylinder engines, the system's Noise, Vibration, and Harshness (NVH) behavior is significantly impacted by the shifted engine firing order and the lighter flywheel. Drivetrain torsional vibrations are due to combustion and inertia forces of the engine rotating components [ 2]. In automatic transmission applications, transmission lock-up clutch dampers are usually installed to isolate the powertrain from engine firing pulses. To avoid damper mode resonance, transmission lock-up must be applied above the damper mode resonant speed range [ 3, 4, and 5]. A lock-up clutch damper resonance map, Figure 1, depicts the relationship between damper resonance and engine firing frequency over the engine operating speed range. For reference, a 4-cylinder engine produces 2nd order excitation while a 6-cylinder engine produces 3rd order excitation. In 4-cylinder applications, the damper mode resonance will be induced within the engine operating speed range, potentially increasing the overall vibration level. Figure 1. Campbell diagram of typical drivetrainAnalytical Evaluation of Integrated Drivetrain NVH Phenomena2015-01-2781 Published 09/29/2015 Rohit Saha, Yonghong Liu, Mahesh Madurai Kumar, Bill Kendrick, and Long-Kung Hwang Cummins Inc. Liyun Lucas and Dinh Ngo Allison Transmission Inc. CITATION: Saha, R., Liu, Y ., Madurai Kumar, M., Kendrick, B. et