INTRODUCTION The growing demand for lower automotive vehicle emissions and higher fuel efficiency has led to the design of lightweight and other technology solutions to automotive vehicles [ 1]. These new proposed solutions can also negatively affect the drivetrain. New technologies, such as start-stop systems [2], downsized engines [3], cylinder deactivation [ 4] and advanced torque lock-up strategies [ 5] are all examples of solutions that can be effective in reducing emissions, but that at the same time can generate undesired vibration issues, mostly propagated through the vehicle driveline. In this scenario, the advance of those technologies raises the importance of an in-depth understanding of torsional vibrations as they negatively impact comfort and are directly related to engine and drivetrain efficiency . The main consequences of these new technologies are: • High torque oscillations: the torque generated by internal combustion engines is irregular, containing ripples due to combustion cycles. Reducing the number of cylinders has the consequence of increasing this torque irregularity. • Lower engine speed: engine efficiency can be higher at lower rotational speeds, making it the tendency to operate engines at lower RPMs. However, these lower speed conditions can excite driveline torsional modes and suspension modes, leading to higher vibration levels. • Lower torsional damping: in automatic transmissions, locking the clutch at lower RPMs can increase the transmission efficiency, with the drawback of having less torsional damping in lower rotational speeds. Figure 1 summarizes these changes in the powertrain and how they affect the overall vibration levels. The first graph indicates how the lock-up condition happens before employing the more efficient methodologies, with the dashed vertical line representing the RPM state in which the clutch is locked, and the peak is related to the drivetrain resonance. By using turbo charged engines with a lower number of cylinders, the direct consequence is higher vibration levels, as shown in step number two of the first graph. Then, the use of a reduced number of cylinders leads to a shift in the excitation Model Based Approach by Combination of Test and Simulation Methodologies for NVH Investigation and Improvement of a Rear Wheel Drive Vehicle Fabio Luis Marques dos Santos, Tristan Enault, Jan Deleener, and Tom Van Houcke Siemens Industry Software ABSTRACT The increasing pressure on fuel economy has brought car manufacturers to implement solutions that improve vehicle efficiency , such as downsized engines, cylinder deactivation and advanced torque lock-up strategies. However , these solutions have a major drawback in terms of noise and vibration comfort. Downsized engines and lock-up strategies lead to the use of the engine at lower RPMs, and the reduced number of cylinders generates higher torque irregularities. Since the torque generated by the engine is transferred through flexible elements (clutch, torsional damper, gearbox, transmission, tire), these also impact the energy that is transferred to the vehicle body and perceived by the driver. This phenomenon leads to low frequency behavior, for instance booming noise and vibration. This paper presents a combined test and CAE modelling approach (1D/3D) to reverse engineer a vehicle equipped with a CPV A (centrifugal pendulum vibration absorber). The objectives were to fully understand and predict vehicle behavior with respect to the drivetrain torsional oscillations and low frequency booming noise and vibration. For this purpose, the procedure was divided in two phases: testing and modelling. The testing phase was used to get insight into the vehicle behavior, noise sources and noise transfer paths, using operational measurements. Moreover, dedicated component tests were carried out to obtain parameters to be used in the modelling phase, with the CPV A being the most complex and important component. The modelling