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In today’s automotive scenario, noise vibration and harshness (NVH) has become a synonym for quality perception. This paper evaluates the problem of vibration and noise experienced in M2 category 40 seat bus and suggests the counter measures. Severe vibration is experienced on the bus floor, predominantly towards rear part of the bus. Vibration along with acoustic boom occurs prominently in 4th gear wide open throttle operating condition between 1300-1600 rpm of the engine. This paper focuses on reducing NVH levels by working on the transfer path with little modifications on power-train. Preliminary torsional measurements conducted on powertrain indicated high torsional excitation in the driveline during the problematic rpm zone. Further, Operational Deflection Shape (ODS) analysis revealed that the transfer path to the cabin is rear differential unit and suspension links. The dominant frequencies were identified along the transfer path and suitable modifications were done.

NVH is becoming one of the major factor for customer selection of vehicle along with parameters like fuel economy and drivability. One of the major NVH challenges is to have a vehicle with aggressive drivability and at the same time with acceptable noise and vibration levels. This paper focuses on the compact utility vehicle where the howling noise is occurring at higher rpm of the engine. The vehicle is powered by three cylinder turbocharged diesel engine. The noise levels were higher above 2500 rpm due to the presence of structural resonance. Operational deflection shapes (ODS) and Transfer path analysis (TPA) analysis was done on entire vehicle and powertrain to find out the major reason for howling noise at higher engine rpm. It is observed that the major contribution for noise at higher rpm is due to modal coupling between powertrain, half shaft and vehicle sub frame.

Accurate quantification of structure borne noise is a challenging task for NVH engineers. The structural excitation sources of vibration and noise such as powertrain and suspension are connected to the passenger compartment by means of elastomer mounts and spring elements. The indirect force estimation methods such as complex dynamic stiffness method and matrix inversion method are being used to overcome the limitations of direct measurement. In many practical applications, the data pertaining to load dependent dynamic stiffness of the connections especially related to mounts is not available throughout the frequency range of interest which limits the application of complex dynamic stiffness method. The matrix inversion method mainly suffers from the drawback that it needs operational data not contaminated by the effect of other forces which are not considered for calculation.

Meeting various customer(s) requirements with the given automotive product portfolio within the stipulated time period is a challenge. Design of product configuration matrix is an intelligent task and it requires information about vehicle performance for different configurations which helps in deciding the level of new development. Most often the situation arises, particularly in the field of NVH, to strike the right balance between engine power and structural parameters of the body. The sensitivity of engine power on the overall NVH behavior is the key information necessary to take major business decisions. In this paper, the effect of change in torsional fluctuation of the engine on the NVH behavior of the rear wheel drive vehicle is experimentally studied. The torsional fluctuation of the driveline is given as an input with the help of an electric motor to the existing test vehicle at its differential end and the current NVH levels are measured.

Mount development and optimization plays an important role in the NVH refinement of vehicle as they significantly influence overall driving experience. Dynamic stiffness is a key parameter that directly affects the mount performance. Conventional dynamic stiffness evaluation techniques are cumbersome and time consuming. The dynamic stiffness of mount depends on the magnitude of load, frequency of application and the working displacement. The above parameters would be far different in the test conditions under which the mounts are normally tested when compared to operating conditions. Hence there is need to find the dynamic stiffness of mounts in actual vehicle operating conditions. In this paper, the dynamic stiffness of elastomeric mounts is estimated by using a modified matrix inversion technique popularly termed as operational path analysis with exogenous inputs (OPAX).

The customer demand for all wheel drive (AWD) vehicles is increasing over the period of time which also requires NVH performance on par with front wheel drive vehicles. AWD vehicles are equipped with power transfer unit, propeller shaft and independent rear differential assembly to achieve their functional requirement. The additional drive train components in AWD vehicles may amplify torsional fluctuations in the drive line. Hence achieving the NVH performance of AWD vehicles on par with FWD vehicles without any major change in the existing design is a major challenge. In this work, an AWD vehicle with severe body vibration and booming noise is studied. The operational measurements are taken throughout the drive train on all sub-systems from engine to the rear part of the body in the problematic operating condition. An operational deflection shape analysis is conducted to visualize the vibration behavior of the drive train.

Tactile vibration during vehicle key on/off is one of the critical factors contributing to the customer perceived quality of the vehicle. Minimization of the powertrain transient vibration in operating conditions such as key on/off, tip in/out and engagement/disengagement of engine in hybrid vehicles must be addressed carefully in the vehicle refinement stage. Source of start/stop vibration depends on many factors like engine cranking, engine rpm at which the combustion process starts and rate of engine rpm rise etc. The transfer path consists of elastomeric mounts of powertrain and the part of vehicle structure from mounts to tactile response location. In this paper, the contribution of rigid body motion of powertrain of a front wheel drive vehicle during key on/off is analyzed in both frequency and time domain. The signal is analyzed in frequency domain by using fast fourier transform, short time fourier transform and wavelet analysis.