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Technical Paper

Measurement Technique for Quantifying Structure Borne and Air Borne Noise Levels in Utility Vehicle

2014-04-01
2014-01-0003
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.
Technical Paper

Experimental Investigation of Effect of Driveline Torsional Fluctuations on Overall NVH Performance of the Vehicle

2015-06-15
2015-01-2192
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.
Technical Paper

Dynamic Stiffness Estimation of Elastomeric Mounts Using OPAX in an AWD Monocoque SUV

2015-06-15
2015-01-2190
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).
Technical Paper

Analysis of Drive Line Vibration and Boom Noise in an All Wheel Drive Utility Vehicle

2014-04-01
2014-01-1975
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.
Technical Paper

NVH Analysis of Powertrain Start/Stop Transient Phenomenon by using Wavelet Analysis and Time Domain Transfer Path Analysis

2015-06-15
2015-01-2293
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.
Technical Paper

Analysis and Reduction of Abnormal Suspension Noise in Sports Utility Vehicle

2024-01-16
2024-26-0217
This paper focuses on reducing abnormal noise originating from suspension when driving on rough road at the speed of 20 kmph. The test vehicle is a front wheel driven monocoque SUV powered by four cylinder engine. Cabin noise levels are higher between 100 to 800 Hz when driven on rough road at 20 kmph. Vibration levels are measured on front and rear suspension components, front and rear subframe, subframe connections on body to identify the noise source locations. Since the noise levels are dominant only in certain rough patches at very narrow band of time, wavelet analysis is used for identification of frequency at which the problem exist. Based on wavelet analysis, it is identified that the vibration levels are dominant on front lower control arm (LCA). The dynamic stiffness of LCA bushes is reduced by ~ 40% to improve the isolator performance which reduced the noise levels by ~ 9 dB (A) at the problematic frequency band.
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