This research aims to develop a method to efficiently reduce the body input force from the chassis due to road-induced excitation. To this end, the frequency response function–based substructuring method is employed to model the vehicle cross member and coupling points. Using this model, the dynamic stiffness modification factor of elastic bushing at the effective path is predicted for reducing road noise. Because of the difficulties in directly obtaining dynamic properties of body mount bushings pressured into the sub-frame, the frequency response function–based substructuring model and inverse formulation method are used to indirectly estimate the bushing’s dynamic properties. Therefore, the primary focus of this study is to validate the feasibility of using the inverse formulation method for deriving road noise improvement factor on a simple cross member application. In this feasibility validation, road excitation is simply substituted with a shaker excitation in vertical direction. The previously developed suspension rig that enables a direct measurement of the body input force at the coupling points and the specially developed cross member jig are used for the validation test.
Numerous previous studies have been conducted on quantifying road noise through transfer path analysis (TPA) using the matrix inversion and the dynamic stiffness methods. However, the matrix inversion method is a calculation that always contains error, even when treated with the best
condition number found by trial and error iteration to match the calculation SPL (sound pressure level) to measured SPL. Furthermore, the caveat of the dynamic stiffness method is that it requires accurate dynamic stiffness value up to the frequency range of interest, which, in reality, is
rarely available and is challenging to obtain. Therefore, TPA using these two methods is only possible when a complete vehicle is available. For the sake of cost and time reduction, circumventing these limitations is crucial within the vehicle production period. The main focus of the present
study is to directly obtain the operational forces at the suspension mounting points neglecting the effect of the vehicle body through a special suspension rig. The suspension rig is verified through a comparative analysis with the actual baseline vehicle measurement up to 250 Hz. In addition,
an example approach for finding suspension's NVH performance improving factor using the rig benchmarking technique is introduced.
This study aims to estimate the change in suspension to body input force transmission due to the softening of the connecting elastomer under rolling excitation. In this respect, the suspension coupled to a vehicle body via an elastomer bushing is modeled using point impedance. A numerical study is performed for achievable force reduction due to a softened bush under the influence of different impedance combinations for the suspension and the vehicle body. Following a numerical study, the proposed model is validated through empirical testing of McPherson strut type suspension in the lateral arm Y direction and multilink type rear suspension in the front mount X direction, which represent extremely stiff and extremely soft coupling cases for the suspension type, respectively. Due to the difficulties in measuring road-induced operational forces within an actual vehicle, a validation test is performed using a previously developed rig that enables direct measurement of the force without modifying the structure of the suspension. Additionally, the rig-measured force, which is potentially misleading due to the large deviation in stiffness between the rig and an actual vehicle, is investigated under varying combinations of suspension and bush stiffness.
<div class="section abstract"><div class="htmlview paragraph">Numerical simulations offer a wide range of benefits. Therefore, they are widely used in research and development. One of the biggest benefits is the possibility of automated parameter variation. This allows testing different scenarios very quickly. Nevertheless, physical experiments in the laboratory or on a test rig are still, and will remain, necessary. Physical experiments offer benefits, e.g., for very complex and/or nonlinear systems and are required for the validation of numerical models. To enhance the quality of experimental NVH investigations and to make use of the benefits of numerical simulation during experimental investigations at the same time, numerical models can be integrated into physical test rigs using the mechanical hardware-in-the-loop (mHIL) method (also referred to as real-time dynamic substructuring, hybrid testing or active control of impedance). During experimental NVH testing, the device under test (DUT) is connected to a mHIL interface which in turn actively emulates the structural dynamics of the boundary condition based on a numerical target impedance model. The goal is to have realistic contact forces instead of blocked forces at the mounting points of the DUT.</div><div class="htmlview paragraph">This paper illustrates the development and characterization of a modular mHIL interface with high bandwidth for NVH testing of a vehicle’s front axle. The physical emulation of structural dynamics based on a target impedance model is demonstrated for synthetic test cases (e.g., emulation of different stiffness settings, or multi-resonant behavior) up to 1 kHz. Furthermore, emulation of the vehicle chassis’ structural dynamics in a single spatial direction is shown for an NVH investigation on a single-axis chassis dynamometer.</div></div>
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