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A low frequency vibration issue around 3.2 Hz occurs during a commercial heavy truck program development process, and it is linked to extremely uncomfortable driving and riding experiences. This work focuses on an analytical effort to resolve the issue by first building a full vehicle MBS (multi-body-system) model, and then carrying out vibration response analyses. The model validation is performed by using full vehicle testing in terms of structural modes and frequency response characteristics. In order to resolve the issue which is excited by tire non-uniformity, the influence of the cab suspension, frame modes, front leaf spring system and rear tandem suspension is analyzed. The root cause of the issue is found to be the poor isolation of the rear tandem suspension system. The analytical optimization effort establishes the resolution measure for the issue.

When a window opens to provide the occupant with fresh air flow while driving, wind throb problems may develop along with it. This work focuses on an analytical approach to address the wind throb issue for passenger vehicles when a front window or sunroof is open. The first case of this paper pertains to the front window throb issue for the current Ford Escape. Early in a program stage, CAA (Computational Aeroacoustics) analysis predicted that the wind throb level exceeded the program wind throb target. When a prototype vehicle became available, the wind tunnel test confirmed the much earlier analytical result. In an attempt to resolve this issue, the efforts focused on a design proposal to implement a wind spoiler on the side mirror sail, with the spoiler dimension only 6 millimeters in height. This work showed that the full vehicle CAA analysis could capture the impact of this tiny geometry variation on the wind throb level inside the vehicle cabin.

When a sunroof opens to let in fresh air while driving, there might be several noise issues associated with it. The most common and painful one is the wind throb issue, which is nevertheless largely resolved by implementing a sufficiently high wind deflector along the front edge of the sunroof. However, with the wind throb suppressed, other sound quality issues might emerge. The most notable one is the hissing noise issue, which becomes increasingly objectionable with the increase of vehicle speed. This work looks into the impact of sunroof deflector on interior sound quality with the consideration of wind throb, hissing noise and booming noise in terms of psychoacoustic attributes that could be felt subjectively. The goal is to achieve a better understanding of the sound quality associated with the sunroof deflector design, and inspire a balanced design, potentially targeting the most NVH demanding customers in the premium vehicle segment.

Wind noise is one of the most influential NVH attributes that impact customer sensation of vehicle interior quietness. Among many factors that influence wind noise performance, the amount of dynamic door deflection under the pressure load due to fast movement of a vehicle plays a key roll. Excessive deflection could potentially lead to loss of sealing contact, causing aspiration leakage, which creates an effectual path through which the exterior aerodynamically induced noise propagates into the vehicle cabin. The dynamic door deflection can be predicted using CFD and CAE approaches which, in addition to modeling the structure correctly, require a correct pressure loading composed of external and internal pressure distributions. The determination of external pressure distributions can be fulfilled fairly straightforward by using commercial CFD codes such as Fluent, Star CCM+, Powerflow and others.

This work carries out complex modal analyses and optimizations to resolve an 1800 Hz front brake squeal issue encountered in a vehicle program development phase. The stability theory of complex modes for brake squeal simulation is briefly explained. A brake system finite element model is constructed, and the model is validated by the measurement in accordance with the SAE 2521 procedure. The key parameters for evaluating the stability of the brake system complex modes are determined. The modal contributions of relevant components to unstable modes are analyzed and ranked. Finally, in order to resolve the squeal issue, the design improvements of rotor, caliper and pad are proposed and numerical simulations are carried out. The obtained results demonstrate that the optimized rotor and pad design can alleviate the squeal issue significantly while the optimized clipper design could essentially eliminate the squeal issue.