Noise, vibration, and harshness (NVH) has been an important factor in the development of modern motor vehicles since the 1980s. One of the challenges is the control of low-frequency powertrain and road noise inside passenger cabin. Traditional passive control approach uses heavier and/or thicker materials for low-frequency noise reduction, which worsens the fuel efficiency of the vehicle due to the added weight. To satisfy the increasing demand for both fuel efficiency and better NVH performance, active noise control (ANC) that works better at low-frequency noise attenuation with slight increase in weight, can be a promising solution. The most common ANC system uses feedforward control approach formulated with filtered-x least mean square (FXLMS) algorithm. However, the conventional method experiences some difficulties when applying to vehicle low-frequency acoustic noise control. The focus of this dissertation is to develop a feasible ANC system with advanced control algorithms for use inside the passenger compartment of motor vehicles.
Powertrain noise that is dominated by a large number of harmonics is most perceivable when vehicle is at idle or changing speed conditions. Because of the tonal nature, it can negatively impact sound quality inside the passenger cabin. The slow convergence behavior of the conventional FXLMS algorithm is one of the factors that degrade the overall performance of powertrain noise control. In this dissertation, virtual secondary path algorithm is proposed to improve the convergence of the adaptive algorithm. Another challenge is to control multiple orders of powertrain response simultaneously. When the conventional FXLMS algorithm is applied, harmonic interference may occur that often results in overshoot at some adjacent orders. Twin-FXLMS algorithm is proposed to address this problem, by splitting the adaptive filter into two sets, such that the adjacent sinusoids are spaced out farther apart. In addition, traditional ANC system is aimed to reduce the sound pressure level as much as possible. However, powertrain response carries some useful information about the engine speed and power. To achieve a better vehicle interior sound quality, active powertrain response tuning system is presented to either enhance or attenuate the powertrain order selectively.
Road noise is the dominant source when the vehicle is driving at middle or high speed. In contrast to powertrain noise, road noise is more fatiguing and irritating than having benefit. Thus, road noise must be well treated. In practice, it is difficult to obtain reference signals that are well correlated with the targeted noise in a broad frequency range. A combined feedforward-feedback control approach is proposed to solve this problem, which is uniquely formulated with subband FXLMS algorithm. In addition, the computational complexity is another important consideration of the control algorithm. However, the conventional FXLMS algorithm can requite huge computational burden, especially for the multi-reference multi-channel control system. Here, time-frequency-domain FXLMS algorithm is utilized to significantly reduce the computational complexity. Furthermore, a novel channel equalization concept is proposed to overcome the channel dependent convergence behavior of the multichannel FXLMS algorithm.
|Advisor:||Lim, Teik C.|
|Commitee:||Huston, Ronald, Kim, Jay, Kumar, Manish, Thompson, David|
|School:||University of Cincinnati|
|School Location:||United States -- Ohio|
|Source:||DAI-B 73/01, Dissertation Abstracts International|
|Subjects:||Mechanical engineering, Acoustics|
|Keywords:||Active noise control, Adaptive control, Powertrain noise, Road noise|
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