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A multichannel active noise control (ANC) system has been developed for a vehicle application, which employs loudspeakers to reduce the low-frequency road noise. Six accelerometers were attached to the vehicle structure to provide the reference signal for the feedforward control strategy, and two loudspeakers and two microphones were applied to attenuate acoustic noise near the headrest of the driver's seat. To avoid large computational burden caused by the conventional time-domain filtered-x least mean square (FXLMS) algorithm, a time-frequency domain FXLMS (TF-FXLMS) algorithm is proposed. The proposed algorithm calculates the gradient estimate and filtered reference signal in the frequency domain to reduce the computational requirement, while also updates the control signals in the time domain to avoid delay. A comprehensive computational complexity analysis is conducted to demonstrate that the proposed algorithm requires significantly lower computational cost as compared to the conventional FXLMS algorithm.

Conventional active control of road noise inside a vehicle cabin generally uses a pure feedforward control system with the conventional filtered-x least mean square (FXLMS) algorithm. While it can yield satisfactory noise reduction when the reference signal is well correlated with the targeted noise, in practice, it is not always possible to obtain a reference signal that is highly coherent with a broadband response typically seen in road noise. To address this problem, an active noise control (ANC) system with a combined feedforward–feedback controller is proposed to improve the performance of attenuating road noise. To take full advantage of the feedforward control, a subband (SFXLMS) algorithm, which can achieve more noise attenuation over a broad frequency range, is used to replace the conventional FXLMS algorithm. Meanwhile, a feedback controller, based on internal model control (IMC) architecture, is introduced to reduce the road noise components that have strong response but are poorly correlated with the reference signals. The proposed combined feedforward–feedback ANC system has been demonstrated by a simulation model with six reference accelerometers, two control loudspeakers and one error microphone, using actual data measured from a test vehicle. Results show that the performance of the proposed combined controller is significantly better than using either a feedforward controller only or a feedback controller only, and is able to achieve about 4 dBA of overall sound pressure level reduction.

An enhanced multiple-input multiple-output (MIMO) filtered-x least mean square (FXLMS) algorithm using improved virtual secondary path is proposed as the basis for an active noise control (ANC) system for treating vehicle powertrain noise. This new algorithm is developed to overcome the limitation caused by the frequency-dependent property of the standard FXLMS algorithm and to reduce the variation of convergence speed inherent in multiple-channel cases, in order to improve the overall performance of the control system. In this study, the convergence property of the proposed algorithm is analyzed in the frequency domain in order to yield a better understanding of the physical meaning of the virtual secondary path. In practice, because of the arrangement and sensitivities of the actuators (speakers), transducers (microphones), and physical environment, the magnitude response of the main secondary paths can be very different from each other. This difference will cause difficulty in the overall convergence of the algorithm, which will result in minimal attenuation at some of the channels. The proposed channel equalized (CE) virtual secondary path algorithm is designed to tackle this difficulty by equalizing the mean magnitude level of the main secondary paths and by adjusting other secondary paths correspondingly to keep the coupling effects among the control channels unchanged. The performance of the proposed algorithm is validated by analyzing a two-input two-output active powertrain noise control system.

Sound radiation characteristics of an annular disk with application to the computer disk are examined analytically. The far‐field and the radiation impedance approaches are employed to calculate radiated sound of a disk vibrating at its elastic or rigid body modes. Modal sound power is formulated by approximating the structural modal functions and is expressed in terms of a power series of the wave number. Predictions show that axisymmetric vibration modes are more efficient radiators compared to those asymmetric disk modes that have the same number of nodal circles. Numerical results obtained by a boundary element program are used to support analytical predictions. Formulations are also extended to include the modal coupling and source rotation effects. The effect of coupling between disk vibration modes on the radiated sound is found to be significant if multimodes are excited. A simple empirical equation has been developed to predict the modal sound radiation efficiency of a rotating disk for selected vibration modes.

Powertrain noise is a major component of vehicle interior noise and thus has a significant effect on the overall sound quality. It is typically dominated by harmonics in the lower audible frequency range, which are directly related to the engine firing orders. In order to achieve a more comfortable environment and pleasing driving experience, an active noise control (ANC) applying advanced filtered-x least mean squares (FXLMS) algorithm is employed to reduce the vehicle interior noise by targeting these harmonics. The proposed ANC system is designed to control multiple orders of the engine noise response simultaneously. It is also uniquely formulated with a twin-FXLMS algorithm to prevent harmonic interference that often resulted in overshoot at some adjacent orders, especially at low engine speed range where the reference sinusoids are close together. In fact, the interference issue is one of the critical problems that previously plagued the use of the conventional FXLMS algorithm. The basic design of the twin-FXLMS algorithm splits the adaptive filter into two sets. This allows different sum of reference sinusoids to be fed into each adaptive filter in order to widen the frequency separation between two adjacent harmonics. Finally, the performances of proposed twin-FXLMS are validated by numerical simulations.

Past studies have shown that NVH CAE tire model quality is not adequate to correctly capture a mid-frequency range (100-300 Hz). A new methodology has been developed to estimate tire forces that are independent of dynamic characteristics of vehicle suspension and rig test fixture. The forces are called tire blocked forces and defined as a force generated by a tire/wheel system whose boundary condition is constrained. The tire blocked force is estimated by removing the dynamic effect of the tire force measurement fixture. The blocked forces can be applied to CAE models to predict vehicle road NVH responses. This new method can also be used as a target setting tool. Tire suppliers can check the blocked tire forces from the rig testing data against a force target before they submit tires to automotive manufacturers for evaluations on a prototype vehicle.

Traditional vehicle active noise control (ANC) is designed to suppress unwanted vehicle response. In this study, an ANC system is proposed for tuning rather than suppressing vehicle interior response. The proposed concept is studied numerically, utilizing simulated control input speakers inside the passenger compartment. The proposed control algorithm is adapted from the basic filtered-x least mean squares (FXLMS) algorithm. In this case, instead of using the FXLMS algorithm to minimize the resultant sound pressure level, a set of target functions is added to the controller for shaping the vehicle interior response. The proposed computer simulation can incorporate either measured or predicted cavity acoustic transfer functions. Using this analysis model, the proposed approach is demonstrated using a powertrain noise example in which individual engine firing orders are targeted for shaping either by reducing or enhancing the spectral content

Currently, passive noise control treatment is widely applied to treat vehicle powertrain noise. However, passive noise control technology is often not effective in the low frequency range where the response is typically the most dominant component. With the rapid development of digital signal processing, active noise control (ANC) can be a feasible alternative. In this study, an enhanced frequency domain filtered-x least mean square (FXLMS) algorithm is proposed as the basis of an active control system for treating powertrain interior noise. Compared to the time domain algorithms, the approach can save computing time especially for long controller's filter length. Furthermore, unlike traditional ANC techniques for suppressing response, the proposed frequency domain FXLMS algorithm is targeted at tuning vehicle interior response in order to achieve a desirable sound quality. Several frequency domain algorithms are studied numerically by applying the analysis to treat vehicle interior noise recorded from an actual vehicle.

Vehicle noise, vibration and harshness (NVH) problems can be analyzed using numerical methods such as finite element and boundary element analyses that are generally complex and time consuming. In order to reduce the analysis time and calculation burden, this paper discusses the development, use and verification of an enhanced, simplified numerical acoustic cavity formulation for the analysis of vehicle NVH problems. The proposed simplified vehicle model can incorporate multiple acoustic cavities, such as an engine compartment, passenger compartment, and connecting bulkhead compartment, joined by several flexible panels. The damping matrix of the model is constructed from measured acoustic absorption data and panel properties. Utilizing this approach, both single-cavity and three-cavity models are created, different floor panel configurations are investigated, and transfer functions predicted by these models are compared with corresponding transfer functions from measured data. The comparison results show that the proposed simplified model can provide reasonable accuracy for the analysis and simulation of vehicle compartment acoustics.

Analysis of brushless D.C. motor (BDCM) torque pulsations is an essential step in the diagnosis and control of vibration and noise generated by many electro-mechanical devices. The broad band spectral content of the torque pulsations, as predicted by a mathematical model which accounts for various complex effects, can often be obtained only by numerical integration which is time consuming while permitting little understanding of the dynamic interactions. Prior analytical approaches, such as the Fourier series technique or the d-q axis theory, are limited by the simplifying assumptions needed to compute the torque spectrum. This paper develops a new semi-analytical formulation for the analysis of nonlinear, time-varying BDCM’s which involve both spatial and temporal domains. A modified multi-term harmonic balance method, based on a transformation of the dual-domain problem to a spatial domain formulation, is developed here specifically to compute the magnitude of several harmonics of the pulsating torque. The interacting effects of key parameters, like dynamic eccentricity, magnetic saturation and open stator slots, on the time-varying inductances and rotor flux density distribution are included explicitly in the formulation. The predicted spectra compare very well with those obtained by direct time domain numerical integration. Yet, the proposed method is computationally efficient especially when the model dimension is reduced. It also provides better insight into the high frequency dynamics of the sample case.