Abstract
This study shows that a concurrent active noise control strategy for engine harmonics and road noise has a complementary effect. In particular, we found that engine booming noise is additionally attenuated when road noise control is concurrently used with engine harmonics control; an additional attenuation of 2.08 dB and 1.25 dB for the C1.5 and C2.0 orders, respectively, was achieved. A parallel multichannel feedforward controller for non-stationary narrowband engine harmonics and broadband road noise was designed and implemented to reduce noise in all four seats. Two control signals were considered independent because the reference signals, engine revolution speed for the engine harmonic controller, and acceleration signal for the road noise controller are uncorrelated. However, if the reference sensor for the road noise controller is installed along the overlapping transfer path between the engine noise and road noise, the engine noise may also be suppressed by the control signal for the road noise attenuation. Based on transfer path analyses for both engine harmonics and road noise, the optimal positions for the reference sensors were selected. In addition, we identified several overlapping transfer paths between the engine booming noise and road noise. A practical active noise control system combined with a remote microphone technique was implemented for a large six-cylinder sedan using a vehicle audio system to evaluate the noise attenuation performance. The experiments showed that the interior noise from the engine and road excitation was effectively suppressed by the proposed concurrent control strategy.
Highlights
Active noise control (ANC) in vehicles has been widely researched to resolve low-frequency noise problems
The engine revolution speed obtained via controller area network (CAN) bus has been used as a reference signal [13] instead of physical sensors such as microphones or accelerometers to reduce the cost of the ANC system
In concurrent control, when selecting the position of the reference sensor in the road noise controller, if an overlapping position is selected among the transfer paths of the two noise sources, the engine harmonics are expected to be controlled through the road noise cancellation (RNC) signal
Summary
Active noise control (ANC) in vehicles has been widely researched to resolve low-frequency noise problems. Fast convergence and stability are critical because the FxLMS algorithm can lead to instability problems, such as nonlinear distortion and divergence This occurs when excessive noise levels overload the secondary source [20]. Coherence analysis considering vibro-acoustic paths has been applied to select optimal reference sensor positions [27] Both ANC technologies have been successfully developed and implemented in practice for their respective targets, concurrent control of powertrain noise and road noise is required to enhance acoustic comfort further. In concurrent control, when selecting the position of the reference sensor in the road noise controller, if an overlapping position is selected among the transfer paths of the two noise sources, the engine harmonics are expected to be controlled through the RNC signal. The primary aim of this study is to design and implement concurrent active noise control to reduce both nonstationary narrowband engine harmonics and broadband road noise.
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