This application claims priority to EP application Serial No. 15190171.7 filed Oct. 16, 2015, the disclosure of which is hereby incorporated in its entirety by reference herein.
The disclosure relates to engine noise control systems and methods.
Engine order cancellation (EOC) technology uses a non-acoustic signal representative of the engine (motor) noise as a reference to synthesize a sound wave that is opposite in phase to the engine noise audible in the car interior. As a result, EOC makes it easier to reduce the use of conventional damping materials. Common EOC systems utilize a narrowband feed-forward active noise control (ANC) framework in order to generate anti-noise by adaptive filtering of a reference signal that represents the engine harmonics to be cancelled. After being transmitted via a secondary path from an anti-noise source to a listening position, the anti-noise has the same amplitude but opposite phase as the signals generated by the engine filtered by a primary path that extends from the engine to the listening position. Thus, at the place where an error microphone resides in the room, for example, at or close to the listening position, the overlaid acoustical result would ideally become zero so that error signals picked up by the error microphone would only record sounds other than the cancelled harmonic noise signals generated by the engine.
Commonly a non-acoustical sensor, for example, a sensor measuring the repetitions-per-minute (RPM), is used as a reference. The signal from the RPM sensor can be used as a synchronization signal for synthesizing an arbitrary number of harmonics corresponding to the engine harmonics. The synthesized harmonics form a basis for noise canceling signals generated by a subsequent narrowband feed-forward ANC system. Even if the engine harmonics mark the main contributions to the total engine noise, they by no means cover all noise components radiated by the engine, such as bearing play, chain slack, or valve bounce. However, an RPM sensor is not able to cover signals other than the harmonics.
An example engine noise control system includes a noise and vibration sensor configured to directly pick up engine noise from an engine of a vehicle and to generate a sense signal representative of the engine noise, and an active noise control filter configured to generate a filtered sense signal from the sense signal. The system further includes a loudspeaker configured to convert the filtered sense signal from the active noise control filter into anti-noise and to radiate the anti-noise to a listening position in an interior of the vehicle. The filtered sense signal is configured so that the anti-noise reduces the engine noise at the listening position.
An example engine noise control method includes directly picking up with a noise and vibration sensor engine noise from an engine of a vehicle at a pick-up position to generate a sense signal representative of the engine noise, and active noise control filtering to generate a filtered sense signal from the sense signal. The method further includes converting the filtered sense signal from the active noise control filtering into anti-noise and radiating the anti-noise to a listening position in an interior of the vehicle. The filtered sense signal is configured so that the anti-noise reduces the engine noise at the listening position.
The disclosure may be better understood by reading the following description of non-limiting embodiments in connection with the attached drawings, in which like elements are referred to with like reference numbers, wherein below:
As the name suggests, EOC technology is only able to control noise that corresponds to engine orders. Other components of the engine noise that have a non-negligible acoustical impact and that cannot be controlled with the signal provided by a narrowband non-acoustic sensor (e.g., RPM sensor) cannot be counteracted with such a system. Noise is generally the term used to designate sound, vibrations, accelerations and forces that do not contribute to the informational content of a receiver, but rather are perceived to interfere with the audio quality of a desired signal. The evolution process of noise can be typically divided into three phases. These are the generation of the noise, its propagation (emission) and its perception. It can be seen that an attempt to successfully reduce noise is initially aimed at the source of the noise itself, for example, by attenuation and subsequently by suppression of the propagation of the noise signal. Nonetheless, the emission of noise signals cannot be reduced to the desired degree in many cases. In such cases the concept of removing undesirable sound by superimposing a compensation signal is applied.
Methods and systems for canceling or reducing emitted noise suppress unwanted noise by generating cancellation sound waves to superimpose on the unwanted signal, whose amplitude and frequency values are for the most part identical to those of the noise signal, but whose phase is shifted by 180 degrees in relation to the unwanted signal. In ideal situations, this method fully extinguishes the unwanted noise. This effect of targeted reduction in the sound level of a noise signal is often referred to as destructive interference or noise control. In vehicles, the unwanted noise can be caused by effects of the engine, the tires, suspension and other units of the vehicle, and therefore varies with the speed, road conditions and operating states in the automobile.
The ENC system 100 uses the filtered-x least mean square (FXLMS) algorithm and includes a primary path 101 which has a (discrete time) transfer function P(z). The transfer function P(z) represents the transfer characteristic of the signal path between a vehicle's engine whose noise is to be controlled and a listening position, for example, a position in the interior of the vehicle where the noise is to be suppressed. The ENC system 100 also includes an adaptive filter 102 with a filter transfer function W(z), and an LMS adaptation unit 103 for calculating a set of filter coefficients w[n] that determines the filter transfer function W(z) of the adaptive filter 102. A secondary path 104 which has a transfer function S(z) is arranged downstream of the adaptive filter 102 and represents the signal path between a loudspeaker 105 that broadcasts a compensation signal y[n] to the listening position. For the sake of simplicity, the secondary path 104 may include the transfer characteristics of all components downstream of the adaptive filter 102, for example, amplifiers, digital-to-analog-converters, loudspeakers, acoustic transmission paths, microphones, and analog-to-digital-converters. A secondary path estimation filter 106 has a transfer function that is an estimation S*(z) of the secondary path transfer function S(z). The primary path 101 and the secondary path 104 are “real” systems essentially representing the physical properties of the listening room (e.g., the vehicle cabin), wherein the other transfer functions may be implemented in a digital signal processor.
Noise n[n] generated by the engine 107, which includes sound waves, accelerations, forces, vibrations, harness etc., is transferred via the primary path 101 to the listening position where it appears, after being filtered with the transfer function P(z), as disturbing noise signal d[n] which represents the engine noise audible at the listening position within the vehicle cabin. The noise n[n], after being picked up by a noise and vibration sensor such as an force transducer sensor (not shown) or an acceleration sensor 109, serves as a reference signal x[n]. Acceleration sensors may include accelerometers, force gauges, load cells, etc. For example, an accelerometer is a device that measures proper acceleration. Proper acceleration is not the same as coordinate acceleration, which is the rate of change of velocity. Single- and multi-axis models of accelerometers are available for detecting magnitude and direction of the proper acceleration, and can be used to sense orientation, coordinate acceleration, motion, vibration, and shock. The reference signal x[n] provided by the acceleration sensor 109 is input into the adaptive filter 102 which filters it with transfer function W(z) and outputs the compensation signal y[n]. The compensation signal y[n] is transferred via the secondary path 104 to the listening position where it appears, after being filtered with the transfer function S(z), as anti-noise y′[n]. The anti-noise y′[n] and the disturbing noise d[n] are destructively superposed at the listening position. A microphone 108 outputs a measurable residual signal, i.e., an error signal e[n] that is used for the adaptation in the LMS adaptation unit 103. The error signal e[n] represents the sound including (residual) noise present at the listening position, for example, in the cabin of the vehicle.
The filter coefficients w[n] are updated based on the reference signal x[n] filtered with the estimation S*(z) of the secondary path transfer function S(z) which represents the signal distortion in the secondary path 104. The secondary path estimation filter 106 is supplied with the reference signal x[n] and provides a filtered reference signal x′[n] to the LMS adaptation unit 103. The overall transfer function W(z)·S(z) provided by the series connection of the adaptive filter 102 and the secondary path 104 converges against the primary path transfer function P(z). The adaptive filter 102 shifts the phase of the reference signal x[n] by 180 degrees so that the disturbing noise d[n] and the anti-noise y′[n] are destructively superposed, thereby suppressing the disturbing noise d[n] at the listening position.
The error signal e[n] as measured by microphone 108 and the filtered reference signal x′[n] provided by the secondary path estimation filter 106 are supplied to the LMS adaptation unit 103. The LMS adaptation unit 103 calculates the filter coefficients w[n] for the adaptive filter 102 from the filtered reference signal x′[n] (“filtered x”) and the error signal e[n] such that the norm (i.e., the power or L2-Norm) of the error signal e[n] is reduced. The filter coefficients w[n] are calculated, for example, using the LMS algorithm. The adaptive filter 102, LMS adaptation unit 103 and secondary path estimation filter 106 may be implemented in a digital signal processor. Of course, alternatives or modifications of the “filtered-x LMS” algorithm, such as, for example, the “filtered-e LMS” algorithm, are also applicable.
Since the acceleration sensor 109 is able to directly pick up noise n[n] in a broad frequency band of the audible spectrum, the system shown in
The exemplary system shown in
A broadband acceleration sensor is able to pick up engine noise up to at least 1.5 kHz, for example, at least 2 kHz as shown in
One or more noise and vibration sensors, for example, acceleration sensors, used in connection with single-channel or multi-channel ENC systems, may be mounted on flat surfaces on specific locations in the vehicle such as the noise and vibration paths between the engine and the gear box, between the engine and structural elements of the chassis/body of the vehicle, between the engine and the exhaust, at the suspension of the exhaust, on the engine casing, at a firewall between engine and vehicle cabin etc. The one or more acceleration sensors may be disposed, for example, on the engine mounts, at the engine mounting casing or mounting brackets, beyond the engine mounts on the vehicle body structure, on the exhaust mounts and the rear body panel.
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The description of embodiments has been presented for purposes of illustration and description. Suitable modifications and variations to the embodiments may be performed in light of the above description or may be acquired by practicing the methods. For example, unless otherwise noted, one or more of the described methods may be performed by a suitable device and/or combination of devices. The described methods and associated actions may also be performed in various orders in addition to the order described in this application, in parallel, and/or simultaneously. The described systems are exemplary in nature, and may include additional elements and/or omit elements.
As used in this application, an element or step recited in the singular and preceded by the word “a” or “an” should be understood as not excluding the plural of said elements or steps, unless such exclusion is stated. Furthermore, references to “one embodiment” or “one example” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. The terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements or a particular positional order on their objects.
Number | Date | Country | Kind |
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15 190 171.7 | Oct 2015 | EP | regional |