Active Sound Management in Noise Cancellation Systems

Abstract

The present disclosure provides a noise cancellation system and method for receiving a reference signal representing noise to be reduced and providing a noise cancellation signal based on the reference signal. Some examples include a feedback signal representing residual noise in an environment. At least one of the reference signal, the noise cancellation signal, or the feedback signal is filtered to remove a component based on the rotation rate of a rotating device associated with the environment (such as an engine of a vehicle). Therefore, the noise cancellation system can not interfere with sounds associated with the engine.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application is related to and claims the benefit of U.S. Provisional Patent Application Serial No. 62 / 827,554, filed on April 1, 2019, entitled “ACTIVE SOUND MANAGEMENT INNOISE CANCELATION SYSTEMS,” which is incorporated herein in its entirety for all purposes. Background Art

[0003] An exemplary road noise cancellation (RNC) system may generate an audio signal intended to counteract road noise, and may use accelerometers at various locations in the vehicle to provide a road noise reference source. A feedback microphone may monitor the acoustic energy generated within the vehicle cabin and adjust various operating characteristics of the road noise cancellation system, such as an adaptive feed-forward filter, etc. In addition, an active sound management (ASM) system may operate to enhance or otherwise change the perceived sound of vehicle operation, such as through engine harmonic cancellation (EHC) and / or engine harmonic enhancement (EHE) (collectively referred to as EHx). In various examples, the signals generated by the ASM system or the RNC system may interact, such as either system may cause the other system to change operation. For example, the active sound generated by the ASM system may be perceived as road noise by the RNC system, so that the RNC system may attempt to reduce the sound that the ASM system is actively operating to generate. If the accelerometer of the RNC system picks up engine vibrations, such effects may be further aggravated. Therefore, it is necessary to address or reduce the interaction between the ASM and RNC systems. Summary of the invention

[0004] The systems and methods disclosed herein relate to noise cancellation systems, methods, and applications that remove selected signal components, such as those associated with the rotation of an engine, from various signals operated by the noise cancellation system to allow the noise cancellation system to operate without interfering with acoustic sounds associated with the engine.

[0005] According to one aspect, a noise cancellation method is provided, the method comprising receiving a reference signal representing noise to be reduced, providing a noise cancellation signal based on the reference signal, receiving a feedback signal representing residual noise in the environment, and filtering at least one of the reference signal, the noise cancellation signal, or the feedback signal based on a rotation rate of a rotating device associated with the environment.

[0006] In various examples, filtering at least one of the reference signal, the noise cancellation signal, or the feedback signal based on a rotation rate of the rotating device includes filtering out a frequency bandwidth based on a change in the rotation rate.

[0007] Some examples include determining a first rotation rate at a first time, determining a second rotation rate at a second time, and determining a difference between the first rotation rate and the second rotation rate as the change in the rotation rate.

[0008] In some examples, the range of the frequency bandwidth is linearly related to the range of variation of the rotation rate.

[0009] In various examples, filtering at least one of the reference signal, the noise cancellation signal, or the feedback signal based on a rotation rate of the rotating device includes filtering a frequency bandwidth based on a rate of change of the rotation rate.

[0010] In some examples, filtering at least one of the reference signal, the noise cancellation signal, or the feedback signal based on a rotation rate of the rotating device includes filtering out a frequency notch centered around a frequency based on the rotation rate. In some examples, the frequency may be a harmonic of the rotation rate.

[0011] According to another aspect, a noise cancellation system is provided, the noise cancellation system including: a noise sensor configured to provide a reference signal representing noise to be reduced in an environment; a controller coupled to the noise sensor to receive the reference signal and provide a noise cancellation signal based on the reference signal; a transducer coupled to the controller to convert the noise cancellation signal into an acoustic signal in the environment; and a filter coupled to the controller to filter a selected signal based on a rotation rate of a rotating device associated with the environment.

[0012] Some examples include a feedback sensor that provides a feedback signal representative of residual noise in the environment, and the selected signal is at least one of the reference signal, the noise cancellation signal, and the feedback signal.

[0013] In various examples, filtering the selected signal based on a rotation rate of the rotating device includes filtering out a frequency bandwidth based on a change in the rotation rate.

[0014] In some examples, the controller determines a first rotation rate at a first time, determines a second rotation rate at a second time, and determines a difference between the first rotation rate and the second rotation rate as the change in the rotation rate.

[0015] In some examples, the range of the frequency bandwidth is linearly related to the range of variation of the rotation rate.

[0016] In various examples, filtering the selected signal based on a rotation rate of the rotating device includes filtering a frequency bandwidth based on a rate of change of the rotation rate.

[0017] In some examples, filtering the selected signal based on a rotation rate of the rotating device includes filtering out a frequency notch centered at a frequency based on the rotation rate.

[0018] According to another aspect, a non-transitory computer-readable medium is provided having instructions stored thereon, which, when executed by a suitable processor, causes the processor to perform a method comprising: receiving a reference signal representing noise to be reduced in an environment; providing a noise cancellation signal based on the reference signal; and filtering a selected signal based on a rotation rate of a rotating device associated with the environment.

[0019] In some examples, the processor also receives a feedback signal representative of residual noise in the environment, and the selected signal is at least one of the reference signal, the noise cancellation signal, and the feedback signal.

[0020] In various examples, filtering the selected signal based on a rotation rate of the rotating device includes filtering out a frequency bandwidth based on a change in the rotation rate.

[0021] In some examples, the processor may determine a first rotation rate at a first time, determine a second rotation rate at a second time, and determine a difference between the first rotation rate and the second rotation rate as the change in the rotation rate.

[0022] In some examples, the range of the frequency bandwidth is linearly related to the range of variation of the rotation rate.

[0023] In some examples, filtering the selected signal based on a rotation rate of the rotating device includes filtering out a frequency notch centered at a frequency based on the rotation rate.

[0024] Other aspects, examples and advantages of these exemplary aspects and examples are still discussed in detail below. The examples disclosed herein may be combined with other examples in any manner consistent with at least one principle disclosed herein, and references to "examples", "some examples", "alternative examples", "various examples", "an example", etc. are not necessarily mutually exclusive and are intended to indicate that the specific features, structures or characteristics described may be included in at least one example. The appearance of such terms herein may not all refer to the same example. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Various aspects of at least one example are discussed below with reference to the accompanying drawings, which are not intended to be drawn to scale. The accompanying drawings are included to provide illustration and further understanding of the various aspects and examples, and are incorporated into and constitute a part of this specification, but are not intended to be used as a definition of limitations of the present invention. In the accompanying drawings, the same or nearly the same components shown in various figures may be represented by similar reference symbols or numbers. For clarity, not every component is labeled in every figure. In the drawings:

[0026] Figure 1 is a schematic block diagram of an exemplary road noise cancellation system;

[0027] Figure 2 It is available with Figure 1 A schematic block diagram of an exemplary signal flow associated with a road noise cancellation system;

[0028] Figure 3 is a schematic block diagram of an exemplary audio system;

[0029] Figure 4 is a schematic block diagram of another exemplary audio system;

[0030] Figure 5 is a graph of an exemplary transfer function of a notch filter;

[0031] Figure 6 is a graph of an exemplary set of filter poles and zeros; and

[0032] Figure 7 is a graph of an exemplary relationship between ΔRPM and notch filter bandwidth. DETAILED DESCRIPTION

[0033] Noise cancellation systems attempt to acoustically reduce (or "cancel") various sounds in an acoustic space. For example, in a vehicle, a road noise cancellation (RNC) system may attempt to reduce or "follow" road noise in the vehicle cabin. Active sound management (ASM) systems, such as engine harmonic cancellation (EHC) and engine harmonic enhancement (EHE) systems, attempt to adjust the sound of the engine (or other rotating equipment) associated with the operation of the vehicle. Various aspects of the present disclosure are directed to systems and methods adapted for use in a vehicle to remove or reduce selected signal components of a noise cancellation system (such as signal components associated with the engine or other rotating equipment) so that the noise cancellation system will not follow or attempt to reduce the selected signal components.

[0034] For example, without the beneficial effects of the present disclosure, the RNC system may alter or reduce the engine sound in the cabin, which may be undesirable. When the RNC system and the EHE system are operated in parallel, the RNC system may attempt to cancel the engine harmonics being generated by the EHE system, especially if the reference signal from the accelerometer contains these harmonics. When the RNC system and the EHC system are operated in parallel, stability may be adversely affected because both adaptive systems attempt to cancel various engine harmonics.

[0035] Various examples disclosed herein filter out (e.g., remove) engine harmonics from various signals of the RNC system. In various examples, the engine harmonics to be removed can be identified through RPM information and / or from the EHx system. In various examples, such filters can be applied directly to one or more reference signals, one or more speaker signals (also referred to as speaker commands or command signals), one or more error or feedback signals (e.g., from a feedback microphone), or any combination of these signals.

[0036] The examples of the methods and devices discussed herein are not limited to application to the construction details and component arrangements listed in the following description or shown in the accompanying drawings. These methods and devices can be implemented in other examples and can be operated or performed in various ways. The examples of specific implementations provided herein are for illustrative purposes only and are not intended to be limiting. In particular, the functions, components, elements, and features discussed in conjunction with any one or more examples are not intended to be excluded from similar effects in any other examples.

[0037] The examples disclosed herein may be combined with other examples in any manner consistent with at least one principle disclosed herein, and references to "examples," "some examples," "alternative examples," "various examples," "an example," etc. are not necessarily mutually exclusive and are intended to indicate that the particular features, structures, or characteristics described may be included in at least one example. The appearances of such terms herein do not necessarily all refer to the same example.

[0038] In addition, the wording and terminology used herein are for the purpose of description and should not be considered as limiting.Any reference to the examples, parts, elements, actions or functions of the systems and methods herein mentioned in the singular form may also cover embodiments including plural numbers, and any reference to any examples, parts, elements, actions or functions herein in the plural form may also cover examples including only singular numbers.Therefore, the reference in the singular or plural form is not intended to limit the system or method disclosed by the present invention, their parts, actions or elements.This paper uses "including", "comprising", "having", "containing", "involving" and its variant forms to cover the items listed thereafter and their equivalents and additional items.The reference to "or" can be understood to be inclusive, so that any term described using "or" can indicate any single, more than one and all of the terms.Any reference to the front and back, left and right, top and bottom, upper and lower parts and vertical and horizontal is for the convenience of description, rather than for limiting the present system and method or their parts to any one position or spatial orientation.

[0039] Figure 1 is a schematic diagram of an exemplary noise cancellation system 100 that can perform standard calculations. The noise cancellation system 100 can be configured to destructively interfere with undesirable sounds in at least one cancellation zone 102 within a predefined volume 104, such as a vehicle cabin. At a high level, one embodiment of the noise cancellation system 100 can include a reference sensor 106, a feedback sensor 108, a transducer 110, and a controller 112.

[0040] In one embodiment, the reference sensor 106 is configured to generate a reference signal 114 that is representative of an undesired sound or a source of an undesired sound within the predefined volume 104. For example, Figure 1 As shown, the reference sensor 106 may be an accelerometer mounted to a vehicle structure 116 and configured to detect vibrations transmitted through the vehicle structure. The vibrations transmitted through the vehicle structure 116 are converted by the structure into undesirable sounds within the vehicle cabin (perceived as road noise), and thus the accelerometer mounted to the structure provides a signal representative of the undesirable sounds. Figure 1 The noise cancellation system 100 only shows an example with a single reference sensor 106 , but various examples may include multiple reference sensors 106 .

[0041] The transducers 110 may be, for example, speakers distributed at discrete locations around the perimeter of a predefined volume. In one example, four or more speakers may be disposed within a vehicle cabin, with each of the four speakers being located within a respective door of the vehicle and configured to project sound into the vehicle cabin. In alternative embodiments, the speakers may be located within headrests or other locations within the vehicle cabin.

[0042] The noise cancellation signal 118 may be generated by the controller 112 and provided to one or more speakers in the predefined volume, which convert the noise cancellation signal 118 into acoustic energy (i.e., sound waves). Since the acoustic energy generated by the noise cancellation signal 118 is approximately 180° out of phase with the undesirable sound within the cancellation zone 102 and therefore destructively interferes with the undesirable sound, the combination of the sound waves generated from the noise cancellation signal 118 and the undesirable noise in the predefined volume results in cancellation of the undesirable noise, which is perceived by a listener in the cancellation zone.

[0043] The feedback sensor 108 disposed within the predefined volume generates a feedback signal 120 based on the detection of residual noise, which is generated by a combination of sound waves generated from the noise cancellation signal 118 and undesired sounds in the cancellation zone. The feedback signal 120 is provided as feedback to the controller 112, and the feedback signal 120 represents the residual noise that is not cancelled by the noise cancellation signal and other acoustic energy. The error sensor 108 can be, for example, at least one microphone mounted in the vehicle cabin (e.g., the roof, headrest, pillar, or other location in the cabin).

[0044] It should be noted that the cancellation zone may be located away from the feedback sensor 108. In this case, the feedback signal 120 may be converted to represent an estimate of the residual noise in the cancellation zone.

[0045] In one embodiment, the controller 112 may include a non-transitory storage medium 122 and a processor 124. In one embodiment, the non-transitory storage medium 122 may store program code that, when executed by the processor 124, implements the various filters and algorithms described below. The controller 112 may be implemented in hardware and / or software. For example, the controller may be implemented by a SHARC floating-point DSP processor, but it should be understood that the controller may also be implemented by any other processor, FPGA, ASIC, or other suitable hardware.

[0046] Go to Figure 2 , which shows a block diagram of one embodiment of a noise cancellation system 100 including a filter component implemented by a controller 112. As shown, the controller 112 may define a control system including an adaptive filter 126 and an adaptive processing module 128.

[0047] The adaptive filter 126 is configured to receive the reference signal 114 of the reference sensor 106 and generate a noise cancellation signal 118. As described above, the noise cancellation signal 118 is input to the transducer 110, where it is converted into a noise cancellation audio signal that destructively interferes with the undesired sounds in the predefined cancellation zone 102. The adaptive filter 126 can be implemented as any suitable linear filter, such as a multiple-input multiple-output (MIMO) finite impulse response (FIR) filter. The adaptive filter 126 employs a set of coefficients that define the noise cancellation signal 118 in response to the reference signal 114 and can be adjusted to adapt to the changing behavior of the vehicle in response to road inputs (or other inputs in the non-vehicle noise cancellation environment).

[0048] Adjustments to the coefficients of the adaptive filter 126 may be performed by an adaptive processing module 128 that receives the feedback signal 120 and the reference signal 114 as inputs and uses these inputs to generate a filter update signal 130. The filter update signal 130 is an update to the filter coefficients implemented in the adaptive filter 126. The noise cancellation signal 118 produced by the updated adaptive filter 126 will minimize the feedback signal 120 (or a projection or translation thereof) and therefore reduce undesired noise in the cancellation zone.

[0049] Figure 3 An exemplary audio system 300 is shown that includes the noise cancellation system 100, for example as a subsystem, and also includes an active sound management system 310 to provide additional audio signals that may be converted by the transducer 110. Various examples may include additional audio sources, such as entertainment, navigation, and driver warning systems that provide audio signals that will also be converted by the transducer 110.

[0050] The active sound management system 310 may provide one or more active sound signals 314 to be rendered by the sound transducer 110. Examples of the active sound management system 310 may include various sound reduction or enhancement systems, such as engine and / or transmission harmonic cancellation and / or enhancement. Such systems may generate sounds for enhancing or reducing the interior acoustic signature of an engine and powertrain, a continuously variable transmission, an electric vehicle, etc., and / or simulate or mask various acoustic characteristics to produce different acoustic experiences associated with the operation of the vehicle.

[0051] In various examples, the sounds that are reduced or enhanced may be related to engine or powertrain harmonics, and such systems may generally be referred to as engine harmonic cancellation (EHC) and / or engine harmonic enhancement (EHE) systems. Such systems may also refer to systems that enhance or reduce vehicle sounds that are not related to harmonics, or create new sounds, such as sound generators for creating sound effects such as backfiring, extinguishing, popping sound effects, etc. In addition, for example, the active sound management system 310 may create an acoustic environment that is intended to make one sound sound like another sound, such as making an electric vehicle sound like a gasoline vehicle, or making a continuously variable transmission sound like shifting gears, etc., or to create an entirely new mechanical sound.

[0052] The active sound management system may receive any number of input signals 312. Exemplary input signals 312 for the EHE / EHC system may include an indication of RPM, torque, load, temperature, etc., of any vehicle rotating equipment (such as the engine, transmission, wheels, etc.), or other operating conditions of any vehicle equipment that may serve as a basis for generating enhanced or cancelled sounds (e.g., position of an accelerator pedal or control, position of a brake pedal or control, steering wheel position, gear position and / or gear change, or other operator control input).

[0053] In various examples, the active sound signal 314 is combined with the noise cancellation signal 118 for conversion by the transducer 110. In other examples, the active sound signal 314 and the noise cancellation signal 118 may be converted by separate transducers 110. In either case, the feedback sensor 108 detects acoustic energy in the environment that may be contributed by each of the noise cancellation signal 118 and the active sound signal 314. As described above, components of the active sound signal 314 may be related to engine harmonics of the vehicle and / or harmonics of other parts of the rotating equipment (such as the powertrain and / or wheels). In addition, the reference sensor 106 may detect vibrations related to these harmonics, such that components in the reference signal 114 are also related to these harmonics. Therefore, the noise cancellation system 100 may follow these harmonic components to try to reduce their presence in the vehicle cabin, while the active sound management system 310 may try to increase these harmonic components in the vehicle cabin. Therefore, the two systems may work against each other in the best case. Each of the noise cancellation system and the active sound management system may also include adaptive operation, so the two systems may cause instability to each other in the worst case.

[0054] Figure 4 An exemplary audio system 400 is shown including exemplary variations from audio system 300 according to a particular implementation for addressing the operation of noise cancellation system 100 that may alter the sound of the vehicle's engine or other rotating equipment. Figure 4The exemplary audio system 400 of the embodiment of the present invention can also address the interaction between the noise cancellation system 100 and the active sound management system 310. In various examples, one or more notch filters configured based on the RPM 450 operate on at least one of the feedback signal 120, the reference signal 114, the noise cancellation signal 118, or a combination of these signals. For example, a filter 410 can be included to modify the feedback signal 120 to remove harmonic components related to the RPM 450. Alternatively or in addition, a filter 420 can be included to modify the reference signal 114 to remove harmonic components related to the RPM 450. In addition to or in place of either or both of the filters 410, 420, a filter 430 can be included to modify the noise cancellation signal 118 to remove harmonic components related to the RPM 450. Any one or more of the filters 410, 420, 430 can reduce the effect of the noise cancellation system 100 on the removal of harmonic components related to the RPM 450.

[0055] For example, filter 410 removes harmonic components from feedback signal 120, effectively causing noise cancellation system 100 to believe that it has successfully removed harmonic components when it has not removed the harmonic components. Filter 420 removes harmonic components from reference signal 114, effectively causing noise cancellation system 100 to believe that harmonic components are not a source of noise to be addressed. Filter 430 removes harmonic components from noise cancellation signal 118, effectively preventing noise cancellation system 100 from affecting harmonic components in the vehicle cabin.

[0056] Each of the various filter positions has the potential to degrade the performance of the noise cancellation system 100 or cause instability. For example, filtering the reference signal 114 may cause the noise cancellation system 100 to increase the adaptive filter values ​​at harmonic frequencies. Filtering the noise cancellation signal 118 may cause instability in the system because it changes the secondary path. To overcome these challenges, and in various examples, the harmonic filters 410, 420, 430 are designed to be as narrow as possible to achieve the desired component removal.

[0057] Such filtering challenges arise when RPM changes rapidly (e.g., a spirited driving scenario), during which the engine harmonics may deviate from their narrowband nature and therefore may not be contained with a narrow notch filter. If this deviation is not taken into account, the noise cancellation system may alter the engine sound, which may be particularly undesirable at the exact moment when enhanced engine sound is needed, such as during rapid acceleration when RPM changes rapidly.

[0058] One or more notch filters at one or more signal path locations in the noise cancellation system are adjusted according to various examples disclosed herein. The notch filter frequency and bandwidth are based on vehicle operating parameters such as RPM, RPM change, and torque. The filter can be, for example, a simple IIR filter with poles and zeros selected by the engine harmonic frequency and RPM rate of change. In various examples, the filtering reduction of the harmonic components does not need to be deep. For example, a reduction of 10 dB or less may be sufficient because the weakened harmonics played back by the RNC in the cabin can be masked by the actual engine sound and / or the active sound management system.

[0059] According to some examples, the notch filter 430 operates on the noise cancellation signal 118, and the notch can be made narrow enough so that stability issues are not observed, for example, the notch filter 430 can be designed to remove a sufficiently narrow portion of the spectrum that the noise cancellation system cannot accommodate such a level of frequency resolution / granularity.

[0060] In some examples, the secondary path is known and a projection of the filtered signal may be added to the feedback signal in order to prevent the RNC system from increasing gain at these frequencies.

[0061] In various examples, multiple notch filters may be cascaded to remove multiple harmonics.

[0062] Figure 5 The transfer function 500 of an exemplary notch filter is shown, which may be, for example, any of the filters 410, 420, 430. The notch filter removes (attenuates) the signal at the center frequency f c is centered and has a frequency from low frequency f l Extended to high frequency f h The notch bandwidth 510 is a narrow frequency range, which in the exemplary notch filter is defined by a 3 dB attenuation from a nominal 0 gain at frequencies outside of the range. In various examples, the notch bandwidth may be defined by other reductions and / or may not have a symmetrical response on either side of the center frequency.

[0063] In various examples, the center frequency is related to RPM, and the notch bandwidth 510 is proportionally related to the rate of change of RPM. When RPM changes rapidly, the engine harmonics occupy a wider bandwidth and may be larger in many cases. As RPM changes, widening the notch bandwidth helps to appropriately reduce harmonics in these cases. In addition, when RPM does not change significantly, the varying notch bandwidth provides flexibility in retaining the most information in the RNC signal. For example, when driving at a substantially constant RPM, a narrower notch removes less signal content, and in this case, road noise may be the dominant noise source and allows the noise cancellation system 100 to search as much of the noise spectrum as possible.

[0064] When the vehicle is traveling at a substantially constant RPM, the narrow notch bandwidth 510 prevents the adaptive filter 126 from adapting to the filtered harmonic levels, for example by making the notch filter bandwidth 510 narrower than the frequency resolution of the adaptive filter 126. In these cases, to account for the slowly changing RPM, in various examples, the notch filter may be made several orders of magnitude narrower than the resolution of the adaptive filter 126.

[0065] As the vehicle accelerates or decelerates and the RPM changes, the wider notch bandwidth 510 accommodates the changing harmonics. In various examples, the filter transfer function 500 for higher order harmonics may have a wider (wider) notch bandwidth 510 than for lower order harmonics. For example, the fifth harmonic may exhibit a wider bandwidth than the second harmonic, and the filter transfer function 500 intended to attenuate the fifth harmonic may have a wider notch bandwidth 510 than the filter transfer function intended to attenuate the second harmonic. In addition, the center frequency of the notch filter is adjusted according to the RPM and therefore changes in this case. Therefore, the adaptive filter 126 does not have time to adapt to any specific operation of the notch filter (e.g., filters 410, 420, and / or 430).

[0066] Additionally, any of filters 410, 420, and / or 430 may change the phase of the signal on which it operates. Thus, in various examples, transfer function 500 is relatively narrow, such that the notch filter introduces only a narrow range of phase inaccuracies.

[0067] Figure 6 An exemplary digital filter design 600 that can be used in various examples is shown. Filter design 600 represents a second order filter having a zero at a center frequency (which is based on the rotation rate, such as RPM) and a pole that is offset from the zero based on the amount or rate of change of the rotation rate. For example, for a given harmonic frequency f n , the center frequency ω in radians per second o It can be expressed according to formula 1:

[0068]

[0069] where f s is the sampling frequency in the digital system and f n are the harmonic frequencies of interest, each expressed in the same unit such as Hertz. The offset between the corresponding pole and zero can be expressed according to Equation 2,

[0070]

[0071] where bandwidth BW is the notch bandwidth as described above, and is proportional to the sampling frequency f s The same units are expressed in Hertz. Various examples select bandwidth BW based on a measure of the rate of change of RPM, as referenced below Figure 7 At least one example thereof is described in further detail. Figure 6 The illustrated filter design 600 shows poles located substantially linearly between corresponding zeros and the origin, but an actual implementation may only be placed approximately as shown. The filter design 600 is only one example of a filter design that can effectively attenuate a narrow frequency range.

[0072] Figure 7 An example of a correlation or mapping 700 of a selected notch bandwidth (y-axis) for a given ΔRPM (x-axis) is shown. In this example, the selected notch bandwidth is linearly related to ΔRPM, but is bounded between a minimum bandwidth and a maximum bandwidth. In various examples, ΔRPM may be understood as, for example, a rate of change of RPM with respect to time, because although ΔRPM is the difference in RPM at two different times, in various examples, the time difference ΔT may remain constant. For example, in some examples, the value of ΔRPM may be determined every 100 milliseconds as the difference between the current RPM value and the RPM value from 100 milliseconds ago. In other examples, the value of ΔRPM may be determined every 10 milliseconds as the difference between the current RPM value and the RPM value from 10 milliseconds ago. In various examples, the value of ΔRPM may be determined in the range of every 10 milliseconds to 100 milliseconds.

[0073] Some filtering of the RPM signal or the ΔRPM signal may be applied to improve its accuracy or smoothness. Examples include smoothing filtering (for noise reduction), prediction (for compensating for vehicle delays in reported RPM), interpolation (for noise reduction), extrapolation (for increased prediction), or any other processing to enhance the accuracy of ΔRPM. In some cases, ΔRPM may be calculated directly from an analog signal source, such as a signal containing a certain number of pulses per engine revolution.

[0074] Revolutions per minute (RPM) is a conventional unit of measurement for rotation rate, and in various examples, rotation rate may be measured based on RPM, or based on a time scale other than minutes, and / or based on other units. A change in rotation rate may be positive (increase) or negative (decrease). In various examples, the absolute value of the change in rotation rate (or the rate of change of rotation rate) may be considered as a basis for selecting notch bandwidth 510.

[0075] As described above, and according to various examples, the notch bandwidth 510 of a given filter transfer function 500 may depend on the harmonic that the notch filter is intended to target. Thus, various examples of mapping delta RPM to notch bandwidth 510 may vary based on the harmonic it is intended for. Additionally, the frequency bandwidth of any given harmonic may depend on the center frequency of the harmonic, e.g., a 1st harmonic at 80 Hz may have a different width than a 2nd harmonic at 80 Hz, and the notch bandwidth 510 may be selected accordingly.

[0076] In operation, various examples can filter out multiple notches (such as based on multiple harmonics) by cascading two or more notch filters. Therefore, in various examples, any of the filters 410, 420, 430 can be a filter that attenuates or removes multiple notches, for example, each filter having its own center frequency and notch bandwidth.

[0077] In various examples, the notch filter frequency and notch bandwidth may be more directly controlled by an active sound management system such as active sound management system 310. The active sound management system may determine which notches and bandwidths are best suited to reduce the interaction of the noise cancellation system with the sounds being managed by the active sound management system. The active sound management system may or may not be based on rotation rate.

[0078] Although various examples have been described above primarily with respect to vehicle engines, the noise cancellation systems and methods herein may be applied to any rotating equipment, such as motors, drivetrains, transmissions, drive axles, wheels, etc., of electric vehicles.

[0079] Although various examples have been described above with respect to vehicles, the noise cancellation systems and methods disclosed herein may be applied to any environment in which rotating equipment may generate noise that may need to be reduced, such as industrial environments, public transportation equipment, and the like.

[0080] Having described several aspects of at least one example above, it should be understood that various changes, modifications and improvements will be readily apparent to those skilled in the art. Such changes, modifications and improvements are intended to be part of this disclosure and are intended to fall within the scope of the present invention. Therefore, the above description and drawings are exemplary only, and the scope of the present invention should be determined by the appropriate construction of the appended claims and their equivalents.

Claims

1. A method of reducing noise in a cabin of a vehicle environment, the method comprising: receiving a reference signal representing noise to be reduced; providing a noise cancellation signal based on the reference signal; receiving a feedback signal representative of residual noise in the environment; as well as filtering at least one of the reference signal, the noise cancellation signal, or the feedback signal based on a rotation rate of a rotating device associated with the environment, Wherein filtering at least one of the reference signal, the noise cancellation signal, or the feedback signal based on a rotation rate of the rotating device includes filtering out a frequency bandwidth based on a change or a rate of change of the rotation rate.

2. The method of claim 1 further comprising determining a first rotation rate at a first time, determining a second rotation rate at a second time, and determining a difference between the first rotation rate and the second rotation rate as the change in the rotation rate.

3. The method of claim 1, wherein a range of the frequency bandwidth is linearly related to a range of the variation of the rotation rate.

4. The method of claim 1, wherein filtering at least one of the reference signal, the noise cancellation signal, or the feedback signal based on a rotation rate of a rotating device comprises filtering out a frequency notch centered at a frequency based on the rotation rate. The method of claim 4 , wherein the frequency is a harmonic of the rotation rate.

6. A noise cancellation system, comprising: a noise sensor configured to provide a reference signal representative of noise to be reduced in a cabin of a vehicle environment; a controller coupled to the noise sensor to receive the reference signal and to provide a noise cancellation signal based on the reference signal; a transducer coupled to the controller to convert the noise cancellation signal into an acoustic signal in the environment; as well as a filter coupled to the controller, the filter filtering a selected signal based on a rotation rate of a rotating device associated with the environment, wherein the selected signal comprises at least one of the reference signal or the noise cancellation signal, Wherein filtering the selected signal based on the rotation rate of the rotating device includes filtering out a frequency bandwidth based on a change or a rate of change of the rotation rate.

7. The noise cancellation system of claim 6, further comprising a feedback sensor that provides a feedback signal representative of residual noise in the environment, and wherein the selected signal also comprises the feedback signal.

8. The noise cancellation system of claim 6, wherein the controller determines a first rotation rate at a first time, determines a second rotation rate at a second time, and determines a difference between the first rotation rate and the second rotation rate as the change in the rotation rate.

9. The noise cancellation system of claim 6, wherein a range of the frequency bandwidth is linearly related to a range of the variation of the rotation rate.

10. The noise cancellation system of claim 6, wherein filtering the selected signal based on a rotation rate of the rotating device comprises filtering out a frequency notch centered at a frequency based on the rotation rate.

11. A non-transitory computer readable medium having stored thereon instructions, which when executed by a suitable processor causes the processor to perform a method comprising: receiving a reference signal representative of noise to be reduced in a cabin of a vehicle environment; providing a noise cancellation signal based on the reference signal; receiving a feedback signal representative of residual noise in the environment; as well as filtering a selected signal based on a rotation rate of a rotating device associated with the environment, wherein the selected signal is at least one of the reference signal, the noise cancellation signal, and the feedback signal, Wherein filtering the selected signal based on the rotation rate of the rotating device includes filtering out a frequency bandwidth based on a change in the rotation rate.

12. The non-transitory computer-readable medium of claim 11, further comprising instructions for causing the processor to determine a first rotation rate at a first time, determine a second rotation rate at a second time, and determine a difference between the first rotation rate and the second rotation rate as the change in the rotation rate.

13. The non-transitory computer readable medium of claim 11, wherein a range of the frequency bandwidth is linearly related to a range of the variation of the rotation rate.

14. The non-transitory computer readable medium of claim 11, wherein filtering the selected signal based on a rotation rate of the rotating device comprises filtering out a frequency notch centered at a frequency based on the rotation rate.

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