Patent Description:
The present disclosure generally relates to systems and methods for cancelling engine harmonics.

The patent application publication <CIT> is known, that describes a noise or vibration control system that reduces a sampling rate and reduces a control rate to improve computation efficiency. It permits the use of a sample frequency that is less than twice the frequency of interest, the sensed signals are filtered to extract a particular frequency range with a lower bound and an upper bound that contain the frequency of interest. The sensed signals are demodulated by multiplication by reference sine and cosine signals at the frequency of interest. The control computations are done on the harmonic components.

The patent publication <CIT> describes a multidimensional feedback system is used to reduce the noise component of a vibrational or acoustic field. Feedback error signals are sensed by the respective sensors, and transmitted as sensor signals to a digital signal processor, which makes up part of a feedback controller. The digital signal processor complex-demodulates the sensor signals to baseband at each of the disturbance frequencies. The feedback algorithm includes a matrix operator that diagonalizes the feedback system.

All examples and features mentioned below can be combined in any technically possible way.

According to the invention, an engine harmonic cancellation system, includes: an accelerometer disposed within a vehicle to detect a harmonic produced by an engine of the vehicle and to produce a harmonic reference signal representative of the harmonic; a controller configured to produce a harmonic cancellation signal that, when transduced into an acoustic signal, cancels the harmonic within at least one cancellation zone within a cabin of the vehicle, wherein the harmonic cancellation signal is based, at least in part, on mixing the harmonic reference signal converted to baseband with a baseband signal output from a look up table; and a speaker disposed within the cabin and configured to receive the harmonic cancellation signal and to transduce the harmonic cancellation signal into an acoustic harmonic cancellation signal, such that the harmonic is cancelled within the cancellation zone.

In an example, the controller implements a down converter configured to receive the harmonic reference signal and to output the harmonic reference signal converted to baseband.

In an example, the baseband signal has an amplitude and a phase, wherein the amplitude is selected to be a constant ratio with an amplitude of the harmonic reference signal converted to baseband, wherein the phase is equal to a phase of the harmonic cancellation signal when summed with a phase of the harmonic reference signal converted to baseband.

In an example, the controller implements a multiplier, wherein the multiplier mixes the harmonic reference signal converted to baseband with the baseband signal output from the look up table to output a baseband harmonic cancellation signal, wherein the controller further implements an up converter configured to receive the baseband harmonic cancellation signal and to up convert the baseband harmonic cancellation signal to output the harmonic cancellation signal.

In an example, the engine harmonic cancellation system further includes an error sensor disposed to produce an error signal representative of a residual harmonic in the cabin of the vehicle, wherein a value of the look up table is updated according to the error signal.

In an example, the error sensor is disposed outside of the cancellation zone, wherein the controller is further configured to implement a projection filter configured to estimate a value of the residual harmonic within the cancellation zone.

In an example, the controller implements a multiplier, wherein the multiplier mixes the harmonic reference signal converted to baseband with the baseband signal output from the look up table to output an intermediate baseband harmonic cancellation signal, wherein the controller further implements a second look up table and a second multiplier, wherein the second multiplier mixes the intermediate baseband harmonic cancellation signal with an output from the second look up table to produce a baseband harmonic cancellation signal.

In an example, a value of the look up table and a value of the second look up table is updated according to an error signal from an error sensor, representative of a residual harmonic in the vehicle cabin, wherein the second look up table is updated to adapt faster to changes in a transfer function between the speaker and the cancellation zone than the look up table.

In an example, a value of the look up table and a value of the second look up table is updated according to an error signal from an error sensor, representative of a residual harmonic in the vehicle cabin, wherein the look up table is updated to adapt faster to changes in a transfer function between the speaker and the cancellation zone than the second look up table.

In an example, the look up table is configured to select a first value at a first torque value and a second value at a second torque value.

According to the invention, a method for cancelling engine harmonics in a vehicle cabin, includes the steps of: receiving a harmonic reference signal representative of a harmonic produced by an engine of the vehicle from an accelerometer disposed within a vehicle to detect the harmonic; producing a harmonic cancellation signal that, when transduced into an acoustic signal, cancels the harmonic within at least one cancellation zone within a cabin of the vehicle, wherein the harmonic cancellation signal is based, at least in part, on mixing the harmonic reference signal converted to baseband with a baseband signal output from a look up table; and providing the harmonic cancellation signal to a speaker disposed within the cabin and configured to receive the harmonic cancellation signal to transduce the harmonic cancellation signal into an acoustic harmonic cancellation signal, such that the harmonic is cancelled within the cancellation zone.

In an example, the method further includes the step of down converting the harmonic reference signal to output the harmonic reference signal converted to baseband.

In an example, the method further includes the steps of: mixing the harmonic reference signal converted to baseband with the baseband signal output from the look up table to output a baseband harmonic cancellation signal; and up converting the baseband harmonic cancellation signal to output the harmonic cancellation signal.

In an example, the method further includes the step of updating a value of the look up table is according to an error signal received from an error sensor disposed to produce an error signal representative of a residual harmonic in the vehicle cabin.

In an example, the method further includes the step of estimating a value of the residual harmonic within the cancellation zone, wherein the error sensor is disposed outside of the cancellation zone.

In an example, the method further includes the step of: mixing the harmonic reference signal converted to baseband with the baseband signal output from the look up table to output an intermediate baseband harmonic cancellation signal, mixing the intermediate baseband harmonic reference signal with the output from a second look up table to produce a baseband harmonic reference signal.

In an example, the method further includes the step of updating a value of the look up table and a value of the second look up table according to an error signal from an error sensor, representative of a residual harmonic in the vehicle cabin, wherein the second look up table is updated to adapt faster to changes in a transfer function between the speaker and the cancellation zone than the look up table.

In an example, the method further includes the step of updating a value of the look up table and a value of the second look up table according to an error signal from an error sensor, representative of a residual harmonic in the vehicle cabin, wherein the look up table is updated to adapt faster to changes in a transfer function between the speaker and the cancellation zone than the second look up table.

Other features, objects, and advantages will be apparent from the description and the drawings, and from the claims.

Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the various aspects.

Vehicle engines (including both internal combustion engines and electric motors) generate pronounced harmonics (sounds emitted at integer multiples of a fundamental frequency) during operation, often due to the rotation of various elements within the engine, such as the crankshaft.

Road noise cancellation systems are not well adapted for cancelling engine harmonics because the road noise tends to dominate the engine harmonics while the vehicle is in motion, thus road noise cancellation system will tend to adapt the dominant road noise and leave the engine harmonics uncancelled. Furthermore, finite impulse response filters, such as those typically employed in road noise cancellation systems, often cannot capture rapid changes in engine harmonic, such as those that occur when the engine is revved.

In addition, previous engine harmonic cancellation systems tended to rely on the use of a microphone disposed in the cabin to detect the engine harmonics to be cancelled. But these systems relied on a feedback signal from an error sensor, such as a microphone, for detecting both the cabin acoustics and the amplitude and phase of the harmonic, limiting the adaptability and accuracy of such systems.

<FIG> is a schematic view of an example engine harmonic cancellation system <NUM>. Engine harmonic cancellation system <NUM> can be configured to destructively interfere with undesired engine harmonics in at least one cancellation zone <NUM> within a predefined volume <NUM> within a vehicle cabin. At a high level, an example of engine harmonic cancellation system <NUM> can include a reference sensor <NUM>, an error sensor <NUM>, a speaker <NUM>, and a controller <NUM>.

In an example, reference sensor <NUM> is configured to generate reference signal(s) <NUM> representative of the undesired sound, or a source of the undesired sound, within predefined volume <NUM>. For example, as shown in <FIG>, reference sensor <NUM> can be an accelerometer, or a plurality of accelerometers, positioned to detect the harmonics produced by an engine. In various examples, the reference sensor <NUM> can be positioned in the engine compartment, in the vehicle cabin, in the vehicle chassis, or any other location suitable for detecting the engine harmonics.

Speaker <NUM> can, for example, be one or more speakers distributed in discrete locations about the perimeter of the predefined volume <NUM>. (Also referred to as actuators, a speaker is any device configured to receive an electrical signal and transduce it into an acoustic signal. ) In an example, four or more speakers can be disposed within a vehicle cabin, each of the four speakers being located within a respective door of the vehicle and configured to project sound into the vehicle cabin. In alternate examples, speakers can be located within a headrest, or elsewhere in the vehicle cabin.

A harmonic cancellation signal <NUM> can be generated by controller <NUM> and provided to one or more speakers <NUM> in the predefined volume <NUM>, which transduce the harmonic cancellation signal <NUM> to acoustic energy (i.e., sound waves). The acoustic energy produced as a result of harmonic cancellation signal <NUM> is approximately <NUM>° (i.e., <NUM>° ± <NUM>°), out of phase with-and thus destructively interferes with-the undesired engine harmonics within the cancellation zone <NUM>. The combination of sound waves generated from the harmonic cancellation signal <NUM> and the undesired harmonics in the predefined volume results in cancellation of the undesired harmonics, as perceived by a listener in a cancellation zone.

Because harmonic cancellation cannot be equal throughout the entire predefined volume, harmonic cancellation system <NUM> is configured to create the greatest harmonic cancellation within one or more predefined cancellation zones <NUM> within the predefined volume. The harmonic cancellation within the cancellation zones <NUM> can effect a reduction in undesired harmonics by approximately <NUM> dB or more (although in varying examples, different amounts of harmonic cancellation can occur). It should thus be understood that "cancellation" as used in this disclosure does not refer to total cancellation but rather than reduction of the undesired engine harmonics in the cancellation zone <NUM>. In certain examples, the engine harmonics can be reduced to a target value. In other examples, the undesired engine harmonics can be reduced to the extent possible. The portion of the engine harmonics that remains uncancelled within the cancellation zone is referred to in this disclosure as "residual" or "uncancelled" harmonics.

Error sensor <NUM>, disposed within the predefined volume, generates an error signal <NUM> representative of the residual harmonics resulting from the combination of the sound waves generated from the harmonic cancellation signal <NUM> and the undesired harmonics in the cancellation zone <NUM>. The error signal <NUM> is provided to controller <NUM> as feedback, error signal <NUM> representing residual harmonics uncanceled by the harmonic cancellation signal. Error sensors <NUM> can be, for example, at least one microphone mounted within a vehicle cabin (e.g., in the roof, headrests, pillars, or elsewhere within the cabin).

It should be noted that the cancellation zone(s) can be positioned remotely from error sensor <NUM>. In this case, as will be discussed below, the error signal <NUM> can be filtered to represent an estimate of the residual noise in the cancellation zone(s). In either case, the error signal will be understood to represent residual undesired harmonics in the cancellation zone.

In an example, controller <NUM> can comprise a non-transitory storage medium <NUM> and processor <NUM>. In an example, non-transitory storage medium <NUM> can store program code that, when executed by processor <NUM>, implements the various filters, modules, components, and algorithms described below. For example, controller can comprise a SHARC floating-point DSP processor programmed as such. However, it should be understood that controller <NUM> can comprise any suitable processor, FPGA, ASIC, or other suitable hardware, which includes combinations of multiple processors/hardware.

<FIG> depicts a block diagram of engine harmonic cancellation system <NUM>, including multiple components implemented by controller <NUM>. As shown, the reference signal <NUM> can be received at down converter <NUM>. A simplified expression of the harmonic content of reference signal <NUM> can be represented in the time domain as a complex exponential by the following equation: <MAT> where A is the amplitude and ω<NUM> the angular frequency and ϕr is the phase of the harmonic content. Not represented in this equation is some modulation that will provide some bandwidth to the signal; however, this equation is useful for illustrative purposes. Furthermore, it should be understood, that the engine noise and the reference signal <NUM> will contain harmonics at multiple frequencies at a single point in time (i.e., at various harmonic numbers). The system and method described herein can be repeated for each such harmonic frequency. Indeed, it should be understood that the equations presented in this disclosure are presented in a simplified form for the purposes of illustration only and should not be deemed exclusive or limiting.

Down converter <NUM> converts the reference signal <NUM> to baseband. Down converter <NUM>, in the example shown, comprises multiplier <NUM> and lowpass filter <NUM>. Multiplier <NUM> multiplies the reference signal <NUM> by a value to shift the reference signal <NUM> frequency ω<NUM> down to baseband. More specifically, multiplier <NUM> receives the complex conjugate o* of the output o of a complex-valued oscillator <NUM>, producing an output that can be mathematically modeled as: <MAT> where ω<NUM> is again the angular frequency of the harmonic content of the reference signal <NUM> and θ represents a phase introduced by the complex-valued oscillator (this phase will be removed later at up convert). The angular frequency ω<NUM> of the oscillator signal o is selected according to information about the state of the engine and vehicle. For example, the revolutions per minute (RPM) of the vehicle engine is related to the harmonic content of the engine noise. For example, generally the harmonic content increases in frequency as the RPM increase. Thus, the RPM of the vehicle engine can be used to select the target harmonic frequency ω<NUM>. In addition, other factors, such as the torque produced by the engine can modify which harmonic frequencies are produced at a particular RPM. For example, an engine that is revved at idle will produce different harmonic frequencies to an engine that is driven under load, although the engine reaches the same RPM in both cases. Thus, torque can be used to determine the harmonic order, and, accordingly, the appropriate target angular frequency ω<NUM>. (A look-up table can be employed to select the appropriate angular frequency ω<NUM> of oscillator signal o according to the state of the engine or vehicle, e.g., RPM and/or torque, etc.).

The complex conjugate of the oscillator signal o, is found by the complex conjugate module <NUM>, and can be modeled as follows: <MAT>.

The complex conjugate o* is input to the multiplier <NUM>, which outputs the down converter signal md. Multiplying the reference signal <NUM> by the complex conjugate o* of the oscillator signal o effectively shifts the ω<NUM> term of the reference signal <NUM> down to baseband and the -ω<NUM> term down to -<NUM>jω<NUM> such that the down converted reference signal md can be mathematically represented as follows: <MAT>.

The down converted reference signal md is then input to a low pass filter <NUM>, the cut off frequency of which is selected to filter nearly everything except the -jθ term, including filtering the -<NUM>jω<NUM> term. As a result, the baseband reference signal r output from the lowpass filter <NUM> (and from down converter <NUM>) is a baseband signal having an amplitude A of the target harmonic content of the reference signal <NUM> and a phase θ equal to the phase difference between the reference signal <NUM> and the oscillator signal o and can be represented as: <MAT> Thus baseband reference signal r can be thought of as a DC signal having a magnitude A and a phase which is the sum of the phase ϕr of the reference signal <NUM> and the phase θ of the complex-valued oscillator <NUM>.

Because this signal is mixed down to baseband, it is represented as not having a frequency component and thus is represented as a DC phasor value having only a magnitude and phase. It should, however, be understood that the baseband reference signal r can include a nominal frequency component, such as <NUM> or <NUM> (depending on the cutoff of LPF <NUM>) to capture fluctuations in the reference signal and rapid shifts in RPM. To further account for this, the cut off frequency of low pass filter <NUM> can depend on parameters such as the change in RPM from sample to sample. In other words, the cut off frequency can be made higher for large changes in RPM and smaller for low changes.

Down converter <NUM> thus performs a dual function of isolating the harmonic content of the accelerometer signal and resulting in a value representative of the harmonic content at DC, which changes, comparatively, very slowly. Thus, the remaining portions of the engine harmonic cancellation system <NUM> (e.g., multiplier <NUM>, LUT <NUM>, up converter <NUM>, etc.) can accordingly be clocked at a value lower than other functions, such as a road-noise cancellation system if one is concurrently employed, without aliasing. This increases the efficiency of operating the engine harmonic cancellation system <NUM> (e.g., through reduced MIPS) without sacrificing performance. In addition, by down converting and operating in the time domain, rather than in the frequency domain, the harmonic frequencies can be operated on without continuity issues that would arise from doing similar operations in the frequency domain.

The output baseband reference signal r of down converter <NUM> is mixed at multiplier <NUM> with the baseband output of look up table (LUT) <NUM>. The baseband output of LUT <NUM> is configured such that, when mixed with baseband reference signal r and mixed to passband at up converter <NUM>, the resulting signal is a harmonic cancellation signal that when transduced by speaker <NUM> an acoustic signal that cancels the harmonic content of the engine noise at cancellation zone <NUM> within the vehicle cabin (e.g., at a passenger's ears).

The LUT <NUM> can be employed in this example, rather than an FIR filter, because the target harmonic is narrowband, rather than broadband such as might exist in an RNC context. In addition, the use of a LUT further provides greater flexibility and shorter times responding to rapid changes in engine harmonic, as might occur when the engine is revved, because retrieving values from the LUT is generally much faster than adapting the coefficients of a filter. Further, the use of a LUT in this context is preferred over an FIR filter because the LUT will not suffer from the same causality problems in translating a phase value as an FIR filter might.

The passband harmonic cancellation signal d output from up converter <NUM> (as will be described below) and input to speaker <NUM> can be modeled as: <MAT> where phase ϕh is a necessary phase change to the phase ϕr of reference signal <NUM> in order to cancel the engine harmonic in the cancellation zone and is informed by the transfer function from the speaker <NUM> to the cancellation zone.

The output of the LUT <NUM> can thus be modeled as <MAT> such that mixing the baseband signal c of LUT <NUM> with the output of the downconverter results in a baseband harmonic cancellation signal s, which can be represented as <MAT> thus, in this example, introducing the amplitude B and a phase equal to sum of the phase ϕr of the reference signal, the phase change ϕh introduced by LUT <NUM> (and needed to cancel the target harmonic in the cancellation zone) and the phase -θ of the complex-valued oscillator <NUM>.

Mixing this signal with the oscillator signal o at multiplier <NUM> of up converter <NUM> yields <MAT> the real portion of which, as found by real value module <NUM>, forms harmonic cancellation signal d. LUT <NUM> thus functions to translate the output of down converter <NUM> to an amplitude and phase value that, when mixed to passband at up converter <NUM>, renders the harmonic cancellation signal d. Thus, mixing the baseband harmonic cancellation signal s with the output o of the complex-valued oscillator <NUM> shifts the baseband reference signal to the angular frequency ω<NUM> of the target harmonic and removes the phase shift θ initially introduced by mixing the complex conjugate signal o*, yielding only the phase of ϕr of the reference signal <NUM> and the phase shift ϕh of LUT <NUM>.

Like complex-valued oscillator <NUM>, LUT <NUM> receives as an input RPM and/or torque, or any other suitable input related to the state of the engine or vehicle from which the angular frequency ω<NUM> can be determined. (Alternatively, LUT <NUM> can receive the angular frequency ω<NUM> from complex-valued oscillator or any other process from which the angular frequency ω<NUM> is determined. ) From this input, LUT <NUM> retrieves the appropriate amplitude B/A and phase value ϕh for baseband signal c. LUT <NUM> thus effectively associates an output baseband signal with the frequency of a target harmonic. When the harmonic of a particular frequency is detected at reference sensor <NUM>, the appropriate baseband signal is retrieved and output to the multiplier <NUM>. The phase ϕh of baseband signal c and ultimately of the harmonic cancellation signal d will be functions of frequency and of the transfer function from the actuator <NUM> to the cancellation zone. The transfer function from the actuator <NUM> to the cancellation zone should typically remain constant during runtime, although changes to it will generally be captured in the adaptation of LUT <NUM>, as discussed below. LUT <NUM> maintains the amplitude B/A of the baseband signal c at a constant ratio, as determined by the magnitude A of the reference signal <NUM> (and down converter output c) and the desired magnitude B of the harmonic cancellation signal d.

Acceleration or deceleration of the vehicle can alter the amplitude and phase of the harmonics in the cancellation zone, and, accordingly, the necessary values of amplitude B and phase ϕh of the harmonic cancellation signal in order to cancel the harmonics in the cancellation zone. To account for this, the torque value (or any other value representative of acceleration or deceleration of the vehicle), can be used to select between LUTs, one LUT being used for acceleration and the other being used deceleration. For example, for a positive torque value indicative of acceleration, LUT <NUM> can implement one LUT storing an association between harmonic frequency ω<NUM> values and an amplitude and phase shift (e.g., Bi and ϕh<NUM>) of baseband signal c; whereas, for a negative torque value indicative of deceleration, LUT <NUM> can implement a second LUT storing an association between harmonic frequency ω<NUM> and a different amplitude and phase shift (e.g., B<NUM> and ϕh<NUM>) of baseband signal c. Alternatively, LUT <NUM> can output a value for the amplitude and phase shift of baseband signal c that is interpolated between the two LUTs, depending on the torque value received. However, in instances where multiple accelerometers (or other reference sensors) are employed, the ability to receive reference signals across multiple axes generally obviates the need for torque as an input and multiple LUTs.

The error signal <NUM> output from error sensor <NUM> is used by LUT adaptation module to adjust the LUT <NUM> to better cancel the harmonic content in the cancellation zone (i.e., to adjust the values of B and ϕh). In an example, LUT adaptation module <NUM> can update the table value Wk at frequency value k and at time n + <NUM> (i.e., the amplitude value and phase value of the output signal c for a given frequency k, such as at angular frequency ω<NUM>) according to the following update equation: <MAT> where R is the frequency-domain reference signal r, M is the downconverted frequency value of the error signal <NUM> as seen at the actuator <NUM>, and µk is the step size, which determines the adaptation rate. Because the harmonics at one angular frequency are canceled, only values for that frequency (e.g., angular frequency ω<NUM>) need to be updated, further improving the efficiency of harmonic cancellation system <NUM>. Because LUT <NUM> provides a baseband output signal, the error signal <NUM> is also downconverted prior to being input to LUT adaptation module <NUM> by down converter <NUM>.

In addition, error sensor <NUM>, as described above, is positioned to detect a magnitude of the residual harmonics within the vehicle cabin. In one example, error sensor <NUM> is positioned within cancellation zone <NUM> (e.g., in a microphone worn in a headset at a user's ears). However, it can often be difficult to position microphone <NUM> in the cancellation zone <NUM>. In these cases, the error signal e will not accurately represent the error of the harmonic cancellation signal d, as error sensor <NUM> is not positioned in the cancellation zone and the magnitude of the engine harmonic varies in space. As a result, the error signal is indicative of the error at the error sensor <NUM>, but not at cancellation zone <NUM>. This will result in undesirably updating LUT <NUM> to cancel the harmonic at the position of error sensor <NUM> instead of at cancellation zone <NUM>.

To account for this, the error signal <NUM> can be filtered to estimate the residual harmonic in cancellation zone <NUM>. For example, as shown in <FIG>, projection filter <NUM> can estimate the residual harmonic at the cancellation zone. In various examples, projection filter <NUM> can include a first filter that is based on an estimate of an acoustic relationship between the location of error sensor <NUM>. This filter receives the error signal <NUM> (converted to baseband) and "projects" (i.e., estimates) the value of the error signal at the cancellation zone. Projection filter <NUM> can further include a second filter that estimates the relationship between the speaker <NUM> and the cancellation zone. The second filter receives the harmonic cancellation signal d and estimates the value of the harmonic cancellation signal d at the cancellation zone. By summing the outputs of the first and second filter, the error at the cancellation zone (converted to baseband) can be estimated. Such a projection filter is described in more detail in <CIT>, titled "Systems and Methods for Noise-Cancellation using Microphone Projection". It is, however, contemplated, that other projection filters could be employed; indeed, any projection filter suitable for estimating the residual engine harmonic at the cancellation zone can be used.

The output of projection filter <NUM> in the feedback loop to LUT adaptation module <NUM> is also input to the <MAT> filter <NUM>, which implements a transpose (time-flipped version) of the transfer function between the driver and the cancellation zone, effectively backing out the time delay between the speaker <NUM> and the cancellation zone. In an alternative example, rather than <MAT> filter <NUM>, a filter implementing the pseudo-inverse could be employed in the MIMO example (i.e., multiple input reference signals and multiple harmonic cancellation signals output to multiple transducers). In either case, the variable M, described above in connection with the Eq. <NUM> represents the output of the feedback loop to LUT Adaptation Module <NUM>, which is a downconverted estimate of the residual engine harmonic at the cancellation zone with the delay from the cancellation zone to the speaker removed.

In one example, LUT adaptation module <NUM> and the feedback loop to it can be omitted, with the LUT <NUM> operating without changing the values of the look up table during runtime. This example, however, will fail to account for changes to the transfer function between the speaker <NUM> and the cancellation zone or to otherwise mitigate error from residual engine harmonics over time.

As described above, the LUT <NUM> will adapt to changes occurring in the transfer function between the speaker <NUM> and the cancellation zone. However, it will not account for rapid changes, such as a passenger opening a window in the vehicle. To account for such rapid changes, <FIG> depicts an alternative example of engine harmonic cancellation system <NUM>, in which a second LUT, shown as LUT-FB <NUM>, is employed. (Although accelerometer <NUM>, down converter <NUM>, oscillator <NUM>, and complex conjugate module <NUM> have been excluded from the view of <FIG>, it should be understood that engine harmonic cancellation system <NUM> in <FIG> is identical to harmonic cancellation system <NUM> except for the inclusion of LUT-FB <NUM>, multiplier <NUM>, and LUT-FB adaptation module <NUM>.

As shown in <FIG>, the output si of multiplier <NUM> is input to multiplier <NUM>, which multiplies output si with the output of with the output c<NUM> of LUT-FB <NUM>. LUT-FB <NUM> is updated by LUT-FB Adaptation Module <NUM> according to the following update equation: <MAT> where λ is a forgetting factor. Likewise, the update equation for LUT <NUM> is modified as follows to include forgetting factor λ: <MAT> As a result, the update to LUT <NUM> will trend toward zero, but the update equation to LUT-FB <NUM> will trend toward one. Thus, rapid changes to the transfer function between speaker <NUM> and the cancellation zone will be captured by LUT-FB <NUM> while LUT <NUM> is still updating. Longer term changes to the transfer function will be captured by LUT <NUM>, as LUT-FB <NUM> trends toward a value of one (thus not impacting the output). Thus, in this example, the combination of LUT <NUM> and LUT-FB <NUM> create the baseband harmonic cancellation signal s<NUM>. It should be understood that the order of LUT <NUM> and LUT-FB <NUM> can be switched without changing the function of harmonic cancellation system <NUM> (e.g., the output c<NUM> of LUT-FB <NUM> can be mixed with the baseband reference signal r first without changing the operation of harmonic cancellation system <NUM>).

While the example of <FIG> has been provided for a single reference sensor <NUM>, speaker <NUM>, error sensor <NUM>, and harmonic cancellation zone <NUM>, it should be understood that, in application, multiple of such sensors, speakers, and cancellation zones are typically employed or created. Generally, the number of look up tables will be equal to the number of reference sensors (M) multiplied by the number of speakers (N). Each reference sensor is down converted and mixed N times, and each speaker signal is then obtained as a summation of M signals. This can be repeated for each desired cancellation zone in the vehicle cabin. It should be also understood that multiple reference sensors, error sensors, speakers, and harmonic cancellation zones can be employed or created in the method described below in connection with <FIG>.

Harmonic cancellation system <NUM> can be employed in addition to a road noise cancellation system. For example, the output of a road noise cancellation system can be summed with the output of harmonic cancellation system <NUM> at each speaker in order to both cancel road noise and engine harmonics in the cancellation zone(s) of the vehicle cabin <NUM>.

<FIG> depicts a flowchart of a method <NUM> for estimating cancelling an engine harmonic in a vehicle cabin. As described above, this method can be implemented by a computing device, such as controller <NUM>. Generally, the steps of the computer-implemented method are stored in a non-transitory storage medium and are executed by the processor of the computing device. However, at least some of the steps can be carried out in hardware rather than by software.

At step <NUM>, a harmonic reference signal representative of a harmonic produced by an engine of the vehicle is received from a reference sensor disposed within a vehicle to detect the harmonic. Reference sensor can be, for example, reference sensor <NUM>, which can be an accelerometer, although any other sensor suitable for detecting the harmonics produced by the engine can be used. The reference sensor can be disposed in a position suitable for detection of the engine harmonics, such as the engine compartment, the vehicle cabin, or elsewhere on the vehicle chassis.

At step <NUM>, the harmonic reference signal is down converted to output the harmonic reference signal converted to baseband. The harmonic reference signal, output from the reference sensor, can be down converted by a down converter such as down converter <NUM>, which includes a multiplier and a low pass filter. The multiplier receives the complex conjugate output of a complex-valued oscillator, such as oscillator <NUM>. The complex-valued oscillator outputs a signal that has a frequency equal to the frequency of the target harmonic, such that the target harmonic of the harmonic reference signal is mixed down to baseband when the harmonic reference signal is multiplied by the complex conjugate of the oscillator at the multiplier. The frequency of the oscillator is selected, for example, according the RPMs of the vehicle engine, which are typically correlated to the frequency of the target harmonic. Although, in alternative examples, other useful metrics related to the state of the engine or the vehicle, such as torque, can be used to determine the appropriate frequency of the target harmonic. Additional potential inputs can include harmonic number to distinguish the particular harmonic to be targeted from the other harmonics produced by the engine at any point in time.

The low pass filter functions to exclude nearly everything except the baseband harmonic reference signal. In an example, the low pass filter can permit a small bandwidth (e.g., <NUM>-<NUM>) of the baseband harmonic reference signal to account for fluctuations in the harmonic reference signal and bandwidth that results from rapidly changing RPMs of the engine. In an example, the cutoff frequency can be changed in accordance with the change in RPMs from sample to sample (i.e., greater changes results in a higher cut off frequency).

At step <NUM>, the harmonic reference signal converted to baseband is mixed with the baseband signal output from the look up table to output a baseband harmonic cancellation signal. In an example, the baseband harmonic reference signal is mixed at a multiplier such as multiplier <NUM> with the output of a LUT such as LUT <NUM>. The LUT is configured to output a baseband signal that, when mixed with the baseband harmonic reference signal, translates the phase and amplitude of the baseband harmonic reference to a value that, when up converted to passband and then transduced by a speaker in the vehicle cabin, will cancel the harmonics in the cancellation zone (this is represented in, for example, Eqs. (<NUM>) and (<NUM>) above). The LUT effectively associates an output baseband signal with the frequency of a target harmonic. When the harmonic of a particular frequency is detected at reference sensor, the appropriate baseband signal is retrieved and output to the multiplier. Like the complex-valued oscillator, the LUT relies on metrics related to the state of the engine or the vehicle, such as RPM, torque, harmonic number, etc. to determine the appropriate value from the LUT to be mixed with the baseband harmonic reference signal. In an alternative example, the LUT can simply retrieve the values associated with the frequency determined for the complex-valued oscillator.

At step <NUM>, the baseband harmonic cancellation signal is up converted to passband to output the harmonic cancellation signal. This can be performed by an up converter such as up converter <NUM>, which includes a multiplier that receives the output of the complex-valued oscillator to return the signal to a signal having the frequency of the target harmonic frequency (but a phase and amplitude being determined by the mixing of the baseband harmonic reference signal with the output of the LUT). This step also involves taking the real portion, such as with real value module <NUM>, of the passband harmonic cancellation signal to put the harmonic cancellation signal in position to be transduced by speaker <NUM>.

At step <NUM>, the harmonic cancellation signal is provided to a speaker disposed within the cabin to transduce the harmonic cancellation signal into an acoustic harmonic cancellation signal, such that the harmonic is cancelled within the cancellation zone. For example, the harmonic cancellation signal can be provided to speaker <NUM> which is disposed within the vehicle cabin to produce the acoustic harmonic signal in a manner that will cancel the target harmonic in the cancellation zone within the vehicle cabin.

Following this step, the method can return to step <NUM> to receive a new sample from the reference sensor, thus operating in a loop to continually track and cancel the engine harmonics during runtime.

In addition, at step <NUM>, shown in <FIG>, a value of the look up table is updated according to an error signal received from an error sensor disposed to produce an error signal representative of a residual harmonic in the vehicle cabin. This signal can be down converted so that the LUT is appropriately updated to produce the baseband signal to be mixed with the baseband harmonic reference signal. Further, error signal from the error sensor can be filtered, such as with projection filter <NUM>, which estimates the value of the error sensor within the cancellation zone, in the instance in which the error sensor is positioned outside the cancellation zone. Further, the error sensor signal can be input to a filter, such as filter <NUM>, which is the transpose of the transfer function between the speaker and the cancellation zone, in order to back out of the delay between the speaker and the cancellation zone. The LUT can be updated according to an update equation such as Eq. (<NUM>), which also relies on the baseband harmonic reference signal; although, it is contemplated that other update equations can be used. Generally, the error signal is used to update the baseband signal that is stored in association with the frequency of the target harmonic, rather than updating each value of the LUT, in order to increase efficiency.

5C depicts a set of steps (<NUM> and <NUM>) that are alternative to step <NUM> as well as an additional step <NUM>. At step <NUM>, the harmonic reference signal converted to baseband is mixed with the baseband signal output from the look up table to output an intermediate baseband harmonic cancellation signal. This basically follows step <NUM>, except that the output is not the baseband harmonic cancellation signal because it is mixed again at step <NUM> to arrive at the baseband harmonic cancellation signal.

At step <NUM>, the intermediate signal is mixed with the output of a second look up table to output the baseband harmonic cancellation signal. The second look up table can be, for example, be LUT-FB <NUM>. The second look up table is employed because the look up tables are updated according to different forgetting factors as described below at step <NUM>. The baseband harmonic cancellation signal is provided, at steps <NUM> and <NUM>, to an up converter and a speaker to be transduced into an acoustic harmonic cancellation signal.

At step <NUM>, a value of the first look up table and a value of the second look up table are updated according to an error signal from an error sensor, representative of a residual harmonic in the vehicle cabin. This generally follows the updating of step <NUM>, described above, (including projecting, down converting, and backing out the delay of the error signal) except that that update equations are amended, as shown in an example in Eqs. (<NUM>) and (<NUM>) to include a forgetting factor and such that the look up table will trend toward zero over time, while the second look up table will trend toward one. As a result, the first look up table will respond slower to changes in the transfer function from the speaker to the cancellation, while the second look up table responds quickly to such changes, so that these changes do not result in pronounced harmonics while the look up table is updating. It should be understood that the orders of the look up table and the second look up table can be switched, so that the second look up table occurs first in the processing chain and outputs the baseband signal that results in the intermediate harmonic cancellation signal.

As mentioned above, the mathematical equations provided in this disclosure are simplified for the purposes of illustrating the principles of the inventive aspects only and should not be deemed exclusive or limiting in any way. Furthermore, variations in the mathematical equations are contemplated, insofar as they fall within the scope of the invention as set forth in the accompanying claims.

Regarding the use of symbols herein, a capital letter, e.g., H, generally represents a term, signal, or quantity in the frequency or spectral domain, and a lowercase letter, e.g., h, generally represents a term, signal, or quantity in the time domain. Relation between time and frequency domain is generally well known, and is described at least under the realm of Fourier mathematics or analysis, and is accordingly not presented herein. Additionally, signals, transfer functions, or other terms or quantities represented by symbols herein may be operated, considered, or analyzed in analog or discrete form. In the case of time domain terms or quantities, the analog time index, e.g., t, and/or discrete sample index, e.g., n, may be interchanged or omitted in various cases. Likewise, in the frequency domain, analog frequency indexes, e. g, f, and discrete frequency indexes, e.g., k, are omitted in most cases. Further, relationships and calculations disclosed herein may generally exist or be carried out in either time or frequency domains, and either analog or discrete domains, as will be understood by one of skill in the art. Accordingly, various examples to illustrate every possible variation in time or frequency domains, and analog or discrete domains, are not presented herein.

The functionality described herein, or portions thereof, and its various modifications (hereinafter "the functions") can be implemented, at least in part, via computer program product, e.g., a computer program tangibly embodied in an information carrier, such as one or more non-transitory machine-readable media or storage device, for execution by, or to control the operation of, one or more data processing apparatus, e.g., a programmable processor, a computer, multiple computers, and/or programmable logic components.

Actions associated with implementing all or part of the functions can be performed by one or more programmable processors executing one or more computer programs to perform the functions of the calibration process. All or part of the functions can be implemented as, special purpose logic circuitry, e.g., an FPGA and/or an ASIC (application-specific integrated circuit).

Components of a computer include a processor for executing instructions and one or more memory devices for storing instructions and data.

Claim 1:
An engine harmonic cancellation system (<NUM>), comprising:
an accelerometer (<NUM>) adapted to be disposed within a vehicle to detect a harmonic produced by an engine of the vehicle and to produce a harmonic reference signal (<NUM>) representative of the harmonic;
a controller (<NUM>) configured to produce a harmonic cancellation signal (<NUM>) that, when transduced into an acoustic signal, cancels the harmonic within at least one cancellation zone (<NUM>) within a cabin of the vehicle; and
a speaker (<NUM>) adapted to be disposed within the cabin and configured to receive the harmonic cancellation signal and to transduce the harmonic cancellation signal into an acoustic harmonic cancellation signal, such that the harmonic is cancelled within the cancellation zone;
and characterized in that the controller is configured to produce the harmonic cancellation signal, wherein the harmonic cancellation signal is based, at least in part, on mixing the harmonic reference signal converted to baseband with a baseband signal output from a look up table (<NUM>) .