WO2013076137A1

WO2013076137A1 - Method and device for controlling an active noise reduction system

Info

Publication number: WO2013076137A1
Application number: PCT/EP2012/073224
Authority: WO
Inventors: Hervé ILLY; Bertrand Andro
Original assignee: Renault S.A.S.
Priority date: 2011-11-25
Filing date: 2012-11-21
Publication date: 2013-05-30
Also published as: FR2983335A1; EP2783364B1; FR2983335B1; EP2783364A1; CN104081451B; CN104081451A

Abstract

The method applies to a vehicle (12) in which an active noise reduction system (15) comprises one or more loudspeakers (13) for producing one or more output sound signals which oppose the noise and one or more microphones (11) for picking up one or more feedback signals which quantify the noise reduction obtained. To implement the method, the vehicle (12) comprises a control device (23) which comprises feedback verification means designed to establish a feedback diagnosis by analyzing at least one feedback signal (umiC) in combination with means of activation (24) and of neutralization of the active noise reduction system (15) which are driven so as to activate, respectively deactivate, the active noise reduction system following a positive feedback diagnosis, respectively following a negative feedback diagnosis.

Description

METHOD AND DEVICE FOR CONTROLLING A SYSTEM

ACTIVE NOISE REDUCTION

The invention relates to a method for treating the appearance of a malfunction in an Active Noise Control (ANC) system.

More specifically, the invention relates to a method for controlling an active noise reduction system, for example in a passenger compartment having one or more loudspeakers for producing one or more sound output signals that oppose the noise and one or more microphones for capturing one or more feedback signals which measure the noise reduction obtained.

The invention also relates to a device and a computer program for implementing said method.

Active noise reduction is an old subject. Henri Coanda thus described in 1930 a method of protection against noise in his patent FR722274 consisting in obtaining a zone of silence by interference of sound waves. The idea was good but not so obvious to realize. A little more in appearance in 1934, Paul Lueg limited his patent US2043416 to the simplified case of a pipe in which he placed a speaker downstream of a sound source with a microphone placed between the source and the speaker for capture the sound to be removed before it reaches the speaker.

Despite numerous scientific developments since that time, particularly in the field of signal processing, the use of this invention, however old, is struggling to become democratized, in other words to become accessible to a wide audience.

The disadvantage is that, in spite of a strong current control of theoretical noise reduction, the slightest defect or unforeseen event on the equipment or the environment of a device for reducing sound waves per generation appropriately out of phase, has consequences contrary to the desired effect, namely those of adding the energy of the phase-shifted sound waves to those of the source instead of cutting them off, with the effect of increasing rather than reduce the noise. Among the many attempts since that time to try to overcome these inconveniences, we can cite, for example, the one described in document EP 1 14341 1 A2 which deactivates the noise control unit when the inverse of a return which measures a noise is not greater than a predetermined threshold. In other words, this prior document describes a method that deactivates the noise control unit when the feedback that measures the noise is greater than the predetermined threshold.

JP05027780 discloses an evaluation function equal to a sum of microphone feedback signals so as to deactivate an active noise controller when the value of the evaluation function exceeds a predetermined threshold for a certain time.

Document US2008 / 159553 discloses a method and system for actively reducing birch in lacquer! a faulty system state is detected when an error signal given back by a sound sensor exceeds a second threshold after exceeding a first one.

Previous solutions are all based on the obvious concept that the noise may increase in the event of a malfunction, so the system should be turned off when the sound picked up by a microphone or some other way exceeds a certain threshold. However the prior methods and systems pose a problem of inefficiency in case the malfunction comes from the sound sensor itself.

These more or less recent solutions, like other known solutions, are not sufficiently complete to bring complete satisfaction.

To overcome the drawbacks of the prior art, the subject of the invention is a method for controlling an active noise reduction system, the method comprising:

an activation step of the active noise reduction system;

a return verification step which establishes a return diagnosis by analyzing at least one return signal and which allows a re-execution of the activation step following a positive feedback diagnosis;

a neutralization step which is executable following a negative feedback diagnosis and which deactivates the active noise reduction system. Remarkably, the return verification step includes a low detection sub-step that calculates an operating return criterion and that negates the return diagnosis when at least one return signal does not meet a minimum criterion value. operating back.

In particular, the operating return criterion corresponds to a plurality of variations of the feedback signal over a given time interval.

Also particularly, the return check step includes a high detection sub-step that negates the return diagnosis when at least one feedback signal is not less than a maximum amplitude value.

Preferably, the control method comprises an output verification step which establishes an output diagnostic by analyzing at least one output signal, which allows a re-execution of the step following a positive output diagnostic and which makes the neutralization step executable as a result of a negative output diagnostic so as to deactivate the active noise reduction system.

Specifically, the output verification step includes a high detection substep that negates the output diagnostic when at least one output signal is not less than a maximum amplitude threshold.

Also particularly, the output verification step includes a sub-step of limiting the amplitude of the output signal to a maximum threshold,

Particularly advantageously, the method comprises a moderation step which allows a re-execution of the activation step following a diagnosis of negative output or feedback until a sufficient number of an output diagnostic or negative feedback occurrence, which triggers the disabling step when there is a sufficient number of output diagnostic or negative feedback occurrences.

More preferably, the control method comprises a state monitoring step of an environment of the active braking reduction system that allows reactivation of the active bit reduction system only when said environment is in a state compatible with said activation.

The subject of the invention is also a device for controlling an active noise reduction system, in particular in a passenger compartment, comprising one or more loudspeakers for producing one or more sound output signals that oppose the noise and one or more microphones for capturing one or more feedback signals that quantify the noise reduction achieved. The control device comprises in particular:

- return verification means arranged to establish a return diagnosis by analyzing at least one feedback signal; and

activation and deactivation means of the activated noise reduction system for activating or respectively deactivating the active noise reduction system following a positive feedback diagnosis, respectively following a return diagnosis; negative.

Remarkably, the return verification means are arranged to calculate an operating return criterion and to make the return diagnosis negative when at least one return signal does not satisfy a minimum value of the operating return criterion.

Advantageously, the return verification means are arranged to make the return diagnosis negative when at least one feedback signal is not less than a maximum amplitude value.

The subject of the invention is also a computer program, comprising program code means for performing all or part of the steps of the method which is the subject of the invention, when the program is running on a computer, in particular on a computer. embedded calculator.

The subject of the invention is in particular a computer program product, comprising program code means, stored on a computer-readable medium, for implementing the method according to the invention, when the program product is running on a computer program product. a computer.

The subject of the invention is in particular a vehicle in which an active noise reduction system in a passenger compartment comprises one or more loudspeakers for producing one or more noise-canceling output signals and one or more pickup microphones. one or more feedback signals which quantify the noise reduction obtained, the vehicle comprising a control device according to the invention.

The invention will be better understood with the aid of exemplary embodiments of a device according to the invention with reference to the appended drawings, in which: Figure 1 is a schematic view of a system on which the invention is applied;

Figure 2 shows process steps according to the invention; Figures 3 and 4 are details of steps of the process according to the invention;

Figures 5 to 7 are behavioral curves obtained in certain process steps.

Figure 1 shows a motor vehicle referenced 12 which comprises an active reduction system bmit (ANC) which some of the elements shown below are shown outside the vehicle 12 simply for ease of explanation.

One or more microphones 1 1, generally three, each receive an error signal u _m j _c at a predetermined delivery point of the vehicle 12. Each delivery point is predetermined during the design and testing phases of a prototype of vehicle so as to obtain an optimal noise reduction at the ears of the driver and preferably each occupant. Thus the microphones can be placed closer to the driver's head and each occupant or at geometrically correlated locations of the vehicle with nodes of sound amplitude of the bmit near the head of the occupants.

One or more boxes or speakers 13, the number of which generally varies between four and five, receive UHP control signals from an electronic device 14 represented in dotted lines.

The electronic device 14 comprises an electronic card 15 which houses an ANC algorithm for active noise reduction, an audio device 16, for example radio, which can also independently include multimedia and / or navigation functions and a mixer 17.

The algorithm hosted by the electronic card 15 generates a signal uc for each speaker 13 to reduce or eliminate the bmit in the cabin 20 of the vehicle 12. The bmiî that one seeks to remove is a bmit frequency or with a frequency spectrum determined by a measurable or calculable RPM rotation of a vehicle member such as, for example, but not necessarily of a power train 21. Sounds coming from other sources such as, for example, the tread of the wheels 22 on the roadway or of a sound emission apparatus, could then also be reduced or eliminated provided they are transmitted at the same frequency or at one or more frequencies controlled spectrum,

The audio device 16 generates a signal u _R intended for one or more of the loudspeakers 13 to generate sound in the passenger compartment 20 of the vehicle 12, for example that of a radio transmission, the music of a multimedia support or audible messages for navigation, vehicle operating status or telecommunication.

The electronic card 15 and the audio device 16 may be contained in the same housing of the electronic device 14 or in separate boxes. The ANC algorithm can also be hosted in an on-board computer shared with the audio device 16 in the form of one or more programs executable by the on-board computer.

The mixer 17 generates UHP signals which result from the signals i¾ and UR to be routed each to that of the loudspeakers 13 which are intended u and u _R signals respectively combined two by two.

The electronic card 15 is connected to a vehicle signal multiplexing bus 18, for example a CAN bus (acronym for C 1 King Area Network), to read in real time various information on the state of the vehicle comprising in particular the engine speed RPM (acronym for Revolutions Per Minute) expressed in revolutions per minute. This information can also be received wireline from point to point. The advantage of the multiplexing bus 18 is to make accessible to the ANC algorithm real-time information on many other states of the known vehicle, for example the state of opening of a door or window or the engine running condition. The advantage of the on-board computer for carrying out the functions of the electronic card 15 is to provide a great flexibility in the progressive operation of the states available on the bus 18.

The electronic card 15 or the on-board computer also receives a supply voltage Va of the electronic components from a battery 19 of the vehicle 12. The ANC algorithm uses, in a manner known otherwise, the theoretical and practical knowledge of active noise reduction without the need to present all the details here.

It is simply recalled that currently there are essentially two types of ANC algorithms for active noise reduction, feedforward algorithms and feedback-based algorithms, usually referred to as feedback loops. reaction.

As for example exposed in French in the article by Emmanuel Frïot "An introduction to active acoustic control" of October 6, 2005, in particular on pages 16 to 21 and 38 to 41, or exposed in English in the article of SJ Klliot « In December 2008, particularly on pages 12 to 14, the predictive action consisted mainly of enslaving a loudspeaker sound to a noise reference, measured by a first microphone or estimated depending for example on a motor speed. A second microphone is used to adapt in real time the transfer function of the servo in order to obtain a cancellation of the br it measured by the second microphone.

As for example disclosed in the international patent application WO2010136661, the retroactive action consists mainly in slaving a speaker sound on an error with respect to a zero reference, as measured by a microphone. A favored noise frequency is used to adapt the transfer function of the servo to obtain a cancellation of the error at said favored frequency. The adaptation of the transfer function can be modified so as to follow the modifications of the preferred frequency which can change, for example as a function of the rotation speed of the motor.

The invention can be used for both the predictive and retroactive action algorithms and for any other type of ANC algorithms for active noise reduction, notably by producing a sound well at a noise frequency that results from the engine rotation speed. .

Nevertheless, a retroactive action type algorithm is preferred. The inventors have noted that the predictive algorithm requires constantly adapting the transfer function to any variation measured by the second microphone. These adaptations require calculations that are perform in real time. The inventors have noted that, on the other hand, retroactive algorithms do not require the transfer function to be constantly adapted to any variation measured by the microphone which conventionally acts as a feedback function with a given transfer function in a closed control loop. The inventors have thus found it advantageous to adapt the transfer function to a favored frequency which corresponds, for example, to the fundamental frequency or to the harmonic of rank of the noise generated by the motor. It is then possible to pre-calculate adaptation parameters of the transfer function for a series of favored frequencies and then quickly select in operation the adaptation of the transfer function which corresponds to the frequency favored as a function of the speed of transmission. motor rotation observed in real time.

The transfer function involves one or more frequency response functions between the signal (s) H sent on the loudspeakers 13 and the signal (s) u _m j _cro measured on the error microphones 11.

It is possible to evaluate a frequency response function at a value

FRF (f) according to a frequency f by sending a UHF signal (0 to one or to one of the loudspeakers 13 in the absence of noise and by collecting the signal u _m j _cro (f) from each microphone 13, using the formula:

FRF (f) = u _{mic [O} (0 / UHP (0

The frequency response functions depend on the audio reproduction system comprising speakers and loudspeakers 13, the acoustic cavity formed by the passenger compartment 20 of the vehicle 12 and the error microphone or microphones 13 including the sensitivity.

It will be noted that the electronic device 14 represented in FIG. 1 comprises a device 23 for controlling the active noise reduction system, in particular the electronic card 15.

The device 23 comprises on the one hand one or more output couplers for transmitting to the mixer 17 one or more sound output signals u _e to the speaker or 13 to oppose the noise in the passenger compartment 20.

The device 23 further comprises one or more input couplers connected to the microphone or microphones 1 1 to capture one or more feedback signals for transmission to the ANC algorithm, for example hosted on the card electronics 15 to quantify the noise reduction obtained. The device 23 may also include an input coupler connected to the battery 19 to observe the voltage level and one or more input couplers connected to the bus 18 to read the engine speed RPM and different states of the vehicle 12 relative to example when opening the doors or windows, the vehicle load acceleration, deceleration, uphill or downhill.

Return verification means are arranged in the device 23 to establish a return diagnosis by analyzing at least one feedback signal u _m ; _c .

The return verification means may perform several analyzes of the return signal.

A first possible analysis consists in calculating an operating return criterion C1, in other words non-zero return specific to the use of the operations performed by the algorithm ANC. The existence of a return signal which does not satisfy a minimum value of the operating feedback criterion C1 then renders the diagnosis of negative feedback

A second possible analysis consists in comparing each return signal u _m j _c with a maximum amplitude value so that the return diagnosis is made negative as soon as a return signal u _nl j _c is not lower than this value. Max.

Control verification means are arranged in the device 23 to establish an exit diagnostic by analyzing all or part of the signals linked to the output of the ANC algorithm, each intended for one of the loudspeakers 13.

Here again, the control verification means can perform several analyzes of the output signal by means of tests.

A first test consists in verifying that the amplitude of the control signal u _c of each of the loudspeakers 13 does not exceed a threshold value. The threshold value is different for each of the loudspeakers because the command signals sent to each of the loudspeakers 13 do not exceed a threshold value. High-wagerers are different. On the other hand, the threshold value depends on the control frequency associated with one or more harmonics, in particular with the harmonic 2 of the engine speed. This threshold value is tabulated and indicated by the constator at the time of manufacture of the vehicle. The control signal sent to the loudspeakers is a sinusoidal type signal or a composition of periodic signals in a predetermined frequency band. The test consists in verifying, at a given engine speed, that the maximum of this control signal never exceeds a threshold value given in the table. If the signal has a value that exceeds the threshold value, then in this case, the amplitude of the signal is replaced by this threshold value so as to limit the amplitude. This operation ensures that the amplitude of the signal emitted by the loudspeakers never exceeds a certain threshold.

The device 23 thus sends the mixer 17 u a _e associated with each monitored signal uc control signal u so that the amplitude of the signal _c is equal to the amplitude of the signal u _c as the amplitude of the signal u _c is less than the threshold value and which is equal to the threshold value when the amplitude of the signal u _c is greater than or equal to the threshold value.

Other tests may be considered to complete the failure detection system, for example a frequency test and a phase test between the signals. It is not absolutely necessary to implement these other tests because the system has shown satisfactory behavior in a large number of situations during tests carried out as part of the development of the invention.

With regard to the detection of a failure on the frequency, the following test can be imagined and easily implemented. The control signal sent to the loudspeakers is a sinusoidal type signal whose frequency must be identical to that of the control relative to the harmonic 2 of the engine speed. It is then a question of verifying that the two signals have the same frequency. One way of realizing it is to calculate a coefficient of temporal inter-correlation C _up between the control signal u (xj, t) of the loudspeaker xi at time t and the sinusoidal signal p (xi, t + τ). which has a frequency identical to the control frequency at time t + τ, represented by the following expression:

where E [] is the mathematical expectation operator, The detection of a failure on the phase between the signals is more delicate because it is essentially the ANC algorithm.

More specifically, the device 23 comprises means 24 for activating and neutralizing the active brait reduction system, comprising, for example, the electronic card 15. The means 24 are driven firstly to activate the active noise reduction system. following a positive return diagnosis. The means 24 are controlled on the other hand to disable the active brait reduction system following a negative return diagnosis.

The device 23 for controlling the active noise reduction system may be implemented by means of an electronic circuit of the FPGA (acronym for Ficld-programmable gate array in English for programmable gate array), AS1C (acronym for English Application) -Specific Integrated Circuit for "application-specific integrated circuit") or other,

Advantageously, the device 23 is made using the resources of the on-board computer or a multimedia computer of the vehicle shared with the ANC algorithm, the radio and the mixer.

The memory of the computer used then contains a computer program, comprising program code means for performing all of the steps of the method set out below, when said program is running on a computer.

The program can thus be loaded on the computer at the factory in the form of a computer program product, comprising program code means, stored on a computer-readable medium, for implementing the method set out below. , when the program product is running on a computer.

An exemplary method according to the invention is now explained with reference to FIG.

First, a failure tree of the Active Noise Control System (ANC) is documented to determine the various possible causes of failure. On the basis of this analysis, a self - diagnosis procedure is established, preferably broken down into three levels of diagnosis: - Level 1: limitation of the amplitude of the control signals sent to the loudspeakers.

- Level 2: use of information from the environment outside the ANC system.

Level 3: A posteriori detection based on tests on the ANC signals of exit and entry, in particular of return.

The process starts in a step 100 when the active braking reduction system, powered up, receives a positive voltage Va of the battery 19.

Step 100 triggers a step 101 which consists in verifying different states of the vehicle that make it possible or not to activate the algorithm ANC under the conditions for which it is intended.

The struts can be binary as for example purely lustrative and non-exhaustive, door open or closed, glass closed or lowered, engine started or stopped.

It will be understood from the recalls given above on the predictive and counter-reaction algorithms that the effectiveness of the ANC algorithm is conditioned by a well-tuned agreement of the frequent response functions here the FRF in the passenger compartment. vehicle. These frequency response functions are disturbed by any modification of the cabin space, including the changes that result from an opening on the outside. It is therefore considered in step 101 that a correct state (OK abbreviated) of the opening of the vehicle corresponds to a closed position of the passenger compartment of the vehicle.

We have also seen above that the noise that is to be suppressed is a frequency or frequency spectrum noise determined by a measurable or calculable RPM rotation of a vehicle member, in particular of the power train 21 It will be understood that it is difficult to agree on a zero frequency in the absence of rotation of the motor. It is therefore considered in step 101 that a correct state (abbreviated OK) of the engine speed corresponds to an RPM value greater than a positive lower limit.

The states can also be quantified on a continuous or discrete scale when they relate to a temperature in the passenger compartment or to a vehicle occupancy rate. To reel if a state is okay no, its value is. read on the vehicle bus. A diagnostic variable Diag () is set to i when all the stalls E of the vehicle necessary for a proper functioning of the algorithm

ANC are 'correct.', The variable Diag (B) is. zeroing as soon as a JE state is not correct

A step 103 is triggered if all the states are detected correctly in step 101 and a tag 102 is turned on in the opposite case, other words if at least one is detected incorrectly.

Step 102 is to block any activation of the ANC algorithm, in other words not to activate or deactivate the ANC algorithm. Step 102 loops back to step 101 so as to be able to turn on the ANC algorithm. step 1 once all étais- are detected correct ^to step 101 years,

Step 103 is to allow the activation of the ANC algorithm, in other ways to enable or maintain the ANC algorithm,

An output release step 1 and a return check step 130 are initiated from step 103.

Step 1 consists in establishing an output diagnostic using at least one output signal, in particular by verifying that the signals, each of which is at a high pitch, are in accordance with pre-established criteria. amplitude, frequency and / or phase to suppress the noise in the passenger compartment 20 of the vehicle 12.

An example of step 1 according to the invention is described in detail with reference to FIG. figure 4.

In step 1 10, a substep 1 1 1 is cyclically triggered as long as the ANC algorithm is activated, for example, a purely non-limiting and nonlimiting one after each engagement of the step. 103. In substep 1 1 i, an index -j is milialisc to zero to designate ^' the first high -parlera' 13 of a list containing a QHF quantity of loudspeakers 13.

For each execution cycle of substep 1 11, a subsampler 12 is reiterated as many times as there are controlled speakers, in other words, step 11 is executed to check whether The set of output signals of index j, j ranging from zero to QHP- A run cycle typically corresponds, but not necessarily at a sampling period on the inputs or a date of the fundamental frequency Ai noise to cancel.

The vcriffcalio-n of an output signal .in the sub-step 1 12 as it is illustrated in Figure 4, consists in -ensuring that the amplitude | uc (j) i of the control signal of ^'high 13) is less than a predetermined threshold value for the first time,

The value is typically predetermined during testing on a vehicle prototype so as to cancel the noise under optimal conditions with a margin margin above said noise actually occurring. The sound power of the noise and therefore the value u _seu it is generally a function of load and speed -from ^'of rotation of the engine _"in -other tarnished RPM regime. Different tests are then carried out for different RPM engine speeds during tests on the vehicle prototype. The

The adjusted values are then stored in an associative-indexed data structure, by the possible RPM engine speed values. Line mime possible value of scheme 'RPM engine can index multiple values u _sc '. _; . each specially adjusted to one of the speakers 13 in relation to its range of octaves, and its position in the vehicle. The data structure thus obtained is then duplicated on data carriers, for example readable by the on-board computer or any other computer of the vehicle so that it can be used on vehicles of the same type at the end of the Abrical chain.

The assurance amp lude the noise cancellation signal less than the threshold value, u intended in particular to prevent signal ^cancellation is greater than the noise cancel with the opposite and disastrous effect of Γ amplified, The amplitude test can be performed in real time in different ways.

A simple way is to compare the. the absolute value of the signal udj) is the period of sampling with the threshold value, in fact any exceeding of the value u _SCBi i by the signal udj) indicates an amplitude greater than the value s _scllii . It is reasonable to consider that an amplitude greater than the threshold value causes one. crossing by at. minus a sample of the signal ucij) when the sampling frequency is significantly greater than the Nyquist-Shannon frequency. A more elaborate way is to raise the sampled signal squared and then filter it by a first-order filter with a time constant substantially greater than the period of the sampled signal. It will be recalled that the squaring of a first signal of sinusoidal nature generates a second signal comprising a DC component equal to the half-amplitude of the first signal and a sinusoidal component with a frequency double that of the first signal. The filtering of the double-frequency sinusoidal component with a sufficiently high time constant then leaves only the continuous component which it is sufficient to multiply by two to reproduce the amplitude of the first signal. It is also possible to take a second threshold value equal to half of the threshold value considered in the previous paragraph and thus directly compare the output of the filter with the second threshold value without having to double the filtered signal. This second way, of course, with respect to the first way, has the advantage of not requiring a sampling frequency much higher than the Nyquist-Shannon frequency to guarantee the detection of at least one peak beyond the value threshold when the amplitude is greater. A sampling frequency at least equal to the Nyquist-Shannon frequency is then sufficient because it reproduces the entirety of properties called signal and therefore of its squaring. This second way also has another advantage which is that of filtering any inadvertent exceeding of the threshold value which could result for example from a parasite or a momentary accumulation of sound energy of several signals and not a real overshoot. amplitude.

Another more elaborate way is to find in the output signal, the amplitude of a component of the frequency signal ωο / 2π corresponding to the expected frequency of the brait generated by the engine for a given RPM regime.

This third way of verification of the amplitude is particularly adapted to the signal iinp from the mixer 17. In fact the signal comprises not only the frequency of the signal u _c theoretically equal to ωο 2π but also the frequencies of the signal u _¾ which scan at least the spectrum of the frequencies audible by the human ear. The signal may also contain the frequency ωο / 2π and this with an amplitude such that, added to that of the signal u _c , a total amplitude greater than the threshold value of the amplitude is obtained, with the risk of saturating the regulation of the ANC algorithm and consequently to cause non-linearities detrimental to the adaptive parameterization.

This third way of verifying the amplitude does not bring any particular advantage to the verification of the amplitude of the single signal u _c , the frequency of which is, unless the ANC algorithm itself is malfunctioning, equal to the expected frequency ωο / 2π, The verification should not relate in this case to the amplitude but more to the frequency itself for which we will see a possible method below.

The third way of verifying the amplitude is implemented by calculating an abscissa B and an ordinate C relating to an amplitude module A by means of the following formulas:

⁵ = f _r ^/ _/ ² ₂ ½ _p (-cos (u) ₀ ) _£ // "| fm"'' ^{/, (,), Sn (f} '' ^{/) </}

Whatever the manner of verifying the amplitude chosen in the sub-step 1 12, a substep 1 13 is executed if the amplitude is not less than the amplitude threshold value and a substep 1 14 is executed if the amplitude is smaller than the threshold value of amplitude u _seu ii.

In the sub-step 1 13, the amplitude of the signal is limited to the value u _scu ji and a variable Diag (S) previously initialized to 1 for example in the sub-step 1 1 1, is set to zero.

In sub-step 1 14, the amplitude of the signal is maintained at its value and the variable Diag (S) retains its previous value.

Thus, it is necessary for the amplitudes of all the verified output signals to be lower than their respective threshold values for the Diag (S) variable to be maintained at 1 and all that is required is an output signal amplitude greater than its threshold value. to set the Diag (S) variable to zero.

The implementation example illustrated in FIG. 4 corresponds to a sequential execution of the method in which a substep 1 increments the index j following each execution of substep 1 13 or the sub-step 1. step 1 4 to re execute substep 1 12 as long as the index j is less than Qm>. A substep 1 17 end of cycle is engaged as soon as a substep 1 16 detects that the index j reaches the number QHP of output signals to verify.

Other implementations of the method than that illustrated in FIG. 4 are possible. For example, in a multitasking or logic circuit implementation, a parallel execution of Q _HP checks each of an output signal, sets to 1 or 0 a separate Diag (S) variable for each signal. A synthesis task or an AND gate then makes the product of all Diag (S) variables to obtain a final value equal to 1 if all the checks are positive or a final value equal to 0 as soon as a check is negative.

Steps 12, 113 and 114 of FIG. 4 illustrate a check on a maximum allowable amplitude of output signal.

Other output signal checks with or without correction are possible.

In particular, it is possible to check whether the frequency of an output signal u ₂ (t) and close or not to the control frequency f - ωο / 2π by means of an inter correlation coefficient Ο, ι ^ ίτ) of the following way.

An arbitrary signal is generated. uj (t) sinusoidal frequency f = ωο / 2π. Three mathematical expectations E [] are calculated using the following approximate formulas:

£ [», ()» 2 C + 1 - - Σ »! (> »2 (" + H)

NOT

£ [", (/)", ^* (')] = -Σ "i (») ", (»)

N " _{= 0}

The inter-correlation coefficient C _U i "2 (O between the two signals ui (1) and i¾ (t) is then calculated using the following formula:

The correlation coefficient C _U | _u2 (x) thus obtained at a value threshold coefficient for example equal to 0.9. If the inter-correlation coefficient C _u i _U 2 ("c) is not greater than the threshold coefficient, the variable Diag (S) is set to zero to signify that the frequencies of the two signals iii (t) and u ₂ (t) are not close enough to each other.

In particular, it can be verified whether the phase of an output signal iic (t) varies over time. Knowing the period T equal to the inverse of the frequency f = ω ₀ / 2π of the signal Uc (t), the values of the signal uc (t) are compared to two times separated by a period T.

For example, the difference u'c (t + T) is evaluated:

* _c (t + T) = ii _c (t + T) - u _c (t)

A non-zero difference then makes it possible to detect a phase variation. For example, the difference u "c (t + T) is further evaluated;

u "c (t + T) = u (tT) - 2u _c (t) + u _c (t + T)

A non-mile difference then makes it even better to detect a variation in phase variation.

Those skilled in the art will of course take the usual precautions in terms of filtering to avoid unwanted phase variation detections so as to position the variable Diag (S) to zero in the event of detection of known phase variation.

The variable Diag (S) is then evaluated in the substep 1 17 after having made all the checks provided on all the output signals to be checked. The positive escapement of substep 1 17 when the variable Diag (S) is at 1 corresponds to the positive escapement of step 1 10 and the negative escape of substep 1 17 when the variable Diag ( S) is 0 corresponds to the negative exhaust of step 1 10.

The positive escaping of step 1 leads to a continuation of the process without taking a particular measurement so as to allow a re-execution of step 103 following a positive output diagnosis, for example as illustrated on FIG. FIG. 2, looping back to step 101 when the variable Diag (S) is equal to 1.

The negative escapement of step 1 triggers a step 120 of testing the occurrences of the variable Diag (S) equal to zero so as to make executable a step 104 of neutralization of the algorithm ANC when the occurrences of Negative output diagnostics are considerable. Step 104 then essentially consists in deactivating the active brait reduction system, preferably at least until a new start of step 100 by energizing after power off, see until further control is performed. in after sales service.

Step 120 essentially consists of detecting whether the Diag (S) non-1 escaped variable of step 1 represents a failure that occurs over a period of time.

is considered too long if it exceeds a predetermined duration TSEUIL during prototype phases of the vehicle and possibly adjustable to sensitize or desensitize the ANC deactivation in the presence of failures. We will see later in the description a possibility of determining a duration TSEUIL common to the outputs and returns. When a duration TSEUIL equal to a duration Ts (S) specific to the outputs is determined, the following test is carried out on a duration Tdef (S) of null diagnostic proper to the outputs:

TdeffS) = T _DIAG = o> TSEUIL = Ts (S)

Step 120 can be implemented in different ways.

A first way is simply to increment a counter every occuiTence of a zero value of the variable Diag (S) for an observation period equal to T _SE UIL counted from the first occurrence of the variable Diag (S) to zero. If the observation time is reached or exceeded without the contents of the counter corresponding to a number of all zero occurrences of the variable Diag (S), the counter is reset. This first way, if it has the merit of being simple, is not entirely satisfactory because each reset of the counter causes an erasure of past events in terms of failure detection.

Advantageously, a second way is to apply a first-order filter with a time constant a on the variable DIAG-Diag (S) to obtain a filtered variable DF;

DF = ^{X "a} , DIA G

l - a, z ^{~ l}

Figure 5 shows a temporal evolution curve of the D1AG variable in the upper part and a temporal evolution curve of the DF variable in the lower part. When at instant to, the variable DIAG initially at the value 1, passes to the value 0, the variable DF up to the value 1, decreases with the time constant until reaching a threshold ε of zero detection. at a time t ₂ provided that the variable DIAG remains at zero.

If at a moment t | after the instant to and before the instant t ₂ , the variable DIAG returns from the value 0 to its value 1, the variable DF then to a value less than 1, increases with the time constant a until that the variable DIAG returns to zero at a time tj. When at the instant ta, the variable DIAG passes to the value 0, the variable DF then to a value greater than that reached at time t | , decreases with the time constant a until the zero detection threshold ε is reached at a time ¾ that is clearly greater than the instant t ₂ . We note here that the rise of the variable DIAG to 1 during a duration tj - 1], causes a crossing of the threshold ε of detection zero with a delay te - h significantly greater than the duration t ₃ - t _t during which the variable DIAG is ironed at 1.

Although the probability of such a phenomenon to occur is very small, one solution may be to lower the time constant a or to raise the threshold ε of zero detection,

Figure 6 shows a time evolution curve of the DF variable when the filter is applied only if the variable DIAG is at zero and the variable DF remains frozen if the variable DIAG is at 1.

This second way of filtering the zero crossings of the variable DIAG is well adapted to the example of implementation of the method illustrated in FIG. 2. The filter is applied in step 120 only in case of escape from the step 1 10 with a null value of the variable DIAG equal to the variable Diag (S). As long as step 1 10 loops back to step 101 with a unit value of the variable Diag (S), the variable DF is not modified in step 120,

When at a time tj after the instant to and preceding the instant t ₂ , the variable DIAG returns from the value 0 to the value 1, the variable DF then at a value less than 1, retains this value until DIAG is reset to zero at a time { ^■ > ,. When at the instant \ _% , the variable DIAG passes to the value 0, the variable DF then to a value equal to that reached at time t | , decreases with the time constant until reaching the threshold ε of zero detection at a time greater than the moment ta but very close to the instant tj. We note here that the rise of the variable DIAG to 1 during the duration tj-ti, causes a crossing of the threshold ε of detection zero with a delay t. - h much less than the time ta - 11 during which the variable DIAG is ironed at 1. It is thus avoided that the DIAG variable's up-to-1 occurrences inadvertently hide zero crossings whose occurrences indicate a system failure .

However, it is observed in FIG. 6 that if the variable DIAG remains at 1 for a duration t ₇ - ti that is significantly greater than ti - to, the variable DF persists in crossing the threshold ε of detection zero at a time tg greater than moment t ₇ but nevertheless as close to time t ₇ as time t ₄ is at time t ₃ . We note here a memory effect of the zero crossings of the variable DIAG which, even of negligible durations in front of those of passages to 1 of this same variable DIAG, have the effect of making the variable DF fall below the threshold ε of detection null by a short transition to zero DIAG variable after a time more or less long and completely unpredictable.

Figure 7 shows a temporal evolution curve of the variable DF when the filter is applied if the variable DIAG is at zero with a time constant a of value lower than if the variable DIAG is at 1.

This third way of filtering the zero crossings of the variable DIAG poses no particular difficulty of realization because the variable DIAG being a binary logical variable, it suffices to type the time constant a in the form of parameter instantiated at a first low value when the variable DIAG is at 0 and at a second high value when the variable DIAG is at 1. The application of the filter during the ascent of the variable can be carried out in a step not represented in FIG. 2 but which is situated easily between step 1 and step 101.

When at time ti, the variable DIAG returns from the value 0 to the value 1, the variable DF then at a value less than 1. increases until the variable DIAG returns to zero at a time h. When at time t3, the variable DIAG passes to the value 0, the variable DP then has a value greater than that reached at time t | but less than that reached at the same instant in FIG. 5 because of the higher value time constant, decreases with the time constant a of low value up to the threshold ε of zero detection at a time ts greater than the instant t ₂ niais less than the instant te of Figure 5. It is noted here that the rise of the variable DIAG to 1 during the duration t ₃ - 1], causes a crossing of the zero detection threshold ε with a delay ts - ti much lower than the duration t ₆ - 1 \ of Figure 5. Compared to the first way of filtering, it is thus easier to avoid that The DIAG variable's 1-to-1 rollovers do not inadvertently mask zero crossings, the occurrences of which indicate a system failure. Compared to the second way of filtering, it is also avoided that descents to 0 of the variable DIAG do not inadvertently hide a predominance of the passages to 1 whose occurrences testify to an acceptable functioning of the system because the time constant has, well that of high value at your ascent, leads to a duration t ₉ - ti of reaching the threshold ε of null detection higher than the duration t ₈ - t [when the duration t ₇ - ti is definitely greater than the duration t [ - ÎQ.

A negative escape of step 120, as long as the negative diagnosis has not persisted long enough, loops back to step 101 at the rate of the signal samplings.

Step 130 consists in establishing a return diagnosis by analyzing at least one return signal, in particular by verifying that the signals u _m j _C each coming from a microphone 11, comply with pre-established criteria of amplitude, frequency and / or phase according to the noise suppression expected in the passenger compartment 20 of the vehicle 12.

An example of step 130 according to the invention is described in more detail with reference to FIG.

In step 130, a substep 131 is cyclically engaged as long as the ANC algorithm is activated, for example purely illustrative and not limiting, following each activation of step 103. step 131, an index i is initialized to zero to denote the first microphone 11 a list containing a Q ■ amount _m i, _ro of microphone 1 1. ·

For each cycle of execution of the substep 131, a substep 132 is repeated as many times as there are controlled microphones, in other words the substep 132 is performed to check all the signals output of index i, i ranging from zero to Q _in j _cro - 1. A run cycle typically corresponds but not necessarily at a sampling period on the inputs or at a date of the fundamental frequency of the noise to be canceled.

The verification of an output signal in your sub-step 132 as illustrated in FIG. 3 consists in ensuring that the amplitude | u _n , j _c (i) | the signal picked up by the microphone 1 1 of index i, is less than a threshold value a _max \ predetermined.

The value u _ma i is typically predetermined during tests on a prototype vehicle in agreement with a sound level bearable by the human ear. The sound power of the noise and therefore the value u _max i are generally a function of the rotational speed and the load of the engine, in other words the RPM regime. Different tests are then carried out for different RPM engine speeds during tests on the prototype vehicle. The adjusted u _max i values are then stored in an associative data structure indexed by the possible RPM engine speed values. The same possible value of RPM engine speed can index several values u _maX j, each specially adjusted to one of the microphones 1 1 in relation to its sensitivity and position in the vehicle. The data structure thus obtained is then duplicated on data carriers, for example readable by the on-board computer or any other computer of the vehicle so as to be usable on vehicles of the same type at the output of the production line.

The assurance on the amplitude of the signal captured below the maximum value, is intended in particular to avoid a feedback effect with the opposite and disastrous effect of unpleasantly amplifying the noise. The amplitude test can be performed in real time in different ways.

A simple way is to compare the absolute value of the signal _m j i _cro (i) at each sampling period with the threshold value. Indeed any exceeding of the value u _max j by the signal ιι _ηΐ ; _ςΓ0 (ί) indicates an amplitude greater than the value

Umicro (I) -

It is possible to perform a finer analysis of the maximum value on the microphone signal. Indeed, the error microphone 1 1 measures a broadband noise, in other words a noise spectrum over a wide frequency range. The active reduction algorithm aims to remove only the noise component at the expected frequency of being canceled. This filtering operation is implicitly performed in the body of the algorithm. But it is possible to perform it also by a simple operation.

It is recalled that, in general, the signal measured by the microphone can be decomposed into a Fouricr series. It is written as:

^U mkra (0 = Σ A COS ("ft ⁾ / + <f>) OR 6∞0Γ ^β :

11

"" _K ro (0 = Σ B "cos (ncot) + C" sin (ne) /)

G) = 2 KIT with T: signal period u _m i _cro (t)

The coefficients of this series are given by the relations:

^B "= | f _{r /} ² ₂ ""im, (.cos (u ⁾ n <//

In the case where we want to extract the component of the signal at the control frequency f = ω ₀ 12π, we only consider the component which is written in the form

"mkro (= 4sin (û ⁾ _o / + 0)

Q i is rewritten again in the following form

" _micro (0 = Seos (oy) + Csin (ey)

with B, C calculated using the following relationships:

The total amplitude A of the signal at the frequency f is then such that A + C ² . This amplitude varies according to the engine speed A. In general, we have A = A (RPM).

In this case, the test on the simple instantaneous module of the signal mentioned in the preceding paragraph is replaced by a test which consists in checking, at a given RPM engine speed in real time, that the amplitude A (RPM) measured by the microphone is less than a threshold amplitude defined for this same engine speed:

A (RPM) <A ^ieuii (RPM)

This second maximum amplitude test is more interesting than the first maximum amplitude test explained above because an anomaly, in other words a threshold overshoot, is detected only at the control frequency f, for a RPM regime. given. It must be borne in mind that the error microphone 1 1 measures at each instant a pressure value which is an average value whereas the pressure fluctuation is the superposition of all the frequency contributions as expressed by the decomposition of Fourier. But only the fluctuation of pressure at the control frequency interests us. Therefore, if the pressure level measured by the error microphone results from broadband excitation or mono-frequency excitation but at a frequency different from the control frequency, the first maximum amplitude test detects a error while the second maximum amplitude test does not detect it. But the purpose of active noise reduction is to remove only the component of the signal that is at the control frequency. The detection of a fault only makes sense at this frequency.

Whatever the manner in which the maximum admitted amplitude is selected which is chosen in the sub-step 132, a sub-step 13 is executed if the amplitude is less than the amplitude threshold value and a sub-step 134 is executed if the amplitude is not less than the threshold value of amplitude u _max j.

In the sub-step 133, it is verified that the microphone 1 1 index i is operational, and other terms that it actually captures a non-zero signal.

At each time t passing through step 133, calculating a criterion C _m _C j (i) which measures a cumulative variations _in u j signal _c (i, t) discretized in M time intervals on the N samplings preceding the instant t current, in other words on a hard observation Τ = ΝΔτ, by means of the formula:

^C1C1

We then check the criterion C l, "j _c (i)> CI _m im. If no signal is measured by the microphone, the value of C l ", j _C (i) is very low, the value of the lower bound Cl mini is also determined during the tests of the prototype system. The advantage of this criterion is that it does not depend on the average value of the signal and that it is quite simple to calculate.

In the exemplary implementation of the method illustrated in FIG. 3, a substep 136 is executed if the criterion C l _m _{C C} (i)> Cl _m i _n i is found and the sub-step 134 is executed. on the other hand.

In step 134, the variable Diag (R) is set to zero so that a negative response to one of the verification steps 132 or 133 is sufficient: to set the variable Diag (R) to zero and the variable Diag (R) remains at 1 if and only if all the responses to verification steps 132 and 133 are positive.

The implementation example illustrated in FIG. 3 corresponds to a sequential execution of the method in which the substep 136 increments the index i following each execution of the substep 133 or of the substep 134 to re-execute the _substep 132 as long as the index i is less than Q _mjcro . A sub-step 138 of the cycle fm is triggered as a substep 137 detects that the index i reaches the number Q _m j _cro return signals to verify.

Other implementations of the method than that illustrated in FIG. 3 are possible. In particular, the order of execution of steps 132 and 133 can be reversed or their execution can be done in parallel. For example yet in multitasking implementation or logic circuit, a parallel execution of Q "i _era verification tasks each of a return signal, positioned in a 1 or 0 Diag variable (R) for each separate signal . A synthesis task or an AND gate then makes the product of all Diag (R) variables to obtain a final value equal to 1 if all the checks are positive or a final value equal to 0 as soon as a check is negative.

The variable Diag (R) is then evaluated in the substep 138 after having made all the checks provided on all the return signals to be checked. The positive escape of the substep 13S when the variable Diag (R) is at 3 corresponds to the positive escapement of the step 130 and the negative escape of the substep 138 when the variable Diag (R) is at 0 corresponds to the negative exhaust of step 130. The positive exhaust of step 130 leads to a continuation of the process without taking part measurement so as to allow a re-execution of the step

103 as a result of a positive feedback diagnosis, for example known as illustrated in FIG. 2, in a reboot on step 101 when the variable Diag (R is equal to 1.

The negative diagram of step 130 triggers a step 140 of testing the occurrences of the variable Diag (R) equal to -siera so as to make the step

104 -neutralization of the ANC algorithm when the occurrences of negative feedback diagnostics are considerable.

Step 140 essentially consists in detecting whether the non-escaping Diag (R) variable of step J30 -radiates a failure that occurs over a too long duration TJ _MA OO. The duration TU _TA O _A is considered too long if it ^'exceeds a duration TS _E UTI during predetermined phases of the test on the vehicle prototype. The duration Tstiii _L is optionally adjustable to sensitize or desensitize the deactivation "!]. ANC in the presence of failures. We will go further in the description a possibility of determining a duration Tsexm. common- to exits and retows. When determining a duration T TIME equal to a duration Ts (R) specific to the outputs, te is performed. next test over a period of time Tdei | R) diagnostic will go clean to the outputs i

Tdef (ït) = TDJACMJ> Tsram. = Ts (R)

Step 1 0 can be implemented in different ways on the model of those of step 120.

A negative exhaust of step 140 ,. as long as the negative diagnosis has not persisted for a long time, re-started on step 101 with the rhythm of the signal samplings.

As we come from, vok, a step 120 distinct from step 140, makes it possible to determine a threshold duration Ts (S) that is customized for the occurrences of the output diagnostics -negatives and a duration -threshold Ts (R) customized. for the occurrences of. negative output diagnostics of different values.

If the threshold values durations Ts (S) and T (R) are identical, the steps 120 and .140 can be grouped in a single step ^'wherein the OCCUITCJICCS of diagnosti ues, output and return are nevertheless considered' éparément or are considered in the same way, in other words in the latter case, a Negative diagnosis is considered to be an occurrence regardless of whether it relates to exit or return.

The invention which has just been described fulfills the purpose of prescribing, during use, that the ANC system does not cause a problem for the user when the system becomes defective, for example because a microphone or a built-in by them is down. We have seen how the invention: to ^'prevent the vehicle speakers emit sound .forte amplîlui when the system fails. The invention thus makes it possible to detect the appearance of the fault in a very short time and to find an adequate correction.

the detection is tight in. what it does not go off unexpectedly.

This simple solution makes it possible to process all the identified lances identified in the fault tree. Erase her. is sufficiently general not to depend on the particular origin of the failure, it has the potential to deal with other unidentified failures so far.

Claims

A method of controlling an active brait reduction system having one or more loudspeakers (13) for producing one or more noise-canceling output signals and one or more pickup microphones (1 1) for sensing one or more return signals which measure the noise reduction obtained, characterized in that it comprises:

a step (103) of activation of the active brait reduction system;

a step (130) of return verification;

- which establishes a return diagnosis by analyzing at least one feedback signal in a low detection substep (132) which calculates an operating return criterion (C1) and renders the return diagnosis negative when at least one signal return does not meet a minimum value of the operating return criterion (C l); and

which authorizes a re-execution of the step (103) following a diagnosis of positive return;

a neutralization step (104) which is executable following a negative feedback diagnosis and which deactivates the active brait reduction system,

2. Control method according to claim 1, characterized in that the criterion (C l) corresponds to a plurality of variations of the feedback signal over a given time interval.

3. Control method according to one of claims 1 to 2, characterized in that the return verification step (130) comprises a sub-step (133) of binding detection which makes the diagnosis of return negative when at minus a feedback signal is not less than a maximum amplitude value.

4. Control method according to one of the preceding claims, characterized in that it comprises:

an output verification step (1 10) in which an output diagnostic is established by analyzing at least one output signal, which allows a re-execution of the step (103) following an exit diagnostic positive and which makes step (104) of neutralization executable following a negative output diagnostic so as to deactivate the active noise reduction system,

5. Control method according to claim 4, characterized in that the output verification step (1 10) comprises a high detecting sub-step (112) which renders the output diagnosis negative when at least one output is not less than a maximum amplitude threshold,

6. Control method according to one of claims 4 or 5, characterized in that the step (1 10) of output verification comprises a substep (1 13) amplitude limitation of the output signal to a threshold maximum,

7. Control method according to one of the preceding claims, characterized in that it comprises a moderation step (120, 140) which allows a re-execution of step (103) following a diagnosis of output or negative feedback as long as there is not a sufficient number of negative output or feedback diagnostic occurrences, especially as long as said diagnosis is not negative for a sufficient duration and triggers the step (104). ) of neutralization when there is a sufficient number of occurrences of diagnostic output or negative feedback, especially as soon as said diagnosis is negative for a sufficient duration.

8. Control method according to one of the preceding claims, characterized in that it comprises a step (101) for monitoring the state of an environment of the active noise reduction system which authorizes the aclivation of the reduction system. active noise only when said environment is in a state compatible with said activation.

9. Apparatus (23) for controlling an active noise reduction system (15) having one or more loudspeakers (13) for producing one or more noise-canceling output signals, one or more microphones (1 1) for sensing one or more feedback signals that quantify the noise reduction obtained, andmeans for activating (24) and neutralizing the active reduction system of noise (15) controlled to activate respectively deactivate the active noise reduction system following a positive feedback diagnosis, respectively following a negative feedback diagnosis, characterized in that it comprises:

- return verification means arranged to calculate an operating return criterion (C1) and to establish a return diagnosis by analyzing at least one return signal (u _m i _c ) so as to render the return diagnosis negative when at least one return signal does not satisfy a minimum value of the operating return criterion (C l).

10. Device (23) according to claim 9, characterized in that said return verification means are arranged to make the return diagnosis negative when at least one return signal (u _mic ) is not less than a value. maximum amplitude.

A computer program, comprising program code means for performing all of the steps of any one of claims 1 to 8, when said program is running on a computer.

A computer program product, comprising program code means, stored on a computer readable medium, for implementing the method of any one of claims 1 to 8, when said program product is operating on a computer program product. computer.

A vehicle (12) in which an active noise reduction system (15) in a passenger compartment (20) has one or more speakers (13) for producing one or more sound output signals which oppose noise and one or more microphones (1 1) for receiving one or more feedback signals which quantify the noise reduction obtained, characterized in that it comprises a control device (23) according to one of the claims 9 to 10 mounted in a manner to control the active reduction system of brait.