FR2786307A1 - PILOTAGE SYSTEM FOR ELECTROACOUSTIC TRANSDUCER ACTIVE ANTI-NOISE FOR MOTOR VEHICLE EXHAUST SYSTEM - Google Patents

Abstract

This system comprising a residual line noise sensor (3), associated with an anti-noise computer (4) adapted to generate, thanks to an estimate of the equivalent transfer function (H) of the line, of the transducer means and of the sensor, a line noise reduction signal suitable for being applied to the electroacoustic transducer means (5), for superimposing noise reduction on the noise generated by the exhaust line, is characterized in that it comprises means (6) for dynamically updating the estimate of the equivalent transfer function (H), comprising means (7, 8) for generating and superimposing on the anti-noise signal, a predetermined analysis signal, means ( 9) analysis of the residual line noise coming from the sensor, to extract the contribution of this analysis signal, the residual noise, and means (10) for calculating a corresponding updated estimate from this signal of analysis and this contribution.

Description

The present invention relates to a system for controlling means at

  electroacoustic active noise canceling transducer for exhaust line

motor vehicle.

  In the state of the art, systems of this type have already been developed.

  type to reduce the level of noise pollution caused by the function-

vehicle engines.

  Conventionally, such systems include a residual line noise sensor, associated with an anti-noise calculator adapted to generate, by means of an estimate of the equivalent transfer function of this line, means with an electroacoustic transducer and the sensor, a signal line noise canceling adapted to be applied to electroacoustic transducer means,

  to superimpose noise reduction on the noise generated by the exhaust line.

  However, such structures present a number of incon-

  because the operating characteristics of the exhaust line

  vary over time due in particular to changes in the conditions

  operation of this exhaust line, wear of parts,

these, etc.

  However, in the systems known in the prior art, the estimate of

  the equivalent transfer function is frozen and we can see that over time

  system response is drifting strongly.

  Such drifts can also be noticed during abrupt

variations in engine load.

  The object of the invention is therefore to solve these problems.

  To this end, the subject of the invention is a system for controlling active anti-noise electroacoustic transducer means for the exhaust line of a motor vehicle, comprising a residual line noise sensor, associated with an anti-noise calculator suitable for generate, by means of an estimate of the equivalent transfer function of the exhaust line, of the electroacoustic transducer means and of the sensor, a line noise reduction signal suitable for being applied to the electroacoustic transducer means, for

  superimpose a noise barrier on the noise generated by the exhaust line, characteristic

  se in that it includes means for updating the dynamics of the

  mée of the equivalent transfer function, comprising:

  - means of generation and superposition on the anti-signal

  noise, of a predetermined analysis signal, - means for analyzing the residual line noise from the sensor, to extract the contribution of this analysis signal, from the residual noise, and - means for calculating a estimated updated from the function of

  transfer from this analysis signal and this contribution.

  Advantageously, the analysis signal is known in amplitude and in phase.

  Advantageously also, the means of calculating the estimated estimate

  include means of calculating it from the transforms

  Fourier mées of the analysis signal and its contribution.

  The invention will be better understood using the description which follows

  given only by way of example and made with reference to the drawings an-

attached, on which:

  - Fig.1 shows a block diagram illustrating the general structure

  line of a control system according to the invention; and

  - Fig.2 illustrates the updating of the estimate.

  In fact, in FIG. 1, one recognizes an exhaust line of

  automobile vehicle which is designated by the general reference 1 and which is associated

  ciée to an anti-noise system designated by the general reference 2.

  As previously indicated, this type of system has been de-

  developed in the state of the art to reduce the level of noise pollution

  generated by the operation of vehicle engines, for example.

  Conventionally, such noise reduction systems include a cap

  level of residual line noise designated by the general reference 3, constituted by

  for example by any suitable microphone or pressure sensor.

  This line residual noise sensor 3 is associated with an anti-noise computer, designated by the general reference 4, which is adapted to generate from the residual line noise, and by virtue of an estimate of transfer function stored in the computer. 4 and which will be described in more detail below, a line noise canceling signal adapted to be applied to active electroacoustic transducer means designated by the general reference 5 in this figure, and

  associated with exhaust line 1.

1I ILFl!

  These transducer means 5 comprise for example a high

  their and are adapted to receive the noise canceling signal from the computer to generate line noise canceling adapted to be superimposed on the noise generated

  through the exhaust line, in a conventional manner.

  The estimate of the transfer function mentioned above is

  then an estimate of the equivalent transfer function of the escape line-

  electroacoustic transducer and sensor means and is desi-

  hindered by the general reference H in this figure.

  This transfer function estimate then allows this calculator to

  determine the line noise canceling signal from the residual line noise.

  However, and as mentioned earlier, this estimated

must be updated.

  The system according to the invention then comprises means designated by

  the general reference 6 in this figure, which make it possible to update in dyna-

  mique this estimate of the equivalent transfer function and which include means 7 for generating a predetermined analysis signal x, for example not audible, and means 8 for superimposing this analysis signal on the noise canceling signal from the computer 4. This predetermined analysis signal can by

  example present characteristics of known amplitude and phase.

  The updating means 6 also include means for analyzing the residual line noise from the sensor 3 and designated by the reference

  general 9 in this figure, to extract from this residual line noise, the contribution

tion x 'of the analysis signal.

  Finally, the updating means also include

  means 10 for calculating the corresponding updated estimate from this

  general analysis and this contribution.

  It is in fact conceivable that, by knowing the analysis signal injected

  in the system, it is possible to retrieve the contribution and then determine

  ner the transfer function of the system to update the estimate of this function

  transfer to the computer.

  This updating can then be carried out periodically to update

  dynamically update the estimate of the stored equivalent transfer function

  in the computer to optimize the generation of the noise canceling signal.

  The means of calculating the updated estimate, designated by the ref-

  general reference 10 in this figure, can be based on the use of trans-

  formed of Fourier corresponding signals that is to say of analysis and con-

tribution, in a classic way.

  This is illustrated in FIG. 2. In this figure: - P (z) is the real transfer function of the exhaust line, - Yp (n), the noise generated by this line, - W (z), the coefficient matrix, - Yc (n), the line noise canceling signal, - Ya (n), the analysis signal, - H (z), the estimated transfer function, and

  - e (n), the residual line noise.

  The analysis signal Ya (n), which is for example a non-audible or low-power signal, is added to the noise canceling signal Yc (n) and contains all the

  harmonics of the useful frequency band of the system.

  The main characteristics of this signal are: - an identical amplitude for all harmonics, - a random phase, - a time signal between -1 and +1, and

- small variance.

  The goal is therefore to find from available information, in

  the occurrence the error signal e (n), the transfer function H (z).

  This error signal is written: j-1 j-1 e (n) = Zhjyc (nj) + Xhjya (nj) + yp (n) j = 0 j = 0 In the frequency space, this expression becomes : E (f) = H (f) Yc (f) + H (f) Y. (f) + YP (f) Considering that the noise canceling signal yc (n) is calculated so that H (f) YC (f) + Y (f) + Y (0 0, an estimate of H is given by the relation: AE (f)

H (f) -

  Ya (f) The transfer function H is completely characterized because the signal

  ya (n) contains no zero frequency.

  In addition, the parameters of interest in the context of filtering the

  trated by the estimate of H are in fact the real and imaginary Fourier coefficients of H. ji1 AA a (f) =: hjcos (27rfj) = Real [H (f) j = o j-1 AA b (f) = E hjsin (27rfj) = - lmagt H (f) j = o It suffices therefore to calculate the Fourier transform of the error signal as it is acquired, the transform of the additional signal being

she perfectly known.

  It goes without saying of course that different embodiments of such a

system can be considered.

Claims (2)

  1. Control system of active electroacoustic transducer means for noise reduction for motor vehicle exhaust line, comprising a sensor (3) of residual line noise, associated with an noise reduction computer (4) adapted to generate thanks to an estimate of the equivalent transfer function   slow (H) line, electroacoustic transducer means and cap-   line, an anti-noise signal adapted to be applied to the means to trans-   electroacoustic conductor (5) for superimposing noise reduction on the noise generated by   the exhaust line, characterized in that it comprises means (6) for re-   dynamic updating of the estimate of the equivalent transfer function (H) comprising: - means (7,8) for generating and superimposing on the anti-noise signal, a predetermined analysis signal, - means (9) for analyzing the residual line noise from the sensor to extract the contribution of this analysis signal, for the residual noise, and - means (10) for calculating the updated estimate of the function of   transfer, from this analysis signal and this contribution.   2. Control system according to claim 1, characterized in that the means (10) for calculating the updated estimate comprise means for calculating the latter from the Fourier transforms of the analysis signal and of his contribution.