Acoustics – Sound-modifying means – By wave interference
Reexamination Certificate
2002-04-12
2004-02-10
Nappi, Robert (Department: 2837)
Acoustics
Sound-modifying means
By wave interference
C381S071500, C381S071130, C381S071900, C381S071400, C381S071140
Reexamination Certificate
active
06688422
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for actively influencing the intake noise of an internal combustion engine, wherein a correcting noise is generated which is superimposed on the intake noise. The invention also relates to an apparatus especially adapted to carry out the method of the invention.
The process of actively influencing the intake noise of an internal combustion engine, such as with a loudspeaker, is known. A possible circuit arrangement with a corresponding electrical process is illustrated in U.S. Pat. No. 5,321,759. The only feature of the arrangement of
FIG. 1
of this document which is relevant in the present context is the intake tract
12
, which emits an intake noise
20
. The control system receives at least one engine speed signal
44
from the internal combustion engine
10
, which is processed in the electronic control system
26
. Additional variables, such as the position
18
of a throttle valve
16
, can also be incorporated into the computing process of the electronic control system.
Using these measured variables, the control system
26
calculates an output signal, which is converted by a loudspeaker
28
into a sound, which is superimposed on the intake noise. The purpose of this measure is to reduce the intake noise. This purpose is achieved by taking advantage of the fact that a broad spectrum of the intake noise emanating from the internal combustion engine is directly dependent on the engine speed, while the frequency of the noise is based on various multiples of the engine speed. By emission of the noise determined in the intake tract by the control system through the loudspeaker
28
, the corresponding partial noise in the intake tube can be reduced. In the ideal case, therefore, the noise emitted by the loudspeaker
28
requires an opposite and equal amplitude, so as to cancel the corresponding noise component.
To be able to measure the degree of noise reduction, an error microphone
30
is installed in the intake tract which absorbs the intake noise affected by the loudspeaker
28
. The correspondingly filtered signal of the error microphone
30
provides the control system with information on the degree of noise reduction in the intake tract, so that the output signal for the loudspeaker
28
can be varied in terms of optimized noise reduction.
The system described above can be used to achieve effective reduction of the intake noise irrespective of the engine speed of the internal combustion engine. In comparison to conventional silencers, such as resonators, no additional volume is needed for active noise minimization. However, effective noise minimization using the method described above is not considered desirable in all operating states of an internal combustion engine. In certain operating states, the driver needs the acoustic information coming from the internal combustion engine for such purposes as to select the correct point at which to change gears during engine operation. Consequently, a consistent minimization of the intake noise across the entire engine speed range of the internal combustion engine would provide the driver with an inaccurate picture of engine characteristics, resulting in improper loading of the internal combustion engine and therefore in increased fuel consumption.
Furthermore, the publication “Adjusting the Tonal Quality of Engine Noise Using Active Noise Control Techniques” (XP 000163374 ISSN:0374-4353) discloses a method for actively influencing the intake noise of an internal combustion engine. This method makes it possible to tailor the intake noise which remains after noise cancellation to a reference noise. In this way the intake noise can be transformed either into a more powerful sound or also into a very quiet noise. For this purpose an LMS (leased mean squares) adaptive filter is utilized which generates a starting signal phase shifted by 180° in order to damp the intake noise. This starting signal is transformed into an analog signal which can be used to activate a loudspeaker arranged in the intake system. The acoustic waves generated by the loudspeaker are superimposed on the intake noise of the internal combustion engine, so that a cancellation is achieved. A microphone collects the instantaneous noise which remains after the cancellation and generates a corresponding feedback signal.
The filter input signal x(n) is read from a table depending on the angular position of the crankshaft. The values stored in the table list the harmonic oscillations of the intake noise which are to be canceled. These have the following form:
x
(
n
)=
A
sin(
aq
)+
B
sin(
bq
)+
C
sin(
cq
)+ . . .
wherein
A,B,C, . . . are the relative magnitudes;
a,b,c, . . . are the generated oscillations; and
q is the angular position of the crankshaft.
To achieve a targeted adjustment of the intake noise of the internal combustion engine, a second generated signal d(n) is required, which is based on the angle of the crankshaft. This second signal forms the reference noise, which should remain after noise cancellation. The values for the reference noise have the following form:
d
(
n
)=
A
′ sin(
a′q
)+
B
′ sin(
b′q
)+
C
′ sin(
c′q
)+ . . .
wherein
A′, B′, C′ . . . are the desired relative magnitudes;
a′, b′, c′ . . . are the desired oscillations or vibrations; and
q is the angle of the crankshaft.
The error signal e(n), which is utilized to correct the coefficients of the LMS-adaptive filter, is generated by subtraction of the feedback signal of the microphone from the reference signal of the reference noise d(n). In this way the signal y(n) emitted from the LMS adaptive filter will assure that the intake noise emitted by the internal combustion engine will be matched or tailored to the reference noise. The reference noise can be maintained over the entire speed range of the internal combustion engine. Inlet or outlet noise vibrations, which are not created by the internal combustion engine, are generated by the active noise control system only depending on the angular position of the crankshaft.
In the described system a constant tailored adaptation of the reference noise depending on the angular position of the crankshaft is achieved. This tailored adaptation has the result that the reference noise is based exclusively on the crankshaft and other influences are not taken into account.
One could deactivate active noise minimization in certain operating states. However, this would result in an abrupt change in the intake noise, which would similarly confuse the driver, as he is not accustomed to such changes in conventional internal combustion engines. Consequently, the problem described above cannot be satisfactorily solved in this manner.
SUMMARY OF THE INVENTION
Therefore, it is the object of the invention to provide a method and/or apparatus for carrying out this method which makes possible better matching or tailoring of the intake noise.
This and other objects are achieved by the method of the invention as described and claimed hereinafter, as well as by the apparatus for carrying out the method, which apparatus is also described and claimed hereinafter.
In the method of the invention, an electromechanical converter or transducer which may, for example, comprise a loudspeaker which generates a correcting noise, is provided in a manner known in the art. This converter is installed in such a way that a correcting noise generated by the transducer can be superimposed on the intake noise. This can, for example, be achieved by securing the loudspeaker to the outside wall of the intake tract so that it emits sound into the interior of the intake duct. However, it is also possible to install the loudspeaker outside the intake system in the engine space. The key element here is that the sound waves emitted by the loudspeaker can be superimposed on the intake noise.
In addition, a sensor, especially a microphone, is provided which is installed in the engine space or in the intak
Fuesser Rolf
Pricken Franc
Schirmacher Rolf
Crowell & Moring LLP
Filterwerk Mann & Hummel GmbH
Martin Edgardo San
Nappi Robert
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