JPH112113A - Noise actively reducing method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the noise as much as possible throughout a wide range of frequency with a minimum structure, by making the first and second volumetic currents exist, and modulating one of them on a specific frequency spectrum. SOLUTION: A piping 2 is branched from a piping 1 in which the first volumetic current 10 for reducing the noise, is flown. The second volumetic current 20 flown in the piping 2 as a part of the first volumetic current 10, is guided to an actuator A, and is modulated to an optimum phase on a specific frequency spectrum, in the actuator A. This modulation is performed so that the noise can be reduced as much as possible throughout the total acoustic spectrum when the first and second volumetic currents 10, 20 are interfered with each other afterward. The both volumetic currents 10, 20 have the same temperature, and the acoustic sources thereof are located on the same position, so that the noise can be almost eliminated by the superposing of the sounds. Further the spectrum of an acoustic wave to be eliminated, of the first volumetic current 10 is detected by a sensor, e.g. a microphone, to be used in control of the actuator A after the cleaning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for silencing a sound according to the preambles of claims 1 and 11.

[0002]

2. Description of the Related Art It is generally known to cancel sound waves by causing sound waves oscillating in opposite phases to interfere with each other. It is also known that sound waves can be generated by modulating the gas flow.

[0003] Known active silencers require a very large volume, which reduces the useful space in the device to be silenced. This is particularly problematic for passenger cars or motorcycles. In German Offenlegungsschrift DE 43 43 951 a method is known for active silencing, for example in an exhaust system of a motor vehicle, in which two volume flows are superimposed. In order to optimize the phase shift of the two volume streams with regard to noise reduction, at least one path length of the two volume streams is varied as a function of the operating temperature. The path length of this volume flow can be varied by means of a variable length tube. In this case, a large space is required for the apparatus, since the area for accommodating the longest change in the tube must always be kept open.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and an apparatus for actively silencing with as small a structure as possible.

[0005]

According to the invention, this object is achieved by a method according to claim 1 and a device according to claim 9.

[0006] In the case of the method according to the invention, in which the sound is actively silenced, there is a first volume flow and a second volume flow, one of which is subsequently modulated by a modulation on a predetermined frequency spectrum. Is changed so as to cause a silencing effect when both volume flows interfere with each other. In the volume flow modulated by the modulation, an acoustic spectrum is created which allows the best muffle over a large frequency range by later interference with other volume flows.

According to the method according to the invention, an active silencer with a volume of less than one is realized. The invention is therefore particularly suitable for use in motor vehicles.

According to the method according to the invention, in contrast to the above-mentioned DE-A 43 41 951, in which only predetermined sound frequencies are best muted,
Silencing over a large acoustic spectrum can be performed.

The method can also be used to generate a predetermined acoustic spectrum independent of silencing (sound design).

In an advantageous embodiment of the invention, one of the two volume streams is taken from the other volume stream. This means that the volume flow containing the sound to be reduced is split into two partial volume flows, which are interfered with each other after the modulation of one volume flow.

Instead of splitting into two partial volume flows, the volume flow containing the sound to be reduced is in any case present in the device and a second volume flow independent of the first volume flow.
(Air flow, traveling vehicle, compressed air, exhaust gas flow).

Thus, in both cases, the existing volume flow is used for the second volume flow required for interference. It is therefore not necessary to provide a special volume flow for this purpose.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to FIGS. FIG. 1 schematically shows the principle of the first method of the present invention. The first that tries to reduce that sound
The pipe 1 in which the volume flow 10 flows is shown. A second pipe 2 branches from the pipe 1. The pipe 2 guides a part of the first volume flow (hereinafter referred to as the second volume flow 20) to the actuator A, and the second volume flow 20 has an appropriate phase in the actuator A for a predetermined frequency spectrum. Is modulated. The modulation is the first volume flow 10
In order to achieve as great a noise reduction as possible over the entire acoustic spectrum in the event of a subsequent interference between the first and second volume flows 20 (the advantageous phase difference between the first and second volume flows 20, 20). Is particularly 180 °). First volume flow 1
The spectrum of the sound wave to be eliminated at zero is detected by a sensor not shown here, for example a microphone that generates a reference signal for acoustic analysis. The reference signal is carefully selected in a known manner and used to control the actuator A.

The method is employed, for example, for silencing in the exhaust gas stream of an internal combustion engine, especially in motor vehicles.
This can also be used advantageously for silencing in the compressed air stream of an air compressor.

Another application of this method is in reducing running noise in traveling vehicles, especially rail vehicles. In an electric locomotive (ICE Zugen), the airflow, especially in a pantograph, generates a loud noise. This is prevented when part of the airflow is modulated in the actuator and subsequently superimposed with the noise-generating airflow. Here, unlike the case shown in FIG. 1, the airflow is of course not guided, so that the pipe 1 is omitted. FIG. 2 schematically illustrates the principle of the second method of the present invention. Shown is a pipe 1 in which a first volume flow 10 whose sound is to be reduced is flowing. Here, unlike FIG. 1, there is a pipe 2 for the second volume flow 20 independent of the pipe 1 and this pipe 2 is connected to the inlet of the actuator A. The second pipe 2 is supplied from the volume flow already present in the vehicle or the equipment, independent of the silencing. The method is advantageously used for the exhaust gas flow of an internal combustion engine in a motor vehicle (first volume flow), wherein the second volume flow is withdrawn, for example, from an existing turbocharger.

The specific structure of the present invention as a silencer for an internal combustion engine is shown in FIG. The exhaust gas stream of the internal combustion engine is split in the front chamber 40 after passing through a typical front silencer 50 and is directed to the actuator A in the form of two coaxial streams 10, 20. A central portion of the exhaust gas flow (first volume flow 10) flows through actuator A almost without obstruction and an annular outer exhaust gas flow (second volume flow 2).
0) is modulated for a given frequency spectrum by the valve (see FIG. 4) and interferes with the central flow 10 at the outlet of the actuator A. The actuator A is controlled by a sensor, here a microphone which detects the acoustic frequency spectrum to be eliminated and possibly residual acoustics. The microphone signal is carefully selected as is known,
Used as an input signal for modulation at actuator A. Since both gas streams 10, 20 have approximately the same temperature (affecting the speed of sound) and the sound sources are at almost the same location, superposition of sound waves optimally reduces unwanted noise in almost all directions (non-directional). Mute the sound.

Instead of being arranged here coaxially in order to improve the directionality, the pipes 1, 2 can also be arranged so that they lie inside and outside one another and extend in parallel without their axes being aligned. .

In another embodiment, the two exhaust gas streams can be guided side by side, for example in parallel.

The actuator can also supply bleed air from an existing turbocharger.

FIG. 4 shows, in cross-section, an advantageous construction of the device according to the invention, as for example employed in the device in FIG. Central pipe 1 for first volume flow 10
Above (in this case, an exhaust pipe for the exhaust gas flow of the internal combustion engine), an electro-pneumatic actuator A having an inlet and an outlet for the second volume flow 20 is installed. The second volume flow 20 in the pipe 2 is withdrawn from the pipe 1 for the first volume flow 10 or from another volume flow present in the vehicle or equipment. The sound wave to be eliminated is detected by one or a plurality of microphones M in the pipe 1.

In this embodiment, the exhaust pipe 1
An annular magnet 60 magnetized in three axial directions is fitted thereon. The outer end faces on both sides of these permanent magnets 60 are N
A pole and an S pole are formed. The magnet 60 is placed on one end in a pot-shaped housing 62 made of cast iron, which together with a pole piece 64 on the other end forms a substantially sealed magnetic circuit. A thin cylindrical coil (valve ring) 66 vibrates in a narrow gap between the pole piece 64 and the housing 62. The coil 66 is supplied with a control signal derived from the output signal of the microphone M. The coil 66 is hung on a plurality of springs (leaf springs 67). The gas flow 20 to be modulated flows around the magnet 60 through an opening in the bottom of the housing and into the front chamber 68 and from there through an annular gap. The width of the gap is varied according to the control signal selected by the vibrating coil 66. The front chamber 68, the gap and the outlet opening are bounded by an outlet cover bolted in front of the pot-shaped housing 62. The outlet side area of the second pipe 2 is formed in a funnel shape.

With the aid of the actuator described above, a freely selectable acoustic frequency spectrum is generated in the second volume flow 20 in relation to the control signal.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a first principle of a method according to the present invention.

FIG. 2 is a schematic diagram of a second principle of the method according to the invention.

FIG. 3 shows a side view of the device according to the invention as a silencer for an internal combustion engine.

FIG. 4 is a sectional view of a different embodiment of the device according to the invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st piping 2 2nd piping 10 1st volume flow 20 2nd volume flow

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventors Ludwig, Schaubecker Daisendorf, Höhnebeek, Germany 21

Claims (21)

[Claims] A first volume flow (10) and a second volume flow (2).
0), and one of the two volume flows (10, 20) changes such that when the two volume flows (10, 20) subsequently interfere, a silencing effect is caused. An active silencing method as claimed in claim 1, wherein the change of one volume flow (20) is effected by modulation on a predetermined frequency spectrum. 2. The method according to claim 1, wherein the second volume flow is a first volume flow.
2. The method according to claim 1, wherein the method is derived from 0). 3. The method according to claim 1, wherein the second volume stream is removed from an already existing volume stream independently of the silencing. 4. The method as claimed in claim 1, wherein at least one of the two volume flows is taken from the exhaust gas stream of the internal combustion engine. 5. A volume flow (10) of one of the two volume flows is taken from the exhaust gas stream of the internal combustion engine and the other volume flow (20).
5. The method according to claim 3, wherein the gas is taken from the gas stream of a supercharger in an internal combustion engine. 6. The method as claimed in claim 1, wherein at least one of the two volume flows is withdrawn from the vehicle. 7. The method as claimed in claim 1, wherein the two volume flows are guided in coaxial pipes (1, 2) located inside and outside one another. 8. The method according to claim 7, wherein the two volume flows are guided in pipes which are located inside and outside of each other and which are arranged in parallel without being aligned. 9. The method according to claim 1, wherein the two volume flows are guided in pipes arranged parallel to one another.
The method according to any one of the preceding claims. 10. The method according to claim 1, wherein the method is used to generate a predetermined acoustic spectrum instead of performing silencing. 11. A first pipe (1) for containing a first volume flow (10) and a second pipe (2) for containing a second volume flow (20), Both of these pipes (1,
One of the pipes (2) of (2) has a volume flow (2) flowing therethrough.
0) is connected to the inlet of a device (A) that changes so that a silencing effect occurs when the first volume flow (10) and the second volume flow (20) subsequently interfere. Active muffling device, characterized in that the changing device (A) is an actuator that changes the volume flow (20) flowing therethrough by modulation over a predetermined frequency spectrum. 12. The two pipes (1, 2) are connected to each other and one of the two volume flows (20) is connected to the other volume flow (10).
12. The device according to claim 11, wherein the device is taken from the device. 13. The device according to claim 11, wherein one of the two pipes has a connection for introducing an already existing volume flow independent of the silencing. 14. The system according to claim 11, wherein at least one of the two pipes is connected to an exhaust gas pipe of the internal combustion engine.
The apparatus according to any one of claims 13 to 13. 15. At least one of the two pipes (1) is connected to an exhaust gas pipe of an internal combustion engine, and the other pipe (2) is for introducing a gas flow of a supercharger present in the internal combustion engine. The apparatus according to claim 13, wherein the apparatus has a connection port. 16. The device according to claim 11, wherein the second pipe has a connection for introducing the airflow of the traveling vehicle. 17. The apparatus according to claim 11, wherein the two pipes are arranged coaxially inside and outside of each other.
An apparatus according to any one of the preceding claims. 18. The apparatus according to claim 17, wherein the two pipes are located inside and outside of each other and are arranged in parallel with their axes not aligned. 19. The device according to claim 11, wherein the two pipes are arranged next to one another. 20. Apparatus according to claim 17, wherein the actuator (A) is provided on one of the two pipes (1). 21. Use according to any one of claims 11 to 20, characterized in that it is used for generating a predetermined acoustic spectrum instead of for silencing.