Method of influencing the exhaust noise of a motor vehicle and exhaust system for a motor vehicle

Abstract

In a method of influencing the exhaust noise of a motor vehicle, a control unit generates noise package signals, the control unit transmits the noise package signals individually or so as to superimpose a basic signal to a loudspeaker associated with an exhaust branch of the motor vehicle, and the loudspeaker converts the individual noise package signals or the basic signal superimposed with the noise package signals into sound waves, with individual noise package signals being emitted by the loudspeaker as time-limited sound wave packages, so-called noise packages. Furthermore, an exhaust system is shown.

Claims

1. A method of influencing the exhaust noise of a motor vehicle, in which (a) a control unit generates colored noise package signals, (b) the control unit transmits the colored noise package signals individually or so as to superimpose a basic signal to a loudspeaker associated with an exhaust branch of the motor vehicle, and (c) the loudspeaker converts the individual colored noise package signals or the basic signal superimposed with the colored noise package signals into sound waves, wherein each of the colored noise package signals is emitted by the loudspeaker as a time-limited sound wave package that corresponds to dynamic noise, wherein the control unit generates the basic signal, the basic signal featuring a superposition of harmonic oscillations which correspond to half the rotational frequency of an engine and higher orders thereof, and wherein amplitudes of envelopes of the colored noise package signals are selected as a function of the amplitude of the basic signal.

2. The method according to claim 1, wherein the colored noise package signals, in particular at least one of their periodicity, their length in time, the shape of their envelopes, the amplitudes of envelopes and their frequency spectrum, are selected as a function of the current operating condition of the vehicle, in particular at least one of the engine load, the engine speed and the temperature of gas in the exhaust branch.

3. The method according to claim 2, wherein the periodicity of the colored noise package signals is equal to or greater than 5 Hz.

4. The method according to claim 3, wherein the periodicity of the colored noise package signals is in the range of from 5 Hz to 500 Hz.

5. The method according to claim 1, wherein synthetically generated noise, or sections of recorded noise stored in the control unit and recorded noise packages stored in the control unit are used for generating the colored noise package signals.

6. The method according to claim 1, wherein at least seven successive colored noise package signals constitute a noise package pattern, wherein the duration of the noise package pattern is longer than at least one second, and wherein the noise package pattern repeats itself.

7. The method according to claim 6, wherein the duration of the noise package pattern is longer than 20 seconds.

8. The method according to claim 1, wherein the control unit generates the basic signal synthetically.

9. The method according to claim 8, wherein the periodicity of the colored noise package signals is synchronous with the frequency of the lowest-frequency harmonic oscillation on the basis of which the colored noise package signals are generated.

10. The method according to claim 9, wherein the amplitudes of envelopes of the colored noise package signals are selected as a function of the amplitude of the harmonic oscillations to which the periodicity of the colored noise package signals is synchronous to.

11. The method according to claim 1, wherein the colored noise package signals are generated as a function of the basic signal, in particular on the basis of one or more selected harmonic oscillations of the basic signal, in particular by amplitude modulation of the noise with the amplitude of the basic signal or with the amplitude of one or more selected harmonic oscillations of the basic signal.

12. The method according to claim 1, wherein the colored noise package signals are also generated on the basis of low-frequency harmonic oscillations which cannot be effectively generated by the loudspeaker.

13. The method according to claim 12, wherein the control unit transmits colored noise package signals to the loudspeaker individually if the colored noise package signals were generated on the basis of low-frequency harmonic oscillations which cannot be effectively generated by the loudspeaker.

14. The method according to claim 1, wherein the colored noise package signals are superimposed on the basic signal to be offset in relation to that point in time of the basic signal that corresponds to the maximum displacement of the loudspeaker diaphragm of the loudspeaker.

15. The method according to claim 1, wherein the colored noise package signals have a constant mean amplitude.

16. An exhaust system for a motor vehicle, comprising: an exhaust branch having exhaust noise that includes at least three components comprising harmonic oscillations as a first component, static noise as a second component, and as a third component dynamic noise caused by momentary peaks in flow velocity of exhaust gas in the exhaust branch of the motor vehicle; a loudspeaker associated with the exhaust branch; and a control unit controlling sound emission of the loudspeaker, the control unit being adapted to generate colored noise package signals and to transmit the colored noise package signals to the loudspeaker individually or so as to superimpose a basic signal, the loudspeaker emitting sound waves corresponding to the individual colored noise package signals or the basic signal superimposed with the colored noise package signals into the exhaust branch, wherein each of the colored noise package signals is emitted by the loudspeaker as a time-limited sound wave package, which creates another dynamic noise that is in addition to the dynamic noise caused by momentary peaks, wherein the control unit generates the basic signal, the basic signal featuring a superposition of harmonic oscillations which correspond to half the rotational frequency of an engine and higher orders thereof, and wherein amplitudes of envelopes of the colored noise package signals are selected as a function of the amplitude of the basic signal.

17. The exhaust system according to claim 16, wherein the control unit is adapted to generate the colored noise package signals, in particular at least one of their periodicity, their length in time, the shape of their envelopes, the amplitude of their envelopes and their frequency spectrum, as a function of the current operating condition of the vehicle, in particular at least one of the engine load, the engine speed and the temperature of the gas in the exhaust branch.

18. The exhaust system according to claim 16, wherein the control unit is adapted to generate the basic signal and further generate the colored noise packages based on one or more selected harmonic oscillations of the basic signal.

19. The exhaust system according to claim 16, wherein the control unit is adapted to generate the colored noise package signals on the basis of low-frequency harmonic oscillations which cannot be effectively converted to sound waves by the loudspeaker, so that the loudspeaker merely emits the colored noise packages of these harmonic oscillations.

20. The exhaust system according to claim 16, wherein the loudspeaker is adapted to emit noise packages with a periodicity which correspond to colored noise package signals, the periodicity being synchronous with the frequency of the lowest harmonic oscillation on the basis of which the control unit has generated the colored noise package signals.

21. The exhaust system according to claim 16, wherein the control unit is adapted to superimpose the colored noise package signals on the basic signal to be offset in relation to that point in time of the basic signal that corresponds to the maximum displacement of the loudspeaker diaphragm of the loudspeaker.

22. A method of influencing the exhaust noise of a motor vehicle having at least three components comprising harmonic oscillations as a first component, static noise as a second component, and as a third component dynamic noise caused by momentary peaks in flow velocity of exhaust gas in an exhaust branch of the motor vehicle, in which (a) a control unit generates colored noise package signals, (b) the control unit transmits the colored noise package signals individually or so as to superimpose a basic signal to a loudspeaker associated with the exhaust branch of the motor vehicle, and (c) the loudspeaker converts the individual colored noise package signals or the basic signal superimposed with the colored noise package signals into sound waves, wherein each of the colored noise package signals is emitted by the loudspeaker as a time-limited sound wave package creating another dynamic noise that is in addition to the dynamic noise caused by momentary peaks, wherein the control unit generates the basic signal, the basic signal featuring a superposition of harmonic oscillations which correspond to half the rotational frequency of an engine and higher orders thereof, and wherein amplitudes of envelopes of the colored noise package signals are selected as a function of the amplitude of the basic signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention will be apparent from the description below and from the accompanying drawings, to which reference is made and in which:

(2) FIG. 1 shows an illustration of existing frequencies and frequencies that are additionally generated by a known method, as a function of the engine speed;

(3) FIG. 2 shows a greatly simplified diagram of the current flow velocity as a function of the engine speed;

(4) FIG. 3 schematically shows an exhaust system according to the invention; and

(5) FIG. 4 shows an illustration of the sound pressure level, and of the components thereof, which is generated by the loudspeaker of the exhaust system according to FIG. 3 when carrying out the method according to the invention.

DETAILED DESCRIPTION

(6) FIG. 3 schematically illustrates an exhaust system 10 of a vehicle (indicated as a dashed line) which has an exhaust branch 12 and a loudspeaker 14.

(7) The exhaust branch 12 continues into a tailpipe 16 which at an outlet 18 emits exhaust gas to the surroundings of the vehicle.

(8) The loudspeaker 14 is fluidically connected with the exhaust branch 12 via a channel 20 and is thus associated with the exhaust branch 12.

(9) The loudspeaker 14 is operated and controlled by a control unit 22 to which it is electrically connected.

(10) The control unit 22, in turn, may be connected to the engine control (not shown) or may form a part thereof.

(11) The control unit 22 is adapted to generate noise package signals and/or a basic signal for transmission to the loudspeaker 14. The loudspeaker 14, for its part, can convert the signals it receives from the control unit 22 to sound waves.

(12) The flow of the exhaust gas runs from the engine (not shown) through the exhaust branch 12 to the tailpipe 16 and via the outlet 18 to the environment. The direction of flow is indicated by arrows.

(13) FIG. 4 illustrates the sound pressure level generated by the loudspeaker 14, and its components. The sound pressure level generated by the loudspeaker 14 is directly proportional to the signal generated by the control unit 22 and applied to the loudspeaker 14, so that FIG. 4 is also made use of for illustrating this signal. For the sake of simplicity, reference will be made in the following only to the signals and not to the sound pressure level.

(14) The graph in the middle, denoted by A, shows the total signal transmitted to the loudspeaker 14 by the control unit 22. The signal is composed of two components, more specifically the basic signal B (top) and the noise package signals C, the chronological sequence of which is illustrated in the lowermost signal of FIG. 4.

(15) The signal A can now be generated by superposition of the basic signal B with the noise package signals C. Generation of the signal A by the control unit 22 is done as follows.

(16) First, the control unit 22 generates the basic signal B. More particularly, generation may be synthetic here.

(17) The basic signal B features a superposition of harmonic oscillations which correspond to half the rotational frequency of the engine, the fundamental order and higher orders thereof.

(18) Furthermore, especially in the case of high engine speeds, the basic signal B may feature continuous noise, which corresponds to the static noise of a natural engine signal.

(19) Further, the noise package signals C are generated by amplitude modulation of a noise having a constant mean amplitude with the amplitude of the basic signal B by the control unit 22. The total basic signal B or single harmonic oscillations of the basic signal B may be used for this purpose.

(20) In doing so, only the exclusively positive portions of the amplitude of the basic signal B are made use of for modulation of the amplitude of the noise, and no noise signal C is generated while the basic signal B is negative.

(21) As an alternative, the basic signal B can be rectified prior to the amplitude modulation, and then the whole signal can be used for modulation of the amplitude of the noise.

(22) The noise package signals C here are individual time-limited wave packages which are generated with a periodicity P, that is, a specific time interval.

(23) The periodicity P of the noise package signals C is equal to or greater than 5 Hz and, more particularly, is in the range of from 5 Hz to 500 Hz.

(24) The frequencies of the wave packages, that is, of the noise package signals C, are between 100 Hz and 4,000 Hz, for example.

(25) For generating a basis for the individual noise package signals C, use is made of synthetically generated noise, in particular colored noise, and/or sections from recorded noise stored in the control unit. The recorded noise may be recorded noise packages and also continuous noise from which short parts are extracted, which then constitute the basis of the noise package signals C.

(26) The noise package signals C may also be generated in that a plurality of recorded noise packages is superposed and in this way forms the basis for the noise package signal C to be generated.

(27) A plurality of, but at least seven, successive noise package signals C can form a noise package pattern D.

(28) Such a noise package pattern D preferably does not repeat itself.

(29) But where a repetition of the noise package pattern D cannot be avoided, the duration d of the noise package pattern D is at least 1 second, preferably at least 5 seconds, particularly preferably at least 20 seconds. Here, the duration d of the noise package pattern D is the time interval between the start of the first noise package signal C and the end of the last noise package signal C of the noise package pattern D.

(30) A repetition is understood to mean, for example, a case when the noise package pattern D starts again within 10 seconds from its end. In this way, tonal oscillations can be effectively prevented from developing since noise package signals C are only regularly repeated at a very low repetition frequency, if at all.

(31) After generating the basis of the noise package signals C, the periodicity P, their length in time L, the shape of their envelopes, the amplitude of their envelopes and/or their frequency spectrum can be adjusted by the control unit 22. The adjustment can be selected here as a function of the operating condition of the vehicle, in particular the engine load, the engine speed and/or the temperature of the exhaust branch.

(32) It is possible here for the control unit 22 to obtain information from the engine control about the operating condition of the vehicle, in particular the engine load, the engine speed and/or the temperature of the exhaust branch.

(33) The adjustment of the noise package signals C, in particular their periodicity P, their length in time L, the shape of their envelopes, the amplitude of their envelopes and/or their frequency spectrum can also be effected by the control unit 22 as a function of one or more harmonic oscillations of the basic signal B.

(34) The amplitudes of the envelopes of the noise package signals C may be selected here as a function of the amplitude of the harmonic oscillations on the basis of which the noise package signals C are generated.

(35) Particularly the periodicity P results from the selected harmonic oscillations of the basic signal B, the periodicity P being synchronous with the frequency of the lowest harmonic oscillation on the basis of which the noise package signals C were generated.

(36) Following the generation of the noise package signals C, the frequency spectrum of the basic signal B can be reduced to those frequencies which are effectively generatable by the loudspeaker 14. As a rule, loudspeakers for exhaust systems cannot effectively generate frequencies below 50 Hz.

(37) The shape of the noise package signals C is generated by amplitude modulation with the basic signal B and is then superimposed thereon by simple addition.

(38) Here the superimposition of the noise package signals C with the basic signal B may occur so as to be offset such that the noise package signals C are not superimposed on the basic signal B at that point in time t.sub.max of the basic signal B which corresponds to the maximum displacement of the loudspeaker diaphragm of the loudspeaker 14. This offset in time can also be seen in FIG. 4, but it is not perceived by the human ear.

(39) For example, the noise package signal C is offset in time relative to the basic signal such that the maxima of the amplitudes of the noise packages will be in the proximity of the zero crossings of the basic signal B.

(40) After the superimposition of the basic signal B with the noise package signals C, the control unit 22 transmits the signal A to the loudspeaker 14. The loudspeaker 14 emits sound waves corresponding to the signal A, that is, corresponding to the basic signal B having the noise package signals C superimposed thereon, into the exhaust branch 12.

(41) In signal generation and transmission to the loudspeaker 14, the control unit 22 can also take the transit time into account which the sound waves require for travelling through the channel 20, in order to avoid any undesirable interferences with the sound waves originating from the engine.

(42) In the event that the entire basic signal B is comprised of frequencies that are so low that they cannot be effectively generated by the loudspeaker 14, in particular of frequencies below 50 Hz, the noise package signals C are transmitted by the control unit 22 to the loudspeaker 14 individually, that is, without a basic signal B. In that case the loudspeaker 14 merely generates noise packages which correspond to the noise package signals C.

(43) This case occurs in particular at low engine speeds since the frequencies of the low-order harmonic oscillations of the engine are frequently below 50 Hz at low engine speeds, i.e. the noise package signals C are generated based on harmonic oscillations which cannot be effectively generated by the loudspeaker 14.

(44) It is also conceivable that the channel 20 also opens into the surroundings of the vehicle in the region of the outlet 18 of the exhaust branch 12, rather than into the exhaust branch 12 itself. In such an arrangement, too, the sound waves generated by the engine and directed through the exhaust branch 12 are superimposed with those that were generated by the loudspeaker 14, so that the loudspeaker 14 is associated with the exhaust branch 12.

(45) Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.