Active design of exhaust sounds

Abstract

A sound generator (1) includes a casing (10) with at least one exhaust gas inlet (11) and at least one exhaust gas outlet (12) that is different from the at least one exhaust gas inlet (11) and at least one electro-acoustical transducer (20). The electro-acoustical transducer (20) is configured to produce sound in dependence on an electrical control signal. The electro-acoustical transducer (20) is located within the casing or directly attached to the casing. An active noise control system (9) includes the sound generator (1). A vehicle (8) with an internal combustion engine (6) includes the active noise control system (9).

Claims

1. A sound generator for an active noise control system for a vehicle with an internal combustion engine, the sound generator comprising: a casing with at least one exhaust gas inlet and at least one exhaust gas outlet different from the at least one exhaust gas inlet; an electro-acoustical transducer configured to produce sound in dependence on an electrical control signal, the electro-acoustical transducer being located directly attached to the casing and the electro-acoustical transducer comprising a moving coil loudspeaker directly attached to the casing, wherein the casing comprises a hole or plural holes at a direct attachment position of the electro-acoustical transducer, the electro-acoustical transducer covering the hole or holes in the casing, wherein sound generated by the electro-acoustical transducer is superimposing sound supplied to the casing together with exhaust gas via the at least one exhaust gas inlet within the casing; and at least one flexible membrane coupled to the casing in an air-tight manner so as to separate the electro-acoustical transducer from the at least one exhaust gas inlet and the at least one exhaust gas outlet, wherein the at least one flexible membrane is provided in addition to the electro-acoustical transducer and the at least one flexible membrane is suitable to prevent corrosive exhaust gas from reaching the electro-acoustical transducer while sound waves generated by the electro-acoustical transducer enter the casing via the flexible membrane.

2. A sound generator according to claim 1, wherein the casing comprises at least one of: a chamber in fluid communication with both the at least one exhaust gas inlet and the at least one gas outlet wherein the chamber is at least one of lined with sound absorbing material and provided with roving fiberglass; and a resonating chamber, harmonically tuned to cause destructive interference comprising a cavity resonator using Helmholtz resonance.

3. A sound generator according to claim 1, wherein the electro-acoustical transducer comprises an acoustic diaphragm, the acoustic diaphragm being located at a spaced location from the at least one flexible membrane.

4. A sound generator according to claim 3, wherein the acoustic diaphragm forms part of a walling of the casing and is comprised of a material different from a material of a remainder of the walling of the casing.

5. A sound generator according to claim 1, further comprising: a bridge wall within the casing and coupled to the casing so as to define at least two chambers separated from one another by the bridge wall; a supply conduit connected to one of the at least one exhaust gas inlet, extending through one of the chambers and communicating with another of the chambers; and an exhaust conduit within the casing and connected to the at least one exhaust gas outlet, extending through one of the chambers and communicating with another of the chambers.

6. A sound generator according to claim 5, wherein the supply conduit comprises a supply conduit section and the exhaust conduit comprises an exhaust conduit section wherein the supply conduit section is supported extending in parallel to the exhaust conduit section.

7. A sound generator according to claim 5, wherein at least one of: the bridge wall is perforated; and one or more of the supply conduit and the exhaust conduit is perforated.

8. A sound generator according to claim 1, further comprising: a bridge wall within the casing and coupled to the casing so as to define first and second chambers separated from one another by the bridge wall; a supply conduit connected to one of the at least one exhaust gas inlet and extending through the first chamber and communicating with the second chamber; and an exhaust conduit connected to the at least one exhaust gas outlet and extending through the first chamber and communicating with the second chamber, wherein the electro-acoustical transducer is arranged opposing an open end of at least one of the supply and exhaust conduits.

9. A sound generator according to claim 8, wherein the supply conduit comprises a supply conduit section and the exhaust conduit comprises an exhaust conduit section wherein the supply conduit section is supported extending in parallel to the exhaust conduit section.

10. A sound generator according to claim 8, wherein at least one of: the bridge wall is perforated; and one or more of the supply conduit and the exhaust conduit is perforated.

11. A sound generator according to claim 1, further comprising: a first bridge wall within the casing and coupled to the casing; a second bridge wall within the casing and coupled to the casing, the first bridge wall, the second bridge wall and the casing cooperating to define first, second and third chambers separated from one another by the bridge walls; a supply conduit connected to the at least one exhaust gas inlet and extending through the first and second chambers and communicating with the third chamber; and an exhaust conduit connected to the at least one exhaust gas outlet and extending through the third and second chamber and communicating with the first chamber, wherein the electro-acoustical transducer is arranged opposing an open end of the supply and exhaust conduits.

12. A sound generator according to claim 11, wherein the supply conduit comprises a supply conduit section and the exhaust conduit comprises an exhaust conduit section wherein the supply conduit section is supported extending in parallel to the exhaust conduit section.

13. The sound generator according to claim 1, further comprising: an additional exhaust gas inlet; an additional exhaust gas outlet; a bridge wall within the casing and coupled to the casing so as to define at least two chambers separated from one another by the bridge wall; a supply conduit connected to the at least one exhaust gas inlet, extending through one of the chambers and communicating with another of the chambers; an additional supply conduit connected to the additional exhaust gas inlet, extending through one of the chambers and communicating with another of the chambers; an exhaust conduit connected to the at least one exhaust gas outlet; an additional exhaust conduit connected to the additional exhaust gas outlet; an additional electro-acoustical transducers, wherein: the electro-acoustical transducer is arranged opposing an open end of the supply conduit connected to the at least one exhaust gas inlet and the additional electro-acoustical transducer is arranged opposing an open end of the additional supply conduit; or the electro-acoustical transducer is arranged opposing an open end of the exhaust conduit connected to the at least one exhaust gas outlet and the additional electro-acoustical transducer is arranged opposing an open end of an exhaust conduit connected to the additional exhaust gas outlet.

14. A sound generator according to claim 1, further comprising a second casing different from the casing, the second casing being attached to the casing, wherein the second casing houses the electro-acoustical transducer.

15. A sound generator according to claim 1, wherein the one or more holes has a hole diameter, the moving coil comprising a diaphragm, the diaphragm having a diaphragm diameter, the diaphragm diameter being greater than the hole diameter, the casing comprising a wall having a first portion and a second portion, the first portion being located opposite the second portion, the wall defining at least one of the one or more holes, wherein the at least one of the one or more holes is located between the first portion of the wall and the second portion of the wall, the moving coil loudspeaker bridging the at least one of the one or more holes, wherein the moving coil loudspeaker engages the first portion of the wall and the second portion of the wall.

16. A sound generator according to claim 1, further comprising: a supply conduit connected to the at least one exhaust gas inlet, wherein a chamber is defined at least by at least a portion of the casing and at least a portion of the at least one flexible membrane, the supply conduit being in fluid communication with the chamber; and an exhaust conduit connected to the at least one exhaust gas outlet, the exhaust conduit being in fluid communication with the chamber.

17. A sound generator according to claim 16, wherein the supply conduit comprises a supply conduit end portion having a supply conduit outlet, the exhaust conduit comprising an exhaust gas end portion having an exhaust conduit gas inlet, the supply conduit outlet and the exhaust conduit gas inlet being arranged in the chamber.

18. An active noise control system comprising: a sound generator comprising a flexible membrane and a casing with at least one exhaust gas inlet and at least one exhaust gas outlet different from the at least one exhaust gas inlet and an electro-acoustical transducer configured to produce transducer sound in dependence on an electrical control signal, the electro-acoustical transducer being directly attached to the casing, the electro-acoustical transducer comprising a moving coil loudspeaker directly connected to the casing, the casing comprising a hole or a plurality of holes, the electro-acoustical transducer covering the hole or the plurality of holes in the casing, the hole or the plurality of holes defining a direct attachment position of the electro-acoustical transducer, the flexible membrane being connected to the casing, the electro-acoustical transducer being sealed from the at least one exhaust gas outlet and the at least one exhaust gas inlet via the flexible membrane, the flexible membrane being impermeable to gas and permeable to at least electro-acoustical transducer sound waves, wherein the electro-acoustical transducer sound waves generated by the electro-acoustical transducer pass through the flexible membrane into an interior of the casing, the sound waves being superimposed on transmitted sound transmitted to the interior of the casing, wherein the interior of the casing receives exhaust fluid; a control unit configured to create an electrical control signal and to supply the electrical control signal to the electro-acoustical transducer of the sound generator, wherein the electrical control signal drives the electro-acoustical transducer to partially or completely cancel exhaust sound waves guided in an exhaust gas system of the vehicle.

19. A vehicle comprising: a combustion engine; and an active noise control system comprising: a sound generator comprising a sound vibration permeable and fluid impermeable flexible membrane and a casing with at least one exhaust gas inlet and at least one exhaust gas outlet different from the at least one exhaust gas inlet and an electro-acoustical transducer configured to produce transducer sound in dependence on an electrical control signal, the electro-acoustical transducer being directly attached to the casing, the casing comprising one or more holes, the electro-acoustical transducer comprising a moving coil loudspeaker, the moving coil loudspeaker being directly attached to the casing, wherein the coil loudspeaker covers each of the one or more holes, the one or more holes defining at least one direct attachment position of the electro-acoustical transducer, the sound vibration permeable and airtight flexible membrane being connected to the casing, wherein a chamber is defined at least by at least a portion of the casing and at least a portion of the sound vibration permeable and fluid impermeable flexible membrane, wherein transmitted sound is transmitted to the chamber, wherein the transducer sound passes through the sound vibration permeable and fluid impermeable flexible membrane into the chamber, the electro-acoustical transducer being sealed from the exhaust gas via the sound vibration permeable and fluid impermeable flexible membrane, wherein the chamber receives the exhaust gas; and a control unit configured to create an electrical control signal and to supply the electrical control signal to the electro-acoustical transducer of the sound generator, wherein the electrical control signal drives the electro-acoustical transducer to partially or completely cancel exhaust sound waves guided in an exhaust gas system of the vehicle, wherein: the exhaust gas inlet of the active noise control system is connected to the combustion engine and the exhaust gas outlet of the active noise control system is connected to an exhaust-pipe end; and the exhaust gas flowing from the combustion engine to a tailpipe is guided via the exhaust gas inlet and exhaust gas outlet of the casing of the sound generator of the active noise control system before reaching the tailpipe.

20. A vehicle according to claim 19, further comprising: a supply conduit connected to the at least one exhaust gas inlet, the supply conduit being in fluid communication with the chamber, the exhaust gas being delivered to the chamber via the supply conduit; and an exhaust conduit connected to the at least one exhaust gas outlet, the exhaust conduit being in fluid communication with the chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a schematic cross-sectional view of a sound generator for an active noise control system according to a first embodiment;

(2) FIG. 1B is a schematic cross-sectional view of a sound generator for an active noise control system according to a second embodiment;

(3) FIG. 1C is a schematic cross-sectional view of a sound generator for an active noise control system according to a third embodiment;

(4) FIG. 2 is a schematic cross-sectional view of an electro-acoustic transducer that may be used in the sound generator of FIG. 1A, 1B or 1C;

(5) FIG. 3 is a block diagram of an active noise control system using in the sound generator of FIG. 1A, 1B or 1C; and

(6) FIG. 4 is a schematic view showing a vehicle using the active noise control system of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) Referring to the drawings, in the exemplary embodiments described below, components that are alike in function and structure are designated as far as possible by alike reference numerals. Therefore, to understand the features of the individual components of a specific embodiment, the descriptions of other embodiments and of the summary of the invention should be referred to.

(8) For the sake of clarity, the figures show only those elements, components and functions that are necessary for an understanding of the present invention. However, embodiments of the invention are not limited to the elements, components or functions explained, but can also contain other elements, components and functions that are deemed necessary for their particular use or functional scope.

(9) A schematic cross-sectional view of a sound generator for an active noise control system according to a first embodiment is shown in FIG. 1A.

(10) The sound generator marked overall with reference number 1 comprises a generally cylinder-shaped casing 10 made of stainless steel. An exhaust gas inlet 11 connected to a supply duct 3 and an exhaust gas outlet 12 connected to an exhaust duct 4 are provided at a basal plane of the casing 10. The supply duct 3 may become fluidly connected to a combustion engine of a vehicle and the exhaust duct 4 may become fluidly connected to a tailpipe. A perforated bridge wall 15 made of stainless steel is coupled to the casing 10 so as to define two chambers A, B within the casing 10. The chambers A, B are separated from one another by the bridge wall 15. The supply duct 3 connected to the exhaust gas inlet 11 continues within the casing 10 as an unperforated supply conduit 17, and the exhaust duct 4 connected to the exhaust gas outlet 12 continues within the casing 10 as an unperforated exhaust conduit 18. Within the casing 10, the supply conduit 17 and the exhaust conduit 18 are arranged in parallel. Exhaust gas flowing in the supply conduit 17 is directed to the opposite direction as exhaust gas flowing in the exhaust conduit 18. Both the supply conduit 17 and the exhaust conduit 18 extend through the chamber A neighboring the exhaust gas inlet 11 and the exhaust gas outlet 12 and communicate with the other chamber B separated from the exhaust gas inlet 11 and the exhaust gas outlet 12 by the bridge wall 15. Sound supplied to chamber B of the casing 10 together with exhaust gas via the supply conduit 17 enters chamber A via holes in the bridge wall 15. The holes in the bridge wall 15 and the dimensions of chamber A are selected such that destructive interference of sound is caused in chamber A. A moving coil loudspeaker 20 used as electro-acoustical transducer is mounted via a mount 13 within the casing 10 at a basal plane of the casing 10 opposite to the exhaust gas inlet 11 and the exhaust gas outlet 12. An acoustic diaphragm made of Poly(p-phenylenterephthalamide) is oriented towards open ends of the supply conduit 17 and the exhaust conduit 18. Thus, the main direction of sound emission of the loudspeaker 20, is oriented towards open ends of the supply conduit 17 and the exhaust conduit 18. The loudspeaker 20 produces sound in dependence on an electrical control signal. A flexible membrane 14 made of heat-resistant silicone is coupled to the casing 10 in between the loudspeaker 20 and the open ends of the supply conduit 17 and the exhaust conduit 18 to separate the loudspeaker 20 from the supply conduit 17 and the exhaust conduit 18 and the exhaust gas inlet 11 and the exhaust gas outlet 12. In the first embodiment, the electro-acoustical transducer is completely contained in the casing 10 of the sound generator and does not have a separate casing.

(11) In the following, a second embodiment of a sound generator 1′ is explained by reference to FIG. 1B. FIG. 1B shows a schematic cross-sectional view of the sound generator 1′.

(12) The sound generator marked overall with reference number 1′ comprises a (first) generally cube-shaped casing 10′ made of zinc coated tinplate. An exhaust gas inlet 11 connected to a supply duct 3 and an exhaust gas outlet 12 connected to an exhaust duct 4 are provided at opposing sides of the casing 10′. Two parallel unperforated bridge walls 15, 15′ made of zinc coated tinplate are coupled spaced-apart from one another to the casing 10′ so as to define three chambers A, B′, C within the casing 10′. The supply duct 3 connected to the exhaust gas inlet 11 continues within the casing 10′ as a supply conduit 17, and the exhaust duct 4 connected to the exhaust gas outlet 12 continues within the casing 10′ as a exhaust conduit 18. Within the casing 10′, the supply conduit 17 and the exhaust conduit 18 are arranged in parallel in section D. Exhaust gas flowing in the supply conduit 17 is directed to the same direction as exhaust gas flowing in the exhaust conduit 18; however, there is an offset between the supply conduit 17 and the exhaust conduit 18. Supply conduit 17 extends through the chamber A neighboring the exhaust gas inlet 11 and the central chamber B′ and communicates with chamber C neighboring the exhaust gas outlet 12. The supply conduit 17 is perforated in the region crossing chambers A and B′. Exhaust conduit 18 extends through the chamber C neighboring the exhaust gas outlet 12 and the central chamber B′ and communicates with chamber A neighboring the exhaust gas inlet 11. The exhaust conduit 18 is perforated in the region crossing chambers C and B′. The holes in the supply conduit 17 and exhaust conduit 18 and the dimensions of chambers A, B′ and C are selected such that a Helmholtz resonance is achieved. A moving coil loudspeaker 20 used as electro-acoustical transducer is mounted to a wall of the casing 10 opposite to the exhaust gas inlet 11 and an open end of the supply conduit 17. At the position of the moving coil loudspeaker 20, the wall of the casing 10 comprises a hole. A diameter of the hole in the casing is the same as a diameter of a diaphragm of the moving coil loudspeaker 20. The diaphragm of the moving coil loudspeaker 20 is made of titanium and thus of a material different from the wall of the casing 10. The diaphragm is covering the hole in the wall of the casing 10. A (second) loudspeaker casing 5 made of zinc coated tinplate and housing the loudspeaker 20 is welded to the casing 10′ in air-tight manner, thus additionally sealing a hole in the casing 10′. The diaphragm of the moving coil loudspeaker 20 is sealed against the loudspeaker casing 5. Thus, the loudspeaker casing 5 and the diaphragm define a closed internal volume of the moving coil loudspeaker 20.

(13) In the following, a third embodiment of a sound generator 1″ is explained by reference to FIG. 1C. FIG. 1C shows a schematic cross-sectional view of the sound generator 1″.

(14) The sound generator marked overall with reference number 1″ comprises a generally cylinder-shaped casing 10″ made of stainless steel. Two exhaust gas inlets 11, 11′ each connected to an supply duct and two exhaust gas outlets 12, 12′ each connected to an exhaust duct are provided at opposing sides of the casing 10″. Two parallel perforated bridge walls 15, 15′ made of stainless steel are coupled spaced-apart from one another to the casing 10″ so as to define three chambers A, B′, C within the casing 10″. The supply ducts connected to the exhaust gas inlets 11, 11′ each continue within the casing 10″ as a supply conduits 17, 17′ and the exhaust ducts connected to the exhaust gas outlets 12, 12′ each continue within the casing 10″ as a exhaust conduits 18, 18′. The supply conduits 17, 17′ are bent such that within the casing 10″ they are arranged in parallel in section E. Exhaust gas flowing in the supply conduits 17, 17′ is directed to opposite directions in section E. Supply conduit 17 extends through the chamber A neighboring the exhaust gas inlet 11 and the central chamber B′ and communicates with chamber C neighboring the other exhaust gas inlet 11′. Supply conduit 17′ extends through the chamber C neighboring the exhaust gas inlet 11′ and the central chamber B′ and communicates with chamber A neighboring the other exhaust gas inlet 11. The supply conduits 17, 17′ are perforated in the region crossing the central chamber B′. The unperforated exhaust conduits 18, 18′ simply leave chambers A and C, respectively, without crossing chamber B′. Roving fiberglass is contained in the central chamber B′ as sound absorbing material. Two moving coil loudspeakers 20, 20′ used as electro-acoustical transducers are mounted to opposing walls of the casing 10. At the position of the moving coil loudspeakers 20, 20′ the wall of the casing 10 comprises holes. A diameter of the holes in the casing is 10% larger than a diameter of each diaphragm of the moving coil loudspeakers 20, 20′. The diaphragm of each moving coil loudspeaker 20 is made of aluminum and thus of a material different from the wall of the casing 10. The diaphragm of each loudspeaker is covering a major part of one of the holes in the wall of the casing 10. The acoustic diaphragm of one loudspeaker 20 is oriented towards an open end of supply conduit 17′ and the acoustic diaphragm of the other loudspeaker 20′ is oriented towards an open end of supply conduit 17. Flexible membranes 14, 14′ made of Polytetrafluoroethylene are coupled to the casing 10″ in between the loudspeakers 20, 20′ and the open ends of the supply conduits 17, 17′ and the exhaust conduits 18, 18′ to separate the loudspeakers 20, 20′ from corrosive exhaust gas. The acoustic diaphragms of the loudspeakers 20, 20′ seal the holes in the casing 10″ in an air-tight manner. Two loudspeaker casings 5, 5′ made of stainless steel are attached to the casing 10″ in a removable manner. Each loudspeaker casing 5, 5′ houses one of the loudspeakers 20, 20′. Together with the diaphragm of the respective loudspeaker, each loudspeaker casing 5, 5′ defines an internal volume of each moving coil loudspeaker 20, 20′.

(15) A schematic cross-sectional view of a moving coil loudspeaker that is used as electro-acoustic transducer in the sound generators of FIG. 1A, 1B or 1C above is shown in FIG. 2.

(16) The loudspeaker marked overall with reference number 20 comprises a sheet metal basket 21, which carries a permanent magnet 22. The basket 21 has the overall shape of a truncated cone. The basket 21 carries an acoustic diaphragm 23 via a surround 24 made from flexible plastic. Titanium is used for the diaphragm 23 and heat-resistant silicone is used for the surround 24 to ensure sufficient resistance against heat and corrosion. The diaphragm 23 has the overall shape of a truncated cone. A dust cap 28 and bobbin 25 are secured to the top surface of the truncated cone formed by the diaphragm 23. The end of the bobbin 25 averted from the diaphragm 23 is arranged in an annular gap provided in the permanent magnet 22, and carries a voice coil 26. As a result, this coil 26 is located in a constant magnetic field generated by the permanent magnet 22. It should be noted that the width of the annular gap on the figure is greatly exaggerated. The bobbin 25 is centered relative to the annular gap by means of a centering spider 27. The centering spider 27 consists of springs radially stretched between the bobbin 25 and basket 21. In the embodiment shown, the basket 21, surround 24, diaphragm 23, dust cap 28, bobbin 25 and permanent magnet 22 are rotationally symmetrical bodies with the same axis of symmetry. Application of an electrical control signal to the voice coil 26 causes movement of the bobbin 25 together with the diaphragm 23 and thus the generation of sound due to the Lorentz force.

(17) FIG. 3 shows a block diagram of an active noise control system using in the sound generator of FIG. 1A, 1B or 1C and the moving coil loudspeaker of FIG. 2. The following will focus only on the special features of the active noise control system. The active noise control system marked overall with reference number 9 is used to actively extinguish or influence sound waves in exhaust systems of a vehicle powered by an internal combustion engine. The exhaust gas inlet 11 of the casing of the sound generator 1 is connected to an exhaust gas outlet of an internal combustion engine 6 via a supply duct 3. The exhaust gas outlet 12 of the casing of the sound generator 1 is connected to a tailpipe 91 via an exhaust duct 4. The active noise control system 9 comprises a controller 90, which in order to exchange control or measuring signals is electrically connected with an engine controller 61 of an internal combustion engine 6 via a CAN-bus. The controller 61 is further electrically connected with an error microphone 7 situated in a duct 4 of an exhaust system, as well as with the loudspeaker 20 of the sound generator 1.

(18) As a function of an operating state of the internal combustion engine 6 acquired by the engine controller 61 of the internal combustion engine 6, the controller 90 calculates electrical control signals, which are fed to the loudspeaker 20 so as to generate sound, which extinguishes airborne noise guided in the supply duct 3 and the exhaust duct 4 at least partially. The electrical control signals can be regulated by using signals output by the error microphone 7, so that airborne noise is emitted at a reduced sound pressure at a tailpipe 91 of the exhaust system.

(19) FIG. 4 schematically shows a vehicle 8 using the above described active noise control system 9 of FIG. 3. The active noise control system is mounted to an undercarriage of the vehicle 6. Besides other features, the vehicle 8 comprises a combustion engine 6 and an exhaust duct 4 terminating in a tailpipe 91.

(20) It is obvious that the above described sound generator may work as sound absorber, in dependency on a control signal used for the at least one electro-acoustical transducer.

(21) While the invention has been described with respect to certain exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention set forth herein are intended to be illustrative and not limiting in any way. Various changes may be made without departing from the spirit and scope of the present invention as defined in the following claims.

(22) While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.