RU2191269C2 - Internal combustion engine muffler - Google Patents

Abstract

FIELD: mechanical engineering; internal combustion engines. SUBSTANCE: proposed muffler has cylindrical housing with end face walls in which four chambers are formed by means of cross partitions: inlet, outlet and two additional ones. It has also coaxially arranged inlet and outlet branch pipes and axially arranged intermediate branch pipes located at both sides from housing axis. Spaces of branch pipes are connected to spaces of chambers by means of open cuts and through perforated sections. In all chambers, except for outlet one, cuts of branch pipes, dynamic or imaginary, (beginning of perforated section being located direction of gas flow) along which gas flow passes in or out from corresponding chamber are located in node zones of lower natural resonance oscillations of gas volume enclosed in space of corresponding chamber, that is way said modes are not excited as pressures in modes in zone of excitation is close to zero value (being theoretically zero). Pulsating gas flows at cut of inlet branch pipes are not exposed to correspond resistance, and they do not convey energy to corresponding modes. EFFECT: improved acoustic efficiency of muffler. 1 dwg

Description

 The invention relates to mechanical engineering, in particular engine manufacturing, and in particular to multi-chamber silencers of exhaust noise of internal combustion engines.

 When a chamber muffler is operating in the place of expansion of the gas pipeline (that is, in the place where the camera itself appears), an abruptly increased wave impedance is created - a “wave plug”, which in certain frequency ranges of the sound spectrum prevents the passage of sound through the muffler with further attenuation of its radiation into the environment . In this design of the silencer (such as a central expansion chamber), there is a predetermined cutoff frequency, starting from which the silencer begins to work effectively (to drown out noise). However, the silencing characteristic of such a silencer is not an ascending inclined line, indicating an increase in acoustic silencing with increasing frequency of the exhaust sound spectrum, but a curve with pronounced silencing maxima in individual frequency ranges and pronounced “dips” at individual discrete frequencies in the silencing characteristic. In some cases, at the frequencies of “dips” in the damping characteristic, not only zero damping of noise is observed, but even some amplification of exhaust noise at these frequencies. It is these numerous “dips” that are the “acoustic defect” of the design of chamber silencers. The frequencies at which these "dips" are observed correspond to multiple harmonics of the half-lengths of the waves that fit in the three-dimensional space of the silencer chamber between the opposite rigid walls of the silencer chamber. To reduce the number of such dips, to minimize them, they also use the internal introduction of cuts of gas pipe nozzles into the cavity of the silencer chamber in areas where these multiple half-long harmonics will not be excited or, if excited, will not be output (transmitted) from the cavity of the chamber further along the exhaust path gas pipeline to the environment. Such zones of excitation of excitation or transmission of the lower eigenmodes of the camera are the nodes (minima) of sound pressure oscillations distributed over the three-dimensional space of the camera on these eigenmodes.

 The principle of attenuation of excitation and / or transmission of lower eigen resonance modes from the chamber cavity to the gas pipeline is implemented in the well-known single-chamber exhaust silencer for an internal combustion engine, USSR author's certificate 1092290, MKI F 01 N 1/00, BI 18/84, containing at least one cylindrical chamber with end walls and coaxial nozzles. A distinctive feature of the known silencer is that to ensure high acoustic efficiency of damping noise by the expansion chamber while achieving minimal hydrodynamic resistance, dynamic (acoustic) sections of the inlet and outlet pipes of the chamber (i.e., conditionally elongated by 0.2 ... 0.4d from its static geometric state, where d is the diameter of the corresponding pipe) are located in the nodal zones of the lower intrinsic resonant longitudinal forms (first and second) of the gas Vågå volume of the muffler chamber, i.e. in areas where the sound pressure on the specified acoustic mode is close to zero, which prevents (weakens) the transmission of sound energy of these forms (modes) of vibrations by an external cut of the outlet pipe into the environment.

 Such a construction of a well-known muffler in some cases fits well, in particular, in the concept of sports cars, some stationary power plants with a fairly limited amount of noise suppression, however, its acoustic performance for mass-produced cars is clearly not enough, since much more stringent requirements of national and international standards on the maximum permissible value of the levels of external and internal noise of vehicles, protection environmental pollution from acoustic pollution.

 A further improvement of the considered type of muffler is the design of a multi-chamber muffler described in the USSR author's certificate 1420193, MKI F 01 N 1/00, BI 32/88 (or for more details see SN Volgin and others. Color illustrated album. VAZ- cars 2110, VAZ-2111, VAZ-2112 and their modifications. Moscow. "Third Rome", 1998, p.30-31), which has a higher efficiency of damping exhaust noise and a wider range of muffling, which, in particular, is currently time is used in a number of models of automobiles of mass production OA "AVTOVAZ".

 The exhaust silencer of an internal combustion engine comprises a housing with end walls and coaxial inlet and outlet nozzles, the dynamic sections of the latter being located inside the central chamber of the housing. The silencer housing is oval and provided with at least one transverse partition to form chambers with end walls. One of the chambers (central) is made longer, its length is equal to the length of the larger axis of the body oval. The internal sections of the nozzles are placed in one of the chambers and are located at a distance of 1 / 4L from the end walls of the latter, where L is the length of the chamber. The length of the major axis of the body oval is (1.6..2.5) d, where d is the diameter of the nozzle. Part of the pipe passing through the chamber is perforated, while the non-perforated part of the pipe from its internal cut is L / 2.

 Some design flaws of the muffler, which appear during its operation, if necessary, further improve the design to meet the more stringent perspective requirements of vehicles in terms of the limit values of their external noise levels and analysis of the design perfection allow us to state the potential for its further improvement. In particular, in all known variants of the considered silencer design shown in Figs. 1-3, it can be seen that the most energy-intensive first (and all subsequent odd) longitudinal lower intrinsic resonance modes of vibration from the middle (central) chamber of the silencer are freely passed into the environment through the exhaust pipe 5. The same thing is observed with the second elevation (radial) intrinsic mode of oscillation of the chamber volume. The resonant transmission of sound from the camera to the environment also occurs at the fourth longitudinal eigenmode of the chamber volume oscillations (f4 = 4c / 2L, where f is the frequency, c is the speed of sound, L is the length of the middle chamber).

 The extreme (side) chambers of the muffler, Fig. 1, according to the graphic description of the prototype, which are identical end-face concentric resonators, are tuned to the same resonant frequency range of noise suppression, which leads to unjustified duplication of suppression of identical resonant modes and, ultimately , limits (narrows) the muffling band, and also in this case promotes undesirable mutual resonant interaction of the side (end) cameras and does not allow the use of each of the cameras for targeted noise reduction of a particular individual resonance range in a given frequency region of the sound spectrum.

In modern designs of noise suppressors of automobile ICEs, sound-absorbing gaskets of chamber cavities with fibrous porous materials are widely used to improve the attenuation of sound transmission on these resonant modes, such as an expansion cylindrical chamber with inner tubes. In particular, almost all automobile companies use the design of one of the exhaust silencers of the exhaust system with filling the cavity of the silencer chamber with basalt fiber packing. Having sufficiently high heat-resistant and sound-absorbing characteristics, such packing, in most cases, attenuates unwanted defective resonant high-frequency “whistles” of the muffler, primarily in the 4th longitudinal and 2nd radial eigenmodes of oscillation of the air volume of the chamber. However, this design has a number of significant drawbacks, the main of which are as follows:
- Porous packing of fibrous basalt fiber actively absorbs and accumulates chemically aggressive condensate contained in the exhaust gases in the cavity, which causes accelerated internal corrosion of the silencer housing, significantly reducing its service life. It should be noted here that it is internal corrosion, and not mechanical stress, that is the main cause of the destruction of silencers in automobile ICEs.

 - The use of fibrous basalt fiber due to the above reason forces, in turn, to use expensive stainless chrome-nickel steels, use additional devices for forced suction of the accumulated condensate from the chamber cavity by various diffuser receivers, which additionally complicates the design and makes it more expensive.

 - During the operation of the vehicle, basalt fibers are partially blown away by the flow of exhaust gases from the silencer cavity into the environment, which leads to harmful and very dangerous for human health air pollution by small particles of basalt fibers.

 - During the long-term operation of the device, the porosity of the fibrous packing of the chamber decreases due to exposure to carbon particles (soot) and liquid condensate ("coking"), which leads to a deterioration in the sound-absorbing characteristics of the fibrous packing and a decrease in the sound-damping capacity of the silencer as a whole.

 - The use of basalt fibers in the production technology of silencers is associated with harmful production conditions due to the possible ingress of small particles of fibers through the respiratory system into the human body.

 As a prototype, the main silencer of the exhaust noise of the exhaust system of the internal combustion engine of the VAZ-2110 series cars was adopted, see Volgin S.N. et al. Color illustrated album. Cars VAZ-2110, VAZ-2111, VAZ-2112 and their modifications. M .: Third Rome, 1998, p.30-31.

 The silencer contains four serial cameras to suppress noise in the wide frequency range. It contains an oval body limited by flat end walls. The chambers in the housing are formed by means of three transverse partitions and communicate with each other by means of perforated nozzles. In the direction of the gas flow, the chambers are sequentially arranged as follows: inlet, outlet and two additional ones. In this case, two nozzles - inlet and outlet, are placed coaxially to the body, and two intermediate pipes are axially and on both sides of the axis of the silencer body. For better corrosion resistance, the silencer housing is made of aluminized steel and has no welding points. All parts of the muffler are interconnected by rolling.

 The considered silencer has high reliability and durability, but at the same time there is a need and opportunities to increase its acoustic efficiency due to the implementation of separate measures for the acoustic tuning of the chamber silencer design to meet more stringent environmental protection requirements from acoustic pollution. This is due, first of all, to the fact that free sections of the inlet, outlet and intermediate pipes in the silencer chamber are placed without an insufficiently “thin” and detailed study of the acoustic field and allowance for the acoustic phenomena occurring in its individual chambers as a result of the excitation of lower resonance eigenvalues in them vibration modes of the gas volume enclosed in the corresponding chamber of the silencer, which causes the corresponding acoustic design flaws (defects). As a result of this, corresponding “noise damping dips” or insufficient damping, which leads to a decrease in the acoustic efficiency of the structure as a whole, are formed in the characteristic of muffling at individual frequencies. The disadvantage is that the second and third (along the gas flow from the engine to the environment) silencer chambers have the same volume (length), which leads to duplication of the frequency range of the damping and the tendency to mutual resonant excitation of the chambers.

 The inventive design of the silencer involves increasing its acoustic efficiency by expanding the frequency range and increasing the degree of silencing, eliminating the defective ranges of resonant sound transmission at the most energy-intensive lower longitudinal and radial resonance modes of vibration of the gas volume of the central chamber, attenuating the interaction of individual cameras, by additional acoustic tuning of the silencer .

 The essence of the invention lies in the fact that in the known silencer of the exhaust exhaust of an internal combustion engine comprising a cylindrical body with end walls, in which four successive chambers are formed by transverse partitions: inlet, outlet and two additional, coaxially arranged inlet and outlet pipes and axially arranged and intermediate nozzles placed on both sides of the housing axis, the cavity of the nozzles being connected to the chamber cavities by means of their open "dynamic cuts "and through perforated sections (" imaginary sections "), in contrast to the prototype, additional cameras are located on both sides of the input and output chambers, the length of the input chamber is at least twice the length of the output chamber; "imaginary dynamic section" (measured from the beginning of the perforation section along the gas flow in the pipe) of the inlet pipe is placed in the zone of the center of gravity of the gas volume (cavity) of the inlet chamber; "open dynamic slices" of the intermediate nozzles are located in the cavity of the additional chamber adjacent to the inlet chamber, at distances 1/4 and 1/2 of the length of the chamber from the transverse partition, while the "imaginary dynamic cut" (the beginning of the perforation section) of one of the intermediate nozzles is located in the cavity of the main chamber, at a distance of 1/4 of its length from the said partition, and the non-perforated solid portion of this nozzle is limited by a transverse plug so that the dead-end resonator thus formed in the nozzle is tuned to suppression of the lower radial intrinsic resonance mode of oscillations of the gas volume of said additional chamber; the "imaginary dynamic section" (the beginning of the perforation section) of the second intermediate pipe is placed in the cavity of the second additional chamber at a distance of 1/4 from the transverse partition, and the "open dynamic section" of the first intermediate pipe is located in the middle of this additional chamber, and part of this pipe located in the output chamber, made in the form of a through perforated section; the part of the outlet pipe, located in the outlet chamber, is made in the form of a through perforated section.

 The invention is illustrated by the drawing, which shows the inventive silencer noise of the exhaust of an internal combustion engine.

 The exhaust silencer of an internal combustion engine comprises a cylindrical body 1 with end walls 2 and 3, in which four chambers are formed by transverse partitions 4, 5 and 6: inlet 7, outlet 8 and two additional 9 and 10, coaxially arranged inlet 11 and outlet 12 nozzles and intermediate nozzles 13 and 14 axially located and placed on both sides of the housing axis, the cavity of the nozzles being connected to the chamber cavities by means of their “open dynamic sections” and through perforated sections (“imaginary sections in "). Unlike the prototype, additional cameras are located on both sides of the input and output cameras; the length of the inlet chamber is at least twice the length of the outlet chamber; "imaginary dynamic slice" 15 (counted from the beginning of the perforation section along the gas flow in the pipe) of the inlet pipe is placed in the zone of the center of gravity of the gas volume of the inlet chamber; “open dynamic sections” of 16 and 17 intermediate nozzles are located in an additional chamber adjacent to the inlet chamber at a distance of 1/4 and 1/2 of the length of the chamber from the transverse partition, while the “imaginary dynamic section” 18 of one of the intermediate nozzles (13) is located in the inlet chamber, at a distance of 1/4 of its length from the said partition, and the non-perforated section 19 of this pipe is limited by the transverse plug 20, so that the dead-end resonator thus formed in the pipe is configured to suppress the lower radial intrinsic ezonansnoy fashion gas volume oscillations of said additional chamber; the "imaginary dynamic slice" 21 of the second intermediate pipe (14) is placed in the second additional chamber at a distance of 1/4 from the transverse partition, and the "open dynamic slice" 22 of the first intermediate pipe (13) is placed in the middle of this additional chamber, and part 23 of this the nozzle located in the outlet chamber is made in the form of a through perforated section; part 24 of the outlet pipe located in the outlet chamber is made in the form of a through perforated section.

 The muffler works in the usual way.

 The flow of exhaust gases from the inlet pipe 11. through the holes 15 of the perforated section enters the inlet chamber 7, where it expands, accompanied by a partial loss of sound energy. From the chamber 7, the exhaust gases through the openings 18 of the perforation section and the open cut 16 of the intermediate pipe 13 enter the cavity of the additional chamber 9, where the secondary expansion of the already partially attenuated gas flow occurs with a corresponding attenuation of sound. From the additional chamber 9, through the open cut 17 of the intermediate pipe 14, through the openings 21 of the perforated section and the open cut adjacent to it (the section), the exhaust gases enter the second additional chamber 10, where once again the gas flow expands and it loses sound energy. From the additional chamber 10, through an open cut of the intermediate pipe 13 and part 23 of this pipe, equipped with a section of through holes for perforation, the gas stream enters the cavity of the output chamber 8, where it expands once again, losing some of the sound energy. From the outlet chamber, through the perforated through holes part 24 of the outlet pipe, the exhaust stream is discharged into the environment.

 The waves incident from the inlet pipe excite at the entrance to the chamber (any of the four chambers presented in the silencer design) volumetric air flow oscillations, which, in turn, excite sound pressure in it (the chamber). The amplitude of the transmitted wave is equal to the average pressure at the cutoff of the branch pipe for this chamber and is determined mainly by the transfer function of the chamber volume. At low frequencies, for which the largest linear size of the camera is less than 1/4 of the wavelength, the sound pressure at all points of the camera is almost the same and it works like an acoustic capacitance. The sound pressure in the chamber and the transmission of sound through it (the chamber) the less, the less the amount of gas falls over half the period of oscillation, the higher the oscillation frequency and the larger the chamber volume. For a chamber of a sufficiently large volume, most of the energy of the incident waves is reflected in the inlet pipe (back to the source). At frequencies for which the wavelengths are commensurate with the geometric dimensions of the chamber, the sound pressure is distributed unevenly throughout the chamber and is equal to the sum of the pressures in the natural forms (modes) of volume fluctuations. The transfer function for these frequencies is resonant in nature. Each camera's own mode corresponds to its own frequency. When the excitation frequency approaches the last (mode frequency), resonant oscillations are excited in the chamber, which undesirably increase the sound transmission. The characteristics of chamber sound reflectors can be significantly improved by suppressing resonant sound transmissions at the lower resonant frequencies indicated above. In this case, the characteristics of the camera in the frequency domain in which resonant transmissions are detected and attenuated (eliminated) are close to the characteristics of the acoustic capacitance.

 To implement such chambers in the inventive silencer, design methods were used, including reducing the excitability of the chambers and transmitting sound by placing open sections of pipes — real dynamic ones, when the geometric section is offset opposite to the gas stream by a distance of about 0.3 diameter of the pipe, from vibration nodes of lower eigenmodes cameras to compensate for additional acoustic fields associated with the presence of the pipe itself in the chamber volume.

 The inventive silencer is constructed in such a way that in all chambers, except for the outlet 8, the sections of the nozzles are dynamic or imaginary (the beginning of the perforation section along the gas flow), along which the gas flow is supplied or removed from the corresponding chamber, located in the nodal zones of the lower intrinsic resonance forms oscillations of the gas volume enclosed in the cavity of the corresponding chamber; therefore, the above-mentioned modes are not excited, since the pressure in these modes in the excitation zone is close to zero (theoretically equal to zero). At the same time, pulsating gas flows at the inlet section of the nozzles do not experience the corresponding resistance and do not, therefore, transfer energy to the corresponding modes.

 Additionally, in comparison with the prototype in the intermediate pipe 13 with its non-perforated section 19 and the plug 20, a dead end resonator is configured to suppress the energy-intensive, lower intrinsic radial shape of the cavity volume of the chamber excited in the additional chamber 9.

 The implementation of the cavity of the inlet chamber 7 of a significant volume (more than twice the volume of the outlet chamber 8) allows you to increase the amplitude of the muffling in the initial stage of the muffler, especially in the medium and low frequencies.

Claims (1)

 An exhaust silencer for an internal combustion engine comprising a cylindrical body with end walls, in which four successive chambers are formed by transverse baffles: an inlet, outlet, and two additional inlet and outlet pipes coaxially located and intermediate pipes located axially and placed on both sides of the body axis moreover, the cavity of the nozzles are connected to the cavity of the chambers through their open sections and through perforated sections, characterized in that The exhaust chambers are located on both sides of the inlet and outlet chambers, the length of the inlet chamber is at least twice the length of the outlet chamber, the beginning of the perforation section along the gas flow in the inlet pipe is located in the center of gravity of the inlet chamber volume, open dynamic sections of the intermediate pipes are located in the cavity of the additional chamber adjacent to the inlet chamber at distances of 1/4 and 1/2 of the length of the chamber from the transverse partition, while the beginning of the perforation section of one of the intermediate pipes is located but in the inlet chamber at a distance of 1/4 of its length from the said partition, and the non-perforated solid portion of this nozzle is limited by the transverse plug so that the dead-end resonator formed in the nozzle is configured to suppress the lower radial intrinsic resonant mode of gas volume oscillations of the said additional chamber, the beginning of the perforation section of the second intermediate pipe is placed in the second additional chamber at a distance of 1/4 from the transverse partition, and the open dynamic section of the first an intermediate nozzle is placed in the middle of this additional chamber, and a part of this nozzle located in the outlet chamber is made in the form of a through perforated section, a part of the outlet nozzle located in the outlet chamber is made in the form of a through perforated section.