RU2172846C2 - Internal combustion engine exhaust muffler - Google Patents

Abstract

FIELD: mechanical engineering; internal combustion engines. SUBSTANCE: proposed muffler has cylindrical housing with end face walls in which three chambers are formed by means of cross partitions, these chambers being inlet, central and outlet ones. Muffler has coaxial inlet and outlet branch pipes hydraulically connected to corresponding chambers by means of perforated sections and free cuts arranged in central chamber. Free dynamic cut of outlet branch pipe is located in node zone of second lower natural longitudinal mode of oscillations of gas volume enclosed in central chamber. Dynamic cut of inlet branch pipe is located in node zone of first lower natural longitudinal mode of oscillations of gas volume enclosed in central chamber. Summary volume of extreme chambers of muffler is equal to volume of its central chamber, and extreme chambers proper are made in form of concentric resonators tuned for suppressing resonant noise frequencies of main chamber at fourth longitudinal and second radial lower natural resonance modes of oscillations of gas volume in central chamber. EFFECT: increased acoustic efficiency of exhaust system preliminary muffler. 2 cl, 8 dwg

Description

 The invention relates to mechanical engineering, in particular engine manufacturing, and in particular to silencers of exhaust noise of an internal combustion engine (ICE).

 Known exhaust silencer for an internal combustion engine, USSR author's certificate N 1092290, MKI F 01 N 1/00, BI N 18/84, containing at least one cylindrical chamber with end walls and coaxial nozzles, sections of which are placed inside the chamber.

 The well-known muffler design allows its successful use in sports cars, since it has the best acoustic performance with minimal hydraulic resistance and is simple and small in size. The efficiency of the silencer is achieved due to the fact that the maximum expansion of the silencing band and the elimination of specific periodic “dips” in the noise suppression characteristic is achieved by placing dynamic sections of the nozzles in the cavity of the silencer chamber at the nodes of the lower natural resonant forms of gas oscillations in the chamber corresponding to the points where the oscillations sound pressure are minimal. Effective (dynamic) sections take into account the actual elongation of pulsating gas columns enclosed in the nozzle cavities due to the influence of the near hydrodynamic field at the nozzle section by attaching some nearby gas mass at the static section of the pipe. The practically dynamic cut is “longer” than the static (geometric) cut by 0.2 ... 0.4d, where d is the diameter of the passage section of the corresponding pipe.

 The described silencer design is compact and has low hydrodynamic drags, since the sections of the nozzles are aligned and the gas flow through the silencer cavity is transported in a straight line (without turns).

 The design of the described silencer fits quite well, in particular, into the concept of sports cars, some stationary power plants, etc., however, for cars of mass production for which the requirements for the maximum permissible noise level are much higher, the effectiveness of such a silencer is clearly insufficient.

 Further improvement of the described silencer is the design (prototype) described in the USSR author's certificate N 1420193, MKI F 01 N 1/00, BI N 32/88 (or for more details see SN Volgin and others. Color illustrated album. Cars VAZ-2110, VAZ-2111, VAZ-2112 and their modifications. Moscow, “Third Rome”, 1998, pp. 30-31), which has increased muffling efficiency and a wider range of muffler band, which is currently used in a number of models cars produced by 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 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 appeared during its operation, if necessary, design improvements to meet more stringent requirements of automobiles with regard to the limit values of their external noise levels, and structural analysis allows us to state the potential for its further improvement. In particular, in all of the silencer designs illustrated in FIG. 1-3 it can be seen that the most energy-intensive first (and all odd) longitudinal lowest intrinsic resonance mode of vibration from the middle (central) chamber of the muffler freely passes into the environment through the exhaust pipe 5. The same thing is observed with the second high-rise (radial) eigenmode camera volume fluctuations. Resonant sound transmission 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 silencer, FIG. 1, according to the graphic description of the prototype, which are identical concentric-type resonators, are tuned to the same resonant frequency range, which leads to unjustified duplication of the suppression of resonant modes and, ultimately, limits (narrows) the damping band, in this case, contributes to an undesirable mutual resonant interaction of the side cameras and does not allow each of the cameras to be used for targeted noise reduction of a particular individual resonance range in a given oh frequency region of the sound spectrum.

In modern designs of noise suppressors of automobile ICEs, sound-absorbing chamber gaskets with fibrous materials are widely used to improve the attenuation of sound transmission at the indicated resonant modes of an expansion cylindrical chamber with internal pipes. Currently, almost all automotive companies use the design of a preliminary silencer for the exhaust system with gasket cavity basalt fiber silencer chamber. Possessing sufficiently high heat-resistant and sound-absorbing characteristics, such packing in some cases attenuates the resonant high-frequency “whistles” of the silencer at 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:
- Fibrous basalt fiber actively absorbs chemically aggressive exhaust condensate, which causes accelerated internal corrosion of the silencer housing, significantly reducing its 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.

 - Fibrous basalt fiber, due to the above reason, forces the use of expensive chrome-nickel steels, the use of additional condensate extraction devices from the chamber cavity by various diffuser gas receivers, which further complicates the design and makes it more expensive.

 - During operation, basalt fibers are partially blown 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 long-term operation, the porosity of the fibrous packing of the chamber changes due to exposure to carbon particles (soot) and liquid condensate, 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 fiber particles through the respiratory system into the human body.

 The silencer design proposed below involves increasing its acoustic efficiency by expanding the frequency range and damping amplitude, eliminating the defective ranges of resonant sound transmission at the most energy-intensive lower (first and fourth longitudinal and second radial) natural resonance modes of gas volume oscillations of the central chamber by additional acoustic tuning of the silencer that is achieved by changing the design parameters of the prototype.

 The essence of the invention lies in the fact that in the known silencer of an exhaust of an internal combustion engine comprising a cylindrical body with end walls, in which three chambers are formed by transverse partitions: an inlet, a central and an outlet, coaxial inlet and outlet pipes hydraulically connected to the respective chambers by perforated portions of the nozzles, and free sections of which are placed in the Central chamber, and a free dynamic section of the outlet pipe is placed in the nodal in the zone of the second lowest intrinsic longitudinal mode of gas volume oscillations enclosed in the central chamber, a dynamic section of the inlet pipe is located in the nodal zone of the first lower intrinsic longitudinal mode of oscillations of the gas volume enclosed in the central chamber, with the total volume of the end silencer chambers being approximately ± 0 , 05 the volume value is equal to the volume of its central chamber and the extreme chambers themselves are made in the form of differently configured concentric resonators tuned to suppress the frequencies of resonant transmissions mind the main chamber at the fourth and second radial longitudinal lowest natural resonant modes of the gas volume of the central chamber oscillations.

для второй радиальной собственной моды колебаний газового объема центральной камеры

где c - скорость звука,
L - длина центральной камеры,
F - суммарная площадь проходного сечения отверстий перфорации в заданной камере (входной, выходной),
h - длина горлышка резонатора (динамическая толщина отверстия перфорации), с присоединенной массой газа Δ h = 2(0,44

),
F_отв - площадь одного отверстия,
V - объем соответственно входной (при настройке на подавление 4-й продольной собственной моды) или выходной (при настройке на подавление 2-й радиальной собственной моды) камеры глушителя,
D - приведенный диаметр корпуса глушителя. Для кругового цилиндра D = D_{цилиндра}; для корпуса, имеющего форму овала D = S/П, где S - площадь поперечного сечения овала и П - периметр этого сечения.The resonators formed by the annular volumes of the outer chambers in communication with the nozzles through the perforation sections are tuned by selecting the degree of perforation of the sections, the dynamic thickness of the perforation holes, taking into account the attached oscillating mass of air in the perforation holes and the volume of the cavities of the corresponding chamber and is calculated by the well-known formula:
for the fourth longitudinal eigenmode of oscillation of the gas volume of the central chamber

for the second radial eigenmodes of oscillation of the gas volume of the Central chamber

where c is the speed of sound,
L is the length of the Central chamber,
F is the total area of the bore of the perforation holes in a given chamber (input, output),
h is the length of the resonator neck (dynamic thickness of the perforation hole), with the attached mass of gas Δ h = 2 (0.44

),
F _holes - one hole area,
V is the volume, respectively, of the input (when setting to suppress the 4th longitudinal eigenmode) or output (when setting to suppress the 2nd radial eigenmode) muffler chamber,
D is the reduced diameter of the silencer body. For a circular cylinder D = D _cylinder ; for an oval-shaped case D = S / P, where S is the cross-sectional area of the oval and P is the perimeter of this section.

 With this design, the silencer minimizes the negative impact on its acoustic efficiency of all the odd and lowest (most energy-intensive) even natural resonance modes of gas volume oscillations in its expansion chamber, associated with the elimination of transmission bands (frequency dips) in the above natural resonance modes. The choice of different volumes and resonant settings of the side chambers of the silencer eliminates the unwanted resonant interaction of these chambers.

The invention is illustrated in the drawings, where
in FIG. 1 shows a general view of an exhaust silencer,
in FIG. 2 shows a diagram of the internal elements of the silencer,
in FIG. 3. ..6 plots of the distribution of sound pressure fields on the lower (first to fourth, respectively) eigen resonant longitudinal modes of gas volume oscillations in the central chamber of the silencer are shown,
in FIG. Figures 7 and 8 show diagrams of the distribution of sound pressure fields on the lower (first and second) eigen resonant radial modes of gas volume oscillations in the central and side chambers of the silencer.

 On the diagrams, the symbol -P- denotes the sound pressure module.

 The exhaust silencer shown in FIG. 1, comprises a cylindrical body 1 with end walls 2 and 3, in which three chambers are formed by transverse partitions 4 and 5: input 6, central 7 and output 8, coaxial input 9 and output 10 nozzles hydraulically connected to the respective chambers 6 and 8 by means of perforated sections 11 and 12, and free sections of which are placed in the central chamber 7, the free dynamic section 13 of the outlet pipe 10 being located in the nodal zone of the second lower proper longitudinal mode, FIG. 4, oscillations of the gas volume enclosed in the central chamber 7, FIG. 2, a dynamic slice 14 of the inlet pipe 9 is located in the nodal zone of the first lower proper longitudinal mode, FIG. 3, oscillations of the gas volume enclosed in the central chamber 7, FIG. 2, while the total volume of the extreme chambers of the silencer, with a volume ratio of 3: 2, is equal to the volume of its central chamber, and the extreme chambers themselves are made in the form of concentric resonators, purposefully tuned to the frequencies of the resonant transmissions of the main chamber on the fourth longitudinal, FIG. 6, and the second radial, FIG. 8, lower eigen resonance modes of oscillations of the gas volume of the central chamber 7.

 The muffler works in the usual way.

 Exhaust gases through the inlet pipe 9 enter through a free cut 14 into the central chamber 7 of the muffler and, due to the sudden expansion of the acoustic waveguide, determined by the ratio of the flow cross sections of the pipe 9 and the chamber 7 are partially reflected back to the radiation source (exhaust valve), and partially transferred to the free cut 13 of the outlet pipe 10, and, due to a sudden narrowing of the passage section of the acoustic waveguide, determined by a similar ratio of the passage sections of the chamber 7 and the pipe 10, similar to the sample the gas are partially reflected towards the radiation source and partially removed from the silencer chamber through the pipe 10 to the atmosphere.

 In the process of continuous reflections of sound waves, the generated backward waves interact with the direct ones, due to antiphase overlays, they are partially compensated in areas of sharp changes in the passage sections of the waveguide and, accordingly, a sharp change in the acoustic impedance of the waveguide and frictional losses, irreversible conversions of sound energy into thermal energy with corresponding attenuation of the environment of sound energy from the engine exhaust system.

 The sound energy transmitted through the gas pipes of the silencer 9 and 10 in the zones of the perforated sections 11 and 12 undergoes resonant attenuation in the individual frequency ranges to which the corresponding acoustic chamber 6 or 8 is tuned.

 In this case, the annular mass of gas concentrated around the nozzle plays the role of an elastic element (spring), and the mass of gas concentrated in the perforation holes plays the role of an oscillating mass on this spring.

 As a result of acoustic resonance (short acoustic short circuit) at a given vibration frequency, the amplitude of these gas mass oscillations in the necks of perforated holes becomes large, the oscillation phase is the opposite phase of forward and backward waves of the same frequency, transmitted along the gas duct and due to significant friction of large-amplitude oscillations against the walls perforated holes, acoustic energy is converted into heat, and thus there is a general attenuation of sound energy at a given deny) frequency range.

 In this case, the dynamic cut 14 of the inlet pipe does not excite the most energy-intensive first in the central chamber 7 of the muffler, FIG. 3, the intrinsic resonant longitudinal vibration mode of the volume of the chamber 7, since it is located in the nodal zone (with a pressure modulus of about zero) of sound pressure on this waveform. This applies to all odd higher-frequency analogous modes, see FIG. 5. At the same time, the second longitudinal eigenmode excited in the chamber 7, FIG. 4, is not transmitted by the outlet pipe 10 from the chamber 7 to the atmosphere, since the dynamic cut 13 of the outlet pipe 10 is located in the node (zero sound pressure value) of this waveform. Excited in the central chamber 7 is a fourth longitudinal one, FIG. 6, the intrinsic resonance mode of vibration is suppressed by the concentric resonator tuned to the frequency of the mode in question, formed by the annular chamber volume 6 and the perforation holes of section 11, in which (holes), as a result of intense resonant vibrations of the sound wave, a significant part of the sound energy is converted into heat. A completely similar mechanism for suppressing the second lowest radial eigenmodes, FIG. 8 is implemented by a concentric resonator formed by the annular volume of the output chamber 8 and the holes of the perforation section 12 and tuned to the dominant frequency of this mode. Regarding the first radial eigenmode, FIG. 7, it is not excited due to the fact that the axis of the outlet pipe 10 passes through the center of gravity of the volume of the central chamber 7, i.e. located in the vibration node of this mode.

 The implementation of cameras of various volumes in combination of 0.3 ± 0.05: 0.5 ± 0.05: 0.2 ± 0.05 allows you to avoid resonant coincidences, it is easier to configure cameras using the same type of perforation, and expand the noise suppression band.

 Thus, by providing more optimal, from the point of view of acoustics, geometric parameters of the silencer elements, an increase in its acoustic efficiency is achieved.

 In comparison with the prototype of the inventive exhaust silencer has a wider frequency range and level of damping and, therefore, greater acoustic efficiency. The expected additional effect of using the proposed muffler in the exhaust system of VAZ automobiles instead of the standard (serial) additional muffler is at least 3 dBA.

Claims (2)

 1. A silencer of the exhaust exhaust of an internal combustion engine, comprising a cylindrical body with end walls, in which three chambers are formed by transverse baffles: inlet, center and outlet, coaxial inlet and outlet pipes hydraulically connected to the inlet and outlet chambers by means of perforated sections and free sections which are located in the Central chamber, and a free dynamic section of the outlet pipe is located in the nodal zone of the second lowest intrinsic longitudinal mode of gas oscillations volume enclosed in the central chamber, characterized in that the free dynamic section of the inlet pipe is located in the nodal zone of the first lowest intrinsic longitudinal mode of oscillation of the gas volume enclosed in the central chamber, while the total volume of the outermost silencer chambers is equal to the volume of its central chamber the outermost chambers are made in the form of concentric resonators tuned to suppress the frequencies of the resonant noise transmission of the main chamber at the fourth longitudinal and second radial lower intrinsic resonances modes of oscillations of the gas volume of the central chamber.  2. The muffler according to claim 1, characterized in that the ratio of the volumes of the input, central and output chambers, respectively, is 0.3 ± 0.05: 0.5 ± 0.05: 0.2 ± 0.05.

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