RU2791855C1 - Method for acoustic research of the intake system of an internal combustion engine - Google Patents

Abstract

FIELD: metrology.

SUBSTANCE: methods for acoustic research of internal combustion engines. The method for acoustic research of the intake system of an internal combustion engine consists in installing an adjustable source of acoustic noise and a measuring microphone in a low-noise room, stage-by-stage formation of sound vibrations by the noise source and data measurement. As a system for collecting, measuring and processing data, a frequency spectrum analyser and a computer are used. As an adjustable source of acoustic noise, a prototypical resonator is used, built into the ICE intake system, made with the possibility of varying, with 0.1 l pitch, the volume of its internal cavity from 0.9V calc _to 1.1 V_calc, where V_calc is the volume of the resonator silencer. The measuring microphone is installed in the near acoustic field at a distance of 0.06 to 0.1 m from the noise source. First, the volume of the resonator is set equal to 1.1 V_calc, after which the ICE is accelerated, sound pressure levels are measured. Then, step by step, with a 0.1 l pitch, the volume of the resonator is reduced to a value of 0.9V_calc, and at each stage of changing the volume of the resonator, the ICE is accelerated from idle speed to maximum speed. During any of the accelerations, sound pressure levels are measured. Then choose the volume of the silencer corresponding to the minimum noise level.

EFFECT: reduction of the cost of finishing work on the ICE intake system by vibroacoustics, as well as creating an intake system with the lowest possible level of acoustic noise.

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Description

The invention relates to the field of acoustics, in particular, to a method for conducting experimental studies and fine-tuning the intake system of an internal combustion engine in terms of vibroacoustics.

One of the most intense sources of vehicle noise is its power plant - an internal combustion engine (ICE), including exhaust gas systems and the intake of a fuel-air mixture into the working cylinders. When studying the sound field emitted by the intake system of an internal combustion engine, two components are distinguished - gas-dynamic sound that occurs at the cut of the air intake pipe, and structural (body) sound resulting from sound re-emission by the vibrating walls of the body elements, in particular - the air intake pipe, air cleaner, expansion chambers , receivers.

Periodic opening of the intake valve (valves) in one of the internal combustion engine cylinders causes a pulsating gas pressure drop with the corresponding generation and propagation of air pulsations and elastic waves along the intake system path before and after the valve (in the cavity of the internal combustion engine cylinder in relation to the environment). Air pulsations and elastic waves of rarefaction-compression of the air along the route of the intake system propagate, at the speed of sound, from the intake valve to the open cut of the air cleaner pipe, as well as in the direction of free outlet dead-end intake pipes with closed intake valves. The pulsation frequency is determined by the formula:

где

Where

n - frequency of rotation of the crankshaft of the internal combustion engine, min ^-1 ;

i is the number of cylinders;

τ is the engine cycle.

The sound gas-dynamic field formed by repeatedly reflected elastic acoustic waves in the complex geometric volume of the intake system, including the re-radiation of the energy of these elastic waves into the environment through dynamic excitation of the walls of the elements of the intake system, causes structural vibrations of the body elements of the exhaust system, which are sources of body noise. noise.

Acoustic studies, in order to optimize the design, in particular, the intake system of the internal combustion engine in terms of vibroacoustics, are performed in acoustic semi-anechoic (with a hard sound-reflecting floor, the ceiling and walls are lined with sound-absorbing material from the inside) or, preferably, anechoic (ceiling, floor and walls are lined with sound-absorbing material from the inside). material) test chambers equipped with a stand, measuring microphones, an internal combustion engine fixed on the stand, a balancing (drive / brake) unit kinematically connected to the crankshaft of the internal combustion engine, units for ensuring the operation of the internal combustion engine, equipment for controlling the operating modes of the internal combustion engine, at least one automated system data collection, measurement and processing and, finally, the tested intake system (acoustic noise source) installed on the internal combustion engine. A more detailed description of the test acoustic chambers and examples of their use as an assessment tool for the vibroacoustic qualities of internal combustion engines, in particular, their intake systems, is given in the article by Fesina M.I., Deryabin I.V., Lomakin V.V., Malkin I.V. . “Motor vibroacoustic stand as an effective tool for research and improvement of noise characteristics of internal combustion engines. Directory. Engineering Journal, No. 11, 2007, pp. 55…62 and No. 1, 2008, (continued) pp. 50…55, as well as in the materials cited in the article. From the same article, the test methodology is also known, which consists in installing measuring microphones in the chamber, at distances specified from the object of assessment (source / emitter of acoustic noise), connecting microphones to a system for collecting, measuring and processing data and then measuring sound pressure levels formed by the object under study.

The article also notes that when conducting research and development work on vibroacoustics, the applicant, in addition to the standard distance between the measuring microphone and one or another surface of the noise emitter, equal to 1 m, uses other measuring distances approved by the relevant approved test instructions, in In particular, the distances of the “near acoustic field” are equal to 0.06 m, 0.1 m and 0.25 m. It is indicated that the displacement of the measuring microphone to the zone of higher concentration of sound energy is not always sufficient to provide the required effective attenuation of the masking background generated by outsiders (directly not related to the object of research) closely spaced intense noise emitters; that in these cases, in order to obtain additional sound insulation from the effects of background noise radiation in the installation area of the measuring microphone, noise-reducing screens are used to some extent additionally absorbing / isolating background noise radiation. The paper also mentions that when assessing intake noise, the most preferred installation point for measuring microphones is a distance of 0.06 m from the plane of the free cut of the air intake pipe or from the wall surface of the housing element of the ICE intake system. Considering that the crankshaft spin-up at full load of the internal combustion engine, for the intake system, is the most “noisy” mode of operation, the frequency of rotation of the internal combustion engine crankshaft, in the process of research, varies from minimum to maximum speed.

In Deryabin I., 2020. “On the issue of reducing the sound level emitted by the intake system of an internal combustion engine”, Journal of Physics: Conference Series 1679 052026, doi:10.1088/1742-6596/1679/5/ 052026 is specified - when studying the sound level emitted by the internal combustion engine intake system, measuring microphones are installed at two points, namely, at a distance of 0.06 m from the geometric center of the open cut of the inlet pipe and at a distance of 0.06 m from the geometric center of the resonator chamber wall; the frequency of rotation of the crankshaft of the internal combustion engine in the process of research is changed from 1500 rpm to 6000 rpm in the mode of simulating the full load of the internal combustion engine. The article also presents the test results.

In the publication of Malkin I.V. "Development of technical means for reducing noise emissions of the gas exchange system of a passenger car engine", Dissertation, State Scientific Center of the Russian Federation FSUE "NAMI", - Moscow, 2014, fig. 2.26, pp. 96-97, a schematic diagram is shown (duplicated in Fig. 1 of the description) of the internal combustion engine intake system of a modern passenger car, where 1 is the inlet valves of the internal combustion engine cylinder head, 2 are inlet pipes, 3 is a gas collection receiver, 4 is a throttle body dampers, 5 - intermediate pipe, 6 - air cleaner chamber (body), 7 - filter element, 8 - air intake pipe, 9 - Helmholtz resonator, 10 - expansion resonator chamber, 11 - quarter-wave resonator, 12 - porous sound-absorbing panel, 13 - open noise-emitting cut of the air intake pipe, 14 - compensation channel (drainage hole), 15 - acoustic pipe, in the form of a cantilever section located in the cavity of the receiver or air cleaner chamber, 16 - perforation holes, 17 - measuring microphone (when performing bench acoustic studies of the intake system) . To summarize, to reduce the noise level emitted by the intake system, various noise-damping devices are used in its design: acoustic pipes, expansion chambers, resonator silencers (quarter-wave and Helmholtz) and noise-absorbing materials. In this case, the resonator silencers are tuned to the frequency of the sound spectrum with the highest (resonant) sound pressure level.

To calculate resonator silencers, the well-known dependencies are used, cited, in particular, in the above-mentioned article by Deryabin I., 2020. “On the issue of reducing the sound level emitted by the intake system of an internal combustion engine”, Journal of Physics: Conference Series 1679 052026, doi: 10.1088/1742-6596/1679/5/052026, as well as in the description of the patent RU 2677621, 6MPK G10K 11/16, E04H 5/00, publ. 01/17/2019.

Natural frequency of the Helmholtz resonator:

- f _R ^III - natural resonant frequency in Hz of the acoustic Helmholtz resonator R ^III ,

- V _k - the volume of the chamber part of the Helmholtz acoustic resonator R ^III , m ³ ,

- K _p - conductivity of the throat part of the Helmholtz acoustic resonator R ^III , m,

- S _g - area of the flow section in the throat part of the acoustic Helmholtz resonator R ^III , m ² ,

- L _R - dynamic length of the throat part of the acoustic Helmholtz resonator R ^III , m,

- h _g - geometric (overall) length of the neck part of the Helmholtz acoustic resonator, m,

- t ^o C - air temperature established in the air cavity of the spatial zone of the installation of the internal combustion engine intake system, ^o C;

- π = 3.14.

Geometric length L ^I _r quarter-wave acoustic resonator:

-f _r is the resonator tuning frequency, Hz,

- d _pr - reduced hydraulic diameter of the passage section of the tubular part of a quarter-wave acoustic resonator of arbitrary geometric shape, m ,

- π = 3.14,

-S _T is the area of the passage section, inm ² , the tubular part of a quarter-wave acoustic resonator.

For the reduced hydraulic diameter of the circular flow section d _pr \u003d d _cr , where d _cr is the diameter of the circle.

However, despite the existing calculation methods for designing resonator mufflers of the internal combustion engine intake system, the decisive and final method is experimental research and refinement of the design designs of various options for the intake system, which includes resonator mufflers (resonators), see the book by Ivanov N.I., Nikiforova A.S. "Fundamentals of vibroacoustics" - St. Petersburg, Polytechnic, 2000, p. 326, the first paragraph under paragraph 15.2 and further to p. 337.

Experimental studies involve the manufacture of a set of prototypes of resonators of various volumes with their subsequent installation / dismantling into the composition of the studied ICE intake system, acoustic measurements and the final choice of the optimal design of the resonator muffler. This method of research is very time-consuming and costly and, due to the limited number of prototypes, does not provide the most optimal choice of the resonator volume.

The objective of the invention is to create a method for acoustic research of the internal combustion engine intake system, which has enhanced technological capabilities, increased accuracy and lower costs when conducting this type of research.

As a prototype, the method of acoustic research of sound absorbers with resonant elements, known from patent RU 2652161, 6MPK B06V 1/00, publ. and a measuring microphone connected to the data collection, measurement and processing system, in the acoustic separation of the noise source by a screen containing the studied sound absorber, in the subsequent phased formation of sound vibrations by the noise source and in the measurement by means of a microphone and a data acquisition, measurement and processing system, at each stage of sound formation, sound pressure levels. In this case, a frequency spectrum analyzer and a computer are used as a system for collecting, measuring and processing data.

The method according to patent RU 2652161 involves shielding, using the studied sound absorber, an adjustable noise source from the microphone and measuring the sound pressure levels after the sound passes through the screen. The process of fine-tuning ICE intake systems according to vibroacoustics excludes the use of any additional noise suppression means, except for those that isolate the microphone from background noise radiation and those that can be used directly as part of ICE intake systems.

Terminological explanations:

1. Resonator mufflers (resonators) - frequency-tuned noise damping devices (Helmholtz resonators, quarter-wave and half-wave acoustic resonators) designed for

dissipative absorption (scattering, damping) of sound (acoustic) energy propagated in the considered gas-dynamic (aerodynamic) system to which they are connected; The most efficient use of acoustic resonators relates to the absorption of resonant sound vibrations at prominent frequency components in the noise emission spectra of a gas-dynamic (aerodynamic) system.

2. Natural (resonant) frequency f - oscillation frequency at which the resonance phenomenon takes place (in this case, the sound frequency f at which acoustic resonance is observed, characterized by a significant increase in sound pressure amplitudes).

3. The quality factor of the frequency response of a resonator oscillatory system is a quantitative characteristic of the resonant properties of an oscillatory system, numerically equal to the ratio of the natural frequency of the resonant system to the bandwidth, at the boundaries of which the energy of the system during forced oscillations is 2 times less than the energy at the resonant frequency.

4. The quality factor of the frequency response of an acoustic resonator is a parametric characteristic of an acoustic resonator, indicating internal dissipative losses that occur both in the composite structures (elements) of an acoustic resonator and due to external energy losses directly related to the process of sound emission into the environment, which also a certain part of the vibrational energy of the acoustic resonator is consumed.

The problem is solved in the method of acoustic research, which consists in installing in a low-noise room equipped with a system for collecting, measuring and processing data, an adjustable source of acoustic noise and a measuring microphone connected to the system for collecting, measuring and processing data, in the subsequent gradual formation of sound vibrations by the noise source and in the measurement by means of a microphone and a system for collecting, measuring and processing data, at each stage of sound formation, sound pressure levels, where a frequency spectrum analyzer and a computer are used as a system for collecting, measuring and processing data.

The technical result is achieved by the fact that

- as an adjustable source of acoustic noise, a mock-up resonator is used, built in advance into the engine intake system, the crankshaft of which is kinematically connected to the balancing unit, made with the possibility of varying, in steps of 0.1 l, the volume of its internal cavity from 0.9 V _calc to 1 ,1V _calc , where V _calc is the volume of the resonator silencer determined by the calculation method,

- the measuring microphone is installed in the near acoustic field, preferably at a distance of 0.06 to 0.1 m, from the sound-emitting (tested) element of the (tested) intake system,

- at the initial stage, the volume of the cavity of the mock-up resonator is set equal to 1.1V _calc, after which the internal combustion engine is accelerated, in the mode of its maximum load, from idle speed to maximum speed, during which the sound pressure levels generated by the source located in front of the microphone are measured and recorded sound,

- then, step by step, with a step of 0.1 l, the volume of the cavity of the prototype resonator is reduced to a value of 0.9V _calc , and at each stage of changing the volume of the resonator, the internal combustion engine is accelerated, in the mode of its maximum load, from idle speed to maximum speed, and during any of the accelerations, the sound pressure levels generated by the sound source located in front of the microphone are measured and recorded,

- after completion of all stages of testing, choose the volume of the breadboard resonator corresponding to the minimum noise level emitted from

sides of the internal combustion engine intake system, the selected volume value is implemented in the design of the working resonator muffler.

The invention is illustrated by drawings:

Fig. 1, which shows a schematic diagram of the internal combustion engine intake system of a modern passenger car; cited from the publication of Malkin I.V. "Development of technical means for reducing noise emissions of the gas exchange system of a passenger car engine", Dissertation, State Scientific Center of the Russian Federation FSUE "NAMI", - Moscow, 2014, fig. 2.26, pp. 96-97. The designation of positions shown in Fig.1 corresponds to the numbering adopted in the cited work.

Fig. 2, which schematically shows the ICE intake system under study, equipped, for the test period, with a mock-up resonator;

Fig. 3, which shows the layout of the prototype resonator.

The positions in FIG. 2 and 3 are marked:

1 - intake module;

2 - acoustic branch pipe;

3 - expansion chamber;

4 - air cleaner;

5 - inlet pipe;

6 – cylinder of a breadboard resonator;

7 – measuring microphone;

8 – prototype resonator piston.

The claimed method of acoustic research of the internal combustion engine intake system can be implemented as follows:

On a motor bench (not shown) located in a low-noise room, preferably in an acoustic anechoic or semi-anechoic test chamber (not shown), the subject is fixed complete with the studied (adjustable/optimized) ICE intake system (not shown in Fig.). The crankshaft of the internal combustion engine is connected to the balancing unit (not shown; is part of the test chamber), the internal combustion engine systems (not shown) are connected to units (not shown; are part of the test chamber) to ensure the operation of the internal combustion engine and equipment (not shown; is part of the test chamber). camera) to control the operating modes of the internal combustion engine.

The studied intake system includes, see Fig.2, the intake module 1, the acoustic pipe 2 of the intake module, the expansion chamber 3, the air cleaner 4 and the inlet pipe 5.

A breadboard resonator is built into the ICE intake system under study. The interface between the mock resonator and the intake system is chosen based on the layout conditions of the engine compartment of the vehicle, where, in the future, it is assumed to use a resonator with a volume optimized according to the test results. In the region of the near sound field, preferably at a distance of 0.06 ... 0.1 m from the sound-emitting element of the intake system, a measuring microphone 7 is installed (in Fig. 2, the microphone 7 is shown installed near the open cut of the intake pipe 5), which is connected to the collection system , measurement and data processing (not shown; included in the test chamber, contains a frequency spectrum analyzer and a computer with pre-installed specialized software).

The dummy resonator can be formed by a cylinder 6, one of the ends of which is plugged (shown graphically), as well as a piston 8 installed in the cylinder with the possibility of axial displacement, and a branch pipe (shown graphically) located on the side of the plugged end of the cylinder (in Fig. 2 and 3 shows the axial, relative to the walls of the cylinder 6, the location of the nozzle).

As part of the investigated system of intake of the internal combustion engine, the cylinder 6 of the mock-up resonator is made fixed; the location of the cylinder pipe is also determined, as mentioned above, by the layout conditions of the engine compartment of the vehicle, where the subsequent use of a volume-optimized resonator is assumed (in Fig. 2, the cylinder pipe is shown located axially to the acoustic pipe 2 of the intake module 1).

The geometric dimensions of the cylinder and the piston stroke are selected based on the possibility of changing the volume of the cylinder located under the piston 8, at least from 0.9V _calc to 1.1V _calc or from 1.1V _calc to 0.9V _calc , where V _calc is the volume resonator silencer, determined by the calculation method. At the same time, the prototype resonator is made with the possibility of alternately fixing the position of the piston 8 in the cylinder 6 with a step (a), providing a staged change in the piston volume of the cylinder by 0.1 l.

The range of change in the volume of the breadboard resonator is selected based on the frequency characteristics of well-known resonator silencers with a high quality factor (see the book by Ivanov N.I., Nikiforov A.S. "Fundamentals of vibroacoustics" - St. Petersburg, Polytechnic, 2000, p 324, table. 15.1, second row from the bottom of the table). The range of change in the volume of the breadboard resonator from 0.9V _calc to 1.1V _calc , with a change step of 0.1 l is optimal for accurately determining the frequency of the resonator silencer, at which the noise level emitted by the internal combustion engine intake system will be minimal.

At the initial stage of research, the piston 8 of the model resonator is set to a position in which the volume of the cavity enclosed between the walls of the cylinder 6, its plugged end and piston 8 (the volume of the model resonator) corresponds to the volume of the internal cavity of the resonator muffler increased by 10%, determined (for a given type of internal combustion engine and the studied intake system) by the calculation method (1.1V _calc ). Then, acceleration (crankshaft spinning) of the ICE is performed from the idle speed to the maximum speed in the ICE full load simulation mode. In the process of acceleration of the internal combustion engine, the sound pressure level generated by the sound source located in front of the microphone 7 (an element of the intake system) is constantly monitored. By means of a system for collecting, measuring and processing data, a spectral analysis of the signals received from the microphone 7 is performed, the measurement of their parameters and the registration of the results obtained.

It is quite obvious that in the presence of a multichannel system for collecting, measuring and processing data, the number of simultaneously used microphones can be increased.

After completion of the first stage of research, the internal combustion engine is stopped. Then piston 8 is displaced towards the muffled end of the cylinder in such a way that the volume of the prototype resonator is reduced by 0.1 l relative to the previous value (in Fig. 3 the piston displacement step is indicated by the letter "a"). After that, the ICE is again promoted in its full load mode, accompanied by constant collection, analysis and recording of signal data generated by microphone 7. After completion of the second stage, the ICE is stopped.

The algorithm described above is repeated, step by step reducing the volume of the mock resonator cavity by 0.1 l, and for each of the volumes of the mock resonator obtained by displacement of the piston 8, the ICE is unwound, followed by a stop, accompanied by constant collection, analysis and recording of signal data generated by microphone 7 .

The final position of the piston 8 is its positioning in the cylinder 6, in which the volume of the cavity of the prototype resonator corresponds to the volume of the internal cavity of the resonator muffler reduced by 10%, determined (for a given type of internal combustion engine and the studied intake system) by the calculation method (0.9V _calc ).

According to the spectral analysis data and according to the results of measuring the parameters of the signals received from the microphone 7, registered during successive changes in the volume of the breadboard resonator, each time accompanied by the spin-up of the internal combustion engine from the idle speed to the maximum speed in its full load mode, the volume of the breadboard resonator is selected, corresponding to the minimum level of noise emitted from the intake system of the internal combustion engine; the result obtained is used in the final (pre-series) testing of the design of the internal combustion engine intake system.

The claimed method of acoustic research of the intake system of an internal combustion engine provides a reduction in the cost of finishing work on the intake system of the internal combustion engine in terms of vibroacoustics, as well as the creation of an intake system with the lowest possible level of acoustic noise.

Claims (1)

The method of acoustic research of the intake system of an internal combustion engine, which consists in installing in a low-noise room equipped with a system for collecting, measuring and processing data, an adjustable source of acoustic noise and a measuring microphone connected to the system for collecting, measuring and processing data, in the subsequent gradual formation of sound fluctuations and in measurement by means of a microphone and a system for collecting, measuring and processing data at each stage of sound formation of sound pressure levels, where a frequency spectrum analyzer and a computer are used as a system for collecting, measuring and processing data, characterized in that as an adjustable source of acoustic noise, a mock-up resonator is used, built in advance into the intake system of an internal combustion engine, the crankshaft of which is kinematically connected to the balancing unit, made with the possibility of varying, in steps of 0.1 l, the volume of its internal cavity from 0.9V _calc up to 1.1V _calc , where V _calc is the volume of the resonator silencer, determined by the calculation method, the measuring microphone is installed in the near acoustic field, preferably at a distance of 0.06 to 0.1 m from the sound-emitting element of the intake system, at the initial stage, the volume of the cavity the prototype resonator is set equal to 1.1V _calc , after which the internal combustion engine is accelerated, in the mode of its maximum load, from idle speed to maximum speed, during which the sound pressure levels generated by the sound source located in front of the microphone are measured and recorded, then step by step, with a step of 0.1 l, the volume of the cavity of the prototype resonator is reduced to a value of 0.9V _calc , and at each stage of changing the volume of the resonator, the internal combustion engine is accelerated, in the mode of its maximum load, from idle speed to maximum speed, and in during any of the overclocking, sound levels are measured and recorded pressure generated by the sound source located in front of the microphone, after completion of all stages of testing, the volume of the resonator muffler is selected corresponding to the minimum noise level emitted from the intake system of the internal combustion engine.

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