RU2292537C2 - Method to determine noise radiated by mufflers of automobile engines - Google Patents

Abstract

FIELD: transport engineering; acoustics.

SUBSTANCE: invention can be used for determining noise radiated by mufflers of automobile engines. Method comes to determining spectrum of noise damping by muffler by delivering acoustic noise to muffler input under laboratory conditions. Noise inside automobile exhaust system in area of its joint with muffler, when automobile runs along measured section under conditions corresponding to maximum level of external noise, is measured additionally, and then spectrum of noise inside exhaust system is determined, and spectrum of noise damping by muffler obtained under laboratory conditions is extracted from noise spectrum inside exhaust system. Then, basing on obtained difference, integral level of noise is calculated and correction corresponding to noise damping at desired distance is subtracted from integral noise level.

EFFECT: possibility of finding of rational method of external noise level.

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Description

The present invention relates to the field of vehicle acoustics and can be used to identify sources of external car noise in order to select rational ways to reduce the external noise of the car and reduce costs during its acoustic refinement.

Before proceeding to the description of known analogues and prototype, the following should be noted. The car’s external noise is the sum of its individual components, which include the engine, engine gas exchange systems (exhaust system and air intake system for the fuel combustion process), transmission units (gearbox, axles), an engine cooling fan, tires, and some others. The main source of external noise, as a rule, is the engine. The next most important source (especially for trucks with powerful diesel engines) is an exhaust system equipped with a silencer. If the efficiency is not high enough, the noise level emitted by the silencer of the exhaust system (gas-dynamic component of the exhaust) may prevail over engine noise. The contribution of the remaining sources to the external noise of the car is insignificant and begins to affect only after a significant reduction in engine and muffler noise. Thus, the engine and the muffler of the exhaust system are the main sources of noise that determine the external noise of the car, and the successful solution of the problem of reducing it substantially depends on determining the contribution of these sources to external noise, since it is necessary to choose one of the directions of work: either reduce engine noise, or increase the efficiency of the muffler.

A known analogue of the invention described in RF patent No. 2096561, IPC 7 E 02 F 5/14, G 01 M 15/00 "Method for measuring external noise emitted by road-building and earth-moving machinery", consisting in measuring external noise with noise sensors, located at measuring points lying on an imaginary measuring surface that surrounds the entire working trajectory of the cyclic movement of the machine. The analogue method allows to determine the integral noise level of the machine, from which it is not possible to identify individual noise sources, which is its drawback.

There is also a method of measuring the external noise of a car, described in GOST R 41.51-99. Uniform provisions concerning the approval of vehicles with at least four wheels in connection with the noise they produce. Standards Publishing House, Moscow, 2000, p. 12, 13, which consists in the fact that the noise level of a car moving in acceleration mode from its left and right sides is measured on a measuring section (the concepts of “left” and “right” sides of a car are determined relative to its direction of movement). Measurements are carried out for various gears. The microphone is installed at a distance of 7.5 ± 0.2 m from the control line CC ¹ (see Fig. 1 on page 15 of the mentioned GOST). The maximum value of the level realized during the measurements is taken as the result of measuring the external noise of the car. The disadvantage of this analogue is that it does not allow to determine the contribution of individual sources to the external noise of the car (in particular, the muffler), since at a distance of 7.5 m, as described in GOST R 41.51-99, the sources cannot be identified with sufficient accuracy. The consequence of this may be the choice of an ineffective way to reduce the external noise of the car, which will not give positive results, entail excessive material and financial costs, etc.

A device for testing silencers for the production of automobile engines, selected as a prototype and described in ed. USSR No. 1296884, 1984, IPC 7 G 01 M 7/00, G 10 K 7/00, including a noise source with exhaust and intake pipes connected thereto and a compressed gas source connected to the intake pipe, the noise source being made in the form of a siren. With this device, the acoustic efficiency of the silencer can be determined in the form of a noise reduction spectrum, for example, 1/3 octave (according to the results of noise measurements with and without a silencer), which allows you to choose from several types of silencers the most effective from the point of view of noise reduction, however the prototype device does not allow to evaluate the contribution of the muffler as a source to the external noise of the car, because for this it is necessary to know the real characteristics of the noise inside the exhaust pipe of the car exhaust system (in front of the muffler), avisyaschie temperature exhaust gases, their chemical composition, the static pressure, the velocity of sound in the exhaust gases, which device can not reproduce, which is its disadvantage.

The tasks solved by the present invention are:

- identification of sources of external vehicle noise by determining the noise emitted by the muffler of the exhaust system;

- reducing the cost of acoustic refinement of the car in terms of reducing external noise.

This is achieved by the fact that:

- additionally measure the noise inside the exhaust system of the car in the area of its junction with the silencer when the car moves along the measured area in the mode corresponding to the maximum level of external noise of the car;

- determine the noise spectrum inside the exhaust system;

- the spectrum of noise reduction by the silencer, obtained in laboratory conditions, is subtracted from the obtained spectrum and the integral noise level is calculated from the obtained difference;

- the correction value corresponding to the attenuation of noise at a distance of interest is subtracted from the integral noise level.

The essence of the proposed method is illustrated in the drawing, which schematically shows a car containing an engine 1, a pipe 2 of the exhaust system, through which the exhaust gases from the engine 1 are supplied to the muffler 3. The car has a front 4 and rear 5 axles on which wheels with tires 6 are mounted. The microphone 7, designed to measure the external noise of the car, is located at a distance of λ = 7.5 m from the longitudinal axis of symmetry α of the car, or at any other distance of interest to the researcher. The direction of movement of the car is shown by an arrow. Inside the pipe 2 of the exhaust system in the area of its junction with the silencer 3, a sensor 8 is installed that measures the noise inside the exhaust system.

The implementation of the proposed method is as follows. First, in laboratory conditions, the acoustic efficiency of the muffler is determined using the prototype device described in ed. USSR No. 1296884, or similar, resulting in a noise reduction spectrum of a silencer, for example 1/3-octave (denoted by L ₀ ), which is the difference of the spectra at the inlet and outlet of the silencer when acoustic noise is applied to the silencer inlet, for example, from a siren as implemented in the prototype device. After that, the vehicle is additionally measured using a sensor 8 (a piezoelectric sensor can be used to measure the alternating pressure in the gas medium) noise inside the pipe 2 of the exhaust system in the area of its junction with the silencer 3 when the car moves along the measured area in the mode corresponding to the maximum level of the external car noise (external car noise is measured by microphone 7). The mode of movement of the car is selected in accordance with the known method of measuring the external noise of the car, given in GOST R 41.51-99. After that, the process registered by the sensor 8 is processed and, for example, using a spectrum analyzer, the noise spectrum inside the exhaust system (denoted by L ₁ ) is determined, for example, 1/3-octave by analogy with the noise reduction spectrum of the muffler L ₀ . Then, the spectral difference L ₂ = L ₁ -L _{0 is} obtained and the integral noise level L _Σ corresponding to the spectrum L _{2 is} calculated. After that, from the noise level L _Σ subtract the magnitude of the correction ΔL, determined by calculation or experimentally, corresponding to the attenuation of noise at a distance of interest. In the case of measurements of the external noise of the car according to GOST R 41.51-99, this distance is 7.5 m. Thus, the obtained value of L _hl = L _Σ -ΔL is the noise level produced by the muffler at a distance of 7.5 m (or other interesting explorer distance) from the car.

The value of L _hl is an important acoustic characteristic of the muffler, since it allows one to judge its effectiveness in terms of reducing noise (for a specific type of automobile engine) of the exhaust system. Knowing the value of L _hl and the level of external noise of the car, the question of work to reduce the external noise of the car is clearly resolved correctly - to increase the efficiency of the muffler, or to reduce the noise of the car engine.

The method claimed by the authors was tested at Ural Automobile Plant OJSC on a Ural-4320 all-terrain vehicle with a 6 × 6 wheel arrangement, with a YaMZ 236 NOT 2 diesel engine, with three types of silencers with sound-absorbing packing manufactured by various companies. According to the test results, a muffler was selected that has the highest noise reduction efficiency, that is, having the lowest noise level generated by the muffler at a distance of 7.5 m. The method error is not more than 1.5 dB.

Given the above, the authors and the applicant believe that the claimed method has novelty, significant differences with respect to known technical solutions and can be protected by a patent for an invention.

Claims (1)

A method for determining the noise emitted by mufflers of an exhaust system of automobile engines, which consists in determining in laboratory conditions a spectrum of noise reduction by a muffler by applying acoustic noise to the input of the muffler, characterized in that the noise is additionally measured inside the exhaust system of the car in the region of its junction with the muffler when the vehicle moves along the measured area in the mode corresponding to the maximum level of external noise of the car, after which the noise spectrum is determined inside the exhaust system and the spec is subtracted from it mp of noise reduction by a silencer obtained in laboratory conditions, and then, based on the obtained difference, the integral noise level is calculated and the correction value corresponding to the noise attenuation at the distance of interest is subtracted from it.