This standard specifies the test method for the exhaust muffler of an internal combustion engine. This standard is applicable to the test of the muffler of a medium and small power internal combustion engine, and can also be used as a reference for the intake muffler. GB/T 4759-1995 Test method for exhaust muffler of an internal combustion engine GB/T4759-1995 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Measurement procedure for exhaust silencers of internal combustion engines
Measurement procedure for exhaust silencers of internal combustion engines1 Subject content and scope of application
This standard specifies the test method for exhaust silencers of internal combustion engines (hereinafter referred to as silencers). GB/T4759—1995
Replaces GB4759--84
This standard is applicable to the test of silencers of medium and small power internal combustion engines, and can also be used as a reference for intake silencers. 2 Reference standards
GB3785 Electrical and acoustic performance and test methods of sound level meter GB3241 1/1 and 1/3 octave filters for sound and vibration analysis GB1105.1~1105.3 Internal combustion engine bench performance test methods GB3947 Acoustic terminology
3 Terminology
3.1 Exhaust muffler
The exhaust muffler is a device with a sound-absorbing lining or a special form of airflow duct that can effectively reduce airflow noise. Note: The exhaust muffler of an internal combustion engine generally includes the entire muffler component starting from the muffler air inlet, excluding the exhaust manifold and exhaust pipe of the internal combustion engine. 3.2 Insertion loss
The insertion loss of the muffler is the difference in the sound power level radiated through the exhaust port before and after the muffler is installed. Symbol: D; Unit: dB. Note: Under normal circumstances, the size, shape and sound field distribution of the pipe mouth remain approximately the same. In this case, the insertion loss is equal to the difference in sound pressure level before and after the muffler is installed at a given measuring point.
3.3 Power loss ratio
The power loss ratio of the muffler is the percentage of the power difference before and after the muffler is used and the power value when the muffler is not used under the calibration conditions of the internal combustion engine. Symbol: r.
4 Measuring instruments
4.1 Acoustic measuring instruments
4.1.1 Type 1 or 2 sound level meters or other acoustic measuring instruments should be used to measure the sound pressure level. The instruments used should comply with the relevant provisions of GB3785.
4.1.2 The 1/1 octave or 1/3 octave filters used for spectrum analysis should comply with the relevant provisions of GB3241. 4.1.3 The measuring instrument should be calibrated before and after each continuous measurement. The accuracy of the sound level calibrator should be better than or equal to ±0.5dB. The difference between the two calibration values ​​should not exceed 1dB.
4.2 The measuring instruments for the internal combustion engine bench test should comply with the relevant provisions of GB1105.3. Approved by the State Bureau of Technical Supervision on June 15, 1995 and implemented on February 1, 1996
5 Measurement conditions
GB/T4759-1995
5.1 In the laboratory test, the internal combustion engine should be operated stably under the calibrated working conditions specified in GB1105.1, that is, the calibrated power and corresponding speed. The oil temperature and water temperature (wind temperature) can be measured only when they are stable. For automotive internal combustion engines, etc., measurements can be made under different working conditions according to the use requirements, and they should be explained in the report.
5.2 The length, diameter and shape of the exhaust system (including muffler and pipe) of the internal combustion engine should be close to its actual use. 5.3 Except for the exhaust noise, all other noises are taken as background noise during measurement. The difference between the sound pressure level of the measured noise and the background noise should be above 10dB. If the difference between the sound pressure level of the measured noise and the background noise is below 3dB, measures should be taken to deal with the background noise source before measurement. If it is between 3dB and 10dB, correction should be made according to Table 1 (i.e., the measured noise minus the correction value). Table 1 Background noise correction value
Difference between measured noise and background
Noise sound level
Correction value
10 and above 10Www.bzxZ.net
5.4 When the wind speed at the measuring point exceeds 2m/s, a wind shield should be used. When the wind speed exceeds 5m/s, measurement should be stopped. 5.5 The measuring point position is required to be at a distance of 500mm at a direction 45° from the axial direction of the exhaust airflow, with the microphone pointing to the exhaust port (Figure 1). If there are two exhaust ports, the measuring point is selected at the intersection of the two assumed circles shown in Figure 2 at a 45° angle to the axes of the two exhaust ports (Figure 2). For large internal combustion engines, the measuring point distance can be appropriately increased, and for small internal combustion engines, it can be appropriately shortened, but the distance from the measuring point to the exhaust port should be greater than 3 times the diameter of the pipe port. And the measurement results should not be affected by airflow. The height of the measuring point from the ground is greater than 1m, and the distance from the measuring point to other reflecting surfaces is greater than twice the measuring distance. During the test, the relative position of the measuring point and the exhaust port remains unchanged. 5.6 In order to keep the sound field distribution unchanged during measurement, the vicinity of the measuring point should meet the free field conditions, or the measuring point and the reflecting surface in the surrounding environment should remain in the same relative position.
Muffler body
Exhaust port
Microphone
Figure 1 Measurement point position of a muffler with one exhaust port 252
6 Measurement method
Muffler body
GB/T4759—1995
Microphone
Microphone position (on the hypothetical line)
Figure 2 Measurement point position of a muffler with two exhaust ports This standard specifies three measurement methods: laboratory measurement method, on-site measurement method and muffler surface radiated noise measurement method. The comprehensive evaluation of muffler performance should be based on the laboratory method, and the main evaluation quantities are A, C weighted sound pressure level insertion loss and power loss ratio. When measuring the exhaust noise without a muffler, an empty pipe with the same length as the muffler and the same diameter as the exhaust pipe should be installed. 6.1 Laboratory measurement method
6.1.1 Measurement content, mainly measure the A, C insertion loss and power loss ratio of the muffler. 6.1.2 Measurement method, first shield the noise of the internal combustion engine and its auxiliary equipment. Measure the A, C sound pressure level or band sound pressure level of the exhaust noise without and with muffler and the power of the internal combustion engine under the calibration conditions. Carry out two measurements, and the difference between the measurement results should be less than 2dB. The measurement results should be recorded, and the average value of the two times should be taken when processing the data. Eliminate the errors caused by atmospheric conditions and other factors. The above measurements should be carried out in one test, and the parking time should not exceed 30 minutes. 6.1.3 When measuring A, C sound pressure levels, the "slow" gear of the sound level meter should be used for measurement. And read the average value of the sound level meter pointer during the observation period. If spectrum analysis is performed, a 1/1 octave or 1/3 octave filter with a center frequency of 31.5 to 8000 Hz should be used. The observation time for reading the average value is 10 seconds for center frequencies of 200 Hz and above, and 30 seconds for center frequencies of 160 Hz and below.
6.1.4 Insertion loss is calculated as follows:
D = L— L,
Insertion loss, dB,
Where: D—
-A, C sound pressure level or frequency band sound pressure level of exhaust noise with an empty pipe without a muffler, dB (reference value 0dB=20μPa); A, C sound pressure level or frequency band sound pressure level of exhaust noise with a muffler, dB (reference value 0dB=20uPa). L,
6.1.5 The measurement of the power of the internal combustion engine P1,P, can be carried out according to the measurement method specified in GB1105. 6.1.6 The power loss ratio is calculated according to the following formula:
Pi= Pz × 100%
Wherein: r-—power loss ratio;
GB/T 4759-1995
P,—power of the internal combustion engine without muffler and with empty pipe, kW; Pz—power of the internal combustion engine with muffler, kW. 6.1.7 If necessary, the power ratio of the muffler under different working conditions can also be used for evaluation. 6.2 Field measurement method
6.2.1 This method is suitable for the measurement of the insertion loss of the muffler of the internal combustion engine (such as vehicles and equipment driven by the internal combustion engine in neutral gear) under actual on-site use conditions. It can only provide a relative comparison of the muffler performance of different mufflers on the same internal combustion engine. 6.2.2 The muffler measurement should be carried out on the matching internal combustion engine. When measuring the insertion loss of different mufflers, the internal combustion engine should maintain the same operating conditions and explain it in the report.
6.2.3 Measure the muffler insertion loss value according to 6.1.3 and 6.1.4. 6.3 Exhaust muffler surface radiation noise measurement method 6.3.1 This method is applicable to the noise measurement of the muffler surface radiation of the internal combustion engine. 6.3.2 Except for the muffler surface radiation noise, other noises are treated as background noise. 6.3.3 The muffler surface radiation noise level measurement point is 0.5m away from the radiation surface. The number of measurement points is related to the length of the muffler. For muffler lengths below 0.5m, one measurement point can be used, and one measurement point is added for every 0.5m increase. The height of the measurement point from the ground should be greater than 1m. 6.3.4 The muffler surface radiation noise level is evaluated by the average value of the A sound pressure level of each measurement point. 6.3.5 The test method shall be carried out in accordance with 6.1.3. 7
Test report
7.1 The test internal combustion engine and muffler parameters are recorded in Table 2. Table 2 Record table of internal combustion engine and muffler parameters
Internal combustion engine model
Manufacturer
Displacement L
Rated power kW
Rated speed/min
Muffler volume L
Muffler mass kg
7.2 The muffler test results are recorded in Table 3.
Measurement time
Ambient temperature ℃
Test location
Measuring instrument
Measuring point distance
Background noise dB
Measurement personnel
Internal combustion engine speed
Oil temperature ℃
Water temperature ℃
Weighted sound pressure level
Band sound pressure level
(Octave band center frequency, Hz)
Additional instructions:
GB/T4759—1995
Table 3 Internal combustion engine muffler performance test data record table P.kw
This standard is proposed by the National Technical Committee for Acoustics Standardization. This standard is under the jurisdiction of the National Technical Committee for Internal Combustion Engine Standardization. This standard was drafted by the Beijing Institute of Labor Protection Science and Tianjin Internal Combustion Engine Research Institute. The main drafters of this standard are Ren Wentang and Zhao Shen. L
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