T/CSAE 147-2020Wind noise test for full scale automobile in aero-acoustical wind tunnel - The measurement method of leakage noise (English PDF)

4.1 Overview

Leakage noise cannot be directly measured. In this standard, the leakage noise is obtained by comparing the interior wind noise of the vehicle under the inspection conditions and the reference conditions.

The indirect result of the noise difference. The leakage noise measurement method is based on the measurement of the wind noise in the car, refer to the standard T/CSAE 113-2019.

4.2 Test environment-acoustic wind tunnel

The types of wind tunnels applicable to this standard are 3/4 opening, recirculation or direct current, low-speed aero-acoustic wind tunnels for the entire vehicle. The performance of the wind tunnel should Meet the requirements of Chapter 4 of T/CSAE 113-2019.

4.3 Test equipment

This standard specifies the use of artificial heads or microphones to measure the noise in the car, and the test equipment should meet the requirements of Chapter 5 of T/CSAE 113-2019.

4.4 Vehicle under test

The prototype vehicle used for measurement in this standard shall meet the following requirements.

a) It is a complete vehicle that can represent the actual wind noise level of the development stage or is approved by the person in charge of performance;

b) All body opening parts (doors, windows, rear doors or trunk lids, sunroofs, fuel filler caps, engine hoods, etc.), antennas, Seals, functional parts, and interior parts should be in the assembled state and closed state that conform to the design definition;

c) The air inlet of the air conditioner is in the closed state, the air outlet is in the free state, and the active control grille is in the open state;

d) The bottom, front face, body, engine room and other parts must not have any additional objects that produce abnormal noise due to wind excitation, such as tape, cable ties, and protection Films, labels, etc.;

e) The posture maintains the free posture behind the servicing quality of the vehicle and the measuring equipment.

4.5 Sealing material

4.5.1 Tape

This standard stipulates that the exterior of the vehicle for measuring leakage noise must be sealed with cloth tape. The tape should meet the following technical requirements.

a) Use cotton thread to weave the cloth base layer;

b) Acrylic coating with thermosetting natural rubber;

c) The thickness of the single layer is 250~350 µm;

d) Adhesive force to steel plate is 3~4 N/cm2;

e) The cloth density is 21.7~23.25 pieces/cm2 (140~150 pieces/square inch).

4.5.2 Clay or glue strip

When the sound insulation capacity of the sealing system needs to be measured, glue or rubber strips can be used to seal the inside of the sealing gap. Mortar or glue Articles shall meet the following technical requirements.

a) Adhesive strip. Hollow foam sealing strip with self-adhesive adhesive;

b) Clay. It has good sound insulation performance and plasticity, and the density is greater than 1500 kg/m³.

This standard recommends the use of glue for sealing.

5.1 Overview

The method of measuring the noise inside the car and the method of sealing inside and outside the car have a significant influence on the result. This chapter discusses the noise measurement method inside the car and the sealing method outside the car.

Regulations and recommendations are made on the law and the sealing method in the car.

5.2 Measurement method

The method of measuring noise in cars in this standard shall meet the requirements of Chapters 6 and 7 of T/CSAE 113-2019.

5.3 Outer seal

The outer tape seal of the vehicle is the main method to measure the leakage noise. The outer tape seal of the vehicle should meet the following technical requirements.

a) The tape does not affect the initial appearance of the car body as much as possible, and the narrower cloth tape is preferred;

b) Each sealing gap that needs to be investigated separately is sealed with an independent tape;

c) Try to keep the original outer surface contour shape as much as possible to avoid cavities and bubbles on the joint surface of the tape and the car body;

d) Ensure that the small boss at the junction of the tape and the tape flows downstream. The order of tape application should be from downstream to upstream in the direction of airflow, that is, the front is sealed the tape is pressed on the rear sealing tape to reduce additional wind noise;

e) The corners and other places with larger curvature should be reinforced with additional tape.

5.4 Interior seal

Car interior sealing should be carried out when the sound insulation performance of the sealing system or cavity noise needs to be measured. The interior sealing should meet the following technical requirements.

a) Adhesive strips or mortar shall be used to strengthen as appropriate, but the type of sealing material shall be recorded in the test report;

b) In the case of sealing with rubber strips, the rubber strips should be fully squeezed to ensure the sound insulation;

c) In the case of sealing with glue, fill the sealing gap with glue to ensure that there is no obvious sound transmission point;

d) It is advisable to seal the gap with adhesive tape before applying the glue to strengthen the seal and facilitate the removal of the glue.

6.1 Overview

This chapter regulates the vehicle test conditions such as the scope of the sealing treatment, the sealing position to be examined separately, and the sequence method. About testing See Chapter 7 of T/CSAE 113-2019 for wind tunnel test conditions such as wind speed and yaw angle.

6.2 Sealing position

The exterior sealing position includes the following parts.

a) Movable seals, that is, the sealing position that can be opened and closed by movement. car door seam, side window guide groove, external water cut, sunroof guide groove, door handle cover Wait;

b) Fixed seal, that is, the components of the combined seal in the automobile manufacturing process. front windshield, rear windshield, fixed triangular window, rearview mirror base, Luggage rack supports, body trim strips, water-cut ends, edges of lap joints, etc. that communicate with the interior of the car.

The best sealing state should strictly seal all the above contents; the partial sealing state should be sealed according to the specific test content. its Other functional ventilation positions, such as the air inlet of the air conditioner, the pressure balance hole, etc., should be kept in the design state and not sealed. In addition, seal the front air inlet the grid can inspect the aerodynamic noise generated by the engine compartment, eliminate the abnormal noise at this location, and choose to seal it as needed.

6.3 Leakage noise of the whole vehicle

The leakage noise of the whole vehicle is the difference between the original state and the best sealed state of the vehicle interior wind noise under the same wind tunnel operating conditions, and the leakage noise is given the operating conditions of the wind tunnel should be stated in the value.

6.4 Local leakage noise

6.4.1 Baseline status selection

When measuring local leakage noise, the reference state is particularly important as the subtracted number. The reference state is based on the local leakage noise test sequence method select.

6.4.2 Test sequence method

The local leakage noise test sequence method mainly includes three methods. windowing method, packet reduction method and packet increase method.

a) Window opening method. First, seal the whole car, remove the tape at the target position after each measurement, restore the fully sealed state after completion, and then Perform the next target position measurement. The reference state of each state of this method is the fully sealed state, and the negative number of the difference is the leakage the magnitude of the noise. It should be noted that the working conditions of the removed sealing tape should not affect the sealing of adjacent working conditions, otherwise the adjacent working conditions should be carried out.

Sealed

b) Package reduction method. First, seal the whole car, remove the tape at the target position after each measurement, and do not restore the tape seal after completion.

Proceed to the next target position measurement. The base state of each state of this method is the previous state, and the negative number of the difference is the leakage the magnitude of noise;

c) Increase package method. The car is not sealed, and the target location tape is added for each measurement. After the completion, the tape is not removed and the tape is sealed directly.

Take the next target position measurement. The reference state of each state of this method is the previous state, and the negative number of the difference is the leakage noise the local leakage noise obtained by different methods are obviously different. The appropriate sequence method can be selected according to actual needs, but the local leakage noise is given.

The method used should be clarified while leaking noise.

6.5 Basic principles of working condition formulation

Leakage noise covers a wide range of auto parts, and the actual situation is complicated. The leakage noise test conditions should follow the following principles.

a) Select the test content and scope according to the test purpose;

b) Consider the feasibility of the actual structural state of the vehicle;

c) The degree of refinement of each seal inspection should be determined according to the available test resources;

d) Arrange the sequence of working conditions reasonably, generally firstly investigate the working conditions with less contribution and less time-consuming;

e) A certain amount of on-site adjustment space should be reserved.

7.1 Preliminary preparations

Before conducting the noise leakage wind tunnel test, the following preparations should be carried out as appropriate.

a) In order to improve the efficiency of the leakage and noise test, the sealing strip gap or static leakage can be detected according to the method in Appendix A before the test.

Judge the possible leakage and noise problems;

b) Check and deal with the locations where abnormal noise may be generated during the wind tunnel test;

c) If the initial working condition is in a sealed state, most of the sealing treatment can be completed in the preparation stage;

d) Record vehicle information and status.

7.2 Formal measurement process

The formal measurement process should be carried out according to the following steps.

a) Install and align the vehicle in the wind tunnel;

b) The tester enters the car and judges the noise level and leakage noise points in the car when the wind blows;

c) Adjust the seat position of the test vehicle and install measuring equipment;

d) Calibrate the measurement system to measure the background noise of the wind tunnel and equipment;

e) Switch the vehicle to the current test state;

f) Operate the wind tunnel to reach the set wind speed and yaw angle;

g) Start measurement and record data for more than 10 seconds;

h) Stop the wind tunnel and switch the vehicle to the next test state;

i) Repeat steps e) ~ h) above until all test conditions are completed;

j) Calibrate the measurement system again.

8.1 Overview

The evaluation indicators of leakage noise specified in this standard include. A-weighted sound pressure level, cumulative sound pressure difference value, speech intelligibility index, loudness and Sharpness. The comprehensive evaluation of this index can reflect the objective amount and subjective feelings of wind noise in the car under the full frequency band. The evaluation source data comes from the measurement data, the calculation should be carried out using software that includes the calculation function of the corresponding parameters or a software that is strictly in accordance with the definition.

8.2 Weighted sound pressure level

The A-weighted sound pressure level is used to process the car interior wind noise data measured by the sensor, and the line spectrum, the 1/3 octave spectrum and the total sound pressure level can be obtained.

The line spectrum and the 1/3 octave spectrum can give the magnitude of the noise in the car in different frequency bands, and the total sound pressure level is a single-value evaluation index.

8.3 Cumulative sound pressure difference value

The cumulative sound pressure difference value compares the difference between the two sets of noise data A weighting the sound pressure level at each center frequency of the 1/3 octave band, and by accumulating each frequency Rate segment to get the total value. This indicator is suitable for the comparison and evaluation of multiple groups of leakage noise inspection conditions, and is more sensitive to local contributions. Cumulative sound pressure difference the calculation formula of the score is shown in formula (1). It should be noted that the calculation center frequency range of local leakage noise is 400 Hz~10000 Hz.

Where.

The number a represents the reference working condition, the letter b represents the investigation working condition, i is the serial number of the center frequency of 1/3 octave, and, are respectively a and b the sound pressure level corresponding to the i-th center frequency point of the working condition 1/3 octave band. When defining,.

8.4 Speech intelligibility index

The Articulation Index (Articulation Index) is the effective ratio of language intelligibility under a given noise environment, as the evaluation index of the wind noise in the vehicle has the same characteristics as the subjective feeling. Refer to GB/T 15485-1995 for calculation method.

8.5 Total loudness

Loudness is the concept of the intensity level by which the human ear judges the sound from light to loud. It not only depends on the intensity of the sound, but also depends on the intensity of the sound.

The frequency is related to the waveform. Refer to ISO 532-1:2017 for the calculation method.

8.6 Sharpness

Sharpness describes the feeling that is related to the frequency components of the sound but has nothing to do with the loudness of the sound. It reflects the sharp sound, the high frequency and uncomfortable feeling is the ratio of the high frequency energy in the sound to the total energy. Refer to DIN 45692 for calculation method.

Sharpness should be used in conjunction with loudness to serve as an auxiliary indicator for evaluating the level of leakage noise.