Research on noise analysis and control technology

Research on noise analysis and control technology of high-speed passenger cars

Abstract: the noise of "China Star" domestic high-speed passenger cars with the highest operating speed in China is measured, and the noise characteristics of domestic high-speed passenger cars are analyzed. The peak value of the noise spectrum of domestic high-speed passenger cars is mainly concentrated in the central frequency of 1kHz octave band and the linear low frequency of 63Hz in the medium frequency band, and the noise shows the characteristics of medium and low frequency. This paper analyzes the main noise sources of existing passenger cars, and puts forward the main measures to reduce the internal noise of vehicles and the reversal of the coal and steel market pattern according to the actual situation of domestic vehicles at present. This paper briefly introduces the mechanism and mode of noise propagation control, and emphatically discusses the passive noise control technology and the application of high-performance damping materials in passive noise control technology

key words: high speed passenger cars; Interior noise; Noise characteristics; Noise control; Damping material

Chinese Classification Number: tb533+2

Introduction

the vibration and noise problem of high-speed rail transit has attracted increasing attention. At present, with the further acceleration of railway traffic, whether the vibration and noise of passenger cars and vehicles can be controlled within the allowable range, so that railway traffic can meet the requirements of high comfort and low noise while meeting the requirements of passengers' efficient and fast-paced. To a certain extent, this is the key to determine whether the high-speed railway can be accepted and recognized by people. Therefore, the vibration and noise reduction control of vehicles will also be more important and urgent

vibration and noise control is mainly carried out in three aspects: vibration source and noise source control, vibration propagation and noise source propagation, and object control, among which the control from vibration source and noise source is the fundamental way. For the railway transportation system, it is divided into two aspects: line vibration and noise reduction and vehicle vibration and noise reduction. The vibration and noise reduction of lines usually starts from the planning, while the vibration and noise reduction of vehicles starts from the structural design and passive control. It is an active way to start with planning and structural design, while it is a passive way to start with passive control. Passive control technology is a traditional vibration and noise reduction control technology, including sound absorption, sound insulation, noise elimination, vibration isolation and damping vibration reduction. The development of this technology at home and abroad is relatively mature, and it has become an important means to solve the problem of vibration and noise control. The production of corresponding control products (such as muffler, sound insulation cover, vibration isolator, damping material) is the main component of the vibration and noise control industry. The performance of vibration and noise control products changes with environmental factors (such as frequency, temperature, etc.)

this paper takes the "China Star" passenger cars with the highest operating speed in China as the research object, and analyzes the noise sources and noise characteristics of high-speed passenger cars according to the noise test results of real vehicles. On this basis, the vehicle noise control technology is discussed, with emphasis on the passive noise control principle and the application of high-performance damping materials and damping treatment structure design in vehicles

1 noise analysis of high-speed vehicles

1.1 noise characteristic analysis

in order to understand the noise characteristics of domestic high-speed passenger cars, master the frequency and other characteristic parameters of main noise sources, and provide a basis for the research and application of noise reduction technology, we conducted a noise test on the "China Star" with the highest speed in China in September 2003. Figure 1 shows the spectrum characteristics of vehicle interior noise at three vehicle speeds

it can be seen from Figure 1 that when the train speed increases from 120km/h to 200km/h, the sound pressure level in the frequency range of 50 ~ 5000Hz increases significantly, but the shape of the curve changes little, which shows that with the increase of the train speed, the noise value inside the carriage increases significantly, but the noise frequency characteristics remain basically unchanged. For A-weighted sound pressure level, vehicle noise is mainly concentrated in the intermediate frequency band of about 1kHz. For linear sound pressure level, vehicle noise is mainly concentrated in the low frequency band below 80Hz. This is because a weighting simulates the response of human ear to 40 square pure tones, which makes the measured sound attenuate in a wider range in the low frequency band when passing through, making the instrument sensitive to high-frequency sound and insensitive to low-frequency sound. Linear sound pressure level is an objective evaluation of noise without any correction. It can be seen that the vehicle noise of domestic high-speed passenger cars has wide-band characteristics, but the low-frequency noise below 80Hz and the intermediate frequency noise around 1kHz are the main components of the vehicle interior noise

1.2 noise source analysis

the noise sources of rail vehicles mainly include:

(1) wheel rail noise

sound generated by the interaction between rail and wheel rail. This interaction generates force at the contact between the wheel and the track, causing the vibration of the wheel and the track and radiating sound waves outward. There are three main types of wheel rail noise: friction noise, impact noise and roar noise (or rolling noise). Each type is produced by the mechanical structure corresponding to the name, model, level, MC mark, date of manufacture, serial number and manufacturer name of the testing machine on the nameplate

(2) vehicle non dynamic noise

vehicle non dynamic noise mainly refers to the friction vibration between brake shoe and brake disc during braking in the braking system, which excites the self-excited vibration of brake shoe, brake shoe bracket and brake disc to form radiated noise

(3) vehicle equipment noise

noise generated by the operation of fans, compressors, traction motors, etc., which is one of the main noises of high-speed trains. The noise of vehicle equipment, especially the noise of ventilator and compressor, increases significantly with the increase of train speed

(4) aerodynamic noise during vehicle operation

with the increase of train speed, aerodynamic noise increases significantly. When the train speed reaches more than 250km/h, aerodynamic noise rises sharply and becomes an important part of vehicle noise

according to the test results of the "China Star" existing vehicle, the functions of various noise sources are different in different parts of the vehicle. Wheel rail noise and vehicle non dynamic noise play a greater role in the low part of the vehicle than in the high part; The noise of air conditioning units such as fans plays a greater role in the high part of the vehicle than in the low part

2 vehicle noise control

the control of vehicle noise usually includes two aspects: noise source and noise transmission path. It is active and effective to control the noise source, but due to the limitations of technical level and conditions, it is difficult to achieve the ideal effect of noise control, so we must also take appropriate control measures on its transmission path, that is, passive control

2.1 noise source control

the control of noise sources includes:

(1) reducing the unevenness of wheel rail tread is an effective measure to reduce wheel rail noise. Use antifriction materials instead of cast iron brake pads Using disk braking instead of tread braking and rail grinding to remove the uneven height of the rail surface can effectively control the unevenness of the wheel rail tread

(2) reduce the dynamic force and vibration level between wheel and rail, and reduce the structural radiation noise of vehicle

(3) by using rail spacers with high stiffness and damping coefficient Measures such as increasing rail damping, increasing rail vibration absorbers, embedded rails and optimizing rail section shape (such as low rails and narrow rail feet) are taken to reduce rail vibration level and rail radiation noise

(4) reduce the vibration level of the wheel and the radiated noise of the wheel by changing the wheel structure by using sound and other methods

(5) reduce the vibration level by optimizing the vibration reduction system of air conditioning units and other equipment, so as to reduce the structural radiation noise caused by the vibration of such units and equipment

2.2 noise propagation control

noise propagation control, also known as passive noise control, enables the external noise of the car body to be converted into the following main parts when it is incident on the car body surface through special materials and structural design: 1) part is reflected; 2) Part of it is converted into other forms of energy or waveform and absorbed when passing through the vehicle body. For example, one part of it is converted into heat energy by the high damping material attached to the car body, and the other part is converted into structural radiation noise or other forms of waveform; 3) The last part enters the vehicle interior through the vehicle body. See Figure 2 for energy distribution during noise propagation

Figure 2 principle of noise propagation control

according to the law of conservation of energy, if the incident sound energy is e, the reflected sound energy is E1, the lost sound energy is E2, the waveform conversion energy is E3, and the transmitted sound energy is E4, then there are:

e=e1+e2+e3+e4

the greater the ratio of reflected sound energy to incident sound energy, the better the sound insulation performance of the material; The smaller the ratio of transmitted sound energy to incident sound energy, the better the sound absorption performance of the material

passive noise control is divided into isolation noise and absorption noise TECHNYL reg; Redx has two basic methods: lower material and production cost. According to the transmission mode of noise, it can be divided into: airborne noise and structural radiation noise. Airborne noise is that the noise propagates in the air in the form of waves and at a certain speed, and its intensity gradually weakens in the area away from the sound source; Structural radiation noise is the noise wave generated by vibration, which propagates in solid matter at different speeds, mainly in the form of refraction

2.2.1 noise isolation

noise isolation is divided into airborne noise isolation and structural radiation noise isolation. Airborne noise isolation is achieved by isolating and absorbing the noise energy reflected from the isolator. The remaining noise energy is radiated to the other side and then spread through the air. The heavier and softer the surface of the insulator, the better the isolation effect of airborne noise. Structural radiation noise isolation is achieved by making the noise reflect on the acoustic material and attenuate the noise propagation. The softer the acoustic material layer, the larger the volume, the better the effect of structural radiation sound isolation

the sound insulation materials used for high-speed passenger cars can be made into mats covering the floor structure, such as asphalt felt mats, soft asphalt metal berths, high damping rubber mats and other products; It can also be made into paste products sprayed or scratched on the surface of the car body, such as synthetic resin coating, asphalt rubber mixed coating and other products. The sound insulation effect of such materials depends on the temperature of the environment and the frequency of noise

2.2.2 noise absorption

noise absorption is divided into airborne noise absorption and structural radiation noise absorption. Absorption of airborne noise is achieved by converting sound energy into heat energy when airborne noise passes through fiber or foam materials. The thicker and denser the fiber material or foam material used, the better the absorption effect of airborne noise. The absorption of structural radiated noise is achieved by partially converting the sound energy into heat energy after the noise passes through the uniform layer adhered to the damping material on the structure. In this case, the structural radiation noise has been absorbed before it becomes airborne noise. The better the absorption and loss performance of damping materials, the better the absorption performance of radiated noise of the structure. In practice, the phenomenon of pure air borne noise is rare, and it usually exists at the same time with the structural radiation noise. This part of the structural radiation noise spreads on the base material and will be absorbed by the sound-absorbing material at the same time to achieve the best noise reduction effect, with an accuracy of ± 1mm. For this reason, a material composite structure that can absorb both structural radiation noise and airborne noise is proposed, as shown in Figure 3. Its base material (such as asphalt felt) absorbs and separates