Discussion on the noise and control theory of the

2022-09-21
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Abstract: This paper briefly describes the significance of noise control of construction machinery for environmental pollution and ride comfort, as well as its impact on the sales market of construction machinery products. At the same time, it briefly analyzes various factors of noise generated by construction machinery in working and driving, and analyzes the basic theories and methods of noise control and measurement

key words: noise control of construction machinery

Introduction

with the rapid development of the construction machinery industry, people have increasingly stringent requirements for the comfort and vibration and noise control of construction machinery. Noise control is not only related to ride comfort, but also related to environmental protection. All noise comes from vibration, which can cause early fatigue damage of some parts, thus reducing the service life of construction machinery; Excessive noise can not only damage the driver's hearing, but also make the driver quickly tired, which poses a great threat to the safety of construction machinery. Noise control is also related to the smoothness, durability and safety of construction machinery products. Therefore, vibration, noise and comfort are closely related. We should not only reduce vibration and noise, but also improve ride comfort, ensure the economy of products, and control the noise of construction machinery products within the standard range

After entering the 21st century, in order to achieve sustainable development, human beings have put forward environmental protection technology and information technology of construction machinery, which has brought the development of construction machinery into a new stage of development. European, American and Japanese markets have imposed stricter requirements on the noise of construction machinery products. Therefore, the environmental protection technology and information technology of construction machinery are the mainstream of the future international engineering development trend. In order to cooperate with the internationalization strategy, take the international advanced product standards as the guidance, improve the product technology level, especially to further explore the international market, XCMG's next development ideas and one of the main objectives is to carry out research on energy conservation, environmental protection, operation comfort and other technologies

1 type of noise

the main factors that produce the noise of construction machinery are aerodynamic, mechanical transmission and hydraulic pressure. Structurally, it can be divided into engine (i.e. combustion noise, exhaust noise, cooling fan noise, generator noise), engine body noise (such as engine vibration, rotation of valve shaft, noise caused by inlet and exhaust valve switches, etc.). Transmission system noise, noise caused by the connection and coordination of chassis components, body noise (vibration of body structure caused by engine, noise caused by unreasonable installation of accessories), hydraulic noise (noise caused by vibration of gear pump, hydraulic valve and pipeline), exhaust noise of braking system, impact noise of working device action. Among them, the noise generated by the engine and its related parts accounts for more than half. Therefore, the vibration and noise reduction of engine has become one of the keys of noise control of construction machinery

2 noise requirements

as early as 1983, some domestic loaders were not issued a license by the Beijing Municipal Public Security Bureau due to high noise, and the purchasing units demanded to return them one after another, which caused a strong impact on the construction machinery production enterprises. In 1984, the Ministry of machinery industry issued the standard of noise limits for construction machinery (jb3774.84); In 1990, the National Environmental Protection Bureau issued the standard of noise limits at the boundary of construction sites (gbl2523-90). On the basis of the above, with reference to the ISO/dis6393-6396:1995 standard, the national standard noise limits for construction machinery (gb16710.1-1996) was issued in 1996. The limits specified in this standard, as the minimum indicators of China's construction machinery products at this stage, are mandatory standards and issued for implementation (more relaxed than jb3774.1-84). The standard stipulates that the noise limit at the driver's position of construction machinery is 92d. The study points out that B (a), and also stipulates the relationship between the sound power level of external radiated noise and the rated power. See Table 1, 2

due to the high level of manufacturing in western developed countries, the running noise of engines, oil pumps, gearboxes, torque converters and other mechanical and hydraulic components is small. For the protection of the environment and human health, the voice limit standards in these countries have been continuously reduced. The European noise limit standard was revised in 1997, which is 4dB (a) lower than the original standard. It stipulates that the maximum noise shall not be greater than 113dB (a). When the engine power is 154kw, the noise sound power level limit shall be less than or equal to 107dB (a), which is 11db (a) lower than the current national standard in China. On January 1, 2002, the European standard was further revised, It is 3dB (a) lower than the standard in 1997. In Japan, the minimum noise limit standard issued and implemented in October 1997 is stricter than the European standard in 1997, which stipulates that the engine power is greater than 105kwlt inch, and the maximum noise shall not be greater than 106db (a), which is 12dB (a) lower than the current national standard in China. Now, it is a global trend to reduce the noise emission limit of construction machinery products

according to the regulation of "environmental noise emission of outdoor equipment" issued by the European Union on May 5, 2000, the second phase of the regulation has been implemented since January 2006. The noise emission standard for equipment with the same engine power is 2 ~ 3dB (a) lower than the European noise limit revised in 1997. See Table 3 for specific noise emission standards

3 noise evaluation and noise control

noise evaluation indicators mainly refer to the noise value and vibration adaptability inside and outside the vehicle. Evaluation methods can be divided into subjective evaluation and objective evaluation. The main factors affecting the subjective evaluation of vehicle noise are comfort, loudness and certainty. In the objective evaluation, the noise measurement device can be used for measurement and analysis; In addition, the finite element method (FEM) and boundary element method (BEM) of sound field analysis in simulation technology are also widely used

foreign countries began to study noise earlier. In 1970, the United States began to study the characteristics of interior noise. In the 1980s, the American Institute of Engineering Mechanics did a lot of research work on the prediction of interior noise characteristics. They systematically studied the finite element modeling method of acoustic modal analysis, and discussed the influence of body structure vibration on interior sound field and the influence of interior sound pressure on boundary vibration, The finite element shear experiment of structure acoustic coupling is established, which is divided into unidirectional shear and bidirectional shear experimental models. The acoustic modal analysis of elastic boundary and the calculation of sound pressure distribution in the car when the body structure is forced to vibrate are completed, and the finite element calculation formula of structural vibration sound pressure fluctuation under the action of external interference forces is derived, which lays a good foundation for the prediction and analysis of interior noise

Japan also attaches great importance to the research on the noise of construction machinery. After the noise of main transmission parts is effectively controlled, the air flow noise formed by different structures is deeply studied and applied to the new generation of excavators and other construction machinery. Domestic research on vehicle noise started late, and the analysis and research of construction machinery noise is even later. In the past two decades, noise control of construction machinery has become an important issue that many manufacturers and scientific research departments urgently need to solve. Due to the requirements of comfort, there are many studies on the vibration and vibration noise of the car body [cab] at home and abroad, and relatively few studies on the analysis of the noise outside the car, but it is also gradually increasing in recent years

noise control first needs to find out the main noise source. Spectrum analysis method is one of the basic methods to identify noise sources. In addition to using amplitude spectrum diagram, power spectrum diagram, coherence function method and cepstrum method are most commonly used in spectrum analysis. Since the 1970s, the theory of acoustic holography has developed rapidly, but it has not been widely used, mainly because the equipment is expensive and the spatial resolution error is greater than the wavelength of sound waves. Sound intensity measurement is a new technology developed in acoustic measurement and signal processing in the early 1980s. It has been widely accepted by people. Because there are too many measurement points, it is difficult to achieve in general manufacturers in China. In recent years, some progress has been made in the research of identifying the main noise sources outside the vehicle using near-field acoustic holography and sound pressure method

according to the mechanism of noise generation and transmission, noise control technologies can be divided into the following three categories: first, the control of noise sources, second, the control of noise transmission routes, and third, the protection of noise receivers. Among them, the control of noise source is the most fundamental and direct measure, including 1 The universal testing machine must check the exciting force and reduce the response of the engine part to the exciting force before the experiment, that is, transform the vibration source and sound source. However, when it is difficult to control the noise source, it is necessary to take measures in the transmission path of noise, such as sound absorption, sound insulation, noise elimination, vibration reduction and isolation. The vibration reduction level of construction machinery products is closely related to the thermal balance, power, economy, reliability, strength, stiffness, quality and manufacturing cost of the whole vehicle

3.1 vibration and noise of engine

reducing engine noise is the focus of noise control of construction machinery products. The engine is the source of vibration and noise. Engine noise is composed of fuel combustion, knocking noise of valve train, timing gear and piston, etc

(1) engine body noise

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to reduce the engine body noise, we need to transform the vibration source and sound source, including using finite element method and other methods to analyze and design the engine, selecting soft combustion working process, improving the structural stiffness of the engine body, and using tight fitting clearance to reduce the cylinder head noise. For example, add stiffeners and diaphragms on the oil pan to improve the stiffness of the oil pan and reduce vibration and noise. In addition, it is also an effective way to coat the engine with damping materials. Damping materials can convert kinetic energy into heat energy. The principle of damping treatment is to combine a damping material with parts to consume vibration energy. It has the following structures: free damping layer structure, interval free damping layer structure, constrained damping layer structure and interval constrained damping layer structure. Its use significantly reduces the amplitude of resonance, accelerates the attenuation of free vibration, reduces the vibration transmission capacity of various parts, and increases the vibration isolation capacity of parts above the critical frequency. At present, experts from some countries have designed an engine active vibration isolation system to reduce engine vibration and noise

(2) intake noise

intake noise is one of the main noise sources of the engine, which is the aerodynamic noise of the engine and increases with the increase of engine speed. The main components of intake noise of non supercharged engine include periodic pressure pulsation noise, eddy current noise, cylinder resonance noise, etc. The intake noise of supercharged diesel engine mainly comes from the compressor of supercharger. For this, the most effective method is to use intake muffler. Types: resistive muffler (sound absorption type), resistant muffler (expansion type, resonance type, interference type and porous dispersion type) and composite muffler. Combining it with the air filter (that is, adding resonance cavity and sound-absorbing material on the air filter) will become the most effective intake muffler

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