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With the rapid development of automobile industry, there is comfort and vehicle vibration and noise control of more and more stringent requirements. According to relevant data shows that 70 percent of the city noise from the traffic noise, and traffic noise is mainly car noise. It is seriously polluting the urban environment, affecting people's life, work and health. So noise control is not only related to comfort, but also related to environmental protection. However, all also from the vibration noise, vibration can cause certain parts of the early fatigue damage, thereby reducing the service life of motor vehicles; excessive noise can damage hearing the driver will enable the rapid driver fatigue, thus driving security constitutes a grave threat. So noise control, is also related to motor vehicle durability and safety. Thus vibration, noise and comfort are the three closely related, it is necessary to reduce vibration, reduce noise, but also improve ride comfort, and ensure the product economy, vehicle noise control in the standard range.
One type of noise arising from car noise are the main factors of air power, mechanical drive, the electromagnetic three parts. From the structure can be divided into the engine (ie, combustion noise), the chassis noise (ie, power train noise, all components connected with the noise), electrical equipment, noise (cooling fan noise, car noise generator), body noise (such as body structure, shape and attachment installation unreasonable noise). One of the engine noise accounted for more than half of motor vehicle noise, including noise and body intake noise (such as engine vibration, the rotational axis Valve, Jin, door switches, such as exhaust noise). Therefore the engine vibration, noise reduction has become a key automotive noise control.
In addition, automobile tires at high speed, it will also cause more noise. This is because of the tire at the ground flows, the pattern is located in the air by ground tank and re-extrusion process caused by inhaling gas pump sound, as well as tread patterns with percussive sound of the road.

2 noise requirements of regulations in Europe, from October 1996 onwards, the external bus 77dBA noise must be reduced to 74dBA, noise was reduced by half energy, the end of the century further reduced to 71dBA. Japan's laws and regulations, small car in the next decade to control noise standards at the following 76dBA. A number of domestic cities are also planning to traffic trunk lines in 2010 to control noise at the average of less than 70dBA. According to the domestic current data indicate that the domestic value of bus noise permit shall not exceed 82dBA, light trucks for 83.5dBA. This shows that our country in the vehicle noise control will have to make do.

3 noise assessment noise evaluation mainly refers to the car, outside noise and vibration adaptive value. Evaluation methods can be divided into subjective evaluation and objective evaluation. Subjective assessment of the impact of vehicle noise is a major factor in comfort, loudness and uncertainties, such as semantic differential method can be used for subjective evaluation. At an objective evaluation, can be used PCNM noise measuring device for measuring test analysis; addition simulation technology in the finite element method (FEM) and boundary element method (BEM) has been widely applied.

4 noise control noise generation and dissemination in accordance with the mechanism of noise control technology can be put into the following three categories: First, the control of noise sources, are two routes of transmission of noise control, noise three recipients are protected. One of the control of noise sources are the most fundamental, the most direct measures, including noise reduction to reduce the exciting force and the engine parts of the exciting force response, which means transformation of acoustic source local oscillator. However, it is difficult to control noise sources when necessary in the route of transmission of noise to take measures, such as sound absorption, sound insulation, noise reduction, vibration and vibration isolation measures. Motor vehicles and vehicle vibration and noise reduction level of power, economy, reliability and strength, stiffness, quality, manufacturing costs and use are closely related.

4.1 engine to reduce vibration and noise of the engine noise is the focus of automotive noise control. Engine vibration and noise are generated at source. Engine noise is from fuel combustion, valve bodies, gears and piston timing noise percussion synthesis.
(1) ontology engine noise
Lower engine noise will be ontological transformation of local oscillator sound sources, including methods such as finite element method analysis and design engines, selection of soft combustion process, improve the structure of the body stiffness, with the use of tight space, reduce noise cylinder cover. For example in the oil pan on an additional stiffener and diaphragm to improve the stiffness of oil pan to reduce vibration and noise. In addition, give the engine Tu damping material is an effective approach. Damping materials can kinetic energy into thermal energy. To deal with the principle of damping is a damping materials and components into its vibrational energy to consume. It has the following structure: Freedom damping layer structure, and spacing of freely damping layer structure, and constrained damping layer structure and spacing of constrained damping layer. It is clear that the adoption of a decrease of resonance amplitude and accelerated the decay of free vibration, reducing the various parts of the Chuan-Zhen capacity, an increase of parts at or above the critical frequency of vibration isolation capacity.
At present, some countries have designed an engine experts active vibration isolation system to reduce engine vibration, in order to achieve the purpose of noise reduction.
(2) intake noise
Engine intake noise is one of the main noise source, the Department of the engine noise of air power, with the engine speed increases to strengthen. Non-supercharged engine intake noise major components, including the cyclical pressure fluctuation noise, vortex noise, the cylinder of the Helmholtz resonance noise. Diesel engine supercharger intake noise mainly from the turbocharger compressor. Two stroke engine noise from the Roots pump. In this regard, the most effective method is the use of intake muffler. There is a resistive type muffler (absorption type), resistant muffler (expansion type, resonance type, interference-type and porous decentralized) and the composite muffler. To combine with the air filter (that is in the air filter on an additional resonance chamber and sound-absorbing material, for example, type R3238) has become the most effective intake muffler, muffler volume of more than 20dBA.

4.2 Chassis Noise

(1) Department of exhaust noise
Department of the chassis exhaust noise is the main noise sources, mainly from the exhaust pressure pulsation noise, air flow through the valve seat when issued by eddy current noise, because of boundary layer airflow disturbance caused by noise and exhaust Office jet noise composition.
Designed to optimize the performance of a good muffler, to reduce car noise are one of the important means. Optimize design method has acoustic finite element method and acoustic boundary element method, but is still in its infancy. Muffler to avoid the transmission characteristics and vibration characteristics of coupled mufflers are designed to be focused on solving a problem. Secondly, to reduce exhaust noise and improve power is also a pair of contradictions, because to reduce exhaust noise and lower exhaust back pressure on the design of the exhaust pipe has a diameter of conflicting demands, the former requires a smaller diameter, which is opposite . In this regard, the use of parallel flow path of the dual function muffler, at reduced air pressure and reduce noise to be effective. In addition, the engine exhaust manifold to the muffler inlet pipe section, the use of flexible pipe vibration, noise reduction effect can be reduced to about 7dBA.
(2) power train noise
Powertrain noise from the vibration caused by变速齿轮meshing and rotating shaft vibration. General measures taken are: First, choose low-noise transmission, engine and gearbox are two and the main reducer, such as rear axle and chassis components for flexible rubber pad connections, so as to achieve the purpose of isolation; are three-axis rotational control balance degrees, to reduce torsional vibration.

4.3 Electric equipment noise

(1) cooling fan noise
Cooling fan noise happened devices are subject to wind retaining ring, water pump, radiator and transmission, but the noise generated depends primarily on the chassis.
(2) automobile generator noise
Automotive generator noise depends on the effects of a variety of sources, these sources have magnet source, mechanical and air power source. Noise level depends on the generator magnetic structure and ventilation systems, as well as generators precision manufacturing and assembly.

4.4 Body Noise

As the speed increased, the body will be more and more noise, and air power are the main causes of noise. Therefore, the following programs to improve the body noise: First, to streamline the design of the body, achieve a smooth transition; two are in between the body and frame components to adopt a flexible connection; three interior is softened, such as Inner Mongolia at the roof and body skin the use of sound-absorbing material.
In addition, the car at high speed when the tire is also a source of noise. Real vehicle Inerting line method has been measured: Tire Tread greater, then the greater the noise. In addition, the tire tread with the noise generated also have a great relationship, there is a reasonable choice of the pattern of steel cord for radial tires to reduce tire noise are an effective way. Materials for the tire, the use of more flexible and soft rubber with high, you can create a low-noise tires.

4.5 Other measures

Automobile noise control, except in the design on the use of optimization methods and optimization of selected components, it can also carry out active control of noise. This is based on sound muffler technology, the principle is: the use of electronic muffler system with the opposite phase of the acoustic noise, vibration so that the two cancel each other out in order to reduce the noise. This muffler device used extremely advanced electronic components, has excellent noise reduction effect can be used to reduce vehicle noise, engine noise, the engine could also be used to proactively support systems, to offset the engine vibration and noise



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