Research And Analysis On Passenger Car 'S Inner Noise Using Statistical Energy Analysis Method

The property of Automotive interior noise is one of the evaluation indexes which is involved in the comfort of the automotive. The manufactures of auto are contriving to curtail the period between model design and manufacture under the increasingly fierce competition. We can assess and calculate the noise level through computer simulation. In this thesis, we predict and analyze the level of inner noise in a domestic car by statistical energy analysis method.This thesis explains the engineering rule how to establish a vehicle noise analysis system based on the Statistical Energy Analysis theory. Based on the three-dimensional CAD data of the domestic car , the car are divided into structure subsystems and Acoustic cavity subsystems. The energy transfer relationship between subsystems is established. The SEA model of the car can be got. The material and physical properties of subsystems are determined. At the same time, the modal density, internal loss factor, coupling loss factor between connected subsystems are also calculated. These results are input into the SEA model.Secondly, the CFD simulation which is about the air pressure fluctuations incentives on the Automotive body surface at high speed are completed. Incentive value is applied to each subsystem. Then the level of inner noise of Automotive can be simulated by software Autosea which is based on the theory of Statistical energy analysis. Through nine time orthogonal test, we can know which body parameter of car has most important impact on the interior noise. The studying results show that: The front windshield angle have the greatest effect on aerodynamic drag for car, which followed by the angle of the front cover, and the least is upturned angle and back windshield angle .Based on the test results, the best combination of value obtained is taken, Specifically, the back windscreen angle of 35°, the front windshield angle value of 42°, the front cover angle of 20°and the upturned angle of 10°. In the vicinity of A column there is strong pressure of air pulse, which is the main source of air noise generated inside. the air pulsating pressure near A column will spread to the car through the windscreen, front side windows and solid way; the major source of noise inside the body when car travel at high speed (speed is 120km/h) is produced by the air wave excitation noise.Then, the body mounting vibration excitation, the vibration excitation of powertrain mounting, the radiation pressure incentive of powertrain and the air pressure fluctuations of car body surface are applied to the SEA model. The noise level of acoustic cavity which near the ears of driver and passenger can be analyzed and forecasted.According to the calculation results, the major subsystem energy flow is obtained, on this basis the vibration noise reduction is put forward, which have been analyzed the influence on the different absorption, sound insulation materials and damping materials for car noise response characteristics. Main achievements are: imposing noise-reducing materials on front panel can dropped the before the tune sound pressure level by an average 0.9 ~ 1.2dB, the noise reduction measures worth to be widely used; the front door and side body panels which was imposed to enhanced pad can be decreased in the interior sound pressure level in the whole band, a drop of about 0.5 ~ 1.5dB; Increasing the thickness of the side windows can reduce interior noise; the effect is obvious when putting damping material on the wall of noise insulation, the noise level which inside the 500 ~ 4000Hz can down 2 ~ 4dB; it is very effective that increasing the insulation wall thickness of 2.5 for the original times under the 4000Hz for noise control, that sound pressure level before and after the tune can be reduced 1 ~ 3dB, but the effect on more than 4000Hz for noise control is poor, not suitable for high-frequency noise reduction; put plywood on the ceiling after the band can 5000Hz noise reduce 1.75dB, in 5000 ~ 10000Hz down 0.4dB; On the coat rack, rear partition and the damping layer increasing absorption material can reduce noise, especially for high-frequency part of the noise reduction, the effect is remarkable; on the engine compartment wall to add damping materials can reduce the car interior noise, it makes the Tune average dropped 2dB; the middle-noise noise control materials of car body material and material thickness of the inner layer is not thicker which is the better, it should be, as the case may be; the thickness of damping and choice of damping material have a great influence on interior acoustic noise of pressure class, it should be noted that how to use the damping layer body.The work above provides some guidance and reference on how to use SEA and Autosea to carry through noise-vibration study, how to effectively reduce the noise level of passenger car.