Research On Noise Source Identification And Noise Control Technology For Medium Excavator

Excavator is one of the most important earthwork construction machinery,which plays an important role in the civil economic construction.China has become the largest excavator market in the world,especially the medium-sized excavator,which accounts for the largest proportion of market sales,and has fierce competition in the international market.Compared with international benchmark excavators,the noise level of domestic medium-sized excavators has a large gap.Due to the complex working conditions and harsh working environment of excavators,operators will be affected by long-term noise during operation,which will cause serious damage to their physical and mental health.Therefore,the international market has strict access standards for excavator noise control,and strict limits for the main indicators measuring the noise level of the whole excavator-the external emission sound power and the noise near the left and right ears of the cab.In the increasingly fierce market competition,reducing the noise level of excavators has become an important task for domestic excavators to improve their product competitiveness.Taking a medium-sized excavator made in China as the research object,aiming at the problems that its noise level cannot reach the European and American standards and it is difficult to enter the international high-end market,the paper conducts research on the key technologies of excavator noise control,and proposes an optimal design scheme for excavator noise control on the basis of revealing the formation principle and influencing factors of the noise such as the aerodynamic noise of the cooling fan,the exhaust noise of the exhaust system,and the noise near the ear in the driving room,It can effectively reduce the emitted sound power outside the excavator and the noise near the left and right ears of the cab.The main work of this paper includes:(1)The test methods for measuring the external acoustic emission power and indoor noise level of excavators were developed,and the external acoustic emission power and indoor noise level of international market benchmark models and domestic research prototypes were compared.The national standard for noise limit of construction machinery is relatively loose compared with the European standard.Similarly,the noise limit of the European standard for engine power is1.5d BA higher than the national standard.There is a certain gap between the research prototype and the benchmark vehicle in terms of overall noise control.The main noise sources of the excavator’s external emission sound power are the engine,fan and main pump,and the contribution of the noise source is different under different working conditions.The main noise sources near the ear of the cab are fan,exhaust noise and engine noise.In addition,according to the coherence function analysis,it is found that the cab glass and panel structure vibration have a great correlation with the indoor noise.(2)The research on the causes of aerodynamic noise during the working process of the cooling fan and the optimization and validation of structural parameters were carried out,and the fan structure fluid acoustic emission multi field coupling model was established,revealing the influence of key structural parameters such as the number of fan blades,the radial clearance between the fan and the shroud,the axial relative position,and the shroud clearance on the aerodynamic noise;A structural optimization design method for the number,size parameters and installation distance of cooling fans with minimum fan noise is proposed.Research shows that the proposed method can effectively reduce fan aerodynamic noise.(3)The acoustic transfer matrix of exhaust system muffler is established,and the frequency domain of muffler structure optimization is obtained.Through mathematical modeling,numerical analysis and experimental verification,the influence of key muffler units on acoustic transmission loss is systematically studied;Based on the orthogonal experimental method,the structural parameters of the muffler are optimized.The installation test results show that the proposed optimization design scheme can effectively reduce the exhaust noise while ensuring the pressure loss level,and achieve the goal of reducing the near-field sound pressure level of the exhaust port by 2.2 d BA at 1meter distance.(4)The acoustic vibration coupling mathematical model of the cab enclosure is established,and the calculation method of the contribution of the cab panel structure to the noise near the cab drivers’ ear is proposed.Based on numerical simulation and experimental verification,the order of contribution of different panels to ear side noise is constructed based on the actual typical working conditions of excavator.Based on the multi-island genetic intelligent optimization algorithm,the thickness and damping of the cab panel structure are optimized,and the sound pressure near the cab ear is reduced by more than 1.25 d BA.The above optimization design method is applied to the research prototype,and the test results verify the effectiveness of the scheme.The results show that the comprehensive application of the optimized cooling fan,muffler,panel structure and damping make the external emission sound power(102.3d BA)of the research prototype lower than that of the benchmark prototype,meets the requirements of the European Noise Directive(103.4d BA),and the cab ear noise(70.3d BA)is lower than that of the benchmark prototype(72d BA),which significantly improves the product performance and market competitiveness.