Vibration And Noise Characteristic Analysis And Noise Reduction Improvement Design Of A Motorcycle Engine Cylinder Head

Motorcycles are mostly single-cylinder engines,so noises caused by the engine are bothering people to a larger extent.With the increasing demand of humans for sound quality,how to reduce the radiated noise of the engine has attracted more and more motorcycle manufacturers ’ attention.Starting from this point,this paper combines with a product produced by a company,using an engine of a motorcycle 150 CC as the research subject,and the characteristics of vibration noise are analyzed,and the effective measures to improve the surface radiation noise are put forward.Firstly,In this paper,the near-field noise test on the surface of a motorcycle engine is carried out.The sound pressure spectrum of 6500 rpm is analyzed,and the noise pressure value of 2500 ～ 5000 Hz in middle and high frequency is determined Then the near-field sound intensity test of the engine was carried out and the noise source of the engine was determined.Secondly,a three-dimensional model of the cylinder head and a finite element analysis model are established,and the natural frequencies and vibration modes of the first six stages are calculated.Then,the experimental mode of cylinder head is obtained by hammering method.By comparing the calculation and experimental modal,the results of the two models match.Therefore,the correctness of the model is verified.Then,the simulation analysis of the noise radiation position of the cylinder head is carried out.this paper studies thelocation ofradiated noise caused by the cylinder head of the first-generation engine.Taking the maximum in-cylinder pressure of the engine,the maximum seating force of the intake valve seating force,the maximum seating force of the exhaust valve,and the maximum impact frequencyas motivating inputs,by using three different engine speeds of 4500 rpm,6500rpm,and 8500 rpm to the finite element model,this paper carries outthe vibration response analysis,calculates the surface vibration speed of the cylinder head of the engine,and gets the maximum vibration speed of the cylinder head surface,which is at 6500 rpm.Then,the sound intensity level of the noise radiated from the cylinder head surface is calculated by using the boundary element method with the vibration velocity of the cylinder head surface at 6500 rpm as the boundary condition.Through the cloud map of the radiated noise on the surface of the cylinder head,the main noise sources of the radiated noise are located at the intake and exhaust ports at both sides,as well as the spark plug and the rear heat sink.Finally,this article proposes improvement measures to reduce vibration and noise fromthe sound source of the cylinder head obtained by simulation: Increase the wall thickness of the connection between the cylinder head heat sink and the cylinder head body from 3mm to4 mm and 5mm respectively.The prediction and analysis of the noise radiation of the two countermeasures are carried out,a scheme with a wall thickness of 5mm is obtained.Engine in the 2500-5000 Hz this band of the largest decline,for about 10 d B.Therefore,the adjustment scheme with 5mm wall thickness is selected.At the same time,through the engine near-field noise test,the radiated noise of the improved cylinder head is reduced by 7-9d B compared with the original engine in the middle and high-frequency range of 2500-5000 Hz.Also,the maximum operating temperature of cylinder head,the maximum power and the maximum torque of engine can meet the requirements of relevant engine enterprise specifications(standards).The improvement is remarkable.