The Improvement Of Motorcycle Engine Vibration Noise

OHV engine has a certain occupancy rate in the Chinese motorcycle market due to its advantages,such as good durability and convenient maintenance.With the increasingly strict noise laws and regulations and higher demands of users to driving noise and comfort,taking a mass-produced prototype engine as the research to analyze the problems of engine idle-speed noise and high-speed noise that users complain.The conclusions of the paper are as follows:(1)Through the combination of subjective evaluation method and near-field noise test,the reason of thermal engine idling abnormal sound is valve clearance enlargement.The near-field noise test and vibration test are used to analyze that the cylinder head heat sinks vibration of the II generation engine(the faulty engine)is larger than that of the I generation engine,resulting in engine high-speed noise.(2)Through theoretical calculations,it is found that the cause of the increase of the valve clearance is the material of the pusher being hot-rolled round steel with low thermal expansion coefficiet.Aluminum alloy material with large thermal expansion coefficient is used to improve the idle-speed noise of the engine being 66 dB,which is reduced by 2dB.The problem of the engine idle-speed noise is then solved.(3)The finite element model of the cylinder head is established the error between the calculated model and experimental model of the cylinder head is within 3.5%,which proves the correctness of the finite element model.The maximum bursting pressure of the engine and the seating force of the intake and exhaust valves,and the impact frequency are taken as excitations and input into the finite element model for the vibration response analysis of the cylinder head.The maximum vibration speed of the prototype cylinder head is large.When the position is at the top of the combustion chamber,and the normal vibration velocity of the peripheral heat sink is also large,indicating that the heat sink of the cylinder head is subjected to high frequency vibration caused by the impact of the mechanical parts,and resulting in the cylinder head high frequency radiation noise.By reducing the length of the cylinder head heat sink and adding two reinforcing ribs and setting ventilation channels,the maximum vibration speed of the modified cylinder head is reduced by 14.5% compared with that of the prototype cylinder head;and the normal vibration speed of peripheral heat sink have a 57% lower than that of the prototype cylinder head.Hence,the vibration of modified cylinder head behaves better than the prototype.In the middle and high frequency region,the radiation noise of the improved cylinder head is reduced by 2-8dB compared with the prototype.The engine temperature field also meets the requirements of the enterprise standard.The performance ofengine and vehicle are comparable to the prototype,and the improvement is remarkable.After the improvement of engine,we apply it to a certain motorcycle and put on the market.The sales volume increase steadily.The surveyed users generally reflecte that the engine idle-speed noise and high-speed noise are decreased than before,and the sales outlets do not receive a complaint about high engine noise.The method of combining the actual vehicle test and numerical simulation technology is used to discuss the above contents and form a relatively complete research idea.The subject focuses on the actual situation of the market problems,and has some reference significance for the current domestic work in vibration and noise improvement.