Research On Modification And Dynamic Characteristics Of Timing Gear System In High Power Diesel Engine

During the strengthening process of high power density diesel engine,the increase of explosion pressure,rotating speed and power results in the increase of load of accessories such as valve train,oil pump,water pump and fuel injection pump,as well as the increase of crankshaft speed and torque fluctuation.This puts forward higher requirements for the performance of timing gears.This paper takes the timing gear system of a 12V150 high power diesel engine as the research object.Two kinds of modification schemes are proposed for the intermediate gear pair of timing gear system,and the vibration characteristics before and after modification are compared and analyzed.In addition,taking the crankshaft gear pair of timing gear system as the research object,the phase tuning theory of planetary gear is introduced into the crankshaft gear pair,and the maximum displacement and load sharing coefficient of peripheral idler gear in different angle arrangement are analyzed.In order to provide theoretical guidance for the modification and the installation angle arrangement of multiple pairs meshing of gears in the timing gear system.Based on the Romax software,the dynamic model of timing gear system is established.Taking the intermediate gear pair as the research object,the load on the tooth surface under the transmission error excitation is analyzed,and two modification schemes are proposed.Taking the size and distribution of the load per unit length of the tooth surface as the standard,the intermediate gear pair is modified.the peak to peak value and fluctuation amplitude of the transmission error,the size and distribution of the load per unit length of the tooth surface and the vibration acceleration are compared and analyzed before and after the modification of different schemes.The dynamic model of the crankshaft gear pair is established based on the gear dynamics theory.Introducing the theory of planetary gear phase tuning into crankshaft gear pair.The effect of the meshing stiffness,meshing damping,tooth backlash and meshing error of including the phase coefficient on the maximum vibration displacement and load sharing coefficient of the timing gear system are analyzed,and the influence law of all time-varying factors including the phase coefficient on the maximum vibration displacement and load sharing coefficient is also studied.The results show that the time-varying factors of including phase coefficient have important effects on the maximum vibration displacement and the load sharing coefficient.Among them,the meshing error is the largest effect factor,the meshing stiffness and backlash are the second,the meshing damping has almost no effect.When all time-varying factors are considered,with variation of the angular,the difference of the maximum displacement and its minimum value is 6.9% and the difference of the maximum load sharing coefficient and its minimum value is 11.8%.In addition,the maximum displacement and the load sharing coefficient take larger values when the phase coefficient is around 0.3 and 0.7,and take smaller values when the phase coefficient is around 0.5 and 0.5,or 0.97 and 0.03.The research results provide the basis for the optimization of installation angle and phase coefficient of strengthening diesel engine,so as to improve the vibration characteristics of timing gear system.