| Lightweight design is an inevitable trend with the development of the automobile industry,requiring engine technology more and more towards the direction of energy-saving emission reduction.The camshaft,the key parts of Valve train which is an important component of the engine,working in high-speed high-temperature environment,wear seriously.It is urgent to prepare new materials with self-lubricating properties in high temperature environment to solve the problem.The new TiAl material which has a light weight,high strength and rigidity at high temperature,good anti-creep and high antioxidant properties,is the ideal alternative to traditional materials.The addition of self-lubricating components can reduce friction and wear by making it to self-lubricating at high temperature.In this paper,the new TiAl alloy was prepared.It was found that the new material could meet the requirements of the valve Lightweight Design of Valve Train by studying the tribological characteristics of the new material and the simulation of dynamic characteristics of the new TiAl alloy as the camshaft material.A new type of TiAl material was prepared by adding Ti44Al2Cr8Nb3V0.5B0.5Al2O3 as the matrix and adding BaF2-CaF2(62:38)co-crystal as solid lubricant.Measured the density of 3.545g/cm3,compared with the traditional carbon steel alloy materials,the same size parts weight reduce more than 50%;measured Rockwell hardness of 55 HRC,the hardness value is in line with the requirements.The results show that the new TiAl material is more suitable for high temperature working condition because the friction coefficient of the new TiAl material at high temperature is lower than that at room temperature.The friction coefficient is consistent with the change trend at both room temperature and high temperature,which decreases with the increase of speed and load,but this trend is more obvious at room temperature.The wear rate increases with the increase of speed and load,but the increase will reduce which trend is more obvious at high temperature.This is because the solid lubricant in the friction process gradually precipitated,play a role in reducing friction.The self-lubricating mechanism of the material is analyzed.It is divided into three stages at room temperature : the first stage of the lower temperature solid lubricant has not yet worked;the second stage,with the effect of friction temperature,solid lubricant began to precipitate to the friction surface toreduce friction effect;the third stage,the solid lubricant in the friction surface to form a complete lubricating film,play a role in lubrication.The mechanism of the wear of the material is discussed.It is found that the effective form of the friction surface is fatigue pitting and adhesive wear,and there is abrasive wear in the dry friction state.Taking the single mass model as an example,the analytical equation of the cam drive mechanism is deduced,and the analytical method is given.The cam contact stress check formula is deduced according to the Hertz contact theory.The modal analysis of the camshaft is carried out.It comes out that the new TiAl material is consistent with the trend of modal change of the traditional material,and the natural frequency does not coincide with the engine excitation frequency avoiding resonance.In a certain range,the natural frequency of each mode decreases with the increase of the speed,but with the further increase in speed,the natural frequency of each stage increased rapidly.The dynamic simulation of the valve train is carried out.It is found that the new TiAl material can reduce the contact force between the cam tappets and its displacement,velocity,acceleration curve meet the design requirements. |
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