Research On Cam Wear Of OHC

Valve train is an important part of engine, while the camshaft is the key part of valve train. Thecam and tappet, which always work at high temperature, high speed, variable load and poorlubrication conditions, are contact in high pair. Its main failure form is wear that will directly affectthe function of valve train and the performance of engine. So, study on the wear and reliability ofcam is necessary. At present, the research on cam wear of OHC was less and not enough systematic,especially the load of cam was lack of experimental date support and a uniform methodology andconclusions.In view of the problem in recent study of cam wear of OHC, in this paper, firstly, it willcalculate the cam loads base on valve train dynamic experiment what had been done earlier by fourdifferent methods and analyze the difference between them. Secondly, it will compute the camcontact stress by modified Hertz contact stress formula. At last, it will reckon the fatigue wear lifeand adhesive wear loss of the cam. The main contents and conclusions are as follows:(1)The valve test bench was designed and built, which included installing the strain gages,laser displacement sensor and acceleration senor. Valve train experiment was done by collecting thesignal of valve acceleration, valve displacement and rocker arm loads. In addition, the test of camprofile and rocker arm stiffness was finished.(2)Put forward one method to calculate cam loads by rocker arm loads, then, the structure andmotion parameter of valve strain was calculated, which was combined with test date to computecam loads by valve loads and rocker arm loads. After analyzing the difference between two methods,it showed that the cam loads result came from rocker arm loads was much better.(3)Single mass dynamic model of valve train was established by writing relative program inVisual C++, was used to calculate cam loads. Multi-rigid body dynamic model was built in Adamsto solve the problem and it showed that the cam loads calculated by this way was much closer toreality.(4)Correction of Hertz contact stress formula by principles of tribology and calculation ofcurvature radius of cam and roller contact points, which was used to calculate the cam contact stressfinally. The result exactly shows the variation of cam contact stress with the speed of camshaft.(5)In this paper, fatigue wear life was reckoned base on modified Miner linear fatigue damagecumulation theory and the S-N curve of cam materials. A new method of calculating the roller’ssliding ratio was put forward to estimate adhesive wear loss of cam at different speed, which wasbased on Archard wear loss theory. The theoretical prediction can provide reference for practical engineering.