Research On Prediction Model Of Engine Valve Fatigue Life And Its Calculation Method

Valve is an important component part of the engine valve mechanism, to ensure that the engine can get good economy, dynamic, reliability and durability. With further optimization of the engine structure, the engine size reduced and power increased, thus make the engine valve working environment worse, and engine valve especially exhaust failure become increasingly significant problem.This paper analyses the failure form of engine exhaust on the basis of expounding the present research methods and achievements about engine valve failure, and make a discussion on the reason of failure about the engine exhaust second hot position:It make the exhaust valve material structure change and the resist of fatigue ability to drop because of the special working environment with high temperature waste gas erosion for long-term, leading to premature fatigue failure of the exhaust. For a variety of reasons may also lead to exhaust in abnormal working state, in engine exhaust in offset or partial pendulum working condition, the stress of the exhaust gets more complicated, it makes the exhaust fatigue fracture more likely to occur in working status about frequent open and close.A model of the engine valve, valve seats and catheter component to analyze stress form of the exhaust under different working conditions has been developed based on ANSYS and through the related fatigue estimation theory to estimate the exhaust s-n curve, and to calculate the loading spectrum of the2nd hot point corresponding with the pressure in the engine cylinder as well the exhaust accumulative total fatigue damage rate. At the same time, it’s more intuitive to study the life of the engine exhaust from the results of fatigue simulation analysis of engine exhaust based on nCode DesignLife software. Results shows that:there are high bending stress at the2nd hot point of engine exhaust valve, and their peak values are respectively happened at combustion impact and the closing impact cases, but the effect of the stress at combustion case on fatigue damage rate is higher than that at closing case. Research also shows that:the fatigue life of the2nd hot point of engine exhaust valve under normal working condition is infinite, but the abnormal condition greatly affects its fatigue life. The relationship between engine working parameters and the exhaust fatigue life also be discussed in this paper based on some examples.