Valve trains are highly burdened powertrain subsystem which has to undergo high fatigue cycles during its service lifespan. Wear enhances valve lash thus depreciating the performance drastically. Analytical advances have helped engineers to predict parameters such as wear, contact stresses, lubrication etc. to uphold the durability of valve train components. Most of the genset and industrial engines running at medium speed use type 5 valve train. In this paper, our study involves about crack induced “wear” due to Hertzian stress on rocker toe and the process followed to resolve the problem for a medium speed diesel engine
We experienced the problem of rocker toe crack resulting in toe wear in field and on test bed. Our investigations led us to evaluate the life of a rocker toe by specifically developing a test cycle to reproduce the wear due to induced cracks as well as to assess the durability. A procedure is developed to characterize the rocker toe wear including dimensional, geometrical, profile measurements along with metallurgical assessment. Thus, the wear characteristics were studied in detail from toe profile and materials viewpoint. A root cause diagram is made to arrive at various affecting parameters in rocker toe wear.
Based on the above, a one dimensional kinematic simulation model is used to improve the cam profile design and to study the sensitivity of rocker forces on valve tip with respect to engine speed. A novel approach of two layer modeling of Hertzian stress is carried out in FEA. The relationship between simulated and experimental results is established.