Numerical study on reducing methods of static strain along the fillet on upper deck of diesel engine cylinder block

Large static strain appears on the fillet on upper deck of diesel engine cylinder block by tightening force of cylinder head bolts. Reducing static strain is necessary to avoid the crack initiation on the fillet. The static strain along the fillet can be reduced, for example, by modifying the depth of thread engagement, and modifying the bead shape and position into the bore grommet of cylinder head gasket. In the present study, the depth of thread engagement was optimized considering four conditions, the overall magnitude of strain, the circumferential fluctuation of strain, the change rate of strain against the depth of thread engagement, and the length of cylinder head bolt. The bead shape or position was optimized considering two conditions, the overall magnitude of strain, and the distribution of contact pressure on the contact area with the cylinder block and the cylinder liner. The analysis results of the circumferential distribution of static strain were agreed with the measurement results. The optimum depth of thread engagement of cylinder head bolt and the optimum type of the cylinder head gasket were evaluated using FEM.