Horizontal Diesel Engine Crankshaft Fatigue Life Studies

The crankshaft endures periodic variations of the cylinder pressure, reciprocating inertia force and rotating mass inertial force.Which can lead to alternating bending and torsional stress in the crankshaft. Because of this, the crankshaft may be fracture and damage. So, to guarantee sufficient fatigue strength of the crankshaft during the process of crankshaft designing is very important. In addition, the stiffness of crankshaft is also very important. The bending rigidity deficiency can exacerbate longitudinal vibration of the block and crankshaft, and bring additional stress, As a result, Deteriorate the working conditions of the connecting rod journals and the main journals. Decrease their fatigue life.Even the pistons and connecting rods can also be influenced. While, torsional rigidity deficiency will reduce the torsional natural frequency of the crankshaft system, which can lead to low-frequency torsional vibration during the working speed range of the engine;Increase crankshaft torsional stress; strengthen the noise and impact load to the driving mechanism. Directly affect the reliability and life of the high-speed internal combustion engine. For these reasons, To improve the working life and reliability of the crankshaft,it is very important to keep sufficient torsional rigidity, bending rigidity, fatigue strength of the crankshaft.In this paper, Based on a two cylinder diesel engine, the detailed finite element model of the Crankshaft, connecting rod and block are established, and subsequently, we do the experimental modal analysis and finite element modal analysis to test and verify the validity of the finite element model and multi-body dynamics model of the crankshaft system.and then, Considering the effects of Hydrodynamic Lubrication, The multi-body dynamic simulation of the crankshaft system and connecting rod-piston pair is carried out by using EXCITE-Power Unit software, According to the calculation results, extract the dynamic load that is obtained by the dynamic simulation. And get a working cycle dynamic stress of the crankshaft. Multiple-spindle fatigue analysis on crankshaft dynamic stress is post-processed with Nsoft5.3software. Finally, in view of the double cylinder horizontal diesel engine crankshaft researched in this paper, make Structural optimization design to give advice for further improvement of the crankshaft system.The results show that:Fist, the minimum oil film thickness of the main bearings is greater than lum, no contact occurs, and meet the design requirements; In addition, the peak oil film pressure of the main bearings is in the allowed range, fatigue spalling will not happen to the working surface of the bearing.Second, the maximum stress of the crankshaft is210MPa,which is in its allowable range; Crankshaft deformation is0.307mm, which is located in the flywheel end; Each cylinder explosive moment, the maximum stress of the crankshaft may easily occur in the fillets which connect the crank arm and the main journal,crank pin. Therefore, for the structure design and optimization of the crankshaft, more importance should be paid to the fillets.Third, the minimum fatigue life of crankshaft is1.6367E10, which is beyond safety design. On the basis of crankshaft fatigue strength, a structure optimization of the crankshaft is carried out to decrease its life to3.3171E9, meanwhile, crankshaft quality reduces0.5kg.