Local Deformation of Hollow Crankshafts under Transient Conditions and their Effect on Durability and Slider Bearing Behavior 2017-01-1331
This paper describes a numerical study of the effect of hollow crankshafts on crankshaft local strength and durability as well as slider bearing contact behavior. Crankshaft dynamic simulation for durability is still a challenging task, although numerical methods are already worldwide established and integrated part of nearly every standard engine development process. Such standard methods are based on flexible multi-body dynamic simulation, combined with Finite Element analysis and multi-axial fatigue evaluation. They use different levels of simplification and consider the most influencing phenomena relevant for durability.
Lightweight design and downsizing require more and more detailed methods due to higher deformation of the crankshaft. This is especially true for hollow shafts, as present in motorsport design or aerospace applications, but also for standard engine having high potential for significant weight savings. Here the local deformation of shaft cross section under dynamic loads during the transient working cycle cannot be neglected, as currently done by typical standard simulation methods. Those use simplifications on coupling the crankshafts to the engine block structure by the bearing models, especially in how the bearing model is connected to the shaft structure. By that, the cross section is artificially stiffened and load introduction is locally not correct. In presented work, accuracy of elasto-hydrodynamic model in slider bearings is improved by considering fully elastic surface-to-surface contact between hollow pins and connecting rods, as well as journals and engine.
The present investigation presents a comparison for a Diesel engine inline 4-cylinder crankshaft to the standard approach and discusses the necessity of using surface-to-surface elasto-hydrodynamic slider bearing model. The main goal of this investigation is the evaluation of durability of the bore regions for hollow crankshafts where the crank pins and/or main journals have mass reduction bores. Focus is set on crankshaft strength in fillets and the mass reduction bores. In addition, the influence of the design/modeling on the slider bearings behavior is evaluated.