Crankshaft Durability Prediction - A New 3-D Approach 920087
New engines must satisfy conflicting customer requirements of higher performance and better fuel economy. These requirements have led us to more sophisticated analyses of crankshafts which must withstand higher gas forces and higher speeds while reducing their contribution to total engine friction.
To face this challenge, the designer needs improved tools to predict friction, dynamic response and durability. It is the problem of crankshaft durability prediction that will be addressed in this paper.
A new crankshaft durability assessment tool has been developed by RENAULT, based on a completely 3-D mechanical analysis. Each step of ‘classical’ durability assessment has been improved. Load calculations include rotating external bearing loads, torsional vibrations and internal centrifugal loads. Stress calculations involve initial 3-D FEM analysis followed by a local BEM fillet zoom technique. Fatigue prediction is made using the multiaxial Dang Van criterion, and fatigue data are obtained through full scale materials testing consistent with the calculation tool.
This new tool allows the designer to optimize a crankshaft more quickly and with more precision than in the past. As an illustration, the design of a 1.9 liter turbocharged diesel engine crankshaft is presented.
Some discussion of remaining difficulties in fatigue life assessment, such as flywheel whirl or statistical aspects of fatigue are also developed in this paper.