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4 Versus 8 Counterweights for an I4 Gasoline Engine Crankshaft - Measurements of Vibration and Bearing Wear
Abstract:
The authors have published SAE paper 2008-01-0088 on the analytical comparison between 4 and 8 counterweight crankshafts for an I4 gasoline engine. This paper showed that for a particular design of a 4 counterweight crankshaft, the differences in bearing force and oil film thickness were very small and the only major difference in terms of bearing shaft tilt angle occurred at mains 2 and 4 (increase of ∼20% compared with 8 counterweight version). The 4 counterweight crankshaft has a significant mass advantage as it was 1.42kg lighter than the 8 counterweight crankshaft.
This new paper addresses the testing performed to validate the analysis results in bearing durability by subjecting the engine to a mixture of high speed and general durability cycles. A comparison was made on the bearing conditions after running a total of 100 hours through prescribed durability cycles on a gasoline engine with both 4 and 8 counterweight crankshafts. Visual bearings inspection and bearing wear measurements were performed on all main bearings and torsional displacement measurements were also made. The torsional vibration measurements were used to correlate the 3D dynamics model of the crankshaft. In addition, the effects of 4 and 8 counterweight crankshafts on the cylinder block and bedplate vibration were also investigated.
This paper concludes that by using the crankshaft counterweight design strategy proposed in 2008-01-0088, it is possible to achieve acceptable bearing durability of a 4 counterweight crankshaft for an I4 gasoline engine while also gaining a significantly lower mass than the 8 counterweight version of the crankshaft for the same engine.