Effects of Crank-Pin Surface Circumferential Waviness on the EHL of a Big-End Bearing in a Diesel Engine

Abstract

The effects of crank-pin surface circumferential waviness, also known as journal lobing or chatter in engineering terms, on bearing performance have been investigated by carrying out an elastohydrodynamic lubrication analysis. The big-end bearing in a 2.0 liter diesel engine has been used for the study. The operating condition is that of maximum torque with engine running at 1800rpm. The crank pin has been assumed to have 2, 3, 5, 9, 15, 30 and 50 lobes. Sufficiently fine meshes have been used to model the lobe profiles. Solutions cover a large range of lobe amplitude and lobe orientation angles. The results show that journal lobing has adverse effects on the bearing's lubrication performance because it severely reduces the oil film thickness and significantly increase the oil film pressure. The combination of large lobe numbers and big lobe amplitudes is particularly detrimental. The only exception is that a 2-lobe journal can have some beneficial effects when the orientation angle is within a range of 90°-105°. Therefore lobe number and lobe amplitude must be carefully controlled to avoid any potential catastrophic damage.