Dynamic Analysis of Engine Bearings

H Hirani,S Biswas,K Athre

doi:10.1155/s1023621x99000251

H Hirani, S Biswas + Show 1 more

Open Access

https://doi.org/10.1155/s1023621x99000251

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Abstract

This paper presents a simple methodology to evaluate the stiffness and damping coefficients of an engine bearing over a load cycle. A rapid technique is used to determine the shaft ‘limit cycle’ under engine dynamic loads. The proposed theoretical model is based on short and long bearing approximations. The results obtained by present approximation are compared with those obtained by numerical method. The influence of thermal effects on the stiffness and damping coefficients is predicted by using a simplified thermal analysis. In order to illustrate the application of the proposed scheme, one engine main bearing and a connecting rod bearing are analysed.

Highlights

The most convenient way to analyse a complete system is to divide it into separate sub-systems or sub-structures (Parszewski, 1989), analyse each sub-system individually with less time-consuming methods, and assemble into the whole system
The gas force due to combustion/compression pressure in the engine cylinder and inertia forces due to reciprocating and unbalanced rotating masses contribute to the engine bearing loads
The dynamic coefficients can be determined by using Reynolds equation with a first order pressure perturbation (Lund and Thomson, 1978)

Summary

INTRODUCTION

The most convenient way to analyse a complete system is to divide it into separate sub-systems or sub-structures (Parszewski, 1989), analyse each sub-system individually with less time-consuming methods, and assemble into the whole system. The behaviour ofthe rotor-bearing system becomes non-linear and to study rotor-bearing dynamics a complete nonlinear transient simulation is used Such an analysis involves the simultaneous solutions of dynamic Reynolds equation and equations of motion, for locating the journal centre at each time step. The dynamic coefficients can be determined by using Reynolds equation with a first order pressure perturbation (Lund and Thomson, 1978) This gives five equations, one for pressure and other four for partial derivatives of pressure with respect to rotor displacement and velocity components. In the present study remaining four equations (Reynolds equation for pressure with perturbation of displacement and velocity components) are solved for short and long bearing approximations. In the present study a simplified thermal analysis is used which is rapid and provides reasonable predictions of the performance

THEORY

THERMAL ANALYSIS

-4. RESULTS AND DISCUSSION