ANALYSIS OF CONNECTING-ROD BIG-END BEARING OF AN INTERNAL COMBUSTION ENGINE

Abstract

The connecting-rod big-end bearing, which is subjected to a complex dynamic loading, is an important component of an internal combustion engine. Gas force, inertia force due to the reciprocating masses (Piston,.gudgeon pin, and small-end of the connecting-rod) and the centrifugal force due to the rotary mass of the connecting-rod big-end, contribute to the total load experienced by the big-end bearing, which varies in magnitude and direction. The relative speed of the bearing with respect to the crank pin is also variable. These factors make the analysis and design of the big-end bearing quite complex. The existence of the fluid-film at all crank angles, consistent with its required minimum thickness in the clearance space of the big-end bearing, is imperative to obviate unnecessary wear and enhance the life of the system. Time history of the minimum film thickness depends on the motion of the bearing centre which has been studied- by various investigators. A review of the available literature on the studies of the big-end bearing is presented in Chapter 1. The literature indicates that some aspects of the big-end bearing analysis need further studies. With this view point, studies were planned in the area of the big-end bearing analysis to include the temperature and pressure (piezo-thermal) effects on viscosity, non- Newtonian lubricant characteristics, misalignment of the bearing and pin axes, effect of grooves, and deformation of the bearing body. Navier-stokes equations are used in the analysis instead of the traditional Reynolds equation so that variations of viscosity may be V accounted for piezoviscous, non-Newtonian and piezo-thermal effects. This thesis work presents the solution of the following problems. 1. Rigid bearing with isoviscous lubricants, 2. Rigid bearing with piezoviscous lunbricants, 3. Rigid bearing with the lubricants having piezo-thermal effects on viscosity, 4. Rigid bearing with non-Newtonian lubricants, 5. Rigid bearing (ungrooved) with axes(i) parallel and (ii) skewed, G. Elastothermohydrodynamic (ETHD) lubrication. The clearance space is discretized using three dimensional isoparametric elements by a mesh of 12x4x1 elements, each containing 20 nodes. Full Sommerfeld boundary condition is used to solve the Navier-Stokes equation and the continuity equation. To account for the cavitation effect, all the negative values of the nodal pressures are replaced by zero. At each crank angle interval, the pressure and velocity fields are established by solving the momentum and continuity equations in the cylindrical coordinates. The finite-element formulation based on Galerkin's method and a direct iterative technique is used. The boundary conditions are substituted at the element stage to reduce the computer storage requirements. The global system equations are solved with each respective column of the right hand side to evaluate the pressure field contributions due to wedge, squeeze, and whirling actions of the fluid-film. In the case of deformation calculation, the three dimensional deformations in the bearing body are obtained by using the forntal solution techinque to reduce the computer storage requirement. For the time marching scheme,Euler-Cauchy's predictor-corrector method is employed which is vi found more suitable in comparison to Runge-Kutta or higher-order predictor-corrector methods(such as Adams-Moulton) for this problem. The algorithm evolved in this work is general and can be used for the solution of any dynamically loaded circular bearings with isoviscous/piezoviscous/non-Newtonian lubricants, and can also handle piezo-thermal effects on viscosity. Using additional subroutines, the elastothermohydrodynamic effect is also studied. Deformations of the bearing body are computed using the hydrodynamic pressure developed in the fluid-film.