Anti-wear additives influence upon hydrodynamic friction mode parameters in bearings of internal-combustion engines

Abstract

An essential condition to ensure an engine life having 300,000 – 1 000,000 km according to race consists in assurance of a minimum wear rate of crankshaft bearings. For such units as connectingrod bearings a maximum allowable value of bearing brass wear makes 100 mkm which corresponds to an integral linear wear intensity of 10-14 …10-13 that is possible only at a hydrodynamic mode of friction actually at all modes of engines operations. Ensuring liquid friction in all range of contact pressures is achieved both through design methods, and technological ones. To the latter belongs first of all the application of lubricants with high wearresistant properties. In this connection arises a problem to reveal a mechanism and degree of the effect of lubricant components upon a range of contact pressure where liquid friction is realized. This paper reports the experimental evidences of the increase of contact pressures at which is achieved a minimum value of a constant of friction at the introduction in lubricant a standard wear-resistant additive – dialkyldithiophosphate of zinc (ZDDP). So, at the introduction in coal oil without additives I-20A (viscosity type ISO 32) 1.25 and 2.5% ZGGP maxi-mum contact pressure at which is realized a hydrody-namic mode of friction increases by 1.8 and 2 times accordingly. Because of impossibility to explain experimental data by a chemical interaction of ZDDP with surface material of tribo-coupling there is offered and substantiated a mechanism of ZDDP influence upon rheological parameters of lubricant in a separation layer. A rheological model allowing the computation of the wearresistant additives influence upon a value of hydrodynamic pressures in a lubrication layer is of-fered. The idea of the initiation by a wearresistant additive of multimolecular adsorption of lubricant on the surface of tribocoupling may be used for the optimization of ZDDP structure and also for the prognostication of changes in pressure coefficient of viscosity in a lubrication layer.