Friction modelling of tribofilm performance in a bench tribometer for automotive engine lubricants

Abstract

Research focusing on the initial stages of the development of an empirical model to predict friction in boundary and mixed lubrication conditions accounting for additive and surface interactions is reported in this article. The regression model was constructed by applying a fractional factorial design statistical approach. The model considers a typical friction modifier, molybdenum dithiocarbamate, in a model automotive engine lubricant also containing zinc dialkyldithiophosphate in a synthetic polyalphaolefin base oil under conditions representative of the cam and follower interface in an automotive engine. Operating temperature, sliding speed, load, initial surface roughness, and the initial lambda ratio were taken as the factors affecting tribological performance. The empirical model predicts friction at 95 per cent confidence level within the specific range of parameters considered in the experiments. Not surprisingly, molybdenum dithiocarbamate is mainly responsible for the reduction of friction of the tribofilm, whereas temperature, sliding speed, and load are the other significant parameters.

Friction modelling in an engine valve train considering the sensitivity to lubricant formulation

“…For lambda ratio <1.0 and contact pressure greater or equal to 0.2 GPa, boundary lubrication is assumed to be the dominant regime within the cam/follower contact for all conditions where the oil film thickness is less than the defined roughness value. The friction force in this regime is based on the tribofilm performance in boundary lubrication condition (F b ) [13]. Mixed lubrication is complicated to treat rigorously.…”

“…A regression model was obtained for the friction response of the tribofilm formed in boundary and mixed lubrication conditions and can be found in detail in reference [13]. The developed tribofilm friction response model was incorporated in the existing valve-train friction model in such a way that it represents additive performance in boundary and mixed lubrication conditions at the interface in a cam cycle.…”

“…Response surface methodology was used to obtain the friction response model as represented by equation (19), and was very useful for predicting the friction response of the tribofilms formed in boundary and mixed lubrication conditions [13]. The model was based on the assumption that there was no great effect of maximum pressure in isolation on the steady-state Table 3 Triboflim performance process parameters, initial lambda ratio, and friction response data [13,17] friction response of the tribofilm and is represented by five independent variables (initial lambda ratio 'λ', MoDTC concentration in the oil 'A', operating temperature 'C', sliding speed 'D', and initial surface roughness of block 'E')…”

“…The friction modelling of the tribofilm performance in the boundary and mixed lubrication conditions was empirically developed by establishing a relationship between the friction response data from a bench tribometer and the chemical sensitivity of the additives under operating conditions representative of the boundary and mixed lubrication conditions at the cam/follower interface [13].…”

Prediction and Analysis of Engine Friction Power of a Diesel Engine Influenced by Engine Speed, Load, and Lubricant Viscosity

“…He also predicted piston ring assembly friction loss under realistic fired conditions of a single cylinder gasoline engine using the indicated mean effective pressure (IMEP) method and validated the model through experimental study. Friction modeling of tribofilm performance was studied by Roshan et al [13] using statistical approach and response surface methodology (RMS). The developed model is based on a bench tribometer and is only pertinent to boundary and mixed lubrication.…”