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The film-forming, friction, and antiwear properties of zinc dialkylphosphates (ZDPs) were investigated and compared with the corresponding zinc dialkyldithiophosphates (ZDDPs). The primary ZDPs generally show similar friction and antiwear performance to the primary ZDDPs, although some differences are seen between them in film-forming properties. For the secondary ZDP and ZDDP, there are some clear differences in their tribological properties. This indicates that the properties of the primary ZDPs and ZDDPs may be controlled predominantly by adsorbed films consisting the intact additives and/or their decomposition compounds, and that the properties of the secondary ones may be controlled by glassy reaction films consisting zinc/iron polyphosphates.

A study has been made of the lubricant film-forming properties of viscosity index improver-containing oils in non-steady state, high-pressure contacts. Two types of non-steady speed condition have been investigated, sudden halting of motion and cyclically-varying entrainment speed. Film thickness has been measured in a ball on flat contact using ultra-thin film interferometry. It has been shown that viscosity index improver polymers in solution exhibit an enhanced squeeze behavior during halting and a viscoelastic response to acceleration/deceleration.

The efficiency of lubricated machine elements such as transmissions, crankcase engines, and hydraulic pumps depends strongly on the friction properties of the lubricant employed. For the design of modern, highly efficient lubricants it is thus essential to understand the influence of the components of the lubricating fluid in terms of film formation and consequent friction. The influence of Polyalkylmethacrylate (PMA) Viscosity Index Improvers on those important parameters has been studied by means of optical interferometry and friction testing. Low friction coefficients and positive contributions to the boundary film thickness of the lubricant were obtained when composition and architecture of the polymeric VII were appropriately designed.

Fuel economy has become the dominant criterion in the design of new automobiles. The globally enacted targets for fleet average emissions pose true challenges to automobile manufacturers. Increasing fuel economy requires enhancements both in hardware as well as in lubricant performance. As a key component of the lubricant, poly(alkyl methacrylate) PAMA viscosity index improvers have been identified as crucial design element due to their multiple modes of action. In their original application, they serve the well-known mechanism of polymer coil expansion at high temperatures and collapse at low temperatures. They help to flatten the viscosity/temperature relationship of the lubricant and allow for reduced low temperature viscosities and reduced internal friction, which directly translates into fuel economy. In addition to this bulk application, interfacial tribological phenomena contribute significantly to efficiency and fuel economy.

The High Frequency Reciprocating Rig (HFRR) commonly used to measure the friction and wear properties of diesel fuels has been modified to study gasoline lubricity. Wear tests have been carried out on a range of gasoline and diesel fuels. The non-additised gasolines tested all give higher wear than severely-refined Class I diesel fuels. The effect of relative humidity on the wear properties of both gasoline and diesel fuels has been compared. Both types of fuel give wear behavior which is almost independent of water vapour pressure down to 0 8 kPa, but show a reduction of wear below this humidity level. In practice most gasoline fuels contain detergent additives. The influence of two commercial gasoline detergent additives of different structure on gasoline lubricity has been studied. Both additives reduce wear, to an extent which is dependent upon additive concentration and also upon the base fuel.

Recent work in the literature has suggested that the poor performance in the ASTM Sequence VI fuel efficiency test may result from an inappropriate balance of ZDDP antiwear agents. This paper describes a study of the friction behavior of ZDDPs. Two recently-developed techniques have been employed to chart the variation of film thickness and friction of ZDDP-containing oils from the EHD through to the boundary lubrication regimes. It is shown that some secondary ZDDP additives give significantly higher friction coefficient in the mixed EHD/boundary regime at temperatures above 80 °C. This behavior is very similar to that seen using formulated ASTM Sequence VI reference oils. Film thickness measurements show that the onset of high friction seen with the ZDDPs correlates with the formation of a solid-like reaction film in the lubricated contact.

Recent work by the authors has indicated that some types of viscosity index improver polymers can form thick boundary films in lubricated contacts. These films appear to result from the adsorption of molecules of polymer on metal surfaces to produce layers, about 20 nm thick, having higher polymer concentration and thus higher viscosity than the bulk solution. In the current paper it is shown that these VII boundary films are able to separate rubbing surfaces in both rolling and sliding contacts and that they make a significant contribution towards reducing friction and wear at temperatures up to at least 140°C. The mechanism by which these polymers reduce friction and wear is elucidated.

A progressive reduction in the permitted level of phosphorus in lubricating oils, coupled with concern to maintain engine and transmission durability, means that it is becoming increasingly important to understand the detailed mechanism of antiwear additive behavior. This paper describes a new experimental technique, which is able to measure both the thickness and distribution of antiwear additive films in rolling/sliding contacts. This enables the kinetics of antiwear film build-up to be investigated and the influence of the reaction film on friction and wear to be monitored. In the current paper, this technique is used to compare the film-forming behavior of ash-containing and ashless antiwear additives.

Polyalkylmethacrylates (PAMAs) are widely used as viscosity index improvers and dispersant boosters in engine, transmission and hydraulic oils. They have been shown to be able to adsorb from oil solution on to metal surfaces, to produce thick, viscous boundary films. These films enhance lubricant film formation in slow speed and high temperature conditions and thus produce a significant reduction of friction and wear. In a recent systematic study a range of dispersant and non-dispersant PAMAs has been synthesized. The influence of different functionalities, molecular weights and architectures on both boundary film formation and friction has been explored using optical interferometry and friction-speed charting. From the results, guidelines have been developed for designing PAMAs having optimal boundary lubricating properties. In the current paper the film forming, friction and wear properties of solutions of two functionalised PAMAs is first described.