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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.

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.

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.

Lubricating films were deposited on friction test specimens from a homogeneous gas phase mixture of nitrogen and various lubricant vapors. The lubricants used were tributylphosphate ester (TBP), tricresylphosphate ester (TCP), trimethylolpropane-triheptanoate ester (TMPTH) and mix-bis-(m-phenoxyphenoxy)benzene (PPE). The volume percent of lubricant vapor in nitrogen ranged from 0.5 to 3.0 percent. The friction tests were performed over a temperature range of 245 to 586°C. The lubrication properties of vapor deposited films were found to be controlled by the specimen temperature, vapor exposure time, lubricant vapor concentration and lubricant chemistry. Lubrication of the tribocontact can be optimized by using the deposition parameters to give the optimum film thickness for a given lubricant.

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.

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.

This paper describes the development of a thin film rheometer able to measure the viscosity of lubricant films of the order of 200 μm thickness on flat, solid surfaces. The rheometer consists of a small cylinder mounted on a piezo bimorph which is divided electrically into two halves. When an AC voltage is applied to the one half of the piezo it causes the flat surface of the cylinder to oscillate in its own plane with an amplitude of a few microns. This motion produces an AC output from the other half of the piezo. The flat face of the cylinder is held parallel to an oily test surface and the latter is supported on a micrometer stage so that the gap between the two surfaces can be adjusted. As the gap is narrowed the oil film dampens the sinusoidal motion of the cylinder and the extent of this damping can be used to determine the viscosity of the oil film between the surfaces.