William Barton

An Analytical Approach for Prediction of Elastohydrodynamic Friction with Inlet Shear Heating and Starvation

An analytical friction model is presented, predicting the coefficient of friction in elastohydrodynamic (EHD) contacts. Three fully formulated SAE 75W-90 axle lubricants are examined. The effect of inlet shear heating (ISH) and starvation is accounted for in the developed friction model. The film thickness and the predicted friction are compared with experimental measurements obtained through optical interferometry and use of a mini traction machine. The results indicate the significant contribution of ISH and starvation on both the film thickness and coefficient of friction. A strong interaction between those two phenomena is also demonstrated, along with their individual and combined contribution on the EHD friction.

Lubrication analysis and sub-surface stress field of an automotive differential hypoid gear pair under dynamic loading:

Film thickness and sub-surface stress distribution in a highly loaded automotive differential hypoid gear pair are examined. A 4-Degree of Freedom torsional gear dynamics model, taking into account the torsional stiffness of the pinion and the gear shafts, is used in order to evaluate the contact load, the surface velocities and the contact radii of curvature of the mating teeth during a full meshing cycle. The torsional gear dynamics model takes into account both the geometric non-linearities of the system (backlash non-linearity) as well as the time varying properties (contact radii, meshing stiffness) and the internal excitations caused by geometrical imperfections of the teeth pair (static transmission error). The input torque used for the study of the film thickness and the sub-surface stress distribution corresponds to the region after the main resonance, where no teeth separation occurs. The contact conditions predicted by the gear dynamics are used as the input for the elastohydrodynamic elliptical point contact analysis. The lubricant film thickness, the corresponding pressure and surface traction distributions are obtained quasi-statically using the output load of the dynamic gear pair model. The variation of the induced sub-surface stress field is determined throughout a meshing cycle. Based on the sub-surface reversing orthogonal shear stresses, marginal differences occur when the viscous shear on the conjunctional surfaces are taken into account, which are mainly influenced by the applied pressure distribution. The numerical prediction of lubricant film thickness agrees reasonably well with that predicted using the well-established extrapolated oil film thickness formulae reported in the literature.

A comparison of verdazyl radicals modified at the 3-position as mediators in the living radical polymerisation of styrene and n-butyl acrylate

Four verdazyl radicals, with varying substituents at the 3-position, were synthesised and used to prepare unimolecular initiators for use in the stable free radical mediated living radical polymerisation of styrene and n-butyl acrylate. The addition of bulky substituents with differing electronic structures at the 3-position of the ring was investigated and the effects of these substituents on the properties of the verdazyl radical studied. The nature of the substituent was discovered to affect the rate and characteristics of polymerisation. The styrene and n-butyl acrylate homopolymers were chain extended to provide evidence of the verdazyl radical as the end group of the polymers.

Nonlinear Dynamics of an Automotive Differential Hypoid Gear Pair

The dynamics of an automotive differential hypoid gear pair is investigated. The gear pair model is a 4 degree-of-freedom torsional model, including the torsional deflections of the supporting shafts of the pinion and the gear. It also includes the dynamic transmission error of the mating teeth pairs. The variations in teeth contact stiffness/contact, principal radii of contact and static transmission error are determined during the meshing cycle, using the CALYX software. The equations of motion are solved using a numerical integration scheme. A preliminary parametric study is presented, enabling identification of different periodic responses as the vehicle cruising speed alters.Copyright

Gear Oil Viscosity Modifiers and Their Impact on Efficiency

The essential functions of an automotive gear lubricant viscosity modifier (VM) are to maintain fluid film protection of gears and bearings as the lubricant warms to operating temperature, to improve cold temperature flow for efficient lubrication in winter and to minimise viscosity loss in a high shear, high load environment. Although a number of different VM technologies can be considered appropriately resistant to permanent shear for automotive gear oils use, their effect on fluid efficiency can vary widely. This paper outlines the study of a series of different VM technologies assessing relationship of operating temperature, operating viscosity and axle efficiency under different load and speed regimes. The fluids presented were formulated to equal kinematic viscosity at 100 °C but vary widely in viscosity index (VI), elastohydrodynamic (EHD) traction and EHD film thickness. The differences observed during efficiency testing were qualitatively related to the rheological properties of the VM technology present and further related to the operating temperature and operating viscosity.