HTHS viscosities

Perhaps the most careful and thorough study of the subject by an ASTM task force in 1990 concluded that HTHS viscosity alone is sufficient to predict oil film thickness in running engines [95]. The key to reaching this conclusion was in establishing the oil temperature at the point of closest contact in the bearing, thus permitting the viscosity to be specified at the relevant temperature. The only VI improver chemistry issue involved is how associative thickeners fit into the total scheme. 

C3 - for high-performance car and light van diesel/gasoline engines vehicles with DPF and TWC with a minimum HTHS viscosity higher than 3.5 mPa.s. These lubricants will increase DPF/TWC operational life. 

The dynamic viscosity r](cai) is conveniently defined under alternating shear-stress conditions. Assuming the fluid velocity along x and the velocity gradient along z, the solvent velocity at the position of the hth atom in the absence of the chain is... 

Alexander, D.L. (1989) Change of high-shear rate viscosity of engine oils during use A review, in high-temperature high-shear (HTHS) oil viscosity Measurement and relationship to engine operation. ASTMSTP 1068, 60-73. 

Cl - with either diesel particulate filters, DPF, or petrol three-way catalysts, TWC, requiring low-friction, low-viscosity lubricants with HTHS minimum of 2.9 mPa.s. These lubricants will increase DPF and TWC life and maintain fuel economy. These lubricants have the lowest sulphated ash/phosphorus/sulphur (SAPS) limits. 

PAO and three different additive packages were studied. Six viscosity modifiers (VM) and three different viscosity grades have been evaluated. Within each viscosity grade it is possible to vary the Newtonian viscosity of the oil (that is the part which is independent of shear rate), and still achieve the same finished oil viscometrics (HTHS and kVlOO). This is achieved by using different amounts of viscosity modifier to boost the viscosity at low and medium shear rates. This is illustrated schematically in Figure 1. 

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