Search Results

This paper outlines the second part in a series on the effect of polymeric additives commonly known as viscosity modifiers (VM) or viscosity index improvers (VII) on gear oil efficiency and durability. The main role of the VM is to improve cold temperature lubrication and reduce the rate of viscosity reduction as the gear oil warms to operating temperature. However, in addition to improved operating efficiency across a broad temperature range compared to monograde fluids the VM can impart a number of other significant rheological improvements to the fluid [1]. This paper expands on the first paper in the series [2], covering further aspects in fluid efficiency, the effect of VM chemistry on these and their relationship to differences in hypoid and spur gear rig efficiency testing. Numerous VM chemistry types are available and the VM chemistry and shear stability is key to fluid efficiency and durability.

In this study, the copper corrosion rates of commercially available lubricants used in electrified and conventional transmissions are measured in both vapor and solution phases simultaneously using an updated version of our previously reported wire resistance test [1]. Unlike the commonly used copper strip tests (versions of the ASTM D130) that generally require high temperatures and long times to differentiate the corrosivity of fluids, the wire resistance test is sufficiently sensitive as to allow real time assessment, thus enabling an efficient and cost-effective way to screen lubricant chemistries over a range of potential operating temperatures. The results of even our small study underscores the importance of understanding both the vapor and solution corrosion across a wide range of temperatures.