821242 Significant Considerations in Selecting Base Stocks for Automatic Transmission Fluids R. A. Bagnall and B. Swinney Research and Development Gulf Canada Limited COPYRIGHT SOCIETY OF AUTOMOTIVE ENGINEERS, INC. ABSTRACT The results of numerous labora- tory bench tests and over-the-road field tests conducted on fluids blended with base stocks of varying physical properties are compared. The effects of using oils derived from solvent-refining versus those manufactured from a hydro- treating process are examined. Other areas investigated include comparisons of high vs. low VI; light vs. medium grade neutrals; and additive response to these differing base stocks. Although high viscosity index (HVI), hydrotreated, medium grade neutrals generally gave superior results in the tests performed, it was determined ATF's blended with light grade hydrotreated neutrals of low viscosity index (LVI) also showed promising results when evaluated against standard industry tests. WITH REVOLUTIONARY CHANGES TAKING PLACE in Canadian crude oil supplies, refineries must be prepared to adjust lubricating oil base stock manufacturing processes to allow for predicted deficiences in feedstocks. Gradually the depleting quantities of light grade, sweet crude are being replaced with lower quality conventional crude oils. Also, increasing output of heavy oil and bitumen derived crudes fromsynthetic plants will increase the level of sulfur and nitrogen contami- nants further. Table 1 compares these three crude types by compositional analysis. From a production viewpoint a lubricating oil process is required that will provide optimum yield and quality without dependence on premium quality crude. One objective of this Paper is to identify the performance qualities of hydrotreated (HT) base stocks in auto- matic transmission fluids. It will be shown how the refining process, irres- pective of crude source, affects the performance of the finished product, (1,2)*. Most lube plants use solvent extraction processes to produce lub- ricant base stocks. These require premium crude oils for economic yields of quality lube base stocks. Hydrotreating processes achieve higher yields from a barrel of crude with consistent high quality and purity. The process adopted by Gulf Canada Limited is carried out in two stages. The first utilizing hydrogen and a catalyst at high temperature and pressure breaks the heavy crude compo- nents into a range of fuels and waxy lubricants while unstable impurities are removed. The products are frac- tionated, dewaxed and again hydro- genated in a second-stage hydrotreater * Numbers in parentheses designate references at end of paper. 107Downloaded from SAE International by University of Edinburgh, Friday, August 10, 2018under more moderate temperature con- ditions but maintaining high pres- sure. The process differs from more conventional lubricating oil designs since fractionation occurs after the major refining step with the severe hydrotreating replacing the more common solvent extraction. A final hydrofinishing step-if included as part of a conventional process-would be conducted at lower temperatures and pressures to further remove sulfur and nitrogen components. High resolution mass spectro- metry shows that a hydrotreating process gives similar products from both Western Canadian and Middle Eastern crude. Both products show high levels of saturated hydrocar- bons, low aromatics and low hetero- organic compounds compared to similar base stock obtained from a Western Canadian crude source by solvent-refining (SR). Table 2. A feature of this study will be a correlation of base stock chemical analysis with blended fluid performance. PERFORMANCE FEATURES OF AUTOMATIC TRANSMISSION FLUIDS There is a continuing trend toward extended automatic transmis- sion fluid change intervals in service applications. Also, new transaxle configurations are ap- pearing more frequently in front- wheel drive (FWD) vehicles incor- porating differential a