Formulation Technology for Low Phosphorus Gasoline Engine Oils 922301
The effect of phosphorus concentration in gasoline engine oils on the valve train wear was experimentally investigated by using the JASO M328-91 3A valve train wear (3A-VTW) test method. The phosphorus concentration is determined proportionally to the amount of zinc dithiophosphate (ZDDP), which is formulated as both antiwear agent and antioxidant.
Lower concentrations of ZDDP generally bring about larger wear in the valve train. However, it was found from the experiments that valve train wear remained low despite a decrease of phosphorus concentration when secondary ZDDPs with short alkyl chain together with appropriate ashless dispersants were selected.
Since adsorptivity of secondary ZDDPs with short alkyl chain lengths onto rubbing metal surfaces is higher than that of primary types, the secondary types give excellent antiwear characteristics.
Ashless dispersants deteriorate the antiwear performance of ZDDPs because the amount of ZDDPs adsorbed onto metal surface is decreased by their complex formation with ashless dispersants in oil. Therefore, the complex formation was investigated quantitatively to optimize the type and dosage of ashless dispersants.
Based on the present work, a low phosphorus SG EC II SAE10W-30 oil which meets 1990 ILSAC GF-1 specification was successfully developed. The newly developed oil was found to provide excellent wear protection in the JASO 3A-VTW test.