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1 Fuel savings by engine oil have been requested for two-wheeled vehicles from the viewpoint of environmental issues. In four-wheeled vehicles, reduction of oil viscosity and addition of friction modifiers have been effective in improving fuel efficiency. However, direct application of engine oil for four-wheeled vehicles to two-wheeled vehicles is difficult. In a four-cycle two-wheeled vehicle, the transmission, gears, and a wet clutch system are imbedded within the engine1). Engine oil must display a remarkable performance as it is required to function as transmission oil and to improve anti-metal fatigue life and clutch performance2), 3). If fuel efficiency is improved by reducing the viscosity of engine oil used in two-wheeled vehicles, the fatigue life tends to worsen. Therefore, reduction in oil viscosity is difficult to achieve.

Just as CO2 reduction is required of four wheeled vehicles for environmental protection, similar environmental concerns drive the development of motorcycle oil technology. Zinc dialkyldithiophosphate (Zn-DTP) type additives are widely used for engine oil formulations. However, phosphorus compounds are environmental load materials. The reduction of the quantity of phosphorus compounds in engine oils is required to reduce poisoning of three-way catalysts used to purify exhaust gases from internal combustion engines. Mr. Ito and his co-authors1) reported that they developed a sulfur-based additive as a substitute for Zn-DTP. Their non-phosphorus engine oil formulation for four-wheeled vehicles with a sulfur-based additive was examined to evaluate its anti-wear performance using the following test methods:JASO M328 for gasoline engines (KA24E) and JASO M354 for Diesel engine (4D34T4).

ASTM D 892 ‘Standard Test Method for Foaming Characteristics of Lubricating Oils is commonly used for evaluating the foaming characteristics of lubricating oils. However, the ASTM test method does not always reproduce the same foaming characteristics of ATF in an actual automatic transmission. A new laboratory test method of foaming characteristics of lubricants has been developed to simulate the foaming characteristics of ATF in the automatic transmission, and it has been named “The Circulation Type Foaming Test Method”. This test method has a high correlation with the foaming characteristics of ATF in the automatic transmission and sufficient repeatability as a test method. Furthermore, a small quantity of sample, short testing time and automated control are key characteristics. In this paper, the development procedure of this test method and each factor relating to the foaming characteristics is reported, such as sample volume, nozzle diameter and height, and impingement time.