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Heavy duty vehicles take a large role in providing global logistics. It is required to have both high durability and reduced CO2 from the viewpoint of global environment conservation. Therefore lubricating oils for transmission and axle/differential gear box are required to have excellent protection and longer drain intervals. However, it is also necessary that the gear oil maintain suitable friction performance for the synchronizers of the transmission. Even with such good performance, both transmission and axle/differential gear box lubricants must balance cost and performance, in particular in the Asian market. The development of gear oil additives for high reliability gear oil must consider the available base oils in various regions as the additive is a global product. In many cases general long drain gear oils for heavy duty vehicles use the group III or IV base oils, but it is desirable to use the group I/II base oils in terms of cost and availability.

Degradation of wet friction materials can cause changes in friction characteristics and a reduction of material strength. The former changes may reduce the friction coefficient or result in a μ-V characteristic with a negative slope. It is well known that the blocking of friction material pores substantially affects changes in characteristics. A decline in strength may reduce the thickness of friction materials and lead to delamination in the worst case. This paper presents the results of a study concerning the effect of the automatic transmission fluid (ATF) on friction material pore blockage and reduction of material strength (delamination life). It was found that the high-temperature detergency of ATFs affects the blocking of friction material pores and that ATF compatibility with cellulose fiber affects the reduction of friction material strength.

An additive package for the automatic transmission fluid (ATF) used in slip lockup control automatic transmissions has been developed that satisfies all the requirements of the DEXRON® III, MERCON® and JASO M315 specifications. The influence of the base oil and viscosity index improver that are combined with this additive package was also investigated with respect to ATF performance.