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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.

The toe-change of road-wheel, so-called compliance-steer(CS), caused by suspension compliance is proved to occur around a steady instantaneous center under steady run at constant speed. The adverse/proverse CS, that increases/decreases the side-slip angle versus the velocity vector of vehicle, is realized by locating the center rearward/forward of the axle. By designing the front/rear wheel CS as a proverse/adverse CS with nonlinear compliance that is large at on-center but small at off-center, vehicle characteristics to reduce lateral deviation caused by disturbance and to improve tracking performance are possible.

The running direction of a vehicle can be controlled by not only wheel steer but also torque steer. This paper introduces the tractive torque steer effect produced by a newly developed electropneumatic control system, the limited-slip differential for large-sized vehicles. This system enhances the vehicle's running stability and controllability by controlling the tractive force of the drive axle. The tractive force maintains a stable running course against disturbances such as road roughness and wind gusts, thereby enhancing the steering response and providing a better feeling of handling to the driver. The system also improves mobility. especially on low-μ roads. It is expected that a single axle equipped with this system will exhibit good performance comparable to that of tandem axle.