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To meet a need identified in earlier valve train friction testing, a tappet rotation monitor was developed and implemented on a cam/tappet tribometer. The system was based on reflecting a light beam from a rotating and translating segmented surface onto a phototransistor. The resulting output was then processed by linear frequency to voltage conversion and multiple cycle integration. The experimental apparatus, signal processing circuit, and the testing circuit are presented. The multiple cycle integration was found to yield average tappet rotation as a function of cam shaft position. These results agreed well with earlier attempts to measure tappet rotation with high speed photography, were repeatable, and correlated with cam shaft speed. Some selected data is also presented which indicates that tappet rotation reduces cam/tappet friction.

Tappet/bore friction and torque at the camshaft were measured for a direct acting bucket tappet using a cam/tappet friction apparatus. Tappet/bore and cam/tappet friction torque and friction coefficient as a function of cam angle were derived from those measurements. The results showed that, for the particular geometry tested, tappet/bore friction torque accounted for about 13% of the total cam/tappet/bore friction torque at 250 cam rpm. This fraction decreased with increasing speed. Tappet bore friction was greatest at about ± 40 degrees of cam angle, where side loads on the tappet bore were highest. In contrast, earlier results for a center pivot rocker arm design showed tappet bore friction to be negligible.

Axle dynamometer tests were carried out to evaluate the effects of rear axle lubricant viscosity-temperature behavior and frictional characteristics on vehicle fuel economy. Using a Ford 9 inch 2.75:1.0 ratio axle, a set of input speed and load conditions was selected to permit simulation of the CVS and EPA highway driving cycles. Lubricant temperature was varied from -30°C to 100°C to simulate seasonal climatic effects. Data obtained for three lubricants differing in viscosity-temperature behavior were interpreted assuming a lubrication model including both elastohydrodynamic and mixed lubrication conditions. From these data, fuel economy projections were made using a vehicle simulation computer program. The results predict that improvements in vehicle fuel economy on the order of a few percent can be made at low temperatures by use of low viscosity synthetic lubricants, but only small effects are projected for the CVS and EPA highway cycles.