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This study examined methods of machining a microsurface texture on the surface of the rolling elements of a toroidal continuously variable transmission (CVT) for improving the traction coefficient. The microsurface texture of the toroidal surfaces consists of tiny circumferential grooves (referred to here as micro grooves) and a mirror-like surface finish similar to the rolling surface of bearings. Hard turning with a cubic boron nitride (cBN) cutting tool, grinding with a cBN wheel and micro forming were applied to machine the micro grooves. The results made clear the practical potential of each method. A micro forming device was also developed for use in actual production. A mirror-like surface finish and micro crowning of the convex portions of the microsurface texture were simultaneously executed by superfinishing them with a fine-grained elastic superfinishing stone.

Due to its lower friction property, a hydrogen-free diamond-like carbon coating (DLC) obtained by an ion-plating physical vapor deposition (PVD) process as an amorphous carbon film (a-C) was applied to an engine valve lifter to reduce mechanical losses. The effect of the a-C coating on reducing friction was evaluated with an engine motoring tester using actual engine parts. To meet the specifications of the valve lifter, a study was made of the typical topography of the a-C coating surface profile and the effect of the film thickness against abrasive wear.

One important development area for obtaining better fuel economy is to reduce mechanical friction losses in engine components. The valvetrain is a significant source of mechanical friction loss in an automobile engine, especially at low speeds where fuel economy is most important. This paper describes the potential use of diamond-like carbon (DLC) coatings at the cam/follower interface in a bucket-type valvetrain. Using a pin-on-disk tester, a motored valvetrain friction apparatus and a bench test rig, the frictional performance of DLC coatings was tested. Experimental data indicate that under a lubricated condition, DLC coatings produced by a plasma CVD (chemical vapor deposition) technique did not show a sufficient effect on reducing friction (only a 20-25% reduction) contrary to our expectations. DLC coatings prepared by arc-ion plating and containing less hydrogen showed superior frictional performance compared with CVD-DLC coatings under a lubricated condition.

Experimental and analytical research were performed on the contact fatigue wear of cam roller follower (needle roller bearing). A new fatigue test machine with a special two-bar loading system was designed to increase the efficiency and the reliability of the tests. The performance test indicated that the end clearance between the roller and rocker had a significant influence on friction and heat generation in the roller follower. The nondestructive testing procedure showed that there were possibly three wear mechanisms in the wear process, but the dominant one was subsurface crack initiation and propagation. Based on the observed wear mechanism two crack initiation dominate contact fatigue models were used to predict the wear life. The life prediction parameters were determined from statistic analysis of the experiment data. The Lundberg-Palmgren model [1] predicts shorter lives and dose not fit with the experiment data.

An investigation was made of techniques for reducing the friction of lightweighted direct-acting valve train systems. The techniques examined included improving the cam/follower surface finish and reducing the valve spring load. The characteristics of each approach and the valve train friction reduction obtained with each one were clarified by experimentation and analysis. As a result, the friction reduction techniques analyzed in this work reduce the friction level of a direct-acting valve train by approximately 40% in comparison with the previous valve train. These techniques have been applied for the direct-acting valve train system of new-generation, lightweight, 3-liter V6 Nissan engine.