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Compromises inherent with fixed valve lift and event timing have prompted engine designers to consider Variable Valve Actuation (VVA) systems for many decades. In recent years, some relatively basic forms of VVA have been introduced into production engines. Greater performance and driveability expectations of customers, more stringent emission regulations set by government legislators, and the mutual desire for higher fuel economy are increasingly at odds. As a solution, many OEM companies are seriously considering large-scale application of higher function VVA mechanisms in their next generation vehicles. This paper describes the continuing development progress of a mechanical VVA system. Design features and operation of the mechanism are explained. Test results are presented in two sections: motored cylinder head test data focuses on VVA system friction, control system performance, valve lift and component stress.

Variable valve actuation (VVA) has been recognized as a potential method to improve engine efficiency, low-end torque, high-end power, idle stability, and emissions. This paper presents a low-friction VVA device that can modulate the valve lift and timing, and potentially provide many of the benefits listed. In order for the VVA-related additional losses not to out-weigh the benefits, energy consumed in friction and activating the VVA mechanism must be comparable to the total energy consumed by friction in a conventional valvetrain. To confirm this point, hardware was built and installed on a General Motors L-4 cylinder head employing 4 valves per cylinder. The frictional-energy loss and the actuation torque for the mechanism were measured at different speeds and oil temperatures. The dynamometer tests confirmed the simulation results that the mechanism consumes less frictional energy than a direct acting, non-roller type valvetrain.