A Low-Friction Variable-Valve-Actuation Device, Part I: Mechanism Description and Friction Measurements 970338
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. Measured torques for activating the mechanism and for maintaining its steady position were reasonable. The tests also verified that the mechanism does provide late valve opening, early valve closing, and reduced-maximum lift simultaneously.