Technical Paper
Analysis of a Lost-Motion-Type Hydraulic System for Variable Valve Actuation
1993-03-01
930822
A general model for the analysis of lost-motion type hydraulic devices used in variable valve actuation is presented. The devices covered by the model include those featuring passive (semi-active) or active bleed control, with external damping. In the case of semi-active bleed control, the bleed-orifice area was fixed during a cam event. However, different orifice areas were considered at different cam-shaft speeds yielding a wide variety of phase, duration, and maximum-lift values. With a fully active bleed control, where the bleed-orifice area was varied as a function of cam-shaft angle during the cam event, independent control of phase, duration, and maximum lift yielded more drastic variations in valve-lift behavior. Governing equations based on dynamic and hydraulic characteristics of the system include Coulomb and hydrodynamic friction forces, inertia forces, an external damping force, and fluid compressibility.