Variable Valve Timing for a Camless Stepping Valve Engine

Abstract

Variable valve timing (VVT) enables the valve events to vary with RPM for optimum engine performance. It alters the timing on the camshaft using pneumatic, hydraulic or electromechanical means. The Cameless Stepping Valve system uses software controlled valve events. Here, VVT is achieved by advancing/retarding valve events using only the direction of the piston and interpolated virtual angles on the flywheel. The engine model used has an optimum RPM of 24000, which translates to a period of 2.5mS. A 10 angle increment on the flywheel corresponds to 6.9µS. As a result, a retardation/advance of 10 would mean that the valve will open/close 6.9µS after the current/previous TDC. A 9bit real-time digital counter was triggered to count the calculated angles at every Otto Cycle so that advance/retard is updated at every RPM. In this project, it was demonstrated that valve event control is possible using interpolation of virtual angles on the flywheel, replacing a multi-tooth timing wheel. The proposed technique is more accurate and robust.