Engine position synchronous control of fuel injection and spark ignition at engine start can reduce regulated emissions, and improve start quality. Synchronous fuel and ignition control requires full 720° engine position information. Emissions and start quality benefits are gained if engine position is available at key-on before initial engine rotation.
Typical engine position sensor sets require substantial engine rotation before engine position is initialized. Tracking engine stop position, for use on the next start, eliminates the initial engine angular travel required for synchronization. The previous stop position of the engine is stored in non-volatile memory, giving engine position immediately at start. This approach is applicable for systems in which the engine controller remains powered for some time after key-off.
As the engine stops, direction reversals are common. The difficulty in tracking engine position as it comes to a stop is that typical engine position sensor sets cannot discern engine direction. Significant position errors occur when travel in the reverse direction is accumulated as travel in the forward direction.
A technique is presented for overcoming this problem. Engine coast-down characteristics and variable reluctance sensor physics are used to implement successful engine stop position tracking, using a non-directional engine position sensor set, in the presence of engine direction reversals.