Flexible fuel control system with fuel transit delay compensation

Abstract

An electronic engine control system for use with differing fuel types, such as gasoline, methanol and mixtures of the two, controls engine operating parameters such as the fuel/air ratio and ignition timing in response to fuel-type indications generated by a fuel type sensor positioned on the fuel line. Changes in the fuel type passing the sensor result in variations in the engine control signals which are effective after a variable delay period elapses. The duration of the variable delay period is altered in response to changes in fuel pump voltage and fuel temperature to form a better estimate of the transport delay experienced by the fuel as it passed from the fuel-type sensor to the engine's fuel intake. A microcontroller delays the control signal changes by retrieving a count value from a two-dimensional lookup table indexed by values reflecting pump voltage and fuel temperature. The count value is placed in a countdown timer which is decremented to zero for establishing a subinterval, at the conclusion of which the current fuel type signal is pushed into a FIFO stack as the oldest stored fuel type value is popped from the stack and supplied to the engine controller. In this way, the stack operates as a variable duration delay device which is updated at the end of subintervals each having a duration dependent upon the estimated fuel transport delay.