Apparatus and method for accurately controlling fuel injection flow rate

A method of controlling a quantity of fuel injected into a cylinder of an internal combustion engine during each injection event comprising the steps of:

• generating a desired fuel quantity signal indicative of a desired fuel quantity to be delivered to the cylinder of the internal combustion engine;
• generating an estimated actuator current signal from said desired fuel quantity signal, said estimated actuator current signal being indicative of an estimated actuator current necessary to deliver said desired fuel quantity to a cylinder of the internal combustion engine;
• generating a fuel rail pressure signal indicative of a measured fuel rail pressure;
• generating an actual fuel quantity signal from said fuel rail pressure signal, said actual fuel quantity signal being indicative of an actual fuel quantity delivered to a cylinder of the internal combustion engine;
• generating a fuel quantity difference signal representing a difference between said desired fuel quantity signal and said actual fuel quantity signal;
• generating an actuator current difference signal from said fuel quantity difference signal, said actuator current difference signal being indicative of a difference between said estimated actuator current and an actual actuator current necessary to achieve delivery of said desired fuel quantity to a cylinder of the internal combustion engine;
• combining said estimated actuator current signal and said actuator current difference signal to generate an actual actuator current signal indicative of said actual actuator current;
• and
• controlling an actuator in accordance with said actual actuator current signal.

A system for controlling a quantity of fuel injected from a fuel rail into a cylinder of an internal combustion engine during each injection event, wherein the fuel pressure in the fuel rail is varied using an actuator to control the desired quantity of fuel to be injected into the cylinder of the internal combustion engine, comprising:

• processing means for generating a desired fuel quantity signal indicative of a desired fuel quantity to be delivered to the cylinder of the internal combustion engine;
• fuel-to-current conversion means connected with said processing means for receiving said desired fuel quantity signal and generating an estimated actuator current signal from said desired fuel quantity signal, said estimated actuator current signal being indicative of an estimated actuator current necessary to deliver said desired fuel quantity to the cylinder of the internal combustion engine during the injection event;
• fuel rail pressure measuring means connected with the fuel rail of the internal combustion engine for measuring a sensed fuel rail pressure and for generating a fuel rail pressure signal in response thereto;
• pressure-to-fuel conversion means connected with said fuel rail pressure measuring means for receiving said fuel rail pressure signal and for generating an actual fuel quantity signal from said fuel rail pressure signal, said actual fuel quantity signal being indicative of an actual fuel quantity delivered to a cylinder of the internal combustion engine;
• first comparison means connected with said processing means and said pressure-to-fuel conversion means for receiving said desired fuel quantity signal and said actual fuel quantity signal, for calculating a difference between said desired fuel quantity signal and said actual fuel quantity signal, and for generating a fuel quantity difference signal representing said difference;
• controller means connected with said first comparison means for receiving said fuel quantity difference signal and for generating an actuator current difference signal from said fuel quantity difference signal, said actuator current difference signal being indicative of a difference between said estimated actuator current and an actual actuator current necessary to achieve delivery of said desired fuel quantity to a cylinder of the internal combustion engine;
• second comparison means connected with said controller means and said fuel-to-current conversion means for receiving said estimated actuator current signal and said actuator current difference signal, and for combining said estimated actuator current signal and said actuator current difference signal to generate an actual actuator current signal indicative of said actual actuator current;
• and
• current control means connected with said second comparison means for controlling the supply of current to the actuator in accordance with said actual actuator current signal.