Fuel injector control strategy for intake vacuum based low pressure fuel system
In at least some implementations, a method of controlling fuel injection events, includes determining at least one engine operating condition, determining timing of a desired pressure in an engine intake chamber or at the outlet of a fuel injector, and initiating a fuel injection event as a function of the at least one engine operating condition and the desired pressure. The fuel injection event is initiated prior to the desired pressure occurring and wherein the fuel injection event occurs for a duration such that the fuel injection event terminates after the desired pressure occurs.
1. A method of controlling fuel injection events, comprising:
determining at least one engine operating condition;
determining timing of a desired pressure in an engine intake chamber or at the outlet of a fuel injector;
initiating a fuel injection event as a function of the at least one engine operating condition and the desired pressure, wherein the fuel injection event is initiated prior to the desired pressure occurring and wherein the fuel injection event occurs for a duration such that the fuel injection event terminates after the desired pressure occurs.
2. The method of claim 1 wherein the desired pressure is a maximum negative pressure.
3. The method of claim 1 wherein the duration of the fuel injection event prior to the desired pressure occurring is equal to the duration of the fuel injection event after the desired pressure occurs, or the duration of the fuel injection event prior to the desired pressure occurring is within 30 degrees of engine revolution of being equal to the duration of the fuel injection event after the desired pressure occurs.
4. The method of claim 1 wherein the desired pressure is a maximum negative pressure, and wherein the duration of the fuel injection event prior to the desired pressure occurring is equal to the duration of the fuel injection event after the desired pressure occurs, or the duration of the fuel injection event prior to the desired pressure occurring is within 30 degrees of engine revolution of being equal to the duration of the fuel injection event after the desired pressure occurs.
5. The method of claim 1 which also includes changing the duration of the fuel injection event to change and air:fuel ratio of a fuel mixture delivered to an engine, and wherein after the change the duration of the fuel injection event prior to the desired pressure occurring is equal to the duration of the fuel injection event after the desired pressure occurs, or the duration of the fuel injection event prior to the desired pressure occurring is within 30 degrees of engine revolution of being equal to the duration of the fuel injection event after the desired pressure occurs.
6. The method of claim 5 wherein, to provide a richer fuel mixture, the fuel injection event duration is increased equally or within 50% of equally before and after the maximum negative pressure point, wherein within 50% is relative to the total duration of the fuel injection event.
7. The method of claim 6 wherein the fuel injection event is offset by up to 60 revolutions compared to a fuel injection event that is equally spaced from the time of the desired pressure.
8. The method of claim 5 wherein, to provide a leaner fuel mixture, the fuel injection event duration is decreased equally or within 50% of equally before and after the maximum negative pressure point, wherein within 50% is relative to the total duration of the fuel injection event.
9. The method of claim 8 wherein the fuel injection event is offset by up to 60 revolutions compared to a fuel injection event that is equally spaced from the time of the desired pressure.
10. The method of claim 1 wherein the at least one engine operating condition is engine speed and the position of a throttle valve.
11. The method of claim 1 wherein the at least one engine operating condition includes ignition timing or engine temperature.
12. The method of claim 1 wherein for a given engine operating condition, the total desired duration during which the fuel injection event occurs is predetermined and stored in a lookup table, map, table or data set, and the step of initiating a fuel injection event includes obtaining the desired duration of the fuel injection event from such stored information.
13. The method of claim 1 wherein the step of initiating a fuel injection event occurs when the pressure in the engine intake chamber or at the outlet of the fuel injector passes a threshold pressure which occurs prior to the desired pressure.
14. The method of claim 13 wherein, for a given engine operating speed and throttle valve position, the threshold pressure varies as a function of the fuel injection event duration.
15. The method of claim 13 wherein the desired pressure is a maximum negative pressure.