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 in a system in which fuel injection occurs at a subatmospheric pressure, comprising:
determining at least two engine operating conditions including an engine speed, a position of a throttle valve, an ignition timing and an engine temperature;
determining a 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 two engine operating conditions and the pressure, wherein the fuel injection event is initiated prior to a maximum subatmospheric pressure occurring and wherein the fuel injection event occurs for a duration such that the fuel injection event terminates after the maximum subatmospheric pressure occurs.
2. The method of claim 1 wherein the duration of the fuel injection event prior to the maximum subatmospheric pressure occurring is equal to the duration of the fuel injection event after the maximum subatmospheric pressure occurs, or the duration of the fuel injection event prior to the maximum subatmospheric pressure occurring is within 30 degrees of engine revolution of being equal to the duration of the fuel injection event after the maximum subatmospheric pressure occurs.
3. The method of claim 1 wherein the pressure is determined at the outlet of the fuel injector.
4. The method of claim 1 wherein the pressure is determined at the engine intake chamber.
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 subatmospheric 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 subatmospheric 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 two engine operating conditions are engine speed and the position of a throttle valve.
11. 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 as a function of the maximum subatmospheric pressure for various engine operating conditions and is 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.
12. 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 maximum subatmospheric pressure.
13. The method of claim 12 wherein, for a given engine operating speed and throttle valve position, the threshold pressure varies as a function of the fuel injection event duration.
14. A method of controlling fuel injection events, comprising:
determining an engine speed;
determining a throttle position;
determining a negative pressure in an engine intake chamber or at the outlet of a fuel injector, where the negative pressure is induced by movement of an engine piston;
initiating a fuel injection event as a function of the engine speed, the throttle position and the negative pressure, wherein the fuel injection event is initiated prior to a maximum negative pressure occurring and wherein the fuel injection event terminates after the maximum negative pressure occurs.
15. The method of claim 14 wherein the fuel injection event is initiated by opening a valve and wherein fuel flows out of the valve at rate that is a function of the magnitude of the negative pressure.
16. The method of claim 15 which also includes providing fuel to the valve at a pressure of 6 psi or less.
17. The method of claim 16 wherein fuel is provided to the valve at atmospheric pressure.
18. The method of claim 17 wherein fuel is provided to the valve from an inlet chamber having a fuel level controlled by a valve that is moved by a float that is buoyant in the fuel in the inlet chamber.
19. The method of claim 14 wherein the negative pressure is determined by a sensor at a location within one inch of an outlet of a fuel injector via which the fuel injection event occurs.