Robust direct injection fuel pump system
A method for a PFDI engine may comprise, during a first condition, comprising direct-injecting fuel to the PFDI engine, estimating a fuel vapor pressure, and setting a fuel lift pump pressure greater than the fuel vapor pressure by a threshold pressure difference, and during a second condition, comprising port-fuel-injecting fuel to the PFDI engine, setting a DI fuel pump command signal greater than a threshold DI fuel pump command signal without supplying fuel to a DI fuel rail.
1. A method for a PFDI engine, comprising:
during a first condition, including direct-injecting fuel to the PFDI engine,
estimating a fuel vapor pressure, and
setting a fuel lift pump pressure greater than an estimated fuel vapor pressure by a threshold pressure difference; and
during a second condition, including port-fuel-injecting fuel to the PFDI engine,
setting a DI fuel pump command signal greater than a threshold DI fuel pump command signal without supplying fuel to a DI fuel rail.
2. The method of claim 1 , wherein estimating the fuel vapor pressure comprises
switching off a fuel lift pump,
measuring a fuel passage pressure compliance while direct-injecting fuel, and
setting the fuel vapor pressure to a fuel passage pressure when the fuel passage pressure compliance is less than a threshold compliance.
3. The method of claim 2 , wherein measuring the fuel passage pressure compliance comprises measuring a pressure compliance of a fuel passage fluidly coupled between the fuel lift pump the DI fuel pump.
4. The method of claim 1 , wherein estimating the fuel vapor pressure comprises
switching off the fuel lift pump, and
setting the fuel vapor pressure to a fuel passage pressure after delivering a threshold fuel volume from a fuel passage fluidly coupled between the fuel lift pump and the DI fuel pump.
5. The method of claim 1 , further comprising during the first condition, enforcing the DI fuel pump duty cycle greater than the threshold duty cycle.
6. The method of claim 1 , wherein the first condition further comprises only direct-injecting fuel to the PFDI engine.
7. The method of claim 1 , further comprising during the second condition, maintaining DI pump lubrication by setting a DI fuel pump duty cycle between 5% and 10%.
8. The method of claim 1 , further comprising during a third condition, maintaining DI fuel pump lubrication by setting a DI fuel pump duty cycle to 0%, the third condition comprising when an engine is idle.
9. The method of claim 8 , wherein maintaining DI fuel pump lubrication comprises maintaining a DI fuel pump compression chamber pressure greater than a fuel lift pump pressure.
10. The method of claim 1 , further comprising during the second condition, maintaining a DI fuel pump compression chamber pressure greater than a fuel lift pump pressure.
11. The method of claim 1 , further comprising detecting a failed fuel lift pump check valve based on a fuel passage pressure decrease when the fuel lift pump is switched off.
12. A method of operating a fuel system for an engine, comprising:
maintaining a fuel lift pump pressure greater than an estimated fuel vapor pressure while fuel is being direct-injected to the engine; and
enforcing a duty cycle of a DI fuel pump to above a threshold duty cycle even when fuel is not being direct-injected to the engine.
13. The method of claim 12 , wherein the estimated fuel vapor pressure is calculated from a stabilized pressure in a fuel line, the pressure stabilizing while direct-injecting fuel after shutting off the fuel lift pump, wherein the fuel line is fluidly coupled between the fuel lift pump and the DI fuel pump.
14. The method of claim 12 , further comprising, enforcing a DI fuel pump duty cycle to 0% during engine idling.
15. The method of claim 12 , wherein the DI fuel pump duty cycle is enforced to a 5% duty cycle when an engine load is above an idle engine load.
16. The method of claim 12 , further comprising maintaining a fuel lift pump pressure greater than an estimated fuel vapor pressure while fuel is only being direct-injected to the engine.
17. The method of claim 12 , further comprising enforcing a DI fuel pump duty cycle above 5% duty cycle while direct-injecting fuel to the engine.
18. The method of claim 12 , wherein enforcing the DI fuel pump duty cycle to above the threshold duty cycle comprises maintaining a DI fuel pump compression chamber pressure greater than a fuel lift pump pressure.
19. An engine system, comprising:
a PFDI engine;
a DI fuel pump;
a fuel lift pump; and
a controller, comprising executable instructions to:
during a first condition, comprising direct-injecting fuel to the PFDI engine,
estimating a fuel vapor pressure, and
setting a pressure of the fuel lift pump greater than the fuel vapor pressure by a threshold pressure difference; and
during a second condition, comprising port-fuel-injecting fuel to the PFDI engine, setting a DI fuel pump duty cycle to a threshold duty cycle without supplying fuel to a DI fuel rail.
20. The engine system of claim 19 , further comprising, during the first condition,
when a desired lift pump pressure is greater than the fuel vapor pressure, controlling the lift pump pressure via feedback control, and
when the desired lift pump pressure is less than the fuel vapor pressure, controlling the fuel lift pump to supply the pressure equivalent to the fuel vapor pressure plus the threshold pressure difference.