Lift pump control for a two pump direct injection fuel system
An economical method for controlling a lift pump operating as part of a direct injection fuel system is described. According to the method, at least two distinct operating modes are provided.
1. A method to operate a lower pressure pump operating as part of a direct injection fuel system, the method comprising:
operating a lower pressure pump in a first mode during a first operating condition of an internal combustion engine, said lower pressure pump supplying fuel to a higher pressure pump that supplies fuel to fuel injectors that directly inject fuel to a cylinder, said first mode comprising adjusting energy supplied to said lower pressure pump as output from a sensor located downstream of said higher pressure pump varies while said higher pressure pump is substantially deactivated;
operating said lower pressure pump in a second mode during a second operating condition of said internal combustion engine, said second mode comprising varying energy supplied to said lower pressure pump as operating conditions of said internal combustion engine vary while said higher pressure pump is activated; and
applying an energy command learned while in said first mode to the lower pressure pump in said second mode.
2. The method of claim 1 wherein said energy is delivered as a voltage or current and wherein a pressure in a fuel rail supplied by said higher pressure pump is adjusted based on a pumped volume and a fuel rail volume.
3. The method of claim 1 wherein said sensor is a pressure sensor.
4. The method of claim 2 further comprising varying said current or voltage as operating conditions of said internal combustion engine vary and wherein a selection of said first mode is related to at least one of ambient air temperature and time since engine start.
5. The method of claim 1 wherein said higher pressure pump is substantially deactivated during said first mode at engine idle.
6. The method of claim 1 wherein operation in said first and second modes is determined from engine operating conditions.
7. The method of claim 2 wherein said higher pressure pump is driven by said internal combustion engine and wherein fuel injection timing is adjusted in response to the adjusted fuel rail pressure.
8. The method of claim 1 wherein said operating conditions of said internal combustion engine are comprised of at least one of a driver torque request, engine speed, engine load, ambient temperature, or engine temperature.
9. The method of claim 1 wherein said higher pressure pump is deactivated in conjunction with deceleration fuel cut-out during said first mode.
10. A method to operate a lift pump operating as part of a direct injection fuel system, the method comprising:
operating a lift pump in a first mode during a first operating condition of an internal combustion engine, said lift pump supplying fuel to an injection pump that supplies fuel to fuel injectors that directly inject fuel to a cylinder, said first mode comprising adjusting energy supplied to said lift pump as output from a sensor located downstream of said injection pump varies while said injection pump is deactivated;
storing a lift pump variable that corresponds to a pressure observed at said sensor as said engine operates in the first mode; and
operating said lift pump in a second mode and adjusting an outlet pressure of said lift pump with said lift pump variable.
11. The method of claim 10 further comprising varying said energy in said first mode when operating conditions of said internal combustion engine vary.
12. The method of claim 10 further comprising operating said injection pump to increase the pressure of fuel delivered from said lift pump.
13. The method of claim 10 wherein said lift pump variable is an amount of current delivered to said lift pump and wherein a pressure in a fuel rail supplied by said higher pressure pump is adjusted based on a pumped volume and a fuel rail volume.
14. The method of claim 10 wherein said lift pump variable is an amount of voltage delivered to said lift pump.
15. The method of claim 13 wherein said lift pump variable is a lift pump temperature and wherein fuel injection timing is adjusted in response to the adjusted fuel rail pressure.
16. The method of claim 10 wherein said lift pump variable is stored in a function, array, or table that is indexed by lift pump operating conditions.
17. A method to operate lift and injection pumps that are part of a direct injection fuel system, the method comprising:
operating a lift pump in a first mode during a first operating condition of an internal combustion engine, said lift pump supplying fuel to an injection pump that supplies fuel to fuel injectors that directly inject fuel to a cylinder, said first mode comprising adjusting energy supplied to said lift pump as output from a sensor located downstream of said injection pump varies while said injection pump is deactivated;
operating said lift pump in a second mode during a second operating condition of said internal combustion engine, said second mode comprising varying energy supplied to said lift pump as operating conditions of said internal combustion engine vary while said injection pump is activated; and
predicting fuel rail pressure during reactivation of said injection pump by counting a number of fuel pump strokes after reactivating said injection pump.
18. The method of claim 17 wherein said energy is delivered as a voltage or current.
19. The method of claim 17 wherein said injection pump is substantially deactivated during said first mode at engine idle.
20. The method of claim 17 wherein said injection pump is deactivated in conjunction with deceleration fuel cut-out.