Adjusting pump volume commands for direct injection fuel pumps
Methods are provided for controlling a direct injection fuel pump, wherein a solenoid spill valve is energized and de-energized according to certain conditions. A control strategy is needed to operate the direct injection fuel pump outside regions where pump operation may be variable and inaccurate, where the regions may be characterized by smaller pump commands as well as smaller displacement volumes. To maintain a suitable range of pump commands and displacements while operating outside the low accuracy regions, a method is proposed that involves clipping calculated pump commands when the calculated pump commands lie within the low accuracy regions.
1. A method, comprising:
in response to a determination that a calculated pump command is between 0 and a zero-flow lubrication command, operating a solenoid spill valve of a direct injection fuel pump with the zero-flow lubrication command;
in response to a determination that the calculated pump command is between the zero-flow lubrication command and a threshold command, operating the solenoid spill valve with the threshold command; and
in response to a determination that the calculated pump command is greater than the threshold command, operating the solenoid spill valve with the calculated pump command, the method including:
operating with the calculated pump command between 0 and the zero-flow lubrication command, operating with the calculated pump command between the zero-flow lubrication command and the threshold command, and operating with the calculated pump command greater than the threshold command.
2. The method of claim 1 , wherein the threshold command and zero-flow lubrication command correspond to displacement volumes of fuel pumped into a direct injection fuel rail by the direct injection fuel pump during a delivery stroke, and further comprising calculating the calculated pump command based on a desired fuel rail pressure and a measured fuel rail pressure.
3. The method of claim 2 , wherein the displacement volumes are controlled by an activating timing of the solenoid spill valve fluidically coupled upstream of a compression chamber inlet of the direct injection fuel pump, and wherein the desired fuel rail pressure is based on engine demand and fuel injector performance.
4. The method of claim 1 , wherein operating the solenoid spill valve with the zero-flow lubrication command includes maintaining an elevated pressure in a compression chamber of the direct injection fuel pump without increasing fuel rail pressure, and wherein while operating the solenoid spill valve with the threshold command, fuel is delivered by the direct injection fuel pump into a direct injection fuel rail coupled to an outlet of the direct injection fuel pump.
5. The method of claim 4 , wherein the elevated pressure forces fuel past a piston-bore interface of the direct injection fuel pump to lubricate and cool the direct injection fuel pump, and wherein the threshold command is based on a boundary between lower accuracy pump commands and higher accuracy pump commands.
6. The method of claim 4 , wherein while operating the solenoid spill valve with the zero-flow lubrication command, no fuel is pumped by the direct injection fuel pump into the direct injection fuel rail.
7. The method of claim 2 , wherein operating the solenoid spill valve with the calculated pump command includes commanding displacement volumes of the direct injection fuel pump based on the desired fuel rail pressure, the measured fuel rail pressure, and a fuel injection volume rate, wherein a displacement volume corresponding to the zero-flow lubrication command is less than a displacement volume corresponding to the threshold command, and wherein the displacement volume corresponding to the threshold command is less than a displacement volume corresponding to the calculated pump command.
8. The method of claim 1 , further comprising operating the solenoid spill valve with the zero-flow lubrication command when a measured fuel rail pressure is greater than a desired fuel rail pressure, the desired fuel rail pressure based on calculations from a controller that issues commands to the solenoid spill valve, and wherein operating the solenoid spill valve includes sending an electric signal corresponding to the zero-flow lubrication command, the threshold command, or the calculated pump command to the solenoid spill valve, the electric signal energizing the solenoid spill valve at a pump displacement corresponding to the command, wherein the energizing closes the solenoid spill valve.
9. A method, comprising:
when a measured fuel rail pressure is less than a desired fuel rail pressure:
calculating a pump command of a direct injection fuel pump based on the measured fuel rail pressure and the desired fuel rail pressure;
in response to the calculated pump command being between 0% and a zero-flow lubrication command greater than 0%, operating the direct injection fuel pump at the zero-flow lubrication command;
in response to the calculated pump command being between the zero-flow lubrication command and a greater, threshold command, operating the direct injection fuel pump at the threshold command; and
in response to the calculated pump command being between the threshold command and 100%, operating the direct injection fuel pump at the calculated pump command; and
when the measured fuel rail pressure is greater than the desired fuel rail pressure, operating the direct injection fuel pump at the zero-flow lubrication command; the method including:
operating with the measured fuel rail pressure less than the desired fuel rail pressure and the calculated pump command between 0% and the zero-flow lubrication command greater than 0%, the calculated pump command between the zero-flow lubrication command and the greater, threshold command, and the calculated pump command between the threshold command and 100%, and operating with the measured fuel rail pressure greater than the desired fuel rail pressure.
10. The method of claim 9 , wherein the desired fuel rail pressure is based on engine demand and fuel injector performance as determined by a controller, and wherein operating the direct injection fuel pump includes closing a solenoid spill valve by energizing the solenoid spill valve with an electrical signal.
11. The method of claim 9 , wherein the measured fuel rail pressure is measured by a pressure sensor positioned in a direct injection fuel rail that is fluidically coupled to an outlet of the direct injection fuel pump, and wherein the threshold command is based on a boundary between lower accuracy pump commands and higher accuracy pump commands.
12. The method of claim 9 , wherein operating at the zero-flow lubrication command includes maintaining an elevated pressure in a compression chamber of the direct injection fuel pump without substantially affecting fuel rail pressure, wherein the zero-flow lubrication command corresponds to a first displacement volume of the direct injection fuel pump and the threshold command corresponds to a second displacement volume of the direct injection fuel pump.
13. The method of claim 12 , wherein the elevated pressure forces fuel past a piston-bore interface of the direct injection fuel pump to lubricate and cool the direct injection fuel pump, and wherein the first displacement volume is less than the second displacement volume.
14. The method of claim 13 , wherein while operating at the zero-flow lubrication command, substantially no fuel is pumped by the direct injection fuel pump into a direct injection fuel rail coupled to an outlet of the direct injection fuel pump, wherein the calculated pump command corresponds to a third displacement volume of the direct injection fuel pump, wherein the second displacement volume is less than the third displacement volume, and wherein while operating the solenoid spill valve with the threshold command, fuel is delivered by the direct injection fuel pump into the direct injection fuel rail.
15. A fuel system, comprising:
a direct injection fuel pump fluidically coupled upstream of a direct injection fuel rail with a plurality of injectors, the direct injection fuel pump including a solenoid spill valve positioned at an inlet of the direct injection fuel pump, wherein the solenoid spill valve is activated and deactivated between closed and open positions, respectively;
a lift pump fluidically coupled upstream of the direct injection fuel pump, the lift pump providing fuel to the inlet of the direct injection fuel pump; and
a controller, with computer-readable instructions stored in non-transitory memory for:
clipping a calculated pump command to a first threshold command when the calculated pump command is within a first region and clipping the calculated pump command to a second threshold command when the calculated pump command is within a second region;
wherein the first threshold command corresponds to a first displacement volume of the direct injection fuel pump, wherein the second threshold command corresponds to a second displacement volume of the direct injection fuel pump, and wherein the first displacement volume is less than the second displacement volume.
16. The system of claim 15 , wherein the first region ranges from 0 to the first threshold command and the second region ranges from the first threshold command to the second threshold command, and wherein the controller includes further instructions for: when the calculated pump command is within the first or second region, issuing the clipped calculated pump command to the direct injection fuel pump, and when the calculated pump command is not within the first or second region, issuing the calculated pump command to the direct injection fuel pump.
17. The system of claim 16 , wherein the first threshold command is a zero-flow lubrication command and the second threshold command is based on a boundary between lower accuracy pump commands and higher accuracy pump commands, and wherein the controller includes further instructions for calculating the calculated pump command based on a desired fuel rail pressure and a measured fuel rail pressure.
18. The system of claim 16 , wherein clipping the calculated pump command when the calculated pump command is in the first or second region operates displacement volumes of the direct injection fuel pump outside the first and second regions, wherein issuing the clipped calculated pump command comprises energizing the solenoid spill valve to close the solenoid spill valve at an angular timing corresponding to the clipped calculated pump command, and wherein while issuing the second threshold command to the solenoid spill valve, fuel is delivered by the direct injection fuel pump into the direct injection fuel rail.
19. The system of claim 15 , wherein the closed position of the solenoid spill valve includes substantially inhibiting fuel from flowing upstream from a compression chamber of the direct injection fuel pump towards the lift pump.
20. The system of claim 15 , wherein the open position of the solenoid spill valve includes allowing fuel to flow upstream and downstream through the solenoid spill valve, and wherein compressed fuel in a compression chamber of the direct injection fuel pump flows upstream through the solenoid spill valve.