Method and apparatus for fuel regulation

Abstract

A method for fuel regulation during a non-motoring operating mode of an internal combustion engine is provided. A fuel regulator employs a first fuel to regulate pressure of a second fuel. The first fuel is communicated to the fuel regulator through a first fuel circuit. The method comprises actuating a fuel injector that introduces the first fuel and the second fuel into a combustion chamber of the internal combustion engine during the non-motoring operating mode. The fuel injector is actuated with an injection command signal having a pulse width below a predetermined maximum value whereby no fuel is injected into the combustion chamber and the first fuel drains from the first fuel circuit through the fuel injector to a supply tank.

Claims

1. A method for fuel regulation during a non-motoring operating mode of an internal combustion engine, a fuel regulator employing a first fuel to regulate pressure of a second fuel, said first fuel communicated to said fuel regulator through a first fuel circuit, the method comprising: actuating a fuel injector, that introduces said first fuel and said second fuel into a combustion chamber of said internal combustion engine during said non-motoring operating mode, said fuel injector actuated with an injection command signal, the injection command signal having a pulse width below a predetermined maximum value whereby no fuel is injected into said combustion chamber and said first fuel drains from said first fuel circuit through said fuel injector to a supply tank; and maintaining a bias between a first fuel injection pressure and a second fuel injection pressure as said first fuel drains from said first fuel circuit.

2. The method of claim 1, wherein said injection command signal activates an actuator in said fuel injector associated with injecting said first fuel into said combustion chamber.

3. The method of claim 1, wherein said injection command signal activates an actuator in said fuel injector associated with injecting said second fuel into said combustion chamber.

4. The method of claim 1, further comprising actuating said fuel injector with said injection command signal during a motoring operating mode, said injection command signal which actuates said fuel injector during the motoring operating mode having a pulse width above a predetermined minimum value whereby fuel is injected into said combustion chamber.

5. The method of claim 1, wherein said first fuel is a pilot fuel and said second fuel is a main fuel.

6. The method of claim 1, wherein said first fuel is a liquid fuel and said second fuel is a gaseous fuel.

7. The method of claim 1, wherein said first fuel is diesel and said second fuel is natural gas.

8. The method of claim 1, further comprising: monitoring a pressure of said first fuel and a pressure of said second fuel; and adjusting said pulse width as a function of said pressure of said first fuel and said pressure of said second fuel.

9. The method of claim 1, wherein said fuel regulator is a dome loaded regulator.

10. A method for fuel regulation during a non-motoring operating mode of an internal combustion engine, a fuel regulator employing a first fuel to regulate pressure of a second fuel, said first fuel communicated to said fuel regulator through a first fuel circuit, said fuel regulator being a dome loaded regulator, the method comprising: actuating a fuel injector that introduces said first fuel and said second fuel into a combustion chamber of said internal combustion engine during said non-motoring operating mode, said fuel injector actuated with an injection command signal having a pulse width below a predetermined maximum value whereby no fuel is injected into said combustion chamber and said first fuel drains from said first fuel circuit through said fuel injector to a supply tank; and maintaining a bias between a first fuel injection pressure and a second fuel injection pressure as said first fuel drains from said first fuel circuit.

11. An apparatus for fuel regulation during a non-motoring operating mode of an internal combustion engine, a fuel regulator employing a first fuel to regulate pressure of a second fuel, said first fuel communicated to said fuel regulator through a first fuel circuit, the apparatus comprising: a fuel injector that introduces said first fuel and said second fuel into a combustion chamber of said internal combustion engine; an electronic controller operatively connected with said fuel injector and programmed to: actuate said fuel injector during said non-motoring operating mode with an injection command signal, the injection command signal having a pulse width below a predetermined maximum value whereby no fuel is injected into said combustion chamber, said first fuel drains from said first fuel circuit through said fuel injector to a supply tank and a bias between a first fuel injection pressure and a second fuel injection pressure is maintained as said first fuel drains from said first fuel circuit.

12. The apparatus of claim 11, further comprising: a first fuel pressure sensor emitting signals representative of said first fuel pressure; and a second fuel pressure sensor emitting signals representative of said second fuel pressure; said electronic controller operatively connected with said first fuel pressure sensor and said second fuel pressure sensor and programmed to determine said pulse width as a function of said signals representative of said first fuel pressure and said second fuel pressure.

13. The apparatus of claim 11, said fuel injector comprising an actuator and a first fuel injection valve associated with said actuator, said actuator responsive to said injection command signal to drain said first fuel to said supply tank.

14. The apparatus of claim 11, said fuel injector comprising an actuator and a second fuel injection valve associated with said actuator, said actuator responsive to said injection command signal to drain said first fuel to said supply tank.

15. The apparatus of claim 11, wherein said electronic controller is further programmed to actuate said fuel injector with said injection command signal during a motoring operating mode, said injection command signal which actuates said fuel injector during the motoring operating mode having a pulse width above a predetermined minimum value whereby fuel is injected into said combustion chamber.

16. The apparatus of claim 11, wherein said first fuel is a pilot fuel and said second fuel is a main fuel.

17. The apparatus of claim 11, wherein said first fuel is a liquid fuel and said second fuel is a gaseous fuel.

18. The apparatus of claim 11, wherein said first fuel is diesel and said second fuel is natural gas.

19. The apparatus of claim 11, wherein said fuel regulator is a dome loaded regulator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a fuel system for a Diesel-cycle internal combustion engine that consumes a pilot fuel and a main fuel.

(2) FIG. 2 is a graphical view of prior art main fuelling command and pilot fuelling command showing a motoring operating mode before time T.sub.1 and a non-motoring operating mode after time T.sub.1.

(3) FIG. 3 is a graphical view of prior art main fuel injection pressure and pilot fuel injection pressure showing a bias within a predetermined range of tolerance between these two pressures before time T.sub.1 and the bias outside the predetermined range of tolerance after time T.sub.1 for the fuelling commands of FIG. 2.

(4) FIG. 4 is a graphical view of main fuelling command and pilot fuelling command according to one embodiment showing a motoring operating mode before time T.sub.1 and a non-motoring operating mode after time T.sub.1.

(5) FIG. 5 is a graphical view of main fuel injection pressure and pilot fuel injection pressure showing a bias within a predetermined range of tolerance between these two pressures before and after time T.sub.1 for the fuelling commands of FIG. 4.

(6) FIG. 6 is a graphical view of pilot injection command signals sent through a wire for actuating a fuel injector of FIG. 1 showing a minimum pulse width PPW.sub.MIN required to inject pilot fuel into a combustion chamber, and a maximum pulse width PPW.sub.MAX that actuates the fuel injector to drain pilot fuel to a supply tank while not injecting pilot fuel into the combustion chamber.

(7) FIG. 7 is a graphical view of main fuelling command and pilot fuelling command according to a second embodiment showing a motoring operating mode before time T.sub.1 and a non-motoring operating mode after time T.sub.1.

(8) FIG. 8 is a graphical view of main injection command signals sent through a wire for actuating a fuel injector of FIG. 1 showing a minimum pulse width MPW.sub.MIN required to inject main fuel into a combustion chamber, and a maximum pulse width MPW.sub.MAX that actuates the fuel injector to drain pilot fuel to a supply tank while not injecting main fuel into the combustion chamber.

(9) FIG. 9 is a schematic view of a fuel system for a Diesel-cycle internal combustion engine that consumes a pilot fuel and a main fuel according to a second embodiment employing a drain orifice from a pilot fuel common rail.

(10) FIG. 10 is a schematic view of a fuel system for a Diesel-cycle internal combustion engine that consumes a pilot fuel and a main fuel according to a third embodiment employing an electronic solenoid valve.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

(11) A technique of preventing hydraulic lock in the pilot circuit that takes advantage of the operation of fuel injector 110 is now discussed. The '959 reference discloses employing the pilot fuel as a controlling fluid for actuating valves inside fuel injectors, such as fuel injector 110 in FIG. 1, for introducing both the pilot fuel and the main fuel (concurrently or separately) into combustion chambers. A pilot fuel actuator (not shown) in fuel injector 110 can be activated by a pilot injection command signal sent through wire 240 to actuate a pilot control valve (not shown) inside fuel injector 110 to drain pilot fuel from a pilot control chamber (not shown). A pilot needle begins to move away from a pilot valve seat resulting in the injection of pilot fuel into the combustion chamber when the pressure in the pilot control chamber decreases below a pilot threshold. In a similar manner, a main fuel actuator (not shown) in fuel injector 110 can be activated by a main injection command signal sent through wire 230 to actuate a main control valve inside fuel injector 110 to drain pilot fuel from a main control chamber. A main needle begins to move away from a main valve seat resulting in the injection of main fuel into the combustion chamber when the pressure in the main control chamber decreases below a main threshold. In other embodiments it is possible to design fuel injector 110 to cause a build-up of pressure in the pilot and main control chambers when the pilot and main actuators are activated, resulting in the displacement of the pilot and main needles respectively. Pilot fuel from the pilot control chamber is returned to supply tank 220 through drain circuit 210 for each activation of the pilot actuator. Pilot fuel from the main control chamber is returned to supply tank 220 through drain circuit 210 for each activation of the main actuator.

(12) Referring to FIG. 4, there is shown main fuelling command 300 and pilot fuelling command 310 according to a first embodiment employed to create injection command signals for fuel injector 110 (seen in FIG. 1). Before time T.sub.1, engine 100 is in a motoring operating mode where main fuelling command 300 has a value of FC.sub.M1 and pilot fuelling command has a value of FC.sub.P1, such that both the main and pilot fuels are injected and combusted in the combustion chambers of engine 100. After time T.sub.1, engine 100 enters a non-motoring operating mode where main fuelling command 300 reduces to zero, but pilot fuelling command 310 decreases to value FC.sub.P2, such that no fuel is injected into the combustion chambers of engine 100. Pilot fuelling command value FC.sub.P2 is below a predetermined maximum value that results in no movement of the pilot needle.

(13) Referring to FIG. 6, each pilot fuelling command value has an associated pilot injection command signal (sent through wire 240), which is an electrical signal that can be represented as a square wave having a pilot pulse width PPW. For the pilot needle to move away from the pilot valve seat, the pressure in the pilot control chamber decreases below the pilot threshold. The pilot actuator is actuated by a pilot injection command signal having minimum pulse width of PPW.sub.MIN for the pressure in the pilot control chamber to decrease below the pilot threshold causing the pilot needle to move away from the pilot valve seat and pilot fuel to be injected into the combustion chamber. Referring now to both FIGS. 4 and 6, when pilot fuelling command 310 has a value of FC.sub.P2 after time T.sub.1, the pilot actuator is actuated by a pilot injection command signal having a pulse width less than or equal to maximum pulse width PPW.sub.MAX such that the pressure in the pilot control chamber does not decrease below the pilot threshold and the pilot needle does not move away from the pilot valve seat, allowing no injection of pilot fuel into the combustion chamber. The difference between PPW.sub.MIN and PPW.sub.MAX is a predetermined range of tolerance allowed between these values, also known as pilot safety factor PSF. When fuel injector 110 is actuated by a pilot injection command signal of pulse width less than or equal to PPW.sub.MAX, no pilot fuel is injected to the combustion chamber but pilot fuel is drained to supply tank 220 through drain circuit 210. During the non-motoring operating mode in FIG. 4 after time T.sub.1, the value of pilot fuelling command 310 is less than a maximum pilot fuelling command value associated with maximum pulse width PPW.sub.MAX such that no pilot fuel is injected into the combustion chamber but pilot fuel is allowed to drain from the pilot circuit during pilot injection events thereby preventing hydraulic lock and loss of fuel regulation by a dome loaded regulator. Pilot pulse width PPW during the non-motoring operating mode can be selected as a function of the bias between main fuel pressure and pilot fuel pressure, as determined by pressure sensors 165 and 195.

(14) Referring now to FIG. 5, the bias between main fuel injection pressure 320 and pilot fuel injection pressure 330 is maintained during the non-motoring operating mode, thereby preventing displacement of pilot fuel by main fuel within pilot fuel cavities inside fuel injector 110. When engine 100 returns to a motoring operating mode both injection and combustion of pilot and main fuel are within normal operating parameters of engine 100.

(15) Referring now to FIG. 7, there is shown main fuelling command 300 and pilot fuelling command 310 according to a second embodiment employed to create main and pilot injection command signals for fuel injector 110 (seen in FIG. 1). This embodiment is similar to the previous embodiment and like parts have like reference numerals and will not be described in detail, if at all. In addition to pilot fuelling command value FC.sub.P2 during the non-motoring operating mode after time T.sub.1, or alternatively, main fuelling command 300 can have value FC.sub.M2 to actuate fuel injector 110 to drain pilot fuel to supply tank 220. Referring to FIG. 8, each main fuelling command value has an associated main injection command signal (sent through wire 230), which is an electrical signal that can be represented as a square wave having a main pulse width MPW. For the main needle to move away from the main valve seat, the pressure in the main control chamber decreases below the main threshold. The main actuator is actuated by a main injection command signal having minimum pulse width of MPW.sub.MIN for the pressure in the main control chamber to decrease below the main threshold causing the main needle to move away from the main valve seat and main fuel to be injected into the combustion chamber. Referring to both FIGS. 7 and 8, when main fuelling command 300 has a value of FC.sub.M2 after time T.sub.1, the main actuator is actuated by a main injection command signal having a pulse width less than or equal to maximum pulse width MPW.sub.MAX such that the pressure in the main control chamber does not decrease below the main threshold and the main needle does not move away from the main valve seat, resulting in no injection of main fuel into the combustion chamber. The difference between MPW.sub.MIN and MPW.sub.MAX is a predetermined range of tolerance allowed between these values, also known as main safety factor MSF. When fuel injector 110 is actuated by a main injection command signal of pulse width less than or equal to MPW.sub.MAX, no main fuel is injected to the combustion chamber but pilot fuel is drained to supply tank 220 through drain circuit 210. During the non-motoring operating mode in FIG. 7 after time T.sub.1, the value of main fuelling command 300 is less than a maximum main fuelling command value associated with maximum pulse width MPW.sub.MAX such that no main fuel is injected into the combustion chamber but pilot fuel is allowed to drain from the pilot circuit during main injection events thereby preventing hydraulic lock and loss of fuel regulation by the dome loaded regulator. Main pulse width PPW during the non-motoring operating mode can be selected as a function of the bias between main fuel pressure and pilot fuel pressure, as determined by pressure sensors 165 and 195.

(16) Both, or either, pilot injection events and main injection events can be employed to provide flow from the pilot circuit to drain circuit 210 thereby preventing hydraulic lock and loss of fuel regulation by the dome loaded regulator. The minimum pulse widths PPW.sub.MIN and MPW.sub.MIN are normally different and the maximum pulse widths PPW.sub.MAX and MPW.sub.MAX are normally different since the mechanical elements (for example springs and needles) employed in the pilot and main injection valves inside fuel injector 110 are normally different.

(17) Referring now to FIG. 9 there is shown engine 400 according to a second embodiment where like parts to previous embodiments have like reference numerals and will not be described in detail, if at all. Pilot fuel common rail 160 comprises orifice 410 which allows pilot fuel to drain to drain circuit 210 at a predetermined flow rate. Since pilot fuel is continuously draining from the common rail, hydraulic lock and loss of fuel regulation by the dome loaded regulator is prevented.

(18) Referring now to FIG. 10 there is shown engine 500 according to a second embodiment where like parts to previous embodiments have like reference numerals and will not be described in detail, if at all. Electronic solenoid valve 510 is actuated by controller 250 to allow pilot fuel to flow to drain circuit 210 preventing hydraulic lock and loss of fuel regulation by the dome loaded regulator.

(19) While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.