Fuel injector method and apparatus

Abstract

One spring and two spring embodiments of a fuel injector having a nozzle body and needle valve with cooperating inner and outer metering rings providing a metering passage which (a) meters fuel at a reduced rate during an initial increment of valve lift, (b) assists in maintaining fuel pressure at the valve seat to reduce fuel dribble and cavitation erosion during a corresponding last increment of valve closure and (c) dampens secondary pressure waves to prevent secondary fuel injection.

Description

Claims

1. A fuel injector comprising a nozzle body with an elongated valve bore, an annular valve seat and longitudinally spaced, coaxial, upper valve guide and lower valve ring above the valve seat; an elongated nozzle needle valve in the valve bore having longitudinally spaced, coaxial, upper guide and lower ring which cooperate with the upper valve guide and lower valve ring respectively of the nozzle body to provide axial movement of the needle valve within the valve bore between a lower closed position in engagement with the valve seat and an upper fully open position with a predetermined maximum lift; the nozzle body having hole means connected to the valve bore below the valve seat for injection of fuel; the nozzle body providing an upper fuel chamber surrounding the needle valve between the upper valve guide and lower valve ring and a lower fuel chamber surrounding the needle valve between the lower valve ring and valve seat; two stage valve closure spring means biasing the needle valve downwardly into engagement with the valve seat, including first stage spring means holding the needle valve in its closed position and biasing the needle valve downwardly as it is lifted upwardly from its closed to its fully open position and second stage spring means biasing the needle valve downwardly as it is lifted upwardly from a predetermined intermediate position with a predetermined intermediate lift to its fully open position; the upper guide of the needle valve having a greater diameter than the valve seat to provide a differential area for hydraulically opening the needle valve against the bias of the valve closure spring means; the upper fuel chamber being connected to receive periodic high pressure pulses of fuel for opening the needle valve against the bias of the spring means and for supplying fuel for fuel injection through the hole means; the lower valve ring forming an outer metering ring with an internal, annular metering surface with an upper metering edge; the lower ring of the needle valve forming an inner metering ring with an external annular, metering surface with a lower metering edge; the inner metering ring, with the needle valve in its closed position, being received within the outer metering ring with the inner ring metering edge below the outer ring metering edge by a predetermined axial overlap substantially less than said predetermined maximum lift and slightly more than said predetermined intermediate lift and with a predetermined annular clearance between the inner and outer metering surfaces providing a metering passageway to regulate fuel flow between the upper and lower fuel chambers during an initial increment of upward movement of the needle valve from its closed position and to its said intermediate position and to regulate the pressure in the lower fuel chamber during the corresponding last increment of downward movement of the needle valve.

2. A fuel injector according to claim 1 wherein the fuel injector is a hole type injector in which the nozzle body has a nozzle tip below the needle valve enclosing the lower end of the valve bore and said hole means comprises one or more spray holes connected to the valve bore below the valve seat.

3. A fuel injector according to claim 1 wherein said axial overlap is approximately one-half said predetermined maximum lift.

4. A fuel injector according to claim 1 wherein said axial overlap is greater than said predetermined intermediate lift in the range of 0.001 to 0.005 inch.

5. A fuel injector according to claim 1 wherein said clearance is a diametrical clearance in the range of 0.0003 to 0.0006 inch.

6. A fuel injector according to claim 1 wherein said axial overlap is no greater than approximately 0.008 inch.

7. A fuel injector according to claim 1 wherein the outer ring metering edge is circular.

8. A fuel injector according to claim 1 wherein the inner ring metering edge is circular.

9. A fuel injector according to claim 1 wherein the inner ring metering surface is cylindrical.

10. A fuel injector according to claim 1 wherein the outer ring metering surface is cylindrical.

11. A fuel injector according to claim 1 wherein the inner metering ring has a diameter greater than that of the valve seat and less than that of the upper guide of the needle valve.

12. A method of fuel injection with a fuel injector comprising a nozzle body with an elongated valve bore, an annular valve seat and longitudinally spaced, coaxial, upper valve guide and lower valve ring above the valve seat; an elongated needle valve in the valve bore having longitudinally spaced, coaxial, upper guide and lower ring which cooperate with the upper valve guide and lower valve ring respectively of the nozzle body to provide axial movement of the needle valve within the valve bore between a lower closed position in engagement with the valve seat and an upper fully open position having a predetermined maximum lift; the nozzle body having hole means connected to the valve bore below the valve seat for injection of fuel; the nozzle body providing an upper fuel chamber surrounding the needle valve between the upper valve guide and lower valve ring and a lower fuel chamber surrounding the needle valve between the lower valve ring and valve seat; closure spring means biasing the needle valve downwardly into engagement with the valve seat, including first stage spring means holding the needle valve in its closed position and biasing the needle valve downwardly as it is lifted upwardly from its closed to its fully open position and second stage spring means biasing the needle valve downwardly as it is lifted upwardly from a predetermined intermediate position with a predetermined intermediate lift to its fully open position; the upper guide of the needle valve having a greater diameter than the valve seat to provide a differential area for hydraulically opening the needle valve against the bias of the valve closure spring means; the upper fuel chamber being connected to receive high pressure pulses of fuel for opening the needle valve against the bias of the spring means and for supplying fuel for fuel injection through the hole means; the method comprising the steps of providing a predetermined fuel metering passage between the lower rings of the nozzle body and needle valve for metering fuel between the upper and lower fuel chambers during only an initial increment of upward movement of the needle valve from its closed position substantially less than said predetermined maximum lift and slightly greater than said predetermined intermediate lift, and a corresponding last increment of downward movement of the needle valve, thereby to regulate the rate of fuel injection during said initial increment of upward movement and the pressure in the lower fuel chamber during said last increment of downward movement.

13. A fuel injection method according to claim 12 wherein said initial increment of opening movement is approximately one half said predetermined lift.

14. A fuel injection method according to claim 12 wherein said initial increment of opening movement is greater than said predetermined intermediate lift in the range of 0.001 to 0.005 inch.

15. A fuel injection method according to claim 12 wherein said initial increment of opening movement is in the range of 0.004 to 0.008 inch.

16. A fuel injection method according to claim 12 wherein said predetermined maximum lift is in the range of 0.008 to 0.016 inch.

17. A fuel injection method according to claim 12 wherein said metering passage is provided by an annular clearance passageway between the lower rings of the nozzle body and needle valve having a diametral clearance in the range of 0.0003 to 0.0006 inch.

18. A fuel injection method according to claim 12 wherein the lower ring of the needle valve has a diameter greater than that of the valve seat and less than that of the upper guide of the needle valve.