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Direct-injection spark ignition engine

Imported: 24 Feb '17 | Published: 06 Jan '04

Takehiko Yasuoka, Noriyuki Ohta, Hiroyuki Yamashita, Masatoshi Seto, Masakazu Matsumoto, Fumihiko Saito, Keiji Araki

USPTO - Utility Patents

Abstract

During stratified-charge combustion operation of a direct-injection spark ignition engine, at the cylinder compression stroke, a tumble is generated which flows between a spark plug electrode and a piston crown surface toward an injector. A fuel is injected from the injector in correspondence with the cylinder ignition timing by controlling the penetration of fuel spray from the injector to correspond to the tumble flow rate so that the fuel spray may go against the tumble, become a flammable mixture at the cylinder ignition timing and stay near the spark plug electrode. In the late stage of the compression stroke, diffusion of the flammable mixture is suppressed with squishes. Thus, fuel spray behavior in the combustion chamber is controlled to allow suitable mixture stratification over a wide engine operating condition range. This improves combustion quality and extends a stratified-charge combustion zone thereby providing enhanced fuel economy and power output.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a condition of a mixture residing in the vicinity of a spark plug electrode at an ignition timing for a cylinder in a direct-injection spark ignition engine according to Embodiment 1 of the present invention.

FIG. 2 is a diagram showing the entire structure of the engine.

FIG. 3 is a perspective view showing the layout of a piston crown surface, an intake port, a spark plug and an injector.

FIG. 4 is a graph showing an exemplary relation between the penetration and spray cone angle of fuel spray from the injector.

FIGS. 5A-B shows schematic diagrams illustrating structures of fuel supply systems.

FIG. 6 is a graph showing an exemplary control map in which respective operation zones where the engine is put into stratified-charge combustion condition and homogeneous-charge combustion condition are set.

FIGS.

7A-C: FIG. 7A is a top view showing the structure of the piston, FIG. 7B is a cross-sectional view cut along the line b—b, and FIG. 7C is a cross-sectional view cut along the line c—c.

FIG. 8 is a diagram illustrating the positional relation among a cavity of the piston crown surface, a tumble and fuel spray when viewed along the center line of the cylinder.

FIG. 9 is a view illustrating the geometrical area, center line and spray cone angle of fuel spray from the injector.

FIGS.

10A-B: FIG. 10A is a diagram illustrating the spray cone angle of fuel spray, and FIG. 10B is a diagram illustrating the penetration of fuel spray.

FIG. 11 is a view corresponding to FIG. 1 at a fuel injection timing for the cylinder.

FIG. 12 is a diagram illustrating change of fuel spray behavior caused by change of the center line of fuel spray.

FIG. 13 is a graph showing the change in the local air fuel ratio around the spark plug electrode in the vicinity of the top dead center in correspondence with the change in the center line of fuel spray.

FIG. 14 is a graph showing the relation between the change in the center line of fuel spray and the change in amount of adhesion of fuel to the piston crown surface.

FIG. 15 is a graph showing the relation between the change in the local air fuel ratio around the spark plug electrode and the change in the spray cone angle of fuel spray.

FIGS. 16A-B show a state of a mixture when the spray cone angle of fuel spray is approximately 20°.

FIGS. 17A-B show a state of a mixture when the spray cone angle of fuel spray is approximately 60°.

FIGS. 18A-B show a state of a mixture when the piston crown surface is formed with a lemon-shaped cavity.

FIG. 19 is a view illustrating the position of the spark plug electrode in comparison with a tumble at an ignition timing for the cylinder.

FIG. 20 is a graph showing the relation between the amount of protrusion of the spark plug electrode and the flow rate of the tumble.

FIG. 21 is a graph showing the relation between the mount of protrusion of the spark plug electrode and the rate of combustion variation.

FIG. 22 is a graph in which the range of percentage of protrusion of the spark plug electrode is set in accordance with the change in the fuel injection timing for the cylinder.

FIG. 23 is a view showing the result of a CFD analysis of flow distribution where the tumble and the fuel spray are balanced one against another in a combustion chamber.

FIGS.

24A-B: FIG. 24A is a view showing a state of a mixture where the tumble moderately impinges against the fuel spray, and FIG. 24B is a view showing a state of a mixture where impingement is too much hard.

FIGS. 25A-B show maps respectively showing the change in the flow rate of the tumble and the penetration of fuel spray in accordance with the revolving speed of the engine.

FIG. 26 is a map showing the relation between the penetration of fuel spay and the fuel injection pressure.

FIGS. 27A-B show maps corresponding to FIG. 25 in a modification.

FIG. 28 is a schematic diagram of the structure of an apparatus for measuring a tumble ratio.

FIG.

29A-B: FIG. 29A is a graph showing the change in temperature conditions of the combustion chamber in relation to the change in the intake temperature and the change in the penetration of fuel spray, and FIG. 29B is a graph showing the change in temperature conditions of the combustion chamber in relation to the change in the fuel injection pressure and the attendant change in the penetration of fuel spray.

FIG. 30 is view corresponding to FIG. 1 at an intake stroke of the cylinder.

FIG. 31 shows graphs of comparison of the relation between engine load and each of the rate of fuel economy improvement, rate of fuel consumption and rate of HC emission at low speed of the inventive engine with that in the case of a conventional type direct-injection engine.

FIG. 32 shows graphs corresponding to FIG. 31 at middle speed of the engines.

FIGS. 33A-C show views corresponding to FIG. 7 according to Embodiment 2 of the present invention.

FIGS. 34A-B show diagrams illustrating another embodiment of the present invention in which the flow rate of the tumble is controlled by changing the valve timing.

FIG. 35 is a graph showing the trade-off relationship between the rate of power output improvement and the rate of fuel economy improvement in a prior-art direct-injection engine.

FIGS. 36A-B show diagrams illustrating a squish area created between the piston crown surface and the ceiling of the combustion chamber in Embodiment 1.

FIG. 37 is a diagram showing the result of a CFD analysis of flow distribution near to the ignition timing for the cylinder in a cross section of the combustion chamber when viewed along the center line of the cylinder.

FIG. 38 is a corresponding diagram of FIG. 36 in a longitudinal cross section of the combustion chamber when viewed from an injector side.

FIGS. 39A-B show corresponding graphs of FIG. 25 according to a second modification of Embodiment 1.

FIGS. 40A-C show corresponding views of FIG. 7 according to Embodiment 3 of the present invention.

FIGS. 41A-C show diagrams schematically illustrating how the center of a tumble vortex moves with upward movement of the piston during a period from the early stage to middle stage of the compression stroke of the cylinder.

FIGS. 42A-C show diagrams of results of a CFD analysis on the change in flow distribution during the period from the early stage to middle stage of the compression stroke of the cylinder.

FIGS. 43A-C show diagrams corresponding to FIG. 41 in the case of a piston of Embodiment 3.

FIGS. 44A-C show corresponding diagrams of FIG. 7 according to another embodiment of the present invention in which the bottom surface of the cavity in the piston crown surface is flat.

Claims

1. A direct-injection spark ignition engine in which a spark plug is disposed in a cylinder at a ceiling of a combustion chamber opposed to a crown surface of a piston, a fuel injection nozzle is disposed in the combustion chamber to inject a fuel from a peripheral portion of the combustion chamber, and the fuel injected from the fuel injection nozzle is stratified around an electrode of the spark plug during stratified-charge combustion operation, said engine comprising:

2. The direct-injection spark ignition engine of claim 1, wherein the electrode of the spark plug is disposed closer to the crown surface of the piston than to the nozzle hole of the fuel injection nozzle when viewed in a direction orthogonal to the center line of the cylinder.

3. The direct-injection spark ignition engine of claim 1, wherein the spray cone angle of fuel spray from the fuel injection nozzle during the compression stroke of the cylinder is at a value within the range of approximately 20° to 60°.

4. The direct-injection spark ignition engine of claim 1, wherein the fuel injection nozzle is disposed so that the fuel spray impinges substantially oppositely against the tumble flowing along the crown surface of the piston during the compression stroke of the cylinder.

5. The direct-injection spark ignition engine of claim 1, wherein

6. The direct-injection spark ignition engine of claim 1, wherein the fuel injection control means controls the penetration of fuel spray from the fuel injection nozzle in accordance with the revolving speed of a crank shaft.

7. The direct-injection spark ignition engine of claim 1, wherein

8. The direct-injection spark ignition engine of claim 7, wherein the fuel injection control means is arranged to correctively control the operation of the injection pressure regulating means in accordance with the temperature conditions of the combustion chamber so that the fuel injection pressure becomes larger as the temperature of the combustion chamber is increased even if the fuel injection quantity and the revolving speed of the crank shaft are substantially constant.

9. The direct-injection spark ignition engine of claim 1, wherein the fuel injection nozzle is provided with a variable spray angle mechanism for adjusting the spray cone angle of fuel spray, and the fuel injection control means is arranged to cause the variable spray angle mechanism to decrease the spray cone angle of fuel spray in increasing the penetration of fuel spray and to increase the spray cone angle of fuel spray in decreasing the penetration of fuel spray.

10. The direct-injection spark ignition engine of claim 1, wherein

11. The direct-injection spark ignition engine of claim 10, wherein the variable tumble means comprises an intake airflow control valve for changing the flowing conditions of the intake air flowing into the combustion chamber.

12. The direct-injection spark ignition engine of claim 10, wherein the variable tumble means is a variable valve timing mechanism for changing the valve timing of at least one of intake and exhaust valves.

13. The direct-injection spark ignition engine of claim 10, wherein the tumble control means correctively controls the operation of the variable tumble means in accordance with the temperature conditions of the combustion chamber so that the flow rate of the tumble is lower as the temperature of the combustion chamber is higher even if the fuel injection quantity and the revolving speed of the crank shaft is substantially constant.

14. A direct-injection spark ignition engine in which a spark plug is disposed in a cylinder at a ceiling of a combustion chamber opposed to a crown surface of a piston, a fuel injection nozzle is disposed in the combustion chamber to inject a fuel from a peripheral portion of the combustion chamber, and the fuel injected from the fuel injection nozzle is stratified around an electrode of the spark plug during stratified-charge combustion operation, wherein

15. The direct-injection spark ignition engine of claim 14, characterized by further comprising:

16. The direct-injection spark ignition engine of claim 14, wherein

17. A direct-injection spark ignition engine in which a spark plug is disposed in a cylinder at a ceiling of a combustion chamber opposed to a crown surface of a piston, a fuel injection nozzle is disposed in the combustion chamber to inject a fuel from a peripheral portion of the combustion chamber, and the fuel injected from the fuel injection nozzle is stratified around an electrode of the spark plug during stratified-charge combustion operation, said engine comprising:

18. The direct-injection spark ignition engine of claim 17, wherein the distance e between the ceiling of the combustion chamber and the electrode of the spark plug is set at a value satisfying the relationship of e≧0.2d where d is the distance on the center line of the cylinder between the ceiling of the combustion chamber and the crown surface of the piston when the cylinder is at a 55° crank angle before the top dead center during the compression stroke thereof.

19. The direct-injection spark ignition engine of claim 17, wherein the electrode of the spark plug is disposed closer to the ceiling of the combustion chamber than to the crown surface of the piston, when viewed along the center line of a geometrical area of fuel spray from the fuel injection nozzle during the compression stroke of the cylinder, with respect to the center line of fuel spray.

20. A direct-injection spark ignition engine in which a spark plug is disposed in a cylinder at a ceiling of a combustion chamber opposed to a crown surface of a piston, a fuel injection nozzle is disposed in the combustion chamber to inject a fuel from a peripheral portion of the combustion chamber, and the fuel injected from the fuel injection nozzle is stratified around an electrode of the spark plug during stratified-charge combustion operation, said engine comprising:

21. A direct-injection spark ignition engine in which a spark plug is disposed in a cylinder at a ceiling of a combustion chamber opposed to a crown surface of a piston, a fuel injection nozzle is disposed in the combustion chamber to inject a fuel from a peripheral portion of the combustion chamber, and the fuel injected from the fuel injection nozzle is stratified around an electrode of the spark plug during stratified-charge combustion operation, said engine comprising:

22. A direct-injection spark ignition engine in which a spark plug is disposed in a cylinder at a ceiling of a combustion chamber opposed to a crown surface of a piston, a fuel injection nozzle is disposed in the combustion chamber to inject a fuel from a peripheral portion of the combustion chamber, and the fuel injected from the fuel injection nozzle is stratified around an electrode of the spark plug during stratified-charge combustion operation, said engine comprising:

23. The direct-injection spark ignition engine of claim 22, wherein the opening width of the cavity in the lateral direction when viewed along the center line of the cylinder is maximized in the vicinity of the electrode of the spark plug.

24. The direct-injection spark ignition engine of claim 23, wherein the opening width of the cavity in the lateral direction in the vicinity of the electrode of the spark plug when viewed along the center line of the cylinder is set to include a geometrical area of fuel spray from the fuel injection nozzle during the compression stroke of the cylinder.

25. The direct-injection spark ignition engine of claim 23, wherein

26. The direct-injection spark ignition engine of claim 22, wherein the squish area sections are provided in the outer portion of the crown surface of the piston to continue from both the lateral locations thereof, which interpose the electrode of the spark plug therebetween, toward the exhaust side.

27. A direct-injection spark ignition engine in which a spark plug is disposed in a cylinder at a ceiling of a combustion chamber opposed to a crown surface of a piston, a fuel injection nozzle is disposed in the combustion chamber to inject a fuel from a peripheral portion of the combustion chamber, and the fuel injected from the fuel injection nozzle is stratified around an electrode of the spark plug during stratified-charge combustion operation, said engine comprising:

28. The direct-injection spark ignition engine of claim 27, wherein

29. A direct-injection spark ignition engine in which a spark plug is disposed in a cylinder at a ceiling of a combustion chamber opposed to a crown surface of a piston, a fuel injection nozzle is disposed in the combustion chamber to inject a fuel from a peripheral portion of the combustion chamber, and the fuel injected from the fuel injection nozzle is stratified around an electrode of the spark plug during stratified-charge combustion operation, said engine comprising: