Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
2001-11-29
2004-01-06
Gimie, Mahmoud (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S301000, C123S305000
Reexamination Certificate
active
06672277
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
This invention relates to a direct-injection spark ignition engine for directly injecting a fuel into a combustion chamber in a cylinder and igniting a mixture thus prepared in a condition of being stratified around an electrode of a spark plug, and more particularly relates to a technique of controlling behavior of fuel spray for promoting suitable stratification of the mixture by effectively using a tumble in the combustion chamber.
(b) Description of the Prior Art
Conventionally, direct-injection spark ignition engines of such type are constructed so that a high-pressure fuel injection nozzle is disposed so as to be presented to a combustion chamber in a cylinder and a cavity of predetermined shape is formed in a piston crown surface, whereby a fuel injected from the fuel injection nozzle is first brought into impingement against an inner wall surface or a bottom surface of the cavity opposed thereto and then confined in the cavity for stratification around a spark plug electrode.
There also exist engines of a type which concentrates a mixture into a cavity or transports it to the vicinity of a spark plug electrode using in-cylinder airflows, such as a swirl flow or a tumble flow, in a combustion chamber. For example, an in-cylinder injection type engine, as disclosed in Japanese Unexamined Patent Publication Gazette No. 11-141338, reverses the direction of fuel injection from that of the tumble, pushes back the mixture which tends to overflow from the cavity to confine it in the cavity by the action of the tumble, and transports the mixture to the vicinity of the spark plug electrode in the cavity while promoting vaporization of fuel droplets or mixture thereof with air.
Alternatively, like an in-cylinder injection type spark ignition engine disclosed in Japanese Unexamined Patent Publication Gazette No. 11-200866, there exist engines of a type which transports a fuel having been spread into a cavity toward a spark plug so as to carry the fuel with a tumble while suppressing adhesion of the fuel to a piston crown surface by forming the cavity substantially in the center of the piston crown surface and into a spherical shape to enhance retentivity of the tumble flow and by widening the spray cone angle of spray from a fuel injection nozzle up to, for example, 70°-90° to damp fuel spray penetration.
However, it is difficult to say that any prior art engines mentioned above suitably stratify the mixture over a wide range of operating conditions different in load and revolving speed. When viewed over a complete range of engine operating conditions, they still have plenty of room to enhance effects such as fuel economy improvement by stratified-charge combustion operation. Specifically, in the engine which requires to confine the mixture in the cavity like the former prior art (Japanese Unexamined Patent Publication No. 11-141338), the range of engine operating conditions within which the mixture can be suitably stratified is strictly constrained by the cavity size and shape, and in fact the range of operating conditions within which the engine is capable of stratified operation is limited to a narrow region on the low-load and low-speed end of its control map. Therefore, the engine can provide only a small effect of fuel economy improvement.
Furthermore, in such a direct-injection engine, since the inner wall surface of the cavity against which fuel spray injected from the fuel injection nozzle impinges is generally located in the vicinity of the center line of the cylinder, it cannot be avoided that the inner wall surface inhibits the growth of a flame core in the initial combustion stage and decreases flame propagation performance, which in fact deteriorates combustion quality. In addition, in this engine, since the fuel spray is caused to impinge against the inner wall surface or the bottom surface of the cavity, the amount of adhesion of the fuel to the wall surface and the like is increased. This invites inconveniences of decrease in fuel economy and increase in unburnt hydrocarbon (HC).
For example,
FIG. 35
comparatively shows results of a test conducted as follows: a plurality of pistons different in their cavity shapes were prepared and the rate of fuel economy improvement and the rate of power output improvement of each engine by direct injection were experimentally obtained. According to the figure, there is a so-called “trade-off relationship” between fuel economy improvement and power output improvement. In the engine (Point A of the figure) in which the cavity in the shape of a deep dish is provided like the former prior art, the effect of fuel economy improvement at low load and low speeds is enhanced because the fuel spray can be confined suitably for stratification, whereas the effect of power output improvement is deteriorated because of degradation in the combustion quality particularly at higher engine speeds.
In a so-called “flat piston” (Point C) in which the crown surface thereof is simply formed in a concave shape, the effect of power output improvement at higher engine speeds is enhanced, whereas the effect of fuel economy improvement is inevitably deteriorated because of the difficulty in suitably stratifying the mixture at low load. As an intermediate between the above two types, there is an engine (Point B) in which the inner wall surface of the cavity opposed to the fuel injection nozzle is largely inclined. However, it cannot be expected that the engine of this type largely improves both fuel economy and power output.
Next, consider the latter prior art (Japanese Unexamined Patent Publication No. 11-200866). It seems that the latter prior art also produces the same inconveniences as caused in the former prior art when its cavity size is small. On the other hand, if its cavity size is large, then suitable stratification of the mixture becomes difficult like the above-mentioned flat piston. Specifically, the engine of this type intends to transport the fuel having been dispersed into the cavity to the spark plug so as to carry it with a tumble. However, when the cavity size is increased, it becomes difficult to concentrate the fuel thus dispersed. And even if the fuel can be concentrated, the fuel goes along with the tumble and passes by the vicinity of the spark plug electrode. Therefore, the period during which the mixture can be ignited by the spark plug is extremely short. Accordingly, it cannot be said that the engine implements suitable mixture stratification.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing points and a major object thereof is to improve fuel economy and power output through improvement of combustion quality and extension of a stratified-charge combustion zone by controlling fuel spray behavior in a combustion chamber to allow suitable mixture stratification over a wide range of operating conditions of a direct-injection spark ignition engine when the engine conducts stratified-charge combustion operation.
To attain the above object, in solutions of the present invention, a tumble is generated to flow from the vicinity of a spark plug electrode toward a fuel injection nozzle at the compression stroke of a cylinder during stratified-charge combustion operation of an engine, and a fuel is injected at a suitable penetration so as to go against the tumble so that a flammable mixture can be retained in the vicinity of the spark plug at an exact ignition timing for the cylinder.
More specifically, the invention of claim 1 is directed to 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. The engine has a configuration which comprises: tumble generat
Araki Keiji
Matsumoto Masakazu
Ohta Noriyuki
Saito Fumihiko
Seto Masatoshi
Gimie Mahmoud
Mazda Motor Corporation
Nixon & Peabody LLP
Studebaker Donald R.
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