Internal-combustion engines – Combustion chamber means having fuel injection only – Injected fuel spraying into whirling fluid
Reexamination Certificate
2002-07-16
2003-04-22
Mohanty, Bibhu (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Injected fuel spraying into whirling fluid
C123S306000, C123S399000, C123S564000
Reexamination Certificate
active
06550445
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a spark-ignition direct injection engine with supercharger, which has been provided with a supercharger for boosting intake air and which stratifies fuel that has been directly injected into the combustion chamber around the electrodes of the spark plugs within the cylinders and combusts it, and in particular relates to the technological field of combustion control in a specific driving region on the high-speed high-load side.
In a conventional example of this type of spark-ignition direct injection engine with supercharger disclosed in JP 2000-274278A, for example, the supercharger is stopped when the engine is in a state of stratified combustion, whereas flow within the cylinder is strengthened by boosting when the engine is in a state of homogenous combustion. This means that during low speeds and low loads at which a state of stratified combustion is assumed, the boosting of intake air by the supercharger is stopped or inhibited to leave a relatively weak state of flow within the cylinder, thereby keeping the air-fuel mixture from diffusing within the combustion chamber and thus achieving suitable stratification. On the other hand, during high-speeds and high-loads at which a state of homogenous combustion is assumed, the flow within the cylinders is strengthened by boosting to adequately mix the intake air with the large volume of fuel injected into the combustion chamber during the intake stroke and form an air-fuel mixture that is as uniform as possible.
In general, in an engine with a supercharger, only a portion of the exhaust is supplied to the supercharger when there is a high exhaust flow and/or pressure, and the rest is released into the air to keep the boost pressure of the intake air due to the supercharger below a target value (maximum boost pressure). This also applies to the above conventional example, where a portion of the exhaust bypasses the supercharger and flows down the exhaust pipe when the engine is in a high-speed high-load driving state. A portion of the energy held by the high pressure exhaust is discarded at this time.
However, due to the structure of a spark-ignition direct injection engine, which directly injects fuel into the combustion chamber within the cylinders of the engine, the period in a single combustion cycle during which fuel injection is possible is restricted to the intake stroke and the compression stroke of the cylinders. Thus, not enough time can be secured between fuel injection and ignition, and during high-load operation where a greater volume of fuel is injected, it is difficult to sufficiently vaporize and atomize the fuel before the cylinders are fired. As a consequence, a portion of the fuel is baked, and this leads to the discharge of particulate matter (hereinafter, referred to as PM) like in diesel engines.
A greater volume of fuel is injected particularly when the engine is in a high-speed high-load driving state, however, the time interval during which the fuel can be injected is shortened inversely proportional to the increase in engine revolution speed. This retards the end of the fuel injection, which further shortens the period between fuel injection and ignition and complicates vaporization and atomization. Also, there is a drop in the flow within the cylinder during the compression stroke of the cylinder compared to during the intake stroke, and thus during the compression stroke it becomes difficult to promote the fuel injected into the cylinder to mix with the air. This also hinders fuel vaporization and atomization.
Additionally, giving consideration to exhaust system reliability, in spark-ignition engines, the air-fuel ratio is generally controlled in a specific driving region on the high-speed or the high-load side so that it is richer than the theoretical air-fuel ratio in order to keep the exhaust temperature from rising due to the latent heat of excess fuel. Thus, even if the intake air is boosted by the supercharger to strengthen the flow within the cylinder when the engine is in this specific driving region, as in the above conventional example, the resulting effect is surpassed by the effect of the large volume of fuel that is supplied, making the above problem of PM even more conspicuous.
The present invention was arrived at in light of the above problems. It is an object of the present invention to exploit the fact that spark-ignition direct injection engines that are provided with a supercharger conventionally discard a portion of the exhaust energy during high-speed high-load engine operation, and a solution has been adopted to control, for example, the boost pressure or the like particularly in a specific driving region on the high-speed high-load side in order to ensure maximum engine output and exhaust system reliability while also achieving a reduction in PM within the exhaust.
SUMMARY OF THE INVENTION
To achieve the above object, one solution presented by the present invention is to collect the portion of exhaust energy that has conventionally been discarded in the specific driving region on the high-speed high-load side, and effectively use it to maximize the strength of the flow within the cylinder.
More specifically, as shown illustratively in
FIG. 1
, it is a premise of a first aspect of the present invention that a spark-ignition type 4-cycle direct injection engine
1
is provided with a supercharger
40
for boosting intake air to the cylinder and a fuel injection valve
18
for directly injecting and supplying fuel to a combustion chamber
6
within the cylinders, and that fuel is injected during the intake stroke of the cylinder
2
by the fuel injection valve
18
in at least a supercharge region on a high-speed high-load side to attain a state of homogenous combustion.
This configuration is also provided with a flow strengthening means
30
for constricting the flow of intake air into the cylinder in order to strengthen the flow within the cylinder, a boost pressure adjustment means
42
for keeping the boost pressure of the intake air due to the supercharger
40
below a target boost pressure, an air-fuel ratio control means
50
b
for controlling an air-fuel ratio A/F in the cylinder to become A/F≦13 in a specific driving region that is established on the high-speed high-load side of the supercharge region, a flow control means
50
c
for increasing the amount of constriction on the intake air caused with the flow strengthening means
30
so as to relatively strengthen the flow in the cylinder in the specific driving region as compared to that in a region that is adjacent to the low-load side of the specific driving region, even if the engine revolution speed is the same, and a boost pressure control means
50
d
for controlling the boost pressure adjustment means
42
to relatively increase the target boost pressure in the specific driving region as compared to that in a region that is adjacent to a low-speed side of the specific driving region.
According to this configuration, first, when the engine
1
is in a predetermined high-speed high-load driving region (specific driving region), the air-fuel ratio within the cylinder
2
of the engine
1
is enriched by the air-fuel ratio control means
50
b
to become A/F≦13, and the temperature of the exhaust is kept from rising due to the latent heat of the overly large volume of fuel compared to the volume of air. Also, the boost pressure adjustment means
42
is controlled by the boost pressure control means
50
d
to raise the target boost pressure, and the flow strengthening means
30
is controlled by the flow control means
50
c
to increase the amount of constriction on the intake air, so that the combination of these actions strengthens the flow within the cylinder as much as possible and sufficiently promotes fuel vaporization and atomization.
That is, in the specific driving region on the high-speed high-load side, the exhaust energy that has conventionally been discarded is utilized to further boost the intake air with the supercharger
40
, and this in
Fujii Mikihito
Uchida Hiroyasu
Umezono Kazuaki
Mazda Motor Corporation
Mohanty Bibhu
Nixon & Peabody LLP
Studebaker Donald R.
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