JP3695056B2 - In-cylinder direct fuel injection spark ignition engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an in-cylinder direct fuel injection spark ignition engine.
[0002]
[Prior art]
Examples of conventional in-cylinder direct fuel injection type spark ignition engines include those shown in FIGS. 14 and 15 (JP-A-5-79370, etc.).
[0003]
This is because an ignition plug 61 is disposed at the center of the combustion chamber wall surface of the cylinder head 60, and a fuel injector 62 is disposed at the periphery of the combustion chamber wall surface, and the crown surface of the piston 63 extends from below the fuel injector 62 to the center of the crown surface. A deep recess (cavity) 64 is formed.
[0004]
The intake port is provided with a helical port 65 and a straight port 66 with an intake control valve (not shown) provided in the middle, and swirl flow (swirl) by intake air flowing into the cylinder from the helical port 65 Is born.
[0005]
In such an engine, when the load on the engine is light, fuel is injected and supplied from the fuel injector 62 in the latter half of the compression stroke, and a combustible air-fuel ratio mixture layer is formed in the vicinity of the spark plug 61. Performing so-called stratified mixture operation with a lean mixture, and inhaling more air than the stoichiometric air-fuel ratio for less fuel, reducing pumping loss and heat loss, improving engine thermal efficiency, and improving fuel efficiency It is possible to improve.
[0006]
[Problems to be solved by the invention]
However, in such an in-cylinder direct fuel injection type spark ignition engine, in order to perform a stratified mixture operation without impairing the stability of the engine even at a low load operation with a small fuel injection amount, In order to form a combustible air-fuel ratio mixture layer in the vicinity of 61, a fuel spray concentrated from the fuel injector 62 or a combustion chamber having a shape and structure for concentrating the injected fuel is required. Then, even in the stratified mixture operating region, in the operating region where the load is relatively high and the fuel injection amount is large, the air-fuel mixture in the vicinity of the spark plug 61 becomes excessively concentrated, causing the generation of smoke, deterioration of ignitability, Contamination may occur.
[0007]
Also, in order to avoid these problems, if the operating region with a so-called homogeneous mixture is made to be in the middle and low load region side, the fuel is injected and supplied in the intake stroke to make the air-fuel ratio in the entire cylinder uniform. As a result, the range of stratified air-fuel mixture operation is narrowed, and the fuel efficiency improvement effect of a practical in-cylinder direct fuel injection spark ignition engine is reduced.
[0008]
The present invention has been made paying attention to such problems, and in a cylinder direct fuel injection type spark ignition engine capable of operating with a stratified mixture, fuel injected by applying an intake swirl and a turning force The air-fuel ratio in the vicinity of the spark plug is made suitable for each region by changing the combination of the swirl direction of the intake swirl and the fuel according to the operation region. The purpose is to solve the above problems.
[0009]
[Means for Solving the Problems]
The first invention is provided with swirl generating means for generating a swirl in the air flowing into the cylinder in a lateral direction that is the circumferential direction of the cylinder, and injecting and supplying fuel toward the combustion chamber in the compression stroke, and combustible near the spark plug In-cylinder direct fuel injection spark ignition engine capable of operating with a stratified mixture that forms a lean mixture as a whole while forming an air / fuel mixture layer and injecting fuel while applying a turning force to the fuel And a swirl direction switching means for switching the swirling direction of the swirl.
[0010]
In a second aspect based on the first aspect, the direction of the swirl is switched according to a predetermined engine load operating condition.
[0011]
According to a third invention, in the first invention, the direction of the swirl is switched according to the stability of the engine or the state of exhaust.
[0012]
In a fourth aspect based on the first aspect, the swirl direction switching means switches the direction of the swirl by switching a plurality of intake ports.
[0013]
In a fifth aspect based on the first aspect, the fuel injection device injects fuel from the peripheral portion of the wall surface of the combustion chamber of the cylinder head.
[0014]
In a sixth aspect based on the first aspect, when viewed substantially from above the cylinder, the swirl direction and the swirl direction of the fuel are opposite to each other when the load in the stratified mixture operation region is low, and in the stratified mixture operation region. Set in the same direction when the load is high.
[0015]
【The invention's effect】
According to the first aspect of the present invention, the fuel spray reaches the spark plug when the fuel injection amount is small in the stratified mixture operation due to the interaction between the fuel injected with the turning force and the direction of the intake swirl. The air-fuel mixture near the spark plug becomes excessively concentrated by forming a sufficiently concentrated air-fuel mixture in the vicinity of the spark plug or by appropriately diffusing the fuel spray when the fuel injection amount is large. And an air-fuel ratio mixture suitable for each condition can be formed in the vicinity of the spark plug.
[0016]
According to the second aspect of the invention, when the fuel injection amount is small and the load is low, an air-fuel mixture having a sufficient concentration is formed in the vicinity of the spark plug so that stable stratified air-fuel mixture operation can be performed. When it is high, the fuel spray is diffused and vaporized appropriately, preventing the air-fuel mixture in the vicinity of the spark plug from becoming excessively rich, avoiding smoke generation, spark plug contamination, etc. Can drive.
[0017]
According to the third aspect of the invention, the stratified mixture operation can be performed accurately while maintaining the stability of the engine and a good exhaust state.
[0018]
According to the fourth aspect of the invention, for example, the intake port is switched through an intake control valve provided in the middle of the intake port, through a variable mechanism of the intake valve, or by a combination of a variable mechanism of the intake control valve and the intake valve. And the direction of the intake swirl is switched.
[0019]
According to the fifth aspect of the present invention, an air-fuel ratio suitable for each condition in the vicinity of the spark plug is obtained by the interaction between the fuel injected by applying a turning force from the periphery of the wall surface of the combustion chamber of the cylinder head and the direction of the intake swirl. Can be formed.
[0020]
According to the sixth aspect of the present invention, the fuel spray is ignited by making the intake swirl direction and the fuel swirl direction opposite to each other when the load in the stratified mixture operation region is low as viewed from above the cylinder. The fuel spray can be appropriately diffused by concentrating in the vicinity and by making the same direction when the load of the stratified mixture operating region is high.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0022]
As shown in FIGS. 1 to 3, a spark plug 15 facing the combustion chamber 2 is disposed on the cylinder center line on the combustion chamber wall surface of the cylinder head 1. In the combustion chamber wall surface around the ignition plug 15 of the cylinder head 1, intake ports 13a and 13b and exhaust ports 14a and 14b are opened, and intake valves 11a and 11b and exhaust valves 12a and 12b are provided at the valve ports, respectively.
[0023]
A fuel injector 5 for injecting and supplying fuel toward the combustion chamber 2 is disposed outside the center of the valve ports of the intake ports 13a and 13b on the periphery of the combustion chamber wall surface of the cylinder head 1.
[0024]
A deep cavity 4 is formed in the crown surface of the piston 3 that reciprocates in the cylinder from the fuel injector 5 side to the center of the crown surface.
[0025]
The intake ports 13a and 13b are respectively provided with intake control valves 17a and 17b that can be opened and closed one by one as swirl generation means and swirl direction switching means, and the intake ports 13a and 13b are switched.
[0026]
When it is sucked into the cylinder from the intake port 13b by closing the intake control valve 17a as shown in FIGS. 1 to 3, lateral is the circumferential direction of the swirl (cylinder of the turning direction 18a (counterclockwise as viewed from the cylinder upward) When the intake control valve 17b is closed and air is sucked into the cylinder from the intake port 13a as shown in FIG. 4 to FIG. 6, swirling direction 18b (clockwise as viewed from above the cylinder) swirl ( cylinder ) The in- cylinder gas flow in the lateral direction, which is the circumferential direction of the gas, is generated.
[0027]
For example, the fuel injector 5 shown in FIGS. 7 to 9 (refer to Japanese Patent Laid-Open No. 5-202825) is used to apply a turning force to the injected fuel.
[0028]
In the figure, 30 is a core that lifts the movable valve 31 by excitation, and 32 is a ball valve that leaves the seat surface 34 of the nozzle 33 by the lift of the movable valve 31 and opens the injection hole 35. A fuel swirling element 38 having swirl chambers 36 and 37 formed therein is provided, and fuel to which a swirling force is applied is injected from the injection hole 35 by the swirl chamber 39 formed by the fuel swirling element 38 and the seat surface 34. Is done.
[0029]
From this fuel injector 5, as shown in FIGS. 2 and 5, fuel is injected while turning in a clockwise direction 9 when viewed from the rear of the fuel injector (substantially above the cylinder).
[0030]
The fuel injection amount and injection timing from the fuel injector 5 are controlled by the control unit. The intake control valves 17a and 17b of the intake ports 13a and 13b are connected to actuators, respectively, and their opening and closing are controlled by the control unit via the actuators.
[0031]
As shown in FIG. 10, as means for detecting engine operating conditions, stability, and exhaust state, a rotational speed sensor (crank angle sensor) 40 for detecting the rotational speed of the engine and an intake air amount sensor 41 for detecting the engine load. , An accelerator opening sensor 42, an in-cylinder pressure sensor 43 for detecting the in-cylinder pressure of the engine, a NOx sensor 44, and the like are provided. Based on these detection signals, the control unit 45 performs fuel injection amount and injection from the fuel injector 5. The opening and closing of the intake control valves 17a and 17b of the intake ports 13a and 13b are controlled at the timing.
[0032]
Next, the contents of control will be described.
[0033]
In the high-load operation region of the engine, the intake control valves 17a and 17b of the intake ports 13a and 13b are kept open, and fuel is injected and supplied from the fuel injector 5 to the intake stroke so that the air-fuel ratio in the entire cylinder is uniform. The operation is performed with a so-called homogeneous mixture.
[0034]
On the other hand, in a light load region where the engine load is not high, either one of the intake control valves 17a and 17b is closed, fuel is injected and supplied from the fuel injector 5 in the latter half of the compression stroke, and the combustible air-fuel ratio is near the spark plug 15. The so-called stratified gas mixture operation is performed in which the air-fuel mixture layer is formed and the entire cylinder is lean. That is, inhaling more air than the stoichiometric air-fuel ratio with respect to less fuel reduces pumping loss and heat loss, improves engine thermal efficiency, and improves fuel efficiency.
[0035]
Hereinafter, the control content of this stratified gas mixture operation is demonstrated based on the flowchart of FIG.
[0036]
In step 1, operating conditions are read from the rotational speed sensor 40, the intake air amount sensor 41, the accelerator opening sensor 42, etc., and in step 2, the engine load is calculated.
[0037]
In step 3, the engine load is compared with a preset low load value.
[0038]
When the engine load is smaller than the low load set value, the routine proceeds to step 4 where the intake control valve 17a is closed so that a swirl in the turning direction 18a (counterclockwise when viewed from above the cylinder) occurs in the cylinder. The intake control valve 17b is opened.
[0039]
When the engine load is larger than the low load set value, it is compared with the high load set value set in advance in step 5.
[0040]
When the engine load is larger than the high load set value, the routine proceeds to step 6, where the intake control valve 17a is opened so that a swirl in the turning direction 18b (clockwise as viewed from above the cylinder) in FIG. The intake control valve 17b is closed.
[0041]
When the engine load is between the low load set value and the high load set value, the intake control valves 17a and 17b maintain the previous state in step 7 so as to provide hysteresis.
[0042]
From the fuel injector 5, a fuel amount calculated based on the operating conditions of the engine is injected and supplied at a predetermined time in the latter half of the compression stroke. The injected fuel turns in the clockwise direction as viewed from above the cylinder.
[0043]
That is, in the low load operation in the stratified mixture operation region, the swirling direction of the injected fuel and the direction of the intake swirl are opposite as shown in FIG.
[0044]
In the reverse direction, the direction of the spray and the direction of the intake swirl are reversed on the lower side of the fuel spray, that is, on the piston 3 side, and the relative speed of that portion increases and the static pressure decreases. For this reason, the fuel spray is concentrated below the combustion chamber 2, that is, in the cavity 4 of the piston 3, and collides and flows in the cavity 4.
[0045]
Due to the flow in the cavity 4, the sprayed fuel reaches the vicinity of the spark plug 15 quickly and smoothly.
[0046]
Therefore, the time until the fuel spray reaches the vicinity of the spark plug 15 can be shortened, and a mixture with a sufficient concentration can be formed in the vicinity of the spark plug 15, and the stratified mixture operation stably in a low load region where the fuel injection amount is small. It can be performed.
[0047]
In this low load region, although smoke is slightly worse, there is no problem because it is originally small.
[0048]
On the other hand, in the high load operation in the stratified mixture operating region, the swirling direction of the injected fuel and the direction of the intake swirl are the same as shown in FIG.
[0049]
In the case of the same direction, the direction of the spray and the direction of the intake swirl are reversed on the upper side of the fuel spray, that is, on the cylinder head 1 side, and the relative speed of that portion becomes slower and the static pressure increases. For this reason, the fuel spray diffuses upward in the combustion chamber 2, and the fuel spray staying in the cavity 4 is reduced, and vaporizes while appropriately diffusing and flowing throughout.
[0050]
As a result, when the fuel injection amount is large, it is possible to prevent the air-fuel mixture in the vicinity of the spark plug 15 from becoming excessively rich, and good ignition and combustion can be performed.
[0051]
Therefore, smoke can be reduced when the fuel injection amount is large and the load is high, the spark plug 15 is not contaminated, and it is possible to operate on the ignition advance side which is particularly excellent in fuel efficiency and HC performance. Good stratified gas mixture operation can be performed.
[0052]
In this way, by utilizing the interaction between the intake swirl and the fuel spray, it is suitable for the vicinity of the spark plug 15 in the low load region where the fuel injection amount is small and the high load region where the fuel injection amount is large in the stratified mixture operation. The air-fuel ratio can be generated, the stratified mixture operation can be performed accurately, and the operation performance can be improved.
[0053]
Here, FIGS. 16 and 17 are diagrams showing the smoke limit when the direction of the intake swirl is switched in the high load operation of the stratified mixture operation. By making the direction of the intake swirl as shown in FIG. 5, it is possible to enlarge the area where smoke is less discharged, and in particular, it is possible to set the ignition timing to a more advanced side. Further, by setting the ignition timing to a more advanced side, it becomes possible to improve fuel consumption and reduce HC emissions.
[0054]
By the way, in order to change the direction of the intake swirl, the intake ports 13a and 13b are switched by using a variable valve mechanism for the intake valves 11a and 11b instead of the intake control valves 17a and 17b, or the intake ports 13a and 13b. The intake swirl is generated by adding a phase difference between the shape of the intake valve 11a and the operation timing of the intake valves 11a and 11b, and the variable valve mechanism of the intake control valve 17a and the intake valve 11b, and the intake control valve 17b and the intake valve 11a. In combination with the variable valve mechanism, the intake ports 13a and 13b may be switched to switch the direction of the intake swirl.
[0055]
FIG. 12 shows another embodiment, in which the direction of the intake swirl is switched to the stratified mixture operation region in accordance with the stability of the engine.
[0056]
In step 11, the engine stability is measured. In this case, the in-cylinder pressure of the engine or the angular velocity of the crankshaft is measured, and this is compared between cylinders and time-series values, and the stability of the engine is measured from the variation.
[0057]
In step 12, it is determined whether the engine stability is better than a set value.
[0058]
When the engine stability is better than the set value (in-cylinder pressure, crankshaft angular speed fluctuation is small, etc.), the process proceeds to step 13, and the turning direction 18b of FIG. ), The intake control valve 17a is opened and the intake control valve 17b is closed.
[0059]
When the engine stability is lower than the set value (in-cylinder pressure, crankshaft angular velocity fluctuations are large, etc.), the process proceeds to step 14, and the turning direction 18a of FIG. The intake control valve 17a is closed and the shut-off valve 17b is opened so that a swirling swirl occurs.
[0060]
In this way, when the stability of the engine deteriorates or is likely to deteriorate from a preset state, the state shown in FIG. 2 is used until the fuel spray from the fuel injector 5 reaches the vicinity of the spark plug 15. Thus, the air-fuel mixture having a sufficient concentration can be formed in the vicinity of the spark plug 15. Therefore, the engine stability can be controlled to a good level.
[0061]
Here, FIGS. 18 and 19 are diagrams showing the allowable limit of stability when the direction of the intake swirl is switched in the stratified mixture operation. It can be understood that the region of good stability can be expanded by setting the direction of the intake swirl to FIG.
[0062]
Note that the determination of switching between the stratified gas mixture operation and the homogeneous gas mixture operation may be performed in accordance with the measured value of the stability of the engine. If stratified mixture operation is performed on the condition of engine stability, the stratified mixture operation range can be expanded, pollution in the combustion chamber and deterioration of exhaust components can be sufficiently prevented, and fuel efficiency can be improved. It can be done well.
[0063]
FIG. 13 shows another embodiment, in which the direction of the intake swirl is switched to the stratified mixture operation region in accordance with the exhaust state of the engine.
[0064]
In step 21, the engine exhaust state is measured. In this case, for example, smoke is measured using a sensor such as a phototube that measures the transmittance of exhaust gas, and HC components are measured using a sensor such as an ion probe.
[0065]
In step 22, it is determined whether the engine exhaust state is better than a set value.
[0066]
When the exhaust state of the engine is better than the set value, the routine proceeds to step 23, where the intake control valve 17a is set so that a swirl in the turning direction 18a of FIG. 2 (counterclockwise when viewed from above the cylinder) occurs in the cylinder. Close and open intake control valve 17b.
[0067]
When the exhaust state of the engine is worse than the set value (smoke starts to be generated, the HC component exceeds a predetermined value), the process proceeds to step 24, in which the turning direction 18b in FIG. ), The intake control valve 17a is opened and the intake control valve 17b is closed.
[0068]
That is, when the smoke and HC components are deteriorated or are likely to deteriorate from the preset state, the mixture in the vicinity of the spark plug 15 is obtained by appropriately diffusing and vaporizing the fuel injector 5 in the state shown in FIG. To avoid over-concentrating. Therefore, a good exhaust state of the engine can be ensured.
[0069]
It is also possible to measure the NOx component in the exhaust gas and thereby control the switching of the direction of the intake swirl. However, when NOx increases, the state shown in FIG. 5 is set.
[0070]
Further, the determination of switching between the stratified gas mixture operation and the homogeneous gas mixture operation may be performed in accordance with the measured value of the exhaust state of the engine. In this case, it is possible to further improve fuel efficiency by expanding the stratified mixture operating region while ensuring the stability of the engine.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an engine showing an embodiment.
FIG. 2 is a cross-sectional view taken along line AA in FIG.
FIG. 3 is a cross-sectional view taken along line BB in FIG.
FIG. 4 is a schematic cross-sectional view showing an operating state.
5 is a cross-sectional view taken along line CC in FIG.
6 is a cross-sectional view taken along the line DD of FIG.
FIG. 7 is a cross-sectional view of a fuel injector.
FIG. 8 is a cross-sectional view of the nozzle portion.
FIG. 9 is a cross-sectional view of the fuel swirl prevention portion.
FIG. 10 is a block diagram showing a control system.
FIG. 11 is a flowchart showing control contents.
FIG. 12 is a flowchart showing another embodiment.
FIG. 13 is a flowchart showing another embodiment.
FIG. 14 is a schematic sectional view of a conventional cylinder.
FIG. 15 is a configuration diagram of the cylinder head portion.
FIG. 16 is a characteristic diagram showing a smoke limit in the case of the intake swirl of FIG. 2;
FIG. 17 is a characteristic diagram showing a smoke limit in the case of the intake swirl of FIG. 5;
FIG. 18 is a characteristic diagram showing an allowable limit of stability in the case of the intake swirl of FIG. 2;
FIG. 19 is a characteristic diagram showing an allowable limit of stability in the case of the intake swirl of FIG. 5;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cylinder head 2 Combustion chamber 3 Piston 4 Cavity 5 Fuel injector 9 Direction 11a, 11b Intake valve 12a, 12b Exhaust valve 13a, 13b Intake port 14a, 14b Exhaust port 15 Spark plug 17a, 17b Intake control valve 18a, 18b Turning direction 31 Movable valve 32 Ball valve 33 Nozzle 34 Seat surface 35 Injection hole 38 Fuel turning element 40 Rotational speed sensor (crank angle sensor)
41 Intake amount sensor 42 Accelerator opening sensor 43 In-cylinder pressure sensor 44 NOx sensor 45 Control unit

Claims (6)

A swirl generating means for generating a swirl in the air flowing into the cylinder in the lateral direction that is the circumferential direction of the cylinder is provided. In-cylinder direct fuel injection spark ignition engine that can be operated with a stratified mixture that forms a lean mixture as a whole while forming
An in-cylinder direct fuel injection spark ignition engine characterized by comprising a fuel injection device for supplying an injection while applying a turning force to the fuel, and further comprising a swirl direction switching means for switching the swirling direction of the swirl.   The in-cylinder direct fuel injection spark ignition engine according to claim 1, wherein the direction of the swirl is switched in accordance with a predetermined operating condition of the engine load.   The in-cylinder direct fuel injection spark ignition engine according to claim 1, wherein the direction of the swirl is switched according to engine stability or exhaust state.   The in-cylinder direct fuel injection spark ignition engine according to claim 1, wherein the swirl direction switching means switches the direction of the swirl by switching a plurality of intake ports.   The in-cylinder direct fuel injection spark ignition engine according to claim 1, wherein the fuel injection device injects fuel from a peripheral portion of a combustion chamber wall surface of the cylinder head.   The swirl direction and the fuel swirl direction are set in the opposite direction when the load in the stratified mixture operation region is low, and in the same direction when the load in the stratified mixture operation region is high, as viewed from above the cylinder. The in-cylinder direct fuel injection type spark ignition engine according to claim 1.

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