JP2005030305A - Lean burn internal combustion engine, and method for forming air-fuel mixture for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lean burn internal combustion engine capable of realizing consistent combustion, reducing NOx emission, and enhancing the fuel consumption. <P>SOLUTION: A lean burn internal combustion engine comprises a fuel injection valve to inject fuel in an air intake passage, a control means to control the injection timing by the fuel injection valve so that a part of fuel required according to the running condition is injected before an air intake valve is opened, and the remaining fuel is injected after the air intake valve is opened, and a piston in which the remaining fuel injected after the air intake valve is opened is stored in a cavity formed in a top surface of the piston, the fuel/air mixture is formed within the cavity, and the fuel/air mixture is lead in a vicinity of an ignition plug in the second half of the compression stroke. The fuel/air mixture of the air-fuel ratio lower than the homogeneous fuel/air mixture formed over the entire combustion chamber is formed in the cavity, and led in a vicinity of the ignition plug in the second half of the compression stroke, and consistent combustion can be realized. NOx emission and the fuel consumption can be reduced by adequately controlling the air-fuel ratio. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lean combustion internal combustion engine provided with a fuel injection valve for injecting fuel into an intake passage.
[0002]
[Prior art]
Conventionally, it has been desired to improve the fuel consumption of an internal combustion engine. As an internal combustion engine to meet this demand, fuel is directly injected into the cylinder, so that a mixture with good ignitability is formed only near the spark plug at the time of ignition. 2. Description of the Related Art An in-cylinder injection spark ignition type internal combustion engine that enables combustion of air is known (see, for example, Patent Document 1).
[0003]
This is because a part of the fuel is injected during the intake stroke to form a lean and homogeneous mixture in the cylinder, and the remaining fuel is injected during the compression stroke to easily ignite around the spark plug. Is formed.
[0004]
Further, in an internal combustion engine having a fuel injection valve at the intake port, fuel is injected during the expansion stroke or exhaust stroke before the intake valve is opened, and fuel vaporization / atomization is promoted to homogenize the cylinder. This makes it possible to burn a lean air-fuel mixture and improve fuel efficiency.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2003-13784
[Patent Document 2]
JP-A-6-317161
[Patent Document 3]
JP 2001-98945 A
[Patent Document 4]
JP 2000-274248 A
[0006]
[Problems to be solved by the invention]
However, in the above-described in-cylinder injection spark ignition internal combustion engine, even if the air-fuel ratio in the cylinder as a whole is lean, the air-fuel mixture formed around the spark plug is injected during the compression stroke. Therefore, the time until ignition is short, and the fuel is difficult to vaporize and atomize, so there is a possibility that the air-fuel ratio will be partially rich. A large amount of nitrogen oxides (NOx) may be discharged due to combustion of the air-fuel mixture that is the rich air-fuel ratio.
[0007]
On the other hand, in an internal combustion engine equipped with a fuel injection valve in the intake port, even if fuel vaporization / atomization is promoted to form a homogeneous mixture, the air-fuel ratio to be ignited is limited. If the air-fuel ratio is lean, there is a risk of misfire during operation of the internal combustion engine, and it is difficult to achieve both stable combustion and improved fuel efficiency.
[0008]
The present invention has been made in view of the above-described problems, and the object of the present invention is a lean combustion capable of reducing the amount of NOx discharged and improving fuel efficiency while realizing stable combustion. It is to provide an internal combustion engine.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, in the lean combustion internal combustion engine according to the present invention, a fuel injection valve for injecting fuel into the intake passage, and a portion of the fuel required according to the operating state of the internal combustion engine are taken in. The injection timing by the fuel injection valve is injected so that at least either the expansion stroke or the exhaust stroke before the valve is opened and the remaining fuel is injected at least in the intake stroke after the intake valve is opened. The control means for controlling and the remaining fuel injected in the intake stroke are accumulated in a cavity provided on the top surface to form an air-fuel mixture in the cavity, and the air-fuel mixture is brought near the spark plug in the latter half of the compression stroke. And a guiding piston.
[0010]
In an internal combustion engine equipped with a fuel injection valve in the intake passage, even if fuel vaporization / atomization is promoted to form a homogeneous mixture in the cylinder, the air-fuel ratio to ignite is limited. If the air / fuel ratio is excessively lean, a misfire may occur during operation of the internal combustion engine, and it may be difficult to achieve stable combustion.
[0011]
On the other hand, in the lean combustion internal combustion engine according to the present invention, the fuel injection valve provided in the intake passage causes a part of the fuel required according to the operation state of the internal combustion engine to open the intake valve. When injected into at least one of the expansion stroke or the exhaust stroke before being performed, vaporization / atomization is promoted before the intake valve is opened, and a lean and homogeneous air-fuel mixture is formed in the cylinder. On the other hand, when the remaining fuel is injected at least in the intake stroke after the intake valve is opened, it is stored in a cavity provided on the top surface of the piston, and an air-fuel mixture is formed in the cavity. . The air-fuel ratio formed in the cavity is more air-fuel ratio than the homogeneous air-fuel mixture because further fuel is added to the homogeneous air-fuel mixture injected before the intake valve is opened. Becomes a low air-fuel mixture. And, since the air-fuel mixture is led to the vicinity of the spark plug in the latter half of the compression stroke by the piston, it becomes easier to ignite than when only the homogeneous air-fuel mixture is present, and even if the air-fuel mixture is a lean air-fuel mixture as a whole Stable combustion can be realized.
[0012]
Furthermore, the control means forms a homogeneous air-fuel mixture that becomes a first lean air-fuel ratio in a part of the required fuel injected before the intake valve is opened over the entire cylinder, The fuel injection valve is configured to form an air-fuel mixture having a second lean air-fuel ratio richer than the first lean air-fuel ratio in the cavity with the remaining fuel injected after the intake valve is opened. By controlling the amount of fuel injected by the air-fuel ratio, the air-fuel mixture formed in the cavity has a lean air-fuel ratio, and the fuel injected in the intake stroke is promoted to vaporize and atomize during the subsequent stroke. Since it is difficult to partially form an air-fuel ratio mixture in the vicinity of stoichiometry, NOx emission can be reduced. Further, since the air-fuel mixture in the cavity is ignited and propagates in the flame, the homogeneous air-fuel mixture that is the first lean air-fuel ratio formed throughout the combustion chamber is also burned. The fuel consumption can be improved.
[0013]
In addition, it is preferable that the apparatus further includes a squish flow generating means that is formed by at least one of a piston and a cylinder head and generates a squish flow so as to hit the discharge portion of the spark plug. When the squish flow hits the discharge part of the spark plug, the combustion speed of the air-fuel mixture increases, and the combustion can be further stabilized.
[0014]
In the lean-burn internal combustion engine formation method according to the present invention, a part of the fuel required in accordance with the operating state of the internal combustion engine is supplied from the fuel injection valve that injects fuel into the intake passage. Before at least the expansion stroke or the exhaust stroke is injected, and the remaining fuel is injected at least after the intake valve is opened, before the intake valve is opened. A part of the required fuel that is injected forms a homogeneous air-fuel mixture throughout the cylinder, and the remaining fuel that is injected after the intake valve is opened. An air-fuel mixture is formed in a cavity located in the vicinity of the spark plug at a point.
[0015]
As described above, when such a method is used, a homogeneous air-fuel mixture is formed throughout the cylinder, and an air-fuel mixture having a lower air-fuel ratio than the homogeneous air-fuel mixture is formed in the cavity. Is led to the vicinity of the spark plug in the latter half of the compression stroke, so that combustion can be stabilized even if the mixture is lean as a whole.
[0016]
Further, a part of the required fuel injected before the intake valve is opened forms a homogeneous mixture of the first lean air-fuel ratio over the entire cylinder, and the intake valve is opened. It is preferable to form a second lean air-fuel ratio mixture richer than the first lean air-fuel ratio in the cavity with the remaining fuel injected after being applied.
[0017]
When the air-fuel mixture formed using such a method is combusted, as described above, NOx emissions can be reduced and fuel efficiency can be improved.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.
[0019]
(First embodiment)
FIG. 1A is a schematic plan view of the internal combustion engine 1 according to the first embodiment of the present invention, and FIG. 1B is a schematic longitudinal sectional view. As shown in FIG. 1B, the combustion chamber 2 is formed by a cylinder head 3, a cylinder block 4, a piston 5, a piston ring 6, an intake valve 7, an exhaust valve 8, a spark plug 9, and the like. A cavity 5a is formed on the top surface of the piston 5, and the electrode at the tip of the spark plug 9 enters the cavity 5a when the piston 5 is located at the top dead center.
[0020]
Further, two intake passages 10 and one exhaust passage 11 are opened in the combustion chamber 2. Basically, the fuel / air mixture injected from the fuel injection valve 12 that injects fuel into the intake passage 10 is lifted by the intake valve 7 driven by an intake cam (not shown), thereby It flows from the passage 10 into the combustion chamber. The combustion gas burned in the combustion chamber 2 flows into the exhaust passage 11 when the exhaust valve 8 driven by an exhaust cam (not shown) is lifted, and enters the atmosphere via an exhaust purification catalyst, a muffler, etc. (not shown). To be discharged.
[0021]
Further, as shown in FIG. 1 (a), the two intake passages 10 merge upstream, and a fuel injection valve 12 is provided so that the injection port protrudes into the intake passage 10 upstream from the junction. Yes. The fuel injection valve 12 is opened by a drive signal from an electronic control unit (ECU: Electronic Control Unit) 13 provided to control the internal combustion engine 1, and the valve opening time is controlled to a desired amount. Inject fuel.
[0022]
The ECU 13 is an arithmetic and logic circuit comprising a CPU, ROM, RAM, backup RAM, and the like. The ECU 13 is a water temperature sensor 14 for detecting the cooling water temperature in the engine, an air flow meter (not shown) for detecting the intake air amount, a crank Various sensors such as a crank position sensor (not shown) for detecting the rotational angle position of the shaft, an accelerator opening sensor (not shown) for detecting the accelerator opening, and an air-fuel ratio sensor (not shown) are connected via electric wiring. The output signals of the various sensors described above are input to the ECU 13.
[0023]
The ECU 13 performs predetermined calculation processing based on the output signals from the various sensors input, such as calculating the engine speed based on the output signal from the crank position sensor, for example, and is provided in the intake passage. Throttle control for controlling the opening of a throttle valve (not shown) for controlling the air amount, fuel injection control for controlling the fuel injection amount and injection timing by the fuel injection valve 12, ignition timing for controlling the ignition timing by the spark plug 9, etc. It is possible to execute control and the like.
[0024]
[First embodiment of fuel injection control]
Next, a first example of the fuel injection control according to the present embodiment will be described in detail.
In the internal combustion engine 1 according to the present embodiment, since the fuel injection valve 12 is provided in the intake passage 10, the fuel injection valve is at least in either the expansion stroke or the exhaust stroke before the intake valve 7 is opened. When the fuel is injected from 12, particularly when the intake passage 10 is at a high temperature, the fuel is vaporized and atomized in the intake passage 10, so that in the process of flowing into the cylinder from the intake passage 10, Mixing with the air sucked into the inside is promoted, and a homogeneous air-fuel mixture is formed throughout the cylinder.
[0025]
On the other hand, the fuel injected after the intake valve 7 is opened, for example, at the beginning of the intake stroke, flows into the cylinder according to the flow of air sucked into the cylinder before being completely vaporized. As shown, it collects in the cavity 5a formed on the top surface of the piston 5 and vaporizes in the cavity 5a.
[0026]
Therefore, by adjusting the amount of fuel injected before and after the intake valve 7 is opened, a predetermined lean air-fuel ratio (for example, A / F = 30, hereinafter “first lean air-fuel ratio” throughout the cylinder). )) And a rich air-fuel ratio (for example, A / F = 20, hereinafter “second lean air-fuel ratio”) that is richer than the first lean air-fuel ratio in the cavity 5a. Can be formed.
[0027]
The air-fuel mixture in the cavity 5a is guided to the vicinity of the spark plug in the compression stroke. Thereafter, when a spark discharge is caused by the spark plug, the air-fuel mixture of the second lean air-fuel ratio is ignitable because it is an air-fuel ratio that can be ignited when the lean air-fuel ratio is, for example, A / F = about 20. Burn. Further, by propagating the flame, even if the air-fuel ratio of the homogeneous air-fuel mixture that is the first lean air-fuel ratio is A / F = about 30, the homogeneous air-fuel mixture also burns.
[0028]
However, just because the fuel is injected after the intake valve 7 is opened, the fuel does not always accumulate in the cavity 5a. Therefore, the fuel from the injection after the intake valve 7 is opened enters the cavity. When an injection timing limit (hereinafter referred to as “injection limit timing”) that can be accumulated is calculated and injection is performed after the intake valve 7 is opened, the injection is terminated before the injection limit timing. To do.
[0029]
This injection limit timing varies depending on the position and orientation of the fuel injection valve, the fuel flow depending on the shape of the intake port, the shape and size of the cavity, the piston speed (engine speed), the intake air amount, and the like.
[0030]
However, when the position and orientation of the fuel injection valve, the shape of the intake port, the shape of the cavity, and the size are fixed for each internal combustion engine 1, the injection limit timing changes according to the engine speed or the intake air amount. . That is, even if injection is performed at the same crankshaft rotation angle, if the engine speed is low, even if it can be accumulated in the cavity, if the engine speed is high, that is, the piston descending speed is fast In such a case, the injected fuel may only collide with the opposing wall surface of the cylinder and may not accumulate in the cavity.
[0031]
Therefore, it is necessary to set the injection limit timing in advance for each operating state of the internal combustion engine 1.
[0032]
By forming the intake port so as to generate a tumble flow that directs the fuel injected after opening the intake valve into the cavity on the flow of the air-fuel mixture flowing into the cylinder, the injection limit timing is set. Can be delayed.
[0033]
In the fuel injection control according to the present embodiment, the fuel injection valve 12 is opened only once as shown in the single injection pattern of FIG. 3 so that the injection limit time is not exceeded, and The injection timing and the injection amount (injection valve opening period) are controlled so as to achieve the air-fuel ratio as described above.
[0034]
Specifically, the ECU 13 executes fuel injection control for controlling the amount of fuel injected by the fuel injection valve 12 and the injection timing as follows. This controls the fuel injection valve 3 according to the control routine shown in the flowchart of FIG.
[0035]
This control routine is a routine that is stored in advance in the ROM of the ECU 13, and is a routine that is executed by the ECU 13 as an interrupt process triggered by the passage of a fixed time or the input of a pulse signal from the crank position sensor described above. .
[0036]
In this routine, first, in step 100, the intake air amount, the accelerator opening, and the engine speed are calculated. This is calculated by the ECU 13 based on the detected values of the air flow meter, accelerator opening sensor, and crank position sensor described above.
[0037]
Thereafter, the routine proceeds to step 101, where the required fuel injection amount is calculated. This is because the target air-fuel ratio is calculated from the accelerator opening calculated in step 100 and the engine speed based on a preset map, and the calculated target air-fuel ratio and the intake air amount calculated in step 100, etc. Is used as a parameter, for example, to calculate the required fuel injection amount based on a preset map. As described above, the target air-fuel ratio is basically the first lean air-fuel ratio (for example, AA) that is fuel injected into at least either the expansion stroke or the exhaust stroke before the intake valve 7 is opened. / F = 30) is formed over the entire cylinder, and is a fuel that is injected at least in the intake stroke after the intake valve 7 is opened, and is richer than the first lean air-fuel ratio. The map is set so that a mixture of lean air-fuel ratio (for example, A / F = 20) can be formed in the cavity 5a.
[0038]
Thereafter, the routine proceeds to step 102, and among the required fuel injection amount, the amount of fuel injected into at least either the expansion stroke or the exhaust stroke before the intake valve is opened and the fuel injected into at least the intake stroke after the intake valve is opened. Determine the amount. This is determined based on a map set in advance as described above. In step 101, the required injection amount is calculated, and in step 102, the fuel amount to be injected before the intake valve is opened and the fuel amount to be injected after the intake valve is opened are not simply determined. The amount of fuel injected before the valve is opened and the amount of fuel injected after the intake valve is opened may be calculated.
[0039]
Thereafter, the routine proceeds to step 103, where the injection end timing after the intake valve is opened is determined. This calculates the valve opening time of the fuel injection valve based on the fuel amount injected after the intake valve opening calculated in step 102 and the pressure of the injected fuel, and the valve opening time is calculated based on the engine speed. Convert to the crankshaft rotation angle. Then, the crankshaft rotation angle obtained by converting the valve opening time is added to the intake valve opening start timing determined by the crankshaft rotation angle, and the injection end timing after the intake valve opening is determined. Note that the target air-fuel ratio, etc. set in the map is set so that the injection end timing after the intake valve opening does not exceed the injection limit timing. Even if the injection end time is determined, the injection limit time is not exceeded.
[0040]
Thereafter, the routine proceeds to step 104, where the injection start timing before intake valve opening is determined. This calculates the valve opening time of the fuel injection valve based on the fuel amount injected before the intake valve opening calculated in step 102 and the pressure of the injected fuel, and the valve opening time is calculated as the engine speed. Based on the crankshaft rotation angle. Then, from the crankshaft rotation angle at the intake valve opening start timing, the valve opening is started so that the fuel amount injected before the intake valve opening at the intake valve opening start timing determined by the crankshaft rotation angle is terminated. The crankshaft rotation angle converted from time is subtracted to determine the injection start timing before the intake valve is opened.
[0041]
Thereafter, the routine proceeds to step 105, where the fuel injection valve is controlled so as to start fuel injection at the injection start timing determined in step 104.
[0042]
In order to dilute by burning a homogeneous air-fuel mixture, there is a limit because the combustion becomes unstable due to misfire or the like, but in this way, at least the expansion stroke before the intake valve 7 is opened or The fuel injected into one of the exhaust strokes forms a homogeneous mixture of the first lean air-fuel ratio, and is richer than the first lean air-fuel ratio with the fuel injected at least in the intake stroke after the intake valve 7 is opened. However, stable combustion is achieved by forming a second lean air-fuel ratio air-fuel mixture in the cavity 5a and igniting the second lean air-fuel mixture in the vicinity of the spark plug. And the improvement of fuel efficiency can be realized.
[0043]
In addition, the air-fuel mixture formed in the cavity has a lean air-fuel ratio, and the fuel injected in the intake stroke is partly near the stoichiometry in the cavity by promoting vaporization and atomization during the subsequent stroke. Since it is difficult to form an air-fuel mixture of the same air-fuel ratio, NOx emissions can be reduced.
[0044]
[Second Embodiment of Fuel Injection Control]
In the first embodiment, the case where the entire target fuel amount is injected by opening the fuel injection valve once has been described. However, in the fuel injection control according to the present embodiment, two times of FIG. As shown in the injection pattern, the fuel injection valve 12 is opened twice so that the total amount of the two injection amounts becomes the target fuel injection amount.
[0045]
Also in such a case, after the intake valve 7 is opened, the first lean air-fuel ratio homogeneous mixture is formed with the fuel injected at least in either the expansion stroke or the exhaust stroke before the intake valve 7 is opened. The amount of fuel to be injected before and after the intake valve 7 is opened so that a fuel mixture injected at least in the intake stroke and having a second lean air-fuel ratio richer than the first lean air-fuel ratio can be formed in the cavity. To be adjusted.
[0046]
By injecting the target fuel injection amount in two times in this way, fuel is injected at an earlier timing before the intake valve 7 is opened than in the single injection pattern as shown in FIG. Therefore, the fuel injected into the intake port can be kept in the port for a long time, and the fuel can be promoted to vaporize and atomize before flowing into the cylinder.
[0047]
However, an interval is required for the fuel injection valve 3 to be closed and opened again, so that it is difficult to open the fuel injection valve 3 twice depending on the target fuel injection amount, engine speed, etc. There is also. For example, in a high-load high-rotation operation state, the target fuel injection amount is large and the engine speed is high, so that the fuel injection valve 3 is opened and closed at least once during either the expansion stroke or the exhaust stroke, and the intake valve 7 is opened. There may be a case where the fuel injection valve 3 cannot be opened again after the valve is opened.
[0048]
Therefore, it is preferable to determine which injection pattern is adopted according to the target fuel injection amount, engine speed, engine temperature, fuel pressure, and the like of the internal combustion engine 1, and the first is determined according to the operating state of the internal combustion engine 1. It is preferable to switch between the single injection pattern of the embodiment and the double injection pattern of the second embodiment.
[0049]
Next, the fuel injection control executed by the ECU 13 according to the present embodiment will be specifically described according to the control routine shown in the flowchart of FIG.
[0050]
In this routine, first, in step 200, the intake air amount, the accelerator opening, and the engine speed are calculated, and then the routine proceeds to step 201, where the required fuel injection amount is calculated. Then, the routine proceeds to step 202, and among the required fuel injection amounts, the fuel amount to be injected in the expansion stroke or the exhaust stroke before the intake valve is opened and the fuel amount to be injected after the intake valve is opened are determined. Since these are the same as the first embodiment, the description thereof is omitted.
[0051]
Thereafter, the routine proceeds to step 203 where the fuel injection timing after the intake valve is opened is determined. This is to calculate the valve opening time by the same method as described above, and to determine it within the range of the injection limit timing described above from the start of opening of the intake valve, for example, determined based on a predetermined map It is what is done.
[0052]
Thereafter, the routine proceeds to step 204 where the injection start timing before intake valve opening is determined. This calculates the valve opening time of the fuel injection valve based on the fuel amount injected before the intake valve opening calculated in step 202 and the pressure of the injected fuel, and the valve opening time is calculated as the engine speed. Based on the crankshaft rotation angle. Then, taking into account the interval from when the fuel injection valve is closed to when it is opened again, the timing for starting injection at least in either the expansion stroke or the exhaust stroke before the intake valve is opened is determined. For example, it is determined based on a predetermined map.
[0053]
Thereafter, the routine proceeds to step 105, where the fuel injection valve is controlled so as to start fuel injection at the injection start timing determined in step 104.
[0054]
By doing in this way, the amount of NOx to be discharged can be reduced and the fuel efficiency can be improved while realizing stable combustion as described above.
[0055]
(Second Embodiment)
In the present embodiment, a squish flow generating means for generating a squish flow so as to be applied to the discharge part of the spark plug 9 is further provided in the first embodiment.
[0056]
Specifically, as shown in FIG. 6, in the pent roof type combustion chamber provided with a cavity 5a in the center of the top surface of the piston 5, and further provided with a squish area, a spark plug 9 is disposed in the vicinity of the squish area. The squish flow is blown horizontally toward the center of the combustion chamber and chamfered on the peripheral edge of the cavity at the top of the piston so that it strikes the discharge part 9a of the spark plug, and its tip is rounded to form a squish flow generation means is doing. The range in which the squish flow generating means is provided is determined for each internal combustion engine, but is preferably provided at least in the vicinity of the spark plug 9.
[0057]
Also in the first embodiment, a squish flow as shown in FIG. 7 is generated and the combustion speed is increased, so that the fuel efficiency is improved. However, if the squish flow as shown in FIG. 7 is simply generated, the squish flow is directed to the top of the combustion chamber, so that the squish flow does not hit the discharge part 9 a of the spark plug 9. Further, since the flame slowly reaches the bottom of the cavity 5a, the combustion speed cannot catch up with the lowering of the piston, and there is a possibility that the combustion may become unstable without properly propagating the flame.
[0058]
Therefore, in the present embodiment, the shape shown in FIG. 6 is used as described above. By adopting such a shape, the squish flow that blows out from the squish area in the horizontal direction as the piston rises in the compression stroke strikes the discharge part 9a of the spark plug 9, thereby promoting the flame propagation and the squish flow in the horizontal direction. By heading in the direction, it goes to the center of the combustion chamber and then reaches the bottom of the cavity 5a, so that the flame propagates quickly to the bottom of the cavity 5a, so that stable combustion can be realized.
[0059]
Further, instead of chamfering the cavity peripheral portion of the piston top portion, as shown in FIG. 8, as a squish flow generating means, a protrusion is provided in the vicinity of the ignition plug 9 of the cylinder head 3 so as to protrude into the combustion chamber 2, The squish flow may be guided to the discharge part of the spark plug. Also in this case, as described above, the squish flow that blows out from the squish area in the horizontal direction due to the piston rising in the compression stroke hits the discharge part of the spark plug, thereby promoting the flame propagation and the squish flow in the horizontal direction. By moving to the center of the combustion chamber, it becomes faster to propagate the flame to the bottom of the cavity and to the bottom of the cavity, so that stable combustion can be realized.
[0060]
Further, as shown in FIG. 9, as a squish flow generating means, the cavity peripheral portion of the top of the piston is chamfered and its tip is rounded, and in the combustion chamber 2 in the vicinity of the spark plug 9 of the cylinder head 3. It is preferable to provide a protruding portion that protrudes. In this case as well, as described above, the squish flow blows out from the squish area in the horizontal direction due to the piston rising in the compression stroke. However, the cavities are simply chamfered or projected into the combustion chamber 2 at the top of the piston. Compared with the provision of the portion on the cylinder head side, the flow velocity is further increased and the flame propagation is further promoted by hitting the discharge portion of the spark plug 9. In addition, since the squish flow is directed in the horizontal direction, the squish flow is directed toward the center of the combustion chamber and propagates to the bottom of the cavity, so that the combustion can be further stabilized.
[0061]
In the first embodiment and the second embodiment described above, an internal combustion engine having two intake valves, one exhaust valve, and two spark plugs is exemplified. As shown in FIG. 10, the present invention can also be applied to an internal combustion engine having two intake valves and two exhaust valves, and having a configuration in which one spark plug is provided at substantially the center of the four valves. . Also in this case, the shape of the intake port, the shape of the cavity, and the like are determined so that the second lean air-fuel ratio mixture is formed in the cavity 5a in the vicinity of the spark plug 9.
[0062]
【The invention's effect】
As described above, according to the present invention, a lean and homogeneous air-fuel mixture is formed over the entire cylinder, and an air-fuel ratio lower than the homogeneous air-fuel mixture is formed in the cavity. Since the air-fuel mixture is led to the vicinity of the spark plug in the latter half of the compression stroke, it is possible to improve fuel efficiency while realizing stable combustion.
[0063]
In addition, a homogeneous air-fuel mixture having a first lean air-fuel ratio is formed in the cylinder by a part of the fuel injected at least in either the expansion stroke or the exhaust stroke before the intake valve is opened, and the intake valve When an air-fuel mixture having a second lean air-fuel ratio richer than the first lean air-fuel ratio is formed in the cavity with the remaining fuel injected at least during the intake stroke after the valve is opened, the intake stroke Since the injected fuel is promoted to vaporize and atomize during the subsequent stroke, it becomes difficult to form an air-fuel ratio mixture near the stoichiometric part of the cavity, and NOx emissions can be reduced. . Further, since the air-fuel mixture in the cavity is ignited and propagates in the flame, the homogeneous air-fuel mixture having the first lean air-fuel ratio formed throughout the combustion chamber is also burned. Since the fuel ratio can also be increased, fuel consumption can be improved.
[Brief description of the drawings]
FIG. 1A is a schematic plan view of an internal combustion engine according to a first embodiment, and FIG. 1B is a schematic longitudinal sectional view.
FIG. 2 is a view showing a state in which fuel injected after an intake valve is opened accumulates in a cavity provided on the top surface of a piston.
FIG. 3 is a diagram showing an injection pattern by fuel injection control according to the embodiment of the present invention.
FIG. 4 is a flowchart showing a control routine according to a first embodiment of fuel injection control.
FIG. 5 is a flowchart showing a control routine according to a second embodiment of fuel injection control.
FIG. 6 is a schematic longitudinal sectional view around the combustion chamber of the internal combustion engine according to the second embodiment.
FIG. 7 is a schematic longitudinal sectional view around the combustion chamber of the internal combustion engine according to the first embodiment.
FIG. 8 is a schematic longitudinal sectional view of the vicinity of a combustion chamber of another internal combustion engine according to the second embodiment.
FIG. 9 is a schematic longitudinal sectional view of the periphery of a combustion chamber of another internal combustion engine according to the second embodiment.
FIG. 10 is a schematic plan view of another internal combustion engine to which the present invention is applicable.
[Explanation of symbols]
1 Internal combustion engine
2 Combustion chamber
3 Cylinder head
4 Cylinder block
5 piston
5a cavity
6 Piston ring
7 Intake valve
8 Exhaust valve
9 Spark plug
10 Intake passage
11 Exhaust passage
12 Fuel injection valve
13 ECU
14 Water temperature sensor

Claims (5)

A fuel injection valve for injecting fuel into the intake passage;
After part of the fuel required according to the operating state of the internal combustion engine is injected into at least the expansion stroke or the exhaust stroke before the intake valve is opened, and the remaining fuel is opened Control means for controlling the injection timing by the fuel injection valve so as to inject at least the intake stroke of
The remaining fuel injected after the intake valve is opened is accumulated in a cavity provided on the top surface to form an air-fuel mixture in the cavity, and the air-fuel mixture is led to the vicinity of the ignition plug in the latter half of the compression stroke. A piston,
A lean burn internal combustion engine. The control means forms a homogeneous air-fuel mixture that becomes a first lean air-fuel ratio over a whole cylinder with a part of required fuel injected before the intake valve is opened, and the intake air Injection by the fuel injection valve so as to form an air-fuel mixture having a second lean air-fuel ratio richer than the first lean air-fuel ratio in the cavity with the remaining fuel injected after the valve is opened The lean combustion internal combustion engine according to claim 1, wherein the fuel amount is also controlled. 3. The lean combustion internal combustion engine according to claim 1, further comprising squish flow generation means that is formed by at least one of a piston and a cylinder head and generates a squish flow so as to be applied to a discharge portion of the spark plug. organ. From a fuel injection valve that injects fuel into the intake passage, a part of the fuel required according to the operating state of the internal combustion engine is injected into at least one of the expansion stroke or the exhaust stroke before the intake valve is opened, The remaining fuel is injected at least during the intake stroke after the intake valve is opened,
A part of the required fuel injected before the intake valve is opened forms a homogeneous mixture throughout the cylinder, and the remaining fuel injected after the intake valve is opened An air-fuel mixture forming method for a lean combustion internal combustion engine, characterized in that an air-fuel mixture is formed in a cavity that is provided on the top surface of the piston and is located near the spark plug at the top dead center. A part of the required fuel injected before the intake valve is opened forms a homogeneous mixture of the first lean air-fuel ratio over the entire cylinder, and the intake valve is opened. 5. The lean-burn internal combustion engine mixture according to claim 4, wherein the remaining fuel injected later forms an air-fuel mixture having a second lean air-fuel ratio richer than the first lean air-fuel ratio in the cavity. Qi formation method.

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