JPH0979079A - In-cylinder injection type spark ignition internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enlarge a load region performing after injection as much as possible while suppressing increase in a harmful discharge gas component. SOLUTION: In a fuel injection control map, the first load region of the first upper limit load or less where fuel injection 81 from a fuel injection valve is placed within a cavity 8 of a piston 7 and the second load region of the second upper limit load or less serving as a smoke generation limit are found, and a overlapping part of both regions is set as an after-injection lean area. That is, serving as the boundary an engine speed Nex in an intersection between the first/second upper limit load lines L1, L2, in a rotational area of this engine speed Nex or less, after-injection is performed in the second limit load region where air-fuel ratio in the cavity 8 is not overrich, and in a rotational area of this engine speed Nex or more, after-injection is performed in the first limit load region where the fuel injection 81 from the fuel injection valve is placed within the cavity 8 of the piston 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder injection type spark ignition internal combustion engine mounted on an automobile or the like, and more specifically to a technique for appropriately setting the early injection mode and the late injection mode according to operating conditions. Regarding

[0002]

2. Description of the Related Art In recent years, in a fuel injection spark ignition type internal combustion engine mounted on an automobile or the like, in order to reduce harmful exhaust gas components and improve fuel efficiency, the conventional intake pipe injection type is directly replaced with a direct combustion chamber. Various in-cylinder injection types for injecting fuel (hereinafter, in-cylinder injection gasoline engine) have been proposed.

In a cylinder injection gasoline engine, for example,
By injecting fuel from the fuel injection valve into the cavity provided at the top of the piston, an air-fuel mixture having an air-fuel ratio close to the stoichiometric air-fuel ratio is generated around the spark plug at the time of ignition. This makes it possible to ignite even with a lean air-fuel ratio as a whole, thereby reducing CO and HC emissions and greatly improving fuel efficiency during idling and low-load driving. In addition, since there is no transfer delay due to the intake pipe even when the fuel injection amount is increased or decreased, the acceleration / deceleration response becomes very good. However, in the method of injecting fuel into the cavity, there is a problem that the stable operation range is narrowed because the air-fuel ratio near the spark plug becomes overrich and misfire occurs during high load operation in which the required fuel injection amount increases. This is because it is difficult to change the injection amount per unit time of the fuel injection valve and the injection direction, so the air-fuel ratio in the vicinity of the spark plug cannot be kept at an optimum value over the entire operating region of the engine, etc. caused by.

In order to solve such a problem, Japanese Patent Laid-Open Publication No.
In JP-A-79370 and JP-A-7-102976, the compression stroke injection mode (late injection mode) and the intake stroke injection mode (early injection mode) are switched according to the load, and the shape of the combustion chamber and the fuel injection are performed. It has been proposed to design the injection direction of the valve in accordance with this. In these engines, during low-load operation, fuel is injected into the cavity (deep bowl or concave groove) during the compression stroke, and the air-fuel ratio (air and fuel A weight ratio of) to form a mixture. As a result, ignition is possible even with a lean air-fuel ratio as a whole, CO and HC emissions are reduced, and fuel efficiency is greatly improved during idle operation and low load running. In addition, during high load traveling, fuel is injected outside the cavity during the intake stroke to form a mixture having a uniform air-fuel ratio in the combustion chamber. As a result, it becomes possible to burn a large amount of fuel, as in the case of the intake pipe injection type, and the output required during acceleration or high speed traveling is secured. In a cylinder-injection gasoline engine, the injection end timing is determined so that the fuel injection is ended during the intake stroke and the compression stroke after the opening time of the fuel injection valve is set from the fuel pressure and the required fuel injection amount. The injection start timing is determined from the injection end timing and the valve opening time. Furthermore, in the late injection mode, the fuel in the cavity must be vaporized at the time of ignition in order to avoid incomplete combustion, and the injection end timing and injection start timing are determined in consideration of the time required for fuel vaporization. To be done.

[0005]

By the way, in a cylinder injection gasoline engine, in consideration of fuel consumption, fuel injection is performed in a late injection mode capable of realizing a lean air-fuel ratio in a wide operating range (load and engine speed). Is desirable. However, when the load range to which the late injection mode is applied is excessively widened, there is a problem that exhaust gas performance is significantly deteriorated. For example, when the load (that is, the target average effective pressure Pe) increases, the required fuel injection amount also increases, and a relatively large amount of fuel is injected into the cavity in the latter injection mode. As a result, the air-fuel ratio in the cavity becomes overrich, misfire occurs and a large amount of unburned fuel is discharged together with the exhaust gas, or incomplete combustion occurs and smoke (black smoke whose main component is carbon soot) is discharged. To be done. Therefore, the late injection mode is
There is no choice but to find the load level that becomes the smoke generation limit and set it to a load region at least below that.

On the other hand, when the latter injection mode is set only by the load and the engine speed increases above a predetermined value, the amount of HC discharged sharply increases. The reason is that when the engine speed increases, the piston speed increases in proportion to this, but the fuel injection amount per unit time from the fuel injection valve and the fuel vaporization speed are constant.
For example, when the fuel injection is started based on the injection start timing determined from the fuel pressure and the required fuel injection amount, as shown in FIG. 8, the fuel spray 81 from the fuel injection valve 4 in the low speed region is generated.
(In the figure, LI is the injection axis of the fuel injection valve 4) is the piston 7
Even if it is accommodated in the cavity 8 (shown by the chain double-dashed line), the injection start timing (crank angle) is advanced in order to secure the same fuel injection amount in the high rotation range where the piston speed is high, so At the start point, the position of the piston 7 (shown by the solid line) is still low, and the fuel spray 81 is injected outside the cavity 8. Then, a part of the fuel spray 81 injected outside the cavity 8 becomes unburned fuel (that is, HC) and is discharged together with the exhaust gas. This tendency becomes remarkable as the engine speed increases, and a large amount of HC is discharged near the maximum speed. Therefore, in order to expand the late injection mode to the high rotation speed side, it is necessary to shorten the valve opening time of the fuel injection valve, that is, reduce the load that is the basis of the required fuel injection amount.

As described above, in the in-cylinder injection gasoline engine, there is a trade-off relationship between the load and the engine speed in the setting of the late injection mode, and the limit load is small in order to carry out the late injection to a relatively high rotation speed range. On the contrary, in order to perform the late injection to a relatively high load range, the limit engine speed must be lowered. Therefore, the latter-stage injection mode has to be set to a relatively low load / low rotation range in accordance with the actual operating state, and a compromise has been forced in improving fuel efficiency.

The present invention has been made in view of the above situation,
An object of the present invention is to provide a cylinder injection type spark ignition type internal combustion engine in which the load range in which the latter-stage injection can be performed is made as wide as possible while suppressing an increase in harmful exhaust gas components.

[0009]

Therefore, in claim 1 of the present invention, when the piston is in the latter stage of the compression stroke, the injection axis thereof is arranged so as to be directed into the cavity formed in the top surface of the piston. Has a fuel injection valve and an ignition plug, which is arranged at a portion where the mixed air flow formed by the cavity reaches when the piston is in the ignition position, in the cylinder head, and the fuel injection is mainly performed in the intake stroke. In a cylinder injection type spark ignition internal combustion engine in which fuel is directly injected into a combustion chamber based on a first-stage injection mode and a second-stage injection mode in which fuel is mainly injected in a compression stroke, the latter-stage injection mode is the fuel injection. It is proposed to set the first load region below a first upper load level where substantially all of the fuel injected from the valve is contained in the cavity.

According to a second aspect of the present invention, in the cylinder injection type spark ignition internal combustion engine of the first aspect, in the latter injection mode, the injection axis of the fuel injection valve at the time of fuel injection deviates from the inner wall surface of the cavity. Suggest what you don't.
Further, in claim 3, when the piston is in the latter stage of the compression stroke, the injection axis is arranged so as to face the inside of the cavity formed in the top surface of the piston, and the piston is in the ignition position. When the cylinder head has a spark plug disposed at a portion where the mixed air flow formed by the cavity reaches, the fuel injection is mainly performed in the intake stroke, and the fuel injection is mainly performed in the compression stroke. In the cylinder injection type spark ignition internal combustion engine in which fuel is directly injected into the combustion chamber based on the latter injection mode performed, the latter injection mode is the second upper limit load level corresponding to the smoke generation limit Propose the one set in the load area.

Further, in claim 4, when the piston is in the latter stage of the compression stroke, the fuel injection valve is arranged so that its injection axis is directed into the cavity formed in the top surface of the piston, and the piston is ignited. When the cylinder head has a spark plug disposed at a position where the mixed airflow formed by the cavity reaches when in the position, the fuel injection is mainly performed in the intake stroke, and the injection stroke is mainly performed in the compression stroke. In the in-cylinder injection spark ignition internal combustion engine in which fuel is directly injected into the combustion chamber based on the latter injection mode in which fuel injection is performed, the latter injection mode is used when the engine rotation speed is equal to or lower than a predetermined value. When the engine speed exceeds the predetermined value and is set in the second load region below the second upper limit load level corresponding to the smoke generation limit, the fuel is Substantially all of the fuel injected proposes those set in the first upper limit load level below the first load region that fits in the cavity from the event.

According to a fifth aspect of the present invention, in the in-cylinder injection spark ignition internal combustion engine of the fourth aspect, the second upper limit load level is set when the engine speed is equal to or lower than the predetermined value. Is set in the load area that exceeds
If the engine rotation speed exceeds the predetermined value, it is proposed that the engine speed is set in the load region that exceeds the first upper limit load level.

Further, in claim 6, claims 1, 2, 4,
In the in-cylinder injection spark ignition internal combustion engine of No. 5, substantially the entire amount of fuel injected from the fuel injection valve is settled in the cavity when the piston rises during the compression stroke in the latter injection mode. It is proposed to provide an injection timing setting means for setting the injection timing of the fuel injection valve.

According to a seventh aspect of the present invention, in the cylinder injection type spark ignition internal combustion engine according to the sixth aspect, the injection timing setting means is at least near the first upper limit load level.
It is proposed that the fuel injection start timing is advanced as the engine speed increases. Further, in claim 8,
7. The direct injection spark ignition internal combustion engine according to claim 6, wherein the injection timing setting means secures a delay time from the end of the fuel injection to the ignition timing or the compression top dead center, in particular, the first upper limit. In the vicinity of the load level, it is proposed that the fuel injection end timing be advanced as the engine speed increases.

[0015]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of an engine control system to which the present invention is applied, and FIG. 2 is a vertical sectional view of a cylinder injection gasoline engine according to the embodiment. In these drawings, reference numeral 1 denotes an in-cylinder in-cylinder in-line in-line four-cylinder gasoline engine (hereinafter simply referred to as an engine), which includes a combustion chamber, an intake device, and
The R device and the like are designed only for in-cylinder injection.

In the case of the present embodiment, the cylinder head 2 of the engine 1 is provided with the spark plug 3 and the electromagnetic fuel injection valve 4 for each cylinder, and the fuel is directly injected into the combustion chamber 5. It is like this. Also, the cylinder 6
A hemispherical cavity 8 is formed on the top surface of the piston 7, which is held slidably in the vertical direction, at a position where fuel spray from the fuel injection valve 4 reaches in the latter stage of the compression stroke. Also,
The theoretical compression ratio of the engine 1 is set higher (about 12 in this embodiment) than that of the intake pipe injection type. A DOHC four-valve system is adopted as a valve mechanism, and an intake side camshaft 11 and an exhaust side camshaft 12 are rotatably provided in an upper portion of the cylinder head 2 so as to drive the intake and exhaust valves 9 and 10, respectively. Is held.

The cylinder head 2 has both camshafts 1
An intake port 13 is formed in a substantially upright direction so as to pass through between the intake ports 1 and 12, and the intake flow passing through the intake port 13 generates a reverse tumble flow described later in the combustion chamber 5. ing. On the other hand, although the exhaust port 14 is formed in a substantially horizontal direction like a normal engine, a large-diameter EGR port 15 (not shown in FIG. 2) branches obliquely downward. In the figure, 16 is the cooling water temperature Tw
The water temperature sensor 17 detects a predetermined crank position of each cylinder (5 ° BTDC and 75 ° BTD in this embodiment).
C) is a vane type crank angle sensor that outputs a crank angle signal SGT, and 19 is an ignition coil that outputs a high voltage to the ignition plug 3. The cylinder discriminating signal S
A cylinder discriminating sensor (not shown) that outputs GC is attached to discriminate which cylinder the crank angle signal SGT belongs to.

As shown in FIG. 2, the intake port 13 is provided with an air cleaner 22, a throttle body 23, and a stepper motor type ISCV (idle speed control valve) 24 via an intake manifold 21 having a surge tank 20. The intake pipe 25 is connected.
Further, the intake pipe 25 is provided with a large-diameter air bypass pipe 26 that bypasses the throttle body 23 and introduces intake air into the intake manifold 21, and a linear solenoid type large-sized ABV is provided in the pipe line. An (air bypass valve) 27 is provided. In addition, the air bypass pipe 2
6 has a flow passage area corresponding to that of the intake pipe 25.
When the V27 is fully opened, the required amount of intake air can be circulated in the low and medium speed range of the engine 1. The throttle body 23 has a butterfly type throttle valve 28 that opens and closes a flow path, and an opening θTH of the throttle valve 28.
There is provided a throttle sensor 29 for detecting the above, and an idle switch 30 for detecting the fully closed state. In the figure, 3
1 is a boost pressure (MAP: Man) for detecting the intake pipe pressure Pb.
ifold Absolute Pressure) sensor, which is connected to the surge tank 20.

On the other hand, an O ₂ sensor 4
An exhaust pipe 43 provided with a three-way catalyst 42 and a muffler (not shown) is connected through an exhaust manifold 41 to which 0 is attached. In addition, the EGR port 15 has a large diameter EG.
It is connected to the upstream side of the intake manifold 21 via an R pipe 44, and has a stepper motor type EG in its pipeline.
An R valve 45 is provided.

The fuel tank 50 is installed at the rear of the vehicle body (not shown). Then, the fuel stored in the fuel tank 50 is sucked up by the electric low-pressure fuel pump 51,
The air is supplied to the engine 1 via the low-pressure feed pipe 52. The fuel pressure in the low-pressure feed pipe 52 is controlled by the first fuel pressure regulator 5 interposed in the return pipe 53.
4, the pressure is adjusted to a relatively low pressure (hereinafter, referred to as low fuel pressure). The fuel supplied to the engine 1 is supplied by a high-pressure fuel pump 55 attached to the cylinder head 2 via a high-pressure feed pipe 56 and a delivery pipe 57.
The fuel is supplied to each fuel injection valve 4. In the case of the present embodiment, the high-pressure fuel pump 55 is a swash plate axial piston type, is driven by the exhaust side cam shaft 12, and generates a discharge pressure of 50 to 60 kg / mm ² or more even during idle operation of the engine 1. The fuel pressure in the delivery pipe 57 is the return pipe 5
The second fuel pressure regulator 59 installed in the conduit 8 regulates the pressure to a relatively high pressure (hereinafter, referred to as high fuel pressure).
In the figure, reference numeral 60 denotes an electromagnetic fuel pressure switching valve attached to the second fuel pressure regulator 59, which relieves fuel in the ON state and reduces the fuel pressure in the delivery pipe 57 to a low fuel pressure. Reference numeral 61 denotes a return pipe for returning the fuel, which has been lubricated or cooled by the high-pressure fuel pump 55, to the fuel tank 50.

In the passenger compartment, an input / output device (not shown), a storage device (ROM, RAM, BURAM, etc.) for storing control programs and control maps, and a central processing unit (C)
An ECU (engine control unit) 70 including a PU), a timer counter, and the like is installed to perform comprehensive control of the engine 1. On the input side of the ECU 70, detection information from the above-mentioned various sensors and the like is input. ECU7
0 determines the ignition timing, the amount of EGR gas introduced, etc., including the fuel injection mode and the fuel injection amount, based on these detection information, and drives and controls the fuel injection valve 4, the ignition coil 19, the EGR valve 45, and the like. To do. The ECU 70 is connected to a large number of switches and sensors (not shown) on its input side, and is connected to various warning lights and devices on its output side.

Next, a basic flow of engine control will be described. When the driver turns on the ignition key in the cold state, the ECU 70 turns on the low-pressure fuel pump 51 and the fuel pressure switching valve 60 to supply the fuel injection valve 4 with fuel having a low fuel pressure. This is because, when the engine 1 is stopped or cranking, the high-pressure fuel pump 55 operates at all or incompletely, so that the required fuel injection amount is set to the discharge pressure of the low-pressure fuel pump 51 and the opening time of the fuel injection valve 4. Because I can only get from. Next, when the driver operates the ignition key to start, the engine 1 is cranked by the cell motor (not shown), and at the same time, the fuel injection control by the ECU 70 is started. At this point, the ECU 7
When 0 is selected, the previous period injection mode is selected, and the fuel is injected so that the air-fuel ratio becomes relatively rich. This is because the vaporization rate of the fuel is low when the engine is cold, so that misfire and discharge of unburned fuel (HC) cannot be avoided when the injection is performed in the late injection mode (that is, the compression stroke). Also, the ECU 70
Since the ABV 27 is closed at the time of starting, the intake air into the combustion chamber 5 is supplied from the gap of the throttle valve 28 and the ISCV 24. In addition, ISCV24 and ABV27 are EC
It is centrally managed by U70 and has a throttle valve 2
Each valve opening amount is determined according to the required introduction amount of the intake air (bypass air) that bypasses 8.

When the engine 1 starts idle operation after the start-up is completed, the high-pressure fuel pump 55 starts the rated discharge operation, so that the ECU 70 turns off the fuel pressure switching valve 60 and supplies the high-pressure fuel to the fuel injection valve 4. Supply. In this case,
As a matter of course, the required fuel injection amount is the high pressure fuel pump 5
It can be obtained from the discharge pressure of 5 and the valve opening time of the fuel injection valve 4. Then, until the cooling water temperature Tw rises to a predetermined value, the ECU 70 selects the first-stage injection mode to inject fuel as at the time of starting, and continuously closes the ABV 27 as well. In addition, the control of the idle speed according to the increase or decrease of the load of the auxiliary equipment such as the air conditioner is the same as that of the intake pipe injection type.
Performed by CV24. Further, when the O ₂ sensor 40 is activated after a lapse of a predetermined cycle, the ECU 70
The air-fuel ratio feedback control is started according to the output voltage of the O ₂ sensor 40, and the harmful exhaust gas component is purified by the three-way catalyst 42. As described above, when the engine is cold, fuel injection control similar to that of the intake pipe injection type is performed.
Since the fuel droplets do not adhere to the wall surface of No. 3, the control response and accuracy are improved.

When the engine 1 is warmed up, the ECU 7
0 is based on the target average effective pressure Pe obtained from the intake pipe pressure Pb, the throttle opening θTH, etc. and the engine rotation speed Ne.
The current fuel injection control region is searched from the fuel injection control map of FIG. 3, the fuel injection mode, the fuel injection amount, and the fuel injection timing are determined, and the fuel injection valve 4 is driven, and the ABV 27 and the EGR valve 45 are opened and closed. It also controls. It should be understood that the fuel injection amount is proportional to the valve opening time width of the fuel injection valve 4.

For example, since the low load region during idle operation or low speed traveling is the late injection lean region in FIG. 3, EC
U70 selects the late injection mode and the ABV27
Is opened, and a lean average air-fuel ratio (in this embodiment, 30-
(About 40) to inject fuel. At this point in time, the vaporization rate of the fuel rises, and as shown in FIG. 4, the intake flow that has flowed in from the intake port 13 forms the reverse tumble flow 80 shown by the arrow, so that the fuel spray 81 inside the cavity 8 of the piston 7. Stored in. As a result, the air-fuel mixture near the stoichiometric air-fuel ratio is formed in a layer around the spark plug 3 at the time of ignition, and ignition is possible even with a lean air-fuel ratio as a whole. As a result, CO and HC emissions are suppressed to an extremely small amount, and fuel consumption is greatly improved in combination with the reduction of pumping loss. The control of the idle speed according to the increase / decrease of the auxiliary machine load and the like is performed by increasing / decreasing the fuel injection amount, so that the control response becomes very high. Further, the ECU 70 controls the EGR in this control region.
By opening the valve 45 and introducing a large amount (30% or more in this embodiment) of EGR gas into the combustion chamber 5, N
O _X also be greatly reduced.

Further, since the medium load range during constant-speed running is the previous period injection lean region or the stoichiometric feedback region in FIG. 3 according to the load state and the engine speed Ne, the ECU 70 causes the previous period injection to be performed. A mode is selected, and fuel is injected so as to have a predetermined air-fuel ratio. That is, the valve opening amount and the fuel injection amount of the ABV 27 are controlled so that the air-fuel ratio becomes relatively lean (about 20 to 23 in the present embodiment) in the early injection lean region, and the ABV 27 in the stoichiometric feedback region. And EGR valve 45 are opened and closed, and air-fuel ratio feedback control is performed according to the output voltage of the O ₂ sensor 40. In this case, as shown in FIG. 5, the intake flow that has flowed in from the intake port 13 forms the reverse tumble flow 80. Therefore, the effect of turbulence due to the reverse tumble flow 80 enables ignition even with a lean air-fuel ratio.
It should be noted that the ECU 70 controls the EGR valve 45 even in this control region.
Is opened and an appropriate amount of EGR gas is introduced into the combustion chamber 5, so that NO _X generated at a lean air-fuel ratio is significantly reduced. Further, in the stoichio feedback region, a large output is obtained due to the relatively high compression ratio, and harmful exhaust gas components are purified by the three-way catalyst 42.

Since the high load range during sudden acceleration or high speed running is the open loop control range in FIG. 3, the ECU
Reference numeral 70 selects the first-stage injection mode, closes the ABV 27, and injects fuel so that the air-fuel ratio becomes relatively rich according to the throttle opening θTH, the engine speed Ne, and the like. At this time, in addition to the high compression ratio and the fact that the intake air flow forms the reverse tumble flow 80, since the intake port 13 is substantially upright with respect to the combustion chamber 5, a high output is obtained by the inertia effect. Can be

Furthermore, during coasting operation during medium-high speed traveling, the fuel cut region in FIG. 3 is reached, so the ECU 70 stops fuel injection. As a result, the fuel economy is improved and, at the same time, no harmful exhaust gas components are emitted. The fuel cut is immediately stopped when the engine rotation speed Ne falls below the return rotation speed or when the driver depresses the accelerator pedal.

Next, the procedure for setting the late injection lean region in the fuel injection control map will be described with reference to FIG. In the present embodiment, when setting the late injection lean region, first, the first load region below the first upper limit load where the fuel spray 81 from the fuel injection valve 4 is contained in the cavity 8 of the piston 7 is obtained. For example, when the required fuel injection amount (that is, the valve opening time of the fuel injection valve 4) is determined from the target average effective pressure Pe, the time required for vaporization of the injected fuel is also obtained by experiments, etc. The start timing is uniquely determined according to the ignition timing. Therefore, for each target average effective pressure (Pe1, Pe2, Pe3 ...), the fuel spray 81 (fuel injection valve 7
Of the engine rotation speed within which the injection axis LI of
1, Ne2, Ne3 ...) is obtained by simulation or the like,
By connecting these, the first upper limit load line L1 shown in FIG. 6 is obtained. The first load region is a region that does not exceed the first upper limit load line L1, and as shown in FIG. 7, the fuel spray 81 does not deviate from the inner wall surface 8a of the cavity 8 in this region. The fuel spray 81 has the highest speed along the injection axis LI of the fuel injection valve 7 and a little behind it in the surrounding areas, so that the injection axis LI does not deviate from the inner wall surface 8a of the cavity 8. The fuel spray 81 does not deviate from the inner wall surface 8a of the cavity 8 due to the ascent of the piston 7 during that time.

In the present embodiment, next, the second load region below the second upper limit load, which is the smoke generation limit, is obtained. The smoke is generated when the air-fuel ratio in the cavity 8 becomes overrich, and the volume of the cavity 8 is constant. Therefore, this is because the absolute value of the fuel injection amount, that is, the average air-fuel ratio is a predetermined value (in the present embodiment, 30) It happens when it becomes above. Since the average air-fuel ratio is uniquely determined by the target average effective pressure Pe, the second upper limit load line L2, which is the smoke generation limit, is defined by the predetermined limit target average effective pressure Pex, as shown in FIG. become. The second load region is a region that does not exceed the second upper limit load line L2, and in principle, smoke does not occur in this region.

In this way, when the first load region and the second load region are obtained, in the present embodiment, a portion where the both overlap is obtained and set as the late injection lean region. That is, the first upper limit load line L1 and the second upper limit load line L2
With the engine rotation speed Nex at the intersection with the boundary, the late injection is performed in the second limit load region where the air-fuel ratio in the cavity 8 does not become overrich in the rotation region below that, and the fuel injection valve 4 in the rotation region above that. The fuel injection 81 is injected into the cavity 8 of the piston 7 in the first limit load region to perform the latter injection. Then, when the load is out of these load regions, the fuel injection is performed in the fuel injection mode, because the fuel injection is in the fuel injection lean region or the stoichio feedback region.

As described above, in the present embodiment, in the load region in which the late injection mode is performed, the first upper limit load level below which the substantially entire amount of the fuel injected from the fuel injection valve 7 is accommodated in the cavity 8 is set. Since the load range and the second load range below the second upper limit load level corresponding to the smoke generation limit are set, the load range in which the latter-stage injection can be performed while suppressing the increase of harmful exhaust gas components such as HC and smoke Can be widened to the limit and fuel efficiency can be significantly improved.

Further, the setting of the fuel injection timing in the latter injection mode in this embodiment will be described. Fuel injection valve 4
There is a delay time until the fuel injected from the inside actually reaches the cavity 8, and the piston 7 continues to rise during the delay time. In other words, when the piston position is used as a reference, even if the fuel injection is performed from a timing (crank angle) earlier than the injection start timing at which the fuel can be supplied into the cavity 8, the arrival at the cavity 8 is reached. Due to the delay time up to, the entire amount of the actual fuel will be stored in the cavity 8. This means that the fuel injection start timing (crank angle) can be advanced in response to an increase in the number of revolutions in consideration of an increase in the rising speed of the piston 7 due to an increase in the number of revolutions. are doing. On the other hand, with respect to the injection end timing, since the injected fuel is ignited in a sufficiently vaporized state, it is preferable to secure a certain time from the injection end timing to the ignition timing near the compression top dead center. This indicates that, considering the rising speed of the piston 7, it is preferable to advance the injection end timing in response to the increase in the rotation speed. In consideration of these points, in the present embodiment, particularly in the latter injection region near the first upper limit load line,
The injection timing is set so that the injection start timing is advanced (the injection end timing is advanced) as the rotational speed is higher. This allows
Since the crank angle range occupied by the injection is wide, the combustion by the late injection is reliably performed even in the vicinity of the first upper limit load line where the flexibility of the injection time is small, and the operating range of the late injection is not unnecessarily narrowed. It was

Although the description of the specific embodiment has been completed, the aspect of the present invention is not limited to this embodiment.
For example, the above-described embodiment is applied to the in-line 4-cylinder in-cylinder injection gasoline engine, but is applied to various engines having different numbers of cylinders and arrangements such as a single-cylinder engine and a V-6 cylinder engine. Alternatively, it may be applied to an engine that uses a fuel other than gasoline, such as methanol. Furthermore, the specific configuration and the like of the control system can be changed without departing from the spirit of the present invention.

[0035]

According to the first aspect of the present invention, when the piston is in the latter stage of the compression stroke, the fuel injection valve is arranged so that its injection axis is directed into the cavity formed on the top surface of the piston. And a spark injection plug disposed in a portion where the mixed airflow formed by the cavity reaches when the piston is in the ignition position, in the cylinder head, and the first-term injection mode in which fuel injection is mainly performed in the intake stroke, ,
In a cylinder injection type spark ignition internal combustion engine in which fuel is directly injected into a combustion chamber based on a late injection mode in which fuel injection is mainly performed in a compression stroke, the late injection mode is injected from the fuel injection valve. Since the substantially entire amount of the fuel is set in the first load region that is equal to or lower than the first upper limit load level in which the fuel is contained in the cavity, the discharge of HC resulting from the deviation of the fuel spray from the cavity is suppressed.

According to a second aspect of the present invention, in the cylinder injection type spark ignition internal combustion engine of the first aspect, in the latter injection mode, the injection axis of the fuel injection valve at the time of fuel injection has an inner wall surface of the cavity. The deviation of the fuel spray from the cavity is more reliably prevented. Further, according to claim 3, when the piston is in the latter stage of the compression stroke, the fuel injection valve is arranged so that its injection axis is directed into the cavity formed on the top surface of the piston, and the piston is at the ignition position. When the cylinder head has a spark plug disposed at a position where the mixed air flow formed by the cavity reaches, the fuel injection is performed mainly in the intake stroke, and the fuel is mainly injected in the compression stroke. In the in-cylinder injection spark ignition internal combustion engine in which fuel is directly injected into the combustion chamber based on the late injection mode in which the injection is performed, the late injection mode is set to the second upper limit load level or less corresponding to the smoke generation limit. Since it is set to the second load region, smoke emission due to the air-fuel ratio in the cavity becoming overrich is suppressed.

Further, according to claim 4, when the piston is in the latter stage of the compression stroke, the fuel injection valve is arranged so that its injection axis is directed into the cavity formed at the top surface of the piston, and the piston. Has a spark plug disposed at a position where the mixed airflow formed by the cavity reaches when the ignition position is in the cylinder head. In the cylinder injection type spark ignition internal combustion engine in which fuel is directly injected into the combustion chamber based on the latter injection mode in which fuel is injected in the stroke, the latter injection mode is the case where the engine speed is equal to or lower than a predetermined value. Is set to a second load region equal to or lower than the second upper limit load level corresponding to the smoke generation limit, and when the engine speed exceeds the predetermined value, Since the substantially entire amount of fuel injected from the fuel injection valve has to be set in the first load range below a first limit load level falls within said cavity, H
Both the emission of C and the emission of smoke are suppressed.

According to a fifth aspect of the present invention, in the cylinder injection type spark ignition internal combustion engine of the fourth aspect, the second upper limit is set in the first injection mode when the engine speed is equal to or lower than the predetermined value. Since the load range is set to exceed the load level and the engine speed exceeds the predetermined value, the load range is set to exceed the first upper limit load level, so that the harmful exhaust gas component is increased. A desired output can be secured while suppressing.

According to claim 6, claims 1, 2 and
In the cylinder injection type spark ignition internal combustion engine of Nos. 4 and 5, substantially all of the fuel injected from the fuel injection valve is accommodated in the cavity when the piston rises during the compression stroke in the latter injection mode. Since the injection timing setting means for setting the injection timing of the fuel injection valve is provided as described above, the discharge of HC caused by the deviation of the fuel spray from the cavity is suppressed.

According to a seventh aspect, in the cylinder injection type spark ignition internal combustion engine according to the sixth aspect, the injection timing setting means has a high engine rotation speed at least near the first upper limit load level. Since the fuel injection start timing is advanced as soon as possible, it is possible to prevent the operating range of the late injection mode from being unnecessarily narrowed. In the eighth aspect, in the direct injection spark ignition internal combustion engine according to the sixth aspect, the injection timing setting means secures a delay time from the end of the fuel injection to the ignition timing or the compression top dead center. Therefore, especially near the first upper limit load level, the fuel injection end timing is advanced as the engine speed increases, so that the time required for vaporization of the injected fuel can be secured even in the high speed region. Further, such setting of the fuel injection end timing is particularly effective in the vicinity of the first upper limit load level where the degree of freedom of the injection timing is small.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an engine control system according to the present invention.

FIG. 2 is a vertical cross-sectional view of a cylinder injection gasoline engine according to an embodiment.

FIG. 3 is a fuel injection control map according to the embodiment.

FIG. 4 is an explanatory diagram showing a fuel injection mode in a latter injection mode in the embodiment.

FIG. 5 is an explanatory diagram showing a fuel injection mode in a first-term injection mode in the embodiment.

FIG. 6 is a graph showing a procedure for setting a late injection mode in a fuel injection control map.

FIG. 7 is an explanatory diagram showing a positional relationship between fuel spray and a piston at a first upper limit load.

FIG. 8 is an explanatory diagram showing the positional relationship between the fuel spray and the piston for explaining the background of the present invention.

[Explanation of symbols]

 1 Engine 2 Cylinder Head 3 Spark Plug 4 Fuel Injection Valve 5 Combustion Chamber 6 Cylinder 7 Piston 8 Cavity 8a Cavity Inner Wall 13 Intake Port 70 ECU 81 Fuel Spray LI Injection Axis

Claims (8)

[Claims] 1. A fuel injection valve arranged so that its injection axis is directed into a cavity formed on the top surface of the piston when the piston is in the latter stage of the compression stroke, and when the piston is in the ignition position. The cylinder head has an ignition plug disposed at a portion where the mixed airflow formed by the cavity reaches, and the fuel injection is performed mainly in the first stroke injection mode in which fuel injection is mainly performed in the intake stroke and the fuel injection is mainly performed in the compression stroke. In the cylinder injection type spark ignition internal combustion engine in which fuel is directly injected into the combustion chamber based on the late injection mode, in the late injection mode, substantially all of the fuel injected from the fuel injection valve is the cavity. An in-cylinder injection type spark ignition internal combustion engine, characterized in that it is set in a first load region equal to or lower than a first upper limit load level that is contained within. 2. The in-cylinder injection spark ignition internal combustion engine according to claim 1, wherein, in the latter injection mode, an injection axis of the fuel injection valve does not deviate from an inner wall surface of the cavity during fuel injection. organ. 3. A fuel injection valve arranged so that its injection axis is directed into a cavity formed on the top surface of the piston when the piston is in the latter stage of the compression stroke, and when the piston is in the ignition position. The cylinder head has an ignition plug disposed at a portion where the mixed airflow formed by the cavity reaches, and the fuel injection is performed mainly in the first stroke injection mode in which fuel injection is mainly performed in the intake stroke and the fuel injection is mainly performed in the compression stroke. In a cylinder injection type spark ignition internal combustion engine in which fuel is directly injected into a combustion chamber based on a late injection mode, the late injection mode is a second load region equal to or lower than a second upper limit load level corresponding to a smoke generation limit. In-cylinder injection spark ignition internal combustion engine characterized in that: 4. A fuel injection valve arranged so that its injection axis is directed into a cavity formed in the top surface of the piston when the piston is in the latter stage of the compression stroke, and when the piston is in the ignition position. The cylinder head has an ignition plug disposed at a portion where the mixed airflow formed by the cavity reaches, and the fuel injection is performed mainly in the first stroke injection mode in which fuel injection is mainly performed in the intake stroke and the fuel injection is mainly performed in the compression stroke. In the cylinder injection type spark ignition internal combustion engine in which fuel is directly injected into the combustion chamber based on the latter injection mode, the latter injection mode is a smoke generation limit when the engine speed is equal to or lower than a predetermined value. When the engine speed is set to a second load region below the corresponding second upper limit load level and the engine speed exceeds the predetermined value, the fuel is injected from the fuel injection valve. Substantially direct injection type spark ignition internal combustion engine, wherein the total amount is set in the first load range below a first limit load level falls within the cavity of the fuel. 5. The first term injection mode is set to a load region that exceeds the second upper limit load level when the engine rotation speed is equal to or lower than the predetermined value, and when the engine rotation speed exceeds the predetermined value. The in-cylinder injection spark ignition internal combustion engine according to claim 4, characterized in that the load region is set to exceed the first upper limit load level. 6. The injection timing of the fuel injection valve is set so that substantially all of the fuel injected from the fuel injection valve is accommodated in the cavity when the piston is raised during the compression stroke in the late injection mode. 5. An injection timing setting means for setting is provided.
5. The in-cylinder spark ignition internal combustion engine according to any one of 5 above. 7. The in-cylinder according to claim 6, wherein the injection timing setting means advances the fuel injection start timing as the engine speed increases, at least near the first upper limit load level. Injection spark ignition internal combustion engine. 8. The injection timing setting means secures a delay time from the end of fuel injection until the ignition timing or the compression top dead center is reached, particularly in the vicinity of the first upper limit load level.
The cylinder injection type spark ignition internal combustion engine according to claim 7, wherein the fuel injection end timing is advanced as the engine speed increases.