JPH10274071A - Cylinder injection type engine with supercharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent misfire and the like by rapidly changing an air-fuel ratio when a condition is switched from a stratified charge combustion condition into an uniform burning condition while improving a fuel consumption improving effect by the stratified charge combustion, and reduce a torque shock. SOLUTION: A device is provided with means 41 for switching a condition between a stratified charge combustion condition and an uniform burning condition, means 44 for setting an operating region so as to set at least a high load side in a stratified charge combustion region to a supercharging operating region, and a bypass opening/closing valve 25 which is interposed in a supercharger bypassing passage and which is capable of charging of an opening, and means 45 for charging an air-fuel ratio in the rich direction by increasing the flow rate of the supercharging bypass passage temporally when a fuel injection mode is switched from the stratified charge combustion condition to the uniform burning condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a supercharger-in-cylinder injection engine having an injector for directly injecting fuel into a combustion chamber of an engine and having a supercharger in an intake passage.

[0002]

2. Description of the Related Art Conventionally, as shown in, for example, Japanese Patent Application Laid-Open No. 4-362221, an injector for directly injecting fuel into a combustion chamber is provided. An in-cylinder injection type that switches the fuel injection mode to a stratified combustion state in which fuel is unevenly distributed around the fuel, and at high load, a uniform combustion state in which fuel is diffused throughout the combustion chamber by injecting fuel from the injector in an intake stroke during the intake stroke. Engines are known.

[0003] In this engine, the air-fuel ratio is set to a large lean state such as about 40 at the time of stratified charge combustion. However, if the air-fuel ratio changes suddenly at the time of switching from stratified combustion to uniform combustion, a shock due to torque fluctuation occurs. Also,
After switching to the uniform combustion state, there is a problem that a misfire occurs if a state leaner than the lean limit during uniform combustion continues due to a delay in air-fuel ratio fluctuation.

As a countermeasure against such a problem, in the engine disclosed in the above-mentioned publication, when the stratified combustion is shifted to the uniform combustion, the stratified combustion state is maintained for a certain period of time while the amount of intake air is gradually increased. The air-fuel ratio is gradually changed in the rich direction by reducing the air-fuel ratio during uniform combustion, and then switched to the uniform combustion state.At the same time, the air-fuel ratio is gradually changed in the rich direction in the stratified combustion state. During this period, the fuel injection amount is corrected so as to compensate for the deterioration of the flammability. In the engine disclosed in the publication, a supercharger is provided in an intake passage, and valves are provided in a supercharger bypass passage and a throttle bypass passage. Each of the valves is controlled when the amount of air is reduced.

[0005]

In the engine disclosed in the above publication, when the operating state shifts from a region where stratified combustion is performed to a region where uniform combustion is performed, stratification is performed before switching to uniform combustion. Since the air-fuel ratio is changed in the rich direction in the combustion state, there is a problem that the effect of improving fuel efficiency by stratified combustion is reduced.

When a supercharger is provided in the intake passage of this type of engine, it is desirable to improve the fuel efficiency by utilizing the supercharging action during stratified charge combustion and uniform combustion, and to improve the supercharger drive state. It is desirable to appropriately adjust the air-fuel ratio and combustion state during stratified combustion and uniform combustion in
There is room for improvement in these respects.

In view of such circumstances, the present invention enhances the fuel efficiency improvement effect of stratified combustion, and quickly changes the air-fuel ratio when switching from a stratified combustion state to a uniform combustion state, thereby deteriorating flammability such as misfire. It is an object of the present invention to provide a supercharger-equipped in-cylinder injection engine that can prevent the occurrence of torque shock and reduce torque shock.

[0008]

The invention according to claim 1 is
An injector that injects fuel directly into the combustion chamber of the engine; and an injector that performs a stratified combustion state while keeping the air-fuel ratio of the entire combustion chamber leaner than the stoichiometric air-fuel ratio in a low load range, and a uniform combustion state in a high load range. Fuel injection mode switching means for switching the fuel injection mode from
In the cylinder-injection type engine with a supercharger provided with a supercharger in the intake passage, at least the high load side of the stratified combustion region, which is the operation region in which the stratified combustion state is set, is set to the intake pressure by the operation of the supercharger. Operating region setting means for setting a supercharging operation region in which the pressure is equal to or higher than the atmospheric pressure, a bypass opening / closing valve having a variable opening provided in a supercharger bypass passage for bypassing the supercharger, The air-fuel ratio is changed to the rich direction by temporarily increasing the flow rate of the supercharging bypass passage when the fuel injection mode is switched from the stratified combustion state to the uniform combustion state in accordance with the shift of the operation state to the load region. And means for changing the supercharging state.

According to this configuration, in the low-load operation region, the stratified combustion is performed, so that the fuel efficiency is sufficiently improved. In particular, the stratified combustion region is expanded to the supercharging operation region, and a relatively high level is obtained by utilizing the supercharging. Since stratified combustion is also performed on the load side, the fuel economy improvement effect is enhanced. In addition, in the stratified combustion state, the air-fuel ratio is significantly lean, but when switching to the uniform combustion state, the supercharging amount decreases due to an increase in the flow rate of the supercharging bypass passage, thereby reducing the uniform combustion. The air-fuel ratio changes quickly to the rich side from the lean limit in the state, and misfire is prevented. Further, the change in the air-fuel ratio is due to a decrease in the intake air amount (a decrease in the supercharging amount), and does not significantly change the fuel injection amount, so that the torque shock is suppressed.

In the present invention, the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio on the low load side of the uniform combustion region, which is the operation region in which the uniform combustion state is set, and when switching from the stratified combustion state to the uniform combustion state, It is preferable to configure the supercharging state changing means so as to change the air-fuel ratio in a rich direction with a predetermined step within a range leaner than the stoichiometric air-fuel ratio (claim 2). In this manner, even in the uniform combustion region, the air-fuel ratio is made relatively lean until the load becomes considerably high, so that the fuel efficiency can be improved over a wide operation region.

In the stratified combustion region, a fuel is injected from the injector in a compression stroke to form a stratified combustion state, while in a predetermined operation region adjacent to the stratified combustion region in the uniform combustion region, the fuel injection from the injector is performed. Is divided into an intake stroke and a compression stroke.
It is preferable that the fuel injection mode switching means be configured so that the fuel injection from the injector is performed in the intake stroke in which only the intake stroke is performed on the load side higher than the predetermined operation range (claim 3). In this case, in particular, when the fuel injection mode is switched from the stratified combustion state by the compression stroke injection to the split injection, the total fuel injection amount is increased by adding the injection in the intake stroke to the constant injection amount in the compression stroke. It is preferable to increase the amount (claim 4).

With this configuration, when the stratified charge combustion mode is switched from the stratified charge combustion mode to the split fuel injection mode, injection is performed in the compression stroke to ensure ignitability, prevent misfiring, and achieve a uniform combustion state. The transition is good.

The bypass on-off valve is preferably driven by an electric driving means (claim 5). In this case, the fuel injection mode is changed from a stratified combustion state to a uniform combustion state. The control for temporarily increasing the flow rate in the supercharging bypass passage when is switched is performed with good responsiveness.

When the supercharger is a mechanical supercharger, a clutch means for switching the mechanical supercharger between a driving state and a stopped state is provided, and a low-load operation region in the stratified combustion region is provided. It is sufficient to provide a clutch control means for controlling the clutch means so as to bring the turbocharger into a stopped state (Claim 6). In this case, the drive resistance of the supercharger in the low-load operation range is reduced. Output loss can be avoided.

[0015] In this case, the turbocharger is stopped in a low rotation speed region below the first set rotation speed on the low load side in the stratified combustion region, and the supercharger is stopped on a high rotation speed side higher than the first set rotation speed. While the clutch control means is configured to be in the machine driving state, the stratified combustion region is set up to a second set rotation speed higher than the first set rotation speed, and a uniform combustion region is set on the higher rotation side than the second set rotation speed. In the stratified charge combustion region, in the operation region where the supercharger is driven, the bypass on-off valve is set to an opening smaller than the full opening, and the engine speed rises from this region and becomes higher than the second set speed. It is preferable that the bypass opening / closing valve be configured to be opened when it is turned on.

In this way, even when the rotational speed increases, the supercharger driving state and the fuel injection mode are switched accordingly, and a misfire is prevented and torque shock is reduced when the fuel injection mode is switched. Is obtained.

Further, in this case, the opening degree of the bypass on-off valve is increased in the low-load, high-rotation-side region of the operation region in which the supercharger is driven in the stratified combustion region, as compared with the high-load, low-rotation side region. In this case, the drive resistance of the turbocharger is reduced on the low-load high-rotation side where the torque does not need to be increased, which is advantageous for improving fuel efficiency.

In the stratified charge combustion region, both the operation region in which the turbocharger is stopped and the operation region in which the supercharger is driven, the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and When the air-fuel ratio is set to be leaner in the operation region in which the engine is in the stop state than in the operation region in which the supercharger is driven, the air-fuel ratio is set to have a predetermined step at the boundary between the two operation regions. 9) When the supercharger is switched from the turbocharger stopped state to the supercharger driving state, the air-fuel ratio changes in the rich direction by a predetermined amount, thereby compensating for the torque reduction due to the supercharger driving resistance.

In the invention of claim 1, NOx in the exhaust gas is adsorbed when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and when the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio, the NOx becomes NOx. The exhaust passage is equipped with a catalyst that reduces and removes air, and the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio on the low-load side of the uniform combustion region to switch from stratified combustion to uniform combustion. At the time of change
If the air-fuel ratio is temporarily changed to the stoichiometric air-fuel ratio or to the extent that the air-fuel ratio becomes richer (claim 1)
0) In addition to preventing misfiring at the time of switching to the uniform combustion state, an effect of recovering the performance of the catalyst can be obtained.

The invention according to claim 11 is an injector for directly injecting fuel into the combustion chamber of an engine, and a stratified combustion state in which the air-fuel ratio of the entire combustion chamber is leaner than the stoichiometric air-fuel ratio in a low load range. An injection mode switching means for switching a fuel injection mode from the injector so as to achieve a uniform combustion state in a high load region, and a supercharger-equipped in-cylinder injection engine having a supercharger in an intake passage. Operating region setting means for setting at least the high load side of the stratified combustion region which is an operation region to be in a combustion state to be a supercharging operation region in which the intake pressure becomes equal to or higher than the atmospheric pressure by the operation of the supercharger. In the stratified combustion region, the fuel is injected from the injector in a compression stroke in the stratified combustion region to achieve a stratified combustion state, while the stratified combustion region in the uniform combustion region is provided. In the adjacent predetermined operation region, the fuel injection from the injector is divided into injections divided into an intake stroke and a compression stroke. On a higher load side than the predetermined operation region, the fuel injection from the injector is performed only in the intake stroke. The fuel injection mode switching means is configured to perform the stroke injection, and when the fuel injection mode is switched from the stratified combustion state by the compression stroke injection to the split injection, the fuel injection mode is switched to the constant injection amount by the compression stroke injection during the intake stroke. The total fuel injection amount is increased by adding the injection.

According to this configuration, a sudden change in the fuel injection mode is avoided by shifting from the stratified combustion state to the uniform combustion state by the intake stroke injection via the split injection, and the injection in the compression stroke during the split injection is prevented. By doing so, ignitability is ensured and misfire is prevented.

In the present invention, NOx in the exhaust gas is adsorbed when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and NOx is reduced and removed when the stoichiometric air-fuel ratio or the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio. In addition to equipping the exhaust passage with such a catalyst, the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio on the low load side in the uniform combustion region, and when switching from the stratified combustion state by the compression stroke injection to the split injection, Alternatively, the air-fuel ratio may be temporarily changed to the stoichiometric air-fuel ratio or to a degree richer than the stoichiometric air-fuel ratio (claim 12).

According to a thirteenth aspect of the present invention, there is provided an injector for directly injecting fuel into a combustion chamber of an engine, and a stratified combustion state in which the air-fuel ratio of the entire combustion chamber is leaner than the stoichiometric air-fuel ratio in a low load range, thereby achieving a high load. Injection mode switching means for switching the mode of fuel injection from the injector so as to achieve a uniform combustion state in the region, and a supercharger-in-cylinder injection engine provided with a mechanical supercharger in the intake passage. An operation region setting in which at least the high load side of the stratified combustion region that is an operation region to be brought into a combustion state is set as a supercharging operation region in which the intake pressure becomes equal to or higher than the atmospheric pressure by the operation of the mechanical supercharger. Means, a clutch means for switching the mechanical supercharger between a driving state and a stopped state, and the clutch for stopping the supercharger in a low load side operation area in the stratified combustion area. And a clutch control means for controlling the switching means, and the air-fuel ratio of the operation region in which the supercharger is stopped and the operation region in which the supercharger is driven in the stratified combustion region are both higher than the stoichiometric air-fuel ratio. Is also lean, and the air-fuel ratio is further leaner in the operating region in which the turbocharger is stopped than in the operating region in which the turbocharger is driven,
The air-fuel ratio is set so that a predetermined level difference occurs at the boundary between the two operation regions.

According to this configuration, when the supercharger is switched from the turbocharger stopped state to the supercharger driving state, the air-fuel ratio changes in the rich direction by a predetermined amount, thereby compensating for the torque reduction due to the supercharger driving resistance. .

According to a fourteenth aspect of the present invention, there is provided an injector for directly injecting fuel into a combustion chamber of an engine, and a stratified combustion state in which the air-fuel ratio of the entire combustion chamber is leaner than the stoichiometric air-fuel ratio in a low load range, thereby achieving a high load. Injection mode switching means for switching the mode of fuel injection from the injector so as to achieve a uniform combustion state in the region, and a supercharger-equipped in-cylinder injection engine provided with a mechanical supercharger in the intake passage. Clutch means for switching the mechanical supercharger between a driving state and a stopped state, and a supercharger stopped state in a low rotation speed region below a first set rotation speed on a low load side in a stratified combustion region,
Clutch control means for controlling the clutch means so that the supercharger is driven on the higher rotation side than the first set rotation number, and stratified combustion up to the second set rotation number higher than the first set rotation number. A region is set, and the higher rotation side than the second set rotation speed is set as a uniform combustion region, and in an operation region where a supercharger is driven in a stratified combustion region, a bypass opening / closing valve is set to an opening smaller than full opening, and from this region, The bypass on-off valve is opened when the engine speed increases and becomes higher than the second set speed.

According to this configuration, even when the rotational speed increases, the supercharger driving state and the fuel injection mode are switched accordingly, and misfire is prevented and torque shock is reduced when the fuel injection mode is switched. Is obtained.

According to the thirteenth or fourteenth aspect of the present invention, in the stratified combustion region, a fuel is injected from the injector in a compression stroke to make a stratified combustion state, while a predetermined operation adjacent to the stratified combustion region in the uniform combustion region is performed. In the region, the fuel injection from the injector is divided into injections divided into an intake stroke and a compression stroke, and on the higher load side than the predetermined operation region, the fuel injection from the injector is set to the intake stroke injection performed only in the intake stroke. It is preferable to configure the fuel injection mode switching means as described above (claim 15).

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings.

FIG. 1 schematically shows a direct injection engine with a supercharger according to an embodiment of the present invention. In this figure, an engine body 1 has a plurality of cylinders 2, each of which has a combustion chamber 4 formed above a piston 3 inserted into a cylinder bore of the cylinder 2.
Has an intake port 5 and an exhaust port 6 open. The intake port 5 and each exhaust port 6 are opened and closed by an intake valve 7 and an exhaust valve 8, respectively.

An ignition plug 9 is disposed at the center of the combustion chamber 4, and the tip of the plug faces the combustion chamber 4.
In addition, the tip of the injector 10 faces the combustion chamber 4 from the side, and fuel is directly injected from the injector 10 into the combustion chamber 4.

The intake passage 11 is connected to the engine body 1.
And an exhaust passage 12, the downstream end of the intake passage 11 communicating with the intake port 5, and the upstream end of the exhaust passage 12 communicating with the exhaust port 6. The above intake passage 1
1 has an upstream common intake passage 13, a surge tank 14 provided downstream thereof, and an independent intake passage 15 branched from the surge tank 14 for each cylinder. The common intake passage 13 is provided with an air cleaner 16, an air flow meter 17 for detecting an intake air amount, a throttle valve 18 driven by a throttle valve driving motor 19, and a supercharger provided downstream of the throttle valve 18. In this embodiment, the rechargeable mechanical supercharger 20 is used.
Is provided. Further, an intercooler 21 is provided downstream of the mechanical supercharger 20.

The mechanical supercharger 20 is driven by an engine output shaft via a belt transmission mechanism 22. An electromagnetic clutch 23 is provided between the pulley of the belt transmission mechanism 22 and the mechanical supercharger 20 to interrupt the transmission of the driving force to the mechanical supercharger 20.

Further, a mechanical supercharger 2 is provided in the intake passage 11.
A supercharger bypass passage 24 that bypasses the zero is provided. One end of the turbocharger bypass passage 24 is connected to the common intake passage 13 between the throttle valve 18 and the mechanical supercharger 20.
The other end is connected to the intake passage 11 downstream of the intercooler 21, and a bypass opening / closing valve (ABV) 25 is provided in the middle of the turbocharger bypass passage 24. The bypass on-off valve 25 is driven by an on-off valve driving motor 26 which is an electric driving means.

The throttle valve drive motor 19 and the opening / closing valve drive motor 26 are step motors, and these motors 19 and 26 and the electromagnetic clutch 23 are controlled by a control unit (ECU) 40. The fuel injection timing and injection amount from the injector 10 are also controlled by the control unit 4.
0 is controlled according to the operating state. The control unit 40 receives detection signals from an accelerator sensor 27 for detecting the amount of depression of an accelerator pedal and a rotation speed sensor 28 for detecting the engine speed.

The exhaust passage 12 is provided with a catalyst device 30 for purifying exhaust gas. This catalyst device 3
0 is for purifying HC, CO, NOx, etc. in the exhaust gas. Preferably, a catalyst having NOx purifying performance even during lean operation in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio is used. .

FIG. 2 shows the control unit 40 shown in FIG.
FIG. 3 is a functional block diagram showing the configuration of the embodiment. In this figure, the control unit 40 includes an injection mode switching unit 41, a fuel injection amount control unit 42, a clutch control unit 43, an operation area setting unit 44, and a supercharging state changing unit 45.

The injection mode switching means 41 switches the mode of fuel injection from the injector 10 to thereby achieve a stratified combustion state in which the injected fuel is unevenly distributed near the ignition plug 9 and a uniform combustion mode in which the injected fuel is diffused throughout the combustion chamber. It can be changed to the state. That is, when the stratified combustion state is set, the fuel is injected from the injector 10 in the compression stroke, and when the uniform combustion state is set, all or a part of the injected fuel is injected from the injector 10 in the intake stroke. Then, based on the region setting as shown in FIG. 3A described later, switching control of the injection mode according to the operating state is performed. In the present specification, a state in which the fuel is divided into an intake stroke and a compression stroke and the stratified layer is weakly stratified by split injection injected from the injector 10 is also included in the uniform combustion state.

The fuel injection amount control means 42 controls the fuel injection amount from the injector 10 by calculating the injection pulse width according to the accelerator opening and the like, and increases the fuel injection amount as the load increases. It is made to let. Further, as described later, the fuel injection amount is increased at the time of switching from the supercharger stopped state to the supercharger drive state.

The clutch control means 43 switches between the supercharger driving state and the supercharger stop state by controlling ON / OFF of the electromagnetic clutch 23, and is shown in FIG. Based on such a region setting, control of the electromagnetic clutch 23 according to the operation state is performed.

The operating region setting means 44 has a memory for storing a map of an operating region set in advance for the control of switching the injection mode according to the operating state and the control of the electromagnetic clutch 23. In the setting means 44, at least the high load side of the stratified combustion region (the operation region in which the stratified combustion is performed) is set to be a supercharging operation region in which the intake pressure becomes equal to or higher than the atmospheric pressure by the operation of the supercharger. Have been.

Specifically, as shown in FIGS. 3 (a) and 3 (b), a map of the operating range is set. In this figure, the vertical axis represents the load (for example, the average effective pressure Pe), and the horizontal axis represents the engine speed. Ne is shown. That is, the electromagnetic clutch 23
As shown in FIG. 3 (b), the area setting for the control of the first set load P1 or less and the first set speed N1
The following low-load low-rotation region C is a clutch-off region, and a region D on a higher load side than the first set load P1 and a higher rotation side than the first set rotation speed N1 is a clutch-on region. The first set load P1 is set near a load at which the intake pressure downstream of the throttle valve becomes the atmospheric pressure (dashed line).

As shown in FIG. 3A, the region A for controlling the injection mode switching is a stratified combustion region where the region A is equal to or less than the second set load P2 and equal to or less than the second set rotational speed N2. The region B on the higher load side than the second set load P2 and on the higher rotational side than the second set rotational speed N2 is a uniform combustion region. The second set load P2 is higher than P1 than the first set load, and the high load side of the stratified combustion region A is set to a supercharging operation region where the intake pressure becomes equal to or higher than the atmospheric pressure by the operation of the supercharger. Is set to Further, the second set speed N2 is higher than the first set speed N1, and the supercharger is driven on the higher speed side of the stratified combustion region A than the first set speed N1. I have.

In the uniform combustion region B, a region (region adjacent to the stratified combustion region A) B1 that is equal to or lower than the third set load P3 and equal to or lower than the third set rotation speed N3 is a region where split injection is performed. Regions B2 and B3 are regions where the intake stroke injection is performed.

Further, the air-fuel ratio is set as follows according to each operation region of the map shown in FIG. That is, in the stratified combustion region A, the air-fuel ratio is significantly lean (for example, about 40) as compared with the stoichiometric air-fuel ratio, and in the divided injection region B1 in the uniform combustion region and the fourth set load P4 in the intake stroke injection region or less. And region B2 equal to or less than the fourth set rotation speed N4
In the range B, the lean region (for example, 17 to 20) does not exceed the lean limit in the uniform combustion state, and the region B is on the higher load side than the fourth set load P4 and on the higher rotational side than the fourth set rotational speed N4.
In No. 3, the air-fuel ratio is stoichiometric or richer (λ ≦ 1). Note that P1 <P2 <P3 <P4, N1 <N
2 <N3 <N4.

The supercharging state changing means 45 includes a motor 26
And controls the bypass on-off valve 25 through the valve. In a region where the supercharger is driven in the stratified combustion region A, the bypass on-off valve 25 is controlled so as to perform supercharging according to the load, as will be described in detail later. The opening degree of the bypass opening / closing valve 25 is made smaller than the full opening state when the switching from the stratified combustion state to the uniform combustion state is performed so as to temporarily increase the supercharging bypass amount (flow rate of the supercharging bypass passage 24). Increase the degree. Further, after switching to the uniform combustion state, the opening degree of the bypass on-off valve 25 decreases as the load increases.

The operation of the above-described in-cylinder injection type engine with a supercharger according to this embodiment will be described with reference to FIGS. 4 and 5. FIG.

FIG. 4 shows an operation corresponding to an increase in the engine load from a low rotation and a low load. As shown in this figure,
In the supercharger stop area C on the low-load low-rotation side, the mechanical supercharger 20 is stopped by turning off the electromagnetic clutch 23, and fuel is injected from the injector 10 in the compression stroke. Thus, stratified combustion is performed, and the amount of intake air and the amount of fuel injected from the injector 10 are controlled so that the air-fuel ratio becomes lean, for example, about 40. Then, as the load increases, the fuel injection amount gradually increases to match the load. However, a large lean state is maintained by adjusting the intake air amount by the throttle valve 18 or the like until the first set load P1 is reached. Stratified combustion is performed while dripping. As a result, the combustion efficiency is increased, the pumping loss is reduced, and the fuel efficiency is improved.

When the engine load exceeds the first set load P1, the electromagnetic clutch 23 is turned on and the mechanical supercharger 20 is driven, but until the second set load P2 is reached, the stratified combustion state is maintained. Will be maintained. In the present embodiment, when the state is switched to the supercharger driving state, the fuel injection amount is increased, so that the torque reduction due to the supercharger driving resistance is compensated, and the torque shock at this time is prevented. At this time, the opening degree of the bypass on-off valve 25 is reduced by a predetermined amount from the fully opened state in order to increase the supercharging amount according to the fuel increase.
Further, the supercharging amount is increased by gradually reducing the opening degree of the bypass on-off valve 25 so as to correspond to the increase in the fuel injection amount accompanying the increase in the load in the stratified combustion region, and the air-fuel ratio becomes 40%.
It is kept lean.

As described above, the stratified combustion in a largely lean state is performed in a wide operating region including the region where the supercharging is performed up to the second set load P2, so that the effect of improving fuel efficiency is enhanced. .

When the load exceeds the second set load P2, the fuel injection mode is switched from stratified combustion by compression stroke injection to uniform combustion, and in this embodiment, is switched to a weakly stratified state by split injection. At this time, by increasing the opening degree of the bypass on-off valve 25, the supercharging bypass amount increases and the supercharging amount decreases. As a result, the air-fuel ratio changes in the rich direction.
Even in a uniform combustion state, combustion stability is ensured and misfire is prevented. In this case, since the bypass on-off valve 25 is driven by the motor 26, which is an electric driving means, the operation is performed with good responsiveness, and the air-fuel ratio changes quickly. In addition, the air-fuel ratio is changed by the adjustment of the supercharging amount, but the torque is not largely changed, and the torque shock is reduced.

At the time of this switching, the fuel injection amount may be kept in a state of linearly changing according to the load as shown by the solid line. Is also good. In particular, when switching from the stratified combustion state by the compression stroke injection to the weakly stratified state by the split injection as in this embodiment, the injection amount in the compression stroke is maintained at the same level as that in the stratified combustion, and the injection in the intake stroke is performed. If the amount of fuel is increased by the addition, ignitability is ensured, misfire is reliably prevented, and control of the fuel injection amount is facilitated. And, since the combustion mode shifts from a stratified combustion state to a uniform combustion state by an intake stroke injection through a weak stratification state by split injection according to an increase in load, the combustion mode does not greatly change suddenly, Transition to a uniform combustion state smoothly.

When the load further increases after exceeding the second set load P2, in the low load side region within the uniform combustion region including the region where the stratified state is formed, the fuel injection amount increases as the load increases. With the increase, the opening degree of the bypass on-off valve 25 is gradually reduced and the supercharged air amount is increased, so that the air-fuel ratio is maintained at an appropriate lean level. Further, after the bypass on-off valve 25 is fully closed and reaches the maximum supercharging state, the air-fuel ratio gradually changes in the rich direction due to an increase in the fuel according to the load. As described above, even in the uniform combustion region, the fuel economy is improved and the output performance is satisfied by making the lean state as high as possible by using the supercharging.

FIG. 5 shows an operation according to an increase in the engine speed from a low rotation speed and a low load. As shown in this figure, when the engine speed changes on the low load side,
In the supercharger stop region C of the first set rotation speed N1 or less, the supercharger is stopped by turning off the electromagnetic clutch 23, and stratified combustion by the compression stroke injection is performed. When N1 is exceeded, the electromagnetic clutch 23 is turned on to switch to the supercharger driving state,
In addition, the stratified combustion state is maintained.

At the time of switching to the supercharger driving state, the bypass opening / closing valve 25 is set to an opening smaller than the full opening to perform supercharging to some extent, and the fuel injection amount is adjusted accordingly. Such a control state is established until it reaches. In this case, since a large torque is not required on the low-load high-rotation side, the amount of supercharging is relatively reduced by increasing the opening degree of the bypass on-off valve 25 as compared with the high-load low-rotation side region. It is desirable to reduce the machine driving resistance.

When the rotation speed exceeds the second set rotation speed N2, a uniform combustion state (in this embodiment, a weak stratification state by split injection).
And the air-fuel ratio is changed to the rich direction by returning the bypass on-off valve 25 to the fully open state.

Thus, even when the engine speed increases, the turbocharger drive state and the fuel injection mode are switched accordingly, and the misfire is prevented and the torque shock is reduced when the fuel injection mode is switched. Is obtained.

In the control operation as shown in FIG. 4, when switching from the stratified combustion state to the uniform combustion state,
As shown by a two-dot chain line in the figure, the air-fuel ratio may be temporarily enriched until λ ≦ 1 by opening the bypass on-off valve 25 widely. Alternatively, the air-fuel ratio may be made rich in this manner by increasing the injection amount due to the injection in the intake stroke in the split injection. This is because the catalyst device 30 in the exhaust passage adsorbs NOx in the exhaust gas when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and the stoichiometric air-fuel ratio becomes higher than the stoichiometric air-fuel ratio. This is to maintain the purification performance of an adsorption-type NOx catalyst that reduces and removes NOx by reacting with HC and CO.

That is, if the adsorption-type NOx catalyst stays lean for longer than the stoichiometric air-fuel ratio for a long time, the NOx adsorption amount is saturated and the purification ability is reduced. Sometimes, if the enrichment is temporarily performed until λ ≦ 1, the purification ability of the catalyst is restored.

FIG. 6 shows another embodiment of the control of the air-fuel ratio. Also in this embodiment, a map for switching control of the fuel injection mode and a map for switching control of the electromagnetic clutch 23 are set as shown in FIGS.
In a low load region equal to or lower than the first set load P1, stratified charge combustion is performed in a turbocharger stopped state. In this state, the air-fuel ratio is significantly lean, for example, about 40.

In the region from the first set load P1 to the second set load P2, stratified charge combustion is performed in the supercharger driving state. In the present embodiment, the air-fuel ratio in this region is smaller than the stoichiometric air-fuel ratio. Although lean, it is richer than during stratified charge combustion with the turbocharger stopped. The reason for this is that, if an attempt is made to increase the lean state by supercharging, the driving resistance of the supercharger increases, so that even if the engine is leaned to a certain degree or more, the fuel efficiency improvement effect cannot be obtained. Also, if the air-fuel ratio has a step between the supercharger driving state and the supercharger stopped state, it is possible to suppress the torque reduction due to the supercharger driving resistance when switching to the supercharger driving state. Is also effective.

Although a mechanical supercharger is used as the supercharger in the above embodiment, a turbocharger may be used. In this case, the electromagnetic clutch is not provided, and control such as turning off the electromagnetic clutch at the time of low-load low-speed rotation to bring the turbocharger into a stopped state is not performed. However, control for switching between the stratified combustion state and the uniform combustion state is not performed. The control of the bypass opening / closing valve of the turbocharger bypass passage may be performed in the same manner as in the above embodiment.

[0062]

As described above, according to the present invention, in the direct injection type engine with a supercharger, at least the high load side of the stratified combustion region is set as the supercharged operation region, and the stratified combustion region including the supercharged operation region is provided. In addition to performing stratified combustion with the air-fuel ratio lean, the air-fuel ratio is increased in the rich direction by temporarily increasing the flow rate in the supercharging bypass passage when switching from the stratified combustion state to the uniform combustion state. The stratified combustion is performed to a relatively high load side by using supercharging, so that the fuel efficiency improvement effect is enhanced.
When switching from the stratified combustion state to the uniform combustion state, the air-fuel ratio quickly changes to the rich side from the lean limit in the uniform combustion state, preventing misfires, improving combustion stability, and cutting off. The torque shock at the time of switching can be suppressed.

In the present invention, if the air-fuel ratio is made lean even on the low load side of the uniform combustion region and the air-fuel ratio is given a predetermined level difference between the stratified combustion and the uniform combustion, the above-described condition can be obtained. And the fuel efficiency improvement effect can be further enhanced.

In the case where the supercharger is a mechanical supercharger and the supercharger is stopped in an operation region on the low load side in the stratified combustion region, the supercharger is stopped in the stratified combustion region. In both the operation region in which the turbocharger is driven and the operation region in which the supercharger is driven, the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and the operation in which the supercharger is driven is performed in the operation region where the supercharger is stopped. If the air-fuel ratio is set to be leaner than the air-fuel ratio and a predetermined level difference occurs in the air-fuel ratio at the boundary between the two operation regions, the air-fuel ratio at the time of switching from the supercharger stopped state to the supercharger drive state Torque reduction due to supercharger driving resistance can be suppressed.

[Brief description of the drawings]

FIG. 1 is an overall view of a direct injection engine with a supercharger according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of a control unit.

3A is a diagram illustrating a map of an operation region for controlling a fuel injection mode, and FIG. 3B is a diagram illustrating a map of an operation region for controlling driving and stopping of a supercharger.

FIG. 4 is a diagram illustrating changes in an electromagnetic clutch, a bypass on-off valve, an air-fuel ratio, and a fuel injection amount according to an engine load.

FIG. 5 is a diagram showing a change in an opening degree of a bypass on-off valve according to an engine speed;

FIG. 6 is a diagram showing a change in an air-fuel ratio according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 4 Combustion chamber 9 Spark plug 10 Injector 15 Intake passage 20 Mechanical supercharger 23 Electromagnetic clutch 24 Supercharger bypass passage 25 Bypass opening / closing valve 30 Catalyst device 40 Control unit 41 Injection mode switching means 43 Clutch control means 44 Operation Area setting means 45 Supercharging state changing means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 23/02 F02D 23/02 H K 41/04 301 41/04 301B 301J 335 335C 41/34 41/34 H 43/00 301 43/00 301R 301J 301H

Claims (15)

[Claims] 1. An injector for directly injecting fuel into a combustion chamber of an engine, a stratified combustion state in which the air-fuel ratio of the entire combustion chamber is leaner than a stoichiometric air-fuel ratio in a low load region, and a uniform combustion state in a high load region. And a fuel injection mode switching means for switching the fuel injection mode from the injector so as to perform a stratified combustion state in a supercharger-in-cylinder injection engine having a supercharger in an intake passage. Operating region setting means for setting at least the high load side of the stratified combustion region as a supercharging operation region in which the intake pressure becomes equal to or higher than the atmospheric pressure by the operation of the supercharger; and bypassing the supercharger. A bypass opening / closing valve provided in the turbocharger bypass passage, the opening of which can be changed, and a fuel injection mode is switched from the stratified combustion state to the uniform combustion state as the operation state shifts to a high load area. A supercharged in-cylinder injection engine comprising: a supercharging state changing means for changing the air-fuel ratio in a rich direction by temporarily increasing a flow rate of a supercharging bypass passage when the engine is replaced. 2. The air-fuel ratio is made leaner than the stoichiometric air-fuel ratio on the low load side in the uniform combustion region, which is an operation region in which a uniform combustion state is set, and the stoichiometric air-fuel ratio is switched from the stratified combustion state to the uniform combustion state. 2. The cylinder-injection engine with a supercharger according to claim 1, wherein the supercharging state changing means is configured to change the air-fuel ratio in a rich direction with a predetermined step within a range in which the fuel ratio is leaner. 3. In a stratified combustion region, a fuel is injected from the injector in a compression stroke to form a stratified combustion state, while in a uniform operation region, a predetermined operation region adjacent to the stratified combustion region causes fuel injection from the injector. Is divided into an intake stroke and a compression stroke, and the fuel injection mode switching means is configured to perform fuel injection from the injector on the high load side of the predetermined operation region so as to perform an intake stroke injection performed only in the intake stroke. The cylinder-injection engine with a supercharger according to claim 1 or 2, wherein: 4. When the fuel injection mode is switched from the stratified combustion state by the compression stroke injection to the split injection, the total fuel injection amount is increased by adding the injection in the intake stroke to the constant injection amount in the compression stroke. The cylinder-injection type engine with a supercharger according to claim 3, wherein the amount is increased. 5. The in-cylinder injection with a supercharger according to claim 1, wherein the bypass on-off valve is driven by an electric driving means. Expression engine. 6. The supercharger is a mechanical supercharger, a clutch means for switching the mechanical supercharger between a driving state and a stopped state is provided, and a low-load operation region in a stratified combustion region is provided. 6. The direct injection engine with a supercharger according to claim 1, further comprising a clutch control means for controlling the clutch means so that the supercharger is stopped. 7. The first on a low load side in a stratified combustion region.
The turbocharger is stopped in the low speed range below the set speed.
While the clutch control means is configured to be in the supercharger drive state on the higher rotation side than the set rotation speed, the stratified combustion region is set up to a second set rotation speed higher than the first set rotation speed,
In the operation region where the supercharger is driven in the stratified charge combustion region, the bypass opening / closing valve is set to an opening smaller than the full opening, and the engine speed increases from this region. 7. The direct injection engine with a supercharger according to claim 6, wherein the bypass on-off valve is opened when the rotation speed becomes higher than the second set rotation speed. 8. In the stratified charge combustion region, the degree of opening of the bypass on-off valve is increased in the low-load high-rotation side region in the operation region in which the supercharger is driven, as compared with the high-load low-rotation side region. The direct injection engine with a supercharger according to claim 6 or 7, wherein: 9. An air-fuel ratio is leaner than a stoichiometric air-fuel ratio in both an operation region in which the supercharger is stopped and an operation region in which the supercharger is driven in the stratified charge combustion region. The air-fuel ratio is set to be leaner in the operation region in which the engine is in the stop state than in the operation region in which the turbocharger is in the driving state, and the air-fuel ratio is set to have a predetermined step at the boundary between the two operation regions. Item 9. An in-cylinder injection type engine with a supercharger according to any one of Items 6 to 8. 10. A method for adsorbing NOx in exhaust gas when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and reducing and removing NOx when the air-fuel ratio becomes a stoichiometric air-fuel ratio or an air-fuel ratio richer than the stoichiometric air-fuel ratio. In addition to installing a catalyst in the exhaust passage, the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio on the low load side of the uniform combustion region, and the air-fuel ratio is temporarily set when switching from the stratified combustion state to the uniform combustion state. 2. The cylinder-injection type engine with a supercharger according to claim 1, wherein the engine is changed to a stoichiometric air-fuel ratio or to an extent that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio. 11. An injector for directly injecting fuel into a combustion chamber of an engine, and a stratified combustion state in which the air-fuel ratio of the entire combustion chamber is leaner than a stoichiometric air-fuel ratio in a low load range.
An injection mode switching means for switching a fuel injection mode from the injector so as to achieve a uniform combustion state in a high load region, and a supercharger-equipped in-cylinder injection engine having a supercharger in an intake passage. At least the high load side of the stratified combustion region which is an operation region to be in a combustion state,
Operating region setting means for setting a supercharging operation region in which the intake pressure becomes equal to or higher than the atmospheric pressure by the operation of the supercharger is provided. In the stratified combustion region, fuel is injected from the injector in a compression stroke from the injector in the stratified combustion range. On the other hand, in the predetermined operation region adjacent to the stratified combustion region in the uniform combustion region, the fuel injection from the injector is divided into the intake stroke and the compression stroke. On the load side, the fuel injection mode switching means is configured so that the fuel injection from the injector is performed in the intake stroke in which only the intake stroke is performed, and the fuel injection mode is switched from the stratified combustion state by the compression stroke injection to the split injection. Sometimes, the total fuel injection amount is increased by adding injection in the intake stroke to the fixed injection amount in the compression stroke. Wherein the supercharged cylinder injection type engine 12. A method for adsorbing NOx in exhaust gas when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and reducing and removing NOx when the air-fuel ratio becomes a stoichiometric air-fuel ratio or an air-fuel ratio richer than the stoichiometric air-fuel ratio. In addition to equipping the exhaust passage with the catalyst that has become active, the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio on the low load side of the uniform combustion region, and the air-fuel ratio is switched from the stratified combustion state by the compression stroke injection to the split injection. 12. The cylinder-injection engine with a supercharger according to claim 11, wherein the fuel ratio is temporarily changed to a stoichiometric air-fuel ratio or to a degree that is richer than the stoichiometric air-fuel ratio. 13. An injector for directly injecting fuel into a combustion chamber of an engine, and a stratified combustion state in which the air-fuel ratio of the entire combustion chamber is leaner than a stoichiometric air-fuel ratio in a low load range.
An injection mode switching means for switching the mode of fuel injection from the injector so as to achieve a uniform combustion state in a high load range, and a supercharger-in-cylinder injection engine in which a mechanical supercharger is provided in an intake passage. An operation in which at least the high load side of the stratified combustion region, which is an operation region to be in the stratified combustion state, is set to be a supercharging operation region in which the intake pressure becomes equal to or higher than the atmospheric pressure by the operation of the mechanical supercharger. Region setting means, clutch means for switching the mechanical supercharger between a driving state and a stopped state, and the clutch means so as to be in a turbocharger stopped state in a low load side operation region in a stratified combustion region. In addition to the clutch control means for controlling the supercharger, the air-fuel ratio of both the operating region in which the supercharger is stopped and the operating region in which the supercharger is driven in the stratified combustion region is lower than the stoichiometric air-fuel ratio. In the operating region where the turbocharger is in the stopped state, the air-fuel ratio is further leaner than in the operating region where the turbocharger is in the driven state, and a predetermined step is generated in the air-fuel ratio at the boundary between the two operating regions. An in-cylinder injection engine with a supercharger, characterized by being set. 14. An injector for directly injecting fuel into a combustion chamber of an engine, and a stratified combustion state in which the air-fuel ratio of the entire combustion chamber is leaner than a stoichiometric air-fuel ratio in a low load range.
An injection mode switching means for switching the mode of fuel injection from the injector so as to achieve a uniform combustion state in a high load range, and a supercharger-in-cylinder injection engine in which a mechanical supercharger is provided in an intake passage. A clutch means for switching the mechanical supercharger between a driving state and a stopped state, and a supercharger stopped state in a low rotation range below a first set rotation speed on a low load side in a stratified combustion region; Clutch control means for controlling the clutch means so that the supercharger is driven on the higher rotation side than the set rotation speed, and the stratified combustion region is increased to a second set rotation speed higher than the first set rotation speed. In the operation region where the supercharger is driven in the stratified combustion region, the bypass on-off valve is set to an opening smaller than the full opening. Supercharged cylinder injection type engine, characterized by being configured to bypass closing valve for opening operation when the engine speed becomes a second set rotation speed from the high speed side rises. 15. In a stratified combustion region, a fuel is injected from the injector in a compression stroke to make a stratified combustion state, and in a predetermined operation region adjacent to the stratified combustion region in the uniform combustion region, fuel injection from the injector is performed. Is divided into an intake stroke and a compression stroke, and the fuel injection mode switching means is configured to perform fuel injection from the injector on the high load side of the predetermined operation region so as to perform an intake stroke injection performed only in the intake stroke. The supercharger-equipped in-cylinder injection engine according to claim 13 or 14, wherein: