JPH10274064A - Engine with mechanical supercharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out internal EGR while driving a mechanical supercharger without increasing mechanical resistance at the time of operation in a low load region, and carry out operation having a lean mixture ratio in a condition in which NOx is reduced. SOLUTION: A device is provided with a mechanical supercharger 20 arranged in an intake passage, a bypass passage for bypassing the supercharger 20, a bypass passage opening/closing valve 25 for opening/closing the bypass passage 24, an injector for injecting and supplying fuel, and a means 18 for regulating the intake distribution area of the intake passage 11, and constituted so as to open the opening/closing valve 25 in a condition in which the supercharger 20 is driven in a low load high rotational region. In at least engine low load high rotational region, overlap periods of an exhaust valve 8 and an intake valve 7 are set largely, the intake distribution area is throttled to such extent that intake pressure becomes negative pressure in a range in which the operation of a lean mixture ratio is obtained, and the fuel injection period of the injector is set after the overlap period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine with a mechanical supercharger having a configuration in which a mechanical supercharger is mounted on an engine that performs combustion in a lean region having an air-fuel ratio of 20 or more.

[0002]

2. Description of the Related Art Conventionally, as shown in, for example, Japanese Patent Application Laid-Open No. 5-256145, by supercharging intake air with a mechanical supercharger, it is possible to increase the amount of intake air and increase the engine torque. An engine with a mechanical supercharger is generally known. In this engine with a mechanical supercharger, usually, a mechanical supercharger is disposed downstream of a throttle valve in an intake passage, and a supercharger bypass passage for bypassing the mechanical supercharger and the supercharger bypass passage. A bypass passage opening / closing valve for opening / closing the feeder bypass passage is provided. When the engine is running at a low speed, the electromagnetic clutch is turned on and off, and when the engine is running at a high speed, it is always turned on. The bypass valve is adjusted to control the supercharging pressure. In addition, when the engine is under low load and high speed, the mechanical supercharger is driven with the bypass passage opening / closing valve open, and a part of the excess air sent from the downstream side of the mechanical supercharger is transferred to the upstream side of the supercharger. It is recirculating. In the case where this type of mechanical supercharger is mounted on a lean burn engine, the lean operation area can be expanded by utilizing the supercharging.

In many cases, the bypass passage opening / closing valve is driven by a pressure-responsive actuator that operates in response to an intake negative pressure or the like. The throttle valve provided on the side is generally mechanically linked with the accelerator pedal.

[0004]

There is an advantage that the lean air-fuel ratio in lean combustion reduces NOx emissions. However, this is the case of a homogeneous air-fuel mixture. If the concentration of the air-fuel mixture in the burning portion is high, the combustion temperature is high, and the amount of air is large, so the NOx generation amount is large. Therefore, for example, even an engine that performs ultra-lean combustion with an air-fuel ratio of about 40, such as a direct injection engine,
It is necessary to suppress NOx emission by applying GR.

Further, in a direct injection type engine equipped with a mechanical supercharger, the supercharging state changes depending on the operating state, so that EGR must be obtained according to the supercharging state. In particular, in operation in a low load range, it is necessary to perform EGR without increasing the mechanical resistance of the supercharger.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and operates a mechanical supercharger without increasing mechanical resistance and performs internal EGR to reduce NOx during operation in a low load range. It is an object of the present invention to provide a mechanical supercharged engine capable of performing a lean mixture operation in a lean state.

[0007]

According to the present invention, there is provided a mechanical supercharger provided in an intake passage, a bypass passage for bypassing the supercharger, and a bypass passage opening and closing for opening and closing the bypass passage. A valve, an injector for injecting fuel, and an intake air flow area adjusting means arranged upstream of the bypass passage connection part on the upstream side of the supercharger to adjust the intake air flow area of the intake passage. In the engine with the mechanical supercharger configured to open the bypass passage opening / closing valve in a state where the mechanical supercharger is driven, the overlap period of the exhaust valve and the intake valve at least in the engine low-load high-speed region. Was set large, the intake air flow area was narrowed to such an extent that the intake pressure became a negative pressure in a range where the operation with a lean mixture ratio was obtained, and the fuel injection timing of the injector was set after the overlap period.械式 is an engine with a supercharger.

The setting of the overlap period to be large means that the crank angle from the opening timing of the intake valve to the closing timing of the exhaust valve defined by a 1 mm lift position is -10 °.
That is all.

According to the third aspect of the present invention, it is preferable to stop the mechanical supercharger in the low-load low-speed range and to narrow the intake flow area when shifting to the low-load high-speed range. Claim 4
In the present invention, a stratified combustion can be performed by providing an injector for directly injecting fuel into the combustion chamber, and injecting fuel from the injector in a compression stroke in a low-load operation region. The engine in the present invention is an in-cylinder injection engine having an injector for directly injecting fuel into a combustion chamber and performing ultra-lean combustion with an air-fuel ratio of about 40 to 50, and a lean burn engine performing lean combustion with an air-fuel ratio of about 22 to 25. However, it is preferable to configure the engine with an in-cylinder injection type engine that can further increase the lean operation range by performing supercharging.

In the fifth aspect of the present invention, it is possible to make the overlap period constant, and to narrow the intake air flow area as the engine speed increases in a low-load high-speed region. Further, as shown in the present invention of claim 6, it is also possible to make the intake air flow area constant and to extend the overlap period as the engine speed increases in the low-load high-speed range.

In the present invention according to claim 7, it is preferable that the period after the intake top dead center is set to be long in the overlap period in the low-load high-speed range. In the low rotation speed range, it is preferable that the overlap period is set to be long before the top dead center of the intake air, and the mechanical supercharger is driven with the bypass passage opening / closing valve being in a non-full open state.

According to the first aspect of the present invention, the mechanical supercharger is driven in a state where the overlap period between the exhaust valve and the intake valve is set large and the bypass passage opening / closing valve is opened in a low load region. If the intake air flow area is reduced to such an extent that the intake pressure becomes a negative pressure, the differential pressure across the turbocharger will decrease, thereby reducing the mechanical resistance of the turbocharger and causing the intake passage to enter a negative pressure state. Performs internal EGR, NO
x can be reduced. In addition, since fuel is injected after the overlap period, blow-by or back-flow of fuel is prevented.

According to the third aspect of the present invention, the mechanical supercharger is stopped in the low-load low-speed range, and when the engine shifts to the low-load high-speed range, the intake flow area is narrowed. The internal EGR is performed effectively even in the driving state.

According to the present invention, the lean operation can be effectively performed. Further, at the time of injection in the compression stroke or the like, a state where fuel is injected into the cylinder after the overlap period is ensured.

According to the fifth aspect of the present invention, since the negative pressure in the intake passage increases as the engine speed increases, the predetermined internal EGR is performed with the overlap period fixed.
The effect can be obtained.

According to the sixth aspect of the present invention, since the overlap period is extended as the engine speed increases, the predetermined internal EGR is performed with the intake air flow area kept constant.
The effect can be obtained.

[0017]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a mechanical supercharged engine according to an embodiment of the present invention. In this figure, reference numeral 1 denotes an engine body having a plurality of cylinders 2. Each cylinder 2 has a combustion chamber 4 formed above a piston 3 inserted into its cylinder bore. The intake port 5 and the exhaust port 6 are open. The intake port 5 and the exhaust port 6 are opened and closed by an intake valve 7 and an exhaust valve 8, respectively. A spark plug 9 is provided at the center of the combustion chamber 4.
Is arranged. Further, an injector 10 is provided so as to face the combustion chamber 4, and fuel is directly injected from the injector 10 into the combustion chamber 4.

An intake passage 11 is provided for the engine body 1.
And an exhaust passage 12. The downstream end of the intake passage 11 communicates with the intake port 5, and the upstream end of the exhaust passage 12 communicates with the exhaust port 6. The intake passage 11 has a common intake passage 13 on the upstream side, 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, and a throttle valve 18 as intake air flow area adjusting means that operates in response to depression of an accelerator pedal. Is provided with a mechanical type supercharger 20 of a reschorm type, and an intercooler 2 is provided downstream of the mechanical supercharger 20.
1 is provided.

The opening of the throttle valve 18 is changed by being driven by a throttle valve driving motor 19. The throttle valve 18 and the throttle valve driving motor 19 change the opening area of the intake passage 11 in the intake passage 11. Is to be adjusted.

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 intermittently transmit 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 passage opening / closing valve (ABV) 25 is provided in the middle of the turbocharger bypass passage 24. The bypass passage opening / closing valve 25 is driven by an opening / closing valve drive motor 26.
The motor 19 for driving the throttle valve and the motor 26 for driving the on-off valve are composed of step motors. These motors 19 and 26 and the electromagnetic clutch 23 are connected to a control unit (E).
CU) 40. In addition, the injector 10
The control unit 40 also controls the fuel injection timing and injection amount from the engine according to the operating state.

The control unit 40 includes an accelerator sensor 2 for detecting an accelerator operation amount (accelerator pedal depression amount).
7 and respective detection signals from a rotation speed sensor 28 for detecting the engine rotation speed. Also,
The exhaust passage 12 is provided with a three-way catalyst device 30 for purifying exhaust gas. An EGR valve 31 for branching from the exhaust passage 12 to the common intake passage 13 for performing external EGR.
Is connected. Thus, a direct injection engine with a mechanical supercharger is configured.

FIG. 2 shows the control unit 40 shown in FIG.
FIG. 3 is a functional block diagram showing the configuration of the embodiment. In the figure, a control unit 40 is an ABV opening setting section 40a that sets the opening of the bypass passage opening / closing valve 25 with respect to the accelerator operation amount.
A throttle opening setting section 40b for setting an opening of the throttle valve 18 with respect to an accelerator operation amount; and an electromagnetic clutch operation setting for setting ON / OFF of an electromagnetic clutch determined based on an engine speed and a throttle opening. A portion 40c, an EGR valve setting portion 40d for setting the opening / closing operation of the EGR valve 31, a fuel injection setting portion 40e, and an ABV 25, a throttle valve 18, an electromagnetic clutch 23, an EGR valve in accordance with instructions output from these setting portions. 31 and a controller 40f for controlling the injector 10.

The ABV opening degree is set such that the bypass passage opening / closing valve 25 is fully opened in a low load region (except for idling) where the accelerator operation amount is small. The opening degree of the on-off valve 25 gradually decreases, and the bypass passage on-off valve 25 is fully closed near the accelerator fully open. In addition, at the time of extremely low load, that is, at the time of idling, the opening operation is partially performed. On the other hand, the throttle opening basically increases as the accelerator operation increases, but is slightly reduced to such a degree that the internal EGR can be obtained during idling.

The fuel injection from the injector 10 is performed in a compression stroke for performing stratified combustion in a low load region including idling, and is performed in an intake stroke for performing uniform combustion in a high load region. I have.

FIG. 3 shows the valve lift characteristics of the intake valve and the exhaust valve by taking the crank angle on the horizontal axis. As shown in FIG. 3, the exhaust valve opens near the bottom dead center BDC at the end of the expansion stroke. The valve is set to close after top dead center TDC, the intake valve is opened before top dead center TDC, and closed after bottom dead center BDC at the end of the intake stroke. However, in this embodiment, the overlap period is set to be longer than that of a general engine, and is basically fixed. More specifically, an overlap period, which is a period from the intake valve opening timing to the exhaust valve closing timing, is a crank angle (CA) from the intake valve opening timing to the exhaust valve closing timing defined at the 1 mm lift position. It is set to be -10 ° CA or more.

Next, the operation of the in-cylinder injection type engine with a mechanical supercharger having the above configuration will be described. FIG. 4 shows each operating condition of the engine. In the figure,
Region 1 shows a low-load low-rotation region, region 2 shows a low-load high-rotation region, and region 3 shows a high-load high-rotation region.

First, in region 1, a large overlap is set.
The supercharger 20 is stopped. With the turbocharger 20 stopped
Throttle valve 18 is required minimum, specifically 50-12
0mm _HGThe internal EGR is performed by narrowing the degree. Follow
In this case, a reduction in the mechanical resistance of the supercharger 20 can be obtained.
On the other hand, internal EGR can be secured.

Next, in the region 2, the large overlap does not change, the electromagnetic clutch 23 is connected, the supercharger 20 is driven, and the lean combustion is secured in a range where the excess air ratio λ = 1 or more. On this assumption, the throttle valve 18 is narrowed down. At this time, the bypass passage opening / closing valve 25 is open, and the amount of supercharging by the supercharger 20 is recirculated upstream of the supercharger 20. However, the higher the rotation speed of the supercharger 20, in other words, the greater the pressure difference between the upstream side and the downstream side of the supercharger 20, the more the supercharging work is performed, and the higher the mechanical resistance. Therefore, if the throttle valve 18 is narrowed down, the pumping loss increases, but the pressure difference between the upstream side and the downstream side of the supercharger 20 becomes small, so that the mechanical resistance of the supercharger 20 becomes small. Further, since the inside of the intake passage has a negative pressure and a large overlap, internal EGR is performed. The internal EGR gas lowers the combustion temperature and reduces NOx in exhaust gas. Further, by re-inhaling and reburning the unburned gas generated in the combustion chamber, H
C is also reduced.

FIG. 5 shows the behavior of the mechanical resistance with respect to the supercharging pressure. P ₁ shows the mechanical resistance of the non-supercharged engine, and P ₂ shows the mechanical resistance of the supercharged engine. I have. In the figure, area A indicates a pumping loss in a non-supercharged engine, and area B indicates a mechanical resistance that increases when a supercharger is provided. in this way,
Under the supercharged engine, below 0 mm _HG , which is the atmospheric pressure, the pumping loss does not increase as much as the non-supercharged engine. As a result, at -500 mm _HG , the mechanical resistance between the supercharged engine and the non-supercharged engine Show almost the same value.

Therefore, if the intake passage is under a negative pressure, even if the supercharger 20 is driven, the pumping loss does not cause a large increase in the resistance as compared with the non-supercharged engine. Supercharger 2
0 can be driven.

In region 2, the control unit 40f adjusts the throttle valve 18 so as to narrow the intake passage area as the engine speed N increases as shown in FIG. Fixed E even if fixed
The GR effect is obtained.

In this embodiment, the amount of overlap is basically fixed. However, the present invention is not limited to this. In order to obtain a constant internal EGR, as shown in FIG. May be variable. That is, the intake flow area is kept constant, and the overlap period is set to be longer as the engine speed increases in the low-load high-speed range. Even with such a configuration, the internal EG
R can be secured. As described above, in the configuration in which the overlap period is changed, the valve timing system (VV) capable of adjusting the valve timing to the advance side or the delay side is provided.
T) 41 (see FIG. 1) is controlled by the ECU 40.

In the low-load high-speed range, it is preferable to delay the exhaust valve closing and shift the overlap period so that the overlap amount after the intake top dead center becomes longer. Thereby, the internal EGR can be secured without unnecessarily increasing the overlap amount.

On the other hand, in an extremely low load low speed range (mainly an idle speed range), it is preferable to shift the overlap period so that the overlap amount before the intake top dead center becomes long. Thereby, scavenging is performed and combustion stability is improved. However, the electromagnetic clutch 23 is turned ON, and the bypass passage opening / closing valve 25 is not fully opened.

Next, in a region 3 where the pressure in the intake passage is higher than the atmospheric pressure, the pressure in the intake passage becomes higher than the pressure in the exhaust passage, so that the internal EGR does not operate. And the external EGR is forcibly performed. Note that the above-described operating conditions are detected by the accelerator sensor 27 and the rotation speed sensor 28.

The engine with a mechanical supercharger according to the present invention has been described in the above embodiment by taking, as an example, an in-cylinder injection engine having an injector for directly injecting fuel into a combustion chamber and performing ultra-lean combustion. The present invention is not limited to this, and can be applied to a lean burn engine that performs lean combustion.

[0038]

As described above, according to the first aspect of the present invention, during operation in a low load region, the mechanical supercharger is driven without increasing the mechanical resistance, and the internal EGR is performed.
Lean combustion can be performed with Ox reduced.

According to the present invention, fuel efficiency can be improved by ultra-lean combustion, and internal EGR is performed while reducing mechanical resistance of the mechanical supercharger, so that NOx can be reduced. According to the fifth and sixth aspects of the present invention, a certain amount of internal E
GR can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an engine with a mechanical supercharger according to an embodiment of the present invention.

FIG. 2 is a functional block diagram showing a configuration of an ECU shown in FIG.

FIG. 3 is an explanatory diagram showing opening and closing timings of an exhaust valve and an intake valve according to the present invention.

FIG. 4 is a graph illustrating operating conditions according to the present invention.

FIG. 5 is a graph illustrating the relationship between supercharging pressure and mechanical resistance according to the present invention.

FIG. 6 is a graph showing a relationship between an engine speed and an intake throttle according to the present invention.

FIG. 7 is a graph illustrating an overlap variable effect according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 5 Intake port 6 Exhaust port 10 Injector 11 Intake passage 12 Exhaust passage 18 Throttle valve 20 Mechanical supercharger 24 Supercharger bypass passage 25 Bypass passage opening / closing valve 40 Control unit 41 Valve timing system

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 9/02 F02D 9/02 C 23/00 23/00 FK P 23/02 23/02 H 41/02 325 41/02 325D 41/04 335 41/04 335D 43/00 301 43/00 301E 301J 301K 301Z 301R

Claims (8)

[Claims] A mechanical supercharger provided in an intake passage;
A bypass passage that bypasses the turbocharger, a bypass passage opening / closing valve that opens and closes the bypass passage, an injector that injects fuel, and an intake passage that is disposed upstream of a bypass passage connection portion on the upstream side of the turbocharger. An intake air flow area adjusting means for adjusting an intake air flow area, with a mechanical supercharger configured to open the bypass passage opening / closing valve in a state where the mechanical supercharger is driven in a low-load high-speed region. In the engine, at least in an engine low load high rotation range, the overlap period between the exhaust valve and the intake valve is set to be large, and the intake flow area is reduced to such an extent that the intake pressure becomes a negative pressure in a range where a lean mixture ratio can be obtained. An engine with a mechanical supercharger, wherein the engine is throttled and the fuel injection timing of the injector is set after the overlap period. 2. The setting of the overlap period to be large means that the crank angle from the intake valve opening timing to the exhaust valve closing timing defined by a 1 mm lift position is -10.
2. The engine with a mechanical supercharger according to claim 1, wherein the angle is not less than °. 3. The mechanical supercharger according to claim 1, wherein the mechanical supercharger is stopped in a low-load low-speed range, and the intake air flow area is narrowed when shifting to the low-load high-speed range. Engine. 4. The fuel injection system according to claim 1, further comprising an injector for directly injecting fuel into the combustion chamber, wherein stratified combustion is performed by injecting fuel from the injector in a compression stroke in a low-load operation range. An engine with a mechanical supercharger according to any of the above. 5. The system according to claim 5, wherein the overlap period is constant, and as the engine speed increases in a low-load high-speed range,
The engine with a mechanical supercharger according to any one of claims 1 to 4, wherein the intake flow area is narrowed. 6. The mechanical supercharger according to claim 1, wherein the intake circulation area is constant, and the overlap period is extended as the engine speed increases in a low-load high-speed range. engine. 7. The engine with a mechanical supercharger according to claim 6, wherein the overlap period in the low-load high-speed region is set to be longer after intake top dead center. 8. The mechanical supercharger is set in an extremely low-load low-speed range, in which the overlap period is set to be long before the intake top dead center, and the bypass passage opening / closing valve is in a non-full-open state. The engine with a mechanical supercharger according to claim 4, wherein the engine is driven.