JPH07310603A - Exhaust gas reflux device for engine - Google Patents

Abstract

PURPOSE:To improve an effect to reduce the generation of NOX owing to EGR as worsening of exhaust gas emission owing to the generation of HC is prevented occurring. CONSTITUTION:Simultaneously with opening of side ports 3 and 4, as main intake ports, to a combustion chamber 2, center port 7 is opened and air-fuel mixture is fed through a center port 7 to the interior of a combustion chamber 2. One end of an EGR passage 32 is connected to an exhaust manifold 28 and the other end thereof is connected to side ports 3 and 4 through an EGR valve 34. An ECU 40 is operated to extend an overlap period between the opening periods of exhaust valves 1 and 14 and the opening periods of intake valves 11 and 12 by delaying the closing times of exhaust valves 13 and 14 in a specified region, where the opening of a throttle valve 17 is below a specified value, through actuation of a VVT timing varying means 10 and open the EGR valve 34 to effect reflux of exhaust gas to the side ports 3 and 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation system for an engine, which is provided with an air-fuel mixture supply section for supplying an air-fuel mixture into the combustion chamber, which is separate from the main intake port. It is a thing.

[0002]

2. Description of the Related Art Conventionally, as an engine exhaust gas recirculation device,
For example, the one disclosed in JP-A-62-28032 is known. In this device, in addition to a main intake port (a first intake port and a second intake port in the publication) having a normal intake valve, a mixture for supplying a mixture of air and fuel in advance into the combustion chamber. The air supply section (third intake port) opens into this combustion chamber. The air-fuel mixture supply unit is provided with an opening / closing valve similar to the intake valve, and its opening timing is set to a timing later than the opening timing of the intake valve. According to such a device, after the intake air is started through the main intake port, the air-fuel mixture that is generated in advance is supplied from the air-fuel mixture supply unit to the combustion chamber independently of the main intake port, so that the combustion chamber is stratified. As a result, good lean combustion is realized.

By the way, in such an apparatus, although the fuel is greatly diluted as a whole, there is a local portion where the air-fuel ratio is apt to generate NOx, and therefore such reduction of NOx is achieved. It becomes an issue. Therefore, in this device, NOx is reduced by recirculating exhaust gas to the air-fuel mixture supply section to slow combustion in the cylinder.

[0004]

As described above, since the air-fuel mixture supply section is intended to stratify the combustion chamber by supplying the air-fuel mixture, the opening area to the combustion chamber is smaller than that of the main intake port. Even if the exhaust gas is recirculated to such a mixture supply portion, it is difficult to expect a sufficient NOx reduction effect by itself. On the other hand, if the exhaust gas is recirculated to the main intake port having a relatively large opening area, it is possible to secure a larger exhaust gas recirculation amount, but with such an increase in the exhaust gas recirculation amount, combustion stability is improved. The decrease may lead to an increase in HC (unburned hydrocarbon), resulting in deterioration of exhaust emission.

In view of such circumstances, it is an object of the present invention to provide an exhaust gas recirculation system for an engine which can effectively reduce the NOx generation amount while suppressing the HC generation.

[0006]

As a means for solving the above problems, the present invention is directed to a main intake port which is opened in a combustion chamber and is opened / closed by an intake valve, and an opening / closed state in the combustion chamber. A mixture supply unit that is opened and closed by a valve and supplies a mixture of air and fuel into the combustion chamber with the opening and closing valve open; and an exhaust port that opens into the combustion chamber and is opened and closed by an exhaust valve. An engine having an opening timing of the opening / closing valve set later than an opening timing of the intake valve, a timing varying means for changing at least the closing timing of the exhaust valve, and the mixture supply section. In a specific region included in the operating region where the air-fuel mixture is supplied from the exhaust valve, the opening period of the exhaust valve and Weight of intake valve opening period A timing control means for delaying the closing timing of the exhaust valve by the timing varying means so as to extend the period, an exhaust gas recirculation means for recirculating exhaust gas to the main intake port, and a specific area in comparison with other areas. An exhaust gas recirculation control means for increasing the amount of exhaust gas recirculation by the exhaust gas recirculation means is provided (Claim 1).

It is desirable that the specific region is a region included in a region where the engine load is below a certain level (claim 2).

In this case, in the specific region, the exhaust gas recirculation control means is constructed so as to reduce the exhaust gas recirculation rate by the exhaust gas recirculation means in accordance with the increase of the engine load (claim 3), or in the mixture mixture supply section. Is a closed space, and at least in the specific region, the opening / closing valve is opened later than a first opening period in which the intake valve is opened later than the intake valve is opened and the exhaust valve is opened in another period. More preferably, it is configured to be opened at both the second valve opening period which is earlier (claim 4). In the device according to the fourth aspect, it is more preferable that the timing control means is configured to delay both the closing timing and the opening timing of the exhaust valve in the specific region as compared with other regions ( Claim 5).

Further, the maximum value of the exhaust gas recirculation amount by the exhaust gas recirculation means is set to an amount substantially equal to the maximum limit exhaust gas recirculation amount within the range where the intake air amount is not reduced (claim 6), or the intake valve is opened. By setting the valve timing at the same time as the piston top dead center or at a time later than this (Claim 7), a more excellent effect as described later can be obtained.

[0010]

According to the apparatus of the first aspect, the so-called internal EGR amount is increased by extending the overlapping period of the exhaust valve opening period and the intake valve opening period in the specific region, and the exhaust gas recirculation means. By increasing the so-called external EGR amount due to, the exhaust gas recirculation amount sufficient for reducing NOx is secured, and the pumping loss is also reduced. Moreover, in this specific region, the combustion chamber is stratified by the air-fuel mixture from the air-fuel mixture supply unit, and the combustion gas containing HC that was once discharged from the exhaust port during the internal EGR is burned again in the overlapping period. Since it is drawn back into the room and re-combusted, even if the exhaust gas recirculation amount is increased as described above, the increase in the amount of generated HC is suppressed and the exhaust emission is kept good.

According to the second aspect of the present invention, since the specific region is a low load region, a sufficient NOx suppressing action and a pumping loss reducing action are secured in the low load region, while the specific region is maintained. In the high load region, which is a region other than the above, by suppressing the internal EGR and the external EGR, the high output required in this high load region is secured.

Further, in the apparatus according to the third aspect, even in the specific region, the external EGR amount is suppressed as the engine load increases, so that the engine output that meets the demand is secured.

Here, if the space in the air-fuel mixture supply unit is a closed space, the air-fuel mixture in the air-fuel mixture supply unit is supplied into the combustion chamber when the on-off valve is opened, and then the combustion gas in the combustion chamber is reversed. By closing the on-off valve after taking it into the mixture supply part, a pressure difference can be generated between the mixture supply part and the pressure in the combustion chamber. By utilizing this pressure difference, special air pressure is applied. It is possible to supply the above-mentioned air-fuel mixture without using any means. Further, as described in claim 4, in addition to the valve opening period (that is, the first valve opening period) at least in the specific region, a second valve opening period (the opening timing of the opening / closing valve is the opening timing of the exhaust valve). If the on-off valve is opened in a period earlier than the valve timing), the high pressure combustion gas in the combustion chamber can be further pushed into the mixture supply section to further increase the pressure in the mixture supply section during the second opening period. It becomes possible to maintain the pressure difference sufficiently. Note that the introduction of such combustion gas itself becomes a factor that lowers the combustion stability of the air-fuel mixture, but in the low load region as described above, the pressure difference increases due to the introduction of the combustion gas and the high heat of the combustion gas. The combustion stability can be maintained by promoting vaporization and atomization of the air-fuel mixture in the air-fuel mixture supply section.

Further, in the device according to the fifth aspect, in the specific region, that is, in the low load region, not only the other regions but the closing timing of the exhaust valve as well as the opening timing of the exhaust valve is delayed.
Due to the delay of the valve opening timing, the overlapping period between the exhaust valve opening period and the second valve opening period is shortened,
During this overlap period, the combustion gas is suppressed from escaping to the exhaust port side, and thereby the pressurizing action in the air-fuel mixture supply section is maintained high. On the other hand, in an area other than the specific area, that is, in a high load operation area or the like in which sufficient internal pressure of the air-fuel mixture supply section can be secured without particularly introducing combustion gas into the air-fuel mixture supply section, the exhaust gas is exhausted more than the specific area. By opening the valve earlier and expanding the overlapping period,
During this overlap period, the combustion gas is positively released to the exhaust port side, the introduction of excess combustion gas into the mixture supply section is prevented, and good combustibility is secured. It is also possible to prevent the pressure inside the air-fuel mixture supply from being excessively increased and adversely affecting the fuel injection.

According to the sixth aspect of the present invention, the maximum value of the exhaust gas recirculation amount by the exhaust gas recirculation means is such that as the exhaust gas recirculation amount increases, the amount of fresh air introduced from the main intake port begins to decrease, and the intake limit exhaust gas return Since the flow rate is set to be approximately equal to the flow rate, the maximum NOx reduction action is ensured within a range that does not adversely affect the engine output.

According to the seventh aspect of the present invention, the opening timing of the intake valve is set at the same time as or later than the piston top dead center, that is, the opening period of the exhaust valve and the opening of the intake valve. Since the overlap period with the valve period is set to the period after the top dead center of the piston, the piston is always descending during this overlap period, and the combustion gas discharged from the exhaust port is lowered by the piston. The negative pressure caused by is more reliably pulled back into the combustion chamber, which causes the internal E
GR amount is increased.

[0017]

Embodiments of the present invention will be described with reference to the drawings.

The engine shown in FIGS. 1 and 2 comprises a plurality of cylinders 1, each of which is provided with a combustion chamber 2 whose volume changes with the operation of a piston (not shown). Each combustion chamber 2 has a pair of left and right first side ports 3 and second side ports 4, which are main intake ports, a pair of left and right first exhaust ports 5 and second exhaust ports 6, and a single center port. And 7 are open, and an ignition plug (not shown) is provided at a substantially central portion of each combustion chamber 2.

The both side ports 3 and 4 are formed from one side of the cylinder head (not shown) to the combustion chamber 2.
Both exhaust ports 5 and 6 are formed from the other side of the cylinder head to the combustion chamber 2. The center port 7 is located between the both side ports 3 and 4 and opens into the combustion chamber 2 at a position close to the spark plug.

The opening portions of the first and second side ports 3 and 4 with respect to the combustion chamber 2 are opened and closed by the first and second intake valves 11 and 12, respectively, and the first and second with respect to the combustion chamber 2, respectively.
The opening portions of the second exhaust ports 5 and 6 are opened and closed by the first and second exhaust valves 13 and 14, respectively, and the opening portion of the center port 7 to the combustion chamber 2 is a timing valve (open / close). It is designed to be opened and closed by a valve 15. These valves 11 to 15 are opened and closed by a valve operating mechanism (not shown) composed of a cam shaft or the like. Particularly, regarding the exhaust valves 13 and 14, a variable valve timing mechanism (timing changing means) connected to the exhaust cam shaft 8 is used. Hereafter, V
It is called VT. ) 10, the phase of the valve opening period is shifted.

More specifically, during the valve opening period of the exhaust valves 13 and 14, when the VVT 10 is off, the curve 4 in FIG.
2A, that is, the period from the time point before the piston bottom dead center to the next piston top dead center is switched, and conversely when the VVT 10 is on, the period shown by the curve 42B, that is, the curve 42A described above. The period from the time point between the valve opening timing and the piston bottom dead center to the time point just past the next piston top dead center is switched. The opening period of the intake valves 11 and 12 is the period shown by the curve 44,
That is, the period is set from the vicinity of the top dead center of the piston to a point slightly after the bottom dead center of the next piston. Therefore, when the opening period of the exhaust valves 13 and 14 is switched to the period shown by the curve 42A, the overlapping period of this opening period and the opening period of the intake valves 11 and 12 is 0 or When the exhaust valve 13, 14 is switched to the period shown by the curve 42B, the valve open period and the intake valve 11, 12 are relatively long. It is supposed to overlap for a period.

The opening period of the timing valve 15 is the curve 46.
Period, that is, the period from a point slightly before the piston bottom dead center to a point before the next piston top dead center (midpoint in the compression stroke) during the opening period of the intake valves 11 and 12. Is set to. Therefore, the opening timing of the timing valve 15 is set to be later than the opening timing of the intake valves 11 and 12, and the intake valves 11 and 12 are closed during the opening period of the timing valve 15. It is supposed to be done.

Air is introduced into each of the side ports 3 and 4 through the intake pipe 16. This intake pipe 16
It has a common intake pipe 16a on the upstream side of intake and a surge tank 16b on the downstream side thereof, and the side ports 3 and 4 are connected to this surge tank 16b. The common intake pipe 16a is provided with a throttle valve 17 that operates in response to an accelerator operation, and a throttle sensor 20 that detects the opening of the throttle valve 17.

Of the two side ports 3 and 4 and the center port 7, a side injector 24 and a center injector 25 are provided at the first side port 3 and the center port 7, respectively, and a side injector 24 and a center injector 25 are provided at the second side port 4, respectively. A swirl control valve 18 for opening and closing is provided, and each swirl control valve 18 is driven to open and close by an actuator (not shown). Then, when the swirl control valve 18 is closed, intake air is only taken from the first side port 3 to form a swirl in the combustion chamber 2.

Each center port 7 is connected to a common surge tank 22, and the center port 7 and the surge tank 22 constitute an air-fuel mixture supply section of the present invention, and the internal space thereof is closed. . Then, the fuel injected from the center injector 25 is mixed with the air in the center port 7, thereby forming an air-fuel mixture.

The exhaust ports 5 and 6 are connected to a common exhaust pipe 30 via an exhaust manifold 28, and these constitute an exhaust passage. An exhaust gas recirculation passage (hereinafter referred to as EG
It is called the R passage. ) 32 has one end connected. The other end of the EGR passage 32 is connected to the surge tank 16b via an EGR valve 34 at an intermediate portion of the intake pipe 16 (a substantially boundary portion between the common intake pipe 16 and the surge tank 16b in the illustrated example). Therefore, when the EGR valve 34 is open, the exhaust gas in the exhaust manifold 28 is returned to the main intake ports 3 and 4 through the EGR passage 32 and the surge tank 16b.

The EGR valve 34 is a diaphragm valve. An air passage 38 arranged in parallel with the common intake pipe 16a and the surge tank 16b is connected to the common intake pipe 16a and the surge tank 16b, and an intermediate portion of the air passage 38 is introduced into the EGR valve 34 via a duty solenoid valve 36. It is connected to each part. Then, the opening degree of each EGR valve 34 can be adjusted by changing the opening degree of each duty solenoid valve 36 by inputting an electric signal.

Detection signals from the sensors such as the throttle sensor 20 are input to an ECU (control unit; timing control means and exhaust gas recirculation control means) 40, and the ECU 40 controls the opening degree of each EGR valve 34. The control, the on / off control of the VVT 10, the opening / closing control of the swirl control valve 18, the fuel injection control of each injector 24, 25, etc. are executed. Specifically,
The ECU 40 is configured to perform the following control operation.

1) Opening / closing control of the swirl control valve 18: As shown in FIG. 3, in a low engine speed region where the engine speed N is less than a preset engine speed N1, the swirl control valve 18 is closed to set the engine speed to the above value. The swirl control valve 18 is opened in a high rotation speed region where N is equal to or higher than the rotation speed N1.

2) Opening control of the EGR valve 34: In the low rotation speed region, as shown by the straight lines 48A and 48B in FIG. 4, the EGR valve is controlled so that the maximum EGR rate is obtained when the throttle valve 17 is fully closed. 34 so that the EGR rate decreases linearly as the opening of the throttle valve 17 increases.
The opening degree of the valve 34 is decreased so that the throttle opening degree becomes a predetermined opening degree θ.
The EGR valve 34 is fully closed in the range of 0 or higher and in the high rotation range. Here, the EGR rate (%) is given by the following equation.

[0031]

## EQU1 ## (EGR rate) = 100 × Ge / (Ge + Ga) where Ge is the exhaust gas recirculation amount and Ga is the intake air amount.

Therefore, as shown in FIG. 3, in the specific region A0 in which the shaft torque T is less than the constant torque T2 in the low rotation region, exhaust gas is recirculated to the side ports 3 and 4 to perform so-called external EGR. As shown in FIG. 2, so-called internal EGR is performed by overlapping the valve opening period of the exhaust valve and the valve opening period of the intake valve (details will be described later), and the axial torque T is equal to or greater than the torque T2 in the low rotation speed region. In the low rotation and high torque region A3 and the high rotation region A4, the external E
The control is performed such that neither GR nor internal EGR is performed.

Although the intake pressure is reduced (that is, the intake negative pressure is decreased) as the exhaust gas recirculates,
As shown in FIG. 5, in the region where the intake negative pressure is equal to or higher than the constant value P ₁ , Qa / A (Qa is the intake flow rate,
In A, the intake passage area) does not decrease, so torque reduction does not occur when the throttle opening is constant. Therefore,
In this embodiment, the ECU 40 sets the intake negative pressure when the throttle valve 17 is fully closed to be substantially equal to the constant value.
Is configured.

3) ON / OFF control of VVT 10: The VVT 10 is turned on in the specific area A0, and the VVT 10 is turned off in the other areas A3 and A4.

4) Fuel injection control: As shown in FIG. 6, the low rotation and low torque region A1 and the low rotation medium torque region A2.
In the low rotation and high torque region A3, the engine rotation speed is further lower than the rotation speed N1 by a predetermined number or more (hatched area in the figure), injection is performed only from the center injector 25, and in other areas, Injection is performed from both the center injector 25 and the side injector 24. In the latter area, injection may be performed only from the side injector 24.

Next, the operation of this device will be described.

First, the engine speed N is a constant speed N1.
In the specific region (low rotation and low load region) A0 where the throttle opening is less than the constant value θo and the throttle opening is less than the constant value θo, the VVT 10 operates and the opening period of the exhaust valves 13 and 14 is delayed as shown by the curve 42B in FIG. Switched to the side. Therefore, in each cycle, the exhaust valve 13,
14 is opened and the combustion gas in the combustion chamber 2 is exhausted to the exhaust ports 5, 6
And the like, the intake valves 11 and 12 are opened before the exhaust valves 13 and 14 are closed at the next piston top dead center, and the intake ports 3 and 4 (the swirl control valve 1
8 is closed, fresh air is introduced through the intake port 3 only), and then the exhaust valves 13 and 14 are closed. Thus, the exhaust valve opening period and the intake valve opening period partially overlap after the piston bottom dead center, so that the combustion gas once discharged to the exhaust ports 5 and 6 has a negative pressure due to the piston descending. When it is generated, it is pulled back into the combustion chamber 2 again (internal EGR).

Further, in the specific area A0, the exhaust gas is directly recirculated to the intake side by opening the EGR valve 34 at an opening according to the throttle opening as shown in FIG. By performing the external EGR and the internal EGR described above at the same time, the center port 7 as in the conventional case can be obtained.
A larger amount of exhaust gas recirculation is ensured as compared with a device that recirculates exhaust gas only through the exhaust gas recirculation, thereby significantly suppressing the generation of NOx and reducing pumping loss.

After the exhaust valves 13, 14 are closed, the timing valve 15 is opened before the next piston bottom dead center, so that the air-fuel mixture formed in the center port 7 is led out into the combustion chamber 2. . Then, when the piston passes through the bottom dead center, the intake valves 11 and 12 are closed, and conversely to this, the gas in the combustion chamber 2 is introduced into the center port 7 as the piston rises, and after this introduction, compression is performed. The timing valve 15 is closed in the middle of the stroke. Here, since the space in the air-fuel mixture supply unit including each center port 7 and the surge tank 22 is a closed space, the timing valve 15 is closed in the middle of the compression stroke as described above, so that the inside of the center port 7 is closed. The pressure of the next timing valve 15
Will be maintained at a pressure higher than the pressure in the combustion chamber 2 at the time of valve opening, and due to this pressure difference, the air-fuel mixture in the center port 7 will return to the inside of the combustion chamber 2 at the next valve opening of the timing valve 15. be introduced. That is, without using a special air pressurizing means, it is possible to use the combustion chamber 2 through the center port 7.
Since the air-fuel mixture is supplied to the inside, the structure of the apparatus is simplified because the air pressurizing means is not necessary, and the engine load due to the driving of the air pressurizing means is not increased.

Incidentally, the increase of the exhaust gas recirculation amount as described above generally lowers the combustibility and increases the amount of generated HC, but according to the apparatus of this embodiment, the external EGR and In the specific area A0 where the internal EGR is performed,
By supplying the air-fuel mixture from the center port 7, the inside of the combustion chamber 2 is stratified and the heat of the combustion gas returned to the inside of the combustion chamber 2 at the time of the internal EGR promotes the vaporization and atomization of the air-fuel mixture for combustion. Since the HC component in the combustion gas is re-combusted in the combustion chamber 2, the generation of HC is suppressed despite the increase in the exhaust gas recirculation amount, and the exhaust gas emission is kept good. Be done.

In contrast to such a specific area A0, the other areas, that is, the low rotation and high load area A3 and the high rotation area A
4, the VVT 10 is switched off, the exhaust valve opening period is switched to the advancing side as shown by the curve 42A in FIG. 2, and the overlapping period of the exhaust valve opening period and the intake valve opening period is 0.
Or it is shortened to an extremely short period and EGR
The valve 34 is also closed. By thus stopping both the external EGR and the internal EGR, the area A
The high engine output required in A3 and A4 is secured.

In this embodiment, the specific area A0 is also used.
4, the opening degree of the EGR valve 34 is narrowed to decrease the EGR rate as the throttle opening degree increases (that is, as the load increases), as shown by the broken line L1 in FIG. It is possible to secure an appropriate engine output. Further, when the EGR rate is maximum, the maximum EGR rate is set to be substantially equal to the limit EGR rate that does not cause engine torque down, so the maximum exhaust gas recirculation amount is set within a range that does not impair the engine output. It is possible to secure it.

Next, a second embodiment will be described with reference to FIGS. 7 and 8.

In this embodiment, the surge tank 22 shown in the first embodiment is connected to the common intake pipe 16a via the air supply passage 60, and an air pump (air pressurizing means) is provided in the middle of the air supply passage 60. ) 58 is provided.
In this embodiment, the air pump 58 is connected to the drive shaft 52 of each timing valve 15 via a drive transmission mechanism 54 and is driven in conjunction with the drive shaft 52. Mechanism 54
An electromagnetic clutch 56 that can switch between a state in which they are connected and a state in which they are disconnected is provided between and.

Inside each center port 7, there is provided a center port throttle valve 26 which is driven to open and close by being interlocked with each other by an actuator (not shown), and inside the center port 7 is changed by the opening change of the center port throttle valve 26. The flow path area of is adjusted.

The ECU 40 is configured to control the opening of the center port throttle valve 26 in addition to the control shown in the first embodiment. Specifically, the opening of the center port throttle valve 26 is maximized in the specific region A0, and in the regions other than the specific region A0, that is, the low speed high torque (high throttle opening) region A3 and the high rotation region A4, Control such that the opening of the center port throttle valve 26 is maximized is performed.

According to such a device, the specific area A is
At 0, the opening degree of the center port throttle valve 26 is minimized, and pressurized air is gradually supplied to the downstream side of the center port throttle valve 26 while the timing valve 15 is closed, so that the timing valve 15 is opened. At this time, the air-fuel mixture is supplied into the combustion chamber 2 at one time, and then the air-fuel mixture is supplied so that the air-fuel mixture supply amount is rapidly reduced. As a result, stratification in the combustion chamber 2 is promoted, and an increase in the amount of HC generated due to exhaust gas recirculation is suppressed. On the other hand, in the low-speed high-torque region A3 and the high-rotation region A4 where relatively high output is required, the center port throttle valve 26 is fully opened to constantly supply the pressurized air, so that the combustion chamber 2 has a larger amount. The air-fuel mixture will be stably supplied.

Next, a third embodiment will be described with reference to FIG.

In this embodiment, in the device shown in the first embodiment, in addition to the first valve opening period shown by the curve 46 in FIG. 2, a second valve opening period shown by the curve 48 in FIG. That is, from the time point after the explosion stroke and before the valve opening timing (the left end of the curve 42A in FIG. 8) of the exhaust valve in the area other than the specific area A0 to the time just after the next piston bottom dead center. The shape of the driving cam is set so that the timing valve 15 is opened even during the period.

According to such an apparatus, in addition to the combustion gas being stored in the center port 7 by the end of the first valve opening period shown by the curve 46, the second gas shown by the curve 48 is added. During the valve opening period, the high temperature and high pressure combustion gas after the explosion is further pushed into the center port 7, so that the heat of this combustion gas further promotes the vaporization and atomization of the air-fuel mixture in the center port 7, and The pressure in the center port 7 when the timing valve 15 is opened (that is, at the start of the first valve opening period) is further increased.
Therefore, even in a low load region where the pressure and temperature in the combustion chamber 2 in each stroke are relatively low, a sufficiently large pressure difference between the pressure in the combustion chamber 2 and the pressure in the center port 7 when the timing valve 15 is opened is secured. With such a pressure difference, it becomes possible to more reliably supply the gas mixture sufficiently vaporized and atomized in the center port 7 to the combustion chamber 2.

The present invention is not limited to the above embodiments, and the following modes can be adopted as examples.

(1) When executing the internal EGR and the external EGR with the low load region as the specific region A0 as in each of the above-described embodiments, the throttle opening is detected as described above, and the intake pressure is detected. You may make it the specific area the area below this. Further, the exhaust gas recirculation may be controlled based on only the engine load regardless of the engine speed.

(2) In the first embodiment, the operation of the VVT 10 delays both the closing timing and the opening timing of the exhaust valves 13 and 14 in the specific region A0.
For example, even if the closing timing of the exhaust valves 13 and 14 is delayed only in the specific area A0 by switching the cam,
It becomes possible to execute the internal EGR. However,
In the third embodiment, the exhaust valve 13,
If both the valve closing timing and the valve opening timing of 14 are delayed, a region where the pressure and temperature in the combustion chamber 2 are higher than the specific region A0 (that is, by introducing the combustion gas in the second valve opening period, In a region where it is less necessary to increase the pressure and temperature in the port 7), the overlapping period between the valve opening period of the exhaust valves 13 and 14 and the second valve opening period can be extended, and such overlapping is possible. By actively releasing the combustion gas to the exhaust ports 5 and 6 side during the period, this combustion gas (that is, an inert gas) is prevented from being introduced into the center port 7 more than necessary, and a high engine output is secured. be able to. Further, it is possible to prevent the fuel injection by the center injector 25 in the center port 7 from being adversely affected by the excessive pressure increase in the center port 7.

(3) The overlapping period of the exhaust valve opening period and the intake valve opening period may be a period between piston top dead center or a period after piston top dead center. Good. However, in the latter case, the piston is always lowered during the overlap period, and the negative pressure due to the lowering of the piston causes the internal EGR amount (from the exhaust ports 5 and 6 to the combustion chamber 2).
There is an advantage that it is possible to secure a larger amount of gas that is drawn back in.

(4) In the first embodiment, the EGR valve 34 is fully closed in the areas A3 and A4 other than the specific area A0.
Although the external EGR is not performed at all, the present invention may set the EGR amount in the region other than the specific region to a minute amount smaller than the EGR amount in the specific region.

(5) In the present invention, regardless of the number of main intake ports, a single one may be used, or three or more main intake ports may be formed.

[0057]

As described above, the present invention is included in the operating region in which the air-fuel mixture is supplied from the air-fuel mixture supply unit in the device in which both the main intake port and the air-fuel mixture supply unit open to the common combustion chamber. In the specified region, the overlap period of the exhaust valve open period and the intake valve open period is within a range in which the exhaust valve open period does not overlap with the open / close valve open period compared to other regions. Is expanded to perform internal EGR, and exhaust gas is recirculated to the main intake port to perform external EGR. Therefore, conventional exhaust gas is simply recirculated to the air-fuel mixture supply section. Compared to the device, NOx is generated by both the internal EGR and the external EGR in the specific region.
The occurrence can be greatly suppressed. Moreover, in this specific region, the combustion chamber is stratified by the air-fuel mixture supply from the air-fuel mixture supply unit, and the vaporization and atomization of the air-fuel mixture is performed by the heat of the combustion gas returned to the combustion chamber during the internal EGR. Since the HC component in the combustion gas returned to the combustion chamber can be promoted again in this combustion chamber, EG
Despite the increase in the amount of R, it is possible to suppress the deterioration of exhaust gas emission due to the generation of HC.

Here, in the apparatus according to the second aspect, since the specific region is the low load region, a sufficient NOx suppressing action and a pumping loss reducing action are ensured in the low load region, while other than the specific region. In the high load region, which is the region of No. 3, by suppressing the internal EGR and the external EGR, there is an effect that the high output required in this high load region can be secured.

Further, in the device according to the third aspect, the external EGR amount is suppressed as the engine load increases even in the specific region, so that the engine output more suitable for the actual operating condition can be secured. There is an effect that can be done.

In the apparatus according to the fourth aspect, the space in the air-fuel mixture supply section is a closed space, and in addition to the valve opening period (that is, the first valve opening period), the second valve opening period (opening and closing). When the valve opening timing is earlier than the exhaust valve opening timing), the on-off valve is opened, and in this second opening period, the high pressure combustion gas in the combustion chamber is further pushed into the mixture supply section to supply the mixture. By increasing the pressure inside the section, a large pressure difference is secured between the inside of the mixture supply section and the combustion chamber when the on-off valve is opened. The air-fuel mixture can be satisfactorily supplied without using the air pressurizing means, and the omission of the air pressurizing means can simplify the structure of the apparatus and reduce the engine load. In addition, although the introduction of the combustion gas into the air-fuel mixture supply unit itself becomes a factor that reduces the combustibility of the air-fuel mixture, in the low load region as described above,
By increasing the pressure difference by introducing the combustion gas and promoting the vaporization and atomization of the air-fuel mixture in the air-fuel mixture supply portion due to the high heat of the combustion gas, the combustibility can be improved rather.

Further, in the device according to the fifth aspect, in the specific region, that is, the low load region, not only the closing timing of the exhaust valve but also the opening timing of the exhaust valve is delayed compared to other regions. By delaying the valve opening timing, the overlap period between the exhaust valve opening period and the second valve opening period can be shortened to maintain a high pressure in the air-fuel mixture supply unit, while the region other than the specific region can be maintained. In particular, in a high load operation region where a sufficient internal pressure of the air-fuel mixture supply section can be secured without introducing the combustion gas into the air-fuel mixture supply section, the opening timing of the exhaust valve should be earlier than that in the specific area and By expanding and actively letting the combustion gas escape to the exhaust port side during this overlap period, it is possible to prevent the introduction of excess combustion gas into the mixture supply section, to ensure good combustibility, and to Rises excessively It is also effective that it is possible to prevent an adverse effect on the fuel injection by.

According to the sixth aspect of the present invention, the maximum value of the exhaust gas recirculation amount by the exhaust gas recirculation means is set to the limit recirculation amount at which the fresh air introduction amount from the main intake port begins to decrease as the exhaust gas recirculation amount increases. Since the amounts are set to be substantially equal, the maximum NOx reduction effect can be obtained within a range that does not adversely affect the engine output.

According to the seventh aspect of the present invention, the valve opening timing of the intake valve is set at the same time as or later than the piston top dead center so that the overlapping period of the exhaust valve opening period and the intake valve opening period is set. Since the period after the piston top dead center is set, that is, the period in which the piston is always descending, the combustion gas discharged from the exhaust port can be reliably returned to the combustion chamber by the negative pressure due to the piston descending. This has the effect that a larger amount of internal EGR can be obtained.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an engine according to a first embodiment of the present invention.

FIG. 2 is a graph showing a valve opening timing of each valve set in the engine.

FIG. 3 is a graph showing the contents of EGR control corresponding to engine speed and shaft torque in the engine.

FIG. 4 is a graph showing the contents of EGR valve opening control and VVT on / off control corresponding to the throttle valve opening in the engine.

FIG. 5 is a graph showing a relationship between intake negative pressure and intake flow velocity in the engine.

FIG. 6 is a graph showing the content of fuel injection control corresponding to engine speed and shaft torque in the engine.

FIG. 7 is an overall configuration diagram of an engine according to a second embodiment of the present invention.

FIG. 8 is a graph showing a valve opening timing of each valve set in the third embodiment of the present invention.

[Explanation of symbols]

 1 Cylinder 2 Combustion Chamber 3 First Side Port (Main Intake Port) 4 Second Side Port (Main Intake Port) 5, 6 Exhaust Port 7 Center Port (Mixture Mixing Unit) 10 VVT (Time Varying Means) 11, 12 Intake valve 13, 14 Exhaust valve 16 Intake pipe 17 Throttle valve 20 Throttle sensor 22 Surge tank (mixture mixture supply part) 25 Center injector 28 Exhaust manifold 32 EGR passage (exhaust gas recirculation means) 34 EGR valve (exhaust gas recirculation means) 40 ECU (timing control means and exhaust gas recirculation control means)

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location F02D 41/34 C 9247-3G 43/00 301 TZ N (72) Inventor Tatsuya Tanaka Fuchu-cho, Aki-gun, Hiroshima Prefecture Shinchi No. 3 Mazda Co., Ltd.

Claims (7)

[Claims] 1. A main intake port that opens into a combustion chamber and is opened and closed by an intake valve; and a main intake port that opens into the combustion chamber and is opened and closed by an on-off valve, and air is introduced into the combustion chamber with the on-off valve opened. It has an air-fuel mixture supply part for supplying a mixture with fuel, and an exhaust port opened in the combustion chamber and opened / closed by an exhaust valve, and the opening timing of the opening / closing valve is the opening timing of the intake valve. In an engine set at a later time, a timing varying means for changing at least the valve closing timing of the exhaust valve, and a specific region included in the operating region in which the air-fuel mixture is supplied from the air-fuel mixture supply unit is other region. In comparison with the above, the timing is variable so as to extend the overlap period of the exhaust valve open period and the intake valve open period within a range in which the exhaust valve open period does not overlap with the open / close valve open period. When the exhaust valve is closed by A timing control means for delaying the period, an exhaust gas recirculation means for recirculating exhaust gas to the main intake port, and an exhaust gas recirculation control means for increasing the amount of exhaust gas recirculation by the exhaust gas recirculation means in the specific region as compared with other regions. An exhaust gas recirculation system for an engine, which is characterized by being provided. 2. The exhaust gas recirculation system for an engine, wherein the specific region is included in a region where an engine load is below a certain level. 3. The exhaust gas recirculation system for an engine according to claim 2, wherein the exhaust gas recirculation control means is configured to reduce the exhaust gas recirculation rate by the exhaust gas recirculation means in the specific region as the engine load increases. An exhaust gas recirculation system for an engine. 4. The exhaust gas recirculation system for an engine according to claim 2, wherein the space in the mixture supply section is a closed space, and the opening / closing valve is opened at least in the specific region. A first valve opening period that is later than the first valve opening period and a second valve valve that is earlier than the valve opening timing of the exhaust valve
An exhaust gas recirculation system for an engine, characterized in that it is configured to open both during the valve opening period. 5. The engine exhaust gas recirculation system according to claim 4, wherein the timing control means is configured to delay both the valve closing timing and the valve opening timing of the exhaust valve in the specific region as compared with other regions. An exhaust gas recirculation system for an engine characterized by the above. 6. The engine exhaust gas recirculation system according to claim 1, wherein the maximum value of the exhaust gas recirculation amount by the exhaust gas recirculation means is a maximum limit exhaust gas recirculation amount within a range in which the intake air amount is not reduced. An engine exhaust gas recirculation device characterized by being set to substantially equal amounts. 7. The exhaust gas recirculation system for an engine according to any one of claims 1 to 6, characterized in that the valve opening timing of the intake valve is set at the same time as or later than the piston top dead center. Engine exhaust gas recirculation system.