JP3365681B2 - Engine intake system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intake system for an engine, in which a mixture supply section for supplying a mixture of air and fuel into the combustion chamber is provided separately from the main intake port. Is.

[0002]

2. Description of the Related Art Conventionally, as an intake device for an engine, one disclosed in, for example, Japanese Patent Laid-Open No. 62-18335 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. Air supply unit (3rd intake port)
Open 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.

[0003]

SUMMARY OF THE INVENTION In the device of the above publication,
A third intake port, which is a mixture supply unit, communicates with an intake passage, and pressurized air for forming a mixture is introduced into the third intake port by using a supercharger provided on the upstream side of the intake passage. Then, the air-fuel mixture is supplied into the combustion chamber due to the pressure difference between the pressure of the air and the pressure in the combustion chamber. However, when the mixture supply port (third intake port) and the main intake port (first intake port and second intake port) are connected to the common intake passage in this way, the inside of the mixture supply port is It is difficult to secure a sufficient pressure difference between the mixed atmospheric pressure and the pressure in the combustion chamber where supercharging is performed from the main intake port, and
The inconvenience occurs that the layout of the intake passage is significantly restricted.

As a means for eliminating such inconvenience,
It is conceivable that an air pressurizing means such as an air pump is connected to the air-fuel mixture supply port to mix the air and the fuel forcibly pressurized by the air pressurizing means. When the means is added, the structure of the entire apparatus becomes complicated, and the engine load increases due to the driving of the air pressurizing means, resulting in deterioration of fuel efficiency.

In view of the above circumstances, the present invention provides an intake system for an engine, which has a simple structure and is capable of stratifying the combustion chamber by supplying an air-fuel mixture without particularly increasing the engine load. With the goal.

[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. And a mixture supply section for supplying a mixture of air and fuel into the combustion chamber when the on-off valve is opened, and the opening timing of the on-off valve is the opening timing of the intake valve. In the engine set at a later time than the above, the space in the air-fuel mixture supply section is made a closed space, and the timing changing means for changing the closing timing of the on-off valve within the compression stroke range, and at the time of engine high-speed operation And a timing control means for controlling the timing varying means so as to delay the closing timing of the on-off valve as compared with the low speed operation.

In this device, it is more preferable that the timing control means is configured to delay the closing timing of the on-off valve during high load operation as compared with during low load operation in a region where the engine speed is below a certain level ( Claim 2).

Further, in the low speed operation region where the engine speed is less than a preset predetermined speed, fuel injection is performed in the air-fuel mixture supply section, and in the medium and high speed operation regions where the engine speed is higher than the low speed operation region. By providing the fuel injection control means for stopping the fuel injection in the air-fuel mixture supply section and performing the fuel injection in the main intake port, a more excellent effect as described later can be obtained (claim 3).

Further, in the low speed operation region where the engine speed is less than a preset predetermined speed, fuel injection is performed in the air-fuel mixture supply section, and in the medium and high speed operation regions where the engine speed is higher than the low speed operation region. In principle, the fuel injection in the air-fuel mixture supply unit is stopped and the fuel injection is performed in the main intake port. Even in the medium-high speed operation range, the operating state of the engine is in the preset required cooling condition. In this case, it may be provided with a fuel injection control means for exceptionally injecting fuel in the air-fuel mixture supply section (claim 4). In this case, as the cooling required condition, the engine speed is in the high speed operation region in the medium and high speed operation region (claim 5), and knocking of a predetermined strength or more is detected (claim 6). Etc.

Further, in each of the above-mentioned devices, a plurality of main intake ports are provided, a swirl control valve is provided only in a part of the main intake ports, and swirl control means for controlling the opening of the swirl control valve is provided. ,
When the engine is in the combustion stable state, the swirl control means is configured to increase the opening degree of the swirl control valve as compared with the case where the engine is in the combustion unstable state (claim 7). It is more preferable to configure the swirl control means so that the degree of opening of the swirl control valve is reduced when knocking of a strength or more occurs than in other cases (claim 8). Become.

[0011]

According to the apparatus of the present invention, since the space inside the air-fuel mixture supply section is a closed space, when the on-off valve is opened, the air-fuel mixture inside the air-fuel mixture supply section is first supplied into the combustion chamber. On the contrary, the combustion gas in the combustion chamber is taken into the air-fuel mixture supply section, and in this state the on-off valve closes during the compression stroke, so that the pressure in the air-fuel mixture supply section becomes lower than the pressure in the combustion chamber when the on-off valve is opened. By maintaining a high pressure and utilizing such a pressure difference, it is possible to supply the air-fuel mixture at the time of opening the next on-off valve without using a special air pressurizing means. It should be noted that during high-speed operation of the engine, one cycle time is shortened and it becomes difficult to supply the air-fuel mixture from the air-fuel mixture supply section into the combustion chamber. The valve timing is delayed, and the combustion gas with a higher pressure is introduced into the mixture supply section, and the pressure difference between this mixture supply section internal pressure and the combustion chamber pressure increases, so mixing is performed regardless of the engine speed. A good mixture supply from the air supply to the combustion chamber is guaranteed.

According to the second aspect of the present invention, the opening / closing valve is closed when the engine load is high even during the low speed operation, that is, when the engine is in the low speed and high load operation range where knocking is likely to occur. Since the valve timing is delayed from the low speed / low load region, higher temperature / high pressure combustion gas is introduced into the air-fuel mixture supply unit. This enhances the function of the air-fuel mixture supply section as a so-called cooling chamber, that is, the function of temporarily storing high-temperature combustion gas, cooling it, and then returning it to the combustion chamber in the next cycle. Therefore,
In the low speed and high load region, the rise in the temperature of the combustion chamber is effectively suppressed, and knocking is suppressed.

In the device according to the third aspect of the present invention, in the low speed operation region, the fuel is injected in the air-fuel mixture supply portion and the air-fuel mixture is supplied, so that the combustibility is enhanced by stratification in the combustion chamber, while the low-speed operation is performed. In the medium to high speed operating region where the engine speed is higher than the operating region, that is, in the region where stratified combustion is difficult and uniform combustion improves rather in combustibility, fuel injection in the mixture supply section is stopped and normal intake By injecting fuel at the main intake port as in the case of the device, fuel injection suitable for the operating state is always executed regardless of the engine speed. Further, since the pressure of the combustion gas introduced into the air-fuel mixture supply unit is high in the medium-high speed operation region as described above, the fuel injection in the air-fuel mixture supply unit is stopped in such a medium-high speed operation region. It becomes unnecessary to use an expensive injector capable of injecting fuel in a high pressure atmosphere. Moreover, even if the fuel injection is stopped in this way, the high-temperature combustion gas in the combustion chamber is taken into the mixture supply section, so that the combustion chamber cooling function as the so-called cooling chamber of the mixture supply section is ensured. .

On the other hand, in the apparatus according to the fourth aspect, even in the medium-high speed operation range, when the operating condition of the engine is a preset cooling requirement, for example, a high speed engine speed is very high. When it is in the operating region (Claim 5) or when knocking is significant (Claim 6), fuel injection is exceptionally executed in the mixture supply unit, so that the heat of vaporization of this fuel is generated. The air in the air-fuel mixture supply unit is cooled, and the excessive rise in engine temperature and knocking are more significantly suppressed.

In each of the above devices, when a swirl control valve is provided in a part of the plurality of main intake ports, the combustion state and pressure state in the combustion chamber are controlled by changing the opening degree of the swirl control valve. Specifically, as the opening of the swirl control valve is throttled, the ventilation resistance of the main intake port increases and the pressure in the combustion chamber decreases, as shown in FIG. 4 (a). As shown in (), the air-fuel mixture easily enters the combustion chamber from the air-fuel mixture supply unit (center port). Then, the swirl formation in the combustion chamber is promoted by the intake air from only some of the main intake ports, and the stratification is promoted.

According to the seventh aspect of the present invention, when the engine is in the combustion stable state, that is, when the stratification in the combustion chamber due to the supply of the air-fuel mixture and the swirl generation is relatively small, the engine burns. Since the opening of the swirl control valve is increased and the amount of the air-fuel mixture is suppressed more than in the unstable state, energy loss due to gas flow between the air-fuel mixture supply unit and the combustion chamber is correspondingly reduced. Is reduced.

Further, in the apparatus according to the eighth aspect, when the engine is remarkably knocked, the opening of the swirl control valve is reduced to promote swirl formation and to supply the air-fuel mixture. The amount of air supplied from the section to the combustion chamber is increased to lower the temperature in the combustion chamber, and thus the knocking is effectively suppressed.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment 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.
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) including a cam shaft and the like. Here, the drive camshaft 8 and the intake camshaft 9 of the open / close valve 15 are configured to interlock with each other, and the drive camshaft 8 of the open / close valve 15 has a valve timing changing mechanism (timing changing means; hereinafter referred to as VTC). 10) are connected, and the operation of the VTC 10 causes the phases of the valve opening periods of the valves 11, 12, 15 to be simultaneously shifted by the same angular amount. This VTC10
Is switched from OFF to ON in response to the hydraulic pressure supplied from the hydraulic circuit 23. The switching of the hydraulic supply is performed by the switching solenoid 23 provided in the hydraulic circuit 23.
It is performed by turning on / off a.

The opening period of the exhaust valves 13 and 14 is set to the period shown by the curve 42, that is, the period from the vicinity of the piston bottom dead center to a point just after the piston top dead center. The opening period of the intake valves 11 and 12 is the above VT.
In the state in which C10 is off, during the period indicated by the curve 44A in FIG. 2, that is, from the time point before the piston top dead center to a time point slightly after the piston bottom dead center (the beginning of the compression stroke). In the state in which the VTC 10 is switched on, and conversely, the period indicated by the curve 44B, that is, from the time point near the piston top dead center to the time point sufficiently past the piston top dead center (time point in the middle of the compression stroke). It is switched to the period.

The opening period of the timing valve 15 is the VT
When C10 is off, the period is switched to the period shown by the curve 46A in FIG. 2, that is, the period from the mid-intake stroke to the mid-compression stroke, and conversely, when the VTC10 is on, it is shown by the curve 46B. The period, that is, the period from the end of the intake stroke to the end of the compression stroke is switched. Therefore, the valve opening timing of the timing valve 15 is always later than the valve opening timing of the intake valves 11 and 12, and the valve closing timing can be switched between the middle stage and the latter stage of the compression stroke.

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, the first side port 3 and the center port 7 are respectively provided with a side injector 24 and a center injector 25, and the second side port 4 is provided with this. 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 its internal space 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 form an exhaust passage.

In this engine, in addition to the air flow sensor 19 and the throttle sensor 20, the engine speed 3
2, equipped with various sensors such as knock sensor,
These detection signals are transmitted to the ECU (control unit;
The timing control means, the fuel injection control means, and the swirl control means 40 are input to the ECU 40, and the ECU 40 controls the on / off of the VTC 10 (that is, the on / off control of the switching solenoid 23a) and the swirl control valve 18.
And the fuel injection control of the injectors 24 and 25 are executed. Specifically, this EC
U40 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 region where the engine speed N is less than a preset engine speed N2, the opening degree of the swirl control valve 18 is minimized, When the rotation speed N is equal to or higher than the rotation speed N2, the swirl control valve 1
The opening degree of 8 is increased. Further, when it is determined that the engine is in the combustion stable state based on the detection signals of the engine speed sensor 32 and the knock sensor 34, the swirl control valve 18 is more than when it is determined that the engine is in the combustion unstable state. The opening degree of is increased by a small amount, and conversely,
When the knocking detected by the knock sensor 34 is equal to or higher than the predetermined strength, the opening degree of the swirl control valve 18 is decreased by a minute amount compared to the other cases.

2) ON / OFF control of VTC 10: VTC 10 is switched off in a region where engine speed N is lower than a preset engine speed N1, and VTC 10 is switched in a region where engine speed N is equal to or higher than N 1 (predetermined operating range). Switch on.

3) Fuel injection control: As for the fuel injection from the center injector 25, as shown by the solid line 51 in FIG. 3, the engine speed N is a predetermined speed N3 (> N1).
In the low speed operation range below, the fuel injection flow rate is increased with the increase of the engine speed up to the engine speed N1, and in the range higher than the engine speed N1, the fuel injection flow rate is reduced with the increase of the engine speed. .
The fuel injection is stopped in the medium-high speed operation region higher than the engine speed N3. As shown by the solid line 52 in the figure, the fuel injection from the side injector 25 is performed only in a region of a predetermined rotational speed or higher, and the fuel injection amount is increased as the engine rotational speed N increases.

Next, the operation of this device will be described.

First, the engine speed N is a constant speed N1.
In the predetermined operation region of, the VTC 10 is off, and the opening periods of the intake valves 11 and 12 and the timing valve 15 are switched to the leading side as shown by the curves 44A and 46A of FIG. 2, respectively. Therefore, in each cycle, the exhaust valves 13 and 14 are opened from before the piston bottom dead center after the explosion and the combustion chamber 2 is opened.
The combustion gas inside is exhausted through exhaust ports 5, 6, etc.,
Then, the intake valves 11 and 12 are opened and fresh air is introduced into the combustion chamber 2 through the side port 3 (the side port 4 is almost closed by the swirl control valve 18). Further, the timing valve 15 is opened before the end of the intake stroke, 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, contrary to the above, the gas in the combustion chamber 2 is introduced into the center port 7 as the piston rises.
After this introduction, the timing valve 15 is closed in the middle of the compression 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. Will be maintained at a pressure higher than the pressure in the combustion chamber 2 at the time of opening the next timing valve 15, and this pressure difference will cause mixing in the center port 7 at the time of opening the timing valve 15 next time. The air is again introduced into the combustion chamber 2.
That is, the air-fuel mixture is supplied from the center port 7 into the combustion chamber 2 without using a special air pressurizing means, and thus the air pressurizing means is unnecessary,
The structure of the device is simplified, and the increase in engine load due to the driving of the air pressurizing means is eliminated.

By the way, in such a device, when the engine speed N rises and the one cycle time is shortened, the valve opening time of the timing valve 15 is also shortened. Therefore, unless any measures are taken, the center port 7 is operated. It becomes difficult to supply the air-fuel mixture or the air into the combustion chamber 2. However, in this device, when the engine speed N enters a predetermined region equal to or higher than the speed N1, the VTC 10 is switched on and the intake valves 11, 12 and the timing valve 15 are turned on as shown by the curves 44B, 46B in FIG. Since the valve opening period is delayed, the pressure in the center port 7 is further increased by that amount, and the pressure difference between the center port 7 and the combustion chamber 2 is increased, so that the engine speed is less than N1. Similar to the region, the supply of the air-fuel mixture or the supply of air can be maintained well.

The reason is as follows. FIG. 5 shows the relationship between the crank advance angle of the engine, the cylinder internal pressure (combustion chamber internal pressure), and the center port 7 internal pressure. As shown in this figure, the in-cylinder pressure increases as the crank advance angle increases (that is, approaches the next piston top dead center).
On the other hand, during the intake stroke period before the piston bottom dead center, the cylinder pressure does not change much even if the crank angle changes. Therefore, by delaying the opening period of the timing valve 15 in the region where the engine speed is N1 or more as described above, it is possible to introduce higher pressure combustion gas into the center port 7 during this opening period. Even if the valve opening period is short, the pressure inside the center port 7 can be maintained at a sufficiently high pressure.

Further, in this embodiment, the following effects can be obtained.

(A) In the medium-high speed operation region where the engine speed is N3 or more, that is, in the region where stratified combustion is difficult and uniform combustion is rather improved in combustibility, the center injector 2
Since the fuel injection by 5 is stopped and the fuel is injected only from the side injector 24 as in the normal intake system, the fuel injection suitable for the engine speed can be executed. Further, in the medium-high speed operation region, since the pressure of the combustion gas introduced into the center port 7 is high as described above,
By stopping the fuel injection by the center injector 25 in such a medium and high speed operation region, there is an advantage that it is not necessary to use an expensive injector capable of fuel injection in a high pressure atmosphere as the center injector 25. Moreover, even if the fuel injection is stopped in this way, the function of the center port 7 as a so-called cooling chamber, that is, the combustion chamber 2 is provided in the center port 7.
Take in the high pressure and high temperature combustion gas inside, store and cool it once,
After that, the function of returning to the combustion chamber 2 is sufficiently ensured.

(B) In the above apparatus, as shown in FIG. 4 (a), as the opening degree of the swirl control valve 18 is reduced, the ventilation resistance in the side port 4 increases and the pressure in the combustion chamber decreases. As shown in FIG. 6B, the air-fuel mixture easily enters the combustion chamber from the air-fuel mixture supply unit (center port). However, in the above embodiment, when the engine is in a stable combustion state, that is, the air-fuel mixture is supplied. When the necessity of stratification in the combustion chamber due to swirl generation is relatively small, the opening degree of the swirl control valve 18 is increased as compared with the case where the engine is in the combustion unstable state.
As a result, by suppressing the air-fuel mixture supply amount, it is possible to reduce energy loss due to gas flow in and out between the center port 7 and the combustion chamber 2. On the contrary, when significant knocking occurs, the opening of the swirl control valve 18 is narrowed, so that the swirl formation is promoted and the pressure in the combustion chamber 2 is lowered to reduce the center port. The air supply amount from 7 to the combustion chamber 2 can be increased to lower the temperature in the combustion chamber, and the knocking can be effectively suppressed by the swirl promotion and the decrease in the temperature in the combustion chamber.

The present invention is not limited to such an embodiment, and the following modes can be adopted as an example.

(1) In the above embodiment, regardless of the engine load, the region where the engine speed is equal to or higher than the predetermined value is set as the predetermined operation region, and the opening period of the timing valve 15 in the other regions is delayed. Since knocking is likely to occur in a region where the engine load is relatively high in the low speed operation region, even in such a low speed and high load region, the opening period of the timing valve 15 is delayed so that the high temperature and high pressure combustion gas is generated in the center port 7. By taking in and enhancing the function of cooling the combustion chamber as the so-called cooling chamber of the center port 7, it becomes possible to avoid the knocking in advance.

(2) In the first embodiment described above, the timing of closing the timing valve 15 and the timing of opening the timing valve 15 are both delayed by the operation of the VTC 10, but the timing valve 15 is closed by switching the cam, for example. You may make it delay only a time. Further, in the above embodiment, the opening period of the intake valves 11 and 12 is changed together with the timing valve 15, but the effect of the present invention can be obtained without changing the opening period of the intake valves 11 and 12. Is.

(3) In the above embodiment, the fuel injection from the center injector 25 is uniformly stopped in the medium and high speed operation range where the engine speed N is N3 or more. However, when the engine operating condition is in the preset cooling required condition, for example, in the high-speed operating region where the engine speed is extremely high, or when knocking is significant, the above center port is exceptional. By configuring the ECU 40 so that the fuel is injected from the center injector 25 in the inside 7, the air in the air-fuel mixture supply unit is cooled by the heat of vaporization of the injected fuel, so that the engine temperature rises excessively and knocking occurs. Can be effectively suppressed. Further, as in the above-described embodiment, the knocking is suppressed to some extent by reducing the opening degree of the swirl control valve 18, and when it is still insufficient, control is performed by injecting fuel from the center injector 25 to further suppress the knocking. With this, knocking can be effectively suppressed over a plurality of stages.

(4) In the present invention, regardless of the number of main intake ports, three or more main intake ports may be formed, or a single swirl control valve 18 may be provided.

[0044]

As described above, according to the present invention, the space inside the air-fuel mixture supply section that opens into the combustion chamber is defined as a closed space, and the opening timing of the on-off valve of this air-fuel mixture supply section is set to the opening of the intake valve in the main intake port. Since the valve closing timing is set later than the valve timing and the valve closing timing is set in the middle of the compression stroke, a sufficiently high pressure can be stored in the air-fuel mixture supply section. By utilizing the difference, it is possible to perform a good air-fuel mixture supply without using a special air pressurizing means, and by omitting such air pressurizing means,
This has the effect of simplifying the structure of the device and reducing the engine load to improve fuel efficiency.

Further, in this device, the closing timing of the on-off valve is delayed during high-speed operation of the engine as compared with during low-speed operation, so that combustion gas of higher pressure is introduced into the mixture supply section in this region. By doing so, it is possible to secure a good mixture supply from the mixture supply unit to the combustion chamber as in the low speed operation, although the opening period of the on-off valve is shortened during the high speed operation.

Further, in the apparatus according to the second aspect of the present invention, the closing timing of the on-off valve is delayed during high load operation as compared with during low load operation even in a region where the engine speed is below a certain level. Due to such a delay, the combustion gas of higher temperature and high pressure is introduced into the air-fuel mixture supply unit to enhance the function of the air-fuel mixture supply unit as a so-called cooling chamber, thereby suppressing an increase in engine temperature in the low speed and high load region. There is an effect that knocking that is particularly likely to occur in this area can be prevented.

According to the third aspect of the present invention, in the low speed operation region, fuel injection is performed in the air-fuel mixture supply section to supply the air-fuel mixture, thereby improving the combustibility by stratification in the combustion chamber, while In the medium to high speed operating region where the engine speed is higher than in the low speed operating region, that is, in the region where stratified combustion is difficult and uniform combustion is more effective in improving combustibility, fuel injection in the air-fuel mixture supply unit is stopped and normal intake air is removed. By injecting fuel at the main intake port as in the case of the device, fuel injection suitable for the operating state can always be executed regardless of the engine speed. Further, in the medium-high speed operation region, since the pressure of the combustion gas introduced into the air-fuel mixture supply unit as described above is high, by stopping the fuel injection in the air-fuel mixture supply unit in such a medium-high speed operation region, It is not necessary to use an expensive injector that can inject fuel in a high pressure atmosphere, and the cost can be further reduced.
Moreover, even if the fuel injection is stopped in this way, the cooling function of the combustion chamber as a so-called cooling chamber of the mixture supply unit, that is, the high temperature combustion gas in the combustion chamber is temporarily stored and cooled and then returned to the combustion chamber. That function can be secured.

On the other hand, in the device according to the fourth aspect, even in the medium-high speed operation range, when the operating condition of the engine is in the preset required cooling condition, for example, the high speed of the engine speed is very high. When the engine is in the operating region (Claim 5) or when knocking is significant (Claim 6), the fuel is exceptionally injected into the air-fuel mixture supply unit. By cooling the air in the air-fuel mixture supply portion, it is possible to more effectively suppress the excessive rise in engine temperature and the occurrence of knocking.

According to the seventh aspect of the present invention, when the engine is in a stable combustion state, that is, when the necessity of stratification in the combustion chamber due to mixture supply and swirl generation is relatively small, the combustion state of the engine is unstable. Since the opening of the swirl control valve is increased more than in the case of, the increase in the pressure in the combustion chamber due to such an increase in the opening of the swirl control valve suppresses the mixture supply amount into this combustion chamber. By doing so, there is an effect that it is possible to reduce the energy loss due to the inflow and outflow of gas between the air-fuel mixture supply section and the combustion chamber.

Further, in the device according to the eighth aspect, when the engine is significantly knocked, the opening degree of the swirl control valve is reduced.
As a result, the swirl formation can be promoted, the mixture gas supply amount can be increased to lower the temperature in the combustion chamber, and the knocking can be effectively suppressed as a whole.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an engine according to an 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 a relationship between an engine speed and a fuel injection flow rate in the engine.

FIG. 4A is a graph showing the relationship between the opening of the swirl control valve and the ventilation resistance of the intake passage in the engine, and FIG. 4B is the opening of the swirl control valve and the air-fuel mixture supply flow rate from the center port. It is a graph which shows the relationship with.

FIG. 5 is a graph showing a relationship among a crank angle, a cylinder internal pressure, and a center port internal pressure in the engine.

[Explanation of symbols]

1 Cylinder 2 Combustion Chamber 3 1st Side Port (Main Intake Port) 4 2nd Side Port (Main Intake Port) 7 Center Port (Mixture Mixing Port) 10 VTC (Timing Variable Means) 11, 12 Intake Valve 18 Swirl Control valve 22 Surge tank (which constitutes a mixture supply unit) 25 Center injector 32 Engine speed sensor 34 Knock sensor 40 ECU (timing control means, fuel injection control means, and swirl control means)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI F02M 67/04 F02M 67/04 (56) References JP-A-57-191451 (JP, A) JP-A-3-134262 (JP , A) JP 6-108907 (JP, A) JP 5-79404 (JP, A) JP 54-96611 (JP, A) JP 5-39756 (JP, A) JP 5-340258 (JP, A) JP 58-28531 (JP, A) Actual development 62-28033 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02D 13/02 F02B 17/00 F02B 29/08 F02B 31/02 F02D 41/34 F02M 67/04

Claims (8)

(57) [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. In an engine having an air-fuel mixture supply unit for supplying an air-fuel mixture with fuel, and the opening timing of the opening / closing valve being set later than the valve opening timing of the intake valve, a space in the air-fuel mixture supply unit As a closed space, and means for changing the closing timing of the on-off valve within a range within the compression stroke, and the above-mentioned timing so as to delay the closing timing of the on-off valve during high-speed operation of the engine as compared with during low-speed operation. An intake system for an engine, comprising: timing control means for controlling the variable means. 2. The engine intake system according to claim 1, wherein the timing control means delays the closing timing of the on-off valve during high load operation compared to during low load operation in a region where the engine speed is below a certain level. An intake system for an engine, which is characterized in that 3. The engine intake system according to claim 1 or 2, wherein fuel injection is performed in the air-fuel mixture supply section in a low speed operation region where the engine speed is less than a preset predetermined speed, and the low speed operation is performed. In a medium-high speed operation region where the engine speed is higher than the region, a fuel injection control means for stopping fuel injection in the air-fuel mixture supply unit and performing fuel injection in the main intake port is provided. Inhaler. 4. The engine intake system according to claim 1, wherein fuel injection is performed in the air-fuel mixture supply section in a low speed operation region where the engine speed is less than a preset predetermined speed, and the low speed operation is performed. In the medium-high speed operation region where the engine speed is higher than the region, in principle, the fuel injection in the air-fuel mixture supply section is stopped and the fuel injection is performed at the main intake port. An intake system for an engine, which is provided with fuel injection control means for exceptionally injecting fuel into the air-fuel mixture supply section when the operating state is in a preset cooling-required condition. 5. The engine intake system according to claim 4, wherein the required cooling condition is that the operating state of the engine is in a high speed operation region of the medium and high speed operation regions. apparatus. 6. The engine intake system according to claim 4 or 5, wherein the cooling requirement is that knocking of a predetermined strength or more is detected. 7. The engine intake system according to claim 1, further comprising a plurality of main intake ports, a swirl control valve being provided only in a part of the main intake ports. And a swirl control means for controlling the opening degree of the swirl control means so as to increase the opening degree of the swirl control valve when the engine is in a combustion stable state compared to when the engine is in a combustion unstable state. An intake system for an engine, which is characterized in that 8. The intake system for an engine according to any one of claims 1 to 6, further comprising a plurality of main intake ports, a swirl control valve being provided only in a part of the main intake ports. The swirl control means is provided so as to control the opening degree, and the swirl control means is configured to reduce the opening degree of the swirl control valve as compared with other cases when knocking of a predetermined intensity or more occurs in the engine. The intake system for the engine, which is characterized by