JP2882265B2 - Intake device for internal combustion engine - 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 internal combustion engine which performs stratified charge under predetermined operating conditions, and more particularly to an improvement in an intake system having two independent intake valves for each cylinder.

[0002]

2. Description of the Related Art In order to improve fuel efficiency, for example, in a predetermined operating range such as a low-load running range, the air-fuel ratio supplied to each cylinder of the internal combustion engine is leaner than the stoichiometric air-fuel ratio (lean air-fuel ratio). However, simply reducing the air-fuel mixture may cause ignition and the like to become unstable.

[0003] Therefore, a relatively dense layer of air-fuel mixture is formed in the vicinity of the spark plug by injecting the fuel into each cylinder in two divided injections to ensure ignitability and combustion stability. A stratified air supply type device is disclosed in, for example,
No. 734, for example.

That is, in the apparatus disclosed in the above publication, first, as a first injection, for example, an amount of fuel corresponding to the operating state of the engine is injected in a compression stroke before a suction stroke, and then a second injection is performed. As the second injection, a small amount of fuel is injected just before the bottom dead center of the piston in the suction stroke, so that a relatively rich air-fuel mixture is retained near the ignition plug, thereby stratifying the air-fuel mixture.

[0005]

However, in recent years,
Market demands for improved fuel efficiency are increasing, and there is a demand for an engine that can operate at a leaner air-fuel ratio. Therefore, there is room for improvement in the stratification of the air-fuel mixture using the conventional device.
In particular, stratification of an air-fuel mixture suitable for a device in which two intake valves are independently provided for each cylinder is required.

[0006]

SUMMARY OF THE INVENTION Therefore, the present invention is to stratify an air-fuel mixture optimally for a device having two intake valves for each cylinder. That is, the intake device for an internal combustion engine according to the present invention is provided for each cylinder of the internal combustion engine, and has a front end side synchronized with an intake passage branched into a first intake port and a second intake port, and synchronized with rotation of the engine. A first intake valve and a second intake valve for opening and closing the first intake port and the second intake port, respectively, and provided in the middle of the intake passage;
A fuel injection valve for injecting fuel toward each intake port; and an intake device for an internal combustion engine in which an ignition plug is disposed near the center of the cylinder. Providing an intake control valve for restricting the amount of air flowing into the second intake port by opening the valve, and setting the closing timing of the first intake valve earlier than the closing timing of the second intake valve;
Further, the injection timing of the fuel injection valve is set immediately before the closing of the second intake valve under the predetermined operating condition.

Further, in the configuration of claim 2, the opening timing of the first intake valve is set earlier than the opening timing of the second intake valve.

[0008]

For example, when a predetermined operating condition such as a low load driving range is satisfied, the first intake valve closes earlier than the second intake valve, while fuel is injected just before the second intake valve closes. Therefore, the fuel that has reached the first intake port from the fuel injection valve cannot flow into the cylinder, but stays in the first intake port and is atomized.

When the intake stroke in the next cycle starts, each intake valve opens, and the fuel atomized in the first intake port flows into the cylinder together with the intake air. Here, under the predetermined operating conditions, the intake control valve closes and the amount of air to the second intake port is limited, so that swirl is generated in the cylinder. Due to this swirl, the air-fuel mixture from the first intake port is uniformly diffused in the cylinder. In addition,
The swirl center of this swirl flow has a lower pressure than the peripheral part.

Next, when the fuel injection valve injects fuel immediately before the second intake valve closes, the injected fuel flows into the first intake port and the second intake port, respectively. Since the first intake port is already closed,
The air-fuel mixture flows into the cylinder only from the second intake port.

Here, since the intake air amount is restricted by the intake control valve on the second intake port side and fuel is injected at the end of the intake stroke just before the second intake valve closes, the cylinder The moving speed of the piston inside is small. Accordingly, the flow rate of the air flowing into the cylinder from the second intake port is small, and the flow rate of the air is low. Therefore, the air-fuel ratio of the air-fuel mixture flowing from the second intake port becomes higher than the stoichiometric air-fuel ratio. It flows into the cylinder at a very slow speed and is drawn to the center of the swirl flow.

Thus, the air-fuel mixture having a very high air-fuel ratio which has flowed in from the second intake port is guided by the swirl to a substantially central portion in the cylinder corresponding to the spark plug, and the air sucked in the early stage of the intake stroke. A stratification with a mixture having a low fuel ratio is performed.

If the opening timing of the first intake valve is set earlier than the opening timing of the second intake valve, the combustion gas is likely to be blown back into the first intake port, and the first intake port is opened. The fuel that has stayed inside can be further atomized.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS.

FIG. 1 is an explanatory view of the structure of an intake device for an internal combustion engine according to a first embodiment of the present invention. The internal combustion engine is provided with a plurality of cylinders 1 (only one is shown). Cylinder 1
The ignition plug 3 facing the inside of the combustion chamber 2 is disposed substantially at the center.

An intake passage 4 is provided for each of the cylinders 1, and the upstream side of the intake passage 4 is connected to an air cleaner (neither is shown) gathering at a collector, and is located downstream of the intake passage 4. The side is bifurcated into a first intake port 4A and a second intake port 4B, and each intake port 4A, 4B communicates with the same combustion chamber 2.

A first intake valve 5A and a second intake valve 5B are provided in each of the intake ports 4A and 4B of the intake passage 4, respectively. These intake valves 5A and 5B are respectively connected to a valve operating mechanism (not shown), and the valve operating mechanisms open and close the intake ports 4A and 4B in conjunction with the rotation of the engine.

The fuel injection valve 6 is provided on a cylinder head (not shown) upstream of a branch portion of each of the intake ports 4A and 4B of the intake passage 4. At the tip of the nozzle of the fuel injection valve 6, an injection hole (not shown) which opens toward each of the intake ports 4A and 4B is formed, and each injection hole is controlled by a control signal from a control unit 12 described later. , And approximately the same amount of fuel is injected at the same time. In addition, each of these injection holes, for example, may form a common flow opening by merging the upstream side thereof, and may be a type in which the common flow opening is opened and closed by a valve body. A type may be formed independently and the upstream end of each injection hole is opened and closed by a valve body.

The swirl control valve 7 as an intake control valve is
The intake passage 4 is provided upstream of the branch portion of each of the intake ports 4A and 4B and downstream of the fuel injection valve 6 and connected to the swirl control valve drive mechanism 8. The portion of the swirl control valve 7 on the fuel injection valve 6 side is the first
Is cut out in a rectangular shape over a range from a portion corresponding to the intake port 4A to a substantially intermediate portion of a portion corresponding to the second intake port 4B to form a cutout portion 7A. When the swirl control valve 7 is closed, the fuel injected in two directions from the fuel injection valve 6 is supplied to each of the intake ports 4A,
4B, and restricts the amount of air flowing into the second intake port 4B.

9 is a crank angle sensor for detecting the crank angle of the engine, 10 is a throttle sensor for detecting the opening of a throttle valve (not shown) provided upstream of the fuel injection valve 6, and 11 is upstream of the throttle valve. The crank angle sensor 9, the throttle sensor 10, and the air flow meter 11 are respectively provided with an oxygen sensor, a water temperature sensor, and a sensor (not shown).
It is connected to the control unit 12 together with an ignition switch and the like.

The control unit 12 for centrally controlling the engine electrically is constructed as a microcomputer system. And the control unit 12
Detects the operating state of the engine based on detection signals from the crank angle sensor 9, the throttle sensor 10, and the air flow meter 11, and closes the swirl control valve 7 when it is determined that the engine has entered a predetermined operating range in which lean combustion is to be performed. As will be described later, the opening and closing timing of each intake valve 5A, 5B is controlled.

Reference numeral 13 denotes an exhaust passage, and the upstream side of the exhaust passage 13 is branched into two forks.
A, a second exhaust port 13B, and a catalytic converter (not shown) is provided downstream of the exhaust passage 13. The exhaust ports 13A and 13B are opened and closed by a first exhaust valve 14A and a second exhaust valve 14B, respectively. The number of exhaust ports does not need to be two, and may be one.

Next, the operation of this embodiment will be described in detail with reference to FIGS.

First, when a predetermined operating condition for starting the engine and performing lean combustion is satisfied, the control unit 12
In order to improve fuel efficiency in the lean burn mode (lean burn), the swirl control valve 7 is closed to generate swirl, the fuel injection timing, and the intake valves 5A, 5B.
Is set as shown in FIG.

That is, the opening timing of each of the intake valves 5A and 5B is set to be the same at the same time, but the closing timing of the first intake valve 5A is set to a predetermined time from the closing timing of the second intake valve 5B. It is set so as to be earlier by the phase difference Δθ.

The fuel injection timing by the fuel injection valve 6 is after the first intake valve 5A is closed, and
Before the intake valve 5B is closed, the injected fuel is supplied to each intake port 4B.
A and 4B are set just before the second intake valve 5B is closed. In other words, the fuel injected from the fuel injection valve 6 is supplied to each intake port after a delay time t determined by the flow path length (the distance from the tip of the fuel injection valve 6 to each of the intake ports 4A and 4B), the engine speed, and the like. 4A and 4B, the fuel injection is started such that the beginning of the arrival is after the closing timing of the first intake valve 5A and the ending of the arrival is before the closing timing of the second intake valve 5B. The timing is set immediately before the second intake valve 5B closes.

Next, the flow of the air-fuel mixture at each time shown in FIG. 2 will be described.

Firstly, at time T ₁ of the in Figure 2, the intake valves 5A intake stroke is started, 5B begins opening, as described later, the air-fuel mixture which has been remaining in the first intake port 4A Figure As shown in FIG. 3, the gas flows into the combustion chamber 2.

Here, in the initial stage of the intake stroke under operating conditions in which lean combustion is performed, the pressure in the intake passage 4 is low in a negative pressure state, so that the first intake valve is overlapped with the exhaust valves 14A and 14B. When the valve 5A is opened, the combustion gas in the combustion chamber 2 and the exhaust passage 13 flows into the first intake port 4A.
Back in the direction of F toward Due to the blown back combustion gas, the air-fuel mixture remaining in the first intake port 4A is atomized before flowing into the combustion chamber 2,
Further, a part thereof evaporates and diffuses into the port 4A. When the pressure in the combustion chamber 2 decreases as the piston descends, the air-fuel mixture (fresh air) diffused into the first intake port 4A and the combustion gas blown back in the F direction enter the combustion chamber 2. The swirl flow S is generated.

That is, the swirl control valve 7 is closed, and the flow of air to the first intake port 4A is permitted by the notch 7A, while the flow of air to the second intake port 4B is restricted. Therefore, the air-fuel mixture flowing from the first intake port 4A has a higher flow velocity and a larger flow rate than the air flowing from the second intake port 4B, and the swirl flow S is generated in the combustion chamber 2. Then, due to the swirl flow S, the air-fuel mixture in the combustion chamber 2 spreads in the combustion chamber 2,
It is homogenized as shown by the dot pattern in FIG.

Next, at time T ₂ in FIG. 2, substantially equal amounts of fuel are injected from the fuel injection valve 6 toward the intake ports 4A and 4B, as shown in FIG.

[0032] Then, at time T ₃ in FIG. 2, the intake ports 4A fuel injected from the fuel injection valve 6, but reaches a 4B, since the first intake valve 5A is already closed, The fuel arriving in the first intake port 4A loses its destination and stays in the port 4A until the next intake stroke is started, as indicated by the hatched portion in FIG.

On the other hand, the second intake valve 5B is closing, but is still slightly open, so that the fuel that has reached the second intake port 4B, as shown in the mesh pattern in FIG. It flows into the combustion chamber 2 from around the second intake valve 5B. Here, since the inflow of the air-fuel mixture is performed at the end of the intake stroke, the inflow speed is low, and the second intake port 4B
Is restricted by the swirl control valve 7. Therefore, the air-fuel ratio of the air-fuel mixture indicated by the mesh pattern in FIG.

The first intake valve 5 is provided in the combustion chamber 2.
Since the swirl flow S is generated by the lean air-fuel mixture flowing from the first intake port 4A before A is closed, the air-fuel ratio flowing from the second intake port 4B is very high. The air slowly flows toward the vortex center of the swirl flow S.

That is, the swirl center of the swirl flow S generated in the combustion chamber 2 is formed substantially at the center of the combustion chamber 2 corresponding to the spark plug 3, and the outlet of the second intake port 4B is Since the air-fuel mixture substantially faces the center of the vortex, the rich air-fuel mixture in the second intake port 4B is attracted by the negative pressure of the center of the vortex and flows into the substantially central portion of the combustion chamber 2, whereby the lean air-fuel mixture ( In the upper part of the center of the dot pattern in FIG.
The middle network pattern portion) is guided in a layered manner, and stratification of the air-fuel mixture is realized. The stratified state is maintained by the swirl flow S until immediately before the ignition timing.

It should be noted that the case where the engine is in the high-speed / high-load region is described below. The swirl control valve 7 is opened to stop the generation of the swirl flow S, and the fuel injection timing is the intake stroke which is the normal injection timing. Is set before.

As described above, according to this embodiment, the closing timing of the first intake valve 5A is advanced by the phase difference Δθ from the closing timing of the second intake valve 5B, and the fuel is injected from the fuel injection valve 6. When the fuel reaches each intake port 4A, 4B, the first
The fuel injection timing is set to be close to the closing of the second intake valve 5B so that the intake valve 5A is already closed and the second intake valve 5B is still open. , The stratification of the air-fuel mixture can be easily realized.

Further, since the swirl flow S generated by the swirl control valve 7 is used, the very swirl center of the swirl flow S whose pressure is lower than that of the surroundings causes a very rich mixture from the second intake port 4B. Can be guided to a substantially central portion of the combustion chamber 2, and the stratified state of the air-fuel mixture can be maintained until ignition.

[0039] Further, around the ignition plug 3, since a structure for guiding the air-fuel mixture air-fuel ratio is higher than the stoichiometric air-fuel ratio, as shown in FIG. 6, the emission of the NO _X can be greatly reduced. That is, FIG. 6 is a characteristic diagram showing a correlation between the air-fuel ratio and the calculated NO _X generation amount when the ratio of the mixture around the spark plug 3 to the total mass of the mixture is 20%. The remaining 80% by weight of the air-fuel mixture is set such that the average air-fuel ratio of the entire air-fuel mixture becomes approximately 23. Under this condition, the air-fuel ratio of the air-fuel mixture present around the ignition plug 3 is set so as to be a high air-fuel ratio equal to or higher than the stoichiometric air-fuel ratio (14.7), preferably in the range of 8 to 12 indicated by oblique lines. Thus, the generation of NO _X can be reduced.

Further, when the swirl control valve 7 is closed, when the piston speed at the end of the intake stroke decreases, a rich air-fuel mixture is introduced from the second intake port 4B. The mixture can be guided to the substantially central portion of the combustion chamber 2 at a very slow speed, and the mixture can be surely stratified while preventing the mixture from diffusing in the combustion chamber 2.

Further, when the engine reaches the high speed / high load range and the operation mode is switched from the lean burn mode to the stoichiometric air-fuel ratio mode, the first cycle of the operation mode switching is performed. Only, already the first in the previous cycle
And the mixture remaining in the intake port 4A is added and supplied. Therefore, when the operation mode is switched, the first
By performing the fuel increase control in consideration of the amount of fuel remaining in the intake port 4A, the air-fuel mixture suitable for the operating state of the engine can be supplied.

Next, a second embodiment of the present invention will be described with reference to FIGS. Note that, in the present embodiment, the first
The same reference numerals are given to the same components as those of the embodiment, and the description thereof will be omitted.

FIG. 7 shows each intake valve 5A, 5A according to this embodiment.
FIG. 8 is an opening / closing characteristic diagram showing the relationship between the opening / closing timing of B and the fuel injection timing, and shows the first intake valve 5 as in the first embodiment.
The closing timing of A is set earlier than the closing timing of the second intake valve 5B by the phase difference Δθ, and the fuel injection timing is set to the second intake valve 5B.
B is set immediately before closing.

In this embodiment, the first intake valve 5A
The opening timing of the second intake valve 5B is greater than the phase difference Δθ
It is set _{one time} earlier.

In this embodiment configured as described above, the first
As a result of opening the intake valve 5A earlier by the phase difference Δθ ₁ , the combustion gas can be blown back more strongly on the first intake port 4A side as shown in FIG.

That is, the inflow initial time T shown in FIG.
_{In 4} , the combustion gas from the combustion chamber 2 and the exhaust pipe 13
For blown back into the first intake port 4A through F ₁ direction, further, atomization of the fuel staying in the first intake port 4A, it is possible to promote atomization.

Further, as a result of opening the first intake valve 5A earlier, the swirl flow S in the combustion chamber 2 becomes stronger than in the first embodiment, the combustion speed increases, and the fuel efficiency improves. Here, the state of the air-fuel mixture at times T ₂ , T ₃ in FIG. 7 is the same as the state shown in FIGS. 4 and 5, and a description thereof will be omitted.

In each of the above embodiments, substantially equal amounts of fuel are injected from the fuel injection valve 6 toward each of the intake ports 4A and 4B. However, the present invention is not limited to this. The fuel may be appropriately distributed by, for example, changing the hole diameter of the fuel cell.

In each of the above embodiments, each intake valve 5A,
The case where the opening / closing timing of the first intake valve 5A is fixed is illustrated as an example. Adjustment may be made to advance the closing timing of the second intake valve 5B, or the like, and in other operating regions, the opening and closing timings of both may be simultaneously set.

[0050]

As described above in detail, according to the intake system for an internal combustion engine according to the present invention, the intake control valve is closed under predetermined operating conditions, and the closing timing of the first intake valve is set to the second timing. In this configuration, fuel is injected just before the second intake valve is closed, so that the fuel that has reached the first intake port is retained for only one cycle to be atomized. Fuel into the cylinder in the next intake stroke,
The swirl flow can homogenize and direct a rich mixture from the second intake port toward the vortex center of the swirl flow. As a result, by one fuel injection, an air-fuel mixture having a high air-fuel ratio can be disposed at a substantially central portion corresponding to the ignition plug, and ignitability and combustion stability can be improved.

Further, by setting the opening timing of the first intake valve earlier than the opening timing of the second intake valve, in addition to the above-described effect, the gas flows backward from the cylinder toward the first intake port. The blowback of the combustion gas can be increased, and the fuel retained in the first intake port can be atomized and atomized more easily.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing an intake device for an internal combustion engine according to a first embodiment of the present invention.

FIG. 2 is an opening / closing characteristic diagram showing the opening / closing timing and the like of each intake valve.

FIG. 3 is an explanatory diagram showing a state when fuel staying in a first intake port flows into a combustion chamber.

FIG. 4 is an explanatory diagram showing a state when fuel is injected.

FIG. 5 is an explanatory diagram showing a state when fuel flows in from a second intake port.

[6] characteristic diagram showing the relationship between the air-fuel ratio and the NO _X generation amount.

FIG. 7 is an opening / closing characteristic diagram showing an opening / closing timing of each intake valve in an intake device for an internal combustion engine according to a second embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a state where fuel staying in a first intake port flows into a combustion chamber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cylinder 2 ... Combustion chamber 3 ... Spark plug 4 ... Intake passage 4A ... 1st intake port 4B ... 2nd intake port 5A ... 1st intake valve 5B ... 2nd intake valve 6 ... Fuel injection valve 7 ... Swirl control valve (intake control valve)

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI F02D 41/34 F02D 41/34 F 43/00 301 43/00 301J 301Z (56) References JP-A-5-231276 (JP, A) JP-A-5-60039 (JP, A) JP-A-64-66434 (JP, A) JP-A-60-122250 (JP, A) JP-A-59-29734 (JP, A) JP-A-59-29734 -77045 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) F02D 41/04 335 F02D 41/04 320 F02D 41/34

Claims (2)

(57) [Claims] 1. An intake passage provided for each cylinder of an internal combustion engine and having a leading end branched into a first intake port and a second intake port, and the first intake port synchronized with rotation of the engine. , A first intake valve and a second intake valve for respectively opening and closing the second intake port, and provided in the middle of the intake passage;
A fuel injection valve for injecting fuel toward each intake port, and an intake device for an internal combustion engine in which an ignition plug is disposed near the center of the cylinder. Providing an intake control valve for restricting the amount of air flowing into the second intake port by opening the valve, and setting the closing timing of the first intake valve earlier than the closing timing of the second intake valve; An intake device for an internal combustion engine, wherein the injection timing of the fuel injection valve is set immediately before closing the second intake valve under the predetermined operating condition. 2. The intake system for an internal combustion engine according to claim 1, wherein the opening timing of the first intake valve is set earlier than the opening timing of the second intake valve.