JP2000213355A - Direct injection spark ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable stable stratified change combustion by promoting fuel transportation under operating conditions in which the tumble flow is damped and broken. SOLUTION: In this direct injection spark ignition engine, a sub intake port 17 is provided near an exhaust valve 10 on an extension between a fuel injection valve 16 and an ignition plug 15. The sub intake port 17 is connected to a port part branched from a branch of an intake manifold 7, and opened or closed by a sub intake valve 18 according to the operating conditions of the engine. Since the tumble flow is damped and broken in the low revolution range in a compression stroke, fuel spray is transported to a part near the ignition plug 15 by the gas flow generated by leakage of gas in a combustion chamber to the sub intake port 17. While, in the range in which stratiforming is enable by the tumble flow, the sub intake valve 18 halts. Control for opening and closing the sub intake valve 18 is achieved by a variable rocker arm 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct in-cylinder injection spark ignition engine, and more particularly to a technique for stabilizing stratified combustion in a low engine speed region such as an idle region.

[0002]

2. Description of the Related Art Conventionally, in a direct in-cylinder injection type spark ignition engine, combustion is performed at an ultra-lean air-fuel ratio in order to improve fuel efficiency under low-speed and low-load operating conditions including an idle range. Therefore, stratification of the air-fuel mixture is achieved by improving the gas flow in the intake air and the combustion chamber.

For example, Japanese Patent Application Laid-Open No. 7-19046 discloses that the swirling flow of intake air flows downward on the exhaust valve side of the combustion chamber, and then is reversed at the concave piston crown surface. Flows upward to form a forward tumble flow toward the ignition plug disposed substantially in the center of the combustion chamber, and transports the injected fuel spray to the vicinity of the ignition plug by the forward tumble flow to form a stratified mixture. Are disclosed.

Japanese Patent Application Laid-Open No. 4-1192931 discloses that a swirling flow of intake air is introduced from an intake valve so as to cross a fuel injection valve disposed below the intake valve in a direction of injection. It is disclosed that a stratified air-fuel mixture is formed by forming a reverse tumble flow that is reversed at a crown surface toward a spark plug.

[0005]

However, in these direct in-cylinder injection spark ignition engines, when the engine is operated in a low rotational speed range such as idling, poor combustion occurs and fluctuations in the generated torque and the However, there is a problem that a misfire may occur.

[0006] This is because the swirling flow of the intake air is weakened by the low-speed operation, so that the tumble flow is attenuated or collapsed, the air-fuel mixture is dispersed, and the combustion pressure is reduced. On the other hand, a method of forcibly transporting the fuel by increasing the penetration of the spray can be considered. However, in this high speed region where the tumble flow develops, the fuel spray reaches the cylinder wall surface on the exhaust valve side. However, there is a concern that the unburned fuel rate increases, and that the liquid film fuel is mixed into the lubricating oil.

[0007] From the viewpoint of fuel transportation, excessively increasing the penetration of the spray is disadvantageous in forming a stratified mixture. In view of these problems, an object of the present invention is to promote the fuel transport in a low rotation speed region such as an idling region, thereby reliably forming a stratified mixture and stabilizing combustion. I do.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a spark plug disposed substantially at the center of a combustion chamber, an intake valve for opening and closing an intake passage for introducing intake air from one side of the combustion chamber, and exhaust gas from the other side. A direct-injection-type spark ignition engine including an exhaust valve for opening and closing an exhaust passage for discharging fuel, and a fuel injection valve for directly injecting fuel into a combustion chamber from near the intake valve. A sub-intake passage communicating with the combustion chamber in the vicinity of the exhaust valve, and a sub-intake valve interposed at an opening of the sub-intake passage and opened at a predetermined time under a specific operating condition of the engine. Provide.

According to this configuration, in the ultra-lean air-fuel ratio region where stratified charge combustion is performed, when the swirl flow of the intake air is weakened and the tumble flow is attenuated or collapsed in the compression stroke, the auxiliary intake valve is temporarily opened. As a result, the gas in the combustion chamber leaks to the auxiliary intake passage, and a gas flow is induced in the combustion chamber.

[0010] The injected fuel is transported along the flow to the vicinity of the spark plug, and the mixture is stratified. Here, it is preferable that the auxiliary intake valve is located on an extension connecting the fuel injection valve and the spark plug (claim 2).

Accordingly, it is preferable that, after branching from the intake passage, the auxiliary intake passage communicates with the combustion chamber, avoiding a spark plug above the combustion chamber. The auxiliary intake valve is controlled to open and close so as to open only in a low rotational speed region such as an idle region in the ultra-lean air-fuel ratio region (claim 3).

Here, it is preferable that the valve opening period of the auxiliary intake valve is set between the fuel injection timing and the ignition, and that the valve lift and operating angle thereof are made minute. Further, a shroud for restricting a leak direction of the gas in the combustion chamber may be provided in the head portion of the auxiliary intake valve.

The shroud is preferably installed on the back surface of the umbrella portion of the auxiliary intake valve so as to surround the valve shaft behind the valve shaft as viewed from the spark plug. Accordingly, an effect is obtained that the leakage of the gas in the combustion chamber from the rear of the valve shaft is regulated, and the gas flow from the tip of the fuel injection valve toward the spark plug is strengthened.

Further, it is preferable that the respective components are arranged such that when the auxiliary intake valve is fully closed, a substantially center of the umbrella portion is located above an edge of a concave portion provided on the piston crown surface ( Claim 6).

Thus, the pressure fluctuation in the combustion chamber due to the leak can be formed most effectively, and the effect of imparting acceleration in the direction of the spark plug to the gas in the concave portion can be obtained to the maximum.

[0016]

According to the first aspect of the present invention, when the engine is operated at an ultra-lean air-fuel ratio, the fuel spray is directed to the spark plug even when the tumble flow is attenuated or collapsed in forming a stratified mixture. And can be transported reliably. Therefore, a stratified mixture can be reliably formed, and stable stratified combustion can be performed.

According to the second aspect of the present invention, the transport direction of the fuel spray is optimized, and an air-fuel mixture optimal for ignition can be collected in the vicinity of the spark plug, so that more stable stratified combustion can be performed.

According to the third aspect of the present invention, the energy consumption can be reduced by stopping the sub intake valve under the operating condition in which the stratified mixture can be formed by the tumble flow. Further, there is no need to consider the restriction of the operating angle of the auxiliary intake valve based on the operating conditions in the high rotation speed region and the reduction of the compression ratio due to the increase in the leak amount, and the control of the auxiliary intake valve becomes easy.

According to the fourth aspect of the present invention, the valve opening period of the auxiliary intake valve is optimized and the amount of gas leaked from the combustion chamber is reduced, so that fuel spray is efficiently transported and the compression ratio is reduced. The fuel economy can be prevented from deteriorating due to the decrease in fuel consumption.

According to the fifth aspect of the present invention, the flow from the fuel injection valve tip toward the spark plug is enhanced by the action of the shroud, so that the fuel spray can be transported more reliably and promptly.

Therefore, the flow rate of the leak gas can be minimized. According to the invention according to claim 6, by applying acceleration in the direction of the spark plug to the gas in the piston crown recess, fuel spray injected toward the piston crown can be guided toward the spark plug. .

Therefore, the stratified mixture is more optimally formed, and the thermal efficiency can be improved.

[0023]

FIG. 1 shows a configuration of a direct in-cylinder injection spark ignition engine according to an embodiment of the present invention.

FIG. 2 is a plan view of the engine body. Referring to these figures, 1 is a cylinder block, 2 is a cylinder head fixed on the cylinder block, 3 is a piston slidably inserted into the cylinder block 1, and 4 is a cylinder block 1 and a cylinder head 2. 2 shows a combustion chamber formed between an inner wall surface and a crown surface of a piston 3.

In the cylinder head 2, an intake port 5 is formed on one side in a direction orthogonal to the cylinder row direction, and an exhaust port 6 is formed on the other side so as to be substantially opposed to the intake port 5. .

The intake port 5 is connected to a branch of the intake manifold 7 to form an intake passage, and introduces intake air into the combustion chamber 4. Further, the exhaust port 6 is connected to a branch portion of the exhaust manifold 8 to form an exhaust passage, and discharges exhaust gas from the combustion chamber 4.

Here, the intake port 5 communicates with the combustion chamber 4 at an angle at which the swirl flow of intake air in the vertical direction (arrow a) is easily formed in the combustion chamber 4, and a tumble flow (not shown) is formed in the intake passage. A valve is provided, and a strong tumble flow is formed for stratification of the air-fuel mixture during combustion at an ultra-lean air-fuel ratio.

The opening of the intake port 5 has an intake valve 9.
However, an exhaust valve 10 is interposed in the opening of the exhaust port 6. Each of the intake valve 9 and the exhaust valve 10 has an end of each valve shaft abutting on the inner surface of the top of the valve lifter 11 or 12 having a closed cylindrical shape, and slidingly in contact with the top of the valve lifter 11 or 12. The reciprocating motion is performed by the function of the exhaust valve operation cam 14.

The cylinder head 2 also has a spark plug 1
5 is buried so as to be located substantially at the center of the combustion chamber 4, and the fuel injection valve 16 is buried in a side portion near the intake valve 9,
The fuel is directly injected into the combustion chamber 4 from the fuel injection valve 16.

Further, a sub-intake port 17 having a smaller diameter than the intake port 5 is formed in the cylinder head 2.
The auxiliary intake port 17 is connected to the intake manifold 7 as shown in the figure.
Connected to the port part branched in a part of the branch of
By avoiding the ignition plug 15 above the combustion chamber 4, it communicates with the combustion chamber 4 near the exhaust valve 10 on the extension connecting the fuel injection valve 16 and the ignition plug 15 to form a sub intake passage.

The sub intake port 17 has an opening at the opening thereof.
8 are interposed. The auxiliary intake valve 18 is slidably inserted into a valve guide (not shown) and a valve spring (not shown).
Owing to the action force in the valve closing direction.

A sub-intake valve operating cam 20 is slidably in contact with the sub-intake valve 18 via a variable rocker arm 19, which will be described later, and reciprocates so as to open at a predetermined time under specific operating conditions of the engine. Exercise.

The variable rocker arm 19 is controlled based on an output signal of an engine control unit 23 which receives detection signals of an accelerator opening sensor 21 and a crank angle sensor 22.

Referring to FIG. 3, the valve operating mechanism of the auxiliary intake valve 18 will be described. The camshaft 31 shown in FIG. 3 is configured to include the exhaust valve operating cam 14, and is formed by integrally forming the auxiliary intake valve operating cam 20 on the same shaft, so that the camshaft 31 is rotationally driven by a crankshaft (not shown). Thus, the power is transmitted to the exhaust valve 10 and the auxiliary intake valve 18.

The exhaust valve 10 reciprocates by the function of the exhaust valve operating cam 14 as described above. On the other hand, the auxiliary intake valve 18
The valve shaft end contacts the bottom surface of the variable rocker arm 19 and reciprocates by the function of the auxiliary intake valve operating cam 20 that slides on the upper surface of the variable rocker arm 19.

The variable rocker arm 19 comprises an operating rocker arm 19a and a stopping rocker arm 19b.
2 is rotatably mounted.

The variable rocker arm 19 has a built-in hydraulic piston 33 for connecting and disconnecting the arms 19a and 19b. The hydraulic piston 33 according to the present embodiment is of a single-acting type (having one cylinder chamber) utilizing a reaction force of an elastic body (such as a spring), and is provided with a switching control valve (not shown) from an oil pump (not shown). Hydraulic oil is circulated through.

The auxiliary intake valve operating cam 20 is connected to each of the arms 1
Corresponding to 9a and 19b, it is composed of an operation part 20a having a cam-shaped cross section and a stop part 20b having a circular shape.

The auxiliary intake valve 18 is provided with the rocker arm 1 for stopping.
9b is in contact with the bottom surface. Here, the hydraulic piston 33
If an operating oil pressure lower than the reaction force of the elastic body is applied to each arm, each arm is driven separately and the auxiliary intake valve 18 is stopped.

On the other hand, if a higher operating oil pressure is applied, the piston moves in the cylinder to connect the arms, and the arms are driven integrally, so that the auxiliary intake valve 18 opens at a predetermined time. I do.

FIG. 4 shows the valve lifts in the ultra-lean air-fuel ratio region. In each curve, Le indicates the exhaust valve,
Li1 indicates an intake valve, and Li2 indicates a sub intake valve. When the engine is operated at an ultra-lean air-fuel ratio, the fuel injection timing is in the latter half of the compression stroke due to the requirements for fuel transport and spray shape.

At this time, in a low rotational speed region such as an idling region, the swirling flow of the intake air is weakened, and the tumble flow is attenuated and collapsed in the middle of the compression stroke, so that the injected fuel is dispersed in the combustion chamber 4. The mixture is not stratified.

This causes abnormal combustion. Therefore, by the function of the variable rocker arm 19 described above, the sub intake valve 18 is opened before and after fuel injection in the idling region (FIG. 4A), and the sub intake valve 18 is stopped in other than the idling region (FIG. 4B). .

Here, the valve opening period (operating angle θa) is changed from the start of fuel injection (crank angle (CA) = Ai1) to ignition (CA = A
ig) (θb in the figure).
In the present embodiment, the operating angle θa and the valve head L are made very small, and the auxiliary intake valve 18 is opened from the start of fuel injection to the end of fuel injection (CA = Ai2), and is closed before ignition. .

As described above, when the auxiliary intake valve 18 is temporarily opened at the latter stage of the compression stroke, a gas flow as shown by an arrow in FIG. This gas flow is caused by gas in the combustion chamber leaking to the sub intake port 17 due to the pressure difference between the combustion chamber 4 and the sub intake port 17.
Since the pressure fluctuation extends throughout the combustion chamber 4, the fuel injection valve 16
Acceleration from the tip of the fuel injection valve 16 to the spark plug 15 is applied to the fuel spray injected from the fuel injection valve 16.

As a result, the fuel spray is transported to the vicinity of the spark plug 15, and the mixture is stratified. On the other hand, in a region other than the idling region, the swirling flow of the intake air is strong and the tumble flow does not collapse during the compression stroke.
The air-fuel mixture can be stratified without opening the air-fuel mixture.

As another embodiment, as shown in FIGS. 6 to 8, a shroud 61 for regulating the leak direction of the gas in the combustion chamber is provided at the head of the auxiliary intake valve 18, as shown in FIGS. May be provided.

As shown in FIGS. 7 and 8, the shroud 61 is provided on the back surface of the umbrella portion of the auxiliary intake valve 18 so as to surround the valve shaft behind the valve shaft as viewed from the spark plug 15.
Accordingly, the approximate center of the umbrella portion of the sub intake valve 18 is
8 is arranged so as to be located above the edge of the concave portion provided on the piston crown when fully closed.

That is, as shown in FIG. 6, the distance from the central axis of the cylinder block 1 to the center of the umbrella portion of the auxiliary intake valve 18 is D1, and the distance from the central axis of the cylinder block 1 to the edge of the concave portion of the piston crown surface. When the distance is D2, they satisfy the following equation (1).

D1 ≒ D2 (1) According to the above configuration, the leakage of the gas in the combustion chamber behind the valve shaft as viewed from the ignition plug 15 is restricted by the shroud 61, and as shown in FIG. Exhaust valve 10
The flow near the (auxiliary intake valve 18) side wall surface weakens,
The flow from the tip of the fuel injection valve 16 toward the spark plug 15 is increased.

As a result, the fuel spray is
5 is reliably and quickly transported to the vicinity, so that the combustion can be further stabilized, and the operating angle θa and the valve lift L of the auxiliary intake valve 18 can be set smaller to reduce energy loss due to leakage. Can be.

Further, the pressure fluctuation due to the leak is optimally formed in the combustion chamber 4, and the gas in the concave portion of the piston crown is subjected to the acceleration toward the spark plug 15 as shown by the arrow b. The fuel spray injected in the direction is guided toward the spark plug 15 as shown by an arrow c.

Thus, the air-fuel mixture is more optimally stratified, so that the thermal efficiency can be improved. As described above, according to the present invention, when the engine is operated at the ultra-lean air-fuel ratio, the fuel spray can be reliably transported to the vicinity of the ignition plug 15 even after the collapse of the tumble flow. Thus, stratified combustion can be performed, and the thermal efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a direct cylinder injection type spark ignition engine according to an embodiment of the present invention.

FIG. 2 is a plan view of the main body of the direct in-cylinder injection spark ignition engine according to the first embodiment;

FIG. 3 is a view showing a valve operating mechanism of a sub intake valve.

FIG. 4 is a diagram showing a relationship between a crank angle and a valve lift.

FIG. 5 is a diagram showing gas flow in a combustion chamber according to an embodiment of the present invention.

FIG. 6 is a view showing a direct cylinder injection type spark ignition engine main body according to another embodiment of the present invention.

FIG. 7 is a diagram showing a setting example of a shroud.

FIG. 8 is a plan view of a direct cylinder injection type spark ignition engine main body according to another embodiment of the present invention.

FIG. 9 is a view showing a gas flow in a combustion chamber according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder block 2 Cylinder head 3 Piston 4 Combustion chamber 5 Intake port 6 Exhaust port 7 Intake manifold 8 Exhaust manifold 9 Intake valve 10 Exhaust valve 15 Ignition plug 16 Fuel injection valve 17 Sub intake port 18 Sub intake valve 19 Variable rocker arm 20 Secondary Intake valve operating cam 21 Accelerator opening sensor 22 Crank angle sensor 23 Engine control unit 31 Cam shaft 32 Rocker shaft 33 Hydraulic piston 61 Shroud

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02B 31/00 F02B 31/00 S F02M 61/14 310 F02M 61/14 310A 310S (72) Inventor Yasuyuki Ito F-term (reference) in Nissan Motor Co., Ltd. 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa 3G023 AA01 AA18 AB03 AC05 AD02 AD03 AD05 AD07 AD09 AD12 AF01 AG01 3G066 AA02 AA05 AB02 AD12 BA02 CC34 CC48 DB07 DC04 DC05

Claims (6)

[Claims] A spark plug disposed substantially at the center of the combustion chamber, an intake valve for opening and closing an intake passage for introducing intake air from one side of the combustion chamber, and an exhaust valve for opening and closing an exhaust passage for discharging exhaust gas from the other side. A fuel injection valve configured to directly inject fuel into the combustion chamber from the vicinity of the intake valve. A sub-intake passage communicating with the chamber, and a sub-intake valve interposed at an opening of the sub-intake passage and opening at a predetermined time under a specific operating condition of the engine. In-cylinder injection spark ignition engine. 2. The direct cylinder injection spark ignition engine according to claim 1, wherein the auxiliary intake valve is located on an extension connecting the fuel injection valve and the spark plug. 3. The direct in-cylinder injection spark ignition engine according to claim 1, wherein the auxiliary intake valve opens only in a low speed range. 4. The valve according to claim 1, wherein the auxiliary intake valve is opened at a predetermined timing between the fuel injection timing and the ignition, and the valve lift and operating angle thereof are made minute. 3. The direct in-cylinder injection spark ignition engine according to any one of 3. 5. A shroud for restricting air flow behind the valve shaft as viewed from the spark plug is provided at an umbrella portion of the auxiliary intake valve.
The direct in-cylinder injection spark ignition engine described in (1). 6. When the auxiliary intake valve is fully closed, a substantially central portion of the umbrella portion of the auxiliary intake valve is located above an edge of a concave portion provided on a piston crown surface. A direct cylinder injection type spark ignition engine according to claim 5.