JP3956518B2 - Direct cylinder injection spark ignition engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct in-cylinder 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]
[Prior art]
Conventionally, direct in-cylinder spark ignition engines perform combustion 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. For this reason, the gas flow in the intake air and the combustion chamber is improved to stratify the air-fuel mixture.
[0003]
For example, in Japanese Patent Application Laid-Open No. 7-19046, the swirling flow of the intake air flows downward on the exhaust valve side of the combustion chamber and then is reversed by the concave piston crown surface so that the intake valve side of the combustion chamber faces upward. A flow that forms 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. It is disclosed.
[0004]
Japanese Patent Laid-Open No. 4-112931 discloses that a swirling flow of intake air is introduced from the intake valve so as to cross an injection direction line of a fuel injection valve disposed below the intake valve, and then is applied to the piston crown surface. In other words, a stratified mixture is formed by forming a reverse tumble flow that is inverted and directed toward the spark plug.
[0005]
[Problems to be solved by the invention]
However, in these direct-in-cylinder spark ignition engines, when the engine is operated in a low engine speed range such as idling, combustion failure occurs, resulting in fluctuations in generated torque, and thus misfires. There was a problem.
[0006]
This is because the swirl flow of the intake air is weakened by 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 is conceivable, but this causes the fuel spray to reach the cylinder wall on the exhaust valve side in a high rotation speed region where the tumble flow develops. There is a concern that the unburned rate will increase and the liquid film fuel will be mixed into the lubricating oil.
[0007]
Also from the viewpoint of fuel transportation, excessively increasing the penetration of the spray is disadvantageous in forming the stratified mixture.
Accordingly, in view of these problems, the present invention aims to reliably form a stratified mixture and stabilize combustion by promoting fuel transportation in a low engine speed region such as an idle region. To do.
[0008]
[Means for Solving the Problems]
For this reason, the present invention provides an ignition plug disposed substantially in the center of the combustion chamber, an intake valve that opens and closes an intake passage that introduces intake air from one side of the combustion chamber, and an exhaust that opens and closes an exhaust passage that discharges exhaust from the other side. A direct in-cylinder injection spark ignition engine configured to include a valve and a fuel injection valve that directly injects fuel into the combustion chamber from the vicinity of the intake valve, branching from the intake passage, and using the ignition plug as a reference An auxiliary intake passage that communicates with the combustion chamber in the vicinity of the exhaust valve on the opposite side of the fuel injection valve and an opening of the auxiliary intake passage are opened at a predetermined time under specific operating conditions of the engine. A secondary intake valve is provided.
[0009]
According to such a configuration, in the ultra lean air-fuel ratio region where stratified combustion is performed, when the swirl flow of the intake air is weakened and the tumble flow is attenuated or collapsed during the compression stroke, the auxiliary intake valve is temporarily opened to perform combustion. The indoor gas leaks into the auxiliary intake passage, and gas flow is induced in the combustion chamber.
[0010]
Then, the injected fuel is transported to the spark plug vicinity riding this flow, the air-fuel 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).
[0011]
Accordingly, it is preferable that the auxiliary intake passage is branched from the intake passage and then communicates with the combustion chamber by avoiding a spark plug above the combustion chamber.
The auxiliary intake valve is controlled to open and close so that it opens only in a low engine speed region such as an idle region in an ultra lean air-fuel ratio region.
[0012]
Herein, the valve opening period of the auxiliary intake valve, and sets in until ignition by jetting or al the spark plug of the fuel by the fuel injection valve, it is desirable that an valve lift and operating angle and small (Claim 4).
Further, a shroud for regulating the leak direction of the combustion chamber gas may be provided in the umbrella portion of the auxiliary intake valve.
[0013]
The shroud, the umbrella portion rear surface of the auxiliary air intake valve, the spark plug is preferably in viewed from the valve shaft rearward installed so as to surround the valve shaft.
As a result, the leakage of the combustion chamber gas from the rear of the valve shaft is regulated, and the gas flow from the tip of the fuel injection valve toward the ignition plug is enhanced.
[0014]
Furthermore, it is preferable that the constituent elements are arranged such that when the auxiliary intake valve is fully closed, the substantially central portion of the umbrella portion is located above the edge of the recessed portion provided on the piston crown surface. ).
[0015]
As a result, the pressure fluctuation in the combustion chamber caused by the leak can be most effectively formed, and the action of applying acceleration in the direction of the spark plug to the gas in the recess can be obtained to the maximum.
[0016]
【The invention's effect】
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 reliably transported toward the spark plug even when the tumble flow attenuates or collapses during the formation of the stratified mixture. be able to. Therefore, the stratified mixture can be reliably formed, and stable stratified combustion becomes possible.
[0017]
According to the second aspect of the present invention, the transport direction of the fuel spray is optimized, and the air-fuel mixture optimal for ignition can be collected in the vicinity of the spark plug, so that more stable stratified combustion becomes possible.
[0018]
According to the third aspect of the present invention, the energy consumption can be reduced by stopping the auxiliary intake valve under the operating condition in which the stratified mixture can be formed by the tumble flow.
Further, it is not necessary to consider the limitation on the operating angle of the auxiliary intake valve based on the operating condition in the high rotation speed region, the decrease in the compression ratio accompanying the increase in the leak amount, and the control of the auxiliary intake valve is facilitated.
[0019]
According to the fourth aspect of the invention, the valve opening period of the auxiliary intake valve is optimized and the amount of leakage of the gas in the combustion chamber is reduced, so that the fuel spray is efficiently transported and the compression ratio is reduced. Deterioration of fuel consumption can be suppressed.
[0020]
According to the fifth aspect of the invention, the flow of fuel spray from the tip of the fuel injection valve toward the spark plug is strengthened by the action of the shroud, so that the fuel spray can be transported more reliably and quickly.
[0021]
For this reason, the leak gas flow rate can be minimized.
According to the invention which concerns on Claim 6, the fuel spray injected to the piston crown surface direction can be guide | induced to the spark plug direction by attaching the acceleration of a spark plug direction to the gas in a piston crown surface recessed part. .
[0022]
For this reason, the formation of the stratified mixture is made more optimal, and the thermal efficiency can be improved.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a configuration diagram of a direct in-cylinder spark ignition engine according to an embodiment of the present invention.
[0024]
FIG. 2 shows a plan view of the engine body.
Referring to these drawings, in the figure, 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 cylinder head 2. The combustion chamber formed between the inner wall surface and the crown surface of the piston 3 is shown.
[0025]
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 positioned substantially opposite to the intake port 5 is formed on the other side.
[0026]
The intake port 5 is connected to a branch portion of the intake manifold 7 to form an intake passage, and introduces intake air into the combustion chamber 4. The exhaust port 6 is connected to a branch portion of the exhaust manifold 8 to form an exhaust passage, and exhausts the exhaust from the combustion chamber 4.
[0027]
Here, the intake port 5 communicates with the combustion chamber 4 at an angle at which it is easy to form a swirling flow in the vertical direction (arrow a) of the intake air in the combustion chamber 4, and a tumble flow generation valve (not shown) is provided in the intake passage. Thus, a strong tumble flow is formed to stratify the air-fuel mixture during combustion at an ultra lean air / fuel ratio.
[0028]
An intake valve 9 is interposed in the opening of the intake port 5, and an exhaust valve 10 is interposed in the opening of the exhaust port 6.
The intake valve 9 and the exhaust valve 10 have respective valve shaft end portions in contact with the top inner surfaces of the covered cylindrical valve lifters 11 and 12, and an intake valve operating cam 13 and a sliding contact with the top portions of the valve lifters 11 and 12, The reciprocating motion is performed by the function of the exhaust valve operating cam 14.
[0029]
An ignition plug 15 is embedded in the cylinder head 2 so as to be positioned substantially in the center of the combustion chamber 4, and a fuel injection valve 16 is embedded in a side portion near the intake valve 9, and combustion is performed from the fuel injection valve 16. The fuel is directly injected into the chamber 4.
[0030]
Further, the cylinder head 2 is formed with a sub-intake port 17 having a smaller diameter than the intake port 5.
The auxiliary intake port 17 is connected to a port portion branched in a part of the branch of the intake manifold 7 as shown in the figure, avoiding the ignition plug 15 above the combustion chamber 4, and connecting the fuel injection valve 16 and the ignition plug 15. An auxiliary intake passage is formed in communication with the combustion chamber 4 in the vicinity of the exhaust valve 10 on the connecting extension.
[0031]
An auxiliary intake valve 18 is interposed in the opening of the auxiliary intake port 17.
The auxiliary intake valve 18 is slidably inserted into a valve guide (not shown) and receives an acting force in the valve closing direction by a valve spring (not shown).
[0032]
The auxiliary intake valve 18 is slidably contacted with an auxiliary intake valve operating cam 20 via a variable rocker arm 19 described later, and reciprocates so as to open at a predetermined time under specific operating conditions of the engine.
[0033]
The variable rocker arm 19 is controlled based on the output signal of the engine control unit 23 that receives the detection signals of the accelerator opening sensor 21 and the crank angle sensor 22.
[0034]
With reference to FIG. 3, the valve operating mechanism of the auxiliary intake valve 18 will be described.
The camshaft 31 shown in FIG. 3 includes the exhaust valve operating cam 14, and the sub-intake valve operating cam 20 is integrally formed on the shaft, so that the camshaft 31 is rotationally driven by a crankshaft (not shown). Thus, power is transmitted to the exhaust valve 10 and the auxiliary intake valve 18.
[0035]
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 reciprocates by the function of the auxiliary intake valve operating cam 20 whose valve shaft end abuts against the bottom surface of the variable rocker arm 19 and slidably contacts the upper surface of the variable rocker arm 19.
[0036]
The variable rocker arm 19 includes an operation rocker arm 19a and a stop rocker arm 19b, and these are separately mounted on the rocker shaft 32 as separate members.
[0037]
The variable rocker arm 19 has a built-in hydraulic piston 33 for connecting and separating the arms 19a and 19b.
The hydraulic piston 33 according to the present embodiment is a single-acting type (one cylinder chamber) utilizing a reaction force of an elastic body (spring or the like), and is not shown from an oil pump (not shown). The hydraulic oil is in circulation.
[0038]
The auxiliary intake valve operating cam 20 includes an operating portion 20a having a cam shape in cross section and a circular stopping portion 20b corresponding to the arms 19a and 19b.
[0039]
The auxiliary intake valve 18 is in contact with the bottom surface of the stop rocker arm 19b.
Here, if a hydraulic pressure lower than the reaction force of the elastic body is applied to the hydraulic piston 33, the arms are driven separately and the auxiliary intake valve 18 is deactivated.
[0040]
On the other hand, if a higher hydraulic pressure is applied, the piston moves in the cylinder to connect the arms, and the arms are driven together, so that the auxiliary intake valve 18 opens at a predetermined timing.
[0041]
FIG. 4 shows valve lifts in the ultra-lean air-fuel ratio region. Of the curves, Le represents an exhaust valve, Li1 represents an intake valve, and Li2 represents a sub-intake valve.
When the engine is operated at an ultra lean air / fuel ratio, the fuel injection timing is late in the compression stroke due to demands for fuel transportation and spray shape.
[0042]
At this time, in a low rotational speed region such as an idle region, the swirl flow of the intake air is weakened, and the tumble flow is attenuated / collapsed during the compression stroke, so that the injected fuel is dispersed in the combustion chamber 4 and the air-fuel mixture Is not stratified.
[0043]
This causes abnormal combustion.
For this reason, the function of the variable rocker arm 19 described above opens the auxiliary intake valve 18 before and after fuel injection in the idle range (FIG. 4a), and deactivates the auxiliary intake valve 18 outside the idle range (FIG. 4b). .
[0044]
Here, it is preferable to set the valve opening period (operating angle θa) from the start of fuel injection (crank angle (CA) = Ai1) to ignition (CA = Aig) (θb in the figure).
In this embodiment, the operating angle θa and the valve lift L are made minute, 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. .
[0045]
As described above, when the auxiliary intake valve 18 is temporarily opened in the latter half of the compression stroke, a gas flow as indicated by an arrow in FIG.
This gas flow is caused by a gas in the combustion chamber leaking to the auxiliary intake port 17 due to a pressure difference between the combustion chamber 4 and the auxiliary intake port 17, and the pressure fluctuation extends throughout the combustion chamber 4. The fuel spray injected from 16 is accelerated from the tip of the fuel injection valve 16 toward the spark plug 15.
[0046]
As a result, the fuel spray is transported to the vicinity of the spark plug 15 and the air-fuel mixture is stratified.
On the other hand, the swirl flow of the intake air is strong outside the idling region, and the tumble flow does not collapse during the compression stroke. Therefore, the air-fuel mixture can be stratified without opening the auxiliary intake valve 18.
[0047]
As another embodiment, in order to further improve the fuel transportation efficiency, a shroud 61 for restricting the leakage direction of the combustion chamber gas is provided in the umbrella portion of the auxiliary intake valve 18 as shown in FIGS. Also good.
[0048]
As shown in FIGS. 7 and 8, the shroud 61 is installed 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 viewed from the spark plug 15.
Accordingly, the substantially central portion of the umbrella portion of the auxiliary intake valve 18 is arranged so as to be positioned above the edge of the recess provided on the piston crown when the auxiliary intake valve 18 is fully closed.
[0049]
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 recess edge of the piston crown surface is D2. In order to satisfy the following equation (1):
[0050]
D1≈D2 (1)
According to the above configuration, the leakage of the combustion chamber gas behind the valve shaft as viewed from the spark plug 15 is regulated by the shroud 61, and as shown in FIG. 9, the exhaust valve 10 (sub intake valve 18) side of the combustion chamber 4 is located. The flow in the vicinity of the wall surface is weakened, and the flow from the tip of the fuel injection valve 16 toward the spark plug 15 is strengthened.
[0051]
As a result, the fuel spray is reliably and quickly transported to the vicinity of the spark plug 15, so that combustion can be further stabilized, and the operating angle θa of the auxiliary intake valve 18 and the valve lift L can be set smaller. , Energy loss due to leakage can be reduced.
[0052]
Further, the pressure fluctuation due to the leak is optimally formed in the combustion chamber 4 and the acceleration in the direction of the spark plug 15 as shown by the arrow b is given to the gas in the concave portion of the piston crown surface. The sprayed fuel is guided toward the spark plug 15 as indicated by an arrow c.
[0053]
As a result, the air-fuel mixture is stratified more optimally, so that the thermal efficiency can be improved.
As described above, according to the present invention, when the engine is operated at an ultra lean air / fuel ratio, the fuel spray can be reliably transported to the vicinity of the spark plug 15 even after the tumble flow collapses. Stratified combustion is possible, and 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 a direct cylinder injection type spark ignition engine main body. FIG. 4 is a diagram showing a mechanism. FIG. 4 is a diagram showing a relationship between a crank angle and a valve head. FIG. 5 is a diagram showing a gas flow in a combustion chamber according to an embodiment of the present invention. FIG. 7 is a view showing an example of installation of a shroud. FIG. 8 is a plan view of a direct in-cylinder injection spark ignition engine body according to another embodiment of the present invention. 9] Diagram showing the gas flow in the combustion chamber according to the embodiment.
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 Spark Plug 16 Fuel Injection Valve 17 Sub Intake Port 18 Sub Intake Valve 19 Variable Rocker Arm 20 Sub 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

Claims (6)

An ignition plug disposed substantially in 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, an exhaust valve for opening and closing an exhaust passage for discharging exhaust from the other side, and the vicinity of the intake valve In a direct in-cylinder injection spark ignition engine configured to include a fuel injection valve that directly injects fuel into the combustion chamber,
A sub intake passage that branches from the intake passage and communicates with a combustion chamber in the vicinity of the exhaust valve on the side opposite to the fuel injection valve with respect to the ignition plug ;
A direct in-cylinder injection spark ignition engine provided with an auxiliary intake valve interposed at an opening of the auxiliary intake passage and opened at a predetermined time under a specific operating condition of the engine.   The direct in-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 rotation speed region. The auxiliary intake valve, while the valve opening at a predetermined time during the up ignition by jetting or al the spark plug of the fuel by the fuel injection valve, and characterized in that the valve lift and operating angle and small The direct in-cylinder injection type spark ignition engine according to any one of claims 1 to 3.   The direct in-cylinder injection according to any one of claims 1 to 4, wherein a shroud for restricting ventilation of a valve shaft rearward as viewed from the spark plug is provided in an umbrella portion of the auxiliary intake valve. Type spark ignition engine.   6. The structure according to claim 1, wherein when the auxiliary intake valve is fully closed, the substantially central portion of the umbrella portion of the auxiliary intake valve is located above the edge of the recess provided in the piston crown surface. The direct in-cylinder injection spark ignition engine according to claim 1.

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