JP2936806B2 - In-cylinder 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 a direct injection internal combustion engine.

[0002]

2. Description of the Related Art A groove is formed on the top surface of a piston to inject fuel into the groove from a fuel injection valve at the end of a compression stroke during low engine load operation, and at the beginning of an intake stroke during high engine load operation. 2. Description of the Related Art A direct injection internal combustion engine in which fuel is injected into a concave groove is known (see JP-A-2-169834). In this internal combustion engine, during engine low load operation with a small fuel injection amount, fuel is injected into the groove at the end of the compression stroke to form an ignitable mixture around the spark plug, and engine high load operation with a large fuel injection amount Sometimes, a fuel-air mixture is formed in the combustion chamber by injecting fuel into the groove at the beginning of the intake stroke.

[0003]

However, even when fuel is injected into the groove during high engine load operation as described above, a large amount of homogeneous fuel-air mixture is promoted by promoting the atomization of a large amount of injected fuel into the combustion chamber. It is difficult to form.

[0004]

According to the present invention, an ignition plug is disposed at the center of an inner wall surface of a cylinder head, and a pair of fuel injection valves is provided at a peripheral portion of the inner wall surface of the cylinder head. In parallel, a groove is formed on the top surface of the piston and extends from below the spark plug toward these fuel injection valves, and fuel is injected from one of the fuel injection valves into the groove during low engine load operation. The peripheral edge of the center of the piston top surface spreading around the end of the groove below the spark plug is formed from an upwardly convex corner so that fuel can flow from a pair of fuel injection valves toward the center of the piston top surface during high engine load operation. And the fuel spray injected from each fuel injection valve is directed toward the center of the piston top surface so as to cross each other during flight.

[0005]

When the fuel spray injected from each fuel injection valve intersects during flight during high engine load operation, the first fuel atomization action is performed, and the injected fuel collides with the center of the piston top surface. Sometimes the second atomization of fuel is performed,
After the fuel flowing on the center of the piston top surface after colliding with the center of the piston top surface passes through the corner of the peripheral edge of the center of the piston top surface, the third atomization of the fuel is performed.

[0006]

2 and 3, reference numeral 1 denotes a cylinder block, 2 denotes a piston reciprocating in the cylinder block 1, 3 denotes a cylinder head fixed on the cylinder block 1, and 4 denotes a cylinder head. The combustion chamber formed between the wall surface 3a and the top surface of the piston 2 is shown. A concave groove 5 is formed on the cylinder head inner wall surface 3a, and a pair of air supply valves 6 are arranged on the cylinder head inner wall surface portion 3b that forms the bottom wall surface of the concave groove 5. On the other hand, the cylinder head inner wall surface portion 3c excluding the concave groove 5 is inclined and substantially flat, and three exhaust valves 7 are arranged on the cylinder head inner wall surface portion 3c. The cylinder head inner wall surface portion 3b and the cylinder head inner wall surface portion 3c are connected to each other via the peripheral wall 8 of the concave groove 5.

The peripheral wall 8 of the concave groove is located between the pair of mask walls 8a, which are disposed very close to the peripheral edge of the air supply valve 6 and extend in an arc along the peripheral edge of the air supply valve 6, and the air supply valve 6. And a pair of fresh air guide walls 8c located between the supply wall 6 and the peripheral wall of the cylinder head inner wall surface 3a. Each mask wall 8a extends toward the combustion chamber 4 below the intake valve 6 at the maximum lift position, so that the opening between the peripheral portion of the intake valve 6 located on the exhaust valve 7 side and the valve seat 9 is formed. The air supply valve 6 is closed by the mask wall 8a throughout the opening period of the air supply valve 6. In addition, each fresh guide wall 8
The fresh air guide walls 8b and 8c extend substantially parallel to a line connecting the centers of the two air supply valves 6. The ignition plug 10 is disposed on the cylinder head inner wall surface portion 3c so as to be located at the center of the cylinder head inner wall surface 3a. On the other hand, the exhaust valve 7 is not provided with a mask wall that covers the opening between the exhaust valve 7 and the valve seat 11, so that when the exhaust valve 7 is opened, the exhaust valve 7
The entire opening formed between the valve seat 11 and the valve seat 11 opens into the combustion chamber 4.

An air supply port 12 is formed in the cylinder head 3 for the air supply valve 6, and an exhaust port is formed for the exhaust valve 7.
13 is formed. On the other hand, a pair of fuel injection valves, that is, a first fuel injection valve,
A fuel injection valve 14a and a second fuel injection valve 14b are arranged, and fuel is injected from the fuel injection valves 14a and 14b into the combustion chamber 4.

As shown in FIG. 1 and FIG. 2, the fuel injection valves 14a, 14a,
A concave groove 15 extending below the tip of 14b is formed. The groove 15 extends from the groove end 15a below the spark plug 10 to the fuel injection valve.
The groove end 15a is defined by a pair of side wall surfaces 15b extending toward the sides 14a and 14b while gradually expanding and a substantially flat bottom wall surface 15c. As shown in FIG. It is formed from a wall extending in the direction. FIG.
As can be seen, the groove end 15a is the ignition plug 10 and the fuel injection valve.
It is formed on a vertical plane KK passing through the center between 14a and 14b, and each side wall surface 15b has a symmetrical shape with respect to this vertical plane KK. Accordingly, the concave groove 15 has a symmetrical shape with respect to the vertical plane KK.

On the other hand, as shown in FIGS. 1 and 2, a center portion 16 of the piston top surface is formed at the center of the top surface of the piston 2 and extends around the groove end 15a. It is formed of a conical surface that gradually descends toward the groove 15. The peripheral edge 16a of the central portion 16 of the piston top surface is formed from a corner that is upwardly convex over the entire length.
As shown in FIG. 2, when the piston 2 reaches the top dead center, there is a gap between the top surface of the piston 2 located on the opposite side of the groove 15 with respect to the ignition plug 10 and the inner wall surface portion 3c of the cylinder head. A squish area 17 is formed.

As shown in FIG. 4, in the embodiment shown in FIGS. 1 to 3, the exhaust valve 7 opens before the air supply valve 6, and the exhaust valve 7 closes before the air supply valve 6. I do. Further, Il in Figure 4 shows the fuel injection timing at the time of engine low load operation, Im ₁ and Im ₂ shows the fuel injection timing during in the engine load operation, Ih _1, Ih ₂ high engine load This shows the fuel injection timing during operation. From FIG. 4, the fuel injections Ih ₁ and Ih ₂ during the high engine load operation are performed when the exhaust valve 7 is closed, and the fuel injection Il during the low engine load operation is performed much later than during the high load operation. It is understood that it is done. Further, the fuel injection Im ₁ and Im ₂ in twice is performed at the time during the engine load operation, the fuel injection Im ₁ of the first round this time is performed at a time substantially the same as the time of engine high load operation, the second time It can be understood that the fuel injection Im ₂ is performed at substantially the same time as during the low-load operation of the engine.

In the embodiment shown in FIGS. 1 to 3, the fuel injection Il at the time of low engine load operation and the second fuel injection Im ₂ at the time of medium engine load operation are performed by the first fuel injection valve.
Performed by 14a, the first fuel injection Im ₁ when while the engine load operation is carried out by the second fuel injection valve 14b, the fuel injection Ih ₁ and Ih ₂ at the time of engine high load operation is first
This is performed by both the fuel injection valve 14a and the second fuel injection valve 14b.

As shown in FIG. 5, when the air supply valve 6 and the exhaust valve 7 are opened, air flows into the combustion chamber 4 through the air supply valve 6. At this time, since the opening of the air supply valve 6 on the exhaust valve 7 side is covered by the mask wall 8a, air is
The gas flows into the combustion chamber 4 from the opening of the air supply valve 6 on the side opposite to the side a. This air descends along the inner wall surface of the cylinder bore below the air supply valve 6 as indicated by the arrow W, and then travels along the top surface of the piston 2 and rises along the inner wall surface of the cylinder bore below the exhaust valve 7, and Will flow in a loop in the combustion chamber 4. The burned gas in the combustion chamber 4 is discharged through the exhaust valve 7 by the air W flowing in the loop, and the swirling flow X swirling in the vertical plane in the combustion chamber 4 by the air W flowing in the loop. Is generated. Next, when the piston 2 starts rising after passing the bottom dead center BDC, fuel injection from the fuel injection valves 14a and 14b is thereafter started.

Next, with reference to FIGS. 6 to 11, a description will be given of a fuel injection method during low engine load operation, medium engine load operation and high engine load operation. FIG. 6 shows the fuel injection Il during the low engine load operation and the second fuel injection Im ₂ during the medium engine load operation.
Shows a first fuel injection Im ₁ during medium load operation the engine, Figure 10 shows a fuel injection Ih ₁ and Ih ₂ at the time of engine high load operation.

As shown in FIG. 6, at the time of the second fuel injection at the time of the engine low load operation and the engine middle load operation, the fuel is obliquely injected from the first fuel injection valve 14a toward the groove bottom wall surface 15c. . The injected fuel collides with the groove bottom wall surface 15c and then proceeds toward the groove end 15a along the groove side wall surface 15b. Next, the behavior of the injected fuel at this time will be described with reference to FIG. In FIG. 7, the chain line R is the bottom wall of the groove.
The collision area of the injected fuel on 15c is shown, and arrows F ₁ and F ₂ show two typical flows of the injected fuel. As shown in FIG. 7, the injected fuels F ₁ and F ₂ continue to travel in the injection direction due to the inertial force even after colliding on the groove bottom wall surface 15c.
Next, after proceeding to the groove side wall surface 15b, it proceeds toward the groove end portion 15a along the groove side wall surface 15b. By the way, each groove side wall surface 15b extends from the groove end 15a to the fuel injection valve 14a, 14b.
Since it extends almost straight toward the side, the concave groove side wall surface 15
The incident angles θ ₁ , θ ₂ of the injected fuels F ₁ , F ₂ with respect to b become smaller as the injected fuel is closer to the injection center.
Each injected fuel F when it starts to proceed along 15b
The flow velocities v ₁ , v ₂ of F ₁ and F ₂ increase as the injected fuel is closer to the injection center.

On the other hand, as shown in FIG.
The contour of the concave groove 15 'formed on the top surface of the
From the fuel injection valve 14 'to the flat bottom wall 15 of the concave groove 15'.
When fuel is injected onto c ', each of the
Injected fuel F₁', F_Two'Incident angle θ₁ ′, Θ_Two′ Is injection
The closer the injection fuel is to the center, the larger it is
Injected fuel F when it starts to proceed along 15b '
₁', F_Two'Flow velocity v₁', V_Two′ Is near the injection center
The slower the injected fuel, the slower it will be. However, like this ₁'>
v_Two′, The flow along each groove side wall surface 15b ′
The fuel or air-fuel mixture collected at the groove end 15a 'at about the same time.
And then rises along the groove end 15a 'at about the same time
As a result, an air-fuel mixture is formed around the ignition plug 10. Obedience
In this case, the ignition plug 10
A mixture is formed around the
The concentration of the mixture formed around the spark plug 10 is the fuel injection amount
Cannot be controlled by any method other than controlling
Will be. Thus, for example, when the fuel injection amount is small
Try to form the optimal mixture around spark plug 10
When the fuel injection amount increases, it is formed around the spark plug 10
The air-fuel mixture becomes excessively rich, thus
Not only can not get the ignition, even if the ignition
This also generates a large amount of unburned HC and CO.

On the other hand, as shown in FIG. 7, v ₁ <
v injected fuel F ₁ even ₂ becomes associated with the injected fuel F ₂ has reached the groove end portion 15a is still in progress toward the groove end 15a, so that each injection fuel F _1, F ₂ is concave Groove end
There will be a time difference to reach 15a. If a time lag occurs between each of the injected fuels F ₁ and F ₂ reaching the groove end 15a, the air-fuel mixture formed around the ignition plug 10 gradually becomes thicker as time passes. In this case, even if the fuel injection amount is constant, it is possible to control the concentration of the air-fuel mixture formed around the ignition plug 10 when the ignition is performed by controlling the time from the fuel injection to the ignition. . In other words, by controlling the ignition timing or the injection timing such that an optimum concentration of the mixture is formed around the ignition plug 10 when the ignition is performed, the optimum around the ignition plug 10 is always achieved when the ignition is performed. An air-fuel mixture can be formed. Therefore, if the concave groove 15 having the shape as shown in FIG. 7 is used, it is possible to secure good ignition by the ignition plug 10 irrespective of the fuel injection amount.

As described above, the injected fuel flows toward the lower side of the spark plug 10 on the groove bottom wall surface 15c by inertia force. By the way, as shown in FIG. 5, the swirling flow X generated in the combustion chamber 4 is attenuated as the piston 2 rises and the swirling radius gradually decreases, and as shown in FIG. 6, when the piston 2 approaches the top dead center. A swirling flow X along the groove bottom wall surface 15c is formed. Therefore, the injected fuel is given a force directed downward of the ignition plug 10 also by the swirling flow X. Also, piston 2
6 further approaches the top dead center, a squish flow is ejected from the squish area 17 as shown by an arrow S in FIG. Therefore, the squish flow S gives the injected fuel a downward force on the ignition plug 10. In addition, the fuel flowing down the spark plug 10 along the groove bottom wall surface 15c is vaporized by the swirl flow X and the squish flow S, and thus, the air-fuel mixture collected around the spark plug 10 is sufficiently vaporized. Become.

On the other hand, at the time of the first fuel injection during the engine middle load operation, as shown in FIG. 9, when the piston 2 is at the low position, the second fuel injection valve 14b moves toward the center 16 of the piston top surface. Fuel is injected. This injected fuel is atomized when it collides with the center 16 of the piston top surface, and the injected fuel that has not been atomized at this time is in a liquid form on the center 16 of the piston top surface, and the periphery of the center portion 16 of the piston top surface. Part 16a
Flows towards Peripheral part 16 of this piston top surface center part 16
Since a is a corner as described above, the fuel flowing on the central portion 16 of the piston top surface is separated from the piston top surface and atomized when passing through the peripheral portion 16a of the central portion 16 of the piston top surface. . As described above, during the first fuel injection during the engine middle load operation, the two-stage atomization action is performed, so that the injected fuel is atomized satisfactorily.
Inside, a homogeneous mixture is formed. This homogeneous mixture is made up of a lean mixture, and the lean mixture is burned by the _second fuel injection Im2 with the mixture formed around the ignition plug 10 serving as an ignition source.

On the other hand, at the time of engine high load operation, FIGS.
As shown in FIG. 11, fuel is injected from both the first fuel injection valve 14a and the second fuel injection valve 14b (not shown in FIG. 10) toward the center 16 of the piston top surface. Hatched area K ₁ in FIG. 11 shows the impact area against the piston 2 the top surface of the fuel injected from the first fuel injection valve 14a, the hatched region K ₂ has a piston of the fuel injected from the second fuel injection valve 14b 2 shows the collision area against the top surface. As can be seen from FIG. 11, each fuel injection valve 14a, 14
The fuel sprays injected from b cross each other during flight toward the center 16 of the piston top surface. When the fuel sprays intersect with each other in this manner, the fuel particles in each fuel spray collide with each other and split, thus atomizing the fuel. As described above, when the engine is under high load operation, the fuel atomization intersects with each other to perform the first atomization action. Next, when each fuel spray collides with the center 16 of the piston top surface, the second atomization action is performed, and the fuel flowing on the center 16 of the piston top surface passes through the peripheral portion 16a of the center 16 of the piston top surface. Then, a third atomization action is performed. As described above, during the high-load operation of the engine, the three-stage atomization action is performed, so that the injected fuel is atomized satisfactorily, and thus a sufficiently vaporized homogeneous mixture is formed in the combustion chamber 4. At the time of engine high load operation, this homogeneous mixture is ignited by the ignition plug 10.

When a swirling flow X as shown in FIG. 5 is generated in the combustion chamber 4, high-temperature burned gas tends to remain in the center of the combustion chamber 4 and is formed in the combustion chamber 4. When the air-fuel mixture is heated by the high-temperature burned gas, self-ignition and knocking are likely to occur. However, as shown in FIGS. 9 and 10, when the injected fuel flies in the center of the combustion chamber 4, the burned gas remaining in the center of the combustion chamber 4 is cooled by the injected fuel. As a result, the occurrence of self-ignition and knocking is suppressed.

Although the present invention has been described with reference to the case where the present invention is applied to a direct injection two-stroke engine, the present invention can also be applied to a direct injection four-cycle engine.

[0023]

According to the present invention, atomization of the injected fuel can be promoted at the time of high load operation of the engine with a large amount of fuel injection, and thus a sufficiently vaporized uniform mixture can be formed in the combustion chamber.

[Brief description of the drawings]

FIG. 1 is a plan view of a piston top surface.

FIG. 2 is a side sectional view of the two-stroke engine.

FIG. 3 is a bottom view of the cylinder head.

FIG. 4 is a diagram showing a valve open period of a supply / exhaust valve and a fuel injection timing.

FIG. 5 is a side sectional view of the two-stroke engine during a scavenging stroke.

FIG. 6 is a side cross-sectional view of a two-cycle engine showing fuel injection during low-load operation and second fuel injection during medium-load operation.

FIG. 7 is an enlarged plan view of the top surface of the piston shown in FIG. 6;

FIG. 8 is a plan view of a piston top surface showing an undesirable example.

FIG. 9 is a side cross-sectional view of the two-cycle engine showing the first fuel injection during the medium load operation.

FIG. 10 is a side sectional view of the two-stroke engine showing fuel injection during high-load operation.

11 is an enlarged plan view of a piston top surface shown in FIG.

[Explanation of symbols]

 2: Pistons 14a, 14b: Fuel injection valve 15: Groove 16: Center of piston top 16a: Peripheral edge

Continued on the front page (72) Inventor Hiroaki Nihei 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Koichi Nakata 1 Toyota Town Toyota City, Aichi Prefecture Toyota Motor Corporation (56) Reference Document JP-A-4-224229 (JP, A) JP-A-2-169834 (JP, A) JP-A-3-3934 (JP, A) JP-A-3-65864 (JP, U) JP-A-4-658 1652 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) F02B 23/10 F02D 41/04 F02D 41/34 F02F 3/26 F02M 61/14

Claims (1)

(57) [Claims] An ignition plug is disposed at the center of an inner wall surface of a cylinder head, and a pair of fuel injection valves are arranged side by side at a peripheral portion of the inner wall surface of the cylinder head. At the time of engine low load operation, fuel is injected from one of the fuel injection valves into the groove, and the center of the piston top surface spreading around the groove end below the spark plug is formed during engine low load operation. The peripheral edge is formed from an upwardly convex corner, and during high engine load operation, fuel is injected from the pair of fuel injection valves toward the center of the piston top surface, and the fuel spray injected from each fuel injection valve is injected into the piston top. An in-cylinder injection internal combustion engine that crosses each other during flight toward the center of the plane.