JP2867772B2 - 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 An ignition plug is disposed at the center of an inner wall surface of a cylinder head, and a fuel injection valve is disposed at a peripheral portion of the inner wall surface of the cylinder head. The fuel injection valve is gradually expanded from below the ignition plug toward the fuel injection valve. While a groove defined by a pair of side walls extending substantially straight and a substantially flat bottom wall is formed on the piston top surface, and the piston top surface around the groove is shown in FIG.
As shown by a broken line 2'a in FIG. 3, a substantially conical surface extending downward from the center of the piston top surface toward the peripheral portion of the piston top surface is formed. When the fuel injection timing is advanced, the fuel injection valve mainly The fuel is obliquely injected toward the conical piston top surface 2'a around the groove, and when the fuel injection timing is delayed, the fuel is injected obliquely from the fuel injection valve toward the bottom wall surface of the groove. The applicant has already proposed a direct injection type internal combustion engine in which the injected fuel colliding with the bottom wall of the groove is directed along the side wall surface of the groove toward the end of the groove below the ignition plug (Japanese Patent Application No. 2002-214,197). (See Japanese Unexamined Patent Publication No. Hei 3-160636)

In this direct injection type internal combustion engine, when the fuel injection timing is advanced, the injected fuel mainly collides with the conical piston top surface 2'a around the concave groove to diffuse the fuel into the combustion chamber. As a result, an air-fuel mixture as uniform as possible is formed in the combustion chamber, and when the fuel injection timing is delayed, fuel is injected into the groove to collect the air-fuel mixture around the spark plug.

[0004]

As described above, in this direct injection type internal combustion engine, when the fuel injection timing is advanced, the injected fuel mainly has a conical piston top surface 2 'around the concave groove.
12, the piston top surface portion 2'a on which the injected fuel collides is lowered in the direction of travel of the injected fuel, as shown in FIG. The angle between the fuel F 'and the collision angle θ' becomes considerably small. However, the atomization effect of the fuel based on the collision effect is promoted as the collision angle θ 'is increased. Therefore, when the collision angle is small as shown by θ' in FIG. Can not be converted.

[0005] When the collision angle θ 'is small, the horizontal velocity component of the injected fuel F' after the collision is large, and the traveling direction of the injected fuel F 'after the collision is close to the horizontal direction as shown by the arrow. Therefore, the distance from the collision point to the inner wall surface of the cylinder bore along the traveling direction of the injected fuel F 'becomes shorter. That is,
The time from when the injected fuel F 'collides with the piston top surface portion 2'a to when the reflected injected fuel F' reaches the inner wall surface of the cylinder bore is shortened. As a result, the reflected fuel F 'is not sufficiently vaporized during this time, and thus the amount of the injected fuel adhering to the inner wall surface of the cylinder bore increases, thereby causing a problem that the lubricating oil is diluted by the injected fuel.

[0006]

According to the present invention, an ignition plug is disposed at the center of the inner wall surface of a cylinder head, and a fuel injection valve is disposed at a peripheral portion of the inner wall surface of the cylinder head. A groove defined by a pair of side wall surfaces and a flat bottom wall surface, which gradually expands from the lower part of the spark plug toward the fuel injection valve, is formed on the piston top surface, and the groove is formed. The top surface of the piston, except for, is formed as a flat surface that is almost perpendicular to the cylinder axis, and when the fuel injection timing is advanced, the fuel is injected diagonally from the fuel injection valve mainly toward the flat piston top surface around the concave groove. Jet,
When the fuel injection timing is delayed, the fuel is injected obliquely from the fuel injection valve toward the bottom wall surface of the groove, and the injected fuel colliding with the bottom wall surface of the groove extends along the side wall surface of the groove, and the end of the groove below the ignition plug. To the club.

[0007]

By forming the piston top surface as a flat surface substantially perpendicular to the cylinder axis, θ in FIG.
As shown by, the collision angle of the injected fuel F increases.

[0008]

1 and 2, reference numeral 1 denotes a cylinder block, 2 denotes a piston which reciprocates 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 8 a which are arranged 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 between 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 over the entire valve open period. 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 arranged 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. Therefore, when the exhaust valve 7 opens, the opening formed between the exhaust valve 7 and the valve seat 11 It opens into the combustion chamber 4.

In the cylinder head 3, an air supply port 12 is formed for the air supply valve 6, and an exhaust port 13 is formed for the exhaust valve 7. On the other hand, a pair of fuel injection valves, that is, a first fuel injection valve 14a and a second fuel injection valve 14b are arranged at the peripheral portion of the cylinder head inner wall surface 3a near each air supply valve 6, as can be seen from FIG. These fuel injection valves 14a,
Fuel is injected from 14b in the cylinder axis direction.

As shown in FIGS. 1 and 3, the fuel injection valve 14 is provided on the top surface of the piston 2 from below the spark plug 10.
A concave groove 15 is formed to extend below the distal ends of the a and b . The groove 15 is formed at a groove end 15a below the ignition plug 10.
, Are defined by a pair of side wall surfaces 15b extending straight and gradually expanding toward the fuel injection valves 14a and 14b , and a flat bottom wall surface 15c. Further, as can be seen from FIG. 3, the end 15a of the concave groove is formed between the ignition plug 10 and the fuel injection valve 1.
It is formed on a vertical plane KK passing through the middle between 4a and 14b, and each side wall surface 15b has a symmetrical shape with respect to this vertical plane KK. Therefore, the concave groove 15 has a vertical plane K
It will have a symmetrical shape with respect to -K. Also,
When the piston 2 reaches the top dead center as shown in FIG.
A squish area 16 is formed between the top surface of the cylinder head and the cylinder head inner wall surface portion 3c.

As shown in FIG. 4, shown in FIGS.
In the embodiment, the exhaust valve 7 opens before the air supply valve 6 and the exhaust valve 7 is opened.
The valve 7 closes before the air supply valve 6. Also, in FIG.
I _lIndicates the fuel injection timing during low engine load operation.
And I_m1And I_m2Is the fuel during medium load operation of the engine.
The fuel injection timing._h1And I_h2Means high engine load
This shows the fuel injection timing during operation. From Fig. 4
Fuel Injection I at High Load Operation_h1And I_h2Is exhaust
This is performed when the valve 7 is closed, and is performed during engine low load operation.
Fuel injection I_lIs much later than during high-load operation.
You can see what happens. In addition, during engine middle load operation, 2
Fuel injection I_m1And I_m2Is done at this time
First fuel injection I_m1Is almost the same as during high engine load operation
The second fuel injection I_m2Means engine low load luck
It can be seen that the operation is performed at about the same time as the turning.

In the embodiment shown in FIGS. 1 to 3, the fuel injection _Il during the low engine load operation and the second fuel injection _Im2 during the intermediate engine load operation are performed by the first fuel injection valve 14a. , the first fuel injection I _m1 during in the engine load operation performed by the second fuel injection valve 14b, the fuel injection at the time of engine high load operation I _h1 and I _h2
Is performed by both the first 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 via 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 each of the fuel injection valves 14a and 14b is thereafter started.

Next, with reference to FIGS. 6 to 8, a description will be given of the fuel injection method at the time of low load operation of the engine, at the time of medium load operation of the engine and at the time of high load operation of the engine. FIG. 6 shows the fuel injection _Il during the low engine load operation and the second fuel injection _Im2 during the medium engine load operation.
Shows the fuel injection I _h2 in the first fuel injection I _m1 and engine high load operation during medium load operation the engine, Figure 8 shows a fuel injection I _h1 at the time of engine high load operation.

As shown in FIG. 6, fuel is injected obliquely from the fuel injection valve 14a toward the concave groove bottom wall surface 15c during the second fuel injection during the low engine load operation and the medium engine load operation. This 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. 9, the dashed line R indicates the collision area of the injected fuel on the groove bottom wall surface 15c, and the arrows F ₁ ,
F ₂ shows two typical flow of injected fuel. As shown in FIG. 9, the injected fuels F ₁ and F ₂ are supplied to the bottom wall 1 of the groove.
Even after the collision on the groove 5c, it proceeds in the injection direction by the inertial force, and then proceeds to the groove side wall surface 15b, and then proceeds to the groove side wall surface 15b.
Along the groove end 15a. By the way, each groove side wall surface 15b is connected to the fuel injection valve 1 from the groove end 15a.
4a, 14b , the incident angle θ of each of the injected fuels F ₁ , F ₂ with respect to the concave groove side wall surface 15b.
₁ and θ ₂ become smaller as the injected fuel is closer to the injection center. Therefore, the flow velocities υ ₁ and υ ₂ of the injected fuels F ₁ and F ₂ when the fuel starts to proceed along the groove side wall surface 15b are equal to the injection fuel. Injected fuel closer to the center is faster.

On the other hand, as shown in FIG.
The contour of the groove 15 'formed on the top surface of the ton 2'
A flat bottom of the groove 15 'from the fuel injection valve 14'
When fuel is injected onto the wall surface 15c ', the groove side wall surface 15b'
Each injected fuel F₁', F_Two'Incident angle θ₁', Θ
_Two′ Is larger for injected fuel closer to the injection center,
When it begins to proceed along the concave groove side wall surface 15b '
Injected fuel F₁', F _Two′ Flow velocity υ₁´, υ_Two′
Injected fuel closer to the injection center is slower. But this is
Unya₁'> Υ_Two′, Each groove side surface 15
The fuel or air-fuel mixture flowing along b '
Gather at the end 15a 'and then at about the same time the groove end 1
Ascend along 5a 'to form an air-fuel mixture around spark plug 10.
Will be achieved. Therefore, in this case, almost all injections
A mixture is formed around the spark plug 10 by the fuel.
And therefore formed around the spark plug 10 at this time.
The concentration of the air-fuel mixture is determined by other methods than controlling the fuel injection amount.
Cannot be controlled. Like this
When the fuel injection amount is small, it is optimal around the spark plug 10.
When the fuel injection amount increases when trying to form an air-fuel mixture
, The mixture formed around the spark plug 10 becomes rich,
Thus, it is not possible to obtain good ignition by the ignition plug 10.
Not a large amount of unburned HC and C even if ignited
O will occur.

[0019] upsilon ₁ as shown contrast in FIG. 9 <
υ 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 There will be a time lag to reach the groove end 15a. As described above, each of the injected fuels F ₁ and F ₂ is in the groove end 15a.
If a time difference occurs between the fuel injection and the fuel injection, the mixture formed around the ignition plug 10 gradually becomes richer as time elapses. By controlling the time until the ignition is performed, the concentration of the air-fuel mixture formed around the ignition plug 10 when the ignition is performed can be controlled. In other words, the ignition plug 1 is controlled when the ignition is performed by controlling the ignition timing or the injection timing so that the mixture having the optimum concentration is formed around the ignition plug 10 when the ignition is performed.
An optimum air-fuel mixture can always be formed around zero. Therefore, if the concave groove 15 having the shape as shown in FIG. 9 is used, it is possible to secure good ignition by the ignition plug 10 regardless 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 due to the inertial 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 swirl flow X. Also,
When the piston 2 further approaches the top dead center, an arrow S in FIG.
As shown by, the squish flow is ejected from the squish area 16, and this squish flow S also advances along the groove bottom wall surface 15c. Accordingly, 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, fuel injection by the second fuel injection valve 14b is started when the piston 2 is at the low position as shown in FIG. During operation, when the piston 2 is at the low position as shown in FIGS. 7 and 8, fuel injection by both the second fuel injection valve 14b and the first fuel injection valve 14a is started. Ra and Rb in FIG. 11 represent the fuel injection valves 14a, 14a with respect to the piston top surface 2a at this time.
4b shows the collision area of the injected fuel from 4b.

As can be seen from FIG.
The fuel injected from the fuel injection valves 14a and 14b mainly
15 hits on the flat top surface 2a of the piston
Thus, the injected fuel is dispersed in the combustion chamber 4.
Become. At the time of engine middle load operation, the first fuel injection I_m1To
Therefore, a lean mixture is formed in the combustion chamber 4, and the lean mixture is formed.
The mixture is the second fuel injection I_m2Around spark plug 10
The air-fuel mixture formed as the ignition source burns
You. On the other hand, during high engine load operation, the injected fuel I _h1,
I_h2The air-fuel mixture formed in the combustion chamber 4 by the ignition plug 10
Is ignited.

In the embodiment according to the present invention, the groove 15
Since the surrounding piston top surface 2a is formed as a flat surface, the collision angle of the injected fuel F with respect to the flat piston top surface 2a increases as indicated by θ in FIG. When the collision angle θ increases, the atomization of fuel due to the collision action is promoted, so that the injected fuel is favorably diffused into the combustion chamber 4. As a result, the injected fuel is mixed well with the air, and thus good combustion is obtained.

When the collision angle θ increases, the amount of fuel atomized by the collision action increases, so that the amount of fuel scattered toward the inner wall surface of the cylinder bore after the collision decreases. When the collision angle θ further increases, the horizontal velocity component of the injected fuel F after the collision decreases, and the traveling direction of the injected fuel F after the collision becomes upward as indicated by the arrow. The distance to the inner wall surface of the cylinder bore along the traveling direction becomes longer. That is, the time from when the injected fuel F collides with the piston top surface 2a to when the reflected injected fuel F reaches the inner wall surface of the cylinder bore becomes longer.

When the piston top surface 2a is formed from a flat surface as described above, the amount of fuel reflected after the collision decreases, and the time required to reach the inner wall surface of the cylinder bore after the collision becomes longer, so that the reflected fuel reaches the inner wall surface of the cylinder bore. It is considerably vaporized by then. As a result, the amount of the injected fuel adhering to the inner wall surface of the cylinder bore is reduced, so that the dilution of the lubricating oil by the injected fuel can be suppressed. Further, when the piston top surface 2a is formed as a flat surface, the surface area of the piston top surface 2a is reduced, so that there is an advantage that heat loss can be reduced and thus thermal efficiency can be improved.

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

[0027]

By forming the piston top surface from a flat surface, it is possible to suppress the dilution of the lubricating oil by the injected fuel while promoting the atomization of the fuel colliding with the piston top surface.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a two-stroke engine.

FIG. 2 is a bottom view of the cylinder head.

FIG. 3 is a plan view of a piston top surface.

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 a side cross-sectional view of the two-stroke engine showing a first fuel injection during a medium load operation and a fuel injection during a high load operation.

FIG. 8 is a side sectional view of the two-stroke engine showing fuel injection during high-load operation.

FIG. 9 is a plan view of a piston top surface similar to FIG. 3;

FIG. 10 is a plan view of a piston top surface showing an undesirable example.

FIG. 11 is a plan view of a piston top surface showing a collision area of injected fuel.

FIG. 12 is a side sectional view of the two-stroke engine for explaining the collision angle of the injected fuel.

[Explanation of symbols]

 2a: piston top surface 10: spark plugs 14a, 14b: fuel injection valve 15: concave groove 15a: concave groove end 15b: concave groove side wall surface 15c: concave groove bottom wall surface

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Nakata 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-1-203613 (JP, A) JP-A-2-125911 (JP, A) Japanese Utility Model 1-124042 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) F02B 1/00-23/10

Claims (1)

(57) [Claims] An ignition plug is arranged at the center of an inner wall surface of a cylinder head, a fuel injection valve is arranged at a peripheral portion of an inner wall surface of the cylinder head, and is gradually expanded from below the ignition plug toward the fuel injection valve. A concave groove defined by a pair of side wall surfaces extending straight and a flat bottom wall surface is formed on the piston top surface, and the piston top surface excluding the concave groove is formed into a flat surface substantially perpendicular to the cylinder axis. When the fuel injection timing is advanced, the fuel is injected obliquely from the fuel injection valve mainly toward the flat piston top surface around the groove, and when the fuel injection timing is delayed, the fuel injection valve forms the groove. An in-cylinder injection internal combustion engine in which fuel is injected obliquely toward the bottom wall surface of the groove and the injected fuel colliding with the bottom wall surface of the groove is directed along the side wall surface of the groove toward the end of the groove below the spark plug.