JP2001227345A - Fuel direct infection-type diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the atomization state of fuel when an injector performs sub fuel injection in timing different from main fuel injection, in a fuel direct injection-type diesel engine. SOLUTION: This fuel direct injection-type diesel engine has a recessed combustion chamber 22 facing a cylinder head 13 on a central part of the top surface 17a of a piston 17 slidably supported on a cylinder 16, and fuel is injected from an injector 23 supported on the cylinder head 13 toward the combustion chamber 22. The top surface 17a of the piston 17 for surrounding the combustion chamber 22 has no valve recess and formed into a flat shape, and sub fuel injection to be performed across main fuel injection by the injector 23 is directed to an opening end 22a of the combustion chamber 22. Accordingly, the sub fuel injection is not affected by the value recess formed by cutting the opening end 22a of the combustion chamber 22, and the atomization state of fuel formed by the sub fuel injection is uniformized in the circumferential direction of the combustion chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a piston which is slidably supported by a cylinder, and has a concave combustion chamber facing the cylinder head at the center of the top surface of the piston. The present invention relates to a direct-injection diesel engine that injects fuel toward a diesel engine.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication (Kokai) No. 4-153563 discloses a fuel direct injection diesel engine having a concave combustion chamber formed at the center of the top surface of a piston. In order to avoid interference between the valve element of the exhaust valve and the piston, a valve recess in which the valve element is fitted is formed on the top surface of the piston.

[0003]

Generally, in a diesel engine, a small amount of auxiliary fuel injection (hereinafter referred to as pilot fuel injection) is performed before main fuel injection to prevent an increase in combustion noise due to fuel ignition delay. It is known that a small amount of secondary fuel injection (hereinafter referred to as post fuel injection) is performed after the main fuel injection is performed in order to improve emission. Since these secondary fuel injections are performed when the piston is located slightly below the top dead center, the fuel that should be injected from the injector toward the interior of the combustion chamber is directed toward the open end of the combustion chamber. It will be injected.

In this case, since the valve recess is formed so as to cut off a part of the opening end of the combustion chamber, a part of the fuel injected from the injector collides with the opening end of the combustion chamber and the other part of the fuel is injected. Will collide with the valve recess. As a result, the atomization state of the fuel becomes uneven, and the effects of the pilot fuel injection and the post fuel injection may not be sufficiently exhibited.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to improve the atomization state of fuel when the injector performs sub-fuel injection at a timing different from the main fuel injection in a direct fuel injection diesel engine. With the goal.

[0006]

According to the first aspect of the present invention, a piston is slidably supported by a cylinder and is opposed to a cylinder head at a central portion of a top surface of the piston. In a fuel direct injection diesel engine that forms a concave combustion chamber and injects fuel toward the combustion chamber from an injector supported by a cylinder head, the top surface of a piston surrounding the combustion chamber is formed flat, and the injector is A direct fuel injection type diesel engine is proposed, wherein the sub fuel injection performed at a different timing from the main fuel injection is directed to the open end of the combustion chamber.

[0007] According to the above configuration, when the injector performs the sub fuel injection at the timing different from the main fuel injection toward the opening end of the combustion chamber, the top surface of the piston surrounding the combustion chamber is formed flat. Therefore, the atomized state of the fuel injected by the auxiliary fuel is made uniform in the circumferential direction of the combustion chamber, and problems such as emission, fuel consumption, noise, and deterioration of vibration can be avoided. Further, since the valve recess is not cut out at the open end of the combustion chamber of the piston, stress concentration on the open end is reduced, and the durability of the piston is improved. In particular, pilot injection is performed at the start of the diesel engine. However, since there is no valve recess at the top surface of the piston, the fuel does not stay in the valve recess in the form of droplets and the startability is not impaired.

The first curved portion 22a of the embodiment corresponds to the open end of the combustion chamber of the present invention.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on embodiments of the present invention shown in the accompanying drawings.

FIGS. 1 to 6 show an embodiment of the present invention. FIG. 1 is a view showing the overall structure of a diesel engine, FIG. 2 is a longitudinal sectional view taken along the cylinder axis of the engine, and FIG. FIG. 4 is a time chart showing fuel injection timing, FIG. 5 is an operation explanatory view of main fuel injection, and FIG.
FIG. 8 is an explanatory diagram of the operation of the auxiliary fuel injection.

As shown in FIG. 1, an in-line four-cylinder diesel engine E includes a crankcase 11 and a cylinder block 12 integrally formed on the upper part of the crankcase 11.
And a cylinder head 13 coupled to an upper part of the cylinder block 12 and an oil pan 14 coupled to a lower part of the cylinder block 12.
A rotatable crankshaft 15 and a piston 17 slidably fitted to a cylinder 16 formed inside the cylinder block 12 are connected via a connecting rod 18. The cylinder head 13 has two intake valves 19, 19 and two exhaust valves 20,
The intake valves 19, 19 and the exhaust valves 20, 20 are driven to open and close by a single camshaft 21 provided on the cylinder head 13 via a rocker arm (not shown). At the center of the top surface of the piston 17, a reentrant combustion chamber 22 is recessed, and an injector 23 is provided in the cylinder head 13 so as to face the center of the combustion chamber 22.

An intake manifold 25 connected to intake ports 24, 24 connected to the intake valves 19, 19,
The surge tank 26 is provided on the upstream side. An exhaust manifold 28 is connected to exhaust ports 27 connected to the exhaust valves 20. The air sucked into the intake passage 30 extending from the air cleaner 29 is pressurized by the intake side impeller 32 of the turbocharger 31 and supplied to the surge tank 26 via the intake passage 33. Exhaust gas discharged from the exhaust manifold 28 is driven to the exhaust side impeller 34 of the turbocharger 31 and then discharged to the outside through an exhaust gas purifying catalyst device 36 provided in an exhaust passage 35.

The fuel supplied from a low pressure pump 38 provided inside the fuel tank 37 is supplied to a high pressure pump 41 via a filter 40 provided in a low pressure feed pipe 39.
The pressurized fuel is supplied to the common rail 43 through the high-pressure feed pipe 42. The high-pressure fuel stored in the common rail 43 is supplied to the four injectors 23 at predetermined timing through four fuel injection pipes 44. Reference numeral 45 denotes a return pipe for returning excess fuel from the high-pressure pump 41 to the fuel tank 37. An EGR valve 50 is provided in the intake manifold 28 so as to return exhaust gas to an upstream position of the surge tank 26 via the EGR gas passage 46.

FIG. 2 is an enlarged vertical sectional view taken along a cylinder axis L of the engine E, and shows a state in which a piston 17 fitted to a cylinder 16 formed in the cylinder block 12 is at a top dead center. The intake valves 19, 19 and the exhaust valves 20, 20 have their stems 19a, 19a;
20a, 20a are arranged in parallel with the cylinder axis L, and the valve seats 47, 4 of the intake valves 19, 19 are arranged.
7 and the valve seats 48, 48 of the exhaust valves 20, 20
Is formed so as to depress the lower surface of the cylinder head 13. Therefore, when the intake valves 19, 19 and the exhaust valves 20, 20 are in the closed state shown in the figure, the valve body 1 of the intake valves 19, 19 and the exhaust valves 20, 20
9b, 19b; the height of the lower surface of 20b, 20b matches the height of the lower surface of the cylinder head 13.

As a result, even if the piston 17 reaches the top dead center, the top surface 17a has the valve bodies 19b and 19b of the intake valves 19 and 19 and the exhaust valves 20 and 20;
Since there is no possibility of interference with the lower surface of Ob, the annular top surface 17a of the piston 17 surrounding the combustion chamber 22 is a flat surface having no valve recess. When the piston 17 is at the top dead center, the lower surface of the cylinder head 13 and each valve 1
9, 19; 20, 20 valve bodies 19b, 19b;
The lower surface of 20b has a slight squish area 49 (see FIG. 5) between itself and the top surface 17a of the piston 17.

The shape of the combustion chamber 22 formed in the piston 17 is of a so-called reentrant type in which the diameter of the inlet is smaller than the maximum diameter inside. That is, as is apparent from FIG. 5, the vertical section of the combustion chamber 22 extends from the point a located at the boundary with the flat top surface 17a of the piston 17 to the point b located below the same toward the cylinder axis L. It is composed of a smooth first curved portion 22a which curves convexly. And b
The first straight portion 22b extends from the point to the point c located therebelow.
And from point c to point d below it,
It is composed of a smooth second curved portion 22c that is concavely curved toward the cylinder axis L, and is located above the point d from above.
The portion up to the point is constituted by the second straight portion 22d, and the portion from the point e to the point d on the cylinder axis L is constituted by a smooth third curved portion 22e which curves upward and convex. At points a to f, the portions located on both sides of each point are connected smoothly, and therefore, in the cross-sectional view shown in FIG. 4, the corners extend from the top surface 17 a of the piston 17 to the entire region of the combustion chamber 22. Does not exist at all.

The first curved portion 22 a of the combustion chamber 22 connected to the top surface 17 a of the piston 17 forms a cavity lip serving as an inlet of the combustion chamber 22. The first straight portion 22b is arranged so as to be inclined such that the point c at the lower end is more distant from the cylinder axis L than the point b at the upper end. The second curved portion 22c is
And the radius of the combustion chamber 22 is maximized near point c at the upper end. 2nd linear part 2
2d is arranged so that the point e at the upper end is closer to the cylinder axis L than the point d at the lower end, and is connected at the point e to the third curved portion 22e which rises up most at the position of the cylinder axis L. I do.

As shown in FIG. 4, the injector 23 starts the main fuel injection when the piston 17 reaches the top dead center (TDC), and also reduces the combustion noise accompanying the main fuel injection at the end of the compression stroke. The pilot fuel injection (sub fuel injection) for the purpose is performed. Also, post fuel injection (auxiliary fuel injection) for the purpose of improving emissions during the expansion stroke and exhaust stroke.

As apparent from FIGS. 3 and 5, the fuel injected from the injector 23 is directed obliquely downward, and is directed in five directions that are equally spaced in the circumferential direction. During the main fuel injection that is started when the piston 17 reaches the top dead center, the injected fuel is directed to the first linear portion 22b of the combustion chamber 22 of the piston 17. That is, the fuel injected in the region A (see FIG. 4) before and after the top dead center is directed to the first straight portion 22b of the combustion chamber 22 (see FIG. 5). On the other hand, when the pilot fuel injection is performed before the area A and when the post fuel injection is performed after the area A, the piston 17 is located below the top dead center. The first fuel 2 is the first curved portion 2 which is the open end of the combustion chamber 22 of the piston 17.
2a (see FIG. 6).

In this embodiment, since the injector 23 injects fuel in five directions at intervals of 72 °, as shown in FIG. 7, a total of four intake valves 19, 19 and exhaust valves 20, 20 are provided. Total 4 valve recesses 17
are formed, the valve recesses 17b are formed.
Is formed in a part of the first curved portion 22a in the circumferential direction, which is the open end of the combustion chamber 22, so that the fuel injected by the pilot fuel injection or the post fuel injection
b (see FIG. 7) and non-collision (see FIG. 6) occur, and as a result, the fuel atomization inside the combustion chamber 22 and the squish area 49 becomes uneven. Noise generation and emission deterioration may occur.

On the other hand, in the present embodiment, the valve recesses 17b are formed in the first curved portion 22a which is the open end of the combustion chamber 22.
Is not formed (see FIG. 6), all the fuel injected by the pilot fuel injection or the post fuel injection collides uniformly with the first curved portion 22a, and therefore the combustion chamber 22
And the squish area 49 are uniformly atomized, so that the effect of reducing noise by pilot fuel injection and the effect of improving emission by post fuel injection can be effectively exhibited.

Further, pilot fuel injection is generally performed when the diesel engine is started. However, since the piston 17 of this embodiment does not have the valve recesses 17b,
There is no danger that the fuel may stay in the valve recesses 17b in the form of droplets and impair the startability. The combustion chamber 22 of the piston 17
The first curved portion 22a, which is the open end of the
Are not formed, the stress concentration on the first curved portion 22a is reduced, and the durability of the piston 17 is also improved.

The fuel injected by the main fuel injection started when the piston 17 reaches the top dead center is shown in FIG.
As shown in FIG. 7, the fuel collides with the first straight portion 22b of the combustion chamber 22 of the piston 17, so that atomization of fuel inside the combustion chamber 22 and inside the squish area 49 is promoted, so that the combustion efficiency is improved, and the fuel consumption is improved. It can contribute to improvement of the rate, improvement of emission, prevention of generation of smoke, and the like.
This is because most of the fuel injected from the injector 23 and colliding with the first linear portion 22b is the first linear portion 22b.
B is guided downward along b, and flows toward the second curved portion 22c, which is a smooth curve having no corners, to generate swirl. On the other hand, part of the fuel that has collided with the first straight portion 22b is
It is guided upward along the first straight portion 22b and further supplied to the squish area 49 formed above the top surface 17a of the piston 17 by being guided by the first curved portion 22a having a smooth curve without corners. You. As a result, the combustion chamber 22
This is because it is possible to atomize the fuel uniformly inside the squish area 49 and inside the squish area 49.

In the case of direct fuel injection, since the injected fuel is directly applied to the combustion chamber 22 of the piston 17, the injected fuel is always burned due to the movement of the piston 17 during the fuel injection period or the shift of the fuel injection timing due to the operation state. It does not impinge on the same part of the chamber 22, but the part which the fuel impinges within a certain range is shifted. Therefore, the injector 23
If the fuel injected from the fuel injector is directed to a curved surface that is convexly curved toward the injector 23, the piston 1
The movement direction of the fuel after hitting the curved surface changes greatly according to the movement of the fuel cell 7 and the fuel injection timing, and there is a possibility that excess fuel is supplied to the squish area 49.
In contrast, in the present embodiment, the first straight portion 22 of the combustion chamber 22
Since the fuel is injected in the direction of b, a substantially constant amount of fuel can be supplied to the squish area 49 even if the position of the piston 17 changes up and down.

Although the embodiments of the present invention have been described in detail above, various design changes can be made in the present invention without departing from the gist thereof.

For example, the diesel engine E of the embodiment is an in-line four-cylinder engine, but the present invention can be applied to a V-type engine or an engine having a different number of cylinders. The diesel engine E of the embodiment has two intake valves 1
9, 19 and two exhaust valves 20, 20, but the number of intake valves and exhaust valves can be changed as appropriate.

[0027]

As described above, according to the first aspect of the present invention, when the injector performs the auxiliary fuel injection toward the opening end of the combustion chamber at a timing different from the main fuel injection, the combustion chamber is opened. Since the top surface of the surrounding piston is formed flat, the atomization state of the fuel injected by the auxiliary fuel is made uniform in the circumferential direction of the combustion chamber, causing problems such as emission, fuel consumption, noise, and deterioration of vibration. Can be avoided. Further, since the valve recess is not cut out at the open end of the combustion chamber of the piston, stress concentration on the open end is reduced, and the durability of the piston is improved. In particular, pilot injection is performed at the start of the diesel engine. However, since there is no valve recess at the top surface of the piston, the fuel does not stay in the valve recess in the form of droplets and the startability is not impaired.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a diesel engine.

FIG. 2 is a longitudinal sectional view taken along the cylinder axis of the engine.

FIG. 3 is a view taken along line 3-3 in FIG. 2;

FIG. 4 is a time chart showing fuel injection timing;

FIG. 5 is an explanatory diagram of an operation of main fuel injection.

FIG. 6 is a diagram for explaining the operation of auxiliary fuel injection.

FIG. 7 is an operation explanatory view corresponding to FIG. 6 when a valve recess exists.

[Explanation of symbols]

 13 Cylinder head 16 Cylinder 17 Piston 17a Top surface 22 Combustion chamber 22a First curved portion (open end) 23 Injector

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) F02M 45/04 F02M 45/04 (72) Inventor Hiroyuki Mamiya 1-4-1 Chuo, Wako-shi, Saitama Stock Inside the Honda R & D Co., Ltd. (72) Inventor Hideki Minami 1-4-1 Chuo, Wako-shi, Saitama F-term in the R & D Co., Ltd. (Reference) 3G023 AA00 AA02 AA03 AA07 AA14 AB05 AC04 AD02 AD07 AD28 AD29 AF03 AG03 3G066 AA07 AA11 AA13 AC09 BA02 BA17 BA22 BA23 BA24 BA46 CC05U CC26 CC34 CC35 CE22 DA09 DA10 DA12 DB01 DC05 3G301 HA02 HA09 HA11 HA13 JA02 JA21 JA24 JA37 KA01 LB04 LB11 MA11 MA18 MA23 MA29 PE04A

Claims (1)

[Claims] A concave combustion chamber (22) facing a cylinder head (13) is formed at the center of a top surface (17a) of a piston (17) slidably supported by a cylinder (16). In a direct injection diesel engine injecting fuel from an injector (23) supported by a head (13) toward the combustion chamber (22), a top surface (17) of a piston (17) surrounding the combustion chamber (22) is provided.
a) is formed flat, and the sub-fuel injection performed by the injector (23) at a different timing from the main fuel injection is directed to the open end (22a) of the combustion chamber (22). diesel engine.