JPS63201315A - Direct injection type diesel engine - Google Patents

Abstract

PURPOSE:To reduce combustion noise and improve output performance by setting the effective sectional area of an injection port smaller the larger is the crossing angle of its center line on the upper course side of a swirl at the intersecting point between said injection port center line and a cavity side wall out of each injection port of a fuel injection valve. CONSTITUTION:A fuel injection valve 6 has plural injection ports 7A-7D on each of both sides of a straight line l0 connecting the center M of the end of the valve 6 and the center N of a cavity 4 formed on the top 3a of a piston 3. And, the center lines L1-L4 of the injection ports have crossing angles theta1-theta4 toward the upper course side part of a swirl at the intersecting point parts P1-P4 to the side wall 5 of the cavity 4, respectively. And, the dimensional relation between each crossing angle is specified in accordance with the displacement conditions of the centers M, N as, e.g., theta4>theta1>theta3<theta2. In this case, each of the port diameters d1-d4, i.e., the effective sectional areas of the injection ports 7A-7D is set as d2>d3>d1>d4 in accordance with the size of each crossing angle theta1-theta4.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a direct injection diesel engine, and more particularly to the structure of a fuel injection valve applied to such a direct injection diesel engine.

(Prior art) In a direct-injection diesel engine, a concave cavity is usually formed at the top of the piston, and the nozzle hole forming part faces the cavity side near the top dead center of the piston, so that the nozzle hole is formed on the cylinder head side. A fuel injection valve is installed, and the fuel injected from each nozzle hole of the fuel injection valve toward the cavity side and the wall is mixed with air using the swirl generated in the cavity and then combusted. ing.

By the way, when a cavity is formed at the top of the piston in this way, if the deviation between the center of the piston and the center of the cylinder becomes large, the swirl generated by the reciprocating motion of the piston will be inhibited from being generated within the cavity. It is desirable to form the cavity as close to the center of the screw as possible.

On the other hand, it is desirable to install the fuel injection valve as close to the center of the cavity as possible in order to equalize the spray, but in reality, as shown in Fig. Since an intake boat and an exhaust boat are provided to sandwich the fuel injection valve from the center of the cylinder, the fuel injection valve is offset from the center of the cylinder in the radial direction to avoid interference with the intake valve and the exhaust valve. Therefore, as shown in FIG. 2, the center M of the tip of the injection valve is inevitably offset from the center N of the cavity in the radial direction of the cavity.

In this way, the center M of the tip of the fuel injector is the center N of the cavity.
For example, four nozzle holes 7
Opening A to 7D in two orthogonal directions (see Figure 4)
When assuming a fuel injection valve 6 with a
As shown in FIG. Swirl upstream side intersection angle 01 that is different between the side parts
~θ.

By the way, in a conventional direct injection diesel engine, even if the fuel injection valve 6 is arranged eccentrically with respect to the center of the cavity as described above, the effective cross-sectional area of each injection hole 7A to 7D of the fuel injection valve 6 is are all set the same (
That is, as shown in FIG. 9, the spray form of the fuel from the nozzle holes 7a' to 7d', which all have the same effective cross-sectional area, is set in the same way), but according to the knowledge of the inventor of the present application, It has become clear that if this is done, problems such as increased combustion noise and decreased output performance will occur for the following reasons.

That is, the fuel is sprayed from each nozzle hole 7&' to 7d' toward the cavity side wall 5, but in this case, a swirl S is generated inside the cavity that flows in the circumferential direction. , the fuel injected from near the center of the cavity across the swirl S toward the cavity side wall 5 is naturally affected by this swirl S, and even if the fuel is sprayed from the nozzle hole of the same diameter, the following will be explained. As a result, the spray form will be different for each.

For example, when comparing the second nozzle hole 7b' (same position as the nozzle hole 7B shown in FIG. 2) and the fourth nozzle hole 7d' (same position as the nozzle hole 7D shown in FIG. 2), The nozzle hole center line of the nozzle hole 7b' has a swirl upstream crossing angle θ with the cavity side wall 5 at the intersection point P with the cavity side wall 5, and the fourth nozzle hole 7d' The nozzle hole center line L4 has a swirl upstream crossing angle θ with the cavity side wall 5, and these two crossing angles θ3. θ, between θ
, 〈θ.

This relationship has been established.

Therefore, regarding the fuel injected from the second nozzle hole 7b', as shown in FIG. The spray part (the part indicated by the hatched part a in Fig. 7, and for the sake of convenience in the following explanation, this is referred to as the swirling component. Note that the hatched parts a and b in Fig. 7 and later-described Fig. 8 are for the sake of explanation) (This is divided for clarity, and there is no clear boundary.) and the spray component that collides with the cavity side wall 5 and is reflected, rides on the flow of the swirl S and flows in layers along the cavity side wall 5 toward the downstream side of the swirl. (The shaded area in Fig. 7 is already shown, and in the following explanation, this will be referred to as a falling component for convenience.) The proportion of the falling component to the rising component is extremely large. .

On the other hand, when looking at the fuel injected from the fourth nozzle hole 7d', as shown in FIG. Since it is larger than the intersection angle θ, the proportion of the swirling component in the sprayed fuel becomes larger than in the case shown in FIG. It is desirable that the amount of this blown-up fuel component be as small as possible because it disperses in large amounts into the air inside the cavity 4 and evaporates early, causing premixed combustion, increasing combustion pressure and increasing combustion noise. .

Furthermore, in this case, when the combustion gas generated by premix combustion is swept downstream by the swirl S, this combustion gas surrounds the fuel that is injected later at the end of injection, and as a result, air flows into the fuel. By blocking the supply,
From this point of view as well, it is preferable that the proportion of the blown-up components in the sprayed fuel be as small as possible, since this may cause deterioration of combustibility and a reduction in engine output.

(Technical Background of the Invention) Based on the above, the inventors of the present application have decided to reduce as much as possible the proportion of the blown-up component in the total sprayed fuel, considering the total sprayed fuel injected into the cavity 4. It has been found that this is effective in reducing combustion noise and maintaining engine output.

Furthermore, the inventors of the present application have proposed that the ratio of the upward components in the sprayed fuel be reduced to increase the ratio of the downstream components. In other words, the fuel that has collided with the cavity side wall 5 and reflected inside the cavity will flow as far downstream as possible in the swirl. In order to make it easier, it is only necessary to weaken the force with which the sprayed fuel collides with the side wall 5 of the cavity (that is, if the force with which the sprayed fuel collides with the side wall 5 of the cavity is weakened, the injection form shown by the solid line in FIG. (The injection form can be changed to the one shown by the chain line in the same figure), and we have come up with the idea that to achieve this, we can reduce the kinetic energy of the atomized fuel by narrowing the effective cross-sectional area of the nozzle hole. It is something.

In addition, as a direct injection diesel engine in which a fuel injection valve with a plurality of injection holes has different injection hole diameters, for example, as disclosed in Japanese Patent Application Laid-Open No. 61-207817, Some devices are designed to equalize the amount of fuel supplied to each part of the cavity side wall by changing the diameter of the hole in proportion to the circumference of the cavity side wall that each hole serves.

Furthermore, as disclosed in Japanese Patent Publication No. 49-16881, for example, the cavity is formed not in a circular shape but in an irregular clover-shaped shape, and a fuel injection valve is disposed in the center of the cavity, and each of its nozzle holes is There is a device in which the swirl upstream crossing angles between the nozzle hole center line and the cavity side wall are all the same size, thereby promoting swirl by the energy of the atomized fuel.

(Objective of the Invention) The present invention is based on such a technical background and attempts to solve the problems pointed out in the above-mentioned section of the prior art. In a direct injection diesel engine located eccentrically at
The purpose is to reduce combustion noise and improve output performance.

(Means for Achieving the Object) As a means for achieving the above object, the present invention provides a fuel injection valve having a plurality of nozzle holes radially formed in a cavity formed at the top of the piston. In a direct injection diesel engine arranged with the center of its tip deviated in the radial direction of the cavity, the nozzle hole at the intersection of the nozzle hole center line and the side wall of the cavity among the nozzle holes of the fuel injection valve. The effective cross-sectional area of a nozzle hole having a larger swirl upstream intersection angle between the center line and the cavity side wall is set to be smaller.

(Function) In the present invention, by the above-described means, among the intake boats of the fuel injection valve, the swirl upstream intersection angle of the nozzle hole center line at the intersection of the nozzle hole center line and the cavity side wall is large. Since the effective cross-sectional area of the nozzle hole is set small, the interlocking energy of the fuel that will be injected from now on is small, and the collision effect of this injected fuel against the side wall of the cavity is weakened, resulting in (1) spraying. (2) Premix combustion: The rate at which fuel is swirled up inside the cavity and dispersed into the air is reduced, promoting stratified mixing of fuel and air and suppressing premix combustion. (2) Premix combustion By the amount that is suppressed, the surrounding phenomenon of the atomized fuel by the combustion gas generated by premix combustion is prevented, and the supply of air to the fuel is promoted.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS. 1 to 8.

FIG. 1 shows the main parts of a direct injection diesel engine for an automobile according to a first embodiment of the present invention, in which reference numeral l is a cylinder block, 2 is a cylinder head, and 3
is a piston.

A circular concave cavity 4 is formed in the top portion 3a of the piston 3, as shown in FIGS. 1 and 2, respectively. Furthermore, a fuel injection valve 6 is attached to the cylinder head 2, and the center M of the tip of the injection valve is located at the second
As shown in the figure, it is arranged to be offset by a predetermined amount in the cavity radial direction with respect to the cavity center N.

As shown in FIG. 3, the fuel injection valve 6 is constructed by mounting a needle 60 inside a valve body 61 with a sack portion 62 at its tip 6a. Furthermore, this valve body 6
Four nozzle holes 7A to 7D are formed in the first sack portion 62, each opening radially in two orthogonal directions. As shown in FIG. 2, this fuel injector 6 has a straight line connecting the cavity center N and the injector tip center M.

The first nozzle hole 7A and the fourth nozzle hole 7 are placed on the blade side of the
D is fixed to the cylinder head 2 side with the second nozzle hole 7B and third nozzle hole 7C positioned on the other side.

Therefore, in the fuel injection valve 6 arranged in this way, the nozzle hole center lines, ~L, of each of the nozzle holes 7A to 7D are the intersections of the six nozzle hole center lines LI-L4 and the cavity side wall 5. Department P
1 to P4, there are swirl upstream intersection angles 01 to θ4 between the swirl upstream side portion of the cavity side wall 5, respectively.
have. Then, each swirl upstream side intersection angle θ
, ~θ4 is defined in accordance with the deviation state between the tip center M of the fuel injector 6 and the cavity center N, and in this embodiment, it is set as θ4>θ1>θ, >θ. There is.

Therefore, when the effective cross-sectional area of each nozzle hole 78 to 7D is the same, the proportion of the swirling component in the fuel injected from each nozzle hole is as follows:
, the fourth nozzle hole 7D → the first nozzle hole 7
The size decreases in the order of A→third nozzle hole 7C→second nozzle hole 7B.

By the way, in order to reduce engine combustion noise and maintain good engine output performance, it is necessary to reduce as much as possible the proportion of blown-up components in the sprayed fuel, which are negative factors in these points, from the perspective of the entire engine. can be said to be effective.

As a specific means for putting this into practice, the inventor of the present application narrows down the effective cross-sectional area of the nozzle hole to reduce the kinetic energy of the fuel that will be injected, as explained in the above section (Technical Background of the Invention). The idea was to weaken the force with which the sprayed fuel collides with the side wall of the cavity so that it is more easily flowed away by the swirl, thereby reducing the ratio of swirling components in the sprayed fuel as much as possible and promoting stratified mixing of the fuel and air. Specifically, as shown in FIG. 4, the aperture, that is, the effective cross-sectional area of each nozzle hole 7A to 7D of the fuel injection valve 6 is set to the swirl upstream cross angle of 01 to θ of each nozzle hole.

The following settings are made in accordance with the size relationship of .

That is, the diameter d+ of the first nozzle hole 7A, the diameter d of the second nozzle hole 7B, the diameter d of the third nozzle hole 7C, and the diameter d4 of the fourth nozzle hole 7D, dz > ds > da > da.

As a result, for example, in the fourth nozzle hole 7D where the swirl upstream crossing angle is large and has the worst conditions, as shown in FIG.
When the effective cross-sectional area is large, the ratio of the upstream component in the sprayed fuel is larger than the downstream component, as shown by the solid line; The shape of the spray is improved at each nozzle hole, such as by reversing the flow and making it easier for the entire swirl to flow downstream.

Therefore, when looking at the fuel injection valve 6 as a whole, each nozzle hole 7A~
Compared to the case where the effective cross-sectional area of 7D is set uniformly, the total fuel injection amount is constant, but the ratio of the swirling component to it is relatively reduced, and the amount of sprayed fuel in the cavity 4 is reduced. The layered mixing between the air and the air is further promoted. As a result, the occurrence of premixed combustion is prevented as much as possible, and combustion noise is reliably reduced based on the high combustion pressure.

(Second Embodiment) FIG. 5 shows the main parts of a direct injection type diesel engine for an automobile according to a second embodiment of the present invention. This embodiment differs from the first embodiment in that the cavity 4 provided at the top 3a of the piston 3 has a circular planar shape, and the fuel injection valve 6 is eccentric to the center of the cavity 4.
In contrast, the planar shape of the cavity 4' is formed into an irregular clover shape, and the fuel injection valve 6' is arranged eccentrically with respect to the center N of this cavity, and each injection hole 7A' to The magnitude relationship of the swirl upstream cross angles θ, ~θ4 of the nozzle hole center lines L1 to L4 of 7D' is θ,〉θ,〉θ4
> θ, and each swirl upstream crossing angle 01 to θ4 are both set to be smaller than 90°. In FIG. 5, symbols U and 114 are perpendicular lines at the intersections P1 to P4 of the nozzle holes 7A' to 7D' and the cavity side wall 5.

In this embodiment, as in the first embodiment, the apertures of the nozzle holes 7A' to 7D' are made to correspond to the magnitudes of the swirl upstream cross angles θ, ˜θ, so that di < dt
< di < ds (see Figure 6).

By doing so, the spray form of the fuel injected from each of the nozzle holes 7A' to 7D' can be made as close as possible to the spray form of the third nozzle hole 70', which has the most favorable conditions among them. As a result, the proportion of the stirred up components in the total atomized fuel decreases, making it easier for the entire atomized fuel to flow downstream of the swirl, further promoting stratified mixing of the fuel, and reducing combustion caused by premixed combustion. Noise will be reduced more effectively.

(Effects of the Invention) The present invention provides a fuel injection valve having a plurality of nozzle holes formed radially with respect to a cavity formed at the top of the piston, with the center of its tip being offset in the radial direction of the cavity. In the direct-injection diesel engine arranged in It is characterized in that the effective cross-sectional area of the hole is set to be smaller.

Therefore, according to the direct injection diesel engine of the present invention,
Among the intake boats of the fuel injection valve, in the nozzle hole where the swirl upstream intersection angle of the nozzle hole center line at the intersection of the nozzle hole 4 center line and the cavity side wall is large, the effective cross-sectional area of the nozzle hole is small. Because of this setting, the kinetic energy of the fuel that will be injected from now on is reduced, and the collision effect of this injected fuel against the side wall of the cavity is weakened.As a result, (1) the sprayed fuel is blown up inside the cavity by a swirl. This reduces the proportion of fuel that is dispersed in the air, promotes stratified mixing between fuel and air, and suppresses premixed combustion, which lowers combustion pressure and reduces engine combustion noise. (2 ) To the extent that premix combustion is suppressed, the phenomenon in which the atomized fuel is surrounded by the combustion gas generated by premix combustion is prevented, and the supply of air to the fuel is promoted, resulting in better mixing of fuel and air. Great effects can be obtained in terms of reducing combustion noise and improving engine output, such as improving engine output.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a main part of a direct injection diesel engine according to a first embodiment of the present invention, FIG. FIG. 4 is an enlarged cross-sectional view taken along IV-IV of FIG. The figure shows an enlarged engine rotational speed of the nozzle hole of the fuel injection valve applied to the engine shown in Figure 5, Figures 7 and 8 are fuel spray state diagrams, and Figure 9 shows the conventional fuel injection valve. FIG. 3 is a cross-sectional view of a nozzle hole portion. l...Cylinder block 2...Cylinder head 3...Piston 4...Cavity 5...Cavity side wall 6...Fuel injection valves 7A to 7D ...Fig. 4, 7, and 8 on the nozzle hole 7

Claims (1)

[Claims] 1. In a direct injection diesel engine, a fuel injection valve having a plurality of injection holes formed radially with respect to a cavity formed at the top of a piston is arranged with its tip center offset in the radial direction of the cavity. Among the nozzle holes of the fuel injection valve, the effective cross-sectional area of the nozzle hole is set to be smaller as the swirl upstream intersection angle between the nozzle hole center line and the cavity side wall at the intersection of the nozzle hole center line and the cavity side wall is larger. A direct injection diesel engine characterized by: