JPH10148129A - Combustion chamber structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure durability against mechanical stress without deteriorating a combustion condition by taking a measure against cracking on a part where cracking is generated in an opening part of a combustion chamber of a reentrant type, and remaining acute angled lip on the other part. SOLUTION: In a combustion chamber 2, a cavity opening part 2a is defined as an acute angled lip 2h, and mixing of fuel at the time of reverse squish with air is promoted. An inclining surface which is contracted in a taper shape in the inner surface of an opening part 2a of a part in the specified direction receiving stress of a combustion chamber opening part 2a, to say concretely, in the piston pin 3 direction, is crossed with a vertical surface along the axial direction of a piston 1, the thickness of its crossing part is thickened, and thereby, durability against mechanical stress is improved. An angle formed by an inclining surface for forming the thick wall part and the vertical surface, is formed into an obtuse angle, air is easily separated in the boundary of both surfaces, and thereby, mixing of air and fuel is accelerated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber structure formed on a piston top surface of a direct injection diesel engine.

[0002]

2. Description of the Related Art As shown in FIGS. 6 and 7, in a direct injection type (hereinafter referred to as "direct injection type") diesel engine, a combustion chamber 11 having a cavity formed in a top surface 10a of a piston 10 is substantially at the center. From the fuel injection nozzle (not shown) attached to the cylinder head
The fuel is injected into the combustion chamber 11 and swirled by the swirl of the intake air to collide with the wall of the combustion chamber 11.
The mixture is stirred by a squish of 0a, and the mixture is burned. In FIG. 6, the dashed line indicates
2 shows the direction of a piston pin. In addition, the top surface 10a sucks,
Exhaust valve recesses 10b and 10c are formed.

There are various types of combustion chambers, and the diameter of the opening (mouth) is formed smaller than the diameter of the inside of the combustion chamber, that is, a reentrant type in which the opening of the combustion chamber is narrowed. In the case of an object, a reverse squish (flow in which fuel and air go out of the combustion chamber) occurs when the piston descends. At this time, the shape of the tip (lip) of the opening largely acts, and FIG.
When the lip 11b of the opening 11a is formed at an acute angle as shown in FIG. 7, the fuel and air tend to be mixed well and the combustion is improved. The opening lip 11b is formed over the entire circumference of the opening of the combustion chamber. That is, the acute angle lip 11b at the opening of the combustion chamber is extremely effective in promoting the mixing of fuel and air during reverse squish and improving combustion.

[0004]

However, tensile stress is applied to the opening of the combustion chamber in the direction of the piston pin due to mechanical stress, or compressive stress is applied in the direction perpendicular to the piston pin due to thermal stress. Fatigue failure occurs and cracks occur. As a countermeasure against the cracks, in the reentrant combustion chamber 11, the opening lip 11b has to be obtuse-angled or provided with a certain thickness. For this reason, the effect of promoting the mixing of fuel and air is reduced, which causes deterioration of output and exhaust gas.

[0005] The present invention has been made in view of the above points, and measures are taken against cracks at the opening of the reentrant type combustion chamber opening, and the other portions are left with an acute lip to prevent combustion. It is an object of the present invention to provide a combustion chamber structure that ensures durability against mechanical stress without deteriorating the pressure.

[0006]

According to the present invention, there is provided a combustion chamber having a cavity formed on a top surface of a piston, wherein the combustion chamber has a cavity opening formed inside the cavity. A reentrant type formed smaller than the inner surface of the cavity, and an inclined surface forming an upper portion of the inner surface of the cavity and tapered toward the opening, and along a piston axis direction in a specific direction receiving stress of the cavity opening. It is a structure that intersects with the vertical surface.

[0007] The reentrant combustion chamber has a sharp opening lip at the cavity opening to promote mixing of fuel and air during reverse squishing. The specific direction in which the stress of the combustion chamber opening is received.Specifically, the inner surface of the opening in the portion in the direction of the piston pin intersects the inclined surface whose diameter is reduced in a tapered shape and the vertical surface along the piston axial direction to intersect. By increasing the thickness, durability against mechanical stress is improved. Also,
By making the ridge angle between the inclined surface and the vertical surface forming the thick portion an obtuse angle, air separation easily occurs at the boundary between these two surfaces, and the mixing of air and fuel is promoted.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below by way of examples. As shown in FIG. 1 and FIG.
A circular cavity is formed substantially at the center of the top surface 1a of the top surface 1a to form a combustion chamber 2. The combustion chamber 2 has an opening (mouth)
2a is smaller in diameter than the inside, and the central portion 2c of the bottom surface 2b has a conical shape and bulges upward. Inner surface (wall surface)
The lower portion 2d forms a donut shape and expands its diameter, and a slightly reduced central portion 2e rises substantially vertically (in the axial direction of the piston 1), and then forms an inclined surface 2f which expands in a tapered shape.
Further, the inclined surface 2g is tapered inward toward the mouth 2a. Thus, the combustion chamber 2 is of a reentrant type in which the substantially central portion 2e of the side wall and the tip 2h of the opening 2a are formed smaller than the diameter of the inside of the combustion chamber.
The central portion 2e and the tip 2h of the opening 2a are respectively called lips, and the combustion chamber 2 is a two-stage lip-shaped reentrant type. The tip 2h of the opening 2a is hereinafter referred to as a lip 2h.

The piston 1 is provided with a piston pin 3 in a vertical direction in FIG. The top surface 1a of the piston 1 has recesses 1b, 1
b and exhaust valve recesses 1c, 1c. By the way, as described above, the crack in the opening of the combustion chamber of the piston in the direct injection diesel engine mainly occurs due to mechanical stress or thermal stress. Since cracks due to mechanical stress occur in the direction of the piston pin 3, countermeasures are taken only in the direction of the piston pin 3 and in the other parts, leaving the opening acute angle lip, without greatly deteriorating combustion , Durability can be ensured.

Therefore, the opening 2a of the combustion chamber 2 is provided with an opening acute angle lip 2h in a portion other than the direction of the piston pin 3, and the portion in the direction of the piston pin 3 is cracked to ensure durability. . That is, as shown in FIG.
In the lip 2h on both sides of the opening 2a except for the direction of the piston pin 3, the ridge angle α formed by the inclined surface 2g forming the inner surface of the opening end and the piston top surface 1a is an acute angle. That is,
The opening lip 2h is an acute angle lip.

The opening 2a of the combustion chamber 2 has a tip 2i on the intake valve side and a tip 2j on the exhaust valve side in the direction of the piston pin 3 as shown in FIG.
And it is made thick as shown in FIG. That is, in FIG. 4, the inclined surface 2 g that forms the intake valve-side tip 2 i of the opening 2 a of the combustion chamber 2 rises vertically (in the axial direction of the piston 1) at a substantially central position to form a vertical surface 2 m, The portion is chamfered in an arc shape and is smoothly connected to the piston top surface 1a. The vertical surface 2m is formed by cutting with the cutter 5 as shown by a two-dot chain line. Therefore, vertical surface 2
m intersects with the inclined surface 2g at an angle, and the inclined surface 2g
Is an obtuse angle with the vertical surface 2m.

As shown in FIG. 5, the end 2j on the exhaust valve side of the opening 2a of the combustion chamber 2 is slightly thicker than the end 2i on the intake side. The temperature on the exhaust side is higher than that on the intake side, resulting in a decrease in fatigue strength. Therefore, the thickness is made thicker than the intake side to ensure durability. In FIG. 5, the inclined surface 2 forming the opening end 2j
g rises vertically (in the axial direction of the piston 1) slightly below the center to form a vertical surface 2n, and its upper end is chamfered in an arc shape and smoothly connected to the piston top surface 1a. Therefore, the vertical surface 2n is the vertical surface 2m on the intake side.
Is slightly longer than the tip 2j
Becomes thicker. This vertical surface 2n is formed by cutting with a cutter in the same manner as the vertical surface 2m. Therefore, the inclined surface 2
g and the vertical surface 2j intersect with a corner, and the ridge angle γ forms an obtuse angle.

In addition, at the intake end 2i and the exhaust end 2j of the opening 2a, a continuous portion between the left and right recesses 1b and 1b on the intake side and a continuous portion between the left and right recesses 1c and 1c on the exhaust side. Alternatively, it may be formed by slightly retreating outward from the opening 2a. Intake end 2i, exhaust end 2j of combustion chamber 2
When the length along the circumferential direction is short, it is difficult to ensure durability, and when the length is long, it becomes difficult to promote mixing of fuel and air. Therefore, in the present invention, the tip 2 of the opening 2a
The lengths of i and 2j along the circumferential direction were set such that the angle θ with respect to the center of the combustion chamber 2 was approximately 60 °. However, the angle θ is not limited to 60 °, and may be 60 ° or less as long as the above-mentioned performance such as durability and improvement of the combustion effect is ensured.

The operation will be described below. The combustion chamber 2 promotes mixing of fuel and air at the time of reverse squishing at the portion of the opening acute angle lip 2h. Further, since the opening ends 2i and 2j in the direction of the piston pin 3 are thick, durability against mechanical stress is secured. At these opening ends 2i and 2j, the ridge angles β and γ formed by the inclined surface 2g and the vertical surfaces 2m and 2n form obtuse angles, so that the inclined surface 2g and the vertical surfaces 2m and 2n At the boundary, the separation of the air from the inclined surface 2g is likely to occur, whereby the fuel and the air are easily mixed. As a result, substantially the same combustion performance and exhaust gas effect as when the entire circumference of the opening 2a of the combustion chamber 2 is formed as an acute lip can be obtained.

In the above embodiment, the case where the present invention is applied to a two-stage lip reentrant type combustion chamber is described. However, the present invention is not limited to this, and the present invention is applied to a normal reentrant type combustion chamber having a lip only at an opening. Of course, it may be applied. However, it is more effective when combined with a two-step lip shape as in the embodiment. Also,
In the above embodiment, the present invention is applied to a four-valve engine, but may be applied to a two-valve engine.

[0016]

As described above, according to the present invention, there is provided a combustion chamber having a cavity formed on the top surface of a piston,
The combustion chamber is a reentrant type in which a cavity opening is formed smaller than the inside of the cavity, and an inclined surface which forms an upper portion of the inner surface of the cavity and has a tapered diameter facing the opening; With a structure that intersects the vertical surface along the piston axis direction in the specific direction that receives the stress of the part, almost the same performance without deteriorating the combustion as compared to the combustion chamber with an acute angle lip all around the opening And durability of the piston against mechanical stress can be ensured.

[Brief description of the drawings]

FIG. 1 is a plan view of a piston to which a combustion chamber structure according to the present invention is applied.

FIG. 2 is a sectional view taken along the line II-II in FIG.

FIG. 3 is an enlarged view of the opening lip of FIG. 2;

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 1;

FIG. 5 is a sectional view taken along the line VV in FIG. 1;

FIG. 6 is a plan view of a piston to which a conventional combustion chamber structure is applied.

FIG. 7 is a sectional view taken along the line VII-VII in FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piston 2 Combustion chamber 2a Opening 2b Bottom surface 2d-2g, 2m, 2n Inner surface 2h Opening lip 2i, 2j Piston pin direction opening tip 3 Piston pin

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuya Watanabe Mitsubishi Motors Corporation, 5-33-8, Shiba 5-chome, Minato-ku, Tokyo

Claims (1)

[Claims] 1. A combustion chamber having a cavity formed on a top surface of a piston, wherein the combustion chamber is a reentrant type in which a cavity opening is formed smaller than the inside of the cavity. A combustion chamber structure, wherein an inclined surface formed and tapered in diameter toward the opening intersects a vertical surface along a piston axis direction in a specific direction subjected to stress of the cavity opening.