JPS62255521A - Pent roof type piston - Google Patents

Abstract

PURPOSE:To suppress a quantity of atomized fuel running over a cavity, by further hollowing an inner wall under an opening of the cavity in a direction perpendicular to the axial direction of a piston pin hole, and thereby enlarging a radial dimension in the cavity. CONSTITUTION:In a pent roof type piston 1, a piston top surface 3 is projected at a portion just over a piston pin hole 2 along the axial direction of the piston pin hole 2, and the portion is inclined at its both ends. The piston top surface 3 is recessed at its central portion to form a cavity 4. An inner wall 6 under an opening 5 of the cavity 4 is further hollowed in a direction perpendicular to the axial direction of the piston pin hole 2 to thereby enlarge a radial dimension in the cavity. Accordingly, there is formed an overhung portion 7 over a small-height portion of the inner wall 6 of the cavity 4 in such a manner as to hang over the small-height portion. Further, the overhang of the overhung portion 7 is widened at the smallest-height portion of the inner wall 6. As a result, it is possible to suppress a quantity of atomized fuel running over the cavity 4 from the small-height portion of the inner wall 6 and thereby reduce the generation of HC and smoke.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a pent roof type piston employed in a direct injection internal combustion engine that directly injects fuel into a combustion chamber, and particularly relates to a pent roof type piston having a cavity shape recessed in the crown surface of the piston. Concerning an improved pent roof type piston.

[Prior art 1] Generally, in internal combustion engines, the cross-sectional area of the flow path of the intake/exhaust boat is increased by increasing the diameter of the intake/exhaust valves or by increasing the number of intake/exhaust valves per cylinder. By increasing , the intake and exhaust efficiency can be improved.

However, if the cross-sectional area of the flow path of the intake/exhaust boat is increased in this manner, the valve shafts of the intake/exhaust valves must be inclined in a V-shape to avoid interference between them. Then, due to the arrangement of the valve mechanism, the combustion chamber formed on the lower surface of the cylinder head is recessed upwards most in the center along the axis of the crankshaft, and gradually slopes on both sides to form a combustion chamber that is approximately perpendicular to the valve axis. It becomes necessary to create a pent roof shape (roof shape) formed so that it becomes 18 to 2.
In order to secure a high compression ratio of 0,
As shown in ``Diesel Engine Combustion Chamber Structure'' proposed in No. 43456, the piston crown surface must necessarily correspond to the lower surface shape of the cylinder head and have a pent roof shape that protrudes upward. .

[Problems to be Solved by the Invention] Incidentally, in the case of a direct injection internal combustion engine, a cavity for forming a substantial combustion chamber is recessed approximately in the center of the crown surface of the piston. As shown in FIG. 6, the cavity b of the conventional pent roof piston a has a circular cross section. Therefore, when the inner circumferential wall surface C of the cavity b is developed, it becomes as shown in FIG. Sahb was changing. For this reason, when the fuel spray injected from the injection nozzle e is swept by the swirl S and turns inside the cavity b, the low part Q of the inner circumferential wall C of the cavity is caused by the influence of centrifugal force, and the piston crown outside the cavity b is It tried to jump out to the upper side of surface i, and the reverse squish was stronger in this part than in other parts, so part of the spray and the flame were likely to spill over into the gap between the piston crown surface and the cylinder head, where the amount of oxygen was low. As a result, a portion of the spray that spilled over and the flame caused a problem in that 02 was insufficient and a large amount of IIc and smoke were generated.

In order to improve this, conventionally, a shelf j was provided in which the inner circumferential wall C on the opening side of the cavity outer pin b protruded radially inward, but there was still room for improvement.

The present invention has been made in view of the above-mentioned problems, and its purpose is to suppress as much as possible the amount of fuel spray spilling over from the low height part of the cavity inner circumferential wall to the outside of the cavity.
An object of the present invention is to provide a pent roof type piston for a direct injection internal combustion engine that can reduce the amount of C and smoke generated.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention makes the piston crown surface directly above the piston pin hole protrude along the axial direction, and both sides thereof are inclined to form a pent roof. A pent roof type piston is formed by forming a cavity in the central part of the piston crown surface under the opening perpendicular to the axial direction of the piston pin hole to form a cavity expanding outward in the radial direction. .

[Function] By further recessing the inner peripheral wall below the opening of the cavity recessed in the center of the piston crown surface in a direction perpendicular to the axial direction of the piston pin hole and expanding radially outward, the cavity is expanded. A shelf part covering the upper part of the inner circumferential wall is formed at a low height part, and the protrusion of the shelf part at the lowest part is made large. This suppresses as much as possible the G of the fuel spray spilling out of the cavity from the low-height portion of the inner circumferential wall.
Reduces the amount of smoke generated.

[Embodiment] A preferred embodiment of the pent roof piston according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a plan view of a pent roof type piston used in a direct injection internal combustion engine such as a direct injection diesel engine, and FIG. 2 is a sectional view taken along the line II--II.

As shown in the figure, the piston 1 has a piston crown surface 3 directly above the piston pin hole 2 in the axial direction of the piston pin hole 2 (
In other words, it protrudes upward along the crankshaft direction, and its both sides are sloped to form a pent roof shape (roof shape). Although this pent roof shape is not shown, the lower surface of the cylinder head This corresponds to the shape of the combustion chamber on the cylinder head side, which is formed in the cylinder head.

Incidentally, a cavity 4 is recessed approximately in the center of the piston crown surface 3 to form a substantial combustion chamber with the cylinder head at the end of the compression stroke. 4 has an inner circumferential wall 6 below the opening 5 which is further depressed in a direction perpendicular to the axial direction of the piston pin hole 2 and expanded radially outward. A part 11 7 is formed in the part where the height is lowered to cover the upper part.

That is, in this embodiment, the cavity 4 below the opening 5 has an elliptical cross section and has a long sleeve in the direction perpendicular to the axial direction of the piston pin hole 2. Therefore, the overhang t2 of the shelf portion 7 is maximized at the portion where the height of the inner peripheral wall 6 of the cavity 4 is the lowest. In addition, in the illustrated example,
The opening 5 of the cavity 4 is opened by extending the periphery of the upper edge of the cavity further inward in the radial direction and narrowing it into a perfect circle. A shelf 7 having the same height from the bottom of the cavity 4 is formed,
The overhang tl of the shelf portion 7 at the highest portion of the cavity inner circumferential wall 6 is the smallest.

The overhang length of this shelf 7 is a minimum value t1=d150 to d/15 with respect to the opening diameter d of the cavity 4. It is desirable to form the maximum value t2=d/10 to about d/3.

On the other hand, as shown in FIG. 1, an injection nozzle 8 is disposed above the approximate center of the cavity 4 and is attached to the cylinder head to inject fuel into the cavity 4. This injection nozzle 8 faces the inner circumferential wall 6 of the cavity 4 and has four injection ports 9 on the right side that inject fuel at an angle of 45° to the axis of the piston pin hole 2, and each of the injection ports 9 The fuel Il# mist F injected from the is directed diagonally downward so as to collide with the lower side of the shelf 7 of the inner peripheral wall 6, and the collided fuel injection iF and the air-fuel mixture G generated thereby are downstream of the swirl S. It is designed to flow downward in the direction.

Therefore, as shown in FIGS. 1 and 3, the fuel injection nF or the mixture G injected toward the A point and the 0 point is flowed into the swirl S and flows along the inner circumferential wall 6 of the cavity 4. The height h6 flows to the lowest part. However, in this case, in the cavity 4 of the present invention, as the height h6 of the inner circumferential wall 6 decreases, the overhang of the shelf 7 increases, and the overhang t2 of the shelf 7 becomes maximum at the lowest part, and the cavity The lower part of the 4th shelf is deep.

Therefore, even if a strong reverse squish occurs above the piston crown surface 3 on both sides of the lower part of the inner peripheral wall height h6 of the cavity 4, the spray, air-fuel mixture, flame, etc. inside the cavity 4 are difficult to flow out. Inner peripheral wall height near the lowest part h6
The spillover chain from the lower part of the piston to the upper side of the piston crown surface 3 is suppressed as much as possible, and as a result, the amount of smoke and HC discharged can be reduced and the output can be increased.

Note that the swirl S in the cavity 4 is generated by intake air from the intake boat, and since the cavity opening 5 is circular, the swirl S easily flows into the cavity 4, and its attenuation is suppressed as much as possible. It is being Further, the shape of the lower part of the shelf of the cavity 4 may be an oval shape as shown in FIG. As the inner circumferential wall 6 on the long axis side gradually moves away from and approaches the long axis, turbulence is induced near the long axis, and a micro swirl of 3 m is created here.
This makes it possible to further measure the mixing of fuel and air.

[Effects of the Invention] To summarize, according to the present invention, the inner circumferential wall below the opening of the cavity recessed in the crown surface of the pent roof piston is enlarged and recessed in a direction perpendicular to the axial direction of the piston pin hole. Therefore, it is possible to increase the overhang of the shelf in the low height part of the cavity inner circumferential wall, thereby reducing as much as possible the fuel spray, air-fuel mixture, and flame inside the cavity that spill over onto the top of the piston crown. It is possible to reduce emissions of smoke, IIC, etc. and improve output.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a preferred embodiment of the pent roof type piston according to the present invention, FIG. 2 is a sectional view taken along the line II-II in FIG. 1, and FIG. FIG. 4 is a sectional view showing a modified example of the shape of the cavity under the opening (below the shelf), FIG. 5 is a plan view of a conventional pent roof piston, and FIG. 6 is a side sectional view of FIG. 5. , FIG. 7 is a developed view of a conventional cavity. In the diagram, 1 is a piston and 2 is a screw!・Piston hole, 3 is the piston crown surface, 4 is the cavity, 5 is the frontage, 6 is the inner peripheral wall,
7 is a shelf.

Claims (3)

[Claims] (1) The area directly above the piston pin hole on the piston crown surface is made to protrude along its axial direction, and its both sides are sloped to form a pent roof shape, and the piston pin hole is formed in the central part of the piston crown surface in the axial direction. A pent roof type piston characterized by forming a cavity that expands radially outward by recessing the inner circumferential wall below the opening perpendicular to the opening. (2) The pent roof type piston according to claim 1, wherein the cavity is formed in an oval or elliptical shape having a long axis in a direction perpendicular to the axial direction of the piston pin hole. (3) The pent roof type piston according to claim 1 or 2, wherein the cavity opening has a shelf portion extending radially inward and narrowed into a perfect circle at its peripheral edge. .