JP2003041937A - Piston structure for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict generation of excessive thermal stress concentration to a protruded part formed between a valve recess or cut part in a piston crown surface and an opening edge of a cavity. SOLUTION: In the crown surface 14a of a piston 14, a recessed cavity 15 to form a combustion chamber, and valve recesses 24-27 to avoid interference with intake and exhaust valves are formed. A cut part 28 to avoid interference with a glow plug is formed in the opening edge 15a of the cavity. Both end parts of the cut part are formed to overlap with inner side parts 24b and 26b of the valve recesses 24 and 26, and protruded parts 29 and 30 formed at overlapping end edges of the valve recesses with the cut part are disposed on the outer circumferential part side of the piston crown surface to be sufficiently apart from the opening edge of the cavity for achieving high heat radiation effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a piston structure of a direct injection diesel engine, and more particularly to a structure such as a crown surface of a piston in which a cavity forming a combustion chamber is formed.

[0002]

2. Description of the Related Art As a piston structure of a conventional diesel engine of this kind, those described in, for example, Japanese Utility Model Laid-Open No. 2-94329 and Japanese Patent Laid-Open No. 11-190217 are known.

First, in the former piston structure, as shown in FIG. 6, a reentrant type cavity 3 is formed at the center position of the crown surface 2 of the piston 1, and the cavity 3 has a substantially circular shape at its upper end. Is formed to define a combustion chamber 4 with the lower surface of the cylinder head.
Further, the piston crown surface 2 has valve recesses 5 and 5 for avoiding interference between the crown surface 2 and each of the two intake valves (not shown) and each umbrella portion of the exhaust valve at the top dead center position of the piston 1. ,
6 and 6 are formed.

Each of the valve recesses 5, 5, 6, 6 is formed in a substantially plane circular shape, and is arranged at four symmetrical positions on the piston crown surface 2 and its inner end portions 5a, 5a. , 6a, 6b are formed so as to communicate with the inside of the cavity 3 from the opening edge 3a of the cavity 3.

On the other hand, in the latter piston structure, a cavity having the same shape as the former is formed at the center position of the crown surface of the piston, and a small circular arc notch is formed at the opening edge of this cavity. The notch prevents the tip of the glow plug held by the cylinder head from interfering with the opening edge of the cavity at the top dead center of the piston.

[0006]

However, in the former piston structure, each valve recess 5, 5, 6,
Since each inner end portion 5a, 5a, 6a, 6b of 6 is formed by cutting out the upper end of the opening edge 3a of the cavity 3,
The opening edge 3a having a high heat load and the inner end portions 5a, 5a, 6
a projecting portion 7 having a sharp tip at the boundary between both edges of a and 6b,
8 are formed respectively.

On the other hand, even in the latter piston structure, similarly protruding projections are formed at the boundaries between both ends of the notch and the opening edge of the cavity.

Therefore, each of the projecting portions 7 and 8 is exposed to the combustion gas during the operation of the engine to increase the heat load and become a so-called heat point where the heat stress is concentrated.

As a result, the protrusions 7 and 8 may be cracked or damaged in some cases, leading to a technical problem that the durability of the piston 1 is reduced.

[0010]

The present invention has been devised in view of the actual situation of the conventional piston, and the invention according to claim 1 is a concave cavity forming a combustion chamber on the crown surface of the piston. And a valve recess for avoiding interference with the engine valve, a notch for avoiding interference with a glow plug is formed at the opening edge of the cavity, and a part of the valve recess is for opening of the cavity. In a piston structure of a diesel engine that communicates with a combustion chamber via an edge, the notch is formed so as to overlap with the part of the valve recess, and is formed at an overlapping edge of the notch and the valve recess. It is characterized in that the protrusion is arranged on the outer peripheral side of the piston crown surface with respect to the opening edge of the cavity.

Therefore, according to the present invention, the protrusion formed on the overlapping edge of the valve recess and the notch is located at a position sufficiently distant from the opening edge of the cavity having a high heat load to the outer peripheral side of the crown surface. Can be formed. Therefore, excessive thermal stress concentration on the protrusion due to combustion is prevented.

The invention according to claim 2 is characterized in that a plurality of the valve recesses are formed on the crown surface of the piston, and the notch is formed so as to extend over the two adjacent valve recesses.

The invention according to claim 3 is characterized in that an annular hole for circulating a cooling liquid therein is formed on the outer peripheral side of the notched portion in the crown portion of the piston.

According to a fourth aspect of the present invention, the notch is formed so as to be inclined downward toward the inside of the cavity.

According to a fifth aspect of the present invention, the cutout portion is
It is characterized in that it is formed in a substantially arc shape along the circular opening edge of the cavity.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a piston structure for a diesel engine according to the present invention will be described in detail below with reference to the drawings.

First, as shown in FIG. 3, the diesel engine in the first embodiment has a cylinder bore 11 inside.
A cylinder block 11 having a, a cylinder head 12 fixed to an upper end of the cylinder block 11, and a cylinder bore 11a are slidably provided and connected to a crankshaft (not shown) through a connecting rod 13. A piston 14 and a reentrant cavity 15 that forms a combustion chamber 16 between the crown 14 a of the piston 14 and the lower surface of the cylinder head 12 at the center thereof.
Are formed.

The cylinder head 12 is internally formed with a pair of intake ports 17 and exhaust ports 18 communicating with the combustion chamber 16, and the open ends of the intake and exhaust ports 17 and 18 are respectively formed. The pair of intake valves 19 and exhaust valves 20 that open and close are slidably supported. An injection nozzle 21 for injecting fuel from the tip portion into the combustion chamber 16 is provided at the center of the inside of the cylinder head 12, and between the intake port 17 and the exhaust port 18 on the one side, Heater part 22 at the tip
A glow plug 22 is provided which a faces the combustion chamber 16 and ignites fuel at the initial stage of engine startup.

A water jacket 23 for circulating engine cooling water is formed inside the peripheral wall of the cylinder block 11.

As shown in FIGS. 1 and 2, the piston 14 has the cavity 1 at a substantially central position of the crown surface 14a.
5 is formed, and the intake valve 19.19 and the exhaust valve 2 are provided at the top dead center position of the piston 14 at four-side symmetrical positions on the crown surface 14a centering on the cavity 15.
Four intake side and exhaust side valve recesses 24, 25, 26, 27 for avoiding interference with each 0.20 umbrella portion are formed, and one intake side and exhaust side valve recess 2 is formed.
A notch 28 for avoiding interference with the tip portion 22a of the glow plug 22 is formed between Nos. 4 and 26.

One of the intake and exhaust valve recesses 2
As shown in FIG. 1, the reference numerals 4 and 26 are formed in a substantially semi-circular shape in which the inside is cut out, and are gradually shallower from the outer end portion side formed in the deepest groove to the inner end portions 24a, 26a side. And both inner ends 24a, 25a
The opposite side edges 24b and 26b are formed up to the circular opening edge 15a of the cavity 15 and communicate with the inside of the cavity 15. On the other hand, the other intake and exhaust side valve recesses 25 and 27 are formed in the same shape as the one valve recesses 24 and 26, and are formed in a substantially semi-circular planar shape with the inside cut out, and formed in the deepest groove. From the end side to the inner end 25
It is formed so as to gradually become shallower toward the a and 27a sides, and the opposite side edge 25 of the inner end portions 25a and 27a.
b and 27 b are formed up to the circular opening edge 15 a of the cavity 15 and communicate with the inside of the cavity 15.

As shown in FIG. 1, the cutout portion 28 is formed at a substantially intermediate position between the intake and exhaust valve recesses 24 and 26 on one side, and is formed along the opening edge 15a so as to straddle these recesses. Has been done. That is, the cutout portion 28 is formed in a substantially arc shape (crescent shape) along the opening edge 15a, and both end portions 28a and 28b thereof are extended to the side end edges 24b and 26b of the valve recesses 24 and 26, respectively. Then, the upper surfaces of the side edges 24b and 26b are cut out. Further, the cutout portion 28 is formed in a downwardly inclined shape from the outer peripheral edge 28c to the inner peripheral edge 28d on the opening edge 15a side. The radius of curvature of the arc-shaped outer peripheral edge 28c of the cutout portion 28 is the same as that of the cavity 15
Is set to be about half the radius of curvature of the opening edge 15a.

Therefore, the outer peripheral edge 28c of the cutout portion 28 is
And the outer peripheral edges 24c and 26 of the valve recesses 24 and 26, respectively.
Protrusions 29 and 30 are formed at positions where c overlaps with each other.
It is arranged on the outer peripheral side of the crown surface 14a from the opening edge 15a.

Therefore, according to this embodiment, each of the projections 29.30 of the crown surface 14a having a high heat dissipation effect is sufficiently separated outward from the opening edge 15a of the cavity 15 where the combustion heat is most likely to be concentrated. Since it can be formed at the position on the outer peripheral side, the heat dissipation of the protrusions 29, 30 is improved, and the generation of a large heat load can be suppressed.

As a result, excessive thermal stress concentration is suppressed, and cracks or damage near the protrusions 29, 30 on the crown surface 14a can be prevented.

Further, the notch 28 is formed in both valve recesses 24,
Since it is formed to be large along the opening edge 15a so as to straddle 26, both end portions 28 of the cutout portion 28 are formed as shown in FIG.
Since the angle θ formed by the tangent line of a and 28b and the tangent line of the opening edge 15a intersecting the tangent line can be set to a large angle close to 180 °, occurrence of excessive thermal stress concentration on the intersection parts 31 and 32 can be prevented. Can be suppressed.

Further, since the notch 28 is formed in a downwardly inclined shape from the outer peripheral edge 28c to the inner peripheral edge 28d, the convex portion formed between the inner peripheral surface of the cavity 15 and the notch 28 as shown in FIG. Since the angle θ1 formed by 33 becomes small,
It is also possible to suppress the occurrence of excessive thermal stress concentration on the convex portion 33.

Further, since the notch portion 28 is formed in an arc shape, the communicating portions 33, 34 with the cavities 15 located at the circumferential edges of the both end portions 28a, 28b can be smoothly communicated. , Such communication parts 33, 3
It is possible to suppress the occurrence of large thermal stress concentration in No. 4.

FIG. 4 shows a second embodiment of the present invention, and on the premise of the piston structure of the first embodiment, the piston 1
An annular hole 36 for circulating the cooling oil is formed between the cavity 15 and the piston ring groove 35 of the crown portion 14b of No. 4, that is, at an inner position on the outer peripheral side of the cutout portion 28.

Therefore, the vicinity of the protrusions 29, 30 is forcibly cooled by the cooling oil flowing through the annular hole 36, so that the thermal stress concentration on the protrusions 29, 30 is more effectively generated. Can be suppressed.

The present invention is not limited to the configurations of the above-described embodiments, and for example, the valve recess 2 on the intake side is used.
It is also possible to apply it to what formed 4,25 in a substantially semicircular shape as shown in FIG. In this case, one of the intake side valve recesses 24 has the cutout 28 as in the case described above.
Since one end 28a of the is formed in a polymerized state,
It goes without saying that the position of the protrusion 29 can be located on the outer peripheral side of the crown surface 14a having a high heat dissipation effect, and the other intake-side valve recess 25 has the opening edge 15 of the cavity 15.
Since it does not communicate with a, it is not affected by the high heat load of the cavity 15.

In addition to the shape of such valve recesses, the present invention corresponds to one intake valve and one exhaust valve per cylinder regardless of the number of the valve recesses, so that the crown surface 14a has two valve recesses on the intake side and the exhaust side. It is also possible to apply it to the one in which the valve is formed or the one having a single valve recess. Further, the shape of the notch 28 can be freely changed as long as the position of the protrusion can be set on the outer peripheral side of the crown surface 14 while avoiding the opening edge 15a of the cavity 15. Is.

[0033]

As is apparent from the above description, claim 1
According to the invention described above, the protrusion formed at the position where the valve recess and the notch intersect with each other is provided on the outer peripheral side of the crown surface having a high heat dissipation effect, which is sufficiently distant outward from the opening edge of the cavity having a high heat load. Since it can be formed, it is possible to prevent excessive thermal stress concentration on the protrusion due to combustion heat.

As a result, it is possible to prevent cracks and damages on the protrusions and their vicinity, and to improve the durability of the piston.

According to the second aspect of the invention, since the notch is formed so as to straddle between the two valve recesses, the opening angle at which both end edges of the notch and the opening edge of the cavity intersect is increased. be able to. For this reason, it is possible to prevent the occurrence of excessive thermal stress concentration on the convex portion at the intersecting position.

According to the third aspect of the present invention, since the vicinity of the protrusion is forcibly cooled by the cooling liquid flowing through the annular hole, the generation of thermal stress concentration on the protrusion is more effective. Can be suppressed.

According to the fourth aspect of the present invention, since the notch is formed so as to be inclined downward toward the opening edge of the cavity, the convex portion formed between the inner peripheral surface of the cavity and the notch makes it. Since the angle can be made small, it is possible to suppress the occurrence of excessive thermal stress concentration on the convex portion.

According to the fifth aspect of the present invention, since the notch is formed in an arc shape, the communicating portions with the cavities located at the circumferential edges of the both ends can be smoothly communicated. Therefore, it is possible to suppress the occurrence of large thermal stress concentration in the communication portion.

[Brief description of drawings]

FIG. 1 is a plan view of a piston used in a first embodiment of the present invention.

FIG. 2 is a sectional view of a main part of a piston according to this embodiment.

FIG. 3 is a vertical sectional view of a diesel engine to which the piston structure of the present embodiment is applied.

FIG. 4 is a sectional view of a main part of a piston showing a second embodiment of the present invention.

FIG. 5 is a plan view of a piston showing another example of the valve recess.

FIG. 6 is a plan view of a piston showing a valve recess having a conventional structure.

[Explanation of symbols]

14 ... Piston 14a ... Crown surface 15 ... Cavity 15a ... Opening edge 16 ... Combustion chamber 19, 20 ... Intake and exhaust valves 22 ... Glow plug 24-27 ... Valve recess 28 ... Notch 29, 30 ... Projection

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Claims (5)

[Claims] 1. A recessed cavity forming a combustion chamber is formed on a crown surface of a piston, and a valve recess for avoiding interference with an engine valve is formed, and interference with a glow plug is avoided at an opening edge of the cavity. A notch is formed,
And in a diesel engine piston structure in which a part of the valve recess communicates with a combustion chamber through an opening edge of the cavity, the cutout is formed so as to overlap with the part of the valve recess, and the cutout is formed. A piston structure for a diesel engine, wherein a protrusion formed on the overlapping end of the valve recess and the valve recess is arranged on the outer peripheral side of the crown surface of the piston with respect to the opening edge of the cavity. 2. The piston for a diesel engine according to claim 1, wherein a plurality of the valve recesses are formed on the crown surface of the piston, and the notch is formed over the two adjacent valve recesses. 3. The piston structure for a diesel engine according to claim 1, wherein an annular hole for circulating a cooling liquid inside is formed on an outer peripheral side of the notch portion in the crown portion of the piston. . 4. The piston structure for a diesel engine according to claim 1, wherein the notch is formed so as to be inclined downward toward the inside of the cavity. 5. The piston structure of a diesel engine according to claim 1, wherein the cutout portion is formed in a substantially arc shape along a circular opening edge of the cavity.