JPS6316124A - Pent roof type piston - Google Patents

Abstract

PURPOSE:To suppress the generation of smoke and improve output because of the superior combustion by making the angle formed by the side wall surface of a cavity formed at the top part of a piston and the tangential line for a piston crown surface, nearly uniform on the whole periphery of the cavity and uniformly dispersing the fuel mist. CONSTITUTION:Since the angle formed by the generating line 6f on the side wall surface of a cavity 6 and the tangential line 3g of a piston crown surface on the opened port edge crossing with the generating line is formed nearly uniform on all the longitudinal sectional surface passing through the piston center line, the introducing angle of a skewish flow V pushed into the cavity 6 in the final period of compression cycle is made uniform over the whole periphery of the cavity 6. Therefore, in the vicinity of the cavity side wall surface 6a, a nearly uniform turbulent flow is generated over the whole periphery. Therefore, the fuel mist injection-supplied from a multiinjection port nozzle 9 can be dispersed uniformly. Therefore, the superior combustion can be achieved by increasing the air utilization rate, and generation of smoke can be reduced, and the output can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a pent-roof type piston adopted between a direct injection internal combustion line for directly injecting fuel into a combustion chamber, and particularly to a pent-roof piston having a cavity shape recessed in the crown surface of the piston. This article relates to a pent roof type piston that has been improved.

[Prior Art] Generally, in internal combustion engines, the cross-sectional area of the flow path of the intake and exhaust ports is increased by increasing the diameter of the intake and exhaust valves or by increasing the number of intake and 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 way, 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 control structure, the combustion chamber that opens on the lower surface of the cylinder head is recessed upward at the center along the axis of the crankshaft, and gradually inclined on both sides to form a combustion chamber approximately relative to the valve shaft. It becomes necessary to create a vertical pent roof shape (ridge shape), and if this pent roof type combustion engine is used in a direct injection internal combustion engine such as a direct injection diesel engine, a high compression ratio of 16 or higher is required. In order to secure the
[Diesel Nada Seki combustion chamber structure] proposed in No. 3456
As shown in Fig. 2, the piston crown surface must necessarily be made into a pent roof shape that protrudes upward, corresponding to the shape of the lower surface of the cylinder head.

[Problems to be Solved by the Invention] By the way, in the case of a direct injection internal combustion engine as shown in FIGS. A high compression ratio of 16 or more is achieved by pushing the piston into a cavity C recessed in the center of the piston crown. The air squeezed between the cylinder head and the lower surface of the cylinder head (not shown) generates a squish flow V on the piston crown surface toward the cavity C in the center, and this squish flow V flows into the cavity C. The fuel spray F introduced and injected from the injection nozzle d and the air are stirred at a constant temperature of 1 to produce a uniform air-fuel mixture.

However, if the piston is a pent roof type piston in which the central part of the piston crown surface is raised upward along the axial direction of the crank (not shown), the side wall surface e of the cavity C is extended over its entire circumference. If they are formed uniformly at the same angle (for example, parallel) to the piston center line f, then the generatrix of the side wall surface e at any point on the opening end Q of the cavity C and the tangent i between the piston crown surface and The angle θ formed by the ridge is not uniform along the circumference but changes, and the angle θ (=β) at the ridge j becomes the maximum (Fig. 7 (A)). The angle θ (=α) of the part perpendicular to is the minimum (
Figure 7(B)).

For this reason, the introduction angle at which the squish flow V generated on the piston crown surface is forced into the cavity C changes along the circumference, and the introduction angle of the squish flow ■ along the ridge j changes. (Fig. 7 (A)), the introduction angle of the squish flow (Fig. 7 (B)) introduced from the direction perpendicular to this (Fig. 7 (B)) is larger than that of the side wall surface e toward the inside of the cavity C.
I will be separated from. As a result, the fuel spray F injected and supplied from the injection nozzle d reaches inside the cavity C, especially on the side wall surface e.
Oxygen is no longer uniformly diffused in the vicinity, and oxygen in the cavity C cannot be sufficiently utilized during combustion, resulting in a decrease in output and the generation of smoke.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention has a side wall surface of a cavity formed at the top of the piston, which is formed in a pent roof shape by raising the crown surface of the piston upward. A pent roof type piston is constructed by forming a cavity by making the angle between the piston and the tangent to the piston crown surface substantially uniform over the entire circumference of the cavity.

[Function] The squish flow generated on the crown surface of the piston at the end of the compression stroke is introduced into the cavity. At this time, since the angle between the side wall surface of the cavity opening end and the piston crown surface is approximately uniform over the entire circumference of the opening end, the squish flow flows from the entire circumference of the cavity opening to the side wall surface. is introduced at an equal angle to the As a result, a turbulent flow caused by the squish flow is generated substantially uniformly around the entire circumference of the cavity side wall surface, and the fuel spray injected into the cavity is uniformly diffused.

[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.

1 and 2 show a first embodiment of the present invention. FIG. 1 is a side sectional view of a pent roof type piston used in a direct injection internal combustion engine such as a direct injection diesel engine, and FIG. FIG. 3 is a plan view of the top of the piston.

As shown in the figure, the piston 1 has a piston crown surface 3 directly above the piston pin 2 that protrudes upward along the axial direction of the piston pin 2 (i.e., the crankshaft direction), and both sides thereof are inclined. It is formed in a pent roof shape (ridge shape), and although this pent roof shape is not shown, it corresponds to the shape of the combustion chamber on the cylinder head side formed on the lower surface of the cylinder head.

Specifically, the piston crown surface 3 has a substantially hexagonal shape and is raised upward, and the ridge line 5 of the ridge portion 4 is formed directly above the axis of the piston pin 2, and is formed symmetrically. A cavity 6 is recessed in the piston top portion 1a approximately at the center of the piston crown surface 3 to form a substantial combustion chamber with the cylinder head (not shown) at the end of the compression stroke. In addition, the inclined surfaces 3a, 3b, 3c, and 3d of the piston crown surface 3 on both axial end sides of the piston pin 2 are curved, and the piston crown surface 3 on both sides of the cavity 6 located in the center of the piston pin 2 is curved. The inclined surfaces 30, 3f are formed substantially flat.

By the way, in all longitudinal sections passing through the center line 1b of the piston 1, the cavity 6 has a generatrix 6b on the cross section of the side wall surface 6a immediately below the open lower part, and a piston crown at the open end 7a on the cross section. The angle θ between the surface 3 and the tangent 13g is formed to be substantially uniform. That is, FIG. 1(A) shows a side cross section along the ridgeline 5 of the ridge portion 4 of the pent roof piston 1, and FIG.
As shown in the figure, the cavity 6 has a generatrix 6b of the side wall surface 6a directly below the open lower part.
and the open end 7 of the piston crown surface 3 intersecting this base 16b.
The tangent line 3g on the opening end 7a intersects substantially equally at any point over the entire circumference of the opening end 7a.

In the first embodiment shown in FIGS. 1 and 2, the bus bar 6b
and the tangent line 3g intersect at θ=90°, and the cavity 6 is formed so that its open lower part is perfectly circular, and the side wall surface 6a is formed so that its generatrix 6b is a straight line up to approximately the cavity bottom 8. is formed. Therefore, since the tangent line 3Q passing over the ridge line 5 of the ridge portion 4 is approximately horizontal, the generatrix 6b of the side wall surface 6a at this portion is close to vertical (FIG. 1(A)) and is perpendicular to the ridge line 5. Since the tangent line 3q passing on the piston center line 1b has the maximum angle of inclination, the generatrix 6b of the side wall surface 6a at this portion is inclined most outwardly with respect to the center line 1b (see Fig. 1( B)). Therefore, the cross-sectional shape of the inside of the cavity 6 becomes flatter toward the cavity bottom 8, and the shape of the cross section becomes more elliptical or oblong with the long axis in the direction of the ridge line 5.

In the pent roof type piston 1 formed in this way,
As shown in Figure 3 (A) and (B), TD at the end of the compression stroke
When the squish flow V generated near C is sandwiched between the lower surface of the cylinder spatula (not shown) and the piston crown surface 3, and is introduced into the cavity 6, the introduction angle (squish flow ) is pushed in from the entire periphery of the open lower at a substantially uniform angle, and the side wall surface 6a of the cavity 6
A substantially uniform turbulent flow is generated in the vicinity over the entire circumference.

Therefore, from each nozzle 10 of the multi-nozzle 9 to the cavity 6
The fuel spray F injected into the cavity 6 is agitated by the turbulence of the squish flow V and diffused into the cavity 6, but at this time, the fuel spray F is dispersed in the vicinity of the side wall surface 6a of the cavity 6 and over its entire circumference. It becomes evenly distributed.

As a result, the oxygen in the cavity 6 can be fully utilized to perform combustion with a high air utilization rate, thereby reducing the generation of smoke and improving the output.

Further, FIGS. 4 and 5 show a second embodiment.

In the case of the pent roof type piston 1 of this second embodiment,
As shown in the figure, the bottom 8 side of the cavity 6 is formed in a perfect circular shape, and therefore the cross-sectional shape on the open lower side is an ellipse with a normal axis in a direction perpendicular to the ridgeline 5, and the aspect ratio is It gets higher towards the lower side. Similar to the first embodiment, the angle formed between the side wall surface 6a of the cavity 6 and the piston crown surface 3 is equal to the generatrix 6b of the side wall surface 6a on any longitudinal section passing through the piston center line 1b. It is formed so that the angle θ (=90°) between the generatrix 6b and the tangent 3g of the piston crown surface 3 on the opening end 7a which intersects with it is approximately uniform, and the effect is the same as in the first embodiment. It has become.

Furthermore, FIG. 6 shows a third embodiment. The pent roof type piston 1 of the third embodiment has a shelf portion 11 which is formed on the side wall surface 6a of the cavity 6 immediately below the same mouth, and whose height from the bottom portion 8 is made equal and whose diameter is reduced inward in the radial direction. The generatrix 6b of the side wall surface 6a forming this shelf 11 is formed linearly with a predetermined length, and the generatrix 6b
The angle θ between the tangent 3q of the piston crown surface 3 on the open end 7a that intersects with the generatrix 6b is substantially uniform in all longitudinal sections passing through the piston center line 1b. In addition, in the third embodiment of this illustrated example, the cross-sectional shape of the lower end of the shelf 11 and the cross-sectional shape of the enlarged diameter cavity 6 below the shelf 11 are formed in a perfect circular shape, and the shelf The cross-sectional shape of the portion 11 is formed into an elliptical shape with the oblateness increasing toward the open lower side and having long sleeves in a direction orthogonal to the ridgeline 5.

In the third embodiment in which the shelf portion 11 is provided in this way, the first
Similarly to the embodiment and the second embodiment, the introduction angle of the squish flow introduced into the cavity 6 from the open lower part is determined by adjusting the introduction angle of the squish flow into the cavity 6 from the open lower part.
Not only can the entire circumference of the cavity 6 be made substantially uniform with respect to a, but also the piston crown surface 3 can be made uniform during the expansion stroke.
Even if a strong reverse squish flow occurs upwards, the spray/air mixture and flame inside the cavity 6 are covered by the shelf 11 on the upper side, making it difficult for them to flow out of the cavity 6. As a result, the amount of smoke and IIc discharged is reduced. It becomes possible to further reduce the amount of heat generated and to further improve the output.

In addition, in all of the first, second, and third embodiments, it is desirable that the fuel spray injected into the cavity 6 be supplied toward a part of the corner on the outer circumferential side of the bottom.

[Effects of the Invention] In summary, the present invention exhibits the following excellent effects.

(1) Since the angle between the generatrix of the cavity side wall surface and the tangent to the piston crown surface on the opening end that intersects this generatrix is approximately uniform in all longitudinal sections passing through the piston center line, The introduction angle of the squish flow that is forced into the cavity from the opening can be made uniform over the entire circumference of the opening with respect to the side wall surface of the cavity.

(2:J Since the introduction angle of the squish flow with respect to the cavity side wall surface is uniform over the entire circumference of the cavity,
The fuel spray that is injected and supplied into the cavity can be uniformly diffused, thereby increasing the air utilization rate and achieving good combustion, which can reduce smoke generation and improve output.

[Brief explanation of drawings]

FIG. 1 is a side sectional view showing a first embodiment of the pent roof type screws 1 to 1 of the present invention, in which (A) is a side sectional view along the ridge direction, and (B) is a side sectional view perpendicular to (A>). 2 is a plan view of the first embodiment, FIG. 3 is a side sectional view for explaining the operation of the first embodiment, and FIG. 4 is a side sectional view of the second embodiment.
FIG. 5 is a plan view of the second embodiment, FIG. 6 is a side sectional view of the third embodiment, and FIG. 7 is a side sectional view showing a conventional pent roof type piston. In the figure, 1a is the top of the piston, 1b is the piston center line, and 3
is a piston crown surface, 3g is a tangent, 4 is a ridge, 6 is a cavity, 6a is a side wall surface, 6b is a generatrix, 7a is an open end, 8 is a cavity bottom, and 11 is a shelf.

Claims (5)

[Claims] (1) The angle between the side wall surface of the cavity formed at the top of the piston, which is formed in a pent-roof shape by raising the piston crown surface upward, and the tangent to the piston crown surface is formed approximately uniformly around the entire circumference of the cavity. A pent roof type piston characterized by: (2) The pent roof type piston according to claim 1, wherein the cavity is formed with a linear generatrix having a predetermined length from the opening end on the side wall surface directly below the opening. (3) The pent roof type piston according to claim 2, wherein the cavity has an open end shaped like a perfect circle. (4) The above-mentioned patent claim, wherein the opening end of the cavity is formed in an elliptical shape with a long axis in a direction perpendicular to the ridge direction of the pent roof-shaped crown surface, and the bottom of the cavity is formed in a perfect circular shape. A pent roof type piston according to item 2 of the range. (5) The pent roof type piston according to claim 4, wherein the cavity has a shelf portion whose diameter is reduced radially inward so as to narrow the cavity toward its opening side.