JPH11200864A - Piston for four-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston for a four-cycle engine wherein both a tumble flow and a squish flow can be generated by a device of piston shape. SOLUTION: In an upper surface of a disk-shaped head part 21, almost a spherical combustion recessed part 21a is hollowly provided, also a recessed part 21b, 21c for avoiding interference with an intake/ exhaust valve is hollowly provided, further, in a peripheral part in an upper surface of the head part 21, a squish part 21d of annular flat surface is formed, a ridge line A of the squish part 21d and the combustion recessed part 21a passes in the recessed part 21b, 21c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for a four-stroke engine, and more particularly to a piston capable of easily generating a tumble flow and a squish flow so as to improve the combustibility.

[0002]

2. Description of the Related Art In a four-stroke engine, it is known that the combustion characteristics can be improved by generating a tumble (longitudinal vortex) in a mixture flow sucked into a cylinder bore. Conventionally, as a structure for generating the tumble flow, various structures such as setting the shape of the intake port to a shape that easily generates the tumble flow, and providing a flow control valve for generating the tumble flow in the intake port are known. Proposed.

[0003]

However, in the case of the above-mentioned conventional intake port having a special shape or a structure in which a flow control valve for generating a tumble flow is provided, the structure becomes complicated and the cost increases. There is. In some cases, the combustibility is improved by devising the shape of the piston, but in reality, a sufficient effect has not been obtained.

[0004] In addition to the above-mentioned tumble flow, various methods such as generation of a squish flow are known to improve the combustibility. However, both the tumble flow and the squish flow are efficiently generated by devising a piston shape. There has not been proposed any device capable of causing the above.

The present invention has been made in view of the above-mentioned conventional circumstances, and has as its object to provide a piston for a four-stroke engine capable of generating both a tumble flow and a squish flow by devising a piston shape. .

[0006]

According to the first aspect of the present invention, a substantially spherical combustion recess 21a is formed on an upper surface of a disk-shaped head portion 21.
And recesses 21b and 21c for avoiding interference with the intake and exhaust valves are formed, and a squish portion 21d is formed in the outer peripheral portion of the upper surface of the head portion 21 as an annular flat surface. The ridge line A between the squish portion 21d and the combustion concave portion 21a is aligned with the recess portions 21b and 21.
c.

[0007]

According to the first aspect of the present invention, when the intake valve 10 is opened and the piston 20 is lowered in the intake stroke, the air-fuel mixture is accordingly passed through the intake valve opening 4d, particularly, a portion closer to the cylinder center side. Inhaled into 7a,
It flows in the cylinder axial direction along the inner surface on the exhaust side of the cylinder bore 7a. In the present invention, the spherical piston-side combustion recess 21a is provided in the center of the upper surface of the piston 20, so that the air-fuel mixture flowing in the cylinder axis direction reverses along the spherical combustion recess 21a. And a tumble flow is likely to occur.

Further, even when the piston 20 rises in the compression stroke, the generated tumble flow is likely to remain due to the spherical combustion concave portion 21a on the upper surface of the piston. Further, as the piston 20 rises, the combustion chamber B is formed by the combustion recess 21a on the piston side and the combustion recess 4b on the cylinder head 4, but the combustion recess 21a on the piston has a spherical shape. As a result, the entire combustion chamber B becomes closer to a spherical shape than a piston whose top surface is flat or protrudes upward, and the tumble flow remains even at the end of the compression stroke from this point.

Further, in the present invention, the squish portion 21d, which is annular and has a flat surface, is formed on the outer peripheral portion of the upper surface of the head portion 21 of the piston 20, so that the squish portion 21d of the piston 20 and the cylinder are closed at the end of the compression stroke. A squish flow that pushes the air-fuel mixture at the outer periphery of the cylinder bore toward the center is likely to be generated by the flat surface flush with the mating surface 4a of the head 4 on the cylinder body side. The atomization of the air-fuel mixture is promoted by the squish flow and the tumble flow, so that the combustibility is improved and the engine performance is improved.

Here, in order to improve the engine performance,
In order to reduce the volume of the combustion chamber and increase the compression ratio, the position of the top dead center of the piston is brought close to the mating side of the cylinder head,
In order to increase the amount of intake air at the time of high-speed rotation, an intake stroke and an exhaust stroke are overlapped.
In this case, it is known to form a recess on the upper surface of the piston in order to avoid interference between the piston and the intake and exhaust valves.

However, since the recess is a recess formed on the upper surface of the piston, the recess acts to inhibit the generation of the tumble flow. Therefore, in the present invention, the spherical combustion concave portion 21a is formed such that the ridge line A between the concave portion 21a and the squish portion 21c is formed in the recess portion 21a.
b, 21c. Therefore, the recess depth of the recess portions 21b and 21c is reduced by the depth of the recess portion of the combustion recess 21a, and as a result, the inhibitory effect of the recess portions 21b and 21c on the tumble flow is reduced.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 to 10 are views for explaining a forged piston for a four-cycle engine according to one embodiment of the present invention. FIG. 1 is a cross-sectional side view of a four-cycle engine provided with the piston, and FIG. FIG. 4 is a cross-sectional side view, FIG. 5 is a partial cross-sectional bottom view, FIGS. 6 and 7 are schematic views, FIGS. 8 and 9 are schematic cross-sectional views of a forging apparatus, FIG. 10 is a schematic diagram for explaining the forging process. It should be noted that the front, rear, left and right in the present embodiment mean front, rear, left and right when the engine is viewed from the intake side.

In FIG. 1, reference numeral 1 denotes a motorcycle engine provided with the piston according to the present embodiment. The engine 1 is a water-cooled parallel 4-cylinder 5-valve engine, in which a cylinder body 3 and a cylinder head 4 are stacked on a crankcase 2 and connected with a head bolt 5, and a head cover 6 is attached to an upper mating surface 4g of the cylinder head 4. And mounted on the body frame with the crankshaft directed in the vehicle width direction.

A piston 20 is slidably inserted into a cylinder bore 7a of the cylinder liner 7 which is inserted into the cylinder body 3 by press fitting or casting. The piston 20 is connected to a crankshaft (not shown) by a connecting rod 8. It is connected to.

The cylinder bore 7a and the piston 20 are provided on the mating face 4a of the cylinder head 4 on the cylinder body side.
A substantially hemispherical head-side combustion recess 4b that forms a combustion chamber B with the upper surface of the combustion chamber B is provided. In the combustion recess 4b, two exhaust valve openings 4i and three intake ports 4j are opened substantially along the outer periphery of the cylinder bore 7a.
i and 4j are led to a front side wall 4e and a rear side wall 4f of the cylinder head 4 through an exhaust port 4c and an intake port 4d, respectively. The electrode of the ignition plug 29 faces substantially the center of the combustion recess 4b. Although not shown, a carburetor is connected to the outer connection opening 4h of the intake port 4d. A fuel injection valve may be attached to the intake port 4d to inject fuel toward the back surface of the head 10a of the intake valve 10.

The combustion chamber side openings 4i and 4j of the exhaust port 4c and the intake port 4d can be opened and closed by umbrella portions 9a and 10a of two exhaust valves 9 and three intake valves 10, respectively. The exhaust valve 9 and each intake valve 10 are urged in the closing direction by valve springs 11a and 11b. The exhaust valve 9 and the intake valve 10 are opened and closed by an exhaust camshaft 13a and an intake camshaft 13b via valve lifters 12a and 12b mounted on the upper end.

Here, the center intake valve of the three intake valves 10 is disposed so that the angle formed with the cylinder bore axis is smaller than that of the left and right intake valves 10 shown in FIG. ing. As a result, the surface shape of the head side combustion concave portion 4b is made closer to a spherical shape, the volume of the combustion chamber is reduced to increase the compression ratio, and the depth of the recess at the piston top surface is made shallow as described later. doing.

The piston 20 has a substantially disk-shaped head portion 21 and a pair of left and right pin boss portions 22a, 22 projecting downward integrally from right and left outer portions of the lower surface of the head portion 21.
b, a pin boss portion 22a on the outer peripheral edge of the head portion 21,
A pair of skirt portions 23 before and after extending integrally from the portion between the boss portions 22b to below the lower ends of the pin boss portions 22a, 22b.
a and 23b.

On the outer peripheral surface of the head portion 21, first and second
Ring grooves 21f, 21f for the compression ring and a ring groove 21g for the oil ring are recessed. A substantially spherical piston-side combustion recess 21a is provided in the center of the upper surface of the head 21. Furthermore, on the upper surface of the head portion 21, two exhaust-side recesses 21b for avoiding interference with the head portion 9a of each of the exhaust valves 9 and interference with the head portion 10a of each of the intake valves 10 are avoided. Are recessed so as to be substantially semicircular and located along the outer periphery of the upper surface. In addition, 21
j is an oil hole that communicates the oil ring groove 21g with the inside of the piston.

Reference numeral 21h denotes a processing boss protruding from the central portion of the combustion recess 21a, which is formed at the time of forging, is used at the time of machining the outer peripheral surface of the piston, and is thereafter cut and removed. Is done. 21i is an arrow indicating the exhaust direction stamped on the piston side combustion recess 21a.

Further, an annular flat squish portion 21d is formed in the outer peripheral portion of the upper surface of the head portion 21 (the hatched region crossing in FIG. 2), and the squish portion 21d and the combustion portion are formed. The ridge line A with the concave portion 21a passes through the inside of the recess portions 21b and 21c. Here, the ridge line A is defined by the recesses 21b and 21c.
The recess depth of each of the recesses 21b and 21c from the upper surface of the piston is reduced by the depth of the recess of the recess 21a. Thereby, as described later, the tumble flow inhibiting action of the recess portion is reduced.

The outer peripheral portion 4k of the cylinder head 4 which is opposed to the squish portion 21d at the outer peripheral portion of the head side combustion concave portion 4b forms a flat surface flush with the cylinder body side mating surface 4a. By thus forming the flat surfaces on the piston side and the cylinder head side, a squish flow is generated at the end of the compression stroke so that the air-fuel mixture is pushed toward the center of the cylinder bore.

The left and right pin boss portions 22a, 22b
Is formed with a piston pin hole 25 in parallel with the crankshaft. A circlip groove 25a for retaining the piston pin is formed in the left and right ends in the axial direction of the inner peripheral surface of the piston pin hole 25.
A pair of front and rear oil grooves 25b are formed in the upper portion of the inner peripheral surface of the inner peripheral surface 5 so as to penetrate in the axial direction. Reference numeral 25c denotes an escape groove of a tool for attaching and detaching the circlip, and reference numeral 25d denotes a seat to which the pushing rod 42 of the pushing cylinder 41 contacts in a forging process.

The front and rear skirt portions 23a and 23b
Of the front and rear skirts 23a and 23b and the right end of the front and rear skirts 23a and 23b and the right side of the pin boss 22a are connected to each other by a pair of left and right ribs 24a and 24a. The right and left rib portions 24b, 24b are connected to the portion 22b. These left and right rib portions 24a and 24b are integrally extended downward from the lower surface of the head portion 21.

The ribs 24a and 24b are formed to be thin for weight reduction, and the lower edge 24c is formed.
The boss-side portion 24d from the connection portion a with the pin boss portions 22a and 22b to the boss-side intermediate portion b is located at substantially the same height as the lower edge of the pin boss portions 22a and 22b. H1 is constant. The boss-side portion 24d is defined as having the dimension H1 equal to the boss-side intermediate portion b.
It may be formed diagonally so as to increase toward the side.

The boss side portion 2 of the lower edge 24c
The central portion 24f following 4d is formed in a substantially arcuate concave shape, and the dimension of the most concave portion of the central portion 24f up to the piston upper surface is Ho (<H1).
In addition, most of the central portion 24f has a dimension up to the piston upper surface smaller than the boss side portion 24d.

Further, the skirt side portion 2 of the lower edge 24c of each of the rib portions 24a, 24b from the connection portion d with the skirt portions 23a, 23b to the skirt side intermediate portion c.
4e is located below the boss side portion 24d, and the dimension up to the piston upper surface is constant H2 (> H1).
The skirt side portion 24e may be formed diagonally so that the dimension H2 increases toward the skirt.

FIG. 8 schematically shows a press device 30 for forging the piston 20. In the figure,
The press device 30 has a lower die holding member 34 that holds the lower die 32 and the side die 33 disposed on the upper surface of the base plate 31 that is disposed and fixed below, and an upper die holding member that holds the upper die 35 above. 36 is fixedly arranged on the lower surface of the slider 37, and the slider 37 is supported by a column 38 so as to be vertically movable,
The slider 37 is connected to the piston rod 4 of the hydraulic cylinder 39.
It is configured to move at zero.

The side mold 33 has a mold hole 33a having a shape corresponding to the outer peripheral surface shape of the piston 20, and a mold surface 32a having a shape corresponding to the inner surface shape of the piston 20 in the mold hole 33a. The lower mold 32 is fitted and arranged.
Here, the portion of the mold surface 32a of the lower mold 32 corresponding to the lower edge 24c of the rib portion is the boss-side portion 24d,
It has shape portions 32b, 32c, 32d corresponding to the central portion 24f and the skirt side portion 24e (see FIG. 10).

An extruding cylinder 41 for removing a forged product is disposed in the base 31 and an extruding rod 42 of the cylinder 41 faces a gap for forming the pin boss. Reference numeral 34a denotes a stopper projecting from the lower mold holding member 34, and the stopper 34a regulates the lowering position of the upper mold holding member 36. Reference numeral 43 denotes a heater disposed in the side mold 33 for maintaining the mold at a predetermined temperature, and reference numeral 43a denotes a power supply lead wire.

The upper mold 35 has at its lower end a mold surface 35a having a shape corresponding to the shape of the upper surface of the piston 20, and a heater 44 for holding the upper mold 35 at a predetermined temperature.
Is inserted and arranged. The upper mold 35 is connected to the upper mold holding member 3.
When the piston 6 is lowered until it comes into contact with the stopper 34a, a space (cavity) corresponding to the pin boss, the skirt, and the rib of the piston 20 is formed. Reference numeral 44a is a power supply lead wire.

In forging the piston 20 of the present embodiment, an aluminum alloy (a material shown in Table 1 can be used) or the like is cut into an ingot or the like of an aluminum alloy to a size required for one piston. It is heated to a suitable temperature, placed in the space formed by the lower mold 32 and the side mold 33, and pressurized by the hydraulic cylinder 39 by the upper mold 35. With the lowering of the upper mold 35, the upper surface of the aluminum material W is formed into a shape corresponding to the mold surface 35a of the upper mold 35, and the pin boss space and the skirt portion space of a part of the aluminum material W are formed. When the upper die 35 is lowered until the lower surface of the upper die holding member 36 contacts the stopper portion 34a of the lower die holding member 34, the forging is completed.

The above forged product has a hardness of 70-80.
(HRB), it is preferable to carry out a heat treatment of holding at 495 ° C. for 2.5 hours, cooling with water, and further holding at 200 ° C. for 6 hours.

[0034]

[Table 1]

In such forging, a part of the piston material W flows into the pin holding portion and the space for the skirt portion, and subsequently flows into the space for the rib portion,
Thus, the ribs 24a and 24b are formed. Therefore, the piston material tends to hardly reach the central portion 24f located at a position apart from the head portion, the pin holding portion, and the skirt portion of the lower edge 24c of the rib portions 24a and 24b. In such a case, there is a concern that cutout-shaped underfill may occur.

In the present embodiment, the rib portions 24a, 24
b is attached to the center portion 24f of the lower edge 24c.
The lower surface 32a of the lower mold 32 has a portion 32c corresponding to the central portion 24f, and the portion 32c of the lower surface 32a has an upwardly convex arc shape. Part and the skirt are alleviated. Therefore, the lower edge 2 of the ribs 24a, 24b
4c is formed according to the shape of the mold surface 32a of the lower mold 32, and the occurrence of underfill is prevented. As a result, it is possible to avoid problems such as breakage of the rib portion due to stress concentration due to a notch-shaped underfill or the like and reduction in rigidity of the skirt portions 23a and 23b and the pin boss portions 22a and 22b.

In this embodiment, the ribs 24a,
The boss side portion 24d of the lower edge 24c of the lower end 24b extends to near the lower end of the pin boss portion 22a, and the skirt side portion 24e extends further below the boss side portion 24d, so that the area of the rib portion increases accordingly. From the point of view, the rigidity of the rib portion itself can be increased, and the rigidity of the pin boss portion and the skirt portion can be increased accordingly.

In the engine 1 of this embodiment, when the intake valve 10 opens and the piston 20 descends during the intake stroke, the air-fuel mixture is sucked into the cylinder bore 7a through the intake valve opening 4j, particularly, near the cylinder center. And
It flows in the cylinder axial direction along the inner surface on the exhaust side of the cylinder bore 7a. Since a piston-side combustion recess 21a having a spherical shape was formed at the center of the upper surface of the piston 20,
The mixture flow flowing in the cylinder axis direction flows while reversing along the spherical combustion concave portion 21a, and a tumble flow is easily generated.

Even when the piston 20 rises during the compression stroke, the generated tumble flow is likely to remain due to the spherical combustion recess 21a on the upper surface of the piston. Furthermore, as the piston 20 rises, the combustion chamber B is formed by the combustion recess 21a on the piston side and the combustion recess 4b on the cylinder head 4, but the combustion recess 21a on the piston side has a spherical shape. Therefore, the entire combustion chamber B is closer to a spherical shape than a piston whose top surface is flat or protrudes upward. From this point, the tumble flow remains even at the end of the compression stroke (FIG. 1).
(See FIG. 10).

In this embodiment, the annular squish portion 21d is formed on the outer peripheral portion of the upper surface of the head portion 21 of the piston 20. The squish portion 21d of the piston side combustion concave portion 21a is formed at the end of the compression stroke. Part 21
It is easy to form a squish flow in which the air-fuel mixture in the outer peripheral portion of the cylinder bore is pushed to the center side by d and the outer peripheral portion 4k of the head side combustion recess 4b. The atomization of the air-fuel mixture is promoted by the squish flow and the tumble flow, so that the combustibility is improved and the engine performance is improved.

Here, in order to improve the engine performance,
In order to reduce the volume of the combustion chamber and increase the compression ratio, the position of the top dead center of the piston is brought close to the mating side of the cylinder head,
In order to increase the amount of intake air at the time of high-speed rotation, an intake stroke and an exhaust stroke are overlapped.
In this case, a recess is formed on the upper surface of the piston in order to avoid interference between the piston and an intake valve or an exhaust valve.

However, since the recess is a recess formed on the upper surface of the piston, the recess acts to inhibit the generation of the tumble flow. Therefore, in the present embodiment, when forming the spherical combustion concave portion 21a on the piston upper surface, the concave portion 21a and the squish portion 21a are formed.
The ridge line A with c is formed so as to pass through the recess portions 21b and 21c. Therefore, the recess depth of the recess portions 21b and 21c is reduced by the depth of the recess portion of the combustion recess 21a, and as a result, the inhibitory effect of the recess portions 21b and 21c on the tumble flow is reduced.

In the present embodiment, since the position of the top dead center of the piston 20 is close to the combustion recess 4b of the cylinder head 4, the overall height of the engine can be reduced accordingly. Further, since the combustion recess 21a is provided on the upper surface of the piston 20, the distance from the recess 21a to the piston ring becomes shorter,
This allows heat to be easily transmitted from the head portion 21 to the cylinder liner 7 via the piston ring, which is advantageous in heat radiation.

[0044]

[Brief description of the drawings]

FIG. 1 is a cross-sectional side view of an engine including a forged piston according to an embodiment of the present invention.

FIG. 2 is a plan view of the piston.

FIG. 3 is a partial cross-sectional side view of the piston.

4 is a sectional side view of the piston (IV-IV in FIG. 3).
FIG.

FIG. 5 is a partial cross-sectional bottom view of the piston.

FIG. 6 is a schematic diagram for explaining a rib portion of the piston.

FIG. 7 is a schematic diagram for explaining a combustion chamber formed by the piston and the cylinder head.

FIG. 8 is a schematic cross-sectional view of a press device for forging a piston.

FIG. 9 is a schematic sectional view of the piston forging press device.

FIG. 10 is a schematic diagram for explaining a forging process of the piston.

[Explanation of symbols]

 14 cycle engine 21 Head 21a Combustion recess 21b, 21c Recess 21d Squish A A ridge

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[Procedure amendment]

[Submission date] January 20, 1998

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG. 2

FIG. 3

FIG.

FIG. 4

FIG. 5

FIG. 6

FIG. 7

FIG. 8

FIG. 9

FIG. 10

Claims (1)

[Claims] A substantially spherical combustion recess is formed on the upper surface of a disk-shaped head portion, and a recess portion for avoiding interference with intake and exhaust valves is formed on the upper surface of the disk-shaped head portion. A piston for a four-stroke engine, wherein an annular flat squish portion is formed in an outer peripheral portion, and a ridge line between the squish portion and the combustion recess passes through the recess.