JP2001164939A - Combustion chamber of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve combustion efficiency by reducing difference between flame propagating distances to respective peripheral parts of a combustion chamber, in the combustion chamber in which an intake valve port, an exhaust valve port, and an ignition plug attaching port are respectively formed in an inner surface of a depression. SOLUTION: A center part of a part 6 between the valve ports is arranged so as to be offset from a position of a cylinder center axial line 9 toward a side opposite to an ignition plug side, and the depression 2 is constituted by comprising at least three surfaces of a pent roof shape surface 21, an ignition plug attaching surface 22, and a side surface 23 opposite to the ignition plug. The pent roof shape surface 21 is constituted such that two surfaces of an inclined surface formed with the intake valve port 3 and an inclined surface formed with the exhaust valve port 4 cross to each other. The ignition plug attaching surface 22 is provided with the ignition plug attaching port 5, and is formed into a gentle inclined surface connected to the pent roof shape surface 21. The side surface 23 opposite to the ignition plug is connected to the pent roof shape surface 21 and is formed into an heavier inclined surface than the inclined surface of the ignition plug attaching surface 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a combustion chamber of an engine.

[0002]

2. Description of the Related Art FIG.
There are the following. This combustion chamber has the following configuration. First, the piston 1 of the cylinder head 101
A depression 102 is provided on a surface facing the cylinder 11, and an intake valve port 103, an exhaust valve port 104, and a spark plug mounting port 105 are provided on the inner surface of the depression 102 when viewed in a direction parallel to the cylinder center axis 109. These openings are opened
4 and 105 are arranged on three sides surrounding the center of the depression 102.

[0003] The recess 102 is provided with an intake valve port 103.
And a pent-roof-shaped surface 121 formed by intersecting two inclined surfaces of a sloping surface formed with an exhaust valve port 104 and the pent-roof-shaped surface 12.
A spark plug mounting port 105 is formed at the position of the first ridgeline 125. An ignition plug 112 is attached to the ignition plug attachment port 105. Further, squish surfaces 107 and 108 are formed on the outer periphery of the depression 102. FIG.
In the figure, reference numeral 106 indicates a portion between valve openings.

[0004]

The above prior art has the following problems. In the configuration of the combustion chamber, FIG.
As shown in (B), since the ignition plug 112 is configured to protrude into the ridgeline 125 of the pentroof-shaped surface 121, the ignition point of the ignition plug 112 is formed at a position far away from the center of the depression 102. Have been. In such a configuration, a large difference occurs in the flame propagation distance to each peripheral portion of the combustion chamber, and it becomes difficult to improve the combustion efficiency.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a combustion chamber of an engine that can solve the above problems. An example of a specific purpose is as follows. (A) In a combustion chamber in which an intake valve port, an exhaust valve port, and a spark plug mounting port are opened one by one on the inner surface of the depression, a difference in flame propagation distance to each peripheral portion of the combustion chamber is reduced. Improve combustion efficiency. (B) In the intake process, the generation of turbulence in the depression is suppressed so that the mixture can smoothly flow into the cylinder. (C) In the intake process, a swirl flow can be generated in the cylinder. It should be noted that the problems of the invention other than those described above and the means for solving the problems will be described in detail in the description in the following specification.

[0006]

The first invention is, for example, shown in FIG.
As shown in FIG. 1, a depression 2 is provided on the surface of the cylinder head 1 facing the piston 11, and the intake valve port 3 and the exhaust valve port 4 are formed on the inner surface of the depression 2 when viewed in a direction parallel to the cylinder center axis 9. In the combustion chamber of the engine in which the spark plug mounting ports 5 are opened one by one, and these ports 3, 4, 5 are arranged on three sides surrounding the center of the recess 2, the center of the valve port portion 6 is The recess 2 includes at least three surfaces of a pent roof-shaped surface 21, a spark plug mounting surface 22, and a non-spark plug side surface 23. The pent roof-shaped surface 21 is formed by intersecting two inclined surfaces of an inclined surface on which the intake valve port 3 is formed and an inclined surface on which the exhaust valve port 4 is formed. The spark plug mounting surface 22 A spark plug mounting port 5 is provided, and has a gentle slope connecting to the pent roof-shaped surface 21. The anti-spark plug side surface 23 is connected to the pent roof-shaped surface 21 and is closer to the spark plug mounting surface 22. Is also characterized by a large slope.

According to a second aspect of the present invention, as shown in FIG. 1, for example, in the first aspect, the pentroof-shaped surface 21 is formed of an inclined surface on which the intake valve port 3 is formed and an inclined surface on which the exhaust valve port 4 is formed. It has a valve opening portion 6 where two inclined surfaces intersect,
The valve opening portion 6 is formed so as to be deepest at the central portion and gradually become shallower toward both sides, so that the ridgeline 25 (FIG. 1) of the pent roof-shaped surface 21 is formed.
(B) is convexly curved upward. In the third invention, for example, as shown in FIG. 1, in the first invention and the second invention, when the recess 2 is viewed in a direction parallel to the cylinder center axis 9, the side face 23 of the anti-ignition plug is positioned at a central portion X thereof. Are characterized by being curved so that the inclination is small and the inclination is large at the peripheral portion Y.

According to a fourth aspect of the present invention, as shown in FIG. 1, for example, in the first to third aspects, the opening 10 of the recess 2 is provided.
Is formed in a substantially chestnut shape, and the intake valve port 3 and the exhaust valve port 4 are arranged on the bottom side of the chestnut shape.
Is arranged on the vertex side of the chestnut real shape. A fifth invention is, for example, as shown in FIG. 1, in the configuration of the fourth invention, the pent roof-shaped surface 21 and the spark plug corresponding to the position of at least one of the oblique sides 30 and 31 of the substantially chestnut-shaped opening 10. It is characterized in that substantially triangular inclined surfaces 32 and 33 that smoothly connect to both of the mounting surfaces 22 are formed.

In a sixth aspect, as shown in FIG. 1, for example, in the first to fifth aspects, at least a plug-side squish surface portion 8 and a non-plug-side squish surface portion 7 are formed. 7 is characterized in that the squish flow is formed in a direction parallel to the ridgeline 25 of the pent roof-shaped surface 21. A seventh invention is, for example, as shown in FIG. 1, in the fourth invention to the sixth invention, a position inside the squish surface portion (including not the squish surface portions 8.7) and a position outside the opening 10 of the depression 2. In addition, gentle slopes 40a and 40b are formed.

[0010] Each of the second to seventh inventions does not depend on the other inventions as needed, and can be combined with the configurations described in the following embodiments to constitute independent inventions.

[0011]

According to the first aspect of the present invention, since the central portion of the portion between the valve ports is disposed deviated from the position of the cylinder center axis toward the anti-spark plug side, the ignition plug is connected to the central portion of the combustion chamber. It is possible to reduce the difference in flame propagation distance from the spark plug to each peripheral portion of the combustion chamber. In addition, compared to a configuration in which a pent roof-shaped surface is provided in the depression and an ignition plug is attached to the ignition plug mounting surface formed by a gentle slope, the ignition plug is inserted in a state of protruding into the ridge line of the pent roof-shaped surface. The spark plug can be made closer to the center of the chamber, and the difference in the flame propagation distance to the periphery of the combustion chamber can be reduced. Furthermore, since the side of the anti-spark plug located on the opposite side to the mounting surface of the spark plug in the recess has a slope that is larger in inclination than the mounting surface of the spark plug, the distance from the spark plug to the side of the anti-spark plug is shortened. The difference in flame propagation distance to each peripheral portion of the combustion chamber can be reduced.
As described above, the configuration that can reduce the difference in the flame propagation distance can increase the combustion efficiency and obtain a high output.

According to the second aspect of the present invention, the pentroof-shaped surface and the spark plug mounting surface, and the pentroof-shaped surface and the anti-spark plug side surface are smoothed in the ridgeline direction by curving the ridge of the pentroof-shaped surface upward. Can be connected to With this configuration, when the air-fuel mixture that has entered through the intake valve port is sucked downward from the cylinder, compared to the case where the ridgeline of the pentroof-shaped surface is straight, the pentroof-shaped surface and the spark plug are attached. The occurrence of turbulence at the connection between the surface and the connection between the pent roof surface and the side of the anti-spark plug can be suppressed, and the flow into the cylinder can be performed smoothly.

According to the third aspect of the invention, a part of the air-fuel mixture sucked from the intake valve port in the suction step is guided by the curved side face of the anti-spark plug, and from the center of the side face of the anti-spark plug to the center of the combustion chamber. Is sucked into the cylinder such that a downward swirling flow is generated. Therefore,
Mixing of fuel and air can be improved as compared to a configuration in which the side of the anti-ignition plug is not curved, and the combustibility can be improved.

In the fourth aspect, the volume of the depression is set to a predetermined value in order to obtain a predetermined compression ratio. By forming the opening of the depression in a substantially chestnut shape, the ridgeline of the pent roof-shaped surface can be formed at a deep position in the depression, and the specific surface area of the depression, that is, the ratio of the surface area to the volume can be reduced. For this reason, the cooling loss from the inner surface of the depression is reduced, the combustion efficiency is high, and a high output can be obtained.

According to the fifth aspect of the invention, by forming the substantially triangular inclined surface, the inner wall of the depression corresponding to the position of the hypotenuse of the substantially chestnut-shaped opening is formed with respect to the region outside the hypotenuse of the opening. The connection can be made smoothly, and the occurrence of turbulence at the position of the oblique side of the opening can be suppressed in the suction process.

According to the sixth aspect, a squish flow can be formed in a direction parallel to the ridgeline of the pent roof surface at a later stage of the compression step, so that the uniformity of the air-fuel mixture around the ignition point of the ignition plug can be improved. Can be. According to the seventh aspect, by forming the gentle slope region, the squish flow generated from the squish surface portion can be moderately weakened as compared with the case where all the gentle slope region is used as the squish surface portion. The inside can be prevented from being disturbed more than necessary by a strong squish flow.

[0017]

Embodiments of the present invention will be described with reference to the drawings. 1 to 4 are views showing one embodiment of a combustion chamber of an engine according to the present invention. As shown in FIGS. 1B and 1C, the piston 11 is fitted into the cylinder 13,
The cylinder head 1 is attached to the cylinder 13. The surface of the cylinder head 1 facing the piston 11 is retracted from the mating surface 14 with the cylinder 13. A part of the surface facing the piston 11 is further retracted, and this is the depression 2. As shown in FIG. 1 (A), when viewed in a direction parallel to the cylinder center axis 9, an intake valve port 3, an exhaust valve port 4, and a spark plug mounting port 5 are respectively opened on the inner surface of the recess 2. ing. These ports 3, 4 and 5 are arranged on three sides surrounding the center of the depression 2.

The surface of the cylinder head 1 facing the piston 11 includes a squish surface and the depression 2. The depression 2 has a region inside the substantially chestnut-shaped opening 10 and the opening 10. It is composed of an outer region. Further, in the embodiment shown in FIG.
The case where the squish surface portion is formed on the entire outer peripheral edge of the surface facing the piston 11 is shown. In the embodiment shown in FIG. 1, it is assumed that the upper surface of the piston 11 is flat.

The configuration of the depression 2 will be described. Hollow 2
As shown in FIG. 1 (A), the opening 10 is formed in a chestnut shape when viewed in a direction parallel to the cylinder center axis 9,
The intake valve opening 3 and the exhaust valve opening 4 are arranged on the bottom side of the chestnut shape,
The configuration is such that the spark plug mounting port 5 is arranged on the vertex side of the chestnut shape. The central portion of the valve opening portion 6 is arranged so as to be deviated from the position of the cylinder center axis 9 to the side opposite to the plug.

The area inside the opening 10 of the depression 2 includes at least three surfaces of a pent roof-shaped surface 21, a spark plug mounting surface 22, and an anti-spark plug side surface 23. The pentroof-shaped surface 21 is configured by two inclined surfaces of an inclined surface on which the intake valve port 3 is formed and an inclined surface on which the exhaust valve port 4 is formed. The intake valve port 3 and the exhaust valve port 4 are arranged on both sides of the valve. As shown in FIG. 1A, the interportion portion 6 has a shape in which the center is narrow and the sides are wide. The spark plug mounting opening 5 is opened in the spark plug mounting surface 22 to form a gentle slope connected to the pent roof surface 21. A spark plug 12 is inserted and fixed in the spark plug mounting opening 5. The connecting portion between the pent roof surface 21 and the spark plug mounting surface 22 is represented as a forked line 41 in FIG.

The anti-spark plug side surface 23 is connected to the pent roof-shaped surface 21 and is an inclined surface having a larger inclination than the spark plug mounting surface 22. The connecting portion between the pent roof surface 21 and the anti-spark plug side surface 23 is shown as a flat normal distribution curve 42 in FIG.

FIG. 2A shows the spark plug mounting surface 22,
FIG. 2 (B) is a diagram for explaining how to set the inclination angle of the anti-ignition plug side surface 23, and FIG. 2 (B) is a diagram showing the hollow space three-dimensionally. It is a figure for explaining the relation with an opening. As shown in FIG. 2A, the inclination angle φ of the anti-spark plug side surface 23 with respect to the cylinder horizontal line 49 is different from the cylinder horizontal line 49 of the spark plug mounting surface 22.
(Φ> θ).

Further, as shown in FIG.
The inner hollow space is composed of two inclined surfaces 44
A part of the pent-roof-shaped surface 21 formed by a part of the part 45 is formed by crossing a spark plug mounting surface 22 intersecting at an angle θ and an anti-spark plug side surface 23 intersecting at an angle φ. It has a shape close to the space composed of parts. For example, a shape close to the hollow space in the opening 10 can be created by cutting out the upper part of the above-mentioned substantially roof shape with a predetermined plane or the like so that the cut end becomes substantially a chestnut shape. In FIG. 2B, FIG.
, And the curved surfaces of the substantially triangular inclined surfaces 32 and 33 and the side surface 23 of the anti-ignition plug are omitted.

The pent roof surface 21 is shown in FIG.
(B), as shown in FIG. 2 (A), the central portion of the valve opening portion 6 is the deepest, and is formed so as to be gradually shallower toward both sides, so that the pent roof surface is formed. The ridgeline 21 is formed so as to be convexly curved upward. By configuring the inter-valve portion 6 in this manner, the connection between the pent roof-shaped surface 21 and the spark plug mounting surface 22 can be improved as compared with the case where the ridgeline 25 is a straight line 43 as shown by a dashed line in FIG. And the connecting portion between the pent roof surface 21 and the anti-spark plug side surface 23 can be connected smoothly.

Next, the configuration of the anti-spark plug side surface 23 in this embodiment will be described. As shown in FIG. 1 (A), the anti-spark plug side surface 23 is configured to be curved so that the inclination is small at the central portion X and large at the peripheral portion Y. FIG. 3A is a longitudinal sectional view showing the flow of the air-fuel mixture when the piston descends.
FIG. 3B is a schematic diagram showing the inside of a concave in which the side of the anti-ignition plug is curved, and FIG. 3C is the case where the side of the anti-ignition plug is formed like a vertically steep cliff (φ = 90 °). FIG. 3D is a vertical cross-sectional view taken along the line DD in FIG. 1A. As can be seen by comparing FIG. 3 (D) with FIG. 1 (B), the central portion X
3D, the inclination of the peripheral portion Y shown in FIG. 3D is larger.

By configuring as shown in FIG. 3B,
As compared with the configuration of FIG. 3C, the flow 46 of the air-fuel mixture escaping to the exhaust valve port 4 side can be reduced, and
As shown in (A), a part of the air-fuel mixture sucked from the intake valve port 3 is guided by the curved anti-spark plug side 23 as the piston descends, and burns from the center of the anti-spark plug side 23. It can be sucked into the cylinder to generate a downward swirling flow 47 toward the center of the chamber. By the swirling flow 47, the mixing of the fuel and the air can be made uniform, and the combustibility can be improved.

Next, the configuration of the substantially triangular inclined surfaces 32 and 33 in this embodiment will be described. As shown in FIG. 1 (A), both oblique sides 30 of the substantially chestnut-shaped opening 10.
Corresponding to the position 31, substantially triangular inclined surfaces 32 and 33 are formed which are smoothly connected to both the pent roof surface 21 and the spark plug mounting surface 22. This substantially triangular inclined surface 32
33 is provided on the inner wall at the boundary between the forked line 41 shown in FIG. 2B and the substantially chestnut-shaped opening 10 to prevent a step 48 as shown in FIG. Have been. That is, the step 48 as shown in FIG.
By providing the substantially triangular inclined surfaces 32 and 33 at the portions where the undulations occur, as shown in FIG.
The inner wall of the depression 2 corresponding to the position of the hypotenuse 30/31 of 0
It can be smoothly connected to the region 35 outside the oblique sides 30 and 31 of the opening 10, and can be connected to the oblique sides 30 and 31 of the opening 10.
The occurrence of turbulence at the position 31 can be suppressed.

Finally, the configuration of the squish surface and the gentle slopes 40a in this embodiment will be described. As shown in FIG. 1A, an anti-plug side squish surface 7 is formed at a location separated from the spark plug mounting port 5 by a valve port portion 6. The non-plug side squish surface 7 is formed in an arc shape along the outer peripheral edge of the surface of the cylinder head 1 facing the piston 11. The gentle slope 40a on the anti-plug side is formed in an arcuate region between the arc-shaped anti-plug side squish surface 7 and the substantially chestnut-shaped bottom.

A plug-side squish surface 8 is formed at a location separated from the non-plug-side squish surface 7 by the inter-valve portion 6 and the spark plug mounting hole 5. The radial width of the plug-side squish surface 8 is substantially the same as the radial width of the non-plug-side squish surface 7.
The plug side squish surface portion 8 is also arranged along the outer peripheral edge of the surface of the cylinder head 1 facing the piston 11, and is formed in an arc shape. Gentle slope 40b on plug side
Is formed in a substantially crescent-shaped region between the arc-shaped plug-side squish surface portion 8 and the two substantially hypotenuse-shaped oblique sides 30 and 31. By forming these gentle slopes 40a and 40b, it is possible to moderately reduce the squish flow generated from the squish surface portion, and it is possible to suppress the inside of the depression 2 from being disturbed more than necessary by the strong squish flow.

In order to obtain a predetermined compression ratio, the depression 2
Is set to a predetermined value. Therefore, the slope 4
When the recesses 0a and 40b are formed, the specific surface area of the recess 2 can be reduced as compared with the case where the recess 2 is expanded to this position. Therefore, the cooling loss from the inner surface of the depression 2 is reduced, the combustion efficiency is high, and a high output is obtained. Further, when the gentle slopes 40a and 40b are formed, the unburned fuel remains less than when the squish surface is expanded so far. Therefore, there is an advantage that the combustion efficiency can be increased and a high output can be obtained.

The present invention is not limited to the above embodiment, and various design changes can be made within the scope of the present invention. (1) In the above-described embodiment, the configuration in which the gentle slopes 40a and 40b are provided in the area 35 outside the substantially chestnut-shaped opening 10 is shown, but the squish surface portion is expanded to the area of the slopes 40a and 40b. It is possible. in this case,
The depression 12 corresponds to the decrease in the volume of the slopes 40a and 40b.
Can be deeper.

(2) In the above-described embodiment, the case where the squish surface portion is formed along the entire outer peripheral edge of the surface of the cylinder head 1 facing the piston 11 has been described. A configuration in which only the non-plug side squish surface portion 7 is formed and the squish surface portion is not formed on the other outer periphery may be adopted.

[Brief description of the drawings]

FIG. 1 is a view for explaining a combustion chamber of an engine according to a first embodiment of the present invention. FIG. 1 (A) is a bottom view of a piston facing surface of a piston head, and FIG. 1 (B) is FIG. 1 (A). 1 (C) is a vertical cross-sectional view taken along line CC of FIG. 1 (A).

FIG. 2 (A) is a diagram for explaining how to set the inclination angle of the spark plug mounting surface and the side surface of the anti-ignition plug, and FIG.
(B) is a figure which shows the hollow space three-dimensionally, and is a figure for demonstrating the relationship between the three surfaces of a pent roof-shaped surface, a spark plug mounting surface, the side opposite a spark plug, and a chestnut-shaped opening. .

FIGS. 3A and 3B are diagrams for explaining an operation in which the side surface of the anti-ignition plug is curved. FIG. 3A is a longitudinal sectional view of a combustion chamber in an intake process, and FIG. FIG. 3 is a diagram showing the flow of the intake air-fuel mixture when the side surface of the spark plug is curved;
FIG. 3C is a diagram showing a flow of the intake air-fuel mixture when the side surface of the anti-ignition plug is not curved, and FIG. 3D is a schematic vertical sectional view taken along line DD of FIG. 1A.

4A and 4B are diagrams for explaining the operation of the substantially triangular inclined surface, FIG. 4A is a longitudinal sectional view showing a configuration in which the substantially triangular inclined surface is not formed, and FIG. It is a longitudinal cross-sectional view which shows the structure at the time of forming a substantially triangular inclined surface.

FIG. 5 is a view for explaining a combustion chamber of an engine according to the related art. FIG. 5 (A) is a bottom view of a piston facing surface of a piston head, and FIG. 5 (B) is a view of FIG. 5 (A). FIG. 5C is a vertical sectional view taken along line BB of FIG. 5A.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cylinder head, 2 ... Depression, 3 ... Intake valve port, 4 ... Exhaust valve port, 5 ... Spark plug mounting port, 6 ... Portion between valve ports, 7 ...
Non-plug side squish surface portion, 8: plug side squish surface portion, 9: cylinder center axis line, 10: recess opening, 11 ...
Piston, 21 ... Pent roof type surface, 22 ... Spark plug mounting surface, 23 ... Anti-ignition plug side surface, 25 ... Pent roof type surface ridgeline, 30/31 ... Hentral side of dent opening, 32.3
3: substantially triangular inclined surfaces, 40a and 40b: inclined surfaces, X: central portion of the side of the anti-spark plug, Y: peripheral portion of the side of the anti-spark plug.

Continuation of the front page F term (reference) 3G019 KA12 KA17 KA18 3G023 AA02 AA07 AB03 AD03 AD04 AD08 AD12 3G024 AA01 AA04 AA06 AA09 AA11 DA01 DA04

Claims (7)

[Claims] A recess (2) is provided on a surface of a cylinder head (1) facing a piston (11), and a cylinder center axis (9) is provided.
When viewed in a direction parallel to
(3), an exhaust valve port (4), and a spark plug mounting port (5) are opened one by one, and these ports (3, 4, 5) are arranged on three sides surrounding the center of the recess (2). In the combustion chamber of the engine, the central portion of the inter-valve portion (6) is disposed so as to be deviated from the position of the cylinder center axis (9) toward the anti-spark plug side, and the depression (2) has a pent roof shape. Surface (21), a spark plug mounting surface (22), and at least three surfaces of an anti-spark plug side surface (23), and the pent roof type surface (21) is provided with an intake valve port (3). The ignition plug mounting surface (22) is formed by intersecting two inclined surfaces, that is, the inclined surface on which the exhaust plug opening (4) is formed, and the inclined surface on which the exhaust plug opening (4) is formed. )
A gently inclined surface connected to the pent roof-shaped surface (21), and the anti-spark plug side surface (23) is provided with the pent roof-shaped surface.
(21) and the spark plug mounting surface (22)
A combustion chamber of an engine, characterized by having an inclined surface having a greater inclination than that of the engine. 2. The combustion chamber of an engine according to claim 1, wherein the pent roof surface (21) has an intake valve opening.
There is an inter-portion portion (6) at which two inclined surfaces intersecting the inclined surface formed with (3) and the inclined surface formed with the exhaust valve port (4), and the inter-portion portion (6) is The ridge line (2) of the pent roof-shaped surface (21) is formed by forming the center portion to be the deepest and to become gradually shallower toward both sides.
5) A combustion chamber of an engine, wherein the combustion chamber is curved upwardly. 3. In the combustion chamber of the engine according to claim 1, when the recess (2) is viewed in a direction parallel to the cylinder center axis (9), anti-ignition occurs. A combustion chamber of an engine, characterized in that a plug side surface (23) is curved so that its inclination is small at a central portion (X) and is large at a peripheral portion (Y). 4. The combustion chamber of an engine according to claim 1, wherein the depression (2) is provided.
Opening (10) is formed substantially in the shape of a chestnut. The intake valve port (3) and the exhaust valve port (4) are arranged on the bottom side of the chestnut shape, and a spark plug mounting port (5) is provided. The combustion chamber of the engine, characterized in that is arranged at the top of the chestnut shape. 5. The pentroof-shaped surface (21) corresponding to the position of at least one oblique side (30, 31) of the substantially chestnut-shaped opening (10) in the combustion chamber of the engine according to claim 4. ) And an ignition plug mounting surface (22), and a substantially triangular inclined surface (32, 33) is formed so as to smoothly connect to the ignition plug mounting surface (22). 6. A combustion chamber for an engine according to claim 1, wherein a squish surface portion (8) on the plug side and a squish surface portion (7) on the opposite side are formed. The combustion chamber of the engine, characterized in that the squish surfaces (8, 7) are formed so as to form a squish flow in a direction parallel to the ridgeline (25) of the pentroof-shaped surface (21). 7. The combustion chamber of an engine according to claim 4, wherein the gradual movement is provided at a position inside the squish surface and outside the opening (10) of the depression (2). A combustion chamber of an engine, characterized in that the slopes (40a, 40b) are formed.