JP3147946B2 - Engine combustion chamber structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber structure of an engine.

[0002]

2. Description of the Related Art In an engine in which a piston is reciprocally slidable in a cylinder formed in a cylinder block, a certain gap is formed between the piston and the cylinder. For this reason, in order to ensure airtightness against the combustion gas in the combustion chamber, for example, in a gasoline engine, three piston ring grooves are formed on the upper outer periphery of the piston, and a compression ring for preventing leakage from the piston top to the two grooves is provided. An oil ring is fitted in the lower one groove so as to prevent the oil of the cylinder from entering the combustion chamber.

[0003] In such a structure, particularly in a high-speed operation region of the engine, abnormal wear may occur on a compression ring (hereinafter, referred to as a top ring) provided on the top of the outer periphery of the piston. The cause of this is that the top ring sticks to the upper wall surface of the ring groove due to the extremely large inertial force generated above the top ring at the time of piston top dead center, and furthermore, the combustion pressure is applied to this top ring. This is because the top ring operates and moves up and down in the ring groove. In other words, the expansion wave due to combustion enters the gap between the piston and the cylinder, and the air column vibration generated in this volume acts on the top ring periodically, causing the top ring stuck to the upper wall surface of the ring groove to ring. A reciprocating motion occurs, which strikes the lower wall surface of the groove. As a result, the inventor has found that abnormal wear occurs in the top ring. Further, as the engine approaches the high-speed operation region, the combustion temperature also increases, and there arises a problem regarding the reliability of the piston and the top ring with respect to the combustion temperature.

Japanese Utility Model Application Laid-Open No. 58-70423 discloses a structure in which the outer peripheral edge of the piston top surface is tapered off to the vicinity of the ring groove of the top ring. The air column resonance generated in the gap and the ring groove can be avoided in the engine rotation speed range. Japanese Utility Model Application Laid-Open No. 61-49020 discloses a structure in which a concave portion for adjusting the volume of a combustion chamber is formed in a cylinder at the upper end of the cylinder.

[0005]

However, in the former structure described above, since the outer peripheral edge of the piston top surface is tapered to the vicinity of the ring groove of the top ring, from the spark plug to the top ring. The path length through which the flame propagates is shortened, and is directly affected by the pressure wave and the combustion temperature caused by the combustion. For this reason, a problem such as breakage of the top ring or a ring stick occurs. Particularly, in the case of a high-speed or high-compression-ratio engine, it is extremely problematic to remove the outer peripheral edge of the piston top surface from the viewpoint of reliability against damage to the piston.

In the latter structure, a recess is formed in the cylinder wall at the upper end of the cylinder, and it becomes difficult for the flame generated by combustion to propagate to the bent portion formed by the recess. Unburned gas accumulates in the air, and the combustion property deteriorates.

Accordingly, an object of the present invention is to provide a combustion chamber structure of an engine capable of improving the reliability of a top ring against a pressure wave and a combustion temperature due to combustion without impairing the combustibility of the engine. .

[0008]

SUMMARY OF THE INVENTION Therefore, the invention according to claim 1 of the present application is directed to a cylinder formed in a cylinder block and a piston disposed in the cylinder so as to be able to reciprocate in the axial direction thereof. And a bottom surface of a cylinder head facing the top surface of the piston. In the combustion chamber structure of an engine in which a spark plug is provided on the bottom surface of the cylinder head, the piston at the time of top dead center of the piston Between the piston land portion above the piston ring groove on the topmost side and the cylinder wall, a substantially wedge-shaped resonance space which communicates with the combustion chamber and whose cross-sectional shape increases toward the combustion chamber side, This is a configuration provided on the cylinder wall.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, the bottom surface of the cylinder head is formed on a bottom surface of the piston starting from a top edge of the resonance space. It is configured to be formed in a concave portion that is depressed in a direction away from the device.

[0010]

Therefore, according to the structure of the first aspect of the present invention, at the time of the top dead center of the piston, the combustion chamber is located between the land above the piston ring groove on the topmost side of the piston and the cylinder wall. By providing a communicating resonance space,
The natural frequency of the expansion wave transmitted to the top ring can be greatly increased without reducing the flame propagation distance from the spark plug. Thereby, the influence of the combustion pressure wave and the combustion temperature acting on the top ring can be reduced. Furthermore,
Air column vibrations acting on the top ring in the engine operating range in the resonance space can be prevented, and abnormal wear of the top ring can be prevented.

According to the structure of the second aspect of the present invention, the first aspect
In addition to the operation of the invention, the bottom surface of the cylinder head is formed in a concave portion that is depressed in a direction away from the top surface of the piston, starting from the upper end peripheral portion of the resonance space, so that the top ring is further formed by the concave portion. The natural frequency of the expansion wave transmitted to is increased. Further, since the refraction part formed in the volume part by the concave part and the resonance space is minimized, the propagation of the flame by the combustion is not hindered.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention. 1 is a cylinder block, 2 is a cylinder head, and the cylinder head 2 is connected to the cylinder block 1 by a bolt or the like via a gasket 3. I have. 4 is a piston,
It is slidably disposed in a cylinder 5 formed in the cylinder block 1 and is located at the top dead center in the drawing.
Between the top surface of the piston 4 and the cylinder head 2,
A combustion chamber recess 6 is formed on the bottom surface of the cylinder head 2 to form a combustion chamber 7. A spark plug 8 faces the combustion chamber 7, and a squish portion S that narrows a gap between the outer peripheral edge of the top surface of the piston 4 and the cylinder head 2 is formed. Three ring grooves 9, 10, 11 are formed on the outer periphery of the upper part of the piston 4.
First and second compression rings 9 and 10 respectively
a (hereinafter referred to as a top ring), a second compression ring 10a, and an oil ring 11a. A land 12 is formed on the outer periphery of the piston 4 above the ring groove 9. An intake port 13 and an exhaust port 14 are respectively opened on the bottom surface of the cylinder head 2 forming the combustion chamber 7, and these ports are selectively opened and closed by an intake valve 15 and an exhaust valve 16, respectively. It has become.

At the upper end of the cylinder 5, a wedge-like shape is formed upward from the position facing the upper wall surface of the ring groove 9 in which the top ring 9 a is fitted at the top dead center position of the piston 4 to the upper end of the cylinder 5. The enlarged resonance space 17 is provided over the entire circumference of the cylinder 5.

A water jacket 18 is formed around the cylinder 5 of the cylinder block 1.
The water jacket 18 further includes the resonance space 17.
And is communicated with the cylinder head 2.
Therefore, the deterioration of the knocking resistance performance caused by the resonance space 17 moving away from the spark plug 8 is suppressed by the temperature of the wall surface of the resonance space 17 being lowered by the water jacket 18 being close to the resonance space 17 side. Is done.

In the above-described embodiment, an expansion wave generated by combustion is generated near the top dead center of the piston by the resonance space 1.
7 to the top ring 9a. This resonance space 1
7, the natural frequency of the expansion wave transmitted to the top ring 9a can be increased, and the air column vibration generated in the resonance space 17 can be excluded from the engine operating range. Therefore, vertical movement of the top ring 9a in the top ring groove 9 due to air column vibration is prevented, and the top ring 9a
Abnormal wear can be reduced.

Further, since the resonance space 17 is provided on the cylinder 5 side, the ignition plug 8 is connected to the top ring 9.
The path length through which the flame propagates to a is not reduced. Therefore, the top ring 9a is not directly affected by the combustion pressure wave and the combustion temperature.
Reliability can be improved. Since the resonance space 17 is formed in a substantially wedge shape that expands toward the combustion chamber side, the pressure wave to be propagated can be attenuated, and the reliability of the top ring 9a can be further improved.

In the above-described embodiment, the resonance space 17 is provided on the entire circumference of the cylinder 5. Alternatively, the resonance space 17 may be partially provided as in the second embodiment shown in FIG. That is, in the end gas zone on the exhaust port 14 side, the temperature becomes locally high, and before the flame propagates from the ignition plug 8, the unburned gas in the end gas zone spontaneously ignites and causes rapid combustion at once. . Therefore, particularly in this portion, the vertical movement of the top ring 9a is promoted and abnormal wear is likely to occur. Therefore, as shown in FIG. 2, the resonance space 17 is provided only in this portion.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that the same members as those in FIG. 1 of the first embodiment are denoted by the same reference numerals, description thereof will be omitted, and only the characteristic structure will be described.

FIG. 3 shows a combustion chamber structure of an engine according to a third embodiment of the present invention. 3, the upper end of the cylinder 5 is formed in a wedge shape from the position facing the upper wall surface of the ring groove 9 in which the top ring 9a is fitted at the top dead center position of the piston 4 to the upper end of the cylinder 5. The enlarged resonance space 17 is provided over the entire circumference of the cylinder 5. Further, starting from the upper peripheral edge of the cylinder 5, that is, the upper peripheral edge of the resonance space 17, a recessed space 19 formed in a tapered shape that is depressed in a direction substantially toward the center of the combustion chamber 7 and away from the top surface of the piston 4. It is provided in the combustion chamber cavity 6.

Accordingly, in the third embodiment, the space between the top surface of the piston 4 and the bottom surface of the cylinder head 3 by the concave space 19 provided at the lower peripheral edge of the recess 6 of the combustion chamber enters the resonance space 17. And the natural frequency of the resonance space can be reliably increased. Therefore, abnormal wear of the top ring 9a can be prevented by removing the air column resonance generated in the above-mentioned volume portion out of the practical rotation range of the engine.

In the above embodiment, the spark plug 8 is arranged at the center of the combustion chamber 7. However, when the spark plug 8 is offset from the center of the combustion chamber 7, the resonance space 17 and the concave space 19 are separated from the ignition plug 8. It may be provided only in the farthest part. Thereby, the most accelerated expansion wave can be effectively attenuated.

[0023]

Therefore, according to the structure of the first aspect of the present invention, at the time of the top dead center of the piston, the piston land portion above the piston ring groove on the topmost side of the piston and the cylinder wall. By providing the resonance space communicating with the combustion chamber, the natural frequency of the expansion wave transmitted to the top ring can be greatly increased without shortening the flame propagation distance from the ignition plug. Thereby, the influence of the combustion pressure wave and the combustion temperature acting on the top ring can be reduced. Furthermore, it is possible to prevent air column vibrations acting on the top ring in the engine operating range in the resonance space, thereby preventing abnormal wear of the top ring. In addition, since the resonance space has a wedge shape that is enlarged upward, the pressure wave is attenuated by the wedge shape and propagates to the top ring, so that the reliability of the top ring can be further improved. .

According to the configuration of the second aspect of the present invention, the first aspect
In addition to the effects of the present invention, the bottom surface of the cylinder head facing the top surface of the piston is formed in a concave portion that is depressed in a direction away from the top surface of the piston, starting from the upper peripheral edge of the resonance space. Therefore, the natural frequency of the expansion wave transmitted to the top ring by the concave portion can be further increased. Further, since the refraction part formed in the volume part by the concave part and the resonance space is minimized, the propagation of the flame by the combustion is not hindered. Therefore, generation of unburned gas is suppressed, and flammability can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view around a combustion chamber of an engine according to a first embodiment of the present invention.

FIG. 2 is a plan view of a combustion chamber of an engine according to a second embodiment of the present invention.

FIG. 3 is a longitudinal sectional view around a combustion chamber of an engine according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cylinder block, 2 ... Cylinder head, 4 ... Piston, 5 ... Cylinder, 7 ... Combustion chamber, 8 ... Spark plug, 9
... top ring groove, 9a ... top ring, 12 ... land part, 17 ... resonance space, 19 ... concave space.

Claims (2)

(57) [Claims] 1. A cylinder formed in a cylinder block, a piston disposed in the cylinder so as to be reciprocally slidable in the axial direction thereof, and a bottom surface of a cylinder head facing a top surface of the piston. In a combustion chamber structure of an engine in which a spark plug is disposed on a bottom surface of the cylinder head, a piston land portion above a piston ring groove on a topmost side of the piston at the time of top dead center of the piston and the cylinder A combustion chamber structure for an engine, wherein a substantially wedge-shaped resonance space which communicates with the combustion chamber and whose cross-sectional shape increases toward the combustion chamber is provided between the cylinder wall and the wall. 2. The cylinder head according to claim 1, wherein the bottom surface of the cylinder head is formed in a concave portion starting from an upper peripheral edge of the resonance space and away from a top surface of the piston.