JP2020165337A - Piston of internal combustion engine - Google Patents

Abstract

To provide a piston capable of realizing uniform combustion by preventing a phenomenon that an air-fuel mixture locally stays in a compression stroke.SOLUTION: A piston 9 used in a pent roof-type internal combustion engine is provided with an intake-side recess 12 at its top face for releasing an intake valve 6 at an initial period of an intake stroke. The intake-side recess 12 is held by an outer ridge line 14 and an inner ridge line 16, and at least the inner ridge line 16 is rounded with a radius of curvature of 3 mm or more. When an air-fuel mixture flows from an outer peripheral side to an exhaust side in a compression stroke, the air-fuel mixture smoothly flows along the inner ridge line 16. Accordingly, a phenomenon that eddy current generates on a part of the inner ridge line 16, and the air-fuel mixture stays, does not occur, and diffusibility of the air-fuel mixture can be improved. As this can be easily applied to an existing piston 9, and only small change not affecting a compression ratio and the like, is needed, versatility is improved with excellent reality.SELECTED DRAWING: Figure 4

Description

The present invention relates to a piston of an internal combustion engine, and particularly preferably a piston of an internal combustion engine having a pent roof type combustion chamber.

In a spark-ignition type internal combustion engine, if a tumble flow is applied to the intake air sucked into the cylinder bore, the mixture of fuel and air is enhanced, which can contribute to the improvement of output and the prevention of deterioration of the exhaust gas component. Therefore, many improvements have been proposed to generate a strong tumble flow, which can be divided into improvements for the intake port and improvements for the piston.

Improvements to the piston often focus on smoothing the flow of the air-fuel mixture, but at the top of the piston there is an intake side recess to allow the intake valve to escape at the beginning of the intake stroke and at the end of the exhaust stroke. If exhaust side recesses are formed to allow the exhaust valve to escape, these recesses can impede the smooth flow of the air-fuel mixture.

Therefore, in Patent Document 1, for the purpose of smoothing the flow of the air-fuel mixture in the intake stroke, the ridgelines located on the outer peripheral side and the axial center side with the recess in between are rounded and the ridgeline on the outer peripheral side is rounded. It is disclosed that the radius of curvature of the roundness of is smaller than the radius of curvature of the roundness of the ridgeline on the axial side.

Japanese Unexamined Patent Publication No. 2014-122589

By the way, in an internal combustion engine having a pent roof type combustion chamber, the flow direction of the tumble flow generated at the beginning of the intake stroke and the compression stroke changes from the intake side to the exhaust side in the compression stroke, and the flow flows as the compression progresses. It is crushed and decomposed into a large number of small streams, eventually forming a collection of fine vortices, and as a result, the flame propagation speed can be increased and uniform combustion can be achieved.

Therefore, in order to fully enjoy the effect of the tumble flow, it is necessary not only to generate a strong tumble flow in the intake stroke, but also to crush the flow evenly in the compression stroke to make it finer. The air-fuel mixture needs to flow smoothly along the top surface of the piston.

However, as analyzed by the inventor of the present application, when a recess is formed on the top surface, a phenomenon of vortex (stagnation), which is thought to be due to a pressure change, is observed when the air-fuel mixture crosses the ridgeline of the recess in the compression stroke. As a result, there is a risk that the mixing of the air-fuel mixture will be suppressed and the uniformity of combustion will be insufficient, or that the air-fuel mixture will partially stay and cause knocking.

On the other hand, Patent Document 1 discloses that the ridgeline is rounded to smooth the flow of the air-fuel mixture, but this is not an analysis of the behavior of the air-fuel mixture in the compression stroke, but the compression stroke. It can be said that it does not suggest the composition of improving the mixing property in.

The present invention has been made in the wake of such a situation, and is intended to realize a configuration in which the tumble flow formed in the intake stroke is evenly dispersed in the compression stroke.

The piston of the present invention
"On the top surface facing the cylinder head, an intake side recess for letting the intake valve escape and an exhaust side recess for letting the exhaust valve escape are formed. Therefore, the recess is an outer ridge line located on the outer peripheral side. It is sandwiched between the inner ridge line located on the axis side. "
In the basic configuration
"At least on the inner ridge of the intake side recess, a roundness with a radius of curvature of 3 mm or more is formed that can prevent the generation of a vortex when the air-fuel mixture flows from the axial center side through the outer circumference in the compression stroke."
It has the feature.

By the way, in the pent roof type internal combustion engine, in the compression stroke, the air-fuel mixture tends to flow from the axis toward the outer peripheral portion and returns to the exhaust side through the outer peripheral portion, but the recess for releasing the valve is exhaust. In the conventional technique in which the intake side is deeper than the side and the edge of the ridge line stands, when the air-fuel mixture flows from the deep intake side recess to the exhaust side in the compression stroke, when the air-fuel mixture crosses the inner ridge line. It is presumed that the pressure change occurred and the vortex flow was likely to occur. Since it is pressurized in the compression stroke, it is possible that the flow velocity becomes faster and eddy currents are more likely to occur.

However, if the inner ridge of the recess on the intake side is rounded with a radius of curvature of 3 mm or more as in the present invention, the air-fuel mixture flows smoothly as if licking the inner ridge, and a pressure change occurs. Absent. Therefore, it is possible to prevent the occurrence of eddy currents (stagnation) at the ridgeline and improve the uniformity of the air-fuel mixture in the entire combustion space. As a result, combustion can be made uniform in the entire combustion space, which can contribute to the improvement of output and fuel efficiency, and can also contribute to the prevention of knocking.

Further, the present invention has a configuration in which the ridgeline is rounded and can be applied to an existing piston as it is, so that it is excellent in reality and versatility. From the viewpoint of smoothing the flow of the air-fuel mixture, it is preferable that the radius of curvature of the roundness of the ridgeline is large, but if it is made excessively large, the volume of the combustion chamber becomes large and each part must be redesigned to maintain the compression ratio. There is a risk that it will not be. In this respect, it is particularly preferable to keep the maximum value of roundness within a radius of curvature of 5 to 6 mm because eddy current can be prevented without causing a change in the compression ratio.

In the present invention, it is possible to give roundness to all the ridgelines, but as described above, since the intake side recess is deep and eddy currents are likely to occur at the inner ridgeline, only the intake side recess is rounded. Even if it is formed, a high effect can be enjoyed. In this case, since there is almost no change in volume even when applied to an existing piston, it is possible to eliminate the trouble of redesigning in relation to the compression ratio.

It is a longitudinal front view of the embodiment. (A) is a plan view of the piston, and (B) is a sectional view taken along line BB of (A). It is a longitudinal front view at the end of the intake stroke. FIG. 2 is a sectional view taken along line IV-IV of FIG. 2 at the end of the compression stroke. It is a figure which shows the comparative example (conventional example).

Next, an embodiment of the present invention will be described with reference to the drawings. This embodiment is applied to a piston of an internal combustion engine for automobiles.

(1). Basic structure The basic structure of the internal combustion engine to which the piston of the present invention is applied is the same as the conventional one, and the cylinder block 2 formed by arranging a plurality of cylinder bores 1 in the direction of the crank axis and fixed to the upper surface thereof. A cylinder head 3 is provided, and the cylinder head 3 is formed with a pair of intake ports 4 and exhaust ports 5 arranged in the direction of the crank axis on both sides of the cylinder bore axis. The intake port 4 is opened and closed by the intake valve 6, and the exhaust port 5 is opened and closed by the exhaust valve 7.

A pent roof type (mountain-shaped) combustion chamber 8 is formed in the cylinder head 3 in a state concentric with each cylinder bore 1, and the intake valve 6 and the exhaust valve 7 are in a state orthogonal to the inclined surface of the combustion chamber 8. Have been placed. A piston 9 is slidably fitted in the cylinder bore 1.

As shown in FIG. 2, a shallow recess 10 extending close to the outer circumference is formed on the top surface of the piston 9, and a portion of the recess 10 near the outer circumference is a gently curved curved surface 10a. Therefore, the generation of the tumble flow 11 shown in FIG. 3 can be promoted. The outer portion of the recess 10 is basically a flat surface orthogonal to the axis, but is formed as a tapered squish surface inclined upwardly constricted at substantially the same angle as the inclination angle of the combustion chamber 8. It is also possible.

An intake side recess 12 and an exhaust side recess 13 are formed on the top surface of the piston 9. Both recesses 12 and 13 have a plan view shape close to a crescent shape because the valves 6 and 7 are inclined with respect to the axis of the cylinder bore 1 (and the axis of the piston 9), and the cross section is It has a mountain shape.

Since the recesses 12 and 13 are recesses, when the recesses 12 and 13 are formed, the outer ridges 14 and 15 located outside the recesses 12 and 13 and the inner ridges 16 and 17 located inside the recesses 12 and 13 are formed. It is formed. The outer sides of the outer ridges 14 and 15 are flat surfaces, and the inner ridges 16 and 17 form a boundary between the recess 10 and the recesses 12 and 13. Further, the inner ridges 16 and 17 are lower in height than the outer ridges 14 and 15.

Then, as shown in FIG. 4 as a representative of the inner ridge line 16 of the intake side recess 12, a roundness having a radius of curvature R of about 5 mm is formed on the entire inner ridge lines 16 and 17 and the outer ridge lines 14 and 15. .. However, it is sufficient if the roundness is formed at least on the inner ridge line 16 of the intake side recess 12. The radius of curvature R of the roundness may be about 3 to 5 mm in each case.

By the way, the tumble flow 11 shown in FIG. 3 is generated in the intake stroke, and the tumble flow 11 is between the two intake side recesses 12 from the exhaust side through the axial center as shown by the dotted arrow in FIG. In many cases, the flow flows toward the intake side through the intake side and is guided by the inner circumference of the cylinder bore 1 and returns to the exhaust side. The tumble flow 11 is enhanced at the initial stage of the compression stroke, and then added. It is crushed by pressure and separated into many turbulent flows.

Then, at the end of the compression stroke, the intake side is shown by the dotted arrow in FIG. 2 (A) because the combustion chamber 8 is a pent roof type and the axial center portion has the largest cross-sectional area. As shown by the arrow 20 in FIG. 4, the air-fuel mixture whose direction has been changed in the above direction tends to flow from the outer peripheral portion toward the exhaust side.

Therefore, the air-fuel mixture whose direction is changed on the intake side flows across the recess 12 on the intake side as shown by the arrow 20 in FIG. 4, but is mixed when the edge of the inner ridge line 16 stands as shown in FIG. When the air flows across the air, a vortex 21 may be generated on the downstream side (axial side) of the inner ridge line 16 to cause stagnation and retention of the air-fuel mixture. When the air-fuel mixture is stagnant or stagnant, the diffusivity of the air-fuel mixture is hindered and the uniformity of combustion is impaired, and knocking is likely to occur due to the local temperature decrease.

On the other hand, when the inner ridge line 16 is rounded by about 3 to 5 mm as in the present embodiment, the air-fuel mixture smoothly passes by licking the inner ridge line 16 as shown by the arrow 20 in FIG. Therefore, no eddy current is generated, and the air-fuel mixture can be uniformly dispersed in the combustion space. Therefore, the tumble flow 11 can be effectively used to improve the output and the fuel consumption, and also to suppress knocking.

Since there is a possibility that a flow crossing the exhaust side recess 13 toward the intake side may occur, it is recommended to form a roundness with a radius of curvature of about 3 to 5 mm on the inner ridge line 17 of the exhaust side recess 13. It is beneficial.

However, since the depth of the exhaust side recess 13 is shallower than that of the intake side recess 12, the degree of generation of eddy current is also low. Further, at the locations of the outer ridges 14 and 15, since the air-fuel mixture is pushed downward in the compression stroke, the frequency of vortex flow is lower than that on the intake side, so that there is no problem even if the roundness is not provided. Therefore, the roundness for the purpose of preventing the generation of eddy current may be formed only on the inner ridge line 16 of the intake side recess 12.

The invention of the present application can be embodied in a piston of an internal combustion engine. Therefore, it can be used industrially.

1 Cylinder bore 2 Cylinder block 3 Cylinder head 4 Intake port 5 Exhaust port 6 Intake valve 8 Combustion chamber 9 Piston 10 Recess 11 Tumble flow 12 Intake side recess 13 Exhaust side recess 14,15 Outer ridgeline 16,17 Inner ridgeline 20 Air-fuel mixture Flow 21 Whirlpool

Claims (1)

An intake side recess for letting the intake valve escape and an exhaust side recess for letting the exhaust valve escape are formed on the top surface facing the cylinder head. Therefore, the recess is the outer ridge line located on the outer peripheral side. It has a structure that is sandwiched between the inner ridge line located on the axis side.
At least on the inner ridge of the intake side recess, a roundness with a radius of curvature of 3 mm or more is formed, which can prevent the generation of a vortex when the air-fuel mixture flows from the axial center side through the outer circumference in the compression stroke.
Internal combustion engine piston.

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