JP2017115586A - Piston of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To merge two tumble flows corresponding to two intake ports to each other, and to enhance the miscibility of intake air as a whole, in a four-valve type internal combustion engine.SOLUTION: A first recess 13 for promoting the generation of a first tumble flow 17 and a second recess 14 for promoting the generation of a second tumble flow 18 are formed on an apex face 5a of a piston 5 while being aligned in a direction of a crank axial line 9. Constitutions such as shapes, magnitudes, depths or the like of the first recess 13 and the second recess 14 are formed asymmetric with an oblong center line 16 orthogonal to the crank axial line 9 and a cylinder axial line 15 sandwiched therebetween. Since guide actions of the tumble flows 17, 18 by the two recesses 13, 14 are different from each other, the symmetry the two tumble flows 17, 18 in flow directions is collapsed, and the two tumble flows 17, 18 are liable to be merged with each other. By this constitution, the miscibility of intake air becomes high.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a piston in an internal combustion engine for a vehicle or the like.

  In an internal combustion engine of a type in which an air-fuel mixture is supplied from an intake port toward a cylinder, a tumble flow is generated in the intake air sucked into the cylinder in order to improve the mixing of air and fuel. This tumble flow is generated by the suction action of the piston moving backward in the intake stroke, and the intake air flows from the inner surface of the cylinder toward the top surface of the piston as viewed from the crank axis direction, and then the top of the piston. The direction is changed from the surface toward the inner surface of the cylinder and then toward the cylinder head. That is, it is a vortex as seen from the crank axis direction.

  In order to promote the generation of the tumble flow, it has been proposed to form a recess for guiding the tumble flow on the top surface of the cylinder head. As an example, Patent Document 1 discloses a recess, It has been disclosed that when viewed from the cylinder axial direction, the intake port side is narrow and the exhaust port side is wide in a convex shape, and the wide part is deeper than the narrow part.

  The tumble flow plays a role in promoting the mixing of the atomized fuel and air in the course of the flow, and is crushed in the compression stroke into many small vortex flows, which promotes the mixing of the air and the atomized fuel. The

JP-A-9-105330

  The tumble flow itself contributes to improving the mixing of fuel and air, but the mixing ratio of the air-fuel mixture supplied from the two intake ports is not always the same. Due to various factors such as the difference in flow resistance between the two intake ports or the variation in EGR gas, there may be variations in the ratio of the ratio of air to fuel in the mixture supplied from the two intake ports.

  The intake air flowing into the cylinder from the two intake ports tends to form a tumble flow independently of each other. However, in a conventional internal combustion engine, the recess for forming the tumble flow has a crank axis direction. Since the shape and depth are formed symmetrically in the longitudinal direction, the independence of the two tumble flows tends to remain maintained. Even if the fuel is injected, there is a possibility that the lean portion and the rich portion are mixed and complete combustion cannot be realized.

  The present invention has been made to improve the current situation.

  The present invention relates to a piston of an internal combustion engine in which two intake ports are open toward one cylinder, and the piston has an intake air supplied from the intake port on a top surface facing the intake port. A concave portion for imparting a tumble flow is formed asymmetrically across a cylinder center and a lateral center line orthogonal to the crank axis.

  In this case, the recess is asymmetrical when the cylinder axis direction is the front-rear direction, the shape and size of the recess is front-rear asymmetric, and the shape is front-rear symmetrical, but the depth and bottom profile are front-rear. Sometimes it is asymmetric.

  Furthermore, the shape and size of the recesses are asymmetrical when two recesses are formed corresponding to two intake ports, and when the shape and size of the two recesses are different from each other, This includes the case where only one recess corresponding to the port is formed and the case where one recess corresponding to the two intake ports is formed in an asymmetrical shape.

  A mode in which two concave portions having the same size and depth are formed symmetrically in the front-rear direction, and the rectifying rib is formed only in one concave portion is also included in the present invention.

  In the present invention, the intake air supplied from the two intake ports becomes a strong tumble flow guided by the recess, but if the recess on the piston top surface is formed asymmetrically in the front-rear direction which is the crank axis direction, The two tumble flows formed by the intake air supplied from the port can be given a guide action and a disturbance action that make the flows non-parallel in the process of passing through the top surface of the piston. For this reason, the two tumble flows can be guided away from the top surface of the piston in a merged state.

  That is, in the present invention, the two tumble flows tend to merge with each other when the flow is unbalanced at the location of the top surface of the piston (parallelism / symmetry is lost). The mixing property as a whole can be improved.

  Therefore, in this invention, the mixing property as the whole intake air is securable, maintaining the production | generation function of a strong tumble flow. As a result, complete combustion can be realized, and output improvement and exhaust gas cleaning can be promoted.

(A) is a longitudinal front view of the first embodiment, and (B) is a cross-sectional view taken along the line BB of (A). (A) is a schematic top view of the combustion chamber of a cylinder head, (B) is a top view of a piston. It is a vertical front view in the intake stroke showing generation of a tumble flow. It is the vertical side view seen from the direction orthogonal to the crankshaft axis in order to show the mixing state of a tumble flow. (A) (B) is a top view of other embodiments.

(1) First Embodiment Next, an embodiment of the present invention will be invented based on the drawings. For example, as shown in FIG. 1, the internal combustion engine includes a cylinder block 2 in which a cylinder 1 is formed, and a cylinder head 4 that is overlapped and fixed to the cylinder block 2 via a gasket 3. Is slidably fitted. A connecting rod connected to the piston 5 is omitted.

  The cylinder head 4 is formed with a substantially roof-shaped or trapezoidal recess (combustion chamber) 6, in which two intake ports 7 and two exhaust ports 8 are connected to a crank axis 9. It is open side by side in the direction. The intake port 7 is opened and closed by an intake valve 10, and the exhaust port 8 is opened and closed by an exhaust valve 11. A spark plug 12 is screwed into the central portion of the recess 6.

  The top surface 5 a of the piston 5 has a first recess 13 that imparts a tumble flow to the intake air supplied from one intake port 7 and a second recess that imparts a tumble flow to the intake air supplied from the other intake port 7. 14 are formed side by side in the direction of the crank axis 9.

  The two recesses 12 and 13 have an elliptical shape that is long in the direction of the horizontally long center line 16 orthogonal to the crank axis 9 and the cylinder axis 15, and the depth gradually changes in both the oval direction and the oval direction. Therefore, as can be understood from FIG. 1B, the cross-sectional shape in the oval direction and the cross-sectional shape in the short circle direction are loosely curved profiles.

  The first recess 13 is larger than the second recess 14 in both the oval direction and the oval direction, and has a greater depth. That is, the first recess 13 is larger than the second recess 14 as a whole. In addition, although the 1st recessed part 13 and the 2nd recessed part 14 are formed in two areas on both sides of the horizontally long center line 16, it forms so that the horizontally long center line 16 may overlap with the 1st recessed part 13 partially. Is also possible.

  In the above configuration, as shown in FIG. 3, in the intake stroke, the intake air that flows straight into the cylinder 1 from the two intake ports 7 is on the opposite side of the intake port 7 on the inner peripheral surface of the cylinder 1. After changing the flow downward along the portion, the flow goes to the top surface 5a of the piston 5 and then flows along the top surface of the piston 5, and then the portion below the intake port 7 on the inner peripheral surface of the cylinder 1 Here, the flow is changed upward so as to go in the direction of the intake port 7. That is, tumble flows 17 and 18 that are vortexes when viewed from the direction of the crank axis 9 are applied to the intake air supplied from the intake port 7 to the cylinder 1.

  And since the recessed part 13 and 14 is formed in the top surface 5a of the piston 5, the directionality of the flow of intake air is strengthened and the tumble flow 17 and 18 is promoted, but the first recessed part 13 becomes the second recessed part 14. Since the first tumble flow 17 passing through the first recess 13 tends to have a lower flow rate than the second tumble flow 18 passing through the second recess 14 because the size and depth are larger, the second recess The second tumble flow 18 passing through 14 tends to flow toward the first recess 13 as the flow velocity increases, and as a result, as shown in FIG. The flows 17 and 18 tend to merge in the process of separating from the piston 5, and thereby the mixing property as a whole of the intake air can be remarkably improved.

  Since the cylinder 1 is circular, the intake air that has passed through the top surface 5a of the piston 5 is subjected to the action of the two tumble flows 17 and 18 being moved toward each other, as indicated by the arrow 19 in FIG. The action is weak. On the other hand, in this embodiment, the tumble flows 17 and 18 are subjected to a forced merging action in the process of passing through the top surface 5a of the piston 5 due to the two asymmetric recesses 13 and 14, so that the mixing property is remarkably improved. You can up.

(2). Other Embodiments FIG. 5 shows another embodiment. Of these, in the second embodiment shown in (A), the first recess 13 is formed only in one area of the top surface 5a of the piston 5 across the horizontally long center line 16, and the other area remains flat. Yes. As indicated by a dotted line, the first recess 13 may cross the lateral center line 16 and cross the other area.

  In this embodiment, when the two tumble flows 17 and 18 pass through the top surface 5a of the piston 5, the imbalance between the flow velocity and the directionality is stronger than in the first embodiment. For this reason, the tendency for the second tumble stream 18 to merge with the first tumble stream 17 is strong.

  More specifically, in the present embodiment, since the second recess 14 of the first embodiment does not exist, the second tumble flow 18 is highly diffusive when passing through the top surface 5a of the piston 5, but the first recess 13 and the pressure difference exists between both sides of the horizontally long center line 16, but the second tumble flow 18 is more likely to flow into the first recess 13 and the two tumbles are increased. It can be said that the merging action of the streams 17 and 18 is also strong.

  The third embodiment shown in FIG. 5B is an example in which one elliptical concave portion 20 that exhibits the guide function of the two tumble flows 17 and 18 is formed on the top surface 5a of the piston 5. The recess 20 inclines the center 21 of the ellipse by a slight angle θ with respect to the horizontally long center line 16 of the piston 5. In the embodiment, the concave portion 20 is inclined so that one end thereof is displaced toward the inflow position of the first tumble flow 17, but it is needless to say that the concave portion 20 may be inclined in the opposite posture.

  In this embodiment, since the recess 20 is inclined with respect to the horizontally long center line 16, the timing at which the two tumble flows 17, 18 flow into the recess 20 is slightly shifted, and the first tumble flow 17 is In addition, since it is forcibly directed by the recess 20 so as to merge with the second tumble flow 18, it can be said that the mixing of the intake air can be further improved.

  In the present embodiment, the tumble flows 17 and 18 are also given a directionality that turns around the axis of the cylinder 1. In this respect as well, it can be said that the mixing of intake air is further enhanced. Furthermore, in this embodiment, since the center of the recessed part 20 is located in the center of the piston 5, thermal expansion can be equalized as much as possible. For this reason, there also exists an advantage that it can prevent that local abnormal temperature rise generate | occur | produces on the top face of the piston 5.

  Although several embodiments of the present invention have been described above, the present invention can be embodied in various ways. For example, it is also possible to form two concave portions in a symmetric shape and vary the depth and bottom surface profile.

  In addition, it can be said that the mixing property of the intake air can be improved by forming the two concave portions in a continuous manner so as to be connected at the downstream side of the tumble flow and forming them in a heart shape or a V shape as a whole.

  The present invention can actually be embodied in a piston. Therefore, it can be used industrially.

1 Cylinder 2 Cylinder block 4 Cylinder head 5 Piston 5a Piston top surface 6 Cylinder head recess (combustion chamber)
7 Intake port 8 Exhaust port 9 Crank axis 10 Intake valve 11 Exhaust valve 13, 14, 20 Recess 15 Cylinder axis 16 Piston horizontal center line 17, 18 Tumble flow

Claims (1)

A piston of an internal combustion engine in which two intake ports open toward one cylinder,
On the top surface facing the intake port, a recess that imparts a tumble flow to the intake air supplied from the intake port is formed asymmetrically across a cylinder center and a horizontal center line orthogonal to the crank axis.
Piston for internal combustion engine.

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