JP2017061901A - piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston which can favorably maintain a tumble flow up to a compression stroke latter stage while improving a compression ratio.SOLUTION: A piston of an engine having tumble formation means comprises: a recess 150 which is formed by recessing a region in the vicinity of both ends of a crown face 100A in a crankshaft direction to a crankshaft side; a salient part 160 which is formed between a center part of the crown face and the recess, is salient to a cylinder head side, and extends substancially along a plane perpendicular to the axis of a crankshaft; and drift means 170 which makes a component flowing along a protrusive end of the salient part in a tumble flow drift to the recess side when viewed from a cylinder axial line direction.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a piston of a reciprocating engine, and more particularly to a piston capable of maintaining a tumble flow well until the latter stage of a compression stroke while improving a compression ratio.

Spark-ignition engines such as gasoline engines are required to improve the isovolume, which shows the deviation from ideal isobaric combustion, by increasing the combustion speed, and to increase the thermal efficiency and improve the output and fuel consumption. ing.
As a technique for improving the combustion speed, it is known to enhance the gas flow (turbulence) in the combustion chamber near the ignition timing.
For example, by generating a tumble flow (longitudinal vortex) swirling around an axis substantially parallel to the crankshaft in the cylinder depending on the shape of the intake port, etc., and by collapsing the tumble flow near the compression top dead center, It is known to form a strong turbulence around the spark plug.
It has also been proposed to form a concave cavity at the center of the crown surface of the piston so as to maintain the tumble flow until the latter stage of the compression stroke and to increase the turbulence of the in-cylinder mixture immediately before ignition.

As a conventional technique for obtaining a desired gas flow in a cylinder or a combustion chamber depending on the shape of the crown surface of the piston, for example, in Patent Document 1, in the slap direction connecting the intake valve and the exhaust valve at the center of the piston crown surface. It is described that a recess having a rectangular bottom surface extending is formed, and a pair of rectifying ribs are formed on both sides sandwiching the recess in the crank axis direction.
In Patent Document 2, a center rib having a triangular shape (wedge shape) when viewed from the cylinder axial direction is formed at the center of the crown surface of the piston, and a tumble flow is generated from the vicinity of the spark plug near the top dead center. It is described to eliminate.

JP-A-11-343851 Japanese Patent Laid-Open No. 8-14048

Since the theoretical thermal efficiency of an engine such as an Otto cycle depends on the compression ratio, it is necessary to set the compression ratio high to some extent in order to obtain good thermal efficiency.
However, as described above, in order to preserve and maintain the tumble flow, when the cavity is formed by recessing the crown of the piston, the combustion chamber volume when the piston is at top dead center is increased and the compression ratio is improved. It tends to be difficult.
For this reason, in order to maintain or improve the compression ratio with respect to the case where no cavity is formed, it is necessary to project (increase) a portion other than the cavity on the crown surface to the cylinder head side.
Conventionally, for such purposes, it has been proposed to provide protrusions formed so as to protrude toward the cylinder head with respect to the average height of the crown surface at both ends of the crown surface in the crank axis direction.

However, with such a crown shape, when the gap between the protrusion and the cylinder head becomes narrower in the latter half of the compression stroke, the air flow (squish flow) ejected from here flows into the center of the bore and becomes tumble. It may interfere with the flow and weaken it.
In view of the above-described problems, an object of the present invention is to provide a piston that can satisfactorily maintain a tumble flow until the latter stage of the compression stroke while improving the compression ratio.

The present invention solves the above-described problems by the following means.
The invention according to claim 1 is a piston of an engine having tumble forming means for forming a tumble flow that turns around an axis substantially parallel to the crankshaft direction inside a cylinder in a compression stroke, wherein the crank on the crown surface A concave portion formed by denting regions near both end portions in the axial direction toward the crankshaft side, and a cylinder with respect to the central portion of the crown surface and the concave portion provided between the central portion of the crown surface and the concave portion A protrusion projecting toward the head and extending substantially along a plane perpendicular to the crankshaft, and a component flowing along the projecting end of the projection in the tumble flow, when viewed from the cylinder axial direction It is a piston characterized by having a drift means deflected to the said recessed part side.
According to this, the squish flow formed by sandwiching a part of the tumble flow in the gap formed when the combustion chamber recess and the protrusion formed in the recess shape in the cylinder head are brought close to each other by the drifting means. By introducing into the recess, the squish flow is prevented from injecting into the cylinder center side (bore inner diameter side) and interfering with the main flow of the tumble flow, and the tumble flow is good until the piston reaches the vicinity of the compression top dead center. Can be maintained.
As a result, even in pistons with a protruding part that improves the compression ratio, the gas flow (turbulence) in the combustion chamber during ignition is strengthened, the combustion speed is increased, the thermal efficiency is improved, and the output and fuel consumption are improved. Can do.

The invention according to claim 2 is such that the tumble flow flows from the exhaust side to the intake side in the vicinity of the crown surface, and when viewed from the cylinder axial direction, When an angle formed by a straight line connecting the center of the crown surface and a straight line that passes through the center of the crown surface and is parallel to the crankshaft is θ, the end portion on the intake side of the recess and the crown surface 2. The piston according to claim 1, wherein the drifting means is arranged in a region where an angular position around the center of the crown surface with respect to a straight line connecting the center is within ½θ.
According to this, most of the squish flow formed so as to flow from the exhaust side to the intake side along the protruding portion by the influence of the tumble flow can be efficiently deflected to the concave portion side.
Further, it is possible to prevent the squish flow deflected toward the concave portion from flowing into the center side of the combustion chamber again.

The invention according to claim 3 is characterized in that the drifting means is formed in a rib shape protruding from the protruding portion toward the cylinder head and inclined with respect to the crankshaft direction. The piston according to claim 1 or claim 2.
According to this, the above-described effects can be reliably obtained with a simple configuration.

According to a fourth aspect of the present invention, there is provided a volume in a region where the protruding portion protrudes toward the cylinder head with respect to the average height of the crown surface, and the recess is located on the crankshaft side with respect to the average height of the crown surface. The piston according to any one of claims 1 to 3, wherein the volume in the projecting region is substantially matched.
According to this, most of the squish flow formed due to the protrusion can be absorbed in the recess, and the main flow of the tumble flow formed in the center of the cylinder is drawn into the recess. The effects described above can be further promoted.

The invention according to claim 5 is a piston of an engine having tumble flow forming means for forming a tumble flow turning around an axis substantially parallel to the crankshaft direction inside the cylinder in the compression stroke, A recess formed by recessing the region in the vicinity of both ends in the crankshaft direction toward the crankshaft, and a center portion of the crown surface and the recess provided between the center portion of the crown surface and the recess. A region projecting toward the cylinder head and extending substantially along a plane perpendicular to the crankshaft, the region projecting toward the cylinder head with respect to the average height of the crown surface And the volume in the region in which the concave portion protrudes toward the crankshaft with respect to the average height of the crown surface is substantially matched.
According to this, by introducing the squish flow that is ejected with a part of the tumble flow sandwiched in the gap between the combustion chamber recess and the protrusion formed in the cylinder head into the recess, the squish flow is moved toward the center of the cylinder. It is possible to prevent the tumbling flow from interfering with the tumble flow and to maintain the tumble flow well to the vicinity of the compression top dead center.
In addition, most of the squish flow formed due to the protrusion can be absorbed in the recess, and the main flow of the tumble flow formed in the central portion is not drawn into the recess. The effect obtained can be further promoted.
As a result, even in a piston that has a protruding portion to improve the compression ratio, the gas flow (turbulence) in the combustion chamber at the time of ignition can be strengthened, the combustion speed can be improved, and the thermal efficiency, output, and fuel consumption can be improved. .

  As described above, according to the present invention, it is possible to provide a piston that can satisfactorily maintain the tumble flow until the latter stage of the compression stroke while improving the compression ratio.

It is a figure which shows the crown surface shape of the piston which is a comparative example of this invention, and the combustion chamber shape of the engine which has this piston. It is a figure which shows typically the time series change of the gas flow in a cylinder in the compression stroke in a comparative example. It is a figure which shows the crown surface shape of Example 1 of the piston to which this invention is applied, and the combustion chamber shape of an engine which has this piston. It is an enlarged view of the combustion chamber shape of the engine which has a piston of Example 1. FIG. It is a figure which shows typically the time series change of the gas flow in a cylinder in the compression stroke in the engine which has a piston of Example 1. FIG. It is a figure which shows typically the state which changed the bottom face height of the recessed part in the piston of Example 1. FIG. It is a figure which shows the crown surface shape of Example 2 of the piston to which this invention is applied, and the combustion chamber shape of an engine which has this piston. It is a figure which shows typically the time series change of the gas flow in a cylinder in the compression stroke in the engine which has a piston of Example 2. FIG.

The present invention aims to provide a piston capable of satisfactorily maintaining the tumble flow until the latter stage of the compression stroke while improving the compression ratio, and forms a recess and a protrusion at both ends of the piston crown surface in the crankshaft direction. This problem has been solved by providing a drifting means for deflecting the squish flow that flows along the protruding end portion toward the concave portion.
Further, by forming recesses and protrusions at both ends in the crankshaft direction on the piston crown surface, and substantially matching the volumes of the regions where the recesses and the protrusions protrude downward and upward from the average crown surface height, respectively. Settled.

Hereinafter, a first embodiment of a piston to which the present invention is applied will be described.
First, prior to the description of the piston of Example 1, a piston that is a comparative example of the present invention will be described.
The piston of the comparative example is used for, for example, a gasoline in-cylinder fuel injection (direct injection) engine used as a driving power source for automobiles such as passenger cars.
The engine has a pent roof type combustion chamber configured by arranging two intake valves and two exhaust valves per cylinder with a predetermined valve sandwich angle.
The combustion chamber is a space portion surrounded by a combustion chamber concave portion 200 formed by denting a cylinder block side surface portion of the cylinder head, a crown surface 100 of the piston, and a part of the inner peripheral surface of the cylinder.
Combustion chamber recess 200 has an ignition plug (spark plug) (not shown) in which an electrode portion is arranged at the center (near the cylinder axis).
Combustion chamber recess 200 has a multi-hole direct injection injector (not shown) in which a nozzle portion is inserted into combustion chamber recess 200 from the interval between the pair of intake ports.
In the latter half of the compression stroke, the direct injection injector ejects a plurality of beam-like fuel sprays radially toward the crown surface 100A of the piston.

FIG. 1 is a diagram showing a crown shape of a piston of a comparative example and a combustion chamber shape of an engine having this piston.
Fig.1 (a) is the figure which looked at the crown of the piston of the comparative example from the cylinder axis (cylinder center axis) direction.
FIG. 1B is a cross-sectional view of the combustion chamber shape when the piston of the comparative example is in the vicinity of the top dead center, and corresponds to a cross section taken along the line bb in FIG. (Same in FIGS. 3 and 7 to be described later)

The piston of the comparative example is formed by, for example, forming a general shape by casting or forging an aluminum-based alloy, and then performing a predetermined machining process or a coating process on the skirt surface.
The crown surface 100 is an end surface of the piston on the side facing the cylinder head, and is formed in a disc shape that is formed substantially along a plane that is substantially orthogonal to the cylinder axis.
The crown surface 100 constitutes a part of the wall surface of the combustion chamber in which the air-fuel mixture is ignited and burned in cooperation with the combustion chamber recess 200 formed in the cylinder head.
The crown surface 100 includes a cavity 110 formed integrally with the piston body, an intake valve recess 120, an exhaust valve recess 130, a protrusion 140, and the like.

The cavity 110 is a recess formed by denting the central portion of the crown surface 100.
The cavity 110 has a function of maintaining and strengthening a tumble flow (longitudinal vortex) T (see FIG. 2) formed in the cylinder when combustion air (fresh air) flows into the cylinder from the intake port 210. .
The cavity 110 is formed in an oval shape having a long axis substantially along the crankshaft direction when viewed from the cylinder axial direction.

The intake valve recess 120 and the exhaust valve recess 130 are concave portions formed for the purpose of preventing interference between the intake port 210 and an exhaust port (not shown) with an intake valve that opens and closes at a predetermined valve timing and a valve body portion of the exhaust valve.
The intake valve recess 120 and the exhaust valve recess 130 are disposed, for example, in pairs in the intake side and exhaust side regions of the crown surface 100.

The projecting portions 140 are portions formed by projecting both end regions in the crankshaft direction of the crown surface 100 toward the cylinder head for the purpose of reducing the combustion chamber capacity and improving the compression ratio of the engine.
The surface of the protrusion 140 is disposed to face the surface of the combustion chamber recess 200 with a narrow gap when the piston is at the compression top dead center.

FIG. 2 is a diagram schematically showing a time-series change of the gas flow in the cylinder in the compression stroke in the comparative example.
2 (A), (B), (C), and (D) are schematic perspective views of the cylinder, from the initial state of the compression process to the state at the end of the compression stroke (compression top dead center). It is shown in time series.
2 (a), (b), (c), and (d) are schematic views viewed from the axial direction of the cylinder, and show in time series from the initial state of the compression process to the state of the compression top dead center. The states at the timings corresponding to FIGS. 2A, 2B, 2C, and 2D, respectively, are shown.

The combustion chamber recess 200 is connected to an intake port 210 that is a flow path for introducing combustion air (fresh air).
For example, a pair of intake ports 210 are provided along the crankshaft direction.
The end of the intake port 210 on the combustion chamber recess 200 side is opened and closed at a predetermined valve timing by an intake valve (not shown).

The intake port 210 is sucked into the cylinder by setting the shape of the cross section of the flow path and the curve, the connection angle to the combustion chamber, the partition wall inside the flow path, and the tumble control valve that closes a part of the flow path. In the fresh air (combustion air), a tumble flow T that is an airflow swirling around an axis substantially parallel to the crankshaft is formed.
The intake port 210 functions as a tumble forming means in the present invention.
When viewed from the cylinder axial direction, the tumble flow T is, on the cylinder head side, from the side provided with the intake port (hereinafter referred to as “intake side”) to the side provided with the exhaust port (hereinafter referred to as “exhaust side”). In the piston side, the flow direction is from the exhaust side to the intake side.

  When the compression stroke is started and the intake valve is closed and the piston starts to be displaced from the state near the bottom dead center shown in FIGS. 2A and 2A to the top dead center side, the tumble flow T is As shown in FIG. 2B and FIG. 2B, the cylinder is compressed and crushed in the cylinder axis direction while maintaining the turning.

Thereafter, when the piston is further displaced and the surface of the protrusion 140 is close to the surface of the combustion chamber recess 200, as shown in FIG. 2C, a part of the tumble flow T sandwiched between the regions therebetween is formed. The squish flow Sq is formed by jetting to the cylinder inner diameter side.
When the squish flow Sq interferes with the main flow of the tumble flow T, the tumble flow T weakens and falls with respect to the cylinder axis, and finally, as shown in FIGS. 2 (D) and 2 (d), The swirl flow Sw is a horizontal vortex swirling around parallel axes.
As described above, in the gas flow in the cylinder immediately before the ignition, when the swirl flow Sw is dominant, the turbulence at the ignition timing is weakened, which is disadvantageous in terms of the combustion speed as compared with the case where the strong tumble flow T can be maintained.
When the combustion speed is lowered, the isovolume is lowered, the thermal efficiency is lowered, and both the output and the fuel consumption are deteriorated.

Next, a first embodiment of the piston to which the present invention is applied will be described.
In Examples 1 and 2 to be described below, portions that are substantially the same as those in the previous comparative example and example are denoted by the same reference numerals, description thereof is omitted, and differences are mainly described.
FIG. 3 is a view showing the crown shape of the first embodiment of the piston to which the present invention is applied and the combustion chamber shape of an engine having the piston.

The piston of Example 1 has a crown surface 100A in which a concave portion 150, a protruding portion 160, and a rib 170 described below are formed instead of the protruding portion 140 of the piston of the comparative example.
The recess 150 is formed by denting the regions of both ends of the crown surface 100A in the crankshaft direction to the crankshaft side with respect to the average height of the crown surface 100A.
The bottom surface of the recess 150 is formed in a planar shape substantially along a plane orthogonal to the cylinder axis.

The protrusion 160 is arranged between the recess 150 in the crown surface 100A and a central region including the cavity 110, and protrudes toward the cylinder head with respect to the average height of the crown 100A. It is the part which was done.
As shown in FIG. 3A, the protrusion 160 is formed in a rib shape extending substantially along a plane orthogonal to the crankshaft when viewed from the cylinder axial direction.
The end surface of the protrusion 160 on the cylinder head side is formed flat along a plane substantially perpendicular to the cylinder axis.
When the crown surface 100A is viewed from the cylinder axis direction, the position, shape, and area of the region occupied by the recess 150 and the protrusion 160 are set substantially equal to the region occupied by the protrusion 140 in the comparative example. Yes.

The rib 170 is a drifting unit that deflects the airflow flowing from the exhaust side to the intake side along the projecting end face (surface facing the cylinder head) of the projecting portion 160 outward (in the recess 150 side) in the crankshaft direction.
The rib 170 is a flat plate-like member formed so as to protrude from the protruding end surface (end surface on the cylinder head side) of the protruding portion 160.
As shown in FIG. 3 (a), the rib 170 has an end on the recess 150 side with respect to the end on the center side of the crown surface 100 when viewed from the cylinder axial direction. It is arranged so as to be inclined with respect to the crank axis so as to be the upper part in a).

  Further, as shown in FIG. 3A, when viewed from the cylinder axial direction, a straight line L1 connecting the center O of the crown surface 100A and the end 151 on the intake side of the recess 150, and passing through the center O and parallel to the crank axis. Assuming that the angle formed by the straight line L2 is θ, all of the ribs 170 are disposed within a region where the angular position around the center O is within 1 / 2θ with respect to the straight line L1.

FIG. 4 is an enlarged view of a combustion chamber shape of the engine having the piston of the first embodiment.
FIG. 4 is an enlarged view of FIG. In FIG. 4, the rib 170 is not shown (the same applies to FIG. 6 described later).
As shown in FIG. 3A, the area of the protrusion 160 when viewed from the cylinder axis direction is A1, and the area of the recess 150 is A2.
Further, as shown in FIG. 4, the height (projection amount) of the projecting portion of the projecting portion 160 with respect to the average height in the cylinder axial direction of the crown surface 100 of the piston (hereinafter referred to as “crown surface average height”) is h1. The height (retraction amount) of the bottom surface of the recess 150 is h2.
At this time, it is preferable to satisfy the relationship shown in Formula 1 below.

h2≈A1 / A2 × h1 (Formula 1)

Equation 1 shows the volume of the portion where the protrusion 160 protrudes toward the cylinder head with respect to the crown surface average height, and the portion where the recess 150 protrudes (concave) toward the crankshaft side with respect to the crown surface average height. It means that the volume substantially matches.

FIG. 5 is a diagram schematically illustrating a time-series change in the gas flow in the cylinder during the compression stroke in the engine having the piston of the first embodiment.
FIGS. 5A, 5B, 5C, and 5D are schematic views seen from the cylinder axis direction, and FIGS. 2A, 2B, 2C, and 2D in the comparative example. ) Shows a timing state corresponding to.
As shown in FIG. 5, in the first embodiment, when the gap between the protruding end portion of the protruding portion 160 and the combustion chamber recessed portion 200 is reduced in FIG. 2C and the squish flow Sq is generated, The squish flow Sq traveling from the exhaust side to the intake side along the end surface collides with the rib 170, and the main flow of the squish flow Sq is deflected toward the concave portion 150.
The deflected squish flow Sq is accommodated in the recess 150 and forms a relatively small tumble flow Tr inside the recess 150.
The air-fuel mixture that forms the tumble flow Tr is substantially isolated from the center of the combustion chamber by the protrusion 160 at the ignition timing, and burns by the propagation of flame from the center of the cylinder in the early stage of the engine expansion stroke. .

  For this reason, the tumble flow T formed at the center of the cylinder is not substantially affected by the squish flow Sq caused by the protrusion 160, and is maintained and stored until the piston reaches the vicinity of the compression top dead center. In the ignition timing, the tumble flow T is crushed, thereby forming a strong turbulence that is effective for improving the combustion speed.

FIG. 6 is a diagram schematically illustrating a state in which the bottom surface height of the recess in the piston of the first embodiment is changed.
FIG. 6A shows the shape of the combustion chamber near the compression top dead center of the engine having the piston of the first embodiment.
6 (b) and 6 (c) show the height h2 of the recessed portion 150 that is made smaller and larger than the piston of the first embodiment.

  When the height h2 of the concave portion 150 is reduced (shallow) and the volume of the concave portion 150 is reduced as in the crown surface 100C of FIG. 6B, the squish flow Sq ejected from the protruding end portion of the protruding portion 160 is the concave portion 150. The squish flow Sq is partly ejected toward the center of the cylinder, interferes with the tumble flow T, and weakens the tumble flow T.

  On the other hand, when the height h2 of the recess 150 is increased (deep) and the capacity of the recess 150 is increased as in the crown surface 100D of FIG. 6C, the squish flow Sq ejected from the protruding end of the protrusion 160 is Although it can be accommodated in the recess 150, a part of the tumble flow T at the center of the cylinder is drawn into the recess 150, and the tumble flow T becomes weak, and the disturbance in the center of the combustion chamber at the ignition timing becomes weak. End up.

  On the other hand, according to the first embodiment shown in FIG. 6A, the volume in which the gas in the combustion chamber is pushed away by the protrusion 160 and the volume in which the recess 150 can store the gas are set substantially equal. Thus, substantially all of the squish flow Sq formed at the protruding end of the protrusion 160 is accommodated in the recess 150 to prevent interference with the main flow of the tumble flow T, and the tumble flow T at the center of the cylinder is recessed. It is possible to prevent the gas from being drawn to the side 150 and maximize the turbulence of the in-cylinder gas at the center of the combustion chamber at the ignition timing.

As described above, according to the first embodiment, the following effects can be obtained.
(1) The squish flow Sq ejected from the gap between the combustion chamber recess 200 formed in the cylinder head and the protrusion 160 is deflected by the rib 170 and introduced into the recess 150, so that the squish flow Sq is centered on the cylinder. , And the tumble flow T is prevented from interfering with the tumble flow T, so that the tumble flow T can be well maintained near the compression top dead center.
As a result, even in the piston with the protruding portion 160 formed to improve the compression ratio, the gas flow (turbulence) in the combustion chamber at the time of ignition is strengthened, the combustion speed is increased, the thermal efficiency is improved, and the output and fuel consumption are improved. be able to.
(2) By disposing the rib 170 close to the end portion on the intake side of the concave portion 150, most of the squish flow Sq formed near the protruding end portion of the protruding portion 160 is efficiently deflected toward the concave portion 150 side. be able to.
Further, it is possible to prevent the squish flow Sq flowing into the concave portion 150 from returning to the combustion chamber center side again.
(3) By deflecting the squish flow Sq toward the concave portion 150 using the flat ribs 170 projecting from the end surface of the projecting end portion of the projecting portion 160, the above-described effects can be reliably obtained with a simple configuration.
(4) The volume of the portion where the protrusion 160 protrudes with respect to the average crown surface height of the piston is substantially matched with the volume of the portion where the recess 150 is recessed with respect to the average height of the crown surface. Thus, most of the squish flow Sq formed due to the protrusion 160 can be absorbed in the recess 150, and the tumble flow T formed in the center of the cylinder is drawn into the recess 150. The effect mentioned above can be promoted more.

Next, a second embodiment of the piston to which the present invention is applied will be described.
FIG. 7 is a diagram illustrating a crown shape of a piston according to a second embodiment and a combustion chamber shape of an engine having the piston.
The piston of the second embodiment is configured substantially in the same manner except that the rib 170 is removed from the piston of the first embodiment on the crown surface 100B.

FIG. 8 is a diagram schematically illustrating a time-series change in the gas flow in the cylinder during the compression stroke in the engine having the piston of the second embodiment.
Also in the piston of the second embodiment, the volume of the recess 150 is appropriately set so as to satisfy the above-described formula 1, and the squish flow Sq generated due to the protrusion 160 is introduced to the recess 150 side. Even when the drift means cannot be provided as in Example 1, the tumble flow T in the center of the cylinder is prevented from collapsing by the squish flow Sq, and the turbulence in the combustion chamber is strengthened to improve the thermal efficiency, output, and fuel consumption. Can be improved.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the technical scope of the present invention.
(1) The structure of the piston and the engine provided with the piston is not limited to the above-described embodiment, and can be changed as appropriate.
(2) The shape of the crown surface of the piston can be changed as appropriate. For example, the drifting means of the first embodiment is formed in a flat rib shape protruding from the protruding end portion of the protruding portion, but the surface portion for changing the airflow may be curved in a concave curved surface shape.
Further, the present invention is not limited to the rib-shaped configuration, and the protruding end portion of the protruding portion may be formed in a stepped shape in which the intake side protrudes with respect to the exhaust side, and the airflow may be deflected using a surface portion formed in the stepped portion.
(3) You may form the recessed part and convex part other than the cavity for tumble flow maintenance like an Example in the piston crown surface. For example, a recess (step) for winding the fuel spray ejected from the direct injection injector toward the spark plug may be formed in place of the cavity or together with the cavity.
(4) In the embodiment, the engine is, for example, a gasoline direct injection engine having a side injector configuration. However, the present invention includes a direct injection engine having a center injector configuration, an engine that performs port injection, and further, port injection and direct injection. It can also be applied to engines used in combination.
Furthermore, the present invention can be applied not only to a gasoline engine but also to a spark ignition engine using other fuel.

100 Crown Surface (Comparative Example) 100A Crown Surface (Example 1)
100B Crown surface (Example 2) 110 Cavity 120 Intake valve recess 130 Exhaust valve recess 140 Projection 150 Depression 160 Projection 170 Rib 200 Combustion chamber T Tumble flow Tr Tumble flow Sq Squish flow Sw Swirl flow

Claims (5)

An engine piston having tumble forming means for forming a tumble flow that turns around an axis substantially parallel to the crankshaft direction inside a cylinder in a compression stroke,
A recess formed by recessing the region in the vicinity of both ends in the crankshaft direction of the crown surface toward the crankshaft side;
Provided between the central portion of the crown surface and the recess, protrudes toward the cylinder head with respect to the central portion of the crown surface and the recess, and extends substantially along a plane orthogonal to the crankshaft. A protrusion,
And a biasing means for deflecting a component flowing along the protruding end of the protruding portion in the tumble flow toward the concave portion when viewed from the cylinder axial direction. The tumble flow flows from the exhaust side to the intake side in the vicinity of the crown surface,
An angle formed by a straight line connecting the intake-side end of the recess and the center of the crown surface and a straight line passing through the center of the crown surface and parallel to the crankshaft when viewed from the cylinder axis direction Is set to be θ in the region where the angular position around the center of the crown surface with respect to the straight line connecting the end of the intake side of the concave portion and the center of the crown surface is within 1 / 2θ. The piston according to claim 1. The said drift means is formed in the rib shape which protrudes from the said protrusion part to the said cylinder head side, and is inclined and arrange | positioned with respect to the said crankshaft direction. piston. The volume in the region where the protrusion protrudes toward the cylinder head with respect to the average height of the crown surface, and the volume in the region where the recess protrudes toward the crankshaft side with respect to the average height of the crown surface, The piston according to any one of claims 1 to 3, wherein the pistons are substantially matched. An engine piston having a tumble flow forming means for forming a tumble flow turning around an axis substantially parallel to a crankshaft direction inside a cylinder in a compression stroke,
A recess formed by recessing the region in the vicinity of both ends in the crankshaft direction of the crown surface toward the crankshaft side;
Provided between the central portion of the crown surface and the recess, protrudes toward the cylinder head with respect to the central portion of the crown surface and the recess, and extends substantially along a plane orthogonal to the crankshaft. With protrusions,
The volume in the region where the protrusion protrudes toward the cylinder head with respect to the average height of the crown surface, and the volume in the region where the recess protrudes toward the crankshaft side with respect to the average height of the crown surface, Piston characterized by substantially matching.

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