JP2006329130A - Combustion chamber structure of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain reduction in engine output, particularly, reduction in wide-open-throttle performance of an engine, by improving combustion stability, exhaust gas performance and fuel economy of the engine. <P>SOLUTION: When a lift quantity of an intake valve 26 driven by a continuously variable valve lift mechanism 27 is small, a flow of intake air flowing in a combustion chamber 17 from the opposite side of the exhaust hole part 21 side among intake hole parts 22 is promoted. When the lift quantity of the intake valve 26 driven by the continuously variable valve lift mechanism 27 is large, a flow promoting part 72 is provided for restraining reduction in a flow rate of the intake air flowing in the combustion chamber 17 via the intake hole parts 22. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

Conventionally, a gasoline engine of a type in which fuel is directly injected into a combustion chamber is mounted on an automobile or the like. Such an engine is generally called an in-cylinder injection engine or a direct injection engine, and has already been put into practical use as an engine having high fuel efficiency.
The following Patent Document 1 is given as a document showing an example of a technique related to such an in-cylinder injection engine. Patent Document 1 discloses a technique for forming a tumble flow (a so-called longitudinal vortex flow) in a combustion chamber by forming a projection called a shroud in a cylinder head that forms a part of the combustion chamber. (For example, refer to the description in the 11th paragraph and FIG. 7 in the specification of Patent Document 1).
Japanese Patent Laid-Open No. 9-151738

However, when a shroud is formed as shown in Patent Document 1, a phenomenon occurs in which the flow of intake air flowing into the combustion chamber is hindered. This phenomenon occurs particularly when the intake air amount is increased due to a high engine load. Becomes prominent.
On the other hand, in recent years, a mechanism capable of continuously changing the lift amount of the intake valve and the exhaust valve (so-called continuously variable valve lift mechanism) has been developed and put into practical use.

  According to this continuously variable valve lift mechanism, since the intake amount of the engine can be changed freely by continuously changing the lift amount of the intake valve, the load that requires the lift amount of the intake valve is required. If it is configured to change according to the fuel consumption, it is possible to reduce fuel consumption by adjusting the intake air amount. In such a configuration, when the lift amount of the intake valve becomes maximum, that is, when the accelerator pedal depression amount is maximum, and when the engine is required to output the maximum torque. is there.

Therefore, if a shroud as disclosed in Patent Document 1 is simply formed as it is on an engine having such a continuously variable valve lift mechanism, the fully open performance of the engine will be significantly reduced.
On the other hand, in the engine of the type in which fuel is injected in the intake port and the air-fuel mixture is introduced into the combustion chamber instead of the in-cylinder injection engine as in Patent Document 1, the wall surface of the intake port is used. There is a problem that the fuel adhering to the fuel flows into the combustion chamber without being atomized, leading to a reduction in exhaust gas performance and fuel consumption.

  The present invention has been devised in view of such problems, and can improve engine combustion stability, exhaust gas performance and fuel consumption, and can suppress a decrease in engine output, in particular, a decrease in engine fully open performance. An object is to provide a combustion chamber structure of an engine.

  In order to achieve the above object, a combustion chamber structure for an engine according to the present invention (Claim 1) includes an intake hole for communicating an intake port and a combustion chamber, and an exhaust hole for communicating an exhaust port and the combustion chamber. A cylinder head formed with fuel, a fuel injection device that injects fuel into the intake port, an intake valve that opens and closes the intake hole, and a continuously variable valve lift mechanism that lifts the intake valve steplessly. When the lift amount of the intake valve driven by the continuously variable valve lift mechanism is small, it flows into the combustion chamber from the opposite side of the intake hole to the exhaust hole side. The flow of the intake air flowing into the combustion chamber through the intake hole when the intake valve driven by the continuously variable valve lift mechanism is large and the lift amount of the intake valve is large is promoted. It is characterized in that it comprises a promoting portion.

Further, the combustion chamber structure of the engine of the present invention according to claim 2 is the content of claim 1, wherein the flow promoting portion extends along the outer edge of the intake hole and projects toward the combustion chamber. And a convex portion formed only on the exhaust hole side of the outer edge of the intake hole.
According to a third aspect of the present invention, there is provided a combustion chamber structure for an engine of the present invention according to the second aspect, wherein a plurality of the intake holes are formed and the convex portions are formed for the plurality of intake holes. The convex portion is formed between the one end portion and the other end portion, and an angle formed by each straight line connecting the one end portion and the other end portion to the corresponding central point of the intake hole portion is at least 90. More than and less than 180 degrees, the one end is formed between the plurality of intake holes.

  According to a fourth aspect of the present invention, there is provided the combustion chamber structure of the engine of the present invention according to the second or third aspect, wherein the cylinder head is inclined downward from a top portion formed above the combustion chamber. A first inclined surface and a second inclined surface extending to both sides are provided, the exhaust hole portion is formed in the first inclined surface, and the intake hole portion is formed in the second inclined surface, The valve has a shaft portion extending in the lift direction and an umbrella portion provided on one end side of the shaft portion, and the umbrella portion is disposed along the inclination of the second inclined surface, The fuel injection device is configured to inject fuel toward the umbrella portion of the intake valve in the intake port.

Further, in the combustion chamber structure of the engine of the present invention according to claim 5, in the content of claim 4, the cylinder head has an air intake port for taking in fresh air on a side surface thereof, and the intake hole portion includes: It is characterized by communicating with the air intake.
In addition, the combustion chamber structure of the engine of the present invention according to claim 6 is characterized in that, in the content of any one of claims 2 to 5, the height of the convex portion is less than 2 millimeters. .

According to the combustion chamber structure of the engine of the present invention, even when the lift amount of the intake valve is small and the intake air amount flowing into the combustion chamber is small, the intake air flow in the combustion chamber is promoted to improve the combustion stability and exhaust gas. It can contribute to the improvement of performance and fuel consumption. Further, even when the lift amount of the intake valve is large, that is, when the output torque demand for the engine is large, it is possible to suppress the decrease in the engine output by suppressing the decrease in the flow rate of the intake air flowing into the combustion chamber as much as possible. Can do. Further, it is possible to generate a vortex flow (reverse tumble) that flows in a direction opposite to the direction in which the exhaust hole portion is formed from the intake hole portion in the combustion chamber, and to promote the flow of the airflow in the combustion chamber. (Claim 1)
In addition, by forming a convex portion only on the exhaust hole portion side of the outer edge of the intake hole portion, it is possible to prevent the flow of intake air from being disturbed while generating a reverse tumble flow. (Claim 2)
In addition, by strengthening the reverse tumble flow generated in the combustion chamber, it is possible to improve the combustion stability, exhaust gas performance, and fuel consumption of the engine while suppressing a reduction in the fully open performance of the engine. (Claim 3)
Moreover, the atomization of the fuel injected toward the umbrella part of the intake valve can be promoted, and the exhaust gas performance can be improved. (Claim 4)
In addition, by introducing the intake air to the combustion chamber from the side, when the lift amount of the intake valve is small, a reverse tumble flow that is a vortex flow directly from the intake hole to the lower side of the combustion chamber is generated. On the other hand, when the opening amount of the intake valve is large, a vertical vortex flow (positive tumble flow) is generated from the intake opening to the lower side of the combustion chamber through the first wall portion of the cylinder head. be able to. (Claim 5)
In addition, by ensuring that the height of the convex portion is less than 2 millimeters, ensuring the fully open performance of the engine and improving the combustion stability, exhaust gas performance and fuel consumption when the intake air flow rate is small are achieved at a high level. be able to. (Claim 6)

  Hereinafter, the combustion chamber structure of an engine according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing the structure of the combustion chamber, and FIGS. 2 and 3 are viewed from the cylinder block side. 4 is a schematic plan view showing the cylinder head, FIG. 4 is a schematic graph showing the relationship between the flow rate of the air flow in the combustion chamber and the lift amount of the intake valve, and FIG. 5 is the ease of flow of the intake air flowing into the combustion chamber. It is a typical graph which shows the relationship between a degree and the lift amount of an intake valve.

  As shown in FIG. 1, the engine 70 is mainly composed of a cylinder block 12 and a cylinder head 71. A cylinder 14 is formed in the cylinder block 12, and an exhaust side inclined surface (first inclined surface) 15 and an intake side inclined surface (second inclined surface) 16 are formed in the cylinder head 71. Further, a side wall portion (combustion chamber peripheral portion) 13 </ b> B is erected from the lower edge of the exhaust side inclined surface 15 and the intake side inclined surface 16 to the lower end surface 13 </ b> A of the cylinder head 71.

A combustion chamber 17 is formed as a space surrounded by the cylinder 14, the exhaust side inclined surface 15, the intake side inclined surface 16, the side wall portion 13B, and the upper surface of the piston (not shown).
Further, the exhaust-side inclined surface 15 and the intake-side inclined surface 16 of the cylinder head 71 are inclined and extended downward from the top portion 18 forming the uppermost portion of the combustion chamber 17, respectively. The upper wall is formed in a pent roof shape. The inclination angle of exhaust side inclined surface 15 relative to the lower end surface 13A of the cylinder head 71 is theta _a, The inclination angle of the intake side inclined surface 16 relative to the cylinder head bottom surface 13A is theta _b.

As shown in FIG. 2, two exhaust hole portions 21 and 21 are formed in the exhaust side inclined surface 15 of the cylinder head 71, and two intake hole portions 22 and 22 are formed in the intake side inclined surface 16. Furthermore, a plug hole 19 for projecting a spark plug (not shown) to the combustion chamber 17 is formed in the top portion 18.
Further, as shown in FIG. 1, an exhaust port 23 and an intake port 24 are formed inside the cylinder head 71. The exhaust port 23 and the intake port 24 are respectively connected to the exhaust holes 21 and 21 and the intake port. It communicates with the holes 22 and 22.

The cylinder head 71 has an air intake (not shown) for taking in fresh air on its side surface. The air intake is in communication with the intake port 23 and the intake holes 22 and 22. Yes.
Thus, air intake is provided on the side of the cylinder head 71, also the intake side inclined surface 16 which the intake hole portions 22 are formed, are formed inclined as shown in FIG. 1 theta _b As a result, the intake air can be introduced obliquely with respect to the combustion chamber 17, whereby the positive tumble flow can be enhanced when the lift amount of the intake valves 26, 26 is large. In this engine 70, when the lift amount of the intake valves 26, 26 is small, a reverse tumble flow that is a tumble flow in the opposite direction to the normal tumble flow can be generated. The point will be described later. Further, the normal tumble flow and the reverse tumble flow will be described later.

  The intake port 23 is provided with an injector (fuel injection device) (not shown), and fuel is injected into the intake port 23 toward the umbrella portion 26B of the intake valve 26. This is intended to promote the vaporization of the fuel by injecting the fuel toward the umbrella portions 26B and 26B of the intake valves 26 and 26 heated by the combustion in the combustion chamber 17.

The exhaust holes 21 and 21 are opened and closed by exhaust valves 25 and 25, and the intake holes 22 and 22 are opened and closed by intake valves 26 and 26.
Among these, the exhaust valve 25 has a shaft portion 25A extending in the lift direction and an umbrella portion 25B provided at the end portion of the shaft portion 25A on the combustion chamber 17 side. The umbrella portion 25 </ b> B of the exhaust valve 25 is disposed along the exhaust-side slope 15.

The intake valve 26 is also formed with a shaft portion 26A extending in the lift direction and an umbrella portion 26B provided at an end portion of the shaft portion 26A on the combustion chamber 17 side. The umbrella portion 26 </ b> B of the intake valve 26 is disposed along the intake side inclined surface 16.
The exhaust valves 25 and 25 open and close (lift) following the movement of an exhaust cam (not shown), while the intake valves 26 and 26 are driven by a continuously variable valve lift mechanism 27 to open and close. It has become.

  Since the continuously variable valve lift mechanism 27 is a well-known technique, a detailed description thereof is omitted here. However, in brief, the intake valves 26 and 26 are driven to open and close, and the lift amount ( (The on-off valve amount) is finely changed, and more specifically, the lift amount is changed continuously (steplessly). Such a continuous lift amount change of the intake valves 26, 26 is performed by changing a displacement amount of a link mechanism (not shown) mechanically connected to the intake valves 26, 26 in accordance with an accelerator pedal depression amount. Realized. Instead of the continuously variable valve lift mechanism 27 that can change the lift amount continuously, a valve lift mechanism that can change the lift amount stepwise may be used.

  Further, shrouds (flow promoting portions; convex portions) 72 and 72 are formed on the outer edges of the intake hole portions 22 and 22 from the one end portions 72A and 72A to the other end portions 72B and 72B, respectively. Generation of a tumble flow can be promoted in the combustion chamber 17. The tumble flow is a vortex having a center of rotation in a direction orthogonal to the reciprocating direction of the piston, and is also called a longitudinal vortex and is an air flow generated in the combustion chamber 17. The tumble flow includes a normal tumble flow and a reverse tumble flow.

Among these, the “normal tumble flow” passes from the intake hole portions 22 and 22 to the cylinder top portion 18 and the exhaust side inclined surface 15 in the counterclockwise direction (positive direction) in the drawing as indicated by an arrow TB ₊ in FIG. This is a tumble flow that flows downward of the combustion chamber 17.
Further, the “reverse tumble flow” is a tumble that flows directly downward from the combustion chamber 17 in the clockwise direction (reverse direction) in the drawing as shown by an arrow _TB− in FIG. Current.

Then, the shroud 72 is formed in the cylinder head 70, the shroud 72, and is capable of promoting the formation of reverse tumble flow T _B-. In particular, the shrouds 72 and 72 can relatively strengthen the generation of the reverse tumble flow T _B− by suppressing the generation of the normal tumble flow T _{B +} when the lift amount of the intake valves 26 and 26 is small. It is like that.

More specifically, the shrouds 72, 72 project toward the combustion chamber 17 on the intake-side inclined surface 16 of the cylinder head 71, and the exhaust hole portions 21, 21 are arranged on the outer edges of the intake hole portions 22, 22. It is formed only on the provided side (that is, on the left half in FIG. 2 among the outer edges of the intake holes 22 and 22).
One end of the shrouds 72, 72 is referred to as one end 72A, 72A, and the other end is referred to as the other end 72B, 72B. One end 72A, 72A of the shroud 72, 72 in this embodiment is These are formed on the straight line L ₁ connecting the center points C ₁ and C ₁ of the intake valves 26 and 26 and between the intake holes 22 and 22.

Further, straight lines L ₃ and L ₃ connecting the center points C ₁ and C _{1 of} the intake hole and the one end portions 72A and 72A, and the center points C ₁ and C _{1 of the} intake hole and the other end portions 72B and 72B are connected. The shrouds 72 and 72 are formed so that the angle θ _S formed by the connecting straight lines L ₄ and L ₄ is about 115.0 degrees. Hereinafter, the straight line L _{3 is referred} to as “one end straight line”, and the straight line L _{4 is referred} to as “other end straight line”, and the angle θ _S formed by the one end straight line L ₃ and the other end straight line L _4. Is referred to as a “shroud angle”. The reference line for the shroud angle θ _S is the one end straight line L ₃ . The basis for setting the shroud angle θ _S to about 115.0 will be described later.

Further, the shroud 72 has a height relative to the intake side inclined surface 16 (see arrows in FIG. 1 h ₂₎ is formed to be about 1.0 millimeters. The height h ₂ is not limited to about 1.0 millimeter, and can be appropriately changed as long as it is less than 2.0 millimeters. Further, the displacement per cylinder of the engine 70 according to the present embodiment is about 165 cc.

Since the combustion chamber structure of the engine according to the embodiment of the present invention is configured as described above, the following operations and effects are achieved.
The graph shown in FIG. 4 is obtained by experiment, and the vertical axis defines the tumble ratio in the combustion chamber 17 and the horizontal axis defines the lift amount of the intake valves 26 and 26.
Here, the tumble ratio in the combustion chamber 17 is a value indicating the number of rotations of the airflow in the combustion chamber 17 generated during one intake stroke. Therefore, the tumble ratio indicates that the larger the absolute value, the better the flow of the airflow in the combustion chamber 17. Note that a positive (plus) tumble ratio indicates a positive tumble, and a negative (minus) tumble indicates an inverse tumble.

Further, in the drawing, the lift amount indicated by reference sign VL _min indicates the minimum lift amount of the intake valves 26, 26, and the lift amount indicated by reference sign VL _max indicates the maximum lift amount of the intake valves 26, 26.
Further, in this graph, a line indicated by a one-dot chain line indicates a case of an engine having a combustion chamber in which no shroud is formed, that is, a general engine.
On the other hand, each line connecting portions indicated by various marks indicates a case where the setting conditions of the shrouds 72 and 72 are changed as shown in FIG. That is, the line connecting the locations indicated by the x marks indicates the case where the shroud angle θ _S is θ ₁ (θ ₁ = about 22.5 degrees), and the line connecting the locations indicated by the ○ marks is the shroud angle θ _{The case where S} is θ ₂ (θ ₂ = about 90.0 degrees) is shown.

A line connecting the locations indicated by □ indicates the case where the shroud angle θ _S is θ ₃ (θ ₃ = about 115.5 degrees), and a line connecting the locations indicated by the Δ marks indicates the shroud angle θ _S. Is set to θ ₄ (θ ₄ = about 180.0 degrees).
Further, the line connecting the portions indicated by ☆ is the shroud angle θ _S is θ ₅ (θ ₅ = about 90.0 degrees), and the center line is the center point C ₁ , C of the intake hole portions 26, 26. _{In FIG. 1} , the case is set so as to be orthogonal to the straight line L ₁ .

When the engine 70 is operated by changing the setting conditions of the shrouds 72 and 72 as described above, as shown in FIG. 3, when the lift amount of the intake valves 26 and 26 is minimum (that is, at VL _min ), the shroud In a general engine in which the engine is not formed, a strong reverse tumble flow cannot be obtained. However, in the engine 70 according to this embodiment including the combustion chamber 17 in which the shrouds 72 and 72 are formed, the general engine does not. Even strong reverse tumble flow can be obtained. In particular, when the shroud angle θ _S is 90 to 180 degrees, a strong reverse tumble flow can be obtained.

In addition, as shown by θ _{5 in} FIG. 3, when the one end portions 72A ′ and 72A ′ are provided at positions that do not coincide with the straight line L ₁ , as shown by the asterisk in FIG. 3, the intake valve When the lift amount of 26, 26 is small, neither the forward tumble nor the reverse tumble can be strengthened.
Next, the relationship between the flow coefficient and the lift amount of the intake valves 26, 26 will be described using the graph shown in FIG. The flow coefficient is a value indicating the easiness of the flow of the intake air flowing into the combustion chamber 17 through the intake holes 22 and 22. The larger the value, the easier the intake air flows into the combustion chamber 17. It is shown that. In the graph shown in FIG. 5, the flow coefficient is defined on the vertical axis, and the lift amounts of the intake valves 26, 26 are defined on the horizontal axis.

In FIG. 5, symbols VL _min and VL _max indicate the minimum lift amount and the maximum lift amount of the intake valves 26, 26, respectively, as in FIG. Also, the objects indicated by the marks used in the graph of FIG. 4 (that is, Δ mark, ○ mark, □ mark, + mark, and ☆ mark) are the same as those in FIG.
As shown in the graph of FIG. 4, when the lift amount of the intake valves 26, 26 is the minimum (VL _min ) to the maximum (VL _max ), that is, the lift amount of the intake valves 26, 26 is increased. in the entire region, the engine 70 according to this embodiment, even when set to either the height h ₂ of the shroud 72, 72, to ensure the engine roughly comparable flow coefficient shroud 72 is not formed Looks like it can.

However, the flow coefficient is not considered only by the value at an arbitrary lift amount, but rather, it is actually considered by examining the flow coefficient from the minimum lift amount to the arbitrary lift amount, that is, by integrating the flow coefficient. In case of
For example, if the lift amount of the intake valves 26, 26 is maximum (VL _max ), the sum of all the flow coefficients from the minimum lift amount to the maximum lift amount is substantially equal to the maximum lift amount. It can be said that the flow rate coefficient is large.

When the graph shown in FIG. 5 is examined by paying attention to such a viewpoint, when the shroud angle θ _S is set to θ ₁ , a substantial flow rate superior to that when the shroud angles θ _{2 to} θ ₅ are set. It can be said that a coefficient can be obtained. However, when the shroud angle θ _S is set to θ ₁ , it is difficult to sufficiently generate a reverse tumble flow when the lift amount of the intake valves 26 is small as described above with reference to FIG.

Therefore, in this embodiment, the shroud angle θ _{S is set} to θ ₃ (θ ₃ = about 115.0 degrees), and the decrease in the flow coefficient is suppressed while strengthening the reverse tumble flow.
When the shroud angle θ _S is set to θ ₅ , that is, when the positions of the one end portions 72A and 72A are not formed between the intake hole portions 26 and 26, a preferable flow coefficient is obtained, but the combustion chamber 17 It is hard to say that the tumble flow is strengthened. Accordingly, in the present embodiment, as shown in FIG. 2, one end portion 72A, a 72A, so as to be located on the straight line L ₁ connecting the and suction hole portions 26 a between the inlet holes 26, 26 Is provided.

As described above, when the lift amount of the intake valves 26, 26 is the minimum (VL _min ), the intake air amount flowing into the combustion chamber 17 becomes small. According to the combustion chamber structure of the engine according to the embodiment, the flow of the airflow in the combustion chamber 17 can be promoted, thereby contributing to the improvement of the combustion stability, exhaust gas performance and fuel consumption of the engine 70. .

Further, even when the lift amount of the intake valves 26, 26 is the maximum (VL _max ), that is, when the output torque request to the engine 70 is the maximum, the combustion chamber structure of the engine according to the embodiment of the present invention. According to the above, since the flow coefficient of the intake air flowing into the combustion chamber 17 is hardly reduced, a situation in which the torque output from the engine 70 is reduced can be avoided.

Further, by generating a reverse tumble flow T _B− in the combustion chamber 17, particularly a strong reverse tumble flow T _B− when the lift amount of the intake valves 26 and 26 is small, the air flow in the combustion chamber 17 is promoted. Can be achieved.
Further, the height h ₂ of the shrouds 72, 72 is set to be less than 2.0 millimeters from the intake side inclined surface 16, so that the fully opening performance of the engine 70 is ensured and the intake flow rate to the combustion chamber 17 is small. Combustion stability, exhaust gas performance, and fuel efficiency improvement in some cases can be achieved at a high level.

In addition, the shroud angle θ _S of the shrouds 72 and 72 is set to 90 to 180 degrees, and the one end portions 72A and 72A are formed between the intake hole portions 22 and 22, thereby ensuring the fully open performance of the engine 70. The combustion stability, the exhaust gas performance, and the improvement in fuel consumption when the intake air flow rate into the combustion chamber 17 is small can be achieved at a high level.
Although the embodiment of the present invention has been described above, the present invention is not limited to the embodiment, and various modifications can be made without departing from the spirit of the present invention.

  In each of the above-described embodiments and modifications thereof, the case where two exhaust holes and two intake holes are formed has been described as an example. However, the present invention is not limited to such a case. For example, one exhaust hole and one intake hole may be formed, or two exhaust holes and three intake holes may be formed. . Of course, the present invention can be applied even when three or more exhaust holes and three intake holes are formed.

  Moreover, although the case where the engine displacement per cylinder of the engine in each of the above-described embodiments and modifications thereof is about 165 cc has been described as an example, for example, the displacement per cylinder may be about 165 to 600 cc.

It is typical sectional drawing which shows the combustion chamber structure of the engine which concerns on embodiment of this invention. It is a typical top view showing the combustion chamber structure of the engine concerning the embodiment of the present invention, and shows the case where a cylinder head is seen from the cylinder block side. It is a typical top view showing the combustion chamber structure of the engine concerning the embodiment of the present invention, and shows the case where a cylinder head is seen from the cylinder block side. It is a typical graph which shows the relationship between the degree of an airflow flow, and the lift amount of an intake valve in the combustion chamber structure of the engine which concerns on embodiment of this invention. 6 is a schematic graph showing the relationship between the degree of intake air flow and the lift amount of the intake valve in the combustion chamber structure of the engine according to the embodiment of the present invention.

Explanation of symbols

13A Cylinder head lower end surface 13B Side wall (combustion chamber circumference)
17 Combustion chamber 21 Exhaust hole portion 22 Intake hole portion 23 Exhaust port 24 Intake port 26 Intake valve 27 Continuously variable valve lift mechanism 70 Engine 71 Cylinder head 72 Shroud (convex portion, flow promoting portion)
72A One end 72B The other end

Claims (6)

A cylinder head formed with an intake hole communicating the intake port and the combustion chamber, and an exhaust hole communicating the exhaust port and the combustion chamber;
A fuel injection device for injecting fuel into the intake port;
An intake valve for opening and closing the intake hole;
A combustion chamber structure of an engine provided with a continuously variable valve lift mechanism that lifts the intake valve steplessly;
When the lift amount of the intake valve driven by the continuously variable valve lift mechanism is small, the flow of intake air flowing into the combustion chamber from the side opposite to the exhaust hole portion of the intake hole portion is promoted, and When the lift amount of the intake valve driven by the continuously variable valve lift mechanism is large, it is provided with a flow promoting portion that suppresses a decrease in the flow rate of the intake air flowing into the combustion chamber through the intake hole portion, Engine combustion chamber structure. The flow promoting portion extends along the outer edge of the intake hole portion, protrudes toward the combustion chamber, and is a convex formed only on the exhaust hole portion side of the outer edge of the intake hole portion. The combustion chamber structure for an engine according to claim 1, wherein the combustion chamber structure is an engine. A plurality of the intake holes are formed,
The convex portion is formed for each of the plurality of intake holes,
The convex portion is formed between one end and the other end,
The angle formed by each straight line connecting the one end and the other end and the corresponding center point of the intake hole is at least 90 degrees and less than 180 degrees,
The combustion chamber structure for an engine according to claim 2, wherein the one end portion is formed between the plurality of intake hole portions. The cylinder head includes a first inclined surface and a second inclined surface extending to both sides while being inclined downward from a top portion formed above the combustion chamber,
The exhaust hole is formed in the first inclined surface,
The intake hole is formed in the second inclined surface,
The intake valve has a shaft portion extending in the lift direction, and an umbrella portion provided on one end side of the shaft portion,
The umbrella portion is disposed along the inclination of the second inclined surface,
The engine combustion chamber structure according to claim 2 or 3, wherein the fuel injection device is set to inject fuel toward the umbrella portion of the intake valve in the intake port. The cylinder head has an air intake for taking in fresh air on its side surface,
The combustion chamber structure of an engine according to claim 4, wherein the intake hole portion communicates with the air intake port. The engine combustion chamber structure according to any one of claims 2 to 5, wherein the convex portion has a height of less than 2 millimeters.

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