Intake port structure of internal combustion engine

This application is a national phase application of International Application No. PCT/IB2007/000754, filed Feb. 15, 2007, and claims the priority of Japanese Application No. 2006-040763, filed Feb. 17, 2006, the contents of both of which are incorporated herein by reference.

1. Field of the Invention

The invention relates to an intake port structure of an internal combustion engine and more particularly to an intake port structure of an internal combustion engine that includes an airflow control valve which is pivotally supported at its proximal end in proximity to the inner wall of the intake port.

2. Description of the Related Art

A known intake port structure of an internal combustion engine includes an airflow control valve that produces vortical flows, such as tumble flows (longitudinal vortexes) and swirl flows (lateral vortexes). Such vortical flows facilitate mixing of fuel and air and help flames propagate within a combustion chamber, thereby improving the combustion efficiency. In addition, by using such vortical flows, it is possible to concentrate dense air-fuel mixtures around each spark plug and perform stratified combustions. Among such intake port structures, there is known an intake port structure in which an airflow control valve which is pivotally supported at its proximal end is fully opened by being retracted into the inner wall of the intake port, which is disclosed, for example, in Japanese Utility Model Application Publication No. 7-25264.

To allow the pivotal motion of the airflow control valve, it is necessary to provide, in each side of the airflow control valve, gaps (clearances) between the side ends of the airflow control valve and the inner walls of the intake port that face the same side ends of the airflow control valve. FIG. 7A to 7C schematically show a conventional intake port structure 100 X of an internal combustion engine (hereinafter, simply referred to as an “intake port structure”) that includes an airflow control valve 1 X which is pivotally supported at its proximal end on a valve shaft 2 . More specifically, FIG. 7A shows the intake port structure 100 X in a state where the airflow control valve 1 X is fully closed, FIG. 7B shows the intake port structure 100 X in a state where the airflow control valve 1 X is fully opened, and FIG. 7C shows, for easier understanding of the shape of the airflow control valve 1 X, the appearance of the airflow control valve 1 X as well as the names of respective portions thereof.

A recess 11 X is formed in the intake port 10 X. The airflow control valve 1 X is retracted into the recess 11 X formed in the inner wall of the intake port 10 X when the airflow control valve 1 X is fully opened, as shown in FIG. 7B . As the recess 11 X is thus formed in the intake port 10 X, the recess 11 X, the inner wall of the intake port 10 X, and the wall substantially perpendicular to these recess and inner wall form a step. In the meantime, the gaps are formed between the side ends of the airflow control valve 1 X and the inner wall of the intake port 10 X. Therefore, when the airflow control valve 1 X is fully closed, the intake air flows through these gaps as gap flow F 2 , in addition to main flow F 1 that flows through the intentionally narrowed intake passage. Some gap flow F 2 , after passing through the gaps, collides with the step and thereby changes its direction upward, just like bouncing up at the step. This gap flow F 2 may disturb the main flow F 1 , making it difficult to stably produce vortical flows in the combustion chamber.

In recent years, an ignition timing retardation control that retards the ignition timing of an internal combustion engine has been widely employed in order to quickly increase the temperature of a catalyst to a reaction temperature after the engine is started. However, when the ignition timing retardation is performed in an internal combustion engine that includes an airflow control valve for producing vortical flows, it is important whether it is possible to maintain a desired stability of combustion using vortical flows, in other words, whether it is possible to stably produce vortical flows, which is fundamentally necessary to achieve stable combustion. That is, unless vortical flows are stably produced, the ignition timing retardation is accordingly limited, and as a result, the effect of reducing emissions from the internal combustion engine is limited inevitably.

The invention provides an intake port structure of an internal combustion engine that can reduce emissions from the internal combustion engine by minimizing adverse effects caused to the main flow of intake air by the gap flow of intake air that flows through gaps on the sides of an airflow control valve.

An aspect of the present invention relates to an intake port structure of an internal combustion engine. The intake port structure has an intake port, a valve shaft provided in proximity to an inner wall of the intake port, and an airflow control valve having a proximal end which is pivotally supported on the valve shaft and a distal end which becomes part of the inner wall of the intake port when the airflow control valve is fully opened. The inner wall of the intake port has a recess into which the airflow control valve is partially or entirely retracted when the airflow control valve is fully opened. The recess has a flow smoothing portion located downstream of the proximal end. In addition, according to an aspect of the present invention, the recess may be formed not to have a step. Furthermore, each side end of the airflow control valve and the inner wall of the intake port that faces the side end form therebetween a gap through which gap flow of intake air passes when the airflow control valve is fully closed. According to the aspect of the present invention, because the intake air that flows through the gap, namely, the gap flow, does not collide with a step and therefore does not disturb the main flow, for example, unevenness in the strength of produced vortical flows can be reduced. That is, according to the above aspect of the present invention, vortical flows can be stably produced, and therefore it is possible to maintain the combustion mode using vortical flows if the ignition timing of the internal combustion engine is further retarded. Accordingly, the temperature of a catalyst quickly increases to its reaction temperature to reduce emissions from the internal combustion engine. Furthermore, according to the aspect of the present invention, since a desired combustion state can be reliably achieved, reduction of the emissions produced due to variation of the combustion state may be expected.

Meanwhile, the sentence “when the airflow control valve is fully opened, a distal end of the airflow control valve becomes part of the inner wall of the intake port” means that the intake port does not include such a partition that, when the airflow control valve is half-open, the distal end of the airflow control valve is located in proximity to the partition, in order to maintain a biased state of the main flow. That is, it is considered that, when the partition is provided in the intake port, the intake air flowing through the gaps on the side ends of the airflow control valve does not reach the main flow. This is what the sentence refers to. It is applicable that a step is partially not formed. Meanwhile, a typical example of “step” is shown in FIG. 7A and FIG. 7B , which is defined by the inner wall of the intake port, the recess, and the surface perpendicular to each of them. However, it is to be understood that the definition of “step” encompasses any shape that is functionally inevitable for allowing an airflow control valve having a substantially constant thickness to be retracted into the inner wall of the intake port. An example of the functionally inevitable shape may be an arc shape formed between the inner wall and the recess so that the portion does not interfere with the distal end of the airflow control valve, based on the fact that the distal end makes an arc-shaped locus during the pivotal motion of the airflow control valve. Another example of the functionally inevitable shape, instead of the arc-shaped surface, may be a surface formed between the inner wall and the recess and slanting to prevent interference with the distal end of the airflow control valve. In other words, according to this aspect of the present invention, in view of the possibility of the main flow being disturbed by the gap flow, the functionally inevitable shape for preventing interference with the distal end of the airflow control valve may be realized without forming a step.

The “functionally inevitable shape” consists of a shape that basically enables the airflow control valve to be retracted into the inner wall of the intake port and that prevents interference between the inner wall of the intake port and the airflow control valve. The “functionally inevitable shape” does not include a shape that accomplishes advantageous effects which are intended according to aspects of the present invention. That is, the shape of the recess may depend upon the shape of the airflow control valve. Therefore, if the airflow control valve is assumed to be a primary element of the intake port structure, some functional shapes may appear to be essential although they are not in fact. However, for example, as long as the shapes employed according to aspects of the present invention, which are described below, correspond to the advantageous effects intended according to aspects of the present invention, they are not considered to be the “functionally inevitable shape” even if the airflow control valve is assumed to be a primary element. Such structures are considered to be aspects of the present invention. Further, although the recess is formed to store the airflow control valve when the airflow control valve is fully opened, the present invention also encompasses a structure including an airflow control valve that is not entirely retracted into the recess when the airflow control valve is fully opened, as long as the advantageous effects intended according to aspects of the present invention, which are described below, are achieved in the same structure.

In an aspect of the present invention, the recess may have a bottom surface that slants inwardly of the intake port from its upstream end to form the flow smoothing portion. In this case, for example, by forming the bottom surface of the airflow control valve into a shape that does not interfere with the bottom surface of the recess when the airflow control valve is fully opened, or by forming the airflow control valve into a shape that is obtained by cutting off the upper portion that becomes a dead volume when the airflow control valve is fully opened, the airflow control valve can be entirely retracted into the inner wall of the intake port when the airflow control valve is fully opened.

In another aspect of the present invention, the bottom surface may be formed partially in correspondence with the gap. Note that “in correspondence with the gap” means “in correspondence with the flowing manner or mode of intake air flowing through the gaps”. That is, in the aspect of the present invention, the bottom surface may be formed partially at a portion where it is necessary to prevent the main flow from being disturbed by the gap flow.

In another aspect of the present invention, the recess has a downstream inner surface that slants inwardly of the intake port from its upstream end to form the flow smoothing portion. In this case, for example, by forming the bottom surface of the airflow control valve into a shape that does not interfere with the downstream inner surface of the recess when the airflow control valve is fully opened, the airflow control valve can be entirely retracted into the inner wall of the intake port when the airflow control valve is fully opened.

In another aspect of the present invention, each side end of the airflow control valve and the inner wall of the intake port that faces the side end form therebetween a gap, and the downstream inner surface may be formed partially in correspondence with the gap.

In another aspect of the present invention, a partition plate that divides an intake passage in the intake port may be provided downstream of the recess. According to this structure, the partition plate effectively prevents the intake air that has passed through the gaps at the airflow control valve from reaching the main flow. If the partition plate is shaped based on the flowing manner or mode of intake air so as not to disturb intake air flow when the airflow control valve is fully opened, resistance against intake air flow can be minimized.

According to the above-described aspects of the present invention, the adverse effects that are caused to the main flow by the intake air flowing through the gaps on the side ends of the airflow control valve are suppressed, and therefore vortical flows can be stably produced, leading to a reduction in the amount of emissions from the internal combustion engine.

The foregoing and further objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1A to FIG. 1C , and FIG. 1E are views schematically showing an intake port structure 100 A according to a first embodiment;

FIG. 1D is a view schematically showing an intake port structure 100 AX that is a modification example of the first embodiment;

FIG. 2A to FIG. 2C are views schematically showing an intake port structure 100 B according to the second embodiment;

FIG. 3A and FIG. 3B are views schematically showing an intake port structure 100 C according to the third embodiment;

FIG. 4A and FIG. 4B are views schematically showing an intake port structure 100 D according to the fourth embodiment;

FIG. 5A and FIG. 5B are views schematically showing an intake port structure 100 E according to the fifth embodiment;

FIG. 6A and FIG. 6B are views schematically showing an intake port structure 100 F according to the sixth embodiment; and

FIG. 6C is a view schematically showing an intake port structure 100 Fa that is a modification example of the sixth embodiment; and

FIG. 7A to FIG. 7C are views schematically showing a conventional intake port structure 100 X having an airflow control valve which is supported at its proximal end on a valve shaft 2 .

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1A to FIG. 1E are views schematically showing an intake port structure 100 A and an intake port structure 100 AX according to a first embodiment of the present invention. Specifically, FIG. 1A is a view showing the intake port structure 100 A together with a cylinder block 51 , a cylinder head 52 A, and a piston 53 A, as the main components of an internal combustion engine 50 A. FIG. 1B is an enlarged view showing the intake port structure 100 A where an airflow control valve 1 A is fully opened. FIG. 1C is an enlarged view showing the intake port structure 100 A in a state where the airflow control valve 1 A is fully closed. FIG. 1D is an enlarged view showing the intake port structure 100 A in a state where the airflow control valve 1 A is replaced by an airflow control valve 1 X. FIG. 1E is a view showing the appearance of the airflow control valve 1 A for easier understanding the shape of the airflow control valve 1 A. Though not indicated in the drawings, the names of the respective portions of the airflow control valve 1 A are the same as those of the airflow control valve 1 X indicated in FIG. 7A to FIG. 7C .

The internal combustion engine 50 A is a direct injection gasoline engine. However, it is to be understood that application of the intake port structure 100 A of the first embodiment is not limited to a so-called lean-burn engine, that is, the intake port structure 100 A may be applied to various other engines, such as non-direct injection gasoline engines, diesel engines. The internal combustion engine 50 A is an inline four-cylinder engine, but the internal combustion engine 50 A may be an engine having more than or less than four cylinders and/or having a non-inline cylinder arrangement. Further, although only the main portions of a cylinder 51 a will be described in this embodiment, it is to be understood that each of other cylinders has the same structure as the cylinder 51 a.

The internal combustion engine 50 A includes the cylinder block 51 , the cylinder head 52 A, and the piston 53 . A cylinder 51 a having a cylindrical shape is formed in the cylinder block 51 , and the piston 53 is arranged in the cylinder 51 a . The cylinder head 52 A is fixed on the top of the cylinder block 51 . A combustion chamber 54 is a space surrounded by the cylinder block 51 , the cylinder head 52 A, and the piston 53 . Within the cylinder head 52 A, an intake port 10 A through which intake air is drawn into the combustion chamber 54 and an exhaust port 20 through which combusted gas is discharged from the combustion chamber 54 are formed. An intake valve, not shown in the drawing, is provided to open and close the passage of the intake port 10 A, and an exhaust valve, not shown in the drawings, is provided to open and close the passage of the exhaust port 20 .

A valve shaft 2 pivotally supports the airflow control valve 1 A and is provided in proximity to the inner wall of the intake port 10 A. An actuator, not shown in the drawings, operates the valve shaft 2 . In this embodiment, the actuator is a step motor. However, it is to be understood that the actuator is not limited to a step motor but may be other device or component. The actuator may be connected to the valve shaft 2 via an appropriate mechanism, such as a link mechanism, a rack-and-pinion mechanism, and a speed-reduction mechanism. The airflow control valve 1 A is a component for changing the flow volume and flow rate of intake air, and the airflow control valve 1 A is pivotally supported at its proximal end on the valve shaft 2 . A cutout portion is formed at the distal end of the airflow control valve 1 A to accelerate the main flow when the airflow control valve 1 A is fully closed. As the actuator changes the angle of the airflow control valve 1 A under the control of ECU (Electric Control Unit), not shown in the drawings, the flow volume and flow rate of intake air change accordingly. The flow of intake air is biased in the intake port 10 A as the airflow control valve 1 A changes its position from the fully-closed position to the half-open position, and strong tumble flows T are thereby produced within the combustion chamber 54 . Note that a cavity for guiding tumble flows T may be formed at the crown of the piston 53 . Further, note that vortical flows produced in the combustion chamber 54 are not limited to tumble flows T, but may include tumble flows that swirl in the opposite direction, swirl flows, or inclined tumble flows, such as those produced by combining tumble flows T and swirl flows.

In this embodiment, the recess 11 A into which the airflow control valve 1 A is retracted when the airflow control valve 1 A is fully opened is formed in the inner wall of the intake port 10 A. The recess 11 A has a bottom surface that slants inwardly of the intake port 10 A from its upstream end, the width of the recess 11 A, as measured in the direction in which the valve shaft 2 extends, is substantially equal to the width of the intake passage. Thus, the recess 11 A provides an additional space that is triangular as viewed in the direction in which the valve shaft 2 extends. That is, the recess 11 A has a triangular cross section that is taken perpendicularly to the direction in which the valve shaft 2 extends. The airflow control valve 1 A has a triangular shape that is substantially the same as or complementary to the triangular shape of the recess 11 A. Specifically, the airflow control valve 1 A has a shape that is obtained by cutting off the upper portion of the airflow control valve 1 X shown in FIG. 7 , which upper portion becomes a dead volume when the airflow control valve 1 X is fully opened, in such a manner that the cut surface becomes flat. This shape of the airflow control valve 1 A is suitable for enabling the airflow control valve 1 A to be retracted into the inner wall of the intake port 10 A, namely, the recess 11 A. Thus, the airflow control valve 1 A is retracted into the inner wall of the intake port 10 A when the airflow control valve 1 A is fully opened, as shown in FIG. 1B . Thus, the airflow control valve 1 A, the valve shaft 2 , and the intake port 10 A constitute the intake port structure 100 A of the first embodiment.

Next, description will be made of how intake air flows when the airflow control valve 1 A is fully closed, with reference to FIG. 1C . When the airflow control valve 1 A is fully closed, the intake air flowing through the cutout portion forms the main flow F 1 . Further, when the airflow control valve 1 A is fully closed, intake air also flows through the gaps, and this flow of intake air forms the gap flow F 2 . In this embodiment, because the recess 11 A has the bottom surface that slants inwardly of the intake port 10 A from its upstream end, no step is formed because of providing the recess 11 A for retracting the airflow control valve 1 A. In this embodiment, the bottom surface may be regarded as a flow smoothing portion of the present invention. Therefore, the gap flow F 2 , after colliding with the inner wall of the intake port 10 A, flows along the inner wall to the downstream side without changing its direction towards the main flow F 1 . As a result, the disturbance from the gap flow F 2 to the main flow F 1 can be minimized and thus tumble flows T can be stably produced within the combustion chamber 54 . Furthermore, according to the above structure, the ignition timing can be further retarded after engine start, so that the temperature of the catalyst increases more quickly to its reaction temperature to reduce emissions from the internal combustion engine.

The recess 11 A is formed to have a flat surface for ease of production, and the like. However, the shape of the bottom surface is not limited to a flat surface, but it may be a single curved surface, a combination of two or more curved surfaces, a combination of flat surfaces, or a combination of flat and curved surfaces. Although it is preferable that the airflow control valve 1 A be shaped such that it can be retracted into the inner wall of the intake port 10 A when the airflow control valve 1 A is fully opened, the airflow control valve 1 X may be used instead of the airflow control valve 1 A, as in the intake port structure 100 AX shown in FIG. 1D . In this case, however, the upper portion that protrudes into the intake passage becomes a dead volume that undesirably increases resistance against intake air flows. In view of this, the intake port structure 100 A of the first embodiment suppresses the adverse effects that are caused to the main flow F 1 by the gap flow F 2 , which enables vortical flows to be stably produced and thereby reduces emissions from the internal combustion engine.

FIG. 2A to FIG. 2C are views schematically showing an intake port structure 100 B according to a second embodiment of the present invention. Specifically, FIG. 2A is a view showing the intake port structure 100 B in a state where an airflow control valve 1 B is fully opened. FIG. 2B is a view showing the intake port structure 100 B where the airflow control valve 1 B is fully closed. FIG. 2C is a view showing the appearance of the airflow control valve 1 B for easier understanding the shape of the airflow control valve 1 B. Though not indicated in the drawings, the names of the respective portions of the airflow control valve 1 B are the same as those of the airflow control valve 1 X shown in FIG. 7A to FIG. 7C . The intake port structure 100 B of the second embodiment is the same as the intake port structure 100 A of the first embodiment except that the intake port 10 A in which the recess 11 A is formed is replaced by an intake port 10 B in which a recess 11 B is formed with a downstream end surface B and that the airflow control valve 1 A is replaced by the airflow control valve 1 B. The configuration of the internal combustion engine in the second embodiment, not shown in the drawings, is the same as the configuration of the internal combustion engine 50 A in the first embodiment except that the intake port structure 100 A is replaced by the intake port structure 100 B. Thus, the airflow control valve 1 B, the valve shaft 2 , and the intake port 10 B constitute the intake port structure 100 B of the second embodiment.

The recess 11 b is formed in the inner wall of the intake port 10 B, and the airflow control valve 1 B is retracted into the recess 11 b when the airflow control valve 1 B is fully opened. The recess 11 b has a downstream inner surface B that slants inwardly of the intake port 10 B from its upstream end. That is, the recess 11 b has a trapezoidal cross section that is taken perpendicularly to the direction in which the valve shaft 2 extends. Meanwhile, the airflow control valve 1 B has a shape that is obtained by cutting off the portion of the airflow control valve 1 X shown in FIG. 7A to FIG. 7C , which interferes with the downstream inner surface B when the airflow control valve 1 X is fully opened, in such a manner that the cut surface becomes flat. Thus, the airflow control valve 1 B is retracted into the inner wall of the intake port 10 B when the airflow control valve 1 B is fully opened, as shown in FIG. 2A . As shown in FIG. 2B , because the downstream inner surface B is provided, that is, because no step that causes adverse effects to the main flow F 1 when the airflow control valve 1 B is fully closed is provided, the gap flow F 2 flows along the downstream inner surface B to the downstream side. As a result, tumble flows T can be stably produced, and therefore emissions from the internal combustion engine can be reduced. Thus, the intake port structure 100 B of the second embodiment suppresses adverse effects that are caused to the main flow F 1 by the gap flow F 2 , which enables vortical flows to be stably produced and thus reduces emissions from the internal combustion engine.

FIG. 3A and FIG. 3B are views schematically showing an intake port structure 100 C according to a third embodiment of the present invention. Specifically, FIG. 3A is a view showing the intake port structure 100 C in a state where an airflow control valve 1 C is fully opened. FIG. 3B is a view showing the intake port structure 100 C in a state where the airflow control valve 1 C is fully closed. The intake port structure 100 C of the third embodiment is the same as the intake port structure 100 A of the first embodiment except that the intake port 10 A in which the recess 11 A is formed is replaced by an intake port 10 C in which a recess 11 C is formed with a downstream inner surface C and the airflow control valve 1 A is replaced by the airflow control valve 1 C. The configuration of the internal combustion engine in the third embodiment, not shown in the drawings, is the same as the configuration of the internal combustion engine 50 A in the first embodiment except that the intake port structure 100 A is replaced by the intake port structure 100 C. The airflow control valve 1 C in the third embodiment is the same as the airflow control valve 1 X shown in FIG. 7A to 7C although they are denoted by different numerals for convenience of description. Thus, the airflow control valve 1 C is retracted into the inner wall of the intake port 10 C when the airflow control valve 1 C is fully opened, as shown in FIG. 3A . Thus, the airflow control valve 1 C, the valve shaft 2 , and the intake port 10 C constitute the intake port structure 100 C of the third embodiment.

The recess 11 C of the intake port 10 C has a downstream inner surface C that slants inwardly of the intake port 10 C from its upstream end. That is, the recess 11 C has a trapezoidal cross section that is taken perpendicularly to the direction in which the valve shaft 2 extends. Thus, no step that causes adverse effects to the main flow F 1 is provided, and therefore the gap flow F 2 flows along the surface C to the downstream side when the airflow control valve 1 C is fully closed. As a result, tumble flows T can be stably produced, and therefore emissions from the internal combustion engine can be reduced. Thus, the intake port structure 100 C of the third embodiment suppresses adverse effects that are caused to the main flow F 1 by the gap flow F 2 , which enables vortical flows to be stably produced and thus reduces emissions from the internal combustion engine.

FIG. 4A and FIG. 4B are views schematically showing an intake port structure 100 D according to a fourth embodiment of the present invention. Specifically, FIG. 4A is a view showing the intake port structure 100 D in a state where an airflow control valve 1 D is fully opened. FIG. 4B is a view schematically showing the intake port structure 100 D as viewed in the direction designated by the arrow Z. The intake port structure 100 D of the fourth embodiment is the same as the intake port structure 100 A of the first embodiment except that the intake port 10 A in which the recess 11 A is formed is replaced by an intake port 10 D in which a recess 11 D is formed with downstream inner surfaces D and that the airflow control valve 1 A is replaced by the airflow control valve 1 D. The configuration of the internal combustion engine in the fourth embodiment, not shown in the drawings, is the same as the configuration of the internal combustion engine 50 A in the first embodiment except that the intake port structure 100 A is replaced by the intake port structure 100 D. The airflow control valve 1 D in the fourth embodiment is the same as the airflow control valve 1 X shown in FIG. 7A to 7C although they are denoted by different numerals for convenience of description. Thus, the airflow control valve 1 D is retracted into the inner wall of the intake port 10 D when the airflow control valve 1 D is fully opened, as shown in FIG. 4A . The airflow control valve 1 D, the valve shaft 2 , and the intake port 10 D constitute the intake port structure 100 D of the fourth embodiment.

The recess 11 D has downstream inner surfaces D that slant inwardly of the intake port 10 D from its upstream end. The downstream inner surfaces D are separately and partially formed in correspondence with the respective gaps. More specifically, the downstream inner surfaces D are formed such that each downstream inner surface D has a certain width as measured, in the direction in which the valve shaft 2 extends, from the portion of the inner wall of the intake port 10 D that faces the corresponding side end of the airflow control valve 1 D. The width of each downstream inner surface D is determined based on the flowing mode or manner of the gap flow F 2 . Note that the position of each of the downstream inner surfaces D may be changed in the direction in which the valve shaft 2 extends, based on the flowing mode or manner of the gap flow F 2 . According to this structure, because no step that causes adverse effects to the main flow F 1 is provided, the gap flow F 2 flows along the downstream inner surfaces D to the downstream side when the airflow control valve 1 D is fully closed, as shown in FIG. 4B . As a result, tumble flows T can be stably produced, and therefore emissions from the internal combustion engine can be reduced. Thus, the intake port structure 100 D of the fourth embodiment suppresses adverse effects that are caused to the main flow F 1 by the gap flow F 2 , which enables vortical flows to be stably produced and thus reduces emissions from the internal combustion engine.

FIG. 5A and FIG. 5B are views schematically showing an intake port structure 100 E according to a fifth embodiment of the present invention. Specifically, FIG. 5A is a view showing the intake port structure 100 E in a state where an airflow control valve 1 E is fully opened. FIG. 5B is a view schematically showing the intake port structure 100 E as viewed in the direction designated by the arrow Z. The intake port structure 100 E of the fifth embodiment is the same as the intake port structure 100 A of the first embodiment except that the intake port 10 A in which the recess 11 A is formed is replaced by an intake port 10 E in which a recess 11 E is formed with downstream inner surfaces E and that the airflow control valve 1 A is replaced by the airflow control valve 1 E. The configuration of the internal combustion engine in the fifth embodiment, not shown in the drawings, is the same as the configuration of the internal combustion engine 50 A in the first embodiment except that the intake port structure 100 A is replaced by the intake port structure 100 E. Thus, the airflow control valve 1 E, the valve shaft 2 , and the intake port 10 E constitute the intake port structure 100 E of the fifth embodiment.

The recess 11 E is formed in the inner wall of the intake port 10 E and the airflow control valve 1 E is retracted into the recess 11 E when the airflow control valve 1 E is fully opened. The recess 11 E has the downstream inner surfaces E that slant inwardly of the intake port 10 E from its upstream end. The downstream inner surfaces E are separately and partially formed in correspondence with the respective gaps. More specifically, the downstream inner surfaces E are formed such that each downstream inner surface E has a certain width as measured, in the direction in which the valve shaft 2 extends, from the portion of the inner wall of the intake port 10 E that faces the corresponding side end of the airflow control valve 1 E. The width of each downstream inner surface E is determined based on the flowing mode or manner of the gap flow F 2 . Note that the position of each of the downstream inner surfaces E may be changed in the direction in which the valve shaft 2 extends, according to the flowing mode or manner of the gap flow F 2 . Meanwhile, the airflow control valve 1 E has a shape that is obtained by cutting off the portions of the airflow control valve 1 X shown in FIG. 7A to FIG. 7C that interfere with the respective surfaces E, in such a manner that the cut surfaces become flat. Thus, the airflow control valve 1 E is retracted into the inner wall of the intake port 10 E when the airflow control valve 1 E is fully opened.

Furthermore, in the fifth embodiment, because the downstream inner surfaces E are formed, that is, because no step that causes adverse effects to the main flow F 1 is provided, the gap flow F 2 flows along the surfaces E to the downstream side. As a result, tumble flows T can be stably produced, and therefore emissions from the internal combustion engine can be reduced. The intake port structure 100 E of the fifth embodiment is an example in which downstream inner surfaces are partially formed, and which corresponds to the intake port structure 100 B of the second embodiment. However, the intake port structure 100 E may alternatively be such that, for example, downstream inner surfaces are partially formed to be suitable in the intake port structure 100 A of the first embodiment. Thus, the intake port structure 100 E of the fifth embodiment suppresses adverse effects that are caused to the main flow F 1 by the gap flow F 2 , which enables vortical flows to be stably produced and thus reduces emissions from the internal combustion engine.

FIG. 6A to FIG. 6C are views schematically showing an intake port structure 100 F according to the sixth embodiment of the present invention. Specifically, FIG. 6A is a view showing the intake port structure 100 F having a partition plate 13 in a state where an airflow control valve 1 F is fully closed. FIG. 6B is a view showing the intake port structure 100 F as viewed in the direction designated by the arrow Z. FIG. 6C is a view showing an intake port structure 100 Fa having partition plates 14 instead of partition plate 13 . The intake port structure 100 F of the sixth embodiment is the same as the intake port structure 100 B of the second embodiment except that the intake port 10 B is replaced by an intake port 10 F. The intake port 10 F has the same structure as the intake port 10 B except for the partition plate 13 additionally provided. The airflow control valve 1 F in the sixth embodiment is the same as the airflow control valve 1 B in the second embodiment although they are denoted by different numerals for convenience of description. A recess 11 F and a downstream inner surface F in the sixth embodiment are the same as the recess 11 B and the downstream inner surface B in the second embodiment. Thus, the airflow control valve 1 F is retracted into the inner wall of the intake port 10 F when the airflow control valve 1 F is fully opened, as shown in FIG. 6A . The airflow control valve 1 F, the valve shaft 2 , the intake port 10 F, and the partition plate 13 constitute the intake port structure 100 F of the sixth embodiment.

The partition plate 13 is arranged downstream of the downstream end of the recess 11 F so that the partition plate 13 divides the intake passage into two passages. The partition plate 13 extends a predetermined distance substantially in parallel to the direction in which the intake port 1 OF extends, and extends from one side of the inner wall to the other side in the direction in which the valve shaft 2 extends. The position of the upstream end of the partition plate 13 and the length of the partition plate 13 are determined based on the flowing mode or manner of the gap flow F 2 . The partition plate 13 prevents the gap flow F 2 from reaching the main flow Fl. Therefore, when the airflow control valve Fl shown in FIG. 6B is fully closed, the gap flow F 2 is blocked by the partition plate 13 such that the gap flow F 2 does not flow towards the main flow Fl after flowing along the respective surfaces F, and this more reliably prevents the main flow Fl from being disturbed by the gap flow F 2 . As a result, tumble flows T can be stably produced, and therefore emissions from the internal combustion engine can be reduced. Note that the partition plates 14 shown in FIG. 6C may replace the partition plate 13 . That is, even when partition plates are provided partially in the direction in which the valve shaft 2 extends, that is, in correspondence with the gaps, it is possible to suppress the flow of the gap flow F 2 towards the main flow Fl.

Further, whether the partition plate 13 or the partition plates 14 are used may be determined based on the flowing mode or manner of the gap flow F 2 . Also, based on the flowing manner or mode of the gap flow F 2 , an appropriate number of partition plates each having desired length, thickness, and width, and formed into a specific shape, such as a curved shape, may be arranged at appropriate positions instead of the partition plates 13 , 14 . While the downstream inner surfaces B to F, which are flat surfaces, are formed in the foregoing embodiments including the sixth embodiment, various non-flat surfaces may alternatively be formed, provided that no step that causes adverse effect to the main flow F 1 is formed. Although it is preferable that the airflow control valves 1 B to 1 F be shaped such that each of them can be retracted into the inner wall of the intake port when fully opened, their shapes are not limited to this. Thus, the intake port structure 100 F of the sixth embodiment suppresses adverse effects that are caused to the main flow F 1 by the gap flow F 2 , which enables vortical flows to be stably produced and thus reduces emissions from the internal combustion engine.

While the invention has been described with reference to the example embodiment thereof, it is to be understood that the invention is not limited to the example embodiment and construction. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the example embodiment are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.