JP2012180811A - Combustion chamber structure of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion chamber structure of an internal combustion engine capable of strengthening a positive tumble flow while suppressing generation of knocking.SOLUTION: In the combustion chamber structure of an internal combustion engine having an intake side slope (41) and an exhaust side slope (42) at a part exposed to a combustion chamber of a cylinder head of the internal combustion engine (5) in which the positive tumble flow is formed in the combustion chamber (40) in an intake process, an intake opening (43) is formed in the intake side slope, an exhaust opening (44) is formed in the exhaust side slope, the exhaust opening is closed by an exhaust valve (60) in the intake process, a valve sheet (70) for an intake valve (50) is disposed in an intake passage, and an upper part of the inner peripheral surface of the valve sheet, positioned in an upper part from a central axis (71) of the valve sheet in the cross section formed by cutting the combustion chamber with the intake side slope and a surface orthogonal to the exhaust side slope, is positioned in a position coming in contact with an extended surface (100) formed by virtually extending the exhaust side slope in the valve sheet direction or in a position of an upper part of the extended surface.

Description

  The present invention relates to a combustion chamber structure of an internal combustion engine, and more particularly to a combustion chamber structure of an internal combustion engine in which a normal tumble flow is formed in the combustion chamber.

  2. Description of the Related Art Conventionally, an internal combustion engine is known in which a normal tumble flow is formed in a combustion chamber, which is guided from an intake opening side to an exhaust opening side and to a piston side (see, for example, Patent Document 1).

JP-A-8-144767

  From the viewpoint of improving the combustion efficiency, the strength of the positive tumble flow formed in the combustion chamber is preferably strong. As a technique for enhancing the normal tumble flow, for example, a technique for increasing the flow velocity of the intake air in the intake passage is conceivable. However, when the flow velocity of the intake air in the intake passage is increased, the intake air temperature may increase. As a result, knocking may occur.

  An object of the present invention is to provide a combustion chamber structure of an internal combustion engine that can reinforce a normal tumble flow while suppressing the occurrence of knocking.

  The combustion chamber structure of the internal combustion engine according to the present invention is such that the combustion chamber of the cylinder head of the internal combustion engine in which a normal tumble flow is formed in an intake stroke in a combustion chamber formed below the cylinder head having an intake passage and an exhaust passage. An intake side slope and an exhaust side slope that are inclined obliquely downward from the center side of the combustion chamber toward the inner peripheral surface side of the combustion chamber, and the intake side slope includes a portion of the intake passage. An intake opening that is an open end is formed, an exhaust opening that is an open end of the exhaust passage is formed on the exhaust-side slope, and the exhaust opening is closed by an exhaust valve in the intake stroke, A valve seat for an intake valve is disposed in the intake passage, and an inner peripheral surface of the valve seat in a cross section obtained by cutting the combustion chamber along a plane perpendicular to the intake side inclined surface and the exhaust side inclined surface Of the upper portion than the central axis of the valve seat is positioned the exhaust side inclined surface above the position or the extended surface contact with the extension surface which virtually is extended in the direction of the valve seat.

  According to the combustion chamber structure according to the present invention, in a cross section obtained by cutting the combustion chamber along a plane perpendicular to the intake side inclined surface and the exhaust side inclined surface, a portion of the inner peripheral surface of the valve seat above the central axis of the valve seat is: The exhaust side inclined surface is positioned in contact with or extending above the extended surface virtually extending in the direction of the valve seat. In the case of a combustion chamber structure that does not have this configuration (hereinafter referred to as a combustion chamber structure according to a comparative example), a portion of the intake air peels off after passing through the valve seat and is stagnated in the vicinity of the exhaust side slope. Do not tumble. On the other hand, according to the combustion chamber structure according to the present invention, by providing the above-described configuration, the intake air after passing through the valve seat is caused to flow along the exhaust-side inclined surface and the surface of the exhaust valve on the combustion chamber side, thereby causing a positive tumble. Can flow. Therefore, according to the combustion chamber structure according to the present invention, it is possible to increase the flow rate of the intake air that becomes a positive tumble flow as compared with the combustion chamber structure according to the comparative example without increasing the flow velocity of the intake air in the intake passage. Thereby, the strength of the normal tumble flow can be increased without increasing the flow velocity of the intake air in the intake passage. As a result, the strength of the positive tumble flow can be increased while suppressing the occurrence of knocking.

  The said structure WHEREIN: The edge part in the side of the said exhaust side slope of the said intake side slope may be located above the edge part in the side of the said intake side slope of the said exhaust side slope. According to this configuration, the valve seat is moved upward as compared with the case where the end of the intake side slope on the exhaust side slope side is not positioned above the end of the exhaust side slope on the intake side slope side. Can be easily arranged on the side. As a result, the portion of the inner peripheral surface of the valve seat that is above the central axis of the valve seat is located at a position where the exhaust side slope is in contact with the extended surface virtually extending in the direction of the valve seat or above the extended surface. Thus, the valve seat can be easily arranged in the intake passage. Thereby, it is possible to easily reinforce the positive tumble flow while suppressing the occurrence of knocking.

  In the above configuration, the valve seat is disposed upstream of the intake opening of the intake passage in the flow direction of intake air, so that a space is formed between the intake opening and the valve seat. It may be a configuration. If there is no space between the intake opening and the valve seat, when the normal tumble flow formed in the combustion chamber flows along the intake side slope, it flows into the valve seat and passes through the intake passage. There is a risk of reverse flow. This phenomenon may occur remarkably when the intake valve is closed late. When such a reverse flow phenomenon occurs, the normal tumble flow is attenuated. On the other hand, according to the above configuration, since a space is formed between the intake opening and the valve seat, when the normal tumble flow formed in the combustion chamber flows along the intake side slope, It is possible to suppress the flow into the valve seat and the backflow of the intake passage. As a result, the attenuation of the positive tumble flow can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the combustion chamber structure of the internal combustion engine which can strengthen normal tumble flow, suppressing generation | occurrence | production of knocking can be provided.

FIG. 1 is a cross-sectional view illustrating the internal combustion engine according to the first embodiment. FIG. 2A is an enlarged cross-sectional view of the combustion chamber according to the first embodiment. FIG. 2B is an enlarged cross-sectional view of the vicinity of the center of the upper portion of the combustion chamber according to the first embodiment. FIG. 3A is an enlarged cross-sectional view of the combustion chamber of the internal combustion engine according to the first comparative example. FIG. 3B is an enlarged cross-sectional view of the vicinity of the upper center of the combustion chamber according to Comparative Example 1. FIG. 4 is a cross-sectional view schematically showing the flow of intake air in the combustion chamber according to Comparative Example 1. FIG. 5 is a cross-sectional view schematically showing the flow mode of intake air in the combustion chamber according to the first embodiment. FIG. 6 is a cross-sectional view illustrating the internal combustion engine according to the second embodiment. FIG. 7A is a cross-sectional view schematically showing the flow of intake air in the combustion chamber of the internal combustion engine according to Comparative Example 1. FIG. 7B is a cross-sectional view schematically illustrating an intake air flow mode in the combustion chamber according to the second embodiment.

  Hereinafter, modes for carrying out the present invention will be described.

  The structure of the combustion chamber 40 of the internal combustion engine 5 according to the first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view showing an internal combustion engine 5 according to this embodiment. The internal combustion engine 5 includes a cylinder block 10, a cylinder head 20 disposed above the cylinder block 10, and a piston 30 disposed in the cylinder block 10. A combustion chamber 40 is formed as a space surrounded by the cylinder block 10, the cylinder head 20, and the piston 30. In the present embodiment, the upper and lower parts do not necessarily need to coincide with the upper and lower parts in the direction of gravity. For example, the upper and lower sides in the present embodiment may be in the horizontal direction.

  The cylinder head 20 has an intake passage 21 for guiding intake air to the combustion chamber 40 and an exhaust passage 22 for discharging exhaust gas from the combustion chamber 40. An intake valve 50 for opening and closing the intake passage 21 is disposed in the intake passage 21. An exhaust valve 60 for opening and closing the exhaust passage 22 is disposed in the exhaust passage 22. The intake valve 50 has an umbrella part 51 and a stem 52. The umbrella portion 51 is disposed at the tip of the stem 52 on the combustion chamber 40 side. The exhaust valve 60 has an umbrella part 61 and a stem 62. The umbrella portion 61 is disposed at the tip of the stem 62 on the combustion chamber 40 side.

  A valve seat 70 for the intake valve 50 is disposed in the intake passage 21. The valve seat 70 is a ring-shaped seat on which the umbrella portion 51 is seated or separated. In this embodiment, the central axis 71 of the valve seat 70 and the central axis of the umbrella portion 51 of the intake valve 50 coincide with each other. The intake passage 21 is closed when the umbrella portion 51 is seated on the valve seat 70. When the umbrella 51 is separated from the valve seat 80, the intake passage 21 is opened.

  A valve seat 80 for the exhaust valve 60 is disposed in the exhaust passage 22. The valve seat 80 is a ring-shaped seat for the umbrella portion 61 of the exhaust valve 60 to be seated or separated. In the present embodiment, the central axis 81 of the valve seat 80 and the central axis of the umbrella portion 61 of the exhaust valve 60 coincide with each other. The exhaust passage 22 is closed when the umbrella portion 61 is seated on the valve seat 80. When the umbrella portion 61 is separated from the valve seat 80, the exhaust passage 22 is opened.

  A positive tumble flow is formed in the combustion chamber 40 of the internal combustion engine 5 during the intake stroke. The configuration of the internal combustion engine 5 for forming a normal tumble flow in the combustion chamber 40 is not particularly limited. For example, the internal combustion engine 5 may have a structure including an airflow control valve that controls the flow direction of the intake air flowing into the combustion chamber 40 on the upstream side of the intake passage 21 in the flow direction of the intake air. The flow direction of the intake air is controlled by the air flow control valve so that the main flow of the intake air passes above the central axis 71 of the valve seat 70, thereby forming a positive tumble flow in the combustion chamber 40 in the intake stroke. Can do. That is, the internal combustion engine 5 according to the present embodiment is an internal combustion engine in which a normal tumble flow is formed in the combustion chamber 40 formed below the cylinder head 20 having the intake passage 21 and the exhaust passage 22 in the intake stroke.

  The internal combustion engine 5 according to the present embodiment has a structure in which the cylinder head 20 is insulated so that the amount of heat transferred in the cylinder head 20 is smaller than the amount of heat transferred in the cylinder block 10. The structure in which the cylinder head 20 is thermally insulated is not particularly limited, but as an example, the internal combustion engine 5 may have a structure in which the cylinder head 20 is thermally insulated from the combustion chamber 40. As this structure, for example, a structure in which a heat insulating member is arranged in a portion exposed to the combustion chamber 40 of the cylinder head 20 can be used. As the heat insulating member, for example, a member having a lower thermal conductivity than a metal that is a material constituting the cylinder head 20 can be used. In this case, heat conduction from the combustion chamber 40 to the cylinder head 20 can be suppressed by the heat insulating member. Thereby, the amount of heat transfer in the cylinder head 20 can be reduced relative to the amount of heat transfer in the cylinder block 10. As a result, the amount of cooling of the cylinder head 20 by the cooling medium (the amount of work of the cooling medium) can be kept low, so that the cooling loss in the cylinder head 20 can be kept low.

  Alternatively, the internal combustion engine 5 has a structure for insulating the cylinder head 20 from the cylinder block 10 in place of the above-described heat insulating structure from the combustion chamber 40 of the cylinder head 20 or together with the heat insulating structure from the combustion chamber 40 of the cylinder head 20. You may have. As this structure, for example, a structure in which a heat insulating member is disposed at the interface of the cylinder head 20 on the cylinder block 10 side can be used. In this case, the heat transfer from the cylinder block 10 to the cylinder head 20 is suppressed, so that the heat transfer amount in the cylinder head 20 can be reduced relative to the heat transfer amount in the cylinder block 10. Even in this case, the cooling loss in the cylinder head 20 can be reduced.

  Alternatively, the internal combustion engine 5 has a cooling capacity of the cooling medium that cools the cylinder head 20 in place of the structure that uses the heat insulating member or together with the structure that uses the heat insulating member. It is also possible to provide a structure for reducing the size. As an example of such a structure, for example, the internal combustion engine 5 includes a first cooling medium circulation passage in which a cooling medium circulates between the cooling medium pump and the cylinder head 20, and a cooling medium that is a cooling medium pump and a cylinder block. And a second cooling medium circulation passage that circulates between the first cooling medium circulation passage and a flow rate adjusting valve in the first cooling medium circulation passage. In this case, the flow rate adjustment valve makes the flow rate of the first cooling medium circulation path smaller than the flow rate of the second cooling medium circulation path, so that the amount of heat transfer between the cooling medium and the cylinder head 20 is reduced. Less than the amount of heat transferred between the cylinder block 10 and the cylinder block 10. That is, the heat insulation between the cylinder head 20 and the cooling medium is higher than the heat insulation between the cylinder block 10 and the cooling medium. Even in this configuration, the cooling loss in the cylinder head 20 can be suppressed.

  When the internal combustion engine 5 has a structure in which the cylinder head 20 is insulated as described above, the fuel consumption of the internal combustion engine 5 can be improved by reducing the cooling loss in the cylinder head 20. Further, the occurrence of knocking can be suppressed by cooling the cylinder block 10 with the cooling medium. Furthermore, the cooling capacity of the cylinder block 10 by the cooling medium can be enhanced by the amount of cooling loss in the cylinder head 20 reduced. In this case, the occurrence of knocking can be further suppressed.

  FIG. 2A is an enlarged cross-sectional view of the combustion chamber 40 according to the present embodiment. In addition, illustration of the intake valve 50 is abbreviate | omitted in Fig.2 (a). The cylinder head 20 has an intake-side inclined surface 41 and an exhaust-side inclined surface 42 inclined obliquely downward from the center side of the combustion chamber 40 toward the inner peripheral surface side of the combustion chamber 40 at a portion exposed to the combustion chamber 40 of the cylinder head 20. have. In FIG. 2A, the surface direction (direction parallel to the surface) of the intake side inclined surface 41 and the exhaust side inclined surface 42 is a direction perpendicular to the paper surface. That is, FIG. 2A illustrates a cross section of the combustion chamber 40 cut along a plane perpendicular to the intake side inclined surface 41 and the exhaust side inclined surface 42.

  An intake opening 43, which is the opening end of the intake passage 21, is formed on the intake side inclined surface 41. An exhaust opening 44 that is an opening end of the exhaust passage 22 is formed in the exhaust-side slope 42. In the present embodiment, the valve seat 70 is disposed at the end of the intake passage 21 on the downstream side in the flow direction of the intake air. The valve seat 80 is disposed at the end of the exhaust passage 22 on the upstream side in the exhaust flow direction.

  The exhaust opening 44 is closed by the exhaust valve 60 in the intake stroke. Specifically, the exhaust opening 44 is closed when the umbrella portion 61 of the exhaust valve 60 is seated on the valve seat 80 in the intake stroke. On the other hand, the intake valve 50 opens the intake opening 43 in the intake stroke.

  In a cross section obtained by cutting the combustion chamber 40 along a plane perpendicular to the intake side inclined surface 41 and the exhaust side inclined surface 42 (that is, a cross sectional view of FIG. 2A), the inner peripheral surface of the valve seat 70 (the surface facing the central axis 71). The portion above the central axis 71 is located at a position in contact with the extended surface 100 which is a virtual surface obtained by virtually extending the exhaust-side inclined surface 42 in the direction of the valve seat 70 or above the extended surface 100. . In FIG. 2A, the portion of the inner peripheral surface of the valve seat 70 above the central axis 71 is in contact with the extended surface 100.

  FIG. 2B is an enlarged cross-sectional view of the vicinity of the center of the upper portion of the combustion chamber 40. In FIG. 2B, illustration of the exhaust valve 60 and the intake valve 50 is omitted. The end 45 on the exhaust side slope 42 side of the intake side slope 41 is positioned above the end 46 on the intake side slope 41 side of the exhaust side slope 42. In the present embodiment, the end portion 45 is also the end portion located at the uppermost position among the end portions of the intake side inclined surface 41. The end portion 46 is also the end portion located at the uppermost position among the end portions of the exhaust-side slope 42.

  Since the end 45 and the end 46 of the combustion chamber 40 have such a configuration, the valve seat 70 is disposed on the upper side as compared with the case where the end 45 is not positioned above the end 46. Can be easily done. Accordingly, the valve seat 70 is disposed in the intake passage 21 such that a portion of the inner peripheral surface of the valve seat 70 above the central axis 71 is in contact with the extended surface 100 or above the extended surface 100. Can be easily done.

  Next, the effect of the structure of the combustion chamber 40 according to the present embodiment will be described while comparing with the structure of the combustion chamber 210 of the internal combustion engine 200 according to the comparative example 1. FIG. 3A is an enlarged cross-sectional view of the combustion chamber 210 of the internal combustion engine 200 according to the first comparative example. In FIG. 3A, the illustration of the intake valve 50 is omitted. FIG. 3B is an enlarged cross-sectional view of the vicinity of the center of the upper portion of the combustion chamber 210 according to the first comparative example. In FIG. 3B, the exhaust valve 60 and the intake valve 50 are not shown.

  In the combustion chamber 210 according to the comparative example 1, the end 45 on the exhaust side slope 42 side of the intake side slope 41 and the end 46 on the intake side slope 41 side of the exhaust side slope 42 are located at the same height. Is different from the combustion chamber 40 according to the present embodiment. As a result, the combustion chamber 210 is above the central axis 71 of the valve seat 70 in the inner peripheral surface of the valve seat 70 in a cross section obtained by cutting the combustion chamber 210 along a plane perpendicular to the intake side inclined surface 41 and the exhaust side inclined surface 42. The portion is not in contact with the extension surface 100 or positioned above the extension surface 100. Specifically, the portion of the inner peripheral surface of the valve seat 70 above the central axis 71 is positioned below the extended surface 100 (FIG. 3B).

  FIG. 4 is a cross-sectional view schematically showing the flow mode of intake air in the combustion chamber 210 according to Comparative Example 1. In FIG. 4, the intake air is shown by arrows. In the combustion chamber 210, a portion of the intake air flowing into the combustion chamber 210 from the intake passage 21 is separated from the main flow of the intake air after passing through the valve seat 70 and stagnates near the exhaust side slope 42. This stagnant intake does not become a positive tumble flow. If the flow velocity of the intake air in the intake passage 21 is increased in order to increase the strength of the normal tumble flow in order to improve the combustion efficiency in the combustion chamber 210, the temperature of the intake air may increase. Specifically, the strength of the positive tumble flow can be increased by increasing the flow rate of the intake air in the intake passage 21 by a method such as reducing the diameter of the intake passage 21. In this case, the intake air in the intake passage 21 is supplied to the cylinder head 20. As a result of an increase in the amount of heat received from the intake air, the temperature of the intake air may increase. If the intake air temperature rises, knocking may occur.

  FIG. 5 is a cross-sectional view schematically showing the flow of intake air in the combustion chamber 40 according to the present embodiment. In FIG. 5, the intake air is indicated by arrows. In the combustion chamber 40, as described above, a portion of the inner peripheral surface of the valve seat 70 above the central axis 71 in the cross section obtained by cutting the combustion chamber 40 along a plane perpendicular to the intake side inclined surface 41 and the exhaust side inclined surface 42. Is disposed at a position in contact with the extended surface 100. As a result, part of the intake air that has passed through the valve seat 70 is prevented from being peeled off and stagnating in the vicinity of the exhaust-side slope 42.

  Specifically, the intake air after passing through the valve seat 70 is directed to the exhaust side inclined surface 42 and the surface on the combustion chamber 40 side of the umbrella portion 61 of the exhaust valve 60 (hereinafter referred to as the surface of the exhaust valve 60 on the combustion chamber 40 side). It flows in line and becomes a positive tumble flow. As a result, according to the structure of the combustion chamber 40, it is possible to increase the flow rate of the intake air that becomes a positive tumble flow as compared with the first comparative example without increasing the flow velocity of the intake air in the intake passage 21. That is, according to the structure of the combustion chamber 40 according to the present embodiment, the strength of the positive tumble flow can be increased without increasing the flow velocity of the intake air in the intake passage 21. As a result, the strength of the positive tumble flow can be increased while suppressing the occurrence of knocking.

  Note that, in a cross section obtained by cutting the combustion chamber 40 along a plane perpendicular to the intake side inclined surface 41 and the exhaust side inclined surface 42, a portion of the inner peripheral surface of the valve seat 70 above the central axis 71 is located above the extended surface 100. Even when it is positioned, the intake air after passing through the valve seat 70 can be made to flow along the exhaust side inclined surface 42 and the surface of the exhaust valve 60 on the combustion chamber 40 side to be a positive tumble flow. As a result, the strength of the positive tumble flow can be increased while suppressing the occurrence of knocking.

  Further, according to the structure of the combustion chamber 40 according to the present embodiment, the end portion 45 of the intake side inclined surface 41 is positioned above the end portion 46 of the exhaust side inclined surface 42 as described above with reference to FIG. ing. Thereby, compared with the case where the end part 45 is not located above the end part 46, the valve seat 70 can be easily arranged on the upper side. As a result, the valve seat 70 is disposed in the intake passage 21 such that a portion of the inner peripheral surface of the valve seat 70 above the central axis 71 is in contact with the extension surface 100 or above the extension surface 100. Can be easily done. Thereby, it is possible to easily reinforce the positive tumble flow while suppressing the occurrence of knocking.

  Then, the structure of the combustion chamber 40a of the internal combustion engine 5a which concerns on Example 2 of this invention is demonstrated. FIG. 6 is a cross-sectional view showing the internal combustion engine 5a according to the present embodiment. In FIG. 6, the illustration of the intake valve 50 is omitted. The combustion chamber 40a includes an intake side inclined surface 41a and an exhaust side inclined surface 42a. The end 45 of the intake side slope 41a and the end 46 of the exhaust side slope 42b are located at the same height. Further, since the valve seat 70 is disposed upstream of the intake opening 43 of the intake passage 21 in the flow direction of the intake air, a space 47 is formed between the intake opening 43 and the valve seat 70. Since the other structure in the combustion chamber 40a of the internal combustion engine 5a is the same as that in the combustion chamber 40 of the internal combustion engine 5 according to the first embodiment, the description thereof is omitted.

  Also in the present embodiment, in the cross section obtained by cutting the combustion chamber 40a along a plane perpendicular to the intake side inclined surface 41a and the exhaust side inclined surface 42a, the portion of the inner peripheral surface of the valve seat 70 above the central axis 71 is the exhaust side inclined surface. It arrange | positions in the position which contacts 42a of the extended surface 100 extended virtually in the direction of the valve seat 70a. In the cross section obtained by cutting the combustion chamber 40a along a plane perpendicular to the intake side inclined surface 41a and the exhaust side inclined surface 42a, a portion of the inner peripheral surface of the valve seat 70 above the central axis 71 is positioned above the extended surface 100. You may do it. Since the combustion chamber 40a has such a configuration, the normal tumble flow can be strengthened while suppressing the occurrence of knocking as in the combustion chamber 40 according to the first embodiment.

  Furthermore, according to the structure of the combustion chamber 40a, the effect demonstrated below can be exhibited. FIG. 7A is a cross-sectional view schematically showing an intake air flow mode in the combustion chamber 210 of the internal combustion engine 200 according to the comparative example 1. FIG. FIG.7 (b) is sectional drawing which shows typically the flow aspect of the intake air in the combustion chamber 40a which concerns on a present Example. In FIG. 7A and FIG. 7B, the intake air is indicated by arrows.

  In the combustion chamber 210 according to the comparative example 1, the valve seat 70 is not disposed on the upstream side of the intake opening 43 in the intake passage 21 in the flow direction of the intake air, so that there is a space between the intake opening 43 and the valve seat 70. Is not formed. In such a structure of the combustion chamber 210, when the normal tumble flow formed in the combustion chamber 210 flows along the intake side inclined surface 41, a phenomenon occurs in which it flows into the valve seat 70 and flows backward through the intake passage 21. There is a fear. This phenomenon may occur remarkably when the intake valve 50 is closed late. When such a reverse flow phenomenon occurs, the normal tumble flow is attenuated.

  On the other hand, according to the structure of the combustion chamber 40a according to the present embodiment, as shown in FIG. 7B, the space 47 is formed, so that the normal tumble flow formed in the combustion chamber 40a is taken into the intake air. The flow into the valve seat 70 when flowing along the side inclined surface 41a is prevented from flowing back through the intake passage 21. As a result, the attenuation of the positive tumble flow is suppressed as compared with Comparative Example 1. Since the attenuation of the positive tumble flow is suppressed, the strength of the positive tumble flow is further increased. As a result, the strength of the positive tumble flow can be further increased without increasing the flow velocity of the intake air in the intake passage 21, so that the strength of the positive tumble flow can be further increased while suppressing the occurrence of knocking.

  In the present embodiment, the end portion 45 of the intake side inclined surface 41a and the end portion 46 of the exhaust side inclined surface 42b are located at the same height, but the present invention is not limited to this. The end portion 45 of the intake side inclined surface 41a may be located above the end portion 46 of the exhaust side inclined surface 42b. Even in this case, if the space 47 is formed, the operational effects of the present embodiment can be exhibited.

  In the first and second embodiments, the internal combustion engine 5 has a structure in which the cylinder head 20 is thermally insulated. However, the present invention is not limited to this. The structure of the combustion chamber according to the first and second embodiments can be applied to an internal combustion engine in which the cylinder head 20 does not have a heat insulating structure.

  However, when the internal combustion engine 5 has a structure in which the cylinder head 20 is insulated, knocking is likely to occur when the internal combustion engine 5 does not have the combustion chamber structure according to the first and second embodiments. Specifically, in the case of such an internal combustion engine, the temperature of the cylinder head 20 is likely to rise because the cylinder head 20 is thermally insulated. As a result, when the flow velocity of the intake air in the intake passage 21 is increased, the temperature of the intake air is likely to increase, and knocking is likely to occur. Therefore, the structure of the combustion chamber according to the first embodiment and the second embodiment is applied to the internal combustion engine 5 in which the cylinder head 20 is insulated, so that the normal tumble flow is not increased without increasing the intake air flow velocity in the intake passage 21. The effect of increasing the strength can be exhibited more effectively.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 5 Internal combustion engine 10 Cylinder block 20 Cylinder head 21 Intake passage 22 Exhaust passage 40 Combustion chamber 41 Intake side slope 42 Exhaust side slope 43 Intake opening 44 Exhaust opening 45 End 46 End 47 Space 50 Intake valve 60 Exhaust valve 70 Valve Seat 71 Center axis 80 Valve seat 100 Extension surface

Claims (3)

In the combustion chamber formed below the cylinder head having the intake passage and the exhaust passage, a positive tumble flow is formed in the intake stroke in the portion exposed to the combustion chamber of the cylinder head of the internal combustion engine. From the intake side slope and the exhaust side slope inclined obliquely downward toward the inner peripheral surface side of the combustion chamber,
An intake opening that is an opening end of the intake passage is formed on the intake side slope, and an exhaust opening that is an opening end of the exhaust passage is formed on the exhaust side slope, and the exhaust opening is the intake stroke. Closed by an exhaust valve,
A valve seat for an intake valve is arranged in the intake passage,
In a cross section obtained by cutting the combustion chamber along a plane perpendicular to the intake-side inclined surface and the exhaust-side inclined surface, a portion of the inner peripheral surface of the valve seat above the central axis of the valve seat defines the exhaust-side inclined surface as the A combustion chamber structure of an internal combustion engine located at a position in contact with an extended surface virtually extended in the direction of the valve seat or above the extended surface.   2. The combustion chamber of the internal combustion engine according to claim 1, wherein an end portion of the intake-side inclined surface on the exhaust-side inclined surface side is located above an end portion of the exhaust-side inclined surface on the intake-side inclined surface side. Construction.   2. The space is formed between the intake opening and the valve seat by disposing the valve seat upstream of the intake opening of the intake passage in the flow direction of intake air. The combustion chamber structure of the internal combustion engine according to 2.

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