JP6268604B2 - Intake structure of internal combustion engine - Google Patents

Description

  According to the present invention, a throttle valve capable of adjusting the intake air amount is interposed in an intake passage that communicates with an intake port of the cylinder head with a passage formed in an intake duct connected to a cylinder head of an engine body as a component. A part of the intake passage downstream of the throttle valve and a part of the intake port are opened and closed by a reed valve attached to a reed valve stay, and bypass the reed valve The present invention relates to an intake structure of an internal combustion engine that is partitioned into a sub-intake passage that is formed and the reed valve stay is formed separately from the intake duct and attached to the intake duct.

  For the purpose of generating a tumble flow in the combustion chamber, a main intake passage in which a part of the intake passage leading to the intake port on the downstream side of the throttle valve and a part of the intake port are opened and closed by the valve, An intake structure for an internal combustion engine that is partitioned into a sub-intake passage that bypasses the reed valve is known from Patent Document 1.

JP-A-7-293255 JP 2007-64146 A

  Patent Document 1 and Patent Document 2 disclose a structure in which various parts are combined to divide the intake passage into a main intake passage and a sub intake passage. By the way, the state of occurrence of the tumble flow in the combustion chamber depends on the configuration of the auxiliary intake passage. In order to generate the tumble flow more efficiently, the configuration of the auxiliary intake passage is simplified while the auxiliary intake passage is being used. Therefore, it is required to keep the flow path resistance at a low level.

  An object of the present invention is to provide an intake structure for an internal combustion engine that can suppress the flow resistance in the auxiliary intake passage for generating the tumble flow to a low level and can simplify the configuration to reduce the cost. .

In order to achieve the above object, the present invention provides an intake air amount in an intake passage that communicates with an intake port of the cylinder head, with a passage formed in an intake duct connected to a cylinder head of an engine body as a component. adjustable throttle valve is interposed, of the intake passage, and a part of the downstream side of the throttle valve, a portion of the intake port, the main which is opened and closed by the reed valve attached to the reed valve Stay In the intake structure of an internal combustion engine, the reed valve is divided into an intake passage and a sub-intake passage that bypasses the reed valve, and the reed valve stay is formed separately from the intake duct and attached to the intake duct. The stay, the intake duct, and the cylinder head are individually formed with individual passages extending in a straight line with a circular cross-sectional shape. Said mutual communicated to another passage auxiliary intake passage is formed, a plurality of said reed valve capable of performing commutation of the intake toward the auxiliary intake passage, wherein the radially outer side of the upstream-side open end of auxiliary air intake passage The first feature is that the reed valve stays are arranged in a circumferential direction .

Further, according to the present invention, a throttle valve capable of adjusting the intake air amount is interposed in an intake passage that communicates with an intake port of the cylinder head with a passage formed in an intake duct connected to the cylinder head of the engine body as a component. A main intake passage that is opened and closed by a reed valve attached to a reed valve stay, and a part of the intake passage that is downstream of the throttle valve and a part of the intake port; and the reed valve In the intake structure of the internal combustion engine, the reed valve stay is formed separately from the intake duct and is attached to the intake duct. Individual passages that extend in a straight line with a circular cross-sectional shape are formed individually in the cylinder head, and these individual passages communicate with each other. The auxiliary air intake passage is constituted Te,
The reed valve stay is arranged at a position corresponding to the top of the virtual quadrangular pyramid by forming three triangular frames corresponding to the three side surfaces of the virtual quadrangular pyramid and the individual passage of the reed valve stay. It has a quadrangular pyramid-shaped frame body integrally provided with the cylindrical portion, and a reed valve is attached to each of the three frame portions .

According to the present invention, in addition to the configuration of the second feature, the plurality of reed valves are attached to the reed valve stay so as to be aligned in the circumferential direction on the radially outer side of the upstream opening end of the auxiliary intake passage. Is the third feature.

In the present invention, in addition to the configuration of the second or third feature, the cylindrical portion is provided at a lower portion of the frame body, the reed valve is attached to an outer surface of the frame portion, and the top of the virtual quadrangular pyramid is provided. guide portion connecting the top three of said frame portion at corresponding positions is formed on the frame upstream of the surface so as to Ren'nara the top of the upstream open end of the cylindrical portion of the guide portion This is the fourth feature.

  In addition to any of the configurations of the first to fourth features, the present invention provides the cylinder head, which is integrally cast with a protruding portion that protrudes inward from the inner periphery of the intake port, A fifth feature is that the individual passage of the head is formed by perforating the raised portion.

  According to the present invention, in addition to any one of the first to fifth features, the intake duct is oblique to the cylinder axis of the engine body on a projection view on a virtual plane orthogonal to the axis of the crankshaft. The intake port connected to the cylinder head so as to extend in an intersecting direction and connected to the intake valve opening that opens to the combustion chamber is curved from the outer end opening connecting the intake duct to the intake valve opening. It is a sixth feature that it is formed.

  According to the present invention, in addition to any one of the first to sixth features, the cylinder head is configured such that a throttle body having a throttle valve is connected to an upstream side of the intake duct so that the intake port is connected. A seventh feature is that a fuel injection valve for injecting fuel toward an intake valve port provided on the throttle valve is attached to any one of the throttle body, the intake duct, and the cylinder head on the downstream side of the throttle valve. And

  Furthermore, in addition to any of the configurations of the first to sixth features, the present invention is characterized in that a carburetor forming a part of the intake passage is connected to the intake duct.

  According to the first aspect of the present invention, the reed valve stay, the intake duct and the cylinder head are individually formed with individual passages extending in a straight line with a circular cross-sectional shape, and these individual passages communicate with each other. Since the auxiliary intake passage is configured, the flow resistance in the auxiliary intake passage is suppressed while securing the intake pipe length of the auxiliary intake passage, thereby increasing the directivity of intake air toward the auxiliary intake passage and rectifying. This facilitates the generation of a tumble flow in the combustion chamber, and simplifies the configuration to reduce the cost.

Also, since multiple reed valve are arranged in the circumferential direction in the radially outer side of the upstream-side open end of the auxiliary air intake passage, rectifying the air toward the auxiliary air intake passage by a plurality of reed valve is resistance Thus, a tumble flow can be effectively generated in the combustion chamber.

According to the second feature of the present invention, three triangular frame portions corresponding to the three side surfaces of the virtual quadrangular pyramid and a cylindrical portion disposed at a position corresponding to the top of the virtual quadrangular pyramid are provided integrally. A quadrangular pyramid-shaped frame has a reed valve stay, and the reed valve attached to the three frame portions acts as a resistance to direct the intake air toward the individual passage side in the cylinder portion, that is, the auxiliary intake passage side. Therefore, rectification can be promoted and a tumble flow can be effectively generated in the combustion chamber.

According to the third feature of the present invention, the plurality of reed valves are arranged in the circumferential direction on the radially outer side of the upstream opening end of the auxiliary intake passage. As a result, the rectification of the intake air is promoted toward the engine, and a tumble flow can be effectively generated in the combustion chamber.

According to the fourth aspect of the present invention, since the upstream surface of the guide portion connecting the top portions of the three frame portions is connected to the upper portion of the upstream opening end of the portion, the intake passage is located upstream of the reed valve stay. When fuel is supplied into the fuel, the fuel adhering to each reed valve can be guided to the auxiliary intake passage side.

  According to the fifth aspect of the present invention, the individual passages of the cylinder head are formed by perforating a raised portion that is integrally formed during casting of the cylinder head so as to rise inward from the inner periphery of the intake port. Therefore, it is easy to form the individual passages in the cylinder head, and it is possible to contribute to manufacturing cost reduction.

  According to the sixth aspect of the present invention, even if the intake port is curved from its outer end opening to the intake valve port, the individual passages that constitute part of the auxiliary intake passage and are provided in the cylinder head are By forming the cross section in a straight line so as to be circular, the flow resistance can be suppressed, and the generation of a tumble flow in the combustion chamber can be promoted.

  According to the seventh feature of the present invention, the present invention can be applied to a fuel injection type internal combustion engine to promote the generation of a tumble flow in the combustion chamber and contribute to the improvement of the combustibility of the internal combustion engine.

  Furthermore, according to the eighth feature of the present invention, the present invention can be applied to a carburetor type internal combustion engine to promote the generation of a tumble flow in the combustion chamber and contribute to the improvement of the combustibility of the internal combustion engine.

1 is a right side view of a motorcycle according to a first embodiment. It is a principal part vertical side view of an internal combustion engine. FIG. 3 is an enlarged view of a portion indicated by an arrow 3 in FIG. 2. It is the perspective view which looked at the reed valve stay from the throttle body side. It is the perspective view which looked at the reed valve stay from the opposite side to the throttle body. It is a perspective view of the cylinder head near an intake port. It is a principal part vertical side view of the internal combustion engine of a low load driving | running state. It is a principal part vertical side view of the internal combustion engine of a high load driving | running state. It is a principal part vertical side view of the internal combustion engine of 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, front and rear, left and right, and top and bottom refer to directions as viewed from the occupant riding the motorcycle.

  A first embodiment of the present invention will be described with reference to FIGS. 1 to 8. First, in FIG. 1, a body frame F of a motorcycle, which is a saddle-ride type vehicle, is a front fork 11 that pivotally supports a front wheel WF. A head pipe 12 that can be steered, a single main frame 13 that is inclined rearwardly downward from the head pipe 12, a pivot plate 14 provided at a rear end of the main frame 13, and the main frame 13 A pair of left and right seat rails 15 that are joined to the middle portion of the main frame 13 and the rear end of the main frame 13 are joined to the head pipe 12 below the connecting portion to the head pipe 12. A single down frame 16 extending downward and a sub-pipe connecting the middle portion of the main frame 13 and the down frame 16 7, and a said pivot plate 14 and the both seat rails pair of right and left connecting the 15 reinforcing frame 18, and the backbone format.

The main frame 13 is integrally formed with a main frame front portion 13a that gently slopes downward from the head pipe 12 and a main frame rear portion 13b that sharply slopes backward from the rear end of the main frame front portion 13a. The pivot plate 14 is provided at a rear end portion, that is, a lower end portion of the main frame rear portion 13b, and a front end of the seat rail 15 is provided at a connecting portion of the main frame front portion 13a and the main frame rear portion 13b. The sub-pipe 17 is joined and provided between an intermediate portion of the main frame front portion 13 a and the down frame 16 .

  Referring also to FIG. 2, an engine main body 21 of an internal combustion engine E that is a single cylinder includes a crankcase 23 that supports a crankshaft 22 that has an axis lined in the width direction of the motorcycle, a cylinder body 24, a cylinder head 25, and The head cover 26 is combined. The engine body 21 is mounted on the vehicle body frame F so as to be disposed below the main frame 13 and in a space surrounded by the main frame 13, the pivot plate 14, and the down frame 16. In the mounted state, the cylinder axis C of the engine body 21 is inclined upward.

  A transmission 27 for shifting the rotational power of the crankshaft 22 is accommodated in the crankcase 23, and one end portion of the output shaft 28 of the transmission 27 is located behind the crankshaft 22 at the crankcase 23. Projecting outwards. Moreover, an endless chain 31 is wound around a driving sprocket 29 fixed to the protruding end of the output shaft 28 and a driven sprocket 30 provided on the rear wheel WR.

  The rear wheel WR is rotatably supported at the rear end portion of the swing arm 32, and the front end portion of the swing arm 32 is arranged around the axis of the connecting shaft 33 that connects the reinforcing frame 18 to the pivot plate 14. The pivot plate 14 is supported so as to be able to swing. A rear cushion unit 34 is provided between a portion where the reinforcing frame 18 is connected to the seat rail 15 and a rear portion of the swing arm 32.

  The cylinder head 25 is provided with an exhaust port 35 that opens to the front side wall thereof. An exhaust pipe 36 that passes through the upstream end of the exhaust port 35 is connected to the front side wall of the cylinder head 25. Is extended from the front of the engine body 21 to the lower side of the crankcase 23 and extended rearward, and the downstream end of the exhaust pipe 36 is connected to an exhaust muffler 37 disposed on the right side of the rear wheel WR.

The cylinder head 25 is provided with an intake port 38 that opens to the side wall thereof. An upstream end of an intake duct 39 that communicates with the intake port 38 is connected to the rear side wall of the cylinder head 25 and is rearward of the cylinder head 25. It is extended to. An air cleaner 40 is fixedly disposed behind the cylinder head 25, and a throttle body 42 is interposed between the connecting tube 41 whose upstream end is connected to the air cleaner 40 and the intake duct 39. .

  In the air cleaner 40, the connecting tube 41, the throttle body 42, and the intake duct 39, an intake air that communicates with the intake port 38 of the cylinder head 25 with a passage 45 formed in the intake duct 39 as a component. A passage 46 is formed, and the throttle body 42 is provided with a throttle valve 43 provided in the intake passage 46 so as to be able to adjust the intake air amount.

  A main intake passage 47 in which a part of the intake passage 46 on the downstream side of the throttle valve 43 and a part of the intake port 38 are opened and closed by a reed valve 50 attached to a reed valve stay 49; The reed valve stay 49 is divided into a sub intake passage 48 that bypasses the reed valve, and the reed valve stay 49 is formed separately from the intake duct 39 and attached to the intake duct 39.

An intake valve provided in the cylinder head 25 so as to connect the intake port 38 to any one of the throttle body 42, the intake duct 39 and the cylinder head 25 on the downstream side of the throttle valve 43. A fuel injection valve 52 for injecting fuel toward the port 51 is attached. In this embodiment, the fuel injection valve 52 is attached to the downstream end of the intake duct 39. A fuel tank 53 for supplying fuel to the fuel injection valve 52 is provided on the main frame 13 of the vehicle body frame F so as to cover the engine body 21 from above.

  3 to 5, the reed valve stay 49, the intake duct 39, and the cylinder head 25 are individually provided with individual passages 54, 55, 56 that have a circular cross section and extend linearly. The auxiliary intake passages 48 are formed by communicating the individual passages 54 to 56 with each other.

The reed valve stay 49 includes a quadrangular pyramid-shaped frame 57 that is inserted into the upstream half of the intake duct 39, a flange 39a that is integrally provided at the upstream end of the intake duct 39, and the throttle. A flange 58 projecting from the frame body 57 so as to be sandwiched between flange portions 59a provided integrally with a connecting cylinder 59 attached to the downstream end of the body 42; 39a, 59a and the flange 58 sandwiched between the flange portions 39a, 59a are fastened by a plurality of bolts 60 screwed into the flange portion 39a, whereby the reed valve stay 49 is connected to the intake duct 39. Mounted on.

  The frame 57 forms three triangular frame portions 57a, 57b, 57c corresponding to the three side surfaces of the virtual quadrangular pyramid, and the individual passage 54 of the reed valve stay 49 to form the top of the virtual quadrangular pyramid. And a cylindrical portion 57d arranged at a position corresponding to each of the three cylindrical portions 57d are formed in a quadrangular pyramid shape, and the triangular openings 61 formed by the three frame portions 57a to 57c are individually formed. The reed valve 50 that opens and closes is attached to the outer surfaces of the frame portions 57a to 57c by the two screw members 62 while contacting and closing the outer surfaces of the frame portions 57a to 57c.

  The frame body 57 is integrally provided with a cylindrical portion 57d that forms the individual passage 54 of the reed valve stay 49 and is disposed at a position corresponding to the top of the virtual quadrangular pyramid. The reed valve stay 49 is disposed in the lower portion of the frame body 57 in a state where the reed valve stay 49 is attached to the intake duct 39, and the individual passage 54 in the cylindrical portion 57 d communicates with the individual passage 55 of the intake duct 39.

  Due to the arrangement of the three frame portions 57a to 57c and the cylindrical portion 57d in the frame body 57, the three reed valves 50 are arranged at the upstream opening end of the cylindrical portion 57d, that is, the upstream opening of the auxiliary intake passage 48. The reed valve stays 49 are attached to the lead valve stays 49 so as to be arranged in the circumferential direction on the radially outer side of the ends.

The surface of the upstream side of the guide portion 57e which connects the top of three of the frame portion 57a~57c at a position corresponding to an apex of the virtual quadrangular pyramid as a reference for configuring the frame body 57, the guide portion 57 e Is formed in the frame body 57 so as to be connected to the upper part of the upstream opening end of the cylindrical portion 57d.

  Referring also to FIG. 6, the cylinder head 25 is formed by casting, and at the time of casting, the cylinder head 25 integrally has a raised portion 25 a that protrudes inward from the inner periphery of the intake port 38. The individual passage 56 of the cylinder head 25 is formed by drilling the raised portion 25a.

Paying attention to FIG. 2, the intake duct 39 is obliquely formed at an angle α with respect to the cylinder axis C of the engine body 21 on a projection view (FIG. 2) onto a virtual plane orthogonal to the axis of the crankshaft 22. The intake port 38 is connected to the cylinder head 25 so as to extend in a direction intersecting with the intake port 39, and an outer end opening for connecting the intake duct 39 and a piston slidably fitted to the cylinder body 24. 63, facing the top of 63 and facing the combustion chamber 64 formed between the cylinder body 24 and the cylinder head 25 so as to open and bend between the intake valve port 51 provided in the cylinder head 25. Formed.

In such an intake structure, in a low load operation state of the internal combustion engine E, the reed valve 50 is in a closed state as shown in FIG. 7, and the air whose flow rate is adjusted by the throttle valve 43 passes through the auxiliary intake passage 48. The gas flows into the combustion chamber 64 from the intake valve port 51, and a tumble flow is generated in the combustion chamber 64. In the high load operation state of the internal combustion engine E, as shown in FIG. 8, the reed valve 50 is opened, and the air whose flow rate is adjusted by the throttle valve 43 flows through the main intake passage 47 from the intake valve port 51. While being introduced into the combustion chamber 64, it flows into the combustion chamber 64 from the intake valve port 51 through the auxiliary intake passage 48.

  Next, the operation of this embodiment will be described. Part of the intake passage 46 on the downstream side of the throttle valve 43 and part of the intake port 38 are opened and closed by the reed valve 50 attached to the reed valve stay 49. The main intake passage 47 and the auxiliary intake passage 48 that bypass the reed valve 50 are partitioned, and the reed valve stay 49 is formed separately from the intake duct 39 and attached to the intake duct 39. The reed valve stay 49, the intake duct 39, and the cylinder head 25 are individually formed with individual passages 54, 55, and 56 having a circular cross-sectional shape and extending linearly, and these individual passages 54 to 56 are mutually connected. Since the auxiliary intake passage 48 is configured to be communicated, the flow resistance in the auxiliary intake passage 48 is suppressed while securing the intake pipe length of the auxiliary intake passage 48. As a result, the directivity of the intake air is increased toward the auxiliary intake passage 48 to promote rectification, and the tumble flow in the combustion chamber 64 can be effectively generated, and the configuration is simplified to reduce the cost. Can be achieved.

  Further, a plurality of, for example, three reed valves 50 are attached to the reed valve stay 49 so as to be arranged in the circumferential direction outside the upstream opening end of the auxiliary intake passage 48 in the circumferential direction. As a result, the rectification of the intake air toward the auxiliary intake passage 48 is promoted, and a tumble flow can be effectively generated in the combustion chamber 64.

  The reed valve stay 49 forms three triangular frame portions 57a, 57b, 57c corresponding to the three side surfaces of the virtual quadrangular pyramid and the individual passage 54 of the reed valve stay 49, thereby Since the cylinder portion 57d disposed at a position corresponding to the top portion has a quadrangular pyramid-like frame body 57 and the reed valve 50 is attached to each of the three frame portions 57a to 57c, the three frames The reed valve 50 attached to the portions 57a to 57c acts as a resistor, and the directivity of intake air can be increased to the individual passage 54 side, that is, the auxiliary intake passage 48 side in the cylinder portion 57d to promote rectification. Can effectively generate a tumble flow.

  In addition, the individual passage 56 of the cylinder head 25 is drilled into the raised portion 25a in the cylinder head 25 integrally formed with the raised portion 25a protruding inward from the inner periphery of the intake port 38. Therefore, it is easy to form the individual passage 56 in the cylinder head 25, and it is possible to contribute to the reduction of the manufacturing cost.

  Further, the intake duct 39 is connected to the cylinder head 25 so as to extend in a direction obliquely intersecting with the cylinder axis C of the engine body 21 on a virtual plane orthogonal to the axis of the crankshaft 22, The intake port 38 connected to the intake valve port 51 that opens to the combustion chamber 64 is formed so as to curve from the outer end opening to which the intake duct 39 is connected to the intake valve port 51. Even if the shape is curved from the outer end opening portion to the intake valve port 51, the individual passage 56 that constitutes a part of the auxiliary intake passage 48 and is provided in the cylinder head 25 is straight so that the cross-sectional shape thereof is circular. By forming it in a shape, the flow resistance can be suppressed and the generation of a tumble flow in the combustion chamber 64 can be promoted.

  Further, a throttle body 42 having a throttle valve 43 is connected to the upstream side of the intake duct 39, and a fuel injection valve 52 that injects fuel toward the intake valve port 51 of the cylinder head 25 is more than the throttle valve 43. At the downstream side, it is attached to any one of the throttle body 42, the intake duct 39 and the cylinder head 25 (in this embodiment, the intake duct 39), and this internal combustion engine E is configured in a fuel injection system. However, the present invention can be applied to such a fuel injection type internal combustion engine E to promote generation of a tumble flow in the combustion chamber 64 and contribute to improvement in combustibility.

  FIG. 9 shows a second embodiment of the present invention. The parts corresponding to those of the first embodiment are indicated by the same reference numerals, and the detailed description is omitted. .

  This second embodiment differs from the first embodiment only in that a carburetor 68 having a throttle body 69 is used in place of the throttle body 42 of the first embodiment. The configuration is basically the same as that of the first embodiment.

  The flange 58 of the reed valve stay 49 is sandwiched between a flange portion 68a that the carburetor 68 has at its downstream end and a flange portion 39a that the intake duct 39 has at the upstream end. The reed valve stay 49 is attached to the intake duct 39 by fastening the flange 58 sandwiched between the flange portions 39a and 68a with a plurality of bolts 60 screwed into the flange portion 39a.

  According to the second embodiment, the present invention can be applied to the carburetor-type internal combustion engine E to promote the generation of a tumble flow in the combustion chamber 64 and contribute to improvement in combustibility. In addition, in the reed valve stay 49, the cylindrical portion 57d is provided at the lower portion of the frame body 57, and the reed valve 50 is attached to the outer surface of the frame portions 57a to 57c, at a position corresponding to the top of the virtual quadrangular pyramid. A guide portion 57e that connects the top portions of the three frame portions 57a to 57c is formed in the frame body 57 so that the inner surface of the guide portion 57e is connected to the upper portion of the upstream opening end of the cylindrical portion 57d. Since the fuel is supplied from the carburetor 68 into the intake passage 46 at the upstream side of the reed valve stay 49, the fuel adhering to each reed valve 50 can be guided to the auxiliary intake passage 48 side by the guide portion 57e. .

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the present invention described in the claims. Is possible.

  For example, in the above-described embodiment, the reed valve stay 49 is configured to have the quadrangular pyramid frame 57 having the three triangular frame portions 57a, 57b, and 57c corresponding to the three side surfaces of the virtual quadrangular pyramid. However, it may be configured to have a triangular pyramid-shaped frame corresponding to the two side surfaces of the virtual triangular pyramid, in which case the reed valves are attached to the two frame portions, respectively.

21 ... Engine body 22 ... Crankshaft 25 ... Cylinder head 25a ... Raised portion 38 ... Intake port 39 ... Intake duct 42 ... Throttle bodies 43, 69 ... Throttle valve 45 ... passage 46 ... intake passage 47 ... main intake passage 48 ... auxiliary intake passage 49 ... reed valve stay 50 ... reed valve 51 ... intake valve port 52 ... fuel Injection valve 54, 55, 56 ... Individual passage 57 ... Frame bodies 57a, 57b, 57c ... Frame portion 57d ... Tube portion 57e ... Guide portion 64 ... Combustion chamber 68 ... Vaporizer C ... Cylinder axis

Claims (8)

Intake air that communicates with the intake port (38) of the cylinder head (25) with a passage (45) formed in an intake duct (39) connected to the cylinder head (25) of the engine body (21) as a part of the constituent elements. A throttle valve (43, 69) capable of adjusting the intake air amount is interposed in the passage (46), and a part of the intake passage (46) on the downstream side of the throttle valve (43, 69), A part of the intake port (38) is opened and closed by a reed valve (50) attached to a reed valve stay (49), and a sub-intake passage (which bypasses the reed valve (50)) ( 48), and the reed valve stay (49) is formed separately from the intake duct (39) and attached to the intake duct (39).
In the reed valve stay (49), the intake duct (39) and the cylinder head (25), individual passages (54, 55, 56) extending in a straight line with a circular cross-sectional shape are individually formed. The auxiliary intake passage (48) is configured by communicating individual passages (54 to 56) with each other, and a plurality of the reed valves (50) capable of rectifying intake air toward the auxiliary intake passage (48), An intake structure for an internal combustion engine, wherein the intake structure is attached to the reed valve stay (49) so as to be aligned in the circumferential direction outside the upstream opening end of the auxiliary intake passage (48) . Intake air that communicates with the intake port (38) of the cylinder head (25) with a passage (45) formed in an intake duct (39) connected to the cylinder head (25) of the engine body (21) as a part of the constituent elements. A throttle valve (43, 69) capable of adjusting the intake air amount is interposed in the passage (46), and a part of the intake passage (46) on the downstream side of the throttle valve (43, 69), A part of the intake port (38) is opened and closed by a reed valve (50) attached to a reed valve stay (49), and a sub-intake passage (which bypasses the reed valve (50)) ( 48), and the reed valve stay (49) is formed separately from the intake duct (39) and attached to the intake duct (39).
In the reed valve stay (49), the intake duct (39) and the cylinder head (25), individual passages (54, 55, 56) extending in a straight line with a circular cross-sectional shape are individually formed. The auxiliary intake passage (48) is configured by communicating the individual passages (54 to 56) with each other,
The reed valve stay (49) includes three triangular frame portions (57a, 57b, 57c) corresponding to the three side surfaces of the virtual quadrangular pyramid and the individual passage (54) of the reed valve stay (49). It has a quadrangular pyramid-shaped frame (57) integrally formed with a cylindrical portion (57d) that is formed and arranged at a position corresponding to the top of the virtual quadrangular pyramid, and the three frame portions (57a to 57c) ) to an intake structure of the inner combustion engine characterized in that the reed valve (50) is attached respectively. The plurality of reed valves (50) are attached to the reed valve stay (49) so as to be arranged in the circumferential direction outside the upstream opening end of the auxiliary intake passage (48) in the circumferential direction. Item 3. An intake structure for an internal combustion engine according to Item 2 . The cylindrical portion (57d) is provided at the lower portion of the frame (57), the reed valve (50) is attached to the outer surface of the frame portions (57a to 57c), and a position corresponding to the top of the virtual quadrangular pyramid The guide part (57e) that connects the top parts of the three frame parts (57a to 57c) connects the upstream surface of the guide part (57e) to the upper part of the upstream opening end of the cylindrical part (57d). The intake structure for an internal combustion engine according to claim 2 or 3, wherein the intake body is formed on the frame (57) so as to be formed.   The individual passage (56) of the cylinder head (25) is formed in the cylinder head (25) integrally formed with a raised portion (25a) that protrudes inward from the inner periphery of the intake port (38). The intake structure for an internal combustion engine according to any one of claims 1 to 4, characterized in that is formed by drilling the raised portion (25a).   The intake duct (39) extends in a direction obliquely intersecting the cylinder axis (C) of the engine body (21) on a projection view on a virtual plane orthogonal to the axis of the crankshaft (22). The intake port (38) connected to the cylinder head (25) and connected to the intake valve port (51) that opens to the combustion chamber (64) is connected to the intake port from the outer end opening that connects the intake duct (39). The intake structure for an internal combustion engine according to any one of claims 1 to 5, wherein the intake structure is formed so as to be curved toward the valve opening (51).   A throttle body (42) having a throttle valve (43) is connected to the upstream side of the intake duct (39), and the intake valve provided in the cylinder head (25) so as to connect the intake port (38). A fuel injection valve (52) for injecting fuel toward the port (51) is located downstream of the throttle valve (43), and the throttle body (42), the intake duct (39) and the cylinder head (25). The intake structure for an internal combustion engine according to any one of claims 1 to 6, wherein the intake structure is attached to any of the above. The intake of the internal combustion engine according to any one of claims 1 to 6, characterized in that a carburetor (68) forming part of the intake passage (46) is connected to the intake duct (39). Construction.

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