JP2018096304A - Suction device of spark ignition type engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a suction device of a spark ignition type engine capable of preventing output shortage in high-load operation.SOLUTION: A suction device of a spark ignition type engine includes a carburetor 1. An air vent pipe 9 is inserted into a passage inlet part 8a of an air vent passage 8. The air vent pipe 9 is directed toward a direction along an axial core 3a direction of a choke valve passage 3. A pipe inlet portion 9a of the air vent pipe 9 is projected to a suction passage 7 on a suctioned air upstream side with respect to an inlet end surface 3b of the choke valve passage 3. An internal passage 9b of the pipe inlet portion 9a is expanded toward the suction passage 7 on the suctioned air upstream side.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an intake device for a spark ignition engine, and more particularly to an intake device for a spark ignition engine that can prevent an output shortage during high load operation.

Conventionally, there are the following intake devices for a spark ignition engine (see, for example, Patent Document 1).
The carburetor includes a venturi passage, a choke valve passage on the intake upstream side of the venturi passage, a throttle valve passage on the intake downstream side of the venturi passage, a float chamber, and a main nozzle protruding from the float chamber to the venturi passage. An air intake passage for a spark ignition engine, comprising an air vent passage for communicating an air intake passage upstream of the float chamber and the choke valve passage.

  According to this type of intake device, when the filter of the air cleaner is clogged, the influence of the intake negative pressure generated in the intake passage extends not only to the venturi passage but also to the float chamber, and excessive fuel flows from the float chamber to the venturi passage. There is an advantage that it is possible to prevent defects that are sucked up.

  In the thing of patent document 1, the bulging space which bulges in the radial direction is provided in the intake passage on the intake upstream side of the inlet surface of the choke valve passage, and the passage inlet of the air vent passage is connected to the passage through the bulged space. It communicates with the intake path.

JP-A-7-139432 (see FIG. 1)

<Problem> Insufficient output during high load operation.
In the thing of patent document 1, at the time of high load operation in which the throttle valve is fully opened, the negative pressure of the intake air passing through the venturi passage at a high speed acts strongly on the float chamber through the choke valve space, the bulging space, and the air vent passage in this order. Due to the decompression of the float chamber, fuel suction from the float chamber to the venturi passage is insufficient, and output shortage is likely to occur.

  The subject of this invention is providing the intake device of the spark ignition type engine which can prevent the output shortage at the time of high load driving | operation.

The invention specific matters of the present invention are as follows.
As illustrated in FIG. 1, a carburetor (1) is provided. The carburetor (1) includes a venturi passage (2), a choke valve passage (3) on the intake upstream side of the venturi passage (2), and a venturi passage (2 ), A throttle valve passage (4), a float chamber (5), a main nozzle (6) protruding from the float chamber (5) to the venturi passage (2), a float chamber (5) and a choke valve In an intake device for a spark ignition engine, comprising an air vent passage (8) for communicating an intake passage (7) on the intake upstream side of the passage (3),
As illustrated in FIG. 1, an air vent pipe (9) is inserted into a passage inlet portion (8a) of an air vent passage (8), and the air vent pipe (9) extends in the direction of the axis (3a) of the choke valve passage (3). The pipe inlet portion (9a) of the air vent pipe (9) is projected in the intake path (7) on the upstream side of the inlet end surface (3b) of the choke valve passage (3). An intake device for a spark ignition engine, characterized in that an internal passage (9b) of the portion (9a) is expanded toward an intake passage (7) on the intake upstream side.

The present invention has the following effects.
<Effect> Insufficient output during high-load operation can be prevented.
In the present invention, as illustrated in FIG. 1, during high load operation in which the throttle valve (4a) is fully opened, the negative pressure generated by the intake air (2a) passing through the venturi passage (4) at high speed is generated in the air vent pipe (9). It is difficult to transmit to the float chamber (5) due to the interposition, the pressure drop in the float chamber (5) is suppressed, and it is possible to prevent insufficient output due to insufficient fuel suction from the float chamber (5) to the venturi passage (2). .
This is because the air vent pipe (9) moves the inlet of the air vent path away from the venturi passage (2) to the upstream side of the intake air, and the negative pressure transmitted to the float chamber (5) is weakened. In addition, the choke valve passage (3) The intake air (7a) in the intake passage (7) on the upstream side of the intake air is pushed into the float chamber (5) through the expanded internal passage (9b) of the pipe inlet portion (9a), and enters the float chamber (5). It is estimated that a part of the transmitted negative pressure is canceled out.

<Effect> Decrease in output shortage prevention function during high load operation is suppressed.
In the present invention, as shown in FIG. 2 (B), the inlet portion of the expanded internal passage (9b) of the pipe inlet portion (9a) has a large cross-sectional area and is deformed by an external force during or before use. However, the change in the cross-sectional area is small, and the deterioration of the output shortage prevention function during high load operation is suppressed.

1 is a longitudinal rear view of an intake device for a spark ignition engine according to an embodiment of the present invention. 2A is an enlarged view of the IIA portion of FIG. 1, and FIG. 2B is a longitudinal sectional view of a modified example of the air vent pipe. FIG. 3 is a view in the direction of arrow III in FIG. 1. FIG. 2 is a cross-sectional plan view of the engine of FIG. 1. It is a side view of the engine of FIG. It is a front view of the engine of FIG.

  1 to 6 are diagrams for explaining a spark ignition type engine according to an embodiment of the present invention. In this embodiment, a vertical water-cooled in-line two-cylinder gasoline engine will be described.

The outline of this engine is as follows.
As shown in FIG. 5, the engine includes a cylinder block (20), a cylinder head (21) assembled to the upper part of the cylinder block (20), and a cylinder head cover (21) assembled to the upper part of the cylinder head (21). 22), a gear case (24) assembled to the front portion of the cylinder block (20), and a timing transmission belt provided at the front portion of the gear case (24) with the installation direction of the crankshaft (23) as the front-rear direction. A case (25), an engine cooling fan (26) disposed at the front of the timing transmission belt case (25), a flywheel (27) disposed at the rear of the cylinder block (20), and a cylinder block ( 20), an oil pan (28) assembled at the bottom of the cylinder block (20), an intake device (29) disposed on one side of the cylinder head (21) with the width direction of the cylinder block (20) as a lateral direction, And it includes apparatus governor lever (30) arranged below the (29).

  As shown in FIG. 6, the gear case (24) accommodates a gear train (not shown) that links the balancer shaft (not shown) and the oil pump (31) with the crankshaft (2.0), and the oil pump (31) and an oil filter mounting seat (32), and the oil filter (33) is mounted on the oil filter mounting seat (32). The timing transmission belt case (24) accommodates a timing transmission belt (35) that interlocks the valve camshaft (34) with the crankshaft (23). The intake device (29) includes a carburetor (1) and an air cleaner (10). As shown in FIG. 5, a fuel supply pump (36) for supplying fuel (5a) to the carburetor (1) is disposed below the carburetor (1), and between the carburetor (1) and the fuel supply pump (36). The governor lever (30) is disposed on the throttle lever (37), and the throttle input lever (38) of the carburetor (1) is linked to the governing lever (37) via the governor spring (43), the governor lever (30) and the interlocking rod (44) in this order. Has been.

  As shown in FIG. 4, the cylinder head (21) includes a V-shaped intake port (39), a pair of exhaust ports (40) and (40), and a water jacket (41), and a port inlet of the intake port (39). The carburetor (1) is attached to the portion (39a) via the insulator (42), the air cleaner (10) is attached to the passage inlet (3c) of the choke valve passage (3) of the carburetor (1), and the carburetor (1) ) To the pair of cylinders (46) and (46) disposed in the front-rear direction through the intake port (39), and the exhaust (47) and (47) become the pair of exhaust ports (40). It is discharged from (40). An exhaust muffler (not shown) is attached to the exhaust ports 40 and 40.

The configuration of the intake device (29) is as follows.
As shown in FIG. 1, the intake device (29) includes a carburetor (1). The carburetor (1) includes a venturi passage (2) and a choke valve passage (3) on the intake upstream side of the venturi passage (2). A throttle valve passage (4) on the intake downstream side of the venturi passage (2), a float chamber (5), a main nozzle (6) protruding from the float chamber (5) to the venturi passage (2), and a float chamber An air vent passage (8) is provided for connecting the intake passage (7) on the intake upstream side of (5) and the choke valve passage (3).

  In this engine, even if the filter of the air cleaner is clogged, the negative intake pressure affects not only the venturi passage (2) but also the float chamber (5), and fuel flows from the float chamber (5) to the venturi passage (2). The problem that (5a) is excessively sucked can be prevented.

  As shown in FIG. 1, in this engine, an air vent pipe (9) is inserted into a passage inlet (8a) of an air vent passage (8), and the air vent pipe (9) is an axis (3a) of a choke valve passage (3). The pipe inlet portion (9a) of the air vent pipe (9) is projected into the intake passage (7) upstream of the inlet end surface (3b) of the choke valve passage (3), The internal passage (9b) of the pipe inlet portion (9a) is expanded toward the intake passage (7) on the intake upstream side.

In this engine, during high load operation in which the throttle valve (4a) is fully opened, negative pressure generated by intake air (2a) passing through the venturi passage (4) at high speed is caused to the float chamber (5) by the air vent pipe (9). It is difficult to transmit, the pressure drop in the float chamber (5) is suppressed, and it is possible to prevent an output shortage due to insufficient fuel suction from the float chamber (5) to the venturi passage (2).
This is because the air vent pipe (9) moves the inlet of the air vent path away from the venturi passage (2) to the upstream side of the intake air, and the negative pressure transmitted to the float chamber (5) is weakened. In addition, the choke valve passage (3) The intake air (7a) in the intake passage (7) on the upstream side of the intake air is pushed into the float chamber (5) through the expanded internal passage (9b) of the pipe inlet portion (9a), and enters the float chamber (5). It is estimated that a part of the transmitted negative pressure is canceled out.

  In this engine, the inlet portion of the expanded internal passage (9b) of the pipe inlet portion (9a) has a large cross-sectional area, and even if it is deformed by an external force during or before use, the change in the cross-sectional area is small and high. Reduction of output shortage prevention function during load operation is suppressed.

As shown in FIG. 2 (A), the internal passage (9b) of the pipe inlet portion (9a) is tapered.
The taper angle (T) of the internal passage (9b) of the pipe inlet portion (9a) is set to an optimum value of 40 °.
The proper range of the taper angle (T) is 24 ° to 80 °, and the optimum range is 30 ° to 60 °.

When the taper angle (T) of the internal passage (9b) of the pipe inlet portion (9a) shown in FIG. 2 (A) is less than 24 °, which is different from the appropriate range of 24 ° to 80 °, during high load operation The function of preventing the shortage of output may be lowered. This is presumably because the taper angle (T) is too small and the intake air (7a) on the intake air upstream side of the choke valve passage (3) is hardly pushed from the internal passage (9b) of the pipe inlet portion (9a). .
Further, unlike the above-mentioned appropriate range of 24 ° to 80 °, even if the taper angle (T) shown in FIG. If it exceeds, the taper angle (T) is too large, and it may be difficult to form the taper.
On the other hand, there is no such problem in the proper range of 24 ° to 80 °, and the function to prevent insufficient output is high, and the function is the highest in the optimal range of 30 ° to 60 °.

FIG. 2 (B) shows a modification of the air vent pipe. The air vent pipe (9) has an internal passage (9b) of the pipe inlet portion (9a) gradually tangent toward the pipe inlet end face (9c) ( A curved portion (9f) having a taper angle (T) of 9d) is provided.
The average value (TA) of the taper angle (T) of the tangent (9d) of the internal passage (9b) of the pipe inlet portion (9a) is set to an optimum value of 40 °.
The appropriate range of the average value (TA) of the taper angle (T) is 15 ° to 110 °, and the optimum range is 25 ° to 90 °.

Unlike the appropriate range of 15 ° to 110 °, the average value (TA) of the taper angle (T) of the tangent line (9d) of the internal passage (9b) of the pipe inlet portion (9a) shown in FIG. If it is less than this, the function of preventing insufficient output during high-load operation may be reduced. This is because the average value (TA) of the taper angle (T) is too small, and the intake air (7a) on the upstream side of the choke valve passage (3) is not easily pushed from the internal passage (9b) of the pipe inlet portion (9a). It is estimated to be.
In addition, unlike the appropriate range of 15 ° to 110 °, even if the average value (TA) of the taper angle (T) shown in FIG. Moreover, if it exceeds 110 °, the average value (TA) of the taper angle (T) is too large, and it may be difficult to form the internal passage (9b) of the pipe inlet portion (9a).
On the other hand, there is no such problem in the proper range of 15 ° to 110 °, and the function to prevent insufficient output is high, and the function is the highest in the optimal range of 25 ° to 90 °.

The curved portion (9f) shown in FIG. 2 (B) is provided at the inlet of the internal passage (9b) of the pipe inlet portion (9a), and the outlet side is tapered.
The curved portion (9f) is not limited to a part of the internal passage (9b) of the pipe inlet portion (9a), and may be formed in the entirety.
The other configurations and functions of the engine having the air vent pipe (9) of this modification are the same as those of the engine having the air vent pipe (9) shown in FIG. 2 (A). 2 (B) is given the same reference numeral as FIG. 2 (A).

As shown in FIGS. 2A and 2B, the passage length (L) of the internal passage (9b) of the pipe inlet portion (9a) is the optimum value, that is, the minimum diameter portion (9e) of the internal passage (9b). ) Is set to a value 0.83 times the diameter (d).
The appropriate range of the passage length (L) is 0.37 to 1.17 times the diameter (d) of the minimum diameter portion (9e) of the internal passage (9b), and the optimum range is 0.53 to 1 .17 times.

Unlike the appropriate range 0.37 times to 1.17 times, the passage length (L) of the internal passage (9b) of the pipe inlet portion (9a) shown in FIGS. ) Is less than 0.37 times the diameter (d) of the minimum diameter portion (9e), the function of preventing output shortage during high-load operation may be reduced. This is presumably because the passage length (L) is too short and the intake air (7a) on the intake upstream side of the choke valve passage (3) is hardly pushed from the internal passage (9b) of the pipe inlet portion (9a). Is done.
Further, unlike the above-mentioned appropriate range of 0.37 times to 1.17 times, even if the passage length (L) shown in FIGS. 2 (A) and 2 (B) exceeds 1.17 times the diameter (d), In the case of 17 times, the output is not improved more than it is, and when it exceeds 1.17 times, the passage length (L) is too long and it becomes difficult to form the internal passage (9b) of the pipe inlet portion (9a). Sometimes.
On the other hand, in the proper range of 0.37 times to 1.17 times, there is no such problem, and the function of preventing insufficient output is high, and in the optimum range of 0.53 times to 1.17 times, the function is the most. high.

  As shown in FIG. 2 (A), the air vent pipe (9) includes a pipe inlet part (9a) and a pipe outlet part (9g), and the pipe inlet part (9a) has a diameter larger than that of the pipe outlet part (9g). The inner passage (9h) of the pipe outlet portion (9g) is a straight passage with a straight uniform diameter. The diameter of the inner passage (9h) of the pipe outlet portion (9g) and the diameter of the air vent passage (8) are The diameter (d) of the minimum diameter portion (9e) of the internal passage (9b) of the pipe inlet portion (9a) is the same.

As shown in FIG. 2A, the projecting dimension (P) of the pipe inlet portion (9a) from the inlet end face (3b) of the choke valve passage (3) is an optimum value, that is, the inside of the pipe inlet portion (9a). It is set to 2.5 times the diameter (D) of the pipe entrance end face (9c) of the passage (9b).
The appropriate range of the projecting dimension (P) is 1.7 to 3.3 times the diameter (d) of the minimum diameter portion (9e) of the internal passage (9b) of the pipe inlet portion (9a), and the optimum range is 2 0.0 times to 3.1 times.

Unlike the appropriate range 1.7 times to 3.3 times, the projecting dimension (P) of the pipe inlet portion (9a) from the inlet end surface (3b) of the choke valve passage (3) shown in FIG. When the diameter (d) of the minimum diameter portion (9e) of the internal passage (9b) of the inlet portion (9a) is less than 1.7 times, the function of preventing output shortage during high load operation is lowered. There is. This is presumably because the protrusion dimension (P) is too short, the inlet of the air vent path approaches the venturi passage (2), and negative pressure is easily transmitted to the float chamber (5).
Also, unlike the above-mentioned proper range of 1.7 times to 3.3 times, even if the protruding dimension (P) shown in FIG. 2 (A) exceeds 3.3 times the diameter (d) of the minimum diameter portion (9e). In the case of 3.3 times, no further improvement in output is observed, and if it exceeds 3.3 times, the projecting dimension (P) is too large and the intake path (7) on the intake upstream side of the choke valve passage (3) (7) ) And the air vent pipe (9) may interfere with each other.
On the other hand, the appropriate range of 1.7 times to 3.3 times does not have such a problem, and the function of preventing insufficient output is high, and the optimum range of 2.0 times to 3.1 times has the highest function. high.

As shown in FIG. 1, the intake device includes an air cleaner (10) attached to a passage inlet (3c) of the choke valve passage (3).
As shown in FIG. 2 (A), the air cleaner (10) includes a receiving plate (11) for receiving the air-fuel mixture blown back from the choke valve passage (3). As shown in FIG. 3, the choke valve passage (3) When the pipe inlet end surface (9c) of the internal passage (9b) of the pipe inlet portion (9a) and the receiving plate (11) are overlapped with each other when viewed in a direction parallel to the axis (3a) of FIG. As shown in (A), the separation distance (E) between the pipe inlet end face (9c) and the receiving plate (11) is an optimum value, that is, 1.75 times the diameter (D) of the pipe inlet end face (9c). Is set to a value.
The appropriate range of the separation distance (E) is 1.0 to 2.1 times the diameter (D) of the pipe inlet end face (9c), and the optimum range is 1.2 to 1.9 times.

Unlike the appropriate range of 1.0 to 2.1, the distance (E) between the pipe inlet end face (9c) and the receiving plate (11) shown in FIG. 2 (A) is the diameter of the pipe inlet end face (9c). When the ratio is less than 1.0 times (D), the function of preventing output shortage during high load operation may be lowered. This is because the separation distance (E) is too short and the intake air (7a) of the intake passage (7) on the intake upstream side of the choke valve passage (3) is pushed from the internal passage (9b) of the pipe inlet portion (9a). This is presumed to be difficult.
In addition, when the separation distance (E) shown in FIG. 2 (A) exceeds 2.1 times the diameter (D), it is 2.1 times unlike the appropriate range of 1.0 times to 2.1 times. The above output improvement is not recognized, and if it exceeds 2.1 times, the separation distance (E) becomes too large, and the air cleaner (10) may be enlarged.
On the other hand, in the proper range of 1.0 to 2.1 times, there is no such problem, and the function to prevent output shortage is high, and in the optimum range of 1.2 to 1.9 times, the function is the most. high.

  As shown in FIG. 1, the carburetor (1) includes a throttle body (48) and a fuel cup (49) attached to the lower portion of the throttle body (48). The throttle body (48) is a choke valve (3d). ) Containing a choke valve passage (3), a venturi passage (2) surrounded by a venturi section (2b), a throttle valve passage (4) containing a throttle valve (4a), and a float chamber (5) The main fuel passage (50) through which the fuel (5a) is supplied via the main jet (50a) and the fuel (5a) from the main fuel passage (50) through the pilot jet (51a) to the slow port (57) and idle A pilot fuel passage (51) branched to the port (58), an air vent passage (8), a main air bleed (50c) for supplying air to the main air bleed chamber (50b) of the main fuel passage (50), a pilot Burning A pilot air bleed (51b) for supplying air to the passage (51) is provided. As shown in FIG. 3, the passage inlet of the air vent passage (8), the passage inlet of the pilot air bleed (51b), and the main air bleed (50c) These passage inlets are all opened at the passage inlet portion (3c) of the choke valve passage (3).

  As shown in FIG. 1, a float valve (52) is accommodated in a fuel cup (49), and the inside of the fuel cup (49) is a float chamber (5). The fuel supply pump (36) is formed by the float valve (52). The amount of fuel supplied to the float chamber (5) is adjusted to maintain the liquid level of the fuel (5a) in the float chamber (5) substantially constant. A valve actuator (53a) of a fuel cut valve (53) is attached to the fuel cup (49), and the fuel cut valve (53) is disposed in a valve chamber (53b) in the middle of the main fuel passage (50), and when the engine is stopped. The main fuel passage (50) is blocked by the fuel cut valve (53). A fuel drain pipe (5b) is suspended from the lower part of the fuel cup (49), and a fuel cock (5c) is provided on the drain pipe (5b). When the engine is stopped for a long time, the fuel drain pipe (5b) is floated via the fuel drain pipe (5b). The fuel (5a) in the chamber (5) is removed.

  As shown in FIG. 1, the air cleaner (10) includes a box-shaped case (54), an air filter (55) housed in the box-shaped case (54), an air filter (55), and an air filter (55). A receiving plate (11) is provided between the air purification chamber (56) on the downstream side of the intake air. The receiving plate (11) faces the inlet end face (3b) of the choke valve passage (3), and is a box-shaped case through a plurality of radial plates (11a) and (11a) led out radially from the receiving plate (11). (54) It is supported by the frame plate (11b) fitted to the inner peripheral surface, and between the radiation plates (11a) and (11a) is an intake opening (11c) and (11c).

  (1) ... carburetor, (2) ... venturi passage, (3) ... choke valve passage, (3a) ... shaft center, (3b) ... inlet end face, (3c) ... passage inlet, (4) ... throttle valve passage (5) ... Float chamber, (6) ... Main nozzle, (7) ... Intake passage, (8) ... Air vent passage, (8a) ... Passage inlet, (9) ... Air vent pipe, (9a) ... Pipe entrance Part, (9b) ... Inner passage, (9c) ... Pipe inlet end face, (9d) ... Tangent, (9e) ... Minimum diameter part, (9f) ... Bent part, (L) ... Passage length, (T) ... Taper angle, (TA) ... average value, (d) ... diameter, (P) ... projection dimension, (10) ... air cleaner, (11) ... receiving plate, (E) ... separation distance, (D) ... diameter.

Claims (8)

The carburetor (1) includes a venturi passage (2), a choke valve passage (3) on the intake upstream side of the venturi passage (2), and a throttle valve on the intake downstream side of the venturi passage (2). A passage (4), a float chamber (5), a main nozzle (6) projecting from the float chamber (5) to the venturi passage (2), an intake upstream side of the float chamber (5) and the choke valve passage (3) In an intake device for a spark ignition engine, comprising an air vent passage (8) for communicating the intake passage (7) of
An air vent pipe (9) is inserted into the passage inlet (8a) of the air vent passage (8), and the air vent pipe (9) is oriented in the direction along the axis (3a) of the choke valve passage (3). The pipe inlet portion (9a) of the pipe (9) projects into the intake passage (7) upstream of the inlet end face (3b) of the choke valve passage (3), and the internal passage (9b) of the pipe inlet portion (9a). ) Is expanded toward the intake passage (7) on the intake upstream side. The intake device for a spark ignition engine according to claim 1,
An intake device for a spark ignition engine, characterized in that the internal passage (9b) of the pipe inlet portion (9a) is tapered. The intake device for a spark ignition engine according to claim 2,
An intake device for a spark ignition engine, characterized in that the taper angle (T) of the internal passage (9b) of the pipe inlet portion (9a) is 24 ° to 80 °. The intake device for a spark ignition engine according to claim 1,
The internal passage (9b) of the pipe inlet portion (9a) includes a curved portion (9f) in which the taper angle (T) of the tangent (9d) gradually increases toward the pipe inlet end face (9c). A spark ignition engine intake system. In the intake device for a spark ignition engine according to claim 1 or 4,
The average value (TA) of the taper angle (T) of the tangent (9d) of the internal passage (9b) of the pipe inlet portion (9a) is set to 15 ° to 110 °. Intake device. In the intake device of the spark ignition engine according to any one of claims 1 to 5,
The passage length (L) of the internal passage (9b) of the pipe inlet portion (9a) is 0.37 to 1.17 times the diameter (d) of the smallest diameter portion (9e) of the internal passage (9b). A spark-ignition engine intake system characterized by that. The intake device for a spark ignition engine according to any one of claims 1 to 6,
The projecting dimension (P) of the pipe inlet portion (9a) from the inlet end surface (3b) of the choke valve passage (3) is the diameter (D) of the pipe inlet end surface (9c) of the inner passage (9b) of the pipe inlet portion (9a). ) And an air intake device for a spark ignition type engine, characterized in that the air intake system is 1.7 times to 3.3 times as large as 3). In the intake device of the spark ignition engine according to any one of claims 1 to 7,
An air cleaner (10) attached to the passage inlet (3c) of the choke valve passage (3);
The air cleaner (10) is provided with a receiving plate (11) for receiving the air-fuel mixture blown back from the choke valve passage (3), and the pipe inlet portion is viewed in a direction parallel to the axis (3a) of the choke valve passage (3). When the pipe inlet end face (9c) of the internal passage (9b) of (9a) and the receiving plate (11) are overlapped, the distance (E) between the pipe inlet end face (9c) and the receiving plate (11) Is an intake device of a spark ignition type engine characterized by being 1.0 to 2.1 times the diameter (D) of the pipe inlet end face (9c).

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