JPH06129252A - Supercharge type four-cycle engine - Google Patents

Abstract

PURPOSE:To prevent much lubricating oil separated from air-fuel mixture from staying inside a supercharging chamber in a supercharge type four-cycle engine for performing supercharging by means of utilizing compression variation inside of a crank chamber. CONSTITUTION:A throttle part 37 where inner diameter of an intake port 31 is contracted is formed inside the intake port 31, and a passage 38 for communicating one end with the bottom part of a supercharging chamber 32, and communicating other end with the intake port 31 at the throttle part 37 or at the combustion chamber side 14 side from the throttle part 37 are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention supplies air-fuel mixture to a combustion chamber through a crank chamber and lubricates each portion in the crank chamber with lubricating oil contained in the air-fuel mixture.
Further, the present invention relates to a supercharged four-cycle engine that compresses the air-fuel mixture and supercharges it by utilizing the pressure fluctuation in the crank chamber due to the reciprocating movement of the piston.

[0002]

2. Description of the Related Art Conventionally, a lubricating oil is mixed with a liquid fuel, and the mixture of the liquid fuel and air is supplied to a combustion chamber through a crank chamber, and at the same time, each part in the crank chamber is controlled by the lubricating oil contained in the mixture. Japanese Patent Application Laid-Open No. 47-35516 discloses a supercharged four-cycle engine that is lubricated and uses the pressure fluctuation in the crank chamber accompanying the reciprocating movement of the piston to compress the mixture to supercharge it. And JP 61-
There is one disclosed in Japanese Patent Publication No. 200330, and a typical structure of such a supercharged four-cycle engine will be described with reference to FIG.

First, FIG. 5 shows the entire structure of a single-cylinder supercharged four-cycle engine, in which a cylinder 2 is mounted on an upper part of a crankcase 1 and a cylinder head 3 is mounted on an upper part of the cylinder 2. There is. A crankshaft 5 rotatably supported by bearings (not shown) is rotatably provided in a crank chamber 4 formed in the crankcase 1, and the crankshaft 5 slides in the cylinder 2. A moving piston 6 is connected via a connecting rod 7. Further, the crank chamber 4
A cam shaft 8 rotatably supported by a bearing (not shown) is rotatably provided therein, and a crank gear 9 press-fitted and fixed to one end of the crank shaft 5 and a press-fit fixed to one end of the cam shaft 8. The engaged cam gear 10 meshes with it. The number of teeth of the cam gear 10 is set to be twice the number of teeth of the crank gear 9, and the camshaft 8 has an intake cam 11 and an exhaust cam for opening and closing an intake valve and an exhaust valve, which will be described later. (Not shown) and are fixed.

A valve operating mechanism housing space 13 surrounded by a rocker cover 12 is formed above the cylinder head 3, and a combustion chamber 14 inside the cylinder 2 is formed in the valve operating mechanism housing space 13. A spring 17 for urging an intake valve 16 that opens and closes an intake port 15 formed in the cylinder head 3 in a valve closing direction, and an exhaust port (not shown) formed in the combustion chamber 14 and the cylinder head 3 A spring (not shown) that urges an exhaust valve (not shown) that opens and closes the valve in the valve closing direction, and a rocker arm 18 that urges the intake valve 16 and the exhaust valve in the valve opening direction. The mechanism 19 is stored. The rocker arm 18 is swingably attached to the upper portion of the cylinder head 3 by an adjusting screw 20, and one end of the rocker arm 18 is in contact with the upper ends of the intake valve 16 and the exhaust valve. Further, one end of the push rod 21 is brought into contact with the other end of the rocker arm 18,
The other end of the push rod 21 is in contact with the intake cam 11 and the exhaust cam via a tappet 22. further,
The valve mechanism storage space 13 and the crank chamber 4 communicate with each other through a communication hole 23.

Next, the carburetor 24 for forming a mixture of liquid fuel mixed with lubricating oil and air is connected to the crank chamber 4 by an intake passage 25. The intake passage 25 and the crank chamber are connected to each other. A reed valve 26 that allows only the air-fuel mixture to be sucked into the crank chamber 4 is provided at the connection portion with the reed valve 4. Further, the crank chamber 4 and the intake port 15 are connected by a supercharging chamber 27, and the air-fuel mixture is discharged into the supercharging chamber 27 at the connecting portion between the supercharging chamber 27 and the crank chamber 4. A reed valve 28 that allows only the above is provided. An intake pipe 29 integrally formed with the cylinder head 3 is provided between the intake port 15 and the supercharging chamber 27, and the inside of the intake pipe 29 serves as a part of the intake port 15. ing. The volume of the supercharging chamber 27 is set to 10 to 20 times the stroke volume in order to reduce pressure fluctuations in the supercharging chamber 27 and obtain a stable output.

In such a structure, during the compression stroke and the exhaust stroke of the engine, the volume of the crank chamber 4 increases as the piston 6 rises, and the pressure in the crank chamber 4 decreases, which causes the reed valve. The valve 26 is opened so as to be in contact with the valve stopper 26a, and the air-fuel mixture formed in the carburetor 24 is sucked into the crank chamber 4. During the engine's explosion stroke and intake stroke, the crank chamber 4 moves as the piston 6 descends.
Is reduced and the pressure in the crank chamber 4 is increased, the reed valve 28 is opened to abut the valve stopper 28a, and the air-fuel mixture in the crank chamber 4 is discharged into the supercharging chamber 27. . Therefore, the compressed and high-pressure air-fuel mixture is stored in the supercharging chamber 27, and the air-fuel mixture is sucked into the combustion chamber 14 when the intake valve 16 is opened during the intake stroke.

Here, the lubricating oil contained in the air-fuel mixture lubricates each part in the crank chamber 4 and enters the valve mechanism storage space 13 through the communication hole 23 to lubricate the valve mechanism 19. Then, after being discharged into the supercharging chamber 27, the combustion chamber 14
It is inhaled and burned.

Further, since such a supercharged four-cycle engine does not have an oil pan for storing the lubricating oil, the crank chamber 4 may be turned upside down in any direction, for example. Can also be used.

[0009]

For the air-fuel mixture discharged into the supercharging chamber 27, the volume of the supercharging chamber 27 is 10 to 10 times the stroke volume.
Since it is 20 times, the residence time in the supercharging chamber 27 becomes long, and the temperature of the wall of the supercharging chamber 27 is increased due to the heat transmitted from the cylinder head 3 and the hot air after cooling the cylinder 2 and the like. It is rising. Therefore, in the supercharging chamber 27, the fuel in the air-fuel mixture is easily vaporized, while the lubricating oil with a high boiling point is easily separated, and depending on the conditions, about half of the lubricating oil contained in the air-fuel mixture is separated. It Then, the separated lubricating oil collects at the bottom of the supercharging chamber 27 adjacent to the reed valve 28.

The lubricating oil accumulated in the position close to the reed valve 28 becomes a resistance when the air-fuel mixture is discharged from the crank chamber 4 to the supercharging chamber 27, so that the air-fuel mixture from the crank chamber 4 to the supercharging chamber 27 is prevented. This has the drawbacks that smooth discharge is hindered, the pressure in the supercharging chamber 27 cannot be increased sufficiently, and the output of the supercharging four-cycle engine decreases.

Further, when a large amount of lubricating oil is accumulated at the bottom of the supercharging chamber 27, the lubricating oil accumulated when the supercharging 4-cycle engine is inverted so that the crank chamber 4 is at the upper side is the combustion chamber 14 In some cases, the pressure in the combustion chamber 14 rises abnormally during the compression stroke, causing damage to the cylinder 2 and the like.

[0012]

The invention according to claim 1 is
An intake passage connecting the air-fuel mixture forming section and the crank chamber, and a supercharging chamber connecting the intake port communicating with the combustion chamber and the crank chamber are provided, and the pressure change in the crank chamber due to the reciprocating motion of the piston. In the supercharged four-cycle engine, the air-fuel mixture containing the lubricating oil is sucked into the crank chamber from the intake passage and the compressed air-fuel mixture in the crank chamber is discharged into the supercharge chamber.
A throttle portion having a reduced inner diameter of the intake port is formed in the intake port, one end of which is communicated with a bottom portion of the supercharging chamber, and the other end of which is the throttle portion or on the combustion chamber side from the throttle portion. A passage communicating with the intake port is provided.

According to a second aspect of the present invention, an intake passage connecting the air-fuel mixture forming portion and the crank chamber, an intake port communicating with the combustion chamber and a supercharging chamber connecting the crank chamber are provided, and the piston is provided. A pressure change in the crank chamber due to the reciprocating movement of the crank chamber causes suction of a mixture containing lubricating oil from the intake passage into the crank chamber and discharge of the compressed mixture in the crank chamber into the supercharging chamber. In the supercharged four-cycle engine described above, a first passage that connects a substantially bottom portion of the supercharging chamber and a valve mechanism storage space that accommodates the valve mechanism is provided, and the inner diameter of the intake port is reduced in the intake port. A second passage having one end communicated with the valve mechanism storage space and the other end communicated with the intake port on the combustion chamber side of the throttle part. Digits.

[0014]

According to the first aspect of the invention, when the air-fuel mixture in the supercharging chamber is sucked into the combustion chamber through the intake port, the sucked air-fuel mixture is throttled in the throttle portion of the intake port. The pressure in the intake port on the combustion chamber side of the throttle becomes lower than that in the supercharging chamber. Therefore, due to this pressure difference, the lubricating oil separated from the air-fuel mixture and accumulated at the bottom of the supercharging chamber flows into the intake port through the passage, and is further sucked into the combustion chamber together with the air-fuel mixture and burned.

According to the second aspect of the invention, when the air-fuel mixture in the supercharging chamber is sucked into the combustion chamber through the intake port, the sucked air-fuel mixture is throttled in the throttle portion of the intake port. The pressure in the intake port on the combustion chamber side of the throttle becomes lower than that in the supercharging chamber. Therefore, due to this pressure difference, the lubricating oil separated from the air-fuel mixture and accumulating at the bottom of the supercharging chamber flows into the valve train housing space through the first passage, and also passes through the second passage and inside the intake port. Flows into the combustion chamber and is burned together with the air-fuel mixture.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the invention described in claim 1 will be described with reference to FIGS. The same parts as those described in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted.
A cylinder 2 is attached to the upper part of the crankcase 1,
A cylinder head 30 is attached to the top of the cylinder 2. A crankshaft 5 and a camshaft 8 are rotatably supported in a crank chamber 4 formed in the crankcase 1.

Next, the carburetor 24, which is an air-fuel mixture forming portion that forms an air-fuel mixture in which the liquid fuel mixed with the lubricating oil and the air are mixed, is connected to the crank chamber 4 by the intake passage 25. A reed valve 26, which allows only the air-fuel mixture to be sucked into the crank chamber 4, is provided at a connecting portion between the crank chamber 4 and the crank chamber 4. Further, the crank chamber 4 and the intake port 31 formed in the cylinder head 30 are connected by a supercharging chamber 32. The crank chamber 4 and the supercharging chamber 32 are connected via a first intake pipe 33, and the air-fuel mixture in the crank chamber 4 is connected to the connecting portion between the first intake pipe 33 and the crank chamber 4. A reed valve 28 that allows only discharge into the supercharging chamber 32 is provided. on the other hand,
The supercharging chamber 32 and the intake port 31 are connected via a second intake pipe 34 integrally formed with the cylinder head 30, and the inside of the second intake pipe 34 is a part of the intake port 31. It is said that. The volume of the supercharging chamber 32 is set to 10 to 20 times the stroke volume in order to reduce the pressure fluctuation in the supercharging chamber 32 and obtain a stable output. Further, at the bottom of the supercharging chamber 32, a sponge 35 for holding the lubricating oil separated from the air-fuel mixture and accumulated in the supercharging chamber 32 in a permeated state is provided.

Next, a ring-shaped throttle member 36 is press-fitted and fixed to the inner peripheral portion of the second intake pipe 34, and the intake port 31 is fixed by press-fitting and fixing the throttle member 36.
A narrowed portion 37 is formed by reducing the inner diameter of the. A passage 38, one end of which communicates with the bottom of the supercharging chamber 32 and the other end of which communicates with the throttle portion 37, is provided in the supercharging chamber 32. The inner diameter dimension "A" of the throttle portion 37 is determined by matching the vertical length "L" of the passage 38 with the full load performance of the supercharged four-cycle engine.

In such a structure, the intake of the air-fuel mixture from the intake passage 25 into the crank chamber 4 and the discharge of the air-fuel mixture from the crank chamber 4 into the supercharging chamber 32 have been described with reference to FIG. Similar to the example, it is performed with the pressure fluctuation in the crank chamber 4 due to the sliding motion of the piston 6. Then, the air-fuel mixture stored in the supercharging chamber 32 in a high pressure state is changed to the intake valve 16
Is sucked into the combustion chamber 14 during the intake stroke when the valve is opened.

Here, when the air-fuel mixture in the supercharging chamber 32 is sucked into the combustion chamber 14 via the intake port 31, the sucked air-fuel mixture is throttled by the throttle portion 37. The pressure becomes lower than the pressure in the supercharging chamber 32. Therefore, due to this pressure difference, the lubricating oil accumulated at the bottom of the supercharging chamber 32 flows into the intake port 31 through the passage 38, and is further sucked into the combustion chamber 14 together with the air-fuel mixture and burned.

Therefore, a large amount of lubricating oil is prevented from collecting at the bottom of the supercharging chamber 32 adjacent to the reed valve 28, and a large amount of lubricating oil accumulated at the bottom of the supercharging chamber 32 is supercharged from the crank chamber 4. The resistance of the air-fuel mixture discharged into the chamber 32 is prevented. Then, the lubricating oil can be smoothly discharged from the crank chamber 4 to the supercharging chamber 32, and the pressure in the supercharging chamber 32 can be sufficiently increased to improve the output of the supercharging 4-cycle engine. it can.

Further, since a large amount of lubricating oil is prevented from accumulating at the bottom of the supercharging chamber 32, a large amount of lubrication is applied even when the supercharging 4-cycle engine is reversed so that the crank chamber 4 is at the top. It is possible to prevent oil from flowing into the combustion chamber 14 all at once, and to prevent damage to the cylinder 2 or the like due to an abnormal increase in pressure in the combustion chamber 14 that occurs when a large amount of lubricating oil flows into the combustion chamber 14. To be prevented.

Next, a second embodiment of the invention described in claim 1 will be described with reference to FIG. 1 and 2 and FIG.
The same parts as those described in 1 are indicated by the same reference numerals, and description thereof will be omitted (the same applies hereinafter). In this embodiment, one end of the passage 39, one end of which communicates with the bottom of the supercharging chamber 32, has the other end of the passage 39.
It is connected to the intake port 31 on the side closer to the combustion chamber 14.

In such a structure, when the air-fuel mixture in the supercharging chamber 32 is sucked into the combustion chamber 14 via the intake port 31, the sucked air-fuel mixture is throttled by the throttle portion 37. The pressure in the portion closer to the combustion chamber 14 than the throttle portion 37 in 31 becomes lower than the pressure in the supercharging chamber 32. Therefore, due to this pressure difference, the lubricating oil accumulated at the bottom of the supercharging chamber 32 flows into the intake port 31 through the passage 39, and is further sucked into the combustion chamber 14 together with the air-fuel mixture and burned.

Therefore, a large amount of lubricating oil is prevented from accumulating at the bottom of the supercharging chamber 32 adjacent to the reed valve 28, and the lubricating oil is smoothly discharged from the crank chamber 4 to the supercharging chamber 32. The pressure in the supercharging chamber 32 can be sufficiently increased to improve the output of the supercharging-type 4-cycle engine. Further, even when the supercharged four-cycle engine is reversed so that the crank chamber 4 is located at the top, a large amount of lubricating oil is prevented from flowing into the combustion chamber 14, and a large amount of lubricating oil is generated. It is possible to prevent damage to the cylinder 2 and the like due to an abnormal increase in the pressure in the combustion chamber 14 that occurs when the cylinder 2 flows in.

Next, an embodiment of the invention described in claim 2 will be described with reference to FIG. A valve mechanism storage space 42 surrounded by a rocker cover 41 is formed above the cylinder head 40, and a valve mechanism 19 including a spring 17 and a rocker arm 18 is formed in the valve mechanism storage space 42. It is stored. It should be noted that the valve mechanism storage space 42 is not communicated with the crank chamber 4.

Next, there is provided a first passage 43, one end of which communicates with the bottom portion of the supercharging chamber 32 and the other end of which communicates with the valve mechanism storage space 42. Further, one end of the first passage 43 is provided with the valve mechanism. A second passage 44 is formed in the cylinder head 40 so as to communicate with the bottom of the storage space 42 and the other end thereof with the intake port 31 on the combustion chamber 14 side of the throttle portion 37.

In such a structure, the intake of the air-fuel mixture from the intake passage 25 into the crank chamber 4 and the discharge of the air-fuel mixture from the crank chamber 4 into the supercharging chamber 32 have been described with reference to FIG. Similar to the example, it is performed with the pressure fluctuation in the crank chamber 4 due to the sliding motion of the piston 6. Then, the air-fuel mixture stored in the supercharging chamber 32 in a high pressure state is changed to the intake valve 16
Is sucked into the combustion chamber 14 during the intake stroke when the valve is opened.

Here, when the air-fuel mixture in the supercharging chamber 32 is sucked into the combustion chamber 14 via the intake port 31, the sucked air-fuel mixture is throttled by the throttle portion 37, so that the air in the intake port 31 is reduced. The pressure in the portion closer to the combustion chamber 14 than the throttle portion 37 becomes lower than the pressure in the supercharging chamber 32. Therefore, due to this pressure difference, the lubricating oil accumulated at the bottom of the supercharging chamber 32 passes through the first passage 43 and the valve operating mechanism storage space 42.
And the intake port 3 through the second passage 44.
1 and flows into the combustion chamber 14 together with the air-fuel mixture and burns.

Therefore, a large amount of lubricating oil is prevented from accumulating at the bottom of the supercharging chamber 32 adjacent to the reed valve 28, and a large amount of lubricating oil accumulated at the bottom of the supercharging chamber 32 is supercharged from the crank chamber 4. The resistance of the air-fuel mixture discharged into the chamber 32 is prevented. Then, the lubricating oil can be smoothly discharged from the crank chamber 4 to the supercharging chamber 32, and the pressure in the supercharging chamber 32 can be sufficiently increased to improve the output of the supercharging 4-cycle engine. it can.

Further, since a large amount of lubricating oil is prevented from accumulating at the bottom of the supercharging chamber 32, a large amount of lubrication oil is retained even when the supercharging 4-cycle engine is inverted so that the crank chamber 4 is at the top. It is possible to prevent oil from flowing into the combustion chamber 14, and prevent a damage accident of the cylinder 2 or the like due to an abnormal increase in pressure in the combustion chamber 14 that occurs when a large amount of lubricating oil flows into the combustion chamber 14. To be done.

Further, in order to allow the lubricating oil separated in the supercharging chamber 32 to flow into the valve mechanism storage space 42, the valve mechanism 1
9 is well lubricated.

[0033]

As described above, according to the first aspect of the invention, the intake passage connecting the mixture forming portion and the crank chamber, the supercharging connecting the intake port communicating with the combustion chamber and the crank chamber. A chamber is provided, and a mixture containing lubricating oil is sucked from the intake passage into the crank chamber due to a pressure change in the crank chamber due to reciprocation of a piston, and the compressed mixture in the crank chamber is supercharged. In a supercharged four-cycle engine for discharging into a room, a throttle part having a reduced inner diameter of the intake port is formed in the intake port so that one end communicates with a bottom part of the supercharge chamber and the other end. Since a passage communicating with the intake port is provided on the throttle portion or on the combustion chamber side from the throttle portion, when the air-fuel mixture in the supercharging chamber is sucked into the combustion chamber through the intake port. Since the intake air-fuel mixture is throttled in the throttle portion, the portion of the throttle portion and the portion of the intake port closer to the combustion chamber than the throttle portion has a lower pressure than the supercharging chamber, and this pressure difference is used to make the bottom of the supercharging chamber. The lubricating oil that has accumulated in the intake chamber can be made to flow into the intake port through the passage, and this lubricating oil can be sucked into the combustion chamber together with the air-fuel mixture and burned. Therefore, a large amount of lubricating oil accumulates at the bottom of the supercharging chamber. It is possible to prevent the discharge of the air-fuel mixture from the crank chamber to the supercharging chamber from being obstructed. Therefore, by smoothly discharging the air-fuel mixture from the crank chamber to the supercharging chamber, the supercharged 4-cycle The output of the engine can be improved and a large amount of lubricating oil flows from the supercharging chamber to the combustion chamber all at once even when the supercharging 4-cycle engine is inverted so that the crank chamber is at the top. It is possible to prevent damage to the cylinder and the like due to an abnormal rise in pressure in the combustion chamber that occurs when a large amount of lubricating oil flows into the combustion chamber, and without installing an oil pump or the like. With a simple structure in which only the throttle portion and the passage are provided, it is possible to process the lubricating oil accumulated at the bottom of the supercharging chamber and to reduce the weight of the supercharging 4-cycle engine.

According to the second aspect of the invention, as described above, the intake passage connecting the mixture forming portion and the crank chamber, the supercharging chamber connecting the intake port communicating with the combustion chamber and the crank chamber. A mixture containing lubricating oil is sucked from the intake passage into the crank chamber by a pressure change in the crank chamber due to reciprocating movement of a piston, and the compressed mixture in the crank chamber is introduced into the supercharge chamber. In a supercharged four-cycle engine for discharging, a first passage is provided which communicates a substantially bottom portion of the supercharging chamber with a valve mechanism storage space in which a valve mechanism is accommodated, and the intake port is provided with the first passage. Forming a throttle part having a reduced inner diameter, one end communicating with the valve mechanism storage space and the other end communicating with the intake port at the throttle part or on the combustion chamber side of the throttle part. Since the second passage is provided, when the air-fuel mixture in the supercharging chamber is sucked into the combustion chamber via the intake port, the air-fuel mixture to be sucked is throttled in the throttle portion, so that the throttle portion in the throttle portion and the intake port is throttled. The pressure on the combustion chamber side of the portion becomes lower than that on the supercharging chamber, and this pressure difference is used to allow the lubricating oil that has accumulated at the bottom of the supercharging chamber to flow into the valve mechanism storage space through the first passage. It can flow into the intake port through the two passages, and can be sucked into the combustion chamber together with the air-fuel mixture and burned. Therefore, a large amount of lubricating oil accumulates at the bottom of the supercharging chamber, and It is possible to prevent the discharge of the air-fuel mixture from being disturbed. Therefore, by smoothly discharging the air-fuel mixture from the crank chamber to the supercharging chamber,
It is possible to improve the output of the cycle engine, and
Even when the supercharged four-cycle engine is turned upside down so that the crank chamber is at the top, a large amount of lubricating oil no longer flows from the supercharging chamber into the combustion chamber all at once, and a large amount of lubricating oil flows into the combustion chamber. In this case, it is possible to prevent damage to the cylinder and the like due to an abnormal rise in the pressure in the combustion chamber, and it is simple to provide the throttle, the first passage and the second passage without providing an oil pump or the like. With such a structure, the lubricating oil accumulated at the bottom of the supercharging chamber can be processed, the weight of the supercharging 4-cycle engine can be prevented from increasing, and the valve mechanism can be satisfactorily lubricated. It has the effect of being able to do so.

[Brief description of drawings]

FIG. 1 is a vertical sectional front view showing a first embodiment of the invention according to claim 1.

FIG. 2 is a vertical sectional front view showing a part of the device in an enlarged manner.

FIG. 3 is a vertical sectional front view showing a second embodiment of the invention according to claim 1;

FIG. 4 is a vertical sectional front view showing an embodiment of the invention described in claim 2;

FIG. 5 is a vertical sectional front view showing a conventional example.

[Explanation of symbols]

 4 Crank Chamber 6 Piston 14 Combustion Chamber 19 Valve Mechanism 24 Mixture Forming Part 25 Intake Passage 31 Intake Port 32 Supercharging Chamber 37 Throttling 38, 39 Passage 42 Valve Mechanism Storage Space 43 First Passage 44 Second Passage

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[Procedure amendment]

[Submission date] November 10, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

[Figure 4]

Claims (2)

[Claims] 1. An intake passage connecting a mixture forming portion and a crank chamber, and a supercharging chamber connecting an intake port communicating with a combustion chamber and the crank chamber, wherein the piston is reciprocally moved. A supercharged four-cycle cycle in which a mixture containing lubricating oil is sucked into the crank chamber from the intake passage due to a pressure change in the crank chamber, and a compressed mixture in the crank chamber is discharged into the supercharging chamber. In the engine, a throttle portion having a reduced inner diameter of the intake port is formed in the intake port, one end of which is communicated with a bottom portion of the supercharging chamber, and the other end of which is the throttle portion or the combustion chamber from the throttle portion. A supercharged four-cycle engine, characterized in that a passage communicating with the intake port is provided on the side. 2. An intake passage connecting the air-fuel mixture forming portion and the crank chamber, and a supercharging chamber connecting the intake port communicating with the combustion chamber and the crank chamber are provided. A supercharged four-cycle cycle in which a mixture containing lubricating oil is sucked into the crank chamber from the intake passage due to a pressure change in the crank chamber, and a compressed mixture in the crank chamber is discharged into the supercharging chamber. In the engine, a first passage that connects the substantially bottom portion of the supercharging chamber and a valve operating mechanism housing space that houses the valve operating mechanism is provided, and a throttle portion that reduces the inner diameter of the intake port is provided in the intake port. And a second passage having one end communicated with the valve mechanism storage space and the other end communicated with the intake port on the throttle portion or on the combustion chamber side of the throttle portion. Supercharged 4-cycle engine.