JP7426511B2 - Pre-chamber combustion 4-stroke engine - Google Patents

Description

The present invention relates to a pre-chamber combustion four-stroke engine having a main combustion chamber and a sub-chamber.

BACKGROUND ART Conventionally, a pre-chamber combustion four-stroke engine is known, which has a main combustion chamber and a sub-chamber that communicate with each other via a plurality of communication holes, as disclosed in Patent Document 1, for example. The air-fuel mixture inside the subchamber is ignited by a spark plug. The subchamber combustion four-stroke engine of Patent Document 1 does not have a subchamber fuel injection valve that injects fuel into the subchamber, but has an intake passage injection valve that injects fuel into an intake passage. The intake manifold injection valve of Patent Document 1 is controlled so that a stoichiometric or air-fuel mixture having an air-fuel ratio richer than stoichiometric is generated in the main combustion chamber.

US Patent No. 10612454

The pre-chamber combustion four-stroke engine of Patent Document 1 has an auxiliary spark plug (ignition auxiliary device) that assists in igniting the air-fuel mixture in the main combustion chamber. The pre-chamber combustion four-stroke engine of Patent Document 1 has an auxiliary spark plug in order to ensure engine performance at low loads. Therefore, if an auxiliary spark plug (ignition auxiliary device) is not provided, it will be difficult to ensure engine performance at low loads.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pre-chamber combustion four-stroke engine that can ensure engine performance at low loads even without the provision of an ignition assist device.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention has the following configuration.
A main combustion chamber having at least one intake port to which an intake passage is connected and at least one exhaust port to which an exhaust passage is connected, and adjusting the amount of air that passes through the intake passage and is drawn into the main combustion chamber. an intake manifold injection valve which injects liquid fuel such as gasoline fuel, alcohol fuel, or gasoline/alcohol mixed fuel into the intake manifold; a auxiliary chamber whose space communicates with the internal space of the main combustion chamber through a plurality of communication holes, and in which a part of the auxiliary chamber spark plug is exposed to the internal space; and the intake passage injection valve and the auxiliary chamber spark plug. This is a pre-chamber combustion four-stroke engine having a control device for controlling the engine. (a) The control device is configured to cause injection of the liquid fuel to end before an intermediate point between exhaust top dead center and intake bottom dead center in at least a portion of a low load region where the opening degree of the throttle valve is small. and the air-fuel mixture mixed in the intake passage and the main combustion chamber has a first air-fuel ratio that can be processed by a three-way catalyst after combustion, or a second air-fuel ratio that is richer than the first air-fuel ratio. Controls the intake manifold injection valve. (b) The subchamber combustion 4-stroke engine includes both a subchamber fuel injection valve that injects fuel into the subchamber and an ignition assist device that assists in igniting the air-fuel mixture in the subchamber or the main combustion chamber. I don't have it. (c) so as to suppress the ratio of the area of the inner surface of the sub-chamber to the volume of the sub-chamber, (i) no protrusion is formed on the inner surface of the sub-chamber except for the sub-chamber spark plug; and (ii) between the length of the internal space of the subchamber in the plug axial direction parallel to the central axis of the subchamber spark plug and the maximum length of the internal space of the subchamber in the direction orthogonal to the plug axial direction. The length of the larger one is less than twice the length of the smaller one. (d) The liquid fuel injected into the intake passage passes from a first intake port included in the at least one intake port through a first intake hole that is one of the plurality of communication holes to the subchamber. (i) When viewed in the axial direction of the plug, the first intake hole is arranged so that the line segment connecting the center axis of the pre-chamber spark plug and the center of the first intake port is the angle θ formed with the center axis of the first intake hole satisfies -17°<θ<17°, and (ii) the first intake hole is parallel to the center axis of the cylinder hole forming the main combustion chamber; In a cross section cut along a plane including the center axis of the hole, the center axis of the first intake hole is aligned with the valve head of the intake valve and the first intake port when the intake valve that opens and closes the first intake port is opened. It is formed to pass between.

According to this configuration, no protrusions are formed on the inner surface of the subchamber except for the subchamber spark plug. Moreover, the larger length of the length of the internal space of the sub-chamber in the plug axial direction and the maximum length of the internal space of the sub-chamber in the direction perpendicular to the plug axial direction is less than twice the smaller length. These two features suppress the ratio of the area of the inner surface of the subchamber to the volume of the subchamber.
Also, when viewed in a direction parallel to the plug axis direction, the center axis of the pre-chamber spark plug and the center of the first intake port are relative to the center axis of the first intake hole, which is one of the plurality of communication holes. The angle θ formed by the line segment connecting these satisfies -17°<θ<17°. In addition, in a cross section cut along a plane that is parallel to the central axis of the cylinder hole and includes the central axis of the first intake hole, the central axis of the first intake hole is The valve head passes between the valve head and the first intake port. These two features facilitate the introduction of a flow of liquid fuel particles spread along the valve head of the intake valve into the first intake hole when the intake valve is opened. Thereby, the liquid fuel injected into the intake passage is easily introduced into the subchamber from the first intake port through the first intake hole. Note that the communication hole through which the liquid fuel introduced into the auxiliary chamber passes is not limited to the first intake hole among the plurality of communication holes.
In at least a portion of the low load region, injection of liquid fuel by the intake manifold injection valve ends before the midpoint between exhaust top dead center and intake bottom dead center. Therefore, fuel injected into the intake passage from the intake passage injection valve is easily introduced into the main combustion chamber from the intake port. At least in part of the low load region, the air-fuel mixture mixed in the intake passage and the main combustion chamber is at the first air-fuel ratio or at a second air-fuel ratio richer than the first air-fuel ratio. The amount of liquid fuel at low load is also larger than when the air/fuel ratio is lean. However, the amount of liquid fuel at low loads is smaller than the amount of liquid fuel at high loads. In addition, when liquid fuel, which is gasoline fuel, alcohol fuel, or gasoline/alcohol mixed fuel, injected from the intake manifold injection valve is introduced into the main combustion chamber from the intake port, the particles of the liquid fuel are relatively large, and the liquid fuel The inertia of fuel particles is relatively large. As described above, the first intake hole is formed so that the flow of liquid fuel particles dispersed along the valve head of the intake valve is easily introduced, and the inner surface area relative to the volume is formed behind the first intake hole. By forming the pre-chamber to suppress the ratio of It can be introduced deep into the interior. Thereby, the ignitability of the air-fuel mixture in the pre-chamber and the injection force of the flame injected from the plurality of communication holes can be increased, and engine performance at low loads can be ensured even without the provision of an ignition assist device. Note that liquid fuel being introduced into the subchamber does not mean that the fuel is introduced into the subchamber in a liquid state, but is a general term for gasoline fuel, alcohol fuel, and gasoline/alcohol mixed fuel in this application. It simply means that liquid fuel is introduced into the subchamber. High ignitability of the air-fuel mixture means that the air-fuel mixture is easily ignited (ignited).

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
When viewed in the axial direction of the plug, and at the center of the first intake hole, so that the liquid fuel introduced into the auxiliary chamber through the first intake hole is difficult to be discharged from the plurality of communication holes. When viewed in a direction perpendicular to both a plane including the axis and the central axis of the cylinder hole, the central axis of the first intake hole is any one of the plurality of communication holes that is not the first intake hole. The plurality of communicating holes are formed so as not to coincide with the central axis of the holes.

According to this configuration, when viewed in the axial direction of the plug, the center axis of the first intake hole does not coincide with the center axis of any communication hole other than the first intake hole. Furthermore, when viewed in a direction perpendicular to both the plane including the central axis of the first intake hole and the central axis of the cylinder hole, the central axis of the first intake hole is the center of any communication hole other than the first intake hole. It doesn't match the axis either. Therefore, the liquid fuel introduced into the auxiliary chamber through the first intake hole becomes difficult to be discharged from the plurality of communication holes. Therefore, it is easy to introduce the liquid fuel deep into the internal space of the auxiliary chamber. As a result, the ignitability of the air-fuel mixture in the sub-chamber and the injection force of the flames injected from the plurality of communication holes in the sub-chamber can be further improved. Therefore, engine performance at low loads can be more reliably ensured.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
If a half straight line that overlaps the central axis of the communication hole and extends from the communication hole toward the main combustion chamber without passing through the internal space of the auxiliary chamber is defined as the direction line of the communication hole, then the plurality of communication The plurality of intake holes, which are any of the holes, have a shortest distance to the at least one intake port in a circumferential direction around the center axis of the sub-chamber spark plug when viewed in the axial direction of the plug. Each of the direction lines is shorter than the shortest distance to the at least one exhaust port in the circumferential direction around the central axis of the chamber spark plug, and includes the first intake hole, and includes the first air intake hole, and the plurality of communication holes. Any one of the plurality of exhaust holes may have a shortest distance to the at least one exhaust port in a circumferential direction centered on the central axis of the subchamber spark plug when viewed in the plug axial direction. Each of the direction lines is shorter than the shortest distance to the at least one intake port in the circumferential direction around the central axis of the plug, and the number of the plurality of intake holes is smaller than the number of the plurality of exhaust holes. .

According to this configuration, since the number of intake holes is less than the number of exhaust holes, the sum of the cross-sectional areas of multiple intake holes and the number of The diameter of the intake hole can be made larger and the diameter of the exhaust hole can be made smaller while maintaining the total cross-sectional area of the exhaust holes. Therefore, it is easy to introduce the liquid fuel injected into the intake passage into the auxiliary chamber from the plurality of intake holes while maintaining the injection force of the flame injected from the plurality of communication holes. As a result, engine performance at low loads can be more reliably ensured. The liquid fuel may be introduced into the subchamber through a plurality of exhaust holes. In addition, the diameter of the exhaust hole can be made smaller while maintaining the total cross-sectional area of the multiple intake holes and the total cross-sectional area of the multiple exhaust holes, which prevents exhaust gas from being introduced into the subchamber from the exhaust hole. It can be suppressed. Note that the communication hole through which the liquid fuel introduced into the auxiliary chamber passes is not limited to the intake hole among the plurality of communication holes.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
If a half straight line that overlaps the central axis of the communication hole and extends from the communication hole toward the main combustion chamber without passing through the internal space of the auxiliary chamber is defined as the direction line of the communication hole, then the plurality of communication The plurality of exhaust holes, which are any of the holes, have a shortest distance to the at least one exhaust port in a circumferential direction around the central axis of the sub-chamber spark plug when viewed in the axial direction of the plug. Each of the direction lines is shorter than the shortest distance to the at least one intake port in the circumferential direction around the center axis of the chamber spark plug, and the minimum diameter of the first intake hole is the largest of the plurality of exhaust holes. larger than the diameter.

According to this configuration, the minimum diameter of the first intake hole is larger than the maximum diameter of the plurality of exhaust holes, so compared to the case where the minimum diameter of the first intake hole is the same as or smaller than the maximum diameter of the plurality of exhaust holes. The liquid fuel injected into the intake passage can be easily introduced into the auxiliary chamber from the first intake hole while maintaining the injection force of the flame injected from the plurality of communication holes. As a result, engine performance at low loads can be more reliably ensured. Further, since the minimum diameter of the first intake hole is larger than the maximum diameter of the plurality of exhaust holes, it is possible to suppress exhaust gas from being introduced into the subchamber from the exhaust hole. Note that the communication hole through which the liquid fuel introduced into the auxiliary chamber passes is not limited to the intake hole among the plurality of communication holes.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
If a half straight line that overlaps the central axis of the communication hole and extends from the communication hole toward the main combustion chamber without passing through the internal space of the auxiliary chamber is defined as the direction line of the communication hole, then the plurality of communication The plurality of exhaust holes, which are any of the holes, have a shortest distance to the at least one exhaust port in a circumferential direction around the central axis of the sub-chamber spark plug when viewed in the axial direction of the plug. Each of the direction lines is shorter than the shortest distance to the at least one intake port in the circumferential direction around the central axis of the chamber spark plug, and the first intake hole has a diameter that is smaller as it is closer to the main combustion chamber. The plurality of exhaust holes are not formed so that their diameter becomes larger closer to the main combustion chamber.

According to this configuration, the diameter of the first intake hole increases as it approaches the main combustion chamber. The liquid fuel injected into the intake passage can be easily introduced into the auxiliary chamber from the first intake hole while maintaining the injection force of the flame injected from the first intake hole. As a result, engine performance at low loads can be more reliably ensured. Also, because the multiple exhaust holes are not formed so that the diameter becomes larger as they get closer to the main combustion chamber, the exhaust gas is It can be suppressed from being introduced into the subchamber through the hole. Note that the communication hole through which the liquid fuel introduced into the auxiliary chamber passes is not limited to the intake hole among the plurality of communication holes.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
The total area of the cross section perpendicular to the central axis of each of the plurality of communicating holes is 5.7 mm ² or more and 7.6 mm ² or less.

According to this configuration, it is easy to ensure the injection force of the flames injected from the plurality of combustion chambers even when the load is low such as when the engine is idling. Therefore, engine performance at low loads can be more reliably ensured. In addition, when the plurality of communication holes include communication holes whose diameter is not constant, the total area of the cross section perpendicular to the central axis of each of the plurality of communication holes is 5.7 mm ² or more and 7.6 mm ² or less. is at least one of the minimum sum of the areas of cross sections perpendicular to the central axis of each of the plurality of communicating holes, and the maximum value of the sum of the areas of cross sections perpendicular to the central axis of each of the plurality of communicating holes, It means 5.7 mm ² or more and 7.6 mm ² or less. Note that each of the plurality of communication holes may have a constant diameter.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
The minimum diameter of the first intake hole is 1.0 mm or more and 1.2 mm or less, and the volume of the subchamber is 328 mm ³ or more and 802 mm ³ or less.

According to this configuration, it is easy to ensure the injection force of the flames injected from the plurality of combustion chambers even when the load is low such as when the engine is idling. Therefore, engine performance at low loads can be more reliably ensured.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
The minimum diameter of the first intake hole is greater than 1.2 mm and less than or equal to 1.4 mm, and the volume of the subchamber is greater than or equal to 328 mm ³ and less than or equal to 1151 mm ³ .

According to this configuration, it is easy to ensure the injection force of the flames injected from the plurality of combustion chambers even when the load is low such as when the engine is idling. Therefore, engine performance at low loads can be more reliably ensured.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
The plurality of communication holes are formed in a sub-chamber wall portion that protrudes into the internal space of the main combustion chamber. When the internal space of the sub-chamber is divided into two spaces by any plane that passes through the internal space of the sub-chamber and is orthogonal to the plug axis direction without passing through the outer surface of the sub-chamber wall, the two spaces The auxiliary chamber is formed such that the volume of the space closer to the main combustion chamber is smaller than the volume of the space farther from the main combustion chamber of the two spaces.

According to this configuration, although the sub-chamber wall portion protrudes into the internal space of the main combustion chamber, the amount of protrusion is small. Therefore, the plurality of communication holes formed in the sub-chamber wall are close to a portion of the inner surface of the main combustion chamber that is not the outer surface of the sub-chamber wall. Therefore, particles of liquid fuel flowing along the inner surface of the main combustion chamber can be easily introduced into the auxiliary chamber from the first intake hole.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
The pre-chamber combustion four-stroke engine does not have a knock sensor. The control device ignites the air-fuel mixture inside the pre-chamber at a predetermined ignition timing based on the output of an operating state detection sensor that detects the operating state of the pre-chamber combustion four-stroke engine, which is not the knock sensor. The pre-chamber spark plug is controlled so as to.

Since the pre-chamber combustion four-stroke engine has the pre-chamber, it is possible to suppress a sudden increase in the likelihood of knocking when the ignition timing is gradually advanced, compared to a case without the pre-chamber. Moreover, in the present invention, as described above, since the liquid fuel injected into the intake passage is easily introduced into the subchamber, it is possible to further suppress a sudden increase in the likelihood of knocking. Therefore, the ignition timing can be brought closer to the optimal ignition timing called MBT (Minimum advance for Best Torque) while avoiding knocking without using a knock sensor.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
It has neither a supercharger nor a turbocharger.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
The main combustion chamber does not have a fuel injection valve that injects fuel into the main combustion chamber.

A pre-chamber combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
The compression ratio of the pre-chamber combustion four-stroke engine is 11 or more.

In the present invention and embodiments, the low load region is the lower region when the region from the lowest to the highest engine load is divided into two equal parts.

In the present invention and embodiments, ending fuel injection before the midpoint between exhaust top dead center and intake bottom dead center means that the crank angle is between exhaust top dead center and intake bottom dead center in one cycle (four strokes). This means that fuel injection ends before the crank angle reaches the midpoint between dead center and dead center. Middle here means the middle.

In the present invention and embodiments, the air-fuel ratio, which is the mixture ratio of fuel and air, is expressed by a first air-fuel ratio, a second air-fuel ratio, and a third air-fuel ratio. The first air-fuel ratio is an air-fuel ratio that can be processed by the three-way catalyst after combustion. The first air-fuel ratio may be a stoichiometric ratio or a window of air-fuel ratios that includes the stoichiometric ratio. The first air-fuel ratio may be an air-fuel ratio near the stoichiometric air-fuel ratio. The first air-fuel ratio may be a window that includes an air-fuel ratio near the stoichiometric air-fuel ratio but does not include the stoichiometric air-fuel ratio. The second air-fuel ratio is richer than the first air-fuel ratio. If the first air-fuel ratio is an air-fuel ratio near the stoichiometric air-fuel ratio or is in a window that does not include the stoichiometric air-fuel ratio, the second air-fuel ratio may or may not be richer than the stoichiometric air-fuel ratio. good. The third air-fuel ratio is an air-fuel ratio that is leaner than the first air-fuel ratio. In the present invention and embodiments, rich means that the mixture is rich in fuel. Lean means that the mixture is lean in fuel. In the present invention and embodiments, the air-fuel ratio that can be processed by a three-way catalyst after combustion is an air-fuel ratio of the air-fuel mixture that allows exhaust gas generated after combustion of the air-fuel mixture to be processed by a three-way catalyst. The control device controls the intake manifold injection valve so that the air-fuel mixture mixed in the intake manifold and the main combustion chamber has a stoichiometric air-fuel ratio or an air-fuel ratio richer than the stoichiometric air-fuel ratio in at least a portion of the low load region. You may. The pre-chamber combustion four-stroke engine of the present invention has a catalyst disposed in the exhaust passage. The pre-chamber combustion four-stroke engine of the present invention may have a three-way catalyst disposed in the exhaust passage. The pre-chamber combustion four-stroke engine of the present invention may have a catalyst other than a three-way catalyst disposed in the exhaust passage. The pre-chamber combustion four-stroke engine of the present invention includes an oxygen sensor that is disposed between the main combustion chamber and the catalyst and detects the oxygen concentration of exhaust gas flowing through the exhaust passage.

In the present invention and embodiments, the ignition assist device that assists in igniting the air-fuel mixture in the auxiliary chamber or the main combustion chamber is, for example, a device that generates microwave discharge, a device that generates dielectric barrier discharge (silent discharge), etc. , or a spark plug that ignites the air-fuel mixture in the main combustion chamber. In the present invention and embodiments, the fact that the pre-chamber combustion 4-stroke engine does not have an ignition auxiliary device means not only that an ignition auxiliary device separate from the pre-chamber spark plug is not provided, but also that the pre-chamber spark plug This also includes the fact that the ignition assist device does not have the function of an ignition assist device.

In the present invention and embodiments, the subchamber having a smaller volume than the main combustion chamber means that the volume of the subchamber is smaller than the minimum volume of the main combustion chamber. Note that the volume of the main combustion chamber changes as the piston moves. The volume of the subchamber is the volume of the internal space of the subchamber. In the present invention and the embodiments, the internal space of the sub-chamber does not include the internal spaces of the plurality of communication holes. In the present invention and embodiments, the inner surface of the subchamber is a surface that forms the internal space of the subchamber. In the present invention and embodiments, the subchamber spark plug forms part of the inner surface of the subchamber. In the present invention and embodiments, "no protrusion is formed on the inner surface of the subchamber except for the subchamber spark plug" means that no protrusion is formed on the inner surface of the subchamber, or the protrusion formed on the inner surface of the subchamber is the subchamber. This means that there is only a protrusion caused by the spark plug in the chamber.

In the present invention and embodiments, the length of the internal space of the sub-chamber in the plug axial direction is the length in the plug axial direction between one end and the other end of the internal space of the sub-chamber in the plug axial direction. In other words, there is a plane that passes through one end of the internal space of the subchamber in the plug axial direction and is perpendicular to the plug axial direction, and a plane that passes through the other end of the internal space of the subchamber in the plug axial direction and is perpendicular to the plug axial direction. is the distance between. In the present invention and the embodiments, the definition of the length of the internal space of the auxiliary chamber in one direction orthogonal to the plug axis direction is also the same as above. In the present invention and embodiments, the maximum length of the internal space of the auxiliary chamber in the direction orthogonal to the plug axial direction refers to the maximum length of the internal space of the auxiliary chamber in a plurality of directions orthogonal to the plug axial direction. It is the length.

In the present invention and the embodiments, the central axis of the cylinder hole is not a line segment that exists only in the region where the cylinder hole exists, but a straight line that extends infinitely.
In the present invention and the embodiments, the central axis of the sub-chamber spark plug is not a line segment that exists only in the area where the sub-chamber spark plug exists, but is a straight line that extends infinitely. The center axis of the subchamber spark plug may or may not be parallel to the center axis of the cylinder hole.

In the present invention and embodiments, the intake port is the end of the annular portion that contacts the valve head of the intake valve that is closer to the main combustion chamber. The exhaust port is the end of the annular portion that is closer to the main combustion chamber and comes into contact with the valve head of the exhaust valve. The number of at least one intake port in the present invention may be one or more.

In the present invention and the embodiments, the central axis of the first intake hole is not a line segment that exists only in the area where the first intake hole (communication hole) exists, but is a straight line that extends infinitely. The definition of the central axis of the communicating hole is also the same.
In the present invention and embodiments, "a half-line that overlaps the central axis of the communication hole and extends from the communication hole toward the main combustion chamber without passing through the internal space of the auxiliary chamber" refers to the communication hole within the central axis of the communication hole. Does not include parts located inside.
In the present invention and embodiments, the diameter of the first intake hole is the diameter of the first intake hole (communication hole) in a cross section perpendicular to the central axis of the first intake hole (communication hole). The diameter of the exhaust hole, which is a communicating hole, is also defined in the same manner. Furthermore, the diameter of the intake hole, which is a communicating hole, is also defined in the same manner. In the present invention and embodiments, when the maximum diameters of the plurality of exhaust holes are different from each other, the term "the minimum diameter of the first intake hole is larger than the maximum diameter of the plurality of exhaust holes" means that the minimum diameter of the first intake hole is larger than the maximum diameter of the plurality of exhaust holes. This means that it is larger than the maximum value of the respective maximum diameters of the exhaust holes. In the present invention and embodiments, the name intake hole is not used to mean a hole for air intake. The name intake hole is used because the intake hole is a communicating hole close to the intake port. In the present invention and embodiments, the first intake hole is a communicating hole close to the first intake port. In the present invention and embodiments, the name exhaust hole is not used to mean a hole for exhaust air. The exhaust hole is a communicating hole close to the exhaust port, so the name exhaust hole is used.

In the present invention and embodiments, "when the exhaust hole is viewed in the axial direction of the plug, the shortest distance from the pre-chamber spark plug to at least one exhaust port in the circumferential direction around the central axis of the pre-chamber spark plug is "has a direction line shorter than the shortest distance to at least one intake port in the circumferential direction around the central axis of the spark plug" means "has a direction line that is shorter than the shortest distance to at least one intake port in the circumferential direction around the central axis of the pre-chamber spark plug" when viewed in the plug axial direction. The shortest distance between the direction line of this exhaust hole and the at least one exhaust port in the circumferential direction is the shortest distance between the direction line of this exhaust hole and the at least one intake port in the circumferential direction centered on the central axis of the pre-chamber spark plug. It means shorter than the distance. When the direction line of the exhaust hole passes through the exhaust port when viewed in the axial direction of the plug, the shortest distance between the direction line of the exhaust hole and the exhaust port when viewed in the plug axial direction is zero. In the present invention and embodiments, "When the intake hole is viewed in the axial direction of the plug, the shortest distance from the center axis of the pre-chamber spark plug to at least one intake port in the circumferential direction is the center of the pre-chamber spark plug. The definition of "having a direction line shorter than the shortest distance to at least one exhaust port in the circumferential direction around the axis" is also the same as above.

In the present invention and embodiments, the plurality of communication holes may be formed in the sub-chamber wall that projects into the internal space of the main combustion chamber, or may be formed in the sub-chamber wall that does not protrude into the internal space of the main combustion chamber. It's okay. The auxiliary chamber wall portion in which the plurality of communication holes are formed is a wall portion that has one surface (outer surface) exposed to the internal space of the main combustion chamber. When the sub-chamber wall portion has a cylindrical portion, the sub-chamber wall portion is formed to protrude into the internal space of the main combustion chamber. The sub-chamber wall portion may be separate from the sub-chamber spark plug, or may be integrated with the sub-chamber spark plug inseparably. The sub-chamber wall is separate from the sub-chamber spark plug because the member including the sub-chamber wall is separated from the sub-chamber spark plug, or the member including the sub-chamber wall is separate from the sub-chamber spark plug. It means possible contact.

In the present invention and embodiments, the compression ratio of the subchamber combustion four-stroke engine is the ratio of the maximum volume to the minimum volume of the main combustion chamber.

In the present invention and embodiments, the engine operating state detection sensor that detects the operating state of the pre-chamber combustion four-stroke engine is a sensor that detects states related to factors that influence when determining ignition timing. For example, it is a sensor that detects accelerator operation amount, load, engine speed, intake air temperature, intake pressure, intake air amount, atmospheric pressure, engine temperature, oil temperature, cooling water temperature, engine wall temperature, exhaust gas temperature, etc. .

In the present invention and embodiments, if the number of an element is not explicitly specified (i.e., expressed in the singular when translated into English), the number of this element is one. There may be more than one. In the present invention and embodiments, components whose numbers are not clearly specified include, for example, the main combustion chamber, intake passage, exhaust passage, throttle valve, intake passage injection valve, subchamber, subchamber spark plug, etc. be.
The subchamber combustion four-stroke engine according to the present invention and embodiments may have a single main combustion chamber or a plurality of main combustion chambers. That is, the pre-chamber combustion four-stroke engine in the present invention and embodiments may be a single cylinder engine unit or a multi-cylinder engine unit. The number of subchambers and subchamber spark plugs are each the same as the number of main combustion chambers. The number of intake manifold injection valves may be the same as the number of main combustion chambers, or may be greater than that. The number of throttle valves may be the same as the number of main combustion chambers or may be less. The intake passage may have a shape that branches into two or more. The number of intake passages connected to one main combustion chamber is one. One branched intake passage may be connected to a plurality of main combustion chambers. The exhaust passage may have a shape that branches into two or more. The number of exhaust passages connected to one main combustion chamber is one. One branched exhaust passage may be connected to a plurality of main combustion chambers.

The pre-chamber combustion four-stroke engine according to the present invention and embodiments has a lighter vehicle weight than an automobile, and can be installed in a straddle-type vehicle that requires a lighter and more compact engine. A straddle-type vehicle refers to any vehicle in which the driver rides while straddling the saddle. Straddle-type vehicles include motorcycles, scooters, motor tricycles, all-terrain vehicles (ATVs), snowmobiles, personal watercrafts, and the like. Further, the pre-chamber combustion four-stroke engine according to the present invention and the embodiments can be installed in a work vehicle that requires a lightweight and compact engine. It goes without saying that the pre-chamber combustion four-stroke engine according to the present invention and the embodiments can be mounted on an automobile. Products equipped with the pre-chamber combustion four-stroke engine according to the present invention and embodiments are not limited to specific products. When the pre-chamber combustion 4-stroke engine, which is an embodiment of the present invention, is mounted on a product, it may be mounted so that the center axis of the cylinder hole is at an angle of 0 degrees or more and 45 degrees or less with respect to the vertical; It may be mounted so that the angle is greater than or equal to 90 degrees.

In the present invention and embodiments, the words "including," "having," "comprising" and their derivatives include the listed items and their equivalents, as well as additional items. is intended and used.

Unless otherwise defined, all terms (including technical and scientific terms) used in the present invention and embodiments have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be construed to have meanings consistent with the relevant art and their meanings in the context of this disclosure, and should not be interpreted as It cannot be interpreted in any meaningful sense.

In the present invention and embodiments, the term "may" is non-exclusive. "You may" means "you may, but are not limited to this." In the present invention and the embodiments, the configuration described as "may be performed" produces at least the above-mentioned effects obtained by the configuration of the present invention.

Before describing embodiments of the invention in detail, it is to be understood that the invention is not limited to the details of construction and arrangement of components that are described in the following description or illustrated in the drawings. The present invention is also possible in embodiments other than those described below. The present invention is also possible in embodiments in which various changes are made to the embodiments described below.

According to the pre-chamber combustion 4-stroke engine of the present invention, the ignitability of the air-fuel mixture in the pre-chamber and the injection force of the flame injected from the plurality of communication holes can be increased, so even if an ignition auxiliary device is not provided, the combustion efficiency is reduced. Engine performance under load can be ensured.

FIGS. 1(a) and 1(b) are schematic diagrams of an example of a pre-chamber combustion four-stroke engine according to a first embodiment of the present invention. FIGS. 2(a) and 2(b) are schematic diagrams of two examples of a pre-chamber combustion 4-stroke engine according to a second embodiment of the present invention, and FIGS. 2(c) and 2(d) are FIG. 2(e) is a schematic diagram of two examples of a pre-chamber combustion 4-stroke engine according to a third embodiment of the present invention, and FIG. 2(e) is a schematic diagram of an example of a pre-chamber combustion 4-stroke engine according to a fourth embodiment of the present invention. It is. FIGS. 3(a) and 3(b) are schematic diagrams of an example of a pre-chamber combustion four-stroke engine according to a fifth embodiment of the present invention. FIG. 4 is a schematic diagram of an example of a pre-chamber combustion four-stroke engine according to a sixth embodiment of the present invention. FIG. 5 is a partial schematic diagram of an example of a pre-chamber combustion four-stroke engine according to a seventh embodiment of the present invention. FIGS. 6(a) and 6(b) are partial schematic diagrams of an example of a pre-chamber combustion four-stroke engine according to an eighth embodiment of the present invention. FIG. 7 is a schematic diagram of an example of a pre-chamber combustion four-stroke engine according to a ninth embodiment of the present invention. FIG. 8 includes a schematic diagram of an example of a pre-chamber combustion four-stroke engine according to a tenth embodiment of the present invention, and a graph of an example of the present invention and a comparative example showing test results related to the tenth embodiment. FIG. 9 is a graph of an example of the present invention and a comparative example, showing test results related to the pre-chamber combustion four-stroke engine of the eleventh embodiment of the present invention. FIGS. 10(a) and 10(b) are graphs of an example of the present invention and a comparative example, showing test results related to a pre-chamber combustion four-stroke engine according to a twelfth embodiment of the present invention. FIG. 11 is a graph of an example of the present invention and a comparative example, showing test results related to a pre-chamber combustion four-stroke engine according to a thirteenth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of a pre-chamber combustion four-stroke engine, which is an embodiment of the present invention, will be described below with reference to the drawings. Note that the embodiment described below is an example. The present invention is not to be construed as being limited by the embodiments described below.

<First embodiment>
A pre-chamber combustion four-stroke engine 1 according to a first embodiment of the present invention will be described with reference to FIGS. 1(a) and 1(b). FIG. 1(a) and FIG. 1(b) show an example of the first embodiment. The subchamber combustion four-stroke engine 1 of the first embodiment has at least one main combustion chamber 2. The main combustion chamber 2 has at least one intake port 3 to which an intake passage 5 is connected and at least one exhaust port 4 to which an exhaust passage 6 is connected. The main combustion chamber 2 is formed by a cylinder head 10, a cylinder hole 11, and a piston 12. That is, the cylinder hole 11 forms the main combustion chamber 2. Intake passage 5 includes a passage formed inside cylinder head 10 and a passage connected to this passage. The exhaust passage 6 includes a passage formed inside the cylinder head 10 and a passage connected to this passage. The prechamber combustion four-stroke engine 1 has at least one throttle valve 7 . The throttle valve 7 adjusts the amount of air that passes through the intake passage 5 and is drawn into the main combustion chamber 2 . The prechamber combustion four-stroke engine 1 has at least one intake passage injection valve 8 . The intake passage injection valve 8 injects liquid fuel, which is gasoline fuel, alcohol fuel, or gasoline/alcohol mixed fuel, into the intake passage 5 . The pre-chamber combustion four-stroke engine 1 has at least one pre-chamber 20. The internal space of the auxiliary chamber 20 communicates with the internal space of the main combustion chamber 2 via a plurality of communication holes 21 . The volume of the auxiliary chamber 20 is smaller than the volume of the main combustion chamber 2. A portion of the subchamber spark plug 23 is exposed to the internal space of the subchamber 20. The relationship between the position of the central axis C11 of the cylinder hole 11 and the position of the central axis C23 of the pre-chamber spark plug 23 is not limited to the positional relationship shown in FIGS. 1(a) and 1(b). Note that FIG. 1(a) is a cross-sectional view taken along the line AA in FIG. 1(b). A direction parallel to the central axis C23 of the sub-chamber spark plug 23 is defined as a plug axial direction DP. In FIGS. 1(a) and 1(b), the plug axial direction DP is parallel to the central axis C11 of the cylinder hole 11, but the plug axial direction DP does not have to be parallel to the central axis C11 of the cylinder hole 11. . The prechamber combustion four-stroke engine 1 has a control device 70 that controls at least one intake manifold injection valve 8 and at least one prechamber spark plug 23 . The control device 70 is configured such that, in at least part of a low load region where the opening degree of the throttle valve 7 is small, liquid fuel injection ends before the midpoint between the exhaust top dead center and the intake bottom dead center, and the intake air The intake manifold injection valve 8 is operated so that the air-fuel mixture mixed in the passage 5 and the main combustion chamber 2 becomes a first air-fuel ratio that can be processed by the three-way catalyst after combustion, or a second air-fuel ratio that is richer than the first air-fuel ratio. Control. For example, the control device 70 controls the intake passage so that the air-fuel mixture mixed in the intake passage 5 and the main combustion chamber 2 has a first air-fuel ratio that can be processed by the three-way catalyst after combustion in at least a part of the low load region. The injection valve 8 may also be controlled. The pre-chamber combustion four-stroke engine 1 may or may not have a three-way catalyst. The pre-chamber combustion four-stroke engine 1 does not have a pre-chamber fuel injection valve that injects fuel into the pre-chamber 20 and an ignition assist device that assists in igniting the air-fuel mixture in the pre-chamber 20 or the main combustion chamber 2. .

The sub-chamber 20 has the following two features so as to suppress the ratio of the area of the inner surface of the sub-chamber 20 to the volume of the sub-chamber 20. The first feature is that no protrusions are formed on the inner surface of the subchamber 20 except for the subchamber spark plug 23. The second feature is the larger of the length L1 of the internal space of the subchamber 20 in the plug axial direction DP and the maximum length L2 of the internal space of the subchamber 20 in the direction perpendicular to the plug axial direction DP. is smaller than twice the length of the smaller one. Although the length L2 is larger than the length L1 in FIG. 1(a), the length L1 may be larger than the length L2. Note that the shape of the internal space of the subchamber 20 is not limited to the shape shown in FIGS. 1(a) and 1(b).

At least one intake port 3 includes a first intake port 3a. FIG. 1(b) is a diagram when the first intake port 3a and the plurality of communication holes 21 are viewed from the main combustion chamber 2 in the plug axial direction DP. FIG. 1B omits illustration of elements other than the main combustion chamber 2, the first intake port 3a, the plurality of communication holes 21, and the subchamber 20. As shown in FIG. 1(b), a line segment connecting the center axis C23 of the pre-chamber spark plug 23 and the center C3a of the first intake port 3a when viewed in the plug axial direction DP is defined as a line segment LSa. The plurality of communication holes 21 include a first intake hole 21ia having the following two characteristics. The first feature is that when viewed in the plug axial direction DP, the angle θ formed by the line segment LSa with respect to the central axis C21ia of the first intake hole 21ia satisfies -17°<θ<17°. (See Figure 1(b)). In FIG. 1(b), the magnitude (absolute value) of the angle θ is greater than 0°, but the angle θ may be 0°. The second feature is that in a cross section taken along a plane that is parallel to the central axis C11 of the cylinder hole 11 and includes the central axis C21ia of the first intake hole 21ia, the central axis C21ia of the first intake hole 21ia is aligned with the first intake port. It passes between the valve head 14 of the intake valve 13 and the first intake port 3a when the intake valve 13 is opened and closed (see FIG. 1(a)). FIG. 1A is a cross-sectional view of the pre-chamber combustion four-stroke engine 1 taken along a plane parallel to the central axis C11 of the cylinder hole 11 and including the central axis C21ia of the first intake hole 21ia. Since the plurality of communication holes 21 have such first intake holes 21ia, the liquid fuel injected into the intake passage 5 is easily introduced into the subchamber 20 from the first intake port 3a through the first intake holes 21ia. . In FIG. 1, the number of communicating holes 21 is five, but the number of communicating holes 21 may be less than or greater than five. The number, position, shape, and size of the plurality of communication holes 21 in the first embodiment are not limited to those shown in FIG. 1. In addition, in FIG. 1, the intersection of the central axis C21ia of the first intake hole 21ia and the central axis C23 of the subchamber spark plug 23 is located at the main axis in the plug axial direction DP from the electrode portion of the central axis C23 of the subchamber spark plug 23. Although it is close to the combustion chamber 2, it is not limited to this configuration.

The first intake hole 21ia is formed so that the flow of liquid fuel particles diffused along the valve head 14 of the intake valve 13 is easily introduced, and the inner surface area relative to the volume is formed behind the first intake hole 21ia. By forming the subchamber 20 so as to suppress the ratio, liquid fuel having relatively large particles and a relatively large inertial force can be introduced deep into the internal space of the subchamber 20. Thereby, the ignitability of the air-fuel mixture in the pre-chamber 20 and the injection force of the flame injected from the plurality of communication holes 21 can be increased, and engine performance at low loads can be ensured even without the provision of an ignition auxiliary device. .

The compression ratio of the pre-chamber combustion four-stroke engine 1 of the first embodiment may be, for example, 11 or more. The pre-chamber combustion four-stroke engine 1 of the first embodiment does not need to have a main combustion chamber fuel injection valve that injects fuel into the main combustion chamber 2. In other words, the only fuel introduced into the internal spaces of the main combustion chamber 2 and the auxiliary chamber 20 is the fuel injected from the intake manifold injection valve 8. The pre-chamber combustion four-stroke engine 1 of the first embodiment does not need to have either a supercharger or a turbocharger. In other words, the subchamber combustion four-stroke engine 1 may be of a naturally aspirated type. The pre-chamber combustion four-stroke engine 1 of the first embodiment does not need to have an external exhaust recirculation device including an external exhaust recirculation passage that bypasses the main combustion chamber 2 and connects the exhaust passage 6 and the intake passage 5. .

<Second embodiment>
A pre-chamber combustion four-stroke engine 1 according to a second embodiment of the present invention will be described with reference to FIGS. 2(a) and 2(b). FIGS. 2(a) and 2(b) show two examples of the second embodiment. The second embodiment has the configuration of the first embodiment. In the second embodiment, the main combustion chamber 2 has two intake ports 3. The two intake ports 3 are a first intake port 3a and a second intake port 3b. The main combustion chamber 2 may have two exhaust ports 4 as shown in FIGS. 2(a) and 2(b). Although not shown, the main combustion chamber 2 may have a single exhaust port 4. FIGS. 2(a) and 2(b) are views of two intake ports 3, two exhaust ports 4, and a plurality of communication holes 21 viewed from the main combustion chamber 2 in the plug axial direction DP. In the second embodiment, the plurality of communication holes 21 include a second intake hole 21ib having the following two characteristics. The first feature is that, when viewed in the plug axial direction DP, the angle θ2 that the line segment LSb makes with the central axis C21ib of the second intake hole 21ib satisfies -17°<θ2<17°. be. The line segment LSb is a line segment that connects the center axis C23 of the subchamber spark plug 23 and the center C3b of the second intake port 3b. In FIGS. 2(a) and 2(b), the magnitude (absolute value) of the angle θ2 is greater than 0°, but the angle θ2 may be 0°. The second feature is that, although not shown, in a cross section cut along a plane that is parallel to the central axis C11 of the cylinder hole 11 and includes the central axis C21ib of the second intake hole 21ib, the central axis C21ib of the second intake hole 21ib. However, when the intake valve (not shown) that opens and closes the second intake port 3b is opened, the second intake port 3b passes between the valve head of the intake valve and the second intake port 3b. That is, the second intake port 3b and the second intake hole 21ib in the second embodiment have the same characteristics as the first intake port and the first intake hole in the present invention. Since the plurality of communication holes 21 have such second intake holes 21ib, the liquid fuel injected into the intake passage 5 is easily introduced into the subchamber 20 from the second intake port 3b through the second intake holes 21ib. . Note that the number of communicating holes 21 in FIG. 2(a) is five, and the number of communicating holes 21 in FIG. 2(b) is six, but the number of communicating holes 21 in the second embodiment, The position, shape, and size are not limited to those shown in FIGS. 2(a) and 2(b).

<Third embodiment>
A pre-chamber combustion four-stroke engine 1 according to a third embodiment of the present invention will be described using FIG. 2(c) and FIG. 2(d). FIGS. 2(c) and 2(d) show two examples of the third embodiment. The third embodiment has the configuration of the first embodiment. In the third embodiment, the main combustion chamber 2 has a single intake port 3. The single intake port 3 is a first intake port 3a. The main combustion chamber 2 may have a single exhaust port 4 as shown in FIGS. 2(c) and 2(d). Although not shown, the main combustion chamber 2 may have two exhaust ports 4. Note that the number of communicating holes 21 in FIG. 2(c) is five, and the number of communicating holes 21 in FIG. 2(d) is six, but the number of communicating holes 21 in the third embodiment, The position, shape, and size are not limited to those shown in FIG. 2(c) and FIG. 2(d).

<Fourth embodiment>
A pre-chamber combustion four-stroke engine 1 according to a fourth embodiment of the present invention will be described using FIG. 2(e). FIG. 2(e) shows an example of the fourth embodiment. The fourth embodiment has at least one configuration of the first to third embodiments. In the fourth embodiment, the plurality of communication holes 21 include a third intake hole 21ic having the following two characteristics. The first feature is that the angle θ3 formed by the line segment LSa with respect to the central axis C21ic of the third intake hole 21ic satisfies -17°<θ3<17° when viewed in the plug axial direction DP. be. The line segment LSa is a line segment that connects the center axis C23 of the subchamber spark plug 23 and the center C3b of the first intake port 3a. The second feature is that, although not shown, in a cross section cut along a plane that is parallel to the central axis C11 of the cylinder hole 11 and includes the central axis C21ic of the third intake hole 21ic, the central axis C21ic of the third intake hole 21ic. , which passes between the valve head 14 of the intake valve 13 and the first intake port 3a when the intake valve 13, which opens and closes the first intake port 3a, is opened. Since the plurality of communication holes 21 have such a third intake hole 21ic, the liquid fuel injected into the intake passage 5 is easily introduced into the subchamber 20 from the first intake port 3a through the third intake hole 21ic. . The first intake hole 21ia and the third intake hole 21ic in the fourth embodiment each correspond to the first intake hole of the present invention. The number, position, shape, and size of the plurality of communicating holes 21 in the fourth embodiment are not limited to those shown in FIG. 2(e).

<Fifth embodiment>
A pre-chamber combustion four-stroke engine 1 according to a fifth embodiment of the present invention will be described with reference to FIGS. 3(a) and 3(b). 3(a) and 3(b) show an example of the fifth embodiment. The fifth embodiment has at least one configuration of the first to fourth embodiments. In the fifth embodiment, the plurality of communication holes 21 are formed as follows so that the liquid fuel introduced into the subchamber 20 through the first intake hole 21ia is difficult to be discharged from the plurality of communication holes 21. ing. When viewed in the plug axial direction DP, the center axis C21ia of the first intake hole 21ia does not coincide with the center axis C21 of any communication hole 21 other than the first intake hole 21ia among the plurality of communication holes 21 (FIG. 3 (see (b)). FIG. 3(b) is a diagram in which the central axis C21 of the communication holes 21 other than the first intake hole 21ia is added to FIG. 1(a). Furthermore, when viewed in a direction perpendicular to both the plane including the central axis C21ia of the first intake hole 21ia and the central axis C11 of the cylinder hole 11, the central axis C21ia of the first intake hole 21ia is It does not coincide with the central axis C21 of any of the communication holes 21 other than the first intake hole 21ia (see FIG. 3(a)). FIG. 3(a) is a diagram in which the central axis C21 of the communication holes 21 other than the first intake hole 21ia is added to FIG. 1(a). That is, FIG. 3A shows the central axis C21 of the plurality of communication holes 21 when viewed in a direction perpendicular to both the plane including the central axis C21ia of the first intake hole 21ia and the central axis C11 of the cylinder hole 11. is displayed. Note that the number, position, shape, and size of the plurality of communication holes 21 in the fifth embodiment are not limited to those shown in FIGS. 3(a) and 3(b). When the fifth embodiment has the configuration of the second embodiment, when viewed in the plug axial direction DP, the plane is perpendicular to both the plane including the central axis C21ib of the second intake hole 21ib and the central axis C11 of the cylinder hole 11. When viewed in the direction shown in FIG.

<Sixth to Eighth Embodiments>
Pre-chamber combustion four-stroke engines 1 according to sixth to eighth embodiments of the present invention will be described with reference to FIGS. 4, 5, 6(a), and 6(b). FIG. 4 is a diagram of at least one intake port 3, at least one exhaust port 4, and a plurality of communication holes 21 as viewed in the plug axial direction DP. 5 and 6(a) are diagrams of the plurality of communication holes 21 viewed in the plug axial direction DP. FIG. 6(b) is a cross-sectional view taken along line BB in FIG. 6(a). The sixth embodiment has at least one configuration of the first to fifth embodiments. The seventh embodiment has at least one configuration of the first to fifth embodiments. The eighth embodiment has at least one configuration of the first to fifth embodiments. First, common definitions of the sixth to eighth embodiments will be explained. A half straight line that overlaps the central axis of the communication hole 21 and extends from the communication hole 21 toward the main combustion chamber 2 without passing through the internal space of the auxiliary chamber 20 is defined as the direction line H21 of the communication hole 21 (FIG. 4 reference). The shortest distance between the direction line H21 of the communication hole 21 and at least one intake port 3 in the circumferential direction centered on the central axis C23 when viewed in the plug axial direction DP is defined as the shortest distance L3 (see FIG. 4). . The shortest distance L3 between the direction line H21 of the first intake hole 21ia and the at least one intake port 3 in the circumferential direction about the central axis C23 is zero. The shortest distance between the direction line H21 of the communication hole 21 and at least one exhaust port 4 in the circumferential direction centered on the central axis C23 when viewed in the plug axial direction DP is defined as the shortest distance L4 (see FIG. 4). . Among the plurality of communication holes 21, the communication hole 21 having a direction line H21 such that the shortest distance L3 is shorter than the shortest distance L4 is defined as an intake hole 21i (see FIG. 4). The first intake hole 21ia corresponds to the intake hole 21i. In the sixth to eighth embodiments, the plurality of communication holes 21 include at least one intake hole 21ia. Among the plurality of communication holes 21, the communication hole 21 having a direction line H21 such that the shortest distance L4 is shorter than the shortest distance L3 is defined as an exhaust hole 21e (see FIG. 4). In the sixth to eighth embodiments, the plurality of communication holes 21 include a plurality of exhaust holes 21e. Although the main combustion chamber 2 in FIG. 4 has two intake ports 3, the main combustion chamber 2 may have a single intake port 3. Although the main combustion chamber 2 in FIG. 4 has two exhaust ports 4, the main combustion chamber 2 may have a single exhaust port 4.

In the sixth embodiment, the plurality of communication holes 21 include a plurality of intake holes 21i whose number is smaller than the number of plurality of exhaust holes 21e (see, for example, FIG. 4). When the sixth embodiment has the configuration of the second embodiment, the plurality of intake holes 21i may be only the first intake hole 21ia and the second intake hole 21ib, or may be three or more intake holes 21i.

In the seventh embodiment, the minimum diameter of the first intake hole 21ia is larger than the maximum diameter of the plurality of exhaust holes 21e (for example, see FIG. 5). In the seventh embodiment, the number of intake holes 21i may be one or more. In the seventh embodiment, the minimum diameter of the plurality of intake holes 21i may be larger than the maximum diameter of the plurality of exhaust holes 21e. When the seventh embodiment has the configuration of the second embodiment, the minimum diameter of the second intake hole 21ib is preferably larger than the maximum diameter of the plurality of exhaust holes 21e.

In the eighth embodiment, the first intake hole 21ia is formed to have a larger diameter as it is closer to the main combustion chamber 2, and the plurality of exhaust holes 21e are formed to have a larger diameter as it is closer to the main combustion chamber 2. (See, for example, FIGS. 6(a) and 6(b)). In the eighth embodiment, the maximum diameter of the first intake hole 21ia is preferably larger than the maximum diameter of the plurality of exhaust holes 21e. In the eighth embodiment, the number of intake holes 21i may be one or more. In the eighth embodiment, all of the plurality of intake holes 21i may be formed such that the closer they are to the main combustion chamber 2, the larger the diameter. In the eighth embodiment, some of the intake holes 21i among the plurality of intake holes 21i may be formed so that the diameter does not change. When the eighth embodiment has the configuration of the second embodiment, it is preferable that the second intake hole 21ib is formed so that the closer it is to the main combustion chamber 2, the larger the diameter thereof.

The seventh embodiment and the eighth embodiment may or may not have the configuration of the sixth embodiment. In the seventh embodiment and/or the eighth embodiment, the plurality of communication holes 21 may include the plurality of intake holes 21i, the number of which is equal to or greater than the number of the plurality of exhaust holes 21e. The sixth embodiment and the eighth embodiment may or may not have the configuration of the seventh embodiment. In the sixth embodiment and/or the eighth embodiment, the minimum diameter of the first intake hole 21ia may be the same as or smaller than the maximum diameter of at least one exhaust hole 21e of the plurality of exhaust holes 21e. The sixth embodiment and the seventh embodiment may or may not have the configuration of the eighth embodiment. In the sixth embodiment and/or the seventh embodiment, the first intake hole 21ia does not have to be formed so that the closer it is to the main combustion chamber 2, the larger the diameter. In the sixth embodiment and/or the seventh embodiment, the plurality of exhaust holes 21e may be formed such that the closer they are to the main combustion chamber 2, the larger the diameter thereof.

<Ninth embodiment>
A pre-chamber combustion four-stroke engine 1 according to a ninth embodiment of the present invention will be described using FIG. 7. The ninth embodiment has at least one configuration of the first to eighth embodiments. In the ninth embodiment, the plurality of communication holes 21 are formed in a sub-chamber wall portion 22 that protrudes into the internal space of the main combustion chamber 2 . Furthermore, in the ninth embodiment, the sub-chamber 20 is formed such that the amount of protrusion of the sub-chamber wall portion 22 is small relative to the volume of the sub-chamber 20. Specifically, when the internal space of the sub-chamber 20 is divided into two spaces by any plane S that passes through the internal space of the sub-chamber 20 and is perpendicular to the plug axial direction DP without passing through the outer surface of the sub-chamber wall 22. The auxiliary chamber 20 is formed such that the volume of the space closer to the main combustion chamber 2 of the two spaces is smaller than the volume of the space farther from the main combustion chamber 2 of the two spaces. There is. The plane S shown in FIG. 7 is only an example of a plane S that does not pass through the outer surface of the sub-chamber wall portion 22 but passes through the internal space of the sub-chamber 20 and is perpendicular to the plug axial direction DP. Note that the outer surface of the sub-chamber wall portion 22 is a surface exposed to the main combustion chamber 2. When the internal space of the sub-chamber 20 is divided into two spaces by any plane S that passes through the internal space of the sub-chamber 20 and is perpendicular to the plug axial direction DP without passing through the outer surface of the sub-chamber wall 22, the two spaces The auxiliary chamber 20 is formed such that the volume of the space closer to the main combustion chamber 2 is smaller than the volume of the space farther from the main combustion chamber 2 among the two spaces. This means that it is not the sub-chamber 20. The sub-chamber 20 is a sub-chamber 20 in which the following relationship holds true for all planes that do not pass through the outer surface of the sub-chamber wall portion 22 but through the internal space of the sub-chamber 20 and are orthogonal to the plug axial direction DP. . The relationship is that when the internal space of the sub-chamber 20 is divided into two spaces by a plane, the volume of the space closer to the main combustion chamber 2 of the two spaces is The relationship is that the volume of the space farthest from is the same as or larger than that.

<Tenth embodiment>
A pre-chamber combustion four-stroke engine 1 according to a tenth embodiment of the present invention will be described using FIG. 8. The tenth embodiment has at least one configuration of the first to ninth embodiments. The pre-chamber combustion four-stroke engine 1 of the tenth embodiment does not have a knock sensor. The control device 70 ignites the air-fuel mixture inside the pre-chamber 20 at a predetermined ignition timing based on the output of an operating state detection sensor 71 that is not a knock sensor and detects the operating state of the pre-chamber combustion 4-stroke engine 1. The pre-chamber spark plug 23 is controlled to do so.

Here, the graph in FIG. 8 is part of the results of experiments conducted by the present inventors. CA50, which is the horizontal axis of this graph, represents 50% mass fraction burned crank angle, which is the crank angle at which the combustion ratio is 50%. This graph shows the knock peak standard deviation [KPa] when CA50 was changed in the four-stroke engines of Examples 1 to 3 and Comparative Example 1. The engine of Comparative Example 1 does not have a subchamber. The engines of Examples 1 and 2 have a cooling jacket around the subchamber spark plug. The engine of Example 3 does not have a cooling jacket around the pre-chamber spark plug. The engine of Example 1 and the engine of Example 2 differ in the configuration of the electrode portion of the pre-chamber spark plug. The engine of Example 3 and the engine of Example 1 have the same structure of the electrode part of the subchamber spark plug. In Examples 1 to 3 and Comparative Example 1, the test conditions other than the above were the same. The operating range of the engine was a high load range and a medium engine speed range. The high load region is the higher region when the region from the lowest to the highest engine load is divided into two equal parts. Note that the medium engine rotational speed region herein refers to the two intermediate regions when the region from the lowest to the highest engine rotational speed is divided into four equal parts. As can be seen from the graph, in the engine of Comparative Example 1 which does not have a pre-chamber, when the ignition timing is advanced, the knock peak standard deviation [KPa] increases very rapidly at a certain point. On the other hand, in the engines of Examples 1 to 3 having a pre-chamber, even if the ignition timing is advanced, the knock peak standard deviation [KPa] does not suddenly increase, but increases gradually. The inventors of the present invention conducted experiments with different load and engine rotational speed conditions, and found that similar trends were observed under other conditions.

<Eleventh embodiment>
A pre-chamber combustion four-stroke engine 1 according to an eleventh embodiment of the present invention will be described. The eleventh embodiment has at least one configuration of the first to tenth embodiments. In the eleventh embodiment, the total area of the cross section perpendicular to the central axis C21 of each of the plurality of communication holes 21 is 5.7 mm ² or more and 7.6 mm ² or less.

Here, the graph in FIG. 9 is part of the results of experiments conducted by the present inventors. In the following description, the total area of the cross section perpendicular to the central axis of each of the plurality of communication holes that communicate the internal space of the main combustion chamber and the internal space of the auxiliary chamber is referred to as the total area of the holes. FIG. 9 shows IMEPcov, which is the rate of change in IMEP (Indicated Mean Effective Pressure) when CA50 is changed in the four-stroke engines of Examples 4 to 7 and Comparative Examples 2 to 4. The meaning of CA50 is as explained in the tenth embodiment. IMEP is the work per cycle divided by the stroke volume of the engine. The lower the value of IMEPcov, the higher the combustion stability. The test conditions of Examples 4 to 7 and Comparative Examples 2 to 4 are the same. The engine of Comparative Example 2 does not have a subchamber. The engine of Comparative Example 2 has the same configuration as the engines of Examples 4 to 7 and Comparative Examples 3 and 4 except for the presence or absence of the subchamber. The total hole area in the engines of Examples 4 to 7 and Comparative Examples 3 and 4 is shown in Table 1 below. The engines of Examples 4 to 7 and Comparative Examples 3 and 4 have the same configuration except for the plurality of communicating holes.

In the graph of FIG. 9, Comparative Example 3, in which the total hole area is smaller than 5.7 mm ² , and Comparative Example 4, in which the total hole area is larger than 7.6 mm ² , have a smaller area than Comparative Example 2, which does not have an auxiliary chamber. combustion stability is low. On the other hand, Examples 4 to 7 in which the total pore area was 5.7 mm ² or more and 7.6 mm ^{2 or} less had higher combustion stability than Comparative Example 2. Examples 5 and 6, which have a larger total pore area than Example 4 and a smaller total pore area than Example 7, have higher combustion stability than Example 4 and Example 7. The combustion stability of Examples 4 and 7 is comparable. Therefore, from the graph of FIG. 9, it can be seen that the total hole area is preferably 5.7 mm ² or more and 7.6 mm ² or less.

<Twelfth embodiment>
A pre-chamber combustion four-stroke engine 1 according to a twelfth embodiment of the present invention will be described. The twelfth embodiment has at least one configuration of the first to eleventh embodiments. In the twelfth embodiment, the minimum diameter of the first intake hole 21ia is 1.0 mm or more and 1.2 mm or less, and the volume of the subchamber 20 is 328 mm ³ or more and 802 mm ³ or less.

Here, the graphs in FIGS. 10(a) and 10(b) are part of the results of experiments conducted by the present inventors. FIG. 10(a) shows IMEPcov when CA50 is changed in the four-stroke engines of Examples 8 and 9 and Comparative Examples 5 and 6. The test conditions of Examples 8 and 9 and Comparative Examples 5 and 6 are the same. The engine of Comparative Example 5 does not have a subchamber. The engine of Comparative Example 5 has the same configuration as the engines of Examples 8 and 9 and Comparative Example 6 except for the presence or absence of the subchamber. The volumes of the subchambers in the engines of Examples 8 and 9 and Comparative Example 6 are shown in Table 2 below. The engines of Examples 8 and 9 and Comparative Example 6 have the same structure except for the subchamber. The minimum diameters of the first intake holes 21ia in the engines of Examples 8 and 9 and Comparative Example 6 are the same, and are 1.0 mm or more and 1.2 mm or less. In the graph of FIG. 10(a), Comparative Example 6 in which the volume of the pre-chamber is larger than 802 mm ³ has lower combustion stability than Comparative Example 5 in which the pre-chamber is not provided. The combustion stability of Example 9, in which the volume of the subchamber was 802 mm ³ , was comparable to that of Comparative Example 5, in which the subchamber was not provided. Example 8, in which the volume of the subchamber is smaller than 802 mm ³ , has higher combustion stability than Example 9 and Comparative Example 5.

FIG. 10(b) shows IMEPcov when the engine rotational speed is changed in the four-stroke engines of Examples 10 to 12 and Comparative Example 7. The test conditions of Examples 10 to 12 and Comparative Example 7 are the same. The engine of Comparative Example 7 does not have a subchamber. The volumes of the subchambers in the engines of Examples 10 to 12 are shown in Table 3 below. The engines of Examples 10 to 12 have the same structure except for the subchamber. Although the volume of the subchamber in Example 10 is listed as 329 mm ³ in Table 3, it is strictly 328.7 mm ³ . The minimum diameter of the first intake hole 21ia in the engines of Examples 10 to 12 and Comparative Example 7 is 1.2 mm. Generally, there are structural restrictions on reducing the volume of the subchamber. The value of the volume of the subchamber of Example 10, 328.7 mm ³ , is the minimum value of the volume of the subchamber determined by structural constraints. As can be seen from the graph in FIG. 10(b), even if the volume of the subchamber is reduced to the minimum value of the volume of the subchamber determined by structural constraints, the combustion stability does not change much.

From the graphs in FIGS. 10(a) and 10(b), when the minimum diameter of the first intake hole 21ia is 1.0 mm or more and 1.2 mm or less, the volume of the subchamber is preferably 328 mm ³ or more and 802 mm ³ or less. can be estimated.

<13th embodiment>
A pre-chamber combustion four-stroke engine 1 according to a thirteenth embodiment of the present invention will be described. The thirteenth embodiment has at least one configuration of the first to eleventh embodiments. In the thirteenth embodiment, the minimum diameter of the first intake hole 21ia is greater than 1.2 mm and less than or equal to 1.4 mm, and the volume of the subchamber 20 is greater than or equal to 328 mm ³ and less than or equal to 1151 mm ³ .

Here, the graph in FIG. 11 is part of the results of experiments conducted by the present inventors. FIG. 11 shows IMEPcov when CA50 is changed in the four-stroke engines of Examples 13 to 19 and Comparative Example 8. The test conditions of Examples 13 to 19 and Comparative Example 8 are the same. The engine of Comparative Example 8 does not have a subchamber. The engine of Comparative Example 8 has the same configuration as the engines of Examples 13 to 19 except for the presence or absence of the subchamber. The volumes of the subchambers in the engines of Examples 13 to 19 are shown in Table 4 below. The engines of Examples 13 to 19 have the same structure except for the subchamber. The minimum diameters of the first intake holes 21ia in the engines of Examples 13 to 19 are the same, and are greater than 1.2 mm and less than 1.4 mm. Generally, there are structural restrictions on increasing the volume of the subchamber. The value of the volume of the subchamber of Example 19, 1151 mm ³ , is the maximum value of the volume of the subchamber determined by structural constraints. In the graph of FIG. 11, Examples 13 to 19 have higher combustion stability than Comparative Example 8, which does not have a subchamber.

Although the test results are omitted, even if the minimum diameter of the first intake hole 21ia is greater than 1.2 mm and less than 1.4 mm, the volume of the subchamber is 328.7 mm, which is the minimum value determined by structural constraints. The combustion stability of an engine with a rating of ³ is higher than that of an engine without a pre-chamber. Therefore, from the graph of FIG. 11, it can be estimated that when the minimum diameter of the first intake hole 21ia is greater than 1.2 mm and less than 1.4 mm, the volume of the subchamber is preferably 328 mm ³ or more and 1151 mm ³ or less.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims. For example, the plurality of communication holes may be formed in a wall portion of the auxiliary chamber that does not protrude into the internal space of the main combustion chamber. The pre-chamber combustion four-stroke engine of the present invention may have a supercharger or a turbocharger. The prechamber combustion four-stroke engine may have a main combustion chamber fuel injection valve that injects fuel into the main combustion chamber. The compression ratio of the pre-chamber combustion four-stroke engine of the present invention may be smaller than 11.

1: Pre-chamber combustion 4-stroke engine, 2: Main combustion chamber, 3: Intake port, 4: Exhaust port, 3a: First intake port, 5: Intake passage, 6: Exhaust passage, 7: Throttle valve, 8: Intake Passage injection valve, 10: cylinder head, 11: cylinder hole, 13: intake valve, 14: valve head, 20: auxiliary chamber, 21: communication hole, 21ia: first intake hole, 21i: intake hole, 21e: exhaust hole , 22: subchamber wall, 23: subchamber spark plug, 70: control device, 71: operating state detection sensor, C3a: center of first intake port, C11: center axis of cylinder hole, C21: center of communication hole Axis line, C21ia: Central axis of the first intake hole, C23: Central axis of the subchamber spark plug, DP: Plug axial direction, H21: Direction line, L1: Length of the internal space of the subchamber in the plug axial direction, L2: Maximum length of the internal space of the subchamber in the direction orthogonal to the plug axis direction, L3, L4: Shortest distance, LSa: Line segment, S: Plane, θ: Angle

Claims (20)

a main combustion chamber having at least one intake port to which an intake passage is connected and at least one exhaust port to which an exhaust passage is connected;
a throttle valve that adjusts the amount of air that passes through the intake passage and is drawn into the main combustion chamber;
an intake passage injection valve that injects liquid fuel that is gasoline fuel, alcohol fuel, or gasoline/alcohol mixed fuel into the intake passage;
an auxiliary chamber formed to have a smaller volume than the main combustion chamber, whose internal space communicates with the internal space of the main combustion chamber through a plurality of communication holes, and in which a part of the auxiliary chamber spark plug is exposed to the internal space; and,
A pre-chamber combustion four-stroke engine comprising a control device for controlling the intake passage injection valve and the pre-chamber spark plug,
(a) The control device is configured to cause injection of the liquid fuel to end before an intermediate point between exhaust top dead center and intake bottom dead center in at least a portion of a low load region where the opening degree of the throttle valve is small. and the air-fuel mixture mixed in the intake passage and the main combustion chamber has a first air-fuel ratio that can be processed by a three-way catalyst after combustion, or a second air-fuel ratio that is richer than the first air-fuel ratio. Controls the intake passage injection valve,
(b) The subchamber combustion 4-stroke engine includes both a subchamber fuel injection valve that injects fuel into the subchamber and an ignition assist device that assists in igniting the air-fuel mixture in the subchamber or the main combustion chamber. do not have,
(c) so as to suppress the ratio of the area of the inner surface of the sub-chamber to the volume of the sub-chamber, (i) no protrusion is formed on the inner surface of the sub-chamber except for the sub-chamber spark plug; and (ii) between the length of the internal space of the subchamber in the plug axial direction parallel to the central axis of the subchamber spark plug and the maximum length of the internal space of the subchamber in the direction orthogonal to the plug axial direction. The length of the larger one is smaller than twice the length of the smaller one,
(d) The liquid fuel injected into the intake passage passes from a first intake port included in the at least one intake port through a first intake hole that is one of the plurality of communication holes to the subchamber. (i) When viewed in the axial direction of the plug, the first intake hole is arranged so that the line segment connecting the center axis of the pre-chamber spark plug and the center of the first intake port is the angle θ formed with the center axis of the first intake hole satisfies -17°<θ<17°, and (ii) the first intake hole is parallel to the center axis of the cylinder hole forming the main combustion chamber; In a cross section cut along a plane including the center axis of the hole, the center axis of the first intake hole is aligned with the valve head of the intake valve and the first intake port when the intake valve that opens and closes the first intake port is opened. A pre-chamber combustion four-stroke engine characterized by being formed so as to pass between the pre-chambers. When viewed in the axial direction of the plug, and at the center of the first intake hole, so that the liquid fuel introduced into the auxiliary chamber through the first intake hole is difficult to be discharged from the plurality of communication holes. When viewed in a direction perpendicular to both a plane including the axis and the central axis of the cylinder hole, the central axis of the first intake hole is any one of the plurality of communication holes that is not the first intake hole. The pre-chamber combustion four-stroke engine according to claim 1, wherein the plurality of communicating holes are formed so as not to coincide with the center axis of the holes. When a half straight line that overlaps with the central axis of the communication hole and extends from the communication hole toward the main combustion chamber without passing through the internal space of the auxiliary chamber is defined as the direction line of the communication hole,
The plurality of intake holes, which are any of the plurality of communication holes, have the shortest distance to the at least one intake port in the circumferential direction around the central axis of the sub-chamber spark plug, when viewed in the axial direction of the plug. each of the direction lines having a distance shorter than the shortest distance to the at least one exhaust port in the circumferential direction around the central axis of the subchamber spark plug, and including the first intake hole;
The plurality of exhaust holes, which are any of the plurality of communication holes, have the shortest distance to the at least one exhaust port in a circumferential direction centered on the central axis of the pre-chamber spark plug when viewed in the axial direction of the plug. each of the direction lines having a distance shorter than the shortest distance to the at least one intake port in the circumferential direction around the central axis of the subchamber spark plug;
The pre-chamber combustion four-stroke engine according to claim 1, wherein the number of the plurality of intake holes is smaller than the number of the plurality of exhaust holes. When a half straight line that overlaps with the central axis of the communication hole and extends from the communication hole toward the main combustion chamber without passing through the internal space of the auxiliary chamber is defined as the direction line of the communication hole,
The plurality of intake holes, which are any of the plurality of communication holes, have the shortest distance to the at least one intake port in the circumferential direction around the central axis of the sub-chamber spark plug, when viewed in the axial direction of the plug. each of the direction lines having a distance shorter than the shortest distance to the at least one exhaust port in the circumferential direction around the central axis of the subchamber spark plug, and including the first intake hole;
The plurality of exhaust holes, which are any of the plurality of communication holes, have the shortest distance to the at least one exhaust port in a circumferential direction centered on the central axis of the pre-chamber spark plug when viewed in the axial direction of the plug. each of the direction lines having a distance shorter than the shortest distance to the at least one intake port in the circumferential direction around the central axis of the subchamber spark plug;
The pre-chamber combustion four-stroke engine according to claim 2, wherein the number of the plurality of intake holes is smaller than the number of the plurality of exhaust holes. When a half straight line that overlaps with the central axis of the communication hole and extends from the communication hole toward the main combustion chamber without passing through the internal space of the auxiliary chamber is defined as the direction line of the communication hole,
The plurality of exhaust holes, which are any of the plurality of communication holes, have the shortest distance to the at least one exhaust port in a circumferential direction centered on the central axis of the pre-chamber spark plug when viewed in the axial direction of the plug. each of the direction lines having a distance shorter than the shortest distance to the at least one intake port in the circumferential direction around the central axis of the subchamber spark plug;
The pre-chamber combustion four-stroke engine according to claim 1, wherein a minimum diameter of the first intake hole is larger than a maximum diameter of the plurality of exhaust holes. When a half straight line that overlaps with the central axis of the communication hole and extends from the communication hole toward the main combustion chamber without passing through the internal space of the auxiliary chamber is defined as the direction line of the communication hole,
The plurality of exhaust holes, which are any of the plurality of communication holes, have the shortest distance to the at least one exhaust port in the circumferential direction around the central axis of the pre-chamber spark plug, when viewed in the axial direction of the plug. each of the direction lines having a distance shorter than the shortest distance to the at least one intake port in the circumferential direction around the central axis of the subchamber spark plug;
The pre-chamber combustion four-stroke engine according to claim 2, wherein a minimum diameter of the first intake hole is larger than a maximum diameter of the plurality of exhaust holes. When a half straight line that overlaps with the central axis of the communication hole and extends from the communication hole toward the main combustion chamber without passing through the internal space of the auxiliary chamber is defined as the direction line of the communication hole,
The plurality of exhaust holes, which are any of the plurality of communication holes, have the shortest distance to the at least one exhaust port in a circumferential direction centered on the central axis of the pre-chamber spark plug when viewed in the axial direction of the plug. each of the direction lines having a distance shorter than the shortest distance to the at least one intake port in the circumferential direction around the central axis of the subchamber spark plug;
The pre-chamber combustion four-stroke engine according to claim 3, wherein a minimum diameter of the first intake hole is larger than a maximum diameter of the plurality of exhaust holes. When a half straight line that overlaps with the central axis of the communication hole and extends from the communication hole toward the main combustion chamber without passing through the internal space of the auxiliary chamber is defined as the direction line of the communication hole,
The plurality of exhaust holes, which are any of the plurality of communication holes, have the shortest distance to the at least one exhaust port in a circumferential direction centered on the central axis of the pre-chamber spark plug when viewed in the axial direction of the plug. each of the direction lines having a distance shorter than the shortest distance to the at least one intake port in the circumferential direction around the central axis of the subchamber spark plug;
The pre-chamber combustion four-stroke engine according to claim 4, wherein a minimum diameter of the first intake hole is larger than a maximum diameter of the plurality of exhaust holes. The plurality of communication holes are formed in a sub-chamber wall portion that protrudes into the internal space of the main combustion chamber,
When the internal space of the sub-chamber is divided into two spaces by any plane that passes through the internal space of the sub-chamber and is orthogonal to the plug axis direction without passing through the outer surface of the sub-chamber wall, the two spaces The auxiliary chamber is characterized in that the sub-chamber is formed such that the volume of the space closer to the main combustion chamber is smaller than the volume of the space farther from the main combustion chamber of the two spaces. The pre-chamber combustion four-stroke engine according to claim 1. The plurality of communication holes are formed in a sub-chamber wall portion that protrudes into the internal space of the main combustion chamber,
When the internal space of the sub-chamber is divided into two spaces by any plane that passes through the internal space of the sub-chamber and is orthogonal to the plug axis direction without passing through the outer surface of the sub-chamber wall, the two spaces The auxiliary chamber is characterized in that the sub-chamber is formed such that the volume of the space closer to the main combustion chamber is smaller than the volume of the space farther from the main combustion chamber of the two spaces. The pre-chamber combustion four-stroke engine according to any one of claims 2 to 8. When a half straight line that overlaps with the central axis of the communication hole and extends from the communication hole toward the main combustion chamber without passing through the internal space of the auxiliary chamber is defined as the direction line of the communication hole,
The plurality of exhaust holes, which are any of the plurality of communication holes, have the shortest distance to the at least one exhaust port in a circumferential direction centered on the central axis of the pre-chamber spark plug when viewed in the axial direction of the plug. each of the direction lines having a distance shorter than the shortest distance to the at least one intake port in the circumferential direction around the central axis of the subchamber spark plug;
The first intake hole is formed so that its diameter increases as it approaches the main combustion chamber,
The pre-chamber combustion four-stroke engine according to any one of claims 1 to 9 , wherein the plurality of exhaust holes are not formed so that their diameters become larger closer to the main combustion chamber. 10. The total area of the cross section perpendicular to the central axis of each of the plurality of communicating holes is 5.7 mm ² or more and 7.6 mm ^{2 or} less, according to any one of claims 1 to 9 . Pre-chamber combustion 4-stroke engine. The total area of the cross section perpendicular to the central axis of each of the plurality of communicating holes is 5.7 mm. ² 7.6mm or more ² The pre-chamber combustion four-stroke engine according to claim 11, characterized in that: The minimum diameter of the first intake hole is 1.0 mm or more and 1.2 mm or less, and the volume of the subchamber is 328 mm ³ or more and 802 mm ³ or less , or
Any one of claims 1 to 9 , wherein the first intake hole has a minimum diameter of greater than 1.2 mm and less than 1.4 mm, and the volume of the auxiliary chamber is 328 mm ³ or more and 1151 mm ³ or less. The pre-chamber combustion 4-stroke engine according to item 1. The minimum diameter of the first intake hole is 1.0 mm or more and 1.2 mm or less, and the volume of the subchamber is 328 mm ³ or more and 802 mm ³ or less, or
The sub-chamber according to claim 11 , wherein a minimum diameter of the first intake hole is greater than 1.2 mm and less than 1.4 mm, and a volume of the sub-chamber is 328 mm ³ or more and 1151 mm ^{3 or} less. Chamber combustion 4-stroke engine. The minimum diameter of the first intake hole is 1.0 mm or more and 1.2 mm or less, and the volume of the subchamber is 328 mm. ³ 802mm or more ³ is less than or equal to, or
The minimum diameter of the first intake hole is greater than 1.2 mm and less than or equal to 1.4 mm, and the volume of the subchamber is 328 mm. ³ 1151mm or more ³ The pre-chamber combustion four-stroke engine according to claim 12, characterized in that: The pre-chamber combustion 4-stroke engine does not have a knock sensor,
The control device ignites the air-fuel mixture inside the pre-chamber at a predetermined ignition timing based on the output of an operating state detection sensor that detects the operating state of the pre-chamber combustion four-stroke engine, which is not the knock sensor. The pre-chamber combustion four-stroke engine according to any one of claims 1 to 9, wherein the pre-chamber spark plug is controlled so as to. The pre-chamber combustion four-stroke engine according to any one of claims 1 to 9 , characterized in that it has neither a supercharger nor a turbocharger. The pre-chamber combustion four-stroke engine according to any one of claims 1 to 9 , characterized in that it does not have a main combustion chamber fuel injection valve that injects fuel into the main combustion chamber. The pre-chamber combustion four-stroke engine according to any one of claims 1 to 9 , wherein the pre-chamber combustion four-stroke engine has a compression ratio of 11 or more.

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