WO2023157088A1

WO2023157088A1 - Pre-chamber combustion four-stroke engine

Info

Publication number: WO2023157088A1
Application number: PCT/JP2022/005988
Authority: WO
Inventors: 周一江頭
Original assignee: ヤマハ発動機株式会社
Priority date: 2022-02-15
Filing date: 2022-02-15
Publication date: 2023-08-24
Also published as: FR3132735A1; TW202334546A; TWI828417B; JPWO2023157088A1; JP2024056986A

Abstract

A pre-chamber combustion four-stroke engine (1) does not comprise an ignition assistance device that assists in ignition of a gaseous mixture, but does comprise a pre-chamber (20) that is in communication with a main combustion chamber (2) via a plurality of communication holes (21), and that is configured so that a portion of a pre-chamber spark plug (23) is exposed to an internal space of the pre-chamber. A control device (70) controls an intake passage injection valve (8) that injects a fuel into an intake passage (5) so that, in at least a part of a low-load region, a gaseous mixture will have a first air–fuel ratio that allows treatment with a three-way catalyst after combustion or a second air–fuel ratio that is richer than the first air–fuel ratio. A cylinder head (10) comprises a cooling section (16) that accommodates a cooling medium that receives heat from an electrode section (24) of the pre-chamber spark plug and a pre-chamber wall section (22) in which the plurality of communication holes are formed. The following are each formed so as to be dispersed in a circumferential direction: a plurality of spark discharges (33) produced by the electrode section of the pre-chamber spark plug; the plurality of communication holes; a plurality of heat paths (14) from the electrode section of the pre-chamber spark plug to the cooling section; and a plurality of heat paths (15) from the pre-chamber wall section to the cooling section.

Description

Pre-combustion 4-stroke engine

This invention relates to a pre-combustion four-stroke engine having a main combustion chamber and a pre-combustion chamber.

Conventionally, there is known a pre-combustion four-stroke engine having a main combustion chamber and a pre-combustion chamber that communicate with each other through a plurality of communication holes, as disclosed in Patent Document 1, for example. The air-fuel mixture inside the pre-chamber is ignited by a spark plug. The pre-combustion four-stroke engine of Patent Document 1 does not have a pre-chamber fuel injection valve that injects fuel into the pre-chamber, but has an intake passage injection valve that injects fuel into the intake passage. The intake manifold injection valve of Patent Document 1 is controlled such that a stoichiometric or richer than stoichiometric air-fuel mixture is produced in the main combustion chamber. The pre-combustion four-stroke engine of Patent Document 1 has a cooling jacket (cooling section) in the cylinder head. Further, the pre-combustion four-stroke engine of Patent Document 1 has an auxiliary spark plug (ignition auxiliary device) that assists the ignition of the air-fuel mixture in the main combustion chamber.

U.S. Patent No. 10612454

In a pre-combustion four-stroke engine such as that disclosed in Patent Document 1, the area around the plurality of communicating holes and the electrode portion of the spark plug become hot. Since these parts become particularly hot under high load, pre-ignition tends to occur in the vicinity of these parts. Note that pre-ignition is a phenomenon in which an air-fuel mixture self-ignites before being ignited by a spark plug. If the volume of the cooling jacket is increased in order to suppress the occurrence of pre-ignition, the size of the cylinder head will be increased.

An object of the present invention is to provide a pre-combustion four-stroke engine that can suppress the occurrence of pre-ignition while suppressing an increase in the size of the cylinder head.

A pre-combustion four-stroke engine according to one embodiment of the present invention has the following configuration.
A main combustion chamber to which an intake passage and an exhaust passage are connected, a throttle valve that adjusts the amount of air that passes through the intake passage and is sucked into the main combustion chamber, gasoline fuel, alcohol fuel, or a mixture of gasoline and alcohol. an intake passage injection valve for injecting liquid fuel, which is fuel, into the interior of the intake passage; A pre-combustion chamber having a pre-chamber communicating with an internal space of the main combustion chamber and exposing a part of the pre-chamber spark plug to the internal space, and a control device for controlling the intake passage injection valve and the pre-chamber spark plug. It is a 4 stroke engine. In at least a part of a low load region in which the opening of the throttle valve is small, the control device provides a first air-fuel ratio or The intake manifold injection valve is controlled so that the second air-fuel ratio is richer than the first air-fuel ratio. The pre-combustion four-stroke engine has neither a pre-combustion fuel injection valve for injecting fuel into the pre-combustion chamber nor an ignition assist device for assisting ignition of the air-fuel mixture in the pre-combustion chamber or the main combustion chamber. . The cylinder head has a cooling portion that accommodates a cooling medium that receives heat from the electrode portion of the pre-chamber spark plug and the sub-chamber wall portion in which the plurality of communication holes are formed. The electrode portion of the pre-chamber spark plug is formed so that a plurality of spark discharges are generated in the electrode portion in a circumferentially distributed manner, and the plurality of communication holes are formed in a circumferentially-distributed manner to provide the pre-chamber spark. The cylinder head is formed such that a plurality of heat paths from the electrode portion of the plug to the cooling portion and a plurality of heat paths from the auxiliary chamber wall portion to the cooling portion are formed separately in the circumferential direction. is formed.

According to this configuration, the liquid fuel, which is gasoline fuel, alcohol fuel, or gasoline-alcohol mixed fuel, is injected into the intake passage from the intake passage injection valve. In at least part of the low load region, the air-fuel mixture mixed in the intake passage and the main combustion chamber has the first air-fuel ratio or a second air-fuel ratio that is richer than the first air-fuel ratio. Therefore, even when the load is low, there are many positions in the interior space of the pre-chamber where the air-fuel mixture is likely to ignite. Therefore, when using, for example, a spark plug having an electrode portion including a plurality of ground electrodes arranged in the circumferential direction or an annular ground electrode as the pre-chamber spark plug, pre-chamber spark A plurality of spark discharges can be dispersively generated in the circumferential direction at the electrode portion of the plug. A plurality of spark discharges dispersively occur in the circumferential direction, thereby dispersively generating heat in the circumferential direction at the electrode portion of the pre-chamber spark plug.
Moreover, a plurality of communication holes are formed dispersedly in the circumferential direction. Therefore, heat is dispersively generated in the circumferential direction in the sub-chamber wall portion in which the plurality of communication holes are formed.
Thus, heat is dispersively generated in the circumferential direction at the electrode portion and the wall portion of the pre-chamber spark plug. Further, the cylinder head is formed such that a plurality of heat paths from the electrode portion of the pre-chamber spark plug to the cooling portion and a plurality of heat paths from the pre-chamber wall portion to the cooling portion are formed separately in the circumferential direction. is formed. Therefore, heat tends to move from the electrode portion and the wall portion of the pre-chamber spark plug, which are particularly hot, to the cooling portion.
Further, if an auxiliary ignition device such as a spark plug is provided in the main combustion chamber, the temperature of the auxiliary ignition device also becomes high, so heat is less likely to move from a position of the auxiliary chamber wall portion close to the auxiliary ignition device. Since no auxiliary ignition device is provided in the main combustion chamber, it is possible to increase the uniformity in the circumferential direction of the ease of heat transfer from the pre-chamber wall to the cooling part, so heat is transferred from the pre-chamber wall. It's easy to do.
Further, if an auxiliary ignition device is provided in the pre-combustion chamber, the temperature of the auxiliary ignition device will also be high, so that heat will not easily move from a position close to the auxiliary ignition device in the electrode portion of the pre-combustion chamber spark plug. Since the pre-chamber spark plug is not provided with an auxiliary ignition device, it is possible to improve the uniformity in the circumferential direction of the ease of heat transfer from the electrode portion of the pre-chamber spark plug to the cooling portion. Heat is easily transferred from the electrodes.
In this way, since heat is easily transferred from the electrode portion and the wall portion of the pre-chamber spark plug to the cooling portion, it is possible to suppress the occurrence of pre-ignition while suppressing an increase in the size of the cooling portion. Moreover, since an ignition auxiliary device is not provided, it is possible to further suppress an increase in the size of the cylinder head. Therefore, it is possible to suppress the occurrence of pre-ignition while suppressing an increase in the size of the cylinder head.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
The base material of the auxiliary chamber wall has a melting point higher than that of the base material of the cylinder head, a value obtained by multiplying specific heat and specific gravity is higher than that of the base material of the cylinder head, and thermal conductivity is the same as that of chromium-based stainless steel. higher than that.

According to this configuration, the base material of the pre-chamber wall has a higher melting point than the base material of the cylinder head. Therefore, the heat resistance of the pre-chamber wall can be ensured. In addition, the value obtained by multiplying the specific heat and the specific gravity of the base material of the auxiliary chamber wall is higher than that of the base material of the cylinder head. Here, the value obtained by multiplying the specific heat by the specific gravity represents the heat capacity per unit volume. The larger the heat capacity per unit volume, the more difficult it is for the temperature to rise. By forming the base material of the pre-chamber wall from a material that has a higher heat capacity per unit volume than the base material of the cylinder head, the temperature rise of the pre-chamber wall can be suppressed and the high-temperature pre-chamber wall can be dissipated from the cylinder head. Heat is easily transferred to the cooling portion formed in the Also, the base material of the pre-chamber wall portion has a thermal conductivity equal to or higher than that of chromium-based stainless steel. Therefore, heat is more easily transferred from the pre-chamber wall portion to the cooling portion. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
Except for the pre-chamber spark plug, no projection is formed on the inner surface of the pre-chamber, and the axial length of the pre-chamber spark plug in the internal space of the pre-chamber extends in the axial direction of the plug in the internal space of the pre-chamber. Less than twice the maximum length in the orthogonal direction.

If projections were formed on the inner surface of the pre-chamber, heat would easily accumulate in the projections. Since no projections are formed on the inner surface of the pre-chamber except for the spark plug in the pre-chamber, heat is easily transferred from the wall of the pre-chamber to the cooling portion. Further, the length of the internal space of the pre-chamber in the axial direction of the plug is smaller than twice the maximum length of the internal space of the pre-chamber in the direction orthogonal to the axial direction of the plug. Therefore, the peripheral length of the pre-chamber can be made longer while securing the volume of the pre-chamber. As a result, more heat paths can be secured from the auxiliary chamber wall portion to the cooling portion. Therefore, heat is more likely to move from the pre-chamber wall portion to the cooling portion. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
The pre-chamber wall portion is formed to protrude into the internal space of the main combustion chamber, and the plug shaft of the pre-chamber spark plug passes through the internal space of the pre-chamber without passing through the outer surface of the pre-chamber wall portion. When the internal space of the pre-combustion chamber is divided into two spaces by any plane orthogonal to the direction, the volume of the space closer to the main combustion chamber out of the two spaces is The sub-chamber is formed so as to have a smaller volume than the space farther from the main combustion chamber.

According to this configuration, although the auxiliary chamber wall protrudes into the internal space of the main combustion chamber, the amount of protrusion is small. Therefore, heat is less likely to accumulate in the pre-chamber wall, and heat is likely to move from the pre-chamber wall to the cooling section. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
A plane passing through the cooling portion and perpendicular to the plug axial direction of the pre-chamber spark plug passes through the pre-chamber spark plug.

According to this configuration, since the pre-chamber spark plug is close to the cooling portion, the heat of the electrode portion of the pre-chamber spark plug is easily transferred to the cooling portion. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
a pre-chamber member, the interior space of which is separate from both the cylinder head body and the pre-chamber spark plug, the interior space of which is partly exposed to the interior space of the main combustion chamber, and which includes the pre-chamber wall portion; It is a space surrounded by the pre-chamber spark plug.

According to this configuration, compared to the case where the internal space of the pre-chamber is a space surrounded by the pre-chamber member including the pre-chamber wall portion, the pre-chamber spark plug, and other members (for example, the cylinder head body), The pre-chamber member can be elongated in the axial direction of the pre-chamber spark plug while maintaining the shape and size of the internal space of the spark plug. Therefore, when the material of the pre-chamber member is made of a material that facilitates heat transfer, the heat is more easily transferred from the pre-chamber wall portion to the cooling portion. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
A plane passing through the cooling portion and perpendicular to the plug axial direction of the pre-chamber spark plug passes through the pre-chamber member.

According to this configuration, since the pre-chamber member is close to the cooling section, heat is more easily transferred from the pre-chamber wall portion to the cooling section. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
A portion of the inner surface of the cooling portion is at least a portion of the outer peripheral surface of the sub chamber member.

According to this configuration, the cooling medium flowing through the cooling portion contacts the outer peripheral surface of the pre-chamber member. Therefore, heat is more easily transferred from the pre-chamber wall portion to the cooling portion. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
A male thread formed on the pre-chamber spark plug engages and contacts a female thread formed on the sub-chamber member.

According to this configuration, the contact area between the pre-chamber spark plug and the pre-chamber member is large. Therefore, heat is easily transferred from the pre-chamber spark plug to the pre-chamber member. Therefore, heat is easily transferred from the electrode portion of the pre-chamber spark plug to the cooling portion via the pre-chamber member. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
A plane passing through the cooling portion and orthogonal to the axial direction of the plug of the pre-chamber spark plug passes through a portion where the male thread formed in the pre-chamber spark plug engages and contacts the female thread formed in the pre-chamber member. .

According to this configuration, since the pre-chamber member is close to the cooling section, heat is more easily transferred from the pre-chamber wall portion to the cooling section. Furthermore, since the threaded contact portion between the pre-chamber spark plug and the pre-chamber member is close to the cooling portion, heat is more easily transferred from the electrode portion of the pre-chamber spark plug to the cooling portion via the pre-chamber member. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
An outer peripheral surface of the sub chamber member is in contact with the cylinder head body.

According to this configuration, heat is more easily transferred from the pre-chamber wall portion to the cylinder head body than when the outer peripheral surface of the pre-chamber member is not in contact with the cylinder head body. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
A plane that passes through the internal space of the pre-chamber and is perpendicular to the plug axial direction of the pre-chamber spark plug passes through a portion of the outer peripheral surface of the pre-chamber member that contacts the cylinder head body.

According to this configuration, the internal space of the pre-chamber is close to the portion of the outer peripheral surface of the pre-chamber member that contacts the cylinder head body. Therefore, the pre-chamber wall portion is close to the portion of the outer peripheral surface of the pre-chamber member that contacts the cylinder head body. Therefore, heat is likely to move from the auxiliary chamber wall portion to the cylinder head body. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
A plane passing through the internal space of the pre-chamber and orthogonal to the axial direction of the plug passes through a portion where a male thread formed in the pre-chamber member meshes and contacts a female thread formed in the cylinder head body.

According to this configuration, the contact area between the pre-chamber member and the cylinder head body is large. Therefore, heat is more easily transferred from the pre-chamber member to the cylinder head body. As a result, the occurrence of pre-ignition can be further suppressed.

A pre-combustion four-stroke engine according to an embodiment of the present invention may have the following configuration.
There is no main combustion chamber fuel injection valve for injecting fuel into the main combustion chamber.

According to this configuration, it is possible to suppress the increase in size of the cylinder head compared to the case where the main combustion chamber fuel injection valve is provided.

In the present invention and the embodiment, 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 the embodiment, 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 air-fuel 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 air-fuel ratios near the stoichiometric air-fuel ratio and does not include the stoichiometric air-fuel ratio. The second air-fuel ratio is a richer air-fuel ratio than the first air-fuel ratio. If the first air-fuel ratio is an air-fuel ratio near the stoichiometric air-fuel ratio or 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 on fuel. In the present invention and the embodiments, the air-fuel ratio that can be processed by the three-way catalyst after combustion is the air-fuel ratio of the air-fuel mixture at which the exhaust gas generated after the combustion of the mixture can be processed by the three-way catalyst. In the present invention and embodiments, the control device controls the air-fuel ratio so that the air-fuel mixture mixed in the intake passage 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 part of the low load region. Alternatively, the intake manifold injection valve may be controlled. The pre-combustion four-stroke engine of the present invention has a catalyst disposed in the exhaust passage. The pre-combustion four-stroke engine of the present invention may have a three-way catalyst arranged in the exhaust passage. The pre-combustion four-stroke engine of the present invention may have a catalyst other than a three-way catalyst located in the exhaust passage. The pre-combustion four-stroke engine of the present invention has an oxygen sensor which is arranged between the main combustion chamber and the catalyst and which detects the oxygen concentration of the exhaust gas flowing through the exhaust passage.

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

In the present invention and the embodiments, that the volume of the pre-chamber is smaller than that of the main combustion chamber means that the volume of the pre-chamber 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 pre-chamber is the volume of the internal space of the pre-chamber. In the present invention and 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 pre-chamber is the surface forming the internal space of the pre-chamber. In the present invention and embodiments, the pre-chamber spark plug forms part of the inner surface of the pre-chamber. In the present invention and the embodiments, "no protrusions are formed on the inner surface of the pre-chamber except for the pre-chamber spark plug" means that no protrusions are formed on the inner surface of the pre-chamber or the protrusions formed on the inner surface of the pre-chamber are not formed on the inner surface of the pre-chamber. Means only the projection by the chamber spark plug. In the present invention, the sub-chamber wall portion in which a plurality of communication holes are formed is a wall portion having one side exposed to the internal space of the main combustion chamber. The auxiliary chamber wall portion may be formed so as to protrude into the internal space of the main combustion chamber, or may be formed so as not to protrude. When the sub-chamber wall is formed to protrude into the internal space of the main combustion chamber, the sub-chamber wall has a cylindrical portion.

In the present invention and embodiments, the cooling medium is liquid or gas. The liquid cooling medium may be, for example, water or lubricating oil. The gaseous cooling medium may be air, for example. In accordance with the invention and embodiments, the cooling section in which the cooling medium is accommodated is at least one chamber or at least one passageway. A cooling medium may flow through the cooling section. A passage through which the cooling medium flowing into the cooling unit flows and a passage through which the cooling medium discharged from the cooling unit flows may be connected to the cooling unit. The cooling section may be multiple chambers or multiple passages that are not in communication with each other.

In the present invention and embodiments, a heat path is a path through which heat moves. In the present invention and the embodiments, the plurality of heat paths from the electrode portion of the pre-chamber spark plug to the cooling portion are not limited to independent heat paths. That is, heat may be transferable between multiple heat paths. The same applies to the definition of a plurality of heat paths from the pre-chamber wall portion to the cooling portion in the present invention and the embodiments.

In the present invention and embodiments, the electrode portion of the pre-chamber spark plug includes at least one center electrode and at least one ground electrode. The electrode section may include, for example, a single center electrode and multiple or annular ground electrodes. The plurality of ground electrodes may be, for example, two ground electrodes. The plurality of ground electrodes may be, for example, three or more ground electrodes. When the electrode section has a single center electrode and multiple ground electrodes, multiple discharge gaps are formed. When the electrode section has a single center electrode and an annular ground electrode, an annular discharge gap is formed. A spark discharge occurs in the discharge gap. In the present invention and the embodiments, the plug axial direction of the pre-chamber spark plug is a direction parallel to the central axis of the pre-chamber spark plug. The plug axial direction of the pre-combustion chamber spark plug may or may not be parallel to the central axis of the cylinder hole forming the main combustion chamber.

In the present invention and the embodiments, "a plurality of spark discharges are distributed in the circumferential direction" means that the positions where the spark discharges occur are distributed in the circumferential direction. The phrase "a plurality of spark discharges are distributed in the circumferential direction" does not mean that a plurality of spark discharges are simultaneously generated at positions distributed in the circumferential direction. A plurality of spark discharges may occur simultaneously at positions dispersed in the circumferential direction. In this case, at least one spark discharge among the plurality of spark discharges generated at the same time serves as the starting point of ignition. The circumferential direction in the sentence "a plurality of spark discharges are dispersed in the circumferential direction" is, for example, the circumferential direction centered on a straight line parallel to the plug axial direction of the pre-chamber spark plug. An example of a case where a plurality of spark discharges are not dispersed in the circumferential direction is a case where the electrode section has a single center electrode and a single ground electrode. Another example of a case in which a plurality of spark discharges are not dispersed in the circumferential direction is that the electrode section consists of a single center electrode, a mainly used first ground electrode, and an auxiliary used second ground electrode. This is the case with the ground electrode. Another example of a case in which a plurality of spark discharges are not dispersed in the circumferential direction is a case in which positions where the air-fuel mixture is likely to ignite are not substantially uniform in the circumferential direction due to variations in the concentration of the air-fuel mixture inside the pre-chamber. Specific examples of the case where a plurality of spark discharges are not distributed in the circumferential direction are not limited to these.

In the present invention and the embodiment, "a plurality of communication holes are formed dispersedly in the circumferential direction" means that the plurality of communication holes are formed side by side in the circumferential direction without extreme bias. When a plurality of communication holes are formed dispersedly in the circumferential direction, the plurality of communication holes are formed side by side in the circumferential direction. "A plurality of communication holes are formed dispersedly in the circumferential direction" does not necessarily mean that the plurality of communication holes are formed at equal intervals in the circumferential direction. The circumferential direction in the sentence "a plurality of communication holes are formed dispersedly in the circumferential direction" is, for example, the circumferential direction centered on a straight line parallel to the plug axial direction of the pre-chamber spark plug.

In the present invention and the embodiments, "a plurality of heat paths from the electrode portion of the pre-chamber spark plug to the cooling portion are formed in a circumferentially distributed manner" means that the heat path from the electrode portion of the pre-chamber spark plug to the cooling portion It means that the amount of heat that moves is distributed in the circumferential direction. In other words, it means that the degree of easiness of heat transfer from the electrode portion of the pre-chamber spark plug to the cooling portion is substantially uniform in the circumferential direction. The circumferential direction in the sentence "a plurality of heat paths from the electrode part of the pre-chamber spark plug to the cooling part are formed in a circumferentially distributed manner" means, for example, a straight line parallel to the plug axial direction of the pre-chamber spark plug. is the circumferential direction centered on . In the present invention and the embodiments, "a plurality of heat paths from the pre-chamber wall portion to the cooling portion are formed in a circumferentially distributed manner" means that the amount of heat transferred from the pre-chamber wall portion to the cooling portion is distributed in the circumferential direction. means that it is distributed over In other words, it means that the degree of easiness of heat transfer from the pre-chamber wall portion to the cooling portion is substantially uniform in the circumferential direction. The circumferential direction in the sentence “a plurality of heat paths from the pre-chamber wall portion to the cooling portion are dispersed in the circumferential direction” means, for example, a straight line parallel to the axial direction of the pre-chamber spark plug. in the circumferential direction. This may be the same as the circumferential direction in which the plurality of communication holes are arranged.
The electrode portion is formed so that a plurality of spark discharges generated in the electrode portion are dispersed in the circumferential direction. That is, the heat generated in the electrode portion is distributed in the circumferential direction. Therefore, in order for a plurality of heat paths from the electrode portion of the pre-chamber spark plug to the cooling portion to be dispersed in the circumferential direction, there must be a space between the cooling portion and the pre-chamber spark plug and the cooling portion in the cylinder head. parts are important. Also, the plurality of continuous holes formed in the auxiliary chamber wall are dispersed in the circumferential direction. That is, the heat generated in the pre-chamber wall portion is distributed in the circumferential direction. Therefore, in order to form a plurality of heat paths distributed in the circumferential direction from the pre-chamber wall portion to the cooling portion, the cooling portion and the portion between the pre-chamber wall portion and the cooling portion in the cylinder head are important. becomes. For example, when the cooling portion is formed in an annular shape, a plurality of heat paths from the electrode portion of the pre-chamber spark plug to the cooling portion and a plurality of heat paths from the sub-chamber wall portion to the cooling portion are arranged in the circumferential direction. It tends to be dispersed and formed. For example, if the structure (shape and material) of the portion between the pre-chamber spark plug and the cooling section in the cylinder head is substantially uniform in the circumferential direction, multiple heat paths from the electrode section of the pre-chamber spark plug to the cooling section are generated. It tends to be dispersed in the circumferential direction. Further, for example, if the structure (shape and material) of the portion between the pre-chamber wall portion and the cooling portion in the cylinder head is substantially uniform in the circumferential direction, a plurality of heat sources from the electrode portion of the pre-chamber spark plug to the cooling portion may be generated. Paths are likely to be formed dispersed in the circumferential direction. An example of a case where a plurality of heat paths from the electrode portion of the pre-chamber spark plug to the cooling portion is not formed in a circumferentially distributed manner is when the cooling portion is formed only in an area of about half of the circumference. This example may be an example in which a plurality of heat paths from the pre-chamber wall portion to the cooling portion are not formed dispersedly in the circumferential direction. Another example of a case in which a plurality of heat paths from the pre-chamber wall to the cooling section is not formed in a distributed manner in the circumferential direction is that the pre-chamber wall to the cooling section is formed in one half area and the other half area of the circumference. This is the case where the materials between are different. A specific example in which the plurality of heat paths from the electrode portion of the pre-chamber spark plug to the cooling portion is not formed in the circumferential direction, and the case where the plurality of heat paths from the pre-chamber wall portion to the cooling portion are formed in the circumferential direction. Specific examples of the case where the particles are not formed dispersedly are not limited to these.

In the present invention and the embodiments, when the pre-chamber wall portion is composed of a plurality of portions made of different materials, the base material of the pre-chamber wall portion is the material of the portion occupying the largest volume among the plurality of portions. . In addition, in the present invention and the embodiments, the auxiliary chamber wall portion does not have to be composed of a plurality of portions made of different materials.
In the present invention and the embodiments, when the cylinder head is composed of a plurality of portions made of different materials, the base material of the cylinder head is the material of the portion occupying the largest volume among the plurality of portions. When the base material of the pre-chamber wall portion and the base material of the cylinder head are different, the portion occupying the largest volume among the plurality of portions of different materials forming the cylinder head does not include the pre-chamber wall portion. Note that, in the present invention and the embodiments, the cylinder head includes the auxiliary chamber wall. In the present invention and embodiments, the cylinder head body partially exposed to the interior space of the main combustion chamber does not include the auxiliary chamber wall. The base material of the cylinder head body is the same as the base material of the cylinder head. The cylinder head body may or may not consist of multiple parts of different materials.

In the present invention and the embodiments, the fact that the base material of the pre-combustion chamber wall has a thermal conductivity equal to or higher than that of chromium-based stainless steel means It means that the thermal conductivity of the base material of the pre-chamber wall is equal to or higher than that of chromium-based stainless steel under temperature conditions. The temperature of the main combustion chamber and the pre-combustion chamber during operation of the pre-combustion four-stroke engine is, for example, about 850 to 1000.degree.

In the present invention and the embodiments, the axial length of the internal space of the pre-chamber is the axial length of the plug between one end and the other end of the internal space of the pre-chamber in the axial direction of the plug. In other words, a plane passing through one end of the internal space of the pre-chamber in the axial direction of the plug and perpendicular to the axial direction of the plug, and a plane passing through the other end of the internal space of the pre-chamber in the axial direction of the plug and perpendicular to the axial direction of the plug. is the distance between In the present invention and the embodiments, the definition of the length of the interior space of the pre-chamber in one direction perpendicular to the axial direction of the plug is the same as above. In the present invention and the embodiments, the maximum length of the interior space of the pre-chamber in the direction perpendicular to the axial direction of the plug is the maximum length among the lengths of the interior space of the pre-chamber in a plurality of directions perpendicular to the axial direction of the plug. length.

In the present invention and the embodiments, "the plane passing through the cooling portion and perpendicular to the plug axial direction of the pre-chamber spark plug passes through the pre-chamber spark plug" It does not mean that all orthogonal planes pass through the pre-chamber spark plug, but means that any plane that passes through the cooling portion and is perpendicular to the axial direction of the pre-chamber spark plug passes through the pre-chamber spark plug. . In the present invention and the embodiments, "the plane passing through the cooling portion and perpendicular to the plug axial direction of the pre-chamber spark plug passes through the pre-chamber member," "the plane passing through the cooling portion and perpendicular to the plug axial direction of the pre-chamber spark plug." The plane passes through the place where the male thread formed in the pre-chamber spark plug engages and contacts the female thread formed in the pre-chamber member," and "the plane passes through the internal space of the pre-chamber and is orthogonal to the plug axial direction of the pre-chamber spark plug. The sentence "the plane that contacts the cylinder head body passes through the portion of the outer peripheral surface of the pre-chamber member that contacts the cylinder head body" is also interpreted in the same manner as above.

In the present invention and the embodiments, "the sub-chamber member is separate from the cylinder head main body partly exposed to the internal space of the main combustion chamber" means that the sub-chamber member is separated from the cylinder head main body. Alternatively, it means that the sub-chamber member is in separable contact with the cylinder head body. In the present invention and the embodiments, the cylinder head main body may be composed of one inseparable member, or composed of a plurality of separable members each partially exposed to the internal space of the main combustion chamber. may be In the case where the cylinder head body is composed of a plurality of separable members, the cylinder head body does not include a member whose part is not exposed to the interior space of the main combustion chamber.
In the present invention and the embodiments, "the pre-chamber member is separate from the pre-chamber spark plug" means that the pre-chamber member is separated from the pre-chamber spark plug, or that the pre-chamber member is separate from the pre-chamber spark plug. It means that they are in separable contact. The pre-chamber member does not include a portion of the electrode portion of the pre-chamber spark plug (for example, the ground electrode).

In the present invention and embodiments, where the number of an element is not explicitly specified (i.e., when translated into English it appears in the singular), the number of that element is one. may be multiple. In the present invention and embodiments, components whose numbers are not clearly specified include, for example, main combustion chambers, intake passages, exhaust passages, throttle valves, intake passage injection valves, pre-chambers, pre-chamber spark plugs, and the like. be.
A pre-combustion four-stroke engine according to the present invention and embodiments may have a single main combustion chamber or may have multiple main combustion chambers. That is, the pre-combustion four-stroke engine according to the present invention and the embodiments may be a single-cylinder engine unit or a multi-cylinder engine unit. The number of pre-chambers and pre-chamber spark plugs are each the same as the number of main combustion chambers. The number of intake manifold injectors may be the same as the number of main combustion chambers or may be greater. The number of throttle valves may be the same as the number of main combustion chambers, or it may be less. The intake passage may have a shape that branches into two or more. One intake passage is connected to one main combustion chamber. A single 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-combustion four-stroke engine according to the present invention and the embodiment can be mounted on a straddle-type vehicle that is lighter in weight than an automobile and requires a lighter and smaller engine. A straddle-type vehicle refers to a vehicle in general in which the driver straddles a saddle. Straddle-type vehicles include motorcycles, scooters, motor tricycles, ATVs (All Terrain Vehicles), snowmobiles, personal water crafts, and the like. Also, the pre-combustion four-stroke engine according to the present invention and the embodiments can be mounted on a work vehicle that requires a lighter and smaller engine. Needless to say, the pre-combustion four-stroke engine according to the present invention and the embodiments can be mounted on automobiles. The product equipped with the pre-combustion four-stroke engine according to the present invention and the embodiments is not limited to a specific product. When the pre-combustion four-stroke engine that is one embodiment of the present invention is mounted on a product, it may be mounted so that the central axis of the cylinder hole is 0 degrees or more and 45 degrees or less with respect to the vertical, or 45 degrees. You may mount so that it may become more than 90 degrees or less.

In the present invention and embodiments, the terms "including, having, comprising and derivatives thereof" are intended to encompass the recited items and their equivalents as well as additional items. is intended and used.

Unless defined otherwise, 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 are to be construed to have a meaning consistent with their meaning in the context of the relevant technology and this disclosure, and are not idealized or overly formal. not be interpreted in any meaningful way.

In the present invention and embodiments, the term "may" is non-exclusive. "May be" means "may be, but is not limited to." In the present invention and the embodiments, the configuration described as "may" has at least the above effect obtained by the configuration of claim 1.

Before describing embodiments of the present invention in detail, it should be understood that the present invention is not limited to the details of construction and arrangement of components set forth 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 modifications are made to the embodiments described later.

According to the pre-combustion four-stroke engine of the present invention, it is possible to suppress the occurrence of pre-ignition while suppressing the enlargement of the cylinder head.

1(a) to 1(f) are schematic diagrams of a pre-combustion four-stroke engine according to a first embodiment of the present invention. FIG. 2(a) is a schematic diagram of a pre-combustion four-stroke engine according to a third embodiment of the present invention, and FIG. 2(b) is a schematic diagram of a pre-combustion four-stroke engine according to a fourth embodiment of the present invention. It is a diagram. 3(a) to 3(c) are schematic diagrams of three examples of a pre-combustion four-stroke engine according to a fifth embodiment of the present invention. 4(a) to 4(e) are schematic diagrams of five examples of a pre-combustion four-stroke engine according to a fifth embodiment of the present invention. 5(a) and 5(b) are schematic diagrams of two examples of a pre-combustion four-stroke engine according to a fifth embodiment of the present invention.

A pre-combustion four-stroke engine that is an embodiment of the present invention will be described below with reference to the drawings. In addition, 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-combustion four-stroke engine 1 according to a first embodiment of the present invention will be described with reference to FIGS. 1(a) to 1(f). FIG. 1(b) shows an example of a part of the AA cross section of FIG. 1(a). FIGS. 1(c) and 1(d) show two examples of a portion of the BB cross-section of FIG. 1(a). FIGS. 1(e) and 1(f) show two examples of a portion of the CC line section of FIG. 1(a). The pre-combustion four-stroke engine 1 according to the first embodiment has at least one main combustion chamber 2 . An intake passage 5 and an exhaust passage 6 are connected to the main combustion chamber 2 . A main combustion chamber 2 is formed by a cylinder head 10 , a cylinder bore 11 and a piston 12 . The intake passage 5 includes a passage formed inside the 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 pre-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 pre-combustion four-stroke engine 1 has at least one intake manifold 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-combustion four-stroke engine 1 has at least one pre-combustion chamber 20 . The internal space of the auxiliary chamber 20 communicates with the internal space of the main combustion chamber 2 through a plurality of communication holes 21 . The auxiliary chamber 20 has a smaller volume than the main combustion chamber 2 . A part of the pre-chamber spark plug 23 is exposed in the internal space of the pre-chamber 20 . A sub chamber 20 is formed in the cylinder head 10 . A plurality of communication holes 21 are formed in the auxiliary chamber wall portion 22 of the cylinder head 10 . The auxiliary chamber wall portion 22 has one side exposed to the internal space of the main combustion chamber 2 . 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). A direction parallel to the central axis C23 of the pre-chamber spark plug 23 is defined as a plug axial direction DP. 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 need not be parallel to the central axis C11 of the cylinder hole 11. . The shape of the internal space of the auxiliary chamber 20 is not limited to the shape shown in FIGS. 1(a) and 1(b). The pre-combustion four-stroke engine 1 has a control device 70 that controls at least one intake manifold injection valve 8 and at least one pre-chamber spark plug 23 . The control device 70 sets the first air-fuel ratio or The intake manifold injection valve 8 is controlled so that the second air-fuel ratio is richer than the first air-fuel ratio. 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 becomes the 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. Injection valve 8 may be controlled. The pre-combustion four-stroke engine 1 may or may not have a three-way catalyst. The pre-combustion four-stroke engine 1 has neither a pre-combustion fuel injection valve for injecting fuel into the pre-combustion chamber 20 nor an ignition assist device for assisting ignition of the air-fuel mixture in the pre-combustion chamber 20 or the main combustion chamber 2. .

As shown in FIGS. 1(a) and 1(b), the cylinder head 10 accommodates a cooling medium (not shown) that receives heat from the electrode portion 24 and the sub chamber wall portion 22 of the pre chamber spark plug 23. It has a cooling part 16 that is Although the cooling portion 16 is annular in FIG. 1(b), the cooling portion 16 may not be annular. The electrode portion 24 of the pre-chamber spark plug 23 is formed so that a plurality of spark discharges 33 are generated in the electrode portion 24 in a circumferentially distributed manner. A plurality of communication holes 21 are formed dispersedly in the circumferential direction. The cylinder head 10 has a plurality of heat paths 14 from the electrode portion 24 of the pre-chamber spark plug 23 to the cooling portion 16 and a plurality of heat paths 15 from the pre-chamber wall portion 22 to the cooling portion 16 distributed in the circumferential direction. It is formed to be formed by For example, the plurality of spark discharges 33, the plurality of communication holes 21, the plurality of heat paths 14, and the plurality of heat paths 15 are distributed in the circumferential direction around the center axis C23 of the pre-chamber spark plug 23. may be formed. The heat path 14 shown in FIG. 1A is merely an example of the heat path 14 from the electrode portion 24 of the pre-chamber spark plug 23 to the cooling portion 16 . The heat path 15 shown in FIG. 1( a ) is merely an example of the heat path 15 from the auxiliary chamber wall portion 22 to the cooling portion 16 . The two spark discharges 33 shown in FIG. 1(c) are merely an example of the plurality of spark discharges 33 distributed in the electrode portion 24 of the pre-chamber spark plug 23 in the circumferential direction. The plurality of spark discharges 33 shown in FIG. 1(d) is merely an example of the plurality of spark discharges 33 distributed in the electrode portion 24 of the pre-chamber spark plug 23 in the circumferential direction. The configuration of the electrode section 24 is not limited to the configurations shown in FIGS. 1(c) and 1(d). The electrode section 24 may have a single center electrode 30 and a plurality of ground electrodes 31, for example, as shown in FIG. 1(c). The electrode section 24 may have a single center electrode 30 and an annular ground electrode 31, for example, as shown in FIG. 1(d). The plurality of ground electrodes 31 are configured such that spaces are formed between the ground electrodes 31 . The plurality of ground electrodes 31 are separated from the center electrode 30 in a direction orthogonal to the plug axial direction DP. The plurality of ground electrodes 31 are not aligned with the center electrode 30 in the plug axial direction DP. An inner peripheral end of the ring-shaped ground electrode 31 is separated from the center electrode 30 in a direction orthogonal to the plug axial direction DP. Between the single center electrode 30 and the plurality of ground electrodes 31 or the annular ground electrode 31, multiple or annular discharge gaps are formed in a direction orthogonal to the plug axial direction DP. The number of ground electrodes 31 may be two, for example. The number, positions, shapes, and sizes of the plurality of communication holes 21 are not limited to those shown in FIGS. 1(e) and 1(f). The number of communication holes 21 may be, for example, three or more.

According to the configuration of the first embodiment, since heat is easily transferred from the electrode portion 24 of the pre-chamber spark plug 23 and the pre-chamber wall portion 22 to the cooling portion 16, the size of the cooling portion 16 is suppressed and pre-ignition is reduced. It can suppress the occurrence. Moreover, since no auxiliary ignition device is provided, it is possible to further suppress the increase in size of the cylinder head 10 . Therefore, it is possible to suppress the occurrence of pre-ignition while suppressing an increase in the size of the cylinder head 10 .

Note that the pre-combustion four-stroke engine 1 in FIG. 1( a ) is formed such that any plane passing through the cooling portion 16 and perpendicular to the plug axial direction DP passes through the pre-chamber spark plug 23 . This plane is, for example, a plane that overlaps the AA line in FIG. 1(a). In FIG. 1( a ), the pre-combustion four-stroke engine 1 is formed so that none of the planes passing through the cooling section 16 and perpendicular to the plug axial direction DP pass through the internal space of the pre-chamber 20 . In the first embodiment, the pre-combustion four-stroke engine 1 may be formed such that any plane passing through the cooling portion 16 and orthogonal to the plug axial direction DP passes through the interior space of the pre-chamber 20 .

The pre-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 . The pre-combustion four-stroke engine 1 of the first embodiment may have neither a supercharger nor a turbocharger. That is, the pre-combustion four-stroke engine 1 may be of a naturally aspirated type. The auxiliary chamber combustion four-stroke engine 1 of the first embodiment need not have an external exhaust gas recirculation device including an external exhaust gas recirculation passage bypassing the main combustion chamber 2 and connecting the exhaust passage 6 and the intake passage 5. .

<Second embodiment>
A pre-combustion four-stroke engine 1 according to a second embodiment of the present invention will be described. The second embodiment has the configuration of the first embodiment. In the second embodiment, the melting point of the base material of the sub chamber wall portion 22 is higher than the melting point of the base material of the cylinder head 10 . The value obtained by multiplying the specific heat and specific gravity of the base material of the sub chamber wall portion 22 is higher than the value obtained by multiplying the specific heat and specific gravity of the base material of the cylinder head 10 . The thermal conductivity of the base material of the auxiliary chamber wall portion 22 is the same as or higher than that of chromium-based stainless steel. A base material of the cylinder head 10 is, for example, aluminum or an aluminum alloy. When the base material of the cylinder head 10 is aluminum or an aluminum alloy, as the base material of the auxiliary chamber wall portion 22, for example, materials shown in Examples 1 to 4 in Table 1 below may be used. The base material of the auxiliary chamber wall portion 22 may be a chromium-zirconium-copper alloy as in the first embodiment. The base material of the auxiliary chamber wall portion 22 may be a chromium-copper alloy. Comparative Examples 1 to 3 shown in Table 1 are examples of materials that are not used as the base material of the auxiliary chamber wall portion 22 when the base material of the cylinder head 10 is aluminum or an aluminum alloy.

The auxiliary chamber wall portion 22 may be composed only of the base material. The auxiliary chamber wall portion 22 may be composed of a base material and a material other than the base material. For example, the sub-chamber wall portion 22 may have a coating layer of a material different from the base material on at least a portion of the outer surface of the sub-chamber wall portion 22 . The thermal conductivity of the coating layer is preferably higher than that of the auxiliary chamber wall portion 22 .

<Third Embodiment>
A pre-combustion four-stroke engine 1 according to a third embodiment of the present invention will be described with reference to FIG. 2(a). The pre-combustion four-stroke engine 1 of the third embodiment has the following configuration in addition to the configuration of the first or second embodiment. No projections are formed on the inner surface of the pre-chamber 20 except for the pre-chamber spark plug 23 . The length L1 of the internal space of the pre-chamber 20 in the axial direction DP of the plug and the maximum length L2 of the internal space of the sub-chamber 20 in the direction perpendicular to the axial direction DP of the plug, whichever is greater is the length of the smaller one. less than twice. Although the length L2 is longer than the length L1 in FIG. 2(a), the length L1 may be longer than the length L2.

<Fourth Embodiment>
A pre-combustion four-stroke engine 1 according to a fourth embodiment of the present invention will be described with reference to FIG. 2(b). The fourth embodiment has at least one configuration of the first to third embodiments. In the fourth embodiment, the auxiliary chamber wall portion 22 is formed so as to protrude into the internal space of the main combustion chamber 2 . Furthermore, in the fourth embodiment, the auxiliary chamber 20 is formed so that the projection amount of the auxiliary chamber wall portion 22 is smaller than the volume of the auxiliary chamber 20 . Specifically, when the internal space of the pre-chamber 20 is divided into two spaces by any plane S1 that passes through the internal space of the pre-chamber 20 without passing through the outer surface of the pre-chamber wall portion 22 and perpendicular to the plug axial direction DP. The pre-chamber 20 is formed such that the volume of the space closer to the main combustion chamber 2 out of the two spaces is smaller than the volume of the space farther from the main combustion chamber 2 out of the two spaces. there is The plane S1 shown in FIG. 2B is merely an example of a plane S1 that does not pass through the outer surface of the pre-chamber wall portion 22 but passes through the internal space of the pre-chamber 20 and is orthogonal to the axial direction DP of the plug. The outer surface of the auxiliary chamber wall portion 22 is the surface exposed to the main combustion chamber 2 .

<Fifth Embodiment>
3(a) to 3(c), 4(a) to 4(e), 5(a) and 5 ( b) is used for explanation. 3(a) to 3(c) show three examples of the fifth embodiment. Figures 4(a) to 4(e) show five examples of the fifth embodiment. Figures 5(a) and 5(b) show two examples of the fifth embodiment. The fifth embodiment has at least one configuration of the first to fourth embodiments. In the fifth embodiment, the inner surface of the pre-chamber 20 is formed by the pre-chamber member 25 including the pre-chamber wall portion 22 and the pre-chamber spark plug 23 . That is, the internal space of the pre-chamber 20 is a space surrounded by the pre-chamber member 25 and the pre-chamber spark plug 23 . The outer peripheral surface of the pre-chamber spark plug 23 and the inner peripheral surface of the pre-chamber member 25 are in contact with each other. The pre-chamber member 25 is separate from the cylinder head body 13 partially exposed to the internal space of the main combustion chamber 2 and separate from the pre-chamber spark plug 23 . The cylinder head body 13 may be composed of one inseparable member, or may be composed of a plurality of separable members each partly exposed to the internal space of the main combustion chamber 2 . When the cylinder head main body 13 is composed of a plurality of separable members, the cylinder head main body 13 does not include a member whose part is not exposed to the internal space of the main combustion chamber 2 .

For example, as shown in FIGS. 3(a) and 3(b), the outer peripheral surface of the sub chamber member 25 may be in contact with the cylinder head body 13. For example, as shown in FIG. 3(b), a male thread 41 formed in the pre-chamber member 25 may mesh with and be in contact with a female thread 40 formed in the cylinder head body 13. As shown in FIG. When the outer peripheral surface of the pre-chamber member 25 is in contact with the cylinder head body 13, for example, as shown in FIGS. Any of the planes S2 may pass through a portion of the outer peripheral surface of the sub chamber member 25 that contacts the cylinder head body 13 . A plane S2 passing through the contact portion may pass through a portion where the male thread 41 formed in the pre-chamber member 25 meshes and contacts with the female thread 40 formed in the cylinder head body 13, as shown in FIG. 3B, for example. good. The plane S2 passing through the contact portion may pass through portions other than the threaded portions (the male thread 41 and the female thread 40) of the pre-chamber member 25 and the cylinder head body 13, as shown in FIG. 3B, for example. The outer peripheral surface of the pre-chamber member 25 shown in FIG. 3(c) may be in contact with the cylinder head body 13 at a location not shown. For example, any plane (not shown) that passes through the pre-chamber spark plug 23 and does not pass through the internal space of the pre-chamber 20 and is orthogonal to the plug axial direction DP contacts the cylinder head main body 13 on the outer peripheral surface of the pre-chamber member 25 . The outer peripheral surface of the auxiliary chamber member 25 shown in FIG. 3(c) may be in contact with the cylinder head main body 13 so as to pass through the portion where the contact point is formed. In this case, the contact portion between the outer peripheral surface of the sub chamber member 25 and the cylinder head main body 13 may be a threaded portion (the male thread 41 and the female thread 40) or may not be a threaded portion.

The outer peripheral surface of the sub chamber member 25 does not have to be in contact with the cylinder head body 13. For example, the outer peripheral surface of the pre-chamber member 25 shown in FIG. 3(c) does not have to come into contact with the cylinder head body. For example, the sub chamber member 25 may be connected to the cylinder head body via a member other than the cylinder head body 13 (for example, a cylinder head cover).

For example, as shown in FIGS. 4( a ) to 4 ( d ), the pre-chamber member 25 and the cooling chamber member 25 are arranged so that any plane S 3 passing through the cooling portion 16 and perpendicular to the axial direction DP of the plug passes through the pre-chamber member 25 . A portion 16 may be formed. When the plane S3 passes through the pre-chamber member 25, for example, as shown in FIGS. There may be. When the plane S3 passes through the pre-chamber member 25, the inner surface of the cooling part 16 does not have to include a part of the outer peripheral surface of the pre-chamber member 25, as shown in FIG. 4D, for example. Further, as shown in FIG. 4E, for example, the pre-chamber member 25 and the cooling section 16 are formed so that none of the planes S3 passing through the cooling section 16 and perpendicular to the axial direction DP of the plug pass through the pre-chamber member 25. may have been The relationship between the sub chamber member 25 and the cylinder head body 13 shown in FIGS. 4(a) to 4(d) is not limited to the same relationship as in FIG. 3(a), and may be any of the relationships described above. good.

When part of the inner surface of the cooling section 16 is at least part of the outer peripheral surface of the pre-chamber member 25, the pre-chamber member 25 protrudes into the internal space of the cooling section 16, as shown in FIG. 4B, for example. It may have at least one heat dissipation part 26 . The heat radiating portion 26 may or may not be annular. For example, the heat radiating portion 26 may have an arc shape larger than a semicircle, or may not have an arc shape. The annular heat radiating section 26 may be formed so as to partition the internal space of the cooling section 16 into a plurality of spaces. The sub chamber member 25 may have a plurality of heat radiating portions 26 arranged in the plug axial direction DP.

When any plane S3 passing through the cooling part 16 passes through the pre-chamber member 25 (for example, FIGS. 4(a) to 4(d)), any plane S3 passing through the cooling part 16 passes through the pre-chamber member 25. The inner peripheral surface may pass through a portion where it contacts the outer peripheral surface of the pre-chamber spark plug 23 . When any plane S3 passing through the cooling part 16 passes through the pre-chamber member 25, for example, as shown in FIGS. The female thread 42 formed on the member 25 may pass through a portion where it meshes and contacts with the male thread 43 formed on the pre-chamber spark plug 23 . The cooling unit 16 in FIG. 5A is the same as the cooling unit 16 in FIG. 4A, but may be the same as the cooling unit 16 in FIG. 4B. The cooling unit 16 in FIG. 5(b) is the same as the cooling unit 16 in FIG. 4(d), but may be the same as the cooling unit 16 in FIG. 4(c). The relationship between the sub chamber member 25 and the cylinder head body 13 shown in FIGS. 5(a) and 5(b) is not limited to the same relationship as that shown in FIG. good. When any plane S3 passing through the cooling part 16 passes through the pre-chamber member 25, any plane S3 passing through the cooling part 16 is such that the inner peripheral surface of the sub-chamber member 25 contacts the outer peripheral surface of the pre-chamber spark plug 23. You don't have to go through the place where you do.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. For example, the pre-combustion four-stroke engine of the present invention may have a supercharger or a turbocharger. A pre-combustion four-stroke engine may have a main combustion chamber fuel injector that injects fuel into the interior of the main combustion chamber.

1: Pre-combustion 4-stroke engine, 2: Main combustion chamber, 5: Intake passage, 6: Exhaust passage, 7: Throttle valve, 8: Intake passage injection valve, 10: Cylinder head, 11: Cylinder hole, 13: Cylinder Head main body 14: Heat path from electrode part of pre-chamber spark plug to cooling part 15: Plural heat paths from wall part of pre-chamber to cooling part 16: Cooling part 20: Pre-chamber 21: Communication hole , 22: pre-chamber wall portion, 23: pre-chamber spark plug, 24: electrode portion, 25: pre-chamber member, 33: spark discharge, 40: female thread of cylinder head body, 41: male thread of pre-chamber member, 42: sub Female thread of chamber member 43: Male thread of pre-chamber spark plug 70: Control device DP: Plug axial direction L1: Length of internal space of pre-chamber in plug axial direction L2: Plug axis of internal space of pre-chamber Maximum length in the direction orthogonal to the direction, S1, S2, S3: plane

Claims

a main combustion chamber to which the intake passage and the exhaust passage are connected;
a throttle valve that adjusts the amount of air that passes through the intake passage and is sucked into the main combustion chamber;
an intake passage injection valve for injecting liquid fuel, which is gasoline fuel, alcohol fuel, or gasoline-alcohol mixed fuel, into the intake passage;
The cylinder head is formed to have a volume smaller than that of the main combustion chamber, and the internal space thereof communicates with the internal space of the main combustion chamber through a plurality of communication holes. A secondary chamber where the part is exposed,
A pre-chamber combustion four-stroke engine having a control device for controlling the intake passage injection valve and the pre-chamber spark plug,
In at least a part of a low load region in which the opening of the throttle valve is small, the control device provides a first air-fuel ratio or controlling the intake manifold injection valve so that the second air-fuel ratio is richer than the first air-fuel ratio;
The pre-combustion four-stroke engine has neither a pre-combustion fuel injection valve for injecting fuel into the pre-combustion chamber nor an ignition assist device for assisting ignition of the air-fuel mixture in the pre-combustion chamber or the main combustion chamber. ,
The cylinder head has a cooling portion that accommodates a cooling medium that receives heat from the electrode portion of the pre-chamber spark plug and the sub-chamber wall portion in which the plurality of communication holes are formed,
the electrode portions of the pre-chamber spark plug are formed so that spark discharges of the plurality of electrode portions are distributed in the circumferential direction;
The plurality of communication holes are formed dispersedly in the circumferential direction,
A plurality of heat paths from the electrode portion of the pre-chamber spark plug to the cooling portion and a plurality of heat paths from the sub-chamber wall portion to the cooling portion are formed so as to be dispersed in the circumferential direction. A pre-combustion four-stroke engine, characterized in that the cylinder head is formed in.
The base material of the auxiliary chamber wall has a melting point higher than that of the base material of the cylinder head, a value obtained by multiplying specific heat and specific gravity is higher than that of the base material of the cylinder head, and thermal conductivity is the same as that of chromium-based stainless steel. 2. Pre-combustion four-stroke engine according to claim 1, higher than that.
Except for the pre-chamber spark plug, no projection is formed on the inner surface of the pre-chamber, and the axial length of the pre-chamber spark plug in the internal space of the pre-chamber extends in the axial direction of the plug in the internal space of the pre-chamber. 3. Pre-combustion four-stroke engine according to claim 1 or 2, characterized in that it is less than twice the maximum length in the orthogonal direction.
the auxiliary chamber wall portion is formed to protrude into the internal space of the main combustion chamber,
When the internal space of the pre-chamber is divided into two spaces by any plane that passes through the internal space of the pre-chamber without passing through the outer surface of the wall portion of the pre-chamber and is perpendicular to the axial direction of the spark plug of the pre-chamber. The auxiliary chamber is formed such that the volume of the space closer to the main combustion chamber out of the two spaces is smaller than the volume of the space farther from the main combustion chamber out of the two spaces. The pre-combustion four-stroke engine according to any one of claims 1 to 3, characterized in that
5. The pre-chamber combustion four-stroke according to any one of claims 1 to 4, wherein a plane passing through the cooling portion and perpendicular to the plug axial direction of the pre-chamber spark plug passes through the pre-chamber spark plug. engine.
a pre-chamber member, the interior space of which is separate from both the cylinder head body and the pre-chamber spark plug, the interior space of which is partly exposed to the interior space of the main combustion chamber, and which includes the pre-chamber wall portion; The pre-combustion four-stroke engine according to any one of claims 1 to 5, wherein the pre-combustion four-stroke engine is a space surrounded by the pre-combustion chamber spark plug.
The pre-chamber combustion four-stroke engine according to claim 6, wherein a plane passing through the cooling portion and perpendicular to the plug axial direction of the pre-chamber spark plug passes through the pre-chamber member.
The pre-combustion four-stroke engine according to claim 7, wherein a part of the inner surface of the cooling part is at least a part of the outer peripheral surface of the pre-combustion chamber member.
9. The pre-combustion chamber 4 according to any one of claims 6 to 8, wherein a male thread formed on the pre-chamber spark plug is in meshing contact with a female thread formed on the pre-chamber member. stroke engine.
A plane passing through the cooling portion and orthogonal to the axial direction of the plug of the pre-chamber spark plug passes through a portion where the male thread formed in the pre-chamber spark plug engages and contacts the female thread formed in the pre-chamber member. 10. Pre-combustion four-stroke engine according to claim 9, characterized in that:
The pre-combustion four-stroke engine according to any one of claims 6 to 10, wherein the outer peripheral surface of the pre-combustion chamber member is in contact with the cylinder head body.
12. A plane of the pre-chamber spark plug passing through the internal space of the pre-chamber and perpendicular to the axial direction of the plug passes through a portion of the outer peripheral surface of the pre-chamber member that contacts the cylinder head body. A pre-combustion four-stroke engine as described.
A plane which passes through the internal space of the pre-chamber and is orthogonal to the axial direction of the plug passes through a portion where a male thread formed in the pre-chamber member meshes and contacts a female thread formed in the cylinder head body. 13. Pre-combustion four-stroke engine according to claim 12.
The pre-combustion four-stroke engine according to any one of claims 1 to 13, characterized in that it does not have a main combustion chamber fuel injection valve for injecting fuel into the main combustion chamber.