FR3132735A1 - Pre-combustion four-stroke engine - Google Patents

Abstract

The cylinder head (10) of a pre-combustion four-stroke engine (1) includes a cooling unit (16) containing a coolant receiving heat from an electrode group (24) of a spark plug pre-chamber ignition (23) and a pre-chamber wall section (22), where connecting holes (21) are formed. At least in part of the low charge region, spark discharges (33) occur on the electrode group (24), where fuel is injected into the intake passage (5) so that the air-fuel mixture becomes a first air-fuel ratio which can be processed by a three-way catalyst after combustion or a second air-fuel ratio richer than said first ratio. The connection ports (21), heat paths (14) from the electrode group (24) to the cooling unit (16), and heat paths (15) from the prechamber wall section (22) to the cooling unit (16), are each formed so as to be distributed circumferentially. Figure for abstract: Fig. 1

Description

Four-stroke pre-combustion engine

The present invention relates to a four-stroke pre-combustion engine comprising a main combustion chamber and a pre-chamber.
State of the art

Until now, four-stroke pre-combustion engines comprising a main combustion chamber and a pre-chamber which communicate via several connecting ports, as disclosed in patent document 1 for example, are known. An internal air-fuel mixture in the prechamber is ignited by a spark plug. The pre-combustion four-stroke engine in Patent Document 1 has an intake injector that injects the fuel into the intake passage, without having a pre-combustion injector that would inject the fuel into the pre-chamber. The intake injector of patent document 1 is controlled so that an air-fuel mixture with a stoichiometric mixture ratio or richer than a stoichiometric ratio is generated in the main combustion chamber. The pre-combustion four-stroke engine in patent document 1 has a cooling jacket (cooling unit) in the cylinder head. Additionally, the pre-combustion four-stroke engine in Patent Document 1 has an auxiliary spark plug (ignition assist device) that assists in the ignition of the air-fuel mixture in the main combustion chamber.
Previous technical documentation
Patent documentation

Patent Document 1: US Patent Application No. 10612454
Overview of the invention
Problems the invention attempts to solve

In a pre-combustion four-stroke engine like that of Patent Document 1, the areas around the connecting ports and an electrode group of the spark plug are subjected to high temperatures. Self-ignition is likely to occur around these areas, due to their rise to particularly high temperatures during heavy loads. Additionally, auto-ignition is a phenomenon in which the air-fuel mixture ignites on its own before ignition by the spark plug. If the volume of the cooling jacket were ever increased to prevent the occurrence of self-ignition, the size of the cylinder head would increase.

The purpose of the present invention is to provide a four-stroke pre-combustion engine capable of preventing the occurrence of self-ignition, while preventing the increase in the size of the cylinder head.
Ways to solve problems

The four-stroke precombustion engine of one embodiment of the present invention has the following configuration:
It is a four-stroke pre-combustion engine comprising:
- a main combustion chamber in which an intake passage and an exhaust passage connect;
- a throttle valve adjusting the quantity of air which passes through said intake passage and which is admitted into said main combustion chamber;
- an intake injector injecting a liquid fuel into said intake passage, said liquid fuel being a gasoline fuel, an alcohol-based fuel, or a mixture of gasoline fuel and alcohol-based fuel 'alcohol ;
- a pre-chamber, formed in a cylinder head,
the volume of said pre-chamber being smaller than the volume of the main combustion chamber, and
an interior space of the prechamber communicates with that of the main combustion chamber via connecting orifices, and
wherein a portion of a prechamber spark plug is exposed in the interior space of the prechamber; And
- a control device controlling said intake injector and said pre-chamber spark plug;
the four-stroke precombustion engine being characterized in that:
said control device controls said intake injector over at least part of a low load zone where an opening angle of said throttle valve is small, so that an air-fuel mixture is mixed in said passage intake and said main combustion chamber, i.e.:
- a first air/fuel ratio, which can be treated in a three-way catalyst after combustion, or
- a second air/fuel ratio richer than said first air/fuel ratio;
said four-stroke pre-combustion engine not having:
- nor a pre-combustion injector, which would inject the fuel into said pre-chamber,
- nor an ignition assistance device, which would assist in the ignition of the air-fuel mixture in said pre-chamber or said main combustion chamber; And
said cylinder head has a cooling unit containing a cooling product receiving heat from an electrode group of said pre-chamber spark plug and a pre-chamber wall section, where said connection ports are formed;
- said group of electrodes of said pre-chamber spark plug is formed so that several spark discharges occur on said group of electrodes and these spark discharges are distributed circumferentially on said group of electrodes ;
- said connecting orifices are formed so as to be distributed circumferentially; And
- said cylinder head is formed in such a way that thermal paths, starting from said group of electrodes of said pre-chamber spark plug to said cooling unit, and thermal paths, starting from said pre-chamber wall section to 'to said cooling unit, are each formed so as to be distributed circumferentially.

According to this configuration, liquid fuel, which is gasoline fuel, alcohol-based fuel or a mixture of gasoline fuel and alcohol, is injected into the intake passage from the fuel injector. admission. Additionally, over at least a portion of the low load area, the air-fuel mixture, mixed in the intake passage and the main combustion chamber, is the first air-fuel ratio or the second air-fuel ratio plus richer than the first. For this reason, there are many places where the air-fuel mixture is likely to ignite in the interior space of the prechamber, even at low load. Thus, by using as a prechamber spark plug a spark plug having an electrode group which includes, for example, several circumferentially arranged ground electrodes or a circularly shaped ground electrode, it is possible to produce multiple spark discharges dispersed circumferentially on the prechamber spark plug electrode group, at low loads and high loads. The generated heat is distributed circumferentially across the electrode group of the prechamber spark plug, due to the production of circumferentially dispersed spark discharges.
In addition, the connection holes are formed circumferentially. For this reason, the generated heat is distributed circumferentially over the prechamber wall section where the connecting ports are formed.
The generated heat is thus distributed circumferentially over the electrode group of the pre-chamber spark plug and over the pre-chamber wall section. In addition, the cylinder head is formed such that the thermal paths, extending from the electrode group of the prechamber spark plug to the cooling unit, and the other thermal paths, extending from the wall section of the pre-chamber up to the cooling unit, are each formed so as to be distributed circumferentially. For this reason, heat transfer occurs easily from the prechamber spark plug electrode group and the prechamber wall section, which have a particularly high temperature.
In addition, if ever a device to assist the ignition of the spark plug for example is installed in the main combustion chamber, heat transfer takes place more difficult inside the wall section of prechamber from a position close to the ignition assistance device, because the ignition assistance device also has a high temperature. Heat transfer is easily done from the pre-chamber wall section without setting up an ignition aid in the main combustion chamber, as it is possible to increase the uniformity of heat transfer easily in circumferential direction from the pre-chamber wall section towards the cooling unit.
In addition, if an ignition assistance device is ever installed in the pre-chamber, heat transfer is more difficult inside the group of electrodes of the pre-chamber spark plug from 'a position close to the ignition assist device, because the ignition assist device also has a high temperature. Heat transfer is easily done from the electrode group of the pre-chamber spark plug without setting up an ignition assist device in the pre-chamber, as it is possible to further increase the uniformity heat transfer easily in circumferential direction from the electrode group of the prechamber spark plug to the cooling unit.
It is thus possible to prevent the occurrence of self-ignition while preventing the increase in the size of the cooling unit, because the heat transfer is easily done from the electrode group of the spark plug of prechamber and the prechamber wall section on the cooling unit. In addition, the increase in the size of the cylinder head can be further prevented because there is no ignition assist device in place. We can therefore prevent the appearance of self-ignition, while preventing the increase in the size of the cylinder head.

The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: a base material of said pre-chamber wall section may have a higher melting point than a base material of said cylinder head, a value of the base material of said pre-chamber wall section which is obtained by a multiplication of the specific heat and the density, may be greater than that of the base material of said cylinder head, and a thermal conductivity of the material of base of said pre-chamber wall section may be greater than or equal to that of a chromium-based stainless steel.

According to this embodiment, the base material of the prechamber wall section has a higher melting point than the base material of the cylinder head. For this reason, it is possible to maintain the thermal endurance of the pre-chamber wall section. In addition, the value obtained by the multiplication of the specific heat and the density of the base material of the prechamber wall section is greater than the base material of the cylinder head. Here, the value obtained by multiplying the specific heat and the density expresses the volumetric heat capacity. The higher the volumetric heat capacity, the more difficult it is for the temperature to rise. Heat transfer is easily done from the high temperature pre-chamber wall section to the cooling unit formed on the cylinder head, while preventing the temperature of the pre-chamber wall section from increasing, forming the cooling material base of the prechamber wall section with a material with a higher volumetric heat capacity than the base material of the cylinder head. In addition, the thermal conductivity of the base material of the pre-chamber wall section is greater than or equal to that of chromium-based stainless steel. For this reason, heat transfer occurs more easily from the prechamber wall section to the cooling unit. Therefore, the occurrence of self-ignition can be further prevented.

The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: a length of the interior space of the pre-chamber along the axial direction of the plug of said pre-chamber spark plug may be smaller than twice the maximum length of the interior space of the pre-chamber in a direction orthogonal to said axial direction of the spark plug, without a protuberance other than said pre-chamber spark plug being formed on a surface internal of said prechamber.

If a protrusion were formed on the internal surface of the prechamber, heat would easily accumulate on the protrusion. Heat transfer is easily accomplished from the pre-chamber wall section to the cooling unit when no protrusions are formed on the inner surface of the pre-chamber other than the pre-chamber spark plug. In addition, the length of the interior space of the prechamber on the axial direction of the spark plug is smaller than twice the maximum length of the interior space of the prechamber on the direction orthogonal to the axial direction of the spark plug. For this reason, we can enlarge the perimeter of the pre-chamber while maintaining the volume of the pre-chamber. This makes it possible to maintain even more thermal paths from the pre-chamber wall section to the cooling unit. Therefore, heat transfer occurs more easily from the pre-chamber wall section to the cooling unit. Therefore, the occurrence of self-ignition can be further prevented.

The pre-combustion four-stroke engine of an embodiment of the present invention may have the following configuration: said pre-chamber wall section may protrude into the interior space of said main combustion chamber; and by separating the interior space of said pre-chamber into two spaces according to one of the plans:
- crossing the interior space of said pre-chamber without crossing the external surface of said pre-chamber wall section, and
- orthogonally intersecting said axial direction of said prechamber spark plug,
said pre-chamber can be formed so that the volume of the space closest to said main combustion chamber among said two spaces is less than the volume of the space furthest from said main combustion chamber among said two spaces.

According to this embodiment, even if the pre-chamber wall section projects onto the interior space of the main combustion chamber, the volume of this projection is small. For this reason, heat is difficult to accumulate on the pre-chamber wall section, and heat transfer is easy from the pre-chamber wall section to the cooling unit. Therefore, the occurrence of self-ignition can be further prevented.

The four-stroke precombustion engine of one embodiment of the present invention may have the following configuration: a plane, passing through said cooling unit and orthogonal to said axial direction of said prechamber spark plug, may pass through said plug prechamber ignition.

According to this embodiment, the heat from the electrode group of the pre-chamber spark plug is easily transferred to the cooling unit, because the pre-chamber spark plug is close to the cooling unit. Therefore, the occurrence of self-ignition can be further prevented.

The four-stroke pre-combustion engine of one embodiment of the present invention may have the following configuration: the interior space of said pre-chamber may be the space surrounded by said pre-chamber spark plug and by a pre-chamber part , the pre-chamber part may comprise said pre-chamber wall section and may be formed to be independent of both said pre-chamber spark plug and a cylinder head body which may be partially exposed in the interior space of said main combustion chamber.

According to this embodiment, it is possible to extend the pre-chamber part in the axial direction of the pre-chamber spark plug, while maintaining the shape and size of the interior space of the pre-chamber, compared to the case where the interior space of the prechamber is surrounded by the prechamber piece, the prechamber spark plug, and other components (e.g., the cylinder head body) including the prechamber wall section. For this reason, if a material facilitating heat transfer has been chosen as the pre-chamber part material, the heat transfer takes place even more easily from the pre-chamber wall section to the cooling unit. Therefore, the occurrence of self-ignition can be further prevented.

The four-stroke precombustion engine of one embodiment of the present invention may have the following configuration: a plane, passing through said cooling unit and orthogonal to said axial direction of said prechamber spark plug, may pass through said part pre-chamber.

According to this embodiment, heat transfer is even easier from the pre-chamber wall section to the cooling unit, because the pre-chamber room is close to the cooling unit. Therefore, the occurrence of self-ignition can be further prevented.

The four-stroke precombustion engine of one embodiment of the present invention may have the following configuration: part of the internal surface of said cooling unit may be at least part of an external cylindrical surface of said part of pre-chamber.

According to this embodiment, the cooling product circulating in the cooling unit is in contact with the external cylindrical surface of the pre-chamber part. For this reason, heat transfer occurs more easily from the prechamber wall section to the cooling unit. Therefore, the occurrence of self-ignition can be further prevented.

The four-stroke pre-combustion engine of one embodiment of the present invention may have the following configuration: an external thread, formed on said pre-chamber spark plug, may be assembled and in contact with an internal thread formed on said pre-chamber room.

According to this embodiment, the contact surface between the pre-chamber spark plug and the pre-chamber part is large. For this reason, heat transfer occurs easily from the prechamber spark plug to the prechamber part. Therefore, heat transfer occurs easily from the electrode group of the pre-chamber spark plug to the cooling unit via the pre-chamber piece. Therefore, the occurrence of self-ignition can be further prevented.

The four-stroke precombustion engine of one embodiment of the present invention may have the following configuration: a plane, passing through said cooling unit and orthogonal to the axial direction of said prechamber spark plug, may pass through the part wherein said external thread formed on said pre-chamber spark plug assembles and is in contact with said internal thread formed on said pre-chamber part.

According to this embodiment, heat transfer is even easier from the pre-chamber wall section to the cooling unit, because the pre-chamber room is close to the cooling unit. In addition, heat transfer occurs even more easily from the electrode group of the pre-chamber spark plug to the cooling unit via the pre-chamber piece, because the part in contact with the spark plug of prechamber and the prechamber room is close to the cooling unit. Therefore, the occurrence of self-ignition can be further prevented.

The four-stroke pre-combustion engine of one embodiment of the present invention may have the following configuration: the external cylindrical surface of said pre-chamber part may be in contact with said cylinder head body.

According to this embodiment, heat transfer takes place easily from the pre-chamber wall section to the cylinder head body, compared to the case where the external cylindrical surface of the pre-chamber part is not in contact with the body. of cylinder head. Therefore, the occurrence of self-ignition can be further prevented.

The four-stroke pre-combustion engine of one embodiment of the present invention may have the following configuration: a plane, crossing the interior space of said pre-chamber and orthogonal to the axial direction of said pre-chamber spark plug, may pass through the part where the external cylindrical surface of said pre-chamber part is in contact with said body of the cylinder head.

According to this embodiment, the interior space of the pre-chamber is close to the part where the external cylindrical surface of the pre-chamber part is in contact with the cylinder head body. Therefore, the pre-chamber wall section is close to the part where the outer cylindrical surface of the pre-chamber part is in contact with the cylinder head body. For this reason, heat transfer occurs more easily from the prechamber wall section to the cylinder head body. Therefore, the occurrence of self-ignition can be further prevented.

The four-stroke precombustion engine of one embodiment of the present invention can have the following configuration: a plane, crossing the interior space of the prechamber and orthogonal to said axial direction of the spark plug, can cross the part where the external thread formed on said pre-chamber part which assembles and is in contact with said thread formed on said cylinder head body.

According to this embodiment, the contact surface between the pre-chamber part and the cylinder head body is large. For this reason, heat transfer takes place even more easily from the pre-chamber part to the cylinder head body. Therefore, the occurrence of self-ignition can be further prevented.

The four-stroke pre-combustion engine of one embodiment of the present invention may have the following configuration: the four-stroke pre-combustion engine may be characterized by the absence of a main combustion chamber fuel injector, which would inject the fuel inside said main combustion chamber.

According to this embodiment, the increase in the size of the cylinder head can be prevented compared to the case where a main combustion chamber fuel injector is provided.

In the present invention and its embodiments, the low load zone is the lowest zone when the load zone of the heat engine is divided into two equal parts going from the lowest zone to the highest zone.

In the present invention and embodiments thereof, the air/fuel ratio, which is the mixing ratio between fuel and air, is represented by a first air/fuel ratio, a second air/fuel ratio, and a third air/fuel ratio. The first air/fuel ratio is the air/fuel ratio that can be treated with a three-way catalyst after combustion. The first air/fuel ratio may be the theoretical mixture ratio (stoichiometric ratio), or an air/fuel ratio range including the theoretical mixture ratio. The first air/fuel ratio may be an air/fuel ratio close to the stoichiometric ratio. The first air/fuel ratio may be a range that includes an air/fuel ratio close to the stoichiometric ratio but does not include the stoichiometric 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 close to the stoichiometric ratio, or a range not including the stoichiometric ratio, the second air/fuel ratio may or may not be richer than the stoichiometric ratio. The third air/fuel ratio is leaner than the first air/fuel ratio. In the present invention and embodiments thereof, "rich" means that the fuel in the air-fuel mixture is denser. “Lean” means the fuel in the air-fuel mixture is weaker. In the present invention and embodiments thereof, the air/fuel ratio treatable with a three-way catalyst after combustion is an air/fuel ratio such that the exhaust gas produced after combustion of the air-fuel mixture can be treated with a three-way catalyst. In the present invention and embodiments thereof, the controller can control the intake injector over at least a portion of the low load area, such that the air-fuel mixture mixed in the intake passage and the main combustion chamber, either the stoichiometric ratio or an air/fuel ratio richer than the stoichiometric ratio. 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 disposed in the exhaust passage. The pre-combustion four-stroke engine of the present invention may have a catalyst that is not a three-way catalyst disposed in the exhaust passage. The four-stroke pre-combustion engine of the present invention has a lambda probe which is disposed between the main combustion chamber and the catalyst, and which detects the oxygen concentration of the exhaust gas flowing in the exhaust passage.

In the present invention and its embodiments, the ignition assistance device, which helps ignite the air-fuel mixture in the prechamber or the main combustion chamber, is for example a device generating discharges by microwave, a device generating dielectric barrier discharges (silent discharges), or, a spark plug that ignites the air-fuel mixture in the main combustion chamber, among others. In the present invention and embodiments thereof, the expression "the pre-combustion four-stroke engine does not have an ignition assist device" does not only include the absence of an ignition assist device to the separate ignition of the pre-chamber spark plug, but also the absence of an ignition assist device function in the pre-chamber spark plug.

In the present invention and its embodiments, the expression “the volume of the pre-chamber is smaller than that of the main combustion chamber” means that the volume of the pre-chamber is less than the minimum volume of the main combustion chamber. Additionally, the volume of the main combustion chamber varies with the movement of the piston. The prechamber volume is the volume of the interior space of the prechamber. In the present invention and its embodiments, the interior space of the prechamber does not include the internal space of the connecting ports. In the present invention and its embodiments, the internal surface of the pre-chamber is the surface which forms the interior space of the pre-chamber. In the present invention and embodiments thereof, the prechamber spark plug forms a portion of the internal surface of the prechamber. In the present invention and its embodiments, the expression "no protrusion is formed on the internal surface of the pre-chamber apart from the pre-chamber spark plug" means that no protrusion is formed on the surface internal of the pre-chamber, or that a protrusion formed on the surface is solely due to the pre-chamber spark plug. In the present invention, the pre-chamber wall section where the connecting ports are formed is the wall section having one side exposed in the interior space of the main combustion chamber. The pre-chamber wall section may be formed to protrude into the interior space of the main combustion chamber, or not. If the pre-chamber wall section is formed to protrude into the interior space of the main combustion chamber, the pre-chamber wall section has a tubular part.

In the present invention and its embodiments, the cooling product is liquid or gaseous. The cooling product in liquid form can be, for example, water or lubricating oil. The cooling product in gaseous form can be air for example. In the present invention and its embodiments, the cooling unit containing the cooling product is at least one chamber, or at least one passage. Coolant may flow through the cooling unit. The passage, where the cooling product flowing into the cooling unit flows, and the passage, where the cooling product discharged from the cooling unit flows, can be connected to the cooling unit. The cooling unit may have several chambers that do not communicate with each other, or several ducts.

In the present invention and embodiments thereof, the thermal path is the heat transfer path. In the present invention and its embodiments, the thermal paths from the electrode group of the pre-chamber spark plug to the cooling unit are not limited to thermal paths independent of each other. In other words, heat transfer is possible between several thermal paths. The definition is identical for the thermal paths going from the prechamber wall section to the cooling unit in the present invention and its embodiments.

In the present invention and embodiments thereof, the electrode group of the prechamber spark plug includes at least one center electrode, and at least one ground electrode. The electrode group may include a single central electrode, and multiple ground electrodes or a circular ground electrode. Several ground electrodes can correspond, for example, to two ground electrodes. Several ground electrodes may correspond, for example, to three or more ground electrodes. If the electrode group has a single central electrode and several ground electrodes, several spark gaps are formed. If the electrode group has a single central electrode and a circular ground electrode, a circular spark gap is formed. Spark discharges occur on the spark gap. In the present invention and embodiments thereof, the plug axial direction of the pre-chamber spark plug corresponds to the direction parallel to the central axis of the pre-chamber spark plug. The axial direction of the spark plug of the pre-chamber spark plug may or may not be parallel to the central axis of the cylindrical hole forming the main combustion chamber.

In the present invention and embodiments thereof, "producing spark discharges circumferentially" means that the positions at which the spark discharges occur disperse in a circumferential direction. “Production of spark discharges circumferentially” does not mean that the production of spark discharges is limited to simultaneous production of spark discharges at positions distributed in the circumferential direction. Multiple spark discharges can occur at the same time at positions dispersed in the circumferential direction. In this case, at least one of the spark discharges occurring at the same time will be the starting point of ignition. The circumferential direction is, for example, around a straight line which is parallel to the axial spark plug direction of the prechamber spark plug. An example of a case where spark discharges do not occur in a dispersed manner in the circumferential direction is where the electrode array has a single center electrode and a single ground electrode. Another example where spark discharges do not form in a dispersed manner in the circumferential direction is where the electrode group has a single central electrode, a primary ground electrode which is primarily used, and a secondary ground electrode which is used as an auxiliary. Another example where spark discharges do not occur in a dispersed manner in the circumferential direction is where the positions, where the air-fuel mixture is likely to ignite, are barely similar in the circumferential direction due to variations in the concentration of the air-fuel mixture inside the pre-chamber. Concrete examples of cases where spark discharges do not occur in a dispersed manner in the circumferential direction are not limited to these.

In the present invention and embodiments thereof, "the connecting holes are formed so as to be distributed circumferentially" means that several connecting holes are formed side by side in a circumferential direction without extreme bias. If the connection holes are formed distributedly in the circumferential direction, the connection holes are formed side by side in the circumferential direction. “The connection holes are formed distributedly in the circumferential direction” does not necessarily mean that the connection holes are formed at regular intervals in the circumferential direction. The circumferential direction found in the sentence "the connection ports are formed distributed in a circumferential direction" is, for example, around a straight line which is parallel to the axial plug direction of the prechamber spark plug .

In the present invention and embodiments thereof, "the thermal paths from the electrode group of the pre-chamber spark plug to the cooling unit are formed distributedly in the circumferential direction" means that the amount of Heat that travels from the electrode group of the prechamber spark plug to the cooling unit disperses in the circumferential direction. In other words, this means that the degree of ease of heat transfer from the electrode group of the prechamber spark plug to the cooling unit is almost equal in the circumferential direction. The circumferential direction in the sentence "the thermal paths from the electrode group of the pre-chamber spark plug to the cooling unit are formed distributedly in the circumferential direction" is, for example, the direction circumferential around a straight line parallel to the axial direction of the spark plug of the prechamber spark plug. In the present invention and its embodiments, "the thermal paths from the pre-chamber wall section to the cooling unit are formed in a distributed manner in the circumferential direction" means that the amount of heat that moves from the section of prechamber wall up to the cooling unit disperses in the circumferential direction. In other words, this means that the degree of ease of heat transfer from the pre-chamber wall section to the cooling unit is almost equal in the circumferential direction. The circumferential direction found in the sentence "the thermal paths from the pre-chamber wall section to the cooling unit are formed distributedly in the circumferential direction" is, for example, around a straight line parallel to the axial spark plug direction of the prechamber spark plug. This may be the same as the circumferential direction on which the connecting holes are arranged.
The electrode group is formed so that the spark discharges generated in the electrode group are produced dispersedly in the circumferential direction. In other words, the heat generated in the electrode group is generated by dispersing in the circumferential direction. For this reason, the cooling unit and the part between the prechamber spark plug and the cooling unit located in the cylinder head are important so that the thermal paths from the spark plug electrode group from prechamber to the cooling unit are formed in a dispersed manner in the circumferential direction. In addition, the connection holes formed on the pre-chamber wall section are formed dispersedly in the circumferential direction. In other words, the heat generated on the prechamber wall section is generated by dispersing in the circumferential direction. For this reason, the cooling unit and the part between the pre-chamber wall section and the cooling unit located in the cylinder head are important so that the thermal paths from the pre-chamber wall section to the cooling unit are formed in a dispersed manner in the circumferential direction. For example, if the cooling unit is circular in shape, the thermal paths, starting from the electrode group of the prechamber spark plug to the cooling unit, and the thermal paths, starting from the section from prechamber wall to the cooling unit, are easily formed in a distributed manner in the circumferential direction. For example, if the structure (shape and material) of the part between the pre-chamber spark plug and the cooling unit located in the cylinder head is almost uniform in the circumferential direction, the thermal paths going from the group of electrodes of the pre-chamber spark plug to the cooling unit are easily formed in a distributed manner in the circumferential direction. Furthermore, if, for example, the structure (shape and material) of the part between the pre-chamber wall section and the cooling unit located in the cylinder head is almost uniform in the circumferential direction, the thermal paths going from group d The electrodes from the pre-chamber spark plug to the cooling unit are easily formed in a distributed manner in the circumferential direction. An example of a case where the thermal paths from the electrode group of the prechamber spark plug to the cooling unit do not form distributed in the circumferential direction is where the cooling unit does not form only about half of the circumferential area. This example can also be that of the case where the thermal paths going from the pre-chamber wall section to the cooling unit are not formed in a distributed manner in the circumferential direction. Another example where the thermal paths from the pre-chamber wall section to the cooling unit are not formed in a distributed manner in the circumferential direction is where the material between the pre-chamber wall section and the cooling unit cooling is different in half of the circumferential zone and half of the remaining zone. Furthermore, the concrete examples of the case where the thermal paths from the electrode group of the prechamber spark plug to the cooling unit are not formed in a distributed manner in the circumferential direction, and the concrete examples where the thermal paths from the pre-chamber wall section to the cooling unit are not formed in a distributed manner in the circumferential direction and are not limited to these.

In the present invention and embodiments thereof, if the pre-chamber wall section is composed of several parts having different materials, the base material of the pre-chamber wall section is the material of the part which occupies the largest volume among these parts. Furthermore, in the present invention and its embodiments, the pre-chamber wall section may not be composed of several parts of different materials.
In the present invention and its embodiments, if the cylinder head is composed of several parts having different materials, the base material of the cylinder head is the material of the part which occupies the largest volume among these parts. If the base material of the pre-chamber wall section and that of the cylinder head are different, the part which occupies the largest volume among the parts of different materials composing the cylinder head does not include the pre-chamber wall section. Furthermore, in the present invention and embodiments thereof, the cylinder head includes the prechamber wall section. In the present invention and its embodiments, the cylinder head body part of which is exposed inside the main combustion chamber does not include the pre-chamber wall section. The basic material of the cylinder head body is the same as that of the cylinder head. The cylinder head body may or may not be made up of several parts of different materials.

In the present invention and embodiments thereof, "the thermal conductivity of the base material of the pre-chamber wall section is greater than or equal to that of chromium-based stainless steel" means that the thermal conductivity of the base material of the pre-chamber wall section is greater than or equal to the thermal conductivity of the chromium-based stainless steel under the temperature conditions of the main combustion chamber and the pre-chamber during operation of the pre-combustion four-stroke engine. The temperature of the main combustion chamber and the pre-chamber during operation of the four-stroke precombustion engine is located, for example, between approximately 850 and 1000°C for high temperatures, and between 500 and 600°C for high temperatures. bass for example.

In the present invention and embodiments thereof, the length of the interior space of the pre-chamber on the spark plug axial direction is the length between the two ends of the interior space of the pre-chamber on the spark plug axial direction. In other words, it is the distance between the plane crossing one end of the interior prechamber space in the axial direction of the candle and orthogonal to the axial direction of the candle, and the plane crossing the other end of the space interior of prechamber on the axial direction of spark plug and orthogonal to the axial direction of spark plug. In the present invention and its embodiments, the definition of the length of the pre-chamber interior space on the direction orthogonal to the spark plug axial direction is also the same as the above. In the present invention and embodiments thereof, the maximum length of the interior space of the prechamber on the direction orthogonal to the axial direction of spark plug is the maximum length among the lengths of the interior space of the prechamber located on several orthogonal directions to the axial direction of spark plug.

In the present invention and its embodiments, "the plane passing through the cooling unit and orthogonal to the plug axial direction of the prechamber spark plug passes through the prechamber spark plug" does not mean that it is limited to the passage through the pre-chamber spark plug of all planes passing through the cooling unit and orthogonal to the axial direction of the plug of the pre-chamber spark plug, but means the passage through the spark plug of prechamber of one of the planes passing through the cooling unit and orthogonal to the axial direction of the spark plug of the prechamber spark plug. In the present invention and its embodiments, the phrases "the plane, passing through the cooling unit and orthogonal to the axial direction of the spark plug of the pre-chamber spark plug, passes through the pre-chamber part", "the plane, passing through the cooling unit and orthogonal to the plug axial direction of the pre-chamber spark plug, passes through the portion where the external thread formed on the pre-chamber spark plug meets and contacts the formed thread on the pre-chamber part", and "the plane which passes through the interior space of the pre-chamber and orthogonal to the axial spark plug direction of the pre-chamber spark plug passes through the part where the external cylindrical surface of the pre-chamber part is in contact with the cylinder head body. » can be interpreted in the same way as the above.

In the present invention and its embodiments, "the pre-chamber part is a part different from the cylinder head body, part of which is exposed in the interior space of the main combustion chamber" means that the pre-chamber part is distant from the body cylinder head, or else, that the pre-chamber part is in contact with the cylinder head body in a dissociable manner. In the present invention and its embodiments, the cylinder head body may be composed of an inseparable part, or may be composed of several separable parts, a part of each of which is exposed in the interior space of the main combustion chamber. If the cylinder head body is composed of several separable parts, the cylinder head body does not include the part of which a part is not exposed in the interior space of the main combustion chamber.
In the present invention and its embodiments, "the pre-chamber part is a different part from the pre-chamber spark plug" means that the pre-chamber part is distant from the pre-chamber spark plug, or else, that the pre-chamber part is in contact with the pre-chamber spark plug in a dissociable manner. The prechamber part does not include part of the prechamber spark plug electrode group (e.g., ground electrode).

In the present invention and embodiments thereof, if the number of components is not clearly specified (i.e., written in the singular in the case of an English translation), the number of components can be one or more. In the present invention and its embodiments, the components whose number is not clearly specified are, for example, the main combustion chamber, the intake passage, the exhaust passage, the throttle valve, the intake injector, the pre-chamber, or even the pre-chamber spark plug.
The pre-combustion four-stroke engine of the present invention and embodiments thereof may have a single main combustion chamber, or may have several. In other words, the pre-combustion four-stroke engine of the present invention and embodiments thereof may have a single-cylinder engine block, or a multi-cylinder engine block. The number of prechambers and prechamber spark plugs are respectively the same as the number of main combustion chambers. The number of intake injectors may be greater than or equal to the number of main combustion chambers. The number of throttle valves may be less than or equal to the number of main combustion chambers. The intake passage may be divided into two or more. There is a single intake passage connected to a main combustion chamber. A single split-shaped intake passage can be connected to multiple main combustion chambers. The exhaust passage may be divided into two or more. There is a single exhaust passage connected to a main combustion chamber. A single split-shaped exhaust passage can be connected to multiple main combustion chambers.

The four-stroke pre-combustion engine of the present invention and embodiments thereof can be mounted on a saddle vehicle, the weight of which is lighter than that of a car and which requires a light and small engine. A saddle vehicle means any vehicle in which the driver rides astride a saddle. A saddle vehicle includes, among others, a motorcycle, a scooter, a three-wheel motor vehicle, a four-wheel buggy (all-terrain vehicle), a snowmobile, or a motorized water vehicle. In addition, the four-stroke pre-combustion engine of the present invention and its embodiments can be mounted on a work vehicle, which requires a light and small engine. Furthermore, it goes without saying that the pre-combustion four-stroke engine can be fitted to a car. Products equipped with the four-stroke pre-combustion engine of the present invention and embodiments thereof are not limited to specific products. If the four-stroke precombustion engine of an embodiment of the present invention is equipped on a product, it can be installed so that the central axis of the cylindrical hole is greater than or equal to 0° and less than or equal to 45°, or so that it is greater than or equal to 45° and less than or equal to 90°.

In the present invention and its embodiments, the terms "including, having, component, possessing and their derivatives" are used with the intention of encompassing all additional elements in addition to the listed elements and their equivalents.

Unless otherwise defined, all terms used in the present invention and its embodiments (including technical and scientific terms) have the same meaning as those generally understood by those skilled in the art to which the invention belongs. Terms such as those defined in commonly used dictionaries should be construed as having a meaning consistent with the meaning in the context of the relevant technology and the present disclosure, and will not be construed ideally or overly formally.

In the present invention and its embodiments, the term “may” is non-exclusive. “May” means “may, but not limited to.” In the present invention and its embodiments, the configuration mentioned with "may" produces at least the aforementioned effects.

Before explaining the details of the embodiments of the present invention, the latter should be interpreted without being limited to the configuration and arrangement details of the configuration elements mentioned in the explanations below or illustrated in the drawings. The present invention may have embodiments other than those described below. The present invention may have embodiments with various additional modifications to the embodiments described below.
Effects of the invention

According to the pre-combustion four-stroke engine of the present invention, the occurrence of self-ignition can be prevented while preventing the increase in the size of the cylinder head.
Brief description of the drawings

: Figures 1(a) to 1(f) are diagrams of the four-stroke precombustion engine according to a first embodiment of the present invention.
: There (a) is a diagram of the four-stroke precombustion engine according to a third embodiment of the present invention, and the (b) is a diagram of the four-stroke pre-combustion engine according to a fourth embodiment of the present invention.
: Figures 3(a) to 3(c) are three examples of diagrams of the four-stroke precombustion engine according to a fifth embodiment of the present invention.
: Figures 4(a) to 4(e) are five examples of diagrams of the four-stroke precombustion engine according to the fifth embodiment of the present invention.
: Figures 5(a) and 5(b) are two examples of diagrams of the four-stroke precombustion engine according to the fifth embodiment of the present invention.
Modes of carrying out the invention

The four-stroke pre-combustion engine, which is an embodiment of the present invention, will be explained below with reference to the drawings. Furthermore, the embodiments described below are examples only. The present invention should not be construed in any way as limited by the embodiment described below.

First embodiment
The four-stroke pre-combustion engine 1 of the first embodiment of the present invention will be explained using Figures 1(a) to 1(f). There (b) shows an example of part of the sectional view along line AA of the (has). Figures 1(c) and 1(d) show two examples of part of the sectional view along line BB of the (has). Figures 1(e) and 1(f) show two examples of part of the sectional view along line CC of the (has). The four-stroke precombustion engine 1 of the first embodiment has at least one main combustion chamber 2. The intake passage 5 and the exhaust passage 6 are connected to the main combustion chamber 2. The combustion chamber main 2 is formed of the cylinder head 10, the cylindrical hole 11, and the piston 12. The inlet passage 5 includes the passage formed inside the cylinder head 10, and the conduit connected thereto. The exhaust passage 6 includes the passage formed inside the cylinder head 10, and the conduit connected thereto. The precombustion four-stroke engine 1 has at least one throttle valve 7. The throttle valve 7 adjusts the amount of intake air into the main combustion chamber 2 passing through the intake passage 5. The engine four-stroke precombustion engine 1 has at least one intake injector 8. The intake injector 8 injects into the intake passage liquid fuel, which is gasoline fuel, fuel based on alcohol, or a mixture of gasoline fuel and alcohol. The four-stroke pre-combustion engine 1 has at least one pre-chamber 20. The interior space of the pre-chamber 20 communicates with that of the main combustion chamber 2 via several connecting orifices 21. The volume of the pre-chamber 20 is smaller than that of the main combustion chamber 2. Part of the pre-chamber spark plug 23 is exposed in the interior space of the pre-chamber 20. The pre-chamber 20 is formed in the cylinder head 10. The connecting orifices 21 are formed on the pre-chamber wall section 22 of the cylinder head 10. The pre-chamber wall section 22 has one side exposed in the interior space of the main combustion chamber 2. The relationship between the position of the central axis C11 of the cylindrical hole 11 and the position of the central axis C23 of the pre-chamber spark plug 23 is not limited to the position relationship shown in Figures 1(a) and 1(b). We consider the axial direction of spark plug DP as the direction parallel to the central axis C23 of the pre-chamber spark plug 23. In Figures 1(a) and 1(b), the axial direction of spark plug DP is parallel to the central axis C11 of the cylindrical hole 11, but it may not be. The shape of the interior space of the prechamber 20 is not limited to the shape indicated in Figures 1(a) and 1(b). The four-stroke precombustion engine 1 has a controller 70 which controls at least one intake injector 8 and at least one pre-chamber spark plug 23. The controller 70 controls the intake injector 8 on at least part of the low load zone where the opening angle of the throttle valve 7 is small, so that the air-fuel mixture, mixed in the intake passage 5 and the main combustion chamber 2 , either a first air/fuel ratio, which can be processed in a three-way catalyst after combustion, or a second air/fuel ratio richer than the first air/fuel ratio. For example, the control device 70 can control the intake injector 8 so that the air-fuel mixture, mixed in the intake passage 5 and the main combustion chamber 2, is the first air/fuel ratio that can be treated with a three-way catalyst after combustion, over at least part of the low load zone. The precombustion four-stroke engine 1 may or may not have a three-way catalyst. The four-stroke precombustion engine 1 has neither a precombustion injector, which injects the fuel into the prechamber 20, nor an ignition assistance device, which assists in the ignition of the air-fuel mixture in the prechamber 20 or the main combustion chamber 2.

As shown in Figures 1(a) and 1(b), the cylinder head 10 has a cooling unit 16 containing the cooling product (not shown) which receives heat from the electrode group 24 of the spark plug d prechamber ignition 23 and the prechamber wall section 22. On the (b), the cooling unit 16 is circular in shape, but it may not be. The electrode group 24 of the pre-chamber spark plug 23 is formed so that the spark discharges 33 in the electrode group 24 are produced dispersedly in the circumferential direction. The connecting orifices 21 are formed distributed in a circumferential direction. The cylinder head 10 is formed so that the thermal paths 14, extending from the electrode group 24 of the pre-chamber spark plug 23 to the cooling unit 16, and the thermal paths 15, extending from the section of pre-chamber wall 22 up to the cooling unit 16, are each formed in a distributed manner in the circumferential direction. For example, the spark discharges 33, the connection orifices 21, the thermal paths 14 and the thermal paths 15 can be formed respectively in a distributed manner in the circumferential direction around the central axis C23 of the pre-chamber spark plug 23 The thermal paths 14 illustrated in (a) are only an example of thermal path 14 from the electrode group 24 of the pre-chamber spark plug 23 to the cooling unit 16. The thermal paths 15 illustrated in (a) are only one example of thermal path 15 from the pre-chamber wall section 22 to the cooling unit 16. The two spark discharges 33 illustrated in (c) are only one example of spark discharges 33 generated in a dispersed manner in the circumferential direction on the electrode group 24 of the prechamber spark plug 23. The spark discharges 33 illustrated in (d) are only one example of spark discharges 33 generated in a dispersed manner in a circumferential direction on the electrode group 24 of the prechamber spark plug 23. The configuration of the electrode group 24 is not limited not to the configuration illustrated in Figures 1(c) and 1(d). The group of electrodes 24 may have a single central electrode 30 and several ground electrodes 31, as indicated for example by (vs). The group of electrodes 24 can have a single central electrode 30 and a ground electrode of circular shape, as indicated for example by (d). The ground electrodes 31 are designed so that a space is formed between the ground electrodes 31. The ground electrodes 31 are spaced away from the central electrode 30 in a direction orthogonal to the axial direction of spark plug DP. The ground electrodes 31 are not aligned with the central electrode 30 in the axial direction of spark plug DP. The internal edge of the ground electrode 31 of circular shape is distant from the central electrode 30 in a direction orthogonal to the axial direction of spark plug DP. Several spark gaps or a spark gap of circular shape are formed in a direction orthogonal to the axial direction of spark plug DP between a single central electrode 30, and several ground electrodes 31 or a ground electrode 31 of circular shape. The number of ground electrodes 31 can be two for example. The number, position, shape, and size of the connection holes 21 are not limited to what is indicated in Figures 1(e) and 1(f). The number of connecting orifices 21 can be, for example, three or more.

According to the configuration of the first embodiment, the occurrence of self-ignition can be prevented while preventing the increase in the size of the cooling unit 16, because the heat transfer is easily done from the electrode group 24 of the pre-chamber spark plug 23 and the pre-chamber wall section 22 on the cooling unit 16. In addition, the increase in the size of the cylinder head 10 can be further prevented because it does not There is no ignition assistance device in place. We can therefore prevent the appearance of self-ignition, while preventing the increase in the size of the cylinder head 10.

In addition, the four-stroke pre-combustion engine 1 of the (a) is formed so that one of the planes passing through the cooling unit 16 and orthogonal to the axial direction of spark plug DP passes through the prechamber spark plug 23. This plane is for example the plane superimposed on the AA line of the (has). On the (a), the four-stroke precombustion engine 1 is formed so that no plane passing through the cooling unit 16 and orthogonal to the axial direction of spark plug DP crosses the interior space of the prechamber 20. In the first embodiment, the four-stroke precombustion engine 1 can be formed so that one of the planes passing through the cooling unit 16 and orthogonal to the axial direction of spark plug DP passes through the interior space of the prechamber 20.

The pre-combustion four-stroke engine 1 of the first embodiment may not have a main combustion chamber fuel injector that injects fuel inside the main combustion chamber 2. The pre-combustion four-stroke engine 1 of the first embodiment may not have both a supercharger or a turbocharger. In other words, the four-stroke precombustion engine 1 can be of the atmospheric type. The four-stroke precombustion engine 1 of the first embodiment may not have an exhaust gas recycling device including an external exhaust gas recycling passage that connects the exhaust passage 6 and the exhaust passage. intake 5 by diverting the main combustion chamber 2.

Second embodiment
The four-stroke pre-combustion engine 1 of the second embodiment of the present invention will be explained below. The second embodiment has the configuration of the first embodiment. In the second embodiment, the melting point of the base material of the pre-chamber wall section 22 is higher than the melting point of the base material of the cylinder head 10. The value obtained by the multiplication of the specific heat and the density of the base material of the pre-chamber wall section 22 is greater than that of the base material of the cylinder head 10. The thermal conductivity of the base material of the pre-chamber wall section is greater than or equal to that of the chromium-based stainless steel. The base material of the cylinder head 10 is, for example, aluminum or an aluminum alloy. If the base material of the cylinder head 10 is an aluminum alloy, the materials indicated in embodiment examples 1 to 4 of Table 1 below can be used as the base material of the prechamber wall section 22, for example example. The base material of the pre-chamber wall section 22 may be a copper-chromium-zirconium alloy as shown in embodiment 1. The base material of the pre-chamber wall section 22 may be a copper alloy to chrome. Comparison examples 1 to 3, shown in Table 1, are examples of materials not used as the base material of the pre-chamber wall section 22, if the base material of the cylinder head 10 is aluminum or a aluminum alloy.

The prechamber wall section 22 may consist of only the base material. The prechamber wall section 22 may be made of the base material and a material other than the base material. For example, the pre-chamber wall section 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 pre-chamber wall section 22. It is preferable that the thermal conductivity of the coating layer is greater than that of the pre-chamber wall section 22.

Third embodiment
The four-stroke precombustion engine 1 of the third embodiment of the present invention will be explained using the (has). The four-stroke precombustion engine 1 of the third embodiment has, in addition to the configuration of the first or second embodiment, the following configuration: No protuberance is formed on the internal surface of the prechamber 20, at the 'except for the pre-chamber spark plug 23. The greatest length, between the length L1 of the interior space of the pre-chamber 20 on the axial direction of the spark plug DP and the maximum length L2 of the interior space of the pre-chamber 20 on the direction orthogonal to the axial direction of spark plug DP, is smaller than twice the smallest length. On the (a), the length L2 is larger than the length L1, but the length L1 can be larger than the length L2.

Fourth embodiment
The four-stroke precombustion engine 1 of the fourth embodiment of the present invention will be explained using the (b). The fourth embodiment has at least one configuration among embodiments 1 to 3. In the fourth embodiment, the pre-chamber wall section 22 protrudes into the interior space of the main combustion chamber 2. Additionally , in the fourth embodiment, the pre-chamber 20 is formed so that the volume of the projection of the pre-chamber wall section 22 is reduced relative to the volume of the pre-chamber 20. More concretely, if we separate the pre-chamber into two spaces the interior space of the pre-chamber 20 according to one of the planes S1 crossing the interior space of the pre-chamber 20 without crossing the external surface of the pre-chamber wall section 22, and intersecting orthogonally the axial direction of spark plug DP, the pre-chamber 20 is formed so that the volume of the space closest to the main combustion chamber 2 among the two spaces is less than the volume of the space farthest from the main combustion chamber 2 among the two spaces. The S1 plan indicated on the (b) is only an example of a plane S1 crossing the interior space of the pre-chamber 20, without crossing the external surface of the pre-chamber wall section 22, and orthogonal to the axial direction of candle DP. Furthermore, the outer surface of the pre-chamber wall section 22 is the surface exposed to the main combustion chamber 2. The pre-chamber 20, formed so that the volume of the space closest to the main combustion chamber 2 among the two spaces is less than the volume of the space farthest from the main combustion chamber 2 among the two spaces if the interior space of the pre-chamber 20 is separated into two spaces according to one of the planes S1 crossing the interior space of the pre-chamber 20 without crossing the external surface of the pre-chamber wall section 22 and intersecting orthogonally the axial direction of candle DP, means that it is not a pre-chamber 20 as it is described below. This prechamber 20 is such that a relationship described below is formed concerning all the planes crossing the interior space of the prechamber 20 without crossing the external surface of the prechamber wall section 22 and intersecting orthogonally the axial direction of candle DP . This relationship is such that the volume of the space closest to the main combustion chamber 2 among the two spaces is equal to or greater than the volume of the space furthest from the main combustion chamber 2 among the two spaces, if we separate the interior space of the pre-chamber 20 into two spaces according to a plan.

Fifth embodiment
The four-stroke pre-combustion engine 1 of the fifth embodiment of the present invention will be explained with the aid of Figures 3(a) to 3(c), 4(a) to 4(e), and 5(a). and 5(b). Figures 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 from embodiments 1 to 4. In the fifth embodiment, the inner surface of the pre-chamber 20 is formed by the pre-chamber part 25 and the pre-chamber spark plug 23 , including the pre-chamber wall section 22. In other words, the interior space of the pre-chamber 20 is the space surrounded by the pre-chamber part 25 and the pre-chamber spark plug 23. The outer cylindrical surface of the pre-chamber spark plug 23 and the internal cylindrical surface of the pre-chamber part 25 are in contact. The pre-chamber part 25 is a separate part, on the one hand, from the cylinder head body 13, part of which is exposed in the interior space of the main combustion chamber 2, and from the pre-chamber spark plug 23, d 'somewhere else. The cylinder head body 13 may be composed of an inseparable part, or may be composed of several separable parts, part of each of which is exposed in the interior space of the main combustion chamber 2. If the cylinder head body 13 is composed of several separable parts, the cylinder head body does not include the part of which a part is not exposed in the interior space of the main combustion chamber 2.

The external cylindrical surface of the pre-chamber part 25 can be in contact with the cylinder head body 13, as shown in Figures 3(a) and 3(b) for example. The external thread 41 formed on the pre-chamber part 25 can assemble and be in contact with the tapping 40 formed on the cylinder head body 13, as shown in (b) for example. If the external cylindrical surface of the pre-chamber part 25 is in contact with the cylinder head body 13, one of the planes S2 crossing the interior space of the pre-chamber 20 and orthogonal to the axial direction of spark plug DP can cross the part of the surface external cylindrical part of the pre-chamber part 25 in contact with the cylinder head body 13, as shown in Figures 3(a) and 3(b) for example. The plane S2 passing through the part in contact can pass through the part where the external thread 41 formed on the pre-chamber part 25 assembles and is in contact with the tapping 40 formed on the cylinder head body 13, as shown in (b) for example. The plane S2 passing through the part in contact can pass through a part which is not a threaded part (external thread 41 and tapping 40) of the pre-chamber part 25 and the cylinder head body 13, as shown in (b). The external cylindrical surface of the pre-chamber part 25 indicated in (c) may be in contact with the cylinder head body 13 on a part not illustrated. For example, the external cylindrical surface of the pre-chamber part 25 indicated on the (c) can be in contact with the cylinder head body 13, so that one of the planes (not illustrated), passing through the prechamber spark plug 23 and orthogonal to the axial direction of spark plug DP does not pass through the The interior space of the pre-chamber 20, passes through the part of the external cylindrical surface of the pre-chamber part 25 in contact with the cylinder head body 13. In this case, the part in contact between the external cylindrical surface of the pre-chamber part 25 and the cylinder head body 13 may be a threaded part (external thread 41 and tapping 40), or not.

The external cylindrical surface of the pre-chamber part 25 may not be in contact with the cylinder head body 13. The external cylindrical surface of the pre-chamber part 25 indicated for example in (c) may not be in contact with the cylinder head body. For example, the prechamber part 25 can be connected to the cylinder head body via a part which is not the cylinder head body 13 (for example, a cylinder head cover).

The pre-chamber part 25 and the cooling unit 16 can be formed so that one of the planes S3 passing through the cooling unit 16 and orthogonal to the axial direction of spark plug DP passes through the pre-chamber part 25, as shown by example Figures 4(a) and 4(d). If the plane S3 passes through the pre-chamber part 25, part of the internal surface of the cooling unit 16 can be at least part of the external cylindrical surface of the pre-chamber part 25, as shown for example in Figures 4 (a) and 4(c). If the plane S3 passes through the pre-chamber part 25, the internal surface of the cooling unit 16 may not include part of the external cylindrical surface of the pre-chamber part 25, as shown for example in (d). In addition, the pre-chamber part 25 and the cooling unit 16 can be formed so that no plane S3 passing through the cooling unit 16 and orthogonal to the axial direction of spark plug DP crosses the pre-chamber part 25, as shown for example by (e). Furthermore, the relationship between the pre-chamber part 25 and the cylinder head body 13 indicated in Figures 4(a) to 4(d) is not limited to the relationship identical to that of the (a), and can be any of the relationships described above.

If part of the internal surface of the cooling unit 16 is at least part of the external cylindrical surface of the pre-chamber part 25, the pre-chamber part 25 may have at least one heat dissipation unit 26 protruding from the interior space of the cooling unit 16, as shown in (b). The heat dissipation unit 26 may or may not be circular in shape. For example, the heat dissipation unit may be shaped like a circular arc larger than a semicircle, or may not be shaped like a circular arc. The circular-shaped heat dissipation unit 26 can be formed to compartmentalize the interior space of the cooling unit 16 into several spaces. The prechamber part 25 may have several heat dissipation units 26 aligned in the axial direction of the candle DP.

If one of the planes S3 passing through the cooling unit 16 passes through the pre-chamber part 25 (Figures 4(a) to 4(d) for example), one of the planes S3 passing through the cooling unit 16 can pass through the part where the internal cylindrical surface of the pre-chamber part 25 is in contact with the external cylindrical surface of the pre-chamber spark plug 23. If one of the planes S3 passing through the cooling unit 16 passes through the pre-chamber part 25, one of the planes S3 passing through the cooling unit 16 can pass through the part where the thread 42 formed on the pre-chamber part 25 assembles and is in contact with the external thread 43 formed on the pre-chamber spark plug 23, as shown for example Figures 5(a) and 5(b). In addition, the cooling unit 16 of the (a) is identical to the cooling unit 16 of the (a), but can be identical to that of the (b). The cooling unit 16 of the (b) is identical to that of (d), but can be identical to that of the (vs). Furthermore, the relationship between the pre-chamber part 25 and the cylinder head body 13 indicated in Figures 5(a) and 5(b) is not limited to the relationship identical to that of the (a), and can be any of the relationships described above. If one of the planes S3 passing through the cooling unit 16 passes through the pre-chamber part 25, one of the planes S3 passing through the cooling unit 16 may not pass through the part where the internal cylindrical surface of the pre-chamber part 25 is in contact with the external cylindrical surface of the prechamber spark plug 23.

The present invention is not limited to the embodiments described above, and may be modified in various ways within the scope of the present invention. For example, the precombustion four-stroke engine of the present invention may have a supercharger or a turbocharger. The pre-combustion four-stroke engine may have a main combustion chamber fuel injector that injects fuel into the main combustion chamber.
Legend

1: Four-stroke pre-combustion engine
2: Main combustion chamber
5: Intake passage
6: Exhaust passage
7: Throttle valve
8: Intake injector
10: Cylinder head
11: Cylindrical hole
13: Cylinder head body
14: Thermal path from the prechamber spark plug electrode group to the cooling unit
15: Thermal paths from the prechamber wall section to the cooling unit
16: Cooling unit
20: Prechamber
21: Connection holes
22: Pre-chamber wall section
23: Prechamber spark plug
24: Electrode group
25: Pre-chamber room
33: Spark discharge
40: Tapping the cylinder head body
41: External thread of the pre-chamber part
42: Tapping the pre-chamber part
43: External thread of the prechamber spark plug
70: Control device
DP: Axial direction of spark plug
L1: Length of the interior space of the prechamber on the axial direction of the spark plug
L2: Maximum length of the interior space of the prechamber in the direction orthogonal to the axial direction of the spark plug
S1, S2, S3: Plan

Claims (14)

Four-stroke precombustion engine (1) comprising:
- a main combustion chamber (2) in which an intake passage (5) and an exhaust passage (6) connect;
- a throttle valve (7) adjusting the quantity of air which passes through said intake passage (5) and which is admitted into said main combustion chamber (2);
- an intake injector (8) injecting a liquid fuel into said intake passage (5), said liquid fuel being a gasoline fuel, an alcohol-based fuel, or a gasoline fuel mixture and alcohol-based fuel;
- a pre-chamber (20), formed in a cylinder head (10),
the volume of said pre-chamber (20) being smaller than the volume of the main combustion chamber (2), and
an interior space of the prechamber (20) communicates with that of the main combustion chamber (2) via connection orifices (21), and
wherein part of a pre-chamber spark plug (23) is exposed in the interior space of the pre-chamber (20); And
- a control device (70) controlling said intake injector (8) and said prechamber spark plug (23);
the four-stroke precombustion engine (1) being characterized in that:
said control device (70) controls said intake injector (8) over at least part of a low load zone where an opening angle of said throttle valve (7) is low, so that a air-fuel mixture, mixed in said intake passage (5) and said main combustion chamber (2), i.e.:
- a first air/fuel ratio, which can be treated in a three-way catalyst after combustion, or
- a second air/fuel ratio richer than said first air/fuel ratio;
said four-stroke precombustion engine (1) not having:
- nor a pre-combustion injector, which would inject the fuel into said pre-chamber (20),
- nor an ignition assistance device, which would assist in the ignition of the air-fuel mixture in said pre-chamber (20) or said main combustion chamber (2); And
said cylinder head (10) has a cooling unit (16) containing a cooling product receiving heat from an electrode group (24) of said pre-chamber spark plug (23) and a wall section pre-chamber (22), where said connection orifices (21) are formed;
- said group of electrodes (24) of said prechamber spark plug (23) is formed so that several spark discharges (33) occur on said group of electrodes (24) and that these discharges of sparks (33) are distributed circumferentially on said group of electrodes (24);
- said connecting orifices (21) are formed so as to be distributed circumferentially; And
- said cylinder head (10) is formed in such a way that thermal paths (14), starting from said group of electrodes (24) of said pre-chamber spark plug (23) to said cooling unit (16) , and thermal paths (15), extending from said pre-chamber wall section (22) to said cooling unit (16), are each formed so as to be distributed circumferentially. The four-stroke pre-combustion engine (1) according to claim 1 characterized in that a base material of said pre-chamber wall section (22) has a higher melting point than a base material of said cylinder head ( 10),
a value of the base material of said pre-chamber wall section (22) which is obtained by multiplication of specific heat and density, is greater than that of the base material of said cylinder head (10), and
a thermal conductivity of the base material of said pre-chamber wall section (22) is greater than or equal to that of a chromium-based stainless steel. The four-stroke pre-combustion engine (1) according to claim 1 or 2, characterized in that a length (L1) of the interior space of said pre-chamber (20) in the axial direction of the spark plug (DP) of said spark plug prechamber ignition (23) is smaller than twice the maximum length (L2) of the interior space of the prechamber (20) in a direction orthogonal to said axial direction of the spark plug (DP), without a protrusion other than said pre-chamber spark plug (23), is formed on an internal surface of said pre-chamber (20). The four-stroke pre-combustion engine (1) according to one of claims 1 to 3 characterized in that said pre-chamber wall section (22) projects into the interior space of said main combustion chamber (2); And
by separating the interior space of said pre-chamber (20) into two spaces according to one of the planes (S1):
- crossing the interior space of said pre-chamber (20) without crossing the external surface of said pre-chamber wall section (22), and
- orthogonally intersecting said axial direction (DP) of said prechamber spark plug (23),
said pre-chamber (20) is formed so that the volume of the space closest to said main combustion chamber (2) among said two spaces is less than the volume of the space furthest from said main combustion chamber ( 2) among said two spaces. The four-stroke precombustion engine (1) according to one of claims 1 to 4 characterized in that a plane (S3), passing through said cooling unit (16) and orthogonal to said axial direction (DP) of said spark plug pre-chamber ignition plug (23), passes through said pre-chamber spark plug (23). The four-stroke precombustion engine (1) according to one of claims 1 to 5 characterized in that the interior space of said pre-chamber (20) is the space surrounded by said pre-chamber spark plug (23) and by a pre-chamber part (25), the pre-chamber part (25) comprises said pre-chamber wall section (22) and is formed to be independent of both said pre-chamber spark plug (23) and a cylinder head body (13) which is partially exposed in the interior space of said main combustion chamber (2). The four-stroke precombustion engine (1) according to claim 6 characterized in that a plane (S3), passing through said cooling unit (16) and orthogonal to said axial direction (DP) of said pre-chamber spark plug (23), passes through said pre-chamber piece (25). The four-stroke precombustion engine (1) according to claim 7 characterized in that a part of the internal surface of said cooling unit (16) is at least a part of an external cylindrical surface of said pre-chamber part ( 25). The four-stroke precombustion engine (1) according to one of claims 6 to 8 characterized in that an external thread (43), formed on said pre-chamber spark plug (23), assembles and is in contact with an internal thread (42) formed on said pre-chamber part (25). The four-stroke precombustion engine (1) according to claim 9 characterized in that a plane (S3), passing through said cooling unit (16) and orthogonal to the axial direction (DP) of said prechamber spark plug (23), passes through the part where said external thread (43) formed on said pre-chamber spark plug (23) assembles and is in contact with said internal thread (42) formed on said pre-chamber part (25). The four-stroke precombustion engine (1) according to one of claims 6 to 10 characterized in that the external cylindrical surface of said pre-chamber part (25) is in contact with said cylinder head body (13). The four-stroke precombustion engine (1) according to claim 11 characterized in that a plane (S2), crossing the interior space of said prechamber (20) and orthogonal to the axial direction (DP) of said spark plug pre-chamber ignition (23), passes through the part where the external cylindrical surface of said pre-chamber part (25) is in contact with said body of the cylinder head (13). The four-stroke precombustion engine (1) according to claim 12 characterized in that a plane (S2), crossing the interior space of the prechamber (20) and orthogonal to said axial direction of the candle (DP), crosses the part where the external thread (41) formed on said pre-chamber part (25) which assembles and is in contact with said thread (40) formed on said cylinder head body (13). The four-stroke precombustion engine (1) according to one of claims 1 to 13 characterized by the absence of a main combustion chamber fuel injector, which would inject the fuel inside said main combustion chamber ( 2).