Four-stroke engine with pre-ignition

Abstract

The cylinder head (10) of a four-stroke pre-combustion engine (1) includes a cooling unit (16) containing a coolant that receives heat from an electrode group (24) of a pre-chamber spark plug (23) and a pre-chamber wall section (22), where connecting ports (21) are formed. At least in a portion of the low-load 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 either a first air / fuel ratio that can be treated by a three-way catalyst after combustion or a second air / fuel ratio richer than said first ratio.The connecting ports (21), the thermal paths (14) from the electrode group (24) to the cooling unit (16), and the thermal paths (15) from the prechamber wall section (22) to the cooling unit (16), are each formed so as to be circumferentially distributed. Figure for the abstract: Fig. 1.

Description

Title of the invention: Four-stroke pre-combustion engine technical field

[0001] The present invention relates to a four-stroke pre-combustion engine comprising a main combustion chamber and a pre-chamber. State of the art

[0002] To date, four-stroke pre-combustion engines comprising a main combustion chamber and a pre-chamber communicating via several connecting ports, such as those disclosed in patent document 1, for example, are known. An air-fuel mixture internal to the pre-chamber is ignited by a spark plug. The four-stroke pre-combustion engine of patent document 1 has an intake injector that injects fuel into the intake passage, but no pre-combustion injector that would inject fuel into the pre-chamber. The intake injector of patent document 1 is controlled so that an air-fuel mixture with a stoichiometric or richer-than-stoichiometric ratio is generated in the main combustion chamber. The four-stroke pre-combustion engine of patent document 1 has a cooling liner (cooling unit) in the cylinder head.Furthermore, the four-stroke pre-combustion engine of patent document 1 has an auxiliary spark plug (ignition aid device) which assists in the ignition of the air-fuel mixture in the main combustion chamber. Previous technical documentation Patent documentation

[0003] Patent document 1: U.S. patent application no. 10612454 Overview of the invention Problems that the invention attempts to solve

[0004] In a four-stroke pre-ignition engine like the one described in patent document 1, the areas around the connecting holes and a group of electrodes of the spark plug are subjected to high temperatures. Pre-ignition is likely to occur around these areas because they reach particularly high temperatures under heavy loads. Furthermore, pre-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 sleeve were increased to prevent pre-ignition, the size of the cylinder head would also need to increase.

[0005] The present invention aims to provide a four-stroke pre-combustion engine that can prevent the occurrence of auto-ignition, while preventing an increase in the size of the cylinder head. Ways to solve problems

[0006] The four-stroke pre-combustion engine of an embodiment of the present invention has the following configuration: This is a four-stroke, pre-ignition engine comprising: - a main combustion chamber in which an intake passage and an exhaust passage connect; - a throttle valve adjusting the amount of air that passes through said intake passage and is admitted into said main combustion chamber; - an intake injector injecting liquid fuel into said intake passage, said liquid fuel being petrol fuel, alcohol-based fuel, or a mixture of petrol fuel and alcohol-based fuel; - 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 ports, and in which a portion of a prechamber spark plug is exposed within the prechamber's interior space; and - a control device controlling said intake injector and said pre-chamber spark plug; The four-stroke pre-combustion engine is characterized in that: said control device controls said intake injector on at least a portion of a low-load zone where the opening angle of said throttle valve is small, so that an air-fuel mixture, mixed in said intake passage and said main combustion chamber, is: - a first air / fuel ratio, which can be treated in a three-way catalyst after combustion, or - a second air / fuel ratio richer than the said first air / fuel ratio; said four-stroke pre-combustion engine not possessing: - nor a pre-combustion injector, which would inject fuel into said pre-chamber, - nor any ignition aid device that 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 in which is contained a coolant which receives heat from a group of electrodes of said spark plug pre-chamber ignition and a pre-chamber wall section, where said connecting orifices are formed; - said electrode group of said pre-chamber spark plug is formed such that several spark discharges occur on said electrode group and that these spark discharges are distributed circumferentially on said electrode group; - said connecting orifices are formed so as to be distributed circumferentially; and - said cylinder head is formed so that thermal paths, from said electrode group of said prechamber spark plug to said cooling unit, and thermal paths, from said prechamber wall section to said cooling unit, are each formed so as to be distributed circumferentially.

[0007] According to this configuration, the liquid fuel, which is gasoline, alcohol-based fuel, or a mixture of gasoline and alcohol, is injected into the intake passage from the intake injector. Furthermore, over at least a portion of the low-load region, the air-fuel mixture, mixed in the intake passage and the main combustion chamber, has a first air / fuel ratio or a second air / fuel ratio richer than the first. For this reason, there are numerous locations where the air-fuel mixture is likely to ignite within the pre-chamber space, even at low load.Thus, by using as a pre-chamber spark plug a spark plug with an electrode group that includes, for example, several circumferentially arranged ground electrodes or a circular ground electrode, it is possible to produce multiple circumferentially dispersed spark discharges across the electrode group of the pre-chamber spark plug, under both low and high loads. The generated heat is distributed circumferentially across the electrode group of the pre-chamber spark plug due to the production of these circumferentially dispersed spark discharges. Furthermore, the connecting orifices are formed circumferentially. For this reason, the generated heat is distributed circumferentially over the prechamber wall section where the connecting orifices are formed. The generated heat is thus distributed circumferentially over the pre-chamber spark plug electrode group and the pre-chamber wall section. Furthermore, the cylinder head is shaped so that the heat paths from the pre-chamber spark plug electrode group to the cooling unit, and the other heat paths from the pre-chamber wall section to the cooling unit, are each formed in such a way as to be distributed circumferentially. For this reason, heat transfer occurs easily from the pre-chamber spark plug electrode group and the pre-chamber wall section, which have a particularly high temperature. Furthermore, if a spark plug ignition aid, for example, is installed in the main combustion chamber, heat transfer becomes more difficult within the pre-chamber wall section from a position close to the ignition aid, because the ignition aid also has a high temperature. Heat transfer occurs easily from the pre-chamber wall section without installing an ignition aid in the main combustion chamber, as it is possible to easily increase the uniformity of heat transfer in a circumferential direction from the pre-chamber wall section to the cooling unit. Furthermore, if an ignition aid is installed in the pre-chamber, heat transfer within the pre-chamber spark plug electrode group becomes more difficult from a position close to the ignition aid, as the ignition aid also has a high temperature. Heat transfer from the pre-chamber spark plug electrode group is easy without an ignition aid installed in the pre-chamber, as it is possible to further increase the uniformity of heat transfer in a circumferential direction from the pre-chamber spark plug electrode group to the cooling unit. This design prevents pre-ignition while also limiting the size of the cooling unit, as heat transfer occurs easily from the pre-chamber spark plug electrode group to the pre-chamber wall section of the cooling unit. Furthermore, it further limits the size of the cylinder head because there is no ignition aid device in place. Therefore, pre-ignition can be prevented while simultaneously limiting the size of the cylinder head.

[0008] 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 density, may be greater than that of the base material of said cylinder head, and a thermal conductivity of the base material of said pre-chamber wall section may be greater than or equal to that of a chromium-based stainless steel.

[0009] 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 prechamber wall section. Furthermore, the value obtained by multiplying the specific heat capacity and density of the base material of the prechamber wall section is greater than that of the base material of the cylinder head. Here, the value obtained by multiplying the specific heat capacity and density expresses the volumetric heat capacity. The higher the volumetric heat capacity, the more difficult it is for the temperature to rise.Heat transfer from the high-temperature pre-chamber wall section to the cooling unit formed on the cylinder head is easily achieved by preventing the pre-chamber wall section's temperature from rising. This is accomplished by using a base material with a higher volumetric heat capacity than the cylinder head base material. Furthermore, the thermal conductivity of the pre-chamber wall section base material is equal to or greater than that of chromium-based stainless steel. Therefore, heat transfer from the pre-chamber wall section to the cooling unit is facilitated, thus further preventing pre-ignition.

[0010] 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 prechamber along the axial direction of the spark plug of said prechamber spark plug may be less than twice the maximum length of the interior space of the prechamber along a direction orthogonal to said axial direction of the spark plug, without a protrusion other than said prechamber spark plug being formed on an internal surface of said prechamber.

[0011] If a protrusion were formed on the inner surface of the prechamber, heat would easily accumulate on the protrusion. Heat transfer occurs easily from the prechamber wall section to the cooling unit when no protrusion is formed on the inner surface of the prechamber, apart from the prechamber spark plug. Furthermore, the length of the prechamber interior space along the axial direction of the spark plug is less than twice the maximum length of the prechamber interior space along the direction orthogonal to the axial direction of the spark plug. For this reason, the perimeter of the prechamber can be increased while maintaining the prechamber volume. It is thus possible to maintain even more heat paths from the prechamber wall section to the cooling unit.Therefore, heat transfer occurs more easily from the prechamber wall section to the unit. Cooling. Consequently, the occurrence of auto-ignition can be further prevented.

[0012] The four-stroke pre-combustion 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 dividing the interior space of said pre-chamber into two spaces along one of the following planes: - traversing the interior space of said prechamber without traversing the external surface of said prechamber wall section, and - cutting orthogonally across the said axial direction of the said pre-chamber spark plug, said pre-chamber may 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.

[0013] According to this embodiment, even though the prechamber wall section protrudes into the interior space of the main combustion chamber, the volume of this protrusion is small. For this reason, heat accumulates with difficulty on the prechamber wall section, and heat transfer occurs easily from the prechamber wall section to the cooling unit. Consequently, the occurrence of auto-ignition can be more effectively prevented.

[0014] The four-stroke pre-combustion engine of an 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 pre-chamber spark plug, may pass through said pre-chamber spark plug.

[0015] According to this embodiment, the heat from the electrode group of the pre-chamber spark plug is easily transferred to the cooling unit, since the pre-chamber spark plug is close to the cooling unit. Consequently, the occurrence of pre-ignition can be further prevented.

[0016] The four-stroke pre-combustion engine of an 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 piece, the pre-chamber piece may include 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.

[0017] According to this embodiment, the pre-chamber piece can be extended along the axial direction of the pre-chamber spark plug, while maintaining the shape and The size of the pre-chamber's internal space, compared to the case where the pre-chamber's internal space is enclosed by the pre-chamber component, the pre-chamber spark plug, and other components (e.g., the cylinder head), including the pre-chamber wall section, is a factor. Therefore, if a heat-transfer-friendly material is chosen for the pre-chamber component, heat transfer from the pre-chamber wall section to the cooling unit is even more efficient. Consequently, pre-ignition can be further prevented.

[0018] The four-stroke pre-combustion engine of an 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 pre-chamber spark plug, may pass through said pre-chamber part.

[0019] According to this embodiment, heat transfer from the prechamber wall section to the cooling unit is even easier because the prechamber section is close to the cooling unit. Consequently, auto-ignition can be further prevented.

[0020] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: a portion of the internal surface of said cooling unit may be at least a portion of an external cylindrical surface of said pre-chamber part.

[0021] According to this embodiment, the cooling product circulating in the cooling unit is in contact with the external cylindrical surface of the prechamber part. For this reason, heat transfer occurs more easily from the prechamber wall section to the cooling unit. Consequently, the occurrence of auto-ignition can be further prevented.

[0022] The four-stroke pre-combustion engine of an 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 tapping formed on said pre-chamber part.

[0023] According to this embodiment, the contact area between the pre-chamber spark plug and the pre-chamber component is large. For this reason, heat transfer occurs easily from the pre-chamber spark plug to the pre-chamber component. Consequently, heat transfer also occurs easily from the electrode group of the pre-chamber spark plug to the cooling unit via the pre-chamber component. Therefore, the occurrence of pre-ignition can be further prevented.

[0024] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: a plane, passing through said unit of cooling and orthogonal to the axial direction of said pre-chamber spark plug, may pass through the part where said external thread formed on said pre-chamber spark plug assembles and is in contact with said internal tapping formed on said pre-chamber part.

[0025] According to this embodiment, heat transfer from the prechamber wall section to the cooling unit is even easier because the prechamber component is close to the cooling unit. Furthermore, heat transfer from the prechamber spark plug electrode group to the cooling unit via the prechamber component is even easier because the contact area between the prechamber spark plug and the prechamber component is close to the cooling unit. Consequently, the occurrence of pre-ignition can be further prevented.

[0026] The four-stroke pre-combustion engine of an 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.

[0027] According to this embodiment, heat transfer occurs easily from the prechamber wall section to the cylinder head body, compared to the case where the external cylindrical surface of the prechamber part is not in contact with the cylinder head body. Consequently, the occurrence of auto-ignition can be more easily prevented.

[0028] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: a plane, passing through the interior space of said prechamber and orthogonal to the axial direction of said prechamber spark plug, may pass through the part where the external cylindrical surface of said prechamber part is in contact with said cylinder head body.

[0029] According to this embodiment, the internal space of the prechamber is close to the point where the external cylindrical surface of the prechamber component is in contact with the cylinder head. Consequently, the prechamber wall section is close to the point where the external cylindrical surface of the prechamber component is in contact with the cylinder head. For this reason, heat transfer occurs more easily from the prechamber wall section to the cylinder head. Therefore, the occurrence of pre-ignition can be more effectively prevented.

[0030] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: a plane, passing through the interior space of the prechamber and orthogonal to said axial direction of the spark plug, may pass through the part where the external thread formed on said prechamber piece is assembled and is in contact with said tapping formed on said cylinder head body.

[0031] According to this embodiment, the contact area between the pre-chamber piece and the cylinder head body is large. For this reason, heat transfer is This is even more easily done from the pre-chamber to the cylinder head. Consequently, the occurrence of pre-ignition can be more easily prevented.

[0032] The four-stroke pre-combustion engine of an 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 fuel into said main combustion chamber.

[0033] 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 installed.

[0034] 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.

[0035] In the present invention and its embodiments, the air / fuel ratio, which is the mixture ratio between the fuel and the 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 a range of air / fuel ratios 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 including an air / fuel ratio close to the stoichiometric ratio but not including the stoichiometric ratio. The second air / fuel ratio is richer than the first air / fuel ratio.If the first air / fuel ratio is close to the stoichiometric ratio, or within a range that does not include 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 its embodiments, "rich" means that the fuel in the air-fuel mixture is denser. "Lean" means that the fuel in the air-fuel mixture is less dense. In the present invention and its embodiments, the air / fuel ratio that can be treated with a three-way catalyst after combustion is an air / fuel ratio such that the exhaust gases produced after combustion of the air-fuel mixture can be treated with a three-way catalyst.In the present invention and its embodiments, the control device can control the intake injector over at least a part of the low load area, so that the air-fuel mixture, mixed in the intake passage and the main combustion chamber, is. The stoichiometric ratio or an air / fuel ratio richer than the stoichiometric ratio. The four-stroke pre-combustion engine of the present invention has a catalyst disposed in the exhaust passage. The four-stroke pre-combustion engine of the present invention may have a three-way catalyst disposed in the exhaust passage. The four-stroke pre-combustion 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 sensor disposed between the main combustion chamber and the catalyst, which detects the oxygen concentration of the exhaust gases flowing through the exhaust passage.

[0036] In the present invention and its embodiments, the ignition aid device, which assists in the ignition of the air-fuel mixture in the pre-chamber or the main combustion chamber, is, for example, a device generating microwave discharges, 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 its embodiments, the expression "the four-stroke pre-combustion engine does not have an ignition aid device" includes not only the absence of an ignition aid device separate from the pre-chamber spark plug, but also the absence of an ignition aid function in the pre-chamber spark plug.

[0037] In the present invention and its embodiments, the expression "the volume of the prechamber is smaller than that of the main combustion chamber" means that the volume of the prechamber is less than the minimum volume of the main combustion chamber. Furthermore, the volume of the main combustion chamber varies with the piston displacement. The volume of the prechamber is the volume of the prechamber's internal space. In the present invention and its embodiments, the prechamber's internal space does not include the internal space of the connecting ports. In the present invention and its embodiments, the internal surface of the prechamber is the surface that forms the prechamber's internal space. In the present invention and its embodiments, the prechamber spark plug forms part of the prechamber's internal surface.In the present invention and its embodiments, the expression "no protrusion is formed on the internal surface of the prechamber apart from the prechamber spark plug" means that no protrusion is formed on the internal surface of the prechamber, or that any protrusion formed on the surface is solely due to the prechamber spark plug. In the present invention, the prechamber wall section where the connecting orifices are formed is the wall section having one side. exposed within the interior space of the main combustion chamber. The prechamber wall section may or may not be shaped to project into the interior space of the main combustion chamber. If the prechamber wall section is shaped to project into the interior space of the main combustion chamber, the prechamber wall section has a tubular portion.

[0038] In the present invention and its embodiments, the coolant is liquid or gaseous. The coolant in liquid form may be, for example, water or lubricating oil. The coolant in gaseous form may be air, for example. In the present invention and its embodiments, the cooling unit containing the coolant is at least one chamber, or at least one passage. The coolant may flow through the cooling unit. The passage through which the coolant flows into the cooling unit, and the passage through which the coolant discharges from the cooling unit flows, may be connected to the cooling unit. The cooling unit may have several chambers that do not communicate with each other, or several conduits.

[0039] In the present invention and its embodiments, the thermal path is the path of heat transfer. In the present invention and its embodiments, the thermal paths from the prechamber spark plug electrode group to the cooling unit are not limited to independent thermal paths. In other words, heat transfer is possible between several thermal paths. The definition is identical for the thermal paths from the prechamber wall section to the cooling unit in the present invention and its embodiments.

[0040] In the present invention and its embodiments, the electrode group of the pre-chamber spark plug includes at least one center electrode and at least one ground electrode. The electrode group may include a single center electrode and several ground electrodes or a circular ground electrode. Several ground electrodes may 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 center electrode and several ground electrodes, several spark gaps are formed. If the electrode group has a single center electrode and a circular ground electrode, a circular spark gap is formed. The spark discharges occur at the spark gap.In the present invention and its embodiments, the axial direction of the spark plug 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. The pre-chamber ignition may or may not be parallel to the central axis of the cylindrical hole forming the main combustion chamber.

[0041] In the present invention and its embodiments, "circumferential spark production" means that the positions at which the spark discharges occur are dispersed in a circumferential direction. "Circumferential spark production" does not mean that spark production is limited to the simultaneous production of spark discharges at positions distributed in the circumferential direction. Several spark discharges may occur at the same time at positions dispersed in a circumferential direction. In this case, at least one of the simultaneous spark discharges will be the starting point of ignition. The circumferential direction is, for example, around a straight line that is parallel to the axial direction of the spark plug of the pre-chamber spark plug.An example of a case where spark discharges do not occur in a circumferentially dispersed manner is when the electrode array has a single center electrode and a single ground electrode. Another example where spark discharges do not occur in a circumferentially dispersed manner is when the electrode array has a single center electrode, a primary ground electrode that is mainly used, and a secondary ground electrode that is used as an auxiliary. A further example where spark discharges do not occur in a circumferentially dispersed manner is when the positions where the air-fuel mixture is likely to ignite are only slightly similar in the circumferential direction due to variations in the air-fuel mixture concentration within the prechamber.Concrete examples of cases where spark discharges do not occur in a dispersed circumferential manner are not limited to these.

[0042] In the present invention and its embodiments, "the connecting ports are formed so as to be distributed circumferentially" means that several connecting ports are formed side by side in a circumferential direction without extreme bias. If the connecting ports are formed in a distributed circumferential manner, the connecting ports are formed side by side in a circumferential direction. "The connecting ports are formed in a distributed circumferential manner" does not necessarily mean that the connecting ports are formed at regular intervals in the circumferential direction. The circumferential direction in the phrase "the connecting ports are formed in a distributed circumferential manner" is, for example, around a straight line that is parallel to the axial direction of the spark plug of the pre-chamber spark plug.

[0043] In the present invention and its embodiments, "the thermal paths from the pre-chamber spark plug electrode group to the cooling unit are formed in a distributed circumferential manner" means that the amount of heat moving from the pre-chamber spark plug electrode group to the cooling unit disperses in a circumferential direction. In other words, this means that the degree of ease of heat transfer from the pre-chamber spark plug electrode group to the cooling unit is virtually equal in the circumferential direction.The circumferential direction in the phrase "the thermal paths from the prechamber spark plug electrode group to the cooling unit are formed in a distributed circumferential manner" is, for example, the circumferential direction around a straight line parallel to the axial direction of the prechamber spark plug. In the present invention and its embodiments, "the thermal paths from the prechamber wall section to the cooling unit are formed in a distributed circumferential manner" means that the amount of heat moving from the prechamber wall section to the cooling unit disperses in a circumferential direction.In other words, this means that the degree of heat transfer from the prechamber wall section to the cooling unit is virtually equal in the circumferential direction. The circumferential direction in the phrase "the thermal paths from the prechamber wall section to the cooling unit are formed in a distributed circumferential manner" is, for example, around a straight line parallel to the axial direction of the prechamber spark plug. This can be identical to the circumferential direction in which the connecting ports are arranged. The electrode group is designed so that the spark discharges generated within it are dispersed circumferentially. In other words, the heat generated within the electrode group is generated by dispersing circumferentially. For this reason, the cooling unit and the area between the pre-chamber spark plug and the cooling unit within the cylinder head are crucial to ensure that the heat paths from the pre-chamber spark plug electrode group to the cooling unit are formed circumferentially. Furthermore, the connection holes formed on the pre-chamber wall section are also formed circumferentially. In other words, the heat generated on the pre-chamber wall section is generated by dispersing circumferentially.For this reason, the cooling unit. The area between the pre-chamber wall section and the cooling unit in the cylinder head is important for the thermal paths from the pre-chamber wall section to the cooling unit to form in a dispersed circumferential manner. For example, if the cooling unit is circular, the thermal paths from the pre-chamber spark plug electrode group to the cooling unit, and the thermal paths from the pre-chamber wall section to the cooling unit, readily form in a distributed circumferential manner.For example, if the structure (shape and material) of the area between the pre-chamber spark plug and the cooling unit in the cylinder head is nearly uniform in the circumferential direction, the thermal paths from the pre-chamber spark plug electrode group to the cooling unit readily form in a distributed circumferential manner. Furthermore, if, for example, the structure (shape and material) of the area between the pre-chamber wall section and the cooling unit in the cylinder head is nearly uniform in the circumferential direction, the thermal paths from the pre-chamber spark plug electrode group to the cooling unit readily form in a distributed circumferential manner.An example of a case where the thermal paths from the prechamber spark plug electrode group to the cooling unit do not form in a circumferentially distributed manner is when the cooling unit comprises only about half of the circumferential area. This can also be the case where the thermal paths from the prechamber wall section to the cooling unit do not form in a circumferentially distributed manner. Another example of a case where the thermal paths from the prechamber wall section to the cooling unit do not form in a circumferentially distributed manner is when the material between the prechamber wall section and the cooling unit differs in half of the circumferential area and half of the remaining area.Furthermore, the concrete examples of the case where the thermal paths from the prechamber spark plug electrode group to the cooling unit do not form in a distributed circumferential direction, and the concrete examples where the thermal paths from the prechamber wall section to the cooling unit do not form in a distributed circumferential direction are not limited to these.

[0044] In the present invention and its embodiments, if the prechamber wall section is composed of several parts made of different materials, the base material of the prechamber wall section is the material of the part that occupies the largest volume among these parts. Furthermore, in the present invention and In its various implementation methods, the prechamber wall section may not be composed of several parts made of different materials. In the present invention and its embodiments, if the cylinder head is composed of several parts made of different materials, the base material of the cylinder head is the material of the part that 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 that occupies the largest volume among the parts made of different materials composing the cylinder head does not include the pre-chamber wall section. Furthermore, in the present invention and its embodiments, the cylinder head includes the pre-chamber wall section. In the present invention and its embodiments, the cylinder head body, a portion of which is exposed inside the main combustion chamber, does not include the pre-chamber wall section. The base material of the cylinder head body is the same as that of the cylinder head. The cylinder head body may or may not be composed of several parts made of different materials.

[0045] In the present invention and its embodiments, "the thermal conductivity of the base material of the prechamber 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 prechamber wall section is greater than or equal to the thermal conductivity of chromium-based stainless steel under the temperature conditions of the main combustion chamber and the prechamber during the operation of the four-stroke pre-combustion engine. The temperature of the main combustion chamber and the prechamber during the operation of the four-stroke pre-combustion engine is, for example, between approximately 850 and 1000°C for high temperatures, and between 500 and 600°C for low temperatures.

[0046] In the present invention and its embodiments, the length of the prechamber interior space along the spark plug axial direction is the length between the two ends of the prechamber interior space along the spark plug axial direction. In other words, it is the distance between the plane passing through one end of the prechamber interior space along the spark plug axial direction and perpendicular to the spark plug axial direction, and the plane passing through the other end of the prechamber interior space along the spark plug axial direction and perpendicular to the spark plug axial direction. In the present invention and its embodiments, the definition of the length of the prechamber interior space along the direction perpendicular to the spark plug axial direction is also identical to the above.In the present invention and its embodiments, the maximum length of the interior space of the prechamber on the direction orthogonal to the axial direction of the candle is the length. maximum among the lengths of the prechamber interior space located on several directions orthogonal to the axial direction of the candle.

[0047] In the present invention and its embodiments, "the plane passing through the cooling unit and orthogonal to the axial direction of the spark plug of the prechamber spark plug passes through the prechamber spark plug" does not mean that it is limited to the passage through the prechamber spark plug of all the planes passing through the cooling unit and orthogonal to the axial direction of the spark plug of the prechamber spark plug, but means the passage through the prechamber spark plug 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 axial direction of the spark plug of the pre-chamber spark plug, passes through the part where the external thread formed on the pre-chamber spark plug is assembled and is in contact with the tapped hole formed on the pre-chamber part", and "the plane which passes through the internal space of the pre-chamber and orthogonal to the axial direction of the spark plug 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 identically to the foregoing.

[0048] In the present invention and its embodiments, "the pre-chamber component is a component separate from the cylinder head body, a portion of which is exposed in the interior space of the main combustion chamber" means that the pre-chamber component is located away from the cylinder head body, or that the pre-chamber component is in contact with the cylinder head body in a separable manner. In the present invention and its embodiments, the cylinder head body may consist of a single, inseparable component, or may consist of several separable components, a portion 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 components, the cylinder head body does not include the component a portion of which is not exposed in the interior space of the main combustion chamber. In the present invention and its embodiments, "the pre-chamber component is a component distinct from the pre-chamber spark plug" means that the pre-chamber component is located away from the pre-chamber spark plug, or that the pre-chamber component is in contact with the pre-chamber spark plug in a separable manner. The pre-chamber component does not include any part of the electrode group of the pre-chamber spark plug (for example, the ground electrode).

[0049] In the present invention and its embodiments, if the number of components is not clearly specified (i.e., if it is written in the singular in the case of an English translation), the number of components may be one or more. In the present invention and its embodiments, components whose number is not clearly specified include, for example, the main combustion chamber, the intake passage, the exhaust passage, the throttle valve, the intake injector, the pre-chamber, or the pre-chamber spark plug. The four-stroke pre-ignition engine of the present invention and its embodiments may have a single main combustion chamber, or may have several. In other words, the four-stroke pre-ignition engine of the present invention and its embodiments may have a single-cylinder engine block, or a multi-cylinder engine block. The number of pre-chambers and pre-chamber spark plugs is respectively identical to 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 only one intake passage connected to a main combustion chamber.A single split-shaped intake passage can be connected to multiple primary combustion chambers. The exhaust passage can be divided into two or more. There is only one exhaust passage connected to a primary combustion chamber. A single split-shaped exhaust passage can be connected to multiple primary combustion chambers.

[0050] The four-stroke pre-ignition engine of the present invention and its embodiments can be mounted on a saddle-mounted vehicle, which is lighter than a car and requires a lightweight, small engine. A saddle-mounted vehicle is defined as any vehicle in which the rider mounts by straddling a saddle. Saddle-mounted vehicles include, among others, motorcycles, scooters, three-wheeled motor vehicles, four-wheeled buggies (all-terrain vehicles), snowmobiles, and personal watercraft. Furthermore, the four-stroke pre-ignition engine of the present invention and its embodiments can be mounted on a work vehicle, which requires a lightweight, small engine. In addition, it goes without saying that the four-stroke pre-ignition engine can be mounted on a car.Products equipped with the four-stroke pre-combustion engine of the present invention and its embodiments are not limited to specific products. If the four-stroke pre-combustion engine of an embodiment of the present invention is fitted to a product, it can be installed so that the shaft... central of the cylindrical hole be 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°.

[0051] 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.

[0052] 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 a person skilled in the art of the invention. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology and this disclosure, and should not be interpreted in an ideal or overly formal manner.

[0053] In the present invention and its embodiments, the term "may" is non-exclusive. "May" means "can, but is not limited to." In the present invention and its embodiments, the configuration mentioned with "may" produces at least the aforementioned effects.

[0054] Before explaining the details of 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 different from those described below. The present invention may have embodiments with various additional modifications to the embodiments described below. Effects of the invention

[0055] According to the four-stroke pre-combustion engine of the present invention, it is possible to prevent the occurrence of auto-ignition, while preventing the increase in the size of the cylinder head. Brief description of the drawings

[0056] [Fig.l]: Figures l(a) to l(f) are diagrams of the four-stroke pre-combustion engine according to a first embodiment of the present invention. [Fig.2]: [Fig.2](a) is a diagram of the four-stroke pre-combustion engine according to a third embodiment of the present invention, and [Fig.2](b) is a diagram of the four-stroke pre-combustion engine according to a fourth embodiment of the present invention. [Fig.3]: Figures 3(a) to 3(c) are three examples of diagrams of the four-stroke pre-combustion engine according to a fifth embodiment of the present invention. [Fig.4]: Figures 4(a) to 4(e) are five examples of diagrams of the four-stroke pre-combustion engine according to the fifth embodiment of the present invention. [Fig.5]: Figures 5(a) and 5(b) are two examples of diagrams of the four-stroke pre-combustion engine according to the fifth embodiment of the present invention. Embodiments of the invention

[0057] The four-stroke pre-ignition engine, which is an embodiment of the present invention, will be explained below with reference to the drawings. Furthermore, the embodiments described below are only examples. The present invention shall not be interpreted in any way as limited by the embodiment described below.

[0058] First embodiment The four-stroke pre-ignition engine 1 of the first embodiment of the present invention will be explained with reference to Figures l(a) to l(f). Figure l(b) shows an example of a portion of the cross-sectional view along line AA of Figure l(a). Figures l(c) and l(d) show two examples of a portion of the cross-sectional view along line BB of Figure l(a). Figures l(e) and l(f) show two examples of a portion of the cross-sectional view along line CC of Figure l(a). The four-stroke pre-combustion 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 main combustion chamber 2 is formed by the cylinder head 10, the cylindrical hole 11, and the piston 12. The intake passage 5 includes the passage formed inside the cylinder head 10, and the conduit connected to it.The exhaust passage 6 includes the passage formed inside the cylinder head 10, and the duct connected to it. The four-stroke pre-combustion 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 four-stroke pre-combustion engine 1 has at least one intake injector 8. The intake injector 8 injects liquid fuel, which is gasoline, alcohol-based fuel, or a mixture of gasoline and alcohol, into the intake passage. The four-stroke pre-combustion engine 1 has at least one pre-chamber 20. The internal space of the pre-chamber 20 communicates with that of the main combustion chamber 2 via several connecting ports 21. The volume of the pre-chamber 20 is smaller than that of the main combustion chamber 2.Part of the prechamber spark plug 23 is exposed in the interior space of the prechamber 20. The prechamber 20 is formed in the cylinder head 10. The connecting ports 21 are formed on the section. of the prechamber wall 22 of the cylinder head 10. The prechamber wall section 22 has one side exposed in the internal space of the main combustion chamber 2. The relationship between the position of the central axis Cl 1 of the cylindrical hole 11 and the position of the central axis C23 of the prechamber spark plug 23 is not limited to the positional relationship shown in Figures l(a) and l(b). The axial direction of spark plug DP is considered to be the direction parallel to the central axis C23 of the prechamber spark plug 23. In Figures l(a) and l(b), the axial direction of spark plug DP is parallel to the central axis Cl 1 of the cylindrical hole 11, but it may not be. The shape of the internal space of the prechamber 20 is not limited to the shape shown in Figures l(a) and l(b). The four-stroke pre-combustion engine 1 has a control device 70 which controls at least one intake injector 8 and at least one pre-chamber spark plug 23.The control device 70 directs the intake injector 8 over at least a portion 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, is either a first air / fuel ratio, which can be treated in a three-way catalytic converter after combustion, or a second air / fuel ratio richer than the first air / fuel ratio. For example, the control device 70 can direct 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 catalytic converter after combustion, over at least a portion of the low-load zone. The pre-combustion four-stroke engine 1 may or may not have a three-way catalytic converter.The four-stroke pre-combustion engine 1 has neither a pre-combustion injector, which injects fuel into the pre-chamber 20, nor an ignition aid device, which helps to ignite the air-fuel mixture in the pre-chamber 20 or the main combustion chamber 2.

[0059] As shown in Figures 1(a) and 1(b), the cylinder head 10 has a cooling unit 16 containing the coolant (not shown) which receives heat from the electrode group 24 of the prechamber spark plug 23 and the prechamber wall section 22. In [Fig. 1(b), the cooling unit 16 is circular, but it may not be. The electrode group 24 of the prechamber spark plug 23 is shaped so that the spark discharges 33 in the electrode group 24 are produced in a dispersed circumferential manner. The connecting orifices 21 are formed in a dispersed circumferential manner. The cylinder head 10 is formed such that the thermal paths 14, from the electrode group 24 of the pre-chamber spark plug 23 to the cooling unit 16, and the thermal paths 15, starting from the prechamber wall section 22 to the cooling unit 16, each are formed in a distributed manner in a circumferential direction. For example, the spark discharges 33, the connecting orifices 21, the thermal paths 14 and the thermal paths 15 can be formed respectively in a distributed circumferential direction around the central axis C23 of the prechamber spark plug 23. The thermal paths 14 illustrated in [Fig. 1](a) are only one example of a thermal path 14 from the electrode group 24 of the prechamber spark plug 23 to the cooling unit 16. The thermal paths 15 illustrated in [Fig. 1](a) are only one example of a thermal path 15 from the prechamber wall section 22 to the cooling unit 16. The two spark discharges 33 illustrated in [Fig.Figures 1(c) are only one example of spark discharges 33 generated in a dispersed circumferential direction on the electrode group 24 of the pre-chamber spark plug 23. The spark discharges 33 illustrated in Figures 1(c) and 1(d) are only one example of spark discharges 33 generated in a dispersed circumferential direction on the electrode group 24 of the pre-chamber spark plug 23. The configuration of the electrode group 24 is not limited to the configuration illustrated in Figures 1(c) and 1(d). The electrode group 24 may have a single central electrode 30 and several ground electrodes 31, as shown, for example, in Figures 1(c). The electrode group 24 may have a single central electrode 30 and a circular ground electrode, as shown for example in [Fig. 1](d). The ground electrodes 31 are designed so that a space is formed between them.The ground electrodes 31 are positioned away from the central electrode 30 in a direction perpendicular to the axial direction of the spark plug DP. The ground electrodes 31 are not aligned with the central electrode 30 in the axial direction of the spark plug DP. The inner edge of the circular ground electrode 31 is positioned away from the central electrode 30 in a direction perpendicular to the axial direction of the spark plug DP. Several spark gaps, or a single circular spark gap, are formed perpendicular to the axial direction of the spark plug DP between a single central electrode 30 and several ground electrodes 31, or a single circular ground electrode 31. The number of ground electrodes 31 may be, for example, two. The number, position, shape, and size of the connecting orifices 21 are not limited to what is shown in Figures 1(e) and 1(f). The number of connection ports 21 can be, for example, three or more.

[0060] According to the configuration of the first embodiment, auto-ignition can be prevented while preventing an increase in the size of the cooling unit 16, because heat transfer occurs easily from the electrode group 24 of the pre-chamber spark plug 23 and the wall section of Pre-chamber 22 on the cooling unit 16. Furthermore, the increase in cylinder head size 10 can be further prevented because there is no ignition aid device in place. Therefore, pre-ignition can be prevented, while simultaneously preventing an increase in cylinder head size 10.

[0061] Furthermore, the four-stroke pre-combustion engine 1 of [Fig. 1](a) is formed such that one of the planes passing through the cooling unit 16 and orthogonal to the axial direction of spark plug DP passes through the pre-chamber spark plug 23. This plane is, for example, the plane superimposed on line AA of [Fig. 1](a). In [Fig. 1](a), the four-stroke pre-combustion engine 1 is formed such that no plane passing through the cooling unit 16 and orthogonal to the axial direction of spark plug DP passes through the interior space of the pre-chamber 20. In the first embodiment, the four-stroke pre-combustion engine 1 can be formed such 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 pre-chamber 20.

[0062] The four-stroke pre-combustion engine 1 of the first embodiment may not have a main combustion chamber fuel injector that injects fuel into the main combustion chamber 2. The four-stroke pre-combustion engine 1 of the first embodiment may not have either a supercharger or a turbocharger. In other words, the four-stroke pre-combustion engine 1 may be naturally aspirated. The four-stroke pre-combustion engine 1 of the first embodiment may not have an exhaust gas recirculation device including an external exhaust gas recirculation passage that connects the exhaust passage 6 and the intake passage 5 by diverting the main combustion chamber 2.

[0063] Second embodiment The four-stroke pre-ignition engine 1 of the second embodiment of the present invention will be explained below. The second embodiment has the same configuration as 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 multiplying the specific heat capacity and 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 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, the base material of the prechamber wall section 22 can be a copper-chromium-zirconium alloy, as shown in embodiment example 1. The base material of the prechamber wall section 22 can be a copper-chromium alloy. Comparison examples 1 to 3, shown in Table 1, are examples of materials not used as the base material for the prechamber wall section 22 if the base material of the cylinder head 10 is aluminum or an aluminum alloy.

[0064] [Tables 1] ivsstiere CondtrclMté thermique iw / m. Density (g / s³) Massive Weight Density Specific Gravity Melting Point Reference Minimum Iron 239.0 2.693 0.917 2.467 660.3 Reference Decarbonate-based stainless steel 26.0 7.700 6.460 3.542 1480 Exempt from production 1 Copper - Chromium - Chromium (C 18150) 320.0 8.900 1111 375 3.346 1050 Example of production 2 Copper 393.0 8.930 0.386 3.447 1085 Exempt from production 3 Iron 804 7.870 0.440 3.463 1538 Exempt from re-evaluation 4 Aluminum ceramic Altsmine 99.7K1 29.0 3.933 0.800 3.120 2072 Comparison example 1 Titans 22.0 4.510 0.527 2.37? 1668 Exempt from comparison 2 1 nconéi 718 deposited • 11.0 8.193 0.440 3.604 1230 Comparison example 3 1 stainless steel 304 16.3 7.930 0.502 3.981 1400-1503

[0065] The prechamber wall section 22 may consist solely of the base material. The prechamber wall section 22 may also consist of the base material and a material other than the base material. For example, the prechamber wall section 22 may have a coating layer of a material different from the base material on at least a portion of the external surface of the prechamber wall section 22. Preferably, the thermal conductivity of the coating layer should be higher than that of the prechamber wall section 22.

[0066] Third embodiment The four-stroke pre-ignition engine 1 of the third embodiment of the present invention will be explained with reference to [Fig. 2](a). The four-stroke pre-ignition engine 1 of the third embodiment has, in addition to the configuration of the first or second embodiment, the following configuration: No protrusion is formed on the internal surface of the prechamber 20, except for the prechamber spark plug 23. The greater length, between the length L1 of the internal space of the prechamber 20 along the axial direction of spark plug DP and the maximum length L2 of the internal space of the prechamber 20 along the direction orthogonal to the axial direction of spark plug DP, is less than twice the smaller length. In [Fig. 2](a), the length L2 is greater than the length L1, but the length L1 can be greater than the length L2.

[0067] Fourth embodiment The four-stroke pre-combustion engine 1 of the fourth embodiment of the present invention will be explained with reference to [Fig. 2](b). The fourth embodiment has at least one configuration among embodiments 1 to 3. In the fourth embodiment, the pre-chamber wall section 22 projects into the interior space of the main combustion chamber 2. Furthermore, in the fourth embodiment, the pre-chamber 20 is formed such 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 specifically, if the interior space of the prechamber 20 is divided into two spaces along one of the SI planes that traverse the interior space of the prechamber 20 without crossing the external surface of the prechamber wall section 22, and intersect orthogonally with the axial direction of spark plug DP, the prechamber 20 is formed such that the volume of the space closest to the main combustion chamber 2 is less than the volume of the space furthest from the main combustion chamber 2. The SI plane shown in [Fig. 2](b) is just one example of an SI plane that traverses the interior space of the prechamber 20 without crossing the external surface of the prechamber wall section 22, and is orthogonal to the axial direction of spark plug DP. Furthermore, the external surface of the prechamber wall section 22 is the surface exposed to the main combustion chamber 2.The prechamber 20, formed such that the volume of the space closest to the main combustion chamber 2 is less than the volume of the space furthest from the main combustion chamber 2 if the interior space of the prechamber 20 is divided into two spaces along one of the planes SI passing through the interior space of the prechamber 20 without crossing the external surface of the prechamber wall section 22 and intersecting orthogonally with the axial direction of spark plug DP, means that it is not a prechamber 20 as described below. This prechamber 20 is such that a relationship described below is formed concerning all planes passing through the interior space of the prechamber 20 without crossing the external surface of the prechamber wall section 22 and intersecting orthogonally with the axial direction of spark plug 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 the interior space of the prechamber 20 is divided into two spaces along a plane.

[0068] Fifth embodiment The four-stroke pre-combustion engine 1 of the fifth embodiment of the present invention will be explained with reference to 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 among embodiments 1 to 4. In the fifth embodiment, the internal surface of the prechamber 20 is formed by the prechamber part 25 and the prechamber spark plug 23, including the prechamber wall section 22. In other words, the internal space of the prechamber 20 is the space enclosed by the prechamber part 25 and the prechamber spark plug 23. The external cylindrical surface of the prechamber spark plug 23 and the internal cylindrical surface of the prechamber part 25 are in contact.The pre-chamber component 25 is a separate component from, on the one hand, the cylinder head body 13, a portion of which is exposed in the interior space of the main combustion chamber 2, and from the pre-chamber spark plug 23, on the other hand. The cylinder head body 13 may consist of a single, inseparable component, or it may consist of several separable components, a portion 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 components, the cylinder head body does not include the component a portion of which is not exposed in the interior space of the main combustion chamber 2.

[0069] The external cylindrical surface of the prechamber 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 prechamber part 25 can engage with and be in contact with the tapped hole 40 formed on the cylinder head body 13, as shown in Figure 3(b), for example. If the external cylindrical surface of the prechamber part 25 is in contact with the cylinder head body 13, one of the planes S2 passing through the internal space of the prechamber 20 and orthogonal to the axial direction of the spark plug DP can pass through the portion of the external cylindrical surface of the prechamber 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 contacting part can pass through the area where the external thread 41 formed on the pre-chamber piece 25 is assembled and is in contact with the tapped hole 40 formed on the cylinder head body 13, as shown, for example, in [Fig. 3](b). The plane S2 passing through the contacting part can also pass through a non-threaded area (external thread 41 and tapped hole 40) of the pre-chamber piece 25 and the cylinder head body 13, as shown in [Fig. 3](b). The external cylindrical surface of the pre-chamber piece 25 shown in [Fig. 3](c) can be in contact with the cylinder head body 13 in an area not shown. For example, the external cylindrical surface of the prechamber part 25 shown in [Fig.3](c) may be in contact with the cylinder head body 13, so that one of the planes (not shown), passing through the prechamber spark plug 23 and orthogonal to the axial direction of spark plug DP does not. passing through the inner space of the prechamber 20, crosses the part of the external cylindrical surface of the prechamber piece 25 in contact with the cylinder head body 13. In this case, the part in contact between the external cylindrical surface of the prechamber piece 25 and the cylinder head body 13 may be a threaded part (external thread 41 and tapped hole 40), or not.

[0070] The external cylindrical surface of the prechamber piece 25 may not be in contact with the cylinder head 13. The external cylindrical surface of the prechamber piece 25 shown, for example, in [Fig. 3](c) may not be in contact with the cylinder head. For example, the prechamber piece 25 may be connected to the cylinder head via a part that is not the cylinder head 13 (for example, a cylinder head cover).

[0071] The prechamber 25 and the cooling unit 16 can be formed such that one of the planes S3 passing through the cooling unit 16 and orthogonal to the axial direction of the spark plug DP also passes through the prechamber 25, as shown, for example, in Figures 4(a) and 4(d). If the plane S3 passes through the prechamber 25, a portion of the internal surface of the cooling unit 16 may be at least a portion of the external cylindrical surface of the prechamber 25, as shown, for example, in Figures 4(a) and 4(c). If the plane S3 passes through the prechamber 25, the internal surface of the cooling unit 16 may not include a portion of the external cylindrical surface of the prechamber 25, as shown, for example, in Figure 4(d).Furthermore, the pre-chamber piece 25 and the cooling unit 16 can be formed such that no plane S3 passing through the cooling unit 16 and orthogonal to the axial direction of spark plug DP crosses the pre-chamber piece 25, as shown for example in [Fig. 4](e). Moreover, the relationship between the pre-chamber piece 25 and the cylinder head body 13 shown in Figures 4(a) to 4(d) is not limited to the relationship identical to that of [Fig. 3](a), and can be any relationship described above.

[0072] If a portion of the internal surface of the cooling unit 16 is at least a portion of the external cylindrical surface of the prechamber part 25, the prechamber part 25 may have at least one heat dissipation unit 26 projecting into the internal space of the cooling unit 16, as shown in [Fig. 4](b). The heat dissipation unit 26 may or may not be circular. For example, the heat dissipation unit may be in the shape of an arc larger than a semicircle, or it may not be arc-shaped. The circular heat dissipation unit 26 may be shaped to compartmentalize the internal 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 spark plug DP.

[0073] If one of the planes S3 passing through the cooling unit 16 passes through the prechamber 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 prechamber part 25 is in contact with the external cylindrical surface of the prechamber spark plug 23. If one of the planes S3 passing through the cooling unit 16 passes through the prechamber part 25, one of the planes S3 passing through the cooling unit 16 can pass through the part where the tapped hole 42 formed on the prechamber part 25 is assembled and is in contact with the external thread 43 formed on the prechamber spark plug 23, as shown for example in Figures 5(a) and 5(b). Furthermore, the cooling unit 16 of [Fig.5](a) is identical to the cooling unit 16 of [Fig.4](a), but may be identical to that of [Fig.4](b). The cooling unit 16 of [Fig.5](b) is identical to that of [Fig.4](d), but may be identical to that of [Fig.4](c). Furthermore, the relationship between the pre-chamber part 25 and the cylinder head body 13 shown in Figures 5(a) and 5(b) is not limited to the relationship identical to that of [Fig.3](a), and may be any relationship 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 pre-chamber spark plug 23.

[0074] The present invention is not limited to the embodiments described above and can be modified in various ways as described in the scope of this invention. For example, the four-stroke pre-ignition engine of the present invention may have a supercharger or a turbocharger. The four-stroke pre-ignition engine may have a main combustion chamber fuel injector that injects fuel into the main combustion chamber. Caption

[0075] 1: Four-stroke pre-combustion engine 2: Main combustion chamber 5: Admission 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 pre-chamber 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 points 22: Prechamber wall section 23: Pre-chamber spark plug 24: Electrode group 25: Pre-chamber room 33: Spark discharge 40: Tapping of the cylinder head body 41: External thread of the prechamber part 42: Tapping of the prechamber piece 43: External thread of the pre-chamber spark plug 70: Control device DP: Axial direction of the spark plug L1: Length of the internal space of the prechamber along the axial direction of the spark plug L2: Maximum length of the prechamber interior space in the direction orthogonal to the axial direction of the spark plug S1, S2, S3: Plan

Claims

1. Demands Four-stroke pre-ignition 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 amount of air that passes through said intake passage (5) and is admitted into said main combustion chamber (2); - an intake injector (8) injecting into said intake passage (5) a liquid fuel, said liquid fuel being a gasoline fuel, an alcohol-based fuel, or a mixture of gasoline fuel 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 connecting ports (21), and in which a portion of a prechamber spark plug (23) is exposed in the interior space of the prechamber (20); and - a control device (70) controlling said intake injector (8) and said pre-chamber spark plug (23); said control device (70) controlling said intake injector (8) over at least a portion of a low-load zone where the opening angle of said throttle valve (7) is small, so that an air-fuel mixture, mixed in said intake passage (5) and said main combustion chamber (2), is: - a first air / fuel ratio, which can be treated in a three-way catalyst after combustion, or - a second air / fuel ratio richer than the said first air / fuel ratio; said four-stroke pre-combustion engine (1) not having: - a pre-combustion injector, which would inject fuel into said pre-chamber (20), - nor any ignition aid device that would assist in the ignition of the air-fuel mixture in said pre-chamber (20) or said main combustion chamber (2); and

2. said cylinder head (10) has a cooling unit (16) in which is contained a coolant receiving heat from a group of electrodes (24) of said pre-chamber spark plug (23) and a pre-chamber wall section (22), where said connecting orifices (21) are formed; the interior space of said prechamber (20) being the space enclosed by said prechamber ignition plug (23) and by a prechamber part (25), the prechamber component (25) comprises said prechamber wall section (22) and is formed to be independent of both said prechamber spark plug (23) and a cylinder head body (13) which is partially exposed in the interior space of said main combustion chamber (2); and a plane (S3), passing through said cooling unit (16) and orthogonal to the axial direction (DP) of said pre-chamber spark plug (23), passes through the part where an external thread (43) formed on said pre-chamber spark plug (23) is assembled and is in contact with an internal tapped hole (42) formed on said pre-chamber part (25); and a portion of the internal surface of said cooling unit (16) being at least a portion of an external cylindrical surface of said prechamber part (25); - said electrode group (24) of said pre-chamber spark plug (23) is formed so that several spark discharges (33) occur on said electrode group (24) and that these spark discharges (33) are distributed circumferentially on said electrode group (24); - said connecting orifices (21) are formed so as to be distributed circumferentially; and - said cylinder head (10) is formed so that thermal paths (14), from said electrode group (24) of said prechamber spark plug (23) to said cooling unit (16), and thermal paths (15), from said prechamber 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 wall section of prechamber (22) has a higher melting point than a base material of said cylinder head (10), a value of the base material of said prechamber wall section (22) which is obtained by a multiplication of the 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 prechamber wall section (22) is greater than or equal to that of a chromium-based stainless steel.

3. The four-stroke pre-combustion engine (1) according to claim 1 or 2, characterized in that a length (L1) of the internal space of said prechamber (20) along the axial direction of the spark plug (DP) of said prechamber spark plug (23) is less than twice the maximum length (L2) of the internal space of the prechamber (20) along a direction orthogonal to said axial direction of the spark plug (DP), without any protrusion other than said prechamber spark plug (23) being formed on an internal surface of said prechamber (20).

4. The four-stroke pre-combustion engine (1) according to any one of claims 1 to 3 characterized in that said pre-chamber wall section (22) protrudes into the interior space of said main combustion chamber (2); and by dividing the interior space of said pre-chamber (20) into two spaces along one of the planes (SI): - passing through the interior space of said pre-chamber (20) without passing through the external surface of said pre-chamber wall section (22), and - cutting orthogonally across said axial direction (DP) of said pre-chamber spark plug (23), said pre-chamber (20) is formed such 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.

5. The four-stroke pre-combustion engine (1) according to any one of claims 1 to 4 characterized in that the external cylindrical surface of said pre-chamber part (25) is in contact with said cylinder head body (13).

6. The four-stroke pre-combustion engine (1) according to claim 5 characterized in that a plane (S2), passing through the internal space of said prechamber (20) and orthogonal to the axial direction (DP) of said prechamber spark plug (23), passes through the part where the external cylindrical surface of said prechamber part (25) is in contact with said cylinder head body (13).

7. The four-stroke pre-combustion engine (1) according to claim 6 characterized in that a plane (S2), passing through the interior space of the prechamber (20) and orthogonal to said axial direction of the spark plug (DP), passes through the part where an external thread (41) formed on said prechamber piece (25) which assembles and is in contact with a tapped hole (40) formed on said cylinder head body (13).

8. The four-stroke pre-combustion engine (1) according to any one of claims 1 to 7 characterized by the absence of a main combustion chamber fuel injector, which would inject fuel into said main combustion chamber (2).

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