Four-stroke engine with pre-ignition

Abstract

The pre-chamber (20) of a four-stroke pre-ignition engine (1) is formed such that the greater length, between the length (L1) of an internal space of the pre-chamber in an axial direction (DP) of a pre-chamber spark plug (23) and the maximum length (L2) of the internal space of the pre-chamber in a direction orthogonal to the axial direction of the spark plug, is less than twice the smaller length. The angle θ formed by the segment (LSa), connecting the central axis (C23) of the pre-chamber spark plug and the center (C3a) of a first intake port (3a), considered along the central axis (C21ia) of the first intake port (21a), is -17° < θ < 17°. The central axis of the first intake port passes between the valve head (14) of an intake valve and the first intake opening when the intake valve (13), which can open and close the first intake opening, is open. (See Figure 1 for abbreviations.)

Description

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

[0001] Technical domain The present invention relates to a four-stroke pre-combustion engine comprising a main combustion chamber and a pre-chamber.

[0002] Prior art We are already aware of four-stroke pre-combustion engines having a main combustion chamber and a pre-chamber connected via several connecting ports, as disclosed in patent document 1, for example. The internal air-fuel mixture in the pre-chamber is ignited by a spark plug. The four-stroke pre-combustion engine in patent document 1 has an intake injector that injects fuel into the intake manifold, but no pre-combustion injector that injects fuel into the pre-chamber. The intake injector in patent document 1 is controlled to generate in the main combustion chamber an air-fuel mixture with a stoichiometric ratio or richer than stoichiometric.

[0003] Prior technical documentation Patent documents Patent Document 1: U.S. Patent Application No. 10612454

[0004] Overview of the invention Problems that the invention attempts to solve The four-stroke pre-ignition engine described in patent document 1 has an auxiliary spark plug (ignition aid device) that assists in igniting the air-fuel mixture in the main combustion chamber. The four-stroke pre-ignition engine described in patent document 1 has an auxiliary spark plug to ensure engine performance under low loads. Therefore, if an auxiliary spark plug (ignition aid device) is not installed, it is difficult to ensure engine performance under low loads.

[0005] The present invention aims to provide a four-stroke pre-combustion engine capable of ensuring engine performance under low loads even if an ignition aid device is not installed. Ways to solve problems

[0006] The four-stroke pre-combustion engine of an embodiment of the present invention has the following configuration: - a main combustion chamber having at least one intake port connected to an intake passage and at least one exhaust port connected to an exhaust passage; - a throttle valve adjusting the amount of air that passes through the intake passage and is admitted into the main combustion chamber; - an intake injector (8) injecting liquid fuel into the intake passage, said liquid fuel being petrol fuel, alcohol-based fuel, or a mixture of petrol fuel and alcohol-based fuel; - a prechamber whose volume is smaller than a 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 part of a prechamber spark plug is exposed in the interior space of the prechamber; - a control device controlling the intake injector and the pre-chamber spark plug; The four-stroke pre-combustion engine is characterized in that: (a) the control device directs the intake injector over at least a portion of a low-load area where an opening angle of said throttle valve is small, so that the injection of liquid fuel terminates before an intermediate point between an exhaust top dead center and an intake bottom dead center, and that an air-fuel mixture, mixed in the intake passage and the main combustion chamber, is either 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; (b) the four-stroke pre-combustion engine not including a pre-combustion injector, which would inject fuel into said pre-chamber, or an ignition aid device, which would assist in the ignition of the air-fuel mixture in the pre-chamber or the main combustion chamber; and (c) to eliminate the ratio of the area of ​​an internal surface of said prechamber to the volume of said prechamber, said prechamber: (i) is formed without protrusion on the internal surface of the prechamber except for said prechamber spark plug, and (ii) is formed such that the greater of a length of the interior space of said prechamber extending along a spark plug axial direction parallel to a central axis of the prechamber spark plug and a maximum length of the interior space of the prechamber orthogonal to the spark plug axial direction, is less than twice the smaller of the two lengths; and (d) in such a way that said liquid fuel injected into the intake passage can easily enter the prechamber by passing through a first intake orifice, which is one of the connecting orifices, from a first intake mouth, said first intake mouth being included in the less one intake port, said first intake port is formed such that: (i) an angle 0, formed by a segment connecting the central axis of said pre-chamber spark plug and the center of said first intake port with a central axis of the first intake port, is between -17° < 0 < 17° according to a view in said axial direction of the spark plug, and (ii) the central axis of the first intake port passes between a valve head of an intake valve and the first intake port when the intake valve is opened, the intake valve opening and closing the first intake port, according to a view in a cutting plane including the central axis of the first intake port and which is parallel to a central axis of a cylindrical hole, said cylindrical hole forming the main combustion chamber.

[0007] According to this configuration, no protrusion is formed on the inner surface of the prechamber, with the exception of the prechamber spark plug. Furthermore, the greater of the two lengths, the length of the inner space of the prechamber along the axial direction of the spark plug and the greater of the length of the inner space of the prechamber along the direction orthogonal to the axial direction of the spark plug, is less than twice the smaller of the two lengths. The ratio of the area of ​​the inner surface of the prechamber to the volume of the prechamber is thus limited by these two characteristics. Furthermore, the angle 0, formed by the segment connecting the central axis of the pre-chamber spark plug and the center of the first intake port, with the central axis of the first intake port, which is one of the connecting ports, viewed in the direction parallel to the axial direction of the spark plug, is between -17° ("minus seventeen degrees") < 0 < 17° ("plus seventeen degrees")°. Moreover, the central axis of the first intake port passes between the valve head of the intake valve and the first intake port during the opening of the intake valve, which opens and closes the first intake port, on a cross-sectional plane parallel to the central axis of the cylindrical bore and including the central axis of the first intake port.The flow of liquid fuel particles spread along the intake valve head can easily enter the first intake port due to these two characteristics when the intake valve opens. The liquid fuel injected into the intake passage can thus easily enter the pre-chamber by passing through the first intake port from the first intake opening. Furthermore, the connecting port through which the liquid fuel introduced into the pre-chamber passes is not limited to the first intake port among the connecting ports. The injection of liquid fuel by the intake injector terminates before the intermediate point between the exhaust top dead center (TDC) and top dead center. The intake manifold is at its lowest point (BMP) over at least part of the low-load region. For this reason, fuel injected into the intake manifold from the intake injector can easily enter the main combustion chamber from the intake port. The amount of liquid fuel present at low loads is greater compared to when the air-fuel mixture has a leaner air / fuel ratio than the first air / fuel ratio. This is because the air-fuel mixture, blended in the intake manifold and the main combustion chamber over at least part of the low-load region, has either a first or second air / fuel ratio richer than the first air / fuel ratio. However, the amount of liquid fuel present at low loads is less than the amount present at high loads.Furthermore, when liquid fuel, which is gasoline fuel, alcohol-based fuel, or a mixture of gasoline and alcohol-based fuel injected from the intake injector, is introduced into the main combustion chamber from the first intake port, the liquid fuel particles are relatively large and the inertial force of the liquid fuel particles is relatively large.It is possible to introduce liquid fuel, in small quantities under low loads such as when idling, but with relatively large particles and a relatively large inertial force, to the bottom of the prechamber interior space by forming a prechamber so that the first intake port is formed to allow the flow of liquid fuel particles spread along the valve head of the intake valve to enter easily, and to limit, in order to eliminate the need for it, the ratio of the area of ​​the internal surface to the volume at the rear of the first intake port, as described above.This makes it possible to increase the ignition capacity of the air-fuel mixture in the pre-chamber and the injection power of the flame injected from the connecting ports, and to ensure engine performance under low loads even if an ignition aid device is not installed. Furthermore, "liquid fuel is introduced into the prechamber" does not mean that the fuel is introduced into the prechamber in liquid form, but simply means that the liquid fuel, which is the generic term for gasoline fuel, alcohol-based fuel, and gasoline-alcohol fuel mixture in this application, is introduced into the prechamber. The "high ignition capacity of the air-fuel mixture" means that the air-fuel mixture ignites (ignites) easily.

[0008] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: the connecting orifices may be formed so that the central axis of the first intake orifice does not coincide with the central axis of any other connecting orifice other than said first intake orifice among said connecting orifices, according to a view in said axial direction of spark plug and in the direction orthogonal to both the plane including the central axis of the first intake orifice and the central axis of the cylindrical hole, so that said liquid fuel introduced into the prechamber by passing through the first intake orifice may be less easily evacuated by the connecting orifices.

[0009] According to this configuration, viewed from the axial direction of the spark plug, the central axis of the first intake orifice does not coincide with the central axis of any other connecting orifice other than the first intake orifice. Furthermore, the central axis of the first intake orifice does not coincide with the central axis of any other connecting orifice other than the first intake orifice when viewed in the direction orthogonal to both the plane containing the central axis of the first intake orifice and the central axis of the cylindrical bore. For this reason, the liquid fuel introduced into the prechamber through the first intake orifice is difficult to evacuate through the connecting orifices. Consequently, it is easy to introduce liquid fuel to the bottom of the prechamber's internal space.As a result, it is possible to further increase the ignition capacity of the air-fuel mixture in the pre-chamber and the injection power of the flame injected from the connecting ports. This makes it possible to ensure even more reliable engine performance under low loads.

[0010] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: by defining a guideline for the connecting ports as a half-line that would overlap the central axis of the connecting ports and extend from the connecting ports towards the main combustion chamber without crossing the interior space of the prechamber, the intake ports, being ports among the connecting ports, may include said first intake port and may each have a guideline arranged such that the shortest distance between the guideline and at least one intake port in a circumferential direction around the central axis of said pre-chamber spark plug is shorter than the shortest distance between the guideline and at least one exhaust port in a circumferential direction around the central axis of said pre-chamber spark plug, according to a view in the axial direction of the spark plug; and The exhaust ports, being ports among the connecting ports, can each have a guide line arranged such that the shortest distance between the guideline and at least one exhaust port in a circumferential direction around the central axis of said pre-chamber spark plug is shorter than the shortest distance between the guideline and at least one intake port in a circumferential direction around the central axis of said pre-chamber spark plug, according to a view in the axial direction of the spark plug, and the number of intake ports may be less than the number of exhaust ports.

[0011] According to this configuration, it is possible to further increase the diameter of the intake ports and decrease the diameter of the exhaust ports, while maintaining the total cross-sectional area of ​​the intake ports and the total cross-sectional area of ​​the exhaust ports, respectively, compared to the case where the number of intake ports is greater than or equal to the number of exhaust ports, since the number of intake ports is less than the number of exhaust ports. For this reason, it is easy to introduce the liquid fuel injected into the intake passage from the intake ports into the pre-chamber, while maintaining the injection power of the flame injected from the connecting ports. It is therefore possible to ensure even more reliable engine performance under low loads.Liquid fuel can be introduced into the pre-chamber from the exhaust ports. Furthermore, it is possible to prevent exhaust gases from entering the pre-chamber from the exhaust ports by reducing the diameter of the exhaust ports while maintaining the full cross-sectional area of ​​both the intake and exhaust ports. Moreover, the connecting ports through which the liquid fuel enters the pre-chamber are not limited to the intake ports.

[0012] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: by defining a guideline for the connecting orifices as a half-line that would overlap the central axis of the connecting orifices and extend from these connecting orifices towards the main combustion chamber without crossing the interior space of the prechamber, The exhaust ports, being ports among the connecting ports, may each have a guide line arranged such that the shortest distance between the guide line and at least one exhaust port in a circumferential direction around the central axis of said pre-chamber spark plug is shorter than the shortest distance between the guide line and at least one intake port in a circumferential direction around the central axis of said pre-chamber spark plug, according to a view in the axial direction of the spark plug, and the smallest diameter of the first intake orifice is greater than the largest diameter of the exhaust orifices.

[0013] According to this configuration, it is easy to introduce the liquid fuel injected into the intake passage from the first intake port into the pre-chamber, while maintaining the injection power of the flame injected from the connecting ports, compared to the case where the smallest diameter of the first intake port is less than or equal to the largest diameter of the exhaust ports, since the smallest diameter of the first intake port is larger than the largest diameter of the exhaust ports. It is therefore possible to ensure even more reliable engine performance under low loads. Furthermore, it is possible to prevent the introduction of exhaust gases into the pre-chamber from the exhaust ports, since the smallest diameter of the first intake port is larger than the largest diameter of the exhaust ports.Furthermore, the connecting orifice through which the liquid fuel introduced into the pre-chamber passes is not limited to the intake orifices among the connecting orifices.

[0014] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: by defining a guideline for the connecting ports as a half-line that would overlap the central axis of the connecting ports and extend from the connecting ports towards the main combustion chamber without crossing the interior space of the prechamber, the exhaust ports, being ports among the connecting ports, may each have a guideline arranged such that the shortest distance between the guideline and at least one exhaust port in a circumferential direction around the central axis of said pre-chamber spark plug is shorter than the shortest distance between the guideline and at least one intake port in a circumferential direction around the central axis of said pre-chamber spark plug, according to a view in the axial direction of the spark plug, and said first intake port may be formed such that the diameter of said first inlet hole increases along its central axis in the direction of the main combustion chamber, and said exhaust ports may be formed so that their diameter does not increase along their central axis in the direction of the main combustion chamber.

[0015] According to this configuration, it is even easier to introduce into the pre-chamber the liquid fuel injected into the intake passage from the first intake orifice, while maintaining the injection power of the flame injected from The first intake port is designed to increase in diameter along its central axis towards the main combustion chamber, unlike a port where its diameter increases as it approaches the main combustion chamber. This allows for even more reliable engine performance under light loads. Furthermore, it prevents exhaust gases from entering the pre-chamber from the exhaust ports, unlike a port where the exhaust ports increase in diameter along their central axis towards the main combustion chamber.Furthermore, the connecting orifice through which the liquid fuel introduced into the pre-chamber passes is not limited to the intake orifices among the connecting orifices.

[0016] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: The total area of ​​a cross-section orthogonal to the central axis of each of said connecting orifices may be between 5.7 mm2 and 7.6 mm2 inclusive.

[0017] According to this configuration, it is easy to ensure the injection power of the flame injected from the combustion chambers, even under low loads such as idle. Consequently, it is possible to ensure engine performance under low loads with even greater certainty. Furthermore, if the connecting ports include connecting ports with non-constant diameters, "the total area of ​​a cross-section perpendicular to the central axis of each of the connecting ports is between 5.7 mm² and 7.6 mm²" means that at least the total minimum or maximum value of the cross-sectional area perpendicular to the central axis of each of the connecting ports is between 5.7 mm² and 7.6 mm². In addition, each of the connecting ports can have a constant diameter.

[0018] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: A minimum diameter of said first inlet orifice may be between 1.0 mm and 1.2 mm inclusive, and a volume of said prechamber may be between 328 mm3 and 802 mm3 inclusive.

[0019] According to this configuration, it is easy to ensure the injection power of the flame injected from the combustion chambers, even under low loads such as idle. Consequently, it is possible to ensure engine performance even more reliably under low loads.

[0020] The four-stroke pre-combustion engine of an embodiment of the present The invention may have the following configuration: A minimum diameter of said first inlet orifice may be greater than 1.2 mm and may be less than or equal to 1.4 mm, and a volume of said prechamber may be between 328 mm3 and 1151 mm3 inclusive.

[0021] According to this configuration, it is easy to ensure the injection power of the flame injected from the combustion chambers, even under low loads such as idle. Consequently, it is possible to ensure engine performance even more reliably under low loads.

[0022] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration - the connecting orifices can be formed on a section of the prechamber wall, the section of the prechamber wall protruding into the interior space of the main combustion chamber; - by dividing the interior space of the prechamber into two spaces along one of the planes traversing the interior space of said prechamber without crossing the external surface of said section of the prechamber wall, and intersecting said axial direction of the spark plug orthogonally, said pre-chamber may be formed such that the volume of the space closest to the 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

[0023] According to this configuration, even though the prechamber wall section protrudes into the interior space of the main combustion chamber, the volume of this protrusion is small. Consequently, the connecting orifices formed on the prechamber wall section are close to the part of the inner surface of the main combustion chamber that is not the outer surface of the prechamber wall section. For this reason, it is easy for liquid fuel particles flowing along the inner surface of the main combustion chamber from the first intake orifice to be introduced into the prechamber.

[0024] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: It can be characterized in that it does not include a knock sensor; and the control device can control the pre-chamber spark plug so as to ignite the air-fuel mixture inside the pre-chamber at a predetermined ignition time, based on an output signal from an operating state detection sensor that can detect the operating state of said pre-combustion four-stroke engine, and that is not a knock sensor.

[0025] The four-stroke engine with pre-combustion having a pre-chamber, it can prevent The present invention addresses the sudden increase in the probability of knocking when the ignition timing is gradually advanced, compared to the case without a pre-chamber. Furthermore, the present invention can further mitigate this sudden increase in the probability of knocking, as it is easy to introduce liquid fuel injected into the intake passage, as described above, into the pre-chamber. For this reason, it is possible to bring the ignition timing closer to the optimal setting, known as the "minimum advance for best torque," while avoiding knocking without the use of a knock sensor.

[0026] The four-stroke pre-combustion engine according to an embodiment of the present invention can be characterized in that it has neither a supercharger nor a turbocharger.

[0027] The four-stroke pre-combustion engine according to an embodiment of the present invention can be characterized by the absence of a main combustion chamber fuel injector, which would inject fuel into said main combustion chamber.

[0028] The four-stroke pre-combustion engine of an embodiment of the present invention may have the following configuration: a compression ratio of the four-stroke pre-combustion engine may be greater than or equal to 11.

[0029] 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.

[0030] In the present invention and its embodiments, "injection ends before an intermediate point between exhaust top dead center and intake bottom dead center" means that injection ends before the crankshaft angle reaches the crankshaft angle of the intermediate point between exhaust top dead center and intake bottom dead center in one cycle (4 strokes). The term "intermediate" here means "in the middle".

[0031] 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 the first air / fuel ratio, the second air / fuel ratio, and the 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 can be the theoretical mixture ratio (stoichiometric ratio), or a range of air / fuel ratios including the theoretical mixture ratio. The first air / fuel ratio can be an air / fuel ratio close to the stoichiometric ratio. The first air / fuel ratio can be a range including an air / 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 such that the exhaust gases produced after combustion of the air-fuel mixture can be treated with a three-way catalyst. The control device can control the intake injector over at least a portion of the low-load range, so that the air-fuel mixture, mixed in the intake passage and the main combustion chamber, is either the stoichiometric ratio or a richer air / fuel ratio 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 which is disposed between the main combustion chamber and the catalyst, and which detects the oxygen concentration of the exhaust gases flowing in the exhaust passage.

[0032] 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.

[0033] In the present invention and its embodiments, the expression "the volume of the The prechamber volume being 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 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 a protrusion formed on the surface is solely due to the prechamber spark plug.

[0034] 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 prechamber interior space in the direction orthogonal to the axial direction of the spark plug is the maximum length among the lengths of the prechamber interior space located in several directions orthogonal to the axial direction of the spark plug.

[0035] In the present invention and its embodiments, the central axis of the cylindrical hole is not a segment that exists only in the area where the cylindrical hole exists, but is a straight line that extends to infinity. In the present invention and its embodiments, the central axis of the pre-chamber spark plug is not a segment existing only in the area where the pre-chamber spark plug is located, but is a straight line extending to infinity. The central axis of the pre-chamber spark plug may or may not be parallel to the central axis of the cylindrical bore.

[0036] In the present invention and its embodiments, the inlet port is The exhaust port is the end closest to the main combustion chamber on the circular portion in contact with the valve head of the intake valve. The number of intake ports in the present invention may be one or more.

[0037] In the present invention and its embodiments, the central axis of the first inlet orifice is not a segment that exists only in the area where the first inlet orifice (connecting orifice) exists, but is a straight line that extends to infinity. The definition of the central axis of the connecting orifices is identical. In the present invention and its embodiments, "the half-line which is superimposed on the central axis of the connecting orifices and which extends towards the main combustion chamber without crossing the interior space of the prechamber from the connecting orifices" does not include the part of the central axis of the connecting orifices located inside the connecting orifices. In the present invention and its embodiments, the diameter of the first intake port is the diameter of the first intake port (connecting port) in cross-section perpendicular to the central axis of the first intake port (connecting port). The diameter of the exhaust port, which is a connecting port, has the same definition. Furthermore, the diameter of the intake port, which is a connecting port, also has the same definition. In the present invention and its embodiments, if the maximum diameters of the exhaust ports differ from one another, "the minimum diameter of the first intake port is greater than the maximum diameter of the exhaust ports" means that the minimum diameter of the first intake port is greater than the maximum value of each of the maximum diameters of the exhaust ports.

[0038] In the present invention and its embodiments, the term "inlet orifice" is not used to designate an orifice used for intake. The term "inlet orifice" is used because it refers to a connecting orifice located near the intake opening. In the present invention and its embodiments, the first inlet orifice is a connecting orifice located near the first intake opening.

[0039] In the present invention and its embodiments, the name "exhaust orifice" is not used to designate an orifice used for exhaust. The name "exhaust orifice" is used because it is a connecting orifice close to the exhaust outlet.

[0040] In the present invention and its embodiments, "the exhaust ports each have a guideline whose shortest distance to at least one exhaust port in a circumferential direction around the central axis of the "The shortest distance between the direct line of these exhaust ports and at least one exhaust port in the circumferential direction around the central axis of the prechamber spark plug, viewed in the axial direction of the spark plug" means that the shortest distance between the direct line of these exhaust ports and at least one exhaust port in the circumferential direction around the central axis of the prechamber spark plug is less than the shortest distance between the direct line of these exhaust ports and at least one intake port in the circumferential direction around the central axis of the prechamber spark plug, viewed in the axial direction of the spark plug.If the guideline of an exhaust port passes through the exhaust port viewed in the axial direction of the spark plug, the shortest distance between the guideline of the exhaust port and the exhaust port viewed in the axial direction of the spark plug is zero. In the present invention and its embodiments, "the intake ports each have a guideline whose distance to at least one intake port in a circumferential direction around the central axis of the pre-chamber spark plug is shorter than the shortest distance to at least one exhaust port in a circumferential direction around the central axis of the pre-chamber spark plug, viewed in the axial direction of the spark plug" has a definition identical to that above.

[0041] In the present invention and its embodiments, the connecting orifices can be formed on the prechamber wall section, which may or may not protrude into the interior space of the main combustion chamber. The prechamber wall section where the connecting orifices are formed is the wall section having an exposed side (external surface) in the interior space of the main combustion chamber. If the prechamber wall section has a tubular portion, the prechamber wall section is formed so as to protrude into the interior space of the main combustion chamber. The prechamber wall section may be a separate component from the prechamber spark plug, or it may be inseparably integrated into the prechamber spark plug."The prechamber wall section is a separate part from the prechamber spark plug" means that the part including the prechamber wall section is separate from the prechamber spark plug, or that the part including the prechamber wall section is in contact with the prechamber spark plug in a separable manner.

[0042] In the present invention and its embodiments, the compression ratio of the four-stroke pre-combustion engine is the ratio of the maximum value to the minimum value of the volume of the main combustion chamber.

[0043] In the present invention and its embodiments, the detection sensor The engine operating status sensor, which detects the operating status of the four-stroke pre-ignition engine, is a sensor that detects the state related to factors that affect the ignition timing decision. It is a sensor that detects, for example, throttle pressure, load, engine speed, intake temperature, intake air quantity, atmospheric pressure, internal combustion engine temperature, oil temperature, coolant temperature, engine wall temperature, and exhaust gas temperature.

[0044] 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.

[0045] 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. A saddle-mounted vehicle includes, among others, a motorcycle, a scooter, a three-wheeled motor vehicle, a four-wheeled buggy (all-terrain vehicle), a snowmobile, or a 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 and compact engine. Furthermore, it goes without saying that the four-stroke pre-ignition engine can be mounted on a car. Products equipped with the four-stroke pre-ignition engine of the present invention and its embodiments are not limited to specific products. If the four-stroke pre-ignition engine of an embodiment of the present invention is fitted to a product, it can be installed so that the central axis of the cylindrical bore 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°.

[0046] 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.

[0047] 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.

[0048] 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 referred to with "may" produces at least the aforementioned effects obtained from the configuration of the present invention.

[0049] 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

[0050] According to the four-stroke pre-combustion engine of the present invention, it is possible to ensure engine performance under low loads even if an ignition aid device is not installed, because it is possible to increase the ignition capacity of the air-fuel mixture of the prechamber and the injection power of the flame injected from the connecting orifices. Brief description of the drawings

[0051] [Fig. 1] Figures 1(a) and 1(b) are an example of a four-way motor diagram pre-combustion time of the first embodiment of the present invention. [Fig.2] Figures 2(a) and 2(b) are two examples of diagrams of the four-stroke pre-combustion engine of the second embodiment of the present invention, Figures 2(c) and 2(d) are two examples of diagrams of the four-stroke pre-combustion engine of the third embodiment of the present invention, and [Fig.2](e) is an example of the four-stroke pre-combustion engine of the fourth embodiment of the present invention. [Fig.3] Figures 3(a) and 3(b) are an example diagram of the four-stroke pre-combustion engine of the fifth embodiment of the present invention. [Fig.4] The [Fig.4] is an example diagram of the four-stroke pre-combustion engine of the sixth embodiment of the present invention. [Fig.5] The [Fig.5] is an example of a partial diagram of the four-stroke pre-combustion engine of the seventh embodiment of the present invention. [Fig.6] Figures 6(a) and 6(b) are an example of a partial diagram of the four-stroke pre-combustion engine of the eighth embodiment of the present invention. [Fig.7] The [Fig.7] is an example diagram of the four-stroke pre-combustion engine of the ninth embodiment of the present invention. [Fig.8] Fig.8 includes an example diagram of the four-stroke pre-combustion engine of the tenth embodiment of the present invention, and a graph of examples of embodiments and comparisons of the present invention showing the results of tests related to the tenth embodiment. [Fig.9] Fig.9 is a graph of examples of embodiment and comparison of the present invention, showing the results of tests relating to the four-stroke pre-combustion engine of the eleventh embodiment of the present invention. [Fig. 10] Figures 10(a) and 10(b) are graphs of embodiments and comparisons of the present invention, showing the results of tests relating to the four-stroke pre-combustion engine of the twelfth embodiment of the present invention. [Fig.l 1] The [Fig.l 1] is a graph of examples of embodiment and comparison of the present invention showing the results of tests relating to the four-stroke pre-combustion engine of the thirteenth embodiment of the present invention. Embodiments of the invention

[0052] The details of the four-stroke pre-ignition engine, according to one 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.

[0053] First embodiment The four-stroke pre-combustion engine 1 of the first embodiment of the present invention will be explained with reference to Figures l(a) and l(b). Figures l(a) and l(b) show an example of the first embodiment. The four-stroke pre-combustion engine 1 of the first embodiment has at least one main combustion chamber 2. The main combustion chamber 2 has at least one intake port 3 connected to an intake passage 5, which may also be an intake duct 5, and at least one exhaust port 4 connected to an exhaust passage 6, which may also be an exhaust duct 6. The main combustion chamber 2 is formed by a cylinder head 10, a cylindrical bore 11, and a piston 12. In other words, the cylindrical bore 11 forms the main combustion chamber 2. The intake passage 5 includes the duct formed inside the cylinder head 10, and the duct connected to it.The exhaust passage 6 includes the duct 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 pre-chamber spark plug 23 is exposed in the interior space of the pre-chamber 20. 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 pre-chamber spark plug 23 is not limited to the positional relationship shown in Figures 1(a) and 1(b). Furthermore, [Fig. 1](a) shows the cross-sectional view of [Fig. 1](b) along line AA. The axial direction of spark plug DP is considered to be 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 Cl 1 of the cylindrical hole 11, but it may not be. 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 controls the intake injector 8 over at least part of the low load area where the opening angle of the throttle valve 7 is small, so that the injection of the liquid fuel ends before the intermediate point between the exhaust top dead center and the bottom dead center. of the intake, and 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 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 pre-combustion four-stroke engine 1 may or may not have a three-way catalyst.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.

[0054] The prechamber 20 has the following two characteristics, in order to limit, and thus eliminate, the ratio of the internal surface area of ​​the prechamber 20 to its volume. The first characteristic is that no protrusion is formed on the internal surface of the prechamber 20, with the exception of the prechamber spark plug 23. The second characteristic is that 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. 1](a), the length L2 is greater than the length L1, but the length L1 can be greater than the length L2. The shape of the interior space of the prechamber 20 is not limited to the shape shown in figures 1(a) and 1(b).

[0055] At least one intake port 3 includes the first intake port 3a. Figure 1(b) shows the first intake port 3a and the connecting ports 21 as seen from the main combustion chamber 2 in the axial direction of spark plug DP. Figure 1(b) omits illustrations of elements other than the main combustion chamber 2, the first intake port 3a, the connecting ports 21, and the prechamber 20. As shown in Figure 1(b), segment LSa is defined as the segment connecting the central axis C23 of the prechamber spark plug 23 and the center C3a of the first intake port 3a, as seen in the axial direction of spark plug DP.The connecting ports 21 include the first intake port 21ia, which has the following two characteristics: The first characteristic is that the angle θ, formed by the segment LSa with the central axis C21ia of the first intake port 21ia viewed in the axial direction of spark plug DP, satisfies -17° < θ < 17° (see [Fig. 1](b)). In [Fig. 1](b), the magnitude of the angle θ (absolute value) is greater than 0°, but . The angle 0 can be equal to 0°. The second characteristic is that the central axis C21ia of the first intake port 21ia passes between the valve head 14 of the intake valve 13 and the first intake port 3a when the intake valve 13 opens and closes the first intake port 3a, on a cross-sectional plane parallel to the central axis Cl 1 of the cylindrical hole 11 and including the central axis C21ia of the first intake port 21ia (see [Fig. 1](a)). [Fig. 1](a) is a cross-sectional view of the four-stroke pre-combustion engine along a cross-sectional plane parallel to the central axis Cl 1 of the cylindrical hole 11 and including the central axis C21ia of the first intake port 21ia. The liquid fuel injected into the intake passage 5 easily enters the prechamber 20 by passing through the first intake port 21ia from the first intake mouth 3a, given that the connecting ports 21 have such a first intake port 21ia.In [Fig. 1], the number of connecting orifices 21 is five, but it may be less than or greater than five. The number, position, shape, and size of the connecting orifices 21 in the first embodiment are not limited to what is shown in [Fig. 1]. Furthermore, in [Fig. 1], the point of intersection between the central axis C21ia of the first intake orifice 21ia and the central axis C23 of the pre-chamber spark plug 23 is closer to the main combustion chamber 2 than to the electrode group of the central axis C23 of the pre-chamber spark plug 23 in the spark plug axial direction, but this is not limited to this configuration.

[0056] It is possible to introduce liquid fuel, with relatively large particles and a relatively high inertial force, to the very bottom of the pre-chamber 20, by forming a pre-chamber 20 such that the first intake port 21ia is formed so that the flow of liquid fuel particles spread along the valve head 14 of the intake valve 13 is easily introduced, and so as to limit, in order to eliminate it, the ratio of the internal surface area to the volume at the rear of the first intake port 21ia. It is thus possible to increase the ignition capacity of the air-fuel mixture in the pre-chamber 20 and the injection power of the flame injected from the connecting ports 21, and to ensure engine performance under low loads even if an ignition aid device is not installed.

[0057] The compression ratio of the four-stroke pre-ignition engine 1 of the first embodiment may be, for example, 11 or higher. The four-stroke pre-ignition engine 1 of the first embodiment may not have a main combustion chamber fuel injector that injects fuel into the main combustion chamber 2. In other words, the fuel introduced into the main combustion chamber 2 and the interior space of the pre-chamber 20 is solely fuel injected by the intake injector 8. The four-stroke engine The pre-combustion four-stroke engine 1 of the first embodiment may not have either a supercharger or a turbocharger. In other words, the pre-combustion four-stroke engine 1 may be naturally aspirated. The pre-combustion four-stroke engine 1 of the first embodiment may not have an exhaust gas recirculation device including an external exhaust gas recirculation duct that connects the exhaust passage 6 and the intake passage 5 by diverting the main combustion chamber 2.

[0058] Second embodiment The four-stroke pre-combustion engine 1 of the second embodiment of the present invention will be explained with reference to Figures 2(a) and 2(b). Figures 2(a) and 2(b) show two examples of the second embodiment. The second embodiment has the same configuration as the first embodiment. In the second embodiment, the main combustion chamber 2 has two intake ports 3. The two intake ports 3 are the first intake port 3a and the second intake port 3b. The main combustion chamber 2 may have two exhaust ports 4, as shown in Figures 2(a) and 2(b). Illustrations are omitted, but the main combustion chamber 2 may have a single exhaust port 4. Figures 2(a) and 2(b) are a figure of the two intake ports 3, the two exhaust ports 4, and the connecting ports 21 seen from the main combustion chamber 2 in the axial direction of spark plug DP.In the second embodiment, the connecting ports 21 include the second intake port 21ib, which has the following two characteristics: The first characteristic is that the angle 02, formed by the segment LSb with the central axis C21ib of the second intake port 21ib viewed in the axial direction of spark plug DP, satisfies -17° < 02 < 17°. The segment LSb is the segment connecting the central axis C23 of the pre-chamber spark plug 23 and the center C3b of the second intake port 3b. In Figures 2(a) and 2(b), the magnitude of the angle 02 (absolute value) is greater than 0°, but the angle 02 can be equal to 0°.Although its illustration is omitted, the second feature is that the central axis C21ib of the second intake port 21ib passes between the valve head of the intake valve and the second intake port 3b when the intake valve opens and closes the second intake port 3b (illustrations omitted), on a cross-sectional plane parallel to the central axis Cl 1 of the cylindrical hole 11 and including the central axis C21ib of the second intake port 21ib. In other words, the second intake port 3b and the second intake port 21ib of the second embodiment have the same characteristics as the first intake port and the first intake port of the present invention. The liquid fuel injected into the intake passage 5 easily enters the prechamber. 20 by passing through the second inlet orifice 21ib from the second inlet mouth 3b, given that the connecting orifices 21 have such a second inlet orifice 21ib. In addition, the number of connecting orifices 21 is five on [Fig.2](a) and six on [Fig.2](b), but the number, position, shape, and size of the connecting orifices 21 of the second embodiment are not limited to what is shown on figures 2(a) and 2(b).

[0059] Third embodiment The four-stroke pre-combustion engine 1 of the third embodiment of the present invention will be explained with reference to Figures 2(c) and 2(d). Figures 2(c) and 2(d) show two examples of the third embodiment. The third embodiment has the configuration of the first embodiment. In the third embodiment, the main combustion chamber 2 has a single intake port 3. The single intake port 3 is the first intake port 3a. The main combustion chamber 2 may have a single exhaust port 4 as shown in Figures 2(c) and 2(d). The illustrations are omitted, but the main combustion chamber 2 may have two exhaust ports 4. Furthermore, the number of connecting ports 21 is five in [Fig. 2(c)] and six in [Fig. 2(d)].2](d), but the number, position, shape, and size of the connecting orifices 21 of the third embodiment are not limited to what is shown in Figures 2(c) and 2(d). .

[0060] 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](e). [Fig. 2](e) shows an example of the fourth embodiment. The fourth embodiment has at least one configuration among embodiments 1 to 3. In the fourth embodiment, the connecting ports 21 include the third intake port 21ic, which has the following two characteristics: The first characteristic is that the angle 03, formed by the segment LSa with the central axis C21ic of the third intake port 21ic viewed in the axial direction of spark plug DP, satisfies -17° < 03 < 17°. The segment LSa is the segment connecting the central axis C23 of the pre-chamber spark plug 23 and the center C3a of the first intake port 3a.Although its illustration is omitted, the second characteristic is that the central axis C21ic of the third intake port 21ic passes between the valve head 14 of the intake valve 13 and the first intake port 3a when the intake valve 13 opens and closes the first intake port 3a (illustrations omitted), on a cross-sectional plane parallel to the central axis Cl 1 of the cylindrical hole 11 and including the central axis C21ic of the third intake port 21ic. The liquid fuel injected into the intake passage 5 easily enters the prechamber 20. passing through the third inlet orifice 21ic from the first inlet orifice 3a, given that the connecting orifices 21 have such a third inlet orifice 21ic. The first inlet orifice 21ia and the third inlet orifice 21ic of the fourth embodiment are each equivalent to the first inlet orifice of the present invention. The number, position, shape, and size of the connecting orifices 21 of the fourth embodiment are not limited to what is shown in [Fig. 2](e).

[0061] 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) and 3(b). Figures 3(a) and 3(b) show an example of the fifth embodiment. The fifth embodiment has at least one configuration among embodiments 1 to 4. In the fifth embodiment, the connecting ports 21 are formed as follows, so that the liquid fuel introduced into the prechamber 20 by passing through the first intake port 21a is difficult to evacuate through the connecting ports 21. Viewed in the axial direction of the spark plug DP, the central axis C21ia of the first intake port 21ia does not correspond to the central axis C21 of any connecting port 21 that is not the first intake port 21ia among the connecting ports 21 (see [Fig. 3](b)). Fig. 3(b) shows Fig.[l](a) to which has been added the central axis C21 of the connecting ports 21 other than the first inlet port 21ia. Furthermore, the central axis C21ia of the first inlet port 21ia does not coincide with the central axis C21 of any connecting port 21 that is not the first inlet port 21ia among the connecting ports 21, when viewed in the direction orthogonal to both the plane including the central axis C21ia of the first inlet port 21ia and the central axis C11 of the cylindrical hole 11 (see [Fig. 3](a)). [Fig. 3](a) shows [Fig. 1](a) to which has been added the central axis C21 of the connecting ports 21 other than the first inlet port 21ia. In other words, [Fig.3](a) shows the central axis C21 of the connecting ports 21 seen in the direction orthogonal to both the plane including the central axis C21ia of the first inlet port 21ia and to the central axis Cl 1 of the cylindrical hole 11.Furthermore, the number, position, shape, and size of the connecting orifices 21 of the fifth embodiment are not limited to what is shown in Figures 3(a) and 3(b). If the fifth embodiment has the configuration of the second embodiment, the central axis C21ib of the second inlet orifice 21ib does not coincide with the central axis C21 of any connecting orifice 21 that is not the second inlet orifice 21ib among the connecting orifices 21, viewed in the axial direction of spark plug DP, and in the direction orthogonal to both the plane including the central axis C21ib of the second inlet orifice 2lib and to the central axis Cl 1 of the cylindrical hole 11.

[0062] Embodiments 6 to 8 The four-stroke pre-ignition engine 1 of embodiments 6 to 8 of the present invention will be explained with reference to Figures 4, 5, 6(a), and 6(b). Figure 4 shows at least one intake port 3, at least one exhaust port 4, and connecting ports 21 viewed in the axial direction of spark plug DP. Figures 5 and 6(a) show the connecting ports 21 viewed in the axial direction of spark plug DP. Figure 6(b) shows the cross-sectional view of Figure 6(a) along line BB. The sixth embodiment has at least one configuration among embodiments 1 to 5. The seventh embodiment has at least one configuration among embodiments 1 to 5. The eighth embodiment has at least one configuration among embodiments 1 to 5. The definitions common to embodiments 6 to 8 will be explained first.A guideline H21 of these connecting ports 21 is defined as the half-line coinciding with the central axis of the connecting ports 21 and extending towards the main combustion chamber 2 without crossing the internal space of the prechamber 20 from these connecting ports 21 (see [Fig. 4]). The shortest distance L3 is defined as the shortest distance between the guideline H21 of the connecting ports 21 and at least one intake port 3 in a circumferential direction around the central axis C23 viewed in the axial direction of spark plug DP (see [Fig. 4]). The shortest distance L3 between the guideline H21 of the first intake port 21a and at least one intake port 3 in a circumferential direction around the central axis C23 is equal to zero.The shortest distance L4 is defined as the shortest distance between the guideline H21 of the connecting ports 21 and at least one exhaust port 4 in a circumferential direction around the central axis C23 viewed in the axial direction of spark plug DP (see [Fig. 4]). Among the connecting ports 21, the intake port 21i is defined as the connecting port 21 having a guideline H21 such that the shortest distance L3 is shorter than the shortest distance L4 (see [Fig. 4]). The first intake port 21ia corresponds to an intake port 21i. In embodiments 6 to 8, the connecting ports 21 include at least one intake port 21ia. Among the connecting ports 21, the exhaust port 21e is defined as the connecting port 21 having a guideline H21 such that the shortest distance L4 is shorter than the shortest distance L3 (see [Fig.4]).In embodiments 6 to 8, the connecting ports 21 include several exhaust ports 21e. The main combustion chamber 2 of [Fig. 4] has two intake ports 3, but may have only one. The main combustion chamber 2 of [Fig. 4] has two exhaust ports 4, but may have only one.

[0063] In the sixth embodiment, the connecting ports 21 include ports intake ports 21i, the number of which is less than that of exhaust ports 21e (see [Fig.4]). If the sixth embodiment has the configuration of the second embodiment, the intake ports 21i may be only the first intake port 21ia and the second intake port 21ib, or may be three or more intake ports 21i.

[0064] In the seventh embodiment, the minimum diameter of the first inlet port 21ia is greater than the maximum diameter of the exhaust ports 21ie (see [Fig. 5], for example). In the seventh embodiment, there may be one or more inlet ports 21i. In the seventh embodiment, any minimum diameter of the inlet ports 21i may be greater than the maximum diameter of the exhaust ports 21e. If the seventh embodiment has the configuration of the second embodiment, it is preferable that the minimum diameter of the second inlet port 21ib be greater than the maximum diameter of the exhaust ports 21e.

[0065] In the eighth embodiment, the first intake port 21ia is formed so that its diameter increases as it approaches the main combustion chamber 2, and the exhaust ports 21e are not formed so that their diameter increases as they approach the main combustion chamber 2 (see Figures 6(a) and 6(b), for example). In the eighth embodiment, it is preferable that the maximum diameter of the first intake port 21ia be greater than the maximum diameter of the exhaust ports 2lie. In the eighth embodiment, there may be one or more intake ports 21i. In the eighth embodiment, the intake ports 21i may all be formed so that their diameter increases as they approach the main combustion chamber 2.In the eighth embodiment, part of the intake ports 21i can be formed so that their diameter does not change. If the eighth embodiment has the configuration of the second embodiment, it is desirable that the second intake port 21ib be formed so that its diameter increases as it approaches the main combustion chamber 2.

[0066] The seventh and eighth embodiments may or may not have the configuration of the sixth embodiment. In the seventh and / or eighth embodiments, the connecting ports 21 may include intake ports 21i, the number of which is greater than or equal to the number of exhaust ports 21e. The sixth and eighth embodiments may or may not have the configuration of the seventh embodiment. In the sixth and / or eighth embodiments, the minimum diameter of the first intake port 21ia may be less than or equal to the maximum diameter of at least one of the exhaust ports 21e. The sixth and seventh The embodiments may or may not have the configuration of the eighth embodiment. In the sixth and / or seventh embodiments, the first intake port 21ia may not be formed so that its diameter increases as it approaches the main combustion chamber 2. In the sixth and / or seventh embodiments, the exhaust ports 21e may be formed so that their diameter increases as they approach the main combustion chamber 2.

[0067] Ninth embodiment The four-stroke pre-combustion engine 1 of the ninth embodiment of the present invention will be explained with reference to [Fig. 7]. The ninth embodiment has at least one configuration among embodiments 1 to 8. In the ninth embodiment, the connecting ports 21 are formed on the prechamber wall section 22, which protrudes into the interior space of the main combustion chamber 2. Furthermore, in the ninth embodiment, the prechamber 20 is formed such that the volume of the protrusion of the prechamber wall section 22 is reduced relative to the volume of the prechamber 20.More specifically, if the interior space of the prechamber 20 is divided into two spaces along one of the planes S that pass through 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 plane S shown in [Fig. 7] is just one example of a plane S that passes through 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 of the two spaces is less than the volume of the space furthest from the main combustion chamber 2 of the two spaces if the interior space of the prechamber 20 is divided into two spaces along one of the planes S 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 relation 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 relation is such that the volume of the space closest to the chamber of . main combustion 2 of the two spaces is equal to or greater than the volume of the space furthest from the main combustion chamber 2 of the two spaces, if the interior space of the prechamber 20 is separated into two spaces along a plane.

[0068] Tenth embodiment The four-stroke pre-ignition engine 1 of the tenth embodiment of the present invention will be explained with reference to [Fig. 8]. The tenth embodiment has at least one configuration among embodiments 1 to 9. The four-stroke pre-ignition engine 1 of the tenth embodiment does not have a knock sensor. The control device 70 controls the pre-chamber spark plug 23 to ignite the air-fuel mixture inside the pre-chamber 20 with a predetermined ignition timing, based on the output of the operating status detection sensor 71, which detects the operating status of the four-stroke pre-ignition engine 1 and is not a knock sensor.

[0069] Here, the graph in [Fig. 8] is part of the results of experiments conducted by the present inventors. The CA50 on the horizontal axis of this graph represents the crankshaft angle at 50% mass fraction burned, which is the crankshaft angle where 50% of the mass is burned. This graph shows the standard deviation of the knock peak kPa as a function of the CA50 variation, for the four-stroke engine of embodiments 1 to 3 and comparison example 1. The internal combustion engine of comparison example 1 does not have a pre-chamber. The internal combustion engine of embodiments 1 and 2 has a cooling sleeve around the pre-chamber spark plug. The internal combustion engine of embodiment example 3 does not have a cooling sleeve around the pre-chamber spark plug. The internal combustion engine in embodiment example 1 and that in embodiment example 2 have a different configuration of the pre-chamber spark plug electrode group.The internal combustion engine in embodiment 3 and embodiment 1 have the same pre-chamber spark plug electrode array configuration. In embodiments 1 through 3 and comparison example 1, the experimental conditions, other than those mentioned above, are identical. The operating range of the internal combustion engine was a mid-range engine speed range with a high-load zone. The high-load zone is the highest point when the engine's load range is divided into two equal parts, from the lowest to the highest range. Furthermore, the mid-range engine speed range corresponds to the two intermediate ranges when the engine speed is divided into four equal parts, from the lowest to the highest range.For the internal combustion engine in comparison example 1, which does not have a pre-chamber, the standard deviation of the knock peak kPa increases very abruptly at a certain point, . When the ignition timing is advanced, as can be seen in the graph. In contrast, for the internal combustion engine in embodiments 1 to 3, which has a pre-chamber, there is no sharp increase in the standard deviation of the knock peak (kPa), but a slight increase even when the ignition timing is advanced. The inventors have discovered similar trends under other conditions, as a result of experiments conducted by changing the load and engine speed conditions.

[0070] Eleventh embodiment The four-stroke pre-combustion engine 1 of the eleventh embodiment of the present invention will be explained below. The eleventh embodiment has at least one configuration among embodiments 1 to 10. In the eleventh embodiment, the total cross-sectional area perpendicular to the central axis C21 of each of the connecting ports 21 is between 5.7 mm² and 7.6 mm².

[0071] Here, the graph in [Fig. 9] represents a portion of the results of experiments conducted by the present inventors. In the following explanation, the total orifice area is defined as the sum of the areas of cross-sections orthogonal to each central axis of the connecting orifices that link the interior space of the main combustion chamber and that of the pre-chamber. [Fig. 9] shows the IMEPcov, which is the rate of change of the mean indicated effective pressure (IMEP) as a function of the CA50, for the four-stroke engine of embodiments 4 to 7 and comparison examples 2 to 4. The meaning of CA50 is identical to the explanation given in the tenth embodiment. IMEP is the work done per cycle divided by the displacement of the heat engine. The lower the IMEPcov values, the greater the combustion stability.The experimental conditions for embodiments 4 to 7 and comparison examples 2 to 4 are identical. The heat engine in comparison example 2 does not have a pre-chamber. The heat engine in comparison example 2 has an identical configuration to the heat engines in embodiments 4 to 7 and comparison examples 3 and 4, except for the presence or absence of the pre-chamber. Table 1 below shows the total area of ​​the ports in the heat engine in embodiments 4 to 7 and comparison examples 3 and 4. The heat engines in embodiments 4 to 7 and comparison examples 3 and 4 have the same configuration in all of them, except for the connecting ports.

[0072] [Tables 1] Total area (mm2) Comparison example 2 (without pre-chamber) Comparison example 3 5.0 Implementation example 4 5.7 Implementation example 5 6.3 Implementation example 6 6.8 Implementation example 7 7.6 Comparison example 4 9.0

[0073] In the graph of [Fig. 9], comparison example 3, where the total orifice area is less than 5.7 mm², and comparison example 4, where the total orifice area is greater than 7.6 mm², have a slightly lower combustion stability than comparison example 2, where no prechamber is installed. Conversely, embodiments 4 to 7, having a total orifice area between 5.7 mm² and 7.6 mm², have a higher combustion stability than comparison example 2. Embodiments 5 and 6, having a total orifice area greater than embodiment 4 but less than embodiment 7, have a higher combustion stability than embodiments 4 and 7. The combustion stability of embodiments 4 and 7 is similar.For this reason, it is understood that it is preferable for the total surface area of ​​the orifices to be between 5.7 mm2 and 7.6 mm2, according to the graph in [Fig.9].

[0074] Twelfth embodiment The four-stroke pre-combustion engine 1 of the twelfth embodiment of the present invention will be explained below. The twelfth embodiment has at least one configuration among embodiments 1 to 11. In the twelfth embodiment, the minimum diameter of the first intake port 21ia is between 1.0 and 1.2 mm, and the volume of the pre-chamber 20 is between 328 mm³ and 802 mm³.

[0075] Here, the graph in Figures 10(a) and 10(b) represents part of the results of experiments conducted by the present inventors. Figure 10(a) shows ITMEPcov as a function of the CA50, for the four-stroke engine of embodiments 8 and 9 and comparison examples 5 and 6. The experimental conditions of embodiments 8 and 9 and comparison examples 5 and 6 are identical. The heat engine of comparison example 5 does not have a pre-chamber. The heat engine of comparison example 5 has an identical configuration to the heat engine of embodiments 8 and 9 and comparison example 6, except for the presence or absence of the pre-chamber. Table 2 below indicates The volume of the prechamber of the internal combustion engine in embodiments 8 and 9 and in comparison example 6. The internal combustion engine in embodiments 8 and 9 and in comparison example 6 has the same configuration in all cases, except for the prechamber. The minimum diameter of the first intake port 21ia of the internal combustion engine in embodiments 8 and 9 and in comparison example 6 is identical in all cases, and is between 1.0 mm and 1.2 mm. In the graph in [Fig. 10](a), comparison example 6, where the volume of the prechamber is greater than 802 mm³, has lower combustion stability than comparison example 5, where no prechamber is installed. The combustion stability of embodiment example 9, whose prechamber volume is 802 mm3, is similar to comparison example 5, where no prechamber is installed.Example embodiment 8, where the prechamber volume is less than 802 mm3, has higher combustion stability than example embodiment 9 and comparison example 5.

[0076] [Tables2] Volume (mm3) Comparison example 5 (without pre-chamber) Implementation example 8 570 Implementation example 9 802 Comparison example 6 919

[0077] Figure 10(b) shows the IMEPcov as a function of engine speed for the four-stroke engine of embodiments 10 to 12 and comparison example 7. The experimental conditions of embodiments 10 to 12 and comparison example 7 are identical. The heat engine of comparison example 7 does not have a pre-chamber. Table 3 below shows the volume of the pre-chamber of the heat engine of embodiments 10 to 12. The heat engine of embodiments 10 to 12 has the same configuration as each other, except for the pre-chamber. Furthermore, the volume of the pre-chamber of embodiment 10 is given as 329 mm³ in Table 3, but its more accurate value is 328.7 mm³. The minimum diameter of the first inlet orifice 21ia of the internal combustion engine of embodiment examples 10 to 12 and of comparison example 7 is equal to 1.2 mm.In general, reducing the prechamber volume has structural constraints. 328.7 mm³, which is the prechamber volume value in embodiment 10, is the minimum prechamber volume determined by the structural constraints. As can be seen in the graph in [Fig. 10](b), the combustion stability remains unchanged. a lot, even if we reduce the volume of the prechamber to the minimum prechamber volume value determined by the structural constraints.

[0078] [Tables3] Volume (mm3) Exempt from comparison 7 (without prechamber) Exempt from implementation 10,329 Exempt from implementation 11,387 Exempt from implementation 12,445

[0079] According to the graphs in figures 10(a) and 10(b), if the minimum diameter of the first inlet orifice 21ia is between 1.0 mm and 1.2 mm, it can be deduced that it is preferable for the volume of the prechamber to be between 328 mm3 and 802 mm3.

[0080] Thirteenth embodiment The four-stroke pre-combustion engine 1 of the thirteenth embodiment of the present invention will be explained below. The thirteenth embodiment has at least one configuration among embodiments 1 to 11. In the thirteenth embodiment, the minimum diameter of the first intake port 21ia is greater than 1.2 mm and less than or equal to 1.4 mm, and the volume of the pre-chamber 20 is between 328 mm³ and 1151 mm³.

[0081] Here, the graph in [Fig. 1 1] is part of the results of experiments conducted by the present inventors. [Fig. 1 1] shows ITMEPcov as a function of the CA50, for the four-stroke engine of embodiments 13 to 19 and of comparison example 8. The experimental conditions of embodiments 13 to 19 and comparison example 8 are identical. The heat engine of comparison example 8 does not have a pre-chamber. The heat engine of comparison example 8 has an identical configuration to the heat engine of embodiments 13 to 19, except for the presence or absence of the pre-chamber. Table 4 below shows the volume of the pre-chamber of the heat engine in embodiment examples 13 to 19. The heat engine in embodiment examples 13 to 19 has the same configuration with each other, except for the pre-chamber.The minimum diameter of the first intake port 21ia of the internal combustion engine in embodiments 13 to 19 is identical for all examples, and is greater than 1.2 mm and less than or equal to 1.4 mm. Generally, the increase in the prechamber volume has structural constraints. 1151 mm³, which is the prechamber volume value of embodiment 19, is the maximum prechamber volume determined by the structural constraints. In the graph in [Fig. 11], embodiments 13 to 19 have greater combustion stability. higher than comparison example 8, where no prechamber is installed.

[0082] [Tables 4] Volume (mm³) Comparison Example 8 (without pre-chamber) Implementation Example 13 570 Implementation Example 14 628 Implementation Example 15 686 Implementation Example 16 802 Implementation Example 17 919 Implementation Example 18 1035 Implementation Example 19 1151

[0083] Although the test results are omitted, the combustion stability of the internal combustion engine, whose pre-chamber volume is the minimum value determined by the structural constraints, i.e., 328.7 mm³, is higher than the combustion stability of the internal combustion engine without a pre-chamber, even if the minimum diameter of the first orifice 21ia is greater than 1.2 mm and less than or equal to 1.4 mm. For this reason, according to the graph in [Fig. 11], if the minimum diameter of the first intake orifice 21ia is greater than 1.2 mm and less than or equal to 1.4 mm, it can be deduced that it is preferable for the pre-chamber volume to be between 328 mm³ and 1151 mm³.

[0084] The present invention is not limited to the embodiments described above and can be modified in various ways as described in the scope of the invention. For example, the connecting ports can be formed on the pre-chamber wall section that does not protrude into the interior space of the main combustion chamber. The four-stroke pre-combustion engine of the present invention may have a supercharger or a turbocharger. The four-stroke pre-combustion engine may have a main combustion chamber fuel injector that injects fuel into the main combustion chamber. The compression ratio of the four-stroke pre-combustion engine of the present invention may be less than 11.

[0085] Reference signs 1: Four-stroke engine with pre-combustion 2: Main combustion chamber 3: Inlet port 4: Exhaust outlet 3a: First intake port 5: Admission Passage 6: Exhaust passage 7: Throat valve 8: Intake injector 10: Cylinder head 11: Cylindrical hole 13: Intake valve 14: Valve head 20: Prechamber 21: Connection points 21ia: First intake port 21i: Admission orifice 2lie: Escape hole 22: Prechamber wall section 23: Pre-chamber spark plug 70: Control device 71: Operating status detection sensor C3a: Center of the first intake outlet Cl 1: Central axis of the cylindrical hole C21: Central axis of the connection holes C21ia: Central axis of the first intake port C23: Central axis of the pre-chamber spark plug DP: Axial direction of the spark plug H21: Guidelines 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 L3, L4: Shortest distance LS has: Segment S: Plan Angle 0:

Claims

Demands

1. Four-stroke pre-ignition engine (1) comprising: - a main combustion chamber (2) having at least one intake port (3) connected to an intake passage (5) and at least one exhaust port (4) connected to an exhaust passage (6); - a throttle valve (7) adjusting the amount of air that passes through the intake passage (5) and is admitted into the main combustion chamber (2); - an intake injector (8) injecting into the intake passage (5) a liquid fuel, said liquid fuel being a petrol fuel, an alcohol-based fuel, or a mixture of petrol fuel and alcohol-based fuel; - a prechamber (20) whose volume is smaller than a volume of the main combustion chamber (2), and an internal space of the prechamber (20) communicates with that of the main combustion chamber (2) via connecting ports (21), and in which (20) a part of a prechamber spark plug (23) is exposed in the internal space of the prechamber (20); - a control device (70) controlling the intake injector (8) and the pre-chamber spark plug (23); the four-stroke pre-combustion engine (1) being characterized in that: (a) the control device (70) controls the intake injector (8) over at least a portion of a low-load area where an opening angle of said throttle valve (7) is small, so that the injection of liquid fuel ends before an intermediate point between an exhaust top dead center and an intake bottom dead center, and that an 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 catalyst after combustion, or a second air / fuel ratio richer than said first air / fuel ratio; (b) the four-stroke pre-combustion engine (1) not comprising a pre-combustion injector, which would inject fuel into said pre-chamber (20), or an ignition aid device, which would assist in the ignition of the air-fuel mixture in the pre-chamber (20) or the main combustion chamber (2); and

2. (c) to eliminate the ratio of the area of ​​an internal surface of said prechamber (20) to the volume of said prechamber (20), said prechamber (20): (i) is formed without protrusion on the internal surface of the prechamber (20) except for said prechamber spark plug (23), and (ii) is formed such that the greater of a length (L1) of the internal space of said prechamber (20) extending along a spark plug axial direction (DP) parallel to a central axis (C23) of the prechamber spark plug (23) and a maximum length (L2) of the internal space of the prechamber (20) orthogonal to the spark plug axial direction (DP), is less than twice the smaller of the two lengths; and (d) in such a way that said liquid fuel injected into the intake passage (5) can easily enter the prechamber (20) by passing through a first intake orifice (2lia), which is an orifice (21ia) among the connecting orifices (21), from a first intake mouth (3a), said first intake mouth (3a) being included in at least one intake mouth (3), said first intake orifice (2lia) is formed such that: (i) an angle 0, formed by a segment (LSa) connecting the central axis (C23) of said pre-chamber spark plug (23) and the center (C3a) of said first intake port (3a) with a central axis (C21ia) of the first intake port (21ia) is between -17° < 0 < 17° according to a view in said axial direction of spark plug (DP), and (ii) the central axis (C21ia) of the first intake port (2lia) passes between a valve head (14) of an intake valve (13) and the first intake port (3a) when the intake valve (13) is opened, the intake valve (13) opening and closing the first intake port (3a), according to a view in a cutting plane including the central axis (C21ia) of the first intake port (21ia) and which is parallel to a central axis (Cil) of a cylindrical hole (11), said cylindrical hole (11) forming the main combustion chamber (2). The four-stroke pre-combustion engine (1) according to claim 1 and having the characteristic that the connecting ports (21) are formed such that the central axis (C21ia) of the first intake port (21ia) does not coincide with the central axis (C21) of any other connecting port (21) other than said first intake port (21ia) among said connecting ports (21), according to a view in said axial direction of spark plug (DP) and in the direction orthogonal to both the plane including the central axis (C21ia) of the first intake orifice (21ia) and to the central axis (Cl 1) of the cylindrical hole (11), so that said liquid fuel introduced into the prechamber (20) by passing through the first intake orifice (21ia) is less easily evacuated through the connecting orifices (21).

3. The four-stroke pre-combustion engine (1) according to claim 1 or 2 and having the following characteristics: by defining a guideline (H21) of the connecting ports (21) as a half-line which would be superimposed on the central axis (C21) of the connecting ports (21) and which would extend from the connecting ports (21) towards the main combustion chamber (2) without crossing the internal space of the pre-chamber (20), the intake ports (21i), being ports (21i) among the connecting ports (21),include said first inlet port (21ia) and each has a guideline (H21) which is arranged such that the shortest distance (L3) between the guideline (H21) and at least one inlet port (3) in a circumferential direction around the central axis (C23) of said pre-chamber spark plug (23) is shorter than the shortest distance (L4) between the guideline (H21) and at least one exhaust port (4) in a circumferential direction around the central axis (C23) of said pre-chamber spark plug (23), in a view in the axial direction of the spark plug (DP); and the exhaust ports (21e), being ports (21e) among the connecting ports (21),each have a guideline (H21) which is arranged such that the shortest distance (L4) between the guideline (H21) and at least one exhaust port (4) in a circumferential direction around the central axis (C23) of said pre-chamber spark plug (23) is shorter than the shortest distance (L3) between the guideline (H21) and at least one intake port (3) in a circumferential direction around the central axis (C23) of said pre-chamber spark plug (23), according to a view in the axial direction of the spark plug (DP), and the number of intake ports (21i) is less than the number of exhaust ports (21e).

4. The four-stroke pre-combustion engine (1) according to any one of claims 1 to 3 and having the following characteristics:

5. by defining a guideline (H21) of the connecting ports (21) as a half-line superimposed on the central axis (C21) of the connecting ports (21) and extending from these connecting ports (21) towards the main combustion chamber (2) without crossing the interior space of the prechamber (20), the exhaust ports (21e), being ports (21e) among the connecting ports (21), each have a guideline (H21) arranged such that the shortest distance (L4) between the guideline (H21) and at least one exhaust port (4) in a circumferential direction around the central axis (C23) of said prechamber spark plug (23) is shorter than the shortest distance (L3) between the guideline (H21) and at least one intake port (3) in a direction circumferential around the central axis (C23) of said pre-chamber spark plug (23),according to a view in the axial direction of the spark plug (DP), and the smallest diameter of the first intake port (21ia) is larger than the largest diameter of the exhaust ports (21e). The four-stroke pre-combustion engine (1) according to any one of claims 1 to 4 and having the following characteristics: by defining a guideline (H21) of the connecting ports (21) as a half-line that would be superimposed on the central axis (C21) of the connecting ports (21) and that would extend from the connecting ports (21) towards the main combustion chamber (2) without crossing the interior space of the prechamber (20), the exhaust ports (21e), being ports (21e) among the connecting ports (21), each have a guideline (H21) arranged such that the shortest distance (L4) between the guideline (H21) and at least one exhaust port (4) in a circumferential direction around the central axis (C23) of said prechamber spark plug (23) is shorter than the shortest distance (L3) between the guideline (H21) and at least one intake port (3) in a circumferential direction around the central axis (C23) of said pre-chamber spark plug (23),according to a view in the axial direction of the spark plug (DP), and said first intake orifice (21a) is formed such that the diameter of said first inlet hole (21a) increases along its central axis in the direction of the main combustion chamber (2), and said exhaust orifices (21e) are formed such that their, diameter does not increase along their central axis in the direction of the main combustion chamber (2).

6. The four-stroke pre-combustion engine according to any one of claims 1 to 5, the total area of ​​a cross-section orthogonal to the central axis of each of said connecting orifices (21) being between 5.7 mm2 and 7.6 mm2 inclusive.

7. The four-stroke pre-combustion engine (1) according to any one of claims 1 to 6, wherein a minimum diameter of the first intake port (21ia) is between 1.0 mm and 1.2 mm inclusive, and a volume of said pre-chamber (20) is between 328 mm3 and 802 mm3 inclusive.

8. The four-stroke pre-combustion engine (1) according to any one of claims 1 to 6, wherein a minimum diameter of the first intake port (21ia) is greater than 1.2 mm and is less than or equal to 1.4 mm, and a volume of said prechamber (20) is between 328 mm3 and 1151 mm3 inclusive.

9. The four-stroke pre-combustion engine (1) according to any one of claims 1 to 8 and having the following characteristics: - the connecting orifices (21) are formed on a pre-chamber wall section (22), the pre-chamber wall section (22) projecting into the interior space of the main combustion chamber (2); - by dividing the interior space of the pre-chamber (20) into two spaces along one of the planes (S) passing through the interior space of said pre-chamber (20) without passing through the external surface of said pre-chamber wall section (22), and intersecting said axial spark plug direction (DP) orthogonally, said pre-chamber (20) is formed such that the volume of the space closest to the 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.

10. The four-stroke pre-combustion engine (1) according to any one of claims 1 to 9, characterized in that it does not include a knock sensor; and that the control device (70) controls the pre-chamber spark plug (23) so as to ignite the air-fuel mixture inside the pre-chamber (20) at a predetermined ignition time, based on an output signal from an operating state detection sensor (71) that detects the operating state of said engine at four-stroke with pre-combustion (1), and which is not a knock sensor.

11. The four-stroke pre-combustion engine (1) according to any one of claims 1 to 10 and having the characteristic of having neither a supercharger nor a turbocharger.

12. The four-stroke pre-combustion engine (1) according to any one of claims 1 to 11 and having the characteristic of the absence of a main combustion chamber fuel injector (2), which would inject fuel into said main combustion chamber (2).

13. The four-stroke pre-ignition engine (1) according to any one of claims 1 to 12 and having a compression ratio of said four-stroke pre-ignition engine (1) greater than or equal to 11.

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