EP4724696A1

EP4724696A1 - Spark plug for spark-ignition engine

Info

Publication number: EP4724696A1
Application number: EP24735153.9A
Authority: EP
Inventors: Antonio GENCARELLI; Thierry Prunier; Laurent SANCHES
Original assignee: Horse Powertrain Solutions SL
Current assignee: Horse Powertrain Solutions SL
Priority date: 2023-06-12
Filing date: 2024-06-12
Publication date: 2026-04-15
Also published as: CN121336041A; WO2024256483A1; FR3149728A1

Abstract

Spark plug for spark-ignition engine Spark plug (4) for spark-ignition engine (2) comprising an electrically insulating body (41), a base (42) delimiting a passive ignition pre-chamber (43), the spark plug (4) further comprising at least one orifice (45) arranged in the base (42) and at least one channel (46) configured to allow the circulation of a flow of drain air (FV) through at least part of the spark plug (4) and at least one means for regulation (47) of the flow of drain air (FV) arranged at the level of the at least one orifice (45) and capable to passively control the circulation of said flow.

Description

DESCRIPTION

Spark plug for spark-ignition engine

The invention describes a spark plug for spark-ignition engine, in particular with a passive pre-chamber, as well as a spark-ignition engine cylinder head with a spark plug of this type. In addition, the invention refers to an engine equipped with the above-mentioned spark plug and/or cylinder head. Lastly, the invention describes an operating method for such a motor.

Increased efficiency of spark-ignition thermal engines is one of the challenges faced by the automotive industry, and boosting the volumetric ratio is a key area for improvement. Nevertheless, boosting the volumetric ratio of a thermal engine entails challenges such as fuel auto-ignition phenomena, also known as knocking, which can potentially damage the engine.

A solution to these challenges is to use pre-chambered spark plugs, more particularly spark plugs with a passive pre-chamber, i.e. one that does not have a fuel injection mechanism operating directly into the pre-chamber. A disadvantage of such spark plugs is the residual-burnt gas, or GBR, that gradually deposits in the pre-chamber until it reaches high proportions, which can impact the carburated mixture's combustion or even render such combustion inefficient.

The invention falls within this context and is intended to offer an alternative to prechamber spark plugs, in particular a passive type, designed to evacuate residual burnt gases that may remain in the pre-chamber after the combustion cycles, in order to guarantee a good quality of the carburated mixture in the pre-chamber before the ignition of the spark plug.

The invention refers to a spark plug for spark-ignition engine with electrically insulating body and conductive base, where the said base delimits an ignition pre-chamber equipped with at least one hole designed for the passage of at least one carburated mixture between a cylinder combustion chamber and the pre-chamber. In addition, the spark plug unit contains at least one orifice and one channel, whereby at least one orifice passes through a wall of the base and is designed for fluid connection to the pre-chamber via at least one channel, in order to circulate a flow of drain air through at least one prechamber. The spark plug also contains at least one means of regulation for the flow of drain air, which is positioned at the level of at least one orifice and is designed to control the flow of drain air passively.

In particular, at least one channel can be delimited by the base and/or the electrically insulating body.

In particular, the base and/or body can extend along a first direction, in addition, the spark plug has primary electrode and one ground electrode, wherein at least one orifice and at least one means of regulation are positioned so that the at least one ground electrode is interposed along the first direction between the at least one orifice on one side and the at least one hole in the pre-chamber on other side.

Alternatively, the spark plug also contains at least one intermediate volume interposed between at least one orifice and all or part of at least one channel, the intermediate volume being delimited by the base and/or the electrically insulating body, and the intermediate volume being connected to the at least one channel and to the pre-chamber through a fluid connection.

According to an example embodiment, at least one means of regulation for the flow of draining air is a non-return valve containing at least one ball and one spring.

The invention also refers to a cylinder head for spark-ignition engine containing at least one intake valve, as well as at least one exhaust valve and at least one cavity delimiting a first volume, wherein the first end of said cavity contains an opening configured to discharge into a cylinder's combustion chamber, the cylinder head also comprising at least one spark plug according to the invention positioned in the first volume at the level of said opening so that the at least one orifice extend into the first volume and the prechamber is configured to implement a fluid connection with the cylinder's combustion chamber.

In particular, a second end which is opposite the first end of at least one spark plug cavity is open, at least in part, in order to facilitate the inflow of a drain air flow into the first volume, the said second end being designed for limiting, or even preventing, the inflow of liquid and/or particles.

The invention also refers to a spark-ignition engine with a cylinder head according to the invention, at least one cylinder delimiting a combustion chamber and a movable piston positioned in the at least one cylinder, the opening of the cylinder head and the prechamber of the at least one spark plugs opening into the combustion chamber.

Alternatively, the engine also has an intake valve control device for regulating an opening, and in particular an opening delay, of the abovementioned valve.

Furthermore, the invention refers to an operating method for a spark-ignition engine as described above, which comprises:

- an intake phase of a flow of intake air (FA) into the cylinder comprising a step of generating a negative pressure in the cylinder in order to allow a flow of drain air (FV) to circulate from the first volume towards the combustion chamber through the pre-chamber of the spark plug, the flow of drain air (FV) being capable to expel residual burnt gases accumulated in the pre-chamber and/or in the spark plug;

- a compression phase comprising a pressure increase in the cylinder so that a portion of a carburated mixture is sent to the pre-chamber and comprising the ignition of said mixture in the pre-chamber; then

- an expansion phase wherein the carburated mixture contained in the cylinder ignites; then

- an exhaust phase comprising the raising of the piston to upper position so as to displace residual burnt gases present in the combustion chamber of the cylinder at least towards the pre-chamber of the spark plug.

Any further details, features and advantages shall be evident from the detailed description given below, which is illustrative and non-restrictive, with reference to the various exemplary embodiments illustrated in the following figures:

Figure 1 is a schematic representation of a vehicle equipped with spark-ignition engine and pre-chamber spark plug operating procedure.

Figure 2 is a schematic representation of engine operation during an intake phase. Figure 3 is a schematic representation of engine operation during an exhaust phase.

Figure 1 illustrates schematically an example of a motor vehicle 1 designed according to the invention. In particular, the motor vehicle 1 is equipped with a spark-ignition engine 2 according to the invention. The spark-ignition engine 2 is a thermal engine of all types. Also, the vehicle 1 could be of any type, for example, a passenger car, a commercial vehicle, a truck or a bus. In particular, the vehicle 1 under consideration may be a connected and/or autonomous vehicle.

The conventional spark-ignition engine 2 is equipped with at least one cylinder 21 , wherein there is a movable piston 22. The at least one cylinder 21 delimits a combustion chamber 23 wherein the piston 22 is moved and wherein an air-fuel mixture is injected.

The engine 2 also comprises a cylinder head 3. According to an exemplary embodiment, the cylinder head 3 comprises an intake duct 31 equipped with an intake valve 32, and an exhaust duct 33 equipped with an exhaust valve 34 in a known manner. The cylinder head 3 is installed in the engine 2 in such a way as to ensure a fluid connection between the intake duct 31 and the exhaust duct 33, on one side, and the combustion chamber 23 of at least one cylinder 21 , on other side. The intake valve 32 and the exhaust valve 34 are conventionally mounted mobile and designed to facilitate or hinder the fluid connection between the duct wherein they are installed and the combustion chamber 23.

The cylinder head 3 also includes at least one spark plug 4 according to the invention, and a cavity 35 configured to house such a spark plug. The cavity 35 delimits a first volume 350 which is open on one side and can accommodate all or part of the spark plug 4. In particular, a first end of the cavity 35 comprises an opening 36 designed to open into the combustion chamber 23 of at least one cylinder 21 when the cylinder head 3 is installed in the engine 2.

A second end of the cavity 35, not illustrated, which is opposite the first end, can be optionally but preferably sealed, at least in part, to protect the cavity 35 from the inflow of liquids and particles which could affect the operation of the spark plug 4. In addition, cavity 35 is designed to let an air flow in, known as the drain air flow FV, which is further detailed below in the first volume 350 of cavity 35. For this purpose, the second end of cavity 35 is at least open in part and optionally has at least one drain air flow FV passage designed for the passage of drain air flow FV while reducing the risk of liquids and particles passing through.

It is understood that the following description is intended to refer to a spark plug 4 of the engine 2, positioned in a spark plug cavity 35 which is opposite a cylinder 21 in question. Nevertheless, it extends to a spark-ignition engine 2 with a plurality of cylinders 21 each equipped with a piston 22 and, alternatively, the cylinder head 3 with a plurality of cavities 35, spark plugs 4, intake valves 32 and exhaust valves 34. In general, the spark plug 4 according to the invention has at least one electrically insulating body 41 and an electrically conductive base 42 extending along a first direction 100, where the base 42 delimits an ignition pre-chamber 43. The ignition pre-chamber 43 has at least one hole 44 designed for the passage of at least one air-fuel mixture between the combustion chamber 23 of the cylinder 21 and the pre-chamber 43, and for the passage of the drain air flow FV to the combustion chamber 23.

The spark plug is positioned in the cavity 35 of the cylinder head 3 so that it extends at least in part into the first volume 350. In particular, the spark plug is positioned at the opening 36 in such a way that, within the engine 2, the pre-chamber 43 is in fluid connection with the combustion chamber 23 of the cylinder 21 through at least one hole 44. Alternatively, but preferably, the cylinder head 3 has at least one sealing element 37, positioned at the interface between the spark plug 4 and the cylinder head 3, for example around the spark plug 4 and/or at the opening 36, in order to prevent the circulation of combustion gases from the combustion chamber 23 to the cavity 35 of the spark plug 4, or in other words the first volume 350, during the compression, expansion and exhaust phases wherein the cylinder pressure is higher than atmospheric pressure, and conversely, the circulation of fresh air flows from the cavity 35, or first volume 350, to the combustion chamber 23 during an engine cycle phase wherein the cylinder 21 may be under negative pressure, for example during the intake phase.

The body 41 has an elongated shape extending along the first direction 100. When the spark plug 4 is arranged in the cylinder head 3 and engine 2, the body 41 comprises, for example, an upper end at which the electrical connection of the spark plug 4 can be made and a lower, opposite end. The body 41 is made of an electrically insulating material, such as ceramic, particularly alumina-based.

The base 42 is made of an electrically conductive material, particularly metal. The base 42 has at least one wall inscribed in a shape that is more or less hollow and designed to surround all or part of the body 41 . For example, the base 42 has a shape that is partly cylindrical, or more or less cylindrical. The base 42 and body 41 extend along the same direction, in this case the first direction, and for example concentrically.

In particular, the base 42 delimits an internal volume 400 of the spark plug 4, including the spark plug pre-chamber 43. Conventionally, the term “pre-chamber” refers to a chamber in the spark plug 4 into which a carburated mixture, also known as the air-fuel mixture, is injected through at least one hole 44 and then spark ignited. A hot jet of combustion gases is then produced and delivered to an external environment, in this case the combustion chamber 23 of cylinder 21 , through at least one hole 44. In particular, according to the invention, the pre-chamber 43 is a passive chamber, i.e. a pre-chamber 43 without a fuel supply device, or injector, enabling fuel to be injected directly into the pre-chamber 43.

The spark plug 4 also comprises at least one orifice 45 and at least one channel 46 fluidically connected to each other and to the pre-chamber 43. In other words, at least one orifice passes right through a wall of the base 42 and can be fluidly connected to the pre-chamber 43 through at least one channel 46. At least one orifice 45 and at least one channel 46 are configured to circulate the drain air flow FV through the internal volume 400 of the spark plug, in particular through the pre-chamber 43 and the at least one hole 44. The “drain air flow” refers to the air flow from the first volume 350 circulating through the spark plug 4, in particular through the pre-chamber 43, in order to evacuate any residual burnt gases that may have collected in the spark plug 4, particularly in the prechamber 43, to the combustion chamber 23. The drain air flow FV therefore circulates from the first volume 350 of the spark plug cavity 35 to the combustion chamber 23 through the internal volume 400 of the spark plug 4, and not into the external environment, so that the pre-chamber 43 can be cleaned. The at least one channel 46 therefore circulates the drain flow FV from the spark plug 4 cavity 35 to the combustion chamber 23, sweeping burnt gases collected in the pre-chamber 43 during a previous combustion to the combustion chamber 23.

In particular, at least one orifice 45 is positioned in one of the walls of the cylinder head 42, so that when the spark plug 4 is equipped in the vehicle 1 , at least one orifice 45 extends into the first volume 350 of at least one cavity 35 in the cylinder head 3.

According to a specific exemplary embodiment, at least one channel 46 is delimited by the base 42 and/or the electrically insulating body 41 . For example, at least one channel 46 extends partly along the first direction 100. At least one channel 46 and at least one orifice 45 are directly or indirectly connected and are designed to implement a fluid connection between the first volume 350 and the pre-chamber 43 in order to allow the drain air flow FV for passage. As a result, at least one orifice 45 and at least one channel 46 are designed to provide a fluid connection between the first volume 350 of the cylinder head 3 and the combustion chamber 23 of at least one cylinder 21 . As illustrated, spark plug 4 may optionally have a plurality of orifices 45 and channels 46 as shown above. According to a non-limiting exemplary embodiment, the spark plug 4 comprises two orifices 45 and two channels 46. The orifices 45 are distributed around the periphery of the base 42, for example.

The spark plug 4 according to the invention also includes at least one means of regulation 47 for the drain air flow FV. The means of regulation 47 is positioned in the passage of the drain air flow FV, within the spark plug 4, particularly in the internal volume 400 of the spark plug 4, in order to control the circulation of said flow passively. The term “to control” is used here for the possibility of obstructing the circulation of said flow in order to interrupt the fluid connection between the first volume 350 and the combustion chamber 23, or for the possibility of circulating the said flow from the first volume 350 to the combustion chamber 23. The term “passive” control means that it does not require motorized actuation.

In particular, the at least one means of regulation 47 is positioned at the level of the at least one orifice 45, for example opposite and/or adjacent thereto. For example, the at least one means of regulation 47 is designed to close the at least one orifice 45 in order to interrupt the drain air flow FV. As a result, the at least one means of regulation 47 is in contact with the edges of the at least one orifice 45. Also, preferentially, the spark plug 4 comprises as many means of regulation 47 as there are orifices 45, each of the said means of regulation 47 being positioned at one of the orifices 45.

According to an exemplary preferred embodiment, illustrated, the at least one means of regulation 47 is a non-return valve comprising at least one ball 47a and a spring 47b. In particular, spring 47b is supported on an intermediate surface 47c, formed by a wall of the base 42 and/or the body 41 , to hold spring 47b in place. On one hand, the ball 47a is positioned in contact with the edges of the at least one orifice 45 and, on other hand, it is in contact with the spring 47b in order to maintain the ball 47a in the internal volume 400 of the spark plug 4. The ball 47a is therefore designed to be shifted between a “closed” configuration, wherein the ball 47a is in contact with the edges of at least one orifice 45 in order to close the latter and interrupt the drain air flow FV in the internal volume 400, and an “open” configuration, wherein the ball 47a exerts a force against the spring 47b and extends at a non-zero distance from at least one orifice 45 in order to allow the drain air flow FV through the internal volume 400. As explained further below, with reference to the method according to the invention, the means of regulation 47 is actuated passively, in this case by shifting the ball 47a, according to a differential pressure defined between a pressure measured in the first volume 350 and a pressure measured in the combustion chamber 23. For example, the spring 47b is preloaded to actuate the means of regulation 47 when a negative pressure is generated in the combustion chamber 23, and by extending into the internal volume 400 and the pre-chamber 43 of the spark plug 4, at the time of an intake phase of the engine cycle 2. The term “negative pressure” is used here to refer to the pressure reduction to a value strictly below atmospheric pressure. As a result, spring 47b is very lightly loaded and serves to hold ball 47a in place within spark plug 4. The ball 47a is subjected to atmospheric pressure on the side of cavity 35, or first volume 350, and to the pressure of cylinder 21 on the side of pre-chamber 43. In this way, when the cylinder 21 pressure falls below atmospheric pressure, the ball 47a is aspirated towards it, and opens the passage to the drain air flow FV. In particular, when a negative pressure is generated in the combustion chamber 23, the ball 47a is aspirated towards the combustion chamber 23 through the passages existing in the internal volume 400 of the spark plug 4, namely through at least one channel 46 and the pre-chamber 43. The ball 47a is then displaced against the spring 47b and compresses the latter against the intermediate surface 47c.

It should be noted that, when using a supercharged engine 2, intake pressure may be higher than atmospheric pressure, depending on operating conditions. As explained below, it is then necessary to delay the opening of intake valve 32 in order to generate an appropriate pressure in cylinder 21 , which is lower than atmospheric pressure due to the piston 22 descent.

Conventionally, the spark plug 4 also comprises at least one primary electrode 5 and at least one ground electrode 51 . The primary electrode 5 passes through the body 41 , for example. The at least one ground electrode 51 is included in the base 42 and constitutes, relative to the at least one primary electrode 5, a primary inter-electrode gap, i.e. a gap between two non-contacting electrodes that is intended to support sparking between the respective electrodes. For example, the at least one ground electrode 51 extends from an internal surface of the base 42, towards the internal volume 400, and extends into the same volume. It is understood that the spark plug 4 may have a plurality of primary electrodes 5 and/or ground electrodes 51 . Alternatively, the vehicle 1 is equipped with a spark ignition system consisting of an ignition control unit and a high-voltage electrical circuit for supplying electrical energy to the at least one primary electrode 5 of the spark plug 4.

According to the preferred embodiment illustrated, the at least one orifice 45 and the at least one means of regulation 47 are positioned in such a way that, along the first direction 100, the at least one ground electrode 51 is interposed between the at least one orifice 45 on one side and the at least one hole 44 in the pre-chamber 43 on its other side. In particular, the at least one orifice 45 and the at least one means of regulation 47 extend at a non-zero distance from the pre-chamber 43 of the spark plug 4. For example, the at least one orifice 45 is positioned in an upper portion, for example in an upper half, of the spark plug 4, which is designed to be positioned in the at least one cavity 35 of the cylinder head 3.

Alternatively, the spark plug 4 also comprises at least one intermediate volume 48 interposed between the at least one orifice 45 and all or part of the at least one channel 46. The intermediate volume 48 comprises the internal volume 400 of the spark plug 4 and differs from a volume of the pre-chamber 43. The intermediate volume 48 is also fluidly connected to the at least one orifice 45, the at least one channel 46 and the prechamber 43. The intermediate volume 48 is delimited by the electrically insulating base 42 and/or the body 41. For example, it has an annular shape that at least partially surrounds the body 41 . The intermediate volume 48 ensures a fluid connection between the at least one orifice and the at least one channel 46, or between different channels 46. It is understood that the shapes of the intermediate volume 48 and the at least one channel 46 illustrated are not restrictive, and the other variants may be envisaged.

The invention also refers to an operating method for the spark-ignition engine 2 according to the invention. This process is implemented during an engine 2 cycle, which typically has intake, compression, expansion and exhaust phases.

During the intake phase, as illustrated in Figure 2, an intake air flow FA is supplied to the at least one cylinder 21 , the process comprises a stage where a negative pressure is generated in the cylinder 21 , particularly in the combustion chamber 23. As mentioned above, the negative pressure here consists of a pressure reduction in the cylinder, and consequently in the internal volume 400 and the pre-chamber 43 of the spark plug 4, at a value strictly below atmospheric pressure. The negative pressure generated activates at least one means of regulation 47, for example by moving the ball to its “open” configuration, so that the drain air flow FV can circulate from the first volume 350 through the spark plug's internal volume 400 to the combustion chamber 23.

The negative pressure can be achieved in different ways, depending on when and how the engine 2 is operated. An initial strategy for obtaining negative pressure in at least one cylinder 21 can be implemented when the engine is operating at low load. The pressure in the intake duct 31 , and more widely in the intake manifold, at engine 2 then reduces to below atmospheric pressure. The engine 2 operates in the atmospheric zone, and a negative pressure is naturally generated in at least one cylinder 21 and the intake duct 31 . The conditions observed in engine 2 are then conducive to actuation of means of regulation 47, with no mechanical intervention required. The means of regulation 47 is preloaded to ensure passive actuation of the means of regulation 47 when such a negative pressure is naturally generated, for example the spring 47b of the non-return valve.

On the other hand, engine 2 can operate at heavy load, i.e. under overload or turbocharging. The pressure in the intake duct 31 , and by extending into the intake manifold, at engine 2 is then significantly above atmospheric pressure at the beginning of the intake phase. The pressure in at least one cylinder 21 and in the intake duct 31 are above the atmospheric pressure, so the negative pressure must be generated mechanically. In this case, the negative pressure is generated by implementing a delayed opening of the intake, or ROA, which consists of keeping the intake valve 32 closed while the piston 22 is initiated to descend. For example, the intake opening delay is implemented by a control device, not illustrated, for intake valve 32, which can trigger a shift in its valve opening actuation in the engine cycle. As indicated above, this delay generates a negative pressure in the cylinder 21 , especially in the combustion chamber 23, and in the internal volume 400 of the spark plug, particularly in the pre-chamber 43, which is sufficient to cause the passive opening 36 of at least one means of regulation 47. When the means of regulation 47 comprises a non-return valve, the valve spring 47b is advantageously preloaded to open the valve opening 36 due to the negative pressure existing in the cylinder 21 .

Advantageously, the process according to the invention offers different strategies for generating a negative pressure within at least one cylinder 21 , which are adapted to different operating points of the engine 2. It should be noted that, preferably, the process according to the invention can be implemented only when the engine is operating at low load, so that the spark plug 4 can be drained without interfering with the operation of engine cycle. The process according to the invention can then be inactive, and no drain is performed, when engine 2 is operating in overload.

By virtue of the natural or generated negative pressure in the cylinder 21 and prechamber 43, the fresh air contained in the first volume 350 of the spark plug cavity 35 is extracted into the internal volume 400 and towards the combustion chamber 23 of the cylinder 21 , the drain air flow FV then passing through the pre-chamber 43 and then through at least one hole 44. For example, the drain air flow FV passes successively through the at least one orifice 45, the intermediate volume 48, the at least one channel 46 and then the pre-chamber 43, thereby eliminating any residual burnt gases collected during preceding combustion in a previous engine cycle 2. The circulation of drain air flow FV through the internal volume 400 of spark plug 4 enables a passive blow-out for expelling residual burnt gases remaining in the internal volume 400 of spark plug 4 following a previous engine cycle. For example, the drain air flow FV expels residual burnt gases remaining in the pre-chamber 43, the at least one channel 46 and/or the intermediate volume 48.

Conventionally, the intake valve 32 is then opened, the cylinder 21 is filled with a flow of intake air FA from the intake duct 33, and fuel injection is initiated. The atomized fuel is mixed with the intake air flow FA in order to form a carburated mixture, also referred to as the air-fuel mixture, in the combustion chamber 23.

Likewise, it is known that engine cycle 2 continues with the compression phase. The fuel injection continues and the carburated mixture is homogenized through turbulence in the combustion chamber 23 of cylinder 21. The piston 22 retracts into the cylinder 21 and the intake valve 32 is closed, which increases the pressure in the combustion chamber 23 and in the internal volume 400 of the spark plug, especially in the pre-chamber 43. The pressure in combustion chamber 23 and by extending into the spark plug's internal volume 400, is then greater than or equal to the pressure in first volume 350, and all means of regulation 47 are closed, which hinders the drain air flow FV. A part of this carburated mixture is then sent to the pre-chamber 43 where the spark ignition system triggers a spark at the spark plug 4 at the end of the compression phase, which causes the compressed carburated mixture to combust in the pre-chamber 43.

The engine cycle 2 then comprises the expansion phase. The flame front propagates into the pre-chamber 43. As the pressure rises in the pre-chamber 43, the ignited gases penetrate into the combustion chamber 23 in the form of fire jets that constitute a multitude of ignition points, thereby optimizing the calibration of the heat release mechanism and combustion efficiency. The intake valve 32, the exhaust valve 34 and all the means of regulation 47 are then closed, and a seal is ensured between the combustion chamber 23 and the first volume 350 of the cavity 35 of the spark plug 4.

Lastly, the exhaust valve 34 opens during the exhaust phase, illustrated in Figure 3. As the piston 22 retracts, it simultaneously displaces residual burnt gases remaining in the combustion chamber 23 of cylinder 21 towards the exhaust duct 33 and the internal volume 400 of spark plug 4, particularly at least towards the pre-chamber 43. For example, some residual burnt gases are sent to at least one channel 46 and throughout the ignition pre-chamber 43, particularly in the intermediate volume 48. Simultaneously, some residual exhaust gases are discharged from the engine 2 through the exhaust duct 33. Any residual burnt gases collected in the internal volume 400 can be discharged from the spark plug 4 during the intake phase of a subsequent engine cycle 2, as described above.

The spark plug 4 and the process according to the invention therefore enable the implementation of a passive drain of the spark plug 4 which limits the collection of residual burnt gases in the pre-chamber 43 at an excessive concentration susceptible to prevent the initiation of the carburated mixture combustion. The draining of residual burnt gases generated during previous combustions, which have been evacuated to cylinder 21 in the intake phase, therefore enables the pre-chamber 43 to be cleaned before being refilled with a carburated mixture.

The invention therefore offers an alternative to pre-chamber spark plugs that can prevent the collection of burnt residual gases in the spark plug. Advantageously, the proposed solution is simple to implement and inexpensive, since it is directly integrated into the spark plug and it can be implemented in a wide range of cylinder heads and internal combustion engines. Furthermore, the invention does not affect the pre-chamber's architecture or operation.

However, this invention is not limited to the methods and configurations described and illustrated herein, and it also extends to any other equivalent methods or configurations, and any technically effective combination of such methods, insofar as they eventually fulfil the functionalities described and illustrated herein.

Claims

1. Spark plug (4) for spark-ignition engine (2) comprising an electrically insulating body (41 ) and an electrically conductive base (42), the said base (42) delimitting an ignition pre-chamber (43) comprising at least one hole (44) capable to allow at least the passage of one carburated mixture between a combustion chamber (23) of a cylinder (21 ) and the pre-chamber (43), the spark plug (4) further comprising:

- at least one orifice (45) and at least one channel (46), the at least one orifice

(45) passing through a wall of the base (42) and being capable to be in fluid connection with the pre-chamber (43) through at least one channel (46) in order to allow the circulation of a flow of drain air (FV) at least through the pre-chamber (43);

- at least one means of regulation (47) of the circulation of the flow of drain air (FV) arranged at the level of the at least one orifice (45) and capable to passively control the circulation of said flow.

2. Spark plug (4) according to the preceding claim, wherein the at least one channel

(46) is delimited by the base (42) and/or the electrically insulating body (41 ).

3. Spark plug (4) according to one of the preceding claims, wherein the base (42) and/or the body (41 ) extend along a first direction (100), the spark plug (4) further comprising at least one primary electrode (5) and at least one ground electrode (51 ), the at least one orifice (45) and the at least one means of regulation (47) being arranged such that, along the first direction (100), the at least one ground electrode (51 ) is interposed between the at least one orifice (45) on one side and the at least one hole (44) of the pre-chamber (43) on the other side.

4. Spark plug (4) according to one of the preceding claims, further comprising at least one intermediate volume (48) interposed between the at least one orifice (45) and all or part of the at least one channel (46), the intermediate volume (48) being delimited by the base (42) and/or the electrically insulating body (41 ) and the intermediate volume (48) being connected to the at least one channel (46) and to the pre-chamber (43) by a fluid connection.

5. Spark plug (4) according to one of the preceding claims, wherein the at least one means of regulation (47) of the circulation of the flow of drain air (FV) is a nonreturn valve comprising at least one ball (47a) and one spring (47b).

6. Cylinder head (3) for spark-ignition engine (2) comprising at least one intake valve (32), an exhaust valve (34) and at least one cavity (35) delimiting a first volume (350), a first end of said cavity (35) comprising an opening (36) configured to open into a combustion chamber (23) of a cylinder (21 ), the cylinder head (3) further comprising at least one spark plug (4) according to one of the preceding claims arranged in the first volume (350) at the level of said opening (36) such that at least one orifice (45) extends into the first volume (350) and such that the pre-chamber (43) is configured to implement a fluid connection with the combustion chamber (23) of the cylinder (21 ).

7. Cylinder head (3) according to the preceding claim, wherein a second end, opposite the first end, of the at least one cavity (35) of spark plug is at least partially open in order to allow the entry of a flow of drain air (FV) into the first volume (350), the said second end being configured to limit, or even eliminate, the entry of liquid and/or particles.

8. Spark-ignition engine (2) comprising a cylinder head (3) according to claim 6 or 7, at least one cylinder (21 ) delimiting a combustion chamber (23) and a movable piston (22) arranged in the at least one cylinder (21 ), the opening (36) of the cylinder head (3) and the pre-chamber (43) of the at least one spark plug (4) opening into the combustion chamber (23).

9. Spark-ignition engine (2) according to the preceding claim, further comprising a device for controlling the intake valve (32), capable to control an opening, in particular a delay in opening, of the said valve.

10. Operating method for a spark-ignition engine (2) according to claim 8 or 9, comprising:

- an intake phase of a flow of intake air (FA) into the cylinder (21 ) comprising a step of generating a negative pressure in the cylinder (21 ) in order to allow a flow of drain air (FV) to circulate from the first volume (350) towards the combustion chamber (23) through the pre-chamber (43) of the spark plug (4), the flow of drain air (FV) being capable to expel residual burnt gases accumulated in the pre- chamber (43) and/or in the spark plug (4);

- a compression phase comprising a pressure increase in the cylinder so that a portion of a carburated mixture is sent to the pre-chamber (43) and comprising the ignition of said mixture in the pre-chamber (43); then - an expansion phase wherein the carburated mixture contained in the cylinder

(21 ) ignites; then

- an exhaust phase comprising the raising of the piston (22) to upper position so as to displace residual burnt gases present in the combustion chamber (23) of the cylinder (21) at least towards the pre-chamber (43) of the spark plug (4).