Prechamber spark plug for a combustion chamber of an internal combustion engine, in particular for a motor vehicle

Abstract

Internal combustion engine (24) for a motor vehicle, with at least one combustion chamber (12), and with a pre-chamber spark plug (10) associated with the combustion chamber (12), which has a pre-chamber (20) fluidically connected to the combustion chamber (12) via several openings (18) and having a volume, characterized in that a ratio of the volume of the pre-chamber (20) to an ignition volume of the combustion chamber (12), which has the ignition volume at the ignition time associated with the combustion chamber (12), which lies before or after the ignition dead center, is in a range of 0.05% to 2% inclusive, wherein the internal combustion engine (24) is designed as a gasoline engine and has direct fuel injection with an injector (14) associated with the combustion chamber (12), by means of which a liquid fuel can be injected directly into the combustion chamber (12), wherein the injector (14) is designed as an outwardly opening injector.whose nozzle needle opens outwards, allowing the liquid fuel to be injected directly into the combustion chamber (12) forming at least one fuel jet (16).

Description

[0001] The invention relates to an internal combustion engine for a motor vehicle according to the preamble of claim 1. Furthermore, the invention relates to a motor vehicle, in particular a motor car, with such an internal combustion engine.

[0002] DE 10 2010 010 109 B4 discloses a pre-chamber spark plug for a combustion chamber of an internal combustion engine. The pre-chamber spark plug has a housing with a pre-chamber having several openings at its front end, an insulator arranged in the housing, a central electrode surrounded by the insulator which carries an ignition electrode arranged in the pre-chamber, the ignition electrode having several electrode arms, each having a rear section extending transversely to the longitudinal direction of the central electrode and a front section running along a pre-chamber wall which forms a spark gap between itself and the pre-chamber wall, the electrode arms being embedded in the central electrode and projecting from a side surface of the central electrode. EP 2 657 479 A1 also discloses a cylinder head for an internal combustion engine. DE 603 ​​10 979 T2 discloses an ignition device as known.Furthermore, an internal combustion engine is known from DE 10 2018 003 465 A1.

[0003] The object of the present invention is to create an internal combustion engine, a motor vehicle and a method that allows for particularly efficient operation of the internal combustion engine in a particularly simple way.

[0004] This problem is solved by an internal combustion engine with the features of claim 1, by a motor vehicle with the features of claim 7, and by a method with the features of claim 8. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0005] A first aspect, not part of the invention, relates to an internal combustion engine, for example a reciprocating piston engine, for a motor vehicle, in particular a car. The internal combustion engine has at least one combustion chamber, which may be partially bounded, for example, by a cylinder, by a piston movably mounted in the cylinder, and by a combustion chamber roof. The internal combustion engine includes a pre-chamber spark plug associated with the combustion chamber, which has a pre-chamber fluidically connected to the combustion chamber via several openings and having a volume.

[0006] To achieve particularly efficient operation of the internal combustion engine, the ratio of the pre-chamber volume to the combustion chamber compression volume is designed to be between 0.2% and 2% inclusive. In other words, the pre-chamber volume has a first value and the compression volume a second value, with the quotient of these two values ​​falling within the specified range. The numerator of the quotient is the first value, and the denominator is the second value.

[0007] The volume of the pre-chamber is also referred to as the internal volume or chamber volume, and the ratio is also called the volume ratio. The aforementioned cylinder is formed, for example, by a housing of the internal combustion engine, which is designed, in particular, as a crankcase, preferably as a cylinder crankcase. The combustion chamber roof is formed, for example, by a cylinder head, which is designed separately from the housing and connected to it. The piston is mounted in the cylinder so as to be translationally movable. The piston is articulated, in particular via a connecting rod, to an output shaft of the internal combustion engine, which is designed, for example, as a crankshaft, in such a way that translational movements of the piston in the cylinder relative to the housing can be converted into a rotational movement or rotation of the output shaft, in particular relative to the housing.The output shaft is rotatably mounted on the housing.

[0008] Particularly during the firing of an internal combustion engine, air and liquid fuel are introduced into the combustion chamber, forming a mixture of air and fuel. At least a portion of the mixture from the combustion chamber flows through the openings and into the pre-chamber, where it is ignited, particularly by at least one spark. This ignites burning flares, also known as lances or flame lances. The flares from the pre-chamber can then flow through the openings into the combustion chamber, also called the main combustion chamber. This ignites the remaining mixture in the combustion chamber.

[0009] The volume ratio now allows for particularly advantageous ignition of the mixture in the pre-chamber, and enables the flame lances penetrating the combustion chamber to propagate in a particularly advantageous manner, especially with regard to their length and extent. In other words, the aforementioned volume ratio improves ignition conditions compared to conventional solutions. This is particularly advantageous, for example, in operating modes with low cylinder filling and / or low pressure in the combustion chamber, resulting, for instance, from low load due to throttling and / or small cam lift. Furthermore, the volume ratio, and thus the improved ignition conditions, are particularly advantageous in operating modes with low charge motion, such as at low engine speeds, small cam lift, etc.Furthermore, the volume ratio or the ignition conditions are particularly advantageous in operating modes with a high exhaust gas recirculation rate (EGR rate) and / or with high charge dilution and / or charge stratification, especially with a combustion air ratio (λ) that is in a range from 1.0 inclusive to 2.2 inclusive.

[0010] The internal combustion engine has an injector, also known as an injection nozzle, located in the combustion chamber, through which the liquid fuel can be injected directly into the combustion chamber. In particular, the injector is preferably designed as a piezo injector. Furthermore, it is conceivable that the injector is designed as a multi-hole nozzle, especially with variable or varying hole geometry and / or variable or varying pressure, whereby, for example, the fuel is injected into the combustion chamber at the aforementioned pressure. In particular, the first aspect allows for very high robustness against pre-ignition, thus preventing ceramic fracture caused by pressure waves.

[0011] The cylinder in question has a total internal volume, which can be divided into a stroke volume and a compression volume. The stroke volume corresponds to the space the piston traverses during its complete stroke, from bottom dead center to top dead center. The compression volume comprises the combustion chamber volume of the cylinder head, any valve pockets in the piston, the piston bowl, and the volume of the piston ring land up to the top compression ring.

[0012] For example, at least one spark can be generated in the prechamber, particularly by means of at least one electrode of the prechamber spark plug, in order to ignite, for example, the mixture (also referred to as the fuel-air mixture) in the prechamber and subsequently in the combustion chamber. In particular, it can be provided that the prechamber is separated from the combustion chamber except for the respective fluidic connections between the prechamber and the combustion chamber realized via the respective openings, in particular by means of a prechamber element of the prechamber spark plug that delimits the prechamber, wherein the openings, for example designed as through-holes, are arranged in or penetrate the prechamber element. The prechamber element is, for example, a component of a housing element of the prechamber spark plug.In particular, the pre-chamber element is a cap which, for example, is formed separately from at least one further housing part of the housing element of the pre-chamber spark plug and is connected to the further housing part. In particular, the pre-chamber spark plug has, for example, the pre-chamber at its front end, which, for example, extends at least partially, and in particular at least predominantly or completely, into the combustion chamber or is contained within the combustion chamber.

[0013] The internal combustion engine is preferably designed as a four-stroke engine. Furthermore, it is preferably provided that exactly one working cycle of the internal combustion engine comprises exactly two complete revolutions of the crankshaft and thus exactly 720 degrees of crank angle. Each working cycle preferably comprises exactly four strokes of the piston and thus of the cylinder or the internal combustion engine. Within each working cycle, the piston moves to its top dead center exactly twice and to its bottom dead center exactly twice. Thus, for example, it is provided that during exactly one complete revolution of the output shaft, the piston is at least once at its top dead center, or moves to its top dead center at least once, or reaches its top dead center once.The first stroke of each working cycle is, for example, the compression stroke, during which the piston moves from bottom dead center to top dead center and compresses the air taken in, at least in the combustion chamber. A second stroke, which follows directly after the first, is, for example, the power stroke, during which the piston moves from top dead center to bottom dead center. A third stroke, which follows directly after the second, is, for example, the exhaust stroke, during which the piston moves from bottom dead center to top dead center and expels gas, particularly exhaust gas, from the combustion chamber.The fourth stroke, which follows the third stroke directly, is called the intake stroke. During this stroke, the piston moves from top dead center to bottom dead center, drawing in or introducing gas, such as air or fresh air, into the combustion chamber. The intake stroke marks the end of the power cycle, and a new power cycle, the compression stroke, begins.

[0014] The invention is based in particular on the following findings: With the aid of the pre-chamber spark plug, when used in an internal combustion engine, for example a gasoline or Otto engine, a stabilization and an improvement in ignition can be achieved, which can be used advantageously to reduce fuel consumption and increase the performance of the internal combustion engine, especially compared to conventional solutions.The pre-chamber spark plug ignites and combusts the fuel-air mixture in the pre-chamber, creating an overpressure relative to the main combustion chamber. This causes the flame jets, acting as reactive combustion gases, to flow through small openings in the pre-chamber element—located between the pre-chamber and the main combustion chamber—into the main combustion chamber. These openings, often referred to as transfer ports, ignite the mixture over a large area. The penetration depth of the reactive combustion gases, or flame jets, into the main combustion chamber depends on the pressure ratio, which in turn depends on the volume ratio between the pre-chamber volume and the compression volume in the main combustion chamber.However, the volume ratio between the pre-chamber volume and the compression volume can, conventionally, lead to a situation where, with an unfavorable choice of volume ratio, the combustible mixture present in the pre-chamber spark plug is not optimally ignited and optimal propagation of the combustion gases entering the combustion chamber is not guaranteed. This makes ignition more difficult, which can now be avoided by the internal combustion engine. It has been found that it is advantageous for the volume ratio between the pre-chamber volume and the compression volume to be in the range of 0.2% to 2% inclusive.This ensures, particularly when the internal combustion engine is operated at low speed and / or low load, that a reliably combustible fuel-air mixture is introduced into the pre-chamber, leading to an ideal propagation of the flame lances penetrating the combustion chamber.

[0015] According to the invention, the internal combustion engine is designed as a gasoline engine, which has a direct fuel injection system with the injector assigned to the combustion chamber, by means of which the liquid fuel can be injected directly into the combustion chamber, wherein the injector is designed as an outwardly opening injector, the nozzle needle of which opens outwards and not inwards, whereby the liquid fuel can be injected directly into the combustion chamber, forming at least one fuel jet.

[0016] In an advantageous embodiment of the first aspect, the ratio of the pre-chamber volume to the combustion chamber compression volume is in the range of 0.5% to 1.5% inclusive. This allows for particularly favorable ignition conditions.

[0017] A second aspect belonging to the invention relates to an internal combustion engine for a motor vehicle, with at least one combustion chamber, and with a pre-chamber spark plug associated with the combustion chamber, which has a pre-chamber that is fluidically connected to the combustion chamber via several openings and has a volume.

[0018] To achieve particularly efficient operation of the internal combustion engine, the invention provides that the ratio between the volume of the pre-chamber and the ignition volume of the combustion chamber, which contains the ignition volume at the ignition point associated with the combustion chamber, lies within a range of 0.05% to 2% inclusive. In other words, the volume of the pre-chamber has a first value, and the ignition volume of the combustion chamber, which contains the ignition volume at the ignition point associated with the combustion chamber, has a second value, the first value being less than the second value, such that the quotient of the first value and the second value lies within the aforementioned range. The numerator of the quotient is the first value, and the denominator is the second value. Particularly advantageous ignition conditions can also be achieved with regard to this second aspect, especially for the aforementioned operating modes.Advantages and beneficial features of the first aspect are to be regarded as advantages and beneficial features of the second aspect, and vice versa.

[0019] Another embodiment is characterized in that a pre-chamber spark plug is used, which has a pre-chamber fluidically connected to the combustion chamber via several openings and which has a volume, wherein the ratio of the volume of the pre-chamber to an ignition volume of the combustion chamber, which has the ignition volume at the ignition time associated with the combustion chamber, lies in a range of 0.1% to 1.5% inclusive. In other words, the ratio of the volume of the pre-chamber to an ignition volume of the combustion chamber, which has the ignition volume at the ignition time associated with the combustion chamber, lies in a range of 0.1% to 1.5% inclusive.In other words, the volume of the pre-chamber has a first value and the ignition volume of the combustion chamber, which has the ignition volume at the ignition time assigned to the combustion chamber, has a second value, where the first value is less than the second value.

[0020] To achieve particularly efficient operation of the internal combustion engine, an advantageous embodiment of the invention provides that the compression ratio of the combustion chamber lies within a range of 8.0 to 16.0 inclusive, particularly within a range of 8.5 to 15.0 inclusive, and most especially within a range of 9.0 to 13.5 inclusive. This means that the compression ratio, which indicates the ratio of the total cylinder volume before compression to the remaining volume after compression (compression volume), in one of the aforementioned ranges, together with the volume ratios of the pre-chamber spark plug and the compression volume or ignition volume according to the invention, allows for the realization of a high thermodynamic efficiency.The tendency to knock, which triggers premature, uncontrolled combustion in the cylinder's combustion chamber, limits the compression ratio and thus the thermodynamic efficiency, especially in gasoline engines. The compression ratio is therefore usually a compromise, aiming to avoid knocking while still achieving high thermodynamic efficiency.

[0021] Furthermore, the invention provides that the internal combustion engine can be operated with an air-fuel ratio ranging from 1.0 to 2.2 inclusive. The air-fuel ratio, also known as lambda, denotes the mass ratio of air to fuel relative to the ideal stoichiometric ratio for a theoretically complete combustion process. Air-fuel ratios with a numerical value greater than 1.0 indicate an excess of air during combustion, meaning that more air participates in the combustion than would be necessary for a stoichiometric reaction. This excess air is achieved through charge stratification in the combustion chamber, resulting in fuel savings.

[0022] It has proven particularly advantageous to inject the fuel directly into the combustion chamber. Therefore, it is preferably provided that the fuel is introduced by means of a direct injection system, also known as direct fuel injection, in which the fuel is injected directly into the combustion chamber, particularly by means of an injector.

[0023] The invention also includes a motor vehicle, preferably designed as a motor vehicle, in particular as a passenger car, which has an internal combustion engine according to the invention.

[0024] Furthermore, the invention also includes a method which is designed for operating an internal combustion engine according to the first aspect of the invention and / or for operating an internal combustion engine according to the second aspect of the invention.

[0025] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned above in the description, as well as those mentioned below in the figure description and / or shown in the figures alone, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

[0026] The attached drawings show in: Fig. 1. A schematic sectional view of an internal combustion engine of a motor vehicle at the point of ignition dead center, and Fig. 2 a schematic sectional view of an internal combustion engine of a motor vehicle at a time which is before or after the ignition dead center.

[0027] In the figures, identical or functionally equivalent elements are provided with the same reference numerals.

[0028] The following section explains, with reference to the figures, an internal combustion engine designed as a reciprocating piston engine with a pre-chamber spark plug integrated in the combustion chamber.

[0029] The Fig. Figure 1 shows a partial schematic sectional view of an internal combustion engine 24 designed as a reciprocating piston engine of a motor vehicle, which is preferably designed as a motor vehicle, in particular as a passenger car and can be driven by means of the internal combustion engine 24, at the time of top dead center.

[0030] The internal combustion engine 24 has a [missing information] in the Fig. 1. A first housing element, not shown, designed for example as a crankcase 22, in particular as a cylinder crankcase, by which at least one cylinder 4 is formed or bounded. Furthermore, the internal combustion engine 24 has at least one piston 6, which is translationally movable in the cylinder 4 and is therefore movable between a bottom dead center and a top dead center.

[0031] The internal combustion engine 24 also has a second housing element, which is, for example, designed separately from the first housing element and connected to it. The second housing element is, for example, a cylinder head 2, through which a combustion chamber 12 is formed. The cylinder 4, the piston 6, and the cylinder head 2 with its combustion chamber roof each form or partially define a combustion chamber 12 of the internal combustion engine 24, which is designed as a reciprocating piston engine. The volume of the combustion chamber 12 at the point of ignition dead center corresponds to the compression volume of the combustion chamber 12.

[0032] Furthermore, the internal combustion engine 24 has an injector 14, also referred to as an injection nozzle, assigned to the combustion chamber 12, by means of which fuel, in particular liquid fuel, can be injected directly into the combustion chamber 12 by forming respective fuel jets 16, for example as cones or clubs. The direct injection of fuel into the combustion chamber 12 is also referred to as direct injection or fuel direct injection.

[0033] The injector 14, which may preferably be designed as a piezo injector or as a multi-hole injector, in particular with variable or varying hole geometry and / or variable or varying pressure, can, for example, introduce the fuel, in particular liquid fuel, into the combustion chamber 12 by forming at least one or more fuel jets 16, also referred to as sprays or spray clubs, in particular by direct injection. Furthermore, it is conceivable that the injector 14 can be designed as an outwardly opening injector whose nozzle needle opens outwards and not inwards.

[0034] The internal combustion engine 24 also has a pre-chamber spark plug 10 associated with the combustion chamber 12, which has a pre-chamber 20 fluidically connected to the combustion chamber 12 via several openings 18 and otherwise separated from the combustion chamber 12. A spark can be generated in the pre-chamber 20, in particular by means of at least one electrode of the pre-chamber spark plug 10. For example, at least a portion of the mixture formed in the combustion chamber 12 can flow from the combustion chamber 12 into the pre-chamber 20 via at least one of the openings 18. If the spark is then generated in the pre-chamber 20, the mixture or the portion of the mixture contained in the pre-chamber 20 is ignited. This results in so-called flame lances, which exit the pre-chamber 20 through the openings 18 and penetrate the combustion chamber 12, subsequently igniting the mixture still present in the combustion chamber 12.As a result, the mixture is burned in the combustion chamber 12 and the piston 6 is driven.

[0035] At least during a firing operation of the internal combustion engine 24, the aforementioned fuel and air are introduced into the combustion chamber 12 within each operating cycle of the internal combustion engine 24, thereby forming a fuel-air mixture, also referred to as charge or mixture, in the combustion chamber 12. At least a portion of the fuel-air mixture can flow from the combustion chamber 12 into the pre-chamber 20 via the openings 18. If, for example, the ignition spark is then generated in the pre-chamber 20, particularly at an ignition point, the portion of the fuel-air mixture received in the pre-chamber 20 and the remaining fuel-air mixture in the combustion chamber 12 are ignited and subsequently combusted, creating an overpressure in the pre-chamber 20 compared to the combustion chamber 12.The resulting burning torches, also called lances or flame lances, can flow from the pre-chamber 20 through the openings 18 and thus into the combustion chamber 12, also called the main combustion chamber. This ignites the remaining mixture in the combustion chamber 12.

[0036] Furthermore, in the Fig. 1 A gas exchange valve 8 of the internal combustion engine 24, assigned to the combustion chamber 12 and designed, for example, as an inlet valve, is recognizable. For example, the aforementioned air can be drawn in, in particular, by forming a Fig. 1 flowing into the combustion chamber 12 via the inlet valve through a tumble-shaped flow 28, resulting, for example, in a tumble-shaped charge movement in the combustion chamber 12.

[0037] The internal combustion engine 24 also features a [missing information] in the Fig. 1 output shaft not shown in the form of a crankshaft, which is rotatably mounted on the crankcase 22, and via which the internal combustion engine 24 can provide torques to drive the motor vehicle.

[0038] The internal combustion engine 24 is, for example, a gasoline or Otto engine with direct fuel injection, so that, for example, the internal combustion engine 24 is operated in its fired operation by an Otto direct injection combustion process.

[0039] The Fig. Figure 2 shows a partial schematic sectional view of an internal combustion engine 24 designed as a reciprocating piston engine of a motor vehicle, which is preferably designed as a motor vehicle, in particular as a passenger car, and can be driven by means of the internal combustion engine 24, at a time which is before or after the ignition dead center. The figure shown in Fig. 2 combustion chamber 12 shown, the ignition volume of the combustion chamber 12, which is present at an ignition time that is before or after the ignition dead center.

[0040] Furthermore, it shows Fig. 2 the internal combustion engine 24, which has a first housing element designed, for example, as a crankcase 22, by which at least one cylinder 4 of the internal combustion engine 24 is bounded or formed and to which the second housing element, which is designed, for example, as a cylinder head 2, is connected.

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