Pre-chamber spark plug with profiled ground electrode

Description

State of the art

[0001] A prechamber spark plug is already known from the prior art, DE 10 2017 221 517 A1. It comprises a housing and a cap arranged on the housing at the combustion chamber end of the housing. The cap and the housing together form a prechamber. Bores are provided in the cap to allow gas to enter and exit the prechamber. An insulator is arranged within the housing, in which a center electrode is located. A ground electrode is also provided, which, together with the center electrode, forms an ignition gap.

[0002] Furthermore, pre-chamber spark plugs are known from DE 10 2011 006597 A1, GB 737 117 A, DE 10 2013 221963 A1, WO 2009 / 059339 A1 and EP 3 173 596 A1.

[0003] When the prechamber spark plug is operated in the combustion chamber of an internal combustion engine, fresh air flows into the prechamber during the compression stroke. This is necessary for the fresh air to reach the ignition gap formed between the electrodes, where a spark is generated during ignition. Due to the significant increase in volume of compressed combustion gases, a sharp increase in pressure occurs after ignition in the prechamber, which in turn causes the hot combustion gases to escape from the prechamber bores in the form of flares at high speed. This allows large portions of the combustion chamber to be ignited virtually simultaneously. By optimizing the timing of this process, the engine's efficiency can be brought closer to its thermodynamic optimum.

[0004] A prerequisite for this is that a sufficient amount of ignitable fresh mixture flows into the prechamber and reaches the area of ​​the ignition gap.

[0005] Furthermore, it is necessary that during the charge exchange of the internal combustion engine, the burnt combustion gases remaining in the prechamber flow out of the prechamber in order to release volume for fresh mixture. Advantage of the inventionj Disclosure of the invention

[0006] The present invention is based firstly on the finding that the geometry of the ground electrode plays an important role for an efficient access of fresh gas to the ignition gap and for an efficient outflow of burnt combustion gases from the prechamber as well as for a homogenization of the gas in the prechamber with regard to its fuel-air ratio.

[0007] The invention is further based on the finding that the cylindrical ground electrode known from the prior art is merely suboptimal with regard to the aforementioned criteria and can be improved by a geometry according to the invention in that the ground electrode has a shape that deviates from a cylindrical shape in order to specifically influence a gas flow within the prechamber.

[0008] In the context of this application, "cylinder" and "cylindrical" generally refer only to a vertical circular cylinder. A further development of the invention involves assuming a "cylinder" in a broad mathematical sense, i.e., as a body defined as the spatial area swept out by a rectilinear displacement of a flat base surface.

[0009] The ground electrode has a longitudinal direction. This can be the direction along which the ground electrode is inserted into a mounting hole in the housing. It can also be the direction along which the main axis of the ground electrode points, in which it has its greatest extension.

[0010] It can be provided that the ground electrode is inserted into the mounting hole of the housing and is also screwed, pressed and / or welded into the mounting hole.

[0011] It is provided that the ground electrode has cross sections perpendicular to the longitudinal direction, of which at least one cross section deviates from a circular shape, wherein the at least one cross section has the shape of an ellipse or the shape of a longitudinal cross section of a drop.

[0012] The shape and orientation of the ground electrode or the shape and orientation of the cross-sections deviating from the circular shape, for example the shape and orientation of the ellipse or the drop, can cause gas flowing into the prechamber through the overflow hole to be directed specifically to the ignition gap and / or flow resistances in the prechamber are reduced and / or gas flowing in through the overflow hole is deflected specifically in such a way that turbulence is created in the prechamber.

[0013] A further development of the invention provides that the ground electrode consists of a base body facing the housing and a precious metal pin facing away from the housing. The precious metal consists predominantly of precious metal (e.g., platinum), while the base body consists predominantly of base metal.

[0014] In a further development, it can be provided that only the base body has a shape other than a cylinder and / or that the precious metal pin has a cylindrical shape. drawing

[0015] The Figure 1 shows a pre-chamber spark plug which is already known.

[0016] The Figure 2 and 3 show an embodiment of the invention. Description of the embodiment

[0017] Figure 1 shows a semi-sectional view of a pre-chamber spark plug 1. The pre-chamber spark plug 1 comprises a housing 2. An insulator 3 is inserted into the housing 2. The housing 2 and the insulator 3 each have a bore along their longitudinal axis. The housing has an outer side 24 and an inner side 23. The longitudinal axis of the housing 2, the longitudinal axis X of the insulator 3, and the longitudinal axis of the pre-chamber spark plug 1 coincide.

[0018] A center electrode 4 is inserted into the insulator 3. Furthermore, an electrical contact extends into the insulator 3, via which the pre-chamber spark plug 1 is electrically connected to a voltage source. The electrical contact forms the end of the pre-chamber spark plug 1 facing away from the combustion chamber. The electrical contact can be formed as a single piece or, as in this example, from multiple components, such as a connecting bolt 8 and a connecting nut 9.

[0019] The insulator 3 is typically divided into three sections: insulator base 31, insulator body 32, and insulator head 33. The three sections differ, for example, in their diameters. The insulator base 31 is the end of the insulator 3 facing the combustion chamber. The center electrode 4 is located within the insulator base 31. The insulator base 31 is usually located entirely within the housing 2. The insulator base 31 generally has the smallest outer diameter on the insulator 3.

[0020] Adjacent to the insulator base 31 is the insulator body 32, which is generally completely enclosed by the housing 2. The insulator body 32 has a larger outer diameter than the insulator base 31. The transition between the insulator base 31 and the insulator body 32 is formed as a shoulder or groove. This transition is also referred to as the base groove or insulator seat 35.

[0021] The insulator head 33 adjoins the end of the insulator body 32 facing away from the combustion chamber and forms the end of the insulator 3 facing away from the combustion chamber. The insulator head 33 protrudes from the housing 2. The outer diameter of the insulator head 33 lies between the outer diameters of the insulator base 31 and the insulator body 32, whereby the regions typically do not have a constant outer diameter over their length, but the outer diameter can vary.

[0022] The housing 2 has a seat 25 on its inside. The insulator rests with its shoulder or insulator seat 35 on the housing seat 25. An inner seal 10 is arranged between the insulator seat 35 and the housing seat 25.

[0023] A resistance element 7, also called a contact element (CCM), is located in the insulator 3 between the center electrode 4 and the terminal bolt 8. The resistance element 7 electrically connects the center electrode 4 to the terminal bolt 8. The resistance element 7 is constructed, for example, as a layered system consisting of a first contact element (CCM), a resistance element (CCM), and a second contact element (CCM). The layers of the resistance element differ in their material composition and the resulting electrical resistance.

[0024] On the inner side 23 of the housing 2, the ground electrode 5 is arranged in a bore 52, so that the ground electrode 5 protrudes radially from the housing inner side 23 into the bore along the longitudinal axis X of the housing 2. The ground electrode 5 and the center electrode 4 together form an ignition gap. The bore 52 extends from the outer side 24 through the housing wall to the inner side 23 of the housing 2.

[0025] The housing 2 has a shaft. A polygon 21, a shrink recess, and a thread 22 are formed on this shaft. The thread 22 serves to screw the prechamber spark plug 1 into an internal combustion engine. An outer sealing element 6 is arranged between the thread 22 and the polygon 21. In this exemplary embodiment, the outer sealing element 6 is designed as a folded seal.

[0026] The bore 52 in the housing wall is formed in the area of ​​the thread 22. The bore 52 for the ground electrode 5, and thus also the ground electrode 5, can be arranged at any height in the area of ​​the thread 22. Depending on the position of the ground electrode 5 in the area of ​​the thread 22, the center electrode 4 and with it the insulator base 31 protrude more or less far into the prechamber 81. Depending on the desired application of the prechamber spark plug, the position of the bore 52 in the area of ​​the thread 22 and the ground electrode 5 on the inside 23 of the housing 2 can be selected.

[0027] The bore 52 is arranged in a recess 51, such as a conical or round groove. The outer diameter of the housing 2 in the recess is smaller than the core diameter of the thread 22.

[0028] The recess 51 can be created, for example, by punching the housing 2 during the manufacture of the pre-chamber spark plug 1. This reduces not only the outer diameter of the housing 2 in the area of ​​the recess 51, but also the inner diameter of the housing 2 in the area of ​​the recess 51.

[0029] A cap 80 is arranged on the end face of the housing 2 facing the combustion chamber. The housing 2 and the cap 80 together form a pre-chamber 81 with a pre-chamber volume. The pre-chamber 81 extends from the cap into the housing 2 and within the housing 2 to the housing seat 25, on which the insulator 3 rests with its shoulder 35. The space between the housing 2 and the insulator 3 is sealed gas-tight at this point by means of an internal seal 10. The pre-chamber 81 and its volume can be divided into a front pre-chamber 81a and a rear pre-chamber 81b. The boundary between the front pre-chamber 81a and the rear pre-chamber 81b is determined by the position of the ground electrode, i.e. the front pre-chamber 81a extends from the cap to a plane which, at the level of the ground electrode, runs perpendicular to the longitudinal axis X of the housing.Accordingly, the rear pre-chamber 81b extends from this plane to the housing seat 25, on which the insulator 3 and the inner seal 10 rest.

[0030] The following differ from the known pre-chamber spark plug 1 with regard to the Figure 2 described embodiments of the invention in that the ground electrode 5 has a shape that deviates from a cylindrical shape in order to specifically influence a gas flow within the prechamber 81.

[0031] The Figure 2The prechamber spark plug 1 shown in detail and by way of example has a ground electrode 5 that has a longitudinal direction y and is preferably inserted into a mounting hole 52 of the housing 2 along the longitudinal direction y. The ground electrode 5 has a base body 5a facing the housing 2 and a precious metal pin 5b facing away from the housing 2. The base body 5a has a shape that deviates from a cylinder, while the precious metal pin 5b has a cylindrical shape.

[0032] Perpendicular to the longitudinal direction y of the ground electrode 5, in the region of the base body 5a, the center electrode 5 has cross sections which correspond to the cross-sectional area along the longitudinal direction of a drop.

[0033] Overall, a ground electrode 5 is designed as a drop-shaped profile. The end of the drop, which protrudes elongated from an imaginary cylindrical shape, can point, for example, in the direction of the cap 80 or in the direction of an overflow bore 82 of the cap 80.

[0034] Enlarged and in plan view, along its longitudinal axis y looking out of the prechamber 81, the ground electrode 5 is in the Figure 3 shown.

[0035] As an aerodynamic shape with particularly low flow resistance, the drop-shaped ground electrode 5 can thus substantially improve the inflow or outflow of gas.

[0036] Alternatively (not shown), it can also be provided that the center electrode 5 has cross-sections that have the shape of an ellipse. Overall, for example, a ground electrode 5 profiled as an ellipsoid or semi-ellipsoid is thus formed. One of the two ends of the ellipsoid, which protrude elongated from an imaginary cylindrical shape, can point, for example, in the direction of the cap 80 or in the direction of an overflow bore 82 of the cap 80. As an aerodynamic shape with particularly low flow resistance, the ground electrode 5 profiled in this way can substantially improve the inflow or outflow of gas.

[0037] Alternatively (not shown), the center electrode 5 can also be eccentrically shaped in a different way or be designed with different eccentric cross-sections. Preferably, the greatest eccentricity 5c occurring in this case is oriented toward the cap 80 or toward an overflow bore 82 of the cap 80.

Claims

1. Pre-chamber ignition plug having a housing (2), and having a cap (80) which is arranged on the combustion-chamber-side end of the housing (2) and which forms together with the housing (2) a pre-chamber (81) and in which provision is made of at least one flow-transfer bore (82) to allow entry of gas into the pre-chamber (81) and exit of gas from the pre-chamber (81), having an insulator (3) which is arranged within the housing (2), having a central electrode (4) which is arranged within the insulator (3), and having an earth electrode (5), wherein the earth electrode (5) and the central electrode (4) are arranged in such a way as to form with one another an ignition gap, and wherein the earth electrode (5) has a shape which is different from a cylindrical shape in order to influence a gas flow within the pre-chamber (81) in a targeted manner, wherein the earth electrode (5) has a longitudinal direction (y) and the earth electrode (5) has perpendicular to the longitudinal direction (y) cross sections of which at least one cross section is different from a circular shape, characterized in that the at least one cross section has the shape of an ellipse or the shape of a longitudinal cross section of a drop.

2. Pre-chamber ignition plug according to the preceding claim, characterized in that the earth electrode (5) is plugged into a fastening bore (52) of the housing (2) along the longitudinal direction (y).

3. Pre-chamber ignition plug according to either of the preceding claims, characterized in that the difference from a cylindrical shape and / or the difference from a circular shape have / has the effect that gas flowing in through the flow-transfer bore (82) is directed in a targeted manner to the ignition gap.

4. Pre-chamber ignition plug according to one of the preceding claims, characterized in that the difference from a cylindrical shape and / or the difference from a circular shape have / has the effect that flow resistances in the pre-chamber (81) are reduced.

5. Pre-chamber ignition plug according to one of the preceding claims, characterized in that the difference from a cylindrical shape and / or the difference from a circular shape have / has the effect that gas flowing in through the flow-transfer bore (82) is diverted in a targeted manner in such a way that turbulence is generated in the pre-chamber (81).

6. Pre-chamber ignition plug according to one of the preceding claims, characterized in that the earth electrode (5) consists of a main body (5a), which is relatively close to the housing (2), and a high-grade-metal pin (5b), which is relatively far from the housing (2), wherein the main body (5a) has a shape which is different from a cylinder and the high-grade-metal pin (5b) has a cylindrical shape.

7. Pre-chamber ignition plug according to one of the preceding claims, characterized in that a further earth electrode is fitted opposite the earth electrode (5) in the housing (2), wherein the further earth electrode has the same shape as or a different shape from the earth electrode (5).

8. Pre-chamber ignition plug according to Claim 7, characterized in that the earth electrode (5) brings about swirling or directing of the flow into the ignition gap, and the further earth electrode brings about improved flushing.