WO2023156390A1

WO2023156390A1 - Prechamber spark plug

Info

Publication number: WO2023156390A1
Application number: PCT/EP2023/053648
Authority: WO
Inventors: Ronald Ritter
Original assignee: Robert Bosch Gmbh
Priority date: 2022-02-16
Filing date: 2023-02-14
Publication date: 2023-08-24
Also published as: DE102022201624A1

Abstract

The invention relates to a prechamber spark plug comprising at least one central electrode (4) and at least one ground electrode (5), an isolator (3) for electrical separation between the central electrode and ground electrode, and a cap (6) which, along with a housing (2), defines a prechamber (16), wherein the cap (6) has a plurality of overflow holes, at least one of which is a radial overflow hole (7) having a central axis (71) arranged at a first angle a between 80° and 100° to a first tangential plane T1 at an intersection of the central axis (71) and an outer casing of the cap (6), wherein at least one of the overflow holes is a tangential-type overflow hole (8) having a second central axis (81) arranged at a second angle b between 5° and 45° to a second tangential plane T2 at an intersection of the second central axis (81) and the outer casing of the cap.

Description

title

prechamber spark plug

State of the art

The present invention relates to a prechamber spark plug of a gas internal combustion engine with an improved design and arrangement of overflow bores that create a fluid connection between a prechamber and a combustion chamber.

Prechamber spark plugs are known from the prior art in different configurations. In this context, it is known to introduce so-called “overflow bores” in the caps of prechamber spark plugs, via which gas exchange takes place between the prechamber and the combustion chamber of an internal combustion engine. On the one hand, the prechamber is flushed by means of the overflow bores and, on the other hand, after ignition in the prechamber, so-called “flare jets” emerge from the overflow bores into the combustion chamber in order to ignite the fuel-air mixture there. One problem with prechamber spark plugs is that after ignition has taken place in the prechamber, fresh gas must flow into the prechamber of the spark plug again during an intake and compression stroke of the internal combustion engine, so that an ignitable mixture is present in the area of the electrodes of the prechamber spark plug, which ignites can be. The overflow bores are usually provided symmetrically. DE 102010 003 899 A1 discloses a laser spark plug with a prechamber, in which overflow bores are provided which have different cross-sectional areas and/or cross-sectional shapes along a longitudinal axis of the overflow bore.

Disclosure of Invention The prechamber spark plug of a gas internal combustion engine according to the invention with the features of claim 1 has the advantage that overflow bores can be arranged in such a way that requirements within a prechamber of the prechamber spark plug can be optimized with regard to their flow conditions in order to ensure reliable ignition in the prechamber. As a result, the efficiency of the internal combustion engine and the exhaust gas behavior of the internal combustion engine can be improved by this design of the prechamber spark plug according to the invention. According to the invention, a high fresh gas content can be obtained in the electrode gap between the center electrode and the ground electrode, and also a moderate flow rate in the electrode gap at the ignition point, as a result of which reliable ignition is possible. According to the invention, this is achieved in that the prechamber spark plug has a center electrode and a ground electrode. An insulator is provided to electrically separate the center electrode and the ground electrode. Furthermore, the prechamber spark plug includes a cap which defines a prechamber with a housing. An arrangement of a large number of overflow bores is provided in the cap, which keep the prechamber in fluid connection with an outer area of the prechamber spark plug, usually a combustion chamber of an internal combustion engine. At least one of the overflow bores is a radial overflow bore, which has a central axis which is at a first angle a in a first angular range of between 80° and 100°, in particular 85° and 95°, more preferably 88° and 92°, to a first Tangential plane T1 is arranged at the intersection of the central axis with an outer shell of the cap. Furthermore, at least one other of the overflow bores is a tangential-type overflow bore, which has a central axis that is arranged at a second angle b in a second angular range of 5° to 45° to a second tangential plane T2 at an intersection of the second central axis with the outer shell of the cap . The present invention thus combines different overflow bores, namely a radial and a tangential-type overflow bore, so that in the electrode gap at the point of ignition a significantly increased flow rate is achieved in comparison with the prior art and also a higher proportion of fresh gas is present in the electrode gap at the point of ignition.

The dependent claims show preferred developments of the invention. The second angular range is preferably in a range between 10° and 30° to the tangential plane at the point of intersection of the central axis of the tangential overflow bore and the outer shell of the cap, in particular in the range from 10° to 20°.

More preferably, the at least one radial and at least one tangential overflow bore are arranged in the cap in such a way that each gas jet that enters the antechamber through one of the overflow bores has a targeted influence on another gas jet of the other overflow bore. That is, the overflow bores are arranged in such a way that the mutual influencing of the gas jets creates a certain turbulence inside the prechamber, which contributes to the desired improved flow rate in the electrode gap at the time of ignition and the improved supply of flammable mixture to the electrode gap. The gas jets entering the antechamber through the overflow bores can be influenced in different ways, for example by deflecting the gas jets or by mixing the gas jets or the like.

A radial overflow bore and a tangential-type overflow bore are particularly preferably arranged in such a way that the gas jets of these two overflow bores meet in the antechamber. As a result, a deflection and change in speed of the flow speed of the two gas jets and additional turbulence can be achieved in a targeted manner.

Particularly preferably, each gas jet that emerges from an overflow bore into the antechamber hits at least one other gas jet in the antechamber. Thus, each gas jet entering the antechamber is influenced by another gas jet with regard to its type of propagation in the prechamber, in particular with regard to a flow rate and a propagation volume.

At least one of the radial overflow bores is particularly preferably directed towards a center point on a central axis of the prechamber spark plug. The The center point is preferably a spatial center of the antechamber, which lies in the center of the antechamber.

More preferably, radial and tangential overflow bores are arranged alternately in the circumferential direction on the cap. As a result, it can be realized in a particularly simple manner that preferably each gas jet entering the antechamber through a radial overflow bore is influenced by a gas jet entering via a tangential-type overflow bore.

More preferably, all overflow bores are cylindrical. That is, a diameter of the overflow bores in the cap does not change. All overflow bores preferably have the same, constant diameter. More preferably, the overflow bores are arranged in such a way that no central axes of the overflow bores are arranged parallel to one another.

According to a further preferred embodiment of the invention, the cap does not have a central overflow bore, which would lie in the central axis of the prechamber spark plug. This can prevent a central gas jet, which would enter the antechamber through such a central overflow bore, from weakening the mutual influence of the other gas jets of the other overflow bores, since the gas jet of a central overflow bore usually determines the fresh gas content due to its arrangement in the central axis at the electrode gap and the flow velocity at the electrode gap at the time of ignition. Alternatively, the cap has a central overflow bore located in the central axis of the prechamber spark plug, and at least one gas jet from another overflow bore strikes the gas jet from the central overflow bore. This prevents the gas jet from the central overflow bore from being directed directly in the direction of the electrode gap between the central electrode and the ground electrode and the gas jet hitting the gas jet from the central overflow bore from lowering and thus changing the direction of this gas jet and also affecting a change in the speed of the inflow behavior of the gas jet. There is preferably an even number of radial overflow bores and an even number of tangential overflow bores. Exactly two or exactly three radial overflow bores and exactly two or exactly three tangential-like overflow bores are particularly preferably provided.

According to a further preferred embodiment of the invention, all overflow bores are arranged in a first peripheral area of the cap, which is between 0° and 300°. An area is thus provided on the cap which extends over 60° and in which there are no overflow bores. In this 60° area, there are therefore no overflow bores in the inner area of the cap, so that this area can serve as a guide area for the gas entering via the overflow bores. This area of the cap without overflow bores is preferably formed between 60° and 90° along the circumference of the cap.

More preferably, the overflow bores are provided in such a way that a flow velocity of the gas jets is at least 4 m/s at the time the overflow bores emerge into the antechamber. The flow rate is preferably in a range from 4 m/s to 15 m/s.

Furthermore, the present invention relates to an internal combustion engine with a prechamber spark plug according to the invention.

drawings

Preferred embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawing is:

FIG. 1 shows a schematic sectional view of a prechamber spark plug according to a first exemplary embodiment of the invention, Figure 2 is a schematic partial sectional view of a cap

Prechamber spark plug of Figure 1 with a radial overflow hole,

Figure 3 is another schematic partial sectional view of the cap of

Figure 1 with a tangential overflow hole,

Figure 4 is a schematic plan view of the prechamber spark plug

Figure 1 from the direction of the cap,

Figure 5 is another schematic sectional view of the cap

Prechamber spark plug of Figure 1, and

Figure 6 is a schematic sectional view of a cap of a

Prechamber spark plug according to a second embodiment of the invention.

Preferred Embodiments of the Invention

A prechamber spark plug 1 according to a preferred exemplary embodiment of the invention is described in detail below with reference to FIGS.

As can be seen from Figure 1, the prechamber spark plug 1 comprises a metallic housing 2 and an insulator 3. The prechamber spark plug also comprises at least one center electrode 4, which lies in a central axis X-X, and at least one laterally positioned ground electrode 5. Housing 2 has an external thread 21 formed, which is set up to be screwed into a cylinder head of an internal combustion engine.

The prechamber spark plug 1 also includes a cap 6 which, together with a portion of the housing 2, defines a prechamber 16. The center electrode and the ground electrode are arranged in the antechamber 16 . A plurality of overflow openings are formed in the cap 6 and produce a fluid connection between the antechamber 6 and a combustion chamber 10 of the internal combustion engine.

Both radial overflow bores 7 and tangential overflow bores 8 are formed in the cap 6 .

Radial overflow bores 7 are overflow bores in which a central axis 71 of the radial overflow bore is at a first angle a in a first angular range between 85° and 95° to a first tangential plane T1, which lies at an intersection of the central axis 71 and an outer shell of the cap 6 , is arranged. Tangential overflow bores 8 are overflow bores which have a central axis 81 which is at a second angle b in a second angular range to a second

Tangential plane T2 are arranged at the intersection of the central axis 81 and the outer shell of the cap 6.

In other words, the radial overflow bores 7 run essentially perpendicular to the outer shell of the cap 6 and the tangential overflow bores 8 run at an acute angle to the outer shell of the cap, the acute angle preferably being in a range of 10° to 30°.

FIG. 2 shows in detail a radial overflow hole 7 in which the central axis 71 is arranged on the outer shell of the cap 6 at a right angle a to the first T angential plane T1.

The central axis 71 of the radial overflow bore 7 is directed in the direction of a center point M, which lies on the central axis X-X of the prechamber spark plug. In this exemplary embodiment, the center M is a center which defines inner radii of the hemispherical cap 6 .

FIG. 3 shows in detail a tangential overflow hole 8 in which the central axis 81 is arranged on the outer shell of the cap 6 at an acute angle b to the second tangential plane T2. The acute angle b is approximately 45°. Thus, the prechamber spark plug 1 according to the invention has a mixture of radial overflow bores 7 and tangential overflow bores 8 . As can be seen from FIGS. 1 and 4, there is no central overflow hole which would be provided in the central axis XX in the cap 6 .

As can also be seen from FIG. 4, all overflow bores 7, 8 are arranged in a first circumferential area 11 of approximately 300°. In a second peripheral area 12, which has approximately 60°, no overflow bores or other openings or the like are provided. Thus, the overflow bores are not distributed over the entire circumference of the cap 6 but are formed exclusively in the first peripheral area 11 .

Thus, the arrangement of radial and tangential overflow bores 7, 8 can result in a targeted influencing of the flow during a gas exchange within the antechamber 16. Tangential overflow bores 8 tend to result in high flow velocities on the inner wall of the cap 6 in the antechamber 16 . During gas exchange in the antechamber 6, radial overflow bores 7 usually produce a gas jet that penetrates deep into the antechamber. The combination of the radial and tangential-type overflow bores can thus make it possible to influence the flow in a targeted manner during gas exchange within the antechamber 6 .

As can be seen from FIG. 4, radial and tangential overflow bores are arranged alternately along the circumference. The arrangement of the overflow bore 7, 8 is such that the internal flow within the antechamber 16 provides an optimal fresh gas concentration in an electrode gap between the center electrode 4 and the ground electrode 5 and an optimal gas velocity in the electrode gap. This also makes it possible for a position of the electrode gap to be arranged, for example, in such a way that noble metal elements which are usually arranged on the electrodes have to be arranged in smaller quantities on the electrodes, while a superior long service life of the prechamber spark plug is nevertheless achieved. Figure 5 shows schematically the mutual interaction of the arrangement of radial overflow bores 7 and tangential overflow bores 8. The radial overflow bore 7 in Figure 5 has an inwardly directed first gas jet 72 during gas exchange, which is directed essentially in the direction of the central axis 71. The tangential-type overflow bore 8 of FIG. The arrangement of the radial and the tangential overflow bore 8 is now such that the first gas jet 72 and the second gas jet 82 meet in the antechamber 16 . As shown schematically in Figure 5, this results in a first deflection 73 of the first gas jet 72 and a second deflection 83 of the second gas jet 82.

The radial overflow bore 7 has a first diameter D1, which is the same as a second diameter D2 of the tangential overflow bore 8. Both the radial and the tangential overflow bore 7, 8 are cylindrical.

Thus, exactly four overflow bores 7 , 8 are provided in this exemplary embodiment, with two overflow bores being radial overflow bores 7 and two overflow bores being tangential-like overflow bores 8 . All overflow bores are designed pointing in different directions.

The design of the radial and tangential overflow bores 7, 8 is based on the requirements within the antechamber 16 in order to ensure reliable ignition. In the prior art, the design of the overflow bores is usually based on the flow conditions in the main combustion chamber, from which the present invention, however, differs. The combination of radial and tangential-type overflow bores 7, 8 thus ensures that a spark generated in the electrode gap enables ignition of a sufficiently large volume of fresh gas in the antechamber 16, with the fresh gas in the pre-chamber remaining in motion at the time of ignition, in particular due to the tangential-type overflow bores 8. This allows a large volume of gas to be ignited. However, the movement in the combustion chamber at the time of ignition must not be too large, since otherwise the spark can break off in the electrode gap and the ignition in the antechamber 16 would thus be terminated. Here, the first gas jets 72 of the radial overflow bores 7 ensure that the speed of movement in the antechamber does not become too great, since these essentially reach deep into the antechamber 6 .

The tangential overflow bores 8 allow essentially a tangential flow in the antechamber, a very good balance for optimal ignition being obtained through the mutual influencing of the gas jets of the two different types of overflow bores.

It is thus possible for higher fresh gas concentrations to be achieved with a simultaneously significantly lower flow rate in the antechamber 16 in the area of the electrode gap. In this way, in particular, much earlier flushing in the area of the electrode gap can be achieved in comparison to the prior art, so that at the ignition point in the electrode gap there is only about 5% residual gas from the previous ignition. This further promotes ignition.

FIG. 6 shows a prechamber spark plug with a cap 6 according to a second exemplary embodiment of the invention. Identical or functionally identical parts are denoted by the same reference symbols as in the first exemplary embodiment.

As can be seen from FIG. 6, in addition to radial overflow bores 7 and tangential overflow bores 8, the prechamber spark plug 1 of the second exemplary embodiment also has a central overflow bore 9 in the cap, which lies in the central axis XX of the prechamber spark plug. The central overflow bore 9 is also a radial overflow bore, since an angle c to a third tangential plane T3 on the outer shell of the cap 6 is approximately 90°. In the second exemplary embodiment, the first gas jet 72 of the radial overflow bore 7 and a third gas jet 92 of the middle overflow bore 9 meet. This results in the first deflection 73 of the first gas jet 72 and a third deflection 93 of the third gas jet 92. The two gas jets 72, 92 are further influenced by the second gas jet 82 of the tangential type Overflow hole 8 obtained. Otherwise, this exemplary embodiment corresponds to the previous exemplary embodiment, so that reference can be made to the description given there.

Claims

Expectations

1 . Prechamber spark plug comprising: at least one center electrode (4) and at least one ground electrode (5), an insulator (3) for electrical separation between center electrode and ground electrode, and a cap (6) which defines a prechamber (16) with a housing (2). , wherein the cap (6) has a large number of overflow bores, at least one of the overflow bores being a radial overflow bore (7) which has a central axis (71) which is at a first angle a in a range between 80° and 100° a first tangential plane T1 at an intersection of the central axis (71) with an outer shell of the cap (6), at least one of the overflow bores being a tangential-type overflow bore (8) which has a second central axis (81) which is at a second angle b is located in a range of 5° to 45° to a second tangent plane T2 at an intersection of the second central axis (81) with the outer shell of the cap.

2. Prechamber spark plug according to claim 1, wherein the range of the first angle is between 85° and 95°, and/or wherein the range of the second angle b is between 10° and 30°.

3. Prechamber spark plug according to one of the preceding claims, wherein the radial and tangential overflow bores (7, 8) are arranged in the cap (6) in such a way that a first gas jet entering the prechamber (16) through one of the overflow bores (7, 8). (72) of a radial overflow bore (7) influences another second gas jet (82) of a tangential overflow bore (8). Prechamber spark plug according to claim 3, wherein the first gas jet (72) and the second gas jet (82) meet in the prechamber (16), so that a first deflection (73) occurs at the first gas jet (72) and at the second gas jet (82) a second deflection (83) occurs. Prechamber spark plug according to Claim 4, in which each gas jet from an overflow bore strikes at least one further other gas jet from another overflow bore in the prechamber (16). Prechamber spark plug according to one of the preceding claims, wherein at least one radial overflow bore (7) is directed towards a center point (M) on a central axis (XX) of the prechamber spark plug. Prechamber spark plug according to one of the preceding claims, radial overflow bores (7) and tangential overflow bores (8) being arranged alternately in the circumferential direction on the cap (6). Prechamber spark plug according to one of the preceding claims, in which all the radial and tangential overflow bores are of cylindrical design and/or in which all the radial and tangential overflow bores have the same diameter. Prechamber spark plug according to one of the preceding claims, wherein the cap (6) has no overflow bore in the central axis (XX) of the prechamber spark plug. Prechamber spark plug according to one of Claims 1 to 8, the cap (6) having a central overflow bore (9) lying in the central axis (XX). Prechamber spark plug according to one of the preceding claims, wherein an even number of radial overflow bores and an even number of tangential overflow bores are formed in the cap (6). Prechamber spark plug according to one of the preceding claims, wherein all overflow bores in the cap (6) are arranged in a first peripheral area (11) of the cap, the first peripheral area (11) encompassing an angular range of 0° to 300°, in particular 0° to 240 °.