EP3235080B1 - Spark plug having a ground electrode having a small cross-section - Google Patents

Description

State of the art

The invention is based on a spark plug according to the preamble of the independent claim.

Due to the increasing reduction in installation space in the engine compartment, there is less space available in the engine compartment for the individual components, such as the spark plug, and the components in the engine compartment must be made smaller. This trend of so-called downsizing of the components creates new challenges in the design of the components and the spark plug.

Downsizing the spark plug and its components increases the thermal, electrical and mechanical stress on the spark plug and its individual components. At the same time, the spark plug should have the same reliability and the same long service life as previous spark plugs that have not been downsized.

The US 2007/0216275 A1 discloses a spark plug according to the preamble of claim 1.

Disclosure of the invention

Due to the downsizing, the housing also has to be changed. This has the result that the end face of the housing on which the ground electrode is arranged becomes narrower. This means that a smaller width of the end face is available for welding on for the ground electrode. The dimensions of the ground electrode must be adapted to this reduced space. At the same time, the ground electrode must also withstand the mechanical, thermal, chemical and electrical loads when a spark plug is operated in an internal combustion engine, so that the spark plug has a similarly good ignition reliability and service life as spark plugs that are not subject to downsizing.

The object of the present invention is to provide a spark plug which can meet the requirements mentioned at the beginning.

This object is achieved by the spark plug according to the invention by the characterizing part of claim 1.

According to the invention it is provided that the ground electrode has a core which is surrounded by a jacket, wherein the cross-sectional area of the ground electrode is not greater than 2.76 mm ² , and wherein the ground electrode has a first area in which the jacket has a wall thickness c of is no larger than 0.4 mm. This ensures that the core in this first area of the ground electrode takes up a sufficiently large volume in the ground electrode so that the ground electrode can withstand the thermal loads during spark plug operation.

The above limit for the cross-sectional area of the ground electrode relates to its largest cross-sectional area. For example, the ground electrode can have several areas with different cross-sectional areas. In a preferred manner, the value of the cross-sectional area is constant over the entire length of the ground electrode, whereby, in the context of this application, constant means that the value does not change by more than 5%.

Advantageous further developments of the invention are the subject of the dependent claims.

In particular, it can be provided that the cross-sectional area of the ground electrode is not greater than 2.64 mm ² or, in a particularly preferred manner, not greater than 2.3 mm ² .

The sheath is advantageously made of a more wear-resistant material than the core. The core is made of a material with a higher thermal conductivity than the material of the jacket. The material of the core preferably has a thermal conductivity of at least 350 W / mK at room temperature. Additionally or alternatively, it can be provided that at room temperature the thermal conductivity of the material of the core is at least 300 W / mK greater than the thermal conductivity of the material of the jacket. For example, the core is made of copper, silver or an alloy with copper and / or silver. The jacket consists for example of an alloy containing nickel. The Ni alloy can, for example, contain at least 20% by weight of chromium, in particular 25 % Chromium by weight. Additionally or alternatively, the nickel-containing alloy can also contain yttrium.

It has been found to be advantageous that the jacket and the core each have a constant cross-sectional area in the first region of the ground electrode. The cross-sectional area of the core preferably corresponds to at least 20% of the total cross-sectional area of the ground electrode in the first area. The cross-sectional area of the ground electrode is the sum of the cross-sectional area of the jacket and the cross-sectional area of the core. By maintaining a lower limit for the cross-sectional area of the core, it is ensured that the heat dissipation within the ground electrode from an end of the ground electrode facing away from the housing to an end of the ground electrode arranged on a spark plug housing is sufficiently large for the spark plug to operate in Heat absorbed by an internal combustion engine at the end of the ground electrode facing away from the housing is dissipated sufficiently quickly to the housing in thermal contact with a cylinder head, so that the ground electrode has a sufficiently high resistance to the thermal, mechanical and chemical loads during operation of the spark plug.

It is preferably provided that the casing of the ground electrode, in particular along its entire length, has a wall thickness c of not less than 0.15 mm, so that the core of the ground electrode is sufficiently well protected against the combustion chamber gases occurring during operation of the spark plug.

Additionally or alternatively, in order to achieve the above-mentioned advantage, it can be provided that in the first area the cross-sectional area of the core corresponds at most to 65% of the total cross-sectional area of the ground electrode.

It is preferred that the first region is preferably formed at an end of the ground electrode which corresponds to an end of the ground electrode arranged on the housing of the spark plug. As a result, a good thermal contact between the ground electrode and the housing is achieved.

In an advantageous development of the invention, an end of the ground electrode facing away from the housing is at a distance b from the core in the ground electrode. The distance b is preferably not greater than 4 mm, and in particular not smaller is than 0.2mm. When using an ignition surface on the end of the ground electrode facing away from the housing, it is preferred that the distance b is in the range from 0.2 mm to 2 mm so that the core, which conducts heat well, is not too far from the ignition surface. The ignition surface typically contains a noble metal or a noble metal alloy and therefore has a higher wear resistance than the jacket material.

If an ignition surface is dispensed with, it has been found to be advantageous that the distance b is at least 2 mm and a maximum of 4 mm. So that there is sufficient volume of the jacket material in the area of the ground electrode in which an ignition spark is formed so that the ground electrode can withstand the thermal and chemical loads during operation of a spark plug for a sufficiently long time. Sufficiently long means operating the spark plugs for at least 50,000 km.

A height and a width can be assigned to the cross-sectional area of the ground electrode. The width x _E and the height y _E correspond to two dimensions of the cross-sectional area that are perpendicular to each other. The width x _E denotes the longer dimension and the height y _E denotes a perpendicular dimension of the cross-sectional area. In the case of a rectangular cross-section, the width x _E and the height y _{E of} the cross-sectional area correspond to the lengths of the sides of the rectangular cross-sectional area. The height y _{E of} the cross section is preferably not greater than 1.2 mm, and in particular not less than 0.8 mm, in particular not greater than 1 mm. The width x _{E of} the cross-sectional area of the ground electrode is, for example, no greater than 2.3 mm, in particular no greater than 2.2 mm or even no greater than 1.9 mm, and in particular no smaller than 1.6 mm.

Analogously to the height y _E and the width x _{E of} the cross-sectional area of the ground electrode, a height y _K and a width x _{K are also} assigned to the core.

The first area is preferably cylindrical. The first region preferably has a length perpendicular to the cross-sectional area, which is equal to or longer than the height y _{E of} the cross-sectional area of the ground electrode. In particular, the length of the first region is at least 1.5 times as long as the height y _{E of} the cross-sectional area of the ground electrode.

The cross-sectional areas of the core and of the ground electrode advantageously have the same shape. This ensures that the ground electrode has a jacket with a constant thickness in this first region.

The ground electrode can be designed as a roof electrode, side electrode or bracket electrode.

• Figur 1 zeigt ein Beispiel für eine Masseelektrode
• Figur 2 zeigt einen Querschnitt der Masseelektrode
• Figur 3 zeigt einen Schnitt einer gebogenen Masseelektrode
• Figur 4 zeigt eine erfindungsgemäße Zündkerze mit einer gebogenen Masseelektrode

drawing

• Figure 1 shows an example of a ground electrode
• Figure 2 shows a cross section of the ground electrode
• Figure 3 shows a section of a bent ground electrode
• Figure 4 shows a spark plug according to the invention with a curved ground electrode

description

Figure 1 shows schematic representations of examples of a ground electrode 10. The ground electrode 10 has a core 12 and a jacket 11 surrounding the core 12. The core 12 consists of a material with a higher thermal conductivity than the material of the jacket 11. Typically, the material of the jacket 11 has a higher wear resistance than the material of the core 12. The core 12 consists of copper, silver or an alloy with copper and / or silver. A Ni alloy is preferably used as the material for the jacket 11, and the alloy can contain chromium and / or yttrium.

Due to the manufacturing process, here an extrusion process, the core 12 of the ground electrode 10 shown here in section has at least one first section 15a, in which the core 12 has relatively constant dimensions (x _K , y _K ) and, associated therewith, a relatively constant cross-sectional area Has. In the context of this application, the term “relatively constant” means that the dimensions or the cross-sectional area change their values by a maximum of 5%.

Within a second section 14a, the dimensions (x _K , y _K ) and the cross-sectional area of the core 12 are reduced. The at least one first section 15a is arranged on a side of the ground electrode 10 facing away from a combustion chamber, for example on the side with which the ground electrode is arranged on the spark plug housing 2. In the direction of the end of the ground electrode 10, which protrudes into the combustion chamber when the ground electrode is used in a spark plug, a second section 14a of the core 12 adjoins the at least one first section 15a of the core 12. In principle, it is conceivable that the core 12 has a plurality of first sections 15a with a constant cross-sectional area, the dimensions (x _K , y _K ) and the cross-sectional areas of the individual first sections 15a being different. This is particularly the case when the ground electrode 10 itself has a plurality of regions with different dimensions (x _E , y _E ) or cross-sectional areas. In the case of a plurality of first sections 15a in the core 12, the section closest to the combustion chamber is the second section 14a with the continuously decreasing cross-sectional area of the core 12.

In the Figure 1 The ground electrode 10 shown has constant dimensions (x _E , y _E ) along its length and, associated therewith, a constant cross-sectional area. In the case of the ground electrode 10, at least three areas 13, 14, 15 can be distinguished. In a first region 15, the ground electrode 10 has a core 12 with a constant cross-sectional area and a jacket thickness c of not greater than 0.4 mm. In a second region 14a, the ground electrode 10 has a core 12 with a continuously reducing cross-sectional area. In a third area 13, the ground electrode 10 does not have a core.

The thickness c of the jacket of the ground electrode 10 results from half the difference between its dimensions (x _E , y _E ) and the core dimensions (x _K , y _K ). If the ground electrode 10 has a constant cross-sectional area in the first region 15, then the jacket thickness c in this first region 15 is constant. It is advantageously provided that in this first region 15 the jacket thickness c of the ground electrode 10 is not less than 0.15 mm, and in particular not greater than 0.4 mm, for example the jacket thickness c is 0.25 mm or less.

In the second region 14, the ground electrode 10 can have constant dimensions (x _E , y _E ) and a constant cross-sectional area, in which case the jacket thickness c increases within the area 14 in the direction of the combustion chamber. The jacket thickness c is at least 0.15 mm thick in the second region 14.

In an alternative example, not shown here and not claimed, the dimensions (x _E , y _E ) or the cross-sectional area of the ground electrode 10 in the second region 14 can likewise be reduced. In this case it applies to the jacket thickness c that it is preferably in the range from 0.15 mm to 0.4 mm. It can be provided that the dimensions (x _E , y _E ) or the cross-sectional area of the ground electrode 10 change at the same rate as the dimensions (x _K , y _K ) or the cross-sectional area of the core 12. This has the advantage that the jacket thickness c remains constant in the second region 14.

There is no core in the third area 13 of the ground electrode 10. The third area 13 preferably has constant dimensions (x _E , y _E ) and a constant cross-sectional _{area which corresponds to the dimensions (x E} , y _E ) or the cross-sectional area of the second area 14 at the transition to the third area 13.

The third region 13 of the ground electrode 10 has a length b which extends from an end 17 of the core 12 on the combustion chamber side to an end face 16 of the ground electrode 10 facing away from the housing. The length b is not greater than 4 mm. If the ground electrode 10 is designed with a noble metal-containing ignition surface 19, the length b can be made shorter than without a noble metal-containing ignition surface 19, as in FIG Figure 1b shown. For example, the length b is then in the range from 0.2 mm to 2 mm. If a noble metal-containing ignition surface 19 is dispensed with, as in Figure 1a As shown, the length b should have a minimum length of 1 mm so that the jacket 11 at the end of the ground electrode 10 facing away from the housing has enough material for a sufficiently long service life of the ground electrode 10.

The dimension of the length b is adjusted to the desired length after the extrusion of the ground electrode 10. The excess length of the jacket 11 is cut off by a cutting process, a shearing process, a punching process or by means of a laser beam. The length b has an influence on the heat dissipation in the ground electrode 10. By selecting the length b accordingly, the heat level of the ground electrode 10 at its end 16 facing away from the housing can be set to a desired value, so that the end 16 facing away from the housing of the ground electrode 10 does not fall below a temperature which is advantageous for igniting the gas mixture in a combustion chamber.

Figure 2 Fig. 13 shows an example of a cross section of the ground electrode 10. In this example, the ground electrode 10 and the core 13 have a rectangular cross section. The area of the cross section of the ground electrode is not larger than 2.76 mm ² . The cross section has a width x _E of not greater than 2.3 mm and a height y _E of not greater than 1.2 mm.

The cross section of the core 12 is arranged in the center of the cross section of the ground electrode 10. The thickness c of the jacket 11 results from half the difference between the height y and width x of the ground electrode 10 (y _E , x _E ) and of the core 12 (y _K , x _K ). The cross-sections of the ground electrode 10 and of the core 12 advantageously have the same geometric shape.

The cross-sectional area of the core 12 is not less than 20%, and in particular not more than 65%, of the cross-sectional area of the ground electrode 10 in the first region 15 of the ground electrode 10. The cross-sectional area of the ground electrode is composed of the area of the jacket 11 and the area of the Core 12 in cross section.

In an example not shown here and not claimed, it can be provided that the shape of the cross section of the ground electrode 10 changes in the course of the length of the ground electrode 10. For example, the ground electrode 10 can have a rectangular cross section at its end 16 facing away from the housing and a cross section at its end arranged on the housing 2 which is adapted to the annular end face 21 of the housing 2. This means that the height y _{E of} the cross section of the ground electrode 10 corresponds to a width of the annular end face 21 or is smaller than this. Correspondingly, the width x _E at the end of the ground electrode 10 facing the housing 2 is longer than at the end 16 of the ground electrode 10 facing away from the housing. The cross section of the ground electrode 10 at its end facing the housing 2 has a curvature, ie the cross section has a banana -shaped profile, corresponding to the curvature of the end face 21 of the housing. The shape of the cross-section is typically changed by means of stamping, either a rectangular cross-section of the end of the ground electrode 10 facing the housing can be formed into a banana-shaped profile by stamping or the end 16 of a ground electrode with a banana-shaped profile facing away from the housing is shown in embossed a flat surface.

Figure 3 shows a section for a ground electrode 10 of the spark plug according to the invention, which differs from the in Figure 1 ground electrodes 10 shown differ only in that the ground electrode in Figure 3 is bent. In a first step, the ground electrode 10 is produced by an extrusion process such as, for example, the cup process. The straight ground electrode 10 is welded to the end face 21 of the spark plug housing in a subsequent step. Depending on the intended use, the ground electrode 10 is bent into the desired position in a subsequent step, so that a top electrode or a side electrode or a bracket electrode is produced. In addition, the ground electrode 10 can also have an ignition surface 19, which is typically welded to the ground electrode before bending.

The three areas 13, 14, 15 of the earth electrode 10 or the two sections 14a, 15a of the core 12 can also be identified in the case of the curved earth electrode 10. The length of the respective areas results as a mean from the longest and shortest length of the area, which result along the surface of the ground electrode 10.

Figure 4 shows a schematic representation of a spark plug 1 according to the invention with a ground electrode 10. The spark plug 1 has a metallic housing 2 with a thread for mounting the spark plug 1 in a cylinder head. The thread can have an outer diameter of at least 8 mm, 10 mm or larger. Furthermore, the housing has a hexagon section 9, on which a tool for mounting the spark plug 1 in the cylinder head is attached. An insulator 3 is arranged inside the housing 2. A center electrode 5 and a connecting bolt 7 are arranged inside the insulator 3 and are electrically connected via a resistance element 6.

The center electrode 5 typically protrudes from the insulator 3 at the end of the spark plug 1 facing away from the housing. The center electrode 5 rests with its electrode head 4 on a seat formed on the inside of the insulator 3. The center electrode 5 and / or the ground electrode 10 have an arranged ignition surface 19. The center electrode can also have a core surrounded by a jacket, the core being made of a material with a higher thermal conductivity than the material of the jacket.

At least one ground electrode 10 according to the invention is arranged on the end of the housing 2 facing away from the housing. Which forms an ignition gap together with the center electrode 5. The ground electrode 10 can be designed as a roof electrode, side electrode or bracket electrode.

Claims (10)

1. Spark plug (1), comprising a housing (2), an insulator (3) arranged in the housing (2), a centre electrode (5) arranged in the insulator (3), and an earth electrode (10) arranged on the housing (2), wherein the earth electrode (10) and the centre electrode (5) are arranged in relation to one another in such a way that the earth electrode (10) and the centre electrode (5) form a spark gap, and wherein the earth electrode (10) has a core (12) and a sheath (11) surrounding the core (12), wherein the core (12) consists of a material that has a higher thermal conductivity than the material of the sheath (11), and wherein a cross-sectional area of the earth electrode (10) is not greater than 2.76 mm², wherein the sheath (11) has a wall thickness c of not greater than 0.4 mm in a first region (15) of the earth electrode (10), wherein the first region (15) forms a region of the earth electrode (10) which is facing away from the combustion space and in which the core (12) has a constant cross-sectional area, wherein the earth electrode (10) has a second region (14), in which the cross-sectional area of the core (12) reduces continuously, wherein the earth electrode has a third region (13), into which the core (12) does not reach and which is arranged at the end (16) of the earth electrode (10) facing away from the housing, wherein the earth electrode (10) is bent, so that it is formed as a roof electrode, side electrode or bow electrode, characterized in that the second region (14) is formed within a bent portion of the earth electrode (10) between the first region (15) and the third region (13) along the longitudinal extent of the earth electrode (10).
2. Spark plug (1) according to Claim 1, characterized in that the sheath (11) and the core (12) respectively have a constant cross-sectional area in the first region (15) of the earth electrode (10) along its longitudinal extent.
3. Spark plug (1) according to either of Claims 1 and 2, characterized in that, in the first region (15), the cross-sectional area of the core (12) corresponds to at least 20% of the entire cross-sectional area of the earth electrode (10).
4. Spark plug (1) according to one of the preceding claims, characterized in that, in the first region (15), the cross-sectional area of the core (12) corresponds to at most 65% of the entire cross-sectional area of the earth electrode (10).
5. Spark plug (1) according to one of the preceding claims, characterized in that, at an end (16) of the earth electrode (10) facing away from the housing, the distance b between the end (16) of the earth electrode (10) and an end (17) of the core (12) is not greater than 4 mm, and in particular not smaller than 0.2 mm.
6. Spark plug (1) according to one of the preceding claims, characterized in that the cross-sectional area of the earth electrode (10) has a height y_E and a width x_E.
7. Spark plug (1) according to Claim 6, characterized in that the height y_E of the cross-sectional area of the earth electrode (10) is not greater than 1.2 mm and/or the width x_E of the cross-sectional area of the earth electrode (10) is not greater than 2.3 mm.
8. Spark plug (1) according to either of Claims 6 and 7, characterized in that the first region (15) is longer than the height y_E of the cross-sectional area of the earth electrode (10).
9. Spark plug (1) according to one of the preceding claims, characterized in that the cross-sectional area of the core (12) and the cross-sectional area of the earth electrode (10) have the same shape.
10. Spark plug (1) according to one of the preceding claims, characterized in that the material of the sheath (11) comprises a nickel-containing alloy, in particular that the alloy comprises at least 20% by weight chromium.

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