spark plug

Abstract

Spark plug (10) comprising an insulator (11) arranged in a spark plug housing (21), the insulator having a longitudinal axis (12) and an opening (13) along the longitudinal axis (12), a center electrode (14) arranged in the opening (13) of the insulator (11), and at least one ground electrode (15) provided on the spark plug housing (21), wherein the insulator (11) has a first insulator section (31) and a second insulator section (32), the first insulator section (31) extending in the direction of the longitudinal axis (12) over a first insulator section length (61) with a first inner diameter (51), and the second insulator section (32) extending in the direction of the longitudinal axis (12) over a second insulator section length (62) with a second inner diameter (52), the first inner diameter (51) being smaller than the second inner diameter (52).wherein the first insulator section (31) transitions directly into the second insulator section (32) in a transition (25), and wherein the central electrode (14) has a central electrode section (44) with a constant diameter extending in the direction of the longitudinal axis (12) over a central electrode section length (64) with a central electrode outer diameter (54), wherein the central electrode section (44) extends at least over the entire insulator section length of the first insulator section (31) and the second insulator section (32), and wherein the central electrode section (44) in the first insulator section (31) has a radial distance to the insulator (11) of at least 40 µm and at most 120 µm.

Description

[0001] The present invention relates to a spark plug with reduced heat absorption at the center electrode. State of the art

[0002] Spark plugs are known in various designs from the prior art. A known spark plug has a center electrode and a ground electrode. The center electrode is arranged in an insulator, which is positively connected to a spark plug housing. An electrically conductive material establishes an electrical connection between the center electrode and an electrical terminal of the spark plug. Spark plugs are used to ignite flammable air-fuel mixtures in a combustion chamber (e.g., an internal combustion engine).

[0003] During spark plug operation in an engine, high temperatures occur at the center electrode, accelerating its wear. Heat is transferred to the center electrode in two ways. First, after ignition of the mixture, the high temperature of the hot residual gas is transferred to the center electrode. Second, heat is transferred from the portion of the insulator protruding into the combustion chamber to the center electrode. This high heat input to the center electrode protruding into the combustion chamber leads to increased heating and consequently to undesirably high wear at the ignition tip of the center electrode.

[0004] To reduce this high heat transfer from the insulator to the center electrode protruding into the combustion chamber, the heat transfer between the insulator and the center electrode is prevented by a gap. This reduces the center electrode temperature and thus the wear of the ignition tip of the center electrode.

[0005] For example, US Patent 5,239,225 A discloses a spark plug in which the center electrode has a diameter step. This step reduces the diameter of the center electrode. The reduced diameter of the center electrode separates it from the insulator opening via a gap. A disadvantage of this design is that the diameter reduction of the center electrode requires complex manufacturing processes (e.g., extrusion or turning). Furthermore, the step reduces the mechanical stability of the center electrode, particularly its bending resistance. Additionally, the reduction in the cross-section of the center electrode also reduces the cross-sectional area of ​​the heat-conducting center electrode core, thus impairing heat dissipation from the center electrode.

[0006] Furthermore, reducing the diameter of the center electrode leads to a decrease in the cross-sectional area of ​​the heat-conducting center electrode core, or to a greater distance between the center electrode core and the end face of the center electrode. These limitations in the center electrode core length and cross-sectional area result in a detrimental reduction in the heat dissipation capacity of the ignition tip along the center electrode.

[0007] Therefore, there is a need for a spark plug with reduced heat input into the center electrode, which is cheaper to manufacture and whose center electrode has increased mechanical stability and increased heat dissipation along the center electrode.

[0008] Other spark plugs are known from DE 11 2008 002 535 T5, DE 689 17 573 T2, DE 10 2013 102 854 A1, DD 126 935 A5, DE 691 12 330 T2, JP 2013 - 165 016 A and EP 2 180 565 A1. Disclosure of the invention

[0009] The spark plug according to claim 1 has the advantages that it is low-wear due to the reduced heat input into the center electrode and the high heat dissipation along the center electrode, has a center electrode with high mechanical stability and can be manufactured cost-effectively.

[0010] According to the invention, a spark plug is provided which comprises an insulator arranged in a spark plug housing, the insulator having a longitudinal axis and an opening along the longitudinal axis. Furthermore, a center electrode is arranged in the opening of the insulator. At least one ground electrode is arranged on the spark plug housing of the spark plug.

[0011] The insulator comprises a first insulator section and a second insulator section. The opening of the insulator extends along the longitudinal axis with a first, essentially constant inner diameter and a substantially cylindrical opening of a certain length. The opening of the insulator extends along the longitudinal axis with a second, essentially constant inner diameter and a similarly cylindrical opening of a certain length. An essentially constant inner diameter is defined as an inner diameter that varies by no more than 10% within the specified range. An essentially cylindrical opening is defined as a cylindrical opening that deviates from the diameter of an ideal cylinder by no more than 10% within the specified range.

[0012] The first inner diameter of the insulator opening is smaller than the second inner diameter of the insulator opening. The first insulator section transitions directly into the second insulator section. The longitudinal extent of this transition from the first to the second insulator section is significantly smaller than the longitudinal length of the second insulator section. The transition can be designed such that the inner diameter of the insulator in the transition area is neither smaller than the first inner diameter of the first insulator section nor larger than the second inner diameter of the second insulator section.

[0013] Furthermore, the central electrode is arranged in the opening of the insulator. The central electrode has a section with a length in the direction of the longitudinal axis and an outer diameter, the central electrode section extending at least over the entire length of the first and second insulator sections. It is advantageous that the reduction in heat absorption by the central electrode from the insulator is achieved due to the increased inner diameter along the second insulator section. This makes it possible to design the central electrode with a substantially constant outer diameter, at least in the region of the first and second insulator sections. A substantially constant outer diameter is one that varies by no more than 10% in the aforementioned region.This, in turn, has the advantage that the center electrode can be manufactured with minimal production effort. Furthermore, it is advantageous that the mechanical strength, particularly the bending resistance, of the center electrode is improved.

[0014] The measures mentioned in the dependent claims enable advantageous further developments of the device specified in the independent claim.

[0015] According to the invention, the central electrode is joined to the first insulator section in the region of the first insulator section length by a gap that varies between at least 40 µm and at most 120 µm in said region. This gap has the advantage that the central electrode can be joined to the insulator with minimal manufacturing effort.

[0016] Furthermore, it is advantageous that the center electrode in the first insulator section can be connected to the insulator by a molten glass, at least partially along the first insulator section's length. This connection of the center electrode to the insulator creates a thermal connection, in addition to the mechanical fastening and gas-tight seal, at least in the sections of the first insulator section connected by the molten glass. This makes it possible to dissipate heat from the center electrode, at least in a portion of the first insulator section, through the insulator into the spark plug housing.

[0017] Furthermore, it is advantageous that the radial distance between the insulator and the center electrode in the second insulator section is at least 100 µm and at most 500 µm. Such an annular gap between the center electrode and the insulator results in thermal decoupling, which reliably prevents the center electrode from being heated by the insulator. The radial distance can be achieved by means of an additional bore in the longitudinal direction of the insulator with a correspondingly larger diameter.

[0018] A particular advantage is that the second insulator section, with its enlarged opening for forming the gap between the central electrode and the insulator, has an insulator section length of at least 0.5 mm and at most 10 mm. This insulator section length ensures effective thermal decoupling through the gap.

[0019] Furthermore, it is advantageous that the first insulator section is arranged on the side of the second insulator section facing away from the combustion chamber. This ensures insulation of the center electrode on the side facing the combustion chamber and heat dissipation on the side of the center electrode section facing away from the combustion chamber.

[0020] A particular advantage is that the enlargement of the insulator's inner opening is compensated, at least in part, by an increase in the outer diameter of the second insulator section. The thermal and mechanical properties of the insulator can be fully or partially maintained by increasing the outer diameter.

[0021] Furthermore, it is advantageous that the center electrode section extends beyond the second insulator section of the insulator opening at the combustion chamber end of the spark plug.

[0022] Advantageously, a center electrode core, surrounded by a center electrode sheath, extends at least along the longitudinal extent of the center electrode section. The material of the center electrode core exhibits a higher thermal conductivity than the material of the center electrode sheath. At the transition from the first to the second insulator section, the center electrode core comprises up to 60% of the cross-sectional area of ​​the center electrode. This advantageously improves the thermal conductivity of the center electrode core and thus the heat dissipation capacity of the ignition tip along the center electrode.

[0023] A particular advantage is that the core of the center electrode, at a distance of 5 mm from the end of the center electrode section facing the combustion chamber, accounts for up to 70% of the cross-sectional area of ​​the center electrode.

[0024] A particular advantage is that the distance between the center electrode core and the end of the center electrode section facing the combustion chamber is at most 2.25 mm. This advantageously enables very good heat dissipation from the center electrode, which leads to an increased service life of the spark plug.

[0025] A particular advantage is that the second insulator section extends to one end face of the insulator. This facilitates robust manufacturing in a beneficial manner.

[0026] Advantageously, the opening of the insulator at the combustion chamber end is at least partially conical in a third insulator section immediately adjoining the second insulator section. This at least partially conical widening of the insulator opening results in a gap between the insulator and the center electrode that changes over a third of the length of the third insulator section. This further increases the distance to the center electrode at the end of the insulator, which is subject to particularly high thermal stress, thereby further reducing the temperature at the ignition tip of the center electrode and extending the service life of the spark plug.

[0027] An advantage is that the third insulator section extends in the direction of the longitudinal axis over a third insulator section length.

[0028] Furthermore, it is advantageous that the middle electrode section extends at least over the entire section length encompassing the first insulator section length of the first insulator section, the second insulator section length of the second insulator section, and the third insulator section length of the third insulator section.

[0029] Furthermore, it is advantageous that the center electrode section at the combustion chamber-side end of the spark plug extends beyond the third insulator section length of the third insulator section of the insulator opening.

[0030] A particular advantage is that the third insulator section extends to the end face of the insulator. This facilitates robust manufacturing in a beneficial manner.

[0031] A particular advantage is that along the at least partially conical widening of the inner opening of the insulator, in the region of the third insulator section length, the radial wall thickness of the insulator is largely constant. A largely constant wall thickness is defined as a wall thickness in a plane perpendicular to the longitudinal axis of the spark plug that varies by no more than 10% in the aforementioned region. The thermal and mechanical properties of the insulator can be fully or partially maintained by increasing the outer diameter.

[0032] Further features and advantages of the present invention will become apparent to the person skilled in the art from the following description of exemplary embodiments, which, however, are not to be interpreted as limiting the invention, with reference to the accompanying drawings. Brief description of the drawings

[0033] They show: Fig. 1: a schematic representation of a spark plug known from the prior art. Fig. 2: a schematic representation of the combustion chamber side of a spark plug according to a first embodiment of the invention Fig. 3: A schematic representation of the combustion chamber side of a spark plug according to a second embodiment of the invention Fig. 4: A schematic representation of the combustion chamber side of a spark plug according to a further embodiment of the invention

[0034] All figures are merely schematic representations of the devices or their components according to exemplary embodiments of the invention. In particular, distances and size relationships are not always shown to scale in the figures. Corresponding elements in the various figures are provided with the same reference numbers. Preferred embodiments

[0035] In Fig. Figure 1 shows a schematic representation of a spark plug 10 known from the prior art, comprising an insulator 11, a spark plug housing 21, a longitudinal axis 12, an opening 13 of the insulator 11, a center electrode 14 with an inner center electrode core 16 and an outer center electrode sheath 24, and at least one ground electrode 15.

[0036] The insulator 11 is arranged in the spark plug housing 21. An opening 13 is provided in the insulator 11 along its longitudinal axis 12. The center electrode 14 is arranged in the substantially cylindrical opening 13 of the insulator 11 such that the center electrode 14 is electrically insulated from the spark plug housing 21 by the insulator 11, while allowing heat conduction from the center electrode 14 to the spark plug housing 21 via the insulator 11. The center electrode 14 has an internal center electrode core 16, the material of which has a higher thermal conductivity than the material of the center electrode sheath 24 that surrounds the center electrode core 16. This ensures good heat conduction along the center electrode 14.

[0037] The ground electrode 15 is arranged at a combustion chamber-side end 18 of the spark plug 10 and is connected to the spark plug housing 21.

[0038] Ignition energy is introduced into the spark plug 10 via one terminal 19. The applied high voltage creates an electric spark at the combustion chamber end 18 of the spark plug 10 between the center electrode 14 and the ground electrode 15, which is suitable to ignite the air-fuel mixture present in the combustion chamber.

[0039] In addition, good heat dissipation from the center electrode 14 to the insulator 11 and from the ground electrode 15 and from the insulator 11 to the spark plug housing 21 is necessary for a long service life of the spark plug 10. The temperatures reached at the center electrode 14 and the ground electrode 15 significantly determine the service life of the spark plug 10. A higher temperature at the center electrode 14 and the ground electrode 15 leads to increased wear on the center electrode 14 and the ground electrode 15 and thus to a reduction in the service life of the spark plug 10.

[0040] The in Fig. Figure 2 shows the combustion chamber-side section 18 of a first embodiment of the invention. Identical elements with respect to Fig. Items 1 are marked with the same reference symbol and are not explained in more detail.

[0041] According to the invention, the opening 13 is formed in the longitudinal direction of the insulator 11 in a substantially cylindrical first insulator section 31 with a first insulator section length 61 and a first substantially constant inner diameter 51, and in an immediately adjoining substantially cylindrical second insulator section 32 with a second insulator section length 62 and a second substantially constant inner diameter 52. The first inner diameter 51 of the opening 13 of the insulator 11 is smaller than the second inner diameter 52 of the opening 13 of the insulator 11.

[0042] The first insulator section 31 transitions directly into the second insulator section 32. The longitudinal extent of the transition 25 from the first insulator section 31 to the second insulator section 32 is significantly smaller than the longitudinal length 62 of the second insulator section 32. The inner diameter of the insulator 11 in the region of the transition 25 is no smaller than the first inner diameter 51 of the first insulator section 31 and no larger than the second inner diameter 52 of the second insulator section 32. The second insulator section 32 extends along the combustion chamber side 18 of the insulator 11 for a length 62 to an end face 20 of the insulator 11.

[0043] Furthermore, a central electrode 14 is arranged in the opening 13 of the insulator 11. The central electrode 14 has a central electrode section 44 with a central electrode section length 64 in the longitudinal direction and a central electrode outer diameter 54 of the central electrode 14, wherein the central electrode section 44 extends at least over the entire length of the first insulator section length 61 of the first insulator section 31 and the second insulator section length 62 of the second insulator section 32.

[0044] The center electrode core 16 is embedded in a center electrode sheath 24. At the level of the transition 25 from the first insulator section 31 to the second insulator section 32, the center electrode core 24 has a cross-sectional area of ​​40% in the present embodiment. The cross-sectional area of ​​the center electrode 14 can be up to 60% at the level of the transition 25 from the first insulator section 31 to the second insulator section 32. At a distance of 5 mm from the end of the center electrode section 44 facing one combustion chamber 23, the center electrode core 24 has a cross-sectional area of ​​20% in the present embodiment. The proportion of the central electrode core 24 to the cross-sectional area of ​​the central electrode 14 can be up to 70% at a distance of 5 mm from the end of the central electrode section 44 facing the combustion chamber 23.The distance between the center electrode core 16 and the end of the center electrode section 44 facing the combustion chamber is at most 2.25 mm.

[0045] The center electrode 14 is joined in the first insulator section 31 of the opening 13 of the insulator 11 by a narrow gap 22 and is at least partially connected via a glass melt 17. The width of this gap 22 is at least 40 µm and at most 120 µm. This connection between the insulator 11 and the center electrode 14 via the glass melt 17 is also used to dissipate heat from the center electrode 14 through the insulator 11 into the spark plug housing 21.

[0046] To reduce the heat absorption of the central electrode 14 from the combustion chamber-side part of the insulator 11, the opening 13 of the insulator 11 in the insulator section 32 is enlarged by an additional bore. This creates a gap in the insulator section 32 between the insulator 11 and the central electrode 14, which has a substantially constant diameter in the central electrode section 44. The width of this gap is at least 100 µm and at most 500 µm. The length of this gap in the longitudinal direction of the central electrode is at least 0.5 mm and at most 10 mm. Fig. Figure 3 shows a schematic representation of the combustion chamber-side section 18 of a second embodiment of the invention, which differs from the first embodiment essentially in that the enlargement of the opening 13 in the insulator section 32 is fully or partially compensated for by an enlarged insulator outer diameter 53. Identical elements with respect to the Fig. 1 and Fig. 2 are marked with the same reference symbol and are not explained in more detail.

[0047] According to the invention, the enlargement of the insulator outer diameter 53 of the insulator 11 in the insulator section 32 is essentially designed in such a way that the enlargement of the opening 13 in the insulator section 13 is compensated.

[0048] The in Fig. Figure 4 shows a schematic representation of the third embodiment of the invention, which shows an extension of the opening 13 of the insulator 11, which is at least partially conical in a third insulator section 33 immediately adjoining the second insulator section and extending to the end face 20 of the insulator 11.

[0049] Equal elements in relation to the Fig. 1, Fig. 2 and Fig. Three are marked with the same reference symbol and are not explained in more detail.

[0050] The at least partially conical widening of the opening 13 results in a gap between insulator 11 and center electrode 14 that changes over a section length 63. This further increases the distance to the center electrode 14 at the particularly hot end of the insulator 11 and achieves a further reduction in temperature at the ignition tip of the center electrode 14.

Claims

[1] Spark plug (10) comprising an insulator (11) arranged in a spark plug housing (21), the insulator having a longitudinal axis (12) and an opening (13) along the longitudinal axis (12), a center electrode (14) arranged in the opening (13) of the insulator (11), and at least one ground electrode (15) provided on the spark plug housing (21), the insulator (11) comprising a first insulator section (31) and a second insulator section (32), the first insulator section (31) extending in the direction of the longitudinal axis (12) over a first insulator section length (61) with a first inner diameter (51), and the second insulator section (32) extending in the direction of the longitudinal axis (12) over a second insulator section length (62) with a second inner diameter (52), the first inner diameter (51) being smaller than the second inner diameter (52),wherein the first insulator section (31) transitions directly into the second insulator section (32) in a transition (25), and wherein the central electrode (14) has a central electrode section (44) with a constant diameter extending in the direction of the longitudinal axis (12) over a central electrode section length (64) with a central electrode outer diameter (54), wherein the central electrode section (44) extends at least over the entire insulator section length of the first insulator section (31) and the second insulator section (32), and wherein the central electrode section (44) in the first insulator section (31) has a radial distance to the insulator (11) of at least 40 µm and at most 120 µm. [2] Spark plug (10) according to claim 1, characterized by , that the central electrode (14) in the first insulator section (31) is connected to the insulator at least partially by a glass melt (17). [3] Spark plug (10) according to at least one of the preceding claims, characterized by , that the central electrode (14) in the second insulator section (32) has a radial distance to the insulator (11) of at least 100 µm and at most 500 µm. [4] Spark plug (10) according to at least one of the preceding claims, characterized by , that the second insulator section length (62) of the second insulator section (32) is at least 0.5 mm and at most 10 mm. [5] Spark plug (10) according to at least one of the preceding claims, characterized by , that the first insulator section (31) is arranged on the side of the second insulator section (32) facing away from a combustion chamber (23). [6] Spark plug (10) according to the preceding claims, characterized by , that the second insulator section (32) has at least in some areas a second outer diameter (53) which is larger than a first outer diameter (55) of the first insulator section (31). [7] Spark plug (10) according to at least one of the preceding claims, characterized by , that the middle electrode section (44) extends beyond the second insulator section (32) on the combustion chamber side (18). [8] Spark plug (10) according to at least one of the preceding claims, characterized by , that the central electrode (14) has at least in certain areas along its longitudinal extent a central electrode core (16) which is surrounded by a central electrode shell (24), wherein the material of the central electrode core (16) has a higher thermal conductivity than the material of the central electrode shell (24) and wherein the central electrode core (16) has a proportion of up to 60% of the cross-sectional area of ​​the central electrode (14) at the level of the transition (25) from the first insulator section (31) to the second insulator section (32). [9] Spark plug (10) according to claim 8, characterized by, that the center electrode core (16) at a distance of 5 mm from the end of the center electrode section (44) facing the combustion chamber (23) has a proportion of up to 70% of the cross-section of the center electrode (14). [10] Spark plug (10) according to claim 8 or 9, characterized by , that the distance between the center electrode core (16) and the end of the center electrode section (44) facing the combustion chamber is at most 2.25 mm. [11] Spark plug (10) according to at least one of the preceding claims, characterized by that the insulator (11) has an end face (20) on the combustion chamber side (18), and that the second insulator section (32) extends to the end face (20) of the insulator (11). [12] Spark plug (10) according to at least one of claims 1 to 10, characterized by, that the second insulator section (32) transitions into a third insulator section (33) on the combustion chamber side (18), wherein the opening (13) of the insulator (11) in the third insulator section (33) is at least partially conical, and that the third insulator section (33) extends in the direction of the longitudinal axis (12) over a third insulator section length (63). [13] Spark plug (10) according to claim 12, characterized by , that the center electrode section (44) of the center electrode (14) extends at least over the entire first insulator section length (61) of the first insulator section (31) and the entire second insulator section length (62) of the second insulator section (32) and the entire third insulator section length (63) of the third insulator section (33). [14] Spark plug (10) according to claim 12 or 13, characterized by , that the middle electrode section (44) extends beyond the third insulator section (33) on the combustion chamber side (18). [15] Spark plug (10) according to claim 12 or 14, characterized by that the third insulator section (33) extends to the front face of the insulator (11). [16] Spark plug (10) according to at least one of claims 12 to 14, characterized by , that the wall thickness of the third insulator section (33) is largely constant, wherein the wall thickness is the radial wall thickness of the third insulator section in a plane perpendicular to the longitudinal axis (12) of the spark plug (10).

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