Title of Invention

A SPARK PLUG

Abstract

The present invention relates to a spark plug (1) which has at least one ground electrode (15) having a reduced temperature level is proposed- The spark plug (1) comprises a tubular, metallic housing; (5) which, on the coinbustion-chaiTiber side, has an outer edge (10) on which at least one ground electrode (15) is arranged. The cross-sectional surface (20, 25; 30, 35, 40, 41, 45, 46) of the at least one ground electrode (15) increases toward the outer edge (10) of the housing (5).

Full Text

Spark plug Prior art The invention is based on a spark plug according to the generic type of the main claim. DE 196 23 989 has already disclosed a spark-plug having a tubular, metallic housing which, on the combustion-chainber side, has an outer edge to which preferably four ground electrodes are fastened. Advantages of the invention In contrast, the spark plug according to the invention having the features of the main claim has the advantage that the cross-sectional surface of the at least one ground electrode increases toward the outer edge of the housing. This, enables the temperature level of the at least one ground electrode to be reduced. As a result, the at least one ground electrode is subject to a smaller amount o£ wear, for example due to corrosion. In addition; spontaneous ignitions or a preliminary ignition are prevented. The measures listed in the subclaims make advantageous developments and improvements of the spark plug specified in the main claim possible. It is particularly advantageous that the ground electrode comprises at .least one core which has better thermal conductivity than a casing of the ground electrode, which casing surrounds the core. This enables the temperature level of the ground electrode to be additionally reduced and therefore enables the temperature resistance of the ground electrode to be further increased. It is also particularly ■ advantageous if the ground electrode has a round cross-sectional surface. in this ' case, the ratio between the surface and the cross-sectional surface of the ground electrode is optimum as regards the lowest possible temperature level and therefore the greatest possible temperature resistance of the ground electrode. A particularly simple realization of the ground electrode can be brought about by the ground electrode comprising a first part having an essentially constant cross-sectional surface and a second part having a cross-sectional surface increasing to the outer edge of the housing. The temperature level of the ground electrode can be further reduced if both the first part and the second part of the ground electrode comprises [sic] a cross-sectional surface increasing in each case toward the outer edge of the housing- ■ It is particularly advantageous if the second part is arranged on the outer edge of the housing and comprises an opening through which the first part is guided, preferably as far as the outer edge of the housing. This enables the heat flow from the ground electrode to be brought with less heat resistance into the colder housing of the spark plug. It is also advantageous that the second part is of trapezoidal design and, in the region of the outer edge of the housing, takes on the radius of the housing. This enables the second part of the ground electrode to be connected in a form-fitting manner to the outer edge of the housing or, from the manufacturing point of view, to be punched or machined in a particularly simple manner from a step of the housing on the combustion-chamber side. Effort can also be saved in terms of the manufacturing by the ground electrode being manufactured with the two parts as a single component, preferably by punching it out or extruding it. The manufacturing is also less complex if the first part and the second part consist of the same material- Drawing Exemplary embodiments of the invention are illustrated in the drawing and are explained in greater detail in the description which follows. In the drawing Figure 1 shows a first exemplary embodiment of the spark plug according to the invention in a front view, Figure 2 shows the first embodiment of the spark plug according to the invention in a side view. Figure 3 shows the first embodiment of the spark plug according to the invention in a plan view. Figure 4 shows a side view of a ground electrode of the spark plug of the first embodiment. Figure 5a) shows a first cross section of the ground electrode of the first embodiment of the spark plug according to the invention, Figure 5b) shows a second cross section of the ground electrode of the first embodiment of the spark plug according to the invention, Figure 5c) shows a third cross section of the ground electrode of the first embodiment of the spark plug according to the invention. Figure 6 shows a second embodiment of a spark plug according to the invention in a front view, Figure 7 shows a side view of the spark plug according to the invention according to the second embodiment. Figure 8 shows a ground electrode of the spark plug according to the invention. Figure 9a) shows a first cross section of the ground electrode of the spark plug according to the invention according to the second embodiment. Figure 9b) shows a second cross section of the ground electrode of the spark plug according to the invention according to the second embodiment, and Figure 9c) shows a third cross section of the ground electrode of the spark plug according to the invention according to the second embodiment. Description of the exemplary embodiments In figure 1, 1 identifies a spark plug. The spark plug 1 comprises a tubular, metallic housing 5 which, on the combustion-chamber side, has an outer edge 10. An insulator 90, from which a central electrode 95 protrudes on the combustion-chamber side, is embedded in the housing 5. The central electrode 95, the insulator 90 and the tubular, metallic housing 5 lie coaxially with one another. The insulator 90 of the central electrode 95 protrudes out of the housing 5 on the combustion-chamber side. In the side view according to figure 2, it can be seen that a ground electrode 15 is fastened to the outer edge 10 of the housing 5. Said ground electrode 15 initially runs parallel to the longitudinal axis 100 of the spark plug 1. The ground electrode 15 is then bent away toward the central electrode 95 and is guided over the end surface 105 of the central electrode 95. The ground electrode 15 is therefore designed in this example as a roof-type electrode. According to the first exemplary embodiment, the spark plug 1 coinprises just one ground electrode. However, the spark plug according to the invention may also comprise a plurality of ground electrodes. Ground electrodes reach high temperatures as a function of the operating state. High temperatures lead to increasing wear of the ground electrodes due to corrosion and may lead to spontaneous ignitions or to preliminary ignition. New engine concepts increasingly require long spark positions wtiich have been brought forward into the combustion chainber and therefore also require relatively great ground-electrode lengths. The temperature loading of the ground electrodes therefore increases. The invention has now made provision for the cross-sectional surface of the at least one ground electrode 15 to increase toward the outer edge 10 of the housing 5, as can be seen in the front view of figure 1. According to figure 1. the ground electrode 15 is of trapezoidal design toward the outer edge 10. This trapezoidal shape results in a region 50 of continuous cross-sectional change for the ground electrode 15, In addition, the cross-sectional change can also be of step-shaped design in a predetermined region 55 of the ground electrode 15, as can be gathered in the form of dashed lines in figure 4. In general, the cross-sectional change of the ground • electrode 15 can either be of just continuous design, as illustrated in figure 1, or just of step-shaped design or of both continuous and step-shaped design, as illustrated, for example, in figure 4. In the plan view according to figure 3,. the width 65 of the ground electrode 15 in the region of the outer edge 10 is illustrated. Furthermore, figure 3 illustrates the width 60 of the outer edge 10 of the housing 5. According to figure 3, the enlargement in the cross-sectional surface of the ground electrode 15 toward the outer edge 10 is made in such a manner that the width 65 of the ground electrode 15 in the region of the outer edge 10 does not protrude beyond the width 60 of the outer edge 10. Rather, the enlargement in the cross-sectional surface of the ground electrode 15 leads to the ground electrode 15, in the region in which it is fastened to the outer edge 10, taking on the radius 85 of the outer edge 10 of the tubular housing 5 and therefore expanding along the circumference -of the outer edge 10. As a rule, the ground electrode 15 is fastened to the outer' edge 10 by a welding connection. According to figure 3, in the region of the outer edge 10, the ground electrode 15 has been expanded by approximately one eighth of the circumference of the outer edge 10 in the direction of the annular, outer edge 10, the outer edge 10, of course, also lying coaxially with the longitudinal axis 100 of the spark plug 1. The smaller the surface of the ground electrode 15, the less heat is absorbed by the ground electrode 15. The larger the cross-sectional surface of the ground electrode 15, the better it conducts away the heat which has been absorbed by the ground electrode 15, with the enlargement of the cross-sectional surface of the ground electrode 15 expediently taking place in the direction to the outer edge 10, so that the heat which has been absorbed can be passed to the relatively cold housing 5 of the spark plug 1 in a manner which is as resistanceless as possible. A particularly favorable ratio between the surface of the ground electrode 15 and the cross-sectional surface of the ground electrode 15 is obtained if the ground electrode 15 has a round cross-sectional surface. A surface area which is as small as possible is thereby obtained for the ground electrode without changing the area of the cross^sectional surface of the ground electrode 15, As has already been described, the width 65 of the ground electrode 15 is restricted in the region of the outer edge 10 to the width 60 of the outer edge 10. If the ground electrode 15 nevertheless has a greater width than the width 60 of the outer edge 10, then the ground electrode 15 can be tapered in the region in which it is fastened to the outer edge 10, in the event of a welding connection in the region of the welding root, by plastic deformation, for example by pressing, to the required width 60 of the outer edge 10. In addition or as an alternative, the width 60 of the outer edge 10 may also be enlarged as far as, at maximiizn/ the inner sealing seat diameter 110 of the housing 5, as can be gathered from the extension of the width 60 of the outer edge 10 illustrated by dashed lines in figure 3. The dashed-line extension bears the reference number 115. In this case, the sealing seat diameter 110 marks the smallest diameter of the tubular, metallic housing 5 of the spark plug 1 r which diameter occurs at the point within the housing 5 at which the insulator 90 rests on an annular projection of the housing 5, Thus, should it be necessary to adapt the width of the ground electrode 15 to the width of the outer edge 10, then this can be undertaken either by a reduction in the width of the ground electrode 15 or by an enlargement in the width of the outer edge 10 or both by a reduction in the width of the ground electrode 15 and by an enlargement in the width of the outer edge 10 in the region in which the ground electrode 15 is connected to the outer edge 10. If the cross-sectional surface of the ground electrode 15 is of round design, as described above, then it can be provided with a planar surface in the region of the spark gap formed between the central electrode 95 and the ground electrode 15, in order to make available the largest possible burning-off surface. In this case, the planar surface can be impressed on the ground electrode 15 on its region facing the end surface 105 of the central electrode 95. This region is identified in figure 2 by the reference number 120. As a further measure for reducing the temperature level of the ground electrode 15, provision may be made for the ground electrode 15 to comprise at least otio^ core 12 5 which is enclosed by a casing 130 of the ground electrode 15 and has better thermal conductivity than the casing 130, A ground electrode of this type is illustrated in figure 8. In this case, the core 125 may, for exair^le, be formed from copper whereas the casing 130 may, for example, consist of a nickel alloy. The ground electrode 15 is thereby designed as a two-component ground electrode. The core 125 can be inserted here into the casing 130 by means of extrusion, for example. A structurally particularly simple solution for producing the ground electrode 15 comprises manufacturing the ground electrode from two parts 70, 75. According to figures 1, 2, 3 and 4, a first part is identified by the reference number 7 0 and a second part by the reference ni^imber 75. It can be gathered in particular from figures 1 and 4 that the first part 70 comprises an essentially constant cross-sectional surface. In contrast, the second part 75 comprises a cross-sectional surface increasing toward the outer • edge 10 of the housing 5 - As an alternative, provision may be made for both the first part 70 and the second part 75 to comprise in each case a cross-sectional surface increasing toward the outer edge 10 of the housing 5- This can be gathered from figures 5a) and 5b) . In figure 5a) , a first cross-sectional surface of the first part 7 0 is illustrated by hatching and identified by the reference number 20 and is of approximately rectangular design. The first cross-sectional surface 20 is at the furthest distance from the outer edge 10. It is significantly smaller than a third cross-sectional surface 30 of the second part 75 in the region in which the ground electrode 15 is connected to the outer edge 10. According to figure 5b), a second cross-sectional Surface 25 of the first part 70 is illustrated by hatching and is of approximately rectangular design, the second cross-sectional surface 25 lying closer to the outer edge 10 than the first cross-sectional surface 20, and also being of larger design than the first cross-sectional surface 20, However, the second cross-sectional surface 25 is still of smaller design than the third cross-sectional surface 30. Finally, figure 5c) shows a cross section of the ground electrode 15 in the region of the third cross-sectional surface 30, i.e. in the region in which the ground electrode 15 is connected to the outer edge 10. The third cross-sectional surface 3 0 can be adapted here to the annular shape of the outer edge 10, as can be seen in figure 3 and figure 5c) . Figures 5a) , 5b) and 5c) therefore show an example with a first part 70 and a second part 7 5 which differ from each other in the shape of their cross-sectional surface. However, provision may also be made for the cross-sectional surfaces of the first part 70 and of the second part 75 to have the same shape. In particular, the first part 7 0 and also the second part 75 can take on a cross section in the form of an annular section having the radius of the outer edge 10. .For the first part 70 and the sQcoxid part 75, any desired shapes can be used for the cross-sectional surfaces, both when the same shape is used for the cross-sectional surfaces of the two parts 70, 7 5 and when different cross-sectional surface shapes are used for the two parts 70, 75. In the latter case, any desired combinations of polygonal, round or elliptical cross-sectiional surfaces can then be provided for the two parts 70, 75, Figures 5a) and 5b) show, as described, a first part 70 which tapers in its cross-sectional surface with increasing distance from the outer edge 10. According to figure 4, the second part 75 has a cross-sectional surface which tapers with increasing distance from the outer edge 10, As an i alternative to this, the second i part 75 can also have; a cross-sectional surface which is constant over its length, but is to be larger than i I the maximum cross-sectional surface of the first part 70 so as to ensure the best possible elimination' of heat from the ground electrode 15 toward the housing 5. In general, a first part 7 0 > having a cross-sectional surface which is constant over its length can be combined with a second part 7 5 having a cross-sectional surface which is constant .over its length or is enlarged toward the outer edge 10. Correspondingly, a first part 7 0 having a cross-sectional surface which is enlarged over its length in the direction of the outer edge 10 can be combined with a second part 7 5 having a cross-sectional surface which is constant over its length or a cross-sectional surface which is enlarged in the direction of the outer edge 10- The tapering of the cross-sectional surface at increasing distance from the Outer edge 10 can take place in a stepped shape, in a conical shape, in a trapezoidal shape or in any other desired shape both for the first part 70 and for the second part 75, The described manners of tapering of the cross-sectional surface at increasing distance from the Outer edge 10 can also be combined with one another in any desired manner for the two parts 70, 75- As illustrated in figures 1, 2, 3 and 4, the second part 75 is arranged between the first part 70 and the outer edge 10 of the housing 5. In the case of the exemplary embodiment described, the first part 70 comprises a cross-sectional surface which is constant over its length, whereas the second part 7 5 comprises a cross-sectional surface which, tapers trapezoidally over its length at increasing distance from the outer edge 10 and, according to the illustration with dashed lines in figure 4, can additionally' also comprise the stepped region 55 for reducing the cross-sectional surface at increasing distance from the outer edge 10, In this case, the second part 75 can be fastened on the outer edge 10 of the housing 5, for example by welding. The first part 70 can then be welded onto the second part i 75.. According to figure 3, in; the region in which it is fastened to the outer edge 10', the second part 75 takes on the radius 85 of the outer edge 10 and, in the region in which it is fastened to the outer edge 10, is expanded approximately to an eighth of the circumference of the outer €:dge 10 and is adapted in its basic area to the annular, outer edge 10. As an alternative to welding the first part 7 0 onto the second part 75, the second part 75 according to figures 6, 7 and 8, in which the same reference numbers identify the same elements as in the previous figures, can be provided parallel to the longitudinal axis 100 with an opening 80, through which the first part 70 is guided and at maximum reaches as far as the outer edge 10. The first part 70 and' the second part 75 are connected to each other in a .frictional or form-fitting manner, for example by welding, and are fastened on the outer edge 10 of the housing 5, for example by welding. The heat flow can thus be brought from the first part 70 into the colder housing 5 of the spark plug 1 with little heat resistance, especially if the first part 70 reaches as far as the outer edge 10, Otherwise, the arrangement of figures 6 and 7 corresponds to the arrangements shown in figures 1 and 2. Figures 6 and 7 describe a second exemplary embodiment, which is characterized by the first part 70 which is inserted into the opening 80 in the. second part 75. In this case, the second part 75 can be tapered, for example again over its length, trapezoidally in its cross-sectional surface at increasing distance from the outer edge 10 whereas the first part 70 can remain constant in its cross-sectional surface over its length, as illustrated in figure 6. in this case too, in the region in which it is fastened to the outer edge 10 of the housing 5, the second part 75 can take on the radius 85 of the housing 5 according to figure 3 and can be expanded there approximately up to an eighth of I I the .circumference of the outer edge 10 and adapted to the annular shape of the outer edffe 10- According to figure 8, the use of the core 125 having better thermal conductivity' in comparison with the casing 130 is illustrated, i In this case, the core according to figure B can extend over the entire length of the second part 7 5 and can continue over part of the length of the first part 70. According to figure 8, again an example is shown, in; which the cross-sectional surface of the first part 7 0, does not change over its length/ whereas the cross-sectional surface of the second part 75 tapers trapezoidally at increasing distance from the outer edge 10 and therefore toward the first part 70, Taking this as a basis, figures 9a) and 9b) show an example, in which the cross^sectional surface of the first part 7 0 also tapers at increasing distance from the outer edge 10. According to figure 9a) , a fourth cross-sectional surface of the first part 70 is illustrated by hatching and is identified by the reference number 35. This fourth cross-sectional surface 3 5 is of approximately rectangular design and is removed so far from the outer edge 10 of the housing 5 that it only intersects the surrounding casing 130, The reference number 30 again^ as also in figure 5a) , illustrates the third cross-sectional surface 30 of the second part 75 in the region- in which the second part 7 5 is fastened to the outer edge 10, The third cross-sectional surface 30 is; significantly larger than the fourth cross-sectional surface 35. According to figure 9b) , ; a fifth cross-sectional surface of the first part 70 is illustrated, which surface lies closer to the , outer edge 10 than the fourth cross-sectional surface 3 5 and intersects both the surrounding casing 13 0 and also the core 125 • It therefore comprises a first part 40 of the surrounding casing 130 and a second part 41 of the core 125. The fifth cross-sectional surface together with the first part 40 and the second part |41 is overall larger than the fourth cross-sectional siirface 35, since the first part 70 in the case of this } embodiment is enlarged in its cross-sectional surface toward the outer edge 10. Figure 9b) also again shows the third cross-sectional surface 3 0 which is still larger than the fifth cross-sectional surface. Fig:ure 9c) shows the third cross-sectional surface 30, j which is composed of a first part 45 of the surrounding casing 13 0 and of a I second part 46 of the core 125- Pure silver or pure nickel can be used as material for i the second part 75. As an alternative, alloys having aluminum, siIver, copper, magnesium and nickel as the main constituents can be used)for the second part 75. The first part 7 0 and the' second part 7 5 can be manufactured from the same material. In this case, the ground electrode 15 can be .'manufactured as a single component together with the! two parts 70, 75. The manufacturing can take place, for example, by punching it out or by extruding it. i Provision may also be made for the second part 7 5 not to be welded onto the outer jedge 10 of the housing 5. In this case, the housing 5 can initially be manufactured on the combustion-chamber side beyond the outer edge 10 with a step j which is sliced off by cutting down to a web of, for example, approximately one eighth of the circumference of the outer edge 10 or is brought into one of the previously described shapes by punching. The web of the j housing 5, which is thus formed in the combustion chairiber in a manner such that it protrudes over the outer' edge 10, then forms the second part 7 5, onto which the first part 70 is welded as an actual ground electrode. Owing to the length of the ground electrode/ which is thereby shortened, this produces a reduction i:m the ground-electrode temperature. In this case, the second part 7 5 is formed i as a single component together with the housing 5. The spark plug 1 can have a plurality of ground electrodes which can each be idesigned according to one I of the described exemplar;:^ embodiments, it being possible for a plurality of ground electrodes of identical design and/or a plurality of ground electrodes of different design to be provided- Only one of these ground electrodes can be designed here as a roof-type electrode, as illustrated in figures 2 and 7. claims 1. A spark plug (1) having a tubular, metallic housing (5) which, on the combustion^chamber side, has an outer edge (10) on which at least one ground electrode (15) is arranged, wherein the cross-sectional surface (20, 25, 30, 35, 40, 41, 45, 45) of the at least one ground electrode 1(15) increases toward the outer edge (10) of the housing (5) . 2. The spark plug (1) as claimed in claim 1, wherein the ground electrode (15) comprises a region (50) of continuous cross-sectional change. 3. The spark plug (1) as claimed in claim 1 or 2, wherein the spark plug (1) comprises a region (55) with a step-shaped cross-sectional!change. i 4. The spark plug (1) as claimed in claim 1, 2 or 3, wherein the ground electrode (15) comprises a core (12 5) which has better tht^rmal conductivity than a casing (130) of the ground electrode (15), which casing surrounds the core (12 5). 5 - The spark plug (1) as claimed in one of the preceding claims, wherein tike cross-sectional ■ surface (20, 25, 30, 35, 40, 41, 45, 46) of the ground electrode (15) is reduced m its width (65) in the region of attachment to the outer edge (10} of the housing (5) to the width (60) of the outer edge (10). 6. The spark plug (1) as claimed in one of the preceding claims, wherein the width (60) of the outer edge (10) of the housing (5) is enlarged to the width (65) of the cross section of the ground electrode (15) in the region of attachment of the ground electrode (15) to the outer edge (10) ojf the housing (5) , 7. The spark plug (1) as claimed in one of the preceding claiins, wherein the ground' electrode (15) has a round cross-sectional surface (20, 25, 30, 35, 40, 41, 45, 46) . I 8 - The spark plug (1) as claimed in one of the preceding claims, wherein the ground electrode (15) comprises a first part (70) having an essentially constant cross-sectional surface (20, 25, 35, 40, 41) and a second part (7 5) having a cross-sectional surface (30, 45, 46) increasing to the outer edge (10) of the housing (5), 9- The spark plug (1) as claimed in one of claims 1 to 7, wherein the ground electrode (15) comprises a first part (70) and a second part (75) having a cross-sectional surface (20, 25, 30, 35, 40, 41, 45, 46) increasing in each case to the outer edge (10) of the housing (5). 10. The spark plug (1) as claimed in claim 8 or 9, wherein the second part (75)' is arranged between the first part (70) and the outer edge (10) of the housing (5) . 11. The spark plug (1) as claimed in claim 8 or 9; wherein the second part (75) is arranged on the outer edge (10) of the housing (5)i and comprises an opening (80) through which the first part (70) is guided; preferably as far as the outer edge (10) of the housing (5), I 12- The spark plug (1) as claimed in one of claims 8 to 11, wherein the second part (75) is of trapezoidal design and, in the region of the outer edge (10) of the housing (5), takes on the radius (85) of the housing (5). ) 13. The spark plug (1) as claimed in one of claims 8 to 12, wherein the second part (75) is formed just from -Ag or from Ni- 14- The spark plug (1) as claimed in one of claims 8 to 12, wherein the second pairt (75) is formed from an alloy with Al, Ag, Cu, Mg, Ni being the main constituents. ' 15. The spark plug (1) as cilaimed in one of claims 8 to 14, wherein the first part (7 0) and the second part (75) are manufactured from the same material, 16. The spark plug (1) as cjlaimed in one of claims 8 to 15, wherein the ground electrode (15) is manufactured with the two parts (70, 75) as a single component, preferably by punching it out or extruding it- 1 ) 17. The spark plug (1) as claimed in one of claims 8 to 15, wherein the second part (75) is formed as' a single component with the housing (5). 18. The spark plug (1) as claimed in one of claims 8 to 17, wherein the cross-sectional surfaces (2 0, 25, 30, 35, 40, 41, 45, 46) of the first part (70) and of the second part (75) differ in their shape, 19 - The spark plug (1) as claimed in one of claims 8 to 17, wherein the cross-sectional surfaces (2 0, 25, 30, 35, 40, 41, 45, 46) of the first part (70) and of the second part (7 5) have thej same shape^ 20. A spark plug substantially as herein described with reference to the accompanying drawings.

Documents:

0264-chenp-2003 abstract duplicate.pdf

0264-chenp-2003 claims duplicate.pdf

0264-chenp-2003 descripition completed duplicate.pdf

0264-chenp-2003 drawings duplicate.pdf

264-chenp-2003-abstract.pdf

264-chenp-2003-claims.pdf

264-chenp-2003-correspondnece-others.pdf

264-chenp-2003-correspondnece-po.pdf

264-chenp-2003-description(complete).pdf

264-chenp-2003-drawings.pdf

264-chenp-2003-form 1.pdf

264-chenp-2003-form 3.pdf

264-chenp-2003-other documents.pdf

264-chenp-2003-pct.pdf