Spark plug including rounded insulator base section

Abstract

A spark plug including a housing, an insulator, a center electrode, and a ground electrode situated at a combustion chamber-side end of the housing. The insulator has an insulator collar, an insulator base, and a transition area, which rests on a projection of the housing. A breathing space is configured at the combustion chamber-side end of the spark plug and is delimited by a section of the inner side of the housing and a section of the insulator base. The section of the insulator base has a rounding including a first leg length and a second leg length angled with respect to the first leg length, the first leg length extending between the intersecting point of the leg lengths with one another and a first end point of the rounding, and the second leg length extending between the intersecting point and a second end point of the rounding.

Claims

1. A spark plug, comprising: a housing, the housing having a longitudinal axis which extends from a combustion chamber-side end of the housing to an end of the housing which faces away from a combustion chamber, the housing having a borehole along the longitudinal axis of the housing as a result of which the housing has an inner side, the housing on the inner side including a projection; an insulator partially situated in the borehole of the housing, the insulator having a longitudinal axis which extends from the combustion chamber-side end of the insulator to an end of the insulator which faces away from the combustion chamber, and the insulator including an insulator collar which is radially surrounded by the housing, an insulator base which is the combustion chamber-side end of the insulator and has a smaller diameter than the insulator collar, and a transition area which connects the insulator collar and the insulator base to one another and rests on the projection of the housing; a center electrode situated in the insulator; a ground electrode situated at the combustion chamber-side end of the housing, the ground electrode and the center electrode being situated in such a way that, together, the ground electrode and the center electrode form an ignition gap; and a breathing space which is configured at a combustion chamber-side end of the spark plug, the breathing space being delimited by a section of the housing and a section of the insulator base and having an opening to the combustion chamber, wherein the section of the insulator base which delimits the breathing space includes a rounding, the rounding, as viewed in cross-section, having a first leg length and a second leg length angled with respect to the first leg length, the first leg length being greater than the second leg length, the first leg length extending between an intersecting point of the first and second leg lengths with one another and a first end point of the rounding, and the second leg length extending between the intersecting point of the leg first and second lengths with one another and a second end point of the rounding.

2. The spark plug as recited in claim 1, wherein the first leg length is at least 1.5 times the second leg length.

3. The spark plug as recited in claim 1, wherein the first leg length is at least 2 times the second leg length.

4. The spark plug as recited in claim 1, wherein the first leg length is 5 times the second leg length.

5. The spark plug as recited in claim 1, wherein the first leg length is no more than 10 times the second leg length.

6. The spark plug as recited in claim 1, wherein the first leg length is no more than 7 times the second leg length.

7. The spark plug as recited in claim 1, wherein the first leg length extends in parallel to the longitudinal axis of the insulator, and the second leg length extends perpendicularly to the longitudinal axis of the insulator.

8. The spark plug as recited in claim 1, wherein the rounding is described by the first leg length L1 and the second leg length L2 and two angles α.sub.1 and α.sub.2, the angle α1 spanning between a tangent of the rounding in the second end point of the rounding and a first parallel, passing through the second end point of the rounding, to the longitudinal axis of the insulator, and the angle α.sub.2 spanning between a tangent of the rounding in the first end point of the rounding and a second parallel, passing through the first end point of the rounding, to the longitudinal axis of the insulator, the angle α1 having a value of greater than or equal to 0° and smaller than or equal to arctan (L2/L1) and/or the angle α.sub.2 having a value of greater than or equal to arctan (L2/L1) and smaller than or equal to 90°, and the second end point of the rounding being closer to the combustion chamber-side end of the spark plug than the first end point of the rounding.

9. The spark plug as recited in claim 1, wherein the rounding is a concave rounding at the insulator base.

10. The spark plug as recited in claim 1, wherein the rounding extends across an entire section of the insulator base which delimits the breathing space.

11. The spark plug as recited in claim 1, wherein a layer is at least partially applied to the section of the insulator base which delimits the breathing space, which is configured to trigger an ignition at the spark plug during irregular combustions in the combustion chamber.

12. A prechamber spark plug, comprising: a housing, the housing having a longitudinal axis which extends from a combustion chamber-side end to an end of the housing which faces away from a combustion chamber, and the housing having a borehole along the longitudinal axis of the housing as a result of which the housing has an inner side, the housing on the inner side including a projection; an insulator partially situated in the borehole of the housing, the insulator having a longitudinal axis which extends from the combustion chamber-side end to an end of the insulator which faces away from the combustion chamber, and the insulator including an insulator collar, which is radially surrounded by the housing, an insulator base, which is the combustion chamber-side end of the insulator and has a smaller diameter than the insulator collar, and a transition area, which connects the insulator collar and the insulator base to one another and rests on the projection of the housing; a center electrode situated in the insulator; a cap which is situated at the combustion chamber-side end of the housing and forms a prechamber; a ground electrode situated at the housing or at the cap, the ground electrode and the center electrode being situated in such a way that, together, the ground electrode and the center electrode form an ignition gap; and a breathing space, which is configured at a combustion chamber-side end of the spark plug, the breathing space being delimited by a section of the housing and a section of the insulator base and having an opening to the combustion chamber enclosed by the cap, wherein the section of the insulator base delimiting the breathing space includes a rounding, the rounding, as viewed in cross-section, having a first leg length and a second leg length angled with respect to the first leg length, the first leg length being greater than the second leg length, the first leg length extending between an intersecting point of the first and second leg lengths with one another and a first end point of the rounding, and a second leg length extending between the intersecting point of the first and second leg lengths with one another and a second end point of the rounding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the present invention are described in detail hereafter with reference to the figures.

(2) FIG. 1 shows a generally conventional spark plug.

(3) FIG. 2 shows a section of the insulator including a rounding according to an example embodiment of the present invention at the insulator base.

(4) FIGS. 3a and 3b show schematic representations of the breathing space for two exemplary embodiments of the present invention.

(5) FIGS. 4a-4i show a plurality of embodiments of the rounding according to an example embodiment of the present invention at the insulator base.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(6) FIG. 1 shows a generally conventional spark plug 1 in a semi-sectional view. This overview figure is used to introduce the different components and sections of the spark plug and to delimit them from one another. The exemplary embodiments for an insulator base including a rounding according to the present invention shown in FIGS. 2 through 4 may be employed in a spark plug according to FIG. 1.

(7) Spark plug 1 includes a housing 2. An insulator 3 is inserted into housing 2. Housing 2 and insulator 3 each have a borehole and each have a longitudinal axis, which coincide with center axis 8 of the spark plug. A center electrode 4 is inserted into insulator 3. Furthermore, a connecting bolt 5 is inserted into insulator 3. A resistance element 6 is situated in insulator 3 between center electrode 4 and connecting bolt 5. Resistance element 6 connects center electrode 4 to connecting bolt 5 in an electrically conducting manner. A ground electrode 7 is connected to housing 2 in an electrically conducting manner on the side facing the combustion chamber. The corresponding ignition spark is generated between ground electrode 7 and center electrode 4. Spark plug 1 extends around center axis 8.

(8) Housing 2 includes a shank 9. A polygon 10, a shrink stitch 11, and a thread 12 are configured at this shaft 9. Thread 12 is used to screw spark plug 1 into an internal combustion engine.

(9) Connecting bolt 5 includes a bolt shank 14, which extends along center axis 8, and a collar 13. Connecting bolt 5 rests with collar 13 on insulator 3.

(10) Insulator 3 includes an insulator head 31, an insulator collar 32, and an insulator base 34. Insulator head 31 is the end of insulator 3 which faces away from the combustion chamber and protrudes from housing 2 on the side of spark plug 1 which faces away from the combustion chamber. Insulator base 34 is the end of insulator 3 which faces the combustion chamber. Insulator collar 32 is situated between insulator head 31 and insulator base 34. Insulator collar 32 is radially surrounded by housing 2. There is a transition area 33 between insulator collar 32 and insulator base 34, with which insulator 3 rests on projection 22 of housing 2. Transitions 33a, 33b from insulator collar 32 to transition area 33 as well as from transition area 33 to insulator base 34 are identified in FIG. 1.

(11) Insulator base 34 extends from base fillet 33b, which is the transition from transition area 33 to insulator base 34 and is typically configured as a rounding, to insulator base tip, which is the combustion chamber-side end of insulator base 34. Insulator base 34 of spark plug 1 in FIG. 1 has a conical shape and may be divided into two sections 341, 348. First section 341 of insulator base 34 directly abuts root fillet 33b. First section 341 of insulator base 34 is radially surrounded by a protrusion 23 situated on the inner side of housing 2. Protrusion 23 is delimited on the side facing away from the combustion chamber by projection 22, on which insulator 3 rests, and on its side facing the combustion chamber by a section 22b in which the housing inside diameter increases again. Protrusion 23 itself has an essentially constant inside diameter. Together with this protrusion 23, first section 341 forms a narrow gap 51, a so-called bottle neck. This narrow gap 51 has a considerably smaller width, and thus a considerably smaller volume, than breathing space 50 and, within the scope of the present application, does not belong to breathing space 50. Breathing space 50 extends from the combustion chamber-side end of gap 51 to the combustion chamber-side end face of housing 2. Breathing space 50 is furthermore delimited by a section 24 of the housing and a second section 348 of insulator base 34.

(12) As an alternative, housing 2 may also only include projection 22 on which insulator 2 rests, and may have a constant or conically increasing inside diameter in the direction of the combustion chamber. In this case, there is no narrow gap 51, and breathing space 50 begins directly at the end of base fillet 33b which faces the combustion chamber.

(13) Not shown in FIG. 1 is an inner seal, which may, for example, be situated between projection 22 of housing 2 and transition area 33 of insulator 3, and thus seals the space between housing 2 and insulator 3.

(14) FIG. 2 shows a schematic representation of insulator base 34. This representation is used to illustrate the different sections of insulator base 34 as well as the representation of leg lengths L1, L2 as well as angles α.sub.1, α.sub.2. In this example, insulator base 34 may be divided into two sections 341, 348. First section 341 has a cylindrical shape and could, for example, delimit narrow gap 51 beneath base fillet 33b. Second section 348 has two segments 342, 343. First segment 342 includes rounding 345 according to the present invention. Second segment 343 has a conical shape and a smaller outside diameter than first section 341.

(15) Rounding 345 has its first end point 346 at the transition point to first section 341 of insulator base 34. The transition point is shown as a corner in this figure. Rounding 345 has its second end point 347 at the transition point to second segment 343. This transition point arises from angle α.sub.1 to a parallel of longitudinal axis 8 of insulator 3 which extends through second end point 347 becoming minimal, and remaining or being minimal or changing the sign. In the example shown here, α.sub.1=0 and remains at 0 since second segment 343 has a cylindrical shape. Leg lengths L1, L2 extend in parallel or perpendicularly to longitudinal axis 8 of insulator 3. In the process, a leg length is always measured between the intersecting point of the legs with one another and first and second end point 346, 347 of rounding 345.

(16) For example, first leg length L1 may be greater than or equal to 3 mm and smaller than or equal to 20 mm. Second leg length L2 then, for example, has a value of equal to or greater than 0.6 mm and smaller than or equal to 3 mm.

(17) FIGS. 3a and 3b show two examples in which section 24 of housing 2 which delimits breathing space 50 and section 348 of insulator base 34 which delimits breathing space 50, and thus also the resulting breathing space 50, are shown. Indicated are projection 23 on the inner side of housing 2 as well as first section 341 of insulator base 34, which together with projection 23 forms narrow gap 51. In the direction of the combustion chamber, breathing space 50 abuts narrow gap 51, which is delimited by a second section 348 of insulator base 34 and a housing section 24. By way of example, it is apparent that in the case of housing 2 and in the case of insulator 3 edges and corners are designed to be angular, conical or with roundings.

(18) In FIGS. 3a and 3b, the second section of insulator base 34 always has a second segment 343, which includes a convex rounding. Rounding 345 according to the present invention has a concave shape. Second end point 347 of rounding 345 according to the present invention arises at the point when angle α1 becomes minimal. In FIG. 3a, thus α1=0°, L1 is 4.2 mm, and L2 is 1.2 mm. A ratio of L1/L2 of 3.5 results for the exemplary embodiment according to FIG. 3a.

(19) In FIG. 3b, al becomes minimal and is dissimilar to 0°. For example, L1=2 mm and L2=1 mm may apply, thereby resulting in a ratio of L1 to L2 of 2. In second segment 343, angle α1 increases again for a tangent along the surface of second segment 343. In other words, the radius of curvature of rounding 345 of first segment 342 has a different sign than the radius of curvature of the rounding of second segment 343. The point at which the radius of curvature changes its sign is second end point 347 of rounding 345 according to the present invention. Rounding 345 according to the present invention does not have to end in a straight line.

(20) FIGS. 4a-4i show a number of different embodiments of insulator base 34, the enumeration not being exhaustive. In all example embodiments here, insulator base 34 has a first section 341, which is designed with rounding 345 according to the present invention between base fillet 33b and section 348 of insulator base 34. Together with a projection 23 formed at housing 2, this first section 341 may form narrow gap 51 or may, measured in parallel to the longitudinal axis, be so short that this section is essentially negligible. Furthermore, all specific embodiments show second section 348 of insulator base 34, which has a first segment 342 including rounding 345 according to the present invention and partially a second segment 343 without the rounding according to the present invention. For all exemplary embodiments, leg lengths L1 and L2 as well as the approximate positions of first and second end points 346, 347 of rounding 345 according to the present invention are plotted.

(21) In FIG. 4a, first section 341 has a cylindrical shape. Rounding 345 according to the present invention has α2=90° at its first end point 346, and α1=0° at its second end point 347. At second end point 347, rounding 345 transitions into a straight line, which transitions into the cylindrical shape of second segment 343.

(22) FIG. 4b differs from FIG. 4a in that first end point 346 of rounding 345 according to the present invention is radially further to the inside, and does not rest directly on the edge and transition to first section 341 of insulator base 34. In this example, rounding 345 also transitions into a straight line in its first end point 346.

(23) FIG. 4c differs from FIG. 4a in that, in first end point 346, the tangent has an angle α2 of smaller than 90° and greater than 45°.

(24) FIG. 4d differs from FIG. 4a in that first section 341 has a conical shape.

(25) FIG. 4e differs from FIG. 4a in that second section 348 of insulator base 34 only includes first segment 342 including rounding 345 according to the present invention.

(26) FIG. 4f differs from FIG. 4a in that, in second end point 347, angle α1 is greater than 0° and smaller than 45°.

(27) FIG. 4g differs from FIG. 4a in that second segment 343 has a conical shape.

(28) FIG. 4h differs from FIG. 4d in that, in first end point 346 of rounding 345 according to the present invention, angle α2 is smaller than 90° and greater than 45°.

(29) FIG. 4i differs from FIG. 4f in that second segment 343 has a conical shape.

(30) All shown edges may also be chamfered or have small convex roundings.

(31) The specific embodiments shown here for an insulator base including a rounding according to the present invention may also be used in a prechamber spark plug.