Spark plug

Abstract

A spark plug includes a housing, an insulator inside the housing, a center electrode inside the insulator, and a connecting pin inside the insulator. At least one fillet is formed at a change of cross section at the housing, at the insulator, at the center electrode, and/or at the connecting pin. The fillet, viewed in cross section, includes a first leg and a second leg at an angle to the first leg. The length of the first leg is greater than the length of the second leg.

Claims

1. A spark plug comprising: a housing; an insulator inside the housing; a center electrode inside the insulator; and a connecting pin inside the insulator; wherein a respective fillet, which, when viewed in cross section parallel to a central longitudinal axis of the spark plug, includes a first leg and a second leg at an angle to the first leg and shorter than the first leg, is formed at each of at least one change between cross sections of at least one of the housing, the insulator, the center electrode, and the connecting pin, the cross sections being perpendicular to the central longitudinal axis, wherein the fillet, when viewed in cross section parallel to the central longitudinal axis of the spark plug, has a continuously curved shape that forms a first transition to a first straight line and forms a second transition to a second straight line, wherein a length of the first leg is measured parallel to the first straight line, and wherein a length of the second leg is measured parallel to the second straight line, so that the continuous curved shape transitions to the first straight line over a distance larger than a distance over which the continuous curved shape transitions to the second straight line.

2. The spark plug of claim 1, wherein the first leg is at least 1.5 times as long as the second leg.

3. The spark plug of claim 1, wherein the first leg is at least twice as long as the second leg.

4. The spark plug of claim 1, wherein the spark plug is arranged such that the first leg is situated perpendicularly to a greatest force acting on the fillet.

5. The spark plug of claim 1, wherein: the connecting pin includes a pin shaft and a collar; the collar rests on the insulator; and one of the at least one fillet is formed at a transition from the collar to the pin shaft.

6. The spark plug of claim 1, wherein the housing includes (a) a thread by which the housing can be screwed into a combustion for screwing in the housing and (b) a shaft, one of the at least one fillet is formed at a transition from the shaft to the thread.

7. The spark plug of claim 1, wherein: the housing includes the shaft, a shrink groove, and a polygon; and the at least one fillet includes a respective fillet at least one of a transition from the shaft to the shrink groove and a transition from the polygon to the shrink groove.

8. The spark plug of claim 1, wherein the center electrode includes a seat at one of the changes between cross sections at which one of the at least one fillet is formed, the seat resting on the insulator.

9. The spark plug of claim 1, wherein the insulator includes a seat at one of the changes between cross sections at which one of the at least one fillet is formed, the seat resting on the housing.

10. The spark plug of claim 1, wherein the insulator includes a housing seat at one of the changes between cross sections at which one of the at least one fillet is formed, a side of the housing facing away from the combustion chamber resting on the housing seat.

11. The spark plug of claim 1, wherein the two legs are defined by respective transition points at which the fillet transitions into a straight line.

12. The spark plug of claim 1, wherein the first leg is at least 1.3 times as long as the second leg.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a spark plug according to an example embodiment of the present invention.

(2) FIG. 2 shows a detail of FIG. 1.

(3) FIG. 3 shows a first view of a fillet of the spark plug according to an example embodiment of the present invention.

(4) FIG. 4 shows a second view of the fillet of the spark plug according to an example embodiment of the present invention.

DETAILED DESCRIPTION

(5) FIG. 1 shows a spark plug 1 in a half-sectioned view. Spark plug 1 includes a housing 2. An insulator 3 is inserted into housing 2. Housing 2 and insulator 3 are each internally hollow. A center electrode 4 is inserted into insulator 3. Furthermore, a connecting pin 5 is inserted into insulator 3. A panat 6 in insulator 3 is located between center electrode 4 and connecting pin 5. Panat 6 electrically conductively connects center electrode 4 to connecting pin 5. A ground electrode 7 is electrically conductively connected to housing 2 on the side facing the combustion chamber. The appropriate ignition spark is generated between ground electrode 7 and center electrode 4. Spark plug 1 extends around a center axis 8.

(6) Housing 2 includes a shaft 9. A polygon 10, a shrink groove 11 and thread 12 are formed on the shaft 9. Thread 12 is used for screwing spark plug 1 into an internal combustion engine.

(7) Connecting pin 5 includes a pin shaft 14, which extends along center axis 8, and a collar 13. Connecting pin 5 rests on insulator 3 with the aid of collar 13.

(8) Insulator 3 has an insulator collar 23 and a foot cone 28.

(9) Insulator 3 includes a center electrode seat 16 at the transition to foot cone 28. Center electrode 4 includes a first seat 15 that rests on the center electrode seat 16. Housing 2 includes an insulator seat 18 at its inside. A second seat 17, formed at insulator 3, rests on insulator seat 18. Depending on the temperature of spark plug 1, a gap may be present between second seat 17 and insulator seat 18. Furthermore, insulator 3 includes a housing seat 19 at its insulator collar 23. Housing 2 rests on the housing seat 19.

(10) Fillets 20 having an appropriate geometry are provided in particular at the described seats, namely first seat 15, center electrode seat 16, second seat 17, insulator seat 18 and housing seat 19.

(11) FIGS. 3 and 4 show the geometry of fillets 20 in detail. A cross section of fillet 20 is apparent in both figures.

(12) FIG. 3 shows that fillet 20 transitions into a straight line at each of its two ends. The transition points from fillet 20 into the straight lines are provided with reference numeral 24. Between both transition points 24, a first leg length 21 and a second leg length 22 are each measured in parallel to a straight line. In an approximately circular fillet, as occurs in the related art, both leg lengths are of equal length, corresponding to both reference numerals 22 and 22′. According to the present invention, it is, however, provided that first leg length 21 is significantly longer than second leg length 22. First leg length 21 is defined according to force 25 acting on fillet 20. In particular, a tensile load occurs in spark plug 1 in the direction of center axis 8, so that first leg length 21 is defined perpendicularly to center axis 8 at corresponding fillets 20.

(13) FIG. 4 also shows fillet 20 viewed in cross section. The final contour of fillet 20 as well as the ratio of both leg lengths 21, 22 are established with the aid of three straight lines 27. For comparison, FIG. 4 shows the curve of a conventional fillet 26 having two legs of equal length.

(14) In addition to the transitions having fillets 20 shown in the detail, fillet 20 according to the present invention can also be used at all cross section transitions of spark plug 1.