Prechamber spark plug having an adapted cap geometry

Abstract

A prechamber spark plug. The prechamber spark plug includes: a housing, and a cap which has at least one pass-through opening, the cap being situated at a combustion chamber-side end of the housing. The cap and the housing form a prechamber. An outer cap surface area of the cap, which faces away from the prechamber, has at least one predefined ratio to respectively one further geometric feature of the cap.

Claims

1. A prechamber spark plug, comprising: a housing; and a cap which has at least one pass-through opening, the cap being situated on a combustion chamber-side end of the housing, the cap and the housing forming a prechamber, wherein an outer cap surface area of the cap, which faces away from prechamber, has at least one predefined ratio with respect to at least one further geometric feature of the cap, wherein the cap has a flange, and the flange is inserted into the housing, wherein a second geometric feature of the at least one further geometric feature is a cross-sectional connection area of the flange and the housing in a common cross-sectional plane in an overlapping area of the flange and the housing, and a second ratio of the outer cap surface area to the cross-sectional connection area being at least 1:1 and maximally 3:1.

2. The prechamber spark plug as recited in claim 1, wherein a first geometric feature of the at least one further geometric feature is an inner cap surface area of the cap, and a first ratio of the outer cap surface area to the inner cap surface area being at least 1:1.

3. The prechamber spark plug as recited in claim 2, wherein the first ratio is maximally 3:1.

4. The prechamber spark plug as recited in claim 2, wherein the first ratio is 2.167:1.

5. The prechamber spark plug as recited in claim 1, wherein the second ration is 1.97:1.

6. The prechamber spark plug as recited in claim 1, wherein a third geometric feature of the least one geometric feature is a cross-sectional opening area of all pass-through openings, and a third ratio of the outer cap surface area to the cross-sectional opening area being at least 2:1 and maximally 8:1.

7. The prechamber spark plug as recited in claim 6, wherein the third ratio is 5:1.

8. The prechamber spark plug as recited in claim 1, wherein a fourth geometric feature of the least one geometric feature is a prechamber volume in combination with the inner cap surface area, and a fourth ratio of a sum of the outer cap surface area and the inner cap surface area to the prechamber volume being at least 0.2:1/mm and maximally 1:1/mm.

9. The prechamber spark plug as recited in claim 8, wherein the fourth ratio is 0.38:1/mm.

10. The prechamber spark plug as recited in claim 1, wherein the cap has a flat front side.

11. The prechamber spark plug as recited in claim 10, wherein the flat front side is situated in a plane perpendicular to a longitudinal axis of the prechamber spark plug.

12. The prechamber spark plug as recited in claim 10, wherein the cap has four pass-through openings, and the pass-through openings are situated in a transitional area between the front side and a lateral surface of the cap.

13. The prechamber spark plug as recited in claim 1, wherein the cap and the housing are connected to each other by a welded connection or a soldered connection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of the present invention is described in detail below, with reference to the figures.

(2) FIG. 1 shows a schematic sectional view of a prechamber spark plug according to a preferred exemplary embodiment of the present invention.

(3) FIG. 2 shows an enlarged detail of FIG. 1.

(4) FIG. 3 shows a further schematic sectional view of the prechamber spark plug, along the sectional line A-A of FIG. 2.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(5) With reference to FIGS. 1 to 3, a prechamber spark plug 1 according to a preferred exemplary embodiment of the present invention is described in detail below.

(6) As may be seen in FIG. 1, prechamber spark plug 1 comprises a housing 2 and a cap 3. Cap 3 is situated on an end of housing 2 facing a combustion chamber 10. Cap 3 and housing 2 together form a prechamber 5 of prechamber spark plug 1. Prechamber spark plug 1 is shown schematically in FIG. 1 and further includes an electrode 21, an insulator 23 and an electrical terminal 24.

(7) As shown schematically in FIG. 1, prechamber spark plug 1 is screwed into a cylinder head 22 of an internal combustion engine in such a way that cap 3 protrudes into combustion chamber 10. Cap 3 is thereby directly exposed to high temperatures in combustion chamber 10.

(8) In order to be able to absorb and dissipate the high temperatures in the best way possible and without damage, prechamber spark plug 1 has a cap 3 that is specially designed in its geometry. Cap 3 is shown in detail in FIGS. 2 and 3. For example, cap 3 is formed from nickel so as to offer good temperature stability and heat conduction.

(9) Cap 3 in general has a cup-like geometric shape and comprises four cylindrical pass-through openings 4 (see FIG. 3), through which torch jets produced by a first ignition of a fuel-air mixture in prechamber 5 are able to enter combustion chamber 10 in order to ignite the fuel-air mixture present therein. Pass-through openings 4 are situated in a rounded-off area of cap 3 between a lateral surface 33 and a flat front side 31 of cap 3. In addition, the respective axes 41 of pass-through openings 4 are situated at an angle 42 of 30° with respect to a longitudinal axis 25 of prechamber spark plug 1.

(10) Lateral surface 33 is provided as a conical lateral surface. Moreover, flat front side 31 is situated perpendicularly to longitudinal axis 25 and has a diameter 34, which amounts to 80% of an inner diameter 35 of cap 3.

(11) Cap 3 further comprises a flange 6, by which cap 3 is fastened to housing 2 of prechamber spark plug 1. The fastening here occurs in a force-locking manner by an H7/m6 press fit and in a form-locking manner by a welded connection 8 on the outer circumference. Adjacent to flange 6, a shoulder 62 is formed on cap 3, which abuts upon a front side 63 of housing 2. On an axial end of flange 6, the latter has a bevel 64.

(12) This specially designed geometry of cap 3, which allows for the optimized heat transfer on cap 3, is described below. In this case, an outer cap surface A of cap 3, which faces away from prechamber 5, is respectively characterized by multiple predefined ratios with respect to a further geometric feature of cap 3. Outer cap surface A corresponds to the entire outer surface of cap 3 that is freely accessible outside of housing 2 and is 130 mm.sup.2 in the preferred exemplary embodiment.

(13) A first geometric feature is an inner cap surface area B of cap 3. Analogous to the definition of outer cap surface area A, inner cap surface area B corresponds to the entire surface of cap 3 facing prechamber 5. A first ratio A/B of outer cap surface area A to inner cap surface area B is in this case 2,167:1. This results in an inner cap surface area B of 60 mm.sup.2.

(14) A second geometric feature is a cross-sectional connection area C of flange 6 and housing 2. Cross-sectional connection area C corresponds to a sum of the cross-sectional areas 91, 92 of flange 6 and housing 2 in an overlapping area 61 of these two components (cf. FIGS. 2 and 3). In detail, a first cross-sectional area 91 of housing 2 and a second cross-sectional area 92 of flange 6 are located in a common cross-sectional plane 60, which is perpendicular to longitudinal axis 25. Cross-sectional plane 60 corresponds to sectional plane A-A. Outer cap surface area A has a second ratio A/C to cross-sectional connection area C of 1.97:1. Cross-sectional connection area C is thus 66 mm.sup.2.

(15) A third geometric feature is a cross-sectional opening area D of pass-through openings 4. Cross-sectional opening area D is the sum of the individual cross-sectional opening areas D1 of all pass-through openings 4. Outer cap surface area A has a third ratio A/D of 5:1 with respect to cross-sectional opening area D. This results in a cross-sectional opening area D of 26 mm.sup.2.

(16) In addition, a fourth geometric feature is a prechamber volume E in connection with inner cap surface area B. Prechamber volume E corresponds to a total volume enclosed between cap 3 and housing 1. That is, prechamber volume E is bounded by inner cap surface B as well as by an inner side 27 of housing 2. A fourth ratio A′/E constitutes a relation between outer cap surface area A, inner cap surface area B and prechamber volume E. In detail, a sum A′ of outer cap surface area A and inner cap surface area B is set into a relationship with prechamber volume E. This fourth ratio A′/E is 0.38 l/mm. This yields a volume of 500 mm.sup.3 for prechamber volume E.

(17) The geometry of cap 3 according to the present invention thus influences in a particularly advantageous manner the heat transfer on cap 3 when operating prechamber spark plug 1. The described geometric ratios are specially adapted so as to effect an optimal heat absorption and heat dissipation on cap 3. This makes it possible to avoid excessively high temperatures, which would damage the cap or could result in unwanted spontaneous ignitions of the fuel-air ratio in combustion chamber 10, in that the heat is optimally transported away from the cap both by heat radiation and well as by heat conduction.