1. Field of the Invention
The invention relates to a method for the production of a spark plug which contains an inner conductor, an insulator surrounding the inner conductor, a spark plug body surrounding the insulator, and two electrodes forming an ignition gap, wherein the first electrode is a center electrode connected to the inner conductor in an electrically conducting manner and the second electrode is a ground electrode connected to the spark plug body in an electrically conducting manner, wherein, according to the method, an iridium component which contains more than 95 percent by weight of iridium is welded onto one of the electrodes.
Furthermore, the invention relates to a spark plug produced according to the method and to an iridium component provided for the same.
2. Description of the Prior Art
A method of the aforementioned type as well as a spark plug and an iridium component are known from EP 1 576 707 B1. The iridium component is produced in a powder metallurgical process by pulverizing the desired iridium alloy and subsequently pressing it isostatically. Thereafter, further steps for forming the iridium component are taken to give it its final shape. Thereafter, the iridium component can be welded onto one of the electrodes of the spark plug, for example, by laser welding.
An iridium alloy having a very high iridium content is described for the iridium component, said iridium alloy being formed from iridium and containing 1 to 3 percent by weight of rhodium, 0.1 to 0.5 percent by weight of tungsten and 0.05 to 0.01 percent by weight of zirconium with no more than minimum amounts of other substances.
An iridium alloy having such a high iridium content is to advantage in that the iridium component and the spark plug elements reinforced therewith are highly resistant to wear and tear. Such spark plugs have a very long service life. In addition, they require only relatively low ignition voltages.
However, a powder metallurgical production of the iridium components with subsequent reworking is highly complex and cost-intensive.
Another method for the production of an iridium component is known from DE 197 19 937 A1. Therein, the iridium component is formed by a wire section which is 0.5 mm to 2.0 mm in length. The semi-finished product used is an iridium wire which has an iridium content of 70 to 100 percent by weight and is cut to the desired length. Cutting is achieved by means of an abrasion procedure, e.g., abrading the wire with an abrasive. The wire can comprise a circular or a polygonal cross-section. The “abrasive cutting procedure” described uses diamond abrasive grains. Furthermore, the document describes that iridium components made of a wire section which is less than 0.5 mm in length are disadvantageous. Likewise, the separation of the iridium components from the wire-shaped semi-finished product by abrasion processes is highly complex and time-consuming.
EP 1 416 599 A2 discloses a rivet-shaped iridium component which is attached to the spark plug electrode by means of an additional component forming an intermediate layer. The rivet-shaped iridium component comprises a relatively large thickness of 0.7 mm, so that it projects far beyond the electrode surface next to the iridium component. As a result, a relatively large amount of material is required for the iridium component. The production of the iridium component in the rivet shape is highly complex. Together, these two factors lead to high production costs. The intermediate layer consists of an iridium alloy having a considerably lower iridium content, for example the intermediate layer contains 40 percent by weight of nickel. The intermediate layer is used to improve the capability of the iridium component to be connected to the base material of the electrode. Since, in this case, the intermediate layer must be handled and attached in addition to the production of the iridium component, this procedure is complex as well.