Spark plug for externally ignited internal combustion engine

Claim 1

Spark plug defining a connection end and a sparking end having a spark cable terminal (27, 28) to receive spark energy, at the connection end; a tubular metal housing (11) having a counter electrode (15) at the sparking end; a tubular insulator (17) within the tubular metal housing; a center electrode (40) sealingly received in the tubular insulator (17) and having a terminal end portion positioned close to, but spaced from, the counter electrode (15) to define a main spark gap (42) therewith; an electrical connection path including an auxiliary or pre-spark gap (33) coupling the cable terminal (27, 28) to the center electrode (40), said spark gap cable terminal (27, 28), the pre-spark gap (33), the center electrode (40), the main spark gap (42) and the counter electrode (15) defining a first circuit branch; and a shunt capacitor (51) having one electrode terminal connected to the spark cable terminal (27, 28), and another electrode terminal connected to the counter electrode (15) to form a shunt path to said first circuit path, comprising, in accordance with the invention, an auxiliary capacitor (37) serially connected in the first circuit path between the pre-spark gap (33) and the main spark gap (42); a first charging resistor (45) having high-resistance value connected in parallel to the pre-spark gap (33) and the auxiliary capacitor (37); and a second charging resistor (46) having high-resistance value being connected in parallel to the auxiliary capacitor (37) and the main spark gap, to form a charging circuit path from the terminal of the auxiliary spark gap remote from the auxiliary capacitor, through the resistor (45) to that one of the electrodes of the auxiliary capacitor (37) which is remote from the auxiliary spark gap (33) and from that one of the electrodes of the auxiliary capacitor (37) which is close to the auxiliary spark gap through the second resistor (46) to the counter electrode (15).