Internal combustion engine

Claim 1

An internal combustion engine comprising a cylinder block defining therein a cylinder, a cylinder head mounted on the top of said cylinder block, a piston reciprocally mounted in said cylinder and cooperating with said cylinder and cylinder head to define a main combustion chamber, a precombustion chamber adapted to be supplied with a charge of an air-fuel mixture, a passage communicating said precombustion chamber with said main combustion chamber, means for supplying a charge of the air-fuel mixture to said main combustion chamber on an intake stroke of said engine, a part of said charge to said main combustion chamber being forced therefrom through said passage into said precombustion chamber on the succeeding compression stroke of said engine to form a substantial part of said charge to said precombustion chamber, and a spark plug so mounted on said cylinder head as to ignite the air-fuel mixture in said precombustion chamber so that the ignited air-fuel mixture is burnt in said precombustion chamber to produce a torch jet which runs along a path through said passage into said combustion chamber for thereby igniting the air-fuel mixture therein, where said spark plug comprises a generally tubular shell of an electrically conductive material, at least one grounded electrode connected to and extending from one of the end faces of said shell, an insulator axially extending through said shell and having a nose portion extending axially beyond said one end face of said shell, and a center electrode supported by said nose portion of said insulator and extending axially beyond said nose portion, said grounded electrode having a bent end portion extending toward said center electrode to cooperate with the peripheral surface thereof to define a spark gap therebetween, and wherein said center and grounded electrodes extend into said passage to an extent where said electrodes and said nose portion of said insulator are exposed to the rim of a torch jet through said passage.