A spark plug having a connection portion disposed between a metal terminal and a center electrode. The connection portion includes: a magnetic substance formed from a Fe-containing oxide; a conductor which is a wire helically disposed on an outer periphery of the magnetic substance and electrically connected to the metal terminal and the center electrode; and an intermediate member which is in contact with the magnetic substance, the conductor, and an inner peripheral surface of the insulator, is disposed between the magnetic substance and the conductor, and the inner peripheral surface of the insulator, and has lower electrical conductivity than the conductor. The conductor is made of one or more of an oxide conductor, carbon, and a carbon compound.

A spark plug having a connection portion disposed between a metal terminal and a center electrode. The connection portion includes: a magnetic substance formed from a Fe-containing oxide; a conductor which is a wire helically disposed on an outer periphery of the magnetic substance and electrically connected to the metal terminal and the center electrode; and an intermediate member which is in contact with the magnetic substance, the conductor, and an inner peripheral surface of the insulator, is disposed between the magnetic substance and the conductor, and the inner peripheral surface of the insulator, and has lower electrical conductivity than the conductor. The conductor is made of one or more of an oxide conductor, carbon, and a carbon compound.

The present invention allows reduction in high frequency noise of a spark plug. A Fe-containing oxide layer is formed on the surface of a beneath-flange rod-shaped portion, of a metal terminal of the spark plug, between a terminal flange portion and an upper end of a metal shell. The surface area of the Fe-containing oxide layer is not less than 10% of the surface area of the beneath-flange rod-shaped portion.

The present invention allows reduction in high frequency noise of a spark plug. A Fe-containing oxide layer is formed on the surface of a beneath-flange rod-shaped portion, of a metal terminal of the spark plug, between a terminal flange portion and an upper end of a metal shell. The surface area of the Fe-containing oxide layer is not less than 10% of the surface area of the beneath-flange rod-shaped portion.

A spark plug having a center electrode that is formed by joining a conductive portion made of a conductive material and an insulating portion made of an insulating material. A sealing member electrically connects the conductive portion to a resistor. The insulating portion includes a protruding portion at a location on the back side of a back end of the sealing member. The protruding portion is embedded in the resistor.

An ignition coil for an internal combustion engine capable of effectively preventing leakage of noise occurring due to, for example, radio waves or unpleasant sounds generated by a spark discharge is provided. When an elastic O-ring 12, which is a main part of the invention and which is made of a annular elastic resin material, is used as securing means, with a simple structure, it is possible to hold a second cap 9 (on a second electrode side) of an electric noise suppressing resistor 10 and to close a gap formed between an inner wall surface of a resistor accommodation section 4 and the second cap 9 of the electric noise suppressing resistor 10. Therefore, this ignition coil is characterized in that, after securing the electric noise suppressing resistor 10 to the resistor accommodation section 4 by using the elastic O-ring 12, even if the inside of the resistor accommodation section 4 is uniformly filled with the insulating material 5, it is possible to prevent leakage to a location below the resistor accommodation section 4 from occurring.

An ignition coil for an internal combustion engine capable of effectively preventing leakage of noise occurring due to, for example, radio waves or unpleasant sounds generated by a spark discharge is provided. When an elastic O-ring 12, which is a main part of the invention and which is made of a annular elastic resin material, is used as securing means, with a simple structure, it is possible to hold a second cap 9 (on a second electrode side) of an electric noise suppressing resistor 10 and to close a gap formed between an inner wall surface of a resistor accommodation section 4 and the second cap 9 of the electric noise suppressing resistor 10. Therefore, this ignition coil is characterized in that, after securing the electric noise suppressing resistor 10 to the resistor accommodation section 4 by using the elastic O-ring 12, even if the inside of the resistor accommodation section 4 is uniformly filled with the insulating material 5, it is possible to prevent leakage to a location below the resistor accommodation section 4 from occurring.

Disclosed is a spark plug capable of suppressing high-frequency noise by improving the material of an electrical connection part between a center electrode and a metal terminal within an axial hole of an insulator. A spark plug has an electrical connection part arranged in an axial hole of an insulator to establish electrical connection between a center electrode and a metal terminal. The electrical connection part includes a conductor having a first crystal phase formed of a Fe-containing oxide and a second crystal phase formed of a conductive metal oxide of perovskite crystal structure.

Disclosed is a spark plug capable of suppressing high-frequency noise by improving the material of an electrical connection part between a center electrode and a metal terminal within an axial hole of an insulator. A spark plug has an electrical connection part arranged in an axial hole of an insulator to establish electrical connection between a center electrode and a metal terminal. The electrical connection part includes a conductor having a first crystal phase formed of a Fe-containing oxide and a second crystal phase formed of a conductive metal oxide of perovskite crystal structure.

A spark gap assembly includes a sealed chamber, at least two discharge electrodes, and a non-radioactive gas fill within the sealed chamber. The sealed chamber includes first and second end plugs and a vitreous tube having opposite ends, each end being sealed by one of said end plugs. The discharge electrodes extend through the first and second end plugs, respectively, from an exposed portion outside of the sealed chamber to an enclosed portion inside the sealed chamber. The discharge electrodes each have a discharge portion that includes a surface from which electrons of a spark discharge exit or are received, with the discharge surfaces of the discharge portions facing each other to thereby define a spark discharge gap between the discharge surfaces of the two discharge electrodes. The gas fill within the sealed chamber includes one or more non-radioactive isotopes of one or more noble gases.