Spark plug and semi-finished product thereof

A spark plug, a side where the spark plug is attached to an internal combustion engine being defined as a front end side and a side opposite thereof as a rear end side;

• the spark plug comprising:
• a tubular main fitting, a tubular insulator inserted in the main fitting, and a discharge gap formed on a front end side of the insulator;
• wherein
• the main fitting includes a first portion, a second portion having an inner diameter smaller than that of the first portion and disposed adjacent to the first portion on a front end side of the first portion, and a third portion having an inner diameter smaller than that of the second portion and disposed adjacent to the second portion on a front end side of the second portion;
• the insulator includes a first opposing portion having a predetermined portion opposed to the first portion, a second opposed portion opposed to the second portion, and a third opposing portion opposed to the third portion and having an outer diameter smaller than that of the second opposing portion;
• the predetermined portion projects in a radially outward direction and is a portion having the largest diameter in the first opposing portion;
• a connecting portion between the second opposing portion and the third opposing portion is supported by a support portion which is a connecting portion between the second portion and the third portion;
• when defining a first interval as an interval between the first portion and the predetermined portion at a rear end portion of the predetermined portion, and a second interval as an interval between the second portion and the second opposed portion at the rear end portion of the second opposed portion,
• a value obtained by dividing the first interval by a length from the support portion to the rear end portion of the predetermined portion is configured to be smaller than a value obtained by dividing the second interval by a length from the support portion to the rear end portion of the second opposed portion;
• and
• a third interval, which is an interval between the second portion and the second opposing portion at a front end portion of the second opposing portion, is configured to be smaller than the first interval.

A spark plug, a side where the spark plug is attached to an internal combustion engine being defined as a front end side and a side opposite thereof as a rear end side;

• the spark plug comprising:
• a tubular main fitting, a tubular insulator inserted in the main fitting, and a discharge gap formed on a front end side of the insulator;
• wherein
• a semi-finished product of the spark plug is a spark plug in a state before the main fitting is crimped to the insulator;
• the main fitting of the semi-finished product of the spark plug includes a first portion, a second portion having an inner diameter smaller than that of the first portion and disposed adjacent to the first portion on a front end side of the first portion, and a third portion having an inner diameter smaller than that of the second portion and disposed adjacent to the second portion on a front end side of the second portion;
• the insulator includes a first opposing portion having a predetermined portion opposed to the first portion at a first interval, a second opposed portion opposed to the second portion at a second interval, and a third opposing portion opposed to the third portion and having an outer diameter smaller than that of the second opposing portion;
• the first portion includes a thin wall portion having a smaller thickness in a radial direction than other portions of the first portion in the main fitting;
• the predetermined portion projects in a radially outward direction and is a portion having the largest diameter in the first opposing portion;
• a rear end portion of the predetermined portion is within a range of the thin wall portion in an axial direction;
• a connecting portion between the second opposing portion and the third opposing portion is supported by a support portion which is a connecting portion between the second portion and the third portion;
• and
• a value obtained by dividing the first interval by a length from the support portion to a rear end portion of the predetermined portion is configured to be smaller than a value obtained by dividing the second interval by a length from the support portion to a rear end portion of the second opposed portion.

A spark plug, a side where the spark plug is attached to an internal combustion engine being defined as a front end side and a side opposite thereof as a rear end side;

• the spark plug comprising:
• a tubular main fitting, a tubular insulator inserted in the main fitting, and a discharge gap formed on a front end side of the insulator;
• wherein
• a semi-finished product of the spark plug is a spark plug in a state before the main fitting is crimped to the insulator;
• the main fitting of the semi-finished product of the spark plug includes a first portion, a second portion having an inner diameter smaller than that of the first portion and disposed adjacent to the first portion on a front end side of the first portion, and a third portion having an inner diameter smaller than that of the second portion and disposed adjacent to the second portion on a front end side of the second portion;
• the insulator includes a first opposing portion having a predetermined portion opposed to the first portion, a second opposed portion opposed to the second portion, and a third opposing portion opposed to the third portion and having an outer diameter smaller than that of the second opposing portion;
• the first portion includes a thin wall portion having a smaller thickness in a radial direction than other portions of the first portion in the main fitting;
• the predetermined portion projects in a radially outward direction and is a portion having the largest diameter in the first opposing portion;
• a rear end portion of the predetermined portion is within a range of the thin wall portion in an axial direction;
• a connecting portion between the second opposing portion and the third opposing portion is supported by a support portion which is a connecting portion between the second portion and the third portion;
• when defining a first interval as an interval between the first portion and the predetermined portion at a rear end portion of the predetermined portion, and a second interval as an interval between the second portion and the second opposed portion at the rear end portion of the second opposed portion,
• a value obtained by dividing the first interval by a length from the support portion to the rear end portion of the predetermined portion is configured to be smaller than a value obtained by dividing the second interval by a length from the support portion to the rear end portion of the second opposed portion;
• and
• a third interval, which is an interval between the second portion and the second opposing portion at a front end portion of the second opposing portion, is configured to be smaller than the first interval.