US 2003/0155850 A1Published application

Spark plug and method for manufacturing the spark plug

AssigneeNgk Spark Plug Co., Ltd.

InventorAkira Suzuki

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Abstract

A spark plug configured such that a metallic shell is joined to an insulator through crimping. The metallic shell is firmly joined to the insulator by means of a sufficient fastening force even when the diameter of the spark plug is reduced, to thereby enhance gastightness and vibration resistance. A rear end portion of a metallic shell (1) is crimped toward an insulator (2) to thereby be formed into a curved, crimped portion (1d). The inside diameter of an insulator insertion hole (40) of the metallic shell (1) is 8-12 mm. The cross-sectional area S of the metallic shell (1) as measured when the metallic shell (1) is cut by plane A-A perpendicular to the axis O at position (1i) where the inner wall surface of the insulator insertion hole (40) transitions to the inner wall surface of the crimped portion (1d) with respect to the direction of axis O of the metallic shell (1), and the carbon content of a steel material used to form the metallic shell (1) satisfy either of the following conditions A and B: condition A: 15≦S<29 mm2 and a carbon content of 0.20%-0.50% by weight; and condition B: 29≦S<35 mm2 and a carbon content of 0.15%-0.50% by weight. A method for manufacturing the spark plug is also disclosed.

Claims6

Dependent claims

A spark plug comprising a rodlike center electrode (3), a rodlike insulator (2) surrounding said center electrode (3) and having a protrusion (2e) at a central portion thereof, a metallic shell (1) assuming an open-ended, tubular shape and surrounding said insulator (2), and a ground electrode (4) facing said center electrode (3) and defining a spark discharge gap (g) in cooperation with said center electrode (3), and characterized in that:

an insulator insertion hole (4) into which said protrusion (2e) of said insulator (2) is inserted is formed in said metallic shell (1) while extending in a direction of an axis (O);
when a side toward said spark discharge gap (g) with respect to the direction of said axis (O) is taken as a front side, a rear end portion of said metallic shell (1) is cold-crimped toward said insulator (2) to thereby form a curved, crimped portion (1d);
two protrusions (1e and 1g) and a thin-walled portion (1h) are formed on an outer surface of said metallic shell (1) such that said thin-walled portion (1h) is located between said two protrusions (1e and 1g), the thin-walled portion (1h) is thinner than said two protrusions (1e and 1g), and assumes an outwardly deflected section and such that one of said protrusions (1e and 1g) is formed to be located adjacent to and on the front side of said crimped portion (1d);
and
an inside diameter of said insulator insertion hole (40) of said metallic shell (1) is 8-12 mm as measured at a position (1i) where an inner wall surface of said insulator insertion hole (40) transitions to an inner wall surface of said crimped portion (1d) with respect to the direction of said axis (O) of said metallic shell (1);
and a cross-sectional area S of said metallic shell (1) as measured when said metallic shell (1) is cut at said position (1i) by a plane perpendicular to said axis (O), and a carbon content of a steel material used to form said metallic shell (1) satisfy either of the following conditions A and B:
condition A:
15≦S<29 mm2 and a carbon content of 0.20%-0.50% by weight;
and
condition B:
29≦S<35 mm2 and a carbon content of 0.15%-0.50% by weight.

8 more elements

A method for manufacturing a spark plug comprising:

a rodlike center electrode (3);
a rodlike insulator (2) having a through-hole (6) formed therein along a direction of an axis (O) and having a protrusion (2e) at a central portion thereof, said center electrode (3) being disposed in said through-hole (6);
a metallic shell (1) surrounding said insulator (2), having an insulator insertion hole (40) formed therein so as to accommodate said protrusion (2e) of said insulator (2), assuming an open-ended, tubular shape, and
having two protrusions (1e and 1g) and a thin-walled portion (1h) formed on an outer surface thereof at a central portion thereof with respect to the direction of said axis (O), the thin-walled portion (1h) being located between said two protrusions (1e and 1g) and being thinner than said two protrusions (1e and 1g);
and
a ground electrode (4), a first end of said ground electrode (4) being joined to said metallic shell (1) and a second end of said ground electrode (4) facing said center electrode (3) to thereby define a spark discharge gap (g);
with a side toward said spark discharge gap (g) with respect to the direction of said axis (O) being taken as a front side, a rear end portion of said metallic shell (1) adjacent to one of said two protrusions (1e and 1g) being crimped toward said insulator (2) to thereby form a curved, crimped portion (1d);
said method comprising:
forming said metallic shell (1) such that an inside diameter of said insulator insertion hole (40) of said metallic shell (1) formed from a steel material having a carbon content of 0.20%-0.50% by weight is 8-12 mm as measured at a position (1i) where an inner wall surface of said insulator insertion hole (40) transitions to an inner wall surface of said crimped portion (1d) with respect to the direction of said axis (O) of said metallic shell (1), and
a cross-sectional area S of said metallic shell (1) as measured when said metallic shell (1) is cut at said position (1i) by a plane perpendicular to said axis (O) satisfies 15≦S<29 mm2;
disposing said insulator (2) in said insulator insertion hole (40) of said metallic shell (1);
and
cold crimping so as to curve radially inward a portion-to-be-crimped (1d40 ) located at a rear end portion of said metallic shell (1), to form said crimped portion (1d).

10 more elements

A method for manufacturing a spark plug comprising:

a rodlike center electrode (3);
a rodlike insulator (2) having a through-hole (6) formed therein along a direction of an axis (O) and having a protrusion (2e) at a central portion thereof, said center electrode (3) being disposed in said through-hole (6);
a metallic shell (1) surrounding said insulator (2), having an insulator insertion hole (40) formed therein so as to accommodate said protrusion (2e) of said insulator (2), assuming an open-ended, tubular shape, and
having two protrusions (1e and 1g) and a thin-walled portion (1h) formed on an outer surface thereof at a central portion thereof with respect to the direction of said axis (O), said thin-walled portion (1h) being located between said two protrusions (1e and 1g), being thinner than said two protrusions (1e and 1g), and assuming an outwardly deflected section;
and
a ground electrode (4), a first end of said ground electrode (4) being joined to said metallic shell (1) and a second end of said ground electrode (4) facing said center electrode (3) to thereby define a spark discharge gap (g);
with a side toward said spark discharge gap (g) with respect to the direction of said axis (O) being taken as a front side, a rear end portion of said metallic shell (1) adjacent to one of said two protrusions (1e and 1g) being crimped toward said insulator (2) to thereby form a curved, crimped portion (1d);
said method comprising:
forming said metallic shell (1) such that an inside diameter of said insulator insertion hole (40) of said metallic shell (1) formed from a steel material having a carbon content of 0.15%-0.50% by weight is 8-12 mm as measured at a position (1i) where an inner wall surface of said insulator insertion hole (40) transitions to an inner wall surface of said crimped portion (1d) with respect to the direction of said axis (O) of said metallic shell (1), and
a cross-sectional area S of said metallic shell (1) as measured when said metallic shell (1) is cut at said position (1i) by a plane perpendicular to said axis (O) satisfies 29≦S<35 mm2;
disposing said insulator (2) in said insulator insertion hole (40) of said metallic shell (1);
and
cold crimping so as to curve radially inward a portion-to-be-crimped (1d′) located at a rear end portion of said metallic shell (1), to form said crimped portion (1d).

10 more elements

Dependencies are inferred from the claim text.