Spark plug

• US 7,432,641 B2
• Filed: 03/14/2007
• Issued: 10/07/2008
• Est. Priority Date: 03/21/2006
• Status: Expired due to Fees

• Current Assignee: NGK Spark PLUG Company Limited
• Original Assignee: NGK Spark PLUG Company Limited
• Inventors: Nunome, Kenji
• Primary Examiner(s): Santiago; Mariceli
• Assistant Examiner(s): Raleigh; Donald L
• Application Number:
  US11/686,128
• Publication Number:
  US 20070222351A1
• Time in Patent Office: 573 Days
• Field of Search: 313118-145, 123/169.R, 123/169.EL, 123/32, 123/41, 123/310
• US Class Current: 313/141
• CPC Class Codes: B28B 1/30 by applying the material on to a core or other moulding surface to form a layer thereon to form a permanent layer B28B19/00
• CPC Class Codes: B28B 11/0863 for profiling, e.g. making grooves
• CPC Class Codes: B28B 3/003 Pressing by means acting upon the material via flexible mould wall parts, e.g. by means of inflatable cores, isostatic presses isostatic presses in general B30B5/02
• CPC Class Codes: H01T 13/20 characterised by features of the electrodes or insulation
• CPC Class Codes: H01T 13/38 Selection of materials for insulation
• CPC Class Codes: H01T 21/02 of sparking plugs

Abstract

A plurality of insulator samples of different dimensions are subjected to multiple regression analysis to thereby induce an expression for estimating the amount of unevenness in wall thickness of an insulator; specifically, 0.01 (17.527+0.141A−0.285B−6.124C−0.14D+1.105E), where A is an overall length of the insulator, B is the outside diameter of a rear trunk portion of the insulator, C is the diameter of a large diameter portion of the axial bore of the insulator, D is the length of the large diameter portion of the bore, and E is the diameter of a small diameter portion of the axial bore. The insulator is designed such that the amount of unevenness in wall thickness thereof estimated through calculation by this expression is less than 0.07 mm.

Claims

1. A spark plug comprising an insulator having a bore extending in an axial direction and holding a center electrode for generating spark discharge in a front end portion of the axial bore and a terminal electrically connected to the center electrode, at a rear end portion of the axial bore,

wherein the axial bore of the insulator comprises a large diameter portion continuous with an opening located at a rear end of the axial bore and a small diameter portion continuous with a front end of the large diameter portion and smaller in diameter than the large diameter portion, and

wherein an axial length A in mm of the insulator, an outside diameter B in mm of a rear trunk portion located rearward of a portion of the insulator having a maximum outside diameter, a diameter C in mm of the large diameter portion, an axial length D in mm of the large diameter portion, and a diameter E in mm of the small diameter portion satisfy the following inequalities:

A≧

80

E≦

3.4

0.01(17.527+0.141A−

0.285B−

6.124C−

0.14D+1.105E)<

0.07.

2. A spark plug comprising an insulator having a bore extending in an axial direction and holding a center electrode for generating spark discharge in a front end portion of the axial bore and a terminal electrically connected to the center electrode in a rear end portion of the axial bore,

wherein the axial bore of the insulator comprises a large diameter portion continuous with an opening located at a rear end of the axial bore and a small diameter portion continuous with a front end of the large diameter portion and smaller in diameter than the large diameter portion,

wherein an axial length A in mm of the insulator, an outside diameter B in mm of a rear trunk portion located rearward of a portion of the insulator having a maximum outside diameter, a diameter C in mm of the large diameter portion, an axial length D in mm of the large diameter portion, and a diameter E in mm of the small diameter portion satisfy the following inequalities and ratios:

A≧

65

E≦

3.4

C/E≧

1.16

C/B≦

0.47

D/A≧

0.09, and

wherein as viewed on a plane which is perpendicular to the axial direction and on which a front end face of the insulator is projected, a distance between the center of a projected outer circumference of the front end face of the insulator and the center of a projected circumference of the opening of the axial bore is less than 0.07 mm.

3. A spark plug comprising, in combination, an insulator having an axial bore which receives a center electrode, a terminal electrically connected to one end of the center electrode and a spark discharge gap at another end of the center electrode,

the insulator defining an axial length A in millimeters, a rear trunk portion having an outside diameter B in millimeters located rearwardly of a portion of the insulator having a maximum outside diameter,

the axial bore of the insulator defining a large diameter portion having a diameter C in millimeters, an axial length D in millimeters and a small diameter portion having a diameter E in millimeters, and

wherein the following inequalities are satisfied:

A≧

80

E≦

3.4

0.01(17.527+0.141A−

0.285B−

6.124C−

0.14D+1.105E)<

0.07.