Spark plug

Patent metadata

Field	Value
Publication number	US-9755404-B2
Application number	US-201615265152-A
Country	US
Kind code	B2
Filing date	Sep 14, 2016
Priority date	Sep 24, 2015
Publication date	Sep 5, 2017
Grant date	Sep 5, 2017

Abstract

A spark plug includes an insulator made of an alumina sintered body containing Al 2 O 3 as a principal component and additional components including; an Si component, a Ba component, an Mg component, a Ca component, an Sr component, and a rare earth element component. When the additional components are expressed as oxides including R SiO2 , R BaO , R MgO , R CaO , R SrO , and R RE2O3 , contents (mass %) of the sub-component satisfy expressions (1) to (6) as follows: (1) 1.0≦R SiO2 ≦5.0; (2) 0.5≦R BaO ≦5.0; (3) 0≦R MgO ≦0.18; (4) 0≦R MgO /R BaO ≦0.36; (5) 0.3≦(R MgO +R CaO +R SrO )≦1.8; and (6) 0≦R RE2O3 ≦0.1.

First claim

The invention claimed is:

1. A spark plug comprising:
an insulator having an axial bore extending in a direction of an axis;
a center electrode provided at a front side of the axial bore;
a metallic shell provided on an outer periphery of the insulator; and
a ground electrode fixed to a front end of the metallic shell, wherein
the insulator is made of an alumina sintered body containing Al 2 O 3 as a principal component and further containing additional components including an Si component, a Ba component, an Mg component, a Ca component, an Sr component, a rare earth element component, and barium hexaaluminate, and
when the additional components are expressed as oxides including R SiO2 , R BaO , R MgO , R CaO , R SrO , and R RE2O3 , contents (mass %) of the additional components satisfy expressions (1) to (6) as follows:
1.0≦ R SiO2 ≦5.0  (1)

0.5≦ R BaO ≦5.0  (2)

0≦ R MgO ≦0.18  (3)

0≦ R MgO /R BaO o≦ 0.36  (4)

0.3≦( R MgO +R CaO +R SrO )≦1.8  (5)

0≦ R RE2O3 ≦0.1  (6).

2. The spark plug according to claim 1 , wherein
the contents of the additional components satisfy an expression (7) as follows:
0.10≦ R CaO /( R MgO +R CaO +R SrO +R BaO )≦0.50  (7).

3. The spark plug according to claim 1 , wherein
the contents of additional components satisfy an expression (8) as follows:
0.06≦( R MgO +R CaO +R SrO )/ R BaO ≦1.25  (8).

4. The spark plug according to claim 1 , wherein
the alumina sintered body further contains a Na component and a K component whose combined content is not less than 0.002 mass % and not greater than 0.050 mass %.

5. The spark plug according to claim 1 , wherein
the alumina sintered body further contains a Ti component and an Fe component whose combined content is not less than 0.01 mass % and not greater than 0.08 mass %.

6. The spark plug according to claim 1 , wherein
the alumina sintered body has a ratio D A /D B that is not smaller than 0.5 and not larger than 5.0, where D A is an average value of maximum diameters of a plurality of alumina crystal grains, and D B is an average value of maximum diameters of crystal grains containing the Ba component.

Assignees

• Ngk Spark Plug Co

Inventors

• Isasa Jumpei
• Yoshida Haruki
• Yokoyama Yutaka
• Tanaka Kuniharu
• Araki Nobuyoshi
• Kon Toshiki

Classifications

• H01T13/38 Primary

  Selection of materials for insulation · CPC title