IP Library › Granted Patent US 9,054,502

Granted Patent B1

US 9,054,502 · App. 14/452,802 · Granted Jun 9, 2015

Ceramic for ignition device insulator with low relative permittivity

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Quick Facts

Patent No.: US 9,054,502
App. No.: 14/452,802
Granted: Jun 9, 2015
Kind: B1

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Abstract

A ceramic insulator for surrounding an electrode of an ignition device, such as a corona igniter or spark plug, is provided. The insulator is formed of a ceramic material including alumina in an amount of 28 to 38 wt. %, silica in an amount of 57 to 67 wt. %, and calcium oxide in an amount of 3 to 7 wt. %, based on the total weight of the ceramic material. The ceramic insulator is typically formed by firing a mixture of Kaolin, calcium carbonate, and silica, wherein the calcium carbonate acts as a flux during firing. The ceramic material has a relative permittivity of about 5.5 to 6.5 and thus improves the electrical efficiency of the ignition device. The ceramic material is also capable of withstanding temperatures of 900 to 1000° C. and has excellent thermal shock resistance, making it suitable for use in internal combustion engines.

Claims (83)

1. An insulator for an ignition device, comprising:

a ceramic material including alumina in an amount of 28 to 38 wt. %, silica in an amount of 57 to 67 wt. %, and calcium oxide in an amount of 3 to 7 wt. %, based on the total weight of said ceramic material.

2. The insulator of claim 1 , wherein said ceramic material includes a mixture of calcium aluminosilicate glass and mullite crystals.

3. The insulator of claim 1 , wherein said alumina is present in an amount of 33 wt. %, said silica is present in an amount of 62 wt. %, and said calcium oxide is present in an amount of 5 wt. %, based on the total weight of said ceramic material.

4. The insulator of claim 1 , wherein said ceramic material has a relative permittivity of 5.5 to 6.5.

5. The insulator of claim 1 , wherein said ceramic material includes crystalline silica in an amount of 0 wt. % to 2 wt. %, based on the total weight of said ceramic material.

6. The insulator of claim 1 , wherein said ceramic material includes alkalis in an amount of 0 wt. % to 2 wt. %, based on the total weight of said ceramic material.

7. The insulator of claim 6 , wherein said alkalis include at least one of sodium, potassium, sodium oxide, and potassium oxide.

8. The insulator of claim 1 , wherein said alumina is present in an amount of 33 wt. %, said silica is present in an amount of 62 wt. %, and said calcium oxide is present in an amount of 5 wt. %, based on the total weight of said ceramic material;

said ceramic material includes a mixture of calcium aluminosilicate glass and mullite crystals;

said ceramic material has a relative permittivity of 5.5 to 6.5;

said ceramic material includes crystalline silica in an amount of 0 wt. % to 2 wt. %, based on the total weight of said ceramic material;

said ceramic material includes alkalis in an amount of 0 wt. % to 2 wt. %, based on the total weight of said ceramic material; and

wherein said insulator is produced by firing a mixture of Kaolin, calcined Kaolin, calcium carbonate, silica, calcium silicate, and/or calcium sulfate.

9. The insulator of claim 1 , wherein said insulator extends longitudinally along a center axis from an insulator upper end to an insulator nose end; and

said insulator presents an insulator inner surface surrounding a bore extending longitudinally from said insulator upper end to said insulator nose end for receiving a central electrode.

10. The insulator of claim 9 , wherein said alumina is present in an amount of 33 wt. %, said silica is present in an amount of 62 wt. %, and said calcium oxide is present in an amount of 5 wt. %, based on the total weight of said ceramic material;

said ceramic material includes a mixture of calcium aluminosilicate glass and mullite crystals;

said ceramic material has a relative permittivity of 5.5 to 6.5;

said ceramic material includes crystalline silica in an amount of 0 wt. % to 2 wt. %, based on the total weight of said ceramic material;

said ceramic material includes alkalis in an amount of 0 wt. % to 2 wt. %, based on the total weight of said ceramic material;

said insulator presents an insulator outer surface having an insulator outer diameter extending across and perpendicular to said center axis;

said insulator outer surface extends longitudinally from said insulator upper end to said insulator nose end;

said insulator outer diameter decreases along a portion of said insulator adjacent said insulator nose end and moving toward said insulator nose end to present an insulator nose region;

said insulator outer diameter decreases along a portion of said insulator spaced from said insulator nose region and moving toward said insulator nose end to present an insulator lower shoulder;

said insulator outer diameter decreases along a portion of said insulator moving toward said insulator upper end at a location spaced from said insulator lower shoulder to present an insulator upper shoulder;

said insulator inner surface presents an insulator inner diameter extending across and perpendicular to said center axis; and

said insulator inner diameter decreases along a portion of said insulator moving toward said insulator nose end for supporting said central electrode.

11. An ignition device including the insulator of claim 1 , and further comprising a central electrode extending from a terminal end to a firing end for igniting a fuel-air mixture; and

said insulator surrounding at least a portion of said central electrode.

12. The ignition device of claim 11 , wherein said ignition device is a corona igniter, and said central electrode includes a firing tip at said firing end for emitting a corona discharge.

13. The ignition device of claim 12 , wherein said alumina is present in an amount of 33 wt. %, said silica is present in an amount of 62 wt. %, and said calcium oxide is present in an amount of 5 wt. %, based on the total weight of said ceramic material after firing;

said ceramic material includes a mixture of calcium aluminosilicate glass, and mullite crystals;

said ceramic material has a relative permittivity of 5.5 to 6.5;

said ceramic material includes crystalline silica in an amount of 0 wt. % to 2 wt. %, based on the total weight of said ceramic material;

said ceramic material includes alkalis in an amount of 0 wt. % to 2 wt. %, based on the total weight of said ceramic material;

said insulator extends longitudinally along a center axis from an insulator upper end to an insulator nose end;

said insulator presents an insulator inner surface surrounding a bore extending longitudinally from said insulator upper end to said insulator nose end for receiving said central electrode;

said insulator inner surface presents an insulator inner diameter extending across and perpendicular to said center axis and decreasing along a portion of said insulator moving toward said insulator nose end for supporting a portion of said center electrode;

said insulator presents an insulator outer surface having an insulator outer diameter extending across and perpendicular to said center axis;

said insulator outer surface extends longitudinally from said insulator upper end to said insulator nose end;

said insulator outer diameter decreases along a portion of said insulator adjacent said insulator nose end and moving toward said insulator nose end to present an insulator nose region;

said insulator outer diameter decreases along a portion of said insulator spaced from said insulator nose region and moving toward said insulator nose end to present an insulator lower shoulder;

said central electrode is formed of an electrically conductive material;

said central electrode has a length extending along said center axis from a terminal end to a firing end, wherein a majority of said length of said central electrode is surrounded by said insulator;

said firing tip of said central electrode includes a plurality of branches extending radially outwardly from said center axis for providing the corona discharge;

and further comprising:

a terminal disposed in said bore of said insulator and engaging said terminal end of said central electrode;

a seal disposed on said terminal end of said central electrode and around a portion of said terminal and filling a portion of said bore;

a shell formed of metal extending along said center axis from a shell upper end to a shell lower end and surrounding a portion of said insulator;

said shell upper end being disposed between said insulator upper shoulder and said insulator upper end and engaging said insulator; and

said shell lower end being disposed adjacent said insulator nose region such that at least a portion of said insulator nose region extends axially outwardly of said shell lower end.

14. The ignition device of claim 11 , wherein said ignition device is a spark plug and said central electrode includes a central firing surface at said firing end for emitting a spark.

15. The ignition device of claim 14 , wherein said alumina is present in an amount of 33 wt. %, said silica is present in an amount of 62 wt. %, and said calcium oxide is present in an amount of 5 wt. %, based on the total weight of said ceramic material after firing;