Misfire sensor

• US 5,837,887 A
• Filed: 03/06/1996
• Issued: 11/17/1998
• Est. Priority Date: 04/01/1994
• Status: Expired due to Fees

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Shibata, Kazuyoshi, Takeuchi, Yukihisa, Shrader, Eric J., Eckerle, Joseph S.
• Primary Examiner(s): Dombroske, George M.
• Assistant Examiner(s): MCCALL, ERIC SCOTT
• Application Number:
  US08/611,508
• Time in Patent Office: 986 Days
• Field of Search: 73/35.01, 73/35.07, 73/35.09, 73/35.11, 73/116, 73/117.3, 73/593, 73/DIG. 1, 310/317, 310/319, 310/329, 701/103
• US Class Current: 73/35.11
• CPC Class Codes: F02B 2075/027 four
• CPC Class Codes: G01L 23/222 using piezoelectric devices

Abstract

A sensor element for detecting misfire in an internal combustion engine includes: a detecting unit including a piezoelectric film consisting essentially of a ceramic material, a first electrode coated onto at least a portion of the outer surface of the piezoelectric film, and a second electrode coated onto at least a portion of the inner surface of the piezoelectric film; a vibrating portion consisting essentially of a second ceramic material, the detecting unit being placed on the vibrating portion so that the second electrode is coated onto at least a portion of the vibrating portion; and a fixing portion for fixing the vibrating portion so that the vibrating portion may vibrate. In the misfire sensor, the piezoelectric film converts the sound of a combustion explosion into an electric signal. The misfire sensor is excellent in precise misfire detection and durability at low cost.

Claims

1. A sensor for detecting misfire in an internal combustion engine, comprising:

a detecting unit including a piezoelectric film consisting essentially of a first ceramic material, a first electrode coated onto at least a portion of an outer surface of said piezoelectric film, and a second electrode coated onto at least a portion of an inner surface of said piezoelectric film;

a substrate having a top surface, a bottom surface, and a cavity formed through the bottom surface and into the substrate thereby providing a relatively thin vibrating portion supported by a relatively thick fixing portion such that said vibrating portion is adapted to vibrate with respect to said fixing portion, said vibrating portion consisting essentially of a second ceramic material and supporting said detecting unit such that said second electrode is coated onto said vibrating portion, wherein said cavity is open externally to said sensor to receive a sound generated by combustion explosion from an internal combustion engine;

first and second leads respectively electrically connected to said first and second electrodes;

an electric insulator having a depression complementary in shape to said detecting unit, said first and second leads extending through said electric insulator and being electrically connected to said first and second electrodes, respectively; and

a housing containing said detecting unit, said substrate, said electrical insulator, and said first and second leads;

wherein said piezoelectric film converts such a sound generated by combustion explosion in an internal combustion engine into an electrical signal.

2. A sensor of claim 1, wherein said substrate has a unitary structure comprised of said second ceramic material such that said vibrating portion and said fixing portion are integrally formed together.

3. A sensor of claim 1, wherein said first ceramic material comprises at least one species selected from a group consisting of lead zirconate, lead magnesium niobate, lead nickel niobate, lead zinc niobate, lead manganese niobate, lead antimony stanate, lead titanate, and barium titanate.

4. A method for detecting misfire in an internal combustion engine, comprising the steps of:

providing a detecting unit including a piezoelectric film consisting essentially of a first ceramic material, a first electrode coated onto at least a portion of an outer surface of said piezoelectric film, and a second electrode coated onto at least a portion of an inner surface of said piezoelectric film; and

a substrate having a top surface, a bottom surface, and a cavity formed through the bottom surface and into the substrate thereby providing a relatively thin vibrating portion supported by a relatively thick fixing portion such that said vibrating portion is adapted to vibrate with respect to said fixing portion, said vibrating portion consisting essentially of a second ceramic material and supporting said detecting unit such that said second electrode is coated onto said vibrating portion, wherein said cavity is open externally to said sensor to receive a sound generated by combustion explosion from an internal combustion engine;

receiving a sound generated by combustion explosion from an internal combustion engine thereby vibrating the vibrating portion and the detecting unit;

converting vibrations of the detecting unit into an electrical signal by the piezoelectric film; and

sending the electrical signal through said first electrode and said second electrode.

5. The method of claim 4, further comprising:

providing first and second leads respectively electrically connected to said first and second electrodes;

an electric insulator having a depression complementary in shape to said detecting unit, said first and second leads extending through said electric insulator and being electrically connected to said first and second electrodes, respectively; and

a housing containing said detecting unit, said substrate, said electrical insulator, and said first and second leads.

6. The method of claim 4, wherein said substrate has a unitary structure comprised of said second ceramic material such that said vibrating portion and said fixing portion are integrally formed together.