Sensor element and particle sensor

• US 5,825,119 A
• Filed: 04/04/1997
• Issued: 10/20/1998
• Est. Priority Date: 04/01/1994
• Status: Expired due to Fees

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Takeuchi, Yukihisa, Shrader, Eric J., Eckerle, Joseph S., Pelrine, Ronald E., Shibata, Kazuyoshi
• Primary Examiner(s): Dougherty, Thomas M.
• Application Number:
  US08/833,115
• Time in Patent Office: 564 Days
• Field of Search: 310/321, 310/324, 310/328, 310/338, 310/358, 73/54.24, 73/54.25
• US Class Current: 310/338
• CPC Class Codes: B06B 1/0644 using a single piezoelectric element B06B1/0688 takes precedence
• CPC Class Codes: G01N 2291/0226 Oils, e.g. engine oils
• CPC Class Codes: G01N 2291/02408 Solids in gases, e.g. particle suspensions
• CPC Class Codes: G01N 2291/02416 Solids in liquids
• CPC Class Codes: G01N 29/046 using the echo of particles imparting on a surface; using acoustic emission of particles investigating concentration of particle suspensions G01N15/06; devices for measuring flow of solids in suspension G01F1/74

Abstract

A sensor element for detecting solid particles in a fluid 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. At least one of the detecting unit and the vibrating portion contacts with a solid particle in the fluid so that the piezoelectric film converts the vibration into an electric signal. A particle sensor includes the sensor element. The sensor element and the particle sensor are excellent in particle detection precision and durability at low cost.

Claims

1. A sensor element for detecting a solid particle in a fluid, comprising:

a substrate comprising (i) a main body having an opening formed therethrough in a thickness direction thereof, and (ii) a thin-walled vibrating portion covering the opening along an upper surface of said main body; and

a detecting unit formed on an upper surface of said thin-walled vibrating portion remote from the opening formed through said main body, said detecting unit comprising a piezoelectric film, a first electrode coated on at least a portion of the outer surface of said piezoelectric film, and a second electrode coated on at least a portion of the inner surface of said piezoelectric film,

wherein the fluid and the solid particles therein pass through the opening formed through said main body and said detecting unit and said thin-walled vibrating portion have sufficiently low mass such that when the solid particles strike said thin-walled vibrating portion said thin-walled vibrating portion and said detecting unit vibrate, and said piezoelectric film converts the resulting vibration into an electric signal, said detecting unit and said thin-walled vibrating portion being substantially motionless when the fluid and particles therein do not pass through the opening.

2. The sensor element of claim 1, wherein said substrate is a unitary ceramic substrate, and said main body and said thin-walled vibrating portion are integral parts thereof.

3. The sensor element of claim 1, wherein said piezoelectric film comprises at least one material selected from the 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. The sensor element of claim 1, wherein the fluid is a lubricant.

5. The sensor element of claim 1, wherein said piezoelectric film has a thickness ranging from 1 to 100 micrometers, and said thin-walled vibrating portion has a thickness ranging from 1 to 100 micrometers.

6. The sensor element of claim 1, wherein said thin-walled vibrating portion comprises stabilized zirconium oxide.

7. The sensor element of claim 1, further comprising a protective cover for shielding the detecting unit from direct collision with particles in the fluid.

8. The sensor element of claim 1, wherein the electric signal generated by said piezoelectric film has a resonant frequency that is detected by said detecting unit.

9. A sensing apparatus for detecting the size of a solid particle in a fluid, comprising:

a sensor element comprising (i) a detecting unit including a piezoelectric film consisting essentially of a first ceramic material, a first electrode coated on at least a portion of the outer surface of said piezoelectric film, and a second electrode coated on at least a portion of the inner surface of said piezoelectric film;

(ii) a vibrating portion consisting essentially of a second ceramic material, said detecting unit being placed on said vibrating portion so that said second electrode is coated on at least a portion of said vibrating portion; and

(iii) a fixing portion for fixing said vibrating portion so that said vibrating portion may vibrate; and

means for colliding the solid particle-containing fluid against said detecting unit and/or said vibrating portion at a predetermined speed,

wherein the solid particle in the fluid strikes said detecting unit and/or said vibrating portion causing said detecting unit and said vibrating portion to vibrate, and said piezoelectric film converts the vibration into an electric signal from which the size of the particle can be determined.

10. A method for detecting solid particles in a fluid, using a sensor element comprising (i) a detecting unit including a piezoelectric film consisting essentially of a first ceramic material, a first electrode coated on at least a portion of the outer surface of said piezoelectric film, and a second electrode coated on at least a portion of the inner surface of said piezoelectric film, (ii) a vibrating portion consisting essentially of a second ceramic material, said detecting unit being placed on said vibrating portion so that said second electrode is coated on at least a portion of said vibrating portion, and (iii) a fixing portion for fixing said vibrating portion so that said vibrating portion may vibrate, said detecting unit and said vibrating portion having a sufficiently low mass for responding to a collision with the solid particles, said method comprising the steps of:

causing a solid particle in the fluid to strike said sensor element so as to vibrate the vibrating portion, said sensor element remaining substantially motionless when the solid particle does not strike said sensor element; and

using said piezoelectric film and said first and second electrodes to convert a vibration of said vibrating portion into an electric signal from which the size of the particle can be determined.

11. The method of claim 10, wherein the solid particle in the fluid strikes a surface of the vibrating portion.