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Ceramic heater and glow plug

  • US 8,378,273 B2
  • Filed: 02/19/2009
  • Issued: 02/19/2013
  • Est. Priority Date: 02/20/2008
  • Status: Active Grant
First Claim
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1. A ceramic heater comprising a substrate formed of an electrically insulative ceramic, and a resistor element buried in the substrate, wherein the resistor element includes a single heat-generating portion formed of an electrically conductive ceramic and folded into a U-like shape, and a pair of lead portions which are joined to opposite end portions of said heat-generating portion, the end portion facing rearward with respect to a direction of an axis XA, and which extend straight rearward with respect to the direction of the axis XA, the ceramic heater being characterized in thatsaid resistor element includes intermediate portions located between said heat-generating portion and said lead portions;

  • when, on cross section S1 and S2 of said ceramic heater taken along a plane perpendicular to said axis XA at a front end side point P1 and a rear end side point P2, which are arbitrary two different points on said axis XA, imaginary circumscribed circles CG1 and CG2 are drawn such that the imaginary circumscribed circles CG1 and CG2 circumscribe and contain two cross sections HS1a and HS1b and two cross sections HS2a and HS2b, respectively, of said resistor element appearing on the cross section S1 and S2, respectively, diameter CL1 and CL2 of the circumscribed circles CG1 and CG2 satisfy a relation CL1<

    CL2; and

    the total cross sectional area HS1S of the two cross sections HS1a and HS1b of said resistor element and the total cross sectional area HS2S of the two cross sections HS2a and HS2b of said resistor element satisfy a relation HS1S<

    HS2S; and

    wherein said ceramic heater is inserted into and held in a tubular member formed of metal such that a front end portion of said ceramic heater is exposed;

    each of said intermediate portions has a portion having a thickness tXVex equal to or less than ⅔

    a maximum thickness tXVmax of said resistor element; and

    a portion of said resistor element whose thickness is 2 (tXVmax)/3 is exposed from said tubular member formed of metal.

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