ION CURRENT DETECTING SPARK PLUG AND ION CURRENT DETECTOR

摘要

PROBLEM TO BE SOLVED: To restrain concentration of electric field in a gap so as to restrict generation of insulation breakage in the gap and generation of corona discharge near the gap by specifying the radial width of a gap between the projecting part of attaching metal fittings and the small diameter part of an insulation body. ;SOLUTION: Attaching metal fittings 31 provided with a screw part 31a for the purpose of being fixed to an engine block 100 include an insulation body 32 in its inside, and is fixed so that the one-end part 321 and the other end part 322 of the insulation body 32 may be exposed. Inside of the insulation body 32, a central electrode 33 is provided and fixed so that its one end part 331 may be exposed. In addition, a packing 36 is arranged between the projecting part 313 of the attaching metal fittings 31 and the stepped part 32b of the insulation body 32. In this case, a gap C having more than 0.5mm in its radial width W₁ is formed between the projecting part 313 of the attaching metal fittings 31 and the small diameter part 324 of the insulation body 32. In addition, the upper limit of the width W₁ of the gap C is so set as an axial overlapping size W₃ between the projection part 313 of the attaching metal fittings 31 and the stepped part 32b may be more than 30% of the radial width W₂ of the stepped part 32b.;COPYRIGHT: (C)1998,JPO