Spark plug and method of manufacturing the same
AssigneeDenso Corporation
InventorMasayuki Tamura
Life of this patent
Estimating the term…
Abstract
A spark plug has a tubular fitting which is assembled with a center electrode, a ground electrode and an insulator. The fitting has a reach length of at least 12 mm for use in high output-type engines. The fitting is formed with a thread part and a taper part so that the fitting is thread engaged with an engine head and seals a combustion chamber from an outside by a contact between the taper part and a seat surface of the engine head. The fitting is made by cold-forging a low carbon steel to provide the taper surface of a surface roughness of less than 10 μm and a column part. The column part is machine-cut to provide the thread part thereon. The deflection between the axes of the thread part and the taper part is limited to be less than 0.15 mm.
Claims20
A spark plug for engines comprising:
- a tubular fitting having a thread part and a taper part in that order on an outer surface of the tubular fitting, from one end thereof toward another end thereof and having a reach length of at least 12 mm, the thread part being for engagement with the engine, and the taper part being for sealing a combustion chamber from an outside by contacting the engine;
- a center electrode held in and insulated from the tubular fitting with one end thereof protruding from the one end of the tubular fitting;
- and
- a ground electrode fixed to the tubular fitting and facing the one end of the center electrode through a discharge gap therebetween,
- wherein the taper part is formed into a tapered shape thereof by a cold-forging.
A spark plug for engines comprising:
- a tubular fitting having a thread part and a taper part in that order on an outer surface of the tubular fitting, from one end thereof toward another end thereof and having a reach length of at least 12 mm;
- a center electrode held in and insulated from the tubular fitting with one end thereof protruding from the one end of the tubular fitting;
- and
- a ground electrode fixed to the tubular fitting and facing the one end of the center electrode through a discharge gap therebetween,
- wherein the taper part of the tubular fitting has a cold-forged surface roughness of less than about 10 μm.
A method of manufacturing a spark plug for an engine having a thread hole comprising:
- cold-forging a low carbon steel into a shape of a tubular fitting having a taper part, which contacts the thread hole of the engine to seal a combustion chamber from an outside, and a column part, the taper part having a cold-forged surface roughness of less than about 10 μm;
- and
- assembling a center electrode and a ground electrode with the tubular fitting.
Dependencies are inferred from the claim text.