Ignition device for internal combustion engine

#This application is based on Japanese Patent Applications No. 2004-152171 filed on May 21, 2004 and No. 2005-042260 filed on Feb. 18, 2005, the contents of which is incorporated herein by reference.

#The present invention relates to an ignition device for an internal combustion engine merging a spark plug for sparking in a spark gap and an ignition coil for supplying a large voltage current to the spark plug.

#Conventionally, an ignition device is known which merges a spark plug and an ignition coil in one housing as disclosed in U.S. Pat. No. 6,694,958-B and its counterpart JP-2003-297654-A for example. As shown in FIGS. 6 and 7, the ignition device has a male screw portion 22 formed on a housing 1 thereof to mount itself on an internal combustion engine. The male screw portion 22 is screw-fastened to a female screw portion 202 formed on a mounting hole 201 of a cylinder head 200 of the internal combustion engine.

#Features and advantages of embodiments will be appreciated, as well as methods of operation and the function of the related parts, from a study of the following detailed description, the appended claims, and the drawings, all of which form a part of this application. In the drawings:

#FIG. 1 is a side view showing a mounting state of an ignition device according to a first embodiment of the present invention on an internal combustion engine;

#FIG. 2 is an enlarged cross-sectional view showing an inner structure of the ignition device according to the first embodiment;

#FIGS. 1 to 3 depict an ignition device according to a first embodiment of the present invention. The ignition device has a cylinder-shaped housing 1, a spark plug 2 and an ignition coil 3. The housing 1 encloses the spark plug 2 and the ignition coil 3 therein. The ignition device is mounted on a mounting hole 201 of a cylinder head 200 of an internal combustion engine to expose both terminals of the spark plug 2 in a combustion chamber of the internal combustion engine. The cylinder head 200 is made of aluminum.

#The mounting hole 201 of the cylinder head 200 has a step as shown in FIGS. 1 and 2. The mounting hole 201 includes a female screw portion 202 formed at its end portion at a side of a combustion chamber 100 and a non-screw portion 203 formed between the step and the female screw portion 202. The non-screw portion 203 has a cylindrical shape and a bore diameter larger than a core diameter of the female screw portion 202. The cylinder head 200 further has a installing hole 204 disposed coaxial with the mounting hole 201 and between the mounting hole 201 and the outer face of the internal combustion engine. The installing hole 204 has a cylindrical shape and a bore diameter larger than the bore diameter of the non-screw portion 203 of the mounting hole 201.

#The housing 1 is made of a conductive metallic material such as AISI 1045 (DIN C45) and AISI 430 (DIN X6Cr17 or DIN X10CrAl18) having a hardness larger than a hardness of the cylinder head 200. The outer circumferential face of the housing 1 has a male screw portion 11 disposed at its tip portion at a side of the combustion chamber 100. The outer circumferential face of the housing 1 further has a clearance portion 13 and a non-screw portion 12 that are contiguous to and coaxial with the male screw portion 11 in a longitudinal direction of the ignition device. The non-screw portion 12 has a cylindrical shape and an outer diameter larger than an outer diameter of the male screw portion 11. The clearance 13 has an outer diameter smaller than the outer diameter of the male screw portion 11.