Protective sleeve for spark plug

Abstract

A protective sleeve for a spark plug includes a center electrode, an insulator, an attachment fitment having an attachment screw section formed on an outer peripheral surface thereof, and a ground electrode. A protective sleeve is disposed in a detachable manner on the outer periphery of the attachment screw section. The attachment fitment includes a flange section that has a diameter larger than that of the attachment screw section on a base end side of the attachment screw section. The protective sleeve includes a main body cylinder section having an inner diameter that is the diameter of the attachment screw section or larger, and smaller than the diameter of the flange section, a large diameter cylinder section having an inner diameter that is the diameter of the flange section or larger, and a step section formed between the large diameter cylinder section and the main body cylinder section.

1 . A protective sleeve for a spark plug comprising:
 a center electrode;   an insulator holding the center electrode therein;   an attachment fitment holding the insulator therein and configured such that an attachment screw section that is screwed into an internal combustion engine is formed on an outer peripheral surface thereof; and   a ground electrode that forms a spark discharge gap with the center electrode; wherein,   a protective sleeve is disposed in a detachable manner on the outer periphery of the attachment screw section,   the attachment fitment includes a flange section on a base end side of the attachment screw section,   the flange section has a diameter that is larger than that of the attachment screw section,   the protective sleeve includes a main body cylinder section having an inner diameter that is the diameter of the attachment screw section or larger, and smaller than the diameter of the flange section,   a large diameter cylinder section having an inner diameter that is the diameter of the flange section or larger; and   a step section formed between the large diameter cylinder section and the main body cylinder section.   
     
     
         2 . The protective sleeve for the spark plug according to  claim 1 , wherein,
 the large diameter cylinder section is configured to be fitted onto the flange section.   
     
     
         3 . The protective sleeve for the spark plug according to  claim 1 , wherein,
 the protective sleeve is configured such as to cover a coating that coats the attachment screw section, and   a coating pool in which the coating accumulates is formed on the inner side of the step section and the large diameter cylinder section when the protective sleeve is mounted onto the outer periphery of the attachment screw section.   
     
     
         4 . The protective sleeve for the spark plug according to  claim 1 , wherein,
 a tilt angle of the step section in relation to an axial direction of the protective sleeve is 45 degrees or less.   
     
     
         5 . The protective sleeve for the spark plug according to  claim 1 , wherein,
 a thickness of the large diameter cylinder section is greater than a thickness of the main body cylinder section.   
     
     
         6 . The protective sleeve for the spark plug according to  claim 1 , wherein,
 the large diameter cylinder section has a shoulder surface facing a tip side in an axial-direction, further from the outer peripheral side than to the step section.