US2301990A - Spark plug having a mica insulator for internal combustion engines - Google Patents

Description

Nov. 17, 1942. E. ZANZI 2,301,990

SPARK PLUG HAVING A MICA INSULATOR FOR INTERNAL COMBUSTION ENGINES Filed 001.. 29, 1940 Fi .1 r Fig.2

Patented Nov. 17; 1942 UNITED STATES PATENT OFFICE SPARK PLUG HAVING A MICA INSULATOR FOR. INTERNAL COMBUSTION ENGINES Enrico Zanzi, Ivrea, Italy; vested in the Alien Property Custodian Application October 29, 1940, Serial No. 363,374 In Italy November 21, 1939 1 Claim.

This invention relates to improvements in spark plugs having a mica insulator. for internal combustion engines. The insulator is generally con- 1 stituted by mica rings fitted on the core and tightly pressed. In spite of the high pressure the current may pass through the capillary interstices between adjacent rings. These rings, in the known constructions, are separated from the metallic core by means of a mica. tube, which constitutes a screen preventing leaks of -15,000 v. 10

current in a radial direction from the core towards the spark plug body through the rings. Current leaks, however, may occur from the core head to the spark plug body first in an axial direction through the gap between the central mica tube and the ring pack and then in a radial direction through the ring pack.

According to this invention the mica rings are also fitted on a central mica tube coating the core and, moreover, the ring pack is introduced into a mica tube covering the inner wall of the spark plug body; the current accidentally flowing from the core head may pass through the central tube and ring pack and then between the rings but cannot reach directly the spark plug body; it

flows to the base of the body passing through a gap between the ring pack and the outer mica tube.

The resistance to the current flow through interstices between mica and mica is thus increased .to nearly twice the former resistance.

According to this invention and in view of the fact that the rings, which are in closer proximity to the-electrodes are more exposed to be damaged by the current, are subdivided into two concentric rings separated by a wide gap, so that when one 01' these rings is damaged, the dispersion current is lead on two paths along the axis or the first undivided ring between the core head and the base of the spark plug-body.

The annexed drawing shows an embodiment of the invention.

Fig. l is an axial section of a spark plug of ordinary construction,

Fig. 2 is an axial section or a sparkplug or a similar type but improved according to this invention.

Spark plugs are constituted (Fig. 1) by a body I connected to the engine mass and a core 2 connected to the source 01. power; the'body and core 5 are insulated from each other.

A mica insulator is preferably used for spark plugs exposed to high temperatures owing to its strength and is generally constituted by a pack oi mica rings 3 Fig.

1) fitted on the core and pressed against the head to with the interposition of a mica tube 4 I and in many cases also of a copper tube 5. be-

, tween the mica tube and core. An annularchamber 1 between the ring pack 3 and body I .forms an extension of the chamber 6 of the spark plug.

Although the mica rings are highly pressed together, a dispersion of 10-1500 v. current may occur through the capillary interstices; the tube 4 prevents a direct dispersion from the core 2; the current may only flow from the head 2a through the narrow gap between the tube 4 and pack 3 and reaches the wall of the body I through the annular chamber 1, in whichcarbonaceous deposits may be collected.

According to this invention the annular cham-.

her I is eliminated and the ring pack 3 fitted, as in the former case, on the core 2 with the interposition of a mica tube 4 and a copper tube I follows a path twice as long as the path in the ordinary construction.

According to a further improvement, the ring pack 3 is provided on the side or the chamber 6 with a wide and deep circular slot ll forming an extension of the chamber 8 and obtained by subdividing, along a section of the pack, each ring into two concentric rings 3a and lb; the rings 3a bear on the head 2a of the core and the rings 3b on the shoulder la of the body or the spark plug. The current escaping between the head 2a and shoulder la must thus follow a path equal at least to twice the depth of the slot II.

The spark plug may be disassemblable or notand I be provided with sparking points or any'shape' and, generally, various changes may be made in the details of construction without departing from the limits of the invention.

What I claim is:

A spark plug for internal combustion enginu, 7

comprising a core of conducting material, amica tube fitted on said core, a pack or'mica rings surrounding said mica tube and having on the spark side a wide and deep slot,

a secondmicatubeinwhichsaidpackotmica ringsisintroducedandacasingotconducting material surrounding said second mica tube.

ENRIOOZANZI,

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