US2071572A - Radio shield for spark plugs - Google Patents

Description

23, 1937. RABEZZANA ET AL 2,071,572

RADI O SHIELD FOR SPARK PLUGS Filed Dec. 50, 1935 Patented Feb. 23, 1937 UNITED STATES RADIO SHIELD ron SPARK PLUGS Hector Rabezzana and Alexander J. Battey, Flint,

Mich assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application December 30, 1935, Serial No. 56,646

6 Claims.

Our invention relates to shielded spark plugs for preventing high tension currents used for.

igniting the combustible mixture supplied to internal combustion engines, from interfering with the operation of radio sending and receiving and analogous sensitive apparatus located adjacent the engine; and the object thereof is to provide shielding means which, while effective for shielding purposes, is so designed and arranged that it will reduce the flow of heat from ,the metallic base of the spark plug, which is in good heat conducting relation to the cylinder of the engine, to the cable whereby current is supplied to the plug to a lesser amount of heat flow than has heretofore commonly been the case. The drawing accompanying and forming a part of this specification illustrates the preferred form of our invention; and the particular features wherein the same consists, and which distinguish it from prior shielded spark plugs, arepointed out in the concluding claims.

In the drawing:

Figure 1 is a sectional view upon a central plane extending longitudinally thereof, showing a shielded spark plug made in accordance with our invention.

Figure 2 is a view showing a section upon a transverse plane indicated by the line 2-2, Figure 1.

Referring to the drawing, the numeral 6 designates a hollow metallic-base member made, ordinarily, from cold rolled steel bar material, and which base has a lower externally threaded part which is threaded externally, as shown, to screw into a threaded spark plug opening in an internal combustion engine cylinder; and which base supports the grounded or shell electrode 1 of the plug. This base is hollow and annular in form, and within the-same and supported therefrom is the central insulated electrode 8 of the plug, the inner end of the latter being arranged adjacent the shell electrode 1 to provide a spark gap at 9. The central electrode may be insulated from the shell or base 6 in any way but asshown said electrode is surrounded by a mica tube or cigarette I0 extending longitudinally thereof, the ends of said tube being in turn surrounded by stacks II, 12 of mica washers, this being an arrangement of insulation common in mica insulated spark plugs. The electrode 8 has an enlarged head I3 at its lower end, and a metallic collar or terminal I at its upper end, which members abut against the washers H, I2 and secure the central electrode and the insulation therefor together.

The central electrode with the insulation therefor may be permanently assembled with the metallic shell 6 but in the preferred form of our invention illustrated said parts are carried by a tubular externally threaded nut l5 which screws into an internally threaded passage l6 at the upper end of the hollow shell; so that the central electrode, the insulation therefor and the supporting nut l5 comprise a single unitary structure which is removable in its entirety from, and replaceable within the interior of the support or shell 6; to which end said nut has a hexagonal portion I! as shown.

The metallic base 6 has a cage portion shown as comprising three circumferentially spaced bars l8 extending upwardly therefrom and beyond the outer insulating member II and terminal l4, and the upper endsof which bars are connected together by an internally threaded ring member IS; the base, the bars and the ring member being preferably made integral with one another.

Surrounding the outer insulating member II and extending beyond the same, and beyond the outer end of the cage bars l8 and the ring I9, is a tubular insulating member 20 made of porcelain, bakelite, or equivalent insulating material; said member being shown as supported by an annular ledge 2! provided by making the mica washers l I next to the tubular nut l5 larger than those next to the terminal M, as shown; a resilient washer 22 being interposed between the ledge 2| and an annular shoulder within and adjacent the lower end of the insulating member, as shown. The lower portion of said insulating member 20 surrounds the upper end of the upper insulating member I l, and said member is shown as provided with an internal annular seat portion or surface at 23 which fits closely around the terminal M. The upper part 24 of said insulating member is tubular in form to receive a depending terminal 25, made of insulating material, of a supply cable connecter indicated by the numeral 26 whereby current is supplied to the central electrode 8; said depending part having a conducting rod 21 the lower end of which carries a spring 28 which contacts with the central electrode terminal It to therebyprovide an electrical connection between a supply cable and the central insulated electrode of the-spark plug. The rod 21 is threaded at 29 and screws into a passage provided for it in the depending part 25 of the cable connecter as shown.

The numeral 30 designates a thin metallic sheath tubular in form and which sheath surupper end of which is inturned to provide a flange 3| which overlies the upper end of said insulating member; a yieldable washer 32 being interposed between said flangeiand upper end. The lower end of the. sheath is preferably turned inward beneath the lower end of the insulating member 20, as shown at 33, so that the sheath and insulating member when thus assembled to- ,gether form a unitary structure. The sheath 30 while in virtual contact with-the exterior surface of the insulating member 20 fits somewhat loosely about the same so that it may move freely along said member as the washer 32 is compressed during the assembling of the parts.

The numeral 34 designates an externally threaded tubular coupling sleeve or connecting member which screws into the internally threaded ring l9, said member having an inturned flange 35 at its upper end which overlies an outwardly extending flange 36 of the usual metallic casing of the supply cable connecter 26, to thereby secure the connecter to the spark plug or, more strictly, to the ring l9 which connects the outer ends of the cage bars I8. Said flange 36 is clamped between the inturned flange 35 and the inturned flange 3| as the coupling member 34 is screwed into the ring I5; and the metallic sheath 36 is free to move downward relative to the insulating member 20 as the washer 32 yields during the assembling of the parts; downward movement of the insulating member itself being prevented by the ledge 2|as will be appreciated.

' After the coupling member or sleeve 34 has been screwed into the ring l9 sufliciently to secure the tubular nut I5 proper tightness between the inturned flange 35, the outwardly extending flange 36, and the inturned flange 3| and washer 32 and the upper end of the insulating member 20, said coupling member is secured in place by a lock nut 31 which engages the upper side of the ring l9 as will be understood. The coupling member 34 is provided with holes 38 adjacent its upper end to help impede the flow of heat to the cable connecter 26 and to permit said member to be grasped by the fingers in screwing said member into the ring l3; and the peripheryof said member as well also as of the lock nut 31 are shown as knurled to facilitate the securing of the cable connecter 26 to the spark plug, and the removal of said connecter from the spark plug. The cable connecter 26 may be disassembled from the plug by unscrewing the coupling sleeve 34, whereupon the sheath 30 be removed through the ring l9; and the central electrode with its insulating members may likewise be removed through the ring by unscrewing from the base 6. 3

The cable connecter 26 has an outer metallic casing, as explained, and tightening of the sleeve member 34 presses the parts 35, 36, and 3| into firm contact with one another; so that the act of securing the connecter to the spark plug grounds both the metallic casing thereof and the metallic sheath 30 upon the metallic base 6 of the plug. Substantially the same grounding action, however, will be secured if the inturned flange 3| is not present, as there will always be a sufficiently good contact between the sheath 30 and the interior of the coupling member 34 to effectively ground the sheath upon the base 6 of the plug.

In our improved spark plug electrical shielding so far as the plug per se is concerned (that is which bars are connected together by an annular and insulating member-20 may not taking into account the usual metallic shield of the supply cable and the metallic casing of the connecter 26, which are grounded upon the base of the plug as hereinbefore explained) is due to the grounded metallic sheath 36, which :may terminate as close as desired to the tubular nut l5 (or to the upper end of the shell or casing 6 if the central electrode and its insulation are. permanently assembled with the shell), thus reducing the length of high tension lead represented by a short section of the central electrode which is not shielded to as short a length as may be desired; and the bars l8 will in fact form a shield for even the short length of central electrode between the lower end of the sheath 3!! and the nut l5, or the upper end of the shell of the plug.

The cage bars l8 being few in number, and comparatively long and of cross-sections not necessarily greater than is necessary for adequate mechanical strength, it follows that the flow of heat to the cable connecter casing 26 and to the usual rubber insulation of the supply cable through the bars will be reduced to a negligible amount; and the wall of the metallic sheath 36, being extremely thin, acts likewise to minimize the flow of heat to the casing 26 and to the supply cable.

vention, we claim and desire to secure by Letters Patent: V

1. In a shielded spark plug, a hollow metallic base member having an externally threaded part adapted to screw into an opening in an engine cylinder; a central electrode and an insulating member therefor, said electrode and insulating member being supported by said base member; circumferentially spaced bars extending upward from the base member, and the upper ends of ring member; a tubular insulating member surrounding the insulating member for said central electrode, and which insulating member extends beyond said ring member; a tubular metallic shield surrounding said last mentioned insulating member, and which shield is electrically connected with said metallic base member so as to be grounded thereupon; and means for connecting the metallic casing of a supply cable connecter with said ring member, said connecting means acting also to ground said casing upon said base member.

2. In a shielded spark plug, a hollow metallic base member having an externally threaded part adapted to screw into an opening in an engine cylinder; a central electrode and an insulating member therefor, said electrode and insulating member being supported by said base member; circumferentially spaced bars extending upward from said base member and beyond the upper ends of said central electrode and insulating member, and the upper ends of which bars are connected together by a threaded ring; a tubular insulating member supported by the insulatinl member for said central electrode and extending beyond the upper end thereof and beyond said threaded ring; a tubular metallic shield surrounding said last named insulating member and extending throughout the length thereof; and threaded means for connecting the metallic can ing of a supply cable connecter to said threaded ring, said connecting means acting to groundl both said casing and said shield upon said metallic base member.

3. In a shielded spark plug, a hollow metallic base member having an externally threaded part adapted to screw into an opening in an engine cylinder; a central electrode and an insulating member therefor, said electrode and insulating member being supported within said base and said insulating member having an annular supporting ledge; circumferentially spaced bars extending upward from said base member and beyond the upper ends of said central electrode and insulating member, and the upper ends of which bars are connected together by an internally threaded ring; a tubular-insulating member having an internal annular shoulder adjacent its lower end which overlies the ledge aforesaid,

and which insulating member surrounds said first named insulating member and extends beyond the upper end thereof and through-and beyond said internally threaded ring; a tubular metal shield surrounding said last named insulating member and extending throughout the length thereof, and having an intumed flange at its upper end which ove lies the upper end of said insulating member; and an externally threaded sleeve engaging said internally threaded ring and having an inturned flange at its upper end for engaging a flange of a metallic casing of a supply cable connecter, and for forcing said last named flange against the inturned flange aforesaid at the upper end of said tubular metallic shield.

4. In a shielded spark plug, a hollow metallic base member having an externally threaded part adapted to screw into an opening in an engine cylinder and an internally threaded passage at its upper end; a tubular externally threaded nut within said internally threaded passage and removable therefromf a central electrode and insulating-means -therefor, said electrode and insulating means being supported by said tubular nut; circumferentially spaced bars extending upward from said basemember and beyond the upper ends of said central electrode and the insulating means therefor, and the upper ends of which bars are connected together by a threaded ring member; a tubular insulating member surrounding said central electrode and the upper end of the insulating means therefor, and which insulating member is supported by the insulating means for said electrode and extends beyond the same and through and beyond said threaded ring member; a tubular metallic shield surrounding said last named insulating member and extending throughout the length thereof, said shield and insulating member being removable through said ring member; and threaded means for connecting the metallic casing of a supply cable connecter to said threaded ring member, said connecting means acting to ground both said casing and said shield upon said metallic base member.

5. As an element of a shielded spark plug, a

tubular insulating member having a lower por-' tion adapted to surround an insulating member of the central electrode of a spark plug, an internal ledgeadjacent its lower end whereby said member may be supported by a shoulder upon said insulating member, and an upper portion adapted to surround a terminal whereby current is supplied to said central electrode; a metallic shield member surrounding said insulating member and extending throughout the length thereof and having an inturned flange at its upper end which overlies the upper end'of said insulating member, said shield member being loose upon said insulating member and capable of slight movement longitudinally thereof and a yieldable washer arranged between said inturned flange and the upper 'end of said insulating mem ber.

6. In a shielded spark plug, a hollow metallic base member having an externally threaded part adapted to screw into an opening in an'engine cylinder, and an internally threaded passage at its upper end; a tubular externally threaded nut within said internally threaded passage and removable therefrom; a central electrode and insulating means therefor, said electrode and insulating means being supported by said tubular nut; circumferentially spaced bars extending upward from said base member and beyond the upper ends of said central electrode and the insulating means therefor, and the upper ends of which bars are connected together by a threaded ring member; a tubular insulating member surrounding said central electrode and the upper end of the insulating means therefor, and which insulating member extends beyond the insulating means forsaid electrode and through and beyond said threaded ring member; a tubular metallic shield surrounding said last named insulating member and extending throughout the length thereof, said shield and insulating member and said tubular nut and the central electrode and insulating means therefor being removable through said ring member; and threaded means for connecting the metallic casing of a supply cable connecter to said threaded ring member, said connecting means acting to ground both said casing and said shield upon said metallic base member.

HECTOR RABEZZANA. ALEXANDER J. BATTEY.

Images