US1977938A - Spark plug - Google Patents

Description

Patented Oct.

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scum. (mm-lee)" between which they are interposed and either have to be accurately made in order to ensure a close fluid-tight fit or have to be of a metal sufllciently soft to enable the sleeve to be distorted so as to conform with small irregularities in the shapes of the casing and insulator. Other known plugs not employing sleeves have, chiefly for the purpose of obtaining fluid-tightness, had

their casings cast directly on insulators surroundf ing central electrodes. This has necessitated the meet an insulator having special heat resisting qualities and, even so, it frequently happened, by reason of play as a result of unequal contractions in cooling, that cohesion between the sleeve and insulator and the molecules comprising the insulator was detrimentally aiiected, the plug thus losing its fluid-tightness and having its useful life considerably shortened. a 85 The primary object of the present invention is to provide a sparking plug in which a high degree of fluid-tightness is ensured without it being necessary specially to construct the metal sleeve or to employ an insulator resistant to high temperatures and molten metal; and according to the present invention a sparking plug having an insulator surrounded by a metal sleeve is characterizedinthatthecasingorbodyoftheplug is cast on the sleeve with the result that the sleeve and easing become fluid-tightly united but molten metal is prevented from directly touching the insulator. The fact that the casing is cast on the sleeve is necessary only to ensure close flt betweenthe insulator and bore of the sleeve, fluidtightness between the sleeve'and' the casing.

The insulatorusedin the present invention is preferably of'the kind comprising anumber of washers arranged face to facearound the central electrode or comprising a number of turns'of mica plates around the said electrode;

Theuseofthesleevealsopermitsofobtaining cast plugs with a hollow electrode or with aircirculating and'still fluid-tight plugs which are capable of being taken to pieces. 1 v

An example of the invention is illustrated in the accompanying drawing which is a side view of one of my plugs chiefly in vertical: section. "Inthisexampletheplughasacentralrod 1 which is screw-threaded at its upper end and so is provided with ahead 5 atits lower end'and a central electrode bent at 2 to form an electrode proper. That part of the rod between the head 5 at its lower end and the screw-threaded portion is closely surrounded by a cylinder 3 comprising a number ofturns of micaand the mica ylinder is surrounded by a number of mica washers 3'.

Thebodvcomprisingparts1,2, 3and3'isin-- serted in a sleeve .4 and, in accordance with the invention, this sleeve has cast on it an extended aluminium bronze or aluminium brass casing 6 of known form 'I, for the retention of -a grounded electrode 8. The electrode 8 comprising a pin which is preferably placed in the mould at the time of casting thecasing. Washers 3' tightly fit the bore of sleeve 4 and when the casing 6 contracts owing to its cooling, sleeve 4 is contracted and tightly grips the peripheries of the The mica washers above the upper end of sleeve 4 preferably have imputed to them in a lathe a slightly conical shape as indicated by 12.

It will be understood that mica cylinder 3 may be dispensed with and the mica washers 3' be suitably fashioned to take the place of said cylinder. 1 v

The mica bodies 3 and 8' are clamped between the enlargement 5 and lower end of the screwby means of nut 15 which "comprises a counter nut to a thumbor terminal nut 16. v

For the purpose of preventing the central electrode from unintentionally falling or being driven throughthecasing etheinnerwallofthecasing extension has an enlargement or boss 7 which lies in the path of the head 5.when the electrode 1 is moved downwardly, but in orderto permit the said electrode to be intentionally removed for cleaning and replacement purposes theenlargementtisgroovedatlsandbyturning thisgrooveintoregisterwithboss'l, electrode 1 may be withdrawn.

Having now particularly described and ascertained the nature-cr m said invention what manner the sameis to be performed! declarethatwhatIclaimisu v 1. A spark plug comprising a central. insulated electrode, c of a mica cylinder, a series o! mica disks embracing the cylinder, a metal sleeve surrounding the mica insulation and a'plug body in cast welded connection with the sleeve.

2. A spark plug as claimed inclaim 1, in which thelowerpartofthecasingisformedwithaproiection to prevent accidental removal of the central electrode.

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