US2365925A - Electrical distributor - Google Patents

Description

26; 1944. E. ZQERLEW ETA; 2,365,925

ELECTRI CAL DI STRIBU'IOR Filed June 2. 1942 4 Jo}: E y John H. Mickey Iii/5) Z INVENTORS. By 654%. 22 5.

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Patented Dec. 26, 1944 ELECTRICAL DISTRIBUTOR Emil Zoerlein, John L. McCloud, and John A. Mickey, Dearborn, Mich., assignors to Ford Mo tor Company, Dearborn, Miclr, a corporation of Delaware Application June 2, 1942, Serial No. 445,462

Claims.

The object of our invention is to provide an internal-combustion engine distributor by means of which high-tension current is selectively conducted to the several spark plugs associated with such engine. Our invention comprises an improved distributor-cap construction in that our cap has an increased dielectric strength over other caps of similar size.

Our invention is particularly useful in aircraft engine distributors because the ceiling of most airplane engines is determined by the minimum atmospheric pressure at which the distributor will handle the current required for ignition. The use of superchargers and pressure-sealed fuselages has increased the ceiling of planes to such an extent that failure of the distributor is the controlling factor. Due to the increased dielectric strength of our cap, the distributor will function at nearly 10 per cent higher altitudes than was heretofore possible.

In the modern airoraftengine a potential of 9,000 to 14,000 volt is required for ignition, due to the high compression pressures. Substantially this same voltage is required up to 30,000 feet because the supercharger of the engine maintains almost a constant compression pressure up to this height. However, at these altitudes the atmospheric pressure inside the distributor cap is so low that the danger of shorting around the plugs is of major importance. The ordinary distributor cap is made from either rubber or phenol condensate and a reduction in barometric pressure reduces both the surface dielectric strength and the volume dielectric strength of the cap. The surface strength is reduced because it is directly proportional to the atmospheric pressure, while the volume dielectric strength is reduced because the material is porous to a slight degree.

A further factor in connection with such distributors is that nitric acid is formed in the atmosphere within the housing due to the continuous sparking between the rotor and the spark plug wire terminals. The acid accumulates upon the walls of the housing and wets the surface, thereby reducing the surface dielectric strength.

We have improved the dielectric strength of our distributor cap by providing a laminar construction, one element of which seals the pores of the cap material, provides an acid-repellent surface for the interior of the cap, and is of such composition that an unexpected increase in volume dielectric strength results.

With these and other objects in View, our invention consists in the arrangement, construction and combination of the various elements comprising our improved distributor and the method of accomplishing the results attained, as described in the specification, claimed in our claims, and illustrated in the accompanying drawing, in which:

Figure 1 is a plan view of an airplane engine distributor cap, and

Figure 2 is a cross-sectional view, taken upon the line 2-2 of Figure 1.

Referring to the accompanying drawing, we have used the reference numeral ID to indicate a housing which is molded of mica-impregnated phenol condensate. Hard rubber or other similar material may, however, be used if desired. The housing is of cup shape having a central terminal II molded therein, which terminal is electrically connected to a threaded eyelet l2 by means of a wire l3. The terminal ll, eyelet I2 and wire I 3 form a unit which is molded in the housing 10. High-tension current is conducted from the magneto coil to the eyelet H by means of a cable which is inserted in a socket M in the housing. A screw, not shown, is screwed into the eyelet and contacts a ferrule on the end of the cable. The current from the terminal H is conducted to individual spark-plug terminals 15 by means of a conventional distributor rotor which is not shown in the drawing. One terminal [5 is provided for each spark plug of the engine, each of which terminals is connected to an eyelet I6 by means of a wire ll. The terminals 15 are arranged in an annulus around the periphery of the housing [0.

Where the engine is provided with upward of eighteen cylinders, a comparatively large distributor cap is required, solely to obtain the necessary annular spacing between the terminals ii. In order to decrease this spacing the surface path between the adjacent connectors 16 is elongated by providing radially extending ribs I8. The spacing of the terminals I5 and height of the ribs l8 control the dielectric strength of the housing and are chosen so that at atmospheric pressure the housing will safely carry a potential of 16,000 volts.

Our distributor differs from the conventional distributor in that the inside of the housing In is coated with a special enamel. Furthermore,

the inserted portions of the terminals II and I5, eyelets l2 and the connecting wires [3 and H are coated with this enamel before they are molded in place. The action of these coatings is not exactly clear to the applicants but the results attained are far superior to those which could be expected from the actual insulating value of the enamel employed. The improvement may be because the layer of enamel forms a water-impregnable surface, sealing the pores in the housing surface, or it may be becaus the coating is acid repellent, thus being unaffected by the dilute nitric acid formed by the arcs at the several terminals within the housing.

In any event the coating which we appiy is only about .010 inch thick but it increases both the surface and volume dielectric strength suiiiciently that the housing withstands over 2,000 additional volts. This increase is entirely out of proportion to the increase that might be expected from the additional .010 inch of dielectric.

The enamel which we have found desirable consists of a resin mixture of 75 per cent alkyd and 25 per cent melamine resins and from to per cent pigment based on the amount of resin.

Such enamel will bake at 175 to 200 degrees, these temperatures being low enough not to warp the housing. The thickness of the coating is not of particular importance, as apparently the increase in dielectric strength does not depend upon the actual thickness of the coating. It should, however, be of sufficient thickness to completely cover the surface. The pigment may be any one of several but should be heat resistant and free from iron oxide. Any of the various silica compounds are suitable for this use.

Some changes may be made in the composition of the above-described coating and the parts to which it is applied without departing from the spirit of our invention, and it is our intention to cover by our claims such changes as may reasonably be included within the scope thereof.

We claim as our invention:

1. An ignition distributor housing comprising melamine as a component part of the surface thereof.

2. A distributor housing comprising dielectric material, the surface of whichis provided with melamine resin.

3. A distributor housing comprising dielectric material and a layer of melamine applied thereto.

4. The structure, as defined in claim 3, in which the melamine resin is present as a film applied to said dielectric material.

5. In a distributor of the class described, a distributor body molded from a. phenolic resin and a mica filler, said body forming an enclosure for a high tension electric spark, the interior or said distributor having a thin dielectric layer of finely divided silica material in a medium comprising a thermosetting alkyd resin'and a thermosetting melamine resin cured in situ on said body, there being a substantial excess of said alkyd over said melamine resin.

6. In a distributor molded from dielectric material, a compartment forming an enclosure for a high tension electric spark, the interior of said compartment having a thin enamel coating applied thereto, the essential ingredient of said enamel being melamine resin.

'7. In a distributor of the class described, a distributor head molded from a slightly porous insulating material, and a conductor having a thin enamel coating thereon, the essential ingredients of said enamel including alkyd and melamine resins, said conductor being imbedded within said head.

8. In a distributor of the class described, a distributor head molded from a phenolic resin insulating material, an enamel-coated conductor partially imbedded within said head, and a layer of enamed formed on the interior surface of said head, the essential ingredient of said enamels including alkyd and melamine resins.

9. In a distributor of the class described, a distributor head molded from mica-impregnated phenolic resin, said head forming an enclosure for a high-tension spark, the interior of said enclosure havin a pigmented enamel coating applied thereto, the essential ingredients of said enamel comprising alkyd and melamine resins and a heat-resistant pigment free from iron oxide.

10. In an electric distributor of th class described, a distributor head molded from micaimpregnated phenolic resin, said head forming an enclosure for a high-tension electric spark, the interior walls of said enclosure having a layer of enamel formed thereon, and an enamel-coated conductor imbedded within said head, said enamels comprising alkyd and melamine resins and a silica pigment.

EMIL ZOERLEIN. JOHN L. MCCLOUD. JOHN A. MICKEY.

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