US 2555488 A
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June 5, 1951 L. R. HETZLER' ET AL DISTRIBUTOR ROTOR Filed Oct. 22, 1947' e 0 @m m. 3 Mad QM T E Patented June 5, 1951 DISTRIBUTOR ROTOR LewisR. Hetzler, Ann Arbor, Mich., and Raymond A. Wilkins, Anderson, Ind., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application October 22, 1947, Serial No. 781,424
This invention relates to the suppression of disturbances to radio receivers by automotive ignition apparatus. I-I'eretofo're, suppressors have been used with ignition apparatus in various ways to eliminate interference with radio receiving sets ordinarily used in homes or on automobiles; but it has been found that those suppressors do not eliminate interference by ignition apparatus with highly sensitive radio receiving sets, for example, television receivers.
It is an object of the present invention to provide suppression of ignition disturbance which is adequate to practically eliminate interference with highly sensitive radio sets. In the disclosed embodiment of the present invention this object is accomplished by the use of a distributor rotor whose spark gap electrode is provided by a resist ance element.
Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.
In the drawings Fig. 1 is a sectional view on an enlarged scale showing a distributor cap with a rotor constructed according to the present invention;
Fig. 2 shows a plan view of the rotor and a wiring diagram of the ignition system;
Fig. 3 is a sectional view on line 3-3 of Fig. 1; and
Fig. 4 is a perspective view of a part adapted to be attached to the suppressor resistance.
A distributor cap III has a central terminal II supporting a conducting button I2 connected through the terminal with the secondary winding I3 of an ignition coil C whose primary winding I4 is connected with the grounded end of the secondary winding I3 and with contacts I5 of the ignition timer T paralleled by a condenser I6. Primary winding I4 is connected by a switch II with a battery B. The timer contacts are controlled by an engine driven cam S which drives a distributor rotor R comprising a rotor block of molded insulating material encasing a metal insert 2| having a tubular rivet portion 22 by which a steel spring 23 and a copper connector can be attached to the insert. Spring 23 supports a metal contact 24 engaging the button I2. Before assembling the rotor parts, a resistance element 26 of carbon or other suitable material having a high value of distributed resistance is attached to a thin copper disc 21 providing the electrode tip and to a suitable connector such as the part 25. For the purpose of 2 facilitating the attachment of parts 25 and 21 to the element 26, molten copper is sputtered on the ends of the element 26 to provide a surface which bonds readily with these parts by soldering or welding. The rotor block 20 has a recess 28 (Fig. 3) for receiving the element 26.
The function of element 26 is to retard capacity discharges of the capacity to ground of the wiring and parts electrically connected with the spark gap in the distributor. We have discovered that the element 26 is most eii'ective when located at the spark gap. Although the element 26 carries a tip 21, for all practical purposes the element 26 is at the spark gap and provides the rotor distributing electrode as it moves past the distributor terminals 30 which are each connected with a spark plug 3| as indicated in Fig. 2. The electrode tip 2'! which is used to increase the durability of the rotor is so small and it is spaced from the rotor body 20 a distance of a plurality of times its thickness in order that its reduction of the effectiveness of the element 26 is practically negligible. The path of electrostatic fiux between the tip 2'! and ground represented by cam S which drives the rotor R is indicated by dot-dash line e) in Fig. 1. Since the electrode 26 extends beyond the rotor body 20 a substantial distance, a substantial part of path e is in an air gap. Therefore the practically negligible capacity, with respect to ground, of the tip 21 is due to the fact that the path of electrostatic flux is through air as well as to the fact that the mass of tip 2! is small. Therefore it is desirable that the rotor body 20 extend toward the posts 30 no farther than is necessary to adequately support the electrode 26.
The suppressor element 26 is the most effective when located at the spark gap in the distributor for the following reason: Before the gap at the end of the distributor rotor ionizes, energy is stored in any capacity that exists between the high tension path and ground. When ionization occurs, the energy which is stored in the capacities on the sparking side of the suppressing resistor is released without having to pass through the suppressor. If this capacity is kept at a minimum this initial burst of energy is not sufficient to cause serious interference. The capacity to ground of the small electrode tip 21 is so small that ignition apparatus which includes the present rotor has practically no disturbing effect on even the most sensitive radio receivers, such as television receivers.
The resistance of the element 26 is usually in the range of 5000 to 10,000 ohms. These limits depend on engine performance and the degree of suppression required. Good results have been obtained with a resistor in length and having 5000 ohms resistance and having an electrode tip of copper about .03 thick.
While the form of embodiment of the present invention as herein disclosed constitutes a preferred form, it is to beunderstood that other forms might be adopted, all coming within the scope of the claim which follows.
What is claimed is as follows:
An ignition distributor rotor having a nonconducting body adapted to be connected with a driving shaft, a contact supported by the body and adapted to engage the center contact of a distributor cap having a circular row of terminals for connection with spark plugs, and a spark gap electrode made of a material such as carbon having a relatively high value of distributed re sistance supported by the body and connected with the contact and extending beyond the rotor body, and a conducting member of arc resisting material attached to the overhanging end of the carbon electrode, said member having such small dimensions and being spaced from the rotor body a distance of a plurality of times the thickness of said member so that the capacity of said member with respect to ground is substantially negligible.
LEWIS R. HE'IZLER.
RAYMOND A. WILKINS.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS