US1997804A - Spark plug resistor - Google Patents

Description

April 16, 1935. 1 H, SANGERS 1,997,804

SPARK PLUG RESISTOR Filed May 25, 1933 IN VEN TOR ATT E Patented Apr. 16, 1935 PATENT OFFICE SPARK PLUG RESISTOR John H. Sangers, Clev eland, Ohio, assig'nor to The Ohio Carbon Company, Cleveland, Ohio, a corporation of Ohio Application May 25, 1933, Serial No. 672,846

,5 Claims.

This invention relates to improvements in electrical resistance units to be employed in situations where the unit is subjected to considerable vibration and, more particularly, to electrical resistors for use in the ignition circuit of an automobile, or the like, equipped with radio apparatus. In the latter instance, the resistor functions to avoid interference arising from-the action of the spark plugs during operation of the automobile.

Radio receiving sets used in automobiles require some means of altering the character of wave effects set up by the spark discharges across the spark plug gap in the usual operation of the vehicle, so that these effects will not interfere with the reception of the set. One manner of doing this is to insert a high resistance in the ignition circuit to each spark plug, the resistance being of the order of 25,000 ohms. Resistor units for lthis purpose are required to provide a constant resistance which is not subject to rapid change as would be the case if the contact with the re- I sistance element were not stable. In other words, any play between the contact surfaces and the surfaces of the element would result in introducing an air gap into the line with consequent large variations in the effective resistance, Establishment of stable contact, avoiding such changes in resistance, constitutes a diiculty in the case of automobiles and similar vehicles having a high po- 3o tentialignition system, since the vibration of the vehicle tends to produce such play between the parts of the resistance unit, with the result that units in which rigid surfaces are in contact have been found to be unsatisfactory.

To avoid such contact between two rigid surfaces, springs have been employed between contact terminals connected with the ignition leads and the resistance unit itself, such spring having the effect of taking up vibration and maintaining constant contact. 'I'he present invention aims to avoid the use of such springs and the attendant expense of manufacturing the same by employing for the purpose of establishing stable contact with a resistance element, masses of soft or plastic,

electrically conductive materials. Where springs are used for mounting resistance elements in devices of the class described, certain disadvantages are encountered such as corrosion of the spring by moisture which often finds its way inside the housing, the extremely small surface of contact between the end of the spring and the resistance element, and the fact that the end of the spring cuts through the copper coating with which the ends of resistance elements of carbon compositions are covered. In contrast to this, the masses (CI. 20L-63) of soft or plastic, electrically conductive material employed in the present construction provide a large area of contact which insures thorough and continuous electrical connection between the parts of the unit. Also, the substance used in -these masses may be a metal which is not greatly subject to corro-sion from moisture in the unit and such corrosion, moreover, if present, cannot affect the electrical resistance of the unit since the surfaces of the mass, in contact with the resistance element, closely engage such element and consequently exclude moisture. In the case of the springs previously used, these cannot be made of a non-corrodible metal suiiiciently inexpensive to he commercially available, since such springs are required to be resilient. On the other hand, the masses employed in the improved construction do not require to have a high degree of resilience and this permits the use of corrosionresisting metals, such as lead, which cannot be used in the form of a spring in a resistor unit. Where a spring cuts through the copper coating on the ends of a composition resistance element of carbon and a binder, frequent changes in the effective resistance of the unit will occur since the small point of contact may from time to time engage either a particle of carbon or a particle of binder, of different conductivity from the carbon. The present invention avoids these objectionable features of spring mountings by utilizing masses of plastic conductive material.

It is, accordingly, an object of the present invention to provide a resistance unit having improved operating characteristics and which is inexpensive to manufacture. Another object of the invention is to provide a spark plug resistor employing masses of plastic, electrically conductive material to connect a resistance element in an ignition circuit. Other objects of the invention will in part be obvious and will in part appear hereinafter.

In the accompanying drawing, there has been illustrated several modifications of the invention, the same being preferred embodiments thereof although it is to be understood that changes may be made therein without departing from the scope of the invention. In said accompanying drawing:

Fig. 1 is a side elevation, partly in longitudinal section, cf the improved resistance unit applied to a spark plug; Fig. 2 is a View, partly in lontudinal section, of a modiiied form of the resistance unit; Fig. 3 is a longitudinal section of still another modification; Figs. 4 and 5 are longitudinal sections taken through a portion of a resistor unit, made in accordance with the terms CII of the invention, illustrating an intermediate stage in the manufacture of the unit; Fig. 6 is a similar section to that of Figs. 4 and 5 illustrating a subsequent step in the process of manufacture; Fig. 7 is a View in elevation of a modified form of resistance element to be employed in the aforementioned resistance unit; and Fig. 8 is a detail of a modified form of screw adapted for use in the resistance unit.

Referring to the drawing, a spark plug I is provided with a stud 2 which carries the terminal bracket 3 of a resistor unit 3. A head member 5 adapted to receive the end of a cable, serves to complete the inclusion of the resistor unit in the circuit, or a spade terminal may be snapped into place between the hexagonal flanges shown.

The resistor unit includes a housing 6 of bakelite, hard rubber, porcelain, or other non-conducting material not subject to being shattered under the conditions of use described. This housing is hollow throughout its length and the bore thereof is threaded at either end as at 'I and 8 to receive threaded terminal contact members 9 and I0, or the bore may be left smooth and terminal contact members which are not threaded may be forced into the bore with a driving fit. Centrally located within the bore of the housing is a resistance element II composed preferably of carbon, such as graphite, carbon compositions including a binder, metal particles and the like, although other materials having a suitable resistance may also b used. The resistance element is shown as being cylindrical in form to conform with the bore of the housing but it will be understood that this element may assume other shapes and the conformation of the housing, both inside and outside, may also be altered without departing from the scope of the invention.

It will be seen from the foregoing that the terminal contact members 9 and I Il are thus mounted in the housing 6 and the resistance element II is also disposed in said housing. AIt remains to provide a means of electrically connecting these terminal contact members with the resistance element in such manner as to insure nonvarying electrical contact under the conditions of use normally prevailing, which result in considerable vibration. In accordance with the present invention, this is done by disposing between the contact members 9 and I0 and the resistance element II, masses I2 and I3 of a plastic, electrically-conductive substance such as one of the softer metals, including lead, zinc, solder, tin and soft alloys. Lead has been found to be particularly suitable for this purpose due to the fact that it is soft and flows easily at normal temperatures under moderate pressure such as can be exerted by the threaded members 9 and I0 against the element II.

In the assembly of the device, the contact member I will ordinarily be screwed into place, the mass I3 inserted in thevbore of the housing in a form of a lead shot I3', the carbon resistance element I I inserted and followed by another mass I2 in the form of a lead shot I2', and the contact member 9 screwed down into place. The contact members 9 and I Il are shown as being provided with points I Il which are forced into the plastic mass of the lead pellets when the contact member 9 is turned, and tend to deform these pellets to force the metal thereof against the walls of the bore and against the end surfaces of the resistance element. In this way. intimate Contact between the terminals and the resistance element is secured, the plastic metal conforming to the confit of further flow under stresses set up by vibration so as to follow movements of the neighboring surfaces and thus always constitutes a continuous mass-contact between the parts to be connected.

The resistance element I I, when composed of carbon, may be provided with an end covering I of sprayed metal, such as atomized copper, which.

coats the ends of the carbon rod and presents a metal surface for making electrical contact with terminal members. Lead or other soft metal may be used in place of copper for this coating in connection with the contact masses employed in the present invention since there is no sharp contact point, as in the case of a coiled spring, the piercing tendency of which must be resisted by a coating of a relatively hard metal.

The terminal contact elements have been shown in the drawing as provided with points IQ so as more effectively to press the metal of the shot or pellet against the Walls of the bore in the housing li, such contact with the walls of the bore helping to anchor the deformed pellet in place and prevent relative movement of the parts of the assembly. Such anchoring of the mass of plastic conducting material will take place whether the pellet lies on one side of the bore before crushing, as shown in Fig. 4, in which case the deformed mass will assume the position shown in Figs. l, 2 or 3 after pressure has been applied, or whether the undeformed pellet is centrally positioned, as shown in Fig. 5, in which instance the subsequent deformation by the points I4 will force the material of the pellet uniformly toward the walls of the bore in all directions, as shown in Fig. 6. In either case, sufficient contact with the wall of the bore will be secured so as to provide adequate anchorage of the crushed mass. While it is preferred to have the inner ends of the terminal contact elements conical or pointed, good results may also be achieved by having the ends of these elements flat or otherwise shaped. As mentioned above, the threaded Contact members 9 and IU may be replaced by unthreaded plugs which t into the bore of the housing with a driving fit and where such plugs are used, the plastic masses will be deformed by the application of direct pressure to such plugs.

The modification of the resistance unit shown in Fig. 2 does not differ from that above described in essential respects, but is provided with a socket Il at one end to be placed over a cable and with a split socket I8 at the other end having prongs I9 to form an electrical contact with a distributor, either by internal or external contact.

Fig.V 3 illustrates still another modification of the invention in which a uniformly cylindrical housing 2| encloses the resistance element II but in which the terminal contact members 22 and 23 are identical in shape and are each provided with hexagonal iianges 24 fitting into enlarged bores 25 and 26, extending a short distance inwardly from the ends of the housing, and

with screws 2T which are adapted to be forced into the conducting core of a cable. This modiicationv is thus adapted to be inserted at any point in the ignition system between the spark plug and the distributor, or between the distributor and the coils. Its characteristics otherwise are the same as those discussed with respect to the modification shown in Fig. l.

By the use of these various modifications, a resistance element can kbe placed between each spark plug and the distributor and a resistance Amay be placed between the distributor and the ignition coils, so that two resistances are placed in the circuit between each spark plug and the coil. If resistance elements of 25,000 ohms capacity are used, 50,000 ohms of resistance will thus be furnished in connection with each spark plug.

While the method of manufacture of the invention hasbeen described above in which separate pellets or masses of lead, zinc, tin, solder and the like are placed in a housing together with a resistance element and the two forced together by the application of pressure, it is also possible to provide a resistance element having masses of plastic electrically conductive materials, such as soft metal, adherently applied thereto as integral parts of its construction. Such a resistance element is shown in Fig. '7 of the drawing, wherein the portion 28, having the ability to interpose resistance to the ow of an electric current and being constituted of carbon or other suitable material, is provided with masses 29 on either end thereof composed of plastic conductive material. For instance, the masses 29, as well as the separate pellets I2 and I3', may consist of lead, tin, solder, zinc or alloys of any two or more of the metals lead, tin, zinc and other metals, provided such alloys are sufliciently plastic, and thesemetals may be sprayed directly on the ends of the resistance element by methods in which the wire of the desired metal is fed into an apparatus where it is melted and atomized onto the ends of the element until a mass of the desired size has been built up. Alternatively, the plastic mass, such as'one of the above mentioned metals, may be molded onto the ends of the resistance element, or may be molded thereon at separatedpoints on the surface of the element, as desired. The conductive masses may either be molded at the same time that the resistance element itself is molded, or the masses may be applied subsequently. Any metal or metal alloy may be used provided only that the .same is soft or plastic and capable of being deformed in the manner above described. Other plastic, electrically conductive materials may also beused. Where the resistance element is thus provided with masses of conductive material on its ends, the coating of atomized copper may be dispensed with.

In Fig. 8, still another modification of the .structure of theresistance unit, falling within the scope of the invention, is illustrated. In this modification, the plastic material, such as lead or other metal or metal alloyyis sprayed onto the ends of the screw means employed for securing the resistance element in rm electrical contact in the unit. Thus, a terminal contact member 3l, similar in form to those shown in Fig. 3 but which may have the form of such members as illustrated in Figs. 1 and 2 of the drawing, or any other suitable conflguration, has a mass of lead 32, or other suitable substance,sprayed or molded or otherwise applied to one end. In such case the end of the screw means will, of course, not be provided with a conical point but will be made flat, or substantially flat, with or without roughening of the surface in order to hold the sprayed metal. The

soft conductive mass so provided will then be crushed into yfirm electrical contact with the ends of the resistance element when the unit is assembled, in similar manner to that which takes place when the conductive material is used in the form of separate pellets or is applied tothe resistance element itself. The crushing action may be brought about either by screwing the terminal contact members into place, where these are threaded, or by direct pressure where the members are not threaded but are made to t into the bore of the housing with a driving t.

It will be apparent from the foregoing description and accompanying drawing that the present invention provides a resistance unit for overcoming interference in a radio set from the ignition system of an automobile or like vehicle, or for other purposes where a uniform resistance is essential, in which the mounting of the resistance element is stable and non-varying so that such uniform resistance is always present, and in which such mounting is readily and inexpensively made without the use of expensive parts or difficult assembling operations.

What I claim is:

1. A resistance unit, comprising a housing, a resistance element within said housing, a terminal contact at each end of said housing, pointed ends on said terminal contacts and masses of plastic electrically conductive substance lying between each of said terminal contacts and the resistance element crushed into firm electrical contact with the surrounding surfaces by said pointed ends.

2. A resistance unit, comprising a housing, a resistance element within said housing, a terminal contact threadably engaged in the ends of said housing, tapered ends on said terminal contacts and masses of readily deformable soft metal between each of said terminal contacts and the resistance element crushed inwardly and laterally into firm electrical contact with the surrounding surfaces by said tapered ends.

3. A resistance unit, comprising a housing, a resistance element within said hou-sing, a termina'l contact at each end of said housing, coneshaped ends on said terminal contacts and masses of lead between each of said terminal contacts and the resistance element crushed into firm electrical contact with the surrounding surfaces by said cone-shaped ends.

4. A resistance unit, comprising a housing, a resistance element within said housing, a terminal contact member at each end of said housing, tapered ends on said terminal contacts and deformed balls of lead penetrated by said tapered ends and crushed between and electrically connesting each of said terminal contacts and the resistance element.

5. A resistance unit, comprising a housing, a longitudinally extendingxresistance element within said housing and having end faces, terminal contact members having threaded connection with opposite ends of said housing. and masses of relatively soft metal, one lying between each of said terminal contact members and an end face of the resistance element and approximately in its longitudinal axis and adapted by screwing motion of the contact member on the housing to be forced into firm electrical contact with adjacent surfaces at approximately the center of the contact member and on the end face of the resistance element. I

JOHN H. SANGERS.

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