Ignition circuit radiation suppression structure

Abstract

A wire wound resistor for use in suppressing ignition circuit radiation which has a very low resistance and a specified inductance connected in an ignition circuit close to and in series with the spark plug electrodes, as within the spark plug or between the spark plug lead wire and the spark plug.

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No. 226,042, filed Feb. 14, 1972, now U.S. Pat. No. 3,771,006.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to ignition circuits of the type used on automobiles having internal combustion engines and refers more specifically to a wire wound resistor which has a very low resistance and a specified inductance which is connected in series with spark plug electrodes so as to be immediately adjacent the sparking electrodes, which resistor is operable to suppress radiation from the ignition circuit due to sparking of the spark plugs.

2. Description of the Prior Art

In the past, suppression of radiation from ignition circuits of automobiles on firing of the spark plugs therein has often been accomplished by inclusion of wire wound resistors in the spark plugs between an upper and lower electrode or connecting such resistors in series between a spark plug lead wire and the spark plug as shown in U.S. Pat. No. 3,212,044 and U.S. Pat. No. 3,529,273, respectively. Such wire wound resistors of the past have usually been of relatively high ohmic value of, for example, 5,000 or 10,000 ohms. These prior wire wound resistors have been specified generally by their resistance value and physical size. Any inductance in the wire wound resistors has been considered irrelevant in the past. Such resistors are necessarily wound of fine wire spaced close together so that at the usual ignition circuit voltages flashover between the turns of the wire wound resistors has been a problem limiting the minimum physical size of the resistors. A compromise has therefore been reached in the past between the flashover point of the wire wound resistors and the length of the resistors and therefore the size of the spark plugs and boots in which they have been installed.

SUMMARY OF THE INVENTION

It has been found that the inductance of the wire wound resistors is of particular importance in suppression of radiation from ignition circuits, especially when the wire wound resistors are placed close to sparking electrodes as, for example, within or closely adjacent to the spark plugs of the ignition circuits. On the other hand, it appears that the actual resistance of the wire wound resistors is of little importance in suppressing radiation in ignition circuits. Therefore, the radiation suppressing resistors according to the invention have a very low resistance and a predetermined inductance.

The low resistance of the resistors of the invention prevents flashover even though the resistors are made relatively short in comparison to prior resistors. The inductance in the wire wound resistors in accordance with the invention provides radiation suppression in the ignition circuits at least as good as that previously supplied by the higher ohmic value resistors of the past.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially broken away view of spark plug construction including an ignition circuit radiation suppression resistor therein constructed in accordance with the invention.

FIG. 2 is a partly broken away view of ignition circuit construction including an ignition circuit radiation suppression resistor constructed in accordance with the invention connected in a boot between a spark plug lead wire and a terminal adapted to be connected to a spark plug.

FIG. 3 is a graph illustrating ignition circuit radiation suppression permissible under the Society of Automotive Engineers recommendations and that obtained by the resistor of the invention, as illustrated in FIGS. 1 and 2 in three separate installations.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, the spark plug 10 includes an outer metallic body member 12, an inner ceramic insulating core 14, a pair of lower electrodes 16 and 18 and an upper electrode 20. The wire wound resistor 22 of the invention is electrically connected between the lower electrode 16 and the upper electrode 20 within the insulating core 14 of the spark plug 10 by the springs 25 and 27.

The spark plug structure 10 as shown is well known and will not be considered in detail herein. Further, it is known to place a wire wound resistor 22 between electrodes 16 and 20 to suppress radiation in an ignition circuit, in which the spark plug 10 is connected, on sparking between the lower electrodes 16 and 18.

It is also known to place a wire wound radiation suppression resistor 22 in an insulating boot construction 34 between a spark plug lead wire 32 and an upper spark plug electrode 20. One such boot constructure 34 is illustrated in FIG. 2.

As shown in FIG. 2, the ends of a wire wound radiation suppression resistor 22 are electrically engaged with the terminals 36 and 38. The terminal 36 is electrically connected to the spark plug lead wire 32, while the terminal 38 is open to provide a slip fit over an electrode 20 of a spark plug. Inner insulation 40 is provided surrounding the radiation suppression resistor 22, the terminal 36 and a portion of the terminal 38. The outer insulation 42 then encompasses the entire structure including the inner insulation 40, radiation suppression resistor 22, terminals 36 and 38 and the end of the spark plug lead wire 32 as shown.

Again, it is not new to place radiation suppression resistors in either spark plugs or spark plug boot constructions.

However, in the past it has been considered that the wire wound resistors must necessarily be of a resistive value such as 5,000 or 10,000 ohms to effectively suppress radiation on sparking between the electrodes 16 and 18 occurring in an ignition circuit. Accordingly, the wire wound resistors of the past have been so specified and limited and have thus been restricted in minimum length due to the possibility of flashover occurring in the wire wound resistors due to the voltage impressed between the electrodes 20 and 16 and the relatively large resistance of the wire wound resistors. In the past, the inductance of the wire wound resistors has been generally ignored by those interested in radiation suppression in ignition circuits.

The wire wound resistors 22 in accordance with the invention may be similar to the usual wire wound resistors in that the wire itself may be, for example, 0.001 inch or 0.0015 inch in diameter and approximately 18 feet long wound on a ceramic core which is, for example, 1/8 inch .+-. 1/16 inch in diameter and 3/8 to 3/4 inch long. The wire wound resistor 22 of the invention, however, differs from the usual wire wound resistors in that the wire wound resistors 22 have very low resistance as, for example, 15 to 30 ohms in contrast to the relatively large resistance of 5,000 to 10,000 ohms of previous wire wound resistors.

In addition, the resistor 22 is designed to have a known inductance as, for example, between 10 and 800 microhenries inductance when calculated in accordance with the known formula: ##EQU1## where: L = inductance in .mu. h

R = radius of the coil

N = number of turns in the coil

l = length of the coil

The low resistance of the wire wound resistor 22 prevents flashover from occurring in the wire wound resistor even though the resistor may be shorter and have the same number of turns thereon since the voltage drop across the resistor of between 15 and 30 ohms will be considerably less than the voltage drop across the previously used high ohmic value resistors.

Further, the specified inductance of the wire wound resistor 22 which is between 10 and 800 microhenries within the scope of the invention as set forth above and which is preferably between 30 and 45 microhenries as measured on a Tektronix LC 130 meter, provides the radiation suppression desired and previously considered obtainable only with wire wound resistors of higher ohmic value. The Tektronix meter is available as an off-the-shelf item from Tektronix in Beaverton, Oregon.

Thus, by providing a wire wound resistor of predetermined inductance rather than predetermined resistance, shorter resistors are possible with less chance of a flashover and the resistors may be made of less exotic alloy wire and will produce equivalent radiation suppression in ignition circuits.

The following chart shows actual tests of different wire wound resistors having the indicated radiation suppression in standard ignition circuits:

Db Attenuation ______________________________________ Frequency 20 50 100 150 200 250 MHz Standard Plug 16 16 16 16 16 16 Resistor Plug 10 0 0 0 0 0 30 Ohm .112 diameter .605 length 30-45.mu.h Resistor Plug 16 0 0 0 0 0 15 Ohm .112 diameter .385 length 30-45.mu.h Resistor Plug 12 0 0 0 0 0 15 Ohm .147 diameter .380 length 30-45.mu.h Resistor Plug 4 0 0 0 0 0 5,000 Ohm .112 diameter .685 length 70.mu.h ______________________________________

Further, in FIG. 3 the radiation suppression provided in standard ignition circuits using the low ohmic value wire wound resistor 22 having an inductance of 30 to 45 h, as measured on a Tektronix L.C. 130 meter, as compared against the Society of Automotive Engineers' recommended standards is presented. The line 24 shows the Society of Automotive Engineers' recommended standard, while the lines 26, 28 and 30 illustrate the equivalent results obtained by placing wire wound resistors 22 in the spark plugs 10 as shown in FIG. 1 in standard ignition circuits.

In the test producing line 28 on the graph of FIG. 3, the ignition circuit was a Ford Galaxie 1971, 351 cubic inch combustion engine ignition circuit having plain wire plug leads of 39 ohms resistance. The test for line 30 on the graph was conducted on a Chrysler 105 horsepower, 4-cylinder outboard marine engine as was the test for line 26. Both the Chyrsler engine circuits had 39 ohms resistance in the spark plug lead. In the case of line 30 there was a coiled wire lead while in the case of line 26 the lead was a plain metallic wire. All ignition circuits had a carbon core lead from the distributor to the ignition coil and resistors such as resistor 22 were used in the spark plugs in the ignition systems.

From the above indicated results it will be obvious that the low resistance, specified inductance wire wound resistor 22 of the invention is at least as efficient in suppression of ignition circuit radiation as the higher resistance resistors thought necessary in the past.

It is hypothesized that the inductance of the resistor 22, especially when place within the spark plug or in the spark plug boot closely adjacent the sparking electrodes provides a back electromotive force which tends to dampen oscillations set up in the ignition circuit on sparking of the spark plugs, which oscillations produce the objectional radiation. The radiation is thus suppressed providing the inductance is sufficient even though the resistance value of the resistors 22 is particularly low.

While one embodiment of the present invention has been considered in detail, it will be understood that other embodiments and modifications thereof are contemplated by the inventor. It is therefore the intention to include within the scope of the invention all embodiments and modifications as are defined by the appended claims.

Claims

What I claim as my invention is:

1. An ignition circuit including a spark plug having a pair of lower spaced apart electrodes, a spark plug lead wire connected in series with the spaced apart electrodes of the spark plug, and a wire wound ignition circuit radiation suppression resistor connected in series with the series connected spark plug lead wire and electrodes of the spark plug and positioned closely adjacent the electrodes of the spark plug, which resistor has an inductance of between 10 and 800 microhenries and a resistance of between 15 and 30 ohms.

2. Structure as set forth in claim 1 wherein the spark plug includes an outer metallic body portion, and an inner ceramic insulator core received within the outer body portion, and the first of the lower electrodes extends through the insulator core, the second of the lower electrodes is secured to the outer body portion in spaced relation to the first lower electrode, and the spark plug further includes an upper electrode secured to the insulator core in spaced relation to the first lower electrode and the wire wound radiation suppression resistor is positioned within the insulator core and connected at opposite ends to the first lower electrode and to the upper electrode.

3. Structure as set forth in claim 1, wherein an insulating spark plug boot construction is provided between the spark plug lead wire and the spark plug, the wire wound ignition circuit radiation suppression resistor is positioned within the boot construction which further includes terminals provided within the boot construction for connecting one end of the radiation suppression resistor to the end of the spark plug lead wire and connecting the other end of the radiation suppression resistor to the spark plug so that the radiation suppression resistor is connected in series between the spark plug lead wire and spark plug.

4. Structure as set forth in claim 1 wherein the resistor has an inductance of between 30 and 45 microhenries as measured on a Techtronic L.C. 130 meter.

5. Structure as set forth in claim 4 wherein the spark plug includes an outer metallic body portion, and an inner ceramic insulator core received within the outer body portion, and the first of the lower electrodes extends through the insulator core, the second of the lower electrodes is secured to the outer body portion in spaced relation to the first lower electrode, and the spark plug further includes an upper electrode secured to the insulator core in spaced relation to the first lower electrode and the wire wound radiation suppression resistor is positioned within the insulator core and connected at opposite ends to the first lower electrode and to the upper electrode.

6. Structure as set forth in claim 4, wherein an insulating spark plug boot construction is provided between the spark plug lead wire and the spark plug, the wire wound ignition circuit radiation suppression resistor is positioned within the boot construction which further includes terminals provided within the boot construction for connecting one end of the radiation suppression resistor to the end of the spark plug lead wire and connecting the other end of the radiation suppression resistor to the spark plug so that the radiation suppression resistor is connected in series between the spark plug lead wire and spark plug.