US2163624A - Radio shielding means - Google Patents

Description

Jw ne 27; 1939. M. F. PETERS 2,163,624

RADIO SHIELDING MEANS Filed May 11, 1938 2 Sheets-Sheet l INVENTOR MELV/LLE F. PETERS BY W mam- ATTORNEY June 27, 1939. M PETERS 2,163,624

RADIO SHIELDING MEANS Filed May 11, 1938 2 Sheets-Sheet 2 INVENTOR MELV/LLE F. PETERS ATTORNEY Patented June 27, 1939 I UNITED STATES PATENT OFFICE 7 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3'10 G. 757) This invention relates to means for shielding the ignition system of an internal combustion engine to prevent interference with the operation of radio receiving sets due to energy-radlated from such ignition system, and more particularly to apparatus adapted to be used on an aircraft in conjunction with the metal cowiing for the engine and the metal of the nacelle.

Among the several objects of this invention are:

To provide simple and effective means for preventing radiation from the ignition system of an internal combustion engine; I

, To provide means for shielding an ignition system wherein the metal of surrounding parts of the structure in which the ignition system is installed assists in the shielding function;

To provide radio shielding means that will introduce no difilculties due to retention of heat by the shielding means;

To utilize readily formed shapes of foraminous electrically conducting material around certain of the partsto be shielded.

Further objects of this invention will become apparent from the description that follows.

In the drawings: Fig. 1 discloses one embodiment of my inven tion wherein the magneto and certain other elements are enclosed in a foraminous electrically conducting shield and the ignition leads are grounded thereon;

Fig. 2 shows a variation of my novel shielding means wherein substantially flat members in the form of shielding walls are disposed on opposite sides of the magneto and certain other parts and are grounded on the engine cowiing;

Fig. 3 shows novel means'for suppressing very short waves.

In Fig. 1 there is depicted, by way of illustration, an aircraft engine 3 mounted in a metal nacelle l and having disposed around it metal cowiing 5. Ignition current is suppliedto the cylinders 6 by way of ignition leads I from 'a magneto 8. grounded to the engine 3 and a foraminous metallic enclosure l0 substantially in the form of a cylinder closed at one end is disposed around the magnetos 8 with the open end thereof closed by and grounded to the ring 9. That portion of each ignition lead I that lies outside the member III is enclosed in a conductive shielding element ii that is grounded at one end to the engine adjacent the respective spark plug and at the other end to the ring 9 or to the member ID, as is most convenient in view of the position of the lead. While the return current could pass through the engine back to the magneto the well known proximity effect results in its following the path through the shielding elements II. It is obvious that all radiation from the magnetos A ring 9 "is disposed around and.

. of several frequencies.

and associated devices from those parts of the leads I within the member I 0 will be eflectively intercepted by the member III. the ring 9 and the portion of the engine structure within the member ID. It is known that if the return current passes through the engine there is resultant radiation and interference with radio equipment adjacent thereto.

The embodiment of my invention shown in Fig. 2 differs from that in Fig. 1 in that, the

foraminous conducting member 15 extends completely across the space within cowiing 5 in the form of a wall, rearwardly of the magneto 8. A second wall .or foraminous shielding member It, extends from the cowiing to engine 3 forwardly of magneto 8, it being understood that both of members l5 and l2 are electrically grounded to the cowiing 5 and that member I2 is also grounded to engine 3. Here, as in Fig. 1, the ignition lead I is shielded exteriorly of the space between members i5 and I! by well-known flexible shielding elements II that are grounded at one end to the engine and at the other end to the foraminous members.

' It has been found that adequate shielding is had when the mesh of members such as I2 is sufficiently large that there is no appreciable increase in air resistance due thereto. There are numerous advantages inherent in mypresent invention not found in the types of shielding heretofore known wherein the ignition wires are carried in a rigid shielding manifold. Among such advantages are ease of removing and replacing ignition leads, the absence of outlets that may result in bends in the leads, ready access of air to the shielded parts to carry off heat conaround the ignition system in such position that radiation therefrom is prevented from passing out into space by repeated reflection from such metallic parts. That is; the auxiliary apparatus such as carburetors, pumps, oil lines, etc., all aid in the shielding and if theleads are' shielded from the magneto to the spark plug most of the noises are cut ofi ,even if the magneto is not itself shielded although it is preferable that this be done.

The radiation from an ignition system consists That resulting from the' ignition current has a frequency of from 4 to megacycles and is adequately suppressed by the shielding means above described. However, the capacity of the spark plug is such that it sets up waves having a length of around one meter, that is, less than the usual length of the shielding apparatus, and radiation of such waves is not prevented by any of-the shielding means heretofore used so far as is known to me. However, I have found that if a resistor iii of suitable value be inserted between the center electrode ll of the spark plug and the conductor IB of the ignition lead, that these waves of length less than the length of the shielding apparatus are likewise suppressed. If such resistor be of too great value, it tends to damp out the long waves and the ignition spark is too weak. My experiments have shown that if such resistor have a value of about 100 ohms it renders the very short waves aperiodic and effectively prevents radiation thereof, while it does not appreciably affect the strength of the ignition current.

The invention herein described and claimed may be used and/or manufactured by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. Radio shielding means for the ignition system of an internal combustion engine, said system including a source of ignition current, comprising a plane ring disposed around the engine between the cylinders thereof and said source, said ring being mechanically and electrically con-o nected to the engine, a foraminous electrically conducting member cooperating with said ring and the engine to enclose said source and grounded on said ring, conducting leads extending from said source through said ring and other leads from said source extending through said member, and a shielding element around each such lead, each said element being grounded at one end on said ring or on said member, respectively, and at the other end to the ground connection of the respective conductor.

2. Radio shielding means ror the ignition system of an internal combustion engine having combustion chamber means and spark plug means therein, said system including a source of ignition current, comprising a plane ring disposed around the engine between the said combustion chamber means and said source, a foraminous electrically conducting member cooperating with said ring and engine to enclose said source and grounded on said, ring, conducting leads extending from said source through said ring to said spark plug means, a resistive element between each conducting lead and the spark plug means to which it supplies current, and a shielding element around each such lead, each said shielding element being grounded at one end on said ring and at the other end on the spark plug shell.

3. Radio shielding means for the ignition system of an aircraft internal combustion engine, said system including a source of ignition current, comprising the combination with cowling around said engine of an electrically conducting ioraminous screen extending across the space within said cowling at one side of said source and grounded to said cowling, a second like screen on the other side of said source extending from said cowling to said engine and grounded to both, and shielding elements around electrically conducting members extending through either said screen, said shielding elements being each grounded at one end to the respective screen and having the other end also grounded.

4. Radio shielding means for the ignition system of an aircraft internal combustion engine having spark plugs, said system including a source of ignition current, comprising the combination with cowling around said engine of an electrically conducting foraminous screen extending across the space within said cowling at one side of said source and grounded to said cowling, a second like screen on the other side of said sourcev extending from said cowling to said engine and grounded to both, conducting leads from said source to said spark plugs, a resistive member in series between each such lead and its respective spark plug, and a shielding element around each said lead grounded to a said foraminous member and to the shell of the respective spark plug.

5. Radio shielding means for the ignition system of an aircraft internal combustion engine having spark plugs, said system including a source of ignition current, comprising the combination with cowling around said engine of an electrically conducting foraminous screen extend-v ing across the space within said cowling at one side of said source and grounded to said cowling, a second like screen on the other side of said source extending from said cowling to said engine and grounded to both, conducting leads from said source to said spark plugs, a resistive member in series between each said lead and its respective spark plug, the value of said resistive member being suflicient to suppress waves of the order of those due to the capacitance of the spark plug but insuflicient to reduce the current detrimentally, and a shielding element around each said lead grounded to a said foraminous member and to the shell of the respective spark plug.

6. Radio shielding means for the ignition system of an aircraft internal combustion engine having spark plugs, said system including a source of ignition current, comprising the combination with cowling around said engine of an electrically conducting foraminous screen extending across the space within said cowling at one side of said source and grounded to said cowling, a second like screen on the-other side of said source extending from said cowling to said engine and grounded to both, conducting leads from said source to said spark plugs, a resistive member in series between each said lead and its respective spark plug, the value of said resistive member being suflicient to suppress waves of length not substantially greater than the distance between a said forarninous member and the spark plug, and a shielding element around each said lead grounded to a said 'foraminous member and the spark plug shell.

7. Radio shielding means for the ignition system of an internal combustion engine, said system including a source of ignition current, comprising a foraminous electrically conducting member cooperating with said engine substantially to enclose said source and grounded through said engine, conducting leads extending from said source through said member and a'shielding element around each such lead, each said element being grounded at one end on said member and at the other end to the ground connection of the respective conductor.

MELVILLE F. PETERS.

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