US2213478A

US2213478A - Ignition distribution system

Info

Publication number: US2213478A
Application number: US328475A
Authority: US
Inventors: Carl E Swanson
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-04-08
Filing date: 1940-04-08
Publication date: 1940-09-03
Anticipated expiration: 1957-09-03

Description

Sept, 3, 1940. c. E. SWANSON IGNITION DISTRIBUTION SYSTEM e 0 4 9 l l n m m m Q E x E Q Q Q ERRL.

Patented Sept. 3, 1940 UNITED? STATES PATENT OFFICE 20 Claims.

My invention relates to an improvement in aircraft ignition systems wherein it is desired to provide an ignition system which will function properly under the extremely adverse conditions to which these craft are subject.

Problems relating to ignition distribution on aircraft engines are much more difiicult than on other types of engines, and most of the troubles peculiar to aircraft installations can be traced to two important points of difference. These are, to wit, first, that the aircraft ignition systems must be completely shielded electrically by metallic conduit if high sensitivity radio receivers are used; and second, that aircraft ignition systems must operate throughout a wide range of atmospheric pressures.

As a consequence of the fact that shielded distribution must be employed, there are formed dead air spaces within the ignition system.

These dead air spaces become contaminated with undesirable and injurious gases, acids, fluids, and oils. Various designs have been employed in an effort to eliminate the presence of these harmful quantities. One very general eifort has been an attempt to produce a system which would be perfectly tight and thereby exclude the entrance of impurities from without. Aside from the fact that it is quite impossible to construct a practical shielding system which is perfectly tight,

to such a design would not offer relief from the gases and acids which are formed within the system due to certain electrical and chemical actions which are associated with the presence of air in regions subject to very high electrical potential gradients. Inasmuch as the presence of these gases, acids, fluids, and oils have the effect of lowering the electrical insulation of the system and that failures from these causes have been observed to occur most frequently within the space inside or the space adjacent to the spark plug shield chamber, numerous constructions have been used which have as their aim the shutting-off or blocking-off of these spaces from the remainder of the ignition system. In some 5 designs tight fitting rubber or Neoprene grommets have been positioned around the wire in the vicinity of the spark plug elbow and elsewhere in the system in an effort to prevent internal conduction or transmission of fluids to these parts. With much the same object in view other ignition distribution systems have been constructed with portions of the shielded system filled with special insulating oils, pastes, or solid materials. Still other constructions have used 58 Wire with the shielding woven tightly around the wire so as to minimize the amount of dead air space between the wire and the shielding. The fault common to all of these systems is that they do not provide ways and means of excluding and removing the aforementioned gases, acids, 5 fluids, and oils from the space inside and the space adjacent to the spark plug shield chamber.

A matter of particular concern in shielded ignition systems is the fact that spark plugs may and frequently do permit considerable quantities of 10 gases, vapors, and fumes from the combustion chamber to leak through the spark plug cores into the spark plug shield chambers and thence into the shielded ignition distribution system or so-called ignition harness. That such leakage 15 is appreciable in quantity is evidenced by the fact that certain spark plug manufacturers specify that leakages as high as one half cubic centimeter per minute per plug at one hundred and fifty pounds per square inch pressure shall 20 not be cause for rejection. Water vapor is one of the products of combustion found in exhaust gases, and when leaded gasoline is used, fumes of hydrobromic acid are also found therein. As

a result of core leakage these and other exhaust 25 vapors and fumes pass through the plug into the spark plug shield chamber. These gases and vapors together with the previously mentioned gases, acids, fluids, and oils which enter the ignition system from without or which are generated 30 from electrical and chemical actions within, accumulate in the ignition distribution system and weaken the electrical insulation thereof.

It is desired to call attention to the fact that while the presence of these impurities in any 5 part of the ignition distribution system is undesirable and injurious, they are particularly undesirable and injurious when present within the spark plug shield chamber and space adjacent to this chamber. It is within these spaces that 40 insulation failure or flash-over is most likely to occur. Other portions of the ignition distribution system can operate for long periods of time with these impurities present, but the space within the shield chamber wherein the distribution cables terminate must be kept free from these impurities, or failure of electrical insulation or flash-over will quickly result. Obviously failure of insulation or flash-over will cause a failure of the plug to operate. This in turn will cause 50 rough'operation and damage to the engine. Failure of insulation or flash-over with its consequent and attendant effect on the ignition system and engine operation require considerable outlay of expense in maintenance to correct and remedy the causes and results of such. In severe cases of this type of ignition trouble, thesafety of flight is imperiled.

Various methods could be employed to interconnect the spark plug shield chambers. The purpose of such interconnections would be to provide a way or means to introduce air free from impurities into all the spark plug shield chambers. This clean air would displace the air containing the impurities and thus provide relief from the troubles associated with the presence of contaminated air within the shield chambers of the spark plugs. Unfortunately such methods would require additional tubing or an additional conduit system of some sort which would in turn entail additional weight, costand problems associated with maintenance, servicing, and repair.

My invention, herein claimed, is a method, process, or art which will clear out contaminated air from within the spark plug shield chambers and spaces adjacent thereto and replace it with air free from harmful gases, acids, fluids, and vapors. In addition, my method, process, or art will prevent fluids and vapors present outside of the engine from entering the spark plug shield chambers and spaces adjacent thereto through leaks or openings in the boundaries of these regions or in the fittings or conduits attached thereto. It is a feature of my method, process, or art to transmit to and into these regions air free from harmful impurities and to provide a way or means by which the contaminated air may be removed from these regions. For reasons hereinafter explained this air which is transmitted to and into these regions is supplied at a pressure which is maintained constantly in excess of the atmospheric pressures existing outside of the ignition system. It is a further feature of my method, process, or art to utilize for the conduction of this air the type of ignition harness which already constitutes a conduit system to the spark plugs because through such a type of harness clean air can be transmitted to and into all the spark plug shield chambers and adjacent spaces without adding tubing or additional conduit systems of any sort.

Airplane engines and their associated ignition systems are more or less constantly covered with films of various kinds of fluids and oils. Some of these are sprayed on the engines during periods of cleaning and inspection. Others accumu late on the engines during periods of flight. In modern planes an anti-icer fluid consisting of a mixture of alcohol and glycerine is applied through nozzles or jets to the blades of the propellers While the airplane is flying in weather conducive to the formation of ice. This fluid sprays over the entire engine and ignition harness with great force from the propeller backwash. All these fluids together with water encountered when flying through rain and sleet have been found to enter the ignition system and cause failures of insulation and flash-overs particularly within the spark plug shield chambers. Rapid descent after a period of high altitude flying supplies an additional force which drives these fluids ,into the ignition system. On descending to lower altitudes there is a time interof these fluids from the ignition system is accomplished by the aforementioned feature of maintaining the pressure within the system constantly and adequately greater than the pressure existing without.

An airplane ignition system is also subject to troubles arising from electrical and chemical phenomena which take place within the system. Reference is here made to conditions and effects associated with the presence of electrical corona within the system. When air is present in regions subject to electrical potential gradients in excess of certain critical values, which in turn are dependent on air density, a phenomenon known as corona occurs. If the potential (voltage) of an electrical conductor be increased sufflciently a faint purplish light will appear at the surface of the conductor and a hissing sound will be heard. The phenomenon, of which the light and sound are indications is called corona. The presence of corona gives rise to the formation of ozone (O3) and an action takes place with nitrogen in the air to form nitric oxide (NO) and nitric dioxide (N02). Nitric oxide is only slightly soluble in water but if water or water vapor is present, nitric dioxide readily combines with it to form nitric acid (HNOs) and nitrous acid (HNOz). These acids have a deteriorating effect on the electrical insulation of the ignition system, but a more injurious effect for-consideration is the fact that these acids make any films of moisture that might exist in the system very good conductors. In particular, if such acid films exist within and on the parts within the spark plug shield chamber, electrical flash-over and so-called carbonization of the flash-over path is almost certain to result. When this happens, the common practice of running the engine at high speed to heat and to thereby dry out the spark plug shield chamber will not restore proper operation to the system, the carbonized path remaining a more or less permanent short-circuit.

The features and the method of my invention will suppress the corona, clear out the nitric oxide and nitric dioxide from within the system, and keep the system dry and free from acid fllms. As before mentioned, the advent and extent of the corona within the system is dependent on the density of the air within. As the density of the air is diminished the minimum potential gradient required to produce corona is diminished. Air density diminishes with an increase in altitude, therefore, the voltage required to produce corona also diminishes with an increase in altitude. By maintaining the air pressure within the ignition system in considerable excess of the air pressure without, that is, by supercharging the ignition system, I increase the density of the air within the system and thereby suppress the corona and the chemical actions associated therewith. Should there still be some nitric oxide or nitric dioxide formed within the system it will be forced out through holes or openings in the system provided for this purpose or forced out through the inherent leaks in the system. Furthermore, by keeping the interior of the ignition system dry, as my invention does, there will exist no moisture in the system to combine with the nitric dioxide to form nitric and nitrous acids.

The fact that the insulation strength of air' decreases rapidly with the decrease in air density which attends an increase in altitude, is a matter of great importance in modern aviation. For one-inch air gap and for plane electrodes, the

difference of potential for break down diminishes from about 83,000 volts at sea level to about 43,000 volts at an altitude of 20,000 feet. To compensate for this loss of insulation solely by means of increases in air gap clearances involves a large increase in the the system and a considerable increase of weight and cost. Now a supercharge pressure of five pounds per square inch over outside atmospheric pressure will maintain approximately sea level pressures within the spark plug shield chambers and all other spaces connected thereto while flying at an altitude of about 11,000 feet. In other words, at the altitude the above mentioned supercharge pressure compensates for a loss of about 23,000 volts per inch of air gap insulation. Higher supercharge pressures will, of course, give even greater insulation gains. As the airplane increases its altitude this type of air insulation failure makes its appearance in the spark plug shield chambers. It is also true that this type of failure frequently appears within magnetos and high tension distributors.

My invention is a method, process, or art which supplies air free from harmful ingredients at a pressure in considerable excess of atmospheric pressure to the spark plug shield chambers and spaces adjacent thereto utilizing for the conduction of this air the type of ignition harness which already constitutes a conduit system to the spark plugs.

The feature of using the ignition harness conduit system for the distribution of this supercharged air will simultaneously make the magneto and the high tension distributor recipient of all the benefits received by the spark plug shield chambers because these units normally have their metallic casings or radio shielding directly attached to the metallic conduit or radio shielding of the ignition harness. Construction of the metallic casings or radio shielding of the magneto and the high tension distributor must, of course, be such as to prevent excessive air leakage therethrough, or else these units will have to be shut off from the ignition harness by means of suitable air seals. Obviously if these units are shut ofl from the ignition harness, they will not receive the aforementioned benefits of the supercharge. Since the magneto and high tension distributor are subject to failures attendant upon loss of air insulation and the presence of gases, acids, and moisture, especially under conditions of exceedingly high altitude operation, construction of these units suitable for supercharging and attachment to the ignition harness is not only desirable but is essentially provident.

The air which is injected into the ignition harness and transmitted therethrough to the spark plug shield chambers, and to the magnetos and distributors if these be a part of the system, should be, as before stated, free from harmful ingredients. Best results can be obtained by providing for this purpose air which is not only clean, but air which has very low moisture content. For

' this reason it has been found desirable to draw this air from a region where the temperature is low and from a region which is protected from rain, sleet, snow and ice; and to pass this air through some chemical drying compound which will remove essentially all of the water vapor content. By'providing extremely dry air for injection into the ignition system, the possibility of having condensation of air borne water vapor take place within the system is eliminated, and the ability of the air to absorb and carry out physical dimensions of any moisture that might already exist within will be greatly increased. It is not to be inferred from these comments that it is always absolutely essential that the input air be subjected to a drying process. An air intake located in a region of low temperature is preferable to one located in a region of high temperature for the reason that the air from the low temperature region will, in general, have the least absolute humidity.

Activated alumina is one of several drying agents considered suitable for drying the input air. Activated alumina has the property of adsorbing moisture at substantially 100% efficiency until it has taken up between twelve and fourteen percent of its dry weight. Beyond this point it continues to adsorb, but at decreasing efliciencies, until saturated, at which time it contains twenty to twenty-five percent adsorbed water. This material is commercially available in a color indicator grade and is indigo in color when fully reactivated. During the adsorption of moisture the material changes progressively through pink to white, and therefore provides an indication of its degree of saturation when used in a transparent container. Reactivation is accomplished by heating the desiccant within the temperature range of 350 to 600 F. Flow rates of approximately 10 to 20 cubic feet per hour per pound of activated alumina are suitable for complete drying of air. Higher flow rates can be employed when complete drying is not required.

As before mentioned, some designs of ignition harnesses employ tight fitting grommets around the wires at various positions between -the ends thereof. These grommets pinch and compress the rubber insulation of the wires. Rubber loses much of its insulation strength when undermea chanical stress, and for this reason puncture of the insulation occurs frequently at these positions of stricture. In my system the need for such grommets does not exist.

In concluding this summary of the features of my invention, attention is directed to the fact that the continuous flow of air through the ignition harness to the spark plug shield chambers has a desirable cooling effect on the wire contained in these shield chambers and on the wire contained in the spaces adjacent thereto. The insulation on the wire in these regions is frequently found burned and charred due to the high temperatures existing within and near the spark plugs. This is especially true when engines are operating with high power output at high altitudes.

In the drawing forming a part of my specification:

Figure 1 illustrates diagrammatically my ignition distribution system in readiness for attachment to its internal combustion engine.

Figure 2 is a sectional view through a portion of the manifold, one of the flexible conduits connected thereto, and through a spark plug.

My ignition distribution system is shown embodying separate harnesses for two internal combustion engines. Obviously the same system can be used for a single engine or for a greater number of engines withoutchanging the invention.

I disclose a pair of magneto-distributor units ID or other suitable devices designed to generate electrical impulses to be transmitted to the engine spark plugs. The magneto-distributor units I may be of a type which can be supercharged, and air under pressure may be introduced into the casings of the units [0. In the case of magnetos and high tension distributors which are not suitable for supercharging, an air seal is provided in the fitting II which will prevent the flow of air from the flexible conduit element l2 to the magneto casing.

The flexible casing l2 may be of any preferred ordesired type for containing the ignition wires and includes a metallic braided casing or armor or other flexible metallic element which provides a shield for the ignition wires contained therein. Various types of this flexible shielding conduit have been constructed and these metallic hose sections ordinarily comprise a flexible tubular metallic conduit covered with one or more protective layers of braided metal. The flexible conduit portion I2 is connected by a suitable fitting 13 to the fitting l I and by a suitable coupling l4 to the metallic tube or conduit I5. The conduit 15 is shown connected at l6 directly to the ignition manifold 11, but it will be understood that other flexible sections such as 12 could be interposed in this conduit if it is desired or necessary.

The ignition manifolds l1 are substantially ring-shaped, but may have a section thereof broken away to facilitate the removal thereof. The ends IQ of the manifold I1 are sealed. Extending outwardly from the manifold are a series of nipples 20 threaded for engagement with nuts 2| on the end of the ignition flexible shielding conduits 22. The conduits 22 are preferably similar to the flexible conduit [2, but are of smaller diameter as they include but a single conductor. In the form of construction illustrated, the flexible conduits 22 comprise a flexible metallic hose or tubing 23 covered with one or more layers of braided metal or braided metal wires 24. These braided wires or braided metal strips form a continuous protective covering over the metallic hose and the conduit acts to shield the ignition wire 25 within the same.

The flexible conduit 22 is terminally connected at 26 to a rigid metallic elbow 21 secured by the lock nut 29 to the radio shielding forming a shield chamber 30 of a spark plug 31. The rigid elbow 21 is preferably provided with an outwardly extending flange 32 engaged by the lock nut 29 to form a substantially air-tight connection which does, however, usually provide a certain amount of leakage.

The spark plug 31 may be of any desired type to suit the internal combustion engine for which it is used. The central conductor 33 within the core is connected to the ignition wire 25 by means i of a suitable resilient connection 34. The ignition wire 25 is covered by an insulation covering 35 which leaves an air space between the wire and the conduits in which the wire is positioned. In other words, this insulation covering is of appreciably smaller diameter than the inner diameter of the spark plug shield chamber 30, the rigid elbow 21, the flexible conduit 22, the manifold l1, as well as the conduit l5 and flexible conduit I2. Thus a continuous air space is provided around the wire between the insulation 35 and the conduits in which it is contained from the magnetmdistributor unit In to the spark plugs 3|.

In order to provide air under pressure within the ignition distribution system described, I provide an intake pipe 36 leading from a relatively dry air supply such as the air within the wheel well or wing section. A cool air supply is desirable'because of its lower absolute moisture content. This air intake leads to an engine driven oil lubricated air pump 31 operatedwith one of the engines of the plane. In the case of multimotored planes, it is preferable to drive the pump 31 by means of the engine on the side of the plane opposite the door thereof, so that the operation of the engine will not interfere with the entrance or exit of persons into or out of the plane. Some planes are regularly equipped with an air pressure supply which may be used. The air pump 31 is connected by the conduit 39 to the oil separator 40. This separator may be provided with a drain line 4| to the engine crank case and is provided with a constrictor hole or passage 42 to limit the passage of air therethrough to a-minimum. The separator 40 is connected by the pipe line 43 containing the check valve 44 to a second oil separator 45. This second oil separator 45 is provided with a relief valve 46 which will open slightly when the air pressure in the system exceeds a certain predetermined amount such as five pounds per square inch. The. relief valve is connected to a surplus air exhaust pipe 41 through which the excessive air may be exhausted.

The separator 45 may be fllled .with flltering material such as copper wool 49 and cotton 56 through which the air must pass before entering the ignition system. From the separator 45 air is conducted through the pressure line 5| to the drive 52 containing drying material such as activated alumina, silica gel, or the like, indicated by the numeral 53, certain properties of which have been described.

After passing through the tank of drying material, the air passes through the conduit 54 to branch lines 55 and 56 leading to the ignition distribution system. Constrictor passages or openings 51 and 59 are formed in the branches 55 and 56 to limit the air escape in case of excessive leakage in either lineand pressure gauges or flow meters 60 are provided in the conduits 55 and 56 to measure pressure and the flow of air therethrough. The conduits 55 and 56 are connected to the fittings l3 at 6| as indicated in Figure 1 of the drawing.

The body of the second 011 separator 45 is connected by a pipe line 62 to an air hose connector 63. A check valve 64 is provided adjacent the air hose connection 63 to prevent the flow of air through this connection in a reverse direction, and a constrictor opening or passage 65 is provided in the line 62 between the valve 64 and the second oil separator 45.

When the plane is on the ground and the motor is not running, the system may be super-. charged by connecting the air hose connection 6-3 with the compressed air line at the airport.

The constrictor opening 65 limits the flow of air from the relatively high pressure airport air line,

and the relief valve 46 maintains a constant pressure differential between the interior of the conduit system and the outer atmosphere. Excessive air from either the airport air line or the pump 31 is exhausted by means of the air relief valve 46.

My invention has been subjected to severe laboratory and flight tests. In the laboratory, the entire ignition manifold together with all the individual conduits to the spark plugs, and the spark plugs themselves, which were in turn fitted to carbon dioxide bombs, were completely submerged in water for twenty-five consecutive hours. At the end of this period the system was still functioning perfectly. A rigorous examination was then made of the interior of the system to determine whether or not any moisture was present therein. The examination disclosedthat the entire system was perfectly dry. Some water short period of time was then purposely admitted within the system and the submersion test was resumed. [After a the interior of the system was re-examined and again found to be perfectly dry, thus proving that the method functioned to remove moisture from within. By special permission of the Civil Aeronautics Authority, my

invention was then installed on one engine of a transport airplane regularly operating from Chicago, Illinois to Seattle, Washington. After and throughout more than four hundred hours of such operation under all conditions of flight and weather, the interior of the ignition distribution system and the spark plug shield chambers remained entirely free from all moisture, fluids, oils, and other impurities. Many of the flights made during this period were made under conditions of heavy rainfall, or under conditions when much anti-icer fluid was used. During the first two hundred fiftyhours of the aforementioned flight test, the ignition harness on the other engine of the same airplane admitted sufficient moisture and anti-leer fluid to necessitate frequent draining of the manifold and drying of several of the leads within the shield chambers. Both ignition harnesses had like construction but during the first two hundred fifty hours of the flight testonly the oneignition system was recipient of the benefits of my invention.

Certain leakages occur in any conduit system such as has been described, and these leakages may be at various points throughout the system. Leakages most often occur, however, adjacent the spark plugs, as at these points the conduit is most often disconnected. If insuflicient leakage is present in a system, it may be purposely provided. Such leakage is best provided by openings adjacent the spark plugs or in or adjacent the shield chambers. As an illustration of such an opening, I disclose the hole 66 in the elbow 21. This hole is merely an illustration of how such a hole might be positioned.

In the discussion of my invention, herein given, I have frequently referred to spark plug shield chambers. When referring to a spark plug shield chamber I refer to the region or space within the spark plug shielding.

In some constructions the spark plug shield is integral with the spark plug itself. In such types of construction the spark plug shield chamber is that region within the spark plug shield or socalled spark plug barrel. An example of such type of construction is the construction illustrated in Figure 2 of the drawing.

In other constructions the spark plug shielding is not integral with the spark plug itself but is a cap, bonnet, housing, or a covering, which is positioned, fitted, attached, or placed over and around the portion of the spark plug projecting outwardly from the cylinder head. In this latter type of construction the spark plug shield chamber is the region or space within this cap, bonnet, housing, or covering.

Electrical failure at the wire terminal might take place either within the spark plug shield, the chamber .or within the adjacent space. In the presence of impurities, current frequently travels from the end of wire 25 along the insulation sleeve usually encircling this wire end externally of the insulation 35, grounding to points on the inner surface of the conduit attached to the spark plug barrel.

In accordance with the patent statutes, I have described the principles of construction and operation of my invention; and while I have enleasing air from the deavored to set forth the best embodiment thereof, I desire to have it understood that this is only illustrative of a means of carrying out my invention, and that changes may be made within the scope of the following claims without departing from the spirit of my invention.

I claim:

1. A method of supercharging electrical ignition systems for internal combustion engines having a container enclosing the ignition system, the container having leaks therein the method consisting in supplying air at a pressure in excess of that of the surrounding atmosphere to the space between the ignition system and the container enclosing the ignition system, maintaining said pressure within the container, and recontainer through the leaks in the container.

2. A method of supercharging electrical ignition systems for internal combustion engines having a container enclosing the ignition system, the method consisting in cleaning and drying air, supplying the clean dry air at a pressure in excess of that of the surrounding atmosphere to the space between the ignition system and the container enclosing the ignition system, maintaining said pressure within the container, and releasing the air from the container.

3. A method of supercharging electrical ignition systems for internal combustion engines having a container enclosing the ignition system, the method consisting in supplying air at a pressure in excess of that of the surrounding atmosphere to the space between the ignition system and the container enclosing the ignition system, maintaining said pressure within the container, and releasing the air from the container in such a manner as to cause fiow of air throughout the container.

4. A method of supercharging electrical ignition systems for internal combustion engines having a container enclosing the ignition system, the method consisting in cleaning and drying air, and supplying the clean dry air at a pressure in excess of that of the surrounding atmosphere to the space between the ignition system and the container enclosing the ignition system, maintaining said pressure within the container, and releasing the air from the container in such manner as to cause flow of air throughout the container.

5. In combination with the ignition system of an internal combustion engine, a closed housing.

surrounding the ignition system, said ignition system not completely filling said housing, leaving space for air therein, said housing having inherent leaks therein, a source of supply of compressed air, and means connecting said compressed air supply to said closed housing to introduce air into the space between said closed housing and said ignition system at a pressure in excess of that of the surrounding atmosphere.

6. In combination with the ignition system of an internal combustion engine, a closed housing spaced from and surrounding the ignition system, said housing providing holes for leakage, a. source of supply of compressed air connected to said housing to introduce compressed air between said ignition system and said closed housing, and means co-operating with said source of compressed air maintaining the air so introduced at a pressure in excess of that of the surrounding atmosphere.

7. In combination with the ignition system of an internal combustion engine, a closed housing surrounding the ignition system, said ignition system not completely filling saidhousing, leaving space for air therein, means compressing air, drying means connected to said air compressing means for drying compressed air, means connecting said air drying means to said closed housing to introduce dried compressed air to the space between the said closed housing and ignition system, and means co-operable with said air compressing means maintaining the dried air so introduced at a pressure in excess of that of the surrounding atmosphere.

8. In combination with the ignition system of an internal combustion engine, a closed housing surrounding the ignition system, said ignition system not completely filling said housing, leaving space for air therein, and said housing having leaks therein, means compressing air, means drying compressed air connected to said air compressing means to receive air therefrom, means connecting said air drying means to said closed housing to introduce dried compressed air to the space between said closed housing and said ignition system, and means co-operating with said air compressing means maintaining the air in said housing at a pressure in excess of .that of the surrounding atmosphere.

9. In combination with the ignition system of an internal combustion engine, a closed housing surrounding the ignition system, said ignition system not completely filling said housing, leaving space for air therein, said housing having restricted openings therein, air compressing means, air drying means for drying compressed air, means connecting said compressing means, drying means, and said closed housing to introduce the dried compressed-air to the space between said closed housing and said ignition system, means co-operating with said air compressing means maintaining the dried air so introduced at a pressure in excess of that of the surrounding atmosphere. 1

10. In combination with the ignition system of an internal combustion engine, a closed housing enclosing the ignition system, said ignition system not completely filling said housing, leaving space for air therein, air compressing means, air drying means, air conducting means connecting said compressing means and said air drying means, means connecting said air drying means to said housing, and means situated in said conducting means efiecting' a release of excess air and co-operating with said compressing means for maintaining the air in said drying means and in said housing at a pressure in excess of that ot the surrounding atmosphere.

11. In combination with the ignition system of an internal combustion engine, a closed housing enclosing the ignition system, said ignition system not completely filling said housing, leave ing space for air therein, air compressing means, air cleaning means for cleaning the compressed air, air drying means for drying the compressed air, means conducting compressed air from said compressing means to said cleaning means, means connecting said cleaning means to said drying means, means connecting said drying means to said housing, and means interposed between said compressing means and said cleaning means efiecting a release of excess air and co-operating with said air compressing means to maintain the air in the dryingimeans and in said closed housing at a pressure in excess of that of the surrounding atmosphere.

12. In combination with the ignition system of an internal combustion engine, a closed housing enclosing the ignition system, said ignition system not completely filling said housing, leaving space for air therein, said housing having restricted openings therein, air compressing means, air drying means, means conducting compressed air from said compressing means to said air drying means, means connecting said air drying means to said closed housing to conduct compressed dried air to said housing, means situated in said conducting means effecting a release of excess air and co-operating with said compressing means to maintain a pressure in said drying means and said closing housing in excess of that of the surrounding atmosphere.

13. In combination with the ignition system of an internal combustion engine, a closed housing enclosing the ignition system, said ignition system not completely filling said housing,-leaving space for air therein, said housing having restricted openings therein, air compressing means, air cleaning means, air drying means, means conducting compressed air from air compressing means to said air cleaning means, means connecting said air cleaning means to said air drying. means to conduct cleaned air to said air drying means, means connecting said air drying means under pressure greater than to said closed housing to conduct cleaned dry air to saidhousing, means interposed between said compressing means and said cleaning -means eflecting a release of excess air and co-operating with said air compressing means to maintain the air in said drying means and in said housing at a pressure in excess of that of the surroundin atmosphere.

14. In combination with an internal combustion engine having spark plugs provided with shielding, air compressing means, and means connecting said compressing means and said shielding to conduct air under pressure to the space within said shielding, said shielding having means providing leakage from the space within said shielding, and means co-operable with said air compressing means maintaining the air within said shielding at a pressure in excess of that of the surrounding atmosphere.

15. In combination with an internal combustion engine having spark plugs, an individual shield for each spark plug, each shield enclosing a portion of its associated spark plug, a conduit connected to each said shield with a connection providing leaks and means maintaining air within said conduit and shields under pressure greater than that of the surrounding atmosphere.

16. In combination with an internal combustion engine having spark plugs, an individual shield for each spark plug, each shield enclosing a portion of its associated spark plug, a conduit connected to each of said shield, each said shield having minute openings therein, and means maintaining air within said conduit and shields v that of the surrounding atmosphere.

17. In combination with an internal combustion engine having spark plugs, an individual shield for each spark plug, each shield, enclosing a portion of its associated spark plug, a conduit connected to each said shield, said conduit having minute openings therein adjacent said shields, and means maintaining air within said conduit and shields under pressure greater than that of the surrounding atmosphere.

18. In combination with an internal combustion engine having spark plugs, a hollow shield enclosing said spark plugs, said shield having holes in the "wall thereof, and means creating and maintaining a pressure differential between the interior and exterior of said hollow shield.

19. In combination with an internal combustion engine having spark plugs, a hollow shield enclosing a portion of said spark plugs, said shield having holes in the wall thereof, and means creating and maintaining a pressure differential between the interior and exterior of 10 said hollow shield.

20. In combination with an airplane engine having spark plugs, a source of supply of electrical current, and .ignition wires connecting said source of current supply and said spark plugs, a conduit system enclosing a portion of said ignition wires and having minute leaks therein, said conduit being of such dimensions as to provide air space between said conduit and said wires, and means maintaining a pressure differential between the interior and exterior of said conduit system.

CARL E. SWANSON.

CERTIFICATE OF CORRECTION. Patent No. 2,215, L78. September 5, 191m.

CARL E. SWANSON.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, first column, line 114., for the article "the" first occurrence, read --this--; page 14., second column, line 27, for "drive 52" read --drier 52-; page 5, second column, line 11, claim 1, after "therein" insert a coma; page 6, second column, line 52, claim 15, after "leaks" insert a comma; line 59, claim 16, strike out "of" before "said"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5th day of November, A. D. 19140.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION. Patent No. 2,215,1(723. September 3, 191 0.

CARL E. SWANSON.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line lip, for the article "the" first occurrence, read -this-; page 14., second column, line 27, for "drive 52 read --drier 52--; page 5, second column, line 11, claim 1, after "therein" insert a comma; page 6, second column, line 52, claim 15, after "leaks" insert a comma; line 59, claim 16, strike out "of" before "said"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record .of the case in the Patent Office.

Signed and sealed this 5th day of November, A. D. 191w.

Henry Van Arsdale (Seal) Acting Commissioner of Patents.