> o@ @a 1946- F. x. RETTENMEYER - 2,408,881 ULTRA HIGH FREQUENCY IGNITION SYSTEM Filed May 29, '1942 5 1mam '111111114 r11',,11111111.14 ßnventor 0X1 M egel', (Iftomeà 2,408,881 Patented Oct. 8, 1946 UNITED vSTATES PATENT OFFICE 2,408,881 ULTRA HIGH FREQUENCY IGNITION SYSTEl‘fI v Francis X. Rettenmeyer, Moorestown, N. J., as signor to Radio Corporation of America, a cor poration of Delaware Application May 29, 1942, Serial No. 445,046 20 Claims. (Cl. 315-39) l This invention relates generally to ignition systems for internal combustion engines and par ticularly to ignition systems utilizing voltages of ultra high frequency suitably coupled to spark ing devices comprising resonant circuits includ 2 method of and apparatus for generating the re quired potentials at ultra high frequency, trans mitting these potentials over a low impedance transmission line, and applying the ultra high frequency potentials to a resonant circuit includ ing a spark gap which is located within the com bustion chamber of the internal combustion en gine. A further object of the invention is to provide an improved method of and means for interference is generated by the high potentials and comparatively low frequencies involved. Nu 10 pulsing the output of an ultra high frequency os~ cillator to provide extremely high instantaneous merous ignition shielding devices are known for power output with equipment of low continuous decreasing the inherent radio interference in power rating. Another object of the invention i's such systems, but such devices have limited util to provide an improved method of and means for ity due to wide variations in moisture, pressure, and temperature gradients encountered in air 15 coupling successively high potentials of ultra high frequency to spark gaps within combustion cham craft work. For example, when an airplane flies bers by means of individual low impedance coax through a cloud, considerable condensation may ial cables suitably coupled to the equivalent of occur within the shielding surrounding the high any odd multiple of quarter~wave resonant de~ tension spark plug leads, resulting in reduced vices, each including a spark gap. .Another ob eilìciency of the ignition system. Moreover at ject is to provide a new and improved spark plug. low pressures spark-over may occur. Various A further object is to provide an improved and methods, including the use of air pumps, have 'simplified means for removing moisture accumu been devised for exhausting the moisture, or in lations within the ignition transmission lines. creasing the air pressure, within the high tension electrostatic shielding, but ‘the additional appa 25 The invention will be described by reference to ratus required adds weight and has other serious - the drawing of which Figure 1 is a schematic cir cuit diagram of one embodiment of the invention: disadvantages. Figure 2 is an elevational view of an improved The instant system utilizes the advantages of low impedance transmission line showing louvres low inherent radiation from low impedance ul tra high frequency transmission lines and, in ad~ 30 for exhausting moisture accumulations, and Fig~ ure 3 is a cros~s~sectional view of Figure 2. Sim~ dition, provides a simple and eflicient means, for ilar reference numerals are app-lied to similar ele removing continuously the moisture which ac ments throughout the drawing. cumulates within the outer shield of the trans Referring to Fig. l., a power genera-ting source mission line. Ey utilizing ignition voltages of ultra-high frequency which are considerably 35 l which may be a suitable D.-C. generator driven by the internal combustion engine is connected above the normal frequencies used for radio to a voltage divider 2, which is grounded at some transmission, and by transmitting the ignition intermediate point. If extremely high. anode voltages over low impedance transmission lines voltages are required, an A.-C. generator and connecting an ultra high frequency generator to the individual spark plugs of the internal com 40 transformer may be substituted for the 13.--C. power supply and voltage divider. Potentials de", bustion engine, radio interference is reduced to rived from the voltage divider 2 are applied to a practical operating level. the electrodes of an ultra high frequency oscil Various methods and apparatus well known in lator tube 3 which includes an ultra high irc» the art may be utilized for generating the ultra quency oscillator circuit comprising a predetern high frequency potentials required for satisfac mined section of coaxial cable 4. However, the tory ignition. It should be understood that the oscillator circuit may be of any other type known apparatus described herein is merely typical of in the art. At extremely high frequencies, a mag~ the type of equipment which will provide sat ing the spark gaps. ` Present ignition 'systems for aircraft use have the distinct disadvantage that considerable radio netron circuit provides satisfactory power out isfactory operation, and that the invention is not 50 put. Pulsing of the oscillations generate-d in the limited t0 the specific apparatus disclosed. thermionic tube circuit is accomplished by means Among the objects of the invention are to pro vide a new and improved method of and appa of a suitable commutator device 5 connected in series with the vacuum tube anode power lead ratus for ultra high frequency ignition in inter connected to the voltage divider 2. In practice, nal combustion engines. Another object of the invention is to provide a new and improved 55 the pulsing commutator may be driven by the 2,408,881 3 interna1 combustion engine, and synchronized with the engine cylinder ñring. High potentials of ultra. high frequency, derived by suitable cou pling to the oscillatory circuit 4, are applied to the rotating element 8 of a contact or capacity type distributor which may be also driven by the 4 the transmission cable. The openings 54 may be arranged at desired intervals around the sheath 5| or, if desired, may be limited to the lower sur faces thereof. Fig. 3 illustrates more clearly the louvre formation. The term “transmission line” as used in t-he internal combustion engine and the switching appended claims is intended to include all known rate of which is synchronized with the switching types of lines, such as for example, coaxial lines, of the pulsing commutator device 5 described balanced lines, single and multi-conductor lines, heretofore. The stationary elements l and 'l' lO and Wave guides. Any suitable known means may of the distributor are connectedihrough a plu be provided for coupling the spark gaps and the rality of individual low impedance transmission distributor to the particular type of transmission lines 8 and B’ which may be conventional co line utilized. axial cable, to a plurality of special spark plug I claim as my invention: devices 9 and 9'. The spark plug have 1. An ignition system including a source of a length which is the equivalent or any cdd mul~ ultra-high frequency oscillations, means for puls tiples of quarter-wave linesl which terminate in ing said oscillations, at least one spark gap de the spark gaps I0 and I0’. The ends of the outer vice comprising a resonant line including one of conductors 9, 9’ of the plugs remote from the said gaps and upon which standing waves may spark gaps. Il), l0', respectively, are short~cir- 20 be established at said ultra high frequency, and cuited to the respective inner conductors ll, Il’ means including separate low impedance trans to provide voltage maxima at the spark due mission lines alternately connecting said source to standing waves thereby provided in the plugs. to each of said spark gap devices at a point inter The short-circuited conductors are preferably mediate a voltage node and voltage loop of said entirely closed to provide a gas seal. It should 25 standing waves on said resonant line. he understood that wave guides may be used as transmission lines, and that they may be coupled 2. An ignition system including a source of ultra-high frequency oscillations, means ior puls to the distributor and spark plugs in any well ing said oscillations, at least one spark gap de known manner. The connection from the low vice comprising an odd multiple of a quarter impedance transmission line 8 passes through. the wave line including one ci said gaps, and means gas tight gasket I3 to the quarter-wave line ll, including separate low impedance `transmission and should preferably be made at a point on the lines successively connecting said source to each line II to obtain maximum power transfer when of said spark gaps. a spark occurs at the spark gap lll. The gasket 3. An ignition system including a source of I3 may be either conductive or insulation, dem ultra-high frequency oscillations, means for puls pending upon whether .it is located at a voltage ing said oscillations, a plurality of spark gap de node, or at some other point. It should be unn vices each comprising an odd multiple of quarter derstood that the mechanical construction of the wave lines including one oi said gaps, low im quarter»\vave spark plug is not a limiting factor pedance transmission lines connected to each of of this invention and that any arrangement other 40 said devices, and switching means for selectively than that shown which provides the equivalent connecting said source to each of said low im of an odd multiple of a quarter-wave load circuit will be equally satisfactory. The plug construc tion should preferably be adapted to he readily demountable from the cylinder head may include the conventional yscrew type spark plug supporting means. The pulsing of the oscillator output by the pulsing commutator will provide an oscillator output of extremely high instantaneous power » characteristics from an oscillator tube of low pedance transmission lines. 4. Apparatus of ,the type described in claim 3 including means for synchronizing the operation f ` of said pulsing means and said switching means. 5. Apparatus of the type described in cla-im 3 characterized by the fact that the frequency o_î said oscillations is in excess of 500 megacycles. 6. Apparatus of the type described in claim 3 characterized by the fact that said source of oscil lations includes a thermionic tube and a section continuous power rating. Any other well known of coaxial cable of predetermined dimensions, pulsing means, which may be suitably synchro 7. An ignition system for an internal combus nized, would be equally satisfactory. As ex tion engine including power generating means, plained heretofore, ‘the -low impedance transmisn 55 ultra-high frequency generating means including sion line 8 will provide minimum radiation. The a thermionic tube and a resonant section of co entire generator system including the oscillator, axial cable, pulsing means, means including said the resonant circuit, the pulsing commutator, the pulsing means for connecting said power generat distributor and the power generator should prei ing means to said ultra~high frequency generat» erably be enclosed within an electrostatic shield 60 ing means, a plurality of spark gap devices each i2. The sheaths 8 and 8' of the low impedance comprising an odd multiple oi quarter wave lines transmission line should preferably be gounded to including one of said gaps, low impedance trans~~ the electrostatic shield and to the common ground mission lines connected to each of said devices, of the internal combustion engine. switching means for connecting selectively said Referring to Fig. 2, a modiñcation of »the low ultra-high frequency generating means to each impedance transmission cable includes an inner conductor 52 connected at a suitable point to the quarter-wave transmission line l l comprising a spark plug. The outer concentric sheath 5| in cludes a plurality of louvres 53 having openings 54. If a column of air is directed coaxially along the transmission line in the direction indicated by the arrow, low pressure areas will occur in the vicinity of each of the openings 54, providing satisfactory exhaustion of the moisture Within of said low impedance lines, and means for syn~ chronizing the opera-tion of said pulsing means and said switching means. 8. Apparatus of »the type described in claim 'l characterized by the fact that said ultra-high frequency is in excess of 500 megacycles. 9. Apparatus of the 4type described in claim 7 including grounded electrostatic shielding means enclosing said system. 10. Apparatus of the type described in claim 3 2,408,881 5 6 including grounded electrostatic shielding means enclosing said system. 11. In an ultra-high frequency ignition system for internal combustion engines including a plu including means for connection to a transmission rality of spark gap devices each comprising an odd multiple of quarter Wave lines including said gaps, the method including generating oscilla tions in excess of 500 megacycles, pulsing said line, characterized by .the fact that said yconnect ing means is connected to said center electrode at a point providing effective impedance match ing between said transmission line and said spark gap. 16. Apparatus of the type described in claim 14 including means for connection to a transmission oscillations, switching said pulsed oscillations, line, 4characterized by the fact that said connect successively transmitting said switched oscilla tions at low potential to each of said spark gap devices and successively applying said low poten ing means is connected to said center electrode at a point providing effective impedance matching between said transmission line and said spark tial oscillations to each of said devices at a point gap. intermediate a voltage loop and a voltage node 17. Apparatus of the type described in claim 13 of said quarter wave line~ 15 including threaded mounting means for support 12. In an ultra Ihigh frequency ignition system ing said cylindrical electrode. including an ultra high frequency generator, a 18. An ignition system including a source of plurality of sparking devices and individual low ultra-high frequency oscillations, a plurality of impedance coaxial lines connecting said generator ignition devices each comprising a resonant struc `to said sparking devices, spaced apertures in said 20 ture upon which standing Waves may be estab coaxial lines, air deflecting means in operable re lished at said ultra-high frequency to raise sub lation to said apertures, and means including said stan-tially the temperature at a predetermined deflecting means for varying the air pressure point in said device, :and means -including separate within said coaxial lines. low impedance transmission lines connecting said 13. A tuned Spark plug for ultra-high frequency source to each of said ignition devices. ignition voltages including an elongated center 19. An ignition system including a source of electrode, a -coaxially disposed :cylindrical elec ultra-high frequency oscillations, means for puls trode surrounding said center electrode, means ing said oscillations, at least one ignition device connecting one end of said center electrode to comprising a resonant structure upon which the proximate end of said cylindrical electrode, 30 standing waves may be established at said ultra means forming a Spark gap between the remain high frequency to raise substantially the temper ing ends of said electrodes, and .connecting means ature at a predetermined point in said device, and for said ultra-high frequency voltages interme means including separate loW impedance trans diate the ends of said center electrode and to said mission lines connecting said source to each of cylindrical electrode. 35 said devices. 14. A tuned spark plug for ultra-high frequency 20. A resonant ignition plug for ultra-high fre ignition voltages including an elongated center quency voltages including an elongated cen-ter electrode of length equivalent to some odd mul electrode of length equivalent to some odd mul tiple of one quarter wavelength of said voltages. tiple of one-quarter Wavelength of said voltages. 1'5. Apparatus of the type described in claim 13 40 FRANCIS X. RETTENMEYER.