US3030549A - Ignition system - Google Patents

Description

April 17, 1962 Filed March '7, 1960 Fig. 3

2 Sheets-Sheet 1 INVENTOR. William J Johnsfon BY 0 I RI MM His Attorney April 17, 1962 w. J. JOHNSTON IGNITION SYSTEM 2 Sheets-Sheet 2 Filed March 7, 1960 INVENVTOR.

W/l/iam .J. Johnsfon (1R. W His Afforney United States Patent Ofifice 3,030,549 Patented Apr. 17, 1962 3,030,549 IGNITION SYSTEM William J. Johnston, Flint, Mich., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Mar. 7, 1969, Ser. No. 13,347 4 Claims. (Cl. 315-188) This invention relates to ignition systems and apparatus for igniting the combustible fuels of gas turbines, rockets and the like.

One of the objects of this invention is to provide an ignition system that is comprised of relatively few parts but which is capable of boosting the input voltage to provide maximum elficiency in the firing of a spark discharge device.

Another object of this invention is to provide an ignition system that is powered by a source of A.C. voltage, the system including a resonant circuit that is resonant at the frequency of the source and further wherein the voltage developed across one of the circuit elements of the resonant circuit is used to fire a spark discharge device.

Still another object of this invention is to provide an ignition system that is powered by a source of A.C. voltage that includes a pair of condensers and a pair of rectifiers, the condensers and rectifiers being so connected that one condenser is charged on a first half cycle of applied voltage and the other condenser is charged on the other half cycle through the first condenser, the other condenser thus charging to approximately twice the peak voltage of the input voltage and this voltage being used to fire a spark discharge device.

A further object of this invention is to provide an igniter that includes .an ignition system and a spark discharge device in one integral unit. In carrying forward this object of the invention, the parts of the ignition system are fitted as a unit within a housing the lower end of which is enclosed by a spark discharge device. The housing is filled with a plastic material such as an epoxy resin which encapsulates the ignition system parts and provides a bond between them and the housing.

Further objects and advantages of the present invention will be apparent from the following description, reference being bad to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 is a circuit diagram of .an ignition system made in accordance with this invention.

FIGURE 2.is a schematic circuit diagram of a modified ignition system made in accordance with this invention.

FIGURE 3 is a sectional view of an integral igniter made in accordance with this invention.

FIGURE 4 is a plan view of a sub-assembly forming a part of the igniter illustrated in FIGURE 3.

FIGURE 5 is an end view of the assembly illustrated in FIGURE 4.

FIGURE 6 is another end view of the assembly illustrated in FIGURE 4.

Referring now to the drawings and more particularly to FIGURE 1, the reference numeral 10 designates a source of A.C. voltage having one side thereof connected to ground via a lead wire 12. The opposite side of the power source 10 is connected with lead wire 14 and it is seen that this lead wire is connected to one side of a condenser 16. The condenser 16 is connected with a junction 18, and a resistor 20 is connected between the junction 18 and a rectifier 22. The rectifier 22 may be of the p-n junction, semi-conductor type and has its opposite side thereof connected directly to ground as shown.

The junction 18 is connected with a resistor 24 which is in turn connected with a rectifier 26 that may be of the same type as the rectifier 22. The opposite side of rectifier 26 is connected with junction 28 and it is seen that a condenser 30 is connected between junction 28 and ground. The junction 28 is connected to one side of a cold cathode discharge tube 32 the opposite side of the tube being connected with a creepage gap or shunted surface gap type of spark plug 34. The opposite side of the spark plug 34 is connected directly to ground as shown in FIGURE 1.

In the operation of the circuit illustrated in FIGURE 1 and when the lead wires 12 and 14 are energized from the source of A.C. voltage, the condenser 16 will be charged on a half cycle of the A.C. voltage when, for example, the lead Wire 14 is positive with respect to the lead wire 12. This charging circuit is through the condenser 16 through the resistor 20 and through the rectifier 22 to ground. On a next half cycle of applied voltage the polarities of lead wires 12 and 14 is reversed so that the lead wire 12 will be positive with respect to the lead wire 14. Under this condition of operation, thev voltage across condenser 16 is adding to the input voltage and current will flow from the A.C. power source through the condenser 30, through rectifier 26, through resistor 24 and through the condenser 16. The condenser 31) will now be charged to approximately twice the peak value of the input voltage.

The cold cathode discharge tube 32 is chosen to have a break-down voltage that is less than the maximum voltage which can be reached across condenser 30. When this break-down voltage is reached, the condenser 30 will discharge through the cold-cathode discharge tube 32 and through the spark gap 34 to provide a spark. The tube 32 will then deionize and the process will be repeated.

It will be appreciated that the spark repetition rate is a function of the value of the resistors 20 and 24 and the value of condensers 16 and 3t) and also will vary according to the input frequency of the voltage source 10. Referring now to FIGURE 2, another circuit for boostmg the input voltage to fire a spark discharge device is illustrated. In this circuit the reference numeral 36 designates a source of A.C. voltage. The A.C. voltage source 36 is connected with lead wires 38 and 40, the lead wire 38 being connected to one side of an inductor 42. The opposite side of inductor 42 is connected with a junction 44 and it is seen that a resistor 46 is interposed between the junction 44 and the lead wire 40. A condenser 50 is connected between lead wires 40 and 48. The lead wire 43 is connected to one side of a cold cathode discharge tube 52 which may be of the same type as the tube 32 illustrated in FIGURE 1. The tube 52 is connected with a creepage gap or shunted surface gap type of spark plug 36, the opposite side of the plug being connected with lead wire 40.

In selecting the components for the circuit of FIGURE 2, the condenser 50 and inductance 42 are selected to provide resonance at the frequency of the voltage source 36. Thus in a typical system the inductance of inductor 42 may be .156 henry, the resistance of resistor 46 one megohm and the capacitor 1 mfd. With this system the inductor 42 and capacitor 50 are resonant at the 400 cycle A.C. input. In addition, the spark rate achieved is approximately 300 to 400 sparks per second.

It will be appreciated that during the operation of this system, the voltage appearing across condenser 50 will be many times the value of the input voltage from source 36. When the condenser 50 is charged to a voltage sufficient to break down the cold cathode discharge tube 52, the condenser discharges through the creepage plug 37. "This system thus greatlydncreasesdheinput voltage and uses this voltage in causing sparking across the spark plug 36. The function of the resistor 46 is to discharge the capacitor Stiwhen the circuit is inoperativeand thus prevent an undesired spark.

Although the system of FIGURE 2 has principle utility for use with a creepage gap plug, the same principles of this invention could bev applied to a high tension plug. With a high tension plug, no discharge tube 52 would be necessary to prevent the condenser from prematurely discharging through the spark gap 37.

Referring now more particularly to FIGURES 3 through 6, a-physical embodiment of the circuit illustrated inFIGURE l is shown. In these figures the ignition circuit and spark plug are formed in one integral unit which.may then be fitted to, an engine for causing ignition of the combustible fuel of the engine. As shown in FIGURE 3, the integral igniter includes a metal can which is designated by reference numeral '54 containing the ignition system "in FIGURE 1. The can 54 contains a sub-'assembly'generally designated by reference numeral 56and shown in FIGURES 4 through 6 of the drawings. The sub-assembly 56 includes plates 58, 60 and 62. The plate 62 supports the condenser 30 whereas the plates 58 and'60 support the resistors 20 and 24 as well as the condenser 16. The cold cathode discharge tube 32 is not visible in'FIGURE 4 but is visible in the end view of FIGURE'G. One side of the cold cathode discharge tube is connectedwith a conductor 64 that is secured to a terminal66.

"The sub-assembly 56" further includes an assembly including-a metal cover member 68 that supports the rectifiers 22 and 26. ,These' rectifiers are supported on brackets-'having-portions that extend downwardly from the cover 68.

The integral igniter' further includes a spark plug portion which is designatedin itsentirety by reference numeral 70. This spark plug portion includes the member 72 formed bimetallic materialand the portion 74 having threads "76. The electrode portion 74 is spaced from a center electrode 78 as is clearly apparent from FIG- UR'E'S. A button-80 or any suitable semi-conductor material" is fitted around the rodportion'82 of the'center electrode 78 and is interposed between this center rod portion and the outer electrode 74. An insulator 84 insulates the rod portion 82 from the outer electrode'portion 74 and is held in place by metal material 86 which is wedged in place.

In assembling the integral 'igniter ofFIGURE '3, the lower electrode portion 70 is fitted to thecan 54 and is silver soldered thereto along the area designated by reference numeralSS. The sub-assembly S6 is then fitted within the container 54, the terminal 66 being secured to the rod portion'82 at this time and the'conductor 64 being formed to the shape illustrated in FIGURE 3. After the lower'connections have been made for the integral igniter as described, the cover member 68 is $01- dered to the can 54 and the can'is'then filledwith a plastic material such as an epoxy resin through an opening that is later closed by the plug 90. It is seen that a connector 92 -is also provided which mayform she power input connection for the integral igniter. The plastic substance 'whicirentirely fills the can -54*whenit is completely -assembled is designated by reference numeral 94 in FIG- URE 3. Only portions of this material are shown so that the ignition system within the can may be illustrated. It will be apparent that the 'epoxyresin 94 completely seals the system so that the parts of the ignition system are encapsulated. in the epoxy resin and this resin-provides a shock absorbing monntingfor all of the partslocated within the can 54. The filling of the can-with epoxy resin also prevents destruction of theintegral igniter where the .igniter is subjected to severe pressure changes in high altitude operation.

While 'the embodiments of the present invention as herein. disclosed constitute preferred forms, his to be understood that other forms might be adopted.

What is claimed is as follows:

1. An electrical ignition system comprising, a source of AC. voltage, a circuit resonant at the frequency of said A.C. source connected across said AC. voltage source including an inductor anda capacitor, a spark plug of the'creepagegap type, and a discharging circuit for said condenser'in cluding said spark plug anda circuit element having a break down voltage which is less than the voltage attained by said capacitor.

2. An electrical ignition system-comprising, a source of A.C. voltage, a circuit resonant at the frequency of said AIC. voltage source connected across said source of 'A'.C. voltage, said circuit including an inductor and a condenser, and a discharging circuit for said condenser including a cold cathode discharge tube and a spark plug of the creepage gap type.

3. An electrical'ignition system comprising, a spark discharge 'device a condenser connected with said spark discharge device=and adapted to discharge therethrough, a source of-A.C. voltage, and a circuit resonant at the frequency of said A.C. voltage source connected across said source and including said capacitor and an inductor.

4.-An.electrical ignition system comprising, a source of AC. voltage, a circuit resonant-at the frequency of said AC. voltage source connected across said'source and including a series connected inductor and a capacitor, a resistor shunting said capacitor, a spark plug of the creepage gap type, and means connecting said spark plug across said capacitor including acold cathode discharge tube.

. ReferencesCited in .the:file of this patent UNITED STAT ESPATENTS 1,484,591 Van Slyke Feb. 19,- 1924 1,982,950 Curtis Dec. 4, 1934 2,378,893 -Berkey etv a1 June 26, 1945 2,392,171 Marsh Jan. 1, 1946 2,551,101 .Debenharnet al.. May-1, 1951 2,589,189 .Tognola Mar. 11, 1952 2,590,168 Felici Marf25, 1952 2,638,565 -Laird -May 12, 1953 2,790,935 'Lautenberger et a1 Apr. 30; 1957 FOREIGN; PATENTS 560,251 Canada e .July 15, 1958

Images