US 3675077 A
A pulse transformer connects a capacitor to an ignition means.
Description (OCR text may contain errors)
United States Patent [151 3,675,077
Minks 1 July 4, 1972 541 HIGH VOLTAGE IGNITION SYSTEM 3,335,320 8/1967 Quinn ..315/209 R TRANSFORMER 3,427,502 2/1969 Minks ....3l5/209 R 3,428,823 2/1969 Pinckaers ....307/106 Inventor: Floyd Minks, Box 41, Klsslm- 3,463,963 8/1969 Fairley et a1. ..315/206 mee, Fla. 32741 22 d: Primary Examiner-Volodymyr Y. Mayewsky 1 l 6 Jan 1971 Attorney-Andrus, Sceales, Starke & Sawall  Appl. No.: 107,051
 ABSTRACT  US. Cl. ..315/209 R, 123/148, 307/106, A pulse transformer connects a capacitor to an ignition 315/240, 317/92, 317/96, 336/83 means- [511 lift. Cl ..H0lg 9/00, HOlt 15/02 A Secondary coil housing is a tubular p d member molded  Field of Search ..317/92, 96, 80; 336/83, 206; about a core leg carrying a flat wound primary coiL An axially 315/206, 209 240, 123/148? 331/] 13; extended coaxial recess receives a multi-turn single layer 307/106 secondary coil wound on a support tube. The recess is filled with a suitable potting material and a U-shaped core assembly References cued is secured to the center core leg to define a closed rectangular UNITED STATES PATENTS Path A high voltage connector is connected to the innermost turn 6/1966 MNultY et 307/106 of the secondary coil with a minimum spacing therebetween. 3,273,099 9/1966 Minks ..336/83 3,302,629 2/1967 Shano 123/148 17 Claims, 7 Drawing Figures CONVERTER rowan zy souRcE PATENTEDJUL 4 I972 3.575.077
PULSE SOURCE FLOYD M. MINKS ATTORNEYS HIGH VOLTAGE IGNITION SYSTEM TRANSFORMER BACKGROUND OF THE INVENTION This invention relates to a high voltage ignition system transformer and particularly to an improved compact high voltage pulse type transformer adapted to interconnect a high voltage capacitor supply to an ignition firing system for an intemal combustion engine and the like.
Solid state ignition systems have been developed particularly since the invention of the solid state transistors and the like. A particularly satisfactory capacitor discharge ignition system is disclosed in applicants US. Pat. No. 3,427,502 which issued Feb. ll, 1969, wherein a blocking oscillator charges a capacitor to a selected level. The capacitor is discharged through a control rectifier and a pulse transformer to provide proper firing of the engines spark plugs. Such capacitor discharge ignition systems provide unusually satisfactory ignition energy and permit use of polar gaps, plugs and the like for relatively long engine operating periods.
One of the significant and limiting components of the ignition system is the coupling transformer which is interposed between the high voltage source such as the capacitor and the firing means. Generally, the ignition pulse should be an exceedingly, rapidly rising pulse which may in and for a period of nano-seconds reach an amplitude of 45,000 volts. In view of the relatively small time period the average power is relatively minimal. Generally, these characteristics require a high ratio of insulation between the primary winding and the secondary winding relative to the conductor area. A satisfactory ignition transformer is disclosed in applicant's issued US. Pat. Nos. 3,273,099 and 3,448,423. The transformer disclosed in the latter patent is a highly satisfactory unit but is a relatively large and commercially expensive construction. However, so far as applicant has any knowledge that patent discloses the first commercially practical pulse transformer for capacitor discharge ignition systems and the like.
One of the principal problems encountered in such high voltage, low average power transformers is the maintaining of sufiicient insulation adjacent the high voltage secondary winding with respect to the adjacent ground surfaces and between adjacent turns at the high voltage end as well as the components at the position of high voltage connection.
SUMMARY OF THE PRESENT INVENTION The present invention is particularly directed to a relatively small and compact high voltage pulse transformer particularly adapted for capacitor discharge ignition systems and the like.
Generally, in accordance with the present invention, a secondary coil housing is formed of a suitable insulating material. The housing is generally a tubular shaped member having a central core and primary winding opening. An axially extended recess is provided in the housing extending axially from one end of the housing and defining a recess within which the secondary winding is disposed. The secondary winding is a multi-turn single layer coil wound of a very substantial number of turns of relatively small diameter insulated wire with the adjacent turns or convolutions closely spaced and preferably in touching engagement. In a practical construction, a tubular form is provided upon which the fine wire is wound; for example, a thousand turns of number 48 wire can be wound on a suitable thin plastic form with the adjacent convolutions or turns in immediate abutting relationship to thus define a cylindrical coil. The coil and form are disposed within the recess with the innermost turn connected to a high voltage terminal at the base of the recess. The primary winding and a core leg project through the opening of the housing and the total assembly potted in a suitable material to establish a completely encapsulated winding construction. Interconnecting core members are connected to the leg and define a closed magnetic path for producing a high pulse transformer construction.
In accordance with a further aspect of the present invention, the core leg is formed as a separate straight, cylindrical member. The primary winding is formed of a flat conductor having a rectangular cross section and is wound about the cylindrical core leg with the flat face of the conductor wound upon the leg and with opposite end connection of the coil extending axially outwardly of the core leg. The primary convolutions or turns are distributed throughout the length of the coil housing and generally the length of the secondary winding. The secondary housing is cast about the preformed core and primary coil. The secondary is inserted in the housing and the recess filled with a suitable potting material. A U-shaped core assembly is secured to the center core leg to define the closed rectangular path.
In a preferred construction, the coil housing is provided with a laterally extending enlargement of the secondary coil recess in alignment with a high voltage tower or connector, which extends axially in the opposite direction from such recess. A high voltage connector is exposed within the base of lateral extension and the secondary coil located in the recess with the terminal end of the, wire extending into the lateral recess and in overlying engagement to the high voltage connector base. The end of the wire is welded to the high voltage connector base to provide the desired electrical interconnection. The recess is then filled with the outer end of the secondary coil interconnected to the corresponding end of the primary coil to provide a corresponding common ground. The opposite or inner end of the secondary and primary coils define the high voltage terminals connected respectfully to the ignition means and to the incoming power supply such as the capacitor.
If desired, the primary coil and housing can be formed as complementing cone shaped members to increase the insulation at the high voltage ends. The core is similarly shaped to minimize the magnetizing current over that required with constant diameter core having sufficient insulation between the high voltage secondary and the high voltage primary end.
The secondary winding is especially wound at the high voltage end to establish essentially immediate interengagement of adjacent convolutions and thereby minimizing the possibility of corona efiects at the high voltage end. The interconnecting extension between the innermost turn of the secondary and high voltage connector is minimized such that the end of the high voltage connector may also function as a corona shield to distribute the high voltage stresses.
In accordance with a still further aspect of the present invention, a high resistivity conductor such as a conductive plastic or a slotted metal ring is interconnected to the innermost high voltage turn to provide corona protection by minimizing the concentration of dielectric stresses in the insulation immediately adjacent to the high voltage turn or turns in the output terminal or high voltage connector. The high resistivity turn should be selected to prevent excessive power dissipation but with sufficient resistivity to properly distribute the electrical stress.
The present invention thus provides a relatively simple and inexpensive transformer construction which can be incorporated in high voltage, pulse output and, in particular, capacitor discharge ignition systems.
BRIEF DESCRIPTION OF THE DRAWING FIG. I is a side elevational view of a pulse transformer interconnected between a diagrammatically illustrated capacitor power supply and an engine ignition system;
FIG. 2 is a perspective view of the transformer shown in FIG. 1;
FIG. 3 is a top plan view of FIG. 2;
FIG. 4 is a vertical section taken generally on line 44 of FIG. 3;
FIG. 5 is an enlarged section of a portion of FIG. 4 illustrating the transformer components assembled;
FIG. 6 is a view showing an alternative construction for the primary winding in accordance with the present invention; and
FIG. 7 is a fragmentary view illustrating an alternative construction for interconnecting of the high voltage power'connector to the secondary winding.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS Referring to the drawing and particularly to FIG. 1, the internal combustion engine 1 is diagrammatically illustrated including a pair of spark plugs 2 and 3 and'a distributor 4 for successively supplying power to the spark plugs 2 and 3 and thereby operating the engine 1. The distributor 4 is coupled to the output side of a high voltage pulse transformer 5 constructed in accordance with the present invention and having an input interconnected to a high voltage capacitor 6 defining a pulse source. The capacitor 6 is connected to be discharged through the transformer 5 by a controlled rectifier 7 having its gate 8 interconnected to a suitable trigger pulse source 9 which is actuated in synchronism with the distributor 4. The controlled rectifier functions as a rapid acting triggered switch which, when closed, transfers power from the capacitor. 6 through the pulse transformer 5 to the spark plugs 2 or 3. The capacitor 6 is charged from a suitable D.C. source such as the battery or altemator-rectifier system of a conventionalinternal combustion engine 1 and is diagrammatically shown connected to a battery 10 by a suitable DC to D.C. converter 11, such as the converter 11 blocking oscillator system disclosed in applicants issued U.S. Pat. No. 3,427,502.
The transformer includes an outer tubular coil assembly 12 having a central opening through which a core leg 13 extends. A generally U-shaped core 14 having a square cross section is telescoped over the coil assembly 12 and interconnected to the outer ends of the central core leg 13 to establish a continuous iron core transformer in contrast to the conventional air spark coil and the like. In the illustrated embodiment of the invention, the leg 13 is generally a cylindrical member within the coil assembly 12 with the outer end provided with generally flat faces 15 against which the corresponding flat faces of the rectangular cross sectional shaped core 14 abut. Suitable clamping means shown as mounting bands 16 having apertured extensions interconnect and hold the cores l3 and 14 in firm abutting relationship to minimize the air gap within the core path.
The coil assembly 12 includes a plastic housing 17 formed of a suitable plastic or other high voltage insulating material having a central opening through which the core leg 13 projects. A primary winding 18 is wound about the core leg 13 with a plurality of individual turns extended axially within the opening of the housing 17. The primary winding or coil 18 is preferably formed from a flat conductor havinga generally rectangular cross section, as most clearly shown in FIG. 4. The rectangular primary conductor is wound about the core on the principal plane or face of the conductor and with the conductor face abutting the core periphery. Connection is made to the opposite ends of the flat conductor and particularly the terminal ends within the housing 17 by axially extending connecting wires 19 and 20 which extend axially outwardly along the core 13 from the opposite ends of the primary coil 18. The core 13 is formed with suitable tubular recesses 24 through which the leads l9 and 20 extend. The inner ends are welded or otherwise secured to the corresponding ends of the opposite end turns of the rectangular primary coil 18. The preformed leg 13 and coil 18 are preferably castinto the housing 17 as shown by mounting of the sub-assembly in a suitable mold. The core leg 13 with the coil 18 wound thereon may, of course, be preformed and assembled with a separate coil housing 17.
The primary winding 18 is shown generally aligned with a secondary winding 26 which is especially constructed as a high turn cylindrical winding within housing 17, as follows.
The secondary winding 26 is wound as a single layer multiple turn coil 26 of a very fine insulated conductor and extended axially of the core leg 13 and primary coil 18. In a practical construction, the secondary coil 26 was wound with a thousandturn's'of a number 48 conductor. The secondary turns are closely wound with the adjacent convolutions or turns immediately adjacent each other and preferably in .touching engagement.
As a practical matter, the coil 26 is prewound or wound on a preformed tubular form 27- with at least the high voltage end sociated secondary winding 26. The secondary winding 26 and form 27 are telescope'deinto the recess 30 immediately adjacent andclosely abutting the face of the inner diameter of the wall of the recess. The innermost turn 28 of the secondary coil 26 includes an outwardly extending integral connecting end 32 which projects laterally into a lateral extension or enlargement 33 provided in the housing 17 co-extensive with the recess 30.
A high voltage secondary tower 34 is integrally formed with the base portion of the housing 17 and projects axially outwardly in alignment with the enlarged lateral opening 33. A cup shaped high voltage connector 35 of brass or other suitable material is molded within the tower 34 with the base coplanar with the base 31 of' the recess 30 and the lateral extension 33 and thus exposed at that location. The connecting lead 32 overlies the high voltage connector 35 and is welded thereto as at 36.
In the construction, the secondary coil 26 is assembled with the housing 17 and the lead 32 accurately located in overlying relationship with the base of the cup shaped high voltage connector 35. A welding electrode can then be extended downwardly through the extension 33 and spot weld or otherwise interconnect the laterally extending lead 32 to the base of the cup shaped high voltage connector 35.
Applicant has found that it is important to maintain the length of the lead 32 minimal with the base of the connector 35 closely adjacent to the secondary coil 26 in order to minimize the high voltage stresses in the adjacent insulation.
Thus, the high voltages encountered in capacitor discharge ignition systems and the like even though of very short duration and therefore of low average power are of such a nature that unless special consideration is given to the construction, the dielectric stresses immediately adjacent to the high voltage turn and the output'terminal may readily rise to a level resulting in corona. This would result in a-rapid deterioration of the insulating characteristics of the electrical insulation and a pretive circuits.
I As shown, a small L-shapedmetal connecting tab 38 is disposed within a rectangular opening 39 in the top wall of recess 37 in housing 17 adjacent the enlargement or extension 33. A primary lead 40 is welded orot herwise attached to the solderedto the ba'nd'16;
The correspondinglow' voltage end 44 of the secondary coil 26 is aligned with the outer leg of tab 38'and soldered thereto. When the recess 28 and extension 33 are filled with the insulating media 45, such as a resin or the like, the secondary connection is encapsulated to protect the fine wire connection from physical and environmental damage. Thus, the insulation forms a physical support as well as a physical seal. This is of substantial practical significance in connection with marine application when the transformer may be subject to severe vibration conditions and corrosive and moist environmental conditions.
In assembly, the center leg 13 of the core and the primary 18 are formed separately from the bobbin or housing 17, and then molded into housing 17 to produce complete encapsulation of the primary winding 18. After assembly and connection of the secondary winding 26, all of the recesses and openings within the housing 17 are filled with a suitable plastic material to essentially eliminate air and other voids which could contribute to deterioration of the coil assembly.
Applicant has found that the illustrated construction of the high voltage transformer substantially minimizes the required insulation and size of the secondary winding. In an actual construction the following approximate dimensions provided a highly satisfactory pulse transformer for marine engines:
Rectangular Iron Core 3.5 X 2.3 with cross section 0.75 inches.
Plastic Housing 2.25 inches diameter, 2 inches deep.
Secondary Recess 1.7 inches deep, 0.1 inch wide.
Insulation between Primary and Secondary 0.4 inches.
Connecting Lead to Center of Cap 0.1 inches.
Primary Coil 6 turns.
Secondary Coil 1,000 turns No. 48 wire.
An alternative construction similar to that shown in FIGS. 2 and 3 is shown in FIG. 5 and corresponding elements are similarly numbered for simplicity and clarity of explanation. As previously noted, the principal area of insulation is that required at the high voltage end of the secondary coil 26. In the embodiment of the invention illustrated in FIG. 5, a special center core leg 46 is formed with a generally cone shape and with the apex generally aligned with the high voltage end of the secondary winding 26. A primary winding 47 is similarly wound about the cone shaped core leg 46 and the assembly is cast with a housing 17. A greater extent and maximum insulation is thereby introduced between the high voltage end of the secondary winding 26 and the high voltage end of the primary winding 47. This construction minimizes the magnetizing flux and current requirements as compared with the constructions such as shown in previous embodiments. However, the construction is somewhat more complicated with the associated expense and has not been found practically necessary in a high voltage capacitor discharge ignition system, such as disclosed in US Pat. No. 3,427,502.
In addition in the embodiment of FIG. 5, the inner or high voltage end of the secondary winding 26 is shown connected with a modified high voltage tower interconnection. In particular, a generally high resistivity conductor member 49 is interconnected to the innermost high voltage turn of the secondary winding 26. In the illustrated embodiment of the invention, the member 49 is a ring having an L-shaped cross section with the one leg extended upwardly behind the inner surface of the plastic secondary form tube 27 and with the opposite leg extended outwardly immediately beneath the tube and slightly beyond the last turn 28 of the secondary coil 26. The last turn 28 of the secondary coil 26 lies immediately adjacent to the extended leg of the ring member 49 and is soldered or otherwise electrically interconnected to member 49 to form essentially a short circuited turn. The member 49 may be formed of a high resistivity material or may be formed with a gap therein to essentially minimize or increase the resistance of the turn. The resistivity should be relatively high in order to minimize excessive power dissipation in the short circuit turn. It must be sufficiently low, however, to permit adequate distribution of the high voltage and contribute to the distribution of the high voltage stresses or potential at the high voltage turn and thereby minimize the stresses in the adjacent insulation. In this manner it will tend to minimize the creation of corona and other damaging stresses or the like.
A high voltage tower 50 is shown to one side of the secondary and includes a high voltage connector cap 51 located within the enlarged lateral extension 52. The tower and connector cap 51 open upwardly through the extension in contrast to the opposite extension of the tower shown in the previous embodiment. A connecting lead 53 interconnects the high resistivity short circuit turn 28 to the base of the high voltage connector.
An alternative high voltage connection can be constructed such as shown in FIG. 7 wherein a high voltage tower 54 is radially aligned with the terminal end of the secondary winding or coil 26 and axially spaced slightly from the high voltage turn 28. The connecting end lead 55 of the last turn 28 is bent at a right angle and projects axially outwardly to the base of the high voltage cap or connector 56. The lead 55 is welded or otherwise similarly secured to the high voltage cap 56 to provide the proper electrical connection therebetween The length of the lead 55 is relatively short compared to the diameter of the base of the high voltage cap 56 such that the large surface area of cap 56 constitutes a potential distributing member and a corona shield; thereby minimizing corona generation.
This invention thus provides a highly improved pulse transformer which is particularly adapted to the transmission of a pulse similar to that encountered in capacitor discharge ignition systems and particularly a pulse which rises to a high level in a very short period of time but conducts for a minimal or very short period of time. Thus, the pulse in a capacitor discharge ignition system rapidly increases and decreases such that the total conduction period is small and the average power is correspondingly low. The dielectric must, however, withstand the momentary extremely high voltages such as 35,000 voltage levels and thus requires special consideration and constructions. Applicant has found that the single layer secondary of the present invention in combination with the insulating structure and magnetic core produces an unusually satisfactory pulse transformer for capacitor discharge ignition systems.
Various modes of carrying out the invention are contemplated as being within the scope of the following claims, particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.
1. In a high voltage ignition system having a pulse source of a voltage of hundred of volts and connected in an output circuit in series with a triggered electronic switch means and a step-up pulse transformer connected to spark igniting means and establishing a rapidly rising voltage to the level of tens of thousands of volts output, the improvement in said pulse transformer comprising a housing of solid insulating material having a central core opening and a radially spaced secondary winding axial opening extending axially from one end of said housing, a multiple turn primary coil within said central opening, a multiple turn single layer cylindrical secondary coil having a substantially greater number of turns than said primary coil, said secondary coil being disposed within said recess and wound concentrically of said core opening with the adjacent turns essentially in abutting relation and wound axially within the recess, an encapsulating medium surrounding said primary coil and filling said secondary coil recess to essentially eliminate voids between said coils, and a magnetic core including a magnetic core leg extended through said primary coil and defining a magnetic path for coupling of said primary and secondary coils.
2. The ignition system of claim 1 wherein said primary coil is a single layer multiple turn coil distributed within said opening and having a diameter essentially corresponding to the diameter of said core opening.
3. The ignition system of claim 1 wherein said housing is a molded plastic member, said multiple turn primary coil is distributed axially of said secondary coil upon said core leg and wound abutting the core leg, said primary coil and core leg being assembled with and molded into said housing.
4. The ignition system of claim 1 wherein said housing is a molded member, said multiple turn primary coil is a single layer coil distributed axially of said secondary coil and formed of a flat conductor, said core leg includes a cylindrical portion coextensive with said primary coil, and said flat conductor is wound on said cylindrical portion with the principal face of the conductor abutting the core, said primary coil and leg being assembled with said housing and molded into said housmg.
5. The ignition system of claim 1 wherein said secondary axial opening includes a base wall, said secondary coil includes a high voltage turn adjacent the base wall of the recess, the end of said turn defining a high voltage end conductor, a high voltage connection means located within said housing adjacent said end conductor and having a terminal member in the plane of the base of said recess, and fusion means joining said end conductor to said terminal member, said terminal member having a relatively large surface to minimize the high voltage stress concentration in the adjacent insulating medi- 6. The ignition system of claim 1 wherein said secondary axial opening includes a base wall, said secondary coil includes a high voltage turn adjacent the base wall of the recess, the end of said turn being extended laterally outwardly to define a high voltage end conductor, a high voltage connection means located within said housing adjacent said end conductor and having a terminal member in the plane of the base of said recess, and fusion means joining said end conductor to said terminal end turn, said terminal member having a relatively large surface to minimize the high voltage stress concentration in the adjacent insulating medium.
7. The ignition system of claim 1 wherein said secondary coil includes at least a thousand turns of an insulated number 48 wire.
8. The ignition system of claim 1 wherein said secondary coil is wound with the adjacent convolutions in contact with each other throughout the length of each convolution.
9. The ignition system of claim 1 wherein the innermost turn of said secondary includes a high resistivity conducting material establishing an operative short circuit turn minimizing concentration of dielectric stress in the insulation immediately adjacent to the high voltage turn and related output connection.
10. The capacitor discharge ignition system of claim 1 wherein said secondary opening includes a base wall and said secondary coil has an innermost turn adjacent the recess base wall connected as the high voltage turn and an outer low voltage turn, and said central leg is a cylindrical member having a constant diameter throughout said opening, and said primary coil is wound abutting said cylindrical member and having low and high voltage end turns adjacent the corresponding turn of the secondary coil, primary power leads connected to corresponding primary end turns and projecting axially outwardly adjacent the core leg, said core including a U-shaped portion connected to the opposite ends of said core leg to define a closed magnetic path, and said housing being molded about said core leg and primary coil.
11. The ignition system of claim 10 wherein said primary coil is wound from a flat conductor having a rectangular cross section, and said conductor is wound with a principal planar surface aubtting the core.
12. The ignition system of claim 11 wherein said primary coil has essentially six turns and said secondary coil has essentially 1,000 turns.
13. The capacitor discharge ignition system of claim 1 wherein said secondary recess has a base wall and said secondary coil has an innermost turn adjacent the recess base wall connected as the high voltage turn and an outer low voltage turn, and said central leg has a substantially cone shaped portion with a narrow portion adjacent the high voltage turn and a wide portion adjacent the low voltage turn, and said primary winding is wound on a cone shaped portion with a corresponding configuration and connected with low and high voltage turns adjacent the corresponding turn of the secondary coil and thereby minimizing the magnetizing current.
14. In a semi-conductor controlled ignition system, an output transformer having an output winding producing a voltage sufficient to excite the ignition means, said winding having an output terminal, and a conducting material disposed adjacent and connected to the high voltage end and arranged to prevent concentration of dielectric stress in the insulation immediately adjacent to the high voltage turns and output terminal connection.
15. An ignition system, comprising a capacitor, a converter connected to charge said capacitor, a pulse transformer, spark igniting means connected to said pulse transformer, an electronic switch connected in series with said capacitor and said pulse transformer, said pulse transformer including tubular single piece molded housing of insulating material having a central core opening and a radially spaced secondary winding recess extending axially from one end of said housing and terminating in a base wall within said housing, a magnetic core including a cylindrical magnetic core leg extended through said central core opening and defining a magnetic path and U- shaped unit having ends abutting the ends of the core leg to define a closed magnetic path, a tubular multiple turn single layer primary coil formed of a flat striplike conductor upon said leg within said central opening with axially distributed coplanar convolutions, a tubular secondary coil form having a diameter corresponding to the smallest diameter of said recess, a multiple turn single layer cylindrical secondary coil wound upon the exterior of said coil and disposed in said recess concentrically of said primary coil, said leg and primary coil being molded into said housing to define said core opening, and an encapsulating medium filling said secondary coil recess.
16. The capacitor discharge ignition system of claim 15 wherein said secondary coil includes a high voltage turn adjacent the base of the recess, the end of said turn being extended laterally outwardly to define a high voltage end conductor, a high voltage connection means located within said housing adjacent said end conductor and having a terminal member in the place of the base of said recess, and a fusion means joining said end conductor to said terminal end turn, said terminal member having a relatively large surface to minimize the high voltage stress concentration in the adjacent insulating medium.
17. The capacitor discharge ignition system of claim 16 wherein said primary coil is of the order of six turns and said secondary coil is of the order of a thousand turns of wire of the order of 48 gauge.