US1908798A - Ignition coil - Google Patents

Description

May 16, 1933.

A. TOELLE IGNITION COIL Filed May 27, 1932 l N V EN TOR.

A TTORNE Y.

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Patented May 16, 1933 AUGUST TOELLE, OF DETROIT, MICHIGAN,

PATENT OFFICE ASSIGNOB TO roan moron. comm, or

DEABBOBN, MICHIGAN, A CORPORATION OF -DELAWARE IGNITION COIL Application filed Kay 27,

The object of my invention is to provide an induction coil especially suitable for supplying the high-voltage electricity required for ignition in high-speed multicylinder automobile engines. The invention herein resides in the novel arrangement of the various elements comprising the coil, whereb$ a material increase in manufacturing e c ency and incidentally in electrical efiiciency 1s obtained.

Ordinarily, an increase in the efliciency of a piece of electrical apparatus which requires only the small amount of current required to operate an ignition coil would not be a material factor in the design of an automobile so that in this installation, the reduced current consumption of m coil is not part cularly important. The eature of utmost importance which arises from this increased efliciency is that a perfectly satisfactory coil suitable for use on high-speed multicylinder motorscan be designed at a substantial saving in cost'of production. It is well known that supplying ignition current for mediumspeed engines is a comparatively simpleproblem because the duration of time for building up the magnetic field is sufiiciently long to ermit the storing u of the required energy in the coil. In hig -speed eight to twelve cylinder engines the interval is too brief to permit of storing sufficient energy in the magnetic circuit to cause a spark in the spgrk plugs. For this reason it has heretofore en the practice with high-speed engines of elght cylinders or more operat ng at comparatively high compressions to provide two ignit on coils, one for each unit of four or more cylinders so that the period available for storing energy in the coil or establishing the magnetic circuit is doubled.

The increased efiiciency of my coil directly results in a higher permissible speed of operation so that a single unit of my desi may besubstituted in place of the two coils ereto; fore provided for such engines. The primary purpose of producing a coil of higher efliciency is therefore to lessen the cost of the installation and not particularly to reducethe current consumption of the coil. The reasons for this result will be brought out 1932. Serial N0. 813,928.

later in the specification, at which time it should be kept in mind that although this unit is considerably smaller than the usual ign tion coil, its capacity is equivalent to the ordinary coil and in fact the capacity of all such coils is determined by the electromotive force required to cause a spark at the spark plug points of the engine in the short interval of time available for this purpose, depending upon the speed oflthe motor.

A further object of my invention is to provide a secondary winding formed by winding a plurality of layers of wire alternated with layers of insulating paper, the paper overlapping the ends of each succeeding layer of wlre to an increasing extent, which winding 15 connected in the circuit so that the potential increases in the succeeding layers, whereby a correspondingly increased insulat1on is provided between each layer of wire and the co e as the potential therein increases.

Other features will appear from the de' tailed description of this device, amon which may be mentioned that this unit is especially simple to construct, is waterproof so that weather will not affect its operation, and is amply proportioned so that even though the primary current is accidentally left on while the engine is not operating, the coil will not be damaged. With these and other objects in view, my invention consists in the arrangement, construction and combination of the various parts of my improved device, as described in the specification, claimed in my claims and illustrated in the accompanying drawing, in which:

Figure 1 shows a wiring diagram, illustrating the electrical connections required for installing this device on an eight-cylinder motor.

Figure 2 shows a full sized plan view of my improved coil.

Figure 3 shows a sectional view, taken on the line 3-3 of Figure 2.

Fi re 4 shows a sectional view, taken on the line 4-4 of Figure 2.

Figu the line 55 of Figure 4, and

re 5 shows a sectional view, taken on I ion Figure 6 shows an enlarged view, illustrating the manner in which the secondary circuit of the coil is wound.

Before taking up the detailed description of this device, it may be well to mention that this coil is conventional in so far as it consists of an open magnetic circuit in which a primary winding of comparatively few turns together with a secondary winding of many turn! is dispwed The primary winding is connected in series with the usual ignition battery and distributor breaker points and a condenser is shunted across the breaker points. The seconda winding is connected to the spa"k pl t rough an ordinary distributor rotor in usual manner. The 0 ration ofuthe coil is conventional in thltr fi current from the batter causes the magnetic circuit to be establ' ed, the

i rapid decay of which, in obedience to well known physical law as the breaker points open generates E. F.s of great enou h d fierence of potential to cause s arks at t e gark plugs, the stre h of t e magnetic ld, hysteresis and dy current losses in the core, the is esition of the secondary winding in the fi d and the distributed capacit in the seconda windin being factors iting the totx iY availab e ener The departures from conventional coi construction, whereby an increase in efliciency is obtained, relate to the disposition of the secondary windin in the ma etic circuit, this winding being ocated in e re ion of hi hest flux densit The novel ape of t is secondary win ing permits the majority .of its turns to be located at the point of highest flux density in the magnetic circuit. The direct result of this novel arrangement is that I am able to provide a coil with a seconda winding of extremely low impedance, resulting in an output high enough to give the desired results.

The specific construction employed for accompli ing these results may be better understood by referring to the accompanying drawing in which the reference numeral 10 is used to indicate a distributor rotor which is gear driven b the motor with which my coil is to be A pair of breaker contact points 11 are 0 ned and allowed to close upon rotation o the cam 10, these points heincluded in the primary circuit together with a fixed resistance 12, ignition switch 13, battery 14, and a rimary winding 15 in my improved coil. condenser 16 is shunted across the breaker contact points 11 in the usual manner. One end of a secondary windmg 17 in my coil is connected to one end of the primary winding 15, both bein grounded through the battery while the ot er end of the secondary winding extends to a rotor element 18 which is, driven in synchronism with the cam 10. The high-tension current .6 generated in the secondary winding is distributed b the rotor 18 to the several spark lugs of t e motor in the ordinary manner.

y coil proper, however, consists only of the primary and secondary windings together with a laminated core for effecting a magnetic circuit therearound.

eferring now to Figures 2, 3 and 4, it will be seen that I have provided a two-part housing which is molded from a henolic resin compound, the lower half of t e housing being numbered 19 and bein of cup-shaped form and having an annu ar shoulder 20 spaced slightly below the upper ed of its mm. A mounting flange 21 extends rom the intermediate portion of this housing, while a high-tension output terminal 22 is molded integrally with the extreme bottom portion thereof. I have also provided a cup-shaped cover 23 which is adapted to be piloted in the rim of the housing 19 and a ket 24 is disosed between this cover an the housing to cm a water and air-tight enclosure in which my coil is disposed. e cover 23 is fixedly secured in place b means of a pair of rivets 25, as shown in igure 5.

It will be noted from F i re 4 that the iron core of m coil assemb consists of a plurality of at strip-like aminations 26 which extend diametrically across the annular opening in the housing 19 and which laminations are grouped in two parts with both ends of these groups being bent circumferentially around in opposite directions so as to almost but not quite meet each other. A circumferential magnetic circuit having a pair of diametrically opposed air gaps therein is thus rovided, each portion of which is connected by a magnetic core extendin diametrically therebetween and perpendicular to slim joining the air gaps. The ositioning of air gaps is important in the unctioning of the coil, as will later be brought out. It will also be noted that the bent-back portions of these laminations 26, formin an annular ring, fit down into the rim 0 the housing 19 and bear against the shoulder 20. The cover 23 is clamped directly against the laminations so that they are ri dly held within the enclosure formed by t e housing 19 and cover 23.

Around the intermediate rtion 6? the laminations 26 I have provi ed a dielectric tube 27 upon which tube the primary winding 15 is wound, this winding and tube extending the full diametric length of the core. A second and somewhat shorter dielectric tube 28 is disposed around the periphery of the winding 15 and around this tube the secondary winding 17 of my coil is disposed. It will be noted from Figures 4 and 6 that the inner lagers of this winding are about two-thirds t e length of the rimary windin and that they extend an tantially the fu l len h of the tube 28. Each succeeding layer 0 this secondary winding is of r length than the la er beneath so that a radial section throug any portion of the coil shows the wire distributed in a flat-topped pyramidal shape. If desired, the wire may e wound in groups of layers of equal length, it only being important that the general shape of the coil be as just described.

It will further be noted that each layer of wire in the secondary winding 17 is alternated with a layer of paper 29 and that all of these paper layers are of the same length. Now, the beginnlng end of the first layer of the coil is grounded so that the potentialof the induced current therein increases with each succeeding layer, but as each succeeding layer is somewhat shorter than the one beneath the paper layers being of uniform length form an insulation of increasing thickness between the high-potential layers of the winding and the bent-back portions of the core laminations. When this coil is assembled in place, the ends of the laminations may be bent back against the corners of the 0011 and actually flatten this portion, as shown at 30, without reducing the insulation thereof. In this case the spark to ground the coil will ordinarily travel from one end of a particular layer of wire out between the layers of paper to the core laminations, which will be seen to be constant whether or not the corner of the coil is flattened.

From the foregoing, it will be seen that the secondary winding assumes a shape, the purpose of which is to allow the major port on of the coil turns to be located in that region in the magnetic circuit having the greatest flux density. The effective coupling between the windings is thereby increased so that a smaller number of secondary turns for the same voltage output is permissible. This feature of-my coil contributes materially to the smaller size of this device.

The method of assembling my coil is almost self-evident and requires very little skill, it being only necessary to wind the two windings and then place one inside of the other and slip the both over the bundle of laminations. The ends of the laminations are then bent back around thecoil and the whole inserted into the housing 19. The several winding terminals are connected to suitable terminals molded in the housing, the outer end of the secondary winding being connected to the terminal 22. The inner end of the secondary winding is connected to one end of the primary winding and both are connected by means of encased leads with the battery through the resistance 12 and switch 13. The other end of the primary winding is connected to a coil spring 31 which is molded in the flange 21. The free end of this spring is pointed so as to automatically make contact upon assembling'the coilin position on the engine.

In the device shown, the condenser 16 has been installed in a cylindrical pocket formed in the flange 21, this pocket having a metallic sleeve 32 and a metallic grommet 33 molded therein in axial alignment with each other but spaced apart so as to be insulated from each other. The grommet 33 is connected by means of an encased lead with the side of the primary winding which is connected to the breaker arm while the sleeve 32 is connected by an encased lead with a terminal 35 to be thus grounded along with the stationary breaker point of the distributor. Thus, the condenser 16 which is provided with a metallic case will be both held in position and the electrical connections made by simply inserting a single screw 34 in the grommet 33 and threading it into the end of the condenser.

The exact size of the windings, the number of turns and other details will not be given as the construction is subject to many variations and inasmuch as the design of any coil for hlgh-speed ignition must of necessity be a compromise subject to considerable variation. The specific novel features of this coil all coact with each other to produce an improved coil having more desirable characteristics than heretofore obtainable. This result is believed attainable irrespective of the size of the coil constructed.

However, in the design of ignition coils certain requirements must be met. For instance, ignition coils for low-compression slow-speed engines are required to develop an output voltage only sufiicient to strike 1 across about of an inch air gap, while ignition coils for high-speed high-compression motors must have an increased voltage, due to the 5 to 6 atmospheres of pressure under which the spark plugs operate. For this reason the voltage of such coils must be increased two to three times the ordinary striking voltage in order to ionize the air across the spark gap in the limited time available. It has been found that an output voltage of between 12000 and 15000 volts is required to insure operation of the coil under all conditions, the time lag due to ionization being particularly noticeable in cold dry weather. The applicant obtains the increased output, not by simply making the coil excessively large but by his novel magnetic core construction and secondary winding. While it is not claimed that this coil is per cent efficient, still it is of considerably higher efficiency than formerly obtainable, which in crease results from the predetermined arrangement and proportion of the parts there- 1n.

The ideal induction coil of this type should have a very low inductance because the speed of the coil is controlled by the inductance. A single coil to operate an eight-cylinder engine at 4000 R. P. M. should have an inductance of no more than .006 to .007 henrys.

The coil should also have a low resistance in the primary winding; the current stren h at the time the breaker points n shoul be as hi h as possible, and the eldstrength shoul be a maximum. It is at once apparent that all of these ideal conditions cannot be incorporated into the same device. Nevertheless, due to the specific construction emloyed a more advantageous combination can chosen than is possible with any conventional type coil known to the applicant. For instance, the inductance of t is coil is reduced to .006 by providing a small number of primary turns having a relatively nigh-current strength, the inductance equalling the number 0 rimary turns times the flux in lines divided by the current strength in amres times The use of this small numr of turns is made gossible by the construction of the core an the unique disposition of the secondary winding in the magnetic circuit.

Still further, the'current stren h in the primary circuit at the moment t 0 contact points open is relatively high. This current depends u n the resistance of the rimary winding, t e battery voltage and the requency required and at high frequencies the voltage in the primary winding does not attain the battery voltage, due to the resistance and inductance. The low resistance and inductance of my primary winding causes the current strength to build up at an abnormally fast rate, thereby providing a high-current strength even when the frequency is very great. It is for this reason that I am enabled to use only one coil on eight-cylinder highspeed engines that formerly required two coils, one for each bank of four cylinders.

Just as it is very important to establish the magnetic circuit in the shortest time possible, it is even more important that the collapsing of the circuit be almost instantaneous to thereby increase the E. M. F. in the primary circuit as much as possible and likewise increase the output secondary voltage. A low inductance facilitates the collapsing of this circuit.

However, a low inductance has heretofore been associated only with induction coils having an o n magnetic circuit. In such coils the num r of primary turns must be increased from five to ten times that required with a closed circuit and this increasein the number of turns directly increases the resistanceso that the time element required to build up the primary circuit is thereby materially increased. It is apparent that if a closed magnetic circuit is provided, the high inductance so slows u the establishment and collapsing of the circuit that the coil would be inoperative. Inversely, if an open magnetic circuit is provided, then the inductive effect of the circuit is reduced so that excessively 66 large primary and secondary windings are required. The applicant has provided a magnetic circuit having an air ga considerab larger than the conventional air gap employed and while the field strength is somewhat less than in the conventional coil, this reduced inductive action is ofiset by his disposition of the major portion of his secondary winding at a point intermediate of the ends of the coil where the flux density is at a maximum to thereby increase the number of effective turns on the secondary windin The applicant contributes his greater e ciency to the novel design of his laminated core and its relation to the particular shape of secondary winding emplo ed.

In this connection, it may well to mention that the applicant is aware that numerous transformers have been suggested in which the core is composed of laminations ,bent back upon themselves, usually havin the ends thereof overlapping to form a close magnetic circuit. However, all of these deices, to the applicants knowledge, relate solely to transformers and not to induction coils. Although both transformers and induction coils depend upon induction, still the problems connected with each are so difierent that they are considered as inde ndent devices. A transformer operates on y upon alternating current while an induction coil operates only upon direct current. Still further, in all types of transformers the magnetic intensity is controlled by the ampere turns per inch of length and is ual at all points in the circuit. Consequent y, induction is not a factor in this device so that the disposition of the secondary winding should theoretically be wound uniformly over the entire magnetic circuit, as in the ordinary torus ring. In an induction coil the intensity of the magnetic circuit is not uniform but reaches a maximum midway between the ends of the primary winding. Thus. while the novel secondary winding provided herein will increase the efliciency of induction coils, still such winding would be detrimental if used in connection with a transformer. These limitations have been mentioned to show that the construction herein is applicable only to inductioncoils.

Among the many advantages arising from the use of my improved device, it ma be well to mention that I have provid an ignition coil a single unit of which is satisfactory for supplying the entire ignition current for operating eight-cylinder motors at speeds upwards of 4000 R. P. M. which requirement was formerly accomplished by the use of two individual spark coils. Still further, the higher efliciency obtained with this device automatically reduces the size thereof for a given output so that a material reduction in cost is obtained thereby. Still further, for the reason that the coil is especially easy to construct and assemble, the manufacturing cost is still further reduced.

Some changes may be made in the arrangement, construction and combination of the various parts of my improved device without departing from the spirit of my invention and it is my intention to cover by my claims such changes as may reasonably be included within the scope thereof.

I claim as my invention:

1. An induction coil for internal-combustion engine ignition system characterized by its low time constant and high eificiency comprising, a cylindrical low tension primary coil winding, a high tension secondary winding wound in layers around said primary coil having each succeeding layer somewhat less in length than the layer beneath to thus form a coil of such shape that a radial section therethrough will show the wire arranged in a pyramidal shape, a ring of insulation disposed between each of said secondary layers, all of said insulating rings having a uniform length whereby the outer edges of said insulating rings, will extend beyond each succeeding secondary layer to a greater extent, and a plurality of flat strip core laminations extending through said primary winding, both ends of each lamination being bent back around the secondary winding in a circumferential path having the axes of said windings forming a diameter thereof, and each lamination being of such length that an air gap is provided between its bent-back ends, whereby a progressively thicker section of insulation is provided between the edges of each succeeding secondary coil and said laminations.

'2. A device, as claimed in claim 1 wherein a cu -shaped dielectric housing is adapted to receive the arcuate ends of said laminations, and a dielectric cover is arranged to clamp down upon the laminations, to thus both form an enclosure for said windings and retain said bent-back ends in their circumferential shape.

3. An induction coil for internal-combustion engine ignition systems characterized by its low time constant and high efiiciency comprising, a cylindrical layer-wound primary coil, a secondary layer-wound coil disposed around said primary coil having a maximum length substantially two-thirds the length of said primary coil, and each succeeding ..ayer of said secondary coil being somewhat less in length than the layer beneath to thus form a coil of such shape that a radial section therethrough will show the wire arranged in a flat-topped pyramidal shape, and a ring of insulation disposed between each of said secondary layers, all of said insulating rings having a uniform length whereby the outer edges of said insulating rings will extend beyond each succeeding secondary layer to a greater extent, and a plurality of flat strip core laminations extending through said primary winding, both ends of each lamination being bent back around the secondary coil, whereby a progressively thicker section of insulation is provided between the edges of each succeeding secondary coil, the layer and bent-back portions of said laminations.

4. A secondar high tension winding especially adapte for use in connection with induction coils having a-substantiall closed metallic circuit comprising, a multipe layerwound coil having each succeeding la er somewhat less in. length than the layer eneath to thus form a coil of such shape that a radial section therethrough will show the wire arranged in a fiat-topped pryramidal shape, and rings of insulation disposed one between each of said layers, all of said insulating rings having a uniform length whereby the outer edges of said rings will extend beyond each succeeding layer to a greater extent, whereby a progressively thicker section of insulation is provided adjacent to the edges of each succeeding layer, for the purpose described.

5. An induction coil for internal-combustion engine ignition systems comprising, a primary coil winding, a secondary coil winding, said primary coil and secondary coil windings having a plurality of core laminations extending therethrough, said laminations being bent back around the coils to form an arcuate ferric path therearound, and a dielectric housing enclosing said coils and laminations having a portion into which said laminations extend to thereby fixedly secure the coils and laminations in position in said housing.

6. A device, as claimed in claim 5, wherein said housing comprises a cup-shaped dielectric member having a recess around its rim which receives said laminations, and a dielectric cover arranged to clamp down over said laminations to thus both form an enclosure for said coils and to retain said laminations and coils within said housing.

7. A device, as claimed in claim 5, wherein both ends of said laminations are bent back around the primary and secondary coils, said ends each coacting with the recess in said housing to fixedly secure the coils in place.

8. A device, as claimed in claim 5, wherein the core laminations are bent back around the primary and secondary coils to form a circular ferric path therearound, which bent back portions are secured in a circular recess in said housing.

9. An induction coil for internal-combustion engine ignition systems, cha' teriaed by its small time constant and high enciency comprising, a cylindrically shaped primary coil winding, a secondary coil. winding disposed around said primary coii having each succeeding layer somewhat less in lei-igth the layer beneath to thus form a coil of such sha e that the radial section therethrou h wil show the wire arra ed in a pyrami al shape,a pluralit of core aminations extending through sai rimary coil, both ends of each ot said lammations being bent back around the secondary coil to form an arcuate ferric path therearound with the length of each lamination being such that an air gap is provided between its bent back ends in position aligned with the center of said coils, and a dielectric housing havin a cylindrical recess therein into which said ent back portions of the laminations are fixedly retained 15 in an arcuate position.

AUGUST TOELLE.

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