US2605753A

US2605753A - Current generating device

Info

Publication number: US2605753A
Application number: US230296A
Authority: US
Inventors: Dorothy H Madle
Original assignee: Briggs and Stratton Corp
Current assignee: Briggs and Stratton Corp
Priority date: 1951-06-07
Filing date: 1951-06-07
Publication date: 1952-08-05
Anticipated expiration: 1969-08-05

Description

Aug. 5, 1952 A. M. MADLE CURRENT GENERATING DEVICE 4 Sheets-Sheet 1 Filed June 7, 1951 L ill-I A MMEJ/ Burnt/7y Hg m n mm MM M 0 0 7A. E

Aug. 5, 1952 A. M. MADLE CURRENT GENERATING DEVICE Filed June 7, 1951 4 Sheets-Sheet 2 I \a; IIIIII'IIIIIIIE W Alan: M Mad/afazcmsw .UJMzZU/HMBJZE,fApM/Msrmrm A. M. MADLE 2,605,753 CURRENT GENERATING DEVICE Filed June 7, 1951 4 Sheets-Sheet 3 v J! ii i/ Alain MMHUZE, 05:01am flamt/zyHMad/ej Aug. 5, 1952 A. M. MADLE I v 2,505,753

CURRENT GENERATING DEVICE Filed June 7, 1951 I 4 Shets-SheetA cRANKrNG' SPEED BREAKER BREAKER PRIMARY CURRENT AND v BREAKER OPEN g L o 5 E MAGNETOMflTIVE FORCE A OPEN 1 b can DUE TO B I D a PRIMAR CURRENT a I I g9: coRE FLUX T I t \y A FL 7 I J I E ICHAN E :FC I I J I I I. i I r V F I I l MAGNETOMOTI I con COR 1 I I I J. E C

0 90 I80 27a 35b 90 m0 270 no so CRANKSHAFT ANGLE-DEGREES 62v RUNN l N G 3 PE E D BREAKER BREAKER v PRIMARY CURRENT AND EREAKER oPE CLOSE I W 123g! I -|N coRE nus T0 PRIMTRY CURRENT I i I I D ICOJL CORE FLux T z FL L. I CHA N G E I l I l \I MQNETOMOTJVE FORCE m 1 com cans nus T0 MAGNET 0 90 I80 no 360 90 mo :70 860 90 CRANKSHAFT A GLE-DEGREES Patented Aug. 5, 1952 GENERATING DEVICE Alain M. Madl, deceased, late of MilWaukecJVis by Dorothy H. Madl, administratrix, Milwau kee, Wis., assignor to Briggs & Stratton Corporation, Milwaukee, Wis., a corporation of Delaware ' Application June "1, 1951, Serial No. 230,296

19 Claims.

This invention has reference to current generating devices andis'a continuation-in-part of the copending application of Alain M. Madl, deceased, Serial No. 108,293, filed August 3, 1949, which in turn was a continuation-impart of application Serial No. 653,493, filed March 11, 1946, both of which applications are now abandoned.

More specifically this invention concerns the provision of an improved current generating system for internal combustion engines and especially single cylinder four stroke cycle engines of the so-called portable type.

The conventional crankshaft driven magneto while capable of performing its intended function of generating a suitable high F. for spark plug operation leaves much to be desired when used on small one cylinder high speed, high compression internal combustion engines.

Such magnetos usually have their magnets mounted on the flywheel to rotate wit-h the engine crankshaft, and the crankshaft is provided with-a cam for effecting separation of breaker contacts stationarily mounted on a wall of the engine covered by the flywheel.

Hence. the whole magneto assembly together with the breaker contacts for controlling firing of the spark plug is located alongside one Wall of the engine and within the hollow interior of the flywheel. Access to any of the generator parts and especially the breaker contacts for adjustment or replacement thereof is thus either extremely difficult, or impossible, without considerable disassembly of the parts including the removal of the flywheel from the crankshaft.

Another disadvantage of the conventional crankshaft driven magneto when used with single cylinder engines wherein no distributor for the spark is required, resides in the fact that the breaker contacts are separated once each revolution of the crankshaft and thus effect firing of the spark plug twice during each four strokes of the engine, whereas only one spark is wanted for each four strokes. i. e., one spark for each two revolutions of the crankshaft.

The unwanted spark occurs at the top of the exhaust stroke of the piston and while it does not actually interfere with 'the operation of the engine, it shortens the life of the spark plug. Separation of the breaker contacts which produces this unwanted spark likewise results in unnecessary wear on the breaker contacts.

While the problem of the breaker produced unwanted spark may be solved by using a conventional cam shaft driven self-contained magneto. there are serious complications involved in 2 the installation and driving of such a magneto on relatively small engines of the type here under consideration. Consequently the use of such cam shaft driven magnetos in small single cylinder engines is hardly practical. In any event the conventional cam shaft driven magneto is of doubtful value as a solution to the problem. Moreover, it is desirable that the magneto be driven by the engine crankshaft so as to obtain the advantage of the higher speed of rotation of the crankshaft for the production of suitably high firing voltages in the magneto.

Conventional two pole flywheel magnetos for high speed, high, compression single cylinder engines having no distributor and wherein the breaker contacts are separated once each revolution of the crankshaft have another'm'ore serious disadvantage, namely the production of non-breaker produced sparks that occur while the breaker contacts are separated. These nonbreaker produced sparks result from a change in coil core flux due solely to rotation of the rotor. In the most common type of bi-pole magneto wherein the poles on the rotor and stator are, respectively, diametrically opposite one another and symmetrical these unwanted nonbreaker produced sparks that take place while the breaker contacts are separated tend to occur twice at equal time intervals each two revolutions of the engine crankshaft so that with the unwanted breaker produced spark which occurs near the top of the exhaust stroke the possibility exists of having three unwanted sparks during each cycle of the engine, once during each explosion and intake stroke and again near the top of each exhaust stroke; and above certain engine speeds all three of these unwanted sparks will occur.

While the cause of these unwanted sparks no doubt is understood by those skilled in the art, it may be helpful to point'out that in each instance, 1. e. breaker produced as well as nonbreaker produced, the sparks result from rapid flux changes .in the coil core. The curve of the magnetomotive force in the coil core due to the permanent magnet as a function of the movement of the rotor in a well designed magneto has an alternating substantially trapezoidal shape. The abrupt reversals in the curve, of course, correspond to the rapid flux changes in the coil core. The breaker produced sparks occur approximately at the end of every other reversal; and the non-breaker produced sparks occur just before the middle of the reversal/since themaximum voltage occurs at the centerof the reversal where the rate of change of the flux is greatest. Thus, since the wanted spark, which of course is breaker produced, should occur about twenty degrees of engine rotation ahead of the piston top dead center at the end of the compression stroke, the position of the rotor with respect to engine rotation is such that the unwanted other breaker produced spark occurs just before the piston reaches the top of the exhaust stroke and the two unwanted non-breaker produced sparks occur during the latter half of the explosion and intake strokes.

The occurrence of unwanted sparks while the breaker contacts are separated depends upon the comparative values of the spark gap breakdown voltage and the voltage induced in the secondary winding. This breakdown voltage is relatively low during the intake and exhaust strokes because of the low pressure existing in the combustion chamber at these times and can, therefore, be easily exceeded by the induced voltage in the coil.

While these non-breaker produced sparks have a lower peak voltage than breaker produced sparks they are nevertheless highly objectionable. The prolonged nature of the unwanted non-breaker produced sparks in high speed engines coupled with the fact that breaker operation each revolution of the engine produces two more sparks each cycle of the engine causes excessive firing of the spark plug and overheating and corrosion of its electrodes; and the overheating results in preignition of the combustible mixture charged into the engine cylinder and loss of power developed by the engine.

As far as is known, little has been done to eliminate the unwanted spark resulting from breaker contact operation at the top of the exhaust stroke in engines equipped with crankshaft driven magnetos, but attempts have been made to minimize the undesirable efiects of non-breaker produced sparks. The use of special cold plugs, and masking of the plug electrodes are two of the expedients resorted to in the past to offset these maverick sparks.

Masking is usually accomplished by a special cylinder head construction wherein the spark plug electrodes are located in the bottom of a well or recess having more or less limited communication with the cylinder. Thus, the weak but prolonged non-breaker produced maverick sparks across the electrodes can be, prevented from causing preignition by the fact that the electrodes are masked by burnt gases from previous cycles. Special cold plugs are employed chiefly because of their ability to better withstand heat, and do not necessarily eliminate preignition.

But the control of non-breaker produced sparks by masking entails a special cylinder head construction and removes the spark plug electrodes from their most effective position within the cylinder. Moreover, it does not eliminate overheating of the spark plug electrodes which condition manifests itself in shorter spark plug life.

The main objection to these expedients which have been employed in the past to control maverick sparks, however, is that they deal not with the cause but the effect of the disturbing condition.

With the foregoing objections in mind, it is one of the main objects of this invention to provide a crankshaft operated magneto for single cylinder four cycle internal combustion engines having breaker contacts controlled by an engine 4 shaft rotating at one-half crankshaft speed so as to eliminate the unwanted breaker produced spark which would occur at the top of the exhaust stroke of the engine if the breaker operated at crankshaft speed.

Thus it will be noted that while the magneto rotor is driven at a speedsuitably high for cilicient operation, breaker contact separation takes place only once for each two revolutions of the engine crankshaft, i. e. once each engine cycle,

at the proper time required to ignite the compressed mixture in the engine cylinder.

Another object of this invention resides in the provision of a magneto for single cylinder high speed, high compression engines wherein unwanted non-breaker produced or maverick sparks are eliminated.

In this respect it is another object of this invention to provide a magneto for single cylinder high speed, high compression internal combustion engines wherein objectionable maverick sparks are eliminated by the particular manner in which circuit breaker operation is effected. Thus by eliminating the cause there is no need for special structural provisions in the combustion chamber to prevent preignition.

A further object of this invention resides in the provision of a magneto for high speed, high compression engines wherein unwanted nonbreaker produced or maverick sparks are eliminated, and wherein novel automatic spark advancing and retarding mechanism is employed.

Another object of this invention resides in the provision of a magneto for single cylinder internal combustion engines wherein the breaker contacts are located substantially remote from the flywheel and on the exterior of the engine crankcase so as to be readily accessible for adjustment or replacement.

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described, and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the 'hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate one complete example of the physical embodiment of the invention constructed in accordance with the best mode so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a side elevational view of an internal combustion engine equipped with the current generating system of this invention;

Figure 2 is an enlarged detail view partially in section of a portion of the engine shown in Figure 1;

- Figure 3 is a cross sectional view taken on the plane of the line 3-3 of Figure 2, with the rotor of the magneto in a position at which its poles bridge the gaps between the poles of the stator and with the breaker cam in spark retarded position and having just allowed the breaker contacts to close;

Figure 4 is a diagrammatic view illustrating the essential elements of the magneto and the manner in which the breaker contacts control firing of the spark plug, the rotor of the magneto in this view being shown in a position partially bridging the gap between the stator poles, and the breaker cam in spark retarded position and shortly about to allow closure of the breaker contacts;

Figure 5 is a front view of the breaker box with its cover removed;

Figure 6 is a fragmentary sectional view taken on the plane of the line 6-6 of Figure 2;

Figure 7 is a view of the cam shaft gear illustrating the automatic spar-k advancing means;

Figure 8 is a cross sectional view taken on the plane of the line 8-8 of Figure 7;

Figure 9 is a diagram illustrating the magneto motive force in the coil core due to the rotor magnets and the fluX-inthe coil core and the current in the primary coil throughout-a complete engine cycle at cranking speedat which time the spark is retarded; and I I Figure 10 is a diagram similar to Figure -9' bu showingthe magnetomotive force in the coil'co'r'e due to the-rotor magnets and the flux in the coil core and the current in the primary coil at normal running speeds.

Referring now more particularly to the accompanying drawings in which like numerals indicate like parts throughout the several views, the numeral I I) generally designates a single cylinder four stroke cycle internal combustion engine of the small portable type, adapted to be operated at high speeds and having a relatively high compression ratio.

The engine is provided with the customary cyl' inder II and spark plug I2, while the crankshaft I3 projects from one side of the crankcase I4 to' mount a flywheel I5 thereon in a more or less conventional manner. The flywheel I5 is of hollow construction, as illustrated, and has its open side facing the adjacent end wall I4 of the crankcase.

Mounted on the crankshaft between the hub of the flywheel and the adjacent end wall I4 of thecrankcase is the rotor I6 of a magneto generally designated IT. The rotor 16 is of special construction and forms the subject matter of a companion application, Serial No. 230,295, filed June 7, 1951.

It has two diametrically opposite poles I0 connected by a pair of permanent magnets II, the poles and magnets being embedded in-a nonmagnetic hub-like body I3. This body is bored to fit the crankshaft I3 to which it is secured to dispose the rotor withi'n'a stator I8 stationarily supported from the wall I4 of the crankcase inside the hollow interior of the flywheel. The stator I3 also has two diametrically opposite poles connected by a coil core I8 upon which the usual primary and secondary windings I9 and 20 respectively are mounted. I

To the extent that the rotor of the magneto is driven by the crankshaft and the magneto parts per se are located within the hollow interior of the flywheel, the magneto of this invention follows conventional practice.

As stated previously, it was the custom in the past to support the breaker contacts for controlling spark plug operation on the end wall of the crankcase inside the flywheel, and to actuate the breaker contacts by means of a cam carried by the crankshaft of the engine. This arrangement, however, is objectionable for single cylinder four cycle engines having no distributor because the breaker contacts are then all butinaccessible, and because with that arrangement the breaker contacts were actuated every revolution'of the crankshaft and thus produced an unwanted spark at the time the piston reached the top of its exhaust stroke. Such an unwanted spark does not interfere with operation of the engine, but it nevertheless shortens the life of theengine spark by relocatingthe breaker contact assembly 2I re-- mote from the flywheel and on the exterior of the side wall 22 of the crankcase which is adjacent to the cam shaft 23, where it is readily accessible for adjustment or replacement of thebreaker contacts. A

As best shown in Figures 5 and 6, the breaker contact assembly 2| is carried by a base plate 24 overlying an aperture (not shown) in the side wall 22 of the engine crankcase. A bearing 25 projecting from the back of the base plate extendsinto the interior of the crankcase toward the cam shaft 23 and has a stub shaft '21 journalled for oscillatory motion therein.

' One end of the stub shaft 21 projects from the front of the base plate 24 to have the movable breaker arm 28 fixed thereon. The outer end of the breaker arm 28 has the movable contact 29 mounted thereon for cooperation with a stationary breaker contact 30.

The stationary contact 30 is carried by an adjustable 'plate 3I supported from the base plate 24 in a manner such that rotation of an eccentric 32 operates to adjust the position of the stationary contact with respect to the movable contact 29, a clamping screw 32 being provided to secure the plate 3| in adjusted position. A

leaf spring 33 having one end anchored to the Fixed on th inner end of the stub shaft 21 which projects into the interior of the crankcase is an arm 35 having a cam follower 36 onits outer extremity arranged to be traversed by a breaker cam 31 carried by the cam shaft gear 38. As will be clear from Figure 2, the cam shaft gear is located on the cam shaft 23 near the wall of the crankcase remote from the flywheel and meshes with a pinion 39 on the crankshaft. Since the pinion has one-half the number of teeth of'the cam shaft gear, the customary oneto-two ratio obtains between the crankshaft and cam shaft.

Inasmuch as the cam shaft rotates at onehalf crankshaft speed, it will be apparent that the cam 31 acting through the arm 35 effects separation of the breaker contacts once each rev olution of the cam shaft or once for each two revolutions of the crankshaft. This is highly advantageous in that it eliminates the unwanted spark which occurs in conventional one cylinder engine ignition systems at the top of the exhaust stroke, and thereby achieves another of the objects of this invention.

Referring to the diagram of Figure 4, it will be seen that one end of the primary winding I9 is electrically connected with the stationary contact 30 of the breaker assembly by means of a conductor 40. The opposite end of the primary winding, along with the adjacent end of the secondary winding, is grounded as at M.

The movable contact '29 of the breaker assembly is also grounded as at 42 so that when the breaker contacts are engaged both ends of the primary winding are grounded and current may flow therein; and since the secondary wind- 31 has a relatively short angular length or dwell so as to only momentarily hold the breaker contacts separated. The separation of the contacts, which, as is well known, should be rapid, occurs when the steeply inclined leading end 31' of the cam rides under the cam follower; and upon such separation of the breaker contacts the spark plug fires. The timing of the breaker separation with respect to the engine cycle is, of course, determined by the position of the cam on the cam shaft gear 38; and this position, as

will be hereinafter brought out, is automatically adjustable to advance the spark as the engine comes up to speed.

Because of the short angular length of the cam the breaker contactsare allowed to be reclosed by the spring 33 very soon after the plug has fired; but since the closure of the breaker contacts need not be as rapid as the opening and moreover cannot be faster than the action of the breaker spring, the trailing end 31 of the cam is not as steep as its leading end.

The breaker contacts remain closed for most of the 360 degrees of rotation of the cam shaft 23 to normally maintain the primary winding connected to ground at both ends and in condition to have current flow therein. In other words, the primary winding is part of a closed circuit at all times except during the short interval the breaker contacts are opened to effect firing of the spark plug.

By keeping the breaker contacts normally closed in this manner and having the open period of the contacts take place when there is substantially no change in magnetomotive force in the coil core due to the permanent magnet, nonbreaker produced or so-called maverick sparks are prevented. Since there is a substantial difference in the length of the arcuate pole faces of the rotor and stator there is a relatively long interval which occurs four times each engine cycle during which the rotor and stator pole faces overlap or oppose each other and the magneto motive force in the coil core due to-the perma-,

nent magnet is substantially uniform and, of course, as the rotor pole faces sweep across the gaps between the stator poles this magneto motive force in the coil core due to the permanent magnet reverses abruptly.

As long as the breaker contacts are closed so that current may flow in the primary winding the abrupt changes in magnetomotive force in the coil core due to the permanent magnet during these reversals are incapable of causing maverick sparks becausethe current flowing in the closed primary circuit produces a magnetomotive force in the coil core in opposition to the magnetomotive force clue to the permanent magnet. This bucking current prevents rapid flux changes and consequently precludes the generation of a maverick spark producing E. M. F. directly in the secondary winding.

In Figure 4, which depicts conditions during cranking, the rotor is shown in a position at which its pole faces partially bridge the gaps between the stator poles; and the cam 31 is about to allow the breaker contacts to close. At running speeds, when the cam 37 actuates the breaker contacts sooner in the engine cycle, the reclosure of the contacts takes place at approximately the instant the rotor pole faces begin to move into positions bridging the gaps between the stator poles. But at all speeds the opening of the breaker contacts takes place after the reversal of magnetomotive force in the coil core due to the permanent magnet directly preceding spark time and closes before the next successive reversal. Y

Reference to Figures 9 and 10 will facilitate an understanding of the manner in which this magneto operates, and since the maverick spark condition to be eliminated exists only at running speeds, attention is particularly directed to Figure 10.

The wave pattern of the magnetomotive force in the coil core due to the permanent magnet, represented by the heavy solid line in Figures 9 and 10 has the relatively flat plateaus shown to depict substantially uniform magnetomotive force because of the difference in the lengths of the rotor and stator pole faces. As already noted, by virtue of this difference the face of each rotor pole is opposite a stator pole face for a substantial angle of rotor rotation, and during this angular interval substantially no change takes place in magnetomotive force in the coil core due to the permanent magnet. Bearing in mind that for maverick sparks to occur requires the concurrence of a change in magnetomotive force in the coil core due to the permanent magnet and an open condition of the primary circuit, it follows that if the breaker contacts are closed during all changes in magnetomotive force in the coil core due to the rotor magnet that maverick sparks will be prevented.

Hence, the breaker cam 31, after opening the breaker contacts to produce the desired spark (at a time when there is no rotor magnet produced change in magnetomotive force) must allow the contacts to reclose before the next change in magnetomotive force due to the rotor magnet. Accordingly the cam 31 must be short enough to assure opening and reclosing of the breaker contacts during the angular interval that the rotor and stator pole faces are substantially opposite one another, but since the breaker mechanism must have time to function it follows that it is essential to have a relatively large difference in the arcuate length of the stator and rotor pole faces.

The sparking voltage is, of course, obtained from the secondary coil in which it is induced by the rapid change in flux in the coil core which occurs when the primary circuit is opened by separation of the breaker contacts. Since the breaker contacts close and open at times when the magnetomotive force due to the magnet is in the same direction no change of flux would occur when the breaker opened if the primary coil and its circuit had zero resistance. Under such a theoretical condition the coil core flux would remain at a constant value for a complete engine cycle which encompasses the four half cycles of of rotor rotation designated A, B, C and D.

However, since the primary circuit has resistance a decaying current, represented by the dotted line in the diagrams, obtains in the primary circuit. Because of this decaying current the coil core flux represented by the dot and dash lines on the diagram also decays, the overall decrease in coil core flux being represented by the dimension FC.

During the half cycle D and directly after the fourth complete reversal of magnetomotive force following closure of the breaker contacts the breaker contacts open and the flux changes abruptly by an amount equal to its net decay.

Since the net flux decay is a function of time, at higher engine speeds the time for decay is less and hence the net flux decay decreases with increasing engine speeds. This decrease in flux decay results in a decrease in the amount of flux change at the instant of breaker contact opening so that the sparking voltage decreases with 'increasing engine speed. I

I Conversely at lower engine speeds the net flux decay is greater as will appear from a comparison of the value FC in the two diagrams Figures 9 and 10. Therefore, at cranking speeds the sparking voltage (which is approximately proportional to thevalue F) is greater than at running speeds. This in an important advantage since it enables the attainment of the most desirable speed-voltage characteristic orcurve.

'Those skilled in the design of magnetos know that the sparking voltage, i. e. the voltage needed to the the spark plug does not rise with increas-- ing engine speed, but'on the contrary drops. With all magnetos heretofore used on single cylinder engines the voltage at the'spark plug continues to rise as the engine speed increases so that at normal runningspeeds it is far in excess of the voltageneeded for proper firing. In fact, it'is so high that the life'of the plugs is far too short for satisfactoryservice. By contrast the speed-voltage curve of the magneto of this invention rises abruptly during starting speeds to reach maximum long before normal running speeds and then drops so that at running speeds the sparking voltage is actuallylower than at starting but still comfortably above minimum requirements. Obviously this reduces the electrical strain upon the spark plug points.

The explanation for this advantage lies in the fact that the breaker points are operated at onc half crankshaft speed and remain uninterruptedly closed for most of the cycle.

In considering the diagrams, Figures 9' and 10, it should be borne in mind'that the low speed diagram (Figure 9) is greatly'condensed along its time axis so that although there'appear to be rapid and abrupt flux changes,actually these changes which are due to the decay of the current are gradual. The important consideration is that no rapid flux changes can occur as long as the breaker contacts are closed and since the magneto is so designed that the breaker contacts are open only when there is no tendency for rotor rotation to rapidly change the flux (which could only occur atrunning speeds) it follows that all unwanted firing of the spark plug is eliminated.

This invention, therefore, not only eliminates the unwanted spark which is normally produced in one cylinder engines having crankshaft operated breaker contacts, but also eliminates the non-breaker produced sparks which seriously interfered with engine operation in the past; and also provides accessibility to the breaker contacts.

The automatic retarding of the spark referred to hereinbefore is achieved by mounting the breaker cam 31 on the free end of a centrifugally actuated weight 45 having an eccentric pivotal connection 46 with the camshaft gear. This weight, as best shown in Figures '7 and 8 is carried by the cam shaft gear at the side. thereof opposite the breaker cam. A coil spring 41 having one end anchored to the cam shaft gear 38 is attached to the free .end of the weight to hold the same in its inner position holding the breaker cam 31 in a retarded spark position. As the engine speed increases centrifugal force acting on the weight rotates the same about its pivot 46 toward the surface 48 on the cam shaft gear to angularly shift the breaker cam 31 in the di- 5| cut into the side of the breaker cam 31.

tarded with one end of the notch of the breaker cam engaged with the pin 50. 1

For the sake of appearance and to afford a degree of protection for the breaker contacts the base plate 24 is preferably provided with a detachable cover 52 to close the breaker assembly. This cover carries a stop button 53 at its exterior which when depressed into the cover engages the terminal 54 of the breaker assembly to ground the magneto primary despite the condition of the breaker contacts and to thereby effect stopping of the engine.

' From theforegoing description taken in connection with the accompanying drawings, it will be readily apparent to those skilled in the art that this invention provides a highly improved magneto and breaker control therefor which is advantageous from the standmint that it enablesthe elimination of all unwanted sparks; that it achieves the ideal speed-voltage characteristic of high voltage at cranking speeds and lower voltage at running speeds; and that it enables the breaker contacts to be placed in a read.- ily accessible location remote from the flywheel.

What is claimed as the invention is:

1. In an ignition system for a single cylinder four cycle internal combustion engine of the type having a crankshaft driven magneto, a crankcaseyand a cam shaft geared to said crankshaft to rotate at one-half crankshaft speed; fixed and movable breaker points mounted on the exterior of the crankcase in a position substantially remote from the magneto but readily accessible from the exterior of the engine; a cam follower in juxtaposition to a face of the cam shaft gear; a motion transmitting connection between said cam follower and. the movable breaker point; and means for effecting momentary separation of said breaker contacts once each two revolutions of the crankshaft, said means including an arm having one of its ends pivoted to a face of the cam shaft gear eccentrically thereof so as to be bodily movable with the gear, and so that the opposite end of the arm is free for arcuate motion in the plane of the gear face and to advance relative to the periphery of the gear in the direction of rotation of the gear as a result of centrifugal force consequent to rotation of the gear; means yieldingly biasing said arm against such advancing motion; and a cam surface carried by said arm and adapted to cooperate with said cam follower to momentarily separate the breaker points only once during each revolution of the cam shaft.

2. In an ignition system for a single cylinder four cycle internal combustion engine of the type having a crankshaft driven magneto and a cam shaft geared to the crankshaft for rotation therewith at'one-half crankshaft speed: a pair of normally engaged breaker contacts; and means for effecting momentary separation of said breaker contacts once each revolution of the cam shaft, said means comprising a part fixed on the cam shaft to rotate therewith, and a cam mounted on saidv part for motion relative thereto in con- Sequence. to centrifugal force, said cam being movable in a direction to effect earlier separation 11 of the breaker contacts as the engine approaches normal operating speeds.

3. In an ignition system for a single cylinder four cycle internal combustion engine of the type having a crankshaft driven magneto and a cam shaft geared to the crankshaft for rotation therewith at one-half crankshaft speed: normally closed fixed and movable breaker points; a cam follower connected with the movable breaker point and operable to eifect separation thereof from the fixed point; a part fixed on the engine cam shaft to rotate therewith; a cam; and means mounting the cam on said part for momentary engagement with and operation of said cam follower once during each revolution of the cam shaft so as to effect momentary separation of the breaker points during such operation of the cam follower, said means providing for motion of the cam relative to said part in a direction to effect earlier separation of said breaker points in response to increased centrifugal force on said part due to an increase in the rate of rotation of the cam shaft.

l. In an ignition system for a single cylinder four cycle internal combustion engine having a crankshaft driven magneto and fixed and movable breaker points: a wheel rotatably driven from the engine crankshaft at a fixed speed with respect to the crankshaft; an arcuate arm having one of its ends pivotally connected to the wheel at one face thereof to swing about an axis spaced from the center of the wheel in response to centrifugal force during rotation of the wheel, said arm having its free end overlying a slot formed in the side of the wheel substantially diametrically opposite the pivot point of the arm; means for momentarily separating the breaker points once each revolution of said wheel, including a cam disposed at the opposite face of said wheel, and means projecting through said arcuate slot in the wheel to connect the cam with the free end of said arm for motion of the cam with the arm; and a spring reacting between the arm and the wheel to hold the arm with the cam in a position at one end of the slot corresponding to retarded opening of the breaker points, said spring being yieldable in response to centrifugal force on the arm to allow the free end of the arm to carry the cam to the other end of the slot during high speed operation of the engine to eifect earlier separation of the breaker points.

5. In an ignition system for a single cylinder four cycle internal combustion engine of the type having a crankshaft driven magneto for effecting spark plug operation: fixed and movable breaker points accessibly mounted on the exterior of the engine remote from the magneto; a cam follower movably supported by the engine remote from the breaker points; a motion transmitting connection between the cam follower and the movable breaker point such that separation of the points is effected by motion of the cam follower in one direction; a rotatable part adjacent to said cam follower; a driving connection between said rotatable part and the engine crankshaft whereby the speed of rotation of the crankshaft determines the speed of rotation of said rotatable part; a member carried by said rotatable part for rotation therewith and for motion relative thereto in response to centrifugal force; and a cam surface on said member engaged by said cam follower for imparting motion to the cam follower in said direction once each revolution of the rotatable part to effect breaker point separation at instants depending upon the speed 12 of crankshaft rotation and the position of said member relative to the rotatable part as determined by the centrifugal force acting on said member.

6. In an ignition system for a single cylinder four stroke cycle internal combustion engine of the type having a crankshaft driven magneto and a cam shaft driven from the crankshaft for rotation therewith at one-half crankshaft speed: a pair of normally engaged breaker contacts; means for effecting momentary separation of said breaker contacts once each revolution of the cam shaft; said means comprising a part fixed on the cam shaft to rotate therewith, a centrifugally responsive breaker cam mounted on said part to rotate therewith and for back and forth motion relative thereto, said cam being movable in one direction relative to said part to effect earlier separation of the breaker contacts in consequence to centrifugal force as the speed of the engine increases; means for limiting back and forth motion of the cam relative to said part so as to define the spark advanced and retarded positions of the cam; and biasing means acting on the cam to yieldingly resist motion thereof in said direction in response to centrifugal force.

'7. In an ignition system for an internal combustion engine of the type having a crankshaft driven magneto for effecting spark plug operation, and fixed and movable breaker points actuated by a cam follower for timing the occurence of the spark with respect to the rotational position of the crankshaft, means for automatically varying the timing of breaker point operation in accordance with the rate of rotation of the crankshaft, comprising: a member rotatably driven in one direction from the crankshaft, said member having opposite faces normal to its axis of rotation; an arm overlying one face of said member and extending laterally thereacross to one side of the axis of the member, the ends of the arm being disposed substantially diametrically opposite one another; means pivotally connecting one end of the arm to said member so that the other end of the arm may swing back and forth across said face of the member, said other end of the arm being centrifugally responsive and being adapted to swing relative to said member in the direction in which the member rotates as the speed of the engine increases;' a projection on said other end of the arm extending through a slot in said member; a cam on said projection adapted to operatively engage the cam follower once during each revolution of the member, said cam overlying the opposite face of the member so that the member is interposed between said cam and the arm to guide the arm in its swinging motion; and means yieldingly urging the arm to swing counter to the direction of rotation of said member so as to yieldingly resist response of the arm to centrifugal force.

8. In an ignition system for an internal combustion engine having a crankshaft and fixed and movable breaker points operated by a cam actuated follower, means for automatically varying the timing of breaker point operation in accordance with the speed of the engine, comprising: a member rotatably driven in one di- ;rection from the crankshaft of the engine, said member having opposite faces normal to its axis of rotation; an arm overlying one face of said member with its ends lying at substantially diametrically opposite sides of the axis of the memher and its body extending around to one side of the axis of the member; means pivotally connecting one end of said arm to the member and constraining the other end of the arm to swinging motion parallel to said face of the member, said other end of the arm being adapted to swing in one direction relative to the member in consequence to centrifugal force as the speed of rotation of the member increases; an axial thrust cam connected with said other end of the arm to be moved thereby, said cam having a cam. surface thereon exposed at the opposite face of the member for engagement with the cam follower to move the same away from said opposite face of the member and effect actuation of the breaker points once each revolution of said member, said cam having a portion overlying and bearing against said opposite face of the member where by reaction of the cam to the thrust of the cam follower is taken by that portion of the member which the cam overlies; biasing means yieldably restraining movement of r the arm in response to centrifugal force; and stop means on said member for defining the limits of motion of the arm in response 'tocentrifugal force and to said biasing means. I

9. In an ignition system for an internal c0mbustion engine having a crankshaft andfixed and movable breaker points operated by a cam actuated follower, means for automatically varying the timing of breaker point operation in accordance with the speed of the engine, com prising: a member rotatably driven from the engine crankshaft; a cam for actuating said follower; means connecting the cam with said member for bodily rotation therewith and for movement relative thereto in a plane substantially perpendicular to the axis of rotation of the member, movement of the cam in one direction relative to said member effecting earlier engage ment of the cam with its follower, said connecting means including a weighted centrifugally responsive arm eccentrically pivoted on the member so as to effect movement of the cam relative to the member in said direction in response to centrifugal force acting on the arm as the speed of rotation of said member increases; a spring reacting between the cam and said -.member and tending to move the cam in the opposite direction so as to yieldingly resist response of said arm to centrifugal force; and a surface on said member along which the cam moves and against which it bears to transmit the thrust of the cam follower to said member.

10. In an ignition system for an internal cornbustion engine having a cam shaft and a timing gear thereon by which the cam shaft is driven from the crankshaft of the engineat one-half crankshaft speed: fixed and movable breaker contacts; a breaker cam; means mounting the cam on said timing gear for bodily rotation therewith and for motion relative thereto in the direction of rotation of the timing gear in response to centrifugal force; a spring reacting between the cam and the timing gear and tending to move the cam in the opposite direction; stop means on the timing gear for limiting motion of the cam relative to the timing gear under the influence of centrifugal force as well as of said springs; a cam follower alongside the timing gear in position to be op-eratively engaged by said cam once each revolution of the timing gear; and a motion transmitting connection between the cam follower and the movable breaker contact.

11. A high speed, high compression, single cylinder internal combustion engine having a spark plug and a crank shaft driven bipolemagneto having stator and rotor elements, provided with inductively coupled primary and secondary windings on a coil core which connects the'poles of one of the magneto elements and a permanent magnet connecting the polesof the other element to produce a magnetomotive force in the coil core which reverses twice for each revolution of the rotor element, wherein the primary circuit is normally closed and is open only when a pair ofnormally closed breaker contacts connected in the primary circuit are opened, and wherein the spark plug is, fired by the high sparking voltage induced in the secondary winding each time the normally closed breaker contacts are opened: characterized by the fact that the longest pole face of one of the magnetoelements is considerably shorter than the shortest pole face of the other magneto element, and the pole faces of one magneto element are of such length and so related to the pole faces of the other magneto element that for an instant the gaps between the pole faces of each magneto element are simultaneously substantially bridged by the pole faces of the other, at which instant the magnetomotive force in the coil core due to the permanent magnet abruptly reverses, the interval of rotor rotation directly following such abrupt reversal producing a high substantially uniform magnetomotive force in the coil core due to the permanent magnet; and furthercharacterizedby the fact that the breaker contacts are controlled by a single lobed breaker cam driven atone-half crankshaft speed, the effective angular length of which is suchthat opening and, reclosure ofthe breaker contacts can take'place during said interval of rotor rotation when the magneto motive force in the coil core due to the permanent magnet is substantially uniform, and by the fact that the cam is so timed withrespect to the rotor position at the desired spark time as to effect opening of the breaker contacts shortly after thereversal in magneto motive force directly preceding said interval of rotor rotation and reclosure of the breaker contacts before the next successive reversal in magnetomotive force so thatwhenever the primary circuit is open the magnetomotive force in the coil core due to the permanent magnet remains substantially unchanged, and whenever the magnetomotive force in the coil core due to the'permanent magnet is changing the primary circuit is closed and current flows through the primary winding to produce a magnetomotive force in the coil in opposition to the magnetomotive force therein due tothe permanent magnet to thereby prevent rapid flux changes in the coil core, which unless prevented, would result in unwanted non-breaker produced firing'of the spark plug. Y I

12. A high speed, high compression, single cylinder internal combustion engine having a spark plug and a crankshaft driven bipole magneto having stator and rotor elements, provided with inductively coupled primary and secondary windings on a coil core which connects the poles of one of the magneto elements and apermanent magnet connecting the poles of the other element to produce a magnetomotive force in the coil core which reverses twice for each revolution of the rotor element, wherein the primary circuit is normally closed and is open only when a pair of normally closed breaker contacts connected in the primary circuit are opened, and wherein the spark plug is fired by the, high sparking voltage induced in the secondary winding each time the normally closed breaker contacts are opened: characterized by the fact that the longest pole face of one of the magneto elements is considerably shorter than the shortest pole face of the other magneto element and the pole faces of one magneto element are of such length and so related to the pole faces of the other magneto element that for an instant the gaps between the pole faces of each magneto element are simultaneously substantially bridged by the pole faces of the other, at which instant the magneto motive force in the coil core due to the permanent magnet abruptly reverses, the interval of rotor rotation directly following such force in the coil core due to the permanent magnet is substantially uniform, and by the fact that the cam is so timed with respect to the rotor position at the desired spark time as to effect opening of the breaker contacts shortly after the reversal in magnetomotive force directly preceding said interval of rotor rotation and reclosure of the breaker contacts before the next successive reversal in magnetomotive force so that whenever the primary circuit is open the magnetomotive force in the coil core due to the permanent magnet remains substantially unchanged, and whenever the magnetomotive force in the coil core due to the permanent magnet is changing the primary circuit is closed and current flows through the primary winding to produce a magnetomotive force in the coil core in opposition to the magnetomotive force therein due to the permanent magnet to thereby prevent rapid flux changes in the coil core, which unless prevented, would result in unwanted nonbreaker produced firing of the spark plug.

13. A high speed, high compression, single cylinder internal combustion engine having a spark plug and a crankshaft driven bipole magneto having stator and rotor elements, provided with inductively coupled primary and secondary windings on a coil core which connects the poles of one of the magneto elements and a permanent magnet connecting the poles of the other element to produce a magnetomotive force in the coil core which reverses twice for each revolution of the rotor element, wherein the primary circuit is normally closed and is open only when a pair of normally closed breaker contacts connected in the primary circuit are opened, and wherein the spark plug is fired by the high sparking voltage induced in the secondary winding each time the normally closed breaker contacts are opened: characterized by the fact that the faces of each magneto element are of equal length and the faces of one of the magneto elements are considerably longer than the faces of the other magneto element and the pole faces of one magneto element are of such length and so related to the pole faces of the other magneto element that for an instant twice each revolution of the rotatable magneto element the gaps between the poles faces of each magneto element are simultaneously substantially bridged by the pole faces of the other, at which instant the magnetomotive force in the coil core due to the permanent magnet abruptly reverses, the interval of rotor rotation directly following such abrupt reversal producing a high substantially uniform magnetomotive force in the coil core due to the permanent magnet; and further characterized by the fact that the breaker contacts are controlled by a single lobed breaker cam driven at one-half crankshaft speed, the elfective angular length of which is such that opening and reclosure of the breaker contacts can take place during one of said intervals of rotor rotation when the magnetomotive force in the coil core due to the permanent magnet is sub stantially uniform, and by the fact that the cam is so timed with respect to the rotor position at the desired spark time as to effect openingof the breaker contacts shortly after the reversal in magnetomotive force directly preceding said interval of rotor rotation and effects reclosure of the breaker contacts before the next successive reversal in magnetomotive force, so that whenever the primary circuit is open the magnetomotive force in the coil core due to the permanent magnet remains substantially unchanged and whenever the magnetomotive force in the coil core due to the permanent magnet is changing the primary circuit is closed and current flows through the primary winding to produce a magnetomotive force in the coil core in opposition to the magnetomotive force therein due to the permanent magnet to thereby prevent rapid flux changes in the coil core, which unless prevented, would result in unwanted non-breaker produced firing of the spark plug.

14. A high speed, high compression, single cylinder internal combustion engine having a spark plug and a crankshaft driven bipole magneto having stator and rotor elements, provided with inductively coupled primary and secondary windings on a coil core which connects the poles of one of the magneto elements and a permanent magnet connecting the poles of the other element to produce a magnetomotive force in the coil core which reverses twice for each revolution of the rotor element, wherein the primary circuit is normally closed and is open only when a pair of normally closed breaker contacts connected in the primary circuit are opened and wherein the spark plug is fired by the high sparking voltage induced in the secondary winding each time the normally closed breaker contacts are opened: characterized by the fact that the faces of each magneto element are of equal length and the faces of one of the magneto elements are considerably longer than the faces of the other magneto element and the pole faces of one magneto element are of such length and so related to the pole faces of the other magneto element that for an instance twice each revolution of the rotatable magneto element the gaps between the pole faces of each magneto element are simultaneously substantially bridged by the pole faces of the other, at which instant the magnetomotive force in the coil core due to the permanent magnet abruptly reverses, the interval of rotor rotation directly following such abrupt reversal producing a high substantially uniform magnetomotive force in the coil core due to the permanent magnet; and further characterized by the fact that the breaker contacts are controlled by an engine driven single lobed breaker cam, the effective angular length of which is such that opening and reclcsure of the breaker contacts can take place during one of said intervals of rotor rotation when the magnetomotive force in the coil core d'ue'to the permanent magnet is substantially uniform, and by the fact that the cam is so timed with respect to the rotor position at the desired spark time as to effect opening of the breaker contacts shortly after the reversal in magnetomotive force directly preceding said interval of rotor rotation and effects reclosure of the breaker contacts before the next successive reversal in magnetomotive force, so that whenever the primary circuit is open the magnetomotive force in the coil core due to the permanent magnet remains substan tially unchanged and whenever the magnetomotive force in the coil core due to the permanent magnet is changing the primary circuit is closed and current flows through the primary winding to produce a magnetomotive force in the coil core in opposition to the magnetomotive force therein due to the permanent magnet to thereby prevent rapid flux changes in the coil core, which unless prevented, would result in unwanted non-breaker produced firing of the spark plug.

15. A high speed, high compression, single cylinder internal combustion engine having a spark plug and a crankshaft driven symmetrical bipole magneto having a stator and a rotor, provided with inductively coupled primary and secondary windings on a coil core which connects the poles of the stator, wherein a permanent magnet connecting the poles of the rotor produces a magnetomotive force in the coil core which reverses twice for each revolution of the rotor, wherein the primary circuit is normally closed and is open only when a pair of normally closed breaker contacts connected in the primary circuit are opened, and wherein the spark plug is fired by the high sparking voltage induced in the secondary winding each time the normally closed breaker contacts are opened: characterized by the fact that the pole faces of the stator which are equal in length are considerably longer than the pole faces of the rotor which are also of equal length, the respective lengths of said pole faces being such that for an instant twice each revolution of the rotor the gaps between the pole faces of each magneto element are simultaneously substantially bridged by the pole faces of the other, at which instant the magnetomotive force in the coil core due to the permanent magnet abruptly reverses, the interval of rotor rotation directly following such abrupt reversal producing a high substantially uniform magnetomotive force in the coil core due to the permanent magnet; and further characterized by the fact that the breaker contacts are controlled by a single lobed breaker cam driven at onehalf crankshaft speed, the effective angular length. of which is such that opening and reclosure of the breaker contacts can take place during one of said intervals of rotor rotation when the magnetomotive force in the coil core due to the permanent magnet is substantially uniform, and by the fact that the cam is so timed with respect to the rotor position at the desired spark time as to effect opening of the breaker contacts shortly after the reversal in magnetomotive force directly preceding said interval of rotor rotation and reclosure of the breaker contacts before the next successive reversal in magnetomotive force so that whenever the primary circuit is open the magnetomotive force in the coil core due to the permanent magnet remains substantially unchanged and whenever the magnetomotive force in the coil core due to the permanent magnet is changing the primary circuit is closed and current flows through the primary winding to produce a magnetomotive force in the coil core in opposition to the magnetomotive force therein due to the permanent magnet to thereby prevent rapid flux changes in the coil core, which unless prevented, would result in unwanted non-breaker produced firing of the spark plug.

16. The combination set forth in claim 11 wherein the position of the breaker cam is adjustable with respect to the rotor element to advance or retard the spark; means biasing the breaker cam in a direction to retard the spark; centrifugally responsive means acting upon the breaker cam to advance the spark with increasing engine speed; and stop means limiting the adjustment of the breaker cam to a range which affords proper spark timing at all speeds and at running speeds effects opening and closing of the breaker contacts within said interval of rotor rotation during which a high substantially uniform magnetomotive force is produced in the coil core due to the permanent magnet.

17. The combination set forth in claim 16 further characterized by the fact that the open period of the breaker contacts at running speeds substantially coincides with said interval of rotor rotation during which a high substantially uniform magnetomotive force is produced in the coil core due to the permanent magnet.

18. The combination set forth in claim 15 wherein the position of the breaker cam is adjustable with respect to the rotor element to advance or retard the spark; means biasing the breaker cam in a direction to retard the spark; centrifugally responsive means acting upon the breaker cam to advance the spark with increasing engine speed; and stop means limiting the adjustment of the breaker cam to a range which affords proper spark timing at all speeds and at running speeds effects opening and closing of the breaker contacts within said interval of rotor rotation during which a high substantially uniform magnetomotive force is produced in the coil core due to the permanent magnet.

19. The combination set forth in claim 18 further characterized by the fact that the open period of the breaker contacts at running speeds substantially coincides with said interval of rotor rotation during which a high substantially uniform magnetomotive force is produced in the coil core due to the permanent magnet.

DOROTHY H. MAD-LE, Administratrir of the Estate of Alain M. Madl,

Deceased.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS