Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ ~95~ 7
This invention relates generally to ignition
systems for internal combustion engines and in particular
to means by which an existing combustion engine having a
conventional ignition system may be provided with a
capacitor discharge ignition system with minimal time
and effort. This ignition system is generally of the
type disclosed in applicant's Canadian Patent No.
1,~34,1~8, issued July 4, 1978.
Previously, the complex nature oP capacitive
discharge ignition systems made them prohibitively
expensive for application to smaller internal combustion
engines presently utilizing simple magneto ignition
systems. With the development of the improved system
disclosed in the above referenced copending applications,
the number of components, package size, complexity and
cost have been reduced sufficiently to allow the
incorporation of such systems into these smaller sized
engines such as are used in lawnmowers, chain saws,
outboard motors, and the like. The ignition system of
the aforementioned patent is generally applicable for
incorporation during original e~uipment~manufacture of
the associated engines. The present invention provides
an inexpensive ignition replacement package whereby
existing conventional magneto ignition systems may be
easily converted to this improved capacitive discharge system
~ by the owner of the engine subsequent to its initial purchase.; The substantial achievement of this invention can be
appreciated when the nature of existing engines and their J
associated ignltion systems is considered. In order for
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a conversion kit to be commercially practical, it must
be adaptable for use with a variety of engine configurations.
Conventional magneto systems may have a rotor rotating
either clockwise or counterclockwise. Also, the Leading
magnetic pole may be either north or south seekin8
; Further, the ignition timing of the existing ignition
system may not be appropriate due to the differing response
characteristics. Additionally, varying existing space
limitations must be considered since a conversion would
not be commercially practical if significant engine
structure modifications were required. The present
invention as described herein bridges wide variations in
engine and existing ignition systems so as to provide a
conversion kit in which a minimum of component structure
variations will accommodate a large variety of engine and
ignition system configurations without structural
modifications.
Specifically, the present invention relates to
a capacitor discharge system for an internal combustion
engine comprising a permanent magnet means rotated about
a circular path in synchronism with the operation of the
engine, a core of ferromagnetic material mounted adjacent
the circular path and having one portion providing a path
for the varying flux generated by the movement of the
magnet means past the core, a charging winding and a
transformer core portion. The charging winding is offset
from the primary and secondary windings with respect to
the circular path, the charging winding and primary winding
being wound on the one core portion such that the voltages
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induced therein by the varying flux each inclLIdes half
wave voltages of opposite polarity. A charging circuit
is provided including a capacitor connected across the
charging winding and a diode poled to pass half wave
voltages of one polarity for charging the capacitor and
maintaining the capacitor charged when the voltage
generated in the charging winding is opposite the one
polarity. Circuit means connect the capacitor with the
primary winding for discharging the capacitor through
the primary winding and include an electronic switch
means having anode, cathode and control electrodes, the
anodecathode junction of the switch means interconnecting
the ends of the charging winding and the primary winding
which are simultaneously at the same polarity. The
control electrode is connected to the other end of the
primary winding, the polarity of which is opposite this
same polarity. The switch means is nonconductive during
the charging of the capacitor by this one polarity of
the voltage generated in the charging coil and is rendered
conductive by voltage generated in the primary winding
opposite this same polarity whereby the capacitor is
charged during one complete half cycle of voltage generated
in the charging coil and discharged during the next half
wa~e voltage generated in the charging winding.
~dditional advantages and features of the present J
invention will become apparent from the following detailed
~ description taken in conjunc~ion with the attached drawings
; and appended claims.
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BRIEF ~ESCRIPTION OF THE DRAWI~GS
.
Figure 1 is a perspective view of a coil wound
upon a stator having ~.wo legs with mounti.ng provisions
contained thereon all in accordance with the present
invention;
Figure 2 is a second embodiment of the present
invention showing a stator structurs with a third leg for
accommodating an existing mounting structure;
Figure 3 is a third embodiment of the present
invention showlng a stator structure employing yet
another mounting arrangement;
Figure 4 is a fourth embodiment of the present
invention similar to that of Figure 3 but employing a
different mounting structure;
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Fi~ure 5 is a sectional ~idc ~icW o~ thc c~il
assembly utilized in conjunction with the co~e structurcs o~
the present invention;
Figure 6 is an edge view o a keywa~ shi~tex ~ox
use ln altering the axisting timing se~uence;
Figure 7 is another view o~ the ke~w~ shi~ter of
Figure 6 as viewed ~rom the direction of arrow A of ~igure
6;
Figure 8 is a sectional perspectiye view of a
portion o~ a crankshaft o~ an internal combust.ion engine
having a rotor mounted thereon and sho~ing a ke~ywa~ shifter
installed in operatiye relation thereto;
Fi~ure 9 is a schematic dia~ram o~ the capacitiye
ignition system in accordance with the present invention;
Figure 10 is a graphical plot of volta~e Vs. time
showing the operating waveforms for a capacitive discharge
ignitio~ system of the present inyention;
Figure 11 is yet another embodiment of the present
~nvention similar to that of Figure 2 but having split leg
sections;
Figure 12 is another embodiment of the present
i~Vention similar to that o~ Figure 1 but also havin~ split
leg sections~thereon;
Figure 13 is yet another embodiment o~ the present
inVention similar to that of ~lgure 3 but haying s~lit le~ J
6ections incorporated thexeon;
Figu~es 14 through 16 ~re o~ ~ t~piaal existing
lawnmower engine with the sheet metal cowlin~ xe~oved and
~howing, in sequence,` a convention~l ignition system inst~lled
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ther~on, the cngine with thc conventional ignition s~ste~ co$e
~nd coil assembl~ remov~d and the engine with ~ core ~nd
coil assembly of the pres~nt invention installcd ther~on; and
Pigur~s 17 through 19 are o~ a typic~l existing
chain saw engine with the sheet metal cowling ~cmoved and
also showing, in se~uence, the existing engine ignition
~yste~, the removal thereoE, and a core and coil of the
present invention installed thereon.
DESCRIPTION OF THE PRE:FERRED EMBODIMENT
Re~erring now to Figure l, a stator 10 is shown
containing a coil assembly 12 on one leq thereo~. Stator
10 has a generally rectangular cross section and is ~enerally
nu" shaped having a pair o~ spaced apart substantially
parallel legs 14 and 16 and an interconnecting por~ion 18
extending between and connecting one end of each of legs 14
and 16. Leg 14 has a protrusion 15 extending outward there-
from and disposed approximately midway along its length.
Leg 14 also has an elongated aperture 2a adjacent pxotrusion
15 and extending along the longitudinal axis thereo~.
Interconnecting portion 18 has one side 22 which is per-
pendicular to the longitudinal axis of legs 14 and 16 and
a second side 24 which is bowed outward Crom side 22 so as
t~ have a maximum width portion 26 at a point slightly
offset toward leg 16 from its ~idpoint. Also, inte~-
connecting portion 18 similarly has an elongated aperture
28 disposed adjacent portion 26 and extendin~ between sides
22 and 24 and parallel to aperture 20. ~pertures 2~ and
2B ar~ located on stator 10 so a~ to coincide with existing
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mounting pads provided on an internal combustion enqine
and are substantially e~ually elonyated, thus p~ovidin~ mcans
by which the air gap ~etween the stator and a rot~ting magnetic
fleld may be adjustea, as is described in greater detail
~elow. Legs 14 and 16 axe substantially equal in length
and have respective convex end surfaces ~0 ~nd 32 thereon.
' Conventionally, the cores o~ magneto ignition
systems are constructed o$ cold rolled steel. Cold rolled
steel cores are used since the cold rolled steel is an
excellent collector of ~lux emanatlng fro~ the permanent
magnets of the rotor~ Althou~h the core material of the
i,gnition systems disclosed herein c~n be' cold rolled steel,
it has been discovered that electric~l steel, i.e.~ steel
containing a silicone alloy as is used in transformer core
constructions, provides a substantial increase ln the output
voltage of the ignition system. For example/ output voltage
increases of 40~ have been obtained using electrical steel.
It is believed that this substantial increase in output
voltage is due to the ~act that cold rolled steel is not a
desirable core material for the ignition coil so that the
voltage rise upon discharging of the capacito into the
primary winding of the ignition coil is hampered. The
electrical s,teel is a more effective core for the ignition
coil than cold xolled steel, and yet has a good capability
of collecting the 1ux emanating from the permanent ma~nets
o the rotor. The usual core matarials for i~nition coils
are errite materials. These materials would not be satis-
iactory as a core material or the ignition system since they
would not be good collectors o~ the flux eman~ting ~rom the
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permanont magnets o~ thc roto~ Accordinql~, stato~ 10 is
preerably constructed of multiple la~inations o~ elect~ic~1
st~el secured by two rivets 34 and 36 as shown in Figure 1
or other like ~astening devices.
Leg 16 o~ stator 10 has coil assembl~ 12 surroundin~
its longitudinal midportion. Coil ~ssembly 12 com~rises
auxiliary coil 38 located adj~cent convex sur~ace 32 and
ignition coils 40 disposed i~mediately behind auxiliary coil
38. Coil assembly 12 will be described in greater detail
belo~
Stator 10 is particularly suited ~o~ use with the
Rope~ 2.5 chain saw engine i~nition syste~. In such an
application, convex sur~aces 30 and 32 haye a curyature
radius o~ between 1.760 and 1.764 inches and are s~metric~l
about a longitudinal axis extending approximately equ~distant
between legs 14 and 16. Further, in such an application,
the stator structure is constructed of 13 la~inations secured
to~ether by two rivets and having a total thickness of
from .305 to .322 inches.
Stator 10 is thus designed to be mounted on
existing mounting pads of an engine with convex surfaces 30
and 32 o~ legs 14 and 16, respectively, immediate adiacent the
outer peripheral surface o~ a rotor o~ an existin~ conventienal
internal combustion engine. The rotor has a pair o~ magnets
disposed on its outer peripheral sur~ace which create a ti~ing
var~ing magnetic flux in statox lQ, as the magnets rotate
past stator lOo Thus, legs 14 ~nd 16 and inte~connec~ing
poxtion 18 de~ine a conductive path for the ~lux created
by thi;s rotating magnetic ~ield. As the ~lux ~s necessarily
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tlme Varying with respec~ to st~tox 10, a ~olt~c will
ther~by bc generated in coil asse~bly 12. The natu~e and
effect of this voltage will be described in gxeatex detail
below.
Figur~ 2 is a second embodiment of the in~ention
~howi~g a stator structure 42 ha~ing three le~s 44, 46 and
~8, spaced apart and extending substantiall~ parallel fxom
an interconnecting portion 50. Le~ 44 has a longitudinally
elongated aperture 52'located near its end opposite that of
interconnecting portion 50. Similarl~, leg 4~ has a longi-
tudinally elongated aperture 54 located near its end opposite
that of interconnecting portion 5Q. Legs 44 and 46 each
have respective conVe~ end surfaces 56 and 58, which have a
radius of curvature similar to that of a rotor ~or which
stator 42 is designed to be used. Also,,apertures 52 and 54
are located on respective leys 44 and 48, so as to coincide
with existing mounting pads on an existing engine which is
desired to be converted to a capacitive discharge ignition
system. Stator 42 is constructed similarly to that of
stator 10, having a plurality of. identical shaped laminations
~f electrical steel or other suitable magnetic material,
secured by rivets 60 and 62 disposed on legs 4~ ~nd 48. Leg
48 is disposed at one end.of interconnectiny me~ber 5~ and
preferably has a rounded end portion'64. Leg 48 is spaced
ap~rt:from leg 46 a slightly greate~ distance than the
distance bet~een leg 46 and leg 44. Stato~ 42 is a,dapted
to be mounted on existing mounting pads o~ an existin~
conventional internal combustion engine ~ith conVex suxfaces
56 and S8 im~ediately ~djacent a rotox si~ilaxl~ to that
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o~ ~tator 10. Thus, legs 44 ~nd 46 ~nd th~t portlon o~
inte~connecting portlon 50 extcndincl thcrebetween, de~ine
conductive path for the ~a~netic ~lux induced by the enJine
rotor. A coil assembly simil~r to that shown ~t 12 in
~gure 1 is mounted on leg 46 of st~tor 42 ~o~ ~ener~ting
the ignition voltages. As leg 48 is spaced apart ~rom the
r~tating magnetic field, it is effectively removed ~om the
magnetic circuit and se~ves to pro~ide means to mount the
stator 42 to the existing engine mountin~ pads while allowin~
the ignition timing Oæ the en~ine to be ~odiied by the
angular displacement of the coil structure.
Stator ~2 is pa~ticulaxly suited ~or use in the
xetxo~it of certain Briggs and Stratton en~ines. Xn suc~ an
application, the radius of curvature ~ox con~ex sur~aces 56
and 58 will be of the order of. 2.885 to 2.890 inches and the
stator will have a thickness on the order of .305 to .322
inches.
~ eferring now to Figure 3, another embodiment of a
stator 64 is shown. Stator 64 has substantially parallel
and spaced apart legs 66 and 68 extending rom interconnecting
portion 70. Interconnecting portion 70 has a slightly wider
portion 72 extending from leg 68 to a poin~ a~proximately
midway between legs 66 and 68. Legs 66 and 68 also have
convex end surfaces 74 and 76 similar to those previo~sl~
aescribed. Leg 68 has a ~ember 78 extending outward ~xo~
stator 64, perpendiculax to the longitudinal axis o~ leg 68
and disposed near convex end surface 76. Leg 68 ~lso has
member 80 extending outward and subst~ntially pa~llel to
mcmbe~ 78 ~ro~ the point of merc~ex between lecl 68 and
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.
lnterconnccting portion 70. Mcmbcr 80 is sli~htly sh~tcr
than mcmber 78. A third membcr 82 extends between the ends
o~ members 7~ and 80 and prot~udes a short distance be~ond
member 78. Member 32 has lon~itudinall~ elongated ~pertures
84 and a6 adjacent opposite ends thereo~. Me~bers 78, 80,
and 82 form a support arm and, with le~ 64~ enclose a
genexally rectangular shaped aperture 88 therebetween~
Skator 64 is similarly constructed as those o~ Figures l
and 2 having multiple laminations secured by rivets 9~
and 92 or the like. A coil assembly si~ilar to that at 12
of Figure 1 is disposed on leg 66. In this embodiment,
legs 66 and 68 and interconnectin~ portion 70 define a
magnetic Elux conducting path. As members 78, 80 and 82
do not extend from the same leg on which the cail assembly
is disposed, any flux conducted by these members must also
flow through leg 66, thereby contributing to the induction
of voltage in the coil assembly. Thus, while members 78, 80
and 82 form an alternative flux path, it will not affect
the voltage induced in coil 12.
Stator 64, described above, is particularly suited
for adapting Beaird Poulan chain saw engine ignition systems
to the capacitive discharge system of the present invention.
In such an application, convex surfaces 74 and 76 have a
curVature radius on the order of 1.229 to 2.239 inches and
are sym~etrical about an axis extending longitudinally
approximately midway between legs 74 and 76.
~ i~ur~ 4 shows another embodiment of a stator 94
~hich is similar to that of Fi~ure 3 and thus like portions
are ~ndicated by like numerals. ~he only exception is th~t
~10-
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member 96 does not extcnd beyond member 7a ~ut ~athex ~a~cs
smoothly into member 78.
Th~ embodimcnt o~ Figure 4 is particul~rly suited
for conversion of Roper 3.7 chain s~w engine ignition syste~s
to the capacitive discharge syste~ of the preSent invcntion.
In such an applici~tion, convex surfaces 74 and 76 will have
a radius of curvature on the order of 2.010 to 2.016 inches
with leg 66 being slightly shorter than leg 68.
~ he coil assembly 12 shown generally in position
o~ a stator structure lD in Figure 1 is illustrated in
isolation and sectionali~ed in ~gure 5~ The coils are
arranged as best seen in Figure 5 with a secondary coil 116
wound over the ~rimary ignition coil 118 and the auxiliary
c~il 38 located forward o~ t~e ignition coils. Primary
iqnition coil 118 and secondary ignition coil 116 comprise
the ignition coils indicated at 40 in Figure 1. It is
important to the operational sequence of the capacitive
. discharge system that neither the primary nor secondary
ignition coil windings be concentric with the auxiliary coil
windings. ~urther, experimentation has shown that optimum
results are obtained when a minimum 3/8" spacing between the
ignition coils and the aux.iliary coil is maintained and the
auxiliary coil is loc~ted forward of the ignition CQils. T~
order to facilitate assembly, the coils are wound on a for~
120 having a rectangular ox s~uaxe opening 121 xunning
longitudinally therethrough and hayins xadially outwaxdly
extending ~langes 122, 124 and 126 serving to aid in secuxin~
the coils in position. Form 120 may be ~abricated fxo~ any
6ult~b1e material such as pl~c~ic ~ox example.
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Experimentation and reseaxch h~s shown th~t,
bec~use o v~riation of dir~ction o;~ xotor xut~tion ~nd
polarity of the leadin~ ma~netic pole, two dlffcrent windin~
configu~ations are required.
; In the ~irst of these coi:L configurations, the
auxiliary, prima~y, ~nd secondary ignition coil windings ~re
wound counterclockwise and all haye their finished ends
connected to ground. This coil configuration is desi~ned to
be used in all applica~ions in which the leading magnetic
pole of the rotor is south see~ing, such as the Roper ~nd
Beaird-Poulan engine previously xeferred to. Further, J
optimum results were achieved when the coil assembly ~as
`
mounted on the first or leadin~ pole o~ the stator structure.
In the second configuration, both the auxiliary
and primary ignition coils are wound counterclockwise and
have the starting end connected to ground whereas the
secondary ignition coil is wound clockwise and has its
` finished end connected to ground. This coil configuration
is designed to ~e used in all applications in which the
leading magnetic pole of the rotor is north seeking, such as
the Briggs and Stratton engines previously re~erred to.
Furtherl op-timum results we~e achieved when the coil assembly
was mounted on the second or trailing pole of the stator
assembl~.
Experimentation has ~urther shown th~t the ~ollowing
number of coil turns hnd wire gauges have given optimu~
performances:
~uxiliary Coil:
~wo ~ycle engine: 2,000 turns number 3~ wire.
Pour cyclc enqine; 4,000 turns number 40 wire.
,
. 12
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Pxim~ry Ignition Coil:
96 turns o~ numbcr 22 wire for both 2 ~nd ~ cycle
engines.
Secondary Ignition Coil:
9,630 turns of number 44 wi~e ~or both 2 and
4 cycle engines.
~ he completed coil asse~bly will pre~erab:ly have
an outer covering such as ~n e~oxy compound or the like to
seal it against moisture or other potentially damaging
- -elements. Also, the coil will have pxoVisions èxtexnally
o~ this coVexing for the connection o~ the high voltage leaa,
a ground connection, and primar~ ~nd auxiliary coil connection
to the ignition module described below. ~lternati~el~, the
coil may be constructed with the ignition module integral
thereto assuming space limitations per~it. This will further
simplify the conversion in that the only electrical connection
required will be the high volta~e leacl.
In converting some engine ignition systems to the
capacitive discharge ignition system, greater timing
adjustment may be required than can be accomplished through
the design of the stator structure alone. ~lternatively,
space limitations of the engine structure may preclude the
use of a modified st~tor structure embodyin~ isnitic.. timin~
corr~ction. Generally, in conventional m~gne~o i~nition
~ystems, the rotor is retained in position relati~e to its
6haft rotation by a woodruff keyway. Substitution o~
replace~ent rotor with a relocated keyway would ~reatly
inC~ase the cost o~ any c~pacitive disch~r~e ignition
~onversion system thus m~king a conversion kit p~ohibitively
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expensive. Accoxdingly, a kcyway shiftcr, as ~hown ~t 98 ln
~iguxe 6, is pro~ided. ~he kcyway shi~tex includes ~Wo
slmilarly shaped disc~ e portions 100 and 102, both
generally round in shape. Section 102 has an aperture 103
therein of a dia~eter equal to o~ slightly larger than the
diameter of a crankshaft to which the keyway shifter iS to
- be fitted so as to allow it to be slipped over the shaft. A J
protrusion 104 extends axially outward from the edge of
aperture 103 and is of cross sectional size appro~imatin~
that of a keyway slot 106 on ~ rotor 107 as shown in Figure
8. Section 100 also has an aperture 109 therein o~ ~
diameter approximatel~ the same as shaft 108 of an engine
and aperture 103. A protrusion 110 extends axially out~ard
-from the ed~e of the aperture and has a transyerse cross
sectional size approximately that of a keyway slot 112 on
shaft 108. The two sections 100 and 102 are welded to~ether
with the angle between the protrustions 110 and 104 bein~
adjusted to accomplish a predetermined timing change of the
rotor. This angular displacement is best seen by reference
to Figure 7 showing a keyway shi~ter of Figure 6 as viewed
along a line indicated ~enerally by arrow ~ of Figure 6.
The installation and operative relationship of
keyway shifter 98 is best seen with reference to Figure 8 in
Which a rotor 107 is illustrated partially broken away but
~therwise in operatiVe relationship to a crankshaft 108 of
a~ internal combustion engine. Crankshaft 108 is disposed
in a cylindrical bore 113 extending thxough Xo-tor 107.
Rotor 107 has a keyway slot 106 disposed on the periphe~al
- ~urface of bore 113 and crankshaft 108 has a similar keyway
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slot 112 disposcd on its p~ripher~l sur~t~ca, As ~x~inally
manufactured with the conventional ignition s~stem keyway
~lots 112 and 10~ are aligned and retain a wood~uP~ key to
prevent relative rotation. In oxder to install .the keyway
8hifter o~ the present invention, the woodru~f key is ~irst
removed thus allowing rotor 107 to he rotated relative to
shaft 108. ~rotrusion 110 of keywa~ shifter 98 is first
inserted in keyway slot 112, rotor 107 is then rota~cd wi~h
xespect to shaft 1~8 to brin~ keyway 106 into alignment with
protrustion 104 of keyway shifter 98 thus allowing section
102 of keyway shifter 98 to engage the upper surface 114 of : :~
rotor 107. A jam nut.115 is then tigh.tened down over keyway
shifter 98 and rotor 107 thus securing th.em to sh.~t lQ8.
It is possible in certain applications that the key~tay slot
on the rotor may not extend completely through to the top
surface thereof or the keyway slot on the crankshaft may not
extend to the upper end of the shaft. This situation usually
occurs whe~ the keyway slots have been formed by a milling
machine. In either case, in order to install the keyway
shifter of the present inventio~,.it will be necessary to
extend the keyway slot so as to provide openings for ~he
keyway shifter to seat in. This ~ay easily be done hy
filing of the rotor or crankshaft.
Refcrring now to Figures 9 and 10, the operation
of the present invention will be described in detail. A
coil assembly is shown schematically at 128 o~ Fl~u~e 9. In
operative positionl the coil and appropriate st~tor structuxe
described above would be securely mounted to the en~lne
adjacent ~he rotor oarrying the magnetic ~ieId ~eneratln~ ~:
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- mcans. An ignition module, ~s shown schem~tically ~t 130 o~
Figure 9 is mounted on the engine in an~ conVenient loca~ion
and ls eleckrically coupled to the c:oil asseJnbl~ b~ conductors
132 and 134. Both the coil assembl~ and i~nition modulc J
have means 136 and 138, xespectivel~, for cre~tin~ ~n electrical
eonnection to ground which, in this case, may be the engine
~tself. Additionally, coil assembly 128 has a hiyh volt~ge
conductor 140 for conducting the ;ignition volta~e to the
spark plug.
~- As the rotating m~gnetic field, carried by the
rotor, passes in close proximity to the stator co~e, it
induces therein a time varYing magnetic ~lux, ~s this ~lux
inereases in magnitude, it induces a voltage in the auxiliary
eoil which causes a current to ~low fxom the coil assembly
along conductor 132 through diode 142 and conductor 144 to
eapacitor 146 creating a positive charge thereon. Diode 148
is eonnected between conductor 132 and ground 138 and serves
to dampen negative spikes induced in the auxiliary coil.
The voltage~ induced in the auxiliary coil, as this ti~e
varying magnetie field increases in intensity, is plotted
against time in gr~ph 150 of Figure 10 with maximum intensity
being achieved at point 152. Graph 154 shows the voltage
vs. time plot o~ the charging of capacitor 196 in response
to the induced voltage on the auxiliary coil. As shown
graphieally, capacitor 146 achieves a maximum charge ~t
point 156 which corresponds in ti~e to the ~aximum rate of
~hange of flux intensity passing through the st~to~ coil.
hs diode 142 only conducts in one direction, the chaxge on
capacltor 146 wlll be maintained.
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A switch moans 158, such ~s a silicone contxollcd
rectiier ~SCR), is pxovided between capacito~ 146 and
pxima~y conductor 13~ connected to the prima~y coil winding.
A xesistor 160 ~nd a diode 162 axe c:onnected in p~rallel
between the cathod~ 164 and gate 166 o~ SCR 158. Diode 162
serves to protect SCR 158 from positiVe t~ansients lnduced
in the primary coil winding during the chargin~ o~ capacitor
146.
As the rotating ma~netic ~ield begins to moye out
. . .
of alignment with the statox, the ~agnetic flux followin~
thexethrough begins to drop. This then causes a negatiye
voltage to be induced in the primar~ coil, thus c~using a
~urrellt to ~low throu~h conductor 134. This will then cause
gate 166 of SCR 158 to be positively biased with respect tQ
cathode 164, thus causing SCR 158 to become conductive.
This is shown pictorially on graph 168 of Figure 10, which
pIots voltage vs. time as measured across the primary winding.
When SCR 158 becomes conductive, capacitor 146 will dis-
charge through SCR 158 and through primary coil 170. As
;~ the primary and secondary ignition coils are magnetically
coupled, the discharge through primary coil 170 cooperatively
with the time varying magnetic flux induces the ignition
spark generating vo'tage in secondari~ coil 172.
In order to maintain maximum operating e~ficiency
o~ the engine~ it is important to insure capacitor 146 will
repetitiYely fire at precisel~ the same time rel~tive to
the an~ular position o~ the cr~nkshat with as little
~ariation as possible over the entire b~oad speed r~nge o~
the en~ine. It has been ~ound through experiment~tion that
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the ignition modul~ circuit o~ ~igure 9 in coope~Atlon
wlth the degxee o~ magnetic~couplincJ of the l~nition ~nd
auxiliary coils and thei~ polarity ~elationships plus the
lack of frequency sensitivit~ in the SCR gate network produc~
gxeater timing stability than found in conventional ignition
s~stems.
In certain applications,.it is desixable to have
,the sp~rk timing retarded during starting of the engine
: ~ut,,when the engine is at operatiny speed, it becomes
necessary to advance the ignition timing in order to obtain
m~ximum engine efficiency, Accordingly, it is desira,ble to
pxovide means which would automatically ~ccomplish this with-
out increasing the costs of the conVersion contemplated herein.
'Fagure 11 shows a stator structure 174 s.imila~
to,that shown in Figure 2 but incorporating a further
,modification which automatically advances.the ignition
' timing'as engine speed increases. Stator 174 is identical
. to stator 42 with the exception of lower leg portions 176
and 178 respectively. Leg portion 176 is divided into
two spaced apart segments 180 and 182. Segment 180 extends
' laterally and lorgitudinally ~rom the main portion of leg
46 and is slightly longer th~n segment 182 so as to provid~
a smaller air gap betwcen the stator and.rotor when installed
on an engine. Both segments h~ve convex end surfaces 184
and 186 as previously described or stator 4 2 of Figu~e 2.
Similarly, leg portion 178 is diyided into twa se~ments
188 and 190. Se~ment 188 extends later~ nd lon~itudinally
. ~om the main portion of leg 44 in the s~me direction a5
~egment 180 and is also slightly.longs~ tha,n seg~ent 190.
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Both segments 188 ~nd 190 have convex end surf~ces 192
and 194 similar to those previously described. There is
thus provided a slow speed flux path co~prising se~ment lB8,
leg 44, interconnecting portion 50, le~ 46, ~nd segment
180, and a high speed flux path comprising segment 190,
leg 44, interconnecting portion 50, leg 46 and seg~ent 182.
At low speed operation, the trailing segments 180
and 188 provide a significantl~ greater operating flux.for
inducing the ignition voltage in the coil due to -the relatively
smaller air gap relative to that created b~ segments 182
and 190. As these sections are shifted slightly in the
dlrection of rotor rotation relative to the ~ain leg of
the stator, the ignition timing during high speed operation
is advanced relative to the ign~tion timing during low
speed operation. As the operational speed increases, the
magnetic flux provided by the leading pair of stator
leg segments 182 and 190 will induce an increasing].y greater
voltage in the coil due to the increased r~te of change of
the magnetic field. This ignition voltage will necessarily
be advanced relati~e to that induced from the flux provided
by the traiIing ssgments 180 and 188 due to the relative
position o~ the sections. Thus,.at a suf~iciently hlgh
operating speed, the time varying ~agnetic flux provided by
the leading pair o stator le~ seg~ents 18~ and 190 will
induce a voltage in the ignition coil sufficiently large to .
cause the associated capacitiVe discharge ignition circuitry, ~.
as described above and in the two prev~ousl~.re~exenced
applications, to operate. There ls thexeby created means r
Which will automat~cally cause.the ignition timing to advance
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ln r~sponse to increased engine speed. The positi~ning o~
the leg secti~s relativc to e~oh othc~ ~nd xel~tive to the
angle of rotation of the rotor will contxal the de~ee o~
timing advance or retardation.
Figuxe 12 shows a st~tor stxuctu~e 196 similar
to that of Figure 1 but having a further modi~ication si~il~x
to that previously described fo~ stator 174 o~ Fi~ure 11
incorporated thereon.- Stator 196 h~s lower leg po~tions 1~8
and 200, e~ch of which is divided into two segments 2Q2, 204,
206 and 208 t respectively. As pre~iously de,sc~ibed with
reference to ~igure 11, segment 202 is slightly longer than
segment 204 and segment 206 is slightl~,'longe~ th~n se~ment
208 and all segments haye conVex end surfaces thereon., The
operation of this modlfication is identical to tha~ des~
cribed with reference to stator 17~ ~f Figure 11.
Figure 13 in like manner sho~s a stator structure
210 similar to that of Figure 3 but incorpor~ting thereon the
modi~ication similar to that previously described for stators
174 and 196 of Figures 11 and 12, respectively. Stator 210
has lower leg portions 212 and 214, each of which is divided
into two segments 216, 218, 220 and 222, respectively,
all of which have convex end surfaces. Segment 216 is
slightly shorter than segment 218 and se~ment 220 ls slightly
shorter than segment 222. The operation of this m~dification
is identical to that previously described ~ith ~e~erence ~o
~tator 174 of Fi~ure 11, a,low speed ~lu~ p~th bein~ defined
by segment 218, leg 6~, interconnecting po~tion 70, le~ 68,
~nd segm~nt 222 and a high s~eed flux path bein~ de~lned b~
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~egmcnt 216~ le~ 66, inte~conncctin~ po~tion 70~ leg 68,
and segm~nt 220, It should also be noted th4t this ~odiica-
: k~on may bc incorporated into the deslgn o~ st~tor 94 o~
Figure 4 in like ~anner as descxibed with re~exence to
stator 210.
Reference is now made to Figures 14 throu~h 16
in which-is illustrated the sequence of operations by which
: . an owner of an existing machïne ha~in~ an iternal combustion
engine with a convent.ional i~nition syste~ may ayail himself
of the advantages of the capacitive discharge ignition
system o~ the present invention. In Figure 14,.there is
illustrated an internal combustion en~ine 224 which was
manufactured with a conventional i~nition system. The
i~nition system comprises a rotor 226 havin~ a north. ma~netic
pole 228 and a south ma~netic pole 230 spaced a short dis-
tance apart and disposed on the peripheral.surface of rotor
226. The original stator 232 and coil assembly 234 is
mounted on engine housing 236 i~mediately adjacent rotor
226 through the agency of bolts 238 and 240.
In order to convert this ignition system to that
. of the present invention, the existing stator 232 and coil
assembly 234 is removed. As shown in Figure 15, there is
then exposed two mounting pads 242 and 244, which cooperate
with bolts 238 and 240 to secure the stator and coil
assembly.
A stator 248 havin~ a coil assembly 246 mounted
thereon, both in accordance with the p~esient inyention, is
the~ securcd to the mounting pads 242 and 244 through the
agency o~ bolts 238 and 240 p~ssing through e}ongated
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apcrtures 239 and ~41. These olon~at~d apcrtures ~ll.ow
~tator 2~6 to then be positioned to a~ d the px~determined
air gap between it and rotor 226, wld bolts 2~8 and 240 are
then tightened thus securing stator 298 in position. The
ignition module previousl~ described may be mounted in any
convenient location on the machine and is electrically
connected to coil assembly 246 b~ means of conductors 250,
252 and 254. ~ltexnatively, the stator and coil assembly
~ay be fabricated with the ignition module bein~ integral
thereto thus further simpli~ying the conversion.p~ocess
throu~h the elimination o~ the electrical connections. High
voltage conductor 256 is connected to the spark plug thus
completing the installation of the ignition s~stem of the
present.invention. It should be noted that the ignition
timing has been adjusted by means of the construction of the
new stator 248, as may be readily seen in a comparison of
Figures 14 and 16.
A similar conversion of an internal combustion
engine of a chain saw is illustrated in Figures 17 thro~gh
19. Figure 17 shows the en~ine.258 having a conventional
ignition system comprising a stator 260 secured to engine
258 by volts 262 ~nd 264, a coil assembly 266 mounted on
stator 260, and a rotor 268. Rotor 268 has ~ north ma~netic
pole and a south magnetic pole spaced sli~h.tl~ apart ~nd
disposed on its outer periphery ~o~ ~eneratin~ the time
varying magnetic ~lux in stator 260.
.
In installing the stator and coil assembly o~ the
. present invention, the existing stator 260 ~nd cQil ~ssembly
26~ are removed from engine 258 by removal o~ bolts 262 and
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264. Thus thcrc is exposed mounting pads 270 ~nd 272
disposed on enyine 258 as best 5een in Figure lB. The new
stato~ 274 and coil assembly 276 o~ the p~esent inyention
are then mounted on engine mountin~ pads 270 and 272 through
the ayency of bolts 262 and 264, St~tor 274 is then positioned
to afford the proper air gap between it and.rotor 268 and
~olts 262 and 264 a~e tightened, thus securing statcr 274
in operative position~ The iynition module previously
described is then mounted in any convenient.location and
electrica}ly connected to coil assembly 276 or alternatively
may be integral with the stator and coil assembly as pre-
~iously described. It will be noted b~ a comparison of
Pigures 17 and 19 that the ignition timing has been shi~ted
approximately 18 through the use of the stator structure
of the present invention, thus eliminating the need for
any structural modification of the engine itself.
~here is thus disclosed herein means by which
. .
. . any individual having a very few basic tools may easily
convert the existing ignition system of his lawnmower or
the like to the capacitive discharge ignition system of the
present invention. As is apparent from the above description r
there is provided means by which the difference in ignition
timing of the capacitive aischarge ignition system relative
to the conventional ignition system may be compensated for
so as to maintain the ignition timing o~ the en~ine.
The absence of any necessity to pexfor~ delicate machinin~
operations or the need for any complex engine ~odific~tions
makes it possible to completely elimin~te the need for any
knowledge whatsoever o~ machinery operations o~ engine
.
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ignitlon system theory by the owncr. Fu~thcr~ ag the re-
placemcnt of parts ls minimized, the individual ~a~ achieve
the advantages inherent in a capacitive dischar~e ic~nition
system at a relatively small investment of money and time.
It is to be undcrstood that the forec~oing des-
cription is that of preferred embodiments of the in~ention.
V~rious changes and modifications ~a~ be made without
departing from the spirit and scope of the inventiQn as
de~ined by the appended claims.
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