U.S. patent number 3,566,202 [Application Number 04/734,006] was granted by the patent office on 1971-02-23 for self-resonant ignition coil and system.
This patent grant is currently assigned to Chrysler Corporation, Highland Park, MI. Invention is credited to Sherman C. Carr.
United States Patent |
3,566,202 |
|
February 23, 1971 |
SELF-RESONANT IGNITION COIL AND SYSTEM
Abstract
An ignition coil of low internal impedance and high energy
storage and transfer characteristics and having an electrostatic
shield between the coil primary and the coil secondary surrounding
the primary and additional capacity resonating the secondary to a
high frequency providing improved operating efficiency and
prolonged spark duration of a spark plug load connected
thereto.
Inventors: |
Sherman C. Carr (Hartford,
WI) |
Assignee: |
Chrysler Corporation, Highland
Park, MI (N/A)
|
Family
ID: |
24949978 |
Appl.
No.: |
04/734,006 |
Filed: |
June 3, 1968 |
Current U.S.
Class: |
361/270; 336/233;
336/84R |
Current CPC
Class: |
H01F
38/12 (20130101); F02P 3/04 (20130101) |
Current International
Class: |
H01F
38/00 (20060101); H01F 38/12 (20060101); F02P
3/02 (20060101); F02P 3/04 (20060101); H01f
015/04 (); H01f 027/24 (); F02p 001/00 () |
Field of
Search: |
;317/157.62
;336/233,84 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lee T. Hix
Assistant Examiner: C. L. Yates
Attorney, Agent or Firm: Harness, Talburtt and Baldwin
Claims
1. An ignition coil comprising a core; a primary winding around
said core; an open-circuited electrostatic shield in the form of an
electrically conducting sheet of material spaced from and wrapped
about the primary winding with the starting and finishing ends of
the wrapped sheet in overlapping but slightly spaced apart relation
to one another; a secondary winding surrounding said electrostatic
shield and having an electrical connection thereto; and an
additional capacitance electrically connected across the secondary
winding to increase the energy storage and current delivery
capability of the coil and to decrease the internal impedance
2. An ignition coil according to claim 1 wherein said additional
capacitance comprises an electrically conducting foil element
spaced from
3. An ignition coil according to claim 2 including: a body portion
enclosing said windings, shield and foil element; and a mounting
clamp surrounding said body portion and electrically cooperating
with said foil element to form the other element of said
additional
4. An ignition coil assembly according to claim 3 wherein, said
mounting clamp is of split, discontinuous formation at the adjacent
ends thereof which are insulatingly spaced apart in open circuit
electrical relation.
5. An ignition coil assembly according to claim 4 and wherein said
coil
6. An ignition coil assembly according to claim 6 wherein said body
portion is composed of a high dielectric material completely
surrounding said
7. An ignition coil assembly according to claim 6 wherein said body
portion is comprised of an epoxy material cast about said core,
windings, shield and foil element all of which are insulatingly
spaced apart by the
8. An ignition coil assembly according to claim 8 wherein said coil
further includes: first and second low voltage terminals extending
through one end of the body portion and connected electrically to
the opposite ends of the primary winding; a high voltage terminal
extending through another end of said body portion and electrically
connected to one end of the secondary winding; and a ground
terminal extending through said one end of the body portion and
electrically connected to the other end of said secondary winding
and to said electrostatic shield.
Description
This invention relates to ignition coils and, more particularly, to
self resonant ignition coils.
2. Prior Art
Conventional ignition systems employing customary forms of ignition
coils are at a serious disadvantage in internal combustion engines
particularly under cold starting conditions, wide open throttle and
full load operating conditions, or partially hot or cold fouled
spark plug conditions. The energy supplied by the conventional
ignition coil does not attain its peak intensity sufficiently
rapidly for cold starting firing of partially fouled plugs, the
coil frequency being too low to provide the fast rise time required
of the pulse energy to initiate combustion under these
conditions.
Such coils are also characterized by high internal impedance and
resistance, which severely limit the energy delivered to the plug,
while the laminated iron core normally employed in these coils
constitutes an additional source of power loss due to eddy current
and hysteresis or molecular friction effects therein. Fouled or
eroded electrode conditions change the impedance of the plug and
affect the energy transferred thereto from the coil, which is
incapable of adjusting its voltage output in accordance with the
plug electrode conditions. Nor are such coils capable of providing
the high current demand of the spark gap for ignition of all common
fuels in engines which operate with various forms of such
fuels.
Accordingly, the present invention has for its object to provide an
ignition coil device that will provide improved operation as a
source of ignition energy for an internal combustion engine under
severe starting and operating conditions with consequent resulting
improvement of engine combustion efficiency, operation and
performance.
Another object is to provide an improved ignition coil for a source
of ignition energy having a rapid voltage rise time to gap break
down characteristic and providing maximum peak energy for severe
starting conditions of an internal combustion engine.
A related object is to provide an improved ignition coil self
resonating at a high frequency providing a rapid rate of rise of
the pulse energy supplied therefrom and promoting burn-off or self
cleaning of fouling deposits on the plug electrodes.
Another object is to provide an improved ignition coil for an
ignition energy storage source capable of providing energy over a
sufficient period of time to a spark plug load to ensure combustion
under high turbulence, high temperature, full load, high engine
r.p.m. and full load throttle conditions.
Another object is to provide an improved ignition energy source
whose output voltage will adjust to spark plug gap growth without
loss of energy to the plug and which will provide high spark plug
gap current in proportion to gap current demand for ignition of
various fuels commonly employed in internal combustion engines.
Towards accomplishment of the foregoing and related objects, the
present invention provides an improved ignition coil of high energy
storage capacity and of low internal impedance and resistance
characteristics. The coil is designed with additional lumped
capacity therein to provide high current delivery therefrom and to
parallel resonate the secondary inductance to an internal impedance
to operate into the external load for maximum energy transfer
thereto. Energy is supplied from the coil at a rate or frequency
providing a rapid rise to gap breakdown time characteristic for
firing under cold starting or fouled plug conditions and is
sustained for a period sufficient to ensure complete combustion
when the engine is operating under high temperature, high
turbulence, full throttle, full load conditions.
The structure and operation of the invention will be explained with
reference to the accompanying drawings first briefly described
below.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevation view of one end of an ignition coil
constructed in accordance with the present invention;
FIG. 2 is a sectional view taken in the direction 2-2 of the coil
of FIG. 1; and
FIG. 3 is an electrical schematic circuit diagram illustrating the
connections of the subject coil in an ignition circuit supplying
energy to a spark plug connected as an electrical load.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As illustrated in FIGS. 1 and 2 of the drawings, the coil 10 is of
elongated cylindrical formation comprising a shell or body portion
12 circumferentially surrounded over the major portion of its axial
length by a split cylindrical mounting clamp or strap 14.
Interiorly, the coil comprises an axially extending central core
structure 16, a primary transformer winding 18, an electrostatic
shield 20, a high tension secondary winding 22, and a foil segment
24 forming an element of a capacitor 23, the other element of which
is formed by the mounting clamp 14.
The body portion 16 is composed of a high dielectric insulating
material such as a cast epoxy in which the foregoing elements
18--24 are potted or embedded. One end of the body portion extends
axially forwardly or beyond the mounting strap 14 and includes a
diametrically reduced, truncated conical portion 26 having a short
axially extending, outwardly opening bore 28 centrally formed
therein. Molded in the bore is a generally cup-shaped, brass
terminal connector 30 the open end of which has a radially
outwardly expanded annular ferrule 32 formed thereon for detachably
receiving a high tension cable 34 exteriorly connected to the spark
plug 36, as shown in FIG. 3.
In the other or rearwardly facing end of the body portion are
molded three brass terminal post connectors 38, 40 and 42, having
reduced and threaded ends for grounding of the core and external
connections to an excitation source therefor. The terminals are
shown located at the same radial distance from the axis of the coil
structure with the terminal 38 equidistantly located between the
oppositely diametrically disposed terminals 40 and 42.
The core structure 16 comprises a ferrite rod 42 of relatively high
magnetic permeability constant in the order of 2000 to 2500 Oersted
per Gauss, and is formed of compressed powdered iron particles in a
suitable binder. The rod is contained within an elongated fiber
tube 44 upon which is would the primary winding 18 of the coil.
The primary winding 18 is comprised of approximately 75 turns of
-16 A.W.G. enameled magnet wire and is wound about a portion of the
length of the tube in three tiered layers. It will be appreciated
that the resistance of the primary of the coil is considerably less
than that of an ignition coil whose primary is wound about the
secondary and therefore requires a greater lineal length of wire by
reason of the increased diameter thereof. As indicated in FIG. 2,
the starting end of the primary winding is interiorly electrically
connected to input terminal post 40, while its other or finish end
is connected to input terminal post 42.
The secondary winding 22 is spaced radially outwardly of and from
the primary winding about which it is concentrically wound with
approximately 4500 turns of -36 gauge magnet wire distributed in a
plurality of layers insulated from each other by intervening paper
insulating material.
The electrostatic or Faraday shield 20, which is located between
the primary and the secondary windings, comprises a thin strip of
copper foil material disposed concentrically of and physically
insulated from the coil windings. The wrapped ends of the foil
extending paraxially of the coil assembly are disposed in
overlapping but slightly separated relation, as indicated in FIG.
1, and are spaced apart by intervening insulating material
therebetween. The electrostatic shield and the starting or low
potential end of the secondary winding are connected interiorly to
the terminal post 38, which is externally connected to electrical
ground.
The foil element 24 forming one side or electrode of the capacitor
structure 23 provided within the coil is a thin strip of copper
having an area of approximately one and a half square inches in the
constructed embodiment of the invention. As illustrated in dashed
outline in FIG. 1 the foil is of semicircular extent and is spaced
radially outwardly from the secondary winding and inwardly of the
inner surface of the mounting strap 14 which cooperates
electrically therewith to form the other side, plate or electrode
of the capacitor.
The mounting strap 14 may be bonded as by cementing to the
periphery of the body portion 16 and is composed of electrically
conducting material, as aluminum. As indicated in FIG. 1, the
mounting strap is shaped in the form of a split ring or circular
clamplike structure and has a pair of radially outwardly extending
bracket or ear portions 46, 48. Each of the ear portions has a pair
of laterally spaced apart apertures 50, 52 therein for attachment
of the coil assembly by the mounting bracket with threaded screws
or bolts, one of which is shown at 54, to a support or mounting
base structure not shown. The inwardly facing surfaces of the ear
portions are spaced apart by phenolic washers of suitable
insulating material 56 interposed therebetween to prevent the
circulation of currents induced in the conducting strap from
changes in the coil field. Likewise, suitable grommets as 58 formed
of insulating material are inserted in the aligned mounting
apertures in the strap ear portions to insulate the head and body
of the attachment bolts from the strap structure and prevent
completing a continuous electrically conducting path therethrough.
The ends of the electrostatic shield 20 are spaced apart for the
same reason, i.e. to avoid power losses therein that would
otherwise result from the short circuited turn effect of a
continuous conducting medium exposed to a changing electromagnetic
field.
In FIG. 3, the subject coil is represented in electrical schematic
form as employed in an engine ignition system and connected between
an excitation source 60 and the spark plug 34. The excitation
source 60 is energized from a storage battery 62 and supplies a
high current, short duration energy pulse therefrom as obtained
from a condenser discharge system, for example. As employed in
engine ignition applications, such condenser discharge systems
include a DC to AC inverter device that inverts the low DC output
voltage of the storage battery to an AC voltage in the order of 300
volts, a rectifier device connected in charging circuit relation
with an energy storage condenser of say to 1--2 ufd. capacity, and
a discharge control circuit connecting the condenser in discharge
circuit relation with the primary side of the ignition coil. The
discharge controlling circuit comprises the engine actuated breaker
or interrupter contacts 63 connected directly or through an
intermediate electronic triggering circuit to the gate control
element of a controlled switch, as an SCR device. The latter is
connected in discharge controlling circuit relation with the
charged energy storage condenser to discharge the condenser through
the coil load device in timed relation with the operation of the
breaker contacts.
In the coil generally designated at 10 in FIG. 3, the electrostatic
shield is represented at 20. The shield serves to minimize the
internal capacitive coupling between the coil primary and secondary
windings and effectively presents a low impedance path to ground
for high frequency currents which are generated in the spark plug
arc and resonate at the natural frequency of the secondary lead
wires and components external to the coil secondary. The shield
prevents this energy from being coupled back into the primary of
the coil and developing a voltage thereacross that could damage the
voltage sensitive electronic components, including the
semiconductor devices of the condenser discharge system, connected
thereto. By isolating these currents from the primary, the shield
prevents them from being dissipated as power losses in the coil
and, instead, converts and utilizes such energy appearing in the
secondary to maintain the oscillations of the coil for sustaining
spark plug ignition.
The lumped capacitor formed by the foil wrap 24 and mounting clamp
14 is shown schematically at 23 in parallel with both the secondary
winding 22 and the inherent distributed capacity effect 64 of the
secondary winding and serves to parallel resonate the secondary to
a frequency providing a rapid rate of rise to the energy supplied
from the coil to break down the plug gap under cold starting
conditions.
In addition to increasing the energy storage capacity of the coil
as a source of energy, the additional capacity provided by the
lumped circuit capacitor 23 enables delivery of sufficiently high
currents from the coil to satisfy the gap current demand of the
plug for operation of the engine with all commonly available fuels
therefor. The additional capacitance parallel resonates the
secondary and effectively reduces the internal impedance of the
coil to adequately or more closely match that of the plug load for
maximum transfer of energy thereto.
The coil thus effectively constitutes a constant current source or
generator that will deliver energy to a variable impedance load and
will adjust its output voltage characteristic in relation to the
voltage requirements of the load for gap breakdown thereof while
supplying the high current level demands and energy requirements of
the load. In distinction to the high impedance, low current
transfer characteristic of the conventional ignition coil, the
reduction of the internal resistance and somewhat lowered primary
inductance of the subject ignition coil renders the primary thereof
a low impedance, high current energy transfer link circuit to the
secondary. The capacitance 23 resonates the secondary as a high Q
oscillatory tank circuit supplying energy therefrom of sufficient
intensity and duration providing successive or multiple firings to
insure combustion under adverse operating conditions of the
engine.
The energy attains a sufficient intensity and is released at such a
rapid rate as to effectively burn off fouling deposits on the plug
electrodes, thereby improving combustion efficiency, delaying the
formation of combustion chamber deposits and reducing the content
of unspent combustion products exhausted from the engine.
* * * * *