Note: Descriptions are shown in the official language in which they were submitted.
- 3 --
FIELI) 0l~` Tll~ ]:NV~NTION
This invention co~cerns improvements in and relating to
apparatus for produc.ing spark ignition of an internal
combustion engine, and is particularly but not exclusively
concerncd with engines for automobiles.
BACKGROUND ~0 THE INVEN1`ION
It is well known that the electrical sparks fed to the
spark plugs of an internal combustion engine are usually
produced by means of an ignition coil having its high
voltage secondary winding connected to the engine's spark
plug through a distributor, the coil having its primary
winding connected to a low voltage source, typically a
12 ~olt battery or an alternator system driven by the l
engine. An engine dri~en switching device, typically a
mechanical contact breaker produces interruptions in the
current flowing the primary winding of the coil and con-
sequentially high voltage pulses are produced in the
secondary winding, which are applied to the spark plugs.
Considerable research has been directed at improving
fuel economy and reducing pollutant emission of internal
combustion engines. Efforts have been made to devise an
engine which will run satisfactorily with a leaner fuel
to air ratio fed to the cylinders of the engine. Such a
leaner fuel to air ratio reduces fuel cons~nption but has
: 25 the disadvantage that the fuel/air mixture becomes more difficult to ignite with a conventional spark ignition sys-
tem. .Also, the increased ratio of air to fuel increases
the likelihood of nitrogenous fuel constituents being ',
: converted by the combustion into oxides of nitrogen~
hereinafter referred to as NOx. Such NOx products are
difficult to extract from the exhaust of the engine, as
is necessary if the engine is to comply with pollutant
emission regulations.
In order to reduce NOx exhaust emission~ recent
35 research has been directed to recirculating engine exhaust I i
gases into the engine~s cylinders so as to reduce the
: ratio of fuel to air in the mixtu~e to be consume~l:i.n the
engines, whilst maintaining a lean fuel content in the
mi,xturc. S~lcll eXllaUfi~ gas reC:irCtllali(JJ~ }~rcinaf-tcr
referred to aS EGR, reducec; N~x emission ~ut cools the
temperature of combustion and makes thc combustible mi~ture
in the enginc's cylinders even more diffjcult to igni-te.
Various proposals have been made to overcome the
difficulties of igniting a lean fuel/air mixture. One
solution involves the redesign of the engine such as
to produce a so-called stratified charge in the cylinders.
In a stratified charge engine, a fuel/air mixture has a
non uniform spatial fuel distribution within the cylinder
such that a higher concentration of fuel occurs adjacent
the spark plug than in,the most part of the cylinder.
When spark ignition occurs, combustion will occur more
readily in the relatively high fuel concentration adjacent
the spark plug and the ensuing heat of combustion will
`` cause the combustion to spread to the leaner mixture in the
other parts of the cylinder. One example of a stratified
charge engine is described in ~A New Concept of Stratified
Charge Combustion - The Ford Combustion Process (FCP)"SAE
Paper No. 680041 January 1968. This engine was developed
into the PROCO engine described in ~'The Ford PROÇO Engine
Updatel' SAE Paper No. 780699 August 1978. It will be
seen that in contrast to the FCP engine, the PROCO engine
has an EGR system to reduce NOX exhaust emissions. More-
over it is to be noted that in order to achieve s,atis-
factory combustion, two spark plugs per cylinder are required
with the EGR assisted PROCO engine~ thus illustrating the
further difficulties that occur in initiating ignition of
a lean burn mixture when EGR is used. It will be
appreciated that when two spark plugs per cylinder are used,
a complex distributor is required and the overall cost of
the igni-tion system is incre~sed substantially. Another
problem resul-ting from the use of two spark plugs per
cylinder is that the PROCO engine concept can only be used
for large engine capacities of typically 5 litres or more.
For smaller engine capacities, there is not enough room in
the cylinder head to receive the spi~rk plugs and the
neccss.1ry valvcs ar~ ctors ugod ror this tyl,e Or
engine.
Another proposal lor igniting a fuel/air mi~ture is
shown in U.S. Patcnt No. 4,033,316 to Birchenough, that
discloses an arrangemcrlt i~l which a high voltage direct
current source is connected in series with the secondary
winding of an ignition coil, in such a manner as to main-
tain the spark initiated by the conventional operation of
the coil. Thus, the spark ignition in the cylinder is
initiated by a typically 20KV pulse produced in a conven-
tional manner by interrupting the current flow in the
coil's primary winding, and the spark is thereafter main-
tained by a high voltage of` typically 2 to ~ KV from the
high voltage d.c. source that is connected in series with
the coil's secondary winding, in a manner broadly analogous
to the way in which a welding arc is initiated by a high
voltage pulse and is sustained by a lower voltage direct
current. It is well known that once an arc has been
struck it can be maintained by a voltage less than that
required to strike the arc.
Birchenough states that the voltage required to sus-
tain the spark is generally constant, and that the voltage
current characteristic of the direct current generator
shouId be such as to deliver a constant current to the
spark.
The circuit shown in Figure 2 of the Birchenough U.S.
Patent achieves this condition by arranging the d.c.
generator to have an output voltage current characteristic
defined by a curve for which a decreased output voltage
results in an increased current, the maximum current at
low voltage being limited by the output impedance of` the
d.c. generator.
I have fo~nd that in practice, whilst the voltage
required to sustain the arc does have a generally constant
mean value, it is subject to transistory fluctuations,
these fluctuations occurring during combustion conditions of
high EGR, high compression)high $as swirl rates within the
cylinder~ ancl extrelllcly le~lrJ burll iuel mixtures. ~uring
such a tr~nsistory f~uctuLItioJls both a relativel~ high
voltage and current may be required to sustain the spark.
}lowever, thc d.c. generator of Birchenough delivers a
relatively low voltage at high current le~els and accor-
dingly will not sustain the spark during such transitory
conditions unless the d.c. generator is made more powerful
and accordingly inefficient for the most part of its
operation.
Another problem occurs with the d.c. generator of
Birchenough in the event that a short circuit occurs across
the spark plug or across the output of the generator.
Such a short circuit condition could occur when an engineer
is checking operation of the ignition circuit. It is
common practice to touch the spark plug's lead against
the engine to see if a spark jumps from the end of the
lead. During such testing a short circuit is likely to
occur across the output of the d.c. generator. Now, the
d.c. generator of Birchenough comprises a free running
oscillator which drives a step up transformer, the output
of which is applied to a diode and capacitor network which
acts as a rectifier and voltage multiplier, to develop a
high voltage d.c. output across an output capacitor. In
the event of a short circuit across the output, the d.c.
generator operates to pump a high current into the
short circuit. As a result the oscillator will
overheat and is likely to fail. The circuit of Birchenough
is accordingly dangerous to maintenance engineers. If an
engineer accidentally touches thehigh voltage spark plug
lead,to produce a short circuit, the d.c. generator will
pump a heavy current into the short, with consequential
hazardous results for the engineer.
Another problem with the Birchenough circuit is that
the operation of the high voltage d.c. source produces
substantial erosion rates of the spark plugs' electrodes
and the electrodes of the distributor and its associated
rotor arm. This problem i~ particu~arly scrlous ir the
~.
energy supplied by the d.c. generator is selected to be high
enough to maintain the spark during combustion with high
EGR rates and high combustion gas swirl for lean burn fuel
mixtures.
A further problem with the Birchenough circuit
is that the output capacitor of the d.c. generator will
remain charged for a substantial time after the circuit
has been switched off. Thus, if an engineer touches the
output of the ignition circuit even after the circuit has
been switched off, he is liable to receive an electric
shock.
OBJECTS AND SUMMARY OF THE INVENTION
__.
It is an object of an aspect of the invention to
provide an improved ignition system for a lean burn engine.
It is an object of an aspect of the invention to
provide an ignition system that will provide satisfactory
combustion of an internal combustion engine provided with
an EGR system.
It is an object of an aspect of the invention to
provide an ignition system in which the sparks produced
by the spark plugs are initiated by the conventional operation
of an ignition coil and are thereafter sustained bv the
use of a d.c. generator, the d.c. generator being so adapted
as to sustain the sparks even during the aforesaid transitGry
arc sustaining voltage and current fluctuations.
It is an object of an aspect of the invention to
provide such a d~c. generator which does not pump heavy
current into an output short circuit, and which is less
likely to produce dangerous electrical shocks to maintenance
engineers.
An object of an aspect of the invention is to provide
a stratified charge internal combustion engine having an
EGR system, with an ignition system including only one
spark plug per engine cylinder.
An object of an aspect of the invention is to provide
a PROCO engine with an ignition system having only one
spark plug per cylinder.
. .
An object of an aspect of the invention is to provide
an ignition system whlch aids in permittiny smaller size
PROCO engines to be constructed.
From one aspect the invention provides apparatus
for producing spark ignition of an internal combustion
engine wherein combustion is effected by means of a spark
plug in a combustion chamber of the engine, comprising:
~a) spark pulse generating means for applying
repetitively to the spark plug an electrical
pulse capable of initiating a spark across
the spark plug; and
Ib) d.c. to d.c. converter means for producing
a continuous constant output voltage for
application to the spark plug to sustain the
spark, said converter means comprising:
~1) a step up transformer having primary,
secondary and feedback windings, and a
saturable core;
~2) oscillator means including a pair of
semiconductor switching means coupled to
said primary winding and to said feedback
winding and operable to produce an oscilIat-
ory current flow in said primary winding,
thereby to induce an oscillatory stepped
up voltage in said secondary winding, said
oscillator means including a resistor
connecting one end of said feedback
winding with the base electrode of one of
said semiconductor switching means, the
other end of said feedback winding being
directly connected with the base electrode
of the other of said semiconductor switching
means, said resistor being operable to adjust
the point at which the bases of the semi-
conductor switching means no longer saturate,
thereby to define the maximum value oE
current beyond which operation o~ ~he
~ 6a -
oscillator means i9 automatically terminated;
(3) rectifying means coupled to said secondary
winding for producing a rectified output
voltaye for application to the spark plug;
and
(4) said converter means being operable upon
short circuit of said output voltage to
ground to damp said oscillator means and
thereby cease operation of said converter
means.
From another aspect the invention provides an apparatus
for producing spark ignition of an internal combustion
engine in which sparks across the spark plugs are initiated
by an electrical pulse and are thereafter sustained by
the use of a d.c. generator which applies a sustaining
voltage to the plugs, the generator being characterised
in that it is adapted to produce a substantially constant
voltage over a predetermined range of current values supplied
~; thereby to sustain the spark, and to cease operation capable
of sustaining the spark in the event that the current supplied
thereby to the spark plug exceeds a predetermined maximum
value. The d.c. generator has the advantage that because
the voltage thereof remains subs~antially constant, the
generator will sustain sparks even under conditions of
high ÆGR, gas swirl load and extremely lean burn. I~ the
spark demands a transitory high current, the voltage of
the; generator can deliver the current without the voltage
dropping below the arc sustaining voltage.
Also, because the generator will cease operation
when~ the~current exceeds a given maximum value thereof,
the~generator will not pump a heavy current into a short
circuit, and thus dangers to maintenance engineers who
accidently touch the spark plug leads, are reduced substantially.
Also, in the event of an output short circuit, the generator
will not overheat or fail.
In accordance with a preferred feature of ~he invention,
the d.c. generator develops its output voltage across a
r~
- 6b -
capacitor which is shunted by resistance elements to allow
the capacitor to discharge when the genexator is inoperative.
In this way, the capacitor will dissipate the charge which
might otherwise give an electrical shock to a maintenance
engineer.
From another aspect the invention provides an appara-
tus for producing spark ignition of an internal combustion
` - 7 -~
ensine in which thc sl)~rk .s~lstuilling voltago produ~ed by
the d.c. generator i~ ol a selectively variable level, the
level being alterable i~ depcndence upon operating para-
meters of thc engine, with the advantage that relatively
; 5 high spark cnergies need only be used for extreme combu~-
; tiOIl conditions and lower spark energies can be used at
other times, so that sparlc plug electrode erosion i6
reduced.
From yet another aspcct the invention provides an
improved ignition system on a stratified charge lean
burn engine, particularly but not exclusively a PROC0
engine t in which sparksacross spark plugs in combustion
chambers in the engine are initiated by electrical pulses
and are thereafter sustained by the use of a d.c. generator
which applies a spark sustaining voltage *o the plugs.
In accordance with this aspect of the invention only one
spark plug per combustion chamber is provided, since in
accordance with my invention satisfactory ignition can be
achieved with only one spark plug, without any reduction
in fuel economy and with an improvement in exhaust pollu-
tion reduction. Furthermore, with my invention the
stratified charge engine can operate at high EGR rates
without the occurrence of substantial harsh running.
Further features objects and advantages of my inven-
tion will appear from the following description of
embodiments thereof given by way of illustrative example
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
_. ~ . __ - ._._
FIGURE 1 is a schematic diagram of an apparatus for
producing spark ignition in accordance with the invention;
FIGURE 2 illustrates in more detail the circuit
diagram of a d.c. generator shown in FIG. 1;
FIGURE 3 shows waveforms illustrative of operation of
the d.c. generator; FIG. 3A showing the current in the
primary winding of the transformer T1 of FIG. 2; FIG. 3B
showing the voltage induced in the secondary winding of
the transformer T1; and FIG. 3C illustrating the voltage
currerlt outl~llt cllaracteristic oi the ~elJerator 7;
FIGUI~E /1 illu.str~te~ ~ modil'ic~tiorl oI' the apparatus
of FIGS. 1 and 2 in whic}l the voltase ~roduced by the
generator 7 is controlled in dependence on operating
parameters of thc engine to reduce spark plug erosion;
FIGURES 5 to 7 illustrato alternative arrangements
to the circuit of FIG. 4;
FIGURE o is a schematic circuit diagram of an
arrangen1ent permitting a separate inductance to be connected
in series with the spark plugs;
FIGURE 9 is a schematic arrangement which allows the
d.c. generator to be used as an add-on unit for a conven-
tional ignition system.
FIGURE 10 is a sectional view of a cylinder of a
PROCO engine;
FIGURE 11 is a sechmatic top plan view of the cylinder
head of the PROCO engine;
FIGURE 12 is a schematic sectional view of a PROCO
engine adapted to have an ignition system according to the
invention, and which has only one spark plug per cylinder;
and
FIGURE i3 is a schematic diagram of another example
of the invention which utilises a conventional alternator.
~SCRIPI`ION !~` Pl~ EI) EMnODIMI~NJ'S
l~eferring to I~IGU~ 1 therc is shown a spark pulsc
generating means which includes an ignition coil 1,
having primary alld secondary windings la, lb, a current
control means 2 which controls a low voltage current flow-
ing in the primary winding, and an engine driven sparktiminS control means 3 which dri~es the currentcontrol means
2. The current control means 2 is adapted to produce a
rapid rate of change of current flow in the primary winding
la in response to operation of the timing control means 3,
so as to induce in the secondary winding lb a high voltage
pulse of typically 20-40 KV. This high voltage pulse is
capable of producing spark ignition in an internal combus
tion engine and the pulse is applied through a distributor
4 which may be any of the well known types, to spark plugs 5
installed in cylinders of the engine (not shown).
The current control means 2 and the timing control means
3 may be constituted by a conventional contact breaker driven
by a cam in the distributor 4, which swi*ches a nominally
12 volt sùpply from the engine's usual ba$tery/alternator
arrangement (not shown) on line 6, to interrupt the current
flow and produce a rapid rate of change of current in the
primary la. Alternatively, the current control means can
be a semiconductor switch~which may operate to discharge a
capacitor through the primary winding la. Also, the spark
timing control means 3 may be constituted by a known
photoelectrlc, infra-red or like detector responsive to the
angular position of rotation of the engine.
Thus, in operation of the spark generating means, high
voltage pulses are produced in the coil's secondary winding
lb in response to successive operations of the spark
timing control means 3, these pulses being appropriately
applied by the distributor 4 to successive ones of the
spark plugs 5 so as to establish sparks in successive ones
of the cylinders and thereby ignite fuel/air mixture in the
cylinders.
Additionally, a d.c. generator 7 is provi~ed~ connectod
in series with the secondary winding lb. 'I`hc generator 7
applies to the sparlc plugs 5 a d.c. voltage capable of
- 10 -
sust~ininS a spark across 1;ilo spark p~ugs a~ter the lligh
voltagc sparl~ initiating pulse produced by operation of
the circuit 2 has died away to a level incapable of
maintaining tile spark. The d.c. generator 7 comprises
a d.c. to d.c. converter arranged to generate a i~igh
voltage OUtpllt of nominally 3KV from the low voltage
supply on li71c 6. The generator 7 produces a rcctified d.c.
output on lille 8, which is fed through the secondary lb
of the coil to the distributor ll and hence to the spark
plugs 5. Thc output voltage of the generator 7 is of a
magnitude selected to sustain but not initiate a spark
across one of the spark plugs5, and the generator is per se
capable of producing a continuous voltage of such a magnitude.
Once the spark has been initiated by a high voltage pulse
produced by operation o~ the current control means 2, the
spark can be sustained by a somewhat lower voltage, and the
d.c. generator 7 is suitable for providing such a sustaining
voltage. The fact that the spark sustaining current is
supplied by a separate generator 7 provides the advantage
of allowing much greater spark currents to be established
for longer periods of time~ which provides for improved fuel
burning and results in improved fuel economy and/or a
reduction in pollutant emission.
In the forms o the invention described herein the
generator 7 develops a continuous output voltage and each
spark is extinguished either by operation of the distributor
to disconnect the applied sustaining voltage and connect it
to a subsequent spark plug, or by virtue of the increased
gas pressure produced in the cylinder by the combustion
initiated by the spark. The increased gas pressure
presents an increased electrical impedance to the arc
established between the spark plug electrodes, and the
voltage level produced by the generator 7 can be appro-
priately selected so that the increased gas pressure will
cause the spark automatically to extinguish when the gas
pressure rises to a given level indicating that satisfactory
combustion has occurred in the cylinder. Thus, when the
given pressure level is reached in the cylinder~ the voltage
_ i 1 -
I)ro~uced ~)y tlle gelleru1,or 7 is i,nsufficient to maintain
the spark, ulld l,he sl)ark will terminate aut~matically.
In an altorllative arrangement, the d.c. generator 7
is switche~l ofi' an(i on a$ain so as to terminate the spark.
Becausc thc generator 7 is per se capable of produc-
ing a continuous high voltage output, the period that the
generator 7 can be switched to supply the spark sustaining
voltage to the sparks, can be selec-ted independently of
the characteristics of the circuit of the generator 7 and
thus the duration of the output voltage can be selected
for example to be from a few milliseconds to an effectively
infinite duration. This arrangement al],ows the spark
duration to be controlled independently of the characteris-
tics of the circuit, and allows the current flowing
through the arc established across the spark plug to be
substantially constant during the entire period that the
spark is sustained by the voltage from the genera-tor 7.
Accordingly, the system of the invention allows the spark
duration to be extended and energy to be increased which
improves engine combustion.
The d.c. to d.c. converter circuit of the generator
will now be described in more detail with reference to
FIGURE~2. The circuit Gf the generator 7 is shown within,
a hatched outline and its interconnections to the rest of
the ignition circuit are shown schematically. The
circuit comprises an oscillator stage 9 which drives a
step up transformer T1 ? the output of the transformer
being fed to a voltage multiplier and rectifier stage 10.
The oscillator stage 9 is powered from the low voltage
12 volt supply line 6 through an interference filter
network comprising capacitors C1 to C3 and an inductor L1.
The filter network prevents spurious transients on the line
6 from disturbing the oscillatorycondition of the oscillator
stage 9. The transformer T1 has a primary winding with
winding portions lla, 'llb and a centre tap CT, a feedback
winding 12, a secondary winding 13 and a saturable core lll.
Transistor9 TR1 and TR2 are arran$ed to control the current
..
flowins from the rai] G in tho l)rimary winding l)ortions
11a~ 11b respectively~ thc bascs of thc transistors
receivin$ a bias switchins voltage derived f~om the feed-
back windin~s 12~ through a biasing resistor R1 and diodes
D1 and D2.
Operation of the oscillator will now be described
with reference to the waveform diagrams of ~IGU~ES 3A and
3~. Assume that the transistor TR1 is conducting.
A current flows from the line 6 through the winding por-
tion 11a from the centre tap CT7 -the current building up
substantially linearly at a rate determined substantially
by the inductance of the winding portion lla. The
resulting current ramp in the winding portion lla is shown
at 15 in FIG. 3A. The effect of this substantially con-
stant rate of change of current in the winding is to inducein the feedback winding a generally constant voltage which
is of such a polarity to bias the base of transistor TR1
appropriately to hold the transistor in a conducting state.
As the current flowing in the winding portion 11a builds
up, the core 14 becomes saturated with magnetic flux, and
the current can increase no further. As a result the
voltage across the feedback winding rapidly collapses,
... and the bias voltage to the transistor TR1 decreases,
which decreases the current flow in the winding portion lla,
thereby inducing an opposite polarity bias voltage across
the feedback winding 12. This opposite polarity bias
voltage rapidly switches on transistor TR2 and turns off
the transistor TR1. The current then builds up in an
opposite sense in the winding portion llb until the
core 14 saturates, in the manner shown at 16 in FIG. 3A,
at which time transistor TR1 will again switch on and
transistor TR2 will switch o~f. The circuit will oscillate
in this matter. The current ramps such as 15 and 16
induce in the transformer secondary winding respective
positive and negative voltages, such as 17 and 18 shown in
FIG. 3B~ the voltages being stepped up rèlative to the
voltage applied to the primary windins por1;ions 11 in
dependence of the turns ratio of the primary windins
I
o~
, ~ , 1 1
)OI'tiOI].'; ~ /1 S(~0~ Y W~ r~L; 1 1 ~ 12. U~ I(J :lo.t-]
collditio~l 10l~ t~lc~ c~ollvcrter 71 switclling ~rarl~ierlts OCCl~
in the oscil]~Jtol w]lic~ rcsu]l; in voltag~^ sJ,ikes 19 (FIG. 3E3)
occurring oll t~lc vo]tagc wavcform of the sccondary winding12.
The vo~t~gc ~lul1,iplier and rcctiIier 10 comprises fast
recovery diodes 1)3, I)~J which respectively pum~) charge into
series connected capacitors C4, C5 during opposite polarities
of the voltuge on thc winding 13. Thus, when the output
voltage across winding 13 is positive diode ~4 conducts and
charges capacitor C5, and when the output voltage is negative
capacitor C4 is charged through diode D3. Since the capaci-
tors are series connected, the output across both of them
constitutes a doubling of the positive voltage swing across
the winding 13. A final output capacitor C6 is connected in
parallel with the capacitors C4, C5 for smoothing purposes.
Connected in parallel with the final output capacitor is a
resistor chain R2, R3 which contributes to smoothing the
output and which also provides a discharge path for the final
output capacitor C6. A function indicator 20, typically a
neon tube, is connected in parallel with the resistor R3 to
indicate that the generator 7 is operative.
The voltage current characteristic of the output of the
generator 7 that is fed to the line o, is shown in FIG. 3C
as a curve 21. It will be seen that the generator 7 delivers
a substantially constant voltage over a predetermined range
of current. Thus when a spark is struck across a spark
plug 5, the generator 7 will maintain a constant voltage
irrespective of the current demand defined by the impedance
of the arc~ up to a maximum value of current 22 (FIG. 3C).
The current value 22 is defined by the point at which the
bases of TR1 and TR2 no longer saturate, this being adjus-
table by adjusting the value of resistor R1. Currents above
the value 22 indicate a short or other fault condition at
the spark plug, and the generator is arranged to shut down
operation automatically if such a condition occurs. The
occurrence of such a short circuit is reflected back to the
output winding 13 of the transformer T1 (~IG. 2) such as
to alter the inductance of _
-
the trarlsi`orlllor eln~ preventtllc o~ciJ~ .ItOr () 1`rorrl working.
Another usei`ul feature of the gcnerat~r 7 can be seerl Irom
FIG~ 3C. ~efore a spark is struck across one of the
spark plugs, substantially no current is drawn on line 8
from the gencrator 7. Under such a condition, the
capacitor cG (FIG. 2) becomes charged to a voltage substan-
tially equal to twice the value of the voltage spikes 19.
This relatively high voltage from the generator 7 aids in
striking the sparks at the spark plugs 5, since this voltage
adds itself to the high voltage pulses induced in the
secondary winding lb of the coil. After the spark has been
struck, current is drawn from the generator 8 and *he
voltage spikes 19 become integrated by the capacitors C4
to C6 with the result that output voltage on line 8 drops
onto a substantially constant plateau depicted in FIG. 3C,
and which is substantially equal to twice the voltage level
the waveform 17 (FIG. 3B)~
The voltage current characteristic of the generator 7
has the advantage of enabling the generator to sustain the
spark under conditions of extreme lean burn combined with
substantial rates of EGR and gas swirl within the cylinders of
the engine. Under such conditions the impedance of the arc
can undergo substantial transitory fluctuations, so as to
draw an increased current from the generator 7. I have
found that to sustain the arc in these extreme conditions,
the generator must be able to deliver an appropriate
current to *he arc without allowing the voltage applied
to the arc to drop. If the voltage drops below a certain
level, even momentarily, the arc will become extinguished
and will not be re-kindled unless another 20 KV pulse is
applied from the ignition coil. In FIG. 3 there is shown
in hatched outline the voltage current characteristic of
generators of the type described in the prior Birchenough
U.S. Patent No. 4,033,316. It will be seen that if the
arc momen*arily demands a relatively high current, the
voltage applied by the generator will drop. Thus, the
arc would either become extinguished or if the generator of
_ I rJ ~
Birchenousl1 were desjp7l~e(l -I,o o1)eratc satisIac-torily undcr
tl~ese conditions~ i1 would co~lsumc much rnors power an~
would normally delivcr urlnecessarily high voltages to
thc spark p]ugs.
It is to be rloted that the gencrator 7 has a low component
count and is therefore cheap to produce and more reliable,
Anotheradvantagc of the generator 7 is that in the
event of an engineer touching the spark plug lead to produce
a short circuit, the oscillator 9 of -the generator becomes
damped and ceases operation. In this way a condition
is avoided in which the generator pumps a heavy current into
the short circuit. Clearly such a condition would be
hazardous to the engineer and would also be likely to cause
the generator to overheat and fail.
A further safety feature o-f the generator 7 is that
the output capacitor C6 (FIG. 2) is shunted by resistors
R2, R3 so that its charge can dissipate when the engine
is turned off.
Without this shunt the capaci*or C6 would retain its
charge for a considerable period of time so that if an
engineer was to work on the engine, he could receive an
electric shock from the capacitor C6 through the ignition
leads. Also with the present generator 7, the neon 20
will readily indica-te to him not only if the system is
operative but also if a charge remains on the capacitor
C6.
A feature of the ignition system just described is
that substantially increased mean spark energies are
achieved compared with a conventional contact breaker
igni-tionjby means of the currents injec~ed into l~he
sparks by the generator 7. When substantial EGR or extreme
lean burns are utilized in an engine, the spark energies
need to be substantial if reliable ignition is to be
achieved. A disadvantage that can occur is that the
increased spark energies can cause unacceptable erosion
rates of the spark plug electrodes and the electrodes of
the distributor 4. In accordance with a feature of my
~ J~
inverltiol-l tl)c e~lersy lovol of t}~e sJ1arkY carl ~JC se:le~ted
jJI ~ependencc ul)on oJ)crati~lg p.lramcters oI thc engi7le such
th~t higher energy sl).-lrks are only produced when extremc
conditions occur. In this way, the mean energy oi the
sl)arks can bc reduced without detracting from the improved
engine running characteristics that result from the
invention. An example of such an arrangement is shown
in EIGURE 4. This Eigure shows the generator 7 coupled
in series to the ignition coi]~ much as shown in FIGURE 2,
but additionally shows a relay 23 which is used to switch
the voltage applied to the oscillator 9. The relay 23
has a coil 2ll, and contacts 25 which are shunted by a vol-
tage dropping resistor R4. Normally the contacts 25 are
open as shown in the drawing, such that a portion of the
12V supply to the oscillator 9 is dropped across the resis-
tor R4, thereby reducing the voltage developed across $he
primary winding 11 to a value less than 12 volts. As a
result the high voltage d.c. output developed on line 8
is reduced below its maximum value. However, when the
contacts 25 of the relay close, the resistor R4 is shorted
out and the voltage applied to the oscillator 9 increases
with the result that the d.c. output voltage on line 8
achieves its maximum value.
The relay is controlled by a logic circuit 26 which
typically provides a switching path to earth for current to
flow through the relay coil 24. The logic circuit is
responsive to sensed operating parameters of the engine sho~n
schematically at 27. The logic circuit 26 determines
when operating parameters of the engine indicate *hat
extreme combustion conditions occur, and the circuit 26
switches the relay 23 accordingly. As shown in FIGURE 4
the engine is provided with an EGR system in which the
gas flow rate is controlled selectively by a control 28.
As will be appreciated by those skilled in the art the
EGR rate is typically controlled as a function of inlet
manifold vacuum level. The logic circuit 26 is responsive
~ 7
to the ~Gl~ lute.
The losic circuit 2G is also resl)onsivc to a iue:L
control 2~) whicll determines the fuel mixturc strength.
In an engirle aspirated by a conventional carburettor, thc
logic circuit would be responsive to the setting of the
conventionul choke whereas with a stratified charge engine
provided with fuel injectors, the flow rate of fuel to
the injectors would bc monitored.
The losic circuit 26 is also responsive to the
engine temperature as sensed by a temperature sensor 30.
Thus, when these parameters jointly or severally define a
condition known to represent extreme combustion conditions,
the relay 23 is switched to provide a maximum output
voltage on line 8,~ but otherwise the output voltage is
switched to a lower level, with a consequential minimization
of spark plug electrode erosion.
FIGU~ES 5 to 7 illustrate alternative ways in which
the relay 25 can be connected to the d.c. generator 7.
In FIGURE 5, the dropping resistor R~ is connected in the
12 volt supply rail 6 rather than in the earth return.
In FIGURE 6, the dropping resistor is connected in the
high outpu-t voltage line 8 of the generator 7. In
FIGURE 7 the dropping resistor is connected in the earth
reference line of rectifier output stage 10 of the
generator.
In the above described embodiments of the invention,
the d.c. generator 7 is connected in series with the
secondary winding lb o~ the ignition coil. This arrange-
ment has the advantage that the inductance of the secondary
winding lb acts to increasethe sustaining voltageabove the
level set by the generator 7 in response ~oincreased arc impedance
that occurs for example during high gas swirl. In certain
circumstances, the inductance of the secondary lb may not
be sufficient for this purpose and it may be desirable to
use a separate inductor to define the ballast.
FIGURE o shows an arrangement in which a separate
inductor coil L2 is connected in the line ~ rather than
using the coil windins lb as the ballast induct~rlce. A
.
voltage iso~atirls mcarls 3~ is l)lovide~ in scries ~ith the
coil's secondary winding 1b irl ordor to prevent the d c.
current from thc go~cra1or 7 frorn flowing through the
winding to earth in prcference to flowing to the spark
pluss throug7l the distribut~r l~.
The voltage isolating means 31 is also adapted to
allow operation of the ignition coil 1 such that a high
voltage pulse induced in the secondary winding relative
to earth can flow to the spark ~)lugs. The voltage isola-
ting means 31 in one form comprises a capacitor whichblocks direct current flow from the generator 7 to earth
through the winding lb. The voltage isolating means can
also comprise a spark gap across which pulses induced in
the secondary lb will jump, or a high voltage diode.
In the above described embodiments, the ignition coil
1 is shown to have four terminals, two for each winding.
Such a coil can be made at low cost by adapting the manufac-
tureof a conventional ignition coil. A conventional
ignition coil has three terminals such that one end of each
of the primary and secondary windings are provided with a
respective terminal and the other ends thereof are connected
to a common terminal for connection to earth. If it is
desired to use the dc generator 7 as an add~on unit for an
existing conventional ignition system, the circuit arrange-
ment as shown in FIGURE 9 may be used.
In FIGURE 9 a conventional three terminal coil 32 isshown, having primary and secondary windings 32a, b each
with their own terminal 33, 347 and a common earthed
terminal 35. The d.c. generator 7 is coupled to the
conventional coil and distributor 4 by means of the ballast
inductor L2 and the aforesaid voltage isolating means 31
connected in series between the generator 7 and the coil's
secondary winding lb. The voltage isolating means 31
serves to direct the current from the generator 7 to the
distributor 4 and hence to the spark pulgs rather than
allowing it to flow through the secondary coil 32b to
earth. The voltage isolating means 31 however allows the
hiSIl VOlt~lSe ]~ .q~ (]IJ~,O~ ill t~ cling ,~ZI~ to 1)ass to
the distribul,or /l. As ~revi-)lls]y s-l,utecl, the isolating
means can for cxamr~le compri,so ;I C~l)aCitOr, a spark gap or
a diode.
It will l>e apT)rcciated thut dlffererlt combina-tions of
the circuit featurcs just describo(~ can be utilized. For
example any of the voltage levc~ sl~7itching arrangements
shown in l;`IGUT~ES 4 to 7 could bc used with the circuits of
FIGURES 8 or 9.
The generator 7 thus can be used,with conventionally
aspirated engines to achieve improvements in ~uel economy
and pollutant emission reduction, as will be illustrated b~
example hereinafter, and also provides for similar improve-
ments with engines provided with EGR, which may or may not
be conventionally aspirated with a car'burettor.
As previously mentioned, one aspect of the invention
concerns stratified charge engines and an example of the
invention ~ill now be described in relation to the Ford
PROCO engine in order to illustrate the advantages achieved
thereby.
Development of the Ford PROCO engine can be seen from
"Exhaust Emission Control by the Ford Programmed Combustion
Process - PROCO~ SAE Paper No. 720052 January 1972, and from
the previously mentioned SAE Paper No. 780699 - "The Ford
PROCO Engine Update".
A schematic illustration of the PROCO engine is shown
in FIGVRES 10 and 11. The engine has a high compression
ratio of typically 11:1 and operates with a lean fuel to
air ratio of typically 15:1. Referring to FIGURE 10,
which shows a sectional view of one cylinder of the engine,
an engine block 36 is bored with a cylinder 37 which recei-~es
a piston 38 formed with a dished combust ion chamber 39.
A cylinder head 40 is bolted onto the block 36. The head
40 receives two spark plugs 41, 42 and also a fuel injector
43 that injects fuel directly into the cylinder such as to
establish a stratified charge therein. The engine has a
EGR system (not shown) in order to red~lcc NOX emiss:ion.
Thc layout ol' the cylin~lcr hcad in plan view is s}lown
schematical]y in l~`IGUl~E 10, from wllic}l it will 'be seen th~t
the head includes inlet and outlet valvcs 4/l, 45 for air
and EGI'~, and an inlet mani,rold l~6. The inlet manifold 46
and the in]et valve are arrangcd to establish,a swirling
gas motion within the cylinder, the gas motion being
indicated scllematically by the arrows 47, 48.
It has been found necessary to use two spark plugs
per cylinder with a PROCO engine because unsatisractory
combustion otherwise results at conditions of high load
and high EGR~ As a result a complex distributor is
required and the overall cost of the ignition system is
undesirably increased. Also, as can be seen from FIGURE
ll~ the cylinder head 40 becomes rather crowded with
components, which makes it difficult to design ~n engine
of this type with a capacity of less than 5 litres, since
the size of the head then is too small to receive all of
the required components.
I have found that a PROCO engine can be made to run
satisfactorily,with only one spark plug per cylinder when
an ignition system of the kin~ shown in FIGURE 1 is used
therewith. Such an arrangement according to the invention
is shown in FIGURE 12 where it can be seen that the engine
has been modified to have only one spark plug 42 which
receives a spark initiating pulse from a spark generating
means and a spark sustaining voltage thereafter from a
d.c. generator~ as described with reference to FIGVRE 1 et
seq. The improvement achieved can be seen from the results
of a test given below, in which a single cylinder of a
PROCO engine was run with a) two spark plugs b) one spark
plug and c) one spark plug with the ignition system of the
invention, the other plug opening being blanked off.
In the results of test c) the system of the
invention is referred to as the BWU ignition system. The
tests were performed without attempting to optimize the
settings of the engine for the BWU systetn except that a /l
ignition timin~ retardation was introduced relative to the
t]le ~irllulll s(3~ s ~r t~ OC~
bolievecl thnt I`urther im~rovelllents in f-lC(hy~rocarbon) an~
CO(carbon monoxide) oxhaust emissions can ~e achieved
wh~n further optimi.zation ol the engine operating paramet~rs
is achi.eved.
TAr3Ll~ 1
Test ~esults 5 Litre PROCO Engine
4000 LB I.W. 12 P.A.U. 2 75 Xear Axle
Test Emissions-GPM Economy
Type HC CO NOx MPG Remarks
Cold .24 .6 .68 16.9 PROCO dual plug baseline
Start
(C/H)
Hot .11 .2 .52 17~7 X-5 plugs, .0201l gap, Z
Start test average
(H/S)
C/H .20 .3 .69 16.4 BWU system, X-7 O.B. plug
~/S .12 .1 .57 16.9 Dummy I.B. plug, .035"
gap, 1 test
C/H .20 .2 59 16.5 BWU system, same as above
H/S .12 .1 .50 17.2 Configuration but ignition
timing retarded 4 - 2 test
average
H/S .o6 ~1 074 16.0 PROCO single O.B.~ X-7,
.035" gap. Rough engine,
weak drive, standard
ignition timing
H/S .11 .2 53 17.7 BWU system, 4 retard
Hot .33 .4 .82 17.6 PROCO, single O~B. ignition7
Transient 4 retard
Hot .26 .4 .65 18.3 BWU system~ 4 retard
Translent
I
Driveability ~ValUat:i.Orl
PI~OCO dual PllOCO single l3WU ~ystem singl~
Plug (.OZO" plug (.035~ plug (,035" gap)
gal) ) gal) )
Cruise Steady Slightly Steady
Rougher
Medium Load Slight Noticeably Steady to slight
(10" servo Roughness Rough roughness
vacuum)
Heavy Load Steady, Noticeably Steady~ harsh with
(5" servo slight rough/weak standard timing:only
vacuum) harshness slight harshness
with ~ retard
Test Conclusions
1. The BWU sy.stem is comparable to the standard
PROCO 2 plug system on emissions and has a comparable
fuel economy.
2. The BWU system is better than a PROCO single
plug system on both emissions and fuel economy.
3. The BWU system i~ at least as good as the PROCO
2 plug system on driveability and a significant impro~re-
ment compared to a PROCO single plug system.
.
The BWU system provides for increased EGR tolerance~
On test the standard 2 plug PROCO engine would run to a
predetermined minimum misfire rate limit with an EGR flow
rate of 66% relative to the flow rate of fresh inlet gas.
However with 1 plug and the BWU system, the PROCO ran to
103% EGR before the misfire limit was approached.
As previously mentioned~ the ignition system of the
invention also provides for substantial fuel economies with
conventionally aspirated engines, with or without EGR.
Given below in Table 2 is the results of tests performed
with three different capacity conventional engines.
'I`AI51,1~, 2
Test 1 2. 3 litre erlgine
Emissions $pm ~uel Hi~hway
]IC CO NOx Consumr~tion Fuel
(m.p.g._) Consumption
Baseline .172 3.~o 1.1218.40 24.75
~WV Ignition. lfio 3.17 1.1619.81 25 O 91
S.H.U. (+85~o) (+5%)
BWU Ignition.301 2.29 1.8221~09 28.30
T Ø0. ( +15%) ( ~14.43%)
Test 2 3.3 litre engin~
Emissions gpm Fuel Highway
HC CO NOx Conswnption Fuel
(m.p.g.) Consumption
Baseline .289 1.71 1.2818.30 23.14
BWU Ignition.52 2.28 1.1119.06 23.57
S.H.U. (+4%~ (~2%)
BWU Ignition.25 1.46 1.7319.97 25.03
TØ0. (+9%) (-~80/o)
Test 3 5.0 litre engine
Emissions gpm ~heI Highway
HC CO NOx Consump-tion Fuel
~n.~g.) Consumption
Baseline. 383 2.15 ,99~6.97 21.97
BWU Ignition 341 2.32 .7017. o6 23.35
S.H.U. -(+5%) (+6.2850)
BWU Ignition~ 347 2.4 8 . 73 19.11 24.92
TØ0. (+12.6%~ (+10.15%)
S.H.U.: Straight hook only (no other alterations).
T.O.O.: Timing optimizing only.
The tests were performed over 4, 200 miles. The figures
in brackets show the overall fuel economy improvement given
by the BWU system in percentase terms relative to a baseline
defined by a comparable run of the engine with its conven-
tional ignition system.
I
