Breakerless electronic ignition system

An electronic ignition system for an internal combustion engine having a timing signal source comprising an oscillator for providing a carrier signal; an electronic network connected to the oscillator and including a sensor means for providing a reactance which varies as a function of the rotational position of the engine, the network further including a reference means for comparing the reactance of the sensor means and providing modulation of said carrier signal; a detector for demodulating the modulated carrier signal and providing an output signal indicative of a predetermined rotational position of the engine. The output signal is supplied to switching circuitry for switching the primary of an ignition coil and providing a high voltage output pulse at a time synchronized with said predetermined rotational position of the engine.

This invention relates to a breakerless electronic ignition system and more 
particularly to an ignition system employing an improved timing signal 
source for controlling the spark or fuel injection timing of an internal 
combustion engine. 
It is well known that the spark ignition timing of an internal combustion 
engine is a very important factor with regard to engine performance, 
efficiency, operational economy and pollution content of the exhaust gases 
of the engine. Because of the ever increasing stringency of pollution 
control requirements as well as the increasing necessity for economical 
engine operation and the resultant conservation of fuel, it is important 
that the ignition system be capable of providing long periods of proper 
adjustment and trouble free operation. Proper breaker point adjustment and 
ignition timing are of prime importance. 
Prior art mechanical breaker ignition systems, as are well known, 
inherently require very frequent adjustments to maintain their initial 
performance characteristics. These mechanical systems although not capable 
of providing the currently desirable and required characteristics were 
previously considered adequate because of the much lesser degree of 
importance placed on both fuel economy and pollution control. Mechanical 
breaker ignition systems have inherent factors affecting their 
performance. In these mechanical systems, breaker contact wear, contact 
erosion, and susceptibility of the contacts to contamination cause 
undesired changes in not only the electrical conductivity and shape of the 
contacts but also result in changes in the gap or spacing of the contacts 
and thus affect ignition timing adjustments. In addition, wear of the 
distributor cam, the rubbing block as well as wear on the distributor 
shaft bearings result in variations in the change of the breaker gap 
spacing and timing adjustments all of which can combine and result in 
highly unpredictable and undesirable changes in the ignition system 
operating characteristics. These prior art mechanical breaker systems are 
also susceptible to changes in engine speed. At high engine speeds, the 
breaker contacts, or points as they are often referred to, tend to bounce 
and float causing unpredictable changes in ignition timing. This latter 
problem is difficult to overcome in mechanical breaker systems because the 
inherent mass of the movable breaker contact arm assembly and the spring 
loading of the arm will not permit the contacts to open and close 
precisely in synchronization with the distributor cam lobes as the engine 
speed is increased even to moderate speeds. 
Breakerless ignition systems are gradually replacing mechanical systems 
because many of the undesired characteristics of the mechanical system are 
overcome by replacing the mechanically activated contacts with 
non-mechanical sensors. Many such breakerless systems using various types 
of sensors and associated electronic circuitry have been proposed; 
however, not all have been entirely satisfactory. Many such breakerless 
systems, while overcoming some of the mechanical system problems, have 
created new and undesirable characteristics not previously present with 
the mechanical breaker ignition systems. 
Prior art breakerless ignition systems combat many of the weaknesses of 
aforementioned mechanical breaker systems by replacing the mechanically 
activated breaker contacts or points with various types of electrical and 
electro-optic sensors and associated electronic circuitry which, in 
effect, sense the rotational position of the engine. In such breakerless 
systems, signals are provided to activate electronic circuitry for either 
switching or driving the primary of the ignition coil as is well known. 
Sensors suitable for use in breakerless ignition systems can be categorized 
in one of two general operational areas. In the first category are those 
sensors which operate as electric signal generators. Such sensors provide 
an electrical output signal as a direct function of the rotational 
position of the engine. The well known magnetoelectric, photo-electric, 
piezo-electric, and Hall effect type transducers can be used as sensors of 
the first category. Examples of prior art ignition systems using 
magneto-electric and photo-electric type sensors are shown in the 
respective U.S. Pat. Nos. 3,087,001 to Short et, al. and 3,613,654 to 
Gilbert. 
In the second category are those sensors which operate to provide some 
change of sensor characteristic or parameter as a function of the 
rotational position of the engine. Systems using these sensors require 
additional means responsive to the change for providing a usable electric 
output signal. Examples of prior art ignition systems in this second 
category where changes in capacity, mutual inductance, and circuit "Q" or 
loading is used are shown in the respective U.S. Pat. Nos. 3,650,260 to 
Silvera; 3,361,123 to Kasama et al.; 3,822,686 to Gallo; and 3,605,714 to 
Hardin et al. 
A high signal to noise ratio is desired in any type ignition system to 
provide reliable operation and reduce the systems susceptibility to 
external noise and spurious signal pickup. In magneto-electric type 
sensors, this not only requires critically small air gaps, but also 
requires strong magnetic fields and large inductances which generally 
requires relatively large physical packaging of this type of sensor. 
Another disadvantage of the magneto-electric sensor is the fact that its 
output signal level is a direct function of engine speed and therefore at 
low cranking speeds the output level is also low. During engine cranking, 
a high output level is usually desired. 
A piezo-electric sensor although relatively reliable is somewhat fragile. 
This type sensor is also susceptible to vibration. Another disadvantage of 
a piezo-electric type sensor is the difficulty in providing an efficient 
mechanical coupling between the piezo-electric element and a rotational 
portion of the engine without involving excessive mass which can cause 
timing inaccuracies as in mechanical breaker systems. 
Use of the type of sensor which for example, operates to provide a change 
of circuit "Q" or loading or a sensor which provides a change of mutual 
inductance generally requires high frequency operation of the circuitry 
which is responsive to the changed characteristic. As an example, the "Q" 
or loading change when used with an oscillator to provide control between 
an oscillating state and a non-oscillating state typically oscillates at a 
frequency of between 300 and 400 KHz. A mutual inductance change is 
typically used as a conventional transformer supplying a signal from a 
primary winding to a secondary winding in, for example, a feedback network 
of an oscillator. A high operating frequency is desirable for this type 
use, to improve the coupling efficiency between the windings as well as 
provide a greater percentage of mutual inductance change. It is also 
desirable to have a high "Q" circuit. The use, however, of relatively high 
operating frequencies and high "Q" circuits in inherently unstable 
circuits such as the oscillatory circuits described, is undesirable since 
circuit performance degradation is much more likely to occur with 
environmental changes such as temperature and humidity as well as with 
changes in circuit component values and operating parameters which 
normally change over a period of time. 
The use of the sensors, mentioned in the previous paragraph, in ignition 
systems wherein the sensor parameter controls the operation of an 
oscillator between an oscillating state and a low level or non-oscillating 
state for providing a timing signal, can also result in timing errors as 
engine speed is varied. These errors are not only undesirable but are in 
some instances unpredictable which increases the difficulty in providing 
for their compensation. In such ignition systems, the errors are primarily 
due to an inability of oscillatory circuits to react synchronously with 
rapid changes in "Q", tuned circuit loading, or oscillator loop gain 
functions as may be provided by the sensor. The rise and decay times of 
the oscillator output signal vary as a function of circuit "Q", frequency 
of operation of the oscillator, as well as the rate at which the 
oscillator is caused to change states. Thus in such type ignition systems, 
the resultant timing signals do not always occur precisely at the desired 
times or rotational positions of the engine as the engine speed is varied. 
Typically, the timing signal is caused to be retarded as the engine speed 
is increased. 
In view of the foregoing, it is an object of the present invention to 
provide an improved breakerless ignition system for use with an internal 
combustion engine. 
It is an object of the present invention to provide a breakerless ignition 
system having improved immunity to environmental changes and externally 
generated electrical interference. 
It is another object of the present invention to provide a timing signal 
source including a sensor and a reference element and having a network 
means for comparing an electrical characteristic or property of the sensor 
with that of the reference element for generating a timing signal 
indicative of a rotational position of the engine. 
It is another object of the present invention to provide a timing signal 
source for internal combustion engines having a variable reactance sensor 
and a predetermined reference reactance in a bridge network for modulating 
a carrier signal and having a demodulator for demodulating the modulated 
carrier signal and providing an ignition timing signal indicative of one 
or more predetermined rotation positions of the engine. 
It is yet another object of the present invention to provide a timing 
signal source for internal combustion engines having a carrier signal 
source for generating a carrier signal and having a modulation means 
including a position sensor element and a position reference element for 
amplitude modulating the carrier signal in accordance with one or more 
predetermined rotational positions of the engine and having a means for 
demodulating the amplitude modulated carrier signal and providing an 
ignition timing signal indicative of one or more of the rotational 
positions of the engine. 
It is still another object of the present invention to provide a timing 
signal source for internal combustion engines having a carrier signal 
source for generating a carrier signal and having a modulation means 
including a position sensor element and a position reference element for 
phase modulating the carrier signal in accordance with one or more 
predetermined rotational positions of the engine and having a means for 
demodulating the phase modulated carrier signal and providing an ignition 
timing signal indicative of one or more of the rotational positions of the 
engine. 
It is yet another object of the invention to provide improved breakerless 
ignition system having a timing signal source which is well adapted to 
implementation using low cost, reliable, and readily available integrated 
circuits. 
SUMMARY OF THE INVENTION 
In accordance with the present invention in one embodiment, there is 
provided a breakerless ignition system for internal combustion engines or 
the like having a sensor means for providing an inductance which varies as 
a function of rotational position of the engine and having a reference 
inductor. The inductance of the sensor means is continuously compared with 
the inductance of the reference inductor in a bridge comparison network. 
The reference inductor having a predetermined inductance value 
corresponding with or bearing a predetermined relationship to one or more 
predetermined rotational positions of the engine at which ignition is 
desired. A carrier signal is supplied to the bridge network from a carrier 
signal source coupled to the network. The bridge network operates to 
provide amplitude modulation of the carrier signal in accordance with the 
one or more rotational positions of the engine. The modulated carrier 
signal from the bridge network is supplied to a demodulator which provides 
a demodulated and filtered output signal comprising a train of pulses 
occurring in time synchronism with the predetermined rotational positions 
of the engine and having pulse widths representing a dwell angle. The 
output signal from the demodulator is coupled to a power switching means 
which operates to supply a switching or drive voltage to the primary 
winding of a high voltage ignition coil for providing spark ignition 
voltage to one or more spark plugs for operation of the engine. 
In another embodiment of the invention, the bridge network provides a phase 
modulated output signal which is in turn demodulated by a phase 
demodulator. 
In still another embodiment of the invention, a low cost and readily 
available operational amplifier in an integrated circuit form is provided 
for detecting and processing the phase modulated signal. 
It will be noted that although the present invention is described in 
relation to an ignition system for an internal combustion engine, the 
invention also has application for use as a tachometer or for determining 
rotational position of an object. The detected or demodulated output 
signal indicates rotational position of an object or can be counted with 
respect to time and used as a tachometer reading instead of being used as 
a signal to initiate a high voltage pulse to a spark plug. 
The subject matter which we regard as our invention is set forth in the 
appended claims. The invention itself, however, together with further 
objects and advantages thereof, may be better understood by referring to 
the following detailed description taken in conjunction with the 
accompanying drawings.

The exemplifications set out herein illustrate the preferred embodiments of 
the invention in one form thereof, and such exemplifications are not to be 
construed as limiting in any manner. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1, there is shown a sensor inductor 1 and tyne 
assembly 2 for use in a breakerless ignition system in accordance with the 
present invention. The sensor inductor 1 and tyne assembly 2 can be 
contained within a distributor housing, if desired. The tyne assembly 2 is 
mounted to rotate with the distributor shaft so as to provide synchronous 
rotation with the engine. The sensor inductor 1 is mounted in a 
substantially fixed position with respect to the rotating tyne assembly 2. 
The sensor inductor 1 is mounted radially and coaxially outward from the 
center of the tyne assembly 2 as shown in FIG. 2 which is a partial cross 
section of the view A--A shown in FIG. 1. In the arrangement shown in 
FIGS. 1 and 2, the sensor inductor 1 is positional between the rotating 
tynes such as tynes 3 and 4 of the tyne pair 5 whereby rotation of the 
tyne assembly 2 will cause each one of the separate tyne pairs 5 to 8 to 
successively approach, enclose, and leave the sensor inductor 1. The tyne 
assembly 2 is positioned on the distributor shaft so that at a given 
predetermined position of the inductor 1 relative to each one of the tyne 
pairs 5 and 8, there is provided ignition spark as will hereinafter be 
apparent. The relationship between the sensor inductor 1 and the rotating 
tyne assembly 2 is much the same as that which exists between the cam and 
breaker contact assembly in a conventional mechanical breaker ignition 
system. The mounting of the sensor inductor 1 can also provide for 
incremental movements of the sensor inductor 1 relative to the tyne 
assembly 2 as a function of one or more operating conditions of the engine 
much the same as the distributor vacuum advance mechanism of the 
convention ignition system. 
The sensor inductor 1 preferably comprises an inductance coil 9 and core 10 
although in some embodiments the core 10 need not be used. As each one of 
the tyne pairs 5, 6, 7 and 8 of the rotating tyne assembly 2 approach, 
enclose, and leave the sensor inductor 1, there is provided a change of 
reactance of the sensor inductor 1. This change of reactance can, for 
example, be provided by an induced shorted turn effect if the tyne 
material is conductive and/or can be provided by a magnetic permeability 
change if the tyne material has magnetic properties. The inductance, 
reactance, and impedance of the sensor 1 are considered as interacting 
characteristics with a change in one, normally affecting a change in the 
others. Although all reference herein to a change in the reactance of the 
sensor 1 is also to be considered to include a change in its impedance, it 
will be apparent that such an impedance change can result from a change in 
the reactance and/or a change in the effective resistance of the sensor 1. 
The material which is used for the tynes of tyne assembly 2 can accentuate 
either a change in the reactance or the effective resistance of the sensor 
1. To exemplify, an electrically conductive and non-magnetic tyne material 
such as brass or aluminum can be used to accentuate eddy current losses 
thereby causing an accentuated change in the effective resistance of the 
sensor 1 with, of course, a change in the sensor impedance. On the other 
hand, a non-conductive, magnetic tyne material such as ferrite can be used 
to accentuate a change in the sensor 1 reactance with a minimal change in 
the effective resistance of the sensor. Likewise, a conductive, magnetic 
material such as stamped or cast iron can result in a change in both the 
effective resistance as well as the reactance of the sensor 1. The use of 
any of these types of tyne material will, however, for all practical 
purposes result in a change in sensor reactance and although any one of 
the above described tyne materials can be used, some will be more suitable 
than others from the standpoint of both cost and operational 
effectiveness. It will be later apparent, that the tyne material used in 
any particular modulation embodiment of the herein disclosed invention is 
chosen to provide an engine position information signal having a maximum 
degree of modulation resulting from the influence of the tynes upon the 
sensor. The tyne material of all of the tyne pairs 5 to 8 of, for example, 
the tyne assembly 2 of FIG. 1 is normally of one type; however, it need 
not be. Although the tyne assembly 2 shown in FIG. 1 has 4 tyne pairs 5 to 
8, a greater or lesser number can be used. The 4 tyne assembly of FIG. 1 
can, for example, be used in a 4 cylinder engine where it is desired to 
successively spark each one of the 4 cylinders separately or it can be 
used in an 8 cylinder engine where pairs of cylinders are sparked 
simultaneously. 
Alternate sensor inductor and tyne configurations are illustrated in FIGS. 
3-6. The arrangement shown in FIG. 3, as in FIG. 2, is suited to provide a 
reactance change due to either the aforementioned shorted turn effect or 
change in permeability whereas the configurations shown in FIGS. 4 and 6 
were found to be best suited to provide permeability changes. The 
configuration shown in FIG. 5 provides a change in the mutual inductance 
between the two series connected sensor coils 9a and 9b. In this 
configuration, the tyne 11 operates to act as a magnetic shutter or shield 
between the coils 9a and 9b thereby effecting a change in the mutual 
coupling between the coils. 
It will be understood that the tyne assembly can be a solid piece of 
material with built-up areas or knobs extending a slight distance from the 
solid body. The knobs would then provide a reactance change as they pass 
adjacent the sensor inductor. Alternatively, the tyne assembly can be an 
essentially solid or continuous tyne and have a slight indentation or gap 
(a void of material). Then the void of material would provide the 
reactance change as the void passes adjacent the sensor inductor. 
Referring now to FIG. 7 there is shown a breakerless ignition system in 
accordance with the present invention and using any desired one of the 
sensor inductor 1 and tyne assembly 2 configurations illustrated in FIGS. 
1-6. A timing signal source 12 operates upon the reactance change of the 
sensor inductor 1 and in response thereto, provides an output signal at 
output terminal 13. The output signal from the timing signal source 12 is 
supplied to a spark coil driver 14. The driver 14 operates to provide 
switching of the primary winding 16 of the high voltage (H.V.) spark coil 
17. The spark coil 17 and a H.V. distributor 18 operate in the 
conventional well known manner to provide sparking or firing of the spark 
plugs 19. The driver 14 can be any well known switching circuit, 
preferably of solid state design, operating to provide switching of the 
primary winding 16 in series with the battery source 20 as shown in FIG. 
7. In this manner of operation, the driver 14 replaces the conventional 
breaker contacts in the primary of the H.V. spark coil 17. The driver 14 
can also operate to provide a voltage or current drive pulse to the 
primary winding 16 of the spark coil 17 in which case the battery 20 is 
not required. It will be apparent to those skilled in the art that the 
timing signal source 12 can also be used in combination with other types 
of H.V. ignition spark generating circuits such as the well known 
capacitive discharge type. 
It should be understood that the revolving tyne assembly 2 and associated 
tynes provide a reactance change in the sensor inductor 1 at times of 
engine rotation when sparking at one or more of the spark plugs 19 is 
desired. The reactance of the sensor inductor 1 is compared against a 
reference inductor 21 in a bridge 22. A signal source input to the bridge 
is provided by the carrier oscillator 23. As will later be apparent, the 
reactance of the reference inductor 21 can be of a predetermined value to 
provide a balance and/or an unbalance condition at any desired positional 
relationship between the sensor inductor 1 and each one of the tynes of 
the tyne assembly 2. The output signal from the bridge 22 being a function 
of the relative position of the one or more tynes and the sensor inductor 
1. The reference inductor 21 is preferably located physically near the 
sensor inductor 1 to minimize effects of surrounding environmental and 
electro-magnetic interference conditions. The output signal of the bridge 
22 is detected and filtered by the demodulator 24. The output signal from 
the demodulator 24 is normally a D.C. pulse having leading and trailing 
edges related to the desired times of sparking and having a pulse width 
normally equal to the desired dwell time. A Schmidt trigger or pulse 
shaping circuit 25 is supplied by the output of the demodulator 24 to 
steepen the leading and trailing edges of the demodulator output pulse 
signal, although in some instances this pulse shaping may not be 
necessary. A Schmidt trigger type of pulse shaper 25 is referenced in the 
description of the invention embodiments, however, any one of other well 
known shaping circuits such as over driven or saturated amplifiers are 
equally suitable. The bridge circuit 22 in effect, operates to modulate 
the output signal from the carrier oscillator 23. In one embodiment of the 
invention, the demodulator 24 operates to detect an amplitude modulated 
output signal from the bridge 22; in another embodiment the demodulator 24 
operates as a phase detector for detecting a phase modulated output signal 
from the bridge 22. In the latter embodiment, a phase reference signal 
from a phase reference signal source is supplied to the demodulator 24 by 
the signal line 27. In one later described embodiment the phase reference 
signal is provided by the bridge 22 although it can be provided by the 
carrier oscillator 23. The component values of the bridge circuit 22 can 
be made to accentuate either amplitude or phase modulation of the bridge 
output signal as a function of the effect of the tynes of the tyne 
assembly 2 upon the sensor inductor 1. In addition, the tyne material can 
be selected to accentuate either an amplitude or phase change. For 
example, it was found that conductive iron tynes created larger phase 
differentials, thus such tyne material is preferable for phase modulation 
systems as will later be described in more detail. 
It should be understood that the term modulation, as used herein, includes 
a process of operating upon a single signal for providing or generating an 
information bearing signal or signals, the information being related to 
the rotational position of the engine. The above definition includes, but 
is not to be limited to, the classic definition of modulation namely, to 
vary the amplitude, frequency, or phase of a electric wave by impressing 
one wave on another wave of constant properties. 
FIG. 8 shows a more detailed diagram of the timing signal source 12 
suitable for use in the breakerless ignition system of FIG. 7. The timing 
signal source 12 shown by FIG. 8 provides amplitude modulation and 
demodulation of the carrier. The output signal of the carrier oscillator 
23, which in one embodiment provides a 700 KHz sine wave output signal, is 
supplied across the bridge signal input terminals 29, 30. The output 
signal from the bridge 22 appears at the output terminals 31, 32. The 
resistor 26 and sensor inductor 1 comprise one arm of the bridge 22 while 
the second arm is comprised of resistor 28 and the reference inductor 21. 
Other bridge or modulator arrangements are of course possible without 
departing from the spirit of the invention. In one embodiment such as 
shown in FIG. 8, the reactances of the reference inductor 21 and the 
sensor inductor 1 and the resistances of the resistors 26, 28, are such 
that the bridge 22 is balanced when the sensor inductor 1 is removed from 
proximity of the tynes of the tyne assembly 2 and conversely unbalanced 
when the sensor inductor 1 is fully acted upon by the tynes of the tyne 
assembly 2. This latter unbalanced condition would, for example, occur 
when the sensor 1 is totally enclosed by the tynes 3 and 4 of tyne pair 5 
when the tyne assembly 2 configuration of FIG. 1 is used. The operation of 
bridge circuits such as bridge 22 under balance and unbalanced conditions 
is well known and is not therefore described in detail herein. 
FIGS. 9a through 9e show various operating waveforms useful in the 
understanding of the invention and in particular with reference to FIG. 8. 
FIG. 9a shows a plot of the change of inductive reactance of the sensor 
inductor 1 as it approaches, is enclosed by, and leaves the tynes of, for 
example the tyne assembly 2 of FIG. 1. The physical width of the tyne is 
preferably larger than the effective width of the sensor inductor 1 and is 
typically on the order of 10 to 1. In other words, if the tyne width is 
0.5 inch, the effective width of the sensor inductor 1 would be 
approximately 0.05 inch. The carrier signal from carrier oscillator 23 
supplied to carrier signal input terminals 29, 30 of the bridge 22 is 
shown by FIG. 9b. The signal output from the bridge 22 and appearing 
across output terminals 31, 32 is represented by FIG. 9c. This waveform 
shown by FIG. 9c is in effect, the signal output from the carrier 
oscillator 23 and shown by FIG. 9b after being amplitude modulated by the 
bridge 22 as a function of the relative position of the sensor inductor 1 
and tynes of the tyne assembly 2. The leading and trailing edges of the 
waveforms shown in FIG. 9 (as well as those shown in FIG. 11 and described 
herein later) are in the actual operating embodiments, much steeper than 
shown in the Figures; likewise the frequency of the signal output from the 
carrier oscillator 23 and shown in the above referenced waveform figures 
is much higher than shown. As a typical example, at a distributor shaft 
rotational speed of 2,000 rpm, a 25.degree. dwell time such as can be 
represented by the tyne width shown by FIG. 9a would encompass 
approximately 1500 cycles of a 700 KHz carrier signal represented by FIG. 
9b. Therefore, steepness of the waveform edges as well as the carrier 
signal frequency are as is illustrated in the figures simply for ease of 
explaining the operation of the system. 
The signal output from the bridge or modulator 22 is shown by FIG. 9c as an 
amplitude modulated waveform although it is apparent that some phase shift 
also occurs in the modulated waveform. The phase shift is identified as 
.DELTA..phi. in FIG. 9b and occurs as a result of the difference of the 
impedance of the bridge arm comprised of the resistor 26 and the inductive 
reactance X.sub.L of the sensor 1 and the impedance of the bridge arm 
comprised of the resistor 28 and the inductive reactance of the reference 
inductor 21. 
The amplitude modulated signal output from the bridge 22 of FIG. 8 and 
appearing across the sensor inductor 1 and the reference inductor 21 and 
existing between the respective output terminals 31, 32 and ground are 
supplied to the input of a balanced output, differential amplifier 33 
comprised of transistors 34, 35, 36 and associated circuitry which is well 
known in the art. The differential amplifier in the FIG. 8 embodiment 
operates to amplify the aforementioned signals appearing across the sensor 
inductor 1 and the reference inductor 21 and provides the amplified 
signals at the respective signal output terminals 37, 38, and ground. Thus 
the waveform shown by FIG. 9c also represents the amplitude modulated 
signal appearing between the output terminals 37, 38. The output signals 
at terminals 37, 38 are in turn supplied to respective amplitude detectors 
comprised of diodes 39, 40 and 41, 42. The unlabeled resistors and 
capacitors shown in the FIG. 8 diagram and associated with the respective 
diode detectors comprise conventional detector load and filter circuits. 
The detector output signals are in turn supplied to the respective input 
terminals 43, 44 of a differential amplifier 45. The output of the 
differential amplifier 45, shown by FIG. 9d, is thus the detected envelope 
of the waveform shown in FIG. 9c. The output of the differential amplifier 
45 is supplied to the Schmidt trigger 25 which operates to trigger on the 
leading and trailing edges of the detected envelope waveform of FIG. 9d. 
The output of the Schmidt trigger 25 is shown by FIG. 9e. The output 
waveform of FIG. 9e is used as previously described with relation to the 
operation of the ignition system of FIG. 7, to switch the primary of the 
H.V. spark coil 17 and provide sparking at a time corresponding to the 
change of level of the waveform shown by FIG. 9e. The timing signal source 
12 illustrated in FIG. 8 thus operates as an amplitude modulated system. 
The reactance X.sub.L.sbsb.2 of the sensor inductor 1 shown by FIG. 9a in 
the above described operation of FIG. 8 represents the reactance of the 
sensor inductor 1 when the tynes 3, 4 of FIG. 1 enclose the sensor under 
which condition the bridge 22 is unbalanced. It will now be apparent that 
changes in operation can be made for other conditions of balance. 
It will be noted that the balanced output differential amplifier 33 shown 
in FIG. 8 can be replaced by two separate conventional amplifiers. In such 
case, the signal appearing at bridge terminal 31 would be amplified by the 
first of the separate amplifiers, while that signal appearing at terminal 
32 would be amplified by the second separate amplifier. An amplitude 
detector circuit as is well known in the art, can also be connected 
directly across the bridge output terminals 31 and 32 for demodulating the 
modulated carrier signal appearing at bridge terminals 31, 32 and 
providing an output timing signal which can be amplified and shaped as 
desired. It is preferred that any circuitry connected to the bridge output 
terminals 31, 32 have a relatively high input impedance to prevent any 
undesired shunting of the bridge circuit 22. 
Now referring to FIG. 10, there is shown a simplified diagram of a timing 
signal source 12 which operates to provide phase demodulation of a phase 
modulated output signal from the bridge 22. The waveforms shown by FIGS. 
11a through 11e are referred to in the following description of operation 
of the timing signal source 12, shown in FIG. 10, in accordance with the 
immediate invention. The carrier signal output from the carrier source 23 
is supplied to the input terminals 29, 30 of the bridge 22. The output 
signal from the bridge 22 appears at the bridge output terminals 31, 32. 
The voltage which appears across the sensor inductor 1 between the output 
terminal 31 and ground and the voltage appearing across the reference 
inductor 21 between output terminal 32 and ground may or may not be in 
phase with each other depending upon the impedance of each one of the 
respective arms of the bridge comprised of resistor 26, sensor inductor 1 
and resistor 28, reference inductor 21. As an example, when the resistors 
26, 28 are made equal in value and the reactance of both the sensor 
inductor 1 and the reference inductor 21 are of equal value, the output 
voltage across both the sensor and reference inductors will be in phase. 
This, of course, assumes that the internal resistance of both inductors 
are identical or practically so. In the FIG. 10 embodiment, the reference 
inductor 21 is of a fixed and predetermined inductive value so that 
variation of the inductance of the sensor resulting from the effect of the 
passing tynes of the tyne assembly 2 upon the sensor inductor 1, will 
provide the two aforementioned signal output voltages from the bridge 22 
to vary in phase with respect to each other. For purposes of explanation, 
the bridge 22 of the FIG. 10 embodiment is adjusted for operation to 
provide the output voltages appearing across the sensor inductor 1 and the 
reference inductor 21 to be in phase with each other when the sensor 
inductor 1 is for example, fully enclosed by the tynes 3, 4 of the tyne 
assembly 2 and out of phase when the sensor inductor 1 is, for example, 
midway between tynes. This operating condition is shown by FIGS. 11a, b, 
c. The change of the reactance from X.sub.L.sbsb.1 to X.sub.L.sbsb.2 of 
the sensor inductor 1 under influence of a passing tyne is shown by FIG. 
11a and is the same as that previously described with reference to FIG. 
9a. The voltage appearing across the reference inductor 21 is supplied to 
the input of amplifier 59 and is shown by FIG. 11b. The voltage appearing 
across the sensor inductor 1 is supplied to amplifier 47 and is shown by 
FIG. 11c. The phase relationship of the voltage of FIG. 11c with respect 
to the voltage of FIG. 11b is shown by the figures to change from an out 
of phase relationship .DELTA..phi. to an in phase condition and again to 
an out of phase relationship .DELTA..phi. as the tyne respectively 
approaches, encloses, and leaves the sensor inductor 1. The value of the 
resistors 26, 28 and the reactances of the sensor inductor 1 and reference 
inductor 21 as well as the tyne material are selected as previously 
described to accentuate a maximum change of the phase .DELTA..phi. such as 
shown in FIGS. 11b, 11c. Although the signal appearing across the sensor 
inductor 1 is shown in FIG. 11c as being constant in level or amplitude 
for the sake of clarity, it should be noted that this signal can change 
somewhat as a function of the change of the reactance X.sub.L of the 
sensor inductor 1. 
In the FIG. 10 embodiment, the phase reference signal supplied to the 
demodulator 24 is provided by the output signal from the bridge 22 and 
appearing between terminal 32 and ground. This signal is supplied to the 
demodulator 22 by signal line 27. The reference signal can also be 
obtained directly from the carrier oscillator 23 or through a phase shift 
network if so desired in lieu of being obtained from the bridge 22. The 
bridge output signal developed across the sensor inductor 1 and appearing 
between the output terminal 31 and ground is supplied to an amplifier 47 
and in turn supplied to the demodulator 24. The purpose of the amplifiers 
47, 59 is to provide isolation between the bridge 22 output and the input 
to the demodulator 24. The amplifiers 47 and 59 can also be operated to 
provide amplitude clipping or limiting if so desired. 
The output signal from the isolation amplifier 47 is supplied to a signal 
input transformer 48 of a synchronous phase detector 49. The phase 
reference signal from the isolation amplifier 59 is supplied to a 
reference phase signal input transformer 50 of the phase detector 49. The 
phase detector 49 comprised of signal diodes 51, 52, 53, and 54 and the 
respective input signal and phase reference signal transformers 48, 50 is 
a conventional ring configured detector which operates to provide a 
demodulated output signal at output terminals 55, 56. The phase reference 
signal appearing at the secondary winding 57 of transformer 50 provides 
alternate switching of the diode pairs 51, 52 and 53, 54 thereby causing a 
detected signal output from the secondary winding 58 of the signal 
transformer 48 to appear at the detector output terminals 55, 56. The 
level of the reference signal at the secondary winding 57 compared to the 
input signal level at the secondary winding 58 is on the order of 10:1 as 
is conventional in ring type detectors. The average output of the detector 
is at a maximum when the input signal at winding 58 is in phase with the 
reference signal at winding 57 and conversely, zero when the two signals 
are 90.degree. out of phase. The phase demodulator 24 thus compares the 
phases of the two input signals and provides an output signal as a 
function thereof. 
The output signal from the detector 49 is supplied to the input of a low 
pass filter 60. The operation of the low pass filter 60 suppresses any 
carrier signal originating from the carrier oscillator 23, and appearing 
at the output of the detector 49. The detected and filtered output signal 
from the low pass filter 60 is supplied to a Schmidt trigger 25 the 
operation of which was previously described in reference to FIG. 8. The 
output of the Schmidt trigger 25 is in turn supplied to output terminal 13 
of the timing signal source. The waveform shown by FIGS. 11d and 11e are 
similar to those shown by the previously described FIGS. 9d and 9e in that 
they are the signal outputs of the respective demodulators 24 and Schmidt 
triggers 25. The waveform shown by FIG. 11d represents the output of the 
phase demodulator 24 of the FIG. 10 timing signal source 12. 
Referring to FIG. 12, there is shown another embodiment of the timing 
signal source 12 suitable for use in the breakerless ignition system of 
FIG. 7. It was discovered that a conventional operational amplifier when 
operated at relatively high signal input levels and at relatively high 
frequencies will operate to provide the functions provided by the 
isolation amplifiers 47, 59, the phase demodulator 24, the low pass filter 
60, and the pulse shaper 25 of the timing signal source shown by FIG. 10. 
Therefore, in the FIG. 12 embodiment, much of the circuitry of the FIG. 10 
embodiment can be replaced by a single integrated circuit type operational 
amplifier 61. Thus the operational amplifier 61 as shown in FIG. 12, 
replaces all of the circuitry shown in FIG. 10 which exists between the 
output terminals 31, 32 of the bridge 22 and the signal output terminal 
13. The use of such an integrated circuit is highly desirable and of a 
distinct advantage since it results in a reduction of the manufacturing 
cost of the breakerless ignition system with an increase in the 
operational reliability of the system as is inherent with integrated 
circuits. 
The operation and function of the carrier oscillator 23, bridge 22, sensor 
and reference inductors 1, 21 as well as the tyne assembly 2 shown in FIG. 
12 has been previously described in relation to the FIG. 10 embodiment and 
is therefore not repeated. The output signal from the bridge 22 is 
supplied to the input terminals of operational amplifier 61. The signal 
output from the operational amplifier 61 is in turn supplied to the output 
terminal 13 of the timing signal source 12. In one embodiment constructed, 
a type 741C, manufactured by Fairchild Semiconductor, was used for the 
operational amplifier 61 shown in FIG. 12; however, other types of 
amplifiers can be used. The mode of operation of the operational amplifier 
61 for providing the functions of phase detection and filtering and 
supplying the previously described timing output signal at terminal 13 is 
believed to be in accordance with the following description with reference 
to FIGS. 12 and 13. 
Referring to FIG. 13, there is shown a greatly simplified diagram of an 
operational amplifier representative in effect of a great many available 
types of operational amplifiers including the aforementioned type 741C. 
Operational amplifiers such as the type 741 are normally utilized or 
operated with relatively low signal input levels and with signal 
frequencies well below the amplifier's maximum published characteristics 
and under such normal operation provide a normally desirable high degree 
of common mode rejection, i.e. identical signals applied to the two input 
terminals are prevented from appearing at the output terminal. The 
operational amplifier 61, as shown in FIG. 12, however, is operated with 
signal input levels at the input terminals on the order of 4 volts peak to 
peak and at the carrier signal frequency from the carrier oscillator 23 of 
700 KHz. Under these conditions of operation, the amplifier 61 functions 
quite differently than would normally be expected or desired. Under this 
latter condition of operation in the timing signal source of FIG. 12, the 
operational amplifier 61 does not exhibit the normal common mode rejection 
characteristic but rather operates to provide a phase detection function 
for signals applied to its input terminals. The amplifier can, of course, 
be used in other applications where a similar phase detection and 
filtering function is desired and similar conditions of operation exist. 
FIG. 13, as previously stated represents a simplified diagram of a common 
operational amplifier useful in explaining the operation of the amplifier 
61 in the FIG. 12 embodiment. The transistor 62 and the associated 
resistors 63-65 function as a constant current source for transistors 66, 
67. The transistors 66, 67 and associated collector load resistors 68, 69 
normally function as a differential amplifier having a balanced output. 
The transistors 70, 71 normally function as a differential amplifier 
having an unbalanced output. Thus the differential amplifier comprising 
transistors 66, 67 normally supply a balanced input signal to the second 
differential amplifier comprised of transistors 70, 71. The unbalanced 
output of the latter differential amplifier developed across the output 
load resistor 72 is in turn supplied as an input signal to a pair of 
complementary connected transistors 73, 74 which function as a D.C. 
amplifier, the output of which is supplied to the output terminal of the 
operational amplifier 61. 
In the present invention, the transistors 66 and 67 do not function as a 
differential amplifier but rather function as separate amplifiers for 
providing amplification of each separate one of the individual signals 
applied to the respective signal input terminals. Likewise, in the present 
invention, the transistors 70, 71 do not function as a differential 
amplifier but rather function as a phase detector and as such provide a 
demodulated signal to the signal output amplifier comprising transistors 
73, 74. 
In normal operation and use of an operational amplifier such as illustrated 
in FIG. 13, any common mode potential existing at the input signal 
terminals are rejected from appearing at the output terminal. This 
rejection ratio can be, for example, on the order of 30,000 to 1 or 90 db 
and results from the fact that under normal conditions, the constant 
current source comprised of transistors 62 and associated resistors 63-65 
exhibits a very high dynamic impedance and the fact that the two branches 
of the differential amplifier comprising transistors 66 and 67 are highly 
matched. Under these normal conditions, the output is mainly a function of 
an amplified version of the difference of the potentials existing on the 
input terminals 2 and 3. 
In the immediate application of the operational amplifier 61, such as in 
the FIG. 12 embodiment of the ignition timing signal source, the above 
described normal operation does not however take place. The published 
voltage gain of, for example, the 741 operational amplifier is unity at an 
operating frequency of 1 MHz and at 700 KHz is only slightly greater. With 
operation of the operational amplifier 61 at the 700 KHz carrier 
frequency, the constant current source comprised of the transistor 62 and 
associated circuitry does not exhibit the aforementioned normal high 
impedance where the current in the emitters of the transistors 66 and 67 
can be exchanged for deriving and providing differential effects. This 
change from normal operation is believed to be caused by the frequency 
response limitations due to, for example, distributed capacity and charge 
storage effects of the operational amplifier circuitry. The current from 
the emitters of transistors 66 and 67 are not equally exchanged and hence 
the normal common mode rejection ratio is greatly reduced. The signals 
supplied to the inputs of the succeeding differential amplifier comprising 
transistors 70 and 71 are now in the immediate application of such a level 
that the latter transistors 70, 71 can be driven into a non-linear 
switching like region of operation in lieu of being operated as the 
normally intended differential amplifier. Thus the transistors 70 and 71 
operate as a synchronous or switching like phase demodulator. This 
demodulator function or operation can also be considered somewhat similar 
to the operation of an AND gate where an output signal is provided for 
coinciding input signals, thus the average value of the resultant output 
signal from the demodulator is a function of the phase relationship of the 
two separate input signals. Operation of the operational amplifier 61 at 
frequencies in excess of those normally intended provide a filtering and 
averaging effect of the output signals. Thus, a conventional operational 
amplifier 61 can be used in the FIG. 12 timing signal source to provide 
the desired phase demodulation, filtering, amplification and signal 
shaping functions. 
It will now be apparent to one skilled in the art that the bridge circuit 
in effect functions as a comparator as well as a modulator and that the 
values of resistance of each one of the bridge resistors 26 and 28 as well 
as the values of reactance or impedance of the sensor inductor 1 and of 
the reference inductor 21 can be of any desired combination to provide a 
balanced condition of the bridge and/or any desired phase relationship of 
the bridge output signals for any given positional relationship between 
the sensor inductor 1 and the individual tynes of the tyne assembly 2. As 
one example, the aforementioned resistance and reactance values can be 
selected to provide a minimum signal output between the bridge output 
terminals 31 and 32 or an output signal between the terminals 31 and 30 
which is in phase with the signal between terminals 32 and 30 when the 
sensor inductor 1 is just entering and leaving the tyne rather than when, 
for example, the sensor inductor 1 is fully enclosed or affected by the 
tyne. As another example, the reactance of the sensor inductor 1 can be 
made part of a series or parallel resonant circuit of the bridge thereby 
providing both a leading and lagging phase condition as the circuit is 
caused to pass through a resonant frequency as a result of a predetermined 
affect of the tyne upon the sensor reactance. Likewise, the resistors 26, 
28 can be replaced by reactances, capacitive or inductive and the 
reference inductor can be replaced by a resistance or a capacitive 
reactance. 
It will now be appreciated that we have provided a new and novel 
breakerless ignition system having a timing signal source for generating a 
timing signal which is not a function of engine speed. The ignition system 
is essentially not sensitive to changes in temperature due to the use of 
the bridge and reference inductance. As mentioned hereinbefore, the 
reference inductance is located as near as possible to the sensor so that 
both inductors are exposed to the same temperature. There are no 
appreciable delays caused by our ignition system from the time of a change 
of position of the engine to generation of the H.V. spark. High or low 
speeds of the internal combustion engine do not affect response time of 
the ignition system. However, in addition to providing a new and improved 
breakerless ignition system we have also provided a scheme that is readily 
adaptable to being used as a tachometer or as a positional indication of 
an object with advantages similar to those achieved for the ignition 
system. A moving object or a rotating shaft can have a tyne or knob or a 
slight gap such as a void of material that causes a change of inductance 
of a sensor and the change of inductance can be processed as set out 
hereinbefore to generate an output signal. The output signal can be used 
as a tachometer input or as a positional indication depending upon the 
desired application. 
Consequently, while in accordance with the Patent Statutes, we have 
described what at present are considered to be the preferred forms of our 
invention it will be obvious to those skilled in the art that numerous 
changes and modifications may be made herein without departing from the 
spirit and scope of the invention, and it is therefore aimed in the 
following claims to cover all such modifications.