Ignition indicator for internal combustion engines

In an ignition indicator system for internal combustion engines, a transformer is interposed in each line between the spark plug and distributor or other timing circuit. The transformer has a sensor element positioned adjacent thereto to be indirectly coupled to the transformer output circuit. Terminal means is provided for connecting the sensor element to detector means which permits analysis of the pulses for firing the spark plug. Preferably, the transformer and the high voltage portion of the ignition system is shielded by a grounded casing or sheath to minimize radiation of signals, as well as to confine any explosion of ignited gases within the casing or sheath. Access to the sensor element does not adversely affect the shielding effect of transformer casing.

The present invention relates to an improved diagnostic indicator system 
for monitoring the pulses produced to fire the spark plugs during 
operation of internal combustion engines, in which the pulses to fire the 
spark plugs are received from a high-voltage transformer in the ignition 
circuit. The present invention is particularly adapted for use in shielded 
ignition systems wherein each spark plug has a separate transformer 
associated therewith and the indicator system includes a sensor element 
mounted with the transformer. 
High-voltage transformers are used in ignition system circuits for 
heavy-duty engines and are positioned in the circuit intermediate the 
electrical generating means and the spark plugs so that the ignition 
system may utilize an electrical generating means which generates a 
relatively low voltage pulse or signal that is increased in potential by 
the transformer to a sufficiently high voltage pulse to fire the spark 
plug. In this arrangement, which is termed a low tension system, the 
electrical generating means is located at some distance from the cylinders 
and spark plugs. The stepped-up signal at the transformer produces 
radio-frequency signals which may be effectively confined by grounded 
shielding surrounding the transformer and its connections to the spark 
plug and to the electrical generating means. Such systems with shielding 
means are particularly adapted for use in offshore drilling rigs, 
airplanes and other applications where radio-frequency signals may 
interfere with radio communications, firing control of explosives or other 
instances where the high voltage of the pulse might cause an arc that 
would ignite any combustible atmosphere in the area. 
Diagnostic instruments are available for use in automotive diagnostic 
centers and in service centers which are equipped to test the ignition 
circuit of conventional automobiles by capacitive coupling to the lead 
wires connected to the spark plugs. In such conventional automotive use, 
the lead wires carry a sufficiently high voltage to generate a signal 
which may be capacitively coupled to the diagnostic instrument for the 
purposes of the testing. However, in heavy-duty engine applications, where 
high-voltage transformers are interposed in the leads to the spark plugs, 
the conductors from the secondary of the high-voltage transformer are 
normally inaccessible. Thus, the standard diagnostic instruments cannot be 
used to sense the pulses from the secondary to the spark plug. This is 
particularly true where shielded ignition systems are employed in which 
all of the circuit leads are encased in grounded sheaths. In large engine 
installations where a continuous diagnosis of ignition pulses of a 
shielded ignition system is desired, a permanent interconnection with a 
high voltage circuit conductor may be provided which permits sensing of 
the pulses emitted by special access openings formed in the sheath of the 
circuit conductor. Such access is adequate to enable sensing of the 
ingnition pulses, but when the diagnosis is not being performed, 
disconnection of the sensing instruments may permit escape of 
radio-frequency signals from the circuit and may leave an opening in the 
pressure-tight shielded enclosure. Such access openings in shielding for 
electrical conductors of an ignition system are shown in the prior U.S. 
patents to Peters et al., U.S. Pat. Nos. 2,181,149 and 2,245,604. 
Furthermore, in systems where the transformer is mounted directly on the 
spark plug to minimize the length of high voltage conductors, such systems 
do not facilitate the use of such conductor access openings to monitor the 
signal between the transformer and spark plug. 
In accordance with the present invention a diagnostic connection for the 
ignition circuit is provided which does not require interruption of the 
shielding of the ignition system and yet enables selective sensing of the 
pulses generated by the secondary circuit of the high-voltage transformer 
during engine operation without affecting the shielding between the 
high-voltage transformer and the spark plug. 
More specifically, the present invention provides a means for sensing the 
pulses generated by the secondary circuit of the high-voltage transformer 
connected with the individual voltage supplies for each spark plug. 
In particular, the present invention provides a novel shielded transformer 
having within the shield an integral sensor in the form of a sensing 
conductor or element which is indirectly coupled to the transformer and 
particularly the output or the secondary circuit of the transformer, the 
sensor being accessible exteriorly of the shielded transformer for either 
permanent or temporary connection to detector or indicating means for 
giving a visual or audible signal of the functioning of the ignition 
system. 
The present invention preferably provides a transformer embodying a sensor 
conductor of the type in which the external terminal of the sensor is 
disposed within a shielded recess to avoid secondary radiation of 
radio-frequency signals, whereby when said detector cirucit is 
disconnected from the sensor terminal, the shielded effect is not 
disrupted. 
The present invention is applicable to high-voltage transformers which are 
coupled directly to the spark plug, as well as to transformers which are 
mounted remote from the spark plug and are connected thereto by a length 
of shielded electrical conduit.

Referring now to the drawings, there is illlustrated in FIG. 1 an overall 
ignition system embodying the present invention. The ignition system is 
used in conjunction with an engine (not shown), which may be a 
conventional internal combustion engine, having at least one cylinder with 
at least one spark plug for each cylinder of the engine for igniting 
combustible fuel in the associated cylinder. Timed firing of the fuel in 
each of the cylinders is provided by an electrical generating device 
generally designated 11 which in the present instance has six outputs 12, 
13, 14, 15, 16, and 17, each adapted to be connected to a spark plug, 
output 17 being shown connected to a spark plug 10. More specifically, the 
ignition system further includes a voltage step-up transformer 18 of a 
high-frequency type having its primary connected to output conductor or 
connecting means 17 of the electrical generating device and its secondary 
connected in a circuit including the plug 10 by connecting means or 
conductor 20. The electrical generating device 11 may be provided by any 
of the conventional electrical generating means or devices for generating 
a plurality of pulses in synchronism with engine operation at output 
conductors 12 to 17, to which are adapted to be connected to associated 
transformers, such as transformer 18, to fire the associated spark plugs. 
The electrical generating means or device 11 may consist of a pulse 
generator or a conventional magneto-type ignition system employing breaker 
points or electronic circuits to replace the breaker points, to produce 
the timed pulses in synchronism with engine operation. The number of 
outputs from the electrical generating device may vary and a distributor 
or electronic circuit with switches may be employed in a conventional 
manner to provide the proper timing of pulses at the outputs. The pulses 
of the electrical generating device are preferably of a low voltage to 
minimize arcing, sparking and other undesired radiation during operation 
of the engine. As indicated in FIG. 1, the electrical generating device 
and its connecting means or conductors are shielded, as indicated at 21, 
as may be required in various applications of ignition systems. The 
shielding 21 may be provided by a casing around the electrical generating 
device and shielding cable around the output lines, such as line 17. The 
transformer and its connection to the spark plug are also shielded as will 
be explained more fully hereinafter. 
In accordance with the present invention, means is provided in the 
transformer 18 for diagnostic testing of the pulses conducted through the 
transformer, and particularly the testing is performed in association with 
the secondary circuit of the transformer as indicated in FIG. 1, where an 
accurate indication of the ignition pulse to fire the spark plug is 
obtained. The access to the secondary circuit of each transformer 18 is 
designed to avoid direct coupling and the danger of exposure to the high 
voltage generated in the secondary of the transformer in the ignition 
circuit. Indirect coupling provides a transfer of electrical energy 
without any direct mechanical interconnection between the secondary 
circuit and the testing circuit. In the present instance, the indirect 
coupling is by means of a sensor element in the form of a rod 22 disposed 
adjacent the secondary output circuit of the transformer 18. In the 
present case, the indirect coupling is obtained by capacitive coupling 
between the sensor rod 22 and an output conductor of the transformer. By 
using an inductive sensor loop or coil, indirect inductive coupling may be 
obtained between the secondary circuit and the sensor loop or coil. 
Indirect coupling between the secondary and the rod provides for a 
generation of a signal in the rod when an ignition pulse is applied to the 
primary of the transformer 18 to create a pulse in the secondary circuit. 
The character of signal generated in the rod by the pulse in the secondary 
is dependent upon the condition of the spark plug and the character of the 
signal may be detected by suitable detector means 23 coupled to the 
detector or sensor rod 22, for example by a lead 24. The detector means 
provides an indication of the character of the signal generated in the 
sensing element. The lead 24 may be shielded, as indicated at 25. The 
level of energy transferred to the rod 22 is sufficiently low to be safe 
and does not detract from the pulse of energy supplied to the spark plug 
in normal operation. When the spark plug functions normally, as required 
by engine operation, the detector means senses the normal signal generated 
by the ignition pulse in the secondary of the transformer 18. Thus, the 
characteristic of the signal in the secondary circuit sensed by the rod 22 
is indicative of the condition of the plug 10 to which the transformer 18 
is connected. The signal pick-up arrangement of the present invention 
permits analysis of the operation of the secondary circuit by observing 
the signals which it reflects. If the spark plug gap breaks down, the 
energy stored in the winding and the secondary lead discharges abruptly, 
giving a high frequency oscillation in the secondary circuit sensed by the 
sensor rod. If the spark plug does not break down, any oscillations 
present are much lower in frequency and the sensed signal is substantially 
reduced. 
A preferred embodiment of transformer assembly is generally designated 30 
in FIG. 2, wherein the transformer is coupled directly to the spark plug 
10 by means of an elongated secondary conductor 43 and a connector 
generally designated 37, which together from the connecting means or 
connection 20 schematically illustrated in FIG. 1. The spark plug 10 is 
mounted in a suitable adapter casing 31, which is mounted in the engine 
block and serves as a grounded shield for the spark plug and transformer 
connection. The adapter casing is tubular in form to provide a shielded 
housing for the spark plug 10. The transformer coils of the assembly 30 
are mounted within a tubular shell 32 having threads adjacent its inner 
end at 33, which are adapted to be threadedly engaged with the adapter 
casing 31. The tubular shell 32 provides a metallic shield surrounding the 
components of the transformer 35 so as to confine any radiated energy or 
any pressure or flame caused by ignition of gases within the shield. The 
transformer coils are wound together as a compact package as indicated at 
35 and are firmly anchored in the shell 32 by a surrounding body of 
insulating material designated 36. The forward end of the body of material 
is formed as a nose 42 to completely surround the output conductor 43 in a 
fashion to permit engagement of the conductor 43 with the connector 37 
which in turn contacts the spark plug 10 within the adapter housing 31. In 
the present instance, the connector 37 assures direct electrical 
connection between the high voltage secondary of the transformer 35 and 
the spark plug 1o. At the end of the transformer assembly 30 remote from 
the spark plug, the metallic shell 32 is povided with a plug assembly 38 
which, as shown in FIG. 3, has prongs 39 to which the connecting line 17 
in FIG. 1 from the electrical generating device may be coupled. The plug 
assembly 38 includes a threaded member 41 which serves as a connector for 
the shielding cable 21 around the connecting line 17. Thus, the threaded 
member 41, the shell 32, and the shielding cable 21 effectively confine 
any radiation from the transformer 35. 
To the extent described above, the high voltage transformer assembly is of 
conventional construction. In accordance with the present invention, the 
transformer structure is modified to include the sensor rod 22 as 
illustrated schematically in FIG. 1. To this end, in FIG. 2 the body of 
insulating material 36 has sensor rod 22 mounted therein. In the present 
instance, the rod is mounted in a Teflon sleeve 44 extending within and 
along the length of the tubular shell or casing 32 substantially parallel 
to the axial dimension of the transformer and the output conductor 43. At 
the rear end of the transformer assembly, the terminal end of the sensor 
rod is mounted in a receptacle or socket 45, preferably formed of a hard 
wear-resistant insulating material. 
The receptacle provides access to the exposed terminal end of the sensor 
rod 22, so as to permit a releasable connection thereto of the lead 24 of 
FIG. 1, the terminal end of the sensor rod and lead 24 providing terminal 
means to connect the sensor rod to the detector means 23. The receptacle 
with the exposed end of the rod therein constitutes a female plug for the 
lead 24 and the construction is such that the rod 22 terminates at the 
bottom of the receptacle a sufficient distance so as to avoid extraneous 
radiation from the end of the rod. The receptacle is embedded within the 
insulating body of material 36 a sufficient distance from the rear end of 
the tubular casing 32 to avoid loss of the shielding effects. When 
disconnected from the detector means 23 and lead 24, the exposed end of 
the rod 22 also provides a convenient means for checking the timing of the 
ignition system to the engine while it is running. 
The position of the rod 22 alongside the transformer assembly 35 permits 
indirect coupling of the rod to the secondary circuit of the transformer, 
and the signals picked up by the rod through the indirect coupling may be 
transmitted to the detector means 23, as by lead 24. The indirect coupling 
enables energy to be picked up by the rod, but the level of energy is 
sufficiently low to be safe and does not detract noticeably from the 
available ignition energy. The degree of coupling may be increased, for 
example, by reducing the spacing between the rod 22 and the secondary 
output conductor 43 of the transformer or by extending or curving the rod 
circumferentially round the output conductor 43. Since the signal 
generated in the secondary circuit is a high frequency signal, the 
indirect coupling is effective to impart sufficient energy to actuate 
desired detector means. 
The detecting means 23 may be provided by a number of different 
arrangements, including a simple neon glow lamp having one terminal 
connected to the rod 22 and the other grounded, so that its flash will 
indicate the firing of the spark plug. Other arrangements include a timing 
light, a spark detector, a cathode ray oscilliscope for a detailed 
analysis operation of the ignition signal, or other electronic circuitry 
for continuous monitoring or providing a warning of a spark plug not 
firing. The detector arrangement may be connected permanently to all of 
the transformers in the ignition circuit to provide continuous monitoring 
of the firing of the plugs, or may be connected temporarily to provide 
sequential monitoring of the respective plugs. The selection of the 
detector means determines the type of indication provided, and the present 
invention permits a wide selection of operable devices. 
The receptacle of socket 45 of this embodiment of the invention is 
particularly adpated to a plug-in connection to the detector means but a 
permanent connector may be used, if desired. Where the ignition system is 
designed for permanent connection to the detector, the plug assembly 38 
may be modified to accommodate an additional connection for the detector 
circuitry, so as to permit continuous diagnostic analysis of the 
functioning of the ignition circuit and pulses. 
In installations where the spark plugs are not readily accessible, the 
present invention may be used by disposing the high-voltage transformer in 
its shielded casing at a position remote from the spark plug and connected 
intermediate the electrical generating device and spark plug by shielded 
leads. To this end, an arrangement such as shown in FIG. 4 may be 
employed, wherein the spark plug is connected to the high-voltage 
transformer assembly 130 by a length of shielded conduit or lead 137. In 
the present instance, the transformer assembly 130 is substantially 
identical to the transformer assembly 30 described in regard to FIG. 2, 
and the shielded connecting means or line 137 is operable to effect an 
electrical connection at one end with the output conductor (not seen) of 
the transformer assembly 130 and at the other end to the spark plug (not 
shown). In the embodiment of FIG. 4, the shielded conduit has a fitting 
131 which engages threads 133 on the exterior of tubular shell 132 of the 
assembly, and the transformer assembly has an internal configuration with 
a secondary output conductor within a nose 142 of insulating material, as 
described in regard to FIG. 2. A sensor rod 122 is mounted in an 
insulating sleeve 144 with a terminal end engageable in a receptacle or 
socket 145 all of which function indentically to the corresponding 
elements of FIGS. 2 and 3. 
The present invention provides an ignition indicator system with a 
transformer assembly in which a sensor element is incorporated into the 
high-voltage transformer assembly so as to permit diagnostic tests of the 
functioning of the spark plugs without substantially affecting the 
operation of the engine, as might occur if the tests should involve an 
interruption of the ignition circuitry or as an addition of direct 
connections to the circuitry, which are particular problems with shielded 
ignition systems with which the present invention is primarily concerned. 
The present invention provides the capability for either continuous or 
intermittent monitoring of the ignition signal. 
While the invention has been illustrated and described in conjunction with 
a particular form of transformer and spark plug, it is apparent that the 
particular configuration of the transformer and spark plug is not 
critical. Elements of other configurations may be used and other changes 
and modifications may be incorporated in the ignition systems without 
departing from the scope and spirit of the present invention as defined by 
the appended claims.