Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND AND SUMMARY OF THE INVENTICN
This invention relates to testing apparatus for internal combustion
engines and more particularly relates to apparatus for displaying
voltage waveforms derived from the ignition systems of internal com-
bustion engines.
Vehicular ignition systems basically consist of a battery, a dis-
tributor including primary and secondary coils, means for periodically
commencing and terminating the conduction of current through the
primary coil so that a high voltage is induced in the secondary coil and
a spark plug for each individual cylinder of the vehicular engine. The
distributor is connected to each spark plug by a wire or lead.
One way to diagnose the system's condition is to study the voltage
waveforms at various points in the system. The waveforms are usually
coupled from these points and displayed on a cathode ray tube of a con-
ventional oscilloscope. One of the most useful waveforms is generated
by the secondary coil of the distributor. In the past, the secondary
coil and distributor have been manufactured as individually separate units.
The secondary coil is normally connected to the distributor cap by a high
tension lead.
In such a system, there are two common- methods for obtaining a
display of the secondary coil voltage waveform:
The first method is to insert a coupling transformer in series with
the high tension lead between the secondary coil and the distributor cap.
This is accomplished by removing the high tension lead from the coil
tower. A specially constructed coupling transformer is then inserted `
into the coil tower, and the high tension lead is reinserted into the
coupling transformer to complete a series circuit between the secondary
coil and the distributor. The voltage waveform from the coupling trans-
former is coupled to an oscilloscope and is displayed.
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The second method uses a capacitive-type pick-up which fits
around or clamps onto the high tension lead. A typical pick-up
of this type is illustrated in U.S. Patent No. 3,477,024
(Pelta - November 4, 1969). Such a probe operates on the
principal of a capacitor and has two opposed metallic plates
which are separated by the high tension lead when the device
is properly positioned. The opposed plates of the pick-up are
capable of responding to time-varying electric fields like a
conventional capacitor.
Recently, automobile manufacturers have developed a
"unitizedl' ignition distributor in which the distributor
primary and secondary coils are integrally formed within the ~-
distributor cap. As a result, there is no external high : -
tension lead between the primary and secondary coils and -
the distributor cap. Therefore, neither a series coupling
transformer nor a clamp-on capacitive pick-up are useful.
The present invention provides a sensor capable of
responding to the time-varying electrical phenomenon produced
by the secondary coil of a distributor without employing
either a transformer or a capacitive pick-up.
The present invention also provides a sensor of the
foregoing type in which no direct access to the conductor
connecting the secondary coil to the distributor cap is
required.
The present invention further provides a probe of the
foregoing type which produces voltages capable of being
displayed on an oscilloscope.
This invention relates to a system for testing an
internal combustion engine ignition system including a source
of common potential, a plurality of fuel ignitors and a
distributor including a housing for distributing voltage
pulses to the fuel ignitors, said distributor including
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within the housing a primary coil, means for starting and
terminating the flow of electrical current through the primary
coil in synchronism with the engine, and a secondary coil
magnetically coupled to the primary coil for generating the
voltage pulses distributed to the ignitors, improved apparatus
for displaying the waveform of the voltage produced by the
secondary coil comprising: an oscilloscope having a first
input and a second input; a conductive sensor; means for
positioning and maintaining the conductive sensor within a
predetermined distance of less than two inches from the
secondary coil; a first conductor for operatively connecting
the sensor to the first input of the oscilloscope; and a
capacitor electrically connected between the first conductor
and the source of common potential, whereby the waveform of
the voltage produced by the secondary coil is displayed on the ,
oscilloscope.
DESCRIPTION OF THE DRAWINGS :-
These and other objects, advantages and features of the
invention will appear in connection with the accompanying
drawings wherein:
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FIGURE 1 is a schematic diagram illustrating a preferred form of
sensor made in accordance with the present invention mounted on a
unitized distributor of a conventional internal combustion engine
FIGURE 2 is a fragmentary, isometric, exploded view of the
distributor and sensor shown in FIGURE l;
FIGURE 3 is a bottom plan view of the sensor shown in FIGURE 2; :~
FIGURE 4 is a cross-sectional view taken along line 4--4 in
FIGURE 3;
FIGURE 5 is a top plan view of the distributor shown in FIGURE 2
FIGURE 6 is an exploded view of the distributor shown in FIGURE 2,
together with a fragmentary, electrical schematic view of the sensor :
shown in FIGURE Z;
FIGURE 7 is a fragmentary, electrical schematic view of the dis-
tributor shown in FIGURE 2, together with the sensor shown in
FIGURE 2; and
FIGURE 8 is an illustration of an exemplary voltage waveform
produced by the secondary coil shown in FIGURE 7.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGURE 1, a preferred form of the invention may be
used in connection with a conventional 6 cylinder internal combustion
engine 10 comprising spark plugs 11-16 that are supplied with high
voltage pulses through spark plug lead. 21-26, respectively. The engine
is fitted with a fan blade 28 and a storage battery 29 having a positive :
terminal 30 and a negative terminal 31. A source of common potential
or chassis ground 32 is connected to negative terminal 31. Positive
terminal 30 is connected to a conventional ignition switch 33. Voltage .
waveforms generated by the ignition system of the engine can be displayed
on the face of a cathode ray tube 39 included within a conventional ~ :
oscilloscope 35 having a positive input 36 and a negative input 37.
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Engine 10 is fitted with a unitized distributor 40 shown in more
detail in FIGURES 2, 6 and 7. The distributor comprises a gear 42
which is turned by the engine. The gear, in turn, rotates a shaft 44.
A housing 46 is positioned on top of the shaft. A rotor 47 is turned by the
shaft in a conventional manner, and the spark advance of the distributor
is controlled by a vacuum unit 48. A distributor cap 49 holds the ends of the
spark plug wires adjacent the revolving rotor so that high voltage pulses
are sequentially distributed to the spark plugs in a well-known manner.
Cap 49 includes a cavity 50 which houses a coil assembly 52 comprising
a primary coil 53 and a cylindrical secondary coil 54 wound on a common
iron core (not shown) so that the coils are magnetically coupled. The
coils are covered by a cylindrical cover 56 including ribs 57.
Referring to FIGURE 7, an electrical circuit for commencing and
terminating current flow through primary coil 53 comprises resistors
58, 59 and a trigger wheel 60 including lobes 61-66 that are driven in
synchronism with the rotation of the engine. The lobes induce a voltage
in additional circuitry (not shown) which results in voltage pulses at the
junction of resistors 68 and 69. In response to the voltage pulses, tran-
sistors 70, 71 are switched between their conductive and nonconductive
states and are further controlled by a resistor 73. The electronic
circuits used to control coils 53 and 54 are generally more detailed than -.
the circuitry shown in FIGURE 7, but such circuits are -well known in
the art. ,~
FIGURE 8 illustrates a typical voltage waveform produced by ~ -
secondary coil 54. Portion 75 of the waveform represents a rapid
increase in voltage due to the interruption of current flow through
primary coil 53. Portion 76 indicates the voltage while a spark plug
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is firing. Portion 77 indicates the rapid decrease in voltage in the
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secondary coil when a spark plug ceases firing. Portion 78 indicates the
voltage induced in the secondary coil by the primary coil after a spark
plug has stopped firing, and portion 79 shows the voltage induced in the
secondary coil when current again begins to flow through the primary
coil due to the switching of transistor 71 to its conductive state. ~
The current flowing through secondary coil 54 produces discontin- -;
uous, exponentially-decaying signals which give rise to time-varying
magnetic fields, electrical fields and electromagnetic radiation. Since
secondary coil 54 is cylindrical, it produces magnetic fie-ld lines which ;~
are nearly parallel throughout the length of the coil and which form loops
from one end of the coil to the other. Since coil 54 carries current, it
also generates electric fièlds of unknown configuration. According to
Maxwell's wave equation, the secondary coil also radiates electromagnetic
waves which are propagated in all directions through space. For example,
if the electromagnetic waves are propagated horizontally, they consist of
electrical fields oriented in vertical planes and magnetic fields oriented
in horizontal plane s . ~ -
The applicant has discovered a sensor requiring no direct connection
to the secondary coil capable of converting one or more of these time-
varying electrical phenomenon in~ avoltage waveform capable of being
displayed on an oscilloscope which corresponds to the voltage waveform
produced by the secondary coil. A preferred form of sensor capable of
achieving this result is shown in FIGURES 2-5 and 7.
The sensor comprises a phenolic frame 80 including sidewalls 81-84 -
and a top member 86. A depressed rectangular area 90 is formed in top -
86 in order to receive the top of cylindrical cover 56. Cut out ribs 92
are formed on a partition 94 in order to receive ribs 57 on distributor
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cover 56. The underside of partition 94 is clad with a planar copper
sensor sheet 88. Area 90 and cut out ribs 92 serve the function of
steadying frame 80 when it is placed over the top of the distributor
cover in the manner shown in FIGURE 2.
A center terminal 96 of a connector 98 is connected to sensor
sheet 88 through a coupling capacitor 100 and to chassis ground 32
through a capacitor 104 (FIGURE 7). Capacitor 104 provides a means :
of tuning sensor sheet 88 and, in addition, prevents the build up of a
dangerous potential on sensor sheet 88 during the production of high
voltage transients by secondary coil 54. Terminal% isconnected to input
36 of oscilloscope 35 through a conductor 106 which is surrounded by a - .
conductive shield 108 that is connected to chassis ground 32.
It should be noted that the frame 80 is positioned over cover 56 so
that copper sheet 88 is arranged parallel to the longitudinal axis 110 of -
coil 54 and is displaced from the coil by an air gap of less than 2 inches.
In addition, sensor sheet 88 extends below the top of cover 56 in order to
improve the quality of the resulting voltage waveform. ~.
By using the foregoing apparatus, the applicant has found that the - -
voltage produced by secondary coil 54 can be accurately sensed and .`
transmitted to oscilloscope 35 for display on CRT 39. This goal has ~
been achieved without the use of a transformer for sensing the magnetic . : :
fields produced by coil 54 or a capacitive probe for sensing the electrical
fields of coil 54. Applicant has found that this result can be reached
by merely using a single conductive sheet 88 which is connected to the
positive input of oscilloscope 36 by a single conductor 106. By using ;:
this discovery, the voltage waveform produced by secondary coil 54
can be accurately detected and displayed without removing any wires or .
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making any direct electrical connections to the distributor. :
Those skilled in the art will recognize that the embodiment
described herein may be altered and modified without departing from . -~
the true spirit and scope of the invention as defined in the appended claims. - . -
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