CA1050113A - Ignition analyzer for use with electronic ignition systems - Google Patents

Abstract

Abstract of the Disclosure An improved automotive ignition analyzer is provided for use with electronic ignition systems. A quadrature field mag-netic pickup is utilized to detect signals in the secondary cir-cuit of the ignition system. An adaptor including a voltage clamp is connected to the tachometer lead of the electronic igni-tion system so that a power balance test may be performed in the conventional manner without harming the electronic ignition system.

Description

1.3 Background of the Invention 1. Field of the Invention The instant invention relates to improved igni-tion ana-lyzers or multi-cylinder internal combustion engines and, in 5. particular relates to improvements therein permitting the use of such analyzers with electronic ignitlon systems.

2. Description of the Prior Art Ignition analyzers for use with multi-cylinder internal combustion engines are well known in the art.~ Conventional igni-10. tion analyzers may be considered to include a tachometer driveand display, a cathode ray oscilloscope drive and display and a power balance test circuit. The test circuit conventionally in-cludes: (a) a counter for identifyiny the individual cylinder firings; (b) a sw1tch for selecting a particular cylinder to be 15. disabled and (c) a selectively operable shorting circuit con-trolled by the counter through the selector switch to disable the ignition system during the normal firing time of the cylin-der selected. This power balance test circuit is normally util-ized by selecting a particular cylinder and by observing the ta-20. chometer reading before and after disabling that cylinder so thatthe effect on engine performance of the normal operation of the cylinder selected, in terms of engine speed, may be determined These conventional analyzers require a first probe 5~)~13 connected to a preselected cylinder, such as cylinder No. 1, for resetting the counter and second and third probes connected to the primary and secondary circuits of the ignition coil in order to display the signals developed therein and also to provide the 5. count input for the counter. The shorting circuit is connected to the ungrounded side of the points. When the shorting circuit is actuated by the counter, the ungrounded side of the points is grounded by the shorting circuit so that the points effectively never open. The energy in the coil is therefore not discharged 10. through the spark plug selected. The probe connected to the sec-ondary circuit is normally a magnetic pickup positioned around the high tension lead between the primary side of the coil and the center of the distributor.
Such conventional analyzers cannot be used to analyze 15. some of the recently developed electronic ignition systems such as the General Motors Corp., HEI, or high energy ignition system.
In such systems the ignition coil is positioned within the dis-tributor cap so that the secondary circuit is not readily acces-sible for signal detecting purposes and the points are replaced 20. by a transistorized ignition circuit. Although a connection to the collector of this transistor is made accessible for connec-tion to the engine tachometer, the remaining components are pro-tected by covers. This prevents convenient access by the mecha-nic to connect probes associated with the analyzer. The power 25. balance connection to the analyzer, which shorts the points to ground during the firing of the cylinder to be balanced, cannot be connected directly to the tachometer lead without harming the internal circuitry of the electronic ignition systems. Further details of the electronic ignition systems described above are 0. not necessary for an understanding of the instant invention.
Summary of the Instant Invention -The instant invention provides a housing which may be sa li3 affixed to the out~ide o the dlstributor cap of an electronic ignition ~ystem. This housing inrludes an L-shaped core and magnetic winding thereon which is positioned by the housing to be in the quadrature field of the ignition coil to develop signal~ related to the secondary circuit of the ignition system. Further, A voltage clamp i6 provided, one side of which may be connected to the tachometer output of the elec-tronic ignition system and the other side of which may then be connected to the power balance probe from the analyzer so 10 that a conventionally configured analyzer may be utilized to power balance an electronic ignition system without causing malfunctions of the ignition system.
Thus, the present invention discloses an improved internal combustion engine ignition analyzer apparatus for use in power balance testing of an internal combustion engine having an electronic ignition system including a tachometer/
primary output terminal, the analy~er including means to generate a pulse in timed relationship to the firing of a se~ected cylinder of the engine and a shorting switch circuit 20 ordinarily adapted to be connected across the points of a standard ignition system and actuated during the pulse to disable the ignition system to prevent ignition of the selected cylinder, wherein the improvement includes a voltage clamp means for maintaining a voltage at a predetermined level, and means for connecting the voltage clamp means in series circuit between the tachometerlprimary terminal and the shorting switch clrcuit whereby the voltage at the tachometerlprimary output terminal may be maintainet at the fixed predetermined level during ~he normal firing period of the selected cylinder.
30 Brief_Descri~tion of the Drawings Fig. 1 shows in symbolic form a typical electronic ignition system9 a conventional ign$tion analyzer lncluding both power balance and oscilloscopic display and an adapter ~ mb/ r~ ~ 3 _-lLOSO~lL3 accordlng to the instant invention lncluding both a quadrature field magnetic plckup probe and a voltage clamp adapter for the power balance circuit;
Fig, 2 is an exploded view of an electronlc ignition system distributor and the housing containing the circuitry and secondary probe of the lnstant invention;
Fig. 3 includes graphs 3A and 3B which show9 respec-tively, the primary circuit display for an individual cylinder under normal operating conditions and the same display during a power balance tes~.
:~ Detailed Description of a Prefçrred Embodiment Fig. 1 shows an electronic ignition system 10 including a distributor 12 having leads 14, 16, 18 and 20 for connection to spark plugs for cylinders No. 1, 2, 3 and 4, respectively, of an internal eombustion engine such as an automobile engine.
'. Contained within distributor 12 is rotor 22 which distrlbutes the energy prea:nt in secondary circuit high tenaion .

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lead 24 of ignition coil 26. The primary side o~ coil 26 is con-nected by battery lead 28 to the battery of the engine. The com-mon side of ignition coil 26 is connected to the collector of pass transistor 30 which is connected through emitter resistor 32 5. to ground. The base of transistor 30 is operated by circuitry 34 in the manner generally of the mechanical points of a convention-al ignition system so that pass transistor 30 is caused to stop conducting when coil 26 is required to cause a spark plug to ion-ize. Circuitry 34 includes a magnetic or optical pickup 36 which lO. detects indicia 38 on rotating cam shaft 40 in order to synchro-nize the operation of pass transistor 30 with that of rotor 22.
The above described electronic ignition system, with the exception of spark plug cables 14, 16, 18 and 20, is pro-vided in a housing access to which is limited to a three wire 15. cable containing a ground connection, battery lead 28 and tacho-meter lead 25 which is connected to the common point of coil 26 ; and therefore the collector of transistor 30. While the connec-tion to the coil-collector common point has been referred to herein as the tachometer lead or output, it should be understood 20. that such designation is not essential and in other ignition sys-tems may be referred to by other nomenclature, such as, the pri-mary output. What is important is that this connection be made to a common point between the coil and transistor so that the coil energy may be dissipated without damage to the system.
25. Lead 25 is connected to a tachometer display system, not shown, associated with the engine and used to indicate the rotational speed thereof. It is important to note that secondary high ten-sion lead 24 is enclosed within the housing so that it is not readily accessible for connection to an ignition analyzer.
30. The electronic ignition system described above has been developed for improved gas mileage, reduced emissions and other reasons associated with the efficient operation of the .

~050~3 engine. These designs do not allow connection to conventional automotive ignition analyzers, such as analyzer 42 shown in Fig.
1. Such analyzers are usually of fairly complex design including many circuits and features not relevant to the instant disclo-5. sure. For the purposes herein, conventional analyzer 42 is shownto include oscilloscopic display section 44, tachometer section 46 and power balance section 48.
Tachometer section 46 includes one shot 50, which re-ceives as an input the ignition signal developed in cylinder No.
10. 1 as detected by probe 52. The output of one shot 50 is inte-grated in capacitor 54. The voltage impressed across capacitor 54 is therefore representative of the speed of the internal com-bustion engine, not shown, and is displayed in meter 56 as a tachometer reading.
15. The oscilloscopic display section 44 includes cathode ray oscilloscope 58 and signal processing circuitry 60 which re-ceives as an input the signals detected by cylinder No. 1 probe 52, the signals developed in the secondary circuit as detected by secondary probe 62, and the signals developed in the primary 20. circuit as detected by primary probe 64. Circuitry 60 includes amplifiers, switches and other circuits in a conventional configuration.
The power balance section of analyzer 42 includes a counter 66 receiving as a count input the ignition signals in 25. the secondary circuit of the ignition system so that counter 66 counts every time any one of the cylinders is fired. In an al-ternate arrangement, counter 66 may receive as an input the ig-nitions signals in the primary circuit of the ignition system.
In either arrangement, if a four-cylinder engine is being tes~ed, 30. counter 66 will include four output states. Counter 66 receives as a reset input the signals impressed on a particular cylinder, for convenience called cylinder No. 1, so that each of these four output states may be associated with a particular cylinder.
These output states are connected to selector switch 68 which is operated by the mechanic or other igni~ion analyzer user to choose one of the cylinders by selecting one of the output states 5. of counter 66. The output state selected is connected through power balance switch 70, when actuated, to the control input of shorting circuit 72. This circuit is connected to the primary of the ignition system by probe 64. Shorting circuitry 72 is shown to include transistor 73 and high ener~y diode 74. When 10. power balance switch 70 is actuated, circuitry 72 is used to short circuit the points of the engine during the normal firing time of the cylinder selected by switch 68. When switch 70 is not actuated, all cylinders are operated normally.
Various details of the circuitry of analyzer 42 have 15. not been shown but include, for example, circuitry to allow ana-lyzer 42 to be used with engines having other than four cylin-ders, circuitry for developing a substitute cylinder No. 1 pulse for counter 66 for use when the ignition of cylinder No. 2 is disabled by shorting switch 72, pulse shaping and amplifying cir-20. cuitry and various other improvements for displaying and measur-ing other functions of the invention.
The improvement for analyzer ~2 according to the in-stant invention, includes adapter 76 having secondary probe sec-tion 78 and voltage clamp 80 all mounted within a mechanical 25. housing shown in Fig. 2.
Voltage clamp 80 may include zener diode 82 and power transistor 84 together with resistor 86 in a conventional con-figuration to improve the power handling capabilities of diode ~; 82. Clamp 80 is connected between power balance lead 88 and 30. tachometer lead 25. In this manner, when pow~r balance push-button 70 is operated, the output sta-te of counter 66 selected by switch 68 causes shorting circuit 72 to ground points probe :

10Sa~13 64, thereby grounding clamp 80. This clamps tachometer lead 25 to the voltage determined by zener diode 82 during the normal firing time of the cylinder selected.
For display purposes, when the power balance test is 5. not being performed, points probe 64 may be connected to primary lead 90 in order to connect tachometer lead 25 to signal proces-sing cixcuitry 60. Switching between leads 88 and 90 may be ac-complished by a switch or conveniently by moving probe 64 physi-cally from lead 88 to lead 90.
10. In a complex automotive ignition analyzer, such as that represented by analyzer 42 of Fig. 1, the signals being sensed are of a critical nature. The display on the cathode ray tube, generated by the analyzer in response to the signals, is used by the mechanic to determine what action is to be taken. Even more 15. important, complex circuitry within the analyzer uses the signals to perform tasks such as the power balance test, described above, wherein timing to the fraction of a second is critical. Because of size limitations and the lack of a shielding case, as em-ployed with a conventional automotive coil, the coil of a HEI ig-20. nition produces three distinct magnetic fields. Additionally, thebalance of the ignition and electrical system such as sparkplug wires, etc. emit magnetic radiations. One o the aforementioned magnetic fields exists around the wires of the primary winding.
A second (and the major) magnetic field exists parallel to the 25. core -- exiting from one end of the core and entering the other.
The third magnetic field, known as the quadrature field, is per-pendicular to the second field -- exiting at the top and enter-ing at the side (as positioned in the HEI distributor). Unlike the first two fields, wherein the magnetic flux can be out-of-30. phase with the current in the ignition system being tested, thequadrature field has a particularly desirable attribute of be-ing in-phase with the current. Moreover, since the quadrature - 1050~3 field exists perpendicularly to the major magnetic field (the second described above) and within a 90 quadrant, it is well positioned for detection without major interference from the other magnetic fields in the area.
5. Secondary probe section 78 contains an L-shaped elec-tromagnetic core of the proper size to fit against the circum-ference of the housing for ignition coil 26 within the quadrature field thereof. An L-shaped section was chosen in order to maxi-mize the available flux linkage for the probe. If more conven-10. ient, the core shape could also be semicircular. Because of the physical arrangements of the housings, an L-shaped core in the quadrature field of the coil is preferred and provides a better signal of interest while rejecting extraneously induced voltages from other magnetic fields of the engine than a straight core in 15. the direct flux path. One leg of the L-shaped core is wrapped with a pickup coil which may conveniently be 1,000 turns of No.
41 wire. The physical configuration of the above-described de-vices may best be understood with reference to Fig. 2.
Fig. 2 shows in pictorial form an electronic ignition 20. system 10 and adapter 76 in an e~ploded view arrangement. Adap-ter 76 includes housing 100 which has been partially cut away to show secondar~ probe section 78 which includes L-shaped core 102 and winding 104. One end of winding 104 is connected to one terminal of coaxial connector 106 which is the point to which 25. secondary pickup lead 62 of analyzer 42 is connected while the j; other end of winding 104 is connected to the other terminal of j coaxial connector 106 which in turn is connected to engine i ground. Also contained within housing 100 is circuit board 108 upon which are mounted the electronic components of clamp 80.
30. Post 90 and post 88 are the connection points for the primary lead and the power balance lead as described above and are con-nected to the circuitry on board 108. Also connected thereto .

10~0~L13 is tachometer lead 25 which may be connected to the tach input position of connector 112.
Electronic ignition system 10 includes rotor base 114 mounted in which is rotor 22 and electronic circuitry 116 which 5. includes pass transistor 30 and the associated circuitry as shown in Fig. 1. Cable 118 is connected to this circuitry and is ter-minated in connector 112 described in part above. Mounted upon housing 114 is distributor cap 120 to which are connected spark plug wires 14, 16, 18 and 20.
10. Coil 26 is mounted in a cavity in the upper surface of cap 120 and is covered by distributor cover 124 which protects the remainder of the ignition system from the environment. Cover 124 includes a molded portion 126 which fits around coil 26.
When assembled, the quadrature field exists as designated by the 15. arrows 127.
Housing 100 is designed so that it may be mounted upon cover 124 so that L-shaped ~ore 102 partially surrounds coil 26.
Core 102 thereby interrupts the flux lines of the quadrature field 127 of coil 26 thereby developing a maximum signal o~ in-20. terest while responding minimally to other magnetic radiations.
The operation of these devices may be clearly seenwith reference to Figs. 3A and 3B. Fig. 3A is a graphical rep-resentation of the oscilloscope trace shown on oscillo~cope 58 for the signal developed in the primary circuit of the ignition 25. system as detected by probe 64 connected to lead 90. At time To pass transistor 30 is caused to stop conducting by circuitry 34 so that coil 26 discharges its energy through rotor 22 into the appropriate spark plug. This results in a 300 to 400 volt spike in the primary circuit as illustrated in Fig. 3A. At time ~ 30. Tl at the end of the initial spike, the voltage across the spark j plug gap decays to a point where approximately 20 volts is im-pressed on the primary circuit,~the level at which ionization is sustained~ At time T2 the energy is insufficient to sustain ion-ization and the voltage at the primary drops to the battery vol-tage of approximately 12 volts. At time T3 the voltage drops to approximately zero when transistor 30 again is caused to conduct.
5. During a power balance test of the cylinder represented in Fig. 3A, probe 64 would be connected to lead 88. The voltage displayed on oscilloscope 58 would appear as shown in Fig. 3B.
Rather than tying lead 25 to ground, clamp 80 serves to limit the voltage at the common point of the coil to 15 volts, which is 10. sufficient to allow coil 26 to discharge through clamp 80 and shorting circuit 72 but insufficient to cause ionization of the gases within the cylinder. In this manner an electronic ignition system may be power balance tested without causing damage thereto.
Although a preferred embodiment of the instant inven-15. tion has been disclosed herein, it must be understood that modi-fications may be made to the design shown herein without depart-ing from the spirit or scope of the invention. For example, the details of the circuitry of analyzer 42 may be altered to provide additional functions and measurements or ~or special purpose test 20. equipment. The power balance test function may be provided in a device without the capability o oscilloscopic display and vice versa. Further, various different orms of electronic ignition systems may require modifications of the general structure of the adapter and housing. Moreover, the voltage clamp need not 25. ~e housed in the adapter but may be made a part of the ignition analyzer with appropriate switch performed when the analyzer is utilized in connection with older, point type ignition systems and the newer electronic ignition systems.

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Improved internal combustion engine ignition ana-lyzer apparatus for use in power balance testing of an internal combustion engine having an electronic ignition system including a tachometer/primary output terminal, said analyzer including means to generate a pulse in timed relationship to the firing of a selected cylinder of the engine and a shorting switch circuit ordinarily adapted to be connected across the points of a stan-dard ignition system and actuated during the pulse to disable the ignition system to prevent ignition of said selected cylin-der, wherein the improvement comprises:
voltage clamp means for maintaining a voltage at a pre-determined level; and means for connecting said voltage clamp means in ser-ies circuit between said tachometer/primary terminal and said shorting switch circuit whereby the voltage at said tachometer/
primary output terminal may be maintained at said fixed predeter-mined level during the normal firing period of said selected cylinder.

2. The improved apparatus of claim 1 wherein said predetermined voltage level is above the voltage level of the engine battery but below the level required to cause ionization of the gases within said selected cylinder.

3. The improved apparatus of claim 2 wherein said predetermined voltage level is approximately 15 volts.

4. The improved apparatus of claim 2 wherein said voltage clamp means includes a zener diode and resistor connected in electrical series circuit between said tachometer/primary out-put terminal and said shorting switch and a power transistor hav-ing an input electrode, an output electrode and a control elec-trode, said input and output electrodes connected in parallel circuit with said zener diode and resistor and said control elec-trode connected to the junction between said zener diode and said resistor.

5. Improved internal combustion engine ignition ana-lyzer apparatus for use in power balance testing of an internal combustion engine having an electronic ignition system including a coil contained within the distributor housing and a tachometer/
primary output terminal, said analyzer including means to gener-ate a pulse in timed relationship to the firing of a selected cylinder of the engine and a shorting switch ordinarily adapted to be connected across the points of a standard ignition system and actuated during said pulse to disable the ignition system to prevent ignition of said selected cylinder, said apparatus comprising:
a magnetic core;
a winding on said core adapted to be connected to the analyzer for detecting ignition signals of said ignition system;
means for positioning the core in the quadrature field of the ignition coil to cause the quadrature field to be the primary source of inductance of a signal in said winding;
voltage clamp means for maintaining a voltage at a predetermined level; and means for connecting said voltage clamp means in ser-ies circuit between said tachometer/primary output terminal and said shorting switch circuit whereby the voltage at said output terminal may be maintained at said fixed predetermined level dur-ing the normal firing period of said selected cylinder.

6. The apparatus of claim 5 wherein the core is shaped to maximize the available flux linkage from the quadra-ture field between said coil and said core whereby the signal induced by the quadrature field will be maximized and voltages induced by other magnetic fields from the engine will be minimized.

7. The apparatus of claim 5 wherein said positioning means comprises a housing for supporting said core and means for securing said housing to said distributor whereby said magnetic core is closely positioned in the quadrature field with respect to said ignition coil whereby the signal induced by the quadra-ture field will be maximized and voltages induced by other mag-netic fields from the engine will be minimized.

8. The apparatus of claim 5 wherein said predeter-mined voltage level is above the voltage level of the engine bat-tery but below the level required for ionization of the gases within said selected cylinder.

9. The apparatus of claim 8 wherein said voltage clamp means includes a zener diode and resistor connected in el-ectrical series circuit between said tachometer/primary output terminal and said shorting switch circuit and a power transistor having an input electrode, an output electrode and a control el-ectrode, said input and output electrodes connected in parallel circuit with said zener diode and resistor and said control el-ectrode connected to the junction between said zener diode and said resistor.

10. The apparatus of claim 7 wherein said predeter-mined voltage level is above the voltage level of the engine battery but below the level required for ionization of the gases within said selected cylinder.

11. The apparatus of claim 10 wherein said voltage clamp means includes a zener diode and resistor connected in electrical series circuit between said tachometer/primary output terminal and said shorting switch circuit and a power transistor having an input electrode, an output electrode and a control electrode, said input and output electrodes connected in paral-lel circuit with said zener diode and resistor and said control electrode connected to the junction between said zener diode and said resistor.