GB1562319A

GB1562319A - Ignition analyzer for use with electronic ignition systems

Info

Publication number: GB1562319A
Application number: GB4912576A
Authority: GB
Original assignee: Beckman Instruments Inc
Current assignee: Beckman Coulter Inc
Priority date: 1975-11-26
Filing date: 1976-11-25
Publication date: 1980-03-12
Also published as: DE2653627C2; JPS5277342U; FR2333133A1; CA1050113A; FR2333133B1; JPS6032391Y2; DE2653627A1

Description

(54) IMPROVED IGNITION ANALYZER FOR USE WITH ELECTRONIC IGNITION SYSTEMS (71) We, BECKMAN INSTRUMENTS, INC., 2500 Harbor Boulevard, Fullerton, California 92634, United States of America, a Corporation organized and existing under the laws of the State of California, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to apparatus for use in power balance testing of an internal combustion engine having an electronic ignition system.

Ignition analysers for use with multicylinder internal combustion engines are well known in the art. Conventional ignition analysers include a tachometer drive and display, a cathode ray oscilloscope drive and display and a power balance test circuit.

The test circuit conventionally includes: (a) a counter for identifying the individual cylinder firing, (b) a switch for selecting a particular cylinder to be disabled and (c) a selectively operable shorting circuit controlled by the counter through the selector switch to disable the ignition .system during the normal firing time of the cylinder selected. This power balance test circuit is normally utilised by selecting a particular cylinder and by observing the tachometer reading before and after disabling that cylinder so that the effect on engine performance of the normal operation of the cylinder selected, in terms of engine speed, may be determined.

These conventional analysers require a first probe 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 count input for the counter. The shorting circuit is connected to the ungrounded side of the point. When the shorting circuit is actuated by the counter, the unwounded slide 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 through the spark plug selected.The probe connected to the secondary circuit is normally a magnetic pick-up positioned around the high tension lead between the primary side of the coil and the centre of the distributor.

Such conventional analysers cannot be used to analyse some of the recently re developed electronic ignition systems such as the General Motors Corporation high energy ignition (HEI) system. In such systems the ignition coil is positioned within the distributor cap so that the secondary circuit is not readily accessible for signal detecting purposes and the points are replaced by a transistorised ignition circuit. Although a connection to the collector of this transistor is made accessible for connection to the engine tachometer, the remaining components are protected by covers.This prevents convenient access by the mechanic to connect probes associates with the analyser. Ihe power balance connection to the analyser, 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 not necessary for an understanding of the present invention.

According to the present invention there is provided apparatus for use in power balance testing of an internal combustion engine having an electronic ignition system with a tachometer/primary output terminal, said apparatus including means to generate a pulse commencing at a given timed rela tionship to the firing of a selected cylinder of the engine, a shorting switch circuit for connection across the points of a breaker point ignition system and actuated during the generated pulse to prevent ignition of said selected cylinder, voltage clamp means for maintaining a voltage at a predetermined level; and means for connecting said voltage clamp means in series circuit between said tachometer/primary output terminal and said shorting switch circuit whereby the voltage at said tachometer-primary output terminal may be maintained at said fixed predetermined level during the normal firing period of said selected cylinder.

Further, according to the present invention there is provided apparatus for use in power balance testing of an internal combustion engine having an electronic ignition system with a coil contained within the distributor housing and a tachometer-primary output terminal, said apparatus including means to generate a pulse commencing at a given timed relationship to the firing of a selected cylinder of the engine, and comprising a winding on a magnetic core adapted to be positioned in the field of the ignition system coil to cause the quadrature field (as hereinafter defined) thereof to induce a signal in said winding; a shorting switch for connection across the points of a breaker point ignition system and actuated during said generated pulse to prevent ignition of said selected cylinder; voltage clamp means for maintaining a voltage at a predetermined level; and means for connection said voltage clamp means in series 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 during the normal firing period of said selected cylinder.

An embodiment of the present invention will now be described, by way of example with reference to the accompanying drawings, in which: Fig. 1 shows in symbolic form a typical electronic ignition system with apparatus according to the present invention; Fig. 2 is an exploded view of part of Fig. 1; and Fig. 3 includes graphs 3A and 3B which show, respectively, the primary circuit display for an individual cylinder under normal operating conditions and the same display during a power balance test.

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 combustion engine such as an automobile engine.

Contained within distributor 12 is rotor 22 which distributes the energy present in secondary circuit high tension lead 24 of ignition coil 26. The primary side of the coil 26 is connected by battery lead 28 to the battery of the engine. The common side of ignition coil 26 is connected to the collector of power transistor 30 which is connected through emitter resistor 32 to ground. The base of transistor 30 is operated by circuitry 34 in the manner generally of the mechanical points of a conventional ignition system so that the transistor 30 is caused to stop conducting when coil 26 is required to cause a spark plug to receive a voltage pulse. Circuitry 34 includes a magnetic or optical pick-up 36 which detects indicia 38 on rotating cam shaft 40 in order to synchronise the operation of the 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 provided in a housing access to which is limited to a three wire cable containing a ground connection, battery lead 28 and tachometer lead 25 which is connected to the common point of coil 26 and therefore the collector of transistor 30. While the connection to the coil collector common point has been referred to herein as the tachometer lead or output, it should be understood that such designation is not esential and in other ignition systems may be referred to by other nomenclature, such as, the primary output. What is important is that this connection be made to a common point between the coil and transist or so that the coil energy may be dissipated without damage to the system.

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 tension lead 24 is enclosed within the housing so that it is not readily accessible for connection to an ignitional analyser.

The electronic ignition system described above has been developed for improved fuel consumption, reduced exhaust gas emissions and other reasons associated with the efficient operation of the engine but does not allow direct connection to conventional automotive ignition analysers, such as analyser 42 shown in Fig. 1. Such analysers are usually of fairly complex design including many circuits and features not relevant to the present disclosure. For the purposes herein, conventional analyser 42 is shown to include an oscilloscopic display section 44, a tachometer section 46 and a power balance section 48.

Tachometer section 46 includes one shot (or monostable vibrator) 50, which receives as an input the ignition signal developed in cylinder No. 1 as detected by probe 52. The output of one shot 50 is integrated in capacitor 54. The voltage impressed across capacitor 54 is therefore representative of the speed of the internal combustion engine, not shown, and is displayed in meter 56 as a tachometer reading.

The oscilloscopic display section 44 includes cathode ray oscilloscope 58 and signal processing circuitry 60 which receives 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 circuit as detected by primary probe 64. Circuitry 60 includes amplifiers, switches and other circuits in a conventional configuration.

The power balance section of analyser 42 includes a counter 66 receiving as a count input the ignition signals in the secondary circuit of the ignition system so that counter 66 counts every time any one of the cylinders is fired. In an alternate arrangement, counter 66 may receive as an input the ignition signals in the primary circuit of the ignition system. In either arrangement, if a four-cylinder engine is being tested, 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 ignition analyser user to choose one of the cylinders by selecting one of the output states 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 energy diode 74. When 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 analyser 42 have not been shown but include, for example, circuitry to allow analyser 42 to be used with engines having other than four cylinders, 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 circuitry and various other improvements for displaying and measuring other functions of the invention.

The analyser 42 is connected to the ignition system 10 by adaptor 76 having secondary probe section 78 and voltage clamp 80 all mounted within a mechanical housing shown in Fig. 2.

Voltage clamp 80 may include zener diode 82 and power transistor 84 together with resistor 86 in a conventional configuration to improve the power handling capabilities of diode 82. Clamp 80 is connected between power balance lead 88 and tachometer lead 25., In this manner, when power balance push-button 70 is oper- ated, the output state of counter 66 selected by switch 68 causes shorting circuit 72 to ground points probe 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 not being performed, points probe 64 may be conencted to primary lead 90 in order to connect tachometer lead 25 to signal processesing circuitry 60. Switching between leads 88 and 90 may be accomplished by a switch or conveniently by moving probe 64 physicaly from lead 88 to lead 90.

In a complex automotive ignition analyser, such as that represented by analyser 42 of Fig. 1, the signals being sensed are of a critical nature. The display on the cathode ray tube, generated by the analyser in response to the signals, is used by the mechanic to determine what action is to be taken. Even more important, complex circuitry within the analyser 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 an electromagnetic field shielding case, as employed with a conventional automotive coil, the coil of a HEl ignition produces three distinct magnetic fields. Additionally, the balance of the ignition and electrical system such as spark plug wires, etc. emit magnetic radiations.One of the aforementioned magnetic fields exists around the wires of the primary winding. A second (and the major) magnetic field exists parallel to the core--exiting from one end of the core and entering the other.

The third magnetic field, known as the quadrature field, is perpendicular to the second field-exiting at the top and entering at the side (as positioned in the HEl distributor). Unlike the first two fields, wherein the magnetic flux can be out-of-phase with the current in the ignition system being tested, the quadrature field has a particularly desirable attribute of being in-phase with the current. Moreover, since the quadrature field exists perpendicularly to the major magnetic field (the second described above) and within a 90" quadrant, it is well posi tioned for detection without major interference from the other magnetic fields in the area.

Secondary probe section 79 contains an L-shaped electromagnetic core of the proper size to fit against the circumference of the housing for ignition coil 26 within the quadrature field thereof. An L-shaped section was chosen in order to maximise the available flux linkage for the probe. If more convenient, the core shape could also be semicricular. 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 the direct flux path. One leg of the L-shaped core is wrapped with a pick-up coil which may conveniently be 1,000 turns of No. 41 wire.

The physical configuration of the abovedescribed devices may best be undersood with reference to Fig. 2.

Fig. 2 shows in pictorial form an electronic ignition system 10 and adaptor 76 in an exploded view arrangement. Adaptor 76 includes housing 100 which has been partially cut away to show secondary 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 secondary pick up lead 62 of analyser 42 is connected while the other end of winding 104 is connected to the other terminal of coaxial connector 106 which in turn is connected to engine ground. Also contained within housing 100 is circuit board 108 upon which are mounted the electronic components of clamp 80. Post 90 and post 88 are the connection points for the primary lead and the power balance lead as described above and are connected to the circuitry on board 108.Also connected thereto 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 includes pass transistor 30 and the associated circuitry as shown in Fig. 1. Cable 118 is connected to this circuitry and is terminated 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.

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 arrows 127.

Housing 100 is designed so that it may be mounted upon cover 124 so that L-shaped core 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 of interest while responding minimally to other magnetic radiations.

The operation of these devices may be clearly seen with reference to Figs. 3A and 3B. Fig. 3A is a graphical representation of the oscilloscope trace shown on oscilloscope 58 for the signal developed in the primary circuit of the ignition system as detected by probe 64 connected to lead 90. At the time To pass transistor 30 is caused to stop conducting by circuitry 34 so that coil 25 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 T1 at the end of the initial spike, the voltage across the spark plug gap decays to a point where approximately 20 volts is impressed on the primary circuit, the level at which ionization is sustained.At time T2 the energy is insufficient to sustain ionization and the voltage at the primary drops to the battery voltage of approximately 12 volts. At time Ts the voltage drops to approximately zero when transistor 30 again is-caused to conduct.

During a power balance test of the cylinder represented in Fig. 3A, probe 64 would be conencted 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 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 present invention has been disclosed herein, it must be understood that modifications may be made to the design shown herein.

For example, the details of the circuitry of analyser 42 may be altered to provide additional functions and measurements or for special purpose test equipment. The power balance test function may be provided in a device without the capability of oscilloscopic display and vice versa. Further, various different forms of electronic ignition systems may require modifications of the general structure of the adapter and housing.

Moreover, the voltage clamp need not be housed in the adaptor but may be made a part of the ignition analyser with appropriate switch performed when the analyser is utilised in connection with older, point type ignition systems and the newer electronic ignition systems.

WHAT WE CLAIM IS: 1. Apparatus for use in power balance testing of an internal combustion engine having an electronic ignition system with a tachometer/primary output terminal, said apparatus including means to generate a pulse commencing at a given timed relationship to the firing of a selected cylinder of the engine, a shorting switch circuit for connection across the points of a breaker point ignition system and actuated during the generated pulse to prevent ignition of said selected cylinder, voltage clamp means for maintaining a voltage at a predetermined level; and means for connecting said voltage clamp means in series circuit between said tachometer/primary output terminal and said shorting switch circuit whereby the' voltage at said tachometer/primary output terminal may be maintained at said fixed predetermined level during the normal firing period of said selected cylinder.

2. Apparatus for use in power balance testing of an internal combustion engine having an electronic ignition system with a coil contained within the distributor housing and a tachometer/primary output terminal, said apparatus including means to generate a pulse commencing at a given timed:rela- tionship to the firing of a selected cylinder of the engine and comprising, a winding on a magnetic core adapted to be positioned in the field of the ignition system coil to cause the quadrature field (as hereinbefore defined) thereof to induce a signal in said winding: a shorting switch for connection across the points of a breaker point ignition system and actuated during said generated pulse to prevent ignition of said selected cylinder, voltage clamp'means for maintaining a voltage at a predetermined level; and means for connecting said voltage clamp means in series 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 during the normal firing period of said selected cylinder.

3. Apparatus as claimed in Claim 2, wherein the core is shaped to maximise the available flux linkage from the quadrature field between said coil and said core whereby the signal induced by the quadrature field will be maximised and voltages induced by other magnetic fields from the engine will be minimised.

4. Apparatus as claimed in Claim 2 or 3, wherein said winding is positioned in a housing which is adapted to be secured 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 quadrature field will be maximised and voltages induced by other magnetic fields from the engine will be minimised.

5. Apparatus as claimed in any preceding claim, 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.

6. Apparatus as claimed in Claim 5, wherein said predetermined voltage level is 15 volts.

7. Apparatus as claimed in any preceding Claim, wherein said voltage clamp means include a zener diode and resistor connected in electrical series circuit and a power transistor having an input electrode, an output electrode and a control electrode, said input and output electrodes being connected in parallel circuit with said zener diode and resistor series circuit and said control electrode being connected to the junction between said zener diode and said resistor.

8. Apparatus as claimed in Claim 1 and substantially as hereinbefore described with refernce to Figs. 1 to 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. is utilised in connection with older, point type ignition systems and the newer electronic ignition systems. WHAT WE CLAIM IS:

1. Apparatus for use in power balance testing of an internal combustion engine having an electronic ignition system with a tachometer/primary output terminal, said apparatus including means to generate a pulse commencing at a given timed relationship to the firing of a selected cylinder of the engine, a shorting switch circuit for connection across the points of a breaker point ignition system and actuated during the generated pulse to prevent ignition of said selected cylinder, voltage clamp means for maintaining a voltage at a predetermined level; and means for connecting said voltage clamp means in series circuit between said tachometer/primary output terminal and said shorting switch circuit whereby the' voltage at said tachometer/primary output terminal may be maintained at said fixed predetermined level during the normal firing period of said selected cylinder.