GB1559210A

GB1559210A - Timing control circuit for an automotive engine ignition analyzer

Info

Publication number: GB1559210A
Application number: GB4912476A
Authority: GB
Original assignee: Beckman Instruments Inc
Current assignee: Beckman Coulter Inc
Priority date: 1975-11-26
Filing date: 1976-11-25
Publication date: 1980-01-16
Also published as: DE2653626C2; DE2653626A1; FR2333134B1; FR2333134A1; CA1054222A

Description

(54) IMPROVED TIMING CONTROL CIRCUIT FOR AN AUTOMOTIVE ENGINE IGNITION ANALYZER (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 desscribed in and by the following statement: This invention relates to internal combus- tion engine ignition analyzers and in partticular, to a new and improved timing circuit for generating sweep signals for the oscilloscope and trigger signals for the strobe lamp of an analyzer and to a method of engine timing using such an analyzer.

Ignition analyzers are utilized at the pr sent time by engine mechanics to provide information regarding the performance of an internal combustion engine, typically the engine for an automobile or truck. A cathode ray oscilloscope is provided for displaying certain types of information, usually with the horizontal sweeps being initiated by an ignition timing event such as points closed or No.

1. plug firing or the like. The usual constant speed sweep is not satisfactory for engine analyzers where the engine speed will vary over a wide range between idling and full speed. It is desirable to have the horizontal sweep utilize the full width of the tube face regardless of sweep repetition rate, which is proportional to engine speed.

A standard accessory incorporated in the conventional engine analyzer is a strobe or timing lamp which provides a pulse of light of very short duration. In a typical internal combustion engine, a fixed reference mark is provided on the engine housing adjacent the flywheel which carries another reference mark. When these two reference marks are aligned, the engine is in the top dead centre position which nonnally corresponds to the firing time for the number 1 cylinder.

The conventional stand-alone strobe lamp is triggered by the number 1 cylinder firing signal during running of the engine producing the repeating short light pulse permitting visual determination by the mechanic of the actual engine flywheel position with respect to the fixed reference mark for any engine speed.

Originally, the mechanic noted the difference between the two reference marks, typically in degrees scribed on the flywheel, to determine the amount of advance of number 1 cylinder firing signal with respect to top dead center.

In improved timing lamps, a variable delay was introduced into the timing ]amp so that the lamp trigger pulse was delayed with respect to the number 1 cylinder firing signal. In using this improved lamp, the mechanic adjusted the delay so that the two reference marks were aligned when the lamp was triggered and read the calibration of the delay adjustment in terms of degrees of advance.

This type of device employed a ramp voltage proportional to engine speed which voltage was used as a reference for the delay circuit. This simple delay timing circuit has been satisfactory for prior engines which were set at some amount of advance.

The present day engines, particularly those equipped with pollution control devices, incorporate both advance and retard mechansms, and some engines are set at a retarded position at idling speed. The simple time delay circuits utilized with the prior art strobe lamps cannot be used for measuring retard settings. That is, the lamps cannot be utilized to advance the lamp firing ahead of the cylinder firing signal.

Prior art ignition analyzer timing circuits have attempted to generate a horizontal sweep signal (ramp voltage) proportional to the engine speed and typically utilize amplitude comparison circuits. Various ways have been utilized in the past and each has had some limitation. The limitations on the prior art sweep signal generators usually show up as variation in the sweep length at different engine speeds. It is desirable to have the sweep generating system stable and therefore relatively large time constants are utilized; however, the large time constants tend to limit the ability of the system to synchronize itself with rapid changes in engine speed.

Attempts have been made to speed up the synchronization by making the circuitry under damped. This results in a horizontal trace which at first is too long and then too short before settling down to the proper trace length.

It is an object of the present invention to provide a new and improved engine ignition analyzer.

According to the present invention there is provided an engine ignition analyzer including an oscilloscope and a strobe lamp for use in the adjustment of the timing of an internal combustion engine having a fixed reference mark and a moving reference mark which to gether define an engine adjustment reference point when said reference marks are aligned said analyzer comprising a timing control cir cuit having: means for producing an increasing ramp voltage synchronized with an engine ignition event; means for producing a decreasing ramp voltage synrronized with an engine ignition event; means for producing a reference voltage including means for varying said reference voltage as a function of the desired amount of deviation of lamp flash from the occurrence of the engine adjustment reference point; a comparator having first and second input terminals and providing an output pulse when a positive going voltage applied to said first terminal enquals a reference voltage applied to said second terminal and when a negative going voltage applied to said second terminal equals a reference voltage applied to said first terminal; first switch means connecting said increas ing ramp voltage and said reference voltage to said first and second terminals respectively of said comparator when in a first position and connecting said decreasing ramp voltage and said reference voltage to said second and first terminals respectively when in a second posi tion whereby advance or retard deviation of lamp flash can be selected; means connecting said comparator output to the strobe lamp as a trigger voltage; and, means connecting said increasing ramp voltage to the oscilloscope as the sweep voltage.

Further, the present invention provides, a method of retarding and advancing the triggering of a strobe lamp and sweeping the oscilloscope of an engine ignition analyzer with respect to a timing adjustment reference point of an engine, including the steps of: detecting the occurrence of engine ignition events; generating an increasing ramp voltage and a decreasing ramp voltage synchronized with an engine ignition event; triggering the oscilloscope sweep with the increasing ramp voltage; generating a reference voltage of a magnitude varying as a function of the desired strobe larnp triggering deviation from the adjustment reference point; selecting one of the ramp voltages depending on whether the strobe lamp triggering is to be retarded or advanced; and triggering the strobe lamp when the selected voltage and the reference voltage are matched.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a block diagram showing part of an engine ignition analyzer according to the present invention and incorporating a sweep generator; Fig. 2 is an electrical schematic of the sweep generator of Fig. 1; Fig. 3 is a circuit similar to that of Fig.

2 showing an alternative embodiment of the sweep generator; and Fig. 4 is an electrical diagram of the strobe lamp control portion of the analyzer of Fig.

1.

The ignition analyzer illustrated in Fig. 1 includes a pickup 10, a sweep generator 11 and an oscilloscope 12. The pickup provides an electrical output signal in the form of a train of pulses 15, which pulses are related in time to some event in the engine ignition system, such as points open or points closed or No. 1 plug firing or the like.

The pickup is coupled to some point in the ignition system by direct coupling cr by inductive coupling or by capacitive coupling as desired, and the pickup may be of conventional design.

The sweep generator 11 provides the horizontal sweep signal for the trace of the oscilloscope 12 in the form of a cyclically repeating ramp voltage 16. The sweep signal is connected to the horizontal deflection plates of the oscilloscope in the conventional manner, and the signal to be displayed is connected to the vertical deflection plate. Sweep generator 11 also provides the input to the strobe lamp driving portion of the circuit to be described hereinafter in detail.

The time interval between pulses 15 varies with the speed of the engine. The function of the sweep generator is to provide the ramp voltage 16 with a substantially constant peak value so that the sweep width is substantially the same regardless of the sweep rate or interval between sweep initiation signals (i.e., regardless of engine speed). This is accomplished by utilizing a phase lock loop in the sweep generator with phase detector 20, integrator 21 and voltage control oscillator 22. The presently preferred embodiment for the sweep generator is shown in Fig. 2.

The phase detector 20 includes flip-flops A and B. The pulses 15 (designated Fret) are con nected as the input of flip-flop A. The input to flip-flop B is another train of pulses 25 (designated Fb). The pulses 25 are produced by a comparator 26 when the ramp voltage E, reaches a predetermined value, as determined by a reference voltage input Vr to the com parator 26.

In the system as illustrated, the flip-flop A is set by the positive going edge of a pulse 15 and the flipflop B is set by the positive going edge of a pulse 25.

The flip-flops are reset by a reset circuit in cluding gates 28, 29 which provide the reset voltage when both flip-flops are set. The sig nal on line 30 is normally high and goes nega tive upon the occurrence of the engine ignition event with which the beginning of the ramp 16 is synchronized. Gate 29 acts as an OR gate and will reset flip-flops A and B either when both A and B are in the set state or upon the occurrence of the negative going portion of the signal on line 30. This later signal assures that both flip-flops A and B are in the normal or reset state at the beginning of the ramp and prevents the system from getting out of synchronization.

Resistors R1 and R2 are connected as a voltage divider with the junction D connected as the input to the integrator 21 through resistor R3. When flip-flop A is in the normal or reset state, resistor R1 is tied to a known voltage (in this case, 0). Similarly, when flip flop B is in the normal state, resistor R2 is tied to a known voltage (designated as Amplifier AR1 of the integrator 21 has its reference input tied to voltage Vv, which is set to be equal to the potential at the juncrion D when both flip-flops are in the reset state (in this example, V/2). Under this condition, there is no current through the resistor R3 and the integrator output E0 does not change.

When only one of the flip-flops is set, the poten tial at D is greater than or less than the poten tial V0 by a step function amount V/2 pro dudng a current in the resistor R3 and a change in the integrator output Eo as will be hereinafter described in greater detail.

The amplifier AR2 of the voltage controlled oscillator 22 provides the output E4 in the form of a ramp the slope of which is proportional to B. When the voltage Er reaches a value equal to Vref, the pulse 25 is generated by the com parator 26. If the Frer pulse 15 occurs before the Ffb pulse 25, flip-flop A is set and resistor R1 is connected to the voltage (V) causing point D to go from a potential of V/2 to V and the output Eo to move in a negative di rection. This causes the ramp E, to change slope and reach Vret sooner than it did in the preceding cycle. After the pulse 25 is gener ated, flip-flop B is set also and then both flip flops are reset causing point D to once again assure a potential of V/2 and output E, to stabilize at its achieved value. If the Fref pulse occurs after the Ftb pulse, the reverse operation occurs with point D going from a potential of V/2 to 0 and the output E, moving in a posi tive direction. This causes the ramp E, to reach Vre, later than it did in the preceding cycle. With this pulsed compensation arrangement, the length of the horizontal sweep is controlled by Vre, and is not subject to voltage or current feedback from a tachometer circuit or other variable related to engine speed.

The voltage controlled oscillator is reset to the initial condition by a switching transistor 33 connected across the output and input of amplifier AR2. The transistor 33 is actuated to the conducting condition by the negative going signal at 30 through a one shot multivibrator 34. In an alternative embodiment shown in Fig. 3, resetting is accomplished by using the signal Ffb for controlling the switching transistor 33. The signal at 30 may be omitted entirely, with the flip-flops being reset by gate 28 when both flip-flops are in the set state.

The time duration of t of the sweep is R,C2dv F, where dv is the maximum voltage of the ramp ;as determined by Fret). The transfer function of the integrator is E, 1 + jor2 E;n j r where r1= [(R1 or R2)+R3]C1 r2=R4 C1 The phase lock loop functions to reduce the phase difference between the inputs to the two flip-flops to a minimum and thereby maintain the maximum voltage of the ramp substantially constant so that the length of the sweep will be substantially constant and independent of the input pulse rates at the flipflops (i.e., engine speed).

Referring now to Fig. 4, the strobe lamp firing portion of the circuit includes an inverter 120, a selection switch 121, and a comparator 122. The ramp voltage 16 is connected to one fixed terminal (A) of one contact set of the advance-retard selection switch 121, and as an input to the inverter 120 through a resistor 123, with the inverter input connected to a negative voltage source through a variable resistor 124 which provides a zero adjustment. The inverter output is an inverted ramp voltage 127 which is connected to a fixed terminal (R) of another contact set of the switch 121.

A reference voltage is connected to a fixed terminal (R) of the first contact set of the switch 121 and to a fixed terminal (A) of the second contact set. In the embodiment illustrated, the reference voltage is provided by an amplifier 130, a control potentiometer 131 and another amplifier 132 to form a positive voltage source. The potentiometer 131 provides for variation of the reference voltage by the mechanic or other person utilizing the strobe lamp. The amplifier 130 provides isolation of the control potentiometer from the voltage source and the amplifier 132 provides inversion of the reference voltage and isolation. A potentiometer 133 is connected across positive and negative voltage sources, with the moving arm connected to the input of amplifier 132 to provide a bias for the advance zero adjustment.

The moving terminals of the first and second contact sets of the switch 121 are connected to the inputs of the comparator 122 through resistors 136 and diodes 137 which protect the input from large differential voltages. In the embodiment illustrated, the output of the comparator is a negative going step 140 generated when the negative input matches the positive inputs When the switch 121 is in the position illustrated, connecting the A terminals as inputs, the circuit is in the advance mode and the comparator output is generated when the rising voltage of the ramp 16 matches the level of the reference voltage. With the switch in the opposite or retard position connecting the R terminals as comparator inputs, the comparator output step 140 is generated when the falling voltage of the ramp 127 reaches the level of the reference voltage.

The comparator output 140 provides the triggering signal for the lamp 145, preferably through a one shot multivibrator 146 and an OR circuit 147. The negative going step 140 is connected to the one shot 146 through a capacitor 148, with the one shot providing a voltage pulse 149 as an output. The OR circuit 147 connects either the voltage pulse 149 or a voltage pulse 150 as the trigger pulse to the lamp 145, depending on the setting of switch 151. With the switch 151 in the open position as shown in Fig. 4, the pulse 150 provides the triggering. With the switch 151 closed, the pulse 149 provides the triggering. Typically the pulse 150 is generated in the engine analyzer and corresponds in time to the firing signal for the number 1 cylinder, that is, top dead center for the engine which is zero degrees advance and retard. The switch 151 preferably is mounted with the potentiometer 131 so that when the operator sets the desired deviation (advance or retard) at or close to zero degrees, the switch 151 is dosed. This provides direct control of the timing lamp from the engine timing signals without advance or retard from the timing control circuit.

The reference voltage is also connected as an input to a meter 160 through a gain adjustment resistor 161 and amplifier 162. The meter may be calibrated to read directly in degrees of advance or retard. A plurality of gain control circuits 163 are connected across the amplifier 192, each comprising a resistor and switch in series. The appropriate switch is closed, depending on whether the engine under test is a four, six or eight cylinder reciprocating engine or a rotary engine to provide the aptro- priate gain for the meter 160.

Ordinarily the timing lamp 145 would be fired for each ramp of the sweep generator output. When there is a ramp for each cylinder firing, this would produce excessive lamp fir ing, since in ordinary engines, the moving reference mark appears adjacent the fixed reference mark only at the time of firing of number 1 cylinder. An inhibit circuit 166 is provided for inhibiting lamp firing except at the time of number 1 cylinder firing. The in hibit circuit includes an OR circuit 167 hav ing as one input a pulse 169 which is true from the firing time of number 1 cylinder to the firing time of number 2 cylinder, and another pulse 168 which is true from the firing time of cylinder N preceding number 1 cylinder to the firing time of number 1 cylinder. While cylinders are referred to herein, the system is equally usable with rotary engines, where the number of rotors usually corresponds to the number of cylinders in a reciprocating engine.

Another contact set of the advance-retard selection switch 121 provides inputs to the OR circuit 167 so that the one shot multivibrator 146 is inhibited except during the number 1 pulse 169 when engine advance setting is desired, or during number N pulse 168 when engine retard setting is desired.

In operation, the potentiometer 131 may initially be set at the zero degrees position with the switch 151 closed and with the switch 121 in the advance position. Then the timing lamp is fired by the number 1 cylinder pulse and the engine condition may be determined by visually observing the distance between the reference marks. When the reference marks are aligned, the timing deviation is zero degrees.

If the potentiometer 131 is moved to a new setting, say three degrees, and one of the switches 163 is closed, say the eight cylinder switch, the meter 160 will indicate three degrees. The comparator will provide the negative step output 140 when the magnitude of the ramp 16 rises to the magnitude of the reference voltage, which delays the firing of the lamp 145 a period of time corresponding to three degrees of flywheel rotation. If the selection switch 121 is moved to the retard position, the comparator output will be provided when the inverted ramp for cylinder N falls to the magnitude of the reference voltage with the result that the timing lamp is fired prior to the firing of the number 1 cylinder by the desired three degrees.

While specific polarities have been used in the preceding description, it will be readily understood that the invention is not so limited and that different polarities may be used as desired.

WHAT WE CLAIM IS:- 1. An engine ignition analyzer including an oscilloscope and a strobe lamp for use in the adjustment of the timing of an internal combustion engine having a fixed reference mark and a moving reference mark which together define an engine adjustment reference point when said reference marks are aligned, said analyzer comprising a timing control circuit having: means for producing an increasing ramp voltage synchronized with an engine ignition event; means for producing a decreasing ramp voltage synchronized with an engine ignition event; means for producing a reference voltage including means for varying said reference voltage as a function of the desired amount of deviation of lamp flash from the occurrence of the engine adjustment reference point; a comparator having first and second input terminals and providing an output pulse when a positive going voltage applied to said first terminal equals a reference voltage applied to said second terminal and when a negative going voltage applied to said second terminal equals a reference voltage applied to said first terminal; first switch means connecting said increasing ramp voltage and said reference voltage to said first and second terminals respectively of said comparator when in a first position and connecting said decreasing ramp voltage and said reference voltage to said second and first terminals respectively when in a second position whereby advance or retard deviation of lamp flash can be selected; means connecting said comparator output to the strobe lamp as a trigger voltage; and means connecting said increasing ramp voltage to the oscilloscope as the sweep voltage.

2. An analyzer as claimed in claim 1 including a deviation-indicating meter; means connecting said reference voltage to said meter for indicating the set amount of deviation.

3. An analyzer as claimed in claim 2 wherein said deviation-indicating-meter connecting means includes an amplifier, a plurality of amplifier gain control circuits corresponding to the number of cylinders of engines, and second switch means for selecting one of said gain control circuits for said amplifier.

4. An analyzer as claimed in any preceding claim wherein said means for producing a decreasing ramp voltage is an inverter having said increasing ramp voltage as an input.

5. An analyzer as claimed in any preceding claim wherein said strobe-lamp-trigger-voltage connecting means includes an OR circuit hav ing as inputs the comparator output and an engine ignition signal corresponding to the adjustment reference point, and third switch means is provided for controlling said OR circuit to select as the output thereof either said comparator output or said engine ignition signal.

6. An analyzer as claimed in claim 5, wherein said means for varying said reference voltage includes a manually-actuated potentio meter, and said third switch means is actuated by said potentiometer when at the zero devia tion position.

7. An analyzer as claimed in either of claims 5 or 6, wherein said strobe-lamp-trigger-vol tage connecting means includes a one shot multivibrator triggered by said comparator output and providing a trigger pulse for said strobe lamp.

8. An analyzer as claimed in any one of claims 1 to 6 wherein said increasing and de creasing ramp voltages repeat for every engine cylinder ignition, and an inhibit circuit is pro vided for preventing strobe lamp triggering except in conjunction with a selected cylinder ignition, said inhibit circuit including an OR circuit having as inputs engine ignition signals corresponding to the number 1 cylinder igni tion and to the number N cylinder ignition, where N is the number of the cylinder firing just before cylnder number 1, and fourth switch means for selecting the number 1 cylinder ignition signal when an advance engine setting is desired and selecting the N cylinder ignition signal when a retard engine setting is desired.

9. An analyzer as claimed in claim 8, and wherein said strobe-lamp-trigger-voltage con necting means includes a one shot multivi brator triggered by said comparator output and providing a trigger pulse for said strobe lamp, and said inhibit circuit is connected to said multivibrator.

10. An analyzer as claimed in any preceding claim wherein said means for producing an increasing ramp voltage comprises: a voltage-controlled-oscillator having an output and an input said oscillator generating a ramp voltage at its output having a slope which is a function of the signal applied at its input; a comparator circuit having a first reference voltage and said ramp voltage output of said oscillator as inputs and producing a feedback signal output when said inputs are equal; an integrator having a pair of inputs and an

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. selection switch 121 is moved to the retard position, the comparator output will be provided when the inverted ramp for cylinder N falls to the magnitude of the reference voltage with the result that the timing lamp is fired prior to the firing of the number 1 cylinder by the desired three degrees. While specific polarities have been used in the preceding description, it will be readily understood that the invention is not so limited and that different polarities may be used as desired. WHAT WE CLAIM IS:-

1. An engine ignition analyzer including an oscilloscope and a strobe lamp for use in the adjustment of the timing of an internal combustion engine having a fixed reference mark and a moving reference mark which together define an engine adjustment reference point when said reference marks are aligned, said analyzer comprising a timing control circuit having: means for producing an increasing ramp voltage synchronized with an engine ignition event; means for producing a decreasing ramp voltage synchronized with an engine ignition event; means for producing a reference voltage including means for varying said reference voltage as a function of the desired amount of deviation of lamp flash from the occurrence of the engine adjustment reference point; a comparator having first and second input terminals and providing an output pulse when a positive going voltage applied to said first terminal equals a reference voltage applied to said second terminal and when a negative going voltage applied to said second terminal equals a reference voltage applied to said first terminal; first switch means connecting said increasing ramp voltage and said reference voltage to said first and second terminals respectively of said comparator when in a first position and connecting said decreasing ramp voltage and said reference voltage to said second and first terminals respectively when in a second position whereby advance or retard deviation of lamp flash can be selected; means connecting said comparator output to the strobe lamp as a trigger voltage; and means connecting said increasing ramp voltage to the oscilloscope as the sweep voltage.

output connected to said input of said oscil lator whereby the output of said integrator will determine the slope of said ramp voltage output of said oscillator, one of said pair of inputs of said integrator being connected to a second reference voltage; logic circuit means having a pair of inputs and an output, one of said inputs being con nected to the output of said comparator circuit and the other of said inputs being connected to the ignition of an engine being analyzed, said logc circuit means producing an output equal to said second reference vol tage when the signals at said pair of inputs are in coincidence, and output greater than said second reference voltage when the signal at one of said inputs is leading the signal at the other of said inputs and an output less than said second reference voltage when the signal at said one input is lagging the signal at said other input; means connecting the output of said logic circuit means to the other of said pair of inputs of said integrator; and, resetting means connected to said input of said oscillator.

11. An analyzer as claimed in claim 10, wherein said logic circuit means includes a first flip-flop having said reference signal as the input, a second flip-flop having said feedback signal as the input, and a voltage divider connected to voltage sources by said flipflops, with a point on said voltage divider forming said output of said logic circuit means.

12. An analyzer as claimed in daim 11, in cluding a reset circuit having flip-flop outputs as inputs for resetting both of said flip-flops when both are set.

13. An analyzer as claimed in claim 12 wherein said reset circuit includes a gate cir cuit having an engine timing pulse as an in put for controlling flip-flop resetting.

14. An analyzer as claimed in claim 10 wherein said resetting means includes a switching circuit interconnecting the input and output of said voltage controlled oscillator.

15. An analyzer as claimed in claim 14, in eluding means connecting said feedback signal to said switching circuit in controlling rela tion.

16. An analyzer as claimed in claim 15, in cluding means connecting an engine cylinder ignition signal to said switching circuit in con tolling relation.

17. An analyzer as claimed in claim 12, wherein said means for resetting includes a switching circuit interconnecting the input and output of said voltage-controlled-oscillator, with said switching circuit and said reset cir cuit controlled by the same timing signal to reset said flip-flops and said oscillator at sub stantially the same time.

18. An analyzer as claimed in claim 17, wherein said timing signal is said feedback signal.

19. An analyzer as claimed in claim 17, wherein said timing signal is an engine cylinder ignition signal.

20. An engine ignition analyzer as claimed in claim 1, and substantially as hereinbefore described with reference to the accompanying drawings.

21. A method of retarding and advancing the triggering of a strobe lamp and sweeping the oscilloscope of an engine ignition analyzer with respect to a timing adjustment reference point of an engine, including the steps of: detecting the occurrence of engine ignition events; generating an increasing ramp voltage and a decreasing ramp voltage synchronised with an engine ignition event; triggering the oscilloscope sweep with the increasing ramp voltage; generating a reference voltage of a magnitude varying as a function of the desired strobe lamp triggering deviation from the adjustment reference point; selecting one of the ramp voltages depending on whether the strobe lamp triggering is to be retarded or advanced; and triggering the strobe lamp when the selected voltage and the reference voltage are matched.

22. The method claimed in claim 21, including the step of triggering the strobe lamp in synchronism with the engine number 1 cylinder ignition event when the desired amount of deviation is zero.

23. The method claimed in claim 21 including the steps of generating a ramp voltage for each cylinder of the engine; and inhibiting strobe lamp triggering except in conjunction with a selected one of the engine cylinder ignition signals.

24. The method claimed in claim 23 including inhibiting strobe lamp triggering except for the number 1 cylinder ignition signal when retarded triggering is desired and inhibiting strobe lamp triggering except for the number N cylinder ignition signal when advanced triggering is desired, where N is the number of the cylinder firing just before cylinder number 1.

25. The method claimed in any one of claims 21-24 wherein said step of generating an increasing ramp voltage synchronized with an engine ignition event includes the steps of: detecting the occurrence of an engine ignition event and providing a reference signal corresponding to such event; generating a ramp voltage; generating a feedback signal when the ramp voltage reaches a predetermined value; and detecting the difference in phase between the reference signal and the feedback signal and when the signals are out of phase, vary ing the slope of the ramp voltage in a direction to decrease the phase difference between the signals.

26. The method claimed in claim 25 including the step of resetting the ramp voltage to the initial value after the voltage reaches the predetermined value.

27. The method claimed in claim 25 including the step of resetting the ramp voltage to the initial value on occurrence of an engine ignition event.

28. A method of retarding and advancing the trigger of a strobe lamp and sweeping the oscilloscope of an engine ignition analyzer substantially as hereinbefore described with reference to the accompanying drawings.