IGNITION SYSTEM TEST INSTRUMENT AND METHOD

• US 3,793,584 A
• Filed: 03/16/1971
• Issued: 02/19/1974
• Est. Priority Date: 03/16/1971
• Status: Expired due to Term

• Current Assignee: Leonard N. Liebermann, Stanley H. Lai
• Original Assignee: Leonard N. Liebermann, Stanley H. Lai
• Inventors: Liebermann, Leonard N., Lai, Stanley H.
• Primary Examiner(s): Lynch, Michael J.
• Application Number:
  US05/124,677
• Time in Patent Office: 1,071 Days
• Field of Search: 324/15,16,16S,73,17,18 73/116-118
• US Class Current: 324/399
• CPC Class Codes: F02P 17/12 Testing characteristics of the spark, ignition voltage or current testing of sparking plugs H01T13/60
• CPC Class Codes: F02P 2017/003 using an inductive sensor, e.g. trigger tongs
• CPC Class Codes: F02P 2017/006 using a capacitive sensor

Abstract

An instrument and method are disclosed for testing an internal combustion engine ignition system to determine that the spark plugs, cables, coil, and other ignition system components are operating properly and for pinpointing sources of ignition system malfunction. The firing voltage, spark intensity and leakage are tested with respect to each spark plug, and the results indicated on an easily readable meter, without the necessity for an oscillosocpe. In a preferred embodiment, a non-ohmic probe is employed to obtain the spark plug signals, making it unnecessary to disconnect the spark plug leads for test purposes or to employ an ohmic ground connection.

Claims

1. A test instrument for an ignition system including spark plugs supplied sequentially with ignition voltage waveforms for causing spark discharges thereat, each such ignition voltage waveform having a peak voltage characteristic, a spark discharge characteristic and an oscillatory characteristic, comprising:

a bistable selector circuit responsive to signals at first and second trigger terminals for switching respectively to SELECT and NONSELECT states;

a probe connected to said first trigger terminal and capable of contacting any selected one of such spark plugs for supplying signals representative of the ignition voltage waveforms at such selected spark plug to actuate the bistable circuit to its SELECT state;

triggering means connected to the second trigger terminal for switching said selector circuit to its NONSELECT state prior to the next sequential ignition voltage waveform supplied to such spark plugs;

at least one test circuit responsive to actuation of the selector circuit to its SELECT state for measuring one of said characteristics of ignition voltage waveforms supplied to the selected spark plug said test circuit having an output meter, the time constant of which is substantially longer than the time between ignition voltage waveforms supplied to such selected spark plug, for indicating the average of such characteristic;

whereby the average characteristic for any spark plug may be determined by contacting said probe thereto.

2. A test instrument as defined in claim 1 wherein said probe is an electrostatic probe formed of a shielded cable with a short length of unshielded conductor extending therefrom.

3. A test instrument as defined in claim 1 contained in a housing having a handle portion forming a quasi-ground terminal for said instrument when held by a human operator.

4. A test instrument as defined in claim 1 wherein said test circuit measures the peak voltage characteristic of the ignition voltage waveform, said test circuit including capacitive storage means for charging to a voltage proportional to such peak voltage;

and amplifying means for supplying a signal representative of said voltage to the output meter;

said amplify means being actuable by the selector circuit when the selector circuit is switched to its SELECT state, whereby the average peak voltage applied to the selected spark plug is indicated by the output meter.

5. A test instrument as defined in claim 1 wherein said test circuit measures the spark discharge characteristic of the ignition voltage waveform, said test circuit including a timing circuit responsive to the ignition voltage waveform for providing timing signals representative of the elapsed time between the peak voltage characteristic and the termination of the spark discharge characteristic of said waveform, said timing circuit being connected to the bistable selector circuit for actuation thereby only when said selector circuit is switched to its SELECT state, whereby the output meter indicates the average spark discharge time for such spark plug.

6. A test instrument as defined in claim 1 wherein said test circuit measures the oscillatory characteristic of such ignition voltage waveform, said test circuit including a threshold device responsive to excursions of a predetermined polarity of the ignition voltage waveform for actuating the output meter proportionally to the time integral of said excursions.

7. A test instrument as defined in claim 1 including a second probe for deriving ignition voltage waveforms from the ignition coil of the ignition system and supplying them to the test circuit, whErein said probe is an electrostatic probe having an unshielded metallic portion of sufficient area to electrostatically derive signals from an adjacent signal source yet small enough in area to preclude interference from other more distant signal sources within the ignition system under test.

8. A test instrument as defined in claim 7 wherein said test circuit measures the peak voltage characteristic of said ignition voltage waveform, said test circuit including capacitive storage means for charging to a voltage proportional to such peak voltage derived by said second probe;

and amplifying means for supplying a signal representative of said voltage to the output meter;

said amplifying means being actuable by the selector circuit when the selector circuit is switched to its SELECT state, whereby the average peak voltage supplied to the selected spark plug is indicated by the output meter;

said triggering means comprising a time delay circuit for switching the selector circuit to its NONSELECT state a predetermined time interval after actuation to its SELECT state.

9. A test instrument as defined in claim 7 wherein said test circuit measures the average spark discharge characteristic of the ignition voltage waveform supplied to the selected spark plug, said test circuit including a timing circuit for providing timing signals representative of the elapsed time between the peak voltage characteristic and the termination of the spark discharge characteristic of said waveform, including second triggering means connected to the second probe for supplying singals therefrom representative of the termination of the spark discharge characteristic in each ignition voltage waveform to said second trigger terminal of the selector circuit for switching the latter to its NONSELECT state.

10. A test instrument as defined in claim 7 wherein said test circuit measures the oscillatory characteristic of such ignition voltage waveform, said circuit including a threshold device connected between the second probe and the output meter responsive to excursions of a predetermined polarity of the ignition voltage waveform for actuating the output meter proportionally to the time integral of said excursions, said threshold device being actuated by the selector circuit when the latter is switched to its SELECT state.

11. A test instrument as defined in claim 8 contained in a housing having a handle portion forming a quasi-ground terminal for said instrument when held by a human operator.

12. A test instrument as defined in claim 9 contained in a housing having a handle portion forming a quasi-ground terminal for said instrument when held by a human operator.

13. A test instrument as defined in claim 10 contained in a housing having a handle portion forming a quasi-ground terminal for said instrument when held by a human operator.

14. A test instrument as defined in claim 11 including a second test circuit for measuring the average spark discharge characteristic and switching means for actuating said second test circuit, said second test circuit including a timing circuit responsive to the ignition voltage waveform for providing to the output meter timing signals representative of the elapsed time between the peak voltage characteristic and the termination of the spark discharge characteristic of said waveform, including means connected to the second probe for supplying signals therefrom representative of the termination of the spark discharge characteristic in each ignition voltage waveform to said second trigger terminal of the selector circuit for switching the latter to its NONSELECT state.

15. A test instrument as defined in claim 14 including a third test circuit capable of being actuated by said switching means to measure the oscillatory characteristic of the ignition voltage waveform, said third circuit including a threshold device connected between the second probe and the output meter and responsive to excursions of a predetermined polarity of the ignition vOltage waveform for actuating the output meter proportionally to the time integral of said excursions, said threshold device being actuated by the selector circuit when the latter is switched to its SELECT state.

16. A test instrument for an ignition system including at least one spark plug supplied with ignition voltage waveforms for causing spark discharges thereat, each such ignition voltage waveform having a peak voltage characteristic, a spark discharge characteristic, and an oscillatory characteristic, comprising:

a probe for deriving signals representative of said ignition voltage waveform, first, second and third test circuits, each for measuring one of said ignition voltage waveform characteristics, switching means for selectively connecting the probe to one of said test circuits, and an output meter connectable by said switching means to the selected test circuit;

said first test circuit measuring the peak voltage characteristic and including capacitance storage means for charging to a voltage proportional to such peak voltage, and amplifying means for supplying a signal representative of said voltage to the output meter for displaying thereon the average peak voltage;

said second test circuit measuring the spark discharge characteristic of the ignition voltage waveform and including a timing circuit for providing to the output meter signals proportional to the length of said spark discharge characteristic;

said third test circuit connectable by said switching means to measure the oscillatory characteristic of such ignition voltage waveform, said third test circuit including a threshold device responsive to excursions of a predetermined polarity of the ignition voltage waveform for actuating the output meter proportionally to the time integral of said excursions.