GB2157007A - Testing an ignition circuit of an internal combustion engine - Google Patents

Abstract

A tester for testing an ignition circuit of an internal combustion engine comprises a pair of points simulating contacts 12 in a test circuit and control means including a relay coil 13 and relay contacts 14 in series with the coil 13 in a control circuit for controlling the operation of the contacts 12. The control circuit includes a time delay capacitor 15 which may be connected in parallel across the relay coil 13 to provide a delay-on configuration or in series with the coil 13 to provide a delay-off configuration. An ignition circuit capacitor simulating means is provided by a capacitor 20 connected in parallel across the contacts 12. A first push-button switch 21 isolates the simulating capacitor 20 from the contacts 12. A second push-button switch 30 isolates the control circuit from a circuit continuity and resistivity indicating light emitting diode 25. <IMAGE>

Description

SPECIFICATION F03A tester for testing an ignition circuit of an internal combustion engine The invention relates to a tester for testing an ignition circuit of an internal combustion engine and in particular to a tester for testing the ignition circuit of a vehicle internal combustion engine.

Various testers have been devised to locate a fault in the ignition circuit of an internal combustion engine. Conventional voltmeters and the like are usually used for testing the circuit up to but excluding he coil and condenser however such equipment is easily damaged in use. Testing the coil and condenser circuit and the high tension circuit is particularly difficult and while bench and floor mounted sophisticated test equipment to measure spark efficiency is available such equipment is generally expensive and inconveneientto use as in some cases the equipment cannot be used without removing the coil and condenser from the vehicle. In other cases, the engine must be brought to the tester and run continually during the test.

The testing devices described in U.S. patent specification No. 2898546 and British Patent specification No. 418,317 include a pair of contacts, the operation of which are controlled by a trembler coil.

The coil and contacts are connected in series with the ignition coil of the ignition circuit so that the quality of the spark obtained depends on the condition of the ignition coil. In addition because of the configuration arcing may occur across the contacts resulting in contact deterioration.

This invention is directed towards providing an improved tester for testing the ignition circuit of an internal combustion engine which will overcome the problems with prior art tester.

According to the invention there is provided a tester for testing an ignition circuit of an internal combustion engine, the tester comprising a points simulating means in a test circuit, and control means provided in a control circuit for controlling the operation of the points simulating means, the control means including a relay means, current flowing in the control circuit controlling the operation of the points sinulating means in the test circuit.

In one embodiment of the invention the points simulating means comprises a pair of points simulating contacts.

Preferably the relay means comprises a relay coil.

In a further embodiment of the invention the time delay means includes a pair of relay contact connected in series with and operable by the relay coil.

In one embodiment of the invention the control means includes a time delay means for maintaining the points simulating means in a desired open or closed position for a desired period. Preferably the time delay means comprises a time delay capacitor.

The time delay capacitor may be connected in parallel with or in series with the relay coil.

In a further embodiment of the invention the control means also includes a resistor. Typically the resistor is connected in parallel across the time delay capacitor.

In a futher embodiment of the invention the tester comprises an ignition circuit capacitor simulating means. Typically the ignition circuit capacitor simulating means comprises a simulating capacitor which may be connected in parallel across the points simulating contacts.

Usually a first isolating means for isolating the simulating capacitor from the point simulating contacts is provided. Typically the first isolating means comprises a switch such as a push-button switch.

In a further embodiment of the invention the tester comprises a circuit continuity indicating means such as a first light emitting diode and associated resistor.

Typically a protecting second diode is connected across the first diode.

In a further embodiment of the invention the tester comprises a second isolating means for isolating the control means for the points simulating contacts from the indicating means. Usually the second isolating means comprises a switch such as a push-button switch.

In another embodiment of the invention the tester includes protection means such as a fuse.

The invention will be more clearly understood from the following description thereof given by way of example only with reference to the accompanying drawings in which: Figure l is a schematic diagram illustrating a typical ignition circuit of an internal combustion engine, Figure2 is a schematic diagram of a tester according to the invention for testing the ignition circuit of an internal combustion engine, Figure 3 is a perspective view of a box for housing the tester of Figure 2, Figure 4 is a schematic diagram illustrating the use of the tester of Figure 2 in checking one part of the ignition circuit of Figure 1, Figure 5 is a schematic diagram illustrating the use of the tester of Figure 2 in checking another part of the ignition circuit of Figure 1, Figure 6 is a schematic diagram illustrating the use of the tester of Figure 2 in checking another part of the ignition circuit of Figure 1, Figure 7 is a schematic diagram illustrating the use of the tester of Figure 2 in testing a further part of the ignition circuit of Figure 1, Figure 8 is a schematic diagram of another tester according to the invention, Figure 9 is a schematic diagram of a further tester according to the invention, Figure 10 is a schematic diagram of yet another tester according to the invention, Figure ii is a schematic diagram illustrating the use of another tester according to the invention, and Figure 12 is a schematic diagram of yet another tester according to the invention.

Referring to the drawings and initially to Figures 1 to 7 there is illustrated in Figures 2 to 7 a tester according to the invention indicated generally by the reference numeral 1 for testing the ignition circuit of a vehicle internal combustion engine, such as the ignition circuit illustrated in Figure 1. The ignition circuit is conventional and comprises a battery 2, fuses 3, an ignition switch 4, a resistor 5, an ignition coil 6, points 7, a capacitor 8, a distributor 9 and sparking plugs 10.

Referring particularly to Figure 2 the tester 1 comprises a points simulating means formed by a pair of normally open contacts 12 and control means incorporating a time delay means for maintaining the contacts 12 in a desired open or close position for a desired period. In this case the control means comprises a relay coil 13, a pair of relay contacts 14 connected in series with the coil 13 and a time delay capacitor 15 which in this case is connected in parallel across the relay coil 13. A diode 16 is also connected across the relay coild 13 to suppress back E.M.F. from the coil.

The tester 1 also includes an ignition circuit capacitor simulating means which in this case is formed by a simulating capacitor 20 connected in parallel across the points simulating contacts 12. A first isolating means for isolating the simulating capacitor 20 from the points simulation contacts 12 is provided by a normally closed push-button switch 21 connected between the contacts 12 and the capacitor 20.

Circuit continuity indicating means which also gives an indication of resistivity in the ignition points circuit is provided by a light emitting diode 25. A resistor 26 is provided on the input side of the light emitting diode 25 to prevent the diode being overloaded and a second diode 27 is connected across the light emitting diode 20 as a safety feature in the event of the input leads being incorrectly connected.

A second isolating means, in this case a second normally open push-button switch 30 is provided for isolating the relay coil 13, the time delay capacitor 15 and the relay contacts 14 from the light emitting diode 25. Another diode 31 is provided on the input side of the second push-button 30 to protect the apparatus in the event of incorrect wiring. Three terminals namely a negative terminal 35, a positive terminal 36 and a points terminal 37 are provided for connecting the tester 1 to various locations in the ignition circuit 2 as will be described in more detail below.

Referring particularly to Figure 3 the tester 1 is typically housed in a hand-held box 40 having a top wall 41, four depending side walls 42 and a removable base 43. The push-buttons 21,30 project through the top wall 41 of the box 40 as does the light emitting diode 25. Typically electrically conducting cables 44,45,46 for the respective terminals 35,36,37 extend through one side wall of the housing and each terminates in a suitable attachment means such as a crocadile clip 47 for connection to a desire location in the vehicle ignition circuit 2. In this case a protection device in the form of a fuse wire 51 is provided in the circuit adjacent the negative terminal 35 to protect the tester in the event of incorrect connection, for example, if the points lead 46 is connected to a positive power supply.The fuse could also be provided adjacent the points terminal or in any suitable location.

In use, and referring particularly to Figures 1 to 7 before testing the ignition circuit 2 of the vehicle the high tension lead is removed from the centre of the distributor cap 9 and the contacts of the ignition switch 4 are closed. The engine however is not started.

Referring particularly to Figure 4 to check the ignition circuit between the battery 2 and the ignition coil 6 the lead 44 from the negative terminal 35 is connected to a suitable earthing point such as the chassis of a car and the lead 45 from the positive terminal 36 is connected to the positive side of the ignition coil 6. No connection is made between the points terminal 37 and the ignition circuit and neither of the push-buttons 30,21 are operated so that the tester is in the configuration illustrated in Figure 1.

Power from the battery of the ignition circuit passes through the resistor 26 and reactivates the light emitting diode 25 before passing to earth through the negative terminal 35. If the ignition circuit between the battery and ignition coil 6 is in order the diode 25 will light. If the light emitting diode 25 is not activated the procedure is repeated while moving the connection from the lead 45 to the positive terminal 36 back along the ignition circuit until the fault is located as evidenced by a failure of the light emitting diode 25 to light.

Referring particularly to Figure 5 the next step is to check the wiring between the ignition coil 6 and the distributor 9. The lead 45 from the positive terminal 36 of the tester is connected to the negative side of the primary winding of the ignition coil 6. The engine is then turned manually and as the points 7 open the light emitting diode 25 should be activated. If the light emitting diode 25 does not illuminate and extinguish as the engine is turned this indicates a possible fault in the points 7 or the wiring in the distributor 9 or coil open circuit. If the light emitting diode 25 is not extinguished completely this indicates a high resistance in the ignition points circuit or dirt on the points.

Referring to Figure 6 to test the ignition coil 6 and capacitor 8 combination the first step is to ensure that the points 7 are open. The lead 45 from the positive terminal 36 of the tester is then connected to the positive side of the coil 6 and the points lead 46 from the points terminal 37 is connected on the points side of the coil 7. With the free end of the high tension lead held approximately half an inch away from the engine block remote from the carburrettor or any petrol lines both push-buttons 21,30 are pressed simultaneously so that the tester 1 acts as a points simulating means and applies an intermittent current through the coil 6 and capacitor 8 of the ignition circuit. Pressing the first push-buttons 21 takes the simulating capacitor 20 out of the tester circuit while pressing the second push-button 30 activates the relay coil 13 and associated control circuit which in turn operates the relay simulating contacts 12.

In more detail and referring particularly to Figure 2 when the second push-button 30 is pressed current is supplied which charges the capacitor 15 which is then discharged activating the relay coil 13 and opening the relay contacts 14 and closing the points simulating contacts 12. The relay coil 13 then discharges and the procedure is repeated until the second push-button 30 is released. It will be appreci ated that the size and type of the capacitor 15 and the relay contacts 14 controls the on/off action of the points simulating contacts 12 and hence the current supplied to the coil 6 and capacitor 8 combination of the ignition circuit through the points terminal 37 of the tester 1. In this configuration the capacitor 15 acts as a delay on the device.The intensity of the spark emitted from the high tension lead of the ignition coil 6 indicates whether the ignition coil 6 and capacitor 8 combination is operating correctly. If the spark is weak or non-existant there may be a fault in either the ignition coil 6 or the capacitor 8.

To test the ignition coil 6 only the tester leads are connected as illustrated in Figure 6. The points 7 and capacitor 8 of the ignition circuit are then removed electrically from the circuit by disconnecting them at a suitable point, for example at the negative terminal on the low tension side of the coil 6. The second push-button 30 only is then pressed so that the tester 1 is configured to simulate both the points and capacitor of the ignition circuit, the points simulation being provided by the points simulating contacts 12 as already described and the capacitor simulating means being provided by the capacitor 20 which is kept in the circuit by leaving the first push-button switch 21 in its normally closed position.Again, the spark from the high tension lead of the ignition coil 6 is evaluated as already described and if the spark is found to be weak the indications are that the ignition coil 6 is faulty. If the spark is weak but has improved from the previous test then the ignition coil 6 and capacitor 8 may be suspect. If the spark from the previous test is weak and the spark from the coil test is good then the capacitor 8 in the ignition circuit is suspect.

To check the distributor cap 9 and rotor arm the tester is connected as illustrated in Figure 7. The high tension lead from the ignition coil 6 is replaced in the distributor cap 9 and the ignition circuit points 7 are opened. The sparking plugs 10 are removed in turn from their sockets and positioned about a half an inch away from the engine block. Again, both push-buttons 21,30 are pressed so that the tester 1 is configured to operate as a points simulating means only and the spark is observed. This procedure is repeated for each of the plugs, a weak or nonexisting spark indicating a fault in the plug, the distributor cap or rotor arm. If the cap is removed from the distributor coil with the leads in place any arcing in the cap may be visually observed.The rotor arm resistance can also be checked by removing the cap and holding the primary lead from the " away from the rotor face no stray spark should enter the arm while inducing a high voltage with the tester.

The leads from the distributor 9 to the sparking plugs 10 may be tested separately by inserting them into the ignition coil 6 during the coil only test described above. Having proved tha the ignition coil is good a lead under the test is inserted into the core of the ignition coil directly and using the tester to generate points simulation as already described, the high voltage spark is checked at the end of the lead.

If the spark is weak the indications are that the lead under test is faulty.

If the capacitor 8 of the ignition circuit is found to be faulty and a replacement is not readily available the simulating capacitor 20 in the tester unit can be used as a replacement by removing the faulty capacitor from the ignition circuit and connecting the tester 1 as illustrated in Figures 7 or 8.

Typically the relay coil 13 is a 12 volt two pole change over relay. The time delay capacitor is typically a 50 volt 22 microforad capacitor however the tupe and capacitance of the capacitor depends on the particular type of relay used. The simulating capacitor 20 is generally a standard suppressor capacitor used on vehicles, for example a 500 volt.18 to .24 microforad capacitor.

One advantage of the tester according to the invention is that it allows a fault at any location in the ignition circuit of an internal combustion engine to be located simply safely and quickly. In experiments it has been possible to complete the various tests described above in approximately 1 to 2 minutes.

The various parts used for the tester can be easily packed into the box 40 which, while a small enough to be hand-held and hence easy to operate, still allows sufficient access for repair, if required and may be easily and cheaply manufactured.

It will be appreciated that any or all of the various elements in the tester may be replaced by integrated circuits without departing from the scope of the invention however the advantage of using capacitor, relay, diode and resistor elements is that the tester can be easily repaired if required. For example a semi conductor switch such as a transistor may provide points simulation and the control means may be provided by a bistate multivibrator.

Referring to Figure 8 there is illustrated another tester according to the invention indicated generally by the reference numeral 50 which is of similar construction to the tester described above with reference to Figures 2 to 7 and like parts are assigned the same reference numerals. Instead of the time delay capacitor 15 being connected across the relay coil 13 it is in this configuration connected in parallel across the relay contacts 14 and a two kiloohm resistor 52 in connected in parallel across the capacitor 15. In this case a multi pole change over relay is also used which has three points simulating contacts 12 arranged in parallel to simulate the points in the ignition circuit. Such a relay may be used for compactness and to extend contact life. The value of the resistor 52 used depends on the impedence of the coil,the time delay capacitor 15 and the buzz speed which is the speed with which the relay contacts are required to charge over repeatedly. Because the capacitor 15 is connected in series with the relay coil 13 it acts as a delay off device.

Referring to Figure 9 there is illustrated another tester 55 according to the invention in which parts similar to the tester described with reference to Figures 2 to 7 are assigned the same reference numerals. In this modification two pairs of normally closed relay contracts 14 arranged in series are used to buzz the relay 13.

Referring to Figure 10 there is illustrated another tester according to the invention indicated generally by the reference numeral 60 in which parts similar to those of the tester described with reference to Figure 8 are assigned the same reference numerals. In this case the relay contacts 14, time delay capacitor 15 and the resistor 52 are located on the positive side of the relay coil 13.

Refering to Figure 11 a modified tester housing box 65 is illustrated. In this case one side wall of the tester box is provided with two electrical connecting lugs 66 to which a capacitor to be tested is attached.

The tester unit is also supplied with a resistor 67 for connection between a battery 68 and a coil 69 which it is desired to test. To test the coil 69 the tester 65 is connected as illustrated in Figure 11. The second push-button 30 is then pressed and the quality of the spark obtained at the plug 10 or at the end of a high tension lead is observed. If the quality of the spark is good then the coil 69 is not faulty. To test a capacitor a coil which has passed the previous test is used and the tester is connected as in Figure 11. The capacitor to be tested is then connected across the lugs 66 and both push-buttons 21,30 are pressed. Again, if the quality of the spark obtained is good then the capacitor being tested is not faulty whereas if no spark or only a weak spark is obtained then indications are that the capacitor is faulty.A typical connection between the lugs 66 and the tester circuit is illustrated by the interrupted line 70 in Figure 10.

Referring to Figure 12 there is illustrated another tester according to the invention indicated generally by the reference numeral 80 which is of similar construction to the tester of Figure 10 and like parts are assigned the same reference numerals. In this case an additional resistor 81 is provided between the diode 31 and the push-button 30.A switch 82 in parallel with the resistor allows the unit to be switched, depending on the resistance of the resistor 81, to operate at different voltages, for example at 12 or 24 volts. In this case each pole of multi-pole contacts 12 has three contacts, one designated negative which is used in all the previously described testers, and another designated positive. The positive contacts are connected to the positive terminal 36 through a switch 85 and a resistor 86.

When the switch 85 is open, as illustrated, the tester is configured to operate in the same manner as the tester of Figure 10, however when the switch 85 is closed positive pulses appear at the points simulating terminal 37 which may be used to simulate either positive and negative pulses or negative only thus enabling various electronic ingnition circuit pick-ups to be simulated and the faultfound in the pick-up or the electronic control circuit. In this connection the term "points" as used herein includes electronic ignition circuit pick-up devices. It will of course be appreciated that any of the previously described testers may be modified in a similar manner to that described with reference to Figure 12.

Claims (27)

1. A tester for testing an ignition circuit of an internal combustion engine, the tester comprising a points simulating means in a test circuit and control means provided in a control circuit for controlling the operation of the points simulating means, the control means including a relay means, current flowing in the control circuit controlling the operation of the points simulating means in the test circuit.

2. A tester as claimed in claim 1 in which the points simulating means comprises a pair of points simulating contacts.

3. A tester as claimed in claim 1 or 2 in which the relay means comprises a relay coil.

4. A tester as claimed in claim 3 in which the control means includes a pair of relay contacts connected in series with and operable by the relay coil.

5. Atester as claimed in any of claims 1 to 3 in which the control means includes a time delay means for maintaining the points simulating means in a desired open or closed position for a desired period.

6. A tester as claimed in claim 4 in which the control means includes a time delay means for maintaining the points simulating means in a desired open or closed position for a desired period.

7. Atester as claimed in claim 5 or 6 in which the time delay means comprises a time delay capacitor.

8. A tester as claimed in claim 7 when dependent on claim 6 in which the time delay capacitor is connected in parallel across the relay coil.

9. Atester as claimed in claim 7 when dependent on claim 6 in which the time delay capacitor is connected in series with the relay coil.

10. A tester as claimed in claim 9 in which the time delay capacitor is connected in parallel across the relay contacts.

11. Atester as claimed in any of claims 7 to 10 in which the control means includes a resistor.

12. Atester as claimed in claim 11 in which the resistor is connected in parallel across the time delay capacitor.

13. Atester as claimed in any preceding claim comprising an ignition circuit capacitor simulating means.

14. Atester as claimed in claim 13 in which the circuit capacitor simulating means comprises a simulating capacitor.

15. Atester as claimed in claim 14 in which the simulating capacitor is connected in parallel across the points simulating means.

16. A tester as claimed in claim 15 comprising a first isolating means for isolating the simulating capacitor from the points simulating means.

17. Atester as claimed in claim 16 in which the first isolating means comprises a switch.

18.1Atester as claimed in claim 16 or 17 in which the first isolating comprises a push-button switch,

19. A tester as clamed in any preceding claim comprising circuit continuity indicating means.

20. Atester as claimed in claim 19 in which the circuit continuity indicating means comprises a first light emitting diode and an associated resistor.

21. A tester as claimed in claim 20 in which a protecting second diode is connected across the first diode.

22. Atester as claimed in any of claims 19 to 21 comprising a second isolating means for isolating the control means for the points simulating means from the indicating means.

23. A tester as claimed in claim 22 in which the second isolating means comprises a switch.

24. A tester as claimed in claim 22 or claim 23 in which the switch comprises a push-button switch,

25. A tester as claimed in any preceding claim including incorrect connection protection means.

26. A tester as claimed in claim 25 in which the protection means comprises a fuse.

27. A tester substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.