GB2267125A

GB2267125A - I.c.engine spark ignition circuit.

Info

Publication number: GB2267125A
Application number: GB9210285A
Authority: GB
Inventors: Joseph Gibson Dawson
Original assignee: Dawson Royalties Ltd
Current assignee: Dawson Royalties Ltd
Priority date: 1992-05-13
Filing date: 1992-05-13
Publication date: 1993-11-24
Also published as: GB9210285D0

Abstract

An inductance 52, e.g. a coil with a ferrite core, is located in the circuit between the coil (12, Fig. 1) and the spark plug or plugs (22). The inductance may be associated with a capacitor and a voltage controller and may be located before or after a distributor 24 and in series or parallel with the plug circuit. Many different arrangements of the inductor and its associated components are disclosed (Figs. 5 to 14). <IMAGE>

Description

ELECTRICAL CIRCUIT The present invention relates to electrical circuits for sparkignition internal combustion engines.

In a conventional spark-ignition internal combustion engine spark plugs are connected to a high voltage source such as an ignition coil -through a distributor. The distributor periodically closes a conductive path between each spark plug and the coil to enable high voltage developed by the coil to be applied across a gap defined by the spark plug electrodes.

The distributor is connected by a single high tension lead to the coil and by respective high tension leads to each of the spark plugs.

It is an object of the present invention to provide improved electrical circuits which enable the spark generated by an ignition coil to be controlled to provide enhanced ignition characteristics in the engine.

According to a first aspect of the present invention there is provided an ignition circuit for a spark ignition internal combustion engine, the circuit including a high voltage source, electrical conductor means for applying the voltage generated by the high voltage source across a spark gap defined in a spark plug wherein the circuit further includes at least one inductive element interposed between the high voltage source and the spark plug.

Preferably, the at least one inductive element is positioned in physically close proximity to the spark plug.

The ignition circuit may further include a capacitor which is also interposed between the high voltage source and the spark plug. The capacitance of the capacitor being such that a high voltage pulse applied across the capacitor by the high voltage source produces a stored charge sufficient to initiate an additional discharge at the spark plug.

The action of a capacitive element in the electrical circuit between the high voltage source and the spark plug has been fully described in International patent application number PCT/GB91/01928 of common ownership herewith.

The electrical circuit according to the present invention may also include distributor means in the case of multi-cylinder engines.

According to a second aspect of the present invention there is provided an electrical circuit for inclusion in an internal combustion engine spark-ignition system having a high-voltage source and at least one spark plug, the electrical circuit comprising at least one inductive element and may also include a capacitor.

In the case of a multi-cylinder engine, the ignition system of the internal combustion engine will also include a distributor.

The at least one inductive element may be an inductive coil, for example. Conventional pot-core technology using ferrite cores may be utilised, the resulting component constituting a complete magnetic circuit, fully screened to avoid stray magnetic fields affecting other electrical devices in a vehicle.

In addition to a capacitor which may be present in the ignition circuit, other components, intended to safeguard the capacitor and/or ensure continued functioning of the ignition circuit in the event of a capacitor failure may also be present.

The at least one inductive element may be present either in series or in parallel with the capacitor, when present, or more than one inductive element may be employed having effect in both series and parallel configurations.

In order that the present invention may be more fully understood, examples will now be described by way of illustration only with reference to the accompanying drawings, of which: Figure 1 shows a schematic illustration of a conventional ignition system for a four cylinder spark-ignition engine; Figure 2 shows a graph illustrating a typical current v. time waveform for a spark generated by an ignition circuit of the type shown in Figure 1; Figure 3 shows a generalised schematic illustration of an ignition circuit according to the present invention; Figures 4 to 8 show a portion of the circuit of Figure 3 indicating examples of configurations of inductance elements which may be employed in the ignition circuit; Figure 9 shows a complete ignition circuit embodying the examples of Figures 3 to 8;; Figure 10 shows an alternative embodiment of a parallel configuration of an inductive element; Figures 11 to 13 shown ignition circuits according to the present invention for firing two spark plugs; and Figure 14 which shows a schematic embodiment of another alternative ignition circuit according to the present invention.

In the following description, the same or similar features are referred to by common reference numerals.

Referring now to Figure 1 of the drawings and where a conventional coil-energised spark-ignition system is indicated generally at 10. The system comprises a high voltage source 12, in this case an ignition coil, a distributor 14 connected to the coil 12 by a high tension lead 16 and to the four spark plugs 18 of a four cylinder engine (not shown) by four high tension leads 20. The coil 12 and spark plugs 18 are connected to a common source of fixed potential indicated by the earth symbols 22. The high voltage from the coil 12 is conducted to each spark plug in a predetermined sequence by a rotor arm 24 which rotates in the distributor 14 in synchronism which the other mechanical components (not shown) of the engine to produce a spark at the appropriate moment to ignite the fuel/air mixture in the engine cylinder (not shown).

Figure 2 illustrates the current versus time relationship for a spark generated by an ignition circuit such as that shown in Figure 1. There is an initial "bright-line" capacitive discharge indicated by the line 30, but the spark terminates with a relatively ineffective inductive "flaring" portion indicated by the line 32.

Referring now to Figure 3 which shows a generalised ignition circuit diagram according to the present invention and which may be incorporated into an ignition circuit of the type shown in Figure 1. The circuit comprises a capacitor 40, a resistor 42 in parallel with the capacitor 40, a voltage control device 44 also in parallel with the capacitor 40, a series diode 46 having a resistor 48 in parallel therewith. The circuit also includes an inductance "network" indicated generally at 50 as a block. The inductance network may comprise one or more separate inductive elements, positioned in this embodiment, in the general position shown. This position may include either series or parallel configurations with the capacitor 40, or both series and parallel configurations together.The manner of operation and values of the components other than the inductance network 50 shown in Figure 3 are described in detail in PCT/GB91/01928. However, it will be appreciated by those skilled in the art that values may change owing to the presence of the inductance network 50.

Figures 4 to 8 illustrate ways in which the inductance network indicated as a block at 50 in Figure 3 may be put into practical effect. The block 50 has been replaced with a coil and bar symbol with reference numeral 52 (and 54 as appropriate) indicating a single inductive element (this symbol will also be used hereinafter to indicate an inductive element of any physical form). The embodiments shown in Figures 4 to 8 are merely illustrative and not exhaustive of the configurations which may be employed.

The embodiments shown in Figures 3 to 8 may provide enhancement of the capacitive spark discharge edges which provide the major part of the fuel igniting action of the spark. The inclusion of the inductive networks in the circuits allows for extended shaping of the current pulse in the spark plug gap enabling improved ignition characteristics to be achieved in the engine.

Figure 9 shows the electrical circuits of Figures 3 to 8 incorporated into an ignition system.

In the embodiments shown in Figures 3 to 9 the electrical circuits are connected in series with one or more of the spark plugs. In the arrangement shown in Figure 10, the electrical circuit of the present invention may alternatively be connected in parallel with the spark plugs to enhance spark performance.

In Figure 10 only one spark plug 18 has been shown in the interests of clarity and the ignition coil 12 has also been omitted. As shown, the capacitor 40, resistor 42, voltage control device 44 and inductance network 50 are connected as a circuit in parallel between the high tension lead 20 connecting the spark plug 18 to the distributor 14, and a fuse 60 which is connected to ground 22. In this embodiment the inductance network 50 may assume any of the configurations indicated with reference to Figures 4 to 8. In this embodiment, if the capacitor, or resistor were to fail by falling to a low impedance, the fuse 60 would fail due to the resulting high current allowing the basic ignition circuit to function although at a reduced efficiency.

Referring now to Figures 11 to 13, these figures illustrate further embodiments of the electrical circuit of the present invention. Two spark plugs are positioned in the same internal combustion engine cylinder and which are in this case intended to fire simultaneously. Such twin-plug arrangements are well known but are generally powered by duplicate ignition circuits.

Such duplicate ignition circuits have the disadvantages of increased cost and lower reliability.

Referring first to Figure 11 and where two spark plugs 70, 72 are indicated in a single engine cylinder (not shown). Each of the plugs 70, 72 are connected to a high tension lead 20 by high tension leads 74, 76 and its own enhancing circuit indicated generally at 78 and 80. Each of the circuits 78 and 80 includes a capacitor 40, resistor 42, voltage control device 44 and inductance network 50. Although in this case the sparks are intended to fire simultaneously, this arrangement allows for the possibility of out of phase sparks by adjustment of the electrical values of the circuit components. Similarly as with the embodiment of Figure 10, the inductance network 50 may assume any of the configurations shown in Figures 4 to 8.

Further spark enhancement may be achieved by the inclusion in series into the circuit in the high tension lead 20 a further circuit of the type shown in 78, 80.

Figure 12 shows a circuit where the spark plugs 70, 72 are connected to inductance networks 50 which are themselves connected by a variable resistor 80 and individually to a capacitor 40 having a variable resistor 82 in parallel therewith. As has been described above, the individual inductance or inductances within the network 50 may be connected in different configurations as indicated in Figures 3 to 8 above.

Figure 13 shows a similar circuit to that shown in Figure 12, but having variable resistors 90, 92 and 94 as indicated.

Again the same comments as made above with regard to Figure 12 apply to the actual configurations of the inductance or inductances in the networks 50.

Figure 14 shows a circuit diagram for a four cylinder sparkignition engine having an inductance indicated by the symbols at 100 in each spark plug high-tension lead 20. In this instance the inductances 100 are placed in close proximity to each spark plug 18 as part of a high-tension lead 20 to spark plug 18 connecting device. However, the inductances 100 may be placed in the lead 20 at a more remote position from the spark plug 18.

Claims

1. An ignition circuit for a spark ignition internal combustion engine, the circuit including a high voltage source, electrical conductor means for applying the voltage generated by the high voltage source across a spark gap defined in a spark plug wherein the circuit further includes at least one inductive element interposed between the high voltage source and the spark plug.

2. An ignition circuit according to claim 1 further including at least one capacitor which is also interposed between the high voltage source and the spark plug.

3. An ignition circuit according to either claim 1 or claim 2 further including distributor means in the case of a multicylinder engine.

4. An ignition circuit according to any one preceding claim wherein the at least one inductive element is an inductive coil.

5. An ignition circuit according claim 4 wherein the at least one inductive coil also has a core.

6. An ignition circuit according to claim 5 wherein the core is a ferrite material.

7. An ignition circuit according to any one preceding claim wherein the at least one inductive element is positioned physically close to its respective spark plug.

8. An ignition circuit according to any one preceding claim from 2 to 7 wherein the at least one inductive element is present in series relationship with the at least one capacitor.

9. An ignition circuit according to any one preceding claim from 2 to 7 wherein the at least one inductive element is present in parallel relationship with the at least one capacitor.

10. An ignition circuit according to any one preceding claim from 2 to 7 wherein there are inductive elements in both series and parallel relationship with the at least one capacitor.

11. An ignition circuit according to any one preceding claim from 2 to 10 wherein the at least one capacitor is associated with other components to assure continued functioning of the circuit in the event of a capacitor failure.

12. An ignition circuit according to claim 11 wherein the other components include a resistor in parallel with the at least one capacitor.

13. An ignition circuit according to claim 11 wherein the other components include a voltage control device in parallel with the at lest one capacitor.

14. An electrical circuit for inclusion in an ignition circuit including a high voltage source and at least one spark plug for a spark ignition internal combustion engine, the electrical circuit comprising at least one inductive element.

15. An electrical circuit according to claim 14 also including at least one capacitor.

16. An electrical circuit according to claim 15 further including other components to ensure continued functioning of the ignition circuit in the event of a capacitor failure.

17. An electrical circuit according to claim 16 wherein the other components include a resistor in parallel with the at least one capacitor.

18. An electrical circuit according to claim 16 wherein the other components include a voltage control device in parallel with the at least one capacitor.

19. An electrical circuit according to any one preceding claim from 14 to 18 which is positioned physically close to the at least one spark plug.

20. An ignition circuit for a spark ignition internal combustion engine substantially as hereinbefore described with reference to the accompanying description and any of Figures 3 to 14 of the drawings.

21. An electrical circuit for inclusion in an ignition circuit including a high voltage source and at least one spark plug for a spark ignition internal combustion engine. Substantially as hereinbefore described with reference to the accompanying description and any of Figures 3 to 14 of the drawings.