GB2172655A

GB2172655A - Ignition system for an internal combustion engine

Info

Publication number: GB2172655A
Application number: GB08604202A
Authority: GB
Inventors: Heinz Decker; Hans-Ulrich Gruber
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1985-02-21
Filing date: 1986-02-20
Publication date: 1986-09-24
Also published as: GB8604202D0; EP0192167A1; JPS61194062A; DE3505998A1

Description

1

SPECIFICATION

Ignitilion system for an internal combustion engine The invention relates to an engine ignition system having a voltage transformer, ignition transformers, and electronic switches for connecting the primary windings of the ignition transformers to the voltage transformer.

A similar ignition system is already known (International Application No. WO 84/00 402), in which it may however happen that the fueI/air mixture does not ignite because the dura- tion or the energy of the ignition spark is inadequate.

The present invention consists of an ignition system for an internal combustion engine having a voltage transformer, a plurality of igni- tion transformers, a plurality of electronic switches and a plurality of breakdown type spark plugs, wherein one of the primary windings belonging to the ignition transformers may be connected to the voltage transformer by way of one of the electronic switches, and one of the second windings belonging to the ignition transformers supplies at least one of the spark plugs with ignition voltage.

Such an ignition system satisfactorily elimi- nates the above shortcoming.

The invention is further described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a circuit diagram of an ignition system according to the invention, and Figure 2 shows a partly sectional view of one of the spark plugs used in said system.

The ignition system shown in Fig. 1 is intended for a four-cylinder, fourstroke internal combustion engine (not shown) in a motor vehicle (also not shown). The ignition system is supplied from a direct current source 1, which may be the battery of the motor vehicle. A lead 3 runs from the negative pole of the current source 1, to earth 2, and a supply lead 5 containing an operating switch 4 leads from the positive pole. The supply lead 5 branches out to a DC/AC converter 6 and to a sensor unit 7. At the output of the con- verter 6 for single or multiple charging is the 115 primary winding 8 of a step-up transformer 9, whose secondary winding charges a storage capacitor 12 during operation by way of a rectifier 11. The circuit elements 6, 9, 11 thus form a DC/DC converter 13 shown by a 120 broken line in the drawing. Furthermore, four ignition transformers 14, four-spark plugs 15 and four electronic switches (preferably thyris tors) 16 are provided, whereby, at the instant of ignition, one of the primary windings 17 125 belonging to the ignition transformers 14 can be connected by way of one of the electronic switches 16 to the storage capacitor 12, and one of the secondary windings 18 belonging to the ignition transformers 14 supplies one of130 GB2172655A 1 the spark plugs 15 with ignition voltage. In accordance with the invention, breakdown spark plugs are used in the present case, which are provided with a capacitor 19 in the region of the point of ignition spark generation.

Using the sensor unit 7, the spark plugs 15 are fired in a prescribed sequence in dependence upon predetermined angular positions of the crankshaft or camshaft.

When assembled, the breakdown spark plug 15, 19 preferably forms a structural unit 20 with the ignition transformer 14 and the electronic switch 16, for example by accomodat- ing the ignition transformer 14 and the electronic switch 16 (as indicated in Fig. 2) in a plug housing 21 which is attachable to the breakdown spark plug 15, 19. The plug housing 20 has two leads, namely a lead 7' lead- ing to the sensor unit 7 and a lead 12' leading to the storage capacitor 12.

The breakdown spark plug 15, 19 is characterised by the fact that the capacitor 19 is in the immediate vicinity of the electric spark- over (ignition spark). The electric spark-over takes place at the air gap 22 between the centre electrode 23 and the earth electrode 24. The earth electrode 24 is joined to a cylindrical metal housing 25 surrounding a die- lectric insulator 26.

The centre electrode 23 contiguous with the secondary winding 18 runs in the direction of the longitudinal centre axis of the insulator 26 and, if necessary, can contain a series spark 100 gap 27 formed by the insertion of a break. This series spark gap 27 forms a series connection with the spark plug 15 in parallel with the capacitor 19, and can, in certain circumstances, cause an improvement in breakdown 105 ignition.

In the present case amongst others, the capacitor 19 is formed by cylindrical plates 28 which are inserted in the insulator 26. The inner plate is formed by the surface of the centre electrode 23, and the outer plate is formed by an elecrically conductive continuation 25' of the insulator housing 25. The electrically conductive continuation 5', which may also be a metal coating sprayed onto the insulator 26, can be used not only in connection with a capacitor, but also, advantageously, to connect the switching arrangement in the plug housing 21 to earth, so that the plug housing 21 may be a sprayed coating of plastic, preferably a heat-resistant plastic, such as polyimide.

Of course, the capacitor 19 may also be a tubular solid-state capacitor or a wound capacitor.

A plurality of spark plugs may also be associated with a secondary winding and these spark plugs may be in different cylinders of the internal combustion engine, as is sometimes used in so-called---steady- ignition distribution. The switches 16 may also be sepa- 2 GB2172655A 2 rated constructionally from the transformers 14.

In the simpliest case, only one ignition coil may be located, as a voltage transformer, at the current source, whereby at the instants of ignition, the current in its primary winding is interrupted and one of the switches 16 closes the secondary circuit of this ignition coil by way of the primary winding 17 of one of the transformers 14.

Claims

1. An ignition system for an internal combustion engine having a voltage transformer, a plurality of ignition transformers, a plurality of electronic switches and a plurality of breakdown type spark plugs, wherein one of the primary windings belonging to the ignition transformers may be connected to the voltage transformer by way of one of the electronic switches, and one of the secondary windings belonging to the ignition transformers supplies at least one of the spark plugs with ignition voltage.

2. An ignition system as claimed in Claim 1, in which a storage capacitor is connected to the voltage converter so as to be charged thereby and, at corresponding instants of ignition, one of the primary windings belonging to the ignition transformers can be connected to the storage capacitor by one of the electronic switches so that the respective breakdown type spark plug obtains its ignition energy from the storage capacitor.

3. An ignition system as claimed in claim 1 or 2, in which each breakdown type spark plug incorporates a capacitor close to the point of ignition and in parallel with the spark electrodes.

4. An engine ignition system constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

Printed in the United Kingdom for Her Majesty's Stationery Office. Dd 8818935, 1986. 4235. Published at The Patent Office. 25 Southampton Buildings, London. WC2A lAY, from which copies may be obtained.