IGNITION SYSTEM

Abstract: An ignition system is described for an engine having four cylinder (51 to 54). Cylinders (52, 53, 54) lag cylinder (51) by 180°, 90° and 270° of camshaft rotation. Each cylinder has a pair of spark plugs (55, 56). The system includes a pair of primary windings (60, 61) coupled respectively to a first and second pair of secondary windings (62 to 65). Winding (62) is connected to plugs (55) in cylinders (51, 52) and wind­ ing (63) is connected to plugs (56) in cylinders (51, 52) Wind­ ings (64, 65) are connected to the plugs in cylinders (53, 54) in a similar manner. Windings (60, 61) are connected to a power supply (70) through switches (73, 74) operated by a control unit (75) so as to produce sparks in each cylinder at appropriate instants during compression strokes. When, for example, sparks are produced in cylinder (51) during a compression stroke, sparks will also be produced in cylin­ der (52) which will be executing an exhaust stroke. Because of the lower pressure associated with an exhaust stroke, the voltage required in windings (62, 63) is less than twice that required to produce the spark in cylinder (51).

Description: IGNITION SYSTEM This invention relates to an ignition system for a multi-cylinder engine. In US-A-4 177 782, there is described an ignition system in which the two ends of the secondary winding of an ignition coil are connected to the insulated terminals of two igniters mounted in an engine cylinder. The other terminal of each igniter is connect to ground. In order'to create a spark in each igniter with a voltage across the secondary winding which is less than twice the breakdown voltage of the individual igniters, an impedence element is connected between one end of the secondary winding and ground. Thus, this system suffers from the disadvantage that an impedence element must be provided. Moreover, if the impedence element fails, no sparks will be created. It is an object of this invention to provide a new or improved ignition system for a multi-cylinder engine in which there are two igniters in each cylinder and in which the above mentioned disadvantage is overcome or reduced. According to this invention, there is provided an ignition system for a multi-cylinder internal combustion engine comprising two igniters in each cylinder of the engine, each igniter having a first terminal and a second terminal and the second terminals being electrically connected to the engine cylinder block, a primary winding arrangement, a set of secondary windings equal in number to the number of cylinders and magnetically coupled to the primary winding arrangement and means for controlling current flow in the primary winding arrangement in accordance with the timing conditions relating to the cylinders characterized, in that the secondary windings are grouped to form one or more pairs, the or each pair being associated with a respective pair of cylinders, and the or each pair of secondary windings is connected to the igniters of the associated pair of cylinders such that the two ends of one winding of the pair are connected to respective first terminals of one igniter in one cylinder and one igniter in the other cylinder and the two ends of the other winding are connected to respective first terminals of the other igniter in said one cylinder and the other igniter in the other cylinder. With the system of the present invention, it may be arranged that, each time one of the secondary windings provides a high voltage, one of the associated igniters will be under compression pressure and the other igniter will be under exhaust pressure. In the igniter under exhaust pressure, a spark will be created at a voltage which is lower than that required in the igniter under compression pressure. Consequently, the present invention provides a system in which sparks are created with a voltage across each secondary winding which is less than twice the breakdown voltage of an igniter under compression pressure without the need to connect an impedance element between one end of the secondary winding and ground. This invention will now be described in more detail, by way of example, with reference to the drawings in which: Figure 1 is a circuit diagram of an ignition system embodying this invention; and Figure 2 is a circuit diagram of another ignition system embodying this invention. Referring now to figure 1, there is shown an ignition system for an internal combustion engine having four cylinders 11 to 14. The cylinders 12, 13 and 14 lag the cylinder 11 in operation respectively by 1800, 900 and 2700 of cam shaft rotation. Each of the cylinders is provided with a pair of igniters in the form of a pair of spark plugs 15, 16. Each spark plug has a central electrode electrically isolated from its metallic body and an earth electrode which is connected to the metallic body. The central electrode provides a first terminal and the earth electrode provides a second electrode. Because the metallic body is mounted in the cylinder block, the earth electrode is electrically connected to the cylinder block. The ignition system also includes four primary windings 21 to 24 each of which is individually magnetically coupled to a respective one of four secondary windings 25 to 28 by magnetic cores 17 to 20. The secondary windings 25 to 28 are grouped to form a first pair comprising windings 25 and 26 and a second pair which comprises windings 27 and 28. The pair of windings 25, 26 is associated with the pair of cylinder 11 and 12, and the pair of windings 27, 28 is associated with the pair of cylinders 13 and 14. The two ends of secondary winding 25 are connected to the central electrode of spark plug 15 in cylinder 11 and the central electrode of spark plug 15 in cylinder 12. The two ends of secondary winding 26 are connected to the central electrode of spark plug 16 in cylinder 11 and the central electrode of spark plug 16 in cylinder 12. The pair of windings 27 and 28 are connected to the spark plugs in the pair of cylinder 13, 14 in a similar manner. The system also includes a power supply 30 supplying positive and negative supply rails 31 and 32. The power supply 30 may simply be a battery or it may be a battery together with a DC/DC converter. A capacitor 33 is connected between rails 31 and 32. The rail 31 is connected to one end of each of the primary windings 21 to 24. The other end of each of primary windings 21 to 24 is connected through a respective one of a set of thyristors 35 to 38 to rail 32. The gates of thyristors 35 to 38 are connected to a control unit 40. The control unit 40 fires the thyristors 35 to 38 with desired timing. Specifically, thyristors 35 and 36 are fired simultaneously, or nearly simultaneously, when one of cylinders 11 and 12 is performing a compression stroke and at the instant that the spark is required in the cylinder performing the compression stroke. Thyristors 37 and 38 are fired in a similar manner. When, for example, cylinder 11 is performing a compression stroke and thyristors 35 and 36 are fired, capacitor 33 will discharge through windings 21 and 22. This will cause a high voltage to be generated across both secondary windings 25 and 26. Because the earth electrodes of plugs 15, 16 are commonly connected, this high voltage will cause a spark to be created in the plugs 15, 16 in both cylinders 11, 12. Thus, sparks will be produced in cylinder 11 at the required instant. Sparks will also be created in cylinder 12. However, because cylinder 12 lags cylinders 11 by 1800, this cylinder will be performing an exhaust stroke and so the sparks will be of no consequence. Each time one of the secondary windings 25 to 28 produces a high voltage, the gap of one of the associated spark plugs will be under compression pressure and the other will be under exhaust pressure. When a gap is under exhaust pressure, a spark is produced with a lower voltage and a lower energy than that required for a gap under compression pressure. Thus, each of the windings 25 to 28 produces sparks in its associated plugs 15, 16 with a voltage and energy which is less than twice that which would be required if both plugs were under compression pressure. Referring now to figure 2, there is shown an ignition system for an engine having four cylinders 51 to 54 which are similar to the cylinders 11 to 14 shown in figure 1. The cylinders 51 to 54 are each provided with a pair of spark plugs 55, 56 which are similar to the plugs 15, 16 shown in figure 1. This ignition system also includes a pair of primary windings 60, 61. The winding 60 is magnetically coupled with a pair of secondary windings 62, 63 by a magnetic core 57 and the winding 61 is magnetically coupled to a pair of secondary windings 64, 65 by a magnetic core 58. The windings 62 to 65 are connected to the plugs 55, 56 in cylinder 51 to 54 in a similar manner to the connections between windings 25 to 28 and plugs 15, 16 in Figure 1. The system further includes a power supply 70 which is similar to. the power supply 30 and which supplies power to a positive supply rail 71 and a negative supply rail 72. The rail 71 is connected to one end of each of primary windings 60, 61. The other end of each of these windings 60, 61 is connected through a respective switch 73, 74, which may be a transistor, to the rail 72. The switches 73, 74 are controlled by a control unit 75. In operation, the control unit 75 turns on and off switches 73 and 74 with desired timing. When, for example, switch 74 is turned on, current flows in the primary winding 60. When this switch is turned off, a high voltage appears across each of secondary windings 62 and 63 thereby causing ignition sparks to be generated in the spark plugs 55, 56 in each of cylinders 51 and 52. Thus, the switch 74 is switched on shortly before sparks are required in either one of cylinders 51 and 52 and turned off at the instant the sparks are required. The system shown in Figure 2 possesses the advantage over the system shown in Figure 1 that only two primary windings are required. Although the ignition system of Figure 1 is of the capacitive discharge type and the system of Figures 2 is of the inductive discharge type, it is to be appreciated that the systems of Figure 1 could be modified so as to be of the inductive discharge type and the systems of Figures 2 could be modified to be of the capacitive discharge type. Also, although the systems of Figure 1 and 2 and are shown with a four cylinder engine, it is to be appreciated that they could be applied with suitable modification to any engine having one or more pairs of cylinder by providing a pair of secondary windings for each pair of cylinders. In both of the systems described above, the two spark plugs of each cylinder are energised without the necessity of providing a complicated distributor. Because a distributor is not provided, the high voltage leads to the spark plug can be kept short thereby minimising the radio frequency interference which is associated with high voltage leads and wet weather ignition problems which are also associated with such leads.

Claims: CLAIMS. 1. An ignition system for a multi-cylinder internal combustion engine comprising two igniters (15, 16; 55, 56) in each cylinder (11 to 14; 51 to 54) of the engine, each igniter (15, 16; 55, 56) having a first terminal and a second terminal and the second terminals being electrically connected to the engine cylinder block, a primary winding arrangement (21 to 24; 60, 61), a set of secondary windings (25 to 28; 62 to 65) equal in number to the number of cylinders (11 to 14; 51 to 54) and magnetically couplied the primary winding arrangement (21 to 24; 60, 61), and means (35 to 38, 40; 72, 73, 75) for controlling current tow in the primary winding arrangement in accordance with the timing conditions relating to the cylinders (11 to 14; 51 to 54), characterized in that the secondary windings (25 to 28; 62 to 65) are grouped to form one or more pairs, the or each pair being associated with a respective pair of cylinders (11 to 14; 51 to 54), and the or each pair of secondary windings (25 to 28; 62 to 65) is connected to the igniters (15, 16; 55, 56) of the associated pair of cylinders (11 to 14; 51 to 54) such that the two ends of one winding of the pair are connected to respective first terminals of one igniter in one cylinder and one igniter in the other cylinder and the two ends of the other winding are connected to respective first terminals of the other igniter in said one cylinder and the other igniter in the other cylinder. 2. An ignition system as claimed in claim 1, characterised in that the two ends of each secondary windings (25 to 28; 62 to 65) are connected directly to the first terminals of the two associated igniters (15, 16; 55, 56). 3. An ignition system as claimed in claim 1 or claim 2, characterised in that the primary winding arrangement comprises an individual primary winding (21 to 24) for each secondary winding (25 to 28), each primary winding being individually magnetically coupled to its associated one of the secondary windings. 4. An ignition system as claimed in claim 1 or claim 2, characterised in that the primary winding arrangement comprises an individual primary winding (60, 61) for the or each pair of secondary windings (62 to 65), each primary winding being individually magnetically coupled to its associated pair of secondary windings.

Inventors: JONES, PETER DAVID, LEE, MICHAEL JOHN, QASRAWI, AZZAM MOHAMMED SAID
Applicants: LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1986
Main classification: F02P15
IPC codes: F02P7, F02P15