GB1583307A

GB1583307A - Ignition circuit for internal combustion engines

Info

Publication number: GB1583307A
Application number: GB1556278A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-12-31
Filing date: 1978-04-20
Publication date: 1981-01-21
Also published as: JPS6149501B2; JPS5496636A; DE2759154A1; DE2759154C2

Description

(54) IGNITION CIRCUIT FOR INTERNAL COMBUSTION ENGINES (71) We, ROBERT BOSCH GMBH, a German Company of Postfach 50, 7 Sturt- gart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to an ignition circuit for the ignition system of an internal combustion engine.

In the case of a known such ignition circuit (see German Patent Specification Auslegeschrift 2 244 781) a particularly favourable current flow time is achieved with the assistance of a closed angle control device.

Ignition systems using such a device may present problems because the ignition voltage changes during loading, especially when a high capacitive load or dirt on the spark-plug produces a reduced ignition voltage or a shorter discharge period.

The object of the invention is to provide an ignition circuit wherein such load changes cannot affect ignition performance.

There is provided by the present invention an ignition circuit system of an internal combustion engine having an ignition coil, the circuit comprising an electronic switch which in use of the circuit is connected in series with the primary winding of the ignition coil and whose current-conductive state determines the closed angle, and a regulating circuit for changing the closed angle in dependence upon an operational variable of the internal combustion engine, wherein the spark discharge period is regulated by the regulating circuit to a constant or predeterminable time value.

The particular advantage in the ignition circuit according to the invention is that load influences on the secondary side of the ignition coil and also influences on the primary side, such as, for example, fluctuating battery voltage, are practically eliminated.

Further, the circuit may be such that the discharge current has a very low loss, and the regulating circuit may be arranged to compare the duration of a specific discharge current level (for example, 5 or lOmA) with a desired time value (for example, 1 millisecond).

When the discharge period is shorter than the desired time value, then the regulating circuit causes the closed time and the closed angle to be increased, and vice versa. Regulation of this type is possible, for example, with the assistance of a known circuit comprising a monostable trigger stage with a capacitor which determines the trigger period and whose discharge current is increased to reduce the trigger period. The desired value for the discharge period may be changed in dependence upon rpm and possibly load and be adapted to the respective requirements of the internal combustion engine; for example, a long discharge period of 2ms can be set at low rpms and a short discharge period of 0.5ms can be set at high rpms.An adaptation of this type is also possible by the closed angle being limited in a simple manner so that there is no possibility of falling below a specific minimum opening time, for example, 400 Ls.

In the event of a so-called misfiring which is caused, for example, by a defective sparkplug cable and produces no discharge, the regulating circuit sets the maximum closed angle for the subsequent ignition process. In the event of a misfiring also occuring again subsequently, though this seldom happens in practice, the known surge-protection measures may be provided to protect the power transistor and the insulating parts used, for example, the insertion of a Zener diode clamping between the base and the collector of the power transistor.

To illustrate the invention, one embodiment is shown in the drawing. Figure 1 shows a block wiring diagram for an ignition system using a circuit of the invention, and Figure 2 shows the time curve of the spark discharge current iF and the desired value of the discharge period tF.

The ignition system shown in Figure 1 comprises a permanent magnetic signal generator G which is connected to the crank shaft or the distributor shaft of an internal combustion engine, not shown, and, during one revolution, supplies four trigger pulses one for each of the ignition processes described hereinafter. The generator G cooperates with a closed angle control circuit K (such as, for example, described in German Offenlegungsschrift 2 424 896 and 2 549 586) comprising a capacitor C which influences the closed/open state of a final stage E connected on the load side. The final stage comprises a power transistor T connected in series with the primary winding W1 of a high-voltage ignition coil ZS, and to the positive pole P of the circuit which is at the battery potential.

The distributor spark gap of a conventional .ignition distributor (not shown) is in series with the secondary winding W2 of the ignition coil ZS, the spark discharge current being conducted to the respective spark-plugs ZK from the distributor electrodes of the distributor spark gap by way of a respective spark-plug cable KK of the several sparkplug cables used in the system. Disposed parallel with the electrodes of the sparkplug ZK is a secondary loading including a loading resistance which secondary loading reduces when the spark-plug becomes dirty, and a parallel capacitance shown in the broken line connection.Between the secondary winding W2 and the lead to the common earth terminal 0 is a current sensor resistance RF of, for example, 100 ohms which, despite its low resistance value, supplies a sufficiently large measuring signal, dependent upon the respective variable of the discharge current iF, to the regulating circuit RS.

As Figure 2 shows, the spark discharge current iF drops from the ignition time to during the discharge period tr until a prescribed discharge current level N is reached.

In the regulating circuit RS, this discharge period tF is compared with a control variable ts of a monostable multivibrator (not shown) whose trigger period can be changed, for ex ample, by the rpm of the internal combustion engine and/or the reduced pressure existing in the induction manifold of the internal com bustion engine. When the difference between the discharge period and the control variable is is negative, as in the embodiment shown i.e. the discharge period is shorter than its desired value, the closed angle is increased and conversely, when the difference A tF is positive, the closed angle is reduced by the regulating circuit RS by way of the feedback lead L.The particular advantages in the igni tion device of the invention are as follows: a) The spark discharge period tF is de pendent upon capacitive and ohmic load on the high-voltage side within the regulating range of the circuit; b) the power loss caused by the regulating circuit is extremely small, and the following comparative values may apply: conventional ignition systems with a current sensor resistance Err 0.2 ohm on the primary side with a primary ignition current of 1,=5 amps produce a power loss of 5 watts, whereas according to the arrangement of the invention there is a power loss of only 10 mW with a secondary ignition current I, of lOma and a regulating resistance RF of 100 ohms.Consequently, the ignition circuit of the invention is particularly suitable for low-loss 1- or 2-component systems; c) the power loss of the ignition system during normal operation is reduced. This signifies less heating and therefore greater reliabilty.

Reference has been made above to the use of a distributor since an ignition system will usually comprise a plurality of spark-plugs and thus require a distributor. However, the present invention is also applicable to systems using only one spark-plug and not, therefore, having a distributor.

WHAT WE CLAIM IS:- 1. An ignition circuit for the ignition system of an internal combustion engine, having an ignition coil, the circuit comprising an electronic switch which in use of the circuit is connected in series with the primary winding of the ignition coil and whose currentconductive state determines the closed angle, and a regulating circuit for changing the closed angle in dependence upon an operational variable of the internal combustion engine, wherein the spark discharge period is regulated by the regulating circuit to a constant or predeterminable time value.

2. A circuit according to claim 1, wherein a resistor is provided connected in use of the circuit between the winding end, remote from the spark-plug or the distributor as the case may be, of the ignition coil secondary winding and earth, to provide a signal to the regulating circuit.

3. A circuit according to claim 2, wherein the regulating circuit comprises a comparing arrangement in which the duration of a predetermined discharge current level is compared with a desired time value, so that the closed time is increased if the discharge period is below the desired value, or decreased if the discharge period is above the desired value.

4. An ignition circuit for the ignition system of an internal combustion engine, substantially as hereinbefore described with reference to the accompanying drawings.

5. An ignition system for an internal combustion engine, whenever incorporating an ignition circuit according to any of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

generator G which is connected to the crank shaft or the distributor shaft of an internal combustion engine, not shown, and, during one revolution, supplies four trigger pulses one for each of the ignition processes described hereinafter. The generator G cooperates with a closed angle control circuit K (such as, for example, described in German Offenlegungsschrift 2 424 896 and 2 549 586) comprising a capacitor C which influences the closed/open state of a final stage E connected on the load side. The final stage comprises a power transistor T connected in series with the primary winding W1 of a high-voltage ignition coil ZS, and to the positive pole P of the circuit which is at the battery potential.

The distributor spark gap of a conventional .ignition distributor (not shown) is in series with the secondary winding W2 of the ignition coil ZS, the spark discharge current being conducted to the respective spark-plugs ZK from the distributor electrodes of the distributor spark gap by way of a respective spark-plug cable KK of the several sparkplug cables used in the system. Disposed parallel with the electrodes of the sparkplug ZK is a secondary loading including a loading resistance which secondary loading reduces when the spark-plug becomes dirty, and a parallel capacitance shown in the broken line connection.Between the secondary winding W2 and the lead to the common earth terminal 0 is a current sensor resistance RF of, for example, 100 ohms which, despite its low resistance value, supplies a sufficiently large measuring signal, dependent upon the respective variable of the discharge current iF, to the regulating circuit RS.

As Figure 2 shows, the spark discharge current iF drops from the ignition time to during the discharge period tr until a prescribed discharge current level N is reached.

In the regulating circuit RS, this discharge period tF is compared with a control variable ts of a monostable multivibrator (not shown) whose trigger period can be changed, for ex ample, by the rpm of the internal combustion engine and/or the reduced pressure existing in the induction manifold of the internal com bustion engine. When the difference between the discharge period and the control variable is is negative, as in the embodiment shown i.e. the discharge period is shorter than its desired value, the closed angle is increased and conversely, when the difference A tF is positive, the closed angle is reduced by the regulating circuit RS by way of the feedback lead L.The particular advantages in the igni tion device of the invention are as follows: a) The spark discharge period tF is de pendent upon capacitive and ohmic load on the high-voltage side within the regulating range of the circuit; b) the power loss caused by the regulating circuit is extremely small, and the following comparative values may apply: conventional ignition systems with a current sensor resistance Err 0.2 ohm on the primary side with a primary ignition current of 1,=5 amps produce a power loss of 5 watts, whereas according to the arrangement of the invention there is a power loss of only 10 mW with a secondary ignition current I, of lOma and a regulating resistance RF of 100 ohms.Consequently, the ignition circuit of the invention is particularly suitable for low-loss 1- or 2-component systems;

c) the power loss of the ignition system during normal operation is reduced. This signifies less heating and therefore greater reliabilty.

Reference has been made above to the use of a distributor since an ignition system will usually comprise a plurality of spark-plugs and thus require a distributor. However, the present invention is also applicable to systems using only one spark-plug and not, therefore, having a distributor.

WHAT WE CLAIM IS:- 1. An ignition circuit for the ignition system of an internal combustion engine, having an ignition coil, the circuit comprising an electronic switch which in use of the circuit is connected in series with the primary winding of the ignition coil and whose currentconductive state determines the closed angle, and a regulating circuit for changing the closed angle in dependence upon an operational variable of the internal combustion engine, wherein the spark discharge period is regulated by the regulating circuit to a constant or predeterminable time value.
2. A circuit according to claim 1, wherein a resistor is provided connected in use of the circuit between the winding end, remote from the spark-plug or the distributor as the case may be, of the ignition coil secondary winding and earth, to provide a signal to the regulating circuit.
3. A circuit according to claim 2, wherein the regulating circuit comprises a comparing arrangement in which the duration of a predetermined discharge current level is compared with a desired time value, so that the closed time is increased if the discharge period is below the desired value, or decreased if the discharge period is above the desired value.
4. An ignition circuit for the ignition system of an internal combustion engine, substantially as hereinbefore described with reference to the accompanying drawings.
5. An ignition system for an internal combustion engine, whenever incorporating an ignition circuit according to any of the preceding claims.