JPS6149501B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides at least one spark plug, an ignition coil having a primary winding and a secondary winding, and an ignition coil connected in series to the primary winding, the conduction state being at a closing angle ( an electronic switch that determines the angle of rotation associated with the crankshaft of the internal combustion engine over which the switch remains conductive; a control circuit, a measuring resistor provided between the end of the secondary winding opposite the spark plug and earth, and a voltage drop occurring across the measuring resistor due to the spark discharge current; The present invention relates to an ignition device for an internal combustion engine, comprising an adjustment circuit for adjusting the spark discharge duration to a predetermined value and comprising a comparison device.

In the known ignition device (German Patent Application No. 244 781), particularly advantageous current flow times are achieved using closing angle control. However, an ignition device in which such closing angle control is performed is accompanied by difficulties. This is because during periods of load, particularly high capacitive loads or fouling of the spark plug, the ignition voltage changes, causing a drop in the ignition voltage or a relatively short discharge duration.

It is therefore an object of the present invention to provide an ignition device in which changes in load of this type are not likely to affect the ignition output.

According to the present invention, this problem is solved as follows. That is, a regulating device is connected to the control circuit, and furthermore in the comparator device the time interval required for the spark discharge current to drop to a predetermined discharge current level is compared with a target time interval and the final If the spark discharge time interval falls below the target time interval, the closing angle is increased via the control circuit, or if the spark discharge time interval exceeds the target time interval, the closing angle is increased via the control circuit. Made it smaller.

A particular advantage of the ignition device according to the invention is that it becomes virtually immune to load effects on the secondary side of the ignition coil as well as effects on the primary side, such as for example fluctuating battery voltages. According to the invention, the regulating circuit compares the duration of time to reach a predetermined discharge current level (eg 5 or 10 mA) with a target value time (eg 1 ms). If the discharge duration is smaller than the setpoint value, the regulating circuit acts to increase the closing time or the closing angle, or vice versa. Adjustments of this kind are possible, for example, using known circuits in which a monostable multivibrator is provided, which has a capacitor that determines the instability time and whose discharge current is increased in order to reduce the instability time. be. The setpoint value of the discharge duration can be varied as a function of the rotational speed and, if appropriate, the load to adapt it to the particular requirements of the internal combustion engine. For example, when the rotation speed is low, a long discharge duration of 2 ms can be set, and when the rotation speed is high, a short discharge duration of 0.5 ms can be set. An adaptation of this kind is also possible by limiting the closing angle in a simple way so that it does not fall below a predetermined minimum release time, for example 400 μs.

In the event of a so-called misfire, which occurs, for example, due to disconnection of the plug cable and no discharge occurs, the regulating circuit sets the maximum closing angle for the next ignition cycle. In the unlikely event that a similar misfire occurs again, a known overvoltage protection device, such as a zener wire between the base and collector of the power transistor, should be used to protect the power transistor and its insulating parts. A diode clamp can be provided.

Next, the present invention will be explained in detail using the drawings.

The ignition device in FIG. 1 is a permanent magnet connected to the crankshaft or distributor shaft of an internal combustion engine (not shown) and which supplies four trigger pulses per revolution for the ignition process described below. It has a generator G consisting of. A closing angle control circuit K (as described, for example, in DE 24 24 896 and DE 2 549 586) is assigned to the generator G and jointly controls the output stage. The closing angle control circuit has a capacitor C which controls the on/off ratio of the downstream output stage E. The power transistor of the output stage is connected in series to the primary coil W1 of the high voltage ignition coil ZS and to the positive pole P to which the potential U _Batt is applied.

A distributor spark gap, not shown in detail, of a conventional ignition distributor ZV is connected in series to the secondary coil of the ignition coil ZS. From a distributor electrode (not shown in detail) of the distributor, a spark discharge current is supplied to each spark plug ZK via a respective one of a plurality of plug cables KK. In parallel with the electrodes of the spark plug ZK shown, there is a secondary load consisting of a load resistance that decreases if the spark plug becomes dirty and a parallel capacitance, which is likewise not shown in detail. For example, a current detection resistor R _F of about 100Ω is provided between the secondary coil W2 and the common ground wire. Despite its low resistance value, this resistor supplies a sufficiently large measuring signal to the regulating circuit RS, which is dependent on the magnitude of the respective discharge current i _F .

As shown in FIG. 2, the spark discharge current i _F falls from the ignition time t _O for a discharge duration t _F until reaching a predetermined discharge current level N. This discharge duration t _F is compared in a regulating circuit RS with a reference value t _s of a monostable multivibrator (not shown). The instability time of the multivibrator is designed to vary, for example, depending on the rotational speed of the internal combustion engine and/or the negative pressure in the intake pipe of the internal combustion engine. When the difference of the discharge duration from the reference value t _s is negative, as in the illustrated embodiment, i.e. when the discharge duration is shorter than its target value, the closing angle is enlarged, and in the opposite case, i.e. the difference △ When t _F is positive, the feedback line L is adjusted by the adjustment circuit RS.
The closing angle is reduced via . Particular advantages of the igniter according to the invention are as follows.

(a) the spark discharge duration t _F is independent of the capacitive and resistive loads on the high voltage side in the regulation region of the circuit; (b) the power losses caused by the regulation circuit are negligibly small, with the The comparison value of can be applied. Thus, an ignition device with a primary current sensing resistor R _r with a primary ignition current of I ₁ =50 results in a power loss of 5 W, whereas in the solution proposed by the device according to the invention Secondary ignition current of 10mA I ₂ and 100
Only 10 mW of power is lost in the regulating resistor R _F of Ω. The ignition device according to the invention is therefore particularly suitable for devices consisting of one or two components (modules) with low losses; (c) the power losses of the ignition device in normal operation are reduced; Heating is reduced and therefore higher reliability is obtained.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of the ignition device of the present invention, and FIG. 2 shows the spark discharge current and discharge duration t _F
FIG. G... Generator, K... Closing angle control circuit, E
...Output stage, ZK...Spark plug, ZS...Ignition coil, RS...Adjustment circuit, RF...Current detection resistor.

Claims (1)

[Claims] 1. At least one spark plug, an ignition coil having a primary winding and a secondary winding, and an electronic switch connected in series with the primary winding, the conduction state of which determines the closing angle. , a control circuit for varying the closing angle at least as a function of the rotational speed; a measuring resistor arranged between the end of the secondary winding opposite the spark plug and earth; and a spark discharge. In an ignition system for an internal combustion engine, the ignition system is provided with a regulating circuit which adds a voltage drop across a measuring resistor due to the current, which regulates the duration of the spark discharge to a predetermined value and which includes a comparator.
The regulating circuit RS is connected to the control circuit K, and furthermore the time interval _{t F} required for the spark discharge current to drop to a predetermined discharge current level N in the comparison device is determined by the target time interval t _S and finally, if the spark discharge time interval _tF falls below the target time interval _tS , the control circuit K
The closing angle is expanded via the control circuit K, or the closing angle is reduced via the control circuit K when the spark discharge time _tF exceeds the target time interval _tS . Ignition system for internal combustion engines.