DE2057520C3 - Electronic ignition circuit for internal combustion engines - Google Patents

Description

The invention relates to an electronic ignition circuit for internal combustion engines with one by one mechanically operated breaker switch triggerable monostable multivibrator, which has a transistor and a three-winding transformer, the first winding of which is in series with the The transistor is connected, the second winding of which is connected to a storage capacitor, which is connected via a thyristor can be discharged into the primary winding of an ignition transformer, the thyristor via a Control circuit is controlled by the circuit breaker, and its third, as a feedback winding Serving winding is part of a control circuit of the transistor.

Such an ignition circuit is known from US Pat. No. 3,465,738. For the transistor and for the A limiting protection circuit is provided for each thyristor. This creates the familiar circuit relatively expensive, which is disadvantageous in series installation in motor vehicles, in which always on it Care is taken to keep costs as low as possible.

A similar electronic ignition circuit is known from FR-PS 15 69 640, in which, however, a Transformer with four windings is required and another one when controlling the transistor Transistor is needed. Also in this known electronic ignition circuit are to protect the The transistor and the thyristor each require a separate switch / circuit.

The object of the present invention is to provide an electronic ignition circuit for internal combustion engines to make available that is very easy and cheap to manufacture and yet very safe and with good Efficiency works.

The solution to this problem consists in an electronic ignition circuit of the type mentioned at the beginning Type, which is characterized in that the control circuit of the transistor with the control circuit of the thyristor die

<-, third winding of the transformer and a diode resistance limiting element has in common

An advantageous development of this electronic ignition circuit is that between the Connection point between transistor and first

κι winding of the transformer and the control input of the transistor facing terminal of the third winding, a resistor is connected

The invention is illustrated below with reference to a schematic drawing of an exemplary embodiment. -, explained the game in more detail

In the illustrated ignition circuit the voltage applied to terminal Vb DC voltage circuit breaker by means of the mono-stable multivibrator Ob, which is in turn controlled by the ·, mechanically actuated Lower P is the machine of the feedback transformer 7rund of the diodes D 3 and DS in a high voltage of about 350 V converted at the storage capacitor CA. The energy stored in the storage capacitor CA is used when the from

r> Interrupter switch P controlled diode DA in the primary winding of the ignition transformer THT. The high ignition voltage for the machine's spark plugs is then generated on the secondary winding of this ignition transformer.

The monostable multivibrator Ob consists of a switching transistor Q 1 and the feedback transformer Tr. The primary winding Np of this feedback transformer is connected in series with the switching transistor Qi to the DC supply voltage Vb. the

η trigger circuit is positively fed back via a resistor R 6 in the manner of a monostable trigger circuit.

When the circuit breaker P of the machine is closed, the transistor Q 1 remains the monostable

.iii len flop at applied supply voltage Vb locked when the circuit breaker is open P, passes through the resistor R1, the capacitor C 1 and diode D I a firing pulse to the flip-flop locked Ob. The transistor Q I is switched on

r, tet and the current in the primary winding Np increases linearly until the core of the transformer Tr is saturated. The current rises rapidly to a value

, o , where I ₁ - is the collector current and h is the base current of transistor Q 1 and hu: is the current gain coefficient with the emitter grounded for large signals. The transistor is then blocked again, the collector-emitter voltage of the transistor Q 1 increases, i increases, the voltage across the primary winding Np and the secondary winding Nf coupled thereto decreases, so that the transistor Q 1 is quickly blocked.

If /, “denotes the maximum current Mi reached in the winding Np during the conduction phase of the transistor Q i and L denotes the inductance of the winding Np , then that is in the core of the transformer

I 2

Trstored energy -, L χ /.

When the transistor Q I is blocked, the energy

,,, transferred to the capacitor CA via the tertiary winding NL of the feedback transformer and the diodes I) 1 and D5. If the losses are neglected, that is the electrostatic energy

the capacitor charge is equal to the inductive energy previously stored in the feedback transformer Tr. This energy arises immediately at the ends of the primary winding of the ignition transformer THT when the controlled diode D 4 becomes conductive.

The resistor A4 is used to limit the base current of the transistor Q 1. The resistor R 3 and the diode D 2 form a limiting element by which the transistor Q 1 is protected against excessively high blocking voltages in the base-emitter path. The controlled diode D 4 is ignited via the capacitor C2 with the same pulse that causes the transistor Q 1 to conduct. The resistor R 7 ensures a positive voltage between the cathode and the control electrode of the controlled diode D 4 during the conduction phase of the transistor Q 1, which voltage is fed back to the winding Nf. With this positive voltage, the controlled diode D 4 remains switched on even in the event of possible oscillations in the output circuit, which would block it again after ignition. Such oscillations occur when the secondary winding of the ignition transformer THT is open and there is no possibility of completely using up the energy stored in the capacitor C4. This energy deficit is unfavorable because it brings the voltage on the storage capacitor C4 to undefined values during the subsequent charging phases. If, however, the controlled diode D 4 can conduct for a certain time after ignition, the full energy output from the storage capacitor CA is achieved.

The controlled diode DA is ignited via

". the limiting element consisting of the diode D 2 and the resistor A3 and provided to protect the transistor Q 1. This limiting element thus also serves to protect the controlled diode from excessively high reverse voltages.

ι »The resistor R5 biases the basic of the transistor Q 1. The capacitor C3 delays the tipping over of the transistor by limiting the maximum voltage values between the collector and emitter. With the diode D 5, the on the transformer THT

ι> recharged energy partially recovered by it extends the spark duration on the spark plugs.

With a circuit according to the invention, maximum voltage values of 24 kV and more (measured at a resistance of 1 ΜΩ between the electrodes of the spark plugs) can be generated on the secondary winding of the ignition transformer THT, with a spark duration of 200 μβε ^ The rising edge of the ignition pulses is around 20 psek. If the supply voltage fluctuates between 8 and 16 V.

π, the energy only changes between 50 and 75 mjoule and the voltage on the storage capacitor CA between 320 and 390 V.

For this purpose I sheet drawings

Claims (2)

Patent claims: 1. Electronic ignition circuit for internal combustion engines with a monostable flip-flop which can be triggered by a mechanically operated breaker switch, which has a transistor and a transformer provided with three windings, the first winding of which is connected in series with the transistor, the second winding of which is connected to a storage capacitor, which can be discharged via a thyristor into the primary winding of an ignition transformer, the thyristor being controlled by the interrupter switch via a control circuit, and the third winding serving as a feedback winding is part of a control circuit of the transistor, characterized in that the control circuit of the transistor (Q 1) with the control circuit of the thyristor (DA) has the third winding (Nf) of the transformer (Tr) and a diode resistance limiting element (D 2, R 3) in common. 2. Ignition circuit according to claim 1, characterized in that between the connection point between the transistor (Q 1) and the first winding (Np) of the transformer (Tr) and the terminal of the third winding (Nf) facing the control input of the transistor (Q 1) Resistance (7-6) is switched.