DE3423949A1 - IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES - Google Patents

Description

β. 19W9 2 3423940

6/19/198 ** Li / Pi

ROBERT BOSCH GMBH, 7000 STUTTGART 1

Ignition system for internal combustion engines
State of the art

The invention is based on an ignition system according to the preamble of the main claim. It is already known (according to DE-PS 25 31 or the corresponding US-PS k 105 006) an ignition system located in this direction, in which, however, the control of the thyristor located in the shunt branch of the primary winding is relatively complex in terms of circuitry.

Advantages of the invention

In the ignition system according to the invention, by application the characterizing measures of the main claim avoided the aforementioned disadvantage to a satisfactory degree.

Advantageous measures for implementing the invention are specified in the subclaims.

drawing

An exemplary embodiment of the invention is shown in the drawing and in the following Description explained in more detail.

Description of the embodiment

The ignition system shown in the drawing is intended for an internal combustion engine, not shown, of a motor vehicle, also not shown. The system ■ is fed from a direct current source 1, which can be the battery of the motor vehicle. At the power source 1, a line 2 connected to ground extends from the negative pole and a supply line k containing an operating switch (ignition switch) 3 extends from the positive pole. The supply line k is the starting point for a circuit branch, which leads via the primary winding 5 of an ignition coil 6 to the collector of an (npn) end transistor 7, and continues there from the emitter via a measuring resistor 8 to the ground line 2. The secondary winding 9 belonging to the primary winding 6 is connected to the ground line 2 via at least one spark plug JO. The base belonging to the output transistor 7 is connected to the emitter of a Cnpn) driver transistor 11, the collector of which is connected to the supply line h via a resistor 12. The base belonging to the driver transistor 11 is connected to the output of an inverter 13, the input of which is connected to the output of a control element 1U.

In the control element 1U, which can be a microcomputer, it is ensured that approximately the same amount of energy is made available for each ignition process. The input of the control element 1 k is connected to the ground line 2 via a signal generator 15, which works like a small alternating current generator and is intended to be coupled to the crankshaft or camshaft of the internal combustion engine.

The one between the emitter of the output transistor 7 and the measuring resistor 8 existing connection is the starting point for

one line that goes to one input of a! Comparator 16 leads. The other input of the! Comparator i6 is via a constant voltage source 17 is connected to the ground line 2. The output of the! Comparator 16 is connected to the input of a monostable multivibrator 18, whose output is at the base of the driver transistor 11.

The connection between the control element 1U and the inverter 13 is the starting point for a line run which leads via a current limiting resistor 19 to the base of a further transistor 20 (of the npn type), the emitter of which is connected to the ground line 2 and the collector to the control electrode of a thyristor 21 lies. The thyristor 21 is arranged in a shunt branch 22 of the primary coil 5 belonging to the ignition coil 6 in such a way that it is current-permeable for the induction current of the primary winding 5. A control branch 23, which leads to the control electrode of the thyristor 21 and contains at least one resistor 2k , starts from the anode of the thyristor 21 connected to the primary winding 5. It is advisable to connect a Zener diode 25 in series with the resistor 2h in such a way that this Zener diode 25 is stressed by the induction current of the primary winding 5 in the reverse direction. Furthermore, it is advisable to add a parallel branch to the resistor 2k which, if necessary, contains a resistor 26 and is at least partially capacitive due to a capacitor 27.

The ignition system just described has the following mode of operation:

As soon as the operating switch 3 is closed, the system is ready for use. It is assumed that the signal generator 15 has influenced the control member 1 k in such a way that

R. I9U69

that at the output of the control element 1 h the pulse shown there, which has at least almost the potential of the ground line 2, is effective. As a result, the transistor 20 is non-conductive at its emitter-collector path and the transistors 11, 7 have a current-conducting state at their emitter-collector paths, whereupon the current increases in the switched-on primary winding 5 and the voltage drop increases with this current increase at the measuring resistor 8 enlarged. If the current value is sufficient for an effective ignition spark, the voltage drop across the measuring resistor 8 is so great that the comparator 16 controls the monostable multivibrator 18 in its unstable state. In the unstable state of the monostable multivibrator 38, the transistors 11, T are non-conductive at their emitter-collector paths. By switching off the primary winding 5, an induction voltage becomes effective at the anode of the tyhristor 21 and an induction current is conducted via the control branch 23 to the control electrode of the thyristor 21 so that its anode-cathode path becomes conductive. The energy stored in the ignition coil β will therefore slowly decay due to the induction current now flowing over the anode-cathode path. This decay is determined in such a way that an amount of energy sufficient for an ignition spark is retained in the ignition coil 6 until the monostable multivibrator 8 returns to its stable state. If this is the case, the transistors 11, T return to the conductive state at their emitter-collector paths, so that the power supply to the primary winding 5 is switched on again by the output transistor and the shunt branch 22 with the thyristor 21 is rendered ineffective. This power supply is now again holds as long as until the voltage drop across the measuring resistor 8 via the comparator 2 6 the monostable multivibrator 18 again in its unstable state

. 34239A9

R. 19 ^ 69

and the functional sequence just described begins again.

At the ignition point, a pulse is made available at the output of the control element 1 k which has at least almost the potential of the supply line k . As a result, the transistor 20 becomes conductive at its emitter-collector path and the control electrode of the thyristor 21 reaches the ground line 2, whereupon the thyristor 21 cannot become effective when the transistors 11, 7 are blocked. Rather, the blocking now occurring at the emitter-collector path of the end transistor 7 induces a high-voltage surge in the secondary winding 9, which results in an electrical flashover (ignition spark) at the spark plug 10.

It is advisable to use a type as thyristor 21 which is easily "ignitable", i.e. very sensitive to control.

The resistor 2k is necessary to limit the current.

The use of the Zener diode 25 is recommended because, without its use, interference pulses are easily undesirable Switching processes on the thyristor 21 can trigger.

The use of the capacitor 27 makes it possible to make the thyristor 21 faster as a function of the induction current to switch through. In addition, this means that the voltage at the anode of the thyristor does not rise as quickly.

Claims (3)

6/19/198 U Li / Le ROBERT BOSCH GMBH, TOOO STUTTGART 1 Expectations 1J ignition system for internal combustion engines with one ignition coil, whose primary winding is the starting point for a tributary branch is, the primary winding gate each ignition point in time only in temporary periods from a direct current source is supplied with current via a final transistor, furthermore the one at the end of such a period of time Induction current generated in the primary winding flows through a thyristor in the bypass branch, and also when Storing the ignition energy of the thyristor in the off-state of the final transistor, current-conducting state and in the current-conducting state of the final transistor has the blocking state and finally being in series with the primary winding and with the final transistor a measuring resistor is located, with the help of which the output transistor can be switched on and off when storing the ignition energy is, characterized in that from the anode of the thyristor (21) lying on the primary winding (5) Control branch (23) goes out, which contains at least one control resistor (2 * 0 and to the control electrode of the thyristor (21) leads. 2. Ignition system according to claim 1, characterized in that in the control indicator (23) the control resistor (2k) is connected in series with a Zener diode (25), which is loaded in the reverse direction by the induction current of the primary winding (5). 3. Ignition system according to claim 1, characterized in that the control resistor (2k) has a parallel branch (.26, 27) which is at least partially capacitive.