GB2163485A

GB2163485A - Ignition systems for internal combustion engines

Info

Publication number: GB2163485A
Application number: GB08520800A
Authority: GB
Inventors: Gunter Bornmann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1984-08-21
Filing date: 1985-08-20
Publication date: 1986-02-26
Also published as: FR2569446A1; JPS6165076A; DE3430660A1; GB8520800D0

Abstract

The primary winding (5) of an ignition coil (6) is connected in series with a transistor (7) which is conductive when a first threshold value switch (18) is "on". An alternating current generator 22 is connected to the input of the threshold value switch (18) for supplying an alternating voltage signal the values of which preceding and following its peak value are used for switching-on and switching off respectively the threshold value switch (18). The input of a second threshold value switch (19) is connected in parallel with the input of the first threshold value switch (18), and the polarity of its switching-on value is the same as that of the first threshold value switch (18), whilst its switching-off value has the opposite polarity, and a logic circuit 17 is provided whereby the transistor is controlled by the second threshold value switch (19) during starting of the internal combustion engine to retard the ignition timing, and by the first threshold value switch (18) during running of the internal combustion engine. <IMAGE>

Description

SPECIFICATION Improvements in or relating to ignition systems for internal combustion engines The present invention relates to ignition systems for internal combustion engines.

One form of ignition system for internal combustion engines has an electronic circuitbreaker which is conductive when a first threshold value switch is in its "on" state, an ignition coil whose primary winding is connected in series with the circuit-breaker, and an alternating current generator connected to the input of the threshold value switch for supplying an alternating voltage signal whose curve portion preceding a peak value on a curve of a voltage/time graph is used for switching-on the threshold value switch, and the curve portion following this peak value is used for switching-off the threshold value switch, the switching-on and the switching-off values having the same polarity relative to the zero value of the alternating voltage signal.

Such a system is disclosed in German Patent Specification No. 2,549,596 and in the corresponding United States Patent Specification No. 4,071,792; however, the internal combustion engine may be difficult to start, or will not start at all, since the portion of the curve following the peak value has a very small slope initially and consequently the instant of ignition is advanced to a relatively great extent relative to the top dead centre of the piston.

According to the present invention there is provided an ignition system for internal combustion engines having an electronic circuitbreaker which is conductive when a first threshold value switch is in its "on" state, an ignition coil whose primary winding is connected in series with the circuit-breaker, and an alternating current generator connected to the input of the threshold value switch for supplying an alternating voltage signal whose curve portion preceding a peak value on a curve of a voltage/time graph is used for switching-on the threshold value switch, and the curve portion following this peak value is used for switching-off the threshold value switch, the switching-on and the switching-off values having the same polarity relative to the zero value of the alternating voltage signal, in which a second threshold value switch is provided for switching-on and switching-off the electronic circuit-breaker and its input is connected in parallel with the input of the first threshold value switch, and, relative to the zero value of the alternating voltage, the polarity of its switching-on value is the same as the polarity of the switching-on value of the first threshold value switch, while its switching-off value has the opposite polarity, and a logic circuit is provided between the outputs of the two threshold value switches and the electronic circuit-breaker, whereby the electronic circuit-breaker is controlled by the second threshold value switch during starting of the internal combustion engine, and by the first threshold value switch during running of the internal combustion engine.

The invention will be further described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram of an ignition system according to one embodiment of the invention; and Figure 2 is a voltage (U)/time (t) graph of the alternating voltage signal intended for controlling the ignition system.

The ignition system illustrated in Fig. 1 is intended for an internal combustion engine (not illustrated) of a motor vehicle (also not illustrated). This ignition system is fed from a d.c. source 1 which may be the battery of the motor vehicle. A lead 2 is connected between the negative pole of the current source 1 and earth, and a supply lead 4 is connected to the positive pole and includes an operating switch 3. A current circuit leads from the supply lead 4 first through the primary winding 5 of an ignition coil 6 and then through an electronic circuit-breaker 7 to the earth lead 2. The electronic circuit-breaker 7 is formed by the emitter-to-collector path of an n-p-n transistor 8, the emitter being connected to the earth lead 2.One end of the secondary winding 9 of the ignition coil 6 is connected to the lead between the primary winding 5 and the electronic circuit-breaker 7, and its other end is connected to the earth lead 2 by way of a spark plug 10.

The base of the transistor 8, whose emitterto-collector path forms the electronic circuitbreaker 7, is connected by way of a currentlimiting resistor 11 to the collector of a p-n-p driver transistor 12, whose emitter is connected to the supply lead 4. The base of the driver transistor 12 is connected to the junction between two series-connected resistors 13, 14 which are connected between the supply lead 4 and the collector of a further n-p-n transistor 15. The emitter of the further transistor 15 is connected to the earth lead 2, and its base is connected to the output 16 of a logic circuit 17.

A first threshold value switch 18 and a second threshold value switch 19 are connected on the input side of the logic circuit 17. In the present embodiment, the threshold value switch 18 is an operational amplifier 20, and the threshold value switch 19 is an operational amplifier 21. The inputs of the threshold value switches 18, 19 are connected in paral lel to an a.c. generator 22 operating as a signal generator, the threshold value switches 18 and 19 also being connected to the supply lead 4 by way of supply lines 23, 24, and to the earth lead 2 by way of supply lines 25, 26.

The logic circuit 17 includes an AND gate 27 and an OR gate 28. The output of the first threshold value switch 18 is connected to the first input 29 of the OR gate 28, and the output of the second threshold value switch 19 is connected to the first input 30 of the AND gate 27. The output 31 of the OR gate 28 is connected to the second input 32 of the AND gate 27, and its second input 33 is connected to a starting contact 34 which forms part of the operating switch 3 such that the second input 33 receives a signal only during starting of the internal combustion engine. The operating switch 3 also has a running contact 35 and a movable contact 36, the contact 34 and the contact 35 being engaged by the contact arm 36 during starting of the internal combustion engine, and only the running contact 35 being engaged during normal operation.When in the off position, the movable contact 36 is not in engagement with either of contacts 34 and 35.

The voltage (U)/time (t) graph of Fig. 2, in which the alternating voltage signal Ua supplied by the a.c. generator 22 is illustrated, shows how the switching thresholds of the threshold value switches 18, 19 are determined. In the first instance, the switching-on value Ub of the first threshold value switch 18, and the switching-on value Uc of the second threshold value switch 19 are located on the curve portion Ue preceding a positve peak value Ud, whereas the switching-off value Uf of the first threshold switch 18 and the switching-off value Ug of the second threshold value switch 19 are located on the curve portion Uh following the peak value Ud.By way of example, the switching-on value Ub of the first threshold value switch 18 and the switching-on value Uc of the second threshold value switch are equal and above the switching-off value Uf and also have the same polarity, namely positive polarity, with respect to the zero value 0 of the alternating voltage signal Ua. The switching-off value UF of the first threshold value switch 18 is to be somewhat lower than the switching-on values Ub, Uc, although with the same polarity as the switching-on values Ub, Uc, that is to say, positive polarity. In contrast to this, the switching-off value Ug of the second threshold value switch 18 is to have the opposite polarity relative to the zero value 0 of the alternating voltage signal Ua, from which it follows that its value also lies below the switching-off value Uf of the first threshold value switch 18.

The mode of operation of the ignition system described above is as follows: When the internal combustion engine is running, that is to say, when the internal combustion engine has been started and the moveable contact 36 is only in engagement with the running contact 35 of the operating switch 3, current is fed through the primary winding 5 as soon as the electronic circuit-breaker 7 is brought into its conductive state. This occurs when the curve portion Ue of the alternating voltage signal Ua made available by the alternating current generator 27 has reached the switching-on values Ub and Uc.A signal is then present at the output of the first threshold switch 18, at the output of the OR gate 28, and at the output of the second threshold value switch 19, so that a signalconsequently present at the output 16 of the logic circuit 17, makes the emitter-to-collector paths of the transistors 15, 12 and 8 conductive and results in the flow of current in the primary winding 5.

When the alternating current signal Ua supplied by the alternating current generator 22 has exceeded the positive peak value Ud, and has then dropped along the following curve portion Uh to the switching-off value Uf of the first threshold value switch 18, the signal is no longer present at the output of the first threshold value switch 18, nor at the output 31 of the OR gate 28, and consequently not at the output 16 of the AND gate 27, whereupon the emitter-to-collector paths of the transistors 15, 12 and 8 become non-conductive, and the electronic circuit-breaker 7 interrupts the flow of current in the primary winding 5. A high-voltage pulse is then induced in the secondary winding 9 and consequently an electrical spark-over (ignition spark) is produced at the spark plug 10.

It will be seen that the instant of ignition is determined by the first threshold value switch 18 during normal running of the internal combustion engine, that is to say, when the movable contact 36 is only in contact with the contact 35. Difficulties would arise if it were also desired to use this instant of ignition, that is to say, the point of intersection of the alternating voltage signal Ua with the switching-off threshold Uf of the first threshold value switch 18, when starting the internal combustion engine.The curve portion Uh following the peak value Ud has a relatively slight slope during starting of the internal combustion engine, so that the instant of ignition, that is to say, the above-mentioned points of intersection Uc, Uf are shifted in the direction of the arrow, that is to say, they are "advanced", though under the condition it is desirable that they should coincide, with respect to time, substantially with the top dead centre position of the piston in the cylinder of the internal combustion engine. The disadvantage may be the reason why an engine is difficult to start or why it does not start at ali. In order to avoid the above-mentioned disadvantage, the second threshold value switch 19 is used to determine the instant of ignition during starting of the internal combustion engine. During starting of the internal combustion engine, the second input 33 of the OR gate 28 permanently carries a signal which, in the preferred embodiment, is fed from the starting contact 34, so that a signal is also permanently avail able at the output 31 of the OR gate 28 and at the second input 32 of the AND gate 27 during starting. The electronic circuit-breaker 7 then cuts off the flow of current in the primary winding 5 only when a signal is no longer present at the output of the second threshold value switch 19. However, this occurs when the alternating voltage signal Ua and the switching-off threshold Ug intersect, and this takes place with opposite polarity to that of the switching-on values Ub, Uc. Consequently, the instant of ignition shifts in the "retard" direction during starting of the inter nal combustion engine, as is indicated by the arrow and which is also desirable when putting the internal combustion engine into operation.

Claims

1. An ignition system for internal combustion engines having an electronic circuitbreaker which is conductive when a first threshold value switch is in its "on" state, an ignition coil whose primary winding is connected in series with the circuit-breaker, and an alternating current generator connected to the input of the threshold value switch for supplying an alternating voltage signal whose curve portion preceding a peak value on a curve of a voltage/time graph is used for switching-on the threshold value switch, and the curve portion following this peak value is used for switching-off the threshold value switch, the switching-on and the switching-off values having the same polarity relative to the zero value of the alternating voltage signal, in which a second threshold value switch is provided for switching-on and switching-off the electronic circuit-breaker and its input is connected in parallel with the input of the first threshold value switch, and, relative to the zero value of the alternating voltage, the polarity of its switching-on value is the same as the polarity of the switching-on value of the first threshold value switch, while its switching-off value has the opposite polarity, and a logic circuit is provided between the outputs of the two threshold value switches and the electronic circuit-breaker, whereby the electronic circuit-breaker is controlled by the second threshold value switch during starting of the internal combustion engine, and by the first threshold value switch during running of the internal combustion engine.

2. An ignition system as claimed in claim 1, in which the logic circuit comprises an OR gate and an AND gate and the output of the first threshold value switch is connected to a first input of the OR gate, the output of the second threshold value switch is connected to a first input of the AND gate, the output of the OR gate is connected to a second input of the AND gate, a starting signal is connected to a second input of the OR gate during starting of the internal combustion engine, and the output of the AND gate is the control signal for the electronic circuit-breaker.

3. An ignition system as claimed in claim 2, in which a starting contact of an operating switch of the internal combustion engine is operatively connected to the second input of the OR gate.

4. An ignition system for internal combustion engines, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in the accompanying drawings.