GB1586649A

GB1586649A - Ignition system especially for internal combustion engines

Info

Publication number: GB1586649A
Application number: GB17067/78A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-11-30
Filing date: 1978-04-28
Publication date: 1981-03-25
Also published as: IT7830335A0; IT1100426B; SE7812297L; DE2753355A1; SE421083B; DE2753355C2

Description

(54) AN IGNiTION SYSTEM ESPECIALLY FOR INTERNAL COMBUSTION ENGINES (71) We, ROBERT BOSCH GmbH, a German company of 50, Postfach, Stuttgart, 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 invention relates to an ignition system of a type in which a plurality of ignition sparks are produced at each ignition instant. This is referred to hereinafter as a spark band ignition system.

German OS 2 616 693 discloses a timing element for limiting the duration of the spark band. However, since the time interval from ignition to ignition varies very greatly in accordance with the speed, it has been shown in practice that it is more preferable to generate the spark band over a predetermined angular region, thus, to control it in accordance with speed. In the state of the art set forth, the limiting of the spark band is also indicated over a pre-determined angular region, wherein the said angular region conforms to the generator signal angle. Once again, this has the disadvantage that in constructing the generator, regard must be had to a further parameter, namely the duration of the spark band. A variation in the duration of the spark band, for example due to a modified layout of the ignition system, requires a modification of the generator for the plurality of sparks.

The present invention provides an ignition system comprising an electronic device responsive to a signal sequence derived from a rotary generator arrangement for generating a spark band consisting of a plurality of ignition sparks at each ignition instant, and a limiting device for limiting the duration of the spark band, said limiting device comprising a first storage device arranged to be charged in accordance with speed for speed dependent control of the limiting device, and a second storage device arranged to be subjected to a further charging procedure, the end of the spark band being established by the second storage device reaching a threshold value whereby the said instant can be predetermined by a determined ratio of the charging value of the first storage device with respect to the charging value of the second storage device.

A preferred form of ignition system in accordance with the invention has the advantage that the duration of the spark band can be varied by altering the setting of electrical and electronic components in the limiting device. Particular curves for the duration of the spark band can be provided by varying the charging and discharging constants of the two storage devices.

It is of particular advantage to provide a closing angle control device known per se through which the device for generating the spark band and/or the limiting device can be triggered. In this manner, it is'guaranteed that the device for generating the spark band is so triggered at the correct instant that sufficient energy is stored in the ignition coil to trigger the first ignition spark at the desired ignition instant.

In order that the present invention be more readily understood embodiments thereof will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a circuit arrangement of a first embodiment; Figure 2 is a signal diagram for explaining the method of operation of the first embodiment illustrated in Figure 1; and Figure 3 a circuit arrangement of a second embodiment.

In the first embodiment illustrated in Figure 1, a generator arrangement 10, preferably connected to the crankshaft of a combustion engine, is connected to a pulse shaping stage 11 preferably formed as a Schmitt-trigger. The generator arrangement 10 is formed in the illustration as an inductive generator however, for example an arrangement as a mechanical contact breaker, as a Hall generator or as an optical generator is also possible. The output from the pulse shaping stage 11 is connected to a closing angle control device 14 through an ignition angle calculating stage 12 and a subsequent connecting terminal 13. An ignition angle calculating stage 12 for displacing the ignition signal in accordance with, for example, the engine data (speed n, inlet manifold depression p, temperature T and throttle valve setting a) is known for example from German OS 2 348 352 or German OS 2 539 113.A closing angle control device 14 is known from the state of the art set forth above as well as from German OS 22 44 781 or from the corresponding United States specification 3 881 458. The output from the closing angle control device 14 is connected through a terminal 15 to the input to an AND gate 16, the output from which is connected to an ignition final stage 17 known per se.

Such an ignition final stage 17, usually consisting of a driving stage, power transistor, ignition coil and at least one sparking plug, is shown and the method of operation described in the state of the art set forth. Furthermore, the terminal 15 is connected to a further input to the AND gate 16 through an electronic device for generating a spark band preferably formed as a frequency generator 18. Such a frequency generator can be a free running oscillator or even an arrangement according to Figure 3 of German OS 2 616 693 in which the frequency of the frequency generator 18 is controlled by reaching a desired current value in the primary current circuit of the ignition coil.

Moreover, the terminal 15 is connected to a further input to the AND gate 16 through a limiting device 19 for limiting the duration of the spark band. Moreover, the terminal 15 is connected to the inverting input to a comparator 21 through a resistor 20. Furthermore, this inverting input is connected to earth through a capacitor 22 and is connected to the terminal 15 through a diode 23. Moreover, the terminal 15 is connected to the noninverting input of the comparator 21 through the series circuit comprising an inverter 24, a resistor 25 and a diode 26.

This non-inverting input is not only connected to earth through a capacitor 27 but is also connected to earth through a Z diode 28. Moreover, the non-inverting input to the comparator 21 is likewise connected to earth through the series circuit of a diode 29 and the collector-emitter path of an npn transistor 30. A diode 31 is connected between the base of the transistor 30 and earth. Furthermore, the base of the transistor 30 is connected to the interconnecting point between the inverter 24 and the resistor 25 through a capacitor 32.

The method of operation of the first embodiment illustrated in Figure 1, will be explained in the following with the aid of the signal diagram illustrated in Figure 2.

The signals from the generator arrangement 10-in the present case two signals per revolution for a four-cylinder combustion engine-are converted into squarewave signals in the pulse shaping stage 11. These signals are displaced by the ignition angle calculating stage 12 in accordance with the parameters controlling them and arrive as a signal sequence U13 at the terminal 13, or at the input to the closing angle control device 14. A signal sequence U15, the start of the signals of which is advanced with respect to the signal sequence U13 by the period To, appears at the output from the closing angle control device 14, thus at the terminal 15. This period To is so set that, during this period, sufficient magnetic energy can be stored in the ignition coil to generate a first ignition spark with sufficient energy at the beginning of a signal U13.During each signal duration U15, the frequency generator 18 can generate a signal sequence U18 whereby each first signal is extended by constructing the said frequency generator according to Figure 3 of German OS 2 616 693. This is advantageous since the current flow during the first ignition spark of each spark band starts from the current value of zero, whilst the current flow during the subsequent ignition sparks is built up to an increased current value by storing magnetic residual energy in the ignition coil and thus requires a shorter period to reach its desired value.

During a pause in the signal sequence U15, a l-signal is present at the output from the inverter 24, through which the capacitor 27 is charged through the resistor 25 and the diode 26. At the beginning of a signal U15 the charging procedure for the capacitor 27 terminates, the capacitor retains its charge since the transistor 30 remains blocked. At the same time charging of the capacitor 22 starts. When the voltage U22 reaches the value U27, then the output from the comparator 21 connected to a terminal 33 changes from a signal to a 0-signal.

The AND gate 16 is blocked by the said 0-signal and no further signals U18 for controlling the ignition final stage 17 can reach the latter. The spark band terminates. At the end of a signal U15, the capacitor 22 is discharged through the diode 23 and the capacitor 27 is discharged through the diode 29 and the collectoremitter path of the transistor 30. The capacitor 32 is temporarily charged by the rising edge generated at this instant at the output from the inverter 24 and thus switches the transistor 30 into its conductive condition. The voltage rise in the capacitor 27, is limited by the Z-diode 28, in place of which an optional threshold value stage can also be used. This causes limiting of the spark band to a maximum value which cannot be exceeded even on further variation of the speed.

In the second embodiment illustrated in Figure 3, the terminal 13 is connected to the anode of a diode 41 through a timing element 40 formed, for example, as a monostable switching stage, the cathode of the diode 41 being connected to earth through a resistor 42. The series circuit of a further resistor 43 and a capacitor 44 is connected in parallel with the resistor 42. The terminal of the capacitor 44 remote from earth is connected through a further resistor 45 to the base of a pnp transistor 46 the collector of which is connected to earth through a capacitor 47 and the emitter of which is connected through a resistor 48 to a terminal 49 which, in its turn, is connected to the positive pole of a supply voltage source. Furthermore, the collector of the transistor 46 is connected through a diode 50 to the terminal 13 and through a threshold value stage 51 to the terminal 33.

The second embodiment of a limiting stage for the spark band duration illustrated in Figure 3, can be used instead of the limiting stage 19 in Figure 1. The circuit arrangement of the second embodiment is shown having the input to the timing element 40 and the diode 50 connected to the terminal 13. However, as an alternative, the input to the timing element 40 and the diode 50 may be connected to the terminal since at that location a speed dependent signal is likewise present the rear edge of which conforms to the rear edge of the signal U13. In either case, the closing angle control device 14 together with AND gate 16 and frequency generator 18 will usually be provided.

With each rising edge (or with each rear edge) of the signals U13, the timing element 40 is triggered and during its forward period, the capacitor 44 is charged through the resistor 43. A discharge of the capacitor 44 through the resistor 43 and the resistor 42 takes place in the static condition of the timing element 40. Due to the continual charging and discharging of the capacitor 44, a swinging DC voltage is applied to it in accordance with the speed, which swings about a central value which is proportional to the speed. The transistor 46 is made more or less conductive in accordance with the said capacitor voltage, whereby a more or less larger charging current flows into the capacitor 47 in accordance with the speed.The capacitor voltage built up thereby is transmitted to the threshold value stage 51 the output from which changes from a l-signal to a 0-signal on reaching its threshold value, which blocks the AND gate 16 according to Figure 1. At the end of each of the signal sequences U13, the capacitor 47 is discharged through the diode 50.

Digital embodiments can also be used instead of the illustrated analog embodiment of the invention. In so doing, the capacitors can be replaced by digital counters and the charging currents can be replaced by charging frequencies.

WHAT WE CLAIM IS:- 1. An ignition system comprising an electronic device responsive to a signal sequence derived from a rotary generator arrangement for generating a spark band consisting of a plurality of ignition sparks at each ignition instant, and a limiting device for limiting the duration of the spark band, said limiting device comprising a first storage device arranged to be charged in accordance with speed for speed dependent control of the limiting device, and a second storage device arranged to be subjected to a further charging procedure, the end of the spark band being established by the second storage device reaching a threshold value whereby the said instant can be predetermined by a determined ratio of the charging value of the first storage device with respect to the charging value of the second storage device.

2. An ignition system according to claim 1 wherein a comparator is provided, the comparison inputs to which are connected to the two storage devices and the two storage devices are arranged to be charged alternately during signal and signal pauses of the signal sequence providing an ignition sequence, whereby when the charging values are equal the end of the spark band is established by the comparator output.

3. An ignition system according to claim 2 wherein both storage devices are arranged to the reset by a signal edge of the signal sequence.

4. An ignition system according to claim 2 or 3 wherein a threshold value stage for rapid discharge of the storage device on reaching the threshold value, is connected in parallel with the first storage device.

5. An ignition system according to claim 1 wherein the first storage device always has a speed dependent charging value due to speed dependent charging

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. capacitor 22 is discharged through the diode 23 and the capacitor 27 is discharged through the diode 29 and the collectoremitter path of the transistor 30. The capacitor 32 is temporarily charged by the rising edge generated at this instant at the output from the inverter 24 and thus switches the transistor 30 into its conductive condition. The voltage rise in the capacitor 27, is limited by the Z-diode 28, in place of which an optional threshold value stage can also be used. This causes limiting of the spark band to a maximum value which cannot be exceeded even on further variation of the speed. In the second embodiment illustrated in Figure 3, the terminal 13 is connected to the anode of a diode 41 through a timing element 40 formed, for example, as a monostable switching stage, the cathode of the diode 41 being connected to earth through a resistor 42. The series circuit of a further resistor 43 and a capacitor 44 is connected in parallel with the resistor 42. The terminal of the capacitor 44 remote from earth is connected through a further resistor 45 to the base of a pnp transistor 46 the collector of which is connected to earth through a capacitor 47 and the emitter of which is connected through a resistor 48 to a terminal 49 which, in its turn, is connected to the positive pole of a supply voltage source. Furthermore, the collector of the transistor 46 is connected through a diode 50 to the terminal 13 and through a threshold value stage 51 to the terminal 33. The second embodiment of a limiting stage for the spark band duration illustrated in Figure 3, can be used instead of the limiting stage 19 in Figure 1. The circuit arrangement of the second embodiment is shown having the input to the timing element 40 and the diode 50 connected to the terminal 13. However, as an alternative, the input to the timing element 40 and the diode 50 may be connected to the terminal since at that location a speed dependent signal is likewise present the rear edge of which conforms to the rear edge of the signal U13. In either case, the closing angle control device 14 together with AND gate 16 and frequency generator 18 will usually be provided. With each rising edge (or with each rear edge) of the signals U13, the timing element 40 is triggered and during its forward period, the capacitor 44 is charged through the resistor 43. A discharge of the capacitor 44 through the resistor 43 and the resistor 42 takes place in the static condition of the timing element 40. Due to the continual charging and discharging of the capacitor 44, a swinging DC voltage is applied to it in accordance with the speed, which swings about a central value which is proportional to the speed. The transistor 46 is made more or less conductive in accordance with the said capacitor voltage, whereby a more or less larger charging current flows into the capacitor 47 in accordance with the speed.The capacitor voltage built up thereby is transmitted to the threshold value stage 51 the output from which changes from a l-signal to a 0-signal on reaching its threshold value, which blocks the AND gate 16 according to Figure 1. At the end of each of the signal sequences U13, the capacitor 47 is discharged through the diode 50. Digital embodiments can also be used instead of the illustrated analog embodiment of the invention. In so doing, the capacitors can be replaced by digital counters and the charging currents can be replaced by charging frequencies. WHAT WE CLAIM IS:-

1. An ignition system comprising an electronic device responsive to a signal sequence derived from a rotary generator arrangement for generating a spark band consisting of a plurality of ignition sparks at each ignition instant, and a limiting device for limiting the duration of the spark band, said limiting device comprising a first storage device arranged to be charged in accordance with speed for speed dependent control of the limiting device, and a second storage device arranged to be subjected to a further charging procedure, the end of the spark band being established by the second storage device reaching a threshold value whereby the said instant can be predetermined by a determined ratio of the charging value of the first storage device with respect to the charging value of the second storage device.

and constant discharging operations, by which charging rate a charging source for the second storage device can be controlled and that the end of the spark band can be established by a threshold value stage connected to the second storage device.

6. An ignition system according to claim 5, wherein the second storage device can be re-set by a signal edge of the signal sequence.

7. An ignition system according to any one of the preceding claims, wherein a gating stage, controlled by the limiting device, is provided, through which the output signals from the electronic device for generating a spark band can be blocked.

8. An ignition system according to any one of the preceding claims, wherein a closing angle control device is provided, through which the electronic device for generating the spark band and/or the limiting device can be triggered.

9. An ignition system substantially as hereinbefore described with reference to the accompanying drawings.