GB1591684A

GB1591684A - Ignition system for internal combustion engines

Info

Publication number: GB1591684A
Application number: GB1027878A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-03-16
Filing date: 1978-03-15
Publication date: 1981-06-24
Also published as: DE2711433A1; FR2393166A1; DE2711433C2; FR2393166B1

Description

(54) AN IGNITION SYSTEM FOR INTERNAL- COMBUSTION ENGINES (71) We, ROBERT BoscH G.m.b.H., 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 present invention relates to an ignition system for an internal combusion engine, and in particular to such an ignition system wherein the ignition tilming is established by means of counting procedures.

One such system is disclosed in U.S. specification No. 3,908,616 in which counting procedures take place in a counting stage at two different frequencies. However, the length of the counting procedure at one frequency is established by the length of a signal generated in response to a predetermined angular rotation of the engine. The closing time of the electrical switch in the primary current circuit of the ignition coil is therefore estab- lished in response to the length of this generated signal. Hence the generator providing this signal must be carefully constructed so that differences in the rising and falling edges of the signal do not result in errors in the closing time or the ignition instant.If, for example, the system is to be adaptable for installation in engines having different numbers of cylinders, careful matching of the generator will be necessary for each installation.

The present invention provides an ignition system for an internal combustion engine comprising angular generating means arranged to generate a signal which is indicative of the engine rotating through a predetermined angle and which is advanced relative to an ignition instant by a fixed angle of rotation, pulse generating means arranged to generate pulse signals at first and second frequencies for counting in counting means and being responsive to said angular-indicative signal to switch counting of pulse signals at the second frequency to those at the first frequency, first decoding means responsive to the counting means attaining a first count value to trigger the closing time of an electrical switch in the primary current circuit of an ignition coil, and second decoding means responsive to the counting means attaining a second count value to switch counting of the pulse signals at the first frequency to those at the second frequency and to establish the beginning of a successive counting cycle.

Embodiments of the invention have the advantage that a comparatively simple generator can be chosen for controlling the ignition system and which, for example for a four cylinder internal combustion engine, has two symmetrical markers per crankshaft rotation. On changing the generator system to a plurality of generator markers per revolution of the rotating shaft, it is sufficient to provide a different number of symmetrically arranged generator markers for a plurality of ignition sparks per revolution.

The preferred embodiment includes a bistable switching stage for establishing the closing time of the electrical switch, the switching condition of which is determined by signals from the two decoding means.

In this manner, not only the beginning but also the end of the closing time is established by the counting procedure in the counting stage and no special closing time control means is required.

Furthermore, the second decoding means for the switching over from the first frequency to the second frequency can Ibe so designed that it delivers an output signal at the lowest counting condition of the counting means. Thus, for example, a minimum count output of the counting means can Ibe used as the decoding means.

By these means, a very exact closing time of the electrical switch and, at least during steady-state operating conditions, a very exact ignition instant can be established by utilising a very simple generator arrangement. Switching over between the second and the first frequencies may be responsive to short pulses from the generator arrangement. These pulses are advanced relative to the ignition point by a fixed angle of rotation of the engine.

Preferably the end of the closing time is established by the second decoding means.

In order that the present invention may be more readily understood, an embodiment .thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram of the em bodiment, and Figure 2 is a signal diagram for explaining the operation of the embodiment shown in Figure 1.

In the embodiment illustrated in Figure 1, a generator arrangement 10, preferably connected to the crankshaft of an internal com bustion engine, is connected to a pulse shaping stage 11 preferably designed as a Schmitt ,trigger. In the illustration, the generator 10 is formed as an inductive generator; however, alternative arrangements, for example in the form of a contact breaker, a Halleffect generator or an optical generator, are possible. A generator disc 12 has two markers ,l3 which are sensed by the pickup element 14. The illustrated arrangement provided with two markers per revolution is, for example, suitable for a four cylinder combustion engine.In a manner not illustrated, the generator arrangement 10 can have a known mcchanical ignition timing adjustment device, or an electronic ignition timing adjustment arrangement can be associated therewith as is likewise known in many forms.

The output from the pulse shaping stage 11 is connected to the resetting input R of a flipflop 15, the output Q of which is connected to the counting direction input V/D of a counting stage 16. Furthermore, the output Q from the flipflop 15 is connected through an AND-gate 17 to one input to an OR-gate 18, the output from which is connected to the clock input C of the counting stage 16. The output Q from the flipflop 15 is connected through a further AND-gate 19 to a further input to the OR-gate 18. A frequency generator 20 is, on the one hand, connected to a further input to the ANDgate 17 and on the other hand, is connected to a further input to the AND-gate 19 through a frequency reducing stage 21.An arrangement of two frequency generators or a single frequency generator which has two different output frequencies, can alternatively be provided instead of the combination of a frequency generator and a frequency reducing stage.

The numerical outputs from the counting stage 16 are connected through a first decoding stage 22 to one input to an AND-gate 23 the second input of which is connected to the counting direction input V/D to the counting stage 16. The output from the AND-gate 23 is connected to the setting input S of a further flipflop 24. The numerical outputs from the counting stage 16 are further connected to the setting input S to the flipflop 15 and to the resetting input R to the flipflop 24 through a second decoding stage 25.The output Q from the flipflop 24 is connected to the control input of a conventional ignition arrangement 26 in which the series circuit of the primary winding of an ignition coil 28 and the switching path of an electrical switch 29, which is preferably formed as a transistor or a thyristor, is connected between earth and a terminal 27 connected to the positive pole of a voltage supply source. The interconnection between the electrical switch 29 and the ignition coil 28 is connected to earth through its secondary winding and an ignition gap 30. The ignition gap 30 is formed in the usual manner as a sparking plug. With a plurality of sparking plugs, a high-tension distributor can be provided in known manner.

The method of operation of the embodiment illustrated in Figure 1 will be explained in the following with the aid of the signal diagram illustrated in Figure 2. In addition, the terms signal and 0-signal used in digital technology will first of all be defined.

A l-signal represents a potential which is of the order of the positive potential of the supply voltage and a 0-signal represents a potential which corresponds substantially to earth potential.

For each revolution of the engine, the illustrated generator arrangement 10 delivers two short signals which appear at the output from the pulse shaping stage 11 as two short pulses A separated by a predetermined angle of rotation '0!k. One such pulse A resets the flipflop 15 as a result of which, at the complementary output Q from the flipflop 15 there appears a signal B which, on the one hand, enables the AND-gate 17 to transmit the clock frequency fl, and on the other hand, changes the counting direction of the counting stage 16 from upwards counting to downwards counting and thirdly, enables the AND-gate 23 for the output signals from the first decoding stage 22. If the counting condition Z at the output from the counting stage 16 reaches a value Zx, then the first decoding stage 22 delivers an output signal which sets the fiipflop 24 through the AND-gate 23 in the form of a signal E. At the output Q of flipflop 24, a signal F appears which starts the closing time of the electrical switch 29, whereupon a current begins to flow through the ignition coil 28. When the counting condition Z at the output from the counter 16 reaches a value Zo at a fixed angle of rotation lao from the first pulse A, then the flipflop 24 is reset, whereupon the signal F is terminated.

The current flow through the ignition coil 28 is interrupted whereupon an ignition spark is induced at the ignition gap 30.

Simultaneously, the flipflop 15 is set by the output signal from the decoding stage 25, whereupon the AND-gate 17 is blocked, the AND-gate 19 is opened allowing transmission of the clock frequency f2, the counting direction input V/D to the counting stage 16 is changed over and the AND-gate 23 is blocked. It can be seen from the upwards and downwards slopes of the counting condition waveform Z in Figure 2 that, in this embodiment, the ratio of the frequencies f2: fl equals ICgO/(rOf;t Decoding stages 22, 25 can, for example, be designed as gating arrangements comprising AND or NOR-gates. If the lowest possible counting condition of the counting stage 16 is selected as a counting condition Zo, then the decoding stage 25 can be designed very simply.Many counting stages have a minimum count output at which a signal appears in the lowest counting condition. Such an output can then comprise the decoding stage.

Instead of the alternating upwards and downwards counting procedures in the counting stage 16, only upwards or only downwards counting procedures comprising two different frequencies can take place in an equivalent manner.

If a special closing time control means has to be provided, then the flipflop 24 can be omitted and the said closing time control means can be controlled directly by the output signal E from the AND-gate 23.

One such special closing time control means is, for example, an apparatus for generating a plurality of ignition sparks at each ignition instant, as described for example in German OS 2606890, 2616693 and 2619556.

Furthermore, with such a multi-spark ignition device, the signal IF can be brought into play for limiting the spark bandwidth.

WHAT WE CLAIM IS: 1. An ignition system for an internal combustion engine comprising angular generating means arranged to generate a signal which is indicative of the engine rotating through a predetermined angle and which is advanced relative to an ignition instant ;;by a fixed angle of rotation pulse generating means arranged to generate pulse signals at first and second frequencies for counting in counting means and being responsive to said angular-indicative signal to switch counting of pulse signals at the second frequency to those at the first frequency, first decoding means responsive to the counting means attaining a first count value to trigger the closing time of an electrical switch in the primary current circuit of an ignition coil, and second decoding means responsive to the counting means attaining a second count value to switch counting of the pulse signals at the first frequency to those at the second frequency and to establish the beginning of a successive counting cycle.

2. An ignition system according to claim 1 wherein said counting means is arranged to change its counting direction in response to said angular-indicative signal and in response to the second decoding means detecting the second count value, the ratio of said second frequency to said first frequency being equal to 'o:,/(otk), wherein zsso is the fixed angle of rotation and k is the predetermined angle.

3. An ignition system according to claim 1 or 2 further including bistable switching means for establishing the closing time of the electrical switch in the primary current circuit, in response to the first and second decoding means.

4. An ignition system according to claim 1, 2 or 3 wherein the second count value is arranged to be the lowest count value of the counting means.

5. An ignition system according to any one of the preceding claims including further bistable switching means for switching between the pulse signals at the first and second frequencies, and for changing the counting direction in the counting means.

6. An ignition system for an internal combustion engine, substantially as hereinbefore described, with reference to the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. coil 28. When the counting condition Z at the output from the counter 16 reaches a value Zo at a fixed angle of rotation lao from the first pulse A, then the flipflop 24 is reset, whereupon the signal F is terminated. The current flow through the ignition coil 28 is interrupted whereupon an ignition spark is induced at the ignition gap 30. Simultaneously, the flipflop 15 is set by the output signal from the decoding stage 25, whereupon the AND-gate 17 is blocked, the AND-gate 19 is opened allowing transmission of the clock frequency f2, the counting direction input V/D to the counting stage 16 is changed over and the AND-gate 23 is blocked. It can be seen from the upwards and downwards slopes of the counting condition waveform Z in Figure 2 that, in this embodiment, the ratio of the frequencies f2: fl equals ICgO/(rOf;t Decoding stages 22, 25 can, for example, be designed as gating arrangements comprising AND or NOR-gates. If the lowest possible counting condition of the counting stage 16 is selected as a counting condition Zo, then the decoding stage 25 can be designed very simply.Many counting stages have a minimum count output at which a signal appears in the lowest counting condition. Such an output can then comprise the decoding stage. Instead of the alternating upwards and downwards counting procedures in the counting stage 16, only upwards or only downwards counting procedures comprising two different frequencies can take place in an equivalent manner. If a special closing time control means has to be provided, then the flipflop 24 can be omitted and the said closing time control means can be controlled directly by the output signal E from the AND-gate 23. One such special closing time control means is, for example, an apparatus for generating a plurality of ignition sparks at each ignition instant, as described for example in German OS 2606890, 2616693 and 2619556. Furthermore, with such a multi-spark ignition device, the signal IF can be brought into play for limiting the spark bandwidth. WHAT WE CLAIM IS:

1. An ignition system for an internal combustion engine comprising angular generating means arranged to generate a signal which is indicative of the engine rotating through a predetermined angle and which is advanced relative to an ignition instant ;;by a fixed angle of rotation pulse generating means arranged to generate pulse signals at first and second frequencies for counting in counting means and being responsive to said angular-indicative signal to switch counting of pulse signals at the second frequency to those at the first frequency, first decoding means responsive to the counting means attaining a first count value to trigger the closing time of an electrical switch in the primary current circuit of an ignition coil, and second decoding means responsive to the counting means attaining a second count value to switch counting of the pulse signals at the first frequency to those at the second frequency and to establish the beginning of a successive counting cycle.