FR2743607A1 - Ignition advance angle control system for internal combustion engine e.g. for motor cycle - Google Patents

Abstract

The ignition advance control system has a first CR circuit which starts to discharge at a point associated with a maximal ignition advance. A second CR circuit starts to charge at the moment associated with the maximal advance angle, and discharges after having charged fully, at a moment associated with the minimal advance angle. An advance angle control circuit generates an ignition signal at the intersection between the discharge curve of the first circuit and the charging curve of the second circuit. The ignition signal can be generated by a circuit (13) independently of the advance circuit, and the advance circuit can be inhibited by a device (14) at low engine speeds.

Description

IGNITION CONTROL SYSTEM
The present invention relates to an ignition control system, used for controlling the ignition advance angle of an internal combustion engine.

An ignition advance angle control in an ignition system for an automobile can be implemented in a variety of circuit configurations. For example, it is possible to obtain a temporal positioning of the ignition which undergoes linear fluctuations relative to the increase or the decrease in the engine rotation speed, this by means of a simple circuit configuration, using CR type waveforms, having a curved characteristic, by providing two circuits
CR, by comparing the discharge form wave of one of the two circuits to a charge wave form of the other, within a range of possible controls of the ignition advance angles and controlling the positioning time of ignition at the point of intersection of the two waveforms. An example of such a circuit configuration is shown in Figure 7.

 FIG. 7 represents a diagram, given by way of example, of a control circuit of an ignition system for a four-stroke engine intended for a motorcycle. A signal from an excitation coil 1 is supplied to an EXT terminal of a control circuit 2 of this system, and is rectified into a positive half-wave signal by a diode D1. The positive half-wave signal electrically charges a main capacitor C1 which can be selectively discharged by an SCR thyristor. The discharge current of the main capacitor C1 is supplied to a main coil of an ignition coil system 3 via an IGN terminal, so that a spark is produced from a connected spark plug 4 to a secondary coil of the ignition coil system 3.

 The signal supplied to the EXT terminal is also transmitted from the thyristor trigger circuit block 6 via an electrical feedback block 5. The thyristor trigger circuit block 6 controls the SCR thyristor gate.

 To a PC terminal of the control circuit 2 is connected a pulsator coil 7 generating a pulse signal at each maximum ignition advance angle and at each minimum ignition advance angle, these angles defining a range of ignition advance angles possible. The pulse signal generated by the pulsator coil 7 is supplied via the PC terminal to a block of the pulsator control circuit 8 located in the control circuit 2.

From circuit block 8, a pulse signal corresponding to the maximum ignition advance angle, and a pulse signal corresponding to the minimum ignition advance angle, are generated and transmitted to a Ignition advance angle control circuit block 10.

The circuit block 10 provides an ignition advance angle control signal to the thyristor trip circuit block 6 which, in response to the ignition advance angle control signal, provides a trigger signal SCR thyristor.

 In the ignition advance angle control circuit block 10, the transistors Q9, Q10 are put into service by the maximum ignition advance angle signal (by the rise of the signal at node D). generated by the pulsator control circuit block 8 at each maximum ignition advance angle, by charging a capacitor C2 with the time constant determined by the circuit CR formed by the capacitor C2 and a resistor Ril (such that represented in the waveform at node E in FIG. 8>. At each minimum ignition advance angle, the transistors Q9 and Q10 are both turned off in response to the signal singing at node D, caused by the pulsator control circuit block 8, while a QH transistor is turned on by the ignition advance angle pulse signal mlnlmal (the low level signal {L} at node C ), which fully charges the capacitor C2 in an instant. The capacitor C2 is discharged by a resistor ce R1 on the disappearance of the minimum ignition advance angle pulse signal (the high level signal (H) at node C), until the subsequent introduction of the angle pulse signal d 'maximum ignition advance, the voltage signal (at node E) of capacitor C2 being supplied to a comparator CP1.

 The comparator CP1 is also supplied with a signal (at node F) which must be compared with the above signal (at node E). This signal (the waveform at node F in FIG. 8) is the voltage signal of a capacitor C3 which is charged / discharged according to the state of a transistor Qil which is put into service in response to the signal d '' maximum ignition advance angle (the rise in signal at node D) and deactivated in response to the minimum ignition advance angle signal (the fall in signal at node D). In other words, when the transistor Qll is out of service the capacitor C3 is charged at a voltage Vd determined by a voltage divider formed by the resistor R2 and R3 and, when the transistor Qll is in service, the capacitor C3 is discharged by a resistor R4.

The voltage of each capacitor C2, C3 (at nodes E, F) is introduced into an ignition angle advance comparator CP1. The output (at node G) of the comparator CP1 activates a transistor Q13 via a transistor Q12 and the output signal of the transistor
Q13 is transmitted to the thyristor trip circuit block b.

 Referring to Figures 8 to 1U, the operation of the ignition control circuit constructed as indicated above will be described below. At node A, shown in Figure 7, a positive pulse signal is generated at each maximum ignition advance angle and a negative pulse signal is generated at each minimum ignition advance angle, as shown by the highest waveform in Figure 8. The pulsator control circuit block 8 generates a low level pulse signal L at each minimum ignition advance angle, as shown by the upper median waveform (at node C) and a rectangular wave which is at a high level H for a period going from a maximum ignition advance angle to a ignition advance angle subsequent minimum (the range of possible controls for the ignition advance angle? as shown by the middle waveform (at node D) in Figure 8.

 The signals present at nodes E and F that are in the ignition advance angle control circuit block read vary, as represented by the lower median waveforms (nodes E, F) on the FIG. 8, following the operation of the circuits CR mentioned above and a signal equivalent to the ignition signal is generated in T1 when the signals E and F cross each other within the limits of the possible range of commands of the angles d ignition advance, as shown by the lowest waveform (at node G) in Figure 8. Therefore, in the region of low engine speeds below an engine speed N1 represented in FIG. 9, when the speed of rotation of the motor decreases the sign that one has at the node E decreases until reaching a lower level as represented by the line in dashed lines in FIG. 8 and the temporal positioning d ignition Td determined by the intersec point tion of the two signals shifts towards the minimum ignition advance angle.

 In a control as described above, it is possible to carry out a control of the preferable time positioning for ignition with respect to the engine rotation speed by modifying the ignition time positioning as a function of the speed range. of engine rotation for an ignition advance angle control which goes from the engine rotation speed N1 for the minimum ignition advance angle DS to the engine rotation speed N2 to the advance angle DF maximum ignition. However, when the maximum engine speed N2 of the engine speed range of the ignition advance angle control is shifted to a higher engine speed, the following problem may arise.

In an ordinary case, the ignition advance angle in a certain range of low engine rotation speeds is controlled for the constant minimum ignition advance angle, as represented by a solid line in FIG. 9 However, in the case where the maximum engine rotation speed N2 of the range relating to the ignition advance angle control is fixed at a certain high engine rotation speed, the discharge waveform at the node
E extends in an almost flat area of the low speed range of the motor and, as a result, the voltage level at node E, when charging begins, becomes roughly constant. In the meantime, the discharge curve at node F also changes, with a permanent time constant.

Thus, the period of time corresponding to the possibility of range of controls of the ignition advance angles is extended (from T1 to T2 in FIG. 10) relatively longer If compared with the extension (from TI1 to T12 in FIG. 10) of the period of time from the start of the range of possible commands for the ignition advance angles to the point of intersection of the two signals. As a result, the ignition advance angle determined by the intersection point of the two signals is advanced. Thus the problem arises that, when the engine rotation speed decreases, the ignition advance angle is advanced, leading to a less preferable engine starting characteristic.

 In view of these problems of the prior art, a main object of the present invention is to provide an ignition control system intended to control the temporal positioning of ignition with respect to the engine rotation speed by using two circuits CR type, without timing ignition timing advance in an area of low engine rotation speed.

 According to the present invention, the present ignition control system comprises first and second CR circuits; an ignition advance angle control circuit for generating an ignition signal at a point of intersection of the discharge curve of the first CR circuit and the charge curve of the second CR circuit; a circuit for generating an ignition signal at the minimum ignition advance angle independent of the ignition advance angle control circuit; and means for disabling the ignition advance angle control circuit in a range of engine rotation speeds less than a prescribed engine rotation speed (N1 in Fig. 9).

 In a preferred embodiment of the present invention, the means for disabling the ignition advance angle control circuit comprises an ignition advance angle control circuit for low engine speed intended to prevent the charge of the second CR circuit on the range of possible commands for the ignition advance angles when a discharge voltage of the second CR circuit is detected below a threshold voltage.

The present invention will now be described below with reference to the accompanying drawings, in which
Figure l shows a circuit diagram of an ignition system according to the present invention suitable for a four-stroke engine intended for a motorcycle;
Figure 2 is a diagram showing a pulsator input circuit block 8a in Figure 1;
Figure 3 is a diagram showing a pulse generator pulse generator block 8b in Figure 1;
FIG. 4 is a diagram showing an ignition advance angle control block 14 of low engine rotation speed as in FIG. 1;
Figure 5 is a diagram of the comparator 11 power supply according to Figure 1
Figure 6 is a time positioning diagram showing waveforms at different points on the control circuit;
Figure 7 is a schematic circuit diagram of a conventional ignition system suitable for a four-stroke engine of a motorcycle;
FIG. 8 is a time positioning diagram showing conventional waveforms of the ignition time positioning control;
Fig. 9 is a graph showing a timing characteristic of conventional ignition;
FIG. 10 is a time positioning diagram showing conventional waveforms of the ignition timing positioning control;
FIG. 11 is a circuit diagram representing a physical trip unit block, such as in FIG. 1.

 Now, the present invention is described below in more detail in terms of concrete embodiment with reference to the accompanying drawings.

 FIG. 1 is a diagram showing a control circuit of an ignition system according to the present invention, suitable for a four-stroke engine intended for a motorcycle. Parts similar to those shown in the prior art are designated by identical reference numbers and their detailed description will be omitted.

 In this embodiment, a pulsator input circuit block 8a and a voltage pulse generation block 8b for controlling the pulsator constitute a circuit which is equivalent to the pulsator control circuit block of the art. anterior, shown in FIG. 1. A pulse signal generated by a pulsator coil 7 is supplied, via a PC terminal, to the pulsator input circuit block 8a, in the control circuit 2. From the circuit 8a a pulse signal corresponding to the maximum ignition advance angle is generated and transmitted to the pulsator control voltage pulse generation block b and a pulse signal corresponding to the angle of Minimum ignition advance is generated and transmitted to both the pulsator control voltage pulse generation block 8b and an ignition advance angle control circuit block 10.

 The pulsator control voltage pulse generation block 8b generates a voltage pulse signal for controlling the pulsator whose pulse width corresponds to the range of possible commands for the ignition advance angles. The pulse control voltage pulse signal is transmitted to the ignition advance angle control circuit block 10 and to a comparator power supply unit 11.

 A physical trigger circuit block 13 which is shown in detail in Figure 11 is also provided. The physical trip circuit block 13 contains a transistor Q19, turned on by the low level signal (the minimum ignition advance angle signal) at node C. The ON signal of the transistor QIY switches the transistor Q13 of the ignition advance angle control circuit block 10 in operation, so that an ignition signal is generated for the minimum ignition advance angle US.

 In addition, an ignition advance angle control block 14 of low engine rotation speed is provided, communicating with the ignition advance angle control circuit block read. The low speed engine advance ignition angle control unit 14 is constructed so as to be activated by the power supply signal from the comparator power supply unit 11. Similarly, the Ignition advance angle control circuit block read is also constructed to be activated by the power supply signal from the comparator power supply block II.

The pulsator input circuit block 8a is constructed as shown in FIG. 2. In this embodiment, the maximum ignition advance angle pulse signal from the pulsator coil 7 is positive and the minimum ignition advance angle pulse signal from the pulsator coil 7 is negative. The maximum ignition advance angle pulse signal switches a transistor Q2 on, while the minimum ignition advance angle signal switches a transistor
Q3 in service. The signal ON from transistor Q2 is supplied to the pulser control pulse generator block 8b, on the other hand, the signal EN
SERVICE of transistor Q3 is supplied to both the pulsator control pulse generator block Hb and the ignition advance angle control circuit block 1U.

 As shown in Fig. 3, in the pulsator control pulse generation block 8b a flip-flop circuit is formed using transistors Q4, Q5, Q6 and Q7. When the transistor Q2 of the pulser input circuit block 8a is turned on in response to the maximum ignition advance angle pulse signal as described above, the transistor 94 is turned on causing the commissioning of transistor Q5. This, in turn, turns on the transistor Q / and the signal ON of the transistor Q7 is transmitted, as a pulse pulse control pulse signal mentioned above, both to the control circuit block d ignition advance angle 10 and to the comparator power supply unit 11.

When the transistor Q3 is turned on in response to the minimum ignition advance angle pulse signal, the transistor Q6 is turned on. This causes transistor Q7 to go out of service, cutting off the output of the pulsator control voltage pulse signal.

As shown in FIG. 4, the ignition advance angle control block 14 for low engine rotation speeds contains a comparator CP3. The output of comparator CP3 controls the transistor Q9 located in the ignition advance angle control circuit block 10. The comparator CP3 supplies the signal to node E in the angle control circuit block. ignition advance 10 and a constant voltage threshold signal VL coming from a voltage divider constituted by resistors R9 and
R10. The electrical supply voltage intended for the comparator CP3 is supplied by the transistor Q20, which is put into service by the electrical supply signal coming from the comparator power supply unit 11.

 The power supply unit 11 of the comparator is constructed in the manner shown in FIG. 5. The ON signal of transistor Q7, which is present in the pulsator control voltage pulse generation block 8b, activates a transistor Q14 which, in turn, activates a transistor Q15. This activates a transistor Q20, which supplies the control power supply voltage to the comparator CPJ mentioned above, as its power supply voltage. Correspondingly, the comparator CP3 is activated only on the range of possible ignition advance angle commands and is disabled when one is outside this range, eliminating any unnecessary power consumption, thereby contributing to reduce the consumption of electrical power.

 The ignition signal is generated in an ordinary manner, as shown in the prior art, at the point of intersection (T1 in FIG. 8), at which the wave of discharge of the signal at the node F exceeds the form of load waves at the signal at node E in the range of possible ignition advance angles. When the motor rotation speed decreases, the period of time necessary for the discharge associated with the node E becomes longer. as a result, as shown by the dashed lines in FIG. 8, the voltage which is obtained at the start of the charge becomes smaller, the point of intersection of the signals E and F shifting towards the angle of minimum ignition advance, thereby giving a delay control of the ignition advance angle, reacting to the decrease in the engine speed.

 When the motor rotation speed further decreases and the signal at node E must decrease below a threshold value VL as shown in FIG. 6, the comparator Cp3, provided in the advance angle control block ignition 14 for low engine rotation speeds, generates a low level signal, so that any commissioning of transistor Q9 is prevented. Thus, the transistor Q10 does not go into service even when the positive rectangular signal which one has at the node D is generated and the charging of the capacitor C2 (the line in dashed lines in FIG. 6) is prevented. In such a case, the ignition signal is generated only by the physical trigger circuit block 13, at the minimum ignition advance angle. Thus, the temporal positioning of the ignition in the range of low engine rotation speeds is regulated for the minimum ignition advance angle.

 When the motor rotation speed decreases and the signal at node E must exceed the threshold value VL so that these curves no longer cross, the transistors Q9 and Q1U are authorized to be put into service and the angle d ' Ignition advance is usually regulated by the point of intersection of signals E and F. The engine speed at which the manner in which the ignition timing control is switched is adjustable by changing the values of the resistors RY and R1U, resistors determining the threshold value VL making it possible to obtain a simple design and adjustment.

 According to the present invention, as described above, in the ignition advance angle control in which the ignition advance angle is controlled by the point of intersection of the discharge waveforms and load of two CR circuits, the load of the CR circuit which must start to be charged from the start of the possible range of ignition advance angle controls is inhibited within the limits of the possible range of angle control Advances on ignition when the discharge voltage of the CR circuit must decrease below a threshold value. This ensures that the ignition timing is maintained for the minimum ignition advance angle within a certain range of low engine rotational speeds allowing the engine rotational speed range of the advance angle control ignition to be enlarged at a higher engine speed. Such a control can be carried out by using a simple circuit, implementing the comparison of the discharge voltage and the threshold value leading to a simple, economical system.

Claims (2)

 1. - Ignition control system for an internal combustion engine characterized in that it comprises  a first CR circuit (C3, R2, R3, R4, Qll) starting to be discharged for a moment, associated with a maximum ignition advance angle, of a range of possible commands of advance angles of engine ignition;  a second CR circuit (C2, R1, R11, Q8, Q9, Q10), starting to be charged from the time associated with the maximum ignition advance angle and discharged after being fully charged at a time associated with a minimum ignition advance angle of the possible control range of ignition advance angles;  an ignition advance angle control circuit (CP1, Q12), designed to generate an ignition signal at a point of intersection between the discharge curve of the first circuit CR and the charge curve of the second circuit CR;  a circuit (13) for generating an ignition signal at the minimum ignition advance angle, independent of the ignition advance angle control circuit; and  means (14) for disabling the ignition advance angle control circuit in a range of engine rotation speeds less than a prescribed engine rotation speed.  2. - ignition control system according to claim 1, wherein the means for disabling the ignition advance control circuit (14) comprises a circuit for controlling the ignition advance angle for low engine rotation speed intended to prevent charging of the second CR circuit over the range of possible commands for the ignition advance angles when there is detection of a discharge voltage of the second CR circuit below a voltage alone .