GB1566319A

GB1566319A - Device for periodically energising a coil

Info

Publication number: GB1566319A
Application number: GB2726277A
Authority: GB
Original assignee: Sev Marchal
Current assignee: Sev Marchal
Priority date: 1976-06-29
Filing date: 1977-06-29
Publication date: 1980-04-30
Also published as: DE2728623A1; IT1143817B; FR2357108A1; FR2357108B1; DE2728623C2; ES460171A1

Description

(54) A DEVICE FOR PERIODICALLY ENERGISING A COIL (71) We, SOCIETE POUR L'EQUIPMENT DE VEHICULES, a French Body Corporate of 26 rue Guynemer, Issy Les Moulineaux 92132, France, 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: It is well known that the energisation of the spark plugs of an internal combustion engine, used for instance to drive motor vehicles, is effected by using the high tension produced in the secondary winding of an induction coil whose primary winding is periodically connected to the vehicle's low tension D.C. electricity supply.The moment when the high tension is produced in the secondary winding, corresponds to the moment when the L.T. supply is interrupted in the primary winding; the moment after the circuit is opened, a discharge current is produced and after an intermission, the primary winding circuit is closed again to re-energise the coil. Generally, the value of the energisation is limited to a predetermined value Il and this value I1 is obtained at the end of a time interval T2 after the supply circuit of the primary winding has been closed.

This current is then maintained during time interval T1 before the circuit is opened again to obtain the secondary coil high tension to generate an ignition spark.

If the duration of the period between two incipient sparks is designated as T, the interval during which the make and break of the primary winding is closed as T3 and the interval during which the switch is open as T4, we obtain: T2 = T1 + T2 and T = T3 + T4 If the commutation of the primary winding is effected electronically, a transistor is generally used, set up as the series current regulator and this transistor is, for instance, in a Darlington pair. In such a device, a major difficulty lies in the fact that the regulating transistor which also fulfils the function of a circuit breaker is the source of an unduly high heat discharge, although it has already been suggested that the charging current of the coil should be given a value considered to be the optimum value.It has therefore been envisaged that the coil should be charged subject to interval T4 being given a constant value or by assigning a constant value to interval T3, but it was found that these imposed regulations of the coil charge were inadequate and still led to unduly high heat discharge in the control transistor which was also performing the function of circuit breaker of the primary winding.

Accordingly the present invention provides a device for periodically energising a coil with current limitation, the period of this periodic energisation being variable and designated as T, the energising current attaining its limit value in time T2 and being then maintained in the coil during time T1, the sum of (T1 + T2) being less than T, and the energisation of the coil being commenced after an interval T4 from the start of each period, such device including a closed loop control device for controlling T4 in such a way that the T1/T ratio should be a constant low predetermined value which is not zero.

It has been found that the heat output released in the control transistor performing the function of circuit breaker was proportional to ratio T1/T and thus the device according to the invention, allowing the T1/T ratio to be kept to a predetermined low constant value, irrespective of the variations of T, makes it possible to obtain at each cycle the same secondary voltage (by virtue of the constant current), and also less transistor heating. Thus the dissipated output of the transistor performing the role of circuit breaker can be kept to a value which is sufficiently low to be tolerated by the transistor.

The control comprised in the device accord ing to the invention determines the start of time interval T3, so that the T1/T ratio remains at a minimum value. This control is achieved by means of the closed loop which allows the effective T1/T ratio to be compared with a predetermined value which is sufficiently low to be tolerated by the said transistor. The more accurate the control device, the more closely will the effective T1/T will then approach the assigned value very closely. The control comprised in the device according to the invention determines the start of the period T3 to that the T1/T ratio remains constant.The closed loop allows the effective T1/T ratio to be compared with the predetermined value which is intended to be maintained, and allows the difference between the two values to be used, by means of a transmittance unit, to determine the end of the time T4.

Preferably, the device comprises, in order to obtain current limitation in the coil, a proportional series regulator which limits the energising current to a constant maximum level during interval T1; the proportional series regulator comprises a transistor in a Darlington pair. The closed loop control device comprises, (a) a device for identification of the mean value of the current limited by the proportional series regulator, the said mean value being a representation of the effective T1/T ratio; (b) a comparison device to compare this mean value with a reference level corresponding to the required tl/T ratio, the said comparison giving rise to a signal at level U; (c) a generator of periodic voltage V of period T, voltage V being timedependent and returning to zero at the end of period T during a time interval of much shorter duration than T; and (d) a device comparing voltages U and V allowing a signal to be generated when these are equal which initiates the charging of the coil.

The signal at level U is obtained by means of a circuit corresponding to a transmittance unit taking into account the characteristics of the control loop. The transmittance unit comprises amplifying and integrating devices. Voltage V is a function of time t of form a + bt + ce dt, a, b, c, and d being given constants. In an advantageous alternative, voltage V may be a time function of the form a + cede, a being positive constant, c and d being negative constants, and (a + c) being positive or zero. The device comprises a unit controlling the opening of the energising circuit of-the coil when interval T exceeds a predetermined limit.

To ensure an adequate discharge time T4 when period T is reduced, after the charging circuit of the coil has begun to be opened, so as to reduce the current in the coil sufficiently before the charging circuit is closed again, the device comprises a means formaintain- ing a minimum open interval T4 as from the beginning of each period T. The means for maintaining a minimum open interval T4 comprises a monostable circuit. The interval T4 of the discharge or of the opening is the time for the return to zero setting of the saw tooth pulse defined by the monostable circuit.

The primary winding of the coil has a resistance which is lower than 1 ohm. The proportional series regulator is exposed to the action of external parameters which affect the limiting value of the charging current.

The external parameters acting on the proportional series regulator will be one or more of: the speed of engine rotation, the duration of the discharge spark generated by the secondary current, the value of the inlet manifold depression, the engine temperature, the temperature of the air taken in for combustion purposes, or any other parameter capable of reducing fuel consumption and/or exhaust gas pollution.

The device according to the invention may be used with advantage to control the current supply of the primary winding of the ignition coil of an internal combustion engine which can be used in particular for motor vehicles.

The ignition spark will then occur at the end of each period T, period T being itself inversely proportional to the speed of the engine revolutions.

In order that the invention may be better understood, the object of the one embodiment which is illustrated in the attached drawings will be described below merely by way of illustration. In these drawings: Figure 1 is a graph showing the current levels, plotted with respect to time (shown on the x axis), of the current circulating in the primary winding of an ignition coil of a motor vehicle which incorporates a charging device according to the invention. The current is plotted on the y axis, and the graph represents one period of energising and of interrupting of the primary winding; Figure 2 represents a block diagram of the device according to the invention applied to the ignition coil of a motor vehicle: and figure 3 shows a detailed circuit diagram corresponding to the block diagram of Figure 2.

The device represented in Figures 2 and 3 is intended to allow the periodic energising of an ignition coil whose primary winding 1 is flux linked with a secondary winding 2 which delivers a high voltage current to the ignitionplugs of an internal combustion engine which is not shown. The common point of windings 1 and 2 is connected to the positive terminal 3 of the continuous L.T. electricity supply of the vehicle. The passage of the current in the primary winding 1 of the coil is controlled by transistor 4 whose emitter is connected to the frame by means of shunt 5.

When transistor 4 is blocked during inter val T4 at the beginning of each period T, the primary winding 1 is not being energised.

When transistor 4 is unblocked, the current establishes itself in winding 1 during time T2 then it attains the imposed maximum value I l and it is limited to this value by the fact that transistor 4 is connected to serve as a proportional series regulator. Current Il is maintained during interval T1 and is then cut at the end of period T when transistor 4 is blocked again, the decay of the current requiring a certain time from the instant when transistor 4 is blocked.

The principle of the energising device according to the invention, is to keep the T1/T ratio constant irrespective of the variations of T, so as to limit the dissipated heat output in transistor 4 to a predetermined value. This principle is illustrated by the diagram of Figure 2. Transistor 4 is controlled by a regulating device 6 which is fed a representation of the current in the coil at the terminals of shunt 5. This signal is fed to circuit 7a which is capable of supplying the mean value of the said signal: this mean value is a voltage which is proportional to the T,/T ratio.

In comparator 7b, the said mean value is compared to a reference value corresponding to a predetermined T1/T ratio. The difference between the two signals is amplified and sent into transmittance unit 7c of the control loop. This transmittance unit gives the system characteristics (stability, error, response time). The assembly of circuits 7a, 7b, 7c corresponds to a transformation device which has in its entirety been designated by 7. Device 7 supplies an output signal depending on the difference between the effective T,/T ratio and the required T1/T ratio. This output signal at level U is despatched to one of the inputs of a comparator 8 whose other input is supplied with voltage V by a voltage generator 9.Voltage generator 9 supplied a saw tooth profile voltage which is reset to zero by the signal received on terminal 10 originating from a sensor (not shown) which supplies the ignition signal, with or without correction for advanced timing. The sensor signal passes at first into a pulse forming circuit 9a which causes the saw tooth generator 9b to be reset to zero. The saw tooth profile voltage V supplied by unit 9 is compared with voltage U by the comparator 8 whose output generates a signal to be fed to regulator 6 to actuate the unblocking of transistor 4 i.e. to actuate the start of energising of winding 1.

Thus it will be seen that interval T4 is determined in terms of the value of the T1/T ratio so that the T,/T ratio is adjusted to the predetermined value which is required. If the effective T1/T ratio is too high, voltage U increases and time T4 is increased which reduces the value of interval T, by the same amount for a period T which is substantially constant; similarly, if the T1/T ratio is too small, voltage U decreases, interval T4 is shortened which increases time T1 and brings back ratio TI/T to the required value.

It should be observed that, if the engine stops, transistor 4 is, in such a device, placed in the unblocked position so that heating can occur, on stopping, by the regulation of the current in the primary coil winding. To avoid this drawback, an opening control 11 has been provided which, if period T exceeds a predetermined time, a second, for instance, despatches a signal to regulator 6 whcih actuates the blocking of transistor 4.

Moreover, when the speed of rotation of the engine, with which the device according to the invention is used, increases the period T decreases and interval T4 may become too short for the primary coil winding to have time for a complete discharge. Under these circumstances, a minimum value may be conveniently provided for the interval T4 which prevents the disappearance of the ignition spark at top engine speeds.

The circuit represented in Figure 3 shows the details of one embodiment of the block diagram of Figure 2. The sub-components of the block diagram have been assigned the same reference numbers on Figure 3. Transistor 4 which fulfils the function of circuit breaker for the primary coil winding is part of a Darlington pair circuit comprising another transistor 12, a Zener diode 13 which is arranged between the base of transistor 12 and the common collectors of transistors 4 and 12, and a capacitor 14 which is arranged in parallel between the collector and emitter of transistor 4. The base of transistor 12 is actuated through diode 15 by transistor 16 whose collector is linked to the positive terminal via resistor 17 and whose emitter is linked to the frame.The base of transistor 16 is linked to the frame by resistor 18 at the output of comparator 8 by resistor 19, and at the output of the operational amplifier 20 by resistor 21 and a Zener diode 22.

Amplifier 20 receives on one of its input terminals the voltage collected at the terminals of the shunt 5 and on its other input terminal (connected to the output by capacitor 23) a reference voltage supplied by a divider bridge formed by resistors 24 and 25 and Zener diode 26.

The mean value of the output signal delivered by amplifier 20 is obtained by means of resistor 27 and capacitor 28. This mean value is applied to one of the input terminals of the operational amplifier 29 and is compared by amplifier 29 with a reference voltage obtained by the divider bridge constituted by resistor 32 to the other input terminal of amplifier 29.

The terminal of amplifier 29 which receives the reference voltage is connected to the output terminal by a resistor 33 and this output is integrated at capacitor 34; two parallel circuits linked to capacitor 34 have been provided, one comprising resistor 35, the other comprising resistor 36 and diode 37: thus two different time constants are obtained for the charging and discharge of the capacitor, the time constant for charging being greater than the time constant for discharge which enables the device to respond rapidly to the engine accelerations.

The output of the transforming device 7, which depends on the difference existing between the effective T1/T ratio and the required T1/T ratio, is fed via resistor 38 to the inverter input of the operational amplifier 39 which constitutes the comparator 8.

The saw tooth profile voltage V supplied by the generator unit 9a, 9b is directed to the follower input of amplifier 39. The positive input of amplifier 39 is connected to the frame by capacitor 57 and to resistor 53 by resistor 58. Voltage V is obtained by a circuit constituted by resistor 40, diode 41 and a capacitor 42 arranged in series between the frame and the positive feed, voltage V being taken between resistor 40 and diode 41. A transistor 43 placed across the terminals of capacitor 42 allows the voltage V to be reset to zero each time a signal is supplied to terminal 10 by the sensor (not shown). This signal is transformed by a pulse forming circuit 9a and is applied via capacitor 44 and resistor 45 to the base of transistor 43. Resistor 46 is interposed between the frame and the junction point of capacitor 44 and resistor 45.

The pulse forming circuit for the signal from the sensor comprises an operational amplifier 47 whose signal input terminal is connected to the output via resistor 48, and to terminal 10 via two resistors 49 and 50.

The mid-point arranged between resistors 49 and 50 is connected to the frame by diode 51 and to the positive power terminal by diode 52 and by resistor 53 which is interposed between terminal 3 and Zener diode 26. The inverting input of amplifier 47 is connected to the frame by resistor 54 and to resistor 53 by resistor 55. The signal input of amplifier 47 is connected to resistor 53 by resistor The opening control circuit 11 takes its information from the output of diode 41.

This circuit is constituted by a capacitor 59 in series with resistor 60, the mid-point between these two components being connected by diode 61 to diode 52, and by diode 62 to the point common to capacitor 42 and diode 41, and finally by diode 63 to the follower input terminal of amplifier 39.

When the saw tooth profile voltage V has become equal to voltage U, the output of amplifier 39 which constitutes comparator 8, delivers a signal which acts on the base of transistor 16 and actuates the unblocking of transistor 4 to the extent that the blocking interval T4 has exceeded a predetermined value, 800,us for instance, to allow a sufficient discharge of the primary winding and thus to prevent a disappearance of the spark at high engine speeds of rotation. The predetermined time is the time of setting the saw tooth (voltage) to zero, defined by the monostable circuit 43 - 44 - 45 - 46.

When the engine is running, it will be seen that in the opening control circuit 11, capacitor 59 is discharged by transistor 43 at the end of each period. The voltage at its terminals is therefore negligible and does not affect the inverter input of amplifier 39. On the other hand, when the engine stops, transistor 43 no longer discharges capacitor 59, so that after one second, the voltage of the inverting input of amplifier 39 is built up by capacitor 59 and exceeds the voltage of the signal input which is limited by the Zener diode 26; thus causing the amplifier to switch over which allows transistor 4 to be blocked and hence to prevent a current consumption in the primary coil winding when the engine is stopped.

It will be seen that the device according to the invention makes it possible to reduce the heat output dissipated in transistor 4 to a very considerable degree and hence to increase its working life at moderate cost.

WHAT WE CLAIM IS: 1. A device for periodically energising a coil with current limitation, the period of this periodic energisation being variable and designated as T, the energising current attaining its limit value in time T2 and being then maintained in the coil during time T1, the sum of (T1 + T2) being less than T, and the energisation of the coil being commenced after an interval T4 from the loop control device for controlling T4 in such a way that the T1/T ratio should be a constant low predetermined value which is not zero.

2. A device according to claim 1 and including, in order to obtain the current limitation in the coil to be discharged, a proportional series regulator in the form of a Darlington pair transistor arrangement which limits the energising current to a constant maximum level during interval T1.

3. A device according to claim 2, wherein the proportional series regulator is subjected to the action of external parameters which affect the limit value of the charging current.

4. A device according to claim 3, wherein the external parameters acting on the proportional series regulator are one or more of: (a) the engine rotation speed, (b) the duration of the spark discharge of the secondary current, (c) the value of the inlet manifold depression for the engine, (d) the engine temperature, (e) the temperature of the air taken in for combustion and (f) any

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the output terminal by a resistor 33 and this output is integrated at capacitor 34; two parallel circuits linked to capacitor 34 have been provided, one comprising resistor 35, the other comprising resistor 36 and diode 37: thus two different time constants are obtained for the charging and discharge of the capacitor, the time constant for charging being greater than the time constant for discharge which enables the device to respond rapidly to the engine accelerations. The output of the transforming device 7, which depends on the difference existing between the effective T1/T ratio and the required T1/T ratio, is fed via resistor 38 to the inverter input of the operational amplifier 39 which constitutes the comparator 8. The saw tooth profile voltage V supplied by the generator unit 9a, 9b is directed to the follower input of amplifier 39. The positive input of amplifier 39 is connected to the frame by capacitor 57 and to resistor 53 by resistor 58. Voltage V is obtained by a circuit constituted by resistor 40, diode 41 and a capacitor 42 arranged in series between the frame and the positive feed, voltage V being taken between resistor 40 and diode 41. A transistor 43 placed across the terminals of capacitor 42 allows the voltage V to be reset to zero each time a signal is supplied to terminal 10 by the sensor (not shown). This signal is transformed by a pulse forming circuit 9a and is applied via capacitor 44 and resistor 45 to the base of transistor 43. Resistor 46 is interposed between the frame and the junction point of capacitor 44 and resistor 45. The pulse forming circuit for the signal from the sensor comprises an operational amplifier 47 whose signal input terminal is connected to the output via resistor 48, and to terminal 10 via two resistors 49 and 50. The mid-point arranged between resistors 49 and 50 is connected to the frame by diode 51 and to the positive power terminal by diode 52 and by resistor 53 which is interposed between terminal 3 and Zener diode 26. The inverting input of amplifier 47 is connected to the frame by resistor 54 and to resistor 53 by resistor 55. The signal input of amplifier 47 is connected to resistor 53 by resistor The opening control circuit 11 takes its information from the output of diode 41. This circuit is constituted by a capacitor 59 in series with resistor 60, the mid-point between these two components being connected by diode 61 to diode 52, and by diode 62 to the point common to capacitor 42 and diode 41, and finally by diode 63 to the follower input terminal of amplifier 39. When the saw tooth profile voltage V has become equal to voltage U, the output of amplifier 39 which constitutes comparator 8, delivers a signal which acts on the base of transistor 16 and actuates the unblocking of transistor 4 to the extent that the blocking interval T4 has exceeded a predetermined value, 800,us for instance, to allow a sufficient discharge of the primary winding and thus to prevent a disappearance of the spark at high engine speeds of rotation. The predetermined time is the time of setting the saw tooth (voltage) to zero, defined by the monostable circuit 43 - 44 - 45 - 46. When the engine is running, it will be seen that in the opening control circuit 11, capacitor 59 is discharged by transistor 43 at the end of each period. The voltage at its terminals is therefore negligible and does not affect the inverter input of amplifier 39. On the other hand, when the engine stops, transistor 43 no longer discharges capacitor 59, so that after one second, the voltage of the inverting input of amplifier 39 is built up by capacitor 59 and exceeds the voltage of the signal input which is limited by the Zener diode 26; thus causing the amplifier to switch over which allows transistor 4 to be blocked and hence to prevent a current consumption in the primary coil winding when the engine is stopped. It will be seen that the device according to the invention makes it possible to reduce the heat output dissipated in transistor 4 to a very considerable degree and hence to increase its working life at moderate cost. WHAT WE CLAIM IS:

1. A device for periodically energising a coil with current limitation, the period of this periodic energisation being variable and designated as T, the energising current attaining its limit value in time T2 and being then maintained in the coil during time T1, the sum of (T1 + T2) being less than T, and the energisation of the coil being commenced after an interval T4 from the loop control device for controlling T4 in such a way that the T1/T ratio should be a constant low predetermined value which is not zero.

other parameter related to fuel consumption and/or exhaust gas pollution.

5. A device according to any one of claims 2 to 4, wherein the closed loop control device comprises, firstly, a device for the identification of the mean value of the current limited by the proportional series regulator, the said mean value being representative of the effective T1/T ratio; secondly, a device for comparing this mean value with a reference level corresponding to the required T1/T ratio, the said comparison giving rise to a signal at level U; thirdly, a generator of periodic voltage V of period T, voltage V being time dependent and being reset to zero at the end of period T during a time interval whose duration if much lower than T; fourthly, a device comparing voltages U and V making it possible, when they are equal, to generate a signal which actuates the power supply for the coil.

6. A device according to claim 5, wherein the signal at level U is obtained by means of a transmittance unit which takes into account the characteristics of the control loop.

7. A device according to claim 6, wherein the transmittance unit comprises amplifier and integrator devices.

8. A device according to claim 5, 6, 7, wherein voltage V is a function of time tin the form of a + bt + cedt, where a, b, c and d are constants.

9. A device according to claim 8, wherein voltage V is a time function of the form a + cedt, where a is a positive constant, c and d are negative constants, (a + c) is positive or equal to zero.

10. A device according to any one of claims 1 to 9, and comprising a unit for actuating the opening of the coil charging current circuit when period T exceeds a predetermined limit.

11. A device according to any one of claims 1 to 10, wherein, in order to ensure that when period T is decreasing the dis charge time T4 should be sufficient after the start of the opening of the coil charging cur rent circuit, means are provided for maintaining a minimum opening interval T4 from the start of each period T.

12. A device according to claim 9, wherein said means for maintaining a minimum opening interval T4 comprise a monostable device.

13. A device according to claim 11 or 12, wherein the interval of discharge or of opening T4 is the time of setting the saw tooth (voltage) defined by the monostable circuit to zero.

14. Adevice according to one of claims 1 to 13, wherein the primary winding of the coil has a resistance which is less than 1 ohm.

15. A device for periodically energising a coil with a limited current, such device being constructed and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

T A TRTs XT O PA