EP0069888A2 - Electronically controlled ignition system - Google Patents

Abstract

The invention relates to an improvement in a detection circuit for misfires in an electronically controlled ignition system according to German patent application P 31 11 856.9. In the already proposed electronically controlled ignition system, in order to avoid misfires in the event of periodic speed fluctuations, it is determined immediately before the ignition timing whether the primary current in the primary winding has reached the value required for the ignition. If this is not the case, the electronic control is switched off for a defined period. To detect misfires, a test pulse is derived from the duration of the primary current in the value required for the ignition. According to the invention it is provided that the test pulse with an integration stage is extended by a time interval and the extended pulse is fed to a first input of a logic circuit. The second input of the logic circuit is supplied with a trigger signal which is obtained from the switch-off edge of the control signal derived from the ignition pulse generator. The logic is designed in such a way that an output pulse which triggers the switch-off of the electronic control only occurs if there is no pulse supplied by the integration stage during the trigger pulse.

Description

The. The invention relates to an electronically controlled ignition system in which the time of use of the primary current (I _pr ) flowing through the primary winding of the ignition coil is regulated in a speed-dependent manner such that this current only reaches the value (I _max ) required for the ignition shortly before the time of ignition and at which immediately before the ignition point it is determined whether the primary current has reached the value required for the ignition by deriving a test pulse (U _te ) from the dwell time (t _e ) of the primary current in the value required for the ignition (I _pr max), with which Help if the primary current does not exist or is not sufficiently large to avoid misfires (ZA), the electronic control is switched off for a defined period of time and the time of use of the primary current is derived directly from the control signal (U _IN ) of the ignition pulse sender and after the end of the switch-off period the electronically controlled control state is continuous and automatically again is brought about.

Such an electronically controlled ignition system is described in German patent application P 31 11 856.9.

In the case of the regulated ignition system already proposed, a test pulse of the time duration: t _e is obtained from the dwell time of the primary current in its value required for the ignition. With this test pulse, a switch is actuated, via which a capacitor, which is charged when there are no t _e pulses, is discharged again. From that it follows that the voltage across the capacitor falls below the value of a comparison voltage when test pulses occur, which is fixed and is, for example, half as large as the maximum possible voltage across the capacitor during the following test pulse. This comparison voltage is compared with the capacitor voltage at a comparator, at whose output a signal only occurs if the capacitor voltage is above the comparison voltage during an existing trigger pulse. This is only possible if the respective trigger pulse was not immediately preceded by a test pulse and therefore the capacitor was not sufficiently discharged. However, a missing test pulse is equivalent to a misfire, since in this case the primary current through the ignition coil has not reached the value required for the ignition. The trigger pulse with which the comparator is activated is obtained from the negative switch-off edge of the control signal when this control signal of the ignition pulse generator goes from its high level to the low level. An output signal on the comparator, for example, converts a monostable multivibrator from its stable state to the quasi-stable state, so that during the period in which this monostable multivibrator remains in its quasi-stable state, the electronic control is switched off and the instant of use of the primary current through the ignition coil directly from Control signal of the ignition pulse generator is derived. When the switch-off period has ended, the electronically controlled control state is continuously and automatically restored in the manner described in the patent application mentioned.

The present invention is based on the object of further improving the known circuit and, in particular, of specifying a circuit which contains small and integration-capable capacitors. This object is achieved according to the invention in an electronically controlled ignition system of the type Ar described in the introduction in that the test pump pulse (U _te ) with an integration stage (1) by a time interval (t _y ) extended and the extended pulse (U _INTEGR )) is fed to a first input (E ₁ ) of a logic circuit (G ₁ ) that a second input (E2) of the logic circuit (G ₁ ) a derived from the switching edge of the control signal (U _IN ) Triggerim ^p uls (U _TRIGGER ) is supplied, and that the logic (G _l ) _is selected _so that an output pulse (U _MF ) which triggers the switch-off of the electronic control only occurs when none of the integration stage supplied during the trigger pulse Pulse is present.

In the case of the electronically controlled ignition system according to the invention, the voltage comparator used there is thus replaced by a logic circuit compared to the circuit arrangement already proposed, which is supplied with the trigger pulse and an extended test pulse. The integration stage now provided contains a capacitor, but this capacitor is considerably smaller than the capacitor of the circuit previously proposed, which was discharged in each case by the test pulses t _e . This makes it possible to fully integrate the capacitors contained in the newly proposed circuit with integrated semiconductor technology in a semiconductor body, so that the otherwise necessary external connection of a capacitor is eliminated.

In the new circuit within the electronically controlled ignition system, the logic preferably consists of a NOR gate, at the first input of which the extended test pulse is applied as a positive pulse and at the second input of which the negative trigger pulses are applied. The extension _- duration of the test pulse must be greater than the duration of the negative trigger pulse.

The invention and its advantageous embodiment will be explained in more detail using an exemplary embodiment. FIG. 1 shows the circuit for the detection of ignition set, while the operation of the circuit results from the diagrams of Figures 2a to 2f.

The circuit according to FIG. 1 consists of an integrator stage 1 and a differentiating stage 2. The output signals of both stages are given to one input of an _N OR gate G ₁ . The output signal of the NOR gate controls a monostable multivibrator MF, via which the electronic control of the ignition system is switched off for a defined period of time when misfires occur.

The integrator stage 1 consists of a transistor T ₄ at the base electrode of which the test signal U _te is applied, which is obtained according to FIG. 2d from the residence time of the primary current in the ignition coil in the value I _{pr max} required for the ignition. The collector branch of the transistor T _{4 contains} the collector resistor R ₅ , to which the series circuit comprising a capacitor C ₂ and a diode D ₂ is connected in parallel. To the junction between capacitor _C2 and diode D _2, the base electrode of the Ausganastransistors T ₅ is connected, the extended P ^Rue F U _INTEGR ^pulse applied to its collector resistor R. ₇ The emitter resistor R _{6 of} this output transistor T ₅ is connected to the positive pole of the supply voltage source. The output voltage U _{INTEGR of} the integration stage 1 is given to the input E _{1 of} the NOR gate G ₁ .

The differentiation stage 2 contains 3 transistor stages connected in series, with the transistors T ₁ , T ₂ and T ₃ . The control signal U _IN , which is tapped at the ignition pulse generator, is given to the base electrode of the input transistor T ₁ . The emitter collector path of this transistor T ₁ is bridged with the differentiating element from the capacitor C ₁ and the diode D ₁ . In addition, the transistor T ₁ . an emitter resistor R ₁ . At the junction between the differentiating capacitor C ₁ and diode D ₁ is the Base electrode of transistor T _{2 is} connected, the emitter resistor R _{2 of which is} connected to the positive pole of the supply voltage. At the collector resistor R ₃ , the input voltage for the transistor T _{3 is} tapped, from whose collector the negative ^{trigger pulses} U _{TRIGGER are} tapped and fed to the input E _{2 of} the NOR gate G ₁ . The collector resistor R _{4 of} the output transistor T _{3 of} the differentiation stage 2 is in turn connected to the positive potential of the supply voltage source. It can also be seen from FIG. 1 that the output connection of the! NOR gate G _{1 is} connected to the monostable multivibrator MF, at whose output the signal U _out occurs, with which the electronic control of the ignition system is interrupted for a defined period of time.

FIG. 2a shows the control signal U _IN which is applied to the control electrode of the transistor T _{1 of} the differentiating stage ₂ . The periods _P1 and P _{2 of} the control signal are, for example, identical in the embodiment shown, while the period P _{3 contains} an error triggered, for example, by acceleration processes. In this period P ₃ , the "low phase" of the control signal was extended at the expense of the "high phase". It is assumed that this error no longer occurs in the period P ₄ . In the Figure 2b the trigger signal ^U TRIGGER ^DAR is set, the dividing stage appears at the output A, and is applied to the input E2 NOR gate G. ₁ This trigger signal is obtained from the negative edge of the control signal when the control signal changes from the "high phase" to the "low phase". First, a pulse is obtained from each edge of the control signal U _IN on the differentiator from the capacitor C ₁ and the diode D ₁ . At the second stage of the differentiating circuit 2 with the transistor T ₂ , the trigger pulses originating from the positive edges of the control signal U _{IN are} suppressed, so that only trigger signals are present at the collector resistor R _{3 of} the transistor T ₂ , which are from the negative edges of the control signals U _IN originate. These trigger pulses are inverted at transistor T ₃ , so that trigger pulses according to FIG. 2b are present at output A of the transistor stage with transistor T ₃ . The trigger time during which the trigger signal U _{TRIGGER has} its “low value” is denoted by t in accordance with FIG. 2b.

The course of the primary current in the ignition coil is shown in FIG. 2c. Up to the ignition point, the primary current can increase or have the value I _{pr max} required for the ignition. The ignition coil is discharged at the time of ignition. As can be seen from FIG. 2c, the P_imärstrom reaches in normal operation and using the electronic control its value I p _{r max} required for the ignition by the time t _e before the ignition point of the respective period. This value is also reached during the periods P ₁ , P ₂ and P ₄ . From FIG. 2c, however, it can be seen that, in the faulty period P _3, the primary current cannot reach its value I p _{r max} required for the ignition, so that a misfire ZA occurs.

A test pulse U _{te is} obtained from the time span in which the primary current remains at its maximum according to FIG. 2c, the pulse width of which is predetermined by the time t _e according to FIG. 2d. Since the prime current in the ignition coil did not reach its value I p _{r max} required for ignition in the third period, no test pulse U _te occurs in this period either.

The test pulse C _te is fed to an integrating amplifier or an integrator stage 1 according to FIG. 1, so that the test pulse is lengthened as shown in FIG. 2e with the aid of the capacitor C ₂ . The extension period is designated t _y . A voltage according to FIG. 2e is thus present at the output of the integrator stage 1, the pulses of which have the pulse width t _e + t _y . This signal U _INNTEGR is the input E _{1 of} the NOR Gate G ₁ supplied. By definition, a "high level" only occurs at the output of NOR gate G ₁ if both input levels at inputs E ₁ and E _{2 are} low. Since the trigger pulses of Figure 2b negative pulses according to which always in the trigger time t _x reach the low level at the output of a _H igh level can of NOR gate G ₁ only occur if t while the trigger time _x within a period of the control signal UIN no extended ^P r m ^{p UEFI} uls U _INTEGR occurs. This is the case with misfires _ZA , so that, as shown in FIG. 2f, an output signal U _{MF is} emitted by the NOR gate G ₁ at the end of the third period P ₃ , by means of which the flip-flop MF is switched. For the circuit to function reliably, it must be ensured that the extension time t _{y of} the test pulses is greater than the duration t _{x of} the trigger signals. For example, t _{y will be} twice the size of t. In one embodiment, the time was for t _x 20 usec and t _{y is} the time of 40 usec nierun by appropriate dimensioning ^g of the capacitors C _l and C ₂ is set. The capacitor C _{1 had} a value of approximately 30 pF and the capacitor C ₂ a value of approximately 60 pF. Capacitors of this size can easily be integrated into integrated semiconductor circuits. are, so that no separate, externally connectable capacitors are required. The small values of the capacitances are also due in particular to the diodes D ₁ and D ₂ inserted into the circuit. _In the integration stage 1, the capacitor C _{2 is} charged only via the base current of the transistor T ₅ and not via the resistor R _{5 of} the parallel RC element, so that the capacitance C ₂ can remain very small. The present invention thus contains a significant improvement and simplification of the otherwise very advantageous electronically controlled ignition system according to the earlier German patent application P 31 11 856.9.

Claims (4)

1) Electronically controlled ignition system, in which the time of use of the primary current (I _pr ) flowing through the primary winding of the ignition coil is regulated in a speed-dependent manner such that this current only reaches the value (I p _{r max} ) required for ignition shortly before the ignition time and at which is determined immediately before the ignition point, whether the primary current has reached the value required for the ignition by deriving a test pulse (U _te ) from the residence time (t) of the primary current in the value (I _pr max) required for the ignition If the primary current is not available or is not sufficiently large to avoid misfires (ZA), the electronic control is switched off for a defined period of time and the point of use of the primary current is derived directly from the control signal (U _IN ) of the ignition pulse generator and, after the switch-off period has ended, the electronically controlled one Control status is continuously and automatically restored, characterized in that the test pulse (U _te ) with an integration stage (1) extends by a time interval (t) and the extended pulse (U _IWTEGR ) is _{fed to} a first input ( ^E ₁ ) of a logic circuit (G ₁ ), that a second Input (E2) of the logic circuit (G ₁ ), a trigger pulse (U _TRIGGER ) derived from the switch-off edge of the control signal (U _IN ) is supplied, and that the logic (G ₁ ) is selected such that the switch-off of the electro African control triggering output pulse (U _MF ) occurs when there is no pulse supplied by the integration stage during the trigger pulse. 2) Electronically controlled ignition system according to claim 1, characterized in that the logic (G _l), a NOR gate is at its first input (E ₁₎ as a positive pulse of comparable Lan ^g erte Prüfim ^p uls (U _INTEGR) and the second input (E ₂ ) of which the negative trigger pulses are present, and that the length of the test pulse is longer than the duration of the negative trigger pulse. 3) Electronically controlled ignition system according to claim 1 or ₂ , characterized in that the ^{trigger pulses} (U _TRIGGER by differentiating the control signal emitted by the ignition pulse ^generator (U _IN ) and - by means of a diode (D _l ) - subsequent suppression of those caused by the positive switch-on edges Pulse is obtained and that the capacitors (C ₁ , C) contained in the differentiating stage and in the integration stage are also integrated in the integrated semiconductor circuit. 4) Electronically controlled ignition system according to one of the preceding claims, characterized in that the integration stage contains two transistors (T ₄ , T ₅ ) that ir .. Collector branch of the transistor T _4, a parallel RC element is arranged that the base electrode of the Transistor T _{5 is} connected to the collector electrode of transistor T ₄ via a diode D _{2 in} such a way that charging of the capacitor C _{2 of} the RC element via the resistor R _{5 of} the RC element is prevented and charging of the capacitor only via the base current of the transistor T ₅ can take place.

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