EP0069888B1 - Electronically controlled ignition system - Google Patents

Description

The invention relates to an electronically controlled ignition system in which the time of use of the primary current (Ip _r ) flowing through the primary winding of the ignition coil is regulated in a speed-dependent manner such that this current only reaches the value (Ip _rmax ) required for the ignition shortly before the time of ignition 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 _e ) of the primary current in the value (Ip _rmax ) 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 time of use of the primary current is derived directly from the control signal (U _IN ) of the ignition pulse generator, and the electronically controlled control state continuously after the end of the switch-off period and automatically is brought about again.

Such an electronically controlled ignition system is described in the older, not prepublished German patent application P 3 111 856.

In the case of the regulated ignition system already proposed, a test pulse of the 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. The result of this is that the voltage across the capacitor falls below the value of a reference voltage when test pulses occur, which is fixed and, for example, half the size of 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 no test pulse immediately preceded the respective trigger pulse and thus the capacitor was not sufficiently discharged. However, a missing test pulse is synonymous with 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 is direct is derived from the control signal of the ignition pulse generator. 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 capacitors which are capable of integration. This object is achieved in an electronically controlled ignition system of the type described in the introduction in 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 (G ₁ ) in that a second input of the logic circuit is switched off the switch-off edge of the control signal derived trigger pulse is supplied, and that the logic is selected so that an output pulse which triggers the switch-off of the electronic control only occurs when there is no pulse supplied by the integration stage during the trigger pulse.

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 the positive pulse and at the second input of which the negative trigger pulses are present. The length of the test pulse must be longer 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 detecting misfires, while the diagrams of FIGS. 2a to 2f show the mode of operation of the circuit.

1 consists of an integrator stage 1 and a differentiation stage 2. The output signals of both stages are given to an input of a NOR 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. The base electrode of the output transistor T _{5 is} connected to the connection point between the capacitor C ₂ and the diode D ₂ , and the extended test pulse U _INTEGR is applied to its collector resistor R ₇ . The emitter resistor R _{e 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 _{i of} the NOR gate G _I.

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 has} an emitter resistor R ₁ . The base electrode of transistor T ₂ , whose emitter resistor R _{2 is} connected to the positive pole of the supply voltage, is connected to the connection point between differentiation capacitor C ₁ and diode D ₁ . The input voltage for the transistor T _{3 is} tapped at the collector resistor R ₃ , the negative trigger pulses U _{TRIGGER are} tapped from the collector thereof and are 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. Fig. 1 can also be seen that the output terminal of the NOR gate G _{1 is} connected to the monostable multivibrator MF, at whose output the signal U _ou t 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 P ₁ and P _{2 of} the control signal are identical in the exemplary 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 . 2b shows the trigger signal U _TRIGGER , which occurs at output A of the differentiating stage and is applied to 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 from the negative edges are present at the collector resistor R _{3 of} the transistor T ₂ of the control signal U _IN . 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 designated t _x according to FIG. 2b.

The course of the primary current in the ignition coil is shown in FIG. 2c. Up to the point of ignition, the primary current can increase or have the value Ip _{r max} required for the ignition. The ignition coil is discharged at the time of ignition. As can be seen from FIG. 2c, the primary current in normal operating mode and using the electronic control reaches its value I _{pr 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 . 2c shows, however, that in the faulty period P ₃ the primary current cannot reach its value I _{pr max} required for the ignition, so that a misfire ZA occurs.

A test pulse U _{te is} obtained from the time period 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 primary current in the ignition coil did not reach its value I _{pr max} required for ignition in the third period, no test pulse U _te occurs in this period either.

The test pulse U _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 indicated by ty. At the output of the integrator stage 1 there is therefore a voltage according to FIG. 2e, the pulses of which have the pulse width t _e + ty. This signal U _INTEGR is _fed to the input E _{1 of} the NOR gate G ₁ . By definition, a "high level" only occurs at the output of NOR gate G ₁ if both input levels at inputs E ₁ and E2 are low. Since the trigger pulses according to FIG. 2b are negative pulses that are always in the If the trigger time t _{x reaches} the low level, a high level can only occur at the output of the NOR gate G ₁ if no extended test pulse U _INTEGR occurs during the trigger time t _x within a period of the control signal U _IN . 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. In order for the circuit to function reliably, it must be ensured that the extension time ty of the test pulses is greater than the duration t _{x of} the trigger signals. For example, ty will be twice the size of t _x . In one exemplary embodiment, the time of 20 μsec for t _{x and} the time of 40 μsec for t _{y was} set by appropriately dimensioning the capacitors C ₁ and C ₂ . 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 very easily be integrated into integrated semiconductor circuits, 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. Thus, 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 3 111 856.9.

Claims (4)

1. Electronically controlled ignition system, wherein the starting time of the primary current (Ip_r) flowing through the primary winding of the ignition coil is controlled in dependence upon speed in such a way that this current only reaches the value (I_{pr max}) required for the ignition shortly before the point of ignition, and wherein it is ascertained immediately before the point of ignition whether the primary current has reached the value required for the ignition by deriving from the dwell time (t_e) of the primary current in the value (I_{pr max}) required for the ignition a test pulse (U_te) with whose aid, in the absence of primary current or in the case of insufficiently large primary current, in order to avoid misfires (ZA), the electronic control is switched off for a defined time, and the starting point of the primary current is directly derived from the control signal (U_IN) of the ignition pulse generator, and after termination of the switch-off time, the electronically controlled control state is initiated again continuously and automatically, characterized in that the test pulse (U_te) is prolonged with an integration stage (1) by a time interval (ty), and the prolonged pulse (U_INTEGR) is fed to a first input (E₁) of a logic circuit (G₁), in that a trigger pulse (U_TRIGGER) derived from the switch-off edge of the control signal (UN) is fed to a second input (E₂) of the logic circuit (G₁), and in that the logic (G₁) is selected such that an output pulse (U_MF) triggering the switching-off of the electronic control only occurs at it if during the trigger pulse no pulse delivered by the integration stage is present.

2. Electronically controlled ignition system according to claim 1, characterized in that the logic (G_i) is a NOR gate, with the prolonged test pulse (U_INTEGR) present as positive pulse at its first input (E₁), and the negative trigger pulses at its second input (E₂), and in that the prolongation time of the test pulse is longer than the duration of the negative trigger pulse.

3. Electronically controlled ignition system according to claims 1 or 2, characterized in that the trigger pulses (U_TRIGGER) are gained by differentiation of the control signal (U_IN) delivered by the ignition pulse generator and - by means of a diode (D₁) - subsequent suppression of the pulses created by the positiv switch-on edges, and in that the capacitors (C₁, C₂) contained in the differentiating stage and in the integration stage are integrated into 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 (T₄, Ts), in that a parallel RC member is arranged in the collector branch of the transistor (T₄), in that the base electrode of the other transistor (T_s) is connected to the collector electrode of the transistor (T₄) via a diode (D₂) in such a way that charging of the capacitor (C₂) of the RC member via the resistor (R_s) of the RC member is prevented, and the capacitor may only be charged via the base current of the other transistor (Ts).

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