EP0502549B1 - Spark survey in spark ignition engine - Google Patents

Description

The invention relates to a method for ignition monitoring of an ignition system with a storage choke, on which the electrical energy required to generate an ignition spark is stored, and an ignition coil, to which this energy is transmitted to generate the ignition spark, and a device for ignition monitoring of an ignition system with a Storage choke on which the supply voltage is connected and an ignition coil connected in parallel.

In the case of an ignition system for an internal combustion engine, it is desirable to detect a misfire, that is to say the absence of an ignition spark, in order, for example, to prevent the fuel supplied to the engine from not being burned, which can lead to destruction of the catalyst, in particular in the case of an exhaust system with a catalyst .

For this purpose, from DE-A-38 29 797 an electronic engine control with a functional test for the ignition output stage is already known, in which a sensor is provided for the occurrence of the ignition voltages and the injection output stage is switched off when a given number of ignition voltages has failed in a row, which is determined via the sensor output signal.

From EP-A-0 344 349 it is also known to determine the absence of the ignition spark, that is to say a misfire of an ignition system, in that the voltage induced in the primary winding of the ignition coil during the generation of the ignition spark is detected and with a reference voltage of a certain level and a certain duration is compared, which is representative of a faultless ignition process.

In these known methods and circuit arrangements for ignition monitoring of an ignition system, current flow is detected inductively, from which, however, it cannot be clearly deduced whether an ignition spark has arisen, since the occurrence of an ignition spark on the spark plug e.g. cannot be distinguished from the existence of a shunt.

The object underlying the invention is therefore to develop a method and an apparatus, i.e. to create a circuit arrangement of the type mentioned at the beginning with which a clear detection is possible as to whether an ignition spark is present between the electrodes of the spark plugs supplied by the ignition system or whether a short circuit or shunt has occurred or the ignition coil is not loaded on the high voltage side, which is e.g. the case is when the ignition cable has fallen off.

This object is achieved in the method according to the invention in that the voltage difference between the excess voltage at the storage inductor and the supply voltage and the voltage difference across the storage inductor are detected and the absence of at least one of these voltage difference signals is evaluated as an indication of a fault in the ignition system.

The circuit arrangement according to the invention stands out by three voltage handles for the supply voltage and for the two voltages on the storage inductor, which supply corresponding voltage signals, and an evaluation circuit which, in the absence of at least one of these voltage signals, generates an error signal.

Since the two voltage peaks at the storage choke are used for evaluation in the method and device according to the invention, a direct statement about the load on the ignition coil and a clear statement as to whether the ignition coil is short-circuited or not is possible.

The design according to the invention furthermore offers the possibility of measuring the spark life, the circuit arrangement according to the invention being able to be produced at low cost and requiring little space.

Particularly preferred refinements and developments of the method according to the invention and the circuit arrangement according to the invention are the subject of claims 2 and 4 to 8.

• Fig. 1 das Schaltbild einer Zündanlage mit einem Ausführungsbeispiel der erfindungsgemäßen Schaltungsanordnung,
• Fig. 2 das Schaltbild im einzelnen des in Fig. 1 dargestellten Ausführungsbeispiels der erfindungsgemäßen Schaltungsanordnung, und
• Fig. 3 und 4 Spannungszeitdiagramme zur Erläuterung der Arbeitsweise des Ausführungsbeispiels der erfindungsgemäßen Schaltungsanordnung.

A particularly preferred exemplary embodiment of the invention is described in more detail below with reference to the accompanying drawing. Show it

• 1 shows the circuit diagram of an ignition system with an exemplary embodiment of the circuit arrangement according to the invention,
• Fig. 2 shows the circuit diagram in detail of the embodiment of the circuit arrangement according to the invention shown in Fig. 1, and
• 3 and 4 voltage timing diagrams to explain the operation of the embodiment of the circuit arrangement according to the invention.

The ignition system shown in Fig. 1 consists of a storage inductor L0, to which the supply voltage + UB is located and in which energy is stored via a transistor T0, which is switched through by a control when closing a switch S0 between the storage inductor L0 and an ignition coil ZSP0 connected in parallel to it, the ignition coil ZSP0 is transmitted. The secondary winding of the ignition coil ZSP0 is connected in the usual way to the spark gap of a spark plug.

For ignition monitoring according to the invention, voltage signals are tapped at the storage choke L0. These voltage signals are the voltages U20 and U21 on both sides of the storage inductor L0, and additionally the supply voltage UB, which are shown in FIGS. 3b and 4c. The voltages U20 and U21 are the voltage increase at the connection of the storage inductor L0, to which the supply voltage + UB is connected, and the voltage increase at the collector of the switching transistor T0.

Between the supply connection for the supply voltage + UB and the storage inductor L0, a diode D0, which only allows a current in the direction of the storage inductor L0, and two capacitors C0, C1 are connected, the other connection of which is connected to ground.

As shown in detail in FIG. 2, the voltage taps for the voltage + U21, + U20 and the supply voltage + UB are direct or via resistors R1, R2 (+ U21, + UB) and a Zener diode ZD1 (+ UB ) connected to a circuit, preferably in the form of two series-connected optocouplers Opt0 and Opt1, with a logical AND function, which logically combines the voltage differences U20-UB and U21-U20.

These voltage differences are transferred to the resistor R3 via the outputs of the optocouplers Opt0 and Opt1, the corresponding voltage drop across the resistor R3 being stored via a diode D1 in a capacitor C2 which, together with a resistor R4 connected in parallel, forms an integration element. A transistor T1, which serves as a switch, is at its base due to the voltage drop controlled at the resistor R3 and is connected with its collector-emitter path, for example via a resistor R6, between the output of the optocoupler Opt0 and ground. A resistor R5, which is connected upstream of the base of the transistor T1, serves to limit the current.

A voltage UA, which is representative of the state of the spark gap of the ignition system, is tapped at the collector of the transistor T1 via the resistor R6. If this voltage UA has a high potential, then there is an error.

wird mit dem Optokoppler Opt1 ausgewertet.The circuit arrangement according to the invention with the structure shown in detail in FIG. 2 operates in the following way:
In order to first be able to tap the voltage surge + U20, the diode D0 is provided, which prevents the voltage surge + U20 from being short-circuited via the mains when the storage inductor L0 is discharged. The capacitors C0 and C1 integrate the pulse occurring when the storage choke L0 is discharged. The voltage rise + U20 at capacitor C1 (see Fig. 4c, d) provides a direct statement about the load on the ignition coil ZSP0 (shunt of the ignition electrodes). The corresponding voltage difference $\text{U = U20-UB}$

is evaluated with the optocoupler Opt1.

Since there is still no clear indication of whether the ignition coil ZSP0 is short-circuited or not, the voltage rise + U21 at the collector of transistor T0 is also used for the evaluation. The corresponding voltage difference U21-U20 is present over a period of time that corresponds to the spark life at the electrodes. The two voltage difference signals U21-U20 and U20-UB are linked via the outputs of the optocoupling Opt0, Opt1 according to the logical AND function. The two optocouplers Opt0, Opt1 therefore form an AND gate.

If at least one of these signals is missing, then occurs on Resistor R3 no voltage drop. As a result, the voltage UA tapped off at the transistor T1 is at a high value. Since the voltage across the resistor R3 is only present as long as a spark is present between the ignition electrodes, this signal can be used to measure the burning duration, which also makes it possible to make a statement about the condition of the electrodes.

Since the signal at resistor R3 is only applied periodically, the integration element consisting of capacitor C2 and resistor R4 is provided. As long as periodic ignition takes place, the transistor T1 conducts, so that the output voltage UA is at a low value.

This output voltage UA of the transistor T1 can therefore be used to make a direct and unambiguous statement about the load on the ignition coil and whether the ignition coil is short-circuited or not. The circuit arrangement according to the invention makes this possible with a simple, inexpensive construction of simple components with a simple connection (no high voltage), and in addition to the clear statement as to whether a spark is present between the electrodes, there is also the possibility of controlling the erosion of the electrodes, since a burn duration measurement is possible.

Claims (8)

1. Process for monitoring the spark of a spark ignition system comprising a storage choke, at which the electrical energy which is necessary to generate an ignition spark is stored, and an ignition coil, onto which this energy is transferred to generate the ignition spark, characterised in that the voltage difference between the voltage magnification at the storage choke and the supply voltage, and the voltage difference across the storage choke, are detected, and the absence of at least one of these voltage difference signals is evaluated as an indication of a malfunction of the spark ignition system.
2. Process according to Claim 1, characterised in that the two voltage difference signals are configured according to the logical AND function.
3. Circuit arrangement for monitoring the spark of a spark ignition system comprising a storage choke (LO), to which the supply voltage (UB) is applied, and an ignition coil (Zspo) which is connected in parallel thereto, characterised by three voltage taps for the supply network (UB) and for the two voltages (U20, U21) across the storage choke (LO), which deliver the appropriate voltage signals, and a evaluation circuit which generates an error signal if at least one of these voltage signals is absent.
4. Circuit arrangement according to Claim 3, characterised in that, between the supply connection of the spark ignition system and the storage choke (LO), there is connected a diode (DO) which only permits a current in the direction towards the storage choke (LO).
5. Circuit arrangement according to Claim 4, characterised in that two capacitors (C0,C1) are located between earth and a point between the diode (DO) and the storage choke (LO).
6. Circuit arrangement according to one of Claims 3 to 5, characterised in that the evaluation circuit consists of a circuit arrangement with a logical AND function, to which the voltage signals of the voltage taps are applied, and a monitoring circuit, which responds to the output signal of the circuit device with the logical AND function and, optionally, generates the error signal.
7. Circuit arrangement according to Claim 6, characterised in that the circuit with the logical AND function consists of two optocouplers (Opt0, Opt1).
8. Circuit arrangement according to Claim 7, characterised in that the monitoring circuit is constructed of a resistor (R3), which is connected to the output of an optocoupler (Opt1), to which the voltage difference between the voltage magnification at the storage choke (LO) and the supply voltage are applied, a capacitor (C2), to which the voltage drop at the resistor (R3) is connected via a diode (D1), and a transistor (T1), to the base of which the voltage of the capacitor (C2) is applied, which transistor is connected by means of its collector to the output of the other optocoupler (Opt0), to which optocoupler the voltage difference is applied across the storage choke (LO) and which transistor is connected to the earth by means of its collector, wherein the voltage is tapped between the collector of the transistor (T1) and earth as the monitoring voltage, which optionally delivers the error signal.

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