EP0790408B1 - Measuring circuit for an ionic current in ignition devices for internal combustion engines - Google Patents

Description

The invention relates to a circuit arrangement for ion current measurement according to the preamble of claim 1.

Such an ion current measuring circuit is known from US 5483818, which a differential amplifier connected as an inverting amplifier has, for this is the low potential side of the secondary winding Ignition coil through a resistor with the inverting input of the Differential amplifier connected while at its non-inverting Input voltage of approx. 40 V is applied. To achieve the inverting amplifier property is the output through a resistor fed back to the inverting input and at the same time the Output signal for evaluating the ion current of a threshold circuit fed. Also on the low potential side of the secondary winding two Zener diodes are connected in series Connection node from another inverting amplifier in such a way is controlled that those occurring during an ion current measurement Leakage currents can be avoided in order to ensure undistorted ion current signals to create. The further inverting amplifier is corresponding how the amplifier connected directly to the secondary winding is constructed, its output via a resistor with the inverting Input of the further amplifier is connected and its non-inverting The same bias voltage is fed to the input.

to avoid the leakage currents generated by the Zener diodes used this known ion current measuring circuit is disadvantageously required Way of a high circuit effort.

The object of the present invention is therefore a circuit arrangement for ion current measurement of the type mentioned at the beginning specify that avoids this disadvantage.

The solution to this problem is due to the characteristic feature of Claim 1 given. According to this, the derivation of the during the Burning time of the spark plug flowing ignition current a first and second Discharge circuit branch provided, each a semiconductor diode have and the second derivative circuit branch parallel to the inverting Amplifier is arranged. The main advantage of this invention The solution lies in the use of normal semiconductor diodes, so that the problem of high leakage currents does not arise and therefore one as in the prior art proposed complex circuit are eliminated can.

Another advantage that can be achieved with the present invention lies in one Lowering the value of the measuring voltage below that in the prior art specified voltage value of 40 V.

In an advantageous development of the invention, for the further semiconductor diode, which forms the second discharge circuit branch, an ignition current measuring resistor connected in series. The at this ignition current measuring resistor The voltage drop that occurs during the burning period of the Spark plug in an advantageous manner as a measurement signal for the amount of ignition current serve. This ignition current measurement signal can be used to to control the ignition sequence for a secondary ignition.

Preferably, the second diverting circuit branch can be via a Output of the inverting amplifier controllable semiconductor switch, in particular a transistor with the ground potential of the circuit arrangement get connected. This allows the Increase the current carrying capacity of the differential amplifier.

According to a further advantageous embodiment of the invention, a Switched differential amplifier provided as an inverting amplifier.

Preferably, the one input of such a differential amplifier connected to the low potential side of the secondary winding of the ignition coil, while a reference voltage is supplied to the other input, whose value corresponds to the measuring voltage and at which the output over a measuring resistor is connected to the one input.

The ion current is thus converted into an as simple as possible Measuring signal serving voltage converted, which then a Evaluation is fed.

The reference voltage supplied to such a differential amplifier becomes generated in the simplest way with a constant voltage source.

Furthermore, the use of a multi-cylinder internal combustion engine Measuring paths of the spark plugs serving as ion current probes in parallel are switched, so that the advantage of low circuit complexity preserved. On the other hand, the measuring sections should be used as an ion current probe serving spark plugs are measured completely independently, but the circuits can also be present several times, the Output signals are then time-multiplexed in a suitable form.

Finally, in a particularly preferred embodiment, the Invention a parallel circuit from a dissipation resistor and at least one Zener diode connected in series to the secondary winding to the energy that is left after the spark has been torn off located in the ignition coil or the secondary capacitances quickly dissipate so that the ion current measurement can then be carried out without great delay is feasible. Advantageously, preferably two antiserially connected zener diodes instead of just one Zener diode used to be compared to use only to achieve a decay behavior of a single Zener diode, the Duration is shorter and also symmetrical.

Figur 1

ein Schaltbild eines elektronischen Zündsystems gemäß der Erfindung und

Figur 2

einen Schaltungsausschnitt des Schaltbildes nach Figur 1 mit einem alternativen zweiten Ableitschaltungszweig A2.

In the following, the invention will be illustrated and explained using an exemplary embodiment in connection with the figure. Show it:

Figure 1

a circuit diagram of an electronic ignition system according to the invention and

Figure 2

a circuit section of the circuit diagram of Figure 1 with an alternative second diverting branch A2.

FIG. 1 shows a transistor ignition system of a 4-cylinder internal combustion engine, each with an ignition output stage assigned to a cylinder, each ignition output stage comprising an ignition coil Tr ₁ ,..., Tr ₄ , a primary winding P ₁ ,..., P ₄ and a secondary winding S ₁ , ..., S ₄ comprises, and an ignition transistor 1a, ..., 1d connected to the primary winding P ₁ , ..., P ₄ with associated spark plug Zk ₁ , ..., Zk _{4 is} constructed. The primary windings P ₁ ,..., P ₄ are connected with one connection to an on-board battery voltage U _B of 12 V, for example, provided by an on-board battery, while the other connection is connected to the associated ignition transistor 1a,..., 1d.

The ignition transistors 1a, ..., 1d are controlled by their control electrodes controlled a circuit 2a for cylinder selection, which in turn with a Control circuit 2 is connected, the corresponding ignition trigger for the individual cylinders of this circuit 2a supplies.

The figure also shows a control unit 4, the function of an engine management takes over and in turn controls the control circuit 2. For this purpose, this control unit 4 receives motor parameters via an input E, such as load, speed and temperature. Corresponding actuators are controlled via outputs A.

The secondary windings S ₁ , ..., S ₄ are each connected with their high voltage side to the associated spark plug Zk ₁ , ..., Zk ₄ , while their low potential side are combined in a circuit node S via a dissipation resistor R ₃ .

This circuit node S is connected to the input of a differential amplifier 3 connected as a non-inverting amplifier, in that this circuit node S is connected to the inverting input of this differential amplifier 3. In contrast, a constant reference voltage U _ref , preferably 20 V, is applied to the non-inverting input of this differential amplifier 3, this constant reference voltage being generated by a constant voltage source 6. This constant reference voltage U _ref is fed to the secondary windings S ₁ , ..., S ₄ via this differential amplifier 3 by means of a measuring resistor R1 fed back to the inverting input and thus reaches the spark plugs Zk ₁ , ... working as ion measuring current paths as the _test voltage U _test . , Mark ₄ .

In order to derive the ignition current which arises during the burning time due to the ignition process, the circuit according to the figure has a first and second diverting circuit branches A1 and A2. The first discharge circuit branch A1 connects the circuit node S to the ground potential of the circuit via a semiconductor diode D ₂ , while the second discharge circuit branch A2 consists of a series connection of an ignition current discharge resistor R ₂ , a further semiconductor diode D ₁ and a pnp transistor T, the ignition current measurement resistor R ₂ is connected to the circuit node S and the collector electrode of the transistor T is at the ground potential of the circuit. The base electrode of this transistor T is driven by the output of the differential amplifier 3.

The first diverting circuit branch A1 serves to derive negative voltage peaks occurring in one of the spark plugs Zk ₁ ,... Zk ₄ at the moment of a high voltage breakdown.

The actual ignition current is derived via the second derivation switching branch A ₂ , which can also be constructed without the transistor T, which only serves to increase the current carrying capacity of the differential amplifier 3. If such a transistor T is dispensed with, the cathode of the semiconductor diode D _{1 is} connected directly to the output of the differential amplifier 3, so that the diverting branch A _{2 is connected in} parallel with the ion measuring resistor R ₁ .

The function of the circuit according to FIG. 1 is explained below become:

The generation of an ignition pulse by the control circuit 2 leads to the activation of the corresponding ignition transistor 1a, ..., 1d. The ignition spark generated in this way on the associated spark plug Zk ₁ ,..., Zk ₄ leads to a certain burning duration, which is accompanied by an ignition current. This ignition current flows through the low-resistance leakage circuit branch A ₂ to a part via the differential amplifier 3 and to another part in accordance with the set operating point of the transistor T to ground potential. This operating point of the transistor T is determined by the output signal U _{ion of} the differential amplifier 3, which, by means of the feedback via the ion measuring resistor R _1, regulates its potential at the inverting input to the U _ref potential, which represents the measuring voltage for the subsequent ion current measurement. An overload of the differential amplifier 3 by the ignition current is thus avoided by using such a transistor T.

During the burning time, the output signal U _{ion of} the differential amplifier 3 indicates the level of the ignition current flowing through the ignition current measuring resistor R ₂ and can therefore be used as a measurement signal of the ignition current after evaluation for charging and burning time control of the internal combustion engine. The value of the ignition current measuring resistor R ₂ is chosen so that its voltage drop U _R2 with the value R ₂ • I _{ignition is} in the range of a few volts. Such a value for the resistor R ₂ would be 15 Ω, for example. At the output of the differential amplifier 3 there is then a voltage U _ion with a value of U _ref - I _ignite • R ₂ -U _D1 -U _BE , U _D1 and U _{BE representing} the diode forward voltage and the base-emitter voltage.

The measuring voltage for the level of the ignition current could also be tapped at the emitter of the transistor T or with high resistance at the anode of the diode D ₁ . The tolerances of the base-emitter voltage of the transistor T or the diode forward voltage of the diode D ₁ would then not be included in the measurement. Another possibility for generating a measuring voltage for the ignition current is given in FIG. 2 explained below.

After the ignition radio has been torn off, that is to say at the end of the burning time, the residual energy still remaining in the corresponding secondary winding S ₁ ,... S ₄ or in the secondary capacitances must be rapidly dissipated. For this purpose, the already mentioned dissipation resistor R ₃ , to which two antiserially connected Zener diodes Z ₁ and Z ₂ are connected in parallel.

Such a parallel connection reduces the duration of the decay the tearing off of the spark significantly shortened, so that immediately then an ion current measurement not affected by the decay behavior is feasible.

Such accelerated energy dissipation is particularly important at high engine speeds. The value of the dissipation resistance R ₃ is preferably chosen so that it corresponds to the value (L _sek / C _sek ) ^1/2 , the quantities L _sek and C _{sek representing} the coil inductance or coil and stray capacitances effective on the secondary side. The value of this dissipation resistance R ₂ will usually be in the range between 10 kΩ and 100 kΩ and thus causes the energy to dissipate rapidly.

The two Zener diodes Z ₁ and Z ₂ are necessary to limit the voltage drop occurring across the dissipation resistor R ₃ , which would otherwise result in a considerable reduction in the ignition energy. For example, an ignition current of 100 mA at a resistor of 50 kΩ, for example, would cause a voltage drop of 5000 V. The Zener voltages of the Zener diodes Z ₁ and Z ₂ are therefore chosen so that there is only a slight reduction in the ignition energy, for example in the amount of 50 V.

Instead of using two Zener diodes Z ₁ and Z ₂ , it is also possible to provide only the Zener diode Z ₂ and to dispense with the Zener diode Z ₁ . However, this would cause the swing-out behavior to be asymmetrical and the swing-out duration to be extended somewhat. On the other hand, it would be advantageous that the voltage loss in ignition mode would be less than 1 V.

Since in both cases the Zener diodes are in series with the secondary winding of the ignition coils Tr ₁ ,... Tr ₄ and the ion current measuring resistor R ₁ , their leakage currents have no negative effect in the subsequent ion current measurement.

After the ignition current has decayed, the reference voltage U _ref serving as measurement voltage U _{test is applied} by the inverting differential amplifier 3 to the secondary windings S ₁ ,... S ₄ , which then generates an ion current at the corresponding spark plug.

The inverting differential amplifier 3 converts this ion current into a voltage signal U _ion , which is now fed to the evaluation unit 5 as a measurement signal of the ion current, the evaluation result of which is then forwarded to the control unit 4. The measuring voltage U _test supplied to the secondary windings S ₁ , ..., S _{4 of} the ignition coils Tr ₁ , ..., Tr ₄ , which can be between 5 and 30 V, preferably 20 V, is constant during the entire ion current measurement period. Since the ion current is in the µ A range, a differential amplifier 3 with a low input current is used, which is available inexpensively today. The low-impedance provision of this measuring voltage U _{test means} that there is no need to recharge stray capacitances, as can occur in other known systems when exposed to alternating current, such as, for example, with knocking combustion. This advantage is particularly noticeable when several ion measuring sections are operated in parallel, as shown in the figure, since effective stray capacities can then be multiplied.

In order to limit the current flowing into the differential amplifier 3, another resistor in the supply line to its inverting input (not shown in the figure) can be provided.

2 shows a detail of the circuit diagram of Figure 1 with the inverting amplifier connected as a differential amplifier 3 and the associated two Ableitschaltungszweigen A ₁ and _A2.

The difference from FIG. 1 lies in the wiring of the ignition current measuring resistor R ₂ , which is now arranged on the ground side, namely between the collector of the transistor T and the ground potential. The measurement voltage U _Zünd , which is proportional to the ignition current, is therefore ground-related, which is advantageous for the further use of this measurement signal.

The additional use of a resistor R ₄ connected between the output of the differential amplifier 3 and the base of the transistor T limits the measurement error resulting from a base current to small values.

The ion current signal can be used to knock the Detect internal combustion engine and control the ignition timing to set up a corresponding knock control.

Another application is to use the ion current signal both for Detection of ignition misfires as well as for the detection of Use camshaft position.

The circuit arrangement according to the invention for ion current measurement is not only in transistor ignition systems, as shown in the exemplary embodiment, usable, but also for alternating current ignitions or High voltage capacitor ignitions.

Claims (10)

1. A circuit arrangement for measuring ion currents in the combustion chamber of an internal combustion engine consisting of:

   a) an ignition coil (Tr₁, ..., Tr₄) having a primary and a secondary winding (P₁, ..., P₄, S₁, ..., S₄),

   b) a spark plug (Zk₁, ..., Zk₄) that simultaneously serves as an ion current probe connected to the secondary winding (S₁, ..., S₄),

   c) an inverting amplifier (3, R₁) for producing a constant test voltage (U_M) for the ion current measurement process connected to the low potential side of the secondary winding (S₁, ..., S₄) of the ignition coil (Tr₁, ..., Tr₄),
   characterised by the following features:

   d) for the purposes of draining-off the ignition current, which flows during the firing of the spark plug, to the earth potential of the circuit arrangement, there is provided

   d1) a first by-pass branch circuit (A₁) provided with a semiconductor diode (D₂) and

   d2) a second by-pass branch circuit (A₂) which incorporates a further semiconductor diode (D₁) and is connected in parallel with the inverting amplifier (3, R₁).
2. A circuit arrangement in accordance with Claim 2 [sic], characterised in that the second by-pass branch circuit (A₂) comprises an ignition current measuring resistance (R₂) which is connected in series with the further semiconductor diode (D₁).
3. A circuit arrangement in accordance with Claim 1 or 2, characterised in that the second by-pass branch circuit in [sic] (A₂) is connected to the earth potential via a semiconductor switch (T), in particular, a transistor, which is controllable by the output of the inverting amplifier (3, R₁).
4. A circuit arrangement in accordance with Claim 3, characterised in that the ignition current measuring resistance (R₂) is disposed in the emitter path of the transistor (T).
5. A circuit arrangement in accordance with Claim 3, characterised in that the ignition current measuring resistance (R2) is disposed in the collector path of the transistor (T).
6. A circuit arrangement in accordance with any of the preceding Claims, characterised in that the inverting amplifier is in the form of a differential amplifier (3).
7. A circuit arrangement in accordance with Claim 6, characterised in that the one input of the differential amplifier (3) is connected to the low potential side of the secondary winding (S₁, ..., S₄) of the ignition coil (Tr₁, ..., Tr₄) and a reference voltage (U_ref) whose value corresponds to the test voltage (U_test) is supplied to the other input, and the output of the differential amplifier (3) is connected to the one input via an ion current measuring resistance (R₁).
8. A circuit arrangement in accordance with any of the preceding Claims, characterised in that a parallel circuit consisting of a dissipating resistance (R₃) and at least one Zener diode (Z₁, Z₂) is connected in series with the secondary winding (S₁, ..., S₄).
9. A circuit arrangement in accordance with Claim 8, characterised in that two back-to-back connected Zener diodes (Z₁, Z₂) are located in parallel with the dissipating resistance (R₂) [sic].
10. The use of the circuit arrangement in accordance with any of the Claims 2 to 9 for measuring an ignition current in that the voltage drop occurring across the ignition current measuring resistance (R₂) serves as a test signal indicative of the magnitude of the ignition current.

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