WO1999031384A1

WO1999031384A1 - Method for measuring ionic current in internal combustion engines and device for measuring ionic current

Info

Publication number: WO1999031384A1
Application number: PCT/EP1998/008006
Authority: WO
Inventors: Peter Bertelshofer; Peter Hohner; Hartung Wilstermann
Original assignee: Temic Telefunken Microelectronic Gmbh; Daimler-Benz Aktiengesellschaft
Priority date: 1997-12-12
Filing date: 1998-12-09
Publication date: 1999-06-24

Abstract

Previous methods for measuring ionic current consisted in determining the ionic current signal within a given time window . Such methods were unsuitable for ignition control engines because the time window was firmly coupled to a crankshaft angle in previous ionic current measurement devices. This can result in substantial differences in the shape of the ionic signal and to errors in the recognition of ignition faults or knocking combustion. According to the invention, the time window follows the ignition point irrespective of the crankshaft angle position, whereby the initial point and/or duration of the time window are automatically determined on the basis of the ignition point signal and at least one variable describing the real operating condition of the internal combustion engine, especially the number of revolutions per minute. This enables the time window to be adapted to the operating condition of the internal combustion engine.

Description

Process for ion current measurement in internal combustion engines and ion current measurement device

The invention relates to a method for ion current measurement in internal combustion engines according to the preamble of claim 1 and an ion current measurement device according to claim 14.

By applying an external voltage, the ion current measurement measures the release of charge carriers during the combustion of the fuel in the combustion chamber of an internal combustion engine and, via the ion current signal obtained in this way, enables conclusions to be drawn about the combustion behavior, in particular for misfire detection and for knocking combustion, the ion current measurement is used.

Various devices and methods for detecting knocking combustion by means of the ion current measurement method are, for example, DE 42 39 592 C2, DE 43 21 782 C2, DE 34 15 948 C2, DE 30 27 103 and GB 2 259 365 remove.

The knocking combustion of an internal combustion engine is an uncontrolled explosion of the not yet burned mixture in the cylinder and can damage the engine if knocked strongly. However, since the engine releases its maximum output precisely at the knock limit, i.e. when the combustion is already knocking slightly, the aim of an engine control is to operate it as close to the knock limit as possible. If knocking occurs, the ignition timing is shifted towards later ignition. Knocking combustion is characterized by vibrations (5 to 20 kHz) in the range after the cylinder pressure maximum and can be determined by means of the ion current. However, the ion current signal already has a first maximum and fluctuations in the ion current with the spreading flame front. This can falsify knock detection, as these fluctuations are due to turbulence in the cylinder, but not to knock.

The methods according to the prior art have the considerable disadvantage that the time windows are activated by means of a crank angle position detector to a fixed crank angle position, and it is Angle position-related control of the time window and simultaneous adjustment of the ignition timing can lead to very strong differences in the ion current signal. The intention is to change the ignition times in such a large range that a time window coupled to a crank angle position only partially or not at all covers the time range relevant for knock detection.

A method for detecting misfires for internal combustion engines with electronic ignition timing is known from DE 196 18 980. However, this method is based on a change and maximum value determination, which is considered to be extremely complex and prone to errors.

DE 43 03 267 A1 also shows an engine control device which has a sensor device for determining an operating state of the engine, an ion current measuring device for determining the ion current and a misfire detection device. The method used here to detect misfires or misfires also detects the ion current within a time window, but in this method only the amplitude of the individual ion current values is compared and the time window selected such that no noise occurs within the time window.

However, the time window is such that it at least partially covers the ignition spark range, that is to say the ion current measurement takes place when the energy supply is switched on (ignition coil drive period). The temporal position of the time window is coupled to a reference position signal which represents a certain crank angle and which is derived from the crank angle by means of an angular position detector. The ignition timing of the engine is subsequently set by means of the engine control device.

However, the detection of the ion current during the ignition duration is subject to errors, since the ionization caused by the ignition spark cannot be easily separated from that by a subsequent combustion.

This method according to the prior art also has the considerable disadvantage that there are very large differences in the ion current signal when the time window is controlled in relation to the crank angle and the ignition timing is adjusted at the same time can. the intention is to change the ignition times in such a large range that a time window coupled to a crank angle position only partially or not at all covers the time range relevant for misfire detection. The control device according to DE 43 03 267 therefore changes the comparative threshold value depending on the operating state of the engine.

The object of the invention is to provide a method for ion current measurement in internal combustion engines, which is technically simple and also fail-safe and suitable for adjusting the ignition timing. It is also an object to specify a suitable ion current measuring device.

This object was achieved by the characterizing features of claim 1 and solved 14, advantageous developments can be found in the dependent claims. The basic idea of the invention is to detach from the crank angle-related time window control and to implement a tracking of the time window after the ignition time by the starting time and / or the duration of the time window from the ignition time and at least one variable describing the current operating state of the internal combustion engine, in particular the variable Speed, is determined automatically. This requires a new type of ion current measuring device which, instead of using a contactor, now uses an ignition timing signal to carry out the control for determining the starting time and / or the duration of the time window, this ignition timing signal being obtained from the electronic ignition timing control. Other preferred operating parameters can also be incorporated into the control as preferred further developments. such as the torque, the exhaust gas recirculation rate and / or the fuel / air mixture, which influence the ion current signal. Corresponding correction values in the form of characteristic curves or fields are stored in the control.

A first time window for misfire detection and a second time window for the detection of knocking combustion are preferably provided, which can be tracked independently of each other so that each time window can be regulated in the optimal range. The integration over a time window to an integral value largely suppresses interference and enables a comparison with a threshold value to be made more reliably. Since the time window is tracked at a predetermined time interval from the ignition point, that is to say outside the ignition area and is independent of the crank position, the same area of the ion current signal is always detected and the influence of the ignition spark on the ion current signal is minimized. Even very extreme adjustments of the ignition timing, as is desired, for example, in certain load conditions, do not lead to falsification of the ion current signal and thus to no errors in the detection.

In order to be able to recognize misfires particularly well, it proves to be very advantageous to bring the time window as close as possible to the end of the ignition period, since at this point in time, when the ignition is successful, the fuel / air mixture burns particularly strongly and thus the ion current signal particularly is meaningful.

Since the course of the ion current signal, in particular the duration of the significant region of the ion current signal, is also dependent on the operating state of the internal combustion engine, it proves to be very advantageous for comparison with a threshold value to change the duration of the time window accordingly.

A particularly advantageous embodiment is the coupling of the duration of the time window to the engine speed, which is stored accordingly in a map. It has proven particularly suitable to use a time window of approximately 100 degrees crank angle at low speeds, which is then reduced to approximately 60 degrees crank angle up to the maximum speed. When specifying degrees in the crank angle, the speed-independent specification only refers to the duration, but not the start time, which is independent of the crank position.

The adaptation for the second time window is analogous to this, the specific areas of the ion current signal to be recorded being different.

The invention is explained in more detail below using an exemplary embodiment and the figures.

Brief description of the figures: FIG. 1 ion current signal during knocking combustion Figure 2 by means of a band pass on the significant for knocking

Frequency range filtered ion current signal according to FIG. 1

FIG. 3 position of the time window (3a), result of the rectified ion current signal within the time window (3b) and integration (3c) of the signal at an early ignition point and faulty knock detection due to rigid time window coupled to the crank angle position

FIG. 4 position of the time window (4a), result of the rectified ion current signal within the time window (4b) and integration (4c) of the signal with a time window coupled to the ignition point and consequently error-free knock detection

FIG. 5 position of the time window (5a), result of the rectified ion current signal within the time window (5b) and integration (5c) of the signal at a late ignition point and faulty knock detection due to rigid time window coupled to the crank angle position

Figure 6 ion current signal in a knock-free combustion

FIG. 7 bandpass-filtered ion current signal according to FIG. 6 FIG. 8 position of the time window (8a), result of the rectified ion current signal within the time window (8b) and integration (8c) of the signal at an early ignition point and due to rigid time window coupled to the crank angle position, an incorrect knock detection FIG. 9 block diagram of an arrangement for carrying out the

Knocking combustion detection method

Figure 10 block diagram of an arrangement for performing the

Misfire detection method

FIG. 11 shows the course of the ion current signal over time and the increase in the integral value dependent on the position of the time window during successful ignition

Figure 12 ion current, time window and integral value with a misfire Figure l3 ion current signal and integral value at a fixed to one

Crank angle position coupled time window

FIG. 14 time window control with two time windows W1 and W2 that are tracked independently of the ignition timing as a function of operating parameters

FIG. 1 first shows the typical course of the ion current signal i in the case of knocking combustion. The two amplitude deflection ranges, which are separated in time, can be clearly seen, while the first oscillation range (flame front signal range 1) characterizes the ionization during the spreading flame front, a second amplitude deflection range (knock signal range 2) occurs with a delay, with a harmonic characteristic of the knocking combustion. While normal knock-free combustion results in a low-frequency amplitude change, knocking causes pulsed, pulsating ionization. This can be seen even more clearly when the bandpass-filtered ion current signal i _f in FIG. 2 is considered. The low-frequency components of the ion current signal are extinguished and the flame front signal area 1 can easily be distinguished from the knock signal area 2. However, the amplitudes in the flame front signal area 1 are markedly higher than the vibrations in the knock signal area 2.

If the effects of a time window rigidly coupled to the crank angle position according to the prior art are now considered in FIG. 3, it becomes clear that the time window 3 begins very late at an early ignition point (time window start is in each case denoted as t ₀ ). The time window 3 / W2 can therefore no longer fully detect the knock signal area 2. The time window 3 / W2 is to be distinguished in its beginning t ₀ and its duration (to t _E ) from other time windows, for example misfire detection, since a much smaller time range is detected for the knock detection. The time-windowed and rectified signal is thus shortened in the knock signal area 2 (cf. FIG. 3b), which leads to an insufficient intralvalue! I dt during integration (cf. FIG. 30) which does not reach the significant knock threshold 4. Detects the knock detection In spite of knocking occurring, knock-free combustion would occur. With certain control methods that optimize performance, the ignition point ZZP would then be shifted further forward in order to get closer to the knock limit that was actually exceeded and was optimal for performance so that the internal combustion engine is brought into an even knocking operating state. Such a control would therefore steer precisely in the wrong direction due to the faulty body detection. In comparison, FIG. 4 shows for a time window W2 that follows the ignition point that the time window always detects the knock signal area 2 exactly, this precisely between the beginning t ₀ and the end t _{E in the} middle of the time window 3. The time-windowed and rectified ion current signal according to 4b can thus be integrated in an unadulterated manner and reaches knocking threshold 4 due to the vibrations in knocking area 2 that are significant for knocking combustion (cf. FIG. 4c). The combustion is correctly recognized as knocking. In contrast, FIG. 5 again shows the effects of a time window 3 rigidly coupled to the crank angle position in accordance with the prior art with knocking combustion, but this time at a late ignition point, so that the time window 3 begins very early (time window start is in each case designated as t ₀ ). At the beginning of the time window 3, the flame front area 1 is then partially detected (cf. FIG. 5a). The time-windowed and rectified ion current signal thus, as can be clearly seen from FIG. 5b, receives not only the knock signal area 2 but also parts of the flame front area 1, which also has a high amplitude. This leads to a rapid increase in the integral value based on the integrated flame front area 1 (cf. FIG. 5c), which in this exemplary embodiment is already sufficient to reach or reach the knock threshold. Even if knocking signals would no longer follow, knocking would already be recognized. The integral value I i dt increases again in the knock signal area 2.

Even more serious are the effects of a time window that is rigidly coupled to the crank angle position if the time window is too early and if the ignition timing is late, if we consider knock-free combustion. FIG. 6 first shows the ion current signal i in which no harmonics can now be determined after the flame front signal area 1, as can be seen even better from FIG. 7, the bandpass-filtered ion current signal i _f . If this is now filtered again in analogy to FIG. 5 with a time window rigidly coupled to the crank angle position and at the same time a very late ignition time occurs, the time window starts again very early and at least partially captures the time Flame front signal area 1, as can also be seen in FIG. 8b with the time-windowed and rectified ion current signal. This leads to a rapid increase in the integral value I i dt based on the integrated flame front area 1 (cf. FIG. 8c), which in this exemplary embodiment is already sufficient to reach or reach the knock threshold. A knock-free combustion is recognized as knocking. In certain control methods in which knocking is to be avoided, the ignition timing would now be shifted back into the supposedly knock-free area based on this faulty knock detection. The rigid time window would then start earlier with respect to the later ignition point and would capture even more of the flame front area 1 and thus steer precisely in the wrong direction. A time window W2 which follows the ignition point proves to be extremely advantageous for knock detection. FIG. 9 shows a block diagram of an ion current measuring device. The ignition control 11.1 receives commands from the ignition timing control 12.1 and influences the ignition timing accordingly. The ignition times are transmitted via a connection 13.1 to the ion current detection unit 15.1, which then activates the time window for the integration of the bandpass-filtered ion current signal i at the predetermined or previously determined distance. The duration and / or the start t _{0 of} the time window 3 is determined from at least one parameter 14.1 describing the operating state of the internal combustion engine (here the speed n is given here as an example and further ones are indicated) and one or more characteristic diagrams from data stored there and changes accordingly. The integer value I i dt determined during the time window is forwarded to knock detection 16.1, which in turn sets one or more knock display signals 17.1 as a function of the comparison result with knock threshold 18. In addition to the exemplary embodiment shown here, the preferred working areas claimed in the subclaims are also suitable for a large number of internal combustion engines, but can still be checked adaptively and adapted accordingly. The implementation of the time window within the ion current detection unit 15.1 as a function of the parameters 14.1 is readily possible for the person skilled in the art. As shown in FIG. 10, a block diagram of an arrangement for misfire detection can be constructed analogously to this by the ignition control 11.2 Receives commands from the ignition timing control 12.2 and influences the ignition timing accordingly. The ignition times are transmitted via a connection 13.2 to the ion current detection unit 15.2, which then activates the time window for the integration of the ion current signal i at the predetermined or previously determined distance ΔT. The duration TF of the time window is determined from at least one parameter 14.2 describing the operating state of the internal combustion engine (the speed n given here as an example and further indicated) using a map from data stored there and changed accordingly. The integral value lidt determined in this way during the time window is passed on to the misfire detection 16.2, which in turn sets one or more misfire display signals 17.2 depending on the comparison result with a threshold value 18.2.

FIG. 11 shows the course of the ion current i over time t as well as the position of the time window W1 and the integral value ji dt resulting from this by integrating the ion current signal i. The position of the time window TF is determined by the start time t2 and the end time t3. The position and duration TK of the time window W1 are dependent on the ignition timing to and the ignition spark _duration T _zf , because the distance ΔT between the ignition timing to and the time window start t2 is specified accordingly, but also the operating state of the internal combustion engine at the distance ΔT and in particular the time window duration TF is taken into account. If the ignition ZF begins at the ignition point in time to, the time window W1 sets in exactly after the distance ΔT and thus regardless of the current crank angle position. The width TK of the time window W1 is selected such that it detects both the ion current signals of the spreading flame front (1) and the pressure maximum during the subsequent combustion (2) when the ignition is successful and is determined according to the current operating state of the internal combustion engine, for example the speed and load, adjusted. Only the actual spark between to and tl is hidden. The immediately following the spark and over a relatively large time window W1 that extends from 100 to 60 degrees crank angle depending on the current operating state, e.g. the speed, is not affected by atypical ignition curves and faults, because compensate for this over time. The ignition can be over a large area before or after the top Dead center OT, shown at a usual point in FIG. 1, can be shifted without causing an error in the ion current signal. Comparing this with FIG. 12, which shows the case of a misfire, it becomes clear that in the case of the misfire, i.e. the misfire, only a small noise in the ion current signal is detected and integrated within the time window W1 following the ignition time, so that the integral value is far below the predetermined threshold.

If one looks at the ignition timing to, which was shifted very late to TDC with a time window rigidly aligned with the crank angle position, it becomes clear that even with a timing window start t2 that is very late after TDC, the ignition spark ZF is at least partially detected by the integration and that resulting integral value I i dt thus becomes very large since the ion current signal during electrical ignition is significantly higher than the ion current during combustion. even a misfire, as indicated in Figure 13, was considered a successful ignition. Such misfiring detection of misfiring led to unfavorable operating conditions and damage to the catalytic converter. It should be emphasized that the ignition time t1 can of course also be used as the reference time for the time window as the reference time for the time window, since only the known ignition spark duration τ _2f lies between the two.

FIG. 14 additionally outlines a time window controller 20 for carrying out the method with two time windows W1 and W2. The time window control 20 receives the ignition timing signal ZZP and the ignition duration TZF as input variables from the ignition control 21, the ignition timing signal acting as a synchronization signal for the entire time window control 20, according to which all elements are aligned in time. This ensures that the time windows W1 and W2 are tracked to the ignition point regardless of the crank angle position. Furthermore, the time window controller 20 receives at least one parameter describing the operating state of the internal combustion engine, in this case the speed n. In particular the duration of the time window TD (W1 ) and TD.W2) depends on the speed n. For this purpose, the time window control 20 is, for example, directly connected to a tachometer 22. It is also for This exemplary embodiment provides to take into account further operating parameters, which are preferably provided by the motor control circuit 23 by connecting it to a series of sensors 24, 25. These sensors record engine parameters, such as the load, the exhaust gas recirculation rate and the fuel-air mixture via hot-film sensors, the lambda sensor or the like. In this exemplary embodiment, at least the load p, the exhaust gas recirculation rate EGR and the fuel-air are used for the time window control Mixture λ is taken into account, the possibility of further signals being sketched out, for example special signals in the case of staggered dual ignition, cylinder deactivation, change in injection or diagnostic settings. All of these input signals are either linked directly, such as the ignition timing signal, by numerical operations 26 or prepared by characteristic curves or characteristic diagrams 27 or look-up tables 28, and fed to four mutually independent evaluation circuits 29 to 32, each of which determines the position of the time window Determine W1 for misfire detection and W2 for knock detection by starting point in time t0 (W1 / 2) and duration of time window TD.W1 / 2) and forward it to the ion current measuring device (not shown in FIG. 14), which corresponds to this time window W1 and W2 detects the ion current, the ion current signal also being generated only once in the overlapping time ranges, of course, and correspondingly two integrators being supplied for the integration over both time windows W1 and W2.

Claims

1) Method for ion current measurement in internal combustion engines, in which an ion current signal that detects an ion current in the combustion chamber is generated by integrating the ion current signal (i) into an integral value (J dt) over at least one time window, the integral value being compared with at least one threshold value, characterized in that an electronic ignition timing is provided and the time window (W1, W2) is tracked to the ignition time (ZZP) by the starting time (tO (W1 / 2)) and / or the duration of the time window (TD (W1, W2) ) from the ignition point (ZZP) and at least one variable (14) describing the current operating state of the internal combustion engine, in particular the speed (n), is determined

2) method according to claim 1, characterized in that the

Starting time (tθ (Wl / 2)) and / or the duration of the time window (TD (Wl / 2)) is determined from the ignition time (ZZP), the speed (n) and the load torque (p)

3) Method according to claim 2, characterized in that in addition the exhaust gas recirculation rate (EGR), and / or the fuel-air mixture ratio (? _) Are taken into account device (22, 24, 25) for determining the current variable (s) become

4) Method according to one of the preceding claims, characterized in that the starting time of the time window is determined by using at least one variable describing the current operating state of the internal combustion engine, via stored characteristic curves and / or characteristic diagrams (27, 28) from this / these variables (n) parameters are automatically derived and these parameters are additively linked with the ignition point (ZZP)

5) Method according to one of the preceding claims, characterized in that an integral value of the ion current is detected within the time window (WD), this is compared with a threshold value, and at an integral value that is less than the threshold value, this is recognized as a misfire.

6) Method according to claim 5, characterized in that the time interval from the end of the ignition time to the start of the time window for misfire detection is not greater than 5 degrees crank angle! is.

7) method according to claim 5 or 6, characterized in that the

The duration of the time window for misfire detection at low engine speeds is approx. 100 degrees crank angle and is reduced to a maximum speed of approx. 60 degrees crank angle.

8) Method according to one of the preceding claims 1 to 4, characterized in that an integral value of the ion current is detected within the time window, this is compared with a threshold value, and for an integral value which is greater than the threshold value, this as a knocking combustion is recognized.

9) Method according to claim 8, characterized in that the time interval from the ignition time to the start time of

Knock detection time window is approximately between 20 and 45 degrees crank angle.

10) Method according to claim 9, characterized in that the time interval from the ignition timing to the starting time of the time window for knock detection at low speed between 20 and 30 degrees crank angle and at high speed between 30 and 40 degrees crank angle.

11) Method according to claim 8, 9 or 10, characterized in that the duration of the time window for knock detection is approximately between 15 and 35 degrees crank angle.

12) Method according to claim 11, characterized in that the duration of the time window at low speeds between 15 and 30 degrees crank angle and at high speeds between 20 and 35 degrees

Crank angle is. 13) Method according to one of claims 5 or 6, characterized in that the misfire detection and in a second time window (W1, W2) the detection of knocking combustion is carried out in a first time window (WD), the time windows (W1, W2) overlapping one another can and both independently of the ignition timing (ZZP) track.

14) Ion current measuring device for an internal combustion engine, wherein the ion current measuring device generates an ion current signal that detects the ion current in the combustion chamber and has at least one time window in which the ion current signal is detected, characterized in that a device for ignition timing control by generating an ignition timing signal and a control device for determining the starting time and / or the duration of the time window is provided, the control device being connected to the device for regulating the ignition timing, in order to determine the starting time of the time window, the ignition timing signal with a variable (14), in particular the speed (14), which describes the current operating state of the internal combustion engine. n) to track the determinable distance.

15) ion current measuring device according to claim 14, characterized in that the controller (20) for determining the start time and / or the duration of the time window (W1, W2) is connected to at least one sensor (22, 24, 25) for generating a current one Operating state signal of the internal combustion engine describing the operating state signal, in particular a speed signal (22), and with a memory device in the controller (20) in which correction values for adapting the time window to this current operating state are applied.

16) Ion current measuring device according to claim 9, characterized in that two time window integrators which can be tracked independently of one another at the ignition timing (ZZP) are provided, a first time window integrator being used for misfire detection and a second time window integrator being used for knock detection.