SE508168C2 - Pinking detection apparatus using adaptive measurement window for internal combustion engine - Google Patents

Abstract

The detection apparatus has a control unit (10) which detects at least the engine speed, temperature and load. Via indicators (11,12,13) the ignition time point and the fed fuel amount are controlled. The one indicator (11) is preferably a conventional pulse indicator which detects cogs on the periphery of the flywheel, with position determination being obtained through one or more cogs having different spacing and width at a specific crankshaft position. The control unit incorporates an arithmetical unit (15) and the necessary memory (14), in which the regulating algorithm, fuel matrix and ignition matrix are stored. In each engine cylinder (4) is at least one spark plug (5). Ignition voltage is produced in an ignition coil (32) with a primary winding (33) and a secondary winding (34). The primary winding at its one end is connected to a battery (6) and in its earth connection is arranged an electrically controlled switch (35).

Description

sus 168 ~ az 20 30 35 the position for maximum combustion pressure, the measuring window can be opened after this fixed crankshaft position.

The control of the measuring window therefore requires information about the current crankshaft position in order for the measuring window to open at the correct position.

A complicating factor is that the position for maximum pressure can change if certain control measures, for example taken during knocking, delay the ignition. Likewise, the mode of maximum pressure can be changed if unsuitable fuel grades are used.

PURPOSE OF THE INVENTION The object of the invention is to obtain an adaptive measuring window for detecting knocking in internal combustion engines, where the measuring window is opened during the part of the combustion where the knocking phenomena occur.

Another purpose is that the measuring window automatically adapts to current combustion parameters which can affect how fast the combustion takes place. Such parameters may be altered fuel quality and actual mixture of fuel-air. Lean fuel-air mixtures, leaner than stoichiometric conditions, cause slower combustion. Increased exhaust gas recirculation also leads to slower combustion. Yet another object is to enable designs of smart ignition coils which contain means for ion current deletion in the spark plug gap, where these smart ignition coils do not require information on speed or crankshaft position for controlling measuring windows for knocking detail. Another object is that the measuring window should adapt to ignition reduction measures, where the ignition reduction means that the optimal combustion maximum is displaced, and thereby also the part of the combustion where the knocking occurs. Ignition measures can be initiated due to, for example, detected knocking, desired power reduction or desired temperature reduction.

BRIEF DESCRIPTION OF THE INVENTION The inventive method is characterized by the characterizing part of claim 1 and the system for carrying out the inventive method is characterized by the characterizing part of claim 6.

Through the inventive method and system, a measuring window for the knock detection is obtained which opens at the correct position in the combustion process when knocking can occur. It also means that autonomous ignition coils with integrated means for ionization measurement in the combustion chamber can control the measuring windows independently without information from other combustion partner networks, such as speed and load. 50 25 30 35 in 508 168 Other features and advantages of the invention appear from the core-defining parts of the other claims and the following description of exemplary embodiments.

The description of exemplary embodiments is made with reference to fi gures specified in the following fi gur list.

LIST OF FIGURES Figure 1 schematically shows an arrangement for controlling an internal combustion engine and detecting the ionization field in the combustion chamber, Figure 2 showing a typical ion current signal detected with an arrangement according to Figure 1, and Figure 3 showing a schematic design circuit which provides an adaptive control of the activation of the knockout pattern.

DESCRIPTION OF EMBODIMENTS Figure 1 shows an arrangement for controlling an internal combustion engine 1. Figure 1 shows a fully electronic control system for both the fuel supply and ignition of the internal combustion engine. With a control unit 10 which detects at least engine speed, engine temperature and engine load, via the sensors 11, 12 and 13, respectively, the ignition time is controlled as well as the amount of fuel supplied. The sensor 11 is preferably a conventional encoder arranged to detect teeth on the pexiferi of the flywheel, where position determination can also be obtained by one or more of the teeth having different tooth gap / tooth width at a certain crankshaft position.

The control unit 10 contains in the usual way an arithmetic unit 15 and the required memories 14, where control algorithms, fuel mice and ignition matrices are stored.

In each cylinder 4 at least one spark plug 5 is arranged, only the spark plug in a cylinder shown in Fig. 1. The ignition voltage is generated in an ignition coil 32 with a primary winding 33 and a section winding 34.

The primary winding 33 is connected at one end to a voltage source, battery 6, and in its ground connection is arranged an electrically controlled switch 35. By the control unit on the trigger output 50 making the switch 35 conductive, a current begins through the primary winding 33, and then the current is broken in the usual way, an uptrarformed ignition voltage is induced in the secondary winding 34 of the ignition coil 32 and an ignition spark is generated in the spark plug gap 5. When the current is to be released and when the current is to be interrupted by the switch 35, so-called dwell-time control. with an ignition cell array stored in the memory of the control unit 14, so that the required primary current has time to develop and that the ignition spark is generated at the ignition time required for the current load case.

One end of the secondary is connected to the spark plug 5 and at its other grounded end there is a detecting circuit which detects the degree of ionization in the combustion chamber. The detection circuit 10 comprises a voltage accumulator, herein in the form of a rechargeable capacitor 40, which energizes the spark gap of the spark plug with a substantially constant measuring voltage. The capacitor corresponds to an equivalent solution to the form of emission shown in EP, C, 188180 where the voltage accumulator is an elevated / transposed voltage fi from the charging circuit in a capacitive ignition system. In the embodiment shown in the diagram, the capacitor 40 is charged to a voltage level given by the breakdown voltage of the zener diode 41 when the ignition voltage pulse is induced in the secondary winding 34. This breakdown voltage can be anywhere between 80-400 volts. When the supernatant ignition voltage nmt about 30-40 kVolts is generated in the secondary winding, the zener diode 41 opens and ensures that the capacitor 40 is not charged to a higher voltage level than the breakdown voltage of the zener diode. Parallel to the measuring resistor 42, a second reverse protection diode 43 is arranged which correspondingly protects against voltages of reversed polarity. Above the meter node position 42, the current flowing in the circuit 5-34-40 / 40-42 soil can then be detected, which current depends on the conductivity of the gases in the dry-burning hour, which conductivity in turn depends on the degree of ionization in the combustion chamber.

Because the measuring resistor 42 is connected closest to earth, only a connection at the measuring point 45 to a detection circuit 44 is required, which detection circuit measures the voltage across the resistor 42 and at the measuring point 45 relative to earth. By analyzing the current, or alternatively the voltage, through the measuring resistance, knock and preignition can be detected, and as prepared in US, A, 4535740, in certain operating cases the current mixing ratio of air-fuel could be detected by measuring how long the ionization current is above a certain level.

By means of a lambda probe 31 in the exhaust gas collector 3 of the dry combustion engine, seen in the direction of the exhaust fate arranged before a catalyst 30 arranged in the exhaust system, the residual amount of oxygen in the exhaust gases can be detected, and thereby the current mixture-related air-fuel is separated. With a conventional narrowband lambda probe, the output of which has a distinct turning point just below a stoichiometric mixing ratio, the amount of fuel specified from a stored fuel matrix can be corrected so that the ideal air-to-fuel mixing ratio is contained. The output signal A of the lambda probe provides a feedback corrective control of the amount of fuel specified by the fuel mouse, which control is performed so that the output signal of the lambda probe is oscillating between high and low output signal up to a few times per second. The combustion engine fuel system contains in a conventional manner pump unit 22 arranged in the fuel tank. From the pump unit 22 the pressurized fuel is then fed on to a pressure equalizer, on to a fuel filter 24 and on to other containers / volumes 20 25 30 35 s “5 0 8 1 6 8 25 including the fuel distribution pipe. In some cases a pressure regulator 26 is arranged at the end of the fuel distribution pipe, which in case of overpressure opens for a return fate in the return line 27 back to the fuel tank 21 or the pump unit 22. An alternative to a pressure regulator 26 which opens at overpressure may be a pressure control of the fuel pump line 27 can be dispensed with. The volumes in the fuel pump unit 22, the pressure equalizer 23, the fuel cell 24 and other cavities or containers 25 are so large that a couple of minutes of operation can take place before a fuel refueled in the fuel tank 21 reaches the injectors 20. The fuel injectors 20 are preferably arranged in the respective cylinder is preferably actuated sequentially in synchronism with the opening of the respective cylinder inlet valve. The amount of fuel injected is determined by the length of the control pulse that the control unit applies to each injector. The amount of fuel, as well as the ignition timing, is controlled depending on current engine parameters in accordance with a fuel or ignition matrix stored in the control unit memory 14, and where the amount of fuel given by the matrix is possibly corrected by the lambda probe. In some fuel systems a fuel quality sensor 28 may be provided. the system. With a fuel quality sensor 28, the fuel control can be adapted to the octane number of the fuel in question or mixture dryness of, for example, methanol and petrol. The control unit 10 receives an input signal K from the fuel quality sensor indicating the current fuel quality.

Figure 2 schematically shows the appearance of an inverted ion current signal Um; obtained on line 56 with a measuring arrangement in accordance with fi gur l. Um is indicated on the Y-axis and is here measured in volts, and can be between the output signal 0 volts to just over 2.5 volts. The X-axis indicates crankshaft degrees ° VC, where 0 ° indicates the upper dead center when the piston is in its uppermost position.

At the SP position, which is a position before the upper dead center, for example 15-20 crankshaft degrees before the upper dead center, the ignition spark is generated with the ignition that is relevant under the prevailing operating conditions, mainly depending on load and speed. The generation of the spark generates a high measuring pulse in the detection layer, caused by the flash in the spark plug gap during the so-called break down phase, but this high measuring pulse can be filtered out, and its measured value is not used in the preferred form of drying.

After the flashover phase, a fl flame ionization phase, in 2 gur 2 called FLAME ION, starts, during which phase the measuring voltage is affected by the establishment of a burning core of the air-fuel mixture in or at the spark plug gap.

After the ionization phase, the post-ionization phase (Post ionization phase), called POST ION, starts in Figure 2, during which phase the measuring voltage is affected by the combustion in the combustion chamber as the number of ionizing particles increases with temperature and combustion pressure. Typically, POST ION reaches a maximum value, indicated by PP in fi clock 2, when the combustion pressure has developed to its highest value and the fr front has reached the walls of the combustion chamber, which results in an increase in pressure. 20 25 30 35 508168 i 46 Figure 2 shows with solid line UNQRM the normal appearance of an idealized ion current signal obtained from a combustion where knocking does not occur. If l-mapping occurs, the ion current signal receives a frequency content superimposed from the knocking process according to the maximum position PP, which is shown by the curve Umm.

One way to find the position of the mapping can be to detect the position of the maximum position PP by, for example, detecting the zero crossing of the first derivative of UION. However, the detection of the zero crossing is not reliable in all operating cases, as the ion current signal UmN during certain operating cases may completely lack a local maximum during the post-ionization phase, POST ION. In some operating cases, a number of local maxima of the ion beam signal UION may also occur during the post-ionization phase, POST ION, which may give an incorrect indication of when the knocking phenomena become relevant.

Figure 3 shows an inventive circuit solution, which is implemented in the detection unit 44 in Figure 1, providing an adaptive adaptation of the network window for knock detection.

The detection circuit 44 supplies two signals to the control unit 10 on the lines 54 and 58.

On line 54 a signal corresponding to the integrated value of the ion current signal obtained via line 56 is provided. The integrated value provides a parameter which is indicative of the quality of the combustion, hereinafter referred to as CQ.

A signal corresponding to the frequency content of the frequency current extracted from the ion current signal is provided on line 58. The filtered value gives a parameter that is indicative of the intensity of the click, hereinafter referred to as Kl.

Based on these detected parameters, CQ and KI, respectively, the required control measures can then be initiated by the control unit 10.

The detection unit 10 contains two signal processing circuits, a circuit 80 which produces the CQ parameter and a circuit 81 which produces the IG parameter. The ion current signal on line 56 is supplied in parallel to the respective circuit via an input buffer 60. Input buffer 60 converts the potential in the measuring point 45 to an inverted signal level, corresponding to fi gur 2, which is suitable for the circuits 80 and 81. The measuring point 45 can the embodiment lie at a negative potential of the order of -50 volts or more. A suitable signal level for the circuits 80.81 can be around +5 volts.

The CQ circuit 80 contains a low-pass filter 61, which filters out uninteresting high-frequency information. The signal from the low-pass filter 61 is fed to an integrator 62, where an integration of the signal takes place when the starting input ST goes high. The ST input goes high when the comparator 63 detects that the signal from the low pass filter, which is fed to the comparator input 63a, exceeds a reference level. The reference level is set to a fixed level of a voltage divider, in the form of two resistors 72,73 connected between a system voltage VCC and ground The fixed reference level is taken out between the resistors 72,73 and connected to the comparator input 63b.

The reference level is suitably set relatively low, corresponding to the level INTREF in Figure 2. The integrator will then integrate the ion current signal from about -5 crankshaft degrees before the upper dead center to about 45 degrees after the upper dead center, with an ion current signal corresponding to that shown in Figure 2.

The KI circuit 81 contains a bandpass filter 67, which filters out the frequency characteristic of the knocking process. In a 2-liter four-cylinder Otto engine, these frequencies superimposed on the ion current signal are in the order of 5-8 kHz, with respect to the fundamental tone. In some cases it may be appropriate to detect the harmonics instead of the fundamental tone, which lie on equal multiples of the fundamental tone. The signal from the bandpass filter 67 is fed to an integrator 68, where an integration of the bandpass filtered signal takes place when the start input ST of the integrator 68 goes high. The ST input goes high when a logic AND circuit 66 detects that two inputs are high at the same time. One input signal to AND circuit 66 is obtained from comparator 63, which is high when the ion current signal UION is above the reference level INTm. The second input signal to the AND circuit 66 is obtained from a comparator 65, which output of the comparator goes high when the current integrated CQ value amounts to a predetermined second reference level. The current integrated CQ value is obtained from the output of the integrator 62 and fed to the input 65a of the comparator 65.

The second predefined reference level is set to a proportion of at least one previous and substantially complete combustion CQ value. This proportion of the CQ value of the previous combustion is obtained via a voltage divider with two resistors 78 and 79. By substantially complete combustion is not meant that all fuel has been burned. Instead, it refers to the main part of the period during which combustion takes place in the cylinder. If the resistor 79 has twice as high a resistance as the resistor 78, a proportion corresponding to 66% of the previous CQ value is obtained. The comparator 64 and the reverse diode 75 are connected as an ideal diode and charge the capacitor 76 to a voltage level corresponding to the proportion of the previous combustion CQ value given by the voltage divider 78.79.

A discharge resistor 77 is connected in parallel with the capacitor 76. This discharge resistor is preferably highly ununified, and so adapted that the capacitor substantially maintains its voltage level over 2 successive combustions.

The AND circuit 66 thus starts the integration in the integrator 68 when the ion current signal Um is above the reference level 1NTm at the same time as the integrated CQ value from the current combustion amounts to the distributed portion of the previous combustion CQ value.

This means that the measuring window for the knock partition will adapt adaptively to the current ion current signal, and open the measuring window when, for example, the current integrated value amounts to the percentage of the previous combustion CQ value given by the voltage divider 78.79. 508 168 s 20 25 30 35 All increases in the CQ value on line 54 will take effect immediately and increase the second predetermined reference level, which is stored in capacitor 76. If, on the other hand, the CQ value were to decrease, the second predetermined reference level would gradually adapt. to the lower level, according to a time function given by the discharge resistor 77. It is essential that the knocking window is correctly positioned at load increases, where knocking risks usually occur. With load increases, the CQ value increases and the second defined reference level is adapted directly to increased CQ values. If, on the other hand, the combustion engine is subjected to load reductions, the risk of knocking is also reduced, which is why an equally rapid adaptation to reduced CQ values is not as necessary.

Figure 2 shows how the measurement window from being closed, WCLOSE, transitions to an open mode, Wopm when the instantaneous integrated value amounts to a predetermined proportion of approximately 70% of an equivalent integrated value from a previous and substantially complete combustion. Substantially equivalent integrated values are obtained at constant load on the internal combustion engine, so-called steady-state condition. In cases where the integration also takes place over a part of the flashover phase, the predetermined proportion is set to a higher value. For each engine type, the current percentage can be determined by testing, so that the knock measurement window is activated after the PP mode. The position for maximum pressure can in these determinations be detected by a special pressure sensor, or via the ion current signal. The measuring window closes when the ion current signal UION falls below the value for INTREF. In Figure 2, this is shown relative to a normal combustion UNORM at about 45 ° VC. If knocking occurs with an ion current signal corresponding to UION, the closure is delayed to just over 55 ° VC.

After each combustion, the control unit 10 receives from the detection circuit 44 a CQ value on the line 54 from the integrator 62 in the CQ circuit 80, and a KI value on the line 58 from the integrator 68 in the K1-lu etch 81. Respective integrator 62,68 is reset before the next combustion of the control unit 10 via reset signals CL1, CL2 on lines 55 and 57. The detecting circuit is then ready to calculate new CQ and K1 values for subsequent combustion.

The reset signals CL; , CL2 can be obtained from one and the same line, whereby simultaneous zeroing takes place. In some embodiments, the reset can take place via trigger signals on lines 50, 50 ', which means that lines 55 and 57 can be completely eliminated.

The invention can be modified in a number of ways within the framework and the definitions given by the appended claims.

The logic circuit structure shown in Figure 3 can of course be replaced by the corresponding processor-based circuit where the activation of the measurement window takes place in a software-controlled manner. The current reference levels can be read into memories and updated by the processor, for example when the CQ value changes. 20 9 "i 5 0 8 16 8 The first reference level INTREF is preferably a fixed predetermined level, but in some forms it can also adaptively adapt to the current load or speed of the combustion engine, or alternatively adapt to the maximum amplitude of the ion current signal. the second reference value, corresponding to a predetermined proportion of an integral value, is formed by a calculation of a rolling average value, which can preferably be calculated over a dozen of the most recent previous burns.

The KI circuit 81 can also be modified so that the second reference value stored in the capacitor 76 is not updated in proportion to changes in the CQ value. To address the large cycle-to-cycle variations in Otto engines, new reference values can be formed in a subdued manner. For example, if the C Q value increases by 10%, the second reference value can be given a smaller increase of a few percent. Such attenuation can be obtained, for example, by connecting a capacitor in parallel across the resistor 79.

As shown in Figure 2, the signal UION increases on knocking, which leads to an increase in the CQ value. If knocking is detected, in some applications the update of the second reference value, stored in the capacitor 76, can be blocked during ongoing knocking. This can be obtained, for example, by arranging a switch before the voltage divider 78.79. The switch can be controlled by the value of the KI signal, and as soon as the KI signal exceeds a predetermined level, the input of the CQ value to the voltage divider 78.79 is broken, while the supply of the CQ value to the comparator 65 is maintained.

Claims (9)

10 20 25 30 508 168 10 PATENT REQUIREMENTS A method of adapting a measuring window for knock detection in internal combustion engines, the ignition being detected via a measuring gap arranged in the combustion chamber of the pre-combustion engine, above which measuring gap a substantially constant measuring voltage is applied to obtain a degree of ionization in characterized in that - the knocking of the knock takes place in a measuring window which is kept open during a part of the combustion, - that an integrated value of the signal corresponding to the degree of ionization from substantially an entire combustion process in the combustion chamber forms a reference value for checking during a combustion when the value integrated from this combustion amounts to a proportion of the reference value. Method according to Claim 1, characterized in that the reference value for a subsequent combustion is obtained from an integrated value of the signal corresponding to the degree of ionization from substantially an entire combustion process in the combustion chamber from at least the immediately preceding combustion. Method according to claim 2, characterized in that the reference value for a subsequent combustion is continuously updated in dependence on an integrated value of the signal corresponding to the degree of ionization from substantially an entire combustion process in the combustion chamber from an immediately preceding combustion. 4. A method according to claim 3, characterized in that the reference value for a subsequent combustion is not updated if cracking with an intensity above a predetermined level is divided. Method according to claim 4, characterized in that the knock measurement window is opened during a combustion when the value integrated from this combustion amounts to between 60-90%, preferably 80% of the reference value. 20 25 30 11 '508 168 A system for adapting a measuring window for knock detection in internal combustion engines with at least one cylinder (4), wherein the internal combustion engine comprises an ion flow sensor (5) arranged in the cylinder which detects the ionization cylinder during combustion and which, depending on the degree of ionization, produces an ion current signal. the ion current signal receiving device (40-44) which contains an integrating circuit (80) which integrates the ion current signal generated during combustion and which produces a value of the ion current signal integrated from each combustion representative of the quality of the combustion, called CQ, and contains a circuit (81 ) for detecting a frequency content representative of knocking in the ion current signal and which produces a value obtained from each är ring representative of the intensity of the knocking, termed KI known as the system including means (76) for storing a CQ value from a previous combustion process in cylinder means for continuously calculating an instantaneous CQ value during combustion, which instantaneous CQ value is preferably obtained from the integrating circuit (80), means (65) for comparing the stored CQ value with instantaneous CQ value, and means (65.66, ST) to start the knock detection when the instantaneous CQ value amounts to a predetermined proportion of the stored CQ value. 7. A system according to claim 6, characterized in that the means for storing a CQ value from a previous complete combustion process in the cylinder, comprises a memory which can preferably be realized by a capacitor (76). A system according to claim 7, characterized in that the means for comparing the stored CQ value with instantaneous CQ value comprise a comparator (65), which comparator on an input (65a) obtains instantaneous CQ value and at a second input (65b), the CQ stored in the memory (75) obtains the value from a previous complete combustion process in the cylinder or a predetermined proportion of this stored CQ value. System according to claim 8, characterized in that the predetermined proportion of the stored CQ value from a previous complete combustion process in the cylinder is obtained via a voltage divider 78.79 which divides the CQ value from a previous complete combustion process in a cylinder.