JP4006781B2 - Internal combustion engine knock detection method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a knock detection method and apparatus for an internal combustion engine, and more particularly to a method and apparatus for detecting knock based on an ionic current in a combustion chamber.
[0002]
[Prior art]
In a gasoline engine, an air-fuel mixture in the vicinity of the spark plug is ignited by a spark given from the spark plug, and the flame is transmitted to the entire air-fuel mixture, thereby causing gasoline combustion. One such abnormal combustion is knocking. Knocking is a phenomenon in which an unburned portion (terminal gas) self-ignites without waiting for the flame to propagate when the pressure becomes abnormally high during the flame propagation. When knocking occurs, the combustion gas vibrates and heat easily propagates. As a result, the engine may be damaged. Knock has a close relationship with the ignition timing. If the ignition timing is advanced, the maximum combustion pressure increases and knocking is likely to occur.
[0003]
On the other hand, it is preferable to achieve a high compression ratio in order to increase the thermal efficiency and reduce the fuel consumption rate. Therefore, control for advancing the ignition timing to near the limit where knocking occurs while detecting the occurrence of knocking is performed as part of the ignition timing control. As such a knock detection method, conventionally, a vibration sensor is attached to a cylinder block or the like to detect knock vibration. However, in recent years, a method using a change in ionic current in a cylinder when a knock occurs is used. Proposed.
[0004]
That is, when the spark plug discharges and the mixture in the combustion chamber burns, the mixture is ionized. When a voltage is applied to the spark plug when the air-fuel mixture is in an ionized state, an ionic current flows. By detecting this ionic current and performing an analysis process, the occurrence of knocking can be detected. Normally, when knocking occurs, a vibration component of 6 to 7 kHz appears in the ionic current. The knock detection method and apparatus based on ion current extracts a frequency component peculiar to the knock with a filter (filter), and performs knock determination based on the magnitude.
[0005]
For example, Japanese Patent Laid-Open No. Hei 6-159129 extracts a frequency component in the vicinity of 6.3 kHz from the output of an ion current detection circuit as a knock vibration component by a bandpass filter (bandpass filter), and the extracted frequency component , And a method for detecting the presence or absence of occurrence of knock based on the integration result is disclosed.
[0006]
[Problems to be solved by the invention]
By the way, when exhaust gas recirculation (EGR) is performed or during low and medium loads, combustion becomes unstable, and vibration components resulting from this may be included in the ion current output signal. The vibration component resulting from such instability of combustion becomes noise (hereinafter referred to as combustion fluctuation noise) when performing knock determination based on the knock vibration component included in the ion current output signal. And since the frequency of this combustion fluctuation noise is 1-7 kHz, it is difficult to isolate | separate a knock vibration component and a combustion fluctuation noise component. That is, when combustion fluctuation noise is present, a component that passes through a bandpass filter provided for extraction of frequency components related to knock vibration appears, and there is no knock even though no knock has actually occurred. Will be misjudged.
[0007]
In view of such circumstances, an object of the present invention is to provide a knock detection method and apparatus for an internal combustion engine that can reliably separate and extract a combustion fluctuation noise component when extracting a knock vibration component from an ion current output signal. By doing so, the knock detection accuracy is further improved.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, an ignition coil, a switching means connected to a primary side of the ignition coil, which switches between energization and cutoff of a primary current, and a secondary side of the ignition coil are connected, A method of detecting knock in an internal combustion engine having an ignition plug that ignites an air-fuel mixture in a cylinder by causing a spark discharge in response to a secondary high voltage generated when the primary current is interrupted by the switching means. (A) an ionic current that flows through the spark plug through ions generated in the cylinder when the mixture is burned by applying a voltage to a closed circuit that does not include the secondary side of the ignition coil and includes the spark plug And (b) masking the ion current output signal generated in step (a) in a period during which discharge noise can occur. (C) extracting a higher-order frequency component of knock vibration from the signal after mask processing in step (b); and (d) a higher-order frequency component of knock vibration extracted in step (c). Determining whether or not there is a knock based on the above.
[0009]
Further, according to the present invention, the ignition coil, the switching means connected to the primary side of the ignition coil and switching between energization and cutoff of the primary current, and the secondary side of the ignition coil connected to the primary side by the switching means A device for detecting knock in an internal combustion engine having a spark plug that ignites an air-fuel mixture in a cylinder by causing a spark discharge in response to a secondary high voltage generated in response to interruption of current, the ignition An ionic current detection means for applying a voltage to a closed circuit not including the secondary side of the coil and including the spark plug, and detecting an ionic current flowing through the spark plug through ions generated in the cylinder when the air-fuel mixture burns; Masking means for masking the output signal of the ion current detection means during a period in which discharge noise can occur, and whether the output signal of the masking means There is provided a knock detection device for an internal combustion engine, comprising: a band pass filter that extracts a high-order frequency component of knock vibration; and a knock determination unit that determines presence or absence of knock based on an output signal of the band pass filter. The
[0010]
In addition, as a high-order frequency component of knock vibration, a frequency component in the vicinity of 10 to 18 kHz is preferable.
[0011]
In the knock detection method and apparatus for an internal combustion engine according to the present invention configured as described above, since the secondary side of the ignition coil does not exist in the path through which the ionic current flows, a high-order frequency component of knock vibration is included. An ionic current is detected in the state. Since only the higher-order frequency components of knock vibration are extracted from the ion current output signal, combustion fluctuation noises in different frequency bands are reliably separated. As a result, it is possible to reliably prevent a situation in which an erroneous determination that there is a knock due to instability of combustion is made, and the knock detection accuracy is improved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but before that, the problems of the prior art that the present invention has as a subject will be analyzed and details of the problem-solving principle of the present invention will be described. . The configuration of the knock detection device based on the ionic current can be classified into two types. One of the configurations includes the ignition coil secondary side in the path through which the ion current flows, and the other includes the configuration in which the ignition coil secondary side is not included in the path through which the ion current flows.
[0013]
FIG. 1 is a block diagram illustrating an example of a knock detection device that employs a configuration in which an ion current flows through a path including an ignition coil secondary side. One end of the primary winding 1a of the ignition coil 1 is connected to the positive electrode of the battery 2, and the other end is connected to the collector of the transistor 3 as switching means. The emitter of the transistor 3 is grounded, and an ignition signal is applied to its base. One end of the secondary winding 1 b of the ignition coil 1 is connected to the center electrode 4 a of the spark plug 4. The outer electrode 4b of the spark plug 4 is grounded.
[0014]
The other end of the secondary winding 1 b of the ignition coil 1 is grounded via the ion current detection circuit 5. The ion current detection circuit 5 charges a capacitor (not shown) serving as an ion current generating power source to a constant voltage by a secondary current generated when the primary current of the ignition coil 1 is interrupted, and after spark discharge, this capacitor and the ignition coil An ionic current flowing in a closed circuit composed of the secondary winding 1b, the spark plug 4, and a current detection resistor (not shown) is detected.
[0015]
First, when the ignition signal goes high and the transistor 3 is turned on, a current flows through the ignition coil primary winding 1a. Next, when the ignition signal is made low and the transistor 3 is turned off to cut off the primary current, a high voltage is induced in the secondary winding 1b of the ignition coil 1, and as a result, the ignition plug 4 Spark discharge occurs. That is, when a negative high voltage is applied to the center electrode 4a of the spark plug 4, a spark discharge occurs between the center electrode 4a and the outer electrode (ground electrode) 4b, and the spark coil secondary winding 1b Then, a current that makes a circuit flows to the secondary winding 1b through the ion current detection circuit 5 and the spark plug 4. In this process, the capacitor in the ion current detection circuit 5 is charged to a constant voltage.
[0016]
When the air-fuel mixture in the combustion chamber is ignited and burned by the spark discharge in the spark plug 4, the air-fuel mixture is ionized. When the air-fuel mixture is in an ionized state, the two electrodes of the spark plug 4 are electrically conductive. In addition, since a voltage is applied between both electrodes of the spark plug 4 due to the charging voltage of the capacitor in the ion current detection circuit 5, an ion current flows. That is, this ion current makes a round from the ion current detection circuit 5 to the ion current detection circuit 5 again via the ignition coil secondary winding 1b and the ignition plug 4. In this process, a voltage corresponding to the magnitude of the ion current appears at both ends of the current detection resistor in the ion current detection circuit 5, and this voltage is an output signal of the ion current detection circuit (hereinafter referred to as an ion current output signal). Become.
[0017]
Then, the ion current output signal is guided to the mask circuit 6. The mask circuit 6 is for masking the ion current output signal while the supplied mask signal is active so as not to transmit a signal in a period during which discharge noise occurs to the subsequent stage. The output of the mask circuit 6 is guided to a band pass filter (BPF) (band pass filter) 7. The BPF 7 receives the output signal of the mask circuit 6 and extracts a frequency component related to knock, that is, a frequency component in the vicinity of 6 to 7 kHz. Further, the integration circuit 8 provided at the subsequent stage of the BPF 7 integrates the output signal of the BPF 7 while the supplied gate signal is active. Note that a peak hold (P / H) circuit may be provided instead of the integration circuit.
[0018]
The A / D conversion circuit 9 converts the analog output voltage of the integration circuit 8 into a digital output voltage. Further, the central processing unit (CPU) 10 performs ignition timing control including knock control. Based on the output signal of the A / D conversion circuit 9, the central processing unit (CPU) 10 knocks when the value exceeds a predetermined reference value. Judge that there is. The CPU 10 detects various operating states based on outputs from the various sensors, comprehensively determines the engine state together with the presence or absence of knock, determines an optimal ignition timing, and outputs an ignition signal. The CPU 10 determines a mask period in the mask circuit 6 and a gate period in the integration circuit 8, and supplies a mask signal and a gate signal to the mask circuit 6 and the integration circuit 8, respectively.
[0019]
2 (A) to (C), FIGS. 3 (A) to (C) and FIGS. 4 (A) to (C) are (A) an ion current output signal and (B) BPF in the knock detection device of FIG. FIG. 2 is a diagram illustrating a time chart of an output signal and (C) an integration circuit output signal. FIG. 2 is a diagram related to a case where combustion is stable and knock does not occur, and FIG. FIG. 4 is a diagram related to the case where combustion is unstable in the low load region or the EGR execution region although knocking has not occurred. The ion current output that appears after the end of the steep discharge noise is a mountain-shaped low-frequency signal synchronized with the in-cylinder pressure. In the case of FIG. 2, the ion current output includes neither a vibration component due to knock nor a vibration component due to combustion fluctuation, and a gate period during which knock vibration component is expected to occur (in this example, 10 after top dead center). Even if the BPF output is integrated in (set to 40 °), the integrated value is small.
[0020]
On the other hand, when knocking occurs, as shown in FIG. 3, the knock vibration component overlaps the ion current output after the maximum in-cylinder pressure. As a result of the knock vibration component being extracted by the BPF, the integral value becomes large and knock detection becomes possible. However, when the combustion is unstable even if no knock has occurred, the ion current output becomes a messy waveform including a vibration component of 1 to 7 kHz as shown in FIG. Appears as a large signal, and as a result, the output of the integration circuit also increases, and knock is erroneously detected.
[0021]
FIGS. 5A, 5B, and 5C respectively show the ion current output signals shown in FIGS. 2A, 3A, and 4A by FFT (Fast Fourier Transform) analysis. It is the characteristic view displayed in the frequency domain, a horizontal axis represents a frequency and a vertical axis | shaft represents a power spectrum density. As can be seen from this figure, when knocking occurs (FIG. 5B), the frequency component of 6 to 7 kHz is larger than when knocking does not occur (FIG. 5A). appear. However, even when knocking does not occur but combustion is unstable (FIG. 5C), a frequency component of 6 to 7 kHz is also considerably included. Therefore, the conventional noise detection method cannot escape from being affected by combustion fluctuation noise.
[0022]
By the way, when the knock phenomenon is examined in detail, the frequency of the vibration is composed of the frequency of various resonance vibration modes determined by the dimensions of the combustion chamber (mainly the bore diameter) and the sound velocity and its harmonics, and the various resonance vibration modes and The resonance frequency is, for example, as illustrated in FIG. If knock detection is performed by paying attention to the primary component of the 6.3 kHz resonance vibration mode shown in the figure, as described above, the influence of combustion fluctuation noise of 1 to 7 kHz cannot be avoided. However, paying attention to the harmonics of the 6.3 kHz vibration mode and other resonance vibration modes, if the knock determination is performed by extracting the higher-order frequency components of the knock vibration, the influence of the combustion fluctuation noise is removed. Can do. As a high-order frequency component, judging from FIG. 6 and the plug mounting position, the vicinity of 10 to 18 kHz is preferable.
[0023]
Therefore, in the present invention, knock determination is performed based on higher-order frequency components of knock vibration. However, in the configuration including the ignition coil secondary winding in the ionic current path as shown in FIG. 1, the secondary winding becomes a kind of filter, and the high frequency component is cut as shown in FIG. Will be. For this reason, the present invention employs a configuration that does not include the ignition coil secondary winding in the ion current path.
[0024]
FIG. 7 is a diagram illustrating a configuration of a knock detection device according to an embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the component same as the component shown by FIG. That is, an ion current detection circuit 15 and a BPF 17 are provided instead of the ion current detection circuit 5 and the BPF 7 in FIG. 1, and the other parts are the same. The BPF 17 does not extract the vicinity of 6 to 7 kHz as the primary frequency component of the knock vibration as in the conventional technique, but extracts the vicinity of 10 to 18 kHz as the high-order frequency component of the knock vibration.
[0025]
FIG. 8 is a circuit diagram showing details of the ion current detection circuit 15 and the ignition circuit shown in FIG. One end of the secondary winding 1 b of the ignition coil 1 is connected to the center electrode 4 a of the spark plug 4 via a diode 21. A connection point between the diode 21 and the spark plug 4 is grounded via a diode 22, a constant voltage power supply 23, and an ion current detection resistor 24. Therefore, a constant voltage is always applied to the spark plug 4 by the constant voltage power source 23.
[0026]
Therefore, after the spark discharge, an ion current that makes a circuit flows from the positive terminal of the constant voltage power supply 23 to the negative terminal of the constant voltage power supply 23 via the ion current detection resistor 24, the spark plug 4, and the diode 22. A voltage of “ion current value × detection resistance value” appears at the connection point between the ion current detection resistor 24 and the constant voltage power supply 23, and the voltage is supplied to the subsequent circuit as an ion current output signal. Thus, since the secondary side of the ignition coil does not exist in the path through which the ionic current flows, the ionic current is detected without cutting the higher-order frequency component of the knock vibration. As described above, the higher-order frequency component of knock vibration is extracted by the BPF 17 at the subsequent stage. Subsequent knock determination processing is the same as that described with reference to FIG.
[0027]
FIG. 9 is a diagram showing the FFT analysis result of the ionic current output signal detected by the circuit configuration shown in FIG. 8, that is, a characteristic diagram in which the ionic current output is displayed in the frequency domain. Represents the power spectral density. Note that FIG. 9A shows a case where no knock has occurred, and FIG. 9B shows a case where a knock has occurred. As can be seen from this figure, when the secondary side of the ignition coil is not included in the ion current path, not only the primary frequency component of the knock vibration is about 6 to 7 kHz, but also the high frequency component of the knock vibration is about 10 to 18 kHz. However, there is a difference depending on whether knocking occurs. Therefore, in order to avoid the influence of combustion fluctuation noise in the vicinity of 1 to 7 kHz, the circuit configuration shown in FIG. 7 makes it possible to perform knock determination by passing the higher-order frequency components 10 to 18 kHz of the knock vibration through the band and detect the knock. Accuracy is improved.
[0028]
【The invention's effect】
As described above, according to the present invention, there is provided a knock detection method and apparatus for an internal combustion engine that can reliably extract and extract a combustion fluctuation noise component when extracting a knock vibration component from an ion current output signal. Provided. In other words, since the secondary side of the ignition coil does not exist in the path through which the ionic current flows, the ionic current is detected in a state including the higher-order frequency component of knock vibration, and only the higher-order frequency component is extracted for knock determination. As a result, combustion fluctuation noise in different frequency bands is reliably removed. Therefore, a situation in which an erroneous determination that there is a knock due to instability of combustion at the time of EGR execution or a low / medium load is reliably avoided, and the knock detection accuracy is improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of a knock detection device that employs a configuration in which an ion current flows through a path including an ignition coil secondary side.
2 is a time chart of (A) ion current output signal, (B) BPF output signal, and (C) integration circuit output signal in the knock detection device of FIG. 1, and combustion is stable. This relates to the case where no knock has occurred.
3 is a diagram showing time charts of (A) ion current output signal, (B) BPF output signal, and (C) integration circuit output signal in the knock detection device of FIG. 1, and when knocking occurs. It is about.
4 is a time chart of (A) an ion current output signal, (B) a BPF output signal, and (C) an integration circuit output signal in the knock detection device of FIG. 1, and no knock has occurred. It relates to the case where combustion is unstable.
5 (A), (B) and (C) are FFT (Fast Fourier Transform) analyzes of the ion current output signals shown in FIG. 2 (A), FIG. 3 (A) and FIG. 4 (A), respectively. FIG. 6 is a characteristic diagram displayed in the frequency domain.
FIG. 6 is a diagram showing various resonance vibration modes and resonance frequencies of knock vibration.
FIG. 7 is a diagram illustrating a configuration of a knock detection device according to an embodiment of the present invention.
FIG. 8 is a circuit diagram showing details of the ion current detection circuit 15 and the ignition circuit shown in FIG.
9 is a diagram showing an FFT analysis result of an ion current output signal detected by the circuit configuration shown in FIG. 8, that is, a characteristic diagram in which an ion current output is displayed in a frequency domain, and FIG. (B) is for the case where knocking occurs.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Ignition coil 1a ... Primary winding 1b ... Secondary winding 2 ... Battery 3 ... Transistor 4 ... Ignition plug 4a ... Center electrode 4b ... Outer electrode 5 ... Ion current detection circuit 6 ... Mask circuit 7 ... Band pass filter 8 ... Integration (or peak hold) circuit 9 ... A / D conversion circuit 10 ... CPU
DESCRIPTION OF SYMBOLS 15 ... Ion current detection circuit 17 ... Band pass filter 21 ... Diode 22 ... Diode 23 ... Constant voltage power supply 24 ... Ion current detection resistance

Claims (2)

An ignition coil, switching means connected to the primary side of the ignition coil and switching between energization and interruption of the primary current, and connected to the secondary side of the ignition coil and generated when the primary current is interrupted by the switching means. A method for detecting knock in an internal combustion engine having an ignition plug that ignites an air-fuel mixture in a cylinder by causing a spark discharge in response to a secondary high voltage,
(a) A voltage is applied to a closed circuit not including the ignition coil secondary side and including the ignition plug, and an ionic current flowing through the ignition plug is detected via ions generated in the cylinder when the air-fuel mixture burns Steps,
(b) masking the ion current output signal generated in step (a) in a period in which discharge noise may occur;
(c) extracting a frequency component of only 10 to 18 kHz from the signal after the mask processing in step (b);
determining the presence or absence of knock based in (d) of the frequency components that will be extracted in step (c),
A knock detection method for an internal combustion engine, comprising: An ignition coil, switching means connected to the primary side of the ignition coil and switching between energization and interruption of the primary current, and connected to the secondary side of the ignition coil and generated when the primary current is interrupted by the switching means. A device for detecting knock in an internal combustion engine having an ignition plug that ignites an air-fuel mixture in a cylinder by causing a spark discharge in response to a secondary high voltage,
Ion current detection for detecting an ionic current flowing through the spark plug through ions generated in the cylinder when the air-fuel mixture burns by applying a voltage to a closed circuit not including the ignition coil secondary side and including the spark plug Means,
Mask means for masking an output signal of the ion current detection means in a period in which discharge noise may occur;
A bandpass filter that extracts only a frequency component of 10 to 18 kHz from the output signal of the mask means;
Knock determination means for determining the presence or absence of knock based on the output signal of the bandpass filter;
A knock detection device for an internal combustion engine, comprising:

Images