JPH07243346A - Knock detection method by ion current - Google Patents

Abstract

PURPOSE:To remarkably improve discrimination performance of knock frequency components and accurately detect generation of knock by adding restriction to ion current just after starting detection including noise components and releasing the restriction after elapse of a prescribed time length period. CONSTITUTION:In the case of detecting knock, ion current Ii which is generated by applying bias voltage on an ignition plug just after ignition is detected. Because knock current In comes to be stacked in the ion current Ii in knock generation, when ion current Ii in which knock current In is stacked is input in a charge amplifier CA, it is set to be restricted by the first FET1. In the EFT1, control voltage Vg applied on the gate G11 is slowly started in the time length period decided by time constant circuit TCC. Afterwards, knock current In is input in an integral circuit, the integral value is averaged so as to detect knock strength, and affirmative/negative generation of knock is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion current knock detection method for detecting knocks generated in an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, as a method of detecting a knock generated in an internal combustion engine, a method using a vibration type knock sensor is generally used, and a signal from the knock sensor is determined in a predetermined section. The knock is detected by. In this case, of the signals from the knock sensor, a signal in a predetermined frequency band is extracted and processed.

Further, as a method of detecting knock using the ion current, for example, as in the method described in Japanese Patent Laid-Open No. 58-7536, the amplitude and width of the ion signal corresponding to the detected ion current are used. A device that detects (determines) a knock is known. Even in this case, in order to prevent the spark noise from being superimposed on the ion signal, the detection of the ion signal is performed after a predetermined time delay from ignition. Even in the case of such an ion current, as in the case of the knock sensor, there is known one in which a signal in a predetermined frequency band (knock frequency component) of the ion current is peak-held and signal-processed. .

[0004]

By the way, in the case of detecting the knock from the ion current as in the latter example described above, when the ion current is detected after a delay of a predetermined time,
Immediately after the detection, the stepwise current signal is detected. This step-shaped current signal contains many frequency components, and the same frequency as that of the knock is also included therein. Therefore, such a stepped current signal needs to be already eliminated at the time of detection of the ion current in order to reliably detect the knock frequency component.

However, when the engine speed increases, the portion where the knock frequency component is superposed comes close to the time when the ion current detection is started, and many current signals of different frequencies continue to the knock signal. Will occur or will overlap, making it difficult to detect only knock frequency components. Therefore, it becomes difficult to accurately detect the knock, and even if the knock occurs, the knock may be missed in the high rotation speed range.

An object of the present invention is to eliminate such a problem.

[0007]

The present invention takes the following means in order to achieve such an object. That is, the knock detection method by the ion current according to the present invention is based on the ion current that detects the occurrence of knock by detecting the knock frequency component that is detected by detecting the ion current flowing in the cylinder from the start of combustion and superimposing it on the ion current. A knock detection method, in which a limit is given so that the ion current gradually increases during a period of a predetermined time from the start of detection of the ion current, and after the end of the period, the limit on the ion current is released and the limit is released. It is characterized in that the knock frequency component is separated and detected from the generated ion current to detect the occurrence of knock.

[0008]

With such a structure, the ion current at the time of starting the detection of the ion current has the minimum amplitude because the limit is applied, and then gradually increases, but it reaches the detectable amplitude. This is after the end of the predetermined period of time during which restrictions are relaxed. That is, since the ion current within that period is smaller than the ion currents thereafter, it can be easily distinguished from the ion currents whose restrictions have been released thereafter. Further, even if the detection operation is started within this period, the amplitude is small, so the detection is impossible even when unnecessary noise or a current that changes stepwise is superposed, and it is not possible to misidentify it as a knock frequency component. Absent. This makes it possible to distinguish the ion current having various frequency components at the time of starting the detection of the ion current from the ion current having the knock frequency component. Therefore, by extracting only the knock frequency component that is superimposed on the ion current after the period of the predetermined time length, it is possible to reliably detect the occurrence of knock.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

An engine 100 schematically shown in FIG. 1 is of a four-cylinder type for an automobile, and its intake system 1 has a throttle valve 2 which opens and closes in response to an accelerator pedal (not shown).
Is provided, and the surge tank 3 is provided on the downstream side thereof. A fuel injection valve 5 is further provided near one end communicating with the surge tank 3, and the fuel injection valve 5 is controlled by the electronic control unit 6 so as to inject independently for each cylinder. ing. Further, the exhaust system 20 includes an air-fuel ratio sensor 21 for measuring the oxygen concentration in the exhaust gas.
Is attached at a position upstream of the three-way catalyst 22 arranged in a pipe line leading to a muffler (not shown). The air-fuel ratio sensor 21 has almost the same configuration as a normal O ₂ sensor, and by applying a constant voltage between the atmosphere-side electrode and the exhaust-side electrode, the theoretical air-fuel ratio at the time of feedback control From the case to the case of the air-fuel ratio in the lean burn region, the current corresponding to the oxygen concentration in the exhaust gas is output with a substantially linear characteristic.

The electronic control unit 6 includes a central processing unit 7
And a memory device 8, an input interface 9, and an output interface 11 are mainly configured, and the input interface 9 is for detecting the pressure in the surge tank 3. Intake pressure signal a output from the intake pressure sensor 13,
Revolution sensor 14 for detecting engine revolution NE
The rotation speed signal b output from the vehicle, the vehicle speed signal c output from the vehicle speed sensor 15 for detecting the vehicle speed, and the idle switch 1 for detecting the open / closed state of the throttle valve 2.
The LL signal d output from the control unit 6, the water temperature signal e output from the water temperature sensor 17 for detecting the cooling water temperature of the engine, the current signal h output from the air-fuel ratio sensor 21, and the like are input. On the other hand, the output interface 11
From the fuel injection signal f to the fuel injection valve 5 and the ignition pulse g to the spark plug 18,
A reset signal RS, which will be described later, is output.

A bias power source 24 for measuring an ion current is connected to the spark plug 18 via a high voltage diode 23. As the circuit for measuring the ion current including the bias power source 24 and the measuring method itself, various methods known in the art can be used. As the ion current measuring circuit 25, for example, FIG.
As shown in, the ion circuit 2 for amplifying the ion current Ii
5a, a bandpass filter 25b that extracts a knock current In from the signal output from the ion circuit 25a, an ABS circuit 25c that creates an absolute value of a signal in a predetermined frequency band that includes the extracted knock current In, and an ABS. Circuit 2
Integrating circuit 25 for integrating the absolute value signal output from 5c
Some consist of d and. The integrating circuit 25d itself is
Various types known in the art may be applied.

In the ion circuit 25a, as shown in FIG. 3, there are two voltage driving elements, first and second field effect transistors FET1 and FET2 and diodes Di1 and D.
A charge amplifier CA including i2, a resistor R1, and a capacitor C1 is incorporated. This charge amplifier C
A is formed in the first stage of the ion circuit 25a, and the output signal is amplified in the ion circuit 25a. The first field effect transistor FET1 has its drain D1.
The ion current Ii is input to the first gate G11, the time constant circuit TCC including the resistor R1 and the capacitor C1 is connected to the first gate G11, and the second gate G12 is connected to the source S1. It is connected to the drain D2 of the transistor FET2. Source S1 and Kland GD
A diode Di1 is connected between and. The source S2 of the second field effect transistor FET2 is the output terminal Tout of the ion circuit 25a, and the first gate G21 thereof has the first field effect transistor FET1.
Is connected to the first gate G11 of
A diode Di2 is connected between D and D. The one end of the resistor R1 is connected to the ion circuit 25a.
Is the control signal input terminal Tcs.

The electronic control unit 6 uses the intake pressure signal a output from the intake pressure sensor 13 and the rotation speed signal b output from the rotation speed sensor 14 as main information, and various types are determined according to the engine state. The fuel injection valve opening time, that is, the injector final energization time T is determined by correcting the basic injection time with the correction coefficient of, and the fuel injection valve 5 is controlled according to the determined energization time to supply the fuel according to the engine load. A program for injecting from the fuel injection valve 5 to the intake system 1 is built in. Also, a program is built in so that the reset signal RS, which is a control signal for controlling the charge amplifier CA, is output to the charge amplifier CA from the ignition timing to the start of combustion, that is, after the end of the period corresponding to the discharge time. There is. In addition, a program for detecting a knock current In, which is a knock frequency component superimposed on the ion current Ii, is incorporated. As a program for detecting knock current In, a program known in this field can be widely used, and a program for extracting knock current In with a bandpass filter and integrating the same can be mentioned. By detecting the ion current flowing in the cylinder from the start,
A program programmed to separate the knock current In having a predetermined frequency characteristic from the ion current, to integrate the separated knock current In, and to detect the occurrence of the knock based on the integration result in order to detect the occurrence of the knock is given. To be In this embodiment, a program for detecting the occurrence of knock based on such an integration result is incorporated.

An outline of this knock detection program is shown in FIG.
And the knock detection operation will be described with the operation of the charge amplifier CA.

The ion current Ii detected when detecting knock is generated by applying a bias voltage from the bypass power supply 24 to the spark plug 18 immediately after ignition, and decreases before the top dead center TDC as shown in FIG. After that, it has the characteristic that it increases again and its value becomes maximum near the crank angle where the combustion pressure becomes maximum. When knock occurs in the ion current Ii having such a low frequency frequency characteristic, a knock current In having a high frequency characteristic is superimposed according to the degree of knock. Knock current In
When the ionic current Ii on which is superimposed is input to the charge amplifier CA, it is limited by the first field effect transistor FET1. That is, at this time, when the reset signal RS that rises in a stepwise manner is input to the control signal input terminal Tcs, the control voltage Vg applied to the first gate G11 of the first field effect transistor FET1 changes to the time constant circuit TCC.
In the period P of the time length determined by the resistor R1 and the capacitor C1 of FIG. By this control voltage Vg, the first and second field effect transistors FE are
The amplification degrees of T1 and FET2 are controlled, and the input ion current Ii is limited. That is, the first and second field effect transistors FET1 and FET2 function as electrically controllable variable resistors.

As a result, the output current Iout appearing at the output end Tout is not the same magnitude as the input ion current Ii in the period P, and is given by the first and second field effect transistors FET1 and FET2. Depending on the size of the limit, the ionic current Ii gradually input from approximately 0
Changes to be equal to. That is, the reset signal R
S changes to the control voltage Vg that changes in a parabolic increasing direction by passing through the time constant circuit TCC, and the limit changes in accordance with the change state of the control voltage Vg. Therefore, the output current Iout output in the period P
Is increased with time, and the pulse-like current change immediately after the start of the detection of the ion current Ii, which is a hindrance to knock detection, is limited and is output only in a very small amount. Therefore, the pulsed current change does not have a magnitude that can be mistakenly recognized as the knock current In when passing through the bandpass filter 25b, and is not erroneously detected.

Next, the knock detection program will be described.

The knock intensity is determined by averaging the integrated value Sn, and the presence or absence of knock is detected. The following formula is shown as an example of the averaging process. Incidentally, KNKCKLVL the current knock intensity _N, KNOCKLVL knock magnitude of last of _O, the integrated value data of the current detected knock current In and KNOCKDATA.

[0020] _{KNOCKLVL N = KNOCKLVL O + (KNOCKDATA} -KNOCKLVL O) / n detection of knock is intended to be performed only for a predetermined period of time referred to as a knock window KW, as described later, the operation of the knock window KW engine Depending on the state, the start time (the same as the start time of applying the reset signal RS) is programmed to be changed with reference to the ignition timing. It should be noted that the reference of the ignition timing basically means that the ignition timing is the starting point and is based on the elapsed time from that point. It is possible to measure the elapsed time from the time point. In this knock detection program, as data for changing the start time of the knock window KW, as shown in FIG. 6, the start time (crank angle) of the knock window KW that changes in response to a change in load using the rotation speed as a parameter. (Conversion)
I have a table. In this case, the higher the rotational speed and the heavier the load, the shorter the start time.

In this embodiment, the time when the knock window KW is started from the end of ignition is determined by detecting the end of ignition. The detection of the end of ignition is performed by the detection circuit SDC shown in FIG. 7 using the signal from the ignition coil 30. This detection circuit SDC detects the voltage Vp from the primary coil 30a of the ignition coil 30 as a transistor T
By turning on and off r, the voltage is applied to one input terminal 31a of the comparator 31, and the reference voltage Vref is applied to the other input terminal 31b of the comparator 31,
The central processing unit 7 judges that the output of the comparator 31 has been inverted, and detects the ignition end point.
That is, in FIG. 8, in the period a, the transistor Tr
Is on, and one input terminal 3 of the comparator 31
No voltage is applied to 1a. After that, when the transistor Tr is turned off in accordance with the ignition timing, a voltage of, for example, about 50 V is applied to the one input terminal 31a due to the start of arc discharge (period b). When the arc discharge ends (the boundary between the period b and the period c), the voltage applied to the one input terminal 31a in the period c is, for example, about 12
Drop to V. During this period b and c, the transistor Tr
Is off. With respect to the input voltage of the comparator 31 showing such a change, the other input terminal 31b
The reference voltage Vref applied to is set to an intermediate value between the voltage Vb in the period b and the voltage Vc in the period c. Therefore, the output of the comparator 31 is inverted when the voltage Vp from the primary coil 30a is switched from the period b to the period c. This is the voltage generated in the secondary coil 30b of the ignition coil 30. Vs
Coincides with the time when the extinguishes and the ignition ends.

In the control of knock window KW, first in step 51, the engine speed and the magnitude of the load are detected, and the window start time TKNKOPN is determined based on the obtained engine speed and the magnitude of the load. That is, in this step, the time required from the end of ignition to the opening of the knock window KW according to the operating state at that time is determined from the above table. Next, at step 52, after the ignition, the knock window KW is opened after the determined window start time TKNKOPN, and at the same time, the reset signal RS is input to the charge amplifier CA. That is, as shown in FIG. 5, the knock window KW is closed during the window start time TKNKOPN from the end of ignition, and the output current Io of the ion circuit 25a corresponding to the ion current Ii is not input to the bandpass filter 25b during this period. Is in a state. Then, when the window start time TKNKOPN has elapsed from the end of ignition, the knock window KW is opened, so the output current Io on which the knock current In is superimposed is input to the bandpass filter 25b, and the knock current In is output from the bandpass filter 25b. It is input to the central processing unit 7 via the ABS circuit 25c and the integrating circuit 25d.

After that, in step 53, after the knock window KW is opened, the set closing time KTLNKCL is set.
After, the knock window KW is closed. The closing time KTLNKCL is, for example, 50 when converted into a crank angle.
It may be about CA. As a result, the ion current input to the bandpass filter 25b disappears, and the integrating circuit 25d outputs the integrated value Sn of the knock current In during the period when the knock window KW was open. As a result, knock is detected by the integrated value Sn of the knock current In at this time. The integrating circuit 25d is reset at the timing of the rising of the ignition pulse g, for example.

With such a configuration, the knock window start time TKNOPN is changed according to the engine speed, and immediately after the detection of the ion current Ii is started, the band-pass filter 25b receives the ion current Ii of a limited size. Since the input current is input, even if a pulse-like current change exists immediately after the start of detection, the current level is low, so that it can be easily distinguished from the knock current In, and the occurrence of knock can be detected without error. That is, even if the engine speed increases and the interval between the knock current In and the detection start of the ion current Ii becomes shorter than that during low speed, the pulse current change is reduced in the charge amplifier CA. Only the presence of In becomes prominent and misidentification is prevented.

Further, since the window start time TKNKOPN is changed according to the operating condition of the engine, it is possible to surely detect the knock at any time after ignition. That is, even if the ignition timing is advanced or, conversely, is retarded, after the ignition ends, a knock window K is released after a predetermined time period according to the operating state of the engine at that time.
Since W is opened, it is possible to always detect at the optimum timing, and it is possible to prevent omission of knock detection. In this way, since knock detection is performed by finally integrating the knock current obtained from the ion current, even if the ion current changes with a high frequency characteristic equivalent to that of the knock current, the durability of the knock current remains unchanged. It is possible to reliably discriminate between such changes that do not exist and knock currents.

The present invention is not limited to the embodiment described above, and the elapsed time until the knock window KW is subsequently opened is changed according to the operating state of the engine, with reference to the output timing of the ignition pulse g. Then, the knock may be detected.

Further, instead of the integrating circuit 25d, the output of the absolute value circuit 25c may be A / D converted and the converted value may be integrated by digital processing.

In addition, the configuration of each part is not limited to the illustrated example, and various modifications can be made without departing from the spirit of the present invention.

[0029]

As described above in detail, the present invention limits the ion current containing a noise component immediately after the start of detection, and releases the limit when the period of a predetermined time length ends. As a result, the distinguishability of the knock frequency component can be remarkably improved, so that the occurrence of knock can be detected with certainty, and the detection accuracy thereof can be improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view showing an embodiment of the present invention.

FIG. 2 is a block diagram of an ion current measuring circuit of the same embodiment.

FIG. 3 is a circuit diagram of a charge amplifier of the same embodiment.

FIG. 4 is a flowchart showing a control procedure of the embodiment.

FIG. 5 is an operation explanatory view of the same embodiment.

FIG. 6 is a data explanatory view showing data of a table for determining a knock window start time in the same embodiment.

FIG. 7 is a schematic circuit diagram of a detection circuit of the same embodiment.

FIG. 8 is an operation explanatory view of the detection circuit of the embodiment.

[Explanation of symbols]

 6 ... Electronic control device 7 ... Central processing unit 8 ... Storage device 9 ... Input interface 11 ... Output interface 14 ... Cam position sensor 24 ... Bias power supply 25 ... Ion current measuring circuit 25d ... Integration circuit FET1 ... First electric field effect Transistor FET ... Second field effect transistor

Claims (1)

[Claims] 1. A knock detection method using an ion current, which detects the occurrence of knock by detecting an ion current flowing in a cylinder from the start of combustion to detect a knock frequency component superimposed on the ion current. A limit is applied so that the ion current gradually increases from the detection start point of time, and after the end of the period, the limit on the ion current is released, and the knock frequency component is released from the released ion current. A method for detecting knock by ion current, characterized in that the occurrence of knock is detected separately.