JPH06101562A - Method for detecting knock by means of ion current - Google Patents

Abstract

PURPOSE:To ensure detection of knock generated, even if ignition timing varies, so as to enable proper ignition timing control based on the detection by causing the starting time of a judgment area in which the knock is detected to be varied depending on the operating state of an engine. CONSTITUTION:The fuel injection valves 5 of an engine 100 are so controlled by an electronic control unit 6 to inject fuel independently at each cylinder. An ignition pulse (g) is output from the output interface of the electronic control unit 6 to a spark plug 18. A bias power source 24 for measuring ion current via a high pressure diode 23 is connected to the spark plug 18. A judgment area in which to recognize changes in the ion current is set and the judgment area is delayed by a delay time during which the judgment area is set in accordance with the operating state of the engine 100 with ignition timing as a reference point. Knock from the ion current is detected within the delayed judgment area. Detection of the knock can thus ensured.

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. The knock window as the predetermined section is set so that mechanical noise such as valve down noise can be avoided and knock can be detected. Such a knock window is usually 10 ° CA to 60 ° C. of ATDC.
It is set to A (crank angle).

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.

[0004]

However, in the conventional example including the above publication, for example, when a knock occurs before the knock window, that is, between the knock window and TDC, or during the delay time, the generated knock occurs. It could not be detected because it did not enter the knock window.

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

[0006]

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 a knock detection method by the ion current that detects the occurrence of knock by detecting the ion current flowing in the cylinder from the start of combustion, and changes the state of the ion current. A determination section to be determined is set, the determination section is delayed by a delay time that sets the determination section according to the operating state of the engine with the ignition timing as a reference point, and knock is detected from the ion current in the delayed determination section. It is characterized by

[0007]

With such a structure, only the delay time set in a variable length according to the engine operating state, that is, the ignition timing changed by the load, the engine speed, etc. Since the ion current determination section is delayed, the determination section is set according to the ignition timing. That is, the determination section for detecting knock is not fixed regardless of the ignition timing, but is set with the ignition timing as a reference point according to the operating condition of the engine. Therefore, even if knocking occurs at any time after ignition, the knocking can always be detected from the ion current in an optimum state.

[0008]

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 a four-cylinder engine 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 storage 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. The intake pressure signal a from the intake pressure sensor 13, the rotation speed signal b from the rotation speed sensor 14 for detecting the engine rotation speed NE, the vehicle speed signal c from the vehicle speed sensor 15 for detecting the vehicle speed, the throttle valve 2 The LL signal d from the idle switch 16 for detecting the open / closed state, the water temperature signal e from the water temperature sensor 17 for detecting the cooling water temperature of the engine, the current signal h from the air-fuel ratio sensor 21 described above, etc. are input. . On the other hand, the output interface 11
From the above, the fuel injection signal f is output to the fuel injection valve 5, and the ignition pulse g is output to the spark plug 18. Also spark plug 18
A bias power supply 24 for measuring an ion current is connected to the 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, as shown in FIG. 2, an ion circuit 25a that amplifies an ion current, a bandpass filter 25b that extracts a knock current In from a signal output from the ion circuit 25a, and an extraction circuit ABS circuit 25c that creates the absolute value of knocked current In and peak hold circuit 2 that holds the maximum value of the absolute value signal output from ABS circuit 25c.
There is one consisting of 5d.

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, in order to detect the occurrence of knock by detecting the ion current flowing in the cylinder from the start of combustion,
A determination section for determining the change state of the ion current is set, the determination section is delayed by a delay time that sets the determination section according to the operating state of the engine with the ignition timing as a reference point, and the ion is generated in the delayed determination section. A program for detecting knock from current is also built in.

An outline of this knock detection program is as shown in FIG. The ionic current detected for detecting knock is generated by applying a bias voltage to the spark plug 18 from the bypass power supply 24 immediately after ignition, and as shown in FIG. 4, decreases before the top dead center TDC and then increases again. However, it has a characteristic that the value becomes maximum near the crank angle where the combustion pressure becomes maximum. Then, for such an ion current having a low frequency frequency characteristic,
When a knock occurs, a knock current In having a high frequency characteristic due to the knock is superimposed on the ion current. Therefore, the knock current In superimposed on the ion current is extracted by the bandpass filter 25b, and the maximum absolute value thereof is detected to detect the occurrence of knock. The detection of this knock is
The knock window KW is performed only for a predetermined period called a knock window KW, and as will be described later, the knock window KW is programmed so that its start time is changed based on the ignition timing according to the operating state of the engine. 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 the data for changing the start time of the knock window KW, as shown in FIG. 5, the start time of the knock window KW (crank angle) that changes corresponding to the change of the load using the rotation speed as a parameter. (Correspondence) and the correlation data are stored in a table.

In this embodiment, the time at which 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. 6 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. 7, 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 above, 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, the determined window start time TKNKOP is set after ignition.
After N, open knock window KW. That is, as shown in the figure, the knock window KW is closed during the window start time TKNKOPN from the end of ignition, and during this period, the ion current is not input to the bandpass filter 25b. When the window start time TKNKOPN elapses from the end of ignition, the knock window K
Since W is opened, the ion current superposed with the knock current In is input to the bandpass filter 25b, and the knock current In
Is output from the bandpass filter 25b, and is input to the central processing unit 7 via the ABS circuit 25c and the peak hold circuit 25d. In step 53, after the knock window KW is opened, the set closing time KTLNK is set.
When CL has elapsed, the knock window KW is closed. The closing time KTLNKCL may be, for example, about 50 ° CA in terms of crank angle. As a result, the ion current input to the bandpass filter 25b disappears, and the peak hold circuit 25d outputs the maximum value of the knock current In during the period when the knock window KW was open. Then, the knock is detected by the maximum value of the knock current In. The peak hold circuit 25d is reset, for example, at the rising edge of the ignition pulse g.

In such a configuration, the knock window KW is changed according to the operating condition of the engine by the window start time TKNKOPN determined in step 51, so that it is certain that the knock occurs at any time after ignition. Can be detected. That is, even if the ignition timing is advanced or, conversely, retarded, the knock window KW is opened after the ignition is completed and after a predetermined time according to the operating state of the engine, so that the optimum timing is always maintained. Therefore, it is possible to prevent the knock from being missed.

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 condition of the engine, with reference to the output timing of the ignition pulse g. Then, the knock may be detected.

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.

[0018]

As described in detail above, according to the present invention, the start time of the determination section for detecting knock is changed according to the operating condition of the engine. The ignition timing can be detected, and more appropriate ignition timing control can be performed based on the detection result.

[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 flowchart showing a control procedure of the embodiment.

FIG. 4 is an operation explanatory view of the same embodiment.

FIG. 5 is a data explanatory view showing data of a table for determining a knock window start time in the embodiment.

FIG. 6 is a schematic circuit diagram of a detection circuit of the same embodiment.

FIG. 7 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 measurement circuit

Claims (1)

[Claims] 1. A knock detection method using an ion current for detecting occurrence of knock by detecting ion current flowing in a cylinder from the start of combustion, wherein a determination section for determining a change state of the ion current is set, and ignition is performed. Knock by ion current characterized by delaying the determination section by a delay time that sets the determination section according to the operating state of the engine with the timing as a reference point, and detecting knock from the ion current in the delayed determination section. Detection method.