JP6005928B2 - Method for determining the combustion state of an internal combustion engine - Google Patents

Description

The present invention relates to a method for determining a combustion state of an internal combustion engine such as an automobile engine, and more particularly to a combustion state determination method using an ionic current.

Conventionally, in a spark ignition type internal combustion engine, pre-ignition occurs in which the temperature in the vicinity of the center electrode of the spark plug rises and the cylinder self-ignites before the piston reaches top dead center during the compression stroke. There are things to do. When such pre-ignition occurs, the combustion efficiency and durability of the internal combustion engine decrease, and several configurations have been proposed for the purpose of detecting and suppressing pre-ignition before occurrence, for example, No. 030545 (hereinafter referred to as “Patent Document 1”) is known.

In the above-mentioned Patent Document 1, an ion current detecting means for detecting an ion current caused by ions in a combustion chamber of a vehicle engine, and an abnormality in the cylinder of the vehicle engine based on the ion current detected by the ion current detecting means. An abnormal combustion determination means for determining combustion, and a control device for a vehicle engine, wherein an increase rate (=) that is a determination value is obtained from an increase dI of ion current with respect to a width dθ of a predetermined crank angle before ignition discharge. dI / dθ) is calculated. The PCM stores data representing the relationship between normal combustion, knocking, pre-ignition (pre-ignition), and the rate of increase in ion current. This data is set in advance by experiments or the like. Further, normal combustion is set when the increase rate is less than the first threshold T1, and knocking is set when the increase rate is greater than or equal to the first threshold T1 and less than the second threshold T2, and the increase rate is the second threshold. Pre-ignition (pre-ignition) generation is set when T2 or more.

Therefore, the PCM can determine whether the subsequent combustion state is normal combustion, knocking, or pre-ignition (pre-ignition) by determining in which range the increase rate of the ion current is. A vehicle engine control device has been proposed.

JP 2009-030545 A

However, the above-described conventional control device for an internal combustion engine has the following problems. That is, it is determined that pre-ignition has occurred in the cylinder of the vehicle engine when the determination value calculated based on the ion current before ignition is equal to or greater than the second threshold value. However, if the rate of increase is calculated from the amount of increase in the ionic current and the width of the predetermined crank angle, even if the ionic current waveform changes sharply, it is not calculated as the rate of increase until it is advanced to the predetermined crank angle, Not determined as pre-ignition. For this reason, the start of the control for suppressing the pre-ignition is delayed, and the reduction of the combustion efficiency during the period in which the pre-ignition is occurring is left unattended.

In addition, if the predetermined crank angle that easily calculates the increase amount is retarded in order to detect the precursor of pre-ignition, normal combustion may be determined as pre-ignition. It is very difficult to set an appropriate predetermined crank angle in consideration of the use state.

The present invention has been made in view of the above problems, and detects a pre-ignition sign generated in the internal combustion engine immediately after it occurs, and detects a pre-ignition sign and pre-ignition generated in the internal combustion engine that are detected with higher accuracy. An object of the present invention is to provide a combustion state determination method for an internal combustion engine.

In order to solve the above-described problems, the present invention has the following configuration of a combustion state determination method for an internal combustion engine. That is, an internal combustion engine having a plurality of cylinders, an ignition plug for igniting a mixture of fuel and air supplied into the cylinder of the cylinder, an ignition coil for supplying a high voltage to the ignition plug, an ignition signal An igniter that controls discharge of the spark plug in response to an on command / off command, an ion current detection circuit that detects an ion current generated in the spark plug due to combustion of the internal combustion engine, and a crank angle of the internal combustion engine A crank angle sensor to detect,
In the combustion state determination method for an internal combustion engine that determines the pre-ignition of the internal combustion engine based on the ion current detected by the ion current detection circuit, the variation in the crank angle from an ion current waveform indicating a correlation between the ion current and the crank angle Calculating a maximum value of the increase rate expressed as a variable of the ion current with respect to the step, detecting the crank angle when the increase rate is maximized, and increasing rate related to the maximum value of the increase rate A step of setting a threshold value and a crank angle threshold value related to the crank angle based on the rotational speed information of the internal combustion engine, a maximum value of the increase rate being larger than the increase rate threshold value, and the crank angle maximum when the crank angle is aura or preignition preignition if the advanced from the crank angle threshold determine among A step of, and be provided with.

When it is determined that the pre-ignition is a pre-ignition or pre-ignition , it is preferable to perform control to lower the temperature in the cylinder of the internal combustion engine, or exhaust gas recirculated into the cylinder in the subsequent combustion cycle Reducing the percentage of the above, or increasing the percentage of cooled exhaust gas recirculated into the cylinder in subsequent combustion cycles, or reducing the compression pressure of the internal combustion engine in subsequent combustion cycles, or A method of increasing the fuel injection amount in the subsequent combustion cycle or retarding the ignition signal in the subsequent combustion cycle may be added.

As described above, the crank angle sensor for detecting the angle of the crank of the internal combustion engine is provided, and the maximum value of the increase rate is calculated from the ion current waveform detected by the ion current detection circuit. The crank angle at the maximum position is detected, and the increase rate of the ion current waveform detected by the ion current detection circuit is greater than the increase rate threshold value, and the crank angle detected by the crank angle sensor is the crank angle threshold value. If it is more advanced, it can be detected immediately after the occurrence of a pre-ignition sign that occurs in the internal combustion engine by determining that it is a pre-ignition sign or pre-ignition, and the pre-ignition that occurs in the internal combustion engine with higher accuracy. It is possible to realize a combustion state determination method for an internal combustion engine that detects the precursor and pre-ignition.

1 is a diagram showing a configuration of an internal combustion engine according to a first embodiment of the present invention. 1 is a circuit diagram of an ignition device for an internal combustion engine according to a first embodiment. It is a figure which shows the determination range of the combustion state of the internal combustion engine which is a 1st Example. It is a time chart which shows the ignition signal waveform (I) of the internal combustion engine which is a 1st Example, and the ion current waveform (B) with respect to an ignition signal. 3 is a time chart showing a precursor of pre-ignition of the internal combustion engine according to the first embodiment. It is a flowchart which shows the combustion state determination method of the internal combustion engine which is a 1st Example.

An example showing the embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a diagram showing a configuration of an internal combustion engine according to a first embodiment of the present invention, FIG. 2 is a circuit diagram of an ignition device for the internal combustion engine, and FIG. 3 is a diagram showing a determination range of a combustion state of the internal combustion engine. FIG. 4 is a time chart showing an ignition signal waveform (A) of an internal combustion engine and an ion current waveform (B) with respect to the ignition signal, FIG. 5 is a time chart showing a precursor of the internal combustion engine, and FIG. A flowchart showing the state determination method is shown in FIG.

1 and 2, the internal combustion engine is a three-cylinder engine including three cylinders 30, and an intake for supplying a mixture of fuel and air into a cylinder 32 formed for each cylinder 30. A manifold 36 is provided. In addition, an injection 50 for injecting fuel into the intake manifold 36 is provided. Further, an exhaust manifold 42 for discharging exhaust gas from the cylinder 32 is provided.

The intake manifold 36 is provided with an intake valve 38 for adjusting the amount of intake air into the cylinder 32, and the exhaust manifold 42 is provided with an exhaust valve 44 for adjusting the amount of exhaust air from the cylinder 32. Further, in order to open and close the intake valve 38 and the exhaust valve 44, an intake cam 40 is provided on the intake valve 38 side, and an exhaust cam 46 is provided on the exhaust valve 44 side.

The internal combustion engine includes a piston 34 for compressing the air-fuel mixture in the cylinder 32, and a crank 48 for converting the vertical motion caused by the combustion in the cylinder 32 transmitted to the piston 34 into a rotational motion. Further, the crank 48, the intake cam 40, and the exhaust cam 46 are driven in conjunction with a timing belt.

The internal combustion engine includes an ignition coil 10 that boosts the voltage of a battery 22 provided in the engine room, and an ignition plug 20 that ignites the air-fuel mixture in the cylinder 32. The ignition coil 10 includes a primary coil 12 wound with a primary winding, a secondary coil 14 wound with a secondary winding, an iron core 16, and an igniter 18 comprising an FET for supplying an ignition signal to the ignition coil 10. It consists of and.

The engine room includes an ECU 54 that performs electrical control of the internal combustion engine, the ECU 54 controls the amount of fuel injected from the injection 50, and the ECU 54 is connected to the ignition coil 10. The ECU 54 supplies an ignition signal corresponding to the combustion cycle of the internal combustion engine to the ignition coil 10. Further, a crank angle sensor 56 for detecting the angle of the crank 48 of the internal combustion engine is provided, and the crank angle sensor 56 is connected to the ECU 54.

Further, the internal combustion engine is provided with an ion current detection circuit 52 for detecting an ion current generated in the spark plug 20 by the combustion of the cylinder 30, and the ion current detection circuit 52 is provided in the secondary coil of the ignition coil 10. 14 is connected to the low pressure side and the ECU 54. Further, the ion current detection circuit 52 has a noise filter for removing noise generated in the detected ion current waveform.

In FIG. 4, the ignition signal waveform supplied from the igniter 18 to the ignition coil 10 is an ignition signal from the ECU 64 for one ignition of the internal combustion engine, as shown in FIG. The waveform is switched on and off. Further, when the ignition signal is switched from on to off, the operation proceeds to a discharge period in which discharge into the cylinder 32 is started.

The ion current waveform detected by the ion current detection circuit 52 is, as shown in FIG. 4B, an ion current is generated in the cylinder 32 by the combustion of the internal combustion engine, and the ignition coil 10 is During the discharge into the cylinder 32, the ion current cannot be detected from the spark plug 20, so that an ion current waveform is generated after the discharge is completed. Further, as shown in FIG. 4B, the ion current waveform has a peak position of the ion current, and the slope of the ion current waveform toward the ion peak position is determined by the increase amount di of the ion current and the crank. The increase rate (= di / dθ) of the ion current waveform is determined from the angle width dθ, and the position where the increase rate (= di / dθ) is maximum is the maximum increase rate.

The ion current waveform is noise-removed by the noise filter provided in the ion current detection circuit 52, and the steep increase rate (= di / dθ) due to noise is not determined as the maximum amplification factor. ing. However, although the noise filter must remove steep noise generated in the ion current waveform, the waveform calculated as the maximum amplification factor is configured as a bandpass filter that is not removed as noise.

Further, in FIG. 5, the ion current waveform at the time of occurrence of a pre-ignition in the internal combustion engine has a steep slope of the maximum increase rate as shown in FIGS. Is a waveform that advances in the direction of the off timing (broken line) of the ignition signal. Further, the pre-ignition sign of the internal combustion engine becomes stronger in the order of (c) <(d) <(e) <(f), and the maximum increase rate increases as the pre-ignition sign of the internal combustion engine becomes stronger. Since the position at which the occurrence occurs advances and the ion peak position also advances, the maximum increase rate and the ion peak position have a correlation.

Further, as the pre-ignition sign of the internal combustion engine becomes stronger, the ion peak position is advanced, so that the maximum increase rate increases.

In FIG. 3, the pre-ignition precursor of the internal combustion engine and the pre-ignition threshold are shown, the vertical axis shows the maximum increase rate at which the increase amount (= di / dθ) is the largest, and the horizontal axis is The crank angle when the maximum increase rate is reached (hereinafter referred to as “maximum crank angle”) is shown. Further, the vertical axis indicates the increase rate threshold for the maximum increase rate by a broken line, and the vertical axis indicates the crank angle threshold for the maximum crank angle by a broken line.

In the increase rate threshold value and the crank angle threshold value, the maximum increase rate is equal to or greater than the increase rate threshold value, and the maximum crank angle is advanced from the crank angle threshold value. Range A is set. Further, the range A is a range in which it is determined that preignition and preignition have occurred in the internal combustion engine because the steep maximum increase rate occurs at a position close to the off timing of the ignition signal. Is set.

A range B is defined when the maximum increase rate is equal to or greater than the increase rate threshold value and the maximum crank angle is retarded from the crank angle threshold value. Further, although the maximum increase rate is steep in the range B, since the maximum increase rate is generated at a position far from the off timing of the ignition signal, the combustion state of the internal combustion engine is referred to as normal combustion. The judgment range is set.

Further, a range C is defined when the maximum increase rate is equal to or less than the increase rate threshold value and the maximum crank angle is advanced from the crank angle threshold value. Further, the range C is generated at a position where the maximum increase rate is close to the off timing of the ignition signal, but since the maximum increase rate is not steep, a range in which the combustion state of the internal combustion engine is determined to be normal combustion. Is set.

A range D is defined when the maximum increase rate is equal to or less than the increase rate threshold and the maximum crank angle is retarded from the crank angle threshold. Further, since the maximum increase rate is not steep and the maximum increase rate is generated at a position close to the off timing of the ignition signal, the range D is a range for determining the combustion state of the internal combustion engine as normal combustion. Is set.

Further, the increase rate threshold value and the crank angle threshold value fluctuate in accordance with the rotational speed of the internal combustion engine, and the ECU 54 optimizes the increase rate threshold value and the crank angle threshold value according to the rotational speed of the internal combustion engine. The crank angle threshold value is appropriately determined.

Next, operation | movement of the combustion state determination method of an internal combustion engine is demonstrated based on FIG.

In FIG. 6, the ion current detection circuit 52 detects an ion current generated in the spark plug 20 due to combustion of the internal combustion engine (S1), and the crank angle sensor 56 detects the ion current waveform detected in (S1). The angle of the crank 48 is detected (S2). The ECU 54 calculates the increase rate (= di / dθ) of the ion current waveform from the increase amount di of the ion current detected in (S1) and the angle width dθ of the crank 48 (S3), and the ECU 54 The maximum crank angle at the position where the maximum increase rate is obtained is calculated from the maximum increase rate at which the increase rate (= di / dθ) calculated in (S3) is maximum and the angle of the crank 48 detected in (S2). (S4). Further, the ECU 54 determines the increase rate threshold value for the maximum increase rate and the crank angle threshold value for the maximum crank angle in accordance with the rotational speed of the internal combustion engine (S5).

Further, the ECU 54 determines whether or not the maximum increase rate calculated in (S4)> the increase rate threshold value determined in (S5) (S6), and the maximum increase rate> the increase in (S6). When the rate threshold value is reached, the ECU 54 determines whether the maximum crank angle calculated in (S4) is advanced from the crank angle threshold value determined in (S5) (S7), (S7). ), The ECU 54 determines that a pre-ignition sign or pre-ignition has occurred in the internal combustion engine (S8).

In addition, when the internal combustion engine is determined to be a pre-ignition precursor or pre-ignition, the ECU 54 reduces the compression pressure of the internal combustion engine in the subsequent combustion cycles, and the pre-ignition precursor generated in the internal combustion engine. Or pre-ignition is suppressed.

With the above configuration, the maximum increase rate of the increase rate (= di / dθ) of the ion current waveform from the increase amount di of the ion current di and the angle width dθ of the crank 48, and the position where the maximum increase rate is obtained. A pre-ignition or pre-ignition of the pre-ignition is determined from the maximum crank angle. Thus, since the position where the increase rate (= di / dθ) is always the maximum increase rate is detected, it is possible to determine immediately after the occurrence of a pre-ignition sign in the combustion of the internal combustion engine. That is, it is possible to start the control for suppressing the pre-ignition quickly after the occurrence of the pre-ignition, and to prevent the combustion efficiency and durability of the internal combustion engine from being lowered.

Further, from the maximum increase rate and the maximum crank angle, only when the maximum increase rate> the increase rate threshold value and the maximum crank angle are advanced from the crank angle threshold value, the internal combustion engine is preloaded. It is determined that an ignition sign or pre-ignition has occurred. From this, the position where the maximum increase rate occurs is advanced, and the ion peak position is also different from the advanced state, so that a pre-ignition or pre-ignition occurs in the internal combustion engine by mistake. Although it is not, it is possible to prevent erroneous determination that a pre-ignition or pre-ignition has occurred.

As a modification of the first embodiment, the internal combustion engine is a three-cylinder engine including three cylinders 30. However, the internal combustion engine may be changed as appropriate as long as the internal combustion engine has a plurality of cylinders. The parts configuration of the engine may be arbitrarily changed according to design circumstances. The increase rate threshold value and the crank angle threshold value may be changed as appropriate according to the configuration of the internal combustion engine. Further, the increase rate threshold value and the crank angle threshold value are the intake pressure of the internal combustion engine or the rotational speed of the internal combustion engine, the temperature in the cylinder 32, the intake air temperature, the EGR amount, the air-fuel ratio, and the variable valve timing mechanism. Further, it may be determined from at least one condition such as a variable valve lift mechanism and a water temperature of the internal combustion engine.

The circuit configuration of the noise filter provided in the ion current detection circuit 52 may be changed as appropriate. Further, the removal of noise generated in the ion current waveform is performed by hardware such as the noise filter provided in the ion current detection circuit 52, as well as a dedicated computer circuit that operates under the control of the ECU 54 and the ECU 54, etc. You may perform from the digital filter process using software.

Further, when it is determined that the internal combustion engine is a pre-ignition precursor or pre-ignition, in the subsequent combustion cycle, the ECU 54 passes through an exhaust gas recirculation passage that connects the intake manifold 36 and the exhaust manifold 42. The ratio of exhaust gas used in exhaust gas recirculation (hereinafter referred to as “EGR”) for recirculation in the cylinder 32 may be reduced. Further, when it is determined that the internal combustion engine is a pre-ignition sign or pre-ignition, the ECU 54 once cools the exhaust gas used for the EGR outside the internal combustion engine in the subsequent combustion cycle, and then the cylinder again. The ratio of the exhaust gas used in the cooled EGR that recirculates within 32 may be increased.

Further, when it is determined that the internal combustion engine is a pre-ignition sign or pre-ignition, the ECU 54 may increase the fuel injection amount from the injection 50 to the intake manifold 36 in the subsequent combustion cycle. Further, when the internal combustion engine is determined to be a pre-ignition sign or a pre-ignition, the ECU 54 may perform control to retard the ignition signal from the igniter 18 in the subsequent combustion cycle.

Further, if the control is to reduce the temperature in the cylinder 30 of the internal combustion engine, a pre-ignition precursor or pre-ignition suppression may be performed by a method other than the above.

10: Ignition coil
12: Primary coil
14: Secondary coil
16: Iron core
18: Igniter
20: Spark plug
30: Cylinder
32: Cylinder
34: Piston
36: Intake manifold
38: Intake valve
40: Intake cam
42: Exhaust manifold
44: Exhaust valve
46: Exhaust cam
48: Crank
50: Injection
52: Ion current detection circuit
54: ECU
56: Crank angle sensor

Claims (7)

An internal combustion engine having a plurality of cylinders, an ignition plug for igniting a mixture of fuel and air supplied into the cylinder of the cylinder, an ignition coil for supplying a high voltage to the ignition plug, An igniter that controls the discharge of the spark plug in accordance with an OFF switching state, an ion current detection circuit that detects an ion current generated in the spark plug due to combustion of the internal combustion engine, and a crank angle of the internal combustion engine A crank angle sensor that
In the combustion state determination method for an internal combustion engine that determines the pre-ignition of the internal combustion engine based on the ion current detected by the ion current detection circuit,
Calculating a maximum value of an increase rate expressed as a variable of the ion current with respect to a variable of the crank angle from an ion current waveform indicating a correlation between the ion current and a crank angle;
Detecting the crank angle when the increase rate is maximized;
Setting an increase rate threshold value related to the maximum value of the increase rate and a crank angle threshold value related to the crank angle based on the rotational speed information of the internal combustion engine;
If the maximum value of the increase rate is larger than the increase rate threshold value, and the maximum crank angle among the crank angles is advanced from the crank angle threshold value, it is a sign of pre-ignition or pre-ignition. A method for determining the combustion state of the internal combustion engine. 2. The combustion state determination method for an internal combustion engine according to claim 1, wherein when it is determined that the pre-ignition is a precursor or a pre-ignition , control is performed to reduce a temperature in the cylinder of the internal combustion engine. 3. 2. The combustion state of the internal combustion engine according to claim 1, wherein when it is determined that the pre-ignition is a precursor or pre-ignition , a ratio of exhaust gas recirculated into the cylinder in a subsequent combustion cycle is decreased. Judgment method. 2. The internal combustion engine according to claim 1, wherein when it is determined that the pre-ignition is a precursor or a pre-ignition , a ratio of the cooled exhaust gas recirculated into the cylinder in a subsequent combustion cycle is increased. Combustion state determination method. 2. The combustion state determination method for an internal combustion engine according to claim 1, wherein the compression pressure of the internal combustion engine in a subsequent combustion cycle is reduced when it is determined that the pre-ignition is a precursor or pre-ignition . 2. The combustion state determination method for an internal combustion engine according to claim 1, wherein, when it is determined that the pre-ignition is a precursor or pre-ignition , a fuel injection amount in a subsequent combustion cycle is increased. 2. The combustion state determination method for an internal combustion engine according to claim 1, wherein the ignition signal in the subsequent combustion cycle is retarded when it is determined that the pre-ignition is a precursor or a pre-ignition .

Images