WO2015033371A1

WO2015033371A1 - Abnormal combustion detection device for engine and abnormal combustion detection method for engine

Info

Publication number: WO2015033371A1
Application number: PCT/JP2013/005196
Authority: WO
Inventors: 安枝　信次
Original assignee: Yasueda Shinji
Priority date: 2013-09-03
Filing date: 2013-09-03
Publication date: 2015-03-12
Also published as: JPWO2015033371A1

Abstract

This abnormal combustion detection device (50) for an engine, said engine (1) being constructed so as to generate engine power by burning an air-fuel mixture that is supplied into a combustion chamber (2), comprises: an acceleration detector (12) for detecting a physical quantity correlating with a combustion state of the combustion chamber; a knock intensity calculation unit (52) for calculating a knock intensity in each combustion cycle on the basis of the physical quantity detected by the acceleration detector (12); and an abnormal combustion determination unit (54) for detecting abnormal combustion, except normal knocking that occurs under normal ignition in the combustion chamber (2), on the basis of at least either frequency, that is, how frequently the knock intensity calculated by the knock intensity calculation unit (52) becomes equal to or greater than a prescribed threshold value, or continuousness, that is, a state wherein the knock intensity stays equal to or greater than the prescribed threshold value over multiple combustion cycles.

Description

Engine abnormal combustion detection device and engine abnormal combustion detection method

The present invention relates to an engine abnormal combustion detection device and an abnormal combustion detection method for detecting abnormal combustion occurring in a combustion chamber of an engine.

In an engine (internal combustion engine), abnormal combustion that causes output fluctuation or combustion noise may occur. Conventionally, a technique for detecting knocking, which is a typical form of abnormal combustion in an engine, has been known. Yes. In this conventional technique, an acceleration sensor is used as a knocking sensor to detect the vibration frequency at the time of abnormal combustion inherent in the engine, and if the intensity is higher than a certain threshold value, it is considered that knocking has occurred and the ignition timing is delayed. Avoidance control such as cornering is performed (see, for example, Patent Document 1).

JP 2004-346876 A

However, in recent years, abnormal combustion caused by self-ignition of lubricating oil (for example, lubricating oil that has risen) in the combustion chamber has become a problem. When abnormal combustion due to this lubricating oil occurs, the combustion pressure in the combustion chamber suddenly increases, and basically knocking occurs simultaneously. However, both require essentially different measures. It is a completely different abnormal phenomenon. However, in the conventional technology, it is difficult to clearly distinguish between normal knocking generated under normal ignition and abnormal combustion due to the lubricating oil, and when abnormal combustion due to the lubricating oil occurs, As a result of incorrect avoidance control, there is a problem of worsening the situation. That is, when abnormal combustion caused by the lubricating oil occurs, if the control for retarding the ignition timing is performed as in the knocking avoidance control, the temperature in the combustion chamber rises further and the lubricating oil is further ignited at multiple points. Doing so will make things worse.

The present invention has been made in view of such a problem, and an engine having a configuration capable of accurately discriminating between normal knocking generated under normal ignition and abnormal combustion other than the knocking. An object of the present invention is to provide an abnormal combustion detection device and an abnormal combustion detection method.

In order to solve the above problems, an abnormal combustion detection apparatus for an engine according to the present invention is an engine that generates engine power by burning a mixture of air and fuel supplied into a combustion chamber. A physical quantity detection means (for example, the acceleration detector 12 in the embodiment) for detecting a physical quantity correlated with the knock quantity, and a knock intensity calculation means for calculating the knock magnitude of each combustion cycle based on the physical quantity detected by the physical quantity detection means ( For example, the knock intensity calculating unit 52) in the embodiment and the frequency at which the knock intensity calculated by the knock intensity calculating means is equal to or higher than a predetermined threshold and the knock intensity are continuously equal to or higher than the predetermined threshold over a plurality of combustion cycles. Based on at least one of the continuity, the abnormal combustion other than normal knocking that occurs under normal ignition Abnormal combustion determination means for output (e.g., abnormal combustion determination section 54 in the embodiment) configured to include a, a.

Also, the abnormal combustion detection method for an engine according to the present invention is a physical quantity correlated with the combustion state of the combustion chamber in an engine that generates engine power by burning a mixture of air and fuel supplied into the combustion chamber. Detecting a physical quantity detected in the physical quantity detecting step, calculating a knock intensity for each combustion cycle based on the physical quantity detected in the physical quantity detecting step, and determining that the knock intensity calculated in the knock intensity calculating step is equal to or greater than a predetermined threshold value. And abnormal combustion other than normal knocking that occurs under normal ignition based on at least one of the continuity in which the frequency and knock intensity continuously exceed a predetermined threshold over a plurality of combustion cycles And an abnormal combustion determination step for detecting.

According to the abnormal combustion detection apparatus for an engine according to the present invention, the frequency at which the knock intensity becomes equal to or higher than a predetermined threshold and the continuity of the knock intensity continuously equal to or higher than the predetermined threshold over a plurality of combustion cycles. Based on at least one of them, knocking generated in the combustion chamber of the engine and abnormal combustion other than the knocking (for example, abnormal combustion caused by lubricating oil, abnormal combustion caused by hot surface ignition, etc.) are accurately discriminated. Therefore, it is possible to perform correct avoidance control according to the type of abnormal combustion, and to quickly return the engine to an appropriate combustion state. Also, since the engine is generally equipped with a knock sensor (physical quantity detection means), the knock intensity is used as an index for detecting abnormal combustion other than normal knocking that occurs under normal ignition. By using this, the abnormal combustion detection device can be realized at low cost.

Further, in the engine abnormal combustion detection device according to the above-mentioned invention, when the knock intensity fluctuates more than a certain value in a plurality of combustion cycles, other abnormal combustion other than normal knocking generated under normal ignition is detected. With such a configuration, it is possible to further improve the detection accuracy of various abnormal combustion based on the combination conditions of frequency and continuity.

Furthermore, in the engine abnormal combustion detection apparatus according to the above-described invention, when the maximum combustion pressure in the combustion chamber rises above a certain level or when the maximum combustion pressure fluctuates above a certain level in a plurality of combustion cycles, By detecting the abnormal combustion other than the normal knocking that occurs in the combustion chamber, it is possible to reliably detect abnormal combustion that causes a sudden increase in the combustion pressure based on multi-point ignition in the combustion chamber. It becomes possible to do.

According to the abnormal combustion detection method for an engine according to the present invention, the frequency at which the knock intensity becomes equal to or higher than a predetermined threshold and the continuity of the knock intensity continuously equal to or higher than the predetermined threshold over a plurality of combustion cycles. Based on at least one, normal knocking that occurs under normal ignition and abnormal combustion other than the knocking (for example, abnormal combustion due to lubricating oil, abnormal combustion due to hot surface ignition, etc.) Since it is possible to accurately determine, it is possible to execute correct avoidance control according to the type of abnormal combustion and to quickly return the engine to an appropriate combustion state.

Further, in the abnormal combustion detection method for an engine according to the above-described invention, when the knock intensity fluctuates more than a certain value in a plurality of combustion cycles, other abnormal combustion other than normal knocking that occurs under normal ignition is detected. With such a configuration, it is possible to further improve the detection accuracy of various abnormal combustion based on the combination conditions of frequency and continuity.

Furthermore, in the engine abnormal combustion detection method according to the above-described invention, when the maximum combustion pressure in the combustion chamber rises above a certain level or when the maximum combustion pressure fluctuates above a certain level in a plurality of combustion cycles, By detecting the abnormal combustion other than the normal knocking that occurs in the combustion chamber, it is possible to reliably detect abnormal combustion that causes a sudden increase in the combustion pressure based on multi-point ignition in the combustion chamber. It becomes possible to do.

It is a mimetic diagram showing an engine concerning one embodiment of the present invention. It is a table | surface which compares an example of the characteristic of various abnormal combustion made into object by this embodiment. It is a graph which shows an example of how knock strength appears in the above-mentioned various abnormal combustion. It is a graph which shows an example of the relationship between a combustion pressure and crank angle when the abnormal combustion resulting from lubricating oil generate | occur | produces. It is a functional block diagram of the abnormal combustion detection apparatus of a 1st embodiment. It is a schematic diagram for demonstrating an example of the method of calculating knocking intensity | strength. It is a flowchart which shows an example of the abnormal combustion detection method in 1st Embodiment. It is a functional block diagram of the abnormal combustion detection apparatus of 2nd Embodiment. It is a flowchart which shows an example of the abnormal combustion detection method in 2nd Embodiment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an abnormal combustion detection apparatus for an engine according to an embodiment of the present invention. First, the basic configuration of the engine will be described with reference to FIG. In the present embodiment, a premixed combustion type gasoline engine is illustrated as an example of an engine (internal combustion engine). However, the present invention can also be applied to other types of engines such as a gas engine.

[Basic engine configuration]
The engine 1 includes a cylinder block 10 having a cylinder space 11, a cylinder head 20 provided so as to cover the upper surface of the cylinder block 10, a piston 30 provided in a reciprocating manner in the cylinder space 11, and a connecting rod 35. And a crankshaft 40 that is coupled to the piston 30 and is driven to rotate by receiving the reciprocating motion of the piston 30. In the engine 1, a combustion chamber 2 (also referred to as “in-cylinder”) is defined by being surrounded by an inner peripheral surface of the cylinder space 11, a cylinder head 20, and a piston 30.

The cylinder head 20 is provided with an intake passage 21 and an exhaust passage 23 connected to the combustion chamber 2. An intake valve that opens and closes the intake port is provided at an intake port which is a communication portion between the combustion chamber 2 and the intake passage 21. 22 is provided, and an exhaust valve 24 for opening and closing the exhaust port is provided at an exhaust port which is a communication portion between the combustion chamber 2 and the exhaust passage 23. The intake valve 22 and the exhaust valve 24 are opened and closed at a predetermined timing by a cam mechanism (not shown) that is rotationally driven in conjunction with the crankshaft 40.

For example, an air-fuel ratio control device 25 (see FIG. 5), a fuel supply device 26, and the like are provided in the middle of or in front of the intake passage 21, and the compressed air and fuel are mixed through the intake passage 21. Gas (premixed gas) is introduced into the combustion chamber 2. There are various types of the air-fuel mixture supply method and the fuel injection method, and any method may be adopted.

The cylinder head 20 is provided with an ignition device 27 with the tip (electrode portion) facing the ceiling of the combustion chamber 2, and the air-fuel mixture introduced into the combustion chamber 2 by the operation of the ignition device 27. Is ignited. The operations of the air-fuel ratio control device 25, the fuel supply device 26, the ignition device 27, etc. are controlled by the electronic control unit ECU. The cylinder head 20 is provided with a combustion pressure detector 28 for detecting the pressure in the combustion chamber 2 (referred to as “combustion pressure”).

On the other hand, an acceleration detector 12 for detecting vibration (vibration acceleration) generated in the cylinder block 10 is attached to the cylinder block 10.

In the present embodiment, as will be described in detail later, when one of the acceleration detector 12 and the combustion pressure detector 28 constitutes a so-called “knock sensor” and the acceleration detector 12 is employed, it is based on the vibration value. Various abnormal combustion is detected using the knock intensity as an index, and when the combustion pressure detector 28 is employed, various abnormal combustion is detected using the knock intensity based on the combustion pressure as an index. Hereinafter, the acceleration detector 12 or the combustion pressure detector 28 may be referred to as a knock sensor 3.

A crank angle detector 41 for detecting the rotation angle of the crankshaft 40 is attached to the crankshaft 40.

As described above, the engine 1 includes both the acceleration detector 12 and the combustion pressure detector 28. However, either one of the acceleration detector 12 or the combustion pressure detector 28 is included. It may be a thing.

[Basic engine operation]
In the four-cycle engine 1 exemplified in the present embodiment, when the piston 30 descends from the top dead center and the crankshaft 40 rotates in a predetermined rotation direction, the intake valve 22 is opened and mixing from the intake passage 21 is performed. Air is drawn into the combustion chamber 2 via the intake port (“intake stroke”). When the piston 30 is lowered to the bottom dead center, the intake valve 22 is closed by the elastic force of the valve spring.

When the piston 30 reaches the bottom dead center, the inertial force of the crankshaft 40 acts through the connecting rod 35 to raise the piston 30, and the air-fuel mixture is compressed in the sealed combustion chamber 2 ("compression stroke"). ).

Subsequently, when the piston 30 reaches the vicinity of the top dead center, the air-fuel mixture compressed by the spark ignition of the ignition device 27 is combusted. Combustion of the air-fuel mixture in the combustion chamber 2 is performed by propagating a portion of the flame ignited by the ignition device 27 in the combustion chamber 2. In response to this combustion energy, the piston 30 descends again (“combustion / expansion stroke”).

When the piston 30 reaches the bottom dead center and further rises, the exhaust valve 24 is opened, and the gas in the combustion chamber 2 is exhausted through the exhaust port (“exhaust stroke”). When the piston 30 rises to the top dead center, the exhaust valve 24 is closed by the elastic force of the valve spring, while the intake valve 22 is opened again. The series of “intake stroke”, “compression stroke”, “combustion / expansion stroke”, and “exhaust stroke” are repeated each time the piston 30 reciprocates up and down twice.

[Abnormal combustion detector]
In the abnormal combustion detection device according to the present embodiment, various abnormal combustions that occur in the engine 1 based on detection information from the

detectors

12, 28, 41, etc., are generated under normal ignition. A function of discriminating between knocking and other abnormal combustion (for example, abnormal combustion caused by lubricating oil, abnormal combustion caused by hot surface ignition, etc.) is provided.

Here, FIG. 2 is a table comparing the characteristics of the abnormal combustion that is the object of the present embodiment, and FIG. 3 is a graph showing how the knocking intensity changes with time in each abnormal combustion. As will be described in detail later, abnormal combustion caused by lubricating oil and abnormal combustion caused by hot surface ignition are basically characterized by simultaneous knocking, and hence knocking that occurs under normal ignition thereafter. May also be referred to as “normal knocking”. That is, “normal knocking” means that that occurs under normal ignition by the ignition device 27. On the other hand, “abnormal combustion other than normal knocking” means abnormal combustion due to abnormal ignition, and knocking often occurs at the same time. The characteristics of normal knocking, abnormal combustion caused by lubricating oil, and abnormal combustion caused by hot surface ignition will be described in order with reference to FIGS.

"Normal knocking" is a phenomenon in which the pressure wave reciprocates in the combustion chamber 2 and resonates due to self-ignition of the unburned portion of the air-fuel mixture in the process of increasing the combustion pressure due to flame propagation. . As shown in FIGS. 2 and 3, normal knocking tends to occur continuously at a relatively high frequency with a predetermined level of knock intensity compared to the other two abnormal combustions, and its cycle fluctuations. Is relatively small. The “knock strength” is an index indicating the degree of knocking generated in the engine. Further, the maximum combustion pressure Pmax obtained from the combustion pressure, the indicated mean effective pressure Pmi, and their cycle fluctuations are also relatively small compared to the other two abnormal combustions.

“Abnormal combustion due to lubricating oil” is a phenomenon in which the lubricating oil staying in the combustion chamber 2 (for example, the lubricating oil that has risen) causes self-ignition to rapidly increase the combustion pressure. In addition, since the lubricating oil is dispersed in the combustion chamber 2 in the form of mist or steam, self-ignition occurs almost simultaneously at multiple points (multiple positions) in the combustion chamber 2 (and thus causes a sudden pressure increase). Will be.) As described above, abnormal combustion caused by the lubricating oil has a feature that knocking occurs simultaneously because the combustion pressure rapidly increases. As shown in FIG. 2 and FIG. 3, in abnormal combustion caused by lubricating oil, a relatively large level of knock strength tends to occur once, accidentally, or intermittently at a relatively low frequency. More specifically, the abnormal combustion caused by the lubricating oil does not occur continuously in most cases, and the frequency of occurrence is low (in particular, the initial occurrence is particularly low). Therefore, the cycle variation of knock strength is large. Further, there is a characteristic that the maximum combustion pressure Pmax and the indicated mean effective pressure Pmi are higher than those of normal combustion due to the above-mentioned multipoint ignition, and the cycle fluctuation is also increased.

Here, FIG. 4 is a graph showing the relationship between the crank angle and the combustion pressure in normal combustion and abnormal combustion (with advance and without advance) due to lubricating oil. As can be seen from FIG. 4, in the abnormal combustion caused by the lubricating oil, the ignition timing does not necessarily advance, and the maximum combustion pressure Pmax increases with multi-point ignition without advance. There are many cases.

“Abnormal combustion due to hot surface ignition” is a phenomenon in which the air-fuel mixture comes into contact with the overheated high-temperature portion in the combustion chamber 2 to cause self-ignition and gradually accelerates the ignition timing of the air-fuel mixture. Therefore, knocking occurs at the same time. In abnormal combustion resulting from hot surface ignition, as shown in FIGS. 2 and 3, a large level of knock intensity is continuously generated and tends to grow severely in a short time. Further, there is a characteristic that the maximum combustion pressure Pmax is significantly higher than that of normal combustion.

In the present embodiment, paying attention to the difference in characteristics as described above, various abnormal combustion detection methods include (I) a detection method based on occurrence frequency, continuity at which the knock intensity is equal to or greater than a threshold value, and (II) knock. A detection method based on the cycle fluctuation value of the intensity, and (III) a detection method based on the cycle fluctuation value of the combustion maximum pressure Pmax, the combustion maximum pressure Pmax, and the cycle fluctuation value of the indicated mean effective pressure Pmi are proposed.

Now, a specific configuration of the abnormal combustion detection device will be described below. First, the configuration of the abnormal combustion detection device 50 according to the first embodiment will be described. FIG. 5 is a functional block diagram of the abnormal combustion detection device 50 according to the first embodiment.

The abnormal combustion detection device 50 is mainly composed of a microcomputer equipped with a CPU, ROM, RAM, etc., and the CPU detects abnormal combustion occurring in the engine 1 in accordance with an abnormal combustion detection control program stored in the ROM. To do. Knock sensor 3 (acceleration detector 12 etc.), crank angle detector 28 etc. are electrically connected to abnormal combustion detector 50.

As shown in FIG. 5, the abnormal combustion detection device 50 includes a knock intensity calculation unit 52 that calculates a knock intensity and its cycle fluctuation value based on detection information from the knock sensor 3, and an abnormality that detects abnormal combustion in the cylinder. A combustion determination unit 54.

On the other hand, the electronic control unit ECU is composed mainly of a microcomputer equipped with a CPU, ROM, RAM, etc., and the CPU is based on detection information from various detectors and the like according to a combustion control program stored in the ROM. Execute control. The electronic control unit ECU is electrically connected with an air-fuel ratio control device 25, a combustion supply device 26, an ignition device 27, and the like. Here, as shown in FIG. 5, the electronic control unit ECU controls the operation of the air-fuel ratio control device 25, the combustion supply device 26, the ignition device 27, and the like to control the combustion control unit 51 that controls the combustion in the cylinder. I have.

(Calculation of knock strength)
The knock intensity calculation unit 52 executes predetermined calculation processing based on the vibration value V detected by the knock sensor 3 (acceleration detector 12 or the like) and the crank angle θ detected by the crank angle detector 41. Then, the knock strength is calculated. Specifically, as shown in FIG. 6A, the vibration waveform is subjected to frequency analysis (fast Fourier transform) in a predetermined analysis window, and the power spectrum shown in FIG. 6B is calculated. The setting range Δθ of the analysis window can be set to an arbitrary range near the top dead center (TDC), and may be set, for example, within a range of 40 degrees near the top dead center.

Subsequently, a bandpass filter is applied to a predetermined frequency band (referred to as “knock frequency band”) centered on the knocking natural frequency calculated by the following equation (1), and the vibration fluctuation width ΔV of the knock frequency band is calculated. An overall value (root mean square value) is calculated, and this is defined as knock intensity. In the following equation (1), the speed of sound in the tube is calculated as a function of the temperature in the tube.
Knocking natural frequency = sound velocity in the pipe / (2 x cylinder diameter) (1)

(Calculation of knock fluctuation cycle fluctuation value)
Knock strength calculator 52 also calculates a cycle variation value of the knock strength. Here, the cycle fluctuation value of the knock intensity is an index indicating the degree of fluctuation of the knock intensity in a plurality of cycles. For example, the difference between the maximum value and the minimum value of the knock intensity, standard deviation, COV (covariance) ). In the present embodiment, the “cycle” means a series of processes of intake, compression, combustion / expansion, and exhaust.

(Abnormal combustion detection)
The abnormal combustion determination unit 54 executes the above detection methods (I) and (II) singly or in combination with each other, thereby causing abnormal combustion due to knocking, lubricating oil, and hot surface ignition. Various abnormal combustion is detected.

(I) Detection Method Based on Knock Strength Occurrence Frequency and Continuity The abnormal combustion determination unit 54 uses at least one of the occurrence frequency and continuity as an index for detecting abnormal combustion. Specifically, the abnormal combustion determination unit 54 records the number of cycles (occurrence frequency) at which the knock intensity is equal to or higher than a predetermined threshold (referred to as “reference threshold”) during a predetermined number of cycles, and the occurrence frequency thereof. Is greater than or equal to the first threshold, that is, when the occurrence frequency is high, it is determined that the abnormal combustion is caused by hot surface ignition. On the other hand, if the occurrence frequency is less than the first threshold and greater than or equal to the second threshold, that is, if the occurrence frequency is medium, it is determined that the knocking is normal. Further, when the occurrence frequency is less than the second threshold, that is, when the occurrence frequency is low, it is determined that the abnormal combustion is caused by the lubricating oil. Note that the first threshold value is larger than the second threshold value (first threshold value> second threshold value). This is because, as described above, abnormal combustion caused by lubricating oil is less frequent than normal knocking, and abnormal combustion caused by hot surface ignition is compared with normal knocking. Therefore, it uses the characteristic that the frequency of occurrence is high. The reference threshold value, the first threshold value, and the second threshold value are variables that can be arbitrarily variably set according to the operating state of the engine 1 or the like.

Further, when the knock intensity that is equal to or greater than the reference threshold value is continuously detected, the abnormal combustion determination unit 54 performs hot surface ignition when the number of consecutive times is equal to or greater than the third threshold value, that is, when continuity is high. It is determined that the combustion is abnormal combustion. On the other hand, when the number of consecutive times is less than the third threshold value and greater than or equal to the fourth threshold value, that is, when the continuity is medium, it is determined that the knocking is normal. Further, when the number of continuous times is less than the fourth threshold, that is, when the continuity is low, it is determined that the abnormal combustion is caused by the lubricating oil. The third threshold value is larger than the fourth threshold value (third threshold value> fourth threshold value). As described above, the abnormal combustion caused by the lubricating oil does not occur continuously in most cases, and the abnormal combustion caused by hot surface ignition occurs almost continuously. It is a thing. The third threshold value and the fourth threshold value are variables that can be variably set according to the operating state of the engine 1 or the like.

(II) Detection Method Based on Knock Intensity Cycle Variation The abnormal combustion determination unit 54 uses the cycle variation value of the knock strength as an index for detecting abnormal combustion. Specifically, the abnormal combustion determination unit 54 determines that abnormal combustion due to the lubricating oil has occurred when the cycle fluctuation value of the knock intensity is equal to or greater than the fifth threshold value. As described above, this utilizes the characteristic that in the case of abnormal combustion caused by lubricating oil, the variation between combustion cycles is larger than that of normal knocking. At this time, the detection method (II) may be used alone, but the detection accuracy of the abnormal combustion can be further improved by combination with the detection method (I). The fifth threshold value is a variable that can be variably set according to the operating state of the engine 1 or the like.

(Avoidance control)
When any abnormal combustion is detected, the abnormal combustion determination unit 54 transmits detection information related to the abnormal combustion to the combustion control unit 51 of the electronic control unit ECU. The combustion control unit 51 of the electronic control unit ECU executes avoidance control according to the type of abnormal combustion based on the detection information from the abnormal combustion determination unit 54, so that each part of the engine (air-fuel ratio control device 25, fuel supply device 26). The operation of the ignition device 27, etc.).

Next, an example of the abnormal combustion detection method executed by the abnormal combustion detection device 50 according to the first embodiment will be described. FIG. 7 is a flowchart showing an example of the abnormal combustion detection method.

First, the knock strength calculation unit 52 calculates the knock strength based on the detection information input from the knock sensor 3 (acceleration detector 12 or the like) (step S101).

Subsequently, the abnormal combustion determination unit 54 determines whether or not the knock intensity exceeds the reference threshold value (step S102).

When the knock magnitude is greater than or equal to the reference threshold (step S102: YES), the abnormal combustion determination unit 54 determines whether the knock intensity is greater than or equal to the reference threshold in the past N cycles or the number of consecutive times that the knock magnitude is greater than or equal to the reference threshold Is calculated (step S103). It is also possible to calculate both the occurrence frequency of knock strength and the number of consecutive times.

The abnormal combustion determination unit 54 compares the occurrence frequency or the continuous number obtained in step S103 with a predetermined threshold value (first to fourth threshold values), and compares the abnormal combustion caused by normal knocking and lubricating oil. Then, it is determined which of the abnormal combustion caused by hot surface ignition has occurred (step S104).

Subsequently, the combustion control unit 51 of the electronic control unit ECU executes avoidance control according to the type of abnormal combustion detected in step S104 (step S105). For example, as avoidance control for knocking, as control for retarding the ignition timing, as avoidance control for abnormal combustion due to hot surface ignition, as control for avoiding abnormal combustion due to lubricating oil, such as control to immediately stop the engine 1 Control for reducing the output of the engine 1 is executed.

Next, the configuration of the abnormal combustion detection device 150 according to the second embodiment will be described. FIG. 8 is a functional block diagram of the abnormal combustion detection device 150 according to the second embodiment.

The abnormal combustion detection device 150 is mainly composed of a microcomputer equipped with a CPU, ROM, RAM, etc., and the CPU detects abnormal combustion occurring in the engine 1 in accordance with the control program for detecting abnormal combustion stored in the ROM. To do. Knock sensor 3 (combustion pressure detector 28), crank angle detector 28, and the like are electrically connected to abnormal combustion detection device 150.

As shown in FIG. 8, the abnormal combustion detection device 150 includes a knock intensity calculation unit 152 that calculates a knock intensity and its cycle fluctuation value based on detection information from the knock sensor 3 (combustion pressure detector 28), and also knocks. Based on the detection information from the sensor 3 (combustion pressure detector 28), the combustion pressure analysis unit 153 that calculates the maximum combustion pressure Pmax, the indicated mean effective pressure Pmi, and their cycle fluctuation values, and the like, and based on the knock intensity and the combustion pressure An abnormal combustion determination unit 154 that detects abnormal combustion in the cylinder.

On the other hand, the electronic control unit ECU is composed mainly of a microcomputer equipped with a CPU, ROM, RAM, etc., and the CPU is based on detection information from various detectors and the like according to a combustion control program stored in the ROM. Execute control. The electronic control unit ECU is electrically connected with an air-fuel ratio control device 25, a combustion supply device 26, an ignition device 27, and the like. Here, as shown in FIG. 8, the electronic control unit ECU controls the operations of the air-fuel ratio control device 25, the combustion supply device 26, the ignition device 27, etc., and controls the combustion control unit 51 that controls the combustion in the cylinder. I have.

(Calculation of knock strength)
Knock intensity calculation unit 152 executes a predetermined calculation process based on combustion pressure P detected by knock sensor 3 (combustion pressure detector 28) and crank angle θ detected by crank angle detector 41. Then, the knock strength is calculated. Specifically, as shown in FIG. 6A, the combustion pressure waveform is subjected to frequency analysis (fast Fourier transform) in a predetermined analysis window, and the power spectrum shown in FIG. 6B is calculated. The setting range Δθ of the analysis window can be set to an arbitrary range near the top dead center (TDC), and may be set, for example, within a range of 40 degrees near the top dead center.

Subsequently, a bandpass filter is applied to a predetermined frequency band (referred to as “knock frequency band”) centered on the knocking natural frequency calculated by the above equation (1), and the combustion pressure fluctuation width ΔP in this knock frequency band. The overall value (root mean square value) is calculated, and this is defined as the knock intensity.

(Calculation of knock fluctuation cycle fluctuation value)
Knock strength calculation unit 152 also calculates a cycle variation value of the knock strength. Here, the cycle fluctuation value of the knock intensity is an index indicating the degree of fluctuation of the knock intensity in a plurality of cycles. For example, the difference between the maximum value and the minimum value of the knock intensity, standard deviation, COV (covariance) ). In the present embodiment, the “cycle” means a series of processes of intake, compression, combustion / expansion, and exhaust.

(Calculation of combustion pressure)
The combustion pressure analysis unit 153 calculates the maximum combustion pressure Pmax, the indicated mean effective pressure Pmi, and their cycle fluctuation values based on the combustion pressure P detected by the knock sensor 3 (combustion pressure detector 28). Here, the maximum combustion pressure Pmax means the maximum value of the combustion pressure (in-cylinder pressure) during one cycle of the combustion chamber 2. The cycle fluctuation value of the maximum combustion pressure Pmax is an index indicating the degree of fluctuation of the maximum combustion pressure Pmax in a plurality of successive cycles. Specifically, the difference between the maximum value and the minimum value of the maximum combustion pressure Pmax. , Standard deviation, COV (covariance), and the like. The indicated mean effective pressure Pmi is a value obtained by dividing the work amount per cycle of each cylinder by the stroke volume. The cycle fluctuation value of the indicated mean effective pressure Pmi is an index indicating the degree of fluctuation of the indicated mean effective pressure Pmi in a plurality of consecutive cycles, and specifically, the maximum value and the minimum value of the indicated mean effective pressure Pmi. Difference, standard deviation, COV (covariance), and the like.

(Abnormal combustion detection)
The abnormal combustion determination unit 154 executes the detection methods (I), (II), and (III) described above alone or in combination with each other to prevent abnormal combustion caused by knocking, lubricating oil, and hot surface ignition. Detect abnormal combustion caused by it.

(I) Detection Method Based on Knock Strength Occurrence Frequency and Continuity The abnormal combustion determination unit 154 uses at least one of the occurrence frequency and continuity as an index for detecting abnormal combustion. Specifically, the abnormal combustion determination unit 154 records the number of cycles (occurrence frequency) at which the knock intensity is equal to or greater than a predetermined threshold (referred to as “reference threshold”) during a predetermined number of cycles, and the occurrence frequency thereof. Is greater than or equal to the first threshold, that is, when the occurrence frequency is high, it is determined that the abnormal combustion is caused by hot surface ignition. On the other hand, when the occurrence frequency is less than the first threshold and greater than or equal to the second threshold, that is, when the occurrence frequency is medium, it is determined that the knocking is normal. Further, when the occurrence frequency is less than the second threshold, that is, when the occurrence frequency is low, it is determined that the abnormal combustion is caused by the lubricating oil. Note that the first threshold value is larger than the second threshold value (first threshold value> second threshold value). This is because, as described above, abnormal combustion caused by lubricating oil is less frequent than normal knocking, and abnormal combustion caused by hot surface ignition is compared with normal knocking. Therefore, it uses the characteristic that the frequency of occurrence is high. The reference threshold value, the first threshold value, and the second threshold value are variables that can be arbitrarily variably set according to the operating state of the engine 1 or the like.

Further, when the knock intensity that is equal to or greater than the reference threshold value is continuously detected, the abnormal combustion determination unit 154 performs hot surface ignition when the number of consecutive times is equal to or greater than the third threshold value, that is, when continuity is high. It is determined that the combustion is abnormal combustion. On the other hand, when the number of consecutive times is less than the third threshold value and greater than or equal to the fourth threshold value, that is, when the continuity is medium, it is determined that the knocking is normal. Further, when the number of continuous times is less than the fourth threshold, that is, when the continuity is low, it is determined that the abnormal combustion is caused by the lubricating oil. The third threshold value is larger than the fourth threshold value (third threshold value> fourth threshold value). As described above, the abnormal combustion caused by the lubricating oil does not occur continuously in most cases, and the abnormal combustion caused by hot surface ignition occurs almost continuously. It is a thing. The third threshold value and the fourth threshold value are variables that can be variably set according to the operating state of the engine 1 or the like.

(II) Detection Method Based on Knock Intensity Cycle Variation The abnormal combustion determination unit 154 uses the knock strength cycle variation value as an index for detecting abnormal combustion. Specifically, the abnormal combustion determination unit 154 determines that abnormal combustion due to the lubricating oil has occurred when the cycle variation value of the knock intensity is equal to or greater than the fifth threshold value. As described above, this utilizes the characteristic that in the case of abnormal combustion caused by lubricating oil, the variation between combustion cycles is larger than that of normal knocking. At this time, the detection method (II) may be used alone, but the detection accuracy of the abnormal combustion can be further improved by combination with the detection method (I). The fifth threshold value is a variable that can be variably set according to the operating state of the engine 1 or the like.

(III) Detection Method Based on Combustion Pressure The abnormal combustion determination unit 154 uses the maximum combustion pressure Pmax, the cycle fluctuation of the maximum combustion pressure Pmax, and the cycle fluctuation value of the indicated mean effective pressure Pmi as an index for detecting abnormal combustion. Use one of the following. Specifically, the abnormal combustion determination unit 154 determines that the abnormal combustion is other than normal knocking when the maximum combustion pressure Pmax is higher than the cycle average value by a sixth threshold or more. Here, the cycle average value means an average value of the combustion maximum pressure Pmax in a plurality of cycles (for example, 100 times). Further, when the cycle variation value of the maximum combustion pressure Pmax is greater than or equal to a preset seventh threshold value, the abnormal combustion determination unit 154 determines that the abnormal combustion is other than normal knocking. Furthermore, when the cycle fluctuation value of the indicated mean effective pressure Pmi is equal to or greater than a preset eighth threshold value, the abnormal combustion determination unit 154 determines that the abnormal combustion is other than normal knocking. At this time, this detection method (III) may be used alone, but the detection accuracy of the abnormal combustion can be further improved by combination with the detection methods (I) and (II). Note that the sixth threshold value, the seventh threshold value, and the eighth threshold value are variables that can be variably set according to the operating state of the engine 1 or the like.

(Avoidance control)
When any abnormal combustion is detected, the abnormal combustion determination unit 154 transmits detection information related to the abnormal combustion to the combustion control unit 51 of the electronic control unit ECU. The combustion control unit 51 of the electronic control unit ECU executes avoidance control according to the type of abnormal combustion based on the detection information from the abnormal combustion determination unit 154, so that each part of the engine (air-fuel ratio control device 25, fuel supply device 26). The operation of the ignition device 27, etc.).

Next, an example of the abnormal combustion detection method executed by the abnormal combustion detection device 150 according to the second embodiment will be described. FIG. 9 is a flowchart showing an example of the abnormal combustion detection method.

First, the knock intensity calculation unit 152 calculates the knock intensity based on the detection information input from the knock sensor 3 (combustion pressure detector 28) (step S201).

Subsequently, the abnormal combustion determination unit 154 determines whether or not the knock intensity is greater than or equal to a reference threshold value (step S202).

When the knock magnitude is equal to or higher than the reference threshold value (step S202: YES), the abnormal combustion determination unit 154 causes the occurrence frequency of knock intensity equal to or higher than the reference value in the past N cycles, or the knock intensity is equal to or higher than the reference threshold value. The number of continuous times is calculated (step S203). It is also possible to calculate both the occurrence frequency of knock strength and the number of consecutive times.

On the other hand, the knock strength calculation unit 152 also calculates the cycle variation value of the knock strength (step S204).

Subsequently, the combustion pressure analysis unit 153 calculates at least one of the maximum combustion pressure Pmax in the cylinder, the cycle variation value of the maximum combustion pressure Pmax, and the cycle variation value of the indicated mean effective pressure Pmi.

Then, the abnormal combustion determination unit 154 obtains (I) knock intensity occurrence frequency, continuity, (II) knock fluctuation cycle fluctuation value, (III) maximum combustion pressure Pmax, obtained in steps S203 to S205 above. Comparing the cycle fluctuation value of the maximum combustion pressure Pmax and the cycle fluctuation value of the indicated mean effective pressure Pmi with the first to eighth threshold values, and comprehensively judging these judgment items, normal knocking and lubrication It is determined which of abnormal combustion caused by oil and abnormal combustion caused by hot surface ignition has occurred. Here, there are various methods for determining abnormal combustion. For example, if any one of the detection items satisfies the determination criteria (I) to (III), abnormal combustion is detected, or all detection items are detected. Then, when the determination criteria (I) to (III) are satisfied, abnormal combustion may be detected, or the weight may be changed for each detection item.

Subsequently, the combustion control unit 51 of the electronic control unit ECU executes avoidance control according to the type of abnormal combustion detected in step S206 (step S207). For example, as avoidance control for knocking, as control for retarding the ignition timing, as avoidance control for abnormal combustion due to hot surface ignition, as control for avoiding abnormal combustion due to lubricating oil, such as control to immediately stop the engine 1 Control for reducing the output of the engine 1 is executed.

If the knock strength is not greater than or equal to the reference threshold (step S202: NO), steps S203 and S204 are skipped and the process proceeds to step S205. This is for improving the reliability of detection accuracy by executing abnormal combustion detection based on the maximum combustion pressure Pmax or the like even when the knock magnitude is not equal to or higher than the reference threshold value.

As described above, according to the present embodiment (the first embodiment and the second embodiment), the frequency at which the knock intensity is equal to or higher than the reference threshold, and the knock intensity is continuously equal to or higher than the reference threshold over a plurality of combustion cycles. Based on at least one of the continuity, the abnormal combustion occurring in the combustion chamber 2 of the engine 1 is accurately determined as normal knocking, abnormal combustion due to lubricating oil, abnormal combustion due to hot surface ignition, or the like. Therefore, it is possible to perform correct avoidance control according to the type of abnormal combustion and to quickly return the engine 1 to an appropriate combustion state. In general, a knock sensor (physical quantity detection means) such as an acceleration detector is mounted on an engine, so that the knock intensity can be used as an index for detecting other abnormal combustion other than normal knocking. The abnormal combustion detection device 50 can be realized at low cost.

As an example of abnormal combustion other than normal knocking, abnormal combustion caused by lubricating oil and abnormal combustion caused by hot surface ignition have been exemplified so far. A major feature is that it is possible to distinguish abnormal combustion from normal knocking.

Further, in this embodiment, when knock intensity fluctuates more than a certain value in a plurality of combustion cycles, it is configured so that abnormal combustion other than normal knocking can be detected. Based on this, it becomes possible to further improve the detection accuracy of various abnormal combustion.

Furthermore, in this embodiment, when the maximum combustion pressure Pmax in the combustion chamber 2 rises above a certain level or when the maximum combustion pressure Pmax fluctuates above a certain level in a plurality of combustion cycles, other abnormal combustion other than normal knocking Therefore, it is possible to reliably detect abnormal combustion that induces a rapid increase in combustion pressure based on multi-point ignition in the combustion chamber 2 or the like.

It should be noted that the present invention is not limited to the above-described embodiment, and can be improved as appropriate without departing from the gist of the present invention. For example, the knocking intensity may be calculated using sound or the ion state in the combustion gas as another physical quantity having a correlation with the combustion state of the combustion chamber.

Further, the abnormal combustion detection device 50 (150) may be integrated in the electronic control unit ECU, or may be configured as a separate device independent of the electronic control unit ECU.

1 Engine 2 Combustion chamber 3 Knock sensor (physical quantity detection means)
12 Acceleration detector (physical quantity detection means)
28 Combustion pressure detector (physical quantity detection means)
30 Piston 40 Crankshaft 41 Crank Angle Detector 50 Abnormal Combustion Detection Device (First Embodiment)
52 Knock strength calculation unit (knock strength calculation means)
54 Abnormal combustion determination unit (abnormal combustion determination means)
150 Abnormal Combustion Detection Device (Second Embodiment)
152 Knock strength calculation unit (knock strength calculation means)
153 Combustion pressure analysis unit 154 Abnormal combustion determination unit (abnormal combustion determination means)
ECU electronic control unit

Claims

In an engine that generates engine power by burning a mixture of air and fuel supplied into a combustion chamber,
Physical quantity detection means for detecting a physical quantity correlated with the combustion state of the combustion chamber;
Knock intensity calculation means for calculating the knock intensity of each combustion cycle based on the physical quantity detected by the physical quantity detection means;
Based on the frequency at which the knock intensity calculated by the knock intensity calculating means is greater than or equal to a predetermined threshold and at least one of the continuity where the knock intensity is continuously greater than or equal to the predetermined threshold over a plurality of combustion cycles, An abnormal combustion detection device for an engine, comprising: abnormal combustion determination means for detecting abnormal combustion other than normal knocking that occurs under normal ignition in the combustion chamber.
2. The abnormal combustion detection of the engine according to claim 1, wherein the abnormal combustion determination means detects the abnormal combustion generated in the combustion chamber when the knock intensity fluctuates more than a predetermined value in a plurality of combustion cycles. apparatus.
The physical quantity detection means has combustion pressure detection means for detecting a combustion pressure in the combustion chamber,
3. The engine abnormality according to claim 1, wherein the abnormal combustion determination unit detects the abnormal combustion generated in the combustion chamber based on a maximum combustion pressure detected by the combustion pressure detection unit. Combustion detection device.
In an engine that generates engine power by burning a mixture of air and fuel supplied into a combustion chamber,
A physical quantity detection step for detecting a physical quantity correlated with the combustion state of the combustion chamber;
A knock intensity calculating step for calculating a knock intensity of each combustion cycle based on the physical quantity detected in the physical quantity detecting step;
Based on the frequency at which the knock intensity calculated in the knock intensity calculating step is equal to or higher than a predetermined threshold and at least one of the continuity where the knock intensity is continuously higher than the predetermined threshold over a plurality of combustion cycles, An abnormal combustion determination method for an engine, comprising: an abnormal combustion determination step for detecting abnormal combustion other than normal knocking that occurs under normal ignition in the combustion chamber.
5. The abnormal combustion detection method for an engine according to claim 4, wherein the abnormal combustion that occurs in the combustion chamber is detected when the knock intensity fluctuates more than a certain value in a plurality of combustion cycles.
A combustion pressure detecting step for detecting a combustion pressure in the combustion chamber;
6. The abnormal combustion detection device for an engine according to claim 4, wherein the abnormal combustion generated in the combustion chamber is detected based on the maximum combustion pressure detected in the combustion pressure detection step.