JP7211244B2 - CONTROL METHOD AND CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE - Google Patents

Description

The present invention relates to a control method and control apparatus for an internal combustion engine that burns air-fuel mixture in cylinders.

It is preferable that the sound generated by the internal combustion engine mounted on the vehicle is small because the passengers of the vehicle feel that it is noise. In particular, in a diesel engine or a partial compression ignition type engine that performs SPCCI combustion, which will be described later, the air-fuel mixture is self-ignited, so there is a risk that the peak pressure in the cylinder will be high and noise will be increased. A technology related to such noise is disclosed in Patent Document 1, for example.

The fuel injection control device disclosed in Patent Document 1 is a device for executing fuel injection including first injection and second injection by a fuel injection valve when the load is in a high load range, and the combustion state is a predetermined fuel injection. The injection state of at least one of the first injection and the second injection is controlled so as to achieve an allowable state, and the increase rate of the pressure in the combustion chamber, which rises due to the execution of the first injection, reaches a predetermined allowable maximum. The injection rate of the first injection is controlled so as to increase the rate. The allowable maximum rate of increase is set in consideration of vibration, noise, and the like caused by combustion of fuel (paragraph [0032] of Patent Document 1). Alternatively, the injection rate of the first injection is adjusted so that the combustion noise does not exceed the allowable maximum volume (paragraph [0049] of Patent Document 1).

JP 2017-96245 A

By the way, in order to keep the noise (combustion noise) generated in the internal combustion engine low, it is good to keep the pressure in the cylinder low, but if the pressure in the cylinder is kept low, thermal efficiency deteriorates. Therefore, it is desirable to appropriately set the upper limit of combustion noise, that is, the upper limit of the in-cylinder pressure of the cylinder.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an internal combustion engine control method and control device capable of appropriately setting the upper limit value of the in-cylinder pressure of a cylinder.

As a result of various studies, the inventors of the present invention have found that the above object can be achieved by the present invention described below. That is, a method of controlling an internal combustion engine according to one aspect of the present invention is a method of combusting an air-fuel mixture in a cylinder, comprising a cylinder pressure measuring step of measuring the cylinder pressure of the cylinder; The first standard deviation when it is assumed that the histogram of the in-cylinder pressure measured in the in-cylinder pressure measurement step in the combustion cycle is normally distributed with the distribution of in-cylinder pressure lower than the most frequent in-cylinder pressure with reference to the most frequent in-cylinder pressure. , a standard deviation processing step of obtaining a second standard deviation when the histogram is assumed to be normally distributed with a distribution of in-cylinder pressure higher than the most frequent in-cylinder pressure, and a standard deviation processing step of obtaining the first and A difference processing step of obtaining a difference of the second standard deviation, and when the absolute value of the difference obtained in the difference processing step is a predetermined value or more, the histogram is determined as a non-normal distribution, and based on the second standard deviation an upper limit value processing step of obtaining an upper limit value of the in-cylinder pressure of the cylinder at the predetermined operating point; and controlling the internal combustion engine so that the upper limit value obtained in the upper limit value processing step or less is reached at the predetermined operating point. and a combustion control step. A control device for an internal combustion engine according to one aspect of the present invention is a device for combusting an air-fuel mixture in a cylinder, comprising a cylinder pressure measurement unit for measuring the cylinder pressure of the cylinder, and one combustion cycle at a predetermined operating point. a first standard deviation when it is assumed that the histogram relating to the in-cylinder pressure measured in the in-cylinder pressure measuring step is normally distributed with a distribution of in-cylinder pressure lower than the most frequent in-cylinder pressure with the most frequent in-cylinder pressure as a reference; and a standard deviation processing unit for obtaining a second standard deviation when the histogram is assumed to be normally distributed with a distribution of in-cylinder pressure higher than the most frequent in-cylinder pressure; A difference processing unit that obtains a difference in standard deviations, and if the absolute value of the difference obtained by the difference processing unit is equal to or greater than a predetermined value, the histogram is determined as a non-normal distribution, and based on the second standard deviation, the an upper limit processing unit that determines an upper limit value of the in-cylinder pressure of the cylinder at a predetermined operating point; and a control unit. Preferably, in these above methods and apparatus, the predetermined operating point is determined according to the number of revolutions (rotational speed) and load (required torque) on the output shaft of the internal combustion engine.

Combustion noise varies in individual combustion cycles even at the same operating point, so a method of setting the upper limit of the in-cylinder pressure of the cylinder based on the standard deviation of a histogram relating to the in-cylinder pressure of the cylinder is conceivable. When the standard deviation is obtained considering that the histogram is a normal distribution, in reality (actually) the histogram may be a non-normal distribution that cannot be regarded as a normal distribution. In this case, the standard deviation is not properly obtained, and the upper limit set based on the standard deviation may not be set appropriately. The control method and apparatus for an internal combustion engine described above provide a first standard deviation when the histogram is assumed to have a normal distribution on the lower pressure side than the most frequent in-cylinder pressure with reference to the most frequent in-cylinder pressure, and the histogram. Finding the difference from the second standard deviation when it is assumed that the distribution on the high pressure side of the most frequent in-cylinder pressure is normal distribution, and determining whether the histogram is a normal distribution or a non-normal distribution based on the obtained difference , the upper limit value of the in-cylinder pressure of the cylinder is obtained based on the determination result. Therefore, the internal combustion engine control method and apparatus can appropriately set the upper limit value of the in-cylinder pressure of the cylinder even when the histogram has a non-normal distribution. If the second standard deviation is greater than the first standard deviation, by setting the upper limit of the in-cylinder pressure based on the second standard deviation, the upper limit of the in-cylinder pressure of the cylinder is determined based on the first standard deviation. The permissible value for suppressing combustion noise by avoiding the generation of combustion noise due to knocking can be appropriately set as compared with the case of setting . Further, when the second standard deviation is smaller than the first standard deviation, the difference between the upper limit value of the in-cylinder pressure of the cylinder set based on the second standard deviation and the upper limit value set based on the first standard deviation It is expected that the thermal efficiency will be improved according to the Therefore, the control method and apparatus for an internal combustion engine can appropriately set the upper limit value of the in-cylinder pressure of the cylinder, so that the thermal efficiency can be improved while the combustion noise is kept within the allowable value.

In another aspect, in the control method for an internal combustion engine described above, the internal combustion engine performs SI combustion of a portion of the air-fuel mixture in the cylinder by pyrotechnic ignition, and then ignites the remaining air-fuel mixture in the cylinder by self-ignition. A vehicle-mounted partial-compression-ignition engine in which CI-combustion partial-combustion-ignition combustion is performed in at least a part of an operating range, and the combustion control step is performed in the upper-limit value processing step at the predetermined operating point. A target mass combustion timing, which is a timing at which a target mass ratio of fuel out of the fuel supplied to the cylinder during one combustion cycle is burned, is set so as to be equal to or less than the upper limit value, and the set target mass combustion timing is set. Control the ignition timing of the firework ignition based on. In another aspect, in the above-described control device for an internal combustion engine, the internal combustion engine performs SI combustion of part of the air-fuel mixture in the cylinder by pyrotechnic ignition, and then ignites the remaining air-fuel mixture in the cylinder by self-ignition. A vehicle-mounted partial-compression-ignition engine in which CI-combustion partial-combustion-ignition combustion is performed in at least a part of an operating range, wherein the combustion control unit determines, at the predetermined operating point, the upper-limit value processing unit A target mass combustion timing, which is a timing at which a target mass ratio of fuel out of the fuel supplied to the cylinder during one combustion cycle is burned, is set so as to be equal to or less than the upper limit value, and the set target mass combustion timing is set. Control the ignition timing of the firework ignition based on.

According to this, it is possible to provide a control method and a control device for a partial compression ignition engine that can appropriately set the upper limit value of the in-cylinder pressure of the cylinder.

According to another aspect of the above-described internal combustion engine control method, the upper limit value processing step obtains the upper limit value of the in-cylinder pressure of the cylinder based on three times the second standard deviation. In another aspect, in the above-described control device for an internal combustion engine, the upper limit value processing section obtains the upper limit value of the in-cylinder pressure of the cylinder based on three times the second standard deviation.

Three times the standard deviation σ (3σ) can typically cover 99.73% of the distribution. Therefore, the control method and apparatus for an internal combustion engine obtains the upper limit value of the in-cylinder pressure of the cylinder based on three times the corrected first standard deviation. In-cylinder pressure can be kept below the upper limit. That is, the internal combustion engine control method and apparatus described above can keep combustion noise within an allowable range.

The control method and control device for an internal combustion engine according to the present invention can appropriately set the upper limit value of the in-cylinder pressure of the cylinder.

1 is a system diagram schematically showing the overall configuration of a compression ignition engine according to an embodiment; FIG. It is a figure for demonstrating an engine main body and a piston. FIG. 2 is a schematic plan view showing the structure of a cylinder and an intake/exhaust system in the vicinity thereof; 3 is a block diagram showing a control system of the engine; FIG. FIG. 2 is a map diagram in which engine operating regions are classified according to differences in combustion mode; 4 is a graph showing a waveform of heat release rate during SPCCI combustion (partial compression ignition combustion). 4 is a flowchart showing details of control executed during SPCCI combustion; FIG. 8 is a subroutine showing the details of control of processing S4 shown in FIG. 7; FIG. This map is used when determining a reference value for combustion noise. 4 is a map that defines the relationship between the CI combustion start timing (θci) and the reference value. As an example, it is a diagram showing a histogram of in-cylinder pressure at one predetermined operating point. 4 is a graph of the function F(a); As an example, it is a figure which shows each histogram of the in-cylinder pressure in knocking and a misfire. 4 is a flowchart showing processing for obtaining standard deviation; It is a figure for demonstrating the effect of embodiment as an example.

One or more embodiments of the invention are described below with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. It should be noted that the configurations denoted by the same reference numerals in each figure indicate the same configurations, and the description thereof will be omitted as appropriate. In the present specification, reference numerals with suffixes omitted are used when referring to generically, and reference numerals with suffixes are used when referring to individual configurations.

(1) Overall Configuration of Engine FIG. 1 is a system diagram schematically showing the overall configuration of a compression ignition engine according to an embodiment. FIG. 2 is a diagram for explaining an engine body and a piston. The upper part of FIG. 2 shows a cross-sectional view of the engine body, and the lower part of FIG. 2 shows a plan view of the piston. FIG. 3 is a schematic plan view showing the structure of a cylinder and an intake/exhaust system in the vicinity thereof.

The compression ignition engine in the embodiment is, for example, a 4-cycle gasoline direct injection engine mounted on a vehicle as a power source for running. This compression ignition engine includes an engine main body 1, an intake passage 30 through which intake air introduced into the engine main body 1 flows, an exhaust passage 40 through which exhaust gas discharged from the engine main body 1 flows, and an exhaust passage 40. and an EGR device 50 that recirculates part of the exhaust gas to the intake passage 30 .

The engine body 1 includes a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to block the cylinder 2 from above, and a reciprocatingly slidable insertion into the cylinder 2. , and a piston 5. The engine body 1 is typically of a multi-cylinder type having a plurality of (for example, four) cylinders, but for the sake of simplification, only one cylinder 2 will be described here.

A combustion chamber 6 is defined above the piston 5 . A fuel containing gasoline as a main component is supplied to the combustion chamber 6 by injection from an injector 15, which will be described later. The supplied fuel is combusted while being mixed with air in the combustion chamber 6, and the expansion force caused by the combustion pushes down the piston 5 to reciprocate in the vertical direction. Note that the fuel injected into the combustion chamber 6 may contain gasoline as a main component, and may contain, for example, a secondary component such as bioethanol in addition to gasoline. A crankshaft 7 that is an output shaft of the engine body 1 is arranged below the piston 5 . The crankshaft 7 is connected to the piston 5 via a connecting rod 8 and is driven to rotate about the central axis according to the reciprocating motion (vertical motion) of the piston 5 .

The geometric compression ratio of cylinder 2 (the ratio of the volume of combustion chamber 6 when piston 5 is at top dead center to the volume of the combustion chamber when piston 5 is at bottom dead center) is determined by SPCCI combustion ( A suitable value for partial compression ignition combustion (Spark Controlled Compression Ignition combustion) is set to 13 or more and 30 or less. Preferably, the geometric compression ratio of cylinder 2 is set to 14 or more and 17 or less in the case of regular specifications using gasoline fuel with an octane number of about 91, and in the case of high-octane specifications using gasoline fuel with an octane number of about 96. is set to 15 or more and 18 or less.

In the cylinder block 3, a crank angle sensor SN1 for detecting the rotation angle (crank angle) of the crankshaft 7 and the rotation speed (engine speed) of the crankshaft 7, and a cooling device that flows through the cylinder block 3 and the cylinder head 4 are provided. A water temperature sensor SN2 is provided to detect the temperature of water (engine water temperature).

The cylinder head 4 is provided with an intake port 9 and an exhaust port 10 that open to the combustion chamber 6 , an intake valve 11 that opens and closes the intake port 9 , and an exhaust valve 12 that opens and closes the exhaust port 10 . As shown in FIG. 2, the valve type of the engine in this embodiment is a four-valve type consisting of two intake valves and two exhaust valves. More specifically, the intake port 9 includes a first intake port 9A and a second intake port 9B, and the exhaust port 10 includes a first exhaust port 10A and a second exhaust port 10B. A total of two intake valves 11 are provided to open and close the first intake port 9A and the second intake port 9B, respectively, and a total of two exhaust valves 12 are provided to respectively open and close the first exhaust port 10A and the second exhaust port 10B. Have two.

As shown in FIG. 3, a swirl valve 18 that can be opened and closed is arranged in the second intake port 9B. The swirl valve 18 is arranged only in the second intake port 9B and is not arranged in the first intake port 9A. When the swirl valve 18 is driven in the closing direction, the ratio of the intake air flowing into the combustion chamber 6 from the first intake port 9A, in which the swirl valve 18 is not arranged, increases, so that the cylinder swirls around the cylinder axis. swirl flow can be strengthened. Conversely, when the swirl valve 18 is driven in the opening direction, the swirl flow can be weakened. The intake port 9 of this embodiment is a tumble port capable of forming a tumble flow (longitudinal vortex). Therefore, the swirl flow formed when the swirl valve 18 is closed becomes an oblique swirl flow mixed with the tumble flow.

The intake valve 11 and the exhaust valve 12 are driven to open and close in conjunction with the rotation of the crankshaft 7 by valve mechanisms 13 and 14 including a pair of camshafts disposed in the cylinder head 4 .

The valve mechanism 13 for the intake valve 11 incorporates an intake VVT 13 a capable of changing at least the opening timing of the intake valve 11 . Similarly, the valve mechanism 14 for the exhaust valve 12 incorporates an exhaust VVT 14a capable of changing at least the closing timing of the exhaust valve 12 . By controlling these intake VVT 13a and exhaust VVT 14a, in this embodiment, the valve overlap period during which both the intake valve 11 and the exhaust valve 12 are opened across the exhaust top dead center can be adjusted. By adjusting the valve overlap period, the amount of burned gas (internal EGR gas) remaining in the combustion chamber 6 can be adjusted. The intake VVT 13a (exhaust VVT 14a) may be a variable mechanism of a type that changes only the opening timing (closing timing) while fixing the closing timing (opening timing) of the intake valve 11 (exhaust valve 12). 11 (exhaust valve 12) may be a phase-type variable mechanism that simultaneously changes the opening timing and the closing timing.

In the cylinder head 4, an injector 15 for injecting fuel (mainly gasoline) into the combustion chamber 6 and a mixture of the fuel injected from the injector 15 into the combustion chamber 6 and the air introduced into the combustion chamber 6 is ignited. A spark plug 16 is provided. The cylinder head 4 is further provided with an in-cylinder pressure sensor SN3 that detects the pressure in the combustion chamber 6 (hereinafter also referred to as in-cylinder pressure).

As shown in FIG. 2 , a cavity 20 is formed in the crown surface of the piston 5 by recessing a relatively wide area including the central portion thereof toward the opposite side (downward) of the cylinder head 4 . At the center of the cavity 20, a substantially conical raised portion 20a that protrudes relatively upward is formed. In other words, the cavity 20 is a doughnut-shaped concave portion formed to surround the raised portion 20a. A region of the crown surface of the piston 5 that is radially outward of the cavity 20 forms a squish portion 21 that is an annular flat surface.

The injector 15 is a multiple injection hole type injector having a plurality of injection holes at its tip, and can radially inject fuel from the plurality of injection holes (F in FIG. 2 indicates the fuel injected from each injection hole). ). The injector 15 is arranged such that its tip faces the center of the crown surface of the piston 5 (the raised portion 20a).

The spark plug 16 is arranged at a position slightly shifted toward the intake side with respect to the injector 15 . A tip portion (electrode portion) of the ignition plug 16 is set at a position overlapping the cavity 20 in plan view.

As shown in FIG. 1 , the intake passage 30 is formed of a predetermined member and connected to one side surface of the cylinder head 4 so as to communicate with the intake port 9 . Air (fresh air) taken from the upstream end of the intake passage 30 is introduced into the combustion chamber 6 through the intake passage 30 and the intake port 9 . The intake passage 30 includes, in order from the upstream side thereof, an air cleaner 31 that removes foreign matter from the intake air, a throttle valve 32 that can be opened and closed to adjust the flow rate of the intake air, a supercharger 33 that compresses and delivers the intake air, and a supercharger 33 . An intercooler 35 and a surge tank 36 are provided to cool the intake air compressed by the air. The intake passage 30 is provided with an airflow sensor SN4 that detects the flow rate of intake air, an intake air temperature sensor SN5 that detects the temperature of the intake air, and an intake pressure sensor SN6 that detects the pressure of the intake air. More specifically, the airflow sensor SN4 is arranged in a portion of the intake passage 30 between the air cleaner 31 and the throttle valve 32, and detects the flow rate of intake air passing through that portion. An intake air temperature sensor SN5 and an intake air pressure sensor SN6 are provided in the surge tank 36 and detect the temperature and pressure of the intake air in the surge tank 36 .

The supercharger 33 is a mechanical supercharger (supercharger) mechanically linked to the engine body 1 . Although the specific type of the supercharger 33 is not particularly limited, any one of known superchargers such as Lysholm type, Roots type and centrifugal type may be used as the supercharger 33 . Between the turbocharger 33 and the engine body 1, an electromagnetic clutch 34 is interposed which can be electrically switched between engagement and disengagement. When the electromagnetic clutch 34 is engaged, driving force is transmitted from the engine body 1 to the supercharger 33, and supercharging by the supercharger 33 is performed. On the other hand, when the electromagnetic clutch 34 is released, the transmission of the driving force is interrupted and the supercharging by the supercharger 33 is stopped.

A bypass passage 38 for bypassing the supercharger 33 is provided in the intake passage 30 . The bypass passage 38 is made of a predetermined member, and connects the surge tank 36 and an EGR passage 51 (described later) to each other. A bypass valve 39 that can be opened and closed is provided in the bypass passage 38 .

The exhaust passage 40 is formed of a predetermined member and connected to the other side surface of the cylinder head 4 so as to communicate with the exhaust port 10 . Burned gas (exhaust gas) generated in the combustion chamber 6 is discharged to the outside through the exhaust port 10 and the exhaust passage 40 . A catalytic converter 41 is arranged in the exhaust passage 40 . The catalytic converter 41 includes a three-way catalyst 41a for purifying harmful components (HC, CO, NOx) contained in the exhaust gas flowing through the exhaust passage 40, and particulate matter (PM) contained in the exhaust gas. A GPF (gasoline particulate filter) 41b for collecting is incorporated. Note that another catalytic converter containing an appropriate catalyst such as a three-way catalyst or a NOx catalyst may be added downstream of the catalytic converter 41 .

The EGR device 50 includes an EGR passage 51 connecting the exhaust passage 40 and the intake passage 30 , and an EGR cooler 52 and an EGR valve 53 provided in the EGR passage 51 . The EGR passage 51 is made of a predetermined member and connects a portion of the exhaust passage 40 downstream of the catalytic converter 41 and a portion of the intake passage 30 between the throttle valve 32 and the supercharger 33 . The EGR cooler 52 cools the exhaust gas (external EGR gas) recirculated from the exhaust passage 40 to the intake passage 30 through the EGR passage 51 by heat exchange. The EGR valve 53 is provided in the EGR passage 51 downstream (closer to the intake passage 30 ) than the EGR cooler 52 so as to be openable and closable, and adjusts the flow rate of the exhaust gas flowing through the EGR passage 51 . The EGR passage 51 is provided with a differential pressure sensor SN7 for detecting the difference between the pressure on the upstream side and the pressure on the downstream side of the EGR valve 53 .

(2) Control System FIG. 4 is a block diagram showing the control system of the engine. FIG. 5 is a map diagram in which the operating regions of the engine are divided according to the difference in combustion mode. The horizontal axis in FIG. 5 is the rotational speed, and the vertical axis is the load (required torque). FIG. 6 is a graph showing the waveform of the heat release rate during SPCCI combustion. The horizontal axis in FIG. 6 is the crank angle, and the vertical axis is the heat release rate.

The control processing unit 100 shown in FIG. 4 is a microprocessor for comprehensively controlling the engine, and includes a well-known CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory) and their peripheral circuits. etc.

Detection signals from various sensors are input to the control processing unit 100 . For example, the control processing unit 100 is electrically connected to a crank angle sensor SN1, a water temperature sensor SN2, an in-cylinder pressure sensor SN3, an air flow sensor SN4, an intake air temperature sensor SN5, an intake pressure sensor SN6 and a differential pressure sensor SN7. (crank angle, engine rotation speed, engine water temperature, cylinder pressure, intake air flow rate, intake air temperature, intake pressure, differential pressure across EGR valve 53, etc.) detected by the control processor 100 are sequentially input.

In this embodiment, the vehicle is provided with an accelerator sensor SN8 for detecting the opening of an accelerator pedal operated by the driver who drives the vehicle, and a vehicle speed sensor SN9 for detecting the running speed of the vehicle (hereinafter referred to as vehicle speed). and are provided. The accelerator sensor SN8 and the vehicle speed sensor SN9 are also electrically connected to the control processing unit 100, and detection signals from the accelerator sensor SN8 and the vehicle speed sensor SN9 are also input to the control processing unit 100 sequentially.

The control processing unit 100 controls each part of the engine according to the function of each part while executing various determination processes, arithmetic processes, etc. according to the operating range of the engine based on the input signals from the above sensors. That is, the control processing unit 100 is electrically connected to the intake VVT 13a, the exhaust VVT 14a, the injector 15, the spark plug 16, the swirl valve 18, the throttle valve 32, the electromagnetic clutch 34, the bypass valve 39, the EGR valve 53, etc. Control signals are output to each of these devices based on the results of processing and arithmetic processing.

As shown in FIG. 5, the operating range of the engine is roughly divided into four first to fourth operating ranges A1 to A4 depending on the combustion mode depending on the rotational speed and load (required torque). The first operating region A1 is a low-speed/low-load region in which both the rotational speed and load are relatively low. At each operating point belonging to the first operating region A1, the control processing unit 100 controls the engine so that the air-fuel mixture is stoichiometrically SPCCI-burned in a state in which supercharging by the supercharger 33 is stopped (state of natural intake). control each part of The second operating region A2 is a low-speed, high-load region in which the rotational speed is relatively low and the load is relatively high. At each operating point belonging to the second operating region A2, the control processing unit 100 controls each part of the engine so that the air-fuel mixture is SPCCI-burned while being supercharged by the supercharger 33 . The fourth operating area A4 is a high speed area in which the rotational speed is relatively high. At each operating point belonging to the fourth operating region A4, the control processing unit 100 controls each part of the engine so that the mixture supercharged by the supercharger 33 undergoes typical SI combustion. The third operating area A3 is a medium speed/medium load area in which both the rotation speed and the load are relatively medium, which is included in the first operating area A1. At each operating point belonging to the third operating region A3, the control processing unit 100 controls each part of the engine so that the air-fuel mixture is supercharged by the supercharger 33 and undergoes lean-burn SPCCI combustion.

The SPCCI combustion is a combustion mode in which SI combustion and CI combustion are mixed. More specifically, first, SI combustion ignites the air-fuel mixture by spark ignition using the spark plug 16, and forcibly burns the air-fuel mixture by flame propagation that expands the combustion area from the ignition point to the surroundings. is. CI combustion is a mode in which an air-fuel mixture is combusted by self-ignition under an environment of high temperature and high pressure due to compression of the piston 5 . In SPCCI combustion, which is a mixture of SI combustion and CI combustion, part of the air-fuel mixture in the combustion chamber 6 is SI-burned by spark ignition performed in an environment just before the air-fuel mixture self-ignites, and after the SI combustion In this combustion mode, the remaining air-fuel mixture in the combustion chamber 6 is self-ignited for CI combustion (due to the further increase in temperature and pressure associated with SI combustion).

SPCCI combustion has the property that heat release during CI combustion is steeper than heat release during SI combustion. For example, in the waveform of the heat release rate due to SPCCI combustion, as shown in FIG. 6, the rising slope at the beginning of combustion corresponding to SI combustion is smaller than the rising slope corresponding to subsequent CI combustion. The waveform of the heat release rate during SPCCI combustion consists of a first heat release rate portion formed by SI combustion with a relatively small rising slope and a second heat release rate portion formed by CI combustion with a relatively large rising slope. and a generator in succession in this order. Corresponding to such a tendency of the heat release rate, in SPCCI combustion, the pressure rise rate (dp/dθ) in the combustion chamber 6 occurring during SI combustion is smaller than that during CI combustion. When the temperature and pressure in the combustion chamber 6 increase due to SI combustion, the unburned air-fuel mixture self-ignites and CI combustion starts. At the timing of this self-ignition (that is, the timing at which CI combustion starts), the gradient of the heat release rate waveform changes from small to large. Therefore, the waveform of the heat release rate in SPCCI combustion has an inflection point (X in FIG. 6) that appears at the timing when CI combustion starts.

After the start of CI combustion, SI combustion and CI combustion are performed in parallel. In CI combustion, the combustion speed of the air-fuel mixture is faster than in SI combustion, so the heat release rate is relatively large. Here, since CI combustion is performed after compression top dead center, the slope of the heat release rate waveform does not become excessive. That is, after the compression top dead center, the piston 5 descends and the motoring pressure drops, which suppresses the rise in the heat release rate, so that dp/dθ during CI combustion does not become excessive. In this way, in SPCCI combustion, CI combustion is performed after SI combustion. ), combustion noise can be suppressed.

SPCCI combustion also ends with the end of CI combustion. Since CI combustion has a faster combustion speed than SI combustion, SPCCI combustion can advance the end of combustion compared to simple SI combustion (when all fuel is SI-burned). In other words, in SPCCI combustion, the end of combustion can be brought closer to compression top dead center in the expansion stroke. As a result, SPCCI combustion can improve fuel efficiency compared to simple SI combustion.

In order to execute such SPCCI combustion, as an example, in the second operating region A2, more specifically, the control processing section 100 controls each section of the engine as follows. In the explanation below, the terms that specify the timing of fuel injection and spark ignition include the terms "early", "middle", and "late" of the ~ stroke, and the terms "early" and "latter" of the ~ stroke. Appropriately used. These are defined as follows. When an arbitrary stroke such as an intake stroke or a compression stroke is divided into three equal periods, each period is defined as "early period", "middle period", and "late period" in order from the front. For this reason, for example, (i) early stage, (ii) middle stage, and (iii) late stage of the compression stroke are respectively (i) 180 to 120° CA before top dead center of compression (BTDC) and (ii) 120 to 60° CA BTDC. , (iii) ranges from BTDC60 to 0°CA. Similarly, when an arbitrary stroke such as an intake stroke or a compression stroke is divided into two equal periods, each period is defined as "first half" and "second half" in order from the front. Therefore, for example, (iv) the first half and (v) the second half of the intake stroke are in the ranges of (iv) BTDC 360 to 270°CA and (v) BTDC 270 to 180°CA, respectively.

In the second operating region A2, the spark plug 16 performs spark ignition once during the period from the latter half of the compression stroke to the beginning of the expansion stroke. This spark ignition initiates SPCCI combustion, a part of the mixture in the combustion chamber 6 burns due to flame propagation (SI combustion), and the rest of the mixture burns due to self-ignition (CI combustion).

The injector 15 performs at least one fuel injection during the intake stroke. For example, the injector 15 performs one fuel injection during the intake stroke to supply the entire amount of fuel to be injected during one cycle. Note that the fuel may be injected twice during the intake stroke.

The opening of the throttle valve 32 is such that the amount of air corresponding to the theoretical air-fuel ratio is introduced into the combustion chamber 6 through the intake passage 30, that is, the weight ratio of the air (fresh air) in the combustion chamber 6 to the fuel. The opening degree is set so that the air-fuel ratio (A/F), which is equal to , substantially coincides with the theoretical air-fuel ratio (14.7). On the other hand, in the second operating region A2, the EGR valve 53 is opened to introduce external EGR gas into the combustion chamber 6, as will be described later. Therefore, in the second operating region A2, the gas air-fuel ratio (G/F), which is the weight ratio of the total gas in the combustion chamber 6 and the fuel, becomes larger than the stoichiometric air-fuel ratio (14.7). Thus, in the present embodiment, the gas air-fuel ratio (G/F) is greater than the stoichiometric air-fuel ratio and the air-fuel ratio (A/F) substantially matches the stoichiometric air-fuel ratio during operation in the second operating region A2. Control is executed to cause the air-fuel mixture to undergo SPCCI combustion while forming an environment (hereinafter referred to as a G/F lean environment).

The supercharger 33 is turned on. When the supercharger 33 is turned on and the intake air is supercharged, the degree of opening of the bypass valve 39 is controlled so that the pressure in the surge tank 36 (supercharging pressure) matches the target pressure.

The intake VVT 13a and the exhaust VVT 14a drive the intake valve 11 and the exhaust valve 12 at timing such that the internal EGR is substantially stopped.

The EGR valve 53 is opened to an appropriate opening so that an amount of external EGR gas suitable for SPCCI combustion in the second operating region A2 is introduced into the combustion chamber 6 . At this time, the opening of the EGR valve 53 is adjusted so as to achieve an in-cylinder temperature suitable for obtaining a desired SPCCI combustion waveform (target SI rate and target θci, which will be described later).

The opening of the swirl valve 18 is set such that more air than the amount of air corresponding to the stoichiometric air-fuel ratio is introduced into the combustion chamber 6 through the intake passage 30 . Alternatively, the opening of the swirl valve 18 is set to a predetermined intermediate opening larger than this.

On the other hand, as another example, in the fourth operating region A4 where typical SI combustion is performed, more specifically, the control processing section 100 controls each section of the engine as follows.

The spark plug 16 performs one spark ignition during the period from the latter half of the compression stroke to the beginning of the expansion stroke. This spark ignition initiates SI combustion, and all of the air-fuel mixture in the combustion chamber 6 is combusted by flame propagation.

The injector 15 injects fuel for a predetermined period of time that overlaps at least the intake stroke. For example, the injector 15 injects fuel over a series of periods from the intake stroke to the compression stroke.

The supercharger 33 is turned on, and supercharging by the supercharger 33 is performed. The boost pressure at this time is adjusted by the bypass valve 39 .

The opening degrees of the throttle valve 32 and the EGR valve 53 are controlled so that the air-fuel ratio (A/F) in the combustion chamber 6 becomes the stoichiometric air-fuel ratio or a slightly richer value than this.

The swirl valve 18 is fully opened. As a result, not only the first intake port 9A but also the second intake port 9B are completely opened, thereby enhancing the charging efficiency of the engine.

(3) SI rate As described above, in the present embodiment, SPCCI combustion in which SI combustion and CI combustion are mixed is executed in the first to third operating regions A1 to A3. It is important to control the ratio of SI combustion and CI combustion according to operating conditions.

In the present embodiment, the SI rate, which is the ratio of the amount of heat release due to SI combustion to the total amount of heat release due to SPCCI combustion (SI combustion and CI combustion), is used as the ratio. FIG. 6 is a diagram for explaining this SI rate, and shows changes in heat release rate (J/deg) with respect to changes in crank angle when SPCCI combustion occurs. An inflection point X in the waveform of FIG. 6 is an inflection point that appears when the combustion mode is switched from SI combustion to CI combustion. The crank angle θci corresponding to this inflection point X can be defined as the start timing of CI combustion. The area R1 of the heat release rate waveform positioned on the advance side of the crank angle θci (CI combustion start timing) is regarded as the amount of heat release due to SI combustion, and the heat release rate positioned on the retard side of θci. The area R2 of the waveform is the heat release rate due to CI combustion. As a result, the SI rate defined by (amount of heat release due to SI combustion)/(amount of heat release due to SPCCI combustion) can be expressed as R1/(R1+R2) by using the areas R1 and R2 (SI rate =R1/(R1+R2)).

The SI rate correlates with the combustion center of gravity, which is the timing at which half the mass (50% mass) of the fuel injected into the combustion chamber 6 is burned during one cycle. For example, the smaller the SI ratio, the greater the ratio of CI combustion, in which the air-fuel mixture burns simultaneously due to self-ignition, so the average combustion speed increases, and the center of gravity of combustion advances, approaching compression top dead center. . While this leads to an improvement in thermal efficiency, it also leads to an increase in combustion noise. Conversely, the higher the SI ratio (the smaller the proportion of CI combustion), the slower the average combustion speed, so the combustion center of gravity is retarded and moved away from compression top dead center. While this leads to suppression of combustion noise, it also leads to a decrease in thermal efficiency. In the present embodiment, considering the correlation between the SI rate and the combustion center of gravity, the optimum combustion center of gravity at which high thermal efficiency can be obtained while suppressing combustion noise to an allowable level or less is predetermined as the target combustion center of gravity. An optimum SI rate corresponding to this target combustion center of gravity is predetermined as a target SI rate.

Here, the target combustion center of gravity changes according to the operating conditions (rotational speed/load) of the engine. For example, under high load conditions where a large amount of heat is generated, the amount of fuel injected is large and the total amount of heat generated in the combustion chamber 6 is large (in other words, combustion noise tends to increase). In order to suppress combustion noise, it is necessary to retard the combustion center of gravity by a large amount from the top dead center of compression compared to when under load conditions. Conversely, under low load conditions, the amount of heat generated is less than under high load conditions, and combustion noise is less likely to increase. For this reason, the target combustion center of gravity is generally set to the more retarded side as the load increases (in other words, to the more advanced side as the load decreases). In addition, since the progress of the crank angle per unit time changes according to the engine speed, the optimum combustion center of gravity considering noise and thermal efficiency also changes depending on the engine speed. Therefore, the target combustion center of gravity is variably set not only by the load but also by the rotational speed.

In this way, the target combustion center of gravity in SPCCI combustion changes according to the rotational speed and load of the engine, and accordingly, the target SI ratio is also variably set according to the rotational speed and load. For example, as described above, the higher the load, the more the target combustion center of gravity is on the retarded side. set so that the rate of combustion is reduced).

In this embodiment, the ignition timing by the spark plug 16, the fuel injection amount/injection timing, and the in-cylinder state quantity are controlled so that the target combustion center of gravity and the target SI ratio set as described above are realized. A setpoint value for the quantity is predetermined depending on the operating conditions (operating point defined by the combination of rotational speed and load). The in-cylinder state quantity is, for example, the temperature in the combustion chamber 6, the EGR rate, or the like. The EGR rate includes the external EGR rate, which is the ratio of the external EGR gas (exhaust gas recirculated to the combustion chamber 6 through the EGR passage 51) to the total gas in the combustion chamber 6, and the internal EGR rate to the total gas in the combustion chamber 6. and an internal EGR rate, which is the proportion of gas (burned gas remaining in the combustion chamber 6).

For example, the more the ignition timing (spark ignition timing) by the spark plug 16 is advanced, the more fuel is burned by SI combustion, and the SI rate increases. Also, for example, the more the fuel injection timing is advanced, the more fuel is burned by CI combustion, and the SI rate becomes lower. Alternatively, the higher the temperature of the combustion chamber 6, the more fuel is burned by CI combustion, resulting in a lower SI rate. Furthermore, since changes in the SI rate are accompanied by changes in the center of gravity of combustion, changes in these control variables (ignition timing, injection timing, in-cylinder temperature, etc.) are factors for adjusting the center of gravity of combustion.

Based on the above trends, in the present embodiment, each target value of ignition timing, fuel injection amount/injection timing, and in-cylinder state quantity (temperature, EGR rate, etc.) realizes the above-described target combustion center of gravity and target SI rate. It is predetermined for each operating condition so that possible combinations can be obtained. When the engine is operated by SPCCI combustion, the control processor 100 controls the injector 15, the spark plug 16, the EGR valve 53, the intake/exhaust VVT 13a, 14a, etc., based on the respective target values of these control variables. For example, the control processing unit 100 controls the spark plug 16 based on the target value of the ignition timing, and controls the injector 15 based on the target value of the fuel injection amount/injection timing. The control processing unit 100 controls the EGR valve 53 and the intake/exhaust VVT 13a, 14a based on the target values of the temperature of the combustion chamber 6 and the EGR rate, and controls the recirculation amount of the exhaust gas (external EGR gas) through the EGR passage 51. and the residual amount of burned gas (internal EGR gas) due to internal EGR.

In this embodiment, in which the target center of gravity of combustion and the target SI rate are predetermined for each operating condition of the engine, the CI combustion start timing θci is naturally determined. In the following description, the CI combustion start timing determined based on the target combustion center of gravity and the target SI ratio is referred to as "standard θci". This standard θci serves as a reference for determining the target θci in a flowchart (process S4 in FIG. 7) to be described later.

(4) Control During SPCCI Combustion Based on Combustion Noise Index Value FIG. 7 is a flow chart showing control executed by the control processor during SPCCI combustion. When the control shown in this flowchart starts, the control processing unit 100 first detects the engine rotation speed detected by the crank angle sensor SN1, the detection value (accelerator opening) of the accelerator sensor SN8, and the detection value (intake air) of the air flow sensor SN4. The injection amount and injection timing of the fuel from the injector 15 are determined based on the engine load specified from the flow rate) and the like (S1). As understood from the above description, the determined fuel injection amount/injection timing is the injection amount/injection timing for realizing the target combustion center of gravity and the target SI ratio.

Next, the control processing unit 100 determines a reference value W (FIG. 9), which is the upper limit value of the in-cylinder pressure that can be tolerated with respect to combustion noise under the current operating conditions (S2). More specifically, the control processing unit 100 controls the engine load specified from the detected value (accelerator opening) of the accelerator sensor SN8, the vehicle speed detected by the vehicle speed sensor SN9, and the map M1 shown in FIG. A reference value W is specified based on.

A map M1 in FIG. 9 defines the reference value W for each vehicle speed/engine load, and is stored in the control processing unit 100 in advance. This map M1 includes a first characteristic Q1 that defines a reference value W1 when the vehicle speed is changed while the engine load is fixed at a predetermined low load, and a first characteristic Q1 that defines a reference value W1 when the vehicle speed is changed while the engine load is fixed at a predetermined high load. and a second characteristic Q2 that defines a reference value W2 when the pressure is applied. The reference value W2 defined by the second characteristic Q2 for high load is set to be larger than the reference value W1 defined by the first characteristic Q1 for low load. Both the first characteristic Q1 (and the second characteristic Q2) have a tendency to rise to the right in which the reference value W1 (W2) increases as the vehicle speed increases. The second characteristic Q2 for high load has a characteristic close to direct proportionality in which the rate of change (slope of the waveform) of the reference value W2 with respect to the vehicle speed is approximately the same at any vehicle speed. On the other hand, in the first characteristic Q1 for low load, the rate of change of the reference value W1 in the region where the vehicle speed is less than the predetermined value V0 (low vehicle speed region) is greater than or equal to the predetermined value V0 (high vehicle speed region). has a nonlinear characteristic that is greater than the rate of change of the reference value W1 of .

In the process S2, the control processing unit 100 compares the current vehicle speed and engine load (current operating conditions) specified from the detected values of the sensors SN8 and SN9 with the map M1 of FIG. A reference value W corresponding to the operating conditions is specified. More specifically, the control processing unit 100 specifies the reference value W1 corresponding to the current vehicle speed from the value on the first characteristic Q1 for low load, and determines the reference value W1 from the value on the second characteristic Q2 for high load. A reference value W2 corresponding to the current vehicle speed is specified, and a reference value W corresponding to the current driving conditions is specified by linear interpolation using these two reference values W1 and W2. For example, when the current engine load is an intermediate value between the load corresponding to the first characteristic Q1 and the load corresponding to the second characteristic Q2, the intermediate value between the reference value W1 and the reference value W2 is It is identified as a reference value W corresponding to the current operating conditions. Further, when the current engine load is lower than the load corresponding to the first characteristic Q1 (or higher than the load corresponding to the second characteristic Q2), a value lower than the reference value W1 (more than the reference value W2) is specified as the reference value W corresponding to the current operating conditions.

Based on the characteristics of the characteristics Q1 and Q2 described above, the reference value W is set to a larger value as the vehicle speed/engine load increases. That is, the reference value W is a value that increases regardless of whether the vehicle speed or the engine load increases. growing. This is because the lower the vehicle speed and lower the load, the easier it is to perceive even a small combustion noise (conversely, the higher the vehicle speed and a higher load, the less perceptible even a large combustion noise is).

Returning to FIG. 7, next, the control processing unit 100 subtracts the allowance y based on the standard deviation σ of the histogram relating to the in-cylinder pressure of the cylinder from the reference value W corresponding to the current operating conditions specified in the process S2. The resulting value is determined as the final reference value Wx (=Wy) (S3). A method of calculating the standard deviation σ of the histogram relating to the in-cylinder pressure of the cylinder will be described later. The margin y may be 1σ (y=1σ), but is preferably 3σ (y=3σ) from the viewpoint of covering 99.73% of the distribution. The reason why the final reference value Wx is determined in consideration of the standard deviation in this way is that if the same reference value W is adopted despite the large variation in combustion noise for each combustion cycle, the This is because there is a high possibility that combustion with a large amount of noise will occur accidentally.

Next, the control processing unit 100 determines a target θci, which is the target CI combustion start timing. This target θci is a target value of the crank angle (crank angle θci shown in FIG. 6) at which SI combustion is switched to CI combustion, and is determined with the aim of suppressing it to the final reference value Wx or less.

FIG. 8 is a subroutine showing details of the process S4 shown in FIG. When the control shown in this subroutine starts, the control processing unit 100 first determines the engine rotation speed detected by the crank angle sensor SN1, the engine load specified from the detection value of the accelerator sensor SN8, etc. Based on the final reference value Wx obtained and the map M2 shown in FIG. 10, the θci limit, which is the start timing of CI combustion that can be suppressed to the final reference value Wx or less, is determined. More specifically, the control processing unit 100 compares the final reference value Wx determined in the process S3 with the map M2 of FIG. Specify as a limit.

A map M2 in FIG. 10 defines a standard relationship between θci (CI combustion start timing) and final reference value Wx, and is stored in control processing unit 100 in advance. More specifically, the map M2 defines standard characteristics of the final reference value Wx obtained when the engine speed is constant (N1) and the engine load is varied. θci and the vertical axis respectively represent the final reference value Wx. For the sake of convenience, FIG. 10 shows only three types of loads, ie, low load, medium load, and high load, but the map M2 also includes the characteristics of loads other than these three types. Further, the map M2 is a map when the engine rotation speed is constant (N1), but maps created for various engine rotation speeds different from this are also controlled in the same manner as the map M2. stored in unit 100 . If the engine speed/load is a value not defined in the map M2, the final reference value Wx is obtained by linear interpolation, for example.

Next, the control processing unit 100 determines whether or not the θci limit determined in the process S21 is on the lag side of the predetermined standard θci (S22). As a result of this determination, if the θci limit is on the retard side of the standard θci (YES), the control processing unit 100 determines the θci limit as the target θci (S23), and terminates this subroutine. On the other hand, as a result of the above determination, if the θci limit is not on the retard side of the standard θci (NO, that is, if the θci limit and the standard θci are the same or the θci limit is on the advance side of the standard θci) , the control processing unit 100 determines the standard θci as the target θci (S24), and terminates this subroutine.

Returning to FIG. 7, next, the control processing unit 100 determines whether or not a predetermined specific crank angle has arrived based on the detection value of the crank angle sensor SN1 (S5). This specific crank angle is predetermined as the timing for determining the ignition timing of the ignition plug 16, and is set, for example, to about 60° CA before the compression top dead center. If the result of this determination is that the specific crank angle has arrived (YES), the control processing unit 100 next executes processing S6. NO), the control processor 100 returns the process to the process S5. That is, this process S5 is repeatedly executed until the specific crank angle is reached.

In the process S6, the control processing unit 100 determines the ignition timing for realizing the target θci determined in the process S4. Here, in this embodiment, for each operating condition of the engine, the target combustion center of gravity and the target SI rate, the standard θci corresponding to these target combustion center of gravity and the target SI rate, the ignition timing and the fuel Since target values for the injection amount/injection timing and the in-cylinder state quantity (temperature, EGR rate, etc.) are predetermined, the control processing unit 100 determines the ignition timing based on these target values. be able to. For example, the ignition timing for realizing the target θci is determined based on the amount of deviation between the standard θci and the target θci and the in-cylinder state quantity at the specific crank angle.

That is, the greater the amount of deviation between the standard θci and the target θci, the greater the deviation from the initial target value (hereinafter referred to as default ignition timing) of the ignition timing determined corresponding to the standard θci is determined as the ignition timing. There is a need. Further, the greater the deviation of the in-cylinder state quantity from the target value at the specific crank angle time, the greater the deviation from the default ignition timing must be set as the ignition timing. On the other hand, in the present embodiment, the initial target values for the fuel injection amount/injection timing are used as they are, so the amount of deviation in the fuel injection amount/injection timing need not be taken into consideration. In the process S6, the control processing unit 100 calculates the amount of deviation between the standard θci and the target θci and the deviation of the in-cylinder state quantity from the target value using a predetermined arithmetic expression prepared in advance based on the circumstances described above. The ignition timing by the spark plug 16 is determined from the quantity. The in-cylinder state quantity, that is, the temperature of the combustion chamber 6, the EGR rate, etc., can be predicted from the detected values of the intake air temperature sensor SN5, the intake air pressure sensor SN6, the differential pressure sensor SN7, and the like.

Next, the control processor 100 ignites the spark plug 16 at the ignition timing determined in the process S6, and the ignition triggers the SPCCI combustion of the air-fuel mixture (S7).

Such operations are performed for each combustion cycle in SPCCI combustion.

(5) Calculation of Standard Deviation of Histogram of Cylinder Pressure In order to process the standard deviation of the histogram of cylinder pressure, the control processing unit 100 includes a control processing program and Various predetermined data are stored in advance. This control processing program includes a control program for controlling each part of the engine according to the function of each part, a histogram of the cylinder pressure measured by the cylinder pressure sensor SN3 in one combustion cycle at a predetermined operating point, and a histogram of the most frequent cylinder pressure. The first standard deviation when it is assumed that the distribution of in-cylinder pressure lower than the most frequent in-cylinder pressure is normal distribution, and the histogram is normal distribution with the distribution of in-cylinder pressure higher than the most frequent in-cylinder pressure A standard deviation processing program for obtaining the second standard deviation when assumed to be, a difference processing program for obtaining the difference between the first and second standard deviations obtained by the standard deviation processing program, and the absolute value of the difference obtained by the difference processing program is a predetermined value or more, the histogram is determined to be non-normal distribution, and based on the second standard deviation, an upper limit value processing program for determining the upper limit value of the in-cylinder pressure of the cylinder at the predetermined operating point; It includes a combustion control program and the like for controlling the internal combustion engine so that the upper limit value obtained by the upper limit value processing program or less is reached at the predetermined operating point. The predetermined data includes each relationship predetermined for each operating condition described above, the maps M1 and M2 described above, the standard deviation up to the previous combustion cycle, and the like. In the control processing unit 100, by executing the control processing program, as shown in FIG. Functionally configured. Further, the control processing unit 100 is functionally configured with a standard deviation storage unit 106 that stores each standard deviation up to the previous combustion cycle in association with each operating point.

The control unit 101 controls each part of the engine according to the function of each part, and governs the overall control of the engine.

Standard deviation processing unit 102 calculates a histogram of in-cylinder pressure measured by in-cylinder pressure sensor SN3 in one combustion cycle at a predetermined operating point, with the most frequent in-cylinder pressure as a reference, and calculates the values of in-cylinder pressure lower than the most frequent in-cylinder pressure. A first standard deviation is obtained when it is assumed that the distribution is normally distributed, and a second standard deviation is obtained when it is assumed that the histogram is normally distributed with an in-cylinder pressure higher than the most frequent in-cylinder pressure. More specifically, standard deviation processing section 102 obtains the first and second standard deviations in the current combustion cycle as follows.

FIG. 11 is a diagram showing, as an example, a histogram of in-cylinder pressure at one predetermined operating point. The horizontal axis in FIG. 11 is the in-cylinder pressure, and the vertical axis is the frequency. FIG. 12 is a graph of the function F(a). The horizontal axis of FIG. 12 is a, and its vertical axis is F(a). FIG. 13 is a diagram showing, as an example, histograms of in-cylinder pressures for knocking and misfiring. FIG. 13A shows a histogram of in-cylinder pressure when knocking occurs, and FIG. 13B shows a histogram of in-cylinder pressure when misfire occurs. Each horizontal axis in FIGS. 13A and 13B is the in-cylinder pressure, and each vertical axis is frequency.

For example, as shown in FIG. 11, the in-cylinder pressure histogram is asymmetric with respect to the most frequent in-cylinder pressure m. It is difficult to regard such a histogram of in-cylinder pressure as a normal distribution, as indicated by the dashed line α. Although illustration is omitted, the histogram of the in-cylinder pressure may have a normal distribution. Therefore, in this embodiment, the histogram of the in-cylinder pressure of this non-normal distribution is the most frequent in-cylinder pressure m and the in-cylinder pressure is less than the most frequent in-cylinder pressure m (− side histogram (x≦m), and the in-cylinder pressure exceeds the most frequent in _- cylinder pressure m (m< _x ). In addition, the distribution is regarded as a normal distribution, and the histogram of the non-normal distribution of the in-cylinder pressure is represented by a solid line β consisting of these solid lines β ₋ and β ₊ . As a result, the cylinder internal pressure histogram can be expressed by the following equation 1, where x is the cylinder internal pressure, s _- is the standard deviation of the - side histogram, and s ₊ is the standard deviation of the + side histogram. Note that Equation 1 becomes a normal distribution when s ₋ =s ₊ , so Equation 1 includes not only non-normal distributions but also normal distributions.

Since each in-cylinder pressure occurs with a certain probability, the histogram of in-cylinder pressure can be viewed as a probability distribution. In probability theory, the expected value can be expressed by the first moment, and the variance σ ² (=s ² , s ₋ ² , s ₊ ² ) can be expressed by the first and second moments . Moments indicate how the data is distributed. The first to third moments E[x], E[x ² ], and E[x ³ ] in Equation 1 are given by Equations 2 to 4 below, respectively. Note that in Equations 2 to 4, √ applies only to 2/π.

Therefore, by successively estimating E[y] by approximating E[y ⁻ _n ] with y=x, x ² , x ³ , and solving the simultaneous equations of the above equations 2 to 4, m, s ₋ , s ₊ can be obtained. Here, E[y ⁻ _n ] is defined by the following equation 5.

ここで、Ｅ［ｙ^－ _ｎ］は、ｘ、ｘ^２、ｘ^３それぞれのｎ燃焼サイクル目の期待値であり、Ｅ［ｙ^－ _ｎ－１］は、ｘ、ｘ^２、ｘ^３それぞれの直近のｎ－１燃焼サイクルまでの期待値である。ｍｉｎ（Ａ、Ｂ）は、Ａ、Ｂの中で小さい方を出力する演算子であり、ｎ_ｍａｘは、逐次推定する際に用いられる過去のデータの個数である（例えば、直近の過去に取得された１００個のデータを逐次推定で用いる場合ではｎ_ｍａｘは、１００である）。

Here, E[y ⁻ _n ] is the expected value of each of x, x ² and x ³ at the n-th combustion cycle, and E[y ⁻ _n−1 ] is each of the nearest values of x, x ² and x ³ is the expected value up to n-1 combustion cycles. min (A, B) is an operator that outputs the smaller one of A and B, and n _max is the number of past data used for sequential estimation (for example, n _max is 100 when 100 data obtained are used for sequential estimation).

Strictly speaking, however, the histogram of the actual in-cylinder pressure cannot be represented by Equation 1. Therefore, the solutions of the simultaneous equations of Equations 2 to 4 may not exist. Information processing becomes complicated. Therefore, M ₂ and M ₃ are defined by the first to third moments E[x], E[x ² ], and E[x ³ ] as shown in the following equations 6 and 7.

Furthermore, when s ₋ and s ₊ are defined as s ₋ =(1−a)s ₀ and s ₊ =(1+a)s ₀ with a and s ₀ , M ₂ and M ₃ are given by the following equation 8: can be represented by a function F(a) of a.

As described above, M ₂ and M ₃ can be successively estimated from E[y] (y=x, x ² , x ³ ) obtained by successive estimation using Equations 6 and 7, so the function F(a ) can be obtained from M ₃ /(M ₂ ) ^(3/2) . Once the value of the function F(a) is determined, the value of a can be determined from Equation 8 above. Actually, the function F(a) is a monotonically increasing function as shown in FIG. By storing it in the control processing unit 100 as _one of the predetermined data, the standard deviation processing unit ¹⁰² calculates the function F ₍ a) The value of a can be obtained from the value of by referring to the lookup table.

Here, the value of the function F(a) obtained by the sequential estimation M ₃ /(M ₂ ) ^(3/2) may exceed the range of ±1, and 3σ (=3s, 3s ₋ , 3s ₊ ). Therefore, the value of a is limited to a predetermined numerical range. That is, when the value of the function F(a) is the first predetermined value or more, it is clipped to the upper limit value of the numerical range of a. Clipped to the lower limit. The numerical range of a is appropriately set in advance from a plurality of samples, for example, set to ±0.7, ±0.75, ±0.8, etc. The first predetermined value is the numerical range of a and the second predetermined value is the value of F(a) at the lower limit of the numerical range of a.

On the other hand, M ₂ can be expressed as in the following equation 9 using a and s ₀ from the above equation 6, and M ₂ is E[x] and E[ x ² ], it can be estimated successively. Therefore, the standard deviation processing unit 102 can obtain _s0 from the equation 9 from _M2 obtained by the sequential estimation and a obtained as described above. Therefore, from a and s ₀ obtained in this way, the standard deviation processing unit 102 can obtain s _- and s ₊ by s _- = (1-a) s ₀ and s ₊ = (1 + a) s ₀ .

Further, when s ₋ and s ₊ are obtained, standard deviation processing section 102 can obtain m from Equation 2 above.

Thus, the standard deviation processing unit 102 can obtain m, s ₋ , and s ₊ . For example, as shown in FIG. 11, in a histogram in which the most frequent in-cylinder pressure m is closer to the high pressure side than the center, 3s ₊ of the standard deviation s ₊ obtained in this way is the standard deviation s 3s, as can be seen from FIG. In the process S3 described above, the final reference value Wx was obtained by subtracting the standard deviation (preferably three times the standard deviation) from the reference value, but the standard deviation s obtained assuming a normal distribution and the non-normal distribution It can be seen that the allowance was set too large by the difference from the standard deviation s ₊ obtained in consideration of the case of . Accordingly, in the present embodiment, an improvement in thermal efficiency can be expected.

Here, as described above, Equation 1 represents not only the case where the histogram has a non-normal distribution (s ₋ ≠s ₊ ), but also the case where the histogram has a normal distribution (s ₋ =s ₊ ). . The standard deviation s ₋ of the negative histogram and the standard deviation s _{2 +} of the positive histogram correspond to the first and second standard deviations, respectively. Therefore, as described above, the standard deviation processing unit 102 sequentially estimates the first to third moments E[x], E[x ² ], E[x ³ ] to obtain m, s ₋ , s ₊ By obtaining , each of the first and second standard deviations can be obtained.

Then, the standard deviation processing unit 102 stores the variance of the standard deviation s ₋ up to the previous combustion cycle, which is associated with the current operating point and stored in the standard deviation storage unit 106, and the current The standard deviation s ₋ of the combustion cycle is averaged with the variance of the combustion cycle, and the final standard deviation s ₋ of the current combustion cycle is found from the variance of the average thus found. In order _to use the standard deviation s ₋ up to the previous combustion cycle in the next combustion cycle as are stored in the standard deviation storage unit 106 in correspondence with each other. Similarly, the standard deviation processing unit 102 calculates the variance of the standard deviation s ₊ up to the previous combustion cycle, which is associated with the current operating point and stored in the standard deviation storage unit 106, and the current Calculate the average of the standard deviation s ₊ variance of the combustion cycle of , calculate the final standard deviation s ₊ in the current combustion cycle from the variance of the calculated average, and use this calculated standard deviation s ₊ as the current operation It is stored in the standard deviation storage unit 106 in association with the points.

The difference processor 103 obtains the difference between the first and second standard deviations obtained by the standard deviation processor 102 . In this embodiment, the difference processing unit 103 obtains the difference Δs (=|s ₋ −s ₊ |) between the first and second standard deviations s ₋ and s ₊ obtained by the standard deviation processing unit 102 .

The upper limit processing unit 104 obtains the upper limit of the in-cylinder pressure of the cylinder at the predetermined operating point based on the difference Δs obtained by the difference processing unit 103 . More specifically, when the in-cylinder temperature is relatively high, for example, when the in-cylinder temperature is relatively high, knocking occurs, and as shown in FIG. A non-normal distribution with a profile. Further, for example, when the in-cylinder temperature is relatively low, a misfire occurs. As a result, the histogram of the in-cylinder pressure has an irregular profile with a tail on the low pressure side extending from the most frequent in-cylinder pressure m, as shown in FIG. 13B. distribution. Therefore, in this embodiment, in order to obtain the upper limit value of the in-cylinder pressure, the standard deviation s ₋ of the minus side histogram and the standard deviation s ₊ of the + side histogram are compared. In some cases, it is determined that the histogram has a non-normal distribution, and an upper limit value for the in-cylinder pressure of the cylinder is set based on the second standard deviation s _{1 +} . The histogram may be regarded as having a non-normal distribution only when the difference Δs is not 0. Therefore, the predetermined value may be set to a value greater than 0, and the histogram may be regarded as having a normal distribution when the difference Δs is less than the predetermined value. Then, when the difference Δs is less than the predetermined value, it is determined that the histogram has a normal distribution. When it is determined that the distribution is normal, the upper limit value of the in-cylinder pressure of the cylinder may be set based on one of the first and second standard deviations s ₋ and s ₊ , but the predetermined value is When it is set to a value greater than 0, the average value of the first and second standard deviations s ₋ and s ₊ is obtained, and the upper limit of the in-cylinder pressure of the cylinder is set based on this average value. Also good.

The standard deviation s ₊ obtained as described above may be used as it is to obtain the allowance y based thereon. By assuming that it consists of a histogram, it can also be used to determine whether knocking or misfire is likely to occur.

The combustion control unit 105 controls the internal combustion engine (partial compression ignition engine in this embodiment) so that the upper limit value obtained by the upper limit processing unit 104 or less is reached at the predetermined operating point. In this embodiment, the combustion control unit 105 executes each of the processes S1, S2, S4, S5, S6 and S7 described above.

FIG. 14 is a flow chart showing the process of obtaining the standard deviation. FIG. 15 is a diagram for explaining the effect of the embodiment as an example. The horizontal axis in FIG. 15 is the combustion cycle, and the vertical axis is the in-cylinder pressure.

The control processing unit 100 having such functional blocks operates as follows with respect to the calculation of the standard deviation of the in-cylinder pressure for each combustion cycle.

In FIG. 14, first, the control processing unit 100 acquires the current operating point and the in-cylinder pressure by the standard deviation processing unit 102 (S41). More specifically, the standard deviation processing unit 102 obtains the engine rotation speed from the detection signal of the crank angle sensor SN1, the detection signal of the accelerator sensor SN8 (accelerator opening), the detection signal of the air flow sensor SN4 (intake flow rate), etc. , the current operating point is obtained, and the detection signal (in-cylinder pressure) of the in-cylinder pressure sensor SN3 is obtained. This acquisition step S41 is executed at the timing when the crank angle reaches a predetermined angle, for example, 180 degrees when the compression top dead center is 0 degrees.

Next, the control processor 100 uses the standard deviation processor 102 to obtain the first and second standard deviations (S42). More specifically, as described above, the standard deviation processing unit 102 sequentially estimates E[y] by approximating it with E[y ⁻ _n ], so that each of the first to third moments E[x ], E[x ² ], and E[x ³ ] are obtained, and from these, M ₂ and M ₃ are obtained using the above equations 6 and 7, and from M ₃ /(M ₂ ) ^(3/2) , function F ( a) is obtained, a is obtained from the value of the function F(a) thus obtained based on the lookup table, s ₀ is obtained from M ₂ and a, standard deviations s ₋ and s are obtained from a and s ₀ Ask for ₊ . Then, the standard deviation processing unit 102 stores the variances of the standard deviations s ₋ and s ₊ up to the previous combustion cycle, which are associated with the current operating point and stored in the standard deviation storage unit 106, as described above. Each average of the standard deviations s _{− and s + of the current combustion cycle obtained is obtained, and the final standard deviations s − and s + of the} current combustion cycle are obtained from the respective dispersions of the obtained averages. , the obtained standard deviations s ₋ and s ₊ are stored in the standard deviation storage unit 106 in association with the current operating point.

Next, the control processing unit 100 causes the difference processing unit 103 to divide the difference Δs (=s ₋ −s ₊ ) between the standard deviations s ₋ and s ₊ obtained by the standard deviation processing unit 102 in processing S42 into the first and It is obtained as a difference of the second standard deviation (S43).

Then, the control processing unit 100 determines whether the histogram of the in-cylinder pressure is a normal distribution or a non-normal distribution based on the difference Δs obtained by the difference processing unit 103 in step S43, and ends this processing. (S44). Then, based on the determination result, the upper limit value of the in-cylinder pressure of the cylinder is set as described above.

As an example, FIG. 15 shows 3s ₋ and 3s ₊ of the standard deviations s ₋ and s ₊ obtained from the actual data of the in-cylinder pressure by the method described above. FIG. 15 also shows 3s of the standard deviation s obtained by regarding the actual data of the in-cylinder pressure as a normal distribution. It can be seen from FIG. 15 that 3s ₊ of standard deviation s ₊ is better than 3s of standard deviation s.

As described above, in the present embodiment, the first standard deviation and the histogram when it is assumed that the histogram is normally distributed on the lower pressure side than the most frequent in-cylinder pressure with the most frequent in-cylinder pressure as a reference. Finding the difference from the second standard deviation when it is assumed that the distribution on the high pressure side of the most frequent in-cylinder pressure is normal distribution, and determining whether the histogram is a normal distribution or a non-normal distribution based on the obtained difference , the upper limit value (final reference value Wx) of the in-cylinder pressure of the cylinder is obtained based on the determination result. Therefore, the present embodiment can appropriately set the upper limit value of the in-cylinder pressure of the cylinder even when the histogram has a non-normal distribution. If the second standard deviation is greater than the first standard deviation, by setting the upper limit of the in-cylinder pressure based on the second standard deviation, the upper limit of the in-cylinder pressure of the cylinder is determined based on the first standard deviation. The permissible value for suppressing combustion noise by avoiding the generation of combustion noise due to knocking can be appropriately set as compared with the case of setting . Further, when the second standard deviation is smaller than the first standard deviation, the difference between the upper limit value of the in-cylinder pressure of the cylinder set based on the second standard deviation and the upper limit value set based on the first standard deviation It is expected that the thermal efficiency will be improved according to the Therefore, the present embodiment can appropriately set the upper limit value of the in-cylinder pressure of the cylinder, so that the thermal efficiency can be improved while keeping the combustion noise within the allowable value.

According to the present embodiment, since the internal combustion engine is, for example, a partial compression ignition engine, it is possible to provide a control method and a control device for a partial compression ignition engine that can appropriately set the upper limit value of the in-cylinder pressure of the cylinder.

When the upper limit value of the in-cylinder pressure of the cylinder is obtained based on three times the second standard deviation σ (y=3σ), in this embodiment, even if the in-cylinder pressure of the cylinder varies, The internal pressure can be suppressed below the upper limit. That is, such an embodiment can keep combustion noise within an acceptable range.

In the above-described embodiment, the internal combustion engine is a partial compression ignition engine, but it is not limited to this, and other types of engines may be used. For example, the internal combustion engine may be a diesel engine, and each of the processes described above may be used to determine the upper limit of the in-cylinder pressure in order to keep the combustion noise of the diesel engine within an allowable range.

Further, in the above-described embodiment, the combustion center of gravity, which is the timing at which half the mass (50% mass) of the fuel injected into the combustion chamber 6 is burned during one combustion cycle, is used, but the present invention is limited to this. It can be changed as appropriate. That is, the target mass combustion timing may be used, which is the timing at which a target mass ratio (for example, 40% mass, 60% mass, etc.) of the fuel supplied to the cylinder burns during one combustion cycle.

Although the present invention has been adequately and fully described above through embodiments with reference to the drawings in order to express the present invention, modifications and/or improvements to the above-described embodiments can easily be made by those skilled in the art. It should be recognized that it is possible. Therefore, to the extent that modifications or improvements made by those skilled in the art do not depart from the scope of the claims set forth in the claims, such modifications or improvements do not fall within the scope of the claims. is interpreted to be subsumed by

SN3 In-cylinder pressure sensor 100 Control processing unit 101 Control unit 102 Standard deviation processing unit 103 Difference processing unit 104 Upper limit value processing unit 105 Combustion control unit 106 Standard deviation storage unit

Claims (6)

A control method for an internal combustion engine that burns an air-fuel mixture in a cylinder,
an in-cylinder pressure measuring step of measuring the in-cylinder pressure of the cylinder;
It is assumed that the histogram of the in-cylinder pressure measured in the in-cylinder pressure measurement step in one combustion cycle at a predetermined operating point is normally distributed with the distribution of in-cylinder pressure lower than the most frequent in-cylinder pressure as a reference. A standard deviation processing step of obtaining a first standard deviation in the case where the cylinder pressure is higher than the most frequent cylinder pressure and a second standard deviation in the case where the histogram is assumed to be normally distributed with a cylinder pressure higher than the most frequent cylinder pressure;
A difference processing step of obtaining a difference between the first and second standard deviations obtained in the standard deviation processing step;
When the absolute value of the difference obtained in the difference processing step is equal to or greater than a predetermined value, the histogram is determined to be non-normal distribution, and based on the second standard deviation, the in-cylinder pressure of the cylinder at the predetermined operating point is calculated. an upper limit processing step of obtaining the upper limit;
a combustion control step of controlling the internal combustion engine so that the upper limit value obtained in the upper limit value processing step or less is reached at the predetermined operating point;
A control method for an internal combustion engine. In the internal combustion engine, partial compression ignition combustion in which part of the air-fuel mixture in the cylinder undergoes SI combustion by pyrotechnic ignition and then the remaining air-fuel mixture in the cylinder undergoes CI combustion by self-ignition is performed in at least a part of the operating range. It is an automotive partial compression ignition engine that runs
In the combustion control step, at the predetermined operating point, a target mass ratio of fuel out of the fuel supplied to the cylinder during one combustion cycle is equal to or lower than the upper limit value obtained in the upper limit value processing step. setting a target mass combustion timing that is the timing of combustion, and controlling the ignition timing of the fireworks ignition based on the set target mass combustion timing;
A control method for an internal combustion engine according to claim 1. The upper limit value processing step obtains an upper limit value of the in-cylinder pressure of the cylinder based on three times the second standard deviation.
The control method for an internal combustion engine according to claim 1 or 2. A control device for an internal combustion engine that burns an air-fuel mixture in a cylinder,
an in-cylinder pressure measurement unit that measures the in-cylinder pressure of the cylinder;
It is assumed that the histogram of the in-cylinder pressure measured in the in-cylinder pressure measurement step in one combustion cycle at a predetermined operating point is normally distributed with the distribution of in-cylinder pressure lower than the most frequent in-cylinder pressure as a reference. a standard deviation processing unit that obtains a first standard deviation in the case where the cylinder pressure is higher than the most frequent in-cylinder pressure, and a second standard deviation in the case that the histogram is assumed to be normally distributed with a cylinder pressure higher than the most frequent in-cylinder pressure;
A difference processing unit for obtaining the difference between the first and second standard deviations obtained by the standard deviation processing unit;
When the absolute value of the difference obtained by the difference processing unit is equal to or greater than a predetermined value, the histogram is determined to be non-normal distribution, and based on the second standard deviation, the in-cylinder pressure of the cylinder at the predetermined operating point is calculated. an upper limit processing unit that obtains the upper limit;
a combustion control unit that controls the internal combustion engine so that the upper limit value obtained by the upper limit value processing unit or less is reached at the predetermined operating point;
A control device for an internal combustion engine. In the internal combustion engine, partial compression ignition combustion in which part of the air-fuel mixture in the cylinder undergoes SI combustion by pyrotechnic ignition and then the remaining air-fuel mixture in the cylinder undergoes CI combustion by self-ignition is performed in at least a part of the operating range. It is an automotive partial compression ignition engine that runs
The combustion control unit controls a target mass ratio of fuel in the fuel supplied to the cylinder during one combustion cycle so that the upper limit value obtained by the upper limit processing unit is equal to or lower than the upper limit value obtained by the upper limit value processing unit at the predetermined operating point. setting a target mass combustion timing that is the timing of combustion, and controlling the ignition timing of the fireworks ignition based on the set target mass combustion timing;
The control device for an internal combustion engine according to claim 4. The upper limit value processing unit obtains an upper limit value of the in-cylinder pressure of the cylinder based on three times the second standard deviation,
6. The control device for an internal combustion engine according to claim 4 or 5.

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