Control device and control method for engine

Abstract

To successfully suppress abnormal combustion when controlling an internal combustion engine.SOLUTION: A PCM 100 as a control device for an engine calculates a first cylinder internal pressure of a cylinder 2, a first pressure change rate and a first heat generation rate at a first crank angle before high-temperature oxidation reaction is generated within a combustion chamber 6, predicts a second cylinder internal pressure, a second pressure change rate and a second heat generation rate at a second crank angle after the high-temperature oxidation reaction is generated on the basis of the first cylinder internal pressure, the first pressure change rate and the first heat generation rate, determines whether or not abnormal combustion occurs in this combustion cycle on the basis of the second cylinder internal pressure, the second pressure change rate and the second heat generation rate, and causes an injector 14 to execute additional fuel injection when the occurrence of the abnormal combustion is determined.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a control device and a control method for an engine including a combustion chamber.

Background Art

[0002] In internal combustion engines, there is a trend towards further improvement in thermal efficiency. As measures for improving thermal efficiency, increasing the compression ratio and lean burn are useful, but it is essential to suppress abnormal combustion caused by these, particularly abnormal combustion accompanied by abnormal noises and vibrations such as knocking and detonation. Patent Document 1 discloses an engine control device that predicts whether strong knocking will occur based on the in-cylinder pressure when the mass combustion ratio is between 5% and 20%, and performs additional fuel injection when it is predicted that strong knocking will occur.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the control of Patent Document 1, the occurrence of knocking is predicted based on the in-cylinder pressure after combustion actually starts. However, after combustion starts, the prediction timing is late, and the timing of additional fuel injection also becomes late. For this reason, suppression of knocking within the same cycle may be insufficient, or there may be problems such that the fuel injected additionally becomes incomplete combustion and generates smoke.

[0005] An object of the present invention is to provide an engine control device and a control method that can favorably suppress abnormal combustion in the control of an internal combustion engine.

Means for Solving the Problems

[0006] The engine control device according to one aspect of the present invention is an engine control device including a combustion chamber in a cylinder and a liquid injection valve that injects liquid into the combustion chamber. The control device calculates a first in-cylinder pressure, a first pressure change rate, and a first heat generation rate at a first crank angle before a high-temperature oxidation reaction occurs in the combustion chamber, and predicts a second in-cylinder pressure, a second pressure change rate, and a second heat generation rate at a second crank angle after the high-temperature oxidation reaction occurs based on the first in-cylinder pressure, the first pressure change rate, and the first heat generation rate. Based on the second in-cylinder pressure, the second pressure change rate, and the second heat generation rate, it is determined whether abnormal combustion occurs in the current combustion cycle. When it is determined that abnormal combustion occurs, the liquid injection valve is made to execute liquid injection.

[0007] According to this aspect, before the high-temperature oxidation reaction occurs in the combustion chamber, that is, at the first crank angle before combustion occurs, it is determined whether abnormal combustion occurs at the second crank angle after the high-temperature oxidation reaction occurs. Therefore, the occurrence of abnormal combustion can be predicted early. Accordingly, liquid injection can also be executed early. Since the latent heat of vaporization of the injected liquid cools the inside of the cylinder to suppress combustion, abnormal combustion can be suppressed well. In addition, the first in-cylinder pressure, the first pressure change rate, and the first heat generation rate are variables that can be derived if there is a sensor for detecting the in-cylinder pressure, and do not require complicated sensing or calculation processing.

[0008] In the above engine control device, the first crank angle may be set within a period from after a low-temperature oxidation reaction occurs in the combustion chamber to before the high-temperature oxidation reaction occurs.

[0009] The high-temperature oxidation reaction is a reaction that generates high thermal energy while accompanied by a flame and is substantially a combustion reaction. In contrast, the low-temperature oxidation reaction is a slow oxidation reaction that occurs before the high-temperature oxidation reaction. According to the above aspect, the occurrence of abnormal combustion is predicted after the start of the low-temperature oxidation reaction. When the low-temperature oxidation reaction starts, characteristic behavior in the in-cylinder pressure is likely to appear. Therefore, the prediction accuracy of the occurrence of abnormal combustion can be improved.

[0010] In the above engine control device, the engine further includes an ignition device that ignites the air-fuel mixture formed in the combustion chamber, and the first crank angle may be set within a period after the ignition operation by the ignition device.

[0011] Triggered by the ignition operation of the ignition device, a low-temperature oxidation reaction occurs or the low-temperature oxidation reaction is promoted. According to the above aspect, it becomes easier to detect the characteristic in-cylinder pressure associated with the low-temperature oxidation reaction.

[0012] In the above engine control device, the liquid injection valve is a fuel injection valve that injects fuel into the combustion chamber, and when it is determined that the abnormal combustion has occurred, it is desirable for the control device to execute additional fuel injection from the fuel injection valve.

[0013] According to this aspect, it is not necessary to equip the combustion chamber with a device for injecting other liquids other than fuel, such as a water injection valve. The latent heat of vaporization of the fuel introduced by the additional fuel injection from the fuel injection valve can lower the in-cylinder temperature and suppress abnormal combustion.

[0014] In the above engine control device, it is desirable for the control device to execute the additional injection at a timing earlier than the second crank angle.

[0015] According to this aspect, since the additional injection is executed at a timing earlier than the second crank angle at which abnormal combustion is predicted to occur, it is easier to further suppress abnormal combustion.

[0016] In the above engine control device, the control device may calculate a first integral value of the heat generation rate at the time of the first crank angle and predict a second integral value of the heat generation rate at the time of the second crank angle.

[0017] According to this aspect, in addition to the above three elements, the integral value of the heat generation rate is also added to the elements for predicting the occurrence of abnormal combustion. Therefore, it becomes possible to predict abnormal combustion with higher accuracy.

[0018] In the above-described engine control device, the control device includes a prediction processing unit having a prediction model that receives an input of explanatory variables and outputs a solution. The prediction processing unit preferably receives inputs of the first cylinder internal pressure, the first pressure change rate, and the first heat generation rate as the explanatory variables, and outputs an index for determining whether or not abnormal combustion occurs.

[0019] According to this aspect, a prediction model is applied for predicting the occurrence of abnormal combustion. The prediction model can be created, for example, by machine learning the relationship between the first cylinder internal pressure, the first pressure change rate, and the first heat generation rate at the time of the first crank angle and the occurrence of abnormal combustion. By applying the prediction model, an index for predicting the occurrence of abnormal combustion can be obtained only by inputting the explanatory variables at the time of the first crank angle during actual combustion control. Therefore, simplification of engine control can be achieved.

[0020] An engine control method according to another aspect of the present invention is an engine control method including a combustion chamber in a cylinder, a liquid injection valve that injects liquid into the combustion chamber, and an ignition device that ignites an air-fuel mixture formed in the combustion chamber. After an ignition operation by the ignition device, at a predetermined crank angle before a high-temperature oxidation reaction occurs, the cylinder internal pressure of the cylinder is detected. Based on the cylinder internal pressure, in the combustion chamber after the high-temperature oxidation reaction, it is predicted whether or not abnormal combustion occurs due to resonance between a main pressure wave generated by combustion of the air-fuel mixture by the ignition operation and a sub-pressure wave generated by self-ignition of a local high-temperature region in the unburned region of the air-fuel mixture. When it is determined that the abnormal combustion occurs, the liquid injection valve executes liquid injection at a predetermined timing after the high-temperature oxidation reaction.

[0021] According to this aspect, before the high-temperature oxidation reaction occurs in the combustion chamber, that is, before combustion occurs, it is determined whether abnormal combustion based on the resonance of the main pressure wave and the sub-pressure wave occurs after the start of the high-temperature oxidation reaction. Therefore, the occurrence of abnormal combustion can be predicted early. Accordingly, liquid injection can also be executed early. The latent heat of vaporization of the injected liquid can effectively suppress abnormal combustion such as knocking and detonation.

Advantages of the Invention

[0022] According to the present invention, in the control of an internal combustion engine, an engine control device and a control method capable of effectively suppressing knocking can be provided.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0024] Hereinafter, based on the drawings, an example of an engine control device according to an embodiment of the present invention will be described in detail.

[0025] [Overall Configuration of Engine] FIG. 1 is a system diagram showing the configuration of an engine system ES to which an engine control device according to an embodiment of the present invention is applied. The engine system ES includes a four-stroke engine body 1, an intake passage 20 for introducing combustion air into the engine body 1, and an exhaust passage 30 for discharging the exhaust generated in the engine body 1.

[0026] The engine body 1 is, for example, an in-line four-cylinder engine in which four cylinders 2 are arranged in series in a direction perpendicular to the plane of FIG. 1. The engine system ES is mounted on a vehicle, and the engine body 1 is used as a drive source for the vehicle. In the present embodiment, the engine body 1 is driven by receiving the supply of fuel containing gasoline. The engine body 1 has a cylinder block 3 in which cylinders 2 are formed, a cylinder head 4 provided on the upper surface of the cylinder block 3, and a piston 5 reciprocally accommodated in the cylinder 2.

[0027] Above the piston 5, a combustion chamber 6 is formed. As the combustion chamber 6, a so-called pent-roof type is exemplified. The ceiling surface of the combustion chamber 6 formed by the lower surface of the cylinder head 4 has a triangular roof shape composed of two inclined surfaces on the intake side and the exhaust side. On the crown surface of the piston 5, a cavity is formed in a region including the central portion thereof so as to be recessed on the side opposite to the cylinder head 4. The combustion chamber 6 is a space between the crown surface of the piston 5 and the ceiling surface of the combustion chamber 6 in the inner space of the cylinder 2.

[0028] The geometric compression ratio of the engine body 1, that is, the ratio of the volume of the combustion chamber 6 when the piston 5 is at the bottom dead center to the volume of the combustion chamber 6 when the piston 5 is at the top dead center is set to be 12 or more and 30 or less (for example, about 20). According to such an engine body 1 with a high compression ratio, high thermal efficiency can be achieved. On the other hand, abnormal combustion such as knocking and detonation tends to occur easily.

[0029] The cylinder head 4 is provided with an intake port 9, an exhaust port 10, an intake valve 11, and an exhaust valve 12. The intake port 9 is a port for introducing the air supplied from the intake passage 20 into the combustion chamber 6. The exhaust port 10 is a port for leading the exhaust generated in the cylinder 2 to the exhaust passage 30. Two intake ports 9 and two exhaust ports 10 are formed for each cylinder 2, respectively.

[0030] The intake valve 11 opens and closes the openings on the cylinder 2 side of the respective intake ports 9. The exhaust valve 12 opens and closes the openings on the cylinder 2 side of the respective exhaust ports 10. 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 a valve operating mechanism including a pair of camshafts disposed in the cylinder head 4. The valve operating mechanism for the intake valve 11 incorporates an intake valve variable mechanism 11a (see FIG. 2) capable of changing the opening and closing timing of the intake valve 11. The intake valve variable mechanism 11a changes the opening timing and closing timing of the intake valve 11 according to the operating conditions and the like. When the opening and closing timing of the intake valve 11 is changed, the effective compression ratio of the cylinder 2 changes.

[0031] The cylinder head 4 is further equipped with an injector 14 (fuel injection valve / liquid injection valve) and a spark plug 13 (ignition device). The injector 14 injects fuel into the combustion chamber 6. The injector 14 is attached to the cylinder head 4 such that the tip portion formed with an injection port projects from the vicinity of the center of the ceiling surface of the combustion chamber 6. A plurality of nozzles are provided in the tip portion of the injector 14. Fuel is injected in a conical shape centered on the central axis of the cylinder 2 from the nozzle located near the center of the ceiling surface of the combustion chamber 6 toward the crown surface of the piston 5. The injector 14 injects the fuel pumped from a high-pressure pump (not shown) into the combustion chamber 6.

[0032] The ignition plug 13 performs an ignition operation on the air-fuel mixture formed in the combustion chamber 6 by fuel injection from the injector 14. An electrode is provided at the tip of the ignition plug 13. The electrode discharges a spark into the air-fuel mixture and performs an ignition operation of imparting ignition energy to the air-fuel mixture. The tip of the ignition plug 13 is disposed near the center of the ceiling surface of the combustion chamber 6 so as to face the center of the combustion chamber 6.

[0033] In the intake passage 20, an air cleaner 21 and a throttle valve 22 are arranged in order from the upstream side. The air cleaner 21 includes a filter for removing foreign matters in the intake air. The throttle valve 22 is a valve for restricting the flow rate of the intake air. During the operation of the engine body 1, the throttle valve 22 is basically maintained at a fully open position or a position close thereto, and is closed only under limited operating conditions such as when the engine is stopped, thereby blocking the intake passage 20. A purification device 31 for purifying the exhaust gas is provided in the exhaust passage 30. The purification device 31 incorporates, for example, a three-way catalyst.

[0034] An EGR device 40 is attached to the exhaust passage 30. The EGR device 40 recirculates a part of the exhaust gas passing through the exhaust passage 30 to the intake passage 20 as EGR gas. The EGR device 40 includes an EGR passage 41, an EGR valve 42, and an EGR cooler 43. The EGR passage 41 communicates a portion of the intake passage 20 downstream of the throttle valve 22 with a portion of the exhaust passage 30 upstream of the purification device 31. The EGR valve 42 opens and closes the EGR passage 41. The EGR cooler 43 cools the EGR gas passing through the EGR passage 41. The EGR gas is cooled by the EGR cooler 43 and then recirculated to the intake passage 20.

[0035] [Engine control system] FIG. 2 is a block diagram showing the engine control system. The engine system ES of the present embodiment is comprehensively controlled by a PCM (Power Train Control Module) 100. The PCM 100 is an example of the engine control device according to the present invention. The PCM 100 is a microprocessor composed of a CPU, a ROM, a RAM, and the like.

[0036] The vehicle is provided with various sensors, and the PCM 100 is electrically connected to these sensors. In FIG. 2, as sensors, a crank angle sensor SN1, an air flow sensor SN2, an intake air temperature sensor SN3, a cylinder internal pressure sensor SN4, and an accelerator opening sensor SN5 are illustrated.

[0037] The crank angle sensor SN1 is attached to the cylinder block 3 and detects the rotation angle of the crankshaft 7. Based on the rotation angle, the engine speed and the vehicle speed are detected. The air flow sensor SN2 and the intake air temperature sensor SN3 are arranged in the intake passage 20. The air flow sensor SN2 detects the amount of air inhaled into each cylinder 2 through the intake passage 20. The intake air temperature sensor SN3 detects the temperature of the air passing through the intake passage 20. The cylinder internal pressure sensor SN4 is attached to each cylinder 2 one by one and detects the cylinder internal pressure which is the pressure in the combustion chamber 6. In the present embodiment, based on the cylinder internal pressure data output by the cylinder internal pressure sensor SN4, a process of predicting the occurrence of abnormal combustion is performed. The accelerator opening sensor SN5 detects the opening of an accelerator pedal (not shown) operated by the driver.

[0038] The PCM 100 executes various calculations based on the input signals from these sensors SN1 to SN5 etc., and controls each part of the engine such as the spark plug 13, the injector 14, the throttle valve 22, the EGR valve 42, and the intake valve variable mechanism 11a.

[0039] FIG. 3 is a control map of the engine body 1 with the engine speed on the horizontal axis and the engine load on the vertical axis. In the control map, the operation region of the engine is partitioned according to the control content. Specifically, it is partitioned into a low load region B where the engine load is equal to or less than a preset reference load Tq1, and a high load region A where the engine load is higher than the reference load Tq1. The high load region A is further partitioned into a high load low speed region A1 where the engine speed is less than a preset reference speed N1, and a high load high speed region A2 where the engine speed is equal to or greater than the reference speed N1.

[0040] The low-load region B is an area where abnormal combustion such as knocking and detonation is relatively unlikely to occur, while the high-load region A is an area where abnormal combustion is likely to occur. In this embodiment, since the geometric compression ratio of the engine body 1 is set to a high compression ratio of 15 or more, the temperature in the combustion chamber 6 is raised to a very high temperature. Therefore, abnormal combustion is particularly likely to occur. The control for suppressing abnormal combustion, which will be described later, is executed exclusively in the high-load region A.

[0041] In the low-load region B and the high-load low-speed region A1, compression self-ignition combustion (SPCCI combustion, SPCCI: Spark Controlled Compression Ignition) assisted by ignition of the ignition plug 13 is executed. In compression self-ignition combustion, first, fuel is injected into the combustion chamber 6 from the injector 14 before top dead center (TDC). The injected fuel is mixed with air by the time it reaches the vicinity of TDC. Discharge is performed from the ignition plug 13 in the vicinity of TDC to this air-fuel mixture formed in the combustion chamber 6. Thereby, the air-fuel mixture around the ignition plug 13 is forcibly ignited. Then, the flame propagates from the vicinity of the ignition plug 13 to the surroundings, and the surrounding air-fuel mixture is heated up and self-ignites.

[0042] On the other hand, in the high-load high-speed region A2, since it becomes difficult to cause the air-fuel mixture to self-ignite at a desired timing, SI combustion (spark ignition combustion, SI: Spark Ignition) employed in a normal gasoline engine is executed. SI combustion is a combustion mode in which almost the entire air-fuel mixture is burned by flame propagation. Discharge is performed from the ignition plug 13 in the vicinity of TDC, and the air-fuel mixture around the ignition plug 13 is forcibly ignited. Then, the flame propagates from around the ignition plug 13 to the surroundings, and the remaining air-fuel mixture is forcibly burned by flame propagation.

[0043] In the low load region B, the fuel quantity injected into the combustion chamber 6 by the injector 14 is set so that the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 becomes the stoichiometric air-fuel ratio. Specifically, the PCM 100 calculates the air quantity corresponding to the required engine torque, and changes the opening degrees of the throttle valve 22 and the EGR valve 42 so that this air quantity is achieved. Next, the PCM 100 calculates the air quantity introduced into the combustion chamber 6, calculates the quantity of fuel for which the air-fuel ratio becomes the stoichiometric air-fuel ratio with respect to this air quantity, and sets it as the injection quantity. Also in the high load region A, basically, the fuel quantity is set so that the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 becomes the stoichiometric air-fuel ratio.

[0044] [Mechanism of abnormal combustion] Subsequently, the mechanism of abnormal combustion occurring in the combustion chamber 6, which causes abnormal noise and vibration, will be described. Here, among the abnormal combustions in the above-described SI combustion, detonation is focused on. FIGS. 4(A) to 4(C) are schematic diagrams for explaining the mechanism of detonation occurrence. Detonation is an abnormal combustion in which the air-fuel mixture in the combustion chamber 6 self-ignites and burns explosively at an abnormally high flame propagation speed. When detonation occurs, not only does the noise and vibration level deteriorate, but it also has an adverse effect on the durability of the engine.

[0045] FIG. 4(A) shows a state in which the air-fuel mixture in the combustion chamber 6 is not completely burned, and a hot spot HS has occurred in the unburned region AR2 in a situation where a burned region AR1 and an unburned region AR2 exist. The burned region AR1 gradually expands in the combustion chamber 6 by flame propagation combustion triggered by the ignition operation of the ignition plug 13. Along with this flame propagation combustion, a pressure wave is generated. The pressure wave is shown as the main pressure wave PW1 in FIGS. 4(A) to 4(C). The main pressure wave PW1 is a relatively large pressure wave generated based on the flame propagation combustion, which is the main combustion in the combustion chamber 6, and travels back and forth in the combustion chamber 6.

[0046] The generation of the burned region AR1 causes the temperature and pressure in the unburned region AR2 to also increase. In the unburned region AR2, there may be a region where the temperature is locally higher compared to the surroundings. Such a locally high-temperature region is the hot spot HS. Since the hot spot HS is at a high temperature, it is an area prone to auto-ignition. In Fig. 4(A), the sub-pressure wave PW2 generated by the auto-ignition of the hot spot HS is shown. The sub-pressure wave PW2 is a small pressure wave compared to the main pressure wave PW1. Note that the auto-ignition of the hot spot HS can be a cause of knocking.

[0047] Fig. 4(B) shows a state where the chemical reaction CR is rapidly progressing in the unburned region AR2. The chemical reaction CR is mainly a high-temperature oxidation reaction. The high-temperature oxidation reaction is induced by the temperature increase associated with the auto-ignition of the hot spot HS. The high-temperature oxidation reaction is a reaction that generates high thermal energy and is essentially a combustion reaction. Such a chemical reaction CR also generates the sub-pressure wave PW2.

[0048] Fig. 4(C) shows a state where the resonance wave PW3 is generated due to the resonance between the main pressure wave PW1 and the sub-pressure wave PW2. The sub-pressure wave PW2 propagates from the regions of the hot spot HS and the chemical reaction CR to the surroundings and travels back and forth in the combustion chamber 6 while being reflected by the wall surface of the combustion chamber 6. Therefore, the sub-pressure wave PW2 may overlap with the main pressure wave PW1 that also travels back and forth in the combustion chamber 6, generating the resonance wave PW3. The resonance wave PW3 may become a large pressure wave exceeding a certain threshold value. Such a rapid progress of the chemical reaction CR to the generation of a large pressure wave is detonation, which is an explosive combustion in the unburned region AR2. Note that if the magnitude of the pressure wave does not exceed the threshold value, it may end up as simple knocking. Simply put, the larger the scale of the auto-ignition of the hot spot HS, the more likely it is to transition to detonation. Either detonation or knocking invariably turns into abnormal combustion accompanied by abnormal noise and abnormal vibration, and suppression of such abnormal combustion is required.

[0049] To suppress abnormal combustion, additional fuel injection is effective. By cooling the inside of the cylinder with the latent heat of vaporization of the additionally injected fuel, abnormal combustion can be suppressed. The abnormal combustion shown in FIGS. 4(A) to 4(C) occurs after the start of flame propagation combustion, which is the main combustion in the combustion chamber 6. The fluctuation of the in-cylinder pressure associated with the self-ignition of the hot spot HS can be detected by the in-cylinder pressure sensor SN4. However, even if the in-cylinder pressure fluctuation due to self-ignition can be detected after the start of flame propagation combustion, it is often too late to suppress abnormal combustion within the same cycle. That is, it is difficult to perform a series of operations of causing the injector 14 to perform additional injection when it is determined whether the in-cylinder pressure sensor SN4 actually detects the in-cylinder pressure fluctuation due to self-ignition and the occurrence of abnormal combustion is predicted based on the in-cylinder pressure fluctuation before the occurrence of abnormal combustion.

[0050] [Prediction of Abnormal Combustion Occurrence] In the present embodiment, in order to solve the above problems, before combustion starts in the combustion chamber 6, that is, before the high-temperature oxidation reaction occurs, it is determined whether abnormal combustion will occur in the current combustion cycle. FIG. 5 is a graph showing the relationship between the in-cylinder pressure p and the crank angle CAD, and shows the prediction period of abnormal combustion, the prediction target period, and the timing of additional fuel injection. FIG. 5 shows a normal combustion pressure waveform and an abnormal combustion pressure waveform when combustion abnormalities such as detonation occur.

[0051] In the latter stage of the compression process in the engine body 1, for example, in the vicinity of the crank angle CAD = -10 deg, since the piston 5 approaches the TDC, the temperature and pressure in the combustion chamber 6 increase. When fuel is injected into the combustion chamber 6, a low-temperature oxidation reaction occurs from the latter stage of the compression process. The low-temperature oxidation reaction is a slow oxidation reaction that occurs before the high-temperature oxidation reaction accompanied by flame combustion. FIG. 5 shows an example in which the ignition operation IGT by the ignition plug 13 is executed at CAD = -6.5 deg, and the high-temperature oxidation reaction occurs after CAD = 3 deg. The in-cylinder pressure of the abnormal combustion pressure waveform begins to increase compared to the normal combustion pressure waveform slightly before the start of the high-temperature oxidation reaction, becomes significant in the vicinity of CAD = 10 deg, and reaches a peak in the vicinity from CAD = 15 deg to 20 deg.

[0052] In this embodiment, the period during which a low-temperature oxidation reaction occurs in the combustion chamber 6 is treated as the "abnormal combustion prediction period". Further, when abnormal combustion occurs after a high-temperature oxidation reaction and it is assumed that the in-cylinder pressure will become particularly large, the period is defined as the "prediction target period". Then, based on the in-cylinder state quantity of the combustion chamber 6 measured at an arbitrarily determined first crank angle during the "abnormal combustion prediction period", the in-cylinder state quantity at an arbitrary second crank angle during the "prediction target period" is predicted. FIG. 5 shows an example in which the second crank angle is set to CAD = 15 deg.

[0053] As a result of the prediction process, when it is determined that abnormal combustion will occur at the second crank angle of the current cycle, additional fuel injection is executed to the injector 14. The additional fuel injection is a fuel injection performed to cool the inside of the combustion chamber 6 in addition to the original fuel injection necessary to perform combustion that satisfies the required torque. By cooling the inside of the cylinder due to the latent heat of vaporization of the injected fuel, the self-ignition and chemical reaction CR of the hot spot HS leading to detonation can be suppressed. According to this embodiment, since the occurrence of abnormal combustion is predicted early before the high-temperature oxidation reaction, additional fuel injection can also be executed early, and abnormal combustion is easily suppressed.

[0054] The first crank angle can be set within the abnormal combustion prediction period after the low-temperature oxidation reaction occurs and before the high-temperature oxidation reaction occurs. When the low-temperature oxidation reaction starts, characteristic behaviors of in-cylinder state quantities such as the in-cylinder pressure are likely to appear. Further, the hot spot HS, which is a sign of the occurrence of abnormal combustion, often occurs during the low-temperature oxidation reaction period. Even if self-ignition does not occur, the generation of the hot spot HS itself leads to fluctuations in the in-cylinder pressure, so characteristic behaviors of the in-cylinder state quantity can occur even during the low-temperature oxidation reaction period. The first crank angle is preferably the crank angle immediately before the high-temperature oxidation reaction occurs. This is because the above characteristic behavior is easier to capture when it is closer to the prediction target period. In FIG. 5, CAD = 3 deg, which is the crank angle immediately before the high-temperature oxidation reaction occurs, is treated as the first crank angle.

[0055] Also, it is desirable that the first crank angle be set within the period after the ignition operation by the ignition plug 13. Triggered by the ignition operation, a low-temperature oxidation reaction may occur in the combustion chamber 6, or an already occurring low-temperature oxidation reaction may be promoted. Therefore, it becomes easier to detect characteristic in-cylinder state quantities associated with the low-temperature oxidation reaction. FIG. 5 also shows an example in which the ignition operation IGT is performed at CAD = -6.5 deg, and the first crank angle is set at CAD = 3 deg on the retard side from the ignition operation IGT.

[0056] When entering the high-temperature oxidation reaction period, the hot spot HS may grow and cause self-ignition. As described with reference to FIGS. 4(A) to 4(C), when the sub-pressure wave PW2 generated by the self-ignition of the hot spot HS resonates with the main pressure wave PW1 generated by the original flame propagation combustion, detonation occurs. In order to suppress detonation, it is desirable to execute additional fuel injection at a timing earlier than the second crank angle at which the in-cylinder pressure becomes the largest. FIG. 5 shows an example in which additional fuel injection is performed at the timing of CAD = 10 deg. By the additional fuel injection, as shown by the dotted line in FIG. 5, the generation pressure of the abnormal combustion pressure waveform can be suppressed.

[0057] In this embodiment, the in-cylinder pressure sensor SN4 is used as a sensing element for acquiring the in-cylinder state quantity of the combustion chamber 6. Based on the in-cylinder pressure detected by the in-cylinder pressure sensor SN4, detonation caused by the self-ignition of the hot spot HS is predicted.

[0058] The heat generation rate dQ / dθ, which is the time change of the heat generation amount Q in the cylinder, can be expressed by the following differential equation. Here, p is the in-cylinder pressure, V is the volume of the combustion chamber 6, and k is the gas composition in the cylinder.

Equation

[0059] In the above differential equation, since the in-cylinder gas composition k cannot be measured, it is treated as constant (dk / dθ = 0). Then, the heat generation rate dQ / dθ is represented by the following differential equation. By solving this differential equation, the in-cylinder pressure p can be obtained. Therefore, the following differential equation is regarded as the basic equation for the in-cylinder pressure. [Number]

[0060] Figure 6 is a diagram showing the variables necessary for predicting abnormal combustion. From the above differential equation, the in-cylinder pressure p is related to the initial value P which is the in-cylinder pressure p at a certain time, dp / dθ, dQ / dθ, the volume V of the combustion chamber 6, and dV / dθ. Here, since the volume V and dV / dθ do not vary between combustion cycles, they can be ignored. Therefore, the in-cylinder pressure p can be predicted if the initial value P, dp / dθ, and dQ / dθ are known. That is, at the time point of the first crank described above, if the in-cylinder pressure p (the first in-cylinder pressure) detected by the in-cylinder pressure sensor SN4, dp / dθ (the first pressure change rate), and dQ / dθ (the first heat generation rate) are obtained, the in-cylinder pressure p (the second in-cylinder pressure), dp / dθ (the second pressure change rate), and dQ / dθ (the second heat generation rate) at the time point of the second crank angle can be predicted. Then, based on whether or not these in-cylinder state quantities at the time point of the second crank angle exceed a predetermined evaluation index threshold value, it can be determined whether abnormal combustion occurs in the current combustion cycle. Based on this determination result, the necessity of executing additional fuel injection is determined. That is, when it is determined that abnormal combustion occurs, additional fuel injection is executed.

[0061] [Control for Suppressing Abnormal Combustion] Figure 7 is a functional block diagram showing an example of the functional configuration of the PCM 100 that executes the abnormal combustion suppression control of the present embodiment. When the abnormal combustion suppression control program is executed, the PCM 100 operates to functionally include a variable calculation unit 51, a prediction processing unit 52, a prediction model 52M, a determination unit 53, and an injection control unit 54.

[0062] The variable calculation unit 51 calculates variables necessary for predicting abnormal combustion. The variable calculation unit 51 acquires measurement data related to the in-cylinder pressure from the in-cylinder pressure sensor SN4 at the time of the first crank angle set within the abnormal combustion prediction period before the high-temperature oxidation reaction occurs in the combustion chamber 6. In the present embodiment, the first crank angle is CAD = 3 deg immediately before the high-temperature oxidation reaction occurs. Based on the acquired measurement data, the variable calculation unit 51 calculates, as the variables, the in-cylinder pressure p (first in-cylinder pressure), dp / dθ (first pressure change rate), and dQ / dθ (first heat generation rate) at the time of the first crank angle. dp / dθ and dQ / dθ can be derived from the above-described in-cylinder pressure basic formula.

[0063] As variables used for predicting abnormal combustion, in addition to the above-described in-cylinder pressure p, dp / dθ, and dQ / dθ, other variables may be used. It is desirable that the other variables can be derived from the measurement data of the in-cylinder pressure sensor SN4, but they may also be derived from the measurement data of other sensor elements. For example, the integrated value of the heat generation rate may be added as a variable for predicting the occurrence of abnormal combustion. In this case, the variable calculation unit 51 calculates the integrated value (first integrated value) of the heat generation rate dQ / dθ, that is, the heat generation amount, at the time of the first crank angle. The integration period is a fixed period on the advancing angle side from the first crank angle. For example, the period from CAD = 0 deg (TDC) to CAD = 3 deg (first crank angle) can be set as the integration period. In addition, the differences between dp / dθ and dQ / dθ at CAD = 0 deg and dp / dθ and dQ / dθ at CAD = 3 deg may be calculated and used as variables for predicting abnormal combustion.

[0064] The prediction processing unit 52 derives the predicted values of the variables during the prediction target period after the high-temperature oxidation reaction occurs, based on the variables calculated by the variable calculation unit 51. Specifically, the prediction processing unit 52 performs a process of predicting the in-cylinder pressure p, dp / dθ, and dQ / dθ at the time of the second crank angle (CAD = 15 deg), based on the in-cylinder pressure p, dp / dθ, and dQ / dθ calculated by the variable calculation unit 51. When the variable calculation unit 51 calculates other variables, such as the integrated value of the heat generation rate, the prediction processing unit 52 also performs a process of predicting the integrated value of the heat generation rate (the second integrated value) at the time of the second crank angle.

[0065] The prediction processing unit 52 has a prediction model 52M that performs the above-described prediction processing. The prediction model 52M is a model formula that receives an input of explanatory variables and outputs a solution. The prediction model 52M receives, as explanatory variables, at least the inputs of the in-cylinder pressure p, dp / dθ, and dQ / dθ at the time of the first crank angle described above, and outputs an index for determining whether or not the abnormal combustion occurs.

[0066] As the prediction model 52M, for example, a random forest model can be used. Random Forest is a machine learning algorithm that combines two techniques of "decision tree" and "ensemble learning". As the explanatory factors of the decision tree, data extractable from the output of the in-cylinder pressure sensor SN4 are used, and whether or not abnormal combustion actually occurs is used as the target variable. In the present embodiment, a large number of decision tree models associating the data including the in-cylinder pressure p, dp / dθ, and dQ / dθ described above with the occurrence or non-occurrence of abnormal combustion are created. In ensemble learning, learning proceeds by majority vote from the judgment results of a large number of decision tree models. In an actual driving scene, the prediction processing unit 52 uses the random forest model created by the above-described method, receives the inputs of the in-cylinder pressure p, dp / dθ, and dQ / dθ at the time of the first crank angle (CAD = 3 deg), and outputs an evaluation index. The evaluation index is created based on the in-cylinder pressure p, dp / dθ, and dQ / dθ at the time of the second crank angle (CAD = 15 deg).

[0067] Based on the evaluation index output by the prediction processing unit 52, the determination unit 53 determines whether abnormal combustion such as detonation or knocking occurs at the time of the second crank angle. For example, a determination threshold value is set in advance for the evaluation index. The determination unit 53 determines whether abnormal combustion occurs based on whether the output evaluation index exceeds the determination threshold value.

[0068] The injection control unit 54 controls the injector 14 to execute fuel injection into the combustion chamber 6 at the necessary timing. For example, when performing SI combustion, the injection control unit 54 substantially completes fuel injection on the advanced angle side from the ignition timing of the ignition plug 13. In addition to such normal fuel injection, when the determination unit 53 predicts the occurrence of abnormal combustion, the injection control unit 54 executes additional fuel injection from the injector 14. Since the latent heat of vaporization of the fuel introduced into the combustion chamber 6 by the additional fuel injection lowers the in-cylinder temperature, abnormal combustion can be suppressed.

[0069] The additional fuel injection is preferably executed at a timing earlier than the second crank angle. If the additional injection is executed at a timing earlier than the second crank angle at which abnormal combustion is predicted to occur, abnormal combustion can be effectively suppressed. In FIG. 5, CAD = 10 deg is illustrated as the timing of the additional fuel injection.

[0070] The injection for lowering the in-cylinder temperature may be an injection of a liquid other than fuel. For example, a water injection device capable of injecting water into the combustion chamber 6 may be provided in the cylinder block 3, and water injection may be executed when abnormal combustion is predicted to occur. However, if the mode is such that additional fuel injection is performed by the injector 14 as in the present embodiment, it is preferable because the installation of a water injection device or the like can be omitted.

[0071] [Control Flow] FIG. 8 is a flowchart showing an example of abnormal combustion suppression control by the PCM 100. During the operation of the engine body 1, the PCM 100 acquires the measured value of the in-cylinder pressure sensor SN4 at the time of the first crank angle (CAD = 3 deg) (step S1). Based on the acquired measured value, the variable calculation unit 51 calculates the explanatory variables to be applied to the prediction model 52M (step S2). Specifically, the in-cylinder pressure p (the first in-cylinder pressure), dp / dθ (the first pressure change rate), and dQ / dθ (the first heat generation rate) at the time of the first crank angle are calculated (step S2).

[0072] Next, the prediction processing unit 52 applies the explanatory variables calculated in step S2 to the prediction model 52M, and predicts the in-cylinder pressure p (the second in-cylinder pressure), dp / dθ (the second pressure change rate), and dQ / dθ (the second heat generation rate) at the time of the second crank angle (CAD = 15 deg) (step S3). Actually, the prediction model 52M outputs an evaluation index indicating the degree of occurrence of abnormal combustion at the second crank angle based on these predicted values.

[0073] Subsequently, the determination unit 53 determines whether abnormal combustion occurs at the second crank angle based on the output of the prediction model 52M (step S4). When it is determined that abnormal combustion occurs (YES in step S4), the injection control unit 54 causes the injector 14 to perform additional fuel injection at a stage faster than the second crank angle in addition to normal fuel injection (step S5).

[0074] Thereafter, the PCM 100 determines whether there is an engine stop instruction for the engine body 1 (step S6). If there is an engine stop instruction (YES in step S6), the PCM 100 ends the process. If there is no engine stop instruction (NO in step S6), the process returns to step S1 and is repeated. Even when it is determined that abnormal combustion does not occur (NO in step S4), the process returns to step S1 and is repeated.

[0075] Summarizing the above-described engine control method by the PCM 100 along with the phenomena occurring in the combustion chamber 6, it is as follows. After the ignition operation by the spark plug 13, the in-cylinder pressure of the cylinder 2 is detected at a predetermined crank angle before the high-temperature oxidation reaction occurs in the combustion chamber 6. (2) Based on the detected in-cylinder pressure, it is predicted whether a large resonance wave PW3 is generated due to the resonance of the main pressure wave PW1 and the sub-pressure wave PW2 in the combustion chamber 6 after the high-temperature oxidation reaction. The main pressure wave PW1 is generated in the burned area AR1 by the combustion of the air-fuel mixture due to the ignition operation. The sub-pressure wave PW2 is generated by the self-ignition of a local high-temperature area, that is, a hot spot HS, in the unburned area AR2 of the air-fuel mixture. The resonance wave PW3 is generated by the resonance of the main pressure wave PW1 and the sub-pressure wave PW2 (see Fig. 4). The generation of a large resonance wave PW3 leads to a large abnormal noise and abnormal vibration associated with abnormal combustion. (3) When it is determined that abnormal combustion has occurred, at a predetermined timing after the high-temperature oxidation reaction, the injector 14 performs additional fuel injection. The injected fuel is immediately vaporized in the combustion chamber 6, and the combustion chamber 6 is cooled by the latent heat of vaporization.

[0076] According to this control method, before the high-temperature oxidation reaction occurs in the combustion chamber 6, that is, before combustion occurs, it is determined whether abnormal combustion based on the resonance of the main pressure wave PW1 and the sub-pressure wave PW2 occurs after the start of the high-temperature oxidation reaction. Therefore, the occurrence of abnormal combustion can be predicted early. For this reason, additional fuel injection to suppress the self-ignition of the hot spot HS can also be executed early, and abnormal combustion can be suppressed.

Description of symbols

[0077] 1 Engine body 1 2 Cylinder 6 Combustion chamber 13 Spark plug (ignition device) 14 Injector (fuel injection valve / liquid injection valve) 100 PCM (engine control device) 52 Prediction processing unit 52M Prediction model ES Engine system AR1 Burned area 1 AR2 Unburned area HS Hot Spot PW1 Main Pressure Wave PW2 Sub Pressure Wave PW3 Resonance Wave SN4 In-cylinder Pressure Sensor

Claims

1. A control device for an engine, comprising a combustion chamber in a cylinder and a liquid injection valve for injecting a liquid into the combustion chamber, wherein the control device calculates a first in-cylinder pressure, a first pressure change rate, and a first heat generation rate of the cylinder at a first crank angle before a high-temperature oxidation reaction occurs in the combustion chamber, predicts a second in-cylinder pressure, a second pressure change rate, and a second heat generation rate at a second crank angle after the high-temperature oxidation reaction occurs based on the first in-cylinder pressure, the first pressure change rate, and the first heat generation rate, determines whether abnormal combustion occurs in the current combustion cycle based on the second in-cylinder pressure, the second pressure change rate, and the second heat generation rate, and when it is determined that the abnormal combustion occurs, causes the liquid injection valve to execute liquid injection. A control device for an engine.

2. In the control device for an engine according to claim 1, the first crank angle is set within a period from after a low-temperature oxidation reaction occurs in the combustion chamber to before the high-temperature oxidation reaction occurs. A control device for an engine.

3. In the control device for an engine according to claim 1, the engine further includes an ignition device for igniting an air-fuel mixture formed in the combustion chamber, and the first crank angle is set within a period after an ignition operation by the ignition device. A control device for an engine.

4. In the control device for an engine according to any one of claims 1 to 3, the liquid injection valve is a fuel injection valve for injecting fuel into the combustion chamber, and when it is determined that the abnormal combustion occurs, the control device causes the fuel injection valve to execute additional fuel injection. A control device for an engine.

5. In the control device for an engine according to claim 4, the control device causes the additional injection to be executed at a timing earlier than the second crank angle. A control device for an engine.

6. In the control device for an engine according to any one of claims 1 to 3, the control device calculates a first integral value of the heat generation rate at the first crank angle and predicts a second integral value of the heat generation rate at the second crank angle. A control device for an engine.

7. In the control device for an engine according to any one of claims 1 to 3, the control device includes a prediction processing unit having a prediction model that receives an input of explanatory variables and outputs a solution. The prediction processing unit receives inputs of the first cylinder internal pressure, the first pressure change rate, and the first heat generation rate as the explanatory variables, and outputs an index for determining whether abnormal combustion occurs, which is a control device for an engine.

8. A control method for an engine including a combustion chamber in a cylinder, a liquid injection valve for injecting a liquid into the combustion chamber, and an ignition device for igniting an air-fuel mixture formed in the combustion chamber, detecting the cylinder internal pressure of the cylinder at a predetermined crank angle point before a high-temperature oxidation reaction occurs in the combustion chamber after an ignition operation by the ignition device; predicting whether abnormal combustion occurs due to resonance between a main pressure wave generated by combustion of the air-fuel mixture by the ignition operation and a sub-pressure wave generated by self-ignition of a local high-temperature region in the unburned region of the air-fuel mixture in the combustion chamber after the high-temperature oxidation reaction, based on the cylinder internal pressure; A control method for an engine, in which when it is determined that abnormal combustion occurs, the liquid injection valve performs liquid injection at a predetermined timing after the high-temperature oxidation reaction.

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