JP6866871B2 - Engine control device and control method - Google Patents

Description

The technology disclosed herein belongs to the technical field relating to engine control devices and control methods.

Conventionally, it has been known that abnormal combustion called knocking occurs in an engine. When knocking occurs, there is a risk of increased noise and damage to the piston and the like. Therefore, in the field of engines, measures are taken to suppress knocking.

For example, in Cited Document 1, when knocking is detected, the ignition timing is retarded based on the load of the engine, and the air-fuel ratio is changed to the lean side to suppress the occurrence of knocking. It is disclosed.

Further, Cited Document 2 discloses that the occurrence of knocking is suppressed by adjusting the fuel injection amount so that the air-fuel ratio becomes lean before the compression top dead center.

Japanese Unexamined Patent Publication No. 2008-291758 Japanese Unexamined Patent Publication No. 2012-041246

By the way, in an engine, it is known that a low-temperature oxidation reaction accompanied by heat generation occurs during a compression stroke before a high-temperature oxidation reaction in which an air-fuel mixture ignites and burns in a combustion chamber occurs. As a result of diligent research by the inventors of the present application, it was found that there is a relationship between the magnitude of knocking and the reaction amount of the low temperature oxidation reaction. Specifically, it was found that a low-temperature oxidation reaction is likely to occur, and that the larger the reaction amount, the greater the knocking. Therefore, if the reaction amount of the low-temperature oxidation reaction can be appropriately detected or estimated and the knocking magnitude can be estimated, it is possible to take appropriate measures according to the knocking magnitude.

The reaction amount of the low temperature oxidation reaction can be estimated, for example, by detecting a change in the in-cylinder pressure. However, when the change in the in-cylinder pressure is small, it becomes difficult to accurately estimate the reaction amount of the low temperature oxidation reaction. Further, even if the in-cylinder pressure changes to the extent that the reaction amount of the low-temperature oxidation reaction can be sufficiently estimated, if the low-temperature oxidation reaction occurs immediately before the ignition of the air-fuel mixture in the combustion chamber, knocking occurs. The period during which countermeasures can be taken will be shortened. As a result, knocking countermeasures may not be properly implemented.

The technique disclosed here has been made in view of these points, and the purpose thereof is to estimate the reaction amount of the low temperature oxidation reaction generated in the combustion chamber of the engine early and accurately. The purpose is to be able to appropriately suppress knocking.

In order to solve the above problems, the technique disclosed here has a cylinder in which a combustion chamber is formed and a crankshaft that is rotationally driven by the reciprocating motion of a piston fitted in the cylinder, and produces gasoline. Targeting an engine control device that burns an air-fuel mixture containing fuel and air in the combustion chamber, an ignition plug configured to ignite the air-fuel mixture in the combustion chamber and pressure in the cylinder are detected. Only when the in-cylinder pressure detecting means, the crank angle detecting means for detecting the crank angle, and the engine load is a high load equal to or higher than a predetermined load, the air-fuel mixture in the cylinder is activated before the middle stage of the combustion stroke. When one ignition is executed and at least the engine load is a high load equal to or higher than the predetermined load, the second ignition by the ignition plug is executed in the vicinity of the compression top dead point separately from the first ignition. and ignition control means for controlling the ignition plug, which is detected by the cylinder pressure detecting means, based on the pressure in the cylinder in the period before a and ignition compression stroke late, caused by the first ignition, the combustion The reaction amount of the low-temperature oxidation reaction amount estimation means for estimating the reaction amount of the low-temperature oxidation reaction of the air-fuel mixture in the room and the reaction amount of the low-temperature oxidation reaction estimated by the above-mentioned low-temperature oxidation reaction amount estimation means are equal to or larger than the preset specific reaction amount. When the above is the case, the knocking suppression control means for executing the knocking suppression control for suppressing the knocking in the combustion chamber is provided .

That is, as a result of diligent studies by the inventors of the present application, it was found that if the air-fuel mixture in the combustion chamber is activated in advance by ignition by a spark plug, the reaction start time of the low-temperature oxidation reaction is accelerated. It was also found that by activating the air-fuel mixture in the combustion chamber in advance, the change in the in-cylinder pressure based on the low-temperature oxidation reaction becomes large, and the reaction amount of the low-temperature oxidation reaction can be easily estimated.

Therefore, before the middle of the compression stroke, the air-fuel mixture in the combustion chamber is activated in advance by executing the first ignition by the spark plug so that the air-fuel mixture in the cylinder is activated. This makes it possible to generate a low temperature oxidation reaction of an estimated size at the earliest possible time in the late compression stroke and in the pre-ignition period. As a result, the reaction amount of the low temperature oxidation reaction can be estimated early and accurately. Then, knocking can be appropriately suppressed by executing the knocking suppression control based on the estimated reaction amount of the low temperature oxidation reaction.

In the control device of the engine, the ignition start time of the first ignition by the ignition control means may be the time within the period on the most advanced side when the period of the compression stroke is divided into three equal parts.

According to this configuration, by activating the air-fuel mixture as early as possible in the compression stroke, the activated air-fuel mixture diffuses throughout the combustion chamber, making it easy for a low-temperature oxidation reaction to occur in the latter half of the compression stroke. Can be done. As a result, the reaction amount of the low-temperature oxidation reaction can be estimated more accurately, and knocking can be suppressed more effectively.

In the engine control device, the ignition control means is described when the operating state of the engine is such that the engine load is a high load equal to or higher than the predetermined load and the engine speed is higher than the predetermined speed. It may be configured to perform a first ignition.

That is, when the engine load is high and the engine speed is high, the actual time from the occurrence of the low temperature oxidation reaction to the start of the high temperature oxidation reaction of the air-fuel mixture is short. Therefore, at high load and high rotation of the engine, the low temperature oxidation reaction itself tends to be small, and further, the actual time from estimating the reaction amount of the low temperature oxidation reaction to executing the knocking suppression control is short. Therefore, it is highly necessary to estimate the low temperature oxidation reaction at an early stage when the engine has a high load and a high rotation speed. Therefore, by executing the first ignition at the time of high load and high rotation of the engine, the effect of estimating the reaction amount of the low temperature oxidation reaction early and accurately can be more appropriately exhibited.

In one embodiment of the engine control device, the knocking suppression control is a control for supplying a cooling medium to the combustion chamber in the first half of a period in which a high temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber.

That is, knocking occurs when the air-fuel mixture existing in the outer peripheral portion of the combustion chamber or the like locally becomes hot and self-ignites. Therefore, in the first half of the period in which the high-temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber, a cooling medium is supplied to the combustion chamber to suppress the generation of a local high-temperature region in the combustion chamber. As a result, knocking can be appropriately suppressed.

In the above embodiment, the knocking suppression control means may be configured to increase the supply amount of the cooling medium as the reaction amount of the low temperature oxidation reaction increases in the knocking suppression control.

That is, in order for the low temperature oxidation reaction to occur, it is a condition that at least one of the temperature and the pressure in the combustion chamber is high. Therefore, the fact that the reaction amount of the low-temperature oxidation reaction is large means that during the high-temperature oxidation reaction of the air-fuel mixture, the inside of the combustion chamber, particularly near the outer peripheral edge portion, tends to be in a high temperature and high pressure state. Therefore, the larger the reaction amount of the low temperature oxidation reaction, the larger the supply amount of the cooling medium. Thereby, knocking can be suppressed more effectively.

In another aspect of the technique disclosed herein, the fuel comprises a cylinder in which a combustion chamber is formed and a crankshaft that is rotationally driven by the reciprocating motion of a piston fitted in the cylinder. An ignition plug configured to ignite the air-fuel mixture in the combustion chamber and an in-cylinder pressure detecting means for detecting the pressure in the cylinder, targeting an engine control device that burns the air-fuel mixture with the air in the combustion chamber. The crank angle detecting means for detecting the crank angle, the ignition controlling means for controlling the ignition by the ignition plug, and the in-cylinder in the cylinder during the period after the compression stroke and before the ignition detected by the in-cylinder pressure detecting means. Based on the pressure, the low-temperature oxidation reaction amount estimating means for estimating the reaction amount of the low-temperature oxidation reaction of the air-fuel mixture in the combustion chamber and the low-temperature oxidation reaction amount estimated by the low-temperature oxidation reaction amount estimating means are preliminarily determined. When the amount is equal to or more than the set specific reaction amount, the knocking suppression control means for executing the knocking suppression control for suppressing knocking in the combustion chamber is provided, and the ignition control means has a high engine load of a predetermined load or more. When it is a load, the first ignition by the ignition plug can be executed so that the air-fuel mixture in the cylinder is activated before the middle stage of the compression stroke, and the ignition control means is the first ignition. Separately, it is configured to execute the second ignition by the ignition plug in the vicinity of the compression top dead point, and the knocking suppression control is the second ignition in order to delay the ignition of the air-fuel mixture in the combustion chamber. The ignition start timing of the ignition is controlled to be retarded from the ignition start timing when the reaction amount of the low temperature oxidation reaction is less than the specific reaction amount .

According to this configuration, the ignition start timing of the second ignition is retarded, so that the ignition timing of the air-fuel mixture is retarded. This makes it possible to reduce the in-cylinder pressure during the high-temperature oxidation reaction. As a result, knocking can be appropriately suppressed.

Further, since the ignition start time of the second ignition is near the compression top dead center, the knocking suppression control may not be in time unless the reaction amount of the low temperature oxidation reaction is estimated as early as possible. Therefore, the effect of estimating the reaction amount of the low-temperature oxidation reaction generated in the combustion chamber of the engine early and accurately can be more appropriately exhibited.

In the other embodiment, the knocking suppression control means is configured to significantly delay the ignition start timing of the second ignition as the reaction amount of the low temperature oxidation reaction increases in the knocking suppression control. May be good.

As described above, when the reaction amount of the low temperature oxidation reaction is large, the temperature and high pressure in the combustion chamber, particularly near the outer peripheral edge portion, tend to be high during the high temperature oxidation reaction of the air-fuel mixture. Therefore, as the reaction amount of the low-temperature oxidation reaction is large, the ignition start timing of the second ignition is greatly retarded to reduce the in-cylinder pressure of the air-fuel mixture during the high-temperature oxidation reaction as much as possible. Thereby, knocking can be suppressed more effectively.

In the control device of the engine, the engine may be an engine having a geometric compression ratio of 15 to 25.

That is, in a relatively high compression engine having a geometric compression ratio of 15 to 25, the operating efficiency of the engine is high, but knocking is particularly likely to occur. Therefore, it is possible to more appropriately exert the effect of estimating the reaction amount of the low-temperature oxidation reaction generated in the combustion chamber of the engine early and accurately so that knocking can be appropriately suppressed.

In yet another aspect of the technique disclosed herein, a fuel comprising a cylinder in which a combustion chamber is formed and a crank shaft that is rotationally driven by the reciprocating motion of a piston fitted in the cylinder. An ignition plug configured to ignite the air-fuel mixture in the combustion chamber and in-cylinder pressure detection for detecting the pressure in the cylinder, targeting an engine control device that burns the air-fuel mixture with the air in the combustion chamber. The means, the crank angle detecting means for detecting the crank angle, the ignition controlling means for controlling the ignition by the ignition plug, and the inside of the cylinder detected by the in-cylinder pressure detecting means in the late compression stroke and before ignition. The low-temperature oxidation reaction amount estimation means for estimating the reaction amount of the low-temperature oxidation reaction of the air-fuel mixture in the combustion chamber based on the pressure of the above, and the reaction amount of the low-temperature oxidation reaction estimated by the low-temperature oxidation reaction amount estimation means are When the reaction amount is equal to or more than a preset specific reaction amount, the ignition control means includes a knocking suppression control means for executing knocking suppression control for suppressing knocking in the combustion chamber, and the ignition control means has an engine load of a predetermined load or more. When the load is high, the first ignition by the ignition plug can be executed so that the air-fuel mixture in the cylinder is activated before the middle stage of the compression stroke, and the control means is the in-cylinder pressure detecting means. Based on the pressure in the cylinder detected by, the heat generation rate in the combustion chamber is estimated, and among the estimated heat generation rates, the maximum value and the minimum value in the late compression stroke and the period before ignition. The reaction amount of the low temperature oxidation reaction was estimated based on the difference from the value .

According to this configuration, when a low-temperature oxidation reaction occurs, heat of reaction is generated, so that the heat generation rate in the combustion chamber increases. Therefore, among the estimated heat generation rates, the reaction amount of the low temperature oxidation reaction is estimated based on the difference between the maximum value and the minimum value in the late compression stroke and in the period before ignition, so that the low temperature oxidation reaction can be carried out. The reaction amount can be estimated appropriately.

The technology according to the present disclosure also covers an engine control method. Specifically, it has a cylinder in which a combustion chamber is formed, a spark plug facing the combustion chamber, and a crankshaft that is rotationally driven by the reciprocating movement of a piston fitted in the cylinder, and contains gasoline. For the control method of the engine that burns the mixture of fuel and air in the combustion chamber, the in-cylinder pressure detection step for detecting the pressure in the cylinder, the crank angle detection step for detecting the crank angle, and the middle stage of the compression stroke. Previously, a first ignition step of executing the first ignition by the spark plug so as to activate the air-fuel mixture in the cylinder, and a second ignition of the second ignition by the spark plug near the shrinkage dead point. A low-temperature oxidation reaction that estimates the reaction amount of the low-temperature oxidation reaction of the air-fuel mixture generated by the first ignition based on the ignition step and the pressure in the cylinder in the late compression stroke and before ignition. When the reaction amount of the low temperature oxidation reaction estimated in the amount estimation step and the low temperature oxidation reaction amount estimation step is equal to or more than a preset specific reaction amount, knocking suppression for suppressing knocking in the combustion chamber is suppressed. The first ignition step includes a knocking suppression step for executing control, and the first ignition step is a step executed only when the engine load is a high load equal to or higher than a predetermined load, and the second ignition step is at least an engine load. Is a step to be executed when the load is higher than the predetermined load .

Even in this configuration, the low temperature oxidation reaction is performed by executing the first ignition by the spark plug so that the air-fuel mixture in the cylinder is activated before the middle of the compression stroke to activate the air-fuel mixture in the combustion chamber in advance. The reaction amount of can be estimated early and accurately. Then, knocking can be appropriately suppressed by executing the knocking suppression control based on the estimated reaction amount of the low temperature oxidation reaction.

In the engine control method, the ignition start time of the first ignition in the first ignition step may be the time within the period on the most advanced side when the period of the compression stroke is divided into three equal parts.

According to this configuration, by activating the air-fuel mixture as early as possible in the compression stroke, the activated air-fuel mixture diffuses throughout the combustion chamber, making it easy for a low-temperature oxidation reaction to occur in the latter half of the compression stroke. Can be done. As a result, the reaction amount of the low-temperature oxidation reaction can be estimated more accurately, and knocking can be suppressed more effectively.

In the engine control method, the first ignition step is executed when the operating state of the engine is such that the engine load is a high load equal to or higher than the predetermined load and the engine speed is higher than the predetermined speed. It may be a process to be performed.

According to this configuration, the low-temperature oxidation reaction itself tends to be small, and the first ignition is performed at high load and high rotation of the engine in which the actual time from estimating the reaction amount of the low-temperature oxidation reaction to executing the knocking suppression control is short. By performing this, the effect of estimating the reaction amount of the low-temperature oxidation reaction early and accurately can be more appropriately exhibited.

In one embodiment of the engine control method, the knocking suppression control is a control for supplying a cooling medium to the combustion chamber in the first half of a period in which a high temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber.

According to this configuration, by supplying the cooling medium to the combustion chamber in the first half of the period in which the high temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber, it is possible to suppress the generation of a local high temperature region in the combustion chamber. .. As a result, knocking can be appropriately suppressed.

In the above-described embodiment of the engine control method, the knocking suppression control may be a control in which the supply amount of the cooling medium increases as the reaction amount of the low-temperature oxidation reaction increases.

According to this configuration, the supply amount of the cooling medium increases as the temperature and pressure tend to be higher in the combustion chamber, particularly in the vicinity of the outer peripheral edge portion. Thereby, knocking can be suppressed more effectively.

In another aspect of the engine control method, the engine has a cylinder in which a combustion chamber is formed, a spark plug facing the combustion chamber, and a crankshaft that is rotationally driven by the reciprocating motion of a piston fitted in the cylinder. , An in-cylinder pressure detection step for detecting the pressure in the cylinder and a crank angle detection step for detecting the crank angle, targeting an engine control method for burning an air-fuel mixture containing gasoline and air in the combustion chamber. In the latter half of the compression stroke and before the middle stage of the compression stroke, based on the first ignition step of executing the first ignition by the spark plug so that the air-fuel mixture in the cylinder is activated, and the pressure in the cylinder. The reaction amount of the low temperature oxidation reaction estimated in the low temperature oxidation reaction amount estimation step of estimating the reaction amount of the low temperature oxidation reaction of the air-fuel mixture in the combustion chamber and the reaction amount of the low temperature oxidation reaction estimated in the low temperature oxidation reaction amount estimation step in the period before ignition are The first ignition step includes a knocking suppression step of executing knocking suppression control for suppressing knocking in the combustion chamber when the reaction amount is equal to or more than a preset specific reaction amount, and the engine load is equal to or more than a predetermined load in the first ignition step. It is a step executed when the load is high, and further includes a second ignition step of executing the second ignition by the spark plug in the vicinity of the compression top dead point, and the knocking suppression control is the mixing in the combustion chamber. In order to delay the ignition of the ki, the ignition start timing of the second ignition in the second ignition step is controlled to be delayed from the ignition start timing when the reaction amount of the low temperature oxidation reaction is less than the specific reaction amount. There is a configuration.

According to this configuration, the ignition start timing of the second ignition is retarded, so that the ignition timing of the air-fuel mixture is retarded. This makes it possible to reduce the in-cylinder pressure during the high-temperature oxidation reaction. As a result, knocking can be appropriately suppressed.

In the other embodiment of the engine control method, the knocking suppression control is a control that significantly retards the ignition start timing of the second ignition in the second ignition step as the reaction amount of the low temperature oxidation reaction increases. It may be.

According to this configuration, as the reaction amount of the low temperature oxidation reaction is large, the ignition start timing of the second ignition is greatly retarded, so that the in-cylinder pressure at the time of the high temperature oxidation reaction of the air-fuel mixture can be lowered as much as possible. Thereby, knocking can be suppressed more effectively.

As described above, according to the technique disclosed here, before the middle of the compression stroke, the first ignition by the spark plug is executed so that the air-fuel mixture in the cylinder is activated, and the air-fuel mixture in the combustion chamber is preliminarily ignited. By activating it, it is possible to generate a low temperature oxidation reaction of an estimated size at the earliest possible time in the late compression stroke and the period before ignition. As a result, the reaction amount of the low temperature oxidation reaction generated in the combustion chamber of the engine can be estimated early and accurately. Then, knocking can be appropriately suppressed by executing the knocking suppression control based on the estimated reaction amount of the low temperature oxidation reaction.

FIG. 5 is a schematic configuration diagram of an engine system to which the control device according to the first embodiment is applied. It is a block diagram which shows the control system of an engine. It is a figure which shows the control map of combustion control. It is a figure which shows an example of the injection timing, the ignition timing, and the heat generation rate when knocking suppression control is not executed in a high load low rotation region. It is a figure which shows an example of the injection timing, the ignition timing, and the heat generation rate when knocking suppression control is not executed in a high load high rotation region. It is a figure which shows the change of the heat generation rate by a low temperature oxidation reaction. It is the figure which calculated the change of the heat generation rate by a low temperature oxidation reaction by a simulation. It is a flowchart which shows the processing operation of the control apparatus when the knocking suppression control is executed based on the reaction amount of a low temperature oxidation reaction. It is a time chart when the knocking suppression control is executed based on the reaction amount of the low temperature oxidation reaction. It is a time chart when the knocking suppression control is executed based on the reaction amount of the low temperature oxidation reaction in the engine to which the control device which concerns on Embodiment 2 is applied.

Hereinafter, exemplary embodiments will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 shows the configuration of the engine 1 to which the control device according to the first embodiment is applied. The engine 1 of the first embodiment is an engine mounted on a vehicle. The engine 1 includes an engine main body 1a, an intake passage 20 for introducing combustion air into the engine main body 1a, and an exhaust passage 30 for discharging the exhaust generated by the engine main body 1a.

The engine body 1a is an in-line 4-cylinder type, and the four cylinders 2 are arranged in series in a direction orthogonal to the paper surface of FIG. The engine body 1a is used as a drive source for the vehicle. In the first embodiment, the engine body 1a is driven by being supplied with fuel including gasoline.

The engine body 1a includes a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 provided on the upper surface of the cylinder block 3, and a piston fitted to the cylinder 2 so as to be reciprocating (moving up and down in this case). Has 5 and.

Cylinder 2 is a cylinder in which a combustion chamber 6 is formed. Specifically, the combustion chamber 6 is formed above the piston 5 in the cylinder 2. The combustion chamber 6 is a so-called pent roof type, and 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, an intake side and an exhaust side. On the upper surface of the piston 5, a cavity is formed in which a region including the central portion thereof is recessed on the opposite side (lower side) of the cylinder head 4. In the following description, the space formed between the upper surface of the piston 5 and the ceiling surface of the combustion chamber 6 in the inner space of the cylinder 2 regardless of the position of the piston 5 and the combustion state of the air-fuel mixture is referred to as the combustion chamber 6.

The piston 5 is connected to the crankshaft 7 via a connecting rod 8 in the cylinder block 4. The crankshaft 7 is rotationally driven by the reciprocating motion of the piston 5.

The geometric compression ratio of the engine body 1a, that is, the ratio of the volume of the combustion chamber 6 when the piston 5 is at the bottom dead center and the volume of the combustion chamber 6 when the piston 5 is at the top dead center is the present implementation. In the first form, it is set to 15 to 25 (for example, about 17).

The cylinder head 4 has an intake port 9 for introducing air supplied from the intake passage 20 into the cylinder 2 (combustion chamber 6), and a mixture of fuel and air burns in the combustion chamber 6. An exhaust port 10 for leading the exhaust generated by the above to the exhaust passage 30 is formed. Two intake ports 9 and two exhaust ports 10 are formed for each cylinder 2.

The cylinder head 4 is provided with an intake valve 11 that opens and closes an opening on the combustion chamber 6 side of each intake port 9, and an exhaust valve 12 that opens and closes an opening on the combustion chamber 6 side of each exhaust port 10. ..

The cylinder head 4 is provided with an injector 14 for injecting fuel. The injector 14 is attached so that the tip end portion on which the injection port is formed is located near the center of the ceiling surface of the combustion chamber 6 and faces the center of the combustion chamber 6. The injector 14 has a plurality of nozzles at its tip, and has a cone shape (specifically, a hollow cone shape) centered on the central axis of the cylinder 2 from the vicinity of the center of the ceiling surface of the combustion chamber toward the crown surface of the piston 5. It is configured to inject fuel. The taper angle (spraying angle) of the cone is, for example, 90 ° to 100 °. The specific configuration of the injector 14 is not limited to this, and may be a single injector.

The injector 14 injects fuel pumped from a high-pressure pump (not shown) into the combustion chamber 6. The injection pressure of the injector 14 is increased to 30 MPa or more in the engine high load region where knocking is likely to occur, and fuel is injected from the injector 14 at a high pressure. The injection pressure is preferably increased up to about 70 MPa. In this case, the fuel is injected at an injection pressure in the range of 30 MPa to 70 MPa in the engine high load region.

The cylinder head 4 is provided with a spark plug 13 configured to ignite the air-fuel mixture in the combustion chamber 6. At the tip of the spark plug 13, an electrode is formed that discharges sparks to ignite the air-fuel mixture and imparts ignition energy to the air-fuel mixture. The spark plug 13 is arranged so that its tip is located near the center of the ceiling surface of the combustion chamber 6 and faces the center of the combustion chamber 6. The engine body 1a is configured to compress the air-fuel mixture in the combustion chamber 6 and to compress and ignite the air-fuel mixture in the combustion chamber 6 by ignition by the spark plug 13. In the present specification, "ignition" means spark discharge by the spark plug 13, and "ignition" means a state in which a flame is generated in the air-fuel mixture in the cylinder 2.

The intake passage 20 is provided with an air cleaner 21 and a throttle valve 22 for opening and closing the intake passage 20 in this order from the upstream side. In the present embodiment, the throttle valve 22 is basically maintained at a fully open position or an opening close to this during the operation of the engine 1, and is closed only under limited operating conditions such as when the engine 1 is stopped. The intake passage 20 is shut off.

The exhaust passage 30 is provided with a purification device 31 for purifying the exhaust gas. The purification device 31 has, for example, a built-in three-way catalyst.

The exhaust passage 30 is provided with an EGR device 40 for returning a part of the exhaust gas passing through the exhaust passage 30 to the intake passage 20 as EGR gas. The EGR device 40 opens and closes the EGR passage 41 and the EGR passage 41 that communicate the portion of the intake passage 20 downstream of the throttle valve 22 and the portion of the exhaust passage 30 upstream of the purification device 31. It has an EGR valve 42. Further, in the first embodiment, the EGR passage 41 is provided with an EGR cooler 43 for cooling the EGR gas passing through the EGR passage 41, and the EGR gas is cooled by the EGR cooler 43 and then in the intake passage 20. It is recirculated.

FIG. 2 is a block diagram showing a control system of the engine 1. The engine 1 of the first embodiment is collectively controlled by a powertrain control module 100 (hereinafter referred to as PCM100) as a control device. As is well known, the PCM 100 is a microprocessor composed of a CPU, a ROM, a RAM, and the like.

The vehicle is equipped with various sensors. The PCM 100 is electrically connected to these sensors, and detection signals from each sensor are input to the PCM 100. For example, the cylinder block 3 is provided with a crank angle sensor (crank angle detecting means) SN1 that detects a crank angle which is a rotation angle of the crankshaft 7. Further, an air flow sensor SN2 for detecting the amount of air sucked into each cylinder 2 through the intake passage 20 is provided. Further, the cylinder head 4 is provided with an in-cylinder pressure sensor (in-cylinder pressure detecting means) SN3 that detects the pressure in the combustion chamber 6. One in-cylinder pressure sensor SN3 is provided for each cylinder 2. Further, the vehicle is provided with an accelerator opening sensor SN4 that detects an opening degree (accelerator opening degree) of an accelerator pedal (accelerator opening degree) which is not shown and is operated by the driver.

The PCM100 calculates the rotation speed (engine rotation speed) of the engine body 1a from the detection result of the crank angle sensor SN1. The PCM100 calculates the engine load from the detection result of the accelerator opening sensor SN4.

As will be described in detail later, the PCM 100 has a heat generation rate estimation unit (heat generation rate estimation means) that estimates the heat generation rate in the combustion chamber 6 based on the in-cylinder pressure detected by the in-cylinder pressure sensor SN3. ) 101 and the low-temperature oxidation reaction amount estimation unit (low-temperature oxidation reaction) that estimates the reaction amount of the low-temperature oxidation reaction of the air-fuel mixture in the combustion chamber 6 based on the estimated heat generation rate estimated by the heat generation rate estimation unit 101. The amount estimation means) 102, the knocking suppression unit (knocking suppression means) 103 that executes knocking suppression control for suppressing knocking in the combustion chamber 6, and the ignition control unit 104 that controls the ignition timing by the ignition plug 13. including.

The PCM 100 executes various calculations based on the input signals from the sensors SN1 to SN4 and controls each part of the engine 1 such as the spark plug 13, the injector 14, the throttle valve 22, and the EGR valve 42.

<Combustion control>
FIG. 3 is a control map in which the horizontal axis is the engine speed and the vertical axis is the engine load. The operating area of the engine 1 is divided into two areas according to the engine speed and the engine load. In the present embodiment, a low load region B in which the engine load is less than the preset reference load Tq1 and knocking is unlikely to occur, and a high load region A in which the engine load is equal to or more than the reference load Tq1 and knocking is likely to occur are set. There is. In the high load region A, the knocking suppression control is performed in order to suppress the occurrence of knocking. In the first embodiment, the geometric compression ratio of the engine body 1a is set to 15 to 25, and the temperature inside the combustion chamber 6 is raised to a very high temperature. Therefore, knocking is particularly likely to occur.

The high load region A is further divided into a high load low rotation region A1 in which the engine speed is less than the reference rotation speed N1 and a high load high rotation region A2 in which the engine speed is equal to or higher than the reference rotation speed N1. ing.

In the first embodiment, compression ignition combustion (SPCCI combustion, SPCCI: Spark Control Compression Ignition) by ignition assist using a spark plug 13 is carried out. In this compression ignition combustion, first, fuel is injected from the injector 14 into the combustion chamber 6 before the compression top dead center (TDC). This fuel mixes with air by near compression top dead center. The second ignition by the spark plug 13 is performed in the vicinity of the compression top dead center in the air-fuel mixture formed in the combustion chamber 6. As a result, the air-fuel mixture around the spark plug 13 is forcibly ignited. Then, the flame propagates from around the spark plug 13 to the surroundings, and the temperature of the surrounding air-fuel mixture is raised to ignite.

FIG. 4 shows an example of the fuel injection timing, ignition timing, and heat generation rate in the high load low rotation region A1 when the normal control is executed (when the knocking suppression control described later is not executed). As shown in FIG. 4, for example, in the high load low rotation region A1, fuel is injected from the injector 14 once in the middle stage and the latter stage of the intake stroke. That is, the fuel injections Q1a and Q1b are carried out in the middle and late stages of the intake stroke. Then, the air-fuel mixture is ignited by the spark plug 13 at the ignition timing set near the compression top dead center (TDC). The fuel injection Q1a is a main injection for achieving the required engine torque, that is, a main injection for injecting fuel for generating engine torque. On the other hand, the fuel injection Q1b is a sub-injection for controlling the ignition / combustion timing. The injection amount Q1b of the sub-injection is about 5% to 15% of the total value of the fuel injections Q1a and Q1b. In the present specification, the first half, the middle half, and the second half of each stroke are the first half, and the most advanced period when the implementation period (the period at the crank angle) in each stroke is divided into three equal parts. The period on the most retarded side corresponds to the latter period, and the period between the first period and the latter period corresponds to the middle period, respectively.

As shown in FIG. 4, in the high load low rotation region A1, the heat generation rate slightly increases before it suddenly increases due to ignition. That is, after the low temperature oxidation reaction, the high temperature oxidation reaction occurs. The low-temperature oxidation reaction is a reaction that generates a slight amount of heat without a flame, and is generated by compressing the air-fuel mixture in the combustion chamber 6. The high-temperature oxidation reaction is a reaction that emits high thermal energy while generating a flame, and is generated when the air-fuel mixture actually ignites. When distinguishing between a low temperature oxidation reaction and a high temperature oxidation reaction based on the temperature, for example, an oxidation reaction having a temperature of less than 1000 K is regarded as a low temperature oxidation reaction, and an oxidation reaction having a temperature of 1000 K or more is regarded as a high temperature oxidation reaction. It can be regarded as a reaction.

In the example shown in FIG. 4, the heat generation rate rises due to the low temperature oxidation reaction in the latter period of the compression stroke and in the period before ignition. Here, since it is in the stage of the low temperature oxidation reaction, the heat generation rate does not increase so much. At the crank angle a while after the ignition energy is applied by the second ignition of the spark plug 13 at the ignition timing, the air-fuel mixture ignites and the high-temperature oxidation reaction starts, and the heat generation rate after the crank angle increases. It rises sharply toward a high value. In the first embodiment, the ignition timing is set to be substantially the same as the timing at which the low temperature oxidation reaction occurs.

FIG. 5 shows an example of fuel injection timing, ignition timing, and heat generation rate in the high load high rotation region A2 when the basic control is executed. For example, in the high load high rotation region A2, the fuel injection Q1 is performed only once from the first half to the second half of the intake stroke. Then, the second ignition of the air-fuel mixture is performed by the spark plug 13 at the ignition timing set near the compression top dead center (TDC). The fuel injection Q1 is the main injection for realizing the required engine torque, and the injection amount is basically an amount corresponding to the required value of the engine torque.

As shown in FIG. 5, the heat generation rate in the high load high rotation region A2 is different from that in the high load low rotation region A1, and the increase in the heat generation rate due to the low temperature oxidation reaction is not clearly seen. This is because when the engine speed is high, the rising speed of the piston 5 and the pressure rising speed in the combustion chamber 6 are high, so that the time during which the low temperature oxidation reaction of the main air-fuel mixture in the combustion chamber 6 occurs becomes very short, or It is considered that the main air-fuel mixture in the combustion chamber 6 is rapidly heated to start the high-temperature oxidation reaction with almost no low-temperature oxidation reaction.

<Knocking suppression control>
Next, the knocking suppression control performed in the high load region A will be described.

In the first embodiment, first, it is determined whether or not the knocking suppression control is executed based on the reaction amount of the low temperature oxidation reaction.

That is, when the air-fuel mixture in the combustion chamber 6 is ignited by the second ignition by the spark plug 13, the flame generated in the vicinity of the ignition plug 13 in the combustion chamber 6 propagates toward the outer peripheral side of the cylinder 2. At this time, the unburned air-fuel mixture is locally compressed in the vicinity of the outer peripheral edge of the combustion chamber 6. As a result, the vicinity of the outer peripheral edge of the combustion chamber 6 is locally in a high temperature and high pressure state. Knocking occurs when the high-temperature and high-pressure air-fuel mixture individually self-ignites.

In order for the low temperature oxidation reaction to occur in the combustion chamber 6, it is a condition that at least one of the temperature and the pressure in the combustion chamber 6 is high. Therefore, when a low-temperature oxidation reaction occurs in the combustion chamber 6, when the flame generated by the high-temperature oxidation reaction compresses the air-fuel mixture near the outer peripheral portion of the combustion chamber 6, the vicinity of the outer peripheral edge of the combustion chamber 6 becomes. It tends to be in a high temperature and high pressure state. Therefore, when a low-temperature oxidation reaction occurs in the combustion chamber 6, knocking is likely to occur. Further, when a low-temperature oxidation reaction occurs, the temperature inside the combustion chamber 6 is likely to be raised by the heat of the reaction. Therefore, when a low-temperature oxidation reaction occurs in the combustion chamber 6, knocking is likely to occur.

When the low-temperature oxidation reaction is large, specifically, when the increase in heat generation rate due to the low-temperature oxidation reaction is large, at least one of the temperature and pressure in the combustion chamber 6 is considerably high, and the low-temperature oxidation reaction is actively generated. This means that knocking is likely to occur. On the other hand, if the low-temperature oxidation reaction does not occur at all, or if the low-temperature oxidation reaction occurs but is considerably small, knocking does not occur, or even if knocking occurs, noise increases due to the knocking or the piston. It may have little effect on damage such as 5. Therefore, in the first embodiment, in order to suppress knocking in the combustion chamber 6 when the reaction amount of the low temperature oxidation reaction estimated by the low temperature oxidation reaction amount estimation unit 102 is equal to or more than a preset specific reaction amount. Knocking suppression control is executed.

In the first embodiment, the low temperature oxidation reaction amount estimation unit 102 estimates the reaction amount of the low temperature oxidation reaction based on the estimated heat generation rate estimated by the heat generation rate estimation unit 101. The heat generation rate estimation unit 101 estimates the estimated heat generation rate based on the in-cylinder pressure detected by the in-cylinder pressure sensor SN3 in the late compression stroke and in the period before ignition.

FIG. 6 is a diagram showing an example of a change in the heat generation rate due to the low temperature oxidation reaction. In the latter half of the compression stroke, the air-fuel mixture is compressed while cooling loss occurs. Therefore, in the period before the low-temperature oxidation reaction occurs, the heat generation rate tends to decrease slightly. When the low temperature oxidation reaction occurs, the heat generation rate, which has been decreasing, increases as the crank angle increases. Then, in the example shown in FIG. 6, the heat generation rate is slightly reduced after the heat generation rate is maximized during the period in which the low temperature oxidation reaction occurs before ignition. After that, the air-fuel mixture is ignited and a high-temperature oxidation reaction occurs, so that the heat generation rate increases sharply.

As described above, during the period in which the low-temperature oxidation reaction occurs in the latter stage of the compression stroke, the heat generation rate shows a change that becomes, for example, a minimum and then a maximum. Here, the change from the minimum value to the maximum value in the heat generation rate becomes larger as the low temperature oxidation reaction is active. Therefore, the difference between the minimum and maximum values of the estimated heat generation rate, that is, the difference between the maximum and minimum values of the estimated heat generation rate in the late compression stroke and before ignition, is the reaction amount of the low temperature oxidation reaction. Can be regarded as.

However, when the low-temperature oxidation reaction is small as in the high-load, high-speed region A2, the change in the heat generation rate is small, and the maximum and minimum estimated heat generation rates are in the late compression stroke and within the period before ignition. It becomes difficult to obtain the value accurately. Further, even in the high load low rotation region A1, for example, when a large amount of EGR gas is introduced, the ratio of EGR gas in the in-cylinder gas (hereinafter referred to as EGR rate) becomes high, and the oxygen concentration of intake air becomes low. .. As a result, even in the high load low rotation region A1, the low temperature oxidation reaction may be small and the change in the heat generation rate may be small.

Further, the knocking suppression control is executed after estimating the reaction amount of the low temperature oxidation reaction. Therefore, in order to properly execute the knocking suppression control, the reaction amount of the low temperature oxidation reaction is estimated as early as possible, and the real time from the estimation of the reaction amount of the low temperature oxidation reaction to the execution of the knocking suppression control. It is necessary to secure as long as possible. When the operating region of the engine 1 is in the high load and high rotation region A2, the actual time from the occurrence of the low temperature oxidation reaction to the start of the high temperature oxidation reaction of the air-fuel mixture is short. It is necessary to estimate as soon as possible.

On the other hand, as a result of diligent research by the inventors of the present application, it is determined that the air-fuel mixture in the combustion chamber 6 is activated in advance by ignition by the spark plug 13 (hereinafter referred to as the first ignition) before the middle stage of the compression stroke. It was found that the reaction start time of the low temperature oxidation reaction was accelerated.

FIG. 7 shows the result of calculating the change in the heat generation rate due to the low temperature oxidation reaction in the high load and high rotation range A2 by simulation. The broken line in FIG. 7 is the change in the heat generation rate when the first ignition is not executed, and the solid line in FIG. 7 is the change in the heat generation rate when the first ignition is executed. The timing of the second ignition is set to the same timing regardless of the presence or absence of the first ignition.

As shown by the broken line in FIG. 7, when the first ignition is not executed, the start time of the change (increase) in the heat generation rate due to the low temperature oxidation reaction is late, and the heat generation rate due to the low temperature oxidation reaction is the compression top dead center. It can be seen that it is the maximum just before. It is considered that this is because the compression rate by the piston 5 is faster than the reaction rate of the low temperature oxidation reaction, and the change in the heat generation rate due to the low temperature oxidation reaction is immediately before the compression top dead center. On the other hand, as shown by the solid line in FIG. 7, when the first ignition is executed, a change in the heat generation rate due to the low temperature oxidation reaction occurs at a time on the advance side as compared with the case where the first ignition is not executed. You can see that it is doing. Further, it can be seen that when the first ignition is executed, the change in the heat generation rate due to the low temperature oxidation reaction is larger than when the first ignition is not executed. This is because the air-fuel mixture in the combustion chamber 6 was activated in advance by the first ignition. More specifically, the fuel oxidation reaction occurs when the HC of the fuel is thermally decomposed and the grade is lowered. When the first ignition is executed, at least a part of the fuel in the air-fuel mixture can be lowered in advance. As a result, the low-temperature oxidation reaction is promoted, the low-temperature oxidation reaction occurs at an early stage, and the reaction amount of the low-temperature oxidation reaction increases. That is, the "activation of the air-fuel mixture by the first ignition" as used herein means "promotion of thermal decomposition of the fuel in the air-fuel mixture by the first ignition".

In addition, in FIG. 7, it can be seen that the reaction start time of the high temperature oxidation reaction is earlier in the case where the first ignition is executed than in the case where the first ignition is not executed. This is because the air-fuel mixture is activated in advance by the first ignition, so that a high-temperature oxidation reaction is likely to occur.

As described above, by executing the first ignition, the low temperature oxidation reaction can be generated at an early stage and the reaction amount of the low temperature oxidation reaction can be increased. As a result, by executing the first ignition, the reaction amount of the low temperature oxidation reaction can be estimated early and accurately. Therefore, in the first embodiment, the ignition control unit 104 is in a state where the reaction amount of the low temperature oxidation reaction tends to be small, specifically, when the operating region (operating state) of the engine 1 is in the high load high rotation region A2, or When the operating region of the engine 1 is in the high load region A and the EGR ratio is equal to or higher than a predetermined value, the first ignition by the spark plug 13 is performed so that the air-fuel mixture in the cylinder 2 is activated in the first half of the compression stroke. Execute. Then, the low temperature oxidation reaction amount estimation unit 102 estimates the difference between the maximum value and the minimum value of the estimated heat generation rate in the late stage of the compression stroke and in the period before ignition as the reaction amount of the low temperature oxidation reaction. As a result, the reaction amount of the low temperature oxidation reaction can be estimated early and accurately. The predetermined value of the EGR rate is, for example, about 20%.

In addition, in the change of the heat generation rate due to the low temperature oxidation reaction, after the heat generation rate becomes the maximum (maximum), the heat generation rate may not decrease and may become a substantially constant value. At this time, for example, the substantially constant value may be regarded as the maximum value of the estimated heat generation rate in the late compression stroke and in the period before ignition, and the reaction amount of the low temperature oxidation reaction may be estimated.

The start time of the first ignition by the ignition control unit 104 is preferably as early as possible in the period before the middle stage of the compression stroke. This is because by activating the air-fuel mixture as early as possible in the compression stroke, the activated air-fuel mixture is diffused throughout the combustion chamber 6 so that a low-temperature oxidation reaction is likely to occur in the latter half of the compression stroke. Is. Therefore, in the first embodiment, the ignition start timing of the first ignition controlled by the ignition control unit 104 is the period of the compression stroke, that is, the period during which the piston 5 moves from the compression bottom dead center to the compression top dead center. It is preferable that the period is within the period on the most advanced angle side when divided into three equal parts, in other words, within the period of the first half of the compression stroke. On the other hand, in order to properly activate the air-fuel mixture, it is preferable that the air-fuel mixture is diffused to some extent in the combustion chamber 6 and the air-fuel mixture is present around the spark plug 13. Therefore, the ignition start time of the first ignition is the time when the fuel is vaporized and the air-fuel mixture can exist around the spark plug 13, specifically, the time within the period of the first half of the compression stroke and the compression bottom dead center. It is more preferable that the time is after 5 °.

The reaction amount of the low temperature oxidation reaction estimated by the low temperature oxidation reaction amount estimation unit 102 is input to the knocking suppression unit 103 of the PCM 100. The knocking suppression unit 103 suppresses knocking when the estimated reaction amount of the low-temperature oxidation reaction is equal to or more than the above-mentioned specific reaction amount, more specifically, a reaction amount that affects an increase in noise or damage to the piston 5 or the like. Take control.

In the first embodiment, the knocking suppression unit 103 supplies a cooling medium into the combustion chamber 6 as knocking suppression control in the first half of the period during which the high temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber 6. Specifically, the knocking suppression unit 103 controls the injector 14 so as to additionally inject fuel as a cooling medium into the combustion chamber 6.

The timing (crank angle) for performing additional injection is set in advance by an experiment or the like. Specifically, the combustion period (the period during which the high-temperature oxidation reaction occurs) when the knocking suppression control (here, additional fuel injection) is not executed is detected or estimated, and half the period is obtained. Next, a crank angle of less than half of the obtained combustion period is set as a standby angle and stored in the PCM 100. Next, the timing after the standby angle from the ignition timing by the spark plug 13 is set as the execution timing of the additional injection Q2. Then, the knocking suppression unit 103 controls the injector 14 so as to execute the additional injection Q2 at the implementation time.

In the first embodiment, the standby angle is set to be equal to or less than the period from the start of combustion to the time of the center of gravity of combustion. The combustion center of gravity period is the period (crank angle) at which 50% of the total amount of heat generated during one combustion cycle is generated. The standby angle is, for example, the period (crank angle) from the start of the high-temperature oxidation reaction to the generation of heat (crank angle) of about 30% of the total amount of heat generated in one combustion cycle, and the compression top dead center. It is about 15 ° after the point.

In the first embodiment, the fuel injection amount in the additional injection Q2 is set according to the reaction amount of the low temperature oxidation reaction. Specifically, the knocking suppression unit 103 increases the fuel injection amount as the reaction amount of the low-temperature oxidation reaction estimated by the low-temperature oxidation reaction estimation unit 102 increases. As described above, in order for the low temperature oxidation reaction to occur, it is a condition that at least one of the temperature and the pressure in the combustion chamber 6 is high. Therefore, the fact that the reaction amount of the low-temperature oxidation reaction is large means that during the high-temperature oxidation reaction of the air-fuel mixture, the inside of the combustion chamber 6, particularly the vicinity of the outer peripheral edge portion, tends to be in a high temperature and high pressure state. Therefore, the larger the reaction amount of the low temperature oxidation reaction, the larger the fuel injection amount in the additional injection Q2. Thereby, knocking can be suppressed more effectively. On the other hand, if too much fuel is injected, the emission may deteriorate. Therefore, the upper limit of the fuel injection amount in the additional injection Q2 is 10% of the total amount of fuel supplied to the combustion chamber 6 in one combustion cycle. It is set.

Next, the processing operation of the PCM 100 when the knocking suppression control is executed will be described with reference to FIGS. 8 and 9. In the processing operation described below, the processing operation for estimating the reaction amount of the low-temperature oxidation reaction is executed by the low-temperature oxidation reaction amount estimation unit 102, and the knocking suppression control is executed by the knocking suppression unit 103. Further, the heat generation rate is estimated by the heat generation rate estimation unit 101. Further, ignition by the spark plug 13 is executed by the ignition control unit 104. The processing operation based on this flowchart is executed every one combustion cycle while the engine 1 is operating.

First, in step S1, the PCM 100 reads information from the sensors SN1 to SN4.

In the next step S2, the PCM 100 determines whether or not the operating region of the engine 1 is the high load region A. When the operating region of the engine 1 is YES, which is the high load region A, the process proceeds to step S3, while when the operating region of the engine 1 is NO, which is the low load region B, the process returns.

In step S3, the PCM 100 determines whether or not the operating region of the engine 1 is a high rotation region. When the operating region of the engine 1 is YES, the process proceeds to step S5, while when the operating region of the engine 1 is NO, the process proceeds to step S4.

In step S4, the PCM 100 determines whether or not the EGR rate is equal to or greater than a predetermined value. If YES, the EGR rate is greater than or equal to the predetermined value, the process proceeds to step S5, while if NO, the EGR rate is less than the predetermined value, the process proceeds to step S6.

In step S5, the PCM 100 executes the first ignition. The ignition start time of the first ignition is a time within the period of the first half of the compression stroke and a time after 5 ° after the compression bottom dead center. After step S5, the process proceeds to step S6.

In step S6, the PCM 100 determines whether or not it is in the latter stage of the compression stroke. Whether or not it is in the latter stage of the compression stroke is determined by the crank angle detected by the crank angle sensor SN1. The PCM100 proceeds to step S5 when YES is in the latter half of the compression stroke, while repeats the determination in step S4 until the latter half of the compression stroke when NO is before the middle of the compression stroke.

In step S7, the PCM 100 estimates the heat generation rate. The heat generation rate is calculated based on the detection result of the in-cylinder pressure sensor SN3.

In the following step S8, the PCM 100 estimates the reaction amount of the low temperature oxidation reaction. The reaction amount of the low-temperature oxidation reaction is estimated by calculating the difference between the maximum value and the minimum value of the estimated heat generation rate in the late compression stroke and in the period before ignition.

In the next step S9, the PCM 100 determines whether or not the reaction amount of the low temperature oxidation reaction is equal to or more than the specific reaction amount. When YES, the reaction amount of the low-temperature oxidation reaction is equal to or greater than the specific reaction amount, the process proceeds to step S10, while when NO, the reaction amount of the low-temperature oxidation reaction is less than the specific reaction amount, the process returns.

In step S10, the PCM 100 executes knocking suppression control. In this knocking suppression control, as described above, fuel is additionally injected into the combustion chamber 6 (execution of the additional injection Q2) in the first half of the period during which the high temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber 6. The injection amount of the additional injection Q2 in step S10 is set based on the reaction amount of the low temperature oxidation reaction estimated in step S8. After step S10, it returns.

By estimating the reaction amount of the low-temperature oxidation reaction as described above, the accuracy of estimating the reaction amount of the low-temperature oxidation reaction can be improved. As a result, the accuracy of determining whether or not knocking may occur is improved, so that knocking can be effectively suppressed.

FIG. 9 is an example of a time chart when the knocking suppression control is executed based on the reaction amount of the low temperature oxidation reaction. Here, the time chart in the high load high rotation region A2 where the reaction amount of the low temperature oxidation reaction tends to be particularly small is shown.

First, fuel injection Q1 is carried out in the intake stroke. After that, it passes through the compression bottom dead center and enters the compression stroke. Then, the first ignition is executed within the period of the first half of the compression stroke.

After the first ignition, after the middle stage of the compression stroke and the latter stage of the compression stroke, when the piston 5 is located near the compression top dead center, a low temperature oxidation reaction occurs and the heat generation rate increases. The PCM100 has a maximum heat generation rate when the minimum value of the heat generation rate (minimum value in the late compression stroke and before ignition) is shown, and a maximum value in the heat generation rate (maximum value in the late compression stroke and before ignition). The reaction amount of the low temperature oxidation reaction is estimated from the difference from the heat generation rate when.

After that, when the estimated reaction amount of the low temperature oxidation reaction is equal to or more than the specific reaction amount, as shown in FIG. 9, the crank angle of the air-fuel mixture in the combustion chamber 6 before ignition, particularly the second ignition by the spark plug 13. At the crank angle before the ignition start time, the knocking suppression control execution flag is set. When the knocking suppression control execution flag is set, the PCM 100 executes the knocking suppression control and executes the additional injection Q2 in the first half of the period during which the high temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber 6. As a result, the generation of a local high temperature region in the combustion chamber 6 is suppressed, and knocking is appropriately suppressed.

Therefore, in the present embodiment, combustion is performed based on the ignition control unit 104 that controls ignition by the spark plug 13 and the pressure in the cylinder 2 in the late compression stroke and pre-ignition period detected by the in-cylinder pressure sensor SN3. The low-temperature oxidation reaction amount estimation unit 102 that estimates the reaction amount of the low-temperature oxidation reaction of the air-fuel mixture in the chamber 6 and the low-temperature oxidation reaction amount estimation unit 102 that estimates the low-temperature oxidation reaction reaction amount are specified in advance. When the reaction amount is equal to or more than the reaction amount, the knocking suppression unit 103 for executing knocking suppression control for suppressing knocking in the combustion chamber 6 is provided, and the ignition control unit 104 has a high engine load of a predetermined load or more. Occasionally, before the middle of the compression stroke, the first ignition is performed by the spark plug 13 so that the air-fuel mixture in the cylinder 2 is activated, so that the low temperature oxidation reaction can be generated early and the reaction of the low temperature oxidation reaction can be generated. The amount can be easily estimated. Thereby, the reaction amount of the low temperature oxidation reaction generated in the combustion chamber 6 of the engine 1 can be estimated early and accurately. Then, knocking can be appropriately suppressed by executing the knocking suppression control based on the estimated reaction amount of the low temperature oxidation reaction.

Further, in the first embodiment, the injection amount of the fuel in the additional injection of the fuel as the knocking suppression control is set as the reaction amount of the low temperature oxidation reaction increases. As a result, knocking suppression control can be executed according to the environment (pressure and temperature in the cylinder 2) in the combustion chamber 6. Knocking can be suppressed more effectively.

Further, since the additional injection of the fuel as the knocking suppression control is the first half of the period in which the high temperature oxidation reaction occurs, the additionally injected fuel can be sufficiently burned. As a result, even if the inside of the combustion chamber 6 is cooled by the additional injection of fuel, it is possible to prevent the engine torque from decreasing.

(Embodiment 2)
Hereinafter, the second embodiment will be described in detail with reference to the drawings. In the following description, the parts common to the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

In the second embodiment, the content of the knocking suppression control is different from that of the first embodiment. Specifically, in the second embodiment, as knocking suppression control, the ignition start timing of the second ignition by the spark plug 13 is delayed from the ignition start timing when the reaction amount of the low temperature oxidation reaction is less than the specific reaction amount. Let me. More specifically, the ignition start timing of the second ignition by the spark plug 13 is set after the compression top dead center. By retarding the ignition start timing of the second ignition, the ignition timing of the air-fuel mixture is retarded. This makes it possible to reduce the in-cylinder pressure during the high-temperature oxidation reaction. As a result, knocking can be appropriately suppressed.

In the second embodiment, when the reaction amount of the low-temperature oxidation reaction estimated by the low-temperature oxidation reaction amount estimation unit 102 is equal to or more than the specific reaction amount, a signal for executing knocking suppression control from the knocking suppression unit 103 to the ignition control unit 104. Is output. The ignition control unit 104, which has received the signal from the knocking suppression unit 103, delays the ignition start timing of the second ignition. That is, in the second embodiment, the ignition control unit 104 also constitutes the knocking suppressing means.

FIG. 10 is an example of a time chart when the knocking suppression control is executed based on the reaction amount of the low temperature oxidation reaction in the second embodiment.

As shown in FIG. 10, first, fuel injection Q1 is carried out in the intake stroke. After that, it passes through the compression bottom dead center and enters the compression stroke. Then, the first ignition is executed within the period of the first half of the compression stroke.

After the first ignition, after the middle stage of the compression stroke and the latter stage of the compression stroke, when the low temperature oxidation reaction occurs, the PCM100 estimates the reaction amount of the low temperature oxidation reaction. After that, when the estimated reaction amount of the low-temperature oxidation reaction is equal to or more than the specific reaction amount, the knocking suppression control execution flag is set at the crank angle before the ignition start timing of the second ignition by the spark plug 13. Then, when the knocking suppression control execution flag is set, the PCM 100 executes the knocking suppression control to set the ignition start timing by the spark plug 13 after the compression top dead center. As a result, as shown in FIG. 10, the start time of the high-temperature oxidation reaction is delayed as compared with the case where the knocking suppression control is not executed (indicated by the alternate long and short dash line in the graph of the heat generation rate). Therefore, the in-cylinder pressure during the high-temperature oxidation reaction is lower than that when the knocking suppression control is not executed. Further, since the start time of the high temperature oxidation reaction is delayed, the change in the heat generation rate due to the high temperature oxidation reaction becomes slower than when the knocking suppression control is not executed. As a result, the generation of a local high-pressure region in the combustion chamber 6 is suppressed, and knocking is appropriately suppressed.

Further, since the ignition start timing of the second ignition when the knocking suppression control is not executed is near the compression top dead center, the knocking suppression control is in time unless the reaction amount of the low temperature oxidation reaction is estimated as early as possible. It may disappear. Therefore, when the ignition start timing of the second ignition is retarded as knocking suppression control, the effect of estimating the reaction amount of the low temperature oxidation reaction generated in the combustion chamber 6 of the engine 1 early and accurately is effective. It is exhibited more appropriately.

Since the estimation of the reaction amount of the low temperature oxidation reaction in the second embodiment is the same as that in the first embodiment, the description thereof will be omitted.

(Other embodiments)
The technique disclosed herein is not limited to the above embodiment, and can be substituted as long as it does not deviate from the gist of the claims.

For example, in the first embodiment, the cooling medium injected into the combustion chamber 6 in the additional injection Q2 is used as the fuel, but the fuel is not limited to this, and water may be used, for example. In this case, it is necessary to separately provide an injector for injecting water.

Further, in the second embodiment, the ignition start timing of the second ignition by the spark plug 13 is retarded to after the compression top dead center, but the present invention is not limited to this, and the second ignition suppression control is not executed. The ignition start time of the second ignition may be earlier than the compression top dead center as long as it is on the retard side of the ignition start time of the ignition and knocking can be suppressed.

The above embodiments are merely examples, and the scope of the present disclosure should not be construed in a limited manner. The scope of the present disclosure is defined by the scope of claims, and all modifications and changes belonging to the equivalent scope of the scope of claims are within the scope of the present disclosure.

The technology disclosed herein includes a cylinder in which a combustion chamber is formed and a crankshaft that is rotationally driven by the reciprocating movement of a piston fitted in the cylinder, and is a mixture of fuel containing gasoline and air. It is useful for engines that burn air in the combustion chamber.

1 Engine 2 Cylinder 5 Piston 6 Combustion chamber 7 Crankshaft 13 Spark plug 101 Heat generation rate estimation unit (heat generation rate estimation means)
102 Low-temperature oxidation reaction amount estimation unit (low-temperature oxidation reaction amount estimation means)
103 Knocking suppression unit (knocking suppression means)
104 Ignition control unit (ignition control means, knocking suppression means)
SN1 crank angle sensor (crank angle detecting means)
SN3 In-cylinder pressure sensor (in-cylinder pressure detecting means)

Claims (16)

It has a cylinder in which a combustion chamber is formed and a crankshaft that is rotationally driven by the reciprocating movement of a piston fitted in the cylinder, and burns a mixture of fuel containing gasoline and air in the combustion chamber. It ’s an engine control device.
A spark plug configured to ignite the air-fuel mixture in the combustion chamber,
In-cylinder pressure detecting means for detecting the pressure in the cylinder and
Crank angle detecting means for detecting the crank angle and
Only when the engine load is a high load equal to or higher than the predetermined load, the first ignition is executed to activate the air-fuel mixture in the cylinder before the middle stage of the compression stroke, and at least the engine load is higher than the predetermined load. when a load, the ignition control means for controlling the ignition plug as the above first ignition separately executes the second ignition by the ignition plug in the vicinity of the compression top dead center,
The reaction amount of the low temperature oxidation reaction of the air-fuel mixture in the combustion chamber generated by the first ignition based on the pressure in the cylinder in the period before the ignition and in the latter stage of the compression stroke detected by the in-cylinder pressure detecting means. Low-temperature oxidation reaction amount estimation means for estimating
When the reaction amount of the low-temperature oxidation reaction estimated by the low-temperature oxidation reaction amount estimation means is equal to or more than a preset specific reaction amount, knocking suppression is performed to suppress knocking in the combustion chamber. and control means, engine control apparatus wherein the this with a. In the engine control device according to claim 1,
An engine control device characterized in that the ignition start timing of the first ignition by the ignition control means is within the period on the most advanced angle side when the period of the compression stroke is divided into three equal parts. In the engine control device according to claim 1 or 2.
The ignition control means executes the first ignition when the operating state of the engine is a high load of the predetermined load or more and the engine speed is a high speed of the predetermined speed or more. An engine control device characterized by being configured in. In the engine control device according to any one of claims 1 to 3.
The knocking suppression control is an engine control device characterized in that the cooling medium is supplied to the combustion chamber during the first half of the period during which the high temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber. In the engine control device according to claim 4,
The knocking suppression control means is an engine control device, characterized in that, in the knocking suppression control, the larger the reaction amount of the low temperature oxidation reaction, the larger the supply amount of the cooling medium. It has a cylinder in which a combustion chamber is formed and a crankshaft that is rotationally driven by the reciprocating movement of a piston fitted in the cylinder, and burns a mixture of fuel containing gasoline and air in the combustion chamber. It ’s an engine control device.
A spark plug configured to ignite the air-fuel mixture in the combustion chamber,
In-cylinder pressure detecting means for detecting the pressure in the cylinder and
Crank angle detecting means for detecting the crank angle and
Ignition control means for controlling ignition by the spark plug and
The amount of low-temperature oxidation reaction that estimates the amount of low-temperature oxidation reaction of the air-fuel mixture in the combustion chamber based on the pressure inside the cylinder during the period before ignition and in the late compression stroke detected by the in-cylinder pressure detecting means. Estimating means and
When the reaction amount of the low-temperature oxidation reaction estimated by the low-temperature oxidation reaction amount estimation means is equal to or more than a preset specific reaction amount, knocking suppression is performed to suppress knocking in the combustion chamber. Equipped with control means
The ignition control means is configured to be able to execute the first ignition by the spark plug so that the air-fuel mixture in the cylinder is activated before the middle stage of the compression stroke when the engine load is a high load equal to or higher than a predetermined load. And
Further, the ignition control means is configured to execute the second ignition by the spark plug in the vicinity of the compression top dead center, separately from the first ignition.
In the knocking suppression control, in order to delay the ignition of the air-fuel mixture in the combustion chamber, the ignition start timing of the second ignition is set to be greater than the ignition start timing when the reaction amount of the low temperature oxidation reaction is less than the specific reaction amount. An engine control device characterized in that it is a control for retarding. In the engine control device according to claim 6,
The knocking suppression control means of the engine is characterized in that, in the knocking suppression control, the larger the reaction amount of the low temperature oxidation reaction, the larger the ignition start timing of the second ignition is delayed. Control device. In the engine control device according to any one of claims 1 to 7.
The engine is an engine control device, characterized in that the engine has a geometric compression ratio of 15 to 25. It has a cylinder in which a combustion chamber is formed and a crankshaft that is rotationally driven by the reciprocating movement of a piston fitted in the cylinder, and burns a mixture of fuel containing gasoline and air in the combustion chamber. It ’s an engine control device.
A spark plug configured to ignite the air-fuel mixture in the combustion chamber,
In-cylinder pressure detecting means for detecting the pressure in the cylinder and
Crank angle detecting means for detecting the crank angle and
Ignition control means for controlling ignition by the spark plug and
The amount of low-temperature oxidation reaction that estimates the amount of low-temperature oxidation reaction of the air-fuel mixture in the combustion chamber based on the pressure inside the cylinder during the period before ignition and in the late compression stroke detected by the in-cylinder pressure detecting means. Estimating means and
When the reaction amount of the low-temperature oxidation reaction estimated by the low-temperature oxidation reaction amount estimation means is equal to or more than a preset specific reaction amount, knocking suppression is performed to suppress knocking in the combustion chamber. Equipped with control means
The ignition control means is configured to be able to execute the first ignition by the spark plug so that the air-fuel mixture in the cylinder is activated before the middle stage of the compression stroke when the engine load is a high load equal to or higher than a predetermined load. And
Further provided with a heat generation rate estimating means for estimating the heat generation rate in the combustion chamber based on the pressure in the cylinder detected by the cylinder pressure detecting means.
The low-temperature oxidation reaction amount estimation means is the difference between the maximum heat generation rate and the minimum heat generation rate in the late compression stroke and the period before ignition among the heat generation rates estimated by the heat generation rate estimation means. An engine control device characterized in that it is configured to estimate the reaction amount of the low temperature oxidation reaction based on the above. It has a cylinder in which a combustion chamber is formed, a spark plug facing the combustion chamber, and a crankshaft that is rotationally driven by the reciprocating motion of a piston fitted in the cylinder, and contains gasoline-containing fuel and air. This is a control method for an engine that burns the air-fuel mixture in the combustion chamber.
The in-cylinder pressure detection process for detecting the pressure in the cylinder and
The crank angle detection process that detects the crank angle and
Before the middle of the compression stroke, the first ignition step of executing the first ignition by the spark plug so that the air-fuel mixture in the cylinder is activated, and
The second ignition step of executing the second ignition by the spark plug in the vicinity of the shrinkage dead center, and
A low-temperature oxidation reaction amount estimation step for estimating the reaction amount of the low-temperature oxidation reaction of the air-fuel mixture in the combustion chamber generated by the first ignition based on the pressure in the cylinder in the late compression stroke and the period before ignition. ,
When the reaction amount of the low-temperature oxidation reaction estimated in the low-temperature oxidation reaction amount estimation step is equal to or more than a preset specific reaction amount, knocking that executes knocking suppression control for suppressing knocking in the combustion chamber is performed. Including the suppression step,
The first ignition step is a step executed only when the engine load is a high load equal to or higher than a predetermined load.
The second ignition step is an engine control method, characterized in that the second ignition step is a step executed when at least the engine load is a high load equal to or higher than the predetermined load. In the engine control method according to claim 10,
A method for controlling an engine, wherein the ignition start time of the first ignition in the first ignition step is a time within the period on the most advanced angle side when the period of the compression stroke is divided into three equal parts. In the engine control method according to claim 10 or 11.
The first ignition step is a step to be executed when the operating state of the engine is a high load of the predetermined load or more and the engine speed is a high speed of the predetermined speed or more. A characteristic engine control method. The engine control method according to any one of claims 10 to 12.
The knocking suppression control is an engine control method characterized in that the cooling medium is supplied to the combustion chamber during the first half of the period during which the high temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber. In the engine control method according to claim 13,
The knocking suppression control is a control method for an engine, characterized in that the larger the reaction amount of the low temperature oxidation reaction, the larger the supply amount of the cooling medium. It has a cylinder in which a combustion chamber is formed, a spark plug facing the combustion chamber, and a crankshaft that is rotationally driven by the reciprocating motion of a piston fitted in the cylinder, and contains gasoline-containing fuel and air. This is a control method for an engine that burns the air-fuel mixture in the combustion chamber.
The in-cylinder pressure detection process for detecting the pressure in the cylinder and
The crank angle detection process that detects the crank angle and
Before the middle of the compression stroke, the first ignition step of executing the first ignition by the spark plug so that the air-fuel mixture in the cylinder is activated, and
A low-temperature oxidation reaction amount estimation step for estimating the reaction amount of the low-temperature oxidation reaction of the air-fuel mixture in the combustion chamber in the latter period of the compression stroke and before ignition based on the pressure in the cylinder.
When the reaction amount of the low-temperature oxidation reaction estimated in the low-temperature oxidation reaction amount estimation step is equal to or more than a preset specific reaction amount, knocking that executes knocking suppression control for suppressing knocking in the combustion chamber is performed. Including the suppression step
The first ignition step is a step executed when the engine load is a high load equal to or higher than a predetermined load.
A second ignition step of executing the second ignition by the spark plug in the vicinity of the compression top dead center is further included.
In the knocking suppression control, in order to delay the ignition of the air-fuel mixture in the combustion chamber, the ignition start timing of the second ignition in the second ignition step is set when the reaction amount of the low temperature oxidation reaction is less than the specific reaction amount. A control method for an engine, which is characterized in that the angle is delayed from the ignition start time of the engine. In the engine control method according to claim 15,
The knocking suppression control is a control method for an engine, characterized in that the larger the reaction amount of the low-temperature oxidation reaction is, the greater the retardation of the ignition start timing of the second ignition in the second ignition step.

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