JP2019183770A - Engine low temperature oxidation reaction detection method and control method, engine low temperature oxidation reaction detection device and control device - Google Patents

Abstract

To perform a high-precision estimation about a reaction amount of low temperature oxidation reaction generated in an engine combustion chamber.SOLUTION: A difference between the maximum value and the minimum value of an estimated heat generation rate at a later stage of a compression stroke and during a period before ignition is calculated as a first estimated reaction amount, a difference between an estimated heat generation rate at a first crank angle set according to an engine speed and an estimated heat generation rate set according to the engine speed and at a second crank angle at a more delayed angle side than the first crank angle is calculated as a second estimated reaction amount. When the first estimated reaction amount is equal to or more than a predetermined reaction amount, a reaction amount of a low temperature oxidation reaction is estimated in reference to the first estimated reaction amount and in turn when the first estimated reaction amount is less than the predetermined reaction amount, a reaction amount of the low temperature oxidation reaction is estimated in reference to the second estimated reaction amount.SELECTED DRAWING: Figure 9

Description

  The technology disclosed herein belongs to a technical field related to a low temperature oxidation reaction detection method and control method for an engine, and a low temperature oxidation reaction detection device and control device for an engine.

  Conventionally, it is known that abnormal combustion called knocking occurs in an engine. If knocking occurs, there is a risk of increased noise and damage to the piston and the like. For this reason, measures for suppressing knocking have been taken in the field of engines.

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

  Also, 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.

JP 2008-291758 A JP 2012-041246 A

  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. The inventors of the present application have conducted extensive research and found that there is a relationship between the magnitude of knocking and the reaction amount of the low-temperature oxidation reaction. Specifically, it has been found that low-temperature oxidation reaction tends to occur, and knocking increases as the reaction amount increases. For this reason, if the amount of knocking can be estimated by appropriately detecting or estimating the reaction amount of the low-temperature oxidation reaction, it is possible to take appropriate measures according to the knocking size.

  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 is difficult to accurately estimate the reaction amount of the low-temperature oxidation reaction. Even when the oxygen concentration in the cylinder is low, the change in the cylinder pressure due to the low-temperature oxidation reaction is small, and it is difficult to accurately estimate the reaction amount of the low-temperature oxidation reaction.

  The technique disclosed herein has been made in view of such a point, and an object thereof is to accurately estimate a reaction amount of a low-temperature oxidation reaction occurring in a combustion chamber of an engine.

  In order to solve the above-described problems, the technology disclosed herein includes a cylinder in which a combustion chamber is formed, and a crankshaft that is rotationally driven by a reciprocating motion of a piston inserted into the cylinder. In an engine that burns an air-fuel mixture containing fuel and air in the combustion chamber, a pressure in the cylinder for a low-temperature oxidation reaction detection method for the engine that detects a low-temperature oxidation reaction of the air-fuel mixture in the combustion chamber. The in-cylinder pressure detecting step of detecting the crank angle, the crank angle detecting step of detecting the crank angle, and the heat generation rate for estimating the heat generation rate in the combustion chamber based on the in-cylinder pressure detected in the in-cylinder pressure detecting step Low-temperature oxidation reaction amount that estimates the reaction amount of the low-temperature oxidation reaction based on the estimated heat generation rate estimated in the estimation step and the heat generation rate estimation step in the later stage of the compression stroke and before the ignition The low temperature oxidation reaction amount estimation step calculates a difference between the maximum value and the minimum value of the estimated heat generation rate as a first estimated reaction amount in the late compression stroke and before the ignition. In accordance with the first reaction amount estimation step and the engine speed, the first crank angle, which is the crank angle in the latter half of the compression stroke and in the period before ignition, and the second crank angle that is retarded from the first crank angle. A second estimation of the difference between the step of setting the crank angle and the estimated heat generation rate when the crank angle is the first crank angle and the estimated heat generation rate when the crank angle is the second crank angle A second reaction amount estimation step calculated as a reaction amount, and when the first estimated reaction amount is equal to or greater than a predetermined reaction amount, the reaction amount of the low-temperature oxidation reaction is estimated based on the first estimated reaction amount, The first estimated reaction amount is When serial is less than the predetermined reaction amount was configured as a process, to estimate the reaction amount of the low-temperature oxidation reaction based on the second estimated reaction amount.

  According to this configuration, the reaction amount of the low-temperature oxidation reaction is estimated based on the estimated heat generation rate estimated based on the in-cylinder pressure. For this reason, when the change in the in-cylinder pressure is small, it is difficult to estimate the maximum value and the minimum value of the estimated heat release rate, and the first estimated reaction amount may not be calculated with high accuracy.

  On the other hand, the inventors of the present application have examined that the time when the heat generation rate becomes the maximum and the time when the heat generation rate becomes the minimum in the late stage of the compression stroke and before the ignition are approximately according to the engine speed. It turned out to be constant. Therefore, in the present invention, when the first estimated reaction amount is less than the predetermined reaction amount, the estimated heat generation rate when the crank angle is the first crank angle and the estimated heat generation when the crank angle is the second crank angle. Based on the second estimated reaction amount calculated from the difference from the rate, the reaction amount of the low-temperature oxidation reaction is estimated. Thereby, the reaction amount of the low temperature oxidation reaction can be accurately estimated.

  In the low-temperature oxidation reaction estimation method for the engine, the first crank angle is a crank angle that is estimated to have a minimum heat generation rate in a later stage of the compression stroke and before ignition, and the second crank angle is It is preferable that the crank angle be estimated that the heat generation rate is maximized in the later stage of the compression stroke and before the ignition.

  According to this configuration, even when the change in the in-cylinder pressure is small and it is difficult to estimate the maximum value and the minimum value of the estimated heat generation rate, the reaction amount of the low-temperature oxidation reaction can be estimated with higher accuracy.

  As a result of further investigation by the inventors of the present invention, as the engine speed increases, the timing at which the heat generation rate becomes maximum and the timing at which the heat generation rate becomes maximum shifts to the advance side in the later period of the compression stroke and before the ignition. I found out that

  Therefore, in the engine low temperature oxidation reaction detection method, in the second reaction amount estimation step, the higher the engine speed, the higher the first crank angle and the second crank angle are set to the advance side. May be.

  Thereby, since the characteristics of the low temperature oxidation reaction are appropriately reflected by the estimation of the reaction amount of the low temperature oxidation reaction, the reaction amount of the low temperature oxidation reaction can be estimated with higher accuracy.

  The technology according to the present disclosure is also directed to an engine control method using the engine low-temperature oxidation reaction detection method. Specifically, for the engine control method using the engine low temperature oxidation reaction detection method, the reaction amount of the low temperature oxidation reaction estimated in the low temperature oxidation reaction amount estimation step is set in advance and the predetermined A knocking suppression step is executed that performs a knocking suppression control that suppresses knocking in the combustion chamber when the reaction amount is equal to or greater than the specific reaction amount that is smaller than the reaction amount.

  That is, when the reaction amount of the low-temperature oxidation reaction is small, even if knocking does not occur or knocking occurs, the engine operation is hardly affected. For this reason, when the reaction amount of the low-temperature oxidation reaction is equal to or greater than the specific reaction amount, knocking suppression control is executed, so that knocking can be appropriately suppressed.

  In one embodiment of the engine control method, the knocking suppression control is a control for supplying a cooling medium into 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 is locally ignited and self-ignited. 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 into the combustion chamber to suppress the occurrence of a local high-temperature region in the combustion chamber. Thereby, knocking can be suppressed appropriately.

  In another embodiment of the engine control method, the engine is an engine that compresses the air-fuel mixture in the combustion chamber and burns the air-fuel mixture in the combustion chamber by ignition by a spark plug, and the knocking suppression control Is control for retarding the ignition start timing by the spark plug 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 timing of the air-fuel mixture is retarded by retarding the ignition start timing by the spark plug. Thereby, the in-cylinder pressure at the time of high temperature oxidation reaction can be reduced. As a result, knocking can be appropriately suppressed.

  Another aspect of the technology according to the present disclosure is a technology related to the engine low-temperature oxidation reaction detection device. Specifically, it has a cylinder in which a combustion chamber is formed and a crankshaft that is rotationally driven by a reciprocating motion of a piston inserted in the cylinder, and the mixture of fuel containing gasoline and air is For a low temperature oxidation reaction detection device for an engine that burns in a combustion chamber, an in-cylinder pressure detecting means for detecting the pressure in the cylinder, a crank angle detecting means for detecting a crank angle, and the in-cylinder pressure detecting means. Heat generation rate estimation means for estimating the heat generation rate in the combustion chamber based on the in-cylinder pressure, and estimated heat generation in the period after the compression stroke and before ignition, estimated by the heat generation rate estimation means A low-temperature oxidation reaction amount estimation means for estimating a reaction amount of a low-temperature oxidation reaction of the air-fuel mixture in the combustion chamber based on the rate, and the low-temperature oxidation reaction amount estimation means is a period after the compression stroke and before ignition Within A first reaction amount estimation unit that calculates a difference between a maximum value and a minimum value of the estimated heat generation rate as a first estimated reaction amount, and the estimated heat generation rate when the crank angle is the first crank angle. A second reaction amount estimation unit that calculates a difference from the estimated heat generation rate when the crank angle is a second crank angle retarded from the first crank angle as a second estimated reaction amount; When the first estimated reaction amount is greater than or equal to the predetermined reaction amount, the first estimated reaction amount is estimated as the reaction amount of the low temperature oxidation reaction, while when the first estimated reaction amount is less than the predetermined reaction amount, The second estimated reaction amount is estimated as a reaction amount of the low-temperature oxidation reaction, and the first crank angle and the second crank angle are set in advance according to the engine speed and are late in the compression stroke. And before ignition A crank angle in a while, and the thing called.

  Even in this configuration, when the change in the cylinder pressure is small and it is difficult to accurately calculate the first estimated reaction amount, the estimated heat generation rate and the crank angle when the crank angle is the first crank angle are the second crank angle. The reaction amount of the low-temperature oxidation reaction is estimated based on the second estimated reaction amount calculated from the difference from the estimated heat generation rate at the time. Thereby, the reaction amount of the low temperature oxidation reaction can be accurately estimated.

  In the low-temperature oxidation reaction detection device for an engine, the first crank angle is a crank angle that is estimated to have a minimum heat generation rate in a later stage of the compression stroke and before ignition, and the second crank angle is It is preferable that the crank angle be estimated that the heat generation rate is maximized in the later stage of the compression stroke and before the ignition.

  According to this configuration, even when the change in the in-cylinder pressure is small and it is difficult to estimate the maximum value and the minimum value of the estimated heat generation rate, the reaction amount of the low-temperature oxidation reaction can be estimated with higher accuracy.

  In the engine low-temperature oxidation reaction detection device, the first crank angle and the second crank angle in the second reaction amount estimation unit are configured to be set to an advance side as the engine speed increases. May be.

  According to this configuration, the characteristics of the low temperature oxidation reaction are appropriately reflected by the estimation of the reaction amount of the low temperature oxidation reaction, so that the reaction amount of the low temperature oxidation reaction can be estimated with higher accuracy.

  The technology according to the present disclosure is also directed to an engine control device using the engine low-temperature oxidation reaction detection device. Specifically, the reaction amount of the low temperature oxidation reaction estimated by the low temperature oxidation reaction amount estimation means is set in advance for the engine control device using the low temperature oxidation reaction detection device for the engine, and the predetermined value is set. It is configured to include a knocking suppression means for executing knocking suppression control for suppressing knocking in the combustion chamber when the specific reaction amount is smaller than the reaction amount.

  According to this configuration, knocking can be appropriately suppressed by performing the knocking suppression step when the reaction amount of the low-temperature oxidation reaction is equal to or greater than the specific reaction amount.

  In one embodiment of the engine control apparatus, the knocking suppression control is a control for supplying a cooling medium into 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 into 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, the occurrence of a local high-temperature region in the combustion chamber is suppressed. Thereby, knocking can be suppressed appropriately.

  In another embodiment of the engine control apparatus, the engine further includes an ignition plug configured to ignite the air-fuel mixture in the combustion chamber, compresses the air-fuel mixture in the combustion chamber, and The mixture is combusted in the combustion chamber by ignition according to the above, and the knocking suppression control is performed when the ignition start timing by the ignition plug is determined when the reaction amount of the low-temperature oxidation reaction is less than the specific reaction amount. This is a control for retarding the ignition start timing.

  According to this configuration, the ignition timing of the air-fuel mixture is retarded by retarding the ignition start timing by the spark plug. Thereby, the in-cylinder pressure at the time of high temperature oxidation reaction can be reduced. As a result, knocking can be appropriately suppressed.

  As described above, according to the technique disclosed herein, when the change in the cylinder pressure is small and it is difficult to estimate the reaction amount of the low temperature oxidation reaction from the maximum value and the minimum value of the estimated heat generation rate, Based on the difference between the estimated heat generation rate when the angle is the first crank angle and the estimated heat generation rate when the crank angle is the second crank angle retarded from the first crank angle, Since the reaction amount is estimated, the reaction amount of the low temperature oxidation reaction can be accurately estimated.

  Moreover, since control for suppressing knocking is executed based on the reaction amount of the low-temperature oxidation reaction, knocking can be appropriately suppressed.

1 is a schematic configuration diagram of an engine system to which a control device according to Embodiment 1 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 at the time of not performing knocking suppression control in a high load low rotation area | region, an ignition timing, and a heat release rate. It is a figure which shows an example of the injection timing at the time of not performing knocking suppression control in a high load high rotation area | region, an ignition timing, and a heat release rate. It is a figure which shows the change of the heat release rate by low temperature oxidation reaction. It is the figure which computed the change of the heat release rate by low-temperature oxidation reaction in the high load high rotation area by simulation. It is a flowchart which shows the processing operation of the control apparatus at the time of performing knocking suppression control based on the reaction amount of a low temperature oxidation reaction. It is a flowchart which shows the subroutine which estimates the reaction amount of a low temperature oxidation reaction. It is a time chart at the time of performing knocking suppression control based on the reaction amount of the low-temperature oxidation reaction estimated from the 2nd estimated reaction amount. It is a figure which shows an example of the injection timing, ignition timing, and heat release rate when performing knock suppression control in the high load high rotation area | region of the engine to which the control apparatus which concerns on Embodiment 2 was applied.

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

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

  The engine main body 1a is an in-line four-cylinder type, and 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 able to reciprocate (in this case, move up and down). And 5.

  The cylinder 2 is a cylinder in which the combustion chamber 6 is formed. Specifically, a 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 constituted 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 upper surface of the piston 5, a cavity is formed in which a region including the center portion is recessed on the opposite side (downward) from 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 through a connecting rod 8 in the cylinder block 3. 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 In Form 1, it is set to 15 to 25 (for example, about 17).

  In the cylinder head 4, an air-fuel mixture of fuel and air burns in the intake port 9 for introducing the air supplied from the intake passage 20 into the cylinder 2 (combustion chamber 6) and the combustion chamber 6. The 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 portion where 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 nozzle holes 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 (spray 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 that of a single nozzle.

  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 an 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 to about 70 MPa at the maximum. In this case, fuel is injected at an injection pressure in the range of 30 MPa to 70 MPa in the engine high load range.

  The cylinder head 4 is provided with a spark plug 13 configured to ignite the air-fuel mixture in the combustion chamber 6. An electrode that discharges sparks to ignite the air-fuel mixture and applies ignition energy to the air-fuel mixture is formed at the tip of the spark plug 13. The spark plug 13 is disposed so that the tip thereof 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 1 a 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 this 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 order from the upstream side. In the present embodiment, during operation of the engine 1, the throttle valve 22 is basically fully opened or maintained at an opening degree close thereto, and is closed only under limited operating conditions such as when the engine 1 is stopped. Then, the intake passage 20 is shut off.

  The exhaust passage 30 is provided with a purification device 31 for purifying the exhaust. The purification device 31 includes, for example, a 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 as EGR gas to the intake passage 20. The EGR device 40 opens and closes an EGR passage 41 that connects a portion of the intake passage 20 downstream of the throttle valve 22 and a portion of the exhaust passage 30 upstream of the purification device 31, and the EGR passage 41. An EGR valve 42 is provided. In the first embodiment, the EGR passage 41 is provided with an EGR cooler 43 for cooling the EGR gas that passes through the EGR passage 41. After the EGR gas is cooled by the EGR cooler 43, Refluxed.

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

  Various sensors are provided in the vehicle. 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 that is a rotation angle of the crankshaft 7. Further, an air flow sensor SN2 that detects the amount of air taken into each cylinder 2 through the intake passage 20 is provided. The cylinder head 4 is provided with an in-cylinder pressure sensor (in-cylinder pressure detecting means) SN3 for detecting 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 the opening degree (accelerator opening degree) of an accelerator pedal (not shown) operated by the driver.

  The PCM 100 calculates the rotational speed (engine rotational speed) of the engine body 1a from the detection result of the crank angle sensor SN1. PCM100 calculates an engine load from the detection result of accelerator opening sensor SN4.

  Although details will be described later, the PCM 100 includes 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 a low-temperature oxidation reaction amount estimation unit (low-temperature oxidation reaction) for estimating 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 (Quantity estimating means) 102 and a knocking suppression unit 103 that executes knocking suppression control for suppressing knocking in the combustion chamber 6. The low-temperature oxidation reaction amount estimation unit 102 calculates a difference between the maximum value and the minimum value of the estimated heat release rate as the first estimated reaction amount in the later stage of the compression stroke and before the ignition. An estimation unit 102a is included. Furthermore, the low-temperature oxidation reaction amount estimation unit 102 includes a first heat generation rate that is the estimated heat generation rate when the crank angle is the first crank angle CA1, and a crank angle that is more retarded than the first crank angle CA1. A second reaction amount estimation unit 102b that calculates a difference from the second heat generation rate that is the estimated heat generation rate when the second crank angle CA2 is the second estimated reaction amount.

The PCM 100 executes various calculations based on input signals from these 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 represents the engine speed and the vertical axis represents the engine load. The operating region of the engine 1 is divided into two regions according to the engine speed and the engine load. In the present embodiment, a low load region B where the engine load is less than a preset reference load Tq1 and knocking is not likely to occur, and a high load region A where the engine load is greater than the reference load Tq1 and knocking is likely to occur are set. Yes. 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 in the combustion chamber 6 is increased to a very high temperature. For this reason, 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 a preset reference rotation number N1, and a high load high rotation region A2 in which the engine rotation number is greater than or equal to the reference rotation number N1. ing.

  In the first embodiment, compression ignition combustion (SPCCI combustion, SPCCI: Spark Controlled Compression Ignition) using ignition plug 13 is performed. In this compression ignition combustion, first, fuel is injected into the combustion chamber 6 from the injector 14 before the compression top dead center (TDC). This fuel mixes with air by the vicinity of compression top dead center. The air-fuel mixture formed in the combustion chamber 6 is ignited by the spark plug 13 near the compression top dead center. Thereby, 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 surrounding air-fuel mixture is heated to ignite.

  FIG. 4 shows an example of fuel injection timing, ignition timing, and heat generation rate in the high-load low-rotation region A1 when normal control is performed (when knocking suppression control described later is not performed). 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 and late stages of the intake stroke. That is, the fuel injections Q1a and Q1b are performed in the middle and later 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 main injection for realizing required engine torque, that is, 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 this specification, the first, middle, and second half of each stroke is the most advanced period when the execution period (crank angle period) in each stroke is equally divided into three. The most retarded period corresponds to the latter period, and the period between the previous period and the latter period corresponds to the middle period.

  As shown in FIG. 4, in the high-load low-rotation region A1, the heat generation rate slightly increases before suddenly increasing due to ignition. That is, the high temperature oxidation reaction is performed after the low temperature oxidation reaction. 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 low temperature oxidation reaction from high temperature oxidation reaction based on temperature, for example, an oxidation reaction with a temperature of less than 1000K is regarded as a low temperature oxidation reaction, and an oxidation reaction with a temperature of 1000K or more is treated with high temperature oxidation. 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 late stage of the compression stroke and before the ignition. Here, since it is a stage of a low temperature oxidation reaction, the heat generation rate does not increase so much. As the air-fuel mixture ignites and the high-temperature oxidation reaction starts at a crank angle after ignition energy is given by ignition of the spark plug 13 at the ignition timing, the heat generation rate is high after the crank angle. It will rise sharply toward. In the first embodiment, the ignition timing is set substantially at the same time as the timing when 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 performed. 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 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 Q1 is a main injection for realizing the required engine torque, and this 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 not clearly seen in the high load low rotation region A1, unlike the high load low rotation region A1. 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 fast, 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 This is because 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.

<Knock 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 to execute knocking suppression control 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 ignition 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 air-fuel mixture in a high temperature and high pressure state is self-ignited individually.

  In order for the low temperature oxidation reaction to occur in the combustion chamber 6, it is necessary that at least one of the temperature and pressure in the combustion chamber 6 is high. For this reason, 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 periphery of the combustion chamber 6, the vicinity of the outer periphery of the combustion chamber 6 is High temperature and high pressure easily. Therefore, knocking is likely to occur when a low-temperature oxidation reaction occurs in the combustion chamber 6. Further, when the low temperature oxidation reaction occurs, the temperature in the combustion chamber 6 is easily raised by the reaction heat. For this reason, 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, the knocking does not occur or the knocking causes an increase in noise or piston. May have little effect on damage such as 5. Therefore, in the first embodiment, knocking in the combustion chamber 6 is suppressed 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 predetermined specific reaction amount. Therefore, the 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 later stage of the compression stroke and in the period before ignition.

  FIG. 6 is a diagram illustrating an example of a change in heat generation rate due to a 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 that has been on a decrease tends to increase as the crank angle increases. In the example shown in FIG. 6, the heat generation rate slightly decreases after the heat generation rate reaches a maximum in the period in which the low temperature oxidation reaction before ignition occurs. Thereafter, the air-fuel mixture is ignited to cause a high-temperature oxidation reaction, whereby the heat generation rate increases rapidly.

  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 changes so as to become a maximum after being minimized, for example. Here, the change in the heat generation rate from the minimum value to the maximum value becomes larger as the low-temperature oxidation reaction becomes more active. Therefore, the difference between the minimum value and maximum value of the estimated heat release rate, that is, the difference between the maximum value and the minimum value of the estimated heat release rate in the latter part of the compression stroke and before ignition is calculated as the reaction amount of the low-temperature oxidation reaction. Can be considered.

  However, when the low-temperature oxidation reaction is small as in the high-load high-rotation region A2, the change in the heat generation rate is small, and the maximum value and the minimum value of the estimated heat generation rate in the late stage of the compression stroke and before the ignition period. It is difficult to obtain the value with high accuracy. Even in the high-load low-rotation region A1, for example, when the recirculation amount of EGR gas is large, the oxygen concentration in the air-fuel mixture tends to be low, and the low-temperature oxidation reaction tends to be small. For this reason, even in the high-load low-rotation region A1, it may be difficult to accurately obtain the maximum value and the minimum value of the estimated heat generation rate in the later stage of the compression stroke and in the period before ignition.

  On the other hand, when the inventors of the present application have made extensive studies, the present inventors have determined that the crank angle at which the heat generation rate is minimized and the crank angle at which the heat generation rate is maximized due to the low-temperature oxidation reaction are the engine rotation speed. It was determined that the number was determined to be substantially constant according to the number. Therefore, in the first embodiment, the low temperature oxidation reaction amount estimation unit 102 uses the first reaction amount estimation unit 102a to calculate the maximum value and the minimum value of the estimated heat generation rate in the period after the compression stroke and before ignition. The difference is calculated as the first estimated response amount. Further, the low temperature oxidation reaction amount estimation unit 102 uses the second reaction amount estimation unit 102b to set a first heat generation rate that is an estimated heat generation rate when the crank angle is the first crank angle CA1, and a crank angle that is the first. A difference from the second heat generation rate, which is an estimated heat generation rate at the second crank angle CA2 on the retard side with respect to the crank angle CA1, is calculated as a second estimated reaction amount. Then, when the first estimated reaction amount is equal to or greater than the predetermined reaction amount, the low temperature oxidation reaction amount estimation unit 102 estimates the reaction amount of the low temperature oxidation reaction based on the first estimated reaction amount, while the first estimated reaction amount is When the amount is less than the predetermined reaction amount, the reaction amount of the low temperature oxidation reaction is estimated based on the second estimated reaction amount. More specifically, in the first embodiment, the low temperature oxidation reaction amount estimation unit 102 estimates the first estimated reaction amount as the reaction amount of the low temperature oxidation reaction when the first estimated reaction amount is greater than or equal to the predetermined reaction amount. When the first estimated reaction amount is less than the predetermined reaction amount, the second estimated reaction amount is estimated as the reaction amount of the low temperature oxidation reaction. In the first embodiment, the predetermined reaction amount is, for example, 1.5 J / deg. Is set to

  FIG. 7 shows the result of calculation by simulation of the change in the heat generation rate due to the low temperature oxidation reaction in the high load high rotation range. The curves L1 to L3 in FIG. 7 have different engine speeds. Specifically, the curve L1 is a curve at the lowest engine speed among the curves L1 to L3, and the curve L3 is a curve at the highest engine speed among the curves L1 to L3. A curve L2 is a curve at an engine speed between the engine speed of the curve L1 and the engine speed of the curve L3.

  As shown in FIG. 7, it can be seen that the curves L1 to L3 change so as to become maximum after being minimized immediately before the high-temperature oxidation reaction in which the heat generation rate rapidly increases. In each of the curves L1 to L3, the change that becomes the maximum after becoming the minimum corresponds to the change in the heat generation rate due to the low-temperature oxidation reaction. In the first embodiment, as shown in FIG. 7, the minimum crank angle is set to the first crank angle CA1 and the maximum crank angle is set during the period in which the heat generation rate is changed by the low temperature oxidation reaction. The second crank angle CA2 is set. The first crank angle CA1 is a crank angle at which the heat generation rate is estimated to be minimum within the period in which the heat generation rate changes due to the low-temperature oxidation reaction, that is, in the late stage of the compression stroke and before the ignition. On the other hand, the second crank angle CA2 is a crank angle at which the heat generation rate is estimated to be maximum within the period in which the heat generation rate changes due to the low-temperature oxidation reaction, that is, in the latter half of the compression stroke and before the ignition. is there. Note that the first crank angle CA1 may be a crank angle at which the heat generation rate is estimated to be minimum, and the actual heat generation rate changes when the crank angle is the first crank angle CA1. Need not be minimal. Further, the second crank angle CA2 may be a crank angle at which the heat generation rate is estimated to be the maximum, and when the crank angle is the second crank angle CA2 in the actual change in the heat generation rate, the heat generation rate is strict. Need not be the largest.

  Further, as shown in FIG. 7, it can be seen that the higher the engine speed, the more the first crank angle CA1 and the second crank angle CA2 are on the advance side. That is, the first crank angle CA1 and the second crank angle CA2 change depending on the engine speed. For this reason, the second reaction amount estimation unit 102b sets the first crank angle CA1 and the second crank angle CA2 according to the engine speed. More specifically, in the first embodiment, the second reaction amount estimation unit 102b is configured to set the first crank angle CA1 and the second crank angle CA2 to the advance side as the engine speed increases. Has been.

  Further, as shown in FIG. 7, even if the engine speed changes, the length of the period from the first crank angle CA1 to the second crank angle CA2, that is, the first crank angle CA1 and the second crank angle CA2 It can be seen that the angle difference is substantially constant. Therefore, in the first embodiment, the second reaction amount estimation unit 102b is configured to set the length of the period from the first crank angle CA1 to the second crank angle CA2 to be substantially constant.

  The PCM 100 stores a map and a relational expression for setting the first crank angle CA1 and the second crank angle CA2 calculated by the above simulation. Actually, the second reaction amount estimation unit 102b reads the map and the relational expression, and sets the first crank angle CA1 and the second crank angle CA2 according to the engine speed.

  Then, the second reaction amount estimation unit 102b uses the set first crank angle CA1 and second crank angle CA2 to calculate the difference between the first heat generation rate and the second heat generation rate as the second estimated reaction amount. Calculate as As a result, even when the change in the in-cylinder pressure is small and it is difficult to estimate the reaction amount of the low-temperature oxidation reaction from the maximum value and minimum value of the estimated heat release rate, the reaction amount of the low-temperature oxidation reaction is accurately determined. Can be estimated.

  As described above, the low temperature oxidation reaction amount estimation unit 102 has a large change in the estimated heat generation rate, and when the actual maximum value and minimum value of the estimated heat generation rate can be accurately estimated, the first reaction amount estimation unit 102 The first estimated reaction amount calculated by 102a is estimated as the reaction amount of the low temperature oxidation reaction. On the other hand, when the change in the estimated heat generation rate is small and it is difficult to accurately estimate the actual maximum value and minimum value of the estimated heat generation rate, the low temperature oxidation reaction amount estimation unit 102 calculates the second reaction amount estimation unit 102b. The estimated second reaction amount is estimated as the reaction amount of the low temperature oxidation reaction. Thereby, the reaction amount of the low temperature oxidation reaction can be accurately estimated.

  In addition, in the change in the heat generation rate due to the low-temperature oxidation reaction, the heat generation rate may become a substantially constant value without decreasing after the heat generation rate reaches the maximum (maximum). At this time, for example, the reaction amount of the low-temperature oxidation reaction may be estimated by regarding the substantially constant value as the maximum value of the estimated heat generation rate in the later stage of the compression stroke and in the period before ignition.

  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 greater than the above-mentioned specific reaction amount, specifically, the reaction amount that affects the increase in noise or damage to the piston 5 or the like. Execute control.

  In the first embodiment, the knocking suppression unit 103 supplies the cooling medium into the combustion chamber 6 in the first half of a period in which the high-temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber 6 as knocking suppression control. 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 the additional injection is set in advance by experiments or the like. Specifically, a combustion period (period in which a high-temperature oxidation reaction occurs) when knocking suppression control (here, additional injection of fuel) is not executed is detected or estimated, and a half period thereof is obtained. Next, a crank angle equal to or 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. And knocking suppression part 103 controls injector 14 so that additional injection Q2 may be performed at the execution time concerned.

  In the first embodiment, the standby angle is set to be equal to or shorter than the period from the start of combustion to the combustion center of gravity. The combustion center-of-gravity time is a time (crank angle) at which heat generation of 50% of the total amount of heat generated during one combustion cycle occurs. The standby angle is, for example, a timing (crank angle) from the start of the high temperature oxidation reaction until the generation of heat of about 30% of the total amount of heat generated during one combustion cycle (crank angle). It is about 15 ° after the point. The fuel injection amount in the additional injection Q2 is set to 10% or less, more specifically, about 5% of the total amount of fuel supplied to the combustion chamber 6 in one combustion cycle.

  Next, the processing operation of the PCM 100 when executing the knocking suppression control will be described with reference to FIGS. 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. The heat generation rate is estimated by the heat generation rate estimation unit 101. The processing operation based on this flowchart is executed for each combustion cycle while the engine 1 is operating.

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

  In the next step S2, the PCM 100 determines whether or not the operation region of the engine 1 is the high load region A. When the operation region of the engine 1 is the high load region A, the process proceeds to step S3, while when the operation region of the engine 1 is the low load region B, the process returns.

  In step S3, the PCM 100 sets a first crank angle CA1 and a second crank angle CA2. In step S3, the PCM 100 calculates the engine speed based on the information from the crank angle sensor SN1, and sets the first crank angle CA1 and the second crank angle CA2 according to the engine speed.

  In the next step S4, the PCM 100 determines whether or not it is the late stage of the compression stroke. Whether or not it is the latter half of the compression stroke is determined by the crank angle detected by the crank angle sensor SN1. When YES is in the latter half of the compression stroke, the PCM 100 proceeds to step S5. On the other hand, when NO is in the middle of the compression stroke, the PCM 100 repeats the determination in step S4 until the latter half of the compression stroke.

  In step S5, 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 subsequent step S6, the reaction amount of the low temperature oxidation reaction is estimated. A flowchart for estimating the reaction amount of the low-temperature oxidation reaction will be described later.

  In the next step S7, the PCM 100 determines whether or not the reaction amount of the low temperature oxidation reaction is greater than or equal to the specific reaction amount. When the reaction amount of the low temperature oxidation reaction is greater than or equal to the specific reaction amount, the process proceeds to step S8, while when the reaction amount of the low temperature oxidation reaction is less than the specific reaction amount, the process returns.

  In step S8, the PCM 100 executes knocking suppression control. In this knocking suppression control, as described above, fuel is additionally injected into the combustion chamber 6 in the first half of the period in which the high-temperature oxidation reaction of the air-fuel mixture occurs in the combustion chamber 6. After step S8, the process returns.

  FIG. 9 is a flowchart showing a subroutine for estimating the reaction amount of the low-temperature oxidation reaction, that is, the contents of step S6.

  In the estimation of the low temperature oxidation reaction, first, steps S101 to S103 for calculating the first estimated reaction amount and steps S104 to S108 for estimating the second estimated reaction amount are executed in parallel.

  In step S101, the PCM 100 calculates the minimum value of the estimated heat generation rate in the latter half of the compression stroke. In the next step S102, the PCM 100 calculates the maximum value of the estimated heat release rate in the latter half of the compression stroke.

  In the subsequent step S103, the PCM 100 determines the difference between the minimum value of the estimated heat generation rate calculated in step S101 and the maximum value of the estimated heat generation rate calculated in step S102, specifically, step S102. The first estimated reaction amount is calculated by obtaining a value obtained by subtracting the minimum value of the estimated heat generation rate calculated in step S101 from the maximum value of the estimated heat generation rate calculated in step S101.

  On the other hand, in step S104, the PCM 100 determines whether or not the crank angle has reached the first crank angle CA1. The first crank angle CA1 is the first crank angle CA1 set in step S3. Whether or not the crank angle has reached the first crank angle CA1 is determined from the detection result of the crank angle sensor SN1. When the crank angle becomes YES at the first crank angle CA1, the PCM 100 proceeds to step S105 and calculates a first heat generation rate that is an estimated heat generation rate when the crank angle is the first crank angle CA1. After step S105, the process proceeds to step S106. On the other hand, when the crank angle is NO which is not the first crank angle CA1, the PCM 100 repeats the determination in step S104 until the crank angle becomes the first crank angle CA1.

  In the next step S106, the PCM 100 determines whether or not the crank angle has reached the second crank angle CA2. The second crank angle CA2 is the second crank angle CA2 set in step S3. Whether or not the crank angle has reached the second crank angle CA2 is determined from the detection result of the crank angle sensor SN1. When the crank angle is YES at the second crank angle CA2, the PMC 100 proceeds to step S107 and calculates a second heat generation rate that is an estimated heat generation rate when the crank angle is the second crank angle CA2. After step S107, the process proceeds to step S108. On the other hand, when the crank angle is NO that is not the second crank angle CA2, the PCM 100 repeats the determination in step S106 until the crank angle becomes the second crank angle CA2.

  In subsequent step S108, the PCM 100 determines the difference between the first heat generation rate calculated in step S105 and the second heat generation rate calculated in step S107, specifically, the second heat generation rate. A value obtained by subtracting the first heat generation rate from the rate is obtained, and the second estimated reaction amount is calculated.

  In step S109 after the first estimated reaction amount and the second estimated reaction amount are calculated, the PCM 100 determines whether or not the first estimated reaction amount is greater than or equal to a predetermined reaction amount. The PCM 100 proceeds to step S110 when the first estimated reaction amount is greater than or equal to the predetermined reaction amount, and proceeds to step S111 when the first estimated reaction amount is less than the predetermined reaction amount.

  In step S110, the PCM 100 employs the first estimated reaction amount as the reaction amount of the low temperature oxidation reaction. On the other hand, in the above step S111, the PCM 100 employs the second estimated reaction amount as the reaction amount of the low temperature oxidation reaction. After step S110 and step S111, the process returns to return to the processing operation for executing the knocking suppression control.

  As described above, the estimation accuracy of the reaction amount of the low-temperature oxidation reaction can be increased by estimating the reaction amount of the low-temperature oxidation reaction. Thereby, since the determination accuracy of whether or not there is a possibility of knocking is increased, knocking can be effectively suppressed.

  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 estimated from the second estimated reaction amount. Here, a time chart in a high-load high-rotation region in which the reaction amount of the low-temperature oxidation reaction tends to be particularly small is shown. The first crank angle CA1 and the second crank angle CA2 are calculated according to the engine speed.

  First, fuel injection Q1 is performed in the intake stroke. Then, it passes through the compression bottom dead center and enters the compression stroke. Then, when the piston 5 is positioned in the vicinity of the compression top dead center through the middle of the compression stroke and after the middle of the compression stroke, a low temperature oxidation reaction occurs and the heat generation rate increases.

  The crank angle becomes the first crank angle CA1 and the detection flag for the first crank angle CA1 is set in the vicinity where the heat generation rate shows a minimum value (the minimum value in the latter half of the compression stroke and before ignition). The PCM 100 calculates the estimated heat generation rate when the detection flag for the first crank angle CA1 is set as the first heat generation rate.

  When the piston 5 approaches the compression top dead center, the low-temperature oxidation reaction proceeds, and the heat generation rate shows a maximum value (the maximum value in the latter half of the compression stroke and before ignition). In the vicinity of the maximum heat generation rate, the crank angle becomes the second crank angle CA2, and the detection flag for the second crank angle CA2 is set. The PCM 100 calculates the estimated heat generation rate when the detection flag for the second crank angle CA2 is set as the second heat generation rate.

  Thereafter, the PCM 100 calculates the second estimated reaction amount, and when the second estimated reaction amount is equal to or greater than the specific reaction amount, as shown in FIG. 10, the crank angle before ignition of the air-fuel mixture in the combustion chamber 6, particularly A knocking suppression control execution flag is set at a crank angle before the ignition start timing of the spark plug 13. 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. Thereby, it is suppressed that a local high temperature area | region generate | occur | produces in the combustion chamber 6, and knocking is suppressed appropriately.

  Therefore, in the present embodiment, the low-temperature oxidation reaction amount estimation unit 102 calculates the difference between the maximum value and the minimum value of the estimated heat generation rate as the first estimated reaction amount in the late stage of the compression stroke and before the ignition. The first reaction amount estimation unit 102a, the estimated heat generation rate when the crank angle is the first crank angle CA1, and the estimation when the crank angle is the second crank angle CA2 that is retarded from the first crank angle CA1 A second reaction amount estimation unit 102b that calculates a difference from the heat generation rate as a second estimated reaction amount, and when the first estimated reaction amount is equal to or greater than a predetermined reaction amount, the first estimated reaction amount is subjected to low temperature oxidation While the reaction amount is estimated as the reaction amount, when the first estimated reaction amount is less than the predetermined reaction amount, the second estimated reaction amount is estimated as the reaction amount of the low temperature oxidation reaction. Small change , From the maximum value and the minimum value of the estimated heat release rate effected even if such is difficult to estimate the reaction amount of the low-temperature oxidation reaction, it is possible to accurately estimate the reaction amount of the low-temperature oxidation reaction.

  Further, when the estimated reaction amount of the low-temperature oxidation reaction is equal to or greater than a predetermined specific reaction amount, additional injection of fuel is executed as knocking suppression control, so that a local high-temperature region is present in the combustion chamber 6. Generation | occurrence | production is suppressed and knocking is suppressed appropriately.

  Furthermore, as the knocking suppression control, the additional fuel injection is in the first half of the period during which the high-temperature oxidation reaction occurs, so that the additionally injected fuel can be sufficiently combusted. Thereby, even if the inside of the combustion chamber 6 is cooled by the additional injection of fuel, it is possible to suppress the engine torque from being lowered.

(Embodiment 2)
Hereinafter, Embodiment 2 will be described in detail with reference to the drawings. In the following description, portions common to the first embodiment are denoted by the same reference numerals, and detailed description thereof is 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 the knocking suppression control, the ignition start timing by the spark plug 13 is retarded from the ignition start timing when the reaction amount of the low-temperature oxidation reaction is less than the specific reaction amount. More specifically, the ignition start timing by the spark plug is made after the compression top dead center. The ignition timing of the air-fuel mixture is retarded by retarding the ignition start timing by the spark plug 13. Thereby, the in-cylinder pressure at the time of high temperature oxidation reaction can be reduced. As a result, knocking can be appropriately suppressed.

  FIG. 11 is an example of a time chart when performing knocking suppression control based on the reaction amount of the low-temperature oxidation reaction estimated from the second estimated reaction amount in the second embodiment. The first crank angle CA1 and the second crank angle CA2 are calculated according to the engine speed.

  As shown in FIG. 11, when the PCM 100 calculates the second estimated reaction amount and the second estimated reaction amount is equal to or greater than the specific reaction amount, knocking suppression is performed at a crank angle before the ignition start timing of the spark plug 13. A control execution flag is set. When the knocking suppression control execution flag is set, the PCM 100 executes knocking suppression control, and sets the ignition start timing by the spark plug 13 later than the compression top dead center. As a result, as shown in FIG. 11, the start time of the high-temperature oxidation reaction is retarded compared to when knocking suppression control is not executed (indicated by a one-dot chain line in the heat generation rate graph). For this reason, the in-cylinder pressure at the time of the high-temperature oxidation reaction is lower than when the knocking suppression control is not executed. As a result, the occurrence of a local high pressure region in the combustion chamber 6 is suppressed, and knocking is appropriately suppressed.

  Note that 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, and a description thereof will be omitted.

(Other embodiments)
The technology disclosed herein is not limited to the above-described embodiment, and can be substituted without departing from the scope of the claims.

  For example, in the first and second embodiments, the crank angle is determined based on the detection result of the crank angle sensor SN1 as to whether or not the crank angle has reached the first crank angle CA1 and the second crank angle CA2. For example, you may make it determine based on the elapsed time from a compression bottom dead center. That is, the time from the compression bottom dead center to the first crank angle CA1 and the time from the compression bottom dead center to the second crank angle CA2 are calculated according to the engine speed, and the calculated time has elapsed. Then, it may be determined that the crank angle has reached the first crank angle CA1 and the second crank angle CA2.

  In the first embodiment, the cooling medium injected into the combustion chamber 6 in the additional injection Q2 is fuel. However, the present invention 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.

  Furthermore, in the first embodiment, the injection amount in the additional injection Q2 is set to 10% or less of the total amount of fuel supplied to the combustion chamber 6 in one cycle. It is good also as above.

  In the second embodiment, the ignition start timing by the spark plug 13 is delayed until after the compression top dead center. However, the present invention is not limited to this, and the ignition start timing can be increased as long as knocking can be suppressed. It may be before the dead point.

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

  The technology disclosed herein has a cylinder in which a combustion chamber is formed, and a crankshaft that is rotationally driven by a reciprocating motion of a piston inserted into the cylinder, and is a mixture of fuel containing gasoline and air This is useful for an engine that burns air in a combustion chamber.

DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder 5 Piston 6 Combustion chamber 7 Crankshaft 13 Spark plug 101 Heat generation rate estimation part (heat generation rate estimation means)
102 Low temperature oxidation reaction amount estimation unit (low temperature oxidation reaction amount estimation means)
102a 1st reaction amount estimation part (1st reaction amount estimation means)
102b 2nd reaction amount estimation part (2nd reaction amount estimation means)
103 Knocking suppression unit (knocking suppression means)
SN1 Crank angle sensor (crank angle detection means)
SN3 In-cylinder pressure sensor (in-cylinder pressure detection means)

Claims (12)

A cylinder having a combustion chamber and a crankshaft that is rotationally driven by a reciprocating motion of a piston inserted in the cylinder, and combusts an air-fuel mixture containing gasoline and air in the combustion chamber. An engine low-temperature oxidation reaction detection method for detecting a low-temperature oxidation reaction of an air-fuel mixture in the combustion chamber in an engine,
An in-cylinder pressure detecting step for detecting the pressure in the cylinder;
A crank angle detection step for detecting the crank angle;
A heat release rate estimation step of estimating a heat release rate in the combustion chamber based on the in-cylinder pressure detected in the in-cylinder pressure detection step;
A low-temperature oxidation reaction amount estimation step for estimating a reaction amount of a low-temperature oxidation reaction based on an estimated heat generation rate in a later stage of the compression stroke and within a period before ignition estimated in the heat generation rate estimation step,
The low temperature oxidation reaction amount estimation step includes:
A first reaction amount estimation step for calculating a difference between the maximum value and the minimum value of the estimated heat generation rate in a later period of the compression stroke and before ignition as a first estimated reaction amount;
Setting a first crank angle that is a crank angle in a later stage of the compression stroke and in a period before ignition according to the engine speed, and a second crank angle that is retarded from the first crank angle; ,
A second reaction that calculates a difference between the estimated heat generation rate when the crank angle is the first crank angle and the estimated heat generation rate when the crank angle is the second crank angle as a second estimated reaction amount. A quantity estimation step,
When the first estimated reaction amount is greater than or equal to the predetermined reaction amount, the reaction amount of the low temperature oxidation reaction is estimated based on the first estimated reaction amount, while when the first estimated reaction amount is less than the predetermined reaction amount A method for detecting a low-temperature oxidation reaction of an engine, which is a step of estimating a reaction amount of a low-temperature oxidation reaction based on the second estimated reaction amount. The low-temperature oxidation reaction detection method for an engine according to claim 1,
The first crank angle is a crank angle that is estimated to have a minimum heat generation rate in a later period of the compression stroke and in a period before ignition.
The method for detecting a low-temperature oxidation reaction of an engine, wherein the second crank angle is a crank angle that is estimated to have a maximum heat generation rate in a later period of a compression stroke and in a period before ignition. The low-temperature oxidation reaction detection method for an engine according to claim 1 or 2,
In the second reaction amount estimation step, the first crank angle and the second crank angle are set to the advance side as the engine speed is higher. An engine control method using the low-temperature oxidation reaction detection method for an engine according to any one of claims 1 to 3,
Knocking suppression that suppresses knocking in the combustion chamber when the reaction amount of the low-temperature oxidation reaction estimated in the low-temperature oxidation reaction amount estimation step is equal to or larger than a specific reaction amount that is set in advance and smaller than the predetermined reaction amount. An engine control method comprising a knocking suppression step for executing control. The engine control method according to claim 4,
The engine control method according to claim 1, wherein the knocking suppression control is control for supplying a cooling medium into 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. The engine control method according to claim 4,
The engine is an engine that compresses the air-fuel mixture in the combustion chamber and burns the air-fuel mixture in the combustion chamber by ignition with a spark plug.
The engine control is characterized in that the knocking suppression control is a control for retarding an ignition start timing by the spark plug from an ignition start timing when a reaction amount of the low-temperature oxidation reaction is less than the specific reaction amount. Method. A cylinder having a combustion chamber and a crankshaft that is rotationally driven by a reciprocating motion of a piston inserted in the cylinder, and combusts an air-fuel mixture containing gasoline and air in the combustion chamber. An engine low temperature oxidation reaction detection device,
In-cylinder pressure detecting means for detecting the pressure in the cylinder;
Crank angle detecting means for detecting the crank angle;
Heat generation rate estimation means for estimating a heat generation rate in the combustion chamber based on the in-cylinder pressure detected by the in-cylinder pressure detection means;
Low-temperature oxidation reaction that estimates the reaction amount of the low-temperature oxidation reaction of the air-fuel mixture in the combustion chamber based on the estimated heat generation rate in the later stage of the compression stroke and within the period before ignition estimated by the heat generation rate estimation means A quantity estimation means,
The low temperature oxidation reaction amount estimation means is:
A first reaction amount estimation unit that calculates a difference between the maximum value and the minimum value of the estimated heat generation rate in the latter half of the compression stroke and before ignition as a first estimated reaction amount;
A difference between the estimated heat generation rate when the crank angle is the first crank angle and the estimated heat generation rate when the crank angle is the second crank angle retarded from the first crank angle is a second. A second reaction amount estimation unit that calculates the estimated reaction amount;
When the first estimated reaction amount is greater than or equal to the predetermined reaction amount, the first estimated reaction amount is estimated as the reaction amount of the low temperature oxidation reaction, while when the first estimated reaction amount is less than the predetermined reaction amount, It is configured to estimate the second estimated reaction amount as the reaction amount of the low temperature oxidation reaction,
The low temperature oxidation reaction of the engine, wherein the first crank angle and the second crank angle are respectively set in advance according to the engine speed, and are crank angles in a period after the compression stroke and before ignition. Detection device. The engine low-temperature oxidation reaction detection device according to claim 7,
The first crank angle is a crank angle that is estimated to have a minimum heat generation rate in a later period of the compression stroke and in a period before ignition.
2. The engine low temperature oxidation reaction detection device according to claim 1, wherein the second crank angle is a crank angle that is estimated to have a maximum heat generation rate in a later stage of the compression stroke and in a period before ignition. The engine low-temperature oxidation reaction detection device according to claim 7 or 8,
The engine low-temperature oxidation reaction detection device, wherein the first crank angle and the second crank angle in the second reaction amount estimation unit are set to an advance side as the engine speed increases. An engine control device using the engine low-temperature oxidation reaction detection device according to any one of claims 7 to 9,
When the reaction amount of the low-temperature oxidation reaction estimated by the low-temperature oxidation reaction amount estimation means is not less than a specific reaction amount that is set in advance and smaller than the predetermined reaction amount, for suppressing knocking in the combustion chamber An engine control device comprising knocking suppression means for performing knocking suppression control. The engine control device according to claim 10, comprising:
The engine control apparatus according to claim 1, wherein the knocking suppression control is control for supplying a cooling medium into 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. The engine control device according to claim 10, comprising:
The above engine
A spark plug configured to ignite the air-fuel mixture in the combustion chamber;
The air-fuel mixture is compressed in the combustion chamber, and the air-fuel mixture is combusted in the combustion chamber by ignition with a spark plug.
The engine control is characterized in that the knocking suppression control is a control for retarding an ignition start timing by the spark plug from an ignition start timing when a reaction amount of the low-temperature oxidation reaction is less than the specific reaction amount. apparatus.

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