JP2019173703A - Control method of engine, knock detection method, and control device of engine - Google Patents

Abstract

To more surely suppress knocking.SOLUTION: A first calculation process for calculating a low temperature oxidation reaction level representing an occurrence rate of low temperature oxidation reaction on the basis of a cylinder internal pressure during a specific period from a compression stroke latter period to an expansion stroke initial period, a second calculation process for calculating a degree of combustion steepness representing steepness of combustion after start of high temperature oxidation reaction with flame, an estimation process for estimating occurrence of knocking on the basis of the low temperature oxidation reaction level calculated in the first calculation process and the degree of combustion steepness calculated in the second calculation process, and a knock suppression process for supplying a refrigerant for lowering a temperature in the cylinder to the cylinder when necessary on the basis of a result of the estimation process, are executed.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a control method, a knock detection method, and a control device for an engine including a cylinder in which a fuel-air mixture containing gasoline burns.

  Conventionally, in the field of engines, it is known that abnormal combustion called knocking may occur locally when the engine load is high. As for knocking, various measures are taken to prevent the occurrence of knocking knocking with high pressure in the cylinder. Specifically, under conditions where the engine load is high and the temperature in the combustion chamber is high, the mixture of fuel and air self-ignites and burns at the outer periphery of the combustion chamber separately from the main combustion, causing a high pressure wave and knocking. That is, vibration of the cylinder or piston occurs. If knocking occurs, noise increases and the piston or the like may be damaged, and it is required to prevent this.

  For example, Patent Document 1 discloses an engine that is provided with a knock sensor that detects knocking in an engine body, and delays the ignition timing when knocking is detected by the knock sensor to avoid the occurrence of knocking. It is disclosed.

JP 2008-291758 A

  In the method of detecting knocking using a knock sensor, it is found that the knocking is likely to occur only when knocking occurs. Therefore, it can only be avoided that knocking occurs continuously, and the occurrence of knocking itself cannot be prevented. That is, the occurrence of knocking cannot be sufficiently suppressed.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an engine control method, a knock detection method, and an engine control device that can more reliably suppress knocking. .

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research and found that knocking may occur when a low-temperature oxidation reaction occurs before combustion of the air-fuel mixture starts, that is, before a high-temperature oxidation reaction starts. Was very expensive.

  The low-temperature oxidation reaction is a reaction accompanied by slight heat generation exceeding the cooling loss. When the temperature in the combustion chamber (cylinder) is high, oxygen is extracted from hydrocarbons constituting the fuel by oxygen radicals or the like. It is a reaction to start. The low-temperature oxidation reaction occurs before a high-temperature oxidation reaction that is a reaction that generates high thermal energy while generating a flame, that is, before so-called combustion is started. Knocking occurs when the temperature in the combustion chamber is high. Therefore, as described above, when the air-fuel mixture undergoes a low-temperature oxidation reaction, it is considered that the subsequent knocking is caused by the high temperature in the combustion chamber.

  Here, as described above, the low-temperature oxidation reaction occurs before the start of combustion of the air-fuel mixture and at a time sufficiently earlier than the time when knocking occurs. Therefore, if the occurrence of knocking is predicted based on the low-temperature oxidation reaction level indicating the degree of occurrence of the low-temperature oxidation reaction, it is possible to predict the occurrence of knocking at a sufficiently early time with respect to the time when knocking occurs. Become.

  On the other hand, although knocking occurs with a very high probability if the low-temperature oxidation reaction level is high, knocking may not occur even when the low-temperature oxidation reaction level is high, and even though the low-temperature oxidation reaction level is low The knowledge that knocking sometimes occurs was obtained. In contrast, the inventors of the present application have further found that knocking is more likely to occur when the combustion after the start of the high-temperature oxidation reaction is sharper.

  The present invention has been made on the basis of the above knowledge, and includes a cylinder in which a mixture of fuel containing gasoline and air burns, and detection means for detecting an in-cylinder pressure that is a pressure in the cylinder. A method for controlling an engine including a low-temperature oxidation reaction level representing a degree of occurrence of a low-temperature oxidation reaction based on an in-cylinder pressure detected by the detection means during a specific period from a late compression stroke to an early expansion stroke A first calculation step, a second calculation step for calculating a combustion steepness representing a steepness of combustion after the start of a high-temperature oxidation reaction accompanied by a flame based on the in-cylinder pressure during the specific period, and the first A prediction step of predicting the occurrence of knocking based on the low temperature oxidation reaction level calculated in the calculation step and the combustion steepness calculated in the second calculation step, and when necessary based on the result of the prediction step, Above A coolant to reduce the temperature in the cylinder and a knock suppression supplying to said cylinder, characterized in that (claim 1).

  According to this method, a low-temperature oxidation reaction level that is correlated with the occurrence of knocking and that indicates the degree of low-temperature oxidation reaction that occurs earlier than the timing at which knocking occurs, and a high-temperature oxidation reaction that is highly correlated with the occurrence of knocking. The occurrence of knocking is predicted based on the combustion steepness that represents the steepness of combustion after the start, so it is possible to detect early that knocking is likely to occur and to accurately predict the occurrence of knocking. can do. And based on this prediction result, a refrigerant | coolant can be effectively supplied in a cylinder and knocking can be suppressed more reliably.

  In the method, the knock suppression step starts the supply of the refrigerant when a first condition that the low-temperature oxidation reaction level calculated in the first calculation step is equal to or higher than a reference level is satisfied. After the step and the first step, when the second condition that the combustion steepness calculated in the second calculation step is equal to or higher than a reference value is satisfied, the supply of the refrigerant is continued, and the second Preferably, the method includes a second step of stopping the supply of the refrigerant when the above condition is not satisfied (claim 2).

  According to this method, when knocking occurs, the refrigerant can be more reliably supplied into the cylinder at an appropriate time to prevent the occurrence of knocking, and when knocking does not occur, the refrigerant can enter the cylinder. It is possible to prevent the temperature in the cylinder from being excessively lowered by being supplied.

  In the method, it is preferable that in the knock suppression step, an additional fuel different from the normal fuel supplied regardless of knocking is injected into the cylinder as the refrigerant.

  According to this method, it is not necessary to separately provide a device for supplying the refrigerant to the cylinder.

  In the method, in the first calculation step, an increase amount of a heat generation rate during a first period that is a part of the specific period is calculated as the low-temperature oxidation reaction level, and in the second calculation step, the combustion is performed. As the steepness, it is preferable to calculate an increase amount of the in-cylinder pressure during the second period that is included in the specific period and set to the retarded side with respect to the first period.

  According to this method, occurrence of knocking can be predicted with high accuracy.

  The present invention is also a method for detecting knocking that occurs in an engine, including a cylinder in which a mixture of gasoline-containing fuel and air burns, and detection means for detecting in-cylinder pressure, which is the pressure in the cylinder. A first calculation step of calculating a low-temperature oxidation reaction level representing the degree of occurrence of the low-temperature oxidation reaction based on the in-cylinder pressure detected by the detection means during a specific period from the latter stage of the compression stroke to the initial stage of the expansion stroke; Based on the in-cylinder pressure during the specific period, it is determined that a high-temperature oxidation reaction accompanied by a flame has occurred, and a second calculation for calculating a combustion steepness that represents the steepness of combustion after the start of the high-temperature oxidation reaction And a prediction step of predicting the occurrence of knocking based on the low-temperature oxidation reaction level calculated in the first calculation step and the combustion steepness calculated in the second calculation step. It provides a knock detecting method for an engine according to claim (Claim 5).

  According to this method, it is possible to detect that knocking is highly likely to occur at an early stage and to accurately predict the occurrence of knocking. Therefore, if this method is used, an operation for suppressing knocking can be performed early and appropriately, and knocking can be more reliably prevented.

  The present invention also relates to an engine control device having a cylinder in which a mixture of fuel containing gasoline and air burns, the detecting means for detecting an in-cylinder pressure that is a pressure in the cylinder, and the cylinder A refrigerant supply means for supplying a refrigerant for lowering the internal temperature into the cylinder, and a control means for controlling the refrigerant supply means. The control means is a specific period from the latter stage of the compression stroke to the initial stage of the expansion stroke. Based on the in-cylinder pressure detected by the detection means, a low temperature oxidation reaction level representing the degree of occurrence of the low temperature oxidation reaction is calculated, and the first condition that the low temperature oxidation reaction level is equal to or higher than a reference level is satisfied. In accordance with the above, the refrigerant supply means starts supply of the refrigerant, and based on the in-cylinder pressure during the specific period, combustion representing the steepness of combustion after the start of the high-temperature oxidation reaction with a flame When the second condition that the steepness is calculated and the combustion steepness is equal to or higher than a reference value is satisfied, the supply of the refrigerant is continued. When the second condition is not satisfied, the supply of the refrigerant is not performed. An engine control device is provided that controls the refrigerant supply means so as to be stopped (Claim 6).

  According to this apparatus, it is possible to detect early that knocking is likely to occur, and to accurately predict the occurrence of knocking. And based on this prediction result, a refrigerant | coolant can be effectively supplied to a cylinder and knocking can be suppressed more reliably.

  As described above, according to the present invention, knocking can be more reliably suppressed.

It is a figure showing composition of an engine system concerning one embodiment of the present invention. It is a block diagram which shows the control system of an engine. It is the figure which showed the control map. It is the figure which showed an example of the fuel injection timing in a high load area | region, ignition timing, and a heat release rate. It is the figure which compared and showed the change of the heat release rate when knocking generate | occur | produces and when it does not generate | occur | produce. FIG. 6 is an enlarged view of FIG. 5. It is the figure which compared and showed the change of the in-cylinder pressure when knocking generate | occur | produces and when it does not occur. It is the flowchart which showed the flow of knock determination and knock avoidance control. It is the figure which showed each crank change of each parameter when knock determination and knock avoidance control are implemented. It is the figure which showed each crank change of each parameter when knock determination and knock avoidance control are implemented. It is the figure which showed each crank change of each parameter when knock determination and knock avoidance control are implemented.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing a configuration of an engine system to which an engine control device of the present invention is applied. The engine system of the present embodiment includes a four-stroke engine main body 1, an intake passage 20 for introducing combustion air into the engine main body 1, and an exhaust passage 30 for discharging exhaust gas generated by the engine main body 1. With.

  The engine body 1 is, for example, an in-line four-cylinder engine in which four cylinders 2 are arranged in series in a direction orthogonal to the paper surface of FIG. This engine system is mounted on a vehicle, and the engine body 1 is used as a drive source for the vehicle. In the present embodiment, the engine main body 1 is driven by receiving supply of fuel including gasoline. The fuel may be gasoline containing bioethanol or the like.

  The engine body 1 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 5 fitted to the cylinder 2 so as to be able to reciprocate (up and down). Have

  A combustion chamber 6 is formed above the piston 5. 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 crown 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. Here, the space between the crown surface of the piston 5 and the ceiling surface of the combustion chamber 6 in the inner space of the cylinder 2 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 geometric compression ratio of the engine body 1, that is, the ratio of the volume of the combustion chamber 6 when the piston 5 is at the bottom dead center to the volume of the combustion chamber 6 when the piston 5 is at the top dead center is 15 or more. It is set to 20 or less (for example, about 17).

  The cylinder head 4 has an intake port 9 for introducing the air supplied from the intake passage 20 into the cylinder 2 (combustion chamber 6), and an exhaust for generating exhaust gas generated in the cylinder 2 to the exhaust passage 30. An exhaust port 10 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 cylinder 2 side of each intake port 9 and an exhaust valve 12 that opens and closes an opening on the cylinder 2 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 a high load region where knocking is likely to occur, and fuel is injected from the injector 14 at a high pressure in the high load region. 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 50 MPa to 70 Ma in the high load region of the engine.

  The cylinder head 4 is provided with a spark plug 13 for igniting 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 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, the throttle valve 22 is basically fully opened or close to the opening, and is closed only when the engine is in a limited operating condition such as when the engine is stopped. The passage 20 is blocked.

  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 exhaust gas passing through the exhaust passage 30, that is, burned gas, to the intake passage 20 as EGR gas. 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 present embodiment, the EGR passage 41 is provided with an EGR cooler 43 for cooling the EGR gas passing therethrough. The EGR gas is cooled by the EGR cooler 43 and then returned to the intake passage 20. The

(2) Control System (2-1) System Configuration FIG. 2 is a block diagram showing an engine control system. The engine system of the present embodiment is centrally controlled by a PCM (powertrain control module, control means) 100. 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, and the PCM 100 is electrically connected to these sensors. For example, the cylinder block 3 is provided with a crank angle sensor SN1 that detects the engine speed. The intake passage 20 is provided with an air flow sensor SN2 that detects the amount of air taken into each cylinder 2 through the intake passage 20. The cylinder head 4 is provided with an in-cylinder pressure sensor SN3 that detects the pressure in the combustion chamber 6. One in-cylinder pressure sensor SN3 is provided for each cylinder 2. Further, the exhaust passage 30 is provided with an exhaust O2 sensor SN4 for detecting an exhaust oxygen concentration that is an oxygen concentration of exhaust gas flowing through the exhaust passage 20. Further, the vehicle is provided with an accelerator opening sensor SN5 that detects the opening degree (accelerator opening degree) of an accelerator pedal (accelerator opening degree) operated by the driver. In the present embodiment, the in-cylinder pressure sensor SN3 functions as detection means in the claims.

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

(2-2) Basic Control FIG. 3 is a control map in which the horizontal axis represents the engine speed and the vertical axis represents the engine load.

  In the present embodiment, there are a low load region B where the engine load is less than a preset first reference load Tq1 and knocking is difficult 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. Is set. In the high load region A, knock determination described later is performed to suppress the occurrence of knocking, and knock avoidance control is appropriately performed according to the result of the knock determination. In the present embodiment, as described above, the geometric compression ratio of the engine body 1 is set to 15 or more, and the temperature in the combustion chamber 6 is raised to a very high temperature. Therefore, knocking is particularly likely to occur.

  The high load area A is further divided into a high load low speed area A1 where the engine speed is less than a preset reference speed N1, and a high load high speed area A2 where the engine speed is equal to or higher than the reference speed N1. .

  In the present embodiment, in a region (region A1 and region B1) where the engine speed is less than the reference speed N1, compression auto-ignition combustion (SPCCI combustion, SPCCI: Spark Controlled Compression Ignition) is performed. In the 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 discharged from the spark plug 13 near the compression top dead center. Thereby, the air-fuel mixture around the spark plug 13 is forcibly ignited. Then, a flame propagates from the periphery of the spark plug 13 to the surroundings, and the surrounding air-fuel mixture is heated to self-ignite.

  On the other hand, in the region where the engine speed is equal to or higher than the reference speed N1 (region A2 and region B2), it is difficult to self-ignite the air-fuel mixture at a desired time, so SI combustion (used in a normal gasoline engine) Spark ignition combustion, SI (Spark Ignition) is performed. SI combustion is a combustion mode in which almost the entire air-fuel mixture is combusted by flame propagation, and discharge is performed from the ignition plug 13 near the compression top dead center, and the air-fuel mixture around the ignition plug 13 is forcibly ignited. . Then, the flame propagates from around the spark plug 13 to the surroundings, and the remaining air-fuel mixture is forcibly burned by the flame propagation.

(2-3) Knock avoidance control (knock suppression process)
Next, the knock avoidance control performed in the high load region A will be described with reference to FIG.

  In the present embodiment, in order to avoid knocking, control for injecting fuel from the injector 14 to the air-fuel mixture during combustion is performed as knock avoidance control.

  FIG. 4 is a diagram showing an example of fuel injection timing, ignition timing, and heat generation rate in a region (A2) in which SI combustion is performed in the high load region A. As shown by the solid line in FIG. 4, for example, in this region, during normal times when knock avoidance control is not performed, the fuel injection Q1 is performed only once in the latter period of the intake stroke. Then, in the vicinity of the compression top dead center (in the example of FIG. 7, at the compression top dead center), the air-fuel mixture is ignited by the spark plug 13. The fuel injection Q1 is a main injection for realizing the required engine torque. That is, the main injection Q1 is performed regardless of the presence or absence of knocking. The injection amount of the main injection Q1 is basically an amount corresponding to the required value of engine torque.

  On the other hand, when the knock avoidance control is performed, as shown by the broken line in FIG. 4, after the combustion of the fuel related to the main injection Q1 starts, the additional injection Q2 is performed. As will be described later, this combustion is a high temperature oxidation reaction, and the additional injection Q2 is performed after the high temperature oxidation reaction is started.

  When fuel is injected into the air-fuel mixture during combustion, the temperature of the air-fuel mixture decreases and the occurrence of knocking is suppressed. In particular, in the present embodiment, the occurrence of knocking is effectively suppressed by injecting fuel at a high pressure. Specifically, knocking occurs when the air-fuel mixture locally becomes hot in the combustion chamber 6. On the other hand, in this embodiment, since fuel is injected into the air-fuel mixture at a high pressure, the air-fuel mixture can be agitated and the local high-temperature field can be eliminated.

  The amount of additional injection Q2 is set sufficiently smaller than the amount of main injection Q1. In the present embodiment, the amount of additional injection Q2 is the sum of the injection amount of main injection Q1 and the injection amount of additional injection Q2, that is, 10% or less of the total amount of fuel injected into combustion chamber 6 in one combustion cycle. The amount is set. For example, the amount of additional injection Q2 is set to about 5% of the total amount of fuel.

  The additional injection Q2 is preferably performed at a time when heat generation of about 20% of the total heat generation amount generated by the main injection Q1 occurs, and the additional injection Q2 is performed at a timing that is excessively retarded from this time. When Q2 is performed, the mixing with air may be deteriorated and the amount of smoke generated may increase. Therefore, in this embodiment, the additional injection Q2 is performed by the preset additional injection end time. The additional injection end timing is set to a timing included in the combustion period (included in a period in which the high temperature oxidation reaction occurs). For example, the additional injection end time is set in advance according to the engine speed and the engine load and stored in the PCM 100 as a map, and the PCM 100 extracts values corresponding to the engine speed and the engine load from this map. .

  Thus, in this embodiment, fuel is used as a refrigerant for cooling the air-fuel mixture, and the injector 14 functions as a refrigerant supply means for supplying the refrigerant to the combustion chamber 6. Moreover, the process of implementing the said additional injection Q2 is a knock suppression process in a claim.

(2-4) Knock determination control (prediction process)
Next, the knock determination control performed in the high load region A will be described.

  In the present embodiment, the first knock determination step and the second knock determination step are performed, and it is determined whether or not knocking occurs based on these determination results (predicting the occurrence of knocking).

  Here, in the present embodiment and claims, the occurrence of knocking is not limited to the fact that knocking occurs strictly, but the knocking strength is higher than the allowable value allowed from the viewpoint of engine reliability. Including. The knock strength is the maximum value of the amplitude of a waveform having a predetermined frequency or higher included in the in-cylinder pressure waveform.

(First knock determination step)
The inventors of the present application have conducted intensive research on a method for determining whether or not knocking occurs earlier. As a result, it was found that when a low-temperature oxidation reaction occurs, the possibility of subsequent knocking is very high.

  The low-temperature oxidation reaction is a reaction accompanied by slight heat generation exceeding the cooling loss, and starts when hydrogen is extracted from the hydrocarbon constituting the fuel by oxygen radicals or the like when the temperature in the combustion chamber 6 is high. It is a reaction. The low-temperature oxidation reaction occurs before a high-temperature oxidation reaction, which is a reaction that generates high thermal energy while generating a flame, that is, before combustion starts.

  Knocking is a phenomenon that occurs when the air-fuel mixture locally becomes high in the combustion chamber 6 as described above, and knocking occurs when the temperature in the combustion chamber 6 is high. Therefore, when the low-temperature oxidation reaction occurs, the possibility of knocking after that is very high. The low-temperature oxidation reaction occurs because the temperature in the combustion chamber 6 is high enough to cause the low-temperature oxidation reaction. This is because knocking is likely to occur in such a state.

  FIG. 5 is a diagram comparing the heat generation rate when the low-temperature oxidation reaction occurs (solid line) and the heat generation rate when the low-temperature oxidation reaction does not occur (broken line). FIG. 6 is an enlarged view of the vicinity of the compression top dead center of FIG.

  The heat generation rate indicated by the broken line in FIG. 6 gradually increases after being minimized at a predetermined crank angle CA10 before compression top dead center, and then rapidly increases with the start of the high-temperature oxidation reaction. . On the other hand, the heat generation rate shown by the solid line in FIG. 6 is the minimum at a predetermined crank angle CA10 as in the broken line, but then increased at a faster rate than the broken line, and the low-temperature oxidation reaction occurred. It is shown. That is, the low temperature oxidation reaction is an exothermic reaction as described above, and the heat generation rate is higher when the low temperature oxidation reaction occurs than when it does not occur. The amount of increase in the heat generation rate accompanying the low-temperature oxidation reaction is small, and the heat generation rate starts to increase at a fast rate as described above, but the increase immediately stops (the heat generation rate decreases, substantially constant, Alternatively, it rises slowly) and then rises rapidly with the start of the high temperature oxidation reaction.

  As is clear from the comparison between the broken line and the solid line in FIG. 6, when the low temperature oxidation reaction occurs, the heat generation rate is after the middle of combustion (high temperature oxidation reaction) compared to when the low temperature oxidation reaction does not occur. Is rising rapidly and knocking occurs.

  Based on the above knowledge, in the first knock determination step, it is determined whether or not a low temperature oxidation reaction has occurred. And when low temperature oxidation reaction arises, it determines with possibility that knocking will arise after that.

  Specifically, the PCM 100 calculates the heat generation rate of the first crank angle CA10 before ignition, which is the crank angle at which the heat generation rate becomes the minimum, as described above, and is more predetermined than the first crank angle before ignition. The heat release rate of the second crank angle CA20 before ignition after the angle is calculated. The second crank angle CA20 before ignition is a crank angle during a period in which the heat generation rate increases with the low-temperature oxidation reaction. Both the first crank angle CA10 before ignition and the second crank angle CA20 before ignition are both compression strokes. The crank angle is included in a specific period from the latter period to the beginning of the expansion stroke, and is within the first period before the combustion of the air-fuel mixture starts. Then, the PCM 100 calculates a pre-ignition heat generation rate increase that is an increase in the heat generation rate of the second crank angle CA20 before ignition relative to the heat generation rate of the first crank angle CA10 before ignition.

  In the present embodiment, this amount of increase in the heat generation rate before ignition is used as the low temperature oxidation reaction level representing the degree of occurrence of the low temperature oxidation reaction in the claims, and the above-described step of calculating the amount of increase in the heat generation rate before ignition is performed. This is the first calculation step.

  In the present specification and claims, the latter stage of the compression stroke means a period from 60 ° CA before compression top dead center to the compression top dead center, and the initial stage of expansion stroke means after compression top dead center from the compression top dead center. The period up to 60 ° CA.

  The PCM 100 determines that the low temperature oxidation reaction has occurred when the pre-ignition heat generation rate increase is equal to or greater than the reference increase amount, and determines that the low temperature oxidation reaction has not occurred when the increase amount is less than the reference increase amount.

  In the present embodiment, the first crank angle CA10 before ignition and the second crank angle CA20 before ignition are preset and stored in the PCM 100. For example, the first crank angle CA10 before ignition is set to about 10 ° CA before compression top dead center, and the second crank angle CA20 before ignition is set to about 5 ° CA before compression top dead center. The reference increase amount is also set in advance and stored in the PCM 100. For example, the reference increase amount is set to about 10 J / ° CA.

  Here, the low temperature oxidation reaction occurs before the start of combustion of the air-fuel mixture (before the high temperature oxidation reaction starts) and at a time sufficiently earlier than the time when knocking occurs. Therefore, if it is possible to determine whether or not knocking occurs based on whether or not a low-temperature oxidation reaction has occurred, this determination can be performed sufficiently early with respect to the time when knocking occurs.

(Second knock determination step)
As described above, knocking occurs with a very high probability if a low-temperature oxidation reaction occurs. However, when the EGR rate, which is the ratio of the burned gas amount to the total gas amount in the combustion chamber, is high in the course of research, the inventors of the present application, knocking occurs even though the low temperature oxidation reaction does not occur. I got the knowledge that there was a case. This is because when the EGR rate is high, even if the temperature in the combustion chamber is high enough to cause knocking, the burned gas inhibits the contact between oxygen radicals and hydrocarbons, and the low-temperature oxidation reaction does not start. Conceivable. In addition, it has been found that knocking may not occur depending on variations in air-fuel ratio, flow, and the like in the combustion chamber despite the low-temperature oxidation reaction.

  Thus, in the present embodiment, as described above, the PCM 100 performs the second knock determination step and determines that knocking may occur when the low-temperature oxidation reaction occurs. However, this determination alone does not determine that knocking occurs, but performs a second knock determination step described below, and finally determines whether or not knocking occurs based on the determination result of this determination step. .

  FIG. 7 is a diagram showing a change in the in-cylinder pressure with respect to the crank angle. 7 indicates the in-cylinder pressure when knocking occurs, and the broken line indicates the in-cylinder pressure when knocking does not occur. As shown in this figure, the in-cylinder pressure increases after the crank angle CA1 at which combustion has started. When knocking occurs, the in-cylinder pressure increases at a faster speed than when knocking does not occur after the crank angle CA1.

  Thus, when the rate of increase of the in-cylinder pressure after the start of combustion, that is, the amount of increase is high, knocking is likely to occur. When the increase amount of the in-cylinder pressure is equal to or greater than a predetermined value, knocking occurs almost certainly. Thus, in the second knock determination step, it is determined that knocking occurs when the amount of increase in the in-cylinder pressure after the start of combustion is equal to or greater than a predetermined value.

  Specifically, the increase amount of the in-cylinder pressure during the second period after the start of combustion, that is, the in-cylinder pressure immediately after the start of combustion, is included in a specific period from the latter stage of the compression stroke to the early stage of the expansion stroke. It is determined that knocking occurs when the rising speed is equal to or higher than a preset reference pressure increase amount.

  In the present embodiment, the PCM 100 reads the in-cylinder pressure at the first crank angle that is included in the specific period from the late stage of the compression stroke to the early stage of the expansion stroke and after the combustion starts. Further, the PCM 100 reads the in-cylinder pressure at the second crank angle that is the second crank angle after the start of combustion during the specific period and that is retarded from the first crank angle. Then, the PCM 100 calculates an increase amount of the in-cylinder pressure at the second crank angle with respect to the in-cylinder pressure at the first crank angle at the second crank angle.

  Further, the PCM 100 is a third crank angle that is included in a specific period from the late stage of the compression stroke to the early stage of the expansion stroke and that is the third crank angle after the start of combustion and that is retarded from the first crank angle. Read the in-cylinder pressure. In addition, the PCM 100 is included in a specific period including the latter half of the compression stroke and the early stage of the expansion stroke, and is the fourth crank angle after the start of combustion and the retarded side of the third crank angle. Read in-cylinder pressure at. Then, the PCM 100 calculates an increase amount of the in-cylinder pressure at the fourth crank angle with respect to the in-cylinder pressure at the third crank angle at the fourth crank angle.

  In the PCM 100, the amount of increase in the in-cylinder pressure at the second crank angle with respect to the in-cylinder pressure at the first crank angle (hereinafter referred to as the first in-cylinder pressure increase amount as appropriate) is equal to or greater than the reference pressure increase amount, and the third crank It is determined that knocking occurs when the increase amount of the in-cylinder pressure at the fourth crank angle with respect to the in-cylinder pressure at the corner (hereinafter, appropriately referred to as the second in-cylinder pressure increase amount) is equal to or greater than the reference pressure increase amount. On the other hand, the increase in the in-cylinder pressure at the second crank angle with respect to the in-cylinder pressure at the first crank angle is less than the reference pressure increase amount, or the increase in the in-cylinder pressure at the fourth crank angle with respect to the in-cylinder pressure at the third crank angle. When the amount is less than the reference pressure increase amount, it is determined that knocking does not occur.

  Each of the first to fourth crank angles is an angle that is more retarded than the first crank angle CA10 before ignition and the second crank angle CA20 before ignition.

  The reference pressure increase amount is the maximum value of the increase amount of the in-cylinder pressure when knocking does not occur, and is preset and stored in the PCM 100. For example, the reference pressure increase amount is set and stored in a map according to the engine speed and the engine load, and the PCM 100 uses the map to determine the reference pressure increase amount corresponding to the current engine speed and the engine load. Is extracted and compared with the amount of increase in the in-cylinder pressure. In this embodiment, the reference pressure increase amount compared with the first in-cylinder pressure increase amount and the reference pressure increase amount compared with the second in-cylinder pressure increase amount are set to the same value, but they are different. It may be.

  The first crank angle to the fourth crank angle are set in advance and stored in the PCM 100. That is, the timing at which combustion starts is determined to some extent for each engine speed, engine load, and the like. Therefore, in the present embodiment, the timing at which the combustion starts is examined by an experiment or the like, and the first crank angle to the angle included in the specific period from the latter stage of the compression stroke to the early stage of the expansion stroke and after the combustion starts. The fourth crank angle is set in advance and stored in the PCM 100. In the present embodiment, the first to fourth crank angles are set for the engine speed and the engine load and stored in the PCM 100 as a map. For example, the first crank angle is TDC (compression top dead center), the second and third crank angles are about ATDC 5 ° CA (5 ° CA after compression top dead center), and the fourth crank angle is ATDC 10 ° CA (compression). It is set to about 10 ° CA after top dead center.

  In the present embodiment, the first in-cylinder pressure increase amount and the second in-cylinder pressure increase amount are used as the combustion steepness indicating the steepness of combustion after the start of the high temperature oxidation reaction in the claims, and are calculated. The above process is a second calculation process.

(2-5) Flow of Knock Determination Control and Knock Avoidance Control As described above, whether or not knocking occurs can be accurately determined based on the amount of increase in the in-cylinder pressure after combustion starts. However, a method for determining whether or not knocking occurs based on the amount of increase in the in-cylinder pressure, that is, in the second knock determination step, whether or not knocking occurs is determined. After. Therefore, even if it is determined that knocking occurs in the second knock determination step and additional injection Q2 is to be performed, additional injection Q2 is actually possible due to a delay in driving of injector 14 when the engine speed is high. The fact that fuel actually starts to be injected from the injector 14 into the combustion chamber 6 may be later than the optimum additional injection timing, which is the time when knocking can be most effectively suppressed.

  Therefore, in this embodiment, if it is determined that there is a possibility that knocking may be started in the first knock determination step, the additional injection Q2 is started (first step). That is, in accordance with the establishment of the first condition that the heat generation rate increase amount before ignition is equal to or greater than the reference increase amount (according to the establishment of the first condition that the low-temperature oxidation reaction level is equal to or greater than the reference level) The first step of starting injection Q2 (starting the supply of fuel as a refrigerant) is performed.

  When it is determined in the second knock determination step that knocking does not occur, the additional injection Q2 is stopped (second step). That is, when the second condition that both the first in-cylinder pressure increase amount and the second in-cylinder pressure increase amount are equal to or greater than the reference pressure increase amount is not satisfied (the second that the combustion steepness is equal to or greater than the reference value). If the above condition is not satisfied), the second step of stopping the additional injection Q2 (stopping the supply of fuel as the refrigerant) is performed.

  On the other hand, if it is determined that knocking occurs in the second knock determination step, the additional injection Q2 is continued even after this determination (second step). That is, when the second condition that both the first in-cylinder pressure increase amount and the second in-cylinder pressure increase amount are equal to or greater than the reference pressure increase amount is satisfied (the second condition that the combustion steepness is equal to or greater than the reference value). When the above is established), the additional injection Q2 is continued (the supply of fuel as the refrigerant is continued).

  The control flow will be described with reference to the flowchart of FIG.

  First, the PCM 100 reads various information of the engine in step S1. For example, the PCM 100 uses the in-cylinder pressure detected by the in-cylinder pressure sensor SN3, the accelerator opening detected by the accelerator opening sensor SN5, the engine speed detected by the crank angle sensor SN1, and the exhaust detected by the exhaust O2 sensor SN4. The oxygen concentration, the intake air amount detected by the air flow sensor SN2, the opening degree of the EGR valve 42, and the like are read.

  After step S1, the process proceeds to step S2. In step S2, the PCM 100 determines whether or not the engine is operating in the high load region A, that is, whether or not the engine load is equal to or higher than the reference load Tq1. The engine load is calculated based on the accelerator opening and the engine speed.

  When the determination in step S2 is NO and the engine is operating in the low load region B, the PCM 100 ends the process as it is (returns to step S1). On the other hand, when the determination in step S2 is YES and the engine is operating in the high load region A, the PCM 100 proceeds to step S3.

  In step S3, the PCM 100 calculates the heat generation rate dQ using the in-cylinder pressure. As a method for calculating the heat release rate dQ, a conventionally used method can be adopted, and the description thereof is omitted here.

  After step S3, the process proceeds to step S4. In step S4, the PCM 100 determines whether a low temperature oxidation reaction has occurred.

  As described above, the PCM 100 calculates a pre-ignition heat generation rate increase, which is an increase in the heat generation rate of the second crank angle CA20 before ignition relative to the heat generation rate of the first crank angle CA10 before ignition. The PCM 100 determines that the low temperature oxidation reaction has occurred when the heat generation rate increase before ignition is equal to or greater than the reference increase amount, and does not cause the low temperature oxidation reaction when the heat generation rate increase before ignition is less than the reference increase amount. It is determined that

  If the determination in step S4 is YES and the low-temperature oxidation reaction has occurred, the PCM 100 proceeds to step S5. In step S5, the PCM 100 determines that knocking may occur.

  After step S5, the PCM 100 proceeds to step S6 and starts driving the injector 14. Here, the injector 14 has a drive delay. Therefore, even if a command to start driving is issued to the injector 14, the fuel is not injected from the injector 14 immediately, and the fuel is injected only after a predetermined time.

  After step S6, the process proceeds to step S7. In step S7, the PCM 100 calculates the first in-cylinder pressure increase amount and the second in-cylinder pressure increase amount, the first in-cylinder pressure increase amount is equal to or greater than the reference pressure increase amount, and the second in-cylinder pressure increase. It is determined whether or not the amount is greater than or equal to the reference pressure increase amount.

  If the determination in step S7 is YES and the first in-cylinder pressure increase amount is not less than the reference pressure increase amount and the second in-cylinder pressure increase amount is not less than the reference pressure increase amount, the PCM 100 proceeds to step S8 and knocks. And the drive of the injector 14 is continued. After step S8, the PCM 100 proceeds to step S9.

  In step S9, the PCM 100 determines whether or not the crank angle has reached the additional injection end time, waits for this determination to be YES, and then proceeds to step S10. In step S10, the PCM 100 stops driving the injector 14.

  On the other hand, if the determination in step S7 is NO and the first in-cylinder pressure increase amount is less than the reference pressure increase amount, or the second in-cylinder pressure increase amount is less than the reference pressure increase amount, the PCM 100 proceeds to step S11. It is determined that knocking does not occur. Then, the process proceeds to step S10, and the PCM 100 stops driving the injector 14.

  Returning to step S4, if the determination in step S4 is NO and it is determined that the low temperature oxidation reaction has not occurred, the PCM 100 proceeds to step S12. In step S12, the PCM 100 determines whether or not the first in-cylinder pressure increase amount is equal to or greater than the reference pressure increase amount and the second in-cylinder pressure increase amount is equal to or greater than the reference pressure increase amount, as in step S7.

  If the determination in step S12 is YES and the first in-cylinder pressure increase amount is equal to or greater than the reference pressure increase amount and the second in-cylinder pressure increase amount is equal to or greater than the reference pressure increase amount, the PCM 100 proceeds to step S13 and knocking is performed. Determine that it occurs. Then, the PCM 100 proceeds to step S14 and starts driving the injector 14. The drive of the injector 14 is started immediately after the determination in step S13 is YES. However, as described above, the fuel is not injected from the injector 14 immediately after the driving is started, and the fuel is injected only after a predetermined time.

  After step S14, the process proceeds to step S15. In step S15, as in step S9, the PCM 100 determines whether or not the crank angle has reached the additional injection end time, waits for this determination to be YES, and then proceeds to step S16. In step S <b> 16, the PCM 100 stops driving the injector 14.

  On the other hand, if the determination in step S12 is NO and the first in-cylinder pressure increase amount is less than the reference pressure increase amount or the second in-cylinder pressure increase amount is less than the reference pressure increase amount, the PCM 100 proceeds to step S17. Then, it is determined that knocking does not occur, and the process ends (returns to step S1).

  9 to 11 show changes in the crank angle of the heat generation rate, the low temperature oxidation reaction flag, the knock generation flag, the drive signal of the injector 14, and the valve opening degree of the injector 14 when the above control is performed. It is a graph. The low temperature oxidation flag is 1 when it is determined in step S4 that the low temperature oxidation reaction has occurred, and is 0 otherwise. The knock generation flag is determined in step S7 or step S12 that knocking occurs when the first in-cylinder pressure increase amount is equal to or greater than the reference pressure increase amount and the second in-cylinder pressure increase amount is equal to or greater than the reference pressure increase amount. It is a flag that becomes 1 when it is set, and 0 otherwise. The drive signal of the injector 14 is a signal sent from the PCM 100 to the injector 14. Here, when the command is issued from the PCM 100 to the injector 14 so as to start driving of the injector 14, it becomes 1, and when this command is stopped. It is represented as a signal that becomes zero.

  FIG. 9 shows that both the determinations in step S4 and step S7 are YES, it is determined that the low-temperature oxidation reaction has occurred, and there is a high possibility that knocking will occur, and the first cylinder pressure increase amount and It is a figure at the time of determining with all the 2nd in-cylinder pressure rise amount being more than the reference pressure rise amount, and judging that knocking occurs. In this case, when it is determined that the low temperature oxidation reaction has occurred at the crank angle t1 and the low temperature oxidation reaction flag is changed from 0 to 1, the drive of the injector 14 is started immediately thereafter. Along with this, after the crank angle t1, the opening degree of the injector 14 increases, and at the crank angle t2, the opening degree of the injector 14 reaches fully open, and the fuel related to the additional injection Q2 is discharged from the injector 14. Be injected. Even after it is determined that knocking occurs at the crank angle t3 and the knock flag is changed from 0 to 1, the drive of the injector 14 is continued. When the additional injection end time is reached at time t4, the drive of the injector 14 is stopped. Even when the drive of the injector 14 is stopped due to the drive delay of the injector 14, the valve opening degree is not immediately closed but is gradually reduced.

  As described above, when the low-temperature oxidation reaction occurs and when the first in-cylinder pressure increase amount and the second in-cylinder pressure increase amount are equal to or greater than the reference pressure increase amount, the PCM 100 is determined to have generated the low-temperature oxidation reaction. The injector 14 continues to be driven for a period from immediately after to the additional injection end timing. As a result, the injector 14 performs additional injection Q <b> 2 during a period from a predetermined time during this period to the end of additional injection, and injects additional fuel into the combustion chamber 6.

  On the other hand, FIG. 10 shows that the determination in step S4 is YES and it is determined that the low-temperature oxidation reaction has occurred, while the determination in step S7 is NO and the first cylinder pressure increase amount or the second cylinder pressure increase amount. Is a figure when it is determined that knocking does not occur because the pressure is less than the reference pressure increase amount. Also in this case, when it is determined that the low-temperature oxidation reaction has occurred at the crank angle t11, the drive of the injector 14 is started immediately after that. Accordingly, after the crank angle t11, the valve opening degree of the injector 14 increases. However, in this case, when it is determined that knocking does not occur at the crank angle t12, the drive of the injector 14 is stopped (a drive stop signal is output from the PCM 100 to the injector 14). Accordingly, after the crank angle t12, the valve opening degree of the injector 14 is gradually reduced.

  As described above, when the low temperature oxidation reaction occurs, and when the first cylinder pressure increase amount or the second cylinder pressure increase amount is less than the reference pressure increase amount, the injector 14 is driven when it is determined that the low temperature oxidation reaction occurs. However, as soon as it is determined that the first cylinder pressure increase amount or the second cylinder pressure increase amount is less than the reference pressure increase amount, the drive of the injector 14 is stopped.

  Further, FIG. 11 shows that the determination in step S4 is NO and it is determined that the low temperature oxidation reaction does not occur, while the determination in step S7 is YES and the first in-cylinder pressure increase amount and the second in-cylinder pressure increase. It is a figure when it is determined that the amount is equal to or greater than the reference pressure increase amount and knocking occurs. In this case, the drive of the injector 14 is started at the crank angle t21 where it is determined that the first in-cylinder pressure increase amount and the second in-cylinder pressure increase amount are equal to or greater than the reference pressure increase amount. When the additional injection end time is reached at the crank angle t22, the drive of the injector 14 is stopped.

  As described above, when the low temperature oxidation reaction does not occur and the first cylinder pressure increase amount and the second cylinder pressure increase amount are equal to or larger than the reference pressure increase amount, the first cylinder pressure increase amount and the second cylinder pressure increase amount are the reference. Immediately after it is determined that the amount of pressure increase is greater than or equal to, the drive of the injector 14 is started.

(3) Action, etc. As described above, according to the present embodiment, knocking is first performed according to whether or not the low temperature oxidation reaction has occurred (whether or not the increase in the heat generation rate before ignition is equal to or greater than the reference increase). The possibility of occurrence is determined, and then the determination of whether or not knocking occurs is determined depending on whether or not the first cylinder pressure increase amount and the second cylinder pressure increase amount are equal to or greater than the reference pressure increase amount. . Therefore, it is possible to detect early that knocking is likely to occur, and to accurately predict the occurrence of knocking.

  Further, the additional injection Q2 is started (driving of the injector 14 is started) when the low temperature oxidation reaction occurs. Therefore, the fuel related to the additional injection Q2 can be injected into the combustion chamber 6 at an appropriate time, and knocking can be reliably prevented.

  When it is determined that the first cylinder pressure increase amount and the second cylinder pressure increase amount are equal to or greater than the reference pressure increase amount, the additional injection Q2 is continued, while the first cylinder pressure increase amount and the second cylinder pressure increase amount are When it is determined that the amount is less than the reference pressure increase amount, the additional injection Q2 is stopped. Therefore, if it is predicted that the first cylinder pressure increase amount and the second cylinder pressure increase amount are less than the reference pressure increase amount and knocking does not occur, the additional injection Q2 is continued and a large amount of fuel is injected into the cylinder. This can prevent the combustion temperature from being lowered.

(4) Modified Example In the embodiment, in the second knock determination step, the amount of increase in the in-cylinder pressure that is included in the specific period from the latter stage of the compression stroke to the early stage of the expansion stroke and after the start of combustion is the reference pressure increase amount. The case where it is determined that knocking occurs at the above time has been described. When the amount of increase in the in-cylinder pressure is high, the amount of increase in the heat generation rate is also high. In other words, the inventors of the present application have found that knocking is likely to occur even when the amount of increase in the heat generation rate after the start of combustion is high, which is included in the specific period from the late stage of the compression stroke to the early stage of the expansion stroke. Got.

  Therefore, the parameter used for the determination in the second knock determination step (the parameter used as the combustion steepness indicating the steepness of combustion after the start of the high temperature oxidation reaction) is used as the amount of increase in the heat generation rate instead of the amount of increase in the in-cylinder pressure. Also good. That is, in the second knock determination step, when the amount of increase in the heat generation rate after the start of combustion is included in the specific period from the latter stage of the compression stroke to the early stage of the expansion stroke is equal to or higher than a preset reference value. It may be determined that knocking occurs, and it may be determined that knocking does not occur when the amount of increase in the heat generation rate is less than a reference value.

  Specifically, it is included in a specific period from the late stage of the compression stroke to the early stage of the expansion stroke, and is set to a retarded side from the first crank angle of heat generation rate determination set in advance as the time after the start of combustion. The heat generation rate at the set heat generation rate determination second crank angle is calculated. Further, the amount of increase in the heat generation rate of the heat generation rate determination second crank angle with respect to the heat generation rate of the heat generation rate determination first crank angle is calculated as the increase amount of the heat generation rate. Then, the amount of increase in the heat generation rate is compared with a reference value to determine whether or not knocking occurs. The heat generation rate determination first crank angle is set to TDC, for example, and the heat generation rate determination second crank angle is set to about ATDC 10 ° CA (10 ° CA after compression top dead center).

  Also with this method and configuration, it can be accurately determined whether or not knocking occurs. Further, the occurrence of knocking can be more reliably prevented based on this determination result, and the amount of refrigerant supplied to the combustion chamber 6 can be prevented from becoming excessive in order to suppress the occurrence of knocking.

  Further, in the above-described embodiment, the case has been described in which it is determined in the second knock determination step that knocking occurs when both the first in-cylinder pressure increase amount and the second in-cylinder pressure increase amount are equal to or greater than the reference pressure increase amount. . Alternatively, it may be determined that knocking occurs when at least one of the first cylinder pressure increase amount and the second cylinder pressure increase amount is equal to or greater than the reference pressure increase amount.

  Moreover, in the said embodiment, when calculating the 1st in-cylinder pressure rise amount and the 2nd in-cylinder pressure rise amount, and determining whether knocking will generate | occur | produce based on the raise amount of the in-cylinder pressure of two periods. As described above, instead of this, only the increase amount of the in-cylinder pressure in one period may be calculated, and it may be determined whether or not knocking occurs based on this.

  In the above-described embodiment, the case where it is determined in the first knock determination step whether or not the low-temperature oxidation reaction has occurred based on the heat generation rate has been described. However, the second knock determination step includes the latter stage of the compression stroke and the initial stage of the expansion stroke. The low temperature oxidation reaction may be determined based on the pressure in the combustion chamber during a specific period including That is, the determination as to whether or not the low temperature oxidation reaction has occurred may not be performed based on the heat generation rate, but may be performed based on the in-cylinder pressure. That is, the parameter used as the low-temperature oxidation reaction level representing the degree of occurrence of the low-temperature oxidation reaction is not limited to the heat generation rate (an increase in the heat generation rate), and may be, for example, an increase in the in-cylinder pressure.

  In the above embodiment, the case where the additional injection for injecting the fuel into the combustion chamber 6 after the main injection Q1 is described as the knock avoidance control, but the specific configuration of the knock avoidance control is not limited to this. For example, another refrigerant that can reduce the temperature of the air-fuel mixture may be supplied into the combustion chamber 6 instead of the fuel. Examples of the refrigerant include water and a part of exhaust gas. However, if it is set as the structure which injects a fuel, since knock avoidance control can be implemented using the injector 14, it is not necessary to provide the apparatus for injecting another refrigerant | coolant separately, and can simplify a structure.

  Further, in the above embodiment, when the injection amount of the additional injection Q2 (the amount of fuel supplied to the combustion chamber 6 by the additional injection) is 10% or less of the total amount of fuel supplied to the combustion chamber 6 during one cycle. However, the injection amount of the additional injection Q2 may be larger than 10%.

  However, if the injection amount of the additional injection Q2 is increased, the temperature in the combustion chamber 6 may be significantly reduced as the fuel is vaporized. In addition, the fuel and air are not sufficiently mixed and smoke is likely to be generated. Therefore, the amount of fuel supplied to the combustion chamber 6 by the additional injection is preferably set as described above.

  Further, the geometric compression ratio of the cylinder is not limited to 15 or more and 20 or less. However, when the geometric compression ratio of the cylinder is 15 or more, knocking is likely to occur. Therefore, it is effective to apply the above embodiment to this engine.

DESCRIPTION OF SYMBOLS 1 Engine main body 2 Cylinder 6 Combustion chamber 13 Spark plug 14 Injector (refrigerant supply means)
100 PCM (control means)
SN3 In-cylinder pressure sensor (detection means)

Claims (6)

A method for controlling an engine including a cylinder in which a mixture of fuel containing gasoline and air burns, and detection means for detecting in-cylinder pressure, which is the pressure in the cylinder,
A first calculation step of calculating a low-temperature oxidation reaction level representing a degree of occurrence of the low-temperature oxidation reaction based on the in-cylinder pressure detected by the detection means during a specific period from the latter stage of the compression stroke to the initial stage of the expansion stroke;
A second calculation step of calculating a combustion steepness representing a steepness of combustion after the start of a high-temperature oxidation reaction involving a flame based on the in-cylinder pressure during the specific period;
A prediction step of predicting the occurrence of knocking based on the low temperature oxidation reaction level calculated in the first calculation step and the combustion steepness calculated in the second calculation step;
And a knock suppression step of supplying a refrigerant for lowering the temperature in the cylinder to the cylinder when necessary based on a result of the prediction step. The engine control method according to claim 1,
The knock suppression step includes
A first step of starting supply of the refrigerant in response to the first condition that the low-temperature oxidation reaction level calculated in the first calculation step is equal to or higher than a reference level;
After the first step, when the second condition that the combustion steepness calculated in the second calculation step is equal to or greater than a reference value is satisfied, the supply of the refrigerant is continued, and the second condition is And a second step of stopping the supply of the refrigerant when it is not established. The engine control method according to claim 1 or 2,
In the knock suppression step, an additional fuel different from the normal fuel supplied regardless of whether knocking is present or not as the refrigerant is injected into the cylinder. The engine control method according to any one of claims 1 to 3,
In the first calculation step, as the low-temperature oxidation reaction level, an increase amount of the heat generation rate during the first period that is a part of the specific period is calculated,
In the second calculation step, the amount of increase in the in-cylinder pressure during the second period that is included in the specific period and set to the retard side than the first period is calculated as the combustion steepness. The engine control method. A method for detecting knocking that occurs in an engine, including a cylinder in which a mixture of fuel containing gasoline and air burns, and a detecting means for detecting an in-cylinder pressure that is a pressure in the cylinder,
A first calculation step of calculating a low-temperature oxidation reaction level representing a degree of occurrence of the low-temperature oxidation reaction based on the in-cylinder pressure detected by the detection means during a specific period from the latter stage of the compression stroke to the initial stage of the expansion stroke;
Based on the in-cylinder pressure during the specific period, it is determined that a high-temperature oxidation reaction accompanied by a flame has occurred, and a second calculation for calculating a combustion steepness that represents the steepness of combustion after the start of the high-temperature oxidation reaction Process,
An engine knock characterized by including a prediction step of predicting the occurrence of knocking based on the low temperature oxidation reaction level calculated in the first calculation step and the combustion steepness calculated in the second calculation step Detection method. An engine control device having a cylinder in which a mixture of fuel containing gasoline and air burns,
Detecting means for detecting an in-cylinder pressure which is a pressure in the cylinder;
Refrigerant supply means for supplying a refrigerant for lowering the temperature in the cylinder into the cylinder;
Control means for controlling the refrigerant supply means,
The control means includes
Based on the in-cylinder pressure detected by the detecting means during a specific period from the latter stage of the compression stroke to the initial stage of the expansion stroke, a low temperature oxidation reaction level representing the degree of occurrence of the low temperature oxidation reaction is calculated, and the low temperature oxidation reaction level is the reference level. In response to the establishment of the first condition, the refrigerant supply means starts supplying the refrigerant,
A second condition that, based on the in-cylinder pressure during the specific period, a combustion steepness that represents a steepness of combustion after the start of a high-temperature oxidation reaction involving a flame is calculated, and the combustion steepness is equal to or greater than a reference value. The refrigerant supply means is controlled so that the supply of the refrigerant is continued when the second condition is satisfied, and the supply of the refrigerant is stopped when the second condition is not satisfied. Control device.