JP2019173701A - Control device of engine - Google Patents

Abstract

To improve fuel consumption performance while preventing knocking.SOLUTION: An engine in which a fuel including gasoline is supplied to a combustion chamber, and an air-fuel mixture of the fuel and air is burned in the combustion chamber, includes ignition means 13 for igniting the air-fuel mixture in the combustion chamber 6 at a prescribed ignition timing, and control means 100 for controlling the same. A geometric compression ratio of a cylinder is determined to 15 or more, the ignition means 13 is controlled to start the combustion after the air-fuel mixture reaches a compression top dead center, when the engine is operated in a high load region, and the ignition timing is delayed in a case of high EGR rate in comparison with a case of low EGR rate.SELECTED DRAWING: Figure 9

Description

  The present invention comprises a cylinder in which a combustion chamber is formed, an intake passage through which intake air introduced into the combustion chamber flows, and an exhaust passage through which exhaust gas discharged from the combustion chamber flows, and contains gasoline. The present invention relates to a control device for an engine in which fuel is supplied to the combustion chamber and a mixture of the fuel and air is combusted in the combustion chamber.

  Conventionally, in the field of engines, various studies have been made to prevent knocking from occurring. Knocking is a phenomenon in which the pressure in the combustion chamber rapidly rises due to the self-ignition of a mixture of fuel and air locally on the outer periphery of the combustion chamber under conditions where the engine load is high and the temperature in the combustion chamber is high. When knocking occurs, noise increases and the piston and the like may be damaged. Therefore, it is required to prevent knocking.

  For example, Patent Document 1 discloses an engine in which a knock sensor for detecting knocking is provided in an engine body, and the ignition timing is retarded when knocking is detected by the knock sensor.

JP 2008-291758 A

  If the ignition timing is retarded, the temperature at which the temperature in the combustion chamber increases with combustion can be made more retarded than the compression top dead center, and knocking can be suppressed by keeping the temperature during combustion low. it can. However, if the ignition timing is simply retarded, the engine torque decreases, that is, the fuel consumption performance deteriorates.

  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 device that can improve fuel efficiency while preventing knocking.

  In order to solve the above-described problems, the present invention provides a cylinder in which a combustion chamber is formed, an intake passage through which intake air introduced into the combustion chamber flows, and an exhaust passage through which exhaust gas discharged from the combustion chamber flows. And an apparatus for controlling an engine in which a fuel containing gasoline is supplied to the combustion chamber and a mixture of the fuel and air burns in the combustion chamber, and the mixture in the combustion chamber is subjected to predetermined ignition. Ignition means for igniting at a timing, and control means for controlling the ignition means, the geometric compression ratio of the cylinder is set to 15 or more, and the control means has an engine load of a predetermined reference load. When the engine is operated in the above high load region, the ignition means is controlled so that the air-fuel mixture starts combustion after compression top dead center, and the amount of burned gas with respect to the total amount of gas in the combustion chamber Percentage of In some cases EGR rate is high to slow the ignition timing than lower, to provide a control apparatus for an engine, characterized in that (claim 1).

  According to this configuration, when the geometric compression ratio of the cylinder is as high as 15 or more, and the engine is operated in a high load region, the mixture is compressed when the temperature in the combustion chamber becomes very high. The ignition means is controlled to start combustion after the top dead center. Therefore, the temperature and pressure in the combustion chamber should be kept low compared to the case where combustion of the air-fuel mixture is started before the compression top dead center and the air-fuel mixture is combusted at the compression top dead center where the temperature and pressure in the cylinder increase. Can do. Therefore, knocking can be prevented from occurring in a high load region while improving the fuel efficiency by setting the geometric compression ratio to 15 or more.

  Moreover, in this configuration, the ignition timing is the EGR rate under the operating conditions in which the engine is operated in a high load region and the ignition means is controlled so that the air-fuel mixture starts to burn after compression top dead center. If it is high, it is slower than if it is low. Therefore, the occurrence of knocking can be more reliably prevented while suppressing the retard amount of the ignition timing and suppressing the deterioration of the fuel consumption performance.

  Specifically, as a result of intensive research to prevent knocking, the inventors of the present application have found that knocking is more likely to occur when the EGR rate is high than when the EGR rate is low under the above operating conditions. I found out.

  Specifically, the burnt gas has a larger specific heat than air. Therefore, the higher the EGR rate, which is the ratio of the burned gas amount to the total gas amount in the combustion chamber, the lower the combustion speed of the mixture. Therefore, it was estimated that knocking is suppressed when the EGR rate is high than when the EGR rate is low. Actually, in the combustion mode in which the air-fuel mixture starts before the compression top dead center, knocking is less likely to occur when the EGR rate is higher. However, when combustion of the air-fuel mixture is started after compression top dead center, it has been found that knocking is more likely to occur when the EGR rate is high than when it is low. This is considered to be due to the following reason. That is, when the compression top dead center is passed, the gas in the combustion chamber expands and cools as the piston decreases. However, the burned gas has a large specific heat as described above. For this reason, the amount of temperature drop can be reduced when the EGR rate is high and the ratio of burned gas is large. Thus, when combustion of the air-fuel mixture is started after the compression top dead center, the combustion chamber is maintained at a higher temperature after the compression top dead center when the EGR rate is high and the ratio of burned gas is large. It is considered that knocking is likely to occur.

  Therefore, as described above, the ignition timing is set to EGR under the operating condition in which the engine is operated in the high load region and the ignition means is controlled so that the air-fuel mixture starts to burn after compression top dead center. If the rate is higher when the rate is higher than when the rate is lower, when the EGR rate is high and knocking is likely to occur, the ignition timing is delayed to reliably prevent knocking, and when the EGR rate is low and knocking is difficult to occur, ignition is performed. By setting the timing to a relatively advanced timing, it is possible to suppress deterioration in fuel consumption performance due to the retard of the ignition timing.

  In the above configuration, the engine includes a plurality of the cylinders and a plurality of ignition means for igniting an air-fuel mixture in the combustion chamber of each cylinder, and the control means operates the engine in the high load region. In this case, it is preferable that the ignition means is controlled so that the ignition timing of the cylinder having the higher EGR rate is retarded than that of the cylinder having the lower EGR rate.

  According to this configuration, the ignition timing of each cylinder can be set to an appropriate time according to the EGR rate, and thus according to the likelihood of knocking. Therefore, it is possible to further improve fuel efficiency while preventing knocking more reliably.

  The EGR rate of each cylinder is likely to vary because an EGR passage that connects the intake passage and the exhaust passage is provided so that a part of the exhaust gas flowing through the exhaust passage is recirculated to the intake passage. Is connected to one place of the intake manifold for distributing the air to each cylinder. Therefore, it is effective to apply the above configuration to such a configuration (claim 3).

  The present invention also includes a cylinder in which a combustion chamber is formed, an intake passage through which intake air introduced into the combustion chamber flows, and an exhaust passage through which exhaust gas discharged from the combustion chamber flows. An apparatus for controlling an engine in which a fuel contained therein is supplied to the combustion chamber and a mixture of the fuel and air burns in the combustion chamber, the ignition means for igniting the mixture in the combustion chamber, and the mixing A refrigerant injection means for injecting a refrigerant for cooling the air-fuel mixture during combustion of the gas into the combustion chamber; and a control means for controlling the ignition means and the refrigerant injection means. The compression ratio is set to 15 or more, and the control means starts the combustion of the air-fuel mixture after compression top dead center when the engine is operating in a high load region where the engine load is equal to or higher than a predetermined reference load. To make the point Control means, and when the EGR rate, which is the ratio of the burned gas amount to the total gas amount in the combustion chamber, is high, the refrigerant injection amount by the refrigerant injection means is increased as compared with a low case. An engine control device is provided.

  Even in this configuration, when the geometric compression ratio of the cylinder is as high as 15 or more and the temperature of the combustion chamber becomes very high because the engine is operated in a high load region, the air-fuel mixture is compressed after the top dead center. The ignition means is controlled to start combustion. Therefore, knocking can be prevented from occurring in a high load region while improving fuel efficiency by setting the geometric compression ratio to 15 or more. Also, the amount of refrigerant injected into the combustion chamber under operating conditions where the engine is operating in a high load region and the ignition means is controlled so that the air-fuel mixture starts to burn after compression top dead center Is increased when the EGR rate is high than when the EGR rate is low, and when the EGR rate is high, the temperature in the combustion chamber is greatly reduced by the refrigerant. Therefore, the occurrence of knocking can be reliably prevented when the EGR rate is high, and the temperature drop in the combustion chamber due to the refrigerant can be suppressed when the EGR rate is low, and the deterioration of fuel consumption performance can be suppressed.

  In the above configuration, the engine includes a plurality of the cylinders and a plurality of refrigerant injection units that inject refrigerant into the combustion chambers of the cylinders, and the control unit is configured to operate the engine in the high load region. It is preferable to control the refrigerant injection means so that the cylinder with the higher EGR rate has a larger injection amount of the refrigerant than the cylinder with the lower EGR rate (Claim 5).

  According to this configuration, the amount of refrigerant injected into each cylinder can be set to an appropriate amount according to the EGR rate, and thus according to the likelihood of knocking. Therefore, it is possible to further improve fuel efficiency while preventing knocking more reliably.

  In addition, an EGR passage that connects the intake passage and the exhaust passage is provided so that a part of the exhaust gas flowing through the exhaust passage is returned to the intake passage, and the EGR passage uses the intake air for distributing the intake air to each cylinder. It is effective if the above configuration is applied to a configuration in which the EGR rate of each cylinder is likely to vary, which is connected to one position of the manifold.

  In the above configuration, when the engine is operated in the high load region and the refrigerant is injected into the combustion chamber by the refrigerant injection unit, the control means generates 1 heat generated in the combustion chamber. It is preferable to control the refrigerant injection means so that the refrigerant is injected at a time when it becomes 10% or more and 50% or less of the total heat generation amount generated in the combustion chamber during the combustion cycle.

  According to this configuration, knocking can be effectively suppressed by the refrigerant.

  In the above configuration, the EGR rate when the engine is operated in the high load region is, for example, 20% or less (claim 8).

  As described above, according to the engine control apparatus of the present invention, it is possible to improve fuel efficiency while preventing knocking.

It is a figure showing composition of an engine system concerning one embodiment of the present invention. It is a schematic diagram of an engine body. 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 graph which showed the knock intensity | strength when changing ignition timing (combustion start time). It is the flowchart which showed the setting procedure of basic ignition timing. It is the flowchart which showed the correction | amendment procedure of basic ignition timing. It is the figure which showed an example of the fuel injection timing in a high-speed high load area | region, an ignition timing, and a heat release rate. It is the flowchart which showed the flow of refrigerant | coolant injection control.

(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 between the volume of the combustion chamber 6 when the piston 5 is at the bottom dead center and the volume of the combustion chamber 6 when the piston 5 is at the top dead center is The geometrical compression ratio of the gasoline engine is set to a high value so that it is 15 or more and 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 region where engine load is high and 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 Ma in the load area of the engine.

  The cylinder head 4 is provided with a spark plug (ignition means) 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

  FIG. 2 is a schematic view of the engine body 1. As shown in FIG. 2, an independent intake passage 24 extends from the surge tank 23 to each cylinder 2. The intake air in the intake passage 20 is distributed from the surge tank 23 to each cylinder 2 via these independent intake passages 24. More specifically, an intake manifold 200 in which a space functioning as a surge tank 23 and an independent intake passage 24 are formed is connected to the engine body 1, and intake air is distributed to each cylinder 2 within the intake manifold 200. Is done.

  The EGR passage 41 is connected to the intake passage 20 at a portion upstream of the independent intake passage 24 in the intake passage 20. In this embodiment, it is connected to one place of the intake manifold 200. Accordingly, the EGR gas is introduced into the intake passage 20 (intake manifold 200) and then distributed to each cylinder 2. More specifically, the EGR passage 41 is connected to one end of the surge tank 23 in the cylinder arrangement direction (the end on the fourth cylinder side in the example of FIG. 2). The EGR gas that has passed through the EGR passage 41 is distributed from the surge tank 23 to each cylinder 2 through each independent intake passage 24.

(2) Control System (2-1) System Configuration FIG. 3 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 30. 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.

  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. 4 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, in a region 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 rotational speed is equal to or higher than the reference rotational speed N1, it is difficult to self-ignite the air-fuel mixture at a desired time, so SI combustion (spark ignition combustion, SI: Spark) employed in a normal gasoline engine is difficult. 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. Also in the SI combustion, the fuel is injected into the combustion chamber 6 from the injector 14 before the compression top dead center (TDC).

  In a full load (a region where the accelerator opening is fully opened), the EGR valve 42 is fully closed in order to introduce a large amount of air corresponding to the required engine torque into the combustion chamber 6. On the other hand, in order to reduce NOx by reducing the combustion speed and the combustion temperature, the EGR valve 42 is opened and EGR gas is introduced into the combustion chamber 6 in the entire region excluding the full load. That is, EGR gas is burnt gas and has a larger specific heat than air. Therefore, if EGR gas is introduced into the combustion chamber 6, the combustion speed of the air-fuel mixture can be reduced to lower the combustion temperature, thereby reducing NOx. it can.

  The PCM 100 sets a target value of the EGR rate that is the ratio of the burned gas amount to the total gas amount in the combustion chamber 6 based on the operating state of the engine, and the EGR valve 42 of the EGR valve 42 so as to realize this EGR rate. Change the opening. In the present embodiment, the target EGR rate, which is the target value of the EGR rate, for the engine speed and the engine load is preset and stored in a map, and the PCM 100 extracts the target EGR rate from this map. In the present embodiment, the target EGR rate at each operation point in the high speed and high load region A1 described later is set to a value of 20% or less.

  The opening / closing timing of the intake valve 11 is set so that the difference between the effective compression ratio and the geometric compression ratio is 2 or less in an area where the engine load is high including at least a high speed and high load area A1 described later.

  Thus, since the geometric compression ratio and the effective compression ratio are set to high values, the compression end temperature / pressure becomes very high in a region where the engine load is high and the engine speed is high. Therefore, if combustion is started before compression top dead center in this region, knocking occurs or the in-cylinder pressure during combustion becomes excessively high. Therefore, the PCM 100 performs control so that the air-fuel mixture starts combustion after the compression top dead center in a region where the engine load is high and the engine speed is high. Specifically, the PCM 100 ignites the ignition timing after the compression top dead center in the region where the engine load is equal to or higher than the reference load Tq1 in the region where the engine speed is equal to or higher than the reference speed N1 and the SI combustion is performed. Set the time to start.

(2-3) Knock Avoidance Ignition Control Next, knock avoidance ignition control performed in the high speed and high load region A1 excluding the full load when the engine speed is equal to or higher than the reference speed N1 and the engine load is equal to or higher than the reference load Tq1. Will be described.

(Outline of ignition control for knock avoidance)
When the engine is operating in the high-speed and high-load region A1, as described above, the compression end temperature and pressure become very high, so that knocking is likely to occur. If the ignition timing is set to the retard side, combustion can be slowed and knocking can be prevented. However, if the ignition timing is retarded, the required engine torque cannot be obtained (fuel consumption performance deteriorates).

  As a result of investigating the ignition timing at which higher engine torque can be obtained in the high speed and high load region A1 and the occurrence of knocking can be prevented, the present inventors have found that there is a high correlation between the knock intensity and the EGR rate. . 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. In the present embodiment and claims, the occurrence of knocking does not mean that knocking occurs strictly, but the knocking strength is higher than an allowable value from the viewpoint of engine reliability. Including.

  Specifically, as described above, the higher the EGR rate, the lower the combustion temperature of the air-fuel mixture. Therefore, it was estimated that knocking can be suppressed when the EGR rate is high than when the EGR rate is low. Actually, in the combustion mode in which the air-fuel mixture starts before the compression top dead center, knocking is less likely to occur when the EGR rate is higher. However, as shown in FIG. 5, when the combustion of the air-fuel mixture is started after the compression top dead center, it has been found that when the EGR rate is high, the knock strength is higher and knocking is more likely to occur. . FIG. 5 is a graph showing the knock intensity when the ignition timing (combustion start timing) is changed. X1 in the figure is the knock intensity when the EGR rate is about 10%, and X2 in the figure is the EGR rate. Knock strength at 0%.

  The above phenomenon is considered to be caused by the following reason. That is, when the compression top dead center is passed, the gas in the combustion chamber 6 expands and falls as the piston 5 is lowered. However, if a large amount of EGR gas having a large specific heat exists in the combustion chamber 6, the temperature drop is suppressed to a low level and the temperature in the combustion chamber 6 is maintained high. From this, when combustion of the air-fuel mixture is started after the compression top dead center, it is considered that the higher the EGR rate, the easier the knocking occurs and the higher the knock strength. In particular, when the combustion start timing is about 10 ° CA to about 20 ° CA after compression top dead center, the temperature in the combustion chamber 6 tends to increase as the EGR rate increases.

  Here, the amount of EGR gas introduced into each cylinder 2 is not uniform, and the amount of EGR gas in each cylinder 2 and thus the EGR rate varies among the cylinders. In particular, in the present embodiment, as described above, the EGR passage 41 is connected to one end of the surge tank 23 in the cylinder arrangement direction, so that variation in the EGR rate (EGR gas amount) among the cylinders increases. Specifically, the EGR rate (EGR gas amount) tends to be larger in the cylinder 2 on one side in the cylinder arrangement direction than in the cylinder 2 on the other side. Therefore, the ignition timing on the most advanced side within the range in which the occurrence of knocking can be prevented, that is, the ignition timing at which a high engine torque can be obtained without causing knocking is different for each cylinder 2.

  Therefore, in the present embodiment, the ratio of the EGR rate of each cylinder 2 is learned, and based on this, the basic ignition timing, which is the basic ignition timing for each cylinder 2 for each operating point in the high speed and high load region A1. Set. If ignition is performed at the basic ignition timing set in each cylinder 2 in the high-speed and high-load region A1, high engine torque can be basically obtained without causing knocking.

  However, when the engine operating point changes due to the acceleration of the vehicle or the like, the actual EGR rate may deviate from the value to be realized at the operating point, that is, the target EGR rate, with the delay of the EGR gas. In this case, knocking may occur or the engine torque may be lower than the target value even if the ignition timing is the basic ignition timing.

  Therefore, in the present embodiment, when the actual EGR rate and the target EGR rate are different, the basic ignition timing is corrected so that the ignition timing is retarded when the EGR rate is high than when the EGR rate is low. To do.

(Basic ignition timing setting)
Details of the setting of the basic ignition timing will be described using the flowchart of FIG.

  In step S1, the PCM 100 reads various information of the engine. For example, the engine speed, accelerator opening, intake air amount, exhaust oxygen concentration, etc. are read.

  After step S1, the process proceeds to step S2. In step S2, the PCM 100 calculates an average value (hereinafter referred to as an average EGR rate) of the EGR rate of each cylinder 2 from the intake air amount and the amount of carbon dioxide contained in the intake air. The amount of carbon dioxide is determined from the intake air amount and the exhaust oxygen concentration.

  After step S2, the process proceeds to step S3. In step S3, the PCM 100 calculates engine torque generated in the combustion stroke of each cylinder 2 from the engine speed.

  After step S3, the process proceeds to step S4. In step S4, the PCM 100 estimates the EGR rate of each cylinder 2 based on the average EGR rate calculated in step S2, the engine torque of each cylinder 2 calculated in step S3, and the intake air amount. For example, it is estimated that the EGR rate is smaller when the engine torque is larger.

  After step S4, the process proceeds to step S5. In step S5, from the EGR rate of each cylinder estimated in step S4, the ratio of the amount of EGR gas distributed to each cylinder 2, that is, the ratio of the EGR rate of each cylinder (hereinafter referred to as the inter-cylinder ratio of the EGR rate) is calculated. . Here, the ratio of the amount of EGR gas distributed to each cylinder 2 is constant regardless of the engine speed and the engine load, and steps S1 to S5 may be performed once after the engine is started.

  After step S5, the process proceeds to step S6. In step S6, the PCM 100 corrects the initial ignition timing of each operation point in the high-speed and high-load region A1 that is set and stored in advance using the inter-cylinder ratio of the EGR rate calculated in step S5. 2 basic ignition timing is calculated. At this time, in the PCM 100, the cylinder 2 with a large EGR gas ratio to which the ratio of the EGR rate is distributed is larger than the cylinder 2 with a smaller ratio, that is, the cylinder 2 with a larger EGR rate is smaller than the cylinder 2 with a smaller EGR rate. The basic ignition timing is set so that the basic ignition timing is on the retard side.

  In the present embodiment, the PCM 100 stores a map of initial ignition timing set in advance for the engine speed and the engine load. In step S6, the PCM 100 corrects each value of the initial ignition timing of the high speed and high load region A1 in the map using the inter-cylinder ratio of the EGR rate, and for each cylinder, the engine speed and the engine load are corrected. Create a map of basic ignition timing.

  In this way, in this embodiment, the cylinder ratio of the EGR rate corresponding to the variation in the EGR rate among the cylinders is learned, and the basic ignition timing of each cylinder 2 in the high speed and high load region A1 is the cylinder with the large EGR rate. 2 is set so as to be on the retard side with respect to the smaller cylinder 2.

(Basic ignition timing correction)
Details of the correction of the basic ignition timing will be described with reference to the flowchart of FIG.

  In step S10, the PCM 100 reads various information of the engine. For example, the engine speed, accelerator opening, intake air amount, exhaust oxygen concentration, etc. are read. The PCM 100 reads a target EGR rate that is set separately based on the engine speed or the like.

  After step S10, the process proceeds to step S11. In step S11, the PCM 100 determines whether or not the engine is operating in the high speed and high load region A1. When this determination is NO and the engine is not operated in the high speed and high load region A1, the process proceeds to step S16. In step S16, the PCM 100 extracts the initial ignition timing corresponding to the current engine speed and engine load from the map of the initial ignition timing, and causes the ignition plug 13 to perform ignition at this initial ignition timing.

  On the other hand, if the determination in step S11 is YES and the engine is operating in the high speed and high load region A1, the process proceeds to step S12. In step S12, the PCM 100 calculates an average EGR rate based on the exhaust oxygen concentration, the intake air amount, and the like.

  After step S12, the process proceeds to step S13. In step S13, the PCM 100 subtracts the target EGR rate from the average EGR rate to calculate a difference between them (hereinafter referred to as an EGR rate deviation amount).

  After step S13, the process proceeds to step S14. In step S14, the PCM 100 corrects the basic ignition timing of each cylinder 2 based on the EGR rate deviation amount calculated in step S13, and calculates a corrected ignition timing for each cylinder 2. At this time, the basic ignition timing is corrected so that the corrected ignition timing is retarded when the EGR rate deviation amount is larger than when the EGR rate deviation amount is small.

  Specifically, when the EGR rate deviation amount is larger than 0 and the average EGR rate is larger than the target EGR rate, the timing that is retarded from the basic ignition timing of each cylinder 2 is set as the corrected ignition timing. The retard amount (retard amount of the corrected ignition timing with respect to the basic ignition timing) is increased as the EGR rate deviation amount increases. For example, the PCM 100 extracts a retardation amount corresponding to the EGR rate deviation amount calculated in step S13 from a map of the EGR rate deviation amount that is set in advance and stored in the PCM 100 and the retardation amount. The timing that is retarded by the retard amount from the basic ignition timing of each cylinder is set as the corrected ignition timing.

  Further, when the EGR rate deviation amount is smaller than 0 and the average EGR rate is smaller than the target EGR rate, the timing on the more advanced side than the basic ignition timing of each cylinder is set as the corrected ignition timing. The advance amount (advance amount of the corrected ignition timing with respect to the basic ignition timing) is increased as the absolute value of the EGR rate deviation amount increases. For example, the PCM 100 calculates the advance amount corresponding to the EGR rate deviation amount calculated in step S13 from the map of the absolute value of the EGR rate deviation amount preset and stored in the PCM 100 and the advance amount. The timing obtained by extracting and advancing this cylinder by the advance amount from the basic ignition timing of each cylinder is set as the corrected ignition timing.

  After step S14, the process proceeds to step S15. In step S15, the PCM 100 causes the spark plug 13 to ignite at the corrected ignition timing set in step S15, and ends the process (returns to step S10).

(3) Operation and the like As described above, in the present embodiment, when the engine is operated in the high speed and high load region A1 in the gasoline engine in which the cylinder geometric compression ratio is set to a high value of 15 or more. The spark plug 13 is controlled so that the air-fuel mixture starts to burn after the compression top dead center. Therefore, it is possible to suppress the temperature and pressure in the combustion chamber 6 from becoming excessively high and the occurrence of knocking.

  Further, when the engine is operated in the high speed and high load region A1, the ignition timing is delayed in the cylinder 2 having a higher EGR rate than in the cylinder 2 having a lower EGR rate. Therefore, the ignition timing of each cylinder 2 can be set to an appropriate ignition timing corresponding to the EGR rate, that is, an ignition timing that can avoid knocking while increasing the engine torque. Therefore, fuel efficiency can be improved while suppressing knocking.

  Further, when the engine is operated in the high speed and high load region A1, when the EGR rate deviates from the target EGR rate, the ignition timing of each cylinder 2 is made slower when the EGR rate is high than when it is low. The Therefore, even if the EGR rate deviates from the target EGR rate, the ignition timing of each cylinder 2 can be set to an appropriate ignition timing corresponding to the EGR rate, that is, an ignition timing that can avoid knocking while increasing the engine torque. Therefore, fuel efficiency can be improved while suppressing knocking.

(4) Second Embodiment In the above-described embodiment, when the engine is operating in the high speed and high load region A1, the ignition timing is set to the retard side timing when the EGR rate is higher than when the EGR rate is low. Therefore, knocking is prevented while ensuring engine torque (while improving fuel efficiency). Instead of this configuration, when the engine is operating in the high-speed and high-load region A1, the control for changing the ignition timing according to the EGR rate is not performed, and as a control for avoiding knocking, mixing is performed during combustion of the air-fuel mixture. Refrigerant injection control for injecting refrigerant for cooling the air into the combustion chamber 6 is implemented, and the amount of this refrigerant is changed by the EGR rate to ensure engine torque (while improving fuel efficiency) and to prevent knocking You may comprise. Next, a second embodiment according to this configuration will be described.

  In the second embodiment, fuel is used as the refrigerant, and an injector 14 is used as refrigerant injection means for injecting the fuel into the combustion chamber 6. Thus, the overall configuration of the engine and the system configuration of the control system of the second embodiment are the same as the overall configuration of the engine of the first embodiment described in (1) and the control system described in (2-1). Same as the configuration. Also in the second embodiment, the basic control described in (2-2) is performed.

  On the other hand, in the second embodiment, the control for setting the basic ignition timing of each cylinder based on the inter-cylinder ratio of the EGR rate and the correction control for the basic ignition timing according to the first embodiment are not performed. And in 2nd Embodiment, refrigerant | coolant injection control is implemented as mentioned above.

  FIG. 8 is a diagram showing an example of fuel injection timing, ignition timing, and heat generation rate when the engine is operated in the high-speed and high-load region A1. As shown by the solid line in FIG. 8, for example, in this region A1, during the normal time when the refrigerant injection control is not performed, the fuel injection Q1 is performed only once in the latter half of the intake stroke. Then, the air-fuel mixture is ignited by the spark plug 13 in the vicinity of the compression top dead center (in the example of FIG. 8, at the compression top dead center). 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.

  On the other hand, when the refrigerant injection control is performed, as shown by the broken line in FIG. 8, the additional injection Q2 is performed after the combustion of the fuel related to the main injection Q1 is started. 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.

  In addition, when the inventors perform this additional injection Q2 when heat generation of an amount of 10% or more and 50% or less of the total heat generation amount generated by the main injection Q1 occurs, it is most effective. It has been found that the occurrence of knocking can be suppressed. Accordingly, the timing of performing the additional injection Q2 is basically when the amount of heat generation is 10% or more and 50% or less of the total heat generation amount generated by the main injection Q1 (hereinafter, optimal as appropriate). It is called additional injection timing). For example, the additional injection Q2 is performed when heat generation of about 20% of the total heat generation amount generated by the main injection Q1 occurs. Specifically, the timing at which the rate of heat generation is as described above is obtained in advance by experiments or the like and stored in the PCM 100, and the PCM 100 performs the additional injection Q2 at this preset timing.

  The injection amount of the additional injection Q2 (the amount of fuel injected into the combustion chamber 6 by the additional injection Q2) is set sufficiently smaller than the amount of the 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 injection amount of the additional injection Q2 is set to about 5% of the total amount of fuel.

  FIG. 9 is a flowchart showing the flow of refrigerant injection control.

  First, in step S30, the PCM 100 reads various information of the engine. For example, the engine speed, accelerator opening, intake air amount, etc. are read.

  Next, in step S31, the PCM 100 determines whether or not the average EGR rate obtained by the same procedure as that of the first embodiment is larger than the target EGR rate obtained by the same procedure as that of the first embodiment. If this determination is NO and the average EGR rate is equal to or less than the target EGR, the processing is terminated as it is (returning to step S31). On the other hand, when this determination is YES and the average EGR rate is larger than the target EGR rate, the process proceeds to step S32.

  In step S32, the PCM 100 calculates an EGR rate deviation amount by subtracting the target EGR rate from the average EGR rate.

  After step S32, the process proceeds to step S33. In step S33, the PCM 100 determines the injection amount of the additional injection Q2 based on the EGR rate deviation amount. At this time, the larger the EGR rate deviation amount, that is, the larger the average EGR rate, the larger the injection amount of the additional injection Q2.

  After step S33, the process proceeds to step S34. In step S34, the PCM 100 performs additional injection Q2. At this time, the PCM 100 sets the injection amount of the additional injection Q2 to the injection amount determined in step S33. After step S34, the process ends (returns to step S31).

  Here, in the second embodiment, the injection amount of the additional injection Q2 is the same for each cylinder 2, and the amount of fuel determined in step S33 is injected into the combustion chamber 6 of each cylinder 2 by the additional injection Q2. .

(Operation of the second embodiment, etc.)
As described above, in the second embodiment, the additional injection Q2 is performed when the average EGR rate is larger than the target EGR rate. Therefore, the additional injection Q2 is performed when the actual EGR rate is higher than the target value, that is, the EGR rate set in advance as an appropriate value, and knocking is likely to occur. Therefore, occurrence of knocking can be prevented more reliably.

  In the second embodiment, when the additional injection Q2 is performed, the injection amount of the additional injection Q2 is increased when the average EGR rate, that is, when the actual EGR rate is high, is lower than when it is low. Therefore, when the actual EGR rate is high and knocking is likely to occur (knock strength tends to be high), it is possible to more reliably prevent knocking by injecting a large amount of fuel and lowering the temperature of the air-fuel mixture. Further, when the actual EGR rate is relatively low and knocking is difficult to occur (the knock strength is easy to be suppressed low), the temperature of the combustion chamber 6 due to the additional injection Q2 is reduced by reducing the injection amount of the additional injection Q2, and thus the engine A decrease in torque and a significant deterioration in fuel efficiency can be suppressed.

(5) Third Embodiment In the second embodiment, the injection amount of the additional injection Q2 is determined according to the difference between the average EGR rate and the target EGR rate, and the same amount of fuel is placed in the combustion chamber 6 of each cylinder 2. Has been described with respect to the injection by the additional injection Q2. Instead, as in the first embodiment, an inter-cylinder ratio of the EGR rate is calculated, and an actual EGR rate of each cylinder 2 is estimated based on the inter-cylinder ratio of the EGR rate and the average EGR rate, The injection amount of the additional injection Q2 of each cylinder 2 may be determined individually according to the difference between the actual EGR rate and the target EGR rate of each cylinder 2. At this time, the injection amount of the additional injection Q2 of each cylinder is increased as compared with the case where the actual EGR rate of each cylinder 2 is low.

  According to this configuration, an appropriate amount of fuel corresponding to the actual EGR rate can be injected into each cylinder 2 by the additional injection Q2, and knocking can be prevented more reliably and fuel consumption performance can be further deteriorated. It can suppress more reliably.

(Modification of the third embodiment)
Further, instead of the above-described configuration, knock strength is estimated by means for estimating knock strength provided separately, a basic value of the injection amount of the additional injection Q2 is determined based on this estimated value, and the basic value and the EGR rate are determined. From the inter-cylinder ratio (the ratio of the amount of EGR gas distributed to each cylinder), the injection amount of the additional injection Q2 for each cylinder may be determined individually. However, at this time as well, the cylinder 2 with a larger EGR rate is configured to increase the injection amount of the additional injection Q2.

(6) Modification In the second and third embodiments, the case where the additional injection Q2 for injecting the fuel into the combustion chamber 6 after the main injection Q1 is performed as the control for avoiding the knock has been described. Instead, another refrigerant that can reduce the temperature of the air-fuel mixture may be supplied into the combustion chamber 6. Examples of the refrigerant include water and a part of exhaust gas. However, if the configuration is such that fuel is injected, the control for avoiding knocking can be performed using the injector 14, so that it is not necessary to separately provide a device for injecting another refrigerant, and the structure is simplified. Can be

  In the second embodiment, 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 Q2 is preferably set as described above.

  Further, in the above-described embodiment, the description has been given of the case where the inter-cylinder ratio of the EGR rate (the ratio of the EGR gas amount distributed to each cylinder) is calculated based on the engine torque, the intake air amount, etc. generated in the combustion stroke of each cylinder. . Alternatively, the oxygen concentration or carbon dioxide concentration of the intake air introduced into each cylinder may be individually measured, and the inter-cylinder ratio of the EGR rate may be calculated based on this measured value. For example, a sensor capable of detecting the concentration is provided in each independent intake passage 24 communicating with each cylinder.

  In the above embodiment, SPCCI combustion is performed in a region where the engine speed is less than the reference speed N1, SI combustion is performed in a region where the engine speed is equal to or higher than the reference speed N1, and the engine speed is equal to or higher than the reference speed N1. Further, the case where the engine load is equal to or higher than the reference load Tq1 and the knock avoidance ignition control is performed only in the high speed and high load region A1 excluding the entire load has been described. In the case where SI combustion is performed in Fig. 1, knock avoidance ignition control may be performed also in this region. Further, knock avoidance ignition control may be performed even in the full load region. That is, the knock avoidance ignition control may be performed in the entire high load region A where the engine load is equal to or higher than the reference load Tq1.

1 Engine body 2 Cylinder 6 Combustion chamber 13 Spark plug (ignition means)
41 EGR passage 14 Injector (refrigerant injection means)
100 PCM (control means)

Claims (8)

A cylinder having a combustion chamber; an intake passage through which intake air introduced into the combustion chamber flows; and an exhaust passage through which exhaust gas discharged from the combustion chamber flows; A device for controlling an engine that is supplied to a chamber and in which the mixture of the fuel and air burns in the combustion chamber,
Ignition means for igniting the air-fuel mixture in the combustion chamber at a predetermined ignition timing;
Control means for controlling the ignition means,
The geometric compression ratio of the cylinder is set to 15 or more,
The control means controls the ignition means so that the air-fuel mixture starts to burn after compression top dead center when the engine is operated in a high load region where the engine load is equal to or higher than a predetermined reference load. An engine control apparatus characterized by delaying the ignition timing when the EGR rate, which is the ratio of the amount of burned gas to the total amount of gas in the combustion chamber, is higher than when it is low. The engine control device according to claim 1,
The engine includes a plurality of the cylinders and a plurality of ignition means for igniting the air-fuel mixture in the combustion chamber of each cylinder,
The control means controls the ignition means such that when the engine is operated in the high load region, the ignition timing is retarded in the cylinder having a higher EGR rate than in the cylinder having a lower EGR rate. An engine control device characterized by that. The engine control device according to claim 2,
An EGR passage communicating the intake passage and the exhaust passage so that a part of the exhaust gas flowing through the exhaust passage returns to the intake passage;
The engine control device according to claim 1, wherein the EGR passage is connected to one portion of an intake manifold for distributing intake air to each cylinder. A cylinder having a combustion chamber; an intake passage through which intake air introduced into the combustion chamber flows; and an exhaust passage through which exhaust gas discharged from the combustion chamber flows; A device for controlling an engine that is supplied to a chamber and in which the mixture of the fuel and air burns in the combustion chamber,
Ignition means for igniting the air-fuel mixture in the combustion chamber;
Refrigerant injection means for injecting into the combustion chamber a refrigerant for cooling the mixture during combustion of the mixture;
Control means for controlling the ignition means and the refrigerant injection means,
The geometric compression ratio of the cylinder is set to 15 or more,
The control means controls the ignition means so that the air-fuel mixture starts to burn after compression top dead center when the engine is operated in a high load region where the engine load is equal to or higher than a predetermined reference load. The engine control apparatus according to claim 1, wherein when the EGR rate, which is the ratio of the burned gas amount to the total gas amount in the combustion chamber, is high, the refrigerant injection amount by the refrigerant injection means is increased as compared with a low case. The engine control device according to claim 4,
The engine includes a plurality of the cylinders and a plurality of refrigerant injection units that inject refrigerant into the combustion chambers of the cylinders,
The control means controls the refrigerant injection means such that when the engine is operated in the high load region, the cylinder having a higher EGR rate has a higher injection amount of the refrigerant than a cylinder having a lower EGR rate. An engine control device. The engine control apparatus according to claim 5,
An EGR passage communicating the intake passage and the exhaust passage so that a part of the exhaust gas flowing through the exhaust passage returns to the intake passage;
The engine control device according to claim 1, wherein the EGR passage is connected to one portion of an intake manifold for distributing intake air to each cylinder. The engine control apparatus according to any one of claims 4 to 6,
When the engine is operated in the high load region and the refrigerant is injected into the combustion chamber by the refrigerant injection means, the control means generates heat generated in the combustion chamber during one combustion cycle. An engine control apparatus characterized by controlling the refrigerant injection means so that the refrigerant is injected at a time when the total heat generation amount generated in the combustion chamber is 10% or more and 50% or less. The engine control apparatus according to any one of claims 1 to 7,
The engine control apparatus, wherein when the engine is operated in the high load region, the EGR rate is 20% or less.