JP6848917B2 - Engine control - Google Patents

Description

The present invention 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, and contains gasoline. The present invention relates to an engine control device in which fuel is supplied to the combustion chamber and a mixture of the fuel and air is burned in the combustion chamber.

Conventionally, in the field of engines, various studies have been conducted to prevent knocking from occurring. Knocking is a phenomenon in which the air-fuel mixture locally ignites locally at the outer periphery of the combustion chamber or the like under the condition that the engine load is high and the temperature in the combustion chamber is high, and the pressure in the combustion chamber rises sharply. When knocking occurs, noise may increase and damage to the piston and the like may occur. 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 the engine body, and when knocking is detected by the knock sensor, the ignition timing is retarded.

Japanese Unexamined Patent Publication No. 2008-291758

By retarding the ignition timing, the time when the temperature in the combustion chamber rises with combustion can be set to the retard side from the compression top dead center, and the temperature during combustion can be kept low to suppress knocking. it can. However, if the ignition timing is simply retarded, the engine torque will decrease, that is, the fuel efficiency will deteriorate.

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 capable of improving fuel efficiency while preventing knocking.

In order to solve the above problems, the present invention presents 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 the 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 as EGR gas , and the fuel containing gasoline burns. An ignition means that controls an engine in which a mixture of fuel and air supplied to a chamber and burns in the combustion chamber, and ignites the air-fuel mixture in the combustion chamber at a predetermined ignition timing, and the ignition means. The geometric compression ratio of the cylinder is set to 15 or more, and the control means is such that the engine is operated in a high load region where the engine load is equal to or higher than a predetermined reference load. when, together with the air-fuel mixture is set to such ignition timing to start combustion at top dead center after a compression as a basic ignition timing of the ignition means, EGR rate ratio of the EGR gas amount to the total gas amount in the combustion chamber The EGR rate deviation amount is calculated by subtracting the predetermined target EGR rate from the EGR rate, and the larger the calculated EGR rate deviation amount is, the larger the deviation is corrected from the basic ignition timing to the retard side. A control device for an engine, characterized in that the ignition means is ignited at an ignition timing (claim 1).

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

Moreover, in this configuration, the EGR rate deviation amount (EGR rate deviation amount) under 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 combustion after the compression top dead center. The larger the value obtained by subtracting the target EGR rate from the EGR rate, the more the ignition timing is corrected to the retard side. Therefore, it is possible to more reliably prevent the occurrence of knocking while suppressing the amount of retardation of the ignition timing to be small and suppressing the deterioration of fuel efficiency performance.

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

Specifically, EGR gas , which is a burnt gas, has a higher specific heat than air. Therefore, the higher the EGR ratio, which is the ratio of the amount of EGR gas to the total amount of gas in the combustion chamber, the lower the combustion rate of the air-fuel mixture. Therefore, it was speculated that knocking was suppressed when the EGR rate was high than when it was low. In fact, 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, it was found that when the combustion of the air-fuel mixture was started after the compression top dead center, knocking was more likely to occur when the EGR rate was high than when it was low. This is considered to be due to the following reasons. That is, after passing the compression top dead center, the gas in the combustion chamber expands and cools down as the piston lowers. However, as described above, the EGR gas has a large specific heat. Therefore, the higher the EGR rate and the higher the proportion of EGR gas , the smaller the amount of temperature decrease. From this, when the combustion of the air-fuel mixture is started after the compression top dead center, the higher the EGR rate and the larger the proportion of EGR gas , the higher the temperature of the combustion chamber is maintained after the compression top dead center. , It is considered that knocking is likely to occur.

Therefore, as described above, the EGR rate deviation amount is under the operating conditions in which the engine is operated in the high load region and the ignition means is controlled so that the air-fuel mixture starts combustion after the compression top dead point. If the ignition timing is corrected to the retard side as the EGR rate is large, knocking can be reliably prevented by delaying the ignition timing when the EGR rate is high and knocking is likely to occur, and the ignition timing is when the EGR rate is low and knocking is unlikely to occur. However, it is possible to suppress the deterioration of fuel efficiency due to the retardation of the ignition timing by setting the timing to the advance side.

In the above configuration, the engine control device has a first detecting means for detecting the amount of intake air introduced into the combustion chamber through the intake passage, and an exhaust oxygen concentration which is an oxygen concentration of exhaust gas flowing through the exhaust passage. The control means calculates the EGR rate based on the detected intake amount and the exhaust oxygen concentration when the engine is operated in the high load region. At the same time, it is preferable to calculate the EGR rate deviation amount by subtracting the target EGR rate from the calculated EGR rate (claim 2).

In the above configuration, the engine may include the plurality of cylinders, the plurality of ignition means for igniting the air-fuel mixture in the combustion chamber of each cylinder, and the intake manifold for distributing the intake air to each cylinder. well, the EGR passage may be connected in one place of the intake manifold (claim 3).

Further, in the present invention, the cylinder in which the combustion chamber is formed, the intake passage through which the intake air introduced into the combustion chamber flows, the exhaust passage through which the exhaust gas discharged from the combustion chamber flows, and the exhaust passage are provided. An EGR passage that communicates the intake passage and the exhaust passage so that a part of the circulated exhaust gas returns to the intake passage as EGR gas is provided, and fuel containing gasoline is supplied to the combustion chamber. A device that controls an engine in which a mixture of fuel and air burns in the combustion chamber, in order to ignite the mixture in the combustion chamber and to cool the mixture during combustion of the mixture. The exhaust gas injection means for injecting the exhaust gas into the combustion chamber and the control means for controlling the ignition means and the refrigerant injection means are provided, and 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 combustion after the compression top dead point 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 calculated percentage of the EGR gas amount to the total gas amount in the combustion chamber as the EGR rate and from the EGR rate default to calculate the EGR ratio deviation amount obtained by subtracting the target EGR rate, the larger the calculated EGR rate deviation amount refrigerant The engine control device is provided, which comprises increasing the injection amount of the refrigerant by the injection means (claim 4).

Even in this configuration, the geometric compression ratio of the cylinder is as high as 15 or more, and when the temperature in the combustion chamber becomes extremely high due to the engine being operated in the high load region, the air-fuel mixture is compressed after top dead center. The ignition means is controlled so as to start combustion at. Therefore, it is possible to prevent knocking from occurring in a high load region while improving fuel efficiency by setting the geometric compression ratio to 15 or more. In addition, under 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 combustion after the compression top dead center, the amount of EGR rate deviation (target from the EGR rate). and the amount of refrigerant minus the EGR rate) is injected into the more the combustion chamber larger multi rot, the temperature in the combustion chamber is reduced more greatly by the refrigerant as the EGR ratio deviation amount is large. Therefore, when the EGR rate is high, knocking can be reliably prevented, and when the EGR rate is low, the temperature drop in the combustion chamber due to the refrigerant can be suppressed, and the deterioration of fuel efficiency can be suppressed.

In the above configuration, the engine control device has a first detecting means for detecting the amount of intake air introduced into the combustion chamber through the intake passage, and an exhaust oxygen concentration which is an oxygen concentration of exhaust gas flowing through the exhaust passage. The control means calculates the EGR rate based on the detected intake amount and the exhaust oxygen concentration when the engine is operated in the high load region. At the same time, it is preferable to calculate the EGR rate deviation amount by subtracting the target EGR rate from the calculated EGR rate (claim 5).

In the above configuration, the engine may include the plurality of cylinders, the plurality of ignition means for igniting the air-fuel mixture in the combustion chamber of each cylinder, and the intake manifold for distributing the intake air to each cylinder. well, the EGR passage may be connected in one place of the intake manifold (claim 6).

In the above configuration, in the control means, 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 amount of heat generated in the combustion chamber is 1. It is preferable to control the refrigerant injection means so that the refrigerant is injected at a time when the total heat generated in the combustion chamber is 10% or more and 50% or less during the combustion cycle (claim 7).

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

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

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

It is a figure which showed the structure of the engine system which concerns on one Embodiment of this 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 a figure which showed the control map. It is a graph which showed the knock strength when the ignition timing (combustion start timing) was changed. It is a flowchart which showed the setting procedure of the basic ignition timing. It is a flowchart which showed the correction procedure of the basic ignition timing. It is a figure which showed an example of fuel injection timing, ignition timing, and heat generation rate in a high-speed and high-load region. It is a flowchart which showed the flow of the refrigerant injection control.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing a configuration of an engine system to which the control device of the engine of the present invention is applied. The engine system of the present embodiment includes a 4-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 the exhaust generated by the engine main body 1. And.

The engine body 1 is, for example, an in-line 4-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 body 1 is driven by being supplied with 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 in the cylinder 2 so as to be reciprocating (up and down). Has.

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 formed by the lower surface of the cylinder head 4 has a triangular roof shape composed of two inclined surfaces, an intake side and an exhaust side. On the crown surface of the piston 5, a cavity is formed in which a region including the central portion thereof is recessed on the opposite side (lower side) of the cylinder head 4. 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 and the volume of the combustion chamber 6 when the piston 5 is at the top dead center is the fuel efficiency performance. Is set to a high value as the geometric compression ratio of the gasoline engine, which is 15 or more and 20 or less (for example, about 17) so as to increase the value.

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 gas generated in the cylinder 2 to be led out 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 end portion on which the injection port is formed is located near the center of the ceiling surface of the combustion chamber 6 and faces the center of the combustion chamber 6. The injector 14 has a plurality of nozzles at its tip, and has a cone shape (specifically, a hollow cone shape) centered on the central axis of the cylinder 2 from the vicinity of the center of the ceiling surface of the combustion chamber toward the crown surface of the piston 5. It is configured to inject fuel. The taper angle (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 a single injector.

The injector 14 injects fuel pumped from a high-pressure pump (not shown) into the combustion chamber 6. The injection pressure of the injector 14 is increased to 30 MPa or more in a region where the 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 up to about 70 MPa. In this case, the 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. At the tip of the spark plug 13, an electrode is formed that discharges sparks to ignite the air-fuel mixture and imparts ignition energy to the air-fuel mixture. The spark plug 13 is arranged so that its tip is located near the center of the ceiling surface of the combustion chamber 6 and faces the center of the combustion chamber 6.

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

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

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

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 for 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 inside is connected to the engine body 1, and intake air is distributed to each cylinder 2 in the intake manifold 200. Will be done.

The EGR passage 41 is connected to the intake passage 20 at a portion of the intake passage 20 on the upstream side of the independent intake passage 24. In this embodiment, it is connected to one place of the intake manifold 200. Along with this, 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 (the end on the fourth cylinder side in the example of FIG. 2) in the cylinder arrangement direction. The EGR gas that has passed through the EGR passage 41 is distributed from the surge tank 23 to each cylinder 2 via 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 this embodiment is collectively controlled by a PCM (powertrain control module, control means) 100. As is well known, the PCM 100 is a microprocessor composed of 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. Further, the intake passage 20 is provided with an air flow sensor SN2 (first detection means) that detects the amount of air taken into each cylinder 2 through the intake passage 20. Further, 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 (second detection means) for detecting the exhaust oxygen concentration, which is the oxygen concentration of the exhaust gas flowing through the exhaust passage 30. Further, the vehicle is provided with an accelerator opening sensor SN5 that detects an opening degree (accelerator opening degree) of an accelerator pedal (accelerator opening degree) which is not shown and is operated by the driver.

The PCM 100 executes various calculations based on the input signals from the sensors SN1 to SN5 and the like to control 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 is the engine speed and the vertical axis is the engine load.

In the present embodiment, in the region where the engine speed is less than the reference speed N1, compression self-ignition combustion (SPCCI combustion, SPCCI: Spark Control Compression Ignition) by ignition assist is carried out. In compression self-ignition combustion, first, fuel is injected from the injector 14 into the combustion chamber 6 before the compression top dead center (TDC). This fuel mixes with air by near compression top dead center. The air-fuel mixture formed in the combustion chamber 6 is discharged from the spark plug 13 near the compression top dead center. As a result, the air-fuel mixture around the spark plug 13 is forcibly ignited. Then, the flame propagates from around the spark plug 13 to the surroundings, the temperature of the surrounding air-fuel mixture is raised, and self-ignition occurs.

On the other hand, in the region where the engine speed is N1 or higher, it becomes difficult to self-ignite the air-fuel mixture at a desired time. Therefore, SI combustion (spark ignition combustion, SI: Spark) adopted in a normal gasoline engine Ignition) is carried out. SI combustion is a combustion form in which almost the entire air-fuel mixture is burned by flame propagation. Discharge is performed from the spark plug 13 near the compression top dead center, and the air-fuel mixture around the spark plug 13 is forcibly ignited. .. Then, the flame propagates from around the spark plug 13 to the surroundings, and the remaining air-fuel mixture is forcibly burned by the flame propagation. Also in SI combustion, the fuel is injected from the injector 14 into the combustion chamber 6 before the compression top dead center (TDC).

At full load (region where the accelerator opening is fully open), 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 the combustion rate and the combustion temperature to reduce NOx, the EGR valve 42 is opened and the EGR gas is introduced into the combustion chamber 6 in the entire region excluding the full load. That is, since the EGR gas is a burned gas and has a larger specific heat than the air, if the EGR gas is introduced into the combustion chamber 6, the combustion speed of the air-fuel mixture can be lowered and the combustion temperature can be lowered, thereby reducing NOx. it can.

The PCM100 sets a target value of the EGR rate, which is the ratio of the amount of burned gas (the amount of EGR gas) to the total amount of gas in the combustion chamber 6, based on the operating state of the engine, so that this EGR rate is realized. The opening degree of the EGR valve 42 is changed to. In the present embodiment, the target EGR rate, which is the target value of the EGR rate, is preset and stored in a map for the engine speed and the engine load, 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 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, at least in the region where the engine load is high, including the high-speed high load region A1 described later.

By setting the geometric compression ratio and the effective compression ratio to high values in this way, the compression end temperature and pressure become extremely high in the region where the engine load is high and the engine speed is high. Therefore, if combustion is started before the compression top dead center in this region, knocking occurs or the in-cylinder pressure during combustion becomes excessively high. Therefore, the PCM 100 controls so that the air-fuel mixture starts combustion after the compression top dead center in the region where the engine load is high and the engine speed is high. Specifically, the PCM100 burns the ignition timing after the compression top dead center in the region where the engine load is the reference load Tq1 or more in the region where SI combustion is performed at the engine speed N1 or more. Set when to start.

(2-3) Knock avoidance ignition control Next, knock avoidance ignition control is performed in the high-speed high load region A1 where the engine speed is the reference speed N1 or more and the engine load is the reference load Tq1 or more and the full load is excluded. Will be described.

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

As a result of investigating the ignition timing that can obtain a higher engine torque and prevent the occurrence of knocking in the high-speed and high-load region A1, the inventors of the present application have found that there is a high correlation between the knock strength and the EGR rate. .. The knock intensity is the maximum value of the amplitude of the waveform contained in the in-cylinder pressure waveform and having a predetermined frequency or higher. In the present embodiment and the claims, the occurrence of knocking does not mean that knocking occurs strictly, but that the knock strength is higher than the permissible value from the viewpoint of engine reliability. Also includes.

Specifically, as described above, the higher the EGR rate, the lower the combustion temperature of the air-fuel mixture. Therefore, it was speculated that knocking could be suppressed when the EGR rate was high than when it was low. In fact, 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, it was found that when the combustion of the air-fuel mixture was started after the compression top dead center, the knock strength was higher when the EGR rate was high than when it was low, and knocking was more likely to occur. .. FIG. 5 is a graph showing the knock strength when the ignition timing (combustion start timing) is changed. X1 in the figure shows the knock strength when the EGR rate is about 10%, and X2 in the figure shows the EGR rate. Knock strength at 0%.

It is considered that the above phenomenon occurs due to the following reasons. That is, when the compression top dead center is passed, the gas in the combustion chamber 6 expands and the temperature drops as the piston 5 lowers. However, when a large amount of EGR gas having a large specific heat is present in the combustion chamber 6, the amount of temperature decrease is suppressed to be small and the temperature in the combustion chamber 6 is maintained high. From this, it is considered that when the combustion of the air-fuel mixture is started after the compression top dead center, the higher the EGR rate, the more easily knocking occurs, and the higher the knock strength. In particular, when the start time of combustion is about 10 ° CA to about 20 ° CA after the compression top dead center, the higher the EGR rate, the higher the temperature in the combustion chamber 6 tends to be.

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 cylinders. In particular, in the present embodiment, as described above, since the EGR passage 41 is connected to one end of the surge tank 23 in the cylinder arrangement direction, the variation in the EGR ratio (EGR gas amount) between cylinders becomes large. 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 angle 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 of each cylinder 2, is obtained for each operation point in the high-speed high load region A1. To set. In the high-speed high-load region A1, if each cylinder 2 is ignited at the set basic ignition timing, it is basically possible to obtain a high engine torque without causing knocking.

However, when the driving point of the engine 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 driving point, that is, the target EGR rate due to the delay of the EGR gas. In this case, even if the ignition timing is set as the basic ignition timing, knocking may occur or the engine torque may be lower than the target value.

Therefore, in the present embodiment, when the actual EGR rate and the target EGR rate deviate from each other, the basic ignition timing is corrected so that the ignition timing is on the retard side when the EGR rate is high and when it is low. To do.

(Setting of basic ignition timing)
The details of setting the basic ignition timing will be described with reference to the flowchart of FIG.

The PCM100 reads various engine information in step S1. For example, the engine speed, accelerator opening, intake amount, exhaust oxygen concentration, etc. are read.

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

After step S2, the process proceeds to step S3. In step S3, the PCM 100 calculates the 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 amount. For example, it is estimated that the larger the engine torque, the smaller the EGR rate.

After step S4, the process proceeds to step S5. In step S5, the ratio of the amount of EGR gas distributed to each cylinder 2, that is, the ratio of the EGR ratio of each cylinder (hereinafter referred to as the ratio between cylinders of the EGR ratio) is calculated from the EGR ratio of each cylinder estimated in step S4. .. 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 or the like.

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 high-load region A1 preset and stored by using the inter-cylinder ratio of the EGR rate calculated in step S5, and each cylinder. Calculate the basic ignition timing of 2. At this time, in the PCM 100, the cylinder 2 having a large ratio of the amount of EGR gas to which the ratio of the EGR ratio is largely distributed is smaller than the cylinder 2, that is, the cylinder 2 having a large EGR ratio is smaller than the cylinder 2. Set the basic ignition timing so that the basic ignition timing is on the retard side.

In the present embodiment, the PCM 100 stores a preset initial ignition timing map 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 high-load region A1 in this map by 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 the present embodiment, the inter-cylinder ratio of the EGR rate corresponding to the variation between the cylinders of the EGR rate is learned, and the basic ignition timing of each cylinder 2 in the high-speed high load region A1 is the cylinder having a large EGR rate. 2 is set so as to be on the retard side of the smaller cylinder 2.

(Correction of basic ignition timing)
The details of the correction of the basic ignition timing will be described with reference to the flowchart of FIG. 7.

The PCM100 reads various engine information in step S10. For example, the engine speed, accelerator opening, intake amount, exhaust oxygen concentration, etc. are read. Further, the PCM 100 reads a target EGR rate separately set based on the engine speed and 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 high-load region A1. If this determination is NO and the engine is not operating in the high-speed 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 the engine load from the map of the initial ignition timing, and causes the spark plug 13 to ignite 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 high-load region A1, the process proceeds to step S12. In step S12, the PCM 100 calculates the average EGR rate based on the exhaust oxygen concentration, the intake 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 these differences (hereinafter, referred to as the 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 the corrected ignition timing for each cylinder 2. At this time, the basic ignition timing is corrected so that the corrected ignition timing is on the retard side when the EGR rate deviation amount is large than when it 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 time on the retard side of the basic ignition timing of each cylinder 2 is set as the corrected ignition timing. Then, this retard angle amount (the retardation amount of the corrected ignition timing with respect to the basic ignition timing) is increased as the EGR rate deviation amount is larger. For example, the PCM 100 extracts the retard angle amount corresponding to the EGR rate deviation amount calculated in step S13 from the map of the EGR rate deviation amount preset and stored in the PCM 100 and the retard angle amount. , The timing of retarding the basic ignition timing of each cylinder by this amount of retardation is set as the corrected ignition timing.

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 advance side of the basic ignition timing of each cylinder is set as the corrected ignition timing. Then, this 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 is larger. For example, the PCM 100 determines the advance angle 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 angle amount. The ignition timing is set as the corrected ignition timing by extracting and advancing the ignition timing by this amount from the basic ignition timing of each cylinder.

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

Further, when the engine is operated in the high-speed and high-load region A1, the ignition timing of the cylinder 2 having a high EGR rate is later than that of the cylinder 2 having a low EGR rate. Therefore, the ignition timing of each cylinder 2 can be set to an appropriate ignition timing according to the EGR rate, that is, an ignition timing that can avoid knocking while increasing the engine torque. Therefore, it is possible to improve fuel efficiency while suppressing knocking.

Further, when the engine is operating in the high-speed and high-load region A1 and the EGR rate deviates from the target EGR rate, the ignition timing of each cylinder 2 is delayed when the EGR rate is high than when it is low. To. 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 according to the EGR rate, that is, an ignition timing that can avoid knocking while increasing the engine torque. Therefore, it is possible to improve fuel efficiency while suppressing knocking.

(4) Second Embodiment In the above embodiment, when the engine is operating in the high-speed high-load region A1, the ignition timing is set to the retard side when the EGR rate is high and when it is low. So, I tried to prevent knocking while ensuring engine torque (improving fuel efficiency). Instead of this configuration, when the engine is operating in the high-speed, high-load region A1, the control to change the ignition timing according to the EGR rate is not performed, and as a control to avoid knocking, the mixture is mixed during combustion of the air-fuel mixture. Knocking is prevented while ensuring engine torque (improving fuel efficiency) by implementing refrigerant injection control that injects a refrigerant for cooling the air into the combustion chamber 6 and changing the amount of this refrigerant according to the EGR rate. It may be configured to do so. A second embodiment relating to this configuration will be described below.

In the second embodiment, fuel is used as the refrigerant, and the injector 14 is used as the refrigerant injection means for injecting the fuel into the combustion chamber 6. From this, the overall configuration of the engine and the system configuration of the control system of the second embodiment are the overall configuration of the engine of the first embodiment described in (1) above and the system of the control system described in (2-1). Same as the configuration. Further, also in the second embodiment, the basic control described in (2-2) is implemented.

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 implemented. Then, in the second embodiment, the refrigerant injection control is carried out as described above.

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

On the other hand, when the refrigerant injection control is executed, as shown by the broken line in FIG. 8, the additional injection Q2 is executed 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 carried out after the high-temperature oxidation reaction has started.

When fuel is injected into the combustion air-fuel mixture, the temperature of the air-fuel mixture drops 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 the present embodiment, since the fuel is injected at a high pressure in the air-fuel mixture, the air-fuel mixture can be agitated and the local high temperature field can be extinguished.

Further, the inventors of the present application most effectively carry out this additional injection Q2 when 10% or more and 50% or less of the total heat generation amount generated by the main injection Q1 is generated. It was found that the occurrence of knocking can be suppressed. From this, the implementation time of the additional injection Q2 is basically when 10% or more and 50% or less of the total heat generation amount generated by the main injection Q1 is generated (hereinafter, appropriately, optimally). It is said to be the additional injection time). For example, the additional injection Q2 is performed when about 20% of the total heat generation amount generated by the main injection Q1 is generated. Specifically, the timing at which the heat generation rate becomes as described above is obtained in advance by an experiment or the like and stored in the PCM 100, and the PCM 100 executes 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 to be sufficiently smaller than the amount of the main injection Q1. In the present embodiment, the amount of the additional injection Q2 is 10% or less of the total amount of the fuel injected into the combustion chamber 6 in one combustion cycle, that is, the total amount of the injection amount of the main injection Q1 and the injection amount of the additional injection Q2. 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 about the engine. For example, the engine speed, accelerator opening, intake amount, and the like are read.

Next, in step S31, the PCM 100 determines whether or not the average EGR rate obtained by the same procedure as in the first embodiment is larger than the target EGR rate obtained by the same procedure as in the first embodiment. If this determination is NO and the average EGR rate is equal to or less than the target EGR, the process ends as it is (returns to step S31). On the other hand, if 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 the amount of EGR rate deviation 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 the 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 as an appropriate value in advance, and knocking is likely to occur. Therefore, the occurrence of knocking can be prevented more reliably.

Then, in the second embodiment, when the additional injection Q2 is carried out, the injection amount of the additional injection Q2 is larger when the average EGR rate, that is, the actual EGR rate is high than when it is low. Therefore, when the actual EGR rate is high and knocking is likely to occur (knock strength is likely to be high), a large amount of fuel is injected to lower the temperature of the air-fuel mixture to more reliably prevent knocking. Further, when the actual EGR rate is relatively low and knocking is unlikely to occur (knock strength is low and easily suppressed), the injection amount of the additional injection Q2 is suppressed to a small value, and the temperature in the combustion chamber 6 due to the additional injection Q2 is lowered, and eventually the engine. It is possible to suppress a decrease in torque and a significant deterioration in fuel efficiency.

(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 charged in the combustion chamber 6 of each cylinder 2. Was injected by the additional injection Q2. Instead, as in the first embodiment, the inter-cylinder ratio of the EGR rate is calculated, and the 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 individually determined according to the difference between the actual EGR rate and the target EGR rate of each cylinder 2. Then, at this time, the injection amount of the additional injection Q2 of each cylinder is increased when the actual EGR ratio of each cylinder 2 is large than when it is low.

According to this configuration, an appropriate amount of fuel according 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 the deterioration of fuel efficiency is further deteriorated. It can be suppressed more reliably.

(Modified example of the third embodiment)
Further, instead of the above configuration, the knock intensity is estimated by a means for estimating the knock intensity separately provided, and the 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. The injection amount of the additional injection Q2 of each cylinder may be individually determined from the inter-cylinder ratio (ratio of the amount of EGR gas distributed to each cylinder). However, even at this time, the injection amount of the additional injection Q2 is made larger in the cylinder 2 having a larger EGR rate.

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

Further, 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 set to 10% or less of the total amount of fuel supplied to the combustion chamber 6 in 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 lowered due to the vaporization of the fuel. In addition, the mixture of fuel and air is insufficient and smoke is likely to occur. 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, a case where the inter-cylinder ratio of the EGR ratio (ratio of the amount of EGR gas distributed to each cylinder) is calculated based on the engine torque, the intake amount, etc. generated in the combustion stroke of each cylinder has been described. .. Instead of this, the oxygen concentration or carbon dioxide concentration of the intake air introduced into each cylinder may be measured individually, 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 the 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 N1 or more, and the engine speed is N1 or more. Moreover, the case where the ignition control for knock avoidance is performed only in the high-speed high load region A1 in which the engine load is the reference load Tq1 or more and the full load is excluded has been described. In the case where SI combustion is carried out in, knock avoidance ignition control may be carried out also in this region. Further, the ignition control for knock avoidance 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 in which 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 in which a combustion chamber is formed, and an intake manifold which intake air flows to be introduced into the combustion chamber, an exhaust passage exhaust gas discharged from the combustion chamber flows, the exhaust gas flowing through the exhaust passage one An EGR passage that communicates the intake passage and the exhaust passage so that the unit returns to the intake passage as EGR gas is provided, and fuel containing gasoline is supplied to the combustion chamber to provide a mixture of the fuel and air. Is a device that controls the engine that burns in the combustion chamber.
An ignition means for igniting the air-fuel mixture in the combustion chamber at a predetermined ignition timing,
A control means for controlling the ignition means is provided.
The geometric compression ratio of the cylinder is set to 15 or more.
Wherein, when the engine load is an engine with a high load region over a predetermined reference load is in operation, the base of said ignition means the ignition timing as the mixture starts to burn at compression top dead center or later The EGR is set as the ignition timing, the ratio of the EGR gas amount to the total gas amount in the combustion chamber is obtained as the EGR rate, and the EGR rate deviation amount obtained by subtracting the predetermined target EGR rate from the EGR rate is calculated and calculated. An engine control device, characterized in that the ignition means is ignited at a corrected ignition timing that is corrected so that the larger the rate deviation amount is, the larger the deviation is from the basic ignition timing to the retard side. In the engine control device according to claim 1,
A first detection means for detecting the amount of intake air introduced into the combustion chamber through the intake passage, and
Further provided with a second detecting means for detecting the exhaust oxygen concentration, which is the oxygen concentration of the exhaust gas flowing through the exhaust passage.
The control means calculates the EGR rate based on the detected intake amount and the exhaust oxygen concentration when the engine is operating in the high load region, and the target EGR rate is calculated from the calculated EGR rate. An engine control device, characterized in that the EGR rate deviation amount is calculated by subtracting. In the engine control device according to claim 1 or 2.
The engine includes a plurality of the cylinders, a plurality of the ignition means for igniting the air-fuel mixture in the combustion chamber of each cylinder, and an intake manifold for distributing the intake air to each cylinder.
The EGR passage is the is connected to one portion of the intake manifold, that the control device for an engine according to claim. A cylinder in which a combustion chamber is formed, and an intake manifold which intake air flows to be introduced into the combustion chamber, an exhaust passage exhaust gas discharged from the combustion chamber flows, the exhaust gas flowing through the exhaust passage one An EGR passage that communicates the intake passage and the exhaust passage so that the unit returns to the intake passage as EGR gas is provided, and fuel containing gasoline is supplied to the combustion chamber to provide a mixture of the fuel and air. Is a device that controls the engine that burns in the combustion chamber.
An ignition means for igniting the air-fuel mixture in the combustion chamber and
Refrigerant injection means for injecting a refrigerant for cooling the air-fuel mixture into the combustion chamber during combustion of the air-fuel mixture, and
A control means for controlling the ignition means and the refrigerant injection means is provided.
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 combustion after the 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. wherein the ratio of the EGR gas amount to the total gas amount in the combustion chamber is determined and calculated EGR rate deviation amount obtained by subtracting the predetermined target EGR rate from the EGR rate as the EGR rate, the higher the calculated EGR rate deviation amount is large An engine control device characterized in that the injection amount of the refrigerant by the refrigerant injection means is increased. In the engine control device according to claim 4,
A first detection means for detecting the amount of intake air introduced into the combustion chamber through the intake passage, and
Further provided with a second detecting means for detecting the exhaust oxygen concentration, which is the oxygen concentration of the exhaust gas flowing through the exhaust passage.
The control means calculates the EGR rate based on the detected intake amount and the exhaust oxygen concentration when the engine is operating in the high load region, and the target EGR rate is calculated from the calculated EGR rate. An engine control device, characterized in that the EGR rate deviation amount is calculated by subtracting. In the engine control device according to claim 4 or 5.
The engine includes a plurality of the cylinders, a plurality of the ignition means for igniting the air-fuel mixture in the combustion chamber of each cylinder, and an intake manifold for distributing the intake air to each cylinder.
The EGR passage is the is connected to one portion of the intake manifold, that the control device for an engine according to claim. In the engine control device according to any one of claims 4 to 6.
In the control means, 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 amount of heat generated in the combustion chamber is generated during one combustion cycle. An engine control device for 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. In the engine control device according to any one of claims 1 to 7.
An engine control device, characterized in that the target EGR rate is 20% or less when the engine is operated in the high load region.

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