JP2008014249A - Combustion control system for compression ignition internal combustion engine - Google Patents

Abstract

The present invention relates to a compression ignition type internal combustion engine that performs a premixed combustion operation by introducing an EGR gas amount of a predetermined amount or more into a cylinder, and from a fuel cut operation to a premixed combustion operation using existing hardware. It is an issue to provide technology that can be quickly transferred to.
In order to solve the above-mentioned problem, the present invention performs sub-injection of fuel in a cylinder after an expansion stroke when the internal combustion engine shifts from a fuel cut operation to a premixed combustion operation. The amount of the burned gas component discharged is increased, so that the amount of the burned gas component contained in the EGR gas per unit amount is increased.
[Selection] Figure 5

Description

  The present invention relates to a compression ignition type internal combustion engine, and more particularly to a combustion control technique for a compression ignition type internal combustion engine capable of a premixed combustion operation.

  As an internal combustion engine mounted on a vehicle or the like, a compression ignition type internal combustion engine capable of switching between a premixed combustion operation and a diffusion combustion operation is known.

  When a compression ignition type internal combustion engine is operated by premix combustion, it is necessary to introduce a larger amount of EGR gas into the combustion chamber than during diffusion combustion operation in order to prevent pre-ignition of fuel (or premixed gas). . By the way, when the internal combustion engine shifts from the diffusion combustion operation state or the fuel cut operation state to the premixed combustion operation state, the EGR gas amount cannot be increased immediately.

In contrast, a method has been proposed in which EGR gas is stored during premixed combustion operation or diffusion combustion operation, and the stored EGR gas is appropriately supplied to the combustion chamber (see, for example, Patent Document 1).
JP 2005-325811 A JP 2004-124732 A

  By the way, in addition to the existing configuration, the conventional technology described above requires a mechanism for storing EGR gas.

  The present invention has been made in view of the above situation, and an object of the present invention is to provide a compression ignition type internal combustion engine that performs a premixed combustion operation by introducing a predetermined amount or more of EGR gas into a cylinder. It is to provide a technology that can quickly shift from fuel cut operation to premixed combustion operation using existing hardware.

  In order to solve the above-described problems, the present invention provides a combustion control system for a compression ignition internal combustion engine in which a predetermined amount or more of EGR gas is introduced into a cylinder to perform a premixed combustion operation. When shifting to the mixed combustion operation, the concentration of the burned gas component contained in the EGR gas is increased.

  Specifically, the present invention relates to a combustion control system for a compression ignition type internal combustion engine that performs a premixed combustion operation by introducing a predetermined amount or more of EGR gas into a cylinder. A control means for increasing the amount of burned gas components contained in the exhaust gas of the internal combustion engine when shifting to operation is provided.

  The burned gas component here is carbon dioxide (CO2), water (H2O), or the like generated when fuel is burned in the cylinder.

  During fuel cut operation of the internal combustion engine, fuel is not combusted in the cylinder, so that the EGR gas circulation path (that is, starting from the combustion chamber of the internal combustion engine, sequentially returns to the combustion chamber through the exhaust passage, the EGR passage, and the intake passage). The route (hereinafter referred to as “EGR circulation route”) is filled with a gas having a high air concentration and a low concentration of burned gas components.

  In addition, after the fuel cut operation is completed, there is a transport delay until the exhaust gas from the first combustion cylinder (the cylinder in which combustion has been resumed first) reaches the internal combustion engine via the EGR circulation path.

  Therefore, during the period from the end of the fuel cut operation to the elimination of the transport delay, the amount of burned gas component introduced into the cylinder is too small. If the internal combustion engine is operated in a premixed combustion state in such a state, the fuel may ignite prematurely and generate excessive noise.

  In contrast, a method of delaying the start timing of the premixed combustion operation until the amount of burned gas component in the cylinder increases to an appropriate amount (specifically, until the amount of burned gas component in the cylinder increases to an appropriate amount, A method in which the internal combustion engine is operated by diffusion combustion is also conceivable.

  However, all the cylinders of the internal combustion engine do not restart the combustion at the same time when the fuel cut operation ends, but sequentially restart the combustion according to the fuel injection sequence. For this reason, it takes a relatively long time for the amount of burned gas component introduced into the cylinder to reach an appropriate amount.

  Therefore, the control means of the present invention increases the amount of burned gas components in the exhaust when the internal combustion engine shifts from the fuel cut operation to the premixed combustion operation. In this case, a large amount of burned gas component flows into the cylinder after the transportation delay is eliminated.

  As a result, the internal combustion engine can quickly shift from the fuel cut operation to the premixed combustion operation, and an increase in combustion noise during the shift can be suppressed.

  Here, as a method of increasing the amount of burned gas component contained in the exhaust gas of the internal combustion engine, a method of performing sub-injection after normal fuel injection (hereinafter referred to as “main injection”) can be exemplified. At this time, the timing of the sub-injection is preferably after the fuel injected by the main injection (hereinafter referred to as “main fuel”) is ignited. Since the proper ignition timing of the main fuel is near the top dead center of the compression stroke, the sub-injection timing is appropriate after the expansion stroke.

  When fuel is sub-injected into the cylinder after the expansion stroke, the amount of burned gas components in the cylinder increases due to the combustion of the fuel injected by the sub-injection (hereinafter referred to as “sub fuel”). Furthermore, since the unburned main fuel is burned together with the auxiliary fuel, the amount of burned gas components in the cylinder further increases.

  Therefore, when the sub-injection is performed into the cylinder after the expansion stroke, the amount of burned gas components in the exhaust gas can be significantly increased with a relatively small amount of sub-fuel.

  Note that when the engine speed of the internal combustion engine is low, the above-described transportation delay period becomes long, and thus the amount of EGR gas introduced into the cylinder is unlikely to increase rapidly.

  Therefore, the control means of the present invention may increase the amount of auxiliary fuel as the amount of EGR gas introduced into the cylinder decreases with respect to the predetermined amount.

  In this case, the amount of burned gas components contained in the exhaust gas of the internal combustion engine increases as the amount of EGR gas introduced into the cylinder decreases. As a result, even if the amount of EGR gas introduced into the cylinder is difficult to increase, the amount of burned gas component introduced into the cylinder can be quickly increased.

By the way, when the auxiliary fuel burns, the torque of the internal combustion engine increases not a little. Therefore, it is preferable to correct the decrease in the main fuel amount according to the auxiliary fuel amount. However, if the main fuel amount is reduced as the auxiliary fuel amount is increased, the timing at which the combustion energy becomes maximum (hereinafter referred to as “combustion peak timing”) is delayed. May occur.

  Therefore, the control means may advance the timing of main injection (main injection timing) as the amount of fuel injected by sub-injection increases. In this case, since an excessive delay in the combustion peak timing is suppressed, torque reduction and fuel consumption deterioration are suppressed.

  In the combustion control system for a compression ignition type internal combustion engine according to the present invention, when the internal combustion engine is shifted from the fuel cut operation to the premixed combustion operation, the control unit temporarily operates the internal combustion engine in the diffusion combustion operation and at the time of the diffusion combustion operation. The amount of burned gas components discharged from the internal combustion engine may be increased.

  When the internal combustion engine continues the fuel cut operation for a long time, the gas in the EGR circulation path is only air. For this reason, during the period from the end of the fuel cut operation of the internal combustion engine to the elimination of the transportation delay, the amount of burned gas component introduced into the cylinder becomes substantially zero. Therefore, if the internal combustion engine is premixed and burned immediately after the fuel cut operation, fluctuations in the ignition timing cannot be avoided.

  On the other hand, if the internal combustion engine is subjected to the diffusion combustion operation during the period from the end of the fuel cut operation until the transportation delay is eliminated, it is possible to suppress premature ignition. Further, if the amount of burned gas component in the exhaust gas is increased during the diffusion combustion operation of the internal combustion engine, a large amount of burned gas component is introduced into the cylinder when the transport delay is eliminated. As a result, it becomes possible to operate the internal combustion engine in a premixed combustion operation at an early time after the transportation delay is eliminated.

  When the internal combustion engine is shifted from the diffusion combustion operation to the premixed combustion operation, it is possible to gradually change the fuel injection parameters such as the fuel injection timing and the number of fuel injections in order to suppress a sudden change in the combustion state. preferable.

  As a method of gradually changing the fuel injection parameter, the fuel injection is divided into the main injection for diffusion combustion operation and the preliminary injection earlier than the main injection, and the number of preliminary injections is increased stepwise. Can be illustrated. According to such a method, since the premixed gas formation time and the formation amount gradually change, a rapid change in the combustion state is suppressed.

  When the advance of the main injection timing accompanying the increase in the amount of secondary fuel is performed when such a method is executed, the fuel injected by the preliminary injection immediately before the main injection is sufficiently mixed with the gas in the cylinder. There is a possibility of ignition before starting.

  Therefore, when the advancement of the main injection timing accompanying the increase in the auxiliary fuel is performed, the control means stops the preliminary injection immediately before the main injection and supplies the stopped fuel for the preliminary injection earlier than the preliminary injection. Added to injection. In this case, it is possible to form the premixed gas while suppressing the torque fluctuation of the internal combustion engine.

  The combustion control system for a compression ignition type internal combustion engine according to the present invention may further include an internal EGR means for increasing the amount of gas remaining in the cylinder for a first predetermined period from the end of the fuel cut operation. .

According to such a configuration, the amount of the burned gas component introduced into the cylinder increases more rapidly. Therefore, the internal combustion engine can shift from the fuel cut operation to the premixed combustion operation earlier.

  As a method of increasing the amount of gas remaining in the cylinder, (1) a method of reducing the opening of the exhaust throttle valve, (2) a method of advancing the closing timing of the exhaust valve, (3) a variable capacity type A method of reducing the opening degree of the nozzle vane of the turbocharger can be exemplified.

  In addition, examples of the first predetermined period include a period until the above-described EGR gas transport delay is eliminated, or a period until the EGR gas amount introduced into the cylinder reaches a predetermined amount. it can.

  Further, the combustion control system for a compression ignition type internal combustion engine according to the present invention may further comprise a heating means for increasing the temperature of the fuel for a second predetermined period from the end of the fuel cut operation.

  During fuel cut operation, low-temperature air passes through the cylinder, so the temperature in the cylinder decreases. Therefore, immediately after the end of the fuel cut operation, the fuel in the cylinder is difficult to vaporize and atomize. On the other hand, when the temperature of the fuel is raised by the heating means, the vaporization and atomization of the fuel are promoted even if the temperature in the cylinder is lowered.

  Examples of the method for raising the temperature of the fuel include a method for directly heating the fuel and a method for indirectly heating the intake air using a medium.

  The second predetermined period can be exemplified by a period until the fuel is burned at least once in all the cylinders of the internal combustion engine.

  According to the present invention, in a compression ignition internal combustion engine that performs a premixed combustion operation by introducing a predetermined amount or more of EGR gas into a cylinder, the fuel cut operation state is changed to the premixed combustion operation state while using the existing configuration. Prompt migration is possible.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) capable of appropriately switching between a premixed combustion operation and a diffusion combustion operation.

  The internal combustion engine 1 includes a fuel injection valve 3 that can inject fuel directly into each cylinder 2 and an intake passage 4 that guides air into each cylinder 2. A compressor 50 and an intercooler 6 of a centrifugal supercharger (turbocharger) 5 are arranged in the intake passage 4.

  The intake air supercharged by the compressor 50 is cooled by the intercooler 6 and then guided into each cylinder 2. The intake air introduced into each cylinder 2 is ignited and burned in the cylinder 2 together with the fuel injected from the fuel injection valve 3.

  The gas burned in each cylinder 2 is discharged to the exhaust passage 7. The exhaust discharged into the exhaust passage 7 is released into the atmosphere via the turbine 51 and the exhaust purification catalyst 8 disposed in the middle of the exhaust passage 7.

  As the exhaust purification catalyst 8, a NOx storage reduction catalyst having oxidation ability and NOx storage ability, a particulate filter having oxidation ability and PM trapping ability, a particulate filter carrying a storage reduction type NOx catalyst, or the like is used. It can be illustrated.

  The intake passage 4 and the exhaust passage 7 described above are connected to each other by an EGR passage 9. In the middle of the EGR passage 9, an EGR valve 10 that adjusts the flow rate of exhaust gas (hereinafter referred to as “EGR gas”) flowing through the EGR passage 9, and an EGR cooler for cooling the EGR gas flowing through the EGR passage 9 11 is arranged.

  In addition, an intake throttle valve 12 is disposed in a portion of the intake passage 4 downstream of the intercooler 6 and upstream of the connection portion of the EGR passage 9.

  The fuel injection valve 3, the EGR valve 10, and the intake throttle valve 12 described above are electrically controlled by the ECU 13. The ECU 13 is attached to the internal combustion engine 1, the measured value of the air flow meter 14 disposed in the intake passage 4, the measured value of the air-fuel ratio sensor (A / F sensor) 15 disposed in the exhaust passage 5 downstream from the exhaust purification catalyst 8. The fuel injection valve 3, the EGR valve 10, and the intake throttle valve 12 are controlled using the measured value of the crank position sensor 16 and the measured value of the accelerator position sensor 17 as parameters.

  For example, the ECU 13 causes the internal combustion engine 1 to perform a premixed combustion operation when the engine operating state determined from the load (accelerator opening) Accp and the engine speed Ne of the internal combustion engine 1 is in the premixed combustion region shown in FIG. On the other hand, when the engine operating state is in the diffusion combustion operation region of FIG. 2, the ECU 13 causes the internal combustion engine 1 to perform the diffusion combustion operation.

  When the internal combustion engine 1 is operated in a premixed combustion mode, the ECU 13 sets the pilot injection amount to zero (stops pilot injection) and sets the main injection timing earlier than the compression top dead center (see FIG. 3). Set at the beginning or middle of the compression stroke.

  On the other hand, when the internal combustion engine 1 is operated by diffusion combustion, as shown in FIG. 4, the ECU 13 sets the pilot injection amount to an amount larger than zero (executes pilot injection) and compresses the main injection timing. Set near the point.

  When the internal combustion engine 1 is operated in a premixed combustion mode, the fuel in the cylinder 2 may ignite prematurely before forming the premixed gas, so a larger amount of EGR gas is used in the cylinder than in the diffusion combustion operation. 2 need to be introduced.

  By the way, since the fuel is not burned in the cylinder 2 during the fuel cut operation of the internal combustion engine 1, the EGR circulation path (starting from the combustion chamber of the internal combustion engine 1 through the exhaust passage 7, the EGR passage 9, and the intake passage 4 in order again) The path returning to the combustion chamber is filled with a gas having a high air concentration and a low burnt gas component concentration. Furthermore, after the fuel cut operation is completed, there is a transport delay until the exhaust of the first combustion cylinder reaches the combustion chamber of the internal combustion engine 1 via the EGR circulation path.

  Therefore, during the period from the end of the fuel cut operation to the elimination of the transport delay, the amount of burned gas component introduced into the cylinder 2 is minimal or zero. For this reason, if the internal combustion engine 1 is immediately subjected to the premix combustion operation after the end of the fuel cut operation, the ignition timing fluctuates (premature ignition), and combustion noise increases and torque fluctuations occur.

On the other hand, a method of causing the internal combustion engine 1 to perform a diffusion combustion operation during a period from the end of the fuel cut operation to the elimination of the transport delay can be considered. However, all the cylinders 2 of the internal combustion engine 1 do not restart the combustion at the same time when the fuel cut operation ends, but sequentially restart the combustion according to the fuel injection sequence. For this reason, the amount of burned gas components introduced into the cylinder 2 at the time when the transport delay is eliminated becomes too small relative to the amount that can suppress the pre-ignition of the fuel. Therefore, it is difficult to promptly shift the internal combustion engine 1 from the diffusion combustion operation to the premixed combustion operation after the transportation delay is eliminated.

  Therefore, in the combustion control system for the internal combustion engine in the present embodiment, the ECU 13 performs the combustion control shown below.

  FIG. 5 is a timing chart showing a combustion control procedure when the internal combustion engine 1 shifts from the fuel cut operation to the premixed combustion operation.

  When the engine operating state at the end of the fuel cut operation is in the premixed combustion operation region of FIG. 2 described above, the ECU 13 first causes the internal combustion engine 1 to perform a diffusion combustion operation. Specifically, when the fuel cut operation of the internal combustion engine 1 is finished (t1 in FIG. 5), the ECU 13 causes a small amount of fuel to be pilot-injected before the compression top dead center and in the vicinity of the compression top dead center (in FIG. 5). The fuel injection valve 3 is controlled to perform main injection at T1).

  Further, the ECU 13 sets the EGR valve 10 so that the EGR gas amount becomes an amount capable of suppressing premature ignition (hereinafter referred to as “target EGR gas amount”) at the end of the fuel cut operation (t1 in FIG. 5). To control the opening degree.

  Since the EGR gas amount correlates with the intake air amount of the internal combustion engine 1, in the example of FIG. 5, the intake air amount (GN1 in FIG. 5) when the EGR gas amount becomes the target EGR gas amount is determined as the target intake air amount. The opening degree of the EGR valve 10 is controlled so that the actual intake air amount (actual GN in FIG. 5) of the internal combustion engine 1 becomes the target intake air amount GN1.

  It should be noted that the response delay due to the EGR gas transport delay from the time when the ECU 13 outputs the command value for the EGR valve 10 (t1 in FIG. 5) to the time when the actual GN starts to change (t2 in FIG. 5). (Period P1 in FIG. 5) occurs. For this reason, the ECU 13 controls the fuel injection valve 3 so as to continue the diffusion combustion operation of the internal combustion engine 1 during the period P1 described above.

  Further, from the time when the actual GN starts to change (t2 in FIG. 5) until the actual GN becomes equal to the target intake air amount GN1 (t3 in FIG. 5), the response due to the combustion order of each cylinder 2 There is a delay (period P2 in FIG. 5). For this reason, in the above-described period P2, the amount of EGR gas introduced into the cylinder 2 becomes smaller than the target EGR gas amount.

  Therefore, in order to prevent premature ignition of the fuel, it is appropriate to switch the internal combustion engine 1 from the diffusion combustion operation to the premixed combustion operation after the end of the period P2. However, there is a problem that a required period (a period obtained by adding the period P1 and the period P2) from the end of the fuel cut operation to the start of the premixed combustion operation becomes long. In particular, when the engine speed is low, the transport delay of EGR gas becomes large, and thus the above required period may become excessively long.

  On the other hand, a method is conceivable in which EGR gas is stored before the internal combustion engine 1 is subjected to fuel cut operation, and the stored EGR gas is supplied to the internal combustion engine 1 after completion of the fuel cut operation. A mechanism to keep it is necessary.

Therefore, in the combustion control of the present embodiment, the ECU 13 sets the sub-injection flag (= 1) at the end of the fuel cut operation t1 (= 1) to increase the burned gas component concentration in the EGR gas. When the sub injection flag is set (= 1), the ECU 13 performs sub injection (post injection) during the expansion stroke after the main injection, as shown in FIG.

  When the post-injection is performed into the cylinder 2 after the expansion stroke, the fuel (sub fuel) injected by the post-injection burns in the cylinder 2 and a burned gas component is generated. Furthermore, since the unburned main fuel is burned together with the auxiliary fuel, the amount of burned gas components generated is further increased.

  Therefore, when post-injection is performed in the cylinder 2 after the expansion stroke, the amount of burned gas components generated in the cylinder 2 is efficiently increased. As a result, the amount of burned gas components contained in the exhaust gas of the internal combustion engine 1 increases.

  When the amount of the burned gas component contained in the exhaust gas of the internal combustion engine 1 is increased by the method described above, the amount of the burned gas component contained in the EGR gas per unit amount is increased (the burned gas component concentration in the EGR gas is increased). To do. When the burned gas component concentration in the EGR gas increases, the amount of burned gas component introduced into the cylinder 2 increases when the EGR gas transport delay is eliminated (t2 in FIG. 5).

  When a large amount of burned gas component is introduced into the cylinder 2 when the EGR gas transport delay is eliminated (t2 in FIG. 5), the internal combustion engine 1 shifts from the diffusion combustion operation to the premixed combustion operation at that time. However, premature ignition of fuel can be avoided.

  However, if the fuel injection parameter is switched suddenly when the internal combustion engine 1 is shifted from the diffusion combustion operation to the premixed combustion operation, the combustion state may change suddenly, resulting in deterioration of exhaust emission, torque fluctuation, and the like. .

  Therefore, the ECU 13 continuously or discretely changes the fuel injection parameter from the parameter for the diffusion combustion operation to the parameter for the premixed combustion operation. Specifically, the ECU 13 decreases the pilot injection amount continuously or discretely and advances the main injection timing continuously or discretely from the vicinity of the compression top dead center (hereinafter, this process is referred to as “transition process”). Called).

  At this time, the change speed of the fuel injection parameters (for example, the amount of decrease in the pilot injection amount per cycle and the advance amount of the main injection timing) is set so that the exhaust emission and torque fluctuation of the internal combustion engine 1 are within an allowable range. Shall be determined.

  When the main injection timing is advanced to the injection timing for the premixed combustion operation and the pilot injection amount is reduced to the minimum injection amount Qpmin of the fuel injection valve 3 (t3 in FIG. 5), the ECU 13 ends the above-described transition processing. To do.

  When the fuel injection parameter is gradually changed by such a transition process, the operation of the internal combustion engine 1 can be switched while suppressing a rapid change in the combustion state.

  Further, during the above-described transition processing execution period (period P2 in FIG. 5), although the EGR gas amount is smaller than the target EGR gas amount, the amount of burned gas components contained in the EGR gas per unit amount greatly increases. Therefore, the occurrence of premature ignition is suppressed, or the generation of noise and vibration due to premature ignition is suppressed.

The sub-injection may be ended simultaneously with the end of the period P2 (t3 in FIG. 5). However, when the EGR gas amount approximates the target EGR gas amount before the end of the period P2, the sub-injection is preferably ended at that point. This is because if the above-described sub-injection is continued even after the EGR gas amount reaches the target EGR gas amount, the amount of burned gas components introduced into the cylinder 2 becomes excessive, leading to misfire and increased smoke. Because.

  Further, during the above-described transition processing execution period (period P2 in FIG. 5), the auxiliary fuel amount may be set to a constant amount, but the amount of EGR gas introduced into the cylinder 2 (in other words, the actual GN) ) Is preferably changed according to.

  Specifically, as shown in FIG. 7, the ECU 13 increases the sub fuel amount as the actual GN increases with respect to the target GN (as the value ΔGN obtained by subtracting the target GN from the actual GN increases).

  In this case, the burned gas component concentration in the EGR gas increases as the amount of EGR gas introduced into the cylinder 2 decreases, and the burned gas in the EGR gas increases as the amount of EGR gas introduced into the cylinder 2 increases. The component concentration is lowered.

  As a result, pre-ignition of fuel can be suppressed when the amount of EGR gas introduced into the cylinder 2 is small, and fuel misfire and smoke increase when the amount of EGR gas introduced into the cylinder 2 is large. Can be suppressed.

  Note that when the auxiliary fuel burns in the expansion stroke, the torque of the internal combustion engine 1 increases not a little. Therefore, when the auxiliary fuel amount is changed as shown in FIG. 7 described above, it is preferable that the main fuel amount is corrected to decrease as the auxiliary fuel amount increases. In this case, it is possible to suppress the torque of the internal combustion engine 1 from deviating from the target torque.

  However, if the auxiliary fuel amount is excessive, the combustion peak timing is excessively delayed (for example, in the middle of the expansion stroke). If the fuel peak timing is excessively delayed, the torque of the internal combustion engine 1 may be lower than the required torque, leading to a decrease in drivability and a deterioration in fuel consumption.

  Therefore, in the example shown in FIG. 7, the auxiliary fuel amount is limited to a predetermined upper limit guard Qpstmax or less. The upper limit guard Qpstmax is, for example, an amount corresponding to 1/2 of the total fuel injection amount (the sum of the pilot injection amount, the main injection amount, and the post injection amount).

  When the auxiliary fuel amount is limited to the upper limit guard Qpstmax or less in this way, the combustion peak timing is suppressed from being excessively delayed. As a result, the torque of the internal combustion engine 1 does not greatly fall below the required torque, and deterioration of fuel consumption and drivability are suppressed.

  According to the embodiment described above, the internal combustion engine 1 can be quickly and suitably shifted from the fuel cut operation to the premixed combustion operation while using the existing hardware.

<Example 2>
Next, a second embodiment of the combustion control system for a compression ignition type internal combustion engine according to the present invention will be described with reference to FIG. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  In the first embodiment described above, the example in which the auxiliary fuel amount is changed based on the difference ΔGN between the actual GN and the target GN during the transition processing execution period has been described. On the other hand, in the present embodiment, an example will be described in which the sub fuel amount is changed based on the transition processing execution time (that is, the elapsed time from t2 in FIG. 5) Δt.

The amount of EGR gas introduced into the cylinder 2 during the transition processing execution period correlates with the transition processing execution time Δt. That is, the amount of EGR gas introduced into the cylinder 2 during the transition processing execution period decreases as the transition processing execution time Δt decreases and increases as the transition processing execution time Δt increases.

  Therefore, as shown in FIG. 8, the ECU 13 increases the sub fuel amount as the transition processing execution time Δt becomes shorter, and decreases the sub fuel amount as the transition processing execution time Δt becomes longer.

  When the auxiliary fuel amount is changed in this way, the amount of burned gas component in the EGR gas increases as the amount of EGR gas introduced into the cylinder 2 decreases, and the amount of EGR gas introduced into the cylinder 2 increases. The greater the amount, the lower the burned gas component concentration in the EGR gas.

  Therefore, similarly to the first embodiment described above, when the amount of EGR gas introduced into the cylinder 2 is small, pre-ignition of fuel can be suppressed, and the amount of EGR gas introduced into the cylinder 2 can be reduced. When there are many, it is possible to suppress fuel misfire and increase in smoke.

  Note that the rate of increase in the amount of EGR gas introduced into the cylinder 2 during the transition processing execution period increases as the engine speed increases and decreases as the engine speed decreases. Therefore, the ECU 13 may correct the auxiliary fuel amount determined based on the transition processing execution time Δt according to the engine speed. For example, the ECU 14 may increase the sub fuel amount as the engine speed decreases, and decrease the sub fuel amount as the engine speed increases.

<Example 3>
Next, a third embodiment of the combustion control system for a compression ignition type internal combustion engine according to the present invention will be described with reference to FIG. Here, configurations different from those of the first and second embodiments described above will be described, and description of similar configurations will be omitted.

  In the first and second embodiments described above, the example in which the auxiliary fuel amount is limited to the predetermined upper limit guard Qpstmax or less has been described. On the other hand, in the present embodiment, an example will be described in which the main injection timing and the sub injection timing are changed according to the sub fuel amount instead of limiting the sub fuel amount to the upper limit guard Qpstmax or less.

  As described in the first embodiment described above, if the amount of auxiliary fuel is excessive, the combustion peak timing is excessively delayed, which may lead to a decrease in drivability and fuel consumption.

  Therefore, as shown in FIG. 9, the ECU 13 advances the main injection timing and the sub-injection timing as the amount of auxiliary fuel increases. At this time, if the interval (interval) between the main injection timing and the sub-injection timing becomes unequal, there is a possibility that variations in the injection amounts of the main injection and the sub-injection may occur due to fluctuations in the injection pressure or pulsation. Therefore, in the present embodiment, the ECU 13 changes both injection timings while keeping the interval between the main injection timing and the sub injection timing constant.

  As described above, when the main injection timing and the sub-injection timing are changed according to the auxiliary fuel amount, it is suppressed that the combustion peak timing is excessively delayed when the auxiliary fuel amount is increased. Therefore, deterioration of fuel consumption and drivability are suppressed during the transition processing execution period.

<Example 4>
Next, a fourth embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from the above-described third embodiment will be described, and description of the same configuration will be omitted.

  In the above-described third embodiment, as a method of shifting the internal combustion engine 1 from the diffusion combustion operation to the premixed combustion operation, a method of gradually advancing the main injection timing while gradually decreasing the pilot injection amount is used. Yes.

  On the other hand, in the present embodiment, as a method of shifting the internal combustion engine 1 from the diffusion combustion operation to the premixed combustion operation, the fuel is divided and injected several times and the start timing of the most recent fuel injection is gradually advanced. The method to make is used.

  FIG. 10 is a timing chart showing a procedure for changing the fuel injection parameters in the process in which the internal combustion engine 1 shifts from the diffusion combustion operation to the premixed combustion operation.

  First, as shown in FIG. 10A, the ECU 13 starts at the same time as the fuel injection timing (Tdf in FIG. 10) during the diffusion combustion operation, and starts earlier than the main injection M. The fuel is injected separately into the preliminary injection S1.

  At this time, the sum of the injection amount of the main injection M and the injection amount of the preliminary injection S is set to be equal to the amount commensurate with the required torque of the internal combustion engine 1. This is for suppressing the torque fluctuation of the internal combustion engine 1.

  Moreover, it is preferable that the injection amount of the preliminary injection S is set as small as possible. This is because the change in the combustion state due to the addition of the preliminary injection S is minimized and the pre-ignition of the fuel injected by the preliminary injection S is suppressed. Therefore, the injection amount of the preliminary injection S may be set to the minimum injection amount Qpmin that can be injected by the fuel injection valve 3.

  Next, the ECU 13 gradually increases the number of preliminary injections S (hereinafter referred to as “preliminary injection number”) (see (b), (c), and (d) of FIG. 10). Specifically, the ECU 13 increases the number of preliminary injections as the actual GN decreases (or the transition process execution time Δt increases).

  When the number of preliminary injections is increased, the ECU 13 subtracts the fuel amount corresponding to the increase in the number of preliminary injections from the injection amount of the main injection M. This is to prevent the torque of the internal combustion engine 1 from deviating from the required torque.

  Further, the ECU 13 makes the fuel injection interval constant (in this case, the interval Δt1 between the main injection M and the preliminary injection S and the interval Δt2 between the preliminary injection S and the preliminary injection S) constant. This is because if the fuel injection interval becomes indefinite, variations in the injection amounts of the main fuel injection S and the preliminary fuel injection S may occur due to fluctuations or pulsations in the injection pressure.

  By the way, if the number of preliminary injections is increased while the fuel injection intervals Δt1 and Δt2 are kept constant, the start timing of the foremost preliminary injection S is advanced every time the number of preliminary injections increases. For this reason, if the fuel injection intervals Δt1 and Δt2 are set to be long, the ignition timing of the fuel may fluctuate abruptly and induce torque fluctuation and noise.

  In contrast, the ECU 13 sets the fuel injection intervals Δt1 and Δt2 as short as possible so that the start timing of the foremost preliminary injection S is not rapidly advanced.

  When the number of preliminary injections is increased by the above-described procedure, the start timing of the previous preliminary injection S reaches a predetermined advance angle guard timing (see (d) in FIG. 10). The advance guard time corresponds to the fuel injection start time during the premixed combustion operation or the earliest fuel injection time within the range of the fuel injection time at which bore flushing can be suppressed.

  After the start timing of the foremost preliminary injection S reaches the advance guard time, the ECU 13 sequentially ends the fuel injection with the latest start timing and supplies the fuel for the ended fuel injection to the fuel for the previous preliminary injection S. Add to the injection amount.

  When the transition process is executed according to such a procedure, the amount of premixed gas gradually increases and the amount of premixed gas gradually increases as the amount of burned gas components in the cylinder 2 increases. Rapid changes in ignition timing are suppressed. As a result, the internal combustion engine 1 can perform a smooth transition without generating torque fluctuations or noise.

  By the way, when the transition process shown in FIG. 10 and the process for changing the main injection timing and the sub injection timing described in the third embodiment are executed in parallel, the main injection M and the preliminary injection S There is a possibility that the interval Δt1 becomes excessively short. If the interval Δt1 between the main injection M and the preliminary injection S becomes excessively short, the fuel injection valve 3 may not be able to follow the injection signal.

  Therefore, as shown in FIG. 11, the ECU 13 stops the preliminary injection S immediately before the main injection M when the injection timings of the main injection M and the sub injection are advanced. As a result, the interval Δt1 between the main injection M and the preliminary injection S is not excessively shortened.

  Further, the ECU 13 may add the canceled preliminary injection fuel to the previous preliminary injection S. In this case, it is possible to prevent the formation timing and the amount of the premixed gas from changing greatly depending on the advance angle of the main injection timing and the sub injection timing.

<Example 5>
Next, a fifth embodiment of the present invention will be described. Here, configurations different from those of the first to fourth embodiments described above will be described, and description of similar configurations will be omitted.

  In the first to fourth embodiments described above, examples have been described in which the amount of burnt gas component contained in the EGR gas per unit amount is increased to advance the transition timing from the diffusion combustion operation to the premixed combustion operation. .

  In contrast, in this embodiment, an example in which the amount of burned gas components contained in the EGR gas per unit amount is increased and the amount of burned gas components remaining in the cylinder 2 is also increased will be described.

  When sub-injection (post-injection) is performed during the diffusion combustion operation after the fuel cut operation is completed, a large amount of burned gas components are introduced into the cylinder 2 when the EGR gas transport delay is eliminated (t2 in FIG. 5). Can do.

  However, during the period until the EGR gas transport delay is eliminated (period P1 in FIG. 5), since the amount of burned gas components introduced into the cylinder 2 is extremely small, the diffusion combustion operation is changed to the premixed combustion operation. The transfer process cannot be executed until the transportation delay is eliminated.

  On the other hand, if the amount of burned gas component remaining in the cylinder 2 is increased after the fuel cut operation is completed, the amount of burned gas component in the cylinder 2 is increased before the above-described transport delay is eliminated. Can do. As a result, even if the transition process is started before the transportation delay is eliminated, the pre-ignition of the fuel is suppressed.

Here, as a method of increasing the amount of burnt gas component remaining in the cylinder 2, in addition to the execution of the sub-injection (post-injection) described above, (1) reducing the opening of the exhaust throttle valve, (2 Examples thereof include a method of advancing the closing timing of the exhaust valve, and a method of reducing the opening of the nozzle vane of the variable displacement turbocharger.

  According to the embodiment described above, the internal combustion engine 1 can shift to the premixed combustion operation earlier than the first to fourth embodiments described above.

<Example 6>
Next, a sixth embodiment of the present invention will be described. Here, configurations different from those of the first to fifth embodiments described above will be described, and description of similar configurations will be omitted.

  In this embodiment, the ECU 13 increases the temperature of the fuel until a predetermined period (second predetermined period) elapses from the end of the fuel cut operation of the internal combustion engine 1.

  During the fuel cut operation, only low-temperature air passes through the cylinder 2, so that the temperature in the cylinder 2 decreases. Therefore, immediately after the end of the fuel cut operation, the fuel in the cylinder 2 is difficult to vaporize and atomize.

  On the other hand, when the temperature of the fuel is raised during a predetermined period after the fuel cut operation of the internal combustion engine 1 is completed, the vaporization and atomization of the fuel are promoted. As a result, it is possible to form a premixed gas in which fuel and air are homogeneously mixed, and to stabilize the ignition timing.

  Here, as a method of raising the temperature of the fuel, a method of directly heating the fuel or a method of heating indirectly using the intake air as a medium can be exemplified. As a method of directly heating the fuel, a method of operating a glow plug can be exemplified. Moreover, as a method of heating the intake air, a method of arranging a heater in the intake passage can be exemplified.

1 is a diagram illustrating a schematic configuration of an internal combustion engine in Embodiment 1. FIG. It is a figure which shows the map for switching a premix combustion operation and a diffusion combustion operation. It is a timing chart which shows the fuel injection timing at the time of a premix combustion operation. It is a timing chart which shows the fuel injection timing at the time of diffusion combustion operation. 3 is a timing chart showing a combustion control procedure in the first embodiment. It is a timing chart which shows the execution method of sub-injection. It is a figure which shows the map for determining the amount of sub fuel in Example 1. FIG. It is a figure which shows the map for determining sub fuel amount in Example 2. FIG. FIG. 10 is a diagram illustrating a map for determining an advance amount of main injection timing in the third embodiment. 10 is a timing chart illustrating a procedure for executing a migration process according to the fourth embodiment. 10 is a timing chart showing an execution procedure of transition processing when the main injection timing is advanced in the fourth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Fuel injection valve 4 ... Intake passage 7 ... Exhaust passage 9 ... EGR passage 10 ... EGR valve 11- ... EGR cooler 12 .... Intake throttle valve 13 .... ECU

Claims (8)

In a combustion control system for a compression ignition internal combustion engine that performs a premixed combustion operation by introducing a predetermined amount or more of EGR gas into a cylinder,
Combustion of a compression ignition type internal combustion engine, characterized by comprising control means for increasing the amount of burned gas components contained in the exhaust of the internal combustion engine when the internal combustion engine transitions from fuel cut operation to premixed combustion operation Control system.   2. The combustion control system for a compression ignition type internal combustion engine according to claim 1, wherein the control means increases the amount of burned gas components in the exhaust gas by performing sub-injection of fuel into the cylinder after the expansion stroke. .   3. The compression ignition type internal combustion engine according to claim 2, wherein the control means increases the amount of fuel injected by the sub-injection as the amount of EGR gas introduced into the cylinder decreases with respect to the predetermined amount. Engine combustion control system. In Claim 2 or 3, when the internal combustion engine shifts from a fuel cut operation to a premixed combustion operation, it further comprises a transition means for shifting the internal combustion engine to a premixed combustion operation after once performing a diffusion combustion operation.
A combustion control system for a compression ignition type internal combustion engine, wherein the control means performs sub-injection of fuel into a cylinder after an expansion stroke when the transition means causes the internal combustion engine to perform a diffusion combustion operation.   5. The combustion control system for a compression ignition type internal combustion engine according to claim 4, wherein the control means advances the main injection timing of the fuel as the amount of fuel injected by the sub-injection increases. 6. The fuel injection system according to claim 5, wherein when the internal combustion engine shifts from the diffusion combustion operation to the premixed combustion operation, fuel injection is performed by dividing into a main injection for the diffusion combustion operation and a preliminary injection earlier than the main injection. An injection control means for increasing the number of injections stepwise;
When the advancement of the main injection timing is performed, the control means stops the preliminary injection immediately before the main injection and adds the stopped fuel for the preliminary injection to the preliminary injection earlier than the preliminary injection. A combustion control system for a compression ignition type internal combustion engine.   The combustion control system for a compression ignition internal combustion engine according to any one of claims 1 to 6, further comprising an internal EGR means for increasing the amount of gas remaining in the cylinder for a first predetermined period from the end of the fuel cut operation.   The combustion control system for a compression ignition type internal combustion engine according to any one of claims 1 to 7, further comprising heating means for increasing the temperature of the fuel for a second predetermined period from the end of the fuel cut operation.

Images