JP4720798B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine that supplies a reducing agent to an exhaust gas purification device to regenerate the exhaust gas purification device.

Conventionally, as a method of performing a regeneration process with a temperature rise on an exhaust purification device, there is a method of supplying a reducing agent to the exhaust purification device while reducing the opening of an exhaust throttle valve disposed downstream of the exhaust purification device. It has been proposed (see, for example, Patent Document 1).
JP 2006-316758 A JP-A-2005-315190 JP 2003-90209 A JP 2004-150319 A

  By the way, when the internal combustion engine is in a premixed combustion operation, the intake air amount is limited by an intake throttle valve or the like, and the EGR gas amount is increased by an EGR mechanism. For this reason, when the exhaust throttle valve is throttled during the premixed combustion operation of the internal combustion engine, the exhaust pressure upstream of the exhaust throttle valve is less likely to rise quickly, and the exhaust flow velocity tends to rise.

  If the reducing agent is supplied when the exhaust pressure is low and the exhaust gas flow rate is high, it is difficult to obtain the effect of the reducing agent supply, and the reducing agent may slip through the exhaust purification device.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to regenerate the exhaust purification device by supplying a reducing agent to the exhaust purification device while reducing the opening of the exhaust throttle valve. In an exhaust gas purification system for an internal combustion engine, there is provided a technique capable of efficiently regenerating the exhaust gas purification device during a premixed combustion operation of the internal combustion engine.

  In order to solve the above-described problems, the present invention first reduces the opening of the exhaust throttle valve when the necessity of regenerating the exhaust purification device occurs when the internal combustion engine is in the premixed combustion operation, After the elapse of time, the supply of the reducing agent was started.

  Specifically, in an exhaust purification system for an internal combustion engine capable of premixed combustion operation, an exhaust purification device disposed in an exhaust passage of the internal combustion engine, an exhaust throttle valve disposed in an exhaust passage downstream of the exhaust purification device, Supply means for supplying a reducing agent to the exhaust gas flowing into the exhaust purification apparatus; and a regeneration means for regenerating the exhaust purification apparatus by using the reduction in the opening of the exhaust throttle valve and the supply of the reducing agent by the supply means in combination. When the exhaust purification device needs to be regenerated by the regeneration means during the premixed combustion operation of the internal combustion engine, the supply means forbids the supply of the reducing agent for a predetermined period after the opening of the exhaust throttle valve is reduced. Prohibiting means to be provided.

  The “exhaust gas purification device” here includes a purification device such as an NOx storage reduction catalyst or a particulate filter. In addition, “regeneration of the exhaust purification device” includes a process for reducing and removing SOx stored in the NOx storage reduction catalyst (S regeneration process), and a process for oxidizing and removing PM collected by the particulate filter ( A process that requires a temperature rise of the exhaust purification apparatus, such as a PM regeneration process.

  When the internal combustion engine is operated by premix combustion, it is necessary to reduce the amount of oxygen introduced into the cylinder. For this reason, when the internal combustion engine performs a premixed combustion operation, the intake air amount is reduced by the intake throttle valve and the EGR gas amount is increased by the EGR mechanism.

  If the opening of the exhaust throttle valve is throttled in such a state, it takes time until the exhaust pressure increases. Furthermore, since the amount of intake air is limited by the intake throttle valve, the exhaust pressure may not rise to a pressure suitable for regeneration of the exhaust purification device.

  On the other hand, a method of releasing the restriction of the intake air amount by the intake throttle valve and stopping the introduction of EGR gas can be considered. However, an increase in the intake air amount and a decrease in the EGR gas amount lead to pre-ignition of the fuel, so the fuel injection pattern is changed from the pattern for premixed combustion operation (fuel injection before compression top dead center) to that for diffusion combustion operation. It is preferable to switch to a pattern (fuel injection near the compression top dead center).

  Incidentally, the intake air amount and the EGR gas amount do not change immediately. For this reason, until the intake air amount increases to some extent, the flow rate of the exhaust gas increases due to the decrease in the opening of the exhaust throttle valve. If the reducing agent is supplied by the supplying means when the exhaust gas flow rate is high, the reducing agent may be discharged into the atmosphere without reacting with the exhaust purification device.

  On the other hand, if the supply of the reducing agent is prohibited by the supplying means from the time when the opening of the exhaust throttle valve is decreased until the predetermined period elapses, the flow rate of the exhaust gas decreases during the predetermined period and the exhaust pressure To rise. For this reason, the effect of supplying the reducing agent can be easily obtained, and the amount of the reducing agent that passes through the exhaust purification device can be reduced. As a result, waste of the reducing agent is suppressed and the exhaust purification device is efficiently regenerated.

  In the exhaust gas purification system for an internal combustion engine according to the present invention, the generated torque of the internal combustion engine is a required torque in a predetermined period from the time when the opening of the exhaust throttle valve is reduced to the time when the supply of the reducing agent by the supply means is started. An adjusting means for adjusting the fuel injection timing so as to approximate to may be further provided.

  If the opening of the exhaust throttle valve is reduced when the operating state of the internal combustion engine shifts from the premixed combustion operation state to the diffusion combustion operation state, the torque of the internal combustion engine decreases due to an increase in pumping loss. On the other hand, a method of compensating for a decrease in torque by increasing the fuel injection amount can be considered.

  However, when the decrease in torque is compensated by the increase correction of the fuel injection amount, there is a concern that the fuel consumption will increase. On the other hand, when the decrease in torque is reduced by adjusting the fuel injection timing, the increase in the fuel injection amount can be suppressed to a small amount.

  The exhaust gas purification system for an internal combustion engine according to the present invention may further include a retarding means for retarding the fuel injection timing to a predetermined time in the predetermined period. The “predetermined timing” here may be the latest fuel injection timing in the range of the fuel injection timing at which misfire can be suppressed.

  If the supply of the reducing agent is prohibited during the above-mentioned predetermined period, the reducing agent that passes through the exhaust purification device decreases, but the exhaust purification device is heated to a temperature range suitable for regeneration (hereinafter referred to as “regeneration temperature region”). There is a possibility that time to do becomes long.

On the other hand, when the fuel injection timing during the predetermined period is delayed to the predetermined time, the exhaust temperature during the predetermined period increases. For this reason, the exhaust gas purification device receives the heat of the exhaust gas and raises the temperature during a predetermined period.
As a result, it is possible to reduce the amount and time of the reducing agent required for raising the temperature of the exhaust purification device to the regeneration temperature range after a predetermined period.

  The exhaust gas purification system for an internal combustion engine according to the present invention may further include an accelerating means for promoting homogeneous mixing of fuel and gas in the cylinder during at least a part of the predetermined period.

  When the operating state of the internal combustion engine transitions from the premixed combustion operation state to the diffusion combustion operation state, if the intake air amount increases and the EGR gas decreases, the ignition / ignition before the fuel in the cylinder premixes with the intake air. It starts to burn. If the fuel in the cylinder is ignited and burned before premixing with the intake air and the gas, the amount of NOx generated may increase.

  On the other hand, when the homogeneous mixing of fuel and gas is promoted by the promoting means, the fuel in the cylinder is ignited and burned after premixed with the gas. That is, in the process in which the operation state of the internal combustion engine shifts from the premixed combustion operation state to the diffusion combustion operation state, the period during which the internal combustion engine performs the premixed combustion operation can be lengthened. As a result, an increase in the amount of NOx generated can be reduced.

  Specific methods for promoting homogeneous mixing of fuel and gas include a method of generating an air flow such as a swirl flow or a tumble flow in the cylinder by reducing the opening of the air flow control valve, and a fuel injection pressure of the fuel injection valve. A method for increasing the fuel atomization by raising the temperature can be exemplified.

Another method for extending the period during which the internal combustion engine performs the premixed combustion operation in the process in which the operation state of the internal combustion engine shifts from the premixed combustion operation state to the diffusion combustion operation state is included in EGR gas per unit amount. A method of increasing the amount of burnt gas component is also conceivable. The burned gas component referred to here is carbon dioxide (CO ₂ ), water (H ₂ O), or the like generated when the fuel burns in the cylinder or when the unburned fuel is oxidized by the exhaust purification device.

  In the process in which the operation state of the internal combustion engine shifts from the premixed combustion operation state to the diffusion combustion operation state, the amount of EGR gas introduced into the cylinder decreases with time. When the amount of EGR gas introduced into the cylinder is reduced, the fuel injected from the fuel injection valve (hereinafter referred to as “injected fuel”) is easily ignited and burned before forming the premixed gas.

  In contrast, when the amount of burned gas component contained in the EGR gas per unit amount increases, the amount of burned gas component introduced into the cylinder decreases even if the amount of EGR gas introduced into the cylinder decreases. Can be reduced. Therefore, in the process in which the operation state of the internal combustion engine shifts from the premixed combustion operation state to the diffusion combustion operation state, the period during which the internal combustion engine performs the premixed combustion operation can be lengthened. As a result, an increase in the amount of NOx generated can be reduced.

  As a method of increasing the amount of burned gas component contained in the EGR gas per unit amount, a method of performing after injection from a fuel injection valve of a cylinder in an expansion stroke or an exhaust stroke can be exemplified.

  The exhaust gas purification system for an internal combustion engine according to the present invention may further include prediction means for predicting in advance the necessity of regeneration of the exhaust gas purification device when the internal combustion engine is in a premixed combustion operation.

In this case, the regeneration means approximates the opening degree of each of the intake throttle valve, the EGR valve, and the exhaust throttle valve to an opening degree suitable for the regeneration process when the prediction means makes a prior prediction. Also good. That is, the regeneration means may increase the opening of the intake throttle valve, decrease the opening of the EGR valve, and decrease the opening of the exhaust throttle valve when the prediction is performed in advance.

  When the opening degree of the intake throttle valve is increased and the opening degree of the EGR valve is decreased while the internal combustion engine is in the premixed combustion operation, the intake air amount and the EGR gas amount are reduced from the amounts suitable for the premixed combustion operation. There is a risk of departure.

  However, when the opening of the exhaust throttle valve is decreased, the differential pressure between the upstream end and the downstream end of the EGR passage increases. When the differential pressure between the upstream end and the downstream end of the EGR passage increases, the amount of EGR gas flowing through the EGR passage increases.

  Therefore, if the opening of the exhaust throttle valve is reduced instead of increasing the opening of the intake throttle valve, the amount of EGR gas introduced into the cylinder is prevented from being reduced, and the air introduced into the cylinder is reduced. Increase in volume is prevented.

  Furthermore, when the opening of the exhaust throttle valve is set so that the differential pressure becomes larger than before the opening of the intake throttle valve is increased, the amount of air introduced into the cylinder and the amount of EGR gas are reduced. The opening degree of the EGR valve can also be reduced without changing it.

  If such processing is performed before the regeneration request of the exhaust purification device is generated, when the regeneration request is generated, the opening of each of the intake throttle valve, the EGR valve, and the exhaust throttle valve is briefly set to an opening suitable for the regeneration processing. Can be changed.

  Therefore, the supply means can be operated at an early time after the generation of the regeneration request. As a result, the execution time of the reproduction process can be shortened.

  When the internal combustion engine is provided with a variable valve mechanism, the regeneration means performs regeneration processing on the respective opening amounts of the intake throttle valve, the EGR valve, and the exhaust throttle valve at the time when the prediction means makes a prior prediction. While changing to an appropriate opening degree, the internal EGR may be increased using a variable valve mechanism. At that time, it is preferable that the regenerating means controls the variable valve mechanism so that the EGR rate equivalent to the EGR rate before the prediction by the predicting means can be maintained.

  If such a process is performed before the regeneration request of the exhaust purification device is generated, the opening of each of the intake throttle valve, the EGR valve, and the exhaust throttle valve is changed to an opening suitable for the regeneration process when the regeneration request occurs. Since there is no need, the supply means can be activated immediately when a regeneration request occurs.

  In the present invention, the predetermined period may be a period from the time when the opening of the exhaust throttle valve is decreased to the time when the exhaust pressure upstream of the exhaust throttle valve reaches the target pressure. When the predetermined period is determined in this way, the flow rate of the exhaust gas when the supply unit operates is sufficiently low, so that the amount of reducing agent that passes through the exhaust gas purification device is extremely small.

  In the present invention, the predetermined period may be a period from the time when the opening of the exhaust throttle valve is reduced to the time when the exhaust temperature upstream of the exhaust throttle valve reaches the target temperature.

  In this case, only when the exhaust purification device regeneration request is generated, only the opening of the exhaust throttle valve is reduced. When the exhaust temperature reaches the target temperature or more, the transition from the premixed combustion operation to the diffusion combustion operation (intake air) Preferably, the throttle valve opening is increased, the EGR valve opening is decreased, and the fuel injection pattern is switched.

According to such a method, the internal combustion engine can be premixed combustion operation from the time when the regeneration request is generated until the exhaust temperature becomes equal to or higher than the target temperature, and the exhaust temperature and the exhaust pressure are increased to some extent during that time. be able to. For this reason, even if the supply means is operated after the lapse of a predetermined period, there is very little reducing agent that passes through the exhaust purification device.

  Therefore, it is possible to lengthen the period during which the internal combustion engine performs the premixed combustion operation during the regeneration process execution period without prolonging the regeneration process execution period.

  According to the present invention, in an exhaust gas purification system for an internal combustion engine that attempts to regenerate the exhaust gas purification device by supplying a reducing agent to the exhaust gas purification device while reducing the opening of the exhaust throttle valve, during the premixed combustion operation of the internal combustion engine The exhaust purification device can be efficiently regenerated.

  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 exhaust gas purification system for an internal combustion engine according to the present invention.

  The exhaust gas purification system for an internal combustion engine shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) having a plurality of cylinders.

  A fuel injection valve 3 capable of directly injecting fuel into each cylinder 2 is attached to each cylinder 2 of the internal combustion engine 1. The fuel injection valve 3 directly injects the fuel boosted in the common rail 30 into the cylinder 2.

  An intake passage 4 communicates with each cylinder 2. A compressor housing 50 and an intercooler 6 of the turbocharger 5 are disposed in the intake passage 4. The intake air supercharged by the compressor housing 50 is cooled by the intercooler 6 and then introduced 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.

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

  The exhaust purification device 8 includes a NOx storage reduction catalyst having oxidation ability and NOx storage ability, a particulate filter having oxidation ability and PM collection ability, or a particulate having oxidation ability, NOx storage ability and PM collection ability. A curative filter (DPNR) etc. can be illustrated.

  The internal combustion engine 1 includes a low pressure EGR mechanism and a high pressure EGR mechanism. The high pressure EGR mechanism is a high pressure EGR passage 9 that guides part of the exhaust gas from the exhaust passage 7 upstream from the turbine housing 51 to the intake passage 4 downstream from the intercooler 6, and the high pressure EGR that changes the cross-sectional area of the high pressure EGR passage 9. A high-pressure EGR cooler 11 that cools the exhaust gas flowing through the valve 10 and the high-pressure EGR passage 9 (hereinafter referred to as “high-pressure EGR gas”) is provided.

  The amount of the high-pressure EGR gas recirculated by the high-pressure EGR mechanism is the opening degree of the second intake throttle valve 12 disposed at a site downstream of the intercooler 6 of the intake passage 4 and upstream of the connection portion of the high-pressure EGR passage 9; And / or metering by the opening degree of the high pressure EGR valve 10.

  The low-pressure EGR mechanism changes the flow cross-sectional area of the low-pressure EGR passage 13 and the low-pressure EGR passage 13 that lead part of the exhaust from the exhaust passage 7 downstream from the exhaust purification device 8 to the intake passage upstream from the compressor housing 50. A low-pressure EGR cooler 15 that cools the exhaust gas (low-pressure EGR gas) flowing through the valve 14 and the low-pressure EGR passage 13 is provided.

  The amount of low-pressure EGR gas recirculated by the low-pressure EGR mechanism depends on the opening of the first intake throttle valve 16 disposed in the intake passage 4 upstream of the connection portion of the low-pressure EGR passage 13 and / or the low-pressure EGR valve 14. It is metered by the opening.

  An exhaust throttle valve 17 is disposed in the exhaust passage 7 upstream of the connection portion of the low pressure EGR passage 13 and downstream of the exhaust purification device 8. Further, the internal combustion engine 1 is provided with a fuel addition valve 18 that injects fuel as a reducing agent into the exhaust manifold 70. The fuel addition valve 18 is an embodiment of the supply means according to the present invention.

  The fuel injection valve 3, the high pressure EGR valve 10, the second intake throttle valve 12, the low pressure EGR valve 14, the first intake throttle valve 16, the exhaust throttle valve 17 and the fuel addition valve 18 are electrically connected to the ECU 18. ing. The ECU 18 is an electronic control unit that includes a CPU, a ROM, a RAM, a backup RAM, and the like.

  The ECU 19 is electrically connected to various sensors such as an air flow meter 20, a water temperature sensor 21, a crank position sensor 22, an exhaust temperature sensor 23, an exhaust pressure sensor 24, and an accelerator position sensor 25.

  The air flow meter 20 is a sensor that measures the amount of air flowing into the intake passage 4 from the atmosphere. The water temperature sensor 21 is a sensor that measures the temperature of cooling water circulating in the internal combustion engine 1. The crank position sensor 22 is a sensor that detects the rotational position of the crankshaft of the internal combustion engine 1. The exhaust gas temperature sensor 23 is a sensor that measures the temperature of the exhaust gas flowing out from the exhaust gas purification device 8. The exhaust pressure sensor 24 is a sensor that measures the exhaust pressure upstream of the exhaust throttle valve 17. The accelerator position sensor 25 is a sensor that measures an operation amount (accelerator opening) of an accelerator pedal.

  The ECU 17 determines the fuel injection valve 3, the high pressure EGR valve 10, the second intake throttle valve 12, the low pressure EGR valve 14, the first intake throttle valve 16, the exhaust throttle valve 17, and the fuel addition based on the measured values of the various sensors described above. The valve 18 is controlled.

  For example, the ECU 13 causes the internal combustion engine 1 to perform a premixed combustion operation when the operating condition determined from the load (accelerator opening) Accp and the engine speed Ne of the internal combustion engine 1 is in the premixed combustion operation region shown in FIG. On the other hand, when the operating condition 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 to the 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 a premixed gas. Therefore, when the internal combustion engine 1 is premixed combustion operation,
It is necessary to reduce the oxygen concentration in the cylinder 2 by introducing a larger amount of EGR gas into the cylinder 2 than in the diffusion combustion operation.

  On the other hand, the ECU 19 reduces the opening degree of the first intake throttle valve 16 or the second intake throttle valve 12 from that during the diffusion combustion operation, and reduces the opening degree of the high pressure EGR valve 10 or the low pressure EGR valve 14 during the diffusion combustion operation. Increase more. In this case, the amount of air (oxygen amount) introduced into the cylinder 2 decreases from the time of diffusion combustion operation, and the amount of EGR gas introduced into the cylinder 2 increases from the time of diffusion combustion operation. As a result, the internal combustion engine 1 can perform a premixed combustion operation without premature ignition.

  By the way, in order for the exhaust purification device 8 to exhibit an appropriate purification capability, an appropriate regeneration process is required for the exhaust purification device 8.

  For example, in the case where the exhaust purification device 8 has a PM collecting ability, if the PM collection amount of the exhaust purification device 8 becomes excessive, the pressure loss increases and causes problems such as a back pressure increase. Therefore, when the amount of PM collected by the exhaust purification device 8 increases, it is necessary to perform a PM regeneration process for oxidizing and removing the PM collected by the exhaust purification device 8.

  The PM collected in the exhaust purification device 8 is oxidized when exposed to a high temperature and lean atmosphere of about 500 ° C. or higher. Therefore, as a method for executing the PM regeneration processing, a method of raising the temperature of the exhaust purification device 8 to about 500 ° C. or more and making the air-fuel ratio of the exhaust flowing into the exhaust purification device 8 lean is preferable.

  Further, in the case where the exhaust purification device 8 has a NOx storage capability, the NOx storage capability decreases as the amount of SOx stored in the exhaust purification device 8 increases. Therefore, when the NOx occlusion amount of the exhaust purification device 8 increases, it is necessary to perform S regeneration processing for reducing and removing SOx occluded in the exhaust purification device 8.

  The SOx occluded in the exhaust purification device 8 is reduced and removed when exposed to an atmosphere having a high temperature of approximately 600 ° C. or higher and a theoretical air-fuel ratio or lower. Therefore, as a method for executing the S regeneration process, a method of raising the temperature of the exhaust purification device 8 to about 600 ° C. or more and setting the air-fuel ratio of the exhaust flowing into the exhaust purification device 8 to be equal to or lower than the stoichiometric air-fuel ratio is preferable.

  When the regeneration process accompanied by the temperature rise of the exhaust purification device 8 is performed as in the above-described PM regeneration process or S regeneration process, the opening degree of the exhaust throttle valve 17 is decreased and the fuel addition valve 18 to the exhaust purification device 8 is reduced. A method of supplying fuel is preferred.

  This is because when the opening degree of the exhaust throttle valve 17 is decreased, the temperature of the exhaust purification device 8 can be increased by increasing the exhaust pressure, and the fuel reaction rate in the exhaust purification device 8 is increased by lowering the fuel flow rate. Because.

  However, since the amount of intake air is small during the premixed combustion operation of the internal combustion engine 1, the exhaust pressure does not rise quickly even if the opening of the exhaust throttle valve is reduced, and the exhaust pressure is used for regeneration of the exhaust purification device 8. May not increase to a suitable pressure.

  On the other hand, when it is necessary to perform the PM regeneration process or the S regeneration process during the premixed combustion operation of the internal combustion engine 1, the first intake throttle valve 16 and the second intake throttle valve 12 (hereinafter collectively referred to as “intake throttle valve”). Is fully opened, and the high pressure EGR valve 10 and the low pressure EGR valve 14 (hereinafter collectively referred to as “EGR valve”) are fully closed to perform the regeneration process.

  When the intake air amount is increased and the EGR gas amount is decreased by the above-described method, the oxygen concentration in the cylinder 2 increases, so that the fuel may be ignited (premature ignition) before premixing with the intake air. There is. Therefore, the fuel injection pattern is preferably switched from the pattern for premixed combustion operation (fuel injection before compression top dead center) to the pattern for diffusion combustion operation (fuel injection near compression top dead center).

  In addition, it takes time until the change in the opening of the intake throttle valve or EGR valve is reflected in the actual intake air amount or EGR gas amount. For this reason, until the intake air amount increases to some extent, the flow rate of the exhaust gas increases as the opening degree of the exhaust throttle valve 17 decreases. When fuel is supplied from the fuel addition valve 18 to the exhaust purification device 8 when the exhaust gas flow rate is high, the fuel supplied from the fuel addition valve 18 (hereinafter referred to as “supplied fuel”) reacts in the exhaust purification device 8. It becomes difficult. As a result, the exhaust emission of the internal combustion engine 1 may be deteriorated.

  Therefore, when it is necessary to regenerate the exhaust gas purification device 8 during the premixed combustion operation of the internal combustion engine 1, the ECU 19 increases the exhaust pressure (measured value of the exhaust pressure sensor 24) from the time when the opening of the exhaust throttle valve 17 is decreased. During the period (predetermined period) until the target pressure is reached, the operation of the fuel addition valve 18 is prohibited.

  Specifically, as shown in FIG. 5, when the exhaust purification device 8 needs to be regenerated during the premix combustion operation of the internal combustion engine 1, the ECU 19 first diffuses the operation state of the internal combustion engine 1 from the premix combustion operation state. Transition to the combustion operation state. That is, the ECU 19 fully opens the intake throttle valve, fully closes the EGR valve, and shifts the fuel injection pattern from the premixed combustion operation pattern to the diffusion combustion operation pattern. Further, the ECU 19 reduces the opening of the exhaust throttle valve 17 simultaneously with the start of the transition of the operation state described above.

  Thereafter, the ECU 19 monitors the measured value (exhaust pressure) of the exhaust pressure sensor 24, and starts supplying fuel from the fuel addition valve 18 to the exhaust purification device 8 when the exhaust pressure reaches the target pressure. When the internal combustion engine 1 does not include the exhaust pressure sensor 24, the ECU 19 may estimate the exhaust pressure from the intake air amount (measured value of the air flow meter 20).

  According to such a method, since fuel supply from the fuel addition valve 18 is not performed until the exhaust pressure reaches the target pressure, the fuel that passes through the exhaust purification device 8 can be reduced. As a result, the reaction rate of the supplied fuel in the exhaust purification device 8 increases, and the regeneration efficiency of the exhaust purification device 8 increases.

  The target pressure described above may be set to be equal to a pressure suitable for regeneration of the exhaust purification device 8, but since the operation start timing of the fuel addition valve 18 may be delayed, the supply fuel may slip through. It may be set to be equal to the lower limit value of no pressure.

  Hereinafter, the execution procedure of the regeneration process during the premixed combustion operation of the internal combustion engine 1 will be described with reference to FIG. FIG. 6 is a flowchart showing a reproduction processing routine in the present embodiment. This regeneration process routine is a routine stored in advance in the ROM of the ECU 19 and is periodically executed by the ECU 19.

  In the regeneration process routine, the ECU 19 first determines in S101 whether or not a regeneration execution condition is satisfied. The regeneration execution condition is, for example, a condition such that the PM collection amount of the exhaust purification device 8 is equal to or greater than a predetermined upper limit amount, or the SOx occlusion amount of the exhaust purification device 8 is equal to or greater than a predetermined upper limit amount. It can be illustrated.

If a negative determination is made in S101, the ECU 19 once ends this routine. On the other hand, if a positive determination is made in S101, the ECU 19 proceeds to S102.

  In S102, the ECU 19 determines whether or not the internal combustion engine 1 is in a premixed combustion operation. For example, the ECU 19 determines whether or not the operating condition determined from the measured value of the accelerator position sensor 25 (accelerator opening degree Accp) and the engine speed Ne belongs to the above-described premixed combustion operation region of FIG.

  When a negative determination is made in S102, it is not necessary to switch the operating state of the internal combustion engine 1. Therefore, in S108, the ECU 19 fully opens the intake throttle valve, fully closes the EGR valve, and further operates the exhaust throttle valve 17 (decreases the opening of the exhaust throttle valve 17). Then, the ECU 19 immediately operates the fuel addition valve 18.

  Further, when an affirmative determination is made in S102, it is necessary to switch the operating state of the internal combustion engine 1. For this reason, in S103, the ECU 19 starts the transition process for shifting the operation state of the internal combustion engine 1 from the premixed combustion operation state to the diffusion combustion operation state, and operates the exhaust throttle valve 17.

  In the above transition processing, the ECU 19 fully opens the intake throttle valve, fully closes the EGR valve, and further switches the fuel injection pattern from the pattern for the premixed combustion operation to the pattern for the diffusion combustion operation.

  In the transition process described above, the amount of air and the amount of EGR gas introduced into the cylinder 2 do not change at a time from the amount suitable for the premixed combustion operation to the amount suitable for the diffusion combustion operation. For this reason, if the fuel injection pattern is switched from the premixed combustion operation pattern to the diffusion combustion operation pattern at a time, there is a possibility of increasing combustion noise due to fluctuations in the ignition timing.

  Therefore, it is preferable that the fuel injection pattern is gradually changed according to changes in the amount of air introduced into the cylinder 2 and the amount of EGR gas. Therefore, the ECU 19 may gradually retard the main injection timing and gradually increase the pilot fuel injection amount in accordance with an increase in the air amount introduced into the cylinder 2 and a decrease in the EGR gas amount. When the fuel injection pattern is gradually changed in this way, fluctuations in the ignition timing are suppressed, so that an increase in combustion noise is suppressed.

  Here, returning to the regeneration processing routine of FIG. 6, the ECU 19 determines whether or not the exhaust pressure upstream of the exhaust throttle valve 17 (measured value of the exhaust pressure sensor 24) has reached the target pressure in S104.

  If a negative determination is made in S104, the ECU 19 returns to S103. On the other hand, if an affirmative determination is made in S104, the ECU 19 proceeds to S105.

  In S105, the ECU 19 operates the fuel addition valve 18 (starts fuel supply from the fuel addition valve 18 to the exhaust purification device 8). At that time, since the flow rate of the exhaust gas passing through the exhaust gas purification device 8 is sufficiently low, the amount of fuel supplied through the exhaust gas purification device 8 is extremely small. Furthermore, since the temperature of the exhaust gas purification device 8 is also increased due to the increase in the exhaust pressure, the supplied fuel is likely to react (oxidize) in the exhaust gas purification device 8.

  Accordingly, substantially all of the fuel supplied from the fuel addition valve 18 is reacted (oxidized) in the exhaust purification device 8. As a result, the exhaust emission control device 8 can be heated to a temperature range suitable for regeneration with a minimum amount of fuel. Further, an increase in exhaust emission due to the supply fuel passing through the exhaust purification device 8 is also suppressed.

  In S106, the ECU 19 determines whether or not a regeneration end condition is satisfied. The regeneration end condition can be exemplified by a condition such that the PM trapping amount of the exhaust purification device 8 is zero, and the SOx occlusion amount of the exhaust purification device 8 is zero.

  If a negative determination is made in S106, the ECU 19 executes the process of S106 again. On the other hand, when an affirmative determination is made in S106, the ECU 19 proceeds to S107.

  In S107, the ECU 19 ends the regeneration process of the exhaust purification device 8. That is, the ECU 19 stops the fuel supply from the fuel addition valve 18 and fully opens the exhaust throttle valve 17. Further, the ECU 19 changes the operation state of the internal combustion engine 1 from the diffusion combustion operation state to the premix combustion operation state if the current operation conditions (accelerator opening degree Accp and engine speed Ne) belong to the premix combustion operation region. Transition.

  As described above, when the ECU 19 executes the regeneration processing routine of FIG. 6, the regeneration means and the prohibition means according to the present invention are realized. Therefore, the exhaust purification device 8 can be efficiently regenerated when the internal combustion engine 1 is in the premixed combustion operation state.

<Example 2>
Next, a second embodiment of the present invention will be described. 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 fuel injection pattern is gradually changed so as to suppress fluctuations in the ignition timing during a predetermined period from when the opening of the exhaust throttle valve 17 is reduced until the fuel addition valve 18 starts to operate. Although an example has been described, in this embodiment, an example will be described in which a decrease in torque due to a decrease in the opening of the exhaust throttle valve 17 is compensated by adjusting the fuel injection timing.

  When the opening degree of the exhaust throttle valve 17 is decreased in order to regenerate the exhaust purification device 8, the pumping loss increases due to the increase in the back pressure. When the pumping loss increases, the torque of the internal combustion engine 1 decreases. On the other hand, a method for suppressing a decrease in torque of the internal combustion engine 1 by correcting the fuel injection amount to be increased can be considered, but the fuel consumption may increase.

  Therefore, in the regeneration process of the present embodiment, the ECU 19 adjusts the fuel injection timing for a predetermined period so that the decrease in torque is minimized (in other words, the torque is maximized). In this way, the adjusting means according to the present invention is realized by the ECU 19 adjusting the fuel injection timing in a predetermined period.

  Note that the fuel injection timing at which the torque of the internal combustion engine 1 becomes highest varies depending on the amount of air introduced into the cylinder 2, the amount of EGR gas, and the like, and therefore it is preferable to experimentally obtain the relationship therebetween. is there.

  In addition, when the decrease in torque cannot be compensated for by adjusting the fuel injection timing, the ECU 19 may compensate for the shortage of torque by increasing the fuel injection amount.

  According to such an embodiment, although there is a possibility that the ignition timing may fluctuate, it is possible to suppress a decrease in torque of the internal combustion engine 1 while suppressing a large increase in the fuel injection amount. As a result, an increase in fuel consumption accompanying the execution of the regeneration process can be minimized.

<Example 3>
Next, a third embodiment of the present invention will be described. 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 fuel injection pattern is gradually changed so as to suppress fluctuations in the ignition timing during a predetermined period from when the opening of the exhaust throttle valve 17 is reduced until the fuel addition valve 18 starts to operate. Although an example has been described, in this embodiment, an example in which the fuel injection timing is determined so that the exhaust temperature becomes high will be described.

  If the operation of the fuel addition valve 18 is prohibited until the predetermined period elapses after the opening of the exhaust throttle valve 17 is reduced, there is a possibility that the execution period of the regeneration process becomes longer.

  Therefore, the ECU 19 retards the fuel injection timing to a predetermined time in a predetermined period. The predetermined timing may be the latest fuel injection timing in the range of fuel injection timing that can suppress misfire. Thus, the ECU 19 delays the fuel injection timing in a predetermined period, thereby realizing the retard means according to the present invention.

  The range of the fuel injection timing at which misfire can be suppressed varies depending on the amount of air introduced into the cylinder 2, the amount of EGR gas, and the like, so the amount of air introduced into the cylinder 2, the amount of EGR gas, etc. It is preferable to change according to. The relationship between the predetermined time, the air amount, and the EGR gas amount may be obtained experimentally in advance.

  According to such an embodiment, the exhaust temperature during the predetermined period increases. For this reason, the exhaust gas purification device 8 receives the heat of the exhaust gas during a predetermined period and raises the temperature. As a result, the exhaust purification device 8 rises to a relatively high temperature by the end of the predetermined period (in other words, at the start of operation of the fuel addition valve 18).

  When the temperature of the exhaust purification device 8 at the end of the predetermined period increases, the amount of fuel and time required for raising the temperature of the exhaust purification device 8 to the regeneration temperature range are reduced. Therefore, the regeneration process execution period is shortened, and an increase in fuel consumption due to the regeneration process is reduced.

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

In the present embodiment, the fuel injected from the fuel injection valve 3 (at least during a predetermined period from when the opening of the exhaust throttle valve 17 is reduced to when the fuel addition valve 18 starts to operate) (
Hereinafter, an example of promoting mixing of the intake air and the “injected fuel” will be described.

  When the amount of air introduced into the cylinder 2 increases and the amount of EGR gas decreases during a predetermined period, the period from when the fuel injection valve 3 injects fuel until the injected fuel ignites and burns (premixing period) Becomes shorter. When the premixing period is shortened, the injected fuel is ignited and burned before forming the intake air and the premixed gas. In such a case, the amount of NOx generated may increase.

  On the other hand, in the regeneration process of the present embodiment, the ECU 19 executes a process for promoting the mixing of the injected fuel and the intake air (hereinafter referred to as “premixing promotion process”) during a predetermined period.

  When mixing of the injected fuel and the intake air is promoted, the injected fuel and the intake air form a premixed gas in a short time. Therefore, even if the premixing period is shortened, the injected fuel is premixed and combusted. As a result, an increase in the amount of NOx generated due to the execution of the regeneration process can be reduced.

  Hereinafter, the execution method of the premixing promotion process will be described.

  FIG. 7 is a view showing a configuration in the vicinity of the connection portion between the internal combustion engine 1 and the intake passage 4. In FIG. 7, the intake passage 4 is branched into four branch pipes downstream from the connection portion of the high pressure EGR passage 9, and each branch pipe is further branched into two branch pipes. Two branch pipes are connected to the combustion chamber of each cylinder 2. An airflow control valve 26 is provided on one of the two branch pipes. When the air flow control valve 26 is closed, a swirl flow is generated when the intake air flows into the cylinder 2. The airflow control valve 26 is electrically controlled by the ECU 19.

  The ECU 19 closes the airflow control valve 26 for a predetermined period. At that time, the ECU 19 may close the air flow control valve 26 during the entire predetermined period. However, as shown in FIG. 8, the amount of EGR gas introduced into the cylinder 2 during the predetermined period is a predetermined amount. The airflow control valve 26 may be closed only during the following period (or the oxygen concentration in the cylinder 2 is equal to or higher than a predetermined concentration). The aforementioned predetermined amount may be set to be equal to the minimum amount of EGR gas that the injected fuel can premix and burn (or the predetermined concentration is the highest concentration of oxygen that the injected fuel can premix and burn).

  When the premixing promotion process is executed in this way, the period during which the injected fuel is premixed and combusted in a predetermined period is expanded. As a result, an increase in the amount of NOx generated due to the execution of the regeneration process can be reduced.

  Next, the execution procedure of the reproduction process in the present embodiment will be described with reference to FIG. FIG. 9 is a flowchart showing a reproduction processing routine in the present embodiment. In FIG. 9, the same reference numerals are assigned to the same processes as those in the first embodiment described above.

  The ECU 19 proceeds to S201 after executing the process of S103. In S201, the ECU 19 determines whether or not the amount of EGR gas introduced into the cylinder 2 has decreased below a predetermined amount. The amount of EGR gas introduced into the cylinder 2 may be estimated based on the amount of intake air (measured value of the air flow meter 20).

  If a negative determination is made in S201, the ECU 19 repeatedly executes the process of S201. On the other hand, if an affirmative determination is made in S201, the ECU 19 proceeds to S202.

  In S202, the ECU 19 closes the airflow control valve 26. In this case, a swirl flow is generated in the cylinder 2 of the internal combustion engine 1. When a swirl flow is generated in the cylinder 2, the injected fuel and the intake air are quickly mixed. As a result, the injected fuel is premixed and burned even if the premixing period is shortened.

  In addition, when an affirmative determination is made in S104, the ECU 19 proceeds to S203. In S203, the ECU 19 starts the operation of the fuel addition valve 18 and opens the airflow control valve 26.

  Thus, when the ECU 19 executes the regeneration processing routine as shown in FIG. 9, the promotion means according to the present invention is realized. As a result, it is possible to obtain the same effect as that of the first embodiment described above, and to reduce the increase in the amount of NOx generated due to the execution of the regeneration process.

  In the present embodiment, an example in which a swirl flow is generated in the cylinder 2 has been described, but a tumble flow may be generated.

  In the present embodiment, the method of closing the airflow control valve 26 is taken as an example of a method for executing the premixing promotion process. However, a method of increasing the fuel injection pressure of the fuel injection valve 3 may be employed. When the fuel injection pressure of the fuel injection valve 3 is increased, atomization of the injected fuel is promoted. When atomization of the injected fuel is promoted, the premixing period can be prolonged by delaying the ignition timing, and homogeneous mixing of the injected fuel and the intake air can be promoted. As a result, it is possible to prolong the period during which the injected fuel is premixed and burned in the predetermined period.

<Example 5>
Next, a fifth embodiment of the present invention will be described. Here, a configuration different from the above-described fourth embodiment will be described, and the same configuration will be omitted.

  In the above-described fourth embodiment, the NOx generation amount is reduced by promoting the mixing of the injected fuel and the intake air in a predetermined period from when the opening of the exhaust throttle valve 17 is reduced until the fuel addition valve 18 starts operating. In the present embodiment, an example in which the increase in the amount of NOx generated is reduced by increasing the amount of burned gas components contained in the EGR gas per unit amount in a predetermined period will be described.

  When the amount of burned gas component contained in the EGR gas per unit amount increases, even if the amount of EGR gas introduced into the cylinder 2 decreases, the amount of burned gas component introduced into the cylinder 2 Reduction can be suppressed.

  When the decrease in the amount of burned gas component introduced into the cylinder 2 during the predetermined period is suppressed, the shortening of the premixing period is suppressed. For this reason, the injected fuel can be premixed and combusted. Further, when the decrease in the amount of burned gas component introduced into the cylinder 2 is suppressed, the increase in the combustion temperature can be suppressed. Therefore, an increase in the amount of NOx generated during the predetermined period is reduced as much as possible.

  In addition, as a method of increasing the burned gas component contained in the EGR gas per unit amount, a method of performing after injection from the fuel injection valve 3 of the cylinder 2 in the expansion stroke or the exhaust stroke can be exemplified.

  The fuel after-injected from the fuel injection valve 3 is oxidized by the combustion heat of the main-injected fuel or is oxidized in the exhaust purification device 8. As a result, the burnt gas component contained in the exhaust gas (EGR gas) per unit amount increases. Therefore, when the ECU 19 causes the fuel injection valve 3 to perform after injection, the increasing means according to the present invention is realized.

<Example 6>
Next, a sixth embodiment of the present invention will be described with reference to FIGS. 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, the example in which the regeneration process is started from the time when the regeneration request of the exhaust gas purification apparatus 8 is generated (the time when the regeneration process execution condition is satisfied) has been described. However, in the present embodiment, the exhaust gas purification apparatus 8 is started. An example in which the pre-processing of the reproduction process is started before the reproduction request is generated will be described.

  The ECU 19 starts the pre-processing of the regeneration process when the PM collection amount or the SOx occlusion amount of the exhaust purification device 8 approximates the upper limit amount. Specifically, when the difference between the PM trapping amount or the SOx occlusion amount of the exhaust purification device 8 and the upper limit amount becomes equal to or less than a predetermined amount (in other words, the grace period until the regeneration request is generated (time or running) Pre-processing is started when (distance) falls below a threshold value).

  As shown in FIG. 10, the pre-processing here refers to a process of reducing the opening of the exhaust throttle valve 17 to the first opening, a process of fully opening the intake throttle valve, and a second opening of the EGR valve. Processing to reduce the degree. The EGR valve in FIG. 10 indicates the high pressure EGR valve 10 and the low pressure EGR valve 14 is fully closed.

  If the opening degree of the intake throttle valve is increased and the opening degree of the high pressure EGR valve 10 is decreased before the regeneration request of the exhaust gas purification device 8 is generated, the amount of air introduced into the cylinder 2 and the amount of EGR gas are increased. There is concern about deviating from an amount suitable for premixed combustion operation.

  However, when the opening degree of the exhaust throttle valve 17 is decreased, the differential pressure between the upstream end and the downstream end of the high pressure EGR passage 9 increases. When the differential pressure between the upstream end and the downstream end of the high pressure EGR passage 9 increases, the amount of exhaust gas (EGR gas) flowing through the high pressure EGR passage 9 increases.

  Therefore, if the opening of the exhaust throttle valve 17 is reduced instead of fully opening the intake throttle valve, the amount of EGR gas introduced into the cylinder 2 is prevented from being reduced, and the amount of air introduced into the cylinder 2 is reduced. Is prevented from increasing. That is, if the opening degree of the exhaust throttle valve 17 is reduced instead of fully opening the intake throttle valve, fluctuations in the EGR rate can be prevented.

  Further, when the first opening is set so that the above-described differential pressure becomes larger than before the pre-processing, the amount of air and EGR gas introduced into the cylinder 2 even if the second opening is set small. Can be prevented.

  If such pre-processing is performed before the regeneration request is generated, it is not necessary to fully open the intake throttle valve when the regeneration request is generated (when the regeneration process is started). Furthermore, since the opening degree of the exhaust throttle valve 17 and the high pressure EGR valve 10 has already been reduced, the time during which these valve opening degrees operate to the opening degree suitable for the regeneration process is also shortened.

  Therefore, the fuel addition valve 18 can be operated early after the regeneration request is generated. As a result, in addition to the effect of the first embodiment described above, an effect that the execution time of the reproduction process can be significantly shortened can be obtained.

  By the way, when the pre-processing as described above is performed, there may be a case where the exhaust pressure has already increased to the target pressure or higher when the regeneration request is generated. In such a case, the fuel addition valve 18 may be operated immediately after the regeneration request is generated. However, if the fuel addition valve 18 operates before the high pressure EGR valve 10 is fully closed, the supplied fuel may flow to the intake passage 4 through the high pressure EGR passage 9. For this reason, it is better to refrain from operating the fuel addition valve 18 until the high pressure EGR valve 10 is fully closed.

  Hereinafter, the execution procedure of the preliminary process and the reproduction process in the present embodiment will be described with reference to FIG. FIG. 11 is a flowchart showing a processing routine including pre-processing and reproduction processing. In FIG. 11, the same reference numerals are assigned to the processes similar to the reproduction process routine of the first embodiment described above.

  In the processing routine of FIG. 11, the ECU 19 executes the processes of S301 to S303 before executing the process of S101.

  In step S301, the ECU 19 determines whether or not a preprocessing execution condition is satisfied. As an execution condition of the pretreatment, it can be exemplified that the difference between the PM collection amount or the SOx occlusion amount of the exhaust purification device 8 and the upper limit amount is a certain amount or less. Thus, when the ECU 19 executes the process of S301, the prediction means according to the present invention is realized.

  If a negative determination is made in S301, the ECU 19 once terminates execution of this routine. On the other hand, if an affirmative determination is made in S301, the ECU 19 proceeds to S302.

  In S302, the ECU 19 determines whether or not the internal combustion engine 1 is in a premixed combustion operation. If a negative determination is made in S302, the ECU 19 sequentially executes S306 and S108. That is, the ECU 19 executes the process of S108 when the regeneration execution condition is satisfied.

  If an affirmative determination is made in S302, the ECU 19 proceeds to S303. In S303, the ECU 19 starts execution of the preliminary process as described above.

  Subsequently, the ECU 19 proceeds to S101 and determines whether or not a regeneration execution condition is satisfied (in other words, whether or not a regeneration request has occurred). If a negative determination is made in S101, the ECU 19 repeatedly executes the process of S101. On the other hand, if an affirmative determination is made in S101, the ECU 19 proceeds to S304.

  In S304, the ECU 19 starts executing the regeneration process. Specifically, the ECU 19 fully closes the EGR valve and reduces the opening of the exhaust throttle valve 17 to an opening suitable for regeneration.

  At that time, since the opening degree of the EGR valve and the opening degree of the exhaust throttle valve 17 are reduced to some extent by the previous pre-processing, the opening degree of the EGR valve and the exhaust throttle valve 17 reaches the target opening degree in a short time.

  The fuel injection pattern switching may be performed simultaneously with the process of S304, or may be performed simultaneously with the process of S105 described later.

  When the ECU 19 finishes executing the process of S304, the ECU 19 proceeds to S104. If a positive determination is made in S104, the ECU 19 proceeds to S305.

  In S305, the ECU 19 determines whether or not the actual opening of the EGR valve is fully closed. If a negative determination is made in S305, the ECU 19 may return to S104, or the process of S305 may be repeatedly executed.

  If an affirmative determination is made in S305, the ECU 19 proceeds to S105 and operates the fuel addition valve 18.

  When the pre-processing and the reproduction process are performed according to the procedure as described above, the effect described in the first embodiment can be obtained, and the execution period of the reproduction process can be remarkably shortened. Obtainable.

  When the internal combustion engine 1 has a variable valve mechanism, the ECU 19 fully closes the EGR valve in the pre-processing and reduces the opening of the exhaust throttle valve 17 to an opening suitable for regeneration. Also good.

  In this case, the amount of EGR gas introduced into the cylinder 2 through the EGR passage becomes substantially zero, but the fluctuation (decrease) in the EGR rate is prevented by increasing the internal EGR using a variable valve mechanism. can do.

As a specific method for increasing the internal EGR, the valve overlap is increased by advancing the valve opening timing of the intake valve, or the valve E is left in the cylinder 2 by advancing the valve closing timing of the exhaust valve. A method for increasing the burned gas to be performed can be exemplified.

  When the variable valve mechanism is used in this way, the fuel addition valve 18 can be operated immediately when a regeneration request is generated, so that the regeneration process execution period can be further shortened.

<Example 7>
Next, a seventh embodiment of 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 operation of the fuel addition valve 18 is prohibited until the exhaust pressure reaches the target pressure after the opening degree of the exhaust throttle valve 17 is reduced has been described. An example in which the operation of the fuel addition valve 18 is prohibited until the exhaust temperature reaches the target temperature after the opening of the exhaust throttle valve 17 is reduced will be described.

  FIG. 12 is a timing chart showing the execution procedure of the reproduction process in this embodiment. In the regeneration process of the present embodiment, the ECU 19 reduces only the opening of the exhaust throttle valve 17 without changing the openings of the intake throttle valve and the EGR valve at the time when the regeneration request is generated. Further, the operation state of the internal combustion engine 1 maintains the premixed combustion operation.

  In this case, the exhaust temperature upstream of the exhaust throttle valve 17 increases due to a decrease in the opening of the exhaust throttle valve 17. When the exhaust temperature (measured value of the exhaust temperature sensor 23) reaches the target temperature, the ECU 19 fully opens the intake throttle valve, fully closes the EGR valve, and further diffuses the fuel injection pattern from the pattern for the premixed combustion operation. Switch to the driving pattern.

  The target temperature described above is the upper limit value of the exhaust temperature that can be achieved by the reaction heat when the unburned fuel component discharged from the internal combustion engine 1 is oxidized by the exhaust purification device 8 and the opening degree reduction of the exhaust throttle valve 17. The temperature is lower than the regeneration temperature range.

  Further, the exhaust pressure is sufficiently high when the exhaust temperature reaches the target temperature. For this reason, even if the operation of the fuel addition valve 18 is started when the exhaust gas temperature reaches the target temperature, the supplied fuel hardly passes through the exhaust gas purification device 8.

  However, since the EGR valve is opened when the exhaust gas temperature reaches the target temperature, the supplied fuel may flow to the intake passage 4 through the EGR passage. Therefore, it is preferable to refrain from starting the operation of the fuel addition valve 18 until the opening of the EGR valve is fully closed.

  When the regeneration process is executed by such a method, the internal combustion engine 1 can be premixed combustion operation from the time when the opening of the exhaust throttle valve 17 is reduced to the time when the exhaust temperature reaches the target temperature. An increase in the amount of NOx generated can be reduced.

  In the present embodiment, an example in which the opening degree of the exhaust throttle valve 17 is decreased when a regeneration request is generated has been described. However, as in the sixth embodiment described above, exhaust gas is pre-processed before a regeneration request is generated. The opening degree of the throttle valve 17 may be decreased.

  In this case, the fuel addition valve 18 can be operated early after the regeneration request is generated, and the amount of fuel and time required for raising the temperature of the exhaust purification device 8 to the regeneration temperature range are reduced. It becomes possible. As a result, an increase in fuel consumption due to the regeneration process can be reduced, and the execution period of the regeneration process can be shortened.

1 is a diagram showing a schematic configuration of an exhaust gas purification system for an internal combustion engine according to the present invention. It is a figure which shows the premixed combustion operation area | region and diffusion combustion operation area | region of an internal combustion engine. It is a figure which shows the fuel-injection pattern at the time of a premix combustion operation. It is a figure which shows the fuel-injection pattern at the time of a diffusion combustion driving | operation. 3 is a timing chart illustrating a method for executing reproduction processing according to the first exemplary embodiment. 3 is a flowchart illustrating a reproduction processing routine in Embodiment 1. FIG. 10 is a diagram illustrating a configuration in the vicinity of a connection portion between an internal combustion engine and an intake passage in a third embodiment. 12 is a timing chart illustrating a method for executing reproduction processing according to the third embodiment. 10 is a flowchart showing a reproduction processing routine in Embodiment 3. 16 is a timing chart illustrating a method for executing a reproduction process according to the sixth embodiment. 18 is a flowchart showing a reproduction processing routine in Embodiment 6. 18 is a timing chart illustrating a method for executing a reproduction process according to the seventh embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Fuel injection valve 4 ... Intake passage 5 ... Centrifugal supercharger (turbocharger)
7... Exhaust passage 8. Exhaust purification device 9... High pressure EGR passage 10... High pressure EGR valve 11... High pressure EGR cooler 12. Throttle valve 13 ... Low pressure EGR passage 14 ... Low pressure EGR valve 15 ... Low pressure EGR cooler 16 ... First intake throttle valve 17 ... Exhaust throttle valve 18 ... Fuel Addition valve 19 ... ECU
20 .... Air flow meter 23 ... Exhaust temperature sensor 24 ... Exhaust pressure sensor 26 ... Air flow control valve

Claims (9)

In an internal combustion engine exhaust purification system capable of premixed combustion operation,
An exhaust purification device disposed in an exhaust passage of the internal combustion engine;
An exhaust throttle valve disposed in an exhaust passage downstream of the exhaust purification device;
Supply means for supplying a reducing agent to the exhaust gas flowing into the exhaust gas purification device;
Regenerating means for regenerating the exhaust purification device by using a reduction in the opening of the exhaust throttle valve and supplying a reducing agent by the supplying means;
When regeneration of the exhaust purification device by the regeneration means becomes necessary during the premixed combustion operation of the internal combustion engine, the supply of the reducing agent by the supply means is prohibited for a predetermined period after the opening of the exhaust throttle valve is reduced. Prohibited means,
An exhaust gas purification system for an internal combustion engine, comprising:   2. The exhaust gas purification system for an internal combustion engine according to claim 1, further comprising adjusting means for adjusting a fuel injection timing so that a torque generated by the internal combustion engine approximates a required torque during the predetermined period.   2. The exhaust gas purification system for an internal combustion engine according to claim 1, further comprising retarding means for retarding the fuel injection timing to the predetermined timing in the predetermined period.   2. The exhaust gas purification of an internal combustion engine according to claim 1, further comprising an accelerating unit that promotes mixing of the fuel injected from the fuel injection valve and the gas in the cylinder during at least a part of the predetermined period. system.   2. The exhaust gas purification system for an internal combustion engine according to claim 1, further comprising increasing means for increasing the amount of burned gas components contained in the EGR gas during at least a part of the predetermined period. The intake throttle valve disposed in the intake passage of the internal combustion engine according to claim 1,
An EGR valve disposed in an EGR passage communicating the exhaust passage of the internal combustion engine and the intake passage;
Predicting means for predicting in advance that regeneration of the exhaust purification device by the regeneration means is required during premixed combustion operation of the internal combustion engine,
The regeneration means is configured to increase the opening degree of the intake throttle valve, decrease the opening degree of the EGR valve, and decrease the opening degree of the exhaust throttle valve when the prediction means makes a prior prediction. An exhaust purification system for an internal combustion engine. The intake throttle valve disposed in the intake passage of the internal combustion engine according to claim 1,
An EGR valve disposed in an EGR passage communicating the exhaust passage of the internal combustion engine and the intake passage;
Predicting means for predicting in advance that regeneration of the exhaust purification device by the regeneration means is required during premixed combustion operation of the internal combustion engine;
A variable valve mechanism for changing valve opening characteristics of the intake valve and / or the exhaust valve of the internal combustion engine,
The regeneration means is configured to increase the opening of the intake throttle valve, fully close the EGR valve, decrease the opening of the exhaust throttle valve, and reduce the opening of the variable throttle mechanism when the prediction is performed in advance. An exhaust purification system for an internal combustion engine characterized by increasing EGR. 8. The predetermined period according to claim 1, wherein the predetermined period is a period from a time when an opening degree of the exhaust throttle valve is reduced to a time when an exhaust pressure upstream of the exhaust throttle valve reaches a target pressure. An exhaust gas purification system for an internal combustion engine. 8. The predetermined period according to claim 1, wherein the predetermined period is a period from a time when an opening degree of the exhaust throttle valve is reduced to a time when an exhaust temperature upstream of the exhaust throttle valve reaches a target temperature. ,
An exhaust purification system for an internal combustion engine, further comprising control means for causing the internal combustion engine to perform a premix combustion operation during the predetermined period.

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