JP2014084763A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an amount of NOx emitted in atmosphere.SOLUTION: A control device of an internal combustion engine comprises a catalyst provided on an exhaust passage of the internal combustion engine to reduce NOx, and purification ratio detection means for estimating or detecting an NOx purification ratio of the catalyst. The control device comprises calculation means for calculating a target value of the amount of NOx emitted from the internal combustion engine on the basis of a tolerance of the amount of NOx flowing nearer a downstream side than the catalyst and the NOx purification ratio of the catalyst during a predetermined period, when the NOx purification ratio of the catalyst is changed from a value higher than a predetermined value to a value not more than the predetermined value.

Description

  The present invention relates to a control device for an internal combustion engine.

  The exhaust passage of the internal combustion engine includes a NO oxidation catalyst and a selective reduction type NOx catalyst (hereinafter also referred to as an SCR catalyst), and further includes a bypass passage that bypasses the NO oxidation catalyst to reduce the oxidation activity of the NO oxidation catalyst. A technique is known that adjusts the amount of gas flowing through the bypass passage so that the NOx purification rate in the SCR catalyst is equal to or higher than a predetermined level while being suppressed. (For example, refer to Patent Document 1).

  By the way, during the deceleration operation of the internal combustion engine 1 and the like, the temperature of the exhaust gas decreases, so the temperature of the SCR catalyst decreases. Thereby, there exists a possibility that a NOx purification rate may fall. In this case, it is desirable to quickly raise the temperature of the SCR catalyst. However, conventionally, even if the amount of gas flowing through the bypass passage is adjusted, it takes time for the temperature of the SCR catalyst to rise, so the NOx purification rate decreases and NOx may be released into the atmosphere. was there.

JP 2007-154819 A JP 11-324661 A JP 2002-332825 A

  The present invention has been made in view of the above-described problems, and an object thereof is to reduce the amount of NOx released into the atmosphere.

In order to achieve the above object, a control apparatus for an internal combustion engine according to the present invention provides:
A catalyst provided in the exhaust passage of the internal combustion engine for reducing NOx;
A purification rate detecting means for estimating or detecting a NOx purification rate in the catalyst;
In a control device for an internal combustion engine comprising:
When the NOx purification rate in the catalyst changes from a state higher than a predetermined value to a state equal to or lower than a predetermined value, an allowable value of the amount of NOx flowing out downstream from the catalyst in a predetermined period, and the NOx in the catalyst And a calculation means for calculating a target value of the NOx amount discharged from the internal combustion engine based on the purification rate.

The predetermined value here is a value that is larger than the lower limit value of the allowable range of the NOx purification rate, and the NOx purification rate at which the NOx purification rate may be lower than the allowable range, or the NOx purification rate is lower than the allowable range. Is the NOx purification rate that is predicted to be low. The predetermined value is the NOx purification rate when the temperature of the catalyst is higher than the activation temperature, and the NOx purification rate at which the catalyst temperature may be lower than the lower limit value of the activation temperature, or the temperature of the catalyst is The NOx purification rate predicted to be lower than the lower limit value of the activation temperature may be used. That is, when the NOx purification rate in the catalyst changes from a state higher than the predetermined value to a state equal to or lower than the predetermined value, the NOx purification rate is still high and the NOx can be purified. And when a NOx purification rate becomes below a predetermined value, a NOx purification rate can be made higher than a predetermined value by raising the temperature of a catalyst. At this time, by allowing an increase in the amount of NOx discharged from the internal combustion engine,
Higher temperature gas can be discharged from the internal combustion engine.

  However, if the amount of NOx discharged from the internal combustion engine is increased too much, the amount of NOx released into the atmosphere may increase. On the other hand, when the NOx purification rate is just below the predetermined value, NOx can still be purified, so even if the amount of NOx discharged from the internal combustion engine increases, the catalyst purifies NOx. Can do. Based on the allowable value of the NOx amount flowing out downstream of the catalyst in the predetermined period and the NOx purification rate in the catalyst, the NOx amount flowing out downstream of the catalyst in the predetermined period becomes an allowable value. In addition, the amount of NOx discharged from the internal combustion engine can be calculated. If the NOx amount discharged from the internal combustion engine is set as a target value, and the NOx amount actually discharged from the internal combustion engine is adjusted to be equal to or less than the target value, the NOx amount flowing out downstream from the catalyst in a predetermined period is an allowable value. Can fit in. Note that the predetermined period and the allowable value can be determined according to a regulation value, a regulation, or the like. In this way, the amount of NOx released into the atmosphere can be reduced.

  In the present invention, when the NOx purification rate in the catalyst changes from a state higher than a predetermined value to a state not higher than a predetermined value, the amount of NOx discharged from the internal combustion engine is not higher than the target value, and the A temperature raising means for raising the temperature of the exhaust gas of the internal combustion engine can be provided.

  Here, when increasing the temperature of the exhaust gas from the internal combustion engine, the temperature of the exhaust gas from the internal combustion engine can be increased more quickly by increasing the amount of NOx discharged from the internal combustion engine. Therefore, since the temperature of the catalyst can be quickly raised, the amount of NOx released into the atmosphere can be reduced.

  In the present invention, the temperature raising means reduces the amount of EGR gas and retards the fuel injection timing into the cylinder of the internal combustion engine or fuel injection into the cylinder of the internal combustion engine, The temperature of the exhaust gas can be raised by at least one of after-injection performed later.

  By reducing the amount of EGR gas, the combustion temperature rises, so the amount of NOx discharged from the internal combustion engine increases. On the other hand, since the combustion state is stabilized by decreasing the EGR gas amount, the after injection amount and the retard amount of the fuel injection timing can be further increased. Thereby, since the temperature of exhaust can be made higher, the temperature of a catalyst can be raised rapidly. Thereby, the amount of NOx released into the atmosphere can be reduced.

  According to the present invention, the amount of NOx released into the atmosphere can be reduced.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, its intake system, and an exhaust system. 4 is a time chart showing changes in vehicle speed, state of temperature rising combustion, SCR catalyst temperature, NOx amount discharged from an internal combustion engine (engine exhaust NOx amount), NOx amount downstream of the SCR catalyst, and CO ₂ emission amount. . It is the figure which showed the relationship between the NOx amount discharged | emitted from an internal combustion engine (engine exhaust NOx amount), and the temperature increase amount (exhaust temperature rising allowance) of the gas discharged | emitted from an internal combustion engine. It is the flowchart which showed the flow of the temperature rising combustion which concerns on an Example.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified.

Example 1
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine, its intake system and exhaust system according to the present embodiment. An internal combustion engine 1 shown in FIG. 1 is a diesel engine having four cylinders 2.

  An exhaust passage 3 is connected to the internal combustion engine 1. In the middle of the exhaust passage 3, a reducing agent injection valve 4 and a selective reduction type NOx catalyst 5 (hereinafter referred to as SCR catalyst 5) are provided in order from the upstream side.

The reducing agent injection valve 4 is opened when the reducing agent is injected, and is closed when the injection of the reducing agent is stopped. Ammonia (NH ₃ ) is used as the reducing agent. The reducing agent injection valve 4 may inject ammonia or urea water. Here, the urea water injected from the reducing agent injection valve 4 is hydrolyzed in the SCR catalyst 5 to become ammonia and is adsorbed by the SCR catalyst 5. That is, ammonia may be supplied from the reducing agent injection valve 4, or a substance that eventually changes to ammonia may be supplied. Further, the reducing agent may be supplied in any state of solid, liquid, and gas.

  The SCR catalyst 5 selectively reduces NOx with the reducing agent that has been adsorbed. Therefore, if ammonia is adsorbed in advance as a reducing agent on the SCR catalyst 5, NOx can be reduced by this ammonia.

  In the present embodiment, the SCR catalyst 5 is provided, but other catalysts may be used as long as they can purify NOx. For example, a three-way catalyst or an occlusion reduction type NOx catalyst (NSR catalyst) may be used. In this embodiment, the SCR catalyst 5 corresponds to the catalyst for reducing NOx in the present invention.

  A temperature sensor 11 for measuring temperature is attached to the exhaust passage 3 upstream of the SCR catalyst 5. Further, a NOx sensor 12 for measuring the NOx concentration is attached to the exhaust passage 3 downstream of the SCR catalyst 5. The temperature sensor 11 can detect the temperature of the gas discharged from the internal combustion engine 1 or the temperature of the exhaust gas flowing into the SCR catalyst 5. Further, the temperature of the SCR catalyst 5 can be estimated from the detection value of the temperature sensor 11. The detection value of the temperature sensor 11 may be the temperature of the SCR catalyst 5.

  The internal combustion engine 1 includes a fuel injection valve 6 that injects fuel into the cylinder 2.

  An intake passage 20 is connected to the internal combustion engine 1. The intake passage 20 is provided with a throttle 21 for adjusting the flow rate of intake air flowing through the intake passage 20.

  Further, the internal combustion engine 1 is provided with an EGR device 30 that recirculates a part of the exhaust gas flowing through the exhaust passage 3 to the intake passage 20. The EGR device 30 includes an EGR passage 31 that connects the exhaust passage 3 upstream of the SCR catalyst 5 and the intake passage 20 downstream of the throttle 21, and an EGR valve 32 that adjusts the cross-sectional area of the EGR passage 31. ing.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 controls the internal combustion engine 1 in accordance with the operating conditions of the internal combustion engine 1 and the driver's request.

In addition to the sensors described above, the ECU 10 outputs an electric signal corresponding to the amount of depression of the accelerator pedal 14 by the driver to detect the engine load, and an accelerator position sensor 15 that detects the engine speed. 16 are connected via electric wiring, and output signals of these various sensors are input to the ECU 10.

  On the other hand, the reducing agent injection valve 4, the fuel injection valve 6, the throttle 21, and the EGR valve 32 are connected to the ECU 10 through electric wiring, and these devices are controlled by the ECU 10.

  Then, the ECU 10 controls the internal combustion engine 1 so as to maintain the temperature of the SCR catalyst 5 at the target temperature. In this case, in this embodiment, an increase in the amount of NOx discharged from the internal combustion engine 1 is allowed in a range where the amount of NOx released into the atmosphere falls within an allowable value.

  Here, by discharging a gas having a high temperature from the internal combustion engine 1, it is possible to suppress a temperature drop of the SCR catalyst 5 or to raise the temperature of the SCR catalyst 5. Thus, when exhausting high temperature gas from the internal combustion engine 1, the amount of NOx emissions can also increase. However, even if the amount of NOx discharged from the internal combustion engine 1 increases, if the SCR catalyst 5 is still active, NOx can be reduced in the SCR catalyst 5. That is, when the SCR catalyst 5 is in an active state and the temperature of the SCR catalyst 5 can be lower than the activation temperature, the increased NOx is discharged from the internal combustion engine 1 by discharging a gas having a high temperature. While reducing at the catalyst 5, the temperature of the SCR catalyst 5 can be raised.

  Note that when NOx in an amount exceeding the NOx purification capacity of the SCR catalyst 5 is discharged from the internal combustion engine 1, the NOx flows out from the SCR catalyst 5 even if the temperature of the SCR catalyst 5 is in an active state. Therefore, in this embodiment, the amount of NOx discharged from the internal combustion engine 1 is adjusted so that the amount of NOx released into the atmosphere does not exceed the allowable range.

  Here, the temperature of the exhaust gas is raised by delaying the injection timing for delaying the timing of the main injection by the fuel injection valve 6 or by performing the secondary injection (after injection) after the main injection by the fuel injection valve 6. be able to. Hereinafter, the combustion for raising the temperature of the exhaust gas is referred to as “temperature rising combustion”. In the case where at least one of the injection timing retarding and the after injection is performed, the temperature rising combustion is performed.

  By the way, if the supply amount of EGR gas increases, the combustion state may become unstable, and therefore, the injection amount in the after injection (after injection amount) and the retard amount of the fuel injection timing (injection timing retard amount) are limited. On the other hand, by reducing the supply amount of EGR gas, it is possible to suppress the deterioration of the combustion state even if the after injection amount is increased or the injection timing retardation amount is increased. However, as the combustion temperature increases, the amount of NOx discharged from the internal combustion engine 1 increases. On the other hand, in the present embodiment, the amount of NOx discharged from the internal combustion engine 1 is adjusted by adjusting the amount of EGR gas so that the amount of NOx released into the atmosphere does not exceed the allowable range.

FIG. 2 shows changes in the vehicle speed, the state of temperature-increasing combustion, the temperature of the SCR catalyst 5, the amount of NOx discharged from the internal combustion engine 1 (the amount of NOx discharged from the engine), the amount of NOx downstream from the SCR catalyst 5, and the CO ₂ emission amount. It is the time chart which showed. A solid line indicates a case where the NOx emission amount from the internal combustion engine 1 is increased, and a broken line indicates a case where the NOx emission amount from the internal combustion engine 1 is decreased (when warming up is performed).

Here, the warm-up is performed mainly when the internal combustion engine 1 is started, etc., when the SCR catalyst 5 does not reach the activation temperature, and is performed to raise the temperature of the SCR catalyst 5 to the activation temperature. Is done. At this time, since it is difficult to purify NOx in the SCR catalyst 5, it is necessary to reduce the amount of engine exhaust NOx. Therefore, it is not possible to reduce the EGR gas that accompanies an increase in the engine exhaust NOx amount. For this reason, the retard amount of the fuel injection timing cannot be increased, and the after injection amount cannot be increased. The broken line in FIG. 2 shows the case where the temperature of the SCR catalyst 5 is at the activation temperature, but warming up is performed in order to suppress the temperature drop of the SCR catalyst 5.

  In FIG. 2, “vehicle speed” is the speed of the vehicle on which the internal combustion engine 1 is mounted, and is a constant speed before the time indicated by A, decelerated during a period indicated by A to C, and indicated by C. It becomes a constant speed after the point. The vehicle speed is lower in the period after C than in the period before A.

  “Temperature rising combustion” is performed when ON, and is not performed when OFF. That is, when increasing the NOx emission amount (hereinafter also referred to as a solid line), the temperature rising combustion is performed in the period from B to D, and the NOx emission amount is reduced (hereinafter, the case of a broken line). In other words, the temperature rising combustion is performed in the period from B to E.

  The “SCR catalyst temperature” indicates the temperature of the SCR catalyst 5, and this temperature decreases with deceleration of the vehicle unless temperature rising combustion is performed. That is, in the period from A to B, since the temperature rising combustion is not performed in any case, the temperature of the SCR catalyst 5 decreases. In the case of the solid line, since the temperature rising combustion is performed in the period from B to D, the temperature of the SCR catalyst 5 rises in this period. On the other hand, in the case of the broken line, since the temperature rising combustion is performed in the period from B to E, the temperature of the SCR catalyst 5 rises in this period. When increasing the amount of NOx discharged from the internal combustion engine 1, the temperature of the gas discharged from the internal combustion engine 1 can be made higher, so that the temperature of the SCR catalyst can be raised more quickly. . Therefore, the solid line has a larger temperature rise per unit time than the broken line.

  The “engine exhaust NOx amount” indicates the NOx amount exhausted from the internal combustion engine 1, and in the case of a solid line, increases in the period (BD) in which the temperature-enhanced combustion is performed. On the other hand, in the case of the broken line, the amount of engine exhaust NOx is suppressed during the period (BE) in which the temperature rising combustion is performed.

  The “downstream NOx amount of SCR catalyst” indicates the NOx amount downstream of the SCR catalyst 5, and this NOx amount may be the amount of NOx flowing out of the SCR catalyst 5 or the amount of NOx released into the atmosphere. . The transition of this value is the same for the solid line and the broken line. That is, since the temperature rising combustion is performed within a range where the NOx discharged from the internal combustion engine 1 can be purified, the amount of NOx flowing out from the SCR catalyst 5 does not increase even in the case of the solid line.

"CO ₂ emissions" is the amount of CO ₂ discharged from the internal combustion engine 1. When the temperature rising combustion is performed, the amount of CO ₂ emission increases. And since the period when temperature rising combustion is implemented is longer in the case of the broken line than in the case of the solid line, the total emission amount of CO ₂ increases.

Thus, according to the present embodiment, the temperature of the SCR catalyst 5 can be quickly raised while suppressing the outflow of NOx downstream from the SCR catalyst 5. For this reason, since the period during which the temperature-enhanced combustion is performed can be shortened, deterioration of fuel consumption can be suppressed, and the amount of CO ₂ emission can be reduced.

  Note that the temperature rising combustion is performed before the temperature of the SCR catalyst 5 becomes lower than the activation temperature when the temperature of the SCR catalyst 5 can be lower than the activation temperature. For this reason, when the temperature of the SCR catalyst 5 is equal to or lower than a predetermined value, or when the temperature of the SCR catalyst 5 is predicted to be lower than the predetermined value, the temperature rising combustion is performed while increasing the engine exhaust NOx amount.

FIG. 3 is a diagram showing the relationship between the amount of NOx discharged from the internal combustion engine 1 (engine exhaust NOx amount) and the amount of increase in the temperature of the gas discharged from the internal combustion engine 1 (exhaust temperature raising allowance). . "Warm-up"
Indicates a case where the temperature rising combustion is performed while decreasing the NOx emission amount, and “NOx increase” indicates a case where the temperature rising combustion is performed while increasing the NOx emission amount. When NOx increases, the amount of engine exhaust NOx is larger and the exhaust gas temperature increase is larger than when warming up.

  In FIG. 3, “EGR increase” indicates the change direction of the engine exhaust NOx amount when the EGR gas amount (which may be the EGR rate) is increased, and “EGR decrease” indicates the EGR gas amount (EGR rate). The change direction of the engine exhaust NOx amount in the case where the amount is reduced is also shown. That is, as the EGR gas amount is increased, the combustion temperature is lowered, so that the engine exhaust NOx amount is decreased. As the EGR gas amount is decreased, the combustion temperature is increased, so the engine exhaust NOx amount is increased.

  In FIG. 3, “injection timing delay, after injection increase” indicates the change direction of the exhaust gas temperature increase when the fuel injection timing in the fuel injection valve 6 is retarded or the after injection amount is increased. Is shown. Further, “injection timing advance, after injection decrease” indicates the direction of change in the exhaust gas temperature increase when the fuel injection timing in the fuel injection valve 6 is advanced or the after injection amount is decreased. . That is, as the fuel injection timing is retarded and the after injection amount is increased, the amount of increase in the exhaust gas temperature increases. Further, the amount of increase in the exhaust gas temperature decreases as the fuel injection timing is advanced or the after injection amount is decreased.

  FIG. 4 is a flowchart showing a flow of temperature rising combustion according to the present embodiment. This routine is executed by the ECU 10 every predetermined time.

  In step S101, the NOx purification rate in the SCR catalyst 5 is calculated. For example, the NOx purification rate can be calculated based on the temperature of the SCR catalyst 5, the intake air amount, and the ammonia amount adsorbed by the SCR catalyst 5.

  The amount of ammonia adsorbed by the SCR catalyst 5 can be obtained, for example, by subtracting the amount of ammonia consumed for NOx purification and the amount of ammonia flowing out of the SCR catalyst 5 from the amount of ammonia supplied. The amount of ammonia consumed for the purification of NOx has a correlation with the amount of NOx flowing into the SCR catalyst 5, and can be calculated based on the amount of NOx flowing into the SCR catalyst 5. Further, the ammonia amount flowing out from the SCR catalyst 5 has a correlation with the temperature of the SCR catalyst 5 and the intake air amount of the internal combustion engine 1, and can be calculated based on this relationship. Note that the ammonia amount adsorbed by the SCR catalyst 5 may be obtained by a known technique. In this embodiment, the ECU 10 that processes step S101 corresponds to the purification rate detection means in the present invention.

  Note that the NOx purification rate can be obtained by attaching NOx sensors upstream and downstream of the SCR catalyst 5. Further, the NOx purification rate may be obtained using a known technique. Furthermore, instead of the current NOx purification rate, the NOx purification rate after the current time may be predicted using a known technique.

  In step S102, it is determined whether the NOx purification rate is equal to or less than a predetermined value. In this step, it is determined whether or not the NOx purification rate may be lower than the allowable range. Note that it may be determined whether or not the NOx purification rate changes from a state higher than a predetermined value to a state equal to or lower than a predetermined value. Further, it may be determined whether or not the NOx purification rate is predicted to be lower than the allowable range. The predetermined value here is a value that is larger than the lower limit value of the allowable range, and the NOx purification rate that may cause the NOx purification rate to be lower than the allowable range or the NOx purification rate is predicted to be lower than the allowable range. Is the NOx purification rate. As this predetermined value, an optimum value is obtained in advance through experiments or simulations.

  If an affirmative determination is made in step S102, the process proceeds to step S103. On the other hand, if a negative determination is made, this routine is terminated.

  In step S103, warm-up for increasing the temperature of the SCR catalyst 5 is performed. That is, the retard of the after injection or the fuel injection timing is performed. At this time, since the EGR gas amount has not yet been reduced, the after injection amount and the injection timing retardation amount are determined so that the NOx amount discharged from the internal combustion engine 1 decreases. The after injection amount and the injection timing retardation amount at this time are obtained in advance through experiments or simulations and stored in the ECU 10.

  In step S104, an allowable value of the NOx amount downstream of the SCR catalyst 5 is calculated. This allowable value is set so that the amount of NOx downstream from the SCR catalyst 5 accumulated in a predetermined traveling period (which may be a traveling distance) is equal to or less than a predetermined value. This predetermined value is an upper limit value of an allowable range determined by a regulation value or the like. Specifically, the predetermined traveling period is defined as a period from a past predetermined time point to a predetermined future time point, based on a NOx amount accumulated during a period from a past predetermined time point to the present time. Since the amount of NOx accumulated in the traveling period is less than or equal to a predetermined value, the amount of NOx that may be discharged during the period from the current time to a predetermined time in the future is calculated. The allowable value is calculated on the assumption that the current state continues. The allowable value may be calculated as an integrated value of the NOx amount from the present time to a predetermined future time, or may be calculated as the NOx amount flowing out from the SCR catalyst 5 per unit time.

  In step S105, the target value of the NOx amount discharged from the internal combustion engine 1 is calculated. In this step, the engine exhaust NOx amount is set as a target value so that the NOx amount downstream of the SCR catalyst 5 is equal to or less than the allowable value calculated in step S104. The target value is calculated based on the allowable value calculated in step S104 and the current NOx purification rate. That is, by multiplying the engine exhaust NOx amount by (1-NOx purification rate), the NOx amount downstream from the SCR catalyst 5 is obtained. Therefore, the engine exhaust NOx amount such that this value is equal to or less than the allowable value is set as the target value. And In this embodiment, the ECU 10 that processes step S105 corresponds to the calculation means in the present invention.

  In step S106, the EGR gas amount is decreased, the after injection amount is increased, and the retardation amount of the fuel injection timing is increased. At least one of the increase of the after injection amount and the increase of the retard amount of the fuel injection timing may be performed. At this time, the EGR gas amount is adjusted based on the target value calculated in step S105. Here, the EGR gas amount, the fuel injection timing retardation amount, and the after injection amount are obtained from the target values calculated in step S105 in accordance with the relationship shown in FIG. Note that the relationship of FIG. 3 is obtained in advance through experiments or simulations and stored in the ECU 10. In this embodiment, the ECU 10 that processes step S106 corresponds to the temperature raising means in the present invention. Further, the EGR gas amount, the after injection amount, and the injection timing retardation amount may be feedback-controlled so that the detected value of the NOx sensor 12 is equal to or less than the allowable value.

  As described above, according to the present embodiment, the NOx purification rate may be lower than the allowable range, and the temperature-enhanced combustion may be performed before the actual lower than the allowable range. it can. Thereby, the NOx purification rate can be maintained within an allowable range.

In addition, when performing the temperature rising combustion, the amount of NOx discharged from the internal combustion engine 1 is allowed to increase, so that the temperature rising amount per unit time can be increased. That is, the temperature of the SCR catalyst 5 can be quickly raised. At this time, the amount of NOx discharged from the internal combustion engine 1 is adjusted so that the amount of NOx flowing out from the SCR catalyst 5 falls within the allowable range, so that the release of NOx into the atmosphere can be suppressed. And by raising the temperature of the SCR catalyst 5 rapidly, deterioration of fuel consumption can be suppressed or the amount of CO ₂ emission can be reduced.

  In the present embodiment, only one SCR catalyst 5 is provided, but a plurality of catalysts capable of purifying NOx may be provided instead. In this case, the amount of NOx discharged from the internal combustion engine 1 is adjusted so that the amount of NOx flowing out from the most downstream catalyst is less than the allowable value.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Exhaust passage 4 Reducing agent injection valve 5 Selective reduction type NOx catalyst (SCR catalyst)
6 Fuel injection valve 10 ECU
11 Temperature sensor 12 NOx sensor 14 Accelerator pedal 15 Accelerator opening sensor 16 Crank position sensor 20 Intake passage 21 Throttle 30 EGR device 31 EGR passage 32 EGR valve

Claims (3)

A catalyst provided in the exhaust passage of the internal combustion engine for reducing NOx;
A purification rate detecting means for estimating or detecting a NOx purification rate in the catalyst;
In a control device for an internal combustion engine comprising:
When the NOx purification rate in the catalyst changes from a state higher than a predetermined value to a state equal to or lower than a predetermined value, an allowable value of the amount of NOx flowing out downstream from the catalyst in a predetermined period, and the NOx in the catalyst A control apparatus for an internal combustion engine, comprising: calculation means for calculating a target value of the amount of NOx discharged from the internal combustion engine based on a purification rate.   When the NOx purification rate in the catalyst changes from a state higher than a predetermined value to a state not higher than a predetermined value, the amount of NOx discharged from the internal combustion engine is not more than the target value and the exhaust of the internal combustion engine is reduced. The control device for an internal combustion engine according to claim 1, further comprising a temperature raising means for raising the temperature.   The temperature raising means reduces the amount of EGR gas and retards the fuel injection timing into the cylinder of the internal combustion engine or the fuel injection into the cylinder of the internal combustion engine, and after injection that is performed after the main injection The control device for an internal combustion engine according to claim 2, wherein the temperature of the exhaust gas is raised by at least one of the following.

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