JP2017150431A - Internal combustion engine and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine which improves a cleaning rate of a nitrogen oxide in a selective reduction catalyst while suppressing discharge of a reducing agent from the selective reduction catalyst for cleaning the nitrogen oxide in an exhaust gas of the internal combustion engine, and a control method of the internal combustion engine.SOLUTION: In the case of a situation where a selective reduction catalyst 23 is activated, a control device 30 performs control for adjusting an addition amount Qr by performing both of opening loop control OLC for adjusting the addition amount Qr to a first target addition amount Qa which is calculated on the basis of a pre-passage content CBx of the nitrogen oxide, and closing loop control CLC for adjusting the addition amount Qr to a second target addition amount Qb which is calculated on the basis of a post-passage content CAx of the nitrogen oxide, and in the case of a situation where the selective reduction catalyst 23 is not activated, the control device performs control for adjusting the addition amount Qr only by the opening loop control OLC.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an internal combustion engine and a control method thereof, and more particularly, selective reduction while suppressing discharge of a reducing agent from a selective reduction catalyst for purifying nitrogen oxides in exhaust gas of the internal combustion engine. The present invention relates to an internal combustion engine that improves the purification rate of nitrogen oxides in a catalyst and a control method thereof.

  In order to purify nitrogen oxides (NOx) in the exhaust gas of the engine (internal combustion engine), an oxidation catalyst and a selective gas are sequentially selected from the upstream side to the downstream side in the exhaust passage through which the exhaust gas discharged from the cylinder passes. There is an engine with a reduction catalyst. In this engine, the reducing agent is added to the exhaust gas from the reducing agent injection valve upstream of the selective reduction catalyst, and the nitrogen oxide is reduced by the selective reduction catalyst by the reducing agent added to the exhaust gas. doing.

  In this regard, the amount of reducing agent added to the exhaust gas from the reducing agent injection valve is closed loop control (feedback control) based on the content of nitrogen oxides contained in the exhaust gas downstream of the selective reduction catalyst. Has been proposed (see, for example, Patent Document 1).

  However, even when the selective reduction catalyst is inactivated, if the amount of reducing agent added is adjusted by closed loop control, the selective reduction catalyst cannot sufficiently reduce the nitrogen oxides by the reducing agent, and the downstream side of the nitrogen oxides As the amount of reducing agent added increases, the amount of reducing agent becomes excessive, and there is a problem that a large amount of reducing agent is discharged from the selective reduction catalyst. There was a problem that the purification rate of nitrogen oxides in the reduction catalyst decreased.

JP 2013-515897 A

  An object of the present invention is to improve the nitrogen oxide purification rate in the selective reduction catalyst while suppressing the discharge of the reducing agent from the selective reduction catalyst for purifying the nitrogen oxide in the exhaust gas of the internal combustion engine. It is to provide an internal combustion engine and a control method thereof.

  The internal combustion engine of the present invention that achieves the above object comprises an oxidation catalyst and a selective reduction catalyst in order from the upstream side to the downstream side of the exhaust passage through which the exhaust gas from the cylinder of the internal combustion engine passes. In an internal combustion engine equipped with a reducing agent injection valve for adding a reducing agent to exhaust gas upstream of the selective reduction catalyst, the activation state of the selective reduction catalyst is monitored, and the reduction according to the activation state A control device that performs control to adjust the addition amount of the reducing agent added to the exhaust gas from the agent injection valve, and when the control device is in a state where the selective reduction catalyst is activated, the addition amount is Open loop control adjusted to the first target addition amount calculated based on the content of nitrogen oxides contained in the exhaust gas before passing through the selective reduction catalyst, and the addition amount is the selective Exhaust gas after passing through the reduction catalyst While performing the control to adjust the addition amount by both the closed loop control adjusted to the second target addition amount calculated based on the post-passage content of nitrogen oxide contained in the In the situation where the reduction catalyst is inactivated, the control is performed to adjust the addition amount only by the open loop control.

  The control method for an internal combustion engine of the present invention that achieves the above object is an internal combustion engine in which an oxidation catalyst, a reducing agent injection valve, and a selective reduction catalyst are arranged in an exhaust passage through which exhaust gas from a cylinder of the internal combustion engine passes. In the engine control method, the activation status of the selective reduction catalyst, the content of nitrogen oxides contained in the exhaust gas before passing through the selective reduction catalyst, and after passing through the selective reduction catalyst The step of acquiring the content of nitrogen oxides contained in the exhaust gas after passing and determining whether or not the acquired activation state of the selective reduction catalyst is a state in which the selective reduction catalyst is activated And, when it is determined that the selective reduction catalyst is activated, the addition amount of the reducing agent added to the exhaust gas from the reducing agent injection valve is contained before the passage. Calculated based on quantity It adjusts by both control of the open loop control adjusted to the first target addition amount and the closed loop control in which the addition amount is adjusted to the second target addition amount calculated based on the content after passing. And a step of adjusting the addition amount only by the open-loop control when it is determined that the selective reduction catalyst is in an inactivated state.

  The activation state of the selective reduction catalyst here is a state indicating whether or not the selective reduction catalyst is in an activated state in which the reduction of nitrogen oxides is stably performed. Specifically, the activation state of the selective reduction catalyst is based on the catalyst temperature inside the selective reduction catalyst and the space velocity of the exhaust gas in the selective reduction catalyst. The space velocity is represented by the reciprocal of the time that the exhaust gas contacts the selective reduction catalyst per unit time, in other words, the exhaust gas flow rate per filling volume of the selective reduction catalyst. Therefore, the activation state of the selective reduction catalyst is also based on the catalyst temperature and the exhaust gas flow rate.

  That is, the selective reduction catalyst is activated because, for example, the catalyst temperature inside the selective reduction catalyst is high or the space velocity of the exhaust gas in the selective reduction catalyst is low. This refers to the situation where the reduction of nitrogen oxides is stable. On the other hand, the situation in which the selective reduction catalyst is inactivated is, for example, that the catalyst temperature inside the selective reduction catalyst is low or the space velocity of the exhaust gas in the selective reduction catalyst is high. This is a situation where the reduction of nitrogen oxides is unstable. This unstable situation indicates that the reduction of nitrogen oxides is not stable because the catalyst is not sufficiently active, and there is no reduction of nitrogen oxides in the selective reduction catalyst. Not that.

  Therefore, in the internal combustion engine, it is desirable to obtain the catalyst temperature and space velocity, and the control method preferably includes a step of obtaining them.

  In addition, the activation state of the selective reduction catalyst, the content before passage, and the content after passage can be exemplified by sensor detection values or calculation values based on model prediction, and the acquisition means is not limited.

  For example, as the catalyst temperature indicating the activation state of the selective reduction catalyst, the detection value of the temperature sensor arranged in the selective reduction catalyst or the temperature sensor arranged in the exhaust passage near the inlet of the selective reduction catalyst can be used. The detected value can be exemplified.

  In addition, the space velocity indicating the activation state of the selective reduction catalyst is a model prediction of the exhaust gas flow rate discharged from the cylinder to the exhaust passage, and the exhaust gas flow rate and the filling volume in the selective reduction catalyst previously obtained. The calculated value calculated from can be illustrated.

The pre-passage content includes the detected value of the NOx sensor disposed in the exhaust passage near the inlet of the selective reduction catalyst, the NOx concentration of exhaust gas discharged from the cylinder to the exhaust passage, and the oxidation in the oxidation catalyst. A calculated value calculated by predicting a change in NOx concentration due to reaction as a model can be exemplified.

  In addition, as the content after passage, the NOx concentration by reduction in the selective reduction catalyst is further calculated from the detected value of the NOx sensor arranged in the exhaust passage downstream of the selective reduction catalyst and the content before passage predicted by the model. The calculated value calculated by predicting the change in the model can be exemplified.

  The open loop control (open loop control) here refers to adjusting the addition amount to the first target addition amount calculated based on the pre-passage content without performing feedback on the post-passage content. By this, it is control which makes content after passage close to the predetermined target content. This open loop control can be rephrased as feedforward control when the oxidation reaction in the oxidation catalyst is a disturbance.

  On the other hand, the closed loop control (closed loop control) referred to here is control for bringing the content after passage closer to the target content by performing feedback on the content after passage.

  According to this internal combustion engine and its control method, only the open loop control and the control for adjusting the addition amount of the reducing agent by both the open loop control and the closed loop control according to the activation state in the selective reduction catalyst, By switching the control to be adjusted at, it is possible to avoid an excessive or insufficient amount of the reducing agent added.

  For example, in a situation where the selective reduction catalyst is activated, the purification rate of nitrogen oxides in the selective reduction catalyst is improved by adjusting the amount of reducing agent added by both open-loop control and closed-loop control. it can. On the other hand, in a situation where the selective reduction catalyst is inactivated, closed loop control is prohibited, and the reducing agent is discharged from the selective reduction catalyst by adjusting the amount of reducing agent added only by open loop control. Can be suppressed.

  In this way, by switching the control to adjust the addition amount according to the activation state of the selective reduction catalyst, while suppressing the discharge of the reducing agent from the selective reduction catalyst, the nitrogen oxides in the selective reduction catalyst are reduced. The purification rate can be improved.

  In particular, the internal combustion engine and the control method thereof are suitable for adjusting the amount of reducing agent added by predicting the content after passage as a model. When the post-passage content is modeled and the amount of reducing agent added is adjusted by closed-loop control, the purification rate of nitrogen oxides can be improved, but in the situation where the selective reduction catalyst is inactivated, the post-passage content is reduced. There are times when model prediction accuracy decreases. On the other hand, in the internal combustion engine and the control method thereof, the addition amount is adjusted regardless of the decrease in the model prediction accuracy by prohibiting the closed loop control in a situation where the selective reduction catalyst is inactivated. Thereby, the improvement in the purification rate of nitrogen oxides by predicting the content after passage can be achieved without the influence of variations such as the reduction agent being discharged from the selective reduction catalyst.

It is a block diagram which illustrates the engine of embodiment of this invention. It is a block diagram which illustrates the control apparatus of FIG. It is the area | region map data of FIG. It is a flowchart which illustrates the control method of the engine of embodiment of this invention. It is a flowchart which illustrates another form of FIG. It is map data which illustrates another form of FIG.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 illustrates an engine 10 according to an embodiment of the present invention. The engine 10 includes an oxidation catalyst 21 and a selective reduction catalyst 23 in the exhaust passage 20, and the selective reduction catalyst 23 generates nitrogen oxides by the reducing agent R 1 added to the exhaust gas G 1 from the reducing agent injection valve 24. It is something to reduce.

  In the engine 10, the intake air A <b> 1 sucked into the intake passage 11 is compressed by the compressor 12 a of the turbocharger 12 and becomes high temperature, and is cooled by the intercooler 13. Thereafter, the intake air A1 is supplied from the intake manifold 14 through the intake valve 15 to the cylinder 16. The intake air A1 supplied to the cylinder 16 is mixed with the fuel injected from the fuel injection valve 17 and burned to generate heat energy, and then becomes exhaust gas G1.

  The exhaust gas G1 is exhausted from the exhaust valve 18 to the exhaust passage 20 via the exhaust manifold 19. The exhaust gas G1 thus exhausted drives the turbine 12b of the turbocharger 12, and then passes through the oxidation catalyst 21, the collection filter 22, and the selective reduction catalyst 23 in this order to be purified and then released into the atmosphere.

  A part of the exhaust gas G1 branches from the exhaust passage 20 to the EGR passage 25, is cooled by the EGR cooler 26, and then recirculates from the EGR valve 27 to the intake passage 11 as EGR gas G2.

  Hereinafter, the purification of the exhaust gas G1 will be described in detail. In the exhaust passage 20, an oxidation catalyst 21, a collection filter 22, and a selective reduction catalyst 23 are arranged in order from the upstream side to the downstream side in the exhaust passage 20. Further, a reducing agent injection valve 24 for adding the reducing agent R1 to the exhaust gas G1 is disposed upstream of the selective reduction catalyst 23.

  The oxidation catalyst 21 is formed, for example, in a state in which rhodium, cerium oxide, platinum, aluminum oxide or the like is supported on a porous ceramic honeycomb structure support such as a cordierite honeycomb. The oxidation catalyst 21 oxidizes unburned fuel such as hydrocarbon (HC) or carbon monoxide (CO) in the exhaust gas G1, and raises the temperature of the exhaust gas G1 by heat generated by the oxidation. Then, the temperature of the downstream collecting filter 22 is raised by the heated exhaust gas G1.

  The collection filter 22 is generally formed of a monolith honeycomb wall flow type filter or the like in which the inlet and outlet of a porous ceramic honeycomb channel are alternately plugged. In many cases, an oxidation catalyst such as platinum or cerium oxide or a PM oxidation catalyst is supported on the filter portion. By this collection filter 22, the particulate matter (PM) in the exhaust gas G1 is collected by a porous ceramic wall.

The selective reduction catalyst 23 is formed in a state in which a noble metal catalyst such as platinum or vanadium, vanadium, copper, or a base metal catalyst is supported on the honeycomb structure. In this selective reduction catalyst 23, nitrogen oxides (NOx) such as nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) are reduced to nitrogen (N ₂ ) and water (H ₂ O) by a reduction reaction. . In this case, NO: NO ₂ can be most effectively reduce nitrogen oxides to nitrogen in the case of 50:50.

  An example of the reducing agent injection valve 24 is a dosing valve that injects urea water, and an example of the reducing agent R1 is ammonia. Ammonia is generated from the urea water injected from the dosing valve by hydrolysis or thermal decomposition, and this ammonia is adsorbed on the selective reduction catalyst 23 as the reducing agent R1.

When the exhaust gas G1 exhausted from the engine 10 passes through each device in a state where each device is activated, the oxidation catalyst 21 causes unburned hydrocarbons, carbon oxides, and nitrogen oxidation contained in the exhaust gas. Things are oxidized.

  Next, in the collection filter 22, the nitrogen oxide is oxidized by the supported catalyst, and the particulate matter contained in the exhaust gas G1 is collected. Further, in the collection filter 22, the particulate matter is oxidized and removed by reacting the collected particulate matter with nitrogen dioxide (hereinafter referred to as passive regeneration).

Next, in the selective reduction catalyst 23, nitrogen oxides are reduced by a reduction reaction by the reducing agent R1 injected from the reducing agent injection valve 24. Typical examples of this reduction reaction include “4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O”, “6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O”, and “NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O”. it can.

  The above-described configuration of the engine 10 is an example. For example, the configuration may not include the collection filter 22 or may include a catalyst that adsorbs the reducing agent R1 on the downstream side of the selective reduction catalyst 23. Good.

  In such an engine 10, the activation state of the selective reduction catalyst 23 is monitored, and the addition amount Qr of the reducing agent R1 added to the exhaust gas G1 from the reducing agent injection valve 24 is adjusted according to the activation state. A control device 30 that performs control is provided.

  The control device 30 is configured to perform control for adjusting the addition amount Qr by control of both the open loop control OLC and the closed loop control CLC when the selective reduction catalyst 23 is activated. The Further, the control device 30 is configured to perform control to adjust the addition amount Qr by the open loop control OLC when the selective reduction catalyst 23 is inactivated.

  The control device 30 includes a CPU that performs various processes, a ROM that temporarily stores programs used to perform the various processes, a RAM that can read and write processing results, and various interfaces. The control device 30 is connected to respective sensors such as a first NOx sensor 31, a temperature sensor 32, a second NOx sensor 33, a rotation speed sensor 34, and an intake air amount sensor 35 via signal lines. The control device 30 is connected to the fuel injection valve 17, the reducing agent injection valve 24, and the EGR valve 27 via a signal line.

  FIG. 2 illustrates an outline of the control device 30. The control device 30 includes a parameter acquisition unit 36, a determination unit 37, and a control unit 38.

  The parameter acquisition unit 36 uses, as parameters, the catalyst temperature Tx and the space velocity Vx indicating the activation state of the selective reduction catalyst 23, the pre-passage content CBx, and the post-passage content CAx as detected by the sensor or model prediction. Obtained as a calculated value. The parameter acquisition unit 36 is constituted by a RAM when all parameters can be acquired from detection values of various sensors. On the other hand, when one of the parameters requires a model prediction calculation value, the RAM and the model prediction are obtained. It consists of a program. The model prediction program is a program that performs model prediction of parameters based on detection values and models of various sensors.

The catalyst temperature Tx is the temperature inside the selective reduction catalyst 23, and in this embodiment, is the detection value of the temperature sensor 32. The temperature sensor 32 is disposed in the exhaust passage 20 near the inlet of the selective reduction catalyst 23, and detects the temperature of the exhaust gas G1 passing through the vicinity of the inlet. When the detected value of the temperature sensor 32 is acquired as the catalyst temperature Tx, map data indicating the relationship between the detected value of the temperature sensor 32 and the actual catalyst temperature Tx is obtained in advance by experiments or tests, and this map data is obtained. The detection value may be corrected with. Note that the catalyst temperature Tx may be directly acquired by a temperature sensor arranged in the selective reduction catalyst 23.

  The space velocity Vx is the space velocity of the exhaust gas G1 passing through the selective reduction catalyst 23, and indicates the exhaust gas flow rate per filling volume of the selective reduction catalyst 23. In this embodiment, the filling volume of the selective reduction catalyst 23 is obtained in advance by experiments and tests, and is obtained by dividing the filling volume from the exhaust gas flow rate predicted by the model prediction program. The model prediction program may be any program that can predict the exhaust gas flow rate. The detected value of the rotation speed sensor 34, the detected value of the intake air amount sensor 35, and the fuel injection amount that is the control value of the fuel injection valve 17 are used. And a program that predicts the exhaust gas flow rate with reference to preset map data.

  Note that an exhaust gas flow rate may be used instead of the space velocity Vx. However, it is preferable that the activation state of the selective reduction catalyst 23 can be acquired more accurately based on the space velocity Vx.

  The pre-passage content CBx is the content of nitrogen oxides contained in the exhaust gas G1 before passing through the selective reduction catalyst 23, and the post-passage content CAx is the exhaust gas after passing through the selective reduction catalyst 23. It is content of the nitrogen oxide contained in G1. Examples of the content include volume concentration, mass concentration, and mass flow rate. In the following, the unit is ppm as the volume concentration with respect to the exhaust gas G1. This pre-passage content CBx is a detection value of the first NOx sensor 31. The first NOx sensor 31 is disposed in the exhaust passage 20 between the collection filter 22 and the selective reduction catalyst 23, and detects the NOx concentration of the exhaust gas G1 after passing through the oxidation catalyst 21 and the collection filter 22. doing. On the other hand, the post-passage content CAx is a detection value of the second NOx sensor 33. The second NOx sensor 33 is disposed in the exhaust passage 20 on the downstream side of the selective reduction catalyst 23, and detects the NOx concentration of the exhaust gas G1 after passing through the selective reduction catalyst 23.

  The determination unit 37 and the control unit 38 are execution programs and are stored in the RAM. These execution programs are read out from the RAM to the ROM by the CPU, thereby performing predetermined processes.

  The determination unit 37 compares the acquired catalyst temperature Tx and space velocity Vx with area map data 40 described later, and whether the activation state of the selective reduction catalyst 23 exists in the first area 41 or This is a program for determining whether or not the two areas 42 exist.

  The area map data 40 includes the catalyst temperature T in the selective reduction catalyst 23 acquired in advance through experiments and tests, and the exhaust gas G1 passing through the selective reduction catalyst 23 acquired in advance through experiments and tests. Is the map data based on the space velocity V. This area map data 40 is stored in the RAM.

  FIG. 3 illustrates this area map data 40. The area map data 40 indicates the activation state of the selective reduction catalyst 23 based on the catalyst temperature T and the space velocity V. This area map data 40 has a first area 41 and a second area 42. The first region 41 is set on the high temperature region side of the region map data 40 and is a region showing a state where the selective reduction catalyst 23 is activated. On the other hand, the second region 42 is a region other than the first region 41 and is set on the low temperature region side of the region map data 40 and is a region indicating a state where the selective reduction catalyst 23 is inactivated. .

The situation where the selective reduction catalyst 23 is activated means a situation where the reduction of nitrogen oxides in the selective reduction catalyst 23 is stable. For example, when the catalyst temperature T is equal to or higher than the temperature Ta, the reduction of nitrogen oxides in the selective reduction catalyst 23 is stable regardless of the space velocity V. Further, when the catalyst temperature T is equal to or higher than the temperature Tb and lower than the temperature Ta, the reduction of the nitrogen oxide in the selective reduction catalyst 23 is stabilized as the space velocity V becomes low.

  On the other hand, the situation where the selective reduction catalyst 23 is inactivated means a situation where the reduction of nitrogen oxides in the selective reduction catalyst 23 is unstable. For example, when the catalyst temperature T is lower than the temperature Tb, the reduction of nitrogen oxides in the selective reduction catalyst 23 becomes unstable regardless of the space velocity V. Further, when the catalyst temperature T is equal to or higher than the temperature Tb and lower than the temperature Ta, the reduction of nitrogen oxides in the selective reduction catalyst 23 becomes unstable as the space velocity V increases. This unstable situation indicates that the reduction of nitrogen oxides is not stable because the catalyst is not sufficiently active, and there is no reduction of nitrogen oxides in the selective reduction catalyst 23. Not that.

  The temperatures Ta and Tb are set to values of 100 ° C. or more and 250 ° C. or less. The temperature Ta can be 200 ° C. and the temperature Tb can be 100 ° C., for example.

  The case where the obtained catalyst temperature Tx and space velocity Vx are (T1, V1) and (T2, V2) will be described as an example. The determination unit 37 determines that the activation state (T1, V1) of the selective reduction catalyst 23 exists in the first region 41. In this activation state (T1, V1), the selective reduction catalyst 23 is It is determined that the situation is activated. On the other hand, it is determined that the activation state (T2, V2) of the selective reduction catalyst 23 exists in the second region 42. In this activation state (T2, V2), the selective reduction catalyst 23 is inactivated. It is determined that the situation is in progress.

  The control unit 38 is a program for adjusting the addition amount Qr of the reducing agent R1 injected from the reducing agent injection valve 24 and added to the exhaust gas G1. More specifically, the control unit 38 has two controls, an open loop control OLC and a closed loop control CLC, and adjusts the addition amount Qr, thereby setting the post-passage content CAx to a preset target content. It is a program that brings it closer to Ca.

  The target content Ca is a target value of the content of nitrogen oxides contained in the exhaust gas G1 exhausted from the engine 10 to the outside. When the engine 10 is a diesel engine, examples of the target content Ca include a value of 950 ppm or less.

  The open loop control OLC is a control for bringing the post-passage content CAx closer to the target content Ca without performing feedback on the post-passage content CAx. Specifically, the control is such that the addition amount Qr is adjusted to the first target addition amount Qa calculated based on the pre-passage content CBx so that the post-passage content CAx becomes the target content Ca.

  This open loop control OLC has map data in which a first target addition amount Qa based on the pre-passage content CBx is set in advance, and the addition amount Qr is calculated based on the map data. The control which adjusts the reducing agent injection valve 24 so that it may become quantity Qa can be illustrated. The first target addition amount Qa has a positive correlation with the pre-passage content CBx.

  The closed loop control CLC is a control for bringing the post-passage content CAx closer to the target content Ca by performing feedback on the post-passage content CAx. More specifically, the control is such that the addition amount Qr is adjusted to the second target addition amount Qb calculated so that the difference ΔC between the post-passage content CAx and the target content Ca is zero.

  The closed loop control CLC has map data in which a second target addition amount Qb based on the difference ΔC is set in advance, and the addition amount Qr becomes the second target addition amount Qb calculated based on the map data. The control which adjusts the reducing agent injection valve 24 can be illustrated. The second target addition amount Qb has a positive correlation with the difference ΔC.

  Hereinafter, the control method of the engine 10 will be described as a function of the control device 30 with reference to the flowchart of FIG. In addition, this control method shall be performed until it stops after the engine 10 starts.

  First, in step S10, the control device 30 acquires parameters (catalyst temperature Tx, space velocity Vx, pre-passage content CBx, post-passage content CAx). Specifically, the control device 30 acquires the detection value of the temperature sensor 32 as the catalyst temperature Tx. Further, the control device 30 acquires the calculated value calculated by the model prediction program as the space velocity Vx. Moreover, the control apparatus 30 acquires the detected value of the 1st NOx sensor 31 as content CBx before passage. Moreover, the control apparatus 30 acquires the detected value of the 2nd NOx sensor 33 as content CAx after passage.

  Next, in step S20, the control device 30 compares the obtained activation status (Tx, Vx) of the selective reduction catalyst 23 with the area map data 40, and the activation status of the selective reduction catalyst 23 is the first. It is determined whether or not the area 41 exists. If the activation state (Tx, Vx) of the selective reduction catalyst 23 is present in the first region 41 in step S20, that is, if the selective reduction catalyst 23 is activated, step S30 is performed. Proceed to On the other hand, when the activation state (Tx, Vx) of the selective reduction catalyst 23 exists in the second region 42, that is, when the selective reduction catalyst 23 is inactivated, the process proceeds to step S70. .

  Next, in step S30, the control device 30 calculates the first target addition amount Qa based on the pre-passage content CBx. Next, in step S40, the control device 30 adjusts the addition amount Qr to the first target addition amount Qa. Steps S30 and S40 are controls corresponding to the open loop control OLC.

  Next, in step S50, the control device 30 calculates the second target addition amount Qb based on the post-passage content CAx. Next, in step S60, the control device 30 adjusts the addition amount Qr to the second target addition amount Qb. Steps S50 and S60 are controls corresponding to the closed-loop control CLC.

  As described above, when it is determined in step S20 that the selective reduction catalyst 23 is activated, the control returns to the start when the addition amount Qr is adjusted by both the open loop control OLC and the closed loop control CLC.

  On the other hand, in step S70, the control device 30 calculates the first target addition amount Qa based on the pre-passage content CBx. Next, in step S80, the control device 30 adjusts the addition amount Qr to the first target addition amount Qa. Steps S70 and S80 correspond to the open loop control OLC.

  Thus, when it is determined in step S20 that the selective reduction catalyst 23 has been deactivated, the process returns to the start when the addition amount Qr is adjusted by the open loop control OLC.

  By performing the control as described above, the addition amount Qr of the reducing agent R1 is adjusted by the control of both the open-loop control OLC and the closed-loop control CLC according to the activation state in the selective reduction catalyst 23. By switching between the control and the control adjusted by the open loop control OLC, it is possible to avoid the excess and shortage of the addition amount Qr of the reducing agent R1.

That is, when the acquired catalyst temperature Tx and space velocity Vx are present in the first region 41 of the region map data 40, the addition amount Qr of the reducing agent R1 is adjusted by the control of both the open loop control OLC and the closed loop control CLC. By doing so, the purification rate of nitrogen oxides in the selective reduction catalyst 23 can be improved. On the other hand, when the acquired catalyst temperature Tx and space velocity Vx exist in the second region 42, the closed loop control CLC is prohibited, and the addition amount Qr of the reducing agent R1 is adjusted only by the open loop control OLC. The reducing agent R1 can be prevented from being discharged from the catalytic reduction catalyst 23.

  As described above, by switching the control for adjusting the addition amount Qr according to the activation state of the selective reduction catalyst 23, the selective reduction catalyst 23 is suppressed while suppressing the discharge of the reducing agent R1 from the selective reduction catalyst 23. The purification rate of nitrogen oxides in can be improved.

  In the above embodiment, the example in which the catalyst temperature Tx is acquired as the detection value of the temperature sensor 32 has been described. However, it can also be acquired as a calculated value using a model prediction program. For example, the temperature of the exhaust gas G1 exhausted from the cylinder 16 is predicted from the model based on the fuel injection amount and the engine speed, and further, the increase due to the oxidation reaction in the oxidation catalyst 21 and the collection filter 22 and the selective reduction catalyst 23 You may use the calculated value calculated by carrying out model prediction of the descent | fall until it reaches | attains.

  Moreover, although the example which acquires content CBx before passage as a detection value of the 1st NOx sensor 31 was demonstrated, it can also acquire as a calculation value using a model prediction program. For example, the NOx concentration of the exhaust gas G1 exhausted from the cylinder 16 is model-predicted from the fuel injection amount, the intake air amount detected by the intake air amount sensor 35, and the opening degree of the EGR valve 27. A calculated value calculated by model prediction of a change in the NOx concentration due to the oxidation reaction in the collection filter 22 may be used.

  In the engine 10, the control device 30 adds the first target addition amount Qa and the second target addition amount Qb to the addition amount Qr when the selective reduction catalyst 23 is activated. It is desirable to perform control to adjust to the addition amount Qc. More specifically, the control unit 38 of the control device 30 adds the calculated second target addition amount Qb to the calculated first target addition amount Qa to calculate the target addition amount Qc, and adds the addition amount. It is desirable that the program is configured by a program for adjusting Qr to the target addition amount Qc.

  FIG. 5 illustrates another form of the control method of FIG. Hereinafter, the control method of the engine 10 will be described as a function of the control device 30 with reference to the flowchart of FIG. In addition, in the step similar to FIG. 4, the description is abbreviate | omitted as using the same code | symbol.

  In this control method, when the control device 30 calculates the first target addition amount Qa based on the pre-passage content CBx in step S30, then, in step S40, the control device 30 uses the post-passage content CAx. The second target addition amount Qb is calculated. Next, in step S90, the controller 30 adds the first target addition amount Qa and the second target addition amount Qb to calculate the target addition amount Qc. Next, in step S100, the control device 30 adjusts the addition amount Qr to the target addition amount Qc.

  When the control as described above is performed, the number of times that the addition amount Qr is adjusted can be reduced. As a result, deterioration due to the operation of the reducing agent injection valve 24 can be suppressed while avoiding complicated control, which is advantageous in improving the durability of the reducing agent injection valve 24.

  In the first region 41, the activation state of the selective reduction catalyst 23 is different between the low temperature region side and the high temperature region side in the region. Therefore, if the same control is performed on the low temperature side and the high temperature side of the first region 41, the amount of the reducing agent R1 discharged from the selective reduction catalyst 23 increases on the low temperature side or on the high temperature side. There is a possibility that the purification rate in the selective reduction catalyst 23 may decrease.

  Therefore, in the engine 10 described above, the first region 41 is further divided into a plurality of regions 43, 44, 45, and each region 43, 44, 45 has different coefficients α1, α2, α3. It is desirable to be configured.

  FIG. 6 illustrates another form of the area map data 40. The first region 41 includes a third region 43, a fourth region 44, and a fifth region 45 in order from the low temperature region side to the high temperature region side. The third area 43 has a coefficient α1, the fourth area 44 has a coefficient α2, and the fifth area 45 has a coefficient α3. The coefficients α1, α2, and α3 are set to values that correct the second target addition amount Qb according to the activation state of the selective reduction catalyst 23, and are set to values that are greater than zero and less than or equal to 1. . Also, the coefficients α1, α2, and α3 are set to increase stepwise in this order. For example, the coefficient α1 is set to 0.3, the coefficient α2 is set to 0.5, and the coefficient α3 is set to 1.0.

  In the closed-loop control CLC, the control device 30 multiplies the value Qd calculated so as to make the difference ΔC between the post-passage content CAx and the target content Ca zero by a coefficient α1, α2, or α3. It is desirable to be configured to calculate the two target addition amount Qb.

  Hereinafter, the control method of the engine 10 will be described as a function of the control device 30. 4 and 5, the control device 30 determines that the activation state of the selective reduction catalyst 23 exists in the first region 41. Next, in a step (not shown), the control device 30 determines in which of the third region 43, the fourth region 44, and the fifth region 45 the activation state of the selective reduction catalyst 23 exists. . Next, in step S50 of FIG. 4 and FIG. 5, a value Qd that makes the difference ΔC between the added amount Qr and the post-passage content CAx and the target content Ca zero is calculated, and coefficients α1, α2, α3 are added to the value Qd. The second target addition amount Qb is calculated by multiplying any of the above.

  When such control is performed, the second target addition amount Qb obtained by correcting the value Qd based on the difference ΔC with any one of the coefficients α1, α2, and α3 is calculated. Can provide feedback according to Thereby, discharge | emission of the reducing agent R1 from the selective reduction catalyst 23 can be suppressed more, and the purification rate of the nitrogen oxide in the selective reduction catalyst 23 can be improved more.

  In this embodiment, the example in which the first region 41 is divided into the three regions of the third region 43, the fourth region 44, and the fifth region 45 has been described, but the number of divided regions is not particularly limited. . However, the second target addition amount Qb corresponding to the difference ΔC can be calculated with higher accuracy by dividing the first region 41 into more regions and assigning a coefficient that increases stepwise to each of the regions. it can.

10 Engine 20 Exhaust passage 21 Oxidation catalyst 23 Selective reduction catalyst 24 Reducing agent injection valve 30 Control device 41 First region 42 Second region G1 Exhaust gas CAx Content after passage CBx Content before passage CLC Closed loop control OLC Open loop control Qa First target addition amount Qb Second target addition amount Qr Addition amount R1 Reducing agent

Claims (7)

An oxidation catalyst and a selective reduction catalyst are provided in order from the upstream side to the downstream side of the exhaust passage through which exhaust gas from the cylinder of the internal combustion engine passes, and the reducing agent is exhausted upstream of the selective reduction catalyst. In an internal combustion engine comprising a reducing agent injection valve added to gas,
A control device that monitors the activation state of the selective reduction catalyst and performs control to adjust the amount of the reducing agent added to the exhaust gas from the reducing agent injection valve according to the activation state;
The control device is
In a situation where the selective reduction catalyst is activated, the first addition amount is calculated based on the nitrogen oxide content before passing through the exhaust gas before passing through the selective reduction catalyst. Open-loop control adjusted to the target addition amount, and the second target addition amount calculated based on the post-passage content of nitrogen oxides contained in the exhaust gas after passing through the selective reduction catalyst. While performing the control to adjust the addition amount by both the closed-loop control adjusted to
An internal combustion engine configured to perform control for adjusting the addition amount by the open loop control in a state where the selective reduction catalyst is inactivated. The activation state of the selective reduction catalyst is based on the catalyst temperature inside the selective reduction catalyst and the space velocity of the exhaust gas passing through the selective reduction catalyst,
The internal combustion engine according to claim 1, wherein the control device acquires the catalyst temperature and the space velocity. The control device has region map data based on the catalyst temperature inside the selective reduction catalyst acquired in advance and the space velocity of the exhaust gas passing through the selective reduction catalyst,
The area map data is arranged in the high temperature region side and shows the situation where the selective reduction catalyst is activated, and the situation where the selective reduction catalyst is inactivated in the low temperature region side. A second region indicating
The control device compares the acquired catalyst temperature and space velocity with the region map data, and the state of the selective reduction catalyst exists in the first region or in the second region. The internal combustion engine according to claim 1, wherein the internal combustion engine is configured to determine whether it exists. The first region is further divided into a plurality of regions, each region having a different coefficient from each other,
In the closed-loop control, the control device multiplies the value calculated so as to make the difference between the post-passage content and a preset target content zero, and the second target addition amount. The internal combustion engine according to claim 3, wherein the internal combustion engine is configured to calculate.   The internal combustion engine according to claim 4, wherein the coefficient increases stepwise from a low temperature region side toward a high temperature region side.   In the situation where the selective reduction catalyst is activated, the control device performs control to adjust the addition amount to a target addition amount obtained by adding the first target addition amount and the second target addition amount. The internal combustion engine according to any one of claims 1 to 5, wherein the internal combustion engine is configured to perform. In an internal combustion engine control method in which an oxidation catalyst, a reducing agent injection valve, and a selective reduction catalyst are arranged in an exhaust passage through which exhaust gas from a cylinder of the internal combustion engine passes,
The activation state of the selective reduction catalyst, the content of nitrogen oxides contained in the exhaust gas before passing through the selective reduction catalyst, and the exhaust gas after passing through the selective reduction catalyst Obtaining a post-passage content of nitrogen oxide;
Determining whether the acquired activation state of the selective reduction catalyst is a state in which the selective reduction catalyst is activated; and
When it is determined that the selective reduction catalyst is activated, the addition amount of the reducing agent added to the exhaust gas from the reducing agent injection valve is determined based on the pre-passage content. Adjusted by both the open loop control adjusted to the calculated first target addition amount and the closed loop control adjusted to the second target addition amount calculated based on the post-passage content. And steps to
And a step of adjusting the amount of addition only by the open loop control when it is determined that the selective reduction catalyst is in an inactivated state.