JP5837319B2 - 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. More specifically, the present invention relates to an exhaust gas purification system including a selective reduction catalyst that reduces NOx in exhaust gas in the presence of a reducing agent such as ammonia (NH ₃ ).

  Conventionally, as an exhaust purification system for purifying NOx in exhaust, a system in which a selective reduction catalyst for selectively reducing NOx in exhaust with a reducing agent such as ammonia is provided in an exhaust passage has been proposed. For example, in a urea addition type exhaust purification system, urea water, which is a precursor of ammonia, is supplied from the upstream side of the selective reduction catalyst, and ammonia is generated from the urea water by thermal decomposition or hydrolysis with the heat of exhaust gas. This ammonia selectively reduces NOx in the exhaust gas. In addition to such a urea addition type system, for example, a system in which ammonia is generated by heating an ammonia compound such as ammonia carbide and this ammonia is directly added has also been proposed. Hereinafter, a urea addition type system will be described.

  Such a selective reduction catalyst has an ability to adsorb ammonia that has not been used to reduce NOx in the exhaust gas. That is, when the amount of urea water supplied is larger than the amount of NOx flowing into the selective reduction catalyst, the excess ammonia that is not used for NOx reduction is adsorbed by the selective reduction catalyst, and conversely flows into the selective reduction catalyst. When the supply amount of urea water is smaller than the NOx amount, ammonia adsorbed on the selective reduction catalyst is used for NOx reduction. Therefore, the adsorption amount of ammonia in the selective reduction catalyst can be controlled by increasing / decreasing the supply amount of urea water.

  From the viewpoint of NOx purification, it is preferable that as much ammonia as possible be adsorbed on the selective reduction catalyst, but the amount of ammonia that can be adsorbed by the selective reduction catalyst is limited. If ammonia exceeding this limit amount is supplied to the selective reduction catalyst, ammonia that cannot be adsorbed will be discharged downstream.

  Patent Document 1 discloses a slip suppression control procedure for suppressing ammonia slip in such a selective reduction catalyst. Specifically, when the estimated rate of change in the temperature of the selective reduction catalyst is large, the supply of new urea water is stopped in anticipation of a decrease in the ammonia adsorption capacity of the selective reduction catalyst, and the adsorbed ammonia Increases NOx emissions from internal combustion engines in anticipation of being released soon. In Patent Document 1, it is assumed that an oxidation catalyst for oxidizing the slipped ammonia is provided on the downstream side of the selective reduction catalyst. When such an oxidation catalyst is provided, it is assumed that ammonia slipped from the selective reduction catalyst is oxidized by the oxidation catalyst, and the increase in the NOx emission amount when the temperature change rate increases. It has been shown to reduce.

Japanese Patent No. 4542455

  As described above, in the slip suppression control of Patent Document 1, it is possible to suppress ammonia slip in the selective reduction catalyst as much as possible by further increasing the NOx emission amount in accordance with stopping the supply of urea water. Since the adsorption amount of ammonia of the selective reduction catalyst after returning from the slip suppression control is excessively reduced, it is considered that the NOx purification performance of the selective reduction catalyst is also greatly reduced.

  In addition, if ammonia is oxidized by the most downstream oxidation catalyst, the supplied urea water is not wasted without contributing to the purification of NOx, and NOx is generated along with the oxidation of ammonia. This results in deterioration of the NOx purification performance. As described above, although it can be said that the slip suppression control of Patent Document 1 is excellent in terms of suppressing ammonia slip, sufficient studies have not been made on the NOx purification performance and the fuel consumption of the reducing agent.

  The present invention relates to an exhaust gas purification system for an internal combustion engine that can suppress the reducing agent slip from the selective reduction catalyst without deteriorating the NOx purification performance or wastefully using the reducing agent in an exhaust gas purification system equipped with a selective reduction catalyst. The purpose is to provide a system.

In order to achieve the above object, the present invention is provided in an exhaust passage (for example, an exhaust pipe 11 to be described later) of an internal combustion engine (for example, an engine 1 to be described later), and in the presence of a reducing agent (for example, NH _{3 to be} described later). A first selective reduction catalyst (for example, a first selective reduction catalyst 231 described later) that purifies NOx in the exhaust gas and adsorbs the reducing agent, and a downstream side of the first selective reduction catalyst in the exhaust passage. A second selective reduction catalyst (for example, a second selective reduction catalyst 232 described later) and a reducing agent or a precursor thereof (for example, a later-described urea water) upstream of the first selective reduction catalyst in the exhaust passage. An exhaust gas purification system for an internal combustion engine (for example, an exhaust gas purification system 2 to be described later) provided with a reducing agent supply means for supplying (for example, a urea injection device 25 to be described later). The exhaust purification system is configured to determine whether or not the first selective reduction catalyst is in a temperature rising state based on the operating state of the internal combustion engine (for example, ECU 3 described later and S21 in FIG. 14). And the supply amount of the reducing agent or the precursor from the reducing agent supply means is set to a limit supply amount larger than 0 (when the temperature increase determination means determines that the temperature increase state is present). GREEA_ORD-ΔST, GUREA_ORD × 0.5, GUREA_ORD × 0.3) reducing agent restriction control (for example, control shown in S43, S46, and S47 in FIG. 16 described later), and NOx emission amount of the internal combustion engine Slip suppression control means (for example, rear control) that executes NOx emission amount increase control (for example, control shown in S49 in FIG. The ECU 3, and a means) according to the execution of the flowchart shown in FIG. 16, characterized in that it comprises a.

According to the present invention, when it is determined by the temperature increase determination means that the temperature is rising, the reducing agent restriction control is executed to reduce the supply amount of the reducing agent or the precursor to a predetermined restricted supply amount. Thereby, it is possible to prevent the newly supplied reducing agent from being discharged without being adsorbed by the first and second selective reduction catalysts. In addition to such reducing agent restriction control, NOx emission increase control for increasing the NOx emission of the internal combustion engine from that during normal control is executed. Thereby, it is possible to prevent the reducing agent adsorbed on the first and second selective reduction catalysts from being discharged without being consumed for the reduction of NOx.
In the present invention, since the second selective reduction catalyst is provided on the downstream side of the first selective reduction catalyst, the reducing agent discharged from the first selective reduction catalyst is adsorbed, and further, the adsorbed reducing agent in the exhaust NOx can be reduced. Therefore, compared with the case where the oxidation catalyst is provided on the downstream side of the first selective reduction catalyst, the NOx purification performance of the exhaust purification system as a whole is maintained high and wasteful consumption of the reducing agent or precursor is suppressed. You can also.
As described above, in the present invention, the second selective reduction catalyst is provided on the downstream side of the first selective reduction catalyst, so that a system that does not waste the supplied reducing agent is constructed, and then the reducing agent restriction control is performed. Then, the reducing agent or precursor is continuously supplied without reducing the supply amount to zero. As a result, the amount of the reducing agent adsorbed on the first and second selective reduction catalysts when returning to the normal control after executing the reducing agent restriction control and the NOx emission increase control can be secured to some extent. . Thereby, it is possible to suppress a significant decrease in the NOx purification performance at the time of return.

  In this case, the exhaust purification system includes inflow NOx amount acquisition means (for example, a NOx sensor 28 and a unit converter 654 described later) for detecting or estimating the amount of NOx that has flowed into the first selective reduction catalyst, and the internal combustion engine. A first purification rate estimating means (for example, a NOx purification rate calculation unit 651b described later) for estimating a NOx purification rate in the first selective reduction catalyst based on an operating state, and purifies NOx flowing into the first selective reduction catalyst. Therefore, the reducing agent consumption corresponding to the amount of reducing agent consumed in the first selective reduction catalyst is converted into the estimated NOx purification rate (η1st) and the detected or estimated NOx amount (QNOx). Reducing agent consumption estimation means (e.g., a consumption rate calculation unit 65 to be described later) estimated based on the temperature acquisition means (e.g., the temperature of the first selective reduction catalyst) , An exhaust gas temperature sensor 27 and an ECU 3 described later) and a first adsorption allowable amount for estimating the reducing agent adsorption allowable amount (ST1st_max) in the first selective reduction catalyst based on the detected or estimated temperature (TSCR). A slip amount for estimating a reducing agent slip amount from the first selective reduction catalyst based on estimation means (for example, a catalyst temperature base calculation unit 642 described later) and the estimated adsorption allowable amount of the first selective reduction catalyst. Estimation means (for example, slip speed calculation unit 64 described later), and the slip suppression control means is configured such that the estimated reducing agent slip amount (V_SLIP) is greater than the estimated reducing agent consumption amount (V_RED). When the amount is large (V_SLIP> V_RED), the NOx emission amount increase control is executed, and the estimated reducing agent slip amount is the estimated return amount. When the amount is less than the base agent consumption, it is preferable not to execute the NOx emission increase control.

  In the present invention, when the estimated amount of reducing agent slip from the first selective reduction catalyst is larger than the estimated amount of reducing agent consumed in the first selective reduction catalyst, the reduction that slips to the second selective reduction catalyst. NOx emission increase control is executed to consume the agent. When the reducing agent slip amount is smaller than the reducing agent consumption amount, it is determined that the reducing agent slip can be suppressed without increasing the NOx emission amount, and the NOx emission amount increase control is not executed. In this way, by determining execution of the NOx emission increase control based on the estimated reducing agent slip amount and reducing agent consumption amount, the NOx emission amount is increased more than necessary, and the reducing agent is wasted. It is possible to suppress consumption.

In this case, the exhaust purification system includes inflow NOx amount acquisition means (for example, a NOx sensor 28 and a unit converter 654 described later) for detecting or estimating the amount of NOx that has flowed into the first selective reduction catalyst, and the internal combustion engine. A first purification rate estimating means (for example, a NOx purification rate calculation unit 651b described later) for estimating a NOx purification rate in the first selective reduction catalyst based on an operating state, and purifies NOx flowing into the first selective reduction catalyst. Therefore, the reducing agent consumption corresponding to the amount of reducing agent consumed in the first selective reduction catalyst is converted into the estimated NOx purification rate (η1st) and the detected or estimated NOx amount (QNOx). Reducing agent consumption estimating means (e.g., a consumption rate calculating unit 65 described later) that estimates based on the reducing agent for exhaust between the first selective reduction catalyst and the second selective reduction catalyst A reducing agent detecting means for detecting the degree (for example, NH3 sensor 26 described later) and a slip amount for estimating a reducing agent slip amount from the first selective reduction catalyst based on the detected reducing agent concentration (VNH3). Estimation means (for example, NH ₃ sensor base calculation unit 641 and slip speed calculation unit 64 described later), and the slip suppression control unit is configured to estimate the estimated reducing agent slip amount (V_SLIP). When the amount of reducing agent consumption (V_RED) is larger (V_SLIP> V_RED), the NOx emission amount increase control is executed. When the estimated amount of reducing agent slip is smaller than the estimated amount of reducing agent consumption, It is preferable not to execute the NOx emission increase control.

  In the present invention, the NOx emission increase control is determined based on the estimated reducing agent slip amount and reducing agent consumption amount, so that the NOx emission amount is increased more than necessary as described above. It is possible to suppress the wasteful consumption of the agent. In particular, in the present invention, the reducing agent slip amount from the first selective reduction catalyst is reduced by using the reducing agent detection means for detecting the reducing agent concentration of the exhaust gas between the first selective reduction catalyst and the second selective reduction catalyst. It can be estimated with higher accuracy.

  In this case, the exhaust gas purification system recirculates a part of the exhaust gas flowing through the exhaust passage as EGR gas to an intake passage (for example, an intake pipe 12 described later) of the internal combustion engine (for example, an EGR described later). A pipe 18) and an EGR valve (for example, an EGR valve 19 described later) provided in the EGR passage for controlling the amount of EGR gas. In the NOx emission increase control, the opening degree of the EGR valve is controlled. The NOx emission amount is increased by correcting the opening degree (VO_ORD) at the normal control to the closing side, and the slip suppression control means is configured to reduce the estimated reducing agent slip amount (V_SLIP) and the estimated reducing agent consumption. It is preferable to determine a correction amount from the opening degree during normal control of the opening degree of the EGR valve based on a deviation from the amount (V_RED).

  In the present invention, the NOx emission amount is increased by correcting the opening degree of the EGR valve to the closed side. The EGR valve has good responsiveness, and can quickly increase the NOx emission amount without greatly impairing drivability. Further, by determining the correction amount from the normal control of the opening degree of the EGR valve based on the deviation between the estimated reducing agent slip amount and reducing agent consumption amount, an appropriate amount corresponding to the slipping amount is determined. Since NOx can be increased, wasteful consumption of the reducing agent can be suppressed while suppressing slippage of the reducing agent.

In this case, the exhaust purification system includes second storage amount estimation means (e.g., an ECU 3 and an NH ₃ sensor described later) for estimating the storage amount of the reducing agent in the second selective reduction catalyst based on the operating state of the internal combustion engine. 26) and target value setting means (for example, ECU 3 to be described later) for setting a target value for the estimated value of the storage amount of the second selective reduction catalyst based on the operating state of the internal combustion engine, When the estimated value of the storage amount of the second selective reduction catalyst is less than or equal to the target value (ST2nd ≦ ST2nd_TRGT), the suppression control means does not execute the NOx emission amount increase control, and the second selective reduction catalyst When the estimated value of the storage amount is larger than the target value (ST2nd> ST2nd_TRGT), the NOx emission amount increase control is executed. It is preferable to do.

  In the present invention, when the estimated value of the storage amount of the second selective reduction catalyst is equal to or less than the target value, it is determined that the second selective reduction catalyst has a margin for adsorbing the reducing agent, and the NOx emission amount increase control is performed. Do not execute. Further, when the estimated value of the storage amount of the second selective reduction catalyst is larger than the target value, it is determined that the second selective reduction catalyst has no room for adsorbing the reducing agent, and therefore slips from the first selective reduction catalyst. NOx emission increase control is executed so that the reducing agent to be consumed is consumed by the increased NOx. Thereby, it is possible to suppress the amount of NOx discharged from the internal combustion engine from being increased more than necessary, and wasteful consumption of the reducing agent. In addition, this makes it possible to bring the storage amount of the second selective reduction catalyst close to its target, so that the NOx purification performance can be kept high.

In this case, the exhaust gas purification system is configured to estimate a storage amount of the reducing agent in the second selective reduction catalyst based on an operating state of the internal combustion engine (for example, ECU 3 and NH ₃ described later). Sensor 26) and second adsorption allowance estimation means (for example, ECU 3 and NH ₃ sensor 26, which will be described later) for estimating the allowance of adsorption of the reducing agent on the second selective reduction catalyst based on the operating state of the internal combustion engine. And the slip suppression control means estimates the storage amount when the estimated value of the storage amount of the second selective reduction catalyst is smaller than the estimated value of the allowable adsorption amount (ST2nd <ST2nd_max). It is preferable to increase the limit supply amount as compared with the case where the value is equal to or greater than the estimated value of the allowable adsorption amount (ST2nd ≧ ST2nd_max). Arbitrariness.

  In the present invention, when the estimated value of the storage amount of the second selective reduction catalyst is smaller than the estimated value of the adsorption allowable amount, it is determined that the second selective reduction catalyst has a margin for adsorbing the reducing agent, and the limited supply amount, That is, the supply amount of the reducing agent or the precursor during the execution of the reducing agent restriction control is increased as compared with the case where the estimated storage amount is equal to or larger than the estimated adsorption allowable amount. Thereby, since the storage amount of the 1st, 2nd selective reduction catalyst when it returns from execution of reducing agent restriction | limiting control can fully be ensured, the fall of each NOx purification performance can be suppressed.

  In this case, the exhaust purification system further includes acceleration determination means (for example, means related to execution of S31 in FIG. 15 described later) for determining that the internal combustion engine has shifted to the acceleration operation state, and the slip suppression control means. When the acceleration determination means determines that the acceleration operation state has been entered, it is preferable to delay the start of execution of the reducing agent restriction control and the NOx emission increase control.

When the internal combustion engine shifts to the acceleration operation state, first, the NOx emission amount from the internal combustion engine increases, and then the temperature of the first and second selective reduction catalysts rises. In the present invention, in order to start execution of the reducing agent restriction control and the NOx emission increase control as the temperature of the first and second selective reduction catalysts increases, these reductions are performed for a predetermined time after shifting to the acceleration operation state. The execution start of the agent restriction control and the NOx emission increase control is delayed. Thereby, the fall of each NOx purification performance can be suppressed, suppressing the slip of the reducing agent from a 1st, 2nd selective reduction catalyst.
Further, for example, when the supply amount of the reducing agent or precursor is controlled based on the detected value of the NOx sensor that detects NOx in the exhaust gas, particularly immediately after shifting to the acceleration operation state, the reducing agent or precursor is delayed by the delay of the NOx sensor. The supply amount of the body is insufficient, and the NOx purification performance of the selective reduction catalyst tends to temporarily decrease. In the present invention, the NOx purification performance is prevented from further deteriorating by delaying the execution of the reducing agent restriction control and the NOx emission increase control as the internal combustion engine shifts to the acceleration operation state. Can do.

In this case, the exhaust purification system further includes a reducing agent concentration detecting means (for example, NH ₃ sensor 26 described later) for detecting the reducing agent concentration of the exhaust gas between the first selective reduction catalyst and the second selective reduction catalyst. The slip suppression control means executes the reducing agent restriction control and does not execute the NOx emission increase control when the output value of the reducing agent concentration detecting means is smaller than a predetermined value (VNH3 ≧ VNH3_th). It is preferable.

  In the present invention, when the output value of the reducing agent concentration detecting means is smaller than the predetermined value, the amount of reducing agent slipping from the first selective reduction catalyst to the second selective reduction catalyst is small, and the NOx emission amount increase control is executed. At least, it is determined that the reducing agent can be prevented from slipping from the second selective reduction catalyst, and only the reducing agent restriction control is executed. As a result, it is possible to prevent the amount of NOx emission from being increased more than necessary, and wasteful consumption of the reducing agent. In addition, this makes it possible to sufficiently secure the storage amounts of the first and second selective reduction catalysts when returning from the execution of the reducing agent restriction control, so that it is possible to suppress a decrease in the respective NOx purification performance.

It is a mimetic diagram showing composition of an engine and its exhaust gas purification system concerning one embodiment of the present invention. It is a block diagram which shows the structure of the catalyst temperature estimation part which concerns on the said embodiment. It is a flowchart which shows the procedure which estimates the value of an engine torque. It is a time chart for demonstrating the procedure which estimates the value of an engine torque. It is a time chart for demonstrating the procedure which estimates the value of an engine torque. It is a block diagram which concerns on determination of the urea injection quantity by the urea injection apparatus which concerns on the said embodiment. It is a block diagram which shows the structure of the normal injection amount calculation part which concerns on the said embodiment. It is a block diagram which shows the structure of the slip suppression correction amount calculation part which concerns on the said embodiment. It is a figure which shows typically the estimated storage capacity | capacitance difference calculated in a slip suppression correction amount calculation part. It is a block diagram concerning the determination of the EGR valve opening for controlling the fresh air amount of the engine to a predetermined target fresh air amount. It is a block diagram which shows the structure of the slip speed calculation part which concerns on the said embodiment. It is a block diagram which shows the structure of the consumption speed calculation part which concerns on the said embodiment. It is a flowchart which shows the specific procedure of urea injection control and intake control which concern on the said embodiment. It is a flowchart which shows the procedure which updates the slip suppression flag which concerns on the said embodiment. It is a flowchart which shows the procedure which updates the delay flag at the time of acceleration which concerns on the said embodiment. It is a flowchart which shows the specific procedure of the slip suppression control which concerns on the said embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing a configuration of an internal combustion engine (hereinafter referred to as “engine”) 1 and an exhaust purification system 2 thereof according to an embodiment of the present invention. The engine 1 is a lean burn operation type gasoline engine or diesel engine, and is mounted on a vehicle (not shown).

The exhaust purification system 2 is provided in an oxidation catalyst 21 provided in the exhaust pipe 11 of the engine 1, a DPF 22 provided in the exhaust pipe 11 as a filter for collecting PM in the exhaust, and provided in the exhaust pipe 11. A urea selective reduction catalyst 23 that purifies nitrogen oxide (NOx) in the exhaust gas flowing through the exhaust pipe 11 in the presence of ammonia (NH ₃ ) as a reducing agent, and upstream of the urea selective reduction catalyst 23 in the exhaust pipe 11. On the side, a urea injection device 25 for supplying urea water, which is a precursor of ammonia, an EGR device 17 for recirculating a part of the exhaust gas flowing through the exhaust pipe 11 into the intake pipe 12 as EGR gas, and an electronic control unit ( (Hereinafter referred to as “ECU”) 3.

  The EGR device 17 includes an EGR pipe 18 that communicates the upstream side of the oxidation catalyst 21 in the exhaust pipe 11 and the intake pipe 12, and an EGR valve 19 that is provided in the EGR pipe 18 and controls the amount of EGR gas. Composed. The EGR valve 19 is connected to the ECU 3, operates according to a control signal from the ECU 3, and in response to this control signal, the flow rate of exhaust gas recirculated into the intake pipe 12 via the EGR pipe 18, and thus the new engine 1. Control your volume.

The urea injection device 25 includes a urea tank 251 and a urea injection valve 253.
The urea tank 251 stores urea water, and is connected to the urea injection valve 253 via a urea supply path 254 and a urea pump (not shown). This urea tank 251 is provided with a urea level sensor 255. The urea level sensor 255 detects the water level of the urea water in the urea tank 251 and outputs a detection signal substantially proportional to the water level to the ECU 3. The urea injection valve 253 is connected to the ECU 3, operates in accordance with a control signal from the ECU 3, and injects urea water into the exhaust pipe 11 in accordance with this control signal.

The oxidation catalyst 21 is provided on the upstream side of the DPF 22 in the exhaust pipe 11 and oxidizes NO in the exhaust to convert it to NO ₂ , thereby promoting NOx reduction in the urea selective reduction catalyst 23.
The DPF 22 is provided on the downstream side of the oxidation catalyst 21 in the exhaust pipe 11, and when the exhaust gas passes through fine holes in the filter wall, the PM mainly containing carbon in the exhaust gas is converted into the surface of the filter wall and the filter. Collect by depositing in holes in the wall.

The urea selective reduction catalyst 23 includes a first selective reduction catalyst 231 and a second selective reduction catalyst 232 provided downstream of the first selective reduction catalyst 231 in the exhaust pipe 11. Each of these selective reduction catalysts 231 and 232 selectively reduces NOx in the exhaust in an atmosphere in which a reducing agent such as NH ₃ exists. Specifically, when urea water is injected by the urea injection device 25, the urea water is thermally decomposed or hydrolyzed by the heat of the exhaust to generate NH ₃ as a reducing agent. The produced NH ₃ is supplied to the selective reduction catalysts 231 and 232, and NOx in the exhaust is selectively reduced by these NH ₃ .

By the way, these selective reduction catalysts 231 and 232 have a function of reducing NOx in the exhaust with NH ₃ generated from urea water, and also have a function of adsorbing the generated NH ₃ by a predetermined amount. In the present embodiment, the amount of NH ₃ adsorbed by the selective reduction catalysts 231 and 232 is referred to as a storage amount, and the limit of the storage amount is referred to as a maximum storage capacity. The NH ₃ adsorbed in this way is also consumed as appropriate for the reduction of NOx in the exhaust gas. For this reason, as the storage amount increases, the NOx purification rate in the selective reduction catalyst increases. Further, when the supply amount of urea water is small with respect to the amount of NOx discharged from the engine, the adsorbed NH ₃ is consumed for the reduction of NOx so as to compensate for the shortage of urea water. Here, when the selective reduction catalysts 231 and 232 generate NH ₃ exceeding the maximum storage capacity, the generated NH ₃ is discharged downstream of the selective reduction catalysts 231 and 232.

The ECU 3 is connected to an NH ₃ sensor 26, an exhaust temperature sensor 27, a NOx sensor 28, an air flow meter 29, a crank angle position sensor 14, an accelerator opening sensor 15, and the like.

The NH ₃ sensor 26 detects the NH ₃ concentration of the exhaust gas between the first selective reduction catalyst 231 and the second selective reduction catalyst 232 in the exhaust pipe 11, and supplies a detection signal VNH3 substantially proportional to the detected value to the ECU 3. To do. The exhaust gas temperature sensor 27 detects the temperature of the exhaust gas downstream of the second selective reduction catalyst 232 and supplies a detection signal TGAS substantially proportional to the detected value to the ECU 3. The NOx sensor 28 detects the NOx concentration of the exhaust gas flowing into the first selective reduction catalyst 231 and supplies the ECU 3 with a detection signal VNOx that is substantially proportional to the detected value. The air flow meter 29 detects the amount of intake air flowing through an intake passage (not shown) and supplies a detection signal substantially proportional to the detected value to the ECU 3.

  The crank angle position sensor 14 detects the rotation angle of the crankshaft of the engine 1, generates a pulse for each predetermined crank angle, and supplies the pulse signal to the ECU 3. The engine speed NE of the engine 1 is calculated by the ECU 3 based on this pulse signal. The accelerator opening sensor 15 detects a depression amount (hereinafter referred to as “accelerator opening”) of an accelerator pedal (not shown) of the vehicle, and supplies a detection signal AP substantially proportional to the detected value to the ECU 3. In the ECU 3, a driver request torque TRQ is calculated according to the accelerator opening AP and the engine speed NE.

  The current temperature of each part in the exhaust pipe 11, such as the temperature TDOC of the oxidation catalyst 21 and the temperature TSCR of the first selective reduction catalyst, is based on inputs such as the exhaust temperature TGAS, the engine speed NE, and the intake air amount QA, for example. Thus, it is estimated by processing not shown in the ECU 3. Further, the exhaust gas flow rate Gex is estimated by processing not shown in the ECU 3 based on the output of the air flow meter 29, the engine speed NE, and the like that are substantially proportional to the intake air amount.

  The ECU 3 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter “ CPU ”). In addition, the ECU 3 includes a storage circuit that stores various calculation programs executed by the CPU, calculation results, and the like, and an output circuit that outputs control signals to the engine 1, the urea injection valve 253, the EGR valve 19, and the like.

  Hereinafter, the ECU 3 includes a catalyst temperature prediction unit 4 related to exhaust system temperature prediction, a urea injection control unit 5 related to urea water injection control, and an intake control unit 6 related to intake system control. Will be described in order.

[Catalyst temperature prediction unit 4]
The configuration of the catalyst temperature predicting unit 4 will be described with reference to FIGS.
FIG. 2 is a block diagram showing a configuration of the catalyst temperature prediction unit 4.
The catalyst temperature prediction unit 4 estimates a future temperature of the first selective reduction catalyst 231, more specifically, a predicted catalyst temperature TSCR_PRE that is a temperature value of the selective reduction catalyst 231 after a predetermined prediction time T_PRE from the present time.

The catalyst temperature prediction unit 4 includes an operation pattern prediction unit 41 and a heat conduction model calculation unit 42.
The driving pattern prediction unit 41 is based on the current values of parameters relating to the driving state of the vehicle, such as engine speed, vehicle speed, and driver request torque (hereinafter, these parameters are collectively referred to as “driving state parameters”). With respect to the generated torque of the engine (hereinafter referred to as “engine torque”) as an internal combustion engine parameter that directly correlates with the exhaust temperature of the engine port, a value from the present to the predicted time T_PRE is estimated.

FIG. 3 is a flowchart showing a procedure for predicting the value of the engine torque. The process shown in this flowchart is executed by the driving pattern prediction unit 41 (see FIG. 2).
4 and 5 are time charts for explaining the procedure for predicting the value of the engine torque. In the examples shown in FIGS. 4 and 5, the current time is T ₀ , the times T ₋₁ , T ₋₂ , and T ₋₃ are past times, and the times T ₁ , T ₂ , T ₃ ,..., T _N−1 , T _N are set as future times. Therefore, the value indicated by the solid line before time T ₀ is the actual value, and the value indicated by the broken line after time T ₀ is the predicted value by the driving pattern prediction unit.
In this embodiment, as indicated by white circles in FIGS. 4 and 5, the time from the present to the predicted time T_PRE is divided into N, and the value at each time is estimated. That is, the TRQ_PRE_0 the current value of the engine torque, and TRQ_PRE_i the predicted value of the engine torque at time _{T i} later than the current.

  First, in S1, the current value TRQ_PRE_0 of the engine torque is estimated based on the current value of the operating state parameter, and the process proceeds to S2.

  In S2, it is determined whether or not the current engine is in a high-load operation state, more specifically, whether or not the current value TRQ_PRE_0 of the engine torque estimated in S1 is greater than a predetermined threshold value TRQ_TH for the engine torque value. If this determination is NO, the process moves to S3, and if this determination is YES, the process moves to S4. The threshold value TRQ_TH for determining whether or not the engine is in a high load operation state is sequentially set by a process (not shown) according to the value of the operation state parameter.

In S3, it is estimated that the engine torque value does not change from the current value TRQ_PRE_0 until after the predicted time T_PRE in response to the determination that the current engine is not in the high load operation state in S2. That is, as shown in the following equation, it is estimated that the predicted engine torque values TRQ_PRE_1,..., TRQ_PRE_N are all equal to the current value TRQ_PRE_0 (see FIG. 4).
TRQ_PRE_i = TRQ_PRE_0 (i = 1,..., N)

  On the other hand, after S4, in response to the determination that the current engine is in a high-load operation state in S2, the engine torque value is decreased from the current value TRQ_PRE_0 from the present to the predicted time T_PRE. Estimate (see FIG. 5). This is generally the case when the engine is operated to maintain a high engine torque value or continue to increase for a long period of time, so that the current engine is in a high-load operating condition. This is because it can be determined that there is a high possibility that the engine torque value will subsequently decrease so as to converge to a value smaller than the current value that allows continuous operation.

More specifically, first, in S4, a torque convergence value TRQ_CNV that is a value predicted to converge the engine torque value is estimated, and the process proceeds to S5. This torque convergence value TRQ_CNV is calculated, for example, by searching a map (not shown) based on the current value of the operation state parameter.
In S5, a convergence time T_CNV that is a time from the present until the engine torque value converges to the torque convergence value TRQ_CNV is estimated, and the process proceeds to S6. This convergence time T_CNV is calculated, for example, by searching a map (not shown) based on the current value of the operating state parameter.

  In S6, the current value TRQ_PRE_0 of the engine torque and the torque convergence value TRQ_CNV that is the value after the convergence time T_CNV are interpolated in a predetermined decreasing manner as indicated by the broken line in FIG. , TRQ_PRE_N is estimated. At this time, the reduction mode for interpolating between the current value TRQ_PRE_0 of the engine torque and the torque convergence value TRQ_CNV is set based on the current value of the driving state parameter, for example.

  Returning to FIG. 2, the heat conduction model calculation unit 42 determines the first selective reduction catalyst 231 after the predicted time T_PRE from the present time based on a predetermined heat conduction model of the exhaust system in which the engine 1 and its exhaust are regarded as heat sources. The estimated catalyst temperature TSCR_PRE, which is the temperature, is estimated. More specifically, the exhaust temperature of the port portion of the engine 1 is predicted based on the values TRQ_PRE_0,..., TRQ_PRE_N from the current engine torque estimated by the operation pattern predicting unit 41 to the time after the predicted time T_PRE. The predicted value of the exhaust gas temperature until after the predicted time T_PRE is input, and the predicted catalyst temperature TSCR_PRE after the predicted time T_PRE is estimated from the present time by the heat conduction model. As the heat conduction model, for example, an exhaust system model formulated according to Newton's cooling law as described in Japanese Patent Application Laid-Open No. 2006-250945 and Japanese Patent No. 4373909 by the applicant of the present application, etc. Conventionally known ones are used.

[Yurea injection control unit 5]
With reference to FIGS. 6-8, the structure of the urea injection control part 5 is demonstrated.
FIG. 6 is a block diagram relating to determination of the urea injection amount GUREA by the urea injection device. The urea injection control unit 5 includes a normal injection amount calculation unit 51 that calculates a normal injection amount GUREA_ORD, a slip suppression correction amount calculation unit 55 that calculates a slip suppression correction amount ΔST, and a normal injection amount GUREA_ORD corresponding to the slip suppression correction amount ΔST. Is configured to include a slip suppression correction unit 58 that corrects the above, a limited injection amount calculation unit 56 that calculates the limited injection amount GUREA_LIM, and an injection amount selector 57 that determines the urea injection amount GUREA. As shown in FIG. 6, the urea injection control unit 5 of the present embodiment is roughly divided into the normal injection amount GUREA_ORD, the normal injection amount GUREA_ORD corrected by the slip suppression correction amount ΔST, and the limited injection amount GUREA_LIM. Is determined as the final urea injection amount GUREA. Hereinafter, the configurations of the normal injection amount calculation unit 51, the slip suppression correction amount calculation unit 55, the slip suppression correction unit 58, the limited injection amount calculation unit 56, and the injection amount selector 57 will be described in order.

FIG. 7 is a block diagram illustrating a configuration of the normal injection amount calculation unit 51.
The normal injection amount calculation unit 51 includes a feedback controller 52, a base injection amount calculation unit 53, and a storage correction input calculation unit 54.
In the normal injection amount calculation unit 51, as shown in the following equation (1), the base injection amount GUREA_BS calculated by the base injection amount calculation unit 53, the feedback injection amount GUREA_FB calculated by the feedback controller 52, and storage correction The normal injection amount GUREA_ORD is determined by adding the corrected injection amount GUREA_ST calculated by the input calculation unit 54.

  Here, the symbol (k) is a symbol indicating the discretized time, and indicates that the data is detected or calculated every predetermined control period. That is, when the symbol (k) is data detected or calculated at the current control timing, the symbol (k-1) indicates data detected or calculated at the previous control timing. In the following description, the symbol (k) is omitted as appropriate.

The feedback controller 52 includes a target ammonia concentration setting unit 521 and a sliding mode controller 522.
The target ammonia concentration setting unit 521 sets a target value VNH3_TRGT of the detection value VNH3 of the NH ₃ sensor. More specifically, the target value VNH3_TRGT is set to a value slightly larger than “0”.
The sliding mode controller 522 calculates the FB injection amount GUREA_FB so that the detection value VNH3 of the NH ₃ sensor converges to the set target value VNH3_TRGT.

  The base injection amount calculation unit 53 calculates the base injection amount GUREA_BS based on the engine speed NE and the driver request torque TRQ so that NOx discharged from the engine is purified by the first and second selective reduction catalysts. That is, the base injection amount GUREA_BS corresponds to the urea water injection amount calculated so that the equivalence ratio α is “1”.

Here, the equivalent ratio α of urea water refers to the inflow amount of urea water per unit time (including the amount that flows in as NH ₃ ) and the inflow amount of NOx per unit time for the target selective reduction catalyst. This ratio (urea water inflow amount / NOx inflow amount) is equal to (1) when the amount of urea water that can reduce NOx without excess or deficiency flows into the inflowing NOx. That is, when the amount of urea water necessary for reducing the inflowing NOx is not supplied to the NOx flowing into the target selective reduction catalyst, the equivalence ratio α becomes smaller than “1” and flows in. When more urea water than the amount necessary for reducing NOx is supplied, the equivalent ratio α becomes a value larger than “1”.

  The storage correction input calculation unit 54 estimates the storage amount of the first selective reduction catalyst, and calculates the correction injection amount GUREA_ST so that the estimated first storage amount converges to a predetermined target storage amount. Further, the storage correction input calculation unit 54 estimates the maximum storage capacity of the first selective reduction catalyst that changes according to the temperature, and is a value that is the same as or slightly smaller than the estimated maximum storage capacity. Set to.

Therefore, by injecting the urea water of the normal injection amount determined as described above, the first selective reduction catalyst can maintain the state in which the maximum storage capacity or an amount of NH ₃ close thereto is adsorbed. Therefore, the NOx purification rate in the first selective reduction catalyst can be maintained high. Further, by setting the target value VNH3_TRGT of the detection value of the NH ₃ sensor to a value slightly larger than “0”, the amount of NH ₃ flowing into the second selective reduction catalyst can be reduced, so that the second selection The storage amount of the reduction catalyst can be maintained at an appropriate size. Therefore, even when the temperature of the first selective reduction catalyst suddenly rises due to high load operation or the like and NH ₃ adsorbed on the first selective reduction catalyst slips, this is adsorbed by the second selective reduction catalyst. As a result, excessive NH ₃ slip from the tail pipe can be suppressed.

It should be noted that a specific method for calculating the normal injection amount GUREA_ORD as described above, that is, specific configurations of the feedback controller 52, the base injection amount calculation unit 53, and the storage correction input calculation unit 54, and the first and second A specific method for calculating the estimated values ST1st and ST2nd of the respective selective reduction catalysts and the estimated values ST1st_max and ST2nd_max of the maximum storage capacity based on the output of the NH ₃ sensor 26 will be disclosed by the applicant. Since it is described in detail in 2009/128169 , further detailed description is omitted here.

FIG. 8 is a block diagram illustrating a configuration of the slip suppression correction amount calculation unit 55.
The slip suppression correction amount calculation unit 55 includes a predicted slip amount calculation unit 551 and a correction amount calculation unit 552.

The predicted slip amount calculation unit 551, for a map relating the temperature of the first selective reduction catalyst and its maximum storage capacity, the maximum storage capacity calculated based on the estimated current temperature TSCR of the first selective reduction catalyst, A difference from the maximum storage capacity calculated based on the predicted catalyst temperature TSCR_PRE calculated by the catalyst temperature prediction unit 4 is calculated, and this is set as a predicted storage capacity difference ΔST1st (see FIG. 9). As described above, in the present embodiment, the first selective reduction catalyst is controlled to maintain a storage amount close to the maximum storage capacity. Therefore, the predicted storage capacity difference ΔST1st corresponds to an estimated value of the amount of NH ₃ discharged from the first selective reduction catalyst to the second selective reduction catalyst between the present time and the prediction time TPRE.

The correction amount calculation unit 552 calculates the slip suppression correction amount ΔST by converting the predicted storage capacity difference ΔST1st into the mass of urea water. More specifically, urea water (CO (NH ₂ ) ₂ + H ₂ O) having a predetermined concentration injected from the urea injection device is thermally decomposed or hydrolyzed in the exhaust pipe and in the first and second selective reduction catalysts. Finally, as shown in the following equation, the slip suppression correction amount ΔST is calculated from the predicted storage capacity difference ΔST1st by assuming that NH ₃ and carbon dioxide (CO ₂ ) are generated. By subtracting ΔST calculated as described above from the normal injection amount GUREA_ORD as shown in FIG. 6, it will not be necessary to supply an extra amount of slip from the first selective reduction catalyst toward the second selective reduction catalyst in the future. Can be.
CO (NH ₂ ) ₂ + H ₂ O → 2NH ₃ + CO ₂

Returning to FIG. 6, when the following conditions are satisfied, the slip suppression correction unit 58 corrects the normal injection amount GUREA_ORD to the decrease side by subtracting the slip suppression correction amount ΔST from the normal injection amount GUREA_ORD. In other cases, the normal injection amount GUREA_ORD is not corrected.
1. A later-described acceleration delay flag is “0” (FDEL = 0).
2. A slip suppression flag described later is “1” (FSLIP = 1).

  The limited injection amount calculation unit 56 multiplies the base injection amount GUREA_BS calculated by the base injection amount calculation unit 53 of the normal injection amount calculation unit 51 by a correction coefficient equal to or less than “1” as a limited injection amount GUREA_LIM. . Here, for example, either “0.5” or “0.3” is used as the correction coefficient to be multiplied by the base injection amount GUREA_BS. As described above, since the base injection amount GUREA_BS corresponds to the injection amount of urea water whose equivalence ratio α is “1”, the limit injection amount GUREA_LIM calculated as described above has the equivalence ratio α of “0. This corresponds to an injection amount of urea water of 5 ”or“ 0.3 ”.

When the estimated value of the NH ₃ storage amount of the second selective reduction catalyst is smaller than the estimated value of the maximum NH ₃ storage capacity of the second selective reduction catalyst (ST2nd <ST2nd_max), the limited injection amount calculation unit 56 performs the second selection. The reduction catalyst is judged to have a margin for adsorbing NH ₃ and the correction coefficient is set to “0.5”. Further, when the estimated value of the NH ₃ storage amount is equal to or greater than the estimated value of the maximum storage capacity (ST2nd ≧ ST2nd_max), the limited injection amount calculation unit 56 has a margin for allowing the second selective reduction catalyst to adsorb NH _3. The correction coefficient is set to “0.3” and the supply amount of urea water is further limited.

The injection amount selector 57 determines the limited injection amount GUREA_LIM as the final urea injection amount GUREA when the following conditions are satisfied, and otherwise outputs the normal injection amount calculation unit 51 (GUREA_ORD or GUREA_ORD). -ΔST) is determined as the urea injection amount GUREA.
1. A later-described acceleration delay flag is “0” (FDEL = 0).
2. A slip suppression flag described later is “1” (FSLIP = 1).
3. The detection value of the NH3 sensor is equal to or greater than a predetermined threshold (VNH3 ≧ VNH3_th)
4). Estimate of the NH ₃ storage is NH ₃ storage amount of more than the target value (ST2nd ≧ ST2nd_TRGT)

[Intake control unit 6]
With reference to FIGS. 10 to 13, blocks related to the new air amount control of the engine 1 in the intake air control unit 6 will be described.
FIG. 10 is a block diagram relating to the determination of the EGR valve opening degree VO for controlling the fresh air amount of the engine to a predetermined target fresh air amount QNEW.

  As shown in FIG. 10, the valve opening VO includes a normal opening VO_ORD calculated by the normal opening calculator 61 and a closed correction opening VO_CLO calculated by the closing correction opening calculator 62. It is determined by selecting one of them with the opening selector 63.

  The normal opening calculation unit 61 receives the target fresh air amount QNEW, which is the target value of the engine fresh air amount, calculates an appropriate EGR valve opening corresponding to the target fresh air amount QNEW, and normally opens it. Output as degree VO_ORD. This target fresh air amount QNEW is determined by a process (not shown) according to the driving state of the vehicle.

The closing side correction opening degree calculation unit 62 is a closing side correction that is corrected closer to the closing side than the normal opening degree VO_ORD based on the NH ₃ slip speed V_SLIP, the NH ₃ consumption speed V_RED, and the target fresh air amount QNEW. The opening degree VO_CLO is calculated.
Here, the NH ₃ slip speed V_SLIP is the amount of NH ₃ discharged per unit time from the first selective reduction catalyst to the second selective reduction catalyst on the downstream side in the process of increasing the temperature of the first selective reduction catalyst. And is calculated by the slip speed calculation unit 64 (see FIG. 11 described later).
The NH ₃ consumption rate V_RED corresponds to the amount of NH ₃ that can be consumed by reducing the inflowing NOx in the first selective reduction catalyst in a state where the temperature rises, and the consumption rate calculation Calculated by the unit 65 (see FIG. 12 described later).

The closed side corrected opening degree calculation unit 62 includes a surplus NH ₃ amount calculation unit 621, a reaction model calculation unit 622, an additional fresh air amount calculation unit 623, a target new air amount correction unit 624, and an opening degree calculation unit 625. It is comprised including.
Surplus NH ₃ amount calculation unit 621, as shown in the following formula (2), by subtracting the NH ₃ consumption rate V_RED from NH ₃ slip speed V_SLIP, calculates the surplus NH ₃ amount ΔNH _3. The surplus NH ₃ amount ΔNH3 calculated here corresponds to the amount of NH ₃ per unit time that can be exhausted downstream without being consumed only by NOx that currently flows into the first selective reduction catalyst. In other words, the surplus NH ₃ amount ΔNH ₃ is a unit of NH ₃ that needs to be consumed excessively in order to prevent the adsorbed NH _{3 from} being discharged in the process of increasing the temperature of the first selective reduction catalyst. Corresponds to the amount per hour.

The reaction model calculation unit 622 assumes that the excess NH ₃ is reduced by assuming that NO and NO ₂ are reduced by NH ₃ under the reactions shown in the following formulas (3-1) to (3-3). The amount of NOx required to consume the amount ΔNH3 of NH ₃ is calculated, and this is set as the additional NOx amount ΔNOX.

  The additional fresh air amount calculation unit 623 calculates an additional amount of fresh air necessary for adding NOx supplied to the first selective reduction catalyst by an amount corresponding to the additional NOx amount ΔNOX, and calculates this. The amount of additional fresh air is ΔQNEW.

As shown in the following equation (4), the target fresh air amount correction unit 624 adds the additional fresh air amount ΔQNEW to the target fresh air amount QNEW, thereby correcting the corrected fresh air amount corresponding to the correction value of the target fresh air amount. QNEW_COR is calculated.

The opening calculation unit 625 receives the corrected fresh air amount QNEW_COR, calculates an appropriate EGR valve opening corresponding to the corrected fresh air amount QNEW_COR, and outputs this as a closed correction opening VO_CLO. For example, when the state shifts to the acceleration operation state and the temperature of the first selective reduction catalyst rises accordingly, NH ₃ that has been adsorbed by the first selective reduction catalyst is discharged so that the surplus NH ₃ amount ΔNH ₃ May become a positive value, and as a result, the additional fresh air amount ΔQNEW may become a positive value. At this time, the corrected fresh air amount QNEW_COR has a larger value than the target fresh air amount QNEW before being corrected, so that the closing side correction opening degree VO_CLO is in accordance with the target fresh air amount QNEW before being corrected. The normal opening degree VO_ORD calculated in this way is corrected to the closing side.

The opening selector 63 includes a slip suppression flag FSLIP, an acceleration delay flag FDEL, a detected value VNH3 of the NH ₃ sensor, an estimated value ST2nd of the NH ₃ storage amount of the second selective reduction catalyst, a target value ST2nd_TRGT, and an NH ₃ slip. One of the normal opening VO_ORD calculated by the normal opening calculation unit 61 and the closing correction opening VO_CLO calculated by the closing correction opening calculation unit 62 according to the speed V_SLIP and the NH ₃ consumption speed V_RED Is selected, and this is determined as the EGR valve opening VO. More specifically, the opening selector 63 determines the closing correction opening VO_COL as the EGR valve opening VO in order to increase the NOx emission amount from the engine when the following conditions are satisfied. The normal opening VO_ORD is determined as the EGR valve opening VO.
1. The slip suppression flag is “1” (FSLIP = 1).
2. The acceleration delay flag is “0” (FDEL = 0).
3. The detection value of the NH ₃ sensor is equal to or greater than a threshold value (VNH 3 ≧ VNH 3 — th)
4). The estimated value of the NH ₃ storage amount of the second selective reduction catalyst is larger than the target value (ST2nd ≧ ST2nd_TRGT)
5. NH ₃ slip speed is faster than NH ₃ consumption speed (V_SLIP> V_RED)

FIG. 11 is a block diagram showing a configuration of the slip speed calculation unit 64.
Slip speed calculating section 64, a NH ₃ sensor base calculation unit 641 which calculates a slip speed based on the detected value of the NH ₃ sensor, catalyst temperature base calculation unit for calculating a slip rate based on the temperature of the first selective reduction catalyst 642 and a comparator 643 that compares the output of the NH ₃ sensor base calculation unit 641 with the output of the catalyst temperature base calculation unit 642 and outputs the larger one.

The NH ₃ sensor base calculation unit 641 converts the NH ₃ sensor detection value VNH ₃ that is approximately proportional to the NH ₃ concentration in the exhaust into units based on the exhaust flow rate Gex, and is discharged from the first selective reduction catalyst per unit time. _Three quantities QNH3 are calculated. Further, the NH ₃ sensor base calculation unit 641 calculates a differential value of the NH ₃ amount QNH3 as shown in the following formula (5), and sets this as the NH ₃ sensor base slip speed dQNH3. Incidentally, since the NH ₃ sensor detects the NH ₃ concentration between the first selective reduction catalyst and the second selective reduction catalyst, the NH ₃ sensor base slip speed dQNH ₃ is selected from the first selective reduction catalyst. This corresponds to an estimated value of the amount of NH ₃ discharged per unit time toward the reduction catalyst.

The catalyst temperature base calculation unit 642 calculates an estimated value ST1st_max of the maximum storage capacity of the first selective reduction catalyst by searching a predetermined map based on the temperature TSCR of the first selective reduction catalyst, and also uses the following equation (6). As shown in FIG. 5, a differential value of the estimated value ST1st_max of the maximum storage capacity is calculated, and this is set as the catalyst temperature base slip speed dST1st_max. As described above, according to the urea injection control unit 5 of the present embodiment, urea injection control is performed for the first selective reduction catalyst so as to maintain the maximum storage capacity or a storage amount close thereto. Therefore, the catalyst temperature base slip speed dST1st_max corresponds to an estimated value of the amount of NH ₃ discharged per unit time from the first selective reduction catalyst to the second selective reduction catalyst.

The comparator 643 compares the NH ₃ sensor base slip speed dQNH3 with the catalyst temperature base slip speed dST1st_max, and outputs the larger one as the final NH ₃ slip speed V_SLIP. Thus, by estimating the slip speed by a plurality of different methods and using the larger one of them, it is possible to more reliably suppress excessive NH ₃ slip.

FIG. 12 is a block diagram showing a configuration of the consumption speed calculation unit 65.
The consumption rate calculation unit 65 includes a unit conversion unit 654, a NOx amount calculation unit 651, and a reaction model calculation unit 652, and calculates the NH ₃ consumption rate V_RED.

  The unit conversion unit 654 converts the detected value VNOx of the NOx sensor, which is substantially proportional to the NOx concentration in the exhaust gas flowing into the first selective reduction catalyst, based on the exhaust flow rate Gex, and converts the detected value VNOx to the first selective reduction catalyst per unit time. An inflow NOx amount QNOx is calculated.

The NOx amount calculation unit 651 includes a NO ₂ / NO amount calculation unit 651a and a temperature increase NOx purification rate calculation unit 651b, and by these, the first selective reduction catalyst out of NOx flowing into the first selective reduction catalyst. calculating the NO ₂ reduction can amount QNO2_RED corresponding to NO reducible amount QNO_RED and reducible NO ₂ amount corresponding to reducible amount of NO.

The NO ₂ / NO amount calculation unit 651a searches for a predetermined map based on the NOx amount QNOx flowing into the first selective reduction catalyst and the temperature TDOC of the oxidation catalyst, thereby obtaining the NO amount flowing into the first selective reduction catalyst. and NO inflow QNO_IN the corresponding, and NO ₂ inflow QNO2_IN corresponding to NO ₂ amount flowing in the first selective reduction catalyst is calculated.
The NOx purification rate calculation unit 651b searches the predetermined map based on parameters that change according to the operating state of the engine, such as the temperature TSCR and space velocity SV of the first selective reduction catalyst. An estimated value η1st of the NOx purification rate is calculated. Here, as the exhaust space velocity SV in the first selective reduction catalyst, for example, the one calculated based on the exhaust flow rate Gex and the volume of the first selective reduction catalyst is used.
The above-described NO reducible amount QNO_RED and NO ₂ reducible amount QNO2_RED are obtained by adding NOx to NO inflow amount QNO _IN and NO ₂ inflow amount QNO2 _IN , as shown in the following equations (7-1) and (7-2). It is calculated by multiplying the purification rate η1st.

The reaction model calculation unit 652 can perform the above NO reduction by assuming that NO and NO ₂ are reduced by NH ₃ under the reactions shown in the above equations (3-1) to (3-3). NO amount QNO_RED, and NO ₂ reducible amount NH ₃ amount consumed in the first selective reduction catalyst is estimated to purify NO ₂ of QNO2_RED, which is referred to as NH ₃ consumption rate V_RED.

  FIG. 13 is a flowchart showing a specific procedure of urea injection control and intake control in the exhaust purification system. The process shown in FIG. 13 is executed by the ECU every predetermined control cycle. Further, in the process shown in FIG. 13, the slip suppression flag FSLIP and the acceleration delay flag FDEL are flags for determining a time suitable for executing the slip suppression control shown in S7. It is updated at every control cycle by the flowchart shown in FIG. 14 and FIG.

In S1, it is determined whether or not the apparatus related to urea injection control is normal. More specifically, for example, whether or not the urea injection device is normal, whether or not the first and second selective reduction catalysts are deteriorated and failed, and the remaining amount of urea water in the urea tank is a specified value. Whether or not warming up after engine startup has been completed, whether or not various sensors such as the NH ₃ sensor, NOx sensor, exhaust temperature sensor have failed, and these sensors have become active. Whether or not the temperature of the first and second selective reduction catalysts is equal to or higher than a specified temperature.

  If the determination in S1 is NO and it is determined that the urea injection device is not normal, the process proceeds to S2, the urea injection amount is set to “0” to stop the urea injection control (GUREA ← 0), and the process proceeds to S3. In S3, the opening degree of the EGR valve is set to the normal opening degree (VO ← VO_ORD), and this process ends.

If the determination in S1 is YES and it is determined that the apparatus is normal, the process proceeds to S4. In S4, it is determined whether or not the slip suppression flag FSLIP is “1”, and in S5, it is determined whether or not the acceleration delay flag FDEL is “0”. Here, if any of the determinations in S4 and S5 is NO, for the time being, it is determined that there is no possibility of NH ₃ slipping from the second selective reduction catalyst, and the process proceeds to S6. In S6, the urea injection amount is set to the normal injection amount in order to execute the normal urea injection control (GUREA ← GUREA_ORD), and the process proceeds to S3, and the opening of the EGR valve is set to the normal opening. If the determinations in S4 and S5 are both YES, it is determined that NH ₃ may slip from the second selective reduction catalyst, and the process proceeds to S7 to suppress this NH ₃ slip, and FIG. Slip suppression control described later with reference to this is executed.

FIG. 14 is a flowchart showing a procedure for updating the slip suppression flag FSLIP in S4. The process shown in FIG. 14 is executed by the ECU separately from the process shown in FIG. 13 every predetermined control cycle. The slip suppression flag FSLIP updated in this process is a flag indicating that it is determined that NH ₃ may slip from the second selective reduction catalyst, and therefore execution of slip suppression control described later is required. It is.

  In S21, it is determined whether or not the first selective reduction catalyst is in a temperature rising state. If this determination is YES, the slip suppression flag FSLIP is set to “1” (S22), and this determination is NO. If there is, the slip suppression flag FSLIP is reset to “0” (S23). Here, the temperature rise state includes not only a state where the temperature of the first selective reduction catalyst is actually rising, but also a state where the temperature is not currently rising but is considered to increase soon. Therefore, in S21, when the differential value of the current temperature TSCR of the first selective reduction catalyst is greater than or equal to a predetermined positive threshold, the difference between the predicted temperature TSCR_PRE and the current temperature TSCR is greater than or equal to a predetermined positive threshold. Alternatively, when the engine is accelerating, it is determined that the first selective reduction catalyst is in a temperature rising state.

  FIG. 15 is a flowchart showing a procedure for updating the acceleration delay flag FDEL in S5. The process shown in FIG. 15 is executed separately from the process shown in FIG. 13 by the ECU every predetermined control cycle. When the engine shifts to the acceleration operation state, the temperature of the first selective reduction catalyst is considered to increase later even if it does not increase during the shift. Further, immediately after shifting to the acceleration operation state, the urea injection amount tends to be insufficient due to the delay of the NOx sensor. Therefore, in the process shown in FIG. 15, even when it is determined that the slip suppression flag FSLIP is “1” and the time is appropriate for executing the slip suppression control, the engine shifts to the acceleration operation state. Then, the acceleration delay flag FDEL is updated to delay the start of the slip suppression control for a predetermined time. In other words, this acceleration delay flag FDEL is a flag indicating that a delay in starting the execution of slip suppression control is requested. While this flag FDEL is set to “1”, FIG. As shown in FIG. 4, the start of the slip suppression control is delayed.

  In S31, it is determined whether or not the engine has shifted to an acceleration operation state. If the determination in S31 is YES, the acceleration delay flag FDEL is set to “1” (S32), the value of the delay timer is set to a predetermined initial value (S33), and the process proceeds to S36. When the determination in S31 is NO, the process proceeds to S34, and it is determined whether or not the acceleration delay flag FDEL is “1”. If the determination in S34 is NO, the process proceeds to S36, and if YES, the value of the delay timer set in S33 is subtracted (S35), and the process proceeds to S36.

  In S36, it is determined whether or not the value of the delay timer is “0”. If the determination in S36 is NO, this process ends. If the determination in S36 is YES, the process proceeds to S37, the acceleration delay flag FDEL is reset to “0”, and then this process ends.

  FIG. 16 is a flowchart showing a specific procedure of the slip suppression control (S7 in FIG. 13) shown in S7 of FIG. In the process shown in FIG. 16, the urea injection amount and the EGR valve are controlled according to the state of the second selective reduction catalyst so as to suppress the deterioration of the NOx purification performance and the unnecessary consumption of urea water when returning from the slip suppression control. Control the opening appropriately.

In S41, it is determined whether or not the detected value of the NH ₃ sensor is equal to or larger than the threshold value and the estimated value of the storage amount of the second selective reduction catalyst is larger than the target value (VNH3 ≧ VNH3_th and ST2nd> ST2nd_TRGT). Here, the target value ST2nd_TRGT for the storage amount of the second selective reduction catalyst is, for example, an estimated value of the maximum storage capacity of the second selective reduction catalyst so that NH ₃ slip from the second selective reduction catalyst can be reliably suppressed. It is set to a value sufficiently smaller than ST2nd_max.

If the determination in S41 is NO, that is, if it can be determined that the second selective reduction catalyst has some allowance for adsorbing NH ₃ slipped from the first selective reduction catalyst, the urea injection amount is controlled during normal control ( It is determined that NH ₃ slip from the second selective reduction catalyst can be suppressed only by slightly limiting from (GUREA_ORD), and the process proceeds to S42. In S42, the slip suppression correction amount ΔST is calculated, and in S43, the urea injection amount is limited from the normal injection amount by the slip suppression correction amount (GUREA ← GUREA_ORD−ΔST), and the process proceeds to S3 in FIG. Is set to the normal opening (VO ← VO_ORD).

If the determination in S41 is NO, that is, if it can be determined that the second selective reduction catalyst does not have much room for adsorbing NH ₃ slipped from the first selective reduction catalyst, the urea injection amount is corrected to the slip suppression correction. The process proceeds to S45 in order to limit more than the amount ΔST. In S45, it is determined whether or not the estimated value of the storage capacity of the second selective reduction catalyst is smaller than the estimated value of the maximum storage capacity (ST2nd <ST2nd_max). If the determination in S45 is YES, the process proceeds to S46 and the urea injection amount is limited to an amount corresponding to the equivalence ratio α = 0.5 (GUREA ← GUREA_BS × 0.5), and if the determination in S45 is NO Then, the process proceeds to S47 to further limit the injection amount, and the urea injection amount is limited to an amount corresponding to the equivalence ratio α = 0.3 (GUREA ← GUREA_BS × 0.3).

In S48, it is determined whether or not the NH ₃ slip speed is faster than the NH ₃ consumption speed (V_SLIP> V_RED). If the determination in S48 is NO, it is determined that NH ₃ slip from the second selective reduction catalyst can be suppressed without increasing the NOx emission amount of the engine, and the process proceeds to S3 in FIG. Is set to the normal opening. If the determination in S48 is YES, in order to suppress the NH ₃ slip from the second selective reduction catalyst, it is necessary to further increase the NOx emission amount from the engine in addition to limiting the urea injection amount. Judge and move to S49. In S49, the opening degree of the EGR valve is corrected closer to the closing side than the normal opening degree (VO ← VO_CLO), and this process is terminated.

In the above embodiment, an example in which the present invention is applied to a urea addition type exhaust gas purification system that uses ammonia as a reducing agent and supplies urea water as a precursor thereof is shown, but the present invention is not limited thereto.
For example, ammonia may be supplied directly without supplying urea water and generating ammonia from the urea water. The ammonia precursor is not limited to urea water, and other additives may be used. Further, the reducing agent for reducing NOx is not limited to ammonia. The present invention can also be applied to an exhaust purification system using, for example, hydrocarbons instead of ammonia as a reducing agent for reducing NOx.

1. Engine (internal combustion engine)
11 ... Exhaust pipe (exhaust passage)
12 ... Intake pipe (intake passage)
18 ... EGR pipe (EGR passage)
DESCRIPTION OF SYMBOLS 19 ... EGR valve 2 ... Exhaust gas purification system 231 ... 1st selective reduction catalyst 232 ... 2nd selective reduction catalyst 25 ... Urea injection device (reducing agent supply means)
26... NH ₃ sensor (reducing agent detection means, second storage amount estimation means, second adsorption allowable amount estimation means)
27. Exhaust temperature sensor (temperature acquisition means)
26 ... NOx sensor (inflow NOx amount acquisition means)
3 ... ECU (temperature acquisition means, temperature rise determination means, slip suppression control means, second storage amount estimation means, target value setting means, second adsorption allowable amount estimation means)
64 ... slip speed calculation section (slip amount estimation means)

Claims (9)

A first selective reduction catalyst that is provided in an exhaust passage of the internal combustion engine, purifies NOx in the exhaust in the presence of the reducing agent, and adsorbs the reducing agent;
A second selective reduction catalyst provided downstream of the first selective reduction catalyst in the exhaust passage;
An exhaust gas purification system for an internal combustion engine, comprising: a reducing agent supply means for supplying a reducing agent or a precursor thereof upstream of the first selective reduction catalyst in the exhaust passage,
A temperature increase determination means for determining whether or not the first selective reduction catalyst is in a temperature increase state based on an operating state of the internal combustion engine;
A reducing agent restriction control for reducing the supply amount of the reducing agent or the precursor from the reducing agent supply means to a restriction supply amount greater than 0 when the temperature rise determination means determines that the temperature is in an elevated state; and Slip suppression control means for executing only the reducing agent restriction control or both the reducing agent restriction control and the NOx emission increase control among the NOx emission increase control for increasing the NOx emission amount of the internal combustion engine from the normal control time. When,
Slip amount estimating means for estimating a reducing agent slip amount from the first selective reduction catalyst;
Reducing agent consumption estimation means for estimating a reducing agent consumption corresponding to the amount of reducing agent consumed in the first selective reduction catalyst in order to purify NOx flowing into the first selective reduction catalyst;
The slip suppression control means executes the NOx emission increase control when the estimated reducing agent slip amount is larger than the estimated reducing agent consumption amount, and the estimated reducing agent slip amount is the estimated amount. The exhaust gas purification system for an internal combustion engine, wherein the NOx emission amount increase control is not executed when the amount of the reducing agent consumed is smaller . Inflow NOx amount acquisition means for detecting or estimating the amount of NOx flowing into the first selective reduction catalyst;
First purification rate estimating means for estimating a NOx purification rate in the first selective reduction catalyst based on an operating state of the internal combustion engine;
Temperature acquisition means for detecting or estimating the temperature of the first selective reduction catalyst;
A first adsorption allowable amount estimating means for estimating an adsorption allowable amount of the reducing agent in the first selective reduction catalyst based on the detected or estimated temperature ;
The reducing agent consumption estimation means estimates the reducing agent consumption based on the estimated NOx purification rate and the detected or estimated NOx amount,
2. The slip amount estimating means estimates a reducing agent slip amount from the first selective reduction catalyst based on the estimated adsorption allowable amount of the first selective reduction catalyst . An exhaust purification system for an internal combustion engine. Inflow NOx amount acquisition means for detecting or estimating the amount of NOx flowing into the first selective reduction catalyst;
First purification rate estimating means for estimating a NOx purification rate in the first selective reduction catalyst based on an operating state of the internal combustion engine;
Reducing agent detection means for detecting a reducing agent concentration of exhaust gas between the first selective reduction catalyst and the second selective reduction catalyst;
The reducing agent consumption estimation means estimates the reducing agent consumption based on the estimated NOx purification rate and the detected or estimated NOx amount,
2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the slip amount estimating means estimates a reducing agent slip amount from the first selective reduction catalyst based on the detected reducing agent concentration. . A first selective reduction catalyst that is provided in an exhaust passage of the internal combustion engine, purifies NOx in the exhaust in the presence of the reducing agent, and adsorbs the reducing agent;
A second selective reduction catalyst provided downstream of the first selective reduction catalyst in the exhaust passage;
An exhaust gas purification system for an internal combustion engine, comprising: a reducing agent supply means for supplying a reducing agent or a precursor thereof upstream of the first selective reduction catalyst in the exhaust passage,
A temperature increase determination means for determining whether or not the first selective reduction catalyst is in a temperature increase state based on an operating state of the internal combustion engine;
A reducing agent restriction control for reducing the supply amount of the reducing agent or the precursor from the reducing agent supply means to a restriction supply amount greater than 0 when the temperature rise determination means determines that the temperature is in an elevated state; and Slip suppression control means for executing only the reducing agent restriction control or both the reducing agent restriction control and the NOx emission increase control among the NOx emission increase control for increasing the NOx emission amount of the internal combustion engine from the normal control time. When,
Second storage amount estimation means for estimating a storage amount of the reducing agent in the second selective reduction catalyst based on an operating state of the internal combustion engine;
Target value setting means for setting a target value for the estimated value of the storage amount of the second selective reduction catalyst based on the operating state of the internal combustion engine,
The slip suppression control means executes the reducing agent restriction control and does not execute the NOx emission increase control when the estimated value of the storage amount of the second selective reduction catalyst is equal to or less than the target value. An exhaust purification system for an internal combustion engine. A first selective reduction catalyst that is provided in an exhaust passage of the internal combustion engine, purifies NOx in the exhaust in the presence of the reducing agent, and adsorbs the reducing agent;
A second selective reduction catalyst provided downstream of the first selective reduction catalyst in the exhaust passage;
An exhaust gas purification system for an internal combustion engine, comprising: a reducing agent supply means for supplying a reducing agent or a precursor thereof upstream of the first selective reduction catalyst in the exhaust passage,
A temperature increase determination means for determining whether or not the first selective reduction catalyst is in a temperature increase state based on an operating state of the internal combustion engine;
A reducing agent restriction control for reducing the supply amount of the reducing agent or the precursor from the reducing agent supply means to a restriction supply amount greater than 0 when the temperature rise determination means determines that the temperature is in an elevated state; and Slip suppression control means for executing only the reducing agent restriction control or both the reducing agent restriction control and the NOx emission increase control among the NOx emission increase control for increasing the NOx emission amount of the internal combustion engine from the normal control time. When,
Second storage amount estimation means for estimating a storage amount of the reducing agent in the second selective reduction catalyst based on an operating state of the internal combustion engine,
The exhaust purification system for an internal combustion engine, wherein the slip suppression control means changes the limit supply amount according to a storage amount of the second selective reduction catalyst. A second adsorbing amount estimating means for estimating an adsorbing amount of the reducing agent in the second selective reduction catalyst based on an operating state of the internal combustion engine;
When the estimated value of the storage amount of the second selective reduction catalyst is smaller than the estimated value of the adsorption allowable amount, the slip suppression control means has an estimated value of the storage amount equal to or larger than the estimated value of the adsorption allowable amount. 6. The exhaust gas purification system for an internal combustion engine according to claim 5, wherein the limited supply amount is increased as compared with the case. A first selective reduction catalyst that is provided in an exhaust passage of the internal combustion engine, purifies NOx in the exhaust in the presence of the reducing agent, and adsorbs the reducing agent;
A second selective reduction catalyst provided downstream of the first selective reduction catalyst in the exhaust passage;
An exhaust gas purification system for an internal combustion engine, comprising: a reducing agent supply means for supplying a reducing agent or a precursor thereof upstream of the first selective reduction catalyst in the exhaust passage,
A temperature increase determination means for determining whether or not the first selective reduction catalyst is in a temperature increase state based on an operating state of the internal combustion engine;
A reducing agent restriction control for reducing the supply amount of the reducing agent or the precursor from the reducing agent supply means to a restriction supply amount greater than 0 when the temperature rise determination means determines that the temperature is in an elevated state; and Slip suppression control means for executing only the reducing agent restriction control or both the reducing agent restriction control and the NOx emission increase control among the NOx emission increase control for increasing the NOx emission amount of the internal combustion engine from the normal control time. When,
Acceleration determination means for determining that the internal combustion engine has shifted to an acceleration operation state,
The internal combustion engine characterized in that the slip suppression control means delays execution of the reducing agent restriction control and the NOx emission increase control when the acceleration determination means determines that the acceleration operation state has been entered. Engine exhaust purification system. A first selective reduction catalyst that is provided in an exhaust passage of the internal combustion engine, purifies NOx in the exhaust in the presence of the reducing agent, and adsorbs the reducing agent;
A second selective reduction catalyst provided downstream of the first selective reduction catalyst in the exhaust passage;
An exhaust gas purification system for an internal combustion engine, comprising: a reducing agent supply means for supplying a reducing agent or a precursor thereof upstream of the first selective reduction catalyst in the exhaust passage,
A temperature increase determination means for determining whether or not the first selective reduction catalyst is in a temperature increase state based on an operating state of the internal combustion engine;
A reducing agent restriction control for reducing the supply amount of the reducing agent or the precursor from the reducing agent supply means to a restriction supply amount greater than 0 when the temperature rise determination means determines that the temperature is in an elevated state; and Slip suppression control means for executing only the reducing agent restriction control or both the reducing agent restriction control and the NOx emission increase control among the NOx emission increase control for increasing the NOx emission amount of the internal combustion engine from the normal control time. When,
Reducing agent concentration detecting means for detecting a reducing agent concentration of exhaust gas between the first selective reduction catalyst and the second selective reduction catalyst;
The internal combustion engine, wherein the slip suppression control means executes the reducing agent restriction control and does not execute the NOx emission increase control when the output value of the reducing agent concentration detection means is smaller than a predetermined value. Exhaust purification system. A first selective reduction catalyst that is provided in an exhaust passage of the internal combustion engine, purifies NOx in the exhaust in the presence of the reducing agent, and adsorbs the reducing agent;
A second selective reduction catalyst provided downstream of the first selective reduction catalyst in the exhaust passage;
Reducing agent supply means for supplying a reducing agent or a precursor thereof upstream of the first selective reduction catalyst in the exhaust passage;
An EGR passage that recirculates a part of the exhaust gas flowing through the exhaust passage as EGR gas to the intake passage of the internal combustion engine;
An exhaust gas purification system for an internal combustion engine comprising an EGR valve provided in the EGR passage for controlling the amount of EGR gas ,
A temperature increase determination means for determining whether or not the first selective reduction catalyst is in a temperature increase state based on an operating state of the internal combustion engine;
A reducing agent restriction control for reducing the supply amount of the reducing agent or the precursor from the reducing agent supply means to a restriction supply amount greater than 0 when the temperature rise determination means determines that the temperature is in an elevated state; and Slip suppression control means for executing only the reducing agent restriction control or both the reducing agent restriction control and the NOx emission increase control among the NOx emission increase control for increasing the NOx emission amount of the internal combustion engine from the normal control time. When,
Slip amount estimating means for estimating a reducing agent slip amount from the first selective reduction catalyst;
Reducing agent consumption estimation means for estimating a reducing agent consumption corresponding to the amount of reducing agent consumed in the first selective reduction catalyst in order to purify NOx flowing into the first selective reduction catalyst;
In the NOx emission amount increase control, the NOx emission amount is increased by correcting the opening degree of the EGR valve to the closed side from the opening degree in the normal control,
The slip suppression control means determines a correction amount from an opening degree during normal control of the opening degree of the EGR valve, based on a deviation between the estimated reducing agent slip amount and the estimated reducing agent consumption amount. An exhaust gas purification system for an internal combustion engine.

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