JP2012052510A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system of an engine capable of supplying a proper quantity of urea-water solution, by accurately estimating a ratio of NO/NOx.SOLUTION: This exhaust emission control system includes: a PM (particulate matter) deposit quantity estimating section 82 for calculating an estimate QPM of a PM deposit quantity in a DPF (diesel particulate filter), an NOx quantity estimating section 81 for calculating an estimate of an NOx quantity in exhaust gas between the DPF and a selective reduction catalyst within an exhaust pipe; an exhaust temperature sensor for detecting the exhaust temperature Ton the downstream side of the DPF; an NO/NOx ratio estimating section 83 for calculating an estimate RNO2 of the NO/NOx ratio of the exhaust gas between the DPF and the selective reduction catalyst within an exhaust system based on an estimate QPM of the PM deposit quantity, an estimate NOXof the NOx quantity and the exhaust temperature T; and an injection quantity determining section 84 for determining a urea-water solution injection quantity by a urea-water solution injection unit based on the estimate NOXof the NOx quantity and the estimate RNO2 of the NO/NOx ratio.

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 for an internal combustion engine including a selective reduction catalyst that reduces NOx in exhaust gas in the presence of a reducing agent.

  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 gas purification system, urea water 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 the exhaust gas. NOx is selectively reduced. 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.

It is known that the NOx purification performance of the selective reduction catalyst changes according to the ratio of NO ₂ and NO (NO ₂ / NOx ratio) constituting NOx. Therefore, for example, in Patent Document 1, the amount of NOx flowing into the selective reduction catalyst and the NO ₂ / NOx ratio are calculated, and urea water supplied to the selective reduction catalyst is calculated based on the NOx amount and the NO ₂ / NOx ratio. A technique for determining the amount of injection is shown.

JP 2004-100700 A

Meanwhile, in Patent Document _1, NO 2 / NOx ratio, engine temperature, has been shown to be estimated by using injection timing, and a parameter indicating the operating state of the engine such as the air-fuel ratio. However, it is considered that the actual NO ₂ / NOx ratio varies depending not only on the operating state of the engine but also on the state of the catalyst and filter provided in the exhaust pipe. Therefore, the technique of Patent Document 1 cannot accurately estimate the NO ₂ / NOx ratio, and as a result, an appropriate amount of urea water cannot be supplied, and the injection efficiency and purification performance of urea water may be reduced.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an exhaust purification system for an internal combustion engine that can accurately estimate the NO ₂ / NOx ratio and supply an appropriate amount of urea water. .

To achieve the above object, the present invention is provided in an exhaust system (for example, an exhaust pipe 30 to be described later) of an internal combustion engine (for example, an engine 1 to be described later), and is selected to reduce NOx in the exhaust in the presence of a reducing agent. A reduction catalyst (for example, a selective reduction catalyst 61 described later), a filter (for example, a DPF 36 described later) that is provided upstream of the selective reduction catalyst in the exhaust system and collects particulate matter in the exhaust; An exhaust gas purification system for an internal combustion engine (for example, described later), comprising reducing agent injection means (for example, urea water injection device 62 described later) for injecting a reducing agent or a precursor thereof into the exhaust gas flowing into the selective reduction catalyst. An exhaust purification system 2) is provided. The exhaust purification system includes a deposition amount estimation unit (for example, a PM deposition amount estimation unit 82 described later) for estimating a particulate matter deposition amount in the filter, and between the filter and the selective reduction catalyst in the exhaust system. NOx amount estimating means for estimating the NOx amount in the exhaust (for example, a NOx amount estimating unit 81 described later), temperature acquiring means for acquiring the temperature of the exhaust system (for example, an exhaust temperature sensor 35 described later), and the estimation The ratio of the amount of NO _{2 to the} amount of NOx in the exhaust between the filter and the selective reduction catalyst in the exhaust system based on the amount of accumulated particulate matter and the amount of NOx and the temperature acquired by the temperature acquisition means _NO 2 / NOx ratio estimation means for estimating the corresponding _NO 2 / NOx ratio (e.g., _NO 2 / NOx ratio estimation unit 83 described later) and the estimated amount of NOx (NOX _HAT ) and NO ₂ / NOx ratio (RNO2) based on the injection amount determination means (for example, an injection amount determination unit 84 described later) that determines the injection amount (G _UREA ) of the reducing agent or precursor by the reducing agent injection means. And).

In the present invention, the amount of particulate matter accumulated in the filter is estimated, and based on the estimated amount of particulate matter accumulated and the acquired temperature of the exhaust system, the exhaust gas between the filter and the selective reduction catalyst on the downstream side thereof is estimated. Estimate the NO ₂ / NOx ratio. The filter particulate matter deposited, the reaction NO ₂ is NO is reduced is produced by particulate matter deposited on the filter progresses. For example, when a filter coated with an oxidation catalyst is used, a reaction in which NO is oxidized and NO ₂ is generated proceeds. Therefore, in the present invention, since the change in the degree of progress of the oxidation reaction of NO and the reduction reaction of NO ₂ due to the temperature change of the exhaust system and the accumulation of particulate matter can be taken into account, as a result The NO ₂ / NOx ratio of the exhaust gas between the filter and the selective reduction catalyst can be estimated with high accuracy. Further, in the present invention, the reducing agent or precursor by the reducing agent injection means is based on the NO ₂ / NOx ratio estimated with such high accuracy and the NOx amount in the exhaust gas estimated separately from the NO ₂ / NOx ratio. Determine the amount of body injection. Thereby, an appropriate amount of reducing agent or precursor according to the amount of NOx and the NO ₂ / NOx ratio can be supplied.

In this case, the NOx amount estimating means estimates the NOx amount in the exhaust gas between the filter and the selective reduction catalyst based on the rotational speed (NE) of the internal combustion engine and the fuel injection amount (G _FUEL ). It is preferable.

  In the present invention, it is necessary to newly provide a sensor for detecting the NOx amount by estimating the NOx amount based on parameters that are always acquired in the control of the internal combustion engine, such as the rotational speed of the internal combustion engine and the fuel injection amount. Disappear. Therefore, the cost and power consumption required for the sensor can be suppressed. Further, existing NOx sensors do not have sufficient response performance to supply the reducing agent or precursor with high accuracy. In particular, a large sensing delay occurs during the transition, and a sufficient amount of reducing agent or precursor cannot be supplied, and the purification performance may be deteriorated. On the other hand, according to the present invention which does not require the use of a NOx sensor, it is possible to prevent such a decrease in purification performance during a transition.

In this case, it is preferable that the NO ₂ / NOx ratio estimation means decreases the estimated value (RNO2) of the NO ₂ / NOx ratio as the estimated value (QPM) of the particulate matter deposition amount increases.

In the filter, the deposition amount of the particulate matter increases, NO ₂ is considered to progress the reaction in which NO is reduced by the carbon that constitutes the particulate matter is generated increases. In the present invention, in consideration of this point, by reducing the estimate of NO 2 _/ NOx ratio in accordance with the estimated value of the particulate matter accumulation amount becomes large can be estimated NO 2 _/ NOx ratio of the exhaust with high precision .

In this case, when the estimated NO ₂ / NOx ratio (RNO2) is larger than a threshold value (for example, a threshold value RNO2 _TH described later), the injection amount determining means performs the injection according to the NO ₂ / NOx ratio. It is preferred to increase the amount.

In the selective reduction catalyst, three types of reduction reactions can proceed mainly: a reaction that reduces NO and NO ₂ simultaneously, a reaction that reduces only NO, and a reaction that reduces only NO ₂ . Here, the reaction for reducing only NO ₂ requires more reducing agent than the other two reactions. Further, it is considered that when the NO ₂ / NOx ratio is increased, the progress of the reaction for reducing only NO ₂ is increased. Therefore, in the present invention, when the NO ₂ / NOx ratio is larger than the threshold value, in the selective reduction catalyst due to the shortage of the reducing agent, the injection amount of the reducing agent or the precursor is increased according to the NO ₂ / NOx ratio. Reduction in NOx purification performance can be suppressed.

  In this case, it is preferable that the NOx amount estimating means estimates the NOx amount based on a neural network configured by connecting a plurality of neurons that output in accordance with a predetermined function.

In the present invention, the NOx amount is estimated based on a neural network excellent in reproducibility of nonlinear dynamic characteristics, so that even when the NOx amount in the exhaust shows a nonlinear behavior, for example, during a transient state, for example. Since this can be estimated with high accuracy, an appropriate amount of reducing agent or precursor according to the amount of NOx and the NO ₂ / NOx ratio can be supplied.

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 module regarding the determination of the urea water injection quantity which concerns on the said embodiment. It is a figure which shows the neural network structure of the NOx amount estimation part which concerns on the said embodiment. It is a figure which shows a sigmoid function. It is a diagram showing a map for determining an estimate of NO 2 _/ NOx ratio according to the embodiment. It is a figure which shows the map which determines the correction coefficient 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 the present embodiment.

  The engine 1 is a lean burn operation type gasoline engine or diesel engine, and is mounted on a vehicle (not shown). The engine 1 is provided with a fuel injection valve that injects fuel into the combustion chamber of each cylinder. These fuel injection valves are electrically connected by an electronic control unit (hereinafter referred to as “ECU”) 8, and the valve opening time and valve closing time of the fuel injection valve are controlled by the ECU 8.

  The exhaust purification system 2 includes an intake pipe 20 connected to the engine 1 through which intake air flows, an exhaust pipe 30 through which exhaust from the engine 1 flows, and a high-pressure exhaust gas recirculation device (hereinafter referred to as “high pressure”) that recirculates part of the exhaust gas to the intake air. 40) and a low pressure exhaust gas recirculation device (hereinafter referred to as “low pressure EGR device”) 45, an exhaust purification filter (hereinafter referred to as “DPF (Diesel Particulate Filter)”) 36, and a selective reduction catalyst 61. And a urea water injector 62 and a turbocharger 50 that pumps intake air to the engine 1.

  The intake pipe 20 is connected to the intake port of each cylinder of the engine 1 through a plurality of branch portions of the intake manifold 21. The exhaust pipe 30 is connected to the exhaust port of each cylinder of the engine 1 through a plurality of branch portions of the exhaust manifold 31. The intake pipe 20 is provided with a turbocharger 50 and an intercooler 59 in this order from the upstream side.

  The turbocharger 50 includes a turbine 51 provided in the exhaust pipe 30 and a compressor 52 provided in the intake pipe 20. The turbine 51 is driven by the kinetic energy of the exhaust flowing through the exhaust pipe 30. The compressor 52 is driven by the rotation of the turbine 51 and pressurizes the intake air. Further, the turbocharger 50 includes a variable vane (not shown) that changes the rotational speed of the turbine 51 by an opening / closing operation. The intercooler 59 cools the intake air pressurized by the turbocharger 50.

  In the exhaust pipe 30, a catalytic converter 34, a DPF 36, a urea water injection device 62, and a selective reduction catalyst 61 are provided in this order from the upstream side downstream of the turbine 51 of the turbocharger 50.

The catalytic converter 34 incorporates an oxidation catalyst and purifies the exhaust gas by a reaction between the oxidation catalyst and the exhaust gas. The catalytic converter 34 is supplied by, for example, post injection (fuel injection that is executed in the expansion stroke or exhaust process and does not contribute to combustion in the cylinder) during DPF regeneration in which PM accumulated in the DPF 36 is removed by combustion. The unburned fuel is burned, and the temperature of the downstream DPF 36 is raised by the heat generated thereby. In this oxidation catalyst, for example, platinum (Pt) or palladium (Pd) acting as a catalyst is supported on an alumina (Al ₂ O ₃ ) carrier, zeolite having excellent HC adsorption action, and HC What was comprised and added rhodium (Rh) excellent in the steam reforming effect | action is used.

When the exhaust gas passes through the fine holes in the filter wall, the DPF 36 causes particulate matter (hereinafter referred to as “PM (Particulate Matter)”) in the exhaust gas to pass through the filter wall surface and the filter wall. Collect by depositing in the pores. As a constituent material of the filter wall, for example, a ceramic porous body such as silicon carbide (SiC) is used. The DPF 36 is coated with an oxidation catalyst that raises the temperature of the exhaust gas with heat generated by the reaction with the exhaust gas and oxidizes NO in the exhaust gas to NO ₂ to promote the reduction of NOx in the selective reduction catalyst 61 described later. Has been. In this oxidation catalyst, for example, platinum (Pt) or palladium (Pd) acting as a catalyst is supported on an alumina (Al ₂ O ₃ ) carrier, zeolite having excellent HC adsorption action, and HC What was comprised and added rhodium (Rh) excellent in the steam reforming effect | action is used.

  The urea water injection device 62 includes a urea water tank 621 and a urea water injection valve 623. The urea water tank 621 stores urea water as a reducing agent precursor in the selective reduction catalyst 61. The urea water injection valve 623 is connected to the ECU 8 and operates in accordance with a control signal from the ECU 8. An amount of urea water corresponding to the control signal is passed between the DPF 36 in the exhaust pipe 30 and the selective reduction catalyst 61, that is, Injection into the exhaust gas flowing into the selective reduction catalyst 61. That is, urea water injection control is executed.

  The selective reduction catalyst 61 selectively reduces NOx in the exhaust in an atmosphere in which a reducing agent such as ammonia exists. Specifically, when urea water is injected by the urea water injection device 62, the urea water is thermally decomposed or hydrolyzed by the heat of the exhaust to generate ammonia as a reducing agent. The produced ammonia is supplied to the selective reduction catalyst 61, and NOx in the exhaust is selectively reduced by these ammonia.

  By the way, the selective reduction catalyst 61 has a function of reducing NOx in the exhaust with ammonia generated from urea water, and also has a function of storing a predetermined amount of the generated ammonia. Hereinafter, the amount of ammonia stored in the selective reduction catalyst 61 is referred to as a storage amount, and the ammonia amount that can be stored in the selective reduction catalyst 61 is referred to as a maximum storage capacity. The ammonia stored in this way is also consumed as appropriate in the reduction of NOx in the exhaust. For this reason, the NOx reduction rate in the selective reduction catalyst 61 increases as the storage amount increases. Further, when the supply amount of urea water is small relative to the amount of NOx discharged from the engine, the stored ammonia is consumed for the reduction of NOx so as to compensate for the shortage of urea water.

  The high pressure EGR device 40 includes a high pressure EGR pipe 41, a high pressure EGR valve 42, and a high pressure EGR cooler 43. The high pressure EGR pipe 41 connects the exhaust manifold 31 and the intake manifold 21. The high pressure EGR valve 42 is provided in the high pressure EGR pipe 41 and controls the flow rate of the exhaust gas recirculated through the high pressure EGR pipe 41. The high pressure EGR cooler 43 cools the exhaust gas recirculated through the high pressure EGR pipe 41. The high pressure EGR valve 42 is connected to the ECU 8 via an actuator (not shown), and the opening degree (lift amount) is electromagnetically controlled by the ECU 8.

  The low pressure EGR device 45 includes a low pressure EGR pipe 46, a low pressure EGR valve 47, and a low pressure EGR cooler 48. The low pressure EGR pipe 46 connects between the DPF 36 and the urea water injection valve 623 in the exhaust pipe 30 and the upstream side of the compressor 52 in the intake pipe 20. The low pressure EGR valve 47 is provided in the low pressure EGR pipe 46 and controls the flow rate of the exhaust gas recirculated through the low pressure EGR pipe 46. The low pressure EGR cooler 48 cools the exhaust gas recirculated through the low pressure EGR pipe 46. The low pressure EGR valve 47 is connected to the ECU 8 via an actuator (not shown), and the opening degree (lift amount) is electromagnetically controlled by the ECU 8.

The ECU 8 is connected to a crank angle position sensor 11 that detects the rotation angle of the crankshaft of the engine 1 and an accelerator sensor 12 that detects the amount of depression of an accelerator pedal of a vehicle driven by the engine 1. The detection signal is supplied to the ECU 8. Here, the rotational speed NE of the engine 1 is calculated by the ECU 8 based on the output of the crank angle position sensor 11. The fuel injection amount G _FUEL indicating the load of the engine 1 is calculated by the ECU 8 based on the output of the accelerator sensor 12.

In addition to these sensors 11 and 12, the ECU 8 includes an intake pressure sensor 24, a first exhaust pressure sensor 32, a second exhaust pressure sensor 33, a first lift sensor 13, and the like that detect physical quantities in each part of the exhaust purification system 2. A second lift sensor 14 and an exhaust temperature sensor 35 are connected.
The intake pressure sensor 24 detects the intake pressure P2 on the downstream side of the intercooler 59 in the intake pipe 20, and transmits a signal substantially proportional to the detected value to the ECU 8. The first exhaust pressure sensor 32 detects the exhaust pressure P3 on the upstream side of the high pressure EGR cooler 43 in the high pressure EGR pipe 41, and transmits a signal substantially proportional to the detected value to the ECU 8. The second exhaust pressure sensor 33 detects the exhaust pressure P4L between the turbine 51 and the DPF 36 in the exhaust pipe 30, and transmits a signal substantially proportional to the detected value to the ECU 8. The first lift sensor 13 detects the lift amount L _{HP_ACT} of the high pressure EGR valve 42 and transmits a signal substantially proportional to the detected value to the ECU 8. The second lift sensor 14 detects the lift amount L _{LP_ACT} of the low pressure EGR valve 47 and transmits a signal substantially proportional to the detected value to the ECU 8. The exhaust temperature sensor 35 detects the exhaust temperature TDPF on the downstream side of the _DPF 36 as the temperature of the exhaust system, and transmits a signal substantially proportional to the detected value to the ECU 8.

  The ECU 8 shapes an input signal waveform from various sensors, corrects a voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter referred to as “a processing unit”). CPU ”). In addition, the ECU 8 stores a storage circuit that stores various calculation programs and calculation results executed by the CPU, a high pressure EGR valve 42, a low pressure EGR valve 47, a turbocharger 50, a urea water injector 62, and a fuel for the engine 1. An output circuit for outputting a control signal to an injection valve or the like.

FIG. 2 is a block diagram showing modules relating to determination of the urea water injection amount _GUREA of the urea water injection device configured in the ECU. As shown in FIG. 2, in this embodiment, the urea water injection amount G _UREA includes a NOx amount estimation unit 81, a PM accumulation amount estimation unit 82, a NO ₂ / NOx ratio estimation unit 83, and an injection amount determination unit 84. , Determined by.

The NOx amount estimation unit 81 is configured to calculate an estimated NOx amount NOX _HAT corresponding to the amount of NOx in the exhaust gas between the DPF and the selective reduction catalyst in the exhaust pipe based on a neural network having a structure described in detail below. calculate.

FIG. 3 is a diagram illustrating a neural network structure of the NOx amount estimating unit 81.
This neural network is configured by connecting a plurality of neurons that output in accordance with a predetermined function, and outputs a value Y (k) according to an m-component input vector U (k). As shown in FIG. 3, the neural network includes an input layer composed of m neurons W _1j (j = 1 to m) and m × (n−1) neurons W _ij (i = 2 to 2). n, j = 1 to m), and a hierarchical type including three layers, that is, an intermediate layer composed of n, j = 1 to m) and an output layer composed of one neuron Y.
Input layer: W _1j (j = 1, 2,..., M)
Intermediate layer: W _ij (i = 2, 3,..., N, j = 1, 2,..., M)
Output layer: Y

  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 in the current control cycle, the symbol (k-1) indicates that the data is detected or calculated in the previous control cycle. In the following description, the symbol (k) is omitted as appropriate.

The operation of m neurons W _1j (j = _{1 to} m) in the input layer will be described.
A signal T _1j (k) is input to the neuron W _1j in the input layer. As this input signal T _1j (k), the j-th component U _j (k) of the input vector U (k) is used as shown in the following equation (1).

The neuron W _{1j in the} input layer is coupled to the m neurons W _2j (j = 1 to m) in the intermediate layer with a predetermined weight, and the signal V _1j (k) is connected to the m neurons W _{2j that} are coupled. Is output. That is, the neuron W _{1j generates} m signals V _1j (k) corresponding to the input signal T _1j (k) according to the sigmoid function f (x) as shown in the following equations (2) and (3). Output to neuron W _2j .

FIG. 4 is a diagram illustrating the sigmoid function f (x). FIG. 4 shows a case where ε = 0 and β = 0.5, 1.0, 2.0, 3.0 in the above formula (3).
The range of the sigmoid function f (x) is [ε, ε + 1]. Also, as shown in FIG. 4, the sigmoid function f (x) approaches a step function centered on x = 0 as β is increased.

  In the above equation (3), the coefficient β represents the slope gain of the sigmoid function f (x), and the coefficient ε represents the offset value of the sigmoid function f (x). The slope gain β is set by learning of a neural network described later. The offset value ε is set by learning of a neural network described later or set to a predetermined value.

Next, the operation of (n−1) × m neurons W _ij (i = 2 to n, j = 1 to m) in the intermediate layer will be described.
An intermediate layer neuron W _ij (i = 2 to n, j = ₁ to m) has a predetermined value for each of m signals V _{i−1, j} (j = ₁ to m) output from the neurons to be coupled. The sum of signals multiplied by the weights ω _{i−1, j} (j = _{1 to m} ) is input. Therefore, a signal T _ij (k) as shown in the following equation (4) is input to the neuron W _ij in the intermediate layer.

Among the neurons in the intermediate layer, the neurons excluding m coupled to the output layer, that is, (n−2) × m neurons W _ij (i = 2 to n−1, j = 1 to m) The layer is connected to m neurons W _{i + 1, j} (j = _{1 to} m) with a weight ω _ij , and a signal V _ij (k) is output to the connected neurons W _{i + 1, j} . That is, the neuron W _ij (i = 2 to n−1, j = 1 to m) is in accordance with the input signal T _ij (k) according to the sigmoid function f (x) as shown in the following equation (5). The signal V _ij (k) is output to m neurons W _{i + 1, j} .

Further, m neurons W _nj (j = 1 to m) in the intermediate layer are connected to the neuron Y in the output layer with a weight ω _nj , and a signal V _nj (k) is output to the neuron Y in the output layer. To do. That is, these neurons W _nj (j = 1 to m) _generate a signal V _nj (k) corresponding to the input signal T _nj (k) according to the sigmoid function f (x) as shown in the following equation (6). Output to neuron Y.

Next, the operation of the neuron Y in the output layer will be described.
The neuron Y of the output layer is multiplied by a predetermined weight ω _{n, j} (j = ₁ to m) by m signals V _{n, j} (j = ₁ to m) output from the neuron of the intermediate layer to be coupled. The sum of the received signals is input. Therefore, a signal T (k) as shown in the following equation (7) is input to the neuron Y in the output layer.

The neuron Y in the output layer outputs a signal Y (k) corresponding to the input signal T (k) according to the sigmoid function g (x) as shown in the following equations (8) and (9).

  The sigmoid function g (x) is qualitatively the same as the function f (x) shown in FIG. 4 described above, but differs from the sigmoid function f (x) in that the range is [δ, δ + α]. . In the above equation (8), the coefficient γ represents the slope gain of the sigmoid function g (x), and the coefficient δ represents the offset value of the sigmoid function g (x). The coefficient α indicates an output gain for setting the degree of freedom that the output of the neural network can take. The slope gain γ and the output gain α are set by learning with a neural network described later. The offset value δ is set by learning of a neural network described later, or set to a predetermined value.

The component of the input vector U (k) for the neural network is defined as shown in the following formula (10). As described above, the components of the input vector U (k) include a plurality of physical quantities (fuel injection amount G _FUEL , intake pressure P2, exhaust pressure P3, exhaust pressure P3L, high pressure EGR valve necessary for estimating the NOx amount. The lift amount detection value L _{HP_ACT} , the low pressure EGR valve lift amount detection value L _{LP_ACT} , and the engine speed NE) are included. In addition, the components of the input vector U (k) include data regarding physical quantities of different types as described above, and also include data regarding physical quantities at different times. Thus, by including data on physical quantities at different times, the reproducibility of the dynamic behavior of the estimated value during transient operation can be further improved.

The neural network outputs Y (k) for such an input vector U (k) as an estimated value NOX _HAT (k) of the NOx amount as shown in the following equation (11). The following learning is performed.

First, by operating the actually prepared engine and its exhaust purification system, the values of the components (G _FUEL , P2, P3, P4L, L _{HP_ACT} , L _{LP_ACT} , NE) of the above equation (10) Then, the relationship between the NOx amount value in the exhaust gas between the DPF and the selective reduction catalyst at that time is recorded, and learning data is prepared.
Next, neural network learning is performed based on the acquired learning data. That is, the function f (x), g of the neuron so that the relationship between the components of the input vector U (G _FUEL , P2, P3, P4L, L _{HP_ACT} , L _{LP_ACT} , NE) and the NOx amount is reproduced by the neural network. Various gains (α, β, γ, δ, ε) of (x) and weights ω _ij (i = 1 to n, j = 1 to m) indicating the strength of connection of each neuron are set. A known method is used as the neural network learning algorithm. Specifically, for example, in addition to a learning algorithm such as a reverse error propagation method, an optimization algorithm such as a genetic algorithm can be used.

Returning to FIG. 2, the PM accumulation amount estimation unit 82 calculates an estimated value QPM of the PM accumulation amount corresponding to the amount of PM accumulated in the DPF. More specifically, as shown in the following formula (12), the PM accumulation amount estimated value QPM (k−1) in the previous control cycle is collected in the DPF from the previous time to the current control cycle. The PM accumulation amount estimated value QPM (k) is calculated by adding the PM amount ΔQPM. Here, the PM amount ΔQPM discharged from the engine and collected in the DPF from the previous time to the current control cycle is a basic value calculated based on, for example, the fuel injection amount G _FUEL and the engine speed NE. It is calculated by adding a correction term calculated based on the engine coolant temperature, the intake air amount, and the like.

The NO ₂ / NOx ratio estimator 83 is based on the estimated value QPM of the PM accumulation amount calculated by the PM accumulation amount estimator 82 and the exhaust gas temperature T _DPF, and between the DPF and the selective reduction catalyst in the exhaust pipe. It calculates an estimated value RNO2 of _NO 2 / NOx ratio corresponding to the ratio of NO ₂ amount for the amount of NOx in the exhaust gas.

The following formula (13) is a reaction formula of NO ₂ in the exhaust gas in the DPF. As shown in the reaction formula (13), in the DPF in which PM is deposited, NO _{2 in} the exhaust is reduced by carbon (C) constituting the PM, and CO and NO are generated.
NO ₂ + C → CO + NO (13)

Further, the following equation (14) is a reaction formula of NO in the exhaust gas in the catalytic converter incorporating the oxidation catalyst and the DPF coated with the oxidation catalyst. As shown in the reaction formula (14), in the catalytic converter and the DPF provided with the oxidation catalyst, NO in the exhaust is oxidized and NO ₂ is generated.
NO + O → NO ₂ (14)

As described above, in the catalytic converter and the DPF, a reaction in which NO and NO ₂ are mutually oxidized or reduced proceeds. Therefore, the NO ₂ / NOx ratio between the DPF and the selective reduction catalyst is determined by these two reactions. It changes according to the degree of progress. Further, it is considered that the progress of these two reactions is mainly characterized by the exhaust gas temperature and the PM deposition amount. _Therefore, in calculating the estimated value RNO2 of NO 2 / NOx ratio, retrieves an estimate RNO2 of _NO 2 / NOx ratio according to the estimated value QPM of the PM accumulation amount as shown in FIG. 5 and the exhaust gas temperature _{T DPF} You can set the map.

Therefore, in the NO ₂ / NOx ratio estimation unit 83, a map set in advance based on an experiment as shown in FIG. 5 based on the estimated value QPM of the PM accumulation amount and the exhaust temperature T _DPF on the downstream side of the _DPF . To calculate an estimated value RNO2 of the NO ₂ / NOx ratio. According to the map shown in FIG. 5, the estimated value RNO2 of the NO ₂ / NOx ratio decreases as the estimated value QPM of the PM accumulation amount increases. Further, the estimated value RNO2 of the NO ₂ / NOx ratio increases as the exhaust gas temperature T _DPF decreases, that is, as the temperature of the DPF decreases. FIG. 5 shows the estimated PM deposition amounts QPM and NO ₂ when the exhaust gas temperature T _DPF is 230 ° C. (solid line), 250 ° C. (dashed line), 270 ° C. (dashed line). Only the relationship with the / NOx ratio is shown.

The injection amount determination unit 84 includes a base injection amount calculation unit 85, a correction coefficient calculation unit 86, and a multiplier 87, and the NOx amount estimated value NOX _HAT calculated by the NOx amount estimation unit 81 and Based on the estimated value RNO2 of the NO ₂ / NOx ratio calculated by the NO ₂ / NOx ratio estimator 83, the urea water injection amount G _UREA is determined.

The following formulas (15) to (17) are reaction formulas showing the reduction reaction of NO and NO ₂ in the selective reduction catalyst. The reaction shown in the equation (15) is a reaction that simultaneously reduces NO and NO ₂ in the exhaust gas. The reaction shown in the equation (16) is a reaction that reduces only NO in the exhaust gas, and the equation (17). The reaction shown in FIG. ₂ is a reaction that reduces only NO ₂ in the exhaust gas.
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (15)
4NO + 4NH ₃ + O ₂ → 4N ₂ + 16H ₂ O (16)
6NO ₂ + 8NH ₃ → 7N ₂ + 16H ₂ O (17)

The selective reduction catalyst by the reaction shown in the equation (15) to (17) proceeds, but so that the NO and NO ₂ in exhaust gas is reduced by NH _3, progress of each reaction, NO ₂ / NOx ratio is considered to change.

For example, when the NO ₂ / NOx ratio is “0.5”, the molar ratio of NO to NO _{2 in} the exhaust gas is 1: 1. Therefore, the selective reduction catalyst mainly performs the reaction represented by the above formula (15). proceed.

When the NO ₂ / NOx ratio is smaller than “0.5” (NO ₂ lean), that is, when NO is more than NO _2, NO remains that cannot be reduced only by the reaction shown in the above formula (15). The surplus NO is reduced by the progress of the reaction shown in the above formula (16). Therefore, when the NO ₂ / NOx ratio is smaller than “0.5”, as the NO ₂ / NOx ratio decreases, the degree of progress of the reaction shown in the above equation (15) decreases, and the above equation (16) The degree of progress of the reaction shown increases.

On the other _hand, NO 2 / if NOx ratio is greater than "0.5" (NO ₂ rich), that is, when there are more NO ₂ than NO, the only reaction shown in the equation (15) can not be reduced NO ₂ However, this excess NO ₂ is reduced by the progress of the reaction shown in the above formula (17). Therefore, when the NO ₂ / NOx ratio is larger than “0.5”, the progress of the reaction shown in the above equation (15) decreases as the NO ₂ / NOx ratio increases, and the above equation (17). The degree of progress of the reaction shown in FIG.

Here, when the amount of NH ₃ consumed for the reduction of NOx combined with NO and NO ₂ is compared in each reaction, the molar ratio of NOx and NH _{3 in the} reactions shown in the above formulas (15) and (16). Is 1: 1, whereas the molar ratio of NOx to NH _{3 in the} reaction shown in the above formula (17) is 6: 8. That is, in order to reduce NOx by the reaction shown in the above formula (17), a larger amount of NHx than in the case of reducing the same amount of NOx by the reaction shown in the above formulas (15) and (16). ₃ is required, and thus more urea water needs to be supplied.

In the injection amount determination unit 84, the amount of NH ₃ required for NOx reduction varies depending on the point at which a plurality of types of NOx reduction reactions proceed in the selective reduction catalyst as described above and the degree of progress of each reduction reaction. The optimum urea water injection amount _GUREA is determined in consideration of the points. The detailed configuration will be described below.

The base injection amount calculation unit 85 multiplies the estimated NOx amount NOX _HAT calculated by the NOx amount estimation unit 81 by the conversion coefficient K _{CONV_NOX_UREA} as shown in the following equation (18), _{thereby obtaining} the base injection amount G _{UREA_BS} is calculated. In the following equation (18), the conversion coefficient K _{CONV_NOX_UREA} is a conversion coefficient for converting the NOx amount into the urea water injection amount. More specifically, this conversion coefficient K _{CONV_NOX_UREA} is assumed when NOx is reduced to NH ₃ under a molar ratio of 1: 1 as in the reaction shown in the above formula (15) or (16). This is a conversion coefficient for converting the amount of NOx into the amount of urea water necessary for reducing this NOx without excess or deficiency. By multiplying the conversion coefficient K _{CONV_NOX_UREA} by the estimated NOx amount NOX _HAT , the base injection amount G _{UREA_BS} that is the amount of urea water necessary to reduce the amount of NOx flowing into the selective reduction catalyst is _obtained . Can be calculated.

The correction coefficient calculation unit 86 estimates the NO ₂ / NOx ratio RNO2 so as to appropriately correct the base injection amount calculated according to the NOx amount in the exhaust gas according to the ratio of NO ₂ constituting this NOx. Based on the above, the correction coefficient K _RNO2 is calculated. More specifically, the correction coefficient K _RNO2 is calculated by searching a map as shown in FIG. 6 based on the estimated value RNO2 of the NO ₂ / NOx ratio.
According to the map shown in FIG. 6, when the estimated value RNO2 of the NO ₂ / NOx ratio is equal to or less than the threshold value RNO2 _TH set to “0.5”, the degree of progress of the reaction shown in the above equation (17) is sufficient. Therefore, the correction coefficient K _RNO2 is set to “1” regardless of the estimated value RNO2 (see the following equation (19)).
Further, when the estimated value RNO2 of the NO ₂ / NOx ratio is larger than the threshold value RNO2 _TH, it is determined that the progress of the reaction shown in the above equation (17) is high, and therefore the correction coefficient K is determined according to the estimated value RNO2. _RNO2 is set to a value larger than “1”. When only NO ₂ flows, it is considered that only the reaction represented by the above formula (17) proceeds in the selective reduction catalyst. Accordingly, as the correction coefficient _{K RNO2} becomes "8/6" in the time estimate RNO2 is "1.0", the correction coefficient _{K RNO2} when the estimated value RNO2 is larger than the threshold RNO2 _TH is represented by the following formula ( 19), it is set to increase in proportion to the estimated value RNO2.

As shown in the following equation (20), the urea water injection amount G _UREA is calculated based on the base injection amount G _{UREA_BS} calculated based on the NOx amount estimated value NOX _HAT and on the basis of the NO ₂ / NOx ratio estimated value RNO _2. It is determined by multiplying the calculated correction coefficient K _RNO2 . _Thus, when the estimated value RNO2 of NO 2 / NOx ratio is larger than the threshold value RNO2 _TH, depending on the NO 2 / NOx ratio, the urea injection amount _{G UREA} is corrected to the increase side.

According to this embodiment, there are the following effects.
(1) In the present embodiment, an estimated value QPM of the PM accumulation amount in the DPF coated with the oxidation catalyst is calculated, and based on the estimated value QPM and the exhaust gas temperature T _DPF , between the DPF and the selective reduction catalyst An estimated value RNO2 of the exhaust NO ₂ / NOx ratio is calculated. In a DPF coated with an oxidation catalyst, a reaction in which NO is oxidized and NO ₂ is generated, and a reaction in which NO ₂ is reduced by PM deposited on the filter and NO is generated proceeds. Therefore, in the present embodiment, since the change in the degree of progress of the above-described NO oxidation reaction or NO ₂ reduction reaction due to the change in exhaust gas temperature or the accumulation of PM can be taken into consideration, as a result, the DPF is selected. The NO ₂ / NOx ratio of the exhaust gas between the reduction catalysts can be estimated with high accuracy. Furthermore, in the present embodiment, based on the estimated value RNO2 of the NO ₂ / NOx ratio calculated with such high accuracy and the estimated value NOX _HAT of the NOx amount in the exhaust gas calculated separately from the estimated value RNO2, the urea The urea water injection amount _GUREA by the water injection device 62 is determined. Thereby, an appropriate amount of urea water according to the NOx amount and the NO ₂ / NOx ratio can be supplied.

(2) In the present embodiment, a sensor for detecting the NOx amount is estimated by estimating the NOx amount based on parameters that are constantly acquired in engine control, such as the engine speed NE and the fuel injection amount G _FUEL. There is no need to provide it. Therefore, the cost and power consumption required for the sensor can be suppressed. In addition, it is possible to prevent a decrease in purification performance at the time of transition that may occur when a NOx sensor is used.

(3) In the DPF coated with the oxidation catalyst, it is considered that when the amount of PM deposited increases, the progress of the reaction in which NO ₂ is reduced by the carbon constituting the PM and NO is generated increases. In the present embodiment, in consideration of this point, by the estimated value QPM PM accumulation amount is reduced estimates RNO2 of _NO 2 / NOx ratio in accordance with increase, estimates the _NO 2 / NOx ratio of the exhaust with high precision it can.

(4) In the selective reduction catalyst, a reaction that reduces NO and NO ₂ simultaneously (see the above formula (15)), a reaction that reduces only NO (see the above formula (16)), and only NO ₂ is reduced. Three types of reduction reactions with the reaction (see the above formula (17)) can proceed. Here, in the reaction of reducing only NO ₂ , more NH ₃ is required than in the other two reactions. Further, it is considered that when the NO ₂ / NOx ratio is increased, the progress of the reaction for reducing only NO ₂ is increased. Therefore, in the present embodiment, when the NO ₂ / NOx ratio is larger than the threshold value RNO 2 _TH , NH ₃ is insufficient by increasing the urea water injection amount G _UREA according to the estimated value RNO ₂ of the NO ₂ / NOx ratio. Thus, it is possible to suppress a decrease in the NOx purification performance of the selective reduction catalyst.

(5) In this embodiment, the NOx amount estimated value NOX _HAT is calculated based on a neural network excellent in reproducibility of nonlinear dynamic characteristics, so that the NOx amount in the exhaust gas has a nonlinear behavior, for example, during a transient state. Even in such a case, since this can be estimated with high accuracy, an appropriate amount of urea water according to the NOx amount and the NO ₂ / NOx ratio can be injected.

The present invention is not limited to the embodiment described above, and various modifications can be made.
The above embodiment calculates the estimated value RNO2 of the ratio of the NO ₂ amount for the amount of NOx in the exhaust gas _NO 2 / NOx ratio, the _NO 2 / urea water injection amount based on the estimated value RNO2 of NOx ratio _{G UREA} However, the present invention is not limited to this. Calculating the estimated value of the proportion of NO ₂ amount to NO amount of NOx components in the exhaust _NO 2 / NO ratio, correcting the urea injection amount _{G UREA} based on the estimated value of the _NO 2 / NO ratio May be.

In the above embodiment, the exhaust temperature sensor 35 is provided as a temperature acquisition means for acquiring the temperature of the exhaust system, and the NO ₂ / NOx ratio is estimated based on the exhaust temperature T _EX downstream of the DPF detected by the exhaust temperature sensor. However, the temperature of the exhaust system used for estimating the NO ₂ / NOx ratio may be the temperature of the DPF itself in addition to the exhaust temperature downstream of the DPF. Further, the temperature acquisition means is not a sensor that directly detects the temperature of the exhaust gas or the DPF, but parameters indicating the operating state of the engine such as the intake air amount, the fuel injection amount, the water temperature, and the rotational speed, the exhaust pipe, A temperature estimation device that estimates the target temperature based on the heat capacity of an oxidation catalyst, DPF, selective reduction catalyst, and the like provided in the exhaust pipe may be used.

  Moreover, in the said embodiment, although the urea water injection valve 623 and the selective reduction catalyst 61 were provided in the downstream rather than the connection part of the low pressure EGR pipe | tube 46 in the exhaust pipe 30, it does not restrict to this. For example, the urea water injection valve and the selective reduction catalyst may be provided in the exhaust pipe on the downstream side of the DPF and on the upstream side of the connection portion of the low pressure EGR pipe.

In the above-described 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 precursors 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.

In the above embodiment, the DPF coated with the oxidation catalyst is provided, and the catalytic converter incorporating the oxidation catalyst is provided on the upstream side of the DPF. However, the present invention is not limited to this. The catalyst built in the catalytic converter may be a three-way catalyst instead of an oxidation catalyst, or a DPF not coated with an oxidation catalyst may be used.
However, when a DPF not coated with an oxidation catalyst is used, unlike the above embodiment, the reaction shown in the reaction formula (14) hardly occurs in the DPF. Therefore, the NO ₂ / NOx ratio estimation unit takes note of this point. It is necessary to calculate the estimated value RNO2 of the NO ₂ / NOx ratio in a manner different from the above embodiment. More specifically, when the estimated value RNO2 is calculated using a map, it is necessary to use a map different from that shown in FIG. 5 as the map referred to by the NO ₂ / NOx ratio calculation unit. In addition, when the DPF not coated with the oxidation catalyst is used as described above, the NO ₂ / NOx ratio estimated value RNO2 is the same as that in the above embodiment because the reaction of oxidizing NO and generating NO ₂ hardly occurs. It is considered that the correction is made on the decrease side in comparison.

1. Engine (internal combustion engine)
2. Exhaust purification system 30 ... Exhaust pipe (exhaust system)
35 ... Exhaust temperature sensor (temperature acquisition means)
36 ... DPF (filter)
61 ... selective reduction catalyst (selective reduction catalyst)
62 ... Urea water injection device (reducing agent supply means)
8 ... ECU
81 ... NOx amount estimating section (NOx amount estimating means)
82 ... PM accumulation amount estimation unit (deposition amount estimation means)
83... NO ₂ / NOx ratio estimation unit (NO ₂ / NOx ratio estimation means)
84: Injection amount determination unit (injection amount determination means)

Claims (5)

A selective reduction catalyst provided in an exhaust system of an internal combustion engine for reducing NOx in the exhaust in the presence of a reducing agent;
A filter provided upstream of the selective reduction catalyst in the exhaust system and collecting particulate matter in the exhaust;
An exhaust gas purification system for an internal combustion engine comprising a reducing agent injection means for injecting a reducing agent or a precursor thereof into the exhaust gas flowing into the selective reduction catalyst,
A deposition amount estimating means for estimating a particulate matter deposition amount in the filter;
NOx amount estimating means for estimating the amount of NOx in the exhaust between the filter and the selective reduction catalyst in the exhaust system;
Temperature acquisition means for acquiring the temperature of the exhaust system;
Based on the estimated particulate matter accumulation amount and NOx amount and the temperature acquired by the temperature acquisition means, the NO ₂ amount relative to the NOx amount in the exhaust between the filter and the selective reduction catalyst in the exhaust system. and _NO 2 / NOx ratio estimation means for estimating the _NO 2 / NOx ratio corresponding to the ratio of
An exhaust amount of the internal combustion engine, comprising: an injection amount determining unit that determines an injection amount of the reducing agent or the precursor by the reducing agent injection unit based on the estimated NOx amount and the NO ₂ / NOx ratio. Purification system.   The NOx amount estimation means estimates the NOx amount in the exhaust gas between the filter and the selective reduction catalyst based on the rotational speed of the internal combustion engine and the fuel injection amount. Exhaust gas purification system for internal combustion engines. _3. The internal combustion engine according to claim 1, wherein the NO ₂ / NOx ratio estimation means decreases the estimated value of the NO ₂ / NOx ratio as the estimated value of the particulate matter accumulation amount increases. Exhaust purification system. The injection quantity determining means, wherein when the estimated NO 2 _/ NOx ratio is larger than the threshold value, the preceding claims, characterized in that increasing the injection quantity in accordance with the NO 2 _/ NOx ratio of 3 An exhaust purification system for an internal combustion engine according to any one of the above.   The exhaust purification of an internal combustion engine according to claim 2, wherein the NOx amount estimating means estimates the NOx amount based on a neural network configured by connecting a plurality of neurons that output in accordance with a predetermined function. system.

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