JP2014163331A - Control method of exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method of an exhaust emission control device capable of improving estimation accuracy of a trap total amount of an exhaust component per unit time.SOLUTION: Estimation means of the trap total amount of the exhaust component calculates a residual trap possible rate on the basis of the maximum value B of the trap total amount of the exhaust component read from first storage means and the trap total amount of the exhaust component calculated last time; the residual trap possible rate is corrected with a trap characteristic substitutive value P which is read from second storage means as a degree; the corrected residual trap possible rate is multiplied by an inflow A per unit time of a specified exhaust component, which is read from third storage means, to calculate the trap amount per unit time at the present point of time; and the trap amount per unit time at the present point of time is added to the trap total amount calculated last time, and the trap total amount at the present point of time is estimated.

Description

  The present invention relates to a method for controlling an exhaust purification device, and more particularly to a method for estimating the total amount of exhaust components trapped in an exhaust component trap purification device that traps specific exhaust components contained in engine exhaust gas.

  In recent years, lean control for making the engine leaner than the stoichiometric air-fuel ratio has been performed for the purpose of improving fuel efficiency. A NOx trap reduction catalyst (NOx catalyst) is used in the exhaust passage in order to reduce NOx, which is one of the exhaust components discharged along with this. This NOx catalyst becomes saturated with the stored NOx when the lean operation continues for a long time. Therefore, when the stored NOx amount exceeds the predetermined stored amount, the NOx catalyst is enriched with the air-fuel ratio of the exhaust gas to enrich the NOx. Needs to be released to restore the NOx trapping capacity of the catalyst.

  By the way, since the total amount of NOx traps, which is a criterion for determining the timing for switching from lean operation to rich operation as described above, cannot be directly measured, it is generally obtained by estimation. A typical example is that a NOx trap amount per unit time is estimated based on an operation state or the like for each predetermined period (for example, a control cycle or a sampling cycle), and the NOx trap amount per unit time is integrated to obtain a total NOx trap amount. Is estimated. At this time, if there is a difference between the estimated value of the total NOx trap amount and the actual total NOx trap amount, the following problem occurs.

  That is, when the total amount of NOx traps larger than the actual amount is estimated, the NOx releasing process is started even though NOx can still be occluded, or the NOx has already been completely released. Therefore, the NOx release process is continued unnecessarily, leading to deterioration in fuel efficiency. On the other hand, when the total amount of NOx trap that is smaller than the actual amount is estimated, the NOx release process is not started even though NOx has not been occluded, or the NOx has not yet been completely released, but soon. As a result, the NOx releasing process ends and the exhaust gas purification performance deteriorates. Therefore, it is important to accurately estimate the total amount of NOx traps.

  For example, Patent Document 1 discloses a method for improving the estimation accuracy of the total amount of NOx traps. In the method of Patent Document 1, the estimation accuracy of the NOx trap amount per unit time is improved by considering that the NOx trap amount per unit time varies depending on the total amount of NOx traps. Specifically, NOx per unit time is multiplied by a NOx trap amount per unit time multiplied by a correction coefficient (hereinafter referred to as a first correction coefficient) set in accordance with a total NOx trap amount prepared in advance. The trap amount is corrected, and the corrected NOx trap amount per unit time is integrated to estimate the total NOx trap amount. Further, in order to further improve the estimation accuracy of the total NOx trap amount, the first correction factor is set according to the second correction factor set according to the NOx emission amount per unit time and the temperature of the NOx trap catalyst. A method of improving the accuracy of correction by multiplying by a third correction coefficient set in the above is disclosed.

Japanese Patent No. 3925273

  In the method described in Patent Document 1, since it is a method that considers that the amount of NOx traps per unit time varies depending on the total amount of NOx traps as described above, improvement in estimation accuracy can be expected in that respect. Seem. However, since the NOx catalyst chemically traps NOx in the trap material inside the NOx catalyst, the NOx trap amount per unit time is the total amount of NOx traps described in Patent Document 1 and the NOx emission amount per unit time. In addition to the temperature of the NOx trap catalyst, etc., the exhaust gas state varies depending on the operating state, for example, the exhaust gas flow rate, the temperature of the exhaust gas, and the total amount of NOx traps that can be trapped at the maximum in the NOx catalyst. Change. If this point is not taken into account, a deviation occurs between the estimated value of the total NOx trap amount and the actual total NOx trap amount, and it cannot be said that the estimation accuracy of the total NOx trap amount is sufficiently improved. Further, as in Patent Document 1, in the method of correcting by multiplying the relationship between the NOx trap amount per unit time and the total NOx trap amount by a plurality of correction coefficients, errors accumulate as the parameters increase. There is a possibility that a deviation between the estimated value of the total trap amount and the actual total NOx trap amount may occur, and the estimation accuracy of the total NOx trap amount may deteriorate.

  As a method for solving the above problem, for example, a method of calculating the NOx trap amount per unit time from a multi-dimensional map with various parameters changing depending on the operation state can be considered. Since a huge memory capacity is required, the cost of the memory is increased. On the other hand, if the memory capacity is reduced in order to avoid an increase in cost, only limited conditions can be taken into account, leading to deterioration in estimation accuracy.

  Further, as another method for solving the above-described problem, the NOx trap amount per unit time is reduced using the fact that the NOx trap amount per unit time has a decreasing tendency as shown in FIG. A method of approximating with a function using time as a parameter and changing the function according to the operating state is conceivable. That is, the NOx trap amount per unit time decreases as time elapses, and becomes zero when reaching the maximum NOx trap amount that can be trapped in the NOx catalyst (hereinafter referred to as the maximum NOx trap amount). It can be considered that when the operating state changes, the time T until the total amount of NOx trap total amount reaches the maximum value changes. On the other hand, the maximum NOx trap amount B can be determined in advance according to the performance specifications of the NOx catalyst, and the maximum NOx trap amount B is the NOx trap amount per unit time from time t = 0 to t = T. The time until the NOx trap total amount large value B is reached so that the area matches the value of the NOx trap total amount maximum value B when the operating state changes because it matches the area of the graph shown in FIG. If a function that changes T is set, correction according to changes in the operating state can be performed. Specifically, using the relational expressions (1) and (2), which are functions using the following time as a parameter, it is possible to estimate the NOx trap amount per unit time in consideration of changes in the operating state.

ｙは単位時間当たりのＮＯｘトラップ量、ｔは現在時刻、ＴはＮＯｘトラップ総量大値に達するまでの時間、次数ｐは運転状態に応じて設定される実数である。ｋはＮＯｘ触媒に流入する単位時間当たりのＮＯｘ流入量Ａに基づいて定められる係数であり、時刻ｔ＝０すなわちＮＯｘトラップ総量が０の時においては、単位時間当たりのＮＯｘトラップ量は単位時間当たりのＮＯｘ流入量Ａと等しくなると考えることにより、関係式（１）より導かれる。

y is the NOx trap amount per unit time, t is the current time, T is the time until the total amount of NOx trap is reached, and the order p is a real number set according to the operating state. k is a coefficient determined based on the NOx inflow amount A per unit time flowing into the NOx catalyst. When the time t = 0, that is, when the total NOx trap amount is 0, the NOx trap amount per unit time is It is derived from the relational expression (1) by considering that it becomes equal to the NOx inflow amount A.

  However, in such a method using a function with time as a parameter, it is necessary to read it as another function every time the operating state changes. That is, every time the operating state changes, T is calculated so that the area of the function becomes equal to the maximum NOx trap total amount B, and the function in the current operating state is determined, and then the current time t in the function is calculated. Since the processing routine time in the NOx trap total amount estimation becomes longer, the interval for updating the NOx trap total amount becomes longer, and the estimation accuracy of the NOx trap total amount is deteriorated. This will be specifically described with reference to FIGS.

  FIG. 9 shows a NOx trap total amount estimation flow in the case where the change of the operation state is not taken into consideration. First, the operating state of the engine is detected in step 1, the state of the NOx catalyst is detected in step 2, and the maximum NOx trap amount B, NOx per unit time to the NOx catalyst, based on the values detected in steps 1 and 2. The inflow amount A is estimated (steps 3 and 4). Thereafter, the NOx trap amount per unit time is determined from the map of the NOx trap amount per unit time and the total NOx trap amount (step 5). Then, the present NOx trap total amount x is calculated by multiplying the NOx trap amount per unit time determined in Step 5 by the predetermined time Δt of the processing routine and adding it to the previous NOx trap total amount (Step). 6).

  On the other hand, FIG. 10 shows a NOx trap total amount estimation flow when a change in the operating state is taken into consideration using a function with time as a parameter. First, the engine operating state is detected in step 1, the NOx catalyst state is detected in step 2, and the NOx trap total maximum value B, the order set in accordance with the operating state, based on the values detected in steps 1 and 2. p, NOx inflow amount A per unit time to the NOx catalyst is estimated (steps 3 to 5).

  Next, in Step 6 to Step 13, the time T until the NOx trap total amount large value B in the current operation state is reached is calculated. First, a temporary time T until the NOx trap total amount B reaches a large value B is set in step 6, and a temporary coefficient k is calculated from the relational expression (2) in step 7 based on the value. Next, using the relational expression (1), the NOx trap amount per unit time is multiplied by the predetermined time Δt of the processing routine until time t = T, and integration is repeated (steps 8 to 12). Subsequently, a difference between the accumulated amount up to the provisional time T, that is, the total NOx trap amount x0 and a predetermined maximum NOx trap amount B is calculated, and it is determined whether or not the difference is equal to or less than a predetermined threshold value. (Step 13). As a result, if the difference is equal to or smaller than a predetermined value, it is determined that T is appropriate, and the process proceeds to step 15. On the other hand, if the difference is equal to or larger than a predetermined value, it is determined that T is not appropriate, T is corrected (step 14), and then steps 6 to 13 are repeated, and T is corrected until T becomes appropriate. . Through the above steps, T in the current operating state is determined, and functions using the time of the NOx trap amount per unit time in the current operating state as parameters, that is, relational expression (1) and relational expression (2) are obtained. It is determined.

  Subsequently, in step 15 to step 20, the current operating state is changed from the current time in the function having the time of the NOx trap amount per unit time in the current operating state as a parameter, that is, the total NOx trap amount is 0. When the operation continues constantly, the time required to reach the previous total NOx trap amount is calculated. First, from time 0 in the relational expression (1), the NOx trap amount per unit time is multiplied by the predetermined time Δt of the processing routine and accumulated, until the previous NOx trap total amount is reached (step). 15-20). Then, the time t0 when the previous total amount of NOx trap is reached is the current time of the relational expression (1) in the current operation state, and the process proceeds to the next step. In step 21, the currently set T and t0 are introduced into the relational expression (1) to determine the NOx trap amount per unit time in the current operating state.

  Next, the current NOx trap total amount x is calculated by multiplying the NOx trap amount per unit time determined in step 21 by the predetermined time Δt of the processing routine and adding it to the previous NOx trap total amount ( Step 22).

  As described above, when estimating the NOx amount per unit time in consideration of the change in the operating state using the above relational expressions (1) and (2), the NOx trap total amount in the current operating state is set to a large value. A calculation for calculating the time T until the current time t and the current time t of the relational expression (1) in the current operating state is required, which increases the calculation load. Accordingly, the calculation time increases and the calculation time (processing routine time Δt) for calculating the NOx trap amount per unit time increases, so the interval for updating the NOx trap total amount becomes longer, and the NOx trap total amount This will cause a deterioration of the estimation accuracy.

  The present invention has been made in view of the above circumstances, and its purpose is to correctly estimate the NOx trap amount per unit time by correctly considering various parameters that affect the NOx trap amount per unit time. In addition, the estimation accuracy of the NOx trap amount per unit time can be improved with a small memory capacity, and the processing routine time is reduced by suppressing an increase in the computation load, and the total NOx trap amount is updated at shorter intervals. An object of the present invention is to provide a control method for an exhaust gas purification apparatus that improves the estimation accuracy of the total amount of NOx traps.

  In order to solve the above-described problems, an exhaust gas purification method for an engine according to the present invention is configured as follows.

That is, the invention according to claim 1 of the present application is
An exhaust gas purification apparatus that includes an exhaust gas component trap purification device that traps a specific exhaust gas component contained in exhaust gas discharged from an engine in an exhaust system of the engine, and that estimates the total amount of exhaust gas component traps trapped in the exhaust gas component trap purification device A control method,
The exhaust purification device stores a first exhaust component trap total maximum value representing a total exhaust component trap amount that can be trapped at maximum in the exhaust component trap purification device determined in advance based on performance specifications of the exhaust component trap purification device. Storage means;
Second storage means for storing a trap characteristic substitute value determined in advance based on the trap characteristic of the exhaust component trap purifying device that changes according to the state of the exhaust gas flowing into the exhaust component trap purifying device that changes according to the operating state of the engine; ,
Third storage means for storing an inflow amount of the specific exhaust component per unit time flowing into the exhaust component trap purifying device that is predetermined according to the operating state of the engine,
The exhaust component trap total amount estimation means calculates a residual trap possibility rate based on the exhaust component trap total amount maximum value read from the first storage means and the exhaust component trap total amount calculated last time,
The remaining trap possibility rate is corrected with the trap characteristic substitute value read from the second storage means as the order,
Multiplying the corrected residual trap possibility rate and the inflow amount of the specific exhaust component per unit time read from the third storage means to calculate the exhaust component trap amount per unit time at present,
The present exhaust component trap amount per unit time is added to the previously calculated exhaust component trap total amount to estimate the current exhaust component trap total amount.

  According to this, the trap characteristic surrogate value indicating the trap characteristic of the exhaust component trap purifying device, which changes the remaining trap possibility rate calculated based on the maximum exhaust component trap total amount and the current exhaust component trap total amount according to the operating state of the engine. And the NOx trap amount per unit time is calculated by multiplying the corrected residual trap possibility rate by the inflow amount of the specific exhaust component per unit time. The relationship between the amount of traps and the total amount of traps varies depending on the operating conditions, more accurately considered, and the accuracy of estimating the amount of traps per unit time is improved. Accuracy can be improved, and moreover, time is not used as a parameter. Since the trap amount is calculated, the calculation of the time T and the current time t until reaching the large total trap amount as described above becomes unnecessary, the calculation load is small, and the processing routine time can be reduced. The total trap amount can be updated at shorter intervals, and the estimation accuracy of the total NOx trap amount is improved.

  In the present invention, preferably, the trap characteristic substitute value is set based on an engine speed, an engine load, an exhaust gas temperature, and an exhaust component trap device temperature.

  According to this, the engine speed and engine load correlated with the amount of exhaust component contained in the exhaust gas and the exhaust gas flow velocity, the exhaust gas temperature correlated with the remaining trap possibility rate, and the temperature of the exhaust component trap device, Therefore, the trap characteristic substitute value is set based on the trap characteristic substitute value, so that the correction with the trap characteristic substitute value can be performed more accurately, and the estimation accuracy of the total trap amount can be improved.

  Still further, in the present invention, preferably, the maximum value of the exhaust component trap total amount is changed according to deterioration of the exhaust component trap purifying device (claim 3).

  According to this, since it is considered that the exhaust component trap total maximum value changes due to deterioration, the estimation accuracy of the residual trap possibility rate is improved, and the estimation accuracy of the trap total amount is improved.

  Still further, in the present invention, preferably, the exhaust component trap purifying device is a NOx occlusion reduction catalyst (claim 4).

  According to this, the present invention is suitably used particularly in an exhaust component trap purifying apparatus in which it is difficult to directly measure the trap amount, such as a NOx storage reduction catalyst.

  According to the present invention, the estimation accuracy of the total amount of NOx traps is improved in consideration of various parameters that affect the amount of NOx traps per unit time, and the estimation is made by considering changes due to the operating state with a small memory capacity. Since the accuracy can be improved and the increase in the calculation load is suppressed, the processing routine time is reduced, and the total amount of NOx traps can be updated at shorter intervals. Therefore, the estimation accuracy of the total amount of NOx traps can be improved.

1 is a block diagram illustrating an overall configuration of a vehicle according to an embodiment of the present invention. It is a figure which shows the control system of the vehicle shown in FIG. It is a flowchart figure of exhaust component trap total amount estimation in embodiment of this invention. It is a flowchart figure of exhaust component trap total amount maximum value setting in embodiment of this invention. It is a flowchart figure of the exhaust-component trap total amount correction coefficient setting in embodiment of this invention. It is a graph which shows the relationship between the NOx trap amount per unit time and the NOx trap total amount. It is a graph for demonstrating the characteristic of the correction | amendment by the trap characteristic substitute value p. It is a figure which shows the relationship between the amount of NOx traps per unit time when the driving | running state of an engine is constant, and time. It is a flowchart figure of NOx trap total amount estimation in case the change of a driving | running state is not considered. It is a flowchart figure of NOx trap total amount estimation at the time of considering the change of an operating state using the function which uses time as a parameter.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following description of the embodiment is merely an example. FIG. 1 is a block diagram showing an overall configuration of a vehicle according to an embodiment of the present invention, and FIG. 2 is a diagram showing a control system for the vehicle shown in FIG.

  As shown in FIG. 1, a vehicle 1 according to an embodiment of the present invention is a so-called series hybrid vehicle, and is charged with an engine 10, a generator 20 driven by the engine 10, and electric power generated by the generator 20. The battery 30 has a possible high voltage and large capacity, and a travel motor 40 driven by the power generated by the generator 20 driven by the engine 10 and the discharged power of the battery 30.

  In the vehicle 1, an inverter 50 is provided between the generator 20, the battery 30, and the traveling motor 40, and the generated power of the generator 20 is supplied to the battery 30 and / or the traveling motor 40 via the inverter 50. In addition, the electric power discharged from the battery 30 can be supplied to the traveling motor 40.

  The traveling motor 40 is driven by being supplied with at least one of the generated power of the generator 20 and the discharged power of the battery 30, and the driving force of the traveling motor 40 is supplied to the left and right driving wheels via the differential device 60. This is transmitted to the front wheels 61 and 62, so that the vehicle 1 can travel. The traveling motor 40 can also operate as a generator, and operates as a generator when the vehicle 1 is decelerated, so that the battery 30 can be charged with the generated electric power.

  In the vehicle 1, the engine 10 is used only for power generation in the generator 20. In the present embodiment, the engine 10 is not limited to this, but is stored in the hydrogen fuel tank 70. A hydrogen engine in which gas is supplied as fuel is used. A hydrogen engine burns at a high temperature when fuel hydrogen or lubricating oil (metalling oil) in the engine burns, and therefore, nitrogen and oxygen in the intake air are combined, so NOx is contained in the exhaust gas.

  As shown in FIG. 2, the engine 10 is a twin-rotor type rotary engine, and includes a rotor 12 that is in contact with the trochoidal surface of the rotor housing 11 at three points to define three working chambers. By rotating, the eccentric shaft 13 as an output shaft is rotated.

  In the engine 10, an intake passage 14 and an exhaust passage 15 are connected to the rotor housing 11, and a hydrogen injector 17 for injecting hydrogen gas when fuel is supplied to the intake passage 14 by a throttle valve 16 and a premixing system. The exhaust passage 15 is provided with a NOx trap reduction catalyst (hereinafter referred to as NOx catalyst) 80, which is an exhaust component trap purifying device for purifying NOx contained in the exhaust gas. The NOx catalyst 80 occludes NOx during the lean operation, while the NOx occluded is purged by the rich operation.

  A hydrogen injector 18 and a spark plug 19 for injecting hydrogen gas are also attached to the rotor housing 11 so as to face the working chamber of the rotor housing 11. In FIG. 2, the arrows shown in the intake passage 14 and the exhaust passage 15 indicate the flow of intake or exhaust.

  In addition, the vehicle 1 includes a battery current / voltage sensor (battery remaining capacity detecting means) 101 that detects a current flowing in and out of the battery 30 and a voltage of the battery 30, and an accelerator that detects an amount of depression of an accelerator pedal (accelerator opening). An opening sensor 102, a vehicle speed sensor 103 for detecting the vehicle speed, an engine speed sensor 104 for detecting the speed of the engine 10, an air-fuel ratio sensor 105 for detecting the air-fuel ratio, and a catalyst for detecting the temperature of the NOx catalyst 80 A temperature detection sensor 106 and an exhaust gas temperature sensor 108 for detecting the exhaust gas temperature upstream of the NOx catalyst are mounted.

  The vehicle 1 is also provided with a control unit 100 that comprehensively controls the configuration related to the vehicle 1. The control unit 100 includes a battery current / voltage sensor 101, an accelerator opening sensor 102, a vehicle speed sensor 103, Various signals are input from the engine speed sensor 104, the air-fuel ratio sensor 105, the catalyst temperature detection sensor 106, and the like. The control unit 100 can also output control signals to the inverter 50, the throttle valve actuator 107, the hydrogen injectors 17 and 18, the spark plug 19, and the like.

  The control unit 100 controls the inverter 50 to drive the traveling motor 40 only with the discharge power from the battery 30, the mode with only the generated power from the generator 20, the battery 30 and the fuel tank It is possible to switch between the modes performed with the power from both of the 20. In addition, a first storage unit to a third storage unit related to the NOx trap total amount estimation described later are provided.

  The engine 10 controlled by the control unit 100 is normally operated at a lean air-fuel ratio (for example, an excess air ratio λ = 2.3) that is leaner than the stoichiometric air-fuel ratio in order to improve fuel efficiency and improve fuel efficiency. Therefore, the constant rotation speed operation is performed at a constant rotation speed (for example, 2000 rpm) at a predetermined rotation speed that is most efficient.

  When the total amount of NOx traps in the NOx catalyst 80 increases to a predetermined amount or more that is set in advance, the engine 10 is switched to a rich operation where the stoichiometric air-fuel ratio or a rich air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio (for example, excess air ratio λ = 1). Driving). The rich operation is executed until the NOx occlusion amount in the NOx catalyst 80 becomes equal to or lower than a certain lower limit value (for example, 0%) that is sufficiently reduced, but in the embodiment, the NOx occlusion amount is reduced to the lower limit value. The operation is performed for a predetermined time (for example, 10 seconds) set to a sufficient time. The engine speed is a constant speed at the same predetermined speed as that during lean operation. Of course, after the NOx occlusion amount in the NOx catalyst 80 is sufficiently reduced, the engine 10 is returned to the lean operation again.

  The total amount of NOx traps, which is a criterion for determining the timing for switching to rich operation in order to purge NOx occluded in the NOx catalyst 80, cannot be directly measured, and is thus obtained by estimation. At this time, if the estimation accuracy of the total amount of NOx traps is poor, the NOx release process is started even though NOx can still be occluded, or NOx is released even though NOx has already been completely released. Processing will be continued, leading to deterioration of fuel efficiency. On the other hand, when the total amount of NOx trap that is smaller than the actual amount is estimated, the NOx release process is not started even though the NOx can not be occluded already, or the NOx is not yet completely released, but soon. As a result, the NOx releasing process ends, and the exhaust gas purification performance deteriorates. Therefore, in the present invention, the total amount of NOx traps is accurately estimated by the method described below.

  FIG. 3 is a flowchart of NOx trap total amount estimation in the present invention. First, in order to observe the operating state of the engine in step 1, engine speed, engine load, exhaust gas temperature, etc. are detected. Next, in step 2, in order to observe the state of the NOx catalyst, the NOx catalyst temperature, the previously calculated total amount of NOx traps, and the like are detected. Since the NOx catalyst chemically traps NOx, it varies depending on the state of the exhaust gas flowing into the NOx catalyst, which varies depending on the engine operating state, that is, the flow rate and temperature of the exhaust gas, and the amount of NOx contained in the exhaust gas. At the same time, the trap characteristics change depending on the state of the NOx catalyst that changes depending on the state of the exhaust gas flowing into the NOx catalyst that changes depending on the operating state of the engine, that is, the NOx catalyst temperature and the total amount of NOx traps trapped in the NOx catalyst. . Therefore, first, the information of step 1 and step 2 is acquired as a parameter for determining such trap characteristics.

  Subsequently, in step 3, the maximum NOx trap amount B is set. Specifically, the NOx trap total amount maximum value using the engine load and engine speed determined in advance as parameters based on the NOx catalyst performance specifications stored in the first storage means is detected in step 1. The maximum NOx trap total value is set by reading the data corresponding to the engine speed and the engine load. The maximum NOx trap total value B varies depending on the operating state of the engine, and its characteristics are determined as performance specifications of the NOx catalyst in various operating states, and can be determined in advance based on experimental results. Specifically, for example, a map of changes in NOx trap total maximum value B with respect to engine speed and engine load that correlate with exhaust gas flow velocity and temperature, and catalyst temperature, based on experimental results. Referring to the NOx trap total amount maximum value B, it is possible to accurately estimate the NOx trap total amount maximum value that changes depending on the operation state. Further, by using the flow shown in FIGS. 4 and 5, it is possible to set the maximum NOx trap total maximum value with higher accuracy. FIG. 4 is a flow chart for setting the maximum NOx trap total amount, and FIG. 5 is a flow for setting the correction coefficient Kn for the maximum NOx trap total amount. As in step 32, the accuracy of the maximum NOx trap total value can be increased by adding the maximum NOx trap value to the engine speed and the engine load and using a map with exhaust gas temperature and NOx catalyst temperature as parameters. it can. Further, by multiplying the NOx trap total amount maximum value by a correction coefficient that is set so as to decrease according to the deterioration of the NOx catalyst, the accuracy of the NOx trap total amount maximum value is further improved by taking the NOx catalyst deterioration into consideration. (Step 33, Step 34). The method for determining the deterioration is not particularly limited. For example, it can be determined according to the number of NOx releasing processes as in the present embodiment (steps 331 to 334).

  Subsequently, in Step 4 of FIG. 3, a trap characteristic substitute value p representing the trap characteristic of the NOx catalyst is set. Specifically, a map of the trap characteristic substitute value p using parameters determined in advance based on the trap characteristics of the NOx catalyst stored in the second storage means, such as engine load, engine speed, exhaust gas temperature, and NOx catalyst temperature. , The trap characteristic substitute value p is set by reading data corresponding to the engine speed, engine load, exhaust gas temperature detected in step 1 and NOx catalyst temperature detected in step 2. As described above, the trap characteristic of the NOx catalyst varies depending on the state of the exhaust gas flowing into the NOx catalyst and the state of the NOx catalyst, which vary depending on the operating state of the engine. Therefore, in the present invention, such trap characteristics of the NOx catalyst are expressed by a trap characteristic substitute value p in which values are set based on various parameters related to trap characteristics that change depending on various operating conditions. For example, the trap characteristic substitute value p is obtained by calculating the engine speed, the engine load correlated with the NOx amount contained in the exhaust gas and the exhaust gas flow velocity, and the exhaust gas temperature and the NOx catalyst temperature correlated with the remaining trap possibility rate. The trap characteristics when changed are determined in advance by experiments or the like.

  Subsequently, in step 5, the NOx inflow amount A per unit time flowing into the NOx catalyst is estimated. Specifically, referring to the map of NOx inflow amount A per unit time using the engine load and engine speed stored in the third storage means as parameters, the engine speed and engine load detected in step 1 are By reading the corresponding data, the NOx inflow amount A per unit time is set.

Subsequently, in step 6, the NOx trap amount y per unit time is estimated. The NOx trap amount y per unit time is calculated based on the NOx trap total amount maximum value B set in step 3 and the NOx trap total amount x calculated last time. Is corrected with the trap characteristic substitution value p set in step 4 as the order, and the corrected residual trap possibility rate is multiplied by the NOx inflow amount A per unit time estimated in step 4. The current trap amount per unit time is calculated. Specifically, in the following relational expression (3), the maximum NOx trap amount B set in step 3, the total NOx trap amount x calculated in the previous step, the trap characteristic substitute value p set in step 4, and the step By introducing the NOx inflow amount A per unit time estimated in 5, the NOx trap amount y per unit time is calculated.

  Next, the concept of deriving the relational expression (3) will be described. As described above, the NOx trap amount per unit time in consideration of changes due to the operating state can be expressed by the relational expression (1) and the relational expression (2) using time as a parameter, but every time the driving state changes. It is necessary to calculate T in which the area of the function is equal to the total NOx trap total value B, determine the function in the current operating state, and then calculate the current time t in the function. Therefore, the processing routine time in the NOx trap total amount estimation is increased, and the estimation accuracy of the NOx trap total amount is deteriorated.

Ｃは積分定数。 Therefore, in the present invention, a relational expression in which the characteristics of the NOx catalyst are correctly expressed with respect to the NOx amount per unit time and does not include the current time t is derived. First, the relational expression (1) is time-integrated so as not to include the current time t. Here, if y is integrated over time, it can be considered that the total amount of NOx traps x is obtained, so the following relational expression is derived.

C is an integral constant.

At this time, because of the characteristics of the NOx catalyst, it can be considered that the total amount of NOx trap x = 0 at the current time t = 0, and therefore, the relational expression (4) can be derived as follows.

Moreover, the following relational expression is obtained by applying the relational expression (1) to the relational expression (5).

Furthermore, since the total NOx trap amount x at time T can be considered to coincide with the maximum NOx trap amount B, the following relational expression is obtained from the relational expression (5) and the relational expression (2).

Here, the following relational expression is obtained by applying relational expression (2) to relational expression (6).

For the sake of simplification, the following relational expression is obtained by applying the relational expression (7) by dividing both sides of the relational expression (8) by (−T) ^{P + 1} .

  Here, p is a trap characteristic surrogate value set according to the operating state, and even if p / (p + 1) is replaced with p, the substantial meaning is the same. Is guided.

  This relational expression (3) indicates that the relationship between the NOx trap amount y per unit time and the total NOx trap amount is a curve relationship as shown in FIG. That is, when the NOx trap total amount x is 0, the NOx trap amount y per unit time becomes equal to the NOx inflow amount A per unit time flowing into the NOx catalyst, and as the NOx trap total amount x increases, the NOx per unit time is increased. The trap amount y decreases, and the NOx catalyst characteristic that the NOx trap amount y per unit time becomes 0 when the NOx trap total amount reaches the NOx trap total maximum value B is correctly expressed. Next, changes in the relationship between the NOx trap amount y and the NOx trap total amount x per unit time when the trap characteristic substitute value p is changed will be described with reference to FIG.

  7A shows a case where the trap characteristic substitute value p set in step 4 of FIG. 3 is large, and FIG. 7B shows a case where the trap characteristic substitute value p set in step 4 of FIG. 3 is small. As described above, when the trap characteristic substitute value p is changed, the NOx trap amount per unit time per unit time flowing into the NOx catalyst when the NOx trap total amount x, which is the basic characteristic of the NOx trap catalyst described above, is zero. NOx trap total amount from 0 to NOx trap while maintaining the feature that NOx trap amount y per unit time becomes zero when NOx trap total amount reaches NOx trap total maximum value B. Since the curvature of the curve up to the total maximum value B can be changed, it is more correctly considered that the relationship between the NOx trap amount per unit time and the total NOx trap amount changes depending on the operating state, so that the NOx trap per unit time The quantity estimation accuracy is improved. In addition, since the trap characteristic that changes according to the operating state is expressed as a single value as the trap characteristic substitute value p, there is little accumulation of errors that occur when multiplying multiple correction factors, and more correct correction can be performed. The estimation accuracy of the NOx trap amount per unit time is improved. Furthermore, since it is possible to consider that the maximum value of the total NOx trap amount varies depending on the operating state, the estimation accuracy of the NOx trap amount per unit time is improved. Further, the trap characteristic substitute value p is determined based on various parameters that affect the trap characteristic of the NOx catalyst, specifically, the engine speed, the engine load, the exhaust gas temperature, and the NOx catalyst temperature. Therefore, more accurate correction is possible, and the estimation accuracy of the NOx trap amount per unit time is improved. Further, the map prepared in advance includes the maximum NOx trap amount B stored in the first storage means, the trap characteristic substitute value p stored in the second storage means, and the NOx trap per unit time stored in the third storage means. Since the inflow amount A is suppressed, the estimation accuracy can be improved by considering the change due to the operation state with a small memory capacity. Further, if the trap characteristic substitute value p is determined based on the engine speed and the engine load that are correlated with the exhaust gas temperature and the NOx catalyst temperature, the memory capacity can be further reduced. Further, since the relational expression (3) is calculated without using the time as a parameter, the calculation of the time T and the current time t until reaching the large amount of trap total amount as described above becomes unnecessary, and the calculation load Since the processing routine time can be reduced, the total NOx trap amount can be updated at shorter intervals, and the estimation accuracy of the total NOx trap amount is improved.

  Subsequently, the current NOx trap total amount x is calculated by multiplying the NOx trap amount per unit time determined in Step 6 by the predetermined time Δt of the processing routine and adding it to the previous NOx trap total amount ( Step 7).

  In step 8, it is determined whether or not the current total NOx trap amount x is equal to or smaller than a predetermined threshold value. If the total NOx trap amount x is equal to or smaller than the predetermined value, it is assumed that NOx can still be trapped in the NOx catalyst. The operation is continued, and the NOx trap total amount estimation flow in the current operation state ends. On the other hand, if the current total NOx trap amount x is equal to or greater than a predetermined value, it is determined that no more NOx can be trapped in the NOx catalyst, and a rich purge is performed for a predetermined time (step 9). When the rich purge is completed, the estimated value of the total NOx trap amount is reset to 0 (step 10), and the lean operation is resumed.

  As described above, the present invention is suitably used particularly in an exhaust component trap purifying apparatus in which it is difficult to directly measure the trap amount such as a NOx catalyst.

  In this embodiment, the present invention is applied to a NOx catalyst. However, the present invention is not limited to a NOx catalyst, and an exhaust component trap for trapping a specific exhaust component contained in exhaust gas discharged from an engine. The present invention can also be applied to a purification device such as a particulate filter. That is, the trap characteristics of the particulate filter vary depending on the state of the exhaust gas flowing into the particulate filter, which varies depending on the operating condition, for example, the amount of particulates contained in the exhaust gas, the total amount of particulate traps trapped in the particulate filter, etc. Changes. Therefore, by applying the present invention, the total amount of particulate traps can be estimated with high accuracy. Further, the engine is not limited to a hydrogen engine. For example, a gasoline engine or an engine using biofuel as fuel may be used.

  As described above, according to the present invention, various parameters affecting the exhaust component trap amount per unit time are properly considered to improve the estimation accuracy of the exhaust component trap total amount, and the estimation accuracy can be reduced with a small memory capacity. Since the improvement can be achieved and the processing load time is reduced by suppressing the increase in the calculation load, the total amount of NOx traps can be updated at shorter intervals, and the accuracy of estimating the total amount of NOx traps can be improved. It may be suitably used in the field of device control.

10: Engine 15: Exhaust passage 17, 18: Fuel injection valve 19: Spark plug 20: Generator 30: Battery 40: Traveling motor 70: Hydrogen tank 80: Exhaust component trap purifier (NOx catalyst)
100: Control unit (control means)

Claims (4)

An exhaust gas purification apparatus that includes an exhaust gas component trap purification device that traps a specific exhaust gas component contained in exhaust gas discharged from an engine in an exhaust system of the engine, and that estimates the total amount of exhaust gas component traps trapped in the exhaust gas component trap purification device A control method,
The exhaust purification device stores a first exhaust component trap total maximum value representing a total exhaust component trap amount that can be trapped at maximum in the exhaust component trap purification device determined in advance based on performance specifications of the exhaust component trap purification device. Storage means;
Second storage means for storing a trap characteristic substitute value determined in advance based on the trap characteristic of the exhaust component trap purifying device that changes according to the state of the exhaust gas flowing into the exhaust component trap purifying device that changes according to the operating state of the engine; ,
Third storage means for storing an inflow amount of the specific exhaust component per unit time flowing into the exhaust component trap purifying device that is predetermined according to the operating state of the engine,
The exhaust component trap total amount estimation means calculates a residual trap possibility rate based on the exhaust component trap total amount maximum value read from the first storage means and the exhaust component trap total amount calculated last time,
The remaining trap possibility rate is corrected with the trap characteristic substitute value read from the second storage means as the order,
Multiplying the corrected residual trap possibility rate and the inflow amount of the specific exhaust component per unit time read from the third storage means to calculate the exhaust component trap amount per unit time at present,
A control method for an exhaust emission control device, wherein the exhaust gas trap amount per unit time is added to the exhaust gas trap total amount calculated previously to estimate the current exhaust gas trap amount.   The control method for an exhaust emission control device according to claim 1, wherein the trap characteristic substitute value is set based on an engine speed, an engine load, an exhaust gas temperature, and an exhaust component trap device temperature. .   3. The exhaust purification device control method according to claim 1, wherein the maximum value of the exhaust component trap total amount is changed according to deterioration of the exhaust component trap purification device.   The exhaust purification device control method according to claim 1, wherein the exhaust component trap purification device is a NOx occlusion reduction catalyst.

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