JP2016079883A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict an estimated value of adsorption amount of NHat the time of restarting against its excessive reduction in respect to an actual adsorption amount of NHin the exhaust emission control system for estimating an adsorption amount of NHof SCR arranged at a discharging passage of an internal combustion engine.SOLUTION: This invention relates to an exhaust emission control system for estimating adsorption amount of NHat the starting time that is adsorption amount of NHof SCR catalyst at the restarting time of an internal combustion engine by subtracting a reduced amount of NHat the stopping time of the internal combustion engine from an adsorption amount of NHat the stopping time that is an adsorption amount of NHof SCR catalyst at the stopping time of the internal combustion engine, when adsorption amount of NHat the stopping time is larger than a prescribed threshold, an amount in which the reduced amount of NHis subtracted from an adsorption amount of NHat the stopping time is estimated as an adsorption amount of NHat the starting time, and when an adsorption amount of NHat the stopping time is less than a prescribed threshold, the adsorption amount of NHat the stopping time is estimated as an adsorption amount of NHat the starting time.SELECTED DRAWING: Figure 7

Description

The present invention relates to an exhaust gas purification system for an internal combustion engine, and more particularly to a technique for estimating the NH ₃ adsorption amount of a selective catalytic reduction catalyst disposed in an exhaust passage of the internal combustion engine.

As an exhaust gas purification system for an internal combustion engine mounted on a vehicle or the like, an exhaust gas purification device including a selective reduction catalyst (SCR (Selective Catalytic Reduction) catalyst), and ammonia (NH ₃ ) or a precursor of NH ₃ to the exhaust gas purification device And a supply device that supplies the additive, and estimates the amount of NH ₃ adsorbed on the SCR catalyst (hereinafter referred to as “NH ₃ adsorption amount”), so that the estimated value becomes the target amount. In addition, those that control the amount of additive added are known.

By the way, NH ₃ adsorbed on the SCR catalyst may be desorbed from the SCR catalyst during the stop period of the internal combustion engine, or may be oxidized by reacting with oxygen (O ₂ ) in the exhaust passage. Therefore, when the internal combustion engine is restarted after being stopped, if the supply amount of the additive is controlled based on the NH ₃ adsorption amount at the previous stop, the actual NH ₃ adsorption amount of the SCR catalyst is set to the target amount. There is a possibility that exhaust emissions will be deteriorated.

Therefore, when the internal combustion engine is restarted after being stopped, the amount of the additive to the amount corresponding to the actual NH ₃ adsorption amount of the SCR catalyst, NH ₃ during the stop period of the internal combustion engine It is necessary to estimate the NH ₃ adsorption amount at the time of restart in consideration of the decrease amount of the adsorption amount (hereinafter referred to as “NH ₃ decrease amount”). NH ₃ as a method of estimating the amount of reduction, the length of the stop period of the engine, and based on the history of the outside air temperature during the stop period, a method of estimating the NH ₃ reduction is known (e.g., patent Reference 1).

JP 2010-209711 A JP 2012-057591 A JP 2010-223178 A JP 2011-241686 A

Incidentally, SCR catalyst, NH ₃ is desorbed friendly environment, or even in the easily oxidized environment NH _3, has a continuously adsorbs NH ₃ in a certain amount of stable characteristics. If the NH ₃ reduction amount is estimated without taking such characteristics into consideration, the estimated value of the NH ₃ adsorption amount when the internal combustion engine is restarted may be excessively smaller than the actual NH ₃ adsorption amount. There is.

The present invention has been made in view of the above situation, and an object of the present invention is to recycle an internal combustion engine in an exhaust purification system for estimating the NH ₃ adsorption amount of an SCR catalyst disposed in an exhaust passage of the internal combustion engine. This is to prevent the estimated value of the NH ₃ adsorption amount at the time of starting from becoming excessively small with respect to the actual NH ₃ adsorption amount.

The present invention, in order to solve the problems described above, the stop adsorbed NH ₃ amount is adsorbed NH ₃ amount of the SCR catalyst at the previous stop of the internal combustion engine, the adsorbed NH ₃ amount in the stop period of the internal combustion engine By subtracting the NH ₃ reduction amount, which is the reduction amount, the SCR at the start of the internal combustion engine
In the exhaust purification system for estimating a starting adsorbed NH ₃ amount NH ₃ is adsorbed amount of catalyst, if stopped adsorbed NH ₃ amount is larger than a predetermined threshold limit adsorbed NH ₃ amount when the starting above a predetermined threshold value and, when stopped adsorbed NH ₃ amount is less than the predetermined threshold has to set the start-time adsorbed NH ₃ amount the stop adsorbed NH ₃ amount.

Specifically, the present invention relates to an exhaust purification device that is disposed in an exhaust passage of an internal combustion engine and includes a selective reduction catalyst (SCR catalyst), and to the exhaust gas flowing into the exhaust purification device, ammonia (NH ₃ ) or NH _And an addition device for adding the additive as the precursor of No. ₃ , and the amount of NO _X flowing into the exhaust purification device and the amount of the additive added from the addition device during the operation period of the internal combustion engine, as parameters An exhaust gas purification system comprising: an NH ₃ adsorption amount that is an amount of NH ₃ adsorbed on the SCR catalyst; and at least an internal combustion engine when the internal combustion engine is restarted after being stopped the temperature of the selective reduction catalyst at the time of engine stop as a parameter, estimates the NH ₃ reduction is a reduction amount of adsorbed NH ₃ amount in the stop period of the internal combustion engine, stopping the internal combustion engine In the NH ₃ reduction by subtracting the amount of NH ₃ that is adsorbed on the SCR catalyst when the internal combustion engine is restarted from the stop adsorbed NH ₃ amount is an operation result of said operation means during further comprising estimating means for estimating the certain starting adsorbed NH ₃ amount when the stop time of adsorbed NH ₃ amount is larger than the predetermined threshold, the estimation means, said NH ₃ decreases from stop adsorbed NH ₃ amount If the difference obtained by subtracting the amount is greater than or equal to a predetermined threshold value, the difference is estimated as the NH ₃ adsorption amount at the time of starting, and if the difference is less than the predetermined threshold value, the predetermined threshold is set to the NH at starting time. ₃ is estimated as an adsorption amount, when the stop time of adsorbed NH ₃ amount is less than the predetermined threshold value, the estimating means, the stop time of adsorbed NH ₃ amount to estimate as the starting NH ₃ adsorption did.

Here, the "predetermined threshold" is likely temperature range temperature away NH ₃ from the SCR catalyst removal of the SCR catalyst, or NH ₃ is even the _{O 2} reaction (oxidation) easily temperature range, the SCR catalyst Is the amount of NH ₃ adsorption that can be adsorbed stably.

In the exhaust purification system configured as described above, when the internal combustion engine is stopped and restarted, the estimation means estimates the NH ₃ reduction amount using the temperature of the SCR catalyst when the internal combustion engine is stopped as a parameter. Here, during the stop period of the internal combustion engine, NH ₃ adsorbed on the SCR catalyst is separated from the SCR catalyst or reacts (oxidizes) with O ₂ in the exhaust passage, thereby reducing the NH ₃ adsorption amount. To do. At that time, the amount and oxidation of NH ₃ in NH ₃ desorbed from the SCR catalyst, the temperature of the SCR catalyst at the time of stop of the internal combustion engine correlates (hereinafter referred to as "stop-time catalyst temperature") and. For example, compared to the case when stop-time catalyst temperature is high is low, becomes large amount of NH ₃ which is oxidized amount of NH ₃ desorbed from the SCR catalyst during the stop period of the internal combustion engine, and in the SCR catalyst. Therefore, the NH ₃ decrease amount can be estimated using the stop catalyst temperature as a parameter by experimentally obtaining a correlation between the stop catalyst temperature and the NH ₃ decrease amount in advance. Since the NH ₃ decrease amount also changes depending on the length of the stop period (stop time) of the internal combustion engine, the relationship between the stop catalyst temperature, the stop time, and the NH ₃ decrease amount is obtained in advance, and the stop catalyst is determined. The NH ₃ reduction amount may be estimated using temperature and stop time as parameters.

When NH ₃ reduction is estimated by the method as described above, the estimation means subtracts the NH ₃ reduction from stop adsorbed NH ₃ amount estimating the starting adsorbed NH ₃ amount. When the startup NH ₃ adsorption amount is estimated in this way, the estimated value of the NH ₃ adsorption amount after the restart of the internal combustion engine is suppressed from being larger than the actual NH ₃ adsorption amount, and accordingly, from the addition device It is suppressed that the amount of additive to be added is less than the amount that can purify NO _X in the exhaust gas without excess or deficiency (hereinafter referred to as “appropriate addition amount”).

By the way, when the stop NH ₃ adsorption amount is larger than the predetermined threshold value, the NH ₃ adsorption amount of the SCR catalyst decreases during the stop period of the internal combustion engine, but the stop NH ₃ adsorption amount is equal to or less than the predetermined threshold value. In this case, the NH ₃ adsorption amount of the SCR catalyst does not decrease during the stop period of the internal combustion engine. Therefore, when the stop time of adsorbed NH ₃ amount is less than the predetermined threshold value, the adsorbed NH ₃ amount at the starting time is estimated by subtracting the NH ₃ reduction from stop adsorbed NH ₃ amount, startup NH ₃ There is a possibility that the adsorption amount becomes excessively small with respect to the actual NH ₃ adsorption amount.

Also, if the stop adsorbed NH ₃ amount is larger than the predetermined threshold value is adsorbed NH ₃ amount of the SCR catalyst is reduced during the stop period of the internal combustion engine, the adsorbed NH ₃ amount of the SCR catalyst is above a predetermined threshold value When the amount is reduced to the same amount, the NH ₃ adsorption amount does not decrease thereafter. Therefore, if the difference obtained by subtracting the NH ₃ reduction from stop adsorbed NH ₃ amount becomes smaller than the predetermined threshold value, the difference is estimated as the start timing adsorbed NH ₃ amount, startup NH ₃ There is a possibility that the adsorption amount becomes excessively small with respect to the actual NH ₃ adsorption amount.

On the other hand, when the stop NH ₃ adsorption amount is equal to or less than a predetermined threshold, the estimation means of the present invention estimates the stop NH ₃ adsorption amount as the start NH ₃ adsorption amount. As described above, when the startup NH ₃ adsorption amount is estimated, it is suppressed that the startup NH ₃ adsorption amount becomes excessively smaller than the actual NH ₃ adsorption amount. Furthermore, estimation means of the present invention, when the stop time of adsorbed NH ₃ amount is larger than the predetermined threshold value, the difference obtained by subtracting the NH ₃ reduction from the stop adsorbed NH ₃ amount is predetermined If it is less than the threshold value, the startup NH ₃ adsorption amount is estimated to be the same amount as the predetermined threshold value. In this way, when the startup NH ₃ adsorption amount is limited to the predetermined threshold value or more, it is possible to more reliably suppress the startup NH ₃ adsorption amount from being excessively smaller than the actual NH ₃ adsorption amount. it can.

Here, the amount of NH ₃ that can be stably adsorbed by the SCR catalyst tends to decrease when the temperature of the SCR catalyst is higher than when the temperature of the SCR catalyst is low. Therefore, the predetermined threshold value may be set to a smaller value when the temperature of the selective catalytic reduction catalyst when the internal combustion engine is stopped is higher than when the temperature is low. When the predetermined threshold is set in this way, the error between the startup NH ₃ adsorption amount and the actual NH ₃ adsorption amount can be reduced more reliably.

According to the present invention, in the exhaust purification system for estimating the adsorbed NH ₃ amount of the SCR catalyst disposed in an exhaust passage of an internal combustion engine, the estimated value of the adsorbed NH ₃ amount at the restart of the internal combustion engine is actually adsorbed NH ₃ It can suppress that it decreases excessively with respect to quantity.

It is a figure which shows schematic structure of the exhaust system of the internal combustion engine to which this invention is applied. It is a diagram showing the relationship between the NO _X purification rate temperature and the SCR catalyst in the exhaust flow and SCR catalyst that passes through the SCR catalyst. NH of the SCR catalyst ₃ is a graph showing the relationship between the temperature and the NH ₃ oxidation amount of adsorption amount and the SCR catalyst. It is a diagram showing a relationship between the adsorbed NH ₃ amount and the NH ₃ concentration in exhaust gas flowing out of the temperature and the SCR catalyst of the SCR catalyst of the SCR catalyst. It is a figure which shows the relationship between the catalyst temperature at the time of a stop in the environment where external temperature is the highest, a stop time, and the amount of reductions. It is a figure which shows the relationship between the catalyst temperature at the time of a stop, and a threshold value. It is a flowchart showing a processing routine executed by the ECU in estimating the starting adsorbed NH ₃ amount.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of an exhaust system of an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) operated in a lean combustion mode. The internal combustion engine 1 may be a spark ignition type internal combustion engine (gasoline engine) capable of lean burn operation.

  The internal combustion engine 1 is connected to an exhaust pipe 2 for circulating burned gas (exhaust gas) discharged from the cylinder. A first catalyst casing 3 is disposed in the middle of the exhaust pipe 2. A second catalyst casing 4 is disposed in the exhaust pipe 2 downstream of the first catalyst casing 3.

  The first catalyst casing 3 includes, for example, an oxidation catalyst and a particulate filter inside a cylindrical casing. In that case, the oxidation catalyst may be carried on a catalyst carrier disposed upstream of the particulate filter, or may be carried on the particulate filter. The first catalyst casing 3 may contain a three-way catalyst or an occlusion reduction type catalyst instead of the oxidation catalyst.

The second catalyst casing 4 accommodates a catalyst carrier on which an SCR catalyst is supported in a cylindrical casing. The catalyst carrier is composed of, for example, an alumina-based or zeolite-based active component (support) on a monolith type substrate having a honeycomb-shaped cross section formed of cordierite, Fe-Cr-Al heat-resistant steel, or the like. It is a coated one. Note that a catalyst carrier on which an oxidation catalyst is supported may be disposed downstream of the SCR catalyst in the second catalyst casing 4. The oxidation catalyst in that case is provided to oxidize NH ₃ that has passed through the SCR catalyst out of NH ₃ supplied to the SCR catalyst. The second catalyst casing 4 corresponds to an “exhaust gas purification device” according to the present invention.

An addition valve 5 for adding (injecting) ammonia (NH ₃ ) or an additive that is a precursor of NH ₃ into the exhaust pipe 2 between the first catalyst casing 3 and the second catalyst casing 4. Is arranged. The addition valve 5 is connected to an additive tank 51 via a pump 50. The pump 50 sucks the additive stored in the additive tank 51 and pumps the sucked additive to the addition valve 5. The addition valve 5 injects the additive pumped from the pump 50 into the exhaust pipe 2. The combination of the addition valve 5, the pump 50, and the additive tank 51 corresponds to the “addition device” according to the present invention.

Here, the additive stored in the additive tank 51 is NH ₃ gas or an aqueous solution such as urea or ammonium carbamate. In this embodiment, an aqueous urea solution is used as the additive. When the urea aqueous solution is injected from the addition valve 5, the urea aqueous solution flows into the second catalyst casing 4 together with the exhaust gas. At that time, the urea aqueous solution is thermally decomposed by the heat of the exhaust or is hydrolyzed by the SCR catalyst. When the urea aqueous solution is thermally decomposed or hydrolyzed, NH ₃ is generated. The NH ₃ thus produced is adsorbed (or occluded) by the SCR catalyst. NH ₃ adsorbed on the SCR catalyst reacts with NO _X contained in the exhaust to generate N ₂ and water (H ₂ O). That is, NH ₃ functions as a NO _X reducing agent.

The internal combustion engine 1 configured as described above is provided with an ECU (Electronic Control Unit) 8. The ECU 8 is an electronic control unit that includes a CPU, ROM, RAM, backup RAM, and the like. Various sensors such as a NO _X sensor 6, an exhaust temperature sensor 7, a crank position sensor 9, an accelerator position sensor 10, and an air flow meter 11 are electrically connected to the ECU 8.

The NO _X sensor 6 is disposed in the exhaust pipe 2 downstream from the second catalyst casing 4, and outputs an electrical signal that correlates with the NO _X concentration of the exhaust gas flowing out from the second catalyst casing 4. When the second catalyst casing 4 contains the SCR catalyst and the oxidation catalyst, the NO _X sensor 6 is desirably arranged between the SCR catalyst and the oxidation catalyst. The exhaust temperature sensor 7 is disposed in the exhaust pipe 2 downstream from the second catalyst casing 4 and outputs an electrical signal correlated with the temperature of the exhaust gas flowing out from the second catalyst casing 4.

  The crank position sensor 9 outputs an electrical signal correlated with the rotational position of the output shaft (crankshaft) of the internal combustion engine 1. The accelerator position sensor 10 outputs an electrical signal that correlates with the operation amount of the accelerator pedal (accelerator opening). The air flow meter 11 outputs an electrical signal correlated with the amount (mass) of air taken into the internal combustion engine 1.

Further, the ECU 8 is electrically connected to various devices (for example, a fuel injection valve) attached to the internal combustion engine 1, the addition valve 5, the pump 50, and the like. The ECU 8 electrically controls various devices of the internal combustion engine 1, the addition valve 5, the pump 50, and the like based on the output signals of the various sensors described above. For example, in addition to known control such as fuel injection control of the internal combustion engine 1, the ECU 8 performs addition control for intermittently injecting the additive from the addition valve 5 during the operation period of the internal combustion engine 1 or failure of the SCR catalyst. Execute diagnosis and so on. In the addition control, the ECU 8 obtains an estimated value (estimated NH ₃ adsorption amount) of the NH ₃ amount adsorbed on the SCR catalyst of the second catalyst casing 4, and controls the addition valve 5 based on the estimated NH ₃ adsorption amount. To do. Further, in the fault diagnosis of the SCR catalyst, ECU 8 is cleaned by the SCR catalyst with respect to the amount of the NO _X estimated adsorbed NH ₃ amount flowing into the NO _X purification rate of the SCR catalyst when at least a predetermined amount (SCR catalyst that _the amount of NO _X ratio) is obtained, if the NO _X purification rate is less than a predetermined threshold value, it is diagnosed that the SCR catalyst is faulty.

Estimated adsorbed NH ₃ amount to be used in the addition control and the fault diagnosis, NH ₃ and urea aqueous NH 3 _(the urea solution supplied to the SCR catalyst is produced is thermally decomposed in the exhaust gas is hydrolyzed in the SCR catalyst It is estimated by adding up a value obtained by subtracting the amount of NH ₃ consumed in the SCR catalyst from the amount of NH ₃ ) generated. Here, the amount of NH ₃ supplied to the SCR catalyst is calculated using the amount of aqueous urea solution added from the addition valve 5 as a parameter. The amount of NH ₃ to be consumed in the SCR catalyst, the amount of NH ₃ that reacts with oxygen in the exhaust _{(O 2)} amount of NH ₃ that reacts with NO _X in the exhaust gas in the SCR catalyst, the SCR catalyst (hereinafter , “NH ₃ oxidation amount”) and the amount of NH ₃ released from the SCR catalyst (hereinafter referred to as “NH ₃ slip amount”).

The amount of NH ₃ that reacts with NO _X in the SCR catalyst is calculated using the NO _X inflow amount and the NO _X purification rate as parameters. At this time, NO _X inflow correlates to the amount of the NO _X discharged from the internal combustion engine 1 (the amount of the NO _X that mixture in the internal combustion engine 1 is generated when the combustion). The amount of the NO _X discharged from the internal combustion engine 1, the amount of oxygen contained in the gas mixture, the amount of fuel contained in the mixture, the fuel injection timing, correlated to the engine speed. The amount of oxygen contained in the air-fuel mixture correlates with the amount of intake air (the output signal of the air flow meter 11). The amount of fuel contained in the air-fuel mixture correlates with the fuel injection amount. Therefore, the ECU 8 may calculate the NO _X inflow amount using the output signal of the air flow meter 11, the fuel injection amount, the fuel injection timing, and the engine rotation speed as parameters. Incidentally, it is advisable to advance and determined experimentally, and stored in ECU8 the ROM in those aspects of the relationship between the map and functional expression the relationship between various parameters and the NO _X flow rate described above. When the NO _X sensor is disposed in the exhaust pipe 2 between the first catalyst casing 3 and the second catalyst casing 4, the ECU 8 detects the detected value (NO _X concentration) of the NO _X sensor and the amount of exhaust. The NO _X inflow amount may be calculated using (the sum of the intake air amount and the fuel injection amount) as a parameter.

On the other hand, NO _X purification rate is estimated and a temperature of the SCR catalyst (the sum of the fuel injection amount per intake air amount and unit time per unit time) the flow rate of the exhaust gas flowing into the SCR catalyst per unit time as a parameter Is done. Figure 2 is a diagram showing the flow rate of the exhaust gas (the sum of the injection amount per intake air amount and unit time per unit time), and the temperature of the SCR catalyst, the relationship between the NO _X purification rate. NO _X purification rate becomes smaller as the exhaust flow rate increases, and the temperature of the SCR catalyst becomes more larger higher (provided that the temperature of the SCR catalyst is an upper limit temperature (for example, exceeding 350 ° C.), high temperature of the SCR catalyst There is a tendency to become smaller. Therefore, ECU 8, based on the relation shown in FIG. 2, obtaining the NO _X purification rate of the SCR catalyst. 2 may be obtained in advance and stored in the ROM of the ECU 8 in a map or function form.

Next, the NH ₃ oxidation amount is calculated using the O ₂ concentration of the exhaust gas flowing into the SCR catalyst and the previous calculated value of the estimated NH ₃ adsorption amount as parameters. FIG. 3 is a diagram showing the relationship between the O ₂ concentration of the exhaust gas flowing into the SCR catalyst and the amount of oxidation of NH ₃ . In FIG. 3, the amount of NH ₃ oxidation increases as the amount of NH ₃ adsorption increases, and increases as the temperature of the SCR catalyst increases. Therefore, the ECU 8 determines the amount of NH ₃ oxidation based on the relationship as shown in FIG. 3 may be experimentally obtained in advance and stored in the ROM of the ECU 8 in a map or function form.

Further, the NH ₃ slip amount is obtained by using the previous calculated value of the estimated NH ₃ adsorption amount, the temperature of the SCR catalyst, and the flow rate of the exhaust gas passing through the SCR catalyst per unit time as parameters. FIG. 4 is a diagram showing the relationship between the NH ₃ adsorption amount, the temperature of the SCR catalyst, and the NH ₃ concentration of the exhaust gas flowing out from the SCR catalyst when the flow rate of the exhaust gas passing through the SCR catalyst is constant. In FIG. 4, the NH ₃ concentration of the exhaust gas flowing out from the SCR catalyst increases as the amount of NH ₃ adsorption increases, and increases as the temperature of the SCR catalyst increases. Therefore, when the flow rate of the exhaust gas passing through the SCR catalyst is constant, it can be said that the NH ₃ slip amount increases as the NH ₃ adsorption amount increases and the temperature of the SCR catalyst increases. On the other hand, if the NH ₃ concentration of the exhaust gas flowing out from the SCR catalyst is constant, the NH ₃ slip amount per unit time increases as the flow rate of the exhaust gas passing through the SCR catalyst per unit time increases. Therefore, the ECU 8 obtains the NH ₃ concentration of the exhaust gas flowing out from the SCR catalyst based on the relationship as shown in FIG. 4, and calculates the exhaust gas flow rate per unit time (the intake air amount per unit time and the NH ₃ concentration). The NH ₃ slip amount is calculated by multiplying the sum of the fuel injection amount per unit time).

The calculation process of the estimated NH ₃ adsorption amount by the method described above is repeatedly performed at a predetermined cycle during the operation period of the internal combustion engine 1. Then, when the estimated NH ₃ adsorption amount becomes smaller than the prescribed amount, the ECU 8 injects the urea aqueous solution from the addition valve 5. Here, the "prescribed amount" is, for example, NH ₃ adsorption amount when the maximum amount of NH ₃ (NH ₃ adsorption rate of the SCR catalyst and the NH ₃ desorption rate capable SCR catalyst is adsorbed in equilibrium ) Minus a predetermined margin. Further, ECU 8 calculates the NO _X purification rate of the SCR catalyst when the estimated adsorbed NH ₃ amount is equal to or larger than the predetermined amount, executing the failure diagnosis of the SCR catalyst by comparing the NO _X purification rate and a predetermined threshold value To do. Note that the “calculation means” according to the present invention is realized when the ECU 8 calculates the estimated NH ₃ adsorption amount by the method described above.

Incidentally, in the case where the internal combustion engine 1 is restarted after being stopped, by using the estimated adsorbed NH ₃ amount (stop adsorbed NH ₃ amount) at the previous stop is added from the addition valve 5 after restarting A method of controlling the amount of the urea aqueous solution is conceivable. However, the NH ₃ adsorption amount of the SCR catalyst may decrease during the stop period of the internal combustion engine 1. Therefore, when the NH ₃ adsorption amount at the time of stop is used as the NH ₃ adsorption amount at the restart of the internal combustion engine 1 (starting NH ₃ adsorption amount), the startup NH ₃ adsorption amount becomes larger than the actual NH ₃ adsorption amount. there is a possibility. In that case, there is a possibility that the amount of urea aqueous solution to be added from the addition valve 5 after the restart of the internal combustion engine 1 is less than the amount (the proper amount) needed to purify NO _X in the exhaust gas without excess or deficiency . As a result, the amount of the NO _X to be purified by the SCR catalyst is reduced, which can lead to deterioration of the exhaust emission. Further, if the NH ₃ adsorption amount at the time of start-up becomes larger than the actual NH ₃ adsorption amount, the amount of urea aqueous solution added from the addition valve 5 during the operation period of the internal combustion engine 1 becomes smaller than the appropriate addition amount. There is also a possibility that the estimated NH ₃ adsorption amount when the failure diagnosis is performed becomes smaller than the predetermined amount. In this case, there is a possibility that the SCR catalyst is erroneously diagnosed as being malfunctioning even though the SCR catalyst is normal.

Therefore, in this embodiment, estimated decrease in the adsorbed NH ₃ amount in the stopping period the internal combustion engine 1 (NH ₃ reduction), by subtracting the NH ₃ reduction from stop adsorbed NH ₃ amount, starting The amount of NH ₃ adsorption was calculated. Then, ECU 8 after restart the internal combustion engine 1, with using the starting NH ₃ adsorption perform calculation of the estimated adsorbed NH ₃ amount, the addition amount of the urea aqueous solution based on the estimated adsorbed NH ₃ amount It is assumed that control or failure diagnosis processing of the SCR catalyst is executed.

The main factors adsorbed NH ₃ amount decreases during the stop period engine 1, NH ₃ adsorbed on the SCR catalyst or disengaged from the SCR catalyst, or NH ₃ adsorbed on the SCR catalyst exhaust by reacting with O ₂ in the tube 2 is to or oxidized. During the stop period the internal combustion engine 1, the amount of NH ₃ which is oxidized by reacting with O ₂ of NH amount of _3, and the exhaust pipe 2 that leaves the SCR catalyst is correlated to the temperature of the SCR catalyst. Therefore, the temperature transition of the SCR catalyst during the stop period of the internal combustion engine 1 may be monitored, and the NH ₃ reduction amount may be obtained based on the temperature transition. However, in order to monitor the temperature transition of the SCR catalyst during the stop period of the internal combustion engine 1, it is necessary to operate the ECU 8, the exhaust temperature sensor 7 and the like even during the stop period of the internal combustion engine 1. The load increases.

Therefore, a method of estimating the NH ₃ reduction amount using the temperature of the SCR catalyst when the internal combustion engine 1 is stopped (catalyst temperature when stopped) as a parameter can be considered. However, even if the catalyst temperature at the time of stoppage is the same, there is a possibility that the NH ₃ decrease amount varies depending on the length of the stop period (stop time). Therefore, it is desirable to estimate the NH ₃ reduction amount using the catalyst temperature at stop and the stop time as parameters. Further, the temperature transition of the SCR catalyst during the stop period of the internal combustion engine 1 may change depending on the transition of the outside air temperature during the stop period. However, as described above, when it is attempted to monitor the transition of the outside air temperature during the stop period of the internal combustion engine 1, the load on the ECU 8 and the battery increases. Therefore, in the present embodiment, assuming the situation where the outside air temperature is the highest during the stop period of the internal combustion engine 1, the relationship among the catalyst temperature during stop, the stop time, and the NH ₃ reduction amount is obtained, Based on this, the NH ₃ decrease amount was estimated.

Here, FIG. 5 shows the relationship between the catalyst temperature at stop, the stop time, and the NH ₃ reduction amount in an environment where the outside air temperature is the highest. As shown in FIG. 5, when the catalyst temperature at the time of stoppage is high, the amount of decrease in NH ₃ increases compared to when it is low. In addition, when the stop period is long, the amount of NH ₃ decrease is greater than when the stop period is short. When NH ₃ reduction on the basis of such a relationship is estimated, without operating the ECU8 and exhaust gas temperature sensor 7 or the like during the stop period the internal combustion engine 1, it is possible to estimate the NH ₃ reduction. Further, by estimating the NH ₃ decrease amount assuming the environment where the outside air temperature is the highest, in other words, the environment where the temperature of the SCR catalyst is most difficult to decrease, the estimated value is excessive with respect to the actual NH ₃ decrease amount. Is reduced. As a result, it is suppressed that the startup NH ₃ adsorption amount obtained using the estimated value of the NH ₃ decrease amount is larger than the actual NH ₃ adsorption amount. Therefore, it is possible to avoid a situation in which the amount of the urea aqueous solution added from the addition valve 5 after the internal combustion engine 1 is started is smaller than the appropriate addition amount, and it is possible to suppress the deterioration of the exhaust emission due to the shortage of the urea aqueous solution. .

Since the amount of NH ₃ desorbed from the SCR catalyst may increase as the amount of NH ₃ adsorbed at the time of stoppage increases, the amount of NH ₃ reduction obtained based on the relationship shown in FIG. it may be corrected in accordance with the stop adsorbed NH ₃ amount. For example, the NH ₃ decrease amount may be corrected so as to increase as the stop NH ₃ adsorption amount increases. As described above, when the NH ₃ decrease amount is estimated in consideration of the stop NH ₃ adsorption amount, the estimation accuracy can be further increased.

By the way, the SCR catalyst stably adsorbs a specific amount (predetermined threshold value) of NH ₃ even when the temperature of the SCR catalyst is in a temperature range where NH ₃ is easily desorbed and in a temperature range where NH ₃ is easily oxidized. It has the property to continue. Therefore, when stop adsorbed NH ₃ amount is less than the predetermined threshold value, even if desorbed easily temperature range of the temperature of NH ₃ SCR catalyst during the stop period the internal combustion engine 1, or oxidizable temperature of the NH ₃ Even in the range, the NH ₃ adsorption amount of the SCR catalyst does not decrease from the NH ₃ adsorption amount at the time of stoppage. Further, during the stop period the internal combustion engine 1, when the adsorbed NH ₃ amount of the SCR catalyst is decreased to the predetermined threshold value, even eliminated easily temperature range of the temperature of NH ₃ SCR catalyst, or oxidizable temperature of the NH ₃ Even in the region, the NH ₃ adsorption amount of the SCR catalyst does not decrease any more.

If the NH ₃ reduction amount is estimated without considering the characteristics of the SCR catalyst as described above, the startup NH ₃ adsorption amount obtained using the estimated value is excessive with respect to the actual NH ₃ adsorption amount. May be less. In particular, as described above, in the method in which the NH ₃ reduction amount is estimated on the assumption that the outside air temperature is highest during the stop period of the internal combustion engine 1, the NH ₃ adsorption amount at the start time is the actual NH ₃ adsorption amount. There is a high possibility that it will be excessively small.

Therefore, in this embodiment, when the stop NH ₃ adsorption amount is equal to or less than the predetermined threshold, the start NH ₃ adsorption amount is estimated to be the same as the stop NH ₃ adsorption amount. Further, when the stop NH ₃ adsorption amount is larger than the predetermined threshold, if the amount obtained by subtracting the NH ₃ decrease amount from the stop NH ₃ adsorption amount is less than the predetermined threshold, the start NH ₃ adsorption amount is set to The amount is estimated to be the same amount as the predetermined threshold value.

As described above, when the startup NH ₃ adsorption amount is estimated in consideration of the characteristics of the SCR catalyst, it is suppressed that the startup NH ₃ adsorption amount becomes excessively smaller than the actual NH ₃ adsorption amount. The As a result, the amount of the urea aqueous solution added from the addition valve 5 after the start of the internal combustion engine 1 is suppressed from being excessively increased with respect to the appropriate addition amount, and unnecessary consumption of the urea aqueous solution can be suppressed to a low level.

It should be noted that the amount of NH ₃ (predetermined threshold) that the SCR catalyst can continue to adsorb stably varies depending on the catalyst temperature at the time of stop. For example, as shown in FIG. 6, the predetermined threshold value is smaller when the catalyst temperature during stoppage is high than when it is low. Therefore, the predetermined threshold value is determined using the catalyst temperature at the time of stop as a parameter.

The procedure for estimating the startup NH ₃ adsorption amount in the present embodiment will be described below with reference to FIG. FIG. 7 is a flowchart showing a processing routine executed by the ECU 8 when estimating the startup NH ₃ adsorption amount. This processing routine is a processing routine that is executed by the ECU 8 when the internal combustion engine 1 is started (for example, when the ignition switch is switched from OFF to ON), and is stored in the ROM of the ECU 8 in advance.

In the processing routine of FIG. 7, the ECU 8 first reads a stop-time NH ₃ adsorption amount ΣNH ₃ stp that is the NH ₃ adsorption amount of the SCR catalyst at the time of the previous stop of the internal combustion engine 1 in the process of S101. The stopped NH ₃ adsorption amount ΣNH ₃ stp is stored in a non-volatile memory such as a backup RAM when the internal combustion engine 1 is stopped last time.

In the process of S102, the ECU 8 reads the temperature of the SCR catalyst (stop catalyst temperature) Tscr when the internal combustion engine 1 was stopped last time. Similarly to the stop NH ₃ adsorption amount ΣNH ₃ stp, the stop catalyst temperature Tscr is also backed up when the internal combustion engine 1 is stopped last time.
It is assumed that it is stored in a non-volatile memory such as AM. The temperature of the SCR catalyst may be estimated from the operation history of the internal combustion engine 1, or the measured value of the exhaust temperature sensor 7 may be substituted.

In the process of S103, the ECU 8 calculates a predetermined threshold ΣNH ₃ thre based on the stop-time catalyst temperature Tscr read in the process of S102 and the relationship shown in FIG. Subsequently, the ECU 8 proceeds to the process of S104, and determines whether or not the stop NH ₃ adsorption amount ΣNH ₃ stp read in the process of S101 is larger than a predetermined threshold ΣNH ₃ thre calculated in the process of S103. Determine.

If an affirmative determination is made in the process of S104 (ΣNH ₃ stp> ΣNH ₃ thre), the ECU 8 proceeds to the process of S105. In the process of S105, the ECU 8 determines the adsorption amount of NH ₃ during the stop period of the internal combustion engine 1 based on the stop-time catalyst temperature Tscr and the stop time read in the process of S102 and the relationship shown in FIG. the NH ₃ reduction DerutaNH ₃ is a reduction of estimating (calculating). At this time, the stop time is calculated from the difference between the date and time when the internal combustion engine 1 was stopped last time and the date and time when the internal combustion engine 1 was restarted this time.

In the process of S106, the ECU 8 subtracts the NH ₃ decrease amount ΔNH ₃ estimated in the process of S105 from the stop-time NH ₃ adsorption amount ΣNH ₃ stp read in the process of S101 (ΣNH ₃ It is determined whether or not (stp−ΔNH ₃ ) is equal to or greater than a predetermined threshold value ΣNH ₃ thre calculated in the process of S103.

If an affirmative determination is made in the process of S106 ((ΣNH ₃ stp−ΔNH ₃ ) ≧ ΣNH ₃ thre), the ECU 8 proceeds to the process of S107, and the NH ₃ decrease is reduced from the NH ₃ adsorption amount ΣNH ₃ stp at the time of stoppage. the amount DerutaNH ₃ the difference obtained by subtracting (ΣNH _{3 stp-ΔNH 3)} to estimate the starting adsorbed NH ₃ amount ΣNH ₃ str. On the other hand, when a negative determination is made in the process of S106 (ΣNH ₃ stp−ΔNH ₃ ) <ΣNH ₃ thre), the ECU 8 proceeds to the process of S108 and sets the predetermined threshold value ΣNH ₃ thre to the startup NH ₃ adsorption amount ΣNH. Estimated as ₃ str.

If a negative determination is made in the process of S104 (ΣNH ₃ stp ≦ ΣNH ₃ thre), the ECU 8 proceeds to the process of S109. In the process of S109, the ECU 8 estimates the stop time NH ₃ adsorption amount ΣNH ₃ stp as a start time NH ₃ adsorption amount ΣNH ₃ str.

As described above, when the ECU 8 executes the processing routine of FIG. 7, the “estimator” according to the present invention is realized. As a result, it is possible to estimate the startup NH ₃ adsorption amount without operating the ECU 8, the exhaust temperature sensor 7, or the like during the stop period of the internal combustion engine 1. Furthermore, while suppressing that the starting adsorbed NH ₃ amount becomes more actual NH ₃ adsorption, possible to suppress the excessively small with respect to the start time of adsorbed NH ₃ amount is actually adsorbed NH ₃ amount Can do. Thus, it is possible to suppress to deviate from the amount required for the amount of the aqueous urea solution to be added from the addition valve 5 after the start of the internal combustion engine 1 for purifying NO _X in the exhaust gas without excess or deficiency (appropriate amount) Therefore, an unnecessary increase in the consumption amount of the urea aqueous solution can be suppressed while suppressing the deterioration of the exhaust emission after starting the internal combustion engine 1. In addition, when a failure diagnosis of the SCR catalyst is executed, it is possible to suppress erroneous diagnosis that the SCR catalyst is abnormal although the SCR catalyst is normal.

Reference Signs List 1 internal combustion engine 2 exhaust pipe 3 first catalyst casing 4 second catalyst casing 5 addition valve 6 NO _X sensor 7 exhaust temperature sensor 8 ECU
50 Pump 51 Additive tank

Claims (2)

An exhaust purification device that is disposed in an exhaust passage of the internal combustion engine and includes a selective reduction catalyst;
An addition device that adds ammonia or an additive that is a precursor of ammonia to the exhaust gas flowing into the exhaust purification device;
During the operation period of the internal combustion engine, and the amount of additive to be added from the amount and the addition device of the NO _X flowing into the exhaust gas purifier as parameters, an amount of ammonia adsorbed on the selective reduction catalyst A computing means for computing a certain NH ₃ adsorption amount;
In an exhaust purification system equipped with
When the internal combustion engine is restarted after being stopped, NH ₃ the temperature of the selective reduction catalyst at the time of stoppage of at least the internal combustion engine as a parameter, an amount of decrease in NH ₃ adsorption in the stop period of the internal combustion engine When the internal combustion engine is restarted by estimating the decrease amount and subtracting the NH ₃ decrease amount from the stop NH ₃ adsorption amount that is the calculation result of the calculation means when the internal combustion engine is stopped, the SCR catalyst further comprising estimation means for estimating starting adsorbed NH ₃ amount is an amount of NH ₃ adsorbed in the,
When the stop NH ₃ adsorption amount is larger than the predetermined threshold, the estimation means is configured such that the difference obtained by subtracting the NH ₃ decrease amount from the stop NH ₃ adsorption amount is equal to or greater than a predetermined threshold. , The difference is estimated as the startup NH ₃ adsorption amount, and if the difference is less than the predetermined threshold, the predetermined threshold is estimated as the startup NH ₃ adsorption amount,
An exhaust purification system wherein the stop adsorbed NH ₃ amount when the is less than a predetermined threshold value, the estimating means, for estimating the stop-period adsorbed NH ₃ amount as the starting adsorbed NH ₃ amount. The exhaust purification system according to claim 1, wherein the predetermined threshold is set to a smaller value when the temperature of the selective catalytic reduction catalyst is high when the internal combustion engine is stopped than when the temperature is low.

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