JPH1162561A - Hydrocarbon adsorbed quantity detector of exhaust emission purifying catalyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately evaluate the poisoning state of a catalyzer due to hydrocarbon. SOLUTION: An inflow quantity per specified time of poisonous hydrocarbon (poisonous HC) flowing into a catalyzer at each specified time is calculated (step 101 to 104), and an amount of consumption per specified time of the poisonous HC reactively consumed by the catalyzer at each specified time is calculated (step 105 to 107). In addition, a adsorptive rate f1 of the poisonous HC to the catalyzer is multiplied to the deducted value of consumption from the inflow quantity per specified time of the poisonous HC at each specified time, and thereby the adsorbed quantity per specified time of the poisonous HC to the catalyzer is calculated (step 108 and 109), whereby a desorbed quantity per specified time of the poisonous HC being adsorbed in the catalyzer at each specified time is calculated (step 110 and 111). Subsequently, the deducted value of the desorbed quantity from the adsorbed quantity per specified time of the poisonous HC at each specified time is integrated, and thereby the poisonous HC adsorbed quantity of the catalyzer at the current point of time is calculated (step 112).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purification system for reducing and purifying nitrogen oxides in exhaust gas by supplying hydrocarbons as a nitrogen oxide reducing agent to a catalyst.
For example, the present invention relates to a device for detecting the amount of hydrocarbon adsorbed on an exhaust purification catalyst which calculates the amount of adsorbed hydrocarbon on the catalyst in order to control the amount of hydrocarbon supplied to the catalyst.

[0002]

2. Description of the Related Art In order to purify nitrogen oxides (NOx) in exhaust gas discharged from an internal combustion engine in which fuel is burned under an excessive amount of oxygen such as a diesel engine, a NO.
An exhaust purification system has been developed in which an x catalyst is installed and hydrocarbons (HC) such as fuel are supplied to a NOx catalyst as a reducing agent to reduce and purify NOx. In recent years, as disclosed in Japanese Patent Application Laid-Open No. Hei 9-14437, in this exhaust purification system, in order to reduce fuel consumption deterioration due to excessive supply of fuel to the catalyst, the HC adsorption ratio of the catalyst and the HC desorption speed from the catalyst are reduced. It has been proposed to control the amount of HC supplied to the catalyst according to the conditions.

[0003]

SUMMARY OF THE INVENTION The present inventors have recently
When the poisoning phenomenon of the NOx catalyst was investigated, the supplied HC
Is adsorbed on the catalyst in a large amount, the catalyst is poisoned by the HC, and it becomes difficult for the catalyst to recover to its original state.
x A phenomenon in which the purification performance was significantly reduced was discovered. Such poisoning of the catalyst starts to occur when the HC adsorption amount of the catalyst exceeds a certain value (hereinafter, the HC adsorption amount at this time is referred to as “poisoning limit value”). Once the catalyst is poisoned, under normal operating conditions of diesel engines, where the exhaust gas temperature is lower than that of gasoline engines, it becomes difficult for HC to be desorbed from the catalyst, making recovery of the catalyst difficult. I knew it. From this survey result, high NOx over a long period
In order to maintain the purification performance, it has been found that it is necessary to control the amount of HC supplied to the catalyst so that the HC adsorption amount of the catalyst does not exceed the poisoning limit value.

[0004] Incidentally, fuel (light oil) is often used as HC supplied to the catalyst, and the fuel contains many types of HC having different chemical structures (carbon numbers), and the boiling points of these HCs are included. Is also different. HC with low boiling point
Even if it is adsorbed by the catalyst, it is volatilized and desorbed from the catalyst in a relatively short time by the exhaust heat, so that the adsorption of HC having a low boiling point does not affect the poisoning of the catalyst.

[0005] The use of the method for controlling the amount of supplied HC disclosed in the above publication makes it possible to estimate the amount of HC adsorbed on the catalyst. Therefore, the poisoning state of the catalyst is overestimated from the estimated HC adsorption amount. Overestimation of the poisoning condition causes the amount of HC supplied to the catalyst to be under-controlled,
Insufficient HC for reducing and purifying NOx causes a reduction in the NOx purification rate.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and accordingly, it is an object of the present invention to provide an apparatus for detecting the amount of hydrocarbon adsorbed on an exhaust purification catalyst, which can accurately evaluate the poisoning state of the catalyst by HC. Is to do.

[0007]

According to a first aspect of the present invention, there is provided an apparatus for detecting the amount of hydrocarbons adsorbed on an exhaust gas purifying catalyst, the method comprising:
The amount of adsorption of a hydrocarbon component (hereinafter referred to as “toxic hydrocarbon”) that causes poisoning of the catalyst is calculated by a toxic hydrocarbon adsorption amount calculating means. Thus, from the hydrocarbons adsorbed on the catalyst, low-boiling HC that does not affect poisoning is excluded, and the amount of adsorption of only toxic hydrocarbons can be obtained.
The poisoning state of the catalyst can be accurately evaluated.

Here, as a specific method of calculating the amount of adsorption of the toxic hydrocarbon, the following procedure may be performed (claim 2). An inflow amount of the poisoned hydrocarbon flowing into the catalyst per predetermined time is calculated every predetermined time. The consumption amount of the poisoned hydrocarbon consumed by the reaction with the catalyst every predetermined time is calculated per predetermined time. The value obtained by subtracting the consumption amount from the inflow amount of the poisonous hydrocarbon per predetermined time at each predetermined time is multiplied by the adsorption rate of the poisonous hydrocarbon to the catalyst, and the value of the poisonous hydrocarbon to the catalyst for the predetermined time Calculate the amount of adsorption per hit. The desorbed amount of the toxic hydrocarbon adsorbed on the catalyst per predetermined time is calculated per predetermined time. At each predetermined time, a value obtained by subtracting the desorption amount from the adsorption amount of the poisonous hydrocarbon per predetermined time is integrated to calculate the current poisoned hydrocarbon adsorption amount of the catalyst.

By calculating the adsorbed amount of the poisoned hydrocarbon by the above-mentioned procedures, the poisoned hydrocarbon of the catalyst at the present time is considered in consideration of the inflow, reaction (consumption) and desorption of the poisoned hydrocarbon to the catalyst. The amount of adsorption can be calculated accurately.

In this case, since the toxic hydrocarbon is also contained in the exhaust gas discharged from the internal combustion engine, the inflow amount of the toxic hydrocarbon per predetermined time is discharged from the internal combustion engine. The amount of toxic hydrocarbons in the exhaust gas
It is preferable to obtain the total amount of the poisoned hydrocarbons added to the exhaust gas upstream of the catalyst. Thereby, the inflow amount of the poisoned hydrocarbon per predetermined time can be accurately evaluated.

Further, the ratio of the poisoned hydrocarbon in the hydrocarbon discharged from the internal combustion engine may be set based on the operating condition of the internal combustion engine. In other words, the proportion of toxic hydrocarbons in the hydrocarbons discharged from the internal combustion engine changes according to the internal combustion engine operating conditions such as the internal combustion engine speed and the accelerator opening. If the ratio is set based on the operating conditions of the internal combustion engine, it is possible to accurately estimate the inflow amount of the poisoned hydrocarbon in accordance with the operating conditions of the internal combustion engine.

Similarly, the ratio of the toxic hydrocarbon in the hydrocarbon added to the exhaust gas upstream of the catalyst may be set based on the temperature of the exhaust gas.
That is, the hydrocarbons added to the exhaust gas are reformed by the heat of the exhaust gas, and some of the poisonous hydrocarbons are changed into low-boiling hydrocarbons that do not affect poisoning. Due to such hydrocarbon reforming, the higher the temperature of the exhaust gas, the lower the proportion of toxic hydrocarbons in the hydrocarbon.Therefore, the proportion of toxic hydrocarbons in the hydrocarbon is reduced to the temperature of the exhaust gas. If it is set based on the temperature, the inflow amount of the poisoned hydrocarbon can be accurately estimated according to the temperature of the exhaust gas.

The consumption (reaction amount) of poisoned hydrocarbons in the catalyst varies depending on the catalyst temperature.
As described above, the consumption amount of the poisoned hydrocarbon in the catalyst per predetermined time may be calculated by using the steady-state purification rate of the poisoned hydrocarbon preset in accordance with the catalyst temperature. Here, the steady-state purification rate of the poisoned hydrocarbon is a purification rate of the poisoned hydrocarbon when the catalyst temperature is kept constant and the steady-state operation is performed, and can be accurately obtained in advance by an experiment or the like. Therefore, by using the steady-state purification rate according to the catalyst temperature, the consumption amount of the toxic hydrocarbon in the catalyst can be accurately calculated.

Further, the adsorption ratio of the toxic hydrocarbon to the catalyst is determined by the adsorption amount of the toxic hydrocarbon of the catalyst obtained in the previous treatment, the concentration of the toxic hydrocarbon in the exhaust gas flowing into the catalyst, and the catalyst temperature. And the exhaust gas flow rate,
As described in claim 7, the adsorption ratio of the toxic hydrocarbon may be set based on at least one of these four parameters. Thereby, the adsorption ratio of the toxic hydrocarbon can be set with high accuracy.

Similarly, the desorption ratio of the poisoned hydrocarbons from the catalyst is determined by the amount of the poisoned hydrocarbons adsorbed by the catalyst obtained in the previous treatment, the concentration of the poisoned hydrocarbons in the exhaust gas flowing into the catalyst, Because it changes depending on the catalyst temperature and the exhaust gas flow rate,
As described in claim 8, the desorption rate of the toxic hydrocarbon may be set based on at least one of these four parameters. This makes it possible to accurately set the desorption ratio of the toxic hydrocarbon.

Further, the amount of hydrocarbon supplied to the catalyst may be controlled so that the amount of poisoned hydrocarbon adsorbed by the catalyst at this time does not exceed a preset poisoning limit value. good. This makes it possible to optimize the amount of hydrocarbon supplied to the catalyst so that the amount of adsorbed toxic hydrocarbons of the catalyst does not exceed the poisoning limit value, and to achieve high NOx purification performance over a long period of time. Can be maintained.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment (1) of the present invention will be described below with reference to FIGS. First, the configuration of the entire system will be described with reference to FIG. A NOx catalyst 13 that reduces and purifies NOx in exhaust gas is provided in the exhaust pipe 12 (exhaust passage) of a diesel engine 11 that is an internal combustion engine. The NOx catalyst 13 has platinum, which is an active metal, supported on a kind of porous zeolite. In the NOx catalyst 13, NOx in exhaust gas reacts with hydrocarbons (HC) to be purified. This NOx catalyst 1
An exhaust gas temperature sensor 14 that detects the temperature of exhaust gas flowing out of the NOx catalyst 13 is installed at the outlet of the exhaust gas sensor 3 to evaluate the catalyst temperature. The exhaust gas temperature sensor 1
4 may be installed at the inlet of the NOx catalyst 13, and even in this case, the catalyst temperature can be evaluated from the temperature of the exhaust gas flowing into the NOx catalyst 13.

The NOx catalyst 13 in the exhaust pipe 12
Upstream of the fuel, such as light oil as HC for the reducing agent
An HC supply nozzle 15 for supplying the Ox catalyst 13 is provided. Fuel pumped by an injection pump 16 from a fuel tank (not shown) is supplied to the HC supply nozzle 15. The amount of fuel injected from the HC supply nozzle 15 is controlled by the engine control circuit 17.

The engine control circuit 17 is mainly composed of a microcomputer, and has an exhaust gas temperature sensor 1.
4. The amount of fuel injected into each cylinder of the diesel engine 11 is controlled based on the output of various sensors that detect engine operating conditions, such as an engine speed sensor (not shown).

Further, this engine control circuit 17
By executing the toxic HC adsorption amount calculation program of FIG. 2 stored in M (storage medium), the current NOx catalyst 1
3 functions as a toxic hydrocarbon adsorption amount calculation means for calculating the adsorption amount of the toxic hydrocarbon (toxic HC), and further executes the HC supply amount control program of FIG.
The HC supply amount is controlled such that the poisoned HC adsorption amount of the x catalyst 13 does not exceed a preset poisoning limit value. Hereinafter, FIG.
And the processing contents of the program in FIG. 3 will be described.

The toxic HC adsorption amount calculation program shown in FIG. 2 is repeatedly executed at predetermined time intervals Δt. When the processing of this program is started, first, in step 101, in order to detect an engine operating condition, the engine speed Ne,
The accelerator opening Ac, the exhaust gas temperature Tex at the outlet of the NOx catalyst 13, and the like are read. Thereafter, at step 102, the toxic HC discharge amount ΔHCex discharged from the diesel engine 11 within the predetermined time Δt is calculated by the following equation.

ΔHCex = ΔHCexo × fex where ΔHCexo is the amount of all HC discharged from the diesel engine 11 within a predetermined time Δt.
A HC emission map in which engine operating conditions such as the engine speed Ne are set as parameters is searched, and an HC emission ΔHCexo according to the engine operating conditions at that time is obtained.

Fex is a coefficient indicating the ratio of toxic HC in the HC discharged from the diesel engine 11, and as shown in FIG. 4, the coefficient fex is determined by the engine speed Ne and the accelerator opening Ac. Are set in accordance with the engine speed Ne and the accelerator opening Ac at that time from a two-dimensional map having the following parameters. The reason for doing this is
The ratio of poisoned HC in the HC discharged from the diesel engine 11 is determined by the engine speed Ne and the accelerator opening Ac.
This is because it changes according to the engine operating conditions such as.
The parameter of the map of the coefficient fex may be only one of the engine speed Ne and the accelerator opening Ac, or another engine operating condition such as the exhaust gas temperature Tex may be added. good.

Then, in the next step 103, the poisoned HC supplied from the HC supply nozzle 15 within a predetermined time Δt.
The supply amount ΔHCfd is calculated by the following equation. ΔHCfd = ΔHCfdo × ffd Here, ΔHCfdo is the supply amount of all HC supplied from the HC supply nozzle 15 within the predetermined time Δt, and
The HC supply amount ΔHCfdo is obtained from the command value (target HC supply amount) given to the supply nozzle 15.

Ffd is a coefficient indicating the ratio of poisoned HC in the HC supplied from the HC supply nozzle 15,
The coefficient ffd is set according to the exhaust gas temperature at that time from a map using the exhaust gas temperature as a parameter, as shown in FIG. The reason for this is that HC added to the exhaust gas is reformed by the heat of the exhaust gas, and some toxic H
This is because C changes to low boiling point HC which does not affect poisoning. As the exhaust gas temperature increases, HC added to the exhaust gas increases.
Because of the characteristic of reducing the ratio of toxic HC in the
From the map, the coefficient f indicating the ratio of toxic HC in HC
fd is set according to the exhaust gas temperature.

Thereafter, at step 104, a predetermined time Δt
HC flow amount ΔHC flowing into the NOx catalyst 13
in is the toxic H calculated in steps 102 and 103 described above.
The C emission amount ΔHCex and the toxic HC supply amount ΔHCfd are obtained by summing them. ΔHCin = ΔHCex + ΔHCfd The processing of steps 102 to 104 described above functions as an inflow amount calculating means described in the claims.

Then, in the next step 105, the exhaust gas amount ΔWin flowing into the NOx catalyst 13 within a predetermined time Δt is calculated from the engine speed Ne using a map or the like.

Thereafter, in step 106, a toxic HC steady-state purification rate map using the catalyst temperature and the exhaust gas amount as parameters is searched, and the toxic HC constant purification according to the catalyst temperature and the exhaust gas amount ΔWin at that time is searched. Calculate the rate Krep. Here, the steady-state purification rate of poisonous HC is the purification rate of poisonous HC when the catalyst is operated at a constant temperature while maintaining the catalyst temperature constant, and can be accurately obtained in advance by experiments or the like. The catalyst temperature is
The exhaust gas temperature Tex at the catalyst outlet detected by the exhaust gas temperature sensor 14 is substituted. Alternatively, the temperature of the exhaust gas at the catalyst inlet may be detected and used as the catalyst temperature, or the temperature of the carrier of the NOx catalyst 13 may be directly detected. Alternatively, the catalyst temperature may be estimated from the engine speed and the accelerator opening.

Then, in the next step 107, the poisoning HC consumption ΔHCrec reacted and consumed in the NOx catalyst 13 within the predetermined time Δt is multiplied by the poisoning HC inflow ΔHCin by the steady-state purification rate Krep. Ask. ΔHCrec = ΔHCin × Krep The processing of steps 105 to 107 described above functions as a consumption calculating means in claims.

Thereafter, at step 108, the NOx catalyst 1
The adsorption coefficient f ₁ indicating the adsorption ratio of the toxic HC to _{No. 3} is calculated by the following equation. f ₁ = f ₁₁ × f ₁₂ × f ₁₃ × f ₁₄

[0031] Here, f ₁₁ is a coefficient determined from the map shown in FIG. 6 (a) in accordance with the poisoning HC adsorption amount HCadso calculated in the previous processing. f ₁₂ is a coefficient determined from the map shown in FIG. 6 (b) in accordance with the poisoning HC concentration flowing into the NOx catalyst 13. f ₁₃ is a coefficient determined from the map shown in FIG. 6 (c) according to the catalyst temperature. f ₁₄ is, the amount of exhaust gas ΔWin
Is a coefficient obtained from the map of FIG. These coefficients f ₁₁ ~f ₁₄ are each take values within the range of 0 to 1, the map of (a) ~ (d) in FIG. 6 is set by an experiment or the like. Note that a part of these coefficients f _{11 to} f ₁₄ may be omitted to simplify the calculation of the adsorption coefficient f ₁ .

Thereafter, at step 109, a predetermined time Δt
Amount of toxic HC adsorbed by NOx catalyst 13 in air ΔH
Ccad is calculated from the HC inflow amount ΔHCin to the HC consumption amount ΔHCre.
determined by multiplying the adsorption coefficient f ₁ to a value obtained by subtracting or c. DerutaHCcad = treatment (ΔHCin-ΔHCrec) × f ₁ the steps 108 and 109 functions as a current adsorption amount calculating means in the appended claims.

Then, in the next step 110, the desorption coefficient f ₂ is calculated by the following equation. f ₂ = f ₂₁ × f ₂₂ × f ₂₃ × f ₂₄

Here, f ₂₁ is a coefficient obtained from the map of FIG. 7A in accordance with the toxic HC adsorption amount HCadso calculated in the previous processing. f ₂₂ is a coefficient determined from the map shown in FIG. 7 (b) in accordance with the poisoning HC concentration flowing into the NOx catalyst 13. f ₂₃ is a coefficient determined from the map shown in FIG. 7 (c) according to the catalyst temperature. f ₂₄ is the exhaust gas amount ΔWin
Is a coefficient obtained from the map of FIG. Each of these coefficients f _{21 to} f ₂₄ takes a value in the range of 0 to 1, and the maps of FIGS. 7A to 7D are set by experiments and the like. Incidentally, it omitted some of these coefficients f ₂₁ ~f _24, may be simplified to calculate the desorption coefficient f _2.

Thereafter, at step 111, a predetermined time Δt
Toxic HC desorption amount ΔH desorbed from the NOx catalyst 13
Cdiso is converted to the toxic HC adsorption amount ΔHCcad by the desorption coefficient f ₂
Multiplied by ΔHCdiso = ΔHCcad × f ₂ The processing of steps 110 and 111 functions as a desorption amount calculation unit referred to in the claims.

Then, at the next step 112, the current time t
NOx catalyst adsorption amount HCadso of NOx catalyst 13 at ₀
(T ₀ ) is calculated by the following equation.

HCadso (t ₀ ) = HCadso (t ₀ -Δ)
t) + ｛ΔHCcad (t ₀ ) −ΔHCdiso (t ₀ −Δ
t)｝ HCadso (t ₀ −Δt): Poisoned HC adsorption amount calculated in previous processing ΔHCcad (t ₀ ): Poisoned HC adsorption amount calculated in current processing ΔHCdiso (t ₀ −Δt): Previous processing HC desorption amount calculated by

By performing such a calculation, the toxic HC adsorption amount adΔHCcad (t) increased from the previous process to the current process is added to the toxic HC adsorption amount HCadso (t ₀ −Δt) in the previous process. ₀ ) −ΔHCdiso (t ₀ −Δt)｝, and the poisoning H of the NOx catalyst 13 at the current time t ₀ is calculated.
The C adsorption amount HCadso (t ₀ ) is obtained. The value of the toxic HC adsorption amount HCadso (t ₀ ) is updated and stored in a backup memory (non-volatile memory) in the engine control circuit 17. As a result, the NOx catalyst 1
3, the toxic HC adsorption amount H at the current time t ₀ is traced.
Cadso (t ₀ ) is determined. This is represented by the following equation.

[0039]

(Equation 1)

Next, the processing contents of the HC supply amount control program of FIG. 3 will be described. This program is also executed every predetermined time Δt. When the processing of this program is started, first, in step 201, the toxic HC adsorption amount HCadso of the present time t ₀ calculated by the toxic HC adsorption amount calculation program of FIG.
(T ₀ ) is compared with a preset poisoning limit value. Here, the poisoning limit value is a limit of the poisoning HC adsorption amount at which the NOx catalyst 13 becomes difficult to recover to the original state when the NOx catalyst 13 adsorbs more poisoning HC.

If the toxic HC adsorption amount HCadso (t ₀ )
If exceeds the poisoning limit, proceed to step 204,
The supply of HC from the HC supply nozzle 15 to the NOx catalyst 13 is stopped. In this case, the supply of HC to the NOx catalyst 13 is stopped until the poisoned HC adsorption amount HCadso becomes equal to or less than the poisoning limit value. As a result, the toxic HC adsorption amount HCadso of the NOx catalyst 13 is prevented from continuing to increase beyond the poisoning limit value, and the NOx purification ability of the NOx catalyst 13 is maintained.

On the other hand, the toxic HC adsorption amount HCadso (t ₀ )
If is equal to or less than the poisoning limit value, the process proceeds to step 202,
A target HC supply map is searched using the engine operating conditions such as the exhaust gas temperature (catalyst temperature) and the engine speed as parameters, and a target HC supply amount according to the engine operating conditions at that time is obtained. Thereafter, in step 203, a signal of the target HC supply amount is output to the HC supply nozzle 15, and an amount of fuel corresponding to the target HC supply amount from the HC supply nozzle 15 is added to the exhaust gas.

The inventor of the present invention uses the program of FIGS. 2 and 3 described above to control the amount of HC supplied so that the adsorbed amount of toxic HC of the NOx catalyst 13 does not exceed a preset poisoning limit value. Since the test for evaluating the effect was performed, the test result will be described with reference to FIGS. 8 and 9.
FIG. 8 shows the behavior of the conventional NOx catalyst system, and FIG. 9 shows the behavior of the NOx catalyst system of the above embodiment.

In the prior art (FIG. 8), since the control of the amount of HC supplied in accordance with the amount of toxic HC adsorbed by the NOx catalyst is not performed, the amount of toxic HC adsorbed continues to increase beyond the poisoning limit value. As a result, it becomes difficult for the NOx catalyst to recover to the original state, and the NOx purification rate decreases.

On the other hand, in the above embodiment (FIG. 9),
When the toxic HC adsorption amount of the NOx catalyst 13 reaches the poisoning limit value, the supply of HC is stopped, and the concentration of HC added to the exhaust gas decreases. As a result, the toxic HC adsorption amount is prevented from continuing to increase beyond the poisoning limit value, the toxic HC adsorption amount is suppressed below the poisoning limit value, and NO
x Reduction of the purification rate is prevented.

In the embodiment (1), the NOx catalyst 13
Although the HC supply nozzle 15 is provided in the exhaust pipe 12 as a means for supplying HC to the fuel cell, in the embodiment (2) shown in FIG. 10, a fuel injection nozzle (not shown) of each cylinder is provided from the pressure accumulation chamber 20 (common rail). In the diesel engine 11 that distributes fuel to the NOx catalyst 13, a small amount of fuel is injected by post-injection from at least one cylinder of fuel injection nozzles in the expansion stroke after the fuel is injected from the fuel injection nozzles and supplied to the NOx catalyst 13. Like that. Therefore, the exhaust pipe 12
Is not provided with an HC supply nozzle.

In the embodiment (1), the temperature of the outlet of the NOx catalyst 13 is measured by the exhaust gas temperature sensor 14. In the embodiment (2), the carrier of the NOx catalyst 13 is replaced with the exhaust gas temperature sensor. The temperature (catalyst temperature) is directly detected by the catalyst temperature sensor 21. The other configuration is the same as that of the embodiment (1).

Also in this embodiment (2), the current poisoned HC adsorption amount of the NOx catalyst 13 is calculated by the same method as in the embodiment (1), and this poisoned HC adsorbed amount is set to a preset poisoning limit. When the value is exceeded, post injection is stopped. In this case, the post injection is stopped until the poisoned HC adsorption amount becomes equal to or less than the poisoning limit value. As a result, the toxic HC adsorption amount is prevented from continuing to increase beyond the poisoning limit value, and the NOx purification capability of the NOx catalyst 13 is maintained. On the other hand, when the poisoned HC adsorption amount is equal to or less than the poisoning limit value, a target post-injection amount map using the engine operating conditions such as the catalyst temperature and the engine speed as parameters is searched, and according to the engine operating conditions at that time, The post injection is executed by obtaining the target post injection amount thus obtained.

In the above embodiments (1) and (2), N
Although fuel (light oil) was used as HC to be supplied to the Ox catalyst 13, liquid HC such as kerosene or gaseous H such as propane was used.
C may be used.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an entire exhaust gas purification system according to an embodiment (1) of the present invention.

FIG. 2 is a flowchart showing a processing flow of a toxic HC adsorption amount calculation program;

FIG. 3 is a flowchart showing a flow of processing of an HC supply amount control program;

FIG. 4 is a diagram conceptually showing a map of a coefficient fex representing a ratio of toxic HC in HC discharged from a diesel engine.

FIG. 5 is a diagram conceptually showing a map of a coefficient ffd representing a ratio of poisoned HC in HC supplied from an HC supply nozzle.

FIG. 6 (a) is an adsorption coefficient f ₁₁ based on the toxic HC adsorption amount.
Conceptually illustrated FIG maps of the (b) conceptually shows FIG maps of Adsorption Factor f ₁₂ by poisoning HC concentration flowing into the NOx catalyst, (c) the map of the adsorption coefficient f ₁₃ by the catalyst temperature diagram conceptually illustrating, (d) is a diagram showing conceptually a map of adsorption factor f ₁₄ by the exhaust gas amount

FIG. 7 (a) shows a desorption coefficient f ₂₁ according to the amount of toxic HC adsorbed.
Diagram conceptually illustrating a map, (b) conceptually shows FIG maps desorption coefficient f ₂₂ by poisoning HC concentration flowing into the NOx catalyst, (c) the desorption coefficient f ₂₃ by the catalyst temperature conceptually shows a map, (d) is a diagram showing conceptually a map of desorption coefficient f ₂₄ by the exhaust gas amount

FIG. 8 is a time chart showing the behavior of a conventional NOx catalyst system.

FIG. 9 is a time chart showing the behavior of the NOx catalyst system of the embodiment (1).

FIG. 10 is a configuration diagram of the entire exhaust gas purification system according to the embodiment (2) of the present invention.

[Explanation of symbols]

11: diesel engine (internal combustion engine), 12: exhaust pipe (exhaust passage), 13: NOx catalyst, 14: exhaust gas temperature sensor, 15: HC supply nozzle, 16: injection pump, 17
… Engine control circuit (toxic hydrocarbon adsorption amount calculation means,
Inflow amount calculation means, consumption amount calculation means, current adsorption amount calculation means, desorption amount calculation means), 20: pressure accumulating chamber, 21: catalyst temperature sensor.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naohisa Oyama 14 Iwatani, Shimowasumi-cho, Nishio City, Aichi Prefecture Inside the Japan Automobile Parts Research Institute (72) Inventor Shinya Hirota 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Inside the corporation

Claims (9)

[Claims] 1. A catalyst installed in an exhaust passage of an internal combustion engine,
By supplying hydrocarbons as reducing agents for nitrogen oxides,
In an exhaust gas purification system for reducing and purifying nitrogen oxides in exhaust gas, a hydrocarbon component causing poisoning of the catalyst (hereinafter referred to as “toxic hydrocarbon”) among hydrocarbons adsorbed on the catalyst.
A device for calculating the amount of adsorbed toxic hydrocarbons, which calculates the amount of adsorbed hydrocarbons. 2. The intoxication hydrocarbon adsorbing amount calculating means includes: an inflow amount calculating means for calculating an inflow amount of a poisoning hydrocarbon flowing into the catalyst per predetermined time every predetermined time; Consumption amount calculating means for calculating the consumption amount of the poisonous hydrocarbon consumed by the reaction with the catalyst per predetermined time; and the consumption amount is subtracted from the inflow amount of the poisonous hydrocarbon per predetermined time every predetermined time. This time multiplying the value by the adsorption rate of the poisoned hydrocarbon to the catalyst to calculate the adsorbed amount of the poisoned hydrocarbon to the catalyst per predetermined time; and A desorption amount calculating means for calculating a desorption amount of the toxic hydrocarbon adsorbed per predetermined time, and a desorption amount subtracted from the adsorption amount of the toxic hydrocarbon per predetermined time every predetermined time. Integrate the value and add the catalyst Hydrocarbon adsorption amount detection device of an exhaust purifying catalyst according to claim 1, characterized in that is composed of a means for calculating the poisoning hydrocarbon adsorption amount. 3. The inflow amount calculating means calculates an inflow amount of the toxic hydrocarbon per predetermined time into an amount of the toxic hydrocarbon in the exhaust gas discharged from the internal combustion engine and the amount of the toxic hydrocarbon into the exhaust gas upstream of the catalyst. 3. The device for detecting the amount of hydrocarbons adsorbed on an exhaust purification catalyst according to claim 2, wherein the amount is determined by adding up the amounts of the poisoned hydrocarbons added. 4. The system according to claim 2, wherein said inflow amount calculating means sets a ratio of toxic hydrocarbons in hydrocarbons discharged from said internal combustion engine based on internal combustion engine operating conditions. A device for detecting the amount of hydrocarbons adsorbed on an exhaust purification catalyst according to claim 1. 5. The system according to claim 2, wherein said inflow amount calculating means sets a ratio of toxic hydrocarbons in hydrocarbons added to the exhaust gas upstream of said catalyst based on a temperature of the exhaust gas. 4. The device for detecting the amount of adsorbed hydrocarbons of an exhaust purification catalyst according to any one of the above items 4. 6. The method according to claim 6, wherein the consumption calculating unit calculates the consumption of the poisoned hydrocarbon per predetermined time using a steady-state purification rate of the poisoned hydrocarbon set in advance according to a catalyst temperature. The device for detecting the amount of adsorbed hydrocarbons on an exhaust purification catalyst according to any one of claims 2 to 5. 7. The present adsorption amount calculation means calculates an adsorption ratio of the toxic hydrocarbons to the catalyst, the adsorption amount of the toxic hydrocarbons of the catalyst obtained in a previous process, and an amount of the exhaust gas flowing into the catalyst. The hydrocarbon adsorption amount of the exhaust purification catalyst according to any one of claims 2 to 6, wherein the hydrocarbon adsorption amount is set based on at least one of the concentration of the toxic hydrocarbon, the catalyst temperature, and the exhaust gas flow rate. Detection device. 8. The desorption amount calculating means calculates a desorption amount by multiplying a desorption ratio by the detoxification ratio of the toxic hydrocarbon adsorbed amount of the catalyst obtained in the previous process, and calculates the desorption ratio in the previous process. It is set based on at least one of the amount of poisoned hydrocarbons adsorbed by the catalyst obtained in the treatment, the concentration of poisoned hydrocarbons in the exhaust gas flowing into the catalyst, the catalyst temperature, and the exhaust gas flow rate. The device for detecting the amount of hydrocarbons adsorbed on an exhaust purification catalyst according to any one of claims 2 to 7. 9. A system for controlling the amount of hydrocarbons supplied to the catalyst so that the amount of toxic hydrocarbons adsorbed by the catalyst at this time does not exceed a preset poisoning limit value. An apparatus for detecting the amount of hydrocarbons adsorbed on an exhaust purification catalyst according to any one of claims 1 to 8.