JPH094437A - Nitrogen oxide purification device for internal combustion engine - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a nitrogen oxide purification device with a high purification rate that controls the amount of HC added finely. A nitrogen oxide purifying device 1 having an HC increasing means 12 for adding a hydrocarbon extender to exhaust gas and a control means 20 for controlling the HC increasing means 12. The control means 20 has a primary HC calculation unit 21 that performs the primary calculation of the amount of the extender, and a final HC calculation unit 22 that corrects the primary calculated amount of the extender and determines the final calculated amount. The primary HC calculation unit 21 primarily calculates the amount of the extender from the exhaust gas state determination means and the catalyst bed temperature estimation means. The final HC calculation unit 22 has an HC adsorption rate estimation means for the catalyst bed, an HC desorption rate estimation means, and an adsorption rate estimation means for estimating the hydrocarbon adsorption rate in the catalyst bed, and the amount is increased based on these. Vary the amount of agent added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrogen oxide purifying apparatus for an internal combustion engine, which purifies nitrogen oxides in an oxygen excess atmosphere.

[0002]

2. Description of the Related Art In the exhaust of excess air with lean air-fuel ratio,
A lean NO _x catalyst that reduces and purifies nitrogen oxides (NO _x ) in the presence of hydrocarbons (HC) is known. This lean NO _x catalyst for reducing nitrogen oxides is required hydrocarbons, hydrocarbons (HC) feed and nitrogen oxides hydrocarbons from increasing means when a lack of high temperature, such as hydrocarbons in the exhaust A method of maintaining a high purification rate has been proposed (see Japanese Patent Laid-Open No. 63-283727).

Similarly, an HC increasing means is provided in advance,
When the catalyst bed temperature is in a low temperature state, the HC increasing means is intermittently operated to improve the purification rate of nitrogen oxides while suppressing the deterioration of fuel efficiency, and at the same time prevent thermal deterioration of the catalyst device. An improved nitrogen oxide purifying device has been proposed (JP-A-4-284117).

[0004]

However, the improved purifying device (JP-A-4-284117) still has the following problems. Since the HC increasing means is operated only by the temperature of the catalyst bed, hydrocarbons become insufficient depending on the operating state, and the purification rate of nitrogen oxides decreases, or conversely, excessive supply of hydrocarbons deteriorates fuel efficiency. It is a situation that causes it. In view of the above conventional problems, the present invention adjusts an optimal hydrocarbon supply amount according to a change in operating conditions to improve the purification rate of nitrogen oxides and suppress the reduction of fuel consumption. The object is to provide a device for purifying things.

[0005]

The present invention relates to a nitrogen oxide purifying device which is interposed in an exhaust passage of an internal combustion engine and reduces and purifies nitrogen oxides discharged from the internal combustion engine.
A catalyst device for purifying nitrogen oxides in an oxygen excess atmosphere, an HC amount increasing means for adding an amount increasing agent such as fuel to the exhaust gas in order to increase the amount of hydrocarbons in the exhaust gas, and a control means for controlling this HC amount increasing means. The control means includes a primary HC calculation unit that calculates the amount of hydrocarbons or extenders that effectively purify nitrogen oxides on average in normal average operating conditions, and every second. And a final HC calculation unit that corrects the first-order calculated amount based on the changing temperature of the catalyst bed, the amount of hydrocarbon adsorption in the catalyst bed, and the like.
The calculation unit has an exhaust gas state determination means for determining the temperature of the exhaust gas, the flow rate of the purified reaction gas, etc., and a catalyst bed temperature estimation means for estimating the temperature of the catalyst bed, and based on the outputs of both these means. First calculate the target amount of hydrocarbon or extender,
On the other hand, the final HC calculation unit includes an HC adsorption rate estimating means for estimating a hydrocarbon adsorption rate in the catalyst bed, an HC desorption rate estimating means for estimating a hydrocarbon desorption rate in the catalyst bed, and a hydrocarbon in the catalyst bed. And an adsorption ratio estimating means for estimating the occupation ratio of the adsorption site. Based on the outputs of these three estimating means and the catalyst bed temperature estimating means, the primary calculated amount is corrected to determine the optimum hydrocarbon content. In the nitrogen oxide purifying apparatus for an internal combustion engine, the amount or the amount of the extender to be added is finally calculated, and the HC increasing means is operated based on the final calculated value.

What is most noticeable in the present invention is that the control means has a primary HC calculation section and a final HC calculation section, and the primary HC calculation section is composed of an exhaust gas state determination means and a catalyst bed. The target hydrocarbon amount is primarily calculated based on the temperature estimating means, while the final HC calculating unit considers the estimated temperature of the catalyst bed, the hydrocarbon adsorption ratio of the catalyst bed, the hydrocarbon adsorption rate and the desorption rate, and the above. It is to correct the primary calculation amount.

Since the exhaust gas state determination can be indirectly estimated by a sensor indicating the operating state, the operating state detecting means may be used as the exhaust gas state determining means. Further, the temperature of the catalyst bed can be estimated, for example, by the temperature of the exhaust gas and the amount of hydrocarbons in the exhaust gas. It can be estimated by a ratio or the like. Further, the hydrocarbon adsorption rate can be estimated by, for example, estimating the adsorption amount and desorption amount of hydrocarbons from the time of engine start and tracking these values (see FIG. 11 described later).

The final HC calculating section is operated so as to decrease the amount of the extender when the adsorption ratio of hydrocarbons in the catalyst device is high, and to increase the amount of the HC extender when the adsorption ratio is small. . Further, the final HC calculation unit decreases or increases the amount of the HC extender in accordance with, for example, the hydrocarbon desorption rate (or a value obtained by subtracting the adsorption rate from the desorption rate).

Further, the final HC calculation unit increases the extender when the temperature of the catalyst bed is in the process of increasing temperature,
Decrease the bulking agent during the cooling process. The final HC calculation unit increases the amount of the extender when the temperature of the catalyst bed is lower than the maximum temperature of the purification efficiency in the steady state (T2 of FIG. 16 described later), and is higher than the maximum temperature. In some cases, reduce the amount of filler.

[0010]

The function and effect of the present invention is to provide a nitrogen oxide purifying apparatus which can obtain a high purification rate of nitrogen oxides with little deterioration of fuel consumption by supplying an optimum amount of HC to any change of operating conditions. It is the one we are trying to provide. The inventor of the present application has studied the mechanism of the catalytic reaction and has clarified the following contents.

HC and nitrogen oxides (NO _x ) when hydrocarbon (HC) is used as a reducing agent in an oxygen excess atmosphere
FIG. 16 shows the purification characteristics at the steady temperature of. Curve A is NO
_x and curve B are the purification characteristics of HC. When the catalyst bed temperature T1 is low, purification of both NO _x and HC starts, and the purification rate is improved. At the catalyst bed temperature T2, the NO _x purification rate becomes the highest. When the temperature becomes higher, the NO _x purification rate decreases, and the NO _x purification rate becomes almost zero at the high catalyst bed temperature T3.

FIG. 17 shows a graph (Arrhenius plot) in which the horizontal axis represents the reciprocal 1 / T of the absolute temperature T of the local catalyst bed at the tip of the catalyst and the vertical axis represents the purification rate in logarithm. . Broken line A'is NO _x , broken line B'is HC
It is the characteristic of. Lower catalyst bed temperature T1 to catalyst bed temperature T
Up to 2, the rising gradients of the purification rates of NO _x and HC are almost the same. However, in the high temperature range from the catalyst bed temperature T2 to the catalyst bed temperature T3, the rising gradient of the purification rate of NO _x and HC is smaller than that from the catalyst bed temperature T1 to the catalyst bed temperature T2, and NO The increasing gradient of the purification rate of _x is lower than the increasing gradient of the purification rate of HC.

That is, as the temperature rises, the NO _x purification rate rises only slowly. Here, as shown by a straight line C in FIG. 17, even in the region of the catalyst bed temperature T2 or higher, if the rising gradient of the NO _x purification rate from the catalyst bed temperature T1 to the catalyst bed temperature T2 is obtained, the NO _x purification is continued. The speed is significantly improved, and the NO _x purification rate is significantly improved.

Next, the reason why the increasing gradient of the purification rate changes with the catalyst bed temperature T2 will be described with reference to FIG. The catalytic reaction consists of the following 5 steps. : Diffusion of reactant ,: Adsorption of reactant to catalyst ,: Conversion of reactant to product on catalyst surface ,: Desorption of product from catalyst,
: Diffusion of product. Here, in the low temperature region below the catalyst bed temperature T2, the rate of conversion of the reactant to the product on the surface of the catalyst at the stage is the lowest, which is the rate-determining step of the catalytic reaction.

On the other hand, in the high temperature region above the catalyst bed temperature T2,
It is considered that the rate of diffusion of the reactant in the step is the lowest, and it is the rate-determining step of the catalytic reaction. As shown in FIG. 17, the reason why the increasing gradient of the NO _x purification rate is lower than the increasing gradient of the HC purification rate is that the concentrations of the local reactants near the catalyst are different between the catalyst bed temperature T2 and below. It is estimated to be. In other words, oxygen and NO _x , which are HC oxidizing agents,
It is the ratio of the concentrations.

Oxygen concentration and NO of exhaust gas flowing into the catalyst
Comparing the _x concentrations, the oxygen concentration is much higher, so
The diffusion rate of oxygen concentration is higher, and oxygen is present in excess in the vicinity of the catalyst beyond the amount required for the oxidation of HC. Comparing the NO _x concentration with respect to the oxygen concentration at the catalyst bed temperature T2 or lower and the NO _x concentration with respect to the oxygen concentration at the catalyst bed temperature T2 or higher, the diffusion rate of NO _x relatively decreases in the high temperature range, NO _{x with} respect to oxygen concentration at temperature T2 or higher
The density ratio is low. Therefore, HC has a higher probability of reacting with oxygen, and as a result, N in HC
It is considered that the selectivity of O _x reduction decreases and the increasing gradient of the NO _x purification rate becomes lower than the increasing gradient of the HC purification rate.

From the above, in order to obtain the characteristics close to the straight line C explained in FIG. 17, it is necessary to increase the diffusion rate of HC,
Although necessary, as another means, it can be realized by adsorbing HC to the catalyst sufficiently at the catalyst bed temperature T2 or lower and desorbing HC at the catalyst bed temperature T2 or higher. In other words, the sum of the diffusion rate of HC and the desorption rate of HC is apparently
The rate is the rate-determining step of the catalytic reaction. The adsorption rate of HC is
Catalyst bed temperature, catalyst HC adsorption ratio (ratio of the number of already adsorbed sites to the total number of adsorbed sites of the catalyst), and H
The desorption rate of HC can be estimated by the catalyst bed temperature and the HC adsorption ratio of the catalyst.

Next, how the HC flowing into the catalyst is purified and discharged will be described. The adsorption rate is higher than the desorption rate at low temperature, and the desorption rate is higher than the adsorption rate at high temperature. In FIG. 16, when the catalyst bed temperature is T1 or lower, HC is hardly purified because the catalyst is below the activation temperature. Therefore, the inflowing HC has a relatively large adsorbed ratio, and the rest is discharged unpurified. Next, when the catalyst bed temperature of the catalyst is from T1 to T2, a certain proportion of the inflowing HC is purified and a relatively small proportion is adsorbed. On the other hand, the amount of desorbed HC that has already been adsorbed gradually increases as the temperature rises.

When the catalyst bed temperature of the catalyst is from T2 to T3, most of the inflowing HC is purified, and the adsorbed ratio is very small. On the other hand, the already adsorbed HC has a large desorption amount because of its high temperature. That is, in order to improve the NO _x purification rate and reduce the deterioration of fuel efficiency, it is important to estimate the adsorption rate and desorption rate of HC and provide the optimal amount of HC in consideration of the characteristics of the purification reaction. .

That is, when the temperature of the catalyst bed is low, it is preferable to sufficiently adsorb hydrocarbons in the catalyst bed and desorb the hydrocarbons at a high temperature to contribute to the purification reaction of nitrogen oxides. Further, it is desirable to estimate the adsorption rate and desorption rate of hydrocarbons, and to prevent the supply of excess hydrocarbons that are not adsorbed and do not contribute to purification to suppress the deterioration of fuel efficiency.

Therefore, in the present invention, first, the state of exhaust gas is estimated by the exhaust gas state determining means, and the temperature of the catalyst bed is estimated by the catalyst bed temperature estimating means,
Based on this information, the amount of hydrocarbons capable of satisfactorily purifying nitrogen oxides in an average operating state is calculated (first HC calculating unit). Next, in the final HC calculation unit, the above-mentioned primary calculation amount is corrected in response to the change of the hydrocarbon adsorption amount which changes every moment.

That is, the adsorption rate of hydrocarbons is estimated by the adsorption rate estimating means, the adsorption rate and desorption rate of hydrocarbons are estimated by the HC adsorption rate estimating means and the HC desorption rate estimating means, and the above catalyst bed is further used. The estimated amount of hydrocarbon is supplied to calculate the optimal amount of hydrocarbons, and the HC increasing means is operated based on this value. As described above, since the purifying device of the present invention supplies hydrocarbons in response to ever-changing operating conditions, the purification rate of nitrogen oxides becomes extremely good and hydrocarbons may become over-supplied. Therefore, fuel efficiency is good.

For example, when the hydrocarbon adsorption ratio θ in the catalyst bed is a small value, the hydrocarbon can be easily adsorbed to the catalyst bed, so that the HC extender is increased and the hydrocarbon adsorption ratio is increased. When θ is large, it is considered that there is little surplus capacity for adsorbing hydrocarbons in the catalyst bed, and therefore the purification rate of nitrogen oxides can be improved by reducing the amount of the extender.

Similarly, when the hydrocarbon desorption rate (or the difference between the desorption rate and the adsorption rate) in the catalyst bed is large,
Since the amount of hydrocarbons supplied to the catalyst (diffusion amount) is large, the amount of extender is reduced, and in the opposite case, the amount of extender is increased to improve the purification rate and avoid the supply of extra extender. can do.

Further, when the temperature of the catalyst bed is in the process of increasing, the amount of the hydrocarbon is changed in the direction in which the amount of hydrocarbon is insufficient in the nitrogen oxide purification reaction, so that the amount of the extender is increased, and conversely, in the temperature decreasing process. By reducing the extender, the purification rate can be improved. Further, as shown in FIG. 17, when the temperature of the catalyst bed is lower than the temperature (T2) at which the purification efficiency is maximum in the normal temperature state, the amount of hydrocarbons is increased in order to raise the catalyst bed temperature by the reaction heat. When the temperature is higher than the above temperature (T2), it is preferable to reduce the amount of hydrocarbons.

Further, as will be described in detail in the embodiments, in a vehicle or the like, an exhaust gas temperature sensor, a rotation sensor, a throttle sensor and the like are usually used in order for the control means to realize the above control calculation. It can be realized based on the information of existing sensors and the accumulated operation data,
It can be realized relatively inexpensively. As described above, according to the present invention, the optimum hydrocarbon supply amount is adjusted according to the change in the operating state, the purification rate of nitrogen oxides is increased, and the reduction of fuel consumption is suppressed. A device can be provided.

[0027]

【Example】

Example 1 As shown in FIG. 2, this example is a nitrogen oxide purification device 1 which is interposed in an exhaust passage 42 of an engine 41 of an automobile and reduces and purifies nitrogen oxides discharged from the engine 41. The purifying device 1 includes a catalyst device 11 for purifying nitrogen oxides in an oxygen-rich atmosphere, and an HC increasing means 12 for adding fuel as an HC increasing agent to the exhaust gas in order to increase hydrocarbons in the exhaust gas. , And a control means 20 for controlling the HC increasing means 12.

As shown in the flow chart of FIG. 1, the control means 20 calculates the amount of the HC extender (fuel) which purifies the nitrogen oxides on average in a normal average operating condition, and which is the primary HC. Based on the calculation unit 21 and the constantly changing temperature of the catalyst bed, the amount of hydrocarbon adsorption in the catalyst bed, etc.
The final HC calculation unit 22 that corrects the first calculated amount of the extender. The primary HC calculation unit 21 includes an exhaust gas state determination means (steps -61, 62) for determining the temperature of exhaust gas, a flow rate of purified reaction gas, etc., and a catalyst bed temperature estimation means (step -61, 62) for estimating the temperature of the catalyst bed ( And the step 63), and based on the results of both means, in step 64, the amount of the extender added is primarily calculated.

On the other hand, the final HC calculating section 22 comprises an HC adsorption rate estimating means (step 66) for estimating the hydrocarbon adsorption rate V ₂ in the catalyst bed and an HC desorption rate for estimating the hydrocarbon desorption rate V ₁ in the catalyst bed. Separation speed estimation means (step 6
5) and an adsorption ratio estimating means (step 69) for estimating the occupation ratio θ of the hydrocarbon adsorption site in the catalyst bed. Then, the primary calculation amount is corrected based on the outputs of the estimating means and the catalyst bed temperature estimating means to finally calculate the amount of the extender.

Further, as shown in the flow chart of FIG. 8 which will be described later, the final HC calculating section increases the amount of the extender based on the output of the adsorption ratio estimating means to a smaller ratio of the hydrocarbon adsorption ratio θ. If the adsorption ratio θ is large, the extender is decreased. And the hydrocarbon desorption rate V
If the value obtained by subtracting the adsorption rate V ₂ from ₁ is positive, the amount of the extender added is decreased, and if it is negative, the amount of the extender added is increased.

The following is a supplementary explanation for each. FIG. 2 shows the overall configuration of the system. A catalyst device 11 capable of purifying nitrogen oxides in an oxidizing atmosphere is installed in an exhaust passage 42 of the internal combustion engine 41, and a muffler 43 is connected downstream of the catalyst device 11. An exhaust gas temperature sensor 26 is provided upstream of the catalyst device 11. Besides, an accelerator sensor 26 and a rotation speed sensor 27 are provided, and signals of the exhaust gas temperature sensor 25, the accelerator sensor 26 and the rotation speed sensor 27 are input to the control means 20.

The fuel injection pump 44 supplies low pressure fuel to the HC
The fuel is supplied to the fuel addition device 12 as the amount increasing means, and the fuel addition device adds the fuel to the exhaust pipe 42. Fuel injection pump 4
4 supplies high-pressure fuel to the injection nozzle 45, and the injection nozzle 45 injects fuel into the cylinder of the internal combustion engine 41. An intake throttle 47 is installed in the intake pipe 46 of the internal combustion engine 41.

The control means 20 performs various calculations based on the input signal to control the operation of the fuel addition device 12 and the intake throttle 47. The control of the intake throttle 47 is performed by reducing the intake air amount and raising the exhaust temperature when the internal combustion engine 41 is under a low load or accelerating, and reducing the intake air amount and raising the exhaust temperature when decelerating the catalyst bed temperature. It will delay the descent of.

Next, a control method of the HC increasing means 12 of the present invention will be described. FIG. 1 shows an outline of the overall control flow of the control means 20. First, the control means 20
In step 61, the signals of the rotation speed sensor 27, the accelerator sensor 26, and the exhaust temperature sensor 26 are read. Next, at step 62, the operating state of the engine 41 and the exhaust gas state are determined.

Next, at step 63, the catalyst bed temperature estimating means estimates the temperature T of the catalyst bed. Then, step 6
In step 4, the addition amount S ₁ of the extender is first calculated. Next, at step 65, the HC desorption rate estimation means calculates the HC desorption rate V ₁
Then, in step 66, the HC adsorption rate V ₂ is estimated by the HC adsorption rate estimation means.

Next, in step 67, the amount of the extender is adjusted to the final H level.
The correction value is corrected by the C calculation unit to calculate the final value S ₀ . Subsequently, at step 68, the HC increasing means 12 is operated to add the addition amount S ₀ of the increasing agent to the exhaust passage 42. Finally, at step 69, the HC adsorption ratio estimating means calculates the HC adsorption ratio θ.
Is estimated.

The steps 61 to 6 will be described below.
9 will be described in detail. In step 62, the state of the exhaust gas is determined from the signals of the rotation speed sensor 27 and the accelerator sensor 26 input to the control means 20 in step 61.
That is, as shown in FIGS. 3 (a) to 3 (c), the amount of nitrogen oxide (NO _x ) emission, carbonization, and Obtain the hydrogen (HC) emissions and exhaust temperature. Note that each curve in FIG. 3 is an equal curve showing a constant value.

Next, at step 63, the catalyst bed temperature T is estimated from the signal of the exhaust temperature sensor 26 input to the control means 20 by the method shown in FIGS. 4 (a) and 4 (b). First, the exhaust temperature and the temporal change of the exhaust temperature (whether the steady state, the temperature rising state, or the temperature falling state) are obtained from the exhaust temperature sensor, and the catalyst bed temperature 1 is obtained from the map of FIG. This map is to correct the delay in the temperature change of the catalyst bed temperature with respect to the inflow gas temperature due to the heat capacity of the catalyst bed.

Next, the obtained catalyst bed temperature 1 and HC in the exhaust gas
The catalyst bed temperature 2 is determined from the amount based on the map of FIG. 4 (b). This is a map for correcting the temperature rise of the catalyst bed temperature due to the heat of reaction of HC. This catalyst bed temperature 2 is defined as the defined catalyst bed temperature T. The amount of HC in the exhaust gas used here is
It can be calculated by the sum of the amount of HC discharged from the engine obtained in step 62 and the amount of HC by the amount increasing agent which is increased by the HC increasing means described later.

In step 64, the first amount of the extender is determined from the map of engine speed and engine tokule shown in FIG. 5 (a).
Next, determine the calculated amount. Alternatively, as shown in FIG. 5B, the catalyst bed temperature estimated in step 63 and the step 62
The primary calculated amount of the extender may be determined from the NO _x emission amount obtained in. In any case, it is desirable that the first-calculated amount of addition of the extender is increased at a catalyst bed temperature with a high NO _x purification rate, and similarly, is increased in an operating state with a large NO _x emission amount. That is, at the catalyst bed temperatures T1 and below and T3 and above shown in FIG. 16, the amount of addition of the extender is set to zero and during that period, the value is set to a value proportional to the NO _x purification rate.

In step 65, the HC desorption rate V1 is calculated from the catalyst bed temperature T estimated in step 63 and the HC adsorption ratio θ described later by the following equation. V1 = A1 · EXP (−E1 / (R · T)) · θ ─────── (1) Where, V1: HC desorption rate, A1: frequency factor (constant), E1: activation energy (constant) ), R: gas constant,
T: catalyst bed temperature, θ: HC adsorption ratio. Control means 2
When the index calculation is difficult at 0, the HC desorption rate constant k1
(Corresponding to A1 · EXP (−E1 / (R · T))) is read from a preset map shown in FIG. 6, and the read value is multiplied by the HC adsorption ratio θ to obtain the HC desorption rate V1. Good.

In step 66, the catalyst bed temperature T estimated in step 63, the HC adsorption ratio θ described later, and the H in exhaust gas are explained.
From the C concentration (which can be calculated from the sum of the amount of HC discharged from the engine obtained in step 62 and the amount of HC increased by the HC increasing means described later), the HC adsorption speed V2 is calculated by the following formula. V2 = A2 · EXP (−E2 / (R · T)) · (1−θ) · P ─── (2) where V2: HC adsorption rate, A2: frequency factor (constant), E2: activation Energy (constant), R: gas constant,
T: catalyst bed temperature, θ: HC adsorption ratio, P: HC in exhaust gas
The concentration.

When it is difficult to calculate the index by the control means 20,
HC adsorption rate constant k2 (A2.EXP (-E2 / (R.
T)) is read from a predetermined map shown in FIG. 7, and the read value is multiplied by (1−θ) · P to obtain H
The C adsorption rate may be obtained. In step 67, the first calculated amount S1 of the extender calculated in step 64 is set to the HC adsorption ratio θ described later, the HC desorption rate V1 estimated in step 65, and the HC adsorption rate V2 estimated in step 66.
Correct with. FIG. 8 shows the control flow.

First, in step 670, it is determined whether the current HC adsorption ratio θ is smaller than the first set value θ ₁ (HC adsorption ratio small). In the case of YES, the routine proceeds to step 671, where the increase set value A _S for correcting (increasing / decreasing) the first calculated amount S1 of the extender is set to the first set value A _1, and the process proceeds to step 672. On the other hand, if NO in step 670, the process immediately proceeds to step 672. Current HC at step 672
Adsorption rate θ is the second set value θ ₂ (HC adsorption rate is large, θ ₂ >
θ ₁ ) Judgment is made. In the case of YES, the routine proceeds to step 673, where the increase set value As of the extender is set to 0, and the routine proceeds to step 674. On the other hand, if NO in step 672, the process immediately proceeds to step 674.

In step 674, the above-mentioned increase set value A _S is added to the first calculated amount S ₁ of the above-mentioned extender to obtain the second calculated amount S ₂ . Next, proceeding to step 675, a value obtained by multiplying the difference between the HC desorption rate V1 and the HC adsorption rate V2 by a constant k3 is subtracted from the second calculated amount S ₂ of the extender corrected in step 674. The increasing set value A _S of the extender with respect to the HC adsorption ratio θ has the characteristics shown in FIG.
Here, it is desirable to correct the first set value θ ₁ and the second set value θ ₂ with respect to the catalyst bed temperature T as shown in FIG. Because, as the temperature rises, the HC adsorption rate V
2 greatly decreases, and the HC desorption rate V1 greatly increases, so that the HC adsorption ratio θ does not easily increase at high temperature. Therefore, if it is not corrected according to FIG.
This is because the fuel consumption will be deteriorated due to an increase in excess HC.

In step 68, the control means 20 outputs a signal based on the final addition amount S ₀ of the extender corrected in step 67 to the fuel addition device 12 which is the HC increasing means. In step 69, the HC adsorption rate θ at a new time is estimated from the HC desorption rate V1 and the HC adsorption rate V2 based on the present HC adsorption rate θ. FIG. 11 shows the control flow.

First, in step 690, it is determined whether the engine is starting. If YES, the HC adsorption ratio θ is set to 0 in step 691, and the process proceeds to step 692. This is because the adsorbed HC is desorbed and the HC adsorption ratio θ becomes 0 when the engine is stopped and time elapses. If NO in step 690, the process immediately proceeds to step 692.

At step 692, a new HC adsorption rate θ is obtained by subtracting the value obtained by subtracting the HC adsorption rate V2 from the HC desorption rate V1 from the current HC adsorption rate by a constant k4.
Ask for. Next, in step 693, it is determined whether the newly obtained HC adsorption ratio θ is smaller than zero. YES
Then, in step 694, the HC adsorption ratio is corrected to 0, and the process proceeds to step 695. If NO in step 693,
Immediately proceed to step 695.

In step 695, the catalyst bed temperature T is set to the first value.
Of the catalyst bed set temperature T _s1 or less and the increase set value A _S for correcting the first calculated amount S1 of the extender is the first increase set value A ₁ (see step 671 in FIG. 8). It is determined whether or not the first predetermined time t ₁ has continued. If YES, the HC adsorption ratio θ is set to the second set value θ _{2 in} step 696, and the process proceeds to step 697. This is the HC adsorption ratio θ
This is to correct the integrated estimation error of the low temperature (T ≦ Ts
_When the amount of the extender is increased in ₁ ) for a certain period of time (t ≧
This means resetting to an appropriate value for t ₁ ).

If NO in step 695, the process advances to step 697. In step 697, the state where the catalyst bed temperature is _{equal to} or higher than the second set temperature T _s2 (T _s2 > T _s1 ) and the increase set value A _S of the extender is 0 is the second predetermined time t.
Determine if ₂ or more continued. If yes, step 69
In step 8, the HC adsorption ratio θ is set to 0, and the process proceeds to step 699. This is to correct the integration error of the HC adsorption ratio θ, and there is no HC increase at high temperature (T ≧ Ts ₂ ) (As =
When the state of (O) is continued, the adsorption ratio θ becomes almost zero, so that the setting is performed again. If NO in step 697, the process advances to step 699. Step 699 is a process for returning to the start.

The first catalyst bed set temperature T _s1 and the second catalyst bed set temperature T _s2 will be described with reference to FIG. As described above, at low temperatures, the HC adsorption rate V ₂ > H
C desorption rate V ₁ , and at high temperature, HC adsorption rate V ₂ <HC desorption rate V ₁ . Therefore, at the first catalyst bed set temperature T _s1 for correcting the adsorption ratio θ, the HC adsorption rate V ₂ is the HC desorption rate V
Set very large temperature than _1, conversely, the second catalyst bed set temperature Ts ₂ is desirably HC desorption rate V ₁ is set at a very large temperature than HC adsorption rate V _2.

As described above, in the purifying apparatus 1 of this embodiment, the amount of the HC extender added is adjusted according to the progress state of the NOx purification reaction, not only the temperature T of the catalyst bed but also the adsorption of hydrocarbons. It is finely controlled according to the ratio θ, the desorption rate V ₁ and the adsorption rate V ₂ . Therefore, the purification rate of nitrogen oxides is improved, and since the extender is not added excessively, fuel consumption does not deteriorate. As described above, according to this example,
It is possible to provide the nitrogen oxide purification device 1 of the internal combustion engine 41 that adjusts the optimal hydrocarbon supply amount according to the change of the operating state of the vehicle, increases the purification rate of nitrogen oxides, and suppresses deterioration of fuel efficiency. .

Embodiment 2 The second embodiment is the same as the first embodiment except that step 6 in FIG.
7 is another embodiment in which No. 7 is changed. In the first embodiment, the correction of the supply amount of the extender is performed only by the HC adsorption ratio θ, but in the second embodiment, the correction amount As by the HC adsorption ratio θ is used.
_{By using 1} and the correction amount As ₂ depending on whether the catalyst bed temperature T is in the temperature rising state or the temperature falling state, a more detailed correction is performed. The detailed control flow of step 67 of the second embodiment is shown in FIG.

First, at step 710, it is determined whether the present HC adsorption ratio θ is smaller than the first set value θ ₁ (HC adsorption ratio is small). If YES, the process proceeds to step 711, where the first increase set value A _S1 for correcting the first calculated amount S1 of the extender is set to the first set value A ₁ (see step 671 in FIG. 8).
And proceed to step 712. NO in step 710
In the case of, the process immediately proceeds to step 712. Step 7
At 12, it is determined whether or not the current HC adsorption ratio θ is larger than the second set value θ ₂ (HC adsorption ratio is large). If YES, the process proceeds to step 713, the value of the first increase set value A _S1 is set to 0, and the process proceeds to step 714.

If NO in step 712, the process immediately proceeds to step 714. In step 714, the second increase set value A for correcting the first calculated amount S1 of the extender is set.
Reset _S2 to 0 and proceed to step 715. In step 715, it is determined whether or not the catalyst bed temperature T is in a temperature rising state. If YES, the process proceeds to step 716, and the second increasing set value A _S2 of the extender is set to the second setting value A _2, and the process proceeds to step 717. If NO in step 715, the process immediately proceeds to step 717.

In step 717, it is determined whether the catalyst bed temperature T is in the temperature decreasing state. If yes, step 71
8, the second increasing set value A _S2 of the extender is set to the minus second setting value (-A ₂ ) and the process proceeds to step 719. If NO in step 717, immediately execute step 7
Proceed to 19. In step 719, the first increasing set value A _S1 and the second increasing set value A _{S2 are} added to the first increasing agent calculated amount S _1.
And are added to calculate the second calculated amount S2. Next, in step 720, a value obtained by multiplying the difference between the HC desorption rate V ₁ and the HC adsorption rate V ₂ by a constant k3 is subtracted from the second calculated amount S ₂ of the extender corrected in step 719. , Final value S ₀ .

As is known from the above control flow, according to this example, when the temperature of the catalyst bed is in the process of increasing the temperature and the amount of hydrocarbon is likely to be insufficient, the amount S _{0 of the} extender added is increased,
Since the amount S ₀ of the extender to be added is decreased when the reaction is decreasing during the temperature decreasing process, the purification rate of nitrogen oxides can be further improved. Others are the same as in the first embodiment.

Embodiment 3 The third embodiment is another embodiment in which step 67 of FIG. 1 is modified in the second embodiment. In the second embodiment, H
The addition amount of the extender was corrected depending on whether the C adsorption ratio θ and the catalyst bed temperature T are in the temperature rising state or the temperature falling state. In the third embodiment, the catalyst bed temperature T itself is further corrected. Compensate according to the size of. The control flow of step 67 of the third embodiment is shown in FIGS. First, in step 750, the first and second set values A of the extender are set.
Reset _S1 and A _S2 to 0, and proceed to step 751.
In step 751, the catalyst bed temperature T is the first set temperature TS
₁ (This temperature is the temperature corresponding to T1 in FIG.
It is determined whether the O _x purification rate is a very low temperature) or less.

In the case of YES here, the process proceeds to step 752. If NO in step 751, step 7
58 (FIG. 15). Steps 752 to 755 are the same as steps 710 to 713 in FIG. 13, and therefore description thereof will be omitted. NO in step 754
In case of, and after step 755, the process proceeds to step 756. Steps 756 to 757 are similar to steps 719 to 720 of FIG.

On the other hand, in step 758 of FIG. 15, the catalyst bed temperature T is set to the second catalyst bed set temperature TS ₂ (this temperature is set in FIG.
In step 6, the temperature is equivalent to T2 and the NO _x purification rate is extremely high). If YES, proceed to step 759. If NO in step 758, proceed to step 767. Steps 759 to 762 are steps 752 to 755 in FIG.
Is the same as

If NO in step 761 and step 7
After 62, the process proceeds to step 763. Steps 763 to 766 are similar to steps 715 to 718 of FIG. In the case of NO at step 765 and after step 766, the process proceeds to step 756 of FIG. On the other hand, in step 767, which proceeds from step 758, the catalyst bed temperature is equal to or lower than the third catalyst bed set temperature TS ₃ (this temperature is the temperature corresponding to T3 in FIG. 16 and the NO _x purification rate is extremely low). Or not. YE
In the case of S, the routine proceeds to step 768, where the first HC increase amount setting value As ₁ is set to 0, and the routine proceeds to step 763, where the second increase setting value As ₂ is determined during step 766 similarly to the above.

If NO in step 767, step 7
Proceed to 69, and set the HC first increase setting value As ₁ to 0,
Immediately, the routine proceeds to step 756 in FIG. 14 (therefore, the increase set value As ₂ is 0). As described above, in this example, the temperature T of the catalyst bed is
Is divided into four areas, and the amount of the extender is determined so as to be suitable for the purification reaction in each area. As described above, if the control mode is finely changed according to the temperature T of the catalyst bed, a more appropriate amount of hydrocarbon corresponding to the purification reaction of nitrogen oxides is added, and the purification rate can be further improved. it can. Others are the same as in the second embodiment.

[Brief description of drawings]

FIG. 1 is an overall flowchart of a purification device according to a first embodiment.

FIG. 2 is a system configuration diagram of the purification device according to the first embodiment.

FIG. 3 is a diagram showing a relationship between an engine speed and torque and an exhaust gas state in the exhaust gas state determination means of the first embodiment.

FIG. 4 is a diagram showing the relationship between the catalyst bed temperature and the state of exhaust gas in the catalyst bed temperature estimation means of the first embodiment.

FIG. 5 is a diagram showing the relationship between the primary calculated amount S ₁ of the extender and other indexes in the purification apparatus of Example 1.

FIG. 6 is a diagram showing a relationship between a catalyst bed temperature and a hydrocarbon desorption rate constant k1 in the purifying apparatus of Example 1.

FIG. 7 is a diagram showing a relationship between a catalyst bed temperature and a hydrocarbon adsorption rate constant k2 in the purification apparatus of Example 1.

FIG. 8 is a detailed flowchart of step 67 of FIG.

9 is a diagram showing a relationship between a hydrocarbon adsorption ratio θ and a first increase set value A _S in the flowchart of FIG.

10 is a diagram showing the relationship between the hydrocarbon adsorption ratio set values θ ₁ and θ ₂ and the catalyst bed temperature T in the flowchart of FIG.

11 is a detailed flowchart of step 69 of FIG.

FIG. 12 is a diagram showing the relationship between the catalyst bed temperature and the hydrocarbon adsorption rate V ₁ and desorption rate V _{2 in} the purification apparatus of Example 1.

FIG. 13 is a detailed flowchart of step 67 of FIG. 1 in the purifying apparatus according to the second embodiment.

FIG. 14 is a detailed flowchart (1) of step 67 of FIG. 1 in the purifying apparatus according to the third embodiment.

FIG. 15 is a detailed flowchart (No. 2) of step 67 of FIG. 1 in the purifying apparatus according to the third embodiment.

FIG. 16 is a graph showing the relationship between the catalyst bed temperature and the nitrogen oxide purification rate in a steady state of the nitrogen oxide purification device.

FIG. 17 is a diagram showing the relationship between the reciprocal of the catalyst bed temperature of the nitrogen oxide purification device and the logarithmic value of the nitrogen oxide purification rate.

FIG. 18 is a schematic diagram showing a process of a purification reaction in a catalyst bed of a nitrogen oxide purification device.

[Explanation of symbols]

 12. . . 20. HC increasing means (fuel adding means), . . Control means, 21. . . 21. Primary HC calculation unit, 22. . . Final HC calculator, 26. . . Temperature sensor,

Front page continuation (72) Koichi Ohata, 1-1, Showa-cho, Kariya city, Aichi prefecture, Nihon Denso Co., Ltd. (72) Inventor, Tsukasa Kuboshima, 1-1, Showa-cho, Kariya city, Aichi prefecture, Nihon Denso Co., Ltd. (72) Inventor Hideaki Ueno 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd.

Claims (5)

[Claims] 1. A nitrogen oxide purifying device, which is interposed in an exhaust passage of an internal combustion engine and reduces and purifies nitrogen oxides discharged from the internal combustion engine, the purifying device comprising: It has a catalyst device for purifying substances, an HC increasing means for adding an increasing agent such as a fuel to the exhaust gas in order to increase the amount of hydrocarbons in the exhaust gas, and a control means for controlling the HC increasing means, The control means includes a primary HC calculation unit that calculates the amount of hydrocarbons or extenders that effectively purify nitrogen oxides on average in normal average operating conditions, and the temperature of the catalyst bed that changes with time. Final HC for correcting the above-mentioned primary calculated amount based on the amount of hydrocarbon adsorption in the catalyst bed, etc.
The primary HC calculator has an exhaust gas state determination means for determining the temperature of the exhaust gas, the flow rate of the purified reaction gas, and the like, and a catalyst bed temperature estimation means for estimating the temperature of the catalyst bed. Based on the outputs of the both means, the target hydrocarbon or the amount of the extender is first calculated, while the final HC calculation unit estimates the hydrocarbon adsorption rate in the catalyst bed. It has an estimating means, an HC desorption rate estimating means for estimating a hydrocarbon desorption rate in the catalyst bed, and an adsorption ratio estimating means for estimating a occupancy rate of a hydrocarbon adsorption site in the catalyst bed. Based on the outputs of the estimating means and the catalyst bed temperature estimating means, the primary calculated amount is corrected to finally calculate the optimum amount of hydrocarbon or the amount of the extender to be added, and based on this final calculated value, the above HC Operate the increasing means DOO nitrogen oxide purification system of an internal combustion engine characterized by. 2. The final HC calculation unit according to claim 1, wherein, based on the output of the adsorption ratio estimation means, the final HC calculation unit increases the extender when the adsorption ratio is small, and increases the adsorption ratio when the adsorption ratio is large. The nitrogen oxide purifier is characterized in that it operates to reduce the extender. 3. The final HC calculation unit according to claim 1 or 2, wherein the hydrocarbon desorption rate or a value obtained by subtracting the adsorption rate from the hydrocarbon desorption rate is greater than a predetermined value. A nitrogen oxide purifying device which is operated so as to decrease the extender and increase the extender when the amount is smaller than a predetermined value. 4. The final HC calculation unit according to claim 1, wherein the final HC calculation unit determines that the temperature of the catalyst bed is in the process of rising based on the output of the catalyst bed temperature estimation means. The nitrogen oxide purifying device is operated so as to increase the extender when the temperature rises, and decrease the extender when it is determined that the temperature is decreasing. 5. The HC calculation unit according to claim 1, wherein the temperature of the catalyst bed is lower than a temperature at which the purification rate of nitrogen oxides is maximized in a steady state. In this case, the nitrogen oxide purifying device is operated so as to increase the amount of the extender and decrease the amount of the extender when the amount is higher than the above value.