JP2001152835A - Exhaust emission control device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rationally exercise temperature rising of an exhaust gas or NOx absorber for releasing an attached sulfur component from the NOx absorber in an exhaust emission passage, while suppressing fuel consumption deterioration, torque drop, and smoke generation. SOLUTION: At high load, the temperature of exhaust gas is raised by dividedly injecting fuel, and in a low load, the temperature of exhaust gas is raised by conducting dividing injection of the fuel and the lag of ignition timing. In the high load, in which the temperature of the exhaust gas is already high and the temperature rise of the exhaust gas is not needed so much, only the divided injection is conducted in the low load in which the temperature of the exhaust gas is still low and the temperature rising of the exhaust gas is considerably needed, retard is conducted together with divided injection, and temperature rising of the exhaust gas or a catalyst device is efficiently, surely conducted, while nonconformities such as deterioration for fuel consumption, drop in torque, smoke generation accompanting the temperature rising of the exhaust gas for releasing sulfur are suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an engine, and more particularly, to an exhaust gas purifying apparatus for an engine in which a NOx absorbent is disposed in an exhaust passage, and belongs to the technical field of exhaust gas purification.

[0002]

2. Description of the Related Art Generally, in an engine for a vehicle or the like, CO (carbon monoxide) and HC contained in exhaust gas are used.
A three-way catalyst is used as a device for removing harmful components such as (hydrocarbon) and NOx (nitrogen oxide). However, in the case of an engine employing a direct injection stratified combustion system or the like for the purpose of improving fuel efficiency in recent years, since the oxygen concentration in the exhaust gas is high, the conventional three-dimensional window in which the window is in a narrow range near the stoichiometric air-fuel ratio is used. A problem arises in that the source catalyst cannot remove NOx sufficiently.

To cope with this, an exhaust passage is
When the air-fuel ratio is lean (excessive oxygen), NOx in the exhaust gas is absorbed, and when the air-fuel ratio becomes rich (oxygen-deficient), the catalytic device (NOx It is known to arrange a catalyst device). According to this, by appropriately controlling the air-fuel ratio, in the lean state, NOx is absorbed by the NOx absorbent and the emission to the outside is suppressed, and in the rich state, NOx is removed from the NOx absorbent. It is released and reacts with a large amount of CO and HC, and the emission to the outside is also suppressed. As a result, it is possible to effectively reduce the NOx emission of the engine employing the stratified combustion method.

[0004] However, the above-mentioned NOx absorbing material is liable to be linked to other substances such as sulfur components contained in fuel, for example, and there is a problem that the NOx absorbing capacity is reduced due to an increase in the amount of the NOx absorbing material. In particular, those using barium, which is highly effective as this type of NOx absorbent, are easily linked to SOx (sulfur oxide), and an increase in the amount of SOx leads to SOx.
It becomes x poisoned and the NOx purification ability is significantly reduced.

[0005] As a method for eliminating SOx poisoning of the NOx absorbent, a NOx absorbent, for example, 600-
It is known that heating to a high temperature of 650 ° C. or more is effective. That is, generally, the amount of the sulfur component adhering to the NOx absorbent is estimated, and when the estimated amount is equal to or more than a predetermined amount, the temperature of the exhaust gas is increased to remove the NOx absorbent from the sulfur. The temperature is raised to a releasable temperature to release the sulfur component from the NOx absorbent. And, by the sulfur component release treatment, N
The amount of sulfur components released from the Ox absorbent is estimated (or the amount of sulfur components remaining in the NOx absorbent is estimated), and the estimated amount is determined to be equal to or greater than a predetermined amount. If this is the case (similarly, if the remaining amount is equal to or less than the predetermined remaining amount), the release of the sulfur component is terminated.

[0006] In this case, as a method of raising the exhaust gas temperature, for example, as disclosed in Japanese Patent Application Laid-Open No. H10-54274, it is known to retard the ignition timing. Japanese Patent Laid-Open Publication No. Hei 8-100639 also discloses that the ignition timing is retarded as a method of increasing the exhaust gas temperature. It is disclosed that the ignition timing is allowed to be retarded. This is to prevent the engine output from becoming unstable if the ignition timing is retarded in other low-speed low-load regions, for example, and to prevent the NOx catalyst from being excessively high when the ignition timing is retarded in the high-speed high-load region. This is to avoid burning due to high temperature.

[0007] The present applicant increases the amount of CO in exhaust gas and the temperature of exhaust gas by retarding the ignition timing and dividing the fuel into an intake process and a compression process and injecting the fuel. A patent application has been filed for promoting the desorption of sulfur components from the NOx absorbent (1998 Patent Application No. 209,674). Therefore, in addition to retarding the ignition timing, split injection of fuel is also an effective method for raising the exhaust gas temperature for sulfur release.

[0008]

However, the retardation of the ignition timing and the split injection of the fuel all increase the unburned component of the fuel, and the unburned component is so-called in an exhaust passage close to the NOx absorbent. By "burning after", NO
Since the temperature of the exhaust gas flowing into the x-absorbing material is raised, a problem such as deterioration of fuel efficiency, reduction of torque, or generation of smoke in the case of a diesel engine accompanies it. Therefore, N
Even for the purpose of releasing sulfur from the Ox absorber,
It is desired to raise the temperature of the exhaust gas and the NOx catalyst device while suppressing the above-mentioned problems as much as possible.

According to the present invention, the temperature rise of the exhaust gas, which is performed to release the attached sulfur component from the NOx absorbent disposed in the exhaust passage, is caused by various problems such as deterioration of fuel efficiency, decrease in torque, and generation of smoke. The task is to carry out rationally while suppressing the above. Hereinafter, the present invention will be described in detail including other problems.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the invention according to claim 1 in the claims of the present application absorbs the NOx component in the exhaust gas in an oxygen-excess atmosphere and reduces the oxygen concentration. A NOx absorbent that releases a NOx component due to a decrease in the NOx component in the exhaust passage, a sulfur component attached amount estimating means for estimating the amount of the sulfur component attached to the NOx absorbent, and a sulfur component estimated by the estimating means. An exhaust gas purifier for an engine having a sulfur component releasing means for releasing a sulfur component from the NOx absorbent by raising the temperature of the exhaust gas and raising the temperature of the NOx absorbent when the adhered amount becomes equal to or more than a predetermined amount. An apparatus, wherein the sulfur component releasing means increases the temperature of the exhaust gas by injecting the fuel in a plurality of times when the load is high, and increases the temperature of the fuel when the load is low. And split injection, characterized in that raising the temperature of the exhaust gas by performing the retarding of the ignition timing.

At high load, the exhaust gas temperature is already high,
It is close to the temperature at which sulfur can be released from the NOx absorber. On the other hand, when the load is low, the exhaust gas temperature is still low and is far from the temperature at which sulfur can be released from the NOx absorbent. The retardation of the ignition timing that can be used as a method of increasing the exhaust gas temperature has a large problem of a decrease in torque as compared with the fuel split injection.

Therefore, according to the present invention, when the exhaust gas temperature is already high and the load of the exhaust gas does not need to be raised so much, at a high load, only the fuel split injection is performed, the exhaust gas temperature is still low, and the exhaust gas temperature is low. The ignition timing is also retarded in conjunction with the split injection only at low loads where the temperature must be raised to a considerable extent, so that the temperature of the exhaust gas and NOx absorbent for SOx poisoning is increased. It is possible to carry out rationally and reliably while minimizing inconveniences that occur.

Next, according to a second aspect of the present invention, in the first aspect of the present invention, the sulfur component releasing means is provided when the load is larger than the predetermined load on the high load side and when the load is low. When the load is lower than the predetermined load on the side, the sulfur component is not released.

According to the present invention, when the load is higher than a predetermined value and when the load is lower than a predetermined value, the sulfur component is not released. And the retard of the ignition timing is not executed.

When the load is higher than a predetermined value, it is possible that the temperature has already reached the temperature at which sulfur can be released even if the temperature of the exhaust gas is not increased. On the other hand, when the load is lower than a predetermined value, the exhaust gas does not reach the temperature at which sulfur can be released even if the split injection or the retard is performed, and there is a possibility that only accompanying problems occur. Therefore, in such a case, by not releasing the sulfur component, it is possible to avoid the loss of fuel efficiency, the decrease in torque, and the generation of smoke due to the above-mentioned wasteful temperature rise of exhaust gas. it can.

According to a third aspect of the present invention, in the first or the second aspect of the present invention, the sulfur component releasing means injects the fuel into an intake step and a compression step while dividing the fuel into a suction step and a compression step. At the time of load, the fuel injection timing in the compression step is delayed as compared with the time of high load.

According to the present invention, when the fuel is dividedly injected, part of the fuel is dividedly injected into the compression step in which the vaporization and atomization of the fuel is not promoted. The temperature rise of the gas is ensured. Then, at a low load when the temperature of the exhaust gas needs to be raised to a considerable extent, the fuel is injected at a later time, so that the vaporization and atomization of the fuel does not progress further, and the degree of the increase of the unburned components, The degree of temperature rise of the exhaust gas is further increased, and the sulfur release treatment that is well suited to the situation is realized.

In this case, it goes without saying that, for example, the fuel may be further divided and injected in a plurality of times in the compression step.

Next, according to a fourth aspect of the present invention, in the first aspect of the present invention, the target value of the exhaust gas temperature for releasing the sulfur component by the sulfur component releasing means is set. Target exhaust gas temperature setting means is provided, and the sulfur component releasing means sets at least one of the fuel split ratio, the injection timing, and the ignition timing such that the exhaust gas temperature becomes the target temperature set by the setting means. It is characterized by correction.

As described above, the later the fuel injection timing in the compression step, the more unburned components increase, and the higher the exhaust gas temperature. Similarly, even if the late injection amount (the injection amount in the compression step) is increased by the split injection of fuel, the unburned component increases accordingly, and the exhaust gas temperature further rises. Further, even if the ignition timing is delayed, the unburned components increase accordingly, and the exhaust gas temperature further rises. That is, the exhaust gas temperature can be controlled by adjusting the fuel split ratio, the fuel injection timing, and the ignition timing.

Therefore, according to the present invention, the exhaust gas temperature is reliably and appropriately controlled to the target temperature by correcting at least one of the fuel split ratio, the fuel injection timing, and the ignition timing. This makes it possible to realize a sulfur release process with no waste and suppressed defects.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the target exhaust gas temperature setting means is configured to output the target exhaust gas temperature when the sulfur component release means starts to release the sulfur component. Is set high.

According to the present invention, the temperature of the exhaust gas rises quickly, reaches the target temperature quickly, and the sulfur release substantially starts at an early stage.

According to a sixth aspect of the present invention, there is provided the fuel cut-off device according to any one of the first to fifth aspects, wherein the fuel cut is inhibited while the sulfur component is being released by the sulfur component release means. Prohibition means is provided.

According to the present invention, once the sulfur release process is started, the sulfur release process using the fuel injection control is stably continued. Hereinafter, the present invention will be described in more detail through embodiments of the present invention.

[0026]

FIG. 1 shows a control system of a direct injection stratified charge combustion engine. A plurality of combustion chambers 4 defined by pistons 3 are provided in a main body 2 of the engine 1 and the combustion is performed. A spark plug 5 is disposed in the upper center of the chamber 4, and an injector 6 for directly injecting fuel into the combustion chamber 4 is provided on a side portion.

The engine 1 is provided with an intake passage 9 and an exhaust passage 10 which communicate with the combustion chamber 4 via an intake valve 7 and an exhaust valve 8, respectively. Air cleaner 11, air flow sensor 1
2, a throttle valve 13 and a surge tank 14 are provided.

The downstream side of the surge tank 14 is an independent intake passage 9a branched for each cylinder, and the downstream end of each independent intake passage 9a facing the combustion chamber 4 is connected to the first passage 9b. And a second passage 9c.
When the swirl generation valve 15 provided at the position c is closed, swirl is generated in the combustion chamber 4 by the intake air introduced into the combustion chamber 4 from the first passage 9b.

On the other hand, the stoichiometric air-fuel ratio (λ
= 1) A three-way catalyst device 16 for simultaneously removing CO, HC and NOx in the exhaust gas in the vicinity is arranged,
Downstream of the three-way catalyst device 16, a NOx catalyst device 17 for removing NOx in exhaust gas is arranged. This NOx catalyst device 17 absorbs NOx that flows in without being purified by the three-way catalyst device 16 during operation in an air-fuel ratio lean state (λ> 1), suppresses exhaust to the outside, and suppresses air exhaust. When the fuel ratio becomes close to the stoichiometric air-fuel ratio or in a rich state (λ ≦ 1), the absorbed NOx is released and a large amount of C present in the exhaust gas in the rich state
It also suppresses NOx emission to the outside by reacting with O and HC. A NOx absorbent containing barium as a main component and containing potassium, magnesium, strontium, lanthanum and the like is provided.

Further, between a predetermined position on the exhaust passage 10 on the upstream side of the three-way catalyst device 16 and a predetermined position on the intake passage 9 on the upstream side of the surge tank 14, the exhaust gas flowing through the exhaust passage 10 is disposed. An exhaust gas recirculation passage 18 that recirculates a part of the exhaust gas to the intake passage 9 is provided, and an exhaust gas recirculation control valve 19 that adjusts the amount of exhaust gas recirculated is installed in the vicinity of the junction of the passage 18 with the intake passage 9. ing.

Further, the engine 1 is provided with a control unit (hereinafter referred to as “ECU”) 20. The ECU 20 receives a signal indicating the amount of intake air from the air flow sensor 12, an opening degree of the throttle valve 13. , A signal from a recirculation amount sensor 22 for detecting the opening of the exhaust gas recirculation control valve 19, a signal from a boost sensor 23 for detecting a negative pressure of intake air in the surge tank 14, an injector A signal from a fuel pressure sensor 24 that detects the pressure of the fuel supplied to the engine 6, a signal from a water temperature sensor 25 that detects the temperature of the cooling water in the engine body 2, the 1O ₂ sensor the air-fuel ratio of the mixture supplied to the combustion chamber 4 from the remaining oxygen concentration is detected whether rich or lean of the stoichiometric air-fuel ratio Signal from the 26, the temperature of the exhaust gas, and more particularly signals from the exhaust temperature sensor 27 for detecting the exhaust gas temperature immediately before flowing into the NOx catalyst device 17,
For example, a signal from the _second O ₂ sensor 28 for detecting the sulfur poisoning state of the NOx catalyst device 17 at a predetermined time, a signal from an engine rotation sensor 29 for detecting the number of revolutions of the engine 1, A signal from an accelerator opening sensor 30 for detecting the amount of depression of an accelerator pedal by an operation, a signal from an intake air temperature sensor 31 for detecting intake air temperature, a signal from an atmospheric pressure sensor 32 for detecting atmospheric pressure, and the like are input. It has become.

The ECU 20 operates the actuator 33 for driving the throttle valve 13, the exhaust gas recirculation control valve 19, the injector 6, and the actuator for driving the swirl generating valve 15 in accordance with the operating state of the engine 1 indicated by these signals. Control signals to the ignition circuit 34 and the ignition circuit 35 for igniting the ignition plug 5 to control the opening of the throttle valve 13, control the recirculation of exhaust gas, control the fuel injection amount and injection timing, control swirl generation, And control of the ignition timing and the like. In particular, as part of these controls, the NOx catalyst device 1
The NOx purification control and the sulfur poisoning elimination control of the catalyst device 17 are performed. Hereinafter, these N
The Ox purification control and the sulfur poisoning elimination control will be described.

First, the NOx purification control will be outlined. FIG.
Is a target air-fuel ratio map of the engine 1. As shown in the figure, in this map, the engine operating region using the engine speed and the engine load as parameters is a first region A of low-medium-speed low-medium load and a second region A of high-speed high load Region B, a third region C provided between these regions A and B, and a low load region that is equal to or higher than a predetermined engine speed, and fuel injection into the combustion chamber 4 is stopped. And a fuel cut region D.

The first region A where the operation frequency is the highest is a lean operation region where the air-fuel ratio (A / F) is increased. During the lean operation in the lean operation region A, the fuel is injected during the compression stroke (late injection), and the fuel is unevenly distributed near the ignition plug 5 to perform stratified combustion. During this lean operation,
While the amount of emission of CO and HC in the exhaust gas is reduced, the concentration of oxygen and the concentration of NOx are increased. However, NOx is NO
Since it is absorbed by the x-catalyst device 17, both the fuel economy performance and the exhaust performance are improved.

The second region B, which is an operation region at the time of high-speed operation or acceleration, is a rich operation region in which the air-fuel ratio is reduced. During the rich operation in the rich operation region B, fuel is injected during the intake stroke (first injection), and the fuel is sufficiently vaporized and atomized in the combustion chamber 4. During this rich operation, the amount of CO and HC emissions in the exhaust gas increases, while the oxygen concentration and NOx concentration decrease. However, since the NOx stored in the NOx catalyst device 17 and the CO and HC undergo an oxidation-reduction reaction, a good torque is obtained and the exhaust performance is improved.

Further, the third region C is a stoichiometric air-fuel ratio operation region (λ1 operation region) in which the air-fuel ratio is set to the stoichiometric air-fuel ratio (A / F = 14.7). During the stoichiometric air-fuel ratio operation in the stoichiometric air-fuel ratio operation region C, similar to the above-described rich operation,
The fuel is injected during the intake stroke (the injection), and the fuel is sufficiently vaporized and atomized in the combustion chamber 4. During this stoichiometric air-fuel ratio operation, CO, HC and NOx in the exhaust gas are reduced by the three-way catalytic converter 16.
Purified at the same time.

As shown in the time chart of FIG. 3, as the lean operation continues, the amount of NOx absorbed by the NOx catalyst device 17 increases. If this is left as it is, it will eventually become saturated and the catalytic function of the NOx catalyst device 17 will decrease. Therefore, in order to release the absorbed NOx, at a predetermined period shown by the symbol a in the figure, only for a predetermined time shown by the symbol a. , The air-fuel ratio is the stoichiometric air-fuel ratio (λ = 1). Obviously, during the predetermined period a, the NOx catalyst device 17
The period is set to be shorter than x saturation. Thus, the NOx storage capacity of the NOx catalyst device 17 is restored, and the NOx can be stably absorbed again.

NOx absorbed by the NOx catalytic device 17
Is periodically and intentionally released in this manner, and in response to the driving operation of the driver, for example, as shown by reference numeral c in the figure, the operation region is switched from the lean operation region A to the rich operation region B. When the engine is switched, or when the engine is switched to the stoichiometric air-fuel ratio operation region C, the fuel is released from the catalyst device 17 and
The NOx storage capacity of the NOx catalyst device 17 is restored.

Next, NOx constituting a characteristic part of the present invention will be described.
The sulfur poisoning elimination control of the catalyst device 17 will be described with reference to the flowchart of FIG. However, the flowchart shown in FIG. 4 shows one example of the specific operation of the sulfur poisoning elimination control, and also shows the operation mainly when the lean operation is continued. The time chart shown in FIG. 5 also shows an example of the operation of the NOx purification control and the sulfur poisoning elimination control at one time during traveling. In particular, the ratio between the NOx absorption amount and the sulfur adhesion amount is accurately determined. It is not intended to show, but to show an example of the directionality that increases and decreases.

First, the basic flow of this control will be described. This sulfur poisoning elimination control is repeatedly executed while the ignition switch is on. The sulfur poisoning elimination control is executed in a cycle irrelevant to each control of the fuel injection amount, the fuel injection timing, and the ignition timing. Then, the amount Sa of the sulfur component adhering to the NOx catalyst device 17, more specifically, the NOx absorbent of the catalyst device 17 with the supply of the fuel is estimated (step S).
3).

Then, the sulfur adhesion amount Sa is equal to the predetermined amount S.
01 or more (positive determination in step S5), and
When a predetermined sulfur release execution permission condition is satisfied (Yes in step S9), a sulfur release process is performed (step S10). This sulfur release process is performed by raising the exhaust gas temperature Tmp by split injection of fuel or retarding the ignition timing, and thereby raising the temperature of the NOx catalyst device 17 to a temperature at which sulfur can be released.

Then, by this sulfur release treatment, N
By estimating the amount of the sulfur component released from the Ox absorbent, the residual amount Sr of the sulfur component in the NOx absorbent is determined.
Is estimated (step S11). As a result, when the sulfur remaining amount Sr in the NOx absorbent becomes zero (positive determination in step S12), the flag F and the timers are reset, and the current sulfur release processing is ended (step S17).

The above is the case where the sulfur release execution permission condition is continuously satisfied and the sulfur release processing is performed satisfactorily until the sulfur remaining amount Sr becomes zero. In contrast,
Even if the execution permission condition is not satisfied by the driving operation of the driver, and as a result, the sulfur adhering amount Sa of the NOx catalyst device 17 becomes equal to or more than the predetermined amount S01 and it is necessary to remove the sulfur, the sulfur release processing is substantially performed. (Step S9: negative determination) or a situation in which the sulfur release process once started must be interrupted halfway (negative determination in Step S13). In such a case, a different measure is taken than when the sulfur release processing has been completed successfully (steps S18 to S20). Hereinafter, the steps will be sequentially described.

First, in step S1, the sulfur poisoning time T
Measure s. The sulfur poisoning time Ts is such that sulfur is N
This is the elapsed time from the start of adhering to the Ox catalyst device 17. This sulfur poisoning time Ts is reset in step S17 only when the sulfur release processing has been completed successfully. However, when a negative determination is made in step S9 and the sulfur release processing cannot be started, or in steps S13 and S13, When a negative determination is made in S16 and the sulfur release process is forcibly interrupted on the way, the measurement is not reset but continued.

Next, in step S2, the continuous continuation time Tln of the lean operation is measured. This lean duration Tln
Is specifically performed according to the flowchart of FIG. 5, and it is determined in step S31 whether or not the vehicle is in the lean operation.
In the case of the lean operation, the lean time Tl is determined in step S32.
n is measured. On the other hand, if it is not the lean operation, the lean time Tln is reset in step S33. However, the lean time T measured in step S32 so far is
The last value of ln is stored in the memory. This allows
Each time the lean operation is periodically interrupted by the NOx purification control or randomly interrupted according to the driver's operation, the continuous continuation time Tln of the lean operation that has been performed remains in the memory.

Returning to the main flow, next, at step S3
Then, the sulfur poisoning state of the NOx catalyst device 17, that is, the sulfur deposition amount Sa is estimated. Specifically, the estimation of the sulfur deposition amount Sa is performed according to the flowchart of FIG. 6, and in step S41, the data from each sensor shown in FIG. To the amount of fuel injected from the injector 6 (fuel supply amount) Tp until the estimated amount of sulfur Sa is estimated this time.
Is calculated.

Next, in step S42, based on the fuel supply amount Tp, the sulfur adhesion amount (that is, the unit of sulfur increase) between the time when the sulfur adhesion amount Sa was estimated last time and the time when the sulfur adhesion amount Sa was estimated this time is estimated. A basic value Sv of the instantaneous amount of sulfur adhering to the NOx catalyst device 17 per hour is set. Here, as shown in FIG. 7, the basic sulfur increase Sv is the supply amount T of the fuel which is the sulfur generation source.
It is approximately proportional to p.

Next, in steps S43 to S45, correction coefficients K1, K2, K3 for the basic sulfur increase Sv are set.
Are set respectively. That is, in step S43, the first correction coefficient K1 is determined based on the exhaust gas temperature Tmp detected by the exhaust gas temperature sensor 27. In step S44, the second correction coefficient K2 is determined based on the lean operation continuation time Tln measured in step S2. In step S45, the previous value of the amount of sulfur attached (the amount of sulfur already attached) Sa [i-1]
The third correction coefficient K3 is set based on

Here, as shown in FIG. 8, the first correction coefficient K1 is set to a small value whether it becomes higher or lower than a predetermined exhaust gas temperature Tmp 'as a peak.
Further, as shown in FIG. 9, the second correction coefficient K2 is set to a small value regardless of whether it is longer or shorter than the predetermined lean operation continuation time Tln '. Also,
As shown in FIG. 10, the third correction coefficient K3 is set to a small value when it exceeds a predetermined sulfur poisoning amount Sa '.

In particular, the reason why the second correction coefficient K2 has the above characteristics is as follows. That is,
When the lean operation time Tln is long, as schematically shown in FIG.
A large amount of NOx or sulfur (S) has already adhered to barium (Ba) which is a main component of the x-absorbing material. Therefore, it becomes difficult for sulfur to newly adhere to barium, and the amount of sulfur adhered per unit time decreases.

When the lean operation time Tln is short, the contact time between sulfur and barium is short, as schematically shown in FIG. 12, so that a strong bond is formed between the sulfur and barium. Then, when switching to the stoichiometric air-fuel ratio operation or rich operation, the sulfur becomes NO
As in the case of x, it is easily released, and the amount of sulfur attached per unit time also decreases.

That is, even if the accumulated amount of sulfur Sa increases with the passage of time, for example, even if the same 5-minute lean operation is performed, compared to the case where the 1-minute lean operation is performed five times, The accumulated total amount of sulfur deposition increases when the lean operation for 5 minutes (corresponding to the predetermined lean operation continuation time Tln ′ shown in FIG. 9) is performed once. Further, for example, even in the same 20-minute lean operation, the lean operation for 5 minutes (similarly, the predetermined lean operation continuation time Tln ′ shown in FIG. 9) is compared with the case where the lean operation for 20 minutes is performed once. (Equivalent to) is performed four times, the accumulated total amount of the attached sulfur is similarly increased.

Therefore, it is advantageous to make the continuous lean operation time shorter or longer than the predetermined time Tln 'from the viewpoint of making it difficult for the sulfur component to adhere to the NOx absorbent. In the purification control, the period (A) in which the air-fuel ratio is periodically set to the stoichiometric air-fuel ratio for NOx release is, for example, the predetermined time Tln ′.
It is set shorter.

By correcting the basic sulfur increase Sv with the second correction coefficient K2 having such characteristics, it is possible to estimate the sulfur adhesion Sa with higher accuracy.

Next, in step S46, according to equation 1,
The first to third correction coefficients K1,
By multiplying K2 and K3, the corrected sulfur increase S
Calculate v '.

[0056]

(Equation 1)

Then, in step S47, the current estimated sulfur adhesion amount Sa is calculated by adding the corrected sulfur increase amount Sv 'to the previously estimated sulfur adhesion amount Sa [i-1] according to Equation 2. .

[0058]

(Equation 2)

The sulfur poisoning, that is, the adhesion of the sulfur component to the NOx absorbent is caused by the NO
It starts preferentially from the upstream part of the x catalyst device 17. That is, the sulfur component does not uniformly adhere to the catalyst device 17, and the sulfur component adheres unevenly along the passage of the exhaust gas.
Therefore, when estimating the sulfur deposition amount Sa, the catalyst device 17 is generally considered to be divided into n blocks along the passage of the exhaust gas, and the sulfur deposition amount Sa is determined for each block.
[J] (j = 1 to the number of divisions n) is estimated, and the sum (S
a [1] +... + Sa [n]) can be used as the sulfur attachment amount Sa of the entire catalyst device 17. Obviously, the sulfur deposition amount Sa [j] of the upstream block is estimated to be larger than that of the downstream block.

Alternatively, the average value of the sulfur adhesion amount Sa [j] estimated for each block ((Sa [1] +... + Sa
[N]) / n) may be handled as a value representative of the sulfur adhesion amount Sa of the catalyst device 17.

Such a concept will be described later in more detail in step S11.

Returning to the main flow, next, at step S4
It is determined whether the flag F is set to 1 or not.
If the flag F has not been set to 1, step S5
Then, it is determined whether or not the sulfur poisoning amount Sa estimated in step S3 is equal to or greater than a predetermined reference amount S01. When the sulfur poisoning amount Sa is equal to or greater than the reference amount S01, the flag F is determined in step S6.
Is set to 1 and steps S7 and subsequent steps are executed. On the other hand, if the flag F has already been set to 1 in step S4, the sulfur poisoning amount Sa becomes equal to the determination reference amount S01.
Step S7 and subsequent steps are immediately executed without determining whether or not this is the case. Also, in step S5, the sulfur adhesion amount S
If a is smaller than the determination reference amount S01, the process returns to step S2.

Here, the determination reference amount S01 is set to, for example, the amount of sulfur attached when the NOx purification efficiency of the catalyst device 17 decreases to 80%. That is, the flag F is a sulfur removal request flag that indicates whether or not the sulfur component is attached to the catalyst device 17 in such an amount that the NOx purification efficiency of the catalyst device 17 decreases so as to affect the NOx emission. is there.

In step S7, a first target temperature T1 which is a standard target value of the exhaust gas temperature Tmp at the time of executing the sulfur release processing for the NOx catalyst device 17 is set. The first target temperature T1 is set based on the sulfur poisoning time Ts measured in step S1. In this case, as shown in FIG. 13, the first target temperature T1 is set to a temperature between 650 ° C. and 700 ° C., and when the sulfur poisoning time Ts is long, the first target temperature T1 is set to a higher temperature than when it is short. Is set. Also,
The first target temperature T1 may be further corrected based on the sulfur amount Sa estimated in step S3. Also in this case, according to FIG. 13, the first target temperature T1 is corrected to a higher temperature when the sulfur deposition amount Sa is larger than when it is small.

As described above, the sulfur poisoning time Ts is determined when the negative determination is made in step S9 and the sulfur release process cannot be started, or when the negative determination is made in steps S13 and S16 and the sulfur release time Ts is determined. If the processing is forcibly interrupted on the way, the measurement is continued without being reset. In such a case, step S
9 and the step S13, the affirmative determination is continued, and the sulfur poisoning elapsed time Ts which is longer than that when the sulfur release processing is completed in the step S17 is set to a higher first target temperature T1. This makes it possible to efficiently and quickly release and remove sulfur components adhering over a long period of time.

Next, in step S8, the final value T0 of the exhaust gas temperature Tmp at the time of executing the sulfur release processing is selected. That is, the first target temperature T1 set in step S7
And the second target temperature T set in step S19 described later.
2, and the higher one is finally selected as the target exhaust gas temperature T0.

Here, step S19 is performed when the sulfur release execution permission condition is not satisfied, so that the sulfur release process cannot be substantially started (when a negative determination is made in step S9), or when the sulfur release process is started. This routine is executed when the release process is forcibly terminated halfway (when a negative determination is made in step S13). Therefore, when the sulfur release processing has been performed to the end (when a positive determination is made in step S12), the second target temperature T2 is not set, and in step S8, the first target temperature set in step S7 is set. Target temperature T
1 is unconditionally selected as the final target exhaust gas temperature T0.

In the sulfur release process in step S10, the final target exhaust gas temperature T0 is realized so as to achieve the final target exhaust gas temperature T0.
Fuel split injection and ignition timing retard are performed, and as a result, sulfur components adhering to the NOx catalyst device 17 are removed. In this case, a temperature higher than the final target exhaust gas temperature T0 by a predetermined temperature may be set as the target temperature for a certain period at the start of the sulfur release processing in step S10. As a result, the rise of the exhaust gas temperature Tmp is promoted, and the sulfur component starts to be removed immediately after the start of the release process. The dashed line shown in FIG.
In the case where 1 is directly selected as the final target exhaust gas temperature T0, a target temperature higher than the final target exhaust gas temperature T0 set only during a certain period at the start of the sulfur release process is illustrated.

Next, in step S9, it is determined whether or not the sulfur release execution permission condition is satisfied. That is, it is determined whether or not the vehicle speed V is equal to or higher than the predetermined vehicle speed V01 at which there is no problem even if the sulfur release processing is executed.

The reason why the sulfur release execution permission condition is set by the vehicle speed is that the exhaust gas temperature Tmp is set to the temperature at which sulfur can be released even when split injection or ignition timing retard is performed for sulfur release processing at low vehicle speed. A certain target temperature T0 (for example, in this embodiment, T0 ≧ 6
(50 ° C) and efficient sulfur release processing cannot be realized, and engine output becomes excessively unstable if split injection or ignition timing retard is performed for sulfur release processing at low vehicle speed. by. However, the sulfur release execution permission condition is not limited to this, and in general, other conditions are set in order to eliminate a situation in which the execution of the sulfur release process involves some trouble or the accompanying trouble becomes relatively large. You may set using a parameter.

When it is determined that the vehicle speed V is equal to or higher than the predetermined vehicle speed V01, the process proceeds to step S10 to execute a sulfur release process. When it is determined that the vehicle speed V is not equal to or higher than the predetermined vehicle speed V01, a sulfur release process is executed. Step S without
Proceed to 18.

FIG. 14 shows the sulfur release process in step S10.
Are performed according to the flowchart shown in FIG. First, in step S51, the currently used normal air-fuel ratio map shown in FIG. 2 is switched to the air-fuel ratio target air-fuel ratio map shown in FIG. Here, in the target air-fuel ratio map at the time of the sulfur release processing, the entire operation region is the stoichiometric air-fuel ratio region C. That is, the current lean operation is prohibited and the stoichiometric air-fuel ratio operation (λ
1 operation) and prohibits fuel cut (F / C). By performing the stoichiometric air-fuel ratio operation, an environment in which the CO concentration in the exhaust gas is increased and the sulfur component attached to the NOx absorbent is easily released is generated. Further, by prohibiting the fuel cut, the fuel is always supplied, and the sulfur release process using the fuel injection control is stably performed.

Then, in a step S52, it is determined whether or not it is a divided injection region. That is, it is determined whether or not the current operating state of the engine 1 is within the operating range in which the temperature of the exhaust gas for releasing sulfur is increased by split fuel injection. Here, the divided injection region is set to the middle rotation middle load region (all hatched portions) in the map at the time of the sulfur release processing in FIG.

If it is the divided injection area, step S5
3. In S54, the late injection amount and the late injection timing of the fuel are set. Here, the late injection refers to injecting the fuel during the compression stroke, as in the normal map in FIG. 2, and the vaporization and atomization of the fuel does not progress as compared with the early injection in which the fuel is injected during the intake stroke. , Unburned components increase.

In step S53, the late injection amount Tpt is set by adding the late injection amount coefficients K4 and K5 (all values less than 1) to the total fuel injection amount Tp separately determined from the intake air amount and the like according to Equation 3. This is performed by multiplication.

[0076]

(Equation 3)

Here, the first correction coefficient K4 as the fourth correction coefficient is the target exhaust gas temperature T0 (including the case where the target exhaust gas temperature T0 is raised by a predetermined temperature during a certain period at the start of the sulfur release processing. ), And is set to a larger value as the target temperature T0 is higher, as shown in FIG. The second correction coefficient K5, which is the fifth correction coefficient, is determined based on the actual exhaust gas temperature Tmp.
As shown in (2), the lower the actual exhaust gas temperature Tmp is, the larger the value is set. Therefore, the higher the target exhaust gas temperature T0 and the lower the actual exhaust gas temperature Tmp, the larger the late injection amount Tpt. As a result, the unburned component of the fuel further increases, and the temperature of the NOx absorbent in the NOx catalyst device 17 is further increased.

On the other hand, in step S54, the late injection timing is set to be later as the engine load is lower. Therefore, at low load, the actual exhaust gas temperature Tmp
Is lower, the late injection timing is later, the vaporization and atomization of the fuel is not further advanced, the unburned component is further increased, and the temperature of the NOx absorbent in the NOx catalyst device 17 is further raised.

The late injection amount Tp set in this way
The t and the late injection timing are output as control signals to the injector 6, and are used for controlling the fuel injection amount and the injection timing for the engine 1.

Then, in a step S55, it is determined whether or not it is in the retard control area. That is, it is determined whether or not the current operating range of the engine 1 is within the operating range in which the temperature of the exhaust gas for releasing sulfur is increased by retarding the ignition timing. Here, the retard control area corresponds to FIG.
In the map at the time of the sulfur release processing of No. 5, it is set so as to overlap with the low-load-side area (the densely shaded area below the line X) in the divided injection areas. That is, in this retard control region, both the fuel split injection and the ignition timing retard are performed.

If it is in the retard control area, the retard amount is set in step S56. In particular, in step S56, the retard amount is feedback-controlled so that the actual exhaust gas temperature Tmp converges to the target temperature T0.

The setting of the retard amount in step S56 and the feedback control thereof are performed according to the flowchart shown in FIG. First, in step S61, the actual exhaust gas temperature Tmp detected by the exhaust gas temperature sensor 27 is read, and then, in step S62, it is determined whether or not the execution of retard control has started.

Then, the process proceeds to step 63 only once at the beginning of the retard control, and it is determined whether or not the actual exhaust gas temperature Tmp is equal to or higher than the target temperature T0. As a result, when the actual exhaust gas temperature Tmp is equal to or higher than the target temperature T0, a preset high-temperature retard amount is set as the basic retard amount in step S64. When the actual exhaust gas temperature Tmp is not equal to or higher than the target temperature T0, the basic retard amount is set in step S65. As the amount, a preset low-temperature retard amount is set.

Here, the low-temperature retard amount is set to a larger retard amount than the high-temperature retard amount.
As a result, when the exhaust gas temperature Tmp is low, a larger temperature rise is achieved than when the exhaust gas temperature Tmp is high.

On the other hand, when the retard control is not started,
That is, when the retard control has already been started, the process directly proceeds to step S66, and it is determined whether or not the actual exhaust gas temperature Tmp is equal to or higher than the target temperature T0. As a result, when the actual exhaust gas temperature Tmp is equal to or higher than the target temperature T0, in step S68, the actual exhaust gas temperature Tmp is higher than the target temperature T0 by the hysteresis increment ΔT0 (T0 + ΔT
0) It is determined whether or not it is not less than. If so, in step S69, the retard amount is reduced by a predetermined amount.

On the other hand, if not so in step S68,
That is, the actual exhaust gas temperature Tmp is equal to or higher than the target temperature T0 and is higher than the target temperature T0 by the hysteresis increment ΔT0 (T0 + Δ
When it is less than T0), the retard amount is maintained as it is.

Further, when it is determined in step S66 that the actual exhaust gas temperature Tmp is not higher than the target temperature T0,
In step S67, the retard amount is increased by a predetermined amount.

The ignition timing retard amount thus set is output as a control signal to the ignition circuit 35 of the ignition plug 5 and used for controlling the ignition timing for the engine 1.

As described above, as is clear from the flowchart of the sulfur release process of FIG. 14 and the air-fuel ratio map at the time of the sulfur release process of FIG. 15, the operating state of the engine 1 is shifted to the high load side in the middle rotation and middle load region. In some cases (in the case of a positive determination in step S52 and a negative determination in step S55), only split injection is performed to increase the temperature of the exhaust gas. Further, when the operating state of the engine 1 is on the low load side in the middle rotation middle load region (in the case of a positive determination in step S52 and a positive determination in step S55),
Split injection and ignition timing retard are performed together.

However, when the operating state of the engine 1 is not originally in the middle rotation and middle load region (in the case of a negative determination in step S52), neither the split injection nor the ignition timing retard is performed. That is, at low rotation and low load and at high rotation and high load, the temperature of the exhaust gas is not substantially increased.

This is because the exhaust gas temperature Tmp is originally low in the low-speed low-load region, and the exhaust gas temperature may not rise to the target temperature T0 at which the sulfur release processing can be executed even if the exhaust gas temperature is raised. Is performed, there is a possibility that the output state of the engine 1 becomes unstable. Therefore, the purpose is to avoid such waste.

On the other hand, in the high-rotation, high-load region, the exhaust gas temperature Tmp is originally high, and there is a possibility that sulfur is released even if the exhaust gas is not heated. As a result, the NOx catalyst device 17 may be damaged due to an excessively high temperature, and the purpose is to avoid such waste.

By taking such measures, problems such as deterioration of fuel efficiency and decrease in torque, which are caused by the rise of exhaust gas temperature using split injection or retard, are also suppressed to the minimum necessary. .

Further, even when the operating state of the engine 1 is in the middle rotation and middle load range and the exhaust gas temperature is raised,
Basically, the temperature of the exhaust gas is increased by split injection, and only when the exhaust gas temperature is relatively low and the low load needs to be increased to a greater extent, the retard is also performed.
The problem of a decrease in torque due to the retard is also minimized.

Returning to the main flow, step S
At 11, the residual amount of sulfur remaining in the NOx absorbent Sr
Is estimated. The estimation of the remaining sulfur amount Sr is performed according to the flowchart of FIG.
In step 1, it is determined whether the exhaust gas temperature Tmp is equal to or higher than 650 ° C. As a result, when the exhaust gas temperature Tmp is lower than 650 ° C, the sulfur release processing time Tr is reset in step S72. Measures the sulfur release processing time Tr in step S73.

That is, as in the case where the first target temperature T1 is set in FIG. 13 in the step S7, the exhaust gas temperature Tmp and, consequently, the temperature of the NOx catalyst 17 are at least 65.
Since the sulfur component can be released when the temperature is 0 ° C. or higher, 650 ° C. is set as the lowest temperature at which the sulfur component can be released. Of course, the temperature at which the sulfur component can be released can be set to various values depending on other environmental conditions such as the air-fuel ratio of the exhaust gas flowing into the NOx catalyst device 17, for example.

Next, in step S74 and thereafter, the sulfur release amount is estimated based on the sulfur release processing time Tr and the exhaust gas temperature Tmp detected by the exhaust gas temperature sensor 27, and the sulfur residual amount Sr is calculated from the sulfur release amount. Is estimated.

First, an outline of the operation of estimating the residual sulfur amount Sr performed in step S74 and subsequent steps will be described. Step S
As described in the estimation operation of the sulfur deposition amount Sa of No. 3, the exhaust gas flows from the upstream portion of the NOx catalyst device 17 first as shown in FIG. Therefore, the above step S10
Also in the sulfur release process performed in the above, the exhaust gas heated to the temperature at which sulfur can be released flows first from the upstream portion of the NOx absorbent, and the upstream portion is heated first, and the release of sulfur is increased by the upstream. Starts preferentially in parts. That is, the catalyst device 17 does not uniformly release and remove the sulfur component, and the sulfur component is unevenly removed along the passage of the exhaust gas and remains unbalanced.

Therefore, the sulfur release amount or residual amount Sr
In estimating, the catalyst device 17 is generally considered to be divided into n blocks (hatched portions) along the passage of the exhaust gas as shown in FIG. [J] (j = 1 to the number of divisions n) is estimated, and the sum (Sr [1] +... + Sr [n]) is used as the sulfur residual amount Sr of the entire catalyst device 17. This makes it possible to accurately estimate the sulfur release amount or the sulfur remaining amount. Obviously, the sulfur remaining amount Sr [j] in the left upstream block in FIG. 20 is estimated to be smaller than that in the downstream block.

Note that, instead of the total (Sr [1] +... + Sr [n]) of the sulfur residual amounts Sr [j] estimated for each block, the sulfur residual amounts Sr estimated for each block are used.
Average value of [j] ((Sr [1] + ... + Sr [n]) /
n) may be handled as a value representing the sulfur remaining amount Sr of the catalyst device 17.

In this embodiment, as an example,
As shown in FIG. 20, the NOx catalyst device 17 is divided into ten blocks (j = 1 to 10). In step S74, the sulfur release processing time Tr and the exhaust gas temperature T
Based on the mp, a region (completely removed region) S in which the sulfur component is completely released and removed in the volume of the total NOx absorbent.
The ratio (%) of A, in other words, the number of blocks is set from a characteristic map as shown in FIG. As shown in FIG. 21, the complete removal area SA increases as the release processing time Tr increases and as the exhaust gas temperature Tmp increases. That is, the number of blocks belonging to the complete removal area SA increases.

The map of FIG. 21 shows, for example, the exhaust gas temperature T
When mp is 700 ° C., the sulfur release treatment time Tr is t
When the exhaust gas temperature Tmp reaches 650,
° C, when the longer t2 is reached, 10
This indicates that sulfur is released from all the blocks, and the complete removal area SA becomes 100%.

In the next step S75, NO is determined based on the sulfur release processing time Tr and the exhaust gas temperature Tmp.
x Ratio (%) (number of blocks) of the SB in which the sulfur component was partially released and removed in the absorber (partially removed region)
Is set from a characteristic map as shown in FIG. As shown in FIG. 22, the partial removal area SB becomes smaller at least as the release processing time Tr becomes longer, and when the complete removal area SA becomes 100% (t1 or t2).
Disappears.

The ratio (%) (the number of blocks) of the unremoved area SC from which the sulfur component has not been removed at all is calculated by adding the ratio of the above-described complete removal area SA and the partial removal area SB to the total. It is obtained by subtracting from the volume of the NOx absorbent.

In the next step S76, the sulfur removal rate α (%) in the partial removal area SB is similarly determined based on the sulfur release processing time Tr and the exhaust gas temperature Tmp in FIG.
It is set from the characteristic map as shown in (1). As shown in FIG. 23, the sulfur removal rate α in the partial removal area SB
(%) Indicates the release processing time T in this embodiment.
Irrespective of r, it is set to increase as the exhaust gas temperature Tmp increases.

The sulfur remaining rate β (%) in the partial removal area SB is (100−α)%, the sulfur removal rate in the complete removal area SA is 100% (the sulfur remaining rate is 0%), The sulfur removal rate in the unremoved area SC is 0% (the sulfur remaining rate is 100%).

In the next step S77, the remaining sulfur amount S of the entire NOx absorbent is finally determined from the data obtained above.
Calculate r. For that purpose, for example, each area SA, S
The amount of the sulfur component released for each of B and SC is estimated, the sum thereof is obtained, and the value is subtracted from the sulfur adhesion amount Sa estimated in step S3. Alternatively, each area S
The amount of the sulfur component released for each of A, SB, and SC is estimated, and the value is set as the amount of the sulfur component attached to each of the regions SA, SB, and SC (for example, “Sa / j (number of blocks)”). ), And the sum thereof may be obtained.

Here, each sulfur remaining amount Sr [j] of the block (upstream block) belonging to the completely removed area SA is zero, and each sulfur remaining amount Sr of the block (downstream block) belonging to the unremoved area SC. [J] remains the respective sulfur adhesion amount (Sa / j) estimated in step S3,
Then, each sulfur remaining amount Sr [j] of the block belonging to the partial removal area SB (the block at the center) is ((Sa /
j) × (100−α)), the total sulfur remaining amount Sr of the entire NOx absorbent is obtained, for example, according to Equation 4.

[0109]

(Equation 4)

Note that “SB” and “SC” described in the formulas
Indicates the ratio (%) of the partially removed region and the unremoved region of the NOx absorbent, respectively. Then, "(j × SB / 100)" and "(j × SC
/ 100) ”indicates the number of blocks belonging to the partially removed area and the unremoved area, respectively.

The total sulfur release amount or the total sulfur residual amount Sr of the entire NOx absorbent determined here is the sulfur release amount or the sulfur residual amount released for each single sulfur release treatment, It is not the cumulative amount of released sulfur or residual sulfur released as a result of the release process.
Then, the sulfur release processing time Tr, which is a parameter for obtaining the release amount or the remaining amount, is determined in step S7.
At 1, S72, it is reset when the exhaust gas temperature Tmp does not become equal to or higher than the sulfur dischargeable temperature (650 ° C.).
It is not an accumulation of the time during which the sulfur release was made.

For example, even if sulfur release processing for one minute is performed five times, the adopted sulfur release processing time Tr is one minute for all the sulfur release processing.
From the map shown in FIG. 23, if the exhaust gas temperature Tmp is the same, the same percentage of the completely removed area SA, the same percentage of the same partially removed area SB, and the sulfur removal rate α in the same partially removed area SB are always read out. Therefore, as a result, the same sulfur release amount and the same sulfur residual amount are calculated, and the sulfur release amount or the sulfur residual amount is not updated. In other words, the sulfur release amount or the sulfur remaining amount calculated as a result of the sulfur release processing for each minute is not a cumulative sum.

Therefore, for example, even when the same sulfur release treatment is performed for 5 minutes, the sulfur release treatment for one minute is performed once compared with the case where the sulfur release treatment for one minute is performed five times. In the case of (1), the sulfur release amount increases and the sulfur remaining amount decreases.

Then, for example, after the sulfur release treatment for one minute is performed and then the sulfur release treatment for two minutes is performed, the value of the sulfur release amount or the residual amount becomes:
The two-minute sulfur release will be updated to a higher sulfur release or a smaller residual value calculated as a result.

That is, as described above, the sulfur release process is started preferentially from the upstream portion of the NOx absorbent into which the heated exhaust gas flows first, and the downstream portion of the NOx absorbent whose heating is delayed takes some time. If not, sulfur is not easily removed. In addition, since the temperature of the NOx absorbent decreases again after one sulfur release process is completed and the next sulfur release process is performed again, even in the second sulfur release process, The NOx absorbent starts to be heated from the upstream part. Therefore, at this time and in the same or shorter time as the previous time, when the second sulfur release processing is completed, no new sulfur is removed in the second sulfur release processing. It will end as it is. Therefore,
It can be said that the shorter the continuous sulfur release time Tr, the lower the overall sulfur removal rate, and the longer the continuous sulfur release time Tr, the higher the overall sulfur removal rate.

In general, during the rich operation and the stoichiometric air-fuel ratio operation, the exhaust gas temperature T is higher than during the lean operation.
mp increases, and the temperature at which sulfur can be released naturally (for example, 6
(50 ° C.) or higher. In other words, the same effect as that of sulfur release may be obtained during rich operation or stoichiometric air-fuel ratio operation without performing the sulfur release processing in step S10.

Therefore, for example, when rich operation or stoichiometric air-fuel ratio operation (λ ≦ 1) and the exhaust gas temperature is equal to or higher than the sulfur dischargeable temperature (Tmp ≧ 650 ° C.)
Estimates the amount of sulfur component released and removed using the same method as the method of estimating the amount of sulfur released or the amount of residual sulfur Sr in step S11 during the sulfur release processing,
It is preferable to correct the estimated amount of sulfur Sa by subtracting it from the amount of sulfur Sa estimated in step S3.

As a result, the accuracy of estimation of the amount Sa of deposited sulfur is further improved, and the sulfur release processing is started at an unnecessarily early time, or the sulfur release processing is continued unnecessarily for a long time. The problem that occurs when the amount of adhesion Sa is estimated is avoided.

Returning to the main flow, next, step S1
In step 2, it is determined whether or not the total sulfur remaining amount Sr obtained in step S11 is zero. That is, it is determined whether or not all the attached sulfur components have been removed and the NOx storage ability or catalytic function of the NOx absorption catalyst 17 has been completely restored.

Until the sulfur remaining amount Sr becomes zero, in step S13, while confirming that the vehicle speed V is equal to or higher than the second determination predetermined vehicle speed V02 as the second sulfur release execution permission condition, The sulfur release process in step S10 and the estimation of the remaining sulfur amount Sr in step S11 are repeated. Here, the second predetermined vehicle speed V02 is set to a vehicle speed lower than the first predetermined vehicle speed V01. As a result, a positive determination is made in step S9, and once the sulfur release process is started, it is difficult to cancel the sulfur release process even if the vehicle speed decreases to some extent, and it is difficult to minimize the decrease in exhaust gas temperature. Can be

Then, in step S12, the remaining sulfur amount S
When it is determined that r is zero, the routine proceeds to step S17, where the sulfur removal request flag F is reset to 0, and a sulfur poisoning time Ts indicating the elapsed time of sulfur deposition and an operation characteristic counter described later are set. Reset each one. After that, the process returns to step S1, and the sulfur poisoning time Ts is measured again from the beginning.

There are various patterns to reach step S17. The best pattern among them is that the first and second sulfur release permission conditions are set in step S6.
In the case where the flag F is set to 1, the condition is continuously satisfied from the beginning, and no negative determination is made in Steps S9 and S13, and the sulfur release process is performed satisfactorily from the beginning and ends. (Reference d in FIG. 3). In this pattern, the NOx catalyst device 17
Is suppressed to the lowest level. This first pattern corresponds to the case of a driver who tends to maintain a higher vehicle speed for a longer time while traveling, as is clear from the fact that a positive determination is always made in steps S9 and S13. The probability of doing is large.

The remaining steps S14 to S16 and steps S18 to S20 are treatments when passing through a path other than the above-mentioned first pattern.

That is, in step S13, the vehicle speed V
Is determined not to be equal to or higher than the second predetermined vehicle speed V02, that is, the vehicle is considerably decelerated during the execution of the sulfur release process,
Even if split injection or retard control is executed, the exhaust gas temperature Tm
When p does not rise to the target temperature T0 and efficient sulfur release processing cannot be continued, or when there is a possibility that the engine output becomes unstable, step S1 is executed.
Steps S4 and S15 are executed to cancel the fuel split injection for raising the exhaust gas temperature and the retard control of the ignition timing. Also, the normal air-fuel ratio shown in FIG. Switching to the map, the forced stoichiometric air-fuel ratio operation (λ1 operation) is released, and the fuel cut (F / C) is restored.

Then, at step S16, the remaining sulfur amount Sr is reduced to a predetermined sulfur release process termination permission determination amount S02.
It is determined whether or not: Here, the termination permission determination amount S02 is set to a relatively small value other than zero. As a result, when the remaining sulfur amount Sr is equal to or less than the end permission determination amount S02 (reference symbol e in FIG. 3),
Proceeding to step S17, the sulfur release process is performed harmoniously from the beginning, and is treated as if it had been completed. That is, the sulfur removal request flag F, the sulfur poisoning time Ts,
When the operation characteristic counter described later is reset, and the process returns to step S1, the sulfur poisoning time Ts is measured again from the beginning.

On the other hand, if it is determined in step S16 that the remaining sulfur amount Sr is not equal to or less than the sulfur release processing end permission determination amount S02, that is, if a large amount of the sulfur component still remains without being removed, the aforementioned step S9 is performed. As in the case where it is determined that the sulfur release execution permission condition is not satisfied, the process proceeds to step S18 and subsequent steps.

In step S18, the operation characteristic counter is counted up. That is, in step S9, the sulfur release execution permission condition is not satisfied by the driver's driving operation, and as a result, the sulfur deposition amount Sa on the NOx catalyst device 17 is determined.
Is greater than or equal to the predetermined amount S01 and the need to remove sulfur arises, even if the sulfur release process cannot be substantially started, or in step S13, the second sulfur release execution permission condition is the driver's driving The operation was not satisfied. As a result, once the sulfur release treatment was started, although many sulfur components still remained (Sr> S0
2) Count the number of times a situation has to be interrupted on the way.

Therefore, it can be said that the greater the count of the driving characteristic counter, the more the driver's driving operation tends to run for a longer time at a lower vehicle speed. In other words, it can be said that the sulfur release processing has an operating characteristic in which it is difficult to complete quickly and smoothly after the flag F is set to 1.

Next, in step S19, a second target temperature T2, which is a supplementary target value of the exhaust gas temperature Tmp at the time of executing the sulfur release processing, is set based on the count number of the operation characteristic counter. The second target temperature T2 is, for example, 700 to 750 ° C., as the count number is larger, that is, when the sulfur release process is difficult to complete quickly and satisfactorily.
Is set higher.

In step S8, the higher of the reinforcing second target temperature T2 and the standard first target temperature T1 set in step S7 is the final target exhaust gas temperature. As a result, since the sulfur release process which is difficult to be performed is once performed, the temperature of the exhaust gas or the catalyst device 17 is raised to a higher temperature, and the sulfur component is efficiently and promptly released and removed. This ensures that the sulfur release process is completed satisfactorily in a short time.

Finally, at step S20, NO
The NOx poisoning of the x catalyst device 17 is suppressed. That is, N
Since a considerable amount of sulfur component has adhered to the Ox catalyst device 17 (Sa ≧ S01 or Sr> S02), and the NOx storage capacity and catalyst function have been reduced, the lean operation is performed in such a state. Then, NOx contained in a large amount in the exhaust gas is released into the atmosphere without being absorbed by the catalyst device 17.

Therefore, for example, the lean operation region A in the target air-fuel ratio map shown in FIG. 2 is reduced to regulate or prohibit the lean operation itself, so that a large amount of NOx is not contained in the exhaust gas. NOx catalyst device 1
Thus, the emission of NOx to the atmosphere due to the reduced catalytic function of the catalyst 7 is suppressed.

In this case, it is more preferable that the degree to which the lean area A is reduced be determined according to the count number of the operation characteristic counter. This is because the magnitude of the count number indicates the degree of decrease in the catalytic function of the NOx catalytic device 17. Obviously, the larger the count number, the more the catalytic function is degraded, so that the lean operation region A is further reduced.

Then, the operation characteristic counter is set to step S1.
Before resetting in step 7, the sulfur removal request flag F
Is also set to 1 continuously, so when returning, steps S5 and S6 are skipped and step S9
When the first sulfur release execution permission condition is satisfied in
Sulfur release processing will be executed. For example, when the sulfur removal request flag F is set to 1,
If sulfur release is not performed to the end (until Sr = 0 or Sr ≦ S02) due to the driver's tendency to drive at low vehicle speed, sulfur is forcibly turned off or turned on after the ignition switch is turned on. Release processing may be performed. Thereby, when it is not necessary to travel, the sulfur release processing can be performed without hindering the travel of the driver. In particular, when starting the engine, it is customary to warm up the air-fuel ratio with a rich air-fuel ratio, so that sulfur can be efficiently released.

However, in this case, it is preferable to notify the driver that the sulfur release processing is being executed by warning means such as a buzzer or a warning light. In particular, it is possible to prevent an uncomfortable feeling that the engine does not stop even though the ignition switch is turned off, and a false recognition that the engine is faulty.

Further, the estimated poisoning amount Sa of the NOx catalyst device 17 obtained in step S3 is changed at a predetermined time or periodically (for example, every time when the sulfur deposition amount Sa reaches a predetermined value, or when the sulfur release process is executed). It is preferable to make corrections afterwards. Since the output change time of the second O ₂ sensor 28 on the downstream side of the NOx catalyst device 17 varies depending on the sulfur poisoning state of the catalyst device 17, the rich spike time (FIG. 3) depends on the total sulfur poisoning amount estimated value Sa. Is changed, and the sulfur poisoning state can be detected based on the maximum value of the output of the _second O ₂ sensor 28. Then, the estimated poisoning amount Sa is corrected according to the detected value.

[0137]

As described above, according to the present invention,
In realizing the temperature rise of the exhaust gas or the NOx absorbent to release the attached sulfur component from the NOx absorbent disposed in the exhaust passage by using the method of split injection of the fuel or the retard of the ignition timing, the load and the Depending on the number of revolutions, which method is used, and depending on the load and the number of revolutions, the temperature rise of the exhaust gas or the NOx absorbent itself is prohibited, so the fuel consumption deteriorates, the torque decreases, or Sulfur can be rationally released from the NOx absorbent while suppressing various problems such as generation of smoke.
INDUSTRIAL APPLICABILITY The present invention is widely and preferably applicable to vehicles in which a NOx catalyst device using a NOx absorbent is disposed in an exhaust passage.

[Brief description of the drawings]

FIG. 1 is a control system diagram of an engine according to an embodiment of the present invention.

FIG. 2 is a map showing an air-fuel ratio control region.

FIG. 3 shows the operation of the NOx purification control and the sulfur poisoning elimination control at one time during traveling, and the air-fuel ratio, NOx
5 is a time chart showing changes in NOx absorption amount and sulfur component adhesion amount of a catalyst.

FIG. 4 is a flowchart illustrating an example of a specific operation of sulfur poisoning elimination control.

FIG. 5 is a flowchart showing an operation of measuring a continuous lean operation time in the same control.

FIG. 6 is a flowchart showing an operation of estimating a sulfur adhesion amount in the same control.

FIG. 7 is a characteristic diagram showing a relationship between a fuel supply amount used in the estimation operation and a basic sulfur increase amount.

FIG. 8 is a characteristic diagram showing a relationship between an exhaust gas temperature and a first correction coefficient.

FIG. 9 is a characteristic diagram showing a relationship between a continuous lean operation time and a second correction coefficient.

FIG. 10 is a characteristic diagram showing the relationship between the amount of sulfur already attached and a third correction coefficient.

FIG. 11 is a schematic diagram illustrating characteristics of a second correction coefficient K2 when the continuous lean operation time is long.

FIG. 12 is a schematic diagram illustrating characteristics of a second correction coefficient K2 when the length is also short.

FIG. 13 is a characteristic diagram showing a relationship between a sulfur poisoning elapsed time and a standard first exhaust gas target temperature.

FIG. 14 is a flowchart showing a sulfur release processing operation in sulfur poisoning elimination control.

FIG. 15 is a map showing an air-fuel ratio control area at the time of sulfur release processing used in the same processing operation.

FIG. 16 is a characteristic diagram illustrating a relationship between an exhaust gas target temperature used in setting a late injection amount during the same processing operation and a fourth correction coefficient.

FIG. 17 is a characteristic diagram showing a relationship between an actual exhaust gas temperature and a fifth correction coefficient.

FIG. 18 is a flowchart showing an operation of setting a retard amount during the same processing operation.

FIG. 19 is a flowchart showing an operation for estimating the remaining amount of sulfur in the sulfur poisoning elimination control.

FIG. 20 is a conceptual diagram of a NOx catalyst device for explaining features of the estimation operation.

FIG. 21 is a characteristic diagram showing the relationship between the sulfur release processing time and the complete sulfur removal area ratio used in setting the complete sulfur removal area ratio during the estimation operation.

FIG. 22 is a characteristic diagram showing the relationship between the sulfur release processing time and the partial sulfur removal area ratio used in setting the partial sulfur removal area ratio.

FIG. 23 is a characteristic diagram showing the relationship between the sulfur release processing time used for setting the sulfur removal rate in the partial sulfur removal area and the removal rate.

[Explanation of symbols]

 Reference Signs List 1 engine 5 spark plug 6 injector 10 exhaust passage 16 three-way catalyst device 17 NOx catalyst device 20 control unit 27 exhaust temperature sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) F02D 41/02 301 F02D 41/02 301A 41/04 325 41/04 325C 325Z 41/32 41/32 D 41 / 34 41/34 H 43/00 301 43/00 301B 301J 45/00 310 45/00 310H 314 314R F02P 5/15 F02P 5/15 K (72) Inventor Yoichi Kuji No. 3 Fuchu-cho, Fuchu-cho, Aki-gun, Hiroshima Prefecture No. 1 Mazda Co., Ltd. (72) Inventor Masayuki Kuroki No. 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima F-term (reference) 3G022 AA03 AA06 AA07 AA09 AA10 BA01 BA06 CA09 DA02 EA08 FA04 FA07 GA01 GA02 GA05 GA07 GA08 GA09 GA10 GA11 GA19 3G084 AA03 AA04 BA05 BA09 BA13 BA14 BA15 BA17 BA20 BA24 DA10 DA22 DA27 EA11 EB01 FA01 FA02 FA05 FA10 FA11 FA20 FA26 FA27 FA 29 FA33 FA37 FA39 3G091 AA02 AA11 AA12 AA17 AA24 AA28 AB03 AB06 AB09 BA11 BA14 BA15 BA19 BA33 CA13 CB02 CB03 CB05 CB07 CB08 DA01 DA02 DA03 DA08 DB06 DB07 DB08 DB09 DB10 DC01 EA00 EA01 EA07 EA17 EA07 EA07 EA07 FA12 FA13 FA14 FB03 FC02 FC08 GA06 GB02Y GB03Y GB04Y HA08 HA18 HA36 HA37 HA42 HB03 HB05 3G301 HA01 HA04 HA06 HA13 HA15 HA16 HA17 HA18 JA15 JA25 JA26 JA33 JB09 LA03 LA05 LB04 MA01 MA11 MA18 NA06 NA07 NA08 NE09 NE11 NE07 NE01 NE13 NE06 PA07B PA07Z PA09A PA09B PA09Z PA10A PA10B PA10Z PA11A PA11B PA11Z PD02A PD02B PD02Z PD11A PD11B PD11Z PD15A PD15B PD15Z PE01A PE01B PE01Z PE03A PE03B PE03Z PE08A PE08B PE08Z PF01A PF01B PF01B PF01B

Claims (6)

[Claims] 1. A NOx absorbent that absorbs NOx components in exhaust gas in an oxygen-excess atmosphere and releases NOx components due to a decrease in oxygen concentration is provided in an exhaust passage, and the amount of sulfur components adhering to the NOx absorbent is provided. Means for estimating the amount of sulfur component adhering, and elevating the temperature of the exhaust gas to raise the temperature of the NOx absorbent when the amount of adhering sulfur component estimated by the estimating means is equal to or greater than a predetermined amount. An exhaust gas purifying apparatus for an engine having a sulfur component releasing means for releasing a sulfur component from a NOx absorbent according to claim 1, wherein the sulfur component releasing means injects fuel in a plurality of times when the load is high. The exhaust gas temperature of the engine is increased by raising the temperature of the exhaust gas and, when the load is low, increasing the temperature of the exhaust gas by performing split injection of the fuel and retarding the ignition timing. Air purifier. 2. The sulfur component releasing means does not release the sulfur component when the load is larger than the predetermined load on the high load side and when the load is lower than the predetermined load on the low load side. The exhaust gas purifying apparatus for an engine according to claim 1, wherein 3. The sulfur component releasing means injects fuel in a divided manner into an intake process and a compression process.
The exhaust gas purifying apparatus for an engine according to claim 1 or 2, wherein the fuel injection timing in the compression step is delayed as compared with the time of high load. 4. A target exhaust gas temperature setting means for setting a target value of an exhaust gas temperature for releasing a sulfur component by the sulfur component releasing means is provided.
4. The fuel supply system according to claim 1, wherein at least one of a fuel split ratio, an injection timing, and an ignition timing is corrected so that the exhaust gas temperature reaches the target temperature set by the setting unit. Engine exhaust purification device. 5. The exhaust gas purifying apparatus for an engine according to claim 4, wherein the target exhaust gas temperature setting means sets the target exhaust gas temperature high when the sulfur component is released by the sulfur component releasing means. . 6. A fuel cut prohibition device for prohibiting a fuel cut during the sulfur component release by the sulfur component discharge device is provided.
An exhaust purification device for an engine according to any one of the above.