DE60116278T2 - Device for purifying the exhaust gas with a nitrogen oxide trap catalyst - Google Patents

Description

Background of the invention:

The The present invention relates to an exhaust gas purification device having a nitrogen oxide absorption-reduction catalyst (hereinafter NOx absorption-reduction catalyst) for cleaning of nitrogen oxides (NOx) from exhaust gases by absorption of NOx, when the air-fuel ratio in the Exhaust gas of the internal combustion engine is lean, and by ejecting and Reducing NOx when the ratio is rich.

Especially the present invention relates to an exhaust gas purification device, which can be used in all lean-burn vehicles and those with a NOx absorption-reduction catalyst and a NOx sensor is equipped, so that the NOx absorption-reduction catalyst can be regenerated after a reasonable period of time, while the detected by the NOx sensor Value for used the operation of an engine with a lean burn system can be.

One Lean combustion system represents one of the most effective technologies to improve the fuel consumption of gasoline engines. This system However, there are problems that the usual used three-way catalyst not used for the purification of NOx can be, because in exhaust gas is a lot of oxygen. Consequently Catalysts have been developed that can purify NOx even when the Exhaust gas in a supersaturated with oxygen the atmosphere is present.

consequently Recently, a NOx absorption-reduction catalyst has been developed and put on the market, where the NOx in the range of a lean Air-fuel ratio from a base such as barium (Ba) or the like and then the absorbed NOx is in the range of a rich air-fuel ratio desorbed and is reduced.

As an example of a conventional NOx absorption-reduction catalyst, there is shown a NOx absorption-reduction catalyst having a NOx absorbing substance as described in Japanese Patent Publication No. 2600492. The arrangement of an active metal on the surface of the support layer of the NOx absorption-reduction catalyst, and the mechanism for reducing and purifying NOx are in 4 shown.

The NOx absorption-reduction catalyst 2 is constructed so that a catalytically active metal 3 and a NOx absorbing substance (R) 4 with NOx absorption properties on the on the support 6 formed carrier layer 5 are worn. The carrier layer 5 It consists of a porous coating material such as porous zeolite or alumina (Al ₂ O ₃ ) or the like. The catalytically active metal 3 is platinum (Pt) and has catalytic oxidation ability. The NOx absorbing substance (R) 4 consists of potassium (K), barium (Ba), lanthanum (La) or the like. Depending on the oxygen concentration in the exhaust gas or the concentration of carbon monoxide, the NOx absorption-reduction catalyst absorbs 2 NOx and emits NOx and cleans it. In other words, the NOx absorption-reduction catalyst 2 has two properties: the absorption of NOx and the discharge and purification of NOx.

The NOx absorption-reduction catalyst 2 exploits the oxidizing ability of the catalytic metal 3 such as platinum, to oxidize nitrogen oxide (NO) in the exhaust gas to nitrogen dioxide (NO ₂ ) by oxygen contained in the exhaust gas, as shown in U.S. Pat 4 (a) for operation with a lean air-fuel ratio, wherein oxygen (O ₂ ) as in normal diesel engines or lean-burn gasoline engines and the like is contained in the exhaust gas. The nitrogen dioxide reacts with barium 4 or the like which is a NOx absorbing substance to form nitrate (for example, Ba (NO ₃ ) ₂ and the like) for absorption. The absorption of nitrogen dioxide purifies NOx from the exhaust gas.

When a state of absorption of nitrogen dioxide continues, barium becomes 4 or the like having NOx absorbing ability completely converted into nitrate, thereby losing the NOx absorbing ability. Therefore, in order to recover the NOx absorbing ability, the operating state of the engine temporarily goes rich, thereby producing exhaust gas called rich spike exhaust gas, and the rich exhaust gas becomes the NOx absorption reducing catalyst 2 fed. The rich exhaust gas is a high-temperature exhaust gas produced when operating at a rich air-fuel ratio (the theoretical air-fuel ratio or an air-fuel ratio approaching the theoretical air-fuel ratio) the oxygen (O ₂ ) concentration contained therein is almost zero.

As in 4 (b) shown, oxygen (O ₂ ) is eliminated in the exhaust gas due to the short-time change to the rich state; As the temperature of the exhaust gas increases, the nitrate that has absorbed NOx releases nitrogen dioxide (NO ₂ ) and becomes barium (Ba) again, which is the original state. Since no oxygen is contained in the exhaust gas is the expelled nitrogen dioxide in the exhaust gas on the catalytic metal 3 with oxidizing ability, such as platinum (Pt), by reducing agents, such as carbon monoxide (CO), hydrocarbon (HC), hydrogen (H ₂ ) or the like, and reduced to water (H ₂ O), carbon dioxide (CO ₂ ) and nitrogen (N ₂ ) cleaned.

Becomes the exhaust gas using the NOx absorption-reduction catalyst cleaned, the absorption of NOx become leaner in operation Combustion and emissions and the purification of NOx during rich-burning operation (short-term Change to the rich state) repeatedly to exhausted from the engine NOx to be cleaned continuously.

There the operation of the engine at a rich air-fuel ratio, the a fat exhaust for the reduction of NOx generates, to a deterioration of the fuel consumption leads, On the other hand, it is necessary to change the fat in the short term Condition as short as possible to keep. If therefore regularly the Method of execution a short-term change to the fat state using a timer is applied, the NOx emission varies depending on of the number of revolutions of the engine or the load considerably. Thus, the change NOx emission is not sufficiently supported, leading to the conclusion that this method is not effective.

For these reasons, in the related art, the ECM control device of the computer is used to control the motor to provide a momentary change to the rich state according to the method of FIG 5 to control the control sequence shown. In other words, the NOx concentration at each time point is calculated from the inputted load and the number of revolutions using previously inputted record data of the NOx concentration. In a next step, using the calculated NOx concentration and the input air intake amount (Q), the emission of NOx (NOxc) is calculated for each operating state of the engine, and then the emission of NOx (NOxc) is integrated. If the integrated value of NOx (NOx mass) reaches a specified limit value (first reference value: NOxSL), a brief change to the rich state is carried out. (See EP-A-733 787.)

in the However, related art is a control with a fixed predetermined limit (first reference value: NOxSL) executed, although the NOx absorption capacity of the catalyst with deterioration of the catalyst during the course the time is decreasing. A problem therefore is that to the Time for Regeneration of the NOx absorbency would be most appropriate short-term change to the rich state can not be performed can.

Furthermore For example, the NOx absorption-reduction catalyst is due to deterioration a sulfur poisoning, the NOx absorption capacity of the catalyst can be susceptible. If therefore a short-term Change to the rich state according to the normal control a short-term change to the rich state is performed, the fuel consumption can worsen.

Around the negative effects caused by sulfur poisoning It is necessary, by regularly performing the operation in regeneration mode, to in which prevents lean-burn operation and the engine at a rich air-fuel ratio is operated, the desorption to promote sulfur. However, in the exhaust gas purification apparatus comprising the NOx absorption-reduction catalyst used in the prior art, is not considered, there is a Problem in that the Operation in regeneration mode at a rich air-fuel ratio not accomplished can be.

The progressive deterioration of the catalyst due to sulfur poisoning varies depending on the composition of the fuel or the course of the engine operation. To find out how big that is Extent of Deterioration of the catalyst, it is therefore necessary to the Monitor condition of deterioration of the catalyst.

Summary of the invention:

in the In view of this situation, it is an object of the present invention, an exhaust gas purification device with a nitrogen oxide absorption-reduction catalyst for the Absorbing as well as reducing and purifying NOx from the exhaust gas wherein the value detected by the NOx sensor used to deal with the deterioration of the catalyst a pending variation in NOx absorbency (the amount that absorbs to monitor, so the existence short-term change to the rich state at appropriate times accomplished and the purification performance with respect to NOx in the exhaust gas as a whole can be significantly improved.

Another object is to provide an exhaust gas purification device wherein the value detected by the NOx sensor is used to control the sulfur caused by sulfur poisoning To monitor the NOx absorption capacity so that the operation in the regeneration mode or the operation at a rich air-fuel ratio at appropriate times to support the desorption of sulfur from the catalyst is performed.

The Exhaust gas purification device with a nitrogen oxide absorption-reduction catalyst, which achieves the objectives described above a arranged in the exhaust pipe of the internal combustion engine, nitrogen oxides absorbent substance for absorbing nitrogen oxides when the air-fuel ratio is lean is, and for the ejection of nitrogen oxides, if the air-fuel ratio is the theoretical air-fuel ratio or is rich, as well as a noble metal catalyst and a control device for calculating the integrated value of NOx from the engine load, Number of revolutions of the engine and the amount of air intake, so that a short-term Change to the rich state is performed when the integrated value of NOx exceeds the predetermined first reference value, characterized that a NOx sensor downstream is provided to the nitrogen oxide absorption-reduction catalyst and that the Control device corrects the predetermined first reference value, when the from the NOx sensor immediately value detected after the momentary change to the rich state exceeds the predetermined second reference value.

Of the short-term change to the rich state is a special operation control of the engine, where the air-fuel ratio temporarily in the rich state is moved to for that expel and reducing NOx to regenerate the NOx absorption capability To supply exhaust gas with low oxygen concentration. The short-term Change to the fat state takes place for a period of one to two Seconds, before the NOx absorption into saturation goes.

In this containing a nitrogen oxide absorption-reduction catalyst Exhaust gas purification device is immediately downstream of the NOx absorption-reduction catalyst a NOx sensor for detecting the concentration of NOx mounted to the condition the deterioration of the catalyst based on the concentration of NOx, after the NOx absorption-reduction catalyst was monitored. Of the Limit value related to the integrated value of NOx emission represents the first reference value to determine if a momentary change may take place in the fat state or not, using the measured value of the NOx concentration corresponding to the NOx absorbing ability (the amount that can be absorbed) are changed.

Therefore can the frequency, with which the reduction of NOx absorption capacity takes place, increased, and the short-term change to the fat state can be done at appropriate times. In other words, a short-term change to the rich state may be appropriate Time points performed are corrected by the first reference value is corrected accordingly the NOx absorption capacity the time of execution to determine a short-term change to the fat state.

The The exhaust gas purification device including the nitrogen oxide absorption reduction catalyst is constructed so that the Control device performs the operation in the regeneration mode at a rich air-fuel ratio, if the predetermined first reference value is smaller than the predetermined one third reference value.

Of the Operation in regeneration mode is an operation for regenerating the NOx absorption ability of the NOx absorption-reduction catalyst, wherein the operation in the theoretical air-fuel ratio continuous, for example 10 to 30 minutes, executed and lean burn operation is prevented.

With This control can be operated in regeneration mode using of the first reference value corresponding to the NOx absorption ability as criterion for the determination of the beginning of the operation in the regeneration mode correct, be started in a suitable manner.

There this operation in the regeneration mode regeneration of the NOx absorption capacity of the catalytic converter, the deterioration of fuel consumption, by frequent execution of short-term change to the fat state due to sulfur poisoning caused to be prevented. The increase in frequency of short-term change to the fat state becomes by one Reduction of the NOx absorption capacity of the catalyst due to an increasing sulfur poisoning of the catalyst by a long operating time of the engine caused.

Furthermore is the one containing a nitrogen oxide absorption-reduction catalyst Emission control device constructed so that the control device determines that the Nitrogen oxides absorption-reduction catalyst is not in the normal state when the from the NOx sensor immediately after execution of the operation in the regeneration mode detected value of the predetermined exceeds the fourth reference value. In this structure, the abnormality of the NOx absorption-reduction catalyst be determined by which the operator is prompted to take an appropriate countermeasure.

Therefore can be in the exhaust gas purification device with the nitrogen oxide absorption-reduction catalyst of the present Invention NOx absorption capability of the nitrogen oxide absorption-reduction catalyst be calculated, and thus the NOx purification rate can always be kept at a high level. Because the frequency of execution of short-term changes to the rich state as low as possible can be, the deterioration of fuel economy be prevented.

Short description of Characters:

1 Fig. 10 is a block diagram of an exhaust gas purification device having a nitrogen oxide absorption-reduction catalyst according to the present invention;

2 FIG. 10 is a flowchart showing a control for executing a short-time rich change according to the present invention; FIG.

3 FIG. 10 is a flowchart of a controller for carrying out the regeneration mode according to the present invention; FIG.

4 (a) FIG. 12 is a schematic diagram of the structure of a nitrogen oxide absorption-reduction catalyst and a mechanism for purifying NOx from the exhaust gas showing how NOx is absorbed in the combustion state at a lean air-fuel ratio; FIG.

4 (b) FIG. 12 is a schematic diagram of the structure of a nitrogen oxide absorption-reduction catalyst and a mechanism for purifying NO x from the exhaust gas, showing how NO x is discharged and reduced in the combustion state at a rich air-fuel ratio, and FIG

5 Fig. 10 is a flow chart showing a control for executing a short-time rich change according to the prior art.

Detailed description of the invention:

Under Referring to the drawings, an exhaust gas purification device with a nitrogen oxide absorption-reduction catalyst according to the present invention Invention described.

As in 1 is shown an exhaust gas purification device 1 with a nitrogen oxide absorption-reduction catalyst (NOx absorption-reduction catalyst) in the discharge pipe 11 arranged the internal combustion engine E. Immediately downstream of the NOx absorption-reduction catalyst 2 is a NOx sensor 13 for detecting the NOx concentration in the purified exhaust gas Gc after it has the NOx absorption-reduction catalyst 2 has flowed through, provided.

As a NOx absorption-reduction catalyst 2 can the in 4 shown known NOx absorption-reduction catalyst 2 be used. The NOx absorption-reduction catalyst 2 includes a carrier 6 , one on the carrier 6 formed carrier layer 5 , a catalyst metal 3 , which of the carrier layer 5 is worn, and a NOx absorbing substance 4 that absorbs nitrogen oxides (NOx) when the air-fuel ratio is lean, and discharges the nitrogen oxides when the air-fuel ratio is rich. The carrier layer 5 is a catalyst carrier formed of a porous coating material such as alumina or the like.

Although the catalyst metal 3 Is platinum (Pt) or the like, and in the temperature range higher than the activation temperature has reduction activity, another catalyst metal may also be used. For platinum, the activation temperature is in the range of about 150 ° C-200 ° C.

As NOx absorbing substances 4 For example, barium (Ba), calcium (Ca) and the like can be used. When barium is used, the temperature at which the discharge of NOx starts is in the range of 450 ° C. As in 4 is shown, the NOx absorbing substance 4 from the catalyst carrier 5 but it is also possible to use the catalyst support 5 instead of the NOx absorbing substance 4 to build.

The Exhaust gas purification device with the NOx absorption-reduction catalyst according to the present Invention is constructed so that the controller for the execution of short - time change to the rich state and control for the execution of the Regeneration mode as described below.

The control for executing the short-time change to the rich state according to the present invention is performed according to the in 2 executed flowchart shown by way of example. The momentary change to the rich state is the operation state of the engine in which the air-fuel ratio is temporarily shifted to the rich state before the NOx absorption is saturated to produce a low oxygen concentration exhaust gas, so that NOx is discharged and reduces and so the NOx absorption capacity is regenerated.

Of the Control sequence occurs simultaneously with the control of the engine operating condition instead, so that he begins at the beginning of the control of the engine operating condition and is interrupted when the control of the engine operating condition ends, whereby, when the control process is interrupted in the middle of the control then it continues and until the end there ends.

at Beginning of the control process in step S11, the burden and the number of revolutions of the load sensor and the RPM sensor and then, in step S12, the NOx concentration increases any time points from the record data of the NOx concentration, in advance using the entered load and the RPM of the engine were entered, calculated.

The in step S13, the air intake amount Q and the calculated one NOx concentration will be used in step S14, the NOx emission NOxc for each To calculate engine operating condition, and then in step S15 summarized, by the integrated value of NOx (integrated amount: NOx mass) too receive. If the engine is stopped before regeneration, the integrated value NOx mass stored at this time, and the stored value will be the next Start as a basis for used the integration.

In Step S16, it is determined whether the integrated value NOx mass of NOx reaches the predetermined first reference value NOxSL or not. If it is reached (YES), in step S17, a start signal for the short-term Change to the fat state issued to a short-term Change to the rich state.

If the integrated value NOx mass of NOx in step S16 is the predetermined one first reference NOxSL not reached (NO), the timer measures A is the time between measurement times and after these has elapsed, the process returns to step S11 back and repeats the steps S11-S16.

In the present invention, after the short time change to the rich state has been carried out in the step S17, the time period of the short time change to the rich state is measured by the timer B, and after the measured time has elapsed, in step S21 immediately after End of the short-term change to the rich state, the NOx concentration by the immediately downstream to the catalyst 2 arranged NOx sensor 13 measured.

The NOx concentration RSNOx immediately after completion of the short-term Change to the rich state becomes the predetermined one in step S22 second reference value RSSL compared to the state of deterioration of the catalyst (RSNOx> RSSL) and if it worsened in State is (RSNOx> RSSL) (YES), is the limit value NOxSL, which is the first reference value, in Step S23 corrected. This correction is done by multiplying the limit value NOxSL of the previous time with a coefficient KNOX (KNOX <1).

If the catalyst 2 If it is not in the deteriorated state (RSNOx <RSSL) (NO) in step S22, the integrated value NOx mass of NOx is initialized in step S24 to repeat the control.

at In the subsequent control, the integrated value NOxmass of NOx from the engine load, the number of revolutions of the engine and the amount of air intake Q calculated and when the integrated value NOx mass of NOx the exceeds predetermined first reference value NOxSL, the controller to perform a short-term change to the fat state is activated, and when the detected by the NOx sensor value RSNOx, the immediate after execution a short-term change to the rich state is obtained exceeds the predetermined second reference value RSSL, the predetermined first reference value NOxSL be corrected.

Now, the control for carrying out the regeneration mode according to the present invention will be described. This control is performed according to the example in 3 shown control flow chart executed.

Of the Operation in the regeneration mode serves to regenerate the NOx absorption capability of the NOx absorption-reduction catalyst and starts the operation with lean burn operation for a predetermined one Duration (for example, about 10-30 minutes) is prevented. The operation in the regeneration mode serves with the deterioration to deal with the fuel consumption caused by frequently performing a short-term change in the fat state according to the above described control for performing a short-term change is caused in the rich state when the NOx absorbency of the catalyst due to the progress of sulfur poisoning is reduced as a result of long-term operation.

This operation is associated with appropriate time intervals or a specific step of the above-described control to make a short-time change to the rich state (for example, immediately after step S23) repeatedly called and executed.

First, will at the beginning of the control sequence, the limit value NOxSL, which the predetermined first reference value is checked in step S31. exceeds the limit value NOxSL the predetermined third reference value RGSL (NO), it is determined that the Operation in regeneration mode is not necessary, and the process returns. On the other hand, if the limit value NOxSL is smaller than the predetermined third one Reference value RGSL (YES), it is determined that the ner than the predetermined third reference value RGSL (YES), it is determined that the operation in the regeneration mode, and in step S32 becomes ON signal for output the regeneration mode to the NOx absorption-reduction catalyst to regenerate. This operation in regeneration mode counts the Time immediately after turning ON by the timer and ends, when the operation is in the regeneration mode for the predetermined period of time accomplished has been.

If in step S43, the period of operation in the regeneration mode was measured by the timer C and after that time elapsed is, in step S33, the NOx concentration RSNOx on the downstream side of the catalyst immediately after End of the regeneration mode measured, and if the NOx concentration RSNOx is less than the predetermined fourth reference value RSSL2 (YES) and it is thus determined in step S34 that the regeneration of the catalyst is completed is, the limit value NOxSL for checking the integrated NOx value initializes to the threshold value NOxSL to the initial value in step S36 Reset NOxSLO, and the process returns.

If however, the determination in step S34 shows that the NOx concentration RSNOx on the downstream side of the catalyst immediately after End of the regeneration mode, the predetermined fourth reference value RSSL2 is over a regeneration of the NOx purification rate of the catalyst itself can not be observed in the regeneration mode. In such a case, it is determined that the catalyst does not is in the normal state, which is the case when the Catalyst for a reason other than sulfur poisoning deteriorates, and the process goes to step S35, in which the deterioration of the catalyst is diagnosed, the test lamp the engine is turned on and then the process returns.

With Such a controller, as has been described so far, can the operation is carried out in the regeneration mode with the theoretical air-fuel ratio, when the predetermined first reference value NOxSL is smaller than that predetermined third reference value RGSL.

In the exhaust gas purification device 3 with the nitrogen oxide absorption-reduction catalyst 2 can the state of deterioration of the catalyst 2 based on the through the NOx sensor 13 measured NOx concentration RSNOx be monitored, so that the first reference value NOxSL with respect to the integrated value NOx mass of the NOx emission can be varied according to the current NOx absorption capacity to determine whether the implementation of a brief change to the rich state possible is or not.

The frequency the execution a short-term change to the rich state can therefore at a Reduction of the NOx absorption capacity can be increased, and thus can short-term change to the rich state at appropriate times are performed.

In the exhaust gas purification device 3 That is, the first reference value NOxSL to be corrected according to the NOx absorbing ability is used as a criterion for determining the execution of the operation in the regeneration mode, so that the execution of the regeneration mode operation can suitably take place.

Since the NOx absorption capacity of the catalyst 2 can be regenerated by the operation in the regeneration mode, the deterioration of the fuel consumption caused by frequent short-term changes to the rich state due to sulfur poisoning can be prevented.

In addition, since the abnormality of the nitrogen oxide absorption-reduction catalyst 2 can be determined, the operator are led to take a suitable countermeasure.

As a result, in the exhaust gas purification device 1 with the nitrogen oxide absorption-reduction catalyst 2 According to the present invention, the NOx absorption ability of the nitrogen oxide absorption-reduction catalyst 2 be calculated, and thus the NOx purification rate can always be maintained at a high level. Since the frequency of execution of the short-time change to the rich state can be kept as low as possible, the deterioration of the fuel consumption can be prevented.

Claims (3)

Exhaust gas purification device ( 1 ) with a nitrogen oxide absorption-reduction catalyst comprising: a nitrogen oxide absorption-reduction catalyst ( 2 ) with a nitrogen oxide absorbing substance ( 4 ) located in the exhaust pipe ( 11 ) of the internal combustion engine (E) is provided to absorb nitrogen oxides when the air-fuel ratio is lean, and to exhaust nitrogen oxides when the air-fuel ratio is equal to the theoretical air-fuel ratio or rich, and a noble metal catalyst ( 3 ) and a control device ( 10 ) for calculating the integrated value of NOx (NOx mass) from the engine load, the number of revolutions of the engine, and the amount of intake air so that a short time change to the rich state is performed when the integrated value of NOx (NOx mass) is a predetermined one first reference value (NOxSL), characterized in that a NOx sensor ( 13 ) downstream of the nitrogen oxide absorption-reduction catalyst ( 2 ) is provided and that the control device ( 10 ) corrects the predetermined first reference value (NOxSL) when passing through the NOx sensor ( 13 ) immediately after the momentary change to the rich state (RSNOx) exceeds a predetermined second reference value (RSSL). An exhaust gas purification device comprising a nitrogen oxide absorption-reduction catalyst according to claim 1, characterized in that the control device ( 10 ) at a rich air-fuel ratio performs the operation in the regeneration mode when the predetermined first reference value (NOxSL) is smaller than a predetermined third reference value (RGSL). An exhaust gas purification device with a nitrogen oxide absorption-reduction catalyst according to claim 2, characterized in that the control device ( 10 ) determines that the nitrogen oxide absorption-reduction catalyst ( 2 ) is in the abnormal state when passing through the NOx sensor ( 13 ) immediately after the operation in the regeneration mode detected value (RSNOx) exceeds a predetermined fourth reference value (RSSL2).