JP2001020729A - Emission control unit for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To regenerate a lean NOx catalyst with deteriorated NOx purification ability by supplying during deceleration unburned gas to the lean NOx catalyst in which an adsorbent is poisoned by SOx so as to increase a catalyst temperature through combustion on the catalyst. SOLUTION: In this unit, air mixed with gasoline in an intake pipe is combusted inside a cylinder and exhaust gas after combustion is emitted from an exhaust pipe 19. An exhaust gas purification catalyst 20 is provided in the exhaust pipe 19, serving as a lean NOx catalyst purifying exhausted combustion gas effectively during operation with a lean air-fuel ratio, in addition to exhausted combustion gas during operation with a stoichiometric air-fuel ratio and a rich air-fuel ratio. For instance, when an accelerator is fully closed and deceleration from 1500 rpm is performed, fuel is injected for only one cylinder for five seconds, while ignition is not performed and the rest of cylinders are not supplied with fuel. Continuing this control until the speed decrease to 1000 rpm or less, adsorbent of the lean NOx catalyst which is poisoned by sulfur is regenerated all the time and thus deterioration of NOx adsorption ability can be prevented.

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 internal combustion engine of an automobile, and more particularly to a catalyst (lean NOx catalyst) having a function of purifying NOx contained in exhaust gas discharged during lean combustion. The present invention relates to a catalyst device and a method capable of regenerating the purification performance when the purification performance of the catalyst decreases.

[0002]

2. Description of the Related Art In recent years, in the course of resource saving and environmental protection, there is a social demand for operating a gasoline engine for a vehicle by lean burn. Accordingly, catalysts (lean NOx catalysts) for effectively purifying NOx in exhaust gas containing oxygen discharged from a lean burn engine have been developed at various places.

One of the technical issues of lean NOx catalysts is
There is a decrease in the NOx purification ability due to SOx contained in the exhaust gas. Various studies have been made on this SOx poisoning phenomenon, and various countermeasures have been proposed. For example, JP-A-8-2
In No. 4643, the particle size of alkaline earth metals, alkali metals, and the like, which are NOx absorbents in the lean NOx catalyst, is controlled,
A method for suppressing the reactivity with x has been proposed. Also,
In JP-A-7-51544, SOx is converted into a composite sulfate of these metals by supporting two kinds of alkaline earth metals or an alkaline earth metal and a rare earth metal in a complex manner, and is decomposed under a stoichiometric-rich atmosphere. Reproduction methods have been proposed.

Japanese Patent Application Laid-Open No. H10-54274 discloses a method for generating a lean misfire or delaying the ignition timing to raise the temperature of a purifying device in order to release sulfur absorbed by a NOx absorbent. Proposed. Similarly, Japanese Patent Application Laid-Open No.
-274031, JP-A-11-44211 and the like.

[0005]

As environmental regulations on automobiles are tightened, lean NOx catalysts are becoming increasingly expensive.
At the same time as the purification rate is required, high SOx resistance that can withstand long-term use is also required. The present invention proposes an exhaust gas purifying apparatus for an internal combustion engine and a method for realizing regeneration of a lean NOx catalyst in which SOx is easily poisoned and NOx purifying performance is reduced without affecting the operability as compared with the above conventional technology. Is what you do.

[0006]

According to the present invention, reproduction is performed by:
An exhaust gas purifying device equipped with a lean NOx catalyst capable of purifying NOx during operation in lean combustion, supplies unburned gas during deceleration to the lean NOx catalyst poisoned by the adsorbent M with SOx, and burns on the catalyst. And raising the catalyst temperature.

Further, the present invention is implemented by appropriately combining the following means.

(1) After starting the means for raising the temperature of the lean NOx catalyst, a reducing gas is circulated.

(2) At the time of deceleration, control is performed such that fuel injection is performed in at least one cylinder but ignition is not performed.

(3) In (2), when the accelerator is fully closed,
Control is performed such that fuel injection is performed but ignition is not performed in at least one cylinder.

(4) In (3), control is performed such that fuel injection is performed but ignition is not performed in at least one cylinder, and fuel cut control is performed for the remaining cylinders.

(5) In (3), control is performed such that fuel injection is performed but not ignition is performed in at least one cylinder, and fuel cut control is performed in at least one cylinder.

(6) In (3), when the accelerator is fully closed, the engine speed is equal to or higher than a predetermined speed (preferably 150
At the time of 0 rotation or more), control is performed to perform fuel injection but not ignition in at least one cylinder.

(7) In (3), when the engine speed is within the predetermined speed range when the accelerator is fully closed, control is performed such that fuel injection is performed in at least one cylinder but ignition is not performed.

(8) In (3), when the vehicle speed at the start of accelerator fully closing is equal to or higher than a predetermined vehicle speed, control is performed such that fuel injection is performed in at least one cylinder but ignition is not performed.

(9) In (3), when the vehicle speed at the start of accelerator fully closing is within a predetermined vehicle speed range, control is performed such that fuel injection is performed in at least one cylinder but ignition is not performed.

(10) In (6) to (9), when the engine speed is equal to or lower than a predetermined engine speed (preferably 1000 engine speed), fuel injection is performed in at least one cylinder but ignition is not performed. Stop.

(11) The adsorbent M of the lean NOx catalyst is
After it is determined that the poisoning is caused by sulfur oxides (SOx) in the exhaust gas, the temperature of the lean NOx catalyst is increased.

(12) In (11), the adsorbent M is
It is determined based on the traveling distance that the compound is poisoned by SOx in the exhaust gas to reduce the NOx adsorption ability.

(13) In (11), the adsorbent M is
It is determined from the fuel consumption that the compound is poisoned by SOx in the exhaust gas to reduce the NOx adsorption ability.

(14) The lean NOx catalyst is a catalyst in which at least one of an alkali metal, an alkaline earth metal, a rare earth and a transition metal oxide and a noble metal are supported on a porous carrier. It is at least one of a metal and an alkaline earth metal.

(15) In (14), the porous carrier is at least one metal oxide selected from alumina, titania and zirconia, the alkali metal is Na, the rare earth metal is Ce, the alkaline earth metal is Mg, The transition metal oxide is titania, the noble metal is Pt, Rh, and the adsorbent M is the aforementioned component Na.

(16) In (14), each component contains 0.5 liter of Na per 1 liter of the honeycomb heat-resistant structure.
~ 30g, Mg is 0.5 ~ 20g, Ti is 0 ~ 20g,
Ce is 5 to 50 g, Pt is 0.5 to 10 g, and Rh is 0.1.
It is carried in the range of ２2 g.

(17) The lean NOx catalyst is a catalyst in which at least one of an alkaline earth metal, a rare earth and a transition metal oxide and a noble metal are supported on a porous carrier. At least one of

(18) In (17), the porous carrier is at least one metal oxide selected from alumina, titania and zirconia, the rare earth metal is Ce, the alkaline earth metal is Sr and Mg, and the transition metal oxide is The substance is titania, the noble metal is Pt, Rh, and the adsorbent M is Sr
It is.

(19) In (18), each component has a Sr content of 5 to 5 per liter of the honeycomb-shaped heat-resistant structure.
0 g, Ti is 0 to 20 g, Mg is 0.5 to 20 g, Ce
Is 5 to 50 g, Pt is 0.5 to 10 g, and Rh is 0.1 to 2
g.

(20) At least one exhaust temperature measuring device is provided downstream of the internal combustion engine.

(21) In (20), an exhaust gas temperature measuring device is provided inside the exhaust gas purifying device.

(22) In (20), an exhaust gas temperature measuring device is provided downstream of the exhaust gas purifying device.

(23) In (20), when the exhaust gas temperature measuring device reaches a predetermined temperature or higher, the temperature of the lean NOx catalyst is raised to a high temperature.

(24) In (20), when the exhaust gas temperature measuring device reaches a predetermined temperature or higher, the temperature of the lean NOx catalyst is stopped from being raised to a high temperature.

(25) In (20), when the exhaust gas temperature measuring device reaches a predetermined temperature or more for a predetermined cumulative time, the temperature of the lean NOx catalyst is stopped from being raised to a high temperature.

(26) The temperature of the lean NOx catalyst is raised to a high temperature for a predetermined time.

(27) The temperature of the lean NOx catalyst is raised to a high temperature for a predetermined traveling distance.

(28) In (2), control for performing fuel injection but not performing ignition is performed a predetermined number of times of non-ignition.

(29) In (1), after the means for raising the temperature of the lean NOx catalyst is completed, stoichiometric or rich running is performed.

(30) In (10) and (24) to (28), after the control for increasing the temperature of the lean NOx catalyst to a high temperature is completed, stoichiometric or rich running is performed.

(31) In (29) and (30), stoichiometric or rich running is performed for a predetermined time.

[0039]

FIG. 1 shows an internal combustion engine system to which the present invention is applied.

FIG. 1 is a system diagram of a fuel injection type gasoline engine for an automobile. In FIG. 1, air required for combustion is taken in from an intake port 2a, is mixed with gasoline in an intake pipe 8 through an air cleaner 2 and an intake flow control throttle valve 5, and is introduced into a cylinder.

Gasoline required for combustion is drawn from a fuel tank 9 by a fuel pump 10, pressurized, passes through a fuel damper 11 and a fuel filter 12, and flows from a fuel injection valve (injector) 13 into an intake pipe 8. It is injected.

The air mixed with gasoline in the intake pipe is
Combustion is performed in the cylinder by electric ignition (spark plug 21).

The exhaust gas generated by the combustion is exhausted by an exhaust pipe 19,
It is discharged outside the system through the catalyst 20.

The combustion is controlled by controlling the intake air amount signal detected by the intake air flow meter 3, the valve opening signal from the throttle sensor 18 provided in the throttle valve 5, and the crank provided in the distributor 16. An angle signal from the angle sensor is input to the control unit 15 to calculate an appropriate fuel injection amount and ignition timing, and to control the fuel injection valve 13 and the spark plug 2. At this time, according to the oxygen concentration signal from the oxygen sensor 51 provided in the exhaust pipe 19,
More precise control can be performed by detecting the combustion state in the cylinder and performing feedback control.

The control unit 15 for performing this control
2 is shown in FIG. The input signal is passed to the MPU via the I / O. In order to perform an appropriate control state, the MPU performs a calculation using an input signal and values of the ROM and the RAM, and outputs a calculation result via an I / O. This output controls the fuel injection valve 13 and the spark plug 21 as a control signal.

According to this control method, the combustion state in the cylinder is controlled to an arbitrary state such as a stoichiometric air fuel consumption state (stoichiometric state), an excess fuel state (rich), and an excess air state (lean).

Here, since the harmful components such as HC, CO, and NOx are contained in the gas discharged from the engine 7, these harmful components must be detoxified and then discharged out of the system. .

For this reason, an exhaust gas purifying catalyst 20 for purifying exhaust gas by using a catalytic action is provided in the exhaust pipe 19. As the exhaust gas purification catalyst 20, a lean NOx catalyst capable of effectively purifying lean exhaust gas in addition to the conventional purification of combustion exhaust gas in stoichiometric rich is used, and the combustion state of the combustion system shown in FIG. Can be set arbitrarily.

Embodiment 1 When deceleration is performed with the accelerator fully closed from a rotational speed of 1500 rpm or more, fuel injection is performed on one cylinder for a maximum of 5 seconds, but ignition is not performed, and all remaining cylinders are cut off. This control is performed until the speed becomes 1000 rpm or less.

By this control, the adsorbent M of the lean NOx catalyst poisoned by sulfur is constantly regenerated, and a decrease in NOx adsorbing ability can be suppressed.

Test Example 1 The following test was performed based on Example 1.

A nitrate-acidic alumina slurry comprising alumina powder and its precursor was coated on a cordierite honeycomb, and the honeycomb had a volume of 1 liter.
An alumina-coated honeycomb coated with 150 g of alumina was obtained. The honeycomb was impregnated with an aqueous solution of Ce nitrate, dried at about 150 ° C., and fired at about 600 ° C. for 1 hour. Subsequently, this honeycomb was impregnated in a mixed solution of Na nitrate, Mg nitrate, and titania sol, dried, and fired at 600 ° C. Next, the honeycomb was impregnated with a mixed solution of a dinitrodiammine Pt nitric acid aqueous solution and a nitric acid Rh, and dried.
The firing was performed at 50 ° C. for 1 hour. Finally, this honeycomb was impregnated with an aqueous solution of Mg nitrate, dried, and fired at 450 ° C. for 1 hour. By the above-mentioned operation, the apparent volume of the honeycomb catalyst is 1 liter (hereinafter, 1 L of honeycomb), and Ce:
27 g, Na: 18 g, Ti: 4 g, Pt: 2.7 g,
A honeycomb catalyst containing 0.225 g of Rh and 2.0 g of Mg was obtained. Hereinafter, this catalyst is referred to as catalyst A. This catalyst A is used for the exhaust gas purification catalyst 20. The catalyst thus obtained does not absorb NOx,
As described in No. 27617, it adsorbs NOx and has high NOx purification performance.

The catalyst A having a capacity of 1.3 liters was added to 180
It was mounted on a 0cc lean burn test vehicle.

After the mounting, the vehicle subjected to the control of Example 1 and the vehicle not subjected to the control were each run for 20,000 km under the condition of a mixture of lean and stoichiometric. At this time, the gasoline used was a regular gasoline with an S content of 30 ppm.

The evaluation was made before and after running 20,000 km. In the evaluation method, the test vehicle was fixed on a chassis dynamo, and the vehicle was driven at a constant speed at a catalyst inlet temperature of 300 ° C. and 400 ° C. (40 km / h and 70 km / h, respectively). The operating state of the test vehicle is switched between lean burn operation with A / F = 22 and stoichiometric operation, and NOx in exhaust gas
Measure the amount. At this time, the NOx amount is measured before and after the catalyst, and the purification rate is calculated by the following equation. Here, the lean purification rate is switched from stoichiometric to lean burn, and the purification rate after one minute is used. Table 1 shows the results.

NOx purification rate = (NOx amount in inlet gas−
NOx amount in outlet gas) ÷ NOx amount in inlet gas × 10
0

[0057]

[Table 1]

By executing the control of the first embodiment, 20
The performance after traveling 000 km can be prevented from deteriorating.

Embodiment 2 Embodiment 2 will be described with reference to FIG.

An exhaust gas temperature sensor 23 is provided downstream of the exhaust gas purifying catalyst 20.

When the travel distance is calculated by the control unit 15 and the deceleration is performed with the accelerator fully closed from the time of 1500 rpm or more at every 5000 km, one cylinder performs fuel injection but does not perform ignition, and all the remaining cylinders do not perform ignition. The fuel was cut, and control was performed to reduce the fuel to 1000 rpm or less. By performing this control until the accumulated time at which the exhaust temperature sensor indicates 600 ° C. or more reaches 15 minutes,
The adsorbent M of the lean NOx catalyst that is poisoned by sulfur is regenerated, and a decrease in NOx adsorbing ability can be suppressed.

Test Example 2 The same test as in Test Example 1 was carried out on the basis of Example 2 using the same catalyst A as in Test Example 1, and the same results were obtained.

[0063]

According to the present invention, it is possible to regenerate a lean NOx catalyst whose NOx purification ability has been reduced by SOx in exhaust gas, and to maintain NOx purification performance during lean combustion for a long period of time. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an automotive internal combustion engine system to which the present invention is applied.

FIG. 2 is a block diagram of a vehicle engine system control unit.

FIG. 3 is an explanatory diagram of an exhaust gas purification device according to a second embodiment of the present invention.

[Explanation of symbols]

2 ... air cleaner, 2a ... intake port, 3 ... intake flow meter, 5
... Throttle valve, 8 ... Intake pipe, 9 ... Fuel tank, 10 ... Fuel pump, 11 ... Fuel damper, 12 ... Fuel filter, 13 ...
Fuel injection valve, 15 control unit, 16 distributor, 18 throttle sensor, 19 exhaust pipe, 20 exhaust gas purification catalyst, 21 spark plug, 22 engine
23 ... Exhaust gas temperature sensor.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/12 330 F02D 41/12 330K 43/00 301 43/00 301A 301H 301N F02P 9/00 304 F02P 9 / 00 304D (72) Inventor: Osamu Kuroda 2520, Daiji Koba, Hitachinaka City, Ibaraki Prefecture Inside the Automotive Equipment Division, Hitachi, Ltd. Within the Equipment Division (72) Inventor Takeshi Inoue 2520 Oji Takaba, Hitachinaka City, Ibaraki Pref.Hitachi, Ltd. Automotive Equipment Division (72) Kojiro Okude, inventor 7-1-1, Omika-cho, Hitachi, Japan EC01 EC03 FA00 FA03 FA05 FA07 FA10 FA20 FA27 FA29 FA36 FA38 FA39 3G091 AA02 AA12 AB06 BA11 BA14 CA16 CB02 CB05 CB06 DA08 DB10 EA01 EA07 EA17 FA19 GB02W GB02Y GB03W GB03Y GB04W GB05W GB06W GB10A GBA A13X GBA10A GBA CA07 CB04 CB05 EA05 EA06 EA08 EA14 EA17 FA17 FA36 GA13 HA09Z HC06X HC08X HD01X HD02X 3G301 HA01 HA07 HA13 HA15 JA25 KA16 LA00 MA01 MA11 NA08 NE13 NE19 NE23 PA01Z PA11Z PA14Z PD02Z PD11Z PE01Z PE03ZPE08Z08

Claims (6)

[Claims] 1. A catalyst (hereinafter, referred to as a lean NOx catalyst) having a function of purifying nitrogen oxides (NOx) discharged from an internal combustion engine capable of performing lean combustion in the presence of oxygen is provided downstream of the internal combustion engine. In the exhaust gas purifying apparatus having the lean NOx catalyst, the lean NOx catalyst is a catalyst that adsorbs at least a part of NOx in the exhaust gas at the time of leaning and reduces and purifies the lean NOx catalyst with a reducing agent in the exhaust gas.
As a means for regenerating when poisoned by sulfur oxides (SOx) in exhaust gas, a misfire is caused during deceleration to achieve lean N.
An exhaust gas purifying apparatus for an internal combustion engine, comprising: means for raising the temperature of an Ox catalyst. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a reducing gas is circulated after the means for increasing the temperature of the lean NOx catalyst is started. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein, at the time of deceleration, fuel injection is performed in at least one cylinder but ignition is not performed. 4. An internal combustion engine according to claim 1, wherein when the engine speed is equal to or higher than a predetermined speed when the accelerator is fully closed, fuel injection is performed in at least one cylinder but ignition is not performed. Exhaust gas purification equipment. 5. The exhaust gas for an internal combustion engine according to claim 4, wherein when the engine speed becomes equal to or lower than a predetermined speed, control for performing fuel injection in at least one cylinder but not performing ignition is stopped. Purification device. 6. The lean NOx catalyst according to claim 1, further comprising at least one exhaust temperature measuring device downstream of the internal combustion engine, wherein when the exhaust temperature measuring device reaches a predetermined temperature or more for a predetermined cumulative time. Exhaust gas purifying apparatus for an internal combustion engine, characterized in that the temperature of the exhaust gas is not increased.