JP2002070542A - Catalyst control device and catalyst purifying device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst control device and a control method for an engine capable of enhancing exhaust emission and fuel economy by supplying an HC and a CO component acting as a reducing agent during lean operation to a NOx catalyst and reducing the NOx component stored in the NOx catalyst, and reducing a cost. SOLUTION: This catalyst control device for the engine has a first catalyst for accelerating oxidation and reduction to an exhaust gas component and a second catalyst for storing nitrogen oxides in the exhaust gas by adsorption or storage reaction, in an exhaust pipe in order. The catalyst control device controls so that when the purification of the second catalyst is required, the oxidation and reduction performance in the first catalyst is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst control device and a catalyst purification method for an engine, and more particularly, to a three-way catalyst and a NO.
The present invention relates to an engine catalyst control device and a catalyst purification method for reducing and purifying NOx components accumulated in the NOx catalyst during lean operation by combining the x catalyst with a x catalyst.

[0002]

2. Description of the Related Art A typical internal combustion engine oxidizes hydrocarbons (HC) and carbon monoxide (CO) contained in exhaust gas discharged from a combustion chamber of the engine to produce nitrogen oxides (NOx). In general, a three-way catalyst having a function of reducing) is installed in an exhaust pipe of an engine. In such an apparatus, during the operation of the internal combustion engine, the exhaust gas is purified by the three-way catalyst that simultaneously promotes the oxidation and reduction actions near the stoichiometric air-fuel ratio, and is discharged into the atmosphere.

[0003] Therefore, an O2 sensor or a linear air-fuel ratio sensor is provided in the exhaust pipe to detect the actual air-fuel ratio, and the air-fuel ratio at which the operation of the three-way catalyst can be utilized to the utmost, that is, HC, CO, NOx. The fuel injection amount and the intake air amount are feedback-corrected in order to maintain the three components at a point where they are efficiently purified.

[0004] In recent years, lean-burn, in-cylinder-type lean-burn engine systems and the like have been put into practical use due to the recent close-up of air pollution and improvement of fuel economy. The actual air-fuel ratio becomes the lean air-fuel ratio. In this case, the inside of the three-way catalyst becomes an oxygen-excess atmosphere, and the oxidation reaction of the HC and CO components is promoted to achieve a high purification rate, while the reducing action is suppressed, and as a result, the purification rate of the NOx component is remarkably increased. The phenomenon of lowering occurs.

For this reason, an NOx catalyst is disposed in the exhaust pipe of the engine downstream of the three-way catalyst, and the NOx component is reduced to achieve both improvement in exhaust emission and improvement in fuel efficiency. ing. The NOx catalyst is for temporarily accumulating the NOx component discharged during the lean operation by an adsorption or occlusion reaction. Various technologies for an exhaust gas purifying apparatus for an engine combining such a three-way catalyst and a NOx catalyst have been proposed (for example, JP-A-5-133260, JP-A-7-310534, JP-A-8-310534). JP-A-121147, JP-A-11-223123, U.S. Pat.
No. 95060, Japanese Patent Application Laid-Open No. H11-336531, etc.).

In each of the techniques disclosed in the above-mentioned publications, a reducing action is performed if a reducing agent such as an HC component is supplied into the NOx catalyst during the lean operation. The three-way catalyst almost completely removes the reducing agent such as the HC component, and the amount of the NOx component accumulated in the NOx catalyst is limited. Will be done.
Therefore, the HC and C as the reducing agents are obtained by performing an operation to achieve a rich air-fuel ratio or a stoichiometric air-fuel ratio according to a predetermined request.
The O component is supplied to the NOx catalyst and N
In the case of reducing and purifying the Ox component, or when the accumulated amount of the NOx component in the NOx catalyst reaches the saturation amount,
This is a technique of reducing the combustion temperature of the engine to suppress the generation of the emission amount of the NOx component itself, or deteriorating the fuel state to increase the amount of the unburned gas to reduce the adsorbed NOx component.

[0007]

By the way, as described above, the reducing agent is supplied to the NOx catalyst by executing the rich air-fuel ratio or the stoichiometric air-fuel ratio in accordance with a predetermined request.
Reducing and purifying the NOx component in the catalyst is performed by the NO
In view of the fact that there is a limit to the amount of NOx component accumulated in the x-catalyst, it imposes restrictions on the lean operation region and the lean operation time, which is not desirable in the lean burn engine system, When the combustion is switched to the combustion mode, torque fluctuations and shocks occur, so that the rebound to fuel efficiency and drivability increases, and there remains a problem.

That is, the inventor of the present invention has proposed a lean combustion system in which an exhaust pipe is provided with a three-way catalyst and a NOx catalyst downstream of the three-way catalyst in order to achieve improved fuel efficiency and drivability, cost advantages, and the like. New knowledge that it is good to intentionally lower the purification rate of the three-way catalyst in the engine performing the above, and supply the reducing agent generated thereby to the NOx catalyst to reduce and purify the NOx component. However, in the conventional technique, the NOx component is reduced and purified by changing a combustion mode or lowering a combustion temperature when a saturated amount is reached, but the redox reaction of the three-way catalyst is performed. No particular consideration has been given to actively manipulating the performance and intentionally lowering the purification rate.

The present invention has been made in view of such a problem, and an object of the present invention is to supply HC and CO components serving as reducing agents to a NOx catalyst during lean operation, and to provide the NOx catalyst It is an object of the present invention to provide an engine catalyst control device and a control method capable of improving exhaust emissions and fuel efficiency by reducing and purifying NOx components accumulated in a catalyst and reducing costs.

[0010]

In order to achieve the above object,
The catalyst control device for an engine according to the present invention basically includes:
First to promote oxidation and reduction of exhaust gas components
And a second catalyst for accumulating nitrogen oxides in the exhaust gas by an adsorption or occlusion reaction in an exhaust pipe, wherein the catalyst control device comprises: If you need to purify the catalyst of 2,
It is characterized in that the first catalyst is controlled so as to reduce the oxidation and reduction reaction performance of the first catalyst.

The engine catalyst control apparatus of the present invention having the above-described structure intentionally lowers the oxidation and reduction reaction performance of the first catalyst itself for promoting the oxidation and reduction of the exhaust gas components. Since the components other than the nitrogen oxides in the exhaust gas that have not been purified by the first catalyst are supplied to the second catalyst as a reducing agent, the nitrogen oxides are reduced by the reducing agent. Further, it is possible to further improve the exhaust emission and the fuel efficiency, and to reduce the rebound to drivability, thereby improving the reliability of the engine.

Further, in a specific embodiment of the catalyst control apparatus for an engine according to the present invention, it is necessary to supply an exhaust gas component serving as a reducing agent to the second catalyst based on an operating state or an environmental state of the engine. Means for determining whether or not
Means for calculating a control amount of the oxidation and reduction reaction performance of the first catalyst based on the determination result.
Or whether or not a means for controlling the first catalyst based on the calculation result of the control amount is provided, or whether or not it is necessary to supply the exhaust gas component by detecting a purification index of the first catalyst. It is characterized in that the means for judging is provided with means for outputting the purification index.

Further, in another specific embodiment of the catalyst control apparatus for an engine according to the present invention, the means for controlling the first catalyst may reduce the catalyst temperature of the first catalyst, or The means for controlling the catalyst of the above-mentioned means that the catalyst temperature is reduced by any one of or a combination of a parameter affecting combustion, cooling of the first catalyst itself, and cooling of exhaust gas temperature. Features.

[0014] Further, the means for controlling the first catalyst may be configured to lower the temperature of the catalyst based on the temperature of exhaust gas of the engine, or the means for controlling the first catalyst may include an ignition timing. The exhaust gas of the engine by one or a combination of the operation and the air-fuel ratio operation, or by any or a combination of the opening and closing timing operation of the exhaust and intake valves, the lift amount operation, or the combustion speed operation. It is characterized in that the temperature of the sample is changed.

Further, the means for controlling the first catalyst includes:
When having a plurality of the first catalysts, reducing the oxidation and reduction reaction performance for each of the plurality of catalysts, or, among the plurality of catalysts, the first catalyst closest to the exhaust port of the engine It is characterized in that the oxidation and reduction reaction performance is reduced. Further, the first catalyst is a three-way catalyst, and the second catalyst is a NOx catalyst.

In order to achieve the above object, a method for purifying a catalyst of an engine according to the present invention basically comprises a first catalyst for promoting an oxidation and a reduction action on an exhaust gas component;
A method for purifying a catalyst of an engine, wherein a second catalyst for accumulating nitrogen oxides in the exhaust gas by an adsorption or occlusion reaction is sequentially provided in an exhaust pipe, by reducing a purification rate of the first catalyst. The exhaust gas component supplied to the second catalyst is operated to reduce and purify the second catalyst.

Further, in a specific embodiment of the method for purifying a catalyst of an engine according to the present invention, the purifying rate of the first catalyst is reduced by lowering the temperature of the first catalyst.
Alternatively, the temperature of the first catalyst is reduced by operating the temperature of the exhaust gas of the engine.

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an engine catalyst control apparatus and a catalyst purification method according to the present invention. FIG. 1 shows a configuration diagram of an engine system provided with an engine catalyst control device of the present embodiment, and shows an engine catalyst control device and a catalyst purification method for controlling a catalyst temperature.

The engine system relates to an in-cylinder injection engine, which is a lean burn system. Air introduced into a cylinder 2 of an engine 1 is taken in from an inlet 6 of an air cleaner 5, passes through an air flow meter 7, It enters the collector 8 under the control of an electronically controlled throttle valve (ETC) 4. The air taken into the collector 8 is distributed to each intake pipe 10 connected to each cylinder 2 of the engine 1 and then formed by the cylinder 2, the piston 3, the intake valve 11, the exhaust valve 12, and the like. It is led into the room 9.

On the other hand, fuel such as gasoline is sucked and pressurized from a fuel tank (not shown) by a fuel pump (not shown), and supplied to a fuel system in which the injector 13 is piped. The pressurized fuel is adjusted to a constant pressure (for example, 5 MPa) by a fuel pressure regulator (not shown), and is directly injected into the fuel chamber 9 from an injector 13 provided in each cylinder 2. The fuel injected into the fuel chamber 9 is ignited by an ignition plug 16 according to an ignition signal whose voltage is increased by an ignition coil 15.

The exhaust pipe 20 has a three-way catalyst 21 which is an embodiment of a first catalyst for promoting the oxidation and reduction of exhaust gas components, and adsorbs or stores nitrogen oxides in the exhaust gas. And a NOx catalyst 23 which is an embodiment of a second catalyst accumulated by the NOx catalyst. The NOx catalyst 23 is provided downstream of the three-way catalyst 21. After passing through the three-way catalyst 21, the exhaust gas in the combustion chamber 9 passes through the NOx catalyst 23 that purifies NOx during lean combustion, and is released into the atmosphere.

A signal indicating the intake flow rate from the air flow meter 7 and a crankshaft 19 from a crank angle sensor 18
And the detection signal from the temperature sensor 22 mounted near the three-way catalyst 21 in the exhaust pipe 20 are input to an engine control unit (control unit) 17 having a catalyst control unit 17A for controlling the catalyst temperature. , A predetermined calculation process, and outputs various control signals calculated as the calculation result.
3 and a predetermined control signal to the ignition coil 15 and the like,
Various controls such as catalyst temperature, fuel injection amount and ignition timing are executed.

FIG. 2 is a control block diagram of the catalyst control device 17A in the engine control device 17. The catalyst control device 17A provides H as a reducing agent for the NOx catalyst 23.
Supply determining means 17B for determining whether supply of C and CO components is required; control amount calculating means 17C for calculating a control amount of the three-way catalyst 21 with respect to a target temperature; and means for controlling the first catalyst A three-way catalyst control means 17E for controlling the three-way catalyst 21 based on a calculation result of a control amount with respect to the target temperature, and a control result performed based on a calculation result of the control amount with respect to the target temperature. Three-way catalyst 21
And a purification index detecting means 17D for detecting the purification index.

The supply determining means 17B is based on one of the signals representing the operating state of the engine 1 (engine parameters such as engine speed, engine load, accelerator operation amount, etc.) and the environmental state such as outside air temperature. NOx
It is determined whether the supply of the HC and CO components serving as the reducing agent to the catalyst 23 is required, and the result of this determination is output to the control amount calculating means 17C.

When the supply determining means 17B determines that the supply of HC and CO components is necessary, the control amount calculating means 17C actively activates the three-way catalyst 21 by the three-way catalyst control means 17E. In order to lower the purification rate intentionally by calculating the target catalyst temperature and the control amount for lowering the purification rate, the actual catalyst temperature such as ignition timing, injection timing, catalyst cooling water circulation, etc. Is calculated and output to the engine 1 and the three-way catalyst 21 via the three-way catalyst control means 17E.

The purification index detecting means 17D responds to the request from the control amount calculating means 17C by the three-way catalyst 21.
Based on each parameter such as the catalyst temperature, the exhaust temperature, the time, and the exhaust gas concentration, it is estimated and determined whether or not the catalyst temperature has actually decreased. The result is output to the supply determining unit 17B, and the feedback correction is performed. Is going.

FIG. 3 is a characteristic diagram showing the purification rate of the three-way catalyst 21 with respect to the air-fuel ratio. The three-way catalyst 21 has a high air-fuel ratio, that is, H in the oxygen-deficient region.
Although the purification rates of the C and CO components decrease, the purification rates of the NOx components increase to the maximum. On the other hand, in the lean air-fuel ratio, that is, in the oxygen excess region, HC, CO
It can be seen that the purification rate of the component increases to the maximum, but the purification rate of the NOx component decreases.

FIG. 4 is a characteristic diagram showing the purification rate with respect to the catalyst temperature. As described above, the three-way catalyst 21 is greatly affected by the value of the air-fuel ratio.
Regarding the oxidation reaction of the components, the purification rate also increases with the increase in the catalyst temperature until the catalyst temperature reaches a predetermined temperature at which the catalyst is completely warmed up. The purification rate changes under the influence.

That is, since the catalyst is more susceptible to the sensitivity characteristic (S-shaped characteristic) based on the catalyst temperature than to the effect of the air-fuel ratio characteristic, the catalyst control device 17A actively controls the catalyst temperature. Control to reduce to
The purification rate of the HC and CO components of the three-way catalyst 21 is intentionally varied.

The S-shaped characteristic of the catalyst has a large gradient with respect to the temperature in a predetermined temperature range, and the change in the purification rate is large even with a slight temperature change. Care must be taken. Therefore, temperature control may be performed using feedback correction or the like based on the target value and the detection result for the target value.

FIG. 5 is an explanatory diagram of the purification rate control. Assuming that the catalyst temperature TA after the catalyst is completely warmed up, the HC and CO purification rates ηA at the catalyst temperature TA, the catalyst temperature is lower than the catalyst temperature TA. Temperature TB, HC and C at the catalyst temperature TB
Assuming that the purification rate of O is ηB, the purification rate ηB is worse than the purification rate ηA. Then, assuming that the change rate Z of the purification rate is represented by the equation (1).

[0032]

X = (ηA−ηB) × X (1) where X is the exhaust gas amount of the engine 1. That is,
The HC and CO components corresponding to the change Z of the purification rate are released from the three-way catalyst 21 as a reducing agent without being purified.

FIG. 6 shows a time chart of the conventional exhaust gas purification. When a three-way catalyst and a NOx catalyst are arranged downstream of the three-way catalyst behind the engine, and when purifying exhaust gas during a steady lean operation, first, the HC and CO amounts X1 discharged from the engine are determined. Then, the HC, CO
The components are efficiently purified by the oxygen-excess atmosphere due to the lean air-fuel ratio of the three-way catalyst that has been completely warmed up, and the HC and CO amounts after passing through the three-way catalyst are reduced to Y1. Thereafter, since the NOx catalyst on the downstream side is used as a reducing agent, the HC and CO amounts are reduced to the Z1 and released into the atmosphere. That is, HC and CO components are almost purified by the three-way catalyst.

On the other hand, the amount of NOx exhausted from the engine U
If it is set to 1, the NOx component is hardly purified by the three-way catalyst because of the lean air-fuel ratio, becomes the NOx amount V1 (≒ U1) after passing through the three-way catalyst, and does not change. Thereafter, in the NOx catalyst on the downstream side, the NOx catalyst is accumulated in the NOx catalyst by an adsorption / occlusion reaction from a position of a purified component (dotted line B) by the reduction reaction using the HC and CO amounts Y1 (indicated by a hatched portion A). , NOx amount W1 and is released to the atmosphere.

However, the currently mainstream NOx catalysts are
In view of the fact that there is a quantitative restriction on the amount of NOx that can be accumulated in the catalyst due to the storage reaction, the NOx amount W1 is apparent, and the actual amount of NOx that can be accumulated depends on the lean operation time, the NOx emission amount, and the like. Have been affected.

That is, as shown in FIG. 7, the amount of NOx that can be stored in the NOx catalyst in the early stage of the lean operation is represented by A.
Then, at time a after the lean operation, the pressure drops to A ′,
Further, at the time point b, it decreases to A ″. At the time point c, the storage capacity of the NOx catalyst itself saturates, the change becomes zero, and this NOx component may be released to the atmosphere. Therefore, in the related art, the lean operation is prohibited by changing the lean operation time or the operating state, and the saturated NOx is purified by performing the stoichiometric operation or the like.

Further, the purified component (dotted line B) by the reduction reaction using the HC and CO amounts Y1 which is the reaction component during the lean operation shown in FIG. 6 is also used as the reducing agent in the three-way catalyst. , The CO component is already small, so that the amount is not as large as expected.

Therefore, the catalyst control device 1 of the present embodiment
7A secures the purifying rate of the oxidation reaction in the three-way catalyst 21 by intentionally lowering the purifying rate by the reduction reaction using the amounts of HC and CO, which are the reacting components during the lean operation, as shown below. Then, the secured HC and CO components are supplied to the NOx catalyst 23 on the downstream side to promote the NOx reduction reaction during the lean operation to eliminate the restriction of the lean continuation time and to reduce the torque fluctuation due to the change in the air-fuel ratio. Have been avoided.

FIG. 8 shows an exhaust gas purification time chart by the catalyst control device 17A. First, assuming that the amount of HC and CO discharged from the engine is X1, the HC and C
The O component is supplied to the supply determining unit 17B and the control amount calculating unit 17.
The catalyst temperature of the three-way catalyst 21 is lowered based on the output signal of the three-way catalyst control means 17E via C to lower the purification rate, and the HC and CO amounts Y2 (Y
1≪Y2). Then, the HC and CO amounts Y2 are supplied to the NOx catalyst 23 as a reducing agent, so that HC and C
O content is reduced to Z2 (≒ 0) and released to the atmosphere.

On the other hand, the NOx amount U
If it is set to 1, the NOx component is hardly purified by the three-way catalyst 21 because of the lean air-fuel ratio, becomes the NOx amount V1 (≒ U1) after passing through the three-way catalyst 21, and does not change. However, after that, the downstream NOx catalyst 23 adsorbs from the position of the purified component (dotted line B1) by the reduction reaction using the HC and CO amounts Y2, which has not been purified by the three-way catalyst 21.
Due to the occlusion reaction, the NOx is accumulated in the NOx catalyst 23 (shaded area A
), And decreases to the NOx amount W2 (W2≪W1),
Released into the atmosphere. That is, the NOx component is NO
It is almost purified by the x catalyst 23, and the NOx emission can be reduced. Further, the accumulated amount in the NOx catalyst 23 is also
Since the purification reaction is performed during the lean operation, the concept of the NOx saturation amount can be eliminated, and desired operation such as extension of the lean operation time can be performed.

FIG. 9 is an operation flowchart of the supply determining means 17B of the catalyst control device 17A. In step 91, as described later, the amount of NOx stored in the NOx catalyst 23 is estimated, and the routine proceeds to step 92.

In step 92, the NOx amount estimated in step 91 is compared with a predetermined value to determine the estimated NOx.
It is determined whether or not the x amount is equal to or greater than a predetermined value. If the x amount is equal to or greater than the predetermined value, that is, if the determination is YES, the process proceeds to step 93 to establish a supply request for the HC and CO components as the reducing agent. On the other hand, when the difference is equal to or less than the predetermined value, the series of operations is terminated. The predetermined value may be changed according to a fixed value or a parameter such as an operating state.

In step 94, after the supply request is satisfied, the catalyst temperature, time, number of times, and the like are compared with a predetermined value as a determination value to determine whether the determination value is equal to or less than a predetermined value. If the value is equal to or smaller than the predetermined value, that is, if YES, the process proceeds to step 95 to cancel the request and end a series of operations. On the other hand, when the value is equal to or more than the predetermined value, the series of operations is terminated.

FIG. 10 is a flowchart showing the operation of the supply judging means 17B.
FIG. 4 is an explanatory diagram of estimating the accumulated amount of NOx in the x catalyst 23. The NOx emission amount of the engine 1 in each operation region is stored in a map or a table composed of the engine rotation and the engine load, and is used for the operation time and the like. NOx based on
Emissions are estimated by integrating them.

FIG. 11 is an operation flowchart of the control amount calculation means 17C and the three-way catalyst control means 17E of the catalyst control device 17A. In step 101, the supply determining means 1
It is determined whether there is a request to supply HC and CO components as reducing agents by 7B, and if there is a supply request, that is, YES
In this case, the chart is started and the process proceeds to step 102. On the other hand, when there is a supply request, the series of operations ends.

In step 102, the catalyst control device 17A
But three-way catalyst 2 to secure the amount of HC and CO to be supplied
In step 103, a target catalyst temperature for lowering the catalyst temperature of the three-way catalyst 21 is calculated. The target catalyst temperature is calculated by a map, a table value, or a calculation based on parameters such as an engine speed, a vehicle speed, a load, and an NOx amount.

In step 103, the calculated target catalyst temperature is compared with a predetermined judgment temperature TW1 to judge whether or not the target catalyst temperature is equal to or higher than the judgment temperature TW1.
If the temperature is equal to or higher than the determination temperature TW1, that is, if YES, the process proceeds to step 104, where mode A is selected, and a series of operations is completed. On the other hand, when the temperature is equal to or lower than the determination temperature TW1, the routine proceeds to step 105, where mode B is selected and a series of operations is ended.

Each of the above modes is selected in order to realize the calculated catalyst temperature. If a temperature reduction request is large, a mode A in which a large catalyst temperature reduction such as circulation of cooling water is obtained is selected. On the other hand, if the request for lowering the temperature is small, a mode B in which a small decrease in the catalyst temperature such as a decrease in the exhaust gas temperature such as a change in the ignition timing and the fuel injection timing is obtained is selected. When the temperature of the three-way catalyst 21 is to be lowered, any one or a combination of a plurality of methods can be selected according to the request.

The temperature of the exhaust gas from the engine 1 is
It is easily affected by the amount of heat generated during combustion, and the sensitivity of the air-fuel ratio is greatly affected. That is, as shown in FIG. 12, while the exhaust gas temperature decreases toward the lean air-fuel ratio side,
On the rich air-fuel ratio side, the exhaust gas temperature rises.

Here, as shown in FIG. 13, during stratified combustion, since fuel is distributed in a stratified form, combustion is rapidly terminated near the plug.
The exhaust temperature will further decrease. Therefore, when a request for lowering the catalyst temperature occurs during the lean burn operation, it can be dealt with by switching the combustion such as shifting from lean combustion to stratified combustion.

FIG. 14 shows the stratified combustion characteristics.
The graph shows the sensitivity of the Ox emission amount and the surge (combustion stability) depending on the ignition timing and the fuel injection timing. That is, if the exhaust temperature itself is the same air-fuel ratio, the exhaust valve 1
Since the ignition timing is advanced, the exhaust gas temperature can be lowered because the temperature depends on the time until the valve 2 opens. Therefore, when a request for lowering the exhaust gas temperature occurs during stratified combustion, the NOx
It can also be dealt with by advancing the ignition timing in a region where the surge does not extremely decrease on the line, that is, by shifting the combustion point from.

Further, as shown in FIG. 15, since the combustion characteristics based on the ignition timing and the injection timing in the stratified combustion region have sensitivity depending on the air-fuel ratio, when a request for lowering the exhaust gas temperature occurs, the ignition By further switching the air-fuel ratio by combining the operation of the timing and the injection timing, it is possible to further reduce the exhaust gas temperature.

FIG. 16 shows the bank type engine 14.
This shows the exhaust purification system in the case of
Engine 1 having a plurality of banks such as bank A and bank B
4, in each of banks A and B, three-way catalysts CA
TA and CAT-B are arranged, and the NOx catalyst is arranged behind the collecting portion on the downstream side. In this system, the desired HC and CO amounts may be secured by lowering the purification rate of all of the plurality of three-way catalysts CAT-A and CAT-B. The purification rate of only one of the three-way catalysts such as the three-way catalyst may be reduced. In addition, a plurality of three-way catalysts CAT
-A, to select the target catalyst from CAT-B,
The selection is made in consideration of the arrangement position, rebound to driving performance, responsiveness, capacity, and the like.

FIG. 17 shows an exhaust gas purification time chart of the bank type engine 14. As shown in FIG. In the present embodiment, the purification rate of only the three-way catalyst CAT-A among the two three-way catalysts CAT-A and CAT-B existing in the bank type engine 14 is reduced.

By lowering the catalyst temperature of the three-way catalyst CAT-A to lower its purification rate, the H from the bank A side is reduced.
C and CO emissions YA (YB≪YA) are supplied to the NOx catalyst, and the NOx component passes through the three-way catalyst CAT-A without being purified due to a lean air-fuel ratio. HC and CO not purified by -A
Together with the discharge amount YA, it is possible to purify NOx components by a reducing action in the NOx catalyst.

FIG. 18 shows the characteristics of the change in engine cylinder pressure and the change in combustion temperature due to combustion. In this figure, the reference characteristic is indicated by a broken line, and the characteristic when the combustion speed is increased is indicated by a solid line. By shortening the catalytic combustion period according to the exhaust temperature reduction request,
The temperature of the exhaust gas when the exhaust valve 12 is opened changes from the temperature A to the temperature B, and as a result, a decrease in the exhaust temperature indicated by the reduction allowance 1 can be obtained.

Further, as a method of shortening the catalytic combustion period, when the request for lowering the exhaust gas temperature is generated, the energy to the ignition coil 15 is increased compared to the normal combustion, or the swirl tumble flow is increased by the intake pipe system. I do. Further, in the case of an engine having a variable valve operating mechanism, when a request for lowering the exhaust gas temperature occurs, the exhaust gas at the time of opening the valve can be controlled by intentionally operating the timing of opening the exhaust valve and the lift operation amount. Temperature from temperature A to temperature C
And the exhaust gas temperature can be reduced by the amount indicated by the reduction allowance 2.

As described above, the above embodiment of the present invention
The following functions are provided by the above configuration. That is, the catalyst control device 17A of the engine 1
NO based on any one of signals representing the operating state of the engine (engine parameters such as engine speed, engine load, accelerator operation amount, etc.) or the environmental state such as outside air temperature
supply determining means 17B for determining whether the supply of the HC and CO components serving as the reducing agent to the x catalyst 23 is required, and the purifying rate of the three-way catalyst 21 is intentionally reduced based on the determination result. To reduce the purification rate.
A control amount calculating means 17C for calculating a control amount for one target temperature, and a three-way catalyst control means 17E for controlling the three-way catalyst 21 based on the calculation result of the control amount for the target temperature.
And a purification index detecting means 17D for detecting a purification index of the three-way catalyst 21 as a control result based on a calculation result of the control amount with respect to the target temperature.
The NOx catalyst 23 can be used efficiently, and it is possible to reliably cope with emission and fuel efficiency regulations which will be strengthened in the future.

Further, since the need for rich spike control or the like is eliminated, there is no occurrence of torque fluctuation and shock, and there is no increase in cost. Furthermore, the restriction of the lean operation time and the operation region, the NOx catalyst 2
The concept of the saturation amount of 3 is not required, and the exhaust gas can be reduced and the fuel efficiency can be further improved. As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiments, and various changes may be made in the design without departing from the spirit of the present invention described in the claims. You can do it.

For example, the catalyst control device 17 of the above embodiment
A shows an example in which the catalyst temperature is lowered by operating the engine or the like in order to intentionally lower the purification rate of the catalyst. However, an external parameter that directly lowers the temperature of the catalyst or the exhaust gas is given. In this case, the same effect as described above can be obtained. When a request for lowering the catalyst temperature occurs, a system configured to circulate cooling water through the exhaust pipe, the catalyst, a system configured to apply traveling wind or intentionally generated cooling air, or a system combining these. It may be.

Further, in order to lower the purification rate of the catalyst, in addition to lowering the temperature of the catalyst, it is conceivable to operate the air-fuel ratio or to deteriorate the catalyst. It is possible to improve the fuel economy by expanding the cost merit, the lean operation time, and the operation area.

[0062]

As can be understood from the above description, the engine catalyst control apparatus and method according to the present invention reduce the HC and CO purification rates of the three-way catalyst itself during lean operation, and NOx accumulated by supplying to the NOx catalyst the HC and CO components not purified by
Since the components are reduced and purified, it is possible to improve exhaust emission and further improve fuel efficiency without impairing drivability.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an engine system including a catalyst control device of the present embodiment.

FIG. 2 is a control block diagram of the catalyst control device of FIG.

FIG. 3 is a characteristic diagram showing a purification rate with respect to an air-fuel ratio of the three-way catalyst of FIG.

FIG. 4 is a characteristic diagram showing a purification rate of the three-way catalyst of FIG. 1 with respect to a catalyst temperature.

FIG. 5 is an explanatory diagram of purification rate control.

FIG. 6 is a time chart of a conventional exhaust gas purification.

FIG. 7 is a saturation characteristic diagram of a storable amount of the NOx catalyst.

FIG. 8 is an exhaust gas purification time chart by the catalyst control device of FIG. 2;

FIG. 9 is an operation flowchart of a supply determining unit in the catalyst control device of FIG. 2;

FIG. 10 is an explanatory diagram of estimating the NOx accumulation amount in the NOx catalyst by the supply determining means of FIG. 2;

FIG. 11 is an operation flowchart of a control amount calculation unit and a three-way catalyst control unit in the catalyst control device of FIG. 2;

FIG. 12 is an air-fuel ratio sensitivity characteristic diagram of exhaust gas temperature.

FIG. 13 is a stratified distribution diagram of fuel.

FIG. 14 is a stratified combustion characteristic diagram.

FIG. 15 is a diagram showing air-fuel ratio sensitivity at ignition timing and injection timing during stratified combustion.

FIG. 16 is a configuration diagram of an exhaust gas purification system of a bank type engine including the catalyst control device of FIG. 2;

FIG. 17 is an exhaust gas purification time chart of the bank type system of FIG. 16;

FIG. 18 is a characteristic diagram of in-cylinder pressure and combustion temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 4 Electronic control throttle valve 7 Air flow meter 11 Intake valve 12 Exhaust valve 13 Injector 15 Ignition coil 16 Spark plug 17A Catalyst control device 17B Means for determining whether supply is required 17C Means for calculating control amount 17D Purification Means for detecting index 17E Means for controlling first catalyst 18 Crank angle sensor 20 Exhaust pipe 21 Three-way catalyst (first catalyst) 22 Temperature sensor 23 NOx catalyst (second catalyst)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 13/02 F02D 13/02 H 41/04 305 41/04 305A 43/00 301 43/00 301B 301E 301T 301Z (72) Inventor Hidefumi Iwaki 2520 Oita Takaba, Hitachinaka City, Ibaraki Prefecture Within the Hitachi, Ltd. Automotive Equipment Group (72) Inventor Kentaro Shiga 2520, Oaza Takaba, Hitachinaka City, Ibaraki Prefecture Hitachi, Ltd. Automotive Equipment Group (72) Inventor Toshio Hori 2520 Takahiro, Hitachinaka-shi, Ibaraki Pref.Hitachi, Ltd.Automotive equipment group (72) Inventor Yoshikuni Kurashima 2520 Ojitakaba, Hitachinaka-shi, Ibaraki Automobile equipment Hitachi, Ltd. Group F-term (reference) 3G084 AA04 BA09 BA17 B A23 BA24 DA02 DA10 FA07 FA10 FA27 FA33 3G091 AA12 AA24 AA29 AB03 AB06 BA07 BA14 BA36 CB02 CB05 CB07 DB10 DC03 EA01 EA03 EA07 EA14 EA17 EA18 EA30 EA33 EA39 FC01 HA36 3G092 AA01 AA02 AA13 A03 3G301 HA01 HA04 HA16 JA02 JA21 LA03 MA01 NE13 PA01Z PA17Z PD11Z PE01Z PF03Z

Claims (16)

[Claims] 1. A first catalyst for accelerating oxidation and reduction of an exhaust gas component and a second catalyst for accumulating nitrogen oxides in the exhaust gas by an adsorption or occlusion reaction are sequentially disposed in an exhaust pipe. A catalyst control device for an engine comprising: a catalyst control device for controlling the oxidation and reduction reaction performance of the first catalyst when purification of the second catalyst is required. An engine catalyst control device, characterized in that: 2. The means for determining whether or not it is necessary to supply an exhaust gas component serving as a reducing agent to the second catalyst based on an operating state or an environmental state of the engine. 2. The engine catalyst control device according to claim 1, further comprising: means for calculating a control amount of the oxidation and reduction reaction performance of the first catalyst based on the determination result. 3. The catalyst control device for an engine according to claim 1, wherein the catalyst control device includes means for controlling the first catalyst based on a calculation result of the control amount. . 4. The catalyst control device for an engine according to claim 3, wherein the means for controlling the first catalyst reduces a catalyst temperature of the first catalyst. 5. The means for controlling the first catalyst may be operated by a parameter affecting combustion, an operation of cooling the first catalyst itself, or an operation of cooling the temperature of exhaust gas, or a combination thereof. The catalyst control device for an engine according to claim 4, wherein the catalyst temperature is reduced. 6. The catalyst control device for an engine according to claim 4, wherein the means for controlling the first catalyst reduces the temperature of the catalyst based on a temperature of an exhaust gas of the engine. 7. The engine according to claim 1, wherein the means for controlling the first catalyst changes the temperature of the exhaust gas of the engine by one or a combination of an ignition timing operation and an air-fuel ratio operation. The catalyst control device for an engine according to claim 6. 8. The means for controlling the first catalyst may change the temperature of the exhaust gas of the engine by any one or a combination of an opening and closing timing operation and a lift amount operation of the exhaust and intake valves. 7. The engine catalyst control device according to claim 6, wherein: 9. The catalyst control device for an engine according to claim 6, wherein the means for controlling the first catalyst changes the temperature of the exhaust gas of the engine by operating a combustion speed. 10. The control means for controlling the first catalyst, when a plurality of the first catalysts are provided, reduces the oxidation and reduction reaction performance for each of the plurality of catalysts. A catalyst control device for an engine according to the above. 11. The control means for controlling the first catalyst, when a plurality of the first catalysts are provided, among the plurality of catalysts, oxidation of the first catalyst closest to an exhaust port of the engine. The catalyst control device for an engine according to claim 3, wherein the reduction reaction performance is reduced. 12. The catalyst control device further comprises means for detecting a purification index of the first catalyst and outputting the purification index to a means for determining whether or not the supply of the exhaust gas component is required. The catalyst control device for an engine according to any one of claims 2 to 11, wherein: 13. The catalyst control device for an engine according to claim 1, wherein the first catalyst is a three-way catalyst, and the second catalyst is a NOx catalyst. . 14. A first catalyst for accelerating oxidation and reduction of an exhaust gas component and a second catalyst for accumulating nitrogen oxides in the exhaust gas by an adsorption or occlusion reaction are sequentially disposed in an exhaust pipe. A method for purifying an engine catalyst, comprising: reducing and purifying an exhaust gas component supplied to the second catalyst by reducing a purification rate of the first catalyst. A method for purifying an engine catalyst, comprising: 15. The method according to claim 14, wherein the purification rate of the first catalyst is reduced by lowering the temperature of the first catalyst. 16. The method according to claim 15, wherein the temperature of the first catalyst is lowered by controlling the temperature of exhaust gas of the engine.