JP4345202B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to NO in exhaust gas when the air-fuel ratio that is an oxygen-excess atmosphere is a lean air-fuel ratio. _x Is stored (absorbed or adsorbed) and stored when the air-fuel ratio is reduced to the stoichiometric or rich air-fuel ratio. _x Catalyst device (NO _x The present invention relates to an exhaust gas purification apparatus for an internal combustion engine having a catalyst) in an exhaust passage.
[0002]
[Prior art]
In recent years, lean combustion internal combustion engines that enable combustion at a lean air-fuel ratio have been put into practical use in order to improve fuel efficiency. In this lean combustion internal combustion engine, NO in the exhaust gas during lean combustion is due to the purification characteristics of the conventional three-way catalyst. _x There is a problem that cannot be sufficiently purified. Therefore, in recent years, for example, NO in exhaust gas during lean combustion _x Occluded and exhausted NO _x Catalyst device (NO _x Catalyst) has been adopted.
[0003]
NO _x The catalyst is NO in an oxygen-rich atmosphere (lean air-fuel ratio). _x NO in the exhaust by storing the catalyst on the catalyst _x When the oxygen concentration decreases (theoretical air-fuel ratio or rich air-fuel ratio), the attached NO _x It is known that it has a function of releasing. That is, NO _x In an atmosphere with excess oxygen concentration, the catalyst is _x To produce nitrates from NO _x In an atmosphere where oxygen concentration is reduced, NO _x Nitrate occluded in the catalyst reacts with CO in the exhaust to produce carbonate, which produces NO. _x Are to be released.
[0004]
NO _x The catalyst is NO in an oxygen-excess atmosphere during lean operation. _x Will be occluded on the catalyst. _x When the amount of occlusion reaches the saturation level, NO in the exhaust _x Most of it will be discharged into the atmosphere. So NO _x Before the amount of occlusion reaches the saturation level, the air-fuel ratio is switched to the stoichiometric or rich air-fuel ratio, and the exhaust is made into an atmosphere in which the oxygen concentration is reduced to NO. _x NO reduction and NO _x NO of catalyst _x I try to restore the storage capacity. And NO _x When the engine air-fuel ratio is switched to the stoichiometric air-fuel ratio or rich air-fuel ratio in order to restore the storage capacity, the air-fuel ratio is gradually changed to the stoichiometric air-fuel ratio or rich side to suppress NO torque while suppressing engine torque shock. _x A technique for releasing and reducing is known, for example, in JP-A-7-66913.
[0005]
NO _x In order to restore the storage capacity, the engine air-fuel ratio is switched to the stoichiometric air-fuel ratio or rich air-fuel ratio (CO is generated and exhausted, ie, NO _x NO supplied to the catalyst) _x When CO is released and reduced, the supplied CO is stored as NO. _x NO is released because some CO is consumed to release _x The remaining CO is consumed to reduce the amount. NO reduced by this remaining reducing agent such as CO and HC _x And the released NO _x If the percentages match, NO _x In addition, the atmospheric emission of CO can be suppressed.
[0006]
However, in the technique actually disclosed in the above publication, NO to be reduced is reduced. _x And released NO _x It is difficult to match the ratio with. First, NO _x NO depending on the type and amount of catalyst components supported on the catalyst _x NO in catalyst _x Occupancy recovery performance, i.e. occluded NO _x Ease of release (NO _x This is because the (release rate) changes.
[0007]
Because of this, NO _x NO with improved recovery performance of storage capacity _x When using a catalyst, NO _x NO released from the catalyst _x Release rate is also improved and NO is reduced by the reducing agent present in the exhaust gas _x NO released _x Below (reduced NO _x <NO released _x ) And the residual NO remaining in the exhaust gas without being reduced _x Will be discharged into the atmosphere. Conversely, NO _x NO with low storage capacity recovery performance _x If a catalyst is used, the reduced NO _x NO released _x (NO to be reduced) _x > NO released _x That is, a reducing agent (CO or the like) remains in the exhaust gas and is released into the atmosphere.
[0008]
Also generally NO _x Since the release speed increases as the air-fuel ratio of the engine shifts to the rich side (as the CO amount increases), when shifting the air-fuel ratio to the theoretical air-fuel ratio or rich air-fuel ratio side as described in the above publication, NO _x The release rate rises from near the stoichiometric air-fuel ratio where the amount of CO increases, and the NO released from the catalyst _x Release amount increases. But increased NO _x NO released relative to the amount released _x Reducing agent (NO _x The remaining CO and HC that have not contributed to the emission) is low, so the released NO remaining in the exhaust gas _x Will not be reduced and will be released into the atmosphere.
[0009]
As a solution to this, it is conceivable to increase the amount of reducing agent by making the air-fuel ratio of the engine more rich, but in this case, the amount of CO as the reducing agent also increases, so that the released NO _x In fact, the above-mentioned reduced NO _x <NO released _x , The relationship is not changed, and in the end, NO remains without being reduced _x Is released into the atmosphere as it is, and the above problem cannot be solved.
[0010]
Therefore, in the technique disclosed in the above publication, NO to be reduced is reduced. _x And released NO _x Is almost impossible to match, NO from the catalyst _x This causes a problem of deteriorating the exhaust gas characteristics when releasing and reducing gas.
[0011]
Therefore, it is considered to supplement the shortage of reducing agent by additionally supplying fuel that does not contribute to combustion. As a conventional example of supplying additional fuel, for example, in Japanese Patent Laid-Open No. 2000-38942, when a rich spike is performed during lean operation, an additional reducing agent is supplied and released by executing secondary fuel injection. NO _x NO _x A technique for preventing spillage of the liquid is disclosed. That is, in the above publication, when the rich spike operation is performed during the lean operation, the rich spike operation is performed when passing through the weak lean air-fuel ratio region, until the target rich air-fuel ratio is reached from the start of the rich spike, or NO released in weak lean operation area by performing secondary fuel injection before _x Has been disclosed that prevents the catalyst from flowing out without being purified due to a shortage of reducing agent.
[0012]
[Problems to be solved by the invention]
However, in the conventional technology described above, NO _x Is not considered until the timing of the release of additional reducing agent and the arrival of additional reducing agent _x However, there is a problem that the amount of reducing agent tends to be excessive and the amount of HC, CO 2 emissions increases.
[0013]
The present invention has been made in view of the above situation, and in a state where the supply delay of the reducing agent is compensated, the catalyst device (NO _x NO released from the catalyst) _x An object of the present invention is to provide an exhaust purification device for an internal combustion engine that can reliably reduce the amount of exhaust gas.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is such that when the exhaust air-fuel ratio of the engine switches from the lean air-fuel ratio to the stoichiometric air-fuel ratio or rich air-fuel ratio, _x NO released from the catalytic device _x NO is supplied without reducing the exhaust gas performance. _x NO released from the catalytic device _x Reduce.
[0015]
The operating time of the reducing agent supply means is NO released _x Is excessive with respect to the reducing agent in the exhaust, and the reducing agent is _x NO that is controlled based on the delay time until the catalyst device is reached and is released when shifting to the operation at the stoichiometric or rich air-fuel ratio _x Balances the timing at which the excess of reducing agent arrives with the timing at which the additional reducing agent arrives, while suppressing the excess of reducing agent while reducing NO _x Surely reduce.
[0016]
In addition, when the engine shifts from a lean air-fuel ratio operation to a stoichiometric or rich air-fuel ratio operation, NO _x NO released from the catalytic device _x The timing when the exhaust gas becomes excessive with respect to the reducing agent in the exhaust gas, _x Until the delay time until the catalyst device is reached, it is prohibited to enrich the air-fuel ratio at the excessive timing, and the released NO _x Prevents NO from becoming excessive with respect to the reducing agent in the exhaust. _x NO released from the catalytic device _x Surely reduce.
[0017]
When the engine is an in-cylinder injection internal combustion engine having an injection valve that directly injects fuel into the combustion chamber, the reducing agent supply means has an expansion stroke after the main injection (intake stroke injection or compression stroke) of the injection valve. Alternatively, a means for injecting fuel during the exhaust stroke is preferable. This eliminates the need for complex devices and NO released from the catalytic device _x Can be reliably reduced.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a schematic configuration of an internal combustion engine equipped with an exhaust purification apparatus according to an embodiment of the present invention, FIG. 2 shows a block configuration of the exhaust purification apparatus, and FIG. _x Figure 4 and Figure 5 show NO emissions from the exhaust purification system. _x The flowchart showing the release status of
[0019]
A multi-cylinder in-cylinder injection internal combustion engine will be described as an example of the internal combustion engine provided with the exhaust emission control device of this embodiment. As the multi-cylinder in-cylinder internal combustion engine, for example, an in-cylinder in-line four-cylinder gasoline engine (in-cylinder injection engine) 1 that directly injects fuel into a combustion chamber is applied. For example, the in-cylinder injection engine 1 can perform fuel injection in the intake stroke (intake stroke injection mode) or fuel injection in the compression stroke (compression stroke injection mode) by switching the combustion mode (operation mode). ing. The in-cylinder injection engine 1 can be operated at a lean air-fuel ratio (lean air-fuel ratio operation) in addition to an operation at a stoichiometric air-fuel ratio (stoichiometric) or an operation at a rich air-fuel ratio (rich air-fuel ratio operation). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio that has a larger air-fuel ratio than a lean air-fuel ratio operation in the intake stroke.
[0020]
As shown in FIG. 1, a spark plug 3 is attached to each cylinder of the cylinder head 2 of the direct injection engine 1, and an electromagnetic fuel injection valve 4 is attached to each cylinder. An injection port of the fuel injection valve 4 is opened in the combustion chamber 5 so that the fuel injected from the fuel injection valve 4 is directly injected into the combustion chamber 5. A piston 7 is supported on the cylinder 6 of the direct injection engine 1 so as to be slidable in the vertical direction, and a hemispherical cavity 8 is formed on the top surface of the piston 7. The cavity 8 generates a clockwise reverse tumble flow in FIG.
[0021]
An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 9 is connected so as to communicate with each intake port. Further, an exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of the exhaust manifold 10 is connected so as to communicate with each exhaust port. The exhaust manifold 10 is provided with an EGR device (not shown).
[0022]
On the other hand, an exhaust pipe (exhaust passage) 11 is connected to the exhaust manifold 10 of the engine 1, and a muffler (not shown) is connected via a small three-way catalyst 12 close to the engine 1 and an exhaust purification catalyst device 13 as a catalyst device. Has been. A portion of the exhaust pipe 11 between the three-way catalyst 12 and the exhaust purification catalyst device 13 is located immediately upstream of the exhaust purification catalyst device 13, that is, NO to be described later. _x A high temperature sensor 14 for detecting the exhaust temperature is provided immediately upstream of the catalyst 15.
[0023]
The exhaust purification catalyst device 13 is NO when the exhaust air-fuel ratio that becomes an oxygen-excess atmosphere is a lean air-fuel ratio. _x NO in the exhaust by storing the catalyst on the catalyst _x NO is deposited when the oxygen concentration decreases and the exhaust air / fuel ratio is the stoichiometric or rich air / fuel ratio. _x NO with the function of releasing and reducing _x Catalyst 15 (NO _x Catalyst device) and CO, HC and NO in a stoichiometric air-fuel ratio atmosphere _x And a three-way catalyst 16 having a three-way function capable of purifying water. Three-way catalyst 16 is NO _x It is disposed downstream of the catalyst 15 and NO. _x NO released from catalyst 15 _x NO _x NO that could not be reduced by catalyst 15 _x The reduction is also performed. The configuration of the exhaust purification catalyst device 13 is NO. _x As long as at least one catalyst 15 is provided, the arrangement, function, and the like are not limited to the above embodiment.
[0024]
NO _x The catalyst 15 is NO in an oxidizing atmosphere. _x In the reducing atmosphere where mainly CO is present. _x N ₂ NO reduced to (nitrogen) etc. _x It has a release reduction function. Specifically, NO _x The catalyst 15 is configured as a catalyst having platinum (Pt), palladium (Pd) or the like as a noble metal, and an alkali metal such as barium (Ba) or an alkaline earth metal is employed as a storage agent. Further, the downstream side of the exhaust purification catalyst device 13 is NO. _x NO to detect concentration _x A sensor 17 is provided.
[0025]
On the other hand, a drive-by-wire (DBW) type electric throttle valve 21 is connected to the intake manifold 9, and the throttle valve 21 is provided with a throttle position sensor 22 for detecting the throttle opening θth. The engine 1 is provided with a crank angle sensor 23 that detects a crank angle, and the crank angle sensor 23 can detect an engine rotational speed Ne.
[0026]
An electronic control unit (ECU) 31 is provided in the vehicle, and the ECU 23 includes an input / output device, a storage device for storing a control program, a control map, and the like, a central processing unit, a timer, and counters. The ECU 31 performs comprehensive control of the exhaust purification system of this embodiment including the in-cylinder injection engine 1. Detection information of various sensors is input to the ECU 31. The ECU 31 determines the ignition timing and the like including the fuel injection mode and the fuel injection amount based on the detection information of the various sensors, and the fuel injection valve 4, the ignition plug 3, etc. Is controlled.
[0027]
In the in-cylinder injection engine 1, the intake air flow that flows into the combustion chamber 5 from the intake manifold 9 forms a reverse tumble flow, and fuel is injected after the middle of the compression stroke to use the reverse tumble flow and the top of the combustion chamber 5. A small amount of fuel is collected only in the vicinity of the spark plug 3 disposed at the center, and an extremely lean air-fuel ratio is obtained at a portion separated from the spark plug 3. By setting only the vicinity of the spark plug 3 to the stoichiometric air-fuel ratio or a rich air-fuel ratio, fuel consumption is suppressed while realizing stable stratified combustion (stratified super lean combustion).
[0028]
In addition, when high output is obtained from the direct injection engine 1, the fuel from the fuel injection valve 4 is injected into the intake stroke to be homogenized throughout the combustion chamber 5, and the inside of the combustion chamber 5 is stoichiometric or lean. Premixed combustion is performed in an air-fuel mixture state at a fuel ratio. Of course, since the stoichiometric air-fuel ratio or the rich air-fuel ratio can provide a higher output than the lean air-fuel ratio, the fuel injection is performed at such a timing that the atomization and vaporization of the fuel is sufficiently performed. I try to get high output well.
[0029]
The ECU 31 calculates a target in-cylinder pressure corresponding to the engine load, that is, a target average effective pressure Pe, based on an accelerator opening from an accelerator opening sensor (not shown) and an engine rotational speed Ne from the crank angle sensor 23. The fuel injection mode is set from a map (not shown) according to the target average effective pressure Pe and the engine speed Ne. For example, when the target average effective pressure Pe and the engine rotational speed Ne are both small, the fuel injection mode is set to the compression stroke injection mode, and fuel is injected in the compression stroke, while the target average effective pressure Pe is increased, or When the engine speed Ne increases, the fuel injection mode is changed to the intake stroke injection mode, and fuel is injected in the intake stroke. Then, a target air-fuel ratio (target A / F) that is a control target in each fuel injection mode is set from the target average effective pressure Pe and the engine rotational speed Ne, and an appropriate amount of fuel injection amount is set to this target A / F. To be determined.
[0030]
NO of the exhaust purification catalyst device 13 _x In the catalyst 15, when the air-fuel ratio in the exhaust gas that becomes an oxygen-rich atmosphere as in the super-lean combustion operation in the lean mode is the lean air-fuel ratio, the NO in the exhaust gas _x Is stored as nitrate to purify the exhaust. On the other hand, when the air-fuel ratio in the exhaust gas in which the oxygen concentration is reduced and the oxygen excess atmosphere is the stoichiometric or rich air-fuel ratio, NO _x The nitrate stored in the catalyst 15 reacts with the CO in the exhaust to produce carbonate and NO. _x Is released. Therefore, NO _x NO to catalyst 15 _x As oxygen storage proceeds, the air concentration is reduced or additional fuel injection is performed to reduce the oxygen concentration and supply CO. _x NO from catalyst 15 _x NO reduction _x Maintain occlusion function.
[0031]
As shown in FIG. 2, the ECU 31 reduces the oxygen concentration in the exhaust gas (NO in the exhaust gas atmosphere). _x NO from catalyst 15 _x NO to release _x Discharge means 32 is provided. NO _x The discharge means 32 is NO _x NO from catalyst 15 _x Based on the command to release (regeneration command), the stored NO _x Occlusion type NO _x When released from the catalyst 15 and reduced (NO _x Purging), a function of setting the exhaust air-fuel ratio to a rich air-fuel ratio or near the stoichiometric air-fuel ratio (theoretical air-fuel ratio or slightly richer than the stoichiometric air-fuel ratio), that is, a regeneration function.
[0032]
Further, the ECU 31 is provided with a reducing agent supply means 33, and the reducing agent supply means 33 in the present embodiment is NO. _x NO by discharge means 32 _x NO released at a predetermined time during the release operation period _x This is a pulse injection means for injecting additional fuel at the latter stage of the expansion stroke (or at the beginning of the exhaust stroke) in order to additionally supply a reducing agent that reduces the amount of fuel.
[0033]
On the other hand, the ECU 31 is provided with a timing deriving unit 51. The timing deriving unit 51 determines NO when the in-cylinder injection engine 1 shifts from a lean air-fuel ratio operation to a stoichiometric or rich air-fuel ratio operation. _x NO discharged from catalyst 15 _x Is determined based on memory or calculation. That is, NO _x NO release _x NO discharged from catalyst 15 _x NO increased and reduced _x NO released _x (NO to be reduced) _x > NO released _x ) NO reduced _x NO released _x Below (reduced NO _x <NO released _x ) Is determined by the timing deriving means 51 with reference to the air-fuel ratio AFP (for example, the theoretical air-fuel ratio) at this time, for example.
[0034]
NO _x As the timing of the excess, the air-fuel ratio AFP (NO _x <NO released _x ) As long as it is correlated with the time ₂ Concentration, NO _x Concentration, NH _Three At least one of the concentrations may be detected by a gas sensor and used.
[0035]
NO to be reduced _x NO released _x Below (reduced NO _x <NO released _x ) Become NO _x The air-fuel ratio when the engine becomes excessive is the exhaust flow rate, intake flow rate, exhaust temperature, catalyst temperature, exhaust pipe temperature, engine speed, net average effective rate, indicated average effective rate, volumetric efficiency, manifold pressure, water temperature, oil A value corresponding to at least one of the operating conditions of the temperature can be obtained on a map. In addition to the map, a fixed value or a value corrected by a gas sensor can be used. That is, the air-fuel ratio AFP can be appropriately obtained by storage or calculation according to the operating state.
[0036]
Further, the ECU 31 is provided with a delay time deriving means 52, and the delay time deriving means 52 causes the reducing agent to be NO from the operation of the reducing agent supply means 33. _x A time (delay time) Tα until the catalyst 15 is reached is obtained based on storage or calculation. That is, even if the reducing agent supply means 33 is operated, depending on the operating conditions, physical and chemical adsorption to the exhaust system, NO _x Due to the delay of the reduction reaction, temporary oxidation of the reducing agent, etc., there is a delay in reaching the reducing agent, and the released NO _x May increase. For this reason, the reducing agent is actually changed to NO by the delay time deriving unit 52 from the operation of the reducing agent supply unit 33. _x A delay time Tα until the catalyst 15 is reached is obtained.
[0037]
Reducing agent is NO _x Delay time to reach the catalyst 15 is exhaust flow rate, intake flow rate, exhaust temperature, catalyst temperature, exhaust pipe temperature, engine speed, net average effective rate, illustrated average effective rate, volume efficiency, manifold pressure, water temperature, oil A value corresponding to at least one of the operating conditions of the temperature can be obtained on a map. In addition to the map, a fixed value or a value corrected by a gas sensor can be used. That is, the delay time can be appropriately obtained by storage or calculation according to the driving state.
[0038]
The timing of the air-fuel ratio AFP obtained by the timing deriving means 51 and the delay time Tα obtained by the delay time deriving means 52 are input to the control means 53, and the reducing agent is supplied based on the timing of the air-fuel ratio AFP and the delay time Tα. The operation of the means 33 is controlled by the control means 53. That is, when the regeneration command is input to the control means 53, the operation of the reducing agent supply means 33 is controlled based on the timing of the air-fuel ratio AFP and the delay time Tα, and pulse injection is executed at a predetermined timing.
[0039]
As a result, the NO released at the time of transition from the operation at the lean air-fuel ratio to the operation at the stoichiometric air-fuel ratio or rich air-fuel ratio is released. _x And when the excess reducing agent is NO _x The timing to reach the catalyst 15 can be balanced, and NO can be reduced while suppressing excessive reducing agent. _x Can be reliably reduced.
[0040]
Further, in the control means 53, the air-fuel ratio becomes higher than the air-fuel ratio AFP obtained by the timing deriving means 51 until the delay time Tα obtained by the delay time deriving means 52 elapses from the operation of the reducing agent supply means 33. NO to avoid enrichment _x The operation of the discharge means 32 is controlled. That is, when the regeneration command is input to the control means 53, the air-fuel ratio AFP at the timing obtained by the timing deriving means 51 becomes richer until the delay time Tα obtained by the delay time deriving means 52 elapses. NO with banned _x The discharge means 32 is activated.
[0041]
As a result, until the delay time Tα elapses, the NO due to enrichment is reduced. _x NO release is suppressed _x Prevents NO from becoming excessive with respect to the reducing agent in the exhaust. _x NO released from catalyst 15 _x Can be reliably reduced.
[0042]
The pulse injection means is NO _x NO by discharge means 32 _x It operates to inject additional fuel at a later stage of the expansion stroke (or at the beginning of the exhaust stroke) at a predetermined time during the release operation period of NO. _x The engine may be operated when the air-fuel ratio of the engine is switched to the stoichiometric air-fuel ratio or the rich air-fuel ratio regardless of the release means 32. That is, when the engine air-fuel ratio switches from the lean air-fuel ratio to the stoichiometric air-fuel ratio or rich air-fuel ratio at the time of acceleration, air-conditioner, power steering operation, etc., when the negative pressure of the brake master bag is ensured, etc. NO _x When the storage amount of the catalyst 15 is reduced (for example, NO _x High temperature conditions where the temperature of the catalyst 15 is 500 ° C. or higher, for example, NO _x Inflow NO of catalyst 15 _x Conditions under which the concentration decreases, etc.) _x Naturally without operating the discharge means 32 _x At this time, it is also possible to operate the pulse injection means at the later stage of the expansion stroke (or early in the exhaust stroke) to inject additional fuel.
[0043]
The basic operation of the above-described exhaust purification device will be described with reference to FIG.
[0044]
NO of the exhaust purification catalyst device 13 _x In the catalyst 15, when the air-fuel ratio in the exhaust gas that becomes an oxygen-rich atmosphere as in the layered super-lean combustion operation in the lean mode is the lean air-fuel ratio, the NO in the exhaust gas _x Is oxidized to form nitrate, which is _x Is stored and the exhaust gas is purified. On the other hand, NO _x When the air-fuel ratio in the exhaust gas in the atmosphere where the oxygen concentration is reduced becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, the catalyst 15 _x Nitrate occluded in the catalyst 15 reacts with CO in the exhaust to produce carbonate, which results in NO. _x Is released. Therefore, NO _x NO to catalyst 15 _x For example, when the accumulated time of lean operation exceeds a predetermined time, the regeneration command is sent via the control means 53 to NO. _x Sent to discharge means 32, NO _x The release means 32 controls the air / fuel ratio to the stoichiometric or rich air / fuel ratio to reduce the oxygen concentration, and NO _x NO from catalyst 15 _x Release NO _x The function of the catalyst 15 is maintained (regeneration operation).
[0045]
That is, as shown in FIG. 3 (a), the target air-fuel ratio is gradually changed to the rich air-fuel ratio side, and the exhaust atmosphere is changed to an oxygen concentration-reduced atmosphere (NO _x Operation of the discharge means 32). When the target air-fuel ratio is changed to the rich air-fuel ratio side, as shown by the dotted line in FIG. _x Due to the nature of the supported noble metal, the catalyst 15 is NO. _x NO by discharge means 32 _x CO is supplied from the vicinity of the theoretical air-fuel ratio immediately after the start of the release operation of NO and NO _x Begins to be released, but released NO _x NO is released because there is no reducing agent (remaining CO, HC, etc.) _x > NO to be reduced _x , Become NO _x NO released from catalyst 15 _x NO not reduced _x Is released into the atmosphere as it is.
[0046]
Therefore, the released NO is released by the reducing agent supply means 33 during the regeneration operation. _x As shown in Fig. 3 (c), because it does not contribute to the combustion, as shown in Fig. 3 (c), it does not contribute to the combustion, so it does not affect the engine output and at the same time uncombusted HC ( After the expansion stroke, which is the timing at which the reducing agent) can be supplied, preferably at the later stage of the expansion stroke (or at the beginning of the exhaust stroke), the drive pulse is started and the fuel injection valve 4 is driven to inject additional fuel (pulse injection). . The additional amount of fuel is NO released _x Is set according to
[0047]
As a result, as indicated by the solid line in FIG. _x NO is reduced and released into the atmosphere _x The amount can be suppressed. Therefore, NO _x And atmospheric emissions of CO can be suppressed, and released NO _x Will not be released into the atmosphere as it is.
[0048]
When supplying the additional fuel for adding the reducing agent, the in-cylinder injection engine 1 is switched from the operation at the lean air-fuel ratio to the operation at the stoichiometric or rich air-fuel ratio. _x NO discharged from catalyst 15 _x The air-fuel ratio AFP is determined by the timing deriving means 51 as the timing at which becomes excessive with respect to the reducing agent in the exhaust gas. In addition, the reducing agent is NO from the operation of the reducing agent supply means 33 _x The delay time Tα until reaching the catalyst 15 is obtained by the delay time deriving means 52. Therefore, as shown in FIG. 3C, the time T of the air-fuel ratio AFP obtained by the timing deriving means 51 is obtained. _Three Time T before delay time Tα ₂ At this point, pulse injection is executed.
[0049]
As described above, the supply of the additional fuel is performed after the expansion stroke, preferably at the later stage of the expansion stroke (or at the beginning of the exhaust stroke), so that the capacity in the combustion chamber 5 is sufficiently secured and immediately after the fuel is supplied. As a result, the exhaust valve is opened and a flow is generated, so that fuel does not adhere to the spark plug 3.
[0050]
NO _x The catalyst 19 is appropriately selected from the noble metal to be supported, and NO. _x Release rate (NO _x Amount released) and NO _x Reduction rate (NO _x It is preferable to adjust so that the difference in reduction amount is as small as possible. Thereby, the amount of additional fuel can be reduced.
[0051]
Specific actions of the above-described exhaust purification device will be described in detail with reference to FIGS. 4 and 5.
[0052]
As shown in FIG. 4, it is determined in step S1 whether or not the temperature T of the three-way catalyst 16 has become equal to or higher than Ts (estimated by the exhaust gas temperature value detected by the high temperature sensor 14). Is determined to be equal to or higher than Ts (that is, the three-way catalyst 16 has reached the activation temperature Ts and the storage type NO. _x NO purged from catalyst 15 _x In step S2, the lean mode duration Lt is equal to or longer than the first specified time t1, or the lean mode duration Lt is equal to or longer than the second specified time t2 and from the lean mode. It is determined whether or not the mode is switched to the stoichiometric mode. The first specified time t1 (lean duration time) is, for example, a determination condition when the operation in the lean mode is continuously performed, which is set to 30 seconds. The second specified time t2 is, for example, This is a determination condition when the acceleration is set to 5 seconds and the vehicle is accelerating from the lean mode.
[0053]
If any of the conditions are met in step S2 (in the case of YES), the stored NO _x Occlusion type NO _x Control to release and reduce from catalyst 15 (NO _x Purge start condition is satisfied, NO _x In step S3, the time for executing the purge and the time for executing the pulse injection are set. NO _x The purge execution time is the last lean mode duration, exhaust flow rate, NO _x It is set based on the degree of deterioration of the catalyst 15 or the like.
[0054]
NO in step S3 _x After setting the time for executing the purge and the time for executing the pulse injection, NO is determined in step S4. _x Perform a purge. NO _x For example, the purge is performed so that the exhaust air-fuel ratio becomes a rich air-fuel ratio for a predetermined time, and then the exhaust air-fuel ratio is released for a predetermined time. _x NO reduced _x The purge is executed so that the AFP is balanced, or the air / fuel ratio is slightly richer than the stoichiometric air / fuel ratio. At this time, the ignition timing, the intake air amount, the fuel injection timing, the target EGR opening degree, and the like are appropriately controlled so that the lean mode and NO _x A torque step is not caused at the time of purging, and air-fuel ratio tailing is performed at the time of switching to reduce a torque shock caused by the switching so that the air-fuel ratio is not changed suddenly.
[0055]
From the operation of the reducing agent supply means 33, the reducing agent is NO. _x The delay time Tα until reaching the catalyst 15 is detected in step S5, and in step S6, the current time T ₁ Is the time T of the air-fuel ratio AFP obtained by the timing deriving means 51. _Three Time T before delay time Tα ₂ Whether or not, i.e. NO released _x > NO to be reduced _x It is determined whether or not it is before the delay time Tα. Current time T ₁ Is the air-fuel ratio AFP time T _Three Time T before delay time Tα ₂ If it is determined in step S6 that the operation has been completed, the flow proceeds to step S7 and pulse injection is executed. In step S6, the current time T ₁ Is time T ₂ If it is determined that it is not, the process proceeds to step S5.
[0056]
For this reason, NO released _x > NO to be reduced _x The pulse injection is executed at the timing before the delay time Tα from the time of the air-fuel ratio AFP at the predetermined timing, and the predetermined amount of reducing agent is NO _x The catalyst 15 is reached. Pulse injection is desirable from the middle stage of the expansion stroke to the early stage of the exhaust stroke, particularly the latter stage of the expansion stroke. By adding fuel at the latter stage of the expansion stroke, unburned fuel (reducing agent) can be introduced into the exhaust passage without burning. NO supplied and released on catalyst _x Used for reduction of Further, even if fuel is injected from the expansion stroke to the exhaust stroke, the output of the direct injection engine 1 is hardly affected.
[0057]
When pulse injection is started, that is, at time T in FIG. ₂ Then, the routine shown in FIG. 5 is executed, and the air-fuel ratio of the main injection is limited to the lean side from the air-fuel ratio AFP or the air-fuel ratio AFP until the delay time Tα elapses. That is, NO released in step S11. _x > NO to be reduced _x A predetermined timing (air-fuel ratio AFP) is detected, and it is determined in step S12 whether or not the delay time Tα has elapsed. When it is determined that the delay time Tα has not elapsed, that is, the current time is T ₂ And T _Three If it is determined that the air-fuel ratio is between, the air-fuel ratio of the main injection is made smaller than the air-fuel ratio AFP (richer than the air-fuel ratio AFP) in step S13. If it is determined in step S12 that the delay time Tα has elapsed, that is, the current time is T _Three If it is determined that it is after that, the prohibition of the air-fuel ratio of the main injection from becoming smaller than the air-fuel ratio AFP (richer than the air-fuel ratio AFP) is canceled in step S14.
[0058]
This prohibits the air-fuel ratio from being made richer than the air-fuel ratio AFP until the delay time Tα elapses. _x NO release is suppressed _x Is prevented from becoming excessive with respect to the reducing agent in the exhaust, NO _x NO released from catalyst 15 _x Can be reliably reduced.
[0059]
When the in-cylinder injection engine 1 shifts from the lean operation to the operation at the stoichiometric air-fuel ratio or the rich air-fuel ratio (regeneration operation or the like), the above-described exhaust purification device NO _x NO released from catalyst 15 _x Is excessive with respect to the reducing agent in the exhaust gas (the timing when the air-fuel ratio becomes AFP), and the reducing agent supplied by the operation of the reducing agent supply means 33 is NO. _x Based on the delay time Tα until reaching the catalyst 15, the operation timing of the pulse injection for supplying the additional reducing agent is controlled. For this reason, NO released when shifting from lean air-fuel ratio operation to stoichiometric or rich air-fuel ratio operation _x And when the excess reducing agent is NO _x The timing of reaching the catalyst 15 can be balanced. Therefore, NO is suppressed while suppressing excessive reducing agent. _x Can be reliably reduced.
[0060]
In addition, the above-described exhaust purification device is configured so that when the in-cylinder injection engine 1 shifts from lean operation to operation at the stoichiometric air-fuel ratio or rich air-fuel ratio (regeneration operation or the like), NO _x NO released from catalyst 15 _x The reducing agent supplied by the operation of the reducing agent supply means 33 is NO with respect to the air / fuel ratio at the timing at which the exhaust becomes excessive with respect to the reducing agent in the exhaust (the timing at which the air / fuel ratio becomes AFP). _x Until the delay time Tα until the catalyst 15 is reached, the enrichment of the air-fuel ratio is prohibited. Because of this, NO _x NO can be suppressed and released _x Prevents NO from becoming excessive with respect to the reducing agent in the exhaust. _x NO released from catalyst 15 _x Can be reliably reduced.
[0061]
In the above embodiment, the control considering the delay time Tα is introduced for both the execution of the pulse injection and the change of the air-fuel ratio. However, the control considering the delay time Tα is introduced only for one of them. It is good also as what to do. In the above embodiment, the spark ignition type engine in which the fuel is directly injected into the combustion chamber is described as an example of the engine to which the exhaust purification device is applied. _x NO with catalyst 15 _x The engine can be applied to a diesel engine or a spark ignition type lean burn engine in which fuel is injected into an intake pipe and an air-fuel mixture is introduced into a combustion chamber. When the present invention is applied to an engine that introduces an air-fuel mixture into the combustion chamber, as a reducing agent supply means, additional fuel may be injected into the exhaust passage to supply additional reducing agent.
[0062]
【The invention's effect】
In the exhaust gas purification apparatus for an internal combustion engine according to claim 1, NO released when shifting from operation at a lean air-fuel ratio to operation at a stoichiometric air-fuel ratio or rich air-fuel ratio. _x And when the excess reducing agent is NO _x The timing to reach the catalytic device can be balanced, so NO _x Can be reliably reduced.
[0063]
In the exhaust gas purification apparatus for an internal combustion engine according to claim 2, the reducing agent supplied by the operation of the reducing agent supply means is NO. _x NO until the delay time to reach the catalyst unit elapses. _x Because the air-fuel ratio is prohibited from being enriched with respect to the air-fuel ratio at the timing when the exhaust gas becomes excessive relative to the reducing agent in the exhaust, _x NO can be suppressed and released _x Prevents NO from becoming excessive with respect to the reducing agent in the exhaust. _x NO released from the catalytic device _x Can be reliably reduced.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an internal combustion engine provided with an exhaust purification device according to an embodiment of the present invention.
FIG. 2 is a block diagram of an exhaust purification device.
[Figure 3] NO _x Time chart showing the release situation of the.
[Fig. 4] NO by exhaust purification device _x The flowchart showing the discharge | release condition of.
[Fig. 5] NO by exhaust purification device _x The flowchart showing the discharge | release condition of.
[Explanation of symbols]
1 In-cylinder injection engine
3 Fuel injection valve
13 Exhaust gas purification catalyst device
15 NO _x catalyst
31 Electronic control unit (ECU)
32 NO _x Release means
33 Reducing agent supply means
51 Timing deriving means
52 Delay time deriving means
53 Control means

Claims (3)

NO _x having a function of storing NO _x in the exhaust when the air-fuel ratio of the exhaust flowing into the engine exhaust passage is a lean air-fuel ratio and releasing the stored NO _x when the air-fuel ratio is the stoichiometric or rich air-fuel ratio A catalytic device;
When the engine shifts from a lean air-fuel ratio operation to a stoichiometric or rich air-fuel ratio operation, the timing at which NO _x released from the NO _x catalyst device becomes excessive with respect to the reducing agent in the exhaust gas is set. Timing deriving means for obtaining based on memory or calculation;
Reducing agent supply means for supplying an additional reducing agent to NO _x released from the NO _x catalyst device;
Delay time deriving means for obtaining a delay time from the operation of the reducing agent supply means until the reducing agent reaches the NO _x catalyst device based on memory or calculation, timing obtained by the timing deriving means, and the delay time An exhaust emission control device for an internal combustion engine, comprising: control means for controlling the operation timing of the reducing agent supply means based on the delay time obtained by the derivation means. NO _x having a function of storing NO _x in the exhaust when the air-fuel ratio of the exhaust flowing into the engine exhaust passage is a lean air-fuel ratio and releasing the stored NO _x when the air-fuel ratio is the stoichiometric or rich air-fuel ratio A catalytic device;
When the engine shifts from a lean air-fuel ratio operation to a stoichiometric or rich air-fuel ratio operation, the timing at which NO _x released from the NO _x catalyst device becomes excessive with respect to the reducing agent in the exhaust gas is set. Timing deriving means for obtaining based on memory or calculation;
Reducing agent supply means for supplying additional reducing agent to NO _x released from the NO _x catalyst device when the engine shifts from a lean air-fuel ratio operation to a stoichiometric air-fuel ratio or rich air-fuel ratio operation When,
A delay time deriving means for obtaining a delay time from the operation of the reducing agent supply means until the reducing agent reaches the NO _x catalyst device based on memory or calculation;
Control means for prohibiting enrichment from the air-fuel ratio at the timing obtained by the timing deriving means until the delay time from the operation of the reducing agent supply means obtained by the delay time deriving means elapses; An exhaust emission control device for an internal combustion engine, comprising: The engine is a cylinder injection type internal combustion engine having an injection valve for directly injecting fuel into the combustion chamber, and the reducing agent supply means is means for injecting fuel in an expansion stroke or an exhaust stroke after the main injection of the injection valve.
The exhaust emission control device for an internal combustion engine according to claim 1 or 2, wherein

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