JP2757698B2 - Exhaust gas purification device for internal combustion engine - Google Patents

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 provided with a NOx absorption / decomposition catalyst in an exhaust passage of the internal combustion engine, which improves acceleration feeling without deteriorating HC emissions. Exhaust purification device.

[0002]

2. Description of the Related Art An internal combustion engine in which the amount of fuel injection is increased during acceleration to improve torque and improve the feeling of acceleration is known from, for example, Japanese Patent Application Laid-Open No. 53-41642.

[0003]

When the air-fuel ratio is shifted to the rich side by increasing the injection during acceleration, the torque is improved.
Emissions also increase, and there is a limit to purification by the three-way catalyst.In practice, the fuel injection amount can be increased only to the extent that the air-fuel ratio becomes richer on the side shallower than the output air-fuel ratio. There were limits to improvement.

[0004] It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine which can further improve the acceleration feeling without deteriorating HC emissions.

[0005]

The exhaust gas purifying apparatus for an internal combustion engine according to the present invention, which achieves the above object, comprises the following. That is,
A lean-burnable internal combustion engine and an exhaust passage thereof, a NOx absorption / decomposition catalyst provided in the exhaust passage for absorbing NOx in an oxidizing atmosphere and decomposing NOx absorbed in a reducing atmosphere, and a current engine operating state. Acceleration determination means for determining whether or not the engine is in a predetermined acceleration state; and NO when the acceleration determination means determines that the current engine operation state is the predetermined acceleration state.
a predetermined acceleration fuel injection amount increasing means for increasing the fuel injection amount further than the normal acceleration increase amount so that the air-fuel ratio approaches the output air-fuel ratio in accordance with the NOx amount absorbed by the x absorption decomposition catalyst. An exhaust gas purification device for an internal combustion engine.

[0006]

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, at the time of a predetermined acceleration, the fuel injection amount increasing means at the time of the predetermined acceleration is used to increase N
Since the fuel injection amount is increased more than the normal acceleration increase according to the NOx amount absorbed by the Ox absorption / decomposition catalyst, the acceleration feeling is improved. The increased fuel injection increases the unburned fuel content and increases the HC in the exhaust gas. At this time, since the exhaust gas is in a reducing atmosphere, the Nx absorbed in the NOx absorption / decomposition catalyst is increased.
Ox is released from the catalyst, and HC in the exhaust gas is consumed for reduction and decomposition of the NOx. In this case, the fuel is increased so that the amount of HC in the exhaust gas by the increased amount of fuel falls within the range of the amount of HC consumed for reduction and decomposition of NOx absorbed by the NOx absorption / decomposition catalyst. Regardless, the increase in HC released into the atmosphere is kept small,
There is no deterioration of HC emission.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments according to the present invention will be described below with reference to the drawings. 1, an exhaust passage 4 of an internal combustion engine 2 (which may be a diesel engine) capable of lean combustion has a NOx absorption / decomposition catalyst 6 that absorbs NOx in an oxidizing atmosphere and decomposes NOx absorbed in a reducing atmosphere.
Are arranged.

As shown in FIG. 3, the NOx absorption / decomposition catalyst 6 comprises a carrier (for example, Al ₂ O ₃ ) 6c and a noble metal (for example, platinum Pt, or platinum Pt and rhodium Rh) 6a having an oxidizing and reducing ability. , Alkaline earth (eg, Ba), lanthanum, alkali metal (eg, K)
And at least one element 6b selected from the group consisting of: Further, a transition metal (for example, Cu) may be supported as needed.

In the NOx absorption / decomposition catalyst 6 shown in FIG. 3, in an oxidizing atmosphere, NO and O ₂ are oxidized on the Pt surface to form NO ₂ , which is deposited on the Ba (Ba (OH) ₂ , BaO) layer.
₃ ^- By solid diffusion in the form of, NOx is absorbed into the Ba layer. Further, in the reducing atmosphere, the absorbed NO ₃ ^- is released to become NO ₂ , and HC, C
It is reduced on the Pt surface by a reducing agent such as O to become N ₂ .

As shown in FIG. 2, the NOx absorption / decomposition catalyst 6 shown in FIG. 1 includes a NOx absorbent 6A and a three-way catalyst 6B located downstream of the NOx absorbent 6A.
May be combined. As the NOx absorbent 6A, a noble metal or a transition metal having an oxidizing ability,
Compounds of alkaline earth, lanthanum, alkali metal, etc. that can absorb x, for example, Ba-Cu-O type.

The NOx absorption / decomposition catalyst 6 absorbs NOx in an air-fuel ratio lean exhaust gas (in an oxidizing atmosphere) and releases NOx in an air-fuel ratio rich exhaust gas (in a reducing atmosphere) to be regenerated. If the air-fuel ratio lean state continues for a long time, the NOx absorption / decomposition catalyst 6 becomes saturated and no longer absorbs NOx.
When the absorption amount approaches the NOx absorption capacity of the catalyst, an air-fuel ratio rich state is created, and it is necessary to release NOx to the catalyst to purify and regenerate the catalyst.

In the actual operation state, the acceleration state appears repeatedly, and the air-fuel ratio is made rich during acceleration, so that the exhaust gas becomes a reducing atmosphere, so that the catalyst 6 is purified. That is, the acceleration rich can be used for regeneration of the NOx absorption / decomposition catalyst 6. Further, by properly controlling the acceleration rich, not only the regeneration of the NOx absorption / decomposition catalyst 6 but also the improvement of the acceleration feeling without deterioration of the HC emission can be achieved.

Various means are provided for performing this control. For example, the catalyst temperature or exhaust temperature T
In order to measure e, an exhaust gas temperature sensor 10 is provided in the exhaust passage 4 upstream of the catalyst. Further, in order to detect engine operating conditions, a load sensor (for example, an intake negative pressure sensor) 12 and an engine rotational speed sensor (an engine rotational speed Ne may be obtained by calculation from a crank angle sensor built in a distributor). Good) 14 is provided. These sensors 10, 1
The outputs of 2 and 14 are supplied to an electronic control unit (electronic control unit, abbreviated as ECU) 8.

The ECU 8 includes a microcomputer, and executes an input / output interface, a read-only memory (ROM) as a read-only memory, a random access memory (RAM) as a temporary storage memory, and an operation, similarly to a normal microcomputer. It has a central processor unit (CPU). The sensors 10, 1
If the signals from 2 and 14 are analog signals, they are converted into digital signals by an analog / digital converter and input to an input interface. CPU
The command signal of the calculation result in is sent from the output interface to the electronically controlled fuel injection valve 16, and the air-fuel ratio and, consequently, the exhaust atmosphere can be controlled by controlling the fuel injection amount.

FIG. 5 shows a fuel injection control routine.
The data is stored in the OM, read out by the CPU, and executed. The routine of FIG. 5 is interrupted at regular intervals or at constant crank angles. This routine is well-known except that _a predetermined acceleration increase Ka that increases further at a predetermined acceleration is added in addition to the normal acceleration increase in steps 56 and 58.

At a step 50, an interruption is made. At a step 52, the engine load P and the engine speed Ne are read.
At 4, the basic fuel injection amount _TP is determined using a map or the like based on P and Ne. Subsequently, in step 56,
The various correction coefficients K ₁ , K ₂ ,..., _Kn are determined using the respective maps. For example, a normal acceleration increase K ₁ that increases the fuel injection amount during acceleration, a start increase K ₂ that increases when starting, a water temperature increase K ₃ that detects the low temperature start at the water temperature and increases the fuel injection amount at that time, and the like. is there. In addition,
At the time of a predetermined acceleration (for example, at the time of a sudden acceleration equal to or more than a predetermined value) unique to the present invention, at the time of a predetermined acceleration equal to or more than the predetermined value, in addition to the increase of K ₁ , the fuel injection amount K which is further increased. _a is read. The K _a is sought pre Ji because in the routine of FIG. 8 to be described later.

Subsequently, at step 58, the final correction coefficient K is determined, for example, as K = 1 + K ₁ + K ₂ +... + K _n + K _a . In step 60, determine the fuel injection amount K · T _p to be currently injected from the basic fuel injection amount T _p and the correction coefficient K, to determine the fuel injection time TAU based thereon. Then, in step 62, TAU is set,
Fuel is injected for the TAU time, and the routine returns to the step 64.

The above-described correction of the fuel injection amount increase during acceleration with respect to Ka is based on the NOx absorbed in the NOx absorption / decomposition catalyst 6.
It should be executed only in accordance with the quantity and at a predetermined acceleration (for example, at an acceleration equal to or higher than a predetermined value). What is necessary is to increase the fuel injection amount at the time of predetermined acceleration, by improving the acceleration feeling,
This is performed for the purpose of purifying and regenerating the NOx absorption / decomposition catalyst 6, so that it is not necessary to increase the amount of fuel when no torque shock is involved, such as during acceleration at or below a predetermined acceleration, and NOx is not accumulated. Do it sometimes or absorb NO
This is because if the injection amount is increased beyond the x amount, the HC emission deteriorates as will be described later.

How much NOx is contained in the NOx absorption / decomposition catalyst 6
The routine shown in FIG. 6 is used to determine whether or not is absorbed. The routine shown in FIG.
The operation is read out to the PU and executed. The routine of FIG. 6 is interrupted at regular intervals. First, an interruption is made in step 100, and in step 102, the current engine operating state, that is, the engine load P, the engine rotation speed Ne, the exhaust temperature (correlated to the catalyst temperature) Te, and the like are read. Subsequently, step 104
In, it had been determined by pre Ji fit test, P, Ne and, NOx absorption amount per unit time from the map of (absorption rate) N _ij, obtaining the N _ij of the current operating conditions. Subsequently, step 106
In, the last of the NOx absorption accumulated amount ΣNOx, N _ij and △ t
(Interruption time interval to the routine) is added to obtain the current NOx absorption integrated amount ΣNOx,
It is regarded as the amount of NOx accumulated in the x absorption / decomposition catalyst 6, and the routine proceeds to step 108 and returns.

Further, in order to determine whether or not the current engine operating state is in a predetermined acceleration state (for example, an acceleration state equal to or higher than a predetermined acceleration), the routine interrupts a routine as acceleration determination means in FIG. This routine is stored in the ROM,
The operation is read out by the CPU and executed. This routine is interrupted at regular intervals.

In step 150, the interrupt is made.
At 2, the engine load P and the engine speed Ne are read. P uses a value measured as an absolute pressure by an intake pressure. Subsequently, at step 154, the change amount (P
). For example, when the accelerator pedal is suddenly depressed to suddenly increase the accelerator opening, the differential value of P is large. Subsequently, the process proceeds to step 156, where it is determined whether or not the differential value of P is equal to or greater than a predetermined value. If the differential value is greater than the predetermined value, it is determined that the vehicle is accelerating at a predetermined speed. Set acceleration timer to O
N. If the differential value of P is smaller than the predetermined value in step 156, it is determined that the vehicle is not at the predetermined acceleration, and step 160
To clear the acceleration flag ACCFLAG to 0.
The process proceeds from Steps 158 and 160 to Step 162 and returns.

Subsequently, the control routine shown in FIG. 8 is started. FIG.
When the acceleration determination means (the routine in FIG. 7) determines that the current engine operating state is at the time of the predetermined acceleration, while the amount of NOx absorbed in the NOx absorption / decomposition catalyst exceeds the predetermined value, NOx A predetermined acceleration fuel injection increasing means for increasing the fuel injection amount further than the normal acceleration increase so that the air-fuel ratio approaches the output air-fuel ratio in accordance with the NOx amount absorbed in the absorption decomposition catalyst, and is stored in the ROM. CPU
And the operation is executed.

The routine of FIG. 8 is interrupted at step 270 at regular intervals. Subsequently, at step 272, N
It is determined whether or not the NOx amount ΣNOx accumulated in the Ox absorption / decomposition catalyst 6 is larger than a predetermined value (for example, 30% of the NOx absorption capacity of the NOx absorption / decomposition catalyst 6). Step 27
4 and the acceleration flag ACCFLAG is determined in step 274.
Is determined to be 1 (at the time of predetermined acceleration), if it is the predetermined acceleration, it is determined that rich control should be performed at the time of predetermined acceleration, and the routine proceeds to step 276, where the fuel injection increase correction at the time of predetermined acceleration is performed. to determine the coefficient K _a. ΣN at step 272
Ox is or is determined to be not accumulated a sufficient amount, when it is determined not to be at a predetermined acceleration in step 274, in order not to perform the predetermined acceleration fuel injection increase, the process proceeds to step 278, K _a Is set to 0. Step 27
From 6,278, the process proceeds to step 279 and returns.

[0024] In the determination of the K _a of step 276,
At a predetermined acceleration, the amount of N absorbed by the NOx absorption / decomposition catalyst
It is determined that the fuel injection amount is increased so that the air-fuel ratio approaches the output air-fuel ratio within a range corresponding to the Ox amount. For example, the output air-fuel ratio to be the A / F = 11, if the A / F is made rich to 13 by conventional acceleration increase (increase by K _1), A by the time a predetermined acceleration increase (increase by K _a) / F is closer to 11, K _a is determined. Calculation steps 56 and 58 described above in FIG. 5 in such a manner was used K _a, which is determined is executed.

[0025] the rich control by the fuel increase of K _a, an exhaust atmosphere of the engine becomes a reducing atmosphere, NOx absorption decomposition catalyst 6 is releasing NOx, it is reproduced in a relatively short time. If the predetermined acceleration rich control is continued even after the catalyst regeneration, the HC is not consumed for the reduction of the released NOx,
Since the HC emission is directly released to the atmosphere and the HC emission deteriorates, when the regeneration of the NOx absorption / decomposition catalyst 6 is completed, the rich control at the time of the predetermined acceleration is stopped, and the NOx is again reduced to a sufficient amount by the catalyst. You should wait for 6. The control for this is performed by the routine of FIG.

The routine shown in FIG. 9 is stored in the ROM, read out by the CPU, and executed. The routine of FIG. 9 is interrupted at regular intervals. At step 280, an interruption is made. At step 282, it is determined whether or not the predetermined acceleration rich control has been completed. This is determined by, for example, turning on the acceleration timer at a predetermined acceleration in step 158 of the routine of FIG. 7 and checking whether or not the count of the timer has exceeded a predetermined value in step 282. Is done. If the predetermined acceleration rich control has not been completed in step 282, the process proceeds to step 286 and returns.
If it is determined in step 282 that the predetermined acceleration rich control has been completed, the process proceeds to step 284, where the NOx absorption amount ΣNOx of the NOx absorption / decomposition catalyst 6 is cleared to 0, the acceleration timer is turned off, and the process returns. Σ Set NOx to 0
After that, ΣNOx calculated in the routine of FIG.
Until the predetermined value is exceeded again in step 272 of the routine in FIG. 8, the predetermined acceleration rich control is not executed.

Next, the operation will be described. When not at the predetermined acceleration, since it is K _a = 0, K in the routine of FIG. 5 _a =
At 0, normal fuel injection control is executed. Becomes at a predetermined acceleration, the routine of FIG. 8, when the NOx absorption amount is absorbed in the NOx absorbent decomposition catalyst 6 .SIGMA.NOx is equal to or greater than a predetermined value is increased by taking the value K _a is not 0, the conventional acceleration increase in addition to the (increased by K ₁ in FIG. 5), further a predetermined acceleration increase (increase by K _a of FIG. 5) is executed,
The air-fuel ratio is made closer to the output air-fuel ratio.

[0028] As is conventional, when only the three-way catalyst is provided in the exhaust passage, HC in the exhaust gas by the fuel increase by K _a (unburned HC is flowing in the exhaust gas) increases, the three Since the HC cannot be purified even by the original catalyst, the concentration of HC released to the atmosphere exceeds the allowable value as shown in FIG. For this reason, conventionally, it was not possible to make the air-fuel ratio rich up to the output air-fuel ratio. As a result, sufficient torque at the time of sudden acceleration was not obtained, and the acceleration feeling was not so good.

However, according to the present invention, at a predetermined acceleration, K ₁
Is implemented increase of both K _a and, since the air-fuel ratio is close to the output air-fuel ratio, acceleration feeling is improved. In this case, the HC in the exhaust gas immediately after flowing out of the engine 2 into the exhaust passage 4 (upstream of the catalyst 6) increases, but when flowing into the NOx absorption / decomposition catalyst 6, the HC shown in the right half of FIG. 6
Reaction with the released NOx and HC are generated from so HC is consumed in the decomposition of the N ₂ in NOx, HC in the exhaust gas after exiting the NOx absorbent decomposition catalyst 6 is small, in FIG. 4 As shown by the solid line, the concentration of HC in the exhaust gas discharged into the atmosphere is sufficiently within an allowable value. Therefore, the acceleration feeling is improved without deteriorating the HC emission. That is, if the fuel amount is within the fuel amount corresponding to the NOx amount absorbed by the NOx absorption / decomposition catalyst, the fuel amount may be increased, and the acceleration feeling is improved by executing the fuel increase.

Further, HC generated by increasing the amount of fuel for improving the acceleration feeling is also used for purifying and regenerating the NOx absorption / decomposition catalyst 6, thereby preventing NOx from being discharged into the atmosphere due to saturation of the catalyst. doing.

[0031]

According to the present invention, the exhaust gas purifying apparatus for the internal combustion engine having the NOx absorption / decomposition catalyst in the exhaust passage is provided with the acceleration determining means and the fuel injection amount increasing means at the time of the predetermined acceleration. The acceleration feeling can be improved without deterioration, and the NOx absorption / decomposition catalyst can be efficiently regenerated.

[Brief description of the drawings]

FIG. 1 is a system diagram of an exhaust gas purifying apparatus for an internal combustion engine according to one embodiment of the present invention.

FIG. 2 is a system diagram of an exhaust gas purification device for an internal combustion engine according to another embodiment of the present invention.

FIG. 3 shows the NO of the NOx absorption / decomposition catalyst that can be used in the present invention.
It is an x absorption and decomposition | disassembly operation principle diagram.

FIG. 4 is a comparison diagram of the HC concentration of the exhaust gas purifying apparatus for an internal combustion engine of the present invention and a conventional exhaust gas purifying apparatus at a predetermined acceleration.

FIG. 5 is a flowchart of a fuel injection control routine used in the exhaust gas purification apparatus for an internal combustion engine of the present invention.

FIG. 6 is a flowchart of a calculation routine for calculating the amount of NOx accumulated in the NOx absorption / decomposition catalyst used in the exhaust gas purification apparatus for an internal combustion engine of the present invention.

FIG. 7 is a flowchart of acceleration determining means used in the exhaust gas purifying apparatus for an internal combustion engine of the present invention.

FIG. 8 is a flowchart of a predetermined acceleration fuel injection amount increasing means used in the exhaust gas purification apparatus for an internal combustion engine of the present invention.

FIG. 9 is a flowchart of a reset routine at the completion of predetermined acceleration rich control used in the exhaust gas purification apparatus for an internal combustion engine of the present invention.

[Description of Signs] 2 Internal combustion engine 4 Exhaust passage 6 NOx absorption / decomposition catalyst 6A NOx absorbent 6B Three-way catalyst 8 ECU 10 Exhaust temperature sensor 12 Engine load sensor 14 Engine rotation speed sensor 16 Fuel injection valve

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02D 41/00-41/40

Claims (1)

(57) [Claims] 1. An internal combustion engine capable of lean combustion and an exhaust passage thereof, and a NOx absorption / decomposition catalyst provided in the exhaust passage for absorbing NOx in an oxidizing atmosphere and decomposing NOx absorbed in a reducing atmosphere. Acceleration determination means for determining whether or not the engine operation state is a predetermined acceleration state; and when the acceleration determination means determines that the current engine operation state is the predetermined acceleration state, the engine is absorbed by the NOx absorption / decomposition catalyst. A predetermined acceleration fuel injection amount increasing means for increasing the fuel injection amount further than a normal acceleration increase amount so that the air-fuel ratio approaches the output air-fuel ratio in accordance with the NOx amount. Purification device.