JPH11315713A - Exhaust purification controlling device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust purification controlling device for engine that realizes both increase of fuel economy and purification of exhaust by controlling regeneration of NOx catalysts without changing the engine torque or increasing amounts of exhaust gas elements such as HC, CO, and NOx, more precisely, by diagnosing the degree of deterioration of the NOx catalyst performance and controlling regeneration thereof in accordance with the degree of deterioration. SOLUTION: An exhaust purification controlling device 10 is applied to the engine comprising a NOx catalyst disposed in the exhaust pipe, and a temperature sensor 9 detecting exhaust temperature of this NOx catalyst. This device has an estimating means 104 that estimates NOx absorption on the NOx catalyst, a diagnostic means 113 that diagnoses purification performance of the NOx catalyst, and a catalyst regeneration control means 114 that controls regeneration of the NOx catalyst. The catalyst's purification performance diagnostic means 113 diagnoses the purification performance of catalyst based on the exhaust temperature detected by the temperature sensor 9, and the catalyst regeneration control means 114 controls regeneration of catalyst by changing the A/F ratio of the exhaust gas based on the diagnosis results by the catalyst's purification performance diagnostic means 113.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification control device for an engine, and more particularly to a method for diagnosing the degree of deterioration of the purification performance of an exhaust purification catalyst during operation of the engine, and determining the purification performance of the catalyst based on the diagnosis. The present invention relates to an exhaust gas purification control device for an engine that performs regeneration control.

[0002]

2. Description of the Related Art In recent years, in order to improve the fuel efficiency of an engine, the amount of air is increased (hereinafter referred to as lean) to exceed the stoichiometric air-fuel ratio of the engine (about 14.7, hereinafter referred to as stoichiometric), and the fuel is burned lean. In particular, in the case of gasoline engines, in-cylinder injection engine systems, in which fuel is injected directly into the cylinders to achieve leaner combustion than conventional systems that inject fuel through the intake pipe It is shifting to.

The in-cylinder injection engine has an air-fuel ratio of 40 to 5
By burning the fuel as an extremely lean fuel such as 0, it is possible to reduce the pumping loss and heat diffusion of the engine and to improve the fuel efficiency. By the way, when the in-cylinder injection engine examines HC, CO, and NOx, which are components of the exhaust gas, HC and CO
Decreases, but NOx tends to increase.

On the other hand, as a device for removing and purifying exhaust components of a gasoline engine, a three-way catalyst has been widely used. However, the three-way catalyst needs to maintain the stoichiometric air-fuel ratio in order to exhibit its performance.
At present, Ox cannot be appropriately purified.
Therefore, a catalyst having an adsorption function has been proposed for NOx purification under lean combustion. This catalyst reduces and adsorbs NOx in exhaust gas in an oxygen-excess atmosphere to prevent exhaustion to the atmosphere (hereinafter, the adsorption catalyst is referred to as a NOx catalyst).

However, in order to purify NOx in exhaust gas using the NOx catalyst, it is necessary to maintain the performance of the catalyst in consideration of the following points. (1) When an amount of NOx that is full of the adsorption capacity of the NOx catalyst has been adsorbed, it is necessary to immediately reduce the amount of oxygen in the exhaust gas to promote the reduction reaction. (2) Since SOx contained in fuel is more easily adsorbed than NOx, if operation is continued as it is, NO
x The performance as a catalyst decreases. In order to prevent this phenomenon, it is necessary to promote the reduction reaction by making the exhaust gas deficient in oxygen as described above. (3) In order to promote the above-described NOx reduction reaction, it is necessary to increase the temperature of the catalyst.

[0006] Such an operation for maintaining the performance of the NOx catalyst is referred to as regeneration control of the NOx catalyst. In order to promote the regeneration control, the temperature of the catalyst is first adjusted by focusing on the characteristics of the NOx catalyst. It is necessary to increase the operating state from a lean operating state to a rich operating state (the air-fuel ratio is more fuel than the stoichiometric state). Conventional specific regeneration control for shifting to the operation state includes a fuel injection amount, an intake air amount,
Alternatively, an operation method in which the ignition timing is changed is performed.

[0007]

In the above-described conventional NOx catalyst regeneration control system, when reducing NOx adsorbed on the NOx catalyst, the air-fuel ratio is changed in order to change the fuel injection amount and the like. There is a problem that it is difficult to appropriately adjust to the specific value instructed. Also, changing the fuel injection amount causes a problem that engine operability is impaired due to fluctuations in engine torque. The present invention has been made in view of such a problem, and an object of the present invention is to provide a NOx catalyst without increasing engine torque fluctuations or increasing exhaust gas components such as HC, CO, and NOx. It is an object of the present invention to provide an exhaust gas purification control device for an engine that performs regeneration control, specifically, diagnoses the degree of deterioration of the performance of the NOx catalyst, performs regeneration control according to the degree of deterioration, and improves the fuel efficiency of the engine and the exhaust An object of the present invention is to provide an exhaust gas purification control device for an engine that realizes both purification.

[0008]

In order to achieve the above object,
An exhaust gas purification control device for an engine according to the present invention is an exhaust gas purification control device applied to an engine including a NOx catalyst disposed in an exhaust pipe and a temperature sensor for detecting an exhaust gas temperature of the NOx catalyst. The purification control device includes means for estimating the NOx adsorption amount of the NOx catalyst, means for diagnosing the purification performance of the NOx catalyst, and means for controlling regeneration of the NOx catalyst. Diagnose the purification performance of the catalyst based on the exhaust temperature detected by the temperature sensor,
The catalyst regeneration control means performs catalyst regeneration control by changing the air-fuel ratio of exhaust gas based on the diagnosis result of the catalyst purification performance diagnosis means. In a specific aspect of the exhaust gas purification control device for an engine according to the present invention, the temperature sensor is disposed downstream of the NOx catalyst, and the catalyst purification performance diagnosing means detects the exhaust gas temperature at the start of catalyst regeneration and the current time. When the temperature difference from the exhaust gas temperature becomes equal to or more than a predetermined value, it is characterized that the regeneration of the NOx catalyst is completed.

The engine exhaust gas purification control apparatus of the present invention having the above-described structure includes:
Based on the data detected by the temperature sensor and the estimated value of the NOx adsorption amount on the NOx catalyst calculated by the NOx adsorption amount estimating means, the performance of the NOx catalyst was diagnosed. As a result, it was diagnosed that the performance of the NOx catalyst was deteriorated. In this case, the NOx catalyst regeneration control means performs the NOx catalyst regeneration control. The catalyst regeneration control means changes the air-fuel ratio of the engine to rich in order to regenerate the NOx catalyst.

When the temperature difference between the exhaust gas temperature at the start of catalyst regeneration detected by the temperature sensor and the present exhaust gas temperature exceeds a predetermined value, regeneration of the NOx catalyst is completed. When the diagnosis is made, the regeneration control by the catalyst regeneration control means is terminated to make the air-fuel ratio of the engine lean.

In another aspect of the exhaust gas purification control device for an engine according to the present invention, the temperature sensors are arranged on the upstream side and the downstream side of the NOx catalyst, and the catalyst purification performance diagnosing means includes the NOx catalyst. The catalyst purification performance is diagnosed based on a change in the difference between each temperature difference between the exhaust temperature at the start of catalyst regeneration and the current exhaust temperature of each of the temperature sensors on the upstream and downstream sides of the catalyst, and the catalyst purification performance diagnosis is performed. The means diagnoses that the regeneration of the catalyst has been completed when the difference between the respective temperature differences of the two temperature sensors is equal to or more than a predetermined value.

Further, in a specific aspect of the engine exhaust purification control apparatus according to the present invention, the predetermined value is determined based on the diagnosis of the NOx
The catalyst regeneration control means changes the value of the air-fuel ratio of the exhaust gas or the catalyst purification regeneration time according to the diagnosed degradation degree of the NOx catalyst. Alternatively, the catalyst regeneration control means sets the catalyst purification regeneration time longer than at least the time constant of the temperature sensor.
As described above, the engine exhaust purification control device of the present invention
Whether or not the regeneration of the NOx catalyst has been effectively performed can be diagnosed using the temperature of the exhaust gas behind the catalyst or the temperature difference between the exhaust gas before and after the catalyst. Further, it is possible to improve the fuel efficiency while preventing the exhaust components from being deteriorated during the regeneration of the NOx catalyst.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an exhaust gas purification control apparatus for an engine according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a conceptual diagram showing an overall configuration of an exhaust gas purification control device for an engine according to an embodiment of the present invention. In FIG. 1, a direct injection engine 1 includes a cylinder 1a and a piston 1
b at the top of the cylinder 1a.
And a spark plug 14, and the intake pipe 12
And the exhaust pipe 13 are connected to each other.
An intake valve 6 and an exhaust valve 7 are arranged at a connection portion between the two.
The intake pipe 12 is provided with a throttle valve 3, and the exhaust pipe 13 is connected to the NOx catalyst 2. The intake pipe 12 is provided with an air amount sensor 4, and the exhaust pipe 13 is provided with an air-fuel ratio sensor 8 and a temperature sensor 9 at an outlet of the NOx catalyst 2.

Further, the in-cylinder injection engine 1 is provided with an engine control device 11, which outputs output signals of the air amount sensor 4, the air-fuel ratio sensor 8, and the temperature sensor 9, an engine speed signal 102, and a crank angle signal 103. , A signal from the NOx adsorption amount estimating means 104 is input, and an operation signal of the throttle valve 3 and a signal to the fuel injection valve 5 and the spark plug 14 are output from the engine control device 11. It is configured as follows.

The engine control device 11 performs all processing by a single-chip microcomputer having an A / D converter, and a part of the engine control device 11 includes the engine exhaust gas purification control device 100 of the present embodiment. Engine torque control means 111 of the engine control device 11
Is executed by taking in the air amount signal 101 and the engine speed signal 102 from the air amount sensor 4, and the engine torque is calculated as a fuel injection amount and output to the fuel injection valve 5. Although not shown here, when determining the torque, a signal of the accelerator opening may be used.
The injected fuel is supplied to the cylinder 1a of the direct injection engine 1.
And the exhaust gas is discharged from the exhaust pipe 13 through the exhaust valve 7 to the N
It flows to the Ox catalyst 2.

The exhaust purification control device 100 has NO
A NOx adsorption amount estimating unit 104 for estimating the amount of NOx adsorbed on the x catalyst and a temperature storage unit 112 are arranged, and a temperature signal obtained from the temperature sensor 9 is input to the temperature storage unit 112. Based on the data in the temperature storage means 112 and the estimated value of the amount of NOx adsorbed on the NOx catalyst calculated by the NOx adsorption amount estimating means 104, the catalyst purification performance diagnosing means 113
In the above, when the performance of the NOx catalyst is diagnosed as a result of the diagnosis of the performance of the NOx catalyst, the regeneration control of the NOx catalyst 2 is executed by the NOx catalyst regeneration control means 114.

The fuel injection amount determined by the catalyst regeneration control means 114 is different from the fuel injection amount calculated by the engine torque control means 111 by the injection amount calculation means 115 at different injection timings. The fuel injection amount is simply added, and an injection signal of the added fuel injection amount is output to the fuel injection valve 5. The catalyst regeneration control means 114
The fuel injection amount for the regeneration control when the regeneration control of the NOx catalyst 2 is performed in a closed loop by the output value of the air-fuel ratio sensor 8 so as not to affect the engine torque amount.
The fuel is injected into the in-cylinder injection engine 1. In other words, the fuel injection amount proportional to the engine torque becomes the value determined by the engine torque control unit 111 and is not affected by the regeneration control.

That is, the fuel for the regeneration control is injected late in the expansion stroke of the direct injection engine 1 so as not to affect the engine torque. In this case, the fuel for determining the engine torque is injected before the ignition timing. That is, when performing the regeneration control of the NOx catalyst 2, the fuel is injected twice during one cycle of intake-compression-expansion-exhaust.

FIG. 2 shows the relationship between the fuel injection pulse width Tc, the engine torque, the concentration of HC (unburned hydrocarbon), and the exhaust gas temperature in the case of the second expansion stroke injection of the engine 1. When the injection pulse width is increased and the injection amount is increased, the amount of HC discharged to the exhaust pipe 13 without burning increases. That is, the ratio of the cylinder filling air weight to the ignition fuel injection weight + the fuel injection weight during the expansion stroke is 14.7.
Can be larger. At this time, the overall air-fuel ratio is lean. However, when the amount of HC increases due to the injection during the expansion stroke, the exhaust pipe 13 becomes a reducing atmosphere with a small amount of oxygen. Further, since the HC is burned in the exhaust pipe 13, the exhaust gas temperature rises. The NOx catalyst 2 can be regenerated by the reducing atmosphere and the increase in the exhaust gas temperature. Closed loop control is performed based on the signal of the air-fuel ratio sensor 8 so that the exhaust gas upstream of the NOx catalyst 2 becomes a reducing atmosphere.

FIG. 3 shows the relationship between the operation timing of the intake and exhaust valves 6 and 7, the fuel injection pulse, and the crank angle. Fuel for torque control is injected at a crank angle θt. This θt is the ignition timing or the crank angle before the compression top dead center. The fuel for regeneration control is crank angle θ
Injected at c. When the respective fuel injection pulse widths are Tp1 and Tp2, the engine torque is Tp
The air-fuel ratio in the exhaust pipe 13 for the regeneration control determined by p1 is determined by Tp2. That is, the pulse width of Tp2 is closed-loop controlled based on the signal of the air-fuel ratio sensor 8.
Next, the performance diagnosis of the NOx catalyst 2 will be described with reference to the control flowchart of FIG.

In step 401, the Nx catalyst 2
The amount of adsorption of Ox is estimated. As a means for estimating the amount of NOx adsorbed on the NOx catalyst 2, the regeneration control of the NOx catalyst 2 is performed, the fuel injection amount is set to be the start point immediately after the air-fuel ratio is returned to lean, and the current time is set as the end point. In general, a method of performing time integration and obtaining from the total fuel injection amount is used.

In step 402, it is determined whether the NOx adsorption amount is equal to or more than a predetermined value. If the adsorption amount is equal to or more than the predetermined value, it is determined that the performance of the NOx catalyst 2 has deteriorated, and in step 403, the regeneration control of the NOx catalyst 2 is performed by injecting the fuel in the expansion stroke as described above. But,
Specific means will be described later. If it is determined in step 402 that the adsorption amount is less than the predetermined value, it is determined that the performance of the NOx catalyst 2 is good, and the regeneration control of the NOx catalyst 2 is not performed. The above-mentioned predetermined value generally differs depending on driving conditions such as the speed of the vehicle and the road surface. At step 404, it is determined whether or not the performance of the NOx catalyst 2 has been regenerated based on the value of the exhaust gas temperature or the like downstream of the NOx catalyst 2. The specific determination means will be described later. If the performance of the NOx catalyst 2 is regenerated, NOx
The regeneration control of the catalyst 2 is ended, and if not, the process returns to step 403.

Next, the regeneration control of the NOx catalyst 2 will be described with reference to the control flowchart of FIG. In step 501, the signal detected by the air-fuel ratio sensor 8 is input,
In step 502, the target air-fuel ratio for catalyst regeneration is compared with the detected current air-fuel ratio. If the current air-fuel ratio is larger than the target value, the process proceeds to step 503. If the current air-fuel ratio is smaller than the target value, the process proceeds to step 504. The fuel injection pulse width Tp2 is calculated according to the fuel injection pulse width equations (1) and (2).
To adjust the current air-fuel ratio to the target air-fuel ratio.

[0024]

Tp2 = Tp2 + ΔTp2 (Equation 1)

[0025]

Tp2 = Tp2-ΔTp2 (Equation 2)

After adjusting the air-fuel ratio, it is determined in step 505 whether or not the crank angle for the injection timing has reached a predetermined angle θc. If the crank angle has reached the predetermined angle θc, the routine proceeds to step 507, where the fuel injection is performed. Fuel is injected from the valve 5 by a predetermined injection pulp width Tp2. If the crank angle has not reached the predetermined angle θc in step 505, the process proceeds to step 506 and waits for injection timing.
Proceeding to step 505, it is determined whether or not the crank angle for the injection timing has reached the predetermined angle θc. As the air-fuel ratio sensor 8 that detects the air-fuel ratio, a sensor that detects the air-fuel ratio in an analog manner is used.

FIG. 6 shows (1) the air-fuel ratio A / F of the engine,
(2) NOx purification rate of the NOx catalyst 2 and (3) NO
FIG. 4 is a characteristic diagram showing the relationship between the temperature of exhaust gas downstream of the x catalyst 2 and the passage of time. As shown in FIG. 6A, when the air-fuel ratio A / F is changed from the lean state to the stoichiometric state at time t1, the NOx purification rate of the NOx catalyst 2 becomes as shown in FIG.
As shown to improve and become higher. FIG.
As shown in (3), when the air-fuel ratio A / F is changed from the lean state to the stoichiometric state, the exhaust gas temperature downstream of the NOx catalyst 2 also becomes higher (increases from the exhaust gas temperature Tr (t1)). . When the NOx purification rate of the NOx catalyst 2 is improved and the air-fuel ratio A / F returns from the stoichiometric state to the lean state at time t2, the exhaust temperature downstream of the NOx catalyst 2 becomes the exhaust temperature Tr (t2). , And the exhaust gas temperature Tr (t3) is settled.

Next, means for determining whether or not the performance of the NOx catalyst 2 has been regenerated will be described with reference to the control flowchart of FIG. As shown in FIG.
The process of regenerating the catalyst 2, that is, the air-fuel ratio A / F
Is changed from the lean state to the stoichiometric state, NOx
The regeneration control of the NOx catalyst 2 is performed by paying attention to the fact that the exhaust gas temperature of the catalyst 2 rises.

In step 701, the exhaust gas temperature Tr downstream of the NOx catalyst immediately before the regeneration control of the NOx catalyst 2 is performed.
(T1) and the current exhaust gas temperature Tr downstream of the NOx catalyst
(T2) is input. In step 702, the temperature difference Δr between the two exhaust temperatures Tr (t1) and Tr (t2)
r, that is, the value of Δrr = Tr (t2) −Tr (t1) is calculated, and in step 703, it is determined whether or not the temperature difference Δrr is equal to or greater than a predetermined value (reference value) ΔTrr2. Temperature difference Δ
If Trr ≧ ΔTrr2, it is determined that the regeneration of the NOx catalyst has been sufficient, and the routine proceeds to step 704, where the regeneration control of the NOx catalyst is ended. That is, the air-fuel ratio is returned to a lean state for the purpose of improving fuel efficiency. In step 703, Δ
If it is determined that Trr <ΔTrr2, it is determined that the regeneration of the NOx catalyst 2 is not sufficient, and the process returns to step 702, where the temperature difference Δrr is calculated again and the regeneration control of the NOx catalyst 2 is continued. That is, the air-fuel ratio is maintained in a stoichiometric or rich state.

A predetermined value (reference value) ΔTrr2 of the temperature difference
The execution time of the regeneration control of the NOx catalyst 2 is set to be larger than the time constant of the temperature sensor 9 in consideration of the measurement accuracy of the temperature sensor 9, as will be described later. next,
Reference value Δ for determining whether to terminate the regeneration control of NOx catalyst 2.
The means for determining Trr2 will be described. The exhaust temperature downstream of the NOx catalyst 2 in the lean state is represented by Tr (t3)
When Tr (t3) -Tr (t1) is small, the regeneration control of the NOx catalyst is carefully performed.
Generally, the value of ΔTrr2 varies depending on driving conditions such as speed and road surface, and a constant determined by these conditions is k
And As a specific method, the value of ΔTrr2 can be calculated by the following Expression 3.

[0031]

ΔTrr2 = k · Tr (t1) / (Tr (t3) −Tr (t1)) (Equation 3)

FIG. 8 is a control flowchart for determining the value of the reference value ΔTrr2. First, at step 801, the exhaust gas temperature Tr downstream of the NOx catalyst NO
(T1) and the exhaust gas temperature Tr (t3) are read, and then, at step 802, a constant k determined by operating conditions is set. At step 803, the constant k and the two exhaust gas temperatures Tr based on the equation (3). (T1) and Tr
From (t3), the value of ΔTrr2 is calculated.

FIGS. 9 and 10 show (1) the air-fuel ratio A / F of the engine, (2) the NOx purification rate of the NOx catalyst 2, and
(3) is a characteristic diagram showing the relationship between the temperature of the exhaust gas downstream of the NOx catalyst 2 and the passage of time, particularly when the value of ΔTrr2 is large (that is, when it is diagnosed that the performance of the catalyst has deteriorated). FIG. 9 and 10, a thin line a indicates a state before changing the value of ΔTrr2, and a solid line b indicates a state after changing the value of ΔTrr2. FIG.
5 shows a relationship diagram in the case where the time for making the air-fuel ratio stoichiometric (rich) is increased in the process of performing the regeneration control of the NOx catalyst 2. FIG. FIG. 9 shows that the catalyst that had a large degree of deterioration was regenerated by increasing the time for setting the air-fuel ratio to stoichiometric (rich). That is, when the value of ΔTrr2 may be small, the time for making the air-fuel ratio rich can be shortened because the NOx catalyst 2 has not deteriorated so much. The air-fuel ratio is returned to a lean state.

FIG. 10 is a relationship diagram in the case where the degree of enrichment of the air-fuel ratio is increased in the process of performing the regeneration control of the NOx catalyst 2. FIG. 10 shows that by making the air-fuel ratio richer, that is, by reducing the air-fuel ratio, the NOx catalyst having a large degree of deterioration was quickly regenerated. Conversely, when the value of ΔTrr2 is small, NOx
Since the catalyst has not deteriorated so much, the degree of making the air-fuel ratio rich can be relatively small.

When regenerating the NOx catalyst according to the present embodiment, the time for regenerating the catalyst needs to be longer than the time constant. This is because when measuring the exhaust gas temperature of the engine with the temperature sensor 9, the temperature cannot be detected in the regeneration process of the catalyst unless the time constant related to the resolution of the temperature sensor 9 is larger than a predetermined value. Specifically, in FIG. 6, the time for regenerating the NOx catalyst is represented by (t2−t1), but this time needs to be larger than the time constant of the temperature sensor 9.

FIG. 11 shows a second embodiment of the present invention. The difference between the second embodiment and the first embodiment is that a second embodiment is provided upstream of the NOx catalyst 2. The other components in the point that the temperature sensor 10 is provided are the same as those in the first embodiment. Also, the means for performing the regeneration control of the NOx catalyst 2 is the same as that of the first embodiment, and therefore the description thereof will be omitted.

The performance diagnosis of the NOx catalyst 2 is almost the same as in the first embodiment. That is, in the control flowchart of FIG. 4, step 401 for estimating the adsorption amount of NOx to the NOx catalyst 2, step 402 for determining whether the adsorption amount of NOx is equal to or more than a predetermined value, and injecting fuel during the expansion stroke to NOx Step 403 of performing catalyst regeneration control
Is the same as the step in the first embodiment, but NOx
The step 404 of determining whether the performance of the catalyst 2 has been regenerated has a different feature from the first embodiment.
The details of this step 404 will be described later. Also, the means for controlling the regeneration of the NOx catalyst 2 is implemented based on the control flowchart of FIG. 5, and a detailed description thereof will be omitted.

Next, using the flowchart of FIG.
The means for determining whether or not the performance of the NOx catalyst 2 has been regenerated will be described. In the process of regenerating the NOx catalyst 2, not only the temperature of the exhaust gas passing through the NOx catalyst 2, but also the change in the difference between the exhaust temperatures upstream and downstream of the catalyst, The regeneration control of the NOx catalyst 2 is performed by paying attention to the fact that a difference occurs in the exothermic reaction based on the difference.

The temperature difference Trf (t1) between the exhaust gas temperature Tr (t1) downstream of the catalyst and the exhaust gas temperature Tf (t1) upstream of the catalyst immediately before the regeneration control is performed, that is, the temperature difference Trf (t1).
= Tr (t1) -Tf (t1), and the current exhaust gas temperature Tr (t2) downstream of the catalyst and the exhaust gas temperature Tf upstream of the catalyst.
(T2) and the temperature difference Trf (t2), that is, the temperature difference Trf
f (t2) = Tr (t2) -Tf (t2)
It is determined whether or not the performance of the Ox catalyst 2 has been regenerated.

In step 1201 of FIG. 12, based on the output signals of the temperature sensors 9 and 10, the exhaust temperatures Tf (t1) and Tf (t2) upstream of the NOx catalyst and the exhaust temperatures Tr (t1) and Tr (t2) downstream thereof are determined. ) And read. In step 1202, the temperature difference Trf (t
1) Calculate Trf (t2). In step 1203, a time difference temperature difference ΔTrf = Trf (t2) −Trf (t1) is calculated by subtracting the temperature difference Trf (t1) immediately before performing the regeneration control from the current temperature difference Trf (t2). In step 1204, the time difference temperature difference ΔTrf = T
rf (t2) -Trf (t1) is a predetermined value (reference value)
It is determined whether or not ΔTrf2 or more. If the time difference temperature difference ΔTrf is larger than a predetermined value, that is, if ΔTrf ≧ ΔTrf2, it is determined that the regeneration of the NOx catalyst 2 has been sufficiently performed. To end. That is, the air-fuel ratio is returned to a lean state in order to improve fuel efficiency.

In step 1204, ΔTrf <Δ
If it is determined that Trf2, it is determined that the regeneration of the NOx catalyst 2 is not sufficient, and the process returns to step 1202, where the temperature differences Trf (t1) and Trf (t2) are calculated again and NO
The regeneration control of the x catalyst 2 is continued. That is, the air-fuel ratio is maintained in a stoichiometric or rich state. The means for determining the predetermined value (reference value) ΔTrf2 will be described later.
The execution time of the NOx catalyst regeneration control is determined by the temperature sensors 9 and 1.
Considering the measurement accuracy of 0, the time constant is made larger than the time constant of the temperature sensors 9 and 10. For reference, the relationship between the air-fuel ratio, the NOx purification rate, and the exhaust temperature behind the catalyst and time are shown in FIG.
3 is shown.

Next, an embodiment of a method for determining the value of ΔTrf2, which is a reference value for determining whether or not to end the regeneration control of the NOx catalyst, will be described. In general, the value of ΔTrf2 is
It depends on operating conditions such as speed and road surface, and a constant determined by these conditions is k2. Then, the difference Trf between the exhaust gas temperature in front of and behind the catalyst in a certain lean state
When (t3), Trf (t3) −Trf (t1)
When is small, the regeneration of the catalyst is carefully performed.
As a specific method, it is conceivable to calculate the value of ΔTrf2 by the following equation (4).

[0043]

ΔTrf2 = k2 · Trf (t1) / (Trf (t3) −Trf (t1)) (Equation 4)

The method for determining the value of ΔTrf2 as described above is shown in the flowchart of FIG. First, in step 1401, the exhaust gas temperature Tr downstream of the NOx catalyst NO
(T1), Tr (t3) and upstream temperature Tf (t1), Tf
(T3) and read the temperature difference Trf at each time point.
(T1), Trf (t3) is calculated. Next, in step 1402, a constant k2 determined by the operating conditions is set. In step 1403, the constant k2 and the two temperature differences Trf (t1) and Trf are determined based on the above equation (4).
From (t3), the value of ΔTrf2 is calculated. Although not shown here, the air-fuel ratio when the value of ΔTrf2 is large (that is, when it is diagnosed that the performance of the catalyst is deteriorated) is NO.
The purification rate of x and the difference and time between the exhaust gas temperature before and after the catalyst have the same relationship as those shown in FIGS.

Further, also in the present embodiment, when the regeneration of the NOx catalyst is performed, the time for performing the regeneration of the NOx catalyst is determined by the temperature sensors 9 and 1 as in the first embodiment.
It must be larger than the time constant of zero. That is, in FIG. 13, the time for regenerating the NOx catalyst is (t2-t)
This time is indicated by the temperature sensors 9 and 1
It must be larger than the time constant of zero. The two embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and may be designed in a manner not departing from the spirit of the present invention described in the appended claims. Various changes can be made.

[0046]

As will be understood from the above description, the engine exhaust gas purification control device of the present invention determines whether the regeneration of the NOx catalyst has been performed effectively by determining the temperature of the exhaust gas behind the catalyst,
Alternatively, the diagnosis can be made using the temperature difference between the exhaust gas before and after the catalyst. Further, it is possible to improve the fuel efficiency while preventing the exhaust components from being deteriorated during the regeneration of the NOx catalyst.

[Brief description of the drawings]

FIG. 1 is an overall conceptual diagram of an engine system provided with an embodiment of an engine exhaust gas purification control device of the present invention.

FIG. 2 is a diagram showing a relationship between a pulse width in an expansion stroke of an engine and parameters of torque, HC, and exhaust gas temperature.

FIG. 3 is a diagram showing a relationship between a crank angle, a fuel injection timing, and a pulse width of the engine shown in FIG. 1;

FIG. 4 is a diagram showing the NO in the engine exhaust gas purification control device of FIG. 1;
9 is a control flowchart showing performance diagnosis of an x catalyst.

FIG. 5 is a diagram showing NO in the engine exhaust gas purification control device of FIG. 1;
9 is a control flowchart showing an x catalyst regeneration operation.

FIG. 6 shows the air-fuel ratio and N of the engine exhaust gas purification control device of FIG.
FIG. 4 is a characteristic diagram showing changes over time of the Ox purification rate and the exhaust gas temperature.

FIG. 7 is a control flowchart for confirming and diagnosing the regeneration of the performance of the NOx catalyst of the engine exhaust gas purification control device of FIG. 1;

FIG. 8 is a control flowchart for diagnosing the degree of deterioration of the NOx catalyst of the engine exhaust purification control device of FIG. 1;

FIG. 9 shows the air-fuel ratio and N of the engine exhaust gas purification control device of FIG.
FIG. 4 is a characteristic diagram showing changes over time of the Ox purification rate and the exhaust gas temperature.

10 is a characteristic diagram showing changes over time of an air-fuel ratio, a NOx purification rate, and an exhaust temperature of the engine exhaust purification control device of FIG. 1;

FIG. 11 is an overall conceptual diagram of an engine system provided with another embodiment of the engine exhaust gas purification control device of the present invention.

12 is a diagram showing NOx of the engine exhaust gas purification control device of FIG. 11;
4 is a control flowchart for performing a check diagnosis of catalyst performance regeneration.

13 is a characteristic diagram showing changes over time of the air-fuel ratio, the NOx purification rate, and the exhaust temperature of the engine exhaust purification control device of FIG. 11;

FIG. 14 is a diagram showing NOx in the engine exhaust gas purification control device of FIG. 11;
5 is a control flowchart for diagnosing the degree of catalyst deterioration.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 engine 2 catalyst for adsorbing exhaust gas 3 throttle valve 4 air amount sensor 5 injector 6 intake valve 7 exhaust valve 8 air-fuel ratio sensor 9 temperature sensor 10 temperature sensor 11 engine control device 100 engine exhaust purification control device 104 NOx adsorption amount estimation means 111 Engine torque control means 112 Temperature storage means 113 Catalyst purification performance diagnosis means 114 Catalyst regeneration control means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/14 330 F02D 41/14 330A 45/00 ZAB 45/00 ZAB 360 360 360C 368 368F (72) Inventor Minoru Osuka Hitachi, Ibaraki Prefecture 7-1-1, Omika-cho, Yokohama-shi Hitachi, Ltd. Hitachi Research Laboratory

Claims (11)

[Claims] An NOx catalyst disposed in an exhaust pipe;
An exhaust purification control device for an engine, comprising: a temperature sensor for detecting an exhaust temperature of an Ox catalyst, wherein the exhaust purification control device estimates a NOx adsorption amount of the NOx catalyst, and diagnoses a purification performance of the NOx catalyst. And a means for controlling regeneration of the NOx catalyst, wherein the catalyst purification performance diagnosing means diagnoses the purification performance of the catalyst based on the exhaust gas temperature detected by the temperature sensor. Control device. 2. The engine according to claim 1, wherein said catalyst regeneration control means performs catalyst regeneration control by changing an air-fuel ratio of exhaust gas based on a diagnosis result of said catalyst purification performance diagnosis means. Exhaust purification control device. 3. The exhaust gas purification control device for an engine according to claim 1, wherein the temperature sensor is disposed downstream of the NOx catalyst. 4. The catalyst purification performance diagnosing means diagnoses that the regeneration of the NOx catalyst has been completed when the temperature difference between the exhaust gas temperature at the start of catalyst regeneration and the present exhaust gas temperature is equal to or greater than a predetermined value. The exhaust gas purification control device for an engine according to claim 3, wherein: 5. The exhaust gas purification control device for an engine according to claim 1, wherein the temperature sensor is disposed on an upstream side and a downstream side of the NOx catalyst. 6. The catalyst purification performance diagnosing means, wherein the NO
The catalyst purification performance is diagnosed based on a change in the difference between each temperature difference between the exhaust gas temperature at the start of catalyst regeneration of each of the temperature sensors on the upstream and downstream sides of the x catalyst and the current exhaust gas temperature. An engine exhaust purification control apparatus according to claim 5. 7. The catalyst purification performance diagnosing means diagnoses that the regeneration of the catalyst has been completed when a difference between the respective temperature differences of the two temperature sensors is equal to or more than a predetermined value. Item 7. An exhaust gas purification control device for an engine according to Item 6. 8. The method according to claim 3, wherein the predetermined value is changed according to a degree of deterioration of the NOx catalyst diagnosed.
8. The exhaust gas purification control device for an engine according to 7. 9. The catalyst regeneration control means according to claim 1, wherein
6. The exhaust gas purification control device for an engine according to claim 2, wherein the value of the air-fuel ratio of the exhaust gas is changed according to the degree of deterioration of the x catalyst. 10. The catalyst regeneration control means according to claim 1, wherein
6. The exhaust gas purification control device for an engine according to claim 2, wherein the catalyst purification regeneration time is changed according to the degree of deterioration of the Ox catalyst. 11. The exhaust gas purification control device for an engine according to claim 2, wherein the catalyst regeneration control means sets a catalyst purification regeneration time longer than at least a time constant of the temperature sensor.