JPH0526031A - Exhaust emission control device for engine - Google Patents

Abstract

PURPOSE:To keep precision of deterioration judgment regardless of the deterioration of a sensor by setting a control constant just before the output value of a second exhaust sensor is inverted as an air-fuel ratio control constant in the deterioration judgment by a catalyst deterioration judging means at the time of catalyst deterioration judgment. CONSTITUTION:The detection value of a first exhaust sensor 12 on the upper stream side of a catalytic converter 11 disposed on the exhaust passage 6 of an engine 1 and the detection value of a second exhaust sensor 13 on the lower stream side of the catalystic converter 11 are inputted, and feedback control of air-fuel ratio is conducted on the basis of the detection value of the first exhaust sensor 12. In an ECU 14 which judges the deterioration of the catalytic convertor 12 on the basis of the detection value of the second exhaust sensor 13, an air-fuel ratio control constant is changed so that the detection value of the second exhaust sensor 13 is inverted at the time of detecting the catalyst deterioration. Further, the air-fuel ratio control constant just before the detection value of the second exhaust sensor 13 is inverted is set as a catalyst deterioration judging control constant, whereby the judging precision of catalyst deterioration can be held.

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 engine, and more particularly, to installing a catalytic converter for reducing harmful components contained in exhaust gas by a catalytic action in an exhaust passage on the downstream side of a combustion chamber. An exhaust sensor that detects the residual oxygen concentration in the exhaust gas is installed on the upstream side, and the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is feedback-controlled to the target air-fuel ratio according to the detection value of this exhaust sensor. Exhaust gas purification device for engine.

[0002]

2. Description of the Related Art Combustion is used in engines for vehicles.
To reduce harmful components contained in later exhaust gas
In addition, of the harmful components listed above, it has a particularly large impact on the environment.
Carbon monoxide (CO ), Hydrocarbons (HC) and nitrogen oxides
(NO_x) Three-dimensional touch that exhibits excellent purification characteristics for the three components
A catalytic converter using a medium is installed in the exhaust system,
To ensure that the catalytic action of the above three-way catalyst is efficiently exhibited,
The air-fuel ratio of the air-fuel mixture supplied to the firing chamber is set to a predetermined target air-fuel ratio.
(For example, the theoretical air-fuel ratio; air / fuel = 14.7)
There is an air-fuel ratio control that is performed. This air fuel
Specifically, the ratio control is performed on the upstream side of the catalytic converter.
Boundary when the excess air ratio λ (actual air-fuel ratio / theoretical air-fuel ratio) is 1
Install an exhaust sensor whose output state changes as
The air-fuel ratio detected value of the air sensor is rich (fuel is rich
State), the fuel supply amount is reduced and the
Note that the detected value is lean when the air-fuel ratio (fuel is lean)
When indicated, combustion is increased by increasing the fuel supply.
The air-fuel ratio of the air-fuel mixture supplied to the chamber converges to the above target air-fuel ratio
To be done.

By the way, the three-way catalyst used in the above-mentioned catalytic converter has impurities attached to the catalyst component by, for example, injecting leaded gasoline, and the performance is improved even within a service period set in accordance with aging. There is a problem of deterioration.

To solve this problem, for example, as disclosed in Japanese Patent Laid-Open No. 63-97852, a second method for detecting the oxygen concentration downstream of a catalytic converter provided in the exhaust system of an engine is used. There is a system in which the exhaust sensor is installed and the deterioration of the catalytic action is determined by the number of output reversals during the air-fuel ratio feedback control of the exhaust sensor. This is intended to indirectly judge the deterioration of the catalyst by paying attention to the fact that the oxygen concentration on the downstream side of the catalyst has almost no difference from that on the upstream side due to the decrease in the oxygen storage capacity when the catalytic action deteriorates.

By the way, the catalyst in the catalytic converter installed in the exhaust passage is adapted to repeat the oxidation-reduction reaction with respect to harmful components due to adsorption and desorption of oxygen.
There is a problem that the oxygen partial pressure on the downstream side of the catalytic converter does not fluctuate easily, and depending on the operating state, it may be in an oxygen excess state or an oxygen deficiency state and may not be constant. That is, since the air-fuel mixture supplied to the combustion chamber of the engine is controlled in the vicinity of the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas discharged from the combustion chamber also has a value that reflects the stoichiometric air-fuel ratio.
Therefore, when the amount of oxygen in the exhaust gas on the upstream side is large, the oxygen concentration downstream of the catalytic converter becomes excessive due to the oxygen overflowing the oxygen storage capacity of the catalyst,
Further, when the amount of oxygen in the exhaust gas is small, all the oxygen is adsorbed by the catalyst, so that the oxygen concentration on the downstream side becomes insufficient. For this reason, even if an attempt is made to determine the deterioration of the catalyst based on the detection value of the exhaust sensor downstream of the catalytic converter, a problem arises in that good determination accuracy cannot be obtained.

[0006] With respect to such a problem, there is a prior art in which the applicant of the present application filed a patent application No. 93518 in 1991. In this prior art, when determining the deterioration of the exhaust gas purification catalyst, a dedicated air-fuel ratio such that the oxygen partial pressure in the vicinity of the exhaust sensor on the catalyst downstream side is biased toward either the excess side or the insufficient side with respect to normal time A feedback control constant is used, which allows the composition of the exhaust gas on the downstream side of the catalyst to be in either an oxygen excess state or an oxygen deficiency state, which improves the accuracy of deterioration determination and improves the normal air-fuel ratio. Control accuracy is not lost,
Exhaust performance will be improved overall.

[0007]

However, it has been found that even if the above feedback control constant dedicated to the catalyst deterioration detection is used, a problem occurs in the following cases.

That is, the exhaust sensor used for detecting the catalyst deterioration also deteriorates over a long period of use, and even if the initially set feedback control constant for detecting the catalyst deterioration is used, the exhaust sensor Due to the decrease in oxygen reactivity,
For example, it is possible to erroneously determine that the catalyst is in a deteriorated state despite having sufficient activity.

According to the present invention, exhaust sensors whose output values are inverted depending on the oxygen concentration are installed upstream and downstream of the catalytic converter installed in the exhaust system of the engine, and the air-fuel ratio of the air-fuel ratio is changed according to the output value of the exhaust sensor on the upstream side. It deals with the above problem in the engine that performs the feedback control and determines the deterioration of the catalyst on the basis of the output value of the exhaust sensor on the downstream side. The purpose is to further improve the deterioration determination accuracy.

[0010]

That is, an engine exhaust gas purification apparatus according to the present invention is installed on the upstream side of an exhaust gas purification catalyst provided in an exhaust system of an engine and contains residual oxygen contained in the exhaust gas. A first exhaust sensor whose output value is inverted depending on the concentration; a second exhaust sensor which is installed on the downstream side of the catalyst and whose output value is inverted depending on the residual oxygen concentration also contained in the exhaust gas; In an engine provided with air-fuel ratio control means for feedback-controlling the air-fuel ratio according to the output value, and catalyst deterioration determination means for performing deterioration determination of the catalyst based on the output value of the second exhaust sensor under predetermined conditions, When the catalyst deterioration is determined, the control constant of the air-fuel ratio control means is changed so that the output value of the second exhaust sensor is inverted, and the output value of the sensor is inverted before the output value is inverted. His constant, characterized in that a catalyst deterioration determination control constant setting means for setting the air-fuel ratio control constants at the time deterioration determination by said catalyst deterioration determining means.

[0011]

According to the above structure, when determining the deterioration of the catalyst, the air-fuel ratio control constant before the output value of the second exhaust sensor on the downstream side of the catalyst is reversed is set as the control constant for catalyst deterioration determination. Therefore, the deterioration determination constant is appropriately set regardless of the deterioration of the sensor,
The accuracy of determining the deterioration of the catalyst is kept good, the accuracy of the air-fuel ratio control during normal operation is not impaired, and the exhaust gas purification performance is improved overall.

[0012]

EXAMPLES Examples of the present invention will be described below.

First, the control system of the engine 1 will be described with reference to FIG. 1. The engine 1 has intake and exhaust valves 2, 3
An intake passage 5 and an exhaust passage 6 are provided which communicate with the combustion chamber 4 via the. In the intake passage 5, an air cleaner 7, an air flow meter 8 and a throttle valve 9 are installed from the upstream side, and a fuel injection valve 10 is installed downstream of the throttle valve 9.

On the other hand, a three-way catalytic converter 11 for purifying the exhaust gas after combustion is installed in the exhaust passage 6, and the residual oxygen concentration in the exhaust gas is detected upstream and downstream of this catalytic converter 11. First and second exhaust gas sensor 1
2 and 13 are installed respectively.

In this control system, the control of the fuel injection amount from the fuel injection valve 10 and the catalytic converter 1 are performed.
An electronically controlled control unit (hereinafter, referred to as ECU) 14 for performing the deterioration determination 1 is provided. The ECU 14 receives an intake air amount signal from the air flow meter 8, a throttle opening signal from a throttle opening sensor 15 that detects the opening of the throttle valve 9, and a vehicle speed from a vehicle speed sensor 16 that detects the vehicle speed of the vehicle. Signal and
The engine speed signal from the rotation sensor 17 for detecting the engine speed, the water temperature signal from the water temperature sensor 18 for detecting the temperature of the engine cooling water, and the first and second exhaust sensors 12, 13 are respectively detected. The oxygen concentration signal is input, and the air-fuel ratio control of the air-fuel mixture supplied to the combustion chamber 4 and the deterioration determination process of the catalytic converter 11 are performed based on these signals. The ECU 14 is the catalytic converter 1
Lighting control of the warning lamp 19 for deterioration warning of No. 1 is also performed.

The air-fuel ratio control carried out by the ECU 14 will be briefly described below. The ECU 14 reads various signals and then based on the intake air amount indicated by the intake air amount signal and the engine speed indicated by the engine speed signal. Then, the amount of air taken into the combustion chamber 4 per cycle is calculated, and the corresponding basic fuel injection amount is set. Next, the ECU 14
Determines whether the air-fuel ratio feedback condition is satisfied. That is, the ECU 14 determines that the operating state of the engine 1 using the throttle opening degree representing the engine load and the engine speed as parameters belongs to a predetermined feedback region, and the engine cooling water temperature indicated by the water temperature signal becomes a predetermined value or more. Then, the air-fuel ratio feedback control is executed.

This air-fuel ratio feedback control is performed roughly as follows. That is, the ECU 14 is the first
When the oxygen concentration signal from the exhaust sensor 12 indicates the lean state of the air-fuel ratio, the feedback correction amount C _FB is set so that the fuel increases, while when the oxygen concentration signal indicates the rich state of the air-fuel ratio, the fuel amount decreases. The feedback correction amount C _FB is set so that Further, the final injection amount is set by correcting the basic fuel injection amount with the feedback correction amount C _FB and the water temperature correction amount. Then, a fuel injection signal is output to the fuel injection valve 10 so as to obtain this final injection amount.

The feedback correction amount C _FB is
Specifically, it is obtained as follows. Ie EC
As shown in FIG. 2, U14 is the first exhaust sensor 12
At the time when the output voltage V ₁ of the fuel cell becomes larger than the predetermined reference voltage V _10, it is determined that the air-fuel ratio has changed from the lean state to the rich state, and the feedback correction amount C at that time is determined.
A value _FB only during the predetermined lean delay constant D _L1 continues to update with the predetermined rich integration constant I _R1, the delay constant D _L1
After the lapse of time, it is decreased by a predetermined lean skip value P _L1 all at once, and then gradually decreased by using a predetermined lean integration constant I _L1 . Then, when the output voltage V ₁ of the first exhaust sensor 12 becomes lower than the reference voltage V _10, it is determined that the air-fuel ratio is inverted from the rich state to the lean state, and the feedback correction amount C at that time is determined. The value of _FB is continuously updated using the lean integration constant I _L1 for a predetermined rich delay constant D _R1 , and after the delay constant D _R1 has elapsed, it is increased by a predetermined rich skip value P _{R1 at} once. It is gradually increased using the rich integration constant I _R1 .

On the other hand, when the ECU 14 determines that the above feedback conditions are not satisfied, the fuel injection amount is read from the fuel injection map set with parameters such as throttle opening, engine speed, and water temperature. Open loop control for outputting a fuel injection signal to the fuel injection valve 10 is executed.

Next, the catalyst deterioration determination processing, which is a characteristic part of the present invention, will be described. This catalyst deterioration determination processing is performed as follows according to the flowchart of FIG.

That is, the ECU 14 determines in step S1 whether a predetermined catalyst deterioration detection condition is satisfied.
That is, the ECU 14 determines that the catalyst deterioration detection condition is satisfied when the air-fuel ratio feedback condition is satisfied and the throttle opening degree, the vehicle speed, and the like satisfy predetermined conditions.

When the ECU 14 determines that the catalyst deterioration detection condition is satisfied, the ECU 14 proceeds to step S2 and compares the output voltage V ₂ of the second exhaust sensor 13 with a predetermined reference voltage V ₂₀ . When it is determined that the output voltage V ₂ is in the rich state higher than the reference voltage V ₂₀ , the step S
A predetermined amount δP in the previous value P _^'L of the lean skip value proceed to 3
The value obtained by adding only is set to the current value P _L , and then it is determined in step S4 whether or not the output voltage V ₂ of the second exhaust sensor 13 is inverted, and the output voltage V ₂ is set to the reference voltage V _20.
If it is determined that the lean state is lower than
A value obtained by subtracting a predetermined amount δP from the previous value P _^'L of the proceeds to the 5 lean skip value P _L in terms of the set to the current value P _L, also the output voltage V of the second exhaust gas sensor 2 in step S4
Determine if ₂ is inverted. In short, the feedback control constant is changed so that the output voltage V ₂ of the second exhaust sensor 13 is inverted.

When the ECU 14 determines in step S4 that the output voltage V ₂ of the second exhaust sensor 13 is reversed, the ECU 14 proceeds to step S6 and uses the feedback control constant at the time when the output voltage V ₂ is reversed to use the lean skip value P for catalyst deterioration determination.
Calculate _L2 . That is, for example, as shown in FIG. 4B, the output voltage V ₂ of the second exhaust sensor 13 is the reference voltage V _20.
At high rich state than, as shown in FIG. (C), changes in the lean skip value of the previous value P ^'present value _L is added ^{_{P L (P L -P' L}} = δP) as described above Will be done. In that case, if the output voltage V ₂ of the second exhaust sensor 13 has a value lower than the reference voltage V ₂₀ and is in the inversion state at time t ₁ , as shown in FIG. If feedback control of the air-fuel ratio is performed using the lean skip value P _L of, the output voltage V ₂ of the second exhaust sensor 13 surely shows a value lower than the reference voltage V ₂₀ , and the catalytic converter 11 Therefore, it is not possible to judge the deterioration of. Therefore, a value obtained by subtracting the predetermined value P _C from the lean skip value P _L when the output voltage V ₂ is inverted is a lean skip value for catalyst deterioration determination P _L2 (P _L2 = P _L −
P _C ). In this way, a value close to the lean skip value immediately before the output voltage V ₂ is inverted is set as the catalyst deterioration determination lean skip value P _L2 . Of course, when the step S5 is executed and the output voltage V ₂ of the second exhaust sensor 13 shifts from a state lower than the reference voltage V ₂₀ to a state higher than the reference voltage V ₂₀ , the lean skip value P _L at that time is set to a predetermined value. Value P _C
The value obtained by adding is set as the catalyst deterioration determination lean skip value P _L2 .

When the ECU 14 obtains the catalyst deterioration determining lean skip value P _L2 in step S5, the ECU 14 subsequently executes the catalyst deterioration determining process of steps S7 to S10. That is, in step S7, the first exhaust sensor 12
_1st output voltage V ₁ input from the reference voltage V ₁₀
The number of inversions N ₁ and the number of second inversions N _{2 of} the output voltage V ₂ input from the second exhaust sensor 13 with respect to the reference voltage V ₂₀ are respectively counted, and the second inversion of the first number of inversions N _{1 is performed in} step S8. It is determined whether the ratio of the number of times N ₂ is greater than a predetermined deterioration determination reference value K, and YES
When it is determined that it is determined in step S9 whether the catalyst deterioration is confirmed, when it is determined that it is YES, step S1 is performed.
0 is executed to turn on the warning light 19. The ECU 1
4 indicates that the catalyst deterioration is determined when the ratio of the second inversion number N ₂ to the first inversion number N ₁ becomes larger than the deterioration determination reference value K three times in succession. ..

When the warning light 19 is turned on, the ECU 14 proceeds to step S11, where the lean skip value P _L is reached.
Is set to the normal lean-skip value P _L1 for air-fuel ratio control, and the catalyst deterioration determination process is ended.

Further, the ECU 14 executes the above steps S8, S
If NO is determined in 9, the process skips step S10 and moves to step S11 to set the lean skip value P _L to the normal lean skip value P _L1 for controlling the air-fuel ratio and end the catalyst deterioration determination process.

Next, the operation of the embodiment will be described with reference to FIG.

That is, at the time of catalyst deterioration determination, as shown in FIG. 5B, the air-fuel ratio is set to the catalyst deterioration determination lean skip value P _L2 close to the value at which the output voltage V ₂ of the second exhaust sensor 13 is inverted. Control is performed. In that case, when the catalytic converter 11 is activated, the output voltage V ₂ of the second exhaust sensor 13 shifts in a state of being biased to the rich side, and the second inversion number N ₂ with respect to the first inversion number N ₁ is changed. The ratio does not become larger than the deterioration determination reference value K, and the deterioration state is not determined.

On the other hand, when the output voltage V ₂ of the second exhaust sensor 13 exceeds the reference voltage V ₂₀ and inverts to the lean side as shown by the broken line in FIG. The ratio of the second reversal number N ₂ to the first reversal number N ₁ often becomes larger than the deterioration determination reference value K, and when the catalyst deterioration is definitely determined, the warning lamp 19 is turned on. It will inform the driver of the abnormality.

In this embodiment, when the catalyst deterioration is detected, the lean skip value for feedback correction is changed to obtain the catalyst deterioration determination control constant, but the rich skip value may be changed. Further, the integration constant and the delay constant may be changed.

[0031]

As described above, according to the engine exhaust gas purification apparatus of the present invention, the air-fuel ratio control constant before the output value of the second exhaust sensor on the downstream side of the catalyst reverses when the catalyst deterioration is determined. Is set as the catalyst deterioration determination control constant, the deterioration determination constant is appropriately set regardless of the deterioration of the sensor, and the catalyst deterioration determination accuracy is kept good. Therefore, the air-fuel ratio control accuracy at the normal time will not be impaired, and the exhaust purification performance will be comprehensively improved.

[Brief description of drawings]

FIG. 1 is a control system diagram of an engine.

FIG. 2 is a time chart diagram showing changes in the feedback correction amount during normal times.

FIG. 3 is a flowchart showing a catalyst deterioration determination process.

FIG. 4 is a time chart showing changes in the feedback correction amount in the process of calculating the feedback control constant for catalyst deterioration determination.

FIG. 5 is a time chart showing changes in the feedback correction amount when determining catalyst deterioration.

[Explanation of symbols]

 1 Engine 6 Exhaust Passage 10 Fuel Injection Valve 11 Catalytic Converter 12 First Exhaust Sensor 13 Second Exhaust Sensor 14 ECU

Claims (1)

Claim: What is claimed is: 1. A first exhaust sensor, which is installed upstream of an exhaust gas purifying catalyst provided in an exhaust system of an engine and whose output value is inverted by the concentration of residual oxygen contained in the exhaust gas. And a second exhaust sensor, which is installed downstream of the catalyst and whose output value is inverted by the residual oxygen concentration similarly contained in the exhaust gas, and the air-fuel ratio is feedback-controlled according to the output value of the first exhaust sensor. An exhaust gas purification apparatus for an engine, comprising: an air-fuel ratio control means; and a catalyst deterioration determination means for determining the catalyst deterioration based on an output value of a second exhaust sensor under a predetermined condition. At
The control constant of the air-fuel ratio control means is changed so that the output value of the second exhaust sensor is inverted, and the control constant before the output value of the sensor is inverted is used when the deterioration determination is made by the catalyst deterioration determination means. An exhaust emission control device for an engine, comprising: a catalyst deterioration determination control constant setting means which is set as an air-fuel ratio control constant.