JPH0466716A - Catalyst converter device for internal combustion engine - Google Patents

Abstract

PURPOSE:To make a 2nd air-fuel ratio sensor feedback cycle shorter and make the air-fuel ratio maximum shift quantity from a theoretical air-fuel ratio small, by setting the oxygen storage capacity of the 1st catalyst smaller than that of the 2nd catalyst. CONSTITUTION:At an engine 11 exhaust passage 18, the 1st air-fuel ratio sensor 19 which detects an intake air mixture air-fuel ratio by detecting oxygen density in exhaust, is provided at a manifold assembly portion, and the 1st ternary catalyst 20 which acts as an exhaust purification catalyst that conducts purification by conducting the oxidization of CO, HC and the reduction of NOX in exhaust, is provided on the lower stream side. Also, the 2nd air-fuel ratio sensor 21 which is the same as above, is provided downstream of the 1st catalyst 20, and the 2nd three way catalyst 22 which is the same as above but a little smaller in its volume, is provided at the downstream part. A catalyst converter device is thus made up of the above. In this instance, the oxygen storage capacity of the 1st catalyst 20 is set relatively, and the oxygen suction capacity limit of the 1st catalyst 20 and an oxygen quantity that can not be sucked, too, are made small.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a catalytic converter device for an internal combustion engine, and in particular includes air-fuel ratio sensors upstream and downstream of an exhaust purification catalyst, The present invention relates to a catalytic converter device for an internal combustion engine used in a device that performs feedback control of an air-fuel ratio with high precision based on a detected value.

<Prior Art> A conventional general air-fuel ratio control device for an internal combustion engine is disclosed in, for example, Japanese Patent Application Laid-Open No. 60-240840.

To give an overview of this, the intake air flow rate Q and rotational speed N of the engine are detected, and the basic fuel supply amount T, (=K・Q/N; K is a constant) corresponding to the amount of air taken into the cylinder, is calculated. This basic fuel supply amount T is calculated and corrected based on engine temperature, etc., and then the air-fuel ratio is set by a signal from an air-fuel ratio sensor (oxygen sensor) that detects the air-fuel ratio of the air-fuel mixture by detecting the oxygen concentration in the exhaust gas. Feedback correction is performed using a feedback correction coefficient (air-fuel ratio correction amount), and correction based on battery voltage is also performed to finally set the fuel supply amount T1.

Then, by outputting a drive pulse signal with a pulse width corresponding to the fuel supply amount T thus set to the fuel injection valve at a predetermined timing, a predetermined amount of fuel is injected and supplied to the engine. .

The air-fuel ratio feedback correction based on the signal from the air-fuel ratio sensor is performed to control the air-fuel ratio to around the target air-fuel ratio (stoichiometric air-fuel ratio). This is installed in the exhaust system and oxidizes Co and HC (hydrocarbons) in the exhaust, as well as NO
This is because the conversion efficiency (purification efficiency) of the exhaust purification catalyst (three-way catalyst) that reduces and purifies the exhaust gas is set so that it functions effectively in the exhaust state during combustion at the stoichiometric air-fuel ratio.

As mentioned above, the electromotive force (output voltage) generated by the air-fuel ratio sensor has a characteristic that it changes suddenly near the stoichiometric air-fuel ratio, and this output voltage v
0 and the reference voltage (slice level) SL equivalent to the stoichiometric air-fuel ratio
It is determined whether the air-fuel ratio of the air-fuel mixture is rich or lean with respect to the stoichiometric air-fuel ratio. For example, when the air-fuel ratio is lean (rich), the feedback correction coefficient α to be multiplied by the basic fuel supply amount TP is increased (decreased) by a large proportionality constant P the first time the basic fuel supply amount TP is changed to lean (rich), and then a predetermined value is set. The air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio by gradually increasing (decreasing) the fuel supply amount T by an integral constant I.

By the way, in the above-mentioned normal air-fuel ratio feedback control device, one air-fuel ratio sensor is used to improve responsiveness.
The air-fuel ratio sensor should be installed in the gathering part of the exhaust manifold as close to the combustion chamber as possible, since the exhaust temperature is high in this part, and the characteristics of the air-fuel ratio sensor are likely to change due to thermal effects and deterioration.
Because the exhaust gas from each cylinder is insufficiently mixed, it is difficult to detect the average air-fuel ratio of all cylinders, and the air-fuel ratio detection accuracy is difficult.
This in turn worsened the accuracy of air-fuel ratio control.

In view of this point, it has been proposed to provide an air-fuel ratio sensor also on the downstream side of the exhaust purification catalyst (hereinafter referred to as the first exhaust purification catalyst) and to feedback-control the air-fuel ratio using the detected values of the two air-fuel ratio sensors. (Refer to Japanese Unexamined Patent Publication No. 58-48756).

In other words, the air-fuel ratio sensor on the downstream side (hereinafter referred to as the second air-fuel ratio sensor) may have difficulty in responding because it is far from the combustion chamber, or it may have difficulty in responding because it is downstream of the first exhaust purification catalyst. Impact (CO, HC.

NOx, CO*, etc.), and the amount of poisoning by toxic components in the exhaust is small, making it less susceptible to changes in characteristics due to poisoning.Moreover, because the mixture state of the exhaust is good, the average air-fuel ratio of the gold cylinder is Upstream air-fuel ratio sensor (
(hereinafter referred to as the first air-fuel ratio sensor), highly accurate and stable detection performance can be obtained.

Therefore, it is possible to combine two air-fuel ratio feedback correction coefficients that are respectively set by calculations similar to those described above based on the detected values of the two air-fuel ratio sensors, or to control the air-fuel ratio feedback correction coefficient that is set by the first air-fuel ratio sensor. The variation in the output characteristics of the upstream air-fuel ratio sensor is compensated for by the second air-fuel ratio sensor by correcting the constant (proportional component or integral component), the comparison voltage of the output voltage of the first air-fuel ratio sensor, and the delay time. Accurate air-fuel ratio feedback control is performed.

By the way, in the case where the air-fuel ratio is feedback-controlled using the detection values of the two air-fuel ratio sensors as described above, along with the feedback control by the second air-fuel ratio sensor,
The air-fuel ratio will fluctuate up to the oxygen adsorption capacity limit of the first exhaust purification catalyst disposed between the two air-fuel ratio sensors.

Here, the oxidation efficiency of carbon monoxide (CO), hydrocarbons (HC), etc. of the first exhaust purification catalyst, as well as the oxidation efficiency of nitrogen oxides (NO,
) etc. decreases near the limit of the air-fuel ratio, so when the air-fuel ratio is swung to near the limit as mentioned above, unburned components in the exhaust cannot be sufficiently purified and emissions increase. There is a fear.

In view of this, an exhaust purification catalyst (hereinafter referred to as the second exhaust purification catalyst) is further provided downstream of the second air-fuel ratio sensor, so that even when the air-fuel ratio swings to near the limit as described above, the There is a second exhaust gas purification catalyst that purifies unburned components in the exhaust gas, thereby achieving good exhaust emissions.

In recent years, monolith catalysts have been used as exhaust purification catalysts, in which catalyst components such as precious metals for purifying engine exhaust gas are supported on an integrally molded ceramic monolith carrier. By the way, when engine exhaust gas is purified using a three-way catalyst supported on a monolithic catalyst, the purification characteristics vary greatly depending on the set air-fuel ratio of the engine. That is, when the air-fuel ratio is low, the amount of oxygen increases even after combustion, and the oxidizing action becomes active, while the reducing action becomes inactive. Conversely, when the air-fuel ratio is high, the oxidizing action becomes inactive and the reducing action becomes active.

For this reason, conventionally, ceria (Ce02) having an oxygen storage ability has been supported in order to sufficiently maintain the catalytic activity of the three-way catalyst and further increase the catalytic activity even if the air-fuel ratio fluctuates.

<Problem to be Solved by the Invention> By the way, in the above-mentioned conventional system in which two exhaust purification catalysts are provided in the exhaust passage, the first exhaust purification catalyst is close to the engine body, so high-temperature exhaust gas passes through it. . Here, since the ceria also has the effect of improving heat resistance,
In order to protect the ceramic monolith support from the high temperature of the exhaust gas, a large amount of ceria is supported on the first exhaust purification catalyst.

However, if the first exhaust purification catalyst supports a large amount of ceria, the oxygen adsorption capacity limit of the first exhaust purification catalyst becomes large. As a result, the feedback cycle of the second air-fuel ratio sensor becomes longer, the maximum deviation of the air-fuel ratio from the stoichiometric air-fuel ratio becomes larger, the usage rate in areas with low conversion efficiency increases, and emissions increase. be.

On the other hand, when the volume of the first exhaust purification catalyst is made smaller than that of the second exhaust catalyst, the conversion efficiency of the first exhaust purification catalyst decreases, and the output characteristics of the first air-fuel ratio sensor by the second air-fuel ratio sensor are reduced. Compensation becomes impossible, making it impossible to perform highly accurate air-fuel ratio feedback control.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional circumstances, it is an object of the present invention to provide a catalytic converter device for an internal combustion engine that can perform highly accurate air-fuel ratio feedback while ensuring good emissions.

Means for Solving the Problems> Therefore, the catalytic converter device for an internal combustion engine according to the present invention includes first and second catalysts for exhaust purification, which are provided on the upstream side and the downstream side of the engine exhaust passage, respectively; A second catalyst is disposed upstream of the first catalyst and between the first catalyst and the second catalyst, and whose output value changes in response to the concentration ratio of a specific gas component in the exhaust gas that changes depending on the air-fuel ratio. 1 and a second air-fuel ratio sensor, the air-fuel ratio control device for an internal combustion engine controls the air-fuel ratio by correcting the amount of fuel supplied to the intake system or the amount of air supplied to the intake system. The configuration is such that the capacity is smaller than the oxygen storage capacity of the second catalyst.

<Function> If the oxygen storage capacity is small and the air-fuel ratio fluctuates greatly, the conversion efficiency of the catalyst will deteriorate. In this case, by reducing the oxygen storage capacity of the first catalyst, the oxygen adsorption capacity limit of the first exhaust purification catalyst becomes smaller. Therefore, the feedback cycle of the second air-fuel ratio sensor becomes shorter, the maximum deviation of the air-fuel ratio from the stoichiometric air-fuel ratio becomes smaller, and the proportion of the catalyst used in the portions with high conversion efficiency increases, resulting in lower emissions.

Furthermore, since the second catalyst has a large oxygen storage capacity, its ability to purify unburned components in the exhaust gas is sufficient even when the air-fuel ratio fluctuates.

Therefore, it is possible to perform highly accurate air-fuel ratio feedback control while ensuring good emissions.

<Example> Embodiments of the present invention will be described below based on the drawings.

In FIG. 1 showing the configuration of one embodiment, an air flow meter 13 for detecting an intake air flow rate Q and a throttle valve 14 for controlling the intake air flow rate Q in conjunction with an accelerator pedal are provided in an intake passage 12 of an engine 11. An electromagnetic fuel injection valve 15 serving as a fuel supply means is provided for each cylinder in the downstream manifold portion.

The fuel injection valve 15 is driven to open by an injection pulse signal from a control unit 16 having a built-in microcomputer, and injects fuel that is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator. Furthermore, a water temperature sensor 17 for detecting the temperature Tw of the cooling water in the cooling jacket of the engine 11 is provided.

On the other hand, the exhaust passage 18 is provided with a first air-fuel ratio sensor 19 that detects the air-fuel ratio of the intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas at the manifold gathering part, and the exhaust gas First three-way catalyst 2 as an exhaust purification catalyst that oxidizes Co and HC and reduces NOx.
Further, a second air-fuel ratio sensor 21 having the same function as the first air-fuel ratio sensor is provided downstream of the first three-way catalyst 20, and furthermore, a second air-fuel ratio sensor 21 having the same function as the first air-fuel ratio sensor is provided. It has the same function as the first three-way catalyst 20 on the downstream side, and
A second three-way catalyst 22 having a slightly smaller volume than the first three-way catalyst 20 is provided.

That is, the first three-way catalyst 20. A catalytic converter device is constituted by the second three-way catalyst 22 and the like.

Further, the distributor (not shown in FIG. 1) has a built-in crank angle sensor 23, and a crank angle signal outputted from the crank angle sensor 23 in synchronization with engine rotation is counted for a certain period of time, or The engine rotation speed N is detected by measuring the period of the crank reference angle signal.

Next, the air-fuel ratio control routine by the control unit 16 will be explained according to the flowchart shown in FIG. Second
The figure shows a fuel injection amount setting routine, and this routine is performed at predetermined intervals (for example, every 10 m5).

In step (denoted as S in the figure) l, the intake air amount per unit rotation is determined based on the intake air flow rate Q detected by the air flow meter 13 and the engine rotation speed N calculated based on the signal from the crank angle sensor 24. The basic fuel injection amount T, which corresponds to T, is calculated using the following equation.

T p = K x Q / N (K is a constant) In step 2, various correction coefficients C0EF are set based on the cooling water temperature Tw etc. detected by the water temperature sensor 17.

In step 3, the feedback correction coefficient α set by another routine is read.

That is, the two air-fuel ratio feedback correction coefficients set respectively based on the detected values of the first and second air-fuel ratio sensors 19.21 are combined, or the first air-fuel ratio sensor 1
A value obtained by compensating for variations in the output characteristics of the first air-fuel ratio sensor 19 by the second air-fuel ratio sensor 22 by correcting the control constant (proportional component or integral component) of the air-fuel ratio feedback correction coefficient set by 9. Load.

In step 4, a voltage correction numerator is set based on the battery voltage value. This is to correct changes in the injection flow rate of the fuel injection valve 15 due to battery voltage fluctuations.

In step 5, the final fuel injection amount (fuel supply amount) T
1 is calculated according to the following formula.

T+=Tp xCOEFxa+Ts In step 6, the calculated fuel injection valve T1 is set in the output register.

As a result, when the predetermined fuel injection timing is synchronized with the engine rotation, a drive pulse signal having a pulse width of the calculated fuel injection amount T1 is applied to the fuel injection valve 15 to perform fuel injection.

Here, the first three-way catalyst 20 and the second three-way catalyst 22 are used as the first and second catalysts for exhaust purification according to the present invention.
is a monolith type catalyst, for example as shown in FIGS. 3 and 4.

That is, a cylindrical carrier 31 made of a heat-resistant alloy or the like.
is formed by a honeycomb-shaped processing gas passage 32 or partition wall 32a that linearly communicates both ends in the axial direction. A partition wall 32 forming a processing gas passage 32 of this carrier 31
Wash coat 3 of the components described below is applied to the inner peripheral wall surface of a.
3 is coated, thereby forming a monolithic catalyst 34.
or configured.

Here, Table 1 shows the components of the wash coat 33 as a first example according to the present invention.

That is, the content of ceria CeO□, which is a component having an oxygen storage ability, in the first catalyst 20 is 1/3 compared to the content of ceria CeO□ in the second catalyst 22.

Table 1 Therefore, the oxygen storage capacity of the first catalyst 20 is small;
The oxygen adsorption capacity limit of the first catalyst 20 and the aforementioned amount of oxygen that cannot be adsorbed are also small. Therefore, according to the configuration of this embodiment, the first air-fuel ratio sensor 19 and the second air-fuel ratio sensor 21 Since the air-fuel ratio is controlled by the second air-fuel ratio sensor 21, the feedback period of the second air-fuel ratio sensor 21 becomes short, and
Compared to the conventional example shown in FIG. 5(b), as shown in FIG. 5(a), the air-fuel ratio is prevented from fluctuating greatly.

Furthermore, the second catalyst 22 has a large content of ceria CeO2, so it has a large oxygen storage capacity, and even if the air-fuel ratio fluctuates, it has sufficient ability to purify unburned components in the exhaust gas, so the emission at the outlet of the second catalyst 22 is sufficient. can be reduced (see Figure 5).

Therefore, according to this embodiment, it is possible to perform highly accurate air-fuel ratio feedback control while ensuring good emissions.

Next, a second embodiment according to the present invention will be described.
The first primary catalyst 20 and the second three-way catalyst 22 as the first and second catalysts for exhaust purification in the catalytic converter device according to the embodiment are the same as those in the first embodiment, so the configuration is as follows. The explanation will be omitted.

In the second example, Otsushu Coat 3 with the ingredients shown in Table 2 was used.
3 was applied.

Table 2 Also in this example, the content of ceria CeO□ in the first catalyst 20 is smaller than the content in the second catalyst 22.
Furthermore, in this example, the content of zirconia (Zr02) and barium oxide (Bad) is increased to compensate for the thermal deterioration of the catalyst noble metal.

Next, a third embodiment of the present invention will be described.

As shown in FIG. 6, the exhaust purification catalytic converter device 30 according to the third embodiment includes a first three-way catalyst 31 in a container 33.
and a second three-way catalyst 32 are provided in series, and a second air-fuel ratio sensor 21 is provided in the exhaust passage 34 between the first three-way catalyst 31 and the second three-way catalyst 32. It is something.

In the third example, a wash coat 33 having the components shown in Table 3 was applied.

Table 3 Also in this example, the content of ceria CeO2 in the first catalyst 31 is smaller than the content in the second catalyst 32, and also in this example, the content of zirconia (ZrO2) and barium oxide (Bad) is The amount is increased to compensate for thermal degradation of the catalytic precious metal.

<Effects of the Invention> As described above, according to the present invention, the first air-fuel ratio sensor is arranged from the upstream side in the engine exhaust passage.

In a device equipped with a first catalyst for exhaust purification, a second air-fuel ratio sensor, and a second catalyst for exhaust purification in this order, the oxygen storage capacity of the first catalyst is made smaller than the oxygen storage capacity of the second catalyst. Therefore, the feedback cycle of the second air-fuel ratio sensor can be shortened, the maximum deviation of the air-fuel ratio from the stoichiometric air-fuel ratio can be reduced, and the ability of the second catalyst to purify unburned components in the exhaust gas can also be sufficiently ensured. I can do it.

Therefore, it is possible to perform highly accurate air-fuel ratio feedback control while ensuring good emissions.

[Brief explanation of drawings]

Fig. 1 is a system configuration diagram according to an embodiment of the present invention, a flowchart showing a fuel injection amount setting routine of the second commercial embodiment, Fig. 3 is a perspective view of a monolith catalyst, and Fig. 4 is a portion of Fig. 3. Enlarged view, Figure 5 is Book 11... Engine 18...
-Exhaust passage 19...first air-fuel ratio sensor 20
...First three-way catalyst 2021...Second air-fuel ratio sensor 22...Second three-way catalyst 3I...Carrier
32a...Partition wall 33...Wash coat patent applicant Nissan Motor Co., Ltd. agent Patent attorney Fujio Sasashima 11...Engine 18...Exhaust passage 19...First air-fuel ratio sensor 20... First three-way catalyst 2゜× 23

Claims (1)

[Scope of Claims] First and second catalysts for exhaust purification provided on the upstream side and downstream side of an engine exhaust passage, respectively, and the first catalyst and the second catalyst on the upstream side of the first catalyst, and the first catalyst and the second catalyst. a catalytic converter device for an internal combustion engine, comprising first and second air-fuel ratio sensors that are respectively disposed between the air-fuel ratio sensor and the air-fuel ratio sensor and whose output value changes in response to the concentration ratio of a specific gas component in the exhaust gas that changes depending on the air-fuel ratio. A catalytic converter device for an internal combustion engine, characterized in that the oxygen storage capacity of the first catalyst is smaller than the oxygen storage capacity of the second catalyst.