JP2623926B2 - Catalytic converter device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a catalytic converter device for an internal combustion engine, and more particularly, to an air-fuel ratio sensor provided 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 for performing feedback control of an air-fuel ratio with high accuracy based on a detected value.

<Prior Art> A conventional general air-fuel ratio control apparatus for an internal combustion engine is disclosed, for example, in JP-A-60-240840.

To explain the outline of this, the intake air flow rate Q of the engine
And detects the rotational speed N corresponding to the quantity of air sucked into the cylinder basic fuel supply quantity _{T P (= K · Q /} N; K is a constant) is calculated, and the engine temperature the basic fuel supply quantity T _P Feedback using the air-fuel ratio feedback correction coefficient (air-fuel ratio correction amount) 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 by correcting the air-fuel ratio in the exhaust gas subjected to correction, finally setting the fuel supply quantity T ₁ also been corrected due battery voltage.

Then, by outputting a driving pulse signal having a pulse width corresponding to the fuel supply amount T ₁ that is set in this manner to the fuel injection valve at a predetermined timing, so that injects supply a predetermined amount of fuel to the engine .

The air-fuel ratio feedback correction based on the signal from the air-fuel ratio sensor is performed so as to control the air-fuel ratio near the target air-fuel ratio (the stoichiometric air-fuel ratio). This is interposed in the exhaust system,
CO in the exhaust, HC function effectively conversion efficiency of the exhaust gas purifying catalyst for purifying by reducing NO _X with oxidizes (hydrocarbon) (three-way catalyst) (purifying efficiency) in the exhaust state during stoichiometric combustion This is because it is set to do so.

The generated electromotive force (output voltage) of the air-fuel ratio sensor has a characteristic that changes rapidly near the stoichiometric air-fuel ratio.
By comparing V ₀ with a reference voltage (slice level) SL corresponding 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. Then, for example, when the air-fuel ratio is lean (rich), after the feedback correction coefficient α to be multiplied to the basic fuel supply quantity T _P lean increases the larger proportional constant P the first time that turned (rich) (reduction) Fuel supply amount gradually increases (decreases) by a predetermined integration constant I
Controlling the air-fuel ratio to the stoichiometric air-fuel ratio near by increasing (reduction) corrects T _1.

By the way, in the ordinary air-fuel ratio feedback control device as described above, one air-fuel ratio sensor is provided in a collective portion of the exhaust manifold as close as possible to the combustion chamber in order to increase the responsiveness, but this portion has a high exhaust temperature. As a result, the characteristics of the air-fuel ratio sensor are likely to change due to thermal effects and deterioration, and the exhaust gas mixture of each cylinder is insufficient, making it difficult to detect the average air-fuel ratio of all cylinders, making it difficult to detect the air-fuel ratio accurately. As a result, the air-fuel ratio control accuracy was deteriorated.

In view of this point, an air-fuel ratio sensor is provided downstream of an exhaust gas purification catalyst (hereinafter, referred to as a first exhaust gas purification catalyst), and the air-fuel ratio is feedback-controlled using detection values of the two air-fuel ratio sensors. (See JP-A-58-48756).

That is, although the downstream air-fuel ratio sensor (hereinafter referred to as the second air-fuel ratio sensor) is far from the combustion chamber, its responsiveness is difficult. However, since it is downstream of the first exhaust gas purification catalyst, the exhaust gas component balance is low. effect (CO, HC, NOx, CO 2 , etc.) less susceptible to hardly characteristic change undergone by poisoning because less poisoning amount by toxic components in the exhaust gas, yet the average of all the cylinders for good mixed state of exhaust For example, a high air-fuel ratio can be detected as compared with an upstream air-fuel ratio sensor (hereinafter, referred to as a first air-fuel ratio sensor).
Highly accurate and stable detection performance can be obtained.

Therefore, the two air-fuel ratio feedback correction coefficients set by the same calculation based on the detection values of the two air-fuel ratio sensors are combined, or the air-fuel ratio feedback correction coefficient set by the first air-fuel ratio sensor is controlled. Variations in the output characteristics of the upstream air-fuel ratio sensor are compensated by the second air-fuel ratio sensor by correcting a constant (proportional component or integral component), a comparison voltage of the output voltage of the first air-fuel ratio sensor, or a delay time. Accurate air-fuel ratio feedback control is performed.

By the way, in the one in which the air-fuel ratio is feedback-controlled using the detection values of the two air-fuel ratio sensors as described above, the air-fuel ratio is increased between the two air-fuel ratio sensors due to the feedback control by the second air-fuel ratio sensor. Will be swung to the oxygen adsorption capacity limit of the first exhaust gas purification catalyst provided in the first stage.

Here, the first exhaust gas purifying catalyst of the carbon monoxide (CO), reducing the efficiency of oxidation efficiency, also nitrogen oxides hydrocarbons (HC) and the like (NO _X), etc. is reduced in the vicinity limit of the air-fuel ratio Therefore, when the air-fuel ratio fluctuates to near the limit as described above, there is a concern that the unburned components in the exhaust cannot be sufficiently purified and the emission increases.

In view of this point, an exhaust purification catalyst (hereinafter, referred to as a second exhaust purification catalyst) is further provided downstream of the second air-fuel ratio sensor.
As mentioned above, even when the air-fuel ratio is swung to near the limit,
There is a catalyst in which unburned components in exhaust gas are purified by the second exhaust gas purification catalyst, so that good exhaust emission can be obtained.

In recent years, as an exhaust purification catalyst, a monolith catalyst in which a catalyst component such as a noble metal for purifying engine exhaust is supported on a monolithic ceramic monolith carrier has been used. By the way, when purifying the engine exhaust using the three-way catalyst carried by the monolith catalyst, the purification characteristics greatly change 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, the oxidizing action becomes active, and the reducing action becomes inactive. On the other hand, when the air-fuel ratio is high, the oxidizing action becomes inactive and the reducing action becomes active.

For this reason, apart from the above-mentioned known example, ceria (CeO ₂ ) having an oxygen storage capacity is conventionally used for the purpose of sufficiently maintaining the catalytic activity of the three-way catalyst and further increasing the catalytic activity even if the air-fuel ratio fluctuates. It is carried.

<Problems to be Solved by the Invention> Meanwhile, in the above-described conventional two exhaust purification catalysts provided in the exhaust passage, the first exhaust purification catalyst is close to the engine body, so that high-temperature exhaust gas passes. . Here, since the ceria also has an action of improving heat resistance performance, in order to protect the ceramic monolith carrier from the high temperature of the exhaust, two exhaust purification catalysts are provided in the exhaust passage. It is conceivable to carry a large amount of ceria.

However, if the first exhaust gas purification catalyst carries a large amount of ceria, the oxygen adsorption capacity limit of the first exhaust gas purification catalyst becomes large. For this reason, the feedback cycle of the second air-fuel ratio sensor becomes longer, the maximum deviation amount of the air-fuel ratio from the stoichiometric air-fuel ratio becomes larger, and the usage ratio in the portion where the conversion efficiency is low increases, and the emission may increase. There is.

On the other hand, when the volume of the first exhaust gas purification catalyst is made smaller than that of the second exhaust gas catalyst, the conversion efficiency of the first exhaust gas 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, so that high-precision air-fuel ratio feedback control cannot be performed.

Accordingly, it is an object of the present invention to provide a catalytic converter device for an internal combustion engine that can perform high-precision air-fuel ratio feedback control while securing good emission in view of the above-described conventional circumstances.

<Means for Solving the Problems> For this reason, a catalytic converter device for an internal combustion engine according to the present invention includes first and second exhaust purification catalysts provided on the upstream and downstream sides of an engine exhaust passage, respectively. An output unit that is disposed upstream of the first catalyst and between the first catalyst and the second catalyst, and whose output value changes in response to a concentration ratio of a specific gas component in exhaust gas that changes according to an air-fuel ratio. An air-fuel ratio control device for an internal combustion engine, comprising: a first catalyst and a second air-fuel ratio sensor for controlling an air-fuel ratio by correcting a fuel supply amount or an air supply amount to an intake system; The oxygen storage capacity of the first catalyst is made smaller than the oxygen storage capacity of the second catalyst while reducing the amount of ceria in the second catalyst. And configured to increase the content of potassium compared with the content of zirconia and barium oxide in the second catalyst.

Further, the volume of the first catalyst may be larger than the volume of the second catalyst.

<Operation> When the oxygen storage capacity is small, the conversion efficiency of the catalyst deteriorates when the air-fuel ratio largely fluctuates. However, the air-fuel ratio control device for the internal combustion engine including the first and second air-fuel ratio sensors to control the air-fuel ratio In the above, by reducing the oxygen storage capacity of the first catalyst, the oxygen adsorption capacity limit of the first exhaust gas purification catalyst is reduced. For this reason, the feedback cycle of the second air-fuel ratio sensor is shortened, the maximum deviation amount of the air-fuel ratio from the stoichiometric air-fuel ratio is also reduced, and the usage ratio of the catalyst in a portion having high conversion efficiency is increased, and the emission is also reduced.

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

Therefore, high-precision air-fuel ratio feedback control can be performed while ensuring good emission.

On the other hand, in order to reduce the oxygen storage capacity of the first catalyst, the content of zirconia and barium oxide of the first catalyst is increased by an amount corresponding to the reduced content of ceria, thereby compensating for thermal deterioration of the catalyst noble metal.

Further, by making the volume of the first catalyst larger than the volume of the second catalyst, the conversion efficiency of the first catalyst is improved, and the compensation of the output of the first air-fuel ratio sensor by the second air-fuel ratio sensor is improved.

<Example> Hereinafter, an example of the present invention will be described with reference to the drawings.

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

The fuel injection valve 15 is driven to open by an injection pulse signal from a control unit 16 containing a microcomputer, and injects fuel supplied from a fuel pump (not shown) under pressure and controlled to a predetermined pressure by a pressure regulator. Further, a water temperature sensor 17 for detecting a cooling water temperature Tw in the cooling jacket of the engine 11 is provided. On the other hand, in the exhaust passage 18, the first air-fuel ratio of the intake air-fuel mixture is detected by detecting the oxygen concentration in the exhaust gas at the manifold collecting portion.
An air-fuel ratio sensor 19 is provided, and a first three-way catalyst 20 as an exhaust gas purifying catalyst for purifying by oxidizing CO and HC in the exhaust gas and reducing NO _X is provided between the exhaust gas downstream thereof, 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.
A second three-way catalyst 22 having the same function as the first three-way catalyst 20 and having a volume slightly smaller than that of the first three-way catalyst 20 is provided downstream of the air-fuel ratio sensor 21.

That is, the first three-way catalyst 20, the second three-way catalyst 22 and the like constitute a catalytic converter device.

Distributors not shown in FIG.
A crank angle sensor 23 is built-in, and a crank unit angle signal output from the crank angle sensor 23 in synchronization with the engine rotation is counted for a certain period of time, or the cycle of the crank reference angle signal is measured to measure the engine rotation. Detect number N.

Next, an air-fuel ratio control routine by the control unit 16 will be described with reference to the flowchart of FIG. Second
The figure shows a fuel injection amount setting routine, which is performed at predetermined intervals (for example, every 10 ms).

In step (denoted by S in the figure) 1, the amount of intake air per unit rotation is determined based on the intake air flow rate Q detected by the air flow meter 13 and the engine speed N calculated based on a signal from the crank angle sensor 24. the basic fuel injection quantity T _P corresponding to operation by the following equation.

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

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

That is, two air-fuel ratio feedback correction coefficients set based on the detection values of the first and second air-fuel ratio sensors 19 and 21 are combined, or the air-fuel ratio feedback correction set by the first air-fuel ratio sensor 19 is used. A value obtained by compensating the variation in the output characteristics of the first air-fuel ratio sensor 19 with the second air-fuel ratio sensor 22 by correcting the control constant (proportional component or integral component) of the coefficient is read.

In step 4, a voltage correction amount T _S is set based on the battery voltage value. This is for correcting a change in the injection flow rate of the fuel injection valve 15 due to the battery voltage fluctuation.

In step 5, the final fuel injection amount (fuel supply amount)
The T ₁ for calculating according to the following equation.

In _{T 1 = T P × COEF ×} α + T S Step 6, is set in the output register the computed fuel injection valve T _1.

Consequently, when a fuel injection timing of the engine rotational synchronization predetermined fuel injection is performed a drive pulse signal having the calculated pulse width of the fuel injection amount T ₁ is given to the fuel injection valve 15.

Here, the first three-way catalyst 20 and the second three-way catalyst 22 as the first and second catalysts for purifying exhaust gas according to the present invention are monolithic catalysts, for example, as shown in FIGS. 3 and 4. It is as shown.

That is, a columnar carrier 31 formed of a heat-resistant alloy or the like.
A honeycomb-shaped processing gas passage 32 linearly communicating both ends in the axial direction is formed by a partition wall 32a. A wash coat 33 of a component to be described later is applied to the inner peripheral wall surface of the partition wall 32a forming the processing gas passage 32 of the carrier 31, thereby forming a monolithic catalyst.

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

That is, the content of ceria CeC ₂ , which is a component having the oxygen storage capacity of the first catalyst 20, is 1 / of the content of ceria CeO ₂ in the second catalyst 22.

Therefore, the oxygen storage capacity of the first catalyst 20 is small,
The oxygen adsorption capacity limit of the first catalyst 20 and the amount of oxygen that cannot be adsorbed are also reduced. Therefore, according to the configuration of the present embodiment, the first air-fuel ratio sensor 19 and the second air-fuel ratio sensor
Since the air-fuel ratio is controlled by the provision of the air-fuel ratio 21, the feedback cycle of the second air-fuel ratio sensor 21 is shortened, and FIG.
As shown in FIG. 5 (a), the air-fuel ratio is prevented from greatly fluctuating as compared with the conventional example shown in FIG.

Further, since the second catalyst 22 has a large content of ceria CeO ₂ , the oxygen storage capacity is large, and even when the air-fuel ratio fluctuates, the ability to purify unburned components in the exhaust gas is sufficient. It can be reduced sufficiently (see FIG. 5).

Therefore, according to the present embodiment, it is possible to perform high-precision air-fuel ratio feedback control while ensuring good emission.

In addition, the content of ceria CeO ₂ in the first
Therefore, the content of zirconia (ZrO ₂ ) and barium oxide (BaO) is increased to compensate for the thermal degradation of the catalytic noble metal of the first catalyst 20 to compensate for the thermal degradation of the catalytic noble metal. doing.

 Next, a second embodiment according to the present invention will be described.

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

In the second embodiment, the components shown in Table 2 were applied to the wash coat 33.

Also in this embodiment, the content of ceria CeO _{2 in} the first catalyst 31 is smaller than the content in the second catalyst 32, and in this embodiment, the content of zirconia (ZrO ₂ ) and barium oxide (BaO) is also contained. The amount is increased to compensate for the thermal degradation of the catalytic noble metal.

<Effects of the Invention> As described above, according to the present invention, the first air-fuel ratio sensor, the first exhaust purification catalyst, the second air-fuel ratio sensor, and the second exhaust purification catalyst are arranged in the engine exhaust passage from the upstream side. Since the oxygen storage capacity of the first catalyst is smaller than the oxygen storage capacity of the second catalyst, the feedback cycle of the second air-fuel ratio sensor can be shortened, and the stoichiometric air-fuel ratio of the air-fuel ratio can be reduced. The maximum deviation amount can be reduced, and the ability of the second catalyst to purify unburned components in exhaust gas can be sufficiently ensured.

Therefore, there is an effect that high-precision air-fuel ratio feedback control can be performed while ensuring good emission.

On the other hand, in order to reduce the oxygen storage capacity of the first catalyst, the content of zirconia and barium oxide of the first catalyst is increased by the reduced content of ceria.
Thermal deterioration of the catalytic noble metal can be compensated.

Also, by making the volume of the first catalyst larger than the volume of the second catalyst, the conversion efficiency of the first catalyst is improved, and the output of the first air-fuel ratio sensor by the second air-fuel ratio sensor is well compensated. Thus, more accurate air-fuel ratio feedback control can be performed.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram according to an embodiment of the present invention, FIG. 2 is a flowchart showing a fuel injection amount setting routine of the embodiment, FIG. 3 is a perspective view of a monolithic catalyst, and FIG. 5 is a diagram for explaining the operation of the present invention, and FIG. 6 is a schematic configuration diagram of a catalytic converter device according to a second embodiment of the present invention. 11 engine, 18 exhaust passage, 19 first air-fuel ratio sensor, 20 first three-way catalyst 20, 21 second air-fuel ratio sensor, 22 second ternary Catalyst, 31 ... Carrier, 32a ... Partition wall, 33 ... Wash coat

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location F02D 43/00 301 F02D 43/00 301T B01D 53/36 B

Claims (2)

(57) [Claims] An exhaust gas purifying first and second catalyst provided on an upstream side and a downstream side of an engine exhaust passage, respectively, and an upstream side of the first catalyst, the first catalyst, and the second catalyst. And a first and a second air-fuel ratio sensor whose output value changes in response to the concentration ratio of the specific gas component in the exhaust that changes according to the air-fuel ratio. The ceria content in the first catalyst is made smaller than the ceria content in the second catalyst, and the oxygen storage capacity of the first catalyst is made smaller than the oxygen storage capacity of the second catalyst. A catalytic converter device for an internal combustion engine, wherein the content of zirconia and barium oxide in one catalyst is larger than the content of zirconia and barium oxide in a second catalyst. 2. The catalytic converter of an internal combustion engine according to claim 1, wherein the volume of the first catalyst is larger than the volume of the second catalyst.