JP3065182B2 - Catalyst purification rate detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting a purification rate of a catalyst for purifying exhaust gas of an engine.

[0002]

2. Description of the Related Art In an air-fuel ratio control of an engine, when an air-fuel ratio sensor (air-fuel ratio control sensor) provided upstream of a catalyst detects excess fuel (rich), excess air (lean) is detected.
When the air-fuel ratio sensor detects excess air, the air-fuel ratio is controlled so that the fuel becomes excessive. As a result, the air-fuel ratio of the engine alternates between rich and lean at a fast cycle around the stoichiometric air-fuel ratio λ = 1. Then, the catalyst purifies exhaust gas that repeats rich and lean, and reduces and emits harmful components such as NOx, HC, and CO. The purification rate of the catalyst decreases due to heat, components in exhaust gas, and the like. For this reason, there is an attempt to detect the deterioration of the catalyst.

[0003]

In this attempt, an air-fuel ratio sensor similar to the air-fuel ratio sensor (upstream sensor) upstream of the catalyst is provided downstream of the catalyst, and the output of the downstream air-fuel ratio sensor (downstream sensor) is measured. It is confirmed whether or not a change in the purification rate of the catalyst can be confirmed from the fluctuation range. In this trial, when a titania air-fuel ratio sensor is used as the air-fuel ratio sensor, as shown by a dashed line D in FIG. 12, if the purification rate of the catalyst is very high (purification rate 70% or more), the purification rate detection The purification rate of the catalyst can be detected by the output width of the air-fuel ratio sensor. However, when the purification rate of the catalyst is slightly reduced (less than 70%), the output quickly follows the fluctuation of the oxygen concentration downstream of the catalyst. As a result, the fluctuation range became maximum, and the purification rate could not be detected. In other words, the conventionally used air-fuel ratio sensor cannot detect the catalyst purification rate when the purification rate of the catalyst drops to 70% or less.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a catalyst having a purification rate of 70%.
It is an object of the present invention to provide a catalyst purification rate detection device capable of detecting a catalyst purification rate even when the catalyst purification rate falls to not more than%.

[0005]

Means for Solving the Problems The catalyst purification rate detecting device of the present invention employs the following technical means. The catalyst purification rate detecting device is provided upstream of the catalyst for purifying exhaust gas, and detects an air-fuel ratio before purification by the catalyst, and is provided downstream of the catalyst to purify the exhaust gas. A downstream sensor for detecting a subsequent air-fuel ratio, and a detecting means for detecting a purification rate of the catalyst from a variation range of an output value of the downstream sensor when the air-fuel ratio of exhaust gas is controlled within a predetermined range by the upstream sensor. And The downstream sensor is provided such that an output response time is delayed by a predetermined amount.

[0006]

Since the downstream sensor is provided with a delayed response time, even if the purification rate of the catalyst is reduced and the air-fuel ratio downstream of the catalyst fluctuates, the output change of the downstream sensor is changed to the air-fuel ratio change. Instead of following quickly, the fluctuation range of the output of the downstream sensor increases with an increase in the fluctuation range of the air-fuel ratio downstream of the catalyst.

[0007]

As described above, according to the purification rate detecting device of the present invention, the fluctuation width of the output of the downstream sensor increases as the fluctuation width of the air-fuel ratio downstream of the catalyst increases.
It is possible to detect the purification rate of the catalyst up to a purification rate that is lower than in the past.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an apparatus for detecting a purification rate of a catalyst according to the present invention will be described based on one embodiment shown in the drawings. FIG. 1 to FIG. 14 show an embodiment of the present invention. FIG. 1 is a schematic diagram of a catalyst purification rate detecting device using a downstream sensor of the catalyst. A three-way catalyst 3 for purifying exhaust gas is disposed in an exhaust gas passage 2 of the engine 1. The three-way catalyst 3 is a well-known catalyst supporting an oxidation or reduction catalyst such as Pt or Rh, and has a well-known structure using a monolith type such as a honeycomb or a particle type such as a pellet, a cylinder, or a sphere. Things. In this embodiment, an electric heater 4 for heating the catalyst is provided around the three-way catalyst 3. The electric heater 4 was provided for experimental use in order to arbitrarily adjust the purification rate of the three-way catalyst 3, and the three-way catalyst 3 itself used had deteriorated equivalent to 120,000 km running. . Reference numeral 5 in FIG. 1 is a temperature sensor that detects the temperature of the three-way catalyst 3,
This is for detecting the temperature of the three-way catalyst 3 and obtaining the purification rate of the three-way catalyst 3 from the temperature using a previously determined relationship between the catalyst purification rate and the temperature.

The three-way catalyst 3 can purify the exhaust gas to the maximum when the engine 1 is burned at the stoichiometric air-fuel ratio. For this reason, the engine 1 is provided with a control device 6 for controlling the air-fuel ratio to the stoichiometric air-fuel ratio. As is well known, the injection amount of the fuel supplied to the engine 1 is determined according to the vehicle operating state such as the accelerator opening. The control device 6 controls the output of the engine 1 and the air-fuel ratio by controlling the fuel injection means 7 for injecting fuel into the engine 1. The fuel ratio is richly controlled, the air-fuel ratio is lean-controlled when the engine brake is used, and the air-fuel ratio is controlled to the stoichiometric air-fuel ratio (λ = 1) when the vehicle is running stably.
As means for detecting the air-fuel ratio of the engine 1, a three-way catalyst 3
An upstream sensor 8 that detects the oxygen concentration of the exhaust gas before the exhaust gas is purified by the three-way catalyst 3 is provided in the exhaust gas passage 2 upstream of the exhaust gas passage 2. The upstream sensor 8 is an air-fuel ratio sensor having a well-known structure for detecting the oxygen concentration in the exhaust gas, and its output changes quickly according to the change in the oxygen concentration of the exhaust gas. For example, if the exhaust gas is rich, an output of about 1 V is generated, and if it is lean, an output of about 0 V is generated. When the output of the upstream sensor 8 is higher than the predetermined determination value (rich), the control device 6 narrows the fuel injection amount to shift the air-fuel ratio to lean, and conversely, the output of the upstream sensor 8 determines the predetermined determination value. If it is lower than the value (lean), the fuel injection amount is increased to shift the air-fuel ratio to rich. By the air-fuel ratio control of the control device 6, during stable driving, the air-fuel ratio of the engine 1 repeats rich and lean at a fast cycle (for example, about 0.8 to 2 Hz), and the average air-fuel ratio is controlled to the stoichiometric air-fuel ratio. You.

In this embodiment, there is provided a purification rate detecting means 9a for detecting the purification rate of the three-way catalyst 3 and informing the occupant of the time for replacing the three-way catalyst 3 by a display means 9 such as an OK monitor. . In order to detect the purification rate of the three-way catalyst 3,
A downstream sensor 1 for detecting the oxygen concentration in the exhaust gas passing through the three-way catalyst 3 is provided in the exhaust gas passage 2 downstream of the three-way catalyst 3.
0 is provided. Then, the purification rate detecting means 9a detects the purification rate of the three-way catalyst 3 from the fluctuation range of the output value of the downstream sensor 10, and when the purification rate falls below the predetermined purification rate, the display means 9a indicates that. To be displayed. The downstream sensor 10 is an air-fuel ratio sensor using a titania oxygen sensor or a zirconia oxygen sensor, and is an upstream sensor 8 provided upstream of the three-way catalyst 3.
The response time from the change in the oxygen concentration in the exhaust gas to the change in the output is delayed by a predetermined amount (for example, 1.3 times or more of the response speed of the upstream sensor 8). .

A method of measuring the response time of the upstream sensor 8 and the downstream sensor 10 will be described with reference to a measuring device 11 shown in FIG. 2 and a graph shown in FIG. When the exhaust gas is rich,
At time t1, the air-fuel ratio is inverted lean, and the response time until 1V of the output voltage of the upstream sensor 8 or the downstream sensor 10 reaches 0.5V which is the center value of the change width is defined as Trs. When the air-fuel ratio is richly inverted at time t2, the upstream sensor 8 or the downstream sensor 1
0 V of the output voltage of 0 is 0.5 V which is the center value of the change width.
Let Tls be the response time to reach. Note that the reaction time shown in the present embodiment is obtained by subtracting the gas replacement time required for the exhaust gas to reach the upstream sensor 8 or the downstream sensor 10 from the time when the inflow gas amount is changed. In addition,
The measuring device 11 is used experimentally to switch the air-fuel ratio, and includes a main gas passage 12 and a main air passage 1.
Combustion of the stoichiometric air-fuel ratio is performed with the adjusted propane gas and the combustion air sent from 3, and the exhaust gas is guided to the upstream sensor 8 or the downstream sensor 10. At this time, the temperature of the exhaust gas was set to 350 ° C., and the temperature of the upstream sensor 8 or the downstream sensor 10 was set to 650 ° C. by a heater in the sensor. The bypass air passage 14 and the bypass gas passage 15
The air-fuel ratio of the exhaust gas is rich (λ =
0.9) and lean (λ = 1.1). Then, the change state of the output voltage of the upstream sensor 8 or the downstream sensor 10 attached to the exhaust gas passage 2 is measured.

Next, the upstream sensor 8 and the downstream sensor 10
An example of the structure will be described. The upstream sensor 8 and the downstream sensor 10 have basically the same structure. As shown in a partially broken air-fuel ratio sensor in FIG. 15, two ceramic substrates 101 and 102 containing alumina as a main component are integrally joined. It is a thing. On one ceramic substrate 101, three terminals 106, 107, 108 connected to three platinum lead wires 103, 104, 105, two detection electrodes 109, 110 connected to these terminals, respectively.
A heater pattern 111 is formed. The other ceramic substrate 102 having a window 112 is laminated and integrated on the surface on which the pattern of the one ceramic substrate 101 is arranged, and a gas-sensitive layer 113 mainly composed of TiO is provided in the window 112. Are formed. In addition, between this gas sensitive layer 113 and one ceramic substrate 101,
Spherical granulated particles for preventing peeling of the gas-sensitive layer 113 are interposed. Further, the gas-sensitive layer 113 contains a noble metal catalyst such as Pt and Rh. Further, the gas-sensitive layer 113
An overcoat layer 114 of, for example, alumina is formed on the outer surface of the substrate.

As a method of delaying the response time of the downstream sensor 10, for example, the following method can be considered. a) Gas-sensitive layer 11 that reacts to exhaust gas of downstream sensor 10
The response time is delayed by adding an oxidation or reduction catalyst such as Rh or Pt, or an oxygen storage material such as CeO _{2 to} 3, or the overcoat layer 114 for protecting the gas-sensitive layer 113, or both. 4 and 5
First, Rh is applied to both the gas-sensitive layer 113 and the overcoat layer 114 of the titania oxygen sensor in which the thicknesses of the gas-sensitive layer 113 and the overcoat layer 114 made of titania are unified to 400 μm (gas-sensitive layer 200 μm, overcoat layer 200 μm). The relationship between the addition amount in the gas-sensitive layer 113 and the delay of the response time when the addition is performed in the following manner is shown. Note that the reaction time in FIG. 4 indicates a time Trs until 1 V of the output voltage of the downstream sensor 10 when the state is inverted from the rich state to the lean state reaches 0.5 V which is the center value of the change width.
Represents the time Tls until the output voltage 0V of the downstream sensor 10 at the time of inversion from the lean state to the rich state reaches 0.5V which is the center value of the change width. b) By providing the gas-sensitive layer 113 and / or the overcoat layer 114 of the downstream sensor 10 thickly, the response time is delayed. 6 and 7, Rh is uniformly added to both the gas-sensitive layer 113 and the overcoat layer 114. At this time, the amount of Rh added to the gas-sensitive layer 113 is 5.
The relationship between the amount of increase in thickness and the delay in response time when the thickness is similarly increased in the gas-sensitive layer 113 and the overcoat layer 114 at 0 mol% is shown. Note that the reaction time in FIG. 6 is such that 1 V of the output voltage of the downstream sensor 10 when the state is reversed from the rich state to the lean state is 0.5% which is the center value of the change width.
The response time in FIG. 7 is 0 V of the output voltage of the downstream sensor 10 at the time of reversing from the lean state to the rich state.
Shows the time Tls to reach V. c) The response time is delayed by providing a small average pore diameter of the gas-sensitive layer 113 and / or the overcoat layer 114 of the downstream sensor 10. 8 and 9, Rh is uniformly added to both the gas-sensitive layer 113 and the overcoat layer 114. At this time, the addition amount of the gas-sensitive layer 113 is 4.0 mol%, and
And the overcoat layer 114 each have a thickness of 200 μm.
The relationship between the average pore diameter and the response time delay when the average pore diameter of the overcoat layer 114 is reduced by m is shown. The reaction time in FIG. 8 is a time Trs until the output voltage 1V of the downstream sensor 10 when the state is inverted from the rich state to the lean state reaches 0.5 V which is the center value of the change width.
The reaction time in FIG. 9 indicates a time Tls until 0 V of the output voltage of the downstream sensor 10 reaches 0.5 V which is the center value of the change width when the state is inverted from the lean state to the rich state. d) In the protective cover that covers the detection unit of the downstream sensor 10, the response time is delayed by providing a small opening ratio of the opening communicating the detection unit and the exhaust gas. e) The response time is delayed by increasing the distance between the detection unit and the opening communicating with the exhaust gas in the protective cover of the downstream sensor 10. FIGS. 10 and 11 show the relationship between the distance between the opening of the protective cover and the detection unit and the delay in response time. Note that the reaction time in FIG. 10 indicates a time Trs until 1 V of the output voltage of the downstream sensor 10 reaches 0.5 V, which is the center value of the change width, when the state is reversed from the rich state to the lean state. Represents the time Tls until the output voltage 0V of the downstream sensor 10 at the time of inversion from the lean state to the rich state reaches 0.5V which is the center value of the change width. f) The response time is delayed by providing a large volume for enclosing the element portion in the protective cover of the downstream sensor 10. When two or more of the above a) to f) are combined, the responsiveness can be further reduced.

[Experimental Example] Next, the effect of the present invention will be described using an experiment in which the response time of the first, second, and third embodiments is delayed and an experiment in comparison with the conventional product. In the experiment, FIG.
Was performed using the measuring device 11 described above.

The manufacturing process of the first, second and third embodiment products and the conventional product used in this experiment will be briefly described. First, the manufacturing process of a conventional product will be described with reference to FIGS. 1) 92 w% of alumina, 3 w% of magnesia, and 5 w% of a sintering aid (silica, calcia, etc.) are mixed in a pot mill for 20 hours. To this mixture, 12 w% of polyvinyl butyral and 4 w% of dibutyl phthalate are added as an organic binder, and methyl ethyl ketone, toluene and the like are added as a solvent. Then, a green sheet for a ceramic substrate is formed by a doctor blade method. The shape of one green sheet is 47.8 × 4.0 × 0.8 (m
m), and the shape of the other green sheet is 47.8 × 4.
It is 0 × 0.26 (mm). And, on the other green sheet, 3.05 × for forming the window 112 is formed.
An opening of 2.0 (mm) is formed. 2) Platinum black and sponge-like platinum are mixed in a ratio of 2: 1. In addition, 10 w% of the material mixture of the green sheet used in 1) is added, and a solvent such as butyl carbitol and toluene is added. Create an electrode paste. 3) Thick film printing using the electrode paste of 2) above
An electrode pattern is formed on the surface of one green sheet (see FIG. 16). 4) Next, the three terminals 10 of the printed electrode pattern
Platinum lead wires 103, 104 and 105 having a diameter of 0.2 mm are connected to 6, 107 and 108, respectively (see FIG. 17). 5) Next, the other green sheet is laminated on the surface of the one green sheet on which the electrode pattern is printed, and thermocompression-bonded to form a laminate. At this time, two detection electrodes 109 are provided in the window 112 of the other green sheet.
The end of 110 is exposed (see FIG. 18). This window 112
Inside, 80-150 mesh spherical granulated particles (secondary particles) made of the same material as the green sheet prepared in 1)
And the above laminated body is sintered at 1500 ° C. for 2 hours in substantially the same atmosphere as the atmosphere to integrate the two ceramic substrates 101 and 102. 6) Next, the window portion 112 is filled with a gas-sensitive metal oxide containing TiO2 as a main component. This metal oxide is first prepared from a TiO2 paste. That is, 1
Ti with an average particle size of 1.2 μm calcined at 200 ° C for 1 hour
3w as binder for 100 parts by weight of O2 powder
% Of ethylcellulose is added only by 2 parts by weight, and these are mixed in petitcarpitol (trade name of 2- (2-butoxyethoxy) ethanol) to adjust the TiO2 paste to a viscosity of 300 poise. And this TiO2
The paste is applied to the detection electrodes 109 and 110 in the window 112 to a thickness of about 200 μm,
Sintering is performed at 00 ° C. for 2 hours to form the gas-sensitive layer 113 (see FIG. 19). 7) Next, a catalyst is supported on the gas-sensitive layer 113. this is,
A mixed aqueous solution of chloroplatinic acid and rhodium acid adjusted to Pt: Rh = 10: 1 (total catalyst amount: 220 g / l) was used for 1.
8 μl of the catalyst is dropped on the gas-sensitive layer 113 and is thermally decomposed at 600 ° C. for 1 hour in the atmosphere to uniformly disperse and support the catalyst on the gas-sensitive layer 113. 8) Next, the overcoat layer 1 is formed on the gas-sensitive layer 113.
After applying a paste made of Al2 O3 having an average particle size of 3 .mu.m to a thickness of about 200 .mu.m, the paste was dried in air at 120 .mu.m.
Bake at 0 ° C. for 1 hour. Through the above steps, a conventional product is formed (see FIG. 20). The conventional product used was one in which the amount of Rh added to the gas-sensitive layer 113 was 0.5 mol% and the pore size of the overcoat layer 114 was about 3.0 μm.

In the first embodiment, the overcoat layer 114 is used.
The pore size of 0.2 μm (alumina particle size about 1 μm),
After the above steps 7) and 8) were carried out in the same manner as the conventional product, a rhodium chloride aqueous solution was further dropped from above the overcoat layer 114, and treated at 150 ° C. for 2 hours in a H 2 furnace.
Heating was performed in the air at 600 ° C. for 1 hour. This allows
Rh of the obtained gas-sensitive layer 113 was 1.5 mol%. In the second embodiment, the pore size of the overcoat layer 114 is set to 1.0 μm (alumina particle size is about 1.5 μm), the concentration of the rhodium chloride aqueous solution is increased, and the R of the gas-sensitive layer 113 is increased.
Except that h was 4.0 mol%, it was prepared in the same manner as in the first example. In the product of the third embodiment, the thickness of the overcoat layer 114 was set to 300 μm, and the Rh of the gas-sensitive layer 113 was set to 4.0 m.
ol% was prepared in the same manner as in the first embodiment. The products of the first, second, and third embodiments correspond to the overcoat layer 1.
14 also contains Rh. The following Table 1 shows the differences between the conventional product and the products of the first, second and third embodiments.

[Table 1]

Next, the experimental results will be shown. The response time of the product of the first embodiment is such that, when the output voltage is inverted from the rich state to the lean state, the time Trs until the output voltage of 1 V reaches 0.5 V which is the center value of the change width is 520 ms, and the response time of the lean state is rich. When the output voltage is inverted to 0 V, the time Tls required for the output voltage to reach 0.5 V, which is the center value of the change width, is 260 ms.
It is. The response time of the product of the second embodiment is such that the time Trs required for the output voltage 1V to reach 0.5 V, which is the center value of the change width, when the state is inverted from the rich state to the lean state is 650 m.
In s, when the state is inverted from the lean state to the rich state, the time Tls until the output voltage of 0 V reaches 0.5 V which is the center value of the change width is 350 ms. The response time of the third embodiment is such that when the output voltage is inverted from the rich state to the lean state, the time Trs until the output voltage of 1 V reaches 0.5 V which is the center value of the change width is 1000 ms, and the response time is 1000 ms. When the output voltage is inverted to 0 V, the time Tls required for the output voltage to reach 0.5 V, which is the center value of the change width, is 470 ms.
It is. In addition, the response time of the conventional product is such that the time Trs required for the output voltage 1V to reach 0.5 V, which is the center value of the change width, is 400 m when the state is inverted from the rich state to the lean state.
In s, when the state is inverted from the lean state to the rich state, the time Tls until the output voltage of 0 V reaches 0.5 V which is the center value of the change width is 200 ms.

FIG. 12 shows three products of the first embodiment (see the solid line A), the second embodiment (see the solid line B), the third embodiment (see the solid line C), and the conventional product (see the broken line D). Original catalyst 3
The relationship between the average purification rate and the output fluctuation width of the output voltage is shown. In this experiment, the three-way catalyst 3 was
By changing the temperature, the average purification rate of the three-way catalyst 3 is changed in the range of 20 to 90%, and the output fluctuation value of the oxygen sensor at that time is measured. As shown in this graph, in the conventional product, when the purification rate is reduced to 70% or less, the output fluctuation width of the output voltage becomes the maximum uniformly,
As a result, a purification rate of 70% or less could not be detected. However, in the product of the first embodiment in which the response time is delayed, it is possible to detect up to a purification rate of 50% at which the output fluctuation width becomes maximum, and in the product of the second embodiment, it is possible to detect up to a purification rate of nearly 20%. In the third embodiment, the purification rate can be detected up to 0%. FIG. 13 shows that, when the three-way catalyst 3 is reversed from rich to lean when the average purification rate of the three-way catalyst 3 is 90%, the output voltage 1V reaches 0.5 V which is the center value of the change width. Time Trs and the downstream sensor 10
5 is a graph showing a relationship between the output fluctuation width and the output fluctuation width. FIG. 14 shows that, when the three-way catalyst 3 is reversed from the lean state to the rich state when the average purification rate of the three-way catalyst 3 is 90%, the output voltage 0 V reaches 0.5 V which is the center value of the change width. 5 is a graph showing the relationship between the time Tls of the first embodiment and the output fluctuation width of the downstream sensor 10.

[Effects of the Embodiment] In the present embodiment, as described above, the response time of the downstream sensor 10 is delayed so that the downstream of the three-way catalyst 3 is increased in proportion to the increase in the air-fuel ratio width. The output fluctuation width of the sensor 10 increases. For this reason, the purification rate of the three-way catalyst 3 has conventionally been detected only up to a range of 100 to 70%. However, according to the present invention, a purification rate lower than 70% can be detected.

[Modifications] The numerical values, materials, and the like disclosed in the above embodiments are merely examples for facilitating understanding of the embodiments, and the present invention is not limited to the numerical values, materials, and the like described in the embodiments. However, the present invention is also applicable to various air-fuel ratio sensors such as a zirconia solid electrolyte type air-fuel ratio sensor, a limiting current type air-fuel ratio sensor, and a pumping current type air-fuel ratio sensor.
Further, in the present embodiment, an example is shown in which the purification rate of the catalyst is detected by the output fluctuation of the air-fuel ratio sensor downstream of the catalyst.
The purification rate of the catalyst may be detected by comparison with an air-fuel ratio sensor upstream of the catalyst.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a purification rate detection device for a catalyst.

FIG. 2 is a schematic diagram of a measuring device for measuring a response time of an air-fuel ratio sensor.

FIG. 3 is a graph showing a response time of an air-fuel ratio sensor.

FIG. 4 is a graph showing the relationship between Rh content and response time (Trs).

FIG. 5 is a graph showing the relationship between Rh content and response time (Tls).

FIG. 6 is a graph showing the relationship between the element thickness and the output reduction speed.

FIG. 7 is a graph showing a relationship between an element thickness and an output rising speed.

FIG. 8 is a graph showing a relationship between a pore diameter and an output reduction speed.

FIG. 9 is a graph showing a relationship between a pore diameter and an output rising speed.

FIG. 10 is a graph showing the relationship between the shape of the protective cover and the output reduction speed.

FIG. 11 is a graph showing the relationship between the shape of the protective cover and the output rising speed.

FIG. 12 is a graph showing a relationship between a purification rate and a fluctuation value of a sensor output.

FIG. 13 is a graph showing a relationship between a rate of decrease in output and a fluctuation value of sensor output.

FIG. 14 is a graph showing a relationship between an output rising speed and a fluctuation value of a sensor output.

FIG. 15 is a partially broken perspective view of the air-fuel ratio sensor.

FIG. 16 is a plan view of a green sheet.

FIG. 17 is a plan view of a green sheet.

FIG. 18 is a plan view of a ceramic laminate.

FIG. 19 is a sectional view of a ceramic laminate.

FIG. 20 is a sectional view of a ceramic laminate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 2 Exhaust gas passage 3 Three-way catalyst 6 Control device (detection means) 8 Upstream sensor 10 Downstream sensor

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁷ Identification code FI F02D 45/00368 F02D 45 / 00368G (56) References JP-A-4-109045 (JP, A) JP-A-2-310453 (JP, A) JP-A-3-281960 (JP, A) JP-A-1-168859 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/26 391 F01N 3 / 00 F01N 3/20 F02D 35/00 368 F02D 41/14 310 F02D 45/00 368

Claims (3)

(57) [Claims] 1. An upstream sensor provided upstream of a catalyst for purifying exhaust gas and detecting an air-fuel ratio before purification by the catalyst, and an upstream sensor provided downstream of the catalyst and purified by the catalyst. A downstream sensor for detecting a fuel ratio, and a detecting means for detecting a purification rate of the catalyst from a fluctuation range of an output value of the downstream sensor when the air-fuel ratio of exhaust gas is controlled within a predetermined range by the upstream sensor. In the catalyst purification rate detecting device, the downstream sensor is provided such that an output response time is delayed by a predetermined amount. 2. When the exhaust gas is changed from a fuel-lean region to a fuel-rich region, the time (Tls) required for the output value of the downstream sensor to reach the center value of the output change range is equal to the time (Tls) of the upstream sensor. 2. The catalyst purification rate detection device according to claim 1, wherein the output value is at least 1.3 times the time (Tls) required to reach the center value of the output change width. 3. 3. The catalyst purification rate detecting device according to claim 1, wherein when the purification rate of the catalyst is 90%, the output fluctuation range of the downstream sensor is within 30% of the maximum output fluctuation range. .