JPH0742854B2 - Exhaust gas purification device for internal combustion engine for automobile - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine in which two catalytic converters are installed in an exhaust system.

[Conventional technology]

In an internal combustion engine equipped with a catalytic converter (particularly a three-way catalyst), an air-fuel ratio sensor is provided in the exhaust pipe upstream of the catalytic converter, and the air amount or the fuel amount is controlled according to the signal from the air-fuel ratio sensor. The fuel ratio is controlled in a narrow region near the stoichiometric air-fuel ratio where the catalytic device has the highest efficiency. In this case, the air-fuel ratio sensor is an oxygen concentration battery that operates according to the difference in oxygen partial pressure between the exhaust gas and the atmosphere, O ₂
Some have adopted sensors. This O ₂ sensor usually uses a zirconia element and a platinum electrode.

Such a catalytic device must be at least 30 for proper operation.
A temperature of 0-350 ° C is necessary. Therefore, by installing it as close to the engine as possible, the temperature of the engine can be used to activate the catalyst device,
It is possible to improve the exhaust gas purification performance immediately after the start. However, if the catalytic converter is installed near the engine, high temperature exhaust gas will not be emitted from the catalytic converter or O ₂ after the engine is warmed up.
It will hit the sensor directly, which is not preferable for its durability.

Therefore, it is proposed that two catalytic converters are installed in series in the exhaust pipe, a bypass passage is provided so as to bypass the upstream catalytic converter, and the bypass passage is opened and closed according to the temperature.

See, for example, JP-A-57-210116. The bypass is opened at high temperature, the hot exhaust gas bypasses the upstream catalytic converter, the hot exhaust gas is prevented from flowing into the upstream catalytic converter, and the problem of heat damage can be eliminated. . The exhaust gas that has flowed into the bypass passage flows into the catalytic converter on the downstream side when the temperature has dropped somewhat, and the catalytic converter on the downstream side is not subject to a thermal load and the desired catalytic action is achieved. To achieve. On the other hand, when the temperature is low, the bypass is closed, so that the exhaust gas is first introduced into the upstream catalytic converter and then flows into the downstream catalytic converter. The upstream catalytic converter is located near the exhaust port of the engine body,
Since the temperature of the exhaust gas introduced into the upstream catalytic converter is relatively high, the efficiency of catalytic action in the upstream catalytic converter can be increased.

[Problems to be Solved by the Invention]

By providing a bypass in the prior art, it is avoided that exhaust gas directly hits the upstream catalytic converter at high temperature. However, from the viewpoint of improving responsiveness, the O ₂ sensor is provided upstream of the catalytic converter and is located in the exhaust pipe upstream of the position where the bypass passage branches. Therefore, there is a problem of heat damage to the O ₂ sensor at high temperatures.
In order to avoid this problem, it may be possible to provide an O ₂ sensor between the switching valve and the catalytic converter. However, in this case, the O ₂ sensor comes to the downstream side of the bypass passage, and the exhaust gas does not hit the O ₂ sensor and the air-fuel ratio cannot be detected during high temperature operation with the bypass open, so feedback control is performed. There is a problem that cannot be done.

In view of the above-mentioned drawbacks, the present invention aims to enable feedback control of an air-fuel ratio in a configuration in which an O ₂ sensor is arranged upstream of a catalytic converter while protecting the upstream catalytic converter and the O ₂ sensor. To do.

[Means for Solving the Problems]

In the exhaust gas purifying apparatus for an automobile internal combustion engine of an internal combustion engine of the present invention, the air-fuel ratio is controlled by a signal from an air-fuel ratio sensor arranged in the exhaust pipe, and two catalysts are arranged in series in the exhaust pipe downstream of the air-fuel ratio sensor. A converter is installed, one end of which is connected to an exhaust pipe at an upstream portion of the air-fuel ratio sensor, and the other end of which is connected to an exhaust pipe at a portion between an upstream catalytic converter and a downstream catalytic converter. A switching valve for switching between a bypass passage, a first position for closing the first bypass passage and opening the exhaust pipe, and a second position for opening the first bypass passage and closing the exhaust pipe, and the switching valve Temperature sensing control means for opening the valve to the first position when the temperature is low and the second position when the temperature is high, one end connected to the exhaust pipe at an upstream portion of the switching valve, and the other end connected to the switching valve and the air-fuel ratio sensor. Connected to the exhaust pipe at the part between Characterized by comprising a second bypass passage that.

[Work]

The switching valve is in the first position when the temperature is low, and the exhaust gas is guided to the downstream catalytic converter via the air-fuel ratio sensor and then the upstream catalytic converter. Therefore, the exhaust gas is introduced into the upstream catalytic converter located near the engine body, and since it is located near the engine body, the temperature drop of the exhaust gas is reduced and the temperature in the catalytic converter is relatively low. Since it increases, a good catalytic action can be obtained.

The switching valve takes the second position when the temperature is high, and therefore most of the exhaust gas bypasses the upstream catalytic converter and is guided to the downstream catalytic converter via the first bypass passage. It is possible to prevent a large amount of high-temperature exhaust gas from directly hitting the upstream catalytic converter, and to prevent the heat damage.
Then, a small amount of exhaust gas is guided to the downstream side catalytic converter via the air-fuel ratio sensor, the upstream side catalytic converter through the second bypass passage. At this time, since the exhaust gas flowing through the second bypass passage contacts the air-fuel ratio sensor,
The air-fuel ratio is detected and feedback control of the air-fuel ratio can be performed.

〔Example〕

In FIG. 1, 10 is a cylinder block, 12 is a piston, 14 is a connecting rod, 16 is a cylinder head,
18 is a combustion chamber, 20 is an intake valve, 22 is an intake port, 24 is an exhaust valve, and 26 is an exhaust port. An intake manifold 28 is connected to the intake port 22. In this embodiment, the internal combustion engine is a carburetor.
It is a carburetor internal combustion engine equipped with 30. However, it can also be applied to a fuel injection type internal combustion engine. Vaporizer 30
, 30a is a throttle valve, 30b is a venturi, 30c
Is a main nozzle, 30d is a fuel passage, and 30e is a float chamber. The carburetor 30 further comprises means for controlling the air-fuel ratio by controlling the air bleed. That is, a bleed passage 32 that opens to the main nozzle 30c is provided, a bleed control valve 34 that is an opening / closing valve for controlling the amount of bleed is arranged on the bleed passage 32, and an air filter 36 is provided at the end of the bleed passage 32. Is installed. The carburetor 30 is set to a value on the rich side as the base air-fuel ratio, and the bleed air amount is changed by opening / closing the bleed control valve 34 to control the air-fuel ratio.

The upper end of the carburetor 30 is connected to the air cleaner 40, and the lower end thereof is connected to the intake manifold 28.

Exhaust port 26 is connected to exhaust manifold 42. The exhaust manifold 42 is connected to the exhaust pipe 44. Two catalytic converters 46 and 48 are arranged in series on the exhaust pipe 44. A bypass pipe 50 is connected to the exhaust pipe 44 so as to bypass the catalytic converter 46 on the upstream side. A first bypass passage 50a that bypasses the upstream side catalytic converter is formed in the bypass pipe 50. A swing type switching valve 52 is installed at a connection point between the upstream end of the bypass pipe 50 and the exhaust pipe 44. One end of the switching valve 52 is a lever 54
Is connected to one end of the rod 56 via. The other end of the rod 56 is connected to the diaphragm 58a of the diaphragm mechanism 58. A negative pressure chamber 58b is formed on one surface of the diaphragm 58, and a spring 58c is arranged in the negative pressure chamber 58b.The spring 58c biases the diaphragm 58a to the left in the figure, and as a result, the switching valve 52 is in an imaginary line. Thus, the first bypass passage 50a is urged toward the open position. When negative pressure is introduced into the negative pressure chamber 58b, the diaphragm 58a moves to the right against the spring 58c, and this movement causes the rod 5 to move.
6. The changeover valve 52 is transmitted via the lever 54, and the changeover valve 52 closes the first bypass passage 50a as indicated by the solid line. The three-way solenoid valve 59 connects the negative pressure chamber 58b of the diaphragm mechanism 58 to the negative pressure port 28a of the intake manifold 28, which is the negative pressure source, and the negative pressure chamber 58b to the atmospheric filter 60, which is the atmospheric pressure source. Switch to the black paint position.

An O ₂ sensor 61 as an air-fuel ratio sensor is installed in the main passage 44a downstream of the switching valve 52 and upstream of the upstream catalytic converter 46. The O ₂ sensor 61 is configured as an oxygen concentration battery that generates two types of voltage signals, large and small, depending on the air-fuel ratio. The present invention can be applied to other types of air-fuel ratio sensors.

The temperature sensor 62 is installed in the exhaust manifold 42 and obtains a signal according to the temperature T of the exhaust gas. The location where the temperature sensor 62 is installed is not necessarily limited to the location shown in the figure, and may be installed in the upstream catalytic converter 46, for example. Further, instead of directly detecting the temperature, it is also possible to detect the condition under which the catalyst overheats based on the rotation speed and the load.

The control circuit 64 controls the solenoid valve 59 for driving the air bleed control valve 34 and the diaphragm mechanism 58 in response to signals from the O ₂ sensor 61 and the temperature sensor 62. Although the control circuit 64 is shown as a theoretical circuit, it may be configured as software of a microcomputer. The control circuit 64 includes a first comparator 64a and a second comparator 64b. The first comparator 64a is connected to the temperature sensor 62, when the exhaust gas temperature T is smaller than a predetermined value T ₀ "0", the temperature T is to generate a signal "1" when greater than a predetermined value T _0. It should be noted that a proper hysteresis can be added on the way back and forth. On the other hand, the second comparator 64b is the air-fuel ratio sensor 6
It is connected to 1 and generates a signal of "1" when the air-fuel ratio is richer than the stoichiometric air-fuel ratio (λ = 1) and generates a signal of "0" when the air-fuel ratio is leaner than the theoretical air-fuel ratio. First comparator 64
The output of a is connected to the driving transistor 64c of the solenoid 59a of the three-way solenoid valve 59. The second comparator 64b is connected to the drive transistor 64d of the solenoid 34a of the air bleed control valve 34.

According to the present invention, when the switching valve 52 takes the position where the first bypass passage 50a is opened as shown by the imaginary line, a small amount of exhaust gas is circulated in the main passage 44a, so that the partition plate 70 is placed in the exhaust pipe 44. A second bypass passage 72 is formed between the inner wall of the exhaust pipe and the partition plate 70. The flow path diameter of the second bypass passage 72 is small enough not to cause heat damage to the catalytic converter 46, but is sufficient to make the atmosphere around the O ₂ sensor 61 coincide with that of the exhaust gas flowing through the first bypass passage 50a. It is set to obtain the flow rate.

The operation of the present invention will be described below. When the temperature T of the exhaust gas is lower than the predetermined value T ₀ , the first comparator 64a outputs a signal “0”, the transistor 64c is turned off, and the three-way solenoid valve 59
The solenoid 59a is demagnetized, the solenoid valve 59 is in the white position, and the negative pressure from the negative pressure port 28a is introduced into the negative pressure chamber 58b of the diaphragm mechanism 58. Therefore, the diaphragm 58a moves to the right, and the switching valve 52 closes the first bypass passage 50 as shown by the solid line. Therefore, the exhaust gas is introduced into the upstream side catalytic converter 46 and the downstream side catalytic converter 48 via the main passage 44a. The air-fuel ratio of the exhaust gas is detected by the O ₂ sensor 61, and a signal of "1" is generated when rich and a signal of "0" is generated when lean. When the rich (“1”) signal is output from the second comparator 64b, the transistor 64d is driven, the air bleed control valve 34 is opened, and the air from the air filter 36 is carbureted through the bleed passage 32. Since it is introduced into 30, the air-fuel ratio set by the carburetor becomes large and is controlled toward the stoichiometric air-fuel ratio. On the other hand, the O ₂ sensor 61
The second comparator when the air-fuel ratio detected by is lean
64b applies a "0" signal to the transistor 64d. Therefore, the air bleed control valve 34 is closed and the air bleed is stopped, so that the air-fuel ratio set in the carburetor 30 becomes small and the air-fuel ratio is controlled toward the stoichiometric air-fuel ratio. By such feedback control of the air bleed by the air-fuel ratio signal O _X from the O ₂ sensor 61, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio, and the catalytic converter can maximize its capacity.

When the temperature T of the exhaust gas becomes higher than the predetermined value T ₀ , the first comparator 64a applies the signal "1" to the transistor 64c. As a result, the transistor 64c is turned on, the three-way solenoid valve 59 takes the black port position, the atmospheric pressure from the air filter 60 is introduced into the negative pressure chamber 58b of the diaphragm mechanism 58, and the spring 5
The diaphragm 58a moves leftward by the force of 8c, and the switching valve 52 is positioned so as to open the first bypass passage 50a as shown by an imaginary line. Thus, most of the exhaust gas bypasses the catalytic converter 46 on the upstream side, the temperature is sufficiently lowered by the time it reaches the downstream side, and passes through the catalytic converter 48 on the downstream side. Therefore, a large amount of high-temperature exhaust gas is prevented from flowing into the O ₂ sensor 61 and the catalytic converter 46, and its heat damage is prevented. However, even if the switching valve 52 is positioned as shown by the imaginary line in order to open the first bypass passage 50a, a small amount of exhaust gas passes through the second bypass passage 72 and the O ₂ sensor.
61 and upstream catalytic converter 46. The O ₂ sensor 61 detects the air-fuel ratio of the exhaust gas flowing through the second bypass passage 72, and opens / closes the air bleed control valve 34 according to the magnitude with respect to λ = 1.0 so that the air-fuel ratio is maintained at the stoichiometric air-fuel ratio. The feedback control is executed even at this high temperature.

Exhaust pipe corresponding to the periphery of the second bypass passage 72 in FIG.
The fins 90 are formed on the wall surface of 44. The fins can cool the exhaust gas flowing through the bypass passage 72. Therefore, the O ₂ sensor can be installed on the upstream side, and the responsiveness can be further improved.

In the embodiment of FIGS. 3 and 4, a gap 92 is formed between the main passage 44a and the second bypass passage 72 so that cooling can be performed efficiently.

In the embodiment of FIGS. 5 and 6, when the cutout 94 or the small hole is formed at the free end of the switching valve 52 and the switching valve 52 opens the first bypass passage 50a as shown by the imaginary line, A second bypass passage 72 is formed between the inner wall of the exhaust pipe 44 and a small amount of exhaust gas to pass through the main passage. Preferably, the fins 96 may be formed on the outer wall surface of the exhaust pipe 44 adjacent to the second bypass passage 72. FIG. 7 shows another shape of the small hole 94 formed in the switching valve 52.

In the embodiment shown in FIG. 8, the second bypass passage is displaced so as to approach the O ₂ sensor 61 so that the change in the air-fuel ratio can be detected more quickly.

The embodiment is a system of controlling the air-fuel ratio by controlling the amount of air bleed in a carburetor type internal combustion engine. Therefore, the present invention can be applied to a system that controls the air-fuel ratio.

The configuration of the present invention can exert the maximum effect when the feedback control is executed even at a high temperature, but it can also be applied to one that performs the rich control by stopping the feed bag control at a high temperature.

〔The invention's effect〕

By providing a second bypass passage that bypasses the switching valve to the first bypass passage and providing an air-fuel ratio sensor and then upstream and downstream catalytic converters downstream thereof, air-fuel ratio control is performed regardless of whether the switching valve is open or closed. The air-fuel ratio sensor upstream of the catalytic converter with high responsiveness, and at the time of high temperature, only a small amount of exhaust gas passing through the second bypass passage comes into contact with the air-fuel ratio sensor to mitigate heat damage to the air-fuel ratio sensor. You can

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention. FIG. 2 is a partial view showing a second embodiment (a view along the line II-II in FIG. 1). FIG. 3 is a view corresponding to a part of FIG. 1 in another embodiment. FIG. 4 is a sectional view taken along the line IV-IV in FIG. FIG. 5 is a view similar to FIG. 3 in another embodiment. FIG. 6 is a sectional view taken along the line VI-VI of FIG. FIG. 7 is a single-part view of a switching valve in another embodiment. FIG. 8 is a view corresponding to a part of FIG. 1 in yet another embodiment. 30 …… vaporizer, 34 …… air bleed control valve, 44 …… exhaust pipe, 44a… main passage, 46,48 …… catalytic converter, 50 …… bypass pipe, 50a …… first bypass passage, 52 …… Switching valve, 58 …… diaphragm mechanism, 61 …… O ₂ sensor, 62 …… temperature sensor, 64 …… control circuit, 72 …… second bypass passage.

Claims (1)

[Claims] 1. An air-fuel ratio is controlled by a signal from an air-fuel ratio sensor arranged in an exhaust pipe, and two catalytic converters are installed in series in an exhaust pipe downstream of the air-fuel ratio sensor, one end of which is upstream of the air-fuel ratio sensor. A first bypass passage connected to the exhaust pipe at a side portion and the other end connected to the exhaust pipe at a portion between the upstream catalytic converter and the downstream catalytic converter, and the first bypass passage is closed. First to open the exhaust pipe
A switching valve that switches between a position and a second position that opens the first bypass passage and closes the exhaust pipe; and a switching valve that holds the first position when the temperature is low and the second position when the temperature is high. And a second bypass passage having one end connected to the exhaust pipe at a portion upstream of the switching valve and the other end connected to the exhaust pipe at a portion between the switching valve and the air-fuel ratio sensor. An exhaust gas purifying device for an internal combustion engine for an automobile, which is characterized in that