JPS6338340Y2 - - Google Patents

Description

[Detailed description of the invention] A. Field of industrial application This invention relates to an exhaust gas purification device for an internal combustion engine using a three-way catalyst.

B. Prior art The air-fuel ratio control methods for the air-fuel mixture used in this type of device have conventionally been one in which the air-fuel ratio is controlled by an intake system including a carburetor, and the other in which the air-fuel ratio is controlled by an exhaust system. The method is known.

The former had the drawback that it took a long time for the catalyst temperature to reach the temperature required for reaction when starting at low temperatures, and the exhaust gas was released into the atmosphere as a harmful gas without being purified. The latter, on the other hand, obtained an air-fuel ratio with a good purification rate by making the mixture from the carburetor rich in advance and mixing air into the exhaust system, but the fuel consumption was high because the extra fuel was supplied in advance compared to the amount directly consumed for output, and especially in a structure in which the air pump for blowing air into the exhaust system was driven by the output of the internal combustion engine, the extra output was required, which also caused an increase in fuel consumption.

In view of this, the object of this invention is to realize an exhaust gas purification device using an air-fuel ratio control method that eliminates the drawbacks of both of the above methods and takes advantage of their advantages.

D. Means for Solving the Problems The exhaust gas purification device of this invention includes a carburetor provided in the intake passage of an internal combustion engine and an air bleed actuator 3 that controls the amount of air bleed from the carburetor according to the drive voltage. and sequentially along the flow direction so as to be in contact with the flow of the exhaust passage _.
A sensor 5, a second O ₂ sensor 6, and a three-way catalyst 4 for exhaust gas purification are arranged, and an air pump 7 whose air volume can be controlled according to the drive voltage is provided to direct the exhaust air to the exhaust gas passage. 1 O ₂ sensor and 2nd O ₂
A temperature sensor 8 is connected to the part between the sensor and detects the temperature of the three-way catalyst, and it is determined whether the voltage obtained by converting the detected temperature of this temperature sensor 8 with the voltage converter 10 is lower or higher than the comparison voltage 11. A comparison circuit 12 outputs a low voltage signal when the voltage is low and a high voltage signal when the voltage is high, and its duty ratio changes depending on the air-fuel ratio detected by the first O ₂ sensor 5. an AND gate 13 which has a rectangular wave signal as one input, the output of the comparator circuit 12 as the other input, and the output as a control signal for the power circuit 14 that drives the air bleed actuator 3;
One input is a rectangular wave signal whose duty ratio changes according to the air-fuel ratio detected by the second O ₂ sensor 6, and the other input is a signal obtained by inverting the output of the comparison circuit 12 by an inverter 15. An OR gate 16 is provided whose output is used as a control signal for the power circuit 17 that drives the air pump 7, and while the temperature detected by the temperature sensor 8 is low, the output is connected to the air-fuel ratio detected by both the O ₂ sensors 5 and 6. The amount of air bleed is reduced without any problem, and the amount of air to the exhaust passage is increased. When the temperature detected by the temperature sensor 8 becomes high, the air bleed is performed so that the air-fuel ratio detected by the first O ₂ sensor 5 approaches the stoichiometric air-fuel ratio. A driving voltage is applied to the actuator 3 and a driving voltage is applied to the air pump 7 so that the total air-fuel ratio detected by the second O ₂ sensor 6 approaches the stoichiometric air-fuel ratio.

E. Effect Because of this configuration, when the temperature detected by the temperature sensor 8 is low, that is, when the temperature of the three-way catalyst has not reached the temperature required for the reaction, especially when starting or warming up in a cold state, , the air-fuel ratio of the mixture supplied from the carburetor 2 becomes slightly rich, and a large amount of air is sent from the air pump 7 to the exhaust passage 10, promoting the oxidation reaction and emitting harmful gases (mainly HC, CO). The temperature of the three-way catalyst 4 is increased while preventing the above, and the active state of the three-way catalyst is brought to an earlier stage.

When the temperature detected by the temperature sensor is high, that is, after the temperature of the three-way catalyst 4 reaches the temperature required for the reaction, the air bleed actuator 3 of the vaporizer 2 is mainly connected to the first O ₂ sensor 5. The air-fuel ratio detected by the first O ₂ sensor 5 is close to the stoichiometric air-fuel ratio by controlling the drive via the electronic control device 9 based on the output. Therefore, it prevents the emission of harmful gases (HC, CO, NOx) and reduces fuel consumption. Furthermore, the amount of air flowing from the air pump 7 to the exhaust passage 10 is measured by a second O ₂ sensor 6.
By controlling via the electronic control device 9 based on the output of , the overall air-fuel ratio detected by the second O ₂ sensor 6 can be obtained close to the stoichiometric air-fuel ratio.

Example Next, an example will be described.

In FIG. 1, 1 is an internal combustion engine, 2 is a carburetor installed in the intake passage of the internal combustion engine 1, and 3 is an air bleed actuator that controls the amount of air bleed to control the air-fuel ratio of the air-fuel mixture supplied from the carburetor 2. Yueta,
Reference numeral 4 denotes a three-way catalyst for exhaust gas purification provided in contact with the flow of the exhaust passage 10; 5 and 6 refer to the flow from the internal combustion engine 1 to the three-way catalyst 4 in contact with the flow of the exhaust passage 10; a first O ₂ sensor and a second O ₂ sensor, respectively, arranged sequentially along the
is driven by an internal combustion engine 1 and can control the amount of air,
An air pump 8 that causes exhaust air to join the exhaust passage 10 between the first O ₂ sensor 5 and the second O ₂ sensor 6 is operated at a temperature of the three-way catalyst 4 or in parallel thereto. Locations that change, e.g. exhaust passage 1
A temperature sensor 9 detects the outside air temperature at or near 0, and receives and responds to the output of the temperature sensor 8 and the first O ₂ sensor, the output of the sensor 5, and the output of the second O ₂ sensor 6. This is an electronic control device that provides control signals to the air bleed actuator 3 and the air pump 7, respectively.

A specific example of the electronic control device 9 is shown in FIG. Three-way catalyst 4
When the temperature has not reached the temperature required for the reaction, the temperature detected by the temperature sensor 8 is low, and the voltage signal obtained by converting the signal of the temperature sensor 8 by the voltage converter 10 is lower than the comparison voltage 11. In addition, the output voltage of the comparator 12 becomes a low level, the AND gate 13 closes, and its output becomes a low level, so that no driving voltage is applied to the air bleed actuator 3. The air bleed actuator 3 is a known actuator, and is a solenoid valve that is opened and closed by an opening/closing signal (driving voltage) from the power circuit 14, and when the driving voltage is not present (that is, when the opening/closing signal is on the closing side), the air bleed actuator 3 is a known actuator. close. Therefore, when the temperature detected by the temperature sensor 8 is low, the air bleed actuator 3 is closed, and the air-fuel ratio of the air-fuel mixture supplied from the carburetor 2 becomes slightly rich. Also, at this time, the comparator 12
The output is inverted by the inverter 15 to become a high level signal and applied to the OR gate 16.
Therefore, the output of the OR gate 16 becomes high level, is amplified by the power circuit 17, and drives the air pump 7, so that the amount of air supplied from the air pump 7 to the exhaust passage 10 is maximized, promoting the oxidation reaction and causing harmful gases. The temperature of the three-way catalyst 4 is raised while preventing the discharge of the three-way catalyst, and the three-way catalyst reaches an active state earlier.

Note that at this time, _one input terminal 13a of the AND gate 13 is
However, as mentioned above, the low level signal from the comparator 12 is applied to the other input terminal 13b of the AND gate 13, and the output is closed. Not affected by the _O2 sensor 5 signal.

Also, at this time, a pulse signal corresponding to the signal from the second O ₂ sensor 6 is applied to one input terminal 16a of the OR gate 16, but the above-mentioned pulse signal is applied to the other input terminal 16b of the OR gate 16. Since the high level signal from the inverter 15 is applied, the output of the OR gate 16 is not affected by the signal from the second O ₂ sensor 6.

As the temperature detected by the temperature sensor 8 becomes higher,
When the output voltage of the voltage converter 10 becomes high and the temperature of the three-way catalyst 4 reaches the temperature required for the reaction, the output voltage of the voltage converter 10 exceeds the value of the comparison voltage 11,
The output of the comparator 12 changes to high level, and the AND gate 13 opens. Therefore, the output of the AND gate 13 changes depending on the pulse signal applied to the input terminal 13a. The pulse signal applied to the input end 13a is a rectangular wave signal whose duty ratio changes according to the air-fuel ratio detected by the first O ₂ sensor 5, and is connected to the air-fuel ratio determination circuit 18, the integrator 19,
It is generated by a known electric circuit consisting of a proportional device 20, a triangular wave oscillator 21, and a comparator 22. _O2 sensor 5
The output voltage of the air-fuel ratio determination circuit 18 has a characteristic of rapidly changing after reaching the stoichiometric air-fuel ratio, and the output voltage level of the air-fuel ratio determination circuit 18 changes depending on whether the air-fuel ratio is rich or lean. An electric circuit is operated to issue a control signal to lean the air-fuel ratio when the fuel is rich, and to produce a control signal to enrich the air-fuel ratio when the fuel is lean. The output voltages of the integrator 19 and the proportional device 20 are added and applied to the minus input terminal of the comparator 22, and compared with the triangular wave voltage of a constant frequency from the triangular wave oscillator 21, and converted into a rectangular waveform pulse signal. , the duty ratio of this pulse signal is determined by the level of the signal applied to the negative input terminal of the comparator 22. When the output voltage of the O ₂ sensor 5 is judged by the air-fuel ratio judgment circuit 18 and it is judged that the air-fuel ratio has become rich, a step voltage is generated by the proportional regulator 20, and the corresponding duty voltage is generated by the comparison circuit 22. The signal is converted into a rectangular wave of the ratio, passes through the AND gate 13 and the power circuit 14, increases the average opening degree of the air bleed actuator 3, and changes the air-fuel ratio by a proportional amount in the direction of making it leaner. However, the output voltage of the O ₂ sensor does not change immediately and remains in a rich state. At this time, due to the operation of the integrator 19, the signal level at the negative input terminal of the comparator 22 gradually changes in the direction of reducing the air-fuel ratio, and the air bleed actuator 3 is driven to open and close at a duty ratio corresponding to the signal level. The average opening gradually increases, and the air-fuel ratio becomes leaner. As a result, when the output voltage of the O ₂ sensor suddenly changes, the air-fuel ratio determination circuit 18 determines that the air-fuel ratio has become leaner than the stoichiometric air-fuel ratio. Therefore, a step voltage in the opposite direction to that in the above case is generated in the proportional device 20, and then the integrator 19 is activated so that the signal level at the negative input terminal of the comparator 22 changes in the direction of gradually enriching the air-fuel ratio. do. Then, the average opening degree of the air bleed actuator 3 gradually becomes smaller and becomes denser. In this way, the first O ₂
The air bleed actuator 3 is operated so that the air-fuel ratio detected by the sensor 5 approaches the stoichiometric air-fuel ratio.

Further, an electric circuit including an air-fuel ratio determination circuit 23, an integrator 24, a proportional device 25, a triangular wave oscillator 26, and a comparator 27 generates a rectangular wave voltage with a duty ratio corresponding to the output voltage of the second O ₂ sensor 6. occurs, OR
The air pump 7 is operated via the gate 16 and the power circuit 17 to perform the same control as the air-fuel ratio control by the first O ₂ sensor. As a result, the second
The overall air-fuel ratio detected by the O ₂ sensor 6 is close to the stoichiometric air-fuel ratio.

G. Effects of the invention As described above, according to this invention, the oxidation reaction of the three-way catalyst is utilized during startup and warm-up in cold conditions.
At high temperatures, the catalyst utilizes oxidation and reduction reactions, resulting in high catalytic efficiency, which purifies exhaust gases, ie reduces harmful gas emissions, and reduces fuel consumption.

Further, the power for driving the air pump can be suppressed to the necessary minimum, and fuel consumption can also be reduced in this respect. Furthermore, AND gate 1 is used to switch control signals to air bleed actuator 3 and air pump 7 according to the temperature of the three-way catalyst.
3 and the OR gate 16, there is no need to provide a switching valve downstream of the air pump.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of one embodiment of this invention, and FIG. 2 is a circuit diagram of an electronic control device. 1... Internal combustion engine, 2... Carburizer, 3... Air bleed actuator, 4... Three-way catalyst, 5...
First O ₂ sensor, 6... Second O ₂ sensor, 7...
...Air pump, 8...Temperature sensor, 9...Electronic control device, 10...Exhaust passage.

Claims (1)

[Scope of utility model registration request] In an internal combustion engine, a carburetor is provided in the intake passage, and an air bleed actuator 3 is provided to control the amount of air bleed from the carburetor according to the drive voltage. , a first O ₂ sensor 5, a second O ₂ sensor 6, and a three-way catalyst 4 for exhaust gas purification are arranged,
Furthermore, an air pump 7 whose air volume can be controlled according to the drive voltage is provided, and the discharged air is sent to the first exhaust passage.
A temperature sensor 8 is connected to the part between the O ₂ sensor and the second O ₂ sensor and detects the temperature of the three-way catalyst.
Then, it is determined whether the voltage detected by the temperature sensor 8 is converted by the voltage converter 10 is lower or higher than that of the comparator circuit 11, and when it is low, a low voltage signal is output, and when it is high, a high voltage signal is output. A comparator circuit 12 that outputs a signal and a rectangular wave signal whose duty ratio changes according to the air-fuel ratio detected by the first O ₂ sensor 5 are input as one input, and the output of the comparator circuit 12 as the other input. An AND gate 13 whose output is used as a control signal for the power circuit 14 that drives the air bleed actuator 3, and a rectangular wave whose duty ratio changes according to the air-fuel ratio detected by the second O ₂ sensor 6. an OR gate 16 whose one input is a signal, whose other input is a signal obtained by inverting the output of the comparator circuit 12 by an inverter 15, and whose output is a control signal for the power circuit 17 that drives the air pump 7; While the temperature detected by the temperature sensor 8 is low, the amount of air bleed is reduced and the amount of air flowing into the exhaust passage is increased, regardless of the air-fuel ratio detected by both the O ₂ sensors 5 and 6, and the temperature detected by the temperature sensor 8 is reduced. When the air-fuel ratio increases, a driving voltage is applied to the air bleed actuator 3 so that the air-fuel ratio detected by the first O ₂ sensor 5 approaches the stoichiometric air-fuel ratio, and the total air-fuel ratio detected by the second O ₂ sensor 6 increases. An exhaust gas purification device for an internal combustion engine, characterized in that a driving voltage is applied to an air pump 7 so as to approach a stoichiometric air-fuel ratio.