JPS5996421A - Exhaust gas purifying device of internal-combustion engine - Google Patents

Abstract

PURPOSE:To improve the purification efficiency of a ternary catalyst by closing and opening a solenoid valve for supplying secondary air to the upper stream of the ternary catalyst at the frequency of 1-2Hz, periodically varying an air-fuel ratio within the range of + or -0.2-+ or -0.1, and extending the closing time when an engine load exceeds a prescribed value. CONSTITUTION:A secondary air supplying hole 60 is provided on an exhaust manifold 3, and secondary air is supplied to the upper stream of a ternary catalyst 5 via a control valve 50 and a check valve 59. Negative pressure is introduced into the negative pressure chamber 53 of the control valve 50 via a solenoid valve 51, and this solenoid valve 51 is closed and opened by a solenoid driving circuit 70 at the frequency of 1-2Hz, allowing an air-fuel ratio to be periodically varied via the control valve 50 within the range of + or -0.2-+ or -1.0 taking a theoretical air-fuel ratio as a center. A negative pressure switch 77 is connected to the driving circuit 70, and when an engine load exceeds a prescribed value, the negative pressure in the negative pressure chamber 79 of the negative pressure switch 77 is reduced, turned off, and pulse generators 71, 72 are changed over to each other via AND gates 73, 74, allowing closing time to be extended.

Description

[Detailed description of the invention] The present invention relates to an exhaust gas purification device for an internal combustion engine.

A three-way catalyst is said to be a catalyst that can simultaneously reduce harmful three-component molecules (C, Co, and NOxf) in exhaust gas.The purification efficiency R of this three-way catalyst is as shown in Figure 1(a). The air-fuel ratio becomes highest when the air-fuel ratio A/F is approximately the stoichiometric air-fuel ratio, and for example, the air-fuel ratio region where a purification efficiency R' of 80 percent or more can be obtained is when the air-fuel ratio is 0.0.
It has a narrow width of about 6 mm.

Usually, the air-fuel ratio region in which a purification efficiency of 80 percent or more can be obtained is called a window W. Therefore, in order to simultaneously reduce the three harmful components in the exhaust gas using a three-way catalyst, K must always maintain M at all times λ at this narrow air-fuel ratio. To this end, in conventional exhaust gas purification systems, an oxygen concentration detector that can determine whether the air-fuel ratio is greater or less than the stoichiometric air-fuel ratio is installed in the engine exhaust passage, and the output signal of the oxygen concentration detector is used to detect the air-fuel ratio. The fuel ratio is controlled to be the same air-fuel ratio as the window W. However, such an exhaust gas purification device using an oxygen concentration detector requires an expensive oxygen concentration detector and an expensive electronic control unit for air-fuel ratio control, which increases the manufacturing cost of the exhaust gas purification device. There is a problem with doing so.

However, recently, SAE paper No.

As described in Japanese Patent Publication No. 760201 and Japanese Patent Publication No. 56-4741, the function of the three-way catalyst was gradually elucidated, and it was found that the three-way catalyst had an acid accumulation function. In other words, when the air-fuel ratio is on the lean side with respect to the stoichiometric air-fuel ratio, the three-way catalyst takes oxygen from NOx and converts it into NOx.
While reducing x, all of this stolen oxygen is retained, and when the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, the retained oxygen is released to oxidize Co and HC. Therefore, if the air-fuel ratio is alternately varied between the lean side and the rich side with respect to the standard air-fuel ratio, even if the standard air-fuel ratio deviates from the stoichiometric air-fuel ratio, the oxygen retention function described above will reduce NOx.
In addition, the oxidation effect of CO and He is promoted, and high purification efficiency can be obtained. Figure 1 (b) shows the air-fuel ratio total
The window Wok of the reference air-fuel ratio A/F is shown when the reference air-fuel ratio is varied by (3) ±1.0 with respect to the reference air-fuel ratio in Hz. From Figures 1(a) and 1(a), window W is obtained when the total fuel ratio is varied at one frequency. It can be seen that the area becomes wider. This means that if the air-fuel ratio is varied over a constant cycle, high purification efficiency can be obtained even if the reference air-fuel ratio deviates somewhat from the stoichiometric air-fuel ratio. -If the air-fuel ratio fluctuation frequency is lowered, that is, if the air-fuel ratio fluctuation period is lengthened, the oxygen retention function of the three-way catalyst will become saturated, and the oxidation-reduction ability based on the oxygen retention function will decrease. Purification efficiency decreases. FIG. 1(C) shows this very clearly. 1st (C)
In FIG. 2, the vertical axis R shows the purification efficiency, and the horizontal axis F shows the fluctuation frequency of the air-fuel ratio. Furthermore, if the air-fuel ratio fluctuation period is made small, the air-fuel ratio cannot be varied alternately between the rich side and the rich side, so the window becomes narrower. Therefore, it can be seen that there is an optimal RC fluctuation period and a period during which the fuel ratio is varied to widen the window width.

As mentioned above, if the width 2 and the fluctuation frequency of the air-fuel ratio fluctuation relative to the standard air-fuel ratio (4) are appropriately selected, the window becomes wider, and therefore high purification efficiency can be achieved even if the standard air-fuel ratio fluctuates somewhat relative to the stoichiometric air-fuel ratio. You can get everything. Of course, this term means that if a narrow fuel supply system is used during fluctuations in the reference air-fuel ratio, a high purification efficiency can be obtained without using the feedback opening l based on the output signal of the oxygen concentration detector. If a fuel injection valve is used as a fuel supply system, it is possible to narrow the fluctuation period of the reference air-fuel ratio, but since the fuel injection device is expensive, there is a problem that the manufacturing cost of the Ic engine increases. If the air-fuel ratio supplied to the engine cylinders is varied in this way, combustion will fluctuate periodically even if the fluctuations are small, resulting in a problem that vehicle drivability will deteriorate.

It is an object of the present invention to provide an exhaust gas purification device that can ensure high exhaust gas purification efficiency without using an oxygen concentration detector and without changing the air-fuel ratio supplied into an engine cylinder. Hereinafter, the invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 2, 1 is an intake manifold, 2 is a variable venturi carburetor installed on the intake manifold 1,
To 3'! The 1P air manifold, 4RA, and catalytic converter are shown respectively, and the 3-way monolith catalyst 5 is arranged inside the catalytic converter 4, the 0 variable bench lily type carburetor 2, the carburetor housing 6, and the 1 housing 6Fl are vertically aligned. An extending intake passage 7, a suction piston 8 that moves all around the intake passage 7, a needle 9 added to the tip surface of the suction piston 8, and an intake passage w57 facing the tip surface of the suction piston 3. The spacer 10 identified on the inner wall surface of the suction piston 8, the throttle valve 11 provided in the intake passage 7 downstream of the suction piston 8, and the float chamber 12 are all included.
A venturi portion 13 is formed in between. A casing 14 having a cylindrical inner wall is fixed to the carburetor housing 6, and a guide sleeve 15 is attached to the casing 14, which extends along the entire length of the casing 14 inside the casing 14. An illumination receiver 17 having a large number of balls 16 is inserted into the guide sleeve 15, and the reeded guide sleeve 15 is closed by a cover 18. Ten thousand,
A guide rod 19 is fixed to the suction piston 8,
This guide rod 19rl: @ guide rod 19 in the receiver 17
Since the suction piston 8 is supported by the casing 14 via the bearing 17, the suction piston 8 can move smoothly in the axial direction inside the casing 14. It is divided into a negative pressure chamber 20 and an atmospheric pressure chamber 21 by the suction piston 8, and a compression spring 22 that constantly presses the suction piston 8 toward the venturi @13 is inserted into the negative pressure chamber 20. The royal chamber 20 is connected to the venturi part 13 through the suction hole 23 formed in the suction piston 8, and the suction piston 8 is connected to the air intake passage of the suction piston 8 through the entire air hole 24 formed in the carburetor housing 6 to the atmospheric pressure chamber 21. 7173.

(7) A fuel passage 25 extending in the axial direction of the needle 9 is formed in the carburetor housing 6 yen so that the needle 9 can enter therein, and a metering jet 26 is provided in this fuel passage 25 yen. # Fuel passage upstream of liver jet 26 kN5.2
5 is a fuel vibrator 27 that extends downward to the float chamber 1.
2, and the fuel in the float chamber 12 is fed into the fuel passage 25 through this fuel pipe 27. Furthermore,
A hollow cylindrical nozzle 28 disposed coaxially with the fuel passage 25 is fixed to the spacer 10 . This nozzle 28 protrudes from the inner wall of the spacer 1o to the venturi portion 13, and further protrudes toward the suction piston 8 from the bank at the tip of the nozzle 28. The needle 9 extends through the nozzle 28 and the metering jet 2617g, and the fuel #+ is metered by the annular gap formed between the needle 9 and the metering jet 26 before being supplied from the nozzle 28 into the intake passage 7. .

As shown in FIG. 2, a raised wall 29 (8) is formed at the upper end of the spacer 10 and projects horizontally toward the intake passage 7, and between this raised wall 29 and the tip of the suction piston 8. At step 2, flow rate control is performed. When engine operation is started, air flows downward through the intake passage 7FE3.At this time, the airflow is narrowed between the suction piston 8 and the raised wall 29, so that the venturi portion 13
Negative pressure is generated, and this negative pressure is guided into the negative pressure chamber 20 through the suction hole 23. The suction piston 8 is designed so that the pressure difference between the negative pressure chamber 20 and the atmospheric pressure chamber 21 is approximately one foot pressure determined by the spring force of the compression spring 22, that is, the negative pressure in the venturi portion 13 is approximately constant. Moving.

Referring to FIG. 32 and FIG. 4, the entire tip surface of the suction piston located on the upstream side of the needle 9 is raised from the multi-light end surface 30 of the needle 9 toward the tip of the needle 9. , a concave groove 31 extending in the @ line direction of the intake vent 1!1i57 on the tip end surface of the suction piston.
is formed. This concave groove 31 RUJ07fa m
31 a n It has a U-shaped cross section and is located on the side closer to the tip of the needle 9 than the needle mounting end surface 30. The remaining concave groove portion 31b extends almost straight from the upstream fHIJ end 31a to the needle attachment end surface 30. Furthermore, the cross-sectional shape of the suction piston tip surface located upstream of the needle 9 is V-shaped, expanding from the concave groove 31 toward the venturi portion 13. A pair of inclined wall surface portions 32a that are inclined toward.

Shoulder 32b.

As can be seen from FIG. 3, when the total intake air volume is small, the raised wall 29 and the inclined wall portions 32a and 32b.

P and the upstream end portion 31a of the groove form an intake air control constriction portion K having a substantially isosceles triangular shape.

By forming the intake air control throttle part K in this way, the lift t of the suction piston 8 is reduced by the intake air control throttle 9.
Therefore, the rift of the suction piston 8) J! The trc increases smoothly as the intake nitrogen amount increases. Furthermore, since the suction piston 8 is supported by the suction piston 8, it moves with good responsiveness to changes in the total intake air volume, and thus, when the suction piston 8 increases the intake air volume, the intake air volume increases. It moves responsively and clearly to the increase in the number of people. As a result, even when the intake air volume changes rapidly, such as during acceleration, the lift of the suction piston 8 increases in proportion to the increase in the intake air volume, so that the amount of fuel supplied from the nozzle 28 increases. The amount will always be proportional to the intake air amount. Furthermore, as can be seen from FIG. 3, when the amount of intake air is small, the intake air is made to flow through the center of the intake passage 7, and as a result, the solvent I/:i is immediately supplied with the intake airflow from the nozzle 28. Therefore, even when the intake air amount is small, the fuel supplied from the nozzle 28 is immediately supplied into the engine cylinder. Even if fC increases rapidly, the amount of fuel supplied from the nozzle 28 is proportional to the amount of intake air as described above, and moreover, the amount of fuel supplied from the nozzle 28 is
Since the fuel is immediately supplied into the engine cylinder, the air-fuel ratio of the mixture supplied into the engine cylinder remains almost constant even if the intake cost and air weight change rapidly. Since it is supported by the bearing 17, the engine temperature does not affect the movement of the suction piston 8, and thus the suction piston 8 can move responsively to changes in the amount of intake air regardless of the engine temperature. can. Thus, when the variable bench carburetor 2 shown in FIG. 2 is used, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinders can be adjusted to approximately a single value, e.g., regardless of the engine temperature 2 and engine operating conditions. It can be maintained at about 14.0.

Therefore, a rich air-fuel mixture with a desirable fuel-fuel ratio of about 14.0 is constantly supplied to the engine cylinders.

Referring to FIG. 2, an annular air chamber 33 is formed around the metering jet 26, and a plurality of air bleed holes 34 communicating with the annular air chamber 33 are formed on the circumferential wall surface of the metering jet 26. The loam-like air chamber 33 is connected to the intake passage 7 upstream of the raised wall 29 via an air bleed passage 35, 36 and an air bleed jet 37, and a wax valve 38 is provided at the connection of these air bleed passages 35, 36. 0 wax valve 38 in which a valve body 39 driven by
A cooling water circulation chamber 39 is formed around the temperature sensing part 38a, and cooling water is introduced into this cooling water circulation chamber 39 from a cooling water inlet 40, and this cooling water is introduced from a cooling water outlet 41 to υ
[When the temperature of the output O engine cooling water rises, the valve body 39 moves to the left, thereby increasing the flow area of the air bleed passage and thus increasing the amount of air bleed. When the warm-up operation is completed, the valve body 39 fully opens the air bleed passage, and at this time, the nitrogen-fuel ratio of the air-fuel mixture supplied into the engine cylinder is 14.
．． The secondary air supply control valve 5 controls the supply of secondary air to the engine exhaust manifold 3 when the mixture becomes a rich mixture of about 0.
0 is attached to the intake manifold 1, and a solenoid valve 51 for controlling the operation of the secondary air supply control valve 50 is attached to the intake manifold 1.

A secondary air supply control valve 51J has a negative pressure chamber 53 and an atmospheric pressure chamber 54 separated by a diaphragm 52, and the negative pressure chamber 53
A compression spring 55 for pressing the diaphragm is inserted inside.
A hollow tube 56 that protrudes along with the diaphragm 52 is fixedly disposed within the atmospheric pressure chamber 54, and a valve boat 56 whose opening and closing are controlled by a valve body 58 fixed to the diaphragm 52 is provided at the tip of the hollow tube 56. 57 is formed 0 this valve boat 5
7 flows into the exhaust manifold 3 from the valve boat 57 through the check valve 59 and the secondary air supply hole 60, which can flow only at the same time as the exhaust manifold 3! ! I will be treated.

Therefore, the valve boat 57 and the secondary viewing supply hole 60 form a secondary air supply passage. On the other hand, the solenoid valve 51 has a valve chamber 62, a valve body 63 disposed in the valve chamber 62FE3, and a valve chamber 62V.
a negative pressure boat 64 that opens into the valve chamber 62 and is connected to the intake manifold 1, an atmospheric boat 65 that opens into the valve chamber 62 and communicates with the atmosphere, and a movable plunger connected to the valve body 63.
66 and a solenoid 67 for suctioning the movable plunger 66, the negative pressure boat 64 and the atmospheric boat 6
5 is operated to the negative pressure chamber 53 of the secondary air supply control valve 50 via a conduit 68 to a zero valve 62 whose opening and closing are controlled by a valve body 63, and a solenoid 67 is connected to a solenoid drive circuit 70. As shown in FIG. 5(a), the solenoid drive circuit 70 includes a first pulse generator 71 that generates rectangular pulses with a frequency of IHz to 2H7 with a duty ratio t/T of 1-50%. , a second pulse generator 72 that generates a rectangular pulse with a frequency of IHz to 2H2 with a duty ratio t/T of approximately 20% to 30%, and the output of the first pulse generator 71 are used as inputs. and a second AND gate 74 that takes the output of the second pulse generator 72 as its input.
and a first AND gate 73 and a second AND gate 74
The output terminal of the power amplifier 75 is connected to the solenoid 67. Further, the other input of the first AND gate 73 is connected to a negative pressure switch 77 , and the other input of the second AND gate 74 is connected to the negative pressure switch 77 via an inverter 76 . The negative pressure switch 77 connects a negative pressure chamber 79 and an atmospheric pressure chamber 80 separated by a diaphragm 78, and is connected to the negative pressure chamber 79 through a negative pressure conduit 81 into the intake manifold l. The first AND gate 73 in the atmospheric pressure chamber 80
and a fixed contact 8 connected to the input of the second AND gate 74
2 and a movable contact 83 fixed to the diaphragm 78 and connected to a power source (not shown). During low-load operation with a small opening of the throttle valve 11, a large negative pressure is generated in the negative pressure chamber 79 of the negative pressure switch 77, so the diaphragm 78 moves to the left, causing the movable IvI contact 83 and the fixed contact 82 to Contact. Therefore, at this time, the output voltage of the first AND gate 73 becomes high level every time the first pulse generator 71 generates a pulse.
Solenoid 6 is maintained at a low level to the output voltage of 4.
The negative pressure chamber 7 of the negative pressure switch 77 is driven and controlled by the output pulse of the first pulse generator 71.
Since the negative pressure inside 9 becomes small, the movable contact 83 and the fixed contact 82 are brought into a non-contact state. As a result, the output voltage of the first AND gate 73 is maintained at a low level, and becomes a high level every time the second pulse generator 72 generates a pulse to the output voltage of the -1 second AND gate 74, so that the output voltage of the solenoid 67i is maintained at a low level.
The drive is controlled by the output pulse of the i2 pulse generator 72.0 As described above, the drive of the solenoid 67 is controlled by the output pulse of the first pulse generator 71 during low engine load operation. The valve body 63 normally closes the negative pressure boat 64 and opens the atmospheric boat 65 to open the first pulse generator 71.
When a pulse is generated, the solenoid 67 is energized and the valve body 64 moves to the right, thereby causing the valve body 63 to open the negative pressure boat 64 and close the atmospheric boat 65. Therefore, negative pressure boat 64'J? and atmospheric boat 65 Lrl
The opening and closing operations are repeated at a frequency of IHz to 2Hz, and thus the negative pressure chamber 53K of the secondary air supply control valve 50
When negative pressure is applied to the negative pressure chamber 53, into which negative pressure and atmospheric pressure are alternately introduced at a frequency of I Hz to 2 Hz, the valve body 58 opens the valve boat 57, and at this time, the exhaust pulsation occurs. 9 due to the negative pressure generated in the exhaust manifold 31KJ.
Air is sucked into the exhaust manifold 3 from the secondary air supply hole 60.Therefore, as described above, the inside of the negative pressure chamber 53 changes from IHz to 2.0Hz. When atmospheric pressure and negative pressure alternate at a frequency of Hz, the valve element 58 changes the valve boat 57 from IHz to 2Hz.
Thus, secondary air is intermittently supplied into the main air manifold 3 at a frequency of IHz to 2Hz. If secondary air is intermittently supplied into the air manifold 3, the oxygen concentration in the exhaust gas in the air manifold 3 will fluctuate periodically, thus causing the air-fuel ratio to fluctuate. , the term air-fuel ratio is used here in a slightly different meaning from the usual meaning, and this air-fuel ratio includes the total nine air volumes (intake air) supplied into the working gas passage upstream of the three-way catalytic converter 4. and secondary air) and the total amount of fuel.The three-way catalyst 5 has the above-mentioned oxygen retention function against the excess oxygen present in the exhaust gas29, and this excess oxygen is is caused by intake air supplied to the intake system or by intake air supplied to the exhaust system.
Therefore, if the air-fuel ratio is periodically varied by varying the amount of secondary air supplied to the exhaust manifold 3, the average of this air-fuel ratio will be the first shift ( b) High purification efficiency can be obtained if it is maintained within the window Wo in the figure. In the second embodiment shown in FIG. 2, when the valve body 58 of the diaphragm 52 repeatedly opens and closes the valve boat 57 in the dimensions of the valve boat 572 and the secondary 9 air supply hole 600, the average value of the air-fuel ratio A/F is the fifth (
b) As shown in the figure, the air-fuel ratio is approximately at the stoichiometric air-fuel ratio, and during the fluctuation of the air-fuel ratio, it is approximately ±0.2 to ±1.
The reason why the average cylinder of 9 fuel ratio A/F can be maintained at almost the stoichiometric air-fuel ratio by repeating the simple opening and closing operation of the valve body 58 is because of the air-fuel mixture formed in the carburetor 2. This is because the fuel ratio is maintained constant. Therefore, regardless of the operating state of the engine, the air-fuel ratio vX, I
It is made to fluctuate in the range of ±0.2 to ±1.0 with respect to the stoichiometric air-fuel ratio at a frequency of H2 to 2 Hz, and moreover, the average value of this air-fuel ratio has a window Wo
Therefore, high purification efficiency can be obtained by fully utilizing the 11R accumulation retention function of the three-way monolith catalyst 5.

On the other hand, the amount of NOx generated increases during high-load operation such as during acceleration operation 2 and during high-load operation, and therefore it is important to actively purify VX and NOx during such high-load operation. It is preferred in soils that reduce harmful components in exhaust gases emitted into the atmosphere. As described above in the present invention, the duty ratio t as shown in FIG. 6(a) is
Since the solenoid 67 is driven and controlled by a small pulse of /T, the valve boat 57 of the secondary vision supply control 9P50
If the opening time of the box boat 57 is short, the closing time of the box boat 57 will be long. As a result, as shown in Figure 6(b), the time during which the air-fuel ratio becomes smaller than the stoichiometric air-fuel ratio becomes longer, and NO
The time spent on the reduction of x is long, and as a result N
Ox purification efficiency can be improved.

In this way, according to the present invention, exhaust gas can be effectively purified using an inexpensive carburetor without using an expensive oxygen concentration change detector or an expensive electronic control unit for fuel ratio control. The manufacturing cost of the gas purification device can be greatly reduced.Furthermore, since the fuel ratio of the air-fuel mixture supplied into the engine cylinder is maintained at a constant level, combustion fluctuations do not occur, thus ensuring smooth combustion. The operation of the engine can be ensured.In addition, when the engine is operated under high load, which generates a large amount of NOx, the purification efficiency of NOx is improved, so harmful components in the exhaust gas released into the atmosphere are eliminated. It can be reduced as follows.

[Brief explanation of drawings]

Figure 1 is a diagram showing exhaust gas purification efficiency, Figure 2 is a side sectional view of the engine intake and exhaust system, Figure 3 is a plan view taken along the arrow ■ in Figure 2, and Figure 4 is a diagram of the suction piston. Side cross-sectional view, Fig. 5 shows the fluctuations in the air-fuel ratio, and Fig. 6 shows the fluctuations in the air-fuel ratio. 02...carburizer;
...Suction piston, 9...Needle, 25...
- Fuel passage, 28... Nozzle, 50... Secondary air supply control valve, 51... Solenoid valve, 60... Secondary air supply hole, 77... Negative pressure switch. Patent applicant Toyota Motor Corporation Patent agent Akira Aoki Patent attorney Kazuyuki Nishidate Patent attorney Kyosuke Nakayama Patent attorney Akira Yamaguchi

Claims (1)

[Claims] In an internal combustion engine that is fully equipped with a fuel supply device to fully supply a rich mixture into the engine cylinders and a three-way catalytic converter installed in the engine exhaust passage, secondary nitrogen gas is generated in the exhaust passage upstream of the three-way catalytic converter. All the supply passages are connected, and a solenoid valve that opens and closes at a constant frequency of about I Hz to 2 Hz is arranged in the secondary nitrogen supply passage, so that when the secondary nitrogen supply passage is opened and closed, the air-fuel ratio is the average value. approximately ±0.2 to ±
1.0, and the flow path surface 8# of the secondary nitrogen supply passage is added so that the average value of the air-fuel ratio becomes approximately the stoichiometric air-fuel ratio, and the load for detecting the engine load is added. A detector is connected to the electromagnetic valve to shorten the opening time of the secondary nitrogen supply passage and the closing time of the secondary nitrogen supply passage when the engine load becomes larger than a predetermined load. The exhaust gas purification system for the ship's engine has a longer length.