JPS59101529A - Exhaust gas purging device of internal-combustion engine - Google Patents

Abstract

PURPOSE:To improve purging of a large amount of unburnt gas, exhuasted when an atmospheric pressure therearound decreases, without using an expensive device, by a method wherein the air-fuel ratio of fuel-air mixture is maintained at a specified value, and a pressure sensitive switch is provided. CONSTITUTION:When an atmospheric pressure therearound is about a standard atmospheric pressure, a solenoid 67 is actuated and controlled by means of an output signal from a pulse generator 71 with 1-2HZ frequency, and secondary air is intermittently fed in an exhaust manifold 3 by a secondary air feed control valve 50. Since the air-fuel ratio of fuel-air mixture produced in a carbretter 2 is normally maintained at a specified value, the air-fuel ratio is vaired at 1- 2HZ frequency within a range of from + or -0.2 to + or -1.0 based on an approximately theoretical air-fuel ratio. Besides, the mean value thereof is maintained within a window W0, and thereby a high purging efficiency may be obtained through utilization of the oxygen holding function of a ternary monolith catalyst 5. When an atmospheric pressure decreases, a bellows 75 is expanded, a switch 76 is turned ON, the solenoid 67 is consecutively energized, secondary air continues to be fed, and this promotes the oxidizing reaction of unburnt HC, CO.

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 known as a catalyst that can simultaneously reduce three harmful components HC, CO, and NOx in exhaust gas. The purification efficiency R of this three-way catalyst is highest when the air-fuel ratio ↑ is approximately the stoichiometric air-fuel ratio, as shown in Figure 1(a). The air-fuel ratio range that can be obtained is an air-fuel ratio of 0.06.
The width is narrow. Usually, the desired fuel-fuel ratio range 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 exhaust gas using a three-way catalyst, the air-fuel ratio must be maintained within this narrow window W. For this reason, in conventional exhaust gas purification systems, several small oxygen concentration detectors are installed in the engine exhaust passage, and the output of the oxygen concentration detectors (g The air-fuel ratio is controlled to be within the window W based on the above-mentioned No. There is a problem in that the manufacturing cost of the exhaust gas purification device increases because it requires an expensive electronic control unit.

However, recently, SAE paper A 76
As described in No. 0201 or 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 oxygen retention function. That is, 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 reduces the NOx, and at the same time retains this taken oxygen, so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio. Then, 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 above-mentioned oxygen retention function will reduce pNOx and Co, HC. The oxidation effect of the gas is promoted and high purification efficiency can be obtained. Figure 1(b) shows the air-fuel ratio at frequency IH.
The window wo from the reference air-fuel ratio is shown when z is varied by ±1.0 with respect to the reference air-fuel ratio. 1st (
It can be seen from FIG. a) and FIG. 1(b) that the window Wo becomes wider when the air-fuel ratio is varied at a constant frequency. This means that if the borrow-fuel ratio is varied at regular intervals, high purification efficiency can be obtained even if the reference air-fuel ratio deviates somewhat from the stoichiometric air-fuel ratio. On the other hand, when the air-fuel ratio fluctuation frequency is lowered, that is, when the air-fuel ratio fluctuation period is lengthened, the oxygen retention capacity of the three-way catalyst becomes saturated, and the oxidation-reduction ability based on the oxygen retention function decreases, resulting in the purification efficiency of the three-way catalyst. decreases. Figure 1(c) clearly shows this. In FIG. 1(c), 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 range of variation in the air-fuel ratio is made smaller, the air-fuel ratio cannot be varied alternately between the rich side and the rich side, so the width of the window becomes narrower. Therefore, it can be seen that there is an optimum air-fuel ratio fluctuation period and fluctuation width in order to widen the window width.

As mentioned above, if the fluctuation range and fluctuation frequency of the air-fuel ratio relative to the reference air-fuel ratio are appropriately selected, the window will become wider.
Therefore, high purification efficiency can be obtained even if the reference air-fuel ratio varies somewhat with respect to the stoichiometric air-fuel ratio. This means that if a fuel supply system with a narrow reference air-fuel ratio fluctuation range is used, high purification efficiency can be obtained without using feedback control based on the output signal of the oxygen concentration detector.

In theory, if a fuel injection valve is used as a fuel supply system, it is possible to narrow the fluctuation range of the standard air-fuel ratio, but since fuel injection devices are expensive, there is a problem that the manufacturing cost of the engine increases. Thus, even if the air-fuel ratio supplied to the engine cylinder is varied, even if the range of variation is small, combustion will fluctuate periodically, resulting in a problem that vehicle drivability will deteriorate.

An object of the present invention is to provide an exhaust gas purification device that can ensure exhaust gas purification efficiency without using an enemy rivet level detector and without changing the air-fuel ratio supplied into the engine cylinder. be.

Hereinafter, the present 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 Pentieri carburetor mounted on the intake manifold 1,
3 indicates an exhaust manifold, 4 indicates a catalytic converter,
A three-way monolith catalyst 5 is arranged inside the catalytic converter 4 . The variable pencil type carburetor 2 includes a carburetor nozzle 6, an intake passage 7 extending vertically within the nozzle 6, a suction piston 8 that moves laterally within the intake passage 7, and a tip of the suction piston 8. A needle 9 attached to the surface, a spacer 10 fixed on the inner wall surface of the intake passage 7 facing the tip i-plane of the suction piston 3, and a throttle valve provided in the intake passage 7 downstream of the suction piston 8. 11 and a float chamber 12, and a pentagonal portion 13 is formed between the distal end surface of the suction piston 8 and the spacer 10. A hollow circular casing 14 is fixed to the carburetor housing 6, and a guide sleeve 15 extending in the axial direction of the casing 14 inside the casing 14 is attached. A bearing 17 with a number of holes 16 is inserted into the guide sleeve 15, and the outer end of the guide sleeve 15 is closed by a blind cover 18. On the other hand, a guide rod 19-1) 1 is fixed to the suction piston 8, and the guide rod 19 is inserted into the bearing 17 so as to be movable in the axial direction of the guide rod 19.

Since the suction piston 8 is thus supported by the casing 14 via the bearing 17, the suction piston 8 can move smoothly in its axial direction. The interior of the casing 14 is divided into a negative pressure chamber 20 and an atmospheric pressure chamber 21 by the suction piston 8, and a compression spring 22 is inserted into the negative pressure chamber 20 to constantly press the suction piston 8 toward the venturi portion 13. be done. The negative pressure chamber 20 has a comb hole 23 formed in the suction piston 8.
The atmospheric pressure chamber 21 is connected to the intake passage 7 upstream of the succilon piston 8 through an air hole 24 formed in the carburetor housing 6 .

On the other hand, a fuel passage 25 extending in the axial direction of the needle 9 is formed in the carburetor housing 6 so that the needle 9 can enter therein, and a metering jet 26 is provided in the fuel passage 25. The fuel passage 25 upstream of the metering jet 26 is connected to the float chamber 12 via a downwardly extending fuel pipe 27, and the fuel in the float chamber 12 is transferred through this fuel pipe 27.
The fuel is sent into the fuel passage 25 through the fuel passageway 25. Furthermore, a hollow cylindrical nozzle 28 arranged coaxially with the fuel passage 25 is fixed to the spacer 10 . This nozzle 28 protrudes into the bench area 13 from the inner wall surface of the spacer 10, and the upper half of the tip of the nozzle 28 further protrudes from the lower half toward the suction piston 8. The needle 9 extends through the nozzle 28 and the metering jet 26 , and the fuel is metered into the annular gap formed between the needle 9 and the metering jet 26 from the nozzle 28 into the intake passage 7 .

As shown in FIG. 2, a raised wall 29 is formed at the upper end of the spacer 10 and projects horizontally into the intake passage 7, and the flow rate is controlled between this raised wall 29 and the tip of the suction piston 8. It is done. When engine operation is started, air flows downward in the intake passage 7. At this time, since the airflow is restricted between the suction piston 8 and the raised wall 29, negative pressure is generated in the pentagonal portion 13.
This negative pressure is guided into the negative pressure chamber 20 through the suction hole 23. The suction piston 8 moves so that the pressure difference between the negative pressure chamber 20 and the atmospheric pressure chamber 21 becomes a substantially constant pressure determined by the spring force of the compression spring 22, that is, the negative pressure inside the venturi portion 13 becomes substantially constant. do.

Referring to FIGS. 3 and 4, the entire tip surface of the suction piston located on the upstream side of the needle 9 is raised from the mounting end direction 30 of the needle 9 toward the tip of the needle 9. A groove 31 extending in the axial direction of the intake passage 7 is formed on the tip end surface of the suction piston. The upstream end 31a of this concave groove 31 has a U-shaped cross section, and the needle 9 also has a U-shaped cross section.
The concave groove part 31 of the remaining υ is located on the side near the tip of the
b is from the upstream end 31a to the needle end face 30″!,
It extends almost straight. Furthermore, the cross-sectional shape of the suction piston tip surface located on the upstream side of the needle 9 is V-shaped, expanding from the concave groove 31 toward the venturi portion 13. Therefore, the suction piston tip surface portion is A pair of inclined wall portions 32 that are inclined toward the concave groove 3
a.

32b.

As can be seen from FIG. 2, when the amount of intake air is small, the raised wall 29 and the inclined wall portions 32a and 32b.

The upstream end portion 31a of the concave groove forms an intake air control restrictor 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 made proportional to the opening area of the intake air control throttle part, so that the lift of the suction piston 8 -it h It increases smoothly as the amount of intake air increases. Furthermore, since the suction piston 8 is supported by the bearing 17, it moves with good response to the liquefaction of the intake air amount, and thus the suction piston 8 responds to the increase in the intake air amount when the intake air amount increases. Moves smoothly and smoothly. As a result, even when the amount of intake air changes rapidly, such as during acceleration, the lift of the suction piston 8 increases in proportion to the increase in the amount of intake air, so that the amount of fuel supplied from the nozzle 28 increases. Busyness is always proportional to the amount of intake air. 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 fuel supplied from the nozzle 28 immediately flows into the engine cylinder together with the intake air flow. Therefore, even when the amount of intake air is small, the fuel supplied from the nozzle 28 is immediately supplied into the engine cylinder. Therefore, even if the amount of intake air increases rapidly as during acceleration, 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 immediately increased. Since the air-fuel mixture is supplied into the engine cylinder, the desired fuel-fuel ratio of the air-fuel mixture supplied into the engine cylinder is maintained substantially constant even if the amount of intake air changes rapidly. In addition, the suction piston 8
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 moves responsively to changes in the intake air pressure regardless of the engine temperature. can do. In this way, when the variable Pencil carburetor 2 shown in FIG. 2 is used, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinders is kept at a substantially constant value, for example 14.0, regardless of the engine temperature and engine operating conditions. can be maintained to a certain extent. Therefore, a rich air-fuel mixture with a desirable fuel-fuel ratio of about 14.0 is always 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 beam air chamber 33 are formed on the inner peripheral wall surface of the metering jet 26. Ru. The annular air chamber 33 is connected into the intake passage 7 upstream of the raised wall 29 via an air bleed passage 35.36 and an air bleed jet 37, the connection of which is actuated by a wax valve 38. A valve body 39 is arranged. wax valve 38
A cooling water circulation chamber 39 is formed around the temperature sensing portion 38a, and cooling water is introduced into the cooling water circulation chamber 39 from a cooling water inlet 40, and is discharged from a cooling water outlet 41. When the engine cooling water temperature rises, the valve body 39 moves to the left, thereby increasing the flow area of the air bleed passage, thereby 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 air-fuel mixture supplied into the engine cylinder has an air-fuel ratio of 14.
The mixture will be as rich as 0.

- The engine exhaust manifold 3 is equipped with a secondary air supply control valve 50 that controls the supply of secondary air, and the intake manifold 1 is equipped with a secondary air supply control valve 50 that controls the operation of the secondary air supply control valve 50.
Several solenoid valves 51 are activated.

The secondary air supply control valve 50 has a negative pressure chamber 53 and an atmospheric pressure chamber 54 defined by a diaphragm 52.
A compression spring 55 for pressing the diaphragm is inserted inside.

A hollow tube 56 protruding toward the diaphragm 52 is fixedly disposed within the atmospheric pressure chamber 54, and a valve port 57 is provided at the tip of the hollow tube 56 and is opened and closed by a valve body 58 fixed to the diaphragm 52. is formed. This valve port 5
7 is connected to the inside of the exhaust manifold 3 via a check valve 59 and a secondary air supply hole 60, which allow flow only from the valve 7-to-57 into the exhaust manifold 3. Therefore valve port 5
7 and the secondary air supply hole 60 form a secondary air supply passage. On the other hand, the solenoid valve 51 includes a valve chamber 62, a pressure body 63 disposed in the valve chamber 62, a negative pressure boat 64 that opens in the valve chamber 62 and is connected to the intake manifold 1, and a valve chamber 62.
2, a movable grunge 166 connected to the valve body 63, and a solenoid 67 for suctioning the movable grunge 66.
The negative pressure port 64 and the atmospheric boat 65 are controlled by the valve body 63. The valve chamber 62 is connected to the negative pressure chamber 53 of the secondary air supply control valve 50 via a conduit 68, and the solenoid 67 is connected to a solenoid drive circuit 70. The solenoid drive circuit 70 has a rectangular shape with a frequency of 1Hz to 2Hz as shown in FIG. A power source connected to the output terminal of the or gate 73 includes a malus generator 71 that generates pulses, an or dirt 73 that uses the output of the pulse generator 71 as one input and the output of the pressure-sensitive switch device 72 as the other input. The output terminal of the power amplifier 74 is connected to the solenoid 67. The pressure-sensitive switch device 72 includes a bellows 75 and a switch 76 actuated by the bellows 75, and the input terminal of the ordart 73 is connected to a power source 77 via the switch 76.

When the atmospheric pressure is about the standard atmospheric pressure, the bellows 75 is in the vertical position as shown in FIG. 2, and at this time the switch 76 is off. Therefore, at this time, the output voltage of the OR gate 73 becomes a high level every time the pulse generator 71 generates a pulse, and thus the solenoid 67 is driven and controlled by the output signal of the pulse generator 71. on the other hand,
When the ambient atmospheric pressure is low, such as when the vehicle is driven at high altitude, bellows 75 expands, resulting in switch 76
turns on. Thus, at this time, the output voltage of OR gate 73 continues to be at a high level, so solenoid 67 continues to be energized.

As mentioned above, when the vehicle is driven at a low altitude and the surrounding atmospheric pressure is approximately standard atmospheric pressure, the solenoid 67 is driven and controlled by the output signal of the pulse generator 7.

The valve body 63 normally closes the negative pressure port 64 and opens the atmospheric port 65. When the pulse generator 71 generates a pulse, the solenoid 67 is energized and the valve body 64 moves to the right. Thereby, the valve body 63 opens the negative pressure port 64 and closes the atmospheric port 65. Therefore, the negative pressure port 64 and the atmosphere port 65 are repeatedly opened and closed at a frequency of IHz to 2Hz, and thus negative pressure is generated in the negative pressure chamber 53 of the secondary air supply control valve 5o at a frequency of 1Hz to 2Hz. , or atmospheric pressure is introduced alternately. When negative pressure is applied in the negative pressure chamber 53, the valve body 58 opens the valve port 57, and at this time, the negative pressure generated in the exhaust manifold 3 due to exhaust pulsation causes air to flow from the secondary air supply hole 6o to the exhaust manifold. Inhaled within 3 days. As a result, as described above, when the inside of the negative pressure chamber 53 becomes atmospheric pressure or negative pressure alternately at a frequency of 1 Hz to 2 Hz, the valve element 58 closes the valve port 57.
f, open with a frequency of I Hz to 2 Hz,
In this way, secondary air is intermittently supplied into the exhaust manifold 3 at a frequency of IHz to 2Hz. When secondary air is intermittently supplied into the exhaust manifold 3, the oxygen concentration in the exhaust gas within the exhaust manifold 3 changes periodically, and thus the air-fuel ratio changes. Note that the term air-fuel ratio is used here in a slightly different meaning from the usual meaning9, and this air-fuel ratio is defined as the total amount of air supplied into the working gas passage upstream of the three-way catalytic converter 4 ( The ratio of the sum of intake air and secondary air) to the total amount of fuel is 19°. It does not matter whether this excess oxygen is due to intake air supplied to the intake system or secondary air supplied to the exhaust system. Therefore, when the air-fuel ratio is periodically varied by varying the amount of secondary air supplied into the exhaust manifold 3, the average value of the air-fuel ratio is maintained within the window Wo in FIG. 1(b). High purification efficiency can be obtained. In the embodiment shown in FIG. 2, the dimensions of the valve boat 57 and the secondary air supply hole 6o are as follows:
8 repeatedly opens and closes the valve port 57, the average value of the air-fuel ratio ~ 5 becomes almost the stoichiometric air-fuel ratio as shown in FIG. It is determined to be approximately ±0.2 to ±1.0. The reason why the average value of the air-fuel ratio ~ 5 can be maintained at approximately the stoichiometric air-fuel ratio by repeating the simple opening and closing operations of the valve body 58 is that the air-fuel ratio of the air-fuel mixture formed in the carburetor 2 is maintained constant. It is from. Therefore, regardless of the operating state of the engine, the air-fuel ratio is made to vary within the range of approximately ±0.2 to ±1.0 with respect to the stoichiometric air-fuel ratio at a frequency of 1Hz to 2Hz, and the average value of this air-fuel ratio is The three-way monolithic catalyst 5 is maintained within the window Wo in FIG. 1(b).
High purification efficiency can be obtained by utilizing the oxygen retention function of

On the other hand, when the surrounding atmospheric pressure is low, such as when a vehicle is driven at high altitudes, the density of the intake air decreases, making the air-fuel mixture supplied to the engine cylinders even richer. A large amount of unburned HC and co is discharged into the exhaust manifold 3. However, in the present invention, when the surrounding atmospheric pressure becomes low, the solenoid 67 is continuously energized as described above, which causes the valve boat 57 of the secondary air supply judgment valve 50 to continue to open, so that the secondary air is not supplied. Continue to be supplied. As a result, even if large amounts of unburned HC and CO are emitted, unburned kIc
, can promote the oxidation reaction of CO, thus achieving high purification efficiency even when the surrounding atmospheric pressure decreases.

As described above, according to the present invention, exhaust gas can be effectively purified using an inexpensive carburetor without using an expensive oxygen concentration detector or an expensive electronic control unit for air-fuel ratio control. can significantly reduce manufacturing costs. Furthermore, since the air-fuel ratio of the air-fuel mixture supplied into the engine cylinders is maintained constant, combustion fluctuations do not occur, thus ensuring smooth engine operation. Also, when the ambient atmospheric pressure is low and the air-fuel mixture supplied into the engine cylinders is excessively incorrect, sometimes a large amount of unburned air is discharged by continuously supplying secondary air into the exhaust manifold. HC, CO'! l-Can be purified well.

[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, W, Figure 3 is a plan view taken along the arrow ■ in Figure 2, and Figure 4 is the suction piston. FIG. 5 is a diagram showing variations in air-fuel ratio. 2... Carburetor, 8... Suction piston, 9 Needle, 25... Fuel passage, 28... Nozzle, 50...
...Secondary air supply control valve, 51...Solenoid valve, 60...
- Secondary air supply hole, 72...pressure-sensitive switch device.

Claims (1)

[Claims] In an internal combustion engine equipped with a fuel supply device for supplying a rich mixture into the engine cylinders and a three-way catalytic converter installed in the engine exhaust passage, secondary air is supplied into the exhaust passage upstream of the three-way catalytic converter. A solenoid valve that opens and closes at a constant frequency of about I Hz to 2 Hz is arranged in the secondary air supply passage, and when the secondary air supply passage is opened and closed, the air-fuel ratio is equal to the average value. Approximately ±0.2 to ±
The flow area of the secondary air supply passage is determined so that the air-fuel ratio periodically fluctuates between 1.0 and the average value of the air-fuel ratio becomes approximately the stoichiometric air-fuel ratio, and the pressure-sensitive switch responds to changes in atmospheric pressure. is connected to the electromagnetic valve to keep the secondary air supply passage fully open when atmospheric pressure falls below a predetermined pressure.