JPS5912114A - Exhaust gas purifying device of internal combustion engine - Google Patents

Abstract

PURPOSE:To obtain high exhaust purifying effect without employing O2 sensor by a structure wherein a solenoid valve controlled in response of the output of a detector to detect the running state at idling is provided in the air bleed passage of a carburetor and at the same time the flow resistance in the air bleed passage is specified. CONSTITUTION:The titled device is applied to an internal combustion engine, in which a variable Venturi type carburetor 2 is installed in a suction manifold 1 and a catalytic converter 4 is installed in an exhaust manifold 3. An annular air chamber 33 formed around a metering jet 26, into and out of which a needle 9 is inserted and drawn, is communicated through a first air bleed passage 35 to a suction passage 7 and simultaneously through a second air bleed passage 36 to the solenoid valve 50, which is opened and closed by a drive circuit 60 at the fixed frequency of 1-2Hz, when non-idling running or the state, in which a throttle switch 60 is OFF, is detected. On the contrary, when idle running is detected, the solenoid valve 50 is opened and closed at a frequency higher than said frequency.

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 the 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 A/F is approximately the stoichiometric air-fuel ratio, as shown in Fig. 1(a). The air-fuel ratio range that 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·volume-cent 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 at all times. 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 within the air-fuel ratio within 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's a problem.

However, recently, SAE paper No. 7
As described in No. 60201 or Japanese Patent Publication No. 56-4741, the function of the three-way catalyst was gradually elucidated.
It was discovered that the three-way catalyst has an oxygen retention 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
At the same time, 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 NOx reduction effect and (3 ) The oxidizing effects of CO and HC are promoted and high purification efficiency can be obtained. Figure 1(b) shows the air-fuel ratio at frequency IH
The window Wo of the reference air-fuel ratio A/F is shown when the reference air-fuel ratio is varied by ±1.0 with respect to the reference air-fuel ratio in z. 1st
Window W when the air-fuel ratio is varied at a constant frequency as shown in FIG. 1(a) and FIG. 1(b). It can be seen that the area becomes wider. This means that if the air-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 shortened, 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 purification of the three-way catalyst. Efficiency 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 air-fuel ratio fluctuation range is made smaller, the air-fuel ratio cannot be varied alternately between the rich side and the lean side, so the width of the window becomes narrower. Therefore, it can be seen that there is an optimal air-fuel ratio fluctuation period and (4) 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, the fluctuation range of the reference air-fuel ratio can be narrowed, but since the fuel injection device is expensive, the manufacturing cost of the engine increases.

Therefore, in order to keep the manufacturing cost of the engine low, it is necessary to use a carburetor. However, with conventional fixed pliers type carburetors, the standard air-fuel ratio fluctuates over a wide range, and with conventional variable venturi type carburetors, the standard air-fuel ratio fluctuates greatly during acceleration or depending on engine temperature. It is difficult to obtain high purification efficiency even by using a vaporizer or a variable venturi type vaporizer.

An object of the present invention is to provide an exhaust gas purification device that can ensure high exhaust gas purification efficiency using an inexpensive carburetor without using an oxygen concentration detector.

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 venturi carburetor installed 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 venturi carburetor 2 includes a carburetor housing 6, an intake passage 7 that extends vertically within the housing 6, a suction piston 8 that moves laterally within the intake passage 7, and is attached to the distal end surface of the suction piston 8. a spacer 10 fixed on the inner wall surface of the intake passage 7 facing the tip surface of the suction piston 3, a throttle valve 11 provided in the intake passage 7 downstream of the suction piston 8, and a float chamber. 12, and a pair of pliers is provided between the tip surface of the suction piston 8 and the suction piston 10.
A curved portion 13 is formed. A hollow cylindrical casing 14 is fixed to the carburetor housing 6.
A guide sleeve 15 is mounted inside the casing 14 and extends in the axial direction of the casing 14 . A bearing 17 with a number of pawls 16 is inserted into the guide sleeve 15, and the outer end of the guide sleeve 15 is closed by a cover 18. On the other hand, a guide rod 19 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 by the suction piston 8 into a negative pressure chamber 20 and an atmospheric pressure chamber 21, 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. The negative royal chamber 20 is connected to the venturi section 13 through a suction hole 23 formed in the suction piston 8, and the atmospheric pressure chamber 21 is connected to the intake passage upstream of the suction piston 8 through an air hole 24 formed in the carburetor housing 6. 7.

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 fuel master cylinder 27 extending downward, and the fuel in the float chamber 12 is delivered into the fuel passage 25 via this fuel cylinder 27. be included. Furthermore, a hollow cylindrical nozzle 28 disposed coaxially with the fuel passage 25 is fixed to the spacer lO. This nozzle 28 protrudes into the venturi portion 13 from the inner wall surface of the spacer 10,
Moreover, the upper half of the tip of the nozzle 28 further protrudes toward the suction piston 8 from the lower half. needle 9
The nozzle 28 extends through the metering jet 26 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 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 air flow is restricted between the compression piston 8 and the raised wall 29, negative pressure is generated in the pliers part 13.
This negative pressure is guided into the negative pressure chamber 20 through the suction hole 23. The suction piston 8 is arranged so that the pressure difference between the negative pressure chamber 20 and the atmospheric pressure chamber 21 becomes an almost constant pressure determined by the spring force of the compression spring 22, that is, the negative pressure inside the pliers part 13 becomes almost constant. Move to.

Referring to FIGS. 3 and 4, the entire tip surface of the suction piston located upstream of the needle 9 is raised from the mounting end surface 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 piston. The upstream end 31a of this concave groove 31 has a U-shaped cross section and is closer to the needle 9 than the needle mounting end surface 30.
The remaining concave groove portion 31
b extends substantially straight from the upstream end 31a to the needle attachment end surface 30. 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 groove 31 toward the venturi portion 13. a pair of inclined wall portions 32 m that are inclined toward 1;
32b.

As can be seen from FIG. 3, 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 amount of the suction piston 8 becomes proportional to the opening area of the intake air control constriction part, and therefore the lift amount B of the suction piston 8 becomes proportional to the opening area of the intake air control constriction part K. It will increase smoothly as the amount increases. Furthermore, since the suction piston 8 is supported by the bearing 17, it moves with good response to changes in the amount of intake air, and thus the suction piston 8 responds to increases in the amount of intake air when the amount of intake air 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 the amount of fuel supplied from the nozzle 28 increases. 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 is immediately supplied 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 accelerated driving, 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 air-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 has a bearing 1
7, 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. . Thus,
When the variable bench type carburetor 2 shown in FIG. 2 is used, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinders can be maintained at an approximately constant value, for example, at approximately the stoichiometric air-fuel ratio, regardless of engine temperature and engine operating conditions. can be maintained.

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 inner peripheral wall surface of the metering jet 26. The annular air chamber 33 connects on the one hand to the intake channel 7 upstream of the raised wall 29 via a first air bleed channel 35.
On the other hand, the second air bleed passage 36 is connected to the solenoid valve 50 . First air bleed passage 3
A first air bleed jet 37 is inserted into the second air bleed passage 36, and a second air bleed jet 38 is inserted into the second air bleed passage 36. In addition, the first air bleed passage 35
An auxiliary air bleed passage 39 branches off from a portion of the air bleed passage common to the second air bleed passage 36 and opens into the fuel passage 25 downstream of the metering jet 26 .

The solenoid valve 50 controls the opening and closing of a valve chamber 52 that communicates with the atmosphere via an air filter 51, a valve port 53 that opens into the valve chamber 52 and is connected to the second air bleed passage 36, and controls the opening and closing of the valve port 53. The valve body 54 includes a valve body 54, a movable syringe 55 connected to the valve body 54, and a solenoid 56 for sucking the movable plunger 55. The solenoid 56 is connected to a solenoid drive circuit 60. Solenoid drive times M6
0 is a pulse generator 61 that generates a rectangular pulse with a frequency of IHz to 2Hz as shown in FIG.
A nine pulse generator 62 is provided which generates a rectangular pulse having a frequency of Hz. These Yarus generators 61°62
are connected to the power amplifier 650 input terminals via respective analog switches 63 and 64, and the output terminal of the power amplifier 65 is connected to the solenoid 56. On the other hand, a throttle switch 66 that responds to opening and closing operations of the throttle valve 11 is connected to the throttle valve 11 . This throttle switch 66 is turned on when the throttle valve 11 is in the idling position, and turned off when the throttle valve 11 is opened. The analog switch 63 is controlled by the output signal of the throttle switch 66 via an inverter 67, and the analog switch 64 is controlled by the output signal of the throttle switch 66.
directly controlled by the output signal of 6.

When the throttle switch 66 is on, that is, when the engine is idling, the analog switch 63 is in a non-conducting state and the analog switch 64 is in a conducting state, so that a rectangular pulse of 5 Hz to 10 Hz is applied to the solenoid 56.
At this time, the valve body 54 changes from 5Hz to 1Hz.
Open the valve port 53 with a frequency of 0 Hz. On the other hand, Mello 1. When the torque switch 66 is off, that is, when the idling operation is slow, the analog switch 64 is in a non-conducting state and the analog switch 63 is in a conducting state, so 1. A rectangular pulse of Hz to 2 Hz is applied to the solenoid 56, such that the valve body 54 is at this time
The valve port 53 will be opened at a frequency of Hz to 2 Hz. When the valve body 54 opens the valve port 53, air flows through the air filter 51, the valve chamber 52, the valve, and the N-to-5.
3 into the second air bleed passage 36 through the air bleed hole 33 and the auxiliary air bleed passage 3.
The amount of air supplied from the nozzle 9 into the fuel passage 25 increases, and as a result, the amount of fuel supplied from the nozzle 28 decreases, making the air-fuel mixture supplied into the engine cylinder leaner. First air bleed jet 37 and second air bleed jet 38
The dimensions are such that the average value of the air-fuel ratio A/F of the mixture supplied to the engine cylinder when the valve body 54 of the solenoid valve 50 repeatedly opens and closes the valve port 53 is as shown in FIG. 5(b). It is set so that the air-fuel ratio becomes approximately the stoichiometric air-fuel ratio, and the air-fuel ratio during fluctuation is approximately ±0.2 to ±1.0 with respect to the stoichiometric air-fuel ratio. Therefore, regardless of the engine temperature, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinders at a frequency of 5Hz to 10Hz during idling, and at a frequency of IHz to 2Hz when not idling, is approximately the same. The air-fuel ratio is varied within a range of ±0.2 to ±1.0 with respect to the stoichiometric air-fuel ratio, and the average value of this air-fuel ratio is
(b) Window W in the figure. Therefore, high purification efficiency can be obtained by utilizing the oxygen retention function of the three-way monolith catalyst 5. Additionally, if the air-fuel ratio is varied from IHz to 2Hz during idling, the combustion state will fluctuate from IHz to 2Hz because a lean mixture and a rich mixture will be supplied into the engine cylinders at a frequency from IHz to 2Hz. However, as a result, the engine speed fluctuates at a cycle of 1 Hz to 2 Hz, so there is a risk that stable idling operation may not be obtained. However, in the present invention, since the period of fluctuation in the air-fuel ratio is shortened during idling, the engine speed actually hardly fluctuates, thus ensuring stable idling.

As described above, according to the present invention, exhaust gas can be effectively purified using a low-grade carburetor without using an expensive oxygen concentration detector or an expensive electronic control unit for air-fuel ratio control. The manufacturing cost of the device can be significantly reduced. Furthermore, since only a solenoid valve is provided in the air bleed passage, the structure is extremely simple, and therefore the reliability of the exhaust gas purification device can be improved. In addition, by shortening the period of fluctuation in the air-fuel ratio during idling, fluctuations in the idling rotational speed can be suppressed, so stable idling can be ensured.

[Brief explanation of the drawing]

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. The side sectional view, FIG. 5, is a diagram showing variations in the air-fuel ratio. 2... Carburetor, 8... Suction piston, 9...
・Needle, 25...Fuel passage, 28...Nozzle,
35゜36... Air bleed passage, 50... Solenoid valve, 60... Solenoid drive circuit. Patent applicant Toda Yu Jidosha Co., Ltd. Patent application representative Patent attorney Akira Aoki Patent attorney Kazuyuki Nishidate Patent attorney Kyo Nakayama Patent attorney Akira Yamaguchi

Claims (1)

[Claims] A carburetor is installed in the engine intake passage, a three-way catalytic converter is installed in the engine exhaust passage, and an air bleed passage is connected to the fuel passage of the carburetor, so that air is supplied from the air bleed passage into the fuel passage. In internal combustion engines,
It is equipped with a detector that detects the engine idling operating state, and a drive control circuit that can generate drive signals of different frequencies in response to the output signal of the detector, and the solenoid valve driven by the drive signal is connected to the air bleed valve. The solenoid valve is provided in the air passage and is opened and closed at a constant frequency of approximately IHz to 2 Hz when not in idling operation, and the solenoid valve is opened and closed at a frequency higher than the above-mentioned constant frequency during idling operation, and the air bleed passage is When opened and closed, the air-fuel ratio is approximately ±0.2 to ±1,00 relative to the average value.
An exhaust gas purification device for an internal combustion engine, wherein the flow resistance of an air bleed passage is determined so as to vary periodically between 1 to 3, and a carburetor is set so that the average value of the air-fuel ratio is approximately the stoichiometric air-fuel ratio.