JPS5993950A - Exhaust-gas purifier for internal-combustion engine - Google Patents

Abstract

PURPOSE:To efficiently purify exhaust gas by using a low-priced carburetor by arranging a solenoid valve which is opened and closed in a constant frequency into an air bleed passage and connecting a temperature sensing switch which detects the temperature of an engine to the solenoid valve. CONSTITUTION:A carburetor 2 is installed into an engine intake passage 7, and a ternary catalysis converter 5 is installed into an exhaust passage 4, and air is supplied into a fuel passage 25 from an air bleed passage 34. In this case, the carburetor 2 is set so that the average value of air-fuel ratio becomes nearly equal to the theoretical air-fuel ratio. Further, a temperature sensor 54 for detecting the temperature of the engine is connected to a solenoid valve 40, which is closed when the engine temperature is below a predetermined value. Thus, exhaust gas can be efficiently purified by using a low-priced carburetor.

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 is approximately the stoichiometric air-fuel ratio, as shown in Figure 1(a). The air-fuel ratio range that can be obtained is narrow, with an air-fuel ratio of about 0.06.

Usually, the air-fuel ratio region in which a purification efficiency of 80/4'-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, an exhaust gas purification device using such 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.

However, recently, SAE paper A760
As described in No. 201 and Japanese Patent Publication No. 56-4741, the function of the three-way catalyst was gradually elucidated, and it was discovered that the three-way catalyst had an oxygen retention function.

In other words, when the air-fuel ratio is on the lean side compared to the stoichiometric air-fuel ratio, the three-way catalyst removes oxygen from NOx and reduces NOx, and retains this removed oxygen, causing the air-fuel ratio to become 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 oxygen retention function described above will reduce NOx and oxidize Co and HC. The action is promoted and high purification efficiency can be obtained. Figure 1) shows the air-fuel ratio at the 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. It can be seen from FIGS. 1(a) and 1(b) that the window Wo becomes wider when the air-fuel ratio is varied at a constant frequency. 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 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. Purification 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 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 can be widened.
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, in conventional fixed venturi type carburetors, the standard air-fuel ratio fluctuates over a wide range, and in conventional variable venturi type carburetors, the standard air-fuel ratio fluctuates greatly during acceleration or depending on engine temperature. Alternatively, it is difficult to obtain high purification efficiency using 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 while also 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 extending vertically within the housing 6, and a suction piston 8 that moves in the direction of the intake i-path 7M.
, a needle 9 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 distal end surface of the suction piston 3 , and a spacer 10 fixed to the inner wall surface of the intake passage 7 downstream of the suction piston 8 . A venturi portion 13 is formed between the tip end surface of the suction piston 8 and the spacer 1o. A hollow cylindrical 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 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. Ru. The negative pressure 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 air upstream of the suction piston 8 through an air hole 24 formed in the carburetor housing 6. It is connected within the passage 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/main tube 27 extending downward, and the fuel in the float chamber 12 is passed through this fuel pipe 2.
7 into the fuel passage 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 venturi portion 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. Needle 9 extends through nozzle 28 and metering jet 26;
After being metered by the annular gap formed between the needle 9 and the metering jet 26, the fuel flows from the nozzle 28 to the intake passage 7.
supplied within.

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 venturi section 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 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 upstream of the needle 9 is V-shaped, expanding from the groove 31 toward the venturi portion 13. A pair of inclined wall surface parts 32a which are inclined toward 31.

32b.

As can be seen from FIG. 3, when the amount of intake air is small, the raised wall 29 and the inclined wall portion 32ap32b.

The upstream end portion 31m of the concave groove forms 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 amount of the suction piston 8 becomes proportional to the opening area of the intake air control throttle part, and therefore the amount of suction piston 8 is equal to the intake air amount. It increases smoothly as the value 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, 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, suction piston 8 bearings 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 venturi 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 a substantially constant value, for example, at approximately the stoichiometric air-fuel ratio, regardless of engine temperature and engine operating conditions. be able to.

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 is connected to the raised wall 2 via an air bleed passage 34 and an air bleed jet 35.
A valve port 36 is connected to the intake passage 7 upstream of the air bleed passage 34 and has an opening area controlled by a solenoid valve 40 formed within the air bleed passage 34 .

The linear solenoid valve 40 includes a valve body 41 that controls the opening area of the valve port 36, a movable plunger 42 connected to the valve body 41, and a solenoid 43 that sucks the movable plunger 42. It is connected to the drive circuit 5o. In this linear slide/id valve 40, the movable plunger 42 moves by a distance proportional to the current flowing through the solenoid 43, and as the current flowing through the solenoid 43 increases, the valve body 41 moves to the right.

Therefore, the opening area of the valve port 36 changes in proportion to the current flowing through the solenoid 43.

The solenoid drive circuit 50 has an I as shown in FIG.
It consists of a sawtooth generator 51 that generates a sawtooth voltage with a frequency of Hz to 2 Hz, and a voltage-current converter 53 connected to the output terminal of the sawtooth generator 51 via a switch 52.
An output terminal of the voltage-current converter 53 is connected to the solenoid 43. The switch 52 is a switch that responds to a temperature sensor 54 that detects the engine cooling water temperature.
2 is turned off when the engine cooling water temperature is below a predetermined temperature. Therefore, when the engine cooling water temperature is above a predetermined temperature, the switch 52 is turned on, and at this time, the output voltage of the sawtooth wave generator 51 is converted into a corresponding current in the voltage-current converter 53, and this current is It is supplied to the solenoid 43. As mentioned above, the opening area of the valve port 36 changes in proportion to the current flowing through the solenoid 43, and since the current is supplied to the solenoid 43 as shown in FIG. 5(a), the opening area of the valve port 36 is It can be seen that it changes in a sawtooth pattern. When the opening area of the valve port 36 changes in a sawtooth pattern as described above, the amount of air supplied from the air bleed hole 33 into the fuel passage 25 also changes in a sawtooth pattern, so that the air-fuel ratio A of the air-fuel mixture supplied into the engine cylinder. /F is the fifth
佽) As shown in the figure, it changes smoothly in a wave-like manner. The dimensions of the air bleed jet 35 and the valve port 36 are such that the valve body 41 of the near solenoid valve 40 is
When the flow area of 6 is repeatedly increased and decreased, the average value of the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes almost the stoichiometric air-fuel ratio as shown in Fig. It is determined to be approximately ±0.2 to ±1.0 with respect to the air-fuel ratio. Therefore, regardless of engine temperature and engine operating conditions, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinders is approximately within the range of ±0.2 to ±1.0 with respect to the stoichiometric air-fuel ratio at frequencies from IHz to 2H2. Moreover, since the average value of this air-fuel ratio is maintained within the Winbow Wo range shown in FIG. 1(b), high purification efficiency can be obtained by utilizing the oxygen retention function of the three-way monolith catalyst 5. Furthermore, as shown in FIG. 5(b), since the air-fuel ratio fluctuates smoothly, the combustion state does not change suddenly.
In this way, stable combustion can be ensured at all times regardless of the operating state of the engine.

On the other hand, when the engine cooling water temperature is lower than a predetermined temperature, the switch 52 is turned off as described above, and as a result, the solenoid 43 is deenergized, so that the valve body 41 closes the valve port 36. In this way, since a rich mixture is supplied into the engine cylinder at this time, stable combustion can be achieved even if the engine temperature is low.

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. The manufacturing cost can be reduced significantly. 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. Further, since the air-fuel ratio of the air-fuel mixture supplied into the engine cylinders is smoothly varied, stable combustion can be ensured. Further, when the engine temperature is low, a rich air-fuel mixture is supplied into the engine cylinders, so that stable combustion can be obtained even when the engine temperature is low.

[Brief explanation of drawings]

Figure 1 is a diagram showing exhaust gas purification efficiency, Figure 2 is a side cross-sectional view of the engine intake and exhaust system, Figure 3 is a plan view overflowing the arrow ■ in Figure 2, and Figure 4 is the suction piston. The side sectional view of FIG. 5 is a microcosm showing the fluctuation of the air-fuel ratio. 2... Carburetor, 8... Suction piston, 9...
・21'le, 25...Fuel passage, 28...Nozzle,
34... Air bleed passage, 40... Linear solenoid valve, 54... Temperature sensor. Patent applicant Toyota Motor Corporation Patent application agent Akira Aoki Patent attorney Kazuyuki Nishidate Patent attorney Kyosuke Tsuchinakayama 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 an internal combustion engine, the air bleed passage is located within the air bleed passage above the bar.
A solenoid valve that opens and closes at a constant frequency of Hz to 2-Hz is arranged, and when the air bleed passage is opened and closed, the air-fuel ratio periodically changes between approximately ±0.2 and ±1.0 with respect to the average value. The flow resistance of the air bleed passage is determined so as to fluctuate, and the carburetor is set so that the average value of the air-fuel ratio is approximately the stoichiometric air-fuel ratio, and a temperature sensor for detecting the engine temperature is connected to the solenoid valve. An exhaust gas purification device for an internal combustion engine, which closes the solenoid valve when the engine temperature is below a predetermined temperature.