JPS5934463A - Exhaust gas purifier for internal combustion engine - Google Patents

Abstract

PURPOSE:To secure a high purification efficiency in the transient operation of an engine, by changing to a larger second value the amplitude of a drive signal for a solenoid valve for opening and closing an air bleed passage, in the transient operation. CONSTITUTION:When the negative pressure in an intake manifold 1 has sharply changed, namely, transient operation is performed, the movable contact 68 of a transient operation detector 60 comes into touch with one of fixed contacts 69, 70 to apply a voltage to turn off a first analogue switch 53 and turn on a second analogue switch 54. As a result, a saw-toothed voltage of larger amplitude is applied to a voltage-current converter 55 to increase the change width of the cross-sectional area of the opening of a valve port 37 to enlarge the fluctuation width of the air-fuel ratio of a mixture. Although the reference air fuel ratio of the mixture slightly differs from a theoretical air-fuel ratio due to the instantaneous evaporation of fuel clinging to the inside surface of the intake manifold 1 or due to the like in the transient operation, a high purification efficiency is attained by the enlargement of the fluctuation width of the air- fuel ratio.

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. The air-fuel ratio range in which this can be done is narrow, with an air-fuel ratio of about 0.06. 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 exhaust gas using a three-way catalyst, the air-fuel ratio must be maintained within this narrow window W at all times (2). 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 with rising prices.

However, recently, S A F paper Nn
As described in No. 760201 or 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 with respect to the stoichiometric air-fuel ratio, the three-way catalyst takes oxygen from NOx and
While reducing Ox, it retains this stolen oxygen,
When the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, the retained oxygen is released to oxygenate Co and HC. Therefore, if the air-fuel ratio is alternately varied between the lean side and the rich side (3), even if the standard air-fuel ratio deviates from the stoichiometric air-fuel ratio, the above-mentioned oxygen retention function will reduce NOx and Co, The oxidation effect of He is promoted and high purification efficiency can be obtained. Figure 1 (b) shows the standard air-fuel ratio A/F when the air-fuel ratio is varied by ±1.0 with respect to the standard air-fuel ratio at a frequency of IHz.
Window W. It shows. From FIG. 1(a) and FIG. 1(b), window W when the air-fuel ratio is varied at a constant frequency. 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 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. 1st (
c) In the figure, 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 is made smaller, the air-fuel ratio (4) 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 are optimal air-fuel ratio fluctuation periods and fluctuation periods in order to widen the window width.

- As mentioned in F, the air-fuel ratio changes and fluctuates appropriately with respect to the standard air-fuel ratio (if you select C, the window becomes wider, so the standard air-fuel ratio power; high purification efficiency even if there is some fluctuation from the stoichiometric air-fuel ratio) This means that
This means that by using a narrow fuel supply system during fluctuations in the reference air-fuel ratio, 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 range of fluctuations in the standard air-fuel ratio, but since fuel injection devices are 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 reference air-fuel ratio fluctuates widely, and in conventional variable bench carburetors, the reference air-fuel ratio varies greatly during acceleration or depending on engine temperature. It is difficult to obtain high purification efficiency even by using a vaporizer or a variable venteri 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 all the accompanying drawings. Referring to FIG. 2, 1 is an intake manifold, 2 is a variable venturi carburetor mounted on the intake manifold l,
3 indicates an exhaust manifold, 4 indicates a catalytic converter,
A ternary seven-gas catalyst 5 is arranged inside the catalytic converter 4 . The variable venturi carburetor 2 includes a carburetor housing 6, an intake passage 7 extending perpendicularly to the inside of the housing 6, a suction piston 8 that moves laterally within the intake passage 7, and a suction piston 8 that 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 front end surface of the suction piston 3; and a melotor valve 11 provided in the intake passage 7 downstream of the suction piston 8. , and a float chamber 12, and a venturi portion 13 is formed between the distal end surface of the suction piston 8 and the spacer 10. 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 balls 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 belt 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 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 (7) 21, and within the negative pressure chamber 20 is a compression spring 22 that constantly presses the suction piston 8 toward the venturi section 13. inserted. The negative pressure chamber 2o has a suction piston 8
The atmospheric pressure chamber 21 is connected to the bench portion 13 through a suction hole 23' formed in the carburetor housing 6.
The Zakujo piston 8 is inserted through the air hole 24 formed in the
It is connected to the upstream intake 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 pipe 27 extending downward, 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 venturi portion 13 from the inner wall surface of the spacer 10, and the upper (8) 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 by 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 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 pressure difference between the negative pressure chamber 20 and the atmospheric pressure chamber 21 is determined by the spring force of the compression spring 22, and the pressure is approximately constant. In other words, the negative pressure inside the bench area 13 is moved to be approximately constant.

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 concave 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 almost straight from the upstream end 31m 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 combined.

As shown in Fig. 3, when the amount of intake air is small, the raised wall 29. The inclined wall portions 32a*32b- and the groove upstream end portion 31a 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 amount of the suction piston 8 becomes proportional to the opening area of the intake air control throttle part, and therefore the lift amount of the suction piston 8 is proportional to the intake air amount. It will increase smoothly as it 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, when the amount of intake air increases, the suction piston lt moves with good response to the increase in the amount of intake air. Move well and smoothly. As a result, even when the amount of intake air changes rapidly, such as during acceleration, the lift of the 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. 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 fuel supplied from the nozzle 28 is immediately supplied into the engine cylinder together with the intake air flow. Even when the amount of 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 ratio of the air-fuel mixture supplied to the engine cylinder is maintained almost constant even if the amount of intake air changes rapidly, the piston 8 has a bearing 17t/C. Since the suction piston 8 is supported, 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. In this way, when the variable venturi type 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, approximately stoichiometric, regardless of the engine temperature and engine operating state. Referring to FIG. 2, the area around the metering jet 26 (12
) is formed with an annular air chamber 33, and a plurality of air bleed holes 34 communicating with the annular air chamber 33 are connected to the metering jet 26.
is formed on the inner peripheral wall surface of the The annular air chamber 33 is connected to the intake passage 7 upstream of the raised wall 29 via an air bleed passage 35 and an air bleed jet 36, and the opening area of the air bleed passage 35 is controlled by a solenoid valve 40. A valve boat 37 is formed.

The linear solenoid valve 40 includes a valve body 41 that controls the opening area of the valve boat 37, 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 50. In this linear solenoid 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 boat 37 changes in proportion to the current flowing through the solenoid 43.1 The solenoid drive circuit 50 is configured to operate as shown in FIG. The first sawtooth generator 51 that generates a full I Hz signal as shown in FIG. 5(a)
a second sawtooth generator 52 that generates a sawtooth voltage with a frequency of 2Hz to 2Hz; a first analog switch 53 connected to the output terminal of the first sawtooth generator 51;
A second analog switch 54 connected to the output terminal of
and a voltage-current converter 55 connected to the output terminals of the first analog switch 53 and the second analog switch 54, and the output leakage of the current-voltage converter 55 is connected to the solenoid 43. As mentioned above, the first sawtooth generator 51
The sawtooth generator 52 and the second sawtooth generator 52 generate a sawtooth voltage of approximately the same frequency IHz to 2Hz, but as can be seen from FIGS. 5(a) and 6(a), the sawtooth generator 51 The amplitude of the wave is smaller than the amplitude of the sawtooth of the second sawtooth generator 52. As mentioned above, the opening area of the valve boat 37 is proportional to the current flowing through the solenoid 43, and the current supplied to the solenoid 43 is proportional to the output voltage of the sawtooth generator 51, 52, so that the opening area of the valve boat 37 is increased or decreased. It can be seen that is proportional to the amplitude of the sawtooth generated by the sawtooth generator 51,52.

On the other hand, as shown in FIG. 2, a transient operation detector 60 is attached to the intake manifold 1.
0 is composed of a diaphragm device 61 and a switch 62. The dianram device 60 has a working pressure chamber 64 and a pressure accumulating chamber 65 separated by a diaphragm 63 , and the working pressure chamber 64 is connected within the intake manifold 2 . In addition, a compression spring 6 for pressing the diaphragm is provided in the operating pressure chamber 64.
6 is inserted, and a diaphragm 67 is further formed in the diaphragm 63. On the other hand, the switch 62 includes a movable switching point 68 actuated by a diaphragm 63 and a pair of fixed contacts 69 and 70 disposed on both sides of the movable contact 68. The movable contact 68 is connected to the power supply 71, and the fixed contact 69.70
is connected to the input terminal of the solenoid drive circuit 50. The first analog switch 53 is controlled via the inverter 72 by the voltage applied to the fixed contacts 69 and 70, and the second
Analog switch 54 is directly controlled by a voltage applied to fixed contacts 69° (15) 70. When the negative pressure in the working pressure chamber 64 of the diaphragm device 61 increases, the diaphragm 63 moves to the left, so that the movable contact 68 comes into contact with the fixed contact 69. Then, after a while, the pressure accumulation chamber 6
Since the negative pressure inside 5 also increases, the diaphragm 63
moves to the right, thus moving the movable contact 68 to the fixed contact 69.
move away from

On the other hand, when the negative pressure in the working pressure chamber 64 of the diaphragm device 61 becomes smaller, the diaphragm 63 moves to the right for a while, so that the movable contact 68 comes into contact with the fixed contact 70 for a while. Therefore, when the negative pressure inside the intake manifold 1 suddenly changes, that is, during transient operation, the movable contact 68 contacts one of the fixed contacts 69 and 70, and when not during transient operation, that is, during steady running, VC contacts the movable contact 68. is the fixed contact 69.
Far from 70. Therefore, during steady operation, the fixed contact 6
Since no voltage is applied to 9.70, the first analog switch 53 becomes conductive, and the second analog switch 5
4 becomes non-conductive, a sawtooth voltage with a small amplitude as shown in FIG. 6(a) is applied to the voltage/current converter 55. On the other hand, during transient operation, voltage is applied to the fixed contacts 69 and 70, so the first analog switch 53 becomes non-conductive, and the second analog switch 5
4 becomes conductive. Therefore, at this time, a sawtooth voltage with a large amplitude as shown in FIG.
5.

As described above, during steady running, a small-amplitude ripple-like voltage as shown in FIG. urge When the valve boat opening area changes in a sawtooth pattern in this way, the air bleed hole 34 is connected to the fuel passage 25.
Since the amount of air supplied into the engine cylinder also changes in a sawtooth pattern, the air-fuel ratio A/F of the mixture supplied into the engine cylinder is 6(b).
As shown in the figure, it changes smoothly in a wave-like manner.

Dimensions of air bleed jet 36 and valve boat 37 When the valve element 41 of the near solenoid valve 4o repeatedly increases and decreases the flow area of the valve boat 37, the average value of the air-fuel ratio of the mixture supplied into the engine cylinder is As shown in FIG. 6(b), the air-fuel ratio is approximately the stoichiometric air-fuel ratio, and the fluctuation range of the air-fuel ratio is determined to be approximately ±0.2 to ±1.0 with respect to the stoichiometric 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 varies within a range of approximately 10.2 to ±1.0 with respect to the stoichiometric air-fuel ratio at a frequency of 2Hz from FiIHz. Moreover, the average value of this air-fuel ratio is window W in FIG. 1(b). Therefore, the oxygen retention function of the three-way monolithic catalyst 5 can be utilized to obtain high purification efficiency. Furthermore, as shown in Figure 6(b), since the air-fuel ratio fluctuates smoothly, the combustion state does not change suddenly, thus ensuring stable combustion at all times regardless of the operating state of the engine. be able to.

On the other hand, during transient operation, as described above, the sawtooth electric wire with a large amplitude as shown in FIG.
is applied to Therefore, at this time, since the opening area of the valve boat 37 increases and decreases, the fluctuation range of the air-fuel ratio A/F' increases as shown in FIG. 5(I). That is, during transient operations such as acceleration and deceleration, the reference fuel ratio of the air-fuel mixture supplied into the engine cylinders may deviate slightly from the stoichiometric air-fuel ratio due to instantaneous evaporation of fuel adhering to the inner wall surface of the intake manifold 1. In such a case, by increasing the fluctuation period of the air-fuel ratio, the air-fuel ratio can be made to swing back and forth between the lean side and the rich side, thereby achieving high purification by utilizing the oxygen retention function of the three-way monolith catalyst 5. You can gain efficiency. Furthermore, during steady running, the fluctuations in the air-fuel ratio are made as small as possible within the range in which high purification efficiency can be obtained, thereby suppressing fluctuations in the engine output torque to obtain stable steady running.

As described above, according to the present invention, exhaust gas can be purified well using an inexpensive carburetor without the need for an expensive acid-based concentration detector or an expensive electronic control unit for fuel ratio control. The manufacturing cost of the device can be reduced by a large amount. 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. Furthermore, the air-fuel ratio is changed depending on the engine operating state (19
) By doing so, it is possible to ensure stable steady operation without torque fluctuation while ensuring high purification efficiency during transient operation.

[Brief explanation of the 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 1 in Figure 2, FIG. 4 is a side sectional view of the Zakujo piston, FIG. 5 is a diagram showing fluctuations in the air-fuel ratio, and FIG. 6 is a diagram showing fluctuations in the air-fuel ratio. 2... Carburetor, 8... Zakujo piston, 9-... Needle, 25... Fuel passage, 28... Nozzle, 35 ...Air bleed passage, 40...Linear solenoid square, 6
0...Transient operation detector. Special Pestle Applicant Toyota Motor Corporation Patent Attorney Akira Aoki Patent Attorney Kazuyuki Nishidate Patent Attorney Takashi Nakayama Patent Attorney Akira Yamaguchi (20)

Claims (1)

[Claims] A carburetor is attached to the engine intake passage, a three-way catalytic converter 1 is attached to 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 includes a drive signal generating circuit capable of generating a drive signal that varies at a constant frequency of 1 Hz to 2 Hz and has at least two mutually different amplitudes; A solenoid valve is provided that increases or decreases the opening area of the air bleed passage at a constant frequency from I Hz to 2 Hz, and is proportional to the amplitude while the opening area is increasing or decreasing, and when the drive signal has a first amplitude, the air bleed passage increases or decreases. The flow area of the air bleed passage is determined so that the fuel ratio periodically varies between approximately ±0.2 and ±1.0 with respect to the average value, and the average value of the air-fuel ratio is approximately the stoichiometric air-fuel ratio, Emergency engine transient operating condition (1)
□ Connect a detectable transient operation detector to the drive signal generation circuit to switch the amplitude of the drive signal from the first amplitude to a second amplitude larger than the first amplitude during engine transient operation. An exhaust gas purification device for an internal combustion engine, wherein the drive vJ signal having the first amplitude is generated when the engine is not in transient operation.