JPS5934465A - Exhaust gas purifier for internal combustion engine - Google Patents

Abstract

PURPOSE:To secure smooth stationary operation, by connecting a stationary operation detector to a drive signal generation circuit for a solenoid valve for opening and closing an air bleed passage, to cause the circuit to produce a drive signal of second constant frequency in stationary operation to suppress torque fluctuation. CONSTITUTION:When a throttle valve 11 is opened for acceleration, a negative pressure port 60 is opened into an intake passage 7 downstream to the throttle valve to apply negative pressure to the port to intensify the negative pressure in the first chamber 65 of a delay valve 62. However, a check valve 67 is closed so that the negative pressure in a negative pressure chamber 70 remains weak and a movable contact 73 is kept off a fixed contact 74 for a period of time. For the period of the low opening degree of the throttle valve 11 and for the period of time after its opening, a saw-tooth voltage of 1Hz to 2Hz in frequency is applied to a voltage-current converter 55 so that the cross-sectional area of the opening of a valve port 37 changes in a saw-toothed manner in proportion to the electrical current of a solenoid 43. For that reason, the air fuel ratio of a mixture fluctuates smoothly so that the state of combustion does not sharply change. Stable combustion is thus always secured regardless of the operating condition of an engine.

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 N is almost the stoichiometric air-fuel ratio, as shown in FIG. 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 range in which a purification efficiency of 80 percent or more can be obtained is referred to as win P and 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.For this reason, in conventional exhaust gas purification devices, An oxygen concentration detector capable of determining whether the air-fuel ratio is larger or smaller than the stoichiometric air-fuel ratio is installed in the engine exhaust passage, and the air-fuel ratio is adjusted to be within the window W based on the output signal of this oxygen concentration detector. is controlled. 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 No.
As described in Japanese Patent Publication No. 760201 and Japanese Patent Publication No. 56-4741, the function of the three-way catalyst was gradually elucidated and it was found that the three-way catalyst 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 above-mentioned oxygen retention function will reduce NOx and oxidize CO and HC. The action is promoted and high purification efficiency can be obtained. FIG. 1(b) shows a window Wo of the standard air-fuel ratio when the air-fuel ratio is varied by ±1.0 with respect to the standard air-fuel ratio at a frequency of I Hz.

It can be seen from FIGS. 1(&) 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 capacity 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 air-fuel ratio is changed during a small period, the air-fuel ratio cannot be varied alternately between rich and lean sides, 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 above, if the air-fuel ratio is fluctuating relative to the standard air-fuel ratio and the fluctuation frequency is 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 by using a narrow fuel supply system during fluctuations in the reference air-fuel ratio, high purification efficiency can be obtained without using feed control based on the output signal of the oxygen concentration detector.

Theoretically, if a fuel injection valve is used as a fuel supply system, it is possible to narrow the fluctuation period of the reference air-fuel ratio, but since the fuel injection device is expensive, 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 venturi type carburetors, the reference air-fuel ratio varies greatly during acceleration or depending on engine temperature. Alternatively, even if a variable Pentieri type vaporizer is used, it is difficult to obtain high purification efficiency.

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 bench s-') type carburetor mounted on the intake manifold 1, 3 is an exhaust manifold, and 4 is a catalytic converter. A ternary monolithic catalyst 5 is disposed at. The variable venturi type carburetor 2 includes a carburetor housing 6, an intake passage 7 extending vertically within 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 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. 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, and a guide sleeve 15 extending in the axial direction of the casing 14 inside the casing 14 is attached thereto. 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 this guide rod 19 is attached to the bearing 1.
7 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 2o and an atmospheric pressure chamber 21 by the suction piston 8, and a compression spring 22 that constantly presses the suction piston 8 toward the venturi portion 13 is inserted into the negative pressure chamber 2o. . 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 upstream side of the suction piston 8 through an air hole 24'e formed in the carburetor housing 6. It is connected to the 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 f27f extending downward, and the fuel in the float chamber 12 is supplied with this fuel.
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 from the inner wall surface of the spacer 10 into the pliers 13, 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 calculation 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 is designed so that #I, where 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, is a constant pressure, that is, the negative pressure inside the venturi part 13 is almost constant. move so that

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 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.
If the side pressure is located near the tip of the lever, the concave groove portion 31 of the remaining
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 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 surface portions 32a that are inclined toward the groove 31.

32b.

As can be seen from FIG. 3, when the amount of intake air is small, the raised wall 29, the inclined wall portions 32a and 32b, and the upstream end portion 31m of the groove form an intake air control restrictor K having a substantially isosceles triangular shape. Ru.

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 1 of the suction piston 8 increases the amount of intake air. It will increase smoothly according to the 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. Move gracefully and cleanly. 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 Penchili 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 a substantially constant value, for example, at approximately the stoichiometric air-fuel ratio, regardless of the engine temperature and engine operating state. 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 volumetric jet 26. . The annular air chamber 33 is connected to the raised wall 2 via an air bleed passage 35 and an air bleed jet 36.
A valve port 37 is connected to the intake passage 7 upstream of the air bleed passage 35 and has an opening area controlled by a solenoid valve 40 formed within the air bleed passage 35 .

The linear solenoid valve 40 is a valve! -) comprises a valve body 41 for controlling the opening area of the 37, a movable sylanger 42 connected to the valve body 41, and a solenoid 43 for completely suctioning the movable granger 42, and the solenoid 43 is connected to a solenoid drive circuit 50. be done. In this linear solenoid valve 40, the movable no-lunger 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 37 changes in proportion to the current flowing through the solenoid 43.

The solenoid drive circuit 50 includes, for example, a first sawtooth generator 51 that generates a sawtooth voltage with a frequency of 11z to 10Hz as shown in FIG. 6(-), and an IHz voltage generator as shown in FIG. a first analog switch 53 connected to the output terminal of the first sawtooth generator 51 and an output of the second sawtooth generator 52; A second analog switch 54 is connected to the terminal, and a voltage-current converter 55 is connected to the output terminals of the first analog switch 53 and the second analog switch 54. The output terminal is connected to the solenoid 43.

On the other hand, a negative pressure port 60 is formed on the inner wall surface of the intake passage 7 near the throttle valve 11. When the opening degree of the throttle valve 11 is below a predetermined opening degree, this negative pressure port 60 opens into the intake passage 7 upstream of the throttle valve 11 as shown in FIG. When the temperature exceeds 50°C, it opens into the intake passage 7 downstream of the throttle valve 11.

This vacuum port 60 is connected to a vacuum diaphragm device 63 via a vacuum conduit 61 and a delay valve 62 . The delay valve 62 has a first chamber 65 and a second chamber 6 separated by a partition wall 64.
6, and the first chamber 65 is connected to the negative pressure port 60. Further, on the partition wall 64, a check valve 67 that allows flow only from the first chamber 65 into the second chamber 66, and a restrictor 8 are provided.

On the other hand, the negative pressure diaphragm device 63 includes a negative pressure chamber 70 and an atmospheric pressure chamber 71 separated by a diaphragm 69. A compression spring 72 for pressing the diaphragm is provided in the negative pressure chamber 70.
is inserted, and this negative pressure chamber 70 is connected to the second chamber 66 of the delay valve 62.
connected to. On the other hand, a movable contact 73 fixed to the diaphragm 69 and a fixed contact 74 arranged opposite to the movable contact 73 are provided in the atmospheric pressure chamber 7. Fixed contact 7
◆4 is connected to the power source 75, and the movable contact 73 is connected to the 500 Å power terminal of the solenoid drive circuit. The second analog switch 52 is controlled via the inverter 57 by the voltage applied to the movable contact 73, and the first analog switch 53
is directly controlled by the voltage applied to the movable contact 73.

As shown in FIG. 2, when the opening degree of the throttle valve 11 is small, the negative pressure applied to the negative pressure port 60 is small, so the diaphragm 69 is moved to the right by the spring force of the compression spring 72. Therefore, at this time, the movable contact 73 is separated from the fixed contact 74 as shown in FIG. Thus the first
Since the analog switch 53 is in a non-conducting state and the second analog switch 54 is in a conducting state, FIG.
) is applied to the voltage-current converter 55 with a frequency from I Hz to 211 z. Next, when the throttle valve 11 is opened to accelerate and the negative pressure port 60 opens into the intake passage 7 downstream of the throttle valve 11, a large negative pressure is applied to the negative pressure port 60, so that the first The negative pressure inside the chamber 65 also increases significantly. However, since the check valve 67 is closed at this time, the negative pressure in the negative pressure chamber 70 is still small, and thus the movable contact 73 is maintained apart from the fixed contact 74. Then, after a while, the air in the negative pressure chamber 70 flows through the restrictor 8 into the first chamber 65.
As the negative pressure in the negative pressure chamber 70 increases, the diaphragm 69 moves to the left and the movable contact 73 contacts the fixed contact 74. As a result, the first analog switch 5
3 becomes conductive, and the second analog switch 54 becomes non-conductive, so that a sawtooth voltage with a high frequency as shown in FIG.

As mentioned above, when the opening degree of the throttle valve 11 is small,
After the throttle valve 11 is opened, a sawtooth voltage with a frequency of IHz to 2Hz is applied to the voltage-current converter 55, and then converted into a corresponding current in the voltage-current converter 55. It is supplied to the solenoid 43. As mentioned above, the opening area of the valve port 37 changes in proportion to the current flowing through the solenoid 43.
3 is supplied with a surface current as shown in FIG. 5(a), it can be seen that the opening area of the valve port 37 changes in a sawtooth shape. When the opening area of the valve port 37 changes in a sawtooth pattern as described above, the amount of air supplied from the air bleed hole 34 into the fuel passage 25 also changes in a sawtooth pattern, so that the air-fuel ratio AIF of the air-fuel mixture supplied into the engine cylinder changes smoothly in a wave-like manner as shown in FIG. 5(b). Dimensions of air bleed jet 36 and valve port 37 When the valve body 41 of the near solenoid valve 40 repeatedly increases and decreases the flow area of the valve port 37, the average value of the air-fuel ratio of the mixture supplied into the engine cylinder is As shown in FIG. 5(b), the air-fuel ratio is set so that it is approximately at the stoichiometric air-fuel ratio, and the fluctuation of the air-fuel ratio is approximately from ±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 mixture supplied into the engine cylinders is IH
With the frequency from z to 2H2, the stoichiometric air-fuel ratio is varied within the range of ±0.2 to ±1.0, and the average value of the original air-fuel ratio is within the window Wo in Figure 1(b). Therefore, high purification efficiency can be obtained by utilizing the oxygen retention function of the three-way monolith catalyst 5. Furthermore, the fifth
(b) As shown in the figure, since the air-fuel ratio fluctuates smoothly, the combustion state does not change suddenly, and thus stable combustion can be ensured at all times regardless of the operating state of the engine.

On the other hand, when the throttle valve 11 is closed for a while, that is, after the acceleration operation is completed, and the steady running state is reached, a high frequency sawtooth pattern as shown in FIG. A voltage is applied to the voltage-current converter 55, and thus the air-fuel ratio A/F changes in short cycles as shown in FIG. 6(b). When the air-fuel ratio fluctuation period is shortened in this way, even if combustion fluctuations occur due to air-fuel ratio fluctuations, fluctuations in the output torque are small, thus ensuring smooth steady operation.

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 one air pull passage, the structure is extremely simple, and therefore the reliability of the exhaust gas purification device can be improved. Furthermore, since torque fluctuations during steady running can be suppressed, smooth steady running can be ensured.

[Brief explanation of drawings]

Figure 1 is a diagram showing exhaust gas purification efficiency, Figure 2 is a side sectional view of the engine intake and exhaust system, Figure 3 is a plan view taken along the arrow ■ in Figure 2, and Figure 4 is a diagram of the suction piston. A side cross-sectional view, 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... Suction piston, 9...
・Needle, 25...Fuel passage, 28...Nozzle,
35...-r--rrv-do passage, 40... Linear solenoid valve. Patent applicant Toyota Motor Corporation Patent application agent - Patent attorney Ao
Akira Ki, Patent Attorney, Kazuyuki Nishitate, 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 internal combustion engines,
The air bleed passage includes a drive signal generation circuit capable of generating a drive signal of a first constant frequency from 1llz to 211z and a drive signal of a second frequency higher in frequency than the first constant frequency. A solenoid valve that opens and closes the air bleed passage at the above-mentioned constant frequency in response to the above-mentioned drive signal is disposed within the air-bleed passage, and when the air-bleed passage is opened and closed, the air-fuel ratio is approximately ±0.2 to ±1 relative to the average value. The flow area of the air bleed passage is determined so that the air-fuel ratio periodically fluctuates between . A capable steady-state operation detector is connected to the drive signal generation circuit to generate the second constant-frequency drive signal during the steady-state operation, and to generate the first constant-frequency drive signal when the steady-state operation is not in progress. An exhaust gas purification device for an internal combustion engine.