JPS5996418A - Exhaust gas purifying device of internal-combustion engine - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a ternary catalyst by closing and opening a solenoid valve for supplying secondary air to the upper stream of the ternary catalyst at the frequency of 1-2Hz, periodically varying an air-fuel ratio within the range of + or -0.2-+ or -1.0, and closing the solenoid valve when an engine load exceeds a prescribed value over a prescribed period of time. CONSTITUTION:A secondary air supplying hole 60 is provided on an exhaust manifold 3, and secondary air is supplied to the upper stream of a ternary catalyst 5 via a control valve 50 and a check valve 59. Negative pressure is introduced into the negative pressure chamber 53 of the control valve 50 via a solenoid valve 51, and this solenoid valve 51 is closed and opened by means of a solenoid driving circuit 70 at the frequency of 1-2Hz, allowing an air-fuel ratio to be periodically varied via the control valve 50 taking a theoretical air-fuel ratio as a center. A negative pressure switch 72 for introducing the negative pressure via a negative pressure delay valve 80 is connected to the solenoid driving circuit 70, and when an engine load exceeds a prescribed value over a started period of time, the negative pressure in the negative pressure chamber 76 of the negative pressure switch 72 is reduced, and the negative pressure switch 72 is turned off, allowing the solenoid valve 51 to be closed via an AND gate 73.

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, Cob, 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 three-way catalyst sound, the air-fuel ratio must be maintained within this narrow window W at all times. For this reason, conventional exhaust gas purification devices require 2. An oxygen concentration detector that can fully determine whether the air-fuel ratio is larger or smaller than the stoichiometric air-fuel ratio is installed in the engine exhaust passage, and based on the output signal of this oxygen concentration detector, the air-fuel ratio is set to the air-fuel ratio within the window W. 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 A7
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 convert 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(b) shows the air-fuel ratio at frequency I
The window Wo of the reference air-fuel ratio A/ is shown when the reference air-fuel ratio is varied by ±1.0 with respect to the reference air-fuel ratio in Hz. Window W when the air-fuel ratio is varied at a constant frequency as shown in FIGS. 1(a) and 1(b). It turns out that this is wide.

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. 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 is made smaller, the air-fuel ratio f cannot change alternately between the rich side and the rich 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 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, even if the reference air-fuel ratio varies somewhat with respect to the stoichiometric air-fuel ratio, high purification efficiency can be obtained. 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 feedbank 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 reference air-fuel ratio, but since fuel injection devices are expensive, there is a problem that the manufacturing cost of the engine increases. If the air-fuel ratio supplied to the engine cylinders is varied in this way, combustion will fluctuate periodically even if the fluctuations are small, resulting in a problem that vehicle drivability will deteriorate.

SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust gas purification device that can ensure high exhaust gas purification efficiency without using an oxygen concentration detector or changing the air-fuel ratio supplied into the engine cylinder.

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 mounted on the intake manifold 1, a re-type carburetor, 3 is an exhaust manifold, and 4 is a catalytic converter. A ternary monolithic catalyst 5 is arranged. The variable bench eri type carburetor 2 includes a carburetor housing 6 and an intake passage 7 extending vertically within the housing 6.
, a suction piston 8 that moves laterally within the intake passage 7 , a letter plate 9 attached to the tip surface of the suction piston 8 , and a letter 9 attached to the tip surface of the suction piston 8 on the inner wall surface of the intake passage 7 . a spacer 10 fixed to;
It includes a throttle valve 11 provided in the intake passage 7 downstream of the suction piston 8 and a float chamber 12, and a bench or IJ section 13 is formed between the tip 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. Inside the guide sleeve 15 is a bearing 17 having a large number of balls 16.
is inserted, and the outer end of the guide sleeve 15 is fitted with a blind lid 18.
Closed by. On the other hand, a guide rod 19 is fixed to the suction piston 8, and this 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 2o and an atmospheric pressure chamber 21 by the suction piston 8, and a compression spring 22 is inserted into the negative chamber 20 to constantly press the suction piston 8 toward the venturi portion 13. . The negative pressure chamber 2o is connected to the venturi section 13 through a suction hole 23 formed in the suction histone 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 downwardly extending fuel pipe 27, and the fuel in the float chamber 12 is transferred through this fuel pipe 27.
The fuel is sent into the fuel passage 25 through the fuel passageway 25. Furthermore, a hollow cylindrical nozzle 28 arranged coaxially with the fuel passage 25 is fixed to the spacer 10 . This nozzle 28 protrudes into the 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. The needle 9 extends through the nozzle 28 and the metering jet 26 , and the fuel is metered into the annular gap formed between the needle 9 and the metering jet 26 from the nozzle 28 into the intake passage 7 .

As shown in FIG. 2, a raised wall 29 that projects horizontally into the intake passage 7 is formed at the upper end of the spacer 1o, and the flow rate is controlled between the raised wall 29 and the tip of the suction piston 8. It will be 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 suction piston 8 and the raised wall 29, negative pressure is generated in the bench recess 13, and this negative pressure is guided into the negative pressure chamber 20 through the suction hole 23. The suction piston 8 has a negative pressure chamber 20 and an atmospheric pressure chamber 2.
1, the pressure difference between the bench area 13 and the bench area 13 becomes a substantially constant pressure determined by the spring force of the compression spring 22, that is, the negative pressure inside the bench area 13 becomes substantially constant.

Referring to FIGS. 3 and 4, the entire tip surface of the suction piston located on the upstream side of the needle 9 is raised from the mounting end 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 the needle 9 also has a U-shaped cross section.
There is a concave groove part 31 located on the side near the tip of the
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 concave groove 31 toward the venturi portion 13. Therefore, the suction piston tip surface portion is concave. A pair of inclined wall portions 32 a inclined toward the groove 31
, 32b.

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 upstream end portion 31a of the concave groove 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 suction piston 8
The amount of lift becomes proportional to the opening area of the intake air control throttle section.

Therefore, the amount of lift of the suction piston 8 smoothly increases as the amount of intake air increases.

Furthermore, since the suction piston 8 is supported by the bearing 17, it moves with good response to 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. the result.

Even when the amount of intake air changes rapidly, such as during acceleration, the amount of fuel supplied from the nozzle 28 increases because the suction piston 8 increases in proportion to the increase in the amount of intake air. It is always proportional to the amount of intake air. Furthermore, as can be seen from FIG. 3, when the amount of intake air is small, the intake air is made to flow through the center of the intake passage 7, and as a result, the fuel supplied from the nozzle 28 immediately flows into the engine cylinder together with the intake air flow. Therefore, even when the amount of intake air is small, the fuel supplied from the nozzle 28 is immediately supplied into the engine cylinder.

Therefore, even if the amount of intake air increases rapidly as during 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, since the suction piston 8 is supported by the bearing 17, the engine temperature does not affect the movement of the suction piston 8, and thus the suction piston 8 responds to changes in the amount of intake air regardless of the engine temperature. can move easily. 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 regardless of the engine temperature and engine operating conditions.

For example, it can be maintained at about 14.0. Therefore, a rich air-fuel mixture with an air-fuel ratio of about 14.0 is constantly supplied into the engine cylinders.

Referring to FIG. 2, an annular air chamber 33 is formed around the metering jet 26, and a plurality of air bleed holes 34 communicating with the annular air chamber 33 are formed on the inner peripheral wall surface of the metering jet 26. The annular air chamber 33 is connected into the intake passage 7 upstream of the raised wall 29 via an air bleed passage 35.36 and an air bleed jet 37, the connection of which is actuated by a wax valve 38. A valve body 39 is arranged. wax valve 38
A cooling water circulation chamber 39 is formed around the temperature sensing portion 38a, and cooling water is introduced into the cooling water circulation chamber 39 from a cooling water inlet 40, and is discharged from a cooling water outlet 41. When the engine cooling water temperature rises, the valve body 39 moves to the left, thereby increasing the flow area of the air bleed passage, thereby increasing the amount of air bleed. When the warm-up operation is completed, the valve body 39 fully opens the air bleed passage, and at this time, the air-fuel mixture supplied into the engine cylinder has an air-fuel ratio of 14.
The mixture becomes a rich mixture of about 0.

On the other hand, a secondary air supply control valve 50 that controls the supply of secondary air is attached to the two-engine exhaust manifold 3, and a solenoid valve 51 that controls the operation of the secondary air supply control valve 50 is attached to the intake manifold 1. .

The secondary air control valve 50 has a negative pressure chamber 53 and an atmospheric pressure chamber 54 separated by a diaphragm 52.

A compression spring 55 for pressing the diaphragm is inserted into the negative pressure chamber 53 . A hollow tube 56 protruding toward the diaphragm 52 is fixedly disposed within the atmospheric pressure chamber 54.
A valve boat 57 whose opening and closing are controlled by a valve body 58 fixed to the diaphragm 52 is formed at the tip of the diaphragm 52 . This valve boat 57 is connected to the inside of the exhaust manifold 3 via a check valve 59 and a secondary air supply hole 60 that allow flow only from the valve boat 57 into the exhaust manifold 3 .

Therefore, the valve boat 57 and the secondary air supply hole 60 form a secondary air supply passage. On the other hand, the solenoid valve 51 includes a valve chamber 62, a valve body 63 disposed within the valve chamber 62, and a negative pressure boat 6 that opens into the valve chamber 62 and is connected to the intake manifold 1.
4, an atmospheric boat 65 opening into the valve chamber 62 and communicating with the atmosphere, a movable plunger 66 connected to the valve body 63, and a solenoid 67 for suctioning the movable plunger 66.
A negative pressure boat 64 and an atmospheric boat 65 are controlled to open and close by a valve body 63. The valve chamber 62 is connected to the negative pressure chamber 53 of the secondary air supply control valve 50 via a conduit 68;
Solenoid 67 is connected to solenoid drive circuit 70. The solenoid drive circuit 70 includes a pulse generator 71 that generates a rectangular pulse with a frequency of I Hz to 2 Hz as shown in FIG. It includes an AND gate 73 whose output is the other input, and a power amplifier 74 connected to the output terminal of the AND gate 73.
The output terminal of is connected to the solenoid 67.

The negative pressure switch 72 includes a negative pressure chamber 76 and an atmospheric pressure chamber 77 separated by a diaphragm 75.

A fixed contact 78 connected to the AND gate 73 and a movable contact 79 fixed to the diaphragm 75 and connected to a power source (not shown) are arranged in the atmospheric pressure chamber 77. On the other hand, the negative pressure chamber 76 is connected to the intake manifold 1 via a negative pressure delay valve 80 and a negative pressure conduit 81. This negative pressure delay valve 80 is equipped with a check valve 81 and a throttle 82 that can flow only from the negative pressure chamber 76 into the intake manifold 1, and the check valve 81 and the throttle 82 are arranged in parallel. .

During low-load operation with a small opening of the throttle valve 11, a large negative pressure is generated within the negative pressure ring 76 of the negative pressure switch 72, and therefore, at this time, the diaphragm 75 moves to the left and is fixed to the movable contact 79. The contacts 78 are in contact with each other.

Thus, at this time, the output voltage of the AND gate 73 becomes a high level every time the pulse generator 71 generates a pulse, so that continuous pulses as shown in FIG. 5(a) are applied to the solenoid 67. . Next, throttle valve 1 is pressed to accelerate.
When valve 1 is opened nearly to full open, the intake manifold l
However, at this time, the check valve 81 is kept closed, so a large negative pressure still acts within the negative ring 76 of the negative pressure switch 72, and the switch 72 is movable. Since the contact 79 and the fixed contact 78 continue to be in contact with each other, continuous pulses as shown in FIG. 5(a) continue to be supplied to the solenoid 67. Then, after a while, the negative pressure in the negative pressure chamber 76 becomes smaller, so the diaphragm 75 moves to the right.

In this way, the movable contact 79 and the fixed contact 78 are in a non-contact state. As a result, the output voltage of AND gate 73 is maintained at a low level and solenoid 67 is deenergized. As described above, in the present invention, continuous pulses are applied to the solenoid 67 for a while after high-load operation is started, and then the solenoid 67 is deenergized. Note that after the throttle valve 11 is opened.

When the throttle valve 11 is closed again within a short period of time, the check valve 81 is immediately opened and a large negative pressure is applied to the negative royal chamber 76. Therefore, in this case, the solenoid 67 is not deenergized and continuous pulses continue to be applied to the solenoid 67.

As described above, continuous pulses as shown in FIG. 5(a) are applied to the solenoid 67 during low load operation of the engine and for a while after transition to high load operation.

The valve body 63 normally closes the negative pressure boat 64 and opens the atmospheric boat 65. When the pulse generator 71 generates a pulse, the solenoid 67 is energized and the valve body 64 moves to the right. Accordingly, the valve body 63 opens the negative pressure boat 64 and closes the atmospheric boat 65. Therefore, the negative pressure boat 64 and the atmospheric boat 65 have a frequency of I Hz to 2 Hz.
The opening and closing operations are repeated at a frequency of IHz to 2H.
Negative pressure or atmospheric pressure is introduced at the z frequency. When negative pressure is applied inside the negative royal chamber 53, the valve body 58 closes to the valve port 5.
7 is opened, and at this time, the exhaust pulsation causes the exhaust manifold 3 to open.
Air is drawn into the exhaust manifold 3 from the secondary air supply hole 60 by the negative pressure generated within. Therefore, as mentioned above, the inside of the negative pressure chamber 53 is alternately atmospheric pressure at a frequency of IHz to 21 (z).

Or when the pressure becomes negative, the valve body 58 opens the valve boat 57 at a frequency of IHz to 2 Hz, and thus secondary air is intermittently supplied into the exhaust manifold 3 at a frequency of I Hz to 2 Hz. It turns out. When secondary air is intermittently supplied into the exhaust manifold 3, the exhaust manifold 3
The oxygen concentration in the exhaust gas within the engine fluctuates periodically, thus causing the air-fuel ratio to fluctuate. Note that the term air-fuel ratio is used here in a slightly different meaning from its usual meaning, and this air-fuel ratio is defined as the total amount of air (intake air) supplied into the working gas passage upstream of the three-way catalytic converter 4. and secondary air) and the total amount of fuel. The three-way catalyst 5 has the above-mentioned oxygen retention function for excess oxygen present in the exhaust gas. It does not matter whether it is due to the secondary air supplied to the Therefore, when the air-fuel ratio is periodically varied by varying the amount of secondary air supplied into the exhaust manifold 3, the average value of this air-fuel ratio is maintained within the window W0 in the first can). High purification efficiency can be obtained. In the embodiment shown in FIG. 2, the dimensions of the valve boat 57 and the secondary air supply hole 600 are such that when the valve body 58 of the diaphragm 52 repeatedly opens and closes the valve boat 57, the average directivity of the air-fuel ratio A/, b)
As shown in the figure, the air-fuel ratio is approximately at the stoichiometric air-fuel ratio, and the fluctuation of the air-fuel ratio is determined to be approximately ±0.2 to ±1.0 with respect to the stoichiometric air-fuel ratio. The reason why the air-fuel ratio can be maintained at approximately the stoichiometric air-fuel ratio by repeating the simple opening and closing operations of the valve body 58 is that the air-fuel ratio of the air-fuel mixture formed in the carburetor 2 is maintained constant. Because there is. Therefore, regardless of the operating state of the engine, the air-fuel ratio will vary from IHz to 2
At a frequency of Hz, the air-fuel ratio is approximately ±0.
2 to ±1.0, and the average value of this air-fuel ratio is maintained within the window W0 shown in FIG. Purification efficiency can be obtained.

On the other hand, in a high-load operating state where the opening degree of the throttle valve 11 is close to fully open, the amount of exhaust gas increases, and if secondary air is supplied while such high-load operating continues, the third A problem arises in that the primary catalyst 5 overheats and the three-way catalyst 5 deteriorates. On the other hand, when the throttle valve 11 is temporarily opened to nearly full opening, the three-way catalyst 5 will not be overheated, and in this case, the secondary air It is preferable to supply it intermittently. However, in the present invention, when high-load operation continues for a certain period of time or more, the negative pressure switch 72 is turned off and the solenoid 67 is deenergized, and as a result, the valve boat 57 of the secondary air supply control valve 50 is closed by the valve body 58. Therefore, the supply of secondary air is stopped. Therefore, deterioration of the three-way catalyst can be prevented while maintaining a good purifying effect when the throttle valve 11 is temporarily opened.

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 the air-fuel ratio of the air-fuel mixture supplied into one engine cylinder is maintained constant, combustion fluctuations do not occur, thus ensuring smooth engine operation. In addition, it is possible to prevent the catalyst from deteriorating due to overheating while maintaining a good purifying effect during the temporary opening operation of the throttle valve, which is normally often performed.

[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 piston. FIG. 5 is a diagram showing variations in air-fuel ratio. 2... Carburetor, 8... Sakushi proverbial piston. 9... Needle, 25... Fuel passage. 28... Nozzle, 50... Secondary air supply control valve. 51... Solenoid valve, 60... Secondary air supply hole. 72... Negative pressure switch, 80... Negative pressure delay valve. Patent applicant Toyota Motor Corporation Patent attorney Akira Aoki Patent attorney Kazuyuki Nishidate Patent attorney Kyosuke Tsuchinakayama Patent attorney Akira Yamaguchi + Onnaku-10
5 =

Claims (1)

[Scope of Claims] An internal combustion engine that is equipped with a fuel supply device for supplying a rich air-fuel mixture into engine cylinders and that is equipped with a three-way catalytic converter in an engine exhaust passage. A secondary air supply passage is connected to the exhaust passage upstream of the three-way catalytic converter, and a solenoid valve that opens and closes at a constant frequency of about I Hz to 2 Hz is arranged in the secondary air supply passage.
When the secondary air supply passage is opened and closed, the air-fuel ratio periodically fluctuates between approximately 0°2 and 1°0 relative to the average value, and the average value of the air-fuel ratio becomes approximately the stoichiometric air-fuel ratio. The flow area of the secondary air supply passage is determined, and a load detector that responds to engine load changes with a delay is connected to the solenoid valve to detect a certain period of time after the engine load exceeds a predetermined load. An exhaust gas purification device for an internal combustion engine, which closes the secondary air supply passage when the time has elapsed.