JPS5934457A - Exhaust gas purifier for internal combustion engine - Google Patents

Abstract

PURPOSE:To enable stable idling, by detecting the idling state of an engine to change to a smaller second value the amplitude of a drive signal for a solenoid valve for opening and closing an air bleed passage, to decrease the fluctuation width of the air fuel ratio of the engine. CONSTITUTION:When a throttle valve 11 is in the idling position, namely, when an engine is being decelerated, a throttle switch 58 and a first analogue switch 53 are turned on and a second analogue switch 54 is turned off so that a saw- tooth voltage of smaller amplitude is applied to a voltage-current converter 55. As a result, the change width of the cross-sectional area of the opening of a valve port 37 is reduced to decrease the fluctuation width of the air fuel ratio of the engine to diminish the fluctuation of its output torque. Stable idling is thus enabled.

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 three harmful components HC, Co, and N emissions in exhaust gas. The purification efficiency R of this three-way catalyst is highest when the air-fuel ratio is approximately the stoichiometric air-fuel ratio, as shown in FIG.
The air-fuel ratio range in which a purification efficiency of 80% or more can be obtained is usually a narrow range in which the air-fuel ratio is about 0.06. 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 systems, an oxygen concentration detector that can determine whether the air-fuel ratio is higher or lower 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 controlled to be 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. However, recently, SAE paper A 76
As described in No. 0201 or 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 had an oxygen retention function. That is, when the air-fuel ratio is on the lean side with respect to the stoichiometric air-fuel ratio, the three-way catalyst removes oxygen from NOx and reduces the NOx, and retains this removed oxygen, so that the air-fuel ratio becomes less than the stoichiometric air-fuel ratio.

When it comes to the hot side, 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 (
b) is ± with respect to the reference air-fuel ratio at the air-fuel ratio total frequency I Hz.
Window W of the standard air-fuel ratio when varied by 1.0. It shows. Window W when the air-fuel ratio is varied at a constant frequency as shown in FIGS. 1(a) and 1(b). It can be seen that the area becomes wider. This means that if the air-fuel ratio is varied at regular intervals, high purification efficiency can be obtained even if the reference air-fuel ratio deviates slightly from the stoichiometric air-fuel ratio. If you lower it,
That is, when the air-fuel ratio fluctuation period is lengthened, the oxygen retention capacity of the three-way catalyst becomes saturated, so the oxidation-reduction capacity based on the oxygen retention function decreases, and the purification efficiency of the three-way catalyst decreases. 1st (c
) figure 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 are optimal air-fuel ratio fluctuation periods and fluctuation periods in order to widen the window [1].

As mentioned above, if the range and frequency of fluctuation 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. If a fuel injection valve is used as a supply system, the variation 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 reference air-fuel ratio fluctuates widely, and in conventional variable pliers type 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 venturi type vaporizer.

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

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 2, 1 is an intake manifold, 2 is a variable venturi carburetor installed on the intake manifold 1,
3 indicates an exhaust manifold, 4 indicates a catalytic converter,
A three-way monolith catalyst 5 is arranged inside the catalytic converter 4 . The variable venturi type carburetor 2 includes a carburetor housing 6, an intake passage 7 extending in the direction perpendicular to the drawing within the housing 6, a piston 8 that moves laterally within the intake passage 7, and a distal end surface of the suction piston 8. The attached needle 9, the spacer 10 fixed on the inner wall surface of the intake passage 7 facing the tip surface of the piston 3, and the throttle valve 11 provided in the intake passage 7 downstream of the 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 mails 16 is inserted into the guide sleeve 15, and the outer end of the guide sleeve 15 is closed by a blind M18. 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.

In this manner, the suction piston 8 is supported by the casing 14 via the bearing 17, so that 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 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. be done. The negative pressure chamber 20 is a suction hole 2 formed in the Zakushore LJ'stone 8.
3 to the venturi section 13, and the atmospheric pressure chamber 2 is connected to the intake passage 7 upstream of the suction piston 8 through an air hole 24 formed in the carburetor housing 6.

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 upstream of the zero metering jet 26. The fuel passage 25 is connected to the float chamber 2 via a fuel pipe f27 extending downward, and the fuel in the float chamber 12 is supplied 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 compression piston 8 (7). 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 toward the intake passage 7 is formed in the spacer 1 (1) lJ section, and a flow rate between this raised wall 29 and the tip of the suction piston 8 is formed. Control takes place. When engine operation is started, air flows downward in the intake passage 7. At this time, the air flow is restricted between the suction piston 8 and the raised wall 29, so negative pressure is generated in the venturi portion 13, and this negative pressure is introduced into the negative pressure chamber 2o through the suction hole 23. , the piston 8 is operated so that the pressure difference between the negative pressure chamber 20 and the atmospheric pressure chamber 21 becomes a constant pressure determined by the spring force of the compression spring 22, that is, the negative pressure inside the venturi section 13 becomes almost constant. Move to.

Referring to FIGS. 3 and 4, the entire tip surface of the suction piston located upstream of the needle 9 (8) 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.
is formed. The upstream end 311 of this groove 31 has a U-shaped cross section and is located closer to the tip of the needle 9 than the needle mounting end surface 30, and the remaining groove portion 31b is on the upstream side. Needle mounting end face 3 from end 31m
Furthermore, the cross-sectional shape of the tip of the piston is V-shaped, expanding from the concave groove 31 toward the venturi portion 13. The front end of the piston has a pair of inclined wall portions 32a that are inclined toward the groove 31.

32b.

As can be seen from FIG. 3, when the number of inhaled nitric oxides is small, the raised wall 29 and the inclined wall portions 32a and 32b.

The upstream end portion 311L 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 - 111 is proportional to the opening area of the intake air control throttle part. It will increase smoothly as the air increases slightly. Furthermore, since the suction piston 8 is supported by the shaft '17, it moves with good response to changes in the amount of intake air, and thus the suction piston 8 moves when the amount of intake air increases. Moves smoothly and responsively. 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 inhalation volume.

Furthermore, as shown in 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,
As a result, the fuel supplied from the nozzle 28 is immediately supplied into the engine cylinder together with the amount of intake air, so even when the amount of intake air is small, the fuel supplied from the nozzle 28 is immediately supplied into the engine cylinder. Ru. Therefore, even if the intake air iIl increases rapidly as during acceleration operation, the amount of fuel supplied from the nozzle 28 is proportional to the intake air wave as described above, and moreover, the fuel supplied from the nozzle 28 is immediately 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. Furthermore, since the suction piston 8 is supported by the bearing 17, the engine temperature does not affect the movement of the suction piston 8.
In this way, the suction piston 8 can move with good responsiveness to changes in the intake air waves, regardless of the engine temperature.

Thus, 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 a constant value, e.g. The air-fuel ratio can be maintained at approximately the stoichiometric air-fuel ratio.

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 35 and an air bleed jet 36.
A valve boat 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 includes a valve body 41 that controls the opening area of the valve port 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. This linear solenoid valve 40
Then, 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 37 changes in proportion to the current flowing through the solenoid 43.

The solenoid drive times %50 is 1 as shown in Figure 6 (,).
A first sawtooth generator 51 that generates a sawtooth voltage with a frequency of A to 2Hz, and a second sawtooth generator 51 that generates a sawtooth voltage of a frequency of IHz to 2Hz, as shown in FIG. 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 the second sawtooth generator 52; A voltage-current converter 55 is connected to the output terminals of an analog switch 53 and a second analog switch 54, and the output terminal of the current-voltage converter 55 is connected to the solenoid 43. As mentioned above, the first sawtooth generator 51 and the second belltooth generator 52 have almost the same frequency I.
A sawtooth voltage from Hz to 2Hz is generated as shown in Figure 5(a).
and the first sawtooth generator 5 as shown in FIG.
The amplitude of the sawtooth of the second sawtooth generator 52 is smaller than the amplitude of the sawtooth of the second sawtooth generator 52. As mentioned above, the opening area of the valve port 37 is proportional to the current flowing through the solenoid 43'i, and the current supplied to the solenoid 43 is proportional to the output voltage of the sawtooth generator 51,52. It can be seen that during the increase and decrease it is proportional to the amplitude of the sawtooth generated by the sawtooth generators 51,52.

On the other hand, as shown in FIG. 2, a throttle switch 58 is connected to the throttle valve 11 and responds to the opening/closing operation of the throttle valve 11, and this throttle switch 58 is turned on when the throttle valve 11 is in the idling position. The first analog switch 53 is an idle switch 58
The second analog switch 54 is controlled by the output signal of the idle switch 58 via an inverter 57. Therefore, the throttle valve 11
When the analog switch 53 is in the idling position, that is, during idle-link operation, the first analog switch 53 is not conductive, and the second
Since the analog switch 54 becomes non-conductive, the state shown in FIG. 6 (
, ) is applied to the voltage-current converter 55 with a small amplitude sawtooth voltage. On the other hand, when the throttle valve 11 is not in the idling position, the first analog switch 53
is in a non-conducting state, and the second analog switch 54 is in a conducting state. Therefore, at this time, a sawtooth voltage with a large amplitude as shown in FIG. 5(,) is applied to the voltage-current converter 55.

When the throttle valve 11 is not in the idling position, a sawtooth voltage with a large amplitude as shown in FIG. 5 (-) is applied to the voltage-current converter 55, as described above. At this time, the valve body 41 reciprocates between the fully open position and the fully closed position to change the opening area of the valve port 37 in a sawtooth pattern. When the opening area of the port 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 of the mixture supplied into the engine cylinder changes. As shown in FIG. 5(b), it changes smoothly in a wave-like manner. Air bleed jet 36 and valve port 370 Dimensions Near solenoid valve 400 Valve body 4
1 repeatedly increases and decreases the flow area of the valve port 37, the average value of the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes approximately the stoichiometric air-fuel ratio as shown in FIG. 5(b))
, the fluctuation width 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 is approximately within the range of ±0.2 to ±1.0 with respect to the stoichiometric air-fuel ratio at frequencies from IHz to 2Hz. The average value of the original air-fuel ratio is
(b) Window W in the figure. Therefore, high purification efficiency can be obtained by utilizing the acid system retention function of the ternary monolith catalyst 5. Furthermore, as shown in Figure 5(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 idling operation, as mentioned above, as shown in Figure 6 (
, ) is applied to the voltage-current converter 55 with a small amplitude sawtooth voltage. Therefore, in this case, valve port 3
In order to reduce the increase and decrease of the aperture area in Fig.
), the range of fluctuation in air-fuel ratio supply becomes narrower. If the air-fuel ratio fluctuates, the engine output torque will fluctuate accordingly, but the fluctuations in the output torque felt by the passenger are most severe during idle-link operation. Therefore, if the air-fuel ratio fluctuation l] is narrowed during idling operation, the purification efficiency will decrease slightly, but since the fluctuation in output torque will be reduced, stable idling operation can be obtained. Note that during idling, the absolute amount of intake air supplied into the engine cylinders is small, and therefore the absolute amount of harmful components in the exhaust gas discharged into the exhaust manifold 3 is small, so even if the purification efficiency slightly decreases. The absolute amount of harmful components released into the atmosphere is small, and thus the amount of exhaust gas released into the atmosphere can be kept low even during idling 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 the air bleed passage, the structure is extremely simple, and therefore the reliability of the exhaust gas purification device can be improved. In addition, stable idling can be achieved by narrowing the period during which the air-fuel ratio fluctuates during idling.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing exhaust gas purification efficiency, Fig. 2 is a side sectional view of the engine intake and exhaust system, Fig. 3 is a plan view taken along the arrow ■ in Fig. 2, and Fig. 4 is a diagram showing the spool and 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... Zakujon Piston, 9...
・Needle, 25...Fuel passage, 28...Nozzle,
35...Air bleed passage, 40...Linear renoid valve, 58...Idle switch〇Patent applicant Toyota Motor Corporation Patent application representative Patent attorney Akira Segi Patent attorney Kazuyuki Nishidate Patent attorney Kyosuke Nakayama 9P Physician Akira Yamaguchi (19)

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 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 of IHz to 2Hz, and is proportional to the amplitude while the opening area is increasing or decreasing, and when the drive signal exceeds the first amplitude, the valve 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, Furthermore, an idle-link operation detector capable of detecting the engine idling operation state is connected to the drive signal generation circuit, and the amplitude of the drive signal is changed from the first amplitude to the first amplitude, which is smaller than the first amplitude, during engine idle-link operation. An exhaust gas purification device for an internal combustion engine configured to switch to an amplitude of 2.