JPS5934456A - Exhaust gas purifier for internal combustion engine - Google Patents

Abstract

PURPOSE:To enable stable deceleration without torque fluctuation, by temporarily opening a solenoid valve in an air bleed passage at the beginning of the deceleration and entirely closing the valve for the ensuring period of the deceleration to prevent engine misfire. CONSTITUTION:When a throttle valve 11 coupled to an idling switch 59 is in the idling position and the rotational frequency of an engine connected to a rotational frequency switch 60 is higher than 1,500r.p.m., namely, when the engine is being decelerated, the output voltage of an AND gate 56 is made high and the output voltage of a monostable multivibrator 57 is temporarily made high so that a constant voltage is temporarily applied to a voltage-current converter 55 at the beginning of the deceleration and made zero after a while, thereby causing a solenoid 43 to entirely open and close a valve port 37. Since fuel supplied from a nozzle 28 is thus temporarily decreased at the beginning of the deceleration, a mixture introduced into the cylinder of the engine is prevented from becoming too thick. Because a too thick mixture is introduced into the cylinder after a while, misfire is not caused. Stable deceleration without torque fluctuation 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 the three harmful components He, Co, and NOx in exhaust gas. As shown in Fig. 1(a), the purification efficiency R of this three-way catalyst is the highest when the air-fuel ratio ~ is approximately the stoichiometric air-fuel ratio, for example, the purification efficiency R of 80.9 cents or more. The air-fuel ratio range that can be obtained is narrow, with an air-fuel ratio of about 0.06.

Usually, the air-fuel ratio region in which a purification efficiency of 80/f-cent or more can be obtained is called a window W. Therefore, in order to simultaneously reduce the three harmful components in exhaust gas using a three-way catalyst, the air-fuel ratio must be maintained within this narrow window W at all times. For this reason, in conventional exhaust gas purification installations, 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 this oxygen concentration detector is used to 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 tli control unit for controlling the air-fuel ratio, which increases the manufacturing cost of the exhaust gas purification device. There is a problem with doing so.

However, recently, SAE paper & 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 No and reduces No while retaining this taken oxygen, causing the air-fuel ratio to become richer than the stoichiometric air-fuel ratio. Then, the retained oxygen is released to oxidize Co and HC. Therefore, if the air-fuel ratio is alternately varied between the lean side and the rich side with respect to the reference air-fuel ratio, even if the reference air-fuel ratio deviates from the stoichiometric air-fuel ratio, the above-mentioned oxygen retention function will reduce NOx and (1).

The oxidation effect of HC is promoted and high purification efficiency is obtained;
can. FIG. 1(b) shows a window W between the reference air-fuel ratio and the reference air-fuel ratio when the air-fuel ratio is varied by ±1.0 with respect to the reference air-fuel ratio at a frequency of IHz. 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, a high purification effect 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
indicates the air-fuel ratio fluctuation frequency. Furthermore, if the range of variation in the air-fuel ratio is made smaller, the air-fuel ratio cannot be varied alternately between the rich side and the lean side, so the width of the window becomes narrower. Therefore, it can be seen that there is an optimal air-fuel ratio fluctuation period and fluctuation width in order to widen the window width.

As mentioned above, if the 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 variation range is used, high purification efficiency can be obtained without using feed control based on the output signal of the oxygen concentration detector.

In theory, if a fuel injection valve is used as a fuel supply system, the fluctuation range of the reference air-fuel ratio can be narrowed, but since the fuel injection device is expensive, the manufacturing cost of the engine increases.

Therefore, in order to keep the manufacturing cost of the engine low, it is necessary to use a carburetor. However, in conventional fixed venturi type carburetors, the standard air-fuel ratio fluctuates over a wide range, and in conventional variable venturi type carburetors, the standard air-fuel ratio fluctuates greatly during acceleration or depending on engine temperature. 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 as well as an oxygen concentration detector.

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

Referring to FIG. 2, 1 is an intake manifold, 2 is a variable venturi carburetor installed on the intake manifold 1,
3 indicates an exhaust manifold, 4 indicates a catalytic converter,
A three-way monolith catalyst 5 is arranged inside the catalytic converter 4 . The variable venturi carburetor 2 includes a carburetor housing 6 and an intake passage 7 extending vertically within the housing 6.
, a suction piston 8 that moves laterally within the intake passage 7 , a needle 9 attached to the tip surface of the suction piston 8 , and a needle 9 fixed on the inner wall surface of the intake passage 7 facing the tip surface of the suction piston 3 . spacer 10,
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 venturi portion 13 is formed between the tip surface of the suction piston 8 and the spacer 10. A hollow cylindrical casing 14 is fixed to the carburetor housing 6, and the casing 1 with
A guide sleeve 15 extending in the axial direction of the casing 14 inside the casing 14 is attached to the guide sleeve 4 . A bearing 17 with a plurality 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 17.
The guide rod 19 is inserted into the guide rod 19 so as to be movable in the axial direction.

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 by the suction piston 8 into a negative chamber 20 and an atmospheric pressure chamber 21, and a compression spring 22 is inserted into the negative chamber 20 to constantly press the suction piston 8 toward the venturi section 13. The negative royal chamber 20 is connected to the venturi section 13 through a suction hole 23 formed in the suction piston 8, and the atmospheric pressure chamber 21 is connected to the intake passage upstream of the suction piston 8 through an air hole 24 formed in the carburetor housing 6. 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 f27 extending downward, and the fuel in the float chamber 12 is transferred to the fuel pipe f27.
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 further protrudes toward the compression piston 8 from the upper half of the tip of the nozzle 28. Needle 9 is nozzle 28
The nozzle 28 extends through the metering jet 26 and the fuel is metered by the annular gap formed between the needle 9 and the metering jet 26 before being supplied to the intake passage 7 from the nozzle 28 .

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 chamber 20 through the suction hole 23. The piston 8 is arranged so that the pressure difference between the negative pressure chamber 20 and the atmospheric pressure chamber 21 becomes an almost 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 like this.

Referring to FIGS. 3 and 4, the entire tip surface of the suction piston located upstream of the needle 9 is raised from the mounting end surface 30 of the needle 9 toward the tip of the needle 9. A groove 31 extending in the axial direction of the intake passage 7 is formed on the tip end surface of the piston. The upstream end 31a of this concave groove 31 has a U-shaped cross section and is closer to the needle 9 than the needle mounting end surface 30.
There is a concave groove part 31 located on the side near the tip of the
b extends almost straight from the upstream end 311L 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 portions 32a inclined toward 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 p 32 b r, and the groove upstream end 31m form an intake air control constriction part K having a substantially isosceles triangular shape. be done.

By forming the intake air control diaphragm part K in this way, the lift amount of the suction piston 8 is made to be proportional to the opening area of the intake air control diaphragm part. It will increase smoothly as the amount increases. Furthermore, since the suction piston 8 is supported by the bearing 17, it moves with good responsiveness to changes in the amount of intake air, and thus, when the amount of intake air increases, the suction piston 8 moves in response to changes in the amount of intake air. Moves smoothly and responsively. the 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. It will always be proportional to the 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 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. 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, and thus the suction piston 8 changes the amount of intake air regardless of the engine temperature. can be moved with good responsiveness. 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. fuel ratio can be maintained.

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 intake passage 7 upstream of the raised wall 29 via an air bleed passage 35 and an air bleed jet 36, and has an opening area within the air bleed passage 35 by a solenoid valve 40. is controlled by the valve port 37
is formed.

The linear solenoid valve 40 includes a valve body 41 for controlling the opening area of the valve &-) 37, a movable 1-lunger 42 connected to the valve body 41, and a solenoid 43 for suctioning the movable sylanger 42. 43 is connected to the solenoid drive circuit 50. This linear solenoid valve 4
At 0, 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 circuit 50 has an I as shown in FIG.
A sawtooth generator 51 that generates a sawtooth voltage with a frequency from Hz to 2H21, a constant voltage source 52, a first analog switch (12) connected to the output terminal of the sawtooth generator 51, and a constant voltage source 53. An analog switch 54 connected to the output terminal of the source 52, a first analog switch 53 and a second
A voltage-current converter 55 is connected to the output terminal of the analog switch 54, and the output terminal of the voltage-current converter 55 is connected to the solenoid 43. The solenoid drive circuit 50 further includes an AND dart 56, a monostable multipipe rake 57 connected to the output terminal of the AND gate 56, and an inverter 58. The first analog switch 54 is controlled by the output voltage of the AND/DART 56 via an inverter 58, and the second analog switch 54 is directly controlled by the output signal of the monostable multivibrator 57. One input terminal of the AND gate 56 is connected to an idle switch 59 that responds to the opening/closing operation of the throttle valve 11, and the other input terminal of the AND gate 56 is connected to a rotation speed switch 60 that responds to the engine speed. The idle switch 59 is turned on when the throttle valve 11 is in the idle link position, and the rotation speed switch 60 is turned on when the engine rotation speed is as high as, for example, 1500 r, p, m. Therefore, when the throttle valve 11 is in the idling position and the engine speed is higher than 150 Or, p, m, that is, during deceleration operation, the output voltage of the and dart 56 is at a high level. When the output voltage of ANDr-) 56 reaches a high level, the first analog switch becomes non-conducting on the one hand, and the monostable multivibrator 5 becomes non-conductive on the other hand.
Since the output voltage of switch 7 temporarily becomes a high level, the second analog switch 54 temporarily becomes conductive and then becomes non-conductive. Therefore, when deceleration operation starts, the constant voltage becomes 1
The voltage that is applied to the voltage-current converter 55 from time to time and then applied to the input terminal of the voltage-current converter 55 becomes zero shortly after the start of the deceleration operation. On the other hand, the throttle valve 11 is at the idling position, or the engine speed is 150.
When Or, p, and m are also low, that is, when not in deceleration operation, the output voltage of the AND/DART 56 is at a high level, so the first analog switch 53 is in a conductive state.
- Since the output voltage of the permanently stable multivibrator 57 is at a low level, the second analog switch 54 is in a non-conducting state. Therefore, at this time, the output voltage of the sawtooth generator 51 is applied to the voltage-current converter 55.

When not in deceleration operation, the sawtooth generator 5 is activated as described above.
An output voltage of 1 is applied to the voltage-current converter 55 and then converted into a corresponding current in the voltage-current converter 55 and supplied to the solenoid 43. As mentioned above, valve i? −
) 37 changes in proportion to the current flowing through the solenoid 43, and since the solenoid 43 is supplied with a current as shown in FIG. 5(a), the opening area of the valve port 37 changes in a sawtooth pattern. I understand that. In this way, the valve port 37
When the opening area changes in a sawtooth pattern, 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 A/ of the air-fuel mixture supplied into the engine cylinder changes.
F changes smoothly in a wave-like manner as shown in FIG. 5(b). Dimensions of air bleed jet 36 and valve port 37 The air-fuel ratio of the air-fuel mixture supplied into the engine cylinder (15) 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
As shown in the figure, the air-fuel ratio is approximately at the stoichiometric air-fuel ratio, and the fluctuation [1] of the air-fuel ratio is approximately ±0.2 to ±1.
It is set to be equal to 0. 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 a frequency of I Hz to 2 Hz. The average value of the original air-fuel ratio is the first (b).
Window W in the figure.

Therefore, high purification efficiency can be obtained by utilizing the oxygen retention function of the three-way 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, when the throttle valve 11 is closed to reduce the speed, the negative pressure inside the intake manifold 1 suddenly increases, and the liquid fuel adhering to the inner wall surface of the intake manifold 1 evaporates, causing the inside of the engine cylinder to evaporate. The air-fuel mixture supplied to the engine temporarily becomes too rich. (16) Since insufficient fuel is supplied to the engine cylinders, a problem arises in that a misfire occurs and torque fluctuations occur. However, in the present invention, when deceleration operation is started, a constant voltage is applied from the constant voltage source 52 to the voltage-current converter 55 for a certain period of time. This constant voltage is set to approximately the maximum value of the sawtooth voltage shown in FIG. 5(a), so that the valve body 41 fully opens the valve port 37 at this time. In this manner, when deceleration operation is started, the fuel supplied from the nozzle 28 is temporarily reduced, so that it is possible to prevent the air-fuel mixture supplied into the engine cylinders from becoming too rich. Then, shortly after the deceleration operation starts, the voltage applied to the input terminal of the voltage-current converter 55 becomes zero, so the solenoid 43 is deenergized.
Valve body 41 thus closes valve port 37. As a result, since a rich air-fuel mixture is supplied into the engine cylinders, misfires do not occur even during deceleration operation, and thus stable deceleration operation without torque fluctuation can be achieved.

As described above, according to the present invention, it is not necessary to use an expensive oxygen concentration detector and an expensive electronic control unit for air-fuel ratio control, and the exhaust gas can be effectively purified using an inexpensive carburetor. The manufacturing cost of the device can be greatly reduced. 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 completely improved. In addition, it is possible to prevent the air-fuel mixture supplied into the engine cylinders from becoming extremely rich immediately after the start of engine deceleration operation, making it possible to effectively purify exhaust gas. Since a suitably rich air-fuel mixture is supplied into the engine cylinders, it is possible to prevent misfires from occurring, and thus stable deceleration operation can be achieved despite large torque fluctuations.

[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 arrow Il+ in Figure 2, and Figure 4 is the Zakujo piston. FIG. 5 is a diagram showing variations in air-fuel ratio. 2... Carburetor, 8... Zakujon Piston, 9...
・Needle, 25...Fuel passage, 28...Nozzle,
35...Air bleed passage, 40...Linear solenoid. 1st time applicant Toyota Motor Corporation Patent application agent Patent attorney Akira Aomizu Patent attorney Kazuyuki Nishidate Patent attorney Kyo Nakayama 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 is equipped with a drive signal generation circuit capable of generating a drive signal that fluctuates at a constant frequency of IHz to 2Hz, and the air bleed passage generates a drive signal that fluctuates at a constant frequency of IHz to 2Hz in response to the drive signal. A solenoid valve that increases or decreases the flow area is provided, and when the solenoid valve increases or decreases the flow area of the air bleed passage, the air-fuel ratio changes periodically between approximately ±0.2 and ±1.0 with respect to the average value. The flow area of the air bleed passage is determined so that the average value of the air-fuel ratio is approximately the stoichiometric air-fuel ratio, and the drive signal generation circuit generates a drive signal that temporarily fully opens the solenoid valve and then fully closes the solenoid valve. A deceleration operation detector capable of detecting engine deceleration operation is connected to the drive signal generation circuit, and the solenoid valve is temporarily fully opened at the start of deceleration operation, and during the subsequent deceleration period, the solenoid valve is An exhaust gas purification device for an internal combustion engine that completely closes the engine.