JPS5934455A - Exhaust gas purifier for internal combustion engine - Google Patents

Abstract

PURPOSE:To secure smooth deceleration, by opening and closing an air bleed passage with higher frequency to suppress the fluctuation in torque under the deceleration. CONSTITUTION:In a solenoid drive circuit 50, a first and a second saw-tooth wave generators 51, 52 produce saw-toothed voltages of 5Hz to 10Hz and 1Hz to 2Hz in frequency. The drive circuit 50 is connected to a solenoid 43 to control the cross-sectional area of the opening of a valve port 37 in an air bleed passage 35. When a throttle valve 11 is in the idling position and the rotational frequency of an engine is higher than 2,000r.p.m. namely, when the engine is being decelerated, the output voltage of an AND gate 56 is made high to turn on a first analogue switch 53 and turn off a second analogue switch 54 to apply the saw-tooth voltage of higher frequency to a voltage-current converter 55 so that the air fuel ratio of the engine fluctuates at a shorter period. As a result, the fluctuation in the output torque of the engine is small even if the combustion of the engine fluctuates. Smooth deceleration is thus secured.

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 R is approximately the stoichiometric air-fuel ratio, as shown in FIG. The air-fuel ratio range in which this is possible is narrow, with an air-fuel ratio of approximately 0.06°. Usually, the air-fuel ratio region in which a purification efficiency of 80 percent or more can be obtained is called a window W. Therefore, in order to simultaneously reduce the three harmful components in exhaust gas using a three-way catalyst, the air-fuel ratio must be maintained within this narrow window W at all times. To this end, in conventional exhaust gas purification systems, an oxygen concentration detector that can determine whether the air-fuel ratio is greater or less than the stoichiometric air-fuel ratio is installed in the engine exhaust passage, and the output signal of the oxygen concentration detector is used to detect the air-fuel ratio. The fuel ratio is controlled to be within the air-fuel ratio within the window W. However, an exhaust gas purification device using such an oxygen concentration detector requires an expensive oxygen concentration detector and an expensive electronic control unit for air-fuel ratio control, which increases the manufacturing cost of the exhaust gas purification device. There is a problem.

However, recently, SAE paper No.

As described in No. 760201 or Japanese Patent Publication No. 56-4741, the function of the three-way catalyst was gradually elucidated, and it was found that the three-way catalyst had an oxygen retention function. In other words, when the air-fuel ratio is on the lean side with respect to the stoichiometric air-fuel ratio, the three-way catalyst takes oxygen from NOx and converts it into NOx.
While reducing x, this taken 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 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 standard air-fuel ratio A/F is shown when I(z is varied by ±1.0 with respect to the standard air-fuel ratio. Figures 1(a) and 1(b) show the air-fuel ratio It can be seen 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 a constant frequency, high purification efficiency can be achieved 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 is saturated, and the redox capacity based on the oxygen retention function is reduced. Figure 1 (c) clearly shows this. In Figure 4 (C), the vertical axis R represents the purification efficiency, and the horizontal axis F represents the empty air. Indicates the fluctuation frequency of the fuel ratio.Also, if the air-fuel ratio fluctuation is made small, the air-fuel ratio cannot alternately fluctuate between the rich side and the rich side, so the window width becomes narrower.Therefore, in order to widen the window width, It can be seen that there is an optimal air-fuel ratio fluctuation cycle and fluctuation 1].

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 feedback control based on the output signal of the oxygen concentration detector.

In theory, if a fuel injection valve is used as a fuel supply system, it is possible to narrow the 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, it is difficult to obtain high purification efficiency even if a variable venturi type vaporizer is used.

The present invention provides 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 bench z') 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 needle 9 attached to the tip surface of the suction piston 8; a fixed spacer 10;
It includes a throttle valve 11 provided in the intake passage 7 downstream of the suction piston 8, and a 71:l-h chamber 12,
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. Inside the guide sleeve 15 is a bearing 17 with a large number of soles 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 the guide rod 19 is inserted into the bearing 17 so as to be movable in the axial direction of the guide rod 19.

Since the suction piston 8 is 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 pressure chamber 20 and an atmospheric pressure chamber 21, 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. The negative chamber 2o is connected to the bench portion 13 through a suction hole 23 formed in the suction piston 8, and the atmospheric pressure chamber 21 is connected to the upstream end of the suction piston 8 through an air hole 24 formed in the carburetor housing 6. It is connected to the intake passage 7.

On the other hand, a fuel passage 25 is formed in the carburetor housing 6 and extends in the axial direction of the needle 9 so that the needle 9 can enter therein.
will be provided. The fuel passage 25 upstream of the metering jet 26 connects to the float chamber 12 via a fuel f27 extending downward.
The fuel in the float chamber 12 is sent into the fuel passage 25 via the fuel pipe 27. Furthermore, a hollow cylindrical nozzle 28 is fixed to the service member 10 and is arranged coaxially with the fuel passage 25.
protrudes into the penetrating 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 by the annular gap formed between the needle 9 and the metering jet 26 from the nozzle 28 into the intake passage 7 .

As shown in FIG. 2, a raised wall 29 is formed at the upper end of the spacer 10 and projects horizontally into the intake passage 7, and the flow rate is controlled between this raised wall 29 and the tip of the suction piston 8. It is done. When engine operation is started, air flows downward in the intake passage 7. At this time, since the airflow is restricted between the 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 spool hole 23. The suction piston 8 is arranged so that the pressure difference between the negative pressure chamber 20 and the atmospheric pressure chamber 2 becomes an almost constant pressure determined by the spring force of the compression spring 22, that is, the negative pressure inside the venturi part 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 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 is closer to the needle 9 than the needle mounting end surface 30.
The remaining concave groove portion 31
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 groove 31 toward the venturi portion 13. A pair of inclined wall 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 and the inclined wall portions 32a and 32b.

The upstream end portion 31a 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 rift) ft of the suction piston 8 becomes proportional to the opening area of the intake air control throttle part, and therefore the rift) ft of the suction piston 8 becomes the suction It will increase smoothly as the amount of air increases. Furthermore, since the Zakujo piston 8 is supported by the bearing 17, it moves with good response to changes in the amount of intake air, and thus the Zakujo 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 amount of intake air.

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 intake air flow, so that the intake air 1
Even when the amount of fuel is low, 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 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 Figure 2 is used, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinders can be kept at an approximately constant value, for example, approximately stoichiometric, regardless of the engine temperature and the engine operating state K. Can be maintained in combustion.

Referring to FIG. 2, an annular air chamber 33 is formed around the metering jet 1-26, 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. be done. The annular air chamber 33 is connected to the intake passage 7 upstream of the raised wall 29 via an air bleed passage 35 and an air bleed jet 36, and the opening area of the air bleed passage 35 is controlled by a solenoid valve 40. A valve port 37 is formed.

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. In this linear solenoid valve 40, the movable plunger 42 moves by a distance proportional to the current flowing through the solenoid 43, and as the current flowing through the solenoid 43 increases, the valve body 41 moves to the right.

Therefore, the opening area of the valve port 37 changes in proportion to the current flowing through the solenoid 43.

The solenoid drive circuit 50 includes a first sawtooth generator 51 that generates a sawtooth voltage with a frequency of, for example, 5Hz to 10Hz as shown in FIG. a second generating a sawtooth voltage with a frequency of
a sawtooth generator 52; a first analog switch 53 connected to the output terminal of the first sawtooth generator 51; and a second analog switch 54 connected to the output terminal of the second sawtooth generator 52. A voltage-current converter 5 connected to the output terminals of the first analog switch 53 and the second analog switch 54
5, and the output terminal of this current-voltage converter 55 is connected to the solenoid 43. Furthermore, the solenoid drive circuit 5
0 comprises an AND gate 56 and an inverter 57, the first analog switch 53 is directly controlled by the output voltage of the AND gate 56, and the second analog switch 54 is controlled by the output voltage of the AND gate 56 via the inverter 57. controlled. One input terminal of the underpass 56 is an idle switch that responds to the opening/closing operation of the throttle valve 11.

The other input terminal of the AND gate 56 is connected to a rotation speed switch 59 which is responsive to the engine rotation speed. The idle switch 58 is turned on when the throttle valve 11 is in the idling position, and the rotation speed switch 58 is turned on when the throttle valve 11 is in the idling position.
9 is turned on when the engine speed is higher than, for example, 2000 r, p, m.

Therefore, when the throttle valve 11 is in the idling position and the engine speed is higher than 200 Or, p, m,
That is, during deceleration operation, the output voltage of the AND gate 56 becomes high level. When the output voltage of the AND gate 56 reaches a high level, the first analog switch 53 becomes conductive and the second analog switch 54 becomes non-conductive, resulting in a sawtooth voltage with a bright frequency as shown in FIG. 6(a). is applied to the voltage-current converter 55. On the other hand, the throttle valve 11 is not in the idling position or the engine speed is 200 Or
. Therefore, at this time, a sawtooth voltage having a frequency of IHz to 2Hz as shown in FIG. 5(,) is applied to the voltage-current converter 55.

When not in deceleration operation, a sawtooth voltage with a frequency of 1 Hz to 2 Hz is applied to the voltage-current converter 55 as described above, and then converted into a corresponding current by the voltage-current converter 55 and supplied to the solenoid 43. . As mentioned above, the opening area of the valve boat 37 changes in proportion to the current flowing through the solenoid 43.
a) The valve port 37 is supplied with current as shown in the figure.
It can be seen that the opening area changes in a sawtooth pattern. 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 A of the air-fuel mixture supplied into the engine cylinder is changed. /F changes smoothly in a wave-like manner as shown in FIG. 5(b). Air bleed jet 36 and valve? - Dimensions of G 37 Near Solenoid Valve 4
When the flow area of the valve port 37 is repeatedly increased and decreased by the zero valve body 41, the average value of the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder is approximately the stoichiometric air-fuel ratio, as shown in FIG. 5(b). It is determined that the air-fuel ratio during fluctuation is 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 mixture supplied into the engine cylinders will vary from I Hz to 2 Hz.
The frequency of the air-fuel ratio is varied within the range of approximately ±0.2 to ±1.0 with respect to the stoichiometric air-fuel ratio, and the original average value of the air-fuel ratio is maintained within the window Wo in FIG. 1(b). Therefore, high purification efficiency can be obtained by utilizing the oxygen 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 deceleration operation, a sawtooth voltage with a high frequency as shown in FIG. 6(1) is applied to the voltage-current converter 55, and thus the air-fuel ratio A/F is changed as shown in FIG. 6(b). F
will fluctuate in short cycles.

When the air-fuel ratio fluctuation cycle is shortened in this manner, even if combustion fluctuations occur due to air-fuel ratio fluctuations, fluctuations in the output torque become smaller, thus ensuring smooth deceleration 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. (manufacturing cost) can be reduced by a large amount. Furthermore, since only a solenoid valve is provided in the air bleed passage, the structure is extremely simple, and therefore the reliability of the exhaust gas purification device can be improved. Furthermore, since torque fluctuations during deceleration operation can be suppressed, smooth deceleration operation can be ensured.

[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 Box 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...Air bleed passage, 40...Linear solenoid valve.

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 provided with a drive signal generation circuit capable of generating a drive signal with a first constant frequency of IHz to 2Hz and a drive signal with a second frequency higher than the first constant frequency. A solenoid valve is arranged to open and close the air bleed passage at the constant frequency in response to the drive signal, and when the air bleed passage is opened and closed, the air-fuel ratio is approximately ±0.2 to ±1. The flow area of the air bleed passage is determined so that the air-fuel ratio periodically fluctuates between 0 and 0, and the average value of the air-fuel ratio becomes approximately the stoichiometric air-fuel ratio. Exhaust gas purification of an internal combustion engine, which is connected to a drive signal generation circuit to generate the drive signal of the second constant frequency during deceleration operation and to generate the drive signal of the first constant frequency when the operation is not deceleration. Device.