JPS628331Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention is a system and exhaust system for feedback controlling the air-fuel ratio of a carburetor so that the air-fuel ratio upstream of a three-way catalyst installed in the exhaust system of an internal combustion engine is approximately the stoichiometric air-fuel ratio. a secondary air supply system to;
The present invention relates to an exhaust gas purification device including a system that recirculates a portion of exhaust gas to an intake system.

Recently, _in order to reduce _NOx in the exhaust gas of internal combustion engines, a part of the exhaust gas has been recirculated to the intake system.
Three-way catalysts are used that act simultaneously on the three harmful components of CO and HC. In this case, the three-way catalyst has the property of being able to purify three-way harmful components at a high purification rate when the air-fuel ratio on the upstream side is approximately the stoichiometric air-fuel ratio. An exhaust sensor that detects the air-fuel ratio is provided, and by increasing or decreasing the amount of fuel to the engine or the amount of air to the air bleed of the carburetor using the exhaust sensor, the air-fuel ratio at the exhaust sensor location is feedback-controlled to approximately the stoichiometric air-fuel ratio. things will be done. However, performing this feedback control of the air-fuel ratio over the entire operating range of the engine causes combustion to become unstable in the operating range where the throttle valve is closed (particularly in the idling operating range), so it is difficult to control the air-fuel ratio at the exhaust sensor location. Since the fuel ratio fluctuates greatly, and the air-fuel ratio of the intake air-fuel mixture that is controlled accordingly also fluctuates greatly, feedback control during idling becomes extremely unstable, and the engine's idling also becomes extremely unstable. It turned out to be so.

Therefore, conventionally, when performing feedback control of the air-fuel ratio, when the throttle valve is closed, the air-fuel ratio of the intake air-fuel mixture is set to the initially set air-fuel ratio (slightly richer than the stoichiometric air-fuel ratio) by a cut of the feedback control. While stabilizing idling, the three-way catalyst achieves high purification by supplying secondary air to the exhaust system so that the air-fuel ratio upstream of the three-way catalyst is approximately the stoichiometric air-fuel ratio. but,
Conventional systems supply secondary air during idling by connecting a secondary air supply passage to the exhaust system separately from the passage connected to the exhaust system to take out the recirculated exhaust gas to the intake air. This is done by opening the secondary air control valve installed in the supply passage using an actuator using a diaphragm or the like that is activated by negative pressure in the intake pipe, so the connection to the exhaust system is extremely complicated. Not only does the space for connection increase, but the secondary air control valve also requires an actuator for opening and closing, making the secondary air control valve complex and large.

The present invention provides an internal combustion engine that is equipped with an air-fuel ratio feedback system for a three-way catalyst, a secondary air supply system to the exhaust system, and an exhaust gas recirculation system. In this case, exhaust gas is not recirculated to the intake system,
Considering that it is necessary to supply secondary air to the exhaust system when the throttle valve is closed, a secondary air supply passage is connected to the exhaust gas recirculation passage from the exhaust system to the intake system, and the exhaust gas recirculation passage is connected to the exhaust gas recirculation passage from the exhaust system to the intake system. A part of the secondary air supply passage is shared by a part of the secondary air supply passage, and a secondary air control valve in the secondary air supply passage is controlled in response to an increase in negative pressure due to the flow of exhaust gas in the exhaust gas recirculation passage. The above-mentioned drawbacks of the conventional device have been solved by providing a simple structure that can be closed.

To explain the example below, in the figure 1
indicates an internal combustion engine, in which a carburetor 5 with an air cleaner 4 is connected to the intake port 2 of the engine 1 via an intake manifold 3, and a three-way catalyst such as a monolith type is installed to the exhaust port 6 via an exhaust manifold 7. Exhaust gas purification devices 8 consisting of the following are connected to each.

The carburetor 5 includes air bleed ports 14 and 15 in a main fuel passage 10 leading to the main nozzle 9, and in a slow fuel passage 13 leading to an idle port 11 and a slow port 12, respectively, and a throttle in the carburetor 5. The valve 16 is ON when the throttle valve 16 is fully closed (idle opening).
On the other hand, the exhaust manifold 7 is provided with a throttle switch 17 that controls O ₂ in the exhaust gas,
An exhaust sensor 18 is provided to detect CO, CO ₂ , HC or NO _x concentration.

Reference numeral 19 denotes a diaphragm type exhaust gas recirculation control valve.The inlet of the exhaust gas recirculation control valve 19 is located upstream of the exhaust sensor 18 in the exhaust manifold 7 via a recirculation passage 21 with an orifice 20, and the outlet thereof is connected to the recirculation passage 22. The valve body 23 of the exhaust gas recirculation control valve 19 is connected to the intake manifold 3 through the spring 2 in the diaphragm chamber 24.
5, it is biased in the normally closed direction.

Reference numeral 26 denotes an exhaust pressure regulating valve, which includes a diaphragm 29 that separates an atmosphere communication chamber 27 and an exhaust pressure chamber 28, and the atmosphere communication chamber 27 communicates with the atmosphere, such as the clean side of the air cleaner 4, through a passage 31 with an orifice 30. The diaphragm 29
It is equipped with a communication pipe 33 that opens and closes with a flap 32,
While the communication pipe 33 is kept open at all times by the spring 34, the exhaust pressure chamber 28 is connected via a passage 35 between the control valve 19 and the orifice 20 in the reflux passage 21, and the communication pipe 33 is 33 is the diaphragm chamber 2 of the exhaust gas recirculation control valve 19 via the passage 36.
4, and is also connected to a reflux port 39 provided at an appropriate location upstream of the closed position of the throttle valve 16 in the carburetor 5 via a negative pressure take-off passage 38 with an orifice 37.

Reference numeral 40 indicates an actuator for air-fuel ratio control, and a movable body 41 in the actuator 40 is provided with two needle valves 45 and 46 for opening and closing two ports 43 and 44 that open into the valve chamber 42. room 4
The first port 43 is connected to the air bleed port 14 of the main system fuel passage 10 via the air bleed passage 48, and the first port 43 is connected to the air bleed port 14 of the main system fuel passage 10 via the air bleed passage 48.
In addition, the second ports 44 are connected to the air bleed ports 15 of the slow system fuel passage 13 via air bleed passages 49, respectively. In this case the first
The second port 43 and its needle valve 45 are set so that the air-fuel ratio of the carburetor 5 is lean when the actuator 40 stops operating, and the second port 44 and its needle valve 46 are actuator 4
The air-fuel ratio at the slow or idle port is set to be slightly richer than the stoichiometric air-fuel ratio when the engine is stopped.

50 is a control circuit which receives signals from the exhaust sensor 18 and the throttle switch 17;
The control circuit 50 compares the output of the exhaust sensor 18 with a control target value and operates the actuator 40 accordingly. For example, when the exhaust sensor 18 detects O ₂ concentration, , When the O ₂ concentration detected by this exceeds the O ₂ concentration at the stoichiometric air-fuel ratio, since the air-fuel ratio at the exhaust sensor location is leaner than the stoichiometric air-fuel ratio, both ports 43 in the actuator 40,
44 was closed and also detected by the exhaust sensor 18.
When the O ₂ concentration is opposite to the above, both ports 43 and 44 in the actuator 40 are opened to perform feedback control so that the air-fuel ratio at the 18 exhaust sensors becomes approximately the stoichiometric air-fuel ratio. , the control circuit 50 is the throttle switch 1
Based on the ON signal from 7, the actuator 40 stops operating.

Reference numeral 51 denotes a secondary air supply device, and the secondary air supply device 51 has a secondary air supply passage 53 connected at one end to the air cleaner 52 for secondary air or to an atmospheric communication point such as the dirty side of the air cleaner 4.
, a check valve 54 and a secondary air control valve 55, which are provided in the passage 53 and will be described in detail later, and the other end of the secondary air supply passage 53 is connected from the exhaust manifold 7 to the recirculation control valve 19. It is connected to the reflux passage 21 of.

Then, the check valve 54 is attached to the elastic valve body 54d on the valve seat 54c with the valve hole 54b in the valve case 54a.
One end is attached, and the elastic valve body 54d is configured to open and close due to exhaust pulsation in the exhaust manifold 7 when the engine is idling (however, reference numeral 54
(e is a stopper for the elastic valve body 54d) On the other hand,
In the secondary air control valve 55, a valve body 55d with a through hole 55c provided in a valve case 55a close to an open valve seat 55b is held open at all times by a spring 55e, and the inside of the recirculation passage 21 is At the negative pressure when the exhaust gas flows toward the intake manifold 3,
The valve body 55d is configured to close the valve seat 55b. In this case, the valve casing 54a of the check valve 54 and the valve casing 55a of the secondary air control valve 55 are shared, in other words, both the check valve and the secondary air control valve are provided in one valve casing. You can also make it into something else. Note that it is desirable that the connection opening position of the secondary air supply device 53 to the exhaust gas recirculation passage 21 be close to the connection part of the recirculation passage 21 to the exhaust system, since this is likely to be affected by exhaust pulsation.

In this configuration, in the operating range where the throttle valve 16 is fully closed, the reflux port 39 is connected to the throttle valve 1.
Since the diaphragm chamber 24 of the recirculation control valve 19 located upstream from the recirculation control valve 6 is at approximately atmospheric pressure, the valve body 23 thereof does not open, and therefore the exhaust gas is not recirculated to the intake system. It will be in a cut state, but if you open the throttle valve 16, the reflux port 39 will open.
The negative pressure increases, and this negative pressure is transmitted to the atmosphere communication chamber 27 of the exhaust pressure regulating valve 26, and the atmosphere communication chamber 2
7 becomes a negative pressure value between the negative pressure and atmospheric pressure, while if the exhaust pressure increases, the diaphragm 29
closes the communication pipe 33, and the negative pressure in the reflux port 39 acts on the diaphragm chamber 24 of the reflux control valve 19 through the passage 36, so that the valve body 23 opens and the exhaust gas is refluxed to the intake system. Due to this reflux of exhaust gas, the negative pressure at the connection part of the secondary air supply device 53 to the reflux passage 21 becomes larger than when the reflux is cut, so that the secondary air control valve 55 communicating with the reflux passage 21 becomes larger than when the reflux is cut.
Since the valve body 55d contacts the valve seat 55b with negative pressure and closes, the secondary air is not supplied from the secondary air supply passage 53 when the exhaust gas is recirculated to the intake system, and the secondary air is not supplied. While in the cut state, the air-fuel ratio upstream of the exhaust gas purification device 8 is under the control of the exhaust sensor 18 and is feedback-controlled so as to be approximately the stoichiometric air-fuel ratio.

Then, when the throttle valve 16 is closed, the feedback to the air-fuel ratio control actuator 40 is cut off by turning on the throttle switch 17, and the air-fuel ratio of the intake air-fuel mixture becomes rich, while the exhaust gas recirculation is cut off. 2 to the reflux passage 21.
Since the negative pressure at the connection part of the secondary air supply passage 53 is smaller than when the exhaust gas is recirculated, the valve body 55d of the secondary air control valve 55 opens by the force of its spring 55e, and a non-return check is performed on the upstream side thereof. The valve 54 includes
The exhaust pulsation within the exhaust manifold 7 is transmitted, and the elastic valve plate 54d opens and closes in response to the exhaust pulsation. Therefore, when the throttle valve is closed, the air-fuel ratio of the intake air-fuel mixture becomes slightly richer than the stoichiometric air-fuel ratio, and at the same time, the exhaust gas recirculation is cut and secondary air is supplied to the exhaust system. The air-fuel ratio on the upstream side becomes approximately the stoichiometric air-fuel ratio due to the supply of secondary air. Note that there also exists a region where secondary air is supplied to the exhaust system and exhaust gas is recirculated to the intake system at the same time due to the negative pressure generated at the connection.

As described above, the present invention provides an exhaust gas recirculation system to the intake system, a secondary air supply system to the exhaust system, and an air-fuel ratio feedback system to the three-way catalyst. In a closed operating range, the air-fuel ratio of the intake air-fuel mixture is made slightly richer than the stoichiometric air-fuel ratio to stabilize idling, while secondary air is supplied to the exhaust system to achieve high purification by the three-way catalyst. By connecting the secondary air supply passage to the recirculation passage that connects the exhaust gas recirculation control valve and the exhaust system, a part of the recirculation passage can be shared with a part of the secondary air supply passage. It is only necessary to connect the exhaust gas recirculation passage, and there is no need to connect the two passages separately as in the past, which greatly simplifies the structure of the connection to the exhaust system and saves space for connection. And the number of parts for connection can be reduced.

When a part of the reflux passage is used as a part of the secondary air supply passage as described above, the present invention provides a valve in the secondary air supply passage that closes when the negative pressure in the reflux passage is large. By providing a secondary air control valve comprising a body, the supply of secondary air to the exhaust system is automatically cut off when exhaust gas is being recirculated to the intake system via the recirculation passage. Therefore, there are problems caused by simultaneously supplying secondary air in the operating range where exhaust gas is recirculated, that is, a reduction in the effect of exhaust gas recirculation.
Moreover, it is possible to reliably prevent malfunctions in air-fuel ratio feedback control.

Moreover, in the present invention, the secondary air control valve is configured to open and close in accordance with changes in the negative pressure generated at the connection portion of the secondary air supply passage to the exhaust gas recirculation passage. It is not necessary to provide the valve with an actuator for opening/closing operation using intake negative pressure or the like as in the conventional case, and the secondary air control valve can be significantly simplified and miniaturized.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an embodiment of the present invention, and Figure 2 is a diagram showing an embodiment of the present invention.
FIG. 2 is an enlarged sectional view of a secondary air supply check valve and a secondary air control valve. 1...Internal combustion engine, 3...Intake manifold, 5
... Carburetor, 7 ... Exhaust manifold, 8 ... Exhaust purification device, 21, 22 ... Reflux passage, 19 ...
Exhaust gas recirculation control valve, 26... Exhaust pressure adjustment valve, 18
... Exhaust sensor, 40 ... Air-fuel ratio control actuator, 53 ... Secondary air supply passage, 54 ... Check valve, 55 ... Secondary air control valve.

Claims (1)

[Scope of utility model registration request] A system for feedback controlling the air-fuel ratio in a carburetor so that the air-fuel ratio at a three-way catalyst in the exhaust system of an internal combustion engine becomes approximately the stoichiometric air-fuel ratio, a secondary air supply system to the exhaust system, and a part of the exhaust gas. In an internal combustion engine equipped with a system that recirculates air to the intake system, the secondary air supply passage to the exhaust system is
The secondary air supply passage is connected to the recirculation passage for exhaust gas from the exhaust system to the intake system, and the secondary air supply passage is provided with a check valve that opens and closes according to the exhaust pulsation of the exhaust system. 1. An exhaust gas purification device for an internal combustion engine, characterized in that a secondary air control valve is provided with a valve body that closes when negative pressure is large.