JPS638301B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas purification device that stabilizes the purification efficiency of a catalytic converter by controlling the amount of secondary air supplied to an intake system and an exhaust system of an engine.

A three-way catalytic converter installed in the exhaust system of an internal combustion engine removes harmful components such as HC,
In an exhaust gas purification system that attempts to simultaneously purify the three components CO and NOx, the air-fuel ratio state of the exhaust gas flowing into the three-way catalytic converter is kept within a very narrow range (hereinafter referred to as the window region) around the stoichiometric air-fuel ratio. It is desirable to control the This is because the purification efficiency of the three-way catalytic converter is best within the above-mentioned window region.

As a method for performing such air-fuel ratio control, the air-fuel ratio of the air-fuel mixture in the intake system (hereinafter referred to as the base air-fuel ratio) set by a carburetor etc. is set to the richer side than the stoichiometric air-fuel ratio, and the catalytic converter There is a method of supplying an appropriate amount of secondary air to the exhaust system upstream of the catalytic converter so that the air-fuel ratio of the exhaust gas flowing into the catalytic converter falls within the above-mentioned window region. In this case, the amount of secondary air supplied is determined by an air-fuel ratio sensor (hereinafter referred to as A/F sensor) installed in the exhaust system of the engine that detects the concentration of a specific component in the exhaust gas, such as the concentration of oxygen components. When it is detected that the air-fuel ratio state of the gas is on the rich side, the control is performed in an increasing direction, and when it is detected that the gas air-fuel ratio state is on the lean side, it is controlled in a decreasing direction.

However, in the above system,
If the air-fuel ratio setting of the air-fuel mixture in the intake system becomes unbalanced due to variations in components such as the carburetor, fuel efficiency will deteriorate, especially if the air-fuel ratio is biased towards the rich side.
Furthermore, since the amount of unburned components in the exhaust gas increases, a problem arises in that the catalytic converter is more likely to overheat.

In order to solve this problem, some of the secondary air is also supplied to the intake system to bring the air-fuel ratio of the air-fuel mixture on the intake side close to the stoichiometric air-fuel ratio, thereby improving fuel efficiency and eliminating unburned components in the exhaust gas. Systems designed to reduce this have already been proposed. However, according to this type of system, the amount of secondary air supplied to the intake system changes faithfully according to changes in the detection signal of the A/F sensor, and the degree of change is too rapid, so the intake system mixture The air-fuel ratio of the exhaust gas fluctuates significantly, and as a result, the air-fuel ratio state of the exhaust gas deviates from the above-mentioned window area of the catalytic converter, causing a deterioration in purification efficiency. The problem has been that the air-fuel mixture ratio fluctuates significantly, resulting in a significant deterioration in operating characteristics.

Therefore, the present invention solves the above-mentioned problems of the prior art, and aims to provide an exhaust gas purification device that can provide a stable purification effect and good operating characteristics even when the base air-fuel ratio fluctuates. It is said that

The features of the present invention that achieve the above-mentioned object include an exhaust gas sensor that detects the concentration of a specific component in exhaust gas, and an exhaust gas sensor that detects the concentration of a specific component in exhaust gas, and an exhaust gas sensor that detects the concentration of a specific component in the exhaust gas, and an exhaust gas sensor that detects the concentration of a specific component in the exhaust gas. an electric circuit for obtaining an air-fuel ratio discrimination signal selectively exhibiting different levels from each other and an average air-fuel ratio signal representing an average value of the air-fuel ratio discrimination signal from the detection signal of the sensor; a first secondary air supply control mechanism that controls increase or decrease in accordance with the air-fuel ratio discrimination signal; and a second secondary air supply control mechanism that controls increase or decrease in secondary air supplied to the intake system in accordance with the average air-fuel ratio signal. and a catalytic converter that purifies harmful components in the exhaust gas after the secondary air is supplied.

The present invention will be described in detail below using examples with reference to the drawings.

The figure is a schematic configuration diagram of an apparatus according to an embodiment of the present invention.

In the figure, 10 is an engine body, 12 is a carburetor, 14 is an intake manifold, 16 is an exhaust manifold, 18 is an exhaust pipe, and 20 is a three-way catalytic converter. The air-fuel mixture having an air-fuel ratio on the richer side than the stoichiometric air-fuel ratio set in the carburetor 14 is sent to a combustion chamber (not shown) of the engine 10 via the intake manifold 14 to be combusted, and then released as exhaust gas. The HC,
After the three components, CO and NOx, are purified, they are discharged to the outside.

22 is an air pump driven by the engine 10 for supplying secondary air. Air pump 22
The air discharged from the first air control valve 26 is guided to the inlet port 28 of the first air control valve 26 via the conduit 24, and a part of the air is passed through the outlet port 30 to the conduit 23 and the check valve 3.
4. The secondary air is sent via the conduit 36 to the secondary air injection port 38 opened in the exhaust manifold 16, and is injected into the exhaust manifold 16 from this port 38, and the remaining air is passed through the relief port 40 and the conduit 42. It is configured such that the air is released into the atmosphere through an air filter 44.

The first air control valve 26 has a valve body 46 that controls the opening area of its outlet port 30 and relief port 40, and the valve body 46 is connected to a diaphragm 48. The diaphragm 48 is driven upward in the drawing against the spring pressing force of the compression coil spring 52 in response to the negative pressure introduced into the diaphragm chamber 50, and the opening area of the outlet port 30 is increased by the valve body 46. Shitsutsu relief port 4
It is configured to reduce the opening area of 0.

Further, a part of the air discharged from the air pump 22 is guided to the inlet port 58 of the second air control valve 56 via the conduit 54, and is exhausted from the outlet port 60 via the check valve 62 and the conduit 64. Secondary air injection port 6 of gas recirculation (EGR) control valve 66
8 and is blown out into the intake manifold 14 through the EGR control valve 66, and the remaining air is discharged into the atmosphere from the air filter 44 through the relief port 70 and the conduit 42.

This second air control valve 56 has a valve body 72 that controls the opening area of its outlet port 60 and relief port 70, and this valve body 72 is connected to a magnetic core 74. The magnetic core 74 is driven upward in the drawing against the spring pressing force of the compression coil spring 80 in accordance with the magnitude of the current supplied to the electromagnetic coil 76 via the wire 78, and is driven upward in the figure by the valve body 60. The opening area of the relief port 70 is decreased while increasing the opening area of the port 60.

The diaphragm chamber 50 of the first air control valve 26 is connected to the port 8 of the three-way solenoid directional valve 84 via a conduit 82.
It is connected to 6. This electromagnetic switching valve 84 has a negative pressure introduction port 88 and an atmosphere intake port 90, and further has a valve body 92 that selectively opens and closes these ports 88 and 90. Valve body 92
is driven downward with respect to the figure against the spring biasing force of the compression coil spring 96 when the electromagnetic coil 94 is energized by the current supplied through the line 95, closing the atmospheric intake port 90; Open the negative pressure introduction port 88. When the electromagnetic coil 94 is not energized, it is driven upward in the drawing by the action of the spring 96, opening the atmospheric intake port 90 and closing the negative pressure introduction port 88.

Negative pressure introduction port 88 is connected to throttle 98 and conduit 100
The atmospheric air intake port 90 is opened to the atmosphere through a throttle 104 and a conduit 106, and further through an air filter 44.

The exhaust manifold 16 has an exhaust gas extraction port 108 for exhaust gas recirculation, and a portion of the exhaust gas extracted by this port 108 is passed through the EGR control valve 66 and the exhaust gas injection port 110. The air is recirculated into the intake manifold 14.

The EGR control valve 66 has a valve body 114 that opens and closes the valve port 112, and the valve body 114 is connected to the diaphragm 116. When the diaphragm 116 is not supplied with negative pressure equal to or higher than a predetermined value within the diaphragm chamber 118, the diaphragm 116 is pressed downward in the figure by the action of the compression coil spring 120, pushing down the valve body 114 and closing the valve port 112, and When negative pressure equal to or higher than a predetermined value is supplied to the diaphragm chamber 118, it is driven upward in the figure against the pressing force of the compression coil spring 120, lifting the valve body 114 and opening the valve port 112. has been done.

The diaphragm chamber 118 is located on the upstream side when the throttle valve 122 of the carburetor 12 is in the fully closed position, and is located on the downstream side when the throttle valve 122 is opened to a predetermined opening degree or more. Connected to port 124 via conduit 126 .

A back pressure regulating valve 128 is provided in the middle of the conduit 126. The back pressure regulating valve 128 is connected to the chambers 130 and 1.
32, and this diaphragm 134 has a compression coil spring 1.
A pressing force is exerted by 36 in a downward direction with respect to the figure. The back pressure regulating valve 128 has a valve port 138 that opens to the aforementioned chamber 130 in the middle of the conduit 126, and this valve port 138 is opened and closed by a valve body 140 supported on the aforementioned diaphragm 134. It is configured as follows. Diaphragm 1
34 is displaced upward in the figure against the pressing force of the compression coil spring 136 when the pressure in the chamber 132 is higher than the pressure in the chamber 130 by a predetermined value or more, and closes the valve port 138 by the valve body 140. When the pressure in the chamber 130 is not higher than the pressure in the chamber 130 by a predetermined value or more, the pressing force of the compression coil spring 136 causes the valve element 140 to be pulled away from the valve port 138 as shown in the figure to open it.

The chamber 132 of the back pressure adjustment valve 128 is the EGR control valve 6
It communicates via a conduit 146 with a control pressure chamber 144 defined between the orifice 142 of No. 6 and the valve port 112, and is configured to introduce back pressure within the pressure chamber 144. In addition, back pressure regulating valve 1
Twenty-eight chambers 130 are open to the atmosphere via a filter 148. This back pressure regulating valve 128 and orifice 142 are used to control the negative pressure in the diaphragm chamber 118 of the EGR control valve 66 so that the exhaust gas pressure (back pressure) in the control pressure chamber 144 is always maintained at a constant value close to atmospheric pressure. This serves to keep the exhaust gas recirculation ratio approximately constant.

Outlet port 60 of the aforementioned second air control valve 56
The secondary air injection port 68 that communicates with this EGR
It opens into the control pressure chamber 144 of the control valve 66 .

Secondary air injection port 1 of exhaust manifold 16
08, there is an A/F sensor 15 that detects the concentration of a specific component in the exhaust gas, such as oxygen component.
0 is set. The detection signal of this A/F sensor 150 is sent to a control circuit 154 via a line 152.

In the control circuit 154, 156 compares the detection signal of the A/F sensor 150 with the reference voltage from the reference voltage generation circuit 158, and determines whether the level of the detection signal is high or low depending on whether the level of the detection signal is higher than the reference voltage. This is a comparison circuit that selectively generates an air-fuel ratio discrimination signal. The air-fuel ratio discrimination signal from the comparison circuit 156 is sent to the drive circuit 160 and the average value calculation circuit 162.
sent to. When the air-fuel ratio determination signal is at a high level, the drive circuit 160 supplies current to the electromagnetic coil 94 of the electromagnetic switching valve 84 via the line 95;
If the level is low, refrain from doing so. The average value calculation circuit 162 generates an output corresponding to the average value of the air-fuel ratio discrimination signal, and the output is sent to the drive circuit 164 to form a current having a value corresponding to the output value. This current is in line 78
through the electromagnetic coil 76 of the second air control valve 56
is supplied to

Next, the operation of this embodiment will be explained. When the A/F sensor 150 is in the active state, it outputs a high level signal of about 0.9 V when the air-fuel ratio state of the exhaust gas is richer than the stoichiometric state, and outputs a high level signal of about 0.1 V when it is on the lean side. Each outputs a low level signal of about 0.2V. The detection signal of this A/F sensor 150 is sent to a comparison circuit 156 that can be easily configured using, for example, an operational amplifier, and a reference voltage generation circuit that can be easily configured using, for example, a constant voltage line and a dividing resistor. 0.5~0.85V set by 158
compared to a reference voltage of approximately As a result, the air-fuel ratio discrimination signal output from the comparison circuit 156 becomes a rectangular wave with a high level when the exhaust gas is in a rich atmosphere and a low level when the exhaust gas is in a lean atmosphere.
The current is applied to a drive circuit 160, which can be configured, for example, by a switch circuit using a constant current source and a transistor, to control the on/off of the current sent out via the line 95. As a result, the electromagnetic switching valve 84 operates at the negative pressure introduction port 88 when the air-fuel ratio discrimination signal is at a high level.
and close the air intake port 90.
When the level is low, the opposite operation is performed to alternately supply atmospheric pressure and negative pressure to the diaphragm chamber 50 of the first air control valve 26 according to the duty ratio of the air-fuel ratio discrimination signal. As a result, the amount of air necessary to correct the air-fuel ratio state of the exhaust gas to the stoichiometric air-fuel ratio is supplied from the air pump 22 to the conduit 24, the first air control valve 26, the conduit 32, the check valve 34, the conduit 36, and Secondary air is pumped into the exhaust manifold 16 via the secondary air injection port 38.

On the other hand, the air-fuel ratio discrimination signal outputted from the comparison circuit 156 is transmitted to the average value calculation circuit 1 which is easily constructed by, for example, an integrator with a very large integration time constant.
62, and a voltage output whose level is averaged is formed. This output is provided by a drive circuit 1 which can be easily configured by, for example, a general current amplifier.
64 , a current having a value depending on its output voltage is created and fed via line 78 to the electromagnetic coil 76 of the second air control valve 56 . As a result, the second air control valve 56 controls the opening area of the outlet port 60 to increase or decrease in an analog manner according to the supplied current, and as a result, the air pump 22 connects the conduit 54 to the second air control valve 56, Check valve 6
2. The amount of secondary air sent into the control pressure chamber 144 of the EGR control valve 66 via the conduit 64 and the secondary air injection port 68 is controlled to increase or decrease according to the average value of the air-fuel ratio discrimination signal.

However, when the throttle valve 122 is in the fully closed position as shown in the figure, the intake pipe negative pressure does not act on the intake pipe negative pressure outlet port 124 and atmospheric pressure appears substantially, so the EGR control valve 66 The valve is closed, so that in this case, that is, during idling and deceleration operation, there is no recirculation of exhaust gas and no secondary air supply to the intake manifold 14.

When the throttle valve 122 is opened beyond the intake pipe negative pressure extraction port 124 and intake pipe negative pressure comes to act on that port 124, the EGR control valve 6
Negative pressure is introduced into the diaphragm chamber 118 of No. 6,
This opens the EGR control valve 66 and exhaust gas recirculation is performed. In this case, the secondary air supplied to the control pressure chamber 144 via the second air control valve 56 is injected into the intake manifold 14 via the exhaust gas injection port 110 together with the recirculated exhaust gas, and the mixture on the intake side is The air-fuel ratio of air is corrected.

As described above, in the device of the present invention, the amount of secondary air supplied to the intake system of the engine is controlled according to the average value of the air-fuel ratio discrimination signal, so the fluctuation in the amount of secondary air supplied is gradual; Therefore, even when the base air-fuel ratio changes, it is possible to prevent the air-fuel ratio of the intake system mixture from changing greatly and, as a result, the air-fuel ratio of the exhaust gas to go outside the window area of the catalytic converter. Since the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is stabilized, deterioration of operating characteristics can be prevented.

Furthermore, when the secondary air supply amount to the intake system is controlled based on the average value of the air-fuel ratio discrimination signal as in the device of the present invention, variations in the average value of the set air-fuel ratio of the carburetor and changes in the air-fuel ratio due to changes over time can be avoided. Automatic compensation can be done. As mentioned above, this improves fuel efficiency and prevents overheating of the catalytic converter. In addition, similar to the above-mentioned carburetor variations, it is possible to automatically correct deviations in the air-fuel ratio when the engine is operated at high altitudes and deviations in the air-fuel ratio due to the driver's habits.

If secondary air is supplied to the intake system via the exhaust gas recirculation passage, a portion of the recirculated exhaust gas will be replaced with secondary air, reducing the amount of exhaust gas recirculated. However, when the air-fuel mixture is enriched, exhaust gas in excess of the required amount is prevented from being recirculated, and deterioration of engine operating characteristics due to exhaust gas recirculation is reduced.

In the above-mentioned embodiment, the second air control valve controls the opening area of the outlet port according to the input current and controls the amount of air passing therethrough in an analog manner. It may be configured to control the on/off duty ratio of an on/off control type solenoid valve. Moreover, various circuits other than the integrator can be applied as the average value calculation circuit.
For example, the same effect can be obtained by using an up-down counter, a clock pulse generator, and a D/A converter and switching the up-down count instruction based on the air-fuel ratio discrimination signal.

As described above in detail, the exhaust gas purification device of the present invention has the special effect of providing a stable exhaust gas purification effect and good operating characteristics even when the base air-fuel ratio fluctuates.

[Brief explanation of the drawing]

The figure is a schematic configuration diagram of an embodiment of the present invention. 10... Engine body, 12... Carburetor, 14... Intake manifold, 16... Exhaust manifold, 20
...Three-way catalytic converter, 22...Air pump, 2
6, 56...Air control valve, 66...EGR control valve, 8
4...Three-way electromagnetic switching valve, 150...A/F sensor, 1
54...Control circuit, 156...Comparison circuit, 158...Reference voltage generation circuit, 160, 164...Drive circuit, 1
62...Average value calculation circuit.

Claims (1)

[Claims] 1. An exhaust gas sensor that detects the concentration of specific components in exhaust gas, and an air-fuel ratio that selectively exhibits different levels depending on whether the air-fuel ratio state of the engine is richer or leaner than a predetermined air-fuel ratio state. an electric circuit that obtains a determination signal and an average air-fuel ratio signal representing an average value of the air-fuel ratio determination signal from the detection signal of the sensor; a secondary air supply control mechanism; a second secondary air supply control mechanism that controls increasing or decreasing the secondary air supplied to the intake system according to the average air-fuel ratio signal; and an exhaust gas after supplying the secondary air. An exhaust gas purification device for an internal combustion engine, characterized by comprising a catalytic converter that purifies harmful components in gas.