JPH0472975B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine exhaust purification device that purifies exhaust gas by providing a catalyst in an exhaust passage of the engine.

(Prior Art) In order to promote the chemical reaction of exhaust gas within the catalyst, the above-mentioned catalyst needs to be maintained at a high temperature that activates the catalyst. The catalyst is supplied with air to promote the combustion of exhaust gas, and the heat of combustion raises the temperature of the catalyst, but since the catalyst deteriorates over time, for example, the supply of secondary air described above is In anticipation of deterioration over time, we supply a higher initial value.

For this reason, at the beginning of the catalyst's use, more purification than necessary occurs.
That is, there are problems in that excessive combustion occurs, and that the temperature of the catalyst must be maintained at a higher temperature than necessary, which causes deterioration over time to occur more quickly.

In addition, there is a conventional catalyst device that increases the exhaust gas contact area on the exhaust gas introduction side of the catalyst when the engine is under high load (for example, Japanese Patent Application Laid-open No. 10018/1983), but in the case of this device, it is partially shielded, so Deterioration of other parts that are not shielded has the same problem as the previous case, which occurs quickly.

(Object of the invention) The object of the invention is to suppress aging deterioration of a catalyst,
An object of the present invention is to provide an engine exhaust purification device that can obtain an effective purification rate over a long period of time.

(Structure of the Invention) The present invention provides an engine control system that controls the air-fuel ratio of the air-fuel mixture supplied to the engine and increases the amount of secondary air when the total operating time of the engine exceeds a predetermined value. It is characterized by being an exhaust purification device.

(Effect of the invention) According to the invention, by supplying the minimum required amount of secondary air to the catalyst until the total operating time of the engine reaches a predetermined value, the exhaust gas is not burned excessively by the catalyst. In other words, the heat load on the catalyst is lowered to prevent early catalyst deterioration, and once the total operating time of the engine reaches a predetermined value, combustibility is increased by enriching the air-fuel ratio and increasing the amount of secondary air. In other words, by increasing the heat load, it is possible to reduce the rate of decrease in the purification rate of the catalyst after its durability, thereby making it possible to effectively purify exhaust gas and obtain long-term use.

(Example) An example of the present invention will be described in detail below based on the drawings.

The drawing shows an engine exhaust purification device. In FIG. 1, an engine 1 includes a cylinder 2, a piston 3, and a cylinder head 4.
An intake passage 5 and an exhaust passage 6 are connected to the intake passage 5 and the exhaust passage 6.

A first air cleaner 7 is provided at the upstream end of the above-mentioned intake passage 5, and a carburetor 8 is provided downstream thereof, and the carburetor 8 adjusts the air-fuel ratio of the air-fuel mixture supplied to the engine 1. An actuator 9 consisting of a solenoid valve is provided, and this actuator 9 is provided on the upstream side of the aforementioned exhaust passage 6, and is based on an output signal of an O2 sensor 10 that outputs a signal corresponding to the oxygen concentration in the exhaust gas. The drive is controlled by the air-fuel ratio control circuit 11.

A three-way catalyst 12 for purifying exhaust gas from the engine 1 is disposed downstream of the exhaust passage 6 described above.
This catalyst 12 is provided with a catalyst temperature sensor 13 that detects the temperature of this catalyst 12.

A secondary air supply passage 14 for supplying secondary air to the catalyst 12 is opened in the exhaust passage 6 on the upstream side of the catalyst 12, and a second air cleaner 15 is provided at the upstream end of this passage 14. An air pump 16 is disposed downstream of this, and this air pump 16
is driven by a motor 17.

A branch passage 18 is formed in the passage 14 downstream of the air pump 16 described above, and this branch passage 18 opens to the exhaust passage 6 near the upstream of the O2 sensor 10 described above. A linear solenoid valve 19 that is driven proportionally to open and close the passage 18 is provided, and secondary air proportional to the opening amount of the valve 19 is supplied to the O2 sensor 10 to richly adjust the air-fuel ratio.

The aforementioned motor 17 and linear solenoid valve 19 are controlled by a secondary air control circuit 20, and this control is performed by the aforementioned catalyst temperature sensor 13, water temperature sensor 21, negative pressure sensor 22, rotation sensor 23,
This is done based on the output signal from the total travel distance sensor 24.

The above-mentioned water temperature sensor 21 detects the temperature of the cooling water of the engine 11 and outputs a water temperature signal, the negative pressure sensor 22 detects the intake negative pressure in the intake passage 5 and outputs a negative pressure signal, and the rotation sensor 23 detects the intake air negative pressure in the intake passage 5 and outputs a negative pressure signal. The rotation of the crankshaft (not shown) of the engine 1 is detected and a rotation signal is output, and the total mileage sensor 24 detects the total mileage of the automobile and outputs a total mileage signal.

FIG. 2A is a characteristic diagram showing the relationship between the operating state of the engine 1 and the supply amount of secondary air, and is a characteristic diagram showing the relationship between the operating state of the engine 1 and the supply amount of secondary air.
D indicates the area that requires the same amount of secondary air supply, and the supply amount is as follows in the low load and low rotation area.
By increasing the amount of secondary air in accordance with the increase in displacement, the exhaust gas purifying action of the catalyst 12 is made effective, and in the high-load, high-speed region, the amount of secondary air is also reduced and the amount of secondary air is increased. By suppressing the heating of
Region A, so as to improve the durability of the catalyst 12;
The amount of secondary air supplied increases in the order of B, C, and D.

Note that region E is a region where the supply of secondary air is stopped. The amount of secondary air supplied in each region A to D is stored in a map of the memory, which will be described later, in correspondence with the operating state of the engine 1.

FIG. 3 shows details of the secondary air control circuit 20 described above. Since the aforementioned catalyst 12 deteriorates over time due to use, it is necessary to increase the purification rate over time. This purification rate can be increased by increasing combustion in the catalyst 12 and activating the catalyst 12, and by supplying a large amount of unburned fuel to the catalyst 12.

On the other hand, the age of the catalyst 12 can be replaced by the total operating time of the engine 1, and this total operating time can also be replaced by the total distance traveled by the vehicle.

The memory 25 stores a coefficient K2 corresponding to the total distance traveled.
is stored, and this coefficient K2 increases the fuel supplied to the catalyst 12 as it ages, and as shown in Figure 2 C, initially the coefficient K2 is
K2 is set to 1 and increases in proportion to the longer the total distance traveled.

The coefficient calculation circuit 26 reads out the coefficient K2 corresponding to the output signal from the total mileage sensor 24 from the memory 25, and the applied voltage calculation circuit 27 reads out the coefficient K2 corresponding to the output signal from the total mileage sensor 24.
An applied voltage value for driving the linear solenoid valve 19 is calculated based on K2, and the linear solenoid valve 19 is driven by this applied voltage value via the linear solenoid valve driving circuit 28.

When the above-mentioned linear solenoid valve 19 is driven, the above-mentioned branch passage 18 is opened in response to aging of the catalyst 12, and the air pump 16 is driven by secondary air corresponding to the opening amount under the control described below. As a result, it is supplied to the upstream side of the O2 sensor 10.

The above-mentioned O2 sensor 10 detects that the air-fuel ratio is leaner than the air-fuel ratio before the secondary air is supplied due to the supply of secondary air, so this detection signal is used to control the air-fuel ratio. By being input to the circuit 11, the control circuit 11 controls the actuator 9 of the carburetor 8 so that the air-fuel ratio becomes richer than the air-fuel ratio before the secondary air is supplied.
control.

As a result, a large amount of unburned fuel is supplied to the exhaust gas as the catalyst 12 deteriorates over time.

Drive control of the motor 17 for supplying secondary air is performed in accordance with the operating state of the engine 1. That is, the basic control signal generation circuit 29 determines the operating state of the engine 1 based on the intake negative pressure signal from the negative pressure sensor 22 and the engine rotation signal from the rotation sensor 23.

On the other hand, the secondary air supply amount is stored in the map 30 in correspondence with the operating ranges A to D shown in FIG.
Map 3 the secondary air supply amount in the determined operating state.
It reads out from 0 and generates a control signal corresponding to the read supply amount.

On the other hand, when the temperature of engine 1 is low, map 3
If secondary air is supplied with the value of the secondary air supply amount set to 0, the combustibility at the catalyst 12 will decrease and the purification rate will decrease. Therefore, when the temperature of the engine 1 cooling water is below the set temperature t0, the coefficient K1 is set so that the amount of secondary air supplied increases as the water temperature decreases.
As shown in FIG. 2B, this coefficient K1 is set to a value of 1 when the temperature is above the set temperature t0, and increases in proportion to the lower water temperature below it.

The function circuit 31 stores the above-mentioned coefficient K1 as a function of water temperature, and outputs a control signal corresponding to the coefficient K1 based on the water temperature signal from the water temperature sensor 21.

The arithmetic circuit 32 is the basic control signal generation circuit 2 at the previous stage.
A control signal corresponding to the basic supply amount of secondary air calculated in step 9 is determined based on a correction signal corresponding to the coefficient K1 outputted from the function circuit 31, and the gate circuit 33 and the drive circuit are controlled by this corrected control signal. The motor 17 is driven and controlled via 34.

By driving the motor 17 in accordance with the operating state of the engine 1, the air pump 16 supplies the necessary amount of secondary air to the catalyst 12 via the secondary air supply passage 14, and the catalyst 12 supplies the required amount of secondary air to the catalyst 12 from this passage 14. The exhaust gas is combusted and purified by the supplied secondary air and the secondary air corresponding to the total traveling distance supplied from the branch passage 18 described above.

Since the catalyst 12 burns out if the temperature becomes too high due to the above-described combustion, it is necessary to temporarily stop combustion of exhaust gas when the temperature exceeds a set temperature.

The set voltage generation circuit 35 generates a voltage corresponding to the above-mentioned set temperature, and the comparison circuit 36 compares this set voltage with the voltage of the temperature detection signal from the catalyst temperature sensor 13, so that the temperature of the catalyst 12 is set. When the temperature exceeds the temperature, a signal is generated from the comparator circuit 36 to close the gate circuit 33 described above. Therefore, motor 1
7 is not driven, and therefore secondary air is not supplied to the catalyst 12, combustion is stopped, excessive combustion of exhaust gas by the catalyst 12 is prevented, and burnout of the catalyst 12 is prevented.

The exhaust purification device configured in this way has a catalyst 12.
The age of use is detected by the total mileage of the vehicle, a coefficient K2 proportional to the age of use is set to an initial value of 1, and the air-fuel ratio control circuit 11 is controlled to enrich the air-fuel ratio in accordance with the age. At the same time, the branch passage 18
The deterioration of the catalyst 12 over time is dealt with by adding the secondary air supplied from the secondary air supply passage 14 corresponding to the age of the catalyst 12 to the basic secondary air supplied from the secondary air supply passage 14.

At this time, the basic amount of secondary air for each of the operating ranges A to D stored in the map 30 does not need to be set in anticipation of aging deterioration of the catalyst 12, and may be set to the minimum necessary amount.

As a result, as shown in FIG. 4, the catalyst 12 has a high initial purification rate, although it decreases after durability.
In order to suppress the high purification rate to the minimum necessary purification rate, the decrease in the purification rate after durability can be reduced as shown by the arrow, and the deterioration will take longer over time, resulting in a longer service life.

In the above-described embodiment, the age of the catalyst 12 is measured based on the total distance traveled by the vehicle, but the total operating time of the engine 1 may also be measured.

Furthermore, although the secondary air control circuit 20 has been shown to be configured using an analog computer, the circuit 20 may also be configured using a digital computer.

In addition, when the total travel distance is equal to or greater than a predetermined value, the amount of secondary air supplied from the secondary air supply passage may be increased.

In addition, the increase rate of the secondary air is smaller than the fuel increase rate when the catalyst is a reduction catalyst, equal to the fuel increase rate when the catalyst is a three-way catalyst, and lower than the fuel increase rate when the catalyst is an oxidation catalyst. If it is made larger, the reaction in each catalyst can be maintained well.

In the reaction between the structure and the embodiment of this invention, the secondary air supply device includes the secondary air supply passage 14, the second
Air cleaner 15, air pump 16, motor 1
7, and the secondary air control circuit 20, the engine total operating time detection means is the total mileage sensor 2.
4, the air-fuel ratio adjusting means corresponds to the carburetor 8 and the actuator 9, and the secondary air adjusting means corresponds to the motor 17, which is controlled by the secondary air control circuit 20.
Linear solenoid valve 19 and motor 17
The control circuit corresponding to the air pump 16 driven by
7. Corresponds to the linear solenoid valve drive circuit 28.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a block diagram of an engine exhaust purification device. Figure 2 A, B,
C is the characteristic of the secondary air supply amount in the engine operating region,
A diagram showing the characteristics of coefficients K1 and K2. Figure 3 is a block diagram of the secondary air control circuit. FIG. 4 is a diagram showing aging deterioration of the catalyst. 1...Engine, 6...Exhaust passage, 10...
O2 sensor, 11... Air-fuel ratio control circuit, 12...
Catalyst, 14... Secondary air supply passage, 16... Air pump, 17... Motor, 18... Branch passage, 1
9... Linear solenoid valve, 20... Secondary air control circuit, 22... Negative pressure sensor, 23... Rotation sensor, 24... Total mileage sensor, 26... Coefficient calculation circuit, 29... Basic control signal Generation circuit, 3
0...Matsupu.

Claims (1)

[Claims] 1. A catalyst disposed in an exhaust passage of an engine to purify exhaust gas; a secondary air supply device supplying secondary air to the exhaust passage upstream of the catalyst; and a total operating time of the engine. a total engine operation time detection means for detecting the total engine operation time; an air-fuel ratio adjustment means for adjusting the air-fuel ratio of the air-fuel mixture supplied to the engine; a secondary air adjustment means for adjusting the amount of secondary air; In response to the output of the time detection means, when the total operating time of the engine exceeds a predetermined value, the air-fuel ratio adjustment means is controlled to enrich the air-fuel ratio of the air-fuel mixture, and the secondary air is controlled to increase the amount of secondary air. 1. An engine exhaust purification device comprising: a control means for controlling an air adjustment means.