JPH06200748A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Purpose] Without affecting the air-fuel ratio control of the engine,
The air-fuel ratio at the inlet of the three-way catalyst during the HC desorption process is controlled. [Structure] When the engine is cold immediately after starting, the exhaust gas is diverted to the sub passage 9 by the change-over valves 11 and 12 and is circulated through the adsorbent 10 to adsorb HC in the exhaust gas. After switching the switching valves 11 and 12 after completion of warming up, air is supplied to the adsorbent 10 by the air pump 13 to desorb HC, and the air containing this HC is introduced upstream of the three-way catalyst 7. Here, the fuel injection amount by the fuel injection valve 5 is controlled by the first control unit 16 based on a signal from the first oxygen sensor 19 mounted upstream of the three-way catalyst 7 and upstream of the air introduction position.
In addition, the second oxygen sensor 22 installed downstream of the three-way catalyst 7
The second control unit 20 controls the amount of air supplied by the air pump 13 based on the signal from the.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to adsorbing hydrocarbons (hereinafter referred to as "HC") in exhaust gas to an adsorbent when the engine is cold and desorbing the hydrocarbon after completion of warming up. The present invention relates to an exhaust gas purification device that is processed by a method.

[0002]

2. Description of the Related Art Immediately after starting an internal combustion engine, a relatively large amount of HC is contained in the exhaust gas from the engine, and the temperature of the three-way catalyst does not reach the activation temperature, so it is difficult to purify the HC. For this reason, for example, in the exhaust gas purifying apparatus disclosed in Japanese Patent Laid-Open No. 55-101715 and Japanese Utility Model Laid-Open No. 2-67020, an auxiliary gas is provided in parallel with the main passage of the exhaust passage upstream or downstream of the three-way catalyst in the exhaust passage. A passage is provided, and an HC adsorbent is provided in this sub passage, while a valve device for controlling the flow of exhaust gas to the main passage and the sub passage is provided to guide the exhaust gas to the sub passage side when the engine is cold. H in the exhaust that is passed through the adsorbent
C is adsorbed on the adsorbent. And after warming up,
The flow of exhaust gas to the adsorbent is stopped, air is supplied to the adsorbent by an air pump to desorb HC, and the desorbed H
Air containing C is introduced upstream of the three-way catalyst to be purified by the three-way catalyst.

[0003]

However, in such a conventional exhaust gas purification apparatus for an internal combustion engine, since the air pump for desorption processing is only ON / OFF control, the air pumped by the air pump and the adsorbed air are adsorbed. Since the ratio with the HC desorbed from the material does not become the stoichiometric air-fuel ratio, there is a problem in that the three-way catalyst does not necessarily perform good purification of HC.

Of course, an oxygen sensor is mounted upstream of the three-way catalyst (exhaust manifold section) in the exhaust passage to detect the air-fuel ratio and feedback control the fuel supply amount to the engine. Since the position is upstream of the position where the air is introduced from the air pump, the air-fuel ratio at the inlet of the three-way catalyst cannot be controlled by this. Also,
It is also possible to control the air-fuel ratio at the inlet of the three-way catalyst by mounting an oxygen sensor upstream of the three-way catalyst and downstream of the position where the air is introduced from the air pump to feedback control the amount of fuel supplied to the engine. However, the air-fuel ratio in the cylinder deviates from the stoichiometric air-fuel ratio, resulting in large torque fluctuation.

In view of the above conventional problems, the present invention can control the air-fuel ratio at the three-way catalyst inlet during the HC desorption process without affecting the air-fuel ratio control of the engine intake air-fuel mixture. The purpose is to do so.

[0006]

Therefore, according to the present invention, when the engine is cold, the exhaust gas is bypassed from the exhaust passage to be guided to the adsorbent so that the hydrocarbon in the exhaust is adsorbed by the adsorbent. An internal combustion engine equipped with a device and a desorption treatment device that supplies air to an adsorbent by an air pump after decommissioning to desorb hydrocarbons and introduces air containing the hydrocarbons upstream of the three-way catalyst in the exhaust passage. In an exhaust emission control device for an engine, a first oxygen sensor that is mounted upstream of a three-way catalyst in an exhaust passage and upstream of an air introduction position to detect oxygen concentration, and a signal from the first oxygen sensor are used. A fuel supply amount control device for controlling the fuel supply amount to the engine is provided, while a second oxygen sensor mounted downstream of the three-way catalyst in the exhaust passage to detect the oxygen concentration, and the second oxygen sensor.
And an air pump controller for controlling the amount of air supplied by the air pump based on the signal from the oxygen sensor.

[0007]

In the above structure, the fuel supply amount to the engine is controlled based on the signal from the first oxygen sensor mounted upstream of the three-way catalyst in the exhaust passage and upstream of the air introduction position. As a result, the air-fuel ratio in the cylinder can be controlled without being affected by the amount of air supplied from the air pump.

On the other hand, by controlling the amount of air supplied by the air pump based on the signal from the second oxygen sensor mounted downstream of the three-way catalyst in the exhaust passage, the air-fuel ratio at the three-way catalyst inlet can be controlled appropriately. Therefore, the separated HC can be effectively purified.

[0009]

EXAMPLES Examples of the present invention will be described below. FIG. 1 shows the system configuration of an embodiment. Air is drawn into the combustion chamber of each cylinder of the engine 1 from the air cleaner 2 through the throttle valve 3 and the intake manifold 4. An electromagnetic fuel injection valve 5 is provided in each branch portion of the intake manifold 4, and an air-fuel mixture is generated by the fuel injected from each fuel injection valve 5 and burns in the combustion chamber.

Exhaust gas from the engine 1 is exhausted from an exhaust manifold 6
To the three-way catalyst 7. On the downstream side of the three-way catalyst 7, the exhaust passage is branched into a main passage 8 and a sub passage 9, and an HC adsorbent 10 containing activated carbon or zeolite as a main component is interposed in the sub passage 9. . And the main passage 8
Further, a first switching valve 11 is provided at a branch portion to the auxiliary passage 9 and a second switching valve 12 is provided at a confluence portion from the main passage 8 and the auxiliary passage 9.

Further, an electric air pump 13 is provided,
A purge air passage 14 from the discharge port is connected to the exhaust outlet side of the adsorbent 10. A purge air passage 15 from the exhaust inlet side of the adsorbent 10 is connected upstream of the three-way catalyst 7. The sub passage 9, the adsorbent 10, the first and second switching valves 1
An HC adsorbing device is configured by 1 and 12, an air pump 13,
The purge air passages 14 and 15 constitute a desorption processing device.

Here, the operation of the fuel injection valve 5 is controlled by a first control unit 16 incorporated in a microcomputer.
Air flow meter 17 for detecting the intake air flow rate Q of the engine 1
And a signal from a crank angle sensor 18 that outputs a rotation signal of the engine 1 and can indirectly detect the engine rotation speed N.
A signal from the oxygen sensor 19 is input.

The first oxygen sensor 20 is mounted upstream of the three-way catalyst 7 in the exhaust passage and upstream of the position where the air is introduced from the air pump 13 (the opening of the purge air passage 15). In addition, the first and second switching valves 11 and 12, the air pump
The operation of 13 is controlled by a second control unit 20 with a built-in microcomputer. This second control unit 20 has a second oxygen sensor in addition to a signal from an adsorbent temperature sensor 21 for detecting the temperature Ta of the adsorbent 10. The signal from 22 is input.

The second oxygen sensor 22 is mounted downstream of the three-way catalyst 7 in the exhaust passage. The first control unit 16 constitutes a fuel supply amount control device, and the second control unit 20 constitutes a controller of the HC adsorption device and desorption treatment device and also serves as an air pump control device.

FIG. 2 is a flow chart of a fuel injection amount calculation routine executed by the first control unit 16 at predetermined time intervals. In step 1 (denoted as S1 in the drawing; the same applies hereinafter), the intake air flow rate Q is detected based on the signal from the air flow meter 17. In step 2,
The engine speed N based on the signal from the crank angle sensor 18
To detect. Then, in step 3, the intake air flow rate Q
And the engine speed N, the basic fuel injection amount Tp = K × Q / N
(K is a constant) is calculated.

In step 4, the output voltage V ₁ of the first oxygen sensor 19 is read. In step 5, this output voltage V ₁
Is compared with a predetermined value (for example, 400 mV) to determine rich / lean. When rich (V ₁ > 400 mV), the routine proceeds to step 6, where the air-fuel ratio feedback correction coefficient α is decreased by a predetermined amount Δα. If lean, the routine proceeds to step 7, where the air-fuel ratio feedback correction coefficient α is increased by a predetermined amount Δα.

In step 8, the fuel injection amount Ti = from the basic fuel injection amount Tp and the air-fuel ratio feedback correction coefficient α.
Calculate Tp × α. When the fuel injection amount Ti is calculated in this way, the drive pulse signal having the pulse width of Ti is output to the fuel injection valve 5 at a predetermined timing synchronized with the engine rotation, and fuel injection is performed.

FIG. 3 is a flow chart of the adsorption / desorption control routine executed by the second control unit 20 when the engine is started. In step 11, the temperature Ta of the adsorbent 10 is detected based on the signal from the adsorbent temperature sensor 21. In step 12, it is judged whether or not the adsorbent temperature Ta exceeds 200 ° C. If it is 200 ° C. or less, the adsorbent has a adsorption capacity, so the process proceeds to step 13.

In step 13, the first and second switching valves 11,
By 12, the exhaust gas from the three-way catalyst 7 is diverted to the sub passage 9 to flow to the adsorbent 10. After this, the process returns to step 11. Therefore, even if a large amount of HC is contained in the exhaust gas because the three-way catalyst 7 is inactive immediately after the engine is cold,
This HC is adsorbed by the adsorbent 10 and prevented from being released into the atmosphere.

When the adsorbent temperature Ta exceeds 200 ° C., the adsorption capacity is lost, and at this time, the three-way catalyst 7 is sufficiently activated.
Proceed to 14. In step 14, the first and second switching valves 11, 12 are
The exhaust gas from the three-way catalyst 7 is discharged through the main passage 8 without being diverted to the sub passage 9.

In step 15, the driving of the air pump 13 is started for the desorption process of the HC adsorbed on the adsorbent 10. As a result, the air from the air pump 13 is supplied to the adsorbent 10 by the purge air passage 14 and the HC adsorbed therein is desorbed, and the air containing the desorbed HC is removed by the purge air passage 15 by the three-way catalyst. It is introduced upstream of 7 and purified by the three-way catalyst 7. In this way, in the method of desorbing HC from the adsorbent 10 with the air from the air pump 13, complete desorption can be performed without exceeding the heat resistant temperature of the adsorbent 10 during desorption.

In step 16, the output voltage V ₂ of the second oxygen sensor 22 is read. In step 17, this output voltage V ₂
Is compared with a predetermined value to determine rich lean. If rich, the routine proceeds to step 18, where the air supply amount by the air pump 13 is increased. If lean, proceed to step 19 to reduce the amount of air supplied by the air pump 13.

Thus, the signal from the second oxygen sensor 22,
That is, the air-fuel ratio at the inlet of the three-way catalyst 7 is detected from the oxygen concentration on the downstream side of the three-way catalyst 7, and the air-fuel ratio at the inlet of the three-way catalyst 7 is constant during the desorption process of HC by air from the air pump 13. The air supply amount of the air pump 13 is controlled to increase or decrease such that The increase / decrease control of the air supply amount of the air pump 13 may be performed by controlling the drive voltage to the air pump 13 by duty control.

In step 20, the temperature Ta of the adsorbent 10 is detected based on the signal from the adsorbent temperature sensor 21. In step 21, it is judged whether or not the adsorbent temperature Ta is lower than 100 ° C., and when it is 100 ° C. or higher, the process returns to step 16 and the desorption process of HC is performed while controlling the air supply amount of the air pump 13. I do. When the adsorbent temperature Ta becomes less than 100 ° C, the determination in step 21 proceeds to step 22 and the air pump
Stop 13 and complete the desorption process. Adsorbent 10 to H
This is because the adsorbent temperature Ta drops to around 100 ° C. when C is completely desorbed.

According to the present embodiment, since the adsorbent 10 and the like are arranged downstream of the three-way catalyst 7, it becomes possible to bring the three-way catalyst 7 and the second oxygen sensor 22 close to the engine 1, and these early activations can be performed. Can be realized. FIG. 4 shows another embodiment. In this embodiment, the adsorbent 10 and the like are arranged upstream of the three-way catalyst 7.

That is, the exhaust gas from the engine 1 reaches the three-way catalyst 7 through the exhaust manifold 6, and on the upstream side of the three-way catalyst 7, the exhaust passages are in parallel with each other in the main passage 8.
And the sub-passage 9, and an HC adsorbent 10 containing activated carbon or zeolite as a main component is interposed in the sub-passage 9. A switching valve 11 is provided at a branch portion to the main passage 8 and the sub passage 9.

The purge air passage 14 from the discharge port of the electric air pump 13 is connected to the exhaust inlet side of the adsorbent 10. Therefore, when cold immediately after starting, the switching valve
By 11, the exhaust gas from the engine 1 is diverted to the sub-passage 9 and circulated to the adsorbent 10, and the HC in the exhaust gas is adsorbed by the adsorbent 10, and then the exhaust gas is guided to the three-way catalyst 7. After warming up,
By switching the switching valve 11, the exhaust gas from the engine 1 is guided to the three-way catalyst 7 through the main passage 8 without being diverted to the sub passage 9. Then, for the desorption process of HC, the air from the air pump 13 is made to flow into the adsorbent 10 from the inlet side of the sub-passage 9 by the purge air passage 14 to desorb the HC, and the air containing this HC is adsorbed to the sub-passage 9. It is introduced upstream of the three-way catalyst 7 from the outlet side of.

The control is the same, and a signal from the first oxygen sensor 19 mounted upstream of the three-way catalyst 7 in the exhaust passage and upstream of the air introduction position (merging portion of the sub passage 9) is sent to the control unit 16. After the input, the fuel injection amount by the fuel injection valve 5 is controlled as shown in the flowchart of FIG. Further, a signal from the second oxygen sensor 22 mounted downstream of the three-way catalyst 7 in the exhaust passage is input to the control unit 20 to control the air supply amount and the like by the air pump 13 as shown in the flowchart of FIG.

According to the present embodiment, the adsorbent 10 is provided upstream of the three-way catalyst 7 and the air is pumped from the air pump 13 to the upstream of the adsorbent 10. Since the flow direction of the purge air is the same, it is possible to prevent pressure loss due to flow reversal during switching of the switching valve. Further, since only one switching valve is required and the number of pipes and the like is reduced, the structure can be simplified.

[0030]

As described above, according to the present invention, H
Torque fluctuations can be prevented without affecting the air-fuel ratio control of the engine during the desorption process of C, and the air-fuel ratio at the inlet of the three-way catalyst can be controlled with high precision, and exhaust purification performance can be greatly improved. The effect is obtained.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart of a fuel injection amount calculation routine.

FIG. 3 Flow chart of adsorption / desorption control routine

FIG. 4 is a system configuration diagram showing another embodiment.

[Explanation of symbols]

 1 engine 5 fuel injection valve 6 exhaust manifold 7 three-way catalyst 8 main passage 9 auxiliary passage 10 adsorbent 11 first switching valve 12 second switching valve 13 air pump 14, 15 purge air passage 16 first control unit 17 air flow meter 18 crank angle Sensor 19 First oxygen sensor 20 Second control unit 21 Adsorbent temperature sensor 22 Second oxygen sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location F01N 3/24 R F02D 41/14 310 F 8011-3G

Claims (1)

[Claims] 1. A hydrocarbon adsorbing device for adsorbing hydrocarbons in the exhaust gas by adsorbing the hydrocarbons in the exhaust gas by diverting and guiding the exhaust gas from an exhaust passage when the engine is cold, and air by an air pump after warming up. An exhaust gas purification device for an internal combustion engine, comprising: a desorption treatment device that supplies hydrocarbons to the adsorbent to desorb hydrocarbons and introduce air containing the hydrocarbons upstream of the three-way catalyst in the exhaust passage. A first oxygen sensor that is mounted upstream of the original catalyst and upstream of the air introduction position to detect the oxygen concentration, and fuel supply that controls the fuel supply amount to the engine based on the signal from the first oxygen sensor. A second oxygen sensor mounted downstream of the three-way catalyst in the exhaust passage to detect the oxygen concentration, and an air pump based on a signal from the second oxygen sensor. Exhaust purification system of an internal combustion engine, characterized by comprising a pump control device for controlling the supply amount.