JP2850657B2 - Exhaust gas purification device for internal combustion engine - Google Patents

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 a method for adsorbing hydrocarbons (hereinafter referred to as "HC") in exhaust gas when the engine is cold, and desorbing the hydrocarbons after completion of warm-up. The present invention relates to an exhaust gas purifying apparatus configured to perform treatment.

[0002]

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

[0003]

However, in such a conventional exhaust gas purifying apparatus for an internal combustion engine, the air pump for the desorption process is only ON / OFF controlled, so that the air pumped from the air pump adsorbs the air. Since the ratio of HC desorbed from the material does not become the stoichiometric air-fuel ratio, there has been a problem that the three-way catalyst does not necessarily purify HC.

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

In view of the above-mentioned 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. In addition, the adsorbent
The purpose is to be able to control appropriately according to the wearing ability
And

[0006]

[SUMMARY OF To this end, the present invention is discharged
A HC adsorbing device for adsorbing the adsorbent to HC in the exhaust gas is circulated to the adsorbent leading to bypass the exhaust from the gas passage, et
In the exhaust purification system of an internal combustion engine and a desorption apparatus for introducing the air containing the HC was the HC is supplied to the adsorbent desorbing upstream of the three-way catalyst in the exhaust passage of air by Aponpu, the suction Adsorbent temperature sensor to detect material temperature
After the engine is started, the adsorbent temperature is set to the first predetermined temperature.
The HC adsorber is operated until the temperature exceeds
After the temperature exceeds the first predetermined temperature, the temperature becomes lower than the first predetermined temperature.
The desorption treatment apparatus until the temperature falls below a second predetermined temperature.
A first oxygen sensor mounted upstream of the three-way catalyst and upstream of the air introduction position in the exhaust passage to detect oxygen concentration, and an engine based on a signal from the first oxygen sensor. while providing a fuel supply amount control apparatus for controlling the amount of fuel supplied to a second oxygen sensor which detects an oxygen concentration is mounted downstream of the three-way catalyst in the exhaust passage, this upon actuation of the desorption apparatus An air pump control device that controls the amount of air supplied by the air pump based on a signal from the second oxygen sensor is provided. Here, the HC adsorber is located downstream of the three-way catalyst.
Of the exhaust passage into a main passage and a sub-passage.
Either the main passage or the sub-passage with the material interposed
And a switching valve that switches to flow to
When the main passage is selected by the switching valve,
Then, after flowing air from the air pump to the adsorbent,
It is recommended to provide a purge air passage leading to the upstream of the source catalyst.
No.

[0007]

In the above configuration, the adsorbing capacity of the adsorbent is known.
To detect the adsorbent temperature, and after starting the engine,
Exhaust gas from the exhaust passage until the temperature exceeds the first predetermined temperature.
Detours and guides through adsorbent to adsorb HC in exhaust
Adsorbed by the material, the temperature of the adsorbent exceeds the first predetermined temperature
Thereafter, the air is pumped until the temperature falls below the second predetermined temperature.
Gas is supplied to the adsorbent to desorb HC and contain this HC.
Air is introduced into the exhaust passage upstream of the three-way catalyst. And
Influence of the air supply amount from the air pump by controlling the fuel supply amount to the engine based on the signal from the first oxygen sensor mounted upstream of the three-way catalyst and upstream of the air introduction position in the exhaust passage The air-fuel ratio in the cylinder can be controlled without receiving the air-fuel ratio.

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

[0009]

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

The exhaust gas from the engine 1 is supplied to an exhaust manifold 6.
Through 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 mainly composed of activated carbon or zeolite is interposed in the sub-passage 9. . And the main passage 8
A first switching valve 11 is provided at a branch to the sub passage 9, and a second switching valve 12 is provided at a junction from the main passage 8 and the sub passage 9.

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. Further, a purge air passage 15 from the exhaust inlet side of the adsorbent 10 is connected upstream of the three-way catalyst 7. Incidentally, the auxiliary passage 9, the adsorbent 10, the first and second switching valves 1
1 and 12 constitute an HC adsorption device, and an air pump 13 and
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 built in the microcomputer.
An air flow meter 17 for detecting an 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 indirectly detects the engine 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 a position for introducing air from the air pump 13 (opening of the purge air passage 15). Also, the first and second switching valves 11 and 12, an air pump
The operation of 13 is controlled by a second control unit 20 built in the microcomputer. The second control unit 20 includes a signal from an adsorbent temperature sensor 21 for detecting the temperature Ta of the adsorbent 10 and a second oxygen sensor. Signal from 22 is input.

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

FIG. 2 is a flowchart 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 figure, the same applies hereinafter), the intake air flow rate Q is detected based on a signal from the air flow meter 17. In step 2,
Based on the signal from the crank angle sensor 18, the engine speed N
Is detected. 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).

[0016] In step 4, reads the output voltage V ₁ of the first oxygen sensor 19. In step 5, this output voltage V ₁
Is compared with a predetermined value (for example, 400 mV) to determine rich / lean. If it is rich (V ₁ > 400 mV), the routine proceeds to step 6, where the air-fuel ratio feedback correction coefficient α is reduced by a predetermined amount Δα. If the engine is 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 is calculated 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 manner, a 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 flowchart of an 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, the adsorbent temperature Ta is 200 ° C. (No.
It is determined whether or not the temperature has exceeded the predetermined temperature (1) .

In step 13, the first and second switching valves 11,
By 12, the exhaust gas from the three-way catalyst 7 is circulated to the adsorbent 10 by bypassing to the auxiliary passage 9. Thereafter, the process returns to step 11. Therefore, even when the exhaust gas contains a large amount of HC because the three-way catalyst 7 is inactive during the cold immediately after the start,
This HC is adsorbed by the adsorbent 10 and is prevented from being released to the atmosphere.

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

In step 15, the operation of the air pump 13 is started for the process of desorbing the HC adsorbed on the adsorbent 10. As a result, the air from the air pump 13 is supplied to the adsorbent 10 through the purge air passage 14 and the HC adsorbed by the air is desorbed. The air containing the desorbed HC is removed by the purge air passage 15 through the three-way catalyst. 7, and is purified by the three-way catalyst 7. In this manner, in the method in which HC is desorbed from the adsorbent 10 by the air from the air pump 13, the desorbing can be performed completely without exceeding the heat-resistant temperature of the adsorbent 10 at the time of desorption.

[0022] At step 16, it reads the output voltage V ₂ of the second oxygen sensor 22. In step 17, the output voltage V ₂
Is compared with a predetermined value to determine rich / lean. If the air condition is rich, the process proceeds to step 18, where the amount of air supplied by the air pump 13 is increased. If the engine is lean, the process proceeds to step 19, where the amount of air supplied by the air pump 13 is reduced.

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 the HC by the air from the air pump 13. The air supply amount of the air pump 13 is controlled to increase or decrease so that In addition, 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, the adsorbent temperature Ta is raised to 100 ° C. (second predetermined
It is determined whether the temperature is lower than ( temperature). If the temperature is 100 ° C. or more, the flow returns to step 16 to perform the HC desorption process while controlling the air supply amount of the air pump 13. The adsorbent temperature Ta
If the temperature is lower than 100 ° C., the process proceeds to step 22 in the determination of step 21, the air pump 13 is stopped, and the desorption process is terminated. This is because the adsorbent temperature Ta drops to around 100 ° C. by the time HC is completely desorbed from the adsorbent 10.

According to the present embodiment, since the adsorbent 10 and the like are disposed downstream of the three-way catalyst 7, the three-way catalyst 7 and the second oxygen sensor 22 can be brought close to the engine 1, and their early activation can be achieved. Can be achieved. FIG. 4 shows another embodiment. In this embodiment, an adsorbent 10 and the like are arranged upstream of a three-way catalyst 7.

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

A 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, in the cold state immediately after starting, the switching valve
By 11, the exhaust gas from the engine 1 is diverted to the sub-passage 9 and circulated through the adsorbent 10, 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 warm-up is complete,
The switching valve 11 is switched to guide the exhaust gas from the engine 1 to the three-way catalyst 7 through the main passage 8 without bypassing the exhaust gas to the sub passage 9. Then, for the HC desorption process, air from the air pump 13 flows into the adsorbent 10 from the inlet side of the sub-passage 9 through the purge air passage 14 to desorb HC, and the air containing the HC is transferred to the sub-passage 9. From the outlet side of the three-way catalyst 7.

The control is the same, and a signal from a first oxygen sensor 19 mounted upstream of the three-way catalyst 7 in the exhaust passage and upstream of the air introduction position (the junction of the sub-passage 9) is sent to the control unit 16. The input is used to control the fuel injection amount by the fuel injection valve 5 as shown in the flowchart of FIG. In addition, a signal from a 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 amount of air supplied 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 air is pressure-fed 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 when switching the switching valve. In addition, since only one switching valve is required and the number of piping and the like is small, the structure can be simplified.

[0030]

As described above, according to the present invention, H
The torque fluctuation 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 accurately controlled, thereby greatly improving the exhaust gas purification performance. The effect is obtained. Also, adsorption
Detecting material temperature to control HC adsorption and desorption
Thus, appropriate control can be performed according to the adsorption capacity.
Furthermore, the exhaust passage downstream of the three-way catalyst is divided into a main passage and a sub passage.
Branches, adsorbent is interposed in the sub-passage, and exhaust gas is
Switch to switch to flow to one of the sub passages
A valve is provided to supply air from the air pump when the main passage is selected.
Purge air that flows to the upstream of the three-way catalyst after flowing to the adsorbent
If a passage is provided, an adsorbent or the like is provided downstream of the three-way catalyst.
The three-way catalyst and the second oxygen sensor
Can be brought closer to
Can be

[Brief description of the 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 is a flowchart of an adsorption / desorption control routine.

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

[Explanation of symbols]

 Reference Signs List 1 engine 5 fuel injection valve 6 exhaust manifold 7 three-way catalyst 8 main passage 9 sub 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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification code FI F02D 41/14 310 F02D 41/14 310F (58) Investigated field (Int.Cl. ⁶ , DB name) F01N 3/22 301 F01N 3/08 F01N 3/20 F01N 3/24 F02D 41/14 310

Claims (2)

(57) [Claims] 1. A hydrocarbon adsorbing device for diverting and guiding exhaust gas from an exhaust passage to flow through an adsorbent and adsorb hydrocarbons in the exhaust gas by the adsorbent, and supplying air to the adsorbent by an air pump to remove hydrocarbons. A desorption treatment device for desorbing and introducing the hydrocarbon-containing air upstream of the three-way catalyst in the exhaust passage, wherein the adsorbent temperature sensor for detecting the temperature of the adsorbent is provided. Establishment
After the engine starts, the adsorbent temperature exceeds the first predetermined temperature.
Until the adsorbent temperature rises.
Is lower than the first predetermined temperature after exceeding the first predetermined temperature.
Until the temperature falls below a second predetermined temperature.
A first oxygen sensor mounted upstream of the three-way catalyst and upstream of the air introduction position in the exhaust passage to detect oxygen concentration, and to the engine based on a 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 operation of the desorption processing device.
Sometimes an exhaust purification system of an internal combustion engine, characterized by comprising a pump controller for controlling the air supply amount of the air pump on the basis of a signal from the second oxygen sensor. (2) The hydrocarbon adsorber is located downstream of the three-way catalyst.
Of the exhaust passage into a main passage and a sub-passage.
Either the main passage or the sub-passage with the material interposed
And a switching valve that switches to flow to
When the main passage is selected by the switching valve,
Then, after flowing air from the air pump to the adsorbent,
A purge air passage leading to the upstream side of the catalyst is provided.
The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein: