JPH06123223A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent a temperature of catalysts from lowering when HC is desorbed and cause catalysts to recover its purification efficiency by causing HC (unburnt gas) adsorbed into an adsorption material to be desorbed under a high temperature condition where exhaust gas purification catalysts is activated and an accelerated condition involving increase of exhaust gas temperature to exceed a specified temperature. CONSTITUTION:An exhaust gas passage 13 of an internal combustion engine 11 is composed of a main passage 13a and a bypass passage 14 which is connected parallel to the exhaust gas passage 13 and has an adsorbent 15 therein. An exhaust gas inlet 14a and an exhaust gas outlet 14b of the bypass passage 14 are arranged thereon with control valves 16a, 16b, respectively. Furthermore, the upstream of the exhaust gas inlet 14a and the downstream of the exhaust gas outlet 14b of the exhaust gas passage 13 are arranged thereon with three- way catalytic converters 19a, 19b, respectively. On this occasion, an acceleration condition involving exhaust gas temperature increase exceeding a specified temperature is judged at an acceleration condition judgment portion 17a of a control unit 17. Under this acceleration condition and under the high temperature where the three-way catalytic converters 19a, 19b are activated, the worsening of exhaust emission is prevented by means of opening respective control valves 16a, 16b of a valve control portion 17b and desorbing HC of the adsorbent 15.

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, when unburned HC contained in the exhaust gas of an engine is adsorbed by an adsorbent and desorbed (purged), The present invention relates to a technique for preventing a reduction in purification efficiency of an exhaust purification catalyst.

[0002]

2. Description of the Related Art In an internal combustion engine for a vehicle, in order to purify exhaust gas, HC (unburned gas) and CO in the exhaust gas are oxidized into H ₂ O and CO ₂ in the exhaust passage, while NO _X is converted into N ₂ . An exhaust gas purification catalyst called a three-way purification catalyst that reduces and purifies is installed. By the way, of the harmful components in the exhaust gas, H
The discharge amount of C is particularly susceptible to the exhaust temperature. In other words, even if a noble metal catalyst is used, it is generally 3
A catalyst temperature of 00 ° C or higher is required. Therefore, in the exhaust gas purification device only including the three-way catalyst, it is difficult to purify the HC by the catalyst when the exhaust gas temperature is low, such as immediately after the engine is started cold.

Therefore, as a conventional exhaust gas purifying apparatus for a vehicle, for example, as shown in JP-A-62-174522, for adsorbing HC in the exhaust passage on the upstream side of the exhaust gas purifying catalyst. It has been proposed to interpose the adsorbent. That is, when the adsorbent has a low temperature,
By utilizing the fact that it has the property of adsorbing the adsorbent and desorbing the adsorbed HC when the temperature becomes high, a bypass passage in which the adsorbent is interposed is connected in parallel to a part of the exhaust passage upstream of the exhaust purification catalyst. The main passage and the bypass passage are selectively opened and closed, and the bypass passage is opened to adsorb HC at the adsorbent at a low temperature before the exhaust purification catalyst is activated.
After the bypass passage is closed once, the temperature becomes high and the exhaust purification catalyst is activated, and then the bypass passage is opened again to desorb the adsorbed HC and the exhaust purification catalyst purifies it. As the adsorbent, for example, a monolith carrier coated with zeolite has been proposed because zeolite has excellent adsorbability.

[0004]

By the way, in the exhaust gas purification apparatus provided with such an adsorbent, when it is detected that the exhaust gas purification catalyst is activated, the bypass passage is fully opened to allow a large amount of exhaust gas to flow therein. However, the HC adsorbed on the adsorbent is rapidly and largely desorbed, and the activated exhaust purification catalyst has its inlet temperature lowered by the inflow of a large amount of HC, resulting in extremely high catalyst purification efficiency. However, there was a problem that the exhaust emission deteriorated.

The present invention has been made in view of the above conventional problems, and controls the catalyst while suppressing a decrease in the temperature of the exhaust gas flowing into the catalyst, thereby maintaining a good purification efficiency of the catalyst and exhausting the exhaust gas. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can prevent deterioration of emissions.

[0006]

Therefore, according to the present invention, as shown in FIG. 1, an exhaust gas purification catalyst is provided in an exhaust passage of an engine, and a part of the exhaust gas passage upstream of the exhaust purification catalyst is provided. Main passage and unburned HC in exhaust gas connected in parallel to the main passage
Is constituted by a bypass passage having an adsorbent having a function of adsorbing at a low temperature and desorbing at a high temperature, and the opening degree control means controls the opening degree of the main passage and the bypass passage according to the exhaust temperature state. While adsorbing the HC in the exhaust gas to the adsorbent in a low temperature state before the activation of the exhaust gas purification catalyst, the HC adsorbed to the adsorbent is provided at least in the high temperature state after the activation of the exhaust gas purification catalyst. In an exhaust gas purification apparatus for an internal combustion engine, which is desorbed and purified by an exhaust gas purification catalyst, an acceleration state determination means for determining an acceleration state involving a rise in exhaust gas temperature above a predetermined level, and the exhaust gas purification catalyst is activated. Desorption start timing for opening the bypass passage and desorbing the HC adsorbed by the adsorbent when the acceleration state determination means determines that the acceleration state is accompanied by a rise in exhaust gas temperature above a predetermined level. Configured to include a control means.

[0007]

According to this structure, based on the outlet temperature of the exhaust gas purification catalyst, before the exhaust gas purification catalyst is activated, the bypass passage is opened to adsorb the HC in the exhaust gas to the adsorbent. After that, the bypass passage is closed and the exhaust gas is guided to the main passage until the exhaust gas purification catalyst is activated. During this time, the exhaust gas temperature reaches the temperature at which HC is desorbed from the adsorbent, but since the exhaust gas is not guided by closing the bypass passage, desorption is not performed.

However, when the exhaust purification catalyst is activated in a high temperature state and the acceleration state determination means determines that the exhaust gas temperature rises above a predetermined level, the bypass passage is opened to adsorb the adsorbent. The removed HC desorbs. That is, as a result, the exhaust gas having a low temperature and a high concentration of HC from the adsorbent is introduced into the exhaust gas purification catalyst inlet through the exhaust gas bypass passage, but at the same time, the high temperature exhaust gas in the acceleration state of the engine is also exhausted. It is introduced from the passage to the exhaust gas purification catalyst inlet.

Therefore, the temperature of the exhaust purification catalyst is prevented from lowering during the desorption of HC, and the purification efficiency of the exhaust purification catalyst can be restored from low purification efficiency to high purification efficiency. Can be prevented from worsening.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. First, referring to FIG. 2, the overall configuration of the exhaust gas purification device according to the present invention will be described. A part of the exhaust passage 13 of the engine 11 is composed of a main passage 13a and an exhaust bypass passage 14 connected in parallel with the main passage 13a. An adsorbent 15 is formed in the exhaust bypass passage 14. The adsorbent 15 is formed, for example, by coating a monolithic ceramic carrier with a substance having an adsorbing property such as zeolite, activated carbon, or γ-alumina.

The exhaust inlet 14 of the bypass passage 14
Control valves 16a and 16b as means for continuously controlling the opening ratio between the main passage 13a and the bypass passage 14 are provided at the "a" and the exhaust outlet 14b, respectively. This control valve 16
Each of a and 16b includes, for example, a diaphragm type actuator, and is formed so that the valve opening degree is controlled by the actuator based on a signal from the control unit 17. The state of the valve opening degree of the control valves 16a and 16b in FIG. 3 is A in a fully closed state, B in a fully open state, and C in a half open state.

The exhaust passage 13 includes an exhaust bypass passage 14
A pre-three-way catalyst 19a and a main three-way catalyst 19b as exhaust purification catalysts are provided on the upstream side of the exhaust inlet 14a and the downstream side of the exhaust outlet 14b, respectively. An exhaust temperature sensor 20 for detecting the temperature of the exhaust gas discharged from the engine 11 is provided at the inlet of the main three-way catalyst device 19b.

The control unit 17 is an acceleration state determination section 17 having a function as an engine acceleration state determination means.
a and a valve control unit 17b having a function as an opening control unit and a desorption start timing control unit are provided as software. Various signals detected by an air flow sensor 21 that detects the intake air amount of the engine, a crank angle sensor 22 that detects the rotational speed of the engine, and an accelerator opening sensor 23 that detects the opening of the accelerator pedal are controlled. The signals detected by the exhaust gas temperature sensor 20 are input to the valve control unit 17b to the acceleration state determination unit 17a of the unit 17, and various controls are performed based on the input signals. Then, the determination result by the acceleration state determination unit 17a is the valve control unit 1
7b, and the opening of the control valves 16a and 16b is controlled.

The accelerator opening sensor 23 may be replaced with a throttle sensor that detects the valve opening of a throttle valve that works in conjunction with the accelerator pedal. Next, the operation will be described with reference to the flowchart shown in FIG. First, in step 1 (hereinafter referred to as "S1"), the states of the control valves 16a and 16b are read, and in step S2, the control valve 1 is read.
It is determined whether the open / closed state of 6a and 16b is the fully closed state, that is, whether the purge is possible if other conditions are met.

If it is in the fully closed state and the purge is possible, the purge determination is performed at S3 and below, and the purge is impossible, that is, the control valves 16a and 16b are in the adsorption state (fully opened state) or the purge completed state. If it is in the (half-opened state), the operation is ended by skipping this flow. In S3, if other conditions are satisfied, purging is possible, that is, the control valve 16
Since a and 16b are fully closed, the exhaust temperature sensor 18
The exhaust temperature T at the exhaust inlet of the main three-way catalyst 19b is detected by, and the activation temperature Ta (350
(Around ° C) is determined.

If the activation temperature is reached, the purging can be performed immediately. However, after the acceleration state of the engine for purging is determined in S5 or less, the purge is performed, and if the activation temperature is not reached, The operation is ended without going through this flow.
In S5, the rate of change dα / dt of the accelerator opening is calculated based on the value detected by the accelerator opening sensor 23.

Then, in S6, the determination value A obtained from the engine speed N and the fuel injection pulse Tp based on the detected value from the crank angle sensor 22 is read from the acceleration state determination map shown in FIG. In the acceleration state determination map of the figure, the exhaust temperature discharged from the engine increases as the engine speed N increases and the fuel injection pulse Tp of the fuel injection valve increases. A small value is given as the acceleration state determination value A.

In the figure, the fuel injection pulse Tp is Tp = Q
_{Obtained by a} / N, Q _a is the intake air flow rate of the engine. Then, in S7, the rate of change of the accelerator opening dα / d
It is determined whether t is larger than the determination value A. If it is larger than the judgment value A, the process proceeds to S8.

At S8, the rate of change of the accelerator opening dα / d
Since t is larger than the determination value A, the temperature decrease due to the purge can be covered by the exhaust gas temperature increase due to acceleration.
Purging is performed with the control valves 16a and 16b in a half-open state. Next, in S9, the exhaust temperature sensor 20 detects the exhaust temperature T at the inlet of the main three-way catalyst device 19b, and the exhaust temperature T is equal to or lower than a predetermined temperature Tb (for example, about 400 ° C.) that inhibits activation of the catalyst. Or not (S
10). And when it is smaller than Tb and falls, that is,
If there is a possibility that the temperature will be below the activation temperature of the catalyst, S
11, the control valves 16a and 16b are closed to complete the purge.

As a result, in the purged state of the adsorbent, the temperature of the catalyst is lowered by the low temperature exhaust gas flowing into the main catalyst through the exhaust bypass passage, but is discharged from the engine which is originally provided in the accelerated state of the engine. The high temperature exhaust gas can compensate for the temperature drop at the main catalyst inlet. Furthermore, so that the air-fuel ratio is temporarily lean mixture during acceleration of the engine, causing a decrease in the purification efficiency of the main catalyst, but NO _X emissions may become a peak state, the hot exhaust during acceleration It is possible to restore the main catalyst to the high purification efficiency zone, so that it is possible to prevent deterioration of exhaust emission.

[0021] In the above embodiment, although the determination of the purge termination is performed by comparing a predetermined temperature Tb by detecting the exhaust temperature T, the O ₂ sensor disposed downstream adsorbent 15, the O ₂ It can also be determined by the air-fuel ratio based on the detection value of the sensor. That is, the relationship between the air-fuel ratio of the exhaust gas and the purification rate of the catalyst is as shown in FIG. 6, and in the three-way catalyst, if the air-fuel ratio of the exhaust gas is not near the stoichiometric air-fuel ratio, CO,
Simultaneous treatment of HC and NO _x becomes insufficient. Therefore,
Whether or not the purge is completed can be determined depending on whether the air-fuel ratio of the exhaust gas is rich or lean with respect to the stoichiometric air-fuel ratio.

In the above embodiment, the control valves 16a,
Purge is performed by opening the opening of 16b halfway, but more precise purge control is performed by finely controlling the opening of the control valves 16a and 16b according to the acceleration state of the engine. You will be able to

[0023]

As described above, according to the present invention,
When the exhaust purification catalyst is activated in a high temperature state and the acceleration state determination means determines that the exhaust gas temperature rises above a predetermined level, the bypass passage is opened to remove the HC adsorbed by the adsorbent. Since the desorption start timing control means for separating the exhaust gas is provided, the exhaust gas having a low temperature and a high concentration of HC from the adsorbent is introduced into the catalyst inlet through the exhaust bypass passage. Since the exhaust gas of H will also be introduced into the catalyst inlet from the exhaust passage at the same time,
It is possible to prevent the temperature of the catalyst from lowering at the time of desorption of C and to recover the purification efficiency of the catalyst from the low purification efficiency to the high purification efficiency, and thus to prevent the exhaust emission from deteriorating.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a system diagram showing the overall configuration of the present invention.

FIG. 3 is a partial cross-sectional view showing an open / closed state of a control valve.

FIG. 4 is a flowchart showing the operation of the present invention.

FIG. 5 is a map for determining the acceleration state of the engine.

FIG. 6 is an explanatory diagram for explaining a relationship between an air-fuel ratio and a purification rate of a three-way catalyst.

[Explanation of symbols]

 11 Engine 13 Exhaust Passage 13a Main Passage 14 Bypass Passage 14a Exhaust Inlet 14b Exhaust Outlet 15 Adsorbent 16a, b Open / close Valve 17 Control Unit 17a Acceleration State Judge 17b Valve Control 19a Pre-Three-Way Catalyst 19b Main Three-Way Catalyst 20 Exhaust Temperature Sensor 21 Airflow sensor 22 Crank angle sensor 23 Accelerator opening sensor

Claims (1)

[Claims] 1. An exhaust gas purification catalyst is provided in an exhaust passage of an engine, and a part of an exhaust passage upstream of the exhaust purification catalyst is connected in parallel to a main passage and the main passage to remove unburned HC in exhaust gas. It is composed of a bypass passage having an adsorbent having a function of adsorbing at a low temperature and desorbing at a high temperature, and controls the opening degree of the main passage and the bypass passage according to the exhaust temperature state by an opening degree control means. Meanwhile, the HC in the exhaust gas is adsorbed by the adsorbent in a low temperature state before the activation of the exhaust purification catalyst, and the HC adsorbed by the adsorbent is required at least in the high temperature state after the activation of the exhaust purification catalyst. In an exhaust gas purification device for an internal combustion engine, which is desorbed and purified by an exhaust gas purification catalyst, an acceleration state determination means for determining an acceleration state with a rise in exhaust gas temperature above a predetermined level, and the exhaust gas purification catalyst is activated. At high temperature, and
And a desorption start timing control means for opening the bypass passage and desorbing the HC adsorbed by the adsorbent when the acceleration state determination means determines an acceleration state accompanied by a rise in exhaust gas temperature above a predetermined level. An exhaust emission control device for an internal combustion engine, which is configured.