JP2626333B2 - Engine exhaust purification device and exhaust purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an exhaust system for an engine.
The present invention relates to an engine exhaust purification device and an exhaust purification method provided with a catalyst such as a C adsorption catalyst (adsorbent) and a three-way catalyst.

[0002]

2. Description of the Related Art Conventionally, there is an engine provided with a three-way catalyst in the exhaust system of the engine for purifying the exhaust of the engine. It is necessary to change the air-fuel ratio of the inflowing exhaust gas at a relatively short cycle near the stoichiometric air-fuel ratio (stoichiometric ratio). Therefore, an oxygen concentration sensor (O
₂ sensors) to perform air-fuel ratio feedback control with little response delay.

On the other hand, recently, it has been required to reduce HC (hydrocarbon) discharged from an engine at a low temperature, and as one of the measures, a Y-type zeolite or the like is provided upstream of a three-way catalyst. A device provided with an HC adsorbent or an adsorption catalyst made of mordenite or the like has been proposed (see JP-A-2-75327).

[0004]

However, with such a conventional combination of a three-way catalyst and an HC adsorbing catalyst, the HC adsorbing catalyst adsorbs HC at a low temperature, and when the temperature rises, the HC adsorbing catalyst adsorbs the HC. However, since the conversion temperature of this HC release is about 150 ° C., this is lower than the activation temperature of the three-way catalyst, which is about 300 ° C., and therefore, the HC adsorption effect is realized. This is limited to a short time immediately after starting. FIG. 5 also shows that the three-way catalyst and HC
The HC emission characteristics (see the solid line characteristic A) of the combination with the adsorption catalyst are those of the three-way catalyst only (see the dotted line characteristic B).
It can be seen that the HC adsorption effect is realized only in a short time (about 50 seconds) immediately after the start, as compared with the case of FIG.

The present invention has been made in view of the above problems, and provides an exhaust gas purifying apparatus and an exhaust gas purifying method for an engine in which HC emission from engine start until catalyst activation can be completely suppressed. The purpose is to:

[0006]

Therefore, an exhaust gas purifying apparatus for an engine according to the present invention includes a first catalyst, an HC adsorbing catalyst, and a second catalyst in an exhaust system of an engine in order from an upstream side. A switching means for providing a bypass which bypasses the HC adsorption catalyst, and for passing exhaust gas having passed through the first catalyst to the HC adsorption catalyst or the bypass; and an HC adsorption for cooling the HC adsorption catalyst Switching means for switching the switching means so that the exhaust gas passing through the first catalyst is temporarily passed to the HC adsorption catalyst side when the engine is started; and An HC adsorbing catalyst cooling control means for operating the HC adsorbing catalyst cooling means is provided (claim 1).

Further, according to the method for purifying exhaust gas of an engine of the present invention, the exhaust system of the engine includes a first catalyst, an HC adsorption catalyst, and a second catalyst in order from the upstream side, and bypasses the HC adsorption catalyst. A switching means for providing a bypass and passing exhaust gas passing through the first catalyst to the HC adsorbing catalyst or the bypass, and an HC adsorbing catalyst cooling means for cooling the HC adsorbing catalyst are provided. When the engine is started, the HC adsorbing catalyst cooling means is operated to cool the HC adsorbing catalyst, and for the exhaust gas passing through the first catalyst,
When the engine is started, it passes through the HC adsorbing catalyst side, then passes through the bypass passage when the first catalyst is activated, and again when the second catalyst is activated.
It is characterized in that it passes through the adsorption catalyst side and, after warm-up , passes through the bypass path again (claim 2).

Further, according to the method for purifying exhaust gas of an engine of the present invention, the exhaust system of the engine includes a first catalyst, an HC adsorption catalyst, and a second catalyst in order from the upstream side, and bypasses the HC adsorption catalyst. A switching means for providing a bypass and passing exhaust gas passing through the first catalyst to the HC adsorbing catalyst or the bypass, and an HC adsorbing catalyst cooling means for cooling the HC adsorbing catalyst are provided. When the engine is started, the HC adsorbing catalyst cooling means is operated to cool the HC adsorbing catalyst, and the exhaust gas that has passed through the first catalyst is passed to the HC adsorbing catalyst side. When the first catalyst is activated, the HC adsorption catalyst cooling means is deactivated and the HC
When the cooling of the adsorption catalyst was stopped, the exhaust gas passing through the first catalyst was passed through the bypass passage, and when the second catalyst was activated, the HC adsorption catalyst cooling means was deactivated. The exhaust gas that has passed through the first catalyst is passed through the HC adsorption catalyst side again, and the exhaust gas that has passed through the first catalyst is passed through the bypass passage again after warming up . Claim 3).

[0009]

Therefore, according to the present invention, at the time of starting the engine, the HC adsorbing catalyst cooling means is operated to cool the HC adsorbing catalyst, and for the exhaust gas passing through the first catalyst, the HC adsorbing catalyst is cooled at the time of starting the engine. After passing through the HC adsorbing catalyst side, thereafter, when the first catalyst is activated, it passes through the bypass passage side.
After passing through the C adsorption catalyst side, after the warm-up is completed , pass through the bypass path side again.

Further, when the engine is started, the HC adsorbing catalyst cooling means is operated to cool the HC adsorbing catalyst, and the exhaust gas passing through the first catalyst is passed to the HC adsorbing catalyst side. When the catalyst becomes active, HC
When the cooling of the HC adsorbing catalyst is stopped by disabling the adsorbing catalyst cooling means, the exhaust gas passing through the first catalyst is passed to the bypass path side, and when the second catalyst is activated, the cooling of the HC adsorbing catalyst is started. With the means inactive,
The exhaust gas that has passed through the first catalyst again may be passed to the HC adsorption catalyst side, and after the warm-up, the exhaust gas that has passed through the first catalyst may be passed again to the bypass path side.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG.
2 is an overall configuration diagram of an engine system to which the present invention is applied, FIG. 3 is a flowchart for explaining the operation of one embodiment of the present invention, and FIG. 4 is a diagram for explaining the operation of one embodiment of the present invention. FIG.

FIG. 2 shows an engine system for carrying out the present invention. In FIG. 2, the engine EG has an intake passage 2 and an exhaust passage 3 leading to a combustion chamber 1 of each cylinder. The communication between the intake passage 2 and the combustion chamber 1 is controlled by an intake valve 4, and the communication between the exhaust passage 3 and the combustion chamber 1 is controlled by an exhaust valve 5.

The intake passage 2 is provided with an air cleaner 6, a throttle valve 7, and an electromagnetic fuel injection valve (injector) 8 in this order from the upstream side. Note that a surge tank 2a is provided in the intake passage 2.

Here, the injectors 8 are provided in the intake manifold portion by the number of cylinders. That is, the engine EG of the present embodiment is configured as, for example, an in-line four-cylinder engine, whereby four injectors 8 are provided. In other words, it can be said that this engine is a so-called multipoint fuel injection (MPI) type multi-cylinder engine.

Further, the throttle valve 7 is connected to an accelerator pedal via a wire cable so that the opening degree changes in accordance with the depression amount of the accelerator pedal. An opening and closing drive is also performed by an ISC motor, so that the opening of the throttle valve 7 can be changed without depressing the accelerator pedal during idling.

With this configuration, the air sucked through the air cleaner 6 in accordance with the opening of the throttle valve 7 is mixed with the fuel from the injector 8 at the intake manifold so as to have an appropriate air-fuel ratio. Then, the ignition plug 35 is ignited at an appropriate timing, so that it is burned to generate engine torque, and then the air-fuel mixture is discharged to the exhaust passage 3 as exhaust gas.

As shown in FIGS. 1 and 2, an exhaust gas purifying catalytic converter (three-way catalyst) 91 as a first catalyst and an HC adsorbing catalyst (HC adsorbing catalyst) Material) 93, an exhaust gas purifying catalytic converter (three-way catalyst) 92 as a second catalyst, and a muffler (muffler) not shown.

Further, an HC adsorption catalyst 93 is provided in the exhaust passage 3.
A bypass passage 94 is provided to bypass the solenoid valve, and an electromagnetic bypass valve 95 for opening and closing the bypass passage 94 is provided in the bypass passage 94. That is, the bypass valve 95
Functions as a switching unit for passing the exhaust gas that has passed through the catalytic converter 91 as the first catalyst to the HC adsorption catalyst 93 or the bypass passage 94.

Further, HC for cooling the HC adsorption catalyst 93
An adsorption catalyst cooling means 96 is provided. That is, H
A cooling passage 96-1 for supplying secondary air for cooling the HC adsorbing catalyst is connected to the upstream side of the C adsorbing catalyst 93. The cooling passage 96-1 is further connected to the cooling passage 96-1.
-1 is provided with an electromagnetic cooling air supply valve 96-2 for opening and closing.

Further, various sensors are provided to control the engine EG. First, on the intake passage 2 side, an air flow sensor 11, which detects an intake air amount from Karman vortex information, an intake air temperature sensor 12, which detects an intake air temperature, and an atmospheric pressure sensor 13, which detects an atmospheric pressure, are provided at the portion where the air cleaner is provided. The throttle valve is provided with a potentiometer type throttle sensor 14 for detecting the opening of the throttle valve 7, an idle switch 15 for detecting an idling state, and the like.

On the exhaust passage 3 side, an oxygen concentration (O ₂ concentration) in the exhaust gas is provided on an upstream side of the catalytic converter 91.
Is provided with an oxygen concentration sensor 17 (hereinafter, simply referred to as an O ₂ sensor 17) for detecting the pressure.

Further, the exhaust passage 3 is provided with a temperature sensor 41 for detecting the temperature T ₁ in the catalytic converter 91 for detecting whether or not the upstream catalytic converter 91 is in an active state. temperature sensor 42 for detecting the temperature T ₂ of the catalyst converter 92 to the catalytic converter 92 side detects whether an active state are provided.

Further, as other sensors, a water temperature sensor 19 for detecting an engine cooling water temperature, a crank angle sensor for detecting a crank angle (this crank angle sensor also serves as a rotation speed sensor for detecting the engine speed), and a second sensor. Each distributor is provided with a TDC sensor (cylinder discrimination sensor) for detecting the top dead center of one cylinder (reference cylinder). A battery sensor for detecting the voltage of the battery and a cranking switch or an ignition switch (key switch) for detecting the start time are also provided.

The detection signal from the above sensor is
The information is input to an electronic control unit (ECU) 23. Here, the ECU 23 includes a CPU, a RAM, an R
Although the OM and the input / output interface have a hardware configuration connected by a bus, the ECU 23 has a functional configuration for performing fuel control (air-fuel ratio control) and ignition timing control of the engine in terms of its functions. (Software or firmware configuration), but now focusing on the point of exhaust purification, the ECU 23 performs a switching control unit 51 for controlling a bypass valve 95 for such exhaust purification as shown in FIG.
And a cooling air supply valve 96 of the HC adsorption catalyst cooling means 96.
-2 for controlling the cooling of the HC adsorption catalyst.

Here, when the engine is started, the switching control means 51 closes the bypass valve 95 and passes the exhaust gas passing through the upstream catalytic converter 91 to the HC adsorption catalyst 93 side. When rendered active temperature up to, through the exhaust that has passed through the catalytic converter 91 on the upstream side to open the bypass valve 95 to the bypass passage 94 side, activity state further up temperature of the catalytic converter 92 on the downstream side When becomes, through the exhaust that has passed through the catalytic converter 91 again upstream closing the bypass valve 95 to 93 side HC adsorption catalyst, followed, if over the duration t ₃ <br/> over to warm-up is completed The opening and closing of the bypass valve 95 is controlled so that the exhaust gas that has passed through the upstream catalytic converter 91 by opening the bypass valve 95 is again passed through the bypass passage 94.

The control means 52 for cooling the HC adsorption catalyst
When the engine is started, the cooling air supply valve 96-2 is opened to cool the HC adsorption catalyst 93. After that, when the temperature of the upstream catalytic converter 91 rises and becomes active, the cooling air supply The cooling air supply valve 96 is closed so that the cooling of the HC adsorption catalyst 93 is stopped by closing the valve 96-2.
-2 for opening and closing control.

An exhaust gas purifying method according to the present invention having the above configuration will be described. First, when the engine is started, in step S1, the temperature T ₁ of the catalytic converter 91 on the upstream side, obtained by the temperature sensor 41 is the set temperature Ts
It is determined whether or not this set temperature Ts is higher than the temperature at which the upstream catalytic converter 91 is reliably activated. Starting the engine, since it is usually T ₁ ≦ Ts, closes the bypass valve 95 (step S
2) Open the cooling air supply valve 96-2 (Step S)
3).

Thus, immediately after the start of the engine, the HC adsorption catalyst 93 is cooled by the cooling air.
The exhaust gas that has passed through the upstream catalytic converter 91 is HC
It is led to the adsorption catalyst 93 side.

That is, in this state, since the upstream catalytic converter 91 has not been activated yet, HC cannot be purified and is discharged toward the downstream HC adsorption catalyst 93. In this way, HC in the exhaust gas that has passed through the upstream catalytic converter 91 is adsorbed by the HC adsorption catalyst 93. At this time, the HC adsorption catalyst 9
3 is cooled, so that its temperature rise is suppressed. Therefore, it takes a considerable time to raise the temperature to the conversion temperature.

In step S1, instead of determining whether T ₁ > Ts, a set time t after the engine is started is set.
_It is determined whether ₁ (this set time t ₁ is a time during which the upstream catalytic converter 91 is reliably activated) has elapsed, and if not, steps S2 and S3
May be performed, and if the time has elapsed, the processing from step S4 described below may be performed.

Thereafter, T ₁ ≧ Ts or set time t ₁
There has elapsed, the catalyst converter 91 on the upstream side becomes active, at step S4, the set temperature T ₂ of the downstream side of the catalytic converter 92 obtained by the temperature sensor 42 is temperature Ts '(this setting temperature Ts' is It is determined whether the temperature is higher than the temperature at which the downstream catalytic converter 92 is reliably activated. At this time, since T ₂ <Ts ′, the bypass valve 95 is opened (step S5),
The cooling air supply valve 96-2 is closed (Step S6).

As a result, the HC adsorbing catalyst cooling means 96 is deactivated, the cooling of the HC adsorbing catalyst 93 is stopped, and the exhaust gas passing through the upstream catalytic converter 91 passes through the bypass passage 94. .

That is, in this state, since the upstream catalytic converter 91 is in an active state, the HC can be purified by the upstream catalytic converter 91. Therefore, the exhaust gas passing through the upstream catalytic converter 91 is HC has been reduced.

Instead of determining whether or not T ₂ > Ts ′ in step S 4, after determining YES in step S 1, the set time t ₂ (this set time t ₂ is determined by the downstream catalytic converter 92 without fail. It is determined whether or not the time of the active state has elapsed. If the time has not elapsed, the processing of steps S5 and S6 is performed.
The processing after step S7 described below may be performed.

Thereafter, T ₂ ≧ Ts ′ or set time t
_{After the} elapse of ₂ and the downstream catalytic converter 92 is activated, in step S7, after determining YES in step S4, a predetermined time t ₃ (this time t ₃ is equal to the time of the HC adsorption catalyst 93)
Is the time that will be at the conversion temperature). Immediately after the determination is YES in step S4, since the predetermined time has not elapsed t _3, at step S8, it is carried out to close the bypass valve 95. At this time, since the cooling air supply valve 96-2 is closed in step S6, the cooling air supply valve 96-2 is closed.
Remains closed.

Thus, the downstream catalytic converter 92
If There becomes active, while the HC adsorption catalyst cooling means 96 inoperative and of being made to pass the exhaust gas has passed through the catalytic converter 91 of the upper stream side 93 side HC adsorption catalyst again.

At this time, since the HC adsorption catalyst 93 is at the conversion temperature, the adsorbed HC is discharged (desorbed).
This desorbed HC is purified by the downstream catalytic converter 92 in an active state. Note that HC contained in the exhaust gas from the engine is converted into the active catalytic converter 91 on the upstream side.
Purified by.

After determining YES in step S4,
When the warm-up is completed after the lapse of the predetermined time t ₃ , step S
At 9, the bypass valve 95 is opened, and the exhaust gas that has passed through the upstream catalytic converter 91 is again passed to the bypass passage 94 side.

At this time, the adsorbed H
C has already been released, and HC contained in the exhaust from the engine is further purified by the active catalytic converter 91 and the catalytic converter 92 on the downstream side, respectively.

The open and closed states of the bypass valve 95 and the cooling air supply valve 96-2 are shown in FIGS.
(B), and each of the catalytic converters 91, 9
2. The temperature rise characteristics of the HC adsorption catalyst 93 are as shown in FIG. Here, the temperature rise characteristic of the catalytic converter 91 is CAT1, and the temperature rise characteristic of the catalytic converter 92 is C
The temperature rise characteristic of the AT2, HC adsorption catalyst 93 is ADS.

Thus, the two catalysts 91, 92, HC
A process catalyst is constituted by the adsorption catalyst 93, the bypass passage 94, and the HC adsorption catalyst cooling means 96, and the upstream catalytic converter heating + HC adsorption process (see section a in FIG. 4) and the downstream catalytic converter heating process (section in FIG. 4). b), the HC desorption process (see section c in FIG. 4), and the normal process after warm-up (see section d in FIG. 4), thereby completely removing HC from the start of the engine to the activation of the catalyst. Can be deterred.

After the cooling air supply valve 96-2 is opened when the engine is started, it may be kept open until the warm-up is completed.

The bypass valve 95 may be closed when the engine is started and then opened after the upstream catalytic converter 91 has been activated.

Further, as the upstream catalytic converter 91 and the downstream catalytic converter 92, a three-way catalyst may be used, or an oxidation catalyst may be used if only reduction of HC is considered.

[0045]

As described above in detail, according to the exhaust gas purifying apparatus and the exhaust gas purifying method for an engine of the present invention, the process type catalyst is constituted by the two catalysts, the HC adsorption catalyst, the bypass, and the HC adsorption catalyst cooling means. By taking the first catalyst heating + HC adsorption process, the second catalyst heating process, the HC desorption process, and the normal process after warm-up, the exhaust of HC from the start of the engine to the activation of the catalyst is completely completed. Has the advantage that it can be suppressed.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of an engine system to which the present invention is applied.

FIG. 3 is a flowchart for explaining the operation of one embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of one embodiment of the present invention.

FIG. 5 is a diagram showing a comparison between both HC emission characteristics when a catalyst is used alone and when an adsorption catalyst is combined with the catalyst.

[Explanation of symbols]

1 the combustion chamber 2 an intake passage 3 exhaust passage 4 intake valve 5 an exhaust valve 6 an air cleaner 7 throttle valve 8 injectors 8a injector solenoid 11 the air flow sensor 12 intake air temperature sensor 13 atmospheric pressure sensor 14 throttle sensor 15 idle switch 17 O ₂ sensor 19 water temperature sensor 23 Electronic control unit (ECU) 35 Spark plug 41, 42 Temperature sensor 51 Switching control means 52 HC adsorption catalyst cooling control means 91 Upstream catalytic converter (first catalyst) 92 Downstream catalytic converter (second catalyst) 93 HC adsorption catalyst 94 Bypass passage 95 Bypass valve 96 HC adsorption catalyst cooling means 96-1 Cooling passage 96-2 Cooling air supply valve EG engine

Claims (3)

(57) [Claims] 1. An exhaust system of an engine is provided in order from an upstream side.
A first catalyst, an HC adsorbing catalyst, and a second catalyst, a bypass passage for bypassing the HC adsorbing catalyst, and an exhaust gas passing through the first catalyst.
A switching means for passing the C adsorbing catalyst or the bypass passage, and a HC adsorbing catalyst cooling means for cooling the HC adsorbing catalyst are provided, and the exhaust gas passing through the first catalyst is temporarily stopped when the engine is started. Switching control means for switching the switching means so as to pass through the HC adsorption catalyst side, and HC adsorption catalyst cooling control means for operating the HC adsorption catalyst cooling means when the engine is started. , Engine exhaust purification device. 2. An exhaust system of an engine is sequentially arranged from an upstream side.
A first catalyst, an HC adsorbing catalyst, and a second catalyst, a bypass path for bypassing the HC adsorbing catalyst, and exhaust gas passing through the first catalyst is supplied to the H catalyst.
A switching device for passing the catalyst through the C adsorbing catalyst or the bypass passage, and a cooling device for the HC adsorbing catalyst for cooling the HC adsorbing catalyst. While the adsorption catalyst has been cooled, the exhaust gas that has passed through the first catalyst passes through the HC adsorption catalyst when the engine is started.
Thereafter, when the first catalyst is activated, it passes through the bypass passage, when the second catalyst is activated, it passes again through the HC adsorption catalyst, and after warming-up, it passes again through the bypass passage. A method for purifying exhaust gas of an engine, comprising: 3. An exhaust system of an engine is provided in order from an upstream side.
A first catalyst, an HC adsorbing catalyst, and a second catalyst, a bypass path for bypassing the HC adsorbing catalyst, and exhaust gas passing through the first catalyst is supplied to the H catalyst.
A switching device for passing the catalyst through the C adsorbing catalyst or the bypass passage, and a cooling device for the HC adsorbing catalyst for cooling the HC adsorbing catalyst. The adsorption catalyst is cooled, and the exhaust gas passing through the first catalyst is
Then, when the first catalyst is activated, the HC adsorption catalyst cooling means is deactivated to stop the cooling of the HC adsorption catalyst and to pass through the first catalyst. When the exhaust gas passes through the bypass passage and the second catalyst is activated, the HC adsorbing catalyst cooling means is kept in an inactive state, and the exhaust gas that has passed through the first catalyst is again discharged to the HC catalyst. An exhaust gas purification method for an engine, wherein the exhaust gas is passed through the adsorption catalyst side, and after warm-up, the exhaust gas that has passed through the first catalyst is passed through the bypass path again.