JP3088543B2 - Engine exhaust system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for purifying exhaust gas of an engine, and more particularly to an exhaust device for an engine in which a reduction catalyst and a three-way catalyst are selectively used in accordance with an operation state of the engine. About.

[0002]

2. Description of the Related Art As for combustion control of an engine, a control technique for improving the fuel efficiency by making the air-fuel ratio leaner than the stoichiometric air-fuel ratio and performing so-called lean burn (lean combustion) is already known. However, in lean air-fuel ratio control, it is known that NO _x (nitrogen oxide) in exhaust gas increases. Therefore, for the purpose of purifying NO _{x and the} like, a reduction catalyst such as a copper ion exchanged zeolite is used. It has been considered to provide in the exhaust system. However, since such a reduction catalyst has a relatively low heat resistance temperature, for example, Japanese Patent Application Laid-Open No. 1-171625 (B01D53)
/ 36) as seen in JP-like, provided with a reduction catalyst while the purifying and NO _X in the exhaust passage as two systems, the three-way catalyst and the other for purifying HC, CO, the three components of the NO _X It is proposed to control the introduction of exhaust gas to one of the exhaust paths by using a switching valve arranged at the branch of the exhaust passage with two systems so that the exhaust gas does not flow to the reduction catalyst side when the temperature is high. Have been.

[0003]

However, there is a concern that the switching valve in the exhaust system may malfunction due to adhesion of carbon or the like. In addition, high-temperature exhaust gas may flow to the side of the reduction catalyst having low heat resistance. Further, when the switching valve fails in the fully closed state, there is a possibility that the engine operation itself cannot be secured.

The present invention has been made in view of the above circumstances, and an object of the present invention is to ensure that even when the switching valve fails, it is possible to appropriately secure the flow of exhaust gas and to prevent the flow of high-temperature exhaust gas into the reduction catalyst. Another object of the present invention is to provide an exhaust device for an engine that can ensure the operation of the engine and protect the reduction catalyst.

[0005]

[Summary of the invention To achieve the above object, is disposed in an exhaust passage, a reducing catalyst for purifying NO _X, etc., secondary branched from the exhaust passage upstream of said reduction catalytic is disposed in an exhaust passage, HC, CO, and three-way catalyst for purifying three components of nO _X, are disposed in the branch portion between the exhaust passage and the auxiliary exhaust passage, the three-way when the control signal is not input A switching valve that normally opens the catalyst side and normally closes the reduction catalyst side, and outputs a control signal to the switching valve to close the three-way catalyst side and open the reduction catalyst side during lean air-fuel ratio control. And a valve control means.

Further, according to the present invention, the reduction catalyst is disposed in the auxiliary exhaust passage instead of the exhaust passage, and the three-way catalyst is disposed in the exhaust passage instead of the auxiliary exhaust passage. It is characterized by the following.

Further, the present invention is characterized in that a control inhibiting means for inhibiting the lean air-fuel ratio control when the switching valve fails.

[0008] Furthermore, the present invention is disposed in the exhaust passage, a reducing catalyst for purifying NO _X, etc., is disposed upstream of the reducing catalyst, and normally closed to said reduction catalytic side when the control signal is not input A first switching valve, and a sub exhaust passage branched from the exhaust passage upstream of the first switching valve;
C, CO, and three-way catalyst for purifying three components of NO _X, are disposed in the auxiliary exhaust passage, a second switching valve to normally open the three-way catalyst side when the control signal is not input, the lean Valve control means for outputting a control signal to the first and second switching valves so as to close the three-way catalyst side and open the reduction catalyst side at the time of air-fuel ratio control.

[0009]

The operation of the present invention will be described. Basically, the switching operation of the switching valve is performed in accordance with the operating state of the engine, specifically, the air-fuel ratio control state, and the reduction catalyst and the three-way catalyst are selectively operated. Will be used. That is, by switching the switching valve, exhaust gas is introduced into the reduction catalyst during lean air-fuel ratio control, and exhaust gas is introduced into the three-way catalyst in a normal control state other than during lean air-fuel ratio control. This switching valve opens the exhaust passage on the side where the reduction catalyst is disposed and only when the control signal is input from the valve control means in the lean air-fuel ratio control, and the three-way catalyst is disposed. In the normal control state other than the lean air-fuel ratio control where the control signal is not input, the exhaust path on the side where the three-way catalyst is disposed is always kept open. .
Therefore, in a normal engine operating state, the switching valve ensures opening of the exhaust passage on the three-way catalyst side.

Furthermore, by prohibiting the lean air-fuel ratio control by the control prohibiting means at the time of failure of the switching valve, it is possible to suppress the emission of NO _x.

The switching valve may be provided independently on the reduction catalyst side and the three-way catalyst side. In this case, the first switching valve on the reduction catalyst side is normally closed with respect to the reduction catalyst, If the second switching valve on the source catalyst side is configured to be normally opened with respect to the three-way catalyst, the same operation as described above can be ensured.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a configuration diagram showing a preferred embodiment of an exhaust system for an engine according to the present invention. FIG. 1 shows an embodiment in which the present invention is applied to a control device for performing air-fuel ratio control.

The engine 1 is provided with an injector 2 for performing fuel injection for each cylinder, and is configured as a so-called fuel injection type. Injector 2 is engine 1
Are provided in an intake passage 4 that communicates each combustion chamber with the air cleaner 3. The air cleaner 3 is provided in the intake passage 4.
An air flow meter 5 for detecting the flow rate of intake air sucked through the air cleaner, a supercharger 6 for increasing the flow rate of the intake air, a throttle valve 7 for appropriately adjusting the flow rate of the intake air, and an injector 2 are provided on the side of the air cleaner 3 From one to the engine 1 side.

The exhaust system is divided into a secondary exhaust passage 10 upstream of the first catalytic converter 8 in addition to an exhaust passage 9 communicating each combustion chamber of the engine 1 with the first catalytic converter 8 to form a two-system exhaust system. It is composed of The auxiliary exhaust passage 10 has a downstream end connected to the first catalytic converter 8 on the exhaust passage 9 side, and a second catalytic converter 11 disposed in the middle thereof. A switching valve 12 is provided at a branch between the exhaust passage 9 and the sub-exhaust passage 10.

In the exhaust passage 9, an O ₂ sensor 13 for detecting an oxygen concentration in the exhaust gas for detecting an air-fuel ratio is provided with a switching valve 1.
2 is provided on the upstream side. Further, an EGR passage 14 for returning a part of the exhaust gas to the intake side and recirculating the exhaust gas is connected to the upstream side. The downstream end of the EGR passage 14 is communicated with the intake passage 4, and an EGR valve 15 for appropriately adjusting the EGR amount is provided in the middle of the EGR passage 14, and a part of the exhaust gas flows downstream of the throttle valve 7. Is to be returned to. The EGR valve 15 is appropriately opened and closed according to the intake negative pressure, and the operation is controlled so that the EGR amount increases as the engine load increases, such as during acceleration.

The first catalytic converter 8 includes a reduction catalyst 16 for purifying such NO _X, HC, CO, in which the three-way catalyst 17 for purifying the three components of the NO _X was serially arranged, communicated to this A reduction catalyst 16 is disposed upstream of the auxiliary exhaust passage 10 and a three-way catalyst 17 is disposed downstream. On the other hand, the second catalytic converter 11 includes only the three-way catalyst 17.

The switching valve 12 opens the exhaust passage 9 and closes the auxiliary exhaust passage 10 when a control signal is input, but closes the auxiliary exhaust passage 10 when no control signal is input. And is closed with respect to the exhaust passage 9 side.

Each part of the engine 1 includes a CPU, a RAM,
It is appropriately controlled by a computer 18 having an OM and an I / O port. That is, the computer 18 has an air flow meter 5 on its input side.
Various switches and sensors such as the O ₂ sensor 13 are connected, and their detection signals are taken in to determine the operating state of the engine 1 and the like.
Various actuators such as the switching valve 12 are connected and control signals are sent to them, and various engine controls such as air-fuel ratio control are performed according to a predetermined control logic.

The present invention relates to the control of the switching valve 12 associated with the air-fuel ratio control of the engine 1, and FIGS. 2 and 3 are flowcharts showing the relevant processing.

As the air-fuel ratio control, basically, the engine 1
The fuel injection amount is increased or decreased in order to obtain an appropriate air-fuel ratio in accordance with the operation state of the fuel cell, and the valve opening time of the injector 2, that is, the fuel injection time is controlled to increase or decrease while maintaining the fuel pressure at a predetermined value. This is, as shown in FIG.
Read the latest data of various signals necessary for the control, such as the rotation speed, the oxygen concentration in the exhaust gas, and the cooling water temperature (S
1), based on the data, the basic injection time T of the fuel
_P is calculated (S2). If the switching valve 12 is normal (S3, YES) and the operating state of the engine 1 is in the lean air-fuel ratio region (S4, YES), a correction calculation for lean air-fuel ratio control is performed (S5). the sum of the correction amount β of the basic injection time T _P Toko, i.e. obtain a final injection time T _a (S6). Then, a control signal corresponding to the injection time T _A is output to the injector 2 (S7).

Whether the switching valve 12 is normal or not (S3) is determined by monitoring the terminal voltage of the switching valve 12 at the time of outputting the control signal, even though the control signal is being output. If the terminal voltage is not a normal value, it is determined that the switching valve 12 is abnormal and has failed (S3, NO). Whether the operating state of the engine 1 is in the lean air-fuel ratio region (S4) is determined by monitoring the rotational speed and the load state of the engine 1, and the control region is as shown in FIG. In addition, a region map that sequentially increases in the order of the lean air-fuel ratio region A <the stoichiometric air-fuel ratio region B <the open region C corresponding to the rotation speed N and the load L is set in advance. By comparing N and load L, it is determined whether or not it is out of the lean air-fuel ratio region A.

When the switching valve 12 has failed (S3, NO) or when the operating state of the engine 1 is not in the lean air-fuel ratio range (S4, NO), the current operating state is detected and the stoichiometric air-fuel ratio range B is detected. If there is (S8, YES), a correction calculation for stoichiometric air-fuel ratio control is performed (S9). On the other hand, if it is not in the stoichiometric air-fuel ratio region B (S8, NO), since the current operating state is in the open region C, a correction operation is performed for open control, that is, for increasing the amount in accordance with the opening of the throttle valve 7 (S8).
10).

On the other hand, the control of the switching valve 12 basically switches the exhaust gas flow path in accordance with the operating state of the engine 1, and first, as shown in FIG. 3, various signals necessary for the control. (T1), and if the operating state of the engine 1 is in the lean air-fuel ratio region A (T1),
2, YES), the first catalytic converter 8 side is opened and the second catalytic converter 8 is opened.
A control signal for performing a switching operation to close the catalytic converter 11 side is output to the switching valve 12 (T3).
On the other hand, if it is not in the lean air-fuel ratio region A (T2, NO),
Since the current operating state is in the stoichiometric air-fuel ratio region B or the open region C, the second catalytic converter 11 is opened and the first catalytic converter 8 is kept closed without outputting a control signal to the switching valve 12. (T4).

As described above, under the control of the computer 18, the switching operation of the switching valve 12 is performed basically according to the operating state of the engine 1, specifically, the air-fuel ratio control state. And the second catalytic converter 11 are selectively used. That is, by switching the switching valve 12, during the lean air-fuel ratio control, the exhaust gas is introduced into the first catalytic converter 8, and is guided from the reduction catalyst 16 to the three-way catalyst 17 in the next stage in order. In the controlled state, exhaust gas is supplied to the three-way catalyst 1 of the second catalytic converter 11.
7 to the three-way catalyst 17 of the first catalytic converter 8. The switching valve 12 opens the exhaust passage 9 on the side where the reduction catalyst 16 is disposed and controls the three-way catalyst 17 only when a control signal is input from the computer 18 in the lean air-fuel ratio control. In the normal control state other than the lean air-fuel ratio control in which the control signal is not input, the exhaust passage 10 on the side of the second catalytic converter 11 provided is closed. The state where the exhaust passage 10 on the side of the catalytic converter 11 is opened is maintained. Therefore, in a normal engine operation state, the switching valve 12 ensures opening of the exhaust passage 10 on the three-way catalyst side. Therefore, even when the switching valve 12 fails, the flow of exhaust gas can be appropriately secured, and the reduction catalyst 16
High temperature exhaust gas can be prevented from flowing into the side. as a result,
Engine operation can be ensured, and the reduction catalyst 16 can be protected from thermal degradation.

When the switching valve 12 fails, the flow S4 and S5 are bypassed, so that the correction calculation for the lean air-fuel ratio control is not performed, that is, the lean air-fuel ratio control is prohibited. Therefore, it is possible to suppress the emission of NO _X when the switching valve 12 fails.

The present invention is not limited to the above-described embodiment. For example, as shown in FIG.
The three-way catalyst 17 is disposed upstream of the first catalytic converter 80 on the side, and the second catalytic converter 110 on the side of the sub-exhaust passage 10 is constituted by the reduction catalyst 16. The switching valve 120 of the branch portion may be set to be closed with respect to the sub exhaust passage 10 when a control signal is not input.

As shown in FIG. 6, a switching signal is not provided at a branch portion between the exhaust passage 9 and the sub-exhaust passage 10, and a control signal is supplied to the exhaust passage 9 upstream of the first catalytic converter 8. A first switching valve 19 that normally closes the first catalytic converter 8 side when not input is provided, and a second catalyst when a control signal is not input to the sub exhaust passage 10 downstream of the second catalytic converter 11. A second switching valve 20 that normally opens the downstream side of the converter 11 may be provided, and the first switching valve 19 and the second switching valve 20 may be communicated with each other through the bypass exhaust passage 21. In this case, the first switching valve 19 on the side of the reduction catalyst 16 is normally closed with respect to the reduction catalyst 16, and the second switching valve 20 on the side of the three-way catalyst 17 is normally opened with respect to the three-way catalyst 17. As a result, even when both valves 19 and 20 fail, appropriate flow of exhaust gas can be secured, and the reduction catalyst 16
High temperature exhaust gas can be prevented from flowing into the side. In the control of the valve operation, a control signal is input at the time of lean air-fuel ratio control to open the first switching valve 19 and close the second switching valve 20, whereby the first catalytic converter 8 During the normal air-fuel ratio control, the first switching valve 19 is kept closed, and the second switching valve 20 is kept open. As a result, exhaust gas is introduced into the second catalytic converter 11.

[0028]

As described above in detail, according to the engine exhaust system of the present invention, the switching operation of the switching valve basically depends on the operating state of the engine, specifically, the air-fuel ratio control state. Is performed, and the reduction catalyst and the three-way catalyst are selectively used. That is, by switching the switching valve, exhaust gas is introduced into the reduction catalyst during lean air-fuel ratio control, and exhaust gas is introduced into the three-way catalyst in a normal control state other than during lean air-fuel ratio control. This switching valve opens the exhaust passage on the side where the reduction catalyst is disposed and only when the control signal is input from the valve control means in the lean air-fuel ratio control, and the three-way catalyst is disposed. In the normal control state other than the lean air-fuel ratio control where the control signal is not input, the exhaust path on the side where the three-way catalyst is disposed is always kept open. . Therefore, in a normal engine operating state, the switching valve ensures opening of the exhaust passage on the three-way catalyst side. Therefore, even when the switching valve fails, it is possible to ensure appropriate flow of exhaust gas and prevent high-temperature exhaust gas from flowing into the reduction catalyst. As a result, the operation of the engine can be ensured, and the reduction catalyst can be protected from thermal degradation.

Furthermore, by prohibiting the lean air-fuel ratio control by the control prohibiting means at the time of failure of the switching valve, it is possible to suppress the emission of NO _x.

The switching valve may be provided independently on the reduction catalyst side and the three-way catalyst side. In this case, the first switching valve on the reduction catalyst side is normally closed with respect to the reduction catalyst, If the second switching valve on the source catalyst side is configured to be normally open with respect to the three-way catalyst, the same effect as described above can be ensured.

[Brief description of the drawings]

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

FIG. 2 is a flowchart schematically showing air-fuel ratio control.

FIG. 3 is a flowchart schematically showing switching valve control.

FIG. 4 is a schematic explanatory diagram of an area map of air-fuel ratio control.

FIG. 5 is a configuration diagram illustrating a main part of another example of the present invention.

FIG. 6 is a configuration diagram illustrating a main part of still another example of the present invention.

[Explanation of symbols]

DESCRIPTION OF REFERENCE NUMERALS 1 engine 9 exhaust passage 10 auxiliary exhaust passage 12, 120 switching valve 16 reduction catalyst 17 three-way catalyst 18 valve operation control means, inhibition control means (computer) 19 first switching valve 20 second switching valve 21 bypass exhaust passage

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI F01N 3/28 301 F01N 3/28 301C (56) References JP-A-4-31615 (JP, A) JP-A-1-171625 (JP, A) JP-A-4-265415 (JP, A) JP-A-4-224223 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08-3 / 28

Claims (4)

(57) [Claims] 1. A is disposed in an exhaust passage, a reducing catalyst for purifying NO _X, etc., are disposed in auxiliary exhaust passage that is branched from the exhaust passage upstream of said reduction catalytic, HC, CO, of the NO _X A three-way catalyst for purifying three components and a branch portion between the exhaust passage and the sub-exhaust passage. When a control signal is not input, the three-way catalyst side is normally opened and the reduction catalyst side is normally closed. And a valve control means for outputting a control signal to the switching valve so as to close the three-way catalyst side and open the reduction catalyst side during lean air-fuel ratio control. Exhaust system. 2. The method according to claim 1, wherein the reduction catalyst is disposed in the auxiliary exhaust passage instead of the exhaust passage, and the three-way catalyst is disposed in the exhaust passage instead of the sub exhaust passage. The exhaust device for an engine according to claim 1, wherein 3. The engine exhaust system according to claim 1, further comprising control inhibition means for inhibiting the lean air-fuel ratio control when the switching valve fails. Is 4. disposed in an exhaust passage, a reducing catalyst for purifying NO _X, etc., is disposed upstream of the reducing catalyst, a reductive catalyst side when the control signal is not input first to normally closed a switching valve is disposed in the auxiliary exhaust passage that is branched from the exhaust passage upstream of the first switching valve, HC, CO, and three-way catalyst for purifying three components of NO _X, in the auxiliary exhaust passage A second switching valve, which is arranged to normally open the three-way catalyst side when a control signal is not input, and controls to close the three-way catalyst side and open the reduction catalyst side during lean air-fuel ratio control. An exhaust system for an engine, comprising: valve control means for outputting a signal to the first and second switching valves.