JPH05312031A - Exhaust emission control device for engine - Google Patents

Abstract

PURPOSE:To prevent deterioration of purification performance of a lean NOx catalyst by providing a control unit which controls a bypass valve so as to flow exhaust gas of an engine to a bypass passage while bypassing the lean NOx catalyst. CONSTITUTION:An exhaust passage 6 of an engine 1 is composed of a main passage 6a and a bypass passage 6b which straightly connects upstream and downstream of the main passage 6a to each other. A lean NOx catalyst 7 is arranged in the main passage 6a for reducing and purifying NOx. A bypass valve 9 is provided on the bypass passage 6b for opening and closing the bypass passage 6b. A fuel injection valve 5 and the bypass valve 9 are controlled by a control unit 10. When fuel supply is stopped, exhaust gas of the engine is flowed to the bypass passage 6b. Excessive oxygen is prevented from flowing to the lean NOx catalyst 7 and being adsorbed thereby. Deterioration of purification performance of the lean NOx catalyst 7 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust control device having an exhaust system provided with a so-called lean NOx catalyst.

[0002]

2. Description of the Related Art As described in Japanese Patent Laid-Open No. 3-225013, a transition metal is used as a catalyst for purifying NOx in engine exhaust gas in a lean air-fuel ratio region where the air-fuel ratio is larger than the theoretical air-fuel ratio. Alternatively, a catalyst, which is made of zeolite supporting a noble metal and reduces NOx in the exhaust gas in the presence of HC in an oxidizing atmosphere, a so-called lean NOx catalyst is provided in the exhaust system, and the lean NOx catalyst is provided.
It is known that a bypass passage that bypasses the x catalyst and a bypass valve that opens this bypass passage are provided, and the flow of exhaust gas is controlled so as to bypass the lean NOx catalyst in the air-fuel ratio rich region. In the exhaust system having the lean NOx catalyst and the bypass passage as described above, when the catalyst temperature exceeds the heat resistant temperature, the bypass passage is opened to prevent the exhaust gas from flowing into the lean NOx catalyst. It is generally known to stop and control the catalyst temperature.

Separately from this, the engine is usually provided with a deceleration fuel stopping means for stopping the fuel supply at the time of deceleration, as described in, for example, JP-A-63-113139. In addition to deceleration, it has been conventionally practiced to operate the fuel stopping means based on the output of the rotation sensor or the vehicle speed sensor in order to prevent the engine from over-rotating or limit the vehicle speed.

[0004]

The lean NOx catalyst adsorbs HC and NOx in the exhaust gas components to reduce and purify NOx. However, if oxygen is adsorbed, the NOx catalyst temporarily deteriorates and the purification performance remarkably deteriorates. To do. In particular, when the exhaust gas contains a large amount of oxygen, such as when the fuel supply is stopped to prevent engine over-rotation or to limit the vehicle speed, or when the deceleration fuel is stopped, the lean NOx catalyst contains exhaust gas. When flowing, a large amount of oxygen is adsorbed on the catalyst, and the deterioration becomes remarkable.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent the purification performance of a lean NOx catalyst from being lowered by adsorbing oxygen when fuel is stopped.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an exhaust control system for an engine, the structure of which reduces NOx in engine exhaust gas at least in a lean air-fuel ratio region where the air-fuel ratio is larger than the theoretical air-fuel ratio. Lean NOx
A catalyst, a bypass passage for bypassing the lean NOx catalyst, and a switching means for switching the exhaust passage of the engine to a passage for flowing exhaust gas to the lean NOx catalyst and a passage for flowing exhaust gas to the bypass passage according to the operating state of the engine. An exhaust system, and a fuel stop means for stopping the supply of fuel to the engine in a predetermined operating region, the exhaust gas of the engine is lean NOx catalyst regardless of the operating state when the fuel stop means is in operation. The fuel bypass catalyst bypass control means is provided for controlling the switching means so that the fuel is bypassed to flow into the bypass passage.

The fuel stopping means may operate in an operating range in which an engine speed equal to or higher than a predetermined rotational speed is detected, and operates in an operating range in which a vehicle speed equal to or higher than a predetermined vehicle speed is detected. Can be

Further, the fuel stopping means can be operated in an operating region where deceleration of the engine is detected.
In this case, the bypass delay means may be provided so as to delay the operation of the lean NOx catalyst bypass control means when the fuel stop means is operated.

FIG. 1 is an overall configuration diagram showing the above configuration of the present invention.

[0010]

The fuel stop means operates in the operating range in which the engine speed equal to or higher than the predetermined speed is detected, the operating range in which the vehicle speed equal to or higher than the predetermined vehicle speed is detected, or the operating range in which the engine deceleration is detected. Then, the supply of fuel to the engine is stopped. When the fuel is stopped, the exhaust path is switched so that the exhaust gas flows through the bypass passage that bypasses the lean NOx catalyst, thereby preventing a large amount of oxygen from flowing and adsorbing to the lean NOx catalyst. .. Further, particularly during engine deceleration, control is performed so that the flow of exhaust gas is switched to the bypass passage side after a predetermined delay time, and at that time, oxygen is lean due to the rich atmosphere due to the intake of adhered fuel at the initial stage of deceleration. NO from the NOx catalyst
x Purification performance is improved.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a system diagram of an embodiment of the present invention. In the figure, reference numeral 1 denotes an engine, a surge tank 3 is provided in an intake passage 2 of the engine 1, a throttle valve 4 is provided upstream of the surge tank 3, and a fuel injection valve 5 is provided downstream thereof.
Is provided. Further, the exhaust passage 6 of the engine 1 is
The main passage 6a is formed to extend laterally and a bypass passage 6b that connects the upstream portion and the downstream portion of the main passage 6a in a straight line.
A lean NOx catalyst 7 that reduces and purifies NOx during lean operation in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio is provided in the bypass portion, and a three-way catalyst 8 is provided downstream of the confluence with the bypass passage 6b. .. The bypass passage 6b is provided with a bypass valve 9 that opens and closes the bypass passage 6b.

The fuel injection valve 5 and the bypass valve 9
Is controlled by the control unit 10 composed of a microcomputer. Therefore, the control unit 10 receives a catalyst temperature signal from a temperature sensor 11 provided in the lean NOx catalyst 7, a throttle opening signal from a throttle sensor 12 attached to the throttle valve 4, and the drawing. The engine speed signal is input from the rotation sensor. A vehicle speed signal is input to the control unit 10 from a vehicle speed sensor (not shown). In addition, the control unit 10
In addition, various signals such as the intake air amount, the intake pipe negative pressure, the engine water temperature, and the oxygen concentration in the exhaust gas are input.

FIG. 3 is a region diagram of the fuel control in the above embodiment, in which the vertical axis represents the load (intake pipe negative pressure) and the horizontal axis represents the engine speed, and the feedback of the air-fuel ratio lean setting (lean F). / B), high load / high speed increase, idle increase, deceleration fuel stop (deceleration F / C) and over-speed fuel stop (overrev F / C).

In the lean F / B zone, the air-fuel ratio (A
/ F) is made larger than the stoichiometric air-fuel ratio, and its set value depends on the engine speed and the load. In the lean F / B zone, the basic fuel injection amount is set based on the engine speed and the intake air amount, and various corrections such as water temperature are added to the basic injection amount, and further feedback correction based on the oxygen concentration signal is added. And the final injection amount. Then, a control pulse corresponding to this final injection amount is applied to the fuel injection valve 5, whereby the air-fuel ratio of the engine 1 is controlled to a predetermined value. Further, in the high load / high rotation increasing zone and the idle increasing zone, the feedback control is stopped to perform the required fuel increase, and in the deceleration F / C zone and the overrev F / C zone (for example, the engine speed is 7,000 rpm or more). The fuel supply is stopped. Although not shown in the above area diagram, the fuel supply is also stopped when the vehicle speed exceeds a predetermined value (for example, 180 km / h).

On the other hand, in the above embodiment, the lean NOx catalyst 7 is used.
By closing the bypass valve 9 when the temperature is lower than the heat resistant temperature and opening the bypass valve 9 when the lean NOx catalyst 7 becomes higher than the heat resistant temperature, the temperature of the lean NOx catalyst 7 is controlled within the heat resistant temperature range. I have to. Further, in the deceleration F / C zone or the overrev F / C zone, or in the region where the vehicle speed exceeds a predetermined value, the bypass valve 9 is forcibly opened regardless of the catalyst temperature, whereby exhaust gas with high oxygen concentration is produced. Gas is prevented from flowing to the lean NOx catalyst 7. Further, among these, in the control of the bypass valve 9 in the deceleration F / C zone, the opening control of the bypass valve 9 is performed with a predetermined delay time after it is detected that the engine 1 has entered the deceleration F / C zone. Executed. During this delay, the adhering fuel sucked in at the initial stage of deceleration flows as it is to the lean NOx catalyst 7, and the oxygen adsorbed on the lean NOx catalyst 7 is released.

FIG. 4 is a flow chart for executing the control of the bypass valve 9, and S1 to S6 show respective steps thereof.

In the flowchart of FIG. 4, when starting, various signals such as catalyst temperature, engine speed, vehicle speed, intake pipe negative pressure and throttle opening are read in S1. Then, in S2, it is checked whether the current temperature T ₀ of the catalyst is lower than the heat resistant temperature T _{1 of the} catalyst.

At S2, the current catalyst temperature T ₀ is the heat resistant temperature T ₁
If it is lower, the process proceeds to S3, and it is determined whether the operating region of the engine 1 is the deceleration F / C or the overrev F / C or the fuel stop (F / C) region due to the vehicle speed exceeding a predetermined value. If it is in the F / C area, the process proceeds to S4, and it is determined whether the F / C is the deceleration F / C. If the F / C is the deceleration F / C, the process proceeds to S5 and a predetermined delay is applied. After the opening, the bypass valve 9 is opened.

In S4, if the F / C other than the deceleration F / C, that is, the overrev F / C or the F / C resulting from the vehicle speed exceeding a predetermined value, the process proceeds to S6 and the bypass valve 9 is immediately opened. open.

Further, the current temperature T ₀ of the catalyst is determined in the determination of S2.
If is higher than the heat resistant temperature T _{1 of the} catalyst, the process also proceeds to S6 and the bypass valve 9 is opened immediately.

If the result of S3 is not F / C, the process directly returns.

[0023]

As described above, the present invention is constructed as described above. By bypassing the lean NOx catalyst when fuel is stopped, the lean NOx catalyst adsorbs oxygen and deteriorates.
x It is possible to prevent deterioration of the purification performance. In addition, by applying a predetermined delay to the bypass of the lean NOx catalyst when the deceleration fuel is stopped, it is possible to separate the oxygen adsorbed by the lean NOx catalyst and improve the NOx purification performance.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of the present invention.

FIG. 2 is a system diagram of an embodiment of the present invention.

FIG. 3 is a region diagram of fuel control in one embodiment of the present invention.

FIG. 4 is a flowchart for executing control of a bypass valve according to an embodiment of the present invention.

[Explanation of symbols]

 1 engine 5 fuel injection valve 6b bypass passage 7 lean NOx catalyst 9 bypass valve 10 control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location F02D 45/00 301 G 7536-3G (72) Inventor Tadataka Nakagaku Shinchi Fuchu-cho, Aki-gun, Hiroshima No. 1 in Mazda Motor Corporation

Claims (5)

[Claims] 1. NO in engine exhaust gas at least in a lean air-fuel ratio region where the air-fuel ratio is larger than the theoretical air-fuel ratio.
lean NOx catalyst for reducing x, a bypass passage for bypassing the lean NOx catalyst, an exhaust path of the engine for flowing exhaust gas to the lean NOx catalyst and an exhaust gas for the bypass passage according to an operating state of the engine. In the engine, the exhaust system is provided with a switching means for switching to a path through which the fuel flows, and a fuel stopping means for stopping the supply of fuel to the engine in a predetermined operating region. An engine exhaust control device characterized in that a fuel stop catalyst bypass control means is provided for controlling the switching means so that exhaust gas of the engine bypasses the lean NOx catalyst and flows into the bypass passage regardless of the state. .. 2. The exhaust control system for an engine according to claim 1, wherein the fuel stopping means operates in an operating region in which an engine speed equal to or higher than a predetermined speed is detected. 3. The exhaust control system for an engine according to claim 1, wherein the fuel stopping means operates in an operating region where a vehicle speed equal to or higher than a predetermined vehicle speed is detected. 4. The exhaust control system for an engine according to claim 1, wherein the fuel stopping means operates in an operating region where deceleration of the engine is detected. 5. The exhaust control device for an engine according to claim 4, further comprising a bypass delay means for applying a predetermined delay to the operation of the lean NOx catalyst bypass control means at the time of operating the fuel stop means.