JP2009228644A - Exhaust emission control system and method therof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system capable of efficiently purifying an exhaust emission from immediately after the start of an engine, while precisely controlling an exhaust emission flowing passage, and a method thereof. <P>SOLUTION: The exhaust emission control system includes a main catalyst provided in a main passage, a bypass passage branching once from the main passage located in an upstream of the main catalyst to again join to the main passage in the upstream of the main catalyst, a bypass passage catalyst provided in the bypass passage, a flow control valve which is provided in the main passage and specifically on more downstream side than a portion where the bypass passage branches and more upstream side than a portion where the bypass passage l joins the main passage and can regulate the exhaust emission volume flowing through the main passage. Further, the exhaust emission control system includes a gas temperature estimating means (steps S2, S3, S5) for estimating exhaust emission temperature based on an engine operational status, and a valve control means (steps S8, S9) for performing opening and closing control of the flow control valve based on the estimated exhaust emission temperature. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an apparatus and method for controlling purification of exhaust gas discharged from an engine.

The conventional exhaust gas purification control apparatus measures the temperature of the main catalyst container provided in the main passage with a sensor, and changes the path through which the exhaust gas flows based on the measured temperature (see Patent Document 1).
JP-A-8-144789

  However, the above-described conventional apparatus measures the temperature of the catalyst container. The exhaust gas temperature varies rapidly and greatly depending on the operating state of the engine, but the temperature of the catalyst container varies more slowly and smaller than the exhaust gas temperature. Therefore, even if the path through which the exhaust gas flows is changed based on the measured temperature of the catalyst container, the control accuracy is poor.

  The present invention has been made paying attention to such conventional problems, and can control the exhaust gas flow path with high accuracy, and can efficiently purify the exhaust gas immediately after the engine is started. An object is to provide a control device and an exhaust gas purification control method.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

  In the present invention, the main catalyst (21) provided in the main passage (20) and the main passage (20) upstream of the main catalyst (21) are once branched, and the main passage (upstream of the main catalyst (21)) ( 20), a bypass passage (30) rejoining, a bypass passage catalyst (31) provided in the bypass passage (30), and a portion of the main passage (20) where the bypass passage (30) branches. A flow rate control valve (40) provided downstream of the bypass passage (30) and upstream of a portion where the bypass passage (30) merges, and capable of adjusting the amount of exhaust gas flowing through the main passage (20), and exhaust gas based on engine operating conditions Gas temperature estimating means (steps S2, S3, S5) for estimating the temperature, and valve control means (steps S8, S9) for opening / closing the flow rate control valve (40) based on the estimated exhaust gas temperature. It is characterized by.

  According to the present invention, the exhaust gas temperature is estimated based on the engine operating state, and the flow control valve is controlled to open and close based on the estimated exhaust gas temperature. Since it did in this way, a flow control valve can be controlled accurately according to the degree of activation of a catalyst, and exhaust gas can be purified efficiently immediately after engine starting. If the flow control valve is closed after a lapse of a predetermined time after the main gas temperature falls below the catalyst activation temperature, the flow control valve will open and close in response to changes in the operating state of the engine. Can be prevented. In addition, particularly when shifting from the valve closing state to the valve opening state, if such a waiting time is not provided, the exhaust gas is purified by the main catalyst immediately after the activation of the main catalyst, so that the exhaust gas can be efficiently purified. If the flow rate control valve is opened immediately even under conditions that can cause thermal deterioration of the bypass passage catalyst, the flow of high-temperature gas into the bypass passage catalyst can be reliably prevented, and the bypass passage catalyst is not thermally deteriorated.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing the activity characteristics of an exhaust gas purification catalyst used in an exhaust gas purification control apparatus according to the present invention.

  First, in order to facilitate understanding of the present invention, a basic technical idea will be described.

  An exhaust gas purification catalyst for purifying exhaust gas is inactive when the exhaust gas temperature is low, and cannot exhibit exhaust gas purification performance. For example, in the exhaust gas purification catalyst used in the exhaust gas purification control apparatus of this embodiment, as shown in FIG. 1, when the exhaust gas temperature exceeds about 260 ° C., the conversion rate of nitrogen oxides NOx and carbon monoxide CO is almost 100%. Become. When the exhaust gas temperature exceeds about 380 ° C., the conversion rate of hydrocarbon HC becomes almost 100% and the exhaust gas purification performance is exhibited. Thus, the exhaust gas purification catalyst exhibits exhaust gas purification performance when the exhaust gas temperature is approximately 400 ° C. or higher. When the exhaust gas temperature is about 200 ° C. or less, the exhaust gas is hardly purified.

  FIG. 2 is a diagram showing the thermal deterioration characteristics of the exhaust gas purification catalyst used in the exhaust gas purification control apparatus according to the present invention.

  However, if the exhaust gas temperature is too high, heat deterioration will occur. For example, when it continues to be exposed to exhaust gas having a temperature of 850 ° C., the T50 temperature (temperature at a conversion rate of 50%) becomes 280 ° C. after an elapsed time of about 34 hours. The T50 temperature becomes 290 ° C. after an elapsed time of about 58 hours. The T50 temperature becomes 300 ° C. after an elapsed time of about 83 hours. The T50 temperature becomes 310 ° C. after an elapsed time of about 105 hours.

  From another viewpoint, the T50 temperature is saturated to 300 ° C. when exposed to an exhaust gas having a temperature of 740 ° C. for 250 hours or longer.

  As the time of exposure to the high temperature exhaust gas becomes longer, the performance of the catalyst deteriorates.

  Based on such knowledge, the inventors of the present invention have provided a main catalyst that can be increased in capacity apart from the engine and a bypass passage catalyst that is close to the engine and difficult to increase in capacity. The exhaust gas is efficiently purified immediately after the engine is started by flowing the exhaust gas to the main catalyst or the bypass passage catalyst according to the exhaust gas temperature flowing through the catalyst. Below, the concrete structure which implement | achieves such a technical idea is demonstrated.

  FIG. 3 is a diagram showing an embodiment of the exhaust gas purification control apparatus according to the present invention.

  The exhaust gas purification control device 1 includes an exhaust gas main passage 20, a main catalyst 21, a bypass passage 30, a bypass passage catalyst 31, and a flow rate control valve 40.

  The main catalyst 21 is provided in the exhaust gas main passage 20. The main catalyst 21 is disposed away from the engine 10. Since it is away from the engine 10, there is no interference with peripheral parts, and the capacity can be increased.

  The bypass passage 30 once branches from the exhaust gas main passage 20 upstream of the main catalyst 21 and joins the exhaust gas main passage 20 upstream of the main catalyst 21 again.

  The bypass passage catalyst 31 is provided in the bypass passage 30. The bypass passage catalyst 31 is disposed in the engine room. Since it is arranged in the engine room, it is close to the surrounding parts and is small.

  The flow control valve 40 is provided in the exhaust gas main passage 20 downstream of the portion where the bypass passage 30 branches and upstream of the portion where the bypass passage 30 joins. The flow control valve 40 is, for example, a butterfly valve. In FIG. 3, only the housing that houses the flow control valve 40 is shown, and the valve itself is not shown. The flow control valve 40 can adjust the amount of exhaust gas flowing through the exhaust gas main passage 20 by changing the opening degree. When the flow control valve 40 is opened, the exhaust gas flows through the exhaust gas main passage 20 and hardly flows into the bypass passage 30. When the flow control valve 40 is closed, the exhaust gas cannot flow through the exhaust gas main passage 20 but flows into the bypass passage 30.

  FIG. 4 is a flowchart of the control logic of the exhaust gas purification control apparatus according to the invention.

  When receiving the engine start command, the controller repeatedly executes the following processing every minute time (for example, 10 milliseconds).

  In step S1, the controller determines whether or not the acceleration is small. If the acceleration is small, the process proceeds to step S2, and if not, the process proceeds to step S9.

  In step S2, the controller estimates the temperature of the exhaust gas flowing out from the engine based on the engine operating state (engine speed, fuel injection pulse width, throttle opening). Specifically, a characteristic map between the engine operating state and the exhaust gas temperature may be stored in advance in the ROM.

  In step S3, the controller further estimates the exhaust gas temperature tm flowing into the main catalyst 21 in consideration of the outside air temperature. Specifically, the characteristic map may be stored in advance in the ROM.

  In step S4, the controller determines whether or not the exhaust gas temperature tm is lower than the catalyst activation temperature ta. If so, the process proceeds to step S5; otherwise, the process proceeds to step S9. The catalyst activation temperature ta is set in advance according to the catalyst characteristics based on the experimental results as shown in FIG.

  In step S5, the controller estimates the exhaust gas temperature tb flowing into the bypass passage catalyst 31 in consideration of the outside air temperature. Specifically, the characteristic map may be stored in advance in the ROM.

  In step S6, the controller determines whether or not the exhaust gas temperature tb is lower than the catalyst deterioration temperature td. If it is low, the process proceeds to step S7, and if it is high, the process proceeds to step S9. The catalyst deterioration temperature td is set in advance according to the required performance (that is, the endurance performance such as the maximum allowable T50 temperature when the characteristics are saturating) based on the experimental results as shown in FIG.

  In step S7, the controller determines whether or not the delay timer is zero. If zero, the process proceeds to step S8, and if not zero, the process proceeds to step S11. The initial value of the delay timer is zero.

  In step S8, the controller closes the flow control valve 40.

  In step S9, the controller opens the flow control valve 40.

  In step S10, the controller sets a delay timer.

  In step S11, the controller decrements the delay timer.

  FIG. 5 is a schematic diagram showing the flow of exhaust gas when the exhaust gas purification control apparatus according to the invention is executed.

  Immediately after starting the engine, the acceleration of the vehicle is small and the exhaust gas temperature is low. The initial value of the delay timer is zero. At this time, steps S1 → S2 → S3 → S4 → S5 → S6 → S7 → S8 are repeated and the flow control valve 40 is closed. Then, the exhaust gas flows through the bypass passage 30 → the bypass passage catalyst 31 as shown in FIG. Since the bypass passage catalyst 31 is disposed closer to the engine 10 than the main catalyst 21, it can be activated earlier than the main catalyst 21 and can efficiently purify exhaust gas immediately after the engine is started.

  When the engine is warmed up and the exhaust gas temperature rises and the exhaust gas temperature tm becomes higher than the catalyst activation temperature ta, the process flows from step S4 to S9, and the flow control valve 40 is opened. Then, the exhaust gas flows through the exhaust gas main passage 20 as shown in FIG. 5B, and the exhaust gas is purified by the main catalyst 21. Even if the exhaust gas temperature tm is lower than the catalyst activation temperature ta, if the exhaust gas temperature tb exceeds the catalyst deterioration temperature td, the process proceeds from step S6 to S9, and the flow control valve 40 is opened. Then, the exhaust gas hardly flows into the bypass passage 30 as shown in FIG. 5 (B), and thermal deterioration of the bypass passage catalyst 31 is prevented. In step S10, a delay timer is set.

  Even when the accelerator pedal is depressed and the acceleration of the vehicle increases, the process proceeds from step S1 to S9, and the flow control valve 40 opens.

  After the next cycle, when the exhaust gas temperature decreases due to the deceleration state or the idle state, the process flows again through steps S1, S2, S3, S4, S5, S6, and S7. Until the delay timer becomes zero, the process proceeds from step S7 to S11. That is, the process is repeated from step S1 to S2 to S3 to S4 to S5 to S6 to S7 to S11. When the delay timer becomes zero, the process proceeds from step S7 to S8, the flow control valve 40 is closed, and the state shown in FIG. If the operating state changes before the delay timer becomes zero, the process proceeds from step S1 to S9 or step S4 to S9 or step S6 to S9, and the flow control valve 40 is closed (the state shown in FIG. 5A). Instead, the valve open state (the state shown in FIG. 5B) continues.

  According to the present embodiment, the flow rate control valve 40 is shifted from the open state to the closed state after waiting for the predetermined operation state to elapse for a certain time. Since it did in this way, it can prevent that the flow control valve 40 reacts sensitively to the operating state change of an engine, and opens and closes. In particular, the delay timer is operated when shifting from the valve open state to the valve closed state, and the delay timer is not operated when shifting from the valve closed state to the valve open state. Since it did in this way, the flow control valve 40 opens as soon as the main catalyst 21 is activated, and the exhaust gas is purified by the main catalyst 21, so that the exhaust gas can be purified efficiently. In addition, when the conditions under which the thermal degradation of the bypass passage catalyst 31 can occur, the flow rate control valve 40 opens quickly, so that the flow of high-temperature gas into the bypass passage catalyst 31 can be reliably prevented and the bypass passage catalyst 31 is thermally degraded. I will not let you.

  Without being limited to the embodiments described above, various modifications and changes are possible within the scope of the technical idea, and it is obvious that these are also included in the technical scope of the present invention.

It is a figure which shows the active characteristic of the exhaust gas purification catalyst used for the exhaust gas purification control apparatus by this invention. It is a figure which shows the heat deterioration characteristic of the exhaust gas purification catalyst used for the exhaust gas purification control apparatus by this invention. It is a figure which shows one Embodiment of the exhaust gas purification control apparatus by this invention. It is a flowchart of the control logic of the exhaust gas purification control apparatus by invention. It is a schematic diagram which shows the flow of exhaust gas when the exhaust gas purification control apparatus by invention is performed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification control apparatus 10 Engine 20 Exhaust gas main path 21 Main catalyst 30 Bypass path 31 Bypass path catalyst 40 Flow control valve Step S2, S3, S5 Gas temperature estimation means / gas temperature estimation process Step S8, S9 Valve control means / valve control Process

Claims (7)

A main catalyst provided in the main passage;
A bypass passage that once branches from the main passage upstream of the main catalyst and rejoins the main passage upstream of the main catalyst;
A bypass passage catalyst provided in the bypass passage;
A flow rate control valve that is provided downstream of a portion where the bypass passage branches and upstream of a portion where the bypass passage merges, and is capable of adjusting the amount of exhaust gas flowing through the main passage;
Gas temperature estimating means for estimating the exhaust gas temperature based on the engine operating state;
Valve control means for controlling the opening and closing of the flow rate control valve based on the estimated exhaust gas temperature;
An exhaust gas purification control device. The gas temperature estimating means estimates a main gas temperature flowing through the main catalyst,
The valve control means opens the flow control valve when the main gas temperature is higher than the catalyst activation temperature, and closes the flow control valve when the temperature is low.
The exhaust gas purification control apparatus according to claim 1. The gas temperature estimating means estimates a bypass gas temperature flowing through the bypass passage catalyst;
The valve control means opens the flow control valve when the bypass gas temperature is higher than the heat deterioration temperature of the bypass passage catalyst, and closes the flow control valve when the temperature is low.
The exhaust gas purification control apparatus according to claim 1 or 2, characterized by the above. The valve control means opens the flow control valve when the acceleration of the vehicle is relatively large, and closes the flow control valve when the vehicle acceleration is relatively small.
The exhaust gas purification control apparatus according to any one of claims 1 to 3, wherein The valve control means closes the flow control valve after the valve closing condition continues for a predetermined time while the flow control valve is open.
The exhaust gas purification control apparatus according to any one of claims 1 to 4, wherein The valve control means immediately opens the flow control valve when a valve opening condition is satisfied while the flow control valve is closed.
The exhaust gas purification control apparatus according to any one of claims 1 to 5, wherein A main catalyst provided in the main passage;
A bypass passage that once branches from the main passage upstream of the main catalyst and rejoins the main passage upstream of the main catalyst;
A bypass passage catalyst provided in the bypass passage;
A flow rate control valve that is provided downstream of a portion where the bypass passage branches and upstream of a portion where the bypass passage merges, and is capable of adjusting the amount of exhaust gas flowing through the main passage;
A method for controlling exhaust gas from an engine having
A gas temperature estimating step for estimating the exhaust gas temperature based on the engine operating state;
A valve control step for opening and closing the flow rate control valve based on the estimated exhaust gas temperature;
An exhaust gas purification control method comprising:

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