JP2006299937A - Exhaust device for internal combustion engine and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent initial exhaust gas of high HC concentration after start of cranking from being discharged to an outside by temporarily trapping the same. <P>SOLUTION: A main passage 3 is connected to an exhaust port 2, and a main catalytic converter 4 is arranged in an downstream side. A flow passage change over valve 5 opening and closing the main passage 3 is provided in a middle of the main passage 3. A bypass passage 7 of small passage cross section area branches off a branch point 6 of the main passage 3 and a small size bypass catalytic converter 8 is installed in a middle thereof. Exhaust gas is guided to a bypass passage 7 side and exhaust emission control is performed right after cold start. Initial exhaust gas of high HC concentration is trapped in a section from the branch point to a merge point 12 by opening a flow passage change over valve 5 at a time of start of cranking and closing the flow passage change over valve 5 after several cycles from start of fuel injection. Since the flow passage change over valve 5 opens after completion of warming up, exhaust gas is simultaneously purified by the main catalytic converter 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust apparatus and a control method therefor, in which exhaust gas is guided by a flow path switching valve to a bypass flow path side provided with a catalytic converter relatively upstream of the exhaust system immediately after a cold start. The present invention relates to an early exhaust treatment technology containing a large amount of components.

  As conventionally known, in a configuration in which the main catalytic converter is disposed relatively downstream of the exhaust system such as under the floor of a vehicle, the temperature of the catalytic converter rises and is activated after a cold start of the internal combustion engine. In the meantime, a sufficient exhaust purification action cannot be expected. On the other hand, the closer the catalytic converter is to the upstream side of the exhaust system, that is, the internal combustion engine side, the lower the durability due to thermal degradation of the catalyst.

Therefore, as disclosed in Patent Document 1, a bypass flow path is provided in parallel with the upstream portion of the main flow path including the main catalytic converter, and another bypass catalytic converter is interposed in the bypass flow path. However, an exhaust device has been conventionally proposed in which exhaust gas is guided to the bypass flow path side immediately after cold start by a switching valve for switching between the two. In this configuration, the bypass catalytic converter is positioned relatively upstream of the main catalytic converter in the exhaust system and is activated relatively early, so that exhaust purification can be started from an earlier stage. it can.
JP-A-5-321644

  In the exhaust system provided with the bypass catalytic converter as described above, although the bypass catalytic converter is activated relatively early, the exhaust containing a large amount of unburned components discharged during several cycles immediately after the start of cranking. However, activation is not in time, and purification cannot be performed. Therefore, in order to prevent the initial HC discharge, it is necessary to use an HC trap catalyst that temporarily adsorbs HC. In particular, in a gasoline engine that performs spark ignition, it is possible to perform ignition in a normal ignition sequence after completing the cylinder discrimination process for determining which cylinder is at the compression top dead center. In addition, since the fuel injection is started before the cylinder discrimination is completed, there is a possibility that a cylinder in which the injected fuel is discharged without being burned is generated. Therefore, the HC concentration is high immediately after the cranking is started. Exhaust is likely to occur.

  Therefore, in the present invention, the volume of the main passage through which exhaust does not flow until the warming-up of the main catalytic converter is completed is used as a kind of trap for temporarily storing exhaust having a high HC concentration immediately after starting.

  That is, according to the first aspect of the present invention, a bypass passage is provided in parallel with a portion between the upstream branch point of the main passage and the downstream junction, and the main catalytic converter is disposed downstream of the junction. An exhaust device for an internal combustion engine comprising a bypass catalytic converter in the bypass passage, and a flow path switching valve that closes the main passage between the branch point of the main passage and the junction point, It is characterized by comprising switching valve control means for controlling opening and closing of the flow path switching valve so as to store exhaust gas immediately after starting at a portion from the branch point to the junction point of the main passage.

  In one specific aspect, the switching valve control means opens the flow path switching valve after the start of cranking until the predetermined cycle elapses after the start of fuel injection, and thereafter until the warm-up of the main catalytic converter is completed. Closed.

  In the control method according to claim 4, a bypass passage is provided in parallel with a portion between the upstream branch point of the main passage and the downstream junction, and the main catalytic converter is disposed downstream of the junction. An exhaust device for an internal combustion engine comprising a bypass catalytic converter in the bypass passage, and a flow path switching valve that closes the main passage between the branch point of the main passage and the junction point, At the time of starting, the flow path switching valve is opened so that the exhaust gas immediately after the start flows into the main passage side, and then the flow path switching valve is closed before the exhaust gas immediately after the start reaches the merging point. The exhaust immediately after start-up is stored in the portion of the main passage from the branch point to the junction.

  In one specific aspect, after the cranking is started, the flow path switching valve is opened during the period from the fuel injection start time to the lapse of a predetermined cycle, then closed, and opened when the main catalytic converter is warmed up. To do.

  That is, even immediately after the cold start to guide the exhaust to the bypass catalytic converter side, the flow path is very short from the start of cranking, for example, until a predetermined number of cycles elapse from the start of fuel injection. The switching valve is open. As a result, the initial exhaust gas having a high HC concentration flows into the main passage. If the flow path switching valve is closed before the exhaust gas having a high HC concentration flows downstream from the merging point, the flow on the main passage side stops, and the HC concentration is high in the section from the branch point of the main passage to the merging point. Exhaust is stored. While the flow path switching valve is closed, the exhaust discharged from the internal combustion engine is guided to the bypass passage side, and exhaust purification is performed by the bypass catalytic converter. Thereafter, when the main catalytic converter is warmed up, that is, activated, the flow path switching valve is opened, and the exhaust flows through the main passage side. Along with this, the exhaust gas having a high HC concentration stored in the main passage is exhausted through the main catalytic converter already in an active state.

  In one desirable mode, the above-mentioned channel change-over valve is arranged in the middle position of the length from the above-mentioned branch point of the main passage to the above-mentioned junction. In other words, at the branch point and the junction point, the portion of the main passage that stores the initial exhaust is an open end that is open to the bypass passage, but the flow passage switching valve in the intermediate position is closed, so that the flow passage Exhaust gas is stored both upstream and downstream of the switching valve.

  According to the present invention, the exhaust gas having a high HC concentration discharged from the engine at the initial stage of the start can be temporarily trapped using the exhaust passage itself and reliably processed after the main catalytic converter is activated. Therefore, it is possible to reduce the initial HC discharge amount without requiring addition of a volume chamber.

  Hereinafter, an embodiment in which the present invention is applied as an exhaust device of an in-line four-cylinder internal combustion engine will be described in detail based on the drawings.

  FIG. 1 is an explanatory view schematically showing the piping layout of the exhaust device. First, the configuration of the entire exhaust device will be described based on FIG.

  In the cylinder head 1, exhaust ports 2 of the cylinders # 1 to # 4 arranged in series are formed so as to open toward the side surfaces, and a main passage is formed in each of the exhaust ports 2. 3 is connected. The four main passages 3 of the # 1 cylinder to the # 4 cylinder merge into one flow path, and the main catalytic converter 4 is disposed on the downstream side thereof. The main catalytic converter 4 has a large capacity disposed under the floor of the vehicle, and a three-way catalyst is used as a catalyst. However, an HC trap catalyst may be included as necessary. The main passage 3 and the main catalytic converter 4 constitute a main passage through which exhaust flows during normal operation. In addition, a flow path switching valve 5 that opens and closes the main passages 3 at the same time is provided as a flow path switching means at the junction of the four main paths 3 from each cylinder. When the flow path switching valve 5 is in the closed state, the mutual communication of the four main passages 3 upstream from this is simultaneously blocked.

  On the other hand, bypass passages 7 each having a smaller passage sectional area than the main passage 3 are branched from the main passages 3 of the respective cylinders as bypass passages. The branch point 6 that is the upstream end of each bypass passage 7 is set to a position on the upstream side of the main passage 3 as much as possible. The four bypass passages 7 merge into one flow path on the downstream side, and a bypass catalytic converter 8 using a three-way catalyst is interposed immediately after the junction. The bypass catalytic converter 8 has a small capacity as compared with the main catalytic converter 4, and preferably uses a catalyst excellent in low-temperature activity. The downstream end of the bypass passage 7 extending from the outlet side of the bypass catalytic converter 8 is connected to the upstream side of the main catalytic converter 4 in the main passage 3 at the junction 12.

  Air-fuel ratio sensors 10 and 11 are disposed at the inlet of the main catalytic converter 4 and the inlet of the bypass catalytic converter 8, respectively.

  In such a configuration, basically, at a stage where the engine temperature or the exhaust temperature after the cold start is low, the flow path switching valve 5 is closed via the appropriate actuator, and the main passage 3 is shut off. Therefore, the entire amount of exhaust discharged from each cylinder flows from the branch point 6 to the bypass catalytic converter 8 through the bypass passage 7. The bypass catalytic converter 8 is located upstream of the exhaust system, that is, at a position close to the exhaust port 2 and is small in size, so that it is activated quickly and exhaust purification is started at an early stage.

  On the other hand, when the engine warms up and the engine temperature or the exhaust temperature becomes sufficiently high, the flow path switching valve 5 is opened. Thus, the exhaust discharged from each cylinder mainly passes through the main catalytic converter 4 from the main passage 3. At this time, the bypass passage 7 side is not particularly cut off, but the bypass passage 7 side has a smaller passage cross-sectional area than the main passage 3 side and the bypass catalytic converter 8 is interposed. Due to the difference, most of the exhaust flow passes through the main passage 3 side and hardly flows into the bypass passage 7 side. Therefore, the thermal deterioration of the bypass catalytic converter 8 is sufficiently suppressed.

  Next, more specific opening / closing control of the flow path switching valve 5 will be described based on the time chart of FIG.

  FIG. 2 shows changes in various parameters and the like after starting. (A) Open / close state of flow path switching valve 5, (b) Starter motor ON / OFF, (c) Start of fuel injection. Cumulative number of cycles (Note: Since it is a 4-cylinder engine, it will be 4 cycles at 720 ° CA), (d) Engine speed NE, (e) Cranking fuel injection amount TIST, (f) Normal fuel injection amount TP , (G) air-fuel ratio, (h) ignition timing ADV, (i) exhaust temperature, and (j) HC concentration discharged outside. Although the horizontal axis represents time, several cycles at the time of starting are particularly enlarged. Between timings T1 and T2, indicated by thin vertical lines, between T2 and T3, and between T3 and T4. Are 360 ° CA. Further, as the fuel injection amount, the fuel injection amount TIST at the time of cranking is calculated based on the injection amount uniquely determined according to the cooling water temperature or the like, and the fuel injection amount TP is calculated based on the intake air amount detected by the air flow meter, etc. The larger one of the cranking fuel injection amount TIST and the normal fuel injection amount TP is the actual injection amount. Accordingly, in this example, the rising of the cranking fuel injection amount TIST is the first fuel injection start.

  In this embodiment, the flow path switching valve 5 is closed or partially closed before cranking is started. However, this is not essential in the present invention. For example, when the flow path switching valve 5 is open when the engine is stopped, the state may be maintained as it is. And with the start of cranking, the flow path switching valve 5 is opened. This open state is determined from the relationship between the volume of the predetermined cycle number from the start of fuel injection (the volume of the section from the branch point 6 to the junction point 12 of the main passage 3 and the exhaust amount of each cylinder, for example, seven cycles in the illustrated example. When the branch point 6 is away from the exhaust port 2, it is desirable to take into account the delay due to the distance.) When the predetermined number of cycles has elapsed, the flow path switching valve 5 Is closed. As a result, the above-described initial exhaust gas having a high HC concentration is filled in the section from the branch point 6 to the junction point 12 of the main passage 3. Thereafter, when it is determined that the catalyst of the main catalytic converter 4 has been activated, the flow path switching valve 5 is opened, and the exhaust mainly flows through the main passage 3 as described above. At the same time, the exhaust gas with a high HC concentration that has been filled is also introduced into the main catalytic converter 4.

  FIG. 3 is an explanatory view showing the opening / closing operation of the flow path switching valve 5 together with the movement of the gas. Before the engine is started, as shown in (1), the flow path switching valve 5 is, for example, partially In the section from the branch point 6 to the junction point 12 of the main passage 3, air or a lean exhaust gas G1 diluted with air remains. At the start of cranking, the flow path switching valve 5 is opened as shown in (2), and the movement of gas in the main passage 3 is allowed. At this time, the gas G1 close to the remaining air passes through the main catalytic converter 4, so that the amount of oxygen storage of the catalyst is increased, which is advantageous for catalyst activation. Thereafter, when fuel injection is started, as shown in (3), the gas G2 having a high HC concentration containing a large amount of unburned components is discharged from the exhaust port 2 and flows into the main passage 3. When the predetermined number of cycles has elapsed since the start of fuel injection, the flow path switching valve 5 is closed as shown in (4). The number of cycles is set so that the gas G2 having a high HC concentration does not go downstream from the junction 12 and the head of the gas G2 is as close to the junction 12 as possible. As shown in (5), in the state where the flow path switching valve 5 is completely closed, no gas flows in the main passage 3 between the branch point 6 and the junction point 12, so that a gas with a high HC concentration is present. G2 is stored in the section from the branch point 6 to the junction 12 of the main passage 3. During this time, the exhaust discharged from the exhaust port 2 flows through the bypass passage 7 as described above. When the main catalytic converter 4 is activated in this state for a certain period of time, the flow path switching valve 5 is opened and most of the exhaust gas flows through the main passage 3 as shown in (6). Then, the gas G2 having a high HC concentration held in the main passage 3 is also introduced into the main catalytic converter 4 at the same time. Note that, in the state shown in (5), both ends of the main passage 3 (that is, the branching point 6 and the junction 12) serving as a trap for the gas G2 are not closed and are open to the bypass passage 7. Since the flow path switching valve 5 prevents the flow of gas, it is only slightly diffused, and in particular, it is disposed at an intermediate position in the length from the branch point 6 to the junction point 12 of the main passage 3. In the vicinity of the flow path switching valve 5, the gas G2 can be held for a sufficiently long time.

  In the HC concentration shown in FIG. 2 (j), the characteristic of the solid line shows that the trap of the gas G2 having a high HC concentration described above is not performed (that is, the flow path switching valve 5 is kept closed from the start of cranking). On the other hand, the broken line indicates the characteristic when the above-described trap of the gas G2 having a high HC concentration is performed. As shown in the figure, according to the present invention, the discharge of HC to the outside at the initial stage of starting can be greatly reduced.

  Here, the HC concentration in the initial stage of the start is very high because there may be a cylinder that does not reach ignition and discharges fuel without being burned. That is, the internal combustion engine of this embodiment is of a port injection type in which a fuel injection valve is arranged at the intake port, and basically injects fuel toward the intake port in the expansion stroke of each cylinder. Immediately after the cranking is started, the cylinder discrimination process of which cylinder is at the top dead center is not completed, so the first fuel injection is considered to be in the expansion stroke or the intake stroke. On the other hand, fuel injection is performed simultaneously. Therefore, in the cylinder that was in the intake stroke at that time, although a part of the fuel flows into the cylinder, it may be discharged to the exhaust port 2 without being properly ignited and unburned. Therefore, although the initial exhaust gas has a very high HC concentration, the discharge of unburned fuel occurs in the very first cycle. Therefore, in the section from the branch point 6 serving as the trap to the junction point 12 described above. If the volume is equivalent to several cylinders of the displacement of one cylinder, the discharge to the outside can be reliably suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the piping layout of the whole exhaust apparatus which concerns on this invention. The time chart which shows the operation | movement etc. of each part at the time of cold start. Explanatory drawing which shows the opening / closing operation | movement of a flow-path switching valve with the motion of gas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Main passage 4 ... Main catalytic converter 5 ... Flow path switching valve 6 ... Branch point 7 ... Bypass passage 8 ... Bypass catalytic converter 12 ... Junction point

Claims (6)

  A bypass passage is provided in parallel with a portion between a branch point on the upstream side of the main passage and a junction on the downstream side, and a main catalytic converter is provided on the downstream side of the junction, and the bypass catalytic converter is provided in the bypass passage. And a flow path switching valve that closes the main passage between the branch point of the main passage and the junction point. An exhaust system for an internal combustion engine, comprising switching valve control means for controlling the opening and closing of the flow path switching valve so as to store exhaust immediately after starting in a portion up to a point.   The switching valve control means opens the flow path switching valve from the start of fuel injection to the passage of a predetermined cycle after cranking starts, and then closes until the main catalytic converter is warmed up. The exhaust system for an internal combustion engine according to claim 1.   3. The exhaust device for an internal combustion engine according to claim 1, wherein the flow path switching valve is disposed at an intermediate position in a length from the branch point to the junction point of the main passage.   A bypass passage is provided in parallel with a portion between a branch point on the upstream side of the main passage and a junction on the downstream side, and a main catalytic converter is provided on the downstream side of the junction, and the bypass catalytic converter is provided in the bypass passage. And an exhaust device for an internal combustion engine comprising a flow path switching valve that closes the main passage between the branch point and the junction of the main passage. The flow path switching valve is opened so as to flow into the passage side, and then the flow path switching valve is closed before the exhaust gas immediately after the start reaches the confluence, so that the branch path from the branch point of the main path is A method for controlling an exhaust device of an internal combustion engine, characterized in that exhaust immediately after starting is stored in a portion up to a junction.   The flow path switching valve is opened from the fuel injection start time to the passage of a predetermined cycle after the cranking is started, and then closed, and is opened when the main catalytic converter is warmed up. 5. A method for controlling an exhaust device of an internal combustion engine according to 4. 6. The method for controlling an exhaust device of an internal combustion engine according to claim 4, wherein the internal combustion engine starts fuel injection before completion of cylinder discrimination at start-up.