JP2008196333A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

An exhaust purification device for an internal combustion engine that prevents exhaust gas that has not been purified from being discharged to the outside is provided.
An exhaust purification system for an internal combustion engine according to the present invention is connected to upper / middle / downstream main exhaust passages (2), (3) and (7) provided with a main catalytic converter (8), and an upstream main exhaust passage and middle / downstream main exhaust passage. The bypass exhaust passages 11 and 14 for connecting the exhaust passage, the bypass catalytic converter 18 provided in the bypass exhaust passage, the first passage opening / closing means 4 for flowing the exhaust of the bypass exhaust passage, and the connection portion of the middle and downstream main exhaust passages It comprises second passage opening / closing means 12 installed in the nearby midstream side main exhaust passage.
[Selection] Figure 1

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that performs exhaust gas purification using a catalytic converter, and in particular, bypass exhaust gas having another catalytic converter immediately after a cold start in which the main catalytic converter disposed in the main exhaust passage is not activated. The present invention relates to an improvement of an exhaust gas purification device for an internal combustion engine that guides exhaust gas to a passage.

  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 main catalytic converter rises and is activated after the internal combustion engine is cold started. Until then, a sufficient exhaust purification action cannot be expected. On the other hand, the closer the main catalytic converter is to the upstream side of the exhaust system, that is, the internal combustion engine side, the lower the durability of the main catalytic converter due to thermal degradation.

Therefore, as disclosed in Patent Document 1, a bypass exhaust passage is provided in parallel with an upstream portion of the main exhaust passage provided with the main catalytic converter, and another bypass catalytic converter is interposed in the bypass exhaust passage. An exhaust device has been conventionally proposed in which exhaust gas is guided to the bypass exhaust passage 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-2005-351088

  In the conventional exhaust purification device, as the main exhaust passage, an upstream main exhaust passage for each cylinder connected to each cylinder, and a plurality of the upstream main exhaust passages merge into one passage. An exhaust passage and a main catalytic converter interposed in the middle of the downstream main exhaust passage. Further, as bypass exhaust passages, an upstream bypass exhaust passage for each cylinder branched from the upstream main exhaust passage, and a downstream bypass exhaust passage formed by joining the plurality of upstream bypass exhaust passages into one passage, A bypass catalytic converter interposed in the middle of the downstream bypass exhaust passage. The downstream end of the downstream bypass exhaust passage is connected to the downstream main exhaust passage at a position upstream of the main catalytic converter. The upstream main exhaust passage is provided with passage opening / closing means for switching the passage so that the exhaust discharged from each cylinder flows to the upstream bypass exhaust passage.

  In this conventional exhaust purification device, since the passage opening / closing means is installed for each upstream main exhaust passage connected to each cylinder, it is difficult to ensure the sealing performance of the passage opening / closing means, and the exhaust leaks downstream of the passage opening / closing means. When the main catalytic converter is not in an active state, exhaust gas that has not been purified may be discharged to the outside.

  Therefore, the present invention provides an exhaust emission control device for an internal combustion engine that prevents exhaust leaking from the passage opening / closing means from being released to the outside when the main catalytic converter at the time of starting the internal combustion engine is not in an active state. Goal.

  The present invention provides an exhaust gas purification apparatus for an internal combustion engine according to the present invention, comprising an upstream main exhaust passage for each cylinder connected to each cylinder of the internal combustion engine and a plurality of upstream main exhaust passages. A middle-stream side main exhaust passage that is joined to the passage, a downstream-side main exhaust passage that is connected downstream of the middle-stream-side main exhaust passage, a main catalytic converter that is interposed in the middle of the downstream-side main exhaust passage, An upstream bypass exhaust passage that branches from the upstream main exhaust passage, and the plurality of upstream bypass exhaust passages merge into one passage, and the downstream ends are the middle flow main exhaust passage and the downstream main exhaust passage. And a bypass catalytic converter interposed in the middle of the downstream bypass exhaust passage, and further exhaust discharged from each cylinder A first passage opening / closing means for opening and closing the upstream main exhaust passage so as to flow from the upstream main exhaust passage to the upstream bypass exhaust passage, and opening and closing the middle flow main exhaust passage, and the downstream main exhaust passage. And a second passage opening / closing means installed in the middle-stream side main exhaust passage in the vicinity of the connecting portion.

  According to the present invention, when the internal combustion engine is warmed up, the second passage opening / closing means is installed even when the exhaust leaks downstream from the first passage opening / closing means that closes to flow the exhaust gas to the bypass exhaust passage. The exhaust gas that has not been purified is reliably prevented from being discharged to the outside.

  Further, since the second passage opening / closing means is installed in the middle-stream side main exhaust passage in the vicinity of the connection portion between the middle-stream side main exhaust passage and the downstream-side main exhaust passage into which the exhaust from the bypass exhaust passage flows, The second passage opening / closing means is heated by the high-temperature exhaust gas, and deposits can be removed.

  FIG. 1 is an explanatory diagram schematically showing the layout of an exhaust emission control device to which the present invention is applied. The exhaust emission control device of the present invention includes a main exhaust passage connected to each cylinder 1 of an internal combustion engine, a main catalytic converter 8 installed in the main exhaust passage for purifying exhaust, and a main branch branched from an upstream portion of the main exhaust passage. The bypass exhaust passage is connected to the upstream portion of the catalytic converter 8 and the bypass catalytic converter 18 is disposed in the bypass exhaust passage and purifies exhaust when the internal combustion engine is cold. Further, a first switching valve 4 for selectively introducing exhaust gas into the bypass exhaust passage when the internal combustion engine is cold is installed in the main exhaust passage, and a second switching that ensures exhaust leakage of the first switching valve 4. A valve 12 is installed.

  The main exhaust passage is composed of an upstream side, a midstream side, and a downstream main exhaust passage 2, 3, 7. The upstream main exhaust passage 2 is connected to each cylinder 1 including cylinders # 1 to # 4 arranged in series in the internal combustion engine at the upstream end, and to each upstream main exhaust passage at the downstream end. A unit valve 5 in which a first switching valve 4 that opens and closes 2 is integrated is installed. Exhausted gas that has passed through the unit valve 5 is introduced into the midstream main exhaust passage 3 and further introduced into the main catalytic converter 8 disposed in the downstream main exhaust passage 7 on the downstream side. The main catalytic converter 8 includes a three-way catalyst and an HC trap catalyst, and purifies the introduced exhaust. A second switching valve 12 that selectively closes the midstream main exhaust passage 3 is installed in the midstream main exhaust passage 3 in the vicinity of the connection portion between the midstream main exhaust passage 3 and the downstream main exhaust passage 7.

  On the other hand, a bypass exhaust passage connecting the upstream portion of each upstream main exhaust passage 2 and the connecting portion of the midstream main exhaust passage 3 and the downstream main exhaust passage 7 is formed. The bypass exhaust passage is composed of upstream and downstream bypass exhaust passages 11 and 14, and the cross-sectional area of each bypass exhaust passage is smaller than the cross-sectional area of the main exhaust passage. The upstream bypass exhaust passages 11 connected to the upstream main exhaust passages 2 are aggregated and connected to the downstream bypass exhaust passage 14. A bypass catalytic converter 18 having a three-way catalyst having a smaller heat capacity than the main catalytic converter 8 is installed in the downstream bypass exhaust passage 14. Since the bypass catalytic converter 18 has a small capacity as described above and is located on the upstream side, the bypass catalytic converter 18 is quickly activated and used for exhaust purification when the engine is cold such as when the internal combustion engine is started.

  FIG. 2 and FIG. 3 are a configuration diagram and a main part sectional view for explaining the configuration of the valve unit 5 in which the first switching valves 4 are integrated. In the valve unit 5, four openings 52 to 55 are provided in a casing 51 to which the upstream main exhaust passage 2 of each cylinder is connected. The exhaust gas that has passed through each opening gathers into one flow in the valve unit 5 and flows out to the middle flow side main exhaust passage 3.

  Each first switching valve 4 installed in each opening 52 to 55 includes a shaft 56 driven in the rotational direction by an actuator (not shown), an arm 57 attached to the shaft 56, and the arm 57. And a supported rectangular valve body 58. In the state where the valve body 58 is closed, the openings 52 to 55 are individually closed over the entire circumference, so that the two adjacent openings 52, 55, 53 and 54 do not communicate with each other. In FIG. 2, for the purpose of explanation, one valve body 58 is shown in an open state and the other valve body 58 is shown in a closed state, but the two shafts 56 are linked by an appropriate link, Two valve bodies 58 are simultaneously opened and closed by an actuator (not shown). Further, the valve body 58 of the first switching valve 4 rotates to the upstream side in the exhaust flow direction to open the upstream main exhaust passage 2, but is not limited thereto, and may be opened downstream.

  FIG. 4 is a cross-sectional view illustrating the configuration of the second switching valve 12. The basic configuration is the same as that of the first switching valve 4 described above. The switching valve 12 is provided with an opening 62 in the casing 61 to which the middle-stream main exhaust passage 6 of each cylinder is connected. Each switching valve 12 includes a shaft 63 that is driven in the rotational direction by an actuator (not shown), an arm 64 attached to the shaft 63, and a rectangular valve body 65 supported by the arm 64. Is done. With such a configuration, when the valve body 65 is closed, the opening 62 is closed over the entire circumference. In FIG. 4, the valve element 65 of the second switching valve 12 rotates downstream in the exhaust flow direction to open the midstream main exhaust passage 3. However, the present invention is not limited thereto, and may be opened upstream. good.

  Needless to say, the first and second switching valves 4 and 12 are not limited to the illustrated embodiment, and various configurations can be used. For example, although the first switching valve 4 has been described as being configured for each cylinder, it may be configured as one switching valve after the upstream main exhaust passage 2 is assembled.

  In the exhaust purification apparatus configured as described above, the first and second switching valves 4 and 12 are closed via appropriate actuators at the stage where the engine temperature or the exhaust temperature after the cold start of the internal combustion engine is low, and the main The exhaust passage is blocked. Therefore, the entire amount of exhaust discharged from each cylinder 1 flows to the bypass catalytic converter 18 through the upstream bypass exhaust passage 11 and the downstream bypass exhaust passage 14. Since the bypass catalytic converter 18 is upstream of the exhaust system, that is, at a position close to the cylinder 1 and is small in size, the bypass catalytic converter 18 is activated quickly and exhaust purification is started at an early stage.

  On the other hand, when the internal combustion engine is warmed up and the engine temperature or the exhaust temperature becomes sufficiently high, the first and second switching valves 4 and 12 are opened. Thereby, the exhaust discharged from each cylinder 1 mainly flows from the upstream main exhaust passage 2 through the middle flow main exhaust passage 3 and the downstream main exhaust passage 7 to the main catalytic converter 8 to be purified. It is discharged outside. At this time, the bypass exhaust passage side is not particularly cut off, but the bypass exhaust passage side has a passage cross-sectional area smaller than that of the main exhaust passage side and the bypass catalytic converter 18 is interposed. Due to the difference, most of the exhaust passes through the main exhaust passage side and hardly flows into the bypass exhaust passage side. For this reason, the thermal deterioration of the bypass catalytic converter 18 is sufficiently suppressed. In addition, since the bypass exhaust passage side is not completely cut off, a part of the exhaust flow flows through the bypass exhaust passage side at a high speed and high load where the exhaust flow rate becomes large, so that a reduction in charging efficiency due to back pressure can be avoided. .

  Furthermore, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the first exhaust gas purifier installed in the upstream main exhaust passage is configured to switch the passage so that the exhaust discharged from each cylinder flows to the upstream bypass exhaust passage 11. A passage opening / closing means (first switching valve) 4 and a second passage opening / closing means that opens and closes the middle flow side main exhaust passage and is installed in the middle flow side main exhaust passage in the vicinity of the connection portion with the downstream main exhaust passage. (Second switching valve) 12. Therefore, when the first passage opening / closing means 4 is closed and the exhaust gas from the internal combustion engine flows into the bypass exhaust passages 11 and 14, the exhaust gas leaks from the first passage opening / closing means 4 on the main exhaust passage side, and unburned fuel. Even if unpurified exhaust gas including the like may be discharged to the outside from the main exhaust passage, the second passage opening / closing means 12 is further provided downstream of the first passage opening / closing means 4, so that the main exhaust passage 2 It is possible to reliably prevent unpurified exhaust gas from leaking from 3 and 7 to the outside.

  Further, by installing the second passage opening / closing means 12 in the middle main exhaust passage 3 in the vicinity of the connection portion with the downstream main exhaust passage 7, the second passage opening / closing means 12 is heated by the heat of the hot exhaust gas flowing through the bypass exhaust passage. It is possible to remove deposits adhering to the surface. Moreover, the 2nd channel | path opening / closing means 12 can make it difficult to adhere a deposit by setting it as the structure which the valve body 65 opens to the downstream side when a main exhaust passage is open | released.

  FIG. 5 is an explanatory view schematically showing the layout of the exhaust emission control device as the second embodiment. The feature of the second embodiment is that the EGR system is applied to the configuration of the first embodiment.

  In the second embodiment, in addition to the configuration of the first embodiment, the intake valve 21 that supplies intake air to each cylinder 1 downstream of the throttle valve 22 in the intake flow direction, the first switching valve 4 and the second switching valve. An EGR passage 23 that communicates with the midstream main exhaust passage 3 between the EGR gas and the valve is provided, and an EGR control valve 24 that controls the recirculation amount of the EGR gas is installed in the EGR passage 23. Further, air-fuel ratio detection sensors 25, 26 are provided upstream of the main catalytic converter 8 in the downstream main exhaust passage 7 and upstream of the bypass catalytic converter 18 in the downstream bypass exhaust passage 14, respectively. , 26 to control the opening / closing of the EGR control valve 24.

  The first switching valve 4 has the configuration shown in FIG. 3 described above, and rotates the valve body 58 upstream in the exhaust flow direction to open the upstream main exhaust passage 2 and has the configuration shown in FIG. The second switching valve 12 rotates the valve body 65 downstream in the exhaust flow direction to open the midstream main exhaust passage 3. In this way, the first switching valve 4 is configured to rotate upstream in the exhaust flow direction, while the second switching valve 12 is configured to rotate downstream. Between the first and second switching valves is in a negative pressure state, the first and second switching valves 4 and 12 are pressed against the mating member, the sealing performance is improved, and exhaust leakage can be more reliably prevented.

  Next, the EGR control will be described with reference to FIG. The flowchart shown in FIG. 6 shows the control when the EGR control is started simultaneously with the start of the internal combustion engine. This control is performed by the aforementioned controller.

  First, in step S1, when the start of the internal combustion engine is detected, the first and second switching valves 4 and 12 are closed, and the exhaust is guided to the bypass exhaust passage. The bypass catalytic converter 18 installed in the bypass exhaust passage has a smaller heat capacity than the main catalytic converter 8 and is located upstream, so that it immediately becomes active and purifies the exhaust. In subsequent step S2, the EGR control valve 24 installed in the EGR passage 23 is opened, and the exhaust gas containing unburned fuel leaked from the first switching valve 2 is recirculated to the intake passage. In this way, the exhaust gas leaked from the first switching valve 4 is recirculated into the intake air to reduce NOx in the exhaust gas.

  In step S3, the temperature of the main catalytic converter 8 is calculated based on the driving history of the vehicle such as the output of the temperature sensor for detecting the catalyst temperature and the depression amount of the accelerator pedal, and the catalyst of the main catalytic converter has reached the active state. Determine whether or not. When the catalyst is in an active state, the process proceeds to a normal operation state, so the process proceeds to step S4, the EGR control valve 24 is closed, the first and second switching valves 4, 12 are opened, and the exhaust is guided to the main exhaust passage. The exhaust gas is purified by the main catalytic converter. On the other hand, when the catalyst has not reached the active state, the process returns to step S2 to continue the EGR and lead the exhaust to the bypass exhaust passage to purify the exhaust by the bypass catalytic converter.

  In this EGR control, the exhaust gas leaked from the first switching valve 4 is returned to the intake passage 21 via the EGR passage 23, whereby the leaked exhaust gas can be purified. Here, since the downstream second switching valve 12 is closed during EGR control, the exhaust gas containing unburned fuel is not discharged to the outside.

  FIG. 7 shows another EGR control. This EGR control is a control for determining whether to perform EGR according to the exhaust amount leaked from the first switching valve. The EGR control shown in FIG. 6 is a control in which the EGR control valve 24 is opened at the same time as the engine is started and the EGR is performed. In contrast, the EGR control in this embodiment is an exhaust gas leaking from the first switching valve 4. When the amount exceeds a threshold value, the EGR control valve 24 is opened to perform EGR. This control is performed at a predetermined interval by a controller (not shown). In the flowchart of FIG. 7, the amount of exhaust leaking from the first switching valve 4 is determined based on, for example, the detected values of the air-fuel ratio detection sensors 25 and 26. And the amount of exhaust leakage is estimated from the calculated exhaust flow rate difference.

  First, when the start of the internal combustion engine is detected in step S1, the first and second switching valves 4 and 12 are closed, and the exhaust is guided to the bypass exhaust passage. In subsequent step S11, the exhaust leakage amount obtained by the above-described calculation method is compared with a threshold value, and it is determined whether or not the threshold value is exceeded. If it is equal to or greater than the threshold value, it is determined that a predetermined amount or more of the exhaust gas is stored between the first switching valve 4 and the second switching valve 12, and the process proceeds to step S2, and if it is less than the threshold value, the process proceeds to step S4. Then, the EGR control valve 24 is closed to finish the control.

  In step S2, the EGR control valve 24 is opened, the stored exhaust gas is returned to the intake system, and EGR is executed. In the subsequent step S3, the temperature of the main catalytic converter 8 is calculated based on the output of the temperature sensor for detecting the catalyst temperature, the vehicle operation history such as the accelerator pedal depression amount, etc., and the catalyst of the main catalytic converter reaches the active state. Determine if you did. When the catalyst is in the active state, the process proceeds to step S4, the EGR control valve 24 is closed, the first and second switching valves 4, 12 are opened, the exhaust is guided to the main exhaust passage, and the exhaust is sent to the main catalytic converter. Shift to normal operation. On the other hand, when the catalyst has not reached the active state, the process returns to step S2 to continue the EGR and lead the exhaust gas to the bypass exhaust passage for purification by the bypass catalytic converter 18.

  As described above, in this embodiment, the amount of exhaust leakage leaked from the first switching valve 4 is calculated, and EGR is performed when the amount of exhaust leakage is equal to or greater than the threshold value. Therefore, the EGR control valve 24 is opened. It is possible to reduce the amount of power consumed at the time, suppress power consumption, and improve fuel efficiency.

  The EGR control valve 24 may be controlled so as to change the opening according to the amount of exhaust leakage as a variable opening valve, and when a fixed opening valve is used, the exhaust leakage Depending on the amount, the valve opening timing (interval) for opening the EGR control valve 24 may be controlled for a certain period of time.

  As mentioned above, one embodiment in which the present invention is applied to an in-line four-cylinder internal combustion engine has been described. However, the present invention can be variously modified and changed within the scope of the technical idea, and these are also equivalent to the present invention. It is clear that there is.

The explanatory view showing typically the layout of the exhaust emission control device concerning the present invention. The block diagram of a valve unit. Sectional drawing of the principal part of a valve unit (cross section AA of FIG. 2). Sectional drawing of a 2nd switching valve. Explanatory drawing which showed typically the layout of the exhaust gas purification apparatus of 2nd Embodiment. The flowchart of EGR control. The other flowchart of EGR control.

Explanation of symbols

2: upstream main exhaust passage 3: middle flow main exhaust passage 4: first switching valve 5: valve unit 7: downstream main exhaust passage 8: main catalytic converter 11: upstream bypass exhaust passage 12: second switching valve 14 : Downstream bypass exhaust passage 18: bypass catalytic converter 23: EGR passage 24: EGR control valve

Claims (6)

An upstream main exhaust passage for each cylinder connected to each cylinder of the internal combustion engine;
A plurality of upstream main exhaust passages that are joined together into a single passage, and a middle flow side main exhaust passage;
A downstream main exhaust passage connected downstream of the midstream main exhaust passage;
A main catalytic converter interposed in the middle of the downstream main exhaust passage;
An upstream bypass exhaust passage branched from the upstream main exhaust passage,
A plurality of upstream bypass exhaust passages merged into one passage, and a downstream bypass exhaust passage having a downstream end coupled to a connection portion between the midstream main exhaust passage and the downstream main exhaust passage;
A bypass catalytic converter interposed in the middle of the downstream bypass exhaust passage;
First passage opening and closing means for opening and closing the upstream main exhaust passage so that the exhaust discharged from each cylinder flows from the upstream main exhaust passage to the upstream bypass exhaust passage;
A second passage opening / closing means that opens and closes the middle-stream side main exhaust passage and is installed in the middle-stream side main exhaust passage in the vicinity of the connection portion with the downstream-side main exhaust passage;
An exhaust emission control device for an internal combustion engine, comprising:   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the second passage opening / closing means rotates to the downstream side in the exhaust flow direction to open the middle flow side main exhaust passage. An upstream main exhaust passage for each cylinder connected to each cylinder of the internal combustion engine;
A plurality of upstream main exhaust passages that are joined together into a single passage, and a middle flow side main exhaust passage;
A downstream main exhaust passage connected downstream of the midstream main exhaust passage;
A main catalytic converter interposed in the middle of the downstream main exhaust passage;
An upstream bypass exhaust passage branched from the upstream main exhaust passage,
A plurality of upstream bypass exhaust passages merged into one passage, and a downstream bypass exhaust passage having a downstream end coupled to a connection portion between the midstream main exhaust passage and the downstream main exhaust passage;
A bypass catalytic converter interposed in the middle of the downstream bypass exhaust passage;
A first passage opening / closing means that is installed in the upstream main exhaust passage and opens and closes the upstream passage so as to switch the passage through which the exhaust flows so that the exhaust discharged from each cylinder flows to the upstream bypass exhaust passage; ,
Second passage opening and closing means for opening and closing the middle-stream side main exhaust passage;
An EGR passage that recirculates exhaust gas leaked from the first passage opening / closing means to the intake system of the internal combustion engine between the first passage opening / closing means and the second passage opening / closing means;
An EGR control valve for opening and closing the EGR passage;
An exhaust emission control device for an internal combustion engine, comprising:   Exhaust leakage amount calculating means for calculating the amount of exhaust gas leaked downstream from the first passage opening and closing means, and a controller for controlling the opening degree of the EGR control valve, the controller comprising the calculated exhaust leakage The exhaust emission control device for an internal combustion engine according to claim 1, wherein the opening degree of the EGR control valve is controlled according to the amount.   The exhaust leakage amount calculating means includes a first air-fuel ratio sensor that detects an air-fuel ratio upstream of the bypass catalytic converter, and a second air-fuel ratio sensor that detects an air-fuel ratio immediately upstream of the main catalytic converter, The controller calculates an exhaust leak amount based on the detection values of the first and second air-fuel ratio sensors, and controls the opening degree of the EGR control valve according to the calculated exhaust leak amount. The exhaust emission control device for an internal combustion engine according to claim 2. The first passage opening / closing means pivots upstream in the exhaust flow direction to open the upstream main exhaust passage,
4. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the second passage opening / closing means rotates to the downstream side in the exhaust flow direction to open the middle flow side main exhaust passage.

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