JP2009215964A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid temporary drop of catalyst temperature when a channel changeover valve 5 opens associated with the completion of warming up. <P>SOLUTION: A main passage 3 is connected to an exhaust port 2 and a main catalyst converter 4 is disposed at a downstream side. A channel 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 having small passage cross section area branches off of the main passage 3, and a small bypass catalytic converter 8 is put in a middle thereof. Exhaust gas is guided to the bypass passage 7 side to control emission right after cold start. The channel changeover valve 5 is controlled to start opening at relatively low opening change speed to prescribed intermediate opening, to be retained at the target intermediate opening during display time, and to open to full open position at the maximum opening change speed, when the same opens associated with the completion of warming up. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust device 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 an exhaust system immediately after a cold start, and more particularly to the flow path switching valve switching. Concerning time control.

  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 and Patent Document 2, a bypass channel is provided in parallel with the upstream portion of the main channel including the main catalytic converter, and another bypass catalyst is provided in the bypass channel. 2. Description of the Related Art Conventionally, there has been proposed an exhaust device that guides exhaust gas to the bypass flow path side immediately after a cold start by a switching valve that interposes a converter and switches both of them. 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 Japanese Patent Laid-Open No. 2005-351088

  In the configuration as described above, when the switching valve is switched so that the warm-up of the main catalytic converter is completed and the exhaust gas flows to the main flow path side, if the switching valve suddenly opens the main flow path, the main flow Since the low-temperature exhaust gas (or air) staying in the passage suddenly flows into the main catalytic converter, the catalyst temperature decreases, and there is a problem that the exhaust gas purification rate by the catalyst temporarily decreases.

  Therefore, the control device for an internal combustion engine according to the present invention is provided with a bypass passage in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side as an exhaust device, and the bypass catalytic converter is provided in the bypass passage. And a means for determining completion of warm-up of the main catalytic converter, and determination of completion of warm-up in an internal combustion engine provided with a flow path switching valve for closing the main passage in the upstream portion of the main passage Sometimes, the flow path switching valve is opened to a predetermined target intermediate opening degree with a first opening degree changing speed, and then fully opened with a second opening degree changing speed larger than the first opening degree changing speed. And a flow path switching valve control means that opens up to.

  In one aspect, after reaching the target intermediate opening, the target intermediate opening is held for a predetermined delay period.

  More preferably, the first opening change speed, the second opening change speed, the delay period, and the target intermediate opening are variably set according to engine operating conditions, temperature conditions, and the like.

  According to this invention, at the time of switching the flow path when the main catalytic converter is activated, first, the flow path switching valve is gradually opened to a predetermined target intermediate opening, so that it has remained in the main flow path. Low-temperature gas does not flow rapidly into the main catalytic converter, and it is possible to avoid a reduction in purification rate due to a temporary temperature drop of the catalyst.

  Hereinafter, an embodiment in which the present invention is applied as a control device for an in-line four-cylinder internal combustion engine will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory view schematically showing the piping layout and control system of the exhaust device of the internal combustion engine. First, the configuration of the exhaust device will be described based on FIG.

  In the cylinder head 1a of the internal combustion engine 1, exhaust ports 2 of cylinders # 1 to # 4 arranged in series are formed so as to open toward the side surfaces, respectively. In addition, the main passage 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 arranged under the floor of the vehicle, and includes, for example, a three-way catalyst and an HC trap catalyst as the catalyst. 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. The flow path switching valve 5 is driven to open and close by an appropriate actuator 5a such as an electric motor.

  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. A downstream end of the bypass passage 7 extending from the outlet side of the bypass catalytic converter 8 is connected to the main passage 3 at a junction 15 upstream of the main catalytic converter 4 in the main passage 3 and downstream of the flow path switching valve 5. ing.

  Air-fuel ratio sensors 10, 11, 12 and 13 are arranged at the inlet and outlet of the main catalytic converter 4 and at the inlet and outlet of the bypass catalytic converter 8, respectively. In addition, an exhaust temperature sensor 14 for detecting the exhaust temperature and thus the temperature of the main catalytic converter 4 is provided at the inlet of the main catalytic converter 4. It is also possible to arrange a temperature sensor in the catalytic converter 4 itself.

  The internal combustion engine 1 includes a spark plug 21, and a fuel injection valve 23 is disposed in the intake passage 22. Furthermore, a so-called electronically controlled throttle valve 24 that is opened and closed by an actuator such as a motor is disposed upstream of the intake passage 22, and an air flow meter 25 that detects the intake air amount is provided downstream of the air cleaner 26. Yes.

  Various control parameters of the internal combustion engine 1, for example, the fuel injection amount by the fuel injection valve 23, the ignition timing by the spark plug 21, the opening degree of the throttle valve 24, the open / closed state of the flow path switching valve 5 (and the opening degree change thereof) The speed) is controlled by the engine control unit 27. In addition to the above-described sensors, the engine control unit 27 includes a coolant temperature sensor 28, an accelerator opening sensor 29 that detects the opening (depression amount) of an accelerator pedal operated by the driver, and a crank angle sensor (not shown). Detection signals of various sensors such as are input.

  In such a configuration, when the engine temperature or the exhaust temperature after the cold start is low, the flow path switching valve 5 is closed via the actuator 5a, and the main passage 3 is blocked. 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 catalyst of the main catalytic converter 4 is activated, the flow path switching valve 5 is opened by a process as described later. 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.

  Here, when the flow passage switching valve 5 opens the main passage 3 as described above, if the flow passage switching valve 5 is suddenly opened to the fully open position, the inside of the main passage 3 having a relatively large passage sectional area. The low-temperature exhaust gas (or air) staying in the air suddenly flows into the main catalytic converter 4 and causes a decrease in the catalyst temperature. The solid line in FIG. 10 shows, as an example, an example of a change in the catalyst temperature when the catalyst temperature of the main catalytic converter 4 suddenly opens from the fully closed position to the fully open position when it reaches the activation temperature.

  Therefore, in this embodiment, as illustrated by a broken line in FIG. 10, the flow path switching valve 5 is opened to the predetermined target intermediate opening degree with the first opening degree changing speed, and the target value is set during the predetermined delay period. After the intermediate opening degree is maintained, the opening operation of the flow path switching valve 5 is controlled so that it opens to the fully opened position with the second opening degree changing speed relatively larger than the first opening degree changing speed. To do. Thereby, as shown with a broken line, the temporary temperature fall of the main catalytic converter 4 is avoided.

  Hereinafter, based on the flowcharts of FIGS. 2 and 3, the control of the opening operation of the flow path switching valve 5 will be specifically described.

  FIG. 2 shows a routine for determining whether or not to open the flow path switching valve 5 as the engine warms up. First, in step 1 (abbreviated as S1 in the figure), the exhaust gas temperature is shown. It is determined whether or not the exhaust temperature detected by the sensor 14 exceeds a predetermined temperature EXHTMP (corresponding to a temperature at which the catalyst can be regarded as being activated). If it exceeds the predetermined temperature EXHTMP, it is determined in step 2 whether air-fuel ratio feedback control is being performed. When the flow path switching valve 5 is opened, a temporary air-fuel ratio fluctuation occurs due to a change in back pressure or the like. Therefore, if the air-fuel ratio feedback control is not in progress, the opening control of the flow path switching valve 5 is not permitted. Further, it is determined in step 3 whether or not the engine is in idle operation. If in idle operation, it is further determined in step 4 whether or not the rotation speed feedback control is being performed. This takes into account the torque fluctuation that occurs when the flow path switching valve 5 is opened. If the idle speed feedback control is being executed, the torque fluctuation is absorbed. Open control of the flow path switching valve 5 is permitted. If the idling operation is not being performed, the process proceeds to step 6 on the condition that the throttle valve opening is less than the predetermined value BYTVO in step 5, and the opening control of the flow path switching valve 5 is permitted. That is, the flow path switching valve 5 is not switched during acceleration with a large throttle valve opening.

  FIG. 3 shows a control routine for opening the flow path switching valve 5. First, in step 11, it is determined whether the control permission in step 6 described above has been granted. If “YES” here, the process proceeds to a step 12 to set a target intermediate opening. The target intermediate opening is, for example, a value of about 10% to 50% as a passage cross-sectional area, and may be a fixed value, but is desirably based on the engine temperature (cooling water temperature, oil temperature, etc.) at the start. Variably set. Specifically, a larger value, for example, a value close to 50%, is set at the time of warm-up restart such that the cooling water temperature at the start is 60 ° C. or higher, and a smaller value at a cold start at a cryogenic temperature. A value, for example, a value close to 10%.

  Next, an initial value (reference value) of an opening change speed (first opening change speed in claims) until the target intermediate opening is reached is set in step 13. This is a fixed value as will be described later. In step 14, it is determined whether or not the initial value needs to be corrected based on the engine operating conditions and the like, and if necessary, the correction is performed in step 15. In the opening control of this embodiment, as shown in FIG. 4, the flow path switching valve 5 changes from fully closed to fully opened by substantially three sections A, B, C. The opening change rate of ˜15 corresponds to the slope of the characteristic of the first section A. If this rate of change in opening is excessively large, the catalyst temperature decreases in the same manner as when the valve is suddenly opened until it is fully opened. Conversely, if it is excessively small, the increase in catalyst temperature due to the high-temperature exhaust discharged from the internal combustion engine is slow. It becomes. FIG. 5 is a plot of the relationship between the change in exhaust temperature at the inlet of the catalytic converter 4 and the opening change rate under a certain exhaust temperature and exhaust flow rate. If an optimum point exists and the opening degree change speed at this optimum point, the temperature rise of the catalytic converter 4 is most effectively obtained. This optimum point basically corresponds to the initial value of step 13. On the other hand, the optimum point in FIG. 5 varies depending on the exhaust flow rate, the exhaust temperature, and the like, so that correction according to the engine operating conditions and the like is necessary. FIG. 6 shows the characteristics of the correction value of the opening change rate with respect to the engine load. If the load is larger than the reference load (the correction value at this time is 0), the correction value is given as a negative value. When the load is small, a positive correction value is given. For example, both have a linear relationship as shown in the figure. In addition, this correction value is added to the initial value of the opening change speed serving as a reference. Similarly, FIG. 7 shows the characteristics of the correction value of the opening change speed with respect to the engine rotational speed. When the speed is higher than the reference rotational speed, a negative correction value is obtained, and when the speed is low, a positive correction value is obtained. Are given in a linear relationship. These corrections relating to the load and the rotational speed mainly take into account changes in the exhaust flow rate. FIG. 8 shows the relationship between the ignition timing and the correction value. Since the exhaust gas temperature increases as the ignition timing is retarded from the MBT point, the negative correction is performed so that the opening change rate becomes small. A value is given. Further, FIG. 9 shows the relationship between the cooling water temperature and the correction value. When the cooling water temperature is lower than the reference water temperature, a negative correction value is given in a linear relationship, and when the cooling water temperature is high, a positive correction value is given in a linear relationship. It is done.

  When the optimum opening change speed is determined in steps 13 to 15, in step 16, the flow path switching valve 5 starts to open with the opening change speed. In step 17, it is repeatedly determined whether or not the target intermediate opening has been reached, and when the target intermediate opening is reached, the routine proceeds to step 18 where the opening operation of the flow path switching valve 5 is temporarily stopped. At the same time, in step 19, a delay time corresponding to the section B in FIG. 4 is set. This delay time may be an appropriate fixed value, but is desirably set variably according to the exhaust temperature at that time. Specifically, the delay time is set so that the shorter the exhaust temperature at that time (that is, when the target intermediate opening is reached), the shorter the time. Then, in step 20, it is determined whether or not the delay time has elapsed. When the delay time has elapsed, in step 21, the opening operation of the flow path switching valve 5 is started again. At this time, the flow path switching valve 5 is opened with the maximum opening change speed determined from the configuration of the actuator or the like (this corresponds to the second opening change speed in the claims). This corresponds to the section C in FIG.

  Thus, according to the above-described embodiment, when the main catalytic converter 4 is activated, the flow path switching valve 5 is temporarily opened to the target intermediate opening degree with a relatively small opening changing speed according to the engine operating conditions. Since the target intermediate opening is maintained for an appropriate delay time, the low-temperature gas staying in the main passage 3 gradually flows into the main catalytic converter 4 to gradually increase the temperature of the main passage 3 as a whole. Switching of the flow path can be achieved without causing a temporary temperature drop of the catalytic converter 4.

  In the above embodiment, the activity of the main catalytic converter 4 is determined based on the actual detected temperature of the exhaust temperature sensor 14, but the catalyst is determined based on other parameters such as the elapsed time after starting and the coolant temperature. The open control of the present invention can be similarly applied when determining the activity of the converter 4.

  Next, another embodiment of the present invention will be described with reference to the characteristic diagram of FIG. This figure shows the characteristics of the opening change from the fully closed position to the fully open position when the main catalytic converter 4 is activated and the opening control of the flow path switching valve 5 is permitted. Unlikely, the flow path switching valve 5 changes substantially from fully closed to fully open by two sections A and D. The section A is the same as that in the above-described embodiment. For example, the section A is gradually opened from the coolant temperature at the time of engine start to the target intermediate opening determined by the first opening change speed corrected by the engine operating conditions. . When the target intermediate opening degree is reached, the second opening degree changing speed, which is a relatively large changing speed, is opened to the fully opened position. The second opening change rate at this time is not a fixed value, but is variably set according to the exhaust temperature at that time. Specifically, a larger second opening change speed is given such that the higher the exhaust gas temperature at that time (that is, when the target intermediate opening is reached), the quicker the opening is. Even with such open control, the flow path switching can be achieved while reliably avoiding a temporary temperature drop of the catalytic converter 4.

  In addition, in the case of having the delay time section B as shown in FIG. 4, it is possible to further change the opening degree change speed of the section C.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows an example of the piping layout and control system of the exhaust apparatus which concerns on this invention. The flowchart which shows the routine which performs permission of opening control of a flow-path switching valve with warming-up. The flowchart which shows the flow of opening control of a flow-path switching valve. The characteristic view which shows an example of the opening degree change of the flow-path switching valve of this Example. The characteristic view which shows the relationship between the change of the exhaust temperature in a catalytic converter inlet_port | entrance, and an opening change speed. The characteristic view which shows the characteristic of the correction value of the opening degree change speed with respect to engine load. The characteristic view which shows the characteristic of the correction value of the opening degree change speed with respect to an engine speed. The characteristic view which shows the characteristic of the correction value of the opening degree change speed with respect to ignition timing. The characteristic view which shows the characteristic of the correction value of the opening degree change speed with respect to cooling water temperature. The characteristic view which shows the change of a catalyst temperature when a flow-path switching valve is opened by contrasting with a prior art example (solid line) and an Example (broken line). The characteristic view which shows an example of the opening degree change of the flow-path switching valve of a different Example.

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 14 ... Exhaust temperature sensor 27 ... Engine control unit

Claims (6)

As an exhaust device, a bypass passage is provided in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side, the bypass passage is provided with the bypass catalytic converter, and the upstream portion of the main passage is provided with the bypass passage. In the internal combustion engine comprising a flow path switching valve that closes the main passage,
Means for determining completion of warm-up of the main catalytic converter;
When the warm-up completion is determined, the flow path switching valve is opened to a predetermined target intermediate opening degree with the first opening degree changing speed, and then the second opening degree larger than the first opening degree changing speed. A flow path switching valve control means that opens to a fully open position with a changing speed;
A control device for an internal combustion engine, comprising:   2. The control device for an internal combustion engine according to claim 1, wherein the first opening change rate is corrected by engine operating conditions.   3. The control apparatus for an internal combustion engine according to claim 1, wherein the target intermediate opening degree is maintained for a predetermined delay period after reaching the target intermediate opening degree.   4. The control apparatus for an internal combustion engine according to claim 1, wherein the delay period is set according to an exhaust gas temperature at that time.   The control apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the target intermediate opening is set according to an engine temperature condition at the time of starting.   6. The control device for an internal combustion engine according to claim 1, wherein the second opening degree change speed is set according to the exhaust temperature at that time.

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