JP4706463B2 - Control device for internal combustion engine - Google Patents

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 the exhaust system immediately after a cold start, and more particularly to the flow path switching valve switching. It relates to correction control at the time.

  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 the 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 configuration as described above, when the switching valve is switched so that the warming-up of the main catalytic converter is completed and the exhaust gas flows to the main flow path side, the exhaust gas flows without passing through the bypass catalytic converter serving as a passage resistance. For this reason, the back pressure rapidly decreases and a torque step (specifically, an increase in torque) occurs.

  On the other hand, when the exhaust gas flows through the bypass passage with a large passage resistance, the engine output or torque is limited, so the engine operating conditions shift to the high speed range or high load range due to the driver's acceleration request. In this case, it is necessary to switch the switching valve. In such a case, the torque step is not a problem.

  Therefore, the present invention provides 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 also includes a bypass catalytic converter in the bypass passage. In the internal combustion engine having a flow path switching valve that closes the main passage in the upstream portion, the internal combustion engine has a plurality of trigger conditions that serve as triggers for switching the flow path switching valve from a closed state to an open state, and each trigger condition In accordance with the above, the control parameter at the time of switching control of the flow path switching valve is made different.

  For example, the activation of the main catalytic converter is set as one of the trigger conditions, and the transition of the engine operating condition from a predetermined closed region to the open region is set as another trigger condition.

  Desirably, for trigger conditions resulting from activation of the main catalytic converter, a control parameter is set so as to suppress the torque step, and an acceleration response is given to trigger conditions resulting from the driver's acceleration request. Set control parameters to give priority.

  The control parameters are, for example, the opening change rate of the flow path switching valve, the ignition timing, the throttle valve opening, and the like.

  For example, for the trigger condition of the activation of the main catalytic converter, the torque step becomes slow by reducing the opening change rate of the flow path switching valve. For example, for the trigger condition caused by the acceleration request, Responsiveness is ensured by increasing the opening change speed of the path switching valve.

  The opening change speed may be further varied according to the engine operating condition when the trigger condition is satisfied. For example, the higher the load, the larger the opening change speed, and the smaller the load, the smaller the opening change speed in order to suppress the torque step.

  That is, in one aspect, the control parameter is set so as to allow a larger torque step as the engine operating condition when the trigger condition is satisfied is on the higher load side.

  Also, in one aspect, when switching the flow path switching valve triggered by the activation of the main catalytic converter, the opening change speed of the flow path switching valve is set to be small and the ignition timing is retarded. Correction and throttle valve opening reduction correction are performed together.

  Although the retard correction of the ignition timing at the time of switching can suppress the torque step with good responsiveness, it is difficult to absorb a large torque step because of the surge limit on the retard side. In contrast, the reduction correction of the throttle valve opening can absorb a relatively large torque step, but its response is low due to a response delay of the intake air amount change. Therefore, a relatively large torque step can be absorbed with good responsiveness by combining both.

  The ignition timing retardation correction and throttle valve opening reduction correction are set to a larger correction amount when the engine operating condition is higher when the trigger condition is satisfied, and the trigger condition is satisfied accordingly. The opening change rate of the flow path switching valve may be set larger as the engine operating condition at that time is on the higher load side.

  According to the present invention, for example, a large torque step does not occur for the switching of the flow path when the main catalytic converter is activated, and for the switching of the flow path due to the driver's aggressive acceleration request, Control can be performed to enhance acceleration response.

  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.

  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 desirably 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 main passage 3 at a junction 12 upstream of the main catalytic converter 4 in the main passage 3 and downstream of the flow path switching valve 5. ing.

Incidentally, the inlet portion and the outlet portion of the main catalytic converter 4, and the inlet and outlet of the bypass catalytic converter 8, the air-fuel ratio sensor 10,11,1 3, 1 4, respectively are arranged.

  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 amount of intake air 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 sensors described above, the engine control unit 27 includes various sensors such as a coolant temperature sensor 28 and an accelerator opening sensor 29 that detects the opening (depression amount) of an accelerator pedal operated by a driver. Detection signal is 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 warm-up progresses and the engine temperature or the exhaust temperature becomes sufficiently high, it is considered that the catalyst of the main catalytic converter 4 is activated as the first trigger condition, and 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.

  Here, when the flow path switching valve 5 opens the main passage 3 as described above, since the passage resistance of the main passage 3 is small, the back pressure is drastically reduced, and if it is left as it is, the torque step, that is, the torque rises. appear. In particular, since the volume of the main passage 3 between the branch point 6 and the junction 12 is very large compared to the volume of the bypass passage 7 between the branch point 6 and the junction 12, the flow path switching valve 5 is When the main passage 3 is opened, the back pressure temporarily decreases further, and the temporary torque increase becomes more prominent.

  On the other hand, when the flow path switching valve 5 is closed and the exhaust flow flows on the bypass passage 7 side, the flow path switching valve 5 is controlled to be closed because the exhaust flow rate cannot be handled in a high speed range or a high load range. The engine operating conditions (load and engine speed) are limited to a predetermined region on the low-speed and low-load side (this is referred to as a valve closed region for convenience), and other regions (also the valve open region and ), The flow path switching valve 5 is opened even if the main catalytic converter 4 is inactive. Therefore, as the second trigger condition, when the operating condition shifts from the valve closed region to the valve open region, the flow path switching valve 5 is switched from closed to open as described above.

  FIG. 2 is a characteristic diagram showing the above-described valve closing region and valve opening region. In particular, in this drawing, the load on the vertical axis is shown by the suction negative pressure (Boost) downstream of the throttle valve 24. As shown in the figure, the valve closed area is on the low speed and low load side. Is shifted, even if the main catalytic converter 4 is inactive, the flow path switching valve 5 is switched from closed to open, and the exhaust flow passes through the main passage 3 side. A torque step is also generated during this switching.

  That is, as a trigger condition serving as a trigger for switching the flow path switching valve 5 from closed to open, in this embodiment, a first trigger condition that the catalyst is activated and a second trigger that the operating condition has shifted to the valve open region. There are conditions. Here, in the case of the first trigger condition, since the switching is performed at an unexpected timing by the driver, it is desirable that the torque step be as small as possible. On the other hand, in the case of the second trigger condition, basically the driver's Since it accompanies the acceleration request, it is desirable to give priority to the acceleration response over the suppression of the torque step.

  Hereinafter, switching of the flow path switching valve 5, particularly control when switching from closed to open will be described.

  FIG. 3 is a time chart showing changes in various control parameters when switching is performed according to the first trigger condition during steady operation. Here, even in the same steady operation, three examples (referred to as Example 1, Example 2, and Example 3, respectively) having different loads in three stages of low, medium, and high are shown together. This corresponds, for example, to the operating points a, b, and c in FIG. Here, it is assumed that the engine speed does not change. In the figure, APO is the accelerator pedal opening, TVO is the throttle valve opening, and ADV is the ignition timing. In these examples, for example, when the catalyst activity determination flag becomes 1 based on the engine coolant temperature or the like, the valve opening permission flag becomes 1, and the switching of the flow path switching valve 5 starts.

  In Example 1 during steady operation at a low load, the opening change speed of the flow path switching valve 5 by the actuator 5a is limited to be small so that a torque step does not occur, and the flow path switching valve 5 gradually opens. The throttle valve opening TVO is controlled based on different control maps in the closed state and the open state of the flow path switching valve 5, and the set value of the open state map is relative to the same operating condition. Small. This takes into account the difference in passage resistance. Therefore, there is a difference in the target throttle valve opening TVO before and after the switching of the flow path switching valve 5 is started. However, as shown in the figure, the opening degree change of the flow path switching valve 5 gradually opens. Correspondingly, the throttle valve opening TVO gradually decreases and shifts to the target value under the open state.

  The ignition timing ADV is also controlled based on different control maps in the closed state and the open state of the flow path switching valve 5, and the set value of the open state map is relatively relative to the same operating condition. It becomes the advance side. This is because the remaining gas increases in the closed state where the passage resistance of the exhaust system is large, and the knock limit is limited to the retard side. Therefore, there is a difference in the target ignition timing ADV before the switching start of the flow path switching valve 5 and after the switching is completed, but as shown in the figure, the ignition timing ADV is such that the flow path switching valve 5 is completely opened. The value on the retard side (the target value in the closed state) is maintained until it is fully opened, and the angle is advanced to the target value in the open state.

  As described above, in Example 1, the change in the opening degree of the flow path switching valve 5 is made slow, and the ignition timing ADV is kept relatively retarded until it is fully opened, so that the torque step is suppressed to be small.

  Further, in Example 3 during high load steady operation, the opening change speed of the flow path switching valve 5 by the actuator 5a is controlled to be relatively large, and the flow path switching valve 5 is fully opened relatively quickly. The throttle valve opening TVO and the ignition timing ADV are controlled in the same manner as in Example 1. In Example 2 during steady operation of an intermediate load, the opening change speed of the flow path switching valve 5 is controlled to an intermediate speed between Example 1 and Example 3, and the throttle valve opening TVO and the ignition timing ADV are similarly controlled. Is done. Also in these cases, the torque step is sufficiently suppressed.

  FIG. 4 is a time chart showing changes in various control parameters when switching is performed according to the second trigger condition in an inactive state of the catalyst. Here, the case where the vehicle speed (engine speed) gradually increases due to slow acceleration (example 4) and the case where the vehicle speed (engine speed) rapidly increases due to rapid acceleration (example 5) are shown in comparison. is there.

  In these examples, for example, when the engine speed Ne increases and exceeds the boundary between the valve closing region and the valve opening region, the valve opening permission flag is set to 1 regardless of the catalyst activation determination flag, and the flow path switching valve 5 is switched. Starts. In Example 4, for example, the boundary is crossed from the point b to the point b 'in FIG. 2, and in Example 5, for example, the boundary is crossed from the point c to the point c'. FIG. 4 shows that the timing when the valve opening permission flag becomes 1 is the same in Example 4 and Example 5.

  In Example 4 which is slow acceleration, the opening change speed of the flow path switching valve 5 by the actuator 5a is limited to a certain degree so that a large torque step does not occur, and the flow path switching valve 5 is gradually opened. However, even under the same operating condition (point b), the opening change rate is larger in Example 4 with the second trigger condition based on the acceleration request than in Example 2 in FIG. 3 with the first trigger condition. It is done. As described above, the throttle valve opening TVO is controlled based on different control maps depending on whether the flow path switching valve 5 is in the closed state or in the open state. However, in the fourth example of slow acceleration, the throttle valve opening TVO corresponds to the opening change of the flow path switching valve 5 that gradually opens as in the case of the first trigger condition. Gradually shrinks to the target value in the open state.

  Further, the ignition timing ADV is also controlled based on different control maps in the closed state and the open state of the flow path switching valve 5 as described above, and the set value of the open state map is set for the same operating condition. However, the value on the retard side (the target value in the closed state) is maintained until the flow path switching valve 5 is completely opened, as in the first trigger condition. When it is fully open, it advances to the target value under the open state.

  As described above, in Example 4, the torque step is suppressed by delaying the change in the opening degree of the flow path switching valve 5 and maintaining the ignition timing ADV on the retard side during that time. In comparison, since the change in the opening degree of the flow path switching valve 5 is fast, a necessary and sufficient acceleration response can be obtained.

  On the other hand, in Example 5, which is rapid acceleration, the flow path switching valve 5 is switched at the maximum speed by the actuator 5a in order to give priority to the acceleration response. Then, unlike the example 4, the throttle valve opening TVO maintains the target value of the control map in the closed state until the flow path switching valve 5 is completely opened. Switch to the target value of the open control map. That is, the throttle valve opening TVO is given relatively larger than that in the first trigger condition. Therefore, a good acceleration response can be obtained.

  As in the case of the first trigger condition, the ignition timing ADV maintains the retarded value (the target value in the closed state) until the flow path switching valve 5 is completely opened, and the ignition timing ADV is completely opened. At this stage, advance to the target value under the open state.

  Next, FIG. 5 is a time chart showing a second embodiment of control when switching is performed under the first trigger condition during steady operation. Here, similarly to FIG. 3, even in the same steady operation, the load corresponds to three examples (for example, operation points a, b, and c in FIG. ) Are collectively shown as Example 1, Example 2, and Example 3.

  In the second embodiment, the torque step is more reliably prevented by positively correcting the throttle valve opening TVO and the ignition timing ADV, and the opening change rate of the flow path switching valve 5 is as follows. The throttle valve opening TVO is corrected so as to be temporarily reduced as soon as the flow path switching valve 5 starts to open, and then controlled so as to become slower as the load is lower, as in the first embodiment. As the opening degree of the flow path switching valve 5 changes, it gradually changes toward the target value of the control map in the open state. This initial correction amount increases as the load increases, that is, the correction amount increases in the order of Example 1, Example 2, and Example 3.

  Further, the ignition timing ADV is temporarily corrected to the retarded side simultaneously with the start of the opening of the flow path switching valve 5, and then the target value of the control map in the open state in accordance with the opening degree change of the flow path switching valve 5. It will gradually change toward. The initial correction amount to the retard side increases as the load increases. That is, the correction amount increases in the order of Example 1, Example 2, and Example 3.

  Thus, the torque decreases immediately by retarding the ignition timing ADV temporarily. Further, the throttle valve opening TVO is temporarily corrected to be greatly reduced, so that the intake air amount is suppressed and the torque is also suppressed. If the reduction in torque in the high load region depends only on the retard of the ignition timing ADV, a surge may occur, but by combining both, the responsiveness can be improved without excessively retarding the ignition timing ADV. Torque step can be absorbed.

  Further, as described above, the correction amount of the initial ignition timing ADV and the correction amount of the throttle valve opening TVO are set to be larger as the engine operating condition at the time when the first trigger condition is satisfied is higher. The opening change rate of the flow path switching valve 5 can be set to be larger as the load is higher when the first trigger condition is satisfied, while absorbing the torque step. As a result, the flow path switching valve 5 is quickly opened on the high load side, and even when a further load request is generated, this can be dealt with reliably.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows an example of the piping layout and control system of the exhaust apparatus concerning this invention. The characteristic view which shows a valve closing area | region and a valve opening area | region. The time chart in case switching is performed by the 1st trigger condition during steady operation. The time chart in case switching is performed by the 2nd trigger condition in a catalyst inactive state. The time chart which shows the Example from which the switching by the 1st trigger condition differs.

Explanation 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 27 ... Engine control unit

Claims (8)

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,
As a trigger condition for triggering the switching of the flow path switching valve from the closed state to the open state, the first trigger condition consisting of the activation of the main catalytic converter and the engine operating condition have shifted from the predetermined closed region to the open region. A control parameter that has an influence on the engine torque during the switching control of the flow path switching valve, and suppresses the torque step with respect to the first trigger condition. And the second trigger condition is set so that the acceleration response is prioritized . 2. The control apparatus for an internal combustion engine according to claim 1 , wherein the control parameter is an opening change speed of the flow path switching valve. The control device for an internal combustion engine according to claim 2 , wherein the opening change rate is further different according to an engine operating condition when the trigger condition is satisfied. 2. The control device for an internal combustion engine according to claim 1, wherein the control parameter is an ignition timing. 2. The control device for an internal combustion engine according to claim 1, wherein the control parameter is a throttle valve opening degree. The control of the internal combustion engine according to any one of claims 1 to 5 , wherein the control parameter is set so as to allow a larger torque step as the engine operating condition when the trigger condition is satisfied is on a higher load side. apparatus. When switching the flow path switching valve according to the first trigger condition, the opening degree change speed of the flow path switching valve is set small, and the ignition timing retardation correction and the throttle valve opening reduction correction are combined. control apparatus for an internal combustion engine according to any one of claims 1 to 6, characterized in that. As the engine operating condition when the first trigger condition is satisfied is higher, the opening change speed of the flow path switching valve is set to be larger, and the ignition timing retard correction amount and the throttle valve opening are adjusted. 8. The control device for an internal combustion engine according to claim 7, wherein the reduction correction amount is given large .

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