JP5040838B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control apparatus for an internal combustion engine in which exhaust gas is guided by a flow path switching valve to a bypass passage side provided with a catalytic converter relatively upstream of an exhaust system immediately after a cold start.

  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 JP 2005-188374 A

  In a predetermined fuel increase region on the high engine speed and high load side, fuel increase control for increasing the fuel injection amount to the rich side is performed in order to protect exhaust system components such as a catalytic converter from high-temperature exhaust gas. Here, the exhaust system components to be protected also differ with the flow path switching by the flow path switching valve. Specifically, in the closed state in which the flow path switching valve is controlled to close, exhaust gas flows through the bypass flow path side, so that the upstream bypass catalytic converter in which the exhaust system component to be protected is close to the combustion chamber On the other hand, in the open state in which the flow path switching valve is controlled to open, exhaust gas flows through the main flow path side, so that the exhaust system parts to be protected become the main catalytic converter on the downstream side far from the combustion chamber. The demand for fuel increase is low compared to the closed state. For this reason, for example, if the fuel increase range is set in accordance with the open state, the increase is not performed even under the condition that the fuel should be increased in the closed state, and there is a concern about thermal deterioration of the bypass catalytic converter or the like. On the other hand, if the fuel increase region is set in accordance with the closed state, the fuel increase is performed in a region where the fuel increase is not necessary in the open state, which may cause a decrease in exhaust emission and fuel consumption.

  Accordingly, 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, the bypass passage provided with the bypass catalytic converter, and the upstream portion of the main passage. In a control device for an internal combustion engine comprising a flow path switching valve for closing the main passage, a fuel increasing means for increasing the fuel injection amount to the rich side in a fuel increasing range determined by the engine speed and engine load, and the flow And a fuel increase area changing means for changing the fuel increase area depending on whether the path switching valve is closed or open.

  According to the control apparatus for an internal combustion engine according to the present invention, by switching the fuel increase range between the open state and the closed state of the flow path switching valve, the high temperature of the exhaust system parts such as the bypass catalytic converter and the main catalytic converter due to the increased fuel amount. It is possible to achieve both protection from exhaust gas and improvement in exhaust gas purification performance and fuel consumption performance by suppressing / avoiding unnecessary increase of fuel.

  Hereinafter, an embodiment in which the present invention is applied to an in-line four-cylinder internal combustion engine will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram schematically showing the piping layout and control system of the exhaust system of the internal combustion engine. First, the configuration of the exhaust system of the internal combustion engine 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 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 main passage 3 at a junction 9 upstream of the main catalytic converter 4 in the main passage 3 and downstream of the flow path switching valve 5. ing.

  Here, a main upstream air-fuel ratio sensor 10 and a main downstream air-fuel ratio sensor 11 are arranged at the inlet and outlet of the main catalytic converter 4, respectively, and at the inlet and outlet of the bypass catalytic converter 8. A bypass upstream air-fuel ratio sensor 12 and a bypass downstream air-fuel ratio sensor 13 are disposed, respectively. The main upstream air-fuel ratio sensor 10 and the main downstream air-fuel ratio sensor 11 are for performing known air-fuel ratio feedback control after the activation of the main catalytic converter 4. The fuel ratio (fuel injection amount) is controlled, and the output signal of the downstream air-fuel ratio sensor 11 is used for correcting variations in the control characteristics. Similarly, the bypass upstream air-fuel ratio sensor 12 and bypass downstream air-fuel ratio sensor 13 are for performing known air-fuel ratio feedback control when the bypass catalytic converter 8 is used. 12, the engine air-fuel ratio (fuel injection amount) is controlled, and the output signal of the downstream-side air-fuel ratio sensor 13 is used for correcting variations in the control characteristics. As these air-fuel ratio sensors 10 to 13, so-called wide-range air-fuel ratio sensors having a substantially linear output characteristic corresponding to the exhaust air-fuel ratio are used, or simply have rich and lean binary output characteristics. An oxygen sensor is used.

  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 / close state of the flow path switching valve 5, etc. 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 proceeds and the engine temperature or the exhaust temperature becomes sufficiently high, it is considered that the catalyst of the main catalytic converter 4 has been activated, 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.

  2 and 3 are control maps showing the fuel increase areas αClose, αOpen determined by the engine speed and the engine load. FIG. 2 is a fuel increase area in the closed state in which the flow path switching valve 5 is controlled to be closed. FIG. 3 shows the fuel increase area αOpen in the open state in which the flow path switching valve 5 is controlled to be in the open state.

  As shown in the figure, the fuel increase region is set to a region on the high-rotation and high-load side where the exhaust temperature becomes very high, and particularly in the closed state, the exhaust gas flows through the bypass catalytic converter 8 close to the combustion chamber. The fuel increase region αClose is set wider than the fuel increase region αOpen in the open state so as not to exceed the guaranteed temperature of the bypass catalytic converter 8 which is an exhaust system component to be protected. On the other hand, in the open state, exhaust gas does not substantially flow into the bypass passage 7 provided with the bypass catalytic converter 8, and the exhaust system component to be protected becomes the main catalytic converter 4 under the floor far from the combustion chamber. It is set narrower than the fuel increase area αClose in the closed state.

  FIG. 4 is a flowchart showing the flow of fuel injection amount setting control. In step S1, the fuel increase regions αClose, αOpen are changed by switching the control maps shown in FIGS. 2 and 3 according to the closed state / open state of the flow path switching valve 5. In step S2, a fuel injection amount is set. That is, referring to the control map set in step S1 based on the engine speed and the engine load, the fuel injection amount is increased to the rich side in the fuel increase range αClose, αOpen. If it is not in the fuel increase range, general normal fuel injection control is performed. For example, the fuel injection amount is set so as to obtain an appropriate air-fuel ratio.

  5 and 6 are flowcharts showing the flow of the switching process of the flow path switching valve 5. Referring to FIG. 5, flow path switching valve 5 is basically controlled to be switched according to the active state of main catalytic converter 4, and when it is determined that main catalytic converter 4 is activated, the process proceeds from step S 4 to step S 5. When it is determined that the catalyst temperature is low and the main catalytic converter 4 is inactive as in the cold start, the process proceeds from step S4 to step S6 and is closed.

  However, in this embodiment, when the predetermined condition is satisfied even in the closed state by the routine shown in FIG. 6, the open position is forcibly switched even when the main catalytic converter 4 is determined to be inactive. It is done.

  With reference to FIG. 6, in step S <b> 11, it is determined whether or not the flow path switching valve 5 is in a closed state. If it is determined that the engine is in the closed state, the process proceeds to step S12, and it is determined whether the fuel increase region αClose is in the open state based on the engine speed and the engine load. If it is the fuel increase range αClose in the open state, the process proceeds to step S13 to determine whether a predetermined open switching condition is satisfied. When the opening switching condition is satisfied, the process proceeds to step S14, and the flow path switching valve 5 is set to the open position.

  For example, in the first example shown in FIG. 7, the above open switching condition is that the fuel injection amount increase rate (TFBYA) exceeds a predetermined determination threshold value L1. Further, in the second example shown in FIG. 8, the exhaust air-fuel ratio downstream of the main catalytic converter 4 detected by the main downstream air-fuel ratio sensor 11 exceeds the predetermined determination threshold L2 on the rich side. It is. Preferably, as an open switching condition, based on the engine speed and the engine load, the fuel increase region αClose in the closed state and the region α1 outside the fuel increase region αOpen in the open state (hatching in FIG. 3) It is included that it is the area). These open switching conditions may be used in combination, or may be used alone. As a result, when the open switching condition is satisfied and the flow path switching valve 5 is switched to the open position (S14), the fuel increase is stopped / stopped and the normal fuel injection control is performed in the region α1. Is called.

  If it is determined in step S12 that the fuel increase region αClose is not in the closed state, the process proceeds to step S15 to predict whether fuel increase will be performed. As shown in FIGS. 9 and 10, it is predicted that fuel increase will be performed when any of acceleration, accelerator opening (APO), and engine speed exceeds the determination threshold values L3 to L5. In step S16, the flow path switching valve 5 is opened. In the example of FIGS. 9 and 10, the flow path switching valve 5 is switched from the closed state to the open position when the acceleration exceeds the determination threshold value L3.

  However, immediately after switching from the closed state to the open position in step S16, it is determined by the routine shown in FIG. 5 that the main catalytic converter 4 is inactive, and the flow path switching valve 5 is closed again. There is a possibility that the opening and closing of the flow path switching valve 5 is repeated. Therefore, in this embodiment, after switching to the open position in step S16, switching from the open position to the closed position of the flow path switching valve 5 is prohibited for a predetermined time in step S17.

  With reference to the present embodiment as described above, the characteristic configuration of the present invention and the effects thereof will be listed.

  [1] A bypass passage 7 is provided in parallel with the upstream portion of the main passage 3 provided with the main catalytic converter 4 on the downstream side, the bypass passage 7 is provided with a bypass catalytic converter 8, and the main passage 3 is In a control device for an internal combustion engine comprising a flow path switching valve 5 that closes the main passage 3 in the upstream portion, the fuel injection amount is made richer in a fuel increase region αclose, αopon determined by the engine speed and engine load. A fuel increase means for increasing the fuel (S2), and a fuel increase area change means for changing the fuel increase areas αclose and αopon between the closed state and the open state of the flow path switching valve 5 (S1). It is said.

  In this way, by switching the fuel increase range between the open state and the closed state of the flow path switching valve 5, thermal deterioration due to high-temperature exhaust gas of exhaust system parts such as the bypass catalytic converter 8 and the main catalytic converter 4 is caused. Therefore, it is possible to suppress / avoid the unnecessary increase of the fuel amount, and to improve the exhaust purification performance and the fuel consumption performance.

  [2] As shown in FIGS. 2 and 3, the fuel increase region αClose in the closed state is set wider than the fuel increase region αOpen in the open state. For this reason, it is possible to achieve both a high level of prevention of thermal deterioration of the upstream bypass catalytic converter 8 in the closed state and suppression of fuel increase in the open state.

  [3] As shown in FIG. 6, in the closed state (S11) and when a predetermined open switching condition is satisfied (S12, S13, S15), the open switching for switching the flow path switching valve 5 to the open position. Means (S14, 16). As described above, when the predetermined opening switching condition is satisfied, even if the flow path switching valve 5 is in the closed state, the switching to the open position is forcibly suppressed, thereby suppressing the opportunity for fuel increase and exhaust performance. And fuel efficiency can be further improved.

  [4] When the open switching condition is a non-fuel increase range other than the fuel increase range in the closed state (S12), at least one of the engine acceleration, the accelerator opening, and the engine speed is a determination threshold value L3 to L5. (S15) is included.

  In this way, by comparing at least one of the engine acceleration, the accelerator opening degree, and the engine speed and the determination threshold values L3 to L5, the fuel increase is predicted, and the case where the fuel increase is predicted, that is, the determination threshold value If the flow rate exceeds the above, the fuel increase can be suppressed beforehand by switching the flow path switching valve 5 to the open position in advance.

  [5] As shown in FIG. 7, the open switching condition includes that the fuel increase region αClose in the closed state and the fuel increase rate exceeds a predetermined determination threshold value L1. Thereby, excessive fuel increase can be prevented, and exhaust performance and fuel consumption performance can be further improved.

[6] As shown in FIG. 8, the open switching condition includes the fuel increase region αClose in the closed state and the exhaust air-fuel ratio passing through the bypass passage is rich.
Thereby, it is possible to suppress / avoid deterioration of exhaust emission and fuel consumption due to excessive enrichment of the air-fuel ratio.

  [7] When the flow path switching valve 5 is switched from closed to open by the open switching means (S16), there is a switching prohibiting means (S17) for prohibiting switching the flow path switching valve to the closed state for a predetermined time. Yes. As a result, as described above, the flow path switching valve 5 is not switched to the closed state immediately after switching to the open position, and the opening and closing of the flow path switching valve 5 can be prevented from being repeated.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the structure of the internal combustion engine which concerns on one Example of this invention. The control map which shows the fuel increase area | region in a closed state. The control map which shows the fuel increase area | region in an open state. The flowchart which shows the flow of setting control of fuel injection amount. The flowchart which shows the flow of switching control of a basic switching valve. The flowchart which shows the flow of the opening switching control of the switching valve concerning a present Example. Explanatory drawing which shows an example of open switching conditions. Explanatory drawing which shows the other example of open switching conditions. The timing chart which shows the determination threshold value of the acceleration as a switching condition, an accelerator opening, and an engine speed. The timing chart which shows before and after the opening switching by the acceleration etc. similarly as an opening switching condition.

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 9 ... Junction point 27 ... Engine control unit

Claims (7)

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 passage, and the main passage is blocked at the upstream portion of the main passage. In a control device for an internal combustion engine comprising a flow path switching valve,
Fuel increase means for increasing the fuel injection amount to the rich side in the fuel increase range determined by the engine speed and engine load;
A fuel increase area changing means for changing the fuel increase area between a closed state and an open state of the flow path switching valve;
A control apparatus for an internal combustion engine, comprising:   2. The control device for an internal combustion engine according to claim 1, wherein the fuel increase area in the closed state is set wider than the fuel increase area in the open state.   3. The control device for an internal combustion engine according to claim 2, further comprising an open switching means for switching the flow path switching valve to an open position when the open condition is satisfied in the closed state.   The open switching condition includes that at least one of the engine acceleration, the accelerator opening, and the engine speed exceeds a determination threshold in a non-fuel increase range other than the fuel increase range in the closed state. The control device for an internal combustion engine according to claim 3.   The internal combustion engine according to claim 3, wherein the open switching condition includes a fuel increase range in the closed state and a fuel increase rate exceeds a predetermined determination threshold value. Control device.   5. The open / close condition according to claim 3, wherein the open air-fuel ratio that is in the fuel increase region in the closed state and that passes through the bypass passage is on a rich side. Control device for internal combustion engine.   7. A switching prohibiting means for prohibiting switching of the flow path switching valve to a closed state for a predetermined time when the flow switching valve is switched from closed to open by the open switching means. A control device for an internal combustion engine according to claim 1.

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