JP4654977B2 - Internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine 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.

  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

  However, in the configuration as described above, when the changeover valve is switched so that the warm-up of the main catalytic converter is completed and the exhaust flows to the main flow path side, the exhaust does not pass through the bypass catalytic converter that becomes a passage resistance. As a result of the flow, the exhaust pressure rapidly decreases and a torque step (specifically, an increase in torque) occurs.

Accordingly, the present invention is provided with a bypass passage having a relatively small total cross-sectional area compared to the total cross-sectional area of the main passage in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side. In an internal combustion engine comprising a bypass catalytic converter in a bypass passage and a flow path switching valve for closing the main passage in the upstream portion of the main passage that is bypassed by the bypass passage,
When there is a valve overlap amount between the exhaust valve closing timing and the intake valve opening timing when the flow path switching valve is switched from the closed state to the open state, prior to the opening operation of the flow path switching valve, The valve overlap amount is gradually reduced. As a result, the amount of residual gas in the cylinder decreases, and the amount of residual gas in the cylinder does not rapidly decrease even if the exhaust pressure decreases when the flow path switching valve switches from the closed state to the open state.

  According to the present invention, when the flow path switching valve is switched from the closed state to the open state, it is possible to prevent the suction efficiency from being relatively increased by replacing the residual gas amount in the cylinder with fresh air. Thus, the torque generated by the internal combustion engine having a flat characteristic without a torque step can be obtained.

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

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

  In the cylinder head 1, exhaust ports 2 of the cylinders # 1 to # 4 arranged in series are formed so as to open toward the side surfaces, and a main passage is formed in each of the exhaust ports 2. 3 is connected. The four main passages 3 of the # 1 cylinder to the # 4 cylinder merge into one flow path, and the main catalytic converter 4 is disposed on the downstream side thereof. The main catalytic converter 4 has a large capacity 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.

  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 at the junction 12 on the upstream side of the main catalyst converter 4 in the main passage 3 (so that the flow path switching valve 5 is upstream of the junction 12). It is connected.

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

  In this embodiment, an exhaust valve side valve operating mechanism for driving an exhaust valve (not shown) includes an exhaust valve side sprocket (not shown) provided at the front end of an exhaust valve side camshaft (not shown), An exhaust valve side sprocket and an exhaust valve side phase control actuator (not shown) for relatively rotating the exhaust valve side sprocket and the exhaust valve side camshaft within a predetermined angle range. The exhaust valve side sprocket is not shown. It is linked to a crankshaft (not shown) via a timing chain or a timing belt.

  The intake valve side valve operating mechanism for driving the intake valve includes an intake valve side sprocket (not shown) provided at a front end portion of an intake valve side camshaft (not shown), the intake valve side sprocket, and the intake valve side cam. An intake valve side phase control actuator (not shown) that relatively rotates the shaft within a predetermined angle range, and the intake valve side sprocket is connected via a timing chain or a timing belt (not shown). It is linked to a crankshaft not shown.

  The exhaust valve side phase control actuator and the intake valve side phase control actuator are, for example, hydraulic rotary actuators. The exhaust valve side sprocket and the exhaust valve side camshaft rotate relatively by the action of the exhaust valve side phase control actuator, and the lift center angle in the valve lift of the exhaust valve is retarded. Similarly, by the action of the intake valve side phase control actuator, the intake valve side sprocket and the intake valve side camshaft rotate relatively, and the lift center angle in the valve lift of the intake valve is retarded. In other words, due to the action of the exhaust valve side phase control actuator and the intake valve side phase control actuator, the lift characteristics curves of the exhaust valve and the intake valve do not change, and the whole is continuously advanced or retarded. Horn.

  In such a configuration, when the engine temperature or the exhaust gas temperature after the cold start is low, the flow path switching valve 5 is closed via an appropriate actuator, 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 engine temperature or the exhaust temperature becomes sufficiently high, the flow path switching valve 5 is opened. Thus, the exhaust discharged from each cylinder mainly passes through the main catalytic converter 4 from the main passage 3. At this time, the bypass passage 7 side is not particularly cut off, but the bypass passage 7 side has a smaller passage cross-sectional area than the main passage 3 side and the bypass catalytic converter 8 is interposed. Due to the difference, most of the exhaust flow passes through the main passage 3 side and hardly flows into the bypass passage 7 side. Therefore, the thermal deterioration of the bypass catalytic converter 8 is sufficiently suppressed.

  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 exhaust pressure rapidly decreases, and the residual gas amount in the cylinder also sharply increases. Decrease. At this time, in the cylinder, the decrease in the residual gas is replaced with fresh air, the suction efficiency is relatively increased, the torque is instantaneously increased, and a torque step is generated.

  Therefore, in the present invention, when there is a valve overlap amount (O / L amount) between the exhaust valve closing timing and the intake valve opening timing when the flow path switching valve 5 is opened, the valve overlap amount is reduced in advance. By reducing the residual gas amount in the cylinder, an instantaneous torque increase caused by a rapid pressure drop in the main passage 3 and the residual gas amount in the cylinder being replaced with fresh air is prevented. .

  FIG. 2 shows a timing chart for explaining various operations in the first embodiment of the present invention.

  When the control command for the flow path switching valve 5 is switched from the fully closed command to the full open command when the warm-up is completed, the residual gas amount in the cylinder is reduced prior to the actual opening operation of the flow path switching valve 5. In order to achieve this, the valve overlap amount between the exhaust valve closing timing and the intake valve opening timing is gradually decreased, and the opening degree of a throttle valve (not shown) disposed in the intake passage is gradually decreased (in-cylinder The air volume of the air is kept almost constant) and torque fluctuations are suppressed. At this time, the valve overlap amount is gradually decreased so that the residual gas amount in the cylinder becomes a predetermined value (residual gas reference value) set in advance. As a method of reducing the valve overlap amount, the intake valve opening timing may be fixed, and only the exhaust valve closing timing may be advanced by the action of the exhaust valve side phase control actuator. The closing timing may be fixed and only the opening timing of the intake valve may be retarded (retarded) by the action of the intake valve side phase control actuator. Alternatively, it is possible to gradually decrease the valve overlap amount by advancing the exhaust valve closing timing and retarding the intake valve opening timing. Then, after the residual gas amount in the cylinder is reduced to the residual gas reference value, the flow path switching valve 5 starts to open.

  Thereby, when the flow path switching valve 5 starts to open from the fully closed state, the residual gas amount in the cylinder decreases, and even if the flow path switching valve 5 starts to open and the exhaust pressure decreases, the residual gas in the cylinder remains. The amount of gas does not decrease rapidly. In other words, it is possible to prevent the intake efficiency from being relatively increased by replacing the residual gas amount in the cylinder with fresh air, and to obtain the generated torque of the internal combustion engine having a flat characteristic without a torque step. it can.

  In other words, when the flow path switching valve 5 is opened, the air-fuel ratio fluctuation (A / F fluctuation) due to the sudden decrease in the residual gas amount in the cylinder can be suppressed. The resulting torque step can be prevented and exhaust performance deterioration can be suppressed.

  Furthermore, by controlling the residual gas amount in the cylinder by reducing the valve overlap amount, the residual gas amount in the cylinder can be reduced without being affected by the valve opening / closing speed (switching speed) of the flow path switching valve 5. Since it becomes possible to control, for example, an actuator of a drive system in which the valve opening / closing speed cannot be controlled can be adopted as a drive source of the flow path switching valve 5, and an actuator that becomes a drive source of the flow path switching valve 5 The degree of freedom of selection increases, and the cost can be reduced.

  When the flow path switching valve 5 is fully opened, the valve overlap amount is gradually increased to a state before a full open command is issued to the flow path switching valve 5, and the valve opening of the throttle valve is changed to flow path switching. The valve 5 is gradually increased to a valve opening smaller than the state before the fully open command is issued to the valve 5. As described above, when the valve overlap amount is gradually increased, the valve opening amount of the throttle valve is also gradually increased to return the valve overlap amount to the state before the switching of the flow path switching valve 5. Torque fluctuation can be suppressed.

  In FIG. 2, A / F indicated by a broken line indicates a case where the amount of residual gas in the cylinder has rapidly decreased (replaced with fresh air). In FIG. 2, the generated torque indicated by a broken line indicates a case where A / F is A / F indicated by a broken line in FIG. 2.

  FIG. 3 shows a timing chart for explaining various operations in the second embodiment of the present invention.

  This second embodiment is controlled in substantially the same manner as the first embodiment described above, but has an exhaust gas recirculation device (not shown) as EGR means for returning the external EGR to the intake system, and the above-described branching is performed. Part of the exhaust gas taken from the upstream side of the point 6 is recirculated to the intake system while controlling the flow rate.

  More specifically, when the control command for the flow path switching valve 5 is switched from the fully closed command to the fully open command at the stage where the warm-up is completed, the residual in the cylinder is prior to the actual opening operation of the flow path switching valve 5. In order to reduce the gas amount, the valve overlap amount between the exhaust valve closing timing and the intake valve opening timing is gradually decreased, and the opening degree of a throttle valve (not shown) disposed in the intake passage is gradually decreased. Further, the external EGR rate is gradually reduced by the exhaust gas recirculation device.

  In FIG. 3, A / F indicated by a broken line indicates a case where the external EGR rate is not gradually decreased along with the valve overlap amount and the opening degree of the throttle valve. Further, in FIG. 3, the generated torque indicated by a broken line indicates a case where A / F is A / F indicated by a broken line in FIG.

  In such a second embodiment, the same operational effects as those of the first embodiment described above can be obtained.

  In each of the above-described embodiments, there is a slight possibility that a change in exhaust pressure when the flow path switching valve 5 is switched from the fully closed state to the fully open state may become a resistance change during the exhaust stroke. When the switching valve 5 is switched from the fully closed state to the fully opened state, the opening degree of the throttle valve may be gradually decreased.

  In addition, the valve overlap amount is not decreased until the residual gas amount in the cylinder reaches the residual gas reference value, but the exhaust valve closing timing coincides with the intake valve opening timing or the exhaust valve closing timing is At least one of the exhaust valve closing timing and the intake valve opening timing may be changed to a state in which the angle is relatively advanced with respect to the intake valve opening timing.

  The technical idea of the present invention that can be grasped from the above embodiment will be listed together with the effects thereof.

  (1) A bypass passage having a relatively small total cross-sectional area compared to the total cross-sectional area of the main passage is provided in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side. An internal combustion engine comprising a bypass catalytic converter and having a flow path switching valve that closes the main passage in the upstream portion of the main passage that is bypassed by the bypass passage, wherein the flow path switching valve is in a closed state If there is a valve overlap amount between the exhaust valve closing timing and the intake valve opening timing when switching from the open state to the open state, the valve overlap amount is gradually reduced prior to the opening operation of the flow path switching valve. Let As a result, the amount of residual gas in the cylinder decreases, and the amount of residual gas in the cylinder does not rapidly decrease even if the exhaust pressure decreases when the flow path switching valve switches from the closed state to the open state. That is, when the flow path switching valve is switched from the closed state to the open state, it is possible to prevent the suction efficiency from being relatively increased by replacing the residual gas amount in the cylinder with the fresh air, and the torque. The generated torque of the internal combustion engine having a flat characteristic without a step can be obtained.

  (2) Specifically, the internal combustion engine according to (1) reduces the valve overlap amount by retarding the intake valve opening timing.

  (3) The internal combustion engine described in (1) specifically reduces the valve overlap amount by advancing the exhaust valve closing timing.

  (4) In the internal combustion engine described in (3) above, specifically, the exhaust valve closing timing is advanced to a state where the exhaust valve closing timing coincides with the intake valve opening timing or is advanced relative to the intake valve opening timing. .

  (5) Specifically, the internal combustion engine according to any one of the above (1) to (4) gradually decreases the valve opening of the throttle valve when the valve overlap amount is gradually decreased.

  (6) The internal combustion engine according to any one of the above (1) to (5) includes EGR means for recirculating a part of the exhaust gas to the intake system while controlling the flow rate, and the flow path switching valve is closed. When the external EGR is recirculated to the intake system by the EGR means when switching from the open state to the open state, the external EGR rate is gradually reduced prior to the opening operation of the flow path switching valve.

  (7) Specifically, the internal combustion engine according to (6) described above gradually decreases the external EGR rate and gradually decreases the valve opening of the throttle valve when the valve overlap amount is gradually decreased. .

  (8) In the internal combustion engine according to any one of the above (1) to (7), when the bypass valve is switched from the closed state to the open state, the valve overlap amount is changed from the closed state to the flow path switching valve. While gradually increasing until the valve overlap amount before switching to the open state, the valve opening of the throttle valve is gradually increased. Thereby, torque fluctuations when increasing the valve overlap amount can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS Configuration explanatory drawing which shows the piping layout of the whole exhaust apparatus of the internal combustion engine which concerns on this invention. The timing chart for demonstrating the various operation | movement in 1st Embodiment of this invention. The timing chart for demonstrating the various operation | movement in 2nd Embodiment of this invention.

Explanation of symbols

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

Claims (8)

A bypass passage having a smaller overall cross-sectional area than the total cross-sectional area of the main passage is provided in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side. And an internal combustion engine comprising a flow path switching valve that closes the main passage in the upstream portion of the main passage that is bypassed by the bypass passage,
When there is a valve overlap amount between the exhaust valve closing timing and the intake valve opening timing when the flow path switching valve is switched from the closed state to the open state, prior to the opening operation of the flow path switching valve, An internal combustion engine characterized by gradually reducing the valve overlap amount.   The internal combustion engine according to claim 1, wherein the valve overlap amount is reduced by retarding an intake valve opening timing.   The internal combustion engine according to claim 1, wherein the valve overlap amount is reduced by advancing the exhaust valve closing timing.   The internal combustion engine according to claim 3, wherein the exhaust valve closing timing is made to coincide with the intake valve opening timing or advanced to a state where the exhaust valve closing timing is relatively advanced with respect to the intake valve opening timing.   The internal combustion engine according to any one of claims 1 to 4, wherein when the valve overlap amount is gradually decreased, the valve opening of the throttle valve is gradually decreased.   EGR means for returning a part of the exhaust gas to the intake system while controlling the flow rate is provided. When the flow path switching valve is switched from the closed state to the open state, the external EGR is returned to the intake system by the EGR means. 6. The internal combustion engine according to claim 1, wherein the external EGR rate is gradually reduced prior to the opening operation of the flow path switching valve.   The internal combustion engine according to claim 6, wherein when the valve overlap amount is gradually decreased, the external EGR rate is gradually decreased and the valve opening of the throttle valve is gradually decreased.   When the bypass valve switches from the closed state to the open state, the valve overlap amount is gradually increased until the valve overlap amount becomes the valve overlap amount before switching the flow path switching valve from the closed state to the open state, and the throttle valve The internal combustion engine according to any one of claims 1 to 7, wherein the valve opening is gradually increased.

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