JP2006112285A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purifying device for an internal combustion engine capable of efficiently purifying toxic gas three components (CO, HC, NOx) in exhaust gas.
In an exhaust gas purifying apparatus, two catalytic converters 16 and 36 each incorporating a three-way catalyst 17 and 37 are disposed in an exhaust passage 3 of an engine 1. Further, the O2 sensor 34 is disposed downstream of the catalytic converter 36 disposed in the subsequent stage. When the elapsed time from when the output voltage Vr of the O2 sensor 34 exceeds the predetermined value V1 reaches the predetermined time T1 (S5: YES), the VVT mechanism 40 is operated to set the opening timing of the intake valve 48. The lead angle is advanced (S7), and NOx emission is reduced by the internal EGR effect.
[Selection] Figure 3

Description

  The present invention relates to an exhaust gas purification device that purifies exhaust gas discharged from an internal combustion engine.

  Conventionally, exhaust gas purification apparatuses that purify harmful components in exhaust gas discharged from an internal combustion engine have been put into practical use. In recent years, in order to further purify harmful components in exhaust gas due to environmental problems and the like, exhaust gas purifying devices having two catalytic converters are increasing. Some of such exhaust gas purification devices are provided with detection means for detecting deterioration of the catalytic converter disposed in the exhaust system of the internal combustion engine.

  One of them is disclosed in Japanese Patent Application Laid-Open No. 11-107741. In the exhaust gas purifying apparatus disclosed herein, a NOx catalyst is disposed in the front stage and a three-way catalyst is disposed in the rear stage. Then, an O2 sensor is provided upstream and downstream of the NOx catalyst arranged in the preceding stage, and if the time until the outputs of these O2 sensors become equal is less than a predetermined time, it is determined that the catalyst has deteriorated. Based on the determination result, the rich operating conditions of the internal combustion engine are controlled to activate the NOx catalyst and reduce NOx in the exhaust gas.

  However, while the NOx catalyst can efficiently purify nitrogen oxides (NOx), the purification rate of carbon monoxide (CO) and hydrocarbons (HC) is low. For this reason, an exhaust gas purification apparatus in which two three-way catalysts are arranged without using a NOx catalyst has been put into practical use. Thereby, the purification rate of carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) is increased. Also in such an exhaust gas purification device, O2 sensors are provided upstream and downstream of the catalyst in the previous stage, respectively, and catalyst deterioration is determined based on the outputs of these O2 sensors.

Japanese Patent Application Laid-Open No. 11-107741 (2nd page, FIG. 1)

  However, the above-described exhaust gas purification device has a problem that NOx in the exhaust gas cannot be efficiently reduced. This is because, in the exhaust gas purification device described above, when the oxygen concentration of the catalyst (three-way catalyst) disposed in the subsequent stage decreases when it is determined that the catalyst has deteriorated, the NOx purification performance in the exhaust gas This is because of a decrease. In particular, when the temperature of the catalyst is low (about 400 ° C.), as shown in FIG. 6, when the oxygen concentration of the catalyst decreases, the NOx purification rate decreases significantly.

  Accordingly, the present invention has been made to solve the above-described problems, and an exhaust gas purification device for an internal combustion engine that can efficiently purify the three harmful gas components (CO, HC, NOx) in the exhaust gas. It is an issue to provide.

An exhaust gas purification apparatus for an internal combustion engine according to the present invention, which has been made to solve the above problems, is disposed in an exhaust system of the internal combustion engine, and is a catalytic converter that purifies harmful components in the exhaust gas, and a downstream of the catalytic converter. At least one of an intake valve and an exhaust valve, an O ₂ sensor disposed at a position, a measuring means for measuring an elapsed time from when the output voltage of the O ₂ sensor exceeds a predetermined value after the internal combustion engine enters a lean state, and One valve opening / closing operation variable means for varying the opening / closing operation characteristics, and the valve opening / closing operation variable means so that the valve overlap period is increased when the elapsed time measured by the measuring means exceeds a predetermined time. And a control means for controlling the operation.

  In this exhaust gas purification device, an O2 sensor is provided downstream of a catalytic converter disposed in the exhaust system of the internal combustion engine. The elapsed time from when the output voltage of the O2 sensor exceeds a predetermined value after the internal combustion engine enters the lean state is measured by the measuring means. Thereafter, when the elapsed time measured by the measuring means reaches a predetermined time or more, the control means controls the operation of the valve opening / closing operation varying means so that the valve overlap period is increased.

  Specifically, the valve overlap period is lengthened by advancing the opening timing of the intake valve or retarding the opening timing of the exhaust valve, and the amount of gas blown back from the exhaust system to the intake system is increased. be able to. Further, by retarding the opening timing of the intake valve or advancing the opening timing of the exhaust valve, the valve overlap period can be lengthened and the amount of gas blown from the intake system to the exhaust system can be reduced. . Therefore, the amount of exhaust gas remaining in the combustion chamber of the internal combustion engine is increased by such an operation control of the intake valve or the exhaust valve, so that the effect of internal EGR can be obtained.

  In addition, what is necessary is just to set the time until a rich state continues and the NOx purification rate of a catalyst falls and NOx begins to be discharged | emitted from a catalyst as predetermined time. Therefore, since this predetermined time varies depending on the specifications of the internal combustion engine, an optimum time is set for each internal combustion engine by experiments or the like.

  For this reason, when the elapsed time measured by the measuring means becomes a predetermined time or more, the oxygen concentration of the catalyst is lowered and the NOx purification rate is deteriorated. Therefore, in this exhaust gas purifying apparatus, when the elapsed time measured by the measuring means becomes a predetermined time or more, the control means controls the operation of the valve opening / closing operation varying means to increase the valve overlap period. As a result, even when the oxygen concentration of the catalytic converter is lowered and the NOx purification rate is deteriorated, the internal EGR effect can be obtained, so that NOx emission can be efficiently reduced. Therefore, according to the exhaust gas purification apparatus of the present invention, even if the NOx purification rate in the catalytic converter is deteriorated, the harmful gas three components (CO, HC, NOx) in the exhaust gas can be efficiently purified. Can do.

  And the said control means should just determine the increase amount of a valve overlap period based on the driving | running condition of an internal combustion engine. This is because the internal EGR effect can be obtained without adversely affecting the performance of the internal combustion engine.

  In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the operating condition of the internal combustion engine includes a vehicle speed, and the overlap period varying means is configured to provide a valve overlap when the vehicle speed is zero. It is desirable to set the period increment to zero.

  This is because if the valve overlap period is increased when the vehicle speed is zero, problems such as knocking occur.

  In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, a plurality of the catalytic converters are arranged in an exhaust system of the internal combustion engine, and the O2 sensor is disposed at the last stage of the plurality of catalytic converters. It is desirable that it is arranged downstream of the arranged one.

  By arranging a plurality of catalytic converters in the exhaust system of the internal combustion engine, it is possible to further reduce the three harmful gas components (CO, HC, NOx) in the exhaust gas. Of the plurality of catalytic converters, the one arranged at the last stage is least likely to rise in temperature. For this reason, when the oxygen concentration of the catalytic converter arranged in the last stage is lowered, the NOx purification rate is further deteriorated. Therefore, by arranging an O2 sensor downstream of the catalytic converter that is arranged at the last stage among a plurality of catalytic converters and increasing the valve overlap period as described above, NOx emissions are efficiently reduced by the internal EGR effect. can do. As a result, the harmful gas three components (CO, HC, NOx) in the exhaust gas can be reduced very efficiently.

  According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, as described above, the three harmful gas components (CO, HC, NOx) in the exhaust gas can be efficiently purified.

  BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a most preferred embodiment that embodies an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described in detail with reference to the drawings. In this embodiment, the exhaust gas purifying apparatus of the present invention is applied to an engine system of an automobile.

  Therefore, the configuration of the engine system according to the present embodiment is shown in FIG. FIG. 1 is a diagram showing a schematic configuration of an engine system mounted on an automobile. In the engine system of FIG. 1, a multi-cylinder engine 1 is of a reciprocating type having a well-known structure. In this embodiment, the multi-cylinder engine 1 has six cylinders, a first cylinder # 1 to a sixth cylinder # 6. The engine 1 explodes and burns a combustible mixture of fuel and air sucked through the intake passage 2 in the combustion chambers of the cylinders # 1 to # 6, and discharges the exhaust gas after the combustion through the exhaust passage 3. Thus, a piston (not shown) is operated to rotate the crankshaft 4 to obtain power.

  The throttle valve 5 provided in the intake passage 2 is opened and closed in order to adjust the amount of air (intake amount) GA taken into each cylinder # 1 to # 6 through the passage 2. This valve 5 operates in conjunction with the operation of an accelerator pedal 6 provided in the driver's seat. A throttle sensor 21 provided for the throttle valve 5 detects an opening degree (throttle opening degree) TA of the valve 5 and outputs an electric signal corresponding to the detected value. An intake pressure sensor 22 provided in the intake passage 2 detects the intake pressure PM in the intake passage 2 downstream from the throttle valve 5 and outputs an electrical signal corresponding to the detected value.

  A plurality of fuel injection valves (injectors) 7 provided corresponding to the cylinders # 1 to # 6 inject fuel into the intake ports of the cylinders # 1 to # 6. These injectors 7 are connected to one delivery pipe 8. A fuel pump 13 built in the fuel tank 9 is connected to the delivery pipe 8 via a fuel pipe 14. A fuel filter 15 is provided in the middle of the fuel pipe 14. The fuel in the fuel tank 9 is discharged to the fuel pipe 14 by the fuel pump 13, the foreign matter is removed by the fuel filter 15, and then pumped to the delivery pipe 8 to be distributed to each injector 7. The distributed fuel is injected into the intake port when each injector 7 is operated, forms a combustible mixture with air, and is taken into each cylinder # 1 to # 6.

  A plurality of spark plugs 10 provided in the engine 1 corresponding to the respective cylinders # 1 to # 6 operate in response to an ignition signal distributed from the distributor 11. The distributor 11 distributes the high voltage output from the igniter 12 to each spark plug 10 in accordance with a change in the rotation angle of the crankshaft 4, that is, “crank angle (° CA)”. The ignition timing by each spark plug 10 is determined by the output timing of the high voltage output from the igniter 12. That is, by controlling the igniter 12, the ignition timing of each spark plug 10 in each cylinder # 1 to # 6 is controlled.

  The catalytic converters 16 and 36 provided in the exhaust passage 3 contain three-way catalysts 17 and 37 for purifying exhaust gas discharged from the engine 1. As is well known, the three-way catalysts 17 and 37 simultaneously perform oxidation of carbon monoxide (CO) and hydrocarbon (HC) in the exhaust gas and reduction of nitrogen oxide (NOx). As a result, the harmful gas three components (CO, HC, NOx) in the exhaust gas are purified into harmless carbon dioxide (CO2), water vapor (H2O) and nitrogen (N2). The exhaust purification characteristics of the three-way catalysts 17 and 37 vary greatly depending on the set air-fuel ratio in the engine 1. That is, when the air-fuel ratio is low, the amount of oxygen (O2) after combustion increases, the oxidation action becomes active, and the reduction action becomes inactive. When this balance between oxidation and reduction is achieved (when approaching the stoichiometric air-fuel ratio), the three-way catalysts 17 and 37 work most effectively.

  In the exhaust passage 3, an O2 sensor 23 is provided on the upstream side of the three-way catalyst 17, and an O2 sensor 24 is provided on the downstream side. An O2 sensor 34 is provided on the downstream side of the three-way catalyst 37. The O2 sensor 23 detects the oxygen concentration Ox in the exhaust gas discharged from the engine 1 to the exhaust passage 3, and outputs an electric signal corresponding to the detected value. The O2 sensor 24 detects the oxygen concentration Ox in the exhaust gas that has passed through the three-way catalyst 17 and outputs an electrical signal corresponding to the detected value. The O2 sensor 34 detects the oxygen concentration Ox in the exhaust gas that has passed through the three-way catalyst 37, and outputs an electrical signal (output voltage Vr) corresponding to the detected value. Then, based on the output voltage of the O2 sensor 23 and the O2 sensor 24, etc., a known catalyst deterioration diagnosis for the three-way catalyst 17 is performed.

  The rotational speed sensor 25 provided in the distributor 11 detects the angular speed of the crankshaft 4, that is, the engine rotational speed NE, and outputs an electrical signal corresponding to the detected value. The distributor 11 incorporates a rotor (not shown) that rotates in conjunction with the rotation of the crankshaft 4 and has a plurality of teeth on the outer periphery. The rotational speed sensor 25 includes this rotor and an electromagnetic pickup (not shown) disposed opposite to the outer periphery of the rotor. Each time the electromagnetic pickup detects the passage of each tooth with the rotation of the rotor, one pulse signal is output from the rotation speed sensor 25. In this embodiment, every time the crank angle advances by 30 ° CA, one pulse signal is output from the rotation speed sensor 25.

  Similarly, the distributor 11 is provided with a cylinder discrimination sensor 26 for detecting a change in crank angle at a predetermined rate according to the rotation of the rotor. In this embodiment, the cylinder discriminating sensor 26 is assumed at a rate of every 720 ° CA on the assumption that all of the first cylinder # 1 to the sixth cylinder # 6 rotate the crankshaft 4 by the end of the combustion stroke. 1 outputs a pulse signal as the reference position signal GS.

  A water temperature sensor 27 provided in the engine 1 detects the temperature (cooling water temperature) THW of the cooling water flowing inside the engine 1 and outputs an electrical signal corresponding to the detected value. This cooling water temperature THW reflects the temperature state of the engine 1.

  A vehicle speed sensor 28 that detects the vehicle speed of the vehicle and outputs an electrical signal corresponding to the detected value is attached to the vehicle side on which the engine system is mounted.

  In this embodiment, the electronic control unit (ECU) 30 inputs various signals output from the various sensors 21 to 28. The ECU 30 executes fuel injection control including ignition control and ignition timing control based on these input signals, and controls each injector 7 and igniter 12. In addition, the ECU 30 controls the operation of the VVT mechanism 40 described later based on the various signals, and corresponds to the control means of the present invention.

  Here, the fuel injection control is to control the fuel injection amount and the fuel injection timing by controlling each injector 7 in accordance with the operating state of the engine 1. The air-fuel ratio control is feedback control of the air-fuel ratio of the engine 1 to a predetermined air-fuel ratio such as the stoichiometric air-fuel ratio by controlling each injector 7 based on at least the output voltage from the O2 sensor 23. The ignition timing control is to control the ignition timing by each spark plug 10 by controlling the igniter 12 according to the operating state of the engine 1.

  As is well known, the ECU 30 includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), a backup RAM, and the like. The ROM stores in advance predetermined control programs related to the various controls described above. The ECU (CPU) 30 executes the various controls described above according to these control programs.

  The engine 1 is also equipped with a known variable valve timing mechanism that variably controls the opening / closing operation timing of the intake valve (or exhaust valve). Therefore, a schematic configuration of the variable valve timing mechanism mounted on the engine 1 will be described with reference to FIG. FIG. 2 is a perspective view showing a schematic configuration of the variable valve timing mechanism.

  A variable valve timing mechanism (hereinafter referred to as a VVT mechanism) 40 is mounted at the tip of an intake camshaft 41 of the engine 1 and is rotatable relative to the intake camshaft 41. An intake cam sprocket 42 is provided at the tip of the intake camshaft 41 so as to rotate integrally with the VVT mechanism 40. On the other hand, an exhaust cam sprocket 44 provided to rotate integrally with the exhaust camshaft 43 is provided at the tip of the exhaust camshaft 43. The VVT mechanism 40 corresponds to the valve opening / closing operation variable means of the present invention.

  An intake cam sprocket 42, an exhaust cam sprocket 44, and a crankshaft sprocket (not shown) provided on the crankshaft 4 of the engine 1 so as to rotate integrally with the crankshaft 4 are connected via a timing chain 45. Drive coupled. The gear ratio between the crankshaft sprocket and the intake cam sprocket 42 (or the exhaust cam sprocket 44) is 1: 2, and the intake cam sprocket 42 (or the exhaust cam sprocket 44) is 2 during one revolution of the crankshaft sprocket. It is designed to rotate.

  A plurality of intake cams 46 and exhaust cams 47 are provided on the intake camshaft 41 and the exhaust camshaft 43, respectively, so as to be integrally rotatable. The intake cam 46 and the exhaust cam 47 are configured to open and close the intake valve 48 and the exhaust valve 49 based on the pressure. The VVT mechanism 40 is hydraulically driven based on a command signal from the ECU 30 and has a function of adjusting a relative rotation phase with the intake camshaft 41 to a desired state. That is, the exhaust camshaft 43 rotates in synchronization with the crankshaft 4, whereas the relative rotation phase between the intake camshaft 41 and the crankshaft 4 is made variable by the VVT mechanism 40. In this way, in the engine 1, the opening / closing valve operation timing of the intake valve 48 (relative operation timing with respect to the exhaust valve 49) can be appropriately changed through the function of the VVT mechanism 40.

  Next, the contents of the exhaust gas purification process executed by the ECU 30 will be described with reference to FIG. FIG. 3 is a flowchart showing the contents of the exhaust gas purification process. Then, the ECU 30 periodically executes this processing routine every predetermined time.

  First, the ECU 30 determines whether or not the three-way catalyst 17 has deteriorated (S1). The deterioration determination of the three-way catalyst 17 may be performed by a known deterioration diagnosis method based on output voltages of the O2 sensor 23 and the O2 sensor 24 or the like. When it is determined that the three-way catalyst 17 has deteriorated (S1: YES), the ECU 30 determines whether or not the output voltage Vr of the O2 sensor 34 exceeds the predetermined voltage V1 (S2). Here, the predetermined voltage V1 may be set to the output voltage at the stoichiometric air-fuel ratio. When the output voltage Vr of the O2 sensor 34 does not exceed the predetermined voltage V1 (S2: NO), the ECU 30 measures the time after the combustion state of the engine 1 has shifted from the lean state to the rich state. The count value of the rich duration time counter is cleared (S3). When the ECU 30 determines in S1 that the three-way catalyst 17 has not deteriorated (S1: NO), this processing routine is terminated.

  When the output voltage Vr of the O2 sensor 34 exceeds the predetermined voltage V1, that is, when the combustion state of the engine 1 shifts from the lean state to the rich state (S2: YES), the ECU 30 counts up the count value of the rich duration time counter (S4). This count-up is continued until the count value of the rich duration time counter reaches a predetermined value T1 (S5: NO).

  Thereafter, when the count value of the rich duration counter reaches a predetermined value T1 (S5: YES), the ECU 30 determines whether or not the vehicle speed is greater than zero based on the output signal of the vehicle speed sensor 28 (S6). At this time, if the vehicle speed is greater than zero (S6: YES), the ECU 30 adds the VVT correction amount to the advance amount in the conventional VVT control, and the VVT mechanism is based on the advance amount after the addition. 40 is activated (S7). As a result, the opening timing of the intake valve 48 is advanced by a predetermined angle, so that the valve overlap period between the intake valve 48 and the exhaust valve 49 increases.

  Here, the VVT correction amount is set to a value that does not adversely affect the performance of the engine 1. Specifically, the VVT correction amount is determined by the engine speed NE and the engine load, as shown in FIG. Then, the VVT correction amount shown in FIG. 4 is mapped and stored in the ROM of the ECU 30. Thereby, the ECU 30 determines the VVT correction amount based on the engine speed NE and the engine load when the counter value of the rich duration time counter reaches the predetermined value T1.

  The count value (time) until the rich state continues and the NOx purification rate of the three-way catalyst 37 deteriorates and NOx starts to be discharged from the three-way catalyst 37 is set as the predetermined value T1. For this reason, even if the NOx purification rate of the three-way catalyst 37 deteriorates, the valve overlap period between the intake valve 48 and the exhaust valve 49 increases, so that NOx discharged from the engine 1 due to the internal EGR effect is reduced. . Therefore, the harmful gas three components (CO, HC, NOx) in the exhaust gas can be efficiently purified.

  If the vehicle speed is zero (S6: NO), ECU 30 sets the VVT correction amount to zero. When the vehicle speed is zero, the VVT advance amount in the conventional VVT control is also zero. That is, when the vehicle speed is zero, the VVT mechanism 40 does not operate. As a result, problems such as knocking do not occur when the vehicle speed is zero.

  Here, see FIG. 5 for the behavior of the air-fuel ratio, NOx emission amount, O2 sensor output Vr, rich duration (count value), intake valve advance amount, and vehicle speed when the above processing routine is executed. While explaining. FIG. 5 shows the NOx emission amount, O2 sensor output Vr, rich duration (count value), intake valve advance amount, and vehicle speed behavior after it is determined that the three-way catalyst 17 has deteriorated. It is a chart.

  First, since it is determined that the three-way catalyst 17 has deteriorated (S1: YES), the process of S2 is performed. At time t1 immediately after the fuel cut is performed at the time of deceleration, the output voltage Vr of the O2 sensor 34 is smaller than the predetermined voltage V1 (S2: NO). For this reason, the count value of the rich duration time counter is cleared (S3). Therefore, the rich continuation time (counter value) is zero. At time t2, the output voltage Vr of the O2 sensor 34 exceeds the predetermined voltage V1 (S2: YES). For this reason, the rich continuation time counter starts counting up (S4).

  At time t3, the count value of the rich continuation time counter reaches a predetermined value T1 (S5: YES). At this time, NOx emission starts to increase. However, in the exhaust gas purifying apparatus according to the present embodiment, when the count value of the rich duration time counter reaches the predetermined value T1, the vehicle speed is not zero (S6: YES), so the opening timing of the intake valve 48 However, it is advanced further than the advance made in the conventional VVT control (S7). The broken line shows the advance amount in the conventional VVT control. Thus, the valve opening timing of the intake valve 48 is advanced, so that the valve overlap period between the intake valve 48 and the exhaust valve 49 increases. As a result, NOx emissions can be reduced due to the internal EGR effect. And compared with the conventional exhaust-gas purification apparatus which does not implement such a process, the NOx emission amount was able to be about 60 to 70%. The broken line indicates the NOx emission amount of the conventional exhaust gas purification device.

  As described above in detail, in the exhaust gas purifying apparatus according to the present embodiment, the two catalytic converters 16 and 36 each including the three-way catalysts 17 and 37 are disposed in the exhaust passage 3 of the engine 1. Then, when the elapsed time from when the output voltage Vr of the O2 sensor 34 disposed downstream of the catalytic converter 36 located at the rear stage exceeds the predetermined value V1 reaches the predetermined time T1, the VVT mechanism 40 is operated. The valve opening timing of the intake valve 48 is advanced. Thereby, even if the NOx purification rate of the three-way catalyst 37 is lowered, the valve overlap period between the intake valve 48 and the exhaust valve 49 is increased, so that NOx discharged from the engine 1 due to the internal EGR effect is reduced. be able to. As a result, the exhaust gas purifying apparatus according to the present embodiment can efficiently purify the three harmful gas components (CO, HC, NOx) in the exhaust gas.

  It should be noted that the above-described embodiment is merely an example and does not limit the present invention in any way, and various improvements and modifications can be made without departing from the scope of the invention. For example, in the above-described embodiment, in order to increase the valve overlap period between the intake valve 48 and the exhaust valve 49, the valve opening timing of the intake valve 48 is advanced. May be retarded.

  Even if the valve opening timing of the intake valve 48 is retarded or the valve opening timing of the exhaust valve 49 is advanced to increase the valve overlap period, the amount of gas blown from the intake system to the exhaust system is reduced. Therefore, the effect of internal EGR can be obtained.

  Furthermore, in the above-described embodiment, the engine system including the two catalytic converters 16 and 36 has been illustrated, but the present invention can be applied to an engine system including one or two or more catalytic converters.

It is a figure showing a schematic structure of an engine system concerning an embodiment. It is a perspective view which shows schematic structure of a valve timing variable mechanism. It is a flowchart which shows the content of the exhaust gas purification process. It is a figure which shows the relationship between the driving | running state of an engine, and VVT correction amount. It is a time chart showing the behavior of NOx emission amount, O2 sensor output Vr, rich continuation time (count value), intake valve advance amount, and vehicle speed after it is determined that the catalyst is deteriorated. It is a figure which shows the change of the NOx purification rate with respect to the oxygen concentration change in a three-way catalyst.

Explanation of symbols

1 Engine 28 Vehicle speed sensor 30 ECU
36 catalytic converter 37 three-way catalyst 34 O2 sensor 40 valve timing variable mechanism

Claims (4)

A catalytic converter disposed in an exhaust system of an internal combustion engine for purifying harmful components in exhaust gas;
An O2 sensor disposed downstream of the catalytic converter;
Measuring means for measuring an elapsed time from when the output voltage of the O2 sensor exceeds a predetermined value after the internal combustion engine is in a lean state;
A valve opening / closing operation variable means for changing an opening / closing operation characteristic of at least one of the intake valve and the exhaust valve;
Control means for controlling the operation of the valve opening / closing operation variable means so that the valve overlap period is increased when the elapsed time measured by the measuring means becomes a predetermined time or more;
An exhaust gas purifying device for an internal combustion engine, comprising: The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The exhaust gas purification apparatus for an internal combustion engine, wherein the control means determines an increase amount of a valve overlap period based on an operating condition of the internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 2,
The operating conditions of the internal combustion engine include vehicle speed,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the control means sets the increase amount of the valve overlap period to zero when the vehicle speed is zero. The exhaust gas purifying device for an internal combustion engine according to any one of claims 1 to 3,
A plurality of the catalytic converters are arranged in the exhaust system of the internal combustion engine,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the O2 sensor is disposed downstream of the plurality of catalytic converters disposed at the last stage.

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