JP2007154814A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce HC and activate an exhaust emission control catalyst 16 in an early stage at a time of demand for temperature raise of the exhaust emission control catalyst 16. <P>SOLUTION: Overlap during which both of an exhaust valve and an intake valve are in open periods is expanded until start of lambda control for controlling air fuel ratio to a theoretical air fuel ratio at the time of demand for temperature raise of the exhaust emission control catalyst 16. After start of the lambda control, overlap is returned and ignition timing is retarded when output ratio of an air fuel ratio sensor 19 reaches the theoretical air fuel ratio. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust purification device that reduces exhaust unburned components such as HC and activates the catalyst at an early stage by reducing exhaust unburned components such as HC when a temperature increase request is made for an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine. .

In Patent Document 1, in an exhaust gas purification apparatus for an internal combustion engine including a variable valve timing mechanism capable of changing the opening / closing timing of an intake valve and an exhaust gas purification catalyst capable of purifying exhaust gas in an exhaust passage, an engine cold start state, etc. During a predetermined period when the temperature of the exhaust purification catalyst is required (from when the engine is started until when the unburned HC is purified to some extent), the variable valve timing mechanism normally causes an overlap in which both the exhaust valve and the intake valve are open. It is disclosed to enlarge more than during driving. After a predetermined period, the overlap is reduced and the ignition timing is retarded.
JP 2002-235647 A

  However, in the internal combustion engine described in Patent Document 1, the reduction in HC is effective by increasing the overlap because the air-fuel ratio is set to the target air-fuel ratio (by the lambda control in which the air-fuel ratio becomes rich due to the fuel-heavy light air-fuel ratio difference. This is before starting feedback control to (theoretical air-fuel ratio). For this reason, after the feedback control is started, there is a problem that early activation of the exhaust purification catalyst due to HC reduction and exhaust gas temperature increase cannot be achieved.

  The present invention has been made in view of the above problems, and aims to reduce the HC and achieve early activation of the exhaust purification catalyst.

  Therefore, in the present invention, when the temperature increase of the exhaust purification catalyst is requested, until the air-fuel ratio feedback control is started, the overlap between the exhaust valve and the intake valve is opened, and the air-fuel ratio feedback control is started. After that, the overlap is returned and the ignition timing is retarded.

  According to the present invention, fuel vaporization is promoted by causing the exhaust gas to blow back into the intake port by expanding the overlap at the time of the temperature increase request of the catalyst, and the difference between the heavy and light air-fuel ratios of the fuel is reduced. The lean air / fuel ratio can be set. As a result, even when the air-fuel ratio sensor for detecting the air-fuel ratio is inactive and the air-fuel ratio feedback control using the sensor cannot be performed, even in a rich state immediately after the start, the HC can be reduced by expanding the overlap. This is effective in that it can be reduced.

  After the feedback control is started, the effect of expanding the overlap is reduced by reducing the surplus fuel. Therefore, the ignition timing is retarded by the amount of returning the overlap and improving the combustion stability, and the HC is reduced by the afterburning. As well as reducing the temperature, it is possible to achieve early activation of the exhaust purification catalyst due to the temperature rise of the exhaust gas.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an exhaust gas purification apparatus for an internal combustion engine.
An intake valve 6 and an exhaust valve 7 are disposed in a combustion chamber 4 defined by each cylinder 2 and piston 3 of the engine 1 so as to surround the spark plug 5.
The intake valve 6 is opened and closed at a predetermined timing by an intake cam 8a formed on the first camshaft 8. The exhaust valve 7 is opened and closed at a predetermined timing by an exhaust cam 9 a formed on the second camshaft 9.

  The first camshaft 8 is provided with a variable valve timing mechanism 10 that can change the opening / closing timing of the intake valve 6. The variable valve timing mechanism 10 changes the phase of the intake valve 6 based on a variable valve timing signal from the ECU 30 in order to change the opening / closing timing of the intake valve 6, thereby opening both the exhaust valve 7 and the intake valve 6. The overlap which becomes a period can be enlarged and reduced.

  In order to control the amount of intake air introduced into the engine 1, an electric throttle valve (butterfly valve) 12 is disposed in the intake passage 11. The electric throttle valve 12 can introduce air into the combustion chamber 4 in accordance with the opening area. The opening area of the electric throttle valve 12 is determined based on an opening degree command of the engine control unit (ECU) 30. A fuel injection valve 14 is provided in each intake port 11 a downstream of the intake passage 11.

The exhaust passage 15 is provided with an exhaust purification catalyst 16 that can purify exhaust unburned components such as HC.
Further, the ECU 30 includes a throttle opening sensor 17, an air flow meter (hot wire flow meter) 18, an air-fuel ratio detection means (air-fuel ratio sensor in this case) 19, an exhaust temperature sensor 20, a crank angle sensor 21, a water temperature sensor 22, and a start. Signals from the switch 23 and the accelerator opening sensor 24 are input.

The throttle opening sensor 17 outputs a signal corresponding to the opening degree of the electric throttle valve 12.
The air flow meter 18 is provided in the intake passage 11 upstream from the electric throttle valve 12 and outputs a signal corresponding to the flow rate of air passing through the electric throttle valve 12.
The air-fuel ratio sensor 19 is provided upstream of the exhaust purification catalyst 16 in the exhaust passage 15 and outputs a signal corresponding to the exhaust air-fuel ratio. The output value of the air-fuel ratio sensor 19 changes in proportion to the air-fuel ratio.

The exhaust temperature sensor 20 outputs a signal corresponding to the temperature of the exhaust gas.
The crank angle sensor 21 outputs a signal corresponding to the crank angle of the engine 1. The engine speed can be detected by a signal from the crank angle sensor 21.
The water temperature sensor 22 is provided in the cylinder block, and outputs a signal corresponding to the temperature of the coolant flowing in the water jacket of the cylinder block (engine water temperature).

The start switch 23 (shown as “ST / SW” in the figure) outputs ON and OFF signals when the engine 1 is started by the operation of the driver.
The accelerator opening sensor 24 outputs a signal corresponding to the opening of the accelerator pedal.
The ECU 30 performs calculations based on signals from various sensors, and performs various controls based on the calculation results. For example, ignition timing control of the spark plug 5, valve timing control (overlap control) of the intake valve 6, opening control of the electric throttle valve 12, fuel injection control of the fuel injection valve 14, etc. are performed.

FIG. 2 is a time chart in the case where the exhaust purification control of the present invention is performed when a temperature increase request of the exhaust purification catalyst 16 is requested. FIG. 3 is a table showing correction amounts of parameters to be corrected among the parameters shown in FIG.
As shown in FIG. 2, as parameters for the elapsed time T after the start of the engine 1, (a) shows the engine speed, (b) shows the air-fuel ratio (shown as “A / F” in the figure), and (c). Is the advance and retard angles of the intake valve 6 by a variable valve timing mechanism (shown as “VTC; Variable Timing Control” in the figure) 10, (D) is the ignition timing of the spark plug 5, and (E) is the electric throttle valve 12. (F) indicates the rate of increase of the fuel injected from the fuel injection valve 14, (G) indicates the amount of HC discharged into the exhaust passage 15, and (H) indicates the temperature of the exhaust gas.

As shown in FIG. 2A, the engine speed converges to the target engine speed (idle speed) after the start switch 23 is switched from ON to OFF.
As shown in FIG. 2 (b), the exhaust air-fuel ratio suddenly becomes rich from the time point t1 to the time point t2 when the start switch 23 is turned from ON to OFF. Thereafter, the air-fuel ratio in the exhaust passage 15 (or in the combustion chamber 4 of the engine 1) under the condition that a predetermined time Tλ has elapsed from the time t1 when the air-fuel ratio sensor 19 is activated and the start switch 23 is turned from ON to OFF. The air-fuel ratio is gradually shifted to the stoichiometric air-fuel ratio (stoichiometric side) until time t4 when lambda control for feedback control of the air-fuel ratio to the target air-fuel ratio is started.

Note that t3 is a time point at which activation determination of the air-fuel ratio sensor 19 is started after the engine 1 is started. t4 is the time when it is determined that the air-fuel ratio sensor 19 is activated. After the activation of the air-fuel ratio sensor 19, lambda control for controlling the air-fuel ratio to the stoichiometric air-fuel ratio based on the output value of the sensor 19 becomes possible.
As shown in FIG. 2C, at the time t2 when the opening / closing timing (phase) of the intake valve 6 is changed (when the VTC drive is permitted) t2, the phase of the intake valve 6 is set to the first phase VTC ₀ on the retard side. Is advanced to the second phase VCT ₁ on the retard side, and the overlap in which both the exhaust valve 7 and the intake valve 6 are open is expanded. Thereafter, the phase VCT ₁ of the intake valve 6 is controlled to the first phase VTC _{0 in} order to return the enlarged overlap from the time t5 when the retarding of the intake valve 6 by the variable valve timing mechanism 10 is started.

When returning the enlarged overlap, the speed (retard speed) for returning the intake valve 6 from the second phase VCT ₁ to the first phase VTC ₀ is set based on the water temperature TW 0 at the start of the engine 1. This setting is performed with reference to the retardation speed correction table shown in FIG. This table shows that the retarding speed is increased as the water temperature TW0 is higher.
As shown in FIG. 2 (d), the ignition timing ADV of the spark plug 5 is set to a first predetermined value ADV ₁ which is an initial value from immediately after the start of the engine 1 to the time t2, while from the time t2 to the time t5. The second predetermined value ADV ₂ advanced by the correction amount accompanying the increase of the overlap is set up to the time point of. Then, from the time t5 to initiate retarding of the phase of the intake valve 6 by the variable valve timing mechanism 10, the ignition timing, the process proceeds to the third predetermined value ADV ₃ was retarded than the first predetermined value ADV ₁ (retard) .

In this case, the speed (retard speed) at which the ignition timing of the spark plug 5 is shifted from the second predetermined value ADV ₂ to the third predetermined value ADV ₃ is set based on the water temperature TW0 when the engine 1 is started and the overlap. To do. This setting is performed with reference to the ignition timing correction map shown in FIG. This map indicates that correction (setting) is performed so that the ignition timing is advanced more as the overlap is larger, and the ignition timing is further advanced as the water temperature TW0 is lower. That is, the greater the overlap and the lower the water temperature TW0, the faster the retarding speed of the ignition timing.

  As a result, after the lambda control is started, the fuel injection amount from the fuel injection valve 14 increases, and the vaporization of the droplet fuel in the intake port 11a, which is the effect of expanding the overlap, decreases. Thus, the ignition timing is retarded by an amount corresponding to the improvement of the combustion stability, the unburned components are reduced by the afterburning, and the early activation of the exhaust purification catalyst 16 by the rise of the exhaust gas temperature can be achieved.

As shown in FIG. 2E, the opening degree TVO of the electric throttle valve 12 is changed from the first predetermined value TVO ₁ which is the initial value at the time t2 immediately after the engine 1 is started to the first predetermined value TVO _1. The second predetermined value TVO ₂ having a larger opening is set. The second predetermined value TVO ₂ is a value obtained by increasing the opening degree of the electric throttle valve 12 by a correction amount associated with an increase in overlap. The opening TVO of the electric throttle valve 12 is maintained at the second predetermined value TVO ₂ from the time t2 to the time t5. Then, the variable from the time t5 to retard the intake valve 6 by the valve timing mechanism 10 is started, the first predetermined value opening TVO of the electronically controlled throttle valve 12 is TVO ₁ and the second predetermined value TVO ₂ smaller than the third The process proceeds to the predetermined value TVO ₃ .

At this time, the speed at which the opening degree TVO of the electric throttle valve 12 is shifted from the second predetermined value TVO ₂ to the third predetermined value TVO ₃ is set based on the overlap. This setting is performed with reference to the throttle valve opening correction table shown in FIG. This table indicates that correction (setting) is performed so that the opening degree TVO of the electric throttle valve 12 increases as the overlap increases.

This makes it easy to return the exhaust gas to the intake port 11a by increasing the opening degree TVO of the electric throttle valve 12 from the time t2 to the time t5 in FIG. 2 while the overlap is expanding. Thus, fuel vaporization can be promoted. For this reason, the air-fuel ratio is made lean and HC can be reduced.
On the other hand, from the time point t5 to the time point t6 in FIG. 2 during the return of the overlap (retarding of the phase of the intake valve 6), the opening degree TVO of the electric throttle valve 12 is reduced. While making it difficult to return the exhaust gas to the intake port 11a, the ignition timing is retarded. As a result, the exhaust gas temperature can be increased due to afterburning to reduce HC, and the exhaust purification catalyst 16 can be activated early.

  As shown in FIG. 2 (f), the fuel increase rate is decreased from the first predetermined value, which is the initial value until the time t1 immediately after the engine 1 is started, to the time t2. At the time t2, the fuel increase rate is decreased by the amount corresponding to the correction associated with the increase in overlap caused by the advance of the phase of the intake valve 6 by the variable valve timing mechanism 10. Then, fuel injection is increased by lambda control from time t5 when the variable valve timing mechanism 10 retards the intake valve 6.

The fuel increase rate by lambda control is set with reference to the fuel increase rate map shown in FIG. This map indicates that if the overlap is large, the fuel increase rate is low, and if the water temperature TW0 at the start of the engine 1 is low, the fuel increase rate is further reduced.
As shown in FIG. 2G, the amount of exhaust of HC, which is an unburned exhaust component, becomes maximum near the time t2 immediately after the start of the engine 1, and thereafter, the time at which lambda control is started (air-fuel ratio) It gradually decreases until t4 when the sensor 19 is activated.

At time t5, the variable valve timing mechanism 10 retards the intake valve 6 (t5 to t6 in FIG. 2 (c)) to return the overlap and retard the ignition timing of the spark plug 5 (FIG. 2 (d) t5 to t6), the HC emission amount is further reduced.
As shown in FIG. 2 (h), the temperature of the exhaust gas gradually rises from immediately after the engine 1 is started to the time when lambda control is started, that is, until the activation time t4 of the air-fuel ratio sensor 19. Then, lambda control based on the output signal of the air-fuel ratio sensor 19 is started. Thereafter, the variable valve timing mechanism 10 starts retarding the intake valve 6 (t5 to t6 in FIG. 2 (c)) to return the overlap, and retards the ignition timing (t5 to t6 in FIG. 2 (d)). As a result, afterburning is generated to reduce HC, and the exhaust gas temperature is raised to achieve early activation of the exhaust purification catalyst 16.

Next, the exhaust purification control of the engine 1 for carrying out FIGS. 2 and 3 when the temperature of the exhaust purification catalyst 16 is requested will be described with reference to the flowchart of FIG.
In step 1 (shown as “S1” in the figure, the same applies hereinafter), it is determined whether the start switch 23 of the engine 1 is ON. It is determined whether the start switch 23 has been switched from ON to OFF. That is, the process proceeds to Step 2 only when the start switch 23 is switched from ON to OFF at time t1 shown in FIG.

In step 2, the initial value 0 is substituted into a timer for counting the elapsed time T after the start switch 23 is switched from ON to OFF. Thereby, the timer count is started from the time t1 shown in FIG.
In step 3, the water temperature TW0 when the engine 1 is started is read and stored.
In step 4, the time until the lambda control is started (the air-fuel ratio sensor 19 is activated) after the start switch 23 is switched from ON to OFF, that is, from the time t1 to the time t4 shown in FIG. It is determined whether the time Tλ is exceeded (T> Tλ). If T> Tλ, the process proceeds to Step 9 described later. On the other hand, if T ≦ Tλ, the process proceeds to step 5.

  In step 5, it is determined whether or not the variable valve timing mechanism 10 is allowed to advance the phase TVO of the intake valve 6 to increase the overlap. If the drive is not permitted, normal control is performed in step 6. On the other hand, if there is drive permission, the process proceeds to step 7 to set each parameter at t2 to t5 in FIGS.

In step 7, the variable valve timing mechanism 10 advances the phase TVO of the intake valve 6 from the first phase VTC ₀ to the second phase VCT ₁ (FIG. 2 (C)). As a result, the overlap in which both the exhaust valve 7 and the intake valve 6 are open is expanded, and the exhaust gas is blown back from the cylinder to the intake port 11a, thereby promoting the vaporization of the fuel in the intake port 11a. .

For this reason, even when the air-fuel ratio sensor 19 is in an inactive state and lambda control cannot be performed, the overlap immediately after the start of the engine 1 where the air-fuel ratio becomes rich (near the time t2 in FIG. 2B). HC can be reduced by enlargement.
In step 8, the ignition timing ADV of the spark plug 5 is based on the overlap expanded by the advancement of the phase TVO of the intake valve 6 by the variable valve timing mechanism 10 and the water temperature TW0 when the engine 1 is started. The opening degree TVO of the electric throttle valve 12 and the fuel increase rate of the fuel injection valve 14 are corrected (set) with respect to those during normal control.

The ignition timing ADV of the spark plug 5 is set to the second predetermined value ADV ₂ advanced by the correction amount for the overlap as shown from the time t2 to the time t5 in FIG.
The throttle opening TVO is set to a second predetermined value TVO ₂ that is increased by a correction amount for the overlap as shown from the time t2 to the time t5 in FIG. Thereby, in a state where the overlap is enlarged, the vaporization of the fuel in the intake port 11a can be promoted by increasing the throttle opening TVO to facilitate the return of the exhaust gas to the intake port 11a.

  As shown in FIG. 2 (f) from the time t2 to the time t5, the fuel increase rate decreases the fuel increase rate by a correction corresponding to the increase in overlap caused by the advance of the phase of the intake valve 6. Let This is because the fuel in the intake port 11a is vaporized by exhaust gas being blown back into the intake port 11a due to an increase in overlap, and this is introduced into the combustion chamber 4, so that the fuel injected from the fuel injection valve 14 This is because the amount can be reduced.

If the process proceeds to step 9, that is, if T> Tλ in step 4, it is determined whether lambda control has already been performed. If lambda control is not performed, the process proceeds to step 10, while if it is performed, the process proceeds to step 12.
In step 10, it is determined whether the air-fuel ratio sensor 19 is active. If it is active, the process proceeds to step 11, while if it is not active, the process proceeds to step 5 described above. Thus, it is determined whether the predetermined time Tλ has elapsed since the timer count was started and whether lambda control for controlling the air-fuel ratio to the stoichiometric air-fuel ratio is possible based on the output of the air-fuel ratio sensor 19.

In step 11, lambda control for controlling the fuel injection amount from the fuel injection valve 14 is started so that the air-fuel ratio detected based on the output of the air-fuel ratio sensor 19 becomes the stoichiometric air-fuel ratio (at time t4 in FIG. 2). ). At the same time as the start of the lambda control, the determination of the return condition (VTC return condition) of the intake valve 6 by the variable valve timing mechanism 10 is started.
When the routine proceeds to step 12, that is, when lambda control is performed in step 9, the return condition of the intake valve 6 is determined. Since the determination of the return condition is performed based on the air-fuel ratio, for example, the air-fuel ratio is calculated based on the output signal of the air-fuel ratio sensor 19.

In step 13, it is determined whether a condition for starting to return the intake valve 6 is satisfied. Whether the return condition is satisfied is determined, for example, based on whether the air-fuel ratio calculated based on the output of the air-fuel ratio sensor 19 has reached the stoichiometric air-fuel ratio (time t5 in FIG. 2).
Alternatively, when the output value of the air-fuel ratio sensor 19 is within a predetermined range (for example, near the theoretical air-fuel ratio) for a predetermined period, it may be determined that the return condition is satisfied. Thereby, it can be determined that the air-fuel ratio has converged to the stoichiometric air-fuel ratio after the start of lambda control. If, after starting lambda control, the air-fuel ratio is unstable and greatly changes to the rich side or lean side with respect to the stoichiometric air-fuel ratio, the air-fuel ratio becomes lean greatly after reaching the stoichiometric air-fuel ratio. If the overlap is started to return at that time, the air-fuel ratio becomes leaner and the drivability deteriorates. However, if it is determined that the return condition is satisfied when the output value of the air-fuel ratio sensor 19 is in the vicinity of the stoichiometric air-fuel ratio, the air-fuel ratio is sufficiently converged to the stoichiometric air-fuel ratio and is stable. The air-fuel ratio can be prevented from becoming excessively lean, and stable drivability can be ensured.

In step 13, if the return condition is satisfied, the process proceeds to step 14. On the other hand, if the return condition is not satisfied, the process proceeds to step 5 described above.
In step 14, it is determined whether the phase VTC of the intake valve 6 by the variable valve timing mechanism 10 is larger than the phase VTC ₀ in the normal control (VTC> VTC ₀ ). If VTC> VTC ₀ , go to step 15. On the other hand, if VTC ≦ VTC ₀ , normal control is performed in step 6 described above.

  In step 15, the retarding speed (retarding amount) of the intake valve 6 by the variable valve timing mechanism 10 is calculated. As shown in FIG. 3 (A), the retarding speed is decreased as the water temperature TW0 at the start of the engine 1 is lower. This is because when the water temperature TW0 is low, the amount of fuel adhering to the wall flow increases, and the change in the wall flow rate when returning the overlap increases, so the change in the air-fuel ratio also increases and the operability is reduced. This is to make it worse. In order to prevent this, the change in the air-fuel ratio is suppressed by slowing down the overlap retarding speed to suppress the deterioration in drivability.

In step 16, the variable valve timing mechanism 10 retards the intake valve 6 at the retarded speed calculated in step 15. As a result, the speed at which the enlarged overlap is returned to the overlap at the time of normal control can be changed, and the period until the phase VTC of the intake valve 6 changes from VTC ₁ to VTC ₀ as shown in FIG. That is, the period from time t5 to time t6 can be changed. By returning the overlap, the amount of exhaust gas blown back to the intake port 11a can be reduced, and the engine rotation can be stabilized.

In step 17, the ignition timing and the throttle opening are corrected (set) as the enlarged overlap is restored.
The ignition timing ADV of the spark plug 5 is retarded based on the overlap due to the phase VTC of the intake valve 6 by the variable valve timing mechanism 10. As shown in FIGS. 2 (d) and 3 (b), the ignition timing ADV is changed from the second predetermined value ADV ₂ to the third predetermined value based on the overlap and the water temperature TW0 when the engine 1 is started. Slowly transition to ADV ₃ . As a result, after the start of lambda control, the ignition timing ADV is retarded by an amount that improves the combustion stability by returning the overlap, thereby reducing the HC due to the afterburning and the early activation of the exhaust purification catalyst 16 due to the temperature increase of the exhaust gas. It can be carried out.

The opening degree TVO of the electric throttle valve 12 is corrected based on the overlap. As a result, as shown in FIG. 2E, the opening degree TVO of the electric throttle valve 12 can be gradually shifted from the second predetermined value TVO ₂ to the third predetermined value TVO ₃ .
In the determination of whether the return condition is satisfied in step 13 described above, it has been described that it is determined that the return condition is satisfied at time t5 when the output value of the air-fuel ratio sensor 19 exceeds the theoretical air-fuel ratio. It is not limited to this. For example, in the determination of the establishment of the return condition in step 13 described above, the amount of change between the current air-fuel ratio A / F calculated based on the output signal of the air-fuel ratio sensor 19 and the previous air-fuel ratio A / F (−1). ΔA / F is calculated, and the return condition may be satisfied only when the amount of change ΔA / F is less than a predetermined value. The predetermined value in this case is a value for determining that the air-fuel ratio has sufficiently converged in a state where lambda control is being performed. As a result, the overlap can be returned after the air-fuel ratio convergence determination is made, and stable operability can be ensured when lambda control is performed.

  It should be noted that the return speed of the intake valve 6 in the above-described steps 15 and 16 is made slow when the output value of the air-fuel ratio sensor 19 is outside the predetermined range regardless of the water temperature TW0 at the start of the engine 1. Also good. For example, when lambda control is performed, if the air-fuel ratio is outside a predetermined range near the stoichiometric air-fuel ratio, the return speed of the intake valve 6 is decreased. As a result, the return speed of the intake valve 6 can be controlled to be slower in consideration of the air-fuel ratio, and the deterioration of drivability when the intake valve 6 is returned can be suppressed.

In addition, not only the air-fuel ratio control by the lambda control but also the control for correcting the change of the air-fuel ratio due to the wall flow in the intake passage 11 (intake port 11a) is performed during the return of the enlarged overlap. The target phase of the valve 6 may be switched instantaneously and the overlap may be changed instantaneously.
In this case, the target phase of the intake valve 6 is set based on, for example, the water temperature TW0 when the engine 1 is started. Thereby, even if the overlap is instantaneously changed, the air-fuel ratio is less disturbed. Therefore, the ignition timing is retarded as early as possible, and the early stage of the exhaust purification catalyst 16 due to the reduction of HC due to afterburning and the increase in exhaust gas temperature. Can be active.

The use of the exhaust air-fuel ratio sensor 19 as the air-fuel ratio detection means has been described so far, but the present invention is not limited to this. For example, an O ₂ sensor whose output value is inverted at the theoretical air / fuel ratio may be used as the air / fuel ratio detecting means.
In this case, in the flowchart of FIG. 4, it is determined in step 10 whether the O ₂ sensor is active, and in step 13, the output value of the O ₂ sensor is reversed from rich to lean with the theoretical air-fuel ratio as a boundary. Then, it is determined that the overlap return condition is satisfied. Alternatively, if the number of times the output value of the O ₂ sensor is inverted from rich to lean or lean to rich at the theoretical air-fuel ratio reaches a predetermined value in step 13, the overlap return condition is satisfied. Make a decision. After these return conditions are satisfied, the phase of the intake valve 6 is retarded and the overlap is started to return. Here the return of overlap, for example, when the output value of the O ₂ sensor is lean or rich over a predetermined period, that is, when the output value of the O ₂ sensor is not inverted over a predetermined time period, the water temperature at the start of the engine 1 Regardless of TW0, the return speed may be decreased.

In addition, although the fuel injection valve 14 was provided in the intake passage 11 (intake port 11a) and demonstrated performing intake port injection, it is not limited to this. For example, in order to inject fuel directly into the combustion chamber 4, a fuel injection valve 14 may be provided in a cylinder head or the like.
According to the present embodiment, the open / close timing of at least one of the air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio to the target air-fuel ratio at least under the condition after activation of the air-fuel ratio detection means and the intake valve 6 and the exhaust valve 7 is set. In an exhaust gas purification apparatus for an internal combustion engine that includes a variable valve timing mechanism 10 that can be changed and an exhaust gas purification catalyst 16 that can purify exhaust gas in an exhaust passage 15, air-fuel ratio feedback control is started when a temperature increase of the exhaust gas purification catalyst is requested. In the meantime, the overlap in which both the exhaust valve 7 and the intake valve 6 are opened is expanded (step 7). After the air-fuel ratio feedback control is started, the overlap is returned and the ignition timing is delayed. Corner (steps 15-17). For this reason, fuel vaporization is promoted by causing the exhaust gas to blow back into the intake port 11a by expanding the overlap when the temperature increase request of the catalyst 16 is requested, and the difference between the heavy and light air-fuel ratios of the fuel is reduced. It is possible to set the lean ratio of the fuel ratio. As a result, the air / fuel ratio sensor 19 for detecting the air / fuel ratio is inactive and the air / fuel ratio feedback control using the sensor 19 cannot be performed. This is effective in that HC can be reduced. After the feedback control is started, the effect of expanding the overlap is reduced by reducing the surplus fuel. Therefore, the ignition timing is retarded by the amount of returning the overlap and improving the combustion stability, and the HC is reduced by the afterburning. As well as reducing the temperature, it is possible to achieve early activation of the exhaust purification catalyst due to the temperature rise of the exhaust gas.

  Further, according to the present embodiment, the return of overlap is started when the output value of the air-fuel ratio detection means satisfies a predetermined condition after the start of the air-fuel ratio feedback control, and the air-fuel ratio detection means responds to the air-fuel ratio. When the output value of the air-fuel ratio sensor 19 changes proportionally, the predetermined condition is that the output value of the air-fuel ratio sensor 19 reaches a predetermined value, or the output value of the air-fuel ratio sensor 19 is predetermined for a predetermined period. This is when it is within the range (for example, near the theoretical air-fuel ratio) (steps 13 to 16). For this reason, it is possible to accurately determine when the overlap is switched based on the output value of the air-fuel ratio sensor 19, and switch from HC reduction due to the overlap expansion to HC reduction due to overlap return and ignition timing during lambda control. . Alternatively, the HC reduction method can be switched after it is determined that the output value of the air-fuel ratio sensor 19 is within a predetermined range for a predetermined period.

  Further, according to the present embodiment, the return of the overlap changes the return speed based on the water temperature TW0 at the start of the internal combustion engine 1, while when the output value of the air-fuel ratio sensor 19 is outside the predetermined range, Regardless of TW0, the return speed is decreased (steps 15 to 16). This is because as the water temperature TW0 is lower, the fuel wall flow adhesion amount at the intake port 11a increases, the wall flow rate change when returning the overlap, and the air-fuel ratio disturbance also increase. Therefore, by changing the overlap return speed according to the water temperature TW0 (for example, the overlap return speed is decreased as the water temperature decreases), the disturbance of the air-fuel ratio can be suppressed.

Further, according to the present embodiment, the return of the overlap is started when the output value of the air-fuel ratio detecting means satisfies a predetermined condition, and the output value is inverted at the stoichiometric air-fuel ratio as a boundary. In the case of the O ₂ sensor, the predetermined condition is when the output value of the O ₂ sensor is inverted or when the number of times the output value of the O ₂ sensor is inverted reaches a predetermined value (steps 13 to 16). For this reason, it is possible to accurately determine when the overlap is switched based on the output of the O ₂ sensor, and to switch from HC reduction due to overlap expansion to HC reduction due to overlap return and ignition timing during lambda control.

Further, according to the present embodiment, the return of the overlap changes the return speed based on the water temperature TW0 at the start of the internal combustion engine 1, while when the output value of the O ₂ sensor does not invert for a predetermined period or more, the return to the water temperature TW0. Regardless, the return speed is decreased (steps 15 to 16). As a result, the lower the water temperature TW0, the greater the disturbance of the air-fuel ratio due to the overlap. Therefore, by changing the return speed of the overlap according to the water temperature TW0, the disturbance of the air-fuel ratio is suppressed and the influence on the drivability is affected. Can be suppressed. When the air-fuel ratio is lean for a predetermined period or longer, the output value of the O ₂ sensor does not reverse for a predetermined period or longer, so that the influence on the drivability can be suppressed by slowing the return speed of the overlap. it can.

Further, according to the present embodiment, the throttle valve opening TVO during the return of the overlap is corrected based on the overlap (step 17). For this reason, it is possible to correct the throttle valve opening TVO based on the overlap, and to suppress the influence (torque step) on the torque change due to the overlap change.
Further, according to the present embodiment, the ignition timing ADV during the return of the overlap is corrected based on the overlap (step 17). For this reason, it is possible to correct the ignition timing ADV based on the overlap, and to perform early activation of the exhaust purification catalyst 16 due to HC reduction due to afterburning and exhaust gas temperature rise.

The figure which shows the structure of the exhaust gas purification device of an internal combustion engine Time chart of exhaust purification of internal combustion engine Diagram showing correction parameters Flow chart of control of internal combustion engine

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 5 Spark plug 6 Intake valve 7 Exhaust valve 8a Intake cam 9a Exhaust cam 10 Variable valve timing mechanism 11 Intake passage 11a Intake port 12 Electric throttle valve 14 Fuel injection valve 15 Exhaust passage 16 Exhaust purification catalyst 19 Air-fuel ratio detection means 30 Engine control unit (ECU)

Claims (10)

An air-fuel ratio feedback control means that feedback-controls the air-fuel ratio to a target air-fuel ratio at least after the activation of the air-fuel ratio detection means; a variable valve timing mechanism that can change the opening / closing timing of at least one of the intake valve and the exhaust valve; In an exhaust gas purification apparatus for an internal combustion engine comprising an exhaust gas purification catalyst capable of purifying exhaust gas in an exhaust passage,
When the temperature of the exhaust purification catalyst is raised, until the air-fuel ratio feedback control is started, the overlap of both the exhaust valve and the intake valve is opened, and after the air-fuel ratio feedback control is started, An exhaust purification device for an internal combustion engine, wherein the overlap is returned and the ignition timing is retarded.   2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the return of the overlap is started when an output value of the air-fuel ratio detection means satisfies a predetermined condition after the start of air-fuel ratio feedback control.   When the air-fuel ratio detection means is an air-fuel ratio sensor whose output value changes proportionally according to the air-fuel ratio, the predetermined condition is that the output value of the air-fuel ratio sensor reaches a predetermined value. The exhaust emission control device for an internal combustion engine according to claim 2, wherein the exhaust gas purification device is an internal combustion engine.   When the air-fuel ratio detection means is an air-fuel ratio sensor whose output value changes proportionally according to the air-fuel ratio, the predetermined condition is that the output value of the air-fuel ratio sensor is within a predetermined range for a predetermined period. The exhaust emission control device for an internal combustion engine according to claim 2, wherein the exhaust gas purification device is provided.   The return of the overlap changes the return speed based on the water temperature at the start of the internal combustion engine. On the other hand, when the output value of the air-fuel ratio sensor is outside a predetermined range, the return speed is reduced regardless of the water temperature. The exhaust emission control device for an internal combustion engine according to claim 3 or 4, characterized in that: Claim wherein the air-fuel ratio detecting means, when an O ₂ sensor output value is inverted as a boundary a theoretical air-fuel ratio, said predetermined condition, characterized in that the output value of the O ₂ sensor is when inverted 3. An exhaust emission control device for an internal combustion engine according to 2. When the air-fuel ratio detection means is an O ₂ sensor whose output value is inverted at the boundary of the theoretical air-fuel ratio, the predetermined condition is when the number of times the output value of the O ₂ sensor is inverted reaches a predetermined value. The exhaust gas purification apparatus for an internal combustion engine according to claim 2. The return of the overlap changes the return speed based on the water temperature at the start of the internal combustion engine. On the other hand, when the output value of the O ₂ sensor does not reverse for a predetermined period or longer, the return speed is reduced regardless of the water temperature. The exhaust emission control device for an internal combustion engine according to claim 6 or 7,   The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 8, wherein a throttle valve opening during the return of the overlap is corrected based on the overlap.   The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 9, wherein an ignition timing during the return of the overlap is corrected based on the overlap.

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