JP4366607B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine capable of switching a combustion mode and changing a valve overlap amount by a variable valve timing means.

In recent years, in-cylinder injection can be performed at a leaner (lean) air-fuel ratio than the stoichiometric air-fuel ratio (stoichiometric), and can switch between the lean combustion mode and the normal stoichiometric combustion mode according to the operating state A lean burn internal combustion engine (lean burn engine) such as a type internal combustion engine is known.
An internal combustion engine having a variable valve timing mechanism that can change the valve overlap amount by changing the intake valve opening timing or the exhaust valve closing timing is also generally known. Normally, the valve overlap amount is controlled according to a map based on the rotational speed and volumetric efficiency of the internal combustion engine.

Here, when the lean burn engine is provided with a variable valve timing mechanism, when the combustion mode is switched, the volumetric efficiency changes even if the torque is maintained, so that the valve overlap amount is also changed.
In general, the valve overlap amount is controlled to be large in the stoichiometric combustion mode with low volume efficiency, and the valve overlap amount is controlled to be small in the lean combustion mode with high volume efficiency.

  However, for example, in the control at the time of switching from the stoichiometric combustion mode to the lean combustion mode, first, the air-fuel ratio is gradually turned to the lean side by increasing the intake air amount, but the air-fuel ratio becomes lean to some extent at the fuel injection timing. The injection is maintained in the intake stroke until the ignition timing is relatively advanced. At this time, the volumetric efficiency increases as the intake air amount increases, and the valve overlap amount is gradually reduced. In particular, fuel injection in the intake stroke, that is, lean combustion operation with uniform mixing, is valve overlap. Combustion is likely to become unstable with respect to exhaust gas recirculation (hereinafter referred to as internal EGR) due to combustion, and if the valve overlap amount is changed according to a map based on volumetric efficiency, internal EGR cannot be reduced in time, and combustion due to excessive EGR There is a problem that the torque is lowered or the misfire is caused and the torque is reduced.

  On the other hand, when switching from the lean combustion mode to the stoichiometric combustion mode, in the normal lean combustion mode, the amount of exhaust gas recirculation (hereinafter referred to as external EGR) from the exhaust passage to the intake passage is set to be relatively large. At the time of switching the mode, the external EGR amount is reduced by the EGR valve that controls the external EGR amount. However, since this causes a delay, a state in which the external EGR amount is large is maintained. In addition to this, when the valve overlap amount is increased due to a decrease in volumetric efficiency, the internal EGR amount also increases. Since the internal EGR has higher responsiveness than the external EGR, the EGR is excessive in the combustion chamber, and there is also a problem that the combustion is delayed or misfire occurs, resulting in a decrease in torque.

Therefore, when switching the combustion mode, if the target value of the valve timing corresponding to the combustion mode of the switching destination becomes the combustion stable side target value, the target value of the valve timing is immediately switched when the required combustion mode is switched, On the other hand, when the target value of the valve timing corresponding to the combustion mode before switching is the combustion stable target value, a technique for switching the valve timing to the target value when the actual combustion mode is switched is disclosed (patent) Reference 1).
JP 2004-232476 A

  However, the technique disclosed in Patent Document 1 compares the valve overlap amount corresponding to the homogeneous (stoichiometric) combustion mode at the time of switching the combustion mode with the valve overlap amount corresponding to the stratified (lean) combustion mode, Only the valve overlap amount on the combustion stable side is selected, and it is not possible to reliably prevent combustion delay or misfire when switching the combustion mode.

  The present invention has been made to solve such a problem, and an object of the present invention is to control an internal combustion engine capable of suppressing a delay in combustion and a misfire at the time of switching a combustion mode and preventing a torque drop. Is to provide.

  In order to achieve the above-described object, in the control apparatus for an internal combustion engine according to claim 1, a first combustion mode in which combustion is performed at an air-fuel ratio leaner than a stoichiometric air-fuel ratio, and a richer side than the first combustion mode. A control device for an internal combustion engine capable of switching between a second combustion mode for performing combustion at an air-fuel ratio, and a combustion mode switching control means for controlling switching between the first combustion mode and the second combustion mode Variable valve timing means capable of changing the timing of at least one of the opening timing of the intake valve and the closing timing of the exhaust valve of the internal combustion engine, and the valve overlap for controlling the valve overlap amount by the variable valve timing means An amount control means, wherein the valve overlap amount control means sets the first valve overlap amount during operation in the first combustion mode, and the second combustion mode. The second valve overlap amount is larger than the first valve overlap amount during the operation, and the first valve overlap amount is larger than the first valve overlap amount when switching between the first combustion mode and the second combustion mode. Control is performed so that the third valve overlap amount is small.

  That is, the internal combustion engine capable of switching between the first combustion mode and the second combustion mode is provided with variable valve timing means, and the first valve corresponding to each of the first combustion mode and the second combustion mode. The overlap amount and the second valve overlap amount are set, and the first valve overlap amount and the second valve overlap amount corresponding to the first combustion mode and the second combustion mode are switched. A small third valve overlap amount is set.

The control apparatus for an internal combustion engine according to claim 2 is characterized in that the variable valve timing means is capable of changing both the opening timing of the intake valve and the closing timing of the exhaust valve of the internal combustion engine.
That is, the valve timing of both the intake valve and the exhaust valve can be changed.

According to the control apparatus for an internal combustion engine of the first aspect of the present invention using the above means, at the time of switching between the first combustion mode and the second combustion mode, the first combustion mode and the second combustion mode By setting the third valve overlap amount to be smaller than the valve overlap amount, the amount of internal EGR at the time of switching the combustion mode can be greatly reduced.
As a result, combustion delay and misfire during combustion mode switching can be suppressed and torque reduction can be prevented.

  According to the control apparatus for an internal combustion engine of claim 2, since both the opening timing of the intake valve and the closing timing of the exhaust valve can be changed, a change amount of the valve overlap amount can be greatly obtained. The internal EGR at the time of switching the combustion mode can be greatly reduced, combustion delay and misfire can be sufficiently suppressed, and torque reduction can be prevented more reliably.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of a control device for an internal combustion engine according to the present invention.
The engine 1 (internal combustion engine) is an in-cylinder injection type four-cycle in-line four-cylinder engine, and FIG. 1 shows a longitudinal section of one of the cylinders. In addition, illustration and description are abbreviate | omitted as what has the same structure also about another cylinder.

As shown in FIG. 1, the engine 1 is configured by mounting a cylinder head 4 on a cylinder block 2.
A piston 12 is provided in the cylinder 10 formed in the cylinder block 2 so as to be slidable up and down. The piston 12 has a shape having a recess on the upper surface, and is connected to a crankshaft 16 via a connecting rod 14.

In correspondence with the cylinder 10, a so-called pent roof type slope is formed on the lower surface of the cylinder head 4, and a combustion chamber 20 is formed surrounded by the lower surface of the cylinder head, the cylinder 10, and the upper surface of the piston 12.
The cylinder head 4 is provided with a fuel injection valve 22 that can inject fuel directly into the combustion chamber 20 and an ignition plug 24 that ignites the air-fuel mixture in the combustion chamber 20.

An intake port 30 is formed from one inclined surface on the lower surface of the cylinder head 4 toward the upper surface of the cylinder head 4, and from the other inclined surface on the lower surface of the cylinder head 4 to the cylinder head 4 from the other inclined surface of the cylinder head 4. An exhaust port 32 is formed toward the side surface.
An intake manifold 34 is connected to the upper surface of the cylinder head 4 so as to communicate with the intake port 30, and an exhaust manifold 36 is connected to the side surface of the cylinder head 4 so as to communicate with the exhaust port 32.

A surge tank 38 is connected to the intake manifold 34 on the intake upstream side, and an electronic throttle valve 40 for adjusting the intake air amount is provided on the intake upstream side of the surge tank 38.
On the other hand, an exhaust pipe 42 is connected to the exhaust manifold 36 on the exhaust downstream side.
An EGR passage 44 is connected to the intake manifold 34 and the exhaust manifold 36 so as to communicate the intake manifold 34 and the exhaust manifold 36. An EGR valve 46 is provided in the EGR passage 44, and the EGR valve 46 has a function of adjusting the amount of external EGR gas recirculated from the exhaust manifold 42 through the EGR passage 44 and into the intake manifold 32. Have.

In addition, the cylinder head 4 is provided with an intake valve 50 that communicates and shuts off the combustion chamber 20 and the intake port 30 and an exhaust valve 52 that communicates and shuts off the combustion chamber 20 and the exhaust port 32.
Camshafts 58 and 60 having cams 54 and 56 for driving the intake valve 50 and the exhaust valve 52 are provided on the cylinder head 4.

One end of each of the camshafts 58 and 60 is provided with a variable valve timing mechanism (hereinafter also referred to as VVT) 62 and 64 (variable valve timing means).
The VVTs 62 and 64 include, for example, a hydraulic actuator built in a cam sprocket that drives the camshafts 58 and 60, and the cam rotation phase angle can be freely advanced by supplying and discharging the hydraulic pressure to the hydraulic actuator. And can be retarded. The hydraulic pressure can be supplied and discharged by, for example, oil control valves (OCV) 66 and 68. The OCVs 66 and 68 are provided in the VVTs 62 and 64, and the hydraulic pressure is supplied to and discharged from the respective hydraulic actuators. Can be done. The OCVs 66 and 68 are controlled by an electronic control unit (ECU) 70 (valve overlap amount control means) mounted on the vehicle.

  The ECU 70 has a function of controlling the valve overlap amount by controlling the VVTs 62 and 64 via the OCVs 66 and 68 and changing the valve opening timing of the intake valve 50 and the valve closing timing of the exhaust valve 52. For example, the valve opening timing of the intake valve 50 is advanced, the valve closing amount of the exhaust valve 52 is retarded, the valve overlap amount is increased, and the valve opening timing of the intake valve 50 is retarded. The valve overlap amount is reduced by advancing the valve closing timing. Normally, the amount of internal EGR tends to increase as the valve overlap amount increases.

Further, the ECU 70 is also electrically connected to various devices such as the fuel injection valve 22, the spark plug 24, the electronic throttle valve 40, and the EGR valve 46, and can control these various devices.
For example, the ECU 70 sets the air-fuel ratio (A / F) of the engine 1 to a predetermined air-fuel ratio (for example, A / F35) that is leaner than the stoichiometric air-fuel ratio (stoichiometric) (A / F14.7). Lean combustion mode (first combustion mode) in which fuel is injected and stratified combustion, and stoichiometric combustion mode (second combustion mode) in which the air-fuel ratio is in the vicinity of the theoretical air-fuel ratio and fuel is injected during the intake stroke to perform homogeneous mixed combustion ) Has a function of performing switching control between the two combustion modes (combustion mode switching control means).

  Further, the ECU 70 stores a control map of the valve overlap amount according to the engine speed and the volume efficiency, and the valve overlap amount is relatively small corresponding to the lean combustion mode based on the map. VOLl for lean combustion mode (for example, 30 to 50 ° in terms of crank angle) and stoichiometric combustion mode VOLs (for example, 55 ° in terms of crank angle) corresponding to the stoichiometric combustion mode and a relatively large valve overlap amount are set. ing. Further, the ECU 70 is made to respond at the time of switching between the lean combustion mode and the stoichiometric combustion mode regardless of the map, and the combustion mode switching VOLc, which is an extremely small valve overlap amount than the lean combustion mode VOLl. (0 to 10 ° in terms of crank angle) is set.

Hereinafter, the combustion mode switching control of the control apparatus for an internal combustion engine according to the present invention will be described.
2 and 3 show a flowchart of a combustion mode switching control routine in the control apparatus for an internal combustion engine of the present invention. Referring to FIG. 4, the combustion mode switching control is performed in the control apparatus for an internal combustion engine of the present invention. The time chart which showed each state at the time in time series is shown. Hereinafter, description will be given along the flowcharts of FIGS.

First, in step 1, it is determined whether or not the engine 1 is operating in the stoichiometric combustion mode. If the determination result is true (Yes), the process proceeds to step S2.
In step S2, it is determined whether or not a lean combustion mode switching condition is satisfied. Specifically, the lean combustion mode switching condition is set based on the vehicle speed, engine load, throttle opening, cooling water temperature, etc., and is set so that the condition is satisfied, for example, at the time of steady operation at low to medium loads. Has been. If the determination result is false (No), the routine is returned and the above procedure is repeated. On the other hand, when the determination result is true (Yes), that is, when the lean combustion mode switching condition is satisfied during the operation in the stoichiometric combustion mode, the process proceeds to step S3.

  In step S3, the valve opening timing of the intake valve 50 and the exhaust gas are exhausted by the VVTs 62 and 64 via the OCVs 66 and 68 so that the valve overlap amount which is the stoichiometric combustion mode VOLs at this time becomes the very small combustion mode switching VOLc. The valve closing timing of the valve 52 is controlled to reduce the valve overlap amount. At this time, since the valve opening timing of the intake valve 50 and the valve closing timing of the exhaust valve 52 are controlled by simultaneously controlling the VVTs 62 and 64, the response is made as compared with the case where only one of the VVTs 62 and 64 is controlled. Excellent in properties.

  In the subsequent step S4, the A / F correction coefficient is tailed to the lean side by gradually opening the throttle opening. At this time, the volumetric efficiency Ev is increased by opening the throttle opening, but the valve overlap amount is reduced in the step S3 regardless of the map based on the engine speed and the volumetric efficiency. The VOLc for mode switching is maintained.

  In step S5, it is determined whether or not the A / F correction coefficient has reached a predetermined air-fuel ratio region. The predetermined air-fuel ratio region is an air-fuel ratio region in which the fuel injection can be switched from the intake stroke injection to the compression stroke injection and from the compression stroke injection to the intake stroke injection. If the determination result is false (No), the process returns to step S4 to maintain tailing of the A / F correction coefficient. If the determination result is true (Yes), the process proceeds to step S6. The control so far corresponds to the period from t1 to t2 shown in FIG.

In step S6, the fuel injection timing that was injected in the intake stroke is switched to the injection in the compression stroke.
Subsequently, in step S7, the ignition timing on the advance side corresponding to the stoichiometric combustion mode is switched to the ignition timing on the retard side corresponding to the lean combustion mode.
In step S8, the A / F correction coefficient is further tailed to the lean side.

  Next, in step S9, it is determined whether or not the A / F correction coefficient has reached the target value (A / F35) for the lean combustion mode. If the determination result is false (No), the process returns to step S8 to maintain tailing of the A / F correction coefficient. If the determination result is true (Yes), the process proceeds to step S10. The control so far corresponds to the period from t2 to t3 shown in FIG.

In step S10, the valve overlap amount, which is the combustion mode switching VOLc at this time, is controlled by the VVTs 62 and 64 via the OCVs 66 and 68, and is increased to the lean combustion mode VOL1 to exit the routine. Simultaneously with this control, the EGR valve 46 is opened to increase the amount of external EGR.
On the other hand, if the determination result in step S1 is false (No), that is, if the vehicle is operating in the lean combustion mode, the process proceeds to step S20.

  In step S20, it is determined whether or not a stoichiometric combustion mode switching condition is satisfied. The stoichiometric combustion mode switching condition is set such that the condition is satisfied, for example, at the time of acceleration of a high load. If the determination result is false (No), the routine is returned and the above procedure is repeated, and if the determination result is true (Yes), the process proceeds to step S21.

  In step S21, the valve opening timing of the intake valve 50 and the exhaust gas are exhausted by the VVTs 62 and 64 via the OCVs 66 and 68 so that the valve overlap amount which is the VOLl for the lean combustion mode at this time becomes the VOLc for switching the combustion mode at a very small amount. The valve closing timing of the valve 52 is controlled to reduce the valve overlap amount. At this time, as in step S3, the VVT 62 and 64 are simultaneously controlled to control the opening timing of the intake valve 50 and the closing timing of the exhaust valve 52, so only one of the VVT 62 and 64 is controlled. Responsiveness is superior compared to the case.

  In the subsequent step S22, the A / F correction coefficient is tailed to the stoichiometric side by gradually closing the throttle opening. At this time, the volumetric efficiency Ev is reduced by closing the throttle opening, but the valve overlap amount is reduced in the step S21 regardless of the map based on the engine speed and the volumetric efficiency. The VOLc for mode switching is maintained. The combustion mode switching VOLc is maintained regardless of the map based on the engine speed and volumetric efficiency.

In step S23, it is determined whether or not the A / F correction coefficient has reached a predetermined air-fuel ratio region. If the determination result is false (No), the process returns to step S22 to maintain the tailing of the A / F correction coefficient. On the other hand, if the determination result is true (Yes), the process proceeds to step S24. The control so far corresponds to the period from t4 to t5 shown in FIG.
In step S24, the fuel injection timing that was injected in the compression stroke is switched to the injection in the intake stroke.

Subsequently, in step S25, the ignition timing on the retard side corresponding to the lean combustion mode is switched to the ignition timing on the advance side corresponding to the stoichiometric combustion mode.
In step S26, the A / F correction coefficient is further tailed to the stoichiometric side.
Next, in step S27, it is determined whether or not the A / F correction coefficient has reached the target value (A / F 14.7) for the stoichiometric combustion mode. If the determination result is false (No), the process returns to step S26 to maintain tailing of the A / F correction coefficient. If the determination result is true (Yes), the process proceeds to step S28. The control so far corresponds to the period from t5 to t6 shown in FIG.

In step S28, the valve overlap amount, which is the combustion mode switching VOLc at this time, is controlled by the VVTs 62 and 64 via the OCVs 66 and 68 to increase to the stoichiometric combustion mode VOLs, and the routine is exited. Simultaneously with the control, the EGR valve 46 is closed to reduce the amount of external EGR.
As described above, in the control apparatus for an internal combustion engine according to the present invention, in each of the lean combustion mode and the stoichiometric combustion mode, the lean combustion mode VOLl and the stoichiometric combustion mode VOLs are set based on the map of the engine speed and the volumetric efficiency. At the same time, regardless of the map, the combustion mode switching VOLc, which is a very small valve overlap amount, is set corresponding to the switching between the lean combustion mode and the stoichiometric combustion mode.

By switching to the combustion mode switching VOLc when the combustion mode is switched, the internal EGR can be reduced earlier than before when switching from the stoichiometric combustion mode to the lean combustion mode. At the time of switching to the combustion mode, the delay of the external EGR can be compensated by reducing the internal EGR having excellent responsiveness.
As a result, the amount of EGR at the time of switching the combustion mode can be greatly reduced, combustion delay and misfire can be suppressed, and torque reduction can be prevented.

Although the description of the embodiment of the control device for an internal combustion engine according to the present invention has been completed, the embodiment is not limited to the above embodiment.
For example, in the above embodiment, a so-called in-cylinder injection type engine that can inject fuel directly into the combustion chamber may be used, but a so-called intake pipe injection type engine may be used as long as the operation in the lean combustion mode is possible.

In the above embodiment, the air-fuel ratio in the second combustion mode is stoichiometric. However, the air-fuel ratio may be richer than that in the first combustion mode.
In the above embodiment, the combustion mode switching VOLc is set to a very small valve overlap amount, but the valve overlap amount may be zero.

It is a schematic block diagram of the control apparatus of the internal combustion engine which concerns on this invention. It is a flowchart of the control routine at the time of combustion mode switching in the control apparatus of the internal combustion engine of this invention. It is the remainder of the flowchart which shows the control routine following FIG. 3 is a time chart showing each state in time series when combustion mode switching control is performed in the control device for an internal combustion engine of the present invention.

Explanation of symbols

1 engine (internal combustion engine)
22 Fuel Injection Valve 24 Spark Plug 50 Intake Valve 52 Exhaust Valve 54, 56 Cam 58, 60 Cam Shaft 62, 64 Variable Valve Timing Mechanism (VVT) (Variable Valve Timing Means)
66, 68 Oil control valve (OCV)
70 ECU (combustion mode switching control means, valve overlap amount control means)

Claims (2)

Control of an internal combustion engine capable of switching between a first combustion mode in which combustion is performed at an air-fuel ratio leaner than the stoichiometric air-fuel ratio and a second combustion mode in which combustion is performed at an air-fuel ratio richer than the first combustion mode A device,
Combustion mode switching control means for controlling switching between the first combustion mode and the second combustion mode;
Variable valve timing means capable of changing the timing of at least one of the opening timing of the intake valve and the closing timing of the exhaust valve of the internal combustion engine;
A valve overlap amount control means for controlling the valve overlap amount by the variable valve timing means,
The valve overlap amount control means sets the first valve overlap amount during operation in the first combustion mode, and is greater than the first valve overlap amount during operation in the second combustion mode. The valve overlap amount is set to 2 and the control is performed so that the third valve overlap amount is smaller than the first valve overlap amount when switching between the first combustion mode and the second combustion mode. A control device for an internal combustion engine characterized by the above.   2. The control apparatus for an internal combustion engine according to claim 1, wherein the variable valve timing means is capable of changing both timings of an intake valve opening timing and an exhaust valve closing timing of the internal combustion engine.

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