JP2013068099A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine which can prevent a combustion chamber from being excessively cooled down in association with a deceleration fuel cut-off.SOLUTION: In the cylinder direct injection type internal combustion engine which has a variable valve timing mechanism for continuously making a rotational phase of an intake camshaft variable with respect to a crankshaft and in which lag closing miller cycle operation is performed, while a deceleration fuel is cut off, a period when an intake valve is closed is advanced from a period when the intake valve is closed during the lag closing miller cycle operation to approach a bottom dead center, thereby increasing an effective compression ratio, raising a compression temperature and preventing the combustion chamber (crown of a piston) from being excessively cooled down by new air during fuel cut-off. In this case, because a period when the intake valve is opened is also advanced in association with advance of the period when the intake valve is closed, which increases valve overlap and decreases charging efficiency, the rotational phase of the intake camshaft is advanced until the period when the intake valve is opened becomes the same period as the period when an exhaust valve is closed, so that the period when the intake valve is closed approaches the bottom dead center.

Description

  The present invention relates to a control device applied to an internal combustion engine provided with a variable valve mechanism that varies the closing timing of an intake valve.

  In Patent Document 1, during deceleration fuel cut, the closing timing of the intake valve is set to a valve timing of about 90 deg after bottom dead center, and the closing timing of the intake valve is advanced during acceleration after fuel cut to cause bottom dead A control device is disclosed that changes near the point.

JP 2009-215956 A

By the way, if the intake valve is closed late after bottom dead center, the effective compression ratio becomes low and the compression temperature becomes low. Further, in the deceleration fuel cut state, the combustion chamber (piston crown surface, etc.) is cooled by fresh air. For this reason, if the intake valve is closed late in the deceleration fuel cut state, the combustion chamber may be excessively cooled.
If the combustion chamber is excessively cooled, the evaporation (atomization) of the fuel injected into the combustion chamber (piston crown surface) is hindered when the fuel injection is restarted from the fuel cut state. It is not formed, combustion becomes unstable, and exhaust properties deteriorate and drivability deteriorates due to torque fluctuations.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a control device for an internal combustion engine that can suppress the combustion chamber from being excessively cooled due to the fuel cut.

  Therefore, in the present invention, when the fuel is cut in the deceleration operation, the variable valve mechanism that makes the intake valve closing timing variable is controlled so that the closing timing of the intake valve is closer to the bottom dead center than before the fuel cut starts. did.

  According to the above invention, since the compression temperature during the fuel cut rises, the combustion chamber (piston crown surface, etc.) can be prevented from being excessively cooled, the combustion immediately after the fuel cut is stabilized, and the exhaust properties are improved. Driving performance can be improved.

1 is a system diagram of an engine in an embodiment of the present invention. It is a flowchart which shows control of the closing timing IVC of the intake valve at the time of deceleration fuel cut. It is a graph which shows an example of the correlation with the closing timing IVC of an intake valve, and compression temperature. It is a graph which shows the characteristic of the advance angle target of closing timing IVC according to engine temperature. 6 is a time chart showing changes in accelerator opening, engine speed, fuel cut, closing timing IVC, and brake switch when shifting from deceleration to acceleration. 6 is a time chart showing changes in accelerator opening, engine speed, fuel cut, and closing timing IVC when shifting from deceleration to idle as it is. 1 is a system diagram of an engine in an embodiment of the present invention. It is a flowchart which shows control of the closing timing IVC of the intake valve at the time of deceleration fuel cut. It is a graph which shows an example of the correlation with the closing timing IVC of an intake valve, and compression temperature.

Embodiments of the present invention will be described below.
FIG. 1 is a system diagram of a vehicle engine including a control device according to the present invention.
An engine 1 shown in FIG. 1 is an in-cylinder direct injection internal combustion engine that performs a delayed closed mirror cycle operation.
The engine 1 includes a fuel injection valve 3 that directly injects fuel into a cylinder.

The fuel injected into the cylinder by the fuel injection valve 3 is mixed with air sucked into the combustion chamber 5 through the intake passage 2 and the intake valve 4 and ignited and burned by spark ignition by the spark plug 6. The combustion gas in the combustion chamber 5 is discharged to the exhaust passage 8 through the exhaust valve 7.
An electronic control throttle 10 that is opened and closed by a throttle motor 9 is disposed in the intake passage 2, and the intake air amount of the engine 1 is adjusted by the opening degree of the electronic control throttle 10.

The engine 1 also includes a variable valve timing mechanism (VTC) 20 that makes the valve timing (opening / closing timing) of the intake valve 4 variable.
The variable valve timing mechanism 20 is a mechanism that continuously varies the central phase of the operating angle (open period) of the intake valve 4 by continuously varying the rotational phase of the intake camshaft 22 with respect to the crankshaft 21. is there.

An ECM (engine control module) 31 having a computer as a control device for controlling fuel injection by the fuel injection valve 3, ignition by the spark plug 6, opening of the electronic control throttle 10, valve timing by the variable valve timing mechanism 20, and the like. Is provided.
The ECM 31 includes an accelerator opening sensor 34 that detects an accelerator pedal depression amount (accelerator opening) ACC (not shown), an air flow sensor 35 that detects an intake air flow rate QA of the engine 1, and a rotation that detects a rotational speed NE of the engine 1. Detection signals from a sensor 36, a water temperature sensor 37 for detecting the coolant temperature TW (engine temperature) of the engine 1, an air-fuel ratio sensor 38 for detecting the air-fuel ratio in the engine 1 according to the oxygen concentration in the engine exhaust, and the like are input. .

Then, the ECM 31 is based on the detection signals of the various sensors described above, the fuel injection amount and injection timing by the fuel injection valve 3, the ignition timing by the ignition plug 6, the opening of the electronic control throttle 10, and the valve by the variable valve timing mechanism 20. Control timing etc.
In the fuel injection control by the fuel injection valve 3, the ECM 31 executes a deceleration fuel cut that stops the fuel injection by the fuel injection valve 3 during the deceleration operation of the engine 1.

In the deceleration fuel cut, the fuel injection by the fuel injection valve 3 is stopped when the condition (cut condition) that allows the fuel injection to be stopped in the deceleration operation state of the engine 1 is satisfied, and after the fuel injection is stopped, the fuel injection is stopped. When the condition for restarting (recovery condition) is satisfied, the fuel injection by the fuel injection valve 3 is restarted.
For example, when the deceleration operation state in which the throttle 10 is fully closed or a low opening near the full close and the engine speed is higher than the cut speed is determined, the fuel injection by the fuel injection valve 3 is stopped. Thereafter, when the engine rotational speed decreases to the recovery rotational speed (recovery rotational speed <cut rotational speed) and / or when the throttle 10 is opened, the fuel injection by the fuel injection valve 3 is resumed.

Note that the cutting conditions and the recovery conditions are not limited to the above, and a deceleration fuel cut that performs fuel cutting according to the known cutting conditions and recovery conditions can be appropriately employed. Further, the deceleration fuel cut can be executed with a delay from the establishment of the cut condition.
Further, the ECM 31 sets the closing timing IVC of the intake valve 4 to 90 deg after the bottom dead center, for example, and sets the opening timing IVO of the intake valve 4 after the top dead center, so that the engine 1 is so-called delayed closing mirror cycle. To drive.

By the way, when the deceleration fuel cut is performed, the combustion chamber 5 (piston crown surface 18 or the like) may be cooled with fresh air and the temperature may be excessively decreased, and the fuel injection is performed in a state where the temperature of the combustion chamber 5 is excessively decreased. Is restarted, the fuel atomization (vaporization) injected into the combustion chamber 5 (piston crown surface 18) is hindered. As a result, the combustion stability of the air-fuel mixture decreases, and the exhaust properties deteriorate. There is a possibility that drivability deteriorates due to torque fluctuation.
Therefore, the ECM 31 performs a control to bring the closing timing IVC closer to the bottom dead center BDC during the deceleration fuel cut than the closing timing IVC (before the deceleration fuel cut) in the slow closing mirror cycle operation, thereby reducing the deceleration fuel cut. The effective compression ratio (compression temperature) in the inside is increased as compared with that before the fuel cut, thereby performing control for suppressing the temperature drop of the combustion chamber 5 during the deceleration fuel cut (hereinafter referred to as IVC control during fuel cut).

Below, the detail of IVC control at the time of fuel cut by ECM31 is demonstrated according to the flowchart of FIG.
The routine shown in the flowchart of FIG. 2 is interrupted and executed by the ECM 31 every set time. First, in step S101, it is determined whether or not the engine 1 is in a cold state.
Whether or not it is in the cold state is determined based on, for example, whether or not the cooling water temperature TW detected by the water temperature sensor 37 is lower than the set temperature TWSL.

The cooler determined in step S101 means that the combustion chamber 5 (piston crown surface 18) is excessively cooled when the deceleration fuel cut is performed with the closing timing IVC (IVC = ABDC90deg) in the mirror cycle operation being performed. Whether or not the low temperature range of the engine 1 where the vaporization of the fuel spray from the fuel injection valve 3 is hindered and the combustion becomes unstable when the injection is resumed, and the set temperature TWSL is the low temperature range. Set a temperature that can be distinguished.
In other words, if it is determined in step S101 that the engine 1 is not in the cold state, the combustion chamber 5 (piston crown surface 18) is excessive even if the deceleration fuel cut is performed with the closing timing IVC in the mirror cycle operation. It is determined that it is a high temperature range of the engine 1 that is not cooled and that can sufficiently atomize the fuel and perform stable combustion.

Whether the engine 1 is in the cold state or not can be determined based on the cooling water temperature TW, and can be determined based on the temperature of the combustion chamber 5 (piston crown surface 18) such as the lubricating oil temperature, the cylinder head temperature, and the cylinder block temperature. Can be based on correlated temperatures.
Whether or not the combustion chamber 5 (piston crown surface 18) is excessively cooled during the deceleration fuel cut is affected by the fresh air temperature. Even at the same engine temperature, the lower the fresh air temperature, the lower the deceleration fuel cut. Further, the combustion chamber 5 (piston crown surface 18) is easily cooled excessively. Therefore, for example, the lower the outside air temperature or the intake air temperature, the higher the set temperature TWSL is changed, so that the lower the fresh air temperature, the higher the engine temperature range can be determined to be cold.

If it is determined in step S101 that the engine 1 is in the cold state, the process proceeds to step S102, and it is determined whether the deceleration fuel is being cut.
Then, when the engine 1 is decelerated in the cold state and the deceleration fuel cut is executed, the process proceeds to step S103.

In step S103, it is determined whether or not the brake pedal is released from the braking state of the vehicle in which the brake pedal is depressed during the deceleration fuel cut and the vehicle is switched to the non-braking state.
Such a determination is made based on the signal of the brake switch 33, and braking is performed when the signal of the brake switch 33 that is turned on when the brake pedal is depressed (braking state) is switched from ON to OFF during the deceleration fuel cut. It is determined that the state has been switched to the non-braking state.
It can be determined from the braking force of the brake pedal, the brake hydraulic pressure, etc. that the braking state has been switched to the non-braking state.

When the brake is switched from the braking state to the non-braking state during the deceleration fuel cut, in other words, when the depression of the brake pedal is released, the accelerator pedal is subsequently depressed, and the engine 1 changes from the deceleration state to the acceleration state. There is a possibility of migration. In other words, the switch from the braking state to the non-braking state indicates the driver's intention to accelerate.
As described above, at the time of deceleration fuel cut, the IVC control at the time of fuel cut is made to advance the closing timing IVC of the intake valve 4 at the time of slow closing mirror cycle operation (for example, ABCC 90 deg) to bring the closing timing IVC closer to the bottom dead center. I do. When the fuel injection is resumed, the IVC control at the time of fuel cut is canceled and returned to the closing timing IVC in the mirror cycle operation, but the closing timing IVC controlled by the variable valve timing mechanism 20 is stepwise. It does not change and gradually changes with a delay.

For this reason, the throttle 10 which has been fully closed is opened, and the control is made to delay the closing timing IVC from the time when the fuel injection is restarted (when shifting from deceleration to acceleration) to return to the closing timing IVC in the mirror cycle operation. When the fuel injection is performed, the closing timing IVC is closer to the bottom dead center than during the mirror cycle operation during the response delay from when the fuel injection is restarted until the closing timing IVC is actually delayed to the closing timing IVC in the mirror cycle operation. Will be driven in a state.
When the closing timing IVC is closer to the bottom dead center than the set timing in the mirror cycle operation, the compression ratio becomes excessively high, which may cause knocking or large torque fluctuation.

Therefore, the transition from deceleration to acceleration (resumption of fuel injection accompanying acceleration) is predicted in advance based on switching from the braking state to the non-braking state, and in other words, before the actual transition to acceleration, Accordingly, the control for delaying the closing timing IVC is started before the fuel injection is resumed. Thereby, when the fuel injection is restarted, the closing timing IVC has changed to the closing timing IVC in the mirror cycle operation, or is retarded until the timing sufficiently close to the closing timing IVC in the mirror cycle operation. Thus, knocking and torque fluctuation due to an excessive compression ratio can be suppressed.
That is, the transition from the braking state to the non-braking state is detected as a previous stage for shifting to the acceleration, and when the braking state is shifted to the non-braking state, the subsequent transition to acceleration (resumption of fuel injection) is performed. Predictingly, control for returning the closing timing IVC to the closing timing IVC in the mirror cycle operation (the closing timing IVC suitable for the fuel injection state) is started in advance.

If the deceleration fuel is being cut in the cold state and there is no transition from the braking state to the non-braking state, the process proceeds to step S104.
In step S104, the cut-time control release rotational speed NCAN is lower than the cut rotational speed NCUT, which is a start condition for decelerating fuel cut, and higher than the recovery rotational speed NRE, which is a fuel injection restart condition. It is determined whether or not (NRE <NCAN <NCUT).

The deceleration fuel cut is canceled along with the shift to acceleration, and is also canceled when the engine rotational speed NE decreases to the recovery rotational speed NRE, and fuel injection is resumed.
Even when the injection is restarted as the engine speed NE decreases, the closing timing IVC is closed in the mirror cycle operation from the time when the engine speed NE reaches the recovery speed NRE and the fuel injection is restarted. When the control to return to the timing IVC is started, the closing timing IVC immediately after the resumption of fuel injection becomes close to the bottom dead center due to a delay in response to the change in the closing timing IVC, and this causes the compression ratio to become excessively high, thereby causing knocking and Large torque fluctuations may occur.

Therefore, even when the fuel injection is restarted as the engine speed NE decreases, the control for returning the closing timing IVC to the closing timing IVC in the mirror cycle operation is started before the fuel injection is actually restarted. When the fuel injection is resumed, the closing timing IVC is changed to the closing timing IVC in the mirror cycle operation or is delayed to a timing sufficiently close to the closing timing IVC in the mirror cycle operation. It is possible to suppress the occurrence of knocking or torque fluctuation due to an excessive compression ratio.
Therefore, when the engine speed NE decreases to the cut-time control release speed NCAN higher than the recovery speed NRE, the IVC control at the time of fuel cut is canceled, and the closing timing IVC reaches the closing timing IVC in the mirror cycle operation. Control for retarding is started.

In other words, the fuel cut-time IVC control is performed until the engine speed NE decreases to the cut-time control release rotational speed NCAN, and the closing timing IVC of the intake valve 4 is brought close to the bottom dead center. When the engine rotational speed NE is between the cut-time control release rotational speed NCAN and the recovery rotational speed, the actual closing timing IVC is returned to the vicinity of the closing timing IVC in the mirror cycle operation.
Accordingly, the control release rotational speed NCAN at the time of cut takes into account the response delay of the retard control of the closing timing IVC by the variable valve timing mechanism 20, and at the time when the engine speed NE has decreased to the control release rotational speed NCAN at the time of cut. If the IVC control at the time of fuel cut is canceled, the closing timing IVC is close to the closing timing IVC in the mirror cycle operation until the engine rotation speed NE reaches the recovery rotation speed NRE, in other words, until the fuel injection is resumed. The compression ratio is set so as to decrease to a compression ratio that can suppress the occurrence of knocking and torque fluctuation when fuel injection is resumed.

If it is determined in step S104 that the engine rotational speed NE is higher than the cut-time control release rotational speed NCAN (NE> NCAN), the process proceeds to step S105.
In step S105, the variable valve timing mechanism 20 is controlled so that the center phase of the operating angle of the intake valve 4 is advanced from that before the fuel cut (during mirror cycle operation), and the closing timing IVC of the intake valve 4 is lowered. Carry out IVC control at the time of fuel cut to bring it close to the dead point.

For example, if the closing timing IVC in the delayed closing mirror cycle operation is 90 deg after bottom dead center (ABDC) before the fuel cut, for example, the IVC control at the time of fuel cut is 90 deg after bottom dead center (ABDC). The closing timing IVC is made closer to the bottom dead center BDC than during the mirror cycle operation so as to be higher than the compression temperature at that time. When the closing timing IVC of the intake valve 4 is brought close to the bottom dead center BDC, the effective compression ratio increases, and as a result, the compression temperature rises.
On the other hand, during the deceleration fuel cut, the fuel is not burned, and the combustion chamber 5 (piston crown surface 18) is cooled by the fresh air sucked into the cylinder. However, the compression temperature is increased by increasing the effective compression ratio. If it becomes high, the temperature fall of the combustion chamber 5 can be suppressed that much.

If the temperature drop (supercooling) of the combustion chamber 5 during the deceleration fuel cut can be suppressed, atomization of the fuel injected toward the combustion chamber 5 (piston crown surface 18) when the fuel injection is resumed. Since inhibition of (vaporization) can be suppressed, formation of an air-fuel mixture capable of maintaining combustion stability can be performed, and deterioration of exhaust properties and drivability due to torque fluctuation can be suppressed.
When the engine 1 is provided with a lubricating oil supply device that injects cooling lubricating oil to the back side of the piston, the injection of the lubricating oil to the back side of the piston is stopped during the fuel cut IVC control. Alternatively, although the injection of the lubricating oil is continued, the injection pressure and the injection amount can be reduced, and the piston temperature can be prevented from transiently decreasing due to the injection of the lubricating oil.

FIG. 3 shows an example of the correlation between the closing timing IVC of the intake valve 4 and the compression temperature during deceleration operation.
The horizontal axis of the graph shown in FIG. 3 is the retard angle (ABDC) from the bottom dead center of the closing timing IVC, and the intake valve 4 is closed at a position delayed from the bottom dead center toward the right side of the horizontal axis. The vertical axis indicates the compression temperature for each closing timing IVC. The condition for determining the compression temperature is a deceleration operation with an intake pressure of −67 kPa (−500 mmHg), and shows a tendency of the compression temperature when the engine speed NE is 2000 rpm and 1200 rpm.

Compared to the case where the closing timing IVC is set to around ABCDC 90 deg in the slow closing mirror cycle operation, the compression temperature gradually increases by advancing the closing timing IVC and approaching the bottom dead center, but in the example shown in FIG. When the closing timing IVC passes ABDC 50 deg and further approaches the bottom dead center, the compression temperature tends to decrease. When the closing timing IVC is set to ABDC 50 deg, the compression temperature shows a peak value (maximum value).
In the case where only the closing timing IVC is focused on, the effective compression ratio shows a maximum value by setting the closing timing IVC near the bottom dead center BDC. However, in order to bring the closing timing IVC closer to the bottom dead center, the intake valve When the central phase of the operating angle of 4 is controlled to advance, the opening timing IVO is also advanced at the same time to increase the valve overlap. When the valve over increases in the low rotation range, the charging efficiency decreases, and the substantial compression ratio is increased. It will decline.

In the example of FIG. 3, when the closing timing IVC is in the vicinity of ABCC 50 deg, the closing timing EVC of the exhaust valve 7 and the opening timing IVO of the intake valve 4 are substantially simultaneous, and the closing timing IVC is advanced by more than ABDC 50 deg. As the valve overlap increases and, on the contrary, the closing timing IVC is retarded from ABDC 50 deg, the interval from the closing timing EVC of the exhaust valve 7 to the opening timing IVO of the intake valve 4 increases, and the valve overlap does not increase. The compression temperature shows a peak value at a position of ABDC 50 deg where the closing timing IVC is advanced as much as possible in the range.
Therefore, in the IVC control at the time of fuel cut, the compression temperature cannot be raised as the closing timing IVC approaches the bottom dead center, and the closing timing is considered in consideration of the influence of valve overlap due to the opening timing IVO that changes the advance angle at the same time. Set IVC goals. That is, the central phase of the operating angle is set to the closing timing IVC when the opening timing IVO of the intake valve 4 is advanced until the closing timing EVC of the exhaust valve 7 is substantially coincident with the closing timing IVC in the fuel cut IVC control. If the target is, the compression temperature can be made as high as possible.

Specifically, for example, when the operating angle of the intake valve 4 is 220 deg. To 260 deg. And the opening timing IVO is near the top dead center TDC, the exhaust valve 7 is close to the closing timing EVC. The target closing timing IVC in the IVC control at the time of fuel cut may be ABDC 40 deg to ABCD 80 deg.
Note that, as the variable valve mechanism, for example, in the engine 1 including the variable valve timing mechanism 20 and the variable lift mechanism that varies the operating angle and the maximum lift amount, the opening timing IVO and the closing timing IVC of the intake valve 4 are set. Since each can be controlled independently, in the fuel cut IVC control, the opening timing IVO of the intake valve 4 is set substantially at the same time as the closing timing EVC of the exhaust valve 7, and the closing timing IVC of the intake valve 4 is set to the bottom dead center. It is possible to obtain a higher compression temperature by controlling to BDC.

Further, the target closing timing IVC (the advance amount target of the closing timing IVC) in the fuel cut IVC control can be variably set according to the temperature of the engine 1.
That is, as the temperature of the engine 1 is lower, the temperature of the engine 1 is lower because the temperature of the combustion chamber 5 (piston crown surface 18) is easily lowered to a temperature at which fuel atomization is inhibited during fuel cut. The higher the compression temperature is required.

On the other hand, when the temperature of the engine 1 is relatively high, the temperature of the combustion chamber 5 is suppressed from decreasing to a temperature at which fuel atomization is inhibited during the fuel cut even if the compression temperature is not so high. If the amount of advance from the closing timing IVC in the mirror cycle operation can be suppressed, the closing timing IVC can be quickly returned to the closing timing IVC in the mirror cycle operation when canceling the IVC control at the time of fuel cut. This can improve the drivability of the engine 1 when fuel injection is resumed.
Therefore, when the target closing timing IVC in the IVC control at the time of fuel cut is made variable according to the engine temperature, as the engine temperature becomes lower, the progress from the closing timing IVC in the mirror cycle operation becomes lower as shown in FIG. The angular amount is increased so that the closing timing IVC is closer to the bottom dead center and the compression temperature is higher.

For example, if the compression temperature reaches a peak value when the closing timing IVC is set to ABDC 50 deg, the advance temperature limit is set to ABDC 50 deg, and the engine temperature is between the closing timing IVC (ABDC 90 deg) in the delayed closing mirror cycle and ABDC 50 deg. By setting the closing timing IVC closer to the bottom dead center as the target is lower, excessive advance angle control can be suppressed.
Instead of omitting the determination of whether or not the engine is cold in step S101, the advance amount is set to zero when the engine temperature is higher than the set temperature in the setting of the target closing timing IVC in the fuel cut IVC control. Thus, the advance angle control of the closing timing IVC is not substantially performed in the high temperature range (the closing timing IVC in the mirror cycle operation is maintained).

Further, by setting the advance amount to zero when the engine temperature is higher than the set temperature, the advance angle control at the closing timing IVC is canceled, while the advance amount is constant when the engine temperature is lower than the set temperature. By setting the value (> 0), it is possible to perform the advance angle control for bringing the closing timing IVC closer to the bottom dead center.
As described above, during the fuel cut IVC control, if the braking state is switched to the non-braking state, the transition to the subsequent acceleration is predicted and the fuel cut IVC control is canceled in advance. A process of retarding (closing away from the bottom dead center) the closing timing IVC of the intake valve 4 toward the closing timing IVC during the mirror cycle operation is started.

FIG. 5 is a time chart showing changes in accelerator opening (throttle opening), engine speed, fuel cut, closing timing IVC, and brake when the fuel cut IVC control is canceled by the process in step S103. is there.
In FIG. 5, when the accelerator pedal is switched to the brake pedal, at time t1, the accelerator is almost fully closed and is in a braking state. The deceleration fuel cut is started from time t2 when the cut delay time TDL has elapsed from time t1.

Then, by starting the deceleration fuel cut, the IVC control at the time of fuel cut is started, and the closing timing IVC of the intake valve 4 is advanced from the closing timing IVC in the delayed closing mirror cycle operation before the fuel cut starts. By approaching the dead center and bringing the closing timing IVC closer to the bottom dead center and increasing the effective compression ratio, the compression temperature rises and the temperature drop of the combustion chamber 5 (piston crown surface 18) during fuel cut is suppressed.
At time t3 during deceleration fuel cut, when the foot is released from the brake pedal and the brake state is switched to the non-brake state, the deceleration fuel cut is continued, but in preparation for the restart of the subsequent fuel injection, IVC at the time of fuel cut The control is canceled and the control for delaying to the closing timing IVC in the delayed closing mirror cycle operation is started.

Here, the actual closing timing IVC is gradually delayed from the time t3 and approaches the closing timing IVC in the mirror cycle operation.
Then, at time t4 after time t3, when the accelerator pedal is depressed and the accelerator opening increases, the deceleration fuel cut is stopped and fuel injection is resumed, but the closing timing IVC is delayed and closed in advance by mirror cycle operation. Since the process for returning to the target is started, at the time t4 when the fuel injection is resumed, the actual closing timing IVC is sufficiently close to the target in the delayed closing mirror cycle operation.

As a result, when fuel injection is resumed from the deceleration fuel cut state in accordance with the transition from deceleration to acceleration, the closing timing IVC is set sufficiently close to the timing at the time of mirror cycle operation immediately after the restart of fuel injection. Even if there is a response delay of the variable valve timing mechanism 20, it is possible to suppress the occurrence of large torque fluctuations, knocking, etc., by restarting fuel injection while the compression ratio is excessively high.
When the engine speed NE decreases to the rotational speed NCAN immediately before the recovery rotational speed NRE during the fuel cut IVC control, the subsequent fuel injection restart is predicted and the fuel cut IVC control is canceled in advance. Then, a process of retarding (closing away from the bottom dead center) the closing timing IVC of the intake valve 4 toward the closing timing IVC during the mirror cycle operation is started.

FIG. 6 is a time chart showing changes in the accelerator opening (throttle opening), the engine speed, the fuel cut, and the closing timing IVC when the fuel cut IVC control is canceled by the processing in step S104.
In FIG. 6, the deceleration fuel cut is started from the time t1 when the accelerator is substantially fully closed and from the time t2 when the cut delay time TDL has elapsed. When deceleration fuel cut is started, IVC control at the time of fuel cut is started, and the closing timing of the intake valve 4 is advanced from the closing timing IVC in the delayed closing mirror cycle operation before the fuel cut is started, and the bottom dead. By bringing the closing timing IVC closer to the bottom dead center and increasing the effective compression ratio, the compression temperature rises and the temperature drop of the combustion chamber 5 (piston crown surface 18) during fuel cut is suppressed.

When the engine speed NE decreases during the fuel cut and reaches the control release rotational speed NCAN immediately before the recovery rotational speed NRE at the time t3, the deceleration fuel cut continues, but the IVC control during the fuel cut is canceled. Then, the control for delaying to the closing timing IVC in the delayed closing mirror cycle operation is started.
Here, the actual closing timing IVC gradually changes from the time t3 to the closing timing IVC in the mirror cycle operation.

Then, at the time t4 when the engine rotational speed NE has decreased to the recovery rotational speed NRE, the deceleration fuel cut is stopped, the fuel injection is resumed, and the state shifts to the idle state as it is. Since the returning process is started, the actual closing timing IVC is sufficiently close to the target in the delayed closing mirror cycle operation at the fuel injection restart time t4.
As a result, when fuel injection is resumed from the decelerated fuel cut state as the engine speed NE decreases, the closing timing IVC is sufficiently close to the closing timing IVC during mirror cycle operation immediately after the restart of fuel injection. Even if there is a response delay of the variable valve timing mechanism 20, it is possible to suppress the occurrence of knocking and large torque fluctuations by restarting fuel injection while the compression ratio is excessively high.

Note that the variable valve mechanism that makes the intake valve closing timing variable is not limited to the variable valve timing mechanism 20 that continuously changes the rotation phase of the intake camshaft 22 with respect to the crankshaft 21. A mechanism for switching cams, a mechanism for driving a valve by displacing a three-dimensional cam whose cam profile changes in the axial direction in the axial direction, and a variable valve timing mechanism 20 and an operating angle can be used. Further, a combination with a variable lift mechanism that makes the maximum lift amount variable, or an electromagnetically driven valve can be used.
When a mechanism that can change the closing timing of the intake valve 4 with good response, such as an electromagnetically driven valve that opens and closes the intake valve 4 using electromagnetic force, or when the injection is resumed, the closing timing BDC is near the bottom dead center. In the engine 1 in which the occurrence of knocking is sufficiently suppressed even when the angle is advanced, the processing of step S103 and step S104 in the flowchart of FIG. Control can be implemented.

Further, even in the engine 1 in which the early closing mirror cycle operation is performed, it is possible to suppress the overcooling of the combustion chamber 5 (piston crown surface 18) during the deceleration fuel cut by performing the fuel cut IVC control.
However, in the delayed closing mirror cycle in which the intake valve 4 is closed after the bottom dead center BDC, the closing timing IVC is advanced to approach the bottom dead center BDC in order to increase the effective compression ratio during the deceleration fuel cut. In the early closing mirror cycle in which the intake valve 4 is closed before the bottom dead center BDC, the closing timing IVC is retarded to approach the bottom dead center BDC in order to increase the effective compression ratio during the deceleration fuel cut.

In the following, the engine 1 that performs an early closing mirror cycle operation is provided with a variable lift mechanism 23 that makes the working angle and the maximum lift amount of the intake valve 4 variable together with the variable valve timing mechanism 20, as shown in FIG. The fuel cut IVC control in the engine 1 will be described with reference to the flowchart of FIG.
In FIG. 7, the same elements as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

The routine shown in the flowchart of FIG. 8 is interrupted at every set time by the ECM 31, and in steps S201 to S204, the same processing as in steps S101 to S104 in the flowchart of FIG. Assuming that is established, the IVC control at the time of fuel cut in step S205 is performed.
That is, the engine 1 is in a cold state, is in a deceleration fuel cut state, is not switched from a braking state to a non-braking state, and the engine rotational speed NE is less than the cut-time control release rotational speed NCAN. If it is also higher, the process proceeds to step S205.

In step S205, the variable valve timing mechanism 20 is controlled to retard the central phase of the operating angle of the intake valve 4, and the variable lift mechanism 23 is controlled to increase the operating angle of the intake valve 4. Then, the fuel cut IVC control is performed to retard the closing timing IVC of the intake valve 4 from the closing timing IVC (for example, 60 deg before bottom dead center) in the early closing mirror cycle toward the bottom dead center.
Here, in the case of the engine 1 provided with the variable valve timing mechanism 20 and the variable lift mechanism 23 as the variable valve mechanism, the opening timing IVO substantially coincident with the closing timing EVC of the exhaust valve 7 and the bottom dead center. It is possible to control the operating angle and the center phase so that the closing timing IVC can be realized at the same time, whereby the compression temperature can be maximized.

Therefore, in the IVC control at the time of fuel cut in step S205, the crank angle from the opening timing IVO to the bottom dead center BDC set substantially at the same time as the closing timing EVC of the exhaust valve 7 is increased by the variable lift mechanism 23. The intermediate point between the opening timing IVO and the bottom dead center BDC, which is set to the target value and set substantially at the same time as the closing timing EVC of the exhaust valve 7, is the target of the retardation control of the center phase by the variable valve timing mechanism 20. By setting the value, the intake valve 4 is opened substantially simultaneously with the closing timing EVC of the exhaust valve 7 during the deceleration fuel cut, and is closed near the bottom dead center BDC.
As described above, the closing timing IVC of the intake valve 4 during the deceleration fuel cut is retarded from the closing timing IVC (before the deceleration fuel cut starts) in the early closing mirror cycle, and is set near the bottom dead center, and If the opening timing IVO is set such that a substantial reduction in the compression ratio due to the expansion of the valve overlap can be suppressed, the temperature of the combustion chamber 5 (piston crown surface 18) is transiently lowered during the deceleration fuel cut. Therefore, it is possible to suppress at a high compression temperature, and it is possible to suppress deterioration of exhaust properties and restartability due to torque fluctuation when fuel injection is resumed.

Similarly to the case where the IVC control at the time of fuel cut is performed according to the flowchart of FIG. 2, even if there is a response delay in the variable valve timing mechanism 20 or the variable lift mechanism 23, the closing timing IVC of the early closing mirror cycle operation is sufficient. The fuel injection can be restarted in a close state, and knocking and torque fluctuation can be suppressed from occurring when the fuel injection is restarted.
FIG. 9 shows the correlation between the closing timing IVC of the intake valve 4 and the compression temperature in the engine 1 that includes the variable valve timing mechanism 20 and the variable lift mechanism 23 and performs the early closing mirror cycle operation.

For example, deceleration from an early closing mirror cycle operation in which the opening timing IVO of the intake valve 4 is set to the vicinity of the top dead center TDC at the same time as the closing timing EVC of the exhaust valve 7 and the closing timing IVC is set to about 60 degrees before the bottom dead center. When the fuel cut is started, the opening timing IVO is maintained at the same level as that in the mirror cycle operation, while the closing timing IVC is lowered when the closing timing IVC is controlled to approach the bottom dead center from the bottom dead center. The closer to the dead point, the higher the effective compression ratio, and the higher the compression temperature.
Here, the opening timing IVO does not change with the delay angle control of the closing timing IVC, and the opening timing IVO maintains the vicinity of the top dead center TDC at the same time as the closing timing EVC of the exhaust valve 7, so that the valve over There is no change in the charging efficiency due to the change in the lap, and the compression temperature becomes higher as the closing timing IVC is retarded. However, after the bottom dead center BDC, the compression ratio tends to decrease because the effective compression ratio decreases. As a result, the compression temperature shows a peak value when the closing timing IVC = bottom dead center BDC.

Therefore, by setting the target of the closing timing IVC in the IVC control at the time of fuel cut in step S205 to the bottom dead center BDC, the compression temperature can be maximized and the temperature drop of the combustion chamber 5 can be effectively suppressed. .
In the engine provided with the variable valve timing mechanism 20 without the variable lift mechanism 23 described above, since the operating angle is constant, when the opening timing IVO is set substantially at the same time as the closing timing EVC of the exhaust valve 7, The closing timing IVC cannot be set to the bottom dead center BDC.

On the other hand, in the engine provided with the variable valve timing mechanism 20 and the variable lift mechanism 23, the operating angle and the central phase of the operating angle can be made variable, so that the closing timing EVC of the exhaust valve 7 and the opening timing IVO substantially at the same time. The closing timing IVC can be set to the bottom dead center BDC, and a higher effective compression ratio (compression temperature) can be obtained.
In the IVC control at the time of fuel cut in step S205, the target of the closing timing IVC can be set closer to the bottom dead center BDC as the engine temperature at that time is lower. In this case, in the mirror cycle operation Within the angle range from the closing timing IVC (for example, 60 deg before the bottom dead center) to the bottom dead center BDC, the target of the closing timing IVC is variably set according to the engine temperature.

Further, even in an engine that performs an early closing mirror cycle operation, an electromagnetically driven valve can be provided as the intake valve 4, and in this case, the closing timing IVC can be changed with good response, so the processing of steps S203 and 204 is omitted. can do.
Although the preferred embodiments have been specifically described above, it is obvious that those skilled in the art can take various modifications.

In the fuel cut IVC control described above, the fuel cut IVC control was canceled when the engine rotational speed NE decreased to the cut control release rotational speed NCAN. However, as the engine rotational speed NE approaches the recovery rotational speed NRE. The target of the closing timing IVC can be gradually approached toward the closing timing IVC during the delayed closing mirror cycle operation or the closing timing IVC during the early closing mirror cycle operation.
In addition, when switching from the braking state to the non-braking state during deceleration fuel cut, the IVC control at the time of fuel cut is not canceled and the closing timing IVC at the time of the slow closing mirror cycle operation or the closing at the time of the early closing mirror cycle operation The closing timing at the time of the delayed closing mirror cycle operation according to the passage of time from the time when the timing IVC is changed to an intermediate value between the timing of IVC control and the closing timing IVC in the IVC control at the time of fuel cut, or from the braking state to the non-braking state It can be gradually returned toward the closing timing IVC during IVC or early closing mirror cycle operation.

  Further, it is possible to apply the IVC control at the time of fuel cut to an intake port injection type internal combustion engine. In the case of an intake port injection type internal combustion engine, the temperature drop of the combustion chamber 5 during the fuel cut can be suppressed, so that the fuel vaporization performance in the combustion chamber 5 when the fuel cut is canceled and the intake stroke injection is resumed. Can be improved, and combustion stability can be improved.

Here, technical ideas other than the claims that can be grasped from the above embodiment will be described together with effects.
(A) In the control device for an internal combustion engine according to claim 1 or 2,
A control device for an internal combustion engine, which cancels the control for bringing the closing timing of the intake valve closer to bottom dead center than before the start of fuel cut when the driver's intention to accelerate is detected during fuel cut.

  According to the above invention, the control for returning the closing timing is started prior to the resumption of fuel injection accompanying the transition from deceleration to acceleration. Therefore, the delay in returning the closing timing with respect to the restart of the fuel injection accompanying the transition from the deceleration to the acceleration can suppress the occurrence of knocking and torque fluctuation by restarting the fuel injection with a high compression ratio. .

(B) In the control device for an internal combustion engine according to claim 1 or 2,
A control device for an internal combustion engine, which cancels the control for bringing the closing timing of the intake valve closer to the bottom dead center than before the start of fuel cut when the brake state is switched to the non-brake state during the fuel cut.

  According to the above invention, when shifting from deceleration to acceleration, generally, the brake pedal is switched to the accelerator pedal, so when the foot is released from the brake pedal and the braking state is switched to the non-braking state, Subsequent acceleration can be predicted, and control for returning the closing timing is started based on the acceleration prediction. Therefore, the delay in returning the closing timing with respect to the restart of the fuel injection accompanying the transition from the deceleration to the acceleration can suppress the occurrence of knocking and torque fluctuation by restarting the fuel injection with a high compression ratio. .

(C) In the control device for an internal combustion engine according to claim 1 or 2,
An internal combustion engine that cancels the control to bring the closing timing of the intake valve closer to the bottom dead center than before the start of fuel cut when the engine speed drops to a higher speed than the recovery speed of fuel injection during fuel cut Control device.

  According to the above invention, when the engine speed decreases and reaches the recovery rotational speed in the deceleration fuel cut state, the fuel injection is resumed, but the control for returning the closing timing is started at a rotational speed higher than the recovery rotational speed. Is done. Therefore, it is possible to suppress the occurrence of knocking or torque fluctuation by restarting the fuel injection with a high compression ratio by delaying the return of the closing timing with respect to the restart of the fuel injection accompanying the decrease in the engine speed.

(D) In the control apparatus for an internal combustion engine according to claim 1 or 2,
The internal combustion engine is an internal combustion engine in which a delayed closed mirror cycle operation is performed;
A control device for an internal combustion engine that is advanced toward the bottom dead center by advancing more than the closing timing in the slow closing mirror cycle operation at the time of fuel cut.

  According to the above-described invention, in an internal combustion engine in which the delayed closing mirror cycle operation with the closing timing after the bottom dead center is performed, when the fuel is decelerated, the closing timing is advanced to approach the bottom dead center so that the effective compression ratio ( (Compression temperature) is increased, and a decrease in the temperature of the combustion chamber (piston crown surface) during deceleration fuel cut is suppressed.

(E) In the control device for an internal combustion engine according to claim 1 or 2,
The internal combustion engine is an internal combustion engine in which a mirror cycle operation is performed that is quickly closed,
A control device for an internal combustion engine that is brought closer to the bottom dead center by delaying the closing timing in the early closing mirror cycle operation when the fuel is cut.

  According to the above-described invention, in an internal combustion engine in which the early closing mirror cycle operation is performed with the closing time before the bottom dead center, when the fuel is decelerated, an effective compression ratio ( (Compression temperature) is increased, and a decrease in the temperature of the combustion chamber (piston crown surface) during deceleration fuel cut is suppressed.

(F) In the control device for an internal combustion engine according to claim 1 or 2,
In the control to bring the intake valve closing timing closer to bottom dead center than before the start of fuel cut, the closing timing is lowered as much as possible while the opening timing of the intake valve is set substantially at the same time as the closing timing of the exhaust valve. A control device for an internal combustion engine that approaches the dead center.

  According to the above-described invention, if the valve overlap is large, the substantial compression ratio is lowered due to the reduction of the charging efficiency, and the compression temperature is lowered. Therefore, the intake valve opening timing is substantially the same as the exhaust valve closing timing. The intake valve is closed close to the bottom dead center as much as possible while maintaining a high compression temperature.

(G) In the control device for an internal combustion engine according to claim 1 or 2,
The internal combustion engine includes, as the variable valve mechanism, a variable valve timing mechanism that varies the rotational phase of the intake camshaft with respect to the crankshaft, and a variable lift mechanism that varies the operating angle of the intake valve, and an early closing mirror Cycle operation is performed,
In the control for bringing the closing timing of the intake valve closer to the bottom dead center than before the start of the fuel cut, the opening timing is substantially the same as the closing timing of the exhaust valve, and the closing timing becomes the bottom dead center. A control device for an internal combustion engine that controls a rotational phase and an operating angle.

  According to the above invention, the target value of the operating angle is determined from the angular interval between the closing timing of the exhaust valve and the opening timing substantially at the same time and the bottom dead center, and the closing timing of the exhaust valve and the opening timing at the substantially same time The midpoint of the bottom dead center is the target value of the rotation phase, and both the closing timing of the exhaust valve and the opening timing at approximately the same time and the closing timing of the bottom dead center are realized, and the compression temperature is as high as possible. Is obtained.

(H) In the control device for an internal combustion engine according to claim 1 or 2,
The internal combustion engine includes a variable valve timing mechanism that varies a rotational phase of an intake camshaft with respect to a crankshaft as the variable valve mechanism, and a slow closing mirror cycle operation is performed.
In the control to bring the closing timing of the intake valve closer to the bottom dead center than before the start of fuel cut,
By changing the rotational phase of the intake camshaft so that the intake valve opening timing is substantially coincident with the exhaust valve closing timing, the intake valve closing timing is delayed and closed in mirror cycle operation. A control device for an internal combustion engine that is closer to bottom dead center than the closing time.

  According to the above invention, when the intake camshaft rotation phase is advanced so that the intake valve opening timing is substantially coincident with the exhaust valve closing timing, the closing timing is advanced by the conversion angle of the opening timing. Then, it approaches the bottom dead center, the effective compression ratio increases, and the compression temperature rises. Here, if the opening timing of the intake valve is advanced more than the closing timing of the exhaust valve, the closing timing of the intake valve will be closer to the bottom dead center, but it will be filled by expanding the valve overlap. Since the efficiency is lowered and the compression temperature is lowered, the compression temperature becomes a peak value at the closing timing when the opening timing of the intake valve is substantially the same as the closing timing of the exhaust valve, and the combustion chamber ( Piston crown surface) Temperature drop can be effectively suppressed.

(I) In the control apparatus for an internal combustion engine according to claim 1 or 2,
The internal combustion engine includes a variable valve timing mechanism that varies a rotational phase of an intake camshaft with respect to a crankshaft as the variable valve mechanism, and a slow closing mirror cycle operation is performed.
In the control to bring the closing timing of the intake valve closer to the bottom dead center than before the start of fuel cut,
By changing the rotational phase of the intake camshaft so that the opening timing of the intake valve is substantially the intake top dead center, the closing timing of the intake valve is set to be slower than the closing timing in the mirror cycle operation. A control device for an internal combustion engine that approaches the bottom dead center.

  According to the above invention, when the rotational phase of the intake camshaft is advanced so that the intake valve opening timing is substantially at the intake top dead center, the closing timing is advanced by the conversion angle of the open timing, and the bottom dead center is reached. The effective compression ratio increases and the compression temperature rises. Here, if the opening timing of the intake valve is substantially the intake top dead center, the valve overlap amount can be made sufficiently small to suppress a decrease in charging efficiency, so that a compression temperature close to the peak value is obtained and the combustion chamber ( Piston crown surface) Temperature drop can be effectively suppressed.

  DESCRIPTION OF SYMBOLS 1 ... Engine (internal combustion engine), 2 ... Intake passage, 3 ... Fuel injection valve, 4 ... Intake valve, 5 ... Combustion chamber, 7 ... Exhaust valve, 18 ... Piston crown, 20 ... Variable valve timing mechanism, 31 ... ECM (Engine control module), 33 ... Brake switch

Claims (2)

A control device applied to an internal combustion engine having a variable valve mechanism that makes the closing timing of an intake valve variable,
A control apparatus for an internal combustion engine, which controls the variable valve mechanism at the time of fuel cut in a deceleration operation so that the closing timing of the intake valve is closer to bottom dead center than before the start of fuel cut.   The control device for an internal combustion engine according to claim 1, wherein the closing timing of the intake valve is made closer to bottom dead center as the temperature of the internal combustion engine is lower.