Control apparatus for internal combustion engine

Abstract

A control apparatus for an internal combustion engine that varies the amount of lift of an intake valve is disclosed. In one embodiment, the control apparatus includes a fuel injection timing correcting device that, when lift of the intake valve is varied, corrects and varies fuel injection termination timing according to the variation of the lift of the intake valve. In another embodiment, an injection quantity correcting device is included that, when lift of the intake valve is varied, corrects and varies an injection quantity. In still another embodiment, a swirl flow generating device is included that generates a swirl flow in the cylinder. In a further embodiment, an intake valve closing timing correcting device is included that, when lift of the intake valve is varied, controls the variable valve timing mechanism so that the valve closing timing of the intake valve remains substantially constant.

Description

CROSS REFERENCE TO RELATED APPLICATION

The following is based on and claims priority to Japanese Patent Application No. 2005-264566, filed Sep. 13, 2005, which is incorporated herein by reference.

FIELD

The present invention relates to a control apparatus for an internal combustion engine that varies the amount of lift of an intake valve.

BACKGROUND

Internal combustion engines have been proposed that include a variable intake valve lifter that varies the amount of lift of an intake valve. An example of this type of variable intake valve lifter is disclosed in Japanese Patent No. 2827768. Specifically, the control mode of the variable intake valve lifter is switched between low lift mode and high lift mode in accordance with the state of operation of the internal combustion engine. In low lift mode, a cam for driving and opening/closing an intake valve is changed to a cam for low lift to reduce the amount of lift of the intake valve. In high lift mode, the cam for driving and opening/closing the intake valve is changed to a cam for high lift to increase the amount of lift of the intake valve. Accordingly, the variable intake valve lifter varies the amount of lift of the intake valve by switching between low lift mode and high lift mode.

Such systems can pose certain problems. For instance, from the intake stroke to the initial stage of the compression stroke, rich gas (i.e., a fuel-air mixture rich with fuel) can be disproportionately distributed near the intake ports in the cylinder. This phenomenon is illustrated in FIG. 10, wherein the variable intake valve lifter is switched from low lift mode to high lift mode (i.e., when the amount of lift of an intake valve is increased). As shown, when the valve closing timing of the intake valve is delayed from Bottom Dead Center (labeled “BDC” in FIG. 10) at this time, the intake valve remains open until the initial stage of the compression stroke. For this reason, back flow may occur, and the rich gas disproportionately distributed in proximity to the intake ports in the cylinder in the initial stage of the compression stroke may be pushed back toward the intake port. As a result, the average air-fuel ratio in the cylinder may be detected as being lean. Thus, immediately after the mode is switched from low lift mode to high lift mode, a lean spike can occur as illustrated in FIG. 11. In other words, the average air-fuel ratio in the cylinder temporarily fluctuates toward lean.

In the second and following cycles after switching to high lift mode, rich gas that flowed back to intake port in the compression stroke of the previous cycle is re-introduced into the cylinder as illustrated in FIG. 10. As a result, the average air-fuel ratio in the cylinder is approximately equal to a target air-fuel ratio.

However, when the mode is thereafter switched from high lift mode to low lift mode (i.e., when the amount of lift of the intake valve is reduced), a phenomenon occurs as illustrated in FIG. 12. Specifically, when the valve closing timing of the intake valve is returned to approximately the BDC, the back flow of rich gas in the cylinder substantially stops. For this reason, the residual volume of rich gas in the cylinder is increased, and the average air-fuel ratio in the cylinder becomes rich. As a result, immediately after the mode is switched from high lift mode to low lift mode, a rich spike occurs as illustrated in FIG. 13. In other words, the average air-fuel ratio in the cylinder temporarily fluctuates toward rich.

More specific description will be given. During the period from the intake stroke to the initial stage of the compression stroke, the air-fuel ratio distribution of the fuel mixture in the cylinder is not uniform. Rich gas is disproportionately distributed in proximity to the intake ports in the cylinder. Therefore, when the valve closing timing of an intake valve is changed by varying the amount of lift of the intake valve by a variable intake valve lifter, the back flow of rich gas disproportionately distributed in proximity to the intake ports in the cylinder is increased or reduced. A lean spike or a rich spike occurs. This lean spike or rich spike can cause torque shock, which can lead to degraded drivability or deteriorated exhaust emission.

SUMMARY OF THE INVENTION

A control apparatus is disclosed for an internal combustion engine that varies the amount of lift of an intake valve. The control apparatus includes a fuel injection timing correcting device that, when the amount of lift of the intake valve is varied, corrects and varies fuel injection termination timing according to the variation of the lift of the intake valve.

A control apparatus is also disclosed for an internal combustion engine that varies the amount of lift of an intake valve for a cylinder. The control apparatus includes a swirl flow generating device that generates a swirl flow in the cylinder.

A control apparatus is further disclosed for an internal combustion engine. The internal combustion engine is equipped with a variable intake valve lifter that varies the amount of lift of an intake valve and a variable valve timing mechanism that varies the opening/closing timing of the intake valve. The control apparatus includes an intake valve closing timing correcting device that, when the amount of lift of the intake valve is varied by the variable intake valve lifter, controls the variable valve timing mechanism so that the valve closing timing of the intake valve remains substantially constant.

A control apparatus is still further disclosed for an internal combustion engine that varies the amount of lift of an intake valve. The control apparatus includes an injection quantity correcting device that, when the amount of lift of the intake valve is varied, corrects and varies an injection quantity.

A method of controlling fuel injection timing is additionally disclosed for an internal combustion engine that varies the amount of lift of an intake valve. The method includes correcting and varying fuel injection termination timing according to the variation of the lift of the intake valve when the amount of lift of the intake valve is varied.

Also, a method of controlling opening/closing timing of an intake valve of an internal combustion engine is disclosed. The internal combustion engine is equipped with a variable intake valve lifter that varies the amount of lift of an intake valve and a variable valve timing mechanism that varies the opening/closing timing of the intake valve. The method includes controlling the variable valve timing mechanism so that the valve closing timing of the intake valve remains substantially constant when the amount of lift of the intake valve is varied by the variable intake valve lifter.

Moreover, a method of controlling an injection quantity of an intake valve is disclosed for an internal combustion engine that varies the amount of lift of the intake valve. The method includes correcting and varying an injection quantity when the amount of lift of the intake valve is varied.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one embodiment of an engine control system with a variable intake valve lifter;

FIG. 2 is a valve lift characteristic diagram for explaining the valve lift characteristic of a variable intake valve lifter in low lift mode;

FIG. 3 is a valve lift characteristic diagram for explaining the valve lift characteristic of a variable intake valve lifter in high lift mode;

FIG. 4 is a flowchart illustrating one embodiment of a fuel injection timing computation program;

FIG. 5 is a flowchart illustrating one embodiment of an injection quantity computation program;

FIG. 6 is a plan view illustrating one embodiment of a swirl valve;

FIG. 7 is a flowchart illustrating one embodiment of a swirl valve control program;

FIG. 8 is a valve lift characteristic diagram for explaining one embodiment of a method for switching from low lift mode to high lift mode;

FIG. 9 is a valve lift characteristic diagram for explaining the method for switching from high lift mode to low lift mode in embodiment of FIG. 8;

FIG. 10 is a valve lift characteristic diagram for explaining a conventional system for switching from low lift mode to high lift mode;

FIG. 11 is a time diagram illustrating air-fuel ratio behavior for the system of FIG. 10;

FIG. 12 is a valve lift characteristic diagram for explaining a conventional system for switching from high lift mode to low lift mode; and

FIG. 13 is a time diagram illustrating air-fuel ratio behavior for the system of FIG. 12.

DETAILED DESCRIPTION

Hereafter, description will be given to various embodiments of the invention.

First Embodiment

Description will be given to the first embodiment of the invention with reference to FIG. 1 to FIG. 4.

First, description will be given to the general configuration of an engine control system with reference to FIG. 1. An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of an internal combustion engine 11. An air flow meter 14 that detects the quantity of intake air is provided downstream of this air cleaner 13. Downstream of this air flow meter 14, there are provided a throttle valve 16 and a throttle angle sensor 17. The angle of the throttle valve 16 is adjusted by a motor 15 (e.g., a DC motor), and the throttle angle sensor 17 detects the angle of the throttle valve 16.

A surge tank 18 is provided downstream of the throttle valve 16, and this surge tank 18 is provided with an intake manifold pressure sensor 19 that detects intake manifold pressure. The surge tank 18 is provided with an intake manifold 20 that guides air into each cylinder of the engine 11. A fuel injection valve 21 for injecting fuel is installed in proximity to the intake ports of each cylinder in the intake manifold 20. Spark plugs 22 for respective cylinders are installed in the cylinder head of the engine 11. The air-fuel mixture injected into the cylinders is ignited by spark discharge from the respective spark plug 22.

The intake valves 29 of the engine 11 are provided with a variable intake valve lifter 30 that varies the amount of lift of the intake valves 29. The variable intake valve lifters 30 can be switched between low lift mode and high lift mode. In low lift mode, as illustrated in FIG. 2, the variable intake valve lifter 30 operates a cam for driving and opening/closing the intake valve 29 for low lift of the intake valve 29. As such, the variable intake valve lifter 30 reduces the amount of lift of the intake valve 29 and reduces a valve opening duration (i.e., the amount of time that the intake valve 29 is open is reduced). In high lift mode, as illustrated in FIG. 3, the variable intake valve lifter 30 operates a cam for driving and opening/closing the intake valve 29 for higher lift of the intake valve 29. As such, the amount of lift of the intake valve 29 is increased, and the valve opening duration is increased (i.e., the amount of time that the intake valve is open is increased).

As illustrated in FIG. 1, a catalyst 24 (e.g., a three way catalyst) is provided in the exhaust pipe 23 of the engine 11 for purifying exhaust gas and reducing CO, HC, NOx, and the like therein. An exhaust gas sensor 25 (e.g., an air-fuel ratio sensor, oxygen sensor, or the like) is provided upstream of the catalyst 24 for detecting the air-fuel ratio of exhaust gas, whether the mixture is rich/lean, or the like.

In the cylinder block of the engine 11, there are installed a cooling water temperature sensor 26 and a crank angle sensor 27. The cooling water temperature sensor 26 detects cooling water temperature, and the crank angle sensor 27 outputs a pulse signal each time the crank shaft of the engine 11 rotates through a predetermined crank angle. Based on the output signal of the crank angle sensor 27, a crank angle and the number of engine revolutions are detected.

The output of these sensors are inputted to an engine control unit 28 (hereafter, referred to as “ECU”). In one embodiment, the ECU 28 is a microcomputer that executes various engine control programs stored in a built-in ROM (i.e., storage media). The ECU 28 thereby controls the injection quantity of the fuel injection valves 21 and the ignition timing of the spark plugs 22 in accordance with the state of engine operation.

The ECU 28 executes a variable intake valve control program and thereby switches the control mode of the variable intake valve lifters 30 between low lift mode and high lift mode in accordance with the state of engine operation. In low lift mode, as illustrated in FIG. 2, the ECU 28 reduces the amount of lift of the intake valve 29 and reduces a valve opening duration. In high lift mode, as illustrated in FIG. 3, the ECU 28 increases the amount of lift of the intake valves 29 and increases a valve opening duration.

To reduce the likelihood of a rich or lean spike, the ECU 28 executes a fuel injection timing computation program. Generally, when the amount of lift of the intake valve is varied (e.g., switching from high lift to low lift mode or from low lift to high lift mode) the fuel injection timing computation program corrects and varies fuel injection termination timing according to the variation of the lift of the intake valve. For instance, when the variable intake valve lifter 30 is switched from low lift mode to high lift mode and the amount of lift of an intake valve 29 is increased, the fuel injection termination timing is corrected and advanced. Also, when a variable intake valve lifter 30 is switched from high lift mode to low lift mode and the amount of lift of an intake valve 29 is reduced, the fuel injection termination timing is corrected and delayed.

When the fuel injection termination timing is corrected and advanced, the mixing time for injected fuel and intake air is accordingly increased, and the air-fuel ratio distribution of fuel mixture in the cylinder can be made uniform. Therefore, when the amount of lift of the intake valve 29 is increased, the fuel injection termination timing is corrected and advanced to make the air-fuel ratio distribution of fuel mixture in the cylinder more uniform. Also, even though the valve closing timing of the intake valve 29 is delayed more and the back flow of fuel mixture in the cylinder is increased, the average air-fuel ratio in the cylinder can be kept substantially constant. As a result, the occurrence of a lean spike is less likely.

When the fuel injection termination timing is corrected and delayed, the quantity of injected fuel sticking to the intake valve 29 is increased. Thus, the quantity of fuel sucked into the cylinder can be reduced. Therefore, when the amount of lift of an intake valve 29 is reduced, the fuel injection termination timing is corrected and delayed to reduce the quantity of fuel sucked into the cylinder. Thus, even though the valve closing timing of the intake valve 29 is advanced and the back flow of rich gas in the cylinder is reduced (i.e., the residual volume of rich gas in the cylinder is increased), the average air-fuel ratio in the cylinder can be kept substantially constant. As a result, the occurrence of a rich spike is less likely.

Hereafter, description will be given to the details of the processing of the fuel injection timing computation program executed by the ECU 28 as illustrated in FIG. 4. The fuel injection timing computation program illustrated in FIG. 4 is executed at predetermined intervals while the engine is in operation. When the program is started, the current amount of lift of the intake valve is computed at Step S101, and the current valve closing timing of the intake valve is computed at Step S102.

Thereafter, the ECU proceeds to Step S103, and computes a basic injection quantity based on the current intake air quantity and the target air-fuel ratio using a map, a mathematical expression, or the like. Thereafter, the ECU proceeds to Step S104, and computes basic fuel injection termination timing based on the current engine revolution speed and quantity of air filled in cylinder. (The basic fuel injection termination timing is time delayed behind the time of initiation of basic fuel injection by a fuel injection time.)

At Step S105, thereafter, the ECU determines whether or not a variation in the amount of lift of the intake valve is equal to or larger than a predetermined value. The variation in the amount of lift is, for example, the difference between the current amount of lift of the intake valve and the previous amount of lift of the intake valve. Next, in Step S106, the ECU determines whether or not a variation in the valve closing timing of the intake valve is equal to or lager than a predetermined value. The variation in the valve closing timing is, for example, the difference between the current valve closing timing of the intake valve and the previous valve closing timing of the intake valve.

In cases where the ECU determines that the variation in the amount of lift of the intake valve is greater than or equal to the predetermined value at Step 105 and that the variation in the valve closing timing of the intake valve is greater than or equal to the predetermined value at Step S106, the ECU determines that the control mode of the variable intake valve lifter 30 has been switched. Then, in Step S107 the ECU computes an amount of correction, A, for the fuel injection termination timing based on the valve closing timing of the intake valve using a map, a mathematical expression, or the like.

The amount of correction, A, is set such that, when the variable intake valve lifter 30 is switched from low lift mode to high lift mode and the valve closing timing of the intake valve is delayed more, the fuel injection termination timing is corrected and advanced. In other words, when the amount of lift of the intake valve is varied and the valve closing timing of the intake valve is delayed more, the fuel injection termination timing is corrected and advanced. Also, when the variable intake valve lifter 30 is switched from high lift mode to low lift mode and the valve closing timing of the intake valve is advanced, the fuel injection termination timing is corrected and delayed. In other words, when the amount of lift of the intake valve is reduced and the valve closing timing of the intake valve is advanced, the fuel injection termination timing is corrected and delayed.

After the computation of the amount of correction, A, the ECU proceeds to Step S108 to obtain a final fuel injection termination timing. Specifically, the ECU corrects the basic fuel injection termination by adding the correction amount, A, to the basic fuel injection termination timing to compute the final fuel injection termination timing (i.e., Final Fuel Injection Termination Timing=Basic Fuel Injection Termination Timing+A).

Thus, when the variable intake valve lifter 30 is switched from low lift mode to high lift mode to increase the amount of lift of the intake valve, the fuel injection termination timing is corrected and advanced. Also, when the variable intake valve lifter 30 is switched from high lift mode to low lift mode to reduce the amount of lift of the intake valve 29, the fuel injection termination timing is corrected and delayed.

In cases where the ECU determines that the variation in the amount of lift of the intake valve is smaller than the predetermined value at Step S105, or in cases where the ECU determines that the variation in the valve closing timing of the intake valve is smaller than the predetermined value at Step S106, the ECU determines that the current control mode of the variable intake valve lifter 30 is maintained, and Step S109 follows. In Step S109, the ECU sets the basic fuel injection termination timing, computed at Step S104, as the final fuel injection termination timing (i.e., Final Fuel Injection Termination Timing=Basic Fuel Injection Termination Timing).

In summary, when the variable intake valve lifter 30 is switched from low lift mode to high lift mode to increase the amount of lift of the intake valve 29, the fuel injection termination timing is corrected and advanced to make the air-fuel ratio distribution of fuel mixture in the cylinder more uniform. Therefore, even though the valve closing timing of the intake valve 29 is delayed and the back flow of fuel mixture in the cylinder is increased, the average air-fuel ratio in the cylinder can be kept substantially constant. Thus, when the amount of lift of the intake valve 29 is increased, the occurrence of a lean spike is less likely. As a result, torque shock due to a lean spike is less likely, drivability is enhanced, and exhaust emissions are improved.

Meanwhile, when the variable intake valve lifter 30 is switched from high lift mode to low lift mode to reduce the amount of lift of the intake valve 29, the fuel injection termination timing is corrected and delayed. The quantity of fuel sucked into the cylinder is thereby reduced. Therefore, even though the valve closing timing of the intake valve 29 is advanced, and the back flow of rich gas in the cylinder is reduced (i.e., the residual volume of rich gas in the cylinder is increased), the average air-fuel ratio in the cylinder can be kept substantially constant. Thus, when the amount of lift of the intake valve 29 is reduced, the occurrence of a rich spike is less likely. As a result, torque shock due to a rich spike is less likely, drivability is enhanced, and exhaust emissions are improved.

Second Embodiment

Next, description will be given to the second embodiment of the invention with reference to FIG. 5. Generally, when the variable intake valve lifter 30 is switched from low lift mode to high lift mode to increase the amount of lift of the intake valve 29, the injection quantity is corrected and increased to reduce the likelihood of a lean spike. Also, when the variable intake valve lifter 30 is switched from high lift mode to low lift mode to reduce the amount of lift of the intake valve 29, the injection quantity is corrected and reduced to reduce the likelihood of a rich spike.

The injection quantity computation program illustrated in FIG. 5 is executed at predetermined intervals while the engine is in operation. When the program is started, the current amount of lift of the intake valve is computed in Step S201, and the current valve closing timing of the intake valve is computed in step S202. Then in Step S203, the ECU computes a basic injection quantity based on the current intake air quantity and a target air-fuel ratio.

Next in Step S204, the ECU determines whether or not a variation in the amount of lift of the intake valve greater than or equal to a predetermined value. In the next Step S205, the ECU determines whether or not a variation in the valve closing timing of the intake valve is greater than or equal to a predetermined value.

In cases where the ECU determines that the variation in the amount of lift of the intake valve is greater than or equal to the predetermined value at Step S204 and that the variation in the valve closing timing of the intake valve is greater than or equal to the predetermined value at Step S205, the ECU determines that the control mode of the variable intake valve lifter 30 has been switched. Then in Step S206, the ECU prohibits purge control such that evaporative gas, produced by fuel in the fuel tank being evaporated, is not purged into the air intake system of the engine 11.

Thereafter, the ECU proceeds to Step S207, and computes a fuel correction factor α based on the variation in the valve closing timing of the intake valve using a map, a mathematical expression, or the like. Thereafter, the ECU proceeds to Step S208 and computes a fuel correction factor β based on the variation in the amount of lift of the intake valve using a map, a mathematical expression, or the like.

In this map of fuel correction factor α and map of fuel correction factor β, the fuel correction factor α and the fuel correction factor β are set so that, when the variable intake valve lifter 30 is switched from low lift mode to high lift mode and the valve closing timing of the intake valve is delayed, the back flow of rich gas in the cylinder is increased (i.e., the residual volume of rich gas in the cylinder is reduced). In other words, when the amount of lift of the intake valve is increased and the valve closing timing of the intake valve is delayed, the back flow of rich gas in the cylinder is increased. Therefore, the injection quantity is corrected and accordingly increased. Also, when the variable intake valve lifter 30 is switched from high lift mode to low lift mode and the valve closing timing of the intake valve is advanced, the back flow of rich gas in the cylinder is reduced (i.e., the residual volume of rich gas in the cylinder is increased). In other words, when the amount of lift of the intake valve is reduced and the valve closing timing of the intake valve is advanced, the back flow of rich gas in the cylinder is reduced. Therefore, the injection quantity is corrected and accordingly reduced.

After the computation of fuel correction factor α and fuel correction factor β, the ECU proceeds to Step S209. Specifically, the ECU corrects the basic injection quantity and computes a final injection quantity by multiplying the basic injection quantity by the fuel correction factor, α, and the fuel correction factor, β (i.e., Final Injection Quantity Basic Injection Quantity×Fuel Correction Factor α×Fuel Correction Factor β).

Thus, when the variable intake valve lifter 30 is switched from low lift mode to high lift mode to increase the amount of lift of the intake valve, the injection quantity is corrected and increased. Also, when the variable intake valve lifter 30 is switched from high lift mode to low lift mode to reduce the amount of lift of the intake valve 29, the injection quantity is corrected and reduced.

In cases where the ECU determines that the variation in the amount of lift of the intake valve is less than the predetermined value at Step S204, or in cases where the ECU determines that the variation in the valve closing timing of the intake valve is less than the predetermined value at Step S205, Step S210 follows. Specifically, the ECU determines that the current control mode of the variable intake valve lifter 30 is maintained, and the ECU sets the basic injection quantity, computed at Step S203, as final injection quantity (i.e., Final Injection Quantity=Basic Injection Quantity).

Thus, when the variable intake valve lifter 30 is switched from low lift mode to high lift mode to increase the amount of lift of the intake valve 29, the injection quantity is corrected and increased. Therefore, even though the amount of lift of the intake valve 29 is increased, the valve closing timing of the intake valve 29 is delayed, and the back flow of rich gas in the cylinder is increased (i.e., the residual volume of rich gas in the cylinder is reduced), the injection quantity can be corrected and accordingly increased to increase the quantity of fuel sucked into the cylinder. Also, the average air-fuel ratio in the cylinder can be kept substantially constant. Thus, when the amount of lift of the intake valve 29 is increased, a lean spike is less likely, drivability is improved, and the exhaust emission is also improved.

Meanwhile, when the variable intake valve lifter 30 is switched from high lift mode to low lift mode to reduce the amount of lift of the intake valve 29, the injection quantity is corrected and reduced. Therefore, even though the amount of lift of the intake valve 29 is reduced, the valve closing timing of the intake valve 29 is advanced, and the back flow of rich gas in the cylinder is reduced (i.e., the residual volume of rich gas in the cylinder is increased), the injection quantity can be corrected and accordingly reduced to reduce the quantity of fuel sucked into the cylinder. Also, the average air-fuel ratio in the cylinder can be kept substantially constant. Thus, when the amount of lift of the intake valve 29 is reduced, a rich spike is less likely, the drivability is improved, and the exhaust emission is also improved.

When the amount of lift of the intake valve 29 is varied, a variation (i.e., increment or decrement) in the back flow of rich gas in a cylinder changes in accordance with a variation in the valve closing timing of the intake valve 29. In the second embodiment, this change is taken into account, and when the amount of lift of the intake valve 29 is varied, a fuel correction factor, α, is set based on a variation in the valve closing timing of the intake valve 29. Therefore, it is possible to appropriately set a fuel correction factor, α, in accordance with a change (i.e., increment or decrement) in variation in the back flow of rich gas corresponding to a variation in the valve closing timing of the intake valve 29. As a result, the occurrence of a lean spike or a rich spike is less likely.

Furthermore in this embodiment, when the amount of lift of the intake valve 29 is varied, purge control is prohibited. Therefore, external disturbance to the air-fuel ratio can be avoided when the amount of lift of the intake valve is varied. Thus, it is possible to enhance the accuracy of controlling the air-fuel ratio of fuel mixture when the amount of lift of an intake valve is varied, and the occurrence of a lean spike or a rich spike is even less likely.

Third Embodiment

Description will be given to the third embodiment of the invention with reference to FIG. 6 and FIG. 7.

As illustrated in FIG. 6, the engine 11 is a four-valve engine having four valves for each cylinder. Each cylinder is provided with two intake ports 31 and two exhaust ports 32. Each intake port 31 is provided with an intake valve 29, and each exhaust port 32 is provided with an exhaust valve 33.

A swirl valve 34 (i.e., a swirl flow generating device) is included in either of the two intake ports 31 of the cylinder. The swirl valve 34 generates a swirl flow in the corresponding cylinder. The swirl valve 34 of each cylinder is so constructed that it is driven and opened/closed by a motor or the like (not shown). The ECU 28 executes the swirl valve control program illustrated in FIG. 7. As such, when the engine is in a predetermined operating range (e.g. low-revolution, low-load operating range, etc.), the swirl valve 34 is closed to generate a swirl flow in the cylinder.

Hereafter, description will be given to the details of the processing of the swirl valve control program carried out by the ECU 28 in the third embodiment, with reference to FIG. 7. The swirl valve control program illustrated in FIG. 7 is executed at predetermined intervals while the engine is in operation. When the program is started, the current engine revolution speed is computed at Step S301. At the next step, Step S302, the current quantity of air filled in cylinder is computed.

Thereafter, the ECU proceeds to Step S303 wherein a basic injection quantity is computed based on the current engine revolution speed and quantity of air filled in cylinder using a map, a mathematical expression, or the like. Thereafter, the ECU proceeds to Step S304, and computes a basic fuel injection termination timing based on the current engine revolution speed and quantity of air filled in cylinder. (The basic fuel injection termination timing is time delayed behind the time of initiation of basic fuel injection by a fuel injection time.)

At Step S305, thereafter, the ECU determines whether or not the engine is in a low-revolution operating range according to whether the engine revolution speed is less than or equal to a predetermined value. At the next step, or Step S306, it determines whether or not the engine is in a low-load operating range according to whether the quantity of air filled in cylinder is less than or equal to a predetermined value.

In cases where the ECU determines that the engine is in a low-revolution operating range at Step S305 and that the engine is in a low-load operating range at Step S306, Step S307 follows, and the swirl valve 34 of each cylinder is closed. As such, intake air is let into each cylinder through only either of the two intake ports 31 of the cylinder to generate a swirl flow in the cylinder. The air-fuel ratio distribution of fuel mixture in the cylinder is thereby made more uniform.

In cases where the ECU determines the engine is in a high-revolution operating range at Step S305 or that the engine is in a high-load operating range at Step S306, Step S308 follows, and the swirl valve 34 is opened for each cylinder. As such, intake air is let into each cylinder through the two intake ports 31 of the cylinder, and a sufficient quantity of air filled in cylinder is ensured.

Thus, when the engine is in a predetermined engine operating range (e.g. low-revolution, low-load operating range), a swirl valve 34 is closed to generate a swirl flow in the relevant cylinder, and the air-fuel ratio distribution of fuel mixture in the cylinder is thereby made more uniform. Therefore, in this engine operating range (i.e., an operating range in which the air-fuel ratio distribution of fuel mixture in each cylinder is made more uniform by a swirl flow), even though the amount of lift of the intake valve 29 is varied by the variable intake valve lifter 30 and the valve closing timing of the intake valve 29 is delayed or advanced to increase or reduce the back flow of fuel mixture in the cylinder, the average air-fuel ratio in the cylinder can be kept substantially constant. Thus, when the amount of lift of the intake valve is varied, the occurrence of a lean spike or a rich spike is less likely, thereby improving the drivability and the exhaust emission.

Fourth Embodiment

Description will be given to the fourth embodiment of the invention with reference to FIG. 8 and FIG. 9.

In the fourth embodiment, a variable valve timing mechanism (not shown) is provided which is capable of varying the valve timing (opening/closing timing) of the intake valve 29 at high speed by a motor or the like. When the amount of lift of the intake valve 29 is varied by the variable intake valve lifter 30, the variable valve timing mechanism is so controlled that the valve closing timing of the intake valve 29 is not changed.

More specific description will be given. When the variable intake valve lifter 30 is switched from low lift mode to high lift mode to increase the amount of lift of the intake valve 29, as illustrated in FIG. 8, the valve timing of the intake valve 29 is instantaneously advanced by the variable valve timing mechanism. As such, the valve closing timing of the intake valve 29 remains constant. Thereafter, the valve timing of the intake valve 29 is gradually delayed by the variable valve timing mechanism to return the valve closing timing of the intake valve 29 to the normal valve closing timing in high lift mode.

When the variable intake valve lifter 30 is switched from high lift mode to low lift mode to reduce the amount of lift of the intake valve 29, as illustrated in FIG. 9, the valve timing of the intake valve 29 is instantaneously delayed by the variable valve timing mechanism. As such, the valve closing timing of the intake valve 29 is not changed. Thereafter, the valve timing of the intake valve 29 is gradually advanced by the variable valve timing mechanism to return the valve closing timing of the intake valve 29 to the normal valve closing timing in low lift mode.

Thus, when variable intake valve lifter 30 varies the amount of lift of the intake valve 29, the variable valve timing mechanism is controlled so that the valve closing timing of the intake valve 29 remains approximately constant. Therefore, when the amount of lift of the intake valve is varied, the back flow of rich gas in the cylinder can remain approximately constant, and the average air-fuel ratio in the cylinder can remain substantially constant. Accordingly, when the amount of lift of the intake valve is varied, the occurrence of a lean spike or a rich spike is unlikely to thereby improve the drivability and the exhaust emission.

In the first to fourth embodiments mentioned above, a system is equipped with a variable intake valve lifter that performs switching between low lift mode and high lift mode and thereby instantaneously varies the amount of lift of an intake valve. The invention is not limited to these embodiments. For instance, it may be applied to systems that are equipped with a variable intake valve lifter that continuously varies the amount of lift of an intake valve by a motor or the like. It may also be applied to an electromagnetically driven intake valve, and the like, and in which the amount of lift of the intake valve can be instantaneously varied.

While only the selected preferred embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the preferred embodiments according to the present invention is provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

Claims

1. A control apparatus for an internal combustion engine that varies the amount of lift of an intake valve, the control apparatus comprising:

a fuel injection timing correcting device that, when the amount of lift of the intake valve is varied, corrects and varies fuel injection termination timing according to the variation of the lift of the intake valve.

2. The control apparatus according to claim 1, wherein the fuel injection timing correcting device corrects and advances fuel injection termination timing when the amount of lift of the intake valve is increased.

3. The control apparatus according to claim 1, wherein the fuel injection timing correcting device corrects and delays fuel injection termination timing when the amount of lift of the intake valve is reduced.

4. A control apparatus for an internal combustion engine that varies the amount of lift of an intake valve for a cylinder, the control apparatus comprising:

a swirl flow generating device that generates a swirl flow in the cylinder.

5. A control apparatus for an internal combustion engine equipped with a variable intake valve lifter that varies the amount of lift of an intake valve and a variable valve timing mechanism that varies the opening/closing timing of the intake valve, the control apparatus comprising:

an intake valve closing timing correcting device that, when the amount of lift of the intake valve is varied by the variable intake valve lifter, controls the variable valve timing mechanism so that the valve closing timing of the intake valve remains substantially constant.

6. A control apparatus for an internal combustion engine that varies the amount of lift of an intake valve, the control apparatus comprising:

an injection quantity correcting device that, when the amount of lift of the intake valve is varied, corrects and varies an injection quantity.

7. A control apparatus according to claim 6, wherein the injection quantity correcting device corrects and increases an injection quantity when the amount of lift of the intake valve is increased by the variable intake valve lifter.

8. A control apparatus according to claim 6, wherein the injection quantity correcting device corrects and reduces an injection quantity when the amount of lift of the intake valve is reduced by the variable intake valve lifter.

9. The control apparatus according to claim 6, wherein the injection quantity correcting device sets an amount of correction for injection quantity based on a variation in the valve closing timing of the intake valve when the amount of lift of the intake valve is varied.

10. The control apparatus according to claim 6, further comprising an evaporative gas purge prohibiting device that, when the amount of lift of the intake valve is varied, prohibits purge of evaporative gas into the air intake system.

11. A method of controlling fuel injection timing for an internal combustion engine that varies the amount of lift of an intake valve, the method comprising:

correcting and varying fuel injection termination timing according to the variation of the lift of the intake valve when the amount of lift of the intake valve is varied.

12. The method of claim 11, wherein the correcting and varying comprises correcting and advancing fuel injection termination timing when the amount of lift of the intake valve is increased.

13. The method of claim 11, wherein the correcting and varying comprises correcting and delaying fuel injection termination timing when the amount of lift of the intake valve is reduced.

14. A method of controlling opening/closing timing of an intake valve of an internal combustion engine equipped with a variable intake valve lifter that varies the amount of lift of an intake valve and a variable valve timing mechanism that varies the opening/closing timing of the intake valve, the method comprising:

controlling the variable valve timing mechanism so that the valve closing timing of the intake valve remains substantially constant when the amount of lift of the intake valve is varied by the variable intake valve lifter.

15. A method of controlling an injection quantity of an intake valve of an internal combustion engine that varies the amount of lift of the intake valve, the method comprising:

correcting and varying an injection quantity when the amount of lift of the intake valve is varied.

16. The method according to claim 15, wherein the correcting and varying comprises correcting and increasing an injection quantity when the amount of lift of the intake valve is increased by the variable intake valve lifter.

17. The method according to claim 15, wherein the correcting and varying comprises correcting and reducing an injection quantity when the amount of lift of the intake valve is reduced by the variable intake valve lifter.

18. The method according to claim 15, further comprising setting an amount of correction for injection quantity based on a variation in the valve closing timing of the intake valve when the amount of lift of the intake valve is varied.

19. The method according to claim 15, further comprising prohibiting purge of evaporative gas into the air intake system when the amount of lift of the intake valve is varied.