WO2010020852A1

WO2010020852A1 - Engine-start control device and method for internal combustion engine

Info

Publication number: WO2010020852A1
Application number: PCT/IB2009/006467
Authority: WO
Inventors: Hideaki Kosuge; Mamoru Yoshioka; Makoto Tomimatsu
Original assignee: Toyota Jidosha Kabushiki Kaisha; Nippon Soken, Inc.
Priority date: 2008-08-22
Filing date: 2009-08-06
Publication date: 2010-02-25
Also published as: JP2010048194A

Abstract

At least in the first engine-start cycle, the closing timing (EVC) of an exhaust valve is controlled so that the closing timing (EVC) is at the advanced side of the intake top dead center, and so that the crank angle from the closing timing (EVC) to the intake top dead center is larger than the crank angle between the opening timing (IVO) of an intake valve and the intake top dead center. Besides, at least in the first engine-start cycle, the fuel injection timing of the fuel injection valve so that the fuel injection period overlaps with the opening timing (IVO) of the intake valve. More particularly, the invention relates to an engine-start control device and method for a port-injection internal combustion engine that injects fuel into intake ports. The in-cylinder gas compressed inside the combustion chamber during the time from the closing timing of the exhaust valve till the opening timing of the intake valve is blown back into the intake port as the intake valve opens. Since the fuel injection period in the first engine-start cycle in the start-up of the engine overlaps with the opening timing of the intake valve, the in-cylinder gas blown back into the intake port collides with the fuel spray-injected from the fuel injection valve. Due to the collision with the in-cylinder gas, the fuel spray is stirred, forming a further vaporized fuel vapor or a further atomized fuel spray.

Description

ENGINE-START CONTROL DEVICE AND METHOD FOR INTERNAL

COMBUSTION ENGINE

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates to an engine-start control device and method for an internal combustion engine. More particularly, the invention relates to an engine-start control device and method for a port-injection internal combustion engine that injects fuel into intake ports. 2. Description of the Related Art

[0002] A known technology for restraining the emission of HC when the internal combustion engine is started is, for example, a system described in Japanese Patent

Application Publication No. 2007-40150 (JP-A-2007-40150). In this system, in the first engine cycle during the start-up of the engine during which combustion gas is not present in the combustion chamber, so-called intake asynchronous injection is performed to provide a long time for the evaporation of fuel inside the intake port, and therefore the vaporization of fuel is promoted. Besides, in the second and later cycles in which combustion gas is present in the combustion chamber, the closing timing of the exhaust valve is advanced than the intake top dead center, and the fuel injection timing is set in accordance with the opening timing of the intake valve, whereby the vaporization of fuel is promoted by high-temperature combustion gas that is blown back into the intake port from inside the combustion chamber.

[0003] However, the system described in Japanese Patent Application Publication No. 2007-40150 (JP-A-2007-40150) has a limitation in the fuel vaporization promoting effect by securing enough vaporization time in the first engine cycle in the start-up of the engine. In the first cycle in the start-up of the engine in which combustion gas is not present, the temperature in the intake port is strongly affected by the ambient temperature. Therefore, when the ambient temperature is low, mere the securing of a good vaporization time may possibly fail to achieve sufficient vaporization of fuel. SUMMARY OF THE INVENTION

[0004] The invention provides an engine-start control device and method for an internal combustion engine that is capable of promoting vaporization or atomization of fuel during a start-up time of the internal combustion engine and, particularly, in the first engine cycle during the start-up time.

[0005] A first aspect of the invention relates to an engine-start control device for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, and an exhaust valve whose closing timing is adjustable. The engine-start control device of the internal combustion engine includes: exhaust valve closing timing control means for, at least in a first engine-start cycle, controlling the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center, and so that a crank angle from the closing timing to the intake top dead center is larger than the crank angle between an opening timing of an intake valve and the intake top dead center; and fuel injection timing control means for, at least in the first engine-start cycle, controlling a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve.

[0006] According to the foregoing aspect, in the first engine-start cycle in the start-up of the engine, since the closing timing of the exhaust valve is controlled so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center, and so that a crank angle from the closing timing to the intake top dead center is larger than the crank angle between an opening timing of an intake valve and the intake top dead center, the pressure in the in-cylinder gas at the opening timing of the intake valve is higher than the pressure of the in-cylinder gas at the closing timing of the exhaust valve. Therefore, the in-cylinder gas compressed inside the combustion chamber during the time from the closing timing of the exhaust valve till the opening timing of the intake valve is blown back into the intake port as the intake valve opens. Since the fuel injection period in the first engine-start cycle in the start-up of the engine overlaps with the opening timing of the intake valve, the in-cylinder gas blown back into the intake port collides with the fuel spray-injected from the fuel injection valve. Due to the collision with the in-cylinder gas, the fuel spray is stirred, forming a further vaporized fuel vapor or a further atomized fuel spray.

[0007] In the foregoing aspect of the invention, the fuel injection timing control means may control the fuel injection timing so that a substantially central portion of the fuel injection period overlaps with the opening timing of the intake valve.

[0008] Since the fuel spray produced during a substantially central portion of the fuel injection period has a small and stable or consistent particle diameter, the foregoing construction is able to heighten the overall effect of promoting the vaporization or atomization of fuel spray through collision with in-cylinder gas.

[0009] In the foregoing aspect of the invention, the fuel injection timing control means may control the fuel injection timing so that the fuel injection period is divided into a plurality of fuel injection periods, and so that one of the divided fuel injection periods overlaps with the opening timing of the intake valve, and so that an other one period of the divided fuel injection periods is within a closure period of the intake valve.

[0010] According to this construction, a portion of the fuel can be vaporized or further atomized through the collision of fuel spray with in-cylinder gas, and the rest of the fuel can be vaporized by securing an enough vaporization time inside the intake port.

[0011] In the foregoing aspect, the amount of fuel injected during the one of the periods may be smaller than the amount of fuel injected during the other one of the periods.

[0012] In the foregoing aspect, in a second and later engine-start cycles, the fuel injection timing control means may reduce the fuel injection period that overlaps with the opening timing of the intake valve, according to rise in the internal combustion engine rotation speed.

[0013] According to this construction, since the fuel injection period that overlaps with the opening timing of the intake valve is shortened in accordance with the blow-back time that shortens with rises in the internal combustion engine rotation speed, the occurrence of the fuel spray that cannot receive the stirring effect of the blow-back can be restrained.

[0014] In the foregoing aspect, the fuel injection timing control means may reduce a fuel injection amount injected during the fuel injection period that overlaps with the opening timing of the intake valve in the second and later engine-start cycles, according to rise in the internal combustion engine rotation speed.

[0015] In the foregoing aspect, the fuel injection timing control means may cause the fuel injection amount injected during the fuel injection period that overlaps with the opening timing of the intake valve in the second and later engine-start cycles to be the amount of fuel that is injectable in a range of 30 degrees or less in crank angle from the opening timing of the intake valve.

[0016] In the foregoing aspect, the fuel injection timing control means may cause a fuel injection end timing that overlaps with the opening timing of the intake valve in the second and later engine-start cycles to be 30 degrees or less in crank angle than a retarded side of the opening timing of the intake valve. [0017] In the foregoing aspect, the fuel injection timing control means may cause a fuel injection start timing that overlaps with the opening timing of the intake valve in the second and later engine-start cycles to be 30 degrees or less in' crank angle than an advanced side of the opening timing of the intake valve.

[0018] In the foregoing aspect, the fuel injection timing control means may control the fuel injection timing if a water temperature of the internal combustion engine is lower than or equal to a predetermined temperature.

[0019] In the foregoing aspect, the engine-start control device of the internal combustion engine may further include intake valve opening timing control means for, at least in the first engine-start cycle, controlling the opening timing of the intake valve so that the opening timing of the intake valve is when pressure in a combustion chamber of the internal combustion engine is higher than pressure in the intake port.

[0020] In the foregoing aspect, the engine-start control device of the internal combustion engine may further include intake valve opening timing control means for, at least in the engine-start-time first cycle, controlling the opening timing of the intake valve so that the opening timing of the intake valve is when a blow-back from the combustion chamber of the internal combustion engine to the intake port occurs.

[0021] A second aspect of the invention relates to an engine-start control device for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, an exhaust valve whose closing timing is adjustable, and an intake valve whose opening timing is adjustable. The engine-start control device for the internal combustion engine includes: exhaust valve closing timing control means for, at least in a first engine-start cycle, controlling the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center; intake valve opening timing control means for, at least in the first engine-start cycle, controlling the opening timing of the intake valve so that the opening timing of the intake valve is when pressure in a combustion chamber of the internal combustion engine is higher than pressure in the intake port; and fuel injection timing control means for, at least in the first engine-start cycle, controlling a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve.

[0022] According to the second aspect of the invention, in the first engine-start cycle in the start-up of the engine, since the closing timing of the exhaust valve is at the advanced side of the intake top dead center, the in-cylinder gas is compressed as the piston ascends after the exhaust valve closes. The pressure in the combustion chamber changes in accordance with the upward and downward movements of the piston afterwards. When the pressure in the combustion chamber of the internal combustion engine is higher than the pressure in the intake port, the intake valve is opened. Therefore, when the intake valve opens, the in-cylinder gas compressed inside the combustion chamber is blown back into the intake port. Since the fuel injection period in the first engine-start cycle in the start-up of the engine overlaps with the opening timing of the intake valve, the in-cylinder gas blown back into the intake port collides with the fuel spray-injected from the fuel injection valve. Due to the collision with the in-cylinder gas, the fuel spray is stirred, forming a further vaporized fuel vapor, or a further atomized fuel spray. [0023] A third aspect of the invention relates to an engine-start control device for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, an exhaust valve whose closing timing is adjustable, and an intake valve whose opening timing is adjustable. The engine-start control device for the internal combustion engine includes: exhaust valve closing timing control means for, at least in a first engine-start cycle, controlling the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center; intake valve opening timing control means for, at least in the first engine-start cycle, controlling the opening timing of the intake valve so that the opening timing of the intake valve is when a blow-back from a combustion chamber to the intake port occurs; and fuel injection timing control means for, at least in the first engine-start cycle, controlling a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve.

[0024] According to the third aspect, in the first engine-start cycle in the start-up of the engine, since the closing timing of the exhaust valve is at the advanced side of the intake top dead center, the in-cylinder gas is compressed as the piston ascends after the exhaust valve closes. The pressure in the combustion chamber changes in accordance with the upward and downward movements of the piston afterwards, and the pressure difference between the pressure in the intake port and the pressure in the combustion chamber correspondingly changes. When the blow-back from the combustion chamber into the intake port occurs, the intake valve is opened. That is, when the intake valve opens in the first engine-start cycle in the start-up of the engine, the in-cylinder gas is blown back into the intake port from the combustion chamber. Since the fuel injection period in the first engine-start cycle in the start-up of the engine overlaps with the opening timing of the intake valve, the in-cylinder gas blown back into the intake port collides with the fuel spray-injected from the fuel injection valve. Due to the collision with the in-cylinder gas, the fuel spray is stirred, forming a further vaporized fuel vapor, or a further atomized fuel spray.

[0025] In the first to third aspects of the invention, the intake valve opening timing control means may cause the opening timing of the intake valve to be at a retarded side of the closing timing of the exhaust valve.

[0026] According to this construction, since the opening timing of the intake valve is set at the retarded side than the closing timing of the exhaust valve, the in-cylinder gas can be compressed in a period from the closing timing of the retarded side till the opening timing of the opening timing.

[0027] In the first to third aspects, the intake valve opening timing control means may cause the opening timing of the intake valve to be a crank angle than an advanced side of an intake top dead center, the crank angle being equal to or smaller than the crank angle from the closing timing of the exhaust valve to the intake top dead center.

[0028] According to this construction, since the opening timing of the intake valve is set at a crank angle than the advanced side of the intake top dead center, the crank angle being equal to or smaller than the crank angle from the closing timing of the exhaust valve to the intake top dead center, the pressure of the in-cylinder gas at the opening timing of the intake valve can certainly be made higher than the pressure of the in-cylinder gas at the closing timing of the exhaust valve.

[0029] In the first to third aspects, the exhaust valve closing timing control means may cause the closing timing of the exhaust valve to be 30 degrees or less in crank angle than an advanced side of an intake top dead center. , [0030] According to this construction, since the closing timing of the exhaust valve is set at 30 degrees or less in crank angle than the advanced side of the intake top dead center, the in-cylinder gas can be appropriately compressed.

[0031] A fourth aspect of the invention relates to an engine-start control method for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, and an exhaust valve whose closing timing is adjustable. The engine-start control method for the internal combustion engine includes: controlling, at least in a first engine-start cycle, the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center, and so that a crank angle from the closing timing to the intake top dead center is larger than the crank angle between an opening timing of an intake valve and the intake top dead center; and controlling, at least in the first engine-start cycle, a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve. [0032] A fifth aspect of the invention relates to an engine-start control method for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, an exhaust valve whose closing timing is adjustable, and an intake valve whose opening timing is adjustable. The engine-start control method for the internal combustion engine includes: controlling, at least in a first engine-start cycle, the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center; controlling, at least in the first engine-start cycle, the opening timing of the intake valve so that the opening timing of the intake valve is when pressure in a combustion chamber of the internal combustion engine is higher than pressure in the intake port; and controlling, at least in the first engine-start cycle, a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve.

[0033] A sixth aspect of the invention relates to an engine-start control method for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, an exhaust valve whose closing timing is adjustable, and an intake valve whose opening timing is adjustable. The engine-start control method for the internal combustion engine includes: controlling, at least in a first engine-start cycle, the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center; controlling, at least in the engine-start-time first cycle, the opening timing of the intake valve so that the opening timing of the intake valve is when a blow-back from a combustion chamber to the intake port occurs; and controlling, at least in the first engine-start cycle, a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG 1 shows a general construction of an internal combustion engine to which an engine-start control device of a first embodiment of the invention is applied;

FIG 2 shows a routine of an exhaust valve timing control that is executed in the first embodiment of the invention; FIG 3 shows diagrams representing the opening/closing timing of an intake valve and an exhaust valve in accordance with the first embodiment of the invention during an exhaust valve early-closure control and during an exhaust valve normal control; ■ FIG 4 illustrates an engine-start-time fuel injection timing control that is executed in the first embodiment of the invention; FIG 5 shows changes in the particle diameter of fuel spray during a fuel injection period;

FIG 6 shows a routine of an engine-start-time fuel injection timing control that is executed in a second embodiment of the invention;

FIG 7 shows the setting of an increase correction rate of the amount of fuel injection with respect to the engine-start-time water temperature;

FIG 8 shows the setting of an injection-timing switch-over reference accumulation with respect to the engine-start-time water temperature;

FIG 9 shows a routine of an engine-start-time fuel injection timing control that is executed in a third embodiment of the invention; FIG 10 shows a routine of an engine-start-time fuel injection timing control that is executed in a fourth embodiment of the in invention;

FIG 11 is a diagram showing the setting of the intake TDC injection time with respect to the engine rotation speed;

FIG 12 is a flowchart showing a routing of an engine-start-time fuel injection timing control that is executed in a fifth embodiment of the invention;

FIG 13 is a flowchart showing a routine of an engine-start-time fuel injection timing control that is executed in a sixth embodiment of the invention;

FIG 14 is a diagram showing the setting range of the opening timing of the intake valve during an exhaust valve early-closure control in accordance with a seventh embodiment of the invention;

FIG 15 is a diagram showing the opening/closing timings of an intake valve and an exhaust valve during an exhaust valve early-closure control in accordance with a seventh embodiment of the invention; and FIG 16 is a diagram showing the opening/closing timing of an intake valve and an exhaust valve during an exhaust valve early-closure control in accordance with an eighth embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS [0035] A first embodiment of the invention will be described with reference to FIGS.

I to 5.

[0036] FIG 1 shows a general construction of an internal combustion engine to which an engine-start control device of the first embodiment of the invention is applied.

An internal combustion engine in accordance with this embodiment is a spark ignition type 4-stroke engine. The internal combustion engine includes a cylinder block 6 in which pistons 8 are disposed, and a cylinder head 4 that is mounted on the cylinder block

6. A space between an upper surface of each piston 8 and the cylinder head 4 forms a combustion chamber 10. The following description will be made mainly with regard to one of the pistons (one of the combustion chambers 10). A top portion of the combustion chamber 10 is provided with an ignition plug 16. Besides, an intake port 36 and an exhaust port 40 that communicate with the combustion chamber 10 are formed in the cylinder head 4.

[0037] A connecting portion between the intake port 36 and the combustion chamber

10 is provided with an intake valve 12 that controls the state of communication between the intake port 36 and the combustion chamber 10. A drive system of the intake valve 12 is equipped with an intake valve timing control device 22 that variably controls the opening/closing timing of the intake valve 12 (hereinafter, referred to as "intake valve timing"). The intake valve timing control device 22 used in this embodiment is a hydraulic type variable valve timing mechanism (VVT) capable of simultaneously altering the opening timing and the closing timing of the intake valve 12 while the operation angle is kept the same, by changing the phase angle of a camshaft relative to a crankshaft 18. The intake valve timing control device 22 has a lock structure for preventing a malfunction in a state where the hydraulic pressure is not sufficiently heightened. This lock structure locks the action of the intake valve timing control device 22 when the hydraulic pressure is low, and automatically releases the lock when the hydraulic pressure rises to a certain level. When the intake valve timing control device 22 is locked by the lock structure, the opening timing of the intake valve 12 is fixed in the vicinity of the intake TDC, more specifically, slightly to the advanced side from the intake TDC.

[0038] A connecting portion between the exhaust port 40 and the combustion chamber 10 is provided with an exhaust valve 14 that controls the state of communication between the exhaust port 40 and the combustion chamber 10. A drive system of the exhaust valve 14 is equipped with an exhaust valve timing control device 24 that variably controls the opening/closing timing of the exhaust valve 14 (hereinafter, referred to as "exhaust valve timing"). The exhaust valve timing control device 24 used herein is a hydraulic type variable valve timing mechanism, similarly to the intake valve timing control device 22. When the exhaust valve timing control device 24 is locked by a lock structure, the exhaust valve timing is fixed at a most advanced position. [0039] An intake pipe 30 is connected to the intake port 36. A throttle valve 32 is disposed in the intake pipe 30. The intake pipe 30 downstream of the throttle valve 32 branches toward each of the cylinders is thus connected to the intake port 36 of each cylinder. In the vicinity of a connecting portion between the intake pipe 30 and the intake port 36 of each cylinder, a fuel injection valve 34 that injects fuel into the intake port 36 is mounted.

[0040] The internal combustion engine in accordance with this embodiment includes an ECU (electronic control unit) 50 as a control device. The output side of the ECU 50 is connected to the intake valve timing control device 22, the exhaust valve timing control device 24, the fuel injection valves 34, the throttle valve 32, the ignition plug 16, a starter 20, and other various devices. The input side of the ECU 50 is connected to various sensors, such as a crank angle sensor 52, a water temperature sensor 54, an air flow sensor 56, and also to various switches, such as a start switch 58. The crank angle sensor 52 outputs a signal commensurate with the rotation angle of the crankshaft 18. The water temperature sensor 54 outputs a signal commensurate with the cooling water temperature of the internal combustion engine. The airflow sensor 56 outputs a signal commensurate with the amount of flow of air that is taken into the intake pipe 30. The start switch 58 receives from a driver, an engine start request to the internal combustion engine. On the basis of the outputs of the sensors and switches, the ECU 50 drives various appliances following predetermined control programs.

[0041] This embodiment has features in a control of the exhaust valve timing and a control of the fuel injection timing that are performed at the time of engine start-up, among the controls of the internal combustion engine executed by the ECU 50. FIG 2 shows a flowchart of the exhaust valve timing control that is executed by the ECU 50 in this embodiment. The routine shown in FIG 2 is executed simultaneously with the cranking of the internal combustion engine is started by the starter 20 in response to the turning-on of the start switch 58. Besides, this routine is executed for each one of the cylinders.

[0042] According to the routine shown in FIG 2, the ECU 50 performs an exhaust valve early-closure control (step S2), as a control of the exhaust valve timing at the time of start of the engine. The exhaust valve early-closure control is continued until the water temperature detected by the water temperature sensor 54 reaches a target water temperature (step S4). The target water temperature used in the determination at step S4 is a reference value for determining whether the internal combustion engine has sufficiently warmed up through the post-start warm-up operation. Then, when the water temperature reaches the target water temperature, the control of the exhaust valve timing is switched from the engine-start-time exhaust valve early-closure control to the exhaust valve normal control (step S6). [0043] Details of the exhaust valve early-closure control and the exhaust valve normal control mentioned above are described with reference to FIG 3. FIG 3 shows the opening/closing timings of the intake valve 12 and of the exhaust valve 14 during the exhaust valve early-closure control and during the exhaust valve normal control. In FIG 3, EVO represents the opening timing of the exhaust valve 14, and EVC represents the closing timing of the exhaust valve 14, and the crank angle (shown by a solid arc) from EVO to EVC represents the period of opening of the exhaust valve 14. Besides, IVO represents the opening timing of the intake valve 12, and IVC represents the closing timing of the intake valve 12, and the crank angle (shown by a blank arc) from FVO to IVC represents the period of opening of the intake valve 12. [0044] As shown in FIG 3, the exhaust valve early-closure control is a control that sets the closing timing of the exhaust valve 14 to the advanced side of the intake TDC as well as to the advanced side of the opening timing of the intake valve 12. The exhaust valve timing control device 24 is provided with the lock structure as described above, and the exhaust valve timing is fixed to the most advanced position until the hydraulic pressure becomes high. Besides, by the lock structure of the intake valve timing control device 22, the intake valve timing is fixed to such a timing that the opening timing thereof is slightly to the advanced side from the intake TDC. Therefore, with regard to the first cycle during the start-up of the internal combustion engine, the exhaust valve early-closure control is automatically performed because of the structure of the exhaust valve timing control device 24 and the intake valve timing control device 22. The first cycle during the start-up of the internal combustion engine at least begins before the opening timing of the intake valve 12.

[0045] The exhaust valve normal control is a control of setting the exhaust valve timing at an appropriate position in terms of the output performance of the internal combustion engine. In the example shown in FIG 3, the exhaust valve timing is controlled so that the opening period of the exhaust valve 14 and the opening period of the intake valve 12 overlap with each other. This exhaust valve normal control becomes possible only after the lock structure of the exhaust valve timing control device 24 is released. When the determination at step S4 is affirmative, that is, when the warm-up of internal combustion engine is completed, the hydraulic pressure has sufficiently risen, and the lock structure of the exhaust valve timing control device 24 has been released.

[0046] As can be understood from the foregoing description, the engine-start-time exhaust valve timing control refers to the exhaust valve early-closure control in this embodiment. Concurrently with the exhaust valve early-closure control, the engine-start-time fuel injection timing control is performed. FIG 4 describes the content of the engine-start-time fuel injection timing control that is executed in the embodiment. FIG 4 shows the exhaust valve timing and the intake valve timing in the exhaust valve early-closure control, and also shows changes in the flow rate at an intake valve portion (a connecting portion between the intake port 36 and the combustion chamber 10) that are brought about by the exhaust valve early-closure control.

[0047] As shown in FIG 4, during the exhaust valve early-closure control, the exhaust valve 14 is closed prior to the intake TDC, and the intake valve 12 is opened near the intake TDC. Therefore, the gas inside the combustion chamber 10 (hereinafter, referred to as "in-cylinder gas") is compressed by the piston 8 to obtain high temperature and high pressure during the period from the closing timing of the exhaust valve 14 till the opening timing of the intake valve 12, and then is blown back into the intake port 36 as the intake valve 12 is opened. This blow-back occurs when the pressure in the combustion chamber 10 of the internal combustion engine is higher than the pressure in the intake port 36. The blow-back brings about a high-speed flow of gas from inside the combustion chamber 10 toward the intake port 36. The gas blown back into the intake port 36 is taken into the combustion chamber 10 again from the intake port 36 as the piston 8 descends. In FIG 4, the flow rate of the gas flowing from the intake port 36 toward the combustion chamber 10 is indicated by +, and the flow rate of the gas flowing from the combustion chamber 10 toward the intake port 36 is indicated by -. Incidentally, during the exhaust valve normal control, both the exhaust valve 14 and the intake valve 12 are open in a period in the vicinity of the intake TDC. During this period, the pressure in the intake port 36 and the pressure in the combustion chamber 10 are substantially the same, and therefore the blow-back of in-cylinder gas toward the intake port 36 is small or almost none.

[0048] The fuel injection period shown in FIG 4 is a fuel injection period brought about by the engine-start-time fuel injection timing control. In this embodiment, the fuel injection timing is controlled so that a substantially central portion of the fuel injection period overlaps with the opening timing of the intake valve 12. In other words, the fuel injection is started prior to (at the advanced side of) the opening timing of the intake valve 12, and fuel continues being injected at the time point of the opening timing of the intake valve 12, and the fuel injection ends after (at the retarded side of) the opening timing of the intake valve 12. Therefore, the high-speed in-cylinder gas that is blown back from the combustion chamber 10 into the intake port 36 as the intake valve 12 opens can be caused to collide with the fuel spray-injected from the fuel injection valve 34. Owing to the collision of the in-cylinder gas, the fuel spray is stirred to form a fuel vapor that is further vaporized, or a fuel spray that is further atomized.

[0049] The engine-start-time fuel injection timing control continues to be performed during a period from the first cycle during the engine start-up until the exhaust valve early-closure control is switched to the exhaust valve normal control. In this case, the in-cylinder gas that is blown back is different between the first cycle and the second and later cycles. During the engine-start second and later cycles, high-temperature and high-pressure combustion gas obtained from the combustion of fuel is blown back. On the other hand, during the first engine-start cycle in the start-up of the engine, high-temperature and high-pressure air resulting from the compression by the piston 8 is blown back. The air blown back in the first engine-start cycle in the start-up of the engine does not have such a high temperature as the combustion gas that is blown back in the engine-start second and later cycles. However, in the first cycle, the effect of stirring fuel spray due to the collision with the blown-back ih-cylinder gas can be achieved to substantially the same degree as in the second and later cycles. Due to the stirring caused by the blown-back gas, the fuel spray becomes further vaporized fuel vapor, or a further atomized fuel spray. Besides, during the first engine-start cycle in the start-up of the engine, the air compressed to high temperature and high pressure by the piston 8 has higher temperature than the air present in the intake port that is strongly affected by the ambient temperature, and therefore causes the fuel spray to become a more vaporized fuel vapor or a more atomized fuel spray, as in the aforementioned system described in Japanese Patent Application Publication No. 2007-40150 (JP-A-2007-40150). Therefore, according to the engine-start control in accordance with this embodiment, it is possible to promote the vaporization or atomization of fuel from the very first cycle in the engine start-up, so that the emission of HC during the engine start-up can be restrain.

[0050] Incidentally, a purpose for which the fuel injection period is set so that a substantially central portion of the period, instead of a portion of the period immediately following the beginning thereof or near the end thereof, overlaps with the opening timing of the intake valve 12 is to bring about the maximum effect of promoting the vaporization or atomization of fuel spray through the collision with the in-cylinder gas. FIG 5 shows changes in the particle diameter of fuel spray in a fuel injection period. The fuel injected immediately following the start of fuel injection collides with the motionless air that is adjacent to the distal end of the fuel injection valve 34, and becomes spray that is large in particle diameter and therefore less readily vaporizes. Besides, as time elapses in the latter half of the injection period, the particle diameter becomes inconsistent because the fuel injection pressure declines. On another hand, the fuel spray produced at and around the center of the fuel injection period has a small and stable or consistent particle diameter. By causing the in-cylinder gas to collide with the fuel spray whose particle diameter is small and stable, the vaporization or atomization promoting effect can be heightened as a whole.

[0051] A second embodiment of the invention will be described with reference to FIG 1, and FIGS. 6 to 8. [0052] An engine-start control device as the second embodiment of the invention is applied to an internal combustion engine that has the construction shown in FIG 1, as in the first embodiment. Therefore, the following description will be made on the basis of the construction shown in FIG 1, as in the first embodiment. [0053] This embodiment is different from the first embodiment in the engine-start-time fuel injection control that is executed by the ECU 50. The engine-start-time exhaust valve timing control in this embodiment is the same as that in the first embodiment. FIG 6 shows a flowchart of the engine-start-time fuel injection control that is executed by the ECU 50 in the second embodiment. The routine shown in FIG 6 is started the instant when the cranking of the internal combustion engine is started by the starter 20 in response to the turning-on of the start switch 58. Besides, this routine is executed for each one of the cylinders.

[0054] In the first step SlOO in this routine, the ECU 50 determines whether the present cycle is the first engine-start cycle in the start-up of the engine. If the present engine cycle is the first engine-start cycle in the start-up of the engine, the fuel injection control is performed through a process of step S 102 and the steps that follow. On the other hand, if the present engine cycle is the engine-start second or later cycle, the fuel injection control is performed through a process of step S114 and the steps that follow.

That is, in this embodiment, the contents of the fuel injection control differ depending on whether the present engine cycle is the first engine-start cycle in the start-up of the engine or the engine-start second or later cycle.

[0055] In the case where the present cycle is the first engine-start cycle in the start-up of the engine, the ECU 50 firstly in step S 102 takes in an engine-start-time water temperature (thws) measured by the water temperature sensor 54. Subsequently in step S 104, the ECU 50 finds an engine-start injection amount (tausta) from a map on the basis of the engine-start-time water temperature (thws). In step S 106, the ECU 50 sets the engine-start injection amount (tausta) as a final injection amount (TAU). The final injection amount (TAU) is converted into a fuel injection period.

[0056] In step S 108, the ECU 50 determines whether the engine-start-time water temperature (thws) is lower than a reference temperature (α). The reference temperature (α) is a water temperature that allows an expectation that injected fuel will sufficiently vaporize inside the intake port 36. An example of the situation in which the engine-start-time water temperature (thws) is higher than the reference temperature (α) is when the engine is restarted from an idle stop. If the engine-start-time water temperature (thws) is higher than the reference temperature (α), the process proceeds to step S 112, in which the normal fuel injection timing control is performed. The normal fuel injection timing control is a fuel injection timing control that is performed in a situation that does not require a special vaporization or atomization promoting effect, and concretely is an intake asynchronous injection control or an intake synchronous injection control. In the intake asynchronous injection control, fuel is injected within the period during which the intake valve 12 is closed. In the intake synchronous injection control, fuel is injected when the intake valve 12 is open.

[0057] In the case where the engine-start-time water temperature (thws) is lower than the reference temperature (α), the ECU 50 performs the process of step SIlO. In step SIlO, the fuel injection timing is controlled so that the fuel injection period overlaps with the opening timing of the intake valve 12. Since the opening timing of the intake valve 12 is near the intake TDC, the fuel injection performed during this time will hereinafter be termed the intake TDC injection control. As described above in conjunction with the first embodiment, according to the intake TDC injection control, the fuel spray can be stirred by the collision with the blown-back in-cylinder gas, and the stirring effect promotes the vaporization or atomization of fuel spray.

[0058] In a case where in step SlOO it is determined that the present engine cycle is the engine-start second cycle, the ECU 50 firstly finds an increase correction rate (fwl) of the amount of fuel injection commensurate with the engine-start-time water temperature (thws) in step S 114. FIG 7 shows a conceptual image of a map for finding the increase correction rate (fwl) from the engine-start-time water temperature (thws). The increase correction rate (fwl) is set greater the lower the engine-start-time water temperature (thws) is. If the engine-start-time water temperature (thws) is higher than or equal to a certain temperature, the increase correction rate (fwl) is set at zero.

[0059] Next, in step S 116, the ECU 50 calculates a basic amount of fuel injection (tau). The basic injection amount (tau) is calculated using an intake air amount (Ga) calculated from a signal from the air flow sensor 56, and an engine rotation speed (NE) calculated from a signal from the crank angle sensor 52.

[0060] In step S118, the ECU 50 calculates a final injection amount (TAU) using the basic injection amount (tau) calculated in step S116, and the increase correction rate (fwl) calculated in step S114, as in the following expression (1). In the following expression (1), fwlk is a damping coefficient for damping the increase correction rate (fwl). The initial value of fwlk is set at 1, and the increase correction rate fwlk is set so that the value thereof decreases every one rotation. TAU=tauχ(l+fwlxfwlk) ...(1)

[0061] Subsequently in step S 120, the ECU 50 calculates a reference value that is used in a determination process described below. The determination process is performed for switching the fuel injection timing, and more specifically determines whether the integrated value of the intake air amount from the engine start-up (hereinafter, termed the accumulation Ga) is greater than an accumulation Ga (gaft) that serves as a switch reference. FIG 8 is a diagram showing a conceptual image of a map for finding a switch reference accumulation Ga (gaft) from the engine-start-time water temperature (thws). The switch reference accumulation Ga (gaft) is set greater the lower the engine-start- time water temperature (thws) is. If the engine-start-time water temperature (thws) is higher than or equal to a certain temperature, the switch reference accumulation Ga (gaft) is set at zero.

[0062] In step S122, the ECU 50 updates the value of the accumulation Ga (gat) accumulated from the start of the engine on the basis of the signals taken in from the air flow sensor 56 during the period from the previous cycle of the routine to the present cycle. Then, in step 124, the ECU 50 determines whether the accumulation Ga (gat) up to the present calculated in step S 122 is greater than the switch reference accumulation Ga (gaft) calculated in step S120. [0063] The result of the determination in step S 124 is that the accumulation Ga (gat) up to the present is not greater than the switch reference accumulation Ga (gaft), the process proceeds to step SIlO, in which the intake TDC injection control is performed as in the first engine-start cycle in the start-up of the engine. That is, in the engine-start second and later cycles, the ECU 50 also controls the fuel injection timing so that the fuel injection period overlaps with the opening timing of the intake valve 12, until the accumulation Ga (gat) exceeds the switch reference accumulation Ga (gaft). Therefore, the high-temperature combustion gas blown back from inside the combustion chamber 10 can be caused to collide with the fuel spray, so that the combination of the heat of the combustion gas and the stirring effect of the collision can promote the vaporization or atomization of fuel spray.

[0064] Then, when the accumulation Ga (gat) up to the present time exceeds the switch reference accumulation Ga (gaft), the process proceeds to step S 126. Due to the selection of step S 126, the control of the fuel injection timing is switched from the intake TDC injection control to the intake asynchronous injection control. Incidentally, when the engine-start-time water temperature (thws) is high and the switch reference accumulation Ga (gaft) is set at zero, the ECU 50 performs the intake asynchronous injection control from the engine-start second step on.

[0065] A third embodiment of the invention will be described with reference to FIG 1 and FIG 9.

[0066] An engine-start control device as the third embodiment of the invention is applied to an internal combustion engine that has the construction shown in FIG 1, as in the first embodiment. Therefore, the following description will be made on the basis of the construction shown in FIG 1, as in the first embodiment. [0067] This embodiment has a feature in the engine-start-time fuel injection control that is executed by the ECU 50. The engine-start-time fuel injection control in accordance with this embodiment is based on the engine-start- time fuel injection control in accordance with the second embodiment. FIG 9 is a flowchart showing the engine-start-time fuel injection control that is executed by the ECU 50 in the third embodiment. Of the processes shown in the flowchart of FIG. 9, the same processes as in the second embodiment are represented by the same step numbers as in the second embodiment. The descriptions of the same processes as those in the second embodiment are omitted or simplified below, and the process different from those in the second embodiment will be mainly described.

[0068] A feature of the routine shown in FIG 9 is a process that is performed in the case where in step S 108 it is determined that the engine-start-time water temperature

(thws) is lower than the reference temperature (α). According to this routine, the _j process of step S200 is performed instead of the process of step SIlO in the second embodiment.

[0069] In step S200, the ECU 50 performs a control of dividing the final injection amount (TAU) calculated in step S106 into a plurality of portions, and injects the divided portions of the final injection amount (TAU) (hereinafter, termed the multiple injection control). Herein, the final injection amount (TAU) is divided into two portions at 1:3, and a quarter of the final injection amount (TAU) is injected by the intake TDC injection control. Then, the three quarters of the final injection amount (TAU) is injected by the intake asynchronous injection control prior to the intake TDC injection control. The injection end timing of the intake asynchronous injection control is set at such a timing

(e.g., 90° BTDC) that the fuel injection period of the control does not overlap with the fuel injection period of the intake TDC injection control.

[0070] As described above, in the engine-start control in accordance with the embodiment, a combination of the intake TDC injection control and the intake asynchronous injection control is used as the fuel injection timing control at least in the first engine-start cycle in the start-up of the engine. According to this control, the following effects can be achieved, in comparison with the case where only the intake TDC injection control is used.

[0071] According to the intake TDC injection control, the in-cylinder gas blown back from the combustion chamber 10 can be caused to collide with fuel spray. However, the time of blow-back of in-cylinder gas is shorter than the fuel injection period as shown in FIG 4. Therefore, fuel spray does not always receive the stirring effect of the blow-back. Therefore, in this embodiment, the amount of fuel that can receive the stirring effect of the blow-back is injected by carrying out the intake TDC injection control, and the rest of the entire amount of fuel is injected earlier by the intake asynchronous injection control. Since the amount of fuel that cannot be stirred by the blow-back is injected relatively early, a time of atomization inside the intake port and a time during which the fuel not atomized dwells in the vicinity of the intake valve 12 due to its own weight can be secured. The fuel dwelling in the vicinity of the intake valve 12 is blown back to an upstream side of the intake port 36 by the blow-back occurring when the intake valve 12 is opened, so that the vaporization or atomization of the fuel is promoted. Therefore, according to the engine-start control in accordance with the embodiment, it becomes possible to promote the vaporization or atomization of the entire amount of injected fuel, and therefore the discharge of HC at the time of start of the engine can be restrained. [0072] Incidentally, although in the routine shown in FIG. 9, the ratio of the separate injections by the intake TDC injection control and the intake asynchronous injection control is set at 1:3, this is a mere example. The separate injection ratio can be appropriately set, for example, at 1:4, or the like.

[0073] A fourth embodiment of the invention will be described with reference to FIG 1, FIG 10, and FIG 11.

[0074] An engine-start control device as the fourth embodiment of the invention is applied to an internal combustion engine that has the construction shown in FIG 1, as in the first embodiment. Therefore, the following description will be made on the basis of the construction shown in FIG 1, as in the first embodiment. [0075] This embodiment has a feature in the engine-start-time fuel injection control that is executed by the ECU 50. The engine-start-time fuel injection control in accordance with this embodiment is based on the engine-start-time fuel injection control in accordance with the third embodiment. FIG 10 is a flowchart showing the engine-start-time fuel injection control that is executed by the ECU 50 in the fourth embodiment. Of the processes shown in the flowchart of FIG 10, the same processes as in the third embodiment are represented by the same step numbers as in the third embodiment. The descriptions of the same processes as those in the third embodiment are omitted or simplified below, and the process different from those in the third embodiment will be mainly described.

[0076] A feature of the routine shown in FIG 10 is a process performed in the engine-start second and later cycles. According to this routine, in the case where step S124 it is determined that the accumulation Ga (gat) up to the present time has not exceeded the switch reference accumulation Ga (gaft), the process of step S300 and later steps is performed in the fourth embodiment, instead of the process of step S200 in the third embodiment.

[0077] Firstly, in step S300, the ECU 50 determines an upper-limit amount of fuel injection (hereinafter, referred to as "intake TDC injection amount") (tautdc) on the basis of the engine rotation speed (NE) at the present time point. The intake TDC injection amount (tautdc) is an upper limit value of the amount of fuel injection that can receive the stirring effect of the blow-back. FIG. 11 is a diagram showing a conceptual image of a map for finding the intake TDC injection amount (tautdc) from the engine rotation speed (NE). In this map, the intake TDC injection amount (tautdc) is made less the higher the engine rotation speed (NE) becomes. This is because in the engine-start second and later cycles, as the engine rotation speed (NE) rises, the blow-back time shortens, and therefore the intake TDC injection amount (tautdc) needs to be lessened correspondingly.

[0078] Subsequently in step S302, the ECU 50 determines whether the final injection amount (TAU) calculated in step S118 is greater than or equal to the intake TDC injection amount (tautdc) obtained in step S300. In the case where the final injection amount (TAU) is greater than or equal to the intake TDC injection amount (tautdc), a portion of the fuel cannot be injected by the intake TDC injection control. In this case, the process proceeds to step S306, in which a multiple injection control of injecting fuel separately by the intake TDC injection control and by the intake asynchronous injection control is performed. Specifically, prior to the intake TDC injection control, a differential amount of fuel between the final injection amount (TAU) and the intake TDC injection amount (tautdc) is injected by the intake asynchronous injection control. Then, the intake TDC injection amount (tautdc) of fuel is injected by the intake TDC injection control. Incidentally, the injection end timing of the intake asynchronous injection control is set at such a timing (e.g., 90° BTDC) that the fuel injection period of the control does not overlap with the fuel injection period of the intake TDC injection control.

[0079] On the other hand, in the case where the final injection amount (TAU) is less than the intake TDC injection amount (tautdc), the entire amount of fuel can be injected by the intake TDC injection control. In that case, the ECU 50 firstly performs the process of step S304. In step S304, the ECU 50 substitutes the value of the intake TDC injection amount (tautdc) with the final injection amount (TAU). After that, the ECU 50 performs the process of step S306. Due to the process of step S304, the difference between the final injection amount (TAU) and the intake TDC injection amount (tautdc) is eliminated, and therefore the amount of fuel injected by the intake asynchronous injection control becomes zero. Then, the entire mount of the final injection amount (TAU) is injected by the intake TDC injection control.

[0080] As described above, in the engine-start control in accordance with the embodiment, during the engine-start second and later cycles when the engine rotation speed rises, as the engine rotation speed rises, the amount of fuel injection provided by the intake TDC injection control is reduced in accordance with the blow-back time, which shortens with increasing engine rotation speed. Therefore, occurrence of the fuel spray that cannot receive the stirring effect of the blow-back can be restrained. Besides, the amount of fuel subtracted during the intake TDC injection control can certainly obtain an atomization time or the like owing to the early injection performed by the intake asynchronous injection control. Therefore, according to the engine-start control in accordance with the embodiment, the vaporization or atomization of the entire amount of injected fuel in the engine-start second and later cycles can be further promoted.

[0081] A fifth embodiment of the invention will be described with reference to FIG 1 and FIG 12. [0082] An engine-start control device as the fifth embodiment of the invention is applied to an internal combustion engine that has the construction shown in FIG 1, as in the first embodiment. Therefore, the following description will be made on the basis of the construction shown in FIG 1, as in the first embodiment. [0083] This embodiment has a feature in the engine-start-time fuel injection control that is executed by the ECU 50. The engine-start-time fuel injection control in accordance with this embodiment is based on the engine-start-time fuel injection control in accordance with the fourth embodiment. FIG 12 is a flowchart showing the engine-start-time fuel injection control that is executed by the ECU 50 in the fifth embodiment. Of the processes shown in the flowchart of FIG 12, the same processes as in the fourth embodiment are represented by the same step numbers as in the fourth embodiment. The descriptions of the same processes as those in the fourth embodiment are omitted or simplified below, and the process different from those in the fourth embodiment will be mainly described. [0084] A feature of the routine shown in FIG 12 is that the upper-limit amount of fuel injection under the intake TDC injection control executed in the engine-start second and later cycles is at an amount that corresponds to a predetermined crank angle range whose center is the IVO. The predetermined crank angle range is a range that allows the stirring effect of the blow-back to be certainly obtained. According to this routine, in the case where it is determined in step S 1124 that the accumulation Ga (gat) up to the present time has not exceeded the switch reference accumulation Ga (gaft), a process of steps S400 and S402 is performed, instead of the process of step S300 in the fourth embodiment.

[0085] In step S400, the ECU 50 determines an injectable amount of fuel in a 60°-crank-angle range whose center is the IVO (hereinafter, termed the 60⁰CA injection amount) (tauca) on the basis of the engine rotation speed (NE) at the present time point. The 60⁰CA injection amount (tauca) decreases as the engine rotation speed (NE) heightens. Next in step S402, the ECU 50 sets the 60⁰CA injection amount (tauca) found in step S400, as the intake TDC injection amount (tautdc). [0086] After the determination in step S302 is performed, the process of step S404 is performed instead of the process of step S306 in accordance with the fourth embodiment, according to this routine. In step S404, the ECU 50 performs a multiple injection control in which fuel is injected separately by the intake TDC injection control and by the intake asynchronous injection control. However, in the case where the final injection amount (TAU) is less than the intake TDC injection amount (tautdc) and therefore the process of step S304 is performed, the entire amount of the injection fuel is injected by the intake TDC injection control.

[0087] The intake TDC injection control performed in step S404 has a feature that the fuel injection period is set with reference to the end timing of the fuel injection.

There is no such limitation regarding the intake TDC injection controls executed in step

S200 or in step S306 in the third embodiment. As for these controls, the fuel injection period by the intake TDC injection control may be set with reference to the start timing of the fuel injection. In step S404, the end timing of the fuel injection by the intake TDC injection control is set around 30° in crank angle from the FVO.

[0088] As described above, in the engine-start control in accordance with the embodiment, the intake TDC injection control is performed with the injection end timing set at 30° crank angle from the IVO so that the fuel injection period is within the range of

60° in crank angle whose center is the IVO. Therefore, the occurrence of a fuel spray that cannot receive the stirring effect of the blow-back can be effectively prevented.

[0089] Incidentally, although in the routine shown in FIG 12 the intake TDC injection amount (tautdc) is the injection amount that corresponds to the range of 60° in crank angle whose center is the IVO, the range of 60° in crank angle whose center is the IVO is a mere example. The foregoing crank angle range may be appropriately set according to a positional relationship between the fuel injection valve 34 and the intake valve 12, and to the structure of the intake port 36. Besides, instead of using the IVO as the center, the crank angle range may be set using a crank angle prior to the FVO and a crank angle following the IVO that are different from each other in absolute value.

[0090] A sixth embodiment of the invention will be described with reference to FIG 1 and FIG 13.

[0091] An engine-start control device as the sixth embodiment of the invention is applied to an internal combustion engine that has the construction shown in FIG 1, as in the first embodiment. Therefore, the following description will be made on the basis of the construction shown in FIG 1, as in the first embodiment.

[0092] This embodiment has a feature in the engine-start-time fuel injection control that is executed by the ECU 50. The engine-start-time fuel injection control in accordance with this embodiment is based on the engine-start-time fuel injection control in accordance with the fifth embodiment. FIG 13 is a flowchart showing the engine-start-time fuel injection control that is executed by the ECU 50 in the sixth embodiment. Of the processes shown in the flowchart of FIG 13, the same processes as in the fifth embodiment are represented by the same step numbers as in the fifth embodiment. The descriptions of the same processes as those in the fifth embodiment are omitted or simplified below, and the process different from those in the fifth embodiment will be mainly described.

[0093] A feature of the routine shown in FIG 13 is that the contents of the intake TDC injection control that is carried out in the engine-start second and later cycles are made different depending on whether the final injection amount (TAU) is greater than or equal to the intake TDC injection amount (tautdc). According to this routine, in the case where in step S302 it is determined that the final injection amount (TAU) is greater than or equal to the intake TDC injection amount (tautdc), the process step S404 is performed as in the fifth embodiment. On the other hand, in the case where it is determined that the final injection amount (TAU) is less than the intake TDC injection amount (tautdc), a process of step S500 is performed, instead of step S404, after the process of step S304. [0094] The intake TDC injection control performed in step S500 has a feature that the fuel injection period is set with reference to the start timing of the fuel injection, instead of the end timing of the fuel injection. In step S500, the start timing of the fuel injection by the intake TDC injection control is set at 30° in crank angle prior to the IVO.

[0095] As described above, in the engine-start control in accordance with the embodiment, the ECU 50 starts the fuel injection at 30° in crank angle prior to the IVO, in the case where the final injection amount (TAU) is within the intake TDC injection amount (tautdc). Therefore, the rate of collision between the blow-back and the fuel spray can be maximized, and the fuel spray stirring effect of the collision can be heightened.

[0096] A seventh embodiment of the invention will be described with reference to FIG 1, FIG 14 and FIG 15.

[0097] An engine-start control device as the seventh embodiment of the invention is applied to an internal combustion engine that has the construction shown in FIG 1, as in the first embodiment. Therefore, the following description will be made on the basis of the construction shown in FIG 1, as in the first embodiment.

[0098] This embodiment has a feature in the opening timing of the intake valve 12 in the first engine-start cycle in the start-up of the engine. The closing timing of the exhaust valve 14 in the first engine-start cycle in the start-up of the engine is at the advanced side of the intake TDC as in the first embodiment. More specifically, in this embodiment, the closing timing of the exhaust valve 14 is set at 30° to the advanced side of the intake TDC. Taking into account the balance between the in-cylinder gas compressing effect of the early closure of the exhaust valve 14 and the load on the cranking by the compressing work, it is preferable that the closing timing of the exhaust valve 14 is about 30°.

[0099] In the case where the closing timing of the exhaust valve 14 is determined as described above, the pressure of the in-cylinder gas at the opening timing of the intake valve 12 can be made higher than the pressure of the in-cylinder gas at the closing timing of the exhaust valve 14 by setting the opening timing of the intake valve 12 within a range from about 30° (30° BTDC) at the advanced side of the intake TDC and to about 30° (30° ATDC) at the retarded side of the intake TDC. That is, blow-back into the intake port 36 can be caused. Therefore, if the opening timing of the intake valve 12 is set within the range shown in FIG 14 and the fuel injection is performed at that opening timing, the fuel spray collides with the blown-back in-cylinder gas. Due to the collision with the in-cylinder gas, the fuel spray is stirred, forming a fuel vapor that is further vaporized, or a fuel spray that is further atomized.

[0100] FIG 15 shows opening/closing timings of the intake valve and the exhaust valve at the time of the exhaust valve early-closure control. As shown in FIG 15, in this embodiment, the opening timing of the intake valve 12 at least during the first engine-start cycle in the start-up of the engine is set in the vicinity of the intake TDC. The closer to the intake TDC the opening timing of the intake valve 12 is brought, the greater the pressure difference between the pressure of the in-cylinder gas at the opening timing of the intake valve 12 and the pressure of the in-cylinder gas at the closing timing of the exhaust valve 14 can be made. Therefore, according to this embodiment, the flow rate of the blow-back of the in-cylinder gas that occurs when the intake valve 12 opens can be heightened, so that the fuel spray stirring effect of the blow-back of the in-cylinder gas can be heightened.

[0101] An eighth embodiment of the invention will be described with reference to FIG 1, and FIG. 16.

[0102] An engine-start control device as the eighth embodiment of the invention is applied to an internal combustion engine that has the construction shown in FIG 1, as in the first embodiment. Therefore, the following description will be made on the basis of the construction shown in FIG 1, as in the first embodiment. [0103] In this embodiment, the opening timing of the intake valve 12 in the first engine-start cycle in the start-up of the engine is able to be controlled, for example, according to the engine operation condition. Besides, the intake valve timing control device 22 used in this embodiment is an electromagnetic type valve operating mechanism that drives the intake valve 12 using a solenoid, or an electric motor drive type valve operating mechanism in which the cams are rotated by an electric motor. What is common between these valve operating mechanisms is that the intake valve 12 can be instantaneously opened by a valve opening signal.

[0104] As stated above in conjunction with the seventh embodiment, in the case where the crank angle from the closing timing of the exhaust valve 14 to the intake TDC is larger than the crank angle between the opening timing of the intake valve 12 and the intake TDC, the blow-back from the combustion chamber 10 into the intake port 36 can be certainly brought about when the intake valve 12 is opened. However, as long as the blow-back occurs, the crank angle from the closing timing of the exhaust valve 14 to the intake TDC may be smaller than the crank angle between the opening timing of the intake valve 12 and the intake TDC as shown in FIG 16. For example, when the internal energy of the in-cylinder gas increases due to the heat applied from outside during a period from the closing timing of the exhaust valve 14 until the opening timing of the intake valve 12, the blow-back can occur even with the opening timing of the intake valve 12 as shown in FIG. 16.

[0105] A condition for the occurrence of the blow-back from the combustion chamber 10 into the intake port 36 is that the pressure in the combustion chamber 10 is higher than the pressure in the intake port 36. Therefore, in order to determine whether the foregoing condition is satisfied, the ECU 50 in accordance with this embodiment measures the pressure in the intake port 36 by an intake pipe pressure sensor (not shown), and measures the pressure in the combustion chamber 10 by an in-cylinder pressure sensor (not shown) that is disposed in the combustion chamber 10. Then, before the pressure in the combustion chamber 10 becomes lower than the pressure in the intake port 36, the intake valve 12 is opened by operating the intake valve timing control device 22.

[0106] Incidentally, during the first engine-start cycle in the start-up of the engine, since the throttle valve 32 is fully open, the pressure in the intake port 36 is substantially equal to the atmosphere pressure. Therefore, as a substitute for the output value of the intake pipe pressure sensor, an output value of an atmosphere pressure sensor may be used for the comparison with the output value of the in-cylinder pressure sensor.

[0107] While embodiments of the invention have been described above, it is to be understood that the invention is not limited to the foregoing embodiments, but may be carried out with various modifications, without departing from the spirit of the invention. For example, the invention may also be carried out with the following modifications. [0108] Although in the first embodiment, a substantially center portion of the fuel injection period overlaps with the opening timing of the intake valve 12, this does not exclude a construction in which the opening timing of the intake valve 12 is apart from the center of the fuel injection period. As long as at least a portion of a period of the fuel injection period immediately following the start of the period and immediately preceding the end thereof overlaps with the opening timing of the intake valve 12, the effect of promoting the vaporization or atomization of fuel spray which is achieved by the collision with in-cylinder gas is brought about.

[0109] Besides, in each of the third to sixth embodiments, the fuel injection timing control of step S200 that is carried out in the first engine-start cycle in the start-up of the engine may also be modified so that the ratio between the separate injections of the intake TDC injection control and of the intake asynchronous injection control is variable. For example, the separate injection ratio may be altered according to the engine-start-time water temperature (thws). [0110] While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.

Claims

CLAIMS:

1. An engine-start control device for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, and an exhaust valve whose closing timing is adjustable, characterized by comprising: exhaust valve closing timing control means for, at least in a first engine-start cycle, controlling the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center, and so that a crank angle from the closing timing to the intake top dead center is larger than the crank angle between an opening timing of an intake valve and the intake top dead center; and fuel injection timing control means for, at least in the first engine-start cycle, controlling a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve.

2. The engine-start control device according to claim 1, wherein the fuel injection timing control means controls the fuel injection timing so that a substantially central portion of the fuel injection period overlaps with the opening timing of the intake valve.

3. The engine-start control device according to claim 1 or 2, wherein the fuel injection timing control means controls the fuel injection timing so that the fuel injection period is divided into a plurality of fuel injection periods, and so that one of the divided fuel injection periods overlaps with the opening timing of the intake valve, and so that an other one of the divided fuel injection periods is within a closure period of the intake valve.

4. The engine-start control device according to claim 3, wherein the amount of fuel injected during the one of the periods is smaller than the amount of fuel injected during the other one of the periods.

5. The engine-start control device according to claim 3 or 4, wherein, in a second and later engine-start cycles, the fuel injection timing control means reduces the fuel injection period that overlaps with the opening timing of the intake valve, according to rise in the internal combustion engine rotation speed.

6. The engine-start control device according to any one of claims 3 to 5, wherein the fuel injection timing control means reduces a fuel injection amount injected during the fuel injection period that overlaps with the opening timing of the intake valve in the second and later engine-start cycles, according to rise in the internal combustion engine rotation speed.

7. The engine-start control device according to claim 6, wherein the fuel injection timing control means causes the fuel injection amount injected during the fuel injection period that overlaps with the opening timing of the intake valve in the second and later engine-start cycles to be the amount of fuel that is injectable in a range of 30 degrees or less in crank angle from the opening timing of the intake valve.

8. The engine-start control device according to claim 7, wherein the fuel injection timing control means causes a fuel injection end timing that overlaps with the opening timing of the intake valve in the second and later engine-start cycles to be 30 degrees or less in crank angle at a retarded side than the opening timing of the intake valve.

9. The engine-start control device according to claim 7, wherein the fuel injection timing control means causes a fuel injection start timing that overlaps with the opening timing of the intake valve in the second and later engine-start cycles to be 30 degrees or less in crank angle at an advanced side than the opening timing of the intake valve.

10. The engine-start control device according to any one of claims 1 to 9, wherein the fuel injection timing control means controls the fuel injection timing if a water temperature of the internal combustion engine is lower than or equal to a predetermined temperature.

11. The engine-start control device according to any one of claims 1 to 10, further comprising intake valve opening timing control means for, at least in the first engine-start cycle, controlling the opening timing of the intake valve so that the opening timing of the intake valve is when a pressure in a combustion chamber of the internal combustion engine is higher than pressure in the intake port.

12. The engine-start control device according to any one of claims 1 to 10, further comprising intake valve opening timing control means for, at least in the engine-start-time first cycle, controlling the opening timing of the intake valve so that the opening timing of the intake valve is when a blow-back from the combustion chamber of the internal combustion engine to the intake port occurs.

13. An engine-start control device for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, an exhaust valve whose closing timing is adjustable, and an intake valve whose opening timing is adjustable, characterized by comprising: exhaust valve closing timing control means for, at least in a first engine-start cycle, controlling the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center; intake valve opening timing control means for, at least in the first engine-start cycle, controlling the opening timing of the intake valve so that the opening timing of the intake valve is when pressure in a combustion chamber of the internal combustion engine is higher than pressure in the intake port; and fuel injection timing control means for, at least in the first engine-start cycle, controlling a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve.

14. An engine-start control device for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, an exhaust valve whose closing timing is adjustable, and an intake valve whose opening timing is adjustable, characterized by comprising: exhaust valve closing timing control means for, at least in a first engine-start cycle, controlling the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center; intake valve opening timing control means for, at least in the first engine-start cycle, controlling the opening timing of the intake valve so that the opening timing of the intake valve is when a blow-back from a combustion chamber to the intake port occurs; and fuel injection timing control means for, at least in the first engine-start cycle, controlling a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve.

15. The engine-start control device according to any one of claims 11 to 14, wherein the intake valve opening timing control means causes the opening timing of the intake valve to be at a retarded side of the closing timing of the exhaust valve.

16. The engine-start control device according to any one of claims 11 to 14, wherein the intake valve opening timing control means causes the opening timing of the intake valve to be a crank angle at an advanced side than an intake top dead center, the crank angle being equal to or smaller than the crank angle from the closing timing of the exhaust valve to the intake top dead center.

17. The engine-start control device according to any one of claims 11 to 14, wherein the exhaust valve closing timing control means causes the closing timing of the exhaust valve to be 30 degrees or less in crank angle than an advanced side of an intake top dead center.

18. An engine-start control method for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, and an exhaust valve whose closing timing is adjustable, characterized by comprising: controlling, at least in a first engine-start cycle, the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center, and so that a crank angle from the closing timing to the intake top dead center is larger than the crank angle between an opening timing of an intake valve and the intake top dead center; and controlling, at least in the first engine-start cycle, a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve.

19. An engine-start control method for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, an exhaust valve whose closing timing is adjustable, and an intake valve whose opening timing is adjustable, characterized by comprising: controlling, at least in a first engine-start cycle, the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center; controlling, at least in the first engine-start cycle, the opening timing of the intake valve so that the opening timing of the intake valve is when pressure in a combustion chamber of the internal combustion engine is higher than pressure in the intake port; and fuel injection timing control means for, at least in the first engine-start cycle, controlling a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve.

20. An engine-start control method for an internal combustion engine that has a fuel injection valve that injects fuel into an intake port, an exhaust valve whose closing timing is adjustable, and an intake valve whose opening timing is adjustable, characterized by comprising: controlling, at least in a first engine-start cycle, the closing timing of the exhaust valve so that the closing timing of the exhaust valve is at an advanced side of an intake top dead center; controlling, at least in the first engine-start cycle, the opening timing of the intake valve so that the opening timing of the intake valve is when a blow-back from a combustion chamber to the intake port occurs; and controlling, at least in the engine-start-time first cycle, a fuel injection timing of the fuel injection valve so that a fuel injection period overlaps with the opening timing of the intake valve.